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Applied Surface Science 307 (2014) 682–688

Contents lists available at ScienceDirect

Applied Surface Science

journa l h om epa ge: www.elsev ier .com/ locate /apsusc

g-Al oxide supported Ni catalysts with enhanced stability forfficient synthetic natural gas from syngas

ei-Ting Fan, Kun-Peng Miao, Jing-Dong Lin ∗, Hong-Bin Zhang, Dai-Wei Liaoepartment of Chemistry, College of Chemistry and Chemical Engineering, State Key Laboratory for Physical Chemistry of Solid Surfaces, Nationalngineering Laboratory for Green Chemical Productions of Alcohols-Ethers-Esters, Institute of Physical Chemistry, Xiamen University, Xiamen 361005, China

r t i c l e i n f o

rticle history:eceived 25 February 2014eceived in revised form 14 April 2014ccepted 15 April 2014vailable online 23 April 2014

eywords:ynthetic natural gasethanation

a b s t r a c t

Mg-Al oxide supported Ni catalysts prepared by co-precipitation method for synthetic natural gas (SNG)from syngas methanation were developed. The properties of the catalysts were investigated by XRD,H2-TPR and nitrogen physisorption, etc. The catalytic syngas methanation activity tests showed that Mg-Al oxide supported Ni catalysts not only showed high activity at low reaction temperature (98.4% CH4

yield at 250 ◦C) compared with Ni/MgO (97.0% CH4 yield at 310 ◦C) but also showed an excellent thermalstability (maintained 95.2% CH4 yield after reaction at 700 ◦C for 8 h) compared with Ni/Al2O3 (12.4%CH4 yield after reaction at 700 ◦C for 8 h). The XRD and nitrogen physisorption results indicated that thehigh catalytic activity of Mg-Al oxide supported Ni catalyst was related to the smaller Ni particle size

g-Al oxidehermal stabilityetal-support interaction

compared with Ni/MgO, which attributed to the higher specific surface area of Mg-Al oxide than that ofMgO. The XRD and H2-TPR results suggested that the excellent thermal stability of Mg-Al oxide supportedNi catalyst was ascribed to the stronger metal-support interaction in comparison with Ni/Al2O3. Thisstudy demonstrates that tailoring the composite oxide catalyst support properties is an effective way todevelop high-performance catalysts for SNG from syngas.

© 2014 Elsevier B.V. All rights reserved.

. Introduction

Moving away from coal to alternatives, such as natural gas, isne of the important acts to prevent serious air pollutions in northhina, which were frequently reported recently. Therefore, produc-ion of synthetic natural gas (SNG) via methanation process fromyngas, which can be derived from coal or renewable biomass, haseceived widespread attention due to the lacking of natural gas inhina [1,2].

The methanation processes of carbon oxides toNG, i.e., CO + 3H2 = CH4 + H2O, �H298K = −206 kJ/mol;O2 + 4H2 = CH4 + 2H2O, �H298K = −165 kJ/mol, are stronglyxothermic and thermodynamically feasible [3,4]. One of theost challenges for SNG from syngas is the large amounts of

eat released from the reaction in comparison with selective COethanation in a H2-rich stream [5]. Ni based catalysts are the

ost commonly used methanation catalysts due to their relatively

igh activity and low cost. Tailoring of Ni-based catalysts both

∗ Corresponding author at: Department of Chemistry, Xiamen University, Xiamen61005, China. Tel.: +86 592 218 3045; fax: +86 592 218 3043.

E-mail addresses: jdlin@xmu.edu.cn, jdlin@189.cn (J.-D. Lin).

ttp://dx.doi.org/10.1016/j.apsusc.2014.04.098169-4332/© 2014 Elsevier B.V. All rights reserved.

with high activity and thermal stability for methanation of syngasto SNG is needed.

Abundant efforts have been made aiming to develop Ni-basedcatalysts with high activity and excellent thermal stability formethanation of carbon monoxide to SNG, including modificationcatalyst support, adding promoters and the preparation methodsof catalysts etc. Among them, catalyst supports have crucial impacton the stability and activity of Ni catalysts. Al2O3 is the most widelyused catalyst support for Ni-based catalysts for SNG from syngas.Hu et al. [6] found that Al2O3 with large surface area, a properNi content (20 wt%) and a moderate interaction between Ni andAl2O3 were in favor of formation of small NiO particles, which lead-ing to high catalytic activities for SNG production. Zhang et al. [7]reported that the performance of MgO-modified NiO/Al2O3 catalystfor CO methanation was better than those of NiO/ZrO2-Al2O3 andNiO/SiO2-Al2O3 prepared by modified grinding-mixing method inthe reaction temperature range 300–700 ◦C. However, Ni/Al2O3catalysts suffered from serious deactivation due to the sintering ofcatalysts during the highly exothermic process [8,9]. Maintaininghigh activity and stability of the catalysts simultaneously is crucial

for the strongly exothermic methanation process.

Generally, the stronger metal-support interaction would resultin more excellent thermal stability of catalysts [10]. For Ni/MgOcatalysts, it is well known that the reduction of NiO-MgO solid

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olution to metal Ni is difficult due to the strong interactionetween Ni and MgO, resulting in a higher thermal stability [11].or example, Tomohiro et al. [12] reported that aggregation ofi metal particle was depressed by MgO during the reduction of

he NiO-MgO solid solution. For CO methanation, small amountf MgO was often used in the supported metal catalysts as atructural promoter [6,7,13]. However, the specific surface area ofgO is much smaller than that of Al2O3, which would result in

ower activity of Ni/MgO than that of Ni/Al2O3 [14,15]. Ni/Al2O3nd Ni/MgO catalysts were also widely studied in catalytic steam-ethane reforming (SMR), a reverse process of CO methanation

16–19]. Mg-Al oxides supported Ni catalysts showed good cat-lytic performance and stability for SMR. For example, Ni/Mg-Alxide supported catalyst with highly dispersed and stable Ni metalarticles prepared by solid phase crystallization method from Mg-l hydrotalcite precursors have been used for SMR and methaneecomposition [20–22]. MgAl2O4 spinel was also used as sup-orts of bimetallic Ni-Fe catalysts for CO methanation [23], whichesulted in enhanced reactivity in comparison with Al2O3 sup-orted catalysts. In view of the advantages and disadvantages ofl2O3 and MgO, Mg-Al oxides are expected to be the suitable sup-ort of Ni-based catalyst not only with higher activity but also withnhanced thermal stability for SNG from syngas.

To the best of our knowledge, very few researches havettempted in-depth studies of the effects of Mg-Al oxides on thectivity and thermal stability of Ni-based catalyst for SNG from syn-as. In order to develop an enhanced thermal stability catalyst forfficient SNG from syngas, in this work, the Mg-Al oxide supportedi catalyst was prepared using modified co-precipitation method

rom Mg-Al hydrotalcite precursors for SNG from syngas. The rolesf Mg-Al oxide in the Ni-based catalyst are hereby discussed.

. Experimental

.1. Catalyst preparation

The Mg-Al oxide supported Ni catalysts were prepared by mod-fied co-precipitation under low saturation method, which waseported for hydrotalcite synthesis [20]. The metal nitrate aqueousolution was obtained by dissolving 10.9 g Ni(NO3)2·6H2O, 12.8 gg(NO3)2·6H2O and 9.4 g Al(NO3)3·9H2O (all in A. R. grade) in

5 mL deionized water. An aqueous solution of NaOH and Na2CO3ith a molar ratio of 4:1 (1.6 mol/L and 0.4 mol/L, respectively) wassed as precipitant. The precursor of mixed oxide was preparedy simultaneously adding these two solutions mentioned aboveery slowly to a container under continuous stirring at room tem-erature, while the pH of the mixed solution was held at 10 ± 0.2y controlling the dropping rate. After aging for 12 h at 90 ◦C, therecipitate was washed with deionized water until the filtrateas neutral, and then it was dried at 110 ◦C for 12 h. The Mg-Al

xide supported Ni catalyst was then obtained by calcining therecipitate at 450 ◦C in air for 5 h. The fresh calcined catalyst wasenoted as Ni/Mg2Al(O), wherein, the molar ratio of Mg/Al was 2/1,nd the precipitate before calcined was noted as the precursor ofi/Mg2Al(O). Ni/Al2O3 and Ni/MgO catalysts were also preparedith the same process for comparison. The Ni content of all therepared catalysts was fixed at 40 wt%.

.2. Characterization

The X-ray diffraction (XRD) patterns were conducted on a

igaku D/MAX-rC X-ray diffractometer with Cu K� radiation� = 0.15418 nm). The tube voltage was 35 kV and the currentas 15 mA. The crystal size of the catalyst was calculated using

he Debye–Scherrer equation. Nitrogen adsorption–desorption

cience 307 (2014) 682–688 683

isotherms were measured by static N2 physisorption at 77 Kusing a Micromeritics TriStar II 3020 surface area and pore ana-lyzer. All samples were outgassed and evacuated at 250 ◦C for2 h before adsorption. The specific surface area was determinedaccording to the Brunauer–Emmett–Teller (BET) method. The aver-age pore diameter and pore size distributions were evaluated bythe Barrett–Joyner–Halenda (BJH) method using the desorptionbranch of isotherms. The pore volumes were evaluated at a rela-tive pressure (P/P0) of 0.99. Hydrogen temperature-programmedreduction (H2-TPR) experiments were performed on a Micromeri-tics Autochem II 2920 instrument. Prior to the H2-TPR test, 50 mgcalcined catalyst was pretreated in a quartz U-tube reactor at 450 ◦Cfor 1 h under a gas flow of Ar to remove physically adsorbed impu-rities. And then the H2-TPR experiments were taken in a gas flowof 5%H2-95%Ar (30 mL min−1) with the temperature elevated from50 ◦C to 900 ◦C at a rate of 5 ◦C min−1. The outlet gas was passedthrough a 5A zeolite trap to remove moisture and then the hydro-gen consumption rate was monitored by a thermal conductivitydetector (TCD).

2.3. Evaluation of catalyst performance

The evaluation of Ni catalysts for syngas methanation was car-ried out in a continuous flow fixed-bed reactor equipped with aquartz tube. Prior to the reactivity measurements, 100 mg of thecatalyst, diluted with 500 mg of quartz sand (both of 40–80 mesh),was reduced at a certain temperature, e.g., 600 ◦C, 650 ◦C and 700 ◦C,for 5 h in a gas flow of 5%H2-95%Ar (30 mL min−1) and then thetemperature was lowered to 200 ◦C. The syngas methanation wasperformed in the feed gas of V(H2)/V(CO)/V(CO2)/V(N2) = 75/15/5/5in a temperature range of 200–350 ◦C at a weight hourly spacevelocity (WHSV) of 40,000 mL g−1 h−1 under atmospheric pressure.The outlet stream was monitored by an online gas chromatograph(GC2060, Shanghai RAMI Instrument Co., Ltd.) equipped with athermal conductivity detector (TCD) and a flame ionization detec-tor (FID). The TCD was equipped with a TDX-01 packed column(1 m in length) and the FID with a Porapak Q-S packed column(2 m in length), respectively. After two hours of steady-state oper-ation at each temperature, the concentrations of CO, CO2 and N2(N2 as an inner standard) were analyzed by the TCD, and the con-centrations of CH4 and other C-containing hydrogenated productswere determined by FID. The conversion of CO and total conver-sion of CO and CO2 were determined by the N2 internal standard.The carbon-based selectivity for CH4 selectivity was calculated byan internal normalization method. And the yield of CH4 was cal-culated by multiplying the value of total conversion of CO and CO2and CH4 selectivity.

3. Results and discussion

3.1. Catalyst characterizations

Nitrogen adsorption–desorption isotherms were measured inorder to obtain the informations of the specific surface area andthe pore structure of the as-synthesized catalysts. The results ofthe specific surface area (SBET), pore volume (VP) and average porediameter (DP) are summarized in Table 1. Both of Ni/Al2O3 andNi/Mg2Al(O) catalysts exhibit substantially higher surface area,200.3 m2 g−1 and 215.0 m2 g−1, respectively, which is about 2.6times than that of Ni/MgO catalyst (76.9 m2 g−1). This result indi-cates that the specific surface area of Ni/Mg2Al(O) is as large asthat of Ni/Al2O3, even if incorporation of MgO, which is with

lower specific surface area, into Ni/Al2O3. Mg-Al oxide and Al2O3both exhibit large specific surface area, which would be ben-eficial for the dispersion of Ni active component. Ni/Mg2Al(O)catalyst shows distinct lager pore volume (0.53 cm3 g−1) than that

684 M.-T. Fan et al. / Applied Surface Science 307 (2014) 682–688

Fig. 1. N2 adsorption–desorption isotherms (a) and BJH desorpti

Table 1Textural property of the fresh calcined catalysts.

Catalyst SBET (m2 g−1) VPa (cm3 g−1) DP

b (nm)

Ni/Al2O3 200.3 0.36 5.7Ni/Mg2Al (O) 215.0 0.53 9.0Ni/MgO 76.9 0.21 7.0

ottFs[hlF

aohNA

metal-support interaction of the prepared catalysts. Fig. 3 shows

a BJH desorption pore volume.b BJH desorption average pore diameter.

f Ni/Al2O3 (0.36 cm3 g−1) and Ni/MgO (0.21 cm3 g−1). Fig. 1 showshe N2 adsorption–desorption isotherms and the pore size distribu-ions. The N2 adsorption–desorption isotherms of the samples (seeig. 1(a)) are of type IV, which is characteristic of the mesoporoustructure with the H2 hysteresis loops ascribed to ink-bottle pores15,24]. In the case of Ni/Mg2Al(O), the hysteresis loop extends toigher relative pressure, implying the existence of mesopores with

arger sizes, which is confirmed by the pore size distribution inig. 1(b).

Fig. 2 shows the XRD patterns of the precursor of oxide cat-lysts and the fresh calcined catalysts. In Fig. 2(a), the precursorf Ni/Mg Al(O) presents the diffraction lines of a well-crystallized

2ydrotalcite (HT) phase (JCPDS No. 22-700), but the precursor ofi/Al2O3 also presents a Al(OH)3 phase (JCPDS No. 01-076-1782).fter calcined at 450 ◦C (see Fig. 2(b)), Ni/Al2O3 catalyst presents

Fig. 2. XRD patterns of Ni catalysts before

on pore size distribution (b) of the fresh calcined catalysts.

board diffraction peaks ascribed to NiO (JCPDS No. 01-078-0643)and NiAl2O4 (JCPDS No. 01-1299). The XRD pattern of calcinedNi/MgO shows strong diffraction peaks at 2� = 37.0, 42.8 and 62.2◦

assigned to MgO (JCPDS No. 01-075-0447) and NiO, which are over-lapped each other. As for calcined Ni/Mg2Al(O), the XRD patternshows smaller diffraction peaks compared to Ni/MgO. After incor-porating of Al2O3, it is noteworthy that the diffraction peaks ofNi/Mg2Al(O) shift from 2� = 42.8 to 43.3◦, from 2� = 62.2 to 62.8◦,respectively, compared to Ni/MgO. The observed board diffractionpeaks of calcined Ni/Mg2Al(O) at 2� = 43.3 and 62.8◦ can be assignedto Mg(Ni, Al)O solid solution, indicating that Al3+ and Ni2+ is incor-porated into the MgO structure [25]. In order to further distinguishthe diffraction peaks of calcined Ni/Mg2Al(O), the XRD characteri-zations of MgO, Al2O3 and Mg2Al(O) were also carried out. As canbe seen from Fig. S2, the diffraction peaks of Mg2Al(O) are assignedto Mg(Al)O solid solution. The formation of Mg(Al)O solid solu-tion would help to improve the stability of the Mg2Al(O) support.Though it is difficult to distinguish NiO due to the formation ofMg(Ni, Al)O solid solution, it can be seen from Fig. 2(b) that Ni wasmore uniformly distributed on Mg2Al(O) and Al2O3 than on MgO.

H2-TPR experiments were carried out to characterize the

the H2-TPR profiles of the Ni catalysts supported on differentsupports. It can be identified that there is mainly a peak of H2-consumption, occurring between 300 ◦C and 860 ◦C, corresponding

(a) and after (b) calcined at 450 ◦C.

M.-T. Fan et al. / Applied Surface S

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Fig. 3. H2-TPR profiles of Ni catalysts with different supports.

o the reduction of NiO to Ni [26–28]. According to peak positionf the reduction temperature in the TPR spectra, the reducibleiO species can be divided into three or four types, corresponding

o different intensity of metal-support interaction [6,29,30]. Theesult of H2-TPR of Ni/MgO shows that there is relatively a broadeak width of H2-consumption, indicating that there are nonuni-orm nickel oxides species dispersed on MgO. The nonuniformickel oxides dispersion may result from the lower specific surfacerea of MgO which is not large enough to disperse the nickel. Aso Ni/Al2O3, there is a big H2 consumption peak at ∼520 ◦C and amall shoulder peak at ∼660 ◦C observed. After incorporation withgO, the H2 consumption peak of Ni/Mg2Al(O) shifts from 520 ◦C

o a higher temperature of 590 ◦C. This result indicates that Mg-Alxide supported Ni catalyst exhibits stronger metal-support inter-ction than that on Al2O3. It is noted, as can been seen from H2-TPRpectra, the dispersion of Ni on Mg2Al(O) is more uniform thanhat on MgO, which are consistent with the XRD results. There-ore, the Mg2Al(O) supported Ni catalysts not only have strong

etal-support interaction, but also possess uniform Ni dispersion.

.2. Catalyst activities

.2.1. Methanation performance at low temperatureFig. 4 shows the syngas methanation activities of the prepared

atalysts reduced at 600 ◦C, noted as Ni/Al2O3-600, Ni/Mg2Al(O)-00 and Ni/MgO-600. It can be seen from Fig. 4(a) and (b) that

he CO + CO2 conversion and the CH4 selectivity increase signif-cantly with increasing temperature from 200 to 350 ◦C for allatalysts. The conversions of CO + CO2 achieve a high level (96.9%nd 98.4%) at a temperature of 240 ◦C over Ni/Al2O3-600 and 250 ◦C

Fig. 4. Catalytic activities of Ni catalysts on different supports: (a

cience 307 (2014) 682–688 685

over Ni/Mg2Al(O)-600, respectively. However, the CO + CO2 conver-sion is not over 97.0% until the reaction temperature rising to 310 ◦Con Ni/MgO-600. The maximum CH4 selectivity over the three cat-alysts can reach about 100%. It is clearly seen from Fig. 4(c) thatthe CH4 yield over Ni/Al2O3-600 and Ni/Mg2Al(O)-600 reach 96.9%and 98.4% at a lower temperature of 240 ◦C and 250 ◦C, respectively,while it goes to 310 ◦C for Ni/MgO-600 to reach 97.0% CH4 yield.These results demonstrate that the Al2O3 and Mg-Al oxide sup-ported Ni catalysts show better activity for syngas methanationthan MgO supported Ni catalyst. It seems that the poor catalystperformance of MgO supported Ni catalyst is caused by the smallspecific surface area of Ni/MgO. The better activity of Al2O3 andMg-Al oxide supported Ni catalysts probably ascribed to the largespecific surface area of Ni/Al2O3 and Ni/Mg2Al(O), which is favor inresulting in smaller Ni particle.

Considering the different reduction temperatures of the Ni cat-alysts obtained from H2-TPR, the catalytic measurements werealso carried out over the catalysts reduced at higher temperature,i.e., 650 ◦C and 700 ◦C, noted as Ni/Al2O3-650, Ni/Mg2Al(O)-650,Ni/MgO-650, Ni/Al2O3-700, Ni/Mg2Al(O)-700 and Ni/MgO-700,respectively, and the results are shown in Fig. 5. Compared withthe catalysts reduced at 600 ◦C, the catalysts perform in an order ofNi/Mg2Al(O) > Ni/Al2O3 > Ni/MgO for CO + CO2 conversion in boththe case of reduction temperature at 650 ◦C and 700 ◦C, as shownin Fig. 5(a and d). Specifically, the temperature of CO + CO2 conver-sion (>96.9%) rises to 250 ◦C over Ni/Al2O3-650 and Ni/Al2O3-700(240 ◦C over Ni/Al2O3-600). However, in the case of Ni/Mg2Al(O)and Ni/MgO, in comparison with the catalysts reduced at 600 ◦C,the temperature of CO + CO2 conversion (>96%) shift to lower val-ues, i.e., 220 ◦C, 240 ◦C over Ni/Mg2Al(O)-650, Ni/Mg2Al(O)-700(250 ◦C over Ni/Mg2Al(O)-600) and 290 ◦C, 275 ◦C, for Ni/MgO-650, Ni/MgO-700 (310 ◦C for Ni/MgO-600), respectively. The mostappropriate reduction temperature for Ni/Al2O3 catalyst perfor-mance is 600 ◦C, while Ni/Mg2Al(O) and Ni/MgO prefer a higherreduction temperature. The decrease in activity for syngas metha-nation over Al2O3 supported Ni catalysts with increasing reductiontemperature, indicating its instability compared with Ni/Mg2Al(O)and Ni-MgO catalysts. The excellent stability of Mg-Al oxideand MgO supported Ni catalysts probably due to the strongermetal-support interaction as shown in H2-TPR profiles, while themetal-support interaction of Ni/Al2O3 is too weak to maintain thecatalytic activity at a higher reduction temperature.

3.2.2. Thermal stability testThermal stability is one of key indexes for methanation cata-

lysts. In order to further explore the stability of the as-prepared

Ni catalysts, a heat treatment experiment was taken at reactiontemperature of 600 ◦C, 650 ◦C and 700 ◦C for 8 h, respectively, fol-lowing by cooling down to 200 ◦C and sampling reaction data. Theresults of the catalytic activities over Ni/Al2O3, Ni/Mg2Al(O) and

) CO + CO2 conversion; (b) CH4 selectivity and (c) CH4 yield.

686 M.-T. Fan et al. / Applied Surface Science 307 (2014) 682–688

(a an

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Fig. 5. Catalytic activities of Ni catalysts reduced at different temperature:

i/MgO catalysts with and without the heat treatment are listed inable 2. For Ni/Al2O3, after reaction at 700 ◦C for 8 h, the CO + CO2onversion and CH4 yield sharply decrease to 19.3% and 12.4% com-aring with that of 96.9% and 96.9% over the catalyst without heatreatment. By contrast, the catalytic activities on Ni/Mg2Al(O) andi/MgO catalysts maintain at a high level (CH4 yield > 94.2%) with

ncreasing heat treatment temperature at 650 ◦C and 700 ◦C for 8 h,espectively. It is to conclude that Mg-Al oxide and MgO supportedi catalysts have much better thermal stability than the Al2O3 sup-orted Ni catalyst for SNG from syngas.

In order to understand the roles of supports in the catalyticctivity and thermal stability of Ni catalysts for SNG from syngas,he XRD characterizations of the used Ni catalysts were carried out.ig. 6 shows the XRD patterns of the used Ni catalysts after the heat

reatments at different temperature for 8 h and the freshly reducedatalysts. The Ni/Al2O3 catalysts (Fig. 6(a)) present group of diffrac-ion peaks at 2� = 44.5, 51.8 and 76.4◦ assigned to metal Ni (JCPDSo. 01-087-0712), and group of diffraction peaks at 2� = 37.6,

able 2omparison of methanation activities of the catalysts after reaction at different temperat

Catalyst Reaction temperature (◦C)a CO + CO2 con

Ni/Al2O3b

– 96.9

600 96.2

650 93.8

700 19.3

Ni/Mg2Al(O)c

– 98.4

600 99.0

650 98.5700 95.2

Ni/MgOd

– 97.0

600 98.4

650 98.5

700 94.2

a The catalyst was reacted in feed gas at a certain temperature (600, 650, 700 ◦C respecampling temperature: b 240 ◦C, c 250 ◦C, d 310 ◦C.

d d) CO + CO2 conversion; (b and e) CH4 selectivity and (c and f) CH4 yield.

45.9 and 66.9◦ assigned to Al2O3 (JCPDS No. 01-077-0396). Thediffraction peaks of Ni and Al2O3 become gradually more intenseand sharper with increasing of heat treatment temperature from600 ◦C to 700 ◦C, especially in the case of 700 ◦C. The XRD resultsindicate that the aggregation of Ni particle and sintering of Al2O3support are one of the keys to the severe deactivation of theNi/Al2O3 catalyst after heat treatment at 700 ◦C for 8 h. However,the grain growth of Ni particle is not significant for Ni/Mg2Al(O)before and after heat treatment at higher temperatures as shownin Fig. 6(b), suggesting a good resistance to sintering and superiorstability of the Mg-Al oxide supported Ni catalyst. Ni/Al2O3 per-forms well at a low reaction temperature for syngas methanation,but is suffered from a rapid deactivation at high temperature dueto severe sintering of Ni particles and Al2O3 support. Mg-Al oxide

supported Ni catalyst, however, provides not only high activity atlow reaction temperature but also an excellent thermal stabilitybenefited from the resistance to sintering of the catalysts. It wasreported that the test of methanation pilot plant was generally run

ures.

version (%) CH4 selectivity (%) CH4 yield (%)

100.0 96.9100.0 96.2100.0 93.8

64.4 12.4

100.0 98.4100.0 99.0100.0 98.5100.0 95.2

100.0 97.0100.0 98.4100.0 98.5100.0 94.2

tively) for 8 h, followed by cooling to 200 ◦C.

M.-T. Fan et al. / Applied Surface Science 307 (2014) 682–688 687

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Fig. 6. XRD patterns of the catalysts before and after the heat treatme

etween 300 ◦C and 700 ◦C [31]. Therefore the results of thermaltability test verify that Ni/Mg2Al(O) catalyst for SNG from syngasould meet the thermal stability requirements of SNG from syngas.

. Conclusions

In summary, Mg-Al oxide supported Ni catalysts prepared by co-recipitation method for synthetic natural gas (SNG) from syngasethanation were developed. Ni/Al2O3 shows a relatively excel-

ent catalytic activity at low temperature for SNG from syngas,ut with a poor thermal stability at high reaction temperature.s for Ni/MgO, an excellent thermal stability for SNG from syn-as is shown, but with a poor catalytic activity at low temperature.owever, Ni catalysts supported on Mg-Al mixed oxide demon-

trate not only a relatively high catalytic activity at low temperatureompared with Ni/MgO, but also an excellent thermal stability com-ared with Ni/Al2O3, which is crucial for the strongly exothermicethanation process. The excellent catalytic activity and thermal

tability of Ni/Mg2Al(O) were ascribed to the large specific surfacerea and strong metal-support interaction, respectively. This studyemonstrates that tailoring the properties of composite oxide cat-lyst support is one of the effective ways to develop catalysts withnhanced thermal stability for efficient SNG from syngas.

cknowledgements

This wok has been supported by the National Key Basic Researchrogram of China (973) (2011CBA00508) and National Found forostering Talents of Basic Science of China (NFFTBS) (No. J1310024).

ppendix A. Supplementary data

Supplementary data associated with this article can beound, in the online version, at http://dx.doi.org/10.1016/j.apsusc.014.04.098.

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