Influence of Time Scale on the Reaction Mechanism of CO Oxidation over a Au/TiO2 Catalystt.

Knowledge of the reaction mechanism is key for rational catalyst improvement. Traditionally mechanistic studies focus on structure and the reaction conditions like temperature, pH, pressure, etc, whereas the time dimension is often overlooked. Here, we demonstrate the influence of time on the mechanism of a catalytic reaction. A dual catalytic mechanism was identified for the CO oxidation over Au/TiO2 by time-resolved infrared spectroscopy coupled with modulation excitation spectroscopy. During the first seconds CO on the gold particles is the only reactive species. As the reaction proceeds the redox properties of TiO2 dominate the catalytic activity through electronic metal-support interaction (EMSI). CO induces the reduction and reconstruction of TiO2 whereas oxygen leads to its oxidation. The activity of the catalyst follows the spectroscopic signature of the EMSI. These findings demonstrate the power of studying the short-time kinetics for mechanistic studies.