H2S photodegradation by TiO2/M-MCM-41 (M = Cr or Ce): Deactivation and by-product generation under UV-A and visible light

M-MCM-41 molecular sieves (M = Ce or Cr) were prepared by a hydrothermal method and impregnated with TiO2. The materials were characterized by XRD, N2 adsorption–desorption, DRS and XPS. Their potential application to photooxidize H2S in a wet gas stream was tested in a continuous flow reactor operating at a flow rate of 110 mL min−1 at 50% relative humidity and using 30 ppmv of the pollutant. The photocatalytic efficiency using UV-A and visible light was compared to the activity of TiO2/MCM-41 without heteroatoms incorporated into the MCM-41 structure. It was found that the incorporation of Ce did not improve the performance of TiO2/MCM-41, but Cr-containing samples presented higher initial efficiency and were able to photooxidize H2S without formation of SO2 as a by-product, in contrast to the other prepared samples and to Degussa P-25 TiO2. Moreover, no other gaseous by-product was detected. The isomorphic incorporation of Cr into the structure of MCM-41 followed by TiO2 incorporation produced photocatalysts that presented good adsorption capacity and were much more active under visible light than under UV-light. This performance represents an important advantage for solar applications. Their photoactivity depended on the concentration of chromium; the highest efficiency was attained with samples with a Si/Cr ratio of 50. Finally, deactivation was observed as a consequence of sulfate accumulation on the surface of the catalyst and reduction of Cr6+.