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

Selective photo-oxidation of liquid benzene was studied using cation-exchanged zeolites dispersed in C6H6/CH3CN/H2O mixture at room temperature by using molecular oxygen. Screening with BEA zeolites exchanged with I I kinds of transition metal cations was performed. Pd2+-, Fe3+- 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 Pd2+-, Fe3+- and Cu2+-BEA, while phenol and CO2 were the main products on TiO2 semiconductor (Degussa P25). The photocatalytic property was greatly changed by immobilization of Pd2+ on BEA; Pd2+-BEA showed higher activity and selectivity for the formation of phenols than [Pd(NH3)(4)]Cl-2 in homogeneous solution, on which unselective photo-oxidation of benzene to CO2 was the main reaction. The turnover number of Pd2+-BEA for the formation of phenols was 35 (based on Pd) in 24 h, indicating that the reaction proceeded catalytically. (C) 2004 Elsevier B.V All rights reserved.