In situ Raman spectroscopy studies of bulk and surface metal oxide phases during oxidation reactions

Israel E. Wachs, Jih Mirn Jehng, Goutam Deo, Bert M. Weckhuysen, Vadim V. Guliants, Jay Burton Benziger

Research output: Contribution to journalArticlepeer-review

91 Scopus citations

Abstract

Bulk V-P-O and model supported vanadia catalysts were investigated with in situ Raman spectroscopy during n-butane oxidation to maleic anhydride in order to determine the fundamental molecular structure-reactivity/selectivity insights that can be obtained from such experiments. The in situ Raman studies of the bulk V-P-O catalysts provided information about the bulk crystalline phases, the hemihydrate precursor and its transformation to vanadyl pyrophosphate. However, the Raman experiments could not provide any molecular structural information about the amorphous and surface phases also present in this bulk metal oxide catalyst because of the strong Raman scattering from the crystalline phases. In contrast, in situ Raman studies of the model supported vanadia catalysts, where the active phase is present as a two-dimensional surface metal oxide overlayer, provided new insights into this important hydrocarbon oxidation reaction. In addition, the surface properties of the supported vanadia catalysts could be molecularly engineered to probe the role of various functionalities upon the structure-reactivity/selectivity relationship of n-butane oxidation to maleic anhydride. These fundamental studies revealed that the oxidation of n-butane required only one surface vanadia site and that the critical rate determining step involved the bridging V-O-P or V-O-support bonds. The selective oxidation of n-butane to maleic anhydride could occur over one surface vanadia site as well as multiple adjacent surface vanadia sites, but the reaction is more efficient with multiple sites. The n-butane oxidation TOF increased with the introduction of both surface Brönsted and Lewis acid sites, but only the surface Lewis acid sites increased the maleic anhydride selectivity.

Original languageEnglish (US)
Pages (from-to)47-55
Number of pages9
JournalCatalysis Today
Volume32
Issue number1-4
DOIs
StatePublished - Dec 16 1996

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)

Keywords

  • Bulk metal oxide phase
  • Metal oxide
  • Oxidation reactions
  • Raman spectroscopy
  • Surface metal oxide phase

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