Catalytic combustion of methane on Pd-Cu/SiO2 catalysts

Different series of Pd/SiO2, Pd-Cu/SiO2 and Cu/SiO2 catalysts prepared by t he soli-gel method and by impregnation on a commercial silica were investig ated. The solids were characterised by evaluating the surface area, porosit y, metal dispersion and surface composition. The activity for the combustio n of methane was measured under stoichiometric and oxidant conditions. In a ll the samples, the excess of oxygen shifts the conversion of methane towar ds lower temperatures. In the impregnated series, copper reduces the activi ty due to a copper-palladium interaction, which modifies the nature of the active site. In the sol-gel catalysts the main effect produced by the prese nce of copper is to modify the porosity of the solid, generating catalysts with high microporosity. The presence of micropores limits the access of th e reactant to the active site, which makes catalyst activity lower. In addi tion,the sol-gel catalyst subjected to stringent reaction conditions exhibi ted an activity enhancement due to the development of some mesoporosity. On the contrary, a slight deactivation was observed in the impregnated Pd-Cu catalysts as a consequence of metal sinterisation. (C) 2000 Elsevier Scienc e B.V. hll rights reserved.