Influence of CuOx additives on CO oxidation activity and related surface and bulk behaviours of Mn2O3, Cr2O3 and WO3 catalysts Original Research Article

CuOx-modified and unmodified Mn2O3, Cr2O3 and WO3 catalysts were prepared by impregnation with Cu(NO3)2 solution and/or calcination at 700°C of appropriate precursor compounds. Bulk phase composition and thermochemical stability were characterized by X-ray diffractometry, infrared spectroscopy and thermogravimetry. The surface area, chemical composition, oxidation state and chemisorption capacity were determined by X-ray photoelectron spectroscopy and sorptometry of N2, O2 and CO gas molecules. The catalytic CO oxidation activity was tested, using a gas circulating system equipped with a fixed-bed microreactor and a gas chromatograph. The CuOx additives were found to promote markedly the otherwise insignificant CO oxidation activity of WO3 at 250–400°C. This was related to concomitant improvement primarily in the lattice oxygen reactivity, and in the O2 chemisorption capacity. The already high CO oxidation activities of Mn2O3 and Cr2O3 catalysts at 150–250°C were found to be, respectively, slightly and hardly improved by CuOx additives, despite a marked improvement in oxygen chemisorption capacity. This was attributed to establishment on the unmodified catalysts of a favourable electron-mobile environment. In oxygen-rich reaction atmosphere, both the modified and unmodified catalysts were thermochemically stable. However, in lean oxygen atmosphere, Cr2O3 and CuOx-modified WO3 were relatively the most stable test catalysts.