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n-Hexane conversion on γ-alumina supported palladium–platinum catalysts

Authors
  • Radlik, Monika1
  • Śrębowata, Anna2
  • Juszczyk, Wojciech2
  • Matus, Krzysztof3
  • Małolepszy, Artur4
  • Karpiński, Zbigniew1
  • 1 Cardinal Stefan Wyszyński University in Warsaw, Faculty of Mathematics and Natural Sciences, ul. Wóycickiego 1/3, Warsaw, PL-01938, Poland , Warsaw (Poland)
  • 2 Polish Academy of Sciences, Institute of Physical Chemistry, ul. Kasprzaka 44/52, Warsaw, 01224, Poland , Warsaw (Poland)
  • 3 Silesian University of Technology, Institute of Engineering Materials and Biomaterials, ul. Konarskiego 18A, Gliwice, 44100, Poland , Gliwice (Poland)
  • 4 Warsaw University of Technology, Faculty of Chemical and Process Engineering, ul. Waryńskiego 1, Warsaw, 00645, Poland , Warsaw (Poland)
Type
Published Article
Journal
Adsorption
Publisher
Springer US
Publication Date
Apr 19, 2019
Volume
25
Issue
4
Pages
843–853
Identifiers
DOI: 10.1007/s10450-019-00083-9
Source
Springer Nature
Keywords
License
Green

Abstract

Two series of Pd–Pt/Al2O3 catalysts, characterized by high metal dispersions were prepared and investigated in the reaction of n-hexane conversion at the temperature < 300 °C. Incipient wetness co-impregnation of γ-alumina with the solutions of Pd(acac)2 and Pt(acac)2 led to relatively good Pd–Pt alloying. However, a similar catalyst preparation using solutions of PdCl2 and H2PtCl6 resulted in unsatisfactory homogenization; furthermore, significant amounts of chlorine were retained in the catalysts. The Pd–Pt alloy homogeneity has a significant effect on the relations of catalytic activities and product selectivities with Pd–Pt alloy composition. The relationship between the catalytic activity of chlorine-free Pd–Pt/Al2O3 catalysts and bulk Pd–Pt composition matches the accepted relation between the surface composition and bulk composition of Pd–Pt, reflecting a high surface enrichment in palladium. In contrast, for the chloride series of Pd–Pt/Al2O3, variations of the turnover frequency are directly correlated with the bulk composition, indicating that unalloyed, more active, Pt particles decide about the catalytic behavior. Pd/Al2O3 shows better than Pt/Al2O3 selectivity for isomerization, especially after reduction at higher temperatures, ≥ 500 °C. On alloying with Pt, for the Cl-free series the isomerization selectivity was very high for nearly all bimetallic catalysts and showed a synergistic effect for 20 at.% Pt. In contrast, for the Cl-containing series, the isomerization selectivity was proportional to the palladium content. The effect of reduction temperature on the isomerization propensity of Cl-containing Pd–Pt/Al2O3 catalysts was rather small, suggesting that possible variations in support acidity associated with chloride presence do not have large catalytic consequences, confirming the metal-only catalytic action in alkane isomerization carried out at the temperatures below 300 °C.

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