Atomistic Studies of Oxidation Catalysis and Surface Poisoning on Transition Metal Oxide Surfaces

Base metal oxides have long been of interest as catalysts for oxidation of small molecules such as CO and NO. As an example, Ru metal becomes active for catalytic oxidation only after partial surface oxidation. The (110) surface of RuO$_2$ is a convenient model for the oxidized metal surface because it is active for CO oxidation and well characterized. In this study we employ plane-wave, supercell DFT calculations to examine the mechanisms of oxygen activation, COO oxidation as well as surface poisoning on RuO2(110) surface.

We first consider O2 adsorption and dissociation, and show that the molecular O$_2$ species observed in TPD experiments and identified as a precursor to O2 dissociation is in fact a spectator present only at high coverages of surface O. We then study the CO and NO oxidation mechanisms on the RuO2(110) surface and compare the fundamental differences that lead to complete different catalytic reactivity of this surface on CO and NO oxidations.

Practical applications of oxidation catalysts are limited by surface poisoning, so it is important to understand and ultimately to learn to bypass surface poisoning. We investigate catalytic CO oxidation and its competition with surface poisoning by employing first-principles thermodynamics as well as micro-kinetic modeling method. We identify both carbonate and bicarbonate surface poisons and show that the coverage of the latter is highly sensitive to water concentration and likely accounts for the surface poisoning observed experimentally.

As an attempt to understand how surface metal oxides develop on metal surfaces and what their exact role is during oxidation, we study the formation of oxide nuclei on Pt surface. We hypothesize that the roughening on Pt surfaces observed in STM experiments initiates from small surface PtxOy clusters. We quantify the stability of these clusters vs. the cluster size and oxygen chemical potential and explore whether these clusters might account for the anomalously high catalytic activity of Pt and other metals at high oxygen pressure.