REALCO2DYN-X2: MOF-derived CO2 methanation catalysts – Mechanisms, activity and stability during industrially relevant, dynamic dropout scenarios using hard X-ray techniques

电能到天然气的应用已经成为一种非常有前途的策略，用于化学储存来自风能或太阳能等可再生能源的多余能量。先前的研究表明，负载型Ni甲烷化催化剂在动态反应条件下容易快速失活，这是由可再生能源氢供应的波动引起的。SPP2080第一期MOFCO2DYN-X2项目的成功证明，金属有机框架（MOF）前驱体的受控热分解是一种非常合适的方法，可以生成具有高稳定性的Ni@C催化剂，即使在Ni颗粒周围形成保护碳壳的氢脱落过程中也不会失活。虽然通过先进的硬x射线光谱和散射方法（例如HERFD-XAS， VtC-XES， PDF）的结合可以获得第一个机制，但Ni@C和NiFe@C催化剂中广泛的粒度分布阻碍了对动态过程的深入了解。因此，后续项目REALCO2DYN-X2在合成方面的主要目标是制备具有窄Ni粒度分布的良好定义的模型体系，并建立真正的mof衍生的Ni和nife基甲烷化催化剂，这些催化剂在工业相关的脱氮条件下具有高活性和稳定性。胶体镍将分别沉积在市售的活性炭和氧化铝上，以产生小（2-4纳米）、中（5-8纳米）和大（10 - 10纳米）镍颗粒的模型系统。对于真正的催化剂，Al-和alfe基mof包覆Ni胶体将在规定的条件下热分解得到Ni@Al2O3和NiFe@Al2O3催化剂。模型催化剂和实际催化剂将在实验室反应器中用于二氧化碳甲烷化，以评估它们在工业上比第一阶段更相关的辍学条件下的稳定性。在光谱和散射方面，将通过进一步利用先前在项目中建立的基于硬x射线的方法来推导结构-活性相关性。这些方法对催化剂的结构（短期、中期和长期顺序）和电子性质提供了补充信息。特别是，将在同步加速器设施上进行原位和操作实验，以研究动态操作甲烷化反应过程中结构变化的动力学，从秒到小时不等，以了解和防止催化剂失活机制。通过结合反向蒙特卡罗模型，光谱学和散射学将更加紧密地联系在一起。综上所述，REALCO2DYN-X2的主要重点是建立催化剂，这些催化剂在工业相关的动态操作条件下（如不同的氢退出场景）保持高活性，并且适用于电力制气过程，以利用多余的可再生能源。

Power-to-gas applications have emerged as a very promising strategy for the chemical storage of excess energy from renewable sources like wind or sunlight. Previous studies could show that supported Ni methanation catalysts are prone to fast deactivation under dynamic reaction conditions, which are caused by the fluctuating supply of hydrogen from renewable energies. The successful project MOFCO2DYN-X2 from the first period of SPP2080 proved that the controlled thermal decomposition of metal-organic-framework (MOF) precursors is a very suitable method to generate Ni@C catalysts with a high stability against deactivation even during hydrogen dropouts due to the formation of a protective carbon shell around the Ni particles. Although first mechanistic insight could be gained by a combination of advanced hard X-ray spectroscopic and scattering methods (e.g. HERFD-XAS, VtC-XES, PDF), the broad particle size distribution in Ni@C and NiFe@C catalysts hampered an in-depth understanding of the dynamic processes.Consequently, the key objectives of the follow-up project REALCO2DYN-X2 on the synthetic side are the preparation of well-defined model systems with a narrow Ni particle size distribution and the establishment of real MOF-derived Ni- and NiFe-based methanation catalysts that feature high activity and stability under industrially relevant dropout conditions. Colloidal Ni species will be deposited onto commercially available activated carbon and alumina, respectively, to generate model systems with small (2-4 nm), medium (5-8 nm) and large (> 10 nm) Ni particles. For the real catalysts, Al- and AlFe-based MOFs with encapsulated Ni colloids will be thermally decomposed under defined conditions to obtain Ni@Al2O3 and NiFe@Al2O3 catalysts. Both model and real catalysts will be applied in the methanation of carbon dioxide in a laboratory reactor to evaluate their stability under industrially more relevant dropout conditions than those in the first period. On the spectroscopic and scattering side, structure-activity correlations shall be derived by further exploiting the hard X-ray-based methods established previously in the project. The methods give complementary information on the structural (short-, medium and long-range order) and electronic properties of the catalysts. In particular, in-situ and operando experiments at synchrotron facilities will be performed to study the kinetics of structural changes during the dynamically operated methanation reaction across time scales from seconds to hours to understand and prevent catalyst deactivation mechanisms. Spectroscopy and scattering will be more tightly connected by combined Reverse Monte Carlo modelling. In summary, the main focus of REALCO2DYN-X2 is the establishment of catalysts, which maintain their high activity under industrially relevant dynamic operating conditions like different hydrogen dropout scenarios and that are suitable for power-to-gas processes to utilize excess renewable energy.