Parametric study of propene oxidation over Pt and Au catalysts supported on sulphated and unsulphated titania

The influence of the experimental parameters such as total flow rate, partial pressure of O-2 and C3H6, the nature of the metal, platinum or gold, and the surface treatment of the titania support, sulphated or not, have been investigated on the reaction of propene oxidation. Analysis including XPS, ICP and TEM were carried out in order to characterize the platinum and gold particles and sulphate compounds (oxidation degree, content, morphology). The XPS analysis revealed the presence of Pt2+ and Au degrees species at the catalyst surface. The TEM micrographs indicated Pt particles less than 5 nm and Au particle size composed between 6 and 15 nm with a heterogeneous dispersion. For the Pt catalyst, catalytical testing displayed that the presence of sulphate compounds at the support surface did not influence the partial pressure order of O-2 and C3H6, 1.5 and 0, respectively. For the Au catalyst, the acidity of the support modified the kinetics by decreasing the partial pressure order from 0.5 to 0.7 for O-2 and from 0 to 0.7 for C3H6. In the steady state conditions, a simple power rate law model was adopted to determine the rate constant and the activation energy; Ea varying between 20 and 50 kJ mol(-1). For the Pt catalysts, the rate determining step was oxygen adsorption whereas for the Au catalysts the limiting step was concluded to be the propene dissociation. The catalytic activity was not linked to the specific surface area or the metal content but could be attributed to the nature of the metal, the sulphated support and to the particle oxidation degree and, to a less extent, the particle size. (C) 2010 Elsevier B.V. All rights reserved.