Synthetic natural gas from CO hydrogenation over silicon carbide supported nickel catalystsYue Yu a ,b ,Guo-Qiang Jin a ,Ying-Yong Wang a ,Xiang-Yun Guo a ,⁎a State Key Laboratory of Coal Conversion,Institute of Coal Chemistry,Taiyuan 030001,PR China bGraduate University of the Chinese Academy of Sciences,Beijing 100039,PR Chinaa b s t r a c ta r t i c l e i n f o Article history:Received 19March 2011Received in revised form 23July 2011Accepted 1August 2011Available online xxxx Keywords:CO methanation Ni/SiC catalyst Ni/TiO 2catalyst StabilitySilicon carbide supported nickel catalysts for CO methanation were prepared by impregnation method.The activity of the catalysts was tested in a fixed-bed reactor with a stream of H 2/CO =3without diluent gas.The results show that 15wt.%Ni/SiC catalyst calcined at 550°C exhibits excellent catalytic activity.As compared with 15wt.%Ni/TiO 2catalyst,the Ni/SiC catalyst shows higher activity and stability in the methanation reaction.The characterization results from X-ray diffraction and transmission electron microscopy suggest that no obvious catalyst sintering has occurred in the Ni/SiC catalyst due to the excellent thermal stability and high heat conductivity of SiC.©2011Elsevier B.V.All rights reserved.1.IntroductionNature gas is a clean fuel in fossil fuels and it has a higher calori fic value comparing with petroleum and coal.In recent years,the production of synthetic natural gas from coal and solid dry biomass has been a concern due to the rising price and exhaustion of natural gas [1,2].As one of the most essential steps in the production of SNG [1],the methane synthesis from carbon monoxide and hydrogen has been paid more attention.Different types of methanation catalysts have been developed and widely investigated since the reaction was first reported by Sabatier and Senderens in 1902[3].Although noble metal catalysts show higher activity [4,5],Ni-based catalysts are widely applied due to the low-cost and good availability [1].Many materials such as TiO 2,Al 2O 3,CeO 2,SiO 2,ZrO 2,MgO,YSZ and MgAl 2O 4have been investigated as the support of nickel catalysts [6–10].It is found that the support materials can strongly in fluence the activity of nickel catalysts.Several groups have reported that the nickel catalyst using TiO 2as the support is effective for CO methanation reaction [8,11,12],and the aim of the above studies is to remove carbon monoxide in hydrogen-rich gas for the use in polymer electrolyte fuel cells or ammonia synthesis.There are also some studies on methanation reaction using higher CO concentrations [13,14].However,it is well known that the reaction of CO methanation is a strongly exothermic reaction (3H 2+CO →CH 4+H 2O,ΔH°=−206kJ·mol −1)[6].When the nickel catalysts using conventional supports are used in the methanation reaction with a stream flow of H 2/CO=3,the reaction heat can rapidly accumulate onthe catalysts and make the catalysts sintered.Eisenlohr et al.reported that commercial methanation catalysts always showed a fast deactivation due to the temperature raise of catalyst bed [15].One way to solve the problem is to connect methanation reactors in series with intermediate gas cooling [1].In addition,the problem can also be solved by employing highly thermo-conductive and thermo-stable materials as the support of CO methanation catalysts.Silicon carbide (SiC)exhibits many superior properties,i.e.excellent thermostability,high mechanical strength,high chemical inertness,low coef ficient of thermal expansion and high thermal conductivity.Due to these properties,SiC could be employed as catalyst support in rigorous conditions,i.e.high endothermic or exothermic reactions,strong acidic or basic solution [16].Nguyen et al.[17]reported that SiC with medium surface area could function as catalyst support in the CO 2reforming of methane.Our group investigated the performance of Ni/SiC catalysts for the partial oxidation of methane and methane combustion,and found that the Ni/SiC catalysts showed high catalytic activity and stability [18,19].However,to our knowledge,nickel catalysts using SiC as the support are less investigated for CO methanation reaction.In this work,the catalytic behavior of Ni/SiC catalysts for CO methanation reaction with a stream flow of H 2/CO=3was investigated.The results showed that the silicon carbide supported nickel catalyst exhibited high catalytic activity and stability in CO methanation.2.Experimental 2.1.Catalyst preparationSiC support was prepared by a sol –gel and carbothermal reduction route [20],and TiO 2support was commercial product,P25.TheFuel Processing Technology 92(2011)2293–2298⁎Corresponding author.Tel.:+863514065282;fax:+863514050320.E-mail address:xyguo@ (X.-Y.Guo).0378-3820/$–see front matter ©2011Elsevier B.V.All rights reserved.doi:10.1016/j.fuproc.2011.08.002Contents lists available at ScienceDirectFuel Processing Technologyj o u r n a l h o me p a g e :w w w.e l s ev i e r.c om /l o c a t e /f u p ro ccatalysts were prepared by conventional impregnation method[18]. To prepare15wt.%Ni/SiC catalyst,1g of above SiC was added into 25.5mL Ni(NO3)2aqueous solution(0.1mol/L)with stirring for12h. Then the slurry was heated at80°C until nearly all the water evaporated and the mixture was dried at100°C for6h.Afterward the dried sample was calcined in air at different temperatures for4h. The similar processes can be used to prepare Ni/SiC catalysts with different nickel loadings.15wt.%Ni/TiO2catalyst was prepared by the similar route to15wt.%Ni/SiC catalyst.1g of TiO2was added into 25.5mL Ni(NO3)2aqueous solution and stirred for12h.After being heated and dried,the catalyst was calcined at550°C for4h in air.2.2.Catalyst testThe performance of the catalysts was tested in afixed-bed reactor (a40cm long stainless steel tube with an inner diameter of6mm). The reactor was heated up by a PID regulated oven and the reaction temperature was measured in the middle of the catalyst bed using a K-type thermocouple.Reaction gases,which consisted of H2and CO (molar ratio of H2/CO=3,without diluent gas),were supplied from high-pressure gas cylinders and theflow rate was controlled by mass-flow controller(MFC)to ensure a space velocity(GSV)of4500h−1.0.8mL of catalyst(sieve fraction40–60mesh)was placed in thecenter of the tubular reactor.All experiments were performed at a pressure of2.0MPa.Before each catalyst test,the catalyst was reduced at500°C in the CO/H2mixture gases for2h,then decreased to reaction temperature and kept for1h.The outlet gases were analyzed by GC-14B gas chromatograph with TDX-01column and a GDX-104 column using thermal conductivity detector andflame ionization detector.The selectivity of a certain product is calculated by the formula,S i=n i C i/∑n i C i,where n i and C i are the number of carbon atoms and the concentration of product“i”,respectively.2.3.Catalyst characterizationThe crystalline phases of the catalysts were analyzed by a Rigaku D-Max/RB X-ray diffractometer(XRD)with Cu Kαradiation with a scanning rate of6°/min.The catalyst morphology and structure were analyzed by a JEOL-2010transmission electron microscopy(TEM).The surface areas of catalysts were calculated from the BET method,which was performed at nitrogen temperature at77K on a Micromeritics Tristar3000analyzer.The nickel amount of catalysts was measured by ICP spectrometer.TG–DSC studies of the catalysts after reaction were performed on NETZSCHSTA409PC thermoanalyzer within a temper-ature range from room temperature to850°C at a heating rate of 10°C/min in airflow.3.Results and discussion3.1.CO methanation over Ni/SiC catalyst3.1.1.Influence of nickel loadingThe effect of metal loading on the activity of Ni/SiC catalysts was investigated,and the results are shown in Fig.1and Table1.It can be seen from Fig.1that the methanation activity of SiC supported catalysts increases with the nickel loading from5wt.%to15wt.%. Reaction rate of CO conversion which is defined as moles of CO converted per gram of Ni per second at250°C is shown in Table1.It can be seen that increasing the nickel loading from10wt.%to15wt.% results in an increase of the rate of CO conversion from1.28to 5.10μmol s−1g−1.However,when the nickel loading further in-creases to20wt.%,the rate of CO conversion at250°C decreases to 1.34μmol s−1g−1.As compared with15wt.%Ni/SiC catalyst,there is no significant increase in methanation activity for20wt.%Ni/SiC catalyst(Fig.1).The metal crystallite sizes calculated by Scherrer's equation[21]are shown in Table2.From the table,the metal crystallite size increases with increasing the nickel loading.The influences of the metal particle size on methanation activity have been studied by several authors.Panagiotopoulou et al.[8]reported that the rate of CO conversion increased by a factor of166with increasing the loading of Ru on TiO2from0.5wt.%to5wt.%.Takenaka et al.[11]reported that the Ni crystallites with relatively large sizes were more effective for CO methanation.Zhou et al.[22]demon-strated that the activity of CO hydrogenation increased with increasing the rhodium particle size in the range of 3.0–5.0nm. Therefore,CO methanation is a structure sensitive reaction and the larger particle size facilitates CO hydrogenation.20wt.%Ni/SiC catalyst has larger metallic particles but lower methanation activity than15wt.%Ni/SiC catalyst.The reason may be that both particle size and amount of active sites affect the methanation activity.It is well known that the larger crystallite size results in the decrease of metal dispersion on the surface of catalyst[8]and the latter one can affect the amount of active sites.Therefore,the lower rate of CO conversion may be due to the less active sites over20wt.%Ni/SiC compared with 15wt.%Ni/SiC catalyst.This is in accordance with the results reported by Aksoylu et al.[23],who found that the methane production per square meter of nickel surface area was enhanced with lower Ni loading over Ni/Al2O3catalysts.On the other hand,the large particle size on20wt.%Ni/SiC catalyst may block the external surface of support and this can also decrease the activity of CO methanation. Therefore,15wt.%is an optimal loading of Ni/SiC catalyst for methanation reaction.It should be noted that the products of CO hydrogenation under present reaction condition include methane,higher hydrocarbons (C2H6,C2H4,C3H8and C3H6),carbon dioxide and water.The forma-tion of CO2may be due to the water-gas-shift reaction,CO+Temperature (o C)EquilibriumCOConversion(%)T emperature (o C)COconversion(%)Fig.1.Influence of nickel loading on the activity of Ni/SiC catalysts and the calculated equilibrium CO conversions under P=2.0MPa,H2/CO=3and GSV=4500h−1.Table1Catalytic performance of Ni/SiC and Ni/TiO2catalysts.Catalyst Ni loading(wt.%)Rate of CO conversionat250°C(μmol s−1g−1)aCH4selectivityat320°C(%)Ni/SiC5–70.8910 1.2890.3115 5.1092.0420 1.3493.60Ni/TiO215 3.5282.21Reaction condition:H2/CO=3,GSV=4500h−1,and P=2.0MPa.a Converted CO per second per gram catalyst.2294Y.Yu et al./Fuel Processing Technology92(2011)2293–2298H2O=CO2+H2.The methane selectivity over the Ni/SiC catalysts at 320°C is shown in Table1.It can be seen that the methane selectivity increases with increasing the Ni loading.For CO methanation reaction, CO is adsorbed and dissociated on the surface of metal particles[24]and the dissociation of C\O bond in adsorbed CO species is the rate-determining step[25].It has been reported that there are three forms of adsorbed CO:linear CO,bridged CO and twin CO[26].The activity of adsorbed CO breaking into surface carbon and surface oxygen on the catalyst surface follows the sequence,bridged CO N linear CO N twin CO[10].According to the methanation mechanism,adsorbed CO is dissociated and converted into CH x as intermediate species by assistance of H on the surface of catalysts,and the concentration of the intermediate species determines the distribution of reaction products [25].For the methanation reaction,there are more active bridged CO on larger metallic particles[27],and then the rate of the dissociation and hydrogenation of intermediate species becomes faster[22,28]. Therefore,the methane selectivity is higher on high loading Ni/SiC catalysts.3.1.2.Thermodynamics and equilibrium conversionFrom Fig.1,the conversion of CO over Ni/SiC catalysts can increase up to100%with increasing the reaction temperature.When the reaction temperature is higher than440°C,however the CO con-version begins to decrease.It is most likely due to thermodynamic limitation.According to the thermodynamic equilibrium,theΔG can become positive when the temperature is higher than530°C[29]. Therefore,high temperature is favorable to the stream reforming of methane—the reverse of methanation.Supposing that the only product of CO hydrocarbon is methane, thermodynamic equilibrium data at the temperature range from100 to500°C are calculated.The calculation is performed under the same operating conditions as our experiments,i.e.H2/CO=3,P=2MPa. From Fig.1,the complete conversion of CO can be obtained below 250°C,and then the conversion slightly decreases with increasing the reaction temperature.The CO conversion decreases to87%when the reaction temperature rises to500°C.These are in agreement with the experimental results.3.1.3.Effect of calcination temperatureThe sizes of metallic particles in15wt.%Ni/SiC catalysts under different calcination temperatures are shown in Table2.It can be seen that the particle size increases with increasing the calcination temperature.It has been established that the methanation reaction is structure sensitive and larger particle size facilitates the cleavage of C\O bond[8,22,27,30].Therefore,the catalysts calcined at higher temperatures have higher catalytic activity for CO methanation.Fig.2 shows the influences of the calcination temperature on the activity of 15wt.%Ni/SiC catalyst for CO methanation.It can be seen that the CO conversion increases with increasing the calcination temperature from450°C to550°C.However,there is a little decrease in the CO methanation activity over the Ni/SiC catalyst calcined at600°C.This is likely due to that oversize particles formed at the high temperature could result in a decrease of active sites.Therefore,550°C is an optimal calcination temperature for15wt.%Ni/SiC catalyst.3.2.Performance of Ni/SiC and Ni/TiO2catalystsAccording to literature,TiO2supported nickel catalysts are effective for the CO methanation[8,11,12].Therefore,15wt.%Ni/SiC and15wt.%Ni/TiO2catalysts were tested under the same conditions for comparison.It can be seen from Table1that15wt.%Ni/SiC catalyst is more active than15wt.%Ni/TiO2catalyst.Fig.3shows the evolution of CO conversion over Ni/SiC and Ni/TiO2catalysts at340°C.For the Ni/SiC catalyst,there is an activity rise in the initial stage of the methanation reaction and CO is nearly converted completely.When the reaction time is longer than40h the activity of Ni/SiC catalyst exhibits a slow drop and the CO conversion decreases from initial97% to91%after100h.The decrease of activity is due to the losing of nickel by the formation of nickel carbonyl.According to ICP analysis,the nickel amount of the Ni/SiC catalyst has decreased by16%after reaction for100h.For Ni/TiO2catalyst,the activity decreases rapidly and the CO conversion decreases from initial98%to below50%afterTable2Particle sizes of different Ni/SiC and Ni/TiO2catalysts.Catalyst Ni loading(wt.%)Calculationtemperature(°C)Metal crystallitesize(nm)aNi/SiC55508.61055015.31545017.450018.155019.060020.92055023.5 Ni/TiO215550–Used Ni/SiC1555021.6b Used Ni/TiO21555023.5ba Calculated from NiO(021)plane by Scherrer's equation.b Calculated from Ni(111)plane by Scherrer's equation.COconversion(%)Temperature(o C)Fig.2.Influence of calcination temperature on the activity of Ni/SiC catalysts under P=2.0MPa,H2/CO=3and GSV=4500h−1.COconversion(%)Time (h)parison of the catalytic performance between15wt.%Ni/SiC and15wt.% Ni/TiO2catalysts under T=340°C,P=2.0MPa,H2/CO=3and GSV=4500h−1.2295Y.Yu et al./Fuel Processing Technology92(2011)2293–2298100h reaction.These results indicate that the Ni/SiC catalyst exhibits an obviously better stability than the Ni/TiO 2catalyst.3.3.TG –DSC analysis of used Ni/SiC and Ni/TiO 2catalystsTG –DSC analysis was performed for the used Ni/SiC and Ni/TiO 2catalysts and the results are shown in Fig.4.From the TG pro file shown in Fig.4A,no weight loss but a viewable increase of weight can be observed,indicating that there are no carbon depositions over both catalysts.The weight increase over both catalysts is likely due to the oxidation of metallic Ni to NiO.As seen in Fig.4B,no remarkable exothermic peaks can be observed for the used Ni/SiC and Ni/TiO 2catalysts,indicating that the oxidation of deposited carbon on the used catalysts does not occur.This is in agreement with the results reported by Zhu et al.[31].Therefore,the decrease in the activity of the Ni/SiC catalyst for methanation reaction is not due to the carbon deposition.3.4.XRD resultsFig.5shows the XRD results of 15wt.%Ni/SiC and 15wt.%Ni/TiO 2catalysts before and after reaction at 340°C for 100h.In the XRD patterns of fresh Ni/SiC catalyst shown in Fig.5A,the diffraction peak at 2θ=43.3°is attributed to NiO (012)plane [18].According to Scherrer's equation [21],the average NiO crystallite size calculated from the peak is about 19.0nm.In the XRD patterns of fresh Ni/TiO 2catalyst,diffraction peaks attributed to NiTiO 3phase can be detected (Fig.5A).Rao et al.[32]reported that NiTiO 3was formed whenNi/TiO 2catalyst was calcined above 500°C.Therefore the NiTiO 3phase in the present XRD patterns may be formed during the calcination.In our experiments,the color of Ni/TiO 2catalyst can become light yellow,which is the color of NiTiO 3[33].From both XRD patterns shown in Fig.5B,no diffraction peak of carbon can be found,indicating that the carbon deposition on the two methanation catalysts can be ignored.This is in accordance with the results of TG –DSC analysis.The diffraction peak at 2θ=44.56°is attributed to metallic Ni (111)[18].Metallic nickel exists in both catalysts,indicating that the active phase for CO methanation is metallic nickel.For the used Ni/SiC catalyst,the mean nickel particle size calculated from Ni (111)plane by Scherrer's equation [21]is about 21.6nm.The nickel particle size only has a slight increment during the reaction,suggesting that no serious sintering has occurred on the Ni/SiC pared with the fresh Ni/TiO 2catalyst,the crystallite size of used Ni/TiO 2increased signi ficantly (particle size from 24.2to 30.3nm and from 26.6to 35.9nm for rutile and anatase,respectively).The increase of particle size may be due to the production of hot spots during the CO methanation,which possibly make TiO 2crystallites sintered.In addition,the speci fic surface areas of Ni/TiO 2catalyst decreased from 32.1to 16.7m 2/g after reaction at 340°C for 100h.Ruckenstein et al.[34]reported that TiO x could1002003004005006007008009092949698100102104Ab aS a m p l e w e i g h t (%)temperature(o C)temperature(o C)a---15 wt.% Ni/SiC b---15 wt.% Ni/TiO 2BD S C /(m W /m g )Fig.4.TG –DSC pro files of used 15wt%Ni/SiC and 15wt.%Ni/TiO 2catalysts.AI n t e n s i t y (c p s )2 Theta (o )2 Theta (o )BI n t e n s i t y (c p s )Fig.5.XRD patterns of 15wt.%Ni/SiC and 15wt.%Ni/TiO 2catalysts before (A)and after (B)methanation reaction at 340°C for 100h.(●)NiTiO 3;(■)anatase;(▲)rutile;(★)SiC;(♦)NiO;(○)Ni.2296Y.Yu et al./Fuel Processing Technology 92(2011)2293–2298migrate onto the surface of metal nickel particles due to the strong interaction of support –metal.During the methanation reaction,the TiO 2may amalgamate with the reduced Ni due to the strong metal –support interaction.This is not favorable for CO absorption and decomposition on metal Ni.Therefore,the Ni/TiO 2catalyst shows a declining activity and stability in the methanation reaction.3.5.TEM characterization of Ni/SiC catalystsTEM images of fresh and used 15wt.%Ni/SiC catalyst are shown in Fig.6.From the two TEM images,it can be seen that the metal particles are well distributed on the support surface.From the image of fresh Ni/SiC catalyst (Fig.6A),the size of NiO particles ranges from 10to 25nm.In Fig.6B,the size of nickel particles in the used catalyst is about 10–30nm.These results are in accordance with those derived from XRD analysis.From both XRD and TEM results,15wt.%Ni/SiC catalyst shows better stability in the methanation reaction due to the excellent thermal conductivity and thermostability of the SiC support.4.ConclusionThe synthesis of methane from syngas was investigated over Ni/SiC catalysts which were prepared by impregnation method.From the present work,15wt.%Ni/SiC catalyst calcined at 550°C exhibits excel-lent catalytic activity for CO pared with Ni/TiO 2catalyst,the Ni/SiC catalyst exhibits higher activity and better stability in the CO methanation due to the excellent thermostability and high heat conductivity of the SiC support,which can ef ficiently avoid the sintering of nickel particles.AcknowledgmentsThe work was financially supported by NSFC (Ref.20973190),the in-house research project of SKLCC (Ref.SKLCC-2008BWZ010),and the National Basic Research Program (Ref.2011CB201405).References[1]J.Kopyscinski,T.J.Schildhauer,S.M.A.Biollaz,Production of synthetic natural gas(SNG)from coal and dry biomass —a technology review from 1950to 2009,Fuel 89(2010)1763–1783.[2]N.R.Udengaard,A.Olsen,C.Wix-Nielsen,Pittsburgh Coal Conf.,2006.[3]P.Sabatier,J.B.Senderens,New synthesis of methane,Académie des Sciences 134(1902)514–516.[4]M.A.Vannlce,R.L.Garten,Supported palladium catalysts for methanation,Industrial and Engineering Chemistry Product Research and Development 18(1979)186–191.[5]O.G őrke,P.Pfeifer,K.Schubert,Highly selective methanation by the use of amicrochannel reactor,Catalysis Today 110(2005)132–139.[6]P.Panagiotopoulou,D.I.Kondarides,X.E.Verykios,Selective methanation of COover supported noble metal catalysts:effects of the nature of the metallic phase on catalytic performance,Applied Catalysis A 344(2008)45–54.[7] A.L.Kustov,A.M.Frey,rsen,T.Johannessen,J.K.Nørskov,C.H.Christensen,CO methanation over supported bimetallic Ni –Fe catalysts:from computational studies towards catalyst optimization,Applied Catalysis A 320(2007)98–104.[8]P.Panagiotopoulou,D.I.Kondarides,X.E.Verykios,Selective methanation of COover supported Ru catalysts,Applied Catalysis B 88(2009)470–478.[9]R.A.Dagle,Y.Wang,G.G.Xia,J.J.Strohma,J.Holladay,D.R.Palo,Selective COmethanation catalysts for fuel processing applications,Applied Catalysis A 326(2007)213–218.[10]R.F.Wu,Y.Zhang,Y.Z.Wang,C.G.Gao,Y.X.Zhao,Effect of ZrO 2promoter on thecatalytic activity for CO methanation and adsorption performance of the Ni/SiO 2catalyst,Journal of Fuel Chemistry and Technology 37(2009)578–582.[11]S.Takenaka,T.Shimizu,K.Otsuka,Complete removal of carbon monoxide inhydrogen-rich gas stream through methanation over supported metal catalysts,International Journal of Hydrogen Energy 29(2004)1065–1073.[12]W.J.Shen,M.Okumura,Y.Matsumura1,M.Haruta,The in fluence of the supporton the activity and selectivity of Pd in CO hydrogenation,Applied Catalysis A 213(2001)225–232.[13]M.A.Vannice, C.C.Twu,S.H.Moon,SMSI effects on CO adsorption andhydrogenation on Pt catalysts,Journal of Catalysis 79(1983)70–80.[14]R.L.Chin,A.Elattar,W.E.Wallance,D.M.Hercules,ESCA studies of methanationcatalysts derived from intermetallic compounds,Journal of Physical Chemistry 84(1980)2895–2898.[15]K.H.Eisenlohr,F.W.Moeller,M.Dry,In fluence of certain reaction parameters onmethanation of coal gas to SNG,ACS Division of Fuel Chemistry 19(1974)1–9.[16]M.J.Ledoux,S.Hantzer,C.P.Huu,J.Guille,M.P.Desaneaux,New synthesis and usesof high-speci fic-surface SiC as a catalytic support that is chemically inert and has high thermal-resistance,Journal of Catalysis 114(1988)176–185.[17] D.L.Nguyen,P.Leroi,M.J.Ledoux,P.C.Huu,In fluence of the oxygen pretreatmenton the CO 2reforming of methane on Ni/β-SiC catalyst,Catalysis Today 141(2009)393–396.[18]W.Z.Sun,G.Q.Jin,X.Y.Guo,Partial oxidation of methane to syngas over Ni/SiCcatalysts,Catalysis Communications 6(2005)135–139.[19]Q.Wang,W.Z.Sun,G.Q.Jin,Y.Y.Wang,X.Y.Guo,Biomorphic SiC pellets as catalystsupport for partial oxidation of methane to syngas,Applied Catalysis B 79(2008)307–312.[20]G.Q.Jin,X.Y.Guo,Synthesis and characterization of mesoporous silicon carbide,Microporous and Mesoporous Materials 60(2003)207–212.[21]Y.H.Ni,F.Wang,H.J.Liu,Y.Y.Liang,G.Yin,J.M.Hong,X.Ma,Z.Xu,Fabrication andcharacterization of hollow cuprous sul fide (Cu 2−x S)microspheres by a simple template-free route,Inorganic Chemistry Communications 6(2003)1406–1408.[22]S.T.Zhou,X.L.Pan,X.H.Bao,Effect of rhodium particle size in Rh/SiO 2catalystprepared by microemulsion method on reaction performance of CO hydrogena-tion,Chinese Journal of Catalysis 27(2006)474–478.[23] A.E.Aksovlu,A.N.Akin,Z.I.Őnsan,D.L.Trimm,Structure/activity relationships incoprecipitated nickel –alumina catalysts using CO 2adsorption and methanation,Applied Catalysis A 145(1996)185–193.[24]R.E.Hayes,W.J.Thomas,K.E.Hayes,A study of the nickel-catalyzed methanationreaction,Journal of Catalysis 92(1985)312–326.[25]T.Morl,H.Masuda,H.Imal,Kinetics,isotope effects,and mechanism for thehydrogenation of carbon monoxide on supported nickel catalysts,Journal of Physical Chemistry 86(1982)2753–2760.[26] C.W.Hu,Y.Q.Chen,P.Li,H.Min,Y.Chen,A.M.Tian,On the interaction of CO andH 2with Ni-based catalyst,Journal of Molecular Catalysis (China)9(1995)435–444.[27]H.Arakawa,T.Fukushima,M.Ichikawa,K.Takeuchi,T.Matsuzaki,Y.Sugi,Highpressure in situ FT-IR study of CO hydrogenation over Rh/SiO 2catalyst,Chemistry Letters 1(1985)23–26.[28]R.P.Underwood, A.T.Bell,In fluence of particle size on carbon monoxidehydrogenation over silica-and lanthana-supported rhodium,Applied Catalysis 34(1987)289–310.100nm A 100nmBFig.6.TEM images of 15wt.%Ni/SiC catalysts before (A)and after (B)reaction at 340°C for 100h.2297Y.Yu et al./Fuel Processing Technology 92(2011)2293–2298[29] F.Haga,T.Nakajima,H.Miya,S.Mishima,Catalytic properties of supported cobaltcatalysts for steam reforming of ethanol,Catalysis Letters48(1997)223–227. [30]M.P.Andersson,F.Abild-Pedersen,I.N.Remediakis,T.Bligaard,G.Jones,J.Engbæk,O.Lytken,S.Horch,J.H.Nielsen,J.Sehested,J.R.R.Nielsen,J.K.Nørskov,I.Chorkendorff,Structure sensitivity of the methanation reaction:H2-induced CO dissociation on nickel surfaces,Journal of Catalysis255(2008)6–19.[31]J.Q.Zhu,X.X.Peng,L.Yao,J.Shen,D.M.Tong,C.W.Hu,The promoting effect of La,Mg,Co and Zn on the activity and stability of Ni/SiO2catalyst for CO2reforming of methane,International Journal of Hydrogen Energy36(2011)7094–7104.[32]G.Sankar, C.N.R.Rao,T.Rayment,Promotion of the metal–oxide supportinteraction in the Ni/TiO2catalyst—crucial role of the method of preparation, the structure of TiO2and the NiTiO3intermediate,Journal of Materials Chemistry 1(1991)299–300.[33]T.H.Wu,Q.G.Yan,H.L.Wan,Partial oxidation of methane to hydrogen and carbonmonoxide over a Ni/TiO2catalyst,Journal of Molecular Catalysis A:Chemical226 (2005)41–48.[34] E.Ruckenstein,Y.H.Hu,Role of support in CO2reforming of CH4to syngas over Nicatalysts,Journal of Catalysis162(1996)230–238.2298Y.Yu et al./Fuel Processing Technology92(2011)2293–2298。
