Study Of Mo-based Sulfur-resistant Methanation Catalysts

Coal to natural gas project can utilize the abundant coal resource to produceclean natural gas which has important meaning in mitigating the energy crises inChina. Methanation reaction is a key step in coal to natural gas process.Sulfur-resistant methanation owns advantage in cost for that it can be carried outwithout deep desulfidation process which makes the process simplified and the costdecreased. Currently, developing high effciency and stability sulfur-resistantmethanation catalyst is the core of the whole methanation process. Hence, thesulfur-resistant mathanation performance of serises of Mo-based catalysts prepared byimpregnation method are investigated.The study of15%MoO3/Al2O3catalysts prepared by different alumina finds thatcatalyst prepared with6#Al2O3shows the best activity and the CO conversion is48%.The specific surface area of alumina has no direct relationship with its catalyticperformance when the loading of MoO3on alumina support is lower than itsmonolayer saturated coverage. Well-crystallized support is not favorable to themethanation reaction; medium amount of acid on per unit area of support is beneficialto methanation reaction; weaker metal support interaction can improve the activity ofthe catalyst. Calcination time of alumina support has no significant effect on thecatalytic performance of the catalyst when support is calcinated at600C. Thecatalytic performance of the catalyst decreases with the increase of calcinationtemperature when the calcination temperature is higher than800C.The performances of15%MoO3/25%CeO2-75%Al2O3catalysts prepared byceria-alumina composite supports are studied. It is found that adding CeO2canenhance sulfur-resistant methanation reaction. Adding critic acid, tartaric acid andmendlic acic in the process of preparing25%CeO2-75%Al2O3support can improvethe catalytic performance of15%MoO3/25%CeO2-75%Al2O3catalysts. Moreover, themore critic acid added, the higher catalytic activity will achieve, this is because thatthe amount of Ce species on the surface of the catalyst increased.The study of MoO3/CeO2catalysts shows that the catalyst reaches its best activitywhen the loading of MoO3is5%, and the CO conversion is72%. The monolayersaturated coverage of MoO3on CeO2support is5%when both the support and the catalyst are calcined at600C; what’s more, Ce2O2S has higher sulfur-resistantmethanation activity. The study of5%MoO3/CeO2(denoted as: Mo-Ce/5) catalystsprepared by different CeO2demonstrates that Mo-Ce/5catalyst prepared by calciningCe(NO3)3·6H2O and impregnates Mo precursor shows the best activity; then isMo-Ce/5catalyst prepared by NH4HCO3precipitating Ce(NO3)3; Mo-Ce/5catalystprepared by NH3·H2O precipitating Ce(NO3)3shows the worst activity, this is becausethat the specific surface area of CeO2prepared by this method is too small and Mospecies can not well dispersed on the CeO2support. The study of Mo-Ce/5catalystevaluated for a long period of time reveals that Mo-Ce/5catalyst has relatively goodactivity for sulfur-resistant methanation reaction at450C, but its stability still needsto be enhanced.