Catalytic cleavage of strong bonds including H-H, C-O, and C-H bonds is a highly desired fundamental transformation for the production of chemicals and fuels. Transition metal-containing catalysts are employed although accompanied with poor selectivity in hydrotreatment; metal-free catalysts have been reported primarily for hydrogenation and oxidative dehydrogenation. We report the nitrogen-assembly carbons (NACs) with closely-spaced graphitic nitrogen as active sites, as the first metal-free catalyst achieving both dihydrogen dissociation and subsequent transformation of oxygenates. NACs exhibit high selectivity towards alkylarenes for hydrogenolysis of aryl ethers as model bio-oxygenates without over-hydrogeneration of arenes. Various kinetic and mechanistic experiments were carried out to demonstrate the assemblies of graphitic N are the active sites supported by DFT calculations. Isotope labelling studies further reveal the cleavage of C-OH is achieved by the formation of reversible C-Nsurf bond as in the chemisorbed species. Moreover, we further show that NAC catalysts are versatile for dehydrogenation of ethylbenzene to styrene and tetrahydroquinoline to quinoline and the observed 100% selectivity is rather rare with conventional catalysts based on transition metals. Hydrogenation of unsaturated functionalities for aromatic substrates was also demonstrated, including ketone, alkene, alkyne, and nitro groups. The discovery of nitrogen assembly as active sites can open up broad opportunities for rational design of new metal-free catalysts for challenging chemical reactions to meet the challenges for a carbon-neutral future.

Knitting nitrogen patterns into carbocatalysts for strong bond activation

ACS Spring 2022

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