The reactivity of adsorbed carbon on vanadium promoted rhodium catalysts

Koerts, T Tijs; Santen, van Ra Rutger

doi:10.1007/bf00764052

Cited by 22 publications

(6 citation statements)

References 28 publications

(22 reference statements)

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“…Also the recent observations of increased chain growth on Rh promoted with vanadium [24] seems to be in line with this. One observes an increased metal-carbon bond strength on Rh promoted with vanadium.…”

Section: Carbon-carbon Bond Formationsupporting

confidence: 82%

The quantum chemical basis of the Fischer-Tropsch reaction

1990

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Fischer-Tropsch synthesis, transition metal surfaces, CO and CH~ reactivity, electronic features in F-T synthesis, bond strength, activation energy, chemisorption, CO dissociation, extended Hiickel method, ASED method, quantum chemistry.The electronic features determining the reactivity of CO and CH x on transition metal surfaces are reviewed. Focus is on the relevant features that control the Fischer-Tropsch synthesis. The CO dissociation reaction path is controlled by the interaction with the CO bond strength weakening 2~r* orbitals. CH 3 fragment adsorption is controlled by o type molecule fragment orbitals. This directs the CH 3 fragment to the atop adsorption site on those late transition metals that have strongly interacting d-valence electrons. Adsorbed C and O have a stronger bond strength than CH 3 because they have also unoccupied atomic p orbitals available to bonding. Because the bond strength of adsorbed C and O increases more rapidly with depletion of d-valence electron occupation than that of CO, the activation energy for CO dissociation decreases for the corresponding transition metals towards the left of the periodic system. The rate of methanation versus chain growth is controlled by the strength of the M-CH 3 bond versus the activation energy of carbon-carbon bond formation. The first appears to be more sensitive to variations in metal carbon bond strength than the latter.

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Section: Carbon-carbon Bond Formationsupporting

confidence: 82%

The quantum chemical basis of the Fischer-Tropsch reaction

1990

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“…Secondly vanadium is thought to act by increasing the metal-carbon bond strength, making C-C coupling reactions more likely than hydrogenation of small carbon fragments to form short-chain hydrocarbons. This conclusion was also reached in previous studies carried out over Rh catalysts [17]. trates the use of the second liquid-nitrogen cooled trap following hydrocarbon separation.…”

Section: Effect Of Vanadium Promotion On Labelled N-hexane Selectivitysupporting

confidence: 78%

Production of 11C-labelled n-hexane for use in positron emission imaging

Cunningham

Mangnus

Grondelle

et al. 1996

Journal of Molecular Catalysis A: Chemical

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“…A moderate dissociation temperature of CH 4 resulted in high selectivity of CH 2 or C R species, which generated higher methane conversion (C 1 C 2 ) and C 2+ hydrocarbons, whereas the high-temperature resulted in a greater C γ species, which hydrogenated with greater difficulty into C 2+ hydrocarbons (Table 5 and Figures 8-11). These suggest CH 2 adspecies having a relatively low reactivity of ruthenium-carbon, 42,43 being more mobile 44 and more combinative to adjective CH x groups at low temperature. In addition, the hydrogenation temperature is also an important parameter in determining the methane conversion (C 1 C 2 ) and C 2+ selectivity.…”

Section: Electronic Structure and Spectra Of Ruthenium Carbonyl Clust...mentioning

confidence: 98%

Intrazeolite Anchoring of Ruthenium Carbonyl Clusters: Synthesis, Characterization, and Their Catalytic Performances

et al. 1998

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This paper focuses attention on the intrazeolite anchoring of ruthenium carbonyl clusters and their catalytic performances. The synthesis involves the adsorption of metal carbonyl species or metal ion exchange into zeolite cages followed by reductive carbonylation under a mixed CO and H 2 atmosphere. The characterization of the structure and properties of these samples was based on a multianalytical approach, including FT-IR, UV-vis, EXAFS spectroscopies, CO/H 2 gas chemisorption, and 13 CO isotopic exchange. Methane homologation was carried out on the zeolitic ruthenium clusters using a two-step process. The research encompassed several key points as follows. (i) [Ru 3 (CO) 12 ] guests in Na 56 Y zeolite were thermally activated in a hydrogen atmosphere, generating intrazeolitic [H 4 Ru 4 (CO) 12 ]. (ii) Hexammineruthenium(III) complexes in Na 56 X zeolite were thermally activated progressively in a mixed CO and H 2 atmosphere. The generation process was considered to occur through conversion of the intermediate [Ru(NH 3 ) 5 (CO)] 2+ and Ru I (CO) 3 to [Ru 6 (CO) 18 ] 2-. (iii) Internal and external confinements of ruthenium carbonyl clusters were compared. (iv) A rapid 13 CO/ 12 CO isotopic exchange was found to reversibly occur for [Ru 6 (CO) 18 ] 2-/Na 56 X under H 2 coexistence. (v) Oxidation fragmentation under an O 2 atmosphere and reductive regeneration under a mixed CO and H 2 atmosphere were found to reversibly occur for the intrazeolite anchoring of [Ru 6 (CO) 18 ] 2-. (vi) Comparison of the orbitally degenerate ground state for free Ru carbonyl clusters versus the intrazeolitic anchoring site provides a theoretical indication of the symmetry distortion. (vii) Surface carbonaceous fragments were generated by CH 4 dissociation on the activated ruthenium clusters based on the analysis of TPD, FT-IR, and mass spectroscopies. These fragments are the precursors for hydrocarbon formation. (viii) The catalytic properties of the intrazeolitic ruthenium clusters showed cluster size dependence. Basic Na 56 X is superior to Na 56 Y in enchancing methane conversion and C 2+ hydrocarbons selectivity.

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The reactivity of adsorbed carbon on vanadium promoted rhodium catalysts

Cited by 22 publications

References 28 publications

The quantum chemical basis of the Fischer-Tropsch reaction

The quantum chemical basis of the Fischer-Tropsch reaction

Production of 11C-labelled n-hexane for use in positron emission imaging

Intrazeolite Anchoring of Ruthenium Carbonyl Clusters: Synthesis, Characterization, and Their Catalytic Performances

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