Decomposition of methane over supported-Ni catalysts: effects of the supports on the catalytic lifetime

Decomposition of methane into carbon and hydrogen over Ni catalysts supported on different supports was studied. The catalytic activities and the lifetimes of the catalysts for the reaction were examined and are discussed. Ni catalysts supported on SiO2, TiO2 and graphite showed high activities and long lifetimes for the reaction, whereas the catalysts supported on Al2O3, MgO and SiO2-MgO were inactive for the reaction. The relation between the catalytic performance of the supported-Ni catalysts and the structure or electronic state of Ni species is discussed on the bases of the results of X-ray diffraction (XRD) and Ni K-edge XANES/EXAFS. In the supported-Ni catalysts effective for the methane decomposition, Ni species were present as crystallized Ni metal particles. On the other hand, the Ni species on the inactive catalysts were present as nickel oxides mainly, suggesting the formation of a compound oxide between Ni and the supports. The catalytic performance of the Ni catalysts supported on silicas with different specific surface areas and pore structures indicated that the catalytic activity and lifetime for the methane decomposition depended significantly on the pore structures of the supports. The silica support with no pore structure was the most favorable one for enhancing the catalytic activity and lifetime of the supported-Ni catalysts. (C) 2001 Elsevier Science B.V. All rights reserved.