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Applied Catalysis B, Environmental (v.72, #3-4)
A new combination of a membrane and a photocatalytic reactor for the depollution of turbid water by K. Azrague; P. Aimar; F. Benoit-Marquié; M.T. Maurette (pp. 197-204).
This paper describes the combination of a dialysis membrane and a photocatalytic reactor into an original membrane photoreactor (MPR) to mineralize organic compounds contained in artificial turbid waters which are obtained by using natural clay named bentonite. Various systems have been described in the literature, combining photocatalysis with pressure-driven membrane techniques, such as nanofiltration (NF) and ultrafiltration (UF), but these systems can lead to membrane fouling. Only the combination of photocatalysis and membrane distillation avoids this problem, but it needs energy to reach pervaporation phenomena. The MPR system presented here works at ambient temperature, with the membrane used as a barrier for particles and to extract the organic compounds from the turbid water without transmembrane pressure. Thus, we were able to separate the polluted turbid water from the photoreactor compartment and to separate TiO2 continuously from the treated water. The photocatalytic reaction and dialysis were studied separately before the MPR process was developed. A model pollutant, 2,4-dihydroxybenzoic acid (2,4-DHBA), was mineralized from turbid waters by photocatalysis. By means of the membrane, the TiO2 remained in the photoreactor compartment without filtration and bentonite was kept away from the photoreactor.A mathematical model, based on diffusion through the membrane, with zero-order reaction in the reactor, is in good agreement with the experimental data.
Keywords: Photocatalytic degradation; Membrane contactor; Water treatment; Turbid water; Organic pollutants
Development of Fe2O3-CeO2-TiO2/γ-Al2O3 as catalyst for catalytic wet air oxidation of methyl orange azo dye under room condition by Yan Liu; Dezhi Sun (pp. 205-211).
In order to develop a catalyst with high activity and stability for catalytic wet air oxidation (CWAO) process at room temperature and atmospheric pressure, we prepared Fe2O3-CeO2-TiO2/γ-Al2O3 by consecutive impregnation, and determined its properties using BET, SEM, XRF, XPS and chemical analysis techniques. The degradation of an azo dye, methyl orange, in CWAO process with Fe2O3-CeO2-TiO2/γ-Al2O3 used as catalyst at room temperature and atmospheric pressure was also investigated, and the results show that the catalyst has an excellent catalytic activity in treating synthetic wastewater containing 500mg/L methyl orange, and 98.09% of color and 96.08% of total organic carbon (TOC) can be removed in 2.5h. The degradation pathway of methyl orange was analyzed by UV–vis and FT-IR spectra. The result of leaching tests shows the catalyst has an excellent stability with negligible leaching ions, and the leaching of Ce is effectively controlled by adding Ti, because Ce and Ti in the catalyst take the form of compound oxides, and the deactivation of the catalyst in successive runs is caused by the adsorption of intermediates on the surface and coverage of the active sites. The catalytic activity of the deactivated catalyst can be generally restored by rinsing it in hydrochloric acid followed by calcination.
Keywords: Catalytic wet air oxidation; Azo dye; Wastewater treatment; Room temperature; Atmospheric pressure
Laboratory deactivation testing for the stability of FCC CO combustion promoters by Lin Luo; Darrell Rainer; Jorge A. Gonzalez (pp. 212-217).
Realistic lab deactivation facilitates the development of low NOx, CO combustion promoters for fluid catalytic cracking (FCC) applications. Cyclic deactivation, which provides a close simulation of the FCC operation, can address many possibilities for the deactivation of CO combustion promoters. Here we present our results using a combination of cyclic deactivation and a coke combustion test to predict additive performance after deactivation. By using this newly developed method, CO combustion promoters with exceptional performance were identified. These novel materials feature CO reduction performance similar to that of Pt-based promoters while still offering significant NOx reduction relative to Pt. Examples are also given using a more traditional hydrothermal deactivation approach.
Keywords: Fluid catalytic cracking; FCC; FCC regenerator; FCC additive evaluation; Additive deactivation; Additive testingAbbreviations; FCC; fluid catalytic cracking; CD; cyclic deactivation; AATU; advanced additive testing unit
Solvent nature effect in preparation of perovskites by flame-pyrolysis by G.L. Chiarello; I. Rossetti; L. Forni; P. Lopinto; G. Migliavacca (pp. 218-226).
The effect of a series of carboxylic acids (C2–C8), as solvents for the preparation by flame spray pyrolysis of LaCoO3 catalyst for the flameless combustion of methane, has been investigated. Acetic acid showed to be unsatisfactory from several points of view: low phase purity of the catalyst, higher amount of unburnt carbonaceous residua, lower catalytic activity and low thermal stability. By increasing the carbon chain length of the solvent, the consequent increase of flame temperature led to an increase of crystal phase purity and of particle size and to a decrease of specific surface area of the catalyst. Catalytic activity showed only marginally affected by the last parameter, phase purity seeming more important. Thermal resistance showed directly related to flame temperature, i.e. to the combustion enthalpy of the solvent, but a relatively high amount of residual organic matter can negatively affect this property.
Keywords: Perovskites; Flame spray pyrolysis; Methane catalytic flameless combustion
Solvent nature effect in preparation of perovskites by flame pyrolysis by G.L. Chiarello; I. Rossetti; L. Forni; P. Lopinto; G. Migliavacca (pp. 227-232).
The effect of either pure alcohols or alcohols+propionic acid mixtures as solvents for the preparation by flame pyrolysis of a standard LaCoO3 catalyst, to be employed for the catalytic flameless combustion of methane, has been investigated. All the catalysts proved very active for the mentioned reaction. Low-MW pure alcohols showed however less suitable than alcohols-propionic acid mixtures, leading to lower perovskite phase purity, less particle size homogeneity and lower specific surface area. The high volatility of the solvent seems to be the major cause, together with the improper behaviour of nitrates (forced by solubility reasons) as perovskite metals precursors. However, the addition of propionic acid to the alcohols allowed to use the acetates as precursors and hence to obtain high perovskitic phase purity, high SSA and uniform particle size. Moreover, the increase of combustion enthalpy of the solvent, through the addition of higher-MW alcohols, leading to progressively higher flame temperature, strongly improved the thermal resistance of the catalyst, without lowering catalytic performance.
Keywords: Perovskites; Flame spray pyrolysis; Methane catalytic flameless combustion
Water-induced bulk Ba(NO3)2 formation from NO2 exposed thermally aged BaO/Al2O3 by Do Heui Kim; Ja Hun Kwak; János Szanyi; Sarah D. Burton; Charles H.F. Peden (pp. 233-239).
Phase changes in high temperature treated (>900°C) 8 or 20wt% BaO supported on γ-Al2O3 model lean NO x trap (LNT) catalysts, induced by NO2 and/or H2O adsorption, were investigated with powder X-ray diffraction (XRD), solid state27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, and NO2 temperature programmed desorption (TPD) experiments. After calcination in dry air at 1000°C, the XRD and solid state27Al MAS NMR results confirm that stable surface BaO and bulk BaAl2O4 phases are formed for 8 and 20wt% BaO/Al2O3, respectively. Following NO2 adsorption over these thermally treated samples, some evidence for nanosized Ba(NO3)2 particles are observed in the XRD results, although this may represent a minority phase. However, when water was added to the thermally aged samples after NO2 exposure, the formation of bulk crystalline Ba(NO3)2 particles was observed in both samples. Solid state27Al MAS NMR is shown to be a good technique for identifying the various Al species present in the materials during the processes studied here. NO2 TPD results demonstrate a significant loss of uptake for the 20wt% model catalysts upon thermal treatment. However, the described phase transformations upon subsequent water treatment gave rise to the partial recovery of NO x uptake, demonstrating that such a water treatment of thermally aged catalysts can provide a potential method to regenerate LNT materials.
Keywords: NO; x; storage; Barium aluminate; Barium nitrate; XRD; Solid state; 27; Al MAS NMR; NO; 2; TPD
Low-temperature H2-SCR of NO on a novel Pt/MgO-CeO2 catalyst by Costas N. Costa; Angelos M. Efstathiou (pp. 240-252).
The selective catalytic reduction of NO by H2 under strongly oxidizing conditions (H2-SCR) in the low-temperature range of 100–200°C has been studied over Pt supported on a series of metal oxides (e.g., La2O3, MgO, Y2O3, CaO, CeO2, TiO2, SiO2 and MgO-CeO2). The Pt/MgO and Pt/CeO2 solids showed the best catalytic behavior with respect to N2 yield and the widest temperature window of operation compared with the other single metal oxide-supported Pt solids. An optimum 50wt% MgO-50wt% CeO2 support composition and 0.3wt% Pt loading (in the 0.1–2.0wt% range) were found in terms of specific reaction rate of N2 production (molsN2/gcats). High NO conversions (70–95%) and N2 selectivities (80–85%) were also obtained in the 100–200°C range at a GHSV of 80,000h−1 with the lowest 0.1wt% Pt loading and using a feed stream of 0.25vol% NO, 1vol% H2, 5vol% O2 and He as balance gas. Addition of 5vol% H2O in the latter feed stream had a positive influence on the catalytic performance and practically no effect on the stability of the 0.1wt% Pt/MgO-CeO2 during 24h on reaction stream. Moreover, the latter catalytic system exhibited a high stability in the presence of 25–40ppm SO2 in the feed stream following a given support pretreatment. N2 selectivity values in the 80–85% range were obtained over the 0.1wt% Pt/MgO-CeO2 catalyst in the 100–200°C range in the presence of water and SO2 in the feed stream. The above-mentioned results led to the obtainment of patents for the commercial exploitation of Pt/MgO-CeO2 catalyst towards a new NOx control technology in the low-temperature range of 100–200°C using H2 as reducing agent. Temperature-programmed desorption (TPD) of NO, and transient titration of the adsorbed surface intermediate NOx species with H2 experiments, following reaction, have revealed important information towards the understanding of basic mechanistic issues of the present catalytic system (e.g., surface coverage, number and location of active NOx intermediate species, NOx spillover).
Keywords: Lean de-NO; x; H; 2; -SCR; NO reduction; NO TPD; Supported-Pt; Transient kinetics
WO3–TiO2 monolithic catalysts for high temperature SCR of NO by NH3: Influence of preparation method on structural and physico-chemical properties, activity and durability by Motonobu Kobayashi; Katsunori Miyoshi (pp. 253-261).
The WO3–TiO2 catalysts with different WO3 loadings prepared by the coprecipitation method were investigated in comparison with those prepared by the conventional impregnation method for the activity and durability in the high temperature SCR of NO by NH3 and the structural and physico-chemical properties which were characterized by BET and XRD measurements, IR, Raman and XPS spectroscopies. The catalyst prepared by coprecipitation, as compared with that prepared by impregnation, was found to exhibit a higher SCR activity at high temperatures and also to possess a larger surface area, higher Brønsted acidity and larger monolayer capacity of the support with WO3. Increasing the WO3 loading of the catalysts enhances the SCR activity and simultaneously increases the Brønsted acidity. The observed improvement of SCR activity for the catalyst prepared by coprecipitation is mainly attributed to the higher Brønsted acidity and the presence of the more highly dispersed WO3 species which is suggested by the larger monolayer capacity of ca. 13μmol(W)/m2 and no crystalline WO3 on TiO2 detected with XRD at the high WO3 loading up to 40wt.%. The catalyst with 20wt.% WO3, as compared with that prepared by impregnation, was found to exhibit a better thermal durability at high temperatures from 550 to 600°C. The better durability is attributed to that the reduction of the surface area and the formation and subsequent growth of crystalline WO3 upon aging are more remarkably inhibited.
Keywords: The high temperature SCR of NO by NH; 3; Durability; WO; 3; –TiO; 2; The thermal stability; Coprecipitation; Acidity; Gas turbine exhaust
Preparation of highly dispersed PEM fuel cell catalysts using electroless deposition methods by K.D. Beard; M.T. Schaal; J.W. Van Zee; J.R. Monnier (pp. 262-271).
A methodology for the electroless deposition (ED) of PtCl62− using dimethylamine borane (DMAB) on a Rh-seeded carbon support has been developed for electrochemical and fuel cell applications. This procedure required seeding the carbon with a Rh-precursor catalyst via wet impregnation prior to the exposure of an aqueous ED bath containing PtCl62−, DMAB, and sodium citrate (complexing/stabilizing agent). Kinetic parameters that affect the extent and rate of PtCl62− deposition include concentrations of PtCl62−, DMAB, and sodium citrate as well as pH and concentrations of Rh seed sites. A linear relationship between rate and extent of PtCl62− deposition and DMAB and Rh concentrations was found while the citrate concentration had little effect on rate and a modest effect on extent. Lastly, extent of PtCl62− deposition showed a maximum with respect to pH. Characterization of the Rh-seeded, carbon support by transmission electron microscopy (TEM) shows that the Rh particle diameters remain constant at 33–43Å as the Rh weight loading increases from 0.4% to 2.2% to 4.4%. Further, after deposition of similar loadings of Pt, TEM analysis shows Pt particle diameters decrease with increasing Rh loading, since equal amounts of Pt were deposited on greater numbers of Rh seed particles. This pattern suggests a shell-core geometry, where Pt is deposited more or less uniformly around a Rh core.
Keywords: Electroless deposition; Platinum; Rhodium; Bimetallic catalysts
Reactivation of sulphated Pt/Al2O3 catalysts by reductive treatment in the simultaneous oxidation of CO and C3H6 by F. Cabello Galisteo; R. Mariscal; M. López Granados; M.D. Zafra Poves; J.L.G. Fierro; V. Kröger; R.L. Keiski (pp. 272-281).
A Pt/Al2O3 catalyst prepared by incipient wetness impregnation was used as a diesel oxidation model catalyst and tested in the simultaneous total oxidation of CO and C3H6. Sulphur incorporation by wet impregnation results in deactivation of the Pt/Al2O3 catalyst in both oxidation reactions. Characterization of the catalysts by evolved gas analysis by mass spectrometry (EGA-MS), X-ray diffraction (XRD), isotherm of adsorbed nitrogen, X-ray photoelectron spectroscopy (XPS), infrared spectroscopy of probe molecules (pyridine and carbon monoxide) and finally temperature-programmed surface reaction (O2-TPSR of chemisorbed CO) demonstrated that the formation of aluminium sulphate modifies the acidic properties of the support and the electronic properties of the platinum particles. Thus, new Brønsted acid sites are formed and, moreover, the capacity of the Pt particles to chemisorb CO and O2, the latter as strongly chemisorbed O species, is seriously deteriorated. The alteration of the electronic properties of the particles (they become electronically deficient) is related to the modification of the acidic properties of the support. Treatment of the deactivated catalysts by a reductive treatment at 873K resulted in the removal of the sulphur due to decomposition of the aluminium sulphate. Thus, the original acidic properties of the support and the electronic properties of the Pt particles were largely recovered and a high degree of catalytic reactivation was achieved.
Keywords: Diesel oxidation catalyst; Deactivation; Aluminium sulphate; Platinum
The removal of dichloromethane from atmospheric pressure air streams using plasma-assisted catalysis by Anna E. Wallis; J.C. Whitehead; Kui Zhang (pp. 282-288).
Plasma-assisted catalysis was used for the destruction of ∼500ppm of dichloromethane, CH2Cl2 (DCM), in gas streams of air using a non-thermal, atmospheric pressure plasma utilising a dielectric packed bed. The combination of plasma and catalyst gave improved destruction of DCM. Eight catalysts which including alumina, TiO2 and various zeolites were investigated with the finding that alumina in a one-stage reactor configuration and TiO2 and HZSM-5 in two-stage configurations gave the best DCM destructions. The sodium zeolites are capable of reducing by ∼50% the unwanted NO x by-products, formed by plasma processing in air. The nature of the catalyst is important in terms of the destruction efficiency, end-product selectivity and NO x reduction.
Keywords: Dichloromethane; Non-thermal plasma; Catalysis; Alumina; Titanium dioxide; Zeolites
Design of new systems for transfer hydrogenolysis of polychlorinated aromatics with 2-propanol using a Raney nickel catalyst by Sergei Zinovyev; Andrei Shelepchikov; Pietro Tundo (pp. 289-298).
A multipurpose study deals with the transfer hydrogenolysis of 1,3,5-trichlorobenzene to benzene in the 2-propanol–Raney nickel system in the presence of KOH. At 70°C, no reaction occurs without KOH or with weaker bases, e.g. amines or poorly soluble inorganic bases; however saturated KOH as well as water over 1% suppress the reaction rate, presumably due to the competitive adsorption of these species on the catalyst. The catalytic activity also drops with time because of the deposition of the solid KCl on the catalyst but can be recovered at washing the catalyst with water. The deactivation by KCl can be mitigated with the addition of promoters, e.g. quaternary ammonium salts (Aliquat 336, CTAC) or trioctylamine. Aliquat 336 also promotes hydrodechlorination in the hydrothermal system using a 10% solution of 2-propanol in water, Raney nickel and potassium carbonate as base at 150–200°C and 10–20bar. Under these conditions, hexachlorobenzene was also selectively dechlorinated to benzene.
Keywords: Hydrogen transfer; Dechlorination; 2-Propanol; Raney nickel; Subcritical water
Comparison of the activity of Ru and Pt catalysts for the oxidation of carbon by NO2 by V. Tschamber; M. Jeguirim; K. Villani; J. Martens; P. Ehrburger (pp. 299-303).
The role of two catalysts Pt/Al2O3 and Ru/NaY on the oxidation of carbon by NO2 was investigated in the temperature range 300–400°C. In the case of Pt/Al2O3 no significant catalytic effect on the carbon oxidation rate is observed although decomposition of NO2 takes place on the noble metal and leads to the formation of NO. This result suggests that the amount of the oxygen atoms transferred from the metallic surface sites to the carbon surface to form C(O) complex is negligible. In contrast, in presence of Ru/NaY the oxidation rate of carbon by NO2 is markedly increased. Hence, a significant part of the formed O through catalytic decomposition of NO2 on Ru surface sites is transferred to the carbon surface leading to a larger amount of C(O) complexes on the carbon surface. Thus, the ruthenium surface is a generator of active oxygen species that are spilled over on the carbon surface at 350°C.
Keywords: Carbon oxidation; Platinum ruthenium catalysts; NO; 2; Reaction mechanism
Gliding arc plasma assisted photocatalytic degradation of anthraquinonic acid green 25 in solution with TiO2 by M.R. Ghezzar; F. Abdelmalek; M. Belhadj; N. Benderdouche; A. Addou (pp. 304-313).
Anthraquinonic acid green 25 (AG 25) removal was investigated by plasmachemistry using non-thermal gliding arc at atmospheric pressure. The gaseous species formed in the discharge, and especially OH radicals, induce strong oxidizing effects in the target solution. The removal of the dye was carried out in the absence and presence of TiO2 as photocatalyst. The decolourization of AG 25 was followed by UV–vis spectrometry (at 643nm), while the degradation was followed by COD measurements. The effects of operating variables such as initial concentration of AG 25 and catalyst concentration were investigated. Experiments were carried out to optimise the amount of TiO2. The results showed that maximum degradation was attained for 2gL−1 TiO2 concentration. At this optimum concentration, the dye (80μM) was totally decolourized within 15min of plasma-treatment time, and 93% removal of initial COD was attained after a 180-min plasma-treatment time. In the absence of catalyst, colour removal was 46% after 15min, while COD abatement reached 84% after 180min. The extent of degradation decreased with initial concentration and the time required for complete degradation increased. In all cases, the plasma-treated samples in the presence or absence of catalyst were found to follow pseudo-first order reaction kinetics. The TiO2-mediated plasmachemical process showed potential application for the treatment of dye solutions, resulting in the mineralization of the dye confirmed by sulfate ion formation.
Keywords: Anthraquinonic dye; Degradation; Gliding arc; Plasmacatalysis; TiO; 2
Size dependent photocatalytic activity of hydrothermally crystallized titania nanoparticles on poorly adsorbing phenol in absence and presence of fluoride ion by Paola Calza; Ezio Pelizzetti; Károly Mogyorósi; Robert Kun; Imre Dékány (pp. 314-321).
The photocatalytic degradation of phenol has been performed by adopting nanosized titanium dioxide, prepared with the sol–gel method, both in presence and absence of fluoride ions. Several catalyst treatments, that is hydrothermal heat treatment and calcination, have been applied in order to increase the crystallinity of the particles. A close relationship was found between the rate of phenol disappearance and the particle size, with an efficiency that becomes maximum when the combination of large particle size (7.8nm) and surficial sites covered by fluoride is fulfilled. Intermediates profiles have been also evaluated, in order to verify if the surficial process occurring in the diverse materials still remains the same. It is accomplished in the case of the fluorinated titania, where both the rate of disappearance and the intermediates formation closely resemble those seen on Degussa P25, while a different formation ratio between catechol and hydroquinone was observed in the case of naked titania.
Keywords: Photocatalysis; Sol–gel method; Titanium dioxide; Size dependence
Preparation and structural characterization of Co/Al2O3 catalysts for the ozonation of pyruvic acid by P.M. Álvarez; F.J. Beltrán; J.P. Pocostales; F.J. Masa (pp. 322-330).
A series of Co/Al2O3 catalysts were prepared by the incipient wetness impregnation method using γ-Al2O3 support and (CH3COO)2Co·4H2O solutions, followed by calcination at 500–800°C. Characterization of catalysts was accomplished by several techniques such as thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), physisorption of nitrogen, mercury and helium-based pycnometries, Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and pH of zero charge (PZC). Impregnation of support produced a moderate decrease of its surface area and pore volume and also led to minor changes of its PZC. Depending on preparation conditions (i.e., calcination atmosphere and temperature and metal loading), one or more of the following Co-containing compounds were identified: CoO, Co3O4 and CoAl2O4. The support and prepared Co/Al2O3 catalysts were tested to catalyze the ozonation of aqueous pyruvic acid at pH 2.5. Pyruvic acid was shown refractory towards single ozonation but the use of γ-Al2O3 and Co/Al2O3 catalysts resulted in 56–96% pyruvic acid conversion and 41–78% decrease in DOC after 2h of ozonation of phosphate-buffered solutions. In the absence of the buffer, conversion rate was enhanced likely as a result of pH increase during the course of the process thus giving rise to the indirect way of ozonation through hydroxyl radicals. Acetic acid was found as the main by-product of pyruvic acid ozonation. Depending on the catalyst used, yield of acetic acid varied from 32 to 49%, values noticeably lower that that obtained from the control non-catalytic ozonation experiment (73%). Differences in catalytic activity amongst the various Co/Al2O3 catalysts investigated were attributed to the different Co active phases deposited on the γ-Al2O3 surface. The following sequence of increasing activity can be inferred from experimental results: CoO, CoAl2O4 and Co3O4. All the Co/Al2O3 catalysts prepared showed good stability as the percentage of cobalt leached out was rather low.
Keywords: Cobalt catalyst; Alumina; Pyruvic acid; Catalytic ozonation; Water treatment
Water vapor sensitivity of nanosized La(Co, Mn, Fe)1− x(Cu, Pd) xO3 perovskites during NO reduction by C3H6 in the presence of oxygen by Runduo Zhang; Houshang Alamdari; Serge Kaliaguine (pp. 331-341).
A series of La(Co, Mn, Fe)1− x(Cu, Pd) xO3 perovskites having high specific surface areas and nanosized crystal domains was prepared by reactive grinding. The solids were characterized by N2 adsorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature programmed desorption (TPD) of O2, NO+O2, C3H6, in the absence or presence of 5% H2O, Fourier transform infrared (FTIR) spectroscopy, as well as activity tests towards NO reduction by propene under the conditions of 3000ppm NO, 3000ppm C3H6, 1% O2, 0 or 10% H2O, and 50,000h−1 space velocity. The objective was to investigate the influence of H2O addition on catalytic behavior. A good performance (100% NO conversion, 77% N2 yield, and 90% C3H6 conversion) was achieved at 600°C over LaFe0.8Cu0.2O3 under a dry feed stream. With the exposure of LaFe0.8Cu0.2O3 to a humid atmosphere containing 10% water vapor, the catalytic activity was slightly decreased yielding 91% NO conversion, 51% N2 yield, and 86% C3H6 conversion. A competitive adsorption between H2O vapor with O2 and NO molecules at anion vacancies over LaFe0.8Cu0.2O3 was found by means of TPD studies here. A deactivation mechanism was therefore proposed involving the occupation of available active sites by water vapor, resulting in an inhibition of catalytic activity in C3H6+NO+O2 reaction. This H2O deactivation was also verified to be strictly reversible by removing steam from the feed.
Keywords: Perovskite; Reactive grinding; NO reduction; Propene; H; 2; O deactivation; TPD; FTIR
The role of platinum as the high voltage electrode in the enhancement of Fenton's reaction in liquid phase electrical discharge by Selma Mededovic; Bruce R. Locke (pp. 342-350).
Pulsed electrical discharges in water produce a variety of oxidative and reductive species including hydroxyl radicals, hydrogen peroxide, and hydrogen. The reaction of ferrous ions with hydrogen peroxide (Fenton's reaction) provides additional hydroxyl radicals. Previous experiments with pulsed electrical discharges in water have shown that when ferrous sulfate is used as an electrolyte with a platinum high voltage electrode significantly higher organic compound degradation can be obtained in comparison to the case with an electrode made of nickel-chromium. In the work presented here, it is shown that particles emitted into solution from the platinum high voltage electrode enhance the production of hydroxyl radicals by forming a catalytic cycle between ferric and ferrous ions. The ferrous ions are converted to ferric ions by the Fenton's reaction utilizing hydrogen peroxide from the electrical discharge and the ferric ions are in turn converted to ferrous ions by reactions on the platinum particles emitted into solution from the high voltage electrode with molecular hydrogen formed by the electrical discharge. Based upon experiments with various scavengers it is concluded that the catalytic effect of the platinum particles is due to the presence of adsorbed hydrogen, while in contrast the nickel-chromium, which does not adsorb hydrogen, high voltage electrode and particles emitted by this electrode have no effect on the ferric ion regeneration.
Keywords: High voltage pulse electrical discharge; Water; Platinum electrode; Fenton's reaction
LaCoO3: Effect of synthesis conditions on properties and reactivity by Marta M. Natile; Elisabetta Ugel; Chiara Maccato; Antonella Glisenti (pp. 351-362).
Two nanostructured bulk LaCoO3 powders were prepared by co-precipitation and with the citrate gel method and compared with the two nanocomposites obtained depositing, by wet impregnation, cobalt oxide on the La2O3 surface. All the prepared samples were characterized by means of X-ray photoelectron (XP) and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopic techniques, X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal analysis.XRD results suggest that only the citrate gel method allows to obtain a single phase lanthanum cobaltite powder having a rhombohedral perovskite structure. Moreover, SEM images confirm the wide scale homogeneity. In contrast, a lanthanum hydroxide phase (hexagonal) is also evident in the sample obtained by co-precipitation method. In the nanocomposite richer in cobalt, besides the rhombohedral perovskite, the hexagonal lanthanum oxide and hydroxide phases are also detectable. Perovskite phase does not form when the amount of deposited cobalt oxide is too low. Both in the nanostructured sample prepared by citrate gel method and nanocomposite with [Co/La]nominal=1.0 XPS, DRIFT and TGA outcomes suggest a lower presence of hydroxyl groups and carbonates species.The reactivity of the powders with respect to carbon monoxide was studied (at atmospheric pressure, between RT and 573K) by means of the diffuse reflectance infrared Fourier transform spectroscopy. A significant signal around 2058cm−1 testifies about the interaction of CO with the Lewis acidic sites distributed on the surface of all the samples. The two nanostructured bulk LaCoO3 show a high reactivity toward CO oxidation since 423K. A similar oxidation capability is observed also for the nanocomposite richer in cobalt. In contrast, a rather low reactivity is displayed from the nanocomposite with lower Co/La nominal atomic ratio and La2O3.
Keywords: LaCoO; 3; Perovskite; La; 2; O; 3; Nanostructured powders; CO reactivity
The effect of platinum and silver deposits in the photocatalytic oxidation of resorcinol by Sai Wei Lam; Ken Chiang; Tuti M. Lim; Rose Amal; Gary K-C. Low (pp. 363-372).
The effects of platinum (Pt) and silver (Ag) metallisation in the photocatalytic oxidation of resorcinol at pH 3±0.5 have been investigated. The photocatalytic degradation of resorcinol was significantly improved by Pt/TiO2, while the presence of Ag/TiO2 enhanced the initial photocatalytic degradation rate of resorcinol slightly. Likewise, the photocatalytic mineralisation of resorcinol continued to be enhanced by Pt/TiO2, but it was retarded when Ag/TiO2 was used.The function of Pt and Ag deposits on the surface of TiO2 has been found to be markedly influenced by the interaction of resorcinol and its degradation products with the metal deposits. The presence of Pt or Ag on the surface of TiO2 altered the distribution of degradation products of resorcinol as well as the production of photoactive species for the photocatalytic oxidation of resorcinol. The X-ray photoelectron spectroscopy (XPS), zeta potential and transmission electron microscopy (TEM) analyses have indicated that the contrasting effect of Pt and Ag deposits were governed by the oxidation states and the catalytic property of metal deposits. In addition to that, it has been found that the roles of metal deposits are specific and should not be generalised.
Keywords: Photocatalysis; Photodeposition; Platinum; Silver; Resorcinol
Mineralization of clofibric acid by electrochemical advanced oxidation processes using a boron-doped diamond anode and Fe2+ and UVA light as catalysts by Ignasi Sirés; Francesc Centellas; José Antonio Garrido; Rosa María Rodríguez; Conchita Arias; Pere-Lluís Cabot; Enric Brillas (pp. 373-381).
This work shows that aqueous solutions of clofibric acid (2-(4-chlorophenoxy)-2-methylpropionic acid), the bioactive metabolite of various lipid-regulating drugs, up to saturation at pH 3.0 are efficiently and completely degraded by electrochemical advanced oxidation processes such as electro-Fenton and photoelectro-Fenton with Fe2+ and UVA light as catalysts using an undivided electrolytic cell with a boron-doped diamond (BDD) anode and an O2-diffusion cathode able to electrogenerate H2O2. This is feasible in these environmentally friendly methods by the production of oxidant hydroxyl radical at the BDD surface from water oxidation and in the medium from Fenton's reaction between Fe2+ and electrogenerated H2O2. The degradation process is accelerated in photoelectro-Fenton by additional photolysis of Fe3+ complexes under UVA irradiation. Comparative treatments by anodic oxidation with electrogenerated H2O2, but without Fe2+, yield much slower decontamination. Chloride ion is released and totally oxidized to chlorine at the BDD surface in all treatments. The decay kinetics of clofibric acid always follows a pseudo-first-order reaction. 4-Chlorophenol, 4-chlorocatechol, hydroquinone, p-benzoquinone and 2-hydroxyisobutyric, tartronic, maleic, fumaric, formic and oxalic acids, are detected as intermediates. The ultimate product is oxalic acid, which is slowly but progressively oxidized on BDD in anodic oxidation. In electro-Fenton this acid forms Fe3+–oxalato complexes that can also be totally destroyed at the BDD anode, whereas in photoelectro-Fenton the mineralization rate of these complexes is enhanced by its parallel photodecarboxylation with UVA light.
Keywords: Boron-doped diamond anode; Catalysis; Electro-Fenton; Photoelectro-Fenton; Drug mineralization
Catalytic behavior of the Fe3+/Fe2+ system in the electro-Fenton degradation of the antimicrobial chlorophene by Ignasi Sirés; José Antonio Garrido; Rosa María Rodríguez; Enric Brillas; Nihal Oturan; Mehmet A. Oturan (pp. 382-394).
The catalytic behavior of the Fe3+/Fe2+ system in the electro-Fenton degradation of the antimicrobial drug chlorophene has been studied considering four undivided electrolytic cells, where a Pt or boron-doped diamond (BDD) anode and a carbon felt or O2-diffusion cathode have been used. Chlorophene electrolyses have been carried out at pH 3.0 under current control, with 0.05M Na2SO4 as supporting electrolyte and Fe3+ as catalyst. In these processes the drug is oxidized with hydroxyl radical (OH) formed both at the anode from water oxidation and in the medium from electrochemically generated Fenton's reagent (Fe2++H2O2, both of them generated at the cathode). The catalytic behavior of the Fe3+/Fe2+ system mainly depends on the cathode tested. In the cells with an O2-diffusion cathode, H2O2 is largely accumulated and the Fe3+ content remains practically unchanged. Under these conditions, the chlorophene decay is enhanced by increasing the initial Fe3+ concentration, because this leads to a higher quantity of Fe2+ regenerated at the cathode and, subsequently, to a greaterOH production from Fenton's reaction. In contrast, when the carbon felt cathode is used, H2O2 is electrogenerated in small extent, whereas Fe2+ is largely accumulated because the regeneration of this ion from Fe3+ reduction at the cathode is much faster than its oxidation to Fe3+ at the anode. In this case, an Fe3+ concentration as low as 0.2mM is required to obtain the maximumOH generation rate, yielding the quickest chlorophene removal. Chlorophene is poorly mineralized in the Pt/O2 diffusion cell because the final Fe3+–oxalate complexes are difficult to oxidize withOH. These complexes are completely destroyed using a BDD anode at high current thanks to the great amount ofOH generated on its surface. Total mineralization is also achieved in the Pt/carbon felt and BDD/carbon felt cells with 0.2mM Fe3+, because oxalic acid and its Fe2+ complexes are directly oxidized withOH in the medium. Comparing the four cells, the highest oxidizing power regarding total mineralization is attained for the BDD/carbon felt cell at high current due to the simultaneous destruction of oxalic acid at the BDD surface and in the bulk solution.
Keywords: Antimicrobials; Electro-Fenton method; Advanced oxidation processes; Degradation; Water treatment
Ethanol combustion over strontium- and cerium-doped LaCoO3 catalysts by Beata Białobok; Janusz Trawczyński; Włodzimierz Miśta; Mirosław Zawadzki (pp. 395-403).
Ce- or Sr-doped LaCoO3 bulk perovskites were prepared by citric acid method as well as 10wt.% of LaCoO3 was deposited on alumina carrier stabilized with lanthanum. Properties of prepared materials were characterized by determination of surface area, acid-basic properties and XRD, XPS, TPDO2, H2-TPR measurements as well as catalytic activity and selectivity for ethanol combustion was tested. It was found that substitution of La in LaCoO3 with either Sr or Ce has only small effect on its activity in ethanol combustion. Strontium inserted into LaCoO3 structure increases basic character of the perovskite surface as well as selectivity to acetaldehyde (ACA). Substitution of La with cerium has no effect on the concentration of basic sites and does not affect the selectivity to ACA. Activity of LaCoO3-based catalysts in ethanol combustion and their selectivity to ACA formation can be explained on the basis of the presence of both α-oxygen species and sites with basic character on the material surface.Acid-basic properties of supported LaCoO3 are dominated by acidic character of the carrier. Results of XPS and H2-TPR measurements of LaCoO3 supported on La–Al2O3 suggest that perovskite remains in strong interaction with carrier and probably is partially decomposed. Deposition of perovskite on stabilized carrier significantly increases the rate of ethanol combustion.
Keywords: Perovskites; Lanthanum–cobalt mixed oxide; Catalyst; Combustion; Carrier; Ethanol