Studies of carbon- and hydrogen-containing adspecies present during CO hydrogenation over unsupported Ru, Ni and Rh

Abstract Isotopic tracer studies have been conducted to determine the coverages of adsorbed CO, carbon, and hydrogen on the surfaces of unsupported Ru, Rh, and Ni powders during CO hydrogenation. Two forms of hydrogen are observed on each catalyst at 298 K: a low-energy form which is in equilibrium with the gas phase and is rapidly displaced from the surface by CO adsorption and a high-energy form which is not in equilibrium with the gas phase and is not displaced by CO adsorption. The low-energy form is ascribed to hydrogen adsorbed on the exterior surfaces of the metal powder. It is proposed that the high-energy form may be hydrogen which has migrated along crystal grain boundaries into the interior of the metal powder. Adsorbed carbon and CO are also observed on each catalyst. It is demonstrated that high methanation activity correlates with the surface coverage of active carbon but not with the coverage of adsorbed hydrogen.

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