The power-to-gas process for the chemical storage of renewable energy in methane as a storage molecule requires a carbon source, for which industrial exhaust gases are very promising because of their availability in large quantities. The composition of these gas streams, however, is often characterized by a mixture of CO and CO2. Because of the rather complex reaction mechanism, though, the methanation of CO/CO2 mixtures using nickel catalysts is not yet fully understood, and appropriate reaction kinetics required for the reactor design are still lacking. Therefore, we report the experimental results on the methanation of various mixtures of CO and CO2. The data are further evaluated by a model-based approach in order to derive reaction kinetics capable for the reactor design in a typical range of operating conditions. The results also reveal two kinetic regimes depending on the fraction of CO in the CO/CO2 mixture, which is accounted for in the proposed kinetics.

Investigating the effect of concentration forcing of the CO2 methanation is not only relevant for power‐to‐gas plants but also for the study of dynamic phenomena of this reaction. In this study a Ni/Al2O3 catalyst is investigated under concentration forcing at industrially relevant conditions. The dynamic experiments allow an evaluation in terms of the reaction rate and enable the study of the reaction mechanism. The experiments show that no methane is formed in the CO2‐rich part of the cycle, whereas a fast hydrogenation of carbonaceous species to methane takes place upon switching to H2.

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CO x hydrogenation reactions for hydrocarbon synthesis, such as methane, are becoming more and more important in terms of the energy transition. The formation of the byproduct water leads to a hydrothermal environment, which necessitates stable catalyst materials under harsh reaction conditions. Therefore, novel nanostructured core-shell catalysts are part of scientific discussion, since these materials offer an exceptional resistance against thermal sintering. Here we report on a core-shell catalyst -Co@mSiO 2 -for the hydrogenation of CO/CO 2 mixtures towards methane. CO methanation experiments reveal a rapid temperature-depended deactivation for temperatures above 350°C caused by coking and possible blocking of the pores. In comparison to a Co/mSiO 2 reference catalyst with the same Co particle size a significantly higher methane selectivity was found for CO 2 hydrogenation, which we attribute to the confinement effect of the core-shell structure and therefore a higher probability of CO readsorption. Finally, the simultaneous CO/ CO 2 co-methanation experiments show a high flexibility of the catalyst materials on different gas feed compositions.[a] J. Ilsemann, + Prof. Dr. M. Bäumer

The Power-to-Gas (PtG) process offers the opportunity to store fluctuating renewable energy in form of chemical energy by hydrogenating carbon oxides into methane. In addition, potential carbon point sources often consist of CO/CO2 (COx) mixtures. Hence, reactor design requires kinetic models valid for unsteady-state operation and a broad spectrum of feed gas compositions. In order to provide the required experimental data basis for derivation of kinetic expressions valid under transient conditions, the dynamic response of a continuously operated fixed-bed methanation reactor is studied by applying periodic step-changes in the feed composition. The obtained results are evaluated based on a simple reactor model, providing the molar flow rate exchanged between the gas bulk and the solid surface for CO, CO2, CH4, and H2O. The results further reveal that the transient kinetic processes at the catalyst surface strongly affect the reactor response under reaction conditions of technical relevance.