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Applied Catalysis B, Environmental (v.62, #1-2)
Reduction of N2O by NH3 on polycrystalline copper and Cu(110): A combined XPS, FT-IRRAS and kinetics investigation by Isabelle Louis-Rose; Christophe Méthivier; Jacques C. Védrine; Claire-Marie Pradier (pp. 1-11).
Kinetics of N2O decomposition and catalytic reduction of N2O by NH3 in the presence or absence of oxygen have been studied on polycrystalline Cu planar chip (3cm×3cm×0.1cm) or Cu(110) single crystal, using catalytic test equipment, XPS and FT-IRRAS techniques. It has been shown that N2O decomposes on metallic Cu, but gives then Cu2O, which is detrimental to N2O decomposition. The presence of a reductant, such as NH3, allowed N2O to react leading to its catalytic reduction to N2; 500°C is the best temperature for catalytic reduction alone, i.e. with low additional self-decomposition of N2O or NH3. The presence of oxygen, in amount less than that of NH3, leads to more efficient NH3 oxidation, oxygen being observed to be more reactive than N2O on NH3. XPS results enabled to identify the active surface as metallic Cu and Cu3N for NH3 oxidation and NH2, NH, N adsorbed species as intermediates of the reaction. At room temperature, in the presence of N2O, O2 and NH3, FT-IRRAS allowed to show the formation of NH2 and NH species (bands at 1550 and 1440cm−1, respectively) and of two N2 δ− species (bands at 2170 and 2204cm−1), the latter one corresponding to adsorbed N2 δ− species close to adsorbed electron accepting O or OH species. This study demonstrated that N2O decomposed to N2 and O species during SCR reaction; it enabled to identify several adsorbed surface species (N, NH, NH2, N2 δ−), both by XPS after catalytic reaction at 500°C on the polycrystalline Cu chip and by IRRAS on Cu(110) single crystal in the presence of the reactants at room temperature. In addition, it was shown that N2 is a powerful IR probe to characterise the surrounding environment of surface sites that cannot be identified by any other way.
Keywords: N; 2; O decomposition; N; 2; O selective catalytic reduction by NH; 3; Effect of oxygen; XPS; FT-IRRAS characterisation; Cu chip; Cu(1; 1; 0)
A review of catalytic processes for the destruction of PCDD and PCDF from waste gases by Elisabetta Finocchio; Guido Busca; Maurizio Notaro (pp. 12-20).
The current literature concerning the catalytic destruction of dioxins and of related model compounds is reviewed. Several different catalyst formulations have been tested, but V-rich vanadia-tungsta-titania catalysts seem to be mostly applied and allow reducing the dioxins concentration well below the limits of 0.1ng TEQ/Nm3, as required by the EU directives. Other catalysts (in particular the noble metal-based ones) seem to be less efficient, due to deactivation effects and/or a considerable amount of polychlorinated by-products formation during oxidation activity. The coupled de-NO x and dioxin destruction systems compete with activated carbon adsorption for efficiency in PCDD/F removal from gases.
Keywords: Dioxins; PCDD/PCDF; Catalytic abatement of CVOC; Vanadia-tungsta-titania catalyst
Effect of surfactant microstructures on photocatalytic degradation of phenol and chlorophenols by D. Fabbri; A. Bianco Prevot; E. Pramauro (pp. 21-27).
The effect of hexadecyltrimethylammonium bromide (HTAB) on the photocatalytic degradation of phenol (Phe), 2,5-dichlorophenol (2,5-DCP) and 2,4,5-trichlorophenol (2,4,5-TCP) in the presence of aqueous TiO2 suspensions at pH ca. 5 was investigated using a laboratory photoreactor equipped with a medium-pressure mercury lamp. Inhibition of substrate decomposition was observed for phenol, both below and above the surfactant critical micellar concentration, whereas a more complex behaviour was exhibited by chlorophenols. It was found that adsorption of these compounds onto the surfactant-modified semiconductor particles facilitates their faster decomposition, but the competitive partition of substrates between adsorbed surfactant structures and micellar aggregates tends to limit the beneficial kinetic effects at higher amphiphile concentrations. The crucial influence of surfactant adsorption was clearly evidenced in some runs performed at pH 3. Relevant inhibition of chloride release from chlorophenols, observed in the presence of HTAB, indicates a higher persistence of reaction intermediates in the reaction media, suggesting the need for a careful investigation of surfactant effects on all the degradation steps of the process.
Keywords: Photocatalysis; Phenol; Chlorophenols; Surfactants; Microstructures
Photocatalytic reduction of chromium and oxidation of organics by polyoxometalates by E. Gkika; A. Troupis; A. Hiskia; E. Papaconstantinou (pp. 28-34).
The photocatalytic reduction of Cr(VI) to the less toxic Cr(III) is presented in the presence of the polyoxometalates (POM) PW12O403− or SiW12O404− as photocatalyst and an organic substrate (salicylic acid or propan-2-ol) as electron donor. Cr(VI), as dichromate, is reduced to Cr(III), according to the 6:1 stoichiometry of PW12O404− versus Cr2O72− indicated from experiments in the dark. Increase of POM or salicylic acid (SA) concentration accelerates, till a saturation value, both the reduction of metal and the oxidation of the organic, suggesting that these two conjugate reactions act synergistically. The photocatalytic action of POM is not so important in the case of highly concentrated solutions of organics that exhibit direct photochemical reduction of Cr(VI), i.e. propan-2-ol (i-prOH), while it becomes important at low concentrations of i-prOH, especially for organics that do not react directly photochemically with Cr(VI), such as SA. Increase of Cr(VI) concentration enhances consumption of SA and Cr(VI) till an optimum value, due to inner filter effect. The method is suitable for a range of chromium concentration from 5–100ppm achieving complete reduction of Cr(VI) to Cr(III) up to non-detected traces (>98%). The presence of oxygen does not influence the efficiency of SA and Cr(VI) consumption. In contrast to the semiconductor-based heterogeneous photocatalysis, the POM-based homogeneous process seems superior in the frame that: (i) it remains catalytic throughout illumination by providing more active sites and (ii) among the two POM used, the one that is more efficient in the degradation of the organic, that is PW12O403− compared to SiW12O404−, is also more efficient in reducing Cr(VI), due to a kinetic effect, and a compromise is not needed.
Keywords: Photocatalytic reduction; Chromium; Polyoxometallates
Kinetics of heterogeneously MgO-catalyzed transesterification by Tanguy F. Dossin; Marie-Françoise Reyniers; Guy B. Marin (pp. 35-45).
The transesterification of ethyl acetate with methanol over magnesium oxide as solid base catalyst was investigated. Intrinsic kinetic data have been obtained in a perfectly mixed slurry batch reactor. The influence of the temperature (283–323K) and the initial methanol to ethyl acetate molar ratio (M/E: from 0.1 to 10) was investigated over a broad ethyl acetate conversion range (1–95%). A kinetic model was developed based on a three-step ‘Eley–Rideal’ type of mechanism applied in liquid phase, describing the experimental data over the investigated range of experimental conditions. Transesterification reaction occurs between methanol adsorbed on a magnesium oxide free basic site and ethyl acetate from the liquid phase. Methanol adsorption is assumed to be rate-determining. Other models derived from other mechanisms were rejected based on statistical analysis, mechanistic considerations and physicochemical interpretation of the parameters. The calculation of activity coefficients accounting for non-ideality had to be incorporated in the parameter estimation procedure.
Keywords: Abbreviations; EtOAc; ethyl acetate; EtOH; ethanol; LHHW; Langmuir–Hinshelwood–Hougen–Watson; M/E; methanol to ethyl acetate; MeOAc; methyl acetate; MeOH; methanol; MgO; magnesium oxide; RSSQ; residual sum of squaresTransesterification; Kinetics; Elementary reactions; Solid base catalyst; Magnesium oxide
Catalytic behavior of potassium containing compounds for diesel soot combustion by Hongmei An; Paul J. McGinn (pp. 46-56).
Alkali doped oxides were synthesized and tested as catalysts for diesel soot combustion using a combinatorial method. It has been found that potassium shows better promotion of the catalytic activity than other alkali elements, and most of the potassium-rich oxides showed similar catalytic behaviors when catalysts and soot were mixed in a slurry. The influence of different mixing methods, including loose contact, tight contact and slurry (wet) mixing with different soot suspensions, on the catalytic behavior of some transition metal oxides, alkali metal carbonates and potassium-containing oxides were studied through thermogravimetry and XRD. The high activity of potassium-containing catalysts is found to be due to the intimate contact between soot and potassium cations caused by polar solvents. Potassium containing catalysts degraded after repeated thermal cycles due to the loss of potassium. It was also found that the addition of transition elements can inhibit the loss of potassium.
Keywords: Diesel soot combustion; Potassium catalysts; Transition metal oxides
Deactivation of a Pd/Al2O3 catalyst used in hydrodechlorination reactions: Influence of the nature of organochlorinated compound and hydrogen chloride by Elena López; Salvador Ordóñez; Fernando V. Díez (pp. 57-65).
The deactivation of a 0.5wt.% Pd on alumina catalyst used for the hydrodechlorination of tetrachloroethylene (TTCE), chlorobenzene (CBZ) and dichloromethane (DCM) in organic matrix in gas phase has been studied in this work. Experiments were carried out in a continuous fixed bed reactor, at a pressure range of 0.1–2MPa. It was found that the reactivity and stability of the catalyst increases as pressure increases. Different compounds present quite different deactivation patterns: fast initial deactivation followed by a plateau for DCM and CBZ, continuous moderate deactivation for TTCE.The effect of hydrogen chloride was studied by adding to the reactor feed different amounts of hydrogen chloride, working at 225–300°C.Fresh and used catalysts were characterised by nitrogen porosimetry, X-ray diffraction, transmission electronic microscopy, scanning electronic microscopy, thermogravimetry and temperature-programmed oxidation. Results indicate that carbonaceous deposits play a key role in the catalyst deactivation, being this phenomenon promoted by the presence of HCl.
Keywords: Tetrachloroethylene; Chlorobenzene; Dichloromethane; Hydrodechlorination; Pd catalyst; Catalyst deactivation; Effect hydrogen chloride
Total oxidation of volatile organic compounds by vanadium promoted palladium-titania catalysts: Comparison of aromatic and polyaromatic compounds by Tomas Garcia; Benjamin Solsona; Diego Cazorla-Amorós; Ángel Linares-Solano; Stuart H. Taylor (pp. 66-76).
Vanadium oxide, palladium oxide and mixed Pd/V-supported on titania catalysts have been prepared and tested in the total oxidation of volatile organic compounds (VOCs). A comparative study with two different aromatic VOCs (benzene and naphthalene) has been carried out. For benzene, the mixed Pd/V-catalysts presented the highest catalytic activity. However, whilst studies with benzene led to the formation of CO2 only, the total conversion of naphthalene to CO2 was not achieved throughout the full temperature range for naphthalene conversion. A naphthalene conversion to CO2 of 99% was obtained over Pd/TiO2, V/TiO2 and Pd/V/TiO2 catalysts at 275, 325 and 300°C, respectively. Therefore, the requirements for an effective benzene total oxidation catalyst cannot be readily extrapolated to larger polycyclic aromatic compounds, as in the naphthalene oxidation the most active catalyst from an environmental point of view is Pd supported on TiO2.
Keywords: VOCs; Benzene; Naphthalene; Catalytic oxidation; Palladium; Vanadium
Catalytic reduction of nitrate on Pt-Cu and Pd-Cu on active carbon using continuous reactor by N. Barrabés; J. Just; A. Dafinov; F. Medina; J.L.G. Fierro; J.E. Sueiras; P. Salagre; Y. Cesteros (pp. 77-85).
The increasing pollution of natural sources of drinking water encourages the development of new emerging technologies and processes for water remediation. This work deals with the study of catalytic reduction of contaminated waters containing nitrates (60ppm) in a continuous reactor working at room temperature and atmospheric pressure and using hydrogen as reducing agent. Optimal proportions of Pt-Cu and Pd-Cu in bimetallic catalysts on activated carbon, obtained by wetness impregnation, have been found. Besides, novel catalysts obtained from copper nanoparticles doped with Pd or Pt and supported on activated carbon, have also been studied. For all catalysts the Pt-Cu pair seems to be more selective in the transformation of the nitrates ions to nitrogen compared to Pd-Cu pair. Furthermore, considering the noble metal amount, the bimetallic nanosphere catalysts are more active (between 20 and 50) than the impregnated ones. The catalysts have been characterized by hydrogen chemisorption, BET, X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analysis. During the reaction, a considerable amount of the noble metal in its oxidised form has been detected. Based on this result an additional step to the generally accepted reaction mechanism of the nitrate reduction has been proposed.
Keywords: Continuous reactor; Nitrate reduction; Pd-Cu and Pt-Cu/AC catalysts; Activated carbon; Bimetallic catalysts; Copper nanoparticles
Zirconia: Selective oxidation catalyst for removal of tar and ammonia from biomass gasification gas by Sami J. Juutilainen; Pekka A. Simell; A. Outi I. Krause (pp. 86-92).
Catalysts containing zirconia and alumina were tested for their activity in the selective oxidation of tar and ammonia in biomass gasification gas. Their performance was compared with that of nickel and dolomite catalysts. Synthetic gasification gas with toluene as tar model compound was used as feed. In the presence of oxygen, zirconia and alumina-doped zirconia gave high toluene and ammonia conversions even below 600°C. They were the most active catalysts for toluene oxidation below 700°C and for ammonia oxidation below 650°C. At higher temperatures than these, the impregnated ZrO2/Al2O3 catalysts performed better: oxidation selectivity was improved and toluene and ammonia conversions were higher. The presence of both zirconia and alumina in the catalyst promoted toluene and ammonia conversions at low temperatures: zirconia enhanced the oxidation activity, while alumina improved the oxidation selectivity. The presence of H2S had little effect on the activity of alumina-doped zirconia.
Keywords: Selective catalytic oxidation; Zirconia; Tar; Ammonia; Gasification; Gas cleaning
Perovskite catalytic ozonation of pyruvic acid in water by F.J. Rivas; M. Carbajo; F.J. Beltrán; B. Acedo; O. Gimeno (pp. 93-103).
The catalytic ozonation of pyruvic acid in the presence of the perovskite LaTi0.15Cu0.85O3 has been carried out. Typical operating parameters like ozone inlet concentration, catalyst dosage, protons concentration (below 0.01M) and temperature (below 303K) exert a positive influence on the pyruvic acid depletion rate. Regarding the pyruvic acid concentration, a zero kinetic order holds for most of experiments. Under the conditions applied, the process is controlled by the chemical reaction. Acetic and oxalic acids are the only intermediates formed with a higher selectivity towards the former (above 90–95%). The similarities between experimental total organic carbon (TOC) and calculated from the contributions of remaining pyruvic acid and formed acetic and oxalic acids corroborate the previous statement. The activity of the catalyst is enhanced after the first usage. Thereafter, four consecutive reutilisations of the catalyst indicate the high stability of the solid. The process is acceptably simulated by a Langmuir–Hinshelwood kinetic expression derived from adsorption of ozone and pyruvic acid onto different active sites.
Keywords: Perovskite; Ozone; Pyruvic acid; Heterogeneous catalysis; Kinetics
Selective catalytic reduction of nitrogen oxides by ammonia on iron oxide catalysts by N. Apostolescu; B. Geiger; K. Hizbullah; M.T. Jan; S. Kureti; D. Reichert; F. Schott; W. Weisweiler (pp. 104-114).
In this study, new Fe2O3 based materials are developed for the selective catalytic reduction (SCR) of NO x by NH3 in diesel exhaust. As a result of the catalyst screening, performed in a synthetic model exhaust, ZrO2 is considered to be the most effective carrier for Fe2O3. The modification of the Fe2O3/ZrO2 system with tungsten leads to drastic increase of SCR performance as well as pronounced thermal stability. These results show that tungsten acts as bifunctional component. The highest catalytic activity is observed for ZrO2 that is coated with 1.4mol% Fe2O3 and 7.0mol% WO3 (1.4Fe/7.0W/Zr). By the use of this catalyst quantitative conversion of NO x is obtained between 285 and 430°C with selective formation of N2. Here, the turnover frequency of NO x per Fe atom is found to be 35×10−5s−1 that indicates a high catalytic performance. The SCR activity of the 1.4Fe/7.0W/Zr material is decreased in the presence of H2O and CO2, whereas it is increased by NO2.Temperature programmed reduction by H2 (HTPR) analyses show that the Fe sites of the 1.4Fe/7.0W/Zr catalyst are mainly in the form of crystalline Fe2O3, whereby relatively small oxide entities are also present. The strongly aggregated Fe2O3 species are associated with the presence of the promoter tungsten. Based upon stationary catalytic examinations as well as diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) studies we postulate an Eley Rideal type mechanism for SCR on 1.4Fe/7.0W/Zr catalyst. The mechanistic model includes a redox cycle of the active Fe sites. As first reaction step, we assume dissociative adsorption of NH3 that leads to partial reduction of the iron as well as to production of very reactive amide surface species. These amide intermediates are supposed to react with gaseous NO to form N2 and H2O. In the final step, the reduced Fe sites be regenerated by oxidation with O2. As a side reaction of SCR, imide species, originated from decomposition of amide, are oxidized by NO2 or O2 into NO.
Keywords: SCR; Diesel exhaust; NO; x; NH; 3; Fe; 2; O; 3; ZrO; 2; WO; 3; Reaction mechanism
Wet air oxidation of phenol at mild conditions with a Fe/activated carbon catalyst by A. Quintanilla; J.A. Casas; J.A. Zazo; A.F. Mohedano; J.J. Rodríguez (pp. 115-120).
A home-made Fe/activated carbon (Fe/AC) catalyst has been tested for the wet oxidation of phenol in a cocurrent down-flow fixed bed reactor at relatively mild conditions (100–127°C andPO2=8atm), initial pH of 3.5 and a wide range of spatial time values (20–320gCATh/gPh). Complete phenol conversion and 80% TOC removal were reached at 127°C and 320gCATh/gPh. The Fe/AC catalyst has also shown a convenient chemical stability in long-term experiments, Fe leaching being almost negligible. It has been proved that oxidation of phenol takes place on the catalyst surface via a heterogeneous mechanism, the contribution of homogeneous reaction being no significant. The oxidation intermediates have been identified, consisting of ring intermediates ( p-benzoquinone, p-hydroxybenzoic and traces of hydroquinone) that are further oxidized to short chain acids (mainly maleic, malonic, acetic and formic acids). The three last showed to be highly resistant to further oxidation, these being the responsible of the TOC remaining after complete removal of phenol.
Keywords: Catalytic wet oxidation; Fe/AC catalyst; Cocurrent down-flow fixed-bed
Washcoating method for Pd/γ-Al2O3 deposition on metallic foams by Leonardo Giani; Cinzia Cristiani; Gianpiero Groppi; Enrico Tronconi (pp. 121-131).
A method for coating open celled metal foams with a thin layer of Pd–Al2O3 was developed. The method makes use of a sol–gel of pseudobohemite as a precursor of γ-Al2O3 to fill the porous structure by percolation whilst the excess of material is flushed away with an air jet. The influence of solid content, acid content and ageing on the sol–gel rheological behaviour was studied to find a sol–gel dispersion with an appropriate viscosity whose deposition resulted in a 20μm thick coating layer. Foam samples of different nominal porosities (10, 20 and 40PPI) were coated with this method and activated with palladium using a wet impregnation procedure with loadings of 3% (w/w) palladium on the alumina.As an alternative approach, dry impregnation of γ-Al2O3 with palladium was performed and a slurry was prepared adding water and nitric acid. The slurry was deposited by percolation through the foam structure. The coating quality was evaluated with adhesion tests and the activity of coated foams was measured by performing catalytic oxidation of CO in a 9mm i.d. tubular reactor. Both methods produced highly active foams, resulting in light off temperatures between 175 and 250°C depending on CO concentration. Moreover, the mass transfer controlled regime was achieved in all runs independently of the coating method. Nevertheless, conversions reached when the sol–gel dispersion was deposited and activated via wet impregnation were higher than the ones obtained with the coating method based on slurry deposition of active powders, indicating that the sol–gel deposition resulted in more uniform coating.
Keywords: Metal foams; Catalyst supports; Coating procedures
TWC deactivation by lead: A study of the Rh/CeO2 system by C. Larese; M. López Granados; F. Cabello Galisteo; R. Mariscal; J.L.G. Fierro (pp. 132-143).
The effect of the incorporation of low amounts of Pb to a Rh/CeO2 catalyst on the typical reactions involved in Three Way Catalysts converters was investigated. The catalytic tests showed no deactivation for CO oxidation and NO reduction whereas for propylene oxidation the deactivation was evident and more intense with the increasing of Pb concentration. The interpretation of this behaviour is discussed on the basis of HREM combined with XEDS analysis, TPR and DRIFT spectroscopy of chemisorbed CO studies. The results provided clear evidence that Pb is not covering the Rh particles neither forming a new phase with Rh nor altering the dispersion of the Rh particles. They also suggest that a mixed oxide is formed in which lead cations are dissolved within the fluorite-like ceria structure. Thus, CeO2 support may act as sink of Pb preventing the formation of a Rh–Pb compound that explains why the CO oxidation and the NO reduction were only slightly affected. However, an electronic interaction between the Rh particles and the Pb-containing CeO2 support is evidenced by TPR and DRIFTS-CO chemisorption data: the Pb present in the Rh-CeO2 interphase as a result of the Pb dissolution in the ceria framework is proposed to be responsible for the electronic donation to Rh metal particles. The possibility that the electronic interaction and/or the modification of the oxygen storage capacity (OSC) of the ceria, both caused by the Pb, bring about the deactivation in the oxidation of propylene is also discussed.
Zinc oxide thin films prepared by thermal evaporation deposition and its photocatalytic activity by O.A. Fouad; A.A. Ismail; Z.I. Zaki; R.M. Mohamed (pp. 144-149).
Thin zinc oxide (ZnO) films have been grown on silicon substrates by thermal physical vapor deposition approach. X-ray diffraction (XRD) analyses reveal that the deposited films are polycrystalline ZnO phase. Atomic force microscopy images (AFM) show needle-like shape highly oriented ZnO crystals. Thin film thickness ranges from 10 to 80nm. X-ray photoelectron spectroscopy (XPS) results declare that the films compose mainly of Zn and O. Nevertheless, Si is not detected in the films and consequently no possibility of any silicide formation as is confirmed by XRD analysis. Photocatalytic decomposition of azo-reactive dye on ZnO films is tested. The results show that the dye decomposition efficiency increases with decreasing pH. Maximum photodecomposition, 99.6% is obtained at pH 2 with 10mg/l dye concentration.
Keywords: ZnO thin films; Vapor deposition; Azo-reactive dye; Photocatalytic activity
Solar-light-induced photocatalytic decomposition of two azo dyes on new TiO2 photocatalyst containing nitrogen by Beata Wawrzyniak; Antoni W. Morawski (pp. 150-158).
The photocatalytic decolourisation of two azo dyes—Reactive Red 198 and Direct Green 99—in an aqueous solution by the artificial visible light radiation was investigated. The industrial metatitanic acid (H2TiO3) obtained directly from the sulphate technology installation was N-doped and used as photocatalyst. H2TiO3 was calcinated at different temperatures, ranging from 300 to 500°C, for 4 or 20h, respectively, in an ammonia atmosphere. The UV–vis/DR spectra of the modified catalysts exhibited an additional maximum in the vis region ( λ≈476.8nm, EG=2.60eV for catalysts calcinated for 4h and λ≈479.5nm, EG=2.59eV for catalysts calcinated for 20h, which may be due to the presence of nitrogen in TiO2 particles. The chemical structure of the modified photocatalysts was investigated using FTIR/DRS spectroscopy and the presence of nitrogen was confirmed. A photocatalytic activity of the investigated catalysts was determined on the basis of a decomposition rate of azo dyes. The decomposition of Reactive Red 99 increased with increasing the calcination temperature of photocatalysts, whereas the activity of the prepared photocatalysts towards Direct Green 198 degradation was as follows: 300–20h<400–20h<500–20h<300–4h<400–4h<500–4h. Both, the calcination time and temperature had no influence on the amount of nitrogen-doped into TiO2 structure. The inversely proportional linear dependence between the decomposition rates of azo dyes and the intensity of the band attributed to the hydroxyl groups for both dissociated water and molecularly adsorbed water was observed. With increasing temperature of calcinations, the amount of the hydroxyl groups decreased, whereas the decomposition of azo dyes increased.
Keywords: Visible light active photocatalyst; The industrial precursor; Nitrogen-doped; Ammonia; Titanium dioxide; Azo dye; Reactive Red; Direct Green
Photocatalytic and sonolytic oxidation of acid orange 7 in aqueous solution by Theodora Velegraki; Ioannis Poulios; Magdalini Charalabaki; Nicolas Kalogerakis; Petros Samaras; Dionissios Mantzavinos (pp. 159-168).
The oxidation of 50mg/L azodye acid orange 7 (AO7) in water was investigated by means of photocatalysis in the presence of various semiconducting catalysts and ultrasound irradiation. The UVA-induced photocatalytic degradation over TiO2 anatase suspensions was found to increase with increasing catalyst concentration, decreasing solution pH, as well as in the presence of dissolved oxygen. The presence of 1,4-benzoquinone, sodium azide or sodium chloride in the reaction mixture decreased degradation due to the scavenging of radicals and other reactive moieties. Interestingly, addition of hydrogen peroxide at various concentrations from 21 to 1050mg/L also inhibited degradation. The sonochemical degradation of AO7 was found to increase with increasing frequency and decreasing temperature. Under similar treatment conditions, ultrasound irradiation resulted in higher conversion than photocatalysis; moreover, the sonochemically irradiated solution consistently contained low aliphatic intermediates, while the photocatalytically treated solution mainly consisted of aromatic intermediates as confirmed by GC–MS analysis. The acute toxicity to marine bacteria V. fischeri decreased following oxidation with either process. Furthermore, deep sonochemical treatment slightly improved the aerobic biodegradability as assessed by shake flask tests.
Keywords: Acid orange 7; Intermediates; Photocatalysis; Toxicity; TiO; 2; Ultrasound; Wastewater
Photocatalytic performance of Ru doped anatase mounted on silica for reduction of carbon dioxide by Natarajan Sasirekha; Sheikh John Sardhar Basha; Kannan Shanthi (pp. 169-180).
Ru doped anatase supported on silica was prepared by solid-state dispersion method and examined for the photocatalytic reduction of carbon dioxide in aqueous medium at ambient conditions. To assist in interpreting the photocatalytic behaviour of Ru-TiO2/SiO2, reference systems consisting of Ru doped TiO2 and TiO2 supported on SiO2 were also analyzed and the conditions were optimized. Ru/TiO2 photocatalysts with metal loadings of 0.1, 0.3, 0.5 and 1.0wt% were prepared by impregnation method and a series of TiO2/SiO2 catalysts with low TiO2 (1, 3, 5 and 10wt%) contents were prepared by solid-state dispersion method. The photocatalysts were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), UV–vis DRS, FT-IR and Raman spectroscopy. The results showed that TiO2 particles with Ru ions have higher photocatalytic activity than undoped TiO2 and the optimum Ru loading was found to be 0.5wt%. Nevertheless, the yield increased notably when TiO2 was supported on SiO2. This strong enhancement suggests that in 10wt% TiO2/SiO2 the efficiency of charge separation is strongly influenced through the presence of TiOSi bridging bonds. On the contrary, Ru-TiO2/SiO2 has no significant improvement in activity over TiO2/SiO2 except that it shows nearly quadruple times higher activity for the formation of methanol than Ru/TiO2. The difference in the photocatalytic activity is related to its physico-chemical properties.
Keywords: Ru/TiO; 2; Reduction of CO; 2; with H; 2; O; TiO; 2; /SiO; 2; Photocatalytic reduction; Hole scavenger