The in-situ infrared reaction system is a device that uses a Fourier transform infrared spectrometer to evaluate the performance of catalysts or materials in multiple environments, and to perform in-situ evaluation of the performance of catalysts/materials under various conditions. It can conveniently track and identify intermediate states and products in the reaction, providing direct evidence for the investigation of the reaction mechanism of catalytic reaction systems. In situ infrared diffuse reflection is mainly used for characterization of gas-solid catalysis and research on catalytic reactions, such as identification of hydroxyl groups on catalyst surfaces, study of species adsorption states on catalyst surfaces, and characterization of catalyst surface acidity and alkalinity. This reaction system can be applied to vacuum to high-pressure environments at temperatures up to 500 ° C (under vacuum), making it an ideal choice for studying multiphase catalysis, gas-solid interactions, photochemical reactions, and oxidation mechanisms. At present, it has been applied to infrared spectroscopy research on gas-solid interface reactions in the fields of photocatalytic degradation of gas-phase organic compounds and thermal catalysis (CO+H2, CO2+H2).