LAUSR

Abstract Bifunctional Palladium (Pd) supported Y-zeolite, with SiO2/Al2O3 ratios 5, 12, 30 and 60, prepared by impregnation method were used for hydroalkylation of benzene. It is found that the reaction condition and catalyst composition influence the hydroalkylation activity and cyclohexylbenzene (CHB) selectivity. CHB selectivity of a hydroalkylation catalyst can be determined by the destiny of the intermediate cyclohexene formed by partial hydrogenation of benzene on the metal site of the catalyst. That is, if the intermediate cyclohexene hydrogenates to cyclohexane on the metal site, the selectivity for CHB decreases whereas, if the intermediate cyclohexene is alkylated with benzene on the acid sites, the selectivity for CHB increases. Thus, there is a requirement of optimum balance of exposed metal and acid sites of the catalyst for enhancing CHB selectivity. At 42.2% of benzene conversion, Pd (0.2 wt%)/HY5 (SiO2/Al2O3 = 5) catalyst gave a CHB selectivity of 75% in comparison to 70.3% for the best patented catalyst. Furthermore, a kinetic model has been developed for the hydroalkylation of benzene, assuming dissociative, non-competitive addition of hydrogen. Finally, the developed kinetic model along with experimental data was used to study the effect of mole ratio of acid sites to exposed metal sites of Pd/HY catalyst system for hydroalkylation reaction. Based on these results, the ratio of number of acid sites to exposed metal sites can be tuned to maximize CHB yield.