THE RATE-LIMITING STEP FOR OLEFIN COMBUSTION ON SILVER - EXPERIMENT COMPARED TO THEORY

The oxidation of propylene by atomically adsorbed oxygen on Ag(110) has been studied over a wide range of oxygen adatom coverages between 0.05 and 0.5 monolayers. Over the entire range of coverage combustion occurs easily, the only products observed are CO2 and H2O, and all absorbed oxygen is found to react readily. The absence of acrolein as a product mitigates against the formation of allyl oxide as a combustion intermediate under these conditions. These results are in contrast to theoretical predictions concerning the mechanism of olefin combustion which invoke both homolytic CH cleavage and oxygen insertion into a CH bond to produce allyl oxide as an intermediate. Combustion of propylene and higher molecular weight 1-alkenes is proposed to occur predominantly via an acid-base reaction with chemisorbed oxygen. © 1993 Academic Press, Inc.