| Autor: |
Colin H. Rochester, James A. Anderson, Geomar J. Arteaga |
| Rok vydání: |
2000 |
| Předmět: |
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| Zdroj: |
Journal of Catalysis. 189:195-208 |
| ISSN: |
0021-9517 |
| Popis: |
Two Pt(0.3%)–Ge/Al2O3 catalysts containing 0.15 and 0.45% Ge have been characterized by CO chemisorption and FTIR spectra of adsorbed CO after series of oxidation/reduction and oxychlorination/reduction cycles and have also been used for the catalytic hydroreforming of heptane. Catalysts after oxychlorination contained chloro- and oxychloro-Pt complexes which were responsible for the efficient spreading of Pt over the support surface and hence for the maintenance of a good Pt dispersion after reduction. XRD study of a more highly loaded catalyst gave no evidence for Pt–Ge alloy formation or for Ge0 species. Reduced Cl-containing catalysts contained small clustered arrays of Pt atoms dispersed possibly as mats rather than particles over the GeOx-modified alumina such that all the exposed Pt atoms were influenced by an electron withdrawing effect of both Ge2+ ions and Cl ions. Germanium did not block low-coordination Pt sites but may have partially decorated arrays of high coordination sites. Germanium partially stabilized Pt/Al2O3 against loss of activity through coking. The dominant mutual effect of Ge and Cl in catalysts was a significant loss in hydrogenolysis selectivity, but gains in the selectivities of aromatization, isomerization, and cyclization reactions. The addition of Ge to Pt/Al2O3 did not compromise the availability of Pt adsorption sites and only reduced by a small amount the turnover frequencies for heptane reforming reactions. Good activities were therefore maintained in the absence of Ge0 or alloy formation during catalyst reduction. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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