Surface Dynamics for Creating Highly Active Ru Sites for Ammonia Synthesis: Accumulation of a Low-Crystalline, Oxygen-Deficient Nanofraction
Surface Dynamics for Creating Highly Active Ru Sites for Ammonia Synthesis: Accumulation of a Low-Crystalline, Oxygen-Deficient Nanofraction
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DOI：
10.1021/acssuschemeng.9b06299
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发表时间：
2020-02-24
影响因子：
8.4
通讯作者：
Nagaoka, Katsutoshi
中科院分区：
文献类型：
--
作者：
Sato, Katsutoshi;Miyahara, Shin-ichiro;Nagaoka, Katsutoshi
为了缓解与能源和全球变暖相关的全球性问题，开发使用在温和条件下具有高活性的催化剂的氨合成方法是有帮助的。在本文中，我们表明，在700 ℃下预还原的Ru/Ba/LaCeOx催化剂的氨合成活性是所报道的氧化物负载的Ru催化剂中最高的，在350 ℃，1.0 MPa下为52.3 mmol h（-1）g（cat）（-1）。Ru/Ba/LaCeOx在350 ℃下的转换频率是Cs+/Ru/MgO的8倍以上，Cs+/Ru/MgO是用作基准的众所周知的活性催化剂;此外，氢中毒，氧化物负载的Ru催化剂的典型缺点，被有效地抑制。扫描透射电子显微镜观察与能量色散X-射线光谱和电子能量损失谱分析表明，低结晶，缺氧纳米fraction，包括Ba 2+，Ce 3+，和La 3+的Ru颗粒上积累。这种独特的结构是通过利用碱土金属化合物和热稳定的稀土氧化物的表面动力学获得的，这些氧化物在异常高温下还原过程中含有氧化还原活性原子。由于所含阳离子的强碱性、碳酸根的去除以及氧缺陷位点的形成，纳米级分与Ru原子之间的界面消除了吸电子的O2-阴离子，因此纳米级分显示出强的供电子能力。因此，电子被有效地捐赠到反键π轨道的N-2分子通过Ru在接触的纳米级，和N-N三键断裂，这是氨合成的速率决定步骤，促进。
To mitigate global problems related to energy and global warming, it is helpful to develop an ammonia synthesis process using catalysts that are highly active under mild conditions. Here we show that the ammonia synthesis activity per weight of catalyst of Ru/Ba/LaCeOx, prereduced at 700 degrees C, is the highest among reported oxide-supported Ru catalysts, 52.3 mmol h(-1) g(cat)(-1) at 350 degrees C, 1.0 MPa. The turnover frequency of Ru/Ba/LaCeOx at 350 degrees C was more than 8 times that of Cs+/Ru/MgO, which is a well-known active catalyst used as a benchmark; furthermore, hydrogen poisoning, a typical drawback for oxide-supported Ru catalysts, was effectively suppressed. Scanning transmission electron microscopy observations with energy dispersive X-ray spectrometry and electron energy loss spectroscopy analysis revealed that a low-crystalline, oxygen-deficient nanofraction including Ba2+, Ce3+, and La3+ had accumulated on the Ru particles. This unique structure was obtained by exploiting the surface dynamics of alkaline earth compounds and thermostable rare earth oxides that contain redox-active atoms during the reduction at an unusually high temperature. The nanofraction showed strong electron-donating ability because of the strong basicity of the included cations, removal of carbonate, and formation of oxygen defect sites that eliminated electron-withdrawing O2- anions from the interface between the nanofraction and Ru atom. Electrons were therefore effectively donated to antibonding pi-orbitals of the N-2 molecules via Ru in contact with the nanofraction, and N N triple bond cleavage, which is the rate-determining step for ammonia synthesis, was promoted.