Silvia Suárez

Influence of NH3 and NO oxidation on the SCR reaction mechanism on copper/nickel and vanadium oxide catalysts supported on alumina and titania

The influence of ammonia and nitric oxide oxidation on the selective catalytic reduction (SCR) of NO by ammonia with copper/nickel and vanadium oxide catalysts, supported on titania or alumina have been investigated, paying special attention to N2O formation. In the SCR reaction, the VTi catalyst had a higher activity than VAl at low temperatures, while the CuNiAl catalyst had a higher activity than CuNiTi. A linear relationship between the reaction rate of ammonia oxidation and the initial reduction temperature of the catalysts obtained by H-2-TPR showed that the formation rate of NH species in copper/nickel catalysts would be higher than in vanadia catalysts. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) showed that copper/nickel catalysts presented ammonia coordinated on Lewis acid sites, whereas ammonium ion adsorbed on Bronsted acid sites dominated on vanadia catalysts. The NO oxidation experiments revealed that copper/nickel catalysts had an increase of the NO2 and N2O concentrations with the temperature. NO could be adsorbed on copper/nickel catalysts and the NO2 intermediate species could play an important role in the reaction mechanism. It was suggested that the presence of adsorbed NO2 species could be related to the N2O formation

Alumina- and titania-based monolithic catalysts for low temperature selective catalytic reduction of nitrogen oxides

Abstract The selective catalytic reduction of NO+NO2 (NOx) at low temperature (180–230°C) with ammonia has been investigated with copper-nickel and vanadium oxides supported on titania and alumina monoliths. The influence of the operating temperature, as well as NH3/NOx and NO/NO2 inlet ratios has been studied. High NOx conversions were obtained at operating conditions similar to those used in industrial scale units with all the catalysts. Reaction temperature, ammonia and nitrogen dioxide inlet concentration increased the N2O formation with the copper-nickel catalysts, while no increase was observed with the vanadium catalysts. The vanadium-titania catalyst exhibited the highest DeNOx activity, with no detectable ammonia slip and a low N2O formation when NH3/NOx inlet ratio was kept below 0.8. TPR results of this catalyst with NO/NH3/O2, NO2/NH3/O2 and NO/NO2/NH3/O2 feed mixtures indicated that the presence of NO2 as the only nitrogen oxide increases the quantity of adsorbed species, which seem to be responsible for N2O formation. When NO was also present, N2O formation was not observed.

Photocatalysis for Continuous Air Purification in Wastewater Treatment Plants: From Lab to Reality

The photocatalytic efficiency of TiO(2)-SiMgO(x) plates to oxidize H(2)S was first evaluated in a flat laboratory reactor with 50 mL min(-1) synthetic air containing 100 ppm H(2)S in the presence of humidity. The use of the photocatalyst-adsorbent hybrid material enhanced the photocatalytic activity in terms of pollutant conversion, selectivity, and catalyst lifetime compared to previous H(2)S tests with pure TiO(2) because total H(2)S elimination was maintained for more than 30 operating hours with SO(2) appearing in the outlet as reaction product only after 18 h. Subsequently, the hybrid material was successfully tested in a photoreactor prototype to treat real polluted air in a wastewater treatment plant. For this purpose, a new tubular photocatalytic reactor that may use solar radiation in combination with artificial radiation was designed; the lamp was turned on when solar UV-A irradiance was below 20 W m(-2), which was observed to be the minimum value to ensure 100% conversion. The efficient distribution of the opaque photocatalyst inside the tubular reactor was achieved by using especially designed star-shaped structures. These structures were employed for the arrangement of groups of eight TiO(2)-SiMgO(x) plates in easy-to-handle channelled units obtaining an adequate flow regime without shading. The prototype continuously removed during one month and under real conditions the H(2)S contained in a 1 L min(-1) air current with a variable inlet concentration in the range of tens of ppmv without release of SO(2).

Solar Photocatalysis for the Elimination of Trichloroethylene in the Gas Phase

In the present work, we have studied the photocatalytic degradation of trichloroethylene (TCE) under sunlight illumination with the aim of determining the feasibility of using this technology for gas purification. For these experiments, a continuous flow reactor was employed. This system is basically constituted by a Pyrex glass tube located in the focus of a compound parabolic collector made of anodized aluminum. Raschig rings of borosilicate glass coated with TiO 2 and randomly packed within the reactor tube were used as photocatalyts. Results obtained using sunlight illumination indicate that this continuous flow solar reactor can achieve complete TCE degradation. Experimentally, it is found that for moderate conversions, the TCE degradation rate increases linearly with solar irradiance, but a dependence of lower order is observed when removal of the pollutant is almost complete. On the other hand, photonic efficiency decreases linearly with solar irradiance, and it is higher when the molar flow fed to the photoreactor increases. In contrast, the selectivity toward the different partial degradation products (dichloroacetyl chloride, COCl 2 , etc.) is basically insensitive to solar irradiance.

Preparation of Photocatalytic Coatings Adapted to the Elimination of Airborne Pollutants: Influence of the Substrate on the Degradation Efficiency

Abstract Immobilized TiO2 is required for most photocatalytic applications, but obtaining the adequate mechanical and chemical resistance without compromising activity can be very challenging. In order to gain further information about the effect of the substrate on photoactivity, the influence of their physicochemical properties on the efficiency of TiO2 coating for photocatalytic air purification has been studied in this work. With this aim, two different chemicals, hydrogen sulfide (H2S) and trichloroethylene (TCE), were selected as model pollutants to determine the behavior of photoactive layers under diverse experimental conditions. Hydrogen sulfide is a widespread compound, which not only causes nuisance due to its unpleasant odor, perceptible at very low concentrations (>0.5 ppbv), but is also responsible for corrosion in devices and materials. In this work, the efficiency for H2S photocatalytic degradation was compared for TiO2 coatings deposited on different UVtransparent substrates: borosilicate glass and two organic polymers, polyethylene terephthalate (PET) and cellulose acetate (CA). In addition, TiO2 was deposited on plates made of either borosilicate glass, or natural magnesium silicates, and the performance of these immobilized photocatalysts was determined for the elimination of trichloroethylene (TCE), as a model pollutant. Comparison of the activity of TiO2 deposited on this ceramic support, with that of TiO2 deposited on glass can provide valuable information about the influence of the substrate porosity on the photocatalytic efficiency. Results presented indicate that TiO2 on sepiolite can be regarded as a hybrid photocatalyst, which combines adsorptive and photocatalytic properties.