Catalysis by supported metal crystallites prepared from metal carbonyl clusters: III. Catalytic vapor-phase hydroformylation of olefins over Rh, bimetallic RhCo, and Co crystallites prepared from the carbonyl cluster compounds dispersed on zinc oxide

Abstract

The carbonyl clusters Rh/sub 4/(CO)/sub 12/, Rh/sub 6/(CO)/sub 16/, RhCo/sub 2/(CO)/sub 12/, RhCo/sub 3/(CO)/sub 12/, and Co/sub 4/(CO)/sub 12/ were deposited on ZnO and activated by pyrolysis (vacuum, 130/sup 0/-145/sup 0/C) or by activation above 90/sup 0/C in ethylene (or propylene), hydrogen, and carbon monoxide mixtures. The method of activation had no effect on the hydroformylation activity or selectivity. The specific rate for hydroformylation of ethylene or propylene to propanol and butyraldehyde, respectively, was 1.5-2.8 times higher on the rhodium derived from Rh/sub 4/(CO)/sub 12/ than on the rhodium derived from Rh/sub 6/(CO)/sub 16/, but the selectivity for the normal aldehyde isomer was higher on the latter catalyst. Relative rates for propylene hydroformylation depended on the catalyst precursor as follows: 100 for Rh/sub 4/(CO)/sub 12/, 60 for Rh/sub 2/Co/sub 2/(CO)/sub 12/, 42 for RhCO/sub 3/(CO)/sub 12/, and 5.2 for Co/sub 4/(CO)/sub 12/. IR spectroscopy suggested that the active species is a rhodium cluster carbonyl formed in situ from the metal crystallites formed upon activation; the role of cobalt in the bimetallic crystallites is apparently to act as electron donor to rhodium.