Product desorption limitations in selective photocatalytic oxidation

Qualitative Approaches Towards Useful Photocatalytic Materials

The long-standing crusade searching for efficient photocatalytic materials has resulted in a vast landscape of promising photocatalysts, as reflected by the number of reviews reported in the last decade. Virtually all of these reviews have focused on quantitative approaches aiming at developing an understanding of the underlying mechanisms behind photocatalytic behavior and the parameters that influence structure–function correlation. Less attention has been paid, however, to qualitative measures around the development and assessment of photocatalysts. These measures will contribute toward narrowing the range of potential photocatalytic materials for widespread applications. The current report provides a critical perspective over some of the main factors affecting the assessment of photocatalytic materials as a code of good practice. A case of study is also provided, where this qualitative analysis is applied to one of the most prolific materials of the last-decade, disorder-engineered, black titanium dioxide (TiO₂).

Cl2 Production by Photocatalytic Oxidation of HCl over TiO2

We studied the photocatalytic aerobic oxidation of HCl over TiO₂ for producing Cl₂ . Steady-state Cl₂ production rates were determined with a photocatalytic fixed-bed gas-phase reactor equipped with UV light-emitting diodes (LEDs) using iodometric titration as online analytics. We found stable Cl₂ production rates of up to 16 mmol h^-1  m^-2 for commercial anatase TiO₂ Hombikat UV100. The rate increased linearly with temperature from 21 to 140 °C, indicating the acceleration of the limiting desorption rate of the coupled product water. Comparing different TiO₂ polymorphs revealed that anatase possesses higher activity than rutile. The adsorption of HCl was monitored in situ by IR spectroscopy. The IR spectra indicated that HCl chemisorption chlorinates the surface of TiO₂ under the reaction conditions, suggesting it to be the first step of the reaction mechanism. High stability opens up the opportunity of developing a promising photocatalytic process of HCl recycling at lower temperatures suitable for reaching full conversion.