Effects of Alkaline Earth Metal Amides on Ru in Catalytic Ammonia Decomposition

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• 作者：Pei Yu ; Jianping Guo ; Lin Liu ; Peikun Wang ; Fei Chang ; Han Wang ; Xiaohua Ju ; Ping Chen
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：February 11, 2016
• 年：2016
• 卷：120
• 期：5
• 页码：2822-2828
• 全文大小：430K
• ISSN：1932-7455

文摘

The effects of alkaline earth metal amides (Mg(NH₂)₂, Ca(NH₂)₂, and Ba(NH₂)₂) on Ru in catalyzing NH₃ decomposition were investigated. The catalytic activities rank in the order of Ru–Ba(NH₂)₂ > Ru–Ca(NH₂)₂ > Ru–Mg(NH₂)₂, among which Ru–Ba(NH₂)₂ and Ru–Ca(NH₂)₂ catalysts have higher intrinsic activities (TOF) and lower apparent activation energies than those of Ru–Mg(NH₂)₂ and Ru/MgO catalysts, indicating that Ca(NH₂)₂ and Ba(NH₂)₂ may have different roles from those of Mg(NH₂)₂ and MgO. The TPR (temperature-programmed reaction) results show that Ca(NH₂)₂ or Ba(NH₂)₂ decomposes to N₂ and H₂ rather than NH₃ in the presence of Ru. Ru may promote the NH_x (x = 1, 2) coupling to H₂ and N₂ and change the decomposition pathways of Ca(NH₂)₂ and Ba(NH₂)₂. Kinetic analyses reveal that the Ru promoted NH_x coupling to H₂ and N₂ may be the rate-determining step for catalytic ammonia decomposition. We suggest that the catalysis is very likely fulfilled via (1) Ru catalyzes the decomposition of amides to form H₂, N₂, and imides through an energy more favorable pathway and (2) imides react with NH₃ to regenerate amides. The presence of Ca(NH₂)₂ or Ba(NH₂)₂ creates a NH_x-rich environment, and Ru mediates the electron transfer from NH_x to facilitate NH_x coupling to N₂ and H₂.