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Showing papers in "Applied Catalysis B-environmental in 1998"


Journal ArticleDOI
TL;DR: In this paper, the open literature concerning chemical and mechanistic aspects of the selective catalytic reduction of NO by ammonia (SCR process) on metal oxide catalysts is reviewed, and the results of spectroscopic studies of the adsorbed surface species, adsorption-desorption measurements, flow reactor and kinetic experiments are analyzed.
Abstract: The open literature concerning chemical and mechanistic aspects of the selective catalytic reduction of NO by ammonia (SCR process) on metal oxide catalysts is reviewed. Catalytic systems based on supported V2O5 (including the industrial TiO2-supported V2O5–WO3 and/or V2O5–MoO3 catalysts) and catalysts containing Fe2O3, CuO, MnOx and CrOx are considered. The results of spectroscopic studies of the adsorbed surface species, adsorption–desorption measurements, flow reactor and kinetic experiments are analyzed. The proposed reaction mechanisms are described and critically discussed. Points of convergence and of disagreement are underlined.

1,946 citations


Journal ArticleDOI
TL;DR: In this article, the steady-state, water-gas-shift kinetics were measured on model, ceria-supported, Pd, Pt, and Rh catalysts and compared to rates obtained on alumina-supported catalysts.
Abstract: Steady-state, water-gas-shift kinetics were measured on model, ceria-supported, Pd, Pt, and Rh catalysts and compared to rates obtained on alumina-supported catalysts. When ceria was calcined at low temperatures prior to addition of the precious metal, the specific rates were found to be identical for each of the metals, with an activation energy of 11 ± 1 kcal/mol and reaction orders of zero and one for CO and H 2 O respectively. For comparison, specific rates on Rh/alumina were at least two orders of magnitude lower. However, ceria structure strongly affected the results. When ceria was calcined to high temperatures to increase crystallite size, prior to the addition of Pd, specific rates were a factor of 50 lower at 515 K and the activation energy was found to be much higher, 21 ± 1 kcal/mol. By comparison with results from an earlier study of CO oxidation [17], we propose that water-gas shift on ceria-supported metals occurs primarily through a bifunctional mechanism in which CO adsorbed on the precious metal is oxidized by ceria, which in turn is oxidized by water. Deactivation of the catalyst following growth in the ceria crystallite size is due to the decreased reducibility of large ceria crystallites. The implications of these results for automotive, emission-control catalysts is discussed.

807 citations


Journal ArticleDOI
TL;DR: In this paper, a low temperature (500°C) route for calcination of hydroxide precipitates and firing mixtures of acetates was investigated and the results showed that the addition of zirconia increased the oxygen storage capacities over ceria alone for both preparation methods.
Abstract: CeO 2 and CeO 2 /ZrO 2 supports were prepared by two low temperature (500°C) routes: calcination of hydroxide precipitates and firing mixtures of acetates. The supports were loaded with 0.5% Pt and characterized both fresh and aged (at 800 and 1000°C). X-ray diffraction analyses show that a CeO 2 /ZrO 2 solid solution is formed in the samples prepared by precipitation of the hydroxides and calcination at 500°C. To our knowledge this is the lowest temperature chemical route (not including high energy ball milling) to CeO 2 /ZrO 2 solid solutions yet reported. Samples prepared by firing the acetate mixtures had almost exclusively CeO 2 and ZrO 2 in separated phases. Oxygen storage measurements showed that the addition of zirconia increased the oxygen storage capacities (on a per gram of catalyst basis) over ceria alone for both preparation methods. In the phase separated materials the amount of reversibly stored oxygen was 1.7–2.5 times more per gram catalyst than that of ceria only. The beneficial effects of zirconia are most pronounced in the solid solutions which had oxygen storage 3–5 times higher than ceria. When the Zr concentration is optimized, the solid solution materials aged at 1000°C showed higher oxygen storage than fresh CeO 2 . For both preparation methods, the optimal (per gram catalyst) Zr concentration was found to be 25 mol% Zr for samples aged at 1000°C, however, the performance of the solid solution materials was somewhat insensitive to Zr loading between 15 and 50 mol% Zr.

492 citations


Journal ArticleDOI
TL;DR: In this article, the photocatalytic degradation of phenol, chosen as an aromatic model molecule, has been performed at room temperature (20°C) in contact with a suspended mixture of titania and activated carbon (AC).
Abstract: The photocatalytic degradation of phenol, chosen as an aromatic model molecule, has been performed at room temperature (20°C) in contact with a suspended mixture of titania and of activated carbon (AC). Non-additive adsorption capacities were observed when the solids were mixed, and this was ascribed to a strong interaction, involving half of the surface of titania and ca. 14% of that of AC. A synergy effect was observed with an increase of the first order rate constant by a factor of 2.5. As for neat titania, the same main intermediate products (hydroquinone and benzoquinone) were found but in much smaller quantities and during a much smaller lifetime, suggesting that the same reaction mechanism occurred in the presence of photoinactive AC. The synergy effect was ascribed to an extended adsorption of phenol on AC followed by a transfer to titania where it is photocatalytically degraded. The synergy effect could not be improved by previous physical treatments of the solid mixture such as grinding and sonication. Some phenol remained adsorbed on AC when no traces of organic compounds were detected in the purified water. This adsorbed phenol could be destroyed by illuminated titania while maintaining UV-irradiation. This combined photocatalytic system may appear as a new performing one, more efficient with a shorter time necessary for decontaminating diluted used waters.

471 citations


Journal ArticleDOI
TL;DR: In this paper, Ni/CeO2-Al2O3, CeO2 and CeO 2-A1(2)O(3) systems were tested for catalytic CO2 reforming of methane into synthesis gas.
Abstract: Ni catalysts supported on gamma-Al2O3, CeO2 and CeO2-A1(2)O(3) systems were tested for catalytic CO2 reforming of methane into synthesis gas. Ni/CeO2-Al2O3 catalysts showed much better catalytic performance than either CeO2- or gamma-Al2O3-supported Ni catalysts. CeO2 as a support for Ni catalysts produced a strong metal-support interaction (SMSI), which reduced the catalytic activity and carbon deposition. However, CeO2 had positive effect on catalytic activity, stability, and carbon suppression when used as a promoter in Ni/gamma-Al2O3 catalysts for this reaction. A weight loading of 1-5 wt% CeO2 was found to be the optimum. Ni catalysts with CeO2 promoters reduced the chemical interaction between nickel and support, resulting in an increase in reducibility and stronger dispersion of nickel. The stability and less coking on CeO2-promoted catalysts are attributed to the oxidative properties of CeO2. (C) 1998 Elsevier Science B.V. All rights reserved.

439 citations


Journal ArticleDOI
TL;DR: In this paper, the degradation kinetics followed a Langmuir-Hinshelwood type equation and the rate was greater in acid media than in neutral and alkaline media, which correlates with the adsorption behavior of eosin on the TiO2 surface.
Abstract: The TiO2-assisted photodegradation of anionic eosin has been examined in TiO2 aqueous dispersions under illumination by visible light. Eosin is easily decomposed photochemically by visible light in the presence of TiO2 particles. The degradation kinetics followed a Langmuir-Hinshelwood type equation. The rate was greater in acid media than in neutral and alkaline media, which correlates with the adsorption behavior of eosin on the TiO2 surface. Adsorption of eosin is a prerequisite for the TiO2-assisted photodegradation. The evolution of CO2 occurred concomitantly with the photodegradation of eosin. A plausible mechanism of degradation is discussed.

437 citations


Journal ArticleDOI
TL;DR: In this article, aniline degradation in acidic medium of pH≈3 under photocatalytic and electrochemical conditions has been investigated, and the role of Fe(II) ions and H 2 O 2 has been made.
Abstract: The aniline degradation in acidic medium of pH≈3 under photocatalytic and electrochemical conditions has been investigated. The efficiency for substrate mineralization in each process has been comparatively analysed by the decrease in TOC of aniline solutions. Particular emphasis has been made on the role of Fe(II) ions and H 2 O 2 . The electrochemical experiments performed in the presence of both species (electro-Fenton conditions) leads to a fast aniline mineralization, which is notably increased by UVA irradiation (photoelectro-Fenton process). In photocatalysis with TiO 2 suspensions, the presence of H 2 O 2 and Fe(II) ions in solution notably increases the aniline degradation rate at the initial stages of the process, whereas the opposite effect occurs at long irradiation times. Benzoquinone, hydroquinone, nitrobenzene, phenol and 1,2,4-benzenetriol were detected as intermediates by HPLC in both, electrochemical and photocatalytic experiments. Short chain aliphatic acids, such as maleic and fumaric acids, were only found in the electrochemical experiments. Ammonium ions (75–80% of initial nitrogen) were generated in all solutions tested. A general reaction pathway that accounts for aniline mineralization to CO 2 involving those products is proposed.

425 citations


Journal ArticleDOI
John Byrne1, Brian R. Eggins1, Norman M.D. Brown1, B. McKinney1, M. Rouse1 
TL;DR: In this paper, the photocatalytic efficiency of the immobilised TiO2 powder was compared using the degradation of phenol in aqueous solution as a standard test system.
Abstract: TiO2 powder was immobilised on solid support substrates (stainless steel, titanium alloy, titanium metal, and tin oxide coated glass) using electrophoretic coating and spray coating. Electrochemical anodisation of titanium metal was also carried out to give a thin film of TiO2 on the surface. The coated substrates were annealed in air at elevated temperatures to improve the adhesion of the catalyst to the supporting substrates. The photocatalytic efficiency of the TiO2 coatings was compared using the degradation of phenol in aqueous solution as a standard test system. In the case of the powder derived films, the photocatalytic efficiency was found not to be markedly dependent upon either the substrate used or the annealing temperature employed in the coating process. Surface analysis of the immobilised TiO2 showed no significant differences in the elemental composition or in band gap energies. The electrophoretic coating method was found to be the most reproducible resulting in highly fractured thick films with high photocatalytic activity. (C) 1998 Elsevier Science B.V.

398 citations


Journal ArticleDOI
TL;DR: In this paper, nanocrystalline titania catalysts with high surface area (68-100m 2 /g) with varying amounts of anatase and rutile phases were tested during the photocatalyzed degradation of p -coumaric acid.
Abstract: Nanocrystalline titania catalysts with high surface area (68–100 m 2 /g) with varying amounts of anatase and rutile phases were tested during the photocatalyzed degradation of p -coumaric acid. This is a pollutant found in agricultural waste waters originating from the wine and olive oil industry. The catalysts were prepared by the same route namely, the hydrolysis of alkoxides followed by densification under hydrothermal conditions (1500–4000 kPa). Hydrolysis of Ti-butoxide gives rise to predominantly anatase containing titania whereas the Ti-ethoxide hydrolysis leads to mixtures of anatase and rutile. Compared to pure anatase or rutile, titania containing both phases shows a significantly higher catalytic activity during the degradation of p -coumaric acid. After preliminary optimization experiments, the degradation of 0.1 mM p -coumaric acid was achieved in 45 min under light irradiation in the presence of H 2 O 2 . The most efficient catalyst is TiO 2 containing 30% rutile and 70% anatase and is prepared by the hydrolysis of tetraisopropyl–orthotitanate. Pore size distribution measurements indicate the presence of mesopores of radii in the range 6–25 A which were responsible for the effective adsorption of the pollutant on the catalyst. Electrophoretic mobility measurements show the isoelectric point for the most efficient catalyst at pH 5.5.

349 citations


Journal ArticleDOI
TL;DR: In this article, a series of supported vanadia catalysts were prepared on various metal-oxide supports: ceria, zirconia, titania, alumina and silica.
Abstract: The objectives of this research are to establish the fundamental kinetics and mechanism of sulfur dioxide oxidation over supported vanadia catalysts and use these insights to facilitate the design of SCR DeNOx catalysts with minimal sulfur dioxide oxidation activity. A series of supported vanadia catalysts were prepared on various metal-oxide supports: ceria, zirconia, titania, alumina and silica. Raman spectroscopy was used to determine the coordination of surface species. At low vanadia loadings, vanadia preferentially exists on oxide support surfaces as isolated tetrahedrally coordinated (M‐O)3V a5 aO species. At higher vanadia loadings, the isolated (M‐O)3V a5 aO species polymerize on the oxide support surface breaking two V‐O‐M bonds and forming two V‐O‐V bridging bonds. The turnover frequency for sulfur dioxide oxidation was very low, 10 ˇ4 to 10 ˇ6 s ˇ1 at 4008C, and was independent of vanadia coverage suggesting that only one vanadia site is required for the oxidation reaction. As the support was varied, sulfur dioxide oxidation activity of the supported vanadia catalysts varied by one order of magnitude (Ce>Zr, Ti>Al>Si). The basicity of the bridging V‐O‐M oxygen appears to be responsible for influencing the adsorption and subsequent oxidation of the acidic sulfur dioxide molecule. Over the range of conditions studied, the rate of sulfur dioxide oxidation is zero-order in oxygen, first-order in sulfur dioxide and inhibited by sulfur trioxide. The turnover frequency for sulfur dioxide oxidation over WO3/TiO2 was an order of magnitude lower than that found for V2O5/TiO2, and no redox synergism between the surface vanadia and tungsten oxide species was evident for a ternary V2O5/ WO3/TiO2 catalyst. This suggests that WO3 promoted catalysts may be suitable for low-temperature SCR where minimal sulfur dioxide oxidation activity is required. # 1998 Elsevier Science B.V. All rights reserved.

314 citations


Journal ArticleDOI
TL;DR: In this article, the redox properties of Cu ions implanted in ZSM-5 and supported on Al2O3, catalysts active in the selective reduction of NO by hydrocarbons such as propane, are investigated.
Abstract: This paper deals with the redox properties of Cu ions implanted in ZSM-5 and supported on Al2O3, catalysts active in the selective reduction of NO by hydrocarbons such as propane. Data on the reducibility of the Cu systems in various atmospheres (vacuum, CO, H2, O2) and on their DeNOx activity are presented. The methods used to obtain informations on the surface and bulk transformations (and their link with catalytic behaviour) are complementary: UV–visible diffuse reflectance spectroscopy being useful to detect the presence of Cu2+ and Cu0, while Cu+ is detected indirectly by the analysis of the IR spectrum of CO bound selectively to this cation. The main contributions to the previous knowledge are the following: it is possible to distinguish CO bound to isolated and non-isolated Cu+ ions; the isolated Cu2+ ions are reducible under vacuum without participation of organic impurities; the more active solids for the NO reduction into N2 are characterized by the presence of isolated Cun+ ions beside the additional influence of the zeolitic framework; after the formation of Cu+ ions the redox cycles are reversible but, after the formation of Cu0, the reversibility or irreversibility of the redox cycles and the restoration of the SCR activity are function of the copper content; the activity decreases after agglomeration into bulk oxides; there is no formation of bulk CuO during the reaction and, with reducing and moderate oxidizing mixtures, part of the copper remains as cuprous ions.

Journal ArticleDOI
TL;DR: In this paper, the photoreduction to the less harmful Cr(III) on the surface of the semiconductor particles was studied as a function of pH of the suspension, initial Cr(VI) concentration, mass of semiconductor in suspension, and different semiconductors as photocatalysts (ZnO, Hombikat UV100, Degussa P25, WO 3 ).
Abstract: A novel technique based on photocatalysis to eliminate Cr(VI) ions, a toxic pollutant in the environment, was applied. The reduction in aqueous suspensions of ZnO (12 g per dm 3 of solution) under air-equilibration and irradiation by a medium pressure mercury lamp (UV/visible) was investigated. The photoreduction to the less harmful Cr(III) on the surface of the semiconductor particles was studied as a function of pH of the suspension, initial Cr(VI) concentration, mass of the semiconductor in suspension, and different semiconductors as photocatalysts (ZnO, Hombikat UV100, Degussa P25, WO 3 ). An increase in the Cr(VI) photoreduced with decreasing pH values was noticed, suggesting an acid-catalysed behaviour. First-order kinetics were observed from the results at different initial concentrations of Cr(VI). A limiting value of the mass of ZnO of 12 g per dm 3 of solution was attained, where a maximum light absorption by ZnO was ascertained. The effect of oxygen in solution of the photoreduction process was studied by experiments performed on either air-equilibrated or nitrogen-purged suspensions, and accordingly the results were compared. A tentative scheme of the possible catalytic reactions for the photoreduction of Cr(VI) over ZnO is given.

Journal ArticleDOI
TL;DR: In this paper, a tentative reaction pathway for propane and propene combustion is proposed based on the reaction products, and a tentative solution for propene and propane combustion is presented.
Abstract: The catalytic oxidation of the C3 organic compounds: propane, propene, 1-propanol, 2-propanol, prop-2-en-1-ol (allyl alcohol), propanal, propanone (acetone) and propenal (acrolein) has been investigated over Mn3O4 in the presence of excess oxygen. Total combustion to CO2 occurs at temperatures >623 K (673 K for propane). However, the production of pollutant products (such as propene from propane, CO from propene, acetaldehyde from propanols, propanal and propanone, carboxylic acids) persists even at very high volatile organic compounds (VOC) conversions. On the basis of the reaction products, a tentative reaction pathway for propane and propene combustion is proposed.

Journal ArticleDOI
TL;DR: In this article, the effects of the support phase and catalyst preparation methods on catalytic activity and carbon deposition were systematically investigated over nickel catalysts supported on Al2O3, SiO2 and MgO for the reforming reaction of methane with carbon dioxide.
Abstract: The effects of the support phase and catalyst preparation methods on catalytic activity and carbon deposition were systematically investigated over nickel catalysts supported on Al2O3, SiO2 and MgO for the reforming reaction of methane with carbon dioxide. It is found that the pore structure of the support and metal-support interaction significantly affected the catalytic activity and coking resistance. Catalyst with well-developed porosity exhibited higher catalytic activity. Strong interaction between metal and the support made the catalyst more resistant to sintering and coking, thus resulting in a longer time of catalyst stability. (C) 1998 Elsevier Science B.V.

Journal ArticleDOI
TL;DR: In this article, the impact of low concentrations of SO 2 on the activity of low loaded alumina supported manganese oxides has been investigated, and it was shown that the deactivation is not due to the formation of (bulk or surface) Al 2 (SO 4 ) 3 or deposition of ammonium sulphates.
Abstract: Low loaded alumina supported manganese oxides exhibit a high activity and selectivity for the selective catalytic reduction (SCR) of NO in the temperature range 383–623 K. The impact of low concentrations of SO 2 on the activity of these catalysts has been investigated. Upon SO 2 addition to the flue gas, the catalysts lose their high initial activity in a few hours due to stoichiometric SO 2 uptake. Analysis of the deactivated samples by mercury porosimetry, FTIR, TPR and TPD shows that the deactivation is not due to the formation of (bulk or surface) Al 2 (SO 4 ) 3 or deposition of ammonium sulphates. Comparison of the results with unsupported Mn 2 O 3 and MnO 2 provides evidence that formation of surface MnSO 4 is the main deactivation route. This process is independent of the oxidation state of the manganese and the presence of oxygen in the gas stream. The formed sulphates decompose at 1020 K and are reduced by H 2 at temperatures above 810 K. This means that regeneration of the catalysts is not very feasible. The results restrict practical application of these catalysts to sulphur free conditions.

Journal ArticleDOI
TL;DR: In this article, a solar photocatalytic plant for the treatment of commercial pesticide rinsates found in the wastewater produced by a pesticide container recycling plant, which includes the correct treatment of this highly contaminating effluent.
Abstract: Particulate suspensions of TiO2 irradiated with natural solar light in a large experimental plant catalyze the oxidation of a typical organic contaminant: pentachlorophenol (PCP). The addition of oxidants, concentration of which is kept constant during treatment, such as hydrogen peroxide, peroxymonosulphate (oxone) and peroxydisulphate increases the rate of photodegradation of PCP in the following order: S2O2−8>Oxone>H2O2. Peroxydisulphate (10 mM), selected as the best oxidant studied, has been applied to the development of a solar photocatalytic plant for the treatment of commercial pesticide rinsates found in the wastewater produced by a pesticide container recycling plant, which includes the correct treatment of this highly contaminating effluent. The first results, without process or hardware optimisation, show that peroxydisulphate enhances the photocatalytic mineralization rate at least five times.

Journal ArticleDOI
TL;DR: In this paper, a pre-doped catalysts, designated as Cu1−xAxFe2O4 (Aǫ: ǫdopant), were studied for the simultaneous NOx-soot removal.
Abstract: Modification of CuFe2O4 catalyst for the simultaneous NOx-soot removal has been studied by doping alkali metals (Li, Na, K, Cs), vanadium and platinum. In pre-doped catalysts, designated as Cu1−xAxFe2O4 (A : dopant), potassium was superior to the other alkali metals and vanadium with respect to enhancing the activity and selectivity to NOx reduction into N2, and the optimum doping level of potassium was x=0.05. Such a promotion effect of potassium was also observed with the impregnated 5 mol% K/CuFe2O4 catalyst. The impregnation of platinum to CuFe2O4 and Cu0.95K0.05Fe2O4 resulted in a decrease in the selectivity to N2 formation with the activity being almost unchanged. The high catalytic performance, especially high selectivity, was realized only when the proper amount of potassium is doped in the Cu–Fe spinel catalyst. XPS analysis showed the segregation (enrichment) of potassium on the surface, and too much doping of potassium might cause the covering of active sites of the Cu–Fe spinel oxide.

Journal ArticleDOI
TL;DR: In this article, the authors performed a pilot scale water detoxification under solar irradiation at the Plataforma Solar de Almeria (Spain) photoreactor, which consisted of a tank (247l) connected to compound parabolic collectors (CPCs) (147l) through which the aqueous suspension of titania (0.2g/l of TiO2 Degussa P-25) was circulated at a flow-rate of 3.5m3/h.
Abstract: The detoxification of water has been performed at a pilot scale under solar irradiation at the Plataforma Solar de Almeria (Spain). The photoreactor consisted of a tank (247 l) connected to compound parabolic collectors (CPCs) (147 l), through which the aqueous suspension of titania (0.2 g/l of TiO2 Degussa P-25) was circulated at a flow-rate of 3.5 m3/h. Two model molecules have been chosen: 2,4-D (2,4-dichlorophenoxyaceticacid), a common herbicide and benzofuran (BZF). Both pollutants disappeared following a first-order kinetics and were completely mineralized according to the total organic carbon (TOC) analysis within a residence time

Journal ArticleDOI
TL;DR: In this paper, a coprecipitation method was used to obtain the reciprocal solubilities calculated from the XRD patterns approach the thermodynamic ones for both propane and propene oxidation.
Abstract: Mn2O3–Fe2O3 powders have been prepared by a coprecipitation method. The pure compounds have been characterized as constituted of α-Fe2O3 (haematite) and α-Mn2O3 (bixbyite) while the mixed oxides are constituted of a mixture of haematite- and bixbyite-structure solid solutions. The observed reciprocal solubilities calculated from the XRD patterns approach the thermodynamic ones. α-Mn2O3 is more active than α-Fe2O3 as catalyst for both propane and propene oxidation. However, α-Mn2O3 is less active than Mn3O4 powder. Propene oxidation is in all cases very selective to CO2 while propane oxidation gives rise to significant amounts of propene on α-Fe2O3. Mn2O3–Fe2O3 powders are slightly more active than α-Mn2O3 as combustion catalysts. The selectivities to propene upon propane oxidation decrease with increasing Mn content.

Journal ArticleDOI
TL;DR: In this article, the combination of TiO 2 -assisted photocatalysis and ozonation in the degradation of aniline in aqueous solution was investigated. And the results showed that the ozonization pretreatment followed by photocata-alysis strongly increased the yield of TOC removal in comparison to either ozoning or photocatalysing separately.
Abstract: The combination of TiO 2 -assisted photocatalysis and ozonation in the degradation of aniline in aqueous solution is investigated. From the experimental results obtained it is observed that the ozonation pretreatment followed by photocatalysis strongly increases the yield of TOC removal in comparison to either ozonation or photocatalysis carried out separately. The opposite sequence (photocatalysis pretreatment followed by ozonation) does not enhance the efficiency of aniline degradation. Nevertheless, the highest TOC removal was achieved by simultaneous ozonation and photocatalysis. A mechanism involving the formation of an ozonide anion radical previous to the generation of OH radicals is suggested to explain the synergic effect between ozone and TiO 2 under illumination.

Journal ArticleDOI
TL;DR: In this article, perovskite-like mixed oxides of general formula La1−xA′xBO3 were prepared by the amorphous citrate method and tested for methane combustion within the 300-600°C temperature range.
Abstract: Some perovskite-like mixed oxides of general formula La1−xA′xBO3 were prepared by the amorphous citrate method and tested for methane combustion within the 300–600°C temperature range. Substitution at A-site with a bivalent (Eu, Sr) or tetravalent (Ce) metal cation led to a decrease or increase of catalytic activity, respectively. La0.9Ce0.1CoO3 proved to be the most active catalyst, showing complete conversion at 500°C. The nature of the metal cation introduced modifies the oxidation state of cobalt, which leads to the formation of cationic or anionic vacancies. TPD-MS analysis confirmed that the catalytic activity is related to the oxygen storage properties of the catalyst. The substitution at B-site (B=Fe, Co, Ni) allowed to find interesting correlations between catalytic activity and the temperature Tmax of maximum oxygen desorption rate.

Journal ArticleDOI
TL;DR: In this article, perovskite-type oxides of the series La1− xAxMnO3 (A Sr, Eu and Ce) were prepared by the amorphous citrate process, leading to high surface area catalysts (up to 45 m2 g−1).
Abstract: Perovskite-type oxides of the series La1− xAxMnO3 (A Sr, Eu and Ce) were prepared by the amorphous citrate process, leading to high surface area catalysts (up to 45 m2 g−1). They were tested in a flow reactor for the total combustion of methane. Complete conversion was obtained over all of the catalysts between 500 and 600°C and catalyst performance did not change significantly after 100 h on-stream. Specific activity was found to decrease monotonically with increasing the temperature of the O2 TPD desorption peak maximum. The rate of methane combustion was low below 500°C, then grew very fast, showing that two kinds of oxygen are active in these catalysts: an adsorbed oxygen species, that reacts at low temperature, and a lattice oxygen species, that becomes available at high temperature, boosting the catalytic activity.

Journal ArticleDOI
TL;DR: In this article, it was found that doping of the TiO2 support with W6+ cations has a positive effect on the activity of Pt catalysts for benzene and ethylacetate oxidation.
Abstract: The oxidation of benzene and ethylacetate, present in trace amounts in air, over Pt supported on γ-Al2O3, SiO2, TiO2 and TiO2 (W6+) carriers has been studied. It was found that doping of the TiO2 support with W6+ cations has a positive effect on the activity of Pt catalysts for benzene and ethylacetate oxidation. A maximum in activity enhancement has been observed at a W6+ content of 0.45 at% in the TiO2 support. The Pt/TiO2 (0.45 at% W6+) catalyst is over two orders of magnitude more active than the Pt/γ-Al2O3 catalyst in the case of ethylacetate oxidation and an order of magnitude more active in the case of benzene oxidation. Doping of TiO2 with W6+ cations enhances its activity for ethylacetate degradation towards smaller organic intermediates, such as ethanol, acetic acid and ethylene, and it also affects product distribution. The enhanced activity of the Pt/TiO2 (W6+) catalysts is attributed to complementary bifunctional steps occuring on sites offered by Pt metal and by the support. During oxidation of benzene-ethylacetate-water mixtures, benzene oxidation is strongly suppressed in the presence of ethylacetate, while water acts as an inhibitor for both volatile organic compounds (VOC) oxidations.

Journal ArticleDOI
TL;DR: In this paper, the performance of both materials was compared in terms of phenol conversion in 240 h tests, and the results showed that the active carbon, without any active metal supported, gives the highest phenol reduction.
Abstract: Catalytic wet air oxidation is a promising alternative for the treatment of phenolic waste water which cannot be treated in conventional sewage plants. Catalytic wet air oxidation of an aqueous phenol solution was conducted in a fixed bed reactor operating in trickle flow regime. Either active carbon or a commercial copper oxide supported over γ-alumina was used as catalyst. The performance of both materials was compared in terms of phenol conversion in 240 h tests. The results showed that the active carbon, without any active metal supported, gives the highest phenol conversion. The supported copper catalyst undergoes a rapid deactivation due to the dissolution of the metal active species in the acidic medium in which the reaction takes place. On the other hand, the active carbon maintains a higher activity throughout the test, although a decrease of the phenol conversion was also observed due to both the loss of active carbon by combustion and the reduction of its surface area. The phenol oxidation was proved to occur through a first order mechanism with respect to phenol. After the ten-day run, the catalytic activity of the active carbon was found to be about eight times higher than that of the commercial catalyst, also showing high selectivity to the production of carbon dioxide.

Journal ArticleDOI
TL;DR: The catalytic transformations of 1,2-dichlorobenzene, chlorobenzenes, 4-chlorobiphenyl, γ-hexachlorocyclohexane (Lindane), naphthalene and phenanthrene were studied over palladium on alumina in hydrogen-saturated water (Pd/Al2O3/H2) at room temperature and ambient pressure as discussed by the authors.
Abstract: The catalytic transformations of 1,2-dichlorobenzene, chlorobenzene, 4-chlorobiphenyl, γ-hexachlorocyclohexane (Lindane), naphthalene and phenanthrene were studied over palladium on alumina in hydrogen-saturated water (Pd/Al2O3/H2) at room temperature and ambient pressure. The chlorinated benzenes were rapidly hydrodechlorinated and Lindane was dehydrochlorinated to benzene. Partial or complete hydrogenation was observed for biphenyl and the polycyclic aromatic hydrocarbons. The phenanthrene ring was cleaved at the 9,10-position. In general dechlorination reactions were faster than hydrogenation reactions.

Journal ArticleDOI
TL;DR: In this paper, the catalytic properties of cobalt containing ZSM-5 zeolites prepared by various methods were compared, including TPR, XRD, N 2 -BET, XPS, FTIR and UV-vis spectroscopy were used for characterizing the samples.
Abstract: The catalytic properties of cobalt containing ZSM-5 zeolites prepared by various methods were compared. TPR, XRD, N 2 -BET, XPS, FTIR and UV–vis spectroscopy were used for characterizing the samples. Well-dispersed cobalt oxide-like species and isolated Co 2+ ions in charge compensation positions were found in the zeolite. Catalysts prepared using a single step cation exchange method showed high activity for N 2 O decomposition in a temperature range 300–550°C, in the presence of 0–5% O 2 , and high stability in the presence of 10% H 2 O to the feed. UV–vis spectra and TPR experiments indicated the presence of some cobalt oxides, not detected by DRX, in a Co-ZSM-5 catalyst containing 3.76 wt% Co, prepared by a solid-state reaction procedure. The N 2 O conversion over this catalyst was strongly affected by addition of both O 2 and H 2 O to the feed.

Journal ArticleDOI
TL;DR: In this article, samples of iron-doped titania prepared by the wet impregnation method from TiO 2 and two different precursors, Fe(NO 3 ) 3.9H 2 O and Fe(III) acetylacetonate, were tested as photocatalysts in two reactions: nitrite oxidation and Cr(VI) reduction at pH 6.5.
Abstract: Samples of iron-doped titania prepared by the wet impregnation method from TiO 2 (Degussa P-25) and two different precursors, Fe(NO 3 ) 3 .9H 2 O and Fe(III) acetylacetonate, were tested as photocatalysts in two reactions: nitrite oxidation and Cr(VI) reduction at pH 6.5. Whereas samples prepared from Fe(NO 3 ) 3 .9H 2 O containing low amounts of iron (less than 2 wt.%) were more efficient for nitrite oxidation than pure TiO 2 , specimens obtained from Fe(III) acetylacetonate were less active. In the case of Cr(VI) reduction, all doped samples were less active than TiO 2 with no sensibly differential activity. Different mechanistic pathways and structural and surface properties of the samples are invoked to explain the observed behavior.

Journal ArticleDOI
TL;DR: In this paper, the authors showed that the Fe in the zeolite cavities is different from Fe2O3 particles, and that a minority of the Fe complexes lose oxygen upon mere heating to ∼500°C; some of the reduced sites are reoxidized only by N2O.
Abstract: Fe/ZSM-5 catalysts with high Fe loading (Fe/Al∼1) have been prepared by sublimation of FeCl3 onto H-ZSM-5 samples of different Si/Al ratios. They catalyze NOx reduction with hydrocarbons in an excess of O2 and H2O. TPR shows that the Fe in the zeolite cavities is different from Fe2O3 particles. Naked Fe3+ ions are absent; oxo-ions, which are equally well reducible by CO and H2, prevail. A minority of the Fe complexes lose oxygen upon mere heating to ∼500°C; some of the reduced sites are reoxidized only by N2O. The population of oxo-complexes that lose oxygen by heating depends on the Si/Al ratio, this dependence is in qualitative agreement with the model of (2+) charged binuclear ions [HO–Fe–O–Fe–OH]2+. Upon reacting with NO, the bridging O atom is transferred and NO2 is formed. This step is not rate limiting for active catalysts with high Al/Si ratio and high Fe loading, but it becomes critical with zeolites of low Al/Si ratio.

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TL;DR: In this paper, a packed bed filled with coated titanium dioxide glass beads was used to study the kinetics of photocatalytic degradation of trichloroethylene under irradiation of 365nm UV light.
Abstract: In this investigation, a packed bed filled with coated titanium dioxide glass beads to study the kinetics of photocatalytic degradation of trichloroethylene under irradiation of 365 nm UV light. In the range of 100–500 ml/min of flowrate, the reaction rate for 6 μM TCE increased with an increasing flowrate upto 300 ml/min, while was not affected by the flowrate at the values higher than 300 ml/min. For moisture in the range of 9.4–1222.2 μM, the reaction rate of TCE was decreased with an increasing humidity. The adsorbed water on the catalyst surface could compete with the adsorption of TCE on the sites. The reaction rate of 6 μM TCE increased as the light intensity increased, and was proportional to the 0.61 order of the light intensity. Among the three L–H bimolecular form models, the experimental data had the best fit for one of models: r=k[K 1 C r /(1+K 1 C r +K 2 C w )][K 4 C w /(1+K 3 C r +K 4 C w )]

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TL;DR: In this paper, the authors examined the performance of supported gallium oxides for the selective reduction of NO by CH 4 in excess oxygen, and compared with supported Ga 2 O 3 /Al 2 O3 and Co-ZSM-5.
Abstract: Catalytic properties of supported gallium oxides have been examined for the selective reduction of NO by CH 4 in excess oxygen. The activity was greatly affected by the support; Ga 2 O 3 /Al 2 O 3 (Al 2 O 3 supported Ga 2 O 3 ) and Ga 2 O 3 –Al 2 O 3 mixed oxide exhibited high activity and selectivity as comparable to Ga-ZSM-5, while unsupported Ga 2 O 3 and the other supported Ga 2 O 3 were ineffective. For Ga 2 O 3 /Al 2 O 3 , the activity changed with Ga 2 O 3 content, and was highest at about 30 wt% Ga 2 O 3 , which corresponds to a theoretical monolayer coverage. Gallium oxide highly dispersed on Al 2 O 3 is considered to be responsible for the high activity and selectivity. The reaction characteristics of Ga 2 O 3 /Al 2 O 3 were studied and compared with Ga-ZSM-5 and Co-ZSM-5. Ga 2 O 3 /Al 2 O 3 exhibited the highest activity and selectivity at high temperature. In addition, Ga 2 O 3 /Al 2 O 3 showed higher tolerance against water than Ga-ZSM-5. C 3 H 8 and C 3 H 6 were also evaluated as reducing agents, and Ga 2 O 3 /Al 2 O 3 showed higher activity than Ga-ZSM-5 above 723 K achieving almost complete reduction of NO to N 2 .