Study On The Preparation Of Nickel-based Catalysts With Bimodal Porous Structure And Their Catalytic Performances In Carbon Dioxide Reforming Of Methane

Carbon dioxide reforming of methane reaction can not only make rational use of methane,but also convert carbon dioxide into useful chemicals,effectively solving the energy crisis and alleviating the greenhouse effect.At present,the reason why this reaction cannot be industrialized is the serious carbon deposition of the catalyst.For the shortage of traditional monomodal catalyst used in carbon dioxide reforming of methane reaction,a catalyst with bimodal structure was designed to its catalytic performance and carbon deposition resistance.Then,the effect of different preparation methods,different nickel loadings and different Zr addition on the catalytic performance was further studied.The paper mainly includes the following aspects:The monomodal and bimodal structure catalysts prepared by impregnation method were compared.The results show that:1.The bimodal structure catalyst has good catalytic activity.The conversion of CH4 and CO2 reaches 69.7%and 81.2%after 100 h of reaction.2.The bimodal structure catalysts have excellent carbon deposition resistance,and the carbon content after the 100 h reaction was only 5.8%.This is attributed to the special pore structure of the catalyst.The mesoporous pores facilitate the dispersion of Ni particles,and the macroporous channels facilitate the rapid transport of molecules,thereby improving the catalytic activity and carbon deposition resistance of the catalyst.The metal-support interaction of the catalyst prepared by the impregnation method is weak,and the reaction at high temperature tends to cause agglomeration of the Ni particles,thereby causing carbon deposition,and thus improved by changing the preparation method.The bimodal structure catalysts prepared by the impregnation method and the one-step method were compared.The results showed that:1.The catalyst prepared by the one-step method has large specific surface area,small particle size of Ni,high dispersion of Ni,strong interaction between metal and support,and a high reduction peak temperature,therefore,the catalyst has excellent catalytic activity,and the conversion rates of CH4 and CO2 after the reaction of 100 h were 71.4%and 81.2%,respectively.2.The catalyst also has strong carbon deposition resistance,and the carbon content after the reaction is only 2.8%.This is attributed to the fact that the Ni particles of the catalyst are supported on the support framework,so that there is a strong metal-support interaction,which inhibits the agglomeration of the Ni particles,thereby reducing the currence of carbon deposition.A series of bimodal structure catalysts with different nickel loadings were prepared by one-step method.The results show that:1.With the increase of Ni loading,the specific surface area and pore volume of the catalyst increase gradually,and the interaction between the metal and the support gradually increases,so the catalytic activity of the catalyst also increases.2.However,the carbon deposition amount and the degree of graphitization are also increasing,so the carbon deposition resistance of the catalyst is gradually reduced.The catalyst with the above data loading of 6 wt.%has good catalytic activity and carbon deposition resistance.There are a large number of Lewis acidic sites on the surface of alumina,which makes the catalyst easy to deposit carbon.The addition of the Zr can effectively adjust the acidity and alkalinity of the catalyst surface,increase the adsorption amount of CO2 by the catalyst,and the addition of a small amount of Zr can improve the mesoporous structure,thereby further improving catalytic activity and carbon deposition resistance of the catalyst.The experimental results show that:1.Catalyst of Zr/Al=0.03 has strong catalytic activity and carbon deposition resistance.After 100 h reaction,the conversion rate of CH4 and CO2 reached 76.7%and 85.5%,which decreased by less than 1%compared with the initial activity.2.The carbon deposit is also very small,and the carbon content is less than 1%.Therefore,the addition of a small amount of Zr further optimizes the catalytic performance and carbon deposition resistance of the catalyst.