HIGHLY SELECTIVE VAPOR-PHASE PROPENE HYDROFORMYLATION CATALYZED BY RHB AND RH-CO/B SYSTEMS ON SILICA/

The reduction of cobalt and rhodium salts coadsorbed on silica by aque ous NaBH4 at 273 K in Ar allows the synthesis of catalytic systems for med by very small rhodium crystallites(< 4 nm) and cobalt oxide/hydrox ide. The presence of an unreduced cobalt species is well documented by TPR and XPS. The cobalt oxide is probably deposited on the rhodium su rface, obscuring a large amount of the active metal centers. As can be judged by FT-IR and XRD data the morphology of the system is not modi fied by thermal treatments in CO acid H-2. The system resulted inactiv e for the atmospheric hydroformylation of propene, but actively cataly zed the reaction when a slight pressure (506 kPa) was applied. The hig h values of chemoselectivity towards hydroformylation (R = 0.75) and r egioselectivity to linear aldehydes (S-L = 96) can be due to the elect ronic and steric effects of the cobalt oxide layer.