Influence of preparation procedure on physical and catalytic properties of carbon supported Pd-Au catalysts

The influence of preparation variables on the physical and catalytic properties of the Pd-Au/C system, taking benzaldehyde hydrogenation as a probe reaction, has been investigated. Catalysts were prepared by wet impregnation (simultaneous and consecutive). TPR, CO chemisorption and WAXS were used for catalyst characterization, in addition to catalytic tests. The chemisorption data point to the absence of Au surface enrichment in the fresh samples. The metal dispersion decreases upon heating at temperatures up to 500°C, independently on Au presence. WAXS data show that coimpregnation gives rise to a Pd-Au alloy, while consecutive impregnation gives progressive alloying only after heat treatment. An appreciable amount of very small Pd particles is likely to be present in all the samples. For monometallic Pd samples the turnover frequency appears to increase with Pd particle size, but this does not occur in the presence of Au. Au addition to Pd catalysts does not increase their activity in the hydrogenation of aromatic aldehydes.