K-,CeO_2-,and Mn-promoted Ni/Al_2O_3 catalysts for stable CO_2 reforming of methane

摘要

Reforming of methane with carbon dioxide into syngas over Ni/gamma-Al_2O_3 catalysts modified by potassium,MnO and CeO_2 was studied.The catalysts were prepared by impregnation technique and were characterized by N_2 adsorption/desorption isotherm,BET surface area,pore volume,and B JH pore size distribution measurements,and by X-ray diffraction and scanning electron microscopy.The performance of these catalysts was evaluated by conducting the reforming reaction in a fixed bed reactor.The coke content of the catalysts was determined by oxidation conducted in a thermo-gravimetric analyzer.Incorporation of potassium and CeO_2(or MnO)onto the catalyst significantly reduced the coke formation without significantly affecting the methane conversion and hydrogen yield.The stability and the lower amount of coking on promoted catalysts were attributed to partial coverage of the surface of nickel by patches of promoters and to their increased CO_2 adsorption,forming a surface reactive carbonate species.Addition of CeO_2 or MnO reduced the particle size of nickel,thus increasing Ni dispersion.For Ni-K/CeO_2-Al_2O_3 catalysts,the improved stability was further attributed to the oxidative properties of CeO_2.Results of the investigation suggest that stable Ni/Al_2O_3 catalysts for the carbon dioxide reforming of methane can be prepared by addition of both potassium and CeO_2(or MnO)as promoters.