Selective photo-oxidation of benzene over transition metal-exchanged BEA zeolite

Abstract

Selective photo-oxidation of liquid benzene was studied using cation-exchanged zeolites dispersed in C 6 H 6 /CH 3 CN/H 2 O mixture at room temperature by using molecular oxygen. Screening with BEA zeolites exchanged with 11 kinds of transition metal cations was performed. Pd 2+ -, Fe 3+ - and Cu 2+ -BEA were shown to be effective for the formation of phenols (hydroquinone, resorcinol, catechol and phenol). The dihydroxybenzenes were mainly produced on Pd 2+ -, Fe 3+ - and Cu 2+ -BEA, while phenol and CO 2 were the main products on TiO 2 semiconductor (Degussa P25). The photocatalytic property was greatly changed by immobilization of Pd 2+ on BEA; Pd 2+ -BEA showed higher activity and selectivity for the formation of phenols than [Pd(NH 3 ) 4 ]Cl 2 in homogeneous solution, on which unselective photo-oxidation of benzene to CO 2 was the main reaction. The turnover number of Pd 2+ -BEA for the formation of phenols was 35 (based on Pd) in 24 h, indicating that the reaction proceeded catalytically.