Chemisorption and catalysis by metal clusters. Hydrogenation of carbon monoxide and carbon dioxide catalysed by supported Ruthenium clusters derived from Ru3(CO)12 and from H4Ru4(CO)12

Abstract

Properties are described for catalysts containing active clusters derived from Ru₃(CO)₁₂ and H₄Ru₄(CO)₁₂ and supported on silica, alumina and titania. The clusters, protected against sintering by retained ligand-CO, ligand-C and a support–cluster interaction, are stable under the range of reaction conditions used (0.10 MPa, 444–635 K) and provide highly reproducible activity for the hydrogenation of carbon monoxide and carbon dioxide. Freshly prepared catalysts each exhibit an initial non-steady state, during which carbon is progressively retained and activity rises, passes through a maximum and declines to a steady state value. Catalysts in the steady state generally exhibited low activity for carbon monoxide hydrogenation. An effect of support on activity was observed such that as the strength of the metal-support interaction increases, the turnover frequency decreases. Carbon-14 tracer studies revealed differences in the mechanism of CO and CO₂ hydrogenation and a detailed mechanism for CO₂ hydrogenation is presented.