Operando Infrared (IR) Coupled to Steady-State Isotopic Transient Kinetic Analysis (SSITKA) for Photocatalysis: Reactivity and Mechanistic Studies

This paper reports the coupling of operando infrared (IR) and steady-state isotopic transient kinetic analysis (SSITKA) for air purification studies from volatile organic campounds (VOCs) by photocatalysis. Methanol photo-oxidation has been used as a model reaction. A new photocatalyst (TiO2-L) has been studied and compared to the reference material TiO2-P25. We show that turnover frequency (TOF) values are not really available in heterogeneous photocatalysis where the number and/or efficiency of active sites can vary from one TiO2 material to another and from one experimental setup to another. The influence of methanol concentration and reaction temperature on photocatalytic activity and on selectivity was also investigated. TiO2-L is as active as TiO2-P25 at low methanol concentration and is more selective at high methanol concentrations. SSITKA clarified the role of the surface formate species in the reaction mechanism. Most of these formate species are spectators and are not the main intermediates in alcohol photo-oxidation. A graduation was found in the efficiency of active sites on photocatalyst surfaces.