SPECTROSCOPIC CHARACTERIZATION AND CATALYTIC PROPERTIES OF SOL-GEL PD/SIO2 CATALYSTS

The present study reports the results obtained by UV-VIS spectroscopy, FT-IR (Fourier transform infrared) spectroscopy, and BET area measurements of Pd/SiO2 catalysts synthesized by the sol-gel process. This preparation technique results in the hydrolysis and polycondensation of a silicon alkoxide, which contains the metal halide salt PdCl2 in the initial solution. The reaction takes place at pH 9, forming intermediates which correspond most probably to surface species [SiO2]-[PdCl-OH The interaction between the silica gel and the palladium precursor has important effects on the specific surface area. The products are solids with BET specific areas up to 800 m2/g. Catalytic tests (hydrogenation of 1-hexene and phenylacetylene) show that sol-gel catalysts exhibit high selectivity in the formation of 2-methylpentane and styrene. To explain the high selectivities shown by the Pd sol-gel catalysts a geometric effect induced by the support is proposed on the structure of the ca. 1-nm-size Pd metal particles. © 1992.