Kinetic study of CO oxidation over CuO/MO2 (M = Si, Ti and Ce) catalysts

Abstract

A series of supported CuO/MO2 catalysts (M=Si, Ti and Ce) were prepared using a chemisorption-hydrolysis method and tested for CO oxidation. Kinetic study was carried out to investigate reaction pathways on these catalysts. The power-rate law reaction expressions over CuO/SiO2, CuO/TiO2 and CuO/CeO2 were r=1.78×10−7Pco0.85Po20.22, r=1.62×10−7Pco0.65Po20.19 and r=1.5×10−7Pco0.7Po20, respectively. Activation energies were calculated to be 74.8, 53.4 and 46.3kJmol−1 for the CuO/SiO2, CuO/TiO2 and CuO/CeO2 catalysts respectively. Elementary steps of CO oxidation were also proposed. For the CuO/SiO2 catalysts, a Langmuir–Hinshelwood (L–H) model involving chemisorption of CO and O2 on surface Cu atoms was proposed; for the CuO/TiO2 catalysts, a L–H model involving chemisorption of CO on Cu atoms and chemisorption of O2 on TiO2 was proposed, which resulted in a interfacial reaction between the two species. For the CuO/CeO2 catalysts, a Mars van–Krevelen model involving chemisorbed CO on Cu atoms reacting with lattice oxygen in CeO2 was proposed. Effect of CuO particle size was also evaluated. It was found that the active site on the periphery of the CuO–TiO2 and CuO–CeO2 interface was more active on large CuO crystallite than that on small one. The enhanced activity could be interpreted by the higher concentration of chemisorbed CO on the active site on the larger CuO crystallite.