Unraveling mechanistic features for the methane reforming by carbon dioxide over different metals and supports by TAP experiments

Four different catalysts (Ni/SiO2, Ni/Al2O3, Ru/SiO2, Ru/Al2O3) were extens ively investigated in the TAP reactor, in order to elucidate the role of th e metal and support in the dry reforming of methane. Over nickel, dissociat ive CH4 adsorption leads to H-2 gas and to an accumulation of carbon specie s on the surface. Dissociative CO2 adsorption lakes place giving CO gas and adsorbed oxygen. The latter reacts with carbon, originating from CH4, on t he surface to give a second CO molecule in the rate determining step. Over ruthenium, the methane activation is the slowest step and CO2 reacts direct ly with adsorbed carbon to CO. The surface oxygen accumulation is minimal a nd therefore, the oxidation hydrogen is suppressed. Whereas, the silica sup port is rather inert, the alumina support participates in the reaction by d elivering oxygen atoms to the metal via hydroxyl groups spill-over. In addi tion, a strong interaction between gaseous CO/CO2 and oxygenated adspecies is observed on alumina. The reverse water gas shift reaction takes place un der the TAP conditions. The different results are discussed in terms of the hydrogen selectivity. (C) 1998 Elsevier Science B.V. All rights reserved.