The Effects of Water on CO Oxidation over TiO2 Supported Au Catalysts

Polarization modulation infrared reflection absorption spectroscopy (PM-IRAS) was used to investigate the effects of water on CO oxidation catalyzed by TiO2 supported Au. The introduction of water into the reactant mixture caused two effects: (1) a decrease in the CO coverage; and (2) the appearance of a carbonate species. Since both effects inhibit CO oxidation, the promotional effects of water found by previous researchers can only be rationalized by its effects on molecular oxygen adsorption and activation. Although this argument is not confirmed by the PM-IRAS data alone, this conclusion is consistent with previous studies. It is further inferred from this study that carbonate species first form on TiO2 sites and then migrate to Au sites. Surface hydroxyl species may play the same promotional role as adsorbed water.