Characterization of supported Pd-Cu bimetallic catalysts by SEM, EDXS, AES and catalytic selectivity measurements

Pd-Cu/gamma-Al2O3 bimetallic catalysts were prepared according to different impregnation sequences of gamma-Al2O3 and characterized by XRD, SEM, EDXS and AES. The catalysts were tested for the selective hydrogenation of aqueous nitrate solutions to nitrogen. The reaction selectivity was found to be dependent on the catalyst preparation procedures, which affect the spatial distribution of metallic copper and palladium phases. A catalyst prepared by impregnating gamma-Al2O3 with copper followed by palladium gives higher selectivity to nitrogen than a catalyst prepared by impregnating the support with palladium followed by copper. The AES examination shows that in the catalyst exhibiting a higher nitrogen production yield, a reaction zone for the liquid-phase nitrate reduction is located in the interior of particles and covered by a layer of Pd atoms.