Use of TiO2/Cr-MCM-41 molecular sieve irradiated with visible light for the degradation of thiophene in the gas phase

Photocatalytic processes using TiO2 and UV radiation to eliminate pollutants are not yet suitable for industrial facilities due to their high consumption of energy. Transition metals incorporated onto mesoporous MCM-41 molecular sieves impregnated with TiO2 constitute an alternative that allows the use of solar light. In this study, Cr-substituted MCM-41 were synthesized (Si/Cr = 100, 50 and ∞) and impregnated with TiO2 (10 and 20 wt.%). Raman results showed the formation of anatase. Electronic spectroscopy and EPR exposed the formation of trivalent chromium after impregnation with TiO2, which is related to a Cr–TiO2 interaction. The synthesized photocatalysts, as well as TiO2 P25, were tested in the degradation of thiophene in gaseous phase. A test with UV lamp showed 100% of conversion for 20%TiO2/Cr-MCM-41(100) and exceeded the activity of TiO2 P25, probably due to the higher dispersion of TiO2 on the surface of the molecular sieve. During tests using visible light and 20%TiO2/Cr-MCM-41(50) higher conversions than those of 20%TiO2/Cr-MCM-41(100) and TiO2 P25 were observed. These results indicate that chromium concentration is a key factor influencing the photocatalytic activity under visible light.