Effect of the preparation method and calcination temperature on the oxidation activity of CO at low temperature on CuO-CeO₂/SiO ₂ catalysts

The effect of preparation method, either coimpregnation or sequential impregnation, and of calcination temperature (between 500 C and 700 C) of CuO-CeO₂/SiO₂ catalysts on the CuO-CeO₂ interface and on their activity in the oxidation of CO with O₂ at low temperatures is studied. The catalysts are characterized by BET, XRD, TPR and UV-vis DRS. The results show that the preparation method has a substantial effect on the kind of CuO species formed on the surface. At calcination temperatures in the 500-600 C range, coimpregnation leads to the formation only of Cu species that interact strongly with CeO₂, while sequential impregnation leads also to the formation of bulk CuO species that do not interact, or interact weakly, with CeO₂. In the case of sequential impregnation the concentration of the different CuO and CeO₂ species and of the sites on the interface depends on the impregnation sequence of the support with the precursors of the oxides of both metals. On the other hand, the activity of the catalysts in the oxidation of CO at low temperatures (less than 180 C) does not differ substantially with the preparation method, provided the calcination temperature remains in the 500-600 C range. If the catalysts are calcined at 700 C, the CuO-CeO₂ interface, and therefore the activity of the catalysts, is strongly dependent on the preparation method and on the impregnation sequence of both oxides. Using sequential impregnation, impregnating first with the Ce precursor, produces a catalyst whose activity is substantially higher than that of the catalysts prepared by the other methods after calcining at 700 C.