Research ArticleThe Influence of Ce or Mn Doping on Cu-Based Catalysts forDe-NOx with NH3-SCR

Lei Jiang1 Yixi Cai1 Miaomiao Jin 1 Zengzan Zhu2 and Yinhuan Wang2

1School of Automotive and Transportation Engineering Jiangsu University Zhenjiang 212013 China2Kailong Lanfeng New Material Technology Co Ltd Zhenjiang 212132 China

Correspondence should be addressed to Miaomiao Jin miaomiaojin2019163com

Received 20 September 2019 Revised 4 March 2020 Accepted 31 March 2020 Published 13 May 2020

Academic Editor Claudia Crestini

Copyright copy 2020 Lei Jiang et al)is is an open access article distributed under theCreative CommonsAttribution License whichpermits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

In this study the de-NOx performance of Cu-based zeolite catalysts supported on topological structure (SSZ-13 BEA ZSM-5) andloaded with different doses of copper (from 2 to 6 wt) was investigated )e preparation of copper-based catalysts adopted theincipient wetness impregnationmethod To analyze the physicochemical properties of the catalysts advanced techniques like BETXRD NH3-TPD H2-TPR and DRS UV-Vis were used)e performance tests suggested the 4CuSSZ-13 catalyst exhibited higherlow-temperature activity and wider temperature window Furthermore compared with Mn-CuSSZ-13 the Ce-CuSSZ-13catalysts exhibited better de-NOx performance

1 Introduction

)e nitrogen oxide (NOx) pollution level has causedwidespread concern calling for effective measures to achieveultralow emission beyond the current efforts )ereforeurea- (ammonia-) selective catalytic reduction technology(urea-SCR) has been widely employed in removing nitrogenoxide emissions [1] In recent years V2O5-WO3TiO2 [2 3]catalysts and copper-based [4ndash6] and iron-based zeolite[5ndash8] catalysts have been extensively studied in the NH3-SCR catalytic system and are gradually being used forcommercialization Vanadium-based catalysts have devel-oped greater sulfur resistance and high NOx conversion overa broad temperature window whereas vanadium-basedcatalysts will lose activity at high temperatures because of theTiO2 support crystal form Moreover the catalyst systemcontains biologically active component (V2O5) then it iseasy to sublimate or fall off during the purification process ofNOx from diesel exhaust which is potentially harmful to theecological environment and human health )e UnitedStates and Japan have already been forbidden the use ofvanadium-based catalytic system for NOx purification ofdiesel exhaust )erefore developing an effective durableand environmentally friendly SCR catalyst becomes more

important for diesel NOx removal in the future to replace thetraditional vanadium-based catalyst of SCR technology

SCR zeolitic materials can be divided into straight-channel zeolites (including MFI BEA and FAU) and cagetype (SSZ-13 and SAPO-34) according to structural char-acteristics )e main channel of the former SCR reaction istheir 3D main channel whereas the latter is the CHA cage[9ndash12] Cu-based zeolite catalysts have attracted extensivefocus due to the wide SCR reaction window and excellent N2selectivity However the upstream process results in poorstability of zeolite in dealumination under severe hydro-thermal conditions )e small channel size of SSZ-13 im-pedes the structural dealumination and thus possesseshigher hydrothermal stability [13]

)e molecular sieves for NH3-SCR catalyst supportmainly include ZSM-5 Beta SSZ-13 SAPO-34 and USY)e CHA structure especially SSZ-13 molecular sieve hasbecome the focus of molecular sieve denitration catalystresearch and development in recent years due to its ex-ceedingly good de-NOx performance N2 selectivity andhydrothermal stability [14ndash16] Considering that Cu- andFe-based zeolites catalysts present excellent activity and lowcost they have been very popular with commercial catalystmanufacturers Wang et al [17] studied the de-NOx

HindawiJournal of ChemistryVolume 2020 Article ID 1462801 8 pageshttpsdoiorg10115520201462801

performance of fresh and hydrothermal aging (HTA) of Cu-and Fe- based zeolite catalysts and discovered that the CuSSZ-13 catalysts exhibited excellent low-temperature per-formance CuSSZ-13 zeolites were proved to exhibit moreexcellent durability as compared with other Cuzeolites byKwak et al [18] It was found by other researchers that CuSSZ-13 maintained a high SCR reactivity at 1100K after16 hhydrothermal treatment [19]

Liu et al [20] prepared Cu-MnSAPO-34 with the in-cipient witness impregnation method finding that the NOconversion achieved 72 at 120degC and the de-NOx per-formance exceeded 90 when the temperature was up to180degC Liu et al [21] doped Ce andor Zr over CuZSM-5zeolite catalysts to study the effect of Ce andor Zr on the de-NOx performance using NH3 and they reported that thehigh SCR activities of cerium-rich catalysts were caused bythe Ce3+Ce4+ redox couple presence Cerium-containingmaterials are considered to be of great research value in theapplication of NOx emission reduction attributed to theability to store oxygen and their excellent redox capacity[22 23] Overall the introduction of transition metals andrare earth elements in zeolite catalysts can improve theircatalytic performance by changing the active sites andsynergistic action (copper) with active components

In this study Cu-based zeolite catalysts were preparedby incipient witness impregnation and their influence onNH3-SCR reaction was investigated Furthermore theoptimal type of zeolite was used as a carrier to study theeffect of different copper loading on the physicochemicalproperties of the catalyst and the de-NOx performance ofSCR reaction

2 Materials and Methods

21 Catalyst Preparation )e preparation of all samples isaccomplished by the incipient wetness impregnationmethod Taking the preparation of the catalysts with 4 wtCu content as an example the detailed preparation processfor different zeolites (BEA ZSM-5 and SSZ-13) is as followsfirst the water absorption of zeolite (BEA ZSM-5 and SSZ-13) was tested and based on its absorption rate a suitablecopper solution was disposed of as an immersion liquid inthe required Cu loading amount )e copper solution wasquickly and uniformly fixed with the above correspondingzeolite powder After the zeolite power was stirred 6 timesevery 5min when being dried at 100degC the obtained sampleswere calcined in themuff furnace at 550degC for 4 h xCu (x 24 6 wt)zeolite catalysts were prepared using the samemethods

Doped Cu-Mzeolite (M= ceriummanganese) catalystpowder was prepared by a wetness impregnation methodAccording to the water absorption rate of SSZ-13 copperand metal loading (1 wt) the impregnating solutionconsists of copper and metallic elements by Ce(NO3)3middot6H2O(AR) or Mn(NO3)2 (50 wt) (AR Sinopharm ChemicalReagent Co Ltd China) After impregnating the solutionquickly and evenly to the carrier the samples were dried andcalcined under the same conditions as above to get Cu-Mzeolites catalyst powder

22 Activity Measurement )e de-NOx performance ofcatalysts was tested by a quartz tubular fixed-bed reactor(id 24mm) with 628 cm3 sample (400 mesh) as shown inFigure 1 )e catalyst was fixed in the middle of the reactiontube and the tests of the SCR reaction temperature werecontrolled by the program precision temperature controller(YuDian AI-708) A Mass flowmeter was applied to regulatethe concentrations of feed gas H2O was provided by asyringe pump (EverSeiko 022 Pulsation Control Single) andmixed with the feed gas in the evaporator

)e simulation gas was composed of 500 ppm NO550 ppm NH3 8 vol O2 5 vol CO2 5 vol H2O and N2balance (300mLmin) )e gas hourly space velocity(GHSV) value was kept about 50000 hminus1 Typically a massflow controller was used to control the gas composition )eNOx conversion (XNOx

) and N2O yield (XN2O)evaluated thecatalyst activities and selectivity by using the followingequation

XNOx

NOx1113858 1113859in minus NOX1113858 1113859outNOx1113858 1113859in

times 100

XN2O 2N2O

NH31113858 1113859in +[NO]intimes 100

(1)

23 Catalyst Characterization BrunauerndashEmmettndashTeller(BET) and BarrettndashJionerndashHalenda (BJH) methods wereutilized to evaluate the specific surface area the pore volumeand the average pore diameter in the experiments )ephysical characteristics of parent zeolites and copper-basedzeolites previously degassed at 200degC for 6 h were measuredbased on nitrogen adsorption performed on a Quantach-rome NOVA2000-e analyzer

)e X-ray diffraction (XRD) was operated using a BrukerD8-ADVANCE device with Ni filter and Cu-Kα radiation(λ 015418 nm 40 kVtimes 200mA) at room temperature witha scanning velocity of 5degmin (2θ 20 to 80deg) Data wereprocessed with the JADE 65 software

)e NH3-temperature-programmed desorption (NH3-TPD) experiment was performed with a CHEMBET 3000chemical adsorption instrument (Quantachrome) In theNH3-TPD experiment a sample of 02 g was taken and fixedat the bottom of the U-shaped quartz reactor In order toremove the surface impurities the pretreatment was carriedout in pure argon (Ar) under 500degC for 30min and thencooled at 45degC after which the gas composition was changedinto a NH3N2 for adsorption When the thermal conduc-tivity detector (TCD) baselines were stable the gas com-position was switched to N2 again for removal of surfacephysically adsorbed NH3 After attaining the stability ofTCD baselines the temperature increased to 850degC in N2atmosphere by a rate of 10degCmin and NH3 desorption wasdetected by TCD )e standard signal peak of a certainamount of NH3 was calibrated with a quantitative loop andthe amount of NH3 desorption of different samples wasquantitatively calculated at corresponding temperatures bycomparison

2 Journal of Chemistry

)e H2-temperature programmed reduction (H2-TPR)experiments were conducted with Quantachrome Firstlypretreatment of the catalyst was performed at 500degC for30min in pure Ar atmosphere in order to remove the surfaceimpurities and then cooled to below 30degC )en the at-mosphere was switched to a 10H2N2mixtureWhen TCDbaselines become stable the temperature increased to 950degCunder the same atmosphere by a rate of 10degCmin After theexhaust was dehydrated by zeolite the hydrogen con-sumption was detected by TCD

)e UV-Vis spectroscopy was operated on a SHI-MADZU UV-2600 device to evaluate the nuclearity statusof the copper species in the zeolite with different Culoadings )e reflectance spectra ranging from 200 to900 nm (wavelength) was recorded using BaSO4 as ref-erence sample

3 Results and Discussion

31 BETAnalysis Table 1 shows the BETresults It could beseen that the purified SSZ-13 had larger surface area andaverage pore diameter and pore volume than copper-con-taining zeolites )e surface area and pore volumes ofsamples were reduced when copper was added to the zeolitewhich indicated that the internal pores of zeolites werecovered or permeated by copper species )e SSZ-13 zeoliteswere in the micropore range

32 XRD Patterns )e crystal structures and phase com-position of xCuSSZ-13 (x 2 4 6 wt) were investigatedby powdered XRDmeasurements and the XRD patterns areexhibited in Figure 2 Peaks of all samples were observed at2θ 209deg 235deg 254deg 263deg 281deg 286deg 310deg 315deg and350deg associated with typical chabazite (CHA) structure [13]Futhermore the XRD pattern of the CuSSZ-13 was notdetected for diffraction peaks of CuOx (2θ 354deg and 365deg)this observation suggested that the copper species presenteda good dispersion on the surface of the zeolite or the Culoadings in the samples used in this work were so low thatthey could not be determined [24]

33 NH3-TPD Analysis )e acidity of zeolitic materials hasan important impact on the extent of NOx reduction andNH3-TPD could be employed to analyze the acidity of Cuzeolites NH3 peaks at 134degC 194degC and 537degC were ob-served in Figure 3 for all the samples )e NH3 desorptionpeaks at 134degC were assigned to loosely bound NH3 speciesdesorption peaks at 194degC were attributed to NH3 adsorbedon Cu2+ ions and the NH3 released from the Broslashnsted acidsites was responsible for the lowest peaks observed at higherthan 500degC [25] Compared with the different coppercontent SSZ-13 zeolites the peaks presented the strongestNH3 desorption from the Cu2+ ions after Cu was loaded 4wt at 194degC )is result suggested 4 CuSSZ-13 catalysthad a higher acid strength than the other two catalysts[10 26]

)en it can be concluded that the rise of copper loadingcould contribute to adding moderate acid intensity whichcould have a promotional effect on the adsorption of NH3When the copper loading in the sample increased to 4 thestrength of acid reached the maximum With further in-creasing the Cu loading Lewis acid sites decreased )eNH3-TPD results showed that the stronger Lewis acid in the4 CuSSZ-13 catalyst possibly possess a higher activationcapacity of NH3

34 H2-TPRResults Reducibility and distribution of copperspecies in the xCuSSZ-13 catalysts were investigated by H2-TPR Figure 4 exhibi two reduction peaks of 2 CuSSZ-13and 4 CuSSZ-13 at 215degC and 413degC and shows one peakof 6 CuSSZ-13 at 193degC Peak A at 215degC was probablyrelated to the reduction of Cu2+ in the SSZ-13 zeolitestructure (CHA cages) Peak B was attributed to that the Cu+ions could be reduced to metallic Cu at 413degC It can beobserved from Figure 4 that Cu2+ and CuO reduction peakswere increased clearly when increasing the content ofcopper while no effect was observed on the reduction peakof Cu+ because of insignificant production of copper oxidespecies In addition the reduction temperature decreasedwith increasing Cu loadings indicating the redox abilityincreased with increasing Cu loadings of Cu-SSZ-13 )is

N2

AirMFC

MFCMFC

MFC

MFC

MFC

NON2

NH3N2

CO2N2

PumpCold-trap

Wat

er v

apor

Qua

rtz t

ube r

eact

or

FTIR nicolet 6700

PC

Vent

Soap film flowmeter

Figure 1 Activity evaluation simulation gas test platform

Journal of Chemistry 3

high redox ability would lead to the nonselective oxidationof NH3 resulting in a relatively poorer SCR activity and N2selectivity of Cu-SSZ-13 with high Cu contents at hightemperatures [27]

35 DRSUV-Vis UV-Vis-DRS spectra are shown in Figure 5which provided us an insight into the copper species in the SSZ-

13 zeolites )e band at approximately 810nm and around254nm could be derived from the d-d transition in isolated Cu(II) )e peak at around 254nm was assigned to the chargetransfer of O2minus⟶ Cu2+ transition from lattice oxygen theband range of 380ndash600nm could be ascribed to transition ofCuxO ([Cu-O-Cu]2+ and CuO species) And those bands ataround 560nm and above are related to the Cu2+ where

Table 1 Physical characteristics of CuSSZ-13 zeolites

Samples Specific area (m2g) Pore volume (cm3g) Pore diameter (nm)SSZ-13 553 02966 19142 CuSSZ-13 549 02875 19134 CuSSZ-13 517 02794 19026 CuSSZ-13 493 02769 1900

Inte

nsity

(au

)

4 CuSSZ-13

2 CuSSZ-13

6 CuSSZ-13

30 40 50202theta (deg)

SSZ-13

Figure 2 XRD patterns of the xCuSSZ-13 (x 2 4 6) catalysts

134

131

133

148

194

200

186

230

537

514

511

582

b

a

c

d

TCD

sign

al (a

rbu

nits)

200 300 400 500 600 700100Temperature (degC)

2 CuSSZ-13SSZ-13 4 CuSSZ-13

6 CuSSZ-13

Figure 3 NH3-TPD profile of copper-modified SSZ-13 catalysts(a) 2 CuSSZ-13 (b) 4 CuSSZ-13 (c) 6 CuSSZ-13 and (d)SSZ-13

TCD

sign

al (a

rbu

nits)

193

200

215

531

4132 CuSSZ-13

4 CuSSZ-13

6 CuSSZ-13

A B

200 300 400 500 600 700100 800Temperature (degC)

Figure 4 TPR patterns of xCuSSZ-13 (x 2 4 and 6) catalysts

205

254

269

279

805810

820

Abso

rban

ce (a

u)

400 800200 600Wavelength (nm)

2 CuSSZ-134 CuSSZ-136 CuSSZ-13

Figure 5 UV-Vis DRS spectra of the CuSSZ-13 (x 2 4 6)catalysts

4 Journal of Chemistry

electronic d-d transitions took place within a distorted octa-hedral structure in CuO particles with oxygen around it )edifferent copper contents in the catalysts could cause variationsof peaks in different degrees in the DRs UV-Vis results It wasfound that the 6 CuSSZ-13 catalyst showed the highest in-tensity at the bands of 254nm Overall this results is similar tophenomenonwith the different copper oxide contents fromH2-TPR curves due to that the band strength of copper oxidespecies increases with the content of Cu loading

36 NOx Conversion of CuZeolite Figure 6 exhibits the NOconversion of different zeolites by comparing ZSM-5 BEAand SSZ-13 CuSSZ-13 catalyst presented the highest de-NOx performance and the lowest ignition temperature andthe SCR active centers were in the form of larger number ofstable single Cu2+ in the CHA (Chabazite) cages In ad-dition CuSSZ-13 catalyst always maintained the high ac-tivity up to 520degC (NOx conversion gt98) and 2 wt CuSSZ-13 sample possessed greater activity up to full con-version at 250degC )is is because the NOx reduction wasdependent on cage structure as well as exhibiting the activewindow in an obvious broadening It was observed that forCuZSM-5 and CuBEA zeolite catalysts the low-temper-ature performance was noticeably worse and especially forCuBEA catalyst NOx conversion capability reached nearly98 at 370degC As the temperature increased the conversionrate dropped rapidly and had dropped below 80 at 470degCA catalyst had narrow active temperature window(230sim460degC) with poor performance at low temperature

In general the catalysts of copper loading on SSZ-13zeolites possessed low ignition temperature wide activewindow and good hydrothermal stability

37 Effect of Cu Loading Figure 7(a) exhibits the NOconversion of the catalysts with different Cu loadings onSSZ-13 zeolites )e samples had Cu-concentration in therange of 2sim6 wt Firstly at low-temperature (lt270degC) theNO conversion was related to copper concentration )e Cucontent from 2 wt to 6 wt improved the low-temper-ature activity and possessed lower ignition temperature Incase of 6 wt CuSSZ-13 a particular performance wasobserved when the NO conversion was around 20 at100degC whereas the NO conversion achieved highest (almost100 of NOx conversion) at 206degC When the reactiontemperature increased to 407degC obviously a decrease in theNO conversion was observed within the active windowrange 300degC As a comparison the 4 wt copper was loadedon SSZ-13 low-temperature activity to catalyst was mod-erated and the NOx conversion achieved highest at 250degC)e NO conversion was around highest at 250degC andremained high in a wide temperature range (almost 100 ofNOx conversion) When temperature increased to 460degCthe de-NOx conversions gradually decreased )is declinewas principally related to NH3 oxidation competition re-action and oxidation reaction produces NOx at hightemperature For minimum copper content catalyst (2wt) the de-NOx conversions were completely achieveduntil temperature reached 270degC with poor low-temperature

activity )erefore the copper loading was up to 4 wtwhich possessed the great de-NOx performance at low-temperatures and widest active temperature window whichhad the best comprehensive de-NOx performance In ad-dition the N2O formation should also be taken into accountFigure 7(b) displays N2O outlet concentrations at differentreaction temperatures One local maximum at 200ndash300degC isfound for each sample )e 6 CuSSZ-13 catalyst generatesthe highest N2O concentration reaching 56 ppm at 254degCthe N2O formation decreased as the copper content declinedfrom 6 to 2 over the temperature range from around 150to 350degC Although 2 CuSSZ-13 generates the lowest N2Oconcentration it is noted that there is a slight differencebetween the N2O concentration generated by 2 CuSSZ-13and 4 CuSSZ-13 which is far lower than 6 CuSSZ-13catalyst

38 Influence of Ce or Mn Doping over CuSSZ-13Figure 8 shows the NOx conversion on all the samples from50 to 600degC Doping cerium and manganese over CuSSZ-13catalysts respectively were simultaneously impregnatedBefore doping with cerium or manganese to CuSSZ-13 thepoor low temperature performance of the catalyst wasexhibited and the high light-off temperature was presentedWhether doped with cerium or manganese the low-tem-perature performance of the catalyst was significantly im-proved and the light-off temperature dropped to 167degC Cu-Mn-SSZ-13 catalyst had a better NO oxidation activitybecause doping Mn promoted the oxidation of Cu+ to Cu2+but the surface area decreased after Mn was doped [28] Cecould add the number of the isolated Cu2+ species andpromote the formation of the bidentate nitrate species [29])e addition of cerium compared with doping manganeseexhibited broadening active window at higher temperaturesand the NOx conversion reached 80 at lower temperaturewhich suggested that the influence of doping cerium over the

NO

x co

nver

sion

()

0

20

40

60

80

100

CuSSZ-13

CuZSM-5CuBEA

0 200 300 400 500 600100

Temperature (degC)

Figure 6 Comparison of SCR activity on Cu with different zeolites

Journal of Chemistry 5

catalysts was more significant Doping Ce promoted the low-temperature catalytic performance with increasing NOxreduction rate

)e doping manganese in CuSSZ-13 presented poorerresistance to hydrothermal aging as can be observed inFigure 9 )e low-temperature activity deteriorated and thelight-off temperature increased after hydrothermal aging for100 hours corresponding to active temperature windownarrowing Ce-doped sample showed the activity temper-ature window similar to the undoped sample However thedoping of Ce significantly improved the low-temperature

activity of the catalyst For example NOx conversionreached 20 at 100degC whereas the temperature increased to160degC the undoped CuSSZ-13 catalysts achieved the sameconversion )e doped Ce in catalysts maintained thestructural characteristics of the hydrothermal aging catalystsurface Compared with CuSSZ-13 catalyst the addition ofCe stabilized the copper active center and reduced the SSZ-13 structure dealuminization which kept the Cu-Ce-SSZ-13catalysts possessing excellent hydrothermal stability [28]

According to the above analysis the rare earth elementCe as an ideal molecular sieve-based SCR catalyst

NO

x co

nver

sion

()

0

20

40

60

80

100

2 CuSSZ-134 CuSSZ-136 CuSSZ-13

100 200 300 400 500 6000

Temperature (degC)

(a)

0

1

2

3

4

5

6

N2O

conc

entr

atio

n (p

pm)

2 CuSSZ-134 CuSSZ-136 CuSSZ-13

100 200 300 400 500 6000Temperature (degC)

(b)

Figure 7 (a) SCR activity of the catalysts (b) N2O concentration during NH3-SCR with xCuSSZ-13 (x 2 4 6) catalysts

100 200 300 400 500 6000

Temperature (degC)

NO

x co

nver

sion

()

0

20

40

60

80

100

CuSSZ-13Cu-CeSSZ-13Cu-MnSSZ-13

Figure 8 NOx conversion using NH3 for addition of Ce or Mn onCuSSZ-13 catalysts

NO

x co

nver

sion

()

0

20

40

60

80

100

100 200 300 400 500 6000

Temperature (degC)

CuSSZ-13-100hCu-CeSSZ-13-100hCu-MnSSZ-13-100h

Figure 9 NOx conversion after aging treatment for 100 h usingNH3 for addition of Ce or Mn on CuSSZ-13 catalysts

6 Journal of Chemistry

modification element could significantly improve the low-temperature performance of the catalyst and broaden thetemperature window

4 Conclusions

In this paper Cu-based zeolite catalysts were investigated interms of NOx conversion using NH3 under the atmospheresof N2 O2 NO NH3 CO2 and H2O It has been found thatthe zeolite topologies Cu loadings and transition metaldoping affect the catalytic performance with regard to NOxconversion)e SSZ-13 possessed a small pore and exhibitedthe optimal SCR activity because of existing high single Cu2+species in the pores

)e CuxSSZ-13 catalysts prepared with wetness im-pregnation possess dispersed Cu2+ species CuxOy clustersand CuO particles compared with 6 CuSSZ-13 and 2CuSSZ-13 4 CuSSZ-13 demonstrated the best catalyticactivity under low temperature the widest active temper-ature window and the highest comprehensive SCR de-NOxperformance Doping rare earth element Ce could effectivelyimprove the low-temperature de-NOx performance of thecatalysts and broaden the reaction temperature window

Data Availability

)e data used to support the findings of this study are in-cluded within the article

Conflicts of Interest

)e authors declare no conflicts of interest

Acknowledgments

)is research was funded by the Key Research Program ofJiangsu Province China grant number BE2016003-2

References

[1] F Liu H He C B Zhang et al ldquoSelective catalytic reductionof NO with NH3 over iron titanate catalyst catalytic per-formance and characterizationrdquo Applied Catalysis B Envi-ronmental vol 96 no 3-4 pp 408ndash420 2010

[2] P G W A Kompio A Bruckner F Hipler G AuerE Loffler and W Grunert ldquoA new view on the relationsbetween tungsten and vanadium in V2O5-WO3TiO2 catalystsfor the selective reduction of NO with NH3rdquo Journal ofCatalysis vol 286 pp 237ndash247 2012

[3] Y Dong and X Fei ldquoEffect of isopropanol on crystal growthand photocatalytic properties regulation of anatase TiO2single crystalsrdquo Materials Technology vol 35 no 2pp 102ndash111 2020

[4] I E Wachs G Deo B M Weckhuysen et al ldquoSelectivecatalytic reduction of NO with NH3 over supported vanadiacatalystsrdquo Journal of Catalysis vol 161 no 1 pp 211ndash2211996

[5] G Busca L Lietti G Ramis and F Berti ldquoChemical andmechanistic aspects of the selective catalytic reduction of NOxby ammonia over oxide catalystsrdquo Applied Catalysis B En-vironmental vol 18 no 1-2 pp 1ndash36 1998

[6] J Li H Chang L Ma J Hao and R T Yang ldquoLow-tem-perature selective catalytic reduction of NOx with NH3 overmetal oxide and zeolite catalystrdquo Catalysis Today vol 175no 1 pp 147ndash156 2011

[7] T V W Janssens H Falsig L F Lundegaard et al ldquoAconsistent reaction scheme for the selective catalytic reductionof nitrogen oxides with ammoniardquoACS Catalysis vol 5 no 5pp 2832ndash2845 2015

[8] S Brandenberger O Krocher A Tissler and R Althoff ldquo)estate of the art in selective catalytic reduction of NOx byammonia using metal-exchanged zeolite catalystsrdquo CatalysisReviews vol 50 no 4 pp 492ndash531 2008

[9] L Xie F Liu L Ren X Shi F-S Xiao and H He ldquoExcellentperformance of one-pot synthesized Cu-SSZ-13 catalyst for theselective catalytic reduction of NOx with NH3rdquo EnvironmentalScience amp Technology vol 48 no 1 pp 566ndash572 2014

[10] J Wang T Yu X Wang et al ldquo)e influence of silicon on thecatalytic properties of CuSAPO-34 for NOx reduction byammonia-SCRrdquo Applied Catalysis B Environmental vol 127pp 137ndash147 2012

[11] A Sultana T Nanba M Sasaki M Haneda K Suzuki andH Hamada ldquoSelective catalytic reduction of NOx with NH3over different copper exchanged zeolites in the presence ofdecanerdquo Catalysis Today vol 164 no 1 pp 495ndash499 2011

[12] B Chen R Xu R Zhang and N Liu ldquoEconomical way tosynthesize SSZ-13 with abundant ion-exchanged Cu+ for anextraordinary performance in selective catalytic reduction(SCR) of NOx by ammoniardquo Environmental Science ampTechnology vol 48 no 23 pp 13909ndash13916 2014

[13] P G Blakeman E M Burkholder H-Y Chen et al ldquo)e roleof pore size on the thermal stability of zeolite supported CuSCR catalystsrdquo Catalysis Today vol 231 pp 56ndash63 2014

[14] C Niu X Shi F Liu et al ldquoHigh hydrothermal stability ofCu-SAPO-34 catalysts for the NH3-SCR of NOxrdquo ChemicalEngineering Journal vol 294 pp 254ndash263 2016

[15] Y Ma X Wu J Zhang R Ran and D Weng ldquoUrea-relatedreactions and their active sites over Cu-SAPO-34 formationof NH3 and conversion of HNCOrdquo Applied Catalysis BEnvironmental vol 227 pp 198ndash208 2018

[16] C Fan Z Chen L Pang et al ldquoSteam and alkali resistant Cu-SSZ-13 catalyst for the selective catalytic reduction of NOx indiesel exhaustrdquo Chemical Engineering Journal vol 334pp 344ndash354 2018

[17] A Wang Y Wang E D Walter et al ldquoNH3-SCR on Cu Feand Cu plus Fe exchanged beta and SSZ-13 catalysts hy-drothermal aging and propylene poisoning effectsrdquo CatalysisToday vol 320 pp 91ndash99 2019

[18] J H Kwak D Tran S D Burton J Szanyi J H Lee andC H F Peden ldquoEffects of hydrothermal aging on NH3-SCRreaction over Cuzeolitesrdquo Journal of Catalysis vol 287pp 203ndash209 2012

[19] J H Kwak R G Tonkyn D H Kim J Szanyi andC H F Peden ldquoExcellent activity and selectivity of Cu-SSZ-13 in the selective catalytic reduction of NOx with NH3rdquoJournal of Catalysis vol 275 no 2 pp 187ndash190 2010

[20] G Liu W Zhang P He et al ldquoH2O andor SO2 tolerance ofCu-MnSAPO-34 catalyst for NO reduction with NH3 at low-temperaturerdquo Catalysts vol 9 no 3 p 289 2019

[21] Y Liu C Song G Lv C Lv and X Li ldquoPromotional effect ofcerium andor zirconium doping on CuZSM-5 catalysts forselective catalytic reduction of NO by NH3rdquo Catalysts vol 8no 8 p 306 2018

[22] R Zhang W Y Teoh R Amal B Chen and S KaliaguineldquoCatalytic reduction of NO by CO over CuCexZr11minusxO2

Journal of Chemistry 7

prepared by flame synthesisrdquo Journal of Catalysis vol 272no 2 pp 210ndash219 2010

[23] M L Fu X H Yue D Q Ye et al ldquoSoot oxidation via CuOdoped CeO2 catalysts prepared using coprecipitation andcitrate acid complex-combustion synthesisrdquo Catalysis Todayvol 153 no 3-4 pp 125ndash132 2010

[24] L Ma Y Cheng G Cavataio R W McCabe L Fu and J LildquoCharacterization of commercial Cu-SSZ-13 and Cu-SAPO-34 catalysts with hydrothermal treatment for NH3-SCR ofNOx in diesel exhaustrdquo Chemical Engineering Journalvol 225 pp 323ndash330 2013

[25] HWang R Xu Y Jin and R Zhang ldquoZeolite structure effectson Cu active center SCR performance and stability of Cu-zeolite catalystsrdquo Catalysis Today vol 327 pp 295ndash307 2019

[26] Y Li J Deng W Song et al ldquo)e nature of Cu species in Cu-SAPO-18 catalyst for NH3-SCR combination of experimentsand DFT calculationsrdquo Ae Journal of Physical Chemistry Cvol 120 no 27 pp 14669ndash14680 2016

[27] C Chen Y Cao S Liu J Chen and W Jia ldquo)e catalyticproperties of Cu modified attapulgite in NH3-SCO and NH3-SCR reactionsrdquoApplied Surface Science vol 480 pp 537ndash5472019

[28] C Pang Y Zhuo QWeng and Z Zhu ldquo)e promotion effectof manganese on CuSAPO for selective catalytic reduction ofNOx with NH3rdquo RSC Advances vol 8 no 11 pp 6110ndash61192018

[29] S Han J Cheng Q Ye S Cheng T Kang and H Dai ldquoCedoping to Cu-SAPO-18 enhanced catalytic performance forthe NH3-SCR of NO in simulated diesel exhaustrdquo Micropo-rous and Mesoporous Materials vol 276 pp 133ndash146 2019

8 Journal of Chemistry

)e H2-temperature programmed reduction (H2-TPR)experiments were conducted with Quantachrome Firstlypretreatment of the catalyst was performed at 500degC for30min in pure Ar atmosphere in order to remove the surfaceimpurities and then cooled to below 30degC )en the at-mosphere was switched to a 10H2N2mixtureWhen TCDbaselines become stable the temperature increased to 950degCunder the same atmosphere by a rate of 10degCmin After theexhaust was dehydrated by zeolite the hydrogen con-sumption was detected by TCD

)e UV-Vis spectroscopy was operated on a SHI-MADZU UV-2600 device to evaluate the nuclearity statusof the copper species in the zeolite with different Culoadings )e reflectance spectra ranging from 200 to900 nm (wavelength) was recorded using BaSO4 as ref-erence sample

3 Results and Discussion

31 BETAnalysis Table 1 shows the BETresults It could beseen that the purified SSZ-13 had larger surface area andaverage pore diameter and pore volume than copper-con-taining zeolites )e surface area and pore volumes ofsamples were reduced when copper was added to the zeolitewhich indicated that the internal pores of zeolites werecovered or permeated by copper species )e SSZ-13 zeoliteswere in the micropore range

32 XRD Patterns )e crystal structures and phase com-position of xCuSSZ-13 (x 2 4 6 wt) were investigatedby powdered XRDmeasurements and the XRD patterns areexhibited in Figure 2 Peaks of all samples were observed at2θ 209deg 235deg 254deg 263deg 281deg 286deg 310deg 315deg and350deg associated with typical chabazite (CHA) structure [13]Futhermore the XRD pattern of the CuSSZ-13 was notdetected for diffraction peaks of CuOx (2θ 354deg and 365deg)this observation suggested that the copper species presenteda good dispersion on the surface of the zeolite or the Culoadings in the samples used in this work were so low thatthey could not be determined [24]

33 NH3-TPD Analysis )e acidity of zeolitic materials hasan important impact on the extent of NOx reduction andNH3-TPD could be employed to analyze the acidity of Cuzeolites NH3 peaks at 134degC 194degC and 537degC were ob-served in Figure 3 for all the samples )e NH3 desorptionpeaks at 134degC were assigned to loosely bound NH3 speciesdesorption peaks at 194degC were attributed to NH3 adsorbedon Cu2+ ions and the NH3 released from the Broslashnsted acidsites was responsible for the lowest peaks observed at higherthan 500degC [25] Compared with the different coppercontent SSZ-13 zeolites the peaks presented the strongestNH3 desorption from the Cu2+ ions after Cu was loaded 4wt at 194degC )is result suggested 4 CuSSZ-13 catalysthad a higher acid strength than the other two catalysts[10 26]

)en it can be concluded that the rise of copper loadingcould contribute to adding moderate acid intensity whichcould have a promotional effect on the adsorption of NH3When the copper loading in the sample increased to 4 thestrength of acid reached the maximum With further in-creasing the Cu loading Lewis acid sites decreased )eNH3-TPD results showed that the stronger Lewis acid in the4 CuSSZ-13 catalyst possibly possess a higher activationcapacity of NH3

34 H2-TPRResults Reducibility and distribution of copperspecies in the xCuSSZ-13 catalysts were investigated by H2-TPR Figure 4 exhibi two reduction peaks of 2 CuSSZ-13and 4 CuSSZ-13 at 215degC and 413degC and shows one peakof 6 CuSSZ-13 at 193degC Peak A at 215degC was probablyrelated to the reduction of Cu2+ in the SSZ-13 zeolitestructure (CHA cages) Peak B was attributed to that the Cu+ions could be reduced to metallic Cu at 413degC It can beobserved from Figure 4 that Cu2+ and CuO reduction peakswere increased clearly when increasing the content ofcopper while no effect was observed on the reduction peakof Cu+ because of insignificant production of copper oxidespecies In addition the reduction temperature decreasedwith increasing Cu loadings indicating the redox abilityincreased with increasing Cu loadings of Cu-SSZ-13 )is

N2

AirMFC

MFCMFC

MFC

MFC

MFC

NON2

NH3N2

CO2N2

PumpCold-trap

Wat

er v

apor

Qua

rtz t

ube r

eact

or

FTIR nicolet 6700

PC

Vent

Soap film flowmeter

Figure 1 Activity evaluation simulation gas test platform

Journal of Chemistry 3

high redox ability would lead to the nonselective oxidationof NH3 resulting in a relatively poorer SCR activity and N2selectivity of Cu-SSZ-13 with high Cu contents at hightemperatures [27]

35 DRSUV-Vis UV-Vis-DRS spectra are shown in Figure 5which provided us an insight into the copper species in the SSZ-

13 zeolites )e band at approximately 810nm and around254nm could be derived from the d-d transition in isolated Cu(II) )e peak at around 254nm was assigned to the chargetransfer of O2minus⟶ Cu2+ transition from lattice oxygen theband range of 380ndash600nm could be ascribed to transition ofCuxO ([Cu-O-Cu]2+ and CuO species) And those bands ataround 560nm and above are related to the Cu2+ where

Table 1 Physical characteristics of CuSSZ-13 zeolites

Samples Specific area (m2g) Pore volume (cm3g) Pore diameter (nm)SSZ-13 553 02966 19142 CuSSZ-13 549 02875 19134 CuSSZ-13 517 02794 19026 CuSSZ-13 493 02769 1900

Inte

nsity

(au

)

4 CuSSZ-13

2 CuSSZ-13

6 CuSSZ-13

30 40 50202theta (deg)

SSZ-13

Figure 2 XRD patterns of the xCuSSZ-13 (x 2 4 6) catalysts

134

131

133

148

194

200

186

230

537

514

511

582

b

a

c

d

TCD

sign

al (a

rbu

nits)

200 300 400 500 600 700100Temperature (degC)

2 CuSSZ-13SSZ-13 4 CuSSZ-13

6 CuSSZ-13

Figure 3 NH3-TPD profile of copper-modified SSZ-13 catalysts(a) 2 CuSSZ-13 (b) 4 CuSSZ-13 (c) 6 CuSSZ-13 and (d)SSZ-13

TCD

sign

al (a

rbu

nits)

193

200

215

531

4132 CuSSZ-13

4 CuSSZ-13

6 CuSSZ-13

A B

200 300 400 500 600 700100 800Temperature (degC)

Figure 4 TPR patterns of xCuSSZ-13 (x 2 4 and 6) catalysts

205

254

269

279

805810

820

Abso

rban

ce (a

u)

400 800200 600Wavelength (nm)

2 CuSSZ-134 CuSSZ-136 CuSSZ-13

Figure 5 UV-Vis DRS spectra of the CuSSZ-13 (x 2 4 6)catalysts

4 Journal of Chemistry

electronic d-d transitions took place within a distorted octa-hedral structure in CuO particles with oxygen around it )edifferent copper contents in the catalysts could cause variationsof peaks in different degrees in the DRs UV-Vis results It wasfound that the 6 CuSSZ-13 catalyst showed the highest in-tensity at the bands of 254nm Overall this results is similar tophenomenonwith the different copper oxide contents fromH2-TPR curves due to that the band strength of copper oxidespecies increases with the content of Cu loading

36 NOx Conversion of CuZeolite Figure 6 exhibits the NOconversion of different zeolites by comparing ZSM-5 BEAand SSZ-13 CuSSZ-13 catalyst presented the highest de-NOx performance and the lowest ignition temperature andthe SCR active centers were in the form of larger number ofstable single Cu2+ in the CHA (Chabazite) cages In ad-dition CuSSZ-13 catalyst always maintained the high ac-tivity up to 520degC (NOx conversion gt98) and 2 wt CuSSZ-13 sample possessed greater activity up to full con-version at 250degC )is is because the NOx reduction wasdependent on cage structure as well as exhibiting the activewindow in an obvious broadening It was observed that forCuZSM-5 and CuBEA zeolite catalysts the low-temper-ature performance was noticeably worse and especially forCuBEA catalyst NOx conversion capability reached nearly98 at 370degC As the temperature increased the conversionrate dropped rapidly and had dropped below 80 at 470degCA catalyst had narrow active temperature window(230sim460degC) with poor performance at low temperature

In general the catalysts of copper loading on SSZ-13zeolites possessed low ignition temperature wide activewindow and good hydrothermal stability

37 Effect of Cu Loading Figure 7(a) exhibits the NOconversion of the catalysts with different Cu loadings onSSZ-13 zeolites )e samples had Cu-concentration in therange of 2sim6 wt Firstly at low-temperature (lt270degC) theNO conversion was related to copper concentration )e Cucontent from 2 wt to 6 wt improved the low-temper-ature activity and possessed lower ignition temperature Incase of 6 wt CuSSZ-13 a particular performance wasobserved when the NO conversion was around 20 at100degC whereas the NO conversion achieved highest (almost100 of NOx conversion) at 206degC When the reactiontemperature increased to 407degC obviously a decrease in theNO conversion was observed within the active windowrange 300degC As a comparison the 4 wt copper was loadedon SSZ-13 low-temperature activity to catalyst was mod-erated and the NOx conversion achieved highest at 250degC)e NO conversion was around highest at 250degC andremained high in a wide temperature range (almost 100 ofNOx conversion) When temperature increased to 460degCthe de-NOx conversions gradually decreased )is declinewas principally related to NH3 oxidation competition re-action and oxidation reaction produces NOx at hightemperature For minimum copper content catalyst (2wt) the de-NOx conversions were completely achieveduntil temperature reached 270degC with poor low-temperature

activity )erefore the copper loading was up to 4 wtwhich possessed the great de-NOx performance at low-temperatures and widest active temperature window whichhad the best comprehensive de-NOx performance In ad-dition the N2O formation should also be taken into accountFigure 7(b) displays N2O outlet concentrations at differentreaction temperatures One local maximum at 200ndash300degC isfound for each sample )e 6 CuSSZ-13 catalyst generatesthe highest N2O concentration reaching 56 ppm at 254degCthe N2O formation decreased as the copper content declinedfrom 6 to 2 over the temperature range from around 150to 350degC Although 2 CuSSZ-13 generates the lowest N2Oconcentration it is noted that there is a slight differencebetween the N2O concentration generated by 2 CuSSZ-13and 4 CuSSZ-13 which is far lower than 6 CuSSZ-13catalyst

38 Influence of Ce or Mn Doping over CuSSZ-13Figure 8 shows the NOx conversion on all the samples from50 to 600degC Doping cerium and manganese over CuSSZ-13catalysts respectively were simultaneously impregnatedBefore doping with cerium or manganese to CuSSZ-13 thepoor low temperature performance of the catalyst wasexhibited and the high light-off temperature was presentedWhether doped with cerium or manganese the low-tem-perature performance of the catalyst was significantly im-proved and the light-off temperature dropped to 167degC Cu-Mn-SSZ-13 catalyst had a better NO oxidation activitybecause doping Mn promoted the oxidation of Cu+ to Cu2+but the surface area decreased after Mn was doped [28] Cecould add the number of the isolated Cu2+ species andpromote the formation of the bidentate nitrate species [29])e addition of cerium compared with doping manganeseexhibited broadening active window at higher temperaturesand the NOx conversion reached 80 at lower temperaturewhich suggested that the influence of doping cerium over the

NO

x co

nver

sion

()

0

20

40

60

80

100

CuSSZ-13

CuZSM-5CuBEA

0 200 300 400 500 600100

Temperature (degC)

Figure 6 Comparison of SCR activity on Cu with different zeolites

Journal of Chemistry 5

catalysts was more significant Doping Ce promoted the low-temperature catalytic performance with increasing NOxreduction rate

)e doping manganese in CuSSZ-13 presented poorerresistance to hydrothermal aging as can be observed inFigure 9 )e low-temperature activity deteriorated and thelight-off temperature increased after hydrothermal aging for100 hours corresponding to active temperature windownarrowing Ce-doped sample showed the activity temper-ature window similar to the undoped sample However thedoping of Ce significantly improved the low-temperature

activity of the catalyst For example NOx conversionreached 20 at 100degC whereas the temperature increased to160degC the undoped CuSSZ-13 catalysts achieved the sameconversion )e doped Ce in catalysts maintained thestructural characteristics of the hydrothermal aging catalystsurface Compared with CuSSZ-13 catalyst the addition ofCe stabilized the copper active center and reduced the SSZ-13 structure dealuminization which kept the Cu-Ce-SSZ-13catalysts possessing excellent hydrothermal stability [28]

According to the above analysis the rare earth elementCe as an ideal molecular sieve-based SCR catalyst

NO

x co

nver

sion

()

0

20

40

60

80

100

2 CuSSZ-134 CuSSZ-136 CuSSZ-13

100 200 300 400 500 6000

Temperature (degC)

(a)

0

1

2

3

4

5

6

N2O

conc

entr

atio

n (p

pm)

2 CuSSZ-134 CuSSZ-136 CuSSZ-13

100 200 300 400 500 6000Temperature (degC)

(b)

Figure 7 (a) SCR activity of the catalysts (b) N2O concentration during NH3-SCR with xCuSSZ-13 (x 2 4 6) catalysts

100 200 300 400 500 6000

Temperature (degC)

NO

x co

nver

sion

()

0

20

40

60

80

100

CuSSZ-13Cu-CeSSZ-13Cu-MnSSZ-13

Figure 8 NOx conversion using NH3 for addition of Ce or Mn onCuSSZ-13 catalysts

NO

x co

nver

sion

()

0

20

40

60

80

100

100 200 300 400 500 6000

Temperature (degC)

CuSSZ-13-100hCu-CeSSZ-13-100hCu-MnSSZ-13-100h

Figure 9 NOx conversion after aging treatment for 100 h usingNH3 for addition of Ce or Mn on CuSSZ-13 catalysts

6 Journal of Chemistry

modification element could significantly improve the low-temperature performance of the catalyst and broaden thetemperature window

4 Conclusions

In this paper Cu-based zeolite catalysts were investigated interms of NOx conversion using NH3 under the atmospheresof N2 O2 NO NH3 CO2 and H2O It has been found thatthe zeolite topologies Cu loadings and transition metaldoping affect the catalytic performance with regard to NOxconversion)e SSZ-13 possessed a small pore and exhibitedthe optimal SCR activity because of existing high single Cu2+species in the pores

)e CuxSSZ-13 catalysts prepared with wetness im-pregnation possess dispersed Cu2+ species CuxOy clustersand CuO particles compared with 6 CuSSZ-13 and 2CuSSZ-13 4 CuSSZ-13 demonstrated the best catalyticactivity under low temperature the widest active temper-ature window and the highest comprehensive SCR de-NOxperformance Doping rare earth element Ce could effectivelyimprove the low-temperature de-NOx performance of thecatalysts and broaden the reaction temperature window

Data Availability

)e data used to support the findings of this study are in-cluded within the article

Conflicts of Interest

)e authors declare no conflicts of interest

Acknowledgments

)is research was funded by the Key Research Program ofJiangsu Province China grant number BE2016003-2

References

[1] F Liu H He C B Zhang et al ldquoSelective catalytic reductionof NO with NH3 over iron titanate catalyst catalytic per-formance and characterizationrdquo Applied Catalysis B Envi-ronmental vol 96 no 3-4 pp 408ndash420 2010

[2] P G W A Kompio A Bruckner F Hipler G AuerE Loffler and W Grunert ldquoA new view on the relationsbetween tungsten and vanadium in V2O5-WO3TiO2 catalystsfor the selective reduction of NO with NH3rdquo Journal ofCatalysis vol 286 pp 237ndash247 2012

[3] Y Dong and X Fei ldquoEffect of isopropanol on crystal growthand photocatalytic properties regulation of anatase TiO2single crystalsrdquo Materials Technology vol 35 no 2pp 102ndash111 2020

[4] I E Wachs G Deo B M Weckhuysen et al ldquoSelectivecatalytic reduction of NO with NH3 over supported vanadiacatalystsrdquo Journal of Catalysis vol 161 no 1 pp 211ndash2211996

[5] G Busca L Lietti G Ramis and F Berti ldquoChemical andmechanistic aspects of the selective catalytic reduction of NOxby ammonia over oxide catalystsrdquo Applied Catalysis B En-vironmental vol 18 no 1-2 pp 1ndash36 1998

[6] J Li H Chang L Ma J Hao and R T Yang ldquoLow-tem-perature selective catalytic reduction of NOx with NH3 overmetal oxide and zeolite catalystrdquo Catalysis Today vol 175no 1 pp 147ndash156 2011

[7] T V W Janssens H Falsig L F Lundegaard et al ldquoAconsistent reaction scheme for the selective catalytic reductionof nitrogen oxides with ammoniardquoACS Catalysis vol 5 no 5pp 2832ndash2845 2015

[8] S Brandenberger O Krocher A Tissler and R Althoff ldquo)estate of the art in selective catalytic reduction of NOx byammonia using metal-exchanged zeolite catalystsrdquo CatalysisReviews vol 50 no 4 pp 492ndash531 2008

[9] L Xie F Liu L Ren X Shi F-S Xiao and H He ldquoExcellentperformance of one-pot synthesized Cu-SSZ-13 catalyst for theselective catalytic reduction of NOx with NH3rdquo EnvironmentalScience amp Technology vol 48 no 1 pp 566ndash572 2014

[10] J Wang T Yu X Wang et al ldquo)e influence of silicon on thecatalytic properties of CuSAPO-34 for NOx reduction byammonia-SCRrdquo Applied Catalysis B Environmental vol 127pp 137ndash147 2012

[11] A Sultana T Nanba M Sasaki M Haneda K Suzuki andH Hamada ldquoSelective catalytic reduction of NOx with NH3over different copper exchanged zeolites in the presence ofdecanerdquo Catalysis Today vol 164 no 1 pp 495ndash499 2011

[12] B Chen R Xu R Zhang and N Liu ldquoEconomical way tosynthesize SSZ-13 with abundant ion-exchanged Cu+ for anextraordinary performance in selective catalytic reduction(SCR) of NOx by ammoniardquo Environmental Science ampTechnology vol 48 no 23 pp 13909ndash13916 2014

[13] P G Blakeman E M Burkholder H-Y Chen et al ldquo)e roleof pore size on the thermal stability of zeolite supported CuSCR catalystsrdquo Catalysis Today vol 231 pp 56ndash63 2014

[14] C Niu X Shi F Liu et al ldquoHigh hydrothermal stability ofCu-SAPO-34 catalysts for the NH3-SCR of NOxrdquo ChemicalEngineering Journal vol 294 pp 254ndash263 2016

[15] Y Ma X Wu J Zhang R Ran and D Weng ldquoUrea-relatedreactions and their active sites over Cu-SAPO-34 formationof NH3 and conversion of HNCOrdquo Applied Catalysis BEnvironmental vol 227 pp 198ndash208 2018

[16] C Fan Z Chen L Pang et al ldquoSteam and alkali resistant Cu-SSZ-13 catalyst for the selective catalytic reduction of NOx indiesel exhaustrdquo Chemical Engineering Journal vol 334pp 344ndash354 2018

[17] A Wang Y Wang E D Walter et al ldquoNH3-SCR on Cu Feand Cu plus Fe exchanged beta and SSZ-13 catalysts hy-drothermal aging and propylene poisoning effectsrdquo CatalysisToday vol 320 pp 91ndash99 2019

[18] J H Kwak D Tran S D Burton J Szanyi J H Lee andC H F Peden ldquoEffects of hydrothermal aging on NH3-SCRreaction over Cuzeolitesrdquo Journal of Catalysis vol 287pp 203ndash209 2012

[19] J H Kwak R G Tonkyn D H Kim J Szanyi andC H F Peden ldquoExcellent activity and selectivity of Cu-SSZ-13 in the selective catalytic reduction of NOx with NH3rdquoJournal of Catalysis vol 275 no 2 pp 187ndash190 2010

[20] G Liu W Zhang P He et al ldquoH2O andor SO2 tolerance ofCu-MnSAPO-34 catalyst for NO reduction with NH3 at low-temperaturerdquo Catalysts vol 9 no 3 p 289 2019

[21] Y Liu C Song G Lv C Lv and X Li ldquoPromotional effect ofcerium andor zirconium doping on CuZSM-5 catalysts forselective catalytic reduction of NO by NH3rdquo Catalysts vol 8no 8 p 306 2018

[22] R Zhang W Y Teoh R Amal B Chen and S KaliaguineldquoCatalytic reduction of NO by CO over CuCexZr11minusxO2

Journal of Chemistry 7

prepared by flame synthesisrdquo Journal of Catalysis vol 272no 2 pp 210ndash219 2010

[23] M L Fu X H Yue D Q Ye et al ldquoSoot oxidation via CuOdoped CeO2 catalysts prepared using coprecipitation andcitrate acid complex-combustion synthesisrdquo Catalysis Todayvol 153 no 3-4 pp 125ndash132 2010

[24] L Ma Y Cheng G Cavataio R W McCabe L Fu and J LildquoCharacterization of commercial Cu-SSZ-13 and Cu-SAPO-34 catalysts with hydrothermal treatment for NH3-SCR ofNOx in diesel exhaustrdquo Chemical Engineering Journalvol 225 pp 323ndash330 2013

[25] HWang R Xu Y Jin and R Zhang ldquoZeolite structure effectson Cu active center SCR performance and stability of Cu-zeolite catalystsrdquo Catalysis Today vol 327 pp 295ndash307 2019

[26] Y Li J Deng W Song et al ldquo)e nature of Cu species in Cu-SAPO-18 catalyst for NH3-SCR combination of experimentsand DFT calculationsrdquo Ae Journal of Physical Chemistry Cvol 120 no 27 pp 14669ndash14680 2016

[27] C Chen Y Cao S Liu J Chen and W Jia ldquo)e catalyticproperties of Cu modified attapulgite in NH3-SCO and NH3-SCR reactionsrdquoApplied Surface Science vol 480 pp 537ndash5472019

[28] C Pang Y Zhuo QWeng and Z Zhu ldquo)e promotion effectof manganese on CuSAPO for selective catalytic reduction ofNOx with NH3rdquo RSC Advances vol 8 no 11 pp 6110ndash61192018

[29] S Han J Cheng Q Ye S Cheng T Kang and H Dai ldquoCedoping to Cu-SAPO-18 enhanced catalytic performance forthe NH3-SCR of NO in simulated diesel exhaustrdquo Micropo-rous and Mesoporous Materials vol 276 pp 133ndash146 2019

8 Journal of Chemistry

high redox ability would lead to the nonselective oxidationof NH3 resulting in a relatively poorer SCR activity and N2selectivity of Cu-SSZ-13 with high Cu contents at hightemperatures [27]

35 DRSUV-Vis UV-Vis-DRS spectra are shown in Figure 5which provided us an insight into the copper species in the SSZ-

13 zeolites )e band at approximately 810nm and around254nm could be derived from the d-d transition in isolated Cu(II) )e peak at around 254nm was assigned to the chargetransfer of O2minus⟶ Cu2+ transition from lattice oxygen theband range of 380ndash600nm could be ascribed to transition ofCuxO ([Cu-O-Cu]2+ and CuO species) And those bands ataround 560nm and above are related to the Cu2+ where

Table 1 Physical characteristics of CuSSZ-13 zeolites

Samples Specific area (m2g) Pore volume (cm3g) Pore diameter (nm)SSZ-13 553 02966 19142 CuSSZ-13 549 02875 19134 CuSSZ-13 517 02794 19026 CuSSZ-13 493 02769 1900

Inte

nsity

(au

)

4 CuSSZ-13

2 CuSSZ-13

6 CuSSZ-13

30 40 50202theta (deg)

SSZ-13

Figure 2 XRD patterns of the xCuSSZ-13 (x 2 4 6) catalysts

134

131

133

148

194

200

186

230

537

514

511

582

b

a

c

d

TCD

sign

al (a

rbu

nits)

200 300 400 500 600 700100Temperature (degC)

2 CuSSZ-13SSZ-13 4 CuSSZ-13

6 CuSSZ-13

Figure 3 NH3-TPD profile of copper-modified SSZ-13 catalysts(a) 2 CuSSZ-13 (b) 4 CuSSZ-13 (c) 6 CuSSZ-13 and (d)SSZ-13

TCD

sign

al (a

rbu

nits)

193

200

215

531

4132 CuSSZ-13

4 CuSSZ-13

6 CuSSZ-13

A B

200 300 400 500 600 700100 800Temperature (degC)

Figure 4 TPR patterns of xCuSSZ-13 (x 2 4 and 6) catalysts

205

254

269

279

805810

820

Abso

rban

ce (a

u)

400 800200 600Wavelength (nm)

2 CuSSZ-134 CuSSZ-136 CuSSZ-13

Figure 5 UV-Vis DRS spectra of the CuSSZ-13 (x 2 4 6)catalysts

4 Journal of Chemistry

electronic d-d transitions took place within a distorted octa-hedral structure in CuO particles with oxygen around it )edifferent copper contents in the catalysts could cause variationsof peaks in different degrees in the DRs UV-Vis results It wasfound that the 6 CuSSZ-13 catalyst showed the highest in-tensity at the bands of 254nm Overall this results is similar tophenomenonwith the different copper oxide contents fromH2-TPR curves due to that the band strength of copper oxidespecies increases with the content of Cu loading

36 NOx Conversion of CuZeolite Figure 6 exhibits the NOconversion of different zeolites by comparing ZSM-5 BEAand SSZ-13 CuSSZ-13 catalyst presented the highest de-NOx performance and the lowest ignition temperature andthe SCR active centers were in the form of larger number ofstable single Cu2+ in the CHA (Chabazite) cages In ad-dition CuSSZ-13 catalyst always maintained the high ac-tivity up to 520degC (NOx conversion gt98) and 2 wt CuSSZ-13 sample possessed greater activity up to full con-version at 250degC )is is because the NOx reduction wasdependent on cage structure as well as exhibiting the activewindow in an obvious broadening It was observed that forCuZSM-5 and CuBEA zeolite catalysts the low-temper-ature performance was noticeably worse and especially forCuBEA catalyst NOx conversion capability reached nearly98 at 370degC As the temperature increased the conversionrate dropped rapidly and had dropped below 80 at 470degCA catalyst had narrow active temperature window(230sim460degC) with poor performance at low temperature

In general the catalysts of copper loading on SSZ-13zeolites possessed low ignition temperature wide activewindow and good hydrothermal stability

37 Effect of Cu Loading Figure 7(a) exhibits the NOconversion of the catalysts with different Cu loadings onSSZ-13 zeolites )e samples had Cu-concentration in therange of 2sim6 wt Firstly at low-temperature (lt270degC) theNO conversion was related to copper concentration )e Cucontent from 2 wt to 6 wt improved the low-temper-ature activity and possessed lower ignition temperature Incase of 6 wt CuSSZ-13 a particular performance wasobserved when the NO conversion was around 20 at100degC whereas the NO conversion achieved highest (almost100 of NOx conversion) at 206degC When the reactiontemperature increased to 407degC obviously a decrease in theNO conversion was observed within the active windowrange 300degC As a comparison the 4 wt copper was loadedon SSZ-13 low-temperature activity to catalyst was mod-erated and the NOx conversion achieved highest at 250degC)e NO conversion was around highest at 250degC andremained high in a wide temperature range (almost 100 ofNOx conversion) When temperature increased to 460degCthe de-NOx conversions gradually decreased )is declinewas principally related to NH3 oxidation competition re-action and oxidation reaction produces NOx at hightemperature For minimum copper content catalyst (2wt) the de-NOx conversions were completely achieveduntil temperature reached 270degC with poor low-temperature

activity )erefore the copper loading was up to 4 wtwhich possessed the great de-NOx performance at low-temperatures and widest active temperature window whichhad the best comprehensive de-NOx performance In ad-dition the N2O formation should also be taken into accountFigure 7(b) displays N2O outlet concentrations at differentreaction temperatures One local maximum at 200ndash300degC isfound for each sample )e 6 CuSSZ-13 catalyst generatesthe highest N2O concentration reaching 56 ppm at 254degCthe N2O formation decreased as the copper content declinedfrom 6 to 2 over the temperature range from around 150to 350degC Although 2 CuSSZ-13 generates the lowest N2Oconcentration it is noted that there is a slight differencebetween the N2O concentration generated by 2 CuSSZ-13and 4 CuSSZ-13 which is far lower than 6 CuSSZ-13catalyst

38 Influence of Ce or Mn Doping over CuSSZ-13Figure 8 shows the NOx conversion on all the samples from50 to 600degC Doping cerium and manganese over CuSSZ-13catalysts respectively were simultaneously impregnatedBefore doping with cerium or manganese to CuSSZ-13 thepoor low temperature performance of the catalyst wasexhibited and the high light-off temperature was presentedWhether doped with cerium or manganese the low-tem-perature performance of the catalyst was significantly im-proved and the light-off temperature dropped to 167degC Cu-Mn-SSZ-13 catalyst had a better NO oxidation activitybecause doping Mn promoted the oxidation of Cu+ to Cu2+but the surface area decreased after Mn was doped [28] Cecould add the number of the isolated Cu2+ species andpromote the formation of the bidentate nitrate species [29])e addition of cerium compared with doping manganeseexhibited broadening active window at higher temperaturesand the NOx conversion reached 80 at lower temperaturewhich suggested that the influence of doping cerium over the

NO

x co

nver

sion

()

0

20

40

60

80

100

CuSSZ-13

CuZSM-5CuBEA

0 200 300 400 500 600100

Temperature (degC)

Figure 6 Comparison of SCR activity on Cu with different zeolites

Journal of Chemistry 5

catalysts was more significant Doping Ce promoted the low-temperature catalytic performance with increasing NOxreduction rate

)e doping manganese in CuSSZ-13 presented poorerresistance to hydrothermal aging as can be observed inFigure 9 )e low-temperature activity deteriorated and thelight-off temperature increased after hydrothermal aging for100 hours corresponding to active temperature windownarrowing Ce-doped sample showed the activity temper-ature window similar to the undoped sample However thedoping of Ce significantly improved the low-temperature

activity of the catalyst For example NOx conversionreached 20 at 100degC whereas the temperature increased to160degC the undoped CuSSZ-13 catalysts achieved the sameconversion )e doped Ce in catalysts maintained thestructural characteristics of the hydrothermal aging catalystsurface Compared with CuSSZ-13 catalyst the addition ofCe stabilized the copper active center and reduced the SSZ-13 structure dealuminization which kept the Cu-Ce-SSZ-13catalysts possessing excellent hydrothermal stability [28]

According to the above analysis the rare earth elementCe as an ideal molecular sieve-based SCR catalyst

NO

x co

nver

sion

()

0

20

40

60

80

100

2 CuSSZ-134 CuSSZ-136 CuSSZ-13

100 200 300 400 500 6000

Temperature (degC)

(a)

0

1

2

3

4

5

6

N2O

conc

entr

atio

n (p

pm)

2 CuSSZ-134 CuSSZ-136 CuSSZ-13

100 200 300 400 500 6000Temperature (degC)

(b)

Figure 7 (a) SCR activity of the catalysts (b) N2O concentration during NH3-SCR with xCuSSZ-13 (x 2 4 6) catalysts

100 200 300 400 500 6000

Temperature (degC)

NO

x co

nver

sion

()

0

20

40

60

80

100

CuSSZ-13Cu-CeSSZ-13Cu-MnSSZ-13

Figure 8 NOx conversion using NH3 for addition of Ce or Mn onCuSSZ-13 catalysts

NO

x co

nver

sion

()

0

20

40

60

80

100

100 200 300 400 500 6000

Temperature (degC)

CuSSZ-13-100hCu-CeSSZ-13-100hCu-MnSSZ-13-100h

Figure 9 NOx conversion after aging treatment for 100 h usingNH3 for addition of Ce or Mn on CuSSZ-13 catalysts

6 Journal of Chemistry

modification element could significantly improve the low-temperature performance of the catalyst and broaden thetemperature window

4 Conclusions

In this paper Cu-based zeolite catalysts were investigated interms of NOx conversion using NH3 under the atmospheresof N2 O2 NO NH3 CO2 and H2O It has been found thatthe zeolite topologies Cu loadings and transition metaldoping affect the catalytic performance with regard to NOxconversion)e SSZ-13 possessed a small pore and exhibitedthe optimal SCR activity because of existing high single Cu2+species in the pores

)e CuxSSZ-13 catalysts prepared with wetness im-pregnation possess dispersed Cu2+ species CuxOy clustersand CuO particles compared with 6 CuSSZ-13 and 2CuSSZ-13 4 CuSSZ-13 demonstrated the best catalyticactivity under low temperature the widest active temper-ature window and the highest comprehensive SCR de-NOxperformance Doping rare earth element Ce could effectivelyimprove the low-temperature de-NOx performance of thecatalysts and broaden the reaction temperature window

Data Availability

)e data used to support the findings of this study are in-cluded within the article

Conflicts of Interest

)e authors declare no conflicts of interest

Acknowledgments

)is research was funded by the Key Research Program ofJiangsu Province China grant number BE2016003-2

References

[1] F Liu H He C B Zhang et al ldquoSelective catalytic reductionof NO with NH3 over iron titanate catalyst catalytic per-formance and characterizationrdquo Applied Catalysis B Envi-ronmental vol 96 no 3-4 pp 408ndash420 2010

[2] P G W A Kompio A Bruckner F Hipler G AuerE Loffler and W Grunert ldquoA new view on the relationsbetween tungsten and vanadium in V2O5-WO3TiO2 catalystsfor the selective reduction of NO with NH3rdquo Journal ofCatalysis vol 286 pp 237ndash247 2012

[3] Y Dong and X Fei ldquoEffect of isopropanol on crystal growthand photocatalytic properties regulation of anatase TiO2single crystalsrdquo Materials Technology vol 35 no 2pp 102ndash111 2020

[4] I E Wachs G Deo B M Weckhuysen et al ldquoSelectivecatalytic reduction of NO with NH3 over supported vanadiacatalystsrdquo Journal of Catalysis vol 161 no 1 pp 211ndash2211996

[5] G Busca L Lietti G Ramis and F Berti ldquoChemical andmechanistic aspects of the selective catalytic reduction of NOxby ammonia over oxide catalystsrdquo Applied Catalysis B En-vironmental vol 18 no 1-2 pp 1ndash36 1998

[6] J Li H Chang L Ma J Hao and R T Yang ldquoLow-tem-perature selective catalytic reduction of NOx with NH3 overmetal oxide and zeolite catalystrdquo Catalysis Today vol 175no 1 pp 147ndash156 2011

[7] T V W Janssens H Falsig L F Lundegaard et al ldquoAconsistent reaction scheme for the selective catalytic reductionof nitrogen oxides with ammoniardquoACS Catalysis vol 5 no 5pp 2832ndash2845 2015

[8] S Brandenberger O Krocher A Tissler and R Althoff ldquo)estate of the art in selective catalytic reduction of NOx byammonia using metal-exchanged zeolite catalystsrdquo CatalysisReviews vol 50 no 4 pp 492ndash531 2008

[9] L Xie F Liu L Ren X Shi F-S Xiao and H He ldquoExcellentperformance of one-pot synthesized Cu-SSZ-13 catalyst for theselective catalytic reduction of NOx with NH3rdquo EnvironmentalScience amp Technology vol 48 no 1 pp 566ndash572 2014

[10] J Wang T Yu X Wang et al ldquo)e influence of silicon on thecatalytic properties of CuSAPO-34 for NOx reduction byammonia-SCRrdquo Applied Catalysis B Environmental vol 127pp 137ndash147 2012

[11] A Sultana T Nanba M Sasaki M Haneda K Suzuki andH Hamada ldquoSelective catalytic reduction of NOx with NH3over different copper exchanged zeolites in the presence ofdecanerdquo Catalysis Today vol 164 no 1 pp 495ndash499 2011

[12] B Chen R Xu R Zhang and N Liu ldquoEconomical way tosynthesize SSZ-13 with abundant ion-exchanged Cu+ for anextraordinary performance in selective catalytic reduction(SCR) of NOx by ammoniardquo Environmental Science ampTechnology vol 48 no 23 pp 13909ndash13916 2014

[13] P G Blakeman E M Burkholder H-Y Chen et al ldquo)e roleof pore size on the thermal stability of zeolite supported CuSCR catalystsrdquo Catalysis Today vol 231 pp 56ndash63 2014

[14] C Niu X Shi F Liu et al ldquoHigh hydrothermal stability ofCu-SAPO-34 catalysts for the NH3-SCR of NOxrdquo ChemicalEngineering Journal vol 294 pp 254ndash263 2016

[15] Y Ma X Wu J Zhang R Ran and D Weng ldquoUrea-relatedreactions and their active sites over Cu-SAPO-34 formationof NH3 and conversion of HNCOrdquo Applied Catalysis BEnvironmental vol 227 pp 198ndash208 2018

[16] C Fan Z Chen L Pang et al ldquoSteam and alkali resistant Cu-SSZ-13 catalyst for the selective catalytic reduction of NOx indiesel exhaustrdquo Chemical Engineering Journal vol 334pp 344ndash354 2018

[17] A Wang Y Wang E D Walter et al ldquoNH3-SCR on Cu Feand Cu plus Fe exchanged beta and SSZ-13 catalysts hy-drothermal aging and propylene poisoning effectsrdquo CatalysisToday vol 320 pp 91ndash99 2019

[18] J H Kwak D Tran S D Burton J Szanyi J H Lee andC H F Peden ldquoEffects of hydrothermal aging on NH3-SCRreaction over Cuzeolitesrdquo Journal of Catalysis vol 287pp 203ndash209 2012

[19] J H Kwak R G Tonkyn D H Kim J Szanyi andC H F Peden ldquoExcellent activity and selectivity of Cu-SSZ-13 in the selective catalytic reduction of NOx with NH3rdquoJournal of Catalysis vol 275 no 2 pp 187ndash190 2010

[20] G Liu W Zhang P He et al ldquoH2O andor SO2 tolerance ofCu-MnSAPO-34 catalyst for NO reduction with NH3 at low-temperaturerdquo Catalysts vol 9 no 3 p 289 2019

[21] Y Liu C Song G Lv C Lv and X Li ldquoPromotional effect ofcerium andor zirconium doping on CuZSM-5 catalysts forselective catalytic reduction of NO by NH3rdquo Catalysts vol 8no 8 p 306 2018

[22] R Zhang W Y Teoh R Amal B Chen and S KaliaguineldquoCatalytic reduction of NO by CO over CuCexZr11minusxO2

Journal of Chemistry 7

prepared by flame synthesisrdquo Journal of Catalysis vol 272no 2 pp 210ndash219 2010

[23] M L Fu X H Yue D Q Ye et al ldquoSoot oxidation via CuOdoped CeO2 catalysts prepared using coprecipitation andcitrate acid complex-combustion synthesisrdquo Catalysis Todayvol 153 no 3-4 pp 125ndash132 2010

[24] L Ma Y Cheng G Cavataio R W McCabe L Fu and J LildquoCharacterization of commercial Cu-SSZ-13 and Cu-SAPO-34 catalysts with hydrothermal treatment for NH3-SCR ofNOx in diesel exhaustrdquo Chemical Engineering Journalvol 225 pp 323ndash330 2013

[25] HWang R Xu Y Jin and R Zhang ldquoZeolite structure effectson Cu active center SCR performance and stability of Cu-zeolite catalystsrdquo Catalysis Today vol 327 pp 295ndash307 2019

[26] Y Li J Deng W Song et al ldquo)e nature of Cu species in Cu-SAPO-18 catalyst for NH3-SCR combination of experimentsand DFT calculationsrdquo Ae Journal of Physical Chemistry Cvol 120 no 27 pp 14669ndash14680 2016

[27] C Chen Y Cao S Liu J Chen and W Jia ldquo)e catalyticproperties of Cu modified attapulgite in NH3-SCO and NH3-SCR reactionsrdquoApplied Surface Science vol 480 pp 537ndash5472019

[28] C Pang Y Zhuo QWeng and Z Zhu ldquo)e promotion effectof manganese on CuSAPO for selective catalytic reduction ofNOx with NH3rdquo RSC Advances vol 8 no 11 pp 6110ndash61192018

[29] S Han J Cheng Q Ye S Cheng T Kang and H Dai ldquoCedoping to Cu-SAPO-18 enhanced catalytic performance forthe NH3-SCR of NO in simulated diesel exhaustrdquo Micropo-rous and Mesoporous Materials vol 276 pp 133ndash146 2019

8 Journal of Chemistry

electronic d-d transitions took place within a distorted octa-hedral structure in CuO particles with oxygen around it )edifferent copper contents in the catalysts could cause variationsof peaks in different degrees in the DRs UV-Vis results It wasfound that the 6 CuSSZ-13 catalyst showed the highest in-tensity at the bands of 254nm Overall this results is similar tophenomenonwith the different copper oxide contents fromH2-TPR curves due to that the band strength of copper oxidespecies increases with the content of Cu loading

36 NOx Conversion of CuZeolite Figure 6 exhibits the NOconversion of different zeolites by comparing ZSM-5 BEAand SSZ-13 CuSSZ-13 catalyst presented the highest de-NOx performance and the lowest ignition temperature andthe SCR active centers were in the form of larger number ofstable single Cu2+ in the CHA (Chabazite) cages In ad-dition CuSSZ-13 catalyst always maintained the high ac-tivity up to 520degC (NOx conversion gt98) and 2 wt CuSSZ-13 sample possessed greater activity up to full con-version at 250degC )is is because the NOx reduction wasdependent on cage structure as well as exhibiting the activewindow in an obvious broadening It was observed that forCuZSM-5 and CuBEA zeolite catalysts the low-temper-ature performance was noticeably worse and especially forCuBEA catalyst NOx conversion capability reached nearly98 at 370degC As the temperature increased the conversionrate dropped rapidly and had dropped below 80 at 470degCA catalyst had narrow active temperature window(230sim460degC) with poor performance at low temperature

In general the catalysts of copper loading on SSZ-13zeolites possessed low ignition temperature wide activewindow and good hydrothermal stability

37 Effect of Cu Loading Figure 7(a) exhibits the NOconversion of the catalysts with different Cu loadings onSSZ-13 zeolites )e samples had Cu-concentration in therange of 2sim6 wt Firstly at low-temperature (lt270degC) theNO conversion was related to copper concentration )e Cucontent from 2 wt to 6 wt improved the low-temper-ature activity and possessed lower ignition temperature Incase of 6 wt CuSSZ-13 a particular performance wasobserved when the NO conversion was around 20 at100degC whereas the NO conversion achieved highest (almost100 of NOx conversion) at 206degC When the reactiontemperature increased to 407degC obviously a decrease in theNO conversion was observed within the active windowrange 300degC As a comparison the 4 wt copper was loadedon SSZ-13 low-temperature activity to catalyst was mod-erated and the NOx conversion achieved highest at 250degC)e NO conversion was around highest at 250degC andremained high in a wide temperature range (almost 100 ofNOx conversion) When temperature increased to 460degCthe de-NOx conversions gradually decreased )is declinewas principally related to NH3 oxidation competition re-action and oxidation reaction produces NOx at hightemperature For minimum copper content catalyst (2wt) the de-NOx conversions were completely achieveduntil temperature reached 270degC with poor low-temperature

activity )erefore the copper loading was up to 4 wtwhich possessed the great de-NOx performance at low-temperatures and widest active temperature window whichhad the best comprehensive de-NOx performance In ad-dition the N2O formation should also be taken into accountFigure 7(b) displays N2O outlet concentrations at differentreaction temperatures One local maximum at 200ndash300degC isfound for each sample )e 6 CuSSZ-13 catalyst generatesthe highest N2O concentration reaching 56 ppm at 254degCthe N2O formation decreased as the copper content declinedfrom 6 to 2 over the temperature range from around 150to 350degC Although 2 CuSSZ-13 generates the lowest N2Oconcentration it is noted that there is a slight differencebetween the N2O concentration generated by 2 CuSSZ-13and 4 CuSSZ-13 which is far lower than 6 CuSSZ-13catalyst

38 Influence of Ce or Mn Doping over CuSSZ-13Figure 8 shows the NOx conversion on all the samples from50 to 600degC Doping cerium and manganese over CuSSZ-13catalysts respectively were simultaneously impregnatedBefore doping with cerium or manganese to CuSSZ-13 thepoor low temperature performance of the catalyst wasexhibited and the high light-off temperature was presentedWhether doped with cerium or manganese the low-tem-perature performance of the catalyst was significantly im-proved and the light-off temperature dropped to 167degC Cu-Mn-SSZ-13 catalyst had a better NO oxidation activitybecause doping Mn promoted the oxidation of Cu+ to Cu2+but the surface area decreased after Mn was doped [28] Cecould add the number of the isolated Cu2+ species andpromote the formation of the bidentate nitrate species [29])e addition of cerium compared with doping manganeseexhibited broadening active window at higher temperaturesand the NOx conversion reached 80 at lower temperaturewhich suggested that the influence of doping cerium over the

NO

x co

nver

sion

()

0

20

40

60

80

100

CuSSZ-13

CuZSM-5CuBEA

0 200 300 400 500 600100

Temperature (degC)

Figure 6 Comparison of SCR activity on Cu with different zeolites

Journal of Chemistry 5

catalysts was more significant Doping Ce promoted the low-temperature catalytic performance with increasing NOxreduction rate

)e doping manganese in CuSSZ-13 presented poorerresistance to hydrothermal aging as can be observed inFigure 9 )e low-temperature activity deteriorated and thelight-off temperature increased after hydrothermal aging for100 hours corresponding to active temperature windownarrowing Ce-doped sample showed the activity temper-ature window similar to the undoped sample However thedoping of Ce significantly improved the low-temperature

activity of the catalyst For example NOx conversionreached 20 at 100degC whereas the temperature increased to160degC the undoped CuSSZ-13 catalysts achieved the sameconversion )e doped Ce in catalysts maintained thestructural characteristics of the hydrothermal aging catalystsurface Compared with CuSSZ-13 catalyst the addition ofCe stabilized the copper active center and reduced the SSZ-13 structure dealuminization which kept the Cu-Ce-SSZ-13catalysts possessing excellent hydrothermal stability [28]

According to the above analysis the rare earth elementCe as an ideal molecular sieve-based SCR catalyst

NO

x co

nver

sion

()

0

20

40

60

80

100

2 CuSSZ-134 CuSSZ-136 CuSSZ-13

100 200 300 400 500 6000

Temperature (degC)

(a)

0

1

2

3

4

5

6

N2O

conc

entr

atio

n (p

pm)

2 CuSSZ-134 CuSSZ-136 CuSSZ-13

100 200 300 400 500 6000Temperature (degC)

(b)

Figure 7 (a) SCR activity of the catalysts (b) N2O concentration during NH3-SCR with xCuSSZ-13 (x 2 4 6) catalysts

100 200 300 400 500 6000

Temperature (degC)

NO

x co

nver

sion

()

0

20

40

60

80

100

CuSSZ-13Cu-CeSSZ-13Cu-MnSSZ-13

Figure 8 NOx conversion using NH3 for addition of Ce or Mn onCuSSZ-13 catalysts

NO

x co

nver

sion

()

0

20

40

60

80

100

100 200 300 400 500 6000

Temperature (degC)

CuSSZ-13-100hCu-CeSSZ-13-100hCu-MnSSZ-13-100h

Figure 9 NOx conversion after aging treatment for 100 h usingNH3 for addition of Ce or Mn on CuSSZ-13 catalysts

6 Journal of Chemistry

modification element could significantly improve the low-temperature performance of the catalyst and broaden thetemperature window

4 Conclusions

In this paper Cu-based zeolite catalysts were investigated interms of NOx conversion using NH3 under the atmospheresof N2 O2 NO NH3 CO2 and H2O It has been found thatthe zeolite topologies Cu loadings and transition metaldoping affect the catalytic performance with regard to NOxconversion)e SSZ-13 possessed a small pore and exhibitedthe optimal SCR activity because of existing high single Cu2+species in the pores

)e CuxSSZ-13 catalysts prepared with wetness im-pregnation possess dispersed Cu2+ species CuxOy clustersand CuO particles compared with 6 CuSSZ-13 and 2CuSSZ-13 4 CuSSZ-13 demonstrated the best catalyticactivity under low temperature the widest active temper-ature window and the highest comprehensive SCR de-NOxperformance Doping rare earth element Ce could effectivelyimprove the low-temperature de-NOx performance of thecatalysts and broaden the reaction temperature window

Data Availability

)e data used to support the findings of this study are in-cluded within the article

Conflicts of Interest

)e authors declare no conflicts of interest

Acknowledgments

)is research was funded by the Key Research Program ofJiangsu Province China grant number BE2016003-2

References

[1] F Liu H He C B Zhang et al ldquoSelective catalytic reductionof NO with NH3 over iron titanate catalyst catalytic per-formance and characterizationrdquo Applied Catalysis B Envi-ronmental vol 96 no 3-4 pp 408ndash420 2010

[2] P G W A Kompio A Bruckner F Hipler G AuerE Loffler and W Grunert ldquoA new view on the relationsbetween tungsten and vanadium in V2O5-WO3TiO2 catalystsfor the selective reduction of NO with NH3rdquo Journal ofCatalysis vol 286 pp 237ndash247 2012

[3] Y Dong and X Fei ldquoEffect of isopropanol on crystal growthand photocatalytic properties regulation of anatase TiO2single crystalsrdquo Materials Technology vol 35 no 2pp 102ndash111 2020

[4] I E Wachs G Deo B M Weckhuysen et al ldquoSelectivecatalytic reduction of NO with NH3 over supported vanadiacatalystsrdquo Journal of Catalysis vol 161 no 1 pp 211ndash2211996

[5] G Busca L Lietti G Ramis and F Berti ldquoChemical andmechanistic aspects of the selective catalytic reduction of NOxby ammonia over oxide catalystsrdquo Applied Catalysis B En-vironmental vol 18 no 1-2 pp 1ndash36 1998

[6] J Li H Chang L Ma J Hao and R T Yang ldquoLow-tem-perature selective catalytic reduction of NOx with NH3 overmetal oxide and zeolite catalystrdquo Catalysis Today vol 175no 1 pp 147ndash156 2011

[7] T V W Janssens H Falsig L F Lundegaard et al ldquoAconsistent reaction scheme for the selective catalytic reductionof nitrogen oxides with ammoniardquoACS Catalysis vol 5 no 5pp 2832ndash2845 2015

[8] S Brandenberger O Krocher A Tissler and R Althoff ldquo)estate of the art in selective catalytic reduction of NOx byammonia using metal-exchanged zeolite catalystsrdquo CatalysisReviews vol 50 no 4 pp 492ndash531 2008

[9] L Xie F Liu L Ren X Shi F-S Xiao and H He ldquoExcellentperformance of one-pot synthesized Cu-SSZ-13 catalyst for theselective catalytic reduction of NOx with NH3rdquo EnvironmentalScience amp Technology vol 48 no 1 pp 566ndash572 2014

[10] J Wang T Yu X Wang et al ldquo)e influence of silicon on thecatalytic properties of CuSAPO-34 for NOx reduction byammonia-SCRrdquo Applied Catalysis B Environmental vol 127pp 137ndash147 2012

[11] A Sultana T Nanba M Sasaki M Haneda K Suzuki andH Hamada ldquoSelective catalytic reduction of NOx with NH3over different copper exchanged zeolites in the presence ofdecanerdquo Catalysis Today vol 164 no 1 pp 495ndash499 2011

[12] B Chen R Xu R Zhang and N Liu ldquoEconomical way tosynthesize SSZ-13 with abundant ion-exchanged Cu+ for anextraordinary performance in selective catalytic reduction(SCR) of NOx by ammoniardquo Environmental Science ampTechnology vol 48 no 23 pp 13909ndash13916 2014

[13] P G Blakeman E M Burkholder H-Y Chen et al ldquo)e roleof pore size on the thermal stability of zeolite supported CuSCR catalystsrdquo Catalysis Today vol 231 pp 56ndash63 2014

[14] C Niu X Shi F Liu et al ldquoHigh hydrothermal stability ofCu-SAPO-34 catalysts for the NH3-SCR of NOxrdquo ChemicalEngineering Journal vol 294 pp 254ndash263 2016

[15] Y Ma X Wu J Zhang R Ran and D Weng ldquoUrea-relatedreactions and their active sites over Cu-SAPO-34 formationof NH3 and conversion of HNCOrdquo Applied Catalysis BEnvironmental vol 227 pp 198ndash208 2018

[16] C Fan Z Chen L Pang et al ldquoSteam and alkali resistant Cu-SSZ-13 catalyst for the selective catalytic reduction of NOx indiesel exhaustrdquo Chemical Engineering Journal vol 334pp 344ndash354 2018

[17] A Wang Y Wang E D Walter et al ldquoNH3-SCR on Cu Feand Cu plus Fe exchanged beta and SSZ-13 catalysts hy-drothermal aging and propylene poisoning effectsrdquo CatalysisToday vol 320 pp 91ndash99 2019

[18] J H Kwak D Tran S D Burton J Szanyi J H Lee andC H F Peden ldquoEffects of hydrothermal aging on NH3-SCRreaction over Cuzeolitesrdquo Journal of Catalysis vol 287pp 203ndash209 2012

[19] J H Kwak R G Tonkyn D H Kim J Szanyi andC H F Peden ldquoExcellent activity and selectivity of Cu-SSZ-13 in the selective catalytic reduction of NOx with NH3rdquoJournal of Catalysis vol 275 no 2 pp 187ndash190 2010

[20] G Liu W Zhang P He et al ldquoH2O andor SO2 tolerance ofCu-MnSAPO-34 catalyst for NO reduction with NH3 at low-temperaturerdquo Catalysts vol 9 no 3 p 289 2019

[21] Y Liu C Song G Lv C Lv and X Li ldquoPromotional effect ofcerium andor zirconium doping on CuZSM-5 catalysts forselective catalytic reduction of NO by NH3rdquo Catalysts vol 8no 8 p 306 2018

[22] R Zhang W Y Teoh R Amal B Chen and S KaliaguineldquoCatalytic reduction of NO by CO over CuCexZr11minusxO2

Journal of Chemistry 7

prepared by flame synthesisrdquo Journal of Catalysis vol 272no 2 pp 210ndash219 2010

[23] M L Fu X H Yue D Q Ye et al ldquoSoot oxidation via CuOdoped CeO2 catalysts prepared using coprecipitation andcitrate acid complex-combustion synthesisrdquo Catalysis Todayvol 153 no 3-4 pp 125ndash132 2010

[24] L Ma Y Cheng G Cavataio R W McCabe L Fu and J LildquoCharacterization of commercial Cu-SSZ-13 and Cu-SAPO-34 catalysts with hydrothermal treatment for NH3-SCR ofNOx in diesel exhaustrdquo Chemical Engineering Journalvol 225 pp 323ndash330 2013

[25] HWang R Xu Y Jin and R Zhang ldquoZeolite structure effectson Cu active center SCR performance and stability of Cu-zeolite catalystsrdquo Catalysis Today vol 327 pp 295ndash307 2019

[26] Y Li J Deng W Song et al ldquo)e nature of Cu species in Cu-SAPO-18 catalyst for NH3-SCR combination of experimentsand DFT calculationsrdquo Ae Journal of Physical Chemistry Cvol 120 no 27 pp 14669ndash14680 2016

[27] C Chen Y Cao S Liu J Chen and W Jia ldquo)e catalyticproperties of Cu modified attapulgite in NH3-SCO and NH3-SCR reactionsrdquoApplied Surface Science vol 480 pp 537ndash5472019

[28] C Pang Y Zhuo QWeng and Z Zhu ldquo)e promotion effectof manganese on CuSAPO for selective catalytic reduction ofNOx with NH3rdquo RSC Advances vol 8 no 11 pp 6110ndash61192018

[29] S Han J Cheng Q Ye S Cheng T Kang and H Dai ldquoCedoping to Cu-SAPO-18 enhanced catalytic performance forthe NH3-SCR of NO in simulated diesel exhaustrdquo Micropo-rous and Mesoporous Materials vol 276 pp 133ndash146 2019

8 Journal of Chemistry

catalysts was more significant Doping Ce promoted the low-temperature catalytic performance with increasing NOxreduction rate

)e doping manganese in CuSSZ-13 presented poorerresistance to hydrothermal aging as can be observed inFigure 9 )e low-temperature activity deteriorated and thelight-off temperature increased after hydrothermal aging for100 hours corresponding to active temperature windownarrowing Ce-doped sample showed the activity temper-ature window similar to the undoped sample However thedoping of Ce significantly improved the low-temperature

activity of the catalyst For example NOx conversionreached 20 at 100degC whereas the temperature increased to160degC the undoped CuSSZ-13 catalysts achieved the sameconversion )e doped Ce in catalysts maintained thestructural characteristics of the hydrothermal aging catalystsurface Compared with CuSSZ-13 catalyst the addition ofCe stabilized the copper active center and reduced the SSZ-13 structure dealuminization which kept the Cu-Ce-SSZ-13catalysts possessing excellent hydrothermal stability [28]

According to the above analysis the rare earth elementCe as an ideal molecular sieve-based SCR catalyst

NO

x co

nver

sion

()

0

20

40

60

80

100

2 CuSSZ-134 CuSSZ-136 CuSSZ-13

100 200 300 400 500 6000

Temperature (degC)

(a)

0

1

2

3

4

5

6

N2O

conc

entr

atio

n (p

pm)

2 CuSSZ-134 CuSSZ-136 CuSSZ-13

100 200 300 400 500 6000Temperature (degC)

(b)

Figure 7 (a) SCR activity of the catalysts (b) N2O concentration during NH3-SCR with xCuSSZ-13 (x 2 4 6) catalysts

100 200 300 400 500 6000

Temperature (degC)

NO

x co

nver

sion

()

0

20

40

60

80

100

CuSSZ-13Cu-CeSSZ-13Cu-MnSSZ-13

Figure 8 NOx conversion using NH3 for addition of Ce or Mn onCuSSZ-13 catalysts

NO

x co

nver

sion

()

0

20

40

60

80

100

100 200 300 400 500 6000

Temperature (degC)

CuSSZ-13-100hCu-CeSSZ-13-100hCu-MnSSZ-13-100h

Figure 9 NOx conversion after aging treatment for 100 h usingNH3 for addition of Ce or Mn on CuSSZ-13 catalysts

6 Journal of Chemistry

modification element could significantly improve the low-temperature performance of the catalyst and broaden thetemperature window

4 Conclusions

In this paper Cu-based zeolite catalysts were investigated interms of NOx conversion using NH3 under the atmospheresof N2 O2 NO NH3 CO2 and H2O It has been found thatthe zeolite topologies Cu loadings and transition metaldoping affect the catalytic performance with regard to NOxconversion)e SSZ-13 possessed a small pore and exhibitedthe optimal SCR activity because of existing high single Cu2+species in the pores

)e CuxSSZ-13 catalysts prepared with wetness im-pregnation possess dispersed Cu2+ species CuxOy clustersand CuO particles compared with 6 CuSSZ-13 and 2CuSSZ-13 4 CuSSZ-13 demonstrated the best catalyticactivity under low temperature the widest active temper-ature window and the highest comprehensive SCR de-NOxperformance Doping rare earth element Ce could effectivelyimprove the low-temperature de-NOx performance of thecatalysts and broaden the reaction temperature window

Data Availability

)e data used to support the findings of this study are in-cluded within the article

Conflicts of Interest

)e authors declare no conflicts of interest

Acknowledgments

)is research was funded by the Key Research Program ofJiangsu Province China grant number BE2016003-2

References

[1] F Liu H He C B Zhang et al ldquoSelective catalytic reductionof NO with NH3 over iron titanate catalyst catalytic per-formance and characterizationrdquo Applied Catalysis B Envi-ronmental vol 96 no 3-4 pp 408ndash420 2010

[2] P G W A Kompio A Bruckner F Hipler G AuerE Loffler and W Grunert ldquoA new view on the relationsbetween tungsten and vanadium in V2O5-WO3TiO2 catalystsfor the selective reduction of NO with NH3rdquo Journal ofCatalysis vol 286 pp 237ndash247 2012

[3] Y Dong and X Fei ldquoEffect of isopropanol on crystal growthand photocatalytic properties regulation of anatase TiO2single crystalsrdquo Materials Technology vol 35 no 2pp 102ndash111 2020

[4] I E Wachs G Deo B M Weckhuysen et al ldquoSelectivecatalytic reduction of NO with NH3 over supported vanadiacatalystsrdquo Journal of Catalysis vol 161 no 1 pp 211ndash2211996

[5] G Busca L Lietti G Ramis and F Berti ldquoChemical andmechanistic aspects of the selective catalytic reduction of NOxby ammonia over oxide catalystsrdquo Applied Catalysis B En-vironmental vol 18 no 1-2 pp 1ndash36 1998

[6] J Li H Chang L Ma J Hao and R T Yang ldquoLow-tem-perature selective catalytic reduction of NOx with NH3 overmetal oxide and zeolite catalystrdquo Catalysis Today vol 175no 1 pp 147ndash156 2011

[7] T V W Janssens H Falsig L F Lundegaard et al ldquoAconsistent reaction scheme for the selective catalytic reductionof nitrogen oxides with ammoniardquoACS Catalysis vol 5 no 5pp 2832ndash2845 2015

[8] S Brandenberger O Krocher A Tissler and R Althoff ldquo)estate of the art in selective catalytic reduction of NOx byammonia using metal-exchanged zeolite catalystsrdquo CatalysisReviews vol 50 no 4 pp 492ndash531 2008

[9] L Xie F Liu L Ren X Shi F-S Xiao and H He ldquoExcellentperformance of one-pot synthesized Cu-SSZ-13 catalyst for theselective catalytic reduction of NOx with NH3rdquo EnvironmentalScience amp Technology vol 48 no 1 pp 566ndash572 2014

[10] J Wang T Yu X Wang et al ldquo)e influence of silicon on thecatalytic properties of CuSAPO-34 for NOx reduction byammonia-SCRrdquo Applied Catalysis B Environmental vol 127pp 137ndash147 2012

[11] A Sultana T Nanba M Sasaki M Haneda K Suzuki andH Hamada ldquoSelective catalytic reduction of NOx with NH3over different copper exchanged zeolites in the presence ofdecanerdquo Catalysis Today vol 164 no 1 pp 495ndash499 2011

[12] B Chen R Xu R Zhang and N Liu ldquoEconomical way tosynthesize SSZ-13 with abundant ion-exchanged Cu+ for anextraordinary performance in selective catalytic reduction(SCR) of NOx by ammoniardquo Environmental Science ampTechnology vol 48 no 23 pp 13909ndash13916 2014

[13] P G Blakeman E M Burkholder H-Y Chen et al ldquo)e roleof pore size on the thermal stability of zeolite supported CuSCR catalystsrdquo Catalysis Today vol 231 pp 56ndash63 2014

[14] C Niu X Shi F Liu et al ldquoHigh hydrothermal stability ofCu-SAPO-34 catalysts for the NH3-SCR of NOxrdquo ChemicalEngineering Journal vol 294 pp 254ndash263 2016

[15] Y Ma X Wu J Zhang R Ran and D Weng ldquoUrea-relatedreactions and their active sites over Cu-SAPO-34 formationof NH3 and conversion of HNCOrdquo Applied Catalysis BEnvironmental vol 227 pp 198ndash208 2018

[16] C Fan Z Chen L Pang et al ldquoSteam and alkali resistant Cu-SSZ-13 catalyst for the selective catalytic reduction of NOx indiesel exhaustrdquo Chemical Engineering Journal vol 334pp 344ndash354 2018

[17] A Wang Y Wang E D Walter et al ldquoNH3-SCR on Cu Feand Cu plus Fe exchanged beta and SSZ-13 catalysts hy-drothermal aging and propylene poisoning effectsrdquo CatalysisToday vol 320 pp 91ndash99 2019

[18] J H Kwak D Tran S D Burton J Szanyi J H Lee andC H F Peden ldquoEffects of hydrothermal aging on NH3-SCRreaction over Cuzeolitesrdquo Journal of Catalysis vol 287pp 203ndash209 2012

[19] J H Kwak R G Tonkyn D H Kim J Szanyi andC H F Peden ldquoExcellent activity and selectivity of Cu-SSZ-13 in the selective catalytic reduction of NOx with NH3rdquoJournal of Catalysis vol 275 no 2 pp 187ndash190 2010

[20] G Liu W Zhang P He et al ldquoH2O andor SO2 tolerance ofCu-MnSAPO-34 catalyst for NO reduction with NH3 at low-temperaturerdquo Catalysts vol 9 no 3 p 289 2019

[21] Y Liu C Song G Lv C Lv and X Li ldquoPromotional effect ofcerium andor zirconium doping on CuZSM-5 catalysts forselective catalytic reduction of NO by NH3rdquo Catalysts vol 8no 8 p 306 2018

[22] R Zhang W Y Teoh R Amal B Chen and S KaliaguineldquoCatalytic reduction of NO by CO over CuCexZr11minusxO2

Journal of Chemistry 7

prepared by flame synthesisrdquo Journal of Catalysis vol 272no 2 pp 210ndash219 2010

[23] M L Fu X H Yue D Q Ye et al ldquoSoot oxidation via CuOdoped CeO2 catalysts prepared using coprecipitation andcitrate acid complex-combustion synthesisrdquo Catalysis Todayvol 153 no 3-4 pp 125ndash132 2010

[24] L Ma Y Cheng G Cavataio R W McCabe L Fu and J LildquoCharacterization of commercial Cu-SSZ-13 and Cu-SAPO-34 catalysts with hydrothermal treatment for NH3-SCR ofNOx in diesel exhaustrdquo Chemical Engineering Journalvol 225 pp 323ndash330 2013

[25] HWang R Xu Y Jin and R Zhang ldquoZeolite structure effectson Cu active center SCR performance and stability of Cu-zeolite catalystsrdquo Catalysis Today vol 327 pp 295ndash307 2019

[26] Y Li J Deng W Song et al ldquo)e nature of Cu species in Cu-SAPO-18 catalyst for NH3-SCR combination of experimentsand DFT calculationsrdquo Ae Journal of Physical Chemistry Cvol 120 no 27 pp 14669ndash14680 2016

[27] C Chen Y Cao S Liu J Chen and W Jia ldquo)e catalyticproperties of Cu modified attapulgite in NH3-SCO and NH3-SCR reactionsrdquoApplied Surface Science vol 480 pp 537ndash5472019

[28] C Pang Y Zhuo QWeng and Z Zhu ldquo)e promotion effectof manganese on CuSAPO for selective catalytic reduction ofNOx with NH3rdquo RSC Advances vol 8 no 11 pp 6110ndash61192018

[29] S Han J Cheng Q Ye S Cheng T Kang and H Dai ldquoCedoping to Cu-SAPO-18 enhanced catalytic performance forthe NH3-SCR of NO in simulated diesel exhaustrdquo Micropo-rous and Mesoporous Materials vol 276 pp 133ndash146 2019

8 Journal of Chemistry

modification element could significantly improve the low-temperature performance of the catalyst and broaden thetemperature window

4 Conclusions

In this paper Cu-based zeolite catalysts were investigated interms of NOx conversion using NH3 under the atmospheresof N2 O2 NO NH3 CO2 and H2O It has been found thatthe zeolite topologies Cu loadings and transition metaldoping affect the catalytic performance with regard to NOxconversion)e SSZ-13 possessed a small pore and exhibitedthe optimal SCR activity because of existing high single Cu2+species in the pores

)e CuxSSZ-13 catalysts prepared with wetness im-pregnation possess dispersed Cu2+ species CuxOy clustersand CuO particles compared with 6 CuSSZ-13 and 2CuSSZ-13 4 CuSSZ-13 demonstrated the best catalyticactivity under low temperature the widest active temper-ature window and the highest comprehensive SCR de-NOxperformance Doping rare earth element Ce could effectivelyimprove the low-temperature de-NOx performance of thecatalysts and broaden the reaction temperature window

Data Availability

)e data used to support the findings of this study are in-cluded within the article

Conflicts of Interest

)e authors declare no conflicts of interest

Acknowledgments

)is research was funded by the Key Research Program ofJiangsu Province China grant number BE2016003-2

References

[1] F Liu H He C B Zhang et al ldquoSelective catalytic reductionof NO with NH3 over iron titanate catalyst catalytic per-formance and characterizationrdquo Applied Catalysis B Envi-ronmental vol 96 no 3-4 pp 408ndash420 2010

[2] P G W A Kompio A Bruckner F Hipler G AuerE Loffler and W Grunert ldquoA new view on the relationsbetween tungsten and vanadium in V2O5-WO3TiO2 catalystsfor the selective reduction of NO with NH3rdquo Journal ofCatalysis vol 286 pp 237ndash247 2012

[3] Y Dong and X Fei ldquoEffect of isopropanol on crystal growthand photocatalytic properties regulation of anatase TiO2single crystalsrdquo Materials Technology vol 35 no 2pp 102ndash111 2020

[4] I E Wachs G Deo B M Weckhuysen et al ldquoSelectivecatalytic reduction of NO with NH3 over supported vanadiacatalystsrdquo Journal of Catalysis vol 161 no 1 pp 211ndash2211996

[5] G Busca L Lietti G Ramis and F Berti ldquoChemical andmechanistic aspects of the selective catalytic reduction of NOxby ammonia over oxide catalystsrdquo Applied Catalysis B En-vironmental vol 18 no 1-2 pp 1ndash36 1998

[6] J Li H Chang L Ma J Hao and R T Yang ldquoLow-tem-perature selective catalytic reduction of NOx with NH3 overmetal oxide and zeolite catalystrdquo Catalysis Today vol 175no 1 pp 147ndash156 2011

[7] T V W Janssens H Falsig L F Lundegaard et al ldquoAconsistent reaction scheme for the selective catalytic reductionof nitrogen oxides with ammoniardquoACS Catalysis vol 5 no 5pp 2832ndash2845 2015

[8] S Brandenberger O Krocher A Tissler and R Althoff ldquo)estate of the art in selective catalytic reduction of NOx byammonia using metal-exchanged zeolite catalystsrdquo CatalysisReviews vol 50 no 4 pp 492ndash531 2008

[9] L Xie F Liu L Ren X Shi F-S Xiao and H He ldquoExcellentperformance of one-pot synthesized Cu-SSZ-13 catalyst for theselective catalytic reduction of NOx with NH3rdquo EnvironmentalScience amp Technology vol 48 no 1 pp 566ndash572 2014

[10] J Wang T Yu X Wang et al ldquo)e influence of silicon on thecatalytic properties of CuSAPO-34 for NOx reduction byammonia-SCRrdquo Applied Catalysis B Environmental vol 127pp 137ndash147 2012

[11] A Sultana T Nanba M Sasaki M Haneda K Suzuki andH Hamada ldquoSelective catalytic reduction of NOx with NH3over different copper exchanged zeolites in the presence ofdecanerdquo Catalysis Today vol 164 no 1 pp 495ndash499 2011

[12] B Chen R Xu R Zhang and N Liu ldquoEconomical way tosynthesize SSZ-13 with abundant ion-exchanged Cu+ for anextraordinary performance in selective catalytic reduction(SCR) of NOx by ammoniardquo Environmental Science ampTechnology vol 48 no 23 pp 13909ndash13916 2014

[13] P G Blakeman E M Burkholder H-Y Chen et al ldquo)e roleof pore size on the thermal stability of zeolite supported CuSCR catalystsrdquo Catalysis Today vol 231 pp 56ndash63 2014

[14] C Niu X Shi F Liu et al ldquoHigh hydrothermal stability ofCu-SAPO-34 catalysts for the NH3-SCR of NOxrdquo ChemicalEngineering Journal vol 294 pp 254ndash263 2016

[15] Y Ma X Wu J Zhang R Ran and D Weng ldquoUrea-relatedreactions and their active sites over Cu-SAPO-34 formationof NH3 and conversion of HNCOrdquo Applied Catalysis BEnvironmental vol 227 pp 198ndash208 2018

[16] C Fan Z Chen L Pang et al ldquoSteam and alkali resistant Cu-SSZ-13 catalyst for the selective catalytic reduction of NOx indiesel exhaustrdquo Chemical Engineering Journal vol 334pp 344ndash354 2018

[17] A Wang Y Wang E D Walter et al ldquoNH3-SCR on Cu Feand Cu plus Fe exchanged beta and SSZ-13 catalysts hy-drothermal aging and propylene poisoning effectsrdquo CatalysisToday vol 320 pp 91ndash99 2019

[18] J H Kwak D Tran S D Burton J Szanyi J H Lee andC H F Peden ldquoEffects of hydrothermal aging on NH3-SCRreaction over Cuzeolitesrdquo Journal of Catalysis vol 287pp 203ndash209 2012

[19] J H Kwak R G Tonkyn D H Kim J Szanyi andC H F Peden ldquoExcellent activity and selectivity of Cu-SSZ-13 in the selective catalytic reduction of NOx with NH3rdquoJournal of Catalysis vol 275 no 2 pp 187ndash190 2010

[20] G Liu W Zhang P He et al ldquoH2O andor SO2 tolerance ofCu-MnSAPO-34 catalyst for NO reduction with NH3 at low-temperaturerdquo Catalysts vol 9 no 3 p 289 2019

[21] Y Liu C Song G Lv C Lv and X Li ldquoPromotional effect ofcerium andor zirconium doping on CuZSM-5 catalysts forselective catalytic reduction of NO by NH3rdquo Catalysts vol 8no 8 p 306 2018

[22] R Zhang W Y Teoh R Amal B Chen and S KaliaguineldquoCatalytic reduction of NO by CO over CuCexZr11minusxO2

Journal of Chemistry 7

prepared by flame synthesisrdquo Journal of Catalysis vol 272no 2 pp 210ndash219 2010

[23] M L Fu X H Yue D Q Ye et al ldquoSoot oxidation via CuOdoped CeO2 catalysts prepared using coprecipitation andcitrate acid complex-combustion synthesisrdquo Catalysis Todayvol 153 no 3-4 pp 125ndash132 2010

[24] L Ma Y Cheng G Cavataio R W McCabe L Fu and J LildquoCharacterization of commercial Cu-SSZ-13 and Cu-SAPO-34 catalysts with hydrothermal treatment for NH3-SCR ofNOx in diesel exhaustrdquo Chemical Engineering Journalvol 225 pp 323ndash330 2013

[25] HWang R Xu Y Jin and R Zhang ldquoZeolite structure effectson Cu active center SCR performance and stability of Cu-zeolite catalystsrdquo Catalysis Today vol 327 pp 295ndash307 2019

[26] Y Li J Deng W Song et al ldquo)e nature of Cu species in Cu-SAPO-18 catalyst for NH3-SCR combination of experimentsand DFT calculationsrdquo Ae Journal of Physical Chemistry Cvol 120 no 27 pp 14669ndash14680 2016

[27] C Chen Y Cao S Liu J Chen and W Jia ldquo)e catalyticproperties of Cu modified attapulgite in NH3-SCO and NH3-SCR reactionsrdquoApplied Surface Science vol 480 pp 537ndash5472019

[28] C Pang Y Zhuo QWeng and Z Zhu ldquo)e promotion effectof manganese on CuSAPO for selective catalytic reduction ofNOx with NH3rdquo RSC Advances vol 8 no 11 pp 6110ndash61192018

[29] S Han J Cheng Q Ye S Cheng T Kang and H Dai ldquoCedoping to Cu-SAPO-18 enhanced catalytic performance forthe NH3-SCR of NO in simulated diesel exhaustrdquo Micropo-rous and Mesoporous Materials vol 276 pp 133ndash146 2019

8 Journal of Chemistry

prepared by flame synthesisrdquo Journal of Catalysis vol 272no 2 pp 210ndash219 2010

[23] M L Fu X H Yue D Q Ye et al ldquoSoot oxidation via CuOdoped CeO2 catalysts prepared using coprecipitation andcitrate acid complex-combustion synthesisrdquo Catalysis Todayvol 153 no 3-4 pp 125ndash132 2010

[24] L Ma Y Cheng G Cavataio R W McCabe L Fu and J LildquoCharacterization of commercial Cu-SSZ-13 and Cu-SAPO-34 catalysts with hydrothermal treatment for NH3-SCR ofNOx in diesel exhaustrdquo Chemical Engineering Journalvol 225 pp 323ndash330 2013

[25] HWang R Xu Y Jin and R Zhang ldquoZeolite structure effectson Cu active center SCR performance and stability of Cu-zeolite catalystsrdquo Catalysis Today vol 327 pp 295ndash307 2019

[26] Y Li J Deng W Song et al ldquo)e nature of Cu species in Cu-SAPO-18 catalyst for NH3-SCR combination of experimentsand DFT calculationsrdquo Ae Journal of Physical Chemistry Cvol 120 no 27 pp 14669ndash14680 2016

[27] C Chen Y Cao S Liu J Chen and W Jia ldquo)e catalyticproperties of Cu modified attapulgite in NH3-SCO and NH3-SCR reactionsrdquoApplied Surface Science vol 480 pp 537ndash5472019

[28] C Pang Y Zhuo QWeng and Z Zhu ldquo)e promotion effectof manganese on CuSAPO for selective catalytic reduction ofNOx with NH3rdquo RSC Advances vol 8 no 11 pp 6110ndash61192018

[29] S Han J Cheng Q Ye S Cheng T Kang and H Dai ldquoCedoping to Cu-SAPO-18 enhanced catalytic performance forthe NH3-SCR of NO in simulated diesel exhaustrdquo Micropo-rous and Mesoporous Materials vol 276 pp 133ndash146 2019

8 Journal of Chemistry