Reaction pathways of carboxylic acids over TiO2 single crystal surfaces: diketene formation from bromo-acetic acid

D J Titheridge, J N Wilson, Hicham Idriss

Research output: Contribution to journalLiterature review

5 Citations (Scopus)

Abstract

work presents the first investigation of a halo-carboxylic acid (Br-CH2COOH) over the surface of an oxide single crystal (the {011}-faceted TiO2(001) single crystal). A very rich chemistry is observed. This is broadly divided into three categories: elimination of HBr to make ketene, dimerisation of two molecules of ketene to 4-methyl-2-oxetanone and 1,3-cyclobutanedione, and further reaction of the latter to a mass spectrometer m/e 70 signal attributed to crotonaldehyde (formed by ring opening). Temperature programmed desorption (TPD) and Scanning Kinetic Spectroscopy (SKS) gave complementary results with SKS opening a simple way for investigating surface chemical reactions in UHV conditions with high surface coverage at still high temperatures. A successful modeling of SKS data was conducted providing the activation energies (Ea) for ketene desorption, with a reaction order n close to 1, for both CH3COOH (E-a = 21.3 kcal/mol) and BrCH2COOH (E-a = 17.2 kcal/mol). In order to further understand the surface reaction of BrCH2COOH semi-empirical PM3 computation of its adsorption and reaction on a Ti8O29H26 cluster representing the (011) TiO2 surface was conducted and compared to that of CH3COOH on the same cluster. Dissociative adsorptions of both the O-H and C-Br bonds are more stable than the non-dissociative adsorption modes. The di-coordinated species, TiOC(O)CH2Os, formed by the simultaneous dissociation of both C-Br and O-H bonds of BrCH2COOH appears the most plausible surface intermediate for the observed carbon coupling reactions.

Original languageEnglish
Pages (from-to)553-574
Number of pages22
JournalResearch on Chemical Intermediates
Volume29
Issue number6
Publication statusPublished - 2003

Keywords

  • TiO2(001)
  • acetic acid
  • bromoacetic acid
  • scanning kinetic spectroscopy
  • ketene
  • diketene
  • HYDRATION REACTION
  • RUTILE TIO2(110)
  • HALOACETIC ACIDS
  • OXIDE SURFACES
  • ADSORPTION
  • KETENE
  • DECOMPOSITION
  • MECHANISMS
  • ABSORPTION
  • PYROLYSIS

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