Electronic Metal-Support Interactions in the Activation of CO Oxidation over a Cu/TiO2 Aerogel Catalyst

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.