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

Reaction pathways of carboxylic acids over TiO2 single crystal surfaces: diketene formation from... This 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 (E a) 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. Research on Chemical Intermediates Springer Journals

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

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Brill Academic Publishers
Copyright © 2003 by VSP 2003
Chemistry; Inorganic Chemistry; Physical Chemistry
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