| Popis: |
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. |
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