A new catalyst enables solvent-free low-temperature selective oxidation of toluene to benzyl benzoate at high yield, report researchers at Cardiff University, Cardiff, U.K., and Lehigh University, Bethlehem, Pa. The catalyst -- gold/palladium nanoparticles on a carbon support -- boasts turnover numbers around 30 times higher than other heterogeneous catalysts for the reaction. "This opens up the possibility of using hydrocarbon feedstocks in a new way to form intermediates and final products for use in the chemical, pharmaceutical and agricultural business sectors," notes Graham Hutchings, a professor in the Cardiff School of Chemistry who was on the research team.
The catalyzed reaction at 160°C produces benzyl alcohol, benzaldehyde, benzoic acid and benzyl benzoate but no carbon dioxide. Selectivity to the benzoate exceeds 94%. "Catalyst activity could be higher, but it is usable," notes Hutchings, who adds that the next step in the development is to increase catalyst activity.
The nanoparticles are 2--5 nm in size and were prepared by sol immobilization. They contain gold and palladium at about a 1:1 ratio by weight -- the addition of palladium significantly enhances the conversion -- and are stable and reusable, the researchers say. More details appear in a report in Science.
The catalyst currently is in the form of a powder but could be made into pellets, adds Hutchings, who foresees use in either a stirred-pot or continuous flow reactor.