Removal of carbonaceous residues by deuterium from Pt catalysts

A. Wootsch, Claude Descorme, Z. Paál, Daniel Duprez

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

Mixtures of hexane (nH) and hydrogen (H2) were reacted over EUROPT-1 (6.3% Pt/SiO2) and Pt black. In addition to gas-phase products, including isomers, methylcyclopentane, fragments, and benzene, firmly chemisorbed entities were also produced. They may be C1 units or - highly dehydrogenated - polymeric deposits. Removal of these surface carbonaceous entities was studied upon exposing them to deuterium between 293 and 673 K. Deuterium "hydrogenated off" surface CHx species and "hydrogenolyzed" polymeric deposits. The amount and the composition in methane isotopomers was monitored as a function of time and removal temperature. The effect of the temperature and the nH/H2 ratio during carbonization was systematically studied over EUROPT-1. The initial mixture removed initially from both catalysts contained mostly CD3H and CD2H2. These methane molecules must have originated from the most reactive surface species (methylidyne and methylene). C1 removed from Pt black contained, as a rule, more deuterium. The estimated H/C ratio in surface precursors was 0.4-0.9 (CD4 ≫ CHD3 > CH2D2 > CH3D). The H/C ratio in the case of EUROPT-1 was, in turn, 1-1.5 (CHD3 > CH2D2 ≈ CD4 > CH3D). The amount of C1 removed from EUROPT-1 showed a maximum as a function of the removal temperature between 350 and 450 K and further increased above 573 K. The removed methane contained more D when the catalyst was heated in the absence of hydrogen before removal. The deuterium content of methanes was indicative of the degree of dehydrogenation of their surface precursors. Dehydrogenation was significantly higher on Pt black. These observations are in good agreement with the propensity of EUROPT-1 to produce more saturated gas-phase products.

Original languageEnglish
Pages (from-to)276-290
Number of pages15
JournalJournal of Catalysis
Volume208
Issue number2
DOIs
Publication statusPublished - 2002

Fingerprint

Deuterium
Methane
deuterium
catalysts
methane
Catalysts
Dehydrogenation
dehydrogenation
Hydrogen
Deposits
Gases
deposits
vapor phases
carbonization
Carbonization
Hexanes
hydrogen
products
Benzene
Hexane

Keywords

  • Carbonaceous deposits
  • Deuterative removal
  • Deuteromethanes
  • EUROPT-1
  • H/D isotopic exchange
  • Hexane
  • Platinum black
  • Platinum-on-silica

ASJC Scopus subject areas

  • Catalysis
  • Process Chemistry and Technology

Cite this

Removal of carbonaceous residues by deuterium from Pt catalysts. / Wootsch, A.; Descorme, Claude; Paál, Z.; Duprez, Daniel.

In: Journal of Catalysis, Vol. 208, No. 2, 2002, p. 276-290.

Research output: Contribution to journalArticle

Wootsch, A. ; Descorme, Claude ; Paál, Z. ; Duprez, Daniel. / Removal of carbonaceous residues by deuterium from Pt catalysts. In: Journal of Catalysis. 2002 ; Vol. 208, No. 2. pp. 276-290.
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AB - Mixtures of hexane (nH) and hydrogen (H2) were reacted over EUROPT-1 (6.3% Pt/SiO2) and Pt black. In addition to gas-phase products, including isomers, methylcyclopentane, fragments, and benzene, firmly chemisorbed entities were also produced. They may be C1 units or - highly dehydrogenated - polymeric deposits. Removal of these surface carbonaceous entities was studied upon exposing them to deuterium between 293 and 673 K. Deuterium "hydrogenated off" surface CHx species and "hydrogenolyzed" polymeric deposits. The amount and the composition in methane isotopomers was monitored as a function of time and removal temperature. The effect of the temperature and the nH/H2 ratio during carbonization was systematically studied over EUROPT-1. The initial mixture removed initially from both catalysts contained mostly CD3H and CD2H2. These methane molecules must have originated from the most reactive surface species (methylidyne and methylene). C1 removed from Pt black contained, as a rule, more deuterium. The estimated H/C ratio in surface precursors was 0.4-0.9 (CD4 ≫ CHD3 > CH2D2 > CH3D). The H/C ratio in the case of EUROPT-1 was, in turn, 1-1.5 (CHD3 > CH2D2 ≈ CD4 > CH3D). The amount of C1 removed from EUROPT-1 showed a maximum as a function of the removal temperature between 350 and 450 K and further increased above 573 K. The removed methane contained more D when the catalyst was heated in the absence of hydrogen before removal. The deuterium content of methanes was indicative of the degree of dehydrogenation of their surface precursors. Dehydrogenation was significantly higher on Pt black. These observations are in good agreement with the propensity of EUROPT-1 to produce more saturated gas-phase products.

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KW - Hexane

KW - Platinum black

KW - Platinum-on-silica

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