Ionic Liquids Boost Anthraquinone Hydrogenation over Pd‐based Bimetallic Pincer Catalysts

Abstract

A series of bimetallic‐ionic liquid (IL) pincer catalysts Pd‐M@IL were synthesized using low Pd‐loading amount (0.3%) and adopting six kinds of ion liquids with the cation containing the imidazole ring, and then evaluated the catalytic activities toward 2‐ethylanthraquinone hydrogenation reaction with the purpose to produce H2O2. Under the reaction conditions of 60 ℃, 0.30 MPa and 15 min reaction time, over the catalysts Pd‐La@[BMIm]Ac/alu and Pd‐La@[VBIM]Br/alu achieved high hydrogenation efficiency(9.4 g/L and 8.5 g/L) but also high selectivity toward the active anthraquinone (98.9% and 99.6%). Through characterizations of STEM, TPD, in‐situ XPS, etc., it illustrates that the pincer catalysts Pd‐La@[BMIm]Ac/alu and Pd‐La@[VBIM]Br/alu have much better dispersity than the bimetallic Pd‐La/alu, these two ionic liquids of [BMIm]Ac and [VBIM]Br provide different local environment around Pd‐La sites, which in turn modulate the catalytic activity of the pincer‐catalysts toward anthraquinone hydrogenation. DFT calculations disclose the unique electron transfer between ILs ([BMIm]Ac and [VBIM]Br) and Pd‐La clusters and subsequent changes of energy barriers for anthraquinone hydrogenation. The work illuminates a facile strategy to design novel hydrogenation catalysts through combining the pincer microenvironment partially encapsulated by the cation and the anion of ionic liquids with the internal bimetallic sites.