Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
Applied Catalysis B, Environmental (v.65, #1-2)
Photocatalytic oxidation of herbicides in single-component and multicomponent systems: Reaction kinetics analysis by Alexander Gora; Bea Toepfer; Valeria Puddu; Gianluca Li Puma (pp. 1-10).
The photocatalytic oxidation (PCO) of the herbicides isoproturon, simazine and propazine over irradiated TiO2 suspensions was studied in single-component and in multicomponent systems. The initial herbicide concentration ranged from 70μgL−1 to 3mgL−1 in order to approach typical concentrations found in contaminated ground- and surface waters. The time-dependent degradation profiles of each herbicide were successfully modelled using an approximation of the Langmuir–Hinshelwood (L–H) rate equation, which takes into account the direct effect of the intermediate reaction products. The L–H rate equations were successfully extended to represent the time-dependent degradation profiles of multicomponent systems of herbicides, using the kinetic parameters determined in single-component experiments. A direct comparison of the binding constants of the herbicides observed under dark adsorption and under PCO shows that these are very similar suggesting that the degradation of isoproturon, simazine and propazine mixtures follows a surface or near-surface reaction according to a competitive L–H mechanism. The above findings were observed only at herbicide concentrations less than approximately 1mgL−1 when monolayer coverage of TiO2 is attained. Above 1mgL−1 there is a departure from the L–H mechanism due to multilayer adsorption of the herbicides leading to faster herbicide degradation kinetics.
Keywords: Water purification; Titanium dioxide; Photocatalysis; Photoreactor; Suspensions; Herbicides; Pesticides; Langmuir–Hinshelwood; Multicomponent
Kinetics and reactional pathway of Imazapyr photocatalytic degradation Influence of pH and metallic ions by Marion Carrier; Nathalie Perol; Jean-Marie Herrmann; Claire Bordes; Satoshi Horikoshi; Jean Olivier Paisse; Robert Baudot; Chantal Guillard (pp. 11-20).
Some of advanced oxidation processes (AOP) are characterised by a special chemical feature: the ability to use the high reactivity ofOH radicals in driving oxidation processes. These radicals are suitable for achieving the complete abatement, even including the mineralization of less reactive pollutants.In this study, a photocatalytic process is used to degrade one herbicide of the imidazolinone family, Imazapyr. It was shown to be photodegraded rapidly and extensively in an aqueous solution. The decline of Imazapyr concentration in the solution followed a first-order kinetics. The apparent first order rate constant was found equal to 0.19min−1 in distilled water at natural pH 3.8. The smaller activities found at acidic and basic pH were explained by considering the ionisation state of Imazapyr and the charge density of TiO2.The present work dealt with the influence of metal ions like Ni2+ and Cu2+ which are frequently present in agricultural wastewater on the photocatalytic efficiency of TiO2 in the elimination of Imazapyr. A detrimental effect of the presence of metallic species was observed only with samples containing amount of copper and nickel in the presence of TiO2. Several hypotheses were proposed to explain this phenomenon, passivation of TiO2 surface by adsorption of Cu2O and/or Cu0, formation of a complex or recombinaison of the e−/h+ pairs. At higher concentrations of metallic species like Cu2+ and Ni2+, a plateau was reached which could be explained by the photo-Fenton like reaction.In an attempt to understand the basic mechanisms of the degradation of Imazapyr in water by TiO2 photocatalysis, we discussed the primary degradation mechanism on the basis of the experimental results together with molecular orbital calculation of frontier electron density and partial charge.
Keywords: Imidazolinones; Photocatalysis; Photodegradation; Frontier electron density; Titanium dioxide
Synthesis and characterisation of La1− xCa xFeO3 perovskite-type oxide catalysts for total oxidation of volatile organic compounds by Bibiana P. Barbero; Julio Andrade Gamboa; Luis E. Cadús (pp. 21-30).
La1− xCa xFeO3 perovskite-type oxides with x=0, 0.2 and 0.4 were prepared by the citrate method and characterised by means of X-ray diffraction (XRD), X-ray fluorescence (XRF), surface area measurement BET, X-ray photoelectron spectroscopy (XPS), Fourier transformed infrared spectroscopy (FT-IR), laser Raman spectroscopy (LRS), oxygen temperature-programmed desorption (O2-TPD) and temperature-programmed reduction (TPR). The citrate method shows to be simple and appropriate to obtain single phases avoiding segregation and/or contamination. Moreover, controlling the calcination temperature, specific surface areas adequate for catalysts to be used in oxidation reactions are achieved. The structure refinement by using the Rietveld method indicates that the partial calcium substitution modifies the orthorhombic structure of the LaFeO3 perovskite towards a less distorted one. From XRF and XPS, a slight surface enrichment in lanthanum and calcium was detected. XRD, FT-IR and TPR results indicated that the electronic debalance caused by the partial substitution for La3+ by Ca2+ is compensated by an oxidation state increase of a part of Fe3+ to Fe4+. O2-TPD results revealed that at a substitution level higher than x=0.2, oxygen vacancies are also formed to preserve the electroneutrality. Finally, an improvement of the catalytic activity in propane and ethanol combustion was observed on the substituted perovskites. Correlating this with the characterisation results, the active sites would be associated to the Fe4+ ions.
Keywords: Lanthanum iron perovskite; Calcium; XRD; XRF; XPS; FT-IR; Raman spectroscopy; O; 2; -TPD; TPR; Rietveld refinement; Propane combustion; Ethanol combustion
Selective hydrogenation of nitrate in water over Cu–Pd/mordenite by Kyosuke Nakamura; Yasuyuki Yoshida; Ikkou Mikami; Toshio Okuhara (pp. 31-36).
Hydrogenation of nitrate (NO3−) in water has been investigated by using Cu–Pd exchanged zeolites in a gas–liquid co-current flow system. Cu–Pd/mordenites prepared by ion-exchange at 383K were highly selective for the hydrogenation of NO3− with H2 to N2 and N2O at 278–333K. Among Cu–Pd/mordenites with various Cu/Pd ratios and loading amounts of metal, 1.2wt.% Cu–0.5wt.% Pd/mordenite (Cu/Pd=4) were shown to display the highest selectivity for N2O (96%) at 278K, with the generation of undesired by-product NH3 being suppressed. In addition, this catalyst was superior in the selectivity to other Cu–Pd/zeolites and Cu–Pd/γ-Al2O3. The concentrations of NH3 formed 1.2wt.% Cu–0.5wt.% Pd/mordenite at 278K were only 1.4 and 2.0ppm at near 100%-conversion for the initial concentrations of 100 and 200ppm of NO3−, respectively. The product N2O being a greenhouse gas was hydrogenated entirely to N2 with 5wt.% Pd/AC placed at the gas phase of outlet of reactor. Kinetic study has determined the activation energy to be 27kJmol−1 and the reaction order to be 0.5 with respect to the concentration of NO3−. Hydrogenation of nitrite (NO2−) also produced N2O selectively over 1.2wt.% Cu–0.5wt.% Pd/mordenite, supporting that the hydrogenation of NO3− proceeds through NO2− as an intermediate. It was confirmed that 1.2wt.% Cu–0.5wt.% Pd/mordenite exhibited a robust stability both in its activity and against the dissolution of metals during reaction at 278–333K.
Keywords: Hydrogenation of nitrate; Cu–Pd catalyst; Zeolite; Groundwater
Catalytic performance and mechanism of a Pt/TiO2 catalyst for the oxidation of formaldehyde at room temperature by Changbin Zhang; Hong He; Ken-ichi Tanaka (pp. 37-43).
The performance of TiO2 supported noble metal (Pt, Rh, Pd and Au) catalysts was examined and compared for the catalytic oxidation of formaldehyde (HCHO). Among them, the Pt/TiO2 was the most active catalyst. The effects of Pt loading and gas hourly space velocity (GHSV) on Pt/TiO2 activity for HCHO oxidation were investigated at a room temperature (20°C). The optimal Pt loading is 1wt.%. At this loading, HCHO can be completely oxidized to CO2 and H2O over the Pt/TiO2 in a GHSV of 50,000h−1 at 20°C. The 1% Pt/TiO2 was characterized using BET, XRD, high resolution (HR) TEM and temperature programmed reduction (TPR) methods. The XRD patterns and HR TEM image show that Pt particles on TiO2 are well dispersed into a size smaller than 1nm, an important feature for the high activity of the 1% Pt/TiO2. The mechanism of HCHO oxidation was studied with respect to the behavior of adsorbed species on Pt/TiO2 surface at room temperature using in situ DRIFTS. The results indicate that surface formate and CO species are the main reaction intermediates during the HCHO oxidation. The formate species could decompose into adsorbed CO species on the catalyst surface without the presence of O2, and the CO was then oxidized to CO2 with the presence of O2. Based on these results, a simplified mechanism for the catalytic oxidation of HCHO over 1% Pt/TiO2 was proposed.
Keywords: Formaldehyde; Noble metal; Pt/TiO; 2; Formate species; In situ DRIFTS
Bi2O3/Al2O3 catalysts for the selective reduction of NO with hydrocarbons in lean conditions by Dennis E. Sparks; Patricia M. Patterson; Gary Jacobs; Nicolas Dogimont; Amanda Tackett; Mark Crocker (pp. 44-54).
Bi2O3/Al2O3 catalysts were prepared by sol–gel and impregnation methods, and their properties in the selective catalytic reduction of NO x with propene and propane investigated. Under simulated diesel exhaust gas conditions (500ppm NO, 10% O2, 6% H2O, GHSV of ca. 30,000h−1) with 525ppm propene as reductant, maximum conversion levels to N2 reached 62% for NO and 47% for NO2, while maximum NO x reduction was observed at 550°C. Increasing the propene concentration to 1315ppm (corresponding to a [ C1]/[NO] ratio of 8) resulted in a maximum NO reduction level of 96%, while the temperature corresponding to the maximum shifted to 525°C. Propane was also found to function as an efficient reductant; maximum NO conversion levels were only slightly lower than for propene, although the temperature window for NO conversion was shifted by ∼25°C to higher temperature relative to propene. While the presence of oxygen was found to be essential for SCR activity, water significantly inhibited NO x reduction by competing for adsorption sites with the propene and/or NO x reactants. Optimum SCR activity was observed for sol–gel catalysts at bismuth loadings of 3–7wt%, XRD and XPS measurements showing that the bismuth oxide in these catalysts was present as a highly dispersed phase. The results of steady-state and transient DRIFTS measurements suggested a reaction scheme in which surface nitrate and acetate groups react to afford N-containing intermediates, including organo-nitrite and/or nitrate species, as well as isocyanate, which react further to form ultimately N2.
Keywords: Bismuth; Bi; 2; O; 3; Selective reduction; NO reduction; NO; Alumina; Al; 2; O; 3
Adsorption and hydrolysis of isocyanic acid on TiO2 by Gaia Piazzesi; Oliver Kröcher; Martin Elsener; Alexander Wokaun (pp. 55-61).
The interaction of isocyanic acid (HNCO) with titania in the anatase modification has been investigated by means of DRIFT spectroscopy and TPD experiments. HNCO adsorbs dissociatively on TiO2 to yield isocyanate (NCO) groups, bound to Ti4+ sites, and hydroxyl (OH) groups. The stability of theseNCO groups decreases with increasing temperatures, and at T>200°C they are very easily removed from the surface. In the presence of water, the hydrolysis of theNCO species to ammonia is also fostered by elevating the temperature. Moreover, HNCO adsorption on a sample previously exposed to ammonia revealed that competitive adsorption occurs on the surface. The catalytic activity of TiO2 for the hydrolyis of HNCO was investigated in a micro plug-flow reactor and correlated with the stability and reactivity of the isocyanate species found by DRIFT spectroscopy. The results are discussed in view of the role of the HNCO hydrolysis in the selective catalytic reduction (SCR) of diesel NO x emissions with urea (urea-SCR process).
Keywords: Isocyanate; Isocyanic acid; HNCO; TiO; 2; Catalytic hydrolysis; urea-SCR
Complete oxidation of ethanol over alkali-promoted Pt/Al2O3 catalysts by George Avgouropoulos; Evaggelos Oikonomopoulos; Dimitrios Kanistras; Theophilos Ioannides (pp. 62-69).
The catalytic performance of alkali (K+ and Na+)-promoted Pt/Al2O3 catalysts for the complete oxidation of ethanol present in trace amounts (500ppm) in air has been investigated. Pure alumina acts mainly as an acidic catalyst producing diethyl ether and ethylene, while complete oxidation of ethanol to CO2 requires temperatures higher than 400°C. Addition of alkalis in alumina neutralizes its acidic sites and suppresses the formation of diethylether and ethylene. Ethanol oxidation over the Pt/Al2O3 catalyst results in the formation of partially oxidized compounds, such as acetaldehyde and acetic acid, as well as CO2 at higher temperatures. Alkali-promoted catalysts do not produce acetic acid and are significantly more active than un-promoted Pt/Al2O3, especially when they have been pre-reduced. The most effective catalyst was Pt/Al2O3 (K/Al=0.10), in which complete oxidation of ethanol to CO2 was achieved at ∼220°C, while complete oxidation of ethanol over the un-promoted catalyst was obtained at 280°C.
Keywords: Ethanol oxidation; Volatile organic compounds (VOCs); Platinum; Alumina; Potassium; Sodium; Promotion
Photocatalytic degradation of diuron in aqueous solution in presence of two industrial titania catalysts, either as suspended powders or deposited on flexible industrial photoresistant papers by M. El Madani; C. Guillard; N. Pérol; J.M. Chovelon; M. El Azzouzi; A. Zrineh; J.M. Herrmann (pp. 70-76).
In the present paper, the practical elimination of pesticides from water by photocatalysis has been studied by using two commercial titania photocatalysts (Degussa P25 (50m2/g) and Millennium PC500 (340m2/g)) and by choosing diuron as a model molecule. These two catalysts have been tested and compared in suspension in a slurry reactor. Their activities have been based on the rates of diuron disappearance diuron. In particular, comparisons have been made on their initial activities, which is independent of the influence of intermediates formed. Under identical conditions, Degussa P25 appeared substantially more active than Millennium PC500. However, since the final filtration of titania powders in suspension for the release of cleaned water and the recovery of the catalysts is a tedious process, titania has been successfully deposited on flexible photo-inert supports to be easily removed and recycled. The binding agent was an amorphous silica, transparent to UV. Depending on the nature of the industrial paper support used, both industrial titania photocatalysts behaved oppositely: for the same quantity of deposited titania samples, Degussa P25 was as active as in suspension when deposited on paper KN47 and substantially (20%) less active when deposited on NW10 whereas Millennium PC-500 behaved oppositely.
Keywords: Photocatalytic degradation; Titanium dioxide; Supported photocatalyst; Kinetics; Diuron; Environmental photocatalysis
Photooxidation of dimethylsulfide in the gas phase: A comparison between TiO2–silica and photosensitizer-silica based materials by C. Cantau; T. Pigot; R. Brown; P. Mocho; M.T. Maurette; F. Benoit-Marque; S. Lacombe (pp. 77-85).
The photooxidation of dimethylsulfide (DMS) in the gas phase was studied with two different materials, under identical conditions. The first material (TiO2-QZ) is based on titanium dioxide (TiO2) deposited on quartz bars by the sol–gel method. The second one (DCA-SG) is based on the well known photosensitizer, 9,10-dicyanoanthracene (DCA) encapsulated in a sol–gel silica network. In spite of non-optimized conditions, both materials allow the oxidation of DMS in air under irradiation. However, the oxidation products are strikingly different: dimethyldisulfide is the main product detected in the gas phase with TiO2-QZ due to a too short residence time to achieve complete mineralization. With DCA-SG no gaseous product is detected in the treated gaseous flow for more than 100h, due to the exclusive formation of polar dimethylsulfoxide and dimethylsulfone which are totally adsorbed on the highly polar silica gel. The efficiency of this latter reaction depends on the DMS concentration, gas flow and light intensity, but is not affected by the presence of small amounts of water. Singlet oxygen appears to be formed efficiently under these conditions. The saturation of DCA-SG by the oxidation products was demonstrated by several complementary methods, and some possible solutions to regenerate the material are proposed. The complementarities of both TiO2-QZ and DCA-SG could be used to achieve the oxidation of different classes of pollutants.
Keywords: Dimethylsulfide; Photooxidation; Photosensitization; Gas–solid reactions; Supported photocatalysts; Titanium dioxide
The kinetics of phenol decomposition under UV irradiation with and without H2O2 on TiO2, Fe-TiO2 and Fe-C-TiO2 photocatalysts by Beata Tryba; Antoni W. Morawski; Michio Inagaki; Masahiro Toyoda (pp. 86-92).
H2O2 used in the photo-Fenton reaction with iron catalyst can accelerate the oxidation of Fe2+ to Fe3+ under UV irradiation and in the dark (in the so called dark Fenton process). It was proved that conversion of phenol under UV irradiation in the presence of H2O2 predominantly produces highly hydrophilic products and catechol, which can accelerate the rate of phenol decomposition. However, while H2O2 under UV irradiation could decompose phenol to highly hydrophilic products and dihydroxybenzenes in a very short time, complete mineralisation proceeded rather slowly. When H2O2 is used for phenol decomposition in the presence of TiO2 and Fe-TiO2, decrease of OH radicals formed on the surface of TiO2 and Fe-TiO2 has been observed and photodecomposition of phenol is slowed down. In case of phenol decomposition under UV irradiation on Fe-C-TiO2 photocatalyst in the presence of H2O2, marked acceleration of the decomposition rate is observed due to the photo-Fenton reactions: Fe2+ is likely oxidized to Fe3+, which is then efficiently recycled to Fe2+ by the intermediate products formed during phenol decomposition, such as hydroquinone (HQ) and catechol.
Keywords: Phenol decomposition; Phenol conversion; Photo-Fenton reaction; H; 2; O; 2
An investigation of a new regeneration method of commercial aged three-way catalysts by Henrik Birgersson; Magali Boutonnet; Fredrik Klingstedt; Dmitry Yu. Murzin; Plamen Stefanov; Anton Naydenov (pp. 93-100).
The ability to modify aged three-way catalysts (TWC) by regaining part of the fresh catalyst surface structure has been verified by both bulk and surface-sensitive characterisation techniques. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM/EDX) techniques were applied to fully evaluate the efficiency of a regeneration procedure of commercial three-way catalysts targeting the washcoat surface. The regeneration comprised combined thermal and liquid chlorine treatments. Structural changes of the washcoat were further investigated with nitrogen adsorption-desorption (BET) and Laser Ablation methods. The investigation showed that the regeneration treatments resulted in an enrichment of the washcoat surface with palladium, thereby increasing the number of catalytically active surface sites. Furthermore, the observed removal of phosphorous and sulphur contaminants resulted in an increase of the relative amount of small pores between 1 and 10nm and washcoat surface area. An increased catalytic activity regarding CO, NO x and HC emissions was observed after regeneration, providing proof of the proposed concept.
Keywords: Three-way automotive catalyst; Regeneration; Characterisation; Pd; Rh; Deactivation; Fouling; Poisoning; Dispersion; XPS; Laser Ablation
Gold catalysts supported on CeO2 and CeO2–Al2O3 for NO x reduction by CO by L. Ilieva; G. Pantaleo; I. Ivanov; A.M. Venezia; D. Andreeva (pp. 101-109).
The reduction of NO x by CO was studied over gold catalyst supported on ceria and ceria–alumina. The mixed supports with different CeO2/Al2O3 ratios were prepared by co-precipitation. The catalysts were characterized by means of XRD, TPR, XPS and Raman spectroscopy. The addition of alumina led to a slight enlargement of the gold particles, while the ceria particle size was decreased. Deeper oxygen vacancies formation in the presence of alumina was detected by TPR, XPS and Raman spectroscopy, compared to the pure ceria support. The samples exhibited a high and stable activity and 100% selectivity towards N2 was reached at 200°C.
Keywords: Gold; Ceria; Ceria–alumina; NO; x; reduction by CO; XRD; TPR; XPS; Raman spectroscopy
Copper-zinc oxide and ceria promoted copper-zinc oxide as highly active catalysts for low temperature oxidation of carbon monoxide by Unnikrishnan R. Pillai; Sarojini Deevi (pp. 110-117).
Copper-zinc oxide catalyst is prepared by co-precipitation technique. The effects of aging the precipitate in the parent solution and addition of CeO2 are investigated. CuO-ZnO catalyst containing 60% CuO and 40% ZnO is found to be active for the ambient temperature oxidation of CO; however the activity can be improved considerably by aging the catalyst during the precipitation process. Alternatively, the catalyst activity can be improved by the addition of CeO2 during the precipitation without aging the precipitate. A much higher CO oxidation activity is achieved for the CuO-ZnO catalyst system than that reported earlier for the same system. X-ray photoelectron spectra (XPS) and XRD results show that aging the catalyst during the precipitation process brings out more ZnO to the surface leading to higher CuO dispersion. This leads to the formation of relatively less crystalline or amorphous CuO that promotes the formation of more linear or weakly bonded CO on the catalyst surface as well as the creation of CuO x species under redox conditions. The metastable copper oxide species is a good electrophilic reagent with superior oxygen transfer capacity and the presence of weakly bonded surface CO ensures a low temperature oxidation activity for the catalyst. It is further seen that addition of ceria to the catalyst also brings out similar advantages. However, increase in the CeO2 content increases the CO bonding strength causing an increase in the light-off temperature (loss of low temperature oxidation activity), in spite of high overall reducibility and CO adsorption capacity of the catalyst. The reducibility and susceptibility to variation in the oxidation states of copper oxide are critical to the activity of the catalyst. It is also found that addition of CeO2 brings out a significant improvement in the catalyst stability over an extended reaction period as well as at elevated reaction temperature.
Keywords: Co-precipitation; CuO-ZnO; Aging; Ceria promoted CuO-ZnO; Room temperature CO oxidation
Influence of the incorporation of palladium on Ru/MCM hydrotreating catalysts by D. Eliche-Quesada; J.M. Mérida-Robles; E. Rodríguez-Castellón; A. Jiménez-López (pp. 118-126).
Zirconium-doped mesoporous silica with a Si/Zr molar ratio of 5 has been used as a support for bimetallic Ru-Pd catalysts. The effect of palladium as a promoter in a catalyst containing ruthenium as active phase, and the influence of the Ru/Pd atomic ratio were studied in the hydrogenation and ring-opening reaction of tetralin. The results indicate the promotional effect of Pd on hydrotreating activity of catalyst since an increase is observed in the formation of hydrogenation products, especially trans-decalin at low temperatures for 5-RuPd(8/1) and 5-RuPd(4/1), while at higher temperatures, there is an enhacement in the production of hydrogenolysis/hydrocracking products. In contrast 5-RuPd(15/1) catalyst shows at low temperatures lower yields of hydrogenation products and higher yields of high molecular weight products (HMW) than 5-Ru catalyst while at higher temperatures than 315°C only produces HMW products. The best catalytic performance is displayed by the 5-RuPd(8/1) catalyst, giving a conversion of tetralin of 98.5% as well as high yields of hydrogenation (20.8%) and ring-opening (70.1%) products under the following experimental conditions: temperature of reaction 350°C; H2/tetralin molar ratio of 10; contact time 2.8s and total pressure of 6MPa ( P(H2)=4.5MPa and P(N2)=1.5MPa). Moreover, this catalyst exhibits good thiotolerance in the presence of 600ppm of dibenzothiophene in the feed, and an excellent tolerance to nitrogen compounds even with 2000ppm of acridine.
Keywords: Bimetallic ruthenium-palladium catalysts; Hydrogenation; Hydrogenolysis/hydrocracking; Tetralin; MCM-41
Neural networks simulation of photo-Fenton degradation of Reactive Blue 4 by A. Durán; J.M. Monteagudo; M. Mohedano (pp. 127-134).
Multivariate experimental design was applied to the degradation of Reactive Blue 4 dye solutions (RB4) in order to evaluate the use of the Fenton reagent under ultraviolet light irradiation. The efficiency of photocatalytic degradation was determined from the analysis of the following parameters: total organic carbon (TOC), color and sulphates and nitrates content.Factorial experimental design allowed to determine the influence of five parameters (initial concentrations of Fe(II), H2O2 and RB4, pH and temperature) on the value of the decoloration and mineralization kinetic rate constants. Experimental data were fitted using neural networks (NNs). The mathematical model reproduces experimental data within 82–86% of confidence and allows the simulation of the process for any value of parameters in the experimental range studied. Also, a measure of the saliency of the input variables was made based upon the connection weights of the neural networks, allowing the analysis of the relative relevance of each variable with respect to the others.Results showed that intermediate compounds compete to react withOH radicals with the different RB4 species present at each pH. Thus, alkaline pHs were found to be more favourable for a faster decoloration process (higher decoloration kinetic constant) whereas acidic pHs were required to remove total organic carbon.The values of kinetic constants obtained from the NNs fittings were implemented in a computational model together with another 24 reactions to simulate the degradation mechanism and assuming a perfectly mixed reactor. The reaction rate equations were built for each chemical specie and the differential equations were solved in Matlab 6.5.
Keywords: Dye; Neural networks; Mineralization; Textile wastewater
Mechanism of aging for a Pt/CeO2-ZrO2 water gas shift catalyst by Wolfgang Ruettinger; Xinsheng Liu; Robert J. Farrauto (pp. 135-141).
An investigation of the practical viability of Pt on CeO2-containing supports as water gas shift catalysts is reported. This paper takes into account the anticipated duty cycles for residential fuel processors integrated to a PEM fuel cell.It was recently found that CeO2 based catalysts deactivate upon start–stop operation of fuel processors due to carbonate build-up and we suggested that ZrO2-CeO2 composites may be a better choice as the support.Aging of Pt-based ZrO2-CeO2 supported WGS catalysts however is observed under relatively mild operating conditions. We investigated the reasons for aging observed under steady-state operation, high temperature stress and start–stop cycling for a Pt/CeO2-ZrO2 water gas shift catalyst by activity testing, transmission electron microscopy (TEM), IR and chemisorption techniques. Substantial aging was observed under both steady-state operation at relatively low temperature (200–250°C) and high temperature stress (up to 450°C), whereas almost no reduction in activity was seen by simulating start–stop cycling, unlike with Pt/CeO2.The loss of activity could be correlated with Pt dispersion measured by CO chemisorption and TEM. Very little formation of hydroxycarbonate and carbonates on the ceria part of the support was observed.
Keywords: Water gas shift; Pt; CeO; 2; ZrO; 2; Sintering; Deactivation
Selective catalytic reduction of NO with methane on γ-Ga2O3-Al2O3 solid solutions prepared by the glycothermal method by Masaru Takahashi; Noriyuki Inoue; Tetsu Nakatani; Tatsuya Takeguchi; Shinji Iwamoto; Tsunenori Watanabe; Masashi Inoue (pp. 142-149).
The γ-Ga2O3-Al2O3 solid solutions prepared by the glycothermal reaction of the mixtures of aluminum isopropoxide and gallium acetylacetonate had extremely high activities for selective catalytic reduction of NO with methane as a reducing agent (CH4-SCR). With the increase in the Al content incorporated in the spinel structure, the catalytic activity increased. The active sites for this reaction were concluded to be the tetrahedral Ga ions with octahedral Al ions in the next-nearest-neighbor sites. Methane activation on the catalysts was the key-step of CH4-SCR. The solid-solution catalysts showed high durability under steaming conditions.
Keywords: γ-Ga; 2; O; 3; -Al; 2; O; 3; solid solution; Glycothermal method; Selective catalytic reduction; NO; CH; 4
Catalytic abatement of volatile organic compounds assisted by non-thermal plasma by Ch. Subrahmanyam; M. Magureanu; A. Renken; L. Kiwi-Minsker (pp. 150-156).
A novel catalytic reactor with dielectric barrier discharge (DBD) at atmospheric pressure was developed for the abatement of volatile organic compounds (VOCs). The novelty of DBD reactor is the metallic catalyst serving also as the inner electrode. The catalytic electrode was prepared from sintered metal fibers (SMF) in the form of a cylindrical tube. Oxides of Mn and Co were deposited on SMF by impregnation. Decomposition of toluene taken as the model VOC compound (<1000ppm in air) was investigated. The catalyst composition, toluene concentration, applied voltage and frequency were systematically varied to evaluate the performance of the DBD reactor. At 100ppm of toluene, the conversion ∼100% was achieved in the DBD reactor using a specific input energy (SIE)∼235J/l independently of the chemical composition of the SMF catalytic electrode, but the selectivity to CO2 was observed to be a function of the catalyst composition. The MnO x/SMF catalytic electrode showed the best performance towards total oxidation. At a SIE of 295J/l, the selectivity to CO2 was 80% with 100% conversion of toluene. No carbon solid residues were deposited on the electrode.
Keywords: Volatile organic compounds abatement; Non-thermal plasma; Dielectric barrier discharge; Plasma-assisted catalysis; Sintered metal fibers
Catalytic abatement of volatile organic compounds assisted by non-thermal plasma by Ch. Subrahmanyam; A. Renken; L. Kiwi-Minsker (pp. 157-162).
Catalytic purification of air containing 250ppm of toluene assisted by non-thermal plasma was carried out with a novel dielectric barrier discharge (DBD) reactor with an inner electrode made of sintered metal fibers (SMF). The optimization of the reactor performance was carried out by modifying the SMF with Mn and Co oxides, varying the voltage from 12.5 to 22.5kV and the frequency in the range of 200–450Hz. Under the experimental conditions used, the MnO x/SMF showed better activity than CoO x/SMF and SMF during the total oxidation of toluene. The complete oxidation of 250ppm of toluene was possible with the MnO x/SMF catalytic electrode at the specific input energy (SIE) of ∼1650J/l. A higher SIE of ∼2100J/l was required with CoO x/SMF for the total oxidation of toluene to CO2. The better performance of the MnO x/SMF compared to other catalytic electrodes seems to be related to the formation of short-lived species by the in situ decomposition of ozone. XPS analysis of the solid deposit formed on the electrode surface shows the formation of carbonaceous species containing oxygen and nitrogen groups.
Keywords: Volatile organic compound abatement; Non-thermal plasma; Dielectric barrier discharge; Plasma-assisted catalysis; Sintered metal fibers
Activity of commercial zeolites with iron impurities in direct N2O decomposition by Arne H. Øygarden; Javier Pérez-Ramírez (pp. 163-167).
Various commercially available zeolite frameworks (MFI, FER, BEA, MOR, FAU) with iron impurities ranging from 85 to 780ppm and nominal Si/Al ratios of 10–15 have been tested in direct N2O decomposition after calcination and steam treatment. Our results show a significant impact of the framework type on the catalytic activity at these high degrees of iron dilution (Fe/Al<0.01). H-beta was the most effective material in the reaction, followed by the other pentasyl-type H-ferrierite and H-ZSM-5 zeolites.
Keywords: Zeolites; Framework type; N; 2; O decomposition; Iron impurities; Steaming