The direct epoxidation of propene over gold–titania catalysts—A study into the kinetic mechanism and deactivation

Abstract

A reaction scheme is presented for the epoxidation of propene over gold-titania catalysts based on information from catalytic experiments and a detailed infrared study. The reaction mechanism involves the formation of a bidentate propoxy species on titania sites by means of a reactive adsorption of propene, which is catalyzed by the gold nanoparticles. The bidentate propoxy species can react with a peroxide species, produced on the gold from hydrogen and oxygen, to produce propene oxide. Catalyst deactivation occurs via a consecutive oxidation of the bidentate propoxy intermediate to strongly adsorbed carboxylate species. A kinetic model including these reaction steps was fitted to a series of catalytic experiments and provided a good description of the measurements and yielded realistic kinetic parameters. #

Nanotechnology and the environment: A European perspective

“…The research activities comprise advanced preparation methods, development of new catalysts, surface chemistry of metal oxides, improvement of catalyst performance, studies of catalytic reactions and catalyst engineering. Many applications involve mixed catalysts consisting of different oxides or noble metals [18][19][20], so that the catalytic activity is determined not only by the constituent atoms, but also by the neighbouring crystal or surface structures. It is therefore necessary to control precisely the synthesis of the nanostructured catalysts and to understand the chemical reactivity of the catalytic active centre and how this is affected by the reaction conditions.…”

Titania-Supported Gold Catalysts: Comparison between the Photochemical Phenol Oxidation and Gaseous CO Oxidation Performances

“…In all these reactions, the catalytic activity and stability of gold catalysts have been described to depend on the nature of the support, the size and distribution of gold particles and the properties of the contact surface gold-support. Among the large number of gold catalysts tested, those using TiO 2 as support are majority [7][8][9][10][11]. The use of gold catalysts in catalytic liquid phase oxidations is more recent.…”

The Epoxidation of Propene over Gold Nanoparticle Catalysts

“…Only in the first half hour of the experiment, a discrepancy exists between the rate predicted by the model and the observed rate. This can be explained by product adsorption on the support as discussed previously [20], which was not included in this model. A more extensive version of this simplified deactivation model, which includes the occupancies of all surface species, is published elsewhere [21].…”

“…previously [20]. In this model, as a first step in the epoxidation, a bidentate propoxy species is formed on the titania (or titania/silica) support.…”