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Pd/CeO 2 , Pd/ZrO 2 and Pd/CeO 2 -ZrO 2 , 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 CeO 4 and ZrO 2 . The dispersions for Pd/ Al 2 O 3 and Pd/Zr/Al 2 O 3 are similar but very different on , increasing 4 and 7 times in relation to the Pd/Al 2 O 3, suggesting re-dispersion of Pd, mainly due to the promoting effect of Ce. EPR signals of Pd/Ce/Al 2 O 3 are related with O 2-species of Ce 4? -O 2-. DRIFTS studies with NO and CH 4 reaction showed that the Pd d? species interacts with Ce ?d , modifying significantly the NO ? CH 4 reaction route.

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