Highly efficient immobilized PN3P-pincer iridium catalyst for dehydrogenation of neat formic acid

Abstract

Formic acid (FA) has been well recognized as one of the most promising hydrogen carriers. The dehydrogenation of the FA could offer an efficient process to on-demand hydrogen generation with a suitable catalyst. Homogeneous catalysts have demonstrated superior activity and selectivity compared to traditional heterogeneous catalysis. However, the latter is preferred for large-scale applications. By incorporating the homogeneous organometallic complex onto an appropriate support, the unique features of both types of catalysts can be combined and utilized effectively. Herein, we synthesized an immobilized PN3P-Ir pincer catalyst (2) supported onto KCC-1, a 3D fibrous silica nanosphere that exhibits a high surface area and contains a tetracoordinate aluminum site. To reduce the use of volatile additives, the choice of cesium formate (CsO2CH) was found to be crucial as at 80–90 °C, CsO2CH could act as a reaction medium and serve as basic additive. Remarkable reactivities under neat conditions were achieved with a TOF of 13,290 h-1 and a TON of up to 540,000. The comparative study indicates a significant improvement of 2 from its homogenous counterpart, PN3P-IrH3 (1).