CHEMICAL SCIENCE

First! Nanjing University developed nitrogen fixation catalysts for nitrogen dual nitrogen functional coordination polymers


On December 16, 2022, Beijing time, Zuo Jinglin, Jin Zhong, Ma Jing, Li Shuhua and other research teams from the School of Chemistry and Chemical Engineering of Nanjing University published a new study in the journal Nature Chemistry, entitled “Photocatalytic nitrogen fixation under an ambient atmosphere using a porous coordination polymer with.” bridging dinitrogen anions”。

This work is the first to develop and study a nitrogen fixing catalyst with a clear molecular active site of dual nitrogen under mild conditions, which provides a new research idea and theoretical basis for the research and application of complex-type molecular catalysts in the research and application of photosynthetic nitrogen fixation.

The co-first authors of the paper are Xiong Yan, Li Bang and Gu Yuming, and Yan Tong and Ni Zhigang participated in this research work.

Nitrogen molecules are highly stable and not easily reduced due to their large bond dissociation energy of the three bonds. Nitrogen conversion into industrial products (such as ammonia, hydrazine, etc.) has important social benefits and economic value, and nitrogen activation is a research direction full of challenges and opportunities. Inspired by biological nitrogenase, there are two necessary conditions for molecular catalysis for nitrogen fixation reduction: a) the molecular center has variable valence metals, which are unsaturated coordination; b) Sufficient supplies of electrons and protons.

In view of this, Zuo Jinglin, Jin Zhong, Ma Jing, Li Shuhua and other research teams from the School of Chemistry and Chemical Engineering of Nanjing University have cooperated closely to successfully prepare a class of charge transfer metal complex materials with dinitrogen anion coordination, metal zinc as the central ion, and stable D-A-D sandwich structureNJUZ-1。 By pairNJUZ-1The characterization and isotope exchange experiments of single crystal structure, infrared, Raman and paramagnetic resonance proved that there was a clear dinitrogen ligand in the porous metal coordination polymer, and the free electron acceptor TCNQ was embedded in the electron donor TTF sandwich in parallel with hydrogen bonding and π-π to form a stable sandwich structure.

Figure 1: NJUZ-1 crystal structure

The results of different physical and chemical characterization resultsNJUZ-1It has excellent light absorption characteristics and nitrogen adsorption capacity. The experimental results of photocatalytic nitrogen fixation showed thatNJUZ-1Nitrogen coordination polymers have excellent nitrogen fixation properties, especially the photocatalytic reduction of nitrogen in air to ammonia, and the catalyst has excellent catalytic stability. Furthermore, the structure and physical properties of the catalyst after long-term catalytic reaction were analyzed, and it was confirmed that the catalyst itself had good physical properties and structural stability.

Figure 2: Light absorption and photocatalytic nitrogen fixation performance of NJUZ-1

Theoretical and experimental studies have shown thatNJUZ-1After light absorption, charge transfer is generated by TTF-TCNQ intramolecular and metal-to-ligand (MLCT), which promotes the separation of electron-hole pairs, and then provides electron-catalytic conversion of nitrogen to ammonia.

Figure 3: NJUZ-1 nitrogen fixation process and possible reaction pathways

The catalytic process and mechanism studies show thatNJUZ-1The coordination unit {Zn2+-(N≡N)−-Zn2+} is used as a catalytic site to form a stable unsaturated coordination supported by a three-dimensional skeleton structure through the process of ammonia deamination[Zn2+•••Zn+]Intermediates, subsequently[Zn2+•••Zn+]The intermediate is refilled with external nitrogen to a {Zn2+-(N≡N)−-Zn2+} coordination saturation state. This nitrogen fixation process is similar to the Mars-van Krevelen (MvK) process. Theoretical studies have shown that the overall reaction pathway may gradually form the “alternating” pathways of *NHNH, *NHNH2 and *NH2NH2 through protonated *N2H, and finally generate NH3.

This work is the first to develop and study a nitrogen fixing catalyst with a clear molecular active site of dual nitrogen under mild conditions, which provides a new research idea and theoretical basis for the research and application of complex-type molecular catalysts in the research and application of photosynthetic nitrogen fixation.

The above research work has been supported or funded by the National Key R&D Program of China, the National Natural Science Foundation of China, the Special Fund for Scientific and Technological Innovation of Carbon Peaking and Carbon Neutrality of Jiangsu Province, the Special Project of Central Universities, the State Key Laboratory of Coordination Chemistry, the Key Laboratory of Mesoscopic Chemistry of the Ministry of Education, and the Collaborative Innovation Center of Artificial Microstructure Science and Technology. (Source: Science Network)

Related paper information:https://doi.org/10.1038/s41557-022-01088-8



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