Abstract

Different series of Pd/SiO2, Pd-Cu/SiO2 and Cu/SiO2 catalysts prepared by the soli-gel method and by impregnation on a commercial silica were investigated. The solids were characterised by evaluating the surface area, porosity, metal dispersion and surface composition. The activity for the combustion of methane was measured under stoichiometric and oxidant conditions. In all the samples, the excess of oxygen shifts the conversion of methane towards lower temperatures. In the impregnated series, copper reduces the activity 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 presence of copper is to modify the porosity of the solid, generating catalysts with high microporosity. The presence of micropores limits the access of the reactant to the active site, which makes catalyst activity lower. In addition,the sol-gel catalyst subjected to stringent reaction conditions exhibited 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 Science B.V. hll rights reserved.