Study On Coke-resistance Of Coated Ni Catalyst For Dry Reforming Of Methane

Dry reforming of methane is a reaction that converting methane and carbon dioxide into syngas.This environmentally green technology not only increases the consumption proportion of natural gas in primary fossil energy,but also reduces the emission of carbon dioxide from industrial exhaust gas.However,the main problem that limits the industrial process of dry reforming of methane is the coke formation on Ni catalysts.In this thesis,we designed and prepared the coated Ni catalysts,and studied the mechanism of coke-resistance on those catalysts.Through the selection and optimization of some kinds of supports and the loading amounts of Ni metal,10 wt%Ni/MgAl2O4 was selected as the uncoated Ni catalyst.The Ni catalysts coated with silica layer were studied emphatically.The optimal preparation condition of the coated Ni catalyst is that,stirring the solution for 20h,and static aging for 1.5h,then filtration and drying,finally,calcined under the temperature that mantained at 150? for 1 h,then mantaine at 550? for 4h.The coated Ni catalyst with the highest activity and stability was obtained under the optimal conditions.The effects of the catalyst bed condition,temperature,space velocity,and the ratio of feed gases toward dry reforming of methane were studied.The selected conditions for evaluation of Ni catalysts were that the catalyst bed consisting of 0.1 g catalyst and 2g quartz sand,temperature of 750?,space velocity of 66000mL·h-1·g-1,and intake ratio of feed gas as CO2:CH4:N2 =5:5:1.Under these conditions,the conversions of CH4 and CO2 evaluated on the coated catalyst were 70%and 80%,and the catalyst has a stable performance during 100h reaction.Finally,based on homogeneously precipitated method(HPM)and solution combustion method(SCM),two series of the uncoated Ni catalysts and coated Ni catalysts were prepared.After analyze the experiment results,we concluded that Ni-HPM@SiO2 catalyst was partially coated with silica,and Ni-SCM@SiO2 catalyst was completely coated with silica.And the coke-resistance mechanism of the coated catalysts is that silica coating layer protects the Ni metallic particles from aggregation,and hence inhibits the formation of carbon deposition.