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Applied Catalysis B, Environmental (v.78, #3-4)
Nano-titania assisted photoreduction of Cr(VI) by G. Cappelletti; C.L. Bianchi; S. Ardizzone (pp. 193-201).
Nanocrystalline TiO2 samples, with controlled phase composition, were obtained by combining reactions in solution with mild hydrothermal or thermal treatments. By using as the starting salt TiCl3, pure phase rutile with crystallite sizes of 6nm and a BET surface area of 130m2g−1 was obtained. The photocatalytic activity of the synthesized samples along with that of several commercially available TiO2 samples, was tested for the photoreduction of Cr(VI). The reaction was performed in TiO2 aqueous slurry in the presence of different sacrificial molecules (formic acid (FA), isopropyl alcohol (IPA) and sodium sulphite (SS)). The pH of the reaction (2.5) was defined on the grounds of the energy level of the TiO2 conduction band and of the reduction potential of the Cr(VI)/Cr(III) couple. The reaction kinetics could be described, for all samples, by a pseudo-first order rate equation.The photocatalytic activity of the anatase–brookite synthesized composite and of the anatase–rutile commercial P25 were found to be the highest (94% at 90min reaction time). Rutile samples, both synthesized (〈 d〉=6nm) and commercial (〈 d〉=93nm), showed a lower activity with respect to the other samples (around 80% at 90min reaction time). This occurrence is discussed also on the grounds of diffuse reflectance spectra.Cr(0) was observed at the surface of TiO2 samples by XPS analyses. Since thermodynamic analysis shows that TiO2 cannot photoreduce Cr(III) to Cr(0), the formation of Cr(0) is attributed to the reducing action of the produced IPA radicals.The different contributions to the global reaction pathway are critically discussed.
Keywords: Chromates; Water remediation; Nanocrystalline TiO; 2; Photocatalysis
Preparation of carbon-coated W18O49 and its photoactivity under visible light by Fumi Kojin; Masanobu Mori; Yumiko Noda; Michio Inagaki (pp. 202-209).
Carbon-coated W18O49 powders were prepared from the mixture of para-ammonium tungstate with poly(vinyl alcohol) by heat treatment in inert atmosphere at a temperature between 750 and 900°C for 1h. The synthesized W18O49 crystals had prismatic morphology in small size, less than 0.5μm in diameter and about 1μm in length. Carbon-coated W18O49 was shown to have photoactivity under visible light irradiation by comparing the concentration changes of methylene blue, phenol and dimethylsulfoxide with time under the irradiation of visible light to that in the dark. Photoactivity of W18O49 was supposed to be due to the formation of OH radicals on the basis of the degradation of dimethylsulfoxide, its quantitative transformation to methanesulfonic acid. Carbon coating seemed to have various roles: to reduce WO3 to W18O49, to inhibit the sintering and crystal growth of W18O49 to keep them small size, and also to concentrate pollutants around W18O49 crystal by adsorption.
Keywords: Visible light active; W; 18; O; 49; Carbon coating
A new concept in high performance ceria–zirconia oxygen storage capacity material with Al2O3 as a diffusion barrier by Akira Morikawa; Tadashi Suzuki; Takaaki Kanazawa; Koichi Kikuta; Akihiko Suda; Hirofumi Shinjo (pp. 210-221).
CeO2–ZrO2 solid solution ((Ce,Zr)O2) is an indispensable oxygen storage capacity (OSC) material for emission control in gasoline-fuelled automobiles. The high performance OSC material developed in this study is composed of Al2O3 as “a diffusion barrier” and (Ce,Zr)O2 particles in intervening layers on a nanometer scale, and is abbreviated as “ACZ”. The Brunauer–Emmett–Teller (BET) specific surface area (SSA) of ACZ after durability testing in air at 1000°C was 20m2/g, which is higher than that of conventional CZ (2m2/g) composed of (Ce,Zr)O2 without Al2O3. After heat treatment at 1000°C in air, the particle size of (Ce,Zr)O2 in ACZ was about 10nm and that without Al2O3 was one-half of the size in pure CZ. The OSC was roughly characterized by the total capacity (OSC-c1) and the oxygen release rate (OSC-r). In a fresh catalyst, ACZ and CZ had almost the same OSC-c1; however, the OSC-r of ACZ was twice as fast as CZ. After durability testing, the OSC-r of both ACZ and CZ were reduced significantly, but the OSC-r of ACZ was about five times as fast as CZ. While the OSC-c1 was hardly influenced by the (Ce,Zr)O2 crystallite size and Pt particle size on the supports, the OSC-r was influenced by both of these parameters. The improvement of the OSC-r in the fresh catalyst and inhibition of the decrease in the OSC-r after durability testing were achieved by suppression of particle growth of (Ce,Zr)O2 in ACZ by introducing Al2O3 as a diffusion barrier with resultant inhibition of sintering of Pt particles.
Keywords: Al; 2; O; 3; CeO; 2; ZrO; 2; Diffusion barrier; Oxygen storage capacity
Influence of the reaction conditions on the electrochemical promotion by potassium for the selective catalytic reduction of N2O by C3H6 on platinum by Antonio de Lucas-Consuegra; Fernando Dorado; Carmen Jiménez-Borja; José L. Valverde (pp. 222-231).
In this work, we have investigated for the first time the selective catalytic reduction of N2O by C3H6 over an electrochemical catalyst (Pt/K-βAl2O3). It was evaluated the influence of the reaction conditions (temperature, oxygen concentration, water vapour presence and time on stream treatment under reaction conditions) on the catalytic performance of the electrochemical catalyst. Electrochemical pumping of potassium ions to the Pt catalyst working electrode strongly increased the N2O reduction rate, activating the catalyst at lower temperatures. However, it was found that the efficiency of the electrochemical promotion decreased as the oxygen concentration increased because of a strong inhibition of propene adsorption and a relative increase of the oxygen coverage. On the contrary, the presence of potassium ions on the Pt catalyst strongly decreased the inhibiting effect of water vapour, increasing the catalytic activity of the catalyst. In addition, the catalyst stability was confirmed by a deactivation study. It was found that a long term treatment at high temperature under operating conditions had a positive effect on the efficiency of the Pt/K-βAl2O3 electrochemical catalyst.
Keywords: Electrochemical promotion; NEMCA effect; Selective catalytic reduction; N; 2; O; Pt catalyst
Gas phase photocatalysis and liquid phase photocatalysis: Interdependence and influence of substrate concentration and photon flow on degradation reaction kinetics by Stephan Brosillon; Ludovic Lhomme; Cédric Vallet; Abdelkrim Bouzaza; Dominique Wolbert (pp. 232-241).
The photocatalytic degradation of metolachlor in water and butyric acid in air on coated TiO2 has been investigated to study the interdependency on the degradation rate of the UV photon flux and the concentration of the organic compound. Experimental results clearly showed that the kinetic change of order with respect to light intensity depended on the value of the concentration of organic compound. The fitting of experimental results with the Langmuir–Hinshelwood (L-H) model emphasized that the corresponding “apparent adsorption constant”, KR, could not be considered as an equilibrium constant in the dark since the value of KR varied with regard to the photon flow. The assumption of a pseudo-steady-state for the concentration of hydroxyl radicals associated either with L-H model (under certain conditions) or Eley–Rideal model explains consistently the dependence of the apparent kinetic parameter, kobs, and KR with the light intensity. A rate expression taking into account the interdependency of the degradation rate on the UV photon flux and the initial concentration of the organic compound is proposed and validated for a liquid and a gas phase reaction. The constants of this correlation are independent of the initial concentration and light intensity.
Keywords: Photocatalysis; Liquid phase; Gas phase; Langmuir–Hinshelwood model; Eley–Rideal model
Potassium-doped Co3O4 catalyst for direct decomposition of N2O by Kimihiro Asano; Chie Ohnishi; Shinji Iwamoto; Yasushi Shioya; Masashi Inoue (pp. 242-249).
Direct decomposition of nitrous oxide (N2O) on K-doped Co3O4 catalysts was examined. The K-doped Co3O4 catalyst showed a high activity even in the presence of water. In the durability test of the K-doped Co3O4 catalyst, the activity was maintained at least for 12h. It was found that the activity of the K-doped Co3O4 catalyst strongly depended on the amount of K in the catalyst. In order to reveal the role of the K component on the catalytic activity, the catalyst was characterized by XRD, XPS, TPR and TPD. The results suggested that regeneration of the Co2+ species from the Co3+ species formed by oxidation of Co2+ with the oxygen atoms formed by N2O decomposition was promoted by the addition of K to the Co3O4 catalyst.
Keywords: N; 2; O decomposition; Co; 3; O; 4; catalyst; Alkali promoting effect; Redox mechanism
Photo-Fenton degradation of 17β-estradiol in presence of α-FeOOHR and H2O2 by Zhao Yaping; Hu Jiangyong (pp. 250-258).
A novel photocatalyst, α-FeOOH-coated resin (α-FeOOHR), was prepared and applied for the photodegradation of natural estrogen 17β-estradiol (E2) in presence of H2O2 under the relatively weak UV irradiation. The continuing loading of ferric oxide on resin was achieved by in situ hydrolysis of Fe3+ in alkaline solution. The effects of initial pH, catalyst loading, oxidant concentration and iron leaching on the photodegradation of E2 were investigated. The batch photodegradation experiment showed that high removal efficiency of E2 and fairly good mechanic stability could be obtained by the spherical photocatalyst α-FeOOHR in aqueous solutions. The photodegradation efficiencies slightly decreased with the increase of initial pH in the wide pH range of 3–11. Increase of oxidant and catalyst will enhance photodegradation efficiencies thus lead to increase the Ferric leaching. Neglected iron leaching showed the stability of the loaded α-FeOOH withstanding the oxidation. X-ray photoelectron spectrum (XPS) shed light on the surface activity change of photocatalyst and heterogeneous catalytic essence of this process.
Keywords: 17β-Estradiol; α-FeOOH-coated resin; Heterogeneous; Fenton reaction; Photocatalysis
Hydrodechlorination of alachlor in water using Pd, Ni and Cu catalysts supported on activated carbon by L. Calvo; M.A. Gilarranz; J.A. Casas; A.F. Mohedano; J.J. Rodríguez (pp. 259-266).
The hydrodechlorination of alachlor with hydrogen in aqueous phase was studied in a trickle bed reactor using different activated carbon-supported catalysts. The reactor was continuously fed with a 50mg/L solution of alachlor in water and a H2/N2 gas stream. The variables studied were space-time (44.8–448.3kgcath/mol), H2:N2 volumetric ratio in the gas phase (1:1–1:4), temperature (308–373K) and pressure (0.24–0.6MPa). The results of the hydrodechlorination experiments were evaluated in terms of alachlor conversion and ecotoxicity of the exit stream. High conversion values and important reductions of ecotoxicity were obtained working under mild conditions of temperature (323–348K) and pressure (0.24MPa). Palladium catalysts supported on activated carbon were found as the most active in the hydrodechlorination of alachlor, although copper and nickel catalysts led also to high conversions in the 80–93% range. The hydrodechlorination of alachlor was performed successfully with metal loads between 0.5 and 2.5wt.% on the catalysts. A significant metal leaching was observed from the nickel and copper catalysts, which negatively affected the ecotoxicity of the final effluents. Oxidative treatment of the activated carbon supports with nitric acid previous to the impregnation with the metal precursor improved the anchorage of the active phase and reduced leaching dramatically. Likewise, the activity was not influenced by the oxidation of the supports and reductions of ecotoxicity by more than 90% were observed.
Keywords: Hydrodechlorination; Alachlor; Ecotoxicity; Activated carbon supported catalysts; Palladium; Nickel; Copper; Leaching
Co3O4 based catalysts for NO oxidation and NO x reduction in fast SCR process by Muhammad Faisal Irfan; Jeong Hoi Goo; Sang Done Kim (pp. 267-274).
Reaction activities of several developed catalysts for NO oxidation and NO x (NO+NO2) reduction have been determined in a fixed bed differential reactor. Among all the catalysts tested, Co3O4 based catalysts are the most active ones for both NO oxidation and NO x reduction reactions even at high space velocity (SV) and low temperature in the fast selective catalytic reduction (SCR) process. Over Co3O4 catalyst, the effects of calcination temperatures, SO2 concentration, optimum SV for 50% conversion of NO to NO2 were determined. Also, Co3O4 based catalysts (Co3O4-WO3) exhibit significantly higher conversion than all the developed DeNO x catalysts (supported/unsupported) having maximum conversion of NO x even at lower temperature and higher SV since the mixed oxide Co-W nanocomposite is formed. In case of the fast SCR, N2O formation over Co3O4-WO3 catalyst is far less than that over the other catalysts but the standard SCR produces high concentration of N2O over all the catalysts. The effect of SO2 concentration on NO x reduction is found to be almost negligible may be due to the presence of WO3 that resists SO2 oxidation.
Keywords: Fast SCR; NO; x; removal; Co; 3; O; 4; NO oxidation; Catalyst
Lean reduction of NO by C3H6 over Ag/alumina derived from Al2O3, AlOOH and Al(OH)3 by Runduo Zhang; Serge Kaliaguine (pp. 275-287).
The effectiveness of Ag/Al2O3 catalyst depends greatly on the alumina source used for preparation. A series of alumina-supported catalysts derived from AlOOH, Al2O3, and Al(OH)3 was studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet–visible (UV–vis) spectroscopy, diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, O2, NO+O2-temperature programmed desorption (TPD), H2-temperature programmed reduction (TPR), thermal gravimetric analysis (TGA) and activity test, with a focus on the correlation between their redox properties and catalytic behavior towards C3H6-selective catalytic reduction (SCR) of NO reaction. The best SCR activity along with a moderated C3H6 conversion was achieved over Ag/Al2O3 (I) employing AlOOH source. The high density of Ag–O–Al species in Ag/Al2O3 (I) is deemed to be crucial for NO selective reduction into N2. By contrast, a high C3H6 conversion simultaneously with a moderate N2 yield was observed over Ag/Al2O3 (II) prepared from a γ-Al2O3 source. The larger particles of Ag mO ( m>2) crystallites were believed to facilitate the propene oxidation therefore leading to a scarcity of reductant for SCR of NO. An amorphous Ag/Al2O3 (III) was obtained via employing a Al(OH)3 source and 500°C calcination exhibiting a poor SCR performance similar to that for Ag-free Al2O3 (I). A subsequent calcination of Ag/Al2O3 (III) at 800°C led to the generation of Ag/Al2O3 (IV) catalyst yielding a significant enhancement in both N2 yield and C3H6 conversion, which was attributed to the appearance of γ-phase structure and an increase in surface area. Further thermo treatment at 950°C for the preparation of Ag/Al2O3 (V) accelerated the sintering of Ag clusters resulting in a severe unselective combustion, which competes with SCR of NO reaction. In view of the transient studies, the redox properties of the prepared catalysts were investigated showing an oxidation capability of Ag/Al2O3 (II and V)>Ag/Al2O3 (IV)>Ag/Al2O3 (I)>Ag/Al2O3 (III) and Al2O3 (I). The formation of nitrate species is an important step for the deNO x process, which can be promoted by increasing O2 feed concentration as evidenced by NO+O2-TPD study for Ag/Al2O3 (I), achieving a better catalytic performance.
Keywords: SCR; NO; Propene; Silver; Alumina; Boehmite; Al(OH); 3; UV–vis; DRIFT; TPD; TPR
Comparative study of structural properties and NO x storage-reduction behavior of Pt/Ba/CeO2 and Pt/Ba/Al2O3 by M. Casapu; J.-D. Grunwaldt; M. Maciejewski; F. Krumeich; A. Baiker; M. Wittrock; S. Eckhoff (pp. 288-300).
Differences in the NO x storage-reduction (NSR) behavior of Pt/Ba/CeO2 and Pt/Ba/Al2O3 have been identified and traced to their different chemical and structural properties. The results show that Pt/Ba/CeO2 exhibits inferior NO x storage and, particularly, reduction (regeneration) activity compared to the Al2O3 supported catalyst. The incomplete reduction of the stored NO x-species in Pt/Ba/CeO2 seems to be caused by a faster and more profound reoxidation of Pt particles during the lean period as evidenced by in situ X-ray absorption spectroscopy. Interestingly, the reduction activity could be significantly improved by a pre-reduction step at mild conditions. Exposure of the Pt/Ba/CeO2 catalyst to reducing H2 atmosphere in the temperature range 300–500°C lead to a moderate increase of Pt particle size which beneficially influenced the regeneration activity. In contrast, pre-reduction at temperatures above 500°C was unfavorable and resulted in a severe decrease of the regeneration activity, probably due to migration of the partially reduced CeO2 onto the surface of Pt particles.
Keywords: NO; x; storage-reduction catalyst; Ceria; Pre-treatment; Thermal analysis; X-ray absorption spectroscopy
SO2 resistant antimony promoted V2O5/TiO2 catalyst for NH3-SCR of NO x at low temperatures by Ha Heon Phil; Maddigapu Pratap Reddy; Pullur Anil Kumar; Lee Kyung Ju; Jung Soon Hyo (pp. 301-308).
To get the low temperature sulfur resistant V2O5/TiO2 catalysts quantum chemical calculation study was carried out. After selecting suitable promoters (Se, Sb, Cu, S, B, Bi, Pb and P), respective metal promoted V2O5/TiO2 catalysts were prepared by impregnation method and characterized by X-ray diffraction (XRD) and Brunner Emmett Teller surface area (BET-SA). Se, Sb, Cu, S promoted V2O5/TiO2 catalysts showed high catalytic activity for NH3 selective catalytic reduction (NH3-SCR) of NO x carried at temperatures between 150 and 400°C. The conversion efficiency followed in the order of Se>Sb>S>V2O5/TiO2>Cu but Se was excluded because of its high vapor pressure. An optimal 2wt% ‘Sb’ loading was found over V2O5/TiO2 for maximum NO x conversion, which also showed high resistance to SO2 in presence of water when compared to other metal promoters. In situ electrical conductivity measurement was carried out for Sb(2%)/V2O5/TiO2 and compared with commercial W(10%)V2O5/TiO2 catalyst. High electrical conductivity difference (Δ G) for Sb(2%)/V2O5/TiO2 catalyst with temperature was observed. SO2 deactivation experiments were carried out for Sb(2%)/V2O5/TiO2 and W(10%)/V2O5/TiO2 at a temperature of 230°C for 90h, resulted Sb(2%)/V2O5/TiO2 was efficient catalyst. BET-SA, X-ray photoelectron spectroscopy (XPS) and carbon, hydrogen, nitrogen and sulfur (CHNS) elemental analysis of spent catalysts well proved the presence of high ammonium sulfate salts over W(10%)/V2O5/TiO2 than Sb(2%)/V2O5/TiO2 catalyst.
Keywords: NO; x; conversion at low temperature; Sb(2%)/V; 2; O; 5; /TiO; 2; Electrical conductivity; Resistance to SO; 2
Selective catalytic reduction of NO with NH3 at low temperatures over iron and manganese oxides supported on mesoporous silica by Jihui Huang; Zhiquan Tong; Yan Huang; Junfeng Zhang (pp. 309-314).
A series of catalysts of iron–manganese oxide supported on mesoporous silica (MPS) with different Mn/Fe ratio were studied for low-temperature selective catalytic reduction (SCR) of NO with ammonia in the presence of excess oxygen. Effects of amounts of iron–manganese oxide and calcination temperatures on NO conversion were also investigated. It was found that the Mn–Fe/MPS with Mn/Fe=1 at the calcination temperature of 673K showed the highest activity. The results showed that this catalyst yielded 99.1% NO conversion at 433K at a space velocity of 20,000h−1. H2O has no adverse impact on the activity when the SCR reaction temperature is above 413K. In addition, the SCR activity was suppressed gradually in the presence of SO2 and H2O, while such effect was reversible after heating treatment.
Keywords: SCR of NO with NH; 3; Mn–Fe; Mesoporous silica; H; 2; O; SO; 2
Impact of copper on the performance and sulfur tolerance of barium-based NO x storage-reduction catalysts by Sonia Hammache; Lindsey R. Evans; Eric N. Coker; James E. Miller (pp. 315-323).
The presence of sulfur in automotive exhaust is known to be detrimental to lean-NO x traps as SO2 is oxidized to SO3 that competes with NO2 for sites on the trap and is difficult to remove. In this study the effect of adding Cu to the prototypical Pt–BaO/γ-Al2O3 formulation on the system's tolerance for sulfur was investigated. It was found that in the absence of sulfur, Cu decreases the performance in terms of both NO x storage capacity and reduction of NO x to N2 during regeneration. In the presence of SO2, Cu provides a significant improvement in sulfur tolerance so that, after sulfur exposure, the storage capacity of the Cu-modified material can exceed that of the baseline material. The sulfur tolerance afforded by Cu is attributed to a moderation in the activity for SO2 oxidation resulting from the formation of a Pt–Cu bimetallic phase. The propensity for NO oxidation is also modified, but to a lesser effect. Evidence for the bimetallic phase is provided by temperature-programmed reduction (TPR) and electron microscopy. The impact of SO2 on the Cu-modified material is greater during the regenerative reduction cycle. In this case, the results suggest that sulfur blocks Pt and possibly Cu sites and that the sulfur is not removed by oxidation during the subsequent storage cycle. Hence, activity lost during the reduction cycle is not restored. In contrast, sulfur that blocks Pt sites on the baseline material during the reduction cycle is subsequently oxidized and desorbs from the Pt, restoring the activity. However, some of the resulting SO3 reacts with the BaO to form BaSO4, and there is a partial loss of storage capacity.
Keywords: Lean-NO; x; trap; NO; x; storage reduction; Deactivation; Pt–BaO/γ-Al; 2; O; 3; Pt–Cu–BaO/γ-Al; 2; O; 3
Combining non-thermal plasma with heterogeneous catalysis in waste gas treatment: A review by Jim Van Durme; Jo Dewulf; Christophe Leys; Herman Van Langenhove (pp. 324-333).
Plasma driven catalysis is a promising technology for waste gas treatment characterized by higher energy efficiencies, high mineralization rates and low by-product formation. The combination of heterogeneous catalysts with non-thermal plasma can be operated in two configurations: positioning the catalyst in the discharge zone (in-plasma catalysis) or downflow the discharge zone (post plasma catalysis).In a first part of the review, changes of plasma properties resulting from the introduction of catalyst material are discussed. It has been reported that discharge types can even change. Accordingly, it was reported that microdischarges are formed within the catalyst pores. Changing plasma characteristics can eventually result in enhanced production of new active species, increasing the oxidizing power of the plasma discharge.In a second part, it is discussed that plasma discharges also affect catalyst properties such as a change in chemical composition, enhancement in surface area or change of catalytic structure. These phenomena partially explain why catalyst adsorption kinetics of airborne pollutants are affected when exposed to plasma discharges.It is also reviewed that the synergy of combining plasma with catalysts can not only be attributed to the production of new reactive species. Also plasma photon emission or thermal hot-spots can initiate catalytic pollutant oxidation reactions.To conclude, an overview of recently published manuscripts concerning plasma catalysis for volatile organic compounds abatement is given. It is also discussed why heterogeneous plasma catalysis has high potential for the simultaneous abatement of NO x and hydrocarbons.
Keywords: Plasma driven catalysis (PDC); In-plasma catalysis (IPC); Post plasma catalysis (PPC); Volatile organic compounds (VOC); Nitrogen oxides (NO; x; ); Waste gas treatment
Experimental design methodology applied to electro-Fenton treatment for degradation of herbicide chlortoluron by Aida Kesraoui Abdessalem; Nihal Oturan; Nizar Bellakhal; Mohamed Dachraoui; Mehmet A. Oturan (pp. 334-341).
The degradation of herbicide chlortoluron in aqueous medium by electro-Fenton process using a carbon felt cathode and a platinum anode was studied. The great oxidation ability of this process is due to the large production of hydroxyl radical (OH) by electrochemically induced Fenton's reagent. Hydroxyl radicals are very powerful oxidizing agents which react on organics up to complete mineralization. The influence of some experimental parameters such as initial concentration, current intensity and processing time on the degradation and mineralization rate of chlortoluron by hydroxyl radicals has been investigated. The evolution of chlortoluron concentration with processing time shows a pseudo first order kinetics ( kabs=(4.8±0.2)×109mol−1Ls−1). A Doehlert matrix was applied for determination of the optimal working conditions. Optimal parameters for maximum mineralization efficiency (TOC removal ratio of 98%) was achieved after 8h of treatment using a chlortoluron initial concentration of 0.125mM and an applied current of 300mA. The mineralization of aqueous chlortoluron solutions was confirmed by identification of the end-products such as carboxylic acids and inorganic ions. Their evolution during electro-Fenton treatment was studied.
Keywords: Chlortoluron; Electro-Fenton process; Mineralization; Experimental design; Hydroxyl radical
N2O decomposition over wet- and solid-exchanged Fe-ZSM-5 catalysts by Joo-Hyoung Park; Jong-Hyun Choung; In-Sik Nam; Sung-Won Ham (pp. 342-354).
The N2O decomposition activity of Fe-ZSM-5 strongly depends on the iron content and the preparation methods, including wet (WIE) and solid state ion exchanges (SSIE). The state of Fe species formed on the surface of a series of Fe-ZSM-5 catalysts containing a variety of Fe contents with respect to the preparation method and their role for N2O decomposition activity have been systematically examined. The general trend for the decomposition activity of Fe-ZSM-5-SSIE is higher than that of Fe-ZSM-5-WIE, indicating the formation of a distinctive local structure of Fe on the catalyst surface during the course of the ion-exchange procedure. Based upon the Fourier transformed Fe K-edge EXAFS spectra for the series of Fe-ZSM-5-SSIE and -WIE catalysts, most of the Fe species on the surface of Fe-ZSM-5-SSIE with high Fe loading are well dispersed in the form of oxygen-bridged binuclear Fe species. The turnover frequency (TOF) for N2O decomposition under dry and wet conditions has been confirmed assuming that Fe-ZSM-5-SSIE samples with Fe/Al=0.20 and Fe/Al=0.65 only contain mononuclear and binuclear Fe species, respectively, as active reaction species on their surface. The high performance of Fe-ZSM-5-SSIE may be mainly due to the formation of the binuclear Fe species onto its surface during the preparation of the catalyst.
Keywords: N; 2; O decomposition; Fe-ZSM-5; EXAFS; Oxygen-bridged binuclear Fe
Comparative study of MTBE photocatalytic degradation with TiO2 and Cu-TiO2 by J. Araña; A. Peña Alonso; J.M. Doña Rodríguez; J.A. Herrera Melián; O. González Díaz; J. Pérez Peña (pp. 355-363).
The photocatalytic techniques have been widely applied to the treatment of wastewaters. However, this work introduces an innovative application of photocatalysis to the treatment in continuous of gaseous contaminants. Packed reactors with different lengths and a spiral one have been designed to study the photocatalytic degradation of methyl tert-butyl ether (MTBE), individual alcohols and mixtures with their corresponding aldehydes. These studies have been performed with TiO2 (Degussa P-25) and TiO2 doped with Cu (Cu-TiO2). The results obtained have shown that these systems can degrade and mineralize the tested compounds, thus achieving the decontamination of their gaseous emissions. Additionally, the reactor with Cu-TiO2 has been more efficient than that with TiO2 at the degradation and mineralization of MTBE, being the photocatalytic behaviour of the former more easily altered by the presence of intermediates.Additionally, it has been observed that reactor morphology plays an important role in degradation efficiency. The spiral reactor with Cu-TiO2, in which the catalyst was thermally deposited on the inner walls, achieved the highest degradation and mineralization of MTBE.The obtained results are particularly interesting as an alternative to reduce emissions of volatile organic compounds to the atmosphere.
Keywords: MTBE; Gas phase photocatalysis; Spiral reactor; Cu-TiO; 2
Effect of sulfur in catalytic partial oxidation of methane over Rh–Ce coated foam monoliths by A. Bitsch-Larsen; N.J. Degenstein; L.D. Schmidt (pp. 364-370).
A potentially important technology to convert natural gas to syngas is catalytic partial oxidation (CPO) over precious metal catalysts. However, natural gas contains small amounts of sulfur compounds which can poison the catalyst. It is therefore of interest to investigate the effect of sulfur on the performance of CPO. In this work CPO experiments have been performed over Rh–Ce coated foam monoliths with CH3SH added to methane. The result of ppm levels of sulfur is a large (∼200°C) temperature increase, along with lower methane conversion and lower hydrogen selectivity. A doubling of the sulfur level from 14 to 28 ppm does not result in significant changes, showing that the effect saturates at a few ppm. The poisoning effect has been investigated by analyzing both effluent and spatially resolved data and is shown to be due to severe hindrance of steam reforming by adsorbed sulfur.
Keywords: Catalytic partial oxidation; Methane; Rhodium; Ceria; Sulfur poisoning; Steam reforming
Dechlorination kinetics of monochlorobiphenyls by Fe/Pd: Effects of solvent, temperature, and PCB concentration by Yuanxiang Fang; Souhail R. Al-Abed (pp. 371-380).
Well-known, yet undefined, changes in the conditions and activity of palladized zerovalent iron (Fe/Pd) over an extended period of time hindered a careful study of dechlorination kinetics in long-term experiments. A short-term experimental method was, therefore, developed to study the effects of temperature and solvent on the dechlorination of monochlorobiphenyls (MCBs), 2-chlorobiphenyl (2-ClBP), in particular by Fe/Pd. The experiments started with specified initial conditions and lasted only for 10min. The average value ( k) of the first-order rate constant for the dechlorination of 2-ClBP was 0.13±0.03Lm−2h−1, not significantly different from the average values for 3-chlorobiphenyl and 4-chlorobiphenyl. The apparent activation energy was 20±4kJmol−1 and 17±7kJmol−1, in a temperature range between 4°C and 60°C, for the dechlorination of 2-ClBP using two batches of Fe/Pd catalyst. The k values decreased significantly in mixtures with a methanol concentration higher than 10%. The values of the rate constant were slightly influenced by the initial concentrations in the experiments at a low temperature and in a solution with a high methanol concentration. The concentration dependence was described with a Langmuir equation, based on the Langmuir–Hinshelwood mechanism that includes an adsorption step of a single species preceding a rate-determining catalytic reaction.
Keywords: Catalytic dechlorination; Kinetics; PCBs; Palladized zerovalent iron; Fe/Pd; Concentration dependence; Solvent effect; Langmuir–Hinshelwood mechanism
Direct alcohol fuel cells: A novel non-platinum and alcohol inert ORR electrocatalyst by Shuqin Song; Yi Wang; Panagiotis Tsiakaras; Pei Kang Shen (pp. 381-387).
In the present investigation, a series of binary Pd xFe y/C electrocatalysts for the oxygen reduction reaction (ORR) was synthesized in a very short time by employing a pulse-microwave assisted polyol method. The physico-chemical properties were obtained by employing the techniques of X-ray diffraction (XRD) and transmission electron microscopy (TEM). The electrochemical activity was studied by the aid of the techniques of cyclic voltammetry and rotating disk electrode. Based on the obtained experimental results, it can be deduced that the addition of Fe increases the activity of Pd towards the reaction of oxygen reduction. More precisely, when the molar ratio between Pd and Fe was 3:1, the highest oxygen reduction activity among all the investigated Pd xFe y/C catalysts was obtained. It was also found that Pd3Fe1/C exhibited an oxygen reduction activity comparable to that of Pt/C, while showed almost no activity for alcohols oxidation. Moreover, in the simultaneous presence of both methanol and oxygen, Pd3Fe1/C displayed an excellent selectivity for oxygen reduction reaction.
Keywords: Oxygen reduction reaction (ORR); Pd; x; Fe; y; /C electrocatalysts; Direct alcohol fuel cells (DAFCs); Alcohol crossover