Synthetic Chemistry in Flow: From Photolysis & Homogeneous Photocatalysis to Heterogeneous Photocatalysis

Abstract

Photocatalytic synthesis of value‐added chemicals has gained increasing attention in recent years owing to its versatility in driving many important reactions under ambient conditions. Selective hydrogenation, oxidation, coupling, and halogenation with a high conversion of the reactants have been realized using designed photocatalysts in batch reactors with small volumes at a laboratory scale; however, scaling‐up remains a critical challenge due to inefficient utilization of incident light and active sites of the photocatalysts, resulting in poor catalytic performance that hinders its practical applications. Flow systems are considered one of the solutions for practical applications of light‐driven reactions and have experienced great success in photolytic and homogeneous photocatalysis, yet their applications in heterogeneous photocatalysis are still under development. In this perspective, we have summarized recent progress in photolytic and photocatalytic synthetic chemistry performed in flow systems from the view of reactor design with a special focus on heterogeneous photocatalysis. The advantages and limitations of different flow systems, as well as some practical considerations of design strategies are discussed.

Heterogeneous Organocatalysts for Light-Driven Reactions in Continuous Flow

“…Generally, defects and doping are detrimental to the material acting as trap states and accelerate the recombination of the charges; however, catalysis can sometimes benefit from this morphological modification, even though the reasons are not well understood [39]. Semiconductors with a wide bandgap, such as TiO 2 (3.2 eV), are of great interest because of their strong activity during photocatalytic reactions; however, this large bandgap requires irradiation with UV light, where absorption in the visible region is more important [40][41][42][43][44]. This can limit their application, but fortunately, several modification techniques were, hence, developed to tune light absorption.…”