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Applied Catalysis B, Environmental (v.79, #3)

Editorial Board (pp. i).

Contents (pp. co4).

IFC Editorial Board (pp. co2).

Benzene hydrogenation over Ni/Al₂O₃ catalysts prepared by conventional and sol–gel techniques by P.G. Savva; K. Goundani; J. Vakros; K. Bourikas; Ch. Fountzoula; D. Vattis; A. Lycourghiotis; Ch. Kordulis (pp. 199-207).

Nickel supported on alumina catalysts have been prepared using various synthesis methods (dry impregnation, co-precipitation, sol–gel) and evaluated for the hydrogenation of benzene contained in gasoline. The evaluation was carried out in a laboratory scale high pressure fixed bed reactor fed with a stream of surrogated reformate gasoline consisted by a mixture of hexane, benzene and toluene. All catalysts have been characterized by the joint use of various physicochemical characterization methods (XRF, BET, TGA, SEM, XRD, UV–vis DRS and XPS) in order to correlate their catalytic performances to their physicochemical properties. The results obtained revealed that sol–gel procedure, especially when it is followed by supercritical drying (aerogel), produced the most promising catalysts for the aforementioned catalytic process. Sol–gel methodology ensured the best compromise between dispersion of the nickel phase and its interaction with the support surface. Co-precipitated catalysts exhibited important activities but lower than those of the sol–gel catalysts. The catalyst prepared by dry impregnation proved to be the less active. Calcination of the catalysts before their activation by reduction decreased their activities.

Keywords: Benzene reduction; Hydrogenation; Gasoline; Catalyst preparation; Nickel supported on alumina; Sol–gel; Aerogel

Zn-doped TiO₂ nanoparticles with high photocatalytic activity synthesized by hydrogen–oxygen diffusion flame by Yin Zhao; Chunzhong Li; Xiuhong Liu; Feng Gu; H.L. Du; Liyi Shi (pp. 208-215).

Zn-doped TiO₂ nanoparticles with high photocatalytic activity were synthesized by the hydrogen–oxygen diffusion flame method and the photocatalytic degradation mechanism of rhodamine B dye under visible light irradiation were elaborated. The Zn dopants presented in the form of small ZnO nuclei dispersing randomly on the surface of anatase TiO₂ nanoparticles. It is found that the photosensitized degradation activity can be enhanced by doping an appropriate amount of Zn. The improved activity by Zn doping can be attributed to the appropriate energetic position between ZnO and the excited state of dye, which enhanced the electron injection into the conduction band of TiO₂ by capturing electron, subsequently promoted the formation of reactive oxygen species. Hence, the enhanced photodegradation of dyes under visible irradiation can be realized.

Keywords: Titanium dioxide; Photocatalytic; Nanoparticles; Zinc oxide; Dopant; Gas flame combustion; Surface oxygen vacancies

Solid-phase photocatalytic degradation of polystyrene with TiO₂ modified by iron (II) phthalocyanine by Wenjun Fa; Ling Zan; Chuqing Gong; Jiacheng Zhong; Kejian Deng (pp. 216-223).

A novel photodegradable polystyrene-FePc-TiO₂ (PS-FePc-TiO₂) nanocomposite was prepared by embedding the FePc-TiO₂ into the commercial polystyrene. The TiO₂ catalyst was modified by iron (II) phthalocyanine in order to improve its photocatalytic efficiency under the visible light irradiation. Solid-phase photocatalytic degradation of the PS-FePc-TiO₂ nanocomposite was carried out in an ambient air at room temperature under ultraviolet lamp and/or sunlight irradiation. The properties of composite films were compared with those of the pure PS films and the polystyrene-TiO₂ (PS-TiO₂) composite films through performing weight loss monitoring, scanning electron microscope (SEM), FT-IR and UV–vis spectroscopy. The photo-induced degradation of PS-FePc-TiO₂ composite films was significantly higher than that of the pure PS films and the PS-TiO₂ composite films both under the UV irradiation and under the sunlight irradiation. The weight loss of the PS-FePc-TiO₂ composite film reached 35% under the sunlight irradiation. FT-IR analysis and weight loss results indicated that the benzene rings in PS matrix of the composite film were cleaved during UV-light irradiation. The photocatalytic degradation mechanism of the composite films was briefly discussed.

Keywords: Polystyrene; FePc-TiO; ₂; Solid-phase photocatalytic degradation

Electro-Fenton and photocatalytic oxidation of phenyl-urea herbicides: An insight by liquid chromatography–electrospray ionization tandem mass spectrometry by I. Losito; A. Amorisco; F. Palmisano (pp. 224-236).

The degradation pathways exhibited by three phenyl-urea herbicides: isoproturon (ISO), chlortoluron (CHLT) and chloroxuron (CHLOX), during photocatalytic (on supported TiO₂ under intense solar radiation) and electro-Fenton (EF) treatment were investigated by HPLC coupled to electrospray ionization single and tandem mass spectrometry (HPLC–ESI-MS and MS/MS). In particular, the dependence of degradation efficiency on the initial concentration ratio between substrate and Fe(III) ion was assessed for the EF treatment and a 1:1 ratio was found to be optimal. A comparison between photocatalytic and EF degradation, in terms of structures, number and evolution on a similar time scale (up to 5h) of by-products, was then performed. Similar reactivities were found in the two cases, hydroxylation (single and multiple, with H, alkyl groups or Cl substitution, depending on the herbicide) and demethylation on the dimethylamino moiety (eventually followed by hydroxylation) being the most relevant processes in by-products generation. The scale of EF degradation efficiency for the three herbicides was almost identical to the photocatalytic one (ISO>CHLT≈CHLOX), yet electro-Fenton proved to be a more efficient process, generally leading to a faster further degradation of by-products.

Keywords: Phenyl-urea herbicides; Electro-Fenton degradation; Photocatalytic degradation; Liquid chromatography–electrospray ionization mass spectrometry

Activated carbon catalytic ozonation of oxamic and oxalic acids by P.C.C. Faria; J.J.M. Órfão; M.F.R. Pereira (pp. 237-243).

The oxidation of hazardous organic compounds leads to the formation of several by-products, being oxalic acid and oxamic acid final oxidation products refractory to ozonation. The present work aimed to study the ozonation of those carboxylic acids in the presence of activated carbon at different solution pH. For comparative purposes, experiments of adsorption on activated carbon, ozonation, and ozonation in the presence of activated carbon were carried out. In order to clarify the reaction mechanism, some experiments were done in the presence of a radical scavenger. With the aim of evaluating the role of the activated carbon surface chemistry during the ozonation, two activated carbon samples were assessed. A significant synergistic effect between ozone and activated carbon was evidenced in the oxidation of oxalic acid. Oxamic acid was found to be refractory to oxidation at pH 7. On the other hand, at pH 3, the mineralization of oxamic acid was significantly enhanced by the presence of activated carbon. Generally, the presence of activated carbon during ozonation increased the rate of degradation of both carboxylic acids leading to mineralization. Best results were achieved with the most basic activated carbon. In both cases, the efficiency of activated carbon promoted ozonation decreases with the increase of solution pH.

Keywords: Catalytic ozonation; Activated carbon; Carboxylic acids; Oxamic acid; Oxalic acid

Oxidation products and pathway of ceramic honeycomb-catalyzed ozonation for the degradation of nitrobenzene in aqueous solution by Lei Zhao; Jun Ma; Zhi-zhong Sun (pp. 244-253).

Semi-continuous experiments on catalytic ozonation of nitrobenzene (NB) in aqueous solution using ceramic honeycomb as catalyst have been investigated. Experimental results showed that the presence of ceramic honeycombs significantly increased the ozonation degradation rate of NB compared to the case of non-catalytic ozonation. With addition of the radical scavenger tert-butanol, the evident reduction of NB removal indicated that NB was oxidized primarily by hydroxyl radical (OH) in the both systems of ozonation alone and ozonation/ceramic honeycomb. The total organic carbon removal suggested that in the process of ozonation/ceramic honeycomb NB was more quickly mineralized than that by ozonation alone. The absorbance of UV–vis spectra confirmed that carboxylic acids and aromatic compounds were predominant oxidative organic products of NB by catalytic ozonation. The oxidative decomposition products ( o-, p-, m-nitrophenols, phenol, 4-nitrocatechol, hydroquinone, p-quinone, 1,2,3-trihydroxy-5-nitrobenzene, maleic acid, malonic acid, oxalic acid, acetic acid and nitrate ion) have been identified by GC/MS and IC, indicating that degradation proceeded viaOH oxidation. A general reaction pathway for the degradation of NB was proposed by the evidence presented in this study.

Keywords: Catalytic ozonation; Ceramic honeycomb; Nitrobenzene; Decomposition products; OH

Influence of CO pretreatment on the activities of CuO/γ-Al₂O₃ catalysts in CO+O₂ reaction by Haiqin Wan; Zhe Wang; Jie Zhu; Xiaowei Li; Bin Liu; Fei Gao; Lin Dong; Yi Chen (pp. 254-261).

The influence of CO pretreatment on the properties of CuO/γ-Al₂O₃ catalysts was investigated by X-ray diffraction (XRD), temperature programmed reduction (TPR), and infrared spectroscopy (IR). The activities of the treated catalysts were measured in low-temperature CO oxidation reaction (≤200°C). It is shown that CO pretreatment at 250°C mainly results in the reduction of crystalline CuO to Cu⁰ and dispersed Cu²⁺ to Cu⁺. CO–Cu⁺ interaction is much stronger than those of CO–Cu²⁺ and CO–Cu⁰, and as a result, CO molecules adsorbed on Cu⁺ are the main species on the fresh and CO pretreated catalysts exposed to CO stream at temperatures of 100°C and higher.For the low-temperature CO oxidation reaction, the activities of CuO/γ-Al₂O₃ catalysts are intimately related to the operation temperature, copper oxide loading amount and CO pretreatment. CO conversions are promoted evidently with increasing operation temperatures. At the set operation temperatures, maximum CO conversions are always reached over the catalysts with a copper oxide loading amount of 0.6mmol Cu²⁺/100m² Al₂O₃, which is close to the dispersion capacity of copper oxide on γ-Al₂O₃, i.e., 0.75mmol Cu²⁺/100m² Al₂O₃. CO conversions over the catalysts following CO treatment are much higher than those over the fresh catalysts with the same amount of copper oxide. It is concluded that for low-temperature CO oxidation, dispersed copper oxide species are the primary active component, and the dispersed Cu⁺ species plays a significant role.

Keywords: CuO/γ-Al; ₂; O; ₃; In situ IR; CO adsorption; CO oxidation; Supported catalyst

Effect of pretreatment method of activated carbon on the catalytic reduction of NO by carbon over CuO by Yuye Xue; Guanzhong Lu; Yun Guo; Yanglong Guo; Yanqin Wang; Zhigang Zhang (pp. 262-269).

The influence of pretreatment method of activated carbon (AC) made from coconut shell, on the NO reduction by AC over CuO was studied, in which AC was used as a reducing agent and pretreated by air oxidation or wet oxidation in the HNO₃(N), H₂O₂(H), H₂SO₄(S) or H₃PO₄(P) aqueous solution. The results show that over the CuO catalyst, the reductive activity of air oxidized AC for NO increases with a rise of the air oxidation temperature of AC, and the order of the reductive activity of wet oxidized AC for NO is AC-H>AC-N>AC-S>AC-P. The surface chemical properties of these ACs were studied by XRD, TPD, Boehm titration and so on. The dispersion of CuO on AC can be improved by treating AC with the HNO₃ or H₂O₂ aqueous solution. AC treated with H₂O₂ is an effective reducing agent for the reduction of NO over CuO, and the temperature of complete reduction of NO by AC-H is 270°C, which is 120°C lower than that by original AC. Both the high concentration of acidic oxygen groups and moderate amount of basic sites on AC-H help to increase the conversion of NO reduced by AC-H.

Keywords: Activated carbon; NO reduction; CuO catalyst; Surface treatment

Iron-nickel bimetallic nanoparticles for reductive degradation of azo dye Orange G in aqueous solution by Alok D. Bokare; Rajeev C. Chikate; Chandrashekhar V. Rode; Kishore M. Paknikar (pp. 270-278).

The degradation of Orange G, a monoazo dye, in aqueous solutions was investigated using Fe-Ni bimetallic nanoparticles. Transmission electron microscopy (TEM) of as-synthesized nanoparticles showed the presence of spherical particles having a size of 20–40nm. X-ray photoelectron spectroscopy (XPS) did not detect the presence of nickel on the nanoparticle surface, which suggested a uniform distribution of both metals inside the particle core. Batch experiments with a minimum nanocatalyst loading of 3g/L showed complete dye degradation after 10min of reaction time. The degradation efficiency was linearly dependent on the initial dye concentration, pH of the solution and total Fe-Ni catalyst concentration. The efficiency increased with increasing Fe-Ni concentration and decreasing pH of the solution, but decreased with an increase in the dye concentration. The degradation rate followed first order reaction kinetics with respect to the dye concentration. High performance liquid chromatography–mass spectrometry (HPLC–MS) analysis of the degradation products revealed that the degradation mechanism proceeds through a reductive cleavage of the azo linkage resulting in the formation of aniline and surface-adsorbed naphthol amine derivatives. The latter are subsequently hydroxylated through an oxidative process.

Keywords: Iron; Nickel; Nanoparticles; Azo dye; Degradation

Synthesis, characterisation and catalytic evaluation of iron–manganese mixed oxide pillared clay for VOC decomposition reaction by T. Mishra; P. Mohapatra; K.M. Parida (pp. 279-285).

A series of iron and manganese mixed oxide pillared clay with varying manganese to iron ratio has been successfully synthesized. Prepared materials were characterized by low angle XRD, TG/DTA, hydrogen TPR and nitrogen adsorption desorption experiment. All the materials were found to be thermally stable up to 500°C having basal spacing ≥16.5Ǻ. Surface area and pore volume increases with the increase in the metal uptake irrespective of manganese to iron ratio. Catalytic decomposition of acetone and trichloroethylene was studied to find out the suitability of the material for VOC decomposition reaction. Catalyst (S-16/4) having high manganese content acts as better catalyst for the acetone decomposition reaction. Time on stream experiment justifies the stability of the prepared catalyst at least for 20h with minor change in the activity. However, in case of trichloroethylene (TCE) decomposition catalyst (S-8/12) with higher iron content shows better activity. Quick deactivation of the catalyst for TCE decomposition is noticed for all the prepared materials.

Keywords: Iron and manganese mixed oxide; Pillared clay; Decomposition; Acetone and trichloroethylene

Adsorption and oxidation of mercury in tail-end SCR-DeNOx plants—Bench scale investigations and speciation experiments by Sandra Straube; Thomas Hahn; Heinz Koeser (pp. 286-295).

The results of a bench scale investigation on mercury adsorption and oxidation under the conditions of tail-end DeNOx plants are reported. It was shown that HCl has a strong influence on mercury adsorption as well as mercury oxidation.Adsorption of elemental mercury and HgCl₂ on a DeNOx catalyst with 2.5wt.% V₂O₅ is appreciably in flue gases that contain HCl in concentrations below 0.5mg/m³. Mercury adsorption increases linearly with the mercury concentration in the flue gas. The amount of HgCl₂ adsorbed on the catalysts is higher than of elemental mercury, under otherwise comparable conditions. Mercury adsorption depends on the V₂O₅ content of the DeNOx catalyst. The nature of the adsorbed mercury species was investigated by sequential chemical extraction and X-ray absorption fine structure spectroscopy. According to these methods mercury does form a Hg–O bond on the surface of the catalysts. In terms of regeneration of mercury loaded catalysts it is of interest, that more than two-third of the adsorbed mercury can be removed by washing the DeNOx catalyst at room temperature with a dilute solution containing acetic and hydrochloric acid.In the presence of higher concentrations of HCl in the flue gas elemental mercury is no longer adsorbed but oxidized by DeNOx catalysts. The rate of oxidation decreases with increasing temperature. NO has compared to HCl only a slightly accelerating influence, whereas NH₃ shows a small detrimental effect. The simultaneous presence of NO and NH₃ inhibits the HCl assisted oxidation of elemental mercury strongly.

Keywords: SCR-DeNOx; Mercury; Adsorption; Oxidation; V; ₂; O; ₅; XAFS

Suppression of dioxin emission in incineration of poly(vinyl chloride) (PVC) as hybridized with titanium dioxide (TiO₂) nanoparticles by Sung Ho Kim; Seong-Yong Ahn; Seung-Yeop Kwak (pp. 296-305).

The present paper has demonstrated suppression of dioxin emission from poly(vinyl chloride) (PVC)/titanium dioxide (TiO₂) nanohybrids. In our previous paper, we suggested a novel idea for the preparation of PVC/TiO₂ nanohybrid through TiO₂ nanoparticle-integrated hyperbranched poly( ɛ-caprolactone) (HPCL-TiO₂), aiming at a breakthrough to solve the unresolved problem in the conventional PVC/TiO₂ composites related to the poor dispersion of TiO₂ nanoparticles in PVC polymer. The integration of TiO₂ nanoparticles onto the HPCL could be successfully carried out by a dip-coating method based on the spontaneous self-assembly between TiO₂ and HPCL. In this study, three kinds of hyperbranched poly( ɛ-caprolactone)s (H_nPCLs) were prepared by varying the number, n, of monomeric units on the branched backbone chains. Thereby, it was possible to control the numbers of functional ends and the contents of TiO₂ in the H_nPCL-TiO₂. The loadings of TiO₂ in the H_nPCL-TiO₂s were found to be 4.37, 3.26, and 2.93wt% for n of 5, 10, and 20, respectively. The preparation of PVC/H_nPCL-TiO₂ (60/40) blends was performed through solution blending of H_nPCL-TiO₂ with PVC in tetrahydrofurane (THF) as solvent, and the dispersities of TiO₂ in the resulting nanohybrids were investigated by field-emission scanning electron microscope (FE-SEM) equipped with energy dispersive spectroscopy (EDS). The FE-SEM/EDS results showed that TiO₂ nanoparticles were dispersed well in PVC matrix, while some agglomerates of TiO₂ was observed in the PVC+TiO₂ sample prepared from the solution blending of PVC with the same amount of TiO₂. The incineration experiments were performed by using a temperature-controllable electric furnace at 350°C under the flow of ambient air, and the exhaust gases resulting from the incineration process were collected. Prior to the identification of the components emitted in the incineration process, the GC experiments for calibration were performed on several commercial standards of dioxin and organic compounds known to be dioxin precursors. The GC results on the exhaust gases from the incineration of samples showed that the emissions of dioxin and precursors were largely suppressed with the increasing content of TiO₂ in PVC/H_nPCL-TiO₂, i.e., the order of PVC/H₅PCL-TiO₂>PVC/H₁₀PCL-TiO₂>PVC/H₂₀PCL-TiO₂, as compared with those in the neat PVC/H_nPCL without TiO₂. Especially, the PVC/H₅PCL-TiO₂ with a maximum TiO₂ loading of 1.6wt% showed removal efficiencies of ca. 60% up to 70% over the dioxin and dioxin precursors, which is equivalent to one and half to several times as much as the PVC+TiO₂ samples prepared through the conventional route. The remarkable enhancement of the suppression of dioxin emission in the PVC/H_nPCL-TiO₂ might be attributed to the improvement of the degree of TiO₂ dispersion in the nanohybrid.

Keywords: Poly(vinyl chloride) (PVC); Titanium dioxide; Nanohybrid; Dioxins; Incineration

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Applied Catalysis B, Environmental (v.79, #3)