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Applied Catalysis B, Environmental (v.84, #1-2)

OFC Editorial Board (pp. co4).

Editorial Board (pp. i).

Contents Continued (pp. i-ii).

IFC Editorial Board (pp. co2).

Synthesis of CoMo-based carbon hydrodesulfurization catalysts: Influence of the order of metal impregnations on the activity by Hamdy Farag (pp. 1-8).

Series of CoMo-based carbon catalysts were synthesized via the successive impregnation method, in which the carbon material was impregnated first with cobalt. The activity of the catalysts in the hydrodesulfurization of dibenzothiophene using a high pressure batch reactor operating at 340°C under 3MPa of hydrogen was investigated. In general, the carbon-supported CoMo catalysts synthesized by the successive impregnation method (in this case cobalt was the first to be introduced) showed higher hydrodesulfurization activities for dibenzothiophene than the reference CoMo-based carbon catalyst prepared by the conventional successive impregnation. The remarkable hydrodesulfurization activities of these CoMo-based carbon catalysts are suggested to be a consequence of forming a new synergy between molybdenum and cobalt. The data provide evidence that the CoMo-bimetallic synergy is affected by the nature of the support and by the order of metal impregnation. The results support the view of the electronic origin of such synergy.

Keywords: Hydrodesulfurization; Dibenzothiophene; Impregnation; Order of impregnation; Carbon

Degradation of Acid Blue 74 using Fe-ZSM5 zeolite as a heterogeneous photo-Fenton catalyst by M.B. Kasiri; H. Aleboyeh; A. Aleboyeh (pp. 9-15).

Decolourisation and mineralization of an indigoid dye, C.I. Acid Blue 74, was conducted using Fe-ZSM5 zeolite as a catalyst in the presence of UV-C light and H₂O₂. The effects of different parameters such as amounts of catalyst, initial concentration of the dye and H₂O₂ and initial pH of the dye solution on the degradation efficiency of the process were assessed. The results indicated that by using 21.4mmoll⁻¹ of H₂O₂ and 0.5gl⁻¹ of the catalyst at pH 5, about 57% total organic carbon of a solution containing 8.56×10⁻⁵moll⁻¹ Acid Blue 74 could be removed after 120min in a 2l batch photo-reactor. Leaching tests indicated that the activity of the catalyst is not due to leached iron ions, although an amount of about 0.3mgl⁻¹ iron ions was found in the aqueous solution. Significantly lower concentration of Fe²⁺ and Fe³⁺ in the solution after the treatment could give a great advantage to UV/Fe-ZSM5/H₂O₂ system over the homogeneous Fenton-type system. It was found that by using this catalyst, it is possible to expand the range of pH values for which Fenton-type oxidation can occur and no iron hydroxide sludge is formed. It was also observed that catalytic behaviour could be reproduced in consecutive experiments without a considerable drop in the process efficiency.

Keywords: Heterogeneous photo-Fenton; Fe-ZSM5; Indigoid dye; Dye degradation; Wastewater treatment

Preparation of TiO₂-embedded carbon nanofibers and their photocatalytic activity in the oxidation of gaseous acetaldehyde by Soonhyun Kim; Sang Kyoo Lim (pp. 16-20).

TiO₂-embedded carbon nanofibers (TiO₂/CNF) have been prepared by a simple method. TiO₂-embedded polyacrylonitrile fibers (TiO₂/PAN) were first prepared from a PAN solution containing TiO₂ particles by a simple electrospinning method, and subsequent carbonization and further oxidation of these led to TiO₂/CNF and oxidized TiO₂/CNF (Ox-TiO₂/CNF), respectively. Gaseous CH₃CHO was efficiently degraded with the concomitant production of CO₂ on the Ox-TiO₂/CNF composites under UV illumination. Although UV-illuminated TiO₂/PAN were also found to be capable of oxidizing gaseous CH₃CHO, these fibers underwent slow but spontaneous degradation. On the other hand, TiO₂/CNF had no effect on the photocatalytic oxidation of CH₃CHO, which may be attributed to the reduction and phase transformation of TiO₂ during carbonization. XPS results have shown that TiO₂ was partly reduced by carbonization and then re-oxidized during the further oxidation process. No anatase phase of TiO₂ was observed in the TiO₂/CNF composites, whereas this phase was unequivocally observed in the Ox-TiO₂/CNF composites. Moreover, the BET surface area was seen to be significantly enhanced by the further oxidation process, and this was responsible for the adsorption of CH₃CHO on the Ox-TiO₂/CNF. Therefore, the further oxidation process not only brings about re-oxidation of TiO₂ but also leads to a surface modification of the carbon nanofibers.

Keywords: Photocatalysis; TiO; ₂; Acetaldehyde; Electrospinning method; Carbon nanofiber

Cu–Ce mixed oxides supported on Al-pillared clay: Effect of method of preparation on catalytic activity in the preferential oxidation of carbon monoxide by Veda Ramaswamy; Sachin Malwadkar; Satyanarayana Chilukuri (pp. 21-29).

The possibility of using Al-pillared montmorillonite (Al-PILC) clay as a high-surface-area support for CuO–CeO₂-based catalysts has been investigated. The preparation of the samples was done by three different methods, viz., amorphous citrate route (ACR), deposition precipitation (DP) and wet impregnation method (WIM). Samples with different CuO–CeO₂ loadings (10–50wt.%) were prepared by each of the three methods. The catalytic activity of these samples was investigated for the preferential oxidation (PROX) of carbon monoxide (CO) in excess of H₂. The samples prepared by DP and WIM methods show better activity than the samples prepared by ACR method. At low Cu content, the samples prepared by DP method have a slight edge over samples prepared by WIM method. The DP-30 sample shows a very high CO conversion of 96.1% at 423K. A higher dispersion of CuO–CeO₂ on pillared montmorillonite clay and better reducibility of copper oxide species may be responsible for the good activity of these samples even at lower reaction temperatures. A higher O₂/CO ratio increased the CO conversion but led to a reduction in oxidation selectivity. No methanation of CO or CO₂ was observed at the reaction temperature. These CuO–CeO₂/Al-PILC samples could be considered as comparable in performance with supported noble metal catalysts for the preferential oxidation of CO in excess hydrogen.

Keywords: Alumina-pillared clay; CuO–CeO; ₂; Clay-supported CuO–CeO; ₂; PROX of CO

Catalytic wet-air oxidation of aqueous solutions of formic acid, acetic acid and phenol in a continuous-flow trickle-bed reactor over Ru/TiO₂ catalysts by Albin Pintar; Jurka Batista; Tatjana Tišler (pp. 30-41).

Catalytic wet-air oxidation of aqueous solutions of formic acid, acetic acid and phenol was carried out in a trickle-bed reactor at T=328–523K and total pressures up to 50bar over various Ru/TiO₂ catalysts. Complete oxidation of formic acid was obtained at mild operating conditions, and no catalyst deactivation occurred that could be attributed to the dissolution of active ingredient material. It was observed that besides oxidation route thermal decomposition contributes significantly to the removal of formic acid; Ru/TiO₂ catalysts could be thus efficiently used for transformation of HCOOH to H₂ and CO₂ in an inert atmosphere. Liquid-phase oxidation of acetic acid was found to be structure sensitive; the highest catalyst activity was obtained, when Ru phase on the catalyst surface prevailed in zero-valent state. Due to simultaneous oxidation of metallic Ru to RuO₂ during the reaction course, correspondingly lower conversion of acetic acid was measured in the reactor outlet. The employed Ru/TiO₂ catalysts enable complete removal of phenol and TOC at temperatures above 483K; at these conditions, no carbonaceous deposits were accumulated on the catalyst surface. Apparent catalyst deactivation observed at temperatures below 463K is attributed to strong adsorption of partially oxidized intermediates on the catalyst surface, which can be avoided by conducting the CWAO process at sufficiently high temperatures. The acute toxicity to Daphnia magna and Vibrio fischeri of end-product solutions compared with that of the feed solutions was significantly reduced by oxidative treatment over Ru/TiO₂ catalysts.

Keywords: Acute toxicity tests; Catalytic wet-air oxidation; Heterogeneous catalysis; Ruthenium catalysts; Titanium oxide; Trickle-bed reactor; Wastewater treatment

The enhancement of WO₃-catalyzed photodegradation of organic substances utilizing the redox cycle of copper ions by Takeo Arai; Masatoshi Yanagida; Yoshinari Konishi; Ami Ikura; Yasukazu Iwasaki; Hideki Sugihara; Kazuhiro Sayama (pp. 42-47).

WO₃ is a visible-light-responsive photocatalyst and an n-type semiconductor photocatalyst, but its photocatalytic activity toward organic substances is low. We utilized several transition metal ions as redox mediators in attempts to improve the photoactivity of WO₃, and a drastic improvement was observed only when Cu²⁺ ions were utilized for WO₃-catalyzed photodegradation of organic substances. More specifically, the CO₂ generation rates for the photodegradation of formaldehyde and methanol in the presence of Cu²⁺ ions were about 1000 and 150 times as high, respectively, as the rates in the absence of Cu²⁺ ions. We confirmed that Cu²⁺ was reduced to Cu⁺ through the transfer of a photoexcited electron from WO₃ and that Cu⁺ was easily re-oxidized to Cu²⁺ by oxygen in air. This redox cycle could assist in the reduction of oxygen in the photocatalytic reaction, and the reaction was particularly efficient when Cu²⁺ was introduced to the system as a CuCl₂ solution. Photodegradation was achieved with a WO₃ photoelectrode in a two-compartment cell in which the Cu²⁺ solution was separated from wastewater containing organic substances by an ion-exchangeable membrane, simulating practical use. The anodic photocurrent generated by the photodegradation of organic substances was observed at the WO₃ photoelectrode without applying any external bias.

Keywords: Photodegradation; Tungsten oxide; Copper redox; Substances

Catalytic ozonation of naproxen and carbamazepine on titanium dioxide by R. Rosal; A. Rodríguez.; M.S. Gonzalo; E. García-Calvo (pp. 48-57).

This study investigates the ozonation of naproxen and carbamazepine during catalytic and non-catalytic semicontinuous oxidation experiments performed at 25°C and in the range of pH 3–7. The results showed that naproxen and carbamazepine were completely consumed in the first few minutes of reaction. The extent of mineralization during non-catalytic runs reached about 50% and essentially took place during a period covering the first 10–20min. Catalytic runs were carried out on a commercial catalyst consisting of fumed colloidal TiO₂ particles. The catalyst increased the extent of mineralization by up to 75% of the initial organic carbon. The results showed that the catalyst enhanced mineralization both in acidic and neutral solutions, but the best results were obtained in a slightly acidic media. This effect was probably linked to the adsorption of reaction intermediates on Lewis acid catalytic sites. The catalyst enhanced the decomposition of ozone in an acid medium, but inhibited it in a neutral solution. This seems to exclude a mechanism based on the surface formation of hydroxyl radicals followed by their migration and bulk reaction with organic compounds. The evolution of the total organic carbon measured in samples taken during the run was modelled as a function of the integral ozone exposure. The kinetic regression model considered that the ozonation products from naproxen or carbamazepine consisted of either oxidizable or refractory compounds, where the latter were necessarily produced from the former. The model assumed a second order reaction between organic compounds and ozone. The higher non-catalytic rate constants for the first mineralization period were 1.048×10⁻²±9.3×10⁻⁴Lmmol⁻¹s⁻¹ for naproxen and 6.16×10⁻³±5.6×10⁻⁴Lmmol⁻¹s⁻¹ for carbamazepine, both at pH 7. The corresponding pseudohomogeneous catalytic rate constants were 7.76×10⁻³±3.9×10⁻⁴ and 4.25×10⁻³±9.7×10⁻⁴Lmmol⁻¹s⁻¹ for naproxen and carbamazepine, respectively, at pH 5 and with a catalyst load of 1g/L. The evolution of carboxylic acids during reaction revealed that the catalyst avoided the accumulation of oxalate especially in comparison with non-catalytic runs, in which it accounted for up to 30% of the final organic carbon. Specific ultraviolet absorbance at 254nm was also followed during the run. The products from naproxen reached a high absorbance from the beginning of the ozonation that was maintained throughout the run. For carbamazepine, however, the absorbance rapidly decreased revealing a different chemical structure of reaction products.

Keywords: Pharmaceuticals; Mineralization; Ozonation; Catalysis; Adsorption; Titanium oxide

An EPR study of physi- and chemisorption of NO on MgO: Effect of outgassing temperature and nature of surface sites by Shinya Higashimoto; Guylène Costentin; Bernard Morin; Michel Che (pp. 58-64).

The interaction of NO molecules with the surface of MgO has been studied by EPR as a function of outgassing temperature. Two different types of paramagnetic species are identified by EPR: physisorbed NO and chemisorbed NO₂²⁻. They are formed upon specific adsorption of NO on Lewis acidic Mg²⁺ and basic O²⁻ sites, respectively. The concentration of NO and NO₂²⁻ radicals depends on the outgassing temperature of MgO reaching a maximum at 1073K. FT-IR measurements suggest that sites liberated upon thermal outgassing by removal of OH and carbonate groups adsorbed on MgO play a significant role in the increase of the concentrations of NO and NO₂²⁻ radicals. The latter are possibly formed on low coordinated oxide ions close to cationic vacancies or O_4C²⁻ of monoatomic step and O_3C²⁻ from kinks and divacancies.

Keywords: MgO; Surface; Low coordination; NO; Probe; Physisorption; Chemisorption; EPR; FT-IR; Acidic sites; Basic sites; Outgassing temperature

Kinetic modeling of photocatalytic degradation reactions: Effect of charge trapping by Asefeh Jarandehei; Mojgan Karimi Golpayegani; Alex De Visscher (pp. 65-74).

This study investigates the important role of charge trapping in a photocatalytic degradation kinetic model. Different charge trapping reactions were coupled with photocatalytic degradation reaction schemes. The resulting kinetic models were applied to formate and trichloroethylene (TCE) in aqueous and gas phase, respectively. In both cases addition of charge trapping improved the reliability of the kinetic models. Hence, two dissipative charge reactions are considered in the new model: electron–hole recombination with second-order kinetics and charge trapping with first-order kinetics. For the formate system, it was shown that accounting for UV irradiance effects on a mechanistic basis requires the incorporation of charge trapping effects in the kinetic model. The improved model fitted literature data to within experimental error. A reasonable mechanism was suggested for degradation of TCE which involves three electron–hole pairs for the complete mineralization of one molecule of TCE. A kinetic model of TCE degradation via three main steps, along with considering charge trapping can explain the kinetic data with the same accuracy as an existing model of Demeestere et al., but with a more realistic electron–hole pair requirement, and added flexibility to account for light intensity effects.

Keywords: Charge trapping; Kinetic modeling; Photocatalytic degradation; UV irradiance

Wet air oxidation of nitro-aromatic compounds: Reactivity on single- and multi-component systems and surface chemistry studies with a carbon xerogel by Ângela C. Apolinário; Adrián M.T. Silva; Bruno F. Machado; Helder T. Gomes; Paulo P. Araújo; José L. Figueiredo; Joaquim L. Faria (pp. 75-86).

The treatment of dinitrophenol (DNP) and trinitrophenol (TNP), typically found in the effluents from the process of mononitrobenzene (MNB) synthesis, was investigated by wet air oxidation in both non-catalytic (WAO) and catalytic (CWAO) conditions, operating as two phase and three phase reactors, respectively. In the first case, the effect of treating DNP and TNP separately (single-component system) or using mixtures of these compounds (multi-component systems) was assessed by analysing the decrease of the individual pollutant concentration, the total organic carbon (TOC) evolution and the reaction by-products. Of the various systems screened, it was possible to conclude that the presence of DNP enhances the overall oxidation in multi-component systems. TNP is not oxidized individually but totally degraded in the presence of DNP. The observed reactivities were correlated with the number and type of functional groups attached to the aromatic ring and the HO induced denitration may be considered as the main reaction mechanism.Concerning the CWAO experiments, two catalysts were synthesized in this study, a carbon xerogel (CX) and a nanosized cerium oxide (CeO₂), using sol–gel and solvothermal methodologies, respectively, and tested for the degradation of the multi-component system. The CX catalyst operating in slurry conditions was found to be highly active and led to practically complete removal of DNP and TNP, total bleaching of color and 83% mineralization after 120min of reaction. The best catalyst was thoroughly characterized. An increase in the concentration of carboxylic acid groups at the catalyst surface was observed by TPD analysis of the catalyst after the reaction, followed by a decrease in the concentration of phenolic and quinone functional groups. The catalyst surface modification was a consequence of the large amounts of nitrates produced from the model compounds. Nitrites were not detected and, therefore, CWAO seems to be a potential treatment which can be coupled with a biological process to remove the nitrates formed during the reaction.

Keywords: Wet air oxidation (WAO); Dinitrophenol; Trinitrophenol; Carbon xerogel; Cerium oxide

Ag promotion of TiO₂-anatase disinfection capability: Study of Escherichia coli inactivation by A. Kubacka; M. Ferrer; A. Martínez-Arias; M. Fernández-García (pp. 87-93).

In this report we investigate the promotion of the TiO₂-anatase disinfection capability by addition of silver. Ag–TiO₂ systems were prepared by two different methods, impregnation and photodeposition, and their anti-microbial properties analyzed as a function of the silver content using Escherichia coli as a benchmark microorganism. Both Ag–TiO₂ series of samples display maximum photokilling activity for a 1wt.% silver loading but behave very differently for higher silver loadings. The noble metal roles played on the E. coli inactivation and their physical grounds were analyzed by a multitechnique approach using XRD, and Raman, UV–vis and electron paramagnetic resonance (EPR) spectroscopies.

Keywords: Photocatalysis; TiO; ₂; Anatase; Silver; Disinfection; E. coli

Antibacterial activity of thin-film photocatalysts based on metal-modified TiO₂ and TiO₂:In₂O₃ nanocomposite by E.V. Skorb; L.I. Antonouskaya; N.A. Belyasova; D.G. Shchukin; H. Möhwald; D.V. Sviridov (pp. 94-99).

Photoinduced bactericidal activity of nanostructured TiO₂ and TiO₂:In₂O₃ films and the effect of deposition of silver and bimetallic Ag/Ni nanoparticles on the pathophysiological properties of titania films were investigated. The antimicrobic activity of the films was assessed against Psedomonas fluorescens В-22 (gram-negative bacterium) and Lactococcus lactis ssp. lactis 411 (gram-positive bacterium). The silver-modified TiO₂ film demonstrates the highest photobiocide efficiency, enhancing the bactericidal activity of UV light ca. 71-fold, that results from radical improvement of microorganism adsorption and suppression of recombination of photoproduced charge carriers. Higher inactivation rate observed for P. fluorescens as compared to L. lactis can be explained in terms of comparative morphologies of the cell envelops of gram-negative and gram-positive microorganisms and the resistance of their outer membranes to the reactive oxygen species generated by photocatalytic reactions.

Keywords: Antibacterial activity; Photocatalysis; TiO; ₂

Hollow core/mesoporous shell carbon as a highly efficient catalyst support in direct formic acid fuel cell by Baizeng Fang; Minsik Kim; Jong-Sung Yu (pp. 100-105).

Spherical carbon capsules with a hollow macroporous core of ca. 260nm and a ca. 40nm thick mesoporous shell were explored for the first time as an anode catalyst support in direct formic acid fuel cell (DFAFC). Hollow core/mesoporous shell carbon (HCMSC) possesses fantastic structural characteristics such as uniform particle size, well-developed three-dimensionally interconnected bimodal porosity, and large specific surface area and pore volume, which are highly desired for a catalyst support in low temperature fuel cells. HCMSC-supported Pt₅₀Ru₅₀ (60wt.%) has exhibited almost two times the power density that delivered by the commonly used catalyst support carbon black Vulcan XC-72 supported one, suggesting that the HCMSC is a highly efficient anode catalyst support in DFAFC.

Keywords: Hollow core/mesoporous shell carbon; Catalyst support; Anode; Pt; ₅₀; Ru; ₅₀; Direct formic acid fuel cell

Cobalt catalysts promoted with cerium and lanthanum applied to partial oxidation of methane reactions by Alessandra F. Lucrédio; Gregory Jerkiewicz; Elisabete M. Assaf (pp. 106-111).

Catalysts of Co/Mg/Al promoted with Ce and La were tested in the catalytic partial oxidation of methane (POM) reaction. The addition of promoters was made by anion-exchange. X-ray diffraction (XRD) confirmed the formation of hydrotalcite phase for precursors. The mixed oxides were characterized as a mixture of Co₃O₄, periclase (Co, Al)MgO and/or spinel structure (Mg, Co)Al₂O₄. In the catalytic POM reaction over the promoted catalysts, a reduction in the carbon formation rate was found.

Keywords: Hydrotalcite; Cobalt; Promoter; Methane partial oxidation

Pt/titania-nanotube: A potential catalyst for CO₂ adsorption and hydrogenation by Kuo-Pin Yu; Wen-Yueh Yu; Ming-Chih Kuo; Yuh-Cherng Liou; Shu-Hua Chien (pp. 112-118).

The titania-nanotube-supported Pt (Pt/Tnt) catalyst was prepared by the photochemical deposition of Pt complex on the titania-nanotube (Tnt) synthesized by the alkaline hydrothermal method. The physicochemical properties of Pt/Tnt catalyst were investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, N₂ adsorption and desorption isotherms, temperature-programmed reduction and X-ray photoelectron spectroscopy. The Pt/Tnt catalyst exhibited mixed-valence Pt nanoparticles (1–3nm) dispersed uniformly on the surface of Tnt with a Brunauer–Emmett–Teller surface area of 187m²/g. The results of the temperature-programmed desorption of CO₂ indicated the CO₂ adsorption capacity of Tnt was highly enhanced by the supported Pt nanoparticles. In situ Fourier-transform infrared spectroscopy demonstrated that the Pt/Tnt catalyst was highly active for the CO₂ hydrogenation toward methane production at relatively low temperature of 100°C.

Keywords: Titania-nanotube; Pt catalyst; CO; ₂; -TPD/MS; CO; ₂; hydrogenation

Role of water in the CO oxidation reaction on Au/CeO₂: Modification of the surface properties by F. Romero-Sarria; A. Penkova; L.M. Martinez T.; M.A. Centeno; K. Hadjiivanov; J.A. Odriozola (pp. 119-124).

A metallic monolith coated with 1% Au/CeO₂ catalyst has been calcined at 300°C and tested in the CO oxidation reaction both in “dry” and “wet” conditions. The light-off curves show a positive effect of the presence of water in the reactive feed on the catalytic activity. With the aim to explain these observations, a FTIR CO adsorption study at liquid nitrogen temperature was performed over a similar powder catalyst. At this low temperature the oxygen mobility from the bulk to the surface is minimized and then surface phenomena are evidenced. Both, the effect of different pre-treatments of the catalysts and the presence of pre-adsorbed water on the surface have been examined. The studies reveal that the previous treatment of the sample deeply affects the surface species and the gold particle size. The water addition provokes oxidation of the surface and improves the CO oxidation activity.

Keywords: Gold; CO oxidation; Water; FTIR; Oxidation state

Multi-step loading of titania on mesoporous silica: Influence of the morphology and the porosity on the catalytic degradation of aqueous pollutants and VOCs by K. De Witte; V. Meynen; M. Mertens; O.I. Lebedev; G. Van Tendeloo; A. Sepúlveda-Escribano; F. Rodríguez-Reinoso; E.F. Vansant; P. Cool (pp. 125-132).

Titania nanoparticles have been deposited on inert porous silica supports with high specific surface area. These materials have potential applications in paint and textile industry as the titania particles selectively deposited on the inner surface of the silica supports act as a photocatalyst. The inert external surface is necessary to avoid photodegradation of the textile material or the paint components. The photocatalytic activity of the catalysts has been evaluated with two catalytic setups. One setup in aqueous phase, for the degradation of dyes such as rhodamine-6G, is commonly used. The second setup is a continuous flow gaseous phase setup which was used for the mineralization of ethanol as a representative volatile organic compound (VOC). The influence of the porosity and the morphology of the silica supports on the photocatalytic activity are discussed.

Keywords: Titania; ACSG; Silica; Photocatalysis; Gaseous phase; Aqueous phase; Morphology

Analysis of catalytic oxidation of aromatic hydrocarbons over supported palladium catalyst with different pretreatments based on heterogeneous adsorption properties by Wang Geun Shim; Jae Wook Lee; Sang Chai Kim (pp. 133-141).

The influence of pretreatments (air and hydrogen) on the Pd based catalyst for the adsorption and catalytic oxidation of different aromatic hydrocarbons (BTX) were investigated. The strong correlation between the catalytic oxidation and the adsorption was explained in terms of adsorption affinity, isosteric heat of adsorption, and adsorption energy distribution.▪We investigated the catalytic oxidation and adsorption of benzene, toluene, and o-xylene (BTX) by using the palladium (Pd)-based catalyst and its pretreated (pre-oxidized and pre-reduced) catalysts. The physico-chemical properties of the catalysts were characterized and confirmed by using several reliable methods such as the Brunauer Emmett Teller (BET) surface area analysis, gravimetric adsorption analysis, light-off curves analysis, and X-ray photoelectron spectroscopy (XPS). The adsorption and catalytic activities of the catalysts were found to be closely connected with the pretreatment methods and temperatures. Especially, the hydrogen treated catalysts with a largely metallic form enhanced the adsorption ability and catalytic activity of toluene compared to that of the parent and air treated catalysts. In addition, the adsorption equilibrium isotherms of BTX on pre-reduced catalyst at three different temperatures were analyzed successfully with the two sites localized Langmuir (L2m) isotherm equation. Moreover, the strong correlations between the catalytic behavior and the adsorption properties of BTX were explained in terms of adsorption affinity, isosteric heat of adsorption, and adsorption energy distributions.

Keywords: Adsorption; Catalytic oxidation; Pretreatment; Supported palladium catalyst; VOCs

Synthesis of effective titania nanotubes for wastewater purification by Han-Jun Oh; Jong-Ho Lee; Young-Jig Kim; Su-Jeong Suh; Jun-Hee Lee; Choong-Soo Chi (pp. 142-147).

In order to synthesize a self-organized, TiO₂ nanotubular layer for wastewater purification, anodizations were performed at constant applied potential in hydrofluoric acid and the anodic TiO₂ layer was heat treated. The anodic nanotube arrays were also influenced by the applied anodic potentials and HF concentrations. The anodic TiO₂ nanotubular structured film with various morphologies and crystal structures can be synthesized by proper electrochemical anodization and additional annealing treatment. The photocatalytic efficiencies were maximized for the anatase-type, TiO₂ nanotubular layer which was prepared by annealing at 550°C.

Keywords: Titania nanotube; Anodization; Anatase; Aniline blue; Photocatalyst

Simultaneous conversion of dye and hexavalent chromium in visible light-illuminated aqueous solution of polyoxometalate as an electron transfer catalyst by Soonhyun Kim; Jiman Yeo; Wonyong Choi (pp. 148-155).

This study reports the simultaneous conversion of dye and hexavalent chromium (Cr(VI)) in visible light-illuminated polyoxometalate (POM) solution. SiW₁₂O₄₀⁴⁻ (SiW₁₂⁴⁻) was used as a homogeneous catalyst that mediates the electron transfer from excited dye to heavy metal ion in the dye/Cr(VI)/POM ternary system. Rhodamine B (RhB), methylene blue (MB), and acid orange 7 (AO7) were chosen as test dyes. The conversion rate of dye and Cr(VI) in visible light-illuminated dye/Cr(VI)/POM system was strongly affected by the charge property of dye. The simultaneous conversion of cationic (RhB and MB) dye and anionic Cr(VI) were synergically enhanced in the presence of SiW₁₂⁴⁻. POM successfully plays the role of the electron transfer mediator from the excited cationic dye to Cr(VI). However, the conversion of anionic dye (AO7) and Cr(VI) was negatively affected by the addition of SiW₁₂⁴⁻. The observation that the initial UV/vis absorption spectrum of the dye/Cr(VI)/POM solution (with RhB or MB) was changed with increasing the concentration of SiW₁₂⁴⁻ indicates the complex formation between POM and cationic dyes. However, no such complex formation was observed with AO7. As for RhB, the dye degradation mechanism in the ternary RhB/Cr(VI)/POM solution was markedly different from that in the binary RhB/POM solution. The effects of various experimental parameters and the proposed mechanisms are discussed in detail.

Keywords: Polyoxometalate; Photocatalysis; Dye; Electron transfer mediator; Visible light

On the role of Pd β-hydride in the reduction of nitrate over Pd based catalyst by Claudio M. Mendez; Hernán Olivero; Daniel E. Damiani; María A. Volpe (pp. 156-161).

Two monometallic palladium catalysts supported on γ-Al₂O₃ were synthesized using different precursors, Pd(AcAc)₂ and Pd(NO₃)₂, while Pd-Cu/γ Al₂O₃ catalysts were prepared from those parent catalysts. The samples were tested for the elimination of nitrate and nitrite from aqueous solutions using hydrogen as a reductant in a standard batch reactor. Besides, the reduction of nitrate was carried out in a series of two reactors by an electrochemical cell mechanism. In this case, nitrate was reduced to nitrite by electrons supplied from the first reactor. The following reduction of nitrite was performed over the monometallic catalyst. Both the conversion and the selectivity to N₂ were higher than in the standard batch reactor. Monometallic samples prepared from Pd(AcAc)₂ showed an extremely high selectivity to the desired product. The catalysts were characterized by transmission electron microscopy (TEM), temperature programmed reduction (TPR) and H₂ chemisorption. Differences in particle size and β-hydride formation were observed for the different samples. The possible role of Pd β-hydride in the formation of overhydrogenated products is discussed.

Keywords: Nitrate reduction; Nitrite reduction; Supported palladium; β-Hydride; Palladium-copper catalyst

Catalytic activity and aging phenomena of three-way catalysts in a compressed natural gas/gasoline powered passenger car by Alexander Winkler; Panayotis Dimopoulos; Roland Hauert; Christian Bach; Myriam Aguirre (pp. 162-169).

The catalytic activity of the pre(p)- and the underfloor(u) three-way catalysts (TWCs), of a bifuel passenger car (compressed natural gas (CNG), gasoline), has been examined at a series of mileage milestones. Over a rather short lifetime of 35,000km, a significant increase of the unburned total hydrocarbons (THC) has been determined during CNG operation. No comparable THC increase in the exhaust was found during gasoline operation. The THC increase was detected at exhaust temperatures well over 633K, excluding methane specific light-off deterioration. Possible explanations for this fuel selective behaviour could be identified by the application of different surface techniques. XPS analysis hints to the formation of a metallic Pd layer formed over the catalytically active PdO core, probably having the highest impact on the decreased methane oxidation during CNG operation. Typical lubricating oil based contaminants like P, Ca, and Mg, have been detected on the catalysts’ surface as well.

Keywords: Abbreviations; BET; Brunauer, Emmett, Teller; CADC; Common Artemis Driving Cycle; CLD; Chemical Luminescence Detector; CNG; Compressed Natural Gas; ECE; Economic Commission for Europe (driving cycle); EUDC; Extra Urban Driving Cycle; FID; Flame Ionisation Detector; GC; Gas Chromatograph; NDIR; Non-Dispersive InfraRed (analyzer); NEDC; New European Driving Cycle; NMHC; Non Methane HydroCarbons; PM; Precious Metal; RSF; Relative Sensitivity Factor; SEM; Scanning Electron Microscopy; SSA; Specific Surface Area; THC; Total HydroCarbons; p-TWC; Pre Three-Way Catalyst; u-TWC; Underfloor Three-Way Catalyst; WS; Washcoat; XPS; X-ray Photoelectron SpectroscopyThree-way catalyst; Catalyst aging; Methane oxidation; Compressed natural gas; XPS; SEM; BET

The effect of different divalent cations on the reduction of hexavalent chromium by zerovalent iron by Meifang Hou; Hongfu Wan; Tinglin Liu; Yanning Fan; Xinming Liu; Xugang Wang (pp. 170-175).

The effects of ferrous cation (Fe²⁺), copper cation (Cu²⁺) and calcium cation (Ca²⁺) on the reduction of hexavalent chromium Cr(VI) by zerovalent iron (Fe⁰) were investigated. The pseudo-first-order kinetic model was used for describing the reduction of Cr(VI). The experimental results showed that Cu²⁺ and Fe²⁺ could improve the reduction of Cr(VI) but Ca²⁺ might inhibit the reduction of Cr(VI) by Fe⁰. The improvement of the reduction of Cr(VI) by Cu²⁺ on Fe⁰ might be ascribed to Cu²⁺ acting as a catalyst or the media of charge transfer during the reaction. Different concentration of Cu²⁺ might lead to the different reduction kinetics of Cr(VI) by Fe⁰. The X-ray diffraction (XRD) results showed that the reacted iron powder was coated by a small amount of β-FeOOH. The results of scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS) and Fourier-transform infra-red (FTIR) showed that the Fe–Cr coprecipitate or Fe–Cr–Cu coprecipitate might be formed during the reaction.

Keywords: Chromium; Divalent cation; Zerovalent iron; Reduction

Total oxidation of propane using nanocrystalline cobalt oxide and supported cobalt oxide catalysts by Benjamin Solsona; Thomas E. Davies; Tomas Garcia; Isabel Vázquez; Ana Dejoz; Stuart H. Taylor (pp. 176-184).

Supported and unsupported nanocrystalline cobalt oxides have been shown to be extremely efficient catalysts for the total oxidation of propane. Total conversion with a high stability has been achieved at reaction temperatures as low as 250°C. In the present work, a comparison between the catalytic performance of bulk and alumina-supported nanocrystalline cobalt oxide catalysts has been made. The influence of crystallite size, nature of the support (alpha, gamma and mesoporous alumina) and cobalt loading, has been probed. Unsupported cobalt oxide catalysts were more active than any supported cobalt oxide catalysts. The catalytic activity was mainly dependent on the crystallite size, decreasing with an increase in the crystallite size. Whilst the TOF of supported catalysts increases with both a decrease in the surface area of the support and an increase of the cobalt content. Only those catalysts with a cobalt content of 50wt% achieve a catalytic activity per cobalt atom similar to that of unsupported Co₃O₄ prepared under similar conditions. High surface area alumina was shown to be a less efficient support especially at low Co-loadings due to the dispersion of cobalt on the surface leading to the formation of inactive Co–O–Al species. The low surface area support (α-Al₂O₃) presents a low capacity to isolate the cobalt oxide species resulting in a lower concentration of inactive Co–O–Al species and, therefore, the highest activity among supported catalysts. In conclusion, two parameters seem to determine the catalytic activity of nanocrystalline cobalt oxide: these are the presence of inactive Co–Al bonds (prevalent in supported catalysts) and also the size of the active Co₃O₄ particles.

Keywords: Propane; Total oxidation; Nanocrystalline Co; ₃; O; ₄; α-Al; ₂; O; ₃; VOC; Alumina

The highly active catalysts of nanometric CeO₂-supported cobalt oxides for soot combustion by Jian Liu; Zhen Zhao; Jiqiu Wang; Chunming Xu; Aijun Duan; Guiyuan Jiang; Qing Yang (pp. 185-195).

Nanometric CeO₂-supported cobalt oxide materials with variable Co/Ce atomic ratios were prepared by the method of ultrasonic-assisted incipient-wetness impregnation. The catalytic behaviors of a series of CoO_x/nmCeO₂ catalysts have been studied for soot combustion. XRD, XPS, Raman, UV–vis DRS and FT-IR spectroscopy characterization results indicated that CoO or cobalt–cerium solid solutions were formed in the samples with the low Co loading amount, while Co₃O₄ was formed in the samples with high Co loading amount. CoO_x/nmCeO₂ catalysts can further promote soot combustion in contrast to nanometric CeO₂. This improvement is related to the increase in the redox properties of the catalysts brought about by loading cobalt oxide on nanometric CeO₂. The TPR experiment results under hydrogen atmosphere indicated that the presence of Co decreases the reduction temperature of catalyst from 555°C (nanometric CeO₂) to 286°C (Co₂₀/nmCeO₂). On the other hand, attributing to nanoparticle effect and NO₂ formation, Co_m/nmCeO₂ oxide catalysts prepared in this study have very high activity for soot combustion. The best catalytic activity was obtained over Co₂₀/nmCeO₂ catalyst that T₁₀, T₅₀, T₉₀ were 286°C, 368°C, 418°C, respectively, andSCO2m was 98.8%. Compared with the blank case (i.e., without catalyst) for soot combustion, T₅₀ decreased by more than 200°C andSCO2m increased by 40% point. And this catalytic activity for the combustion of soot particle is as good as supported Pt catalysts, which is the best catalyst system so far reported for soot combustion under loose contact conditions. This temperature of soot combustion can ensure immediate activation of the catalyst on the filter under the conditions of diesel engine emissions.

Keywords: Nanometric CeO; ₂; -supported cobalt oxides; Catalysts; Soot combustion; Ceria; Cobalt

Characterization and enhancement of carbon nanotube-supported PtRu electrocatalyst for direct methanol fuel cell applications by Ning-Yih Hsu; Chun-Ching Chien; King-Tsai Jeng (pp. 196-203).

In this study, a carbon nanotube-supported PtRu electrocatalyst (PtRuCNT) was prepared, characterized and investigated for methanol electro-oxidation by catalytic activity enhancement using an electrochemical treatment. From XPS analyses, the as-prepared catalyst was found to mainly composed of Pt(0)/Pt(II) states for the Pt element and Ru(0)/Ru(IV) states for the Ru element. When the electrocatalyst was subjected to an enhancement treatment, the Ru(IV) state increased substantially from 29.50% to 44.11%. Both CO-stripping experiments and open-circuit cell voltage measurements indicated that the treated PtRuCNT has given rise to an improved performance on methanol electro-oxidation caused mainly by the increase of the Ru(IV) state in this particular case. The single-cell test also revealed that a direct methanol fuel cell (DMFC) can be put into its full operation in a short time. A direct application of this finding is to significantly shorten the activation time of a new DMFC stack. However, the electrochemically treated PtRuCNT catalyst still needs a continuous enhancement mechanism to sustain its enhanced activity. A promotional model is proposed to explain the phenomenon observed and a remedial approach is also suggested to solve the problem for practical applications.

Keywords: Direct methanol fuel cell; Carbon nanotube; Electrocatalyst; Catalyst oxidation states; CO stripping; Activation time

Characterisation and catalytic activity in de-NO_x reactions of Fe-ZSM-5 zeolites prepared via ferric oxalate precursor by Mickaël Rivallan; Gloria Berlier; Gabriele Ricchiardi; Adriano Zecchina; Mircea-Teodor Nechita; Unni Olsbye (pp. 204-213).

This paper deals with the spectroscopic characterisation and catalytic activity of Fe-ZSM-5 samples prepared by aqueous exchange with ferric oxalate and Mohr salt as precursors. NH₄⁺-ZSM-5 zeolites with different Si/Al ratios were employed as starting materials, as such and after Na⁺-exchange. The catalytic activity of the samples was tested in the selective catalytic reduction of NO with propane in the 473–773K range, and the nature of extraframework Fe species was investigated by UV–vis and FTIR spectroscopies, using NO as a probe molecule. The catalytic activity was found to be dependent upon the exchange method, the Si/Al ratio and the presence of Na⁺ ions. The results are discussed in terms of the relative concentration of isolated and clustered sites, as estimated by spectroscopic analysis. We propose that isolated sites are active in SCR, while clustered sites favour propane oxidation, having a detrimental effect on the activity for NO activation.

Keywords: Fe-ZSM-5; FTIR; UV–vis; Nitric oxide; Selective catalytic reduction

Plasma catalytic oxidation of methane on alumina-supported noble metal catalysts by Patrick Da Costa; Rui Marques; Stéphanie Da Costa (pp. 214-222).

The methane oxidation reaction was studied as a function of temperature for a gas mixture representative of a combined heat power (CHP) within a dielectric barrier discharge (DBD) reactor. The effect of energy deposition was studied, with energy deposition ranging from 36 to 58JL⁻¹, to maintain a low NO_x formation at high temperature. In the current study, we also investigated the combined process of a dielectric barrier discharge and γ-alumina noble metal catalysts such as platinum and palladium. In order to separate the catalytic effects from the plasma activation, the work included both purely catalytic and plasma activation processes using a complete CHP mixture with 4% of water in the feed. It was found that the presence of water leads to increase the methane conversion in purely plasma activation processes. Moreover, a higher efficiency for methane oxidation in CHP conditions was observed with the plasma–Pd( X)/Al₂O₃ systems.

Keywords: Methane oxidation; Plasma DBD; Catalyst; Palladium; Platinum

Zirconia-supported bimetallic RhPt catalysts: Characterization and testing in autothermal reforming of simulated gasoline by Reetta K. Kaila; Andrea Gutiérrez; Riku Slioor; Marianna Kemell; Markku Leskelä; A. Outi I. Krause (pp. 223-232).

The behavior of ZrO₂-supported RhPt catalysts was studied in the autothermal reforming of simulated gasoline to produce fuel gas (H₂, CO, CO₂, CH₄, and H₂O) suitable for solid oxide fuel cell applications.The bimetallic catalysts were superior to the monometallic Rh and Pt catalysts, and only a small addition of Rh increased the activity of the Pt catalyst markedly. Moreover, the reforming selectivity and the stability of bimetallic RhPt catalysts against carbon deposition improved with increasing Rh/Pt molar ratio.Strong synergism between Rh and Pt was observed, leading to excellent catalytic performance. Based on TPR-, SEM-, and EDX-results a Rh-Pt-O ternary system with Rh_xPt1−_x–Rh₂O₃ equilibrium is suggested for the bimetallic catalysts, where Rh₂O₃ is the active site.

Keywords: Hydrogen; Solid oxide fuel cell; Autothermal reforming; Simulated gasoline; Bimetallic; Zirconia; Rh-Pt-O ternary system; Rh; _x; Pt; 1−; _x; alloy; Rh; ₂; O; ₃; Characterization

Photodegradation of dye pollutant under UV light by nano-catalyst doped titania thin films by Sunil Dutta Sharma; K.K. Saini; Chander Kant; C.P. Sharma; S.C. Jain (pp. 233-240).

Undoped and manganese ion-doped TiO₂ powders and thin films have been prepared by sol–gel route. The concentration of the manganese in TiO₂ powders and films varied from 2 to 10mol%. These powders were annealed at different temperatures from 300 to 1000°C while films were annealed at 450°C for 1h. Prepared samples were characterized by XRD, SEM, XPS, spectroscopic and contact angle measurement techniques.Photocatalytic activity, in terms of rate constant measured by degradation of methylene blue dye, under UV exposure was found to increase from 0.27 to 0.36 for 5mol% doping while very small photo activity has been observed under visible light exposure. Hydrophillicity also shows the same behavior. Optical studies revealed the generation of allowed energy band in the forbidden gap at ∼0.63eV below the conduction band. It has been concluded that Mn doping increases photocatalytic activity by scavenging the photogenerated electrons, thereby increasing the life time of charge carriers and increasing the exposed surface area by reducing the crystallite size.

Keywords: Mn-doped TiO; ₂; films; Sol–gel; Photodegradation; Methylene blue

Stability of hexaaluminate-based catalysts for high-temperature catalytic combustion of methane by Erik Elm Svensson; Magali Boutonnet; Sven G. Järås (pp. 241-250).

Lanthanum hexaaluminate with a nominal composition of LaAl₁₁O₁₈ was used to support 20wt.% of LaMnO₃ and CeO₂. LaAl₁₁O₁₈ was prepared through co-precipitation of metal nitrates within the water phase of an isooctane/CTAB/1-butanol microemulsion. The stabilities of the prepared catalysts were assessed by measuring the activities for combustion of methane before and after aging at 1000°C for 100h in air with 10vol.% H₂O. The activities were compared with LaMnAl₁₁O₁₉, due to its well-documented stability. It was shown that by using hydrothermal treatment of the microemulsion, a significantly higher surface area was obtained for the LaAl₁₁O₁₈. For LaMnO₃, the reference support (Al₂O₃) was shown to be superior to LaAl₁₁O₁₈ as support, both in terms of activity and stability. Reactions between LaMnO₃ and support were observed for all supports included in the study. For CeO₂, LaAl₁₁O₁₈ was superior to Al₂O₃ as support. Deactivations of the CeO₂ catalysts were linked to crystal growth of CeO₂. LMHA deactivated strongly during aging; LaMnO₃ on Al₂O₃ and several of the catalysts with CeO₂ supported on LaAl₁₁O₁₈ showed a much more stable behavior.

Keywords: Catalytic combustion; Hexaaluminate; Methane; LaMnO; ₃; CeO; ₂; Microemulsion

Catalytic oxidation of chlorobenzene over Pd/perovskites by J.-M. Giraudon; A. Elhachimi; G. Leclercq (pp. 251-261).

The catalytic performances of pre-reduced palladium catalysts supported on lanthanum based perovskites LaBO₃ (B=Co, Mn, Fe, Ni) were investigated for the total oxidation of chlorobenzene (PhCl; 1000ppmv) in air. The catalysts were prepared using a wet impregnation technique and Pd-nitrate was used as a palladium precursor. The catalytic performances were compared to those of a reference palladium catalyst supported on a conventional support, namely γ-Al₂O₃. Easiness of chlorobenzene destruction was found to follow the sequence based on the T₅₀ values (temperature at which 50% of chlorobenzene was converted into products): Pd/LaMnO3+_δ (243°C)>Pd/LaFeO₃ (270°C)>Pd/Al₂O₃ (348°C)>Pd/LaCoO₃ (360°C)>Pd/LaNiO₃ (408°C). Complete conversion of chlorobenzene is reached at ca. 320–500°C, but at those temperatures substantial amounts of polychlorinated benzenes are formed. Quasi in situ XPS studies were monitored on Pd/LaCoO₃ and Pd/LaFeO₃ after each stage of the global process, namely after calcination, reduction and exposure to the flowing reactive mixture (1000ppmv PhCl in air) from room temperature to 230 and 310°C (Pd/LaFeO₃) and to 280°C (Pd/LaCoO₃). It was shown that the calcination treatment leads to a palladium which a BE higher than that of PdO and to a (B/La)_XPS<1 which attests of a lanthanum enrichment at the XPS surface. After H₂ treatment it was shown that palladium is totally reduced while the B cation is either unreduced (Fe³⁺) or reduced (Co³⁺ into Co²⁺ and Co⁰). In the reactive atmosphere, Pd⁰ is progressively (oxi)chlorined while the perovskite network is reconstructed with productions of LaOCl and Co₃O₄. The pre-reduced Pd/LaBO₃ are more active than the perovskite alone for PhCl transformation but substantially increase the chlorination rate of PhCl. Among the different catalysts Pd/LaFeO₃ shows the best compromise between PhCl oxidation and chlorination rates.

Keywords: Chlorinated VOC; Catalytic oxidation; Palladium; Perovskite

Grafted multifunctional titanium dioxide nanotube membrane: Separation and photodegradation of aquatic pollutant by Xiwang Zhang; Alan Jianhong Du; Peifung Lee; Darren Delai Sun; James O. Leckie (pp. 262-267).

Titanium dioxide (TiO₂) nanotube membrane has been fabricated by an energy efficient and environmentally friendly method, grafting anatase TiO₂ nanotubes in the channels of alumina microfiltration (MF) membrane using TiF₄ solution through liquid-phase deposition. The inner diameters of the TiO₂ nanotubes are controllable from 5 to 100nm by varying the grafting time. The TiO₂ nanotube membrane exhibited good photocatalytic activity on photodegradation of HA (humic acid) in batch tests. The satisfying permeability of the TiO₂ nanotube membrane was demonstrated by filtration of distilled water and HA. The experiment results of continuous filtration under UV irradiation showed that not only HA was rejected and photodegraded by the TiO₂ nanotube membrane, but also the membrane fouling was alleviated dramatically.

Keywords: Nanotube; Titanium dioxide; Membrane; Photodegradation; Fouling

Regenerable ceria-based SO_x traps for sulfur removal in lean exhausts by Lisa Kylhammar; Per-Anders Carlsson; Hanna Härelind Ingelsten; Henrik Grönbeck; Magnus Skoglundh (pp. 268-276).

Bare and Pt-containing CeO₂, Al₂O₃:MgO mixed oxide and Al₂O₃ have been investigated as potential regenerable sulfur oxides (SO_x) traps. The samples were evaluated by lean SO_x adsorption and temperature programmed desorption using synthetic gas compositions. In addition, combined DRIFT spectroscopy and mass spectrometry were employed to obtain mechanistic information on the adsorption of SO_x. The results suggest Pt/CeO₂ as promising SO_x trap material owing to a high storage capacity at 250°C in combination with efficient release above 600°C. The presence of Pt is generally found to enhance the lean SO_x storage capacity at 250°C for CeO₂-based samples. Lean SO₂ adsorption on CeO₂ is found to proceed via the formation of surface and bulk sulfates, where the latter is formed more rapidly for the Pt-containing CeO₂ sample. Ceria samples pre-exposed to high amounts of SO₂ at 250 and 400°C show lower SO_x storage capacity and higher SO_x release as compared to fresh samples. This indicates that under the conditions used in this study, a part of the storage sites on CeO₂ are non-regenerable.

Keywords: FTIR spectroscopy; Storage mechanism; CeO; ₂; Pt; Sulfur oxide

Nitrous oxide decomposition over transition metal exchanged ZSM-5 zeolites prepared by the solid-state ion-exchange method by Bahaa M. Abu-Zied; Wilhelm Schwieger; André Unger (pp. 277-288).

This paper studied nitrous oxide decomposition over a series of transition metal exchanged ZSM-5 zeolites prepared by solid-state ion-exchange method. Crystallographic structure of the catalysts has been investigated with the aid of XRD analysis. The texture of the prepared catalysts was investigated using nitrogen sorption. FTIR measurements applying pyridine as a probe molecule have been carried out in order to investigate the nature of the acid sites of the different catalysts. In situ electrical conductivity measurements were carried out in order to relate the activity of this series of catalysts to their electrical conductivity variation in the presence of N₂O. The obtained results revealed that the N₂O decomposition activity is related to the relative conductivity decrease upon the admission of N₂O over metal exchanged ZSM-5 zeolites. Further studies have been performed over Co-, Cu- and Fe-ZSM-5 catalysts since they showed the highest activity patterns among all the tested catalysts. Such studies included the effect of changing Si/Al ratio, the exchange level, the calcination temperature and the milling time.

Keywords: Nitrous oxide; Solid-state ion-exchange; Co-ZSM-5; Cu-ZSM-5; Fe-ZSM-5

Selective catalytic reduction of NO with C1–C3 reductants over solvothermally prepared Ga₂O₃–Al₂O₃ catalysts: Effects of water vapor and hydrocarbon uptake by Yuya Miyahara; Masaru Takahashi; Takeo Masuda; Seiichiro Imamura; Hiroyoshi Kanai; Shinji Iwamoto; Tsunenori Watanabe; Masashi Inoue (pp. 289-296).

The influence of reducing agents (C1–C3 hydrocarbons) upon the selective catalytic reduction (SCR) of nitrogen oxide (NO) on γ-Ga₂O₃–Al₂O₃ solid solutions was explored. Under dry conditions, the γ-Ga₂O₃–Al₂O₃ solid solutions having large crystallite size had high activity for the SCR of NO with various hydrocarbons. However, under wet conditions, NO conversion on the catalyst decreased drastically for all the hydrocarbons. The decrease of NO conversion caused by the presence of water is due to the preferential adsorption of water which inhibits hydrocarbon adsorption on the catalyst surface. Among reductants of C1–C3 hydrocarbons, the most atom-efficient NO abatement was achieved with C2 hydrocarbons. C3 hydrocarbons were less selective for NO reduction than the other hydrocarbons. It was suggested that only one carbon atom per molecules were used for the SCR reaction, and the other carbon atoms were consumed by the simple combustion reaction.

Keywords: Selective catalytic reduction; NO; Ga; ₂; O; ₃; –Al; ₂; O; ₃; solid solution; Hydrocarbon; DME

Comparative study of the electrocatalytic oxidation and mechanism of nitrophenols at Bi-doped lead dioxide anodes by Yuan Liu; Huiling Liu; Yan Li (pp. 297-302).

The electrocatalytic oxidation of o-nitrophenol ( o-NP), m-nitrophenol ( m-NP) and p-nitrophenol ( p-NP) has been studied at Bi-doped lead dioxide anodes on acid medium by cyclic voltammetry and bulk electrolysis. The results of voltammetric studies indicated that these nitrophenol isomers were indirectly oxidized byOH radical in the solutions. Within the present experimental conditions used (50mg of nitrophenol L⁻¹, pH 4.3, 30mAcm⁻², 303K), the complete decomposition of nitrophenols (NPs) was achieved. The electrocatalytic oxidation of NPs lay in the order: p-NP> m-NP> o-NP. Molecular configuration including the electron character and hydrogen bonds of NPs significantly influenced the electrocatalytic oxidation of these isomers. Hydroquinone, catechol, resorcinol, benzoquinone, aminophenols, glutaconic acid and maleic acid and oxalic acid have been detected as soluble products during the electrolysis of NPs. The possible degradation pathways of these isomers were proposed. The first stage is the release of nitro group from the aromatic rings. As a consequence, hydroquinone, catechol, resorcinol and benzoquinone are formed. These organic compounds are oxidized initially to carboxylic acids (glutaconic acid, maleic acid and oxalic acid) and later to carbon dioxide and water. Simultaneously, the reduction of NPs to aminophenols takes place at the cathode.

Keywords: Nitrophenols; Electrocatalytic oxidation; Bi-doped lead dioxide anodes; Mechanisms; Hammett constant

VOC oxidation over MnO_x–CeO₂ catalysts prepared by a combustion method by Dimitrios Delimaris; Theophilos Ioannides (pp. 303-312).

MnO_x–CeO₂ catalysts were prepared by a urea combustion method and their performance in the oxidation of ethanol, ethyl acetate and toluene was evaluated. XRD, XPS, H₂-TPR and N₂ physisorption were employed in catalyst characterization. Mn²⁺ and Mn³⁺ ions are present in the catalysts. In ceria-rich materials, crystalline manganese oxide phases are absent and Mn ions are homogeneously distributed between the bulk and the surface suggesting incorporation of Mn ions in ceria structure. In Mn-rich materials, segregation of a Mn₃O₄ phase takes place. The mixed oxides get reduced by H₂ at lower temperatures than the corresponding single oxides and Mn ions promote reduction of ceria. The surface area of MnO_x–CeO₂ catalysts is larger than the one of single oxides prepared with the same method. The larger surface area of MnO_x–CeO₂ catalysts counterbalances their smaller specific activity allowing complete conversion of the examined VOCs at lower temperatures compared to the single oxides.

Keywords: VOC; Oxidation; Ethanol; Ethyl acetate; Toluene; Ceria; Manganese oxide; Compensation effect

A comparative study on the empirical modeling of photo-Fenton treatment process performance by M. Pérez-Moya; M. Graells; P. Buenestado; H.D. Mansilla (pp. 313-323).

This paper investigates the Fenton photo-assisted degradation of 4-chlorophenol (4-CP). The experimental work was planned according to the Design of Experiments (DOE) scheme, and degradation performance was measured in terms of TOC reduction at different reaction times. Appropriate reagent ratios have been obtained for effective 4-CP degradation.The modeling of the process performance as a function of the reaction conditions was then studied by fitting different models to the degradation data. The models are compared and discussed according to the degree of correlation they provide. The widely used second order polynomial equation (including bilinear terms) is questioned and alternative models are proposed (potential model, Hoerl equation) for a better empirical representation of the performance of the degradation process.The disparate estimations given by the different models studied suggest that further research is required in model selection in order to obtain reliable characterization of Fenton, Fenton-like and photo-Fenton treatment performance.

Keywords: Modeling; Experimental design; Photo-Fenton; 4-Chlorophenol

Autothermal reforming of simulated and commercial diesel: The performance of zirconia-supported RhPt catalyst in the presence of sulfur by Reetta K. Kaila; Andrea Gutiérrez; A. Outi I. Krause (pp. 324-331).

Simulated and commercial low-sulfur diesel fuels (S<10ppm) were studied in autothermal reforming (ATR) on Rh and Pt and bimetallic RhPt catalysts supported on ZrO₂ with the aim of obtaining fuel gas suitable for solid oxide fuel cell applications.In ATR of the simulated fuels, the catalysts deactivated markedly in the presence of H₂S, whereas in ATR of simulated fuels in the presence of 4,6-dimethyldibenzothiophene (4,6-DMDBT) and in ATR of commercial diesel the catalyst deactivated only slightly over several hours. In view of its different effect, H₂S cannot be considered a suitable model compound for heterocyclic sulfur compounds present in commercial low-sulfur fuels.In ATR of commercial low-sulfur diesel, carbon formation increased with the Pt loading, whereas sulfur deposition on the catalyst was strongest on the monometallic Rh/ZrO₂. Furthermore, less carbon was deposited on the RhPt catalyst in the presence than absence of H₂S, as sulfur blocked the catalyst active sites. The catalyst could be reactivated by stopping the H₂S flow.

Keywords: Autothermal reforming; Solid oxide fuel cell; Low-sulfur diesel; 4,6-DMDBT; H; ₂; S adsorption; RhPt/ZrO; ₂; catalyst

Photocatalytic hydrogen production over flame spray pyrolysis-synthesised TiO₂ and Au/TiO₂ by Gian Luca Chiarello; Elena Selli; Lucio Forni (pp. 332-339).

A set of titanium dioxide and gold-modified titanium dioxide samples were prepared by flame spray pyrolysis (FP) and characterized by BET, XRD, HRTEM and UV–vis reflectance analysis. Their photocatalytic activity in hydrogen production in water suspension, either from water photosplitting or from methanol photoreforming, was tested in an expressly set up, closed recirculation laboratory scale photoreactor and compared to those of commercial TiO₂ samples, including Degussa P25, pure rutile and pure anatase. The rate of hydrogen evolution (rH2) increased with increasing the anatase content, pure anatase being the most active photocatalyst. Surface area and crystallinity, both key properties of photocatalysts, can be tuned up by properly setting FP operation parameters, including the selection of the organic solvent/fuel. In particular, FP-made TiO₂ prepared from a xylene solution showed more active than P25. Finally,rH2 increased by one order of magnitude in water photosplitting and by ca. 30 times in methanol photoreforming upon 1% gold addition on TiO₂.

Keywords: Photocatalytic water splitting; Methanol photoreforming; H; ₂; production; Flame spray pyrolysis; Au/TiO; ₂

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Applied Catalysis B, Environmental (v.84, #1-2)