MgO-supported bimetallic catalysts consisting of segregated, essentially molecular rhodium and osmium species

Abstract

[EN] A family of supported bimetallic samples was prepared by the reactions of Rh(C2H4)(acac) (acac = acetylacetonate) and Os-3(CO)(12) with MgO. The samples were characterized by infrared and extended X-ray absorption fine structure spectroscopies, before and after various treatments with hydrogen at temperatures up to 393 K. The spectra identify the following combinations of supported species: (a) [Os-3(CO)(11)](2-) + Rh(C2H4)(2), (b) [Os-3(CO)(11)](2-) + Rh(CO)(2), and (c) [Os-3(CO)(11)](2-) + rhodium clusters containing approximately 4 to 6 atoms each, on average. No bimetallic clusters formed. The triosmium frame remained intact while the rhodium surface species were reduced in the presence of H-2. The samples were tested as catalysts for ethylene hydrogenation at 298 K, and the catalytic activity matched that of the rhodium complexes alone; evidently the rhodium complexes were responsible for all the catalysis, with the osmium clusters remaining inactive because of the presence of the carbonyl ligands on them.