Effects of Altervalent Cation Doping of TiO2 on Kinetic Parameters of CO Hydrogenation and CO Oxidation on Supported Rh

T. Ioannides, X. E. Verykios, M. Tsapatsis, C. Economou

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Abstract

The reactions of CO hydrogenation and CO oxidation over Rh are used to determine the influence of altervalent cation doping of a TiO2 support on kinetic parameters. Rh crystallites are dispersed on TiO2 doped with W6+ cations at concentration levels up to 0.67 at%. It is shown that turnover frequencies of CO hydrogenation increase monotonically with increasing dopant content in the TiO2 matrix, apparent activation energy is reduced, and selectivity shifts towards smaller-chain saturated hydrocarbons. Turnover frequencies of CO oxidation at low CO/O2 ratios are shown to pass through a maximum with increasing W6+ dopant content of TiO2. A small activity enhancement is observed at higher CO pressures. The apparent activation energy is found to vary with W6+ content. It is proposed that charge transferred from the doped semiconducting carrier to the metal crystallites alters the chemical potential of the crystallites and, therefore, the work function of surface metal atoms, while a strong electrostatic field is caused by the dipole developed at the metal-semiconductor interface. As a result, the mode of H2 and CO adsorption is altered, as well as the intrinsic kinetic parameters of the reactions investigated.

Original languageEnglish (US)
Pages (from-to)491-500
Number of pages10
JournalJournal of Catalysis
Volume145
Issue number2
DOIs
StatePublished - Jan 1 1994

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