Ruthenium (Ru) loaded catalysts are of significant interest for ammonia synthesis under mild reaction conditions. The B5 sites have been reported as the active sites for ammonia formation, i.e., Ru with other coordinations were inactive, which has limited the utilization efficiency of Ru metal. The implantation of Ru into intermetallic compounds is considered to be a promising approach to tune the catalytic activity and utilization efficiency of Ru. Here we report an acid-durable electride, LnRuSi (Ln = La, Ce, Pr and Nd), as a B5-site-free Ru catalyst. The active Ru plane with a negative charge is selectively exposed by chemical etching using disodium dihydrogen ethylenediaminetetraacetate (EDTA-2Na) acid, which leads to 2–4-fold enhancement in the ammonia formation rate compared with that of the original catalyst. The turnover frequency (TOF) of LnRuSi is estimated to be approximately 0.06 s–1, which is 600 times higher than that of pure Ru powder. Density functional theory (DFT) calculations revealed that the dissociation of N2 occurs easily on the exposed Ru plane of LaRuSi. This systematic study provides firm evidence that layered Ru with a negative charge in LnRuSi is a new type of active site that differs significantly from B5 sites.
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机译:负载钌(Ru)的催化剂对于在温和的反应条件下合成氨具有重大意义。据报道,B5位点是氨形成的活性位点,即Ru与其他配位基团是不活泼的,这限制了Ru金属的利用效率。将Ru植入金属间化合物中被认为是调节Ru的催化活性和利用效率的一种有前途的方法。在这里,我们报告了一种耐酸的电子体LnRuSi(Ln = La,Ce,Pr和Nd),作为无B5位的Ru催化剂。通过使用乙二胺四乙酸二氢二钠(EDTA-2Na)酸进行化学蚀刻,选择性地暴露带负电荷的活性Ru平面,与原始催化剂相比,氨的形成速率提高了2-4倍。 LnRuSi的周转频率(TOF)估计约为0.06 s –1 sup>,是纯Ru粉的600倍。密度泛函理论(DFT)计算表明,N2的解离容易在LaRuSi的暴露Ru平面上发生。这项系统的研究提供了有力的证据,表明LnRuSi中带负电荷的Ru层是一种新型的活性位点,与B5位点明显不同。
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