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Applied Catalysis B, Environmental (v.77, #3-4)
Chemical deactivation of V2O5/WO3–TiO2 SCR catalysts by additives and impurities from fuels, lubrication oils, and urea solution by Oliver Kröcher; Martin Elsener (pp. 215-227).
The influence of the combustion products of different lubrication oil additives (Ca, Mg, Zn, P, B, Mo) and impurities in Diesel fuel (K from raps methyl ester) or urea solution (Ca, K) on the activity and selectivity of vanadia-based SCR catalysts were investigated. Standard V2O5/WO3–TiO2 catalysts coated on metal substrates (400cpsi) were impregnated with water soluble compounds of these elements and calcined at 400 and 550°C, in order to investigate the chemical deactivation potential of different elements and combinations of them.It was found that potassium strongly reduced the adsorption equilibrium constantKNH3of ammonia. At small ammonia concentrations in the feed, only part of the active sites were covered with ammonia resulting in a reduced SCR reaction rate. At high ammonia concentrations, the surface coverage and SCR reaction rate increased, but high SCR activity at concurrent low ammonia emissions was impossible. Calcium caused less deactivation than potassium and did not affect the ammonia adsorption to the same extent, but it lowered the intrinsic SCR reaction rate. Moreover, deactivation by calcium was much reduced if counter-ions of inorganic acids were present (order of improvement: SO42−>PO43−>BO33−). Zinc was again less deactivating than calcium, but the positive effect of the counter-ions was weaker than in case of calcium. The degree of N2O production at T>500°C, which is typical for V2O5/WO3–TiO2 catalysts, was not influenced by the different compounds, except for molybdenum, which induced a small increase in N2O formation.
Keywords: Selective catalytic reduction; DeNO; x; SCR catalyst; Vanadia; Deactivation; Ammonia adsorption
Chemical deactivation of V2O5/WO3–TiO2 SCR catalysts by additives and impurities from fuels, lubrication oils and urea solution by D. Nicosia; I. Czekaj; O. Kröcher (pp. 228-236).
A characterization study on a practice-oriented V2O5/WO3–TiO2 SCR catalyst deactivated by Ca and K, respectively, was carried out using NH3-TPD, DRIFT spectroscopy, and XPS as well as theoretical DFT calculations. It was found from NH3-TPD experiments that strongly basic elements like K or Ca drastically affect the acidity of the catalysts. Detailed DRIFT spectroscopy experiments revealed that these poisoning agents mostly interact with the Brønsted acid sites of the V2O5 active phase, thus affecting the NH3 adsorption. Moreover, these experiments also indicated that the V5+=O sites are much less reactive on the poisoned catalysts. XPS investigations of the O 1s binding energies showed that the oxygen atoms of the V5+=O sites are affected by the presence of the poisoning agents. Based on these results and on DFT calculations with model clusters of the vanadia surface, the poisoning mechanism is explained by the stabilization of the non atomic holes of the (010) V2O5 phase as a result of the deactivation element. Consequently, V–OH Brønsted acid sites and V5+=O sites are inhibited, which are both of crucial importance in the SCR process. The deactivation model also gives an explanation to the very low concentrations of potassium needed to deactivate the SCR catalyst, since one metal atom sitting on such a non-atomic hole site deactivates up to four active vanadium centers.
Keywords: Catalyst deactivation; SCR catalyst; Ammonia adsorption; DRIFT; XPS; DFT
High catalytic activity and stability of Pd doped hexaaluminate catalysts for the CH4 catalytic combustion by A. Baylet; S. Royer; P. Marécot; J.M. Tatibouët; D. Duprez (pp. 237-247).
In this work, different procedures, namely carbonate coprecipitation and modified solid–solid diffusion, were used to prepare hexaaluminate samples, unsupported or supported onto θ-Al2O3. These samples were used as catalyst for the methane total oxidation as synthesized or after impregnation of 1wt% Pd. It was observed that the modified solid–solid diffusion procedure is an efficient method to obtain the hexaaluminate structure. At a theoretical ratio x of hexaaluminate onto Al2O3 less than 0.6 ( xLa0.2Sr0.3Ba0.5MnAl11O19+(1− x)·Al2O3, with x=0.25, 0.60), samples with high specific surface area and θ-Al2O3 structure are then obtained. Large differences in catalytic activity can be observed among the series of sample synthesized. All the pure oxide samples (i.e. without palladium) present low catalytic activity for methane total oxidation compared to a reference Pd/Al2O3 catalyst. The highest activity was obtained for the samples presenting a θ-Al2O3 structure (with x=0.60) and a high surface area. Impregnation of 1wt% palladium resulted in an increase in catalytic activity, for all the solids synthesized in this work. Even if the lowest light-off temperature was obtained on the reference sample, similar methane conversions at high temperature (700°C) were obtained on the stabilized θ-Al2O3 solids ( x=0.25, 0.60). Moreover, the reference sample is found to strongly deactivate with reaction time at the temperature of test (700°C), due to a progressive reduction of the PdO x active phase into the less active Pd° phase, whereas excellent stabilities in reaction were obtained on the pure and palladium-doped hexaaluminate and supported θ-Al2O3 samples. This clearly showed the beneficial effect of the support for the stabilization of the PdO x active phase at high reaction temperature. These properties are discussed in term of oxygen transfer from the support to the palladium particle. Oxygen transfer is directly related to the Mn3+/Mn2+ redox properties (in the case of the hexaaluminate and stabilized θ-Al2O3 samples), that allows a fast reoxidation of the metal palladium sites since palladium sites reoxidation cannot occur directly by gaseous dioxygen adsorption and dissociation on the surface.
Keywords: Methane combustion; Hexaaluminate; Noble metals; Activity; Thermal stability
Assessment of the low-temperature EnviNOx® variant for catalytic N2O abatement over steam-activated FeZSM-5 by Miguel A.G. Hevia; Javier Pérez-Ramírez (pp. 248-254).
Remarkable progress towards implementation of catalytic technology for N2O mitigation in nitric acid plants has been experienced in recent years. EnviNOx®, one of the commercial processes developed by Uhde, accomplishes the tail-gas abatement of N2O and NO x over a single reactor using iron-containing zeolite catalysts. Two variants of the process are available depending on the tail-gas temperature. This manuscript evaluates the low-temperature abatement process (<700K), where NO x and N2O are selectively reduced by NH3 and CH4, respectively. To this end, activity tests in mixtures with N2O, O2, NO, NH3, and CH4 at different temperatures and partial pressures of reactants were carried out over steam-activated FeZSM-5. Ammonia and nitric oxide strongly inhibit the selective catalytic reduction (SCR) of N2O by CH4, shifting the temperature for N2O conversion over 700K. Controlled ammonia dosing is required for the efficient operation of the low-temperature EnviNOx® variant over the particular iron zeolite used in this study. The optimal inlet NH3 concentration is determined by the NO concentration in the tail-gas and its temperature. In the absence of NO and NH3, the CH4-SCR of N2O over FeZSM-5 is effective above 623K. Still, this process cannot retrofit a number of existing plants with lower tail-gas temperatures.
Keywords: EnviNOx; ®; N; 2; O abatement; Decomposition; Reduction; Iron zeolites; FeZSM-5; Tail-gas; Nitric acid plant
Catalytic oxidation of chlorophenol over V2O5/TiO2 catalysts by Casey E. Hetrick; Janine Lichtenberger; Michael D. Amiridis (pp. 255-263).
Catalytic and in situ Fourier Transform Infrared (FTIR) spectroscopic studies were conducted to investigate the adsorption and oxidation of o- and p-chlorophenol over a 3.6wt.% V2O5/TiO2 catalyst. At a space velocity of approximately 53,000cm3g−1h−1, this catalyst was found to be active for the oxidation of o- and p-chlorophenol at temperatures as low as 200°C, yielding CO2 and HCl as the main products. Trace amounts of higher molecular weight products were also detected at the reactor outlet indicating the operation of additional condensation, coupling and chlorination/dechlorination side reactions in parallel to the main complete oxidation scheme. The in situ FTIR studies revealed that different phenols adsorb on the V2O5/TiO2 catalyst through their hydroxyl group. Furthermore, the formation of similar surface species (i.e., maleates, acetates, formates and an aldehyde-type species) was observed. The results were compared with those of previous studies on the oxidation of m-dichlorobenzene ( m-DCB) and benzene and suggest that a similar reaction mechanism is operating in all cases, although the relative kinetic significance of the different steps varies with the presence and the position of the hydroxyl and chlorine groups on the aromatic ring.
Keywords: Catalytic oxidation; Chlorinated aromatics; Chlorophenol; Catalytic vanadium oxide; FTIR
Visible light photocatalysis on praseodymium(III)-nitrate-modified TiO2 prepared by an ultrasound method by Wenyue Su; Jianxiong Chen; Ling Wu; Xinchen Wang; Xuxu Wang; Xianzhi Fu (pp. 264-271).
Nanocrystalline TiO2 incorporated with praseodymium(III) nitrate has been prepared by an ultrasound method in a sol–gel process. The prepared sample is characterized by X-ray diffraction (XRD), nitrogen adsorption (BET surface area), UV–vis diffuse reflectance spectroscopy (UV–Vis DRS) and X-ray photoelectron spectroscopy (XPS). The prepared material consists of TiO2 nanocrystalline with 5nm size incorporated with highly dispersed Pr(NO3)3. Visible light absorptions at 444, 469, 482 and 590nm are observed in the prepared sample. These bands are attributed to the 4f transitions3H4→3P2,3H4→3P1,3H4→3P0 and3H4→1D2 of praseodymium(III) ions, respectively. This sample Pr(NO3)3-TiO2, as a novel visible light photocatalyst, shows high activity and stability in the decomposing rhodamine-B (RhB) and 4-chlorophenol (4-CP) under visible light irradiation. Results examined by electron spin resonance spectroscopy (ESR) reveal that the irradiation (>420nm) of the photocatalyst dispersed in RhB aqueous solution induces the generation of highly active hydroxyl radicals (OH), leading to the cleavage of the whole conjugated chromophore structure of RhB. A mechanism based on local excitation of praseodymium(III) nitrate chromophore and interfacial charge transfer from the chromophore to TiO2 is proposed to explain the formation of active hydroxyl radicals in the photocatalytic system under visible light irradiation.
Keywords: Visible light photocatalysis; Titania; Praseodymium nitrate; Ultrasound preparation
Carbon-based monolithic supports for palladium catalysts: The role of the porosity in the gas-phase total combustion of m-xylene by A.F. Pérez-Cadenas; S. Morales-Torres; F. Kapteijn; F.J. Maldonado-Hódar; F. Carrasco-Marín; C. Moreno-Castilla; J.A. Moulijn (pp. 272-277).
Three different carbon-based monoliths have been studied in their performance as Pd catalyst supports in the total gas-phase combustion of m-xylene at low temperatures. The first monolithic support (HPM) was a classical square channel cordierite modified with α-Al2O3, blocking the macroporosity of the cordierite and rounding the channel cross-section, on which a carbon layer was applied by carbonization of a polyfurfuryl alcohol coating obtained by dipcoating. The other two monolithic supports were composite carbon/ceramic monoliths (MeadWestvaco Corporation, USA), microporous (WA) and a mesoporous (WB) sample.All the catalysts have a comparable total Pd loading and very similar Pd particle size (around 5–6nm). In sample Pd/WA the Pd is situated only in the macropores, while in the case of Pd/WB the Pd is distributed throughout the mesoporous texture. In the case of Pd/HPM, Pd particles are clearly situated at the external surface of the carbon layer.The catalytic activities of the samples were very different, decreasing in the order: Pd/WB>Pd/WA>Pd/HPM. These results show that the carbon external surface area, the macropores and mainly mesopores, play an important role in this kind of gas-phase reactions, improving the contact between the Pd particles and the m-xylene molecules. The catalytic activity of the Pd supported on carbon-based monoliths correlates with the surface area developed in macro- and mesopores of the monolithic support.
Keywords: Carbon support; Monolithic catalysts; Textural properties; VOC combustion; Porosity; Palladium
Alkali-metal promoted rhodium-on-alumina catalysts for nitrous oxide decomposition by Jerzy Haber; Małgorzata Nattich; Tadeusz Machej (pp. 278-283).
Catalytic activity of γ-alumina supported rhodium catalysts in nitrous oxide decomposition into dinitrogen and dioxygen has been determined, the total conversion being reached at 450°C. Rhodium is present at alumina surface in three forms: metal particles, Rh2O3 and rhodium zero valent atoms interacting with oxygen ions at the metal/support interface. Linear dependence of the catalytic activity on rhodium dispersion has been found. Deposition of alkali metal cations: Li, Na, K and Cs as promoters at the surface of alumina results in a considerable increase of rhodium dispersion and hence catalytic activity. The effect of promoters depends strongly on the speciation of alkali metals and rhodium used in the preparation of the catalyst. Both alkali metal cations and rhodium compete for the same OH groups at the alumina surface. The electronegativity of alkali metal oxides is much greater than that of alumina and their deposition increases the negative charge of surface oxide ions hindering the diffusion of rhodium and preventing the growth of its larger particles.
Keywords: N; 2; O decomposition; Rhodium catalyst; Alkali metal promoters
Enhancement of the photocatalytic activity of pelletized TiO2 for the oxidation of propene at low concentration by N. Bouazza; M.A. Lillo-Ródenas; A. Linares-Solano (pp. 284-293).
In a previous study we have shown that the pelletization of titanium dioxide, a convenient step for gas phase applications, causes an important activity lost. Such activity lost can be partially recovered pelletizing in presence of carbon materials. Porosity, as well as carbon conductivity of the selected carbon material, is important. Based on these previous results, we analyze the pelletization of TiO2 in presence of “white additives”, such as MCM-41, zeolites, metal–organic framework, SiO2, Al2O3, glass wool and quartz wool. Our results show that the activities of these composite photocatalytic pellets are higher than that of 100% TiO2-pellets. Pellets containing MCM-41, precipitated SiO2, glass wool and quartz wool present the highest propene conversions. Attention has been paid to the effect of porosity and UV-absorbance on the resulting photocatalytic activity. Although it is difficult to find a correlation between the porosity of these “white additives” and the photocatalytic activity of the TiO2-based materials, additives with no porosity or with some mesoporous contribution seem to be desired to maximize the activity. The different catalytic activities for the studied photocatalysts could not be explained on basis of their UV-absorption and further research is currently being performed trying to deep into the reasons for such behaviour. Comparison of the photocatalytic activities for pellets containing the above-mentioned “white additives” with those of a TiO2/carbon photocatalyst having the highest porosity and conductivity among all those studied highlights the superior performance of the samples containing “white additives”.
Keywords: Photocatalysis; TiO; 2; Adsorbents; Oxidation; Propene
Potassium-doped sodalite: A tectoaluminosilicate for the catalytic material towards continuous combustion of carbonaceous matters by Masaru Ogura; Kazumasa Morozumi; S.P. Elangovan; Hiroshi Tanada; Hiromitsu Ando; Tatsuya Okubo (pp. 294-299).
A novel approach has been proposed for stabilization of potassium in combustion of carbonaceous soot matters emitted from diesel engine vehicles. Sodalite, a clathrate aluminosilicate zeolite, is employed as a support for holding catalytically active potassium species. This approach resulted in a high-catalytic activity and the activity is further enhanced after hydrothermal treatment at 800°C. Such kinds of tectoaluminosilicate hold potassium strongly and possess high stability against high temperatures and alkaline conditions induced by hydrated potassium ions under practical driving conditions.
Keywords: Sodalite; Tectoaluminosilicate; Zeolite; Potassium; Carbon; Diesel particulate
Heterogeneous activation of peroxymonosulfate by supported cobalt catalysts for the degradation of 2,4-dichlorophenol in water: The effect of support, cobalt precursor, and UV radiation by Qiujing Yang; Hyeok Choi; Yongjun Chen; Dionysios D. Dionysiou (pp. 300-307).
In order to generate sulfate radicals (SRs) as oxidizing species for the degradation of 2,4-dichlorophenol (2,4-DCP) in water, we explored heterogeneous activation of peroxymonosulfate (PMS) by supported cobalt catalysts. More attention was given to the effect of support materials (Al2O3, SiO2, TiO2) and cobalt precursors (Co(NO3)2, CoCl2, CoSO4) on cobalt–support interaction, cobalt leaching, and reactivity of the catalysts. Especially, the feasibility of simultaneous generation of SRs and hydroxyl radicals (HRs) in PMS-Co/TiO2 systems was first studied under ultraviolet (UV) radiation. Much lower cobalt leaching was observed in Co/Al2O3 and Co/TiO2 systems than that of Co/SiO2 most probably due to their relatively strong cobalt-support interaction. Co/TiO2 catalyst prepared with Co(NO3)2, compared to CoCl2 or CoSO4 (where Cl− and SO42−, respectively, were not completely removed upon heat treatment at 500°C), showed strong cobalt–support interaction, and thereby exhibited negligible cobalt leaching. Under UV radiation, Co/TiO2 at Co/Ti molar ratio of 0.001 showed significant improvement in the degradation of 2,4-DCP due to HRs. The effective generation of HRs in the system can be explained with Co(III)-mediated charge transfer from the photoinduced electrons to PMS, inducing facilitation of photoinduced electron-hole separation. However, high cobalt loading (i.e., Co/Ti molar ratio of 0.1) on TiO2 surface exhibited negligible enhancement of 2,4-DCP transformation under UV radiation since the penetration of UV light to TiO2 was prohibited by the cobalt.
Keywords: 2,4-Dichlorophenol; Advanced oxidation processes (AOPs); Advanced oxidation technologies (AOTs); Cobalt; Heterogeneous reaction; Hydroxyl radicals; Leaching; Nanoparticles; Oxone; Peroxymonosulfate; Precursor; Support materials; Sulfate radicals; Titanium dioxide; Titania; TiO; 2; UV; Water treatment; Water purification
Enhancement of dye sonochemical degradation by some inorganic anions present in natural waters by Claudio Minero; Paolo Pellizzari; Valter Maurino; Ezio Pelizzetti; Davide Vione (pp. 308-316).
The sonochemical degradation rate of the charged substrates Acid Blue 40 (AB40) and methylene blue (MB) is enhanced by scavengers of hydroxyl radicals such as bicarbonate, carbonate, bromide, iodide and (only in the case of AB40) nitrite. No rate variation was observed with chloride, nitrate or sulphate, excluding a mere ionic strength effect. Oxidation of bicarbonate, carbonate, bromide, iodide and nitrite yields the corresponding radicals CO3−, Br2−, I2− andNO2, reactive but less thanOH. Degradation enhancement can occur if these radicals are sonochemically formed on the surface of the collapsing cavitation bubbles and undergo there radical–radical recombination at a lesser extent thanOH. In this way the radicals would be more available thanOH for substrate degradation, both at the bubble surface and in the solution bulk, which could more than compensate for their lower intrinsic reactivity. The varied reactivity toward different substrates of the sonochemically formed radical species could then explain why nitrite inhibits MB degradation while enhancing that of AB40. The sonochemical formation of Br2−, I2− andNO2 can give rise to halogenation and nitration in addition to oxidation processes. In fact bromo-, iodo- and nitrophenols were detected upon sonication of phenol in the presence of the corresponding anions, but only at quite elevated concentration values of nitrite, bromide or iodide (above 10mM). Formation of harmful halogeno- and nitroderivatives could therefore take place on sonication of some wastewater rather than of typical natural waters.
Keywords: Ultrasound; Sonication; Cavitation; Hazardous by-products; Wastewater
Formation of hydrogen peroxide from coal tar as hydrogen sources using 9-mesityl-10-methylacridinium ion as an effective photocatalyst by Hiroaki Kotani; Kei Ohkubo; Shunichi Fukuzumi (pp. 317-324).
Visible light irradiation of an O2-saturated acetonitrile (MeCN) solution containing 9-mesityl-10-methylacridinium ion (Acr+–Mes) and MeCN-extracted coal tar results in formation of hydrogen peroxide (H2O2). Anthracene and other aromatic hydrocarbons contained in coal tar act as hydrogen sources in the photocatalytic reduction of O2 to produce H2O2. The photocatalytic formation of H2O2 is initiated by photoexcitation of Acr+–Mes, which results in formation of the electron-transfer state: Acr–Mes+, followed by electron-transfer from coal tar to the Mes+ moiety and electron-transfer from the Acr moiety to O2.
Keywords: Hydrogen peroxide; Coal tar; Photocatalyst; Electron-transfer; Molecular oxygen
Effect of copper species and the presence of reaction products on the activity of methane oxidation on supported CuO catalysts by Gonzalo Águila; Francisco Gracia; Joaquín Cortés; Paulo Araya (pp. 325-338).
The activity of the various CuO species found in supported copper catalysts and the effect of the presence of reaction products, CO2 and H2O, was studied during the complete oxidation of methane. Series of copper catalysts supported on ZrO2, Al2O3 and SiO2 with different metal concentrations were analyzed under identical experimental conditions of reactant concentration and temperature. The catalysts were characterized by TPR, UV–vis spectroscopy and XRD. The results show that the activity of supported CuO is closely related to the kind of Cu species formed on the different supports. It was found that the Cu species formed on ZrO2 and Al2O3 are dependent on the metal loading/support's surface area ratio, and that the activity of highly dispersed Cu is substantially higher than that of bulk CuO. In the case of silica, only the formation of bulk CuO was detected, accounting for the low activity of CuO/SiO2 catalysts. The activity of highly dispersed Cu species formed on ZrO2 is higher than those formed over Al2O3, and it is not significantly affected by the formation of bulk CuO on the surface. On the contrary, the activity of copper species formed on alumina decreases continuously as the Cu loading is increased. Thus, for the range of copper loading studied in this work, the activity of the catalysts, per gram of loaded Cu, follows the sequence: CuO/ZrO2>CuO/Al2O3≫CuO/SiO2. It was also found that CO2 does not inhibits the activity of the CuO/ZrO2 catalysts, while water inhibits the combustion reaction of methane, with an estimated reaction order of about −0.2 for temperatures between 360°C and 420°C.
Keywords: Copper catalyst; Copper oxide; Methane; ZrO; 2; Al; 2; O; 3; SiO; 2
Surface-enhanced Raman study of electrochemical and photocatalytic degradation of the azo dye Janus Green B by Carlos E. Bonancêa; Gustavo M. do Nascimento; Michele L. de Souza; Marcia L.A. Temperini; Paola Corio (pp. 339-345).
The photocatalytic degradation of Janus Green B azo dye over silver modified titanium dioxide films was investigated by surface-enhanced Raman spectroscopy (SERS). An optimized SERS-active substrate was employed to study the photodegradation reaction of Janus Green B. Considering that photocatalytic degradation processes of organic molecules adsorbed on TiO2 might involve either their oxidation or reduction reaction, the vibrational spectroelectrochemical study of the dye was also performed, in order to clarify the transformations involved in initial steps of its photochemical decomposition. In order to understand the changes in Raman spectra of Janus Green B after photodegradation and/or electrochemical processes, a vibrational assignment of the main Raman active modes of the dye was carried out, based on a detailed resonance Raman profile. Products formed by electrochemical and photochemical degradation processes were compared. The obtained results revealed that the first steps of the degradation process of Janus Green B involve a reductive mechanism.
Keywords: Advanced oxidative processes; Photocatalytic degradation; Environmental electrochemistry; TiO; 2; Azo dyes; Spectroelectrochemistry; SERS; Janus Green B
CO2 reforming of CH4 over nanocrystalline zirconia-supported nickel catalysts by M. Rezaei; S.M. Alavi; S. Sahebdelfar; Peng Bai; Xinmei Liu; Zi-Feng Yan (pp. 346-354).
Mesoporous nanocrystalline zirconia with high-surface area and pure tetragonal crystalline phase has been prepared by the surfactant-assisted route, using Pluronic P123 block copolymer surfactant. The synthesized zirconia showed a surface area of 174m2g−1 after calcination at 700°C for 4h. The prepared zirconia was employed as a support for nickel catalysts in dry reforming reaction. It was found that these catalysts possessed a mesoporous structure and even high-surface area. The activity results indicated that the nickel catalyst showed stable activity for syngas production with a decrease of about 4% in methane conversion after 50h of reaction. Addition of promoters (CeO2, La2O3 and K2O) to the catalyst improved both the activity and stability of the nickel catalyst, without any decrease in methane conversion after 50h of reaction.
Keywords: Zirconia; Nanocrystal; Ni catalysts; Carbon dioxide reforming
Catalytic activity of iron species in layered clays for photodegradation of organic dyes under visible irradiation by Mingming Cheng; Wenjing Song; Wanhong Ma; Chuncheng Chen; Jincai Zhao; Jun Lin; Huaiyong Zhu (pp. 355-363).
The iron species in layered clays are active for catalytically oxidizing synthetic dyes with H2O2 under visible irradiation ( λ>420nm). Three layered clays, Montmorillonite, Laponite, and Nontronite, in which the iron species exist in different chemical environment, were used to investigate the role of the iron species in the clays. It was found that the reactivity of the iron species greatly depends on their chemical environments. The exchangeable interlayer iron ions in the clay exhibit much better ability to catalyze the mineralization of malachite green (MG) than the structural iron at the centers of octahedrons that are sandwiched by two layers of SiO4 tetrahedrons. The interactions among the foreign ligands, such as phosphate and EDTA, and the two types of iron species are dissimilar, causing the different effects of the ligands on the degradation kinetics. The EPR results show explicitly that the reaction over the two iron species proceeds through different pathways. This explains the differences in the degradation kinetics for the photodegradation of MG by H2O2 over different clays. These iron-containing clay minerals are chemically and mechanically stable, we do not observe any noticeable loss of activity and damage of the clay structure after 14 recycles.
Keywords: Iron species; Clay; Photodegradation; Dye
Design of new gold catalysts supported on mechanochemically activated ceria-alumina, promoted by molybdena for complete benzene oxidation by D. Andreeva; P. Petrova; L. Ilieva; J.W. Sobczak; M.V. Abrashev (pp. 364-372).
Gold catalysts, supported on mechanochemically activated ceria-alumina, nonpromoted and promoted by molybdena, were studied in the reaction of complete benzene oxidation. Higher activity of Au-Mo catalysts was established in the low temperature region, while high temperatures samples, containing only gold exhibit higher benzene conversion and the cross-point of the curves depends on alumina content. The addition of alumina by mechanochemical treatment leads to a surface modification of ceria, e.g. oxygen vacancies are formed prevailing on the ceria surface. The molybdena loading leads to the oxygen vacancies occupation. The calculated hydrogen consumption and the enhanced reduction of ceria surface layers in general correlate with the activities of the catalysts. The XPS data supported the role of Ce3+ and partially charged gold particles in the formation of the complex AuV0Ce3+ as the active site for the redox processes. The modification of ceria in the presence of gold and the formation of oxygen vacancies in close contact with Ce3+ ensure the enhanced electron transfer.
Keywords: Gold; Gold-molybdena; Ceria-alumina; Mechanochemical activation; Hydrocarbon oxidation
Investigation of various ionomer-coated carbon supports for direct methanol fuel cell applications by M. Aulice Scibioh; In-Hwan Oh; Tae-Hoon Lim; Seong-Ahn Hong; Heung Yong Ha (pp. 373-385).
High-performance fuel cell electrodes require architectures that offer appropriate electrochemical and nanoscopic catalytic reaction zones. In this direction, ionomer (perfluoro sulfonic acid)-coated carbon supports were prepared by adopting a simple and cheap synthetic strategy to offer both electronic and protonic contacts to the catalyst particulates. Pt–Ru bimetallic anode catalysts were prepared on these modified carbon supports by a colloidal method. The role of surface area of carbon supports and the influence of ionomer content in them towards the catalytic activities of Pt–Ru catalysts has been probed by using three kinds of carbon black powders with different physical properties. Their electrocatalytic efficiencies toward methanol oxidation were scrutinized via half-cell measurements in cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. Catalysts particulates dispersed on carbon supports coated with ionomer exhibited better performance than those on the plain carbon supports, owing to the reduced micropores and increased interfacial area between catalyst particles and ionomer. Plain and modified carbon (MC) supports were characterized by using FTIR, BET-PSD and TEM techniques. Physico-chemical characterizations of supported catalyst systems were done by using XRD and TEM.
Keywords: Direct methanol fuel cell (DMFC); Ionomer-coated carbon support; Ionomer content; Pt–Ru; Active surface area; High surface area carbon supports; Methanol oxidation
Environmentally friendly solid acid catalyst prepared by modifying TiO2 with cerium sulfate for the removal of volatile organic chemicals by Jong Rack Sohn; Dong Cheol Shin (pp. 386-394).
An environmentally friendly solid acid catalyst, Ce(SO4)2/TiO2 was prepared simply by modifying TiO2 with Ce(SO4)2 for acid catalysis of volatile organic chemicals, 2-propanol and cumene. The characterization of prepared catalysts was performed using FTIR, XRD and DSC. The surface area of 7-Ce(SO4)2/TiO2 calcined at 300°C was very high (206.0m2/g) compared to that of unmodified TiO2 (115.2m2/g) due to the interaction between Ce(SO4)2 and TiO2. 7-Ce(SO4)2/TiO2 containing 7wt% Ce(SO4)2 and calcined at 300°C exhibited maximum catalytic activities for both reactions, 2-propanol dehydration and cumene dealkylation. The catalytic activities for both reactions were correlated with the acid amounts of catalysts measured by an ammonia chemisorption method. The role of Ce results in an increase in the thermal stability of the surface sulfate species and consequently the acid amount of Ce(SO4)2/TiO2 is increased. The asymmetric stretching frequency of the SO bonds for Ce(SO4)2/TiO2 catalysts was related to the acidic properties and to the catalytic activity for acid catalysis to remove volatile organic chemicals, 2-propanol and cumene.
Keywords: Environmentally friendly acid catalyst; Volatile organic chemicals; TiO; 2; modified with Ce(SO; 4; ); 2; Cumene dealkylation; 2-Propanol dehydration
Experimental and microkinetic modeling of steady-state NO reduction by H2 on Pt/BaO/Al2O3 monolith catalysts by Jin Xu; Robert Clayton; Vemuri Balakotaiah; Michael P. Harold (pp. 395-408).
Experimental results describing the product distribution during the reduction of NO by H2 on Pt/Al2O3 and Pt/BaO/Al2O3 catalysts are presented in the temperature range 30–500°C and H2/NO feed ratio range of 0.9–2.5. A microkinetic model that describes the kinetics of NO reduction by H2 on Pt/Al2O3 is proposed and most of the kinetic parameters are estimated from either literature data or from thermodynamic constraints. The microkinetic model is combined with the short monolith flow model to simulate the conversions and selectivities corresponding to the experimental conditions. The predicted trends are in excellent qualitative and reasonable quantitative agreement with the experimental results. Both the model and the experiments show that N2O formation is favored at low temperatures and low H2/NO feed ratios, N2 selectivity increases monotonically with temperature for H2/NO feed ratios of 1.2 or less but goes through a maximum at intermediate temperatures (around 100°C) for H2/NO feed ratios 1.5 or higher. Ammonia formation is favored for H2/NO feed ratios of 1.5 or higher and intermediate temperatures (100–350°C) buts starts to decompose at a temperature of 400°C or higher. The microkinetic model is used to determine the surface coverages and explain the trends in the experimentally observed selectivities.
Keywords: NO; x; Platinum; Barium; Storage; Reduction; Ammonia; Hydrogen
FTIR study of aqueous nitrate reduction over Pd/TiO2 by Jacinto Sá; James A. Anderson (pp. 409-417).
The interactions between Pd/TiO2 catalyst and the reactants and potential reaction intermediates present during aqueous nitrate reduction, including NO3−, NO2− and NO in the presence of H2 and H2O were studied by infrared spectroscopy. Adsorbed forms of NO, nitrite and nitrate could all be detected in the presence of water. In the presence of water/H2, nitrate was the most stable surface species followed by nitrite and then highly reactive NO, suggesting that the reduction of nitrate to nitrite is the rate-limiting step. High concentrations of adsorbed nitrite appear to be linked to the detection of gaseous N2O while the formation of ammonia is related to reactions on the Pd surface and the extent of formation is linked to high levels of adsorbed NO in addition to the surface hydrogen availability and the presence of water.
Keywords: Nitrate hydrogenation; FTIR; Water treatment; Pd/TiO; 2
Kinetics of phase transfer catalyzed reduction of nitrochlorobenzenes by aqueous ammonium sulfide: Utilization of hydrotreater off-gas for the production of value-added chemicals by Sunil K. Maity; Narayan C. Pradhan; Anand V. Patwardhan (pp. 418-426).
The reduction of nitrochlorobenzenes (NCBs) was carried out in an organic solvent, toluene, under liquid–liquid mode with phase transfer catalyst, tetrabutylammonium bromide (TBAB). The selectivity of chloroanilines (CANs) was found to be 100%. The reaction rate of m-nitrochlorobenzene (MNCB) was found to be highest among the three NCBs followed by o- and p-nitrochlorobenzene (ONCB and PNCB). The reactions were found to be kinetically controlled with apparent activation energies of 22.8, 19.6 and 9.4kcal/mol for ONCB, PNCB and MNCB, respectively. The effects of different parameters such as TBAB concentration, NCB concentration, sulfide concentration, ammonia concentration, and elemental sulfur loading on the conversion and reaction rate of NCBs were studied to establish the mechanism of the reaction. The rate of reaction of NCBs was found to be proportional to the concentrations of the catalyst and NCBs and to the cube of the concentration of sulfide. A generalized empirical kinetic model was developed to correlate the experimentally obtained conversion versus time data for the three NCBs.
Keywords: Hydrogen sulfide; Amine treatment unit; Nitrochlorobenzenes; Chloroanilines; Liquid–liquid phase transfer catalysis; Kinetics