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

对于CO2还原为CO，基于Ce+3/Ce4+氧化还原体系的(太阳能)热循环是非常合适的。关于纯氧化铈(CeO2)的热力学，特别是含同价(Zr)氧化物或阳离子价态较低的氧化物(Gd，Sm，Y，Ca，Mg，...)的固溶体热力学的信息虽然广泛，但部分是不完整和相互矛盾的，主要包括氧的化学计量比对温度、氧分压和掺杂的依赖。关于CeO2表面整体CO2裂解反应中氧的表面交换动力学，以及氧在(掺杂/非掺杂)CeO2基质中的输运动力学，信息更加匮乏。因此，协调行动的目的是提供具有潜在技术相关性的固体溶液的可靠热力学信息，并在实验上量化表面交换系数K、扩散系数D和氧的平衡交换速率R°与CO2裂解过程的工艺变量(温度、氧势或CO2/CO比、掺杂剂的种类和浓度)的关系，并提出一致的模型。为此，申请人最近发布的一种模式应予以扩展。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，在这种协同作用中，如果可能的话，在相同的样品上结合了两种互补的实验方法。第一种方法是交换稀有稳定同位素(13C、18O)，并结合SIMS深度剖面法。第二种方法包括时间相关的重量分析和膨胀热分析，以检测氧势变化后块体样品的松弛动力学。这些补充实验所获得的数据将与上述模型进行一致性检验。它们将在各自的表面产生K，D和氧的平衡交换率R°。设想的协调行动将有助于收集必要的信息，以便了解和应用在技术上相关的固体溶液中使用氧化还原系统Ce+3/Ce4+分解二氧化碳。从而，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，申请人开发的现象学动力学模型的现状支持这样的期望，即该模型还将能够定量地描述流体和固体相交换公共组分的其他反应体系。

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.