The Influence of the Support Nature and the Metal Precursor in the Activity of Pd-based Catalysts for the Bromate Reduction Reaction

摘要

Palladium catalysts supported on different materials (alumina, activated carbon and mixed oxide derived from hydrotalcite) and prepared with different metal precursors (nitrate, chloride and acetate) have been characterized and tested for the bromate reduction reaction. The catalytic behavior depends on the support nature and on the metallic precursor used for the catalyst preparation. Pd catalyst supported on a mixed oxide has a low activity due to the high affinity of the reconstructed support for the Br- formed, preventing the reactants to approximate the active Pd sites. Pd catalyst supported on activated carbon has a surface negative charge and a microporous structure, making difficult the interaction of the active sites with the reactants. The best results are obtained with the catalyst supported on alumina due to its physical-chemical properties, i. e. mesoporosity, positive surface charge and reversible adsorption of reactants and products. These characteristics make easy bromate and H-2 adsorption on the active sites and subsequent reaction, thus resulting in a better activity. The Pd precursor salt also influences the catalytic activity as it has an effect on the Pd nanocrystal size. The best results are obtained with the metal precursor that produces homogeneous and large Pd metallic crystallites.