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

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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.