ROLE OF TILTED CO IN DYNAMICS OF CO INSERTION ON CE-RH SIO2/

CO insertion is an important reaction step in the fields of both heter ogeneous and homogeneous catalysis for the production of oxygenated fu els and useful C-2+ oxygenates. Enhancement of CO insertion rate on th e supported Rh catalysts by the addition of oxophilic promoters (i.e., Ce, Mn, Fe, and La oxide) has been suggested to result from the high activity of a postulated tilted CO of which oxygen interacts with the oxophilic promoter. Investigation of the reactivity of adsorbed CO by in situ infrared spectroscopy combined with transient studies reveals that tilted CO on Ce-Rh/SiO2 is inactive for CO insertion at 303 K. Th e reactivities of CO species toward CO insertion were determined to be as follows: Rh(CO)(4) > linear CO > gem-dicarbonyl CO. Steady-state i sotopic transient studies show that gaseous CO rapidly exchanges with adsorbed CO and Ce decreases the residence time of intermediates leadi ng to propionaldehyde formation.