Mn-Promoted Ni/Al2O3 Catalysts for Stable Carbon Dioxide Reforming of Methane

Abstract

Based on previous observation that the addition of manganese onto Ni/Al2O3 catalysts reduced the coke formation in the carbon dioxide reforming of methane, effects of the preparation method for Mn-promoted Ni/Al2O3 catalysts on the catalytic activity and stability were investigated. A coprecipitated catalyst, Ni–MnOx/MnAl2O4, showed higher coke resistance and more stable activity than an impregnated Ni/MnO/γ-Al2O3 catalyst and the well-known Ni0.03Mg0.97O catalyst at 923 K with a feed gas ratio CH4/CO2 of 1 without a diluent gas. In coprecipitated Ni–MnOx/MnAl2O4 catalysts, MnAl2O4, γ-Al2O3, and Ni(0) were observed as major crystalline phases with XRD and potassium was detected on the surface with EPMA. Comparison of H2 chemisorption and XRD suggested that the surface of large metallic nickel particles was partly blocked by manganese oxides, and the structure was confirmed by XAFS. For impregnated Ni/MnO/γ-Al2O3 catalysts, addition of potassium stabilized its catalytic activity further, to the level achieved by coprecipitated Ni–MnOx/MnAl2O4 catalysts. These results indicate that very stable Ni/Al2O3 catalysts for the carbon dioxide reforming of methane can be prepared by addition of both potassium and manganese as promoters.