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Applied Catalysis B, Environmental (v.68, #3-4)

Editorial board, scope (pp. co2).

Editorial board (pp. i).

Catalytic detoxification of 1,1-dimethylhydrazine aqueous solutions in heterogeneous Fenton system by O.A. Makhotkina; E.V. Kuznetsova; S.V. Preis (pp. 85-91).

The experimental study into catalytic properties of FeZSM-5 was undertaken into oxidation of 1,1-dimethylhydrazine (UDMH) aqueous solutions using hydrogen peroxide. The performances of heterogeneous and homogeneous Fenton systems were compared. UDMH complete mineralization was achieved. Formic and acetic acids, as well as nitromethane, were identified as oxidation by-products. Adsorption properties of FeZSM-5 with respect to hydrogen peroxide, 1,1-dimethylhydrazine and N-nitrosodimethylamine have been studied. The effects of the oxidant and the target compound concentrations, temperature and pH of aqueous solution were established.

Keywords: Hydrogen peroxide; Heterogeneous Fenton; FeZSM-5; Unsymmetrical dimethylhydrazine; UDMH; N; -Nitrosodimethylamine

Combination of a non-thermal plasma and a catalyst for toluene removal from air: Manganese based oxide catalysts by Sophie Delagrange; Ludovic Pinard; Jean-Michel Tatibouët (pp. 92-98).

A series of manganese based catalysts have been tested in a combined plasma-catalyst reactor in the reaction of toluene removal from air. In the standard conditions (toluene=240ppm, energy density=172J/L, 1g of catalyst, 315mL/min), the best catalyst (manganese oxide supported on active carbon) is able to transform 55% of the toluene into carbon oxides. According to the study of the reaction mechanism, it appears that the toluene is oxidized both in-plasma by short-lived species generated by plasma and in post-plasma on the catalyst surface by the ozone formed in the plasma, the reaction on the catalyst being more selective in carbon dioxide formation than the reaction in plasma. We have shown that the toluene conversion increases when the toluene concentration in air decreases. A model able to describe the behavior of the plasma reactor and the plasma-catalyst reactor is proposed.

Keywords: Toluene removal; Non-thermal plasma; Plasma-catalyst reactor; Kinetic study

Preparation of freestanding and crack-free titania–silica aerogels and their performance for gas phase, photocatalytic oxidation of VOCs by Shengli Cao; King Lun Yeung; Po-Lock Yue (pp. 99-108).

Freestanding and crack-free titania–silica aerogels with high titanium content (i.e., Ti/Si=1) were successfully prepared by adjusting the hydrolysis of the two alkoxide precursors to a comparable rate during the sol–gel processing. Two titania–silica aerogels were prepared by ethanol and CO₂ supercritical drying methods. Well-dispersed, nanometer-sized anatase crystal domains (ca. 10nm) were crystallized by high temperature, ethanol supercritical drying. The crystalline domains were solidly anchored to the aerogel network by Ti–O–Si bonds. Titania–silica aerogels prepared by CO₂ supercritical drying method were devoid of TiO₂ crystals. A molecular-level mixing was achieved and anatase TiO₂ was only crystallized with difficulty by high temperature calcination (1073K). Both aerogels were mesoporous and displayed similar open pore structure that is readily accessible to reactant molecules. However, only the titania–silica aerogel with anatase TiO₂ prepared by ethanol supercritical drying was active for the gas phase, photocatalytic oxidation of volatile organic compounds (i.e., isopropanol and trichloroethylene). Catalysts prepared from Degussa P25 TiO₂ displayed lower activity under similar reaction conditions.

Keywords: Nanostructured titanium dioxide; Sol–gel processing; Gas diffusion; Photooxidation; Isopropanol; Trichloroethylene

Rules of chemical promotion by S. Brosda; C.G. Vayenas; J. Wei (pp. 109-124).

The recently established rules of electrochemical promotion of catalysis (EPOC or NEMCA effect) are compared with all combined promotional and kinetic studies published in the Journal of Catalysis and other journals during the last 10 years. In all 33 cases surveyed the promotional rules are found to be in agreement with experiment. These rules enable one to predict the desired type of promoter on the basis of the unpromoted reaction kinetics or the type of kinetics on the basis of the rate dependence on promoter coverage. This validation of the electrochemical promotion rules by the classical promotion literature underlines the functional similarity and only operational difference of electrochemical and classical promotion. It also shows that electrostatic interactions in the double layer formed at the catalyst–gas interface are a key element of promotion in catalysis.

Keywords: Promotion; Electrochemical promotion; Catalytic kinetics; Promotional rules; Promoter selection; Work function; Catalytic reaction classification; Volcano-type reactions; Electrophobic and electrophilic reactions

Study of the electronic structure and photocatalytic activity of the BiOCl photocatalyst by Ke-Lei Zhang; Cun-Ming Liu; Fu-Qiang Huang; Chong Zheng; Wen-Deng Wang (pp. 125-129).

A novel bismuth oxychloride (BiOCl) was synthesized by a hydrolysis method. The powder sample was characterized by X-ray diffraction, field emission scanning electron microscope and UV–vis spectrophotometer. The layered compound BiOCl was the first oxyhalide to be used as a photocatalyst. The prepared material has an optical indirect band-gap of 3.46eV. For its photocatalytic reactivity, the methyl orange (MO) dye degradation was chosen to be investigated. In a comparison of a three-cycle measurement of BiOCl with that of TiO₂ (P25, Degussa), it was found that BiOCl had better performance than P25 at every recycle. The calculated electronic structure of BiOCl confirms that it has an indirect band-gap, and the Cl 3p and Bi 6p states dominate the highest occupied molecular orbitals (HOMO) and the lowest unoccupied orbitals (LUMO), respectively. The open crystal structure and indirect optical transitions of BiOCl play important roles in its excellent photocatalytic activity.

Keywords: Photocatalyst; UV–vis; BiOCl; Band-gap; Methyl orange

Vanadium loaded carbon-based catalysts for the reduction of nitric oxide by M.J. Lázaro; M.E. Gálvez; C. Ruiz; R. Juan; R. Moliner (pp. 130-138).

Carbon-based SCR catalysts for the reduction of NO with NH₃ at low temperatures have been prepared using activated carbons obtained from a local Spanish coal, doped with several vanadium compounds. Among them, the ashes of a petroleum coke (PCA) were also employed. Both the catalysts and the carbon supports have been characterized by means of N₂ and CO₂ physisorption, NH₃ and O₂ chemisorption and temperature programmed desorption (TPD). The activity of the catalysts has been tested in a laboratory-scale unit, measuring significant conversions of NO (above 50%) with almost 100% selectivity toward N₂ at 150°C. The feasibility of using the petroleum coke ashes as the active phase was confirmed comparing the activity of the catalysts doped with these residues, with the one measured for the catalysts prepared using model vanadium compounds. The physical–chemical features of the carbon support resulted of key importance for achieving a considerable catalytic activity. The values of apparent energy of activation calculated for the catalysts presented in this paper were very similar to other carbon-based catalysts and smaller than the ones corresponding to TiO₂-supported systems. The gas residence time on the catalytic bed influences the catalytic activity to a great extent, thus being a determinant parameter for designing the SCR de-NO_x unit. To avoid ammonia slip, inlet concentrations of NH₃ has to be little under the stoichometric NH₃/NO ratio (∼0.7). The catalysts stability was tested in terms of carbon support gasification followed by termogravimetric analysis and gas chromatography. The activity of the catalysts was maintained at least over 24h of reaction.

Keywords: Activated carbon; Nitric oxide; Vanadium catalysts

On the photooxidative behavior of TiO₂ and PW₁₂O₄₀³⁻: OH radicals versus holes by P. Kormali; T. Triantis; D. Dimotikali; A. Hiskia; E. Papaconstantinou (pp. 139-146).

Parallel experiments under similar conditions, using various substrates (atrazine, fenitrothion, 4-chlorophenol and 2,4-D) and OH radical scavengers (Br⁻, isopropyl alcohol, tertiary butyl alcohol and acetone), have shown that the photooxidizing mode of PW₁₂O₄₀³⁻ and TiO₂, i.e., OH radicals and/or holes (h⁺), depends on the nature of substrate and the mode of investigation. This provides an explanation for the controversial results reported in the literature. Atrazine shows that both PW₁₂O₄₀³⁻ and TiO₂ operate, mainly, via OH radicals and to a lesser extent with holes (h⁺), whereas, fenitrothion suggests that both systems operate almost exclusively, via OH radicals. Differences in the action of the catalysts are encountered in the photodegradation of 4-chlorophenol (4-ClPh) and 2,4-dichlorophenoxyacetic acid (2,4-D). PW₁₂O₄₀³⁻ appears to operate essentially via OH radicals, whereas, h⁺ appear to be the major oxidant with TiO₂. Overall, though, the action of OH radicals relative to h⁺ appears to be more pronounced with PW₁₂O₄₀³⁻ than TiO₂.

Keywords: Photocatalysis; Polyoxometallates; TiO; ₂; OH radicals; Holes

Microwave-enhanced catalytic degradation of phenol over nickel oxide by Teh-Long Lai; Chia-Chan Lee; Kuen-Shian Wu; Youn-Yuen Shu; Chen-Bin Wang (pp. 147-153).

A mix-valenced nickel oxide, NiO_x, was prepared from nickel nitrate aqueous solution through a precipitation with sodium hydroxide and an oxidation by sodium hypochlorite. Further, pure nickel oxide was obtained from the NiO_x by calcination at 300, 400 and 500°C (labeled as C300, C400 and C500, respectively). They were characterized by thermogravimetry (TG), X-ray diffraction (XRD), nitrogen adsorption at −196°C and temperature-programmed reduction (TPR). Their catalytic activities towards the degradation of phenol were further studied under continuous bubbling of air through the liquid phase. Also, the effects of pH, temperature and kinds of nickel oxide on the efficiency of the microwave-enhance catalytic degradation (MECD) of phenol have been investigated. The results indicated that the relative activity affected significantly with the oxidation state of nickel, surface area and surface acidity of nickel oxide, i.e., NiO_x (>+2 and S_BET=201m²g⁻¹)≫C300 (+2 and S_BET=104m²g⁻¹)>C400 (+2 and S_BET=52m²g⁻¹)>C500 (+2 and S_BET=27m²g⁻¹). The introduction of microwave irradiation could greatly shorten the time of phenol degradation.

Keywords: Nickel oxide; Microwave; Degradation of phenol

Production of ketones from sewage sludge over zirconia-supporting iron oxide catalysts in a steam atmosphere by Eri Fumoto; Yosuke Mizutani; Teruoki Tago; Takao Masuda (pp. 154-159).

Recovering useful hydrocarbons from sewage sludge using zirconia-supporting iron oxide catalysts was investigated. Zirconia has activity for decomposing water molecules to generate active oxygen and hydrogen species. These oxygen species spill over to the surface of iron oxide and react with hydrocarbons to produce oxygen-containing organic chemicals such as acetone. Thus, zirconia-supporting iron oxide catalyst has two kinds of active sites on zirconia and on iron oxide. Sewage sludge was hydrothermally liquefied at 573K in advance, yielding black water containing various hydrocarbons, to enhance the contact of reactant molecules with the catalysts. It was found that the hydrocarbons in the black water converted well to a mixture containing primarily acetone without any carbonaceous residue over zirconia-supporting iron oxide catalysts under the conditions of one atmospheric pressure and superheating steam atmosphere. Furthermore, it was confirmed that acetone was produced continuously from the sewage-derived black water over the catalysts using a bench scale flow reactor.

Keywords: Biomass waste; Sewage sludge; Iron oxide catalyst; Partial oxidative reaction; Acetone

Development of Ni catalysts for tar removal by steam gasification of biomass by Takeo Kimura; Tomohisa Miyazawa; Jin Nishikawa; Shigeru Kado; Kazu Okumura; Toshihiro Miyao; Shuichi Naito; Kimio Kunimori; Keiichi Tomishige (pp. 160-170).

Catalytic performance of Ni/CeO₂/Al₂O₃ catalysts prepared by a co-impregnation and a sequential impregnation method in steam gasification of real biomass (cedar wood) was investigated. Especially, Ni/CeO₂/Al₂O₃ catalysts prepared by the co-impregnation method exhibited higher performance than Ni/Al₂O₃ and Ni/CeO₂/Al₂O₃ prepared by the sequential impregnation method, and the catalysts gave lower yields of coke and tar, and higher yields of gaseous products. The Ni/CeO₂/Al₂O₃ catalysts were characterized by thermogravimetric analysis, temperature-programmed reduction with H₂, transmission electron microscopy and extended X-ray absorption fine structure, and the results suggested that the interaction between Ni and CeO₂ became stronger by the co-impregnation method than that by sequential method. Judging from both results of catalytic performance and catalyst characterization, it is found that the intimate interaction between Ni and CeO₂ can play very important role on the steam gasification of biomass.

Keywords: Steam gasification; Steam reforming; Biomass; Ni; CeO; ₂; Tar; Coke; Synthesis gas; Hydrogen

Photocatalytic oxidation of multicomponent solutions of herbicides: Reaction kinetics analysis with explicit photon absorption effects by Bea Toepfer; Alexander Gora; Gianluca Li Puma (pp. 171-180).

The intrinsic reaction kinetics of the photocatalytic oxidation (PCO) of the herbicides isoproturon, simazine and propazine over irradiated TiO₂ (Degussa P25) suspensions was studied in single-component and in multicomponent systems. Experiments were carried out at different photon fluxes and different herbicide concentrations in the range below 1mgL⁻¹. The results were analyzed in terms of a Langmuir–Hinshelwood (L–H) kinetic model previously established for multicomponent solutions of herbicides, but including the explicit effect of photon absorption. This was accomplished by modeling the radiation field in the reactor with the Six-Flux Absorption-Scattering Model (SFM) (i.e., scattered photons follow the route of the six directions of the Cartesian coordinates) using optical parameters averaged across the spectrum of the incident radiation. The intrinsic reaction kinetic constants of isoproturon, simazine and propazine independent of the radiation field in the reactor were determined. The oxidation rate of the herbicides was found to follow half-order dependence with respect to the local volumetric rate of photon absorption (LVRPA), in the range of photon fluxes investigated. The established model was found to be appropriate to predict the time-dependent degradation profiles of the herbicides in single- and multicomponent systems not only at all radiation intensities investigated in this study but also when one or two herbicides were present in excess of the others in the mixture. Using this simple approach, intrinsic kinetic data can be obtained.

Keywords: Water purification; Titanium dioxide; Photocatalysis; Photoreactor; Suspensions; Pesticides; Radiation absorption; Radiation scattering; Radiation field; Reaction kinetics

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Applied Catalysis B, Environmental (v.68, #3-4)