Check out our New Publishers' Select for Free Articles

Applied Catalysis B, Environmental (v.95, #1-2)

IFC Editorial Board (pp. co2).

Editorial Board (pp. i).

Contents Continued (pp. iii).

Contents (pp. co4).

Decomposition of 2-chlorophenol employing goethite as Fenton catalyst. I. Proposal of a feasible, combined reaction scheme of heterogeneous and homogeneous reactions by Guadalupe B. Ortiz de la Plata; Orlando M. Alfano; Alberto E. Cassano (pp. 1-13).

A study has been conducted on the decomposition of 2-chlorophenol (2-CP) applying a heterogeneous Fenton reaction using goethite as catalyst at pH 3. The research was aimed at obtaining a workable kinetic expression apt for developing a kinetic model for scaling up purposes. Several aspects of the reaction have been described in the available literature but, for the moment, without a reasonable representation of the entire reaction behavior. In order to provide a more comprehensive and probable explanation of the whole observed performance, a set of experiments was carried out varying systematically all the significant variables. The proposal considers that the reaction is essentially a combination of four heterogeneous processes associated with one typical homogeneous Fenton reaction. Three of the surface reactions explain a very small iron leaching to the medium by a proton induced solubilization, a reductive dissolution reaction and a non-reductive iron release produced by detected 2-CP chemical decomposition byproducts, particularly, chlorohydroquinone (ClHQ) and oxalic acid (OxA). Iron concentration in the solution may be further increased in the final stages of the reaction after most of the 2-CP has been degraded, by the appearance of OxA that takes part in a third surface reaction. The fourth heterogeneous reaction rationalizes the unusual hydrogen peroxide consumption at high catalyst loadings. During the homogeneous reaction, the presence of ClHQ and ClBQ produces a homogeneous autocatalytic beneficial enhancement of the Fe³⁺→Fe²⁺ transformation. Consequently, the existence of phenolic derivatives either in the mixture or as reaction byproducts produces a beneficial enhancement of the reaction rate. Very low iron leaching is required to produce the onset of the homogeneous Fenton reaction, which was shown to be strongly dependent upon the reaction temperature. All the experimental findings were satisfactorily described by a set of 19-step feasible reaction scheme. The process could be useful for the treatment of wastewaters containing pollutants with phenolic derivatives, as long as iron leaching remains within tolerable limits.

Keywords: Abbreviations; 2-CP; 2-chlorophenol; ClBQ; chlorobenzoquinone; ClHQ; chlorohydroquinone; ClSQ; chlorosemiquinone; OxA; oxalic acid; PH; phenolic ring; M; _W–P; Weisz–Prater criterion for internal diffusionHeterogeneous Fenton reaction; Goethite; 2-Chlorophenol; Surface reactions; Catalytic effects; Feasible reaction scheme

Decomposition of 2-chlorophenol employing goethite as Fenton catalyst II: Reaction kinetics of the heterogeneous Fenton and photo-Fenton mechanisms by Guadalupe B. Ortiz de la Plata; Orlando M. Alfano; Alberto E. Cassano (pp. 14-25).

The kinetics of the degradation of 2-chlorophenol (2-CP) employing both the heterogeneous Fenton and photo-Fenton reactions using goethite as the solid catalyst is studied. The photoreactor was irradiated with a 350–400nm wavelength light. The kinetics is based on 19 steps of a combined heterogeneous–homogeneous mechanism derived for the thermal Fenton reaction [see companion article by the authors: Ortiz de la Plata et al. (2009)] . For the photo-Fenton alternative, two more steps are needed. Some of the specific kinetic constants of the reaction scheme are approximately known. However, for the heterogeneous “thermal” Fenton reaction, three new unknown constants were required and were attained from experimental data obtained in this and the previous work. The parameters were (i) the reaction of the HO radical with 2-CP, (ii) the proton induced iron dissolution and (iii) the reductive induced iron dissolution . In the case of the heterogeneous photo-Fenton reaction steps, the radiation field in the reacting system was described by solving the complete radiative transfer equation inside the reactor. With this purpose, the knowledge of the needed goethite optical properties were previously characterized . Combining the dark and the irradiated experiments 21 kinetically consistent parameters were achieved for the proposal of a feasible mechanism. They are valid for both systems; making the two primary quantum yields of the photoreaction equal to zero, the “dark” Fenton reaction performance is properly described by the remaining 19 specific rate constants. These results are independent of the used experimental apparatus and can be safely used for scaling-up purposes within the range of the explored variables.

Keywords: Abbreviations; 2-CP; 2-chlorophenol; ClBQ; chlorobenzoquinone; ClHQ; chlorohydroquinone; ClSQ; chlorosemiquinone; LVRPA; the local volumetric rate of photon absorption (Einstein; cm; ⁻³; s; ⁻¹; ); ODE; ordinary differential equation; RTE; the radiative transfer equationAOT; Heterogeneous; Fenton and photo-Fenton; Reaction kinetics; Goethite; 2-Chlorophenol

Kinetic modeling of the total oxidation of propane over CuO-CeO₂/γ-Al₂O₃ by M. Philippe Heynderickx; Joris W. Thybaut; Hilde Poelman; Dirk Poelman; Guy B. Marin (pp. 26-38).

The total oxidation of propane is studied by means of steady-state experiments over a CuO–CeO₂/γ-Al₂O₃ catalyst at propane inlet partial pressures of 0.2–1.0kPa, oxygen inlet partial pressures of 2.7–27.6kPa and temperatures from 543 to 648K. The inlet ratio of oxygen to propane is varied between 6.1 and28.0molO2,0molC3H8,0−1. Water and carbon dioxide inlet partial pressures up to 12.4kPa are investigated. The complete experimental dataset was regressed with a priori possible Langmuir–Hinshelwood (LH), Eley–Rideal (ER) and Mars–van Krevelen (MVK) rate equations. A LH rate equation, the rate-determining step being the surface reaction between one adsorbed propane species and one dissociatively adsorbed oxygen species, allows the best description of the data.The surface reaction activation energy amounts to 74.4±4.6kJmol⁻¹. All adsorption steps in the selected reaction mechanism are quasi-equilibrated. The values of the preexponential factors of the adsorption equilibrium coefficients correspond to rather mobile surface species. Molecular water adsorption is followed by a dissociation of the adsorbed water by interaction with a dissociatively adsorbed oxygen species to form two hydroxyl species.

Keywords: Abbreviations; DOF; degrees of freedom; ER; Eley–Rideal; GC; gas chromatograph; LH; Langmuir–Hinshelwood; MVK; Mars–van Krevelen; NLV; number of lumped variables; NLP; number of lumped parameters; VOC; volatile organic compoundTotal oxidation; Kinetics; Modeling; Langmuir–Hinshelwood; Eley–Rideal; Mars–van Krevelen

High-throughput study of the effects of inorganic additives and poisons on NH₃-SCR catalysts—Part I: V₂O₅–WO₃/TiO₂ catalysts by M. Klimczak; P. Kern; T. Heinzelmann; M. Lucas; P. Claus (pp. 39-47).

The influence of phosphorus, alkaline and alkaline earth metals, chromium and copper on the catalytic activity and selectivity of a V₂O₅–WO₃/TiO₂ catalyst for the selective catalytic reduction (SCR) of nitrogen oxides with ammonia has been studied. These components are put through a catalytic aftertreatment system of a diesel engine as impurities of biodiesel (K, Na, P), urea solution (K, Na, Ca, Mg) and abrasion of the engine (Cr, Cu). The catalysts were exposed to corresponding nitrates or ammonium compounds in diluted solution by wet impregnation or deposition of inorganic aerosol particles. The second approach allows a more realistic investigation using catalysts and reaction conditions close to mobile application. Hereby, the effects of single catalyst poisons have been investigated. Furthermore, the influence of combinations of poisons using Design of Experiments (DOE) has been determined in case of impregnated catalysts. Physical and chemical characterization methods focusing on NH₃-TPD, penetration profiles and chemical analysis have been carried out to gain insight into the extent and the mechanism of deactivation. Both impregnated and aerosol deactivated catalysts show a strong poisoning effect of alkaline metals due to a reduced ammonia adsorption capacity. This effect could be weakened by a simultaneous doping of phosphates or sulphates. Chromium and copper are moderate catalyst poisons but have the ability to increase the N₂O production.

Keywords: V; ₂; O; ₅; –WO; ₃; /TiO; ₂; Catalyst deactivation; Selective catalytic reduction (SCR); DeNOx activity; High-throughput experiments; Design of Experiments (DOE)

High-throughput study of the effects of inorganic additives and poisons on NH₃-SCR catalysts. Part II: Fe–zeolite catalysts by P. Kern; M. Klimczak; T. Heinzelmann; M. Lucas; P. Claus (pp. 48-56).

This study was carried out to identify potential deactivating effects of inorganic materials which are put through an aftertreatment system of a diesel engine as combustion products of lubricant oil additives (i.e. Ca, Mg, Zn, P, B, Mo), impurities of (bio-)diesel fuel, urea solution (K, Ca) and aerosol particulate from intake air (Na, Cl). The effects of adding inorganic additives to an industrial Fe–MFI-SCR catalyst (Fe-BEA) have been evaluated by means of high-throughput methods. The results indicate the impact of different inorganic additives and poisons to Fe–zeolite–NH₃-SCR catalysts in case of addition to the catalyst after catalyst preparation by ion exchange and molding of a washcoat by dip-coating procedures. Results of high-throughput screening are supplemented by experiments in more realistic scale, using catalysts and conditions close to the industrial application. As the mechanism of the uptake of inorganic poisons into the catalytic washcoat of an aftertreatment system is not yet quantitatively understood, thereby the addition of the additive to the as-sold catalyst was conducted in different ways, i.e. by wet-chemical impregnation and by exposure to aerosols generated from thermal decomposition of aqueous precursor solutions of potential poisons. It was found that alkaline metals, which are severe poisons to the established vanadia-based catalysts (see Part I), also exhibit deactivating potential towards Fe–zeolite catalysts and induce the reduction of the ammonia storage capability. However, their effect to the catalytic activity is dependant on the operation mode of the catalyst, and is far less pronounced than the effect of alkaline metals to vanadia-based catalysts. The exposure of Fe–zeolite catalysts to phosphates leads to a strong deactivation of the catalyst.

Keywords: Fe zeolites; Catalyst deactivation; Selective catalytic reduction (SCR); DeNOx activity; High-throughput experiments; Ammonia slip

Influence of H₂, CO₂ and H₂O on the activity and deactivation behavior of Au/CeO₂ catalysts in the water gas shift reaction at 300°C by A. Abd El-Moemen; G. Kučerová; R.J. Behm (pp. 57-70).

The effect of H₂, CO₂ and H₂O on the activity, stability and deactivation behavior of an oxidatively (O400) and a reductively (H400) pretreated 4.5wt.% Au/CeO₂ catalyst in the water gas shift (WGS) reaction at 300°C was studied by kinetic and spectroscopic measurements, using different gas mixtures, going stepwise from idealized to a semi-realistic reaction atmosphere. The results were compared with data for the WGS reaction determined under similar reaction conditions at a lower reaction temperature of 180°C [Y. Denkwitz, A. Karpenko, V. Plzak, R. Leppelt, B. Schumacher, R.J. Behm, J. Catal. 246 (2007) 74]. The formation/removal of adsorbed reaction intermediates and side products (surface carbonates, formates, OH_ad, CO_ad) was followed by in situ IR spectroscopy (DRIFTS). Variation of the reaction gas mixture led to significant effects on the initial activity and the stability of the catalysts, which depend also on the pre-treatment of the catalysts. The resulting trends are compared with those obtained for reaction at 180°C, consequences for the reaction mechanism and for applications in fuel gas processing at medium temperatures will be discussed.

Keywords: Water gas shift reaction; High temperature reaction; Reaction kinetics; Deactivation; Au catalysts; Au/CeO; ₂; Realistic reformate; DRIFTS

Influence of alkali carbonates on benzyl phenyl ether cleavage pathways in superheated water by Virginia Roberts; Sebastian Fendt; Angeliki A. Lemonidou; Xuebing Li; Johannes A. Lercher (pp. 71-77).

Benzyl phenyl ether conversion in superheated water yields a broad product distribution. In addition to the hydrolysis products, phenol and benzyl alcohol, a large amount of consecutive products are formed depending on the operating conditions. The influence of Li₂CO₃, Na₂CO_3, and K₂CO₃ on these reactions is explored between 270 and 370°C. It is shown that high selectivity towards hydrolysis can be achieved at low temperatures and short reaction times. At higher severities the yields of phenol and especially benzyl alcohol decrease and higher molecular weight compounds are formed by consecutive reactions. Alkali carbonates effect this distribution by decreasing the concentration of protons in the system and by providing and enhancing parallel and secondary reaction mechanisms. The yields of toluene, 2 and 4-benzyl phenol are strongly enhanced in the presence of an alkali carbonate, by formation of a cation–BPE adduct in which the ether bond is strongly polarized.

Keywords: Benzyl phenyl ether; Cleavage; Alkali carbonate; Water; Hydrolysis

Photo-induced carbonation of lime-TiO₂ mortars by Ioannis Karatasios; Marios S. Katsiotis; Vlassis Likodimos; Athanasios I. Kontos; Georgios Papavassiliou; Polycarpos Falaras; Vassilis Kilikoglou (pp. 78-86).

In this work, titanium dioxide (TiO₂) has been used as an additive in lime binder (Ca(OH)₂), in order to benefit from its photocatalytic properties and study both the photocatalytic properties of the produced mixtures and the effect of photocatalytically produced carbon dioxide on the carbonation process of lime. TiO₂ was added in three different portions (3, 6 and 10% w/w) in lime mixtures and their physicochemical and photocatalytic properties were studied and compared to those of a reference, made exclusively of lime. The photocatalytic properties of the mixtures were studied through the photo-oxidation of an organic model pollutant solution (methyl orange) to a colorless form, as well as by studying the microstructure and carbonation depth in different groups of mixtures subjected to photocatalysis cycles in the laboratory and exposed for a 2 month period in the open air (urban environment).Laboratory results confirmed that lime-TiO₂ composite mixtures exhibit photocatalytic properties in both UV radiation conditions and direct exposure to sunlight. Moreover, analytical results indicated an enhanced carbonation of lime-TiO₂ composites. TiO₂ can be added to lime successfully and can have applications in lime-based mortars used in the conservation of architectural heritage, enhancing their performance against soiling and amenity loss.

Keywords: Lime; Carbonation; Photocatalysis; TiO; ₂; Mortars; Conservation; Cultural heritage

Steam reforming of methanol over ceria and gold-ceria nanoshapes by Nan Yi; Rui Si; Howard Saltsburg; Maria Flytzani-Stephanopoulos (pp. 87-92).

In this work we have found that a small amount (∼1at.%) of gold deposited on ceria nanorods exhibits excellent catalytic activity for the low-temperature steam reforming of methanol (SRM). Gold clusters (<1nm, TEM invisible) dispersed on the {110} faces of ceria nanorods catalyze the reaction in a cooperative mechanism with ceria. Gold nanoparticles (∼3nm) on the {100} surfaces of ceria nanocubes are inactive. The apparent activation energy of the SRM reaction on Au-ceria is ∼110kJmol⁻¹. On the basis of TPSR/MS analysis, we determined that the SRM reaction on Au-ceria involves methanol dehydrogenation, methyl formate hydrolysis and formic acid decomposition steps to produce CO₂ and H₂. Better than 97% catalyst selectivity to CO₂ was found over the temperature range from 175 to 250°C. In the presence of methanol, the water–gas shift (WGS) reaction is suppressed and is not part of the mechanism at temperatures below 250°C. The SRM stability of the Au-ceria system is good for practical application of this type catalyst.

Keywords: Gold; Cerium oxide nanoparticles; Steam reforming of methanol; Water–gas shift reaction; Methanol decomposition; Shape effect

Supported cobalt oxide on MgO: Highly efficient catalysts for degradation of organic dyes in dilute solutions by Wei Zhang; Hui Lin Tay; Sze Sheng Lim; Yongsheng Wang; Ziyi Zhong; Rong Xu (pp. 93-99).

Cobalt oxide catalysts immobilized on various oxides (MgO, ZnO, Al₂O₃, ZrO₂, P25, SBA-15) were prepared for degradation of organic dyes in dilute solutions via a sulfate radical approach. Their efficiency in activation of peroxymonosulfate (PMS) was investigated for the degradation of methylene blue (MB). Among the catalysts employed, the Co/MgO catalyst was found the most active. The complete degradation of MB occurred in <7min when the Co/MgO catalyst with an optimum Co₃O₄ loading of 5wt% was used. The performance of the Co/MgO catalyst is found better than both the homogeneous cobalt ions and heterogeneous Co₃O₄ catalyst. XPS analysis indicates that the surface of the MgO support is extensively covered by the hydroxyl groups. Hence, it is suggested that the alkaline MgO support plays several important roles in (i) dispersing the cobalt oxide nanoparticles well, (ii) minimizing the leaching of cobalt ions into the liquid phase, and (iii) facilitating the formation of surface Co–OH complex which is a critical step for PMS activation. Besides MB, other organic dyes such as orange II and malachite green, can also be degraded within a few minutes using the Co/MgO catalyst. It is believed that the highly efficient and environmentally benign Co/MgO catalyst developed in this work can be widely applied in advanced oxidation technologies towards degradation of organic pollutants.

Keywords: Advanced oxidation technologies (AOTs); Peroxymonosulfate (PMS); Oxone; Sulfate radicals; Cobalt oxides; Magnesium oxide (MgO); Support materials; Organic dyes; Methylene blue (MB); Orange II; Malachite green

On the kinetics and mechanisms of photolytic/TiO₂-photocatalytic degradation of substituted pyridines in aqueous solutions by David R. Stapleton; Ioannis K. Konstantinou; Dionissios Mantzavinos; Dimitra Hela; Maria Papadaki (pp. 100-109).

Pyridine and pyridine derivatives are extensively used for the production of pesticides, medicinal drugs, industrial solvents, dyes, rubber chemicals etc. They are encountered in their wastewaters and due to their hazardous effects on ecosystems and human health, their removal is imperative. However, the methods for their treatment need to be improved or replaced by more effective alternatives. With this in mind and following our previous work on photolytic treatment of 2-halogenated pyridines (2-HalPys), the combined photolytic/photocatalytic (TiO₂ P-25) at 254nm degradation and mineralisation of 2-chloropyridine (2-CPY), 2-fluoropyridine (2-FPY) and 2-hydroxypyridine (2-HPY), a major photolytic product of all 2-HalPys but 2-FPY are studied in a range of conditions. In order to probe into the mechanisms and factors affecting their degradation, the effects of pH, radical scavenger tert-butanol and inorganic ions, were examined. The former had a substantial impact on 2-CPY photocatalytic removal rate, which, however, remained practically unaffected by the latter. 2-CPY photocatalytic removal was faster at near neutral pH. 2-HPY degradation was faster in the presence of TiO₂, low pH and in the presence of F⁻ or SO₄²⁻ anions. On the contrary, Cl⁻ anions or the presence of tert-butanol had a pronouncedly detrimental effect on 2-HPY degradation rate. Main reaction by-products accompanying the purely photocatalytic destruction of 2-CPY and 2-FPY were identified. Complete total organic carbon removal was achieved in all cases.

Keywords: 2-Chloropyridine; 2-Pyridinol; 2-Hydroxypyridine; 2-Fluoropyridine; TiO; ₂; photocatalysis

FeAl₁₂-Keggin type cation as an active site source for Fe,Al-silica mesoporous catalysts by M.N. Timofeeva; M.E. Malyshev; V.N. Panchenko; A.N. Shmakov; A.G. Potapov; M.S. Mel’gunov (pp. 110-119).

Iron-containing mesoporous mesophase materials Fe,Al-MMM-2 have been synthesized according to a sol-mesophase route under mild acidic conditions (pH 2.3–4.4) using Keggin type cation [FeAl₁₂O₄(OH)₂₄(H₂O)₁₂]⁷⁺ (FeAl₁₂⁷⁺) as Al and Fe sources. Effect of pH of the synthetic solution on structural and physicochemical properties of Fe,Al-MMM-2 has been evaluated by means of small- and wide-angle XRD, FTIR, DR-UV–vis, and N₂-adsorption/desorption analysis. It has been established that deviation of stability of FeAl₁₂⁷⁺ cation at various pH determines Al/Fe ratio in the resulting material as 12/1 (material synthesized at pH 4.4), and 6/1 (pH 2.4 and 3.3). Correlation between incorporation of Al and Fe in different forms and resulting materials texture is discussed. Fe,Al-MMM-2 materials have been tested as catalysts for wet phenol oxidation with H₂O₂. Insertion of Al species into the framework of the silicate matrix increases the activity comparing to a reference Fe,Al-pillared clay due to both higher surface acidity and lower diffusion limitations that correspond to Fe,Al-MMM-2.

Keywords: Fe,Al-containing mesoporous mesophase materials; Fe,Al-pillared clay; Hydrogen peroxide; Phenol; Oxidation

Catalytic degradation of Orange II in a ferrioxalate-assisted photo-Fenton process using a combined UV-A/C–solar pilot-plant system by J.M. Monteagudo; A. Durán; I. San Martín; M. Aguirre (pp. 120-129).

The catalytic degradation of Orange II in a ferrioxalate-assisted photo-Fenton process with combined solar and artificial ultraviolet light sources and continuous addition of H₂O₂ was investigated. The reaction was carried out in a pilot plant consisting of a compound parabolic collector (CPC) solar reactor in series with a UV-A/C reactor. An optimization study was done using a multivariate experimental design including the following variables: pH, H₂O₂ flow rate, UV-lamp exposure time, average temperature, average solar power and initial concentrations of Fe(II) and oxalic acid. The photocatalytic degradation efficiency was determined by the analysis of color and total organic carbon (TOC) removal. Under the optimum conditions, TOC removal increased to 99% in only 45min, and this system permitted the use of a low ferrous concentration of only 2mgL⁻¹. In addition, oxalic acid was used for pH adjustment. Thus, the operating costs of Fe removal, chemicals and electric power were reduced. Artificial UV-A/C light can be used either to increase the efficiency of the single-solar process or as an alternative to solar CPC on cloudy days. The overall rate constant was split into three components: direct oxidation by hydrogen peroxide, photolytic breakdown of dye–oxalate complexes chromophore group and oxidation by hydroxyl radicals. The influence of the Fe catalyst on the molecular and/or radical reactions was studied by conducting the reaction in the presence and absence of tert-butyl alcohol; the radical mechanism's contribution to the overall degradation increased with increasing iron levels.

Keywords: Orange II; Ferrioxalate; Photo-Fenton; Neural networks; CPC

TiO₂–MCM-41 for the photocatalytic abatement of NOx in gas phase by M. Signoretto; E. Ghedini; V. Trevisan; C.L. Bianchi; M. Ongaro; G. Cruciani (pp. 130-136).

Nanotitania supported on mesoporous silica systems were synthesized by a reliable procedure based on an incipient wetness impregnation post-synthetic approach. Characterization by X-ray diffraction, N₂ physisorption, TEM, X-ray photoelectron spectroscopy, ICP has been carried out in order to investigate the chemical–physical properties of the catalysts with particular attention to the chemical nature of the titanium species. The photocatalytic activity of the samples was evaluated for the degradation of NOx in the gas phase. The influence of both the textural properties and the nature of titanium species on the photocatalytic activity is discussed.

Keywords: Nanotitania; Mesoporous silica; NOx oxidation; Photocatalysis

Nanoparticle-assembled Co-B thin film for the hydrolysis of ammonia borane: A highly active catalyst for hydrogen production by N. Patel; R. Fernandes; G. Guella; A. Miotello (pp. 137-143).

Nanoparticle-assembled Co-B thin films were synthesized by Pulsed Laser Deposition (PLD) and used as catalysts for the hydrolysis of NH₃BH₃ (ammonia borane, AB) to produce molecular hydrogen. Amorphous Co-B-based catalyst powders, produced by chemical reduction of cobalt salts, were used as target material for Co-B thin film catalysts preparation through PLD. Surface morphology of Co-B powder and film catalyst was studied using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Compositional and structural characterizations were carried out using X-photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) techniques, respectively. The efficiency of both powder and film catalysts was tested by comparative kinetic analysis of the AB hydrolysis for hydrogen production. It was observed that nanoparticles produced during the laser ablation process act as active catalytic centers to produce significantly higher rate (about 6 times) of H₂ than the same amount of the corresponding Co-B powders. Almost complete conversion (95%) of AB was obtained, as confirmed by¹¹B NMR, by using Co-B films at room temperature. Active Co-B nanoparticles on the surface of the PLD-deposited films is able to decrease the activation energy, for hydrolysis of AB, to the very low value of 34kJmol⁻¹. We also found that by adding small amount of NaBH₄ to the NH₃BH₃ solution increases the efficiency of the Co-B catalyst films, thus generating H₂ with higher rate. Maximum H₂ generation rate of about ∼8.2LH₂min⁻¹(g of Co)⁻¹ and ∼13LH₂min⁻¹(g of Co)⁻¹ was measured by hydrolysis of AB and mixture of (AB+NaBH₄) solutions, respectively.

Keywords: Hydrogen generation; Ammonia borane; Cobalt boride; Thin film; Nanoparticles; Laser ablation

Studies on surface structure of M_xO_y/MoO₃/CeO₂ system (M=Ni, Cu, Fe) and its influence on SCR of NO by NH₃ by Jie Zhu; Fei Gao; Lihui Dong; Wujiang Yu; Lei Qi; Zhe Wang; Lin Dong; Yi Chen (pp. 144-152).

MoO₃/CeO₂ and M_xO_y/MoO₃/CeO₂ (M=Fe, Cu, Ni) catalysts had been characterized by XRD, TPR, LRS, NH₃-adsorbed in situ FT-IR and activity test for selective catalytic reduction (SCR) of NO by NH₃. The results suggested that the addition of NiO, CuO and Fe₂O₃ to MoO₃/CeO₂ catalysts had led to the different structures of surface molybdena species, i.e., isolated regular tetrahedral, highly distorted tetrahedral and polymerized octahedral molybdena species, revealing that the intensities of interaction between molybdena species and these metal oxides could be listed as: NiO/MoO₃/CeO₂>CuO/MoO₃/CeO₂>Fe₂O₃/MoO₃/CeO₂. Furthermore, it exhibited the same order for the surface acid intensities of the Lewis acid sites of these samples. The reactivity of “NO+NH₃+O₂” reaction is tightly related to acid properties of the catalysts (no matter Brønsted or Lewis acid sites): At low temperature, a weak Lewis acid site (L1) is the main active site for “NO+NH₃+O₂” reaction; at middle temperature range, the Brønsted acid site is the primary active site; while at high temperature, another strong Lewis acid site (L2) can also promote the reaction.

Keywords: Molybdena species; Surface structures; Acid sites; “NO; +; NH; ₃; +; O; ₂; ”

Novel synthesis and high visible light photocatalytic activity of SnS₂ nanoflakes from SnCl₂·2H₂O and S powders by Yong Cai Zhang; Zhen Ni Du; Shi Yin Li; Ming Zhang (pp. 153-159).

A novel method based on heating the mixture of SnCl₂·2H₂O and excess S powders in air at 200–240°C for 0–10h ( t=0h, that is, the heating of the reactants was stopped immediately once temperature reached the designed degree), coupled with a subsequent washing treatment, was proposed for the synthesis of SnS₂ nanoflakes. X-ray diffraction, transmission electron microscopy, selected area electron diffraction and Raman spectra revealed the formation of bulk-pure hexagonal phase SnS₂ nanoflakes. UV–vis diffuse reflectance spectra disclosed that the as-synthesized SnS₂ nanoflakes had optical bandgaps in the range of about 2.21–2.25eV. Besides, the photocatalytic performances of the as-synthesized SnS₂ nanoflakes were evaluated by degrading methyl orange (MO) in deionized water under both the visible light ( λ>420nm) and real sunlight irradiation. The results demonstrated that all the SnS₂ products had high visible light photocatalytic activity, and the most efficient photocatalyst among them was the one synthesized at 200°C for 0h, which was able to achieve a MO degradation ratio of nearly 100% after 60min illumination in the first cycle and 86% in the fifth cycle (each cycle lasted for 120min). Moreover, the best sample also possessed much higher photocatalytic activity than the commercial Degussa P25 TiO₂ photocatalyst under the real sunlight irradiation, and can be easily recovered from the suspension by filtration after the photocatalysis.

Keywords: Semiconductors; Tin disulfide; Nanomaterials; Photocatalysis

Sulfur poisoning resistant mesoporous Mn-base catalyst for low-temperature SCR of NO with NH₃ by Jian Yu; Feng Guo; Yingli Wang; Jianhong Zhu; Yunyi Liu; Fabing Su; Shiqiu Gao; Guangwen Xu (pp. 160-168).

Mesoporous MnO₂-Fe₂O₃-CeO₂-TiO₂ was prepared with sol–gel method and demonstrated to have good low-temperature activity and sulfur-poisoning resistance for selective catalytic reduction (SCR) of NO with NH₃ in SO₂-containing gases. In comparison with this, the catalyst with the same composition but made according to the conventional impregnation method exhibited obviously lower SO₂-poisoning resistance and selectivity to the formation of N₂ in the SCR reactions. FTIR analysis of the spent catalysts after SCR reactions for 16h and 60h in a SO₂-contaning gas demonstrated that there was little difference in the amount of deposited ammonium sulfate over the mesoporous catalyst between the two cases. The mesopore channels existing in the mesoporous catalyst enabled probably a dynamic balance between the formation and decomposition of ammonium sulfate in SCR reactions. This concern was justified through comparing the N₂ adsorptions and XPS spectra for the catalysts made with the impregnation and sol–gel methods. The article clarified as well the facilitation effects of introducing Ce and Fe into the mesoporous catalyst on activity, selectivity and SO₂-poisoning resistance.

Keywords: Mesoporous catalyst; Manganese; Low-temperature SCR; SO; ₂; poisoning; Mechanism

Preferential photodegradation of contaminants by molecular imprinting on titanium dioxide by Dovrat Sharabi; Yaron Paz (pp. 169-178).

The photocatalytic degradation of organic contaminants on titanium dioxide is basically non-selective. While this seems at first glance to be an advantage, this is not the case when a stream containing low concentrations of highly toxic substances together with high concentrations of low toxic organics has to be treated. A method for obtaining preferential degradation by means of preparation of molecularly imprinted photocatalyst is presented hereby. The method is demonstrated with two model compounds simulating the nerve gas sarin: diisopropyl methylphosphonate (DIMP) and diethylhydroxy methylphosphonate (DEHMP).An improvement by a factor of 3–4 in the mineralization rates was observed upon using the imprinted substrates. This enhancement in photocatalytic rates cannot be explained by the modest growth in the surface area (not more than 20–30%), hence it can be concluded that the enhancement resulted from the conformity between the target molecules and the molecular cavities on the imprinted sites. This conclusion is further supported by the lower extent of enhancement upon degrading benzene and heptane.Of particular interest is the fact that substrates that were imprinted with DEHMP were found to be very effective in the degradation of the homolog DIMP. This observation suggests the use of molecules having good affinity to the matrix as a means to obtain high surface concentration of molecular active sites, thus detouring the problem of aggregation that might arise in cases where the target contaminants have low affinity to the matrix. Another benefit is the possibility of using non-toxic homolog molecules for constructing the imprinted photocatalyst. This benefit is in particular important when designing a photocatalyst for WMD warfare agents, as in the case of sarin.

Keywords: Titanium dioxide; Molecular imprinting; Photocatalysis; DIMP; DEHMP

Sections

Personal tools

Applied Catalysis B, Environmental (v.95, #1-2)

Sections

Personal tools

Local resources

Applied Catalysis B, Environmental (v.95, #1-2)