2D-COFs-derived heteroatom-doped carbon nanosheets as high-efficiency all-solid frustrated lewis pair metal-free hydrogenation catalyst

Abstract

Metal-free catalysts without metal active sites participating in the reactions have obtained growing attraction under the drive of the economic and environmental problems. Here, 2D-COFs-drived B/N co-doped carbon nanosheets as metal-free catalyst was synthesized by Schiff-based coupling reaction and self-templated carbonization. It shows excellent catalytic performance in nitro compound hydrogenation reaction as all-solid FLP catalyst in H2 system (100 % conversion of nitrobenzene and 99.89 % selectivity to aniline) without any metal active species in the catalyst. This result is the most promising compared to the previous literatures. In the study, the high crystallinity of precursor 2D-COFs is imperative for catalytic stability, and the function of B atoms modification and the B-N synergism were investigated carefully. The formation of B-N bond as a fixed all-solid FLP active center was verified, and it also indicates that B atoms introduction can make the carbon nanosheets orderly and enhance the strength and amount of the acid and base sites. The catalytic mechanism of hydrogen activation was also studied by combining the characterization results and density functional theory (DFT) calculations. The results show that the B atoms doping and defects formation efficiently accelerate the charges aggregation between B-N bonds to form Lewis pairs, and the TS searching calculations shows the significant decrease of H2 dissociation barrier energy and the reaction energy, demonstrating the effectiveness of N and B co-doping strategy. This work is very promising and the metal-free catalyst is the potential alternative to traditional metal catalysts.