Kinetic and mechanistic study of CO oxidation over nanocomposite Cu-Fe-Al oxide catalysts

The oxidation of CO has been studied over Fe-Al and Cu-Fe-Al oxide nanocomposite catalysts prepared by melting of copper, iron, and aluminum nitrates. It was shown that the addition of copper significantly increases the catalytic activity of the Fe-Al nanocomposites. The catalysts were characterized by low-temperature nitrogen adsorption, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). It was found that the catalysts contain Fe(2)O(3)with the hematite structure modified by aluminum. Copper in the three-component catalyst is in the Cu(2+)state, forming CuO and CuFeO(x)clusters on the catalyst surface. An increase in the copper content leads to the formation of a Cu(x)Al(y)Fe(3-x-y)O(4)spinel phase.In situXPS study showed that a treatment of the catalysts in a CO flow leads to the reduction of both copper and iron cations into the metallic state. In contrast, a treatment in a CO/O(2)flow leads only to partial reduction of Cu(2+)to Cu1+, while Fe(3+)are not reduced. The tests of catalytic activity performed in a flow fixed bed reactor using a CO pulse technique showed that the light-off temperature in the oxidation of CO over the Cu-Fe-Al nanocomposite catalysts depends on the copper content. The minimal light-off temperature was achieved over the catalyst containing 5 wt% CuO. In addition, we performed kinetic measurements in a differential reactor and obtained the activation energy and the reaction orders with respect to the reactants. The reaction mechanism of the catalytic oxidation of CO and the origin of active species are discussed.