Physicochemical properties of copper oxide loaded alumina in methane combustion

Abstract

Copper oxide was deposited on gamma alumina with loadings between 2.1 and 9.2 wt % of CuO. The activity of these solids was measured in the catalytic combustion of methane before and after an aging test performed at 1340 K. The state and the environment of the copper species was followed by UV–VIS reflectance spectroscopy. Carbon monoxide adsorption on fresh and aged samples was performed and studied by infrared spectroscopy. For fresh samples, the number of active centres decreases when the copper loading increases. At low amounts of CuO, copper oxide does not have the spectral features of bulk oxide whereas the 9.2 wt % CuO sample behaves like bulk CuO. At moderate conversion levels the catalytic activity is directly proportional to the absorbance of the v_CO band of carbon monoxide bonded to surface Cu^II ions of the copper oxide phase, showing that the sites responsible for the catalytic activity are revealed by carbon monoxide adsorption. After the ageing test, the catalytic activity strongly decreases because of the formation of copper aluminate, copper being in the oxidation state + 1 or +2 according to the stoichiometry of the reactants mixture. In that case, the remaining activity is also proportional to the absorbance of the v_CO band of carbon monoxide bonded to Cu^II ions of the copper oxide phase.