Influence of CuO x additives on CO oxidation activity and related surface and bulk behaviours of Mn 2O 3, Cr 2O 3 and WO 3 catalysts

Abstract

CuO x -modified and unmodified Mn 2O 3, Cr 2O 3 and WO 3 catalysts were prepared by impregnation with Cu(NO 3) 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 N 2, O 2 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 CuO x additives were found to promote markedly the otherwise insignificant CO oxidation activity of WO 3 at 250–400°C. This was related to concomitant improvement primarily in the lattice oxygen reactivity, and in the O 2 chemisorption capacity. The already high CO oxidation activities of Mn 2O 3 and Cr 2O 3 catalysts at 150–250°C were found to be, respectively, slightly and hardly improved by CuO x 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, Cr 2O 3 and CuO x -modified WO 3 were relatively the most stable test catalysts.