Transition metal-like carbocatalyst

Zhicheng Luo,Aaron Sadow,Wenyu Huang,Abhranil Biswas,Renfeng Nie,Xun Wu,Vy T Nguyen,Ranjan K Behera,Bin Wang,Long Qi,Takeshi Kobayashi

doi:10.1038/s41467-020-17909-8

Zhicheng Luo, Aaron Sadow + Show 9 more

Open Access

https://doi.org/10.1038/s41467-020-17909-8

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Abstract

Catalytic cleavage of strong bonds including hydrogen-hydrogen, carbon-oxygen, and carbon-hydrogen bonds is a highly desired yet challenging fundamental transformation for the production of chemicals and fuels. Transition metal-containing catalysts are employed, although accompanied with poor selectivity in hydrotreatment. Here we report metal-free nitrogen-assembly carbons (NACs) with closely-placed graphitic nitrogen as active sites, achieving 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. Activities originate from cooperating graphitic nitrogen dopants induced by the diamine precursors, as demonstrated in mechanistic and computational studies. We further show that the NAC catalyst is versatile for dehydrogenation of ethylbenzene and tetrahydroquinoline as well as for hydrogenation of common unsaturated functionalities, 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.

Highlights

Catalytic cleavage of strong bonds including hydrogen-hydrogen, carbon-oxygen, and carbonhydrogen bonds is a highly desired yet challenging fundamental transformation for the production of chemicals and fuels
The unexpected, unique reactivity present in this study primarily originates from the nitrogen assemblies introduced by the diamine precursors into the graphitic carbons, which enables the nonoxidative dehydrogenation of ethylbenzene and tetrahydroquinoline (THQ) and the selective hydrogenation of unsaturated functional groups in aromatics
The diamine-carbon tetrachloride condensation results in irreversible formation of C–N bonds, as evidenced by the presence of secondary amines formed as crosslinked acyclic chains and imidazolidine, shown by dynamic nuclear polarization (DNP)-enhanced 15N{1H} cross-polarization magic-angle spinning (CPMAS) NMR (Fig. 1b and Supplementary Fig. 1)[19,20]

Summary

Introduction

Catalytic cleavage of strong bonds including hydrogen-hydrogen, carbon-oxygen, and carbonhydrogen bonds is a highly desired yet challenging fundamental transformation for the production of chemicals and fuels. The metal-free NAC materials catalyze hydrogenolysis of C–O bonds in 2-phenoxy-1-phenylethan-1-ol (PPE, 1) with 20-bar H2 (Fig. 2a), which typically require transition metal catalysts. The NAC-800 catalyst gives the highest conversion (30%), compared with NAC-650 (7%), NAC-700 (15%), and NAC-900 (25%) in experiments performed in 2-propanol (2-PrOH) for 8 h at 230 °C, while NAC-600 is inactive (Fig. 2b and Supplementary Table 5).

Results

Conclusion