The effect of an oxidative atmosphere (300°C) is studied on fresh and sintered unchlori nated naphtha reforming catalysts containing 0.6-1 % Pt. The TPR profiles show that only one species is formed using our experimental conditions, regardless of the mean crystallite size of the metal particles. The structural information supplied by EXAFS compared with cuboctahedral particle modeling, implies that such species is a surface platinum oxide, the structure of which is close to that of Pt02, but largely distorted. This is true whether the catalyst is sintered or not.

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Redispersion of sintered Pt (0.6−1.0%)/Al2O3 catalysts at 773 K under HCl/H2O/O2/N2 atmospheres was studied by hydrogen chemisorption, temperature-programmed reduction (TPR), transmission electron microscopy (TEM) and in situ X-ray absorption spectroscopy (EXAFS) experiments. TPR and H2 chemisorption results showed that the concentration of hydroxychlorided Pt species on the alumina carrier and, as a consequence, the metallic dispersion constantly augmented during the 8 h redispersion treatment. In situ EXAFS experiments indicated that Pt(OH)4Cl2 2- species, which are formed by the attack of gaseous/surface chlorided species to partially oxidized metallic Pt particles, are responsible for Pt redispersion. EXAFS studies also suggested that once the Pt−Cl/Pt−O coordination number ratio was stable, the Pt atoms were present on the alumina carrier either in the form of small rafts containing Cl and O atoms in a slighly distorted octahedral environment or in relatively large metallic particles covered by Pt(OH)4Cl2 2- species. This suggestion was supported by the bimodal distribution of metal platinum particles observed by TEM when the redispersed samples where examined after its reduction with H2.

Niobium oxide supported Pd-Co catalysts were characterized through XPS (X-ray photoelectron spectroscopy), (XPS), temperature-programmed reduction (TPR), magnetic measurements, X-ray diffraction, and extended X-ray absorption fine structure (EXAFS). XPS analyses suggested the presence of Co 3 O 4 particles and Co 2+ surface phase. TPR and magnetic measurements showed that the palladium addition promoted not only the reduction of Co 3 O 4 particles but also the cobalt surface phase. Magnetic measurements and EXAFS analyses revealed the Pd-Co alloy formation during reduction. A model represented by bimetallic particles enriched with palladium and particles containing only cobalt was proposed.

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