Pore size independent regioselective cyclohexylation of ethylbenzene

Al-MCM-41 (Si/Al = 52 and 105) and Al-MCM-48 (Si/Al = 47 and 102) molecular sieves were synthesised by hydrothermal method. These materials and commercial HY zeolite were characterised by XRD, BET, 27Al MAS-NMR, pyridine adsorbed FT-IR and ICP-AES techniques. The vapour phase cyclohexylation of ethylbenzene (EB) with cyclohexene was carried out between 200 and 400 °C over all the catalysts. The major products were found to be p-cyclohexyl ethylbenzene (p-CEB) and o-cyclohexyl ethylbenzene (o-CEB). The activity of the catalysts followed the order Al-MCM-41 (52) > Al-MCM-41 (105) > Al-MCM-48 (47) > Al-MCM-48 (102) > HY. Al-MCM-41 and Al-MCM-48 are more active than HY although the density of acid sites of the former catalysts is less than the latter. This is due to the large pore size of Al-MCM-41 and Al-MCM-48 catalysts that permits simultaneous entry of more reactants into the pores and expulsion of products freely out of the pores. Al-MCM-41 catalysts are more active than Al-MCM-48 catalysts due to more density of acid sites on the channel surface of Al-MCM-41. The selectivity of p-CEB is higher than o-CEB due to less steric hindrance for its formation. The effects of feed ratio and WHSV on ethylbenzene conversion and product selectivities were evaluated in the above reaction.

Vapour phase cyclohexylation of ethylbenzene with cyclohexene was carried out over HY, Hβ, Al-MCM-41 and Al-MCM-48 catalysts. Al-MCM-41 catalyst is suggested to be the best for this reaction. In addition to high conversion obtained with these catalysts, absence of isomerisation of ortho and para isomers to meta isomer is also an important result observed in this reaction. Figure optionsDownload as PowerPoint slide