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

电力天然气应用已经成为一种非常有前途的战略，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易于快速失活，这是由来自可再生能源的氢气供应波动引起的。SPP 2080第一阶段的成功项目MOFCO2DYN-X2证明，金属有机骨架（MOF）前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，即使在氢气脱落期间，由于在Ni颗粒周围形成保护性碳壳，也可以防止失活。虽然通过结合先进的硬X射线光谱和散射方法，（例如HERFD-XAS、VtC-XES、PDF），Ni@C和NiFe@C催化剂中的宽粒度分布阻碍了对动态过程的深入理解。合成方面后续项目REALCO2DYN-X2的主要目标是准备好-具有窄Ni粒度分布的定义的模型系统和真实的M0F衍生的Ni和NiFe基甲烷化催化剂的建立，其特征在于在工业相关的失活条件下的高活性和稳定性。将胶体Ni物质分别沉积在市售活性炭和氧化铝上，以产生具有小（2 - 4 nm）、中等（5 - 8 nm）和大（> 10 nm）Ni颗粒的模型系统。对于真实的催化剂，具有包封的Ni胶体的基于Al和AlFe的MOF将在限定的条件下热分解以获得Ni@Al2O3和NiFe@Al2O3催化剂。模型和真实的催化剂都将应用于实验室反应器中的二氧化碳甲烷化反应中，以评价它们在比第一阶段更相关的工业辍学条件下的稳定性。在光谱和散射方面，应通过进一步利用该项目先前建立的基于硬X射线的方法来推导结构-活性相关性。该方法提供了催化剂的结构（短，中，长程顺序）和电子性质的补充信息。特别是，在同步加速器设施的原位和operando实验将进行研究动态操作的甲烷化反应过程中的结构变化的动力学跨越时间尺度从秒到小时，以了解和防止催化剂失活机制。光谱学和散射将更紧密地联系在一起，结合反向蒙特卡罗建模。总之，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保持其高活性，如不同的氢气流失情况，并适用于电力到天然气工艺，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.