Heterogeneous photocatalysis runs in two worlds, gas-solid and liquid-solid, and they demand different reactors. Choosing by system rather than by convenience is the first step toward data that means anything.
The classic suspension: catalyst powder in solvent, light through the wall, stirring for transport. Advantages: simple, well-mixed, easy sampling. Constraints: light scatters and attenuates in the slurry, so photon delivery is statistical rather than uniform; product separation from catalyst is a standing chore; and gas reactants must dissolve before reacting, adding a transfer step.
Vapor or gas flows over an immobilized catalyst bed under illumination. Advantages: every photon reaches the catalyst without scattering losses, products leave promptly (protecting reactive intermediates), and continuous operation is natural. Constraints: heat management without a liquid bath, immobilized catalyst must not detach or deactivate fast, and the reactor must be sealed against dilution by leaks, air ingress changes chemistry silently.
Liquid systems transport reactants by convection and diffusion through a thick medium, often limited by gas solubility. Gas systems deliver reactants at diffusion rates orders of magnitude faster, but residence time is short, so flow rate, bed depth and reactor volume become the levers of conversion.
Synthesis in solvent, degradation of dissolved species and slurry-friendly catalysts: liquid-solid. Gas-phase conversion, selective partial oxidation where liquid residence would over-react products, and continuous processing: gas-solid. When in doubt, follow the chemistry's native phase, not the lab's habit.
Perfectlight builds both: gas-phase systems and liquid-phase photoreactors; see solutions.
