Study On Nickel-based Catalysts For Dry Reforming Of Methane

Dry reforming of methane is of particular interest because it uses twogreenhouse effect pollutant gases. Recently, there have been many attemptsto convert the concentration of CO₂and CH₄into synthesis gas with theratio of H₂/CO about1, which is the synthetic chemical raw material forF-T synthesis and carbonyl synthesis in the atmosphere through theirutilization. And by using modern technology synthesis gas can furtherconvert into synthetic ammonia, methanol and so on a series of importantchemical products, to meet the demand for energy shortage.At present studying on the high activity and high stability goodcatalyst to realize industrialization is one of the key issues. Series ofcatalysts have been investigated for dry reforming of methane includingsupported noble metal catalysts due to its high activity and stability.However, considering the limited resources, numerous researches focusedon non-noble metal catalysts, particularly developing of Ni-based catalystsexhibited high catalytic activity in dry reforming of methane. However, thegreatest problem of nickel-based catalysts is the deactivation due to carbon deposition and Ni particle sintering. This paper is focused on preparation ofnickel-based catalysts with good catalytic properities through supportmodification、adding promoters to support and changing the preparationmethods.In the present work, the silica support was modified by ethyleneglycol （EG） before impregnation of nickel precursor indicating thatpretreatment by EG significantly modified surface properties of silicasupport. The surface properties of pretreated silica support were determinedby FT-IR, the bond at3743cm1is the non-H-bonded O-H，the lowercoverage of H-bonded SiOHs of pretreated silica could contribute toforming smaller supported nickel particle to realize high dispersion ofsupported nickel. C-H bands were detected indicating that the modifiedsilica supports decreased the coverage of OHs、formed oxyls groups andenhanced the Si-O-Si band to increase negative charge on surface ofpretreated silica support contributing to increased supported nickel andsilica interaction resulting in higher supported nickel dispersion. Throughthe XRD data, The Ni/SiO₂catalyst, prepared by non-pretreated silicasupport, exhibits sharp and strong nickel peaks, and the crystalline size is12nm, Ni/SiO₂-EG catalyst exhibited remarkable smaller particle size anddistributed homogeneously. The particle size of two catalysts was alsodetermined by hydrogen chemisorption, as3.2nm for Ni/SiO₂-EG and7.5nm for Ni/SiO₂respectively. The Ni/SiO₂-EG catalyst realized less carbon deposition due to stronger interaction of metal and support, as proved byTPR, contributing to good reaction stability. The reduction degree ofNi/SiO₂-EG catalyst （29.3%） was much lower than that of Ni/SiO₂（54.5%）.The broad and higher temperature reduction peak of Ni/SiO₂-EG catalystindicates that the modified silica support increased the nickel–silicainteraction, contributing to the decreased reducibility and the increaseddispersion of supported nickel. Ni/SiO₂-EG catalyst realized72%CH₄conversion after9h, which is two times higher than that of Ni/SiO₂catalyst，moreover, Ni/SiO₂-EG catalyst is much stable than Ni/SiO₂catalyst. The coke was easily formed on the surface of larger sized Niparticles. The weight loss of carbon deposition for used Ni/SiO₂catalyst is55%, which is two times higher than that of Ni/SiO₂-EG catalyst. Thesmaller supported Ni particles of Ni/SiO₂-EG catalyst reduced carbondeposition and promoted CO2activation to remove the deposited carbon,resulting in not only high activity but also stability in dry reforming ofmethane. Furthermore, TEM images of used catalysts clearly proved thesevere sintering and carbon deposition of Ni/SiO₂catalyst. Ni/SiO₂-EGcatalyst realized excellent stability in dry reforming of methane.The activity and stability of different catalysts modified by promoters（MgO、CeO2、Pt、Pd、Ru） to nickel-based catalysts present a differentdegree of improvement in the same reaction condition. Ni-CeO2/SiO2catalyst realized60%CH4conversion after a period of time which is slightly higher than Ni-MgO/SiO2. The activity and coke resistance ofsupported noble metal catalysts decreased according to the order:Ni-1%Pt/SiO₂>Ni-1%Ru/SiO₂>Ni-1%Pd/SiO₂. The catalytic performanceimpact on CeO2loading, reduction temperature and airspeed ofNi-CeO2/SiO2catalysts were studied.Ni_0.2Mg_0.8O catalyst was prepared by co-precipitation catalyst. Thepretreatment Ni_0.2Mg_0.8O-EG catalyst exhibited the higher activity at673Kcalcination temperature in dry reforming of methane.