Effect of the Cr6+ concentration in Cr-incorporated TiO2-loaded MCM-41 catalysts for visible light photocatalysis

All the TiO2/Cr-MCM-41 catalysts deactivate gradually under visible light due to the reduction of Cr6+ in the catalysts. TPR and temperature program oxidation (TPO) results clearly indicated that the average oxidation state of chromium in TiO2/Cr-MCM-41 (Si/Cr = 20) was +2 after 23 h of photoreaction. The reduced chromium in the photocatalyst can be completely reoxidized by heating the catalyst at 450 °C for 3 h.