In situ DRIFTS and CO-TPD studies of CeO2 and SiO2 supported CuOx catalysts for CO oxidation

Abstract

Gas adsorption-desorption processes on oxide supported metal catalysts are critical steps for understanding catalytic CO oxidation mechanism. This report investigates the support structure (shape and exposed crystal planes)-catalytic activity relationship of irreducible SiO2 and reducible CeO2 nanorods (NR) and nanocubes (NC) supported CuOx via various structural and surface characterization methods, including XRD, Raman spectroscopy, BET surface area, H2-TPR, CO-TPD, in situ DRIFTS, XPS, and HRTEM. Evidence is presented that both isolated Cu+/Cu2+ redox pair and lattice oxygen of oxide supports from different crystal planes (111, 011, and 001) of CeO2 play important role towards CO oxidation by supporting Langmuir–Hinshelwood mechanism. The Cu+/Cu2+ and Ce3+/Ce4+ species at CuOx-CeO2 interfaces can facilitate the charge and mass transfer between CuOx nanoclusters and CeO2 by electronic interaction which was highly promoted by reducible CeO2 NR support. In addition, CeO2 NR contains significantly higher amount of surface defects including oxygen vacancy, steps, voids, and lattice distortion on various crystal facets, which promote surface oxygen release of CeO2 and CO adsorption and oxidation on catalytically active sites at lower temperature. According to the CO oxidation results, the oxidized CuO/CeO2 NR sample showed 62.8% CO conversion at 100°C and up to 98.9% conversion at 397 °C.