Competition of CO and H2 for Active Oxygen Species during the Preferential CO Oxidation (PROX) on Au/TiO2 Catalysts

Aiming at an improved mechanistic understanding of the preferential oxidation of CO on supported Au catalysts, we have investigated the competition between CO and H-2 for stable, active oxygen (O-act) species on a Au/TiO2 catalyst during the simultaneous exposure to CO and H-2 with various CO/H-2 ratios at 80 degrees C and 400 degrees C by quantitative temporal analysis of products (TAP) reactor measurements. It is demonstrated that, at both higher and lower temperature, the maximum amount of active oxygen removal is (i) independent of the CO/H-2 ratio and (ii) identical to the amount of active oxygen removal by CO or H-2 alone. Hence, under preferential CO oxidation (PROX) reaction conditions, in the simultaneous presence of CO and H-2, CO and H-2 compete for the same active oxygen species. In addition, also the dependency of the selectivity towards CO oxidation on the CO/H-2 ratio was evaluated from these measurements. Consequences of these findings on the mechanistic understanding of the PROX reaction on Au/TiO2 will be discussed.