Direct synthesis of benzyl acetate and optimisation of reaction conditions for the gas phase acetoxylation of toluene A. Benhmid, Kalevaru V. Narayana, A. Martin * , B. Lu ¨cke, M.-M. Pohl Institut fu ¨r Angewandte Chemie Berlin-Adlershof e.V. 1 , Richard-Willsta ¨tter-Str. 12, D-12489 Berlin, Germany Available online 4 January 2006 Abstract TiO 2 supported Pd-Sb catalysts were prepared by impregnation method and tested for the selective vapour phase acetoxylation of toluene to benzyl acetate (BA). Investigations were carried out to optimise reaction variables such as effects of reaction temperature, acetic acid/toluene mole ratio, O 2 /toluene mole ratio, contact time, etc. to obtain better performance of the catalysts. Additionally, the influence of Sb/Pd ratio on catalytic performance was also checked under optimised reaction conditions. The activity of the catalysts was found to increase continuously with increasing Sb/Pd ratio up to 0.7 and then decreased with further increase in Sb/Pd ratio to 1.75. The catalyst with Sb/Pd ratio of 0.7 exhibited the best performance among all other catalysts of this series giving a conversion of toluene as high as ca. 68% with BA selectivity of 85%. All these catalysts were observed to deactivate with time on stream due to considerable amount of coke deposition. However, these catalysts can be regenerated in air and reused for more number of cycles with consistent performance. # 2005 Elsevier B.V. All rights reserved. Keywords: Gas phase acetoxylation; Toluene; Sb-Pd/TiO 2 catalysts; Optimization of process parameters; Sb/Pd ratio 1. Introduction The direct partial oxidation of methyl aromatics to their corresponding aldehydes or alcohols is often unselective as the desired products undergo further oxidation. Therefore, these oxidation reactions rather continue to yield more thermo- dynamically stable end products, for instance benzoic acid from toluene [1]. Therefore, an important challenge for the future is to develop more attractive processes/effective catalysts to obtain the desired compounds as stable end products. This problem may be solved to a considerable extent if the selective oxidation is carried out using suitable catalysts and appropriate auxiliary reagents. Acetoxylation of methyl aromatics to produce benzyl esters in a single step is one such good example for preventing over-oxidations and producing stable target products, which are resistant to further oxidation. Literature survey reveals that the acetoxylation of ethylene [2], propylene [3] and butadiene [4,5] are well-known processes and commercialised several years ago. In addition, various research groups also investigated acetoxylation of toluene over Pd based catalysts e.g. [6–9]. However, no catalyst was successful till date for commercialisation of this reaction. Most of the work reported so far was carried out under liquid phase conditions [6–11]. The literature reports on gas phase acetoxylation of toluene are very rare [12,13] on the one hand and on the other hand no considerable success has been achieved so far in terms of achieving higher benzyl acetate (BA) yields. From the state of the art, it is known that vapour phase acetoxylation is still under developmental stage and hence only a limited data available. The vapour phase acetoxylation of toluene, in particular, is of great interest from both academic as well as industrial viewpoints as the target product BA is widely used in perfumery, food and chemical industries. We have reported earlier the superior performance of Pd-Sb/TiO 2 catalysts with different Pd loadings for the selective gas phase acetoxylation of toluene [14,15]. However, the catalyst deactivation still remained unsolved over these catalysts. In another study, we have also successfully solved the deactivation problem by www.elsevier.com/locate/cattod Catalysis Today 112 (2006) 192–196 * Corresponding author. Tel.: +49 30 6392 4306; fax: +49 30 6392 4454. E-mail address: a.martin@aca-berlin.de (A. Martin). 1 A member of the EU-funded Coordination Action of Nanostructured Catalytic Oxide Research and Development in Europe (CONCORDE). 0920-5861/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.cattod.2005.11.041