Hydrogen production at low temperature from methane on cerium and nickel based mixed oxides

Partial oxidation of methane (POM) to synthesis gas, CO + H2, was investigated between 50 °C and 700 °C as a function of metal loading over cerium and nickel based CeNiXOY catalysts. At high temperature, 700 °C, a H2 yield of 100% is obtained. At 200 °C, an interesting yield of 34% is reached with a stable methane conversion of 70% and a H2 selectivity of 49%, only when the solid is previously in situ treated in H2 at 200 °C. Activated in H2 CeNixOY solids are hydrogen reservoirs. Different physico-chemical techniques were used to characterize the structural, dispersion and reduction properties of the solids. Depending on composition, a solid solution and/or a highly dispersed nickel oxide on ceria can be obtained. Ion sputtering followed by XPS analysis was very useful for estimating the size of small NiO crystallites present in the compounds. It is found that active nickel species belong to small clusters and/or to solid solution. Correlations among species present in solid and catalytic performances are discussed. An active site based on formation of anionic vacancies and a mechanism involving a heterolytic abstraction of a hydride species from methane are proposed.