Surface chemistry and catalysis of SiO2-supported RhCo3(CO)(12)

The interaction of the RhCo3 cluster with the SiO2 surface has been investigated via decarbonylation of RhCo3(CO)(12)/SiO2 under different atmospheres by TR spectroscopy. The bimetallic RhCo3 framework is intactly preserved on the surface after thermal treatments of RhCo3(CO)(12)/SiO2 at 623 K under vacuum, hydrogen and oxygen (or air), which is able to regenerate the initial bimetallic carbonyl cluster under a CO atmosphere. In contrast, the RhCo3/SiO2 sample without undergoing any thermal treatment is readily disintegrated by CO to result in Rh+(CO)(2) and Co2+ With the aid of a concerted oxidation by surface OH-. IR study also shows that RhCo3(CO)(12) is reversibly dissociated to Rh-6(CO)(16) and Co-2(CO)(8) on the surface by CO. In situ IR observations reveal that the equilibrium favoring the regeneration of RhCo3(CO)(12) is established at 423 K under atmospheric hydroformylation pressure in terms of the interconversion between the bimetallic cluster and the monometallic clusters, and that RhCo3(CO)(12)/SiO2 is stable and responsible itself for the catalysis toward ethylene hydroformylation. Atmospheric catalytic results illustrate that RhCo3(CO)(12)/SiO2 has high activity and stability for the formation of propanal and n-propanol. (C) 1997 Elsevier Science B.V.