Base
metal oxides have long been of interest as catalysts for oxidation of small molecules such as CO or NO, but practical applications are limited by surface
poisoning processes. With growing interest in the oxidation activity of
metal oxides, it is important to understand and ultimately to learn to bypass surface
poisoning. RuO(2), as a model
metal oxide oxidation catalyst, is active for CO oxidation under UHV conditions but is deactivated by some surface
poisoning processes at ambient pressures. In this work, we use plane-wave, supercell DFT calculations to characterize the structures of
carbonate and
bicarbonate on the RuO(2)(110) surface and determine their thermodynamic stability by constructing phase diagrams. We find that while a surface
carbonate (CO) is stable at low O(2) pressures and high CO(2) pressures, it is not stable under practical catalytic conditions. A surface
bicarbonate (HCO) is more stable and deactivates the RuO(2) surface over a wide range of CO(2) and
oxygen pressures in the presence of trace amounts of water. Therefore,
bicarbonate is likely the species responsible for experimentally observed surface
poisons that deactivates RuO(2) during CO oxidation.
OH* might also be a candidate responsible for surface
poisoning when CO(2) pressure is very low. This study demonstrates that surface
poisoning is sensitive to reaction environments such as water and CO(2) pressures.