K-, CeO2-, and Mn-promoted Ni/Al2O3 catalysts for stable CO2 reforming of methane

Reforming of methane with carbon dioxide into syngas over Ni/gamma-Al2O3 catalysts modified by potassium, MnO and CeO2 was studied. The catalysts were prepared by impregnation technique and were characterized by N-2 adsorption/desorption isotherm, BET surface area, pore volume, and BJH 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 CeO2 (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 CO2 adsorption, forming a surface reactive carbonate species. Addition of CeO2 or MnO reduced the particle size of nickel, thus increasing Ni dispersion. For Ni-K/CeO2-Al2O3 catalysts, the improved stability was further attributed to the oxidative properties of CeO2. Results of the investigation suggest that stable Ni/Al2O3 catalysts for the carbon dioxide reforming of methane can be prepared by addition of both potassium and CeO2 (or MnO) as promoters. (c) 2005 Elsevier B.V. All rights reserved.