How Temperature Affects the Mechanism of CO Oxidation on Au/TiO2: A Combined EPR and TAP Reactor Study of the Reactive Removal of TiO2 Surface Lattice Oxygen in Au/TiO2 by CO

Despite enormous breakthroughs in our understanding of the reaction mechanism of the low-temperature CO oxidation on gold catalysts, in particular on Au/TiO2 and down to temperatures as low as -150 degrees C, there are still many contradictory proposals about the dominant reaction pathway. In this work, we will demonstrate that these discrepancies often originate from the rather different reaction conditions applied in numerous studies, most notably from different reaction temperatures. By combining temporal analysis of products reactor measurements with electron paramagnetic resonance spectroscopy, we will show that removal of TiO2 surface lattice oxygen from a Au/TiO2 catalyst upon exposure to CO (i) readily takes place at 120 degrees C, where it represents the active oxygen species for CO oxidation, (ii) is still possible at -20 C, although much slower and to a much lower extent, and (iii) is completely inhibited at -90 degrees C. Consequences of these findings for our understanding of the dominant reaction pathway for the CO oxidation on Au/TiO2 catalysts, in particular its dependency on the reaction temperature, will be discussed.