Intensification strategies for improving the performance of photocatalytic processes: A review

Green and efficient technologies are one of the biggest challenges in Chemical Engineering. Photocatalysis has been reported as one of the most promising eco-friendly technologies, allowing it to work at milder operating conditions than the conventional processes when using cost-effective light sources for the photonic activation instead of thermal activation. Numerous studies have focused on heterogeneous photocatalysis for several applications, such as air and water purification, organic synthesis, and hydrogen production. Although some of these processes can be found industrially implemented, they are mainly related to water and wastewater treatment. Sustainable processes imply high productivities with reduced costs, requiring high selectivity and kinetic rates, mainly in synthesizing fine chemicals and fuels via photocatalysis. These parameters are deeply linked to mass and photon transfer resistance, which have triggered much research in the process intensification field to overcome these drawbacks. In this way, process intensification strategies have been proposed in the open literature to increase yield and selectivity values towards more sustainable processes from the industrial point of view. Nevertheless, there is still a lack of feasible information on photocatalytic processes at the pilot or industrial scale for other applications rather than aqueous streams treatment. This review aims to systematize novel approaches based on multicomponent hybrid systems and innovative photoreactor design (singles units) for enhanced photocatalytic processes, focusing on the respective advantages and limitations of the application field. For some applications, a comparison between different process intensification methods is presented. Thus, this work can be a helpful tool for the development of new strategies for emerging sustainable and more efficient photocatalytic processes. Moreover, challenges and future perspectives are also addressed.