Methanol is a valuable chemical energy carrier and C1 feedstock, with significant research efforts directed toward its production via CO2 hydrogenation. Here, we report a surfactant-free, non-aqueous synthesis of Cu–ZnO core–shell catalysts (Cu2O core and ZnO shell), featuring uniform morphology and high performance. This enables a better understanding of the Cu–ZnO synergy, providing insights into the formation of highly active and selective sites as well as catalyst stability. The optimal core–shell catalyst achieved 53% CO2 conversion and 84% methanol selectivity. Comprehensive characterization, including operando X-ray diffraction at 184–331 bar reactant pressure, was performed on both the core–shell material and a commercial Cu/ZnO/Al2O3 catalyst, before and after the reaction. The results revealed that the highly active state of the catalyst promotes the carbonation of ZnO, leading to the formation of ZnCO3 during the reaction. This is likely driven by the acidic reaction medium formed from the dissolution of CO2 in water under high conversion conditions. While ZnCO3 formation may contribute to catalyst deactivation, it could also offer a rigid structure that supports highly active and selective, dispersed Cu–Zn interactions.

Monolithic aerogels composed of crystalline nanoparticles enable photocatalysis in three dimensions, but they suffer from low mechanical stability and it is difficult to produce them with complex geometries. Here, an approach to control the geometry of the photocatalysts to optimize their photocatalytic performance by introducing carefully designed 3D printed polymeric scaffolds into the aerogel monoliths is reported. This allows to systematically study and improve fundamental parameters in gas phase photocatalysis, such as the gas flow through and the ultraviolet light penetration into the aerogel and to customize its geometric shape to a continuous gas flow reactor. Using photocatalytic methanol reforming as a model reaction, it is shown that the optimization of these parameters leads to an increase of the hydrogen production rate by a factor of three from 400 to 1200 µmol g⁻¹ h⁻¹. The rigid scaffolds also enhance the mechanical stability of the aerogels, lowering the number of rejects during synthesis and facilitating handling during operation. The combination of nanoparticle-based aerogels with 3D printed polymeric scaffolds opens up new opportunities to tailor the geometry of the photocatalysts for the photocatalytic reaction and for the reactor to maximize overall performance without necessarily changing the material composition.