Investigation of CO oxidation over Au/TiO2 catalyst through detailed temperature programmed desorption study under low temperature and Operando conditions

Using a temperature-programmed online MS system, gas products are directly analyzed at low temperature to understand the reactivity of the surface intermediates on an Au/TiO2 catalyst that exhibits catalytic activity for CO oxidation. CO oxidation was performed over Au/TiO2 catalysts with Au particle size of 3 nm, and a 7.3 wt% loading, focusing on CO-TPD, steady state isothermal titration, high temperature TPR, and low temperature selective TPO experiments. With CO-TPD, we were able to observe directly, the presence of two different CO species adsorbed on the catalyst surface, as well as the respective desorption energies. Steady state isothermal titrations showed two transient processes with different redox sequences, both forming catalytic layers for intermediate storage and subsequent CO2 product formation. High temperature CO titration transients with 200 degrees C pre-oxidation following either isothermal CO titration or high temperature TPR highlights the presence of two oxidative surface intermediate species with different kinetics, with the intermediates purposed as atomic oxygen at the Au NP perimeter and neighboring lattice sites. Finally, low temperature selective TPO beginning at -165 degrees C showed that pre-reduction following oxidation up to -100 degrees C is able to partially convert surface CO species into stable CO2 intermediates, as a higher activation energy was required to fully desorb the CO2 product from the catalyst surface. (c) 2017 Elsevier B.V. All rights reserved.