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Boosting selective nitrogen reduction to ammonia on electron-deficient copper nanoparticles.

ABSTRACT: Production of ammonia is currently realized by the Haber-Bosch process, while electrochemical N₂ fixation under ambient conditions is recognized as a promising green substitution in the near future. A lack of efficient electrocatalysts remains the primary hurdle for the initiation of potential electrocatalytic synthesis of ammonia. For cheaper metals, such as copper, limited progress has been made to date. In this work, we boost the N₂ reduction reaction catalytic activity of Cu nanoparticles, which originally exhibited negligible N₂ reduction reaction activity, via a local electron depletion effect. The electron-deficient Cu nanoparticles are brought in a Schottky rectifying contact with a polyimide support which retards the hydrogen evolution reaction process in basic electrolytes and facilitates the electrochemical N₂ reduction reaction process under ambient aqueous conditions. This strategy of inducing electron deficiency provides new insight into the rational design of inexpensive N₂ reduction reaction catalysts with high selectivity and activity.

SUBMITTER: Lin YX

PROVIDER: S-EPMC6763479 | biostudies-literature | 2019 Sep

REPOSITORIES: biostudies-literature

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Boosting selective nitrogen reduction to ammonia on electron-deficient copper nanoparticles.

Lin Yun-Xiao YX Zhang Shi-Nan SN Xue Zhong-Hua ZH Zhang Jun-Jun JJ Su Hui H Zhao Tian-Jian TJ Zhai Guang-Yao GY Li Xin-Hao XH Antonietti Markus M Antonietti Markus M Chen Jie-Sheng JS

Nature communications 20190926 1

Production of ammonia is currently realized by the Haber-Bosch process, while electrochemical N<sub>2</sub> fixation under ambient conditions is recognized as a promising green substitution in the near future. A lack of efficient electrocatalysts remains the primary hurdle for the initiation of potential electrocatalytic synthesis of ammonia. For cheaper metals, such as copper, limited progress has been made to date. In this work, we boost the N<sub>2</sub> reduction reaction catalytic activity ...[more]

PMID: 31558716

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Project description:Nitrogenase is a fascinating enzyme in biology that reduces dinitrogen from air to ammonia through stepwise reduction and protonation. Despite it being studied in detail by experimental and computational groups, there are still many unknown factors in the catalytic cycle of nitrogenase, especially related to the addition of protons and electrons and their order. A recent biomimetic study characterized a potential dinitrogen-bridged diiron cluster as a synthetic model of nitrogenase. Using strong acid and reductants, the dinitrogen was converted into ammonia molecules, but details of the mechanism remains unknown. In particular, it was unclear from the experimental studies whether the proton and electron transfer steps are sequential or alternating. Moreover, the work failed to establish what the function of the diiron core is and whether it split into mononuclear iron fragments during the reaction. To understand the structure and reactivity of the biomimetic dinitrogen-bridged diiron complex [(P2P'PhFeH)2(μ-N2)] with triphenylphosphine ligands, we performed a density functional theory study. Our computational methods were validated against experimental crystal structure coordinates, Mössbauer parameters, and vibrational frequencies and show excellent agreement. Subsequently, we investigated the alternating and consecutive addition of electrons and protons to the system. The calculations identify a number of possible reaction channels, namely, same-site protonation, alternating protonation, and complex dissociation into mononuclear iron centers. The calculations show that the overall mechanism is not a pure sequential set of electron and proton transfers but a mixture of alternating and consecutive steps. In particular, the first reaction steps will start with double proton transfer followed by an electron transfer, while thereafter, there is another proton transfer and a second electron transfer to give a complex whereby ammonia can split off with a low energetic barrier. The second channel starts with alternating protonation of the two nitrogen atoms, whereafter the initial double proton transfer, electrons and protons are added sequentially to form a hydrazine-bound complex. The latter split off ammonia spontaneously after further protonation. The various reaction channels are analyzed with valence bond and orbital diagrams. We anticipate the nitrogenase enzyme to operate with mixed alternating and consecutive protonation and electron transfer steps.

Dataset Information

Boosting selective nitrogen reduction to ammonia on electron-deficient copper nanoparticles.

Publications

Boosting selective nitrogen reduction to ammonia on electron-deficient copper nanoparticles.

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