Effect of promoter thallium for a novel selectivity oxidation catalyst studied by X-ray photoelectron spectroscopy

A series of novel catalysts consisting of V-Cs-Cu-Tl supported on TiO2 and SiC were prepared by impregnation method and tested for their catalytic properties to selectivity oxidation from p-tert-butyl toluene to p-tert-butyl benzaldehyde. A very significant effect was obtained with a selectivity of about 80 mol% and the conversion of 12 mol% over the series of catalysts. The surface properties of the series of V-Cs-Cu-Tl catalyst were discussed by X-ray photoelectron spectroscopy (XPS) analysis. The results of XPS analysis pointed out the small decrease of the vanadium binding energies and increase in the peak area of nucleophilic oxygen (O2-) with the promoter thallium adding into V-Cs-Cu catalyst. The optimum catalytic activity for the series of V-Cs-Cu-Tl catalyst was probably ascribed to the promoter thallium which effectively enhanced the redox cycle of V5+ <----> V4+. In addition, O 1s analysis of catalyst indicated that the nucleophilic oxygen on the catalyst surface plays an important role in this selectivity oxidation. Such typical results were summarized and the role of thallium promoter was explained. (C) 2003 Elsevier Science B.V. All rights reserved.