Highly active and low moisture sensitive supported thallium oxide catalysts for Friedel-crafts-type benzylation and acylation reactions: Strong thallium oxide-support interactions

Liquid-phase benzylation of benzene by benzyl chloride (at 80 degreesC) ove r basic TIOx, (without support) and supported TIOx, prepared using differen t low and high surface area commonly used catalyst carriers has been invest igated. The catalysts have been characterized by their surface area and als o by XRD, FTIR, and XPS. Strong TIOx-support interactions (which are chemic al in nature) have been observed for the catalysts prepared using high surf ace area (HS), supports, such as Si-MCM-41, silica get (HS), silica-alumina (HS), alumina (HS), and zirconia (HS), which have surface hydroxyl groups. These catalysts are found to be inactive for benzene benzylation or benzoy lation reaction. However, the TIOx supported on sintered low surface area ( LS) macroporous catalyst carriers [viz. zirconia (LS), silica (LS), and sil ica-alumina (LS)], which have no surface hydroxyl groups, showed high benze ne benzylation activity. TIOx/zirconia (LS) is a highly promising catalyst for both the benzylation and acylation of benzene and other aromatic compou nds and it shows high activity, even in the presence of moisture. The activ ity of this catalyst for the benzylation of benzene and substituted benzene s is in the following order: benzene > toluene > p-xylene > anisole. The in duction period for the benzylation and acylation reactions over the catalys t, however, depends strongly on the moisture present in the catalyst and/or in the reaction mixture. The induction period is drastically reduced by th e HCl gas pretreatment of the catalyst before the benzylation or acylation reaction. Only the catalyst that contains Tl2O3 shows activity for the benz ylation and acylation reactions. A redox mechanism for these reactions over the supported TIOx catalysts has been proposed. (C) 2001 Academic Press.