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.

Efficient mass transfer and light utilization are essential for high photocatalytic production rates. Here, we present a hierarchical three-dimensional (3D)-printed aerogel photocatalyst that unites both aspects by taking inspiration from the light scattering in clouds during photochemical processes and from mass transfer in plants during photosynthesis. We combine the geometric freedom of additive manufacturing with computational fluid dynamics and Monte Carlo simulations to guide the implementation of a self-supported aerogel in a continuous gas flow reactor. Here, 3D microstructuring reduced the pressure drop of a monolithic aerogel by 5 orders of magnitude without compromising the gas permeation and the light-harvesting efficiency of the intrinsic nanoporous material. We match the macroscopic thickness with the ultraviolet (UV) light penetration depth and show that the 3D aerogel of 1.1 mm thickness improves photocatalytic hydrogen production rates relative to the nanoparticle powder by a factor of five from 1.3 to 6.6 μmol g^-1h^-1for TiO₂and from 30.0 to 141.8 μmol g^-1h^-1for Au/TiO₂, respectively. Ultimately, our approach can be applied for other nanomaterials to boost the overall performance of a variety of photochemical processes and reactor designs.