XPS structural characterization of Pd/SiO2 catalysts prepared by cogelation

Abstract

Nanostructured Pd/SiO2 xerogel catalysts prepared via cogelation were characterized by X-ray photoelectron spectroscopy. The preparation route allowed highly porous silica particles to be formed along with embedded Pd nanocrystals. After heat-treating the catalysts in vacuum, Pd was found to be in the metallic state. To obtain information on the xerogel catalyst texture and, in particular, on the size of the silica particles, a theoretical formalism was developed based on measuring the relative intensities of Pd 3d doublet and the associated background tail due to inelastically scattered photoelectrons. The suggested procedure also involved the measurement of the background tails accompanying Si 2p and O 1s spectral lines as internal standards. Using the developed formalism, the size of the silica particles in the catalysts after different treatments was evaluated and compared with TEM data. The results obtained indicate that the textural properties of the sol–gel catalysts start to develop already at the level of co-condensation of alkoxides with the network-forming reagent. Calcination causes these properties to run to completion.