Interaction of methane with supported Pd catalysts studied by adsorption microcalorimetry and TPD/TPSR techniques Original Research Article

The interaction of methane with the surfaces of silica-, alumina- and titania-supported Pd catalysts has been studied by means of adsorption microcalorimetry and temperature-programmed surface reaction (TPSR) with hydrogen in a flow system at atmospheric pressure. For adsorption temperatures ranging between 300 and 700 K, a complete dissociation of CH4 occurred which resulted in the formation of C(ads) clusters of different sizes as well as graphitic carbon. The subsequent temperature-programmed hydrogenation of C(ads) mainly produced CH4 together with trace amounts of C2H6 and C2H4. With an increasing number of Pd surface atoms, more C(ads) was formed upon contact with CH4; the reactivity towards hydrogenation was, however, not markedly affected. Compared to Pd/SiO2, the reactivity of deposited carbon to hydrogenation, the C2 yield and the C2H4/C2H6 ratio were higher for Pd/TiO2 and Pd/Al2O3 catalysts, while the tendency for the formation of graphitic carbon was lower.