Microprocess engineering is an alternative approach to design reactors for CO2 methanation, which are used in power-to-gas applications. Microreactors offer advantages, e.g., in terms of heat removal. In the present work, design criteria evolved from transport phenomena are applied to derive preliminary reactor dimensions. The developed 1D model is used for parametric studies and reveals heat transport as limiting factor. More detailed 3D models confirm the results and demonstrate the effect of the metal matrix on heat transport. For further optimization a multi-stage reactor design is proposed.