Breaking scaling relations to achieve low-temperature ammonia synthesis through LiH-mediated nitrogen transfer and hydrogenation
Breaking scaling relations to achieve low-temperature ammonia synthesis through LiH-mediated nitrogen transfer and hydrogenation
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DOI：
10.1038/nchem.2595
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发表时间：
2017-01-01
期刊：
影响因子：
21.8
通讯作者：
Chen, Ping
中科院分区：
文献类型：
--
作者：
Wang, Peikun;Chang, Fei;Chen, Ping
在温和条件下合成氨是人们长期以来追求的目标。先前的研究表明，该过程中中间体在过渡金属（TM）上的吸附和过渡态能量彼此成比例。这阻碍了这些能量的独立优化，从而产生理想的催化剂：一种能够很好地活化反应物，但与中间体的结合相对较弱的催化剂。在这里，我们证明了可以通过使用第二个催化位点 LiH 干预 TM 介导的催化来打破这些比例关系。 LiH 带负电的氢原子充当强还原剂，从 TM 或其氮化物 (TMN) 中去除活化的氮原子，并作为氢的直接来源，与氮原子结合形成 LiNH2。 LiNH2进一步异解分裂H-2，释放出NH3并再生LiH。 TM（或TMN）和LiH之间的这种协同作用创造了一条有利的途径，使早期和晚期3d TM-LiH复合材料表现出前所未有的低温催化活性。
Ammonia synthesis under mild conditions is a goal that has been long sought after. Previous investigations have shown that adsorption and transition-state energies of intermediates in this process on transition metals (TMs) scale with each other. This prevents the independent optimization of these energies that would result in the ideal catalyst: one that activates reactants well, but binds intermediates relatively weakly. Here we demonstrate that these scaling relations can be broken by intervening in the TM-mediated catalysis with a second catalytic site, LiH. The negatively charged hydrogen atoms of LiH act as strong reducing agents, which remove activated nitrogen atoms from the TM or its nitride (TMN), and as an immediate source of hydrogen, which binds nitrogen atoms to form LiNH2. LiNH2 further splits H-2 heterolytically to give off NH3 and regenerate LiH. This synergy between TM (or TMN) and LiH creates a favourable pathway that allows both early and late 3d TM-LiH composites to exhibit unprecedented lower-temperature catalytic activities.