CO 2 methanation is a well-known reaction that is of interest as a capture and storage (CCS) process and as a renewable energy storage system based on a power-to-gas conversion process by substitute or synthetic natural gas (SNG) production. Integrating water electrolysis and CO 2 methanation is a highly effective way to store energy produced by renewables sources. The conversion of electricity into methane takes place via two steps: hydrogen is produced by electrolysis and converted to methane by CO 2 methanation. The effectiveness and efficiency of power-to-gas plants strongly depend on the CO 2 methanation process. For this reason, research on CO 2 methanation has intensified over the last 10 years. The rise of active, selective, and stable catalysts is the core of the CO 2 methanation process. Novel, heterogeneous catalysts have been tested and tuned such that the CO 2 methanation process increases their productivity. The present work aims to give a critical overview of CO 2 methanation catalyst production and research carried out in the last 50 years. The fundamentals of reaction mechanism, catalyst deactivation, and catalyst promoters, as well as a discussion of current and future developments in CO 2 methanation, are also included.

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The rapid separation and efficient recycling of catalysts after a catalytic reaction are considered important requirements along with the high catalytic performances. In this view, although heterogeneous catalysis is generally less efficient if compared to the homogeneous type, it is generally preferred since it benefits from the easy recovery of the catalyst. Recycling of heterogeneous catalysts using traditional methods of separation such as extraction, filtration, vacuum distillation, or centrifugation is tedious and time-consuming. They are uneconomic processes and, hence, they cannot be carried out in the industrial scale. For these limitations, today, the research is devoted to the development of new methods that allow a good separation and recycling of catalysts. The separation process should follow a procedure economically and technically feasible with a minimal loss of the solid catalyst. The aim of this work is to provide an overview about the current trends in the methods of separation/recycling used in the heterogeneous catalysis.

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