Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
Applied Catalysis B, Environmental (v.55, #2)
Photocatalytic degradation of azo dyes by organic-capped anatase TiO2 nanocrystals immobilized onto substrates by R. Comparelli; E. Fanizza; M.L. Curri; P.D. Cozzoli; G. Mascolo; R. Passino; A. Agostiano (pp. 81-91).
The UV-induced photocatalytic degradation of two azo dyes, Methyl Red and Methyl Orange, has been carried out in aqueous media in the presence of oleic acid (OLEA)- and tri- n-octylphosphine oxide (TOPO)-capped anatase TiO2 nanocrystal powders (mean particle size: 6nm) deposited onto a quartz substrate. The progress of photodegradation was followed by combining UV–vis absorption measurements with HPLC–MS analysis. The abatement efficiency for the two organic compounds was compared with that obtained with commercial TiO2 P25 Degussa by evaluating a few significant variables, such as the dye chemical structure, pH of the solution, and catalyst surface status. Identification of several by-products by HPLC–MS analysis has allowed to propose a reasonable degradation pathway for both target molecules. Significantly, although all titania catalysts were effective in removing both parent dyes and their related derivatives, the degradation rate by the OLEA-capped TiO2 nanocrystals was double as that obtained with both its TOPO-capped analogous and TiO2 P25 Degussa. It is suggested that efficient catalysis strictly depends on microscopic mechanisms that occur at the catalyst surface, basically involving specific dye adsorption and local density of terminalOH moieties.
Keywords: Organic-capped nanocrystals; TiO; 2; UV-induced photocatalysis; Azo dyes
Partial oxidation of CH4 to synthesis gas using Ni-catalyst/Au|YSZ|Ag electrochemical membrane reactor by Katsuomi Takehira; Junpei Shimomura; Satoshi Hamakawa; Tetsuya Shishido; Tomonori Kawabata; Ken Takaki (pp. 93-103).
Spc-Ni/MgAl ( spc-: solid phase crystallization method) catalyst has been prepared from Mg–Al hydrotalcite-like compounds containing Ni at the Mg site as the precursors and successfully used as a catalyst on an electrochemical membrane reactor for partial oxidation of CH4 at 1173K. The precursors based on[Mg2+A1−xl3+(OH)2x]x+(CO3−)x· mH2O, in which a ratio of Mg/Al varied and a part of Mg2+ ions were replaced by Ni2+ ions, were prepared by co-precipitation method, thermally decomposed, calcined and reduced to spc-Ni/MgAl catalyst. The electrochemical reactor, using yttria-stabilized zirconia (YSZ) as a solid electrolyte, has been employed as an oxygen permeable membrane reactor. The Ni catalyst coupled with Au paste was used as the catalyst-anode, while Ag paste was used as the cathode of the electrochemical cell. The reaction was carried out over the catalyst-anode film under oxygen pumping through the YSZ, and the results were compared with those obtained by various supported Ni catalysts prepared by impregnation ( imp-) method. Spc-Ni/MgAl catalysts showed higher activity than imp-Ni catalysts and the best composition of metals in the catalyst was spc-Ni0.5/Mg2.5Al. This catalyst showed the CH4 conversion following the thermodynamic equilibrium between 1023 and 1173K, while the other catalysts of different compositions or imp-Ni catalysts showed a clear decrease in the CH4 conversion with decreasing temperature. Moreover, spc-Ni0.5/Mg2.5Al catalyst showed stable activity during the reaction for 40h. It is concluded that the high and stable activity for the partial oxidation of CH4 is due to highly dispersed and stable Ni metal particles formed on spc-Ni0.5/Mg2.5Al catalyst film.
Keywords: CH; 4; oxidation; Synthesis gas; Ni-catalyst; Oxygen permeable membrane; YSZ; Electrochemical reactor
Enhancement of photocatalytic activity of TiO2 by adsorbed aluminium(III) by Maria Isabel Franch; José Peral; Xavier Domènech; Russell F. Howe; José A. Ayllón (pp. 105-113).
The photocatalytic activity of TiO2 (Degussa P-25) in the mineralization of maleic acid in aqueous solution at pH = 3 is greatly enhanced by the previous adsorption of aluminium(III) on the catalyst surface. The nature of the intermediates detected during maleic acid degradation is also affected by the presence of Al(III). The observed differences can be related to an oxygen reactivity enhancement. The effect of aluminium(III) in the maleic acid adsorption over the TiO2 surface has also been investigated by using the ATR–FT-IR technique. The UV–vis diffuse reflectance spectra of the catalyst shows a red shift due to aluminium adsorption. At neutral pH, the positive effect of adsorbed Al(III) is not observed.
Keywords: Photocatalysis; Aluminium(III); Maleic acid degradation
Nanosized CeO2-supported metal oxide catalysts for catalytic reduction of SO2 with CO as a reducing agent by Chun-Liang Chen; Hung-Shan Weng (pp. 115-122).
Nanosized CeO2 was synthesized by sol–gel method and used as the support to prepare six kinds of supported metal oxide catalysts by incipient wetness impregnation method. These catalysts were investigated for the catalytic reduction of SO2 to elemental sulfur with CO as a reducing agent. Experimental results indicate that Cr2O3/nano-CeO2 was the most active catalyst. Using this catalyst, a kinetic study was performed on the reduction of SO2 and the optimal feed ratio of CO/SO2 was found to be 2.5/1, and low concentrations of SO2 and CO provide a high SO2 conversion and sulfur yield. We also found that the catalyst presulfided by CO + SO2 exhibits a higher performance than those pretreated with CO, SO2 or He. The discrepancy in the stability and activity resulted in the pretreatment has been rationally explained. The temperature-programmed desorption patterns of SO2 and CO illustrate that Cr2O3/nano-CeO2 can adsorb and desorb SO2 and CO more easily than can other catalysts. These results may properly explain why Cr2O3/nano-CeO2 has a higher activity for the reduction of SO2.
Keywords: Reduction of SO; 2; Conversion of SO; 2; Yield of elemental sulfur; Nanoparticle of CeO; 2; Supported Cr; 2; O; 3; catalyst
Effect of charge trapping species of cupric ions on the photocatalytic oxidation of resorcinol by S.W. Lam; K. Chiang; T.M. Lim; R. Amal; G.K.-C. Low (pp. 123-132).
The photocatalytic oxidation of resorcinol, a potent endocrine disrupting chemical, in oxygenated aqueous suspensions of pure and cupric ions modified Degussa P25 titanium dioxide has been investigated at pH 3.0 ± 0.5. The initial rate of photocatalytic oxidation of resorcinol increased until an optimum dissolved cupric ions concentration was reached at 1.04mM. At the optimum concentration of cupric ions, the initial rate of photocatalytic mineralisation and degradation of resorcinol was improved by 400%. The observed beneficial effect of cupric ions on the initial rate of resorcinol oxidation could be attributed to the formation of complex and its participation in the photoredox cyclic reaction.Two of the initial oxidation intermediates detected were 1,2,3-trihydroxybenzene and 1,2,4-trihydroxybenzene. These intermediates were formed via hydroxylation of the aromatic ring of resorcinol. Evidences have revealed that 1,2,4-trihydroxybenzene interacted strongly with cupric ions forming copper(II)-trihydroxybenzoate complexes that possessed good adsorption onto TiO2 surface. These dual-effects help to draw the metal ions closer to the photocatalyst surface and subsequently trigger the electron trapping mechanism by cupric ions. As a result, this improved the charge carriers’ separation. Furthermore, in the presence of oxygen, reoxidation of photoreduced cupric ions occurred and this eliminated the possibility of copper photodeposition, while inducing a photoredox cyclic reaction to regenerate copper species that may potentially act as co-catalyst for the oxidation of 1,2,4-trihydroxybenzene. In contrast, no obvious complex formation was seen between 1,2,3-trihydroxybenzene and cupric ions. This pointed to an intriguing finding which indicates that the positioning of functional group on benzene ring influences the role of cupric ions.
Keywords: Photocatalytic; Titanium dioxide; Resorcinol; Dissolved cupric ions
Effect of preparation method on activity and stability of LaMnO3 and LaCoO3 catalysts for the flameless combustion of methane by E. Campagnoli; A. Tavares; L. Fabbrini; I. Rossetti; Yu.A. Dubitsky; A. Zaopo; L. Forni (pp. 133-139).
A set of LaMnO3 and LaCoO3 catalysts was prepared through different synthesis procedures. The selected techniques included the sol–gel method, flame hydrolysis from aqueous solution, complexation through EDTA and solid-state reaction. The last was accomplished through reactive grinding by ball-milling either in a vibration mill or in a planetary mill. EDTA complexation was applied for LaCoO3 only and did not improve significantly catalyst activity or stability, with respect to other techniques. Ball-milling never allowed obtaining a pure perovskitic phase, at least under the most energetic grinding conditions permitted by our apparatus. The highest activity for the catalytic flameless combustion of methane was obtained with the sol–gel prepared samples, though thermal resistance revealed insufficient for high temperature applications. A bit lower activity, but coupled with good thermal stability was obtained with the samples prepared through flame hydrolysis.
Keywords: Perovskite-like catalysts; Preparation method; Methane; Catalytic flameless combustion
Degradation of hydrophobic organic pollutants by titania pillared fluorine mica as a substrate specific photocatalyst by Ken-ichi Shimizu; Hitoshi Murayama; Ayumi Nagai; Aiko Shimada; Tsuyoshi Hatamachi; Tatsuya Kodama; Yoshie Kitayama (pp. 141-148).
The photocatalytic degradation of a highly hydrophobic and stable organic pollutant, γ-hexachlorocyclohexane (γ-HCH), was performed in aqueous suspended mixture of TiO2-containing catalysts. Unlike most of the organic pollutants, γ-HCH was very stable under the conventional photocatalytic condition with TiO2 (P25). Among various catalysts, TiO2 pillared fluorine mica (Ti-mica) showed highest activity. The effect of preparation method of Ti-mica was also examined. The hydrothermal treatment increased the crystallinity of anatase pillar of Ti-mica, though the treatment at high temperature resulted in a decrease in the surface area and an increase in the pore size. Consequently, Ti-mica treated at lowest temperature (373K), Ti-mica-373, was the most effective photocatalyst. The catalytic activity of TiO2 and Ti-mica-373 was compared for 13 kinds of organic compounds with various hydrophobicity. Ti-mica-373 showed 5–66 times higher rate than TiO2 for the degradation of hydrophobic organic pollutants (α, β, γ and δ-HCH, trans- and cis-chlordane, DDE, DDD and DDT) of low concentration (10ppb). In contrast, TiO2 showed higher rate than Ti-mica-373 for the degradations of less hydrophobic compounds (benzonitrile, chlorobenzene, 4-chloroacetophenone and 4-chloronitrobenzene). Over TiO2-mica-373, organic compounds with higher log POW value, i.e. more hydrophobic compounds, were decomposed with higher rate. A positive effect of the fluorine mica support is suggested to be caused by the interaction of hydrophobic reactant with the hydrophobic interlayer surface of pillared-clay.
Keywords: Photocatalysis; Degradation; TiO; 2; pillared clays; Persistent organic pollutants
Selective catalytic reduction of nitric oxide with ammonia on Fe-ZSM-5 catalysts prepared by different methods by Gérard Delahay; David Valade; Ariel Guzmán-Vargas; Bernard Coq (pp. 149-155).
Fe-ZSM-5 catalysts, prepared by different methods, have been characterized by TPR and XRD and tested in the NO-SCR by NH3. The sublimation method leads to the most active catalysts. Nevertheless the preparation starting from Fe(acac)3, which is a preparation easy to implement from an industrial point of view, seems to be a very attractive alternative way.On the most active catalyst, Fe(0.83)subZSM-5, prepared starting from FeCl3, a study of the mechanism was undertaken. In the initial step of the SCR reaction, the oxidation of NO in NO2, the re-oxidation of FeII species in the active iron oxo species is the slow phase.
Keywords: Nitric oxide; Reduction; Iron; Zeolite ZSM-5; NH; 3