Applied Catalysis B, Environmental (v.24, #1)
The comparative studies of titanium dioxide in gas-phase ethanol photocatalytic oxidation by the FTIR in situ method by D.V Kozlov; E.A Paukshtis; E.N Savinov (L7-L12).
Gas-phase ethanol photocatalytic oxidation on the series of TiO2 samples has been studied by the FTIR in situ method. The TiO2 samples were prepared by the usual method and they possessed similar physicochemical properties (porosity, specific area), but were found to have different photocatalytic activities. The acidity and concentration of the Lewis centers have been measured. The TiO2 photocatalytic activity has been found to correlate with the surface acidity, and the Ti3+ and carbonate surface concentrations.
Keywords: Photocatalysis; TiO2; FTIR; Surface acidity;
Photocatalytic degradation of 17-β-oestradiol on immobilised TiO2 by Heather M Coleman; Brian R Eggins; J.Anthony Byrne; Fiona L Palmer; Emma King (L1-L5).
Micro-molar concentrations of aqueous 17-β-oestradiol were 98% destroyed in 3.5 h by photocatalysis over the titanium dioxide powder immobilised on Ti-6Al-4V alloy. The concentration of oestradiol was determined by HPLC with fluorescence detection. The degradation kinetics were fitted to a Langmuir–Hinshelwood model with k(S) = 4.4 × 10−2 μmol dm−3 min−1 and K(S) = 0.347 dm3 μmol−1. The pseudo-first-order rate constant (1.57 × 10−2 min−1) was in line with the 50% degradation time of 40 min. The apparent quantum yield per electron was φ e′ = 0.41%. The effect of pH on the initial rate of degradation was similar to that reported for phenol.
Keywords: Titanium dioxide; Oestrogen; Photocatalysis; Water treatment;
Selective catalytic reduction of NO with ammonia over V2O5 doped TiO2 pillared clay catalysts by R.Q. Long; R.T. Yang (13-21).
A series of vanadia doped TiO2-pillared clay (TiO2-PILC) catalysts with various amount of vanadia were studied for selective catalytic reduction (SCR) of NO by ammonia in the presence of excess oxygen. It was found that the V2O5/TiO2-PILC catalysts were highly active for the SCR reaction. The catalysts showed a broad temperature window, and the maximum NO conversion was higher than that on V2O5/TiO2 catalyst and was the same as the commercial V2O5 + WO3/TiO2 catalyst. The V2O5/TiO2-PILC catalysts also had higher N2/N2O product selectivities as compared to V2O5 doped TiO2 catalysts. In addition, H2O + SO2 slightly increased the activities at high temperatures (>350°C) for the V2O5/TiO2-PILC catalysts. Addition of WO3 to V2O5 further increased the activities of the PILC catalysts. These results indicate that TiO2-PILC is a good support for vanadia catalysts for the SCR reaction. In situ FT–IR experiment indicated that both Brønsted acid sites and Lewis acid sites exist on the catalyst surface, but with a large proportion being Brønsted acid sites at low temperatures (e.g., 100°C). The reaction path for NO reduction by NH3 on the V2O5/TiO2-PILC is similar to that on V2O5/TiO2 catalyst, i.e., N2 originates from the reaction between gaseous NO and NH3 adspecies.
Keywords: Selective catalytic reduction; SCR of NO by NH3; TiO2-pillared clay; Vanadia doped TiO2-pillared clay;
Effect of ex situ treatments with SO2 on the activity of a low loading silver–alumina catalyst for the selective reduction of NO and NO2 by propene by F.C Meunier; J.R.H Ross (23-32).
A 1.2 wt.% Ag/γ-Al2O3 catalyst for the selective catalytic reduction of NO with propene (C3H6-SCR) was rapidly and permanently deactivated following the addition of 100 ppm of SO2 to the gas stream. DRIFTS studies performed on the deactivated silver–alumina material showed the formation of two different types of surface sulphate species. One of these surface species was a surface aluminium sulphate whereas the other corresponded to a sulphate associated with the silver phase. Treatment at higher temperatures in the deNO x feed did not regenerate the catalytic activity fully whereas reduction with H2 was able to do so by removing only the sulphate species associated with the silver phase. When NO2 was used as reactant, there was no need for a promoter for either the alumina or the sulphated alumina, both of those giving high conversions of the NO2 to N2 over a wide temperature window. The decrease in the SCR activity observed over the Ag/γ-Al2O3 upon sulphation is thought to be associated with a decrease of the activity for the oxidation of NO to ad-NO x species (x > 1) promoted by the silver. It is suggested that the reduction of ad-NO x species and NO2 by propene over the 1.2 wt.% Ag/γ-Al2O3 catalyst (plain or sulphated) mostly occurred on the alumina (clean or sulphated).
Keywords: Propene; NO; NO2; Sulphate; Silver; Alumina; DRIFTS;
Enhancement of the catalytic oxidation of hydrogen-lean chlorinated VOCs in the presence of hydrogen-supplying compounds by J.R. González-Velasco; A. Aranzabal; R. López-Fonseca; R. Ferret; J.A. González-Marcos (33-43).
The complete catalytic oxidation of trichloroethylene (TCE) over alumina-supported noble metal catalysts (Pt and Pd) and in the presence of hydrogen-rich compounds, i.e. water, hexane and toluene was evaluated. Experiments were performed at conditions of lean TCE concentration (around 1000 ppm) in air, between 250 and 550°C in a conventional fixed-bed reactor. Hexane and toluene were added to the feedstream in a concentration of around 1000 ppm and water concentration varied from 1000 to 15 000 ppm. TCE oxidation occurred faster in the presence of hexane and toluene over both catalysts. Over palladium catalysts, water did not alter catalytic activity, whereas over platinum catalysts water enhanced TCE oxidation at low temperatures (<400°C) but inhibited it at higher temperatures (>400°C). Selectivity to HCl was much improved by feeding water as a hydrogen-supplying reactant; 7500 ppm of water enhanced HCl outputs from 39.4 to 78.0% with Pd, and from 37.5 to 58.9% with Pt. Selectivities to C2Cl4, formed by chlorination of the feed, and Cl2 were greatly reduced. On the other hand water promoted complete oxidation of TCE to CO2, and thus reduced selectivity to CO. In the presence of hexane and toluene, formation of HCl was also enhanced. Hexane showed higher inhibition ability than toluene over both catalysts for the C2Cl4 and Cl2 formation. Unlike in the presence of water, selectivity to CO increased, as a consequence of partial oxidation of both hydrocarbons.
Keywords: Catalytic oxidation; Selectivity; Trichloroethylene; Noble metal catalysts; VOC;
Catalytic activity of chromium spinels in SCR of NO with NH3 by J. Słoczyński; J. Janas; T. Machej; J. Rynkowski; J. Stoch (45-60).
Series of chromium spinels MCr2O4 (M = Mg, Zn, Fe, Co, Ni, Cu, Mn) were tested in the selective catalytic reduction (SCR) of NO with NH3. Catalytic activity and selectivity to N2O depend on the nature of the divalent metal M. The studies by TPR, XPS and chemical analysis lead to the conclusion that the surface layer of all chromium spinels decomposes to simple oxide species containing M2+/M3+ and Cr3+/Cr6+ redox systems. An increase in the oxidation potential of the redox system is accompanied by a decrease in the selectivity to N2O in agreement with the mechanism of the reaction proposed by the Niiyma group.
Keywords: Selective catalytic reduction of NO with NH3; Transition metal chromites;