Understanding the enhancement of CaO on water gas shift reaction for H2 production by density functional theory
Understanding the enhancement of CaO on water gas shift reaction for H2 production by density functional theory
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用密度泛函理论理解CaO对水煤气变换制氢反应的增强作用
DOI：
10.1016/j.fuel.2021.121257
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发表时间：
2021-11
期刊：
影响因子：
7.4
通讯作者：
Wang Zeyan
中科院分区：
文献类型：
--
作者：
Yan Xianyao;Li Yingjie;Zhang Chunxiao;Wang Yuzhuo;Zhao Jianli;Wang Zeyan
水煤气变换反应是各种工业应用中制氢的重要反应。 CaO的存在可以促进无需任何催化剂的水煤气变换反应的反应活性，但CaO在此反应中的增强机制很难仅通过实验确定。在这项工作中，通过密度泛函理论 (DFT) 分析研究了 CaO 表面上四种可能路径的水煤气变换反应。分析了沿路径的能垒，以确定最可能的反应路径和 CaO 表面的作用。 DFT计算结果表明，WGS反应更容易沿着氧化还原途径进行，可能是：当H2O和CO共吸附在CaO表面时，H2O自发解离成羟基和原子H，然后羟基继续解离，CO被生成的原子O氧化。随后，由两个原子H生成H分子，然后CO2在CaO表面上同时吸附和H2解吸。 CaO 表面能够使 H2O 自发解离，这是 WGS 反应的限速步骤。促进了 CO2 的生成，CaO 表面的能垒从 2.304 eV 降低到 0.757 eV。此外，表面CO32−的形成避免了CO2解吸的能垒，同时CO2也占据了活性位点并降低了CaO对WGS反应的增强作用。计算结果加强了对CaO对WGS反应机理的理解。
The water gas shift reaction is an important reaction for H2production in various industrial applications. The presence of CaO can promote the reactivity of the water gas shift reaction without any catalysts, but the enhancement mechanism of CaO in this reaction is difficult to determine just by the experiment. In this work, the water gas shift reaction along four possible pathways on the CaO surface were studied by density functional theory (DFT) analysis. The energy barriers along the pathways were analyzed to determine the most possible reaction pathway and role of the CaO surface. The DFT calculation results show that the WGS reaction is more prone to proceed along theredox-apathway probably: H2O dissociates into hydroxyl and atomic H spontaneously when H2O and CO co-adsorb on the CaO surface, then the hydroxyl continues to dissociate and CO is oxidized by the generated atomic O. Afterwards, H2molecule generates from two atomic H, and then CO2adsorbs and H2desorbs simultaneously on the CaO surface. The CaO surface enables the spontaneous dissociation of H2O, which is the rate-limiting step of WGS reaction. The generation of CO2is facilitated, and the energy barrier is reduced from 2.304 to 0.757 eV on the CaO surface. Besides, the formation of CO32−on the surface avoids the energy barrier for CO2desorption, while the CO2also occupies the active site and reduces the enhancement of CaO on WGS reaction. The calculation result reinforces the comprehension on the mechanism of CaO on WGS reaction.
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