XPS structural characterization of Pd/SiO2 catalysts prepared by cogelation

Nanostructured Pd/SiO2xerogel catalysts prepared via cogelation were characterized by X-ray photo-electron spectroscopy. The preparation route allowed highly porous silica particles to be formed alongwith embedded Pd nanocrystals. After heat-treating the catalysts in vacuum, Pd was found to be in themetallic state. To obtain information on the xerogel catalyst texture and, in particular, on the size of thesilica particles, a theoretical formalism was developed based on measuring the relative intensities of Pd 3ddoublet and the associated background tail due to inelastically scattered photoelectrons. The suggestedprocedure also involved the measurement of the background tails accompanying Si 2p and O 1s spectrallines as internal standards. Using the developed formalism, the size of the silica particles in the catalystsafter different treatments was evaluated and compared with TEM data. The results obtained indicate thatthe textural properties of the sol–gel catalysts start to develop already at the level of co-condensation ofalkoxides with the network-forming reagent. Calcination causes these properties to run to completion

Catalytic CO oxidation over well-defined cobalt oxide nanoparticles: size-reactivity correlation

Co nanoparticles of well-defined size were synthesized by temperature-controlled injection of Co-2(CO)(8) into dichlorobenzene. After intercalation into mesoporous MCF-17 and temperature-programmed oxidation, Co3O4/MCF-17 model catalysts were obtained with cobalt oxide particle sizes varying between 3.5 and 12.2 nm. We demonstrate here the occurrence of a distinct particle size effect for the CO oxidation. Maximum reaction rates of about 0.77 nm(-2) s(-1) at 150 degrees C were observed for Co3O4 particles with a size in the range of 5 to 8 nm. The reaction rates decreased for either smaller or larger sizes. X-ray photoelectron spectroscopy allowed establishing a clear correlation between the Co3+ trivalent oxidation state and the CO oxidation rate