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Hydrogen production from carbon dioxide

reforming of methane over highly active and stable

MgO promoted CoeNi/g-Al2O3catalyst

In Hyuk Son a,**, Seung Jae Lee a, Hyun-Seog Roh b,*aEnvironment Group, Energy & Environment Research Center, Samsung Advanced Institute of Technology (SAIT),

Samsung Electronics Co. LTD, Gyounggi-Do 446-712, Republic of Koreab Department of Environmental Engineering, Yonsei University, 1 Yonseidae-gil, Wonju, Gangwon 220-710,

Republic of Korea

a r t i c l e i n f o

Article history:

Received 5 July 2013

Received in revised form

18 December 2013

Accepted 24 December 2013

Available online 25 January 2014

Keywords:

Carbon dioxideReforming

Methane

Magnesia

Intimate interaction

a b s t r a c t

CoNi/Al2O3and MgCoNi/Al2O3catalysts are investigated for hydrogen production from CO2reforming of CH4reaction at the gas hourly space velocity of 40,000 mL g

1 h1. The MgO

promoted CoNi/Al2O3 catalyst shows much higher conversions (97% for CO2 and 95% for

CH4at 850 C) than the CoNi/Al2O3catalyst. In addition, the stability is maintained for 200 h

in CO2reforming of CH4. The outstanding catalytic activity and stability of the MgO pro-

moted CoNi/Al2O3catalyst is mainly due to the basic nature of MgO, an intimate interac-

tion between Ni and the support, and rapid decomposition/dissociation of CH4 and CO2,

resulting in preventing coke formation in CO2reforming of CH4.

Copyright 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rightsreserved.

1. Introduction

The production of H2

or synthesis gas from carbon dioxide

reforming of methane (CDR: CH4 CO2 / 2H2 2CO) is an

emerging and challenging issue for the chemical utilization of

green house gases such as carbon dioxide and methane[1e4].

The CDR reaction becomes industrially advantageous

compared to steam reforming of methane (SRM:

CH4H2O/ 3H2CO) in synthesis gas production since H2/

CO ratio of product is close to 1.0. The synthesis gas with low

H2/CO ratio is suitable for direct use in FeT synthesis or oxo-

synthesis, and both of which require lower H2/CO ratio than

that obtained from conventional SRM.

Supported Ni catalysts have been employed for the target

reaction from an economical point of view [5e8]. However,supported Ni catalysts easily deactivate on account of either

coke formation and/or sintering of Ni metal. Therefore, the

primary difficultyin CDR is developing nano-sizedNi catalysts

with high activity and stability under severe conditions. Ac-

cording to the literature, the nature of supports affects the

catalytic performance of supported Ni catalysts in CDR[9e11].

Many commercial Ni/Al2O3-based catalysts are available

for fuel reforming[12]. These catalysts are more economical

* Corresponding author. Tel.:82 33 760 2834; fax: 82 33 760 2571.** Corresponding author. Tel.: 82 31 280 1852; fax: 82 31 280 9359.

E-mail addresses:[email protected](I.H. Son),[email protected](H.-S. Roh).

Available online atwww.sciencedirect.com

ScienceDirect

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i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 9 ( 2 0 1 4 ) 3 7 6 2 e3 7 7 0

0360-3199/$ e see front matter Copyright 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

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than noble metals and can operate stably with high activity

under excess steam. However, severe carbon deposition is

observed on the Ni/Al2O3catalyst in CDR, which does not use

excess steam[13].

Recently, extensive research has been performed to develop

a highly active and stable catalyst. A Ni alloy with precious

metals suchas Pt, Rh, Ru,and Pd showed excellent performance

in CDR resulting from preventing coke formation [14e18]. Inaddition, it wasreported that thestrong interaction between Ni

and supports such as TiO2, CeO2, and ZrO2enhanced the resis-

tance against sintering of Ni and coke formation[19e24].

However, the typical catalyst for reforming reaction is

composed of Ni particles deposited on an alumina support

[25e29]. This is due to the lower cost and availability of Al2O3.

Likewise, many commercial catalysts for reforming are Ni/

Al2O3-based catalysts, such as Ni-0309S (Engelhard Company),

ICI-46-1 (Imperial Chemical Industries), and FCR-4 (Sud-

Chemie). However, the problem of coke formation and sin-

tering could not be addressed completely.

For this reason, Ni/Al2O3 catalyst compositions have been

intensively investigated to minimize coke formation by prepar-ing a Nialloy with othertransition metalssuchas Cu,Co, and Sn

[30e34]. Especially, researchers have been interested in bime-

tallicNieCo systems due to thefactthatthe addition of cobalt to

nickel catalysts reduces coke formation in CDR [35e39]. They

ascribed the enhanced performance to the improved catalyst

resistance to metal oxidation. Therefore, it is possible that

bimetallic catalysts may exhibit superior performance for CDR

compared with the corresponding monometallic catalysts[40].

Considerable studies also have been conducted on the

modification of catalyst supports using promoters to over-

come the catalyst deactivation[40e47]. Choudhary et al. [41]

reported that the catalyst precoated with MgO and CaO

showed high activity compared to that of catalyst withoutprecoating. Koo et al.[42]reported that the MgO promoted Ni/

Al2O3catalyst forms MgAl2O4spinel phase, which is stable at

high temperature and effectively prevents coke formation by

increasing the CO2 adsorption due to the increase in base

strength on the surface of catalyst.

In this study, we have designed a MgO promoted CoNi/g-

Al2O3catalyst to enhance coke resistance and have found that

this catalyst showed much higher activity and stability than

CoNi/g-Al2O3 catalystat 800 C for 200h in CDR. Detailedstudies

on the characterization and catalytic activity for CDR are fur-

nished in this study. Namely, the beneficial effects of MgO on

the performance over CoNi/g-Al2O3catalyst for CDR were sys-

tematically investigated. Especially, we tried to explain excel-lent catalytic performance of MgCoNi/g-Al2O3catalyst with the

location of each element by using the SEM-EDS elemental

mapping technique for the first time. Moreover, we confirmed

that the adsorbed chemical species strongly affects on catalytic

performance using the in situ DRIFTS analysis.

2. Experimental procedures

2.1. Catalyst preparation

Magnesium (MgN2O6$6H2O, Aldrich), Cobalt (Co(NO3)2$6H2O,

Aldrich) and Nickel (Ni(NO3)2$6H2O, Aldrich) were co-

impregnated over g-Al2O3 (SBET 150 m2/g, w3 mm 4;

Aldrich) using the incipient wetnessmethod with quantitative

loading (Mg 3 wt.%, Ni 3 wt.%, and Co 3 wt.%)[48e51].

The prepared catalysts were dried at 120 C for 24 h and

calcined in air (300 ml/min) at 500 C for 5 h. The calcined

catalyst was reduced in pure H2with increasing temperature

(10 C/min) and maintained at 850 C for 1 h.

2.2. CDR reaction test unit

The reaction temperature was changed from 700 to 850 C.

The reaction pressure was fixed at 1 atm. CDR reaction was

conducted in a micro-tubular quartz reactor. Prior to each

catalytic measurement, the catalyst was reduced in pure H2at

850 C for 1 h. The detailed procedure for theCDR reaction was

explained in the literature[12]. The reactant feed comprised a

gaseous mixture of CH4:CO2:N2(1:1:1). N2was employed as a

reference for calculating CH4and CO2conversions. To screen

the catalysts effectively, a gas hourly space velocity (GHSV) of

40,000 mL g1 h1 was used in this study. The conversions of

CH4and CO2were calculated using the following formulas.

CH4conversion% CH4inCH4out

CH4in100

CO2conversion% CO2in CO2out

CO2in100

2.3. Characterization

The BET surface area of support and catalyst was measured by

N2 adsorption at 196 C using a BET instrument (BELsorp,

BEL, Japan). X-ray diffraction (XRD) patterns were obtained by

a Philips Xpert Pro X-ray diffractometer. The crystalline sizeof the Ni particle was estimated using the DebyeeScherrers

equation [52]. CO2 temperature-programmed desorption (TPD)

was performed on a Chemisorption Analyzer (Micrometrics

ASAP 2010). The detailed procedure for CO2-TPD was

described earlier [12]. To check coke amount of the used

samples, TGA study was carried out from 30 to 850 C in air

using a METTLER TOLEDO TGA/DSC1 with a heating rate of

5 C/min. Temperature-programmed reduction (TPR) experi-

ments were conducted in a Chemisorption Analyzer

(AutoChem II 2920). The detailed procedure for TPR was

described in the previous paper[12,53]. In situ diffuse reflec-

tance infrared Fourier transform spectroscopy (DRIFTS) study

was carried out on a Nicolet 5700 FTIR spectrometer with aMCT detector. A powder catalyst sample was put into a reac-

tion cell (Harricks, Praying Mantis) and reduced in situ at

800 C for 30 min in H2flow. For in situ reaction monitoring,

the reaction temperature was set to 300 C. A mixture flow of

100 ml/min (CH4:CO2:N2 1:1:1) was introduced at that tem-

perature. For all the spectra recorded, a 32-scan data accu-

mulation was carried out at a resolution of 4 cm1. The

catalysts were also examined using the ultra-high-resolution

field emission scanning electron microscopy (UHR-FE-SEM;

Hitachi S-5500, resolution 0.4 nm) with transmission electron

microscopy operating at 30 kV. Elemental composition was

assessed using an energy dispersive X-ray spectroscopy (EDS)

in conjunction with UHR-FE-SEM.

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3. Results and discussion

Table 1 summarizes physical properties of CoNi/Al2O3(marked as CoNi in figures) and MgCoNi/Al2O3 (marked as

MgCoNi in figures) catalysts (Mg 3 wt.%, Ni 3 wt.%, and

Co 3 wt.%). The BET surface area of reduced CoNi/Al2O3is

relatively lower than that of reduced MgCoNi/Al2O3. However,the decrease of the BET surface area is ca. 50% (from 156.3 m2/

g to 78.8 m2/g) for used CoNi/Al2O3catalyst after the CDR re-

action, while only ca. 30% decrease (from 167.3 m2/g to

117.4 m2/g) is measured for the catalyst with MgO. Likewise,

the pore volume of CoNi/Al2O3 decreased from 0.44 m2/g to

0.32 m2/g. On the contrary, there was no change of the pore

volume for the MgCoNi/Al2O3catalyst. The crystallite size of

Ni was estimated using XRD. The crystallite size of Ni

increased significantly after the CDR reaction. In the case of

MgCoNi/Al2O3, the Ni crystallite size of used MgCoNi/Al2O3(9.5 nm) is slightly bigger than that of reduced MgCoNi/Al2O3(6.9 nm). In the case of CoNi/Al2O3, however, the reduced

catalyst shows 5.8 nm but the used catalyst 18.9 nm. Thus, ithas been confirmed that sintering took place severely for the

CoNi/Al2O3 catalyst. On the contrary, sintering of Ni crystallite

could be prevented effectively for the MgCoNi/Al2O3catalyst

due to the beneficial role of MgO.

XRD patterns of reduced catalysts are shown inFig. 1. XRD

patterns of both CoNi/Al2O3and MgCoNi/Al2O3show diffrac-

tion lines associated with pseudo-amorphousgamma alumina

(JCPDS 750921) with a slight shift to lower angle. This in-

dicates the presence of Ni aluminate (JCPDS 100339) [54]. The

XRD patterns of MgCoNi/Al2O3 show the formation of Mg

spinel (MgAl2O4, JCPDS 705187) because a shift in the

diffraction lines of alumina is observed. The MgAl2O4is stable

and efficient support, due to its spinel structure and basicproperty [32]. In addition,both metallic Co andNi peaks appear

at 51.4 and 76.0. Other peaks originate from the support[54].

Fig. 2shows H2-TPR patterns of CoNi/Al2O3 and MgCoNi/

Al2O3 catalysts. The CoNi/Al2O3 catalyst shows two major

peaks. The first peak appears at 360 C and the other at 750 C.

The first reduction peak is due to the reduction of relatively

free NiO species, which have weak interaction with the sup-

port[55]. The peak appearing at 750 C can be assigned to the

reduction of NiAl2O4[33]. In addition, the reduction of Co ox-

ides occurs with the two-step process: Co3O4/ CoO/ Co0.

The reduction peaks of Co3O4 and CoOappear at ca. 400 Cand

at ca. 700 C, respectively[56]. However, it is hard to distin-

guish theCo3O4 peak from the relatively free NiO peak and theCoO peak from the NiAl2O4peak because peaks overlap each

other.

The TPR pattern of MgCoNi/Al2O3is different from that of

CoNi/Al2O3. The reduction peak of NiAl2O4 is remarkablydecreased. This result indicates that NiAl2O4 formation is

effectively prevented due to the addition of MgO. In addition,

the first peak shifts toward lower temperature. It is known

that the addition of MgO has a beneficial effect in the reduc-

tion of free NiO species[57e59].

Fig. 3shows CO2-TPD patterns of reduced CoNi/Al2O3and

MgCoNi/Al2O3catalysts. Compared with CoNi/Al2O3, MgCoNi/

Al2O3shows higher peak intensity from 150 to 400 C. This is

mainly due to the increase of basicity resulting from the

addition of MgO. It has been reported that the basic catalyst

supplies the surface oxygen by acidic CO2gas to prevent coke

formation [60e63]. Choudhary et al. [64] reported that the

catalytic performance depends significantly on the basicityand strength of basic sites of the catalyst. Thus, it is expected

that the MgCoNi/Al2O3 catalyst can have strong resistance

against coke formation due to the beneficial effect of MgO.

Fig. 4illustrates the results of ultra-high-resolution SEM/

TEM dual mode microscopy showing images in both the

scanning and transmission modes and energy-dispersive X-

ray analysis in the same position. MgCoNi particles are visible

both in the SEM image and in the TEM image. According to

Fig.4(c), Mgis presenton CoNi particles. Dueto this structure,it

is expected that MgCoNi/Al2O3 canhave enhancedactivityand

strong resistance against coke formation in CDR. In addition,

the surface of the MgCoNi particles is partially covered by

alumina. Alumina is located at the same position as theMgCoNi particles. This result indicates that MgCoNi particles

are not isolated, but surrounded with alumina supports.

Table 1ePhysical properties of the catalysts. The used catalysts indicate after 200 h of CDR reaction (Reaction conditions:T[ 850 C, P [ 1 atm, GHSV [ 40,000 mL gL1 hL1, CH4:CO2:N2 [ 1:1:1).

Catalyst description BET surface area (m2/g) Pore volume (cm3/g) Pore diameter (nm) Ni crystallite diameter (nm)a

Reduced CoNi/Al2O3 156.3 0.44 11.18 5.8

Used CoNi/Al2O3 78.8 0.32 16.15 18.9

Reduced MgCoNi/Al2O3 167.3 0.40 9.48 6.9

Used MgCoNi/Al2O3 117.4 0.40 13.49 9.5

a

Data obtained from Ni(220) diffraction peak broadening using the Scherrer equation.

Fig. 1 e XRD patterns of reduced CoNi/Al2O3and MgCoNi/

Al2O3catalysts.

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Fig. 5depicts the in-situ DRIFT spectra of CO2 reforming

over CoNi/Al2O3and MgCoNi/Al2O3catalysts. In CH4eCO2co-

feeding conditions, large amount of formate (nS,

C]O1588 cm1) and carbonate (nS, C]O1431 cm

1) species

were formed. It was reported that the adsorption of CO2 on

basic support forms carbonate CO23 /hydrocarbonate HCO3

species which react with H atoms produced from CH4decomposition to form formate (HCOO) intermediates [65],

which are subsequently decomposed into CO and adsorbed

OH groups. Efstathiou et al. [66] found that the formate species

on Al2O3surface was stable under CH4/CO2reforming condi-

tions. Generally, the spectra of CoNi/Al2O3are similar to those

of MgCoNi/Al2O3. Interestingly, with the addition of MgO, the

adsorption of formate species was clearly increased. This

result indicates that the addition of MgO helps to accelerate

the decomposition/dissociation of CH4 and CO2, resulting in

increasing the formation of formate intermediate.

The CO2reforming reaction was performed with the feed

ratio of CH4:CO2:N2 1:1:1 at gas hourly space velocity

(GHSV) 40,000 mL g1 h1 from 700 to 850 C. CDR reaction

data with reaction temperature over CoNi/Al2O3and MgCoNi/

Fig. 3e CO2-TPD patterns of reduced CoNi/Al2O3and

MgCoNi/Al2O3catalysts.

Fig. 4 e (a) SEM, (b) TEM and (c) line-scan EDX analysis for

reduced MgCoNi/Al2O3catalyst at the same position.

Fig. 2e TPR patterns of CoNi/Al2O3and MgCoNi/Al2O3catalysts.



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Al2O3catalysts are presented inFig. 6. MgCoNi/Al2O3catalyst

exhibited much higher CH4 and CO2 conversion than CoNi/

Al2O3catalyst within the temperature range between 700 and

850 C. It is very interesting to see that CO2 conversion is

relatively higher than CH4conversion for both catalysts. This

is due to the reverse water gas shift reaction. As a result, the

H2/CO ratio is less than unity for both catalysts. However, with

increasing the temperature, CH4 conversion is close to CO2conversion.

To check the stability of CoNi/Al2O3 and MgCoNi/Al2O3catalysts with time on stream, CO2 reforming reaction data

were collected for 200 h.Fig. 7shows CH4and CO2conversionand H2/CO ratio with time on stream over CoNi/Al2O3 and

MgCoNi/Al2O3catalysts. MgCoNi/Al2O3catalyst revealed very

high CH4and CO2conversion. Surprisingly, the stability was

maintained for 200 h without detectable catalyst deactivation.

On the contrary, CoNi/Al2O3 catalyst continuously deactivated

with time on stream. Both CH4and CO2conversion dropped

with time on stream.

Table 2summarizes CH4and CO2 conversion, H2 and CO

yield, H2/CO ratio and coking rate. In the case of initial data,

CO2conversion of CoNi/Al2O3was lower than that of MgCoNi/

Al2O3. After 200 h of CDR, however, the former showed 89.3%

CO2conversion and the latter 96.7%. These data indicate that

MgCoNi/Al2O3is more active and stable than CoNi/Al2O3. Thetrend of CH4conversion was similar to that of CO2conversion.

In the case of CoNi/Al2O3, CH4conversion was decreased from

88.3 to 85.5%. On the contrary, the MgCoNi/Al2O3 catalyst

exhibited still high CH4 conversion (95.1%) at the GHSV of

40,000 mL g1 h1. It is a rare case that a supported Ni catalyst

shows very high activity as well as stability at the GHSV of

40,000 mL g1 h1 in CDR for 200 h. H2yield was lower than CO

yield due to the reverse water gas shift reaction (RWGS:

H2CO2/H2OCO). As a result, the H2/CO ratio value was

lower than 1.0.

To evaluate the effect of coke, used catalysts were charac-

terized by TGA in air. Fig. 8 depicts the Thermo-gravimetric

(TG) profiles for the quantitative analysis of carbonaceous

species in the used catalysts (CoNi/Al2O3and MgCoNi/Al2O3).

According to previous reports[67e70], up to 300 C, the initial

weight loss is assigned to the thermal desorption of water and

removal of easily oxidizable carbonaceous species. Above

500 C, the large weight loss can be assigned to theoxidationof

coke to CO and CO2. In other words, the oxidation of amor-

phous carbonaceous species occurs at low temperature, while

graphitic carbon is oxidized at high temperature[61,71]. In the

Fig. 5e In-situ DRIFT spectra of CO2reforming on CoNi/Al2O3and MgCoNi/Al2O3catalysts at 300 C.

Fig. 6 e CH4and CO2conversion and H2/CO ratio of CoNi/

Al2O3and MgCoNi/Al2O3catalysts with various

temperatures (Reaction conditions: P [ 1 atm,

GHSV [ 40,000 mL gL1 hL1, CH4:CO2:N2 [ 1:1:1).



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case of MgCoNi/Al2O3, about 5% weight loss was measured due

to theremoval ofboth amorphousand graphiticcarbon. On the

contrary, CoNi/Al2O3 showed the drastic weight loss (16%)

between 450 and660 C. As a consequence, CoNi/Al2O3 showedthe coking rate of0.80mgc/gcat h, while MgCoNi/Al2O3 revealed

the coking rate of 0.25 mgc/gcath. It should be noted that the

coking rate of MgCoNi/Al2O3 is 3 timeslowerthanthatof CoNi/

Al2O3. This clearly confirms that MgCoNi/Al2O3 has much

stronger coke resistance than CoNi/Al2O3in CDR. It suggests

that the addition of MgO effectively stabilizes the catalyst in

CDR. This is possibly related to a strong interaction between Ni

and MgO, confirmed from TPR. As a result, the MgCoNi/Al2O3catalyst exhibited the outstanding performance under severe

condition (GHSV of 40,000 mL g1 h1 for 200 h). In addition, to

elucidatethe beneficial effect of MgOin preventing sintering of

Ni, used catalysts were characterized by XRD (Fig. 9). At the

initial stage, the Ni crystallite size of CoNi/Al2O3 is slightlysmaller than that of MgCoNi/Al2O3. After the reactionfor 200h,

however, the former shows 18.9 nm Ni crystallite size and the

latter 9.5 nm (Table 1).Thus, itis confirmedthat the additionof

MgOis highly effective in preventing the sintering of Ni in CDR.

Nitrogen adsorption/desorption isotherms were used to

confirm the structural properties of CoNi/Al2O3and MgCoNi/

Al2O3 catalysts and the results are shown in Fig. 10. All iso-

therms present a sharp step at intermediate relative pressure

(P/P0) of 0.5e0.9. All the samples give type IV adsorption iso-

therms with a hysteresis loop, indicating that the mesoporous

framework of Al2O3can be well-retained after the impregna-

tion of Mg, Co, and Ni [72]. It is clear that the pore volume of

CoNi/Al2O3was significantly decreased, which is due to coke

formation and sintering, while the pore volume of MgCoNi/

Al2O3did not change significantly.

4. Conclusions

MgCoNi/Al2O3exhibited higher CH4and CO2conversion than

CoNi/Al2O3with the temperature range from 700 to 850 C at

the GHSV of 40,000 mL g1 h1 in CDR. In addition, the

MgCoNi/Al2O3 catalyst showed stable activity at 850 C for

200 h, while the CoNi/Al2O3catalyst deactivated with time on

stream. The remarkable catalytic performance of the MgCoNi/

Al2O3 catalyst is mainly ascribed to the beneficial effect of

MgO, resulting from the basic nature of MgO, a strong inter-

action between Ni and MgO, and rapid decomposition/disso-ciation of CH4and CO2. As a result, the MgCoNi/Al2O3catalyst

can possess stronger resistance againstcoke formation and Ni

Fig. 7e CH4and CO2conversion and H2/CO ratio of CoNi/

Al2O3and MgCoNi/Al2O3catalysts over reaction for 200 h

(Reaction conditions: T[ 850 C, P [ 1 atm,

GHSV [ 40,000 mL gL1 hL1, CH4:CO2:N2 [ 1:1:1).

Table 2e Reaction data of the catalysts. Final data were obtained after 200 h of CDR reaction.

Catalyst description Conversion (%) Yield (%) H2/CO ratio Coking rate (mgC/gcath)

CH4 CO2 H2 CO

Initial CoNi/Al2O3 88.3 92.1 88.9 92.4 0.92 e

Final CoNi/Al2O3 85.5 89.3 86.6 89.9 0.90 0.80

Initial MgCoNi/Al2O3 95.0 96.6 94.2 96.9 0.97 e

Final MgCoNi/Al2O3 95.1 96.7 94.1 97.0 0.96 0.25

(Reaction conditions:T 850

C,P 1 atm, GHSV 40,000 mL g

1

h

1

, CH4:CO2:N2 1:1:1).

Fig. 8 e Thermogravimetric and differential

thermogravimetric profile of CoNi/Al2O3and MgCoNi/Al2O3catalysts after reaction for 200 h (Reaction conditions:

T[ 850 C, P [ 1 atm, GHSV [ 40,000 mL gL1 hL1,

CH4:CO2:N2 [ 1:1:1).



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sintering than the CoNi/Al2O3 catalyst. Therefore, MgCoNi/

Al2O3 catalyst can be a promising catalyst for CDR, which

utilizes two major green house gases (CO2and CH4).

Acknowledgments

The authors gratefully acknowledge financial support from

the Samsung Advanced Institute of Technology (SAIT), Sam-

sung Electronics Co. Ltd.

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Fig. 10e Nitrogen adsorption/desorption isotherms of

reduced (filled symbol) and used (open symbol) catalysts

after reaction for 200 h.

Fig. 9eXRD patterns of used CoNi/Al2O3and MgCoNi/Al2O3catalysts (Reaction conditions: T[ 850 C, P [ 1 atm,

TOS [ 200 h).

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