Different mechanisms of FLP-catalyzed photocatalytic dehalogenation of BDE47 in polar/non-polar solvents: Insight into the vital role of solvents

Abstract

Recently, the hydrogenation reactions of heterogeneous frustrated Lewis pairs (FLP) catalysis based on metal oxides and corresponding reaction mechanisms were extensively studied. Generally, the hydrogenation performance of metal oxides in FLP catalysis was considered to be mainly related to the physicochemical properties of oxygen defects while the effect of solvents was ignored. Thus, the development of strategies for increasing the performances of catalysts is restricted to the regulation of oxygen defects. Herein, we reported different mechanisms for the FLP-catalyzed photocatalytic dehalogenation of 2,2′,4,4′-tetrabromodiphenyl ether (BDE47) by In2O3 in polar/non-polar solvents. Namely, in polar solvents, the Lewis basic sites of FLP transferred to the solvent molecules bonded with oxygen defects while it remains at the In2O3 surface in non-polar solvents. Thus, in different non-polar solvents, the photocatalytic activities for the dehalogenation of BDE47 remained almost unchanged. On the contrary, in reactions with polar solvents, because of the inactivation of original Lewis basic sites, the photocatalytic performances were largely determined by charge densities of the Lewis basic sites in solvent molecules. The above fundamental insight into the different mechanisms of FLP-catalyzed dehalogenation in polar/non-polar solvents could provide a new strategy for the improvement of heterogeneous FLP catalysts for hydrogenation reactions.