We initiated our research by developing a reactor assembly tailored to evaluating catalysts for hightemperature light-driven processes, particularly relevant for light-assisted carbon dioxide reduction. This assembly features a heated stainless steel tank with a quartz window for irradiation, which can house glass microchannel photoreactors. A transparent silicon oil was employed to ensure efficient and uniform heat transfer between the tank and the reactor. The reflective properties of stainless steel, combined with the high refractive index of the oil and quartz, optimize photon utilization and confinement within the reactor unit. Moreover, the oil-filled tank offers versatility, accommodating various reactors, resulting in a highly modular system (Figure ) with broad applicability. Our investigation primarily focused on commercially available microchannel photoreactors, well-suited for continuous-flow reactions within our experimental framework. These reactors were filled with an immobilized catalyst, uniformly coated onto glass beads (Figure , Supplementary Information), creating a packed-bed system. This configuration facilitated a large irradiation area and ensured reproducible packing, enhancing the reliability of our experimental setup.