揭示 IrO2 在乙烷化学链氧化脱氢中的表面态演变,ACS Catalysis

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揭示 IrO2 在乙烷化学链氧化脱氢中的表面态演变
ACS Catalysis ( IF 11.3 ) Pub Date : 2023-01-09 , DOI: 10.1021/acscatal.2c05770
Lulu Ping _{1,

2} , Yuan Zhang ₁ , Baojun Wang _{1,

2} , Maohong Fan _{3,

4,

5} , Lixia Ling ₂ , Riguang Zhang _{1,

2}

Affiliation

基于乙烷氧化脱氢有利的热力学和抗结焦的优点以及乙烯选择性低的挑战，研究了IrO ₂催化剂上的化学链氧化脱氢（CL-ODH），包括脱氢和再生过程。考虑了化学计量的 S-IrO ₂和还原的 R-IrO ₂催化剂作为具有动态变化的 IrO _{2表面结构的两个极端状态。}密度泛函理论(DFT) 计算和动力学蒙特卡罗模拟表明乙烷在S-IrO ₂和R-IrO ₂催化剂上的脱氢机理完全不同。在 S-IrO ₂催化剂，乙烷氧化脱氢为C ₂ H ₄ (g)，H ₂ O(g)、CO(g)和CO ₂ (g)带走表面晶格氧，随后晶格氧从本体迁移到表面，导致S-IrO ₂催化剂的还原。在 R-IrO ₂催化剂上，乙烷直接脱氢为 C ₂ H ₄ (g) 和 H ₂ (g)。此外，再生过程中的氧化度大于脱氢过程中的_Ov浓度，容易实现再生过程中的氧气补给。更重要的是，IrO ₂催化剂在脱氢过程中既不能完全还原，也不能在再生过程中完全氧化， IrO ₂催化剂同时存在S-IrO ₂和R-IrO ₂，750 K和0.8 bar C ₂ H ₆ (g)获得最佳反应条件的压力；因此，对于 IrO _{2上的乙烷 CL-ODH}催化剂，所提出的机理从氧化脱氢过程开始；随着表面晶格氧的消耗和氧从本体迁移到表面，氧化脱氢和非氧化脱氢同时发生，直至再生。本研究拓宽了对乙烷 CL-ODH 对金属氧化物催化剂的理解，并为优化 CL-ODH 工艺和开发其他烷烃 CL-ODH 工艺中的其他高性能金属氧化物催化剂提供了有价值的信息。

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Unraveling the Surface State Evolution of IrO2 in Ethane Chemical Looping Oxidative Dehydrogenation

Based on the advantages of favorable thermodynamics and coking resistance of ethane oxidative dehydrogenation and the challenge of low ethylene selectivity, chemical looping oxidative dehydrogenation (CL-ODH) over the IrO₂ catalyst was examined, including the dehydrogenation and regeneration processes. The stoichiometric S-IrO₂ and reduced R-IrO₂ catalysts as two extreme states of the IrO₂ surface structure with dynamic changes were considered. Density functional theory (DFT) calculations and kinetic Monte Carlo simulations showed that the mechanisms of ethane dehydrogenation over S-IrO₂ and R-IrO₂ catalysts were quite different. Over the S-IrO₂ catalyst, ethane oxidative dehydrogenation to C₂H₄(g) with H₂O(g), CO(g), and CO₂(g) taking away surface lattice oxygen, followed by lattice oxygen migration from the bulk to the surface, leads to the reduction of the S-IrO₂ catalyst. Over the R-IrO₂ catalyst, ethane directly dehydrogenates to C₂H₄(g) and H₂(g). Furthermore, the oxidation degree in the regeneration process is greater than the O_v concentration in the dehydrogenation process, which can easily achieve oxygen replenishment in the regeneration process. More importantly, the IrO₂ catalyst can be neither completely reduced in the dehydrogenation process nor completely oxidized in the regeneration process, both S-IrO₂ and R-IrO₂ simultaneously exist for the IrO₂ catalyst, and both 750 K and 0.8 bar C₂H₆(g) pressure were obtained to be the optimal reaction conditions; thus, for ethane CL-ODH over the IrO₂ catalyst, the proposed mechanism starts from the oxidative dehydrogenation process; with the consumption of surface lattice oxygen and the oxygen migration from the bulk to the surface, the oxidative and nonoxidative dehydrogenations occur simultaneously until the regeneration. The present study broadens the understanding of ethane CL-ODH over metal oxide catalysts and provides valuable information for the optimization of the CL-ODH process and the development of other high-performance metal oxide catalysts in other alkane CL-ODH processes.

更新日期：2023-01-09

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