Complex redox chemistry on the RuO₂(110) surface: experiment and theory

Employing temperature-programmed reaction and desorption, we studied the reduction of RuO2(110) by CO exposure under various conditions. RuO2(110) is mildly and heavily reduced by CO exposure when the reaction temperature is below 400 K and above 500 K, respectively. The restoration of the reduced RuO2(110) surface was investigated by low energy electron diffraction and Auger electron spectroscopy. CO molecules adsorb over the under-coordinated Ru atoms and recombine with the under-coordinated lattice O atoms on the RuO2(110) surface. The initial conversion probability for this process is as high as 80%. The mildly reduced RuO2(110) surface is characterized by the removal of bridging O atoms. A mildly reduced surface, where all bridging O atoms are consumed, is inactive in oxidizing CO below 450 K. However, temperature treatment (greater than or equal to 550 K) or oxygen exposure at room temperature is able to reactivate the mildly reduced surface. Heavy reduction of RuO2(110) leads to a roughening of the surface, which is partly restored by annealing at 700-800 K. The activation barriers of various reaction pathways, motivated by the present experiments, are determined by state-of-the-art density function theory calculations and compared with experiments