Oxidation of carbon monoxide over Cu- and Ag-NaY catalysts with aqueous hydrogen peroxide

A novel oxidation reaction of CO with aqueous H2O2 over Cu-NaY (2-15 wt%) and Ag-NaY (5-15 wt%) catalysts has been achieved at low temperatures (55-70 deg. C) using a flow mode system. The employed catalysts were prepared by the incipient wetness impregnation of NaY zeolite (Si/Al = 5.6, surface area = 910 m2/g) with an aqueous solution of known concentrations of copper acetate and silver nitrate. Solids were subjected to thermal treatment at 300-450 deg. C prior to catalytic measurements unless subjected to subsequent reduction with hydrogen at 350 deg. C. The physicochemical characterization of the catalysts was probed using X-ray diffraction (XRD), FT-IR and combined thermal analyses TGA-DrTGA. The XRD data indicated that, the Ag particles have an ordered location in the sodalite cavity and the center of a single six-ring. The FT-IR data also proved the presence of a new peak at 1385 cm-1 that is assigned to Ag-coordinated with the framework. A slow induced oxidation of CO (induction period, tind) took place at the initial stage of the CO oxidation reaction after which the reaction obeyed first-order kinetics. The utilized metal ions are proposed to be reduced to lower oxidation states such as Cu+ and Ag0 during the first period of reaction, tind, where the reaction proceeded favorably on such sites. Such argument was evidenced by carrying out the oxidation reaction over H2-reduced Cu10-NaY and Ag10-NaY catalysts. The reduction caused a decrease in the tind, giving an evidence that the lower oxidation states Cu+ and Ag0 are the active sites in the studied oxidation reaction. The enhancement in catalytic activity was interpreted in terms of the facile adsorption of CO on the low oxidation state species