No abstract

M-MCM-41 molecular sieves (M = Ce or Cr) were prepared by a hydrothermal method and impregnated with TiO 2 . The materials were characterized by XRD, N 2 adsorption-desorption, DRS and XPS. Their potential application to photooxidize H 2 S 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 ppm v of the pollutant. The photocatalytic efficiency using UV-A and visible-light was compared to the activity of TiO 2 /MCM-41 without heteroatoms incorporated into the MCM-41 structure. It was found that the incorporation of Ce did not improve the performance of TiO 2 /MCM-41, but Cr-containing samples presented higher initial efficiency and were able to photooxidize H 2 S without formation of SO 2 as a by-product, in contrast to the other prepared samples and to Degussa P-25 TiO 2 . Moreover, no other gaseous by-product was detected. The isomorphic incorporation of Cr into the structure of MCM-41 followed by TiO 2 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 Cr 6+ .

No abstract

Photocatalytic oxidation of the sulfur-containing compounds, trimethylene sulfide (C 3 H 6 S), propylene sulfide (C 3 H 6 S), thiophene (C 4 H 4 S), and methyl disulfide (C 2 H 6 S 2 ), was carried out using an annular plug flow reactor with TiO 2 in a supported form. Formation of products and byproducts was monitored in real time using a mass spectrometry online system. Mineralization of the sulfur-containing compounds was confirmed by mass balance of CO 2 and SO 4 2-. Dilute contaminated atmospheres of trimethylene sulfide and propylene sulfide were completely mineralized. For thiophene and methyl disulfide, however, partial oxidation was observed, generating sulfur dioxide (SO 2 ) and sulfur oxide (SO) as byproducts, which were confirmed by parent ion MS/MS spectra as well as by chemical ionization. Sensory analysis showed that for trimethylene sulfide and propylene sulfide, odor intensity after TiO 2 /UV treatment was below the olfactive threshold limit of the panel.

a b s t r a c tA novel versatile tubular reactor that may use both types of radiation, solar and/or artificial, and different types of suspended or immobilized photocatalysts is proposed. The photocatalytic reactor was evaluated for air treatment at laboratory scale and semi-pilot-plant scale. UV-A transparent immobilized photocatalysts were employed, which allowed an efficient use of radiation. Two different types of photocatalytic modules were tested: (a) TiO 2 -coated PET monoliths and (b) TiO 2 -coated glass slides, arranged in monolith-like units with the help of especially designed star-shaped polygonal structures. Both types of units were easy to handle and assured the adequate distribution of the photocatalyst inside the tubular reactor. The efficiency of the photocatalytic system with both solar and artificial radiation to oxidize the H 2 S contained in an air stream was demonstrated at the laboratory roof and in the treatment of real air of a wastewater treatment plant located in Madrid (Spain). As a consequence of the chemical nature of the pollutant, the photocatalytic activity decayed over time due to the accumulation of sulfate on the surface, but easy regeneration of the exhausted photocatalyst was achieved by washing with water.