DECOMPOSITION OF N20 IN THE NITRIC ACID INDUSTRY · DECOMPOSITION OF N20 IN THE NITRIC ACID INDUSTRY: Definition of structure-activity relations as a tool to develop new catalysts

ECN-RX--05-080

DECOMPOSITION OF N20 IN THE NITRIC ACID INDUSTRY:

Definition of structure-activity relations as a tool to develop new catalysts

I. Melian-Cabrera R.W. van den Brink

J.A.Z. Pieterse G. Mul

F. Kapteijn J.A. Moulijn

13th International Congress on Catalysis

11 - 16 July, 2004

Palai des Congrès, Paris, France.

MARCH 2005

Decomposition of N2O in the nitric acid industry: Definition of structure-activity relations as a tool to develop new catalysts

I. Melían-Cabrerab, R.W. van den Brinka, J.A.Z. Pietersea, G. Mulb, F. Kapteijnb, J.A. Moulijnb

a. Energy Research Center of the Netherlands ECN, Westerduinweg 3, NL-1755 ZG PETTEN, The Netherlands, [email protected]. b. Reactor & Catalysis Engineering, Delft University of Technology, Julianalaan 136, NL-2628 BL DELFT, The Netherlands. Introduction The nitric acid industry is one of the major sources of the greenhouse gas N2O, which is 310 times more effective than CO2 in trapping heat in the atmosphere. One of the most promising techniques is direct decomposition of N2O in the tail gases of nitric acid plants (1). The state-of-the-art catalysts are only active at temperatures above 400°C, which means that they can be used only in a limited number of plants. The aim of this research is to develop a catalyst that lowers the temperature for N2O decomposition to below 350°C. This will increase the number of plants that can use the direct decomposition technique for N2O removal and will improve the cost efficiency for plants with a higher temperature. Many researchers have investigated iron-zeolites in recent years. They are active for N2O decomposition, show a high stability in the tail gases of nitric acid plants and are promoted by the presence of NOx in the tail gases (2,3). Noble metal catalysts for N2O decomposition have been studied less thoroughly than iron zeolites. They show high N2O decomposition activity in in diluted N2O streams, but are inhibited by the oxygen, water and NOx present in nitric acid plant tail gases (4). This paper defines relationships between the structure of iron-zeolite and noble metal catalysts and their activity for N2O decomposition. Several parameters of preparation and post-modification were evaluated for their importance in the formation of active species. Based on the knowledge of the structure activity relations, novel catalysts were found with a higher activity for N2O decomposition than the state-of-the-art catalysts. Results Iron zeolites prepared by wet ion exchange in air showed higher activity than catalysts prepared by sublimation of FeCl3 (5), in spite of the fact that by wet ion exchange not all the charge compensation sites are occupied with iron ions and that iron oxide clusters are formed on the outer surface of the zeolite. The catalyst can be further improved by controlling the pH during the ion exchange, in order to keep the iron in the preferred oxidation state. An Fe-FER catalyst prepared at a stable pH of 2.5 showed higher N2O conversion than the same catalyst for which the pH was not controlled during preparation. Iron-zeolite catalysts have been characterized by TPR, FTIR, MAS-NMR and Mössbauer spectroscopy. It was found that tuning the pH prevented the formation of iron oxides to a significant extent. A relation was found between the occurrence of a Fe2+-species and the activity for N2O decomposition. Figure 1 shows that the height of the Fe2+-NO peak at 1874 cm–1 in an in situ DRIFT NO-adsorption experiment on Fe-BEA catalysts correlates with the activity for N2O decomposition (6). Mössbauer spectroscopy confirmed the existence of Fe2+ species in the most active catalysts. Figure 1 also shows that pre-treatment of the catalyst in an inert gas improves N2O decomposition.

180020002200Wavenumbers / cm-1

0.05A

bsor

banc

e / -

1910

, Fe2

+-(

NO

) 218

74, F

e2+-N

O

2160

, NO

+

2193

, NO

2δ+

Fe-BEA from FeSO4pre-treated in Ar Fe-BEA from FeSO4pre-treated in Ar

Fe-BEA from Fe(NO3)3pre-treated in airFe-BEA from Fe(NO3)3pre-treated in air

Fe-BEA from Fe(NO3)3pre-treated in Ar Fe-BEA from Fe(NO3)3pre-treated in Ar

350 400 450 5000

20

40

60

80

100

N 2O

con

vers

ion

[%]

T [°C]550

Fe-BEA from FeSO4pre-treated in airFe-BEA from FeSO4pre-treated in air

1850

, Fe2

+-N

O18

20, F

e2+-(

NO

) 2

Figure 1: Left: DRIFT spectra of NO adsorbed on various Fe-BEA catalysts at 50 °C in flowing 5% NO/He. Right: N2O decomposition activity vs. Conditions: 1500 ppmv N2O in He, W/FN2O = 8.65 105 g.s.mol–1, p = 4 bar(a).

Figure 2: Conditions: 1500 ppmv N2O, 200 ppmv NO, 0.5% H2O, 2.5% O2, p = 4 bar(a), W/FN2O = 30 g.s.mol–1

0

25

50

75

100

275 300 325 350 375 400 425

Temperature inlet [°C]

N2O

con

ver

sion

[%

]

Co-Rh-MOR, 1 bar(a)

Co-Rh-MOR, 4 bar(a)

Fe-FER, 1 bar(a)

Fe-FER, 4 bar(a)

Co-Rh-MOR, 1 bar(a)

Co-Rh-MOR, 4 bar(a)

Fe-FER, 1 bar(a)

Fe-FER, 4 bar(a)

Figure 2 shows that with both a Co-Rh-zeolite and an Fe-zeolite high N2O conversions are reached at temperatures around 350 °C. Interestingly, N2O conversion on the Co-Rh-MOR catalyst did not improve when pressure was increased from atmospheric to 4 bar(a) (with unchanged W/F). For Fe-FER, on the ohand, the N

ther to 2O conversion curve was shifted

lower temperatures at 4 bar(a). Both catalysts were stable for over 500 hours time-on-stream in simulated nitric acid plant off gas. Conclusions By unraveling the structure-activity relations, novel, more active catalysts were developed for the direct decomposition of N2O. This reduces the emission of greenhouse gases. References (1) J. Pérez-Ramírez, F. Kapteijn, K. Schöffel and J.A. Moulijn, Appl. Catal. B 44 (2003) 117 (2) J. Pérez-Ramírez, F. Kapteijn, G. Mul and J.A. Moulijn, Appl. Catal. B 35 (2002) 227 (3) M. Kögel, B.M. Abu-Zied, M. Schwefer, T. Turek, Catal. Commun. 2 (2001) 273 (4) Y. Li and J.N. Armor, Appl. Catal. B 1 (1992) L21 (5) J.A.Z. Pieterse, S. Booneveld and R.W. van den Brink, submitted to Appl. Catal. B (7) G. Mul, J. Peréz-Ramírez, F. Kapteijn and J.A. Moulijn, Cat. Lett. 80 (2002) 129

Decomposition of N2O in the nitric acid industry:

Ruud van den BrinkJean-Pierre PieterseCatalytic Emission Reduction ECN Clean Fossil FuelsEnergy Research Center of the Netherlands

Ignacio Melián-CabreraGuido MulFreek KapteijnJacob MoulijnReactor & Catalysis Engineering DelftChemTech, Delft University of Technology

Definition of structure-activity relations as a tool to develop new catalysts

Nitrous oxide is a potent greenhouse gas

‘N2O is 310 times as effective in trapping heat in the atmosphere than CO2 over a 100-year time period’

GWP

CO2

CH4

N2O

HFC-23

1

21

310

11.700

N N O

N2O concentrations in the atmosphere are rising…

Earth trends 2002 World Resources Institute

290

295

300

305

310

315

320

1978

1980

1982

1984

1986

1988

1990

1992

1994

1996

1998

2000

[ppb]

Pre-industrial concentration:~ 270 ppb

2001: 315 ppb(+ 15%)

Petten

Delft

Nitrous oxide is a potent greenhouse gas

Energy IndustryIndustrial

Sources(23%)

Transport

Agriculture

WasteOther

European Environmental agency, 1999

N2O sources in the EU, 1998

The chemical industry is an important source of N2O

Nylon production (adipic acid)Fertiliser production (HNO3)

Fertiliser useLeguminous crops

Three-way catalystDiesel Engines

Industrial Sources••Agriculture••Transport••

N2O removal in a nitric acid plant

Tail Gas :1500 ppm N2O200 ppm NOx

2.5% O2

0.5% H2O

NOx absorption

Pt/RhGauzes

HeatExchanger

AirNH3

Stack

Expander

NitricAcid

p = 3 to10 baraT = 200 - 500°C

T = 850°C

Direct decomposition of N2O

N2O N2 + ½ O2

Catalysts:•

--

•

-

Zeolite supported iron catalystsFe-ZSM-5 active > 400°CN2O conversion promoted by NO

Zeolite supported (promoted) noble metal catalysts

Shown to be very active in pure N2O

Iron Zeolites

Noble metals

Direct decomposition of N2O

Goals

Means

• N2O removal at 350°C under nitric acid plant tail gas conditions

• Stability of the catalyst• Costs < 1€ / ton CO2-equivalents removed

• Structure-activity relation to aid catalyst optimisation

Different ways to prepare Fe-zeolite catalysts

Fe-ZSM-5

Sublimation of FeCl3(Sachtler, Prins, Centi, van Santen)

Solid State Ion exchange(AlSi Penta, Turek)

ex-Framework(Panov, Moulijn)

Wet ion exchange(Hall, ECN, etc.)

N2O decomposition and SCR

NOx SCR

Selective oxidationBenzene to phenol

Iron Zeolites:Preparation

Fe-ZSM-5:Influence of preparation method

Wet Ion Exchange

# 50% is inactive Fe2O3

Si/Al Fe wt% Fe/Al

11.5 2.3 0.37#

CVD (TU/e)* 19.4 3.6 0.97

CVD (ECN) 11.5 2.6 0.45

25

50

75

100

350 400 450 500Temperature [°C]

N2O

con

vers

ion

[%]

1500 ppm N2O, 200 ppm NO, 0.5% H2O, 2.5% O2, W/F = 11 g.s.mol-1

ex-[Fe,Al]-ZSM-5** 31.5 0.7 0.15

Wet ion exchange in air yields active catalystsPieterse, Booneveld, van den Brink, App. Cat. B 51 (2004) 215* Zhu, Hensen, Mojet, van Wolput, van Santen, Chem. Commun. (2002) 123** Peréz-Ramírez, Mul, Kapteijn, Moulijn, Chem. Commun (2001) 693.

Deactivation Fe-ZSM-5

40

90

50

60

70

80

0 20 40 60 80 100 120 140Time [hours]

N2O

con

vers

ion

[%]

0% H2O

0.5 % H2O

5% H2O

T = 450°C, p = 3 bar(a), 1500 ppm N2O, 200 ppm NO, VAR.% H2O, 2.5% O2

Fe-ZSM-5 prepared by WIE deactivatesDeactivation caused by steam

Iron Zeolites

T = 450°C

Mössbauer spectroscopy:Fe2+ species disappear

-10 -5 0 5 10

3.55

3.60

Velocity mm/s)

3.15

3.20

3.39

3.42

Inte

nsity

(*10

6co

unts

)

10.1

10.2

-10 -5 0 5 107.92

8.04

Velocity (mm/s)

7.5

7.6

Inte

nsity

(*10

6co

unts

)

11.2

11.3

5.04

5.11

300 K, air

300 K, 1*10-6 mbar

77 K, 1*10-6 mbar

4.2 K, 1*10-6 mbarFe2+

Fe2+ Fe2+,missing

Fresh calcined Fe-ZSM-5 Deactivated Fe-ZSM-5

Iron Zeolites

FTIR of adsorbed NO:NO-peaks on Fe2+ are decreased

NO(g)

Abs

orba

nce

[ a

.u. ]

Fresh calcinedFe-ZSM-5

0.125

2400 2000 1600

2133

1877

1598

,

1890

, Fe2+

-NO

2146

, NO

+

Iron Zeolites:Stability

DeactivatedFe-ZSM-5in 5% H2O

Wavenumber [ cm-1]

De-activated catalyst has less Fe2+

Is this a clue to the active species ?

Different zeolites:Fe-FER and Fe-BEA also very active

5000

25

50

75

100

350 400 450Temperature [°C]

N2O

con

vers

ion

[%] Fe-FER

F

Iron Zeolites

1500 ppm N2O, 200 ppm NO, 0.5% H2O, 2.5% O2, W/F = 11 g.s.mol-1

Fe-ZSM-5

Fe-BEA

Fe-MOR

e-FER and Fe-BEA comparable to Fe-ZSM-5

Stability Fe-BEA catalyst:no deactivation at 10% H2O

75

80

85

90

0 20 40 60 80 100 120 140 160 180 200time [h]

N2O

con

vers

ion

[%]

0.5% H2O

5% H2O

10% H2O

T = 400°C, 1500 ppm N2O, 200 ppm NO, x% H2O, 2.5% O2 Iron Zeolites

Fe-BEA shows no deactivation in 10% H2O

FTIR of adsorbed NO on Fe-BEA

Abs

orba

nce

[-]

180020002200Wavenumbers [cm-1]

0.05

Fe-BEA(9)Fe-BEA(7)Fe-BEA(8)

1910

, Fe2

+ -(N

O) 2

1820

, Fe2

+ -(N

O) 2

1850

, Fe2

+ -N

O

1874

, Fe2+

-NO

On

Iron Zeolites

2160

, NO

+

2193

, NO

2δ+

ly Fe2+ sites react with nitrogen oxide

Mul, Pérez-Ramírez, Kapteijn, Moulijn, Cat.Lett. 80 (2002) 129

FTIR of adsorbed NO:correlation between activity and Fe2+-NO

N2O

con

vers

ion

at 4

50 °

C [%

]

Area of 1874 cm-1 peak

0

10

20

30

40

50

60

0 2 4 6 8 10 12

Iron Zeolites

IR vibration at 1874 cm-1 correlates with activityNO on Fe2+ is the active site ?


Fe-FER with or without NO in the feed

0

25

50

75

100

350 400 450 500T [°C]

N2O

con

vers

ion

[%]

0 ppm NO

200 ppm NO1500 ppm N2O, 0 or 200 ppm NO, 0.5% H2O, 2.5% O2, W/F = 11 g.s.mol-1

Iron Zeolites

Nitrogen oxide has a large promoting effect

In-situ FTIR experiments

IR beam

gas in

oven

after Van Neer, Ph.D. Thesis UvA

gas out

IR beam

gas in

oven

after Van Neer, Ph.D. Thesis UvA

gas outMS

In situ FTIR - switch NO to N2O at 350 °C

Delay (30 s)

16 2

t=1.6 min

gas phaseN2O

3Fe2+-NO Fe-NO2

Abs

orba

nce

1600 1800 2000 2200 2400 Wavenumbers [cm-1]

NO → N2O @ t=0

1886 1874

adorbed NO oxidised to adsorbed NO2No nitrate formation !


Iron Zeolites

1400

MS signal - switch N2O to NO at 350°C

00 5050 100100 150150 200200 250250

NONO

NN22

NN22OO

Time [s]Time [s]

Inte

nsity

[a.u

.]In

tens

ity [a

.u.]

delay (~30 s)delay (~30 s)


Same delay in N2 evolution as in adsorbed NO2formation

Iron Zeolites:NO effect

NONO22

In situ FTIR - switch N2O to NO at 350 °C

1600 1800 2000 2200 2400

t=0.5 min

Abs

orba

nce

Wavenumbers [cm-1]

gas phaseN2O

Fe-NO

Fe-NO2 Iron Zeolites:NO effect

NO displaces NO2 rapidly


00 5050 100100 150150 200200 250250 300300

NONO

NN22

NN22OO

NONO22

Time [s]Time [s]

Inte

nsity

[a.u

.]In

tens

ity [a

.u.]

delay (~30 s)delay (~30 s) instantaneouslyinstantaneouslyNN22 and NOand NO22


MS signal - switch N2O to NO at 350 °C

Iron Zeolites

In-situ IR observations

Fe-NO + N2O Fe-NO2 + N2 (1)Fe-NO2 + NO (+N2O) Fe-NO + NO2 (+N2) (2)

Iron Zeolites

Process (1) is delayed : Requires NO to desorb, creating free sites for N2O activation Delay time decreases with increasing temperatureNO2 slowly desorbsNO displaces NO2

•

•••

Fe2+ species involved in N2O conversion

•

-•

--

The presence of specific Fe2+ species is essential in the N2O decomposition.

Nature of active site not knownHow to increase number of Fe2+ species?

Pre-treatmentDuring preparation

Iron Zeolites

(Auto)reduction instead of calcination of Fe-BEA

Fe-BEA pre-treated in O2/N2

Fe-BEA pre-treated in Argon

180020002200Wavenumbers / cm-1

0.05

Abs

orba

nce

/ -

1910

, Fe2+

-(NO

) 2

1820

, Fe2

+ -(N

O) 2

1850

, Fe2+

-NO

1874

, Fe2+

-NO

Iron Zeolites

2160

, NO

+

2193

, NO

2δ+

Peak at 1874 cm-1 increasesHigher activity for N2O decomposition?

Reduction instead of calcination of Fe-FER

60

65

70

75

80

85

90

0 50 100 150 200 250 300 350 400

time [h]

N2O

Con

vers

ie[%

]

Fe-FER pre-treated in O2/N2

Fe-FER pre-treated in hydrogen

Initial activity of reduced catalyst is higherSlow convergence to activity of calcined sample

1500 ppm N2O, 200 ppm NO, 0.5% H2O, 2.5% O2 Iron ZeolitesT = 375°C

Preparation of Fe-zeolitesChemistry of iron ions in solutions

0

1

Fe3+

Fe2O3

Fe2+

2 4 6 8

Pourbaix and De Zoubov, in: Pourbaix, M, Atlas of Electrochemical Equilibria in Aquous Solutions, 1966.Flynn, Chem. Rev. 84 (1984) 31

pH

E [V

]

in H2O + O2 Iron Zeolites

pH below approx. 3: no precipitationExclusion of oxygen has no effect on activity

Preparation of FER at controlled pH

0

20

40

60

80

100

0

20

40

60

80

100

Temperature [°C]

N2O

Con

vers

ion

[%]

300 400 500300 400 500

0.5Fe-FER no pH control (3.5 - 5.0)

0.5Fe-FER pH=4.0

0.5Fe-FER pH=2.5

0.5Fe-FER pH=1.0

1500 ppm N2O, W/F = 11 g.s.mol-1

N2O decomposition highest for pH = 2.5N2O decomposition decreases at lower pH

Iron Zeolites

TPR spectrum of Fe-FER:more iron reduction at low temperature

uncontrolled pH

pH=2.5

Fe-FER

Hyd

roge

n up

take

[a.u

.]

300 500 700 900Temperature [°C]

FeOx

Iron Zeolites

Low-temperature reduction peak is high

Rh-MOR with and without NO in the feed

0

25

50

75

100

300 350 400 450 500T [°C]

N2O

con

vers

ion

[%]

RhMOR0 ppm NO

1500 ppm N2O, 0 or 200 ppm NO, 0.5% H2O, 2.5% O2, W/F = 11 g.s.mol-1

Noble metals

Fe-FER

Rh-MOR with and without NO in the feed

0

25

50

75

100

300 350 400 450 500T [°C]

N2O

con

vers

ion

[%]

RhMOR0 ppm NO

CoRhMOR + NO

RhMOR + NO

Rhodium is inhibited by traces of NOAddition of Cobalt improves activity


Noble metals0.35 wt% Rh2.3 wt% Co

In situ FTIR – NO adsorption at 350 °C on Rh-ZSM-5

1400 1600 1800 2000 Wavenumbers [cm-1]

Nitrate

Rh-NO

Rh-O-NO

Abs

orba

nce

0.1

Development in NONoble metals

NO adsorbes strongly Rh at 350°CNitrates are formed

Combination of Fe en Ru

0

25

50

75

100

350 400 450 500T [°C]

N2O

con

vers

ion

[%]

FeFER0 ppm NO

FeFER 200 ppm NO

FeRuFER0 ppm NO

FeRuFER 200 ppm NO RuFER 200 ppm NO

RuFER 0 ppm NONoble metals


0.4 wt% Ru

Addition of Fe to Ru catalyst improves activity

Larger-scale tests of Co-Rh-MOR and Fe-FER

500 ppm N2O, 200 ppm NO, 0.5% H2O, 2.5% O2, S.V. = 8500 h-1

Noble metals

0

20

40

60

80

100

250 300 350 400 450

N2O

-con

vers

ion

(%)

0

20

40

60

80

100

250 300 350 400 450

Temperature [°C]

N2O

-con

vers

ion

(%)

Fe-FER

Co-Rh-MOR

Fe-ZSM-5Iron Zeolites

Co-Rh-MOR and Fe-FER have about equal activity under realistic conditions

4 bar(a)

Stability test under ‘severe’ conditions

60

65

70

75

80

85

90

0 100 200 300 400 500time [h]

N2O

con

vers

ion

[%] Tin= 460°C

Tout=472°C

1500 ppm N2O, 200 ppm NO, 1% H2O, 2.5% O2, 60.000 hr-1

Noble metals

Co-Rh-MOR is stable for over 500 h

Conclusionsiron zeolites

•

--

•-

Relation between activity for N2O decomposition and activity:

specific Fe2+-species is involved in active siteconcentration can be increased by preparation at pH = 2.5

NO promotes N2O decompositionremoval of adsorbed NO2 left after N2O decomposition

Iron Zeolites

Conclusionsnoble metals

•-

•

•••

--

NO inhibits N2O decompositionNO adsorption on active site, followed by formation of nitrates

Combination of iron and ruthenium is promising

Catalyst active at 350°C Stable for > 500 hCosts with Rh > 1.2 € per ton CO2

costs much lower at higher temperaturescurrent price of CO2 ca. 5 € per ton

Noble metals

Future plans

•--

•

•

Characterisation of promoted noble metalsin situ FTIR NO/N2O reactionTransient studies

Lower amount of noble metal, improve Ru catalyst.

Test in side-stream of a nitric acid plant

Noble metals

Iron Zeolites

Acknowledgements

• Novem, Ministry of the Enivironment of the Netherlands

• Javier Peréz-Ramírez (YARA)• DSM

• Arjan Overweg, IRI Delft for Mössbauer measurements

• Q. Zhu, Eindhoven Universisty of Technology

Documents

DECOMPOSITION OF N20 IN THE NITRIC ACID INDUSTRY · DECOMPOSITION OF N20 IN THE NITRIC ACID INDUSTRY: Definition of structure-activity relations as a tool to develop new catalysts