Kinetic Study of Oxygen Adsorption over Nanosized Au/γ-Al(2)O(3) Supported Catalysts under Selective CO Oxidation Conditions

O(2) adsorption is a key process for further understanding the mechanism of selective CO oxidation (SCO) on gold catalysts. Rate constants related to the elementary steps of O(2) adsorption, desorption and surface bonding, as well as the respective activation energies, over a nanosized Au/γ-Al(2)O(3) catalyst, were determined by Reversed-Flow Inverse Gas Chromatography (RF-IGC). The present study, carried-out in a wide temperature range (50–300 °C), both in excess as well as in the absence of H(2), resulted in mechanistic insights and kinetic as well as energetic comparisons, on the sorption processes of SCO reactants. In the absence of H(2), the rate of O(2) binding, over Au/γ-Al(2)O(3), drastically changes with rising temperature, indicating possible O(2) dissociation at elevated temperatures. H(2) facilitates stronger O(2) bonding at higher temperatures, while low temperature binding remains practically unaffected. The lower energy barriers observed, under H(2) rich conditions, can be correlated to O(2) dissociation after hydrogenation. Although, H(2) enhances both selective CO reactant’s desorption, O(2) desorption is more favored than that of CO, in agreement with the well-known mild bonding of SCO reactant’s at lower temperatures. The experimentally observed drastic change in the strength of CO and O(2) binding is consistent both with well-known high activity of SCO at ambient temperatures, as well as with the loss of selectivity at higher temperatures.