The Interaction of Oxides of the Pd/Ce/Zr/Al2O3 Catalysts Prepared by Impregnation Over Alumina and Promoting Effects on Surface Properties

Pd/CeO2, Pd/ZrO2 and Pd/CeO2-ZrO2, were prepared by impregnation on a well defined alumina support. The oxides are finely dispersed over alumina support. TPR results on promoted Zr and Ce catalysts indicate partial reduction of CeO4 and ZrO2. The dispersions for Pd/Al2O3 and Pd/Zr/Al2O3 are similar but very different on Pd/Ce/Al2O3 and Pd/Ce/Zr/Al2O3, increasing 4 and 7 times in relation to the Pd/Al2O3, suggesting re-dispersion of Pd, mainly due to the promoting effect of Ce. EPR signals of Pd/Ce/Al2O3 are related with O2- species of Ce4+-O2-. DRIFTS studies with NO and CH4 reaction showed that the Pd delta+ species interacts with Ce+delta, modifying significantly the NO + CH4 reaction route.