The reactivity of O2/H2, O2/CO and O2/C3H6 gas mixtures on Cu(111)

The reactivity of O2/CO, O2/H2 and O2/C3H6 gas mixtures on Cu(111) was investigated at 475, 550, 650 and 750 K. For these three gas mixtures steady state oxygen coverages exist intermediate between a completely reduced surface and an oxygen saturated surface. For O2/CO mixtures the coverage dependence behaves according to the kinetic expressions of the reaction models of the separate oxidation and reduction step. Oscillations were never noticed. The sticking probability for oxygen is not significantly influenced by hydrogen and carbon monoxide but is enlarged by propene at 750 K. A model involving assisted sticking is proposed to explain this surprising effect. For the reactions between H2 and O2 and CO and O2, however, the Mars and Van Krevelen mechanism is applicable to describe the overall kinetics.