A highly efficient Ni/N–C catalyst was synthesized by facile pyrolysis of a Ni-containing metal–organic framework (Ni-MOF), and its catalytic hydrogenolysis performance towards C–O bonds in lignin was evaluated in detail using diphenyl ether (DPE) as a model compound. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses show that the flower-like nanosheets of the Ni-MOF shrink, forming a loose and ordered spherical structure during pyrolysis. Under the optimal conditions, DPE was completely converted and the selectivity to monomers (benzene, cyclohexanol and cyclohexane) reached 99.1%. During the catalytic hydrogenolysis conversion (CHC) of DPE, the direct cleavage of the Caromatic–O bond affording benzene and phenol is the major reaction pathway, and a low H2 pressure is crucial to increase the monomer selectivity. Furthermore, Ni/N–C-450 shows high hydrogenolysis activity for other lignin-derived aryl ethers, such as benzyl phenyl ether, dibenzyl ether, dinaphthalene ether, benzyl 2-naphthyl ether and 3-methoxyphenol.
Jianguo Liu,Jiangmin Sun,Thishana Singh,Shanshan Lin,Longlong Ma
Although precious transition metals such as palladium, platinum, and iridium are widely used in hydrogenation reactions, the earth-abundant transition metal-catalyzed highly selective semi-hydrogenation of terminal alkynes to terminal alkenes remains poorly developed and a challenge. Herein we demonstrate the excellent selective, cost-effective semi-hydrogenation of terminal alkynes via a novel graphene encapsulated Ni@N/C catalyst. The graphene layer encapsulated nano-catalyst Ni@N/C could significantly avoid metal leaching and improve the stability of the catalyst. The strong interaction of nitrogen with the Ni nanoparticles regulates the activity of Ni towards selective semi-hydrogenation of terminal alkynes. Substrates having un-functionalized as well as functionalized substituents, and substrates having sensitive functional groups (olefins, ketones) which pose a challenge to hydrogenate, were semi-hydrogenated with excellent conversion (up to 99%) and selectivity (up to 99%) under optimized reaction conditions.
Atomically dispersed catalytic metal sites anchored on N-doped carbon support catalysts (M-N-C) show great prospects for CO 2 electroreduction. Here, single-layer NiZn layered double hydroxides (NiZn-LDHs) was used as a sacrificial assistant to fabricate single-Ni atom anchored on ultrathin porous carbon catalyst. NiZn-LDHs were exfoliated to single-layer by polyhydroxy compounds which took as the carbon resource in Ni-N-C, and single layer NiZn LDHs taking as the Ni resource could avoid the agglomeration of Ni atoms during calcining. The CO Faradaic efficiency (FE CO ) of the synthesized Ni-N-C catalyst exceeded 90% at −0.6 to −1.0 V and a FE CO of 95.2% with a current density of 24 mA cm −2 at −0.9 V. This work not only provides a new method for preparing M-N-C catalysts, but also offers an effective and controllable strategy for large-scale production of high-performance single-atom catalysts.
In this work, by the simple pyrolysis of Fe 2+ , Co 2+ or Ni 2+ and 1,10-phenanthroline (Phen) complexes under the presence of activated carbon and dicyandiamide in nitrogen atmosphere, different nonprecious transition metal-based species that well confined in nitrogen doped carbon (M-N-C, M = Fe, Co or Ni) were prepared. The Fe-N-C showed the best catalytic performance for the transfer hydrogenation of halogenated nitrobenzenes. More importantly, through the catalytic results comparison of the three catalysts estimated by gas chromatography-mass spectrometer, two speculations might be presented for the reaction pathway depending on the catalyst used. The transfer hydrogenation reaction route over Fe-N-C might follow the indirect way like the Co-N-C and Ni-N-C. Another assumption was the Fe-N-C might go through the direct pathway in contrast to the Co-N-C and Ni-N-C which resulted in formation of azoxybenzene and azobenzene intermediates before complete conversion to aniline. Those differences were found to be correlated with the different valence states and active metal components in different catalysts. In addition, the optimal Fe-N-C could be efficiently recovered by using an applied magnetic field and reused without significant decrease of activity. Therefor the catalyst may possess important potential for the industrial application in the selective hydrogenation of halogenated nitrobenzenes.
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