Liquid-phase oxidation of benzene under ambient conditions

Abstract

Oxidation of benzene on silica-supported palladium catalysts has been studied under ambient conditions. Products are phenol and three quinones/quinols (benzoquinone, hydroquinone and catechol), with some minor products produced in negligible amount. Two types of catalyst, Pd alone and Cu–Pd composite catalysts, both being supported on silica gel, were found to behave in remarkably different ways. The palladium catalyst is effective only when hydrogen and oxygen are both present in the reaction system simultaneously and produces phenol almost exclusively [the highest yield of phenol being 200 µmol g^–1 cat. h^–1 in benzene (100 cm³) and the selectivity >90%]. On the other hand, the selectivity shifts towards quinones when the Cu–Pd composite catalyst is used (selectivity for quinones: 28%). The effects of various factors, such as temperature, feeding mode of reaction gases and catalyst composition including moisture content are discussed.