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Kinetic Study of Oxygen Adsorption over Nanosized Au/γ-Al2O3 Supported Catalysts under Selective CO Oxidation Conditions
Physical Chemistry Laboratory, Department of Chemistry, University of Patras, Patras 26504, Greece
School of Science and Technology, Hellenic Open University, Patras 26223, Greece
* Author to whom correspondence should be addressed.
Received: 13 February 2012; in revised form: 8 April 2012 / Accepted: 18 April 2012 / Published: 27 April 2012
Abstract: O2 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 O2 adsorption, desorption and surface bonding, as well as the respective activation energies, over a nanosized Au/γ-Al2O3 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 H2, resulted in mechanistic insights and kinetic as well as energetic comparisons, on the sorption processes of SCO reactants. In the absence of H2, the rate of O2 binding, over Au/γ-Al2O3, drastically changes with rising temperature, indicating possible O2 dissociation at elevated temperatures. H2 facilitates stronger O2 bonding at higher temperatures, while low temperature binding remains practically unaffected. The lower energy barriers observed, under H2 rich conditions, can be correlated to O2 dissociation after hydrogenation. Although, H2 enhances both selective CO reactant’s desorption, O2 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 O2 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.
Keywords: nanoparticles; Au/γ-Αl2Ο3; catalysts; SCO; PROX; reversed-flow inverse gas chromatography; inverse gas chromatography; rate constants; oxygen; carbon monoxide
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Gavril, D.; Georgaka, A.; Karaiskakis, G. Kinetic Study of Oxygen Adsorption over Nanosized Au/γ-Al2O3 Supported Catalysts under Selective CO Oxidation Conditions. Molecules 2012, 17, 4878-4895.
Gavril D, Georgaka A, Karaiskakis G. Kinetic Study of Oxygen Adsorption over Nanosized Au/γ-Al2O3 Supported Catalysts under Selective CO Oxidation Conditions. Molecules. 2012; 17(5):4878-4895.
Gavril, Dimitrios; Georgaka, Aglaia; Karaiskakis, George. 2012. "Kinetic Study of Oxygen Adsorption over Nanosized Au/γ-Al2O3 Supported Catalysts under Selective CO Oxidation Conditions." Molecules 17, no. 5: 4878-4895.