Electronic Metal–Support Interactions in the Activation of CO Oxidation over a Cu/TiO<sub>2</sub> Aerogel Catalyst
Andrew J. Maynes, Darren M. Driscoll, Paul A. DeSario, Jeremy J. Pietron, Ashley M. Pennington, Debra R. Rolison, John R. Morris
Abstract
Carbon monoxide (CO) oxidation is not only an important industrial reaction but also a useful model system for investigations into reaction dynamics involving new catalyst designs. In this work, we use CO oxidation to probe the metal−support interactions between Cu nanoparticles and a TiO2 aerogel support. We utilized a packed-bed reactor to demonstrate the activity of a Cu/TiO2 aerogel catalyst for CO oxidation at temperatures above 463 K. In situ infrared spectroscopic methods revealed that the reaction proceeds primarily by a Cu-assisted Mars-van-Krevelen type mechanism. Results indicate that Ti4+ sites are reduced by CO to generate Ti3+ sites adjacent to oxygen vacancies. Lattice oxygen extraction appears to be accompanied by interfacial charge transfer from lower work function copper nanoparticles to the TiO2 support, as evidenced by variable-temperature infrared spectroscopic studies of adsorbed CO. The charge transfer is evidenced by differences in the nature of CO bound to Ti4+ sites within aerogels in the presence and absence of Cu. The Cu particles on the TiO2 support lower the vibrational frequency for CO bound to Ti4+ sites by 3 cm–1 and increase the binding enthalpy by 7 kJ/mol. Infrared spectroscopic probes of oxidation state cycling during catalysis contribute toward the development of an overall CO oxidation reaction mechanism on the Cu/TiO2 aerogel.