Highly selective vapor phase propene hydroformylation catalyzed by and systems on silica

The reduction of cobalt and rhodium salts coadsorbed on silica by aqueous NaBH4 at 273 K in Ar allows the synthesis of catalytic systems formed by very small rhodium crystallites (< 4 nm) and cobalt oxide/hydroxide. The presence of an unreduced cobalt species is well documented by TPR and XPS. The cobalt oxide is probably deposited on the rhodium surface, 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 modified by thermal treatments in CO and H2. The system resulted inactive for the atmospheric hydroformylation of propene, but actively catalyzed the reaction when a slight pressure (506 kPa) was applied. The high values of chemoselectivity towards hydroformylation (R = 0.75) and regioselectivity to linear aldehydes (SL = 96) can be due to the electronic and steric effects of the cobalt oxide layer.