Highly efficient Pd-Sb-TiO2 catalysts for the vapour phase acetoxylation of toluene to benzyl acetate

A series of Pd-Sb-TiO2 (anatase) catalysts has been prepared over a wide range of Pd loadings from 0.5 to 20 wt% and tested for the selective vapour-phase acetoxylation of toluene to benzyl acetate at a reaction temperature of 210 °C and a pressure of 2 bar. The catalysts were characterised by nitrogen adsorption, XRD, XPS, and TEM. The BET surface areas and pore volumes were observed to decrease considerably with increasing Pd content of the catalysts. XPS revealed that there is loss of both Pd and Sb in the surface region in the used catalysts. The particle size of Pd (measured by TEM) is found to increase dramatically in the used catalysts compared with the fresh ones. Pd particle size is observed to exhibit a strong influence on the catalytic performance of the catalysts. The activity of the catalysts was found to increase continuously with increasing Pd loading, which is associated with an increase in the Pd particle size of the catalysts. The catalyst with 20 wt% Pd has been found to display the best performance, giving conversion of toluene as high as ca. 92 mol% with a benzyl acetate selectivity of 85%. Nevertheless, the solids were observed to deactivate with time on stream due to a considerable amount of coke deposition on the surface. However, the catalysts can be regenerated in air and reused for more number of cycles with consistent performance.