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Applied Catalysis B, Environmental (v.77, #1-2)

IFC Editorial Board (pp. co2).

Contents (pp. co4).

Editorial Board (pp. i).

Contents Continued (pp. iv).

Photocatalytic degradation of azo dye Metanil Yellow: Optimization and kinetic modeling using a chemometric approach by Mohamad Sleiman; Daniel Vildozo; Corinne Ferronato; Jean-Marc Chovelon (pp. 1-11).

The photocatalytic degradation of an azo dye Metanil Yellow was carried out in aqueous solution using TiO₂ as photocatalyst under UV irradiation. The decolorization and degradation kinetics were investigated and both followed a pseudo first order kinetic according to Langmuir–Hinshelwood model. Using HPLC/DAD and GC/MS analyses, more than 10 major reaction intermediates were identified and a tentative degradation pathway was proposed. Furthermore, ion chromatography (IC) and TOC measurements revealed a complete mineralization of Metanil Yellow into CO₂, N₂, H₂O and inorganic ions (NH₄⁺, NO₃⁻ and SO₄²⁻).On the other hand, an experimental design based on the surface response methodology was applied to assess the individual and interaction effects of several operating parameters (dye concentration, TiO₂ concentration, pH, light flux, etc.) on the treatment efficiency (dye removal time). Based on the experimental design data, a semi-empirical expression was obtained, permitting to predict and optimize the dye removal time. This model was very consistent with experiment results (correlation factor: 99.5%). Moreover, additional experimental results obtained under near optimal conditions were found to be very close to the predicted values.This work demonstrates well the utility and benefits of the experimental design approach for screening and modeling the reaction parameters. Furthermore, it contributes significantly to the improvement and better understanding of photocatalytic processes.

Keywords: Azo dye; Metanil Yellow; TiO; ₂; photocatalysis; Experimental design; Optimization

The dependence of NO₂ and CO₂ uptake and release on BaO content for NO_x storage catalysts made using different precursor salts by Noel W. Cant; Irene O.Y. Liu; Michael J. Patterson (pp. 12-18).

Here we compare the uptake of CO₂ on BaO–Al₂O₃ with that of NO₂ for nine samples made by one, two or three incipient wetness impregnations using acetate and nitrates as the precursor salts. The amounts of CO₂ and NO₂ adsorbed to the point of breakthrough at 300°C are similar, proportional to the BaO content and largely independent of the preparation method. The breakthrough of CO₂ is sharp. Its desorption occurs over a wide range of temperatures. Displacement by NO₂ will remove the one-quarter retained at 550°C. Unlike the adsorption of CO₂, the uptake of NO₂ continues for prolonged period after initial breakthrough. It occurs with disproportionation of NO₂ to gaseous NO and stored nitrate. Measurement of the overall O:N ratio in the gaseous decomposition products shows that the material stored to the point of breakthrough retains the overall stoichiometry NO₂. It decomposes in two stages, initially by disproportionation to NO and nitrate followed by decomposition of the latter to NO and O₂ in the ratio 4:3 starting at 450°C. The O:N ratio of material stored after prolonged exposure corresponds to nitrate. In accordance with the literature, these species decompose to NO₂ and a small amount of O₂ with maximum evolution rates below 500°C and to NO and O₂ in the 4:3 ratio above that. The amount of NO₂ produced is largely independent of the BaO content while that of NO is proportional to it.

Keywords: BaO–Al; ₂; O; ₃; NO; _x; storage; CO; ₂; uptake; Barium content; Precursor salts

An opening route to the design of cathode materials for fuel cells based on PtCo nanoparticles by Patricia Hernández-Fernández; Sergio Rojas; Pilar Ocón; José Luis Gómez de la Fuente; Pilar Terreros; Miguel Antonio Peña; José Luis García-Fierro (pp. 19-28).

The performance of PtCo/C electrocatalysts in the oxygen reduction reaction is enhanced after thermal treatment in hydrogen. In fact, the intrinsic activity (per gram of Pt) of PtCo/C electrocatalyst after the adequate treatment is far superior to that of the commercial sample. The PtCo nanoparticles were prepared from the water-in-oil microemulsion technique. The total metal loading of the catalyst was 30wt%, and two reduction temperatures, 300 and 875°C, were studied. Electrochemical measurements were carried out using the rotating disk electrode method in 0.5M H₂SO₄ at room temperature, while the Pt real surface area was determined by CO stripping voltammetry. Analyses from XPS and TPR revealed that the amount of Co and Pt reduced species as well as the particle size (XRD), increased with the thermal treatment. Results derived from the electrochemical analyses were in agreement with those obtained in a H₂/O₂ single cell. These results demonstrate the important role of the cobalt as well as the reduction temperature and atmosphere, and open new ways for the design of improved bimetallic catalyst.

Keywords: Fuel cell; Electrocatalysts; Thermal treatment; PtCo

Promoting functions of H₂ in diesel-SCR over silver catalysts by V. Houel; P. Millington; R. Rajaram; A. Tsolakis (pp. 29-34).

During the selective reduction of NO_x over silver, the known promoting effect of H₂ has been found to vary with the nature of the hydrocarbon reductant. The promoting effect is more pronounced when the reductants are short-chain alkanes, such that the steady-state NO_x conversion at low temperature follows the order: n-C₈H₁₈> n-C₁₀H₂₂> n-C₁₂H₂₆>GTL-fuel>ultra-low sulphur diesel fuel. This reactivity pattern is almost the reverse of that observed in the absence of H₂, where the initial activity is higher for the longer, more reactive alkanes. It has become clear that silver can initially achieve very high NO_x conversion irrespective of the reductant speciation when H₂ is present, but the beneficial effect can be negated (when diesel fuels are used as reductants) by deposition of carbon-rich surface species. By optimising the fuel injection strategy (i.e., the hydrocarbon:NO_x ratio), the promoting effect can be made to dominate, even at relatively low concentrations of H₂ (300–600ppm), which could be produced in an exhaust gas by re-calibrating the engine. When diesel fuel is the reductant, we suggest that a key function of H₂ is to enhance the formation of NO₂, which is very effective at oxidising the carbon-rich species at low temperatures, so allowing the good initial activity to be maintained.

Keywords: Hydrocarbon-SCR; Silver; Hydrogen; Diesel fuel

Influence of mesoporous and platinum-modified titanium dioxide preparation methods on photocatalytic activity in liquid and gas phase by Ekaterina A. Kozlova; Alexander V. Vorontsov (pp. 35-45).

Mesoporous titanium dioxide photocatalysts have been synthesized by template method using widely used precursors and templates with the purpose of choosing the best method for liquid and gas phase photocatalytic oxidation. Titanyl sulphate (TS) and tetrabutyl titanate (TBT) were precursors and cetyl trimethylammonium bromide (CTAB) and dodecylamine (DDA) were templates. Hydrothermal treatment temperature was optimized for the best obtained photocatalyst. The catalysts were characterized by N₂ adsorption–desorption measurements, XRD and UV–vis diffuse reflectance spectroscopy. Samples obtained from TBT contained significant amounts of brookite. Activity was measured in liquid phase for dimethyl methylphosphonate (DMMP) and in gas phase for acetone complete oxidation. The highest activity in liquid phase was observed for catalyst prepared from TS and DDA and aged at 160°C. Activity was higher than that of TiO₂ Degussa P25 in the low concentration range. The highest activity in gas phase was observed for catalyst prepared from TBT and CTAB. Activity of mesoporous catalysts correlates with their surface area and pore volume for gas phase reaction, whereas in the case of liquid phase DMMP oxidation, there is no sufficient correlation. The effect of DMMP initial concentration on initial oxidation rate is well fitted by Langmuir–Hinshelwood competitive adsorption model. Mesoporous catalysts possess higher adsorption constant but lower reaction rate constant than TiO₂ P25. Platinum was deposited by impregnation and soft chemical reduction (SCR) or photodeposition methods (PD). Catalysts obtained by PD were 50% more active than by SCR and 4.5-fold more active than TiO₂ P25 in aqueous phase. The reasons for extraordinarily high activity of this mesoporous catalyst are discussed.

Keywords: Photocatalysis; Oxidation; Template synthesis; Pt; TiO; ₂; Phosphonate; Chemical warfare agent; Decontamination; Sarin; Soman

Cu/ZnO/Al₂O₃ catalysts for oxidative steam reforming of methanol: The role of Cu and the dispersing oxide matrix by Maria Turco; Giovanni Bagnasco; Claudia Cammarano; Pasquale Senese; Umberto Costantino; Michele Sisani (pp. 46-57).

Cu/ZnO/Al₂O₃ catalysts (5–45 Cu at.%) derived from layered double hydroxide (LDH) precursors were studied for oxidative steam reforming of methanol (OSRM). The precursors were prepared by homogeneous precipitation with urea. The catalysts were obtained by thermal decomposition of the precursors and subsequent reduction in H₂ stream. XRD, SEM, N₂ adsorption, TPR and NH₃ TPD techniques were employed for characterization. Catalytic activity tests were carried out in a fixed bed flow reactor at T=200–400°C, H₂O/CH₃OH/O₂ molar ratios=1.1/1/0.12 (CH₃OH concentration=17.8%), GHSV=6×10⁴h⁻¹. Tests of simple steam reforming (SRM), partial oxidation (POM) and CH₃OH decomposition (DEC) were also carried out. TPR measurements showed that redox properties depended on the composition of the samples and on the nature of the phases present in the precursors. The area of metallic Cu, measured by N₂O passivation method, was correlated to Cu content. The size of Cu particles was smaller than 10nm for Cu content up to 18at.%. NH₃ TPD measurements showed acid sites with a wide strength distribution, the strongest ones being mainly related to Al₂O₃ or Zn aluminate. Catalytic activity was influenced by the chemical composition: kinetic constants for OSRM varied unevenly with Cu surface area, while those for SRM increased with Cu surface area. A reaction mechanism agreeing with OSRM, SRM and DEC data was hypothesized. The mechanism involved an oxidation-reduction cycle of Cu and also the participation of the oxide matrix.

Keywords: Methanol; Oxidative steam reforming; Cu/ZnO/Al; ₂; O; ₃; catalysts; Layered double hydroxide; Cu dispersion; Reaction mechanism

Electrochemical degradation of 4-chlorophenol using a novel Pd/C gas-diffusion electrode by Hui Wang; Jianlong Wang (pp. 58-65).

Pd/C catalyst was prepared by hydrogen reduction method and used for the Pd/C gas-diffusion electrode. It was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV) techniques. The electrochemical degradation of 4-chlorophenol was investigated in a diaphragm electrolysis device, by two different feeding gas modes, using the Pd/C gas-diffusion electrode and the carbon/polytetrafluoroethylene (C/PTFE) gas-diffusion electrode as a cathode, respectively. The results indicated that Pd particles with an average size of 4.0nm were highly dispersed in the activated carbon with an amorphous structure; Pd content on the surface of the Pd/C catalyst reached 1.3 at.%. Furthermore, feeding with hydrogen gas firstly and then with air was in favor of improving 4-chlorophenol removal efficiency. The Pd/C gas-diffusion cathode can not only reductively dechlorinate 4-chlorophenols by feeding hydrogen gas, but also accelerate the two-electron reduction of O₂ to hydrogen peroxide (H₂O₂) by feeding air. Therefore, the removal efficiency of 4-chlorophenol by using the Pd/C gas-diffusion cathode was better than that of the C/PTFE gas-diffusion cathode. And both the removal efficiency and the dechlorination degree of 4-chlorophenol reached about 100% after 60min, and the average removal efficiency of 4-chlorophenol in terms of chemical oxygen demand (COD) exceeded 70% after 120min. The analysis of high-performance liquid chromatography (HPLC) identified that phenol was the dechlorination product, and hydroquinone, benzoquinone, maleic, fumaric, crylic, malonic, oxalic, acetic and formic acids were the main oxidation intermediates. A reaction pathway involving all these intermediates was proposed.

Keywords: Electrochemical oxidation; Gas-diffusion cathode; Pd/C catalyst; Chlorophenol; Priority pollutant

Simultaneous and/or separate SO₂/NO reduction by CO over high surface area Cu/Ce containing mesoporous silica by C.C. Pantazis; D.E. Petrakis; P.J. Pomonis (pp. 66-72).

In this work the catalytic performance of a highly thermal-stable mesoporous silica network of large specific surface area >800m²g⁻¹containing Cu and Ce at a load >15 wt.%, in NO reduction by CO, SO₂ reduction by CO as well as the simultaneous reduction of SO₂ and NO by CO is reported.The results indicate a highly active and stable redox catalyst in the above reactions. The variation of the feeding concentration of CO leads to control over COS yield which can be eliminated at a ratio of CO/SO₂ around 2.5, regarding the reaction of the reduction of SO₂ by CO. As far as the simultaneous reduction of SO₂ and NO by CO is concerned, the catalyst proved able to completely reduce NO and SO₂ simultaneously by CO at a relevantly high GHSV 32000h⁻¹ to N₂ and elemental sulfur, respectively, producing at the same time negligible amount of COS, while the results imply a competitive behavior between SO₂ and NO.

Keywords: Simultaneous SO; ₂; /NO reduction; CO oxidation; Mesoporous silica; Copper-ceria catalyst

New approach to enhance the NO x storage performance at high temperature using basic MgAl₂O₄ spinel support by Naoki Takahashi; Shin’ichi Matsunaga; Toshiyuki Tanaka; Hideo Sobukawa; Hirofumi Shinjoh (pp. 73-78).

With the purpose of improving the NO x storage performance of NO x storage and reduction (NSR) catalysts above 673K, a new approach using a support with a higher basicity than γ-Al₂O₃ was proposed and exemplified by using the MgAl₂O₄ spinel as the support for an NSR catalyst containing the potassium NO x storage material. The NO x storage amounts on the fresh and thermally-aged K/Pt/MgAl₂O₄ catalysts at 873K were apparently higher than those on the K/Pt/Al₂O₃ catalysts. The higher potassium basicity resulting from the interaction between the basic MgAl₂O₄ support and the potassium NO x storage material enhanced the stability of the stored NO x over the fresh and thermally-aged K/Pt/MgAl₂O₄ catalysts, which leads to their competitive NO x storage amounts versus those of the K/Pt/Al₂O₃ catalysts. These results indicated a breakthrough that improved the performance of the NSR catalysts at high temperature.

Keywords: NO; x; storage and reduction catalyst; MgAl; ₂; O; ₄; spinel; Potassium; Thermal-aging; Basicity

Preparation, characterization, catalytic activity and CO₂ absorption/desorption studies of Ln/K (Ln=La, Sm, Y) catalysts for diesel soot elimination by Yongheng Zhang; Xiaoting Zou; Fei Yu; Junhong Xu (pp. 79-91).

Ln/K oxide catalysts (Ln=La, Sm, Y) supported on the alumina substrate have been prepared and their catalytic activities of diesel soot oxidation were tested by TPR system. The results showed that all La/K, Sm/K and Y/K catalysts showed a similar change of catalytic activity with the variation of K content. Nevertheless, Y/K catalyst was more active for diesel soot oxidation with a soot ignition temperature of about 350°C at a loose soot/catalyst contact mode. XRD, TG/DSC analyses were employed to investigate the structures and thermal behaviors of catalysts. It was found that the oxides would react with KNO₃ to form the solid solution and the K⁺ saturation level was related to the ionic radii of the Ln³⁺. The Ln/K catalysts showed a physical CO₂ absorption ability that was further enhanced at higher temperature. However, when the temperature was above a critical temperature, the absorption ability was reduced. The CO₂ absorption characteristics was believed to be diffusion controlled and was attributable to the lattice defects (oxygen vacancies) caused by the solid solution formation. The dynamic CO₂ transportation within the catalyst could play an important role on the catalytic oxidation process.

Keywords: Diesel soot; Oxidation; La; ₂; O; ₃; Sm; ₂; O; ₃; Y; ₂; O; ₃; Catalytic activity; CO; ₂; absorption and desorption

Involvement of NCO species in promotion effect of water vapor on propane-SCR over Co-MFI zeolite by Akira Shichi; Tadashi Hattori; Atsushi Satsuma (pp. 92-99).

The effect of water vapor on the SCR of NO by propane over Co-MFI zeolite was investigated with respect to behavior of surface NCO species. In the absence of water vapor, the NO conversion at lower temperatures below 648K decreased with time-on-stream. In the presence of water vapor, on the other hand, the NO conversion was higher than in the absence of water vapor and the catalyst deactivation was not observed. From the measurement of in situ IR spectra, it was found that NCO species accumulates on the catalyst in the absence of water vapor and then leads to deactivation of catalyst. In the presence of water vapor, however, it was found that the NCO species were easily hydrolyzed to ammonia and carbon dioxide, and therefore, the higher SCR activity was obtained. Thus, NCO species, which are known to be an important intermediate to form nitrogen in HC-SCR, could cause self-poisoning in the absence of water vapor.

Keywords: Selective catalytic reduction; Water vapor; Co-MFI; IR spectra; Deactivation

Photocatalytic decolorization of Remazol Black 5 (RB5) and Procion Red MX-5B—Isotherm of adsorption, kinetic of decolorization and mineralization by K. Sahel; N. Perol; H. Chermette; C. Bordes; Z. Derriche; C. Guillard (pp. 100-109).

The isotherm of adsorption and the kinetic of photocatalytic degradation of two azo dyes, Remazol Black 5 (RB5) and Procion Red MX-5B are reported and compared using different concentrations of dyes. The photocatalytic degradation is performed in aqueous solutions in the presence of TiO₂ Degussa P25 under artificial UV light radiation ( λ>290nm).The isotherms of adsorption of the both dyes are very different. These differences are discussed considering the pH of the solution and the structure of the dye. In opposition to the isotherm of adsorption, the kinetic of both dyes are very similar, and fit well with the Langmuir–Hinshelwood model in the concentration range 5–60μmol/L. However, at higher dyes concentration, the initial rate of decolorization decreases. The important absorption of light by the dyes was suggested to be at the origin of this decrease of the decolorization. The absence of correlation between isotherm of adsorption in the dark and the decolorization kinetics is discussed.The attribution of main UV–vis bands of each dye has been performed by molecular modelisation using Density Functional Theory (DFTT). Their evolution as a function of time, the evolution of pH during the photocatalytic process and the determination of the decrease of Total Organic Carbon (TOC) and of the evolution of inorganic ions are used to better understand the decolorization mechanism occurring for these both dyes.

Keywords: Photocatalysis; TiO; ₂; Dyes; Isotherm; Kinetic; Mechanism

Nanoscale Pd/Fe bimetallic particles: Catalytic effects of palladium on hydrodechlorination by Hsing-Lung Lien; Wei-Xian Zhang (pp. 110-116).

Reported herein is a study on the catalytic properties of palladium for hydrodechlorination using nanoscale zero-valent iron particles. Temperature-dependent experiments and X-ray diffraction (XRD) are conducted to characterize reactions of chlorinated ethylenes with nanoscale Fe and Pd/Fe particles. XRD results suggest bimetallic structures are created as a result of Pd(II) reduction by zero-valent iron and the degree of surface palladium loading is proportional to the initial amount of palladium applied. The optimal content of palladium in the bimetallic particles for dechlorination is in the range of 1–5% by weight. XRD analyses further suggest that oxidation of iron produces mainly iron oxides. No oxidized species of palladium (e.g., PdO) is found before or after the reactions. Activation energies of the dechlorination reactions with the nanoscale Pd/Fe and Fe particles are estimated to be 31.1 and 44.9kJ/mol, respectively. A conceptual model for the catalytic hydrodechlorination by the nanoscale Pd/Fe particles is presented.

Keywords: TCE; Palladium; Iron; Hydrodechlorination; Nanoparticles; Groundwater remediation

Preparation of highly active AlSBA-15-supported platinum catalyst for thiophene hydrodesulfurization by Yasuharu Kanda; Tomohiro Aizawa; Takao Kobayashi; Yoshio Uemichi; Seitaro Namba; Masatoshi Sugioka (pp. 117-124).

The catalytic activities of various noble metals (Pt, Pd, Rh, and Ru) supported on siliceous SBA-15 and Al-containing SBA-15 (AlSBA-15) for hydrodesulfurization (HDS) of thiophene at 350°C were investigated. AlSBA-15 was prepared by a grafting method using aluminum isopropoxide (Al(OC₃H₇)₃) hexane solution. The HDS activity of Pt/AlSBA-15 catalyst was the highest among those of various supported noble metal catalysts, and this activity was higher than that of commercial CoMo/Al₂O₃ HDS catalyst. The catalysts were characterized by XRD analysis, hydrogen adsorption, 2-propanol dehydration, cumene cracking, and FT-IR. Dispersion of Pt on SBA-15 was remarkably enhanced by Al grafting. It was revealed that the acidity of AlSBA-15 was higher than that of SBA-15. Furthermore, Brønsted acid sites were observed on AlSBA-15. FT-IR spectra of thiophene adsorbed on AlSBA-15 indicate that thiophene molecules interact with Brønsted acid sites on the surface of AlSBA-15 and that the strength of this interaction was stronger than that of SBA-15. Based on these results, thiophene molecules activated on Brønsted acid site of AlSBA-15 and hydrogen molecules activate to form spillover hydrogen on Pt particles in Pt/AlSBA-15 catalyst in the HDS of thiophene.

Keywords: Acid rain prevention; Hydrodesulfurization; Thiophene; SBA-15; Noble metal catalyst

The nature of surface acidity and reactivity of MoO₃/SiO₂ and MoO₃/TiO₂–SiO₂ for transesterification of dimethyl oxalate with phenol: A comparative investigation by Yue Liu; Xinbin Ma; Shengping Wang; Jinlong Gong (pp. 125-134).

This paper presents results of a comparative investigation of the transesterification of dimethyl oxalate (DMO) with phenol to produce methyl phenyl oxalate (MPO) and diphenyl oxalate (DPO) over MoO₃/SiO₂ and MoO₃/TiO₂–SiO₂ catalysts. The evaluation results show that MoO₃/TiO₂–SiO₂ is much more active and selective than MoO₃/SiO₂. The surface structure and acidity of MoO₃/SiO₂ and MoO₃/TiO₂–SiO₂ were investigated by a series of characterization approaches. XRD and FT-IR demonstrated that the incorporation of amorphous TiO₂ could not only enhance the interaction between MoO₃ and SiO₂, but also improve the dispersion state of MoO₃ on the surface of SiO₂. NH₃-TPD and FT-IR of adsorbed pyridine measurements indicated that amorphous TiO₂ incorporation into and further interaction with MoO₃ and SiO₂ formed more weak acid sites on the surface of the catalysts. However, Brönsted acid sites were also detected on the surface of the MoO₃/TiO₂–SiO₂ catalysts, which further motivated us to study the nature of Brönsted acid sites in detail. Several conventional Brönsted acids were also tested in the transesterification. The results unexpectedly showed that conventional Brönsted acids have better reactivities than those of conventional Lewis acids from selective point of view. In addition, the combination of reactivity tests, NH₃-TPD spectra, and FT-IR measurements of adsorbed pyridine strongly suggest that the strong Lewis acid is more responsible for the production of the by-product anisole than the strong Brönsted acid. The results indicated that the improvement of catalytic efficiency of MoO₃/TiO₂–SiO₂, compared to MoO₃/SiO₂, could be ascribed to the increased dispersion capacity of MoO₃ and the dominant weak acid sites (including the synergistic effect of the weak Lewis acid sites with the weak Brönsted acid sites). A tentative mechanism for the transesterification reaction over Brönsted acid was proposed.

Keywords: Phosgene-free; Diphenyl carbonate; Transesterification; Dimethyl oxalate; Diphenyl oxalate; Methyl phenyl oxalate; MoO; ₃; /TiO; ₂; –SiO; ₂; MoO; ₃; /SiO; ₂; Brönsted acid; Lewis acid

Heterogeneous photocatalytic degradation of the pharmaceutical agent salbutamol in aqueous titanium dioxide suspensions by V.A. Sakkas; P. Calza; C. Medana; A.E. Villioti; C. Baiocchi; E. Pelizzetti; T. Albanis (pp. 135-144).

The present paper deals with the photocatalytic transformation of salbutamol [2-( tert-butylamino)-1-(4-hydroxyl-3-hydroxymethylphenyl)ethanol] under simulated solar irradiation using titanium dioxide as a photocatalyst. The investigation has involved a kinetic study of the drug decomposition, the identification of intermediate compounds, the assessment of mineralization, as well as toxicity evaluation. The variation of TiO₂ concentration and pH on the reaction rate was investigated. The use of the response surface methodology allowed to fit the optimal values of the parameters leading to the degradation of the micro-pollutant. High resolution mass spectrometry was employed in assessing the temporal course of the photocatalyzed process. According to our findings, a tentative degradation pathway is proposed for the photocatalytic degradation of salbutamol based on the formation of both oxidative and reductive compounds. 2-(Methylamino)-1-(4-hydroxyl-3-methylphenyl)ethanol, 2-( tert-butylamino)-1-(4-hydroxylphenyl)ethanol, 2-( tert-butylamino)-1-(3,4-dihydroxyphenyl)ethanol, 2-( tert-butylamino)-1-(4-hydroxyl-3-methylphenyl)ethanol, and 2-( tert-butylamino)-1-(3,4-dihydroxyphenyl)ethanone are initially formed, which are then transformed into 2-( tert-butylamino)-acetic acid and hydroquinone. All these intermediates are easily degraded themselves and until 2h of irradiation 2-( tert-butylamino)-acetic acid is the only compound recognized to endure.Photomineralization of the substrate was rather a quick process; within 2h of irradiation nitrogen is completely mineralized, where the amino moiety is mainly transformed into NH₄⁺ and in a lesser extent into NO₃⁻ ions (ratio 2:1). Carbon complete mineralization is achieved within 3h of irradiation. Finally, Microtox bioassay ( Vibrio fischeri) was employed in evaluating the ecotoxicity of solutions treated by photocatalysis.

Keywords: Photocatalysis; TiO; ₂; Experimental design; Mineralization; Toxicity; Salbutamol

Sulfur impact on NO_x storage, oxygen storage, and ammonia breakthrough during cyclic lean/rich operation of a commercial lean NO_x trap by Jae-Soon Choi; William P. Partridge; C. Stuart Daw (pp. 145-156).

The objective of the present study was to develop an improved understanding of how sulfur affects the spatiotemporal distribution of reactions and temperature inside a monolithic lean NO_x trap (LNT). These spatiotemporal distributions are believed to be major factors in LNT function, and thus, we expect that a better understanding of these phenomena can benefit the design and operation of commercial LNTs. In our study, we experimentally evaluated a commercial LNT monolith installed in a bench-flow reactor with simulated engine exhaust. The reactor feed gas composition was cycled to simulate fast lean/rich LNT operation at 325°C, and spatiotemporal species and temperature profiles were monitored along the LNT axis at different sulfur loadings. Reactor outlet NO_x, NO, N₂O, and NH₃ were also measured. Sulfur tended to accumulate in a plug-like fashion in the reactor and progressively inhibited NO_x storage capacity along the axis. The NO_x storage/reduction (NSR) reactions occurred over a relatively short portion of the reactor (NSR zone) under the conditions used in this study, and thus, net NO_x conversion was only significantly reduced at high sulfur loading. Oxygen storage capacity (OSC) was poisoned by sulfur also in a progressive manner but to a lesser extent than the NO_x storage capacity. Global selectivity for N₂O remained low at all sulfur loadings, but NH₃ selectivity increased significantly with sulfur loading. We conjecture that NH₃ breakthrough increased because of decreasing oxidation of NH₃, slipping from the NSR zone, by downstream stored oxygen. The NSR and oxygen storage/reduction (OSR) generated distinctive exotherms during the rich phase and at the rich/lean transition. Exotherm locations shifted downstream with sulfur accumulation in a manner that was consistent with the progressive poisoning of NSR and OSR sites.

Keywords: Lean NO; _x; trap; NO; _x; storage/reduction; Sulfation; Oxygen storage capacity; Regeneration; Ammonia; Spatiotemporal distribution

Preparation, characterization and application of Nd–TiO₂ photocatalyst for the reduction of Cr(VI) under UV light illumination by S. Rengaraj; S. Venkataraj; Jei-Won Yeon; Younghun Kim; X.Z. Li; G.K.H. Pang (pp. 157-165).

A novel photocatalyst, titanium dioxide (TiO₂) doped with neodymium (Nd), was prepared by the sol–gel method and used for the photocatalytic reduction of Cr(VI) under UV illumination, in order to determine its photocatalytic properties. A series of Nd³⁺–TiO₂ catalysts prepared with different Nd³⁺ dosages were characterized by XRD, Raman spectroscopy, SEM, EDX, TEM, EDS and XPS spectroscopy. In the experiments, formic acid was used as a hole scavenger to enhance the photocatalytic reduction reaction. The experiments demonstrated that Cr(VI) was effectively reduced in aqueous Nd³⁺–TiO₂ suspension by more than 95% within 60min, while the pH of the solution increased from 3.1 to 3.35 due to the consumption of formic acid. The experimental results indicate that the presence of Nd³⁺ in TiO₂ catalysts substantially enhances the photocatalytic reaction of chromium(VI) reduction. It was found that the optimal dosage of 1–3wt% Nd³⁺ in TiO₂ achieved the fastest reaction of Cr(VI) reduction under the experimental conditions. The neodymium ions deposited on the TiO₂ surface behave as sites at which electrons accumulate. The improved separation of electrons and holes on the modified TiO₂ surface allows more efficient channeling of the charge carriers into useful reduction and oxidation reactions rather than recombination reactions. The presence of sacrificial electron donors such as formic acid enhances the photocatalytic reduction of Cr(VI). The Cr(VI) adsorbed on the surface of the TiO₂ particles was observed to be almost completely photoreduced to Cr(III).

Keywords: Chromium(VI); Neodymium; Photocatalysis; Reduction; Titanium dioxide

Catalytic wet peroxide photo-oxidation of phenolic olive oil mill wastewater contaminants by Samia Azabou; Wahiba Najjar; Adel Gargoubi; Abdelhamid Ghorbel; Sami Sayadi (pp. 166-174).

Wet hydrogen peroxide photodegradation, catalyzed by aluminium–iron pillared montmorillonite (Al–Fe)PILC, of a mixture of eight model phenolic compounds present in olive mill wastewater (OMW), has been studied. Important percentages of phenol abatement after the wet hydrogen peroxide photocatalytic oxidation (WHPCO) (86% and 70%) have been achieved after 24h of the o-diphenolic compounds caffeic acid and hydroxytyrosol, respectively. Monophenolic compounds tyrosol, p-hydroxyphenylacetic acid and p-coumaric acid were the most resistant towards the WHPCO. The apparent rate constant kphenolic_molecule decreased with increasing initial pollutant concentration of organic molecule when the other parameters remained unchanged. Almost similar results were obtained with real OMW obtained by ultrafiltration of crude OMW. The toxicity of model and real OMW against the bioluminescent bacteria Vibrio fisheri was significantly decreased by 74% and 68%, respectively after the WHPCO. The subsequent biological treatment using a methanogenic consortium removed the remaining phenolic compounds by more than 70% even with the most recalcitrant compounds.

Keywords: OMW; Low-molecular mass phenolic compounds; Wet hydrogen peroxide photocatalytic oxidation (WHPCO); UV light; Microtoxicity

Structural properties and photocatalytic behaviour of phosphate-modified nanocrystalline titania films by László Kőrösi; Albert Oszkó; Gábor Galbács; Andre Richardt; Volker Zöllmer; Imre Dékány (pp. 175-183).

A series of phosphate-modified titanium dioxide samples (P-TiO₂) with varying P/Ti atomic ratio was prepared by sol–gel method. The influence of the surface-bound phosphate on the structural behaviour of the titania samples was studied by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and nitrogen sorption measurements. The ratio of the numbers of phosphorus and titanium atoms was compared by XPS and inductively coupled plasma atomic emission spectrometry (ICP-AES). In each of the samples the P/Ti ratio was greater than expected from the chemical composition or found by ICP-AES. Taking into account the surface sensitivity of the XPS one can conclude that the surface region is richer in phosphorus than the bulk phase. A practically constant P/Ti ratio was determined at different X-ray incident angles for the P-TiO₂/0.05 sample, which means that the P-abundant layer is thicker than the escape depth of the P 2p electrons from the sample. The presence of phosphate retards the amorphous titania→anatase and anatase→rutile phase transformations during calcination. It was shown that the specific surface area of the P-TiO₂ samples strongly depends on their phosphate content.The photocatalytic activity of the phosphate-modified samples was compared with that of Degussa P25 titanium dioxide by ethanol photooxidation in gas phase, with and without water vapor. The presence of water vapor increased the rate of ethanol degradation on P-TiO_2. At high relative humidity (∼70%) the initial rate of CO₂ formation on the phosphate-modified sample with optimal phosphate content was ∼3 times higher with respect to Degussa P25.

Keywords: Titania; Phosphate-modified titania; Nanocrystaline thin films; Photocatalytical properties; XRD; XPS investigations

Hydrogen production by photocatalytic alcohol reforming employing highly efficient nanocrystalline titania films by Nikoleta Strataki; Vlasoula Bekiari; Dimitris I. Kondarides; Panagiotis Lianos (pp. 184-189).

Hydrogen production by photocatalytic alcohol reforming has been studied in the presence of a Pt/TiO₂ photocatalyst. Nanocrystalline titania was deposited on glass slides by using a sol–gel process in the presence of surfactant template. Band-gap excitation of titania was made by using a low-energy Black-Light source. Water–ethanol mixtures proved the most efficient substrate for hydrogen production. This system demonstrated an impressive efficiency, which reached up to 74% active electron to incident photon ratio and 32% energy conversion efficiency.

Keywords: Photocatalytic alcohol reforming; Nanocrystalline titania films

A NO_x reduction system using ammonia-storage selective catalytic reduction in rich/lean excursions by Tadao Nakatsuji; Manabu Matsubara; Juhana Rouistenmäki; Naohiro Sato; Hiroshi Ohno (pp. 190-201).

NO_x reduction in a different reaction mechanism from the NO_x storage reduction was investigated. NO_x is found to be reduced over a specified catalyst in the following steps: in lean conditions, NO is partially oxidized into NO₂, followed by NO and NO₂ adsorption, in rich conditions, the adsorbed NO_x is reduced mainly into ammonia, followed by ammonia adsorption and finally, during the subsequent cycle of the lean conditions, the adsorbed ammonia selectively reacts with gaseous NO_x. In this reaction, nitrogen is mainly not formed in the rich operation, but in the lean operation. On the other hand, nitrogen is formed only in the rich operation over the NO_x storage-reduction catalyst. The newly developed catalyst is composed of a noble metal/an oxygen storage capacity (OSC) material and a solid acid.

Keywords: NO; _x; reduction; Ammonia storage; NH; ₃; -SCR; Adsorption; Solid acid; Rich/lean operations

Hydrogen assisted urea-SCR and NH₃-SCR with silver–alumina as highly active and SO₂-tolerant de-NO_x catalysis by Ken-ichi Shimizu; Atsushi Satsuma (pp. 202-205).

Addition of 0.5% H₂ in the selective catalytic reduction of NO by urea (urea-SCR) caused a drastic improvement of NO reduction activity of Ag/Al₂O₃. Among various silver-based catalysts Ag/Al₂O₃ showed highest activity for H₂ assisted urea-SCR, and high NO conversion (above 84%) and no formation of N₂O were achieved over wide temperature range (200–500°C) at GHSV of 75,000h⁻¹. After H₂ assisted urea-SCR at 250°C with 10% H₂O and 50ppm SO₂ under GHSV of 380,000h⁻¹ for 24h, NO conversion over Ag/Al₂O₃ decreased from 48 to 30%, though original activity was recovered when the deactivated catalyst was heated at 500°C in the urea-SCR condition for 1h. The catalyst also showed high SO₂-tolerance in H₂ assisted NH₃-SCR at 200°C.

Keywords: Nitrogen oxides; Silver alumina; Urea; Sulfur oxide

Catalysts for the hydrolysis of aqueous borohydride solutions to produce hydrogen for PEM fuel cells by Palanichamy Krishnan; Kan-Lin Hsueh; Sung-Dae Yim (pp. 206-214).

The objective of the present study was to understand the superior catalytic performance of PtRu-LiCoO₂ catalyst for hydrogen (H₂) generation from aqueous sodium borohydride (NaBH₄) solutions by comparing the catalytic activity of various PtRu-supported catalysts. Three of the support materials namely cobalt oxide (Co₃O₄), lithium nickel oxide (LiNiO₂) and lithium manganese oxide (LiMnO₂) were synthesized and characterized using XRD. The PtRu-supported catalysts with eight different support materials were prepared and characterized using XRD and BET surface area measurements. The results revealed excellent hydrogen generation activity of Co₃O₄ and LiCoO₂ for the hydrolysis of NaBH₄. Actually, the catalytic activity of Co₃O₄ and LiCoO₂ is due to the formation of cobalt boride (CoB) by the reduction of these oxides by NaBH₄. A model is proposed to explain the hydrogen generation profile of the above catalysts. The CoB formation is confirmed by XPS studies. Further, the performance of Co₃O₄ and LiCoO₂ was compared with various noble metal catalysts. The performance of Co₃O₄ is at par with the noble metal based catalysts at low concentration of NaBH₄ and far superior to noble metal based catalysts at higher concentration.

Keywords: Borohydride hydrolysis; Hydrogen; PEM fuel cells; Cobalt oxide (Co; ₃; O; ₄; ); Lithium cobalt oxide (LiCoO; ₂; ); PtRu-supported catalysts

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Applied Catalysis B, Environmental (v.77, #1-2)

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Applied Catalysis B, Environmental (v.77, #1-2)