N, B dual-doped carbons as metal-free catalysts for hydrogenation of quinoline with formic acid

Metal-free catalyst with good biocompatibility and sustainability is a fascinating alternative for metal-based catalyst, especially in the production of fine chemicals sensitive to metal impurities. Catalytic hydrogenation with formic acid (FA) is regarded as a sustainable and green strategy for organic hydrogenation, in which the development of metal-free catalyst is an arduous but significant challenge. In this work, a dual-doping strategy of N and B was chosen to build the desired base and acid sites in carbon materials for simultaneous activation of hydrogen donor FA and acceptor quinoline. In the additive-free system, N, B dual-doped metal-free catalyst BNC-900 showed outstanding catalytic performance for the hydrogenation of quinoline with FA, 91.64% conversion of quinoline and 93.62% selectivity for 1,2,3,4-tetrahydroquinoline were achieved. Moreover, it exhibited satisfying stability and tolerance for diverse substrates. According to the experimental data and DFT calculation results, pyridinic N and BC2O were revealed to be the primary active sites for FA and quinoline respectively and act synergistically. Besides, it was found that the formation of B-N bond derived from the neutralization of the electron donor and acceptor may hinder the construction of highly active sites.