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Catalysis Letters

, Volume 27, Issue 3–4, pp 243–249 | Cite as

Lewis acidity as an explanation for oxide promotion of metals: implications of its importance and limits for catalytic reactions

  • A. B. Boffa
  • C. Lin
  • A. T. Bell
  • G. A. Somorjai
Article

Abstract

Sub-monolayer quantities of metal oxides are found to influence CO hydrogenation, CO2 hydrogenation, acetone hydrogenation, ethylene hydroformylation, ethylene hydrogenation, and ethane hydrogenolysis over Rh foils. The metal oxides investigated include AlOx, TiOx, VOx, FeOx, ZrOx, NbOx, TaOx, and WOx. Only those reactions involving the hydrogenation of C-O bonds are enhanced by the oxide overlayers. The coverage at which maximum rate enhancement occurs is approximately 0.5 ML for each oxide promoter. Titanium, niobium, and tantalum oxides are the most effective promoters. XPS measurements after reaction show that of the oxides studied titanium, niobium, and tantalum oxide overlayers are stable in the highest oxidation states. The trend in promotion effectiveness is attributed to the direct relationship between oxidation state and Lewis acidity. For the oxide promoters, bonding at the metal oxide/metal interface between the O-end of adsorbed CO and the Lewis acidic oxide is postulated to facilitate C-O bond dissociation and subsequent hydrogenation.

Keywords

oxide promotion acidity CO and CO2 hydrogenation Rh 

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Copyright information

© J.C. Baltzer AG, Science Publishers 1994

Authors and Affiliations

  • A. B. Boffa
    • 1
    • 2
  • C. Lin
    • 1
    • 3
  • A. T. Bell
    • 1
    • 3
  • G. A. Somorjai
    • 1
    • 2
  1. 1.Materials Science Division, Center for Advanced Materials, Lawrence Berkeley LaboratoryUniversity of CaliforniaBerkeleyUSA
  2. 2.Department of ChemistryUniversity of CaliforniaBerkeleyUSA
  3. 3.Department of Chemical EngineeringUniversity of CaliforniaBerkeleyUSA

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