Mechanism Switching of Ammonia Synthesis Over Ru-Loaded Electride Catalyst at Metal鈥揑nsulator Transition
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- 作者：Shinji Kanbara ; Masaaki Kitano ; Yasunori Inoue ; Toshiharu Yokoyama ; Michikazu Hara ; Hideo Hosono
- 刊名：Journal of the American Chemical Society
- 出版年：2015
- 出版时间：November 18, 2015
- 年：2015
- 卷：137
- 期：45
- 页码：14517-14524
- 全文大小：446K
- ISSN：1520-5126
文摘
The substitution of electrons for O2鈥?/sup> anions in the crystallographic cages of [Ca24Al28O64]4+(O2鈥?/sup>)2 was investigated to clarify the correlation between the electronic properties and catalytic activity for ammonia synthesis in Ru-loaded [Ca24Al28O64]4+(O2鈥?/sup>)2鈥?i>x(e鈥?/sup>)2x (0 鈮?x 鈮?2). This catalyst has low catalytic performance with an electron concentration (Ne) lower than 1 脳 1021 cm鈥? and a high apparent activation energy (Ea) for ammonia synthesis comparable to that for conventional Ru-based catalysts with a basic promoter such as alkali or alkaline earth compounds. Replacement of more than half of the cage O2鈥?/sup> anions with electrons (Ne 鈮?1 脳 1021 cm鈥?) significantly changes the reaction mechanism to yield a catalytic activity that is an order higher and with half the Ea. The metal鈥搃nsulator transition of [Ca24Al28O64]4+(O2鈥?/sup>)2鈥?i>x(e鈥?/sup>)2x also occurs at Ne 鈮?1 脳 1021 cm鈥? and is triggered by structural relaxation of the crystallographic cage induced by the replacement of O2鈥?/sup> anions with electrons. These observations indicate that the metal鈥搃nsulator transition point is a boundary in the catalysis between Ru-loaded [Ca24Al28O64]4+(O2鈥?/sup>)2 and [Ca24Al28O64]4+(e鈥?/sup>)4. It is thus demonstrated that whole electronic properties of the support material dominate catalysis for ammonia synthesis.