Characterization of Pd–Au/SiO2 Catalysts by X-ray Diffraction, Temperature-Programmed Hydride Decomposition, and Catalytic Probes

Two series of Pd–Au/SiO2 catalysts, differing widely in metal particle size distribution, were prepared by a direct redox method, which involves reductive deposition of gold onto prereduced palladium particles. The method yields good results; i.e., a significant Pd–Au alloying was achieved in reduced bimetallic catalysts. The catalysts were investigated at various stages of their preparation by X-ray diffraction and temperature-programmed hydride decomposition. These techniques appear valuable in assessing the degree of alloying. Being sensitive to palladium particle size, the temperature-programmed hydride decomposition could also be applied to estimate the palladium dispersion. 2,2-Dimethylpropane conversion carried out on Pd–Au/SiO2 also appeared to be a useful probe. Apparent activation energy decreased considerably with gold addition. This result is contrary to a relative constancy of the activation energy observed earlier for Pd–Au/SiO2 catalysts, which were prepared by an incipient wetness coimpregnation when the resulting bimetallic samples were not satisfactorily homogenized.