This work presents a comparative study toward the development of efficient microreactors based on three-dimensional (3D)-printed structures. Thus, the study evaluates the influence of the metal substrate geometry on the performance of structured catalysts for the CO2 methanation reaction. For this purpose, the 0.5%Ru–15%Ni/MgAl2O4 catalyst is washcoated over two different micromonolithic metal substrates: a conventional parallel channel honeycomb structure and a novel 3D-printed structure with a complex gyroid geometry. The effect of metal substrate geometry is analyzed for several CO2 sources including ideal flue gas atmospheres and the presence of residual CH4 and CO in the flue gas, as well as simulated biogas sources. The advantages of the gyroid 3D complex geometries over the honeycomb structures are shown for all evaluated conditions, providing in the best-case scenario a 14% improvement in CO2 conversion. Moreover, this contribution shows that systematically tailoring geometrical features of structured catalysts becomes an effective strategy to achieve improved catalyst performances independent of the flue gas composition. By enhancing the transport processes and the gas–catalyst interactions, the employed gyroid 3D metal substrates enable boosted CO2 conversions and greater CH4 selectivity within diffusion-controlled regimes.

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For the purpose of this research, single track details were manufactured in the shape of thin walls with a length of 100 mm and a height of 80 mm. Two welding speeds were chosen for this experiment–13.3 mm/s and 20.0 mm/s corresponding to the following heat inputs: 120 J/mm and 80 J/mm. The gas metal arc welding (GMAW) method was used for the build-up of the specimens in the cold arc pulse mode. The structure of the specimens was studied using X-ray diffraction (XRD) analysis carried out with CuKα radiation with a wavelength of 1.5406 Ǻ, optical microscopy, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). Furthermore, the Vickers hardness of the samples was determined using a ZwickRoell DuraScan 10/20 G5 unit at a force of 1 N. A preferred crystallographic orientation towards the (200) plane was observed in all cases, however a vastly textured structure was observed with inclusions of peaks in the (111), (220), and (311) crystallographic planes. The full width at half maximum (FWHM) of samples taken from different stages of build-up was calculated indicating an increase of the dislocation density at the more advanced stages of specimen growth. Despite that an increase of the hardness was observed towards the top of both specimens. This is attributed to the change in the structure of the αAl + Si formations from an irregular one at the bottom of the specimens, towards a fibrous one at the top. The results are discussed in regard to the optimization of the build-up process during wire arc additive manufacturing (WAAM).