Homogeneous catalysis of the water gas shift reaction by ruthenium and other metal carbonyls. Studies in alkaline solutions

Homogeneous catalysis of the water gas shift reaction (H/sub 2/O + CO reversible H/sub 2/ + CO/sub 2/) has been demonstrated for a number of metal carbonyl complexes under alkaline conditions. Characterization of the catalysts based on ruthenium carbonyl in alkaline, aqueous ethoxyethanol solution demonstrates that the principal species present under the reaction conditions are the carbonyl hydride anions H/sub 3/Ru/sub 4/(CO)/sub 12//sup -/ and HRu/sub 3/CO)/sub 11//sup -/. (The room temperature synthesis of the latter ion by the reaction of Ru/sub 3/(CO)/sub 12/ in alcoholic KOH is described). The catalysis rate shows a first-order dependence on both the CO partial pressure and the total ruthenium concentration. Cyclic mechanisms proposed to explain these observations involve nucleophilic attack of water or of hydroxide on coordinated CO followed by decarboxylation to give hydridic species from which H/sub 2/ is eliminated in a CO-assisted, rate-limiting step. It is noted that catalysts prepared by adding both iron and ruthenium carbonyls to the same solution are more active than either the ruthenium-based or the iron-based catalysts alone. These mixed metal catalyst solutions are shown to contain mixed metal clusters, and it is proposed that the synergetic effect on catalytic activity may result from greater reactivity of the mixed metal clusters toward elimination of dihydrogen.