Investigation on the structure-activity relationship of BaO promoting Pd/CeO2-ZrO2 catalysts for CO, HC and NOx conversions.

Four different synthetic routes (co-precipitation, oxidation-precipitation, citric acid sol-gel and reversed microemulsion) are adopted to prepare barium modified Pd/CeO2-ZrO2 catalysts and their catalytic activity towards CO, HC and NOx conversions is studied. The surface and bulk properties of these catalysts are characterized via XRD, N2 adsorption, XPS, UV-Raman, H2-TPR, and in situ DRIFTS. The catalyst prepared via the co-precipitation method exhibits the optimum three-way catalytic behavior, which is mainly due to its superior redox ability, whereas the oxidation-precipitation synthesis renders the catalyst with the best homogeneity and thermal resistance. However, for the catalyst prepared via the sol-gel route, its worst NOx reduction capacity is verified by the scarce appearance of negatively charged Pd0-N[double bond, length as m-dash]Oδ- species, which is related to the faster dissociation of NO based on in situ DRIFTS, and the abundance of surface CO-Pd+ species reveals its unsatisfactory deep oxidizability of the HC reactant.