Contribution of Nitrogen Vacancies to Ammonia Synthesis over Metal Nitride Catalysts.
Contribution of Nitrogen Vacancies to Ammonia Synthesis over Metal Nitride Catalysts.
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DOI：
10.1021/jacs.0c06624
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发表时间：
2020-08
影响因子：
15
通讯作者：
Tiannan Ye;Sang-Won Park;Yangfan Lu;Jiang Li;M. Sasase;M. Kitano;H. Hosono
中科院分区：
文献类型：
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作者：
Tiannan Ye;Sang-Won Park;Yangfan Lu;Jiang Li;M. Sasase;M. Kitano;H. Hosono
氨是化肥生产最重要的原料之一，也是潜在的能源载体。 LaN等氮化物最近引起了人们的广泛关注，因为它们的氮空位可以激活N2用于氨合成。在这里，我们提出了用于氨合成的氮化物基催化剂设计的一般规则，其中氮空位形成能（ENV）主导催化性能。 CeN 相对较低的 ENV（约 1.3 eV）意味着它可以在负载 Ni 时作为有效且稳定的催化剂。 Ni/CeN的催化活性达到6.5 mmol·g-1·h-1，出水NH3浓度(ENH3)为0.45 vol %，在400 ℃和0.1 MPa下达到热力学平衡(ENH3 = 0.45 vol %)，从而绕过了氮结合能极弱的Ni金属上N2活化的瓶颈。其活性远远超过其他钴基和镍基催化剂，甚至可以与钌基催化剂相媲美。确定CeN本身可以在几乎相同的活化能下在不负载Ni的情况下产生氨。动力学分析和同位素实验结合密度泛函理论（DFT）计算表明，CeN中的氮空位可以在反应过程中同时活化N2和H2，这使得其比其他报道的无负载氨合成催化剂具有更高的催化性能。
Ammonia is one of the most important feedstocks for the production of fertilizer and as a potential energy carrier. Nitride compounds such as LaN have recently attracted considerable attention due to their nitrogen vacancy sites that can activate N2 for ammonia synthesis. Here, we propose a general rule for the design of nitride-based catalysts for ammonia synthesis, in which the nitrogen vacancy formation energy (ENV) dominates the catalytic performance. The relatively low ENV (ca. 1.3 eV) of CeN means it can serve as an efficient and stable catalyst upon Ni loading. The catalytic activity of Ni/CeN reached 6.5 mmol·g-1·h-1 with an effluent NH3 concentration (ENH3) of 0.45 vol %, reaching the thermodynamic equilibrium (ENH3 = 0.45 vol %) at 400 °C and 0.1 MPa, thereby circumventing the bottleneck for N2 activation on Ni metal with an extremely weak nitrogen binding energy. The activity far exceeds those for other Co- and Ni-based catalysts, and is even comparable to those for Ru-based catalysts. It was determined that CeN itself can produce ammonia without Ni-loading at almost the same activation energy. Kinetic analysis and isotope experiments combined with density functional theory (DFT) calculations indicate that the nitrogen vacancies in CeN can activate both N2 and H2 during the reaction, which accounts for the much higher catalytic performance than other reported nonloaded catalysts for ammonia synthesis.