Methane formation by metal-catalyzed hydrogenation of solid calcium carbonate

Abstract

A study of the hydrogenation of solid CaCO₃ has shown that the addition of Pd and Ir catalysts causes a change in the gaseous product and, consequently, in the kinetics of the reaction. In the absence of catalyst, CO is formed at higher than 700 K with the activation energy of 236 kJ/mol and a nearly half order with respect to H₂ pressure, which is explained by the mechanism consisting of predecomposition and reduction. In the presence of the catalysts, CH₄ is exclusively formed even at 573 K at which the equilibrium decomposition pressure of CaCO₃ is extremely low, 1.1 × 10⁻⁵ Torr. Activation energies found in the range 105–118 kJ/mol and the H₂-pressure dependence of the initial rate suggest the direct interaction of CaCO₃ with spilt-over hydrogen atoms.