ChBE Seminar Series: Robert J. Davis
Tuesday, February 19, 2008
11:00 a.m.-12:00 p.m.
Room 2110 Chemical & Nuclear Engineering Bldg.
Professor F. Joseph Schork
Selective Oxidation Reactions Catalyzed by Supported Gold Nanoparticles
Presented by Robert J. Davis
Department of Chemical Engineering
University of Virginia
Bulk gold is normally considered to be inert in catalytic reactions. In contrast, supported gold nanoparticles have demonstrated exceptional low-temperature catalytic activity in the oxidation of CO, and the presence of water vapor in the feed accelerates the oxidation reaction. Perhaps more importantly, gold catalysts selectively oxidize low levels of CO in a great excess of H2, which could be an important process for a future hydrogen economy. Very recently, supported Au catalysts exhibited excellent activity and selectivity in the oxidation of aqueous-phase glycerol to glycerate at high pH. In the work presented here, a variety of gold catalysts were prepared and characterized to examine the role of support composition, gold metal particle size, water and OH- on oxidation reactions. X-ray absorption spectroscopy at the Au LIII edge revealed that as-prepared samples contained cationic Au that was reduced to a predominately metallic state following treatment in He at 623 K. Scanning transmission electron microscopy confirmed the Au particle sizes estimated by X-ray absorption spectroscopy. Isotopic transient analysis involving 13C and 18O was used to evaluate the intrinsic turnover rate and coverage of active intermediates during CO oxidation. The pseudo-first-order rate constant was independent of temperature and fairly independent of support, approximately 3.4 and 2.1 s-1 for Au/TiO2 (261 303 K) and Au/Al2O3 (272 343 K), respectively. Both the rate constant and coverage of intermediates were enhanced by water vapor in the feed. Interestingly, both CO and glycerol in aqueous solutions at high pH are oxidized by gold catalysts with large metal particles that were previously inactive for vapor phase CO oxidation catalysis. These results suggest an oxidation path that depends critically on the availability of hydroxyl groups.