A model of the surface and catalytic activity of supported bimetallic Fe- and Co-containing complexes in CO+H2, synthesis reactions

Abstract The catalytic properties of the complexes Cp(CO) 2 Fe-Co(CO) 4 ( I ), Cp(CO) 2 Fe-Fe(CO) 2 Cp ( II ) and Ph 2 Co 2 (CO) 6 ( III ), and of Fe(CO) 5 + Co 2 (CO) 8 ( IV ), Fe(CO) 5 ( V ) and Co 2 (CO) 8 ( VI ) carbonyls supported on γAl 2 O 5 in the CO hydrogenation reaction at atmospheric pressure and 220–280 °C have been studied. The ratios of Fe and Co metallic and ionic forms formed by interaction of the complexes with the support before and during the catalytic reaction were measured by means of Mossbauer spectroscopy and magnetic susceptibility. It was found that catalysts prepared from complex I exhibited both the high catalytic activity characteristic of catalyst III and the high selectivity in olefin production typical of catalyst II . In contrast, although the catalysts produced from a mixture of carbonyls ( IV ) showed quite high activity comparable with that of sample VI , they exhibited a very low selectivity towards olefins. Mossbauer and magnetic susceptibility data showed that a Fe/Co-intermetallic phase was formed as a result of the interaction of complex I with γ-Al 2 O 3 , while such a phase was not present in catalysts derived from the mixture of carbonyls ( IV ). Samples I and II are characterized by higher Fe 2+ /Fe 3+ ratios relative to that in sample IV where oxidation of Fe 2+ to Fe 3+ took place under the reaction conditions. The mechanism of formation of metallic and ionic form on the catalyst surface is discussed.