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.