Thermodynamics and kinetics of CO2 splitting with the redox system Ce3+/Ce4+ at high temperatures

氧化还原系统Ce3/Ce4在高温下CO2分解的热力学和动力学

• 批准号: 433306682
• 负责人: Professor Dr.-Ing. Günter Borchardt
• 金额: --
• 依托单位: Deutsches Zentrum für Luft- und Raumfahrt (DLR)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/433306682?language=en
• 关键词: Thermodynamics; kinetics; CO2; splitting; redox

For the reduction of CO2 to CO, (solar) thermal cycles based on the Ce+3/Ce4+ redox system are well suited. The information on the thermodynamics of pure cerium oxide (CeO2) and, especially, on the thermodynamics of solid solutions with homovalent (Zr) oxides or oxides with lower cation valences (Gd, Sm, Y, Ca, Mg, ...), albeit extensive, is partially incomplete and contradictory and comprises primarily only the dependency of the oxygen stoichiometry on temperature, oxygen partial pressure and dopants. With respect to the kinetics of the surface exchange of oxygen in the global CO2 splitting reaction at the CeO2 surface, as well as for the oxygen transport in the (doped/undoped) CeO2 matrix information is even more scarce. Therefore, the aim of the concerted action is to provide reliable thermodynamic information on the solid solutions with potential technological relevance, and to experimentally quantify the dependency of the surface exchange coefficient K, the diffusion coefficient D and the equilibrium exchange rate of oxygen, R°, on the process variables (temperature, oxygen potential or CO2/CO ratio, kind and concentration of dopants) of the CO2 splitting process, and to present a consistent model. To this purpose, a model published recently by the applicants shall be expanded. This model quantitatively describes the relation between K, D and R°.In order to gain the necessary experimental data two complementary experimental approaches are combined in this concerted action, if possible on the same samples. The first method is the exchange of rare stable isotopes (13C, 18O) in combination with SIMS depth profiling. The second method comprises the time dependent gravimetric and dilatometric thermal analysis in order to detect the relaxation kinetics of bulk samples after an oxygen potential change.The data gained from these complementary experiments will be checked for consistency with the above mentioned model. They will yield K, D and the equilibrium exchange rate of oxygen, R°, at the respective surface. The envisaged concerted action will enable the gathering of the information needed to understand and apply CO2 splitting with the redox system Ce+3 /Ce4+ in technologically relevant solid solutions. Thus, it will simultaneously supply the scientific basis for a technological realization. This implies that the results can be principally transferred to other material systems. Further, the present state of the phenomenological kinetic model developed by the applicants supports the expectation that the model will also enable to quantitatively describe other reaction systems where a fluid and a solid phase exchange a common component.

对于将 CO2 还原为 CO，基于 Ce+3/Ce4+ 氧化还原系统的（太阳能）热循环非常适合。关于纯氧化铈 (CeO2) 的热力学信息，特别是关于同价 (Zr) 氧化物或具有较低阳离子价态的氧化物 (Gd、Sm、Y、Ca、Mg...) 的固溶体的热力学信息，虽然广泛，但部分不完整且矛盾，并且主要仅包括氧化学计量对温度、氧分压和 掺杂剂。关于 CeO2 表面全局 CO2 分解反应中氧的表面交换动力学，以及（掺杂/未掺杂）CeO2 基体中氧传输的信息更是稀缺。因此，协同行动的目的是提供具有潜在技术相关性的固溶体的可靠热力学信息，并通过实验量化表面交换系数 K、扩散系数 D 和氧的平衡交换率 R° 对 CO2 分解过程的过程变量（温度、氧势或 CO2/CO 比率、掺杂剂的种类和浓度）的依赖性，并提出 一致的模型。为此，应扩展申请人最近发布的模型。该模型定量地描述了 K、D 和 R° 之间的关系。为了获得必要的实验数据，在这种协调一致的操作中结合了两种互补的实验方法，如果可能的话，在相同的样品上进行。第一种方法是交换稀有稳定同位素（13C、18O）并结合 SIMS 深度剖析。第二种方法包括时间相关的重量分析和膨胀热分析，以检测氧势变化后大块样品的弛豫动力学。将从这些补充实验获得的数据将检查与上述模型的一致性。它们将在各自的表面产生 K、D 和氧的平衡交换率 R°。设想的协调行动将能够收集所需的信息，以了解和在技术相关的固体解决方案中使用氧化还原系统 Ce+3 /Ce4+ 进行二氧化碳分解。因此，它将同时为技术实现提供科学依据。这意味着结果可以主要转移到其他材料系统。此外，申请人开发的唯象动力学模型的现状支持这样的期望：该模型还将能够定量地描述其中流体和固相交换共同组分的其他反应系统。