Sintering of Pt/Al2O3 reforming catalysts: EXAFS study of the behavior of metal particles under oxidizing atmosphere

The effect of an oxidative atmosphere (300 °C) is studied on fresh and sintered unchlorinated 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 PtO₂, but largely distorted. This is true whether the catalyst is sintered or not.     

Thermal Transformation of Transition Aluminas

JOM - This paper records conventional (CTEM) and scanning (STEM) microstructural examination of four transition aluminas (γ, δ, χ and κ) prepared from beohmite and...     

Characterization and catalytic activity of Al2O3-supported Pt-Co catalysts

A series of Pt-Co supported on γ-alumina have been prepared from acetylacetonate precursors with 2 wt% as total metal loading and different atomic contents. The catalysts were characterized by hydrogen chemisorption, TPR, TEM, XPS and they were tested in two different reactions: methylcyclohexane dehydrogenation and n-butane hydrogenolysis. The results have shown that platinum is in reduced state and cobalt is mainly in an oxidized state. Additionally, TEM results evidence an increase in the particle size as cobalt content is increased, in agreement with chemisorption results. Monometallic platinum and cobalt supported catalysts showed large differences in the dehydrogenation of methylcyclohexane, while the bimetallic catalysts have activities in the same order of magnitude with respect to the pure platinum catalyst. In n-butane hydrogenolysis all the catalysts show a large decrease in activity compared to other, previously studied Pt-based bimetallic catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Partial oxidation of methane to synthesis gas. Behaviour of different Ni supported catalysts

The behaviour of Ni supported catalysts, obtained using Ni(NO₃)₂ and Ni-acetylacetonate as precursor compounds, is analyzed. It is observed that initial activities and selectivities are similar for both systems, but the stability differs significantly. The systems show different carbon structures and sintering rates, depending on the precursor compound employed.     

Influence of the nature of the platinum precursor on the surface properties and catalytic activity of alumina-supported catalysts

The influence of the nature of the metal precursor — platinum acetylacetonates and chloroplatinic acid — on the surface properties and catalytic activity of Pt/Al₂O₃ catalysts is reported. The obtained results indicate that the catalysts prepared by the organometallic route present higher metal dispersion and lower acidity compared with those prepared from H₂PtCl₆. On the other hand, XPS results showed that the state of platinum is essentially Pt⁰ in the catalysts obtained from Pt(acac)₂ while in the solids prepared by impregnation of H₂PtCl₆ there exists an important contribution of Pt⁺ species which plays a positive role in the hydrogenation of toluene. An additional hydrogen spillover due to the presence of more acidic support is also suggested as an explanation of the observed catalytic results.