Multiscale Design of CO2 Methanation Systems: From Fundamentals to Industrial Deployment

Recent years have seen increased efforts to decarbonize energy systems by converting pollutants into valuable products, integrating renewable energy, promoting carbon circularity, and enabling large‑scale energy storage. In this context, carbon dioxide (CO2) methanation has become an important Power‑to‑Gas (PtG) pathway, producing synthetic natural gas (SNG) as methane (CH4). The CO2 for this process can be obtained from industrial flue gases, such as those from cement and steel production, from biogas upgrading, or directly from the air. Other CO2 conversion routes, such as reverse water‑gas shift, methanol synthesis, or CO2 electrolysis, turn CO2 into different products. Methanation stands out because it gives a fuel that works directly with existing gas networks for storage and distribution. While most past reviews focused on individual aspects of the methanation process, we present a multi‑scale view that connects catalyst development, reactor design, and process optimization, based on recent advances relevant to industrial use. We bridge knowledge across scales: from fundamental reaction mechanisms and comparisons of noble, non‑noble, bimetallic, and alloy catalysts, to the engineering of scalable fixed‑bed, fluidized-bed, structured, process‑intensified, and hybrid reactors. Beyond catalysts and reactors, we also cover process intensification and optimization strategies, including dynamic operation, AI‑driven performance tuning, and multi‑scale integration, to translate concepts into industrial deployment.