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Applied Catalysis B, Environmental (v.87, #3-4)

IFC Editorial Board (pp. co2).

Editorial Board (pp. i).

Contents (pp. co4).

Decontamination of wastewaters containing synthetic organic dyes by electrochemical methods: A general review by Carlos A. Martínez-Huitle; Enric Brillas (pp. 105-145).

Effluents of a large variety of industries usually contain important quantities of synthetic organic dyes. The discharge of these colored compounds in the environment causes considerable non-aesthetic pollution and serious health-risk factors. Since conventional wastewater treatment plants cannot degrade the majority of these pollutants, powerful methods for the decontamination of dyes wastewaters have received increasing attention over the past decade. This paper presents a general review of efficient electrochemical technologies developed to decolorize and/or degrade dyeing effluents for environmental protection. Fundamentals and main applications of typical methods such as electrocoagulation, electrochemical reduction, electrochemical oxidation and indirect electro-oxidation with active chlorine species are reported. The influence of iron or aluminium anode on decolorization efficiency of synthetic dyes in electrocoagulation is explained. The advantages of electrocatalysis with metal oxides anodes and the great ability of boron-doped diamond electrodes to generate heterogeneous hydroxyl radical as mediated oxidant of these compounds in electrochemical oxidation are extensively discussed. The effect of electrode material, chloride concentration, pH and temperature on the destruction of dyestuffs mediated with electrogenerated active chlorine is analyzed. The degradation power of these pollutants with an emerging electrochemical advanced oxidation process such as electro-Fenton, based on the mediated oxidation by homogeneous hydroxyl radical formed from Fenton's reaction between cathodically produced hydrogen peroxide and catalytic Fe²⁺, is examined. Recent progress of emerging photoassisted electrochemical treatments with UV irradiation such as photoelectro-Fenton and photoelectrocatalysis is also described.

Keywords: Abbreviations; ACF; activated carbon fiber; AOP; advanced oxidation process; ABS; ^M; average absorbance; BDD; boron-doped diamond; DSA; dimensionally stable anode; EAOP; electrochemical advanced oxidation process; EO; electrochemical oxidation; EC; electrocoagulation; EF; electro-Fenton; EBT; Eriochrome Black T; GC–MS; gas chromatography–mass spectrometry; HPLC; high-performance liquid chromatography; PEF; photoelectro-Fenton; PTFE; polytetrafluoroethylene; ROS; reactive oxygen species; RVC; reticulated vitreous carbon; SCE; saturated calomel electrode; SHE; standard hydrogen electrode; UV; ultraviolet; UVA; ultraviolet A; UVB; ultraviolet B; UVC; ultraviolet C; UV-Vis; ultraviolet-visibleDyes removal; Electrocoagulation; Electrocatalysis; Hydroxyl radical; Active chlorine; Electro-Fenton; Photoelectro-Fenton; Photoelectrocatalysis

Oxidative removal of 4-nitrophenol using activated carbon fiber and hydrogen peroxide to enhance reactivity of metallophthalocyanine by Wangyang Lu; Wenxing Chen; Nan Li; Minhong Xu; Yuyuan Yao (pp. 146-151).

We have developed a novel heterogeneous metallophthalocyanine catalyst, Co-TDTAPc–ACF, by immobilizing cobalt tetra(2,4-dichloro-1,3,5-triazine)aminophthalocyanine (Co-TDTAPc) on activated carbon fiber (ACF) covalently. The oxidative removal of 4-nitrophenol (4-NP) in the Co-TDTAPc–ACF/H₂O₂ system, based on phase transfer catalytic oxidation, was investigated in aqueous solution by ultra-performance liquid chromatography (UPLC). The results indicated that 4-NP could be removed efficiently by catalytic oxidation in the presence of Co-TDTAPc–ACF and H₂O₂. In addition, the removal of total organic carbon of 4-NP accounted for about 90% in 300min of reaction. Gas chromatography/mass spectrometry (GC–MS) analysis showed that the residue products were mainly small molecular compounds such as maleic acid and succinic acid, etc. This system exhibited high catalytic activity across a wide pH and temperature range. Importantly, compared with homogeneous Co-TDTAPc used alone, the introduction of ACF contributed specifically to the activity enhancement of Co-TDTAPc. Controlled experiments showed that the presence of 2-propanol, as hydroxyl radicals scavenger, has little influence on 4-NP oxidation. The further result of electron paramagnetic resonance (EPR) spin-trap experiments indicated that free radicals did not dominate the reaction in our system. This paper discusses a possible catalytic oxidation mechanism of the Co-TDTAPc–ACF/H₂O₂ system. Repetitive tests showed that Co-TDTAPc–ACF can maintain high catalytic activity over several cycles, and it has a better regeneration capability under mild conditions. We conclude that phase transfer catalytic oxidation has proven itself to be a feasible approach which may be potentially applied to the elimination of widely existing pollutants.

Keywords: 4-Nitrophenol; Catalytic oxidation; Removal; Activated carbon fiber; Cobalt phthalocyanine

Hydrogen production by steam gasification of polypropylene with various nickel catalysts by Chunfei Wu; Paul T. Williams (pp. 152-161).

Several nickel-based catalysts (Ni/Al₂O₃, Ni/MgO, Ni/CeO₂, Ni/ZSM-5, Ni-Al, Ni-Mg-Al and Ni/CeO₂/Al₂O₃) have been prepared and investigated for their suitability for the production of hydrogen from the two-stage pyrolysis–gasification of polypropylene. Experiments were conducted at a pyrolysis temperature of 500°C and gasification temperature was kept constant at 800°C with a catalyst/polypropylene ratio of 0.5. Fresh and reacted catalysts were characterized using a variety of methods, including, thermogravimetric analysis, scanning electron microscopy with energy dispersive X-ray spectrometry and transmission electron microscopy. The results showed that Ni/Al₂O₃ was deactivated by two types of carbons (monoatomic carbons and filamentous carbons) with a total coke deposition of 11.2wt.% after reaction, although it showed to be an effective catalyst for the production of hydrogen with a production of 26.7wt.% of the theoretical yield of hydrogen from that available in the polypropylene. The Ni/MgO catalyst showed low catalytic activity for H₂ production, which might be due to the formation of monoatomic carbons on the surface of the catalyst, blocking the access of gaseous products to the catalyst. Ni-Al (1:2) and Ni-Mg-Al (1:1:2) catalysts prepared by co-precipitation showed good catalytic abilities in terms of both H₂ production and prevention of coke formation. The ZSM-5 zeolite with higher surface area was also shown to be a good support for the nickel-based catalyst, since, the Ni/ZSM-5 catalyst showed a high rate of hydrogen production (44.3wt.% of theoretical) from the pyrolysis–gasification of polypropylene.

Keywords: Polypropylene; Nickel; Catalyst; Gasification

The influence of ultrasound on the RuI₃-catalyzed oxidation of phenol: Catalyst study and experimental design by Ekaterina V. Rokhina; Manu Lahtinen; Mathias C.M. Nolte; Jurate Virkutyte (pp. 162-170).

The influence of ultrasound at 24kHz on the heterogeneous aqueous oxidation of phenol over RuI₃ with hydrogen peroxide (H₂O₂) was studied isothermally at 298K. Effect of ultrasound irradiation on catalytic properties and performance of RuI₃ has been studied in details by means of scanning electron microscopy (SEM), X-ray powder diffraction (XRD), dispersion analyzer and a surface analyzer. Turn over frequency of the catalyst was also calculated. In this work, experimental design methodology was applied to optimize the degradation of phenol in aqueous solution, while minimizing an excessive consumption of chemical reagents. The independent variables considered were the catalyst load and oxidant concentration. The multivariate experimental design allowed the development of empiric non-linear quadratic models for total organic carbon (TOC) removal after 120 and 240min of the reaction, and the time needed for total hydrogen peroxide consumption, which were adequate to predict responses in all of the range of experimental conditions used. Ruthenium leaching was not detected from samples studied at different stages of the reaction, indicating stability of the chosen catalyst. A reaction scheme involving radical species (OH,HO₂) was proposed to explain phenol conversion. Ultrasound-assisted catalytic oxidation demonstrated nearly two-fold increase in phenol conversion (up to 70%), contrary to 31% obtained during silent process. High catalytic activity of RuI₃ associated with isothermal reaction conditions at circum neutral pH was capable to extend the applicability of such catalyst in ultrasound-assisted oxidation processes.

Keywords: Ultrasound; Phenol; Ruthenium iodide; Oxidation; Experimental design

Mesoporous silica–alumina as support for Pt and Pt–Mo sulfide catalysts: Effect of Pt loading on activity and selectivity in HDS and HDN of model compounds by Daniela Gulková; Yuji Yoshimura; Zdeněk Vít (pp. 171-180).

The potential of mesoporous silica–alumina (MSA) material as support for the preparation of sulfided Pt and Pt–Mo catalysts of varying Pt loadings was studied. The catalysts were characterized by their texture, hydrogen adsorption, transmission electron microscopy, temperature programmed reduction (TPR) and by activity in simultaneous hydrodesulfurization (HDS) of thiophene and hydrodenitrogenation (HDN) of pyridine. Sulfided Pt/MSA catalysts with 1.3 and 2wt.% Pt showed almost the same HDS and higher HDN activities per weight amounts as conventional CoMo and NiMo/Al₂O₃, respectively. The addition of Pt to sulfided Mo/MSA led to promotion in HDS and HDN with an optimal promoter content close to 0.5wt.%. The results of TPR showed strong positive effect of Pt on reducibility of the MoS₂ phase which obviously reflects in higher activity of the promoted catalysts. The activity of the MSA-supported Pt–Mo catalyst containing 0.5wt.% Pt was significantly higher than the activity of alumina-supported Pt–Mo catalyst. Generally, Pt–Mo/MSA catalysts promoted by 0.3–2.3wt.% Pt showed lower HDS and much higher HDN activities as compared to weight amounts of CoMo and NiMo/Al₂O₃. It is proposed that thiophene HDS and pyridine hydrogenation proceed over Pt/MSA and the majority of Pt–Mo/MSA catalysts on the same type of catalytic sites, which are associated with sulfided Pt and MoS₂ phases. On the contrary, piperidine hydrogenolysis takes place on different sites, most likely on metallic Pt fraction or sites created by abstraction of sulfur from MoS₂ in the presence of Pt.

Keywords: Platinum; Molybdenum sulfide catalyst; MSA; Hydrodesulfurization; Hydrodenitrogenation

Structure and photocatalytic performance of magnetically separable titania photocatalysts for the degradation of propachlor by V. Belessi; D. Lambropoulou; I. Konstantinou; R. Zboril; J. Tucek; D. Jancik; T. Albanis; D. Petridis (pp. 181-189).

A magnetic photocatalyst was prepared by modification of TiO₂ nanoparticles (Degussa P25) with nanocrystalline γ-Fe₂O₃ nanoparticles through a protective lining made up of two oppositely charged polyelectrolytes. As-prepared magnetically separable photocatalysts differing in γ-Fe₂O₃ loading (3, 8, 13, 20 and 30wt.%) were characterized by XRD, TEM, thermal analysis, Mössbauer and magnetic measurements. The photocatalytic efficiency of the nanocomposite catalysts was evaluated using a chloroacetanilide herbicide (propachlor) in water as model compound. The primary degradation of propachlor followed pseudo-first-order kinetics according to the Langmuir–Hinshelwood model. Generally, all magnetic photocatalysts exhibit good catalytic activity towards organic pollutants, do not suffer from photodissolution and can be reused several times without any decrease in their photocatalytic activity.

Keywords: TiO; ₂; γ-Fe; ₂; O; ₃; Magnetically separated photocatalysts; Organic pollutants

Effects of oxidative modification of carbon surface on the adsorption of sulfur compounds in diesel fuel by Anning Zhou; Xiaoliang Ma; Chunshan Song (pp. 190-199).

This work examines the effects of modification of activated carbons (ACs) by HNO₃ oxidation and gas-phase O₂ oxidation, respectively, on the liquid-phase adsorption of sulfur compounds in diesel fuel. The adsorption characteristics of the oxidized and the original AC samples were evaluated in a fixed-bed flow system by using a model diesel fuel containing 400 parts per million by weight (ppmw) of sulfur as thiophenic compounds and 10wt% of aromatics in a paraffinic solvent. The pore structure and surface properties of the AC samples were characterized by N₂ adsorption, SEM, FTIR, XPS and surface pH measurements. The adsorptive selectivity factor of the AC samples increases in the order of benzothiophene (BT)≈naphthalene (Nap)<2-methyl naphthalene (2-MNap)3 oxidation was an efficient method in improvement of the adsorption performance of the AC for sulfur compounds. The improved adsorption performance upon the HNO₃ oxidation can be attributed mainly to an increase in the acidic oxygen-containing functional groups. However, the improved adsorption capacity upon oxidation is unlikely due to an increase in mesoporous or microporous surface/volume, although such attribution might have been inferred from the literature. An excellent correlation between the concentration of the surface oxygen-containing functional groups and the adsorption capacity per unit area as well as a good relationship between the adsorption capacity and the surface pH value were observed in this work, which suggest that the adsorption of the sulfur compounds over AC from the liquid hydrocarbon fuel may involve an interaction of the acidic oxygen-containing groups on AC with the sulfur compounds.

Keywords: Oxidative modification; Carbon surface; Adsorption; Adsorptive desulfurization; Sulfur compounds; Diesel fuel; Activated carbon; Dibenzothiophene; Dimethyldibenzothiophene

Detailed kinetic modeling of NO_x adsorption and NO oxidation over Cu-ZSM-5 by Louise Olsson; Hanna Sjövall; Richard J. Blint (pp. 200-210).

Detailed kinetic modeling was used in combination with flow reactor experiments to investigate the NO_x adsorption/desorption and NO oxidation over Cu-ZSM-5. NO oxidation is likely an important step for selective catalytic reduction (SCR) using urea and hydrocarbons, and thus was investigated separately. First the NO₂ adsorption on Brönstedt acid sites in H-ZSM-5 was modeled using an NO₂ temperature programmed desorption (TPD) experiment. These results, together with the results of the NO₂ TPD and NO oxidation experiments, were used in developing the model for Cu-ZSM-5. A substantial amount of NO₂ was adsorbed on the catalyst. However, the results from a corresponding NO TPD experiment showed that only very small amounts of NO were adsorbed on the catalyst and therefore this step was not included in the model. The model consists of reversible steps for NO₂ and O₂ adsorption, O₂ dissociation, NO oxidation and two steps for nitrate formation. The first nitrate formation step was disproportionation of NO₂ to form NO and nitrates. This step enabled us to describe the NO production during NO₂ adsorption. Further, in the reverse step the NO reacts with the nitrates and decreased their stability. Without this step the nitrates blocked the surface resulting in to low NO oxidation activity. However, we observe that nitrates can be decomposed also without the presence of NO and in the second reversible step were the nitrates decomposed to form NO₂ and oxygen on the copper. These steps enabled us to describe both the TPD and activity measurement results. NO oxidation was observed even at room temperature. Interestingly, the NO₂ decreased when increasing the temperature up to 100°C and then increased as the temperature increased further. We suggest that this low-temperature NO oxidation occurs with species loosely bound on the surface and that is included in the detailed mechanism. An additional NO₂ TPD at 30°C was also modeled to describe the loosely bound NO₂ on the surface. The detailed model correctly describes NO₂ storage, NO oxidation and low-temperature NO oxidation.

Keywords: NO; ₂; Detailed kinetic modeling; Zeolite; Copper; TPD; Low-temperature activity

Deactivation and regeneration of Pt/Al₂O₃ catalysts during the hydrodechlorination of carbon tetrachloride by T.F. Garetto; C.I. Vignatti; A. Borgna; A. Monzón (pp. 211-219).

Deactivation and regeneration of Pt/Al₂O₃ catalysts during the hydrodechlorination of carbon tetrachloride were studied. The effect of reactant partial pressures and temperature on the catalyst deactivation was investigated. A deactivation model with residual activity was developed to quantify the kinetic deactivation parameters. The effect of the regeneration atmosphere was also investigated. Regeneration under air allowed for the full recovery of the catalytic performance of fresh catalysts while treatments under flowing hydrogen resulted in a superior catalytic performance, increasing both the initial and residual activities. This was ascribed to a combined effect, redispersion of the metallic phase and formation of surface defects.

Keywords: Carbon tetrachloride; Hydrodechlorination; Pt catalysts; Deactivation; Regeneration

Quantitative photocatalyzed soot oxidation on titanium dioxide by Paul Chin; Christine S. Grant; David F. Ollis (pp. 220-229).

We report here the titanium dioxide (TiO₂) photocatalyzed oxidation of deposited hurricane lamp soot. Sol–gel derived TiO₂ was coated on quartz crystal microbalance (QCM) elements. Characterization by spectroscopic ellipsometry ( SE) and atomic force microscopy (AFM) revealed low surface roughness of 0–17%, and SE showed a linear variation of the TiO₂ thickness versus the number of sol–gel spin coats.Soot was deposited on the calcined TiO₂ film using an analytical rotor passing through a hurricane lamp flame, and subsequently irradiated with near-UV light. Varying the soot mass on the TiO₂-coated QCM crystals revealed behaviors over 20,000min ranging from total soot destruction of a single pass soot layer to minimal oxidation of an eight pass soot layer, the latter caused by soot screening of the incident UV light. A series/parallel reaction mechanism [P. Chin, G.W. Roberts, D.F. Ollis, Industrial & Engineering Chemistry Research 46 (2007) 7598] developed to describe previous literature data on TiO₂-catalyzed soot photooxidation was successfully employed to capture the longer time changes in presumably graphitic soot mass as a function of UV illumination time from 1000 to 20,000min and of soot layer thickness. Short time soot mass loss is attributed to oxidation of organic carbons deposited on the graphitic soot components. This kinetic model can be used to predict the rate of TiO₂-catalyzed soot destruction as a function of near-UV illumination time and initial soot layer thickness.

Keywords: Titania; Photocatalysis; Soot; Kinetic model; Oxidation; Formal quantum efficiency

Utilization of carbon dioxide as soft oxidant for oxydehydrogenation of ethylbenzene to styrene over V₂O₅–CeO₂/TiO₂–ZrO₂ catalyst by Benjaram M. Reddy; Seung-Cheol Lee; Dae-Soo Han; Sang-Eon Park (pp. 230-238).

Vanadium oxide and cerium oxide doped titania–zirconia mixed oxides were explored for oxidative dehydrogenation of ethylbenzene to styrene utilizing carbon dioxide as a soft oxidant. The investigated TiO₂–ZrO₂ mixed oxide support with high specific surface area (207m²g⁻¹) was synthesized by a coprecipitation method. Over the calcined support (550°C), a monolayer equivalent (15wt.%) of V₂O₅, CeO₂ or a combination of both were deposited by using wet-impregnation or co-impregnation methods to make the V₂O₅/TiO₂–ZrO₂, CeO₂/TiO₂–ZrO₂ and V₂O₅–CeO₂/TiO₂–ZrO₂ combination catalysts, respectively. These catalysts were characterized using X-ray diffraction (XRD), Raman, scanning electron microscopy (SEM), transmission electron microscopy (TEM), temperature preprogrammed reduction (TPR), CO₂ temperature preprogrammed desorption (TPD) and BET surface area methods. All characterization studies revealed that the deposited promoter oxides are in a highly dispersed form over the support, and the combined acid–base and redox properties of the catalysts play a major role in this reaction. The V₂O₅–CeO₂/TiO₂–ZrO₂ catalyst exhibited a better conversion and product selectivity than other combinations. In particular, the addition of CeO₂ to V₂O₅/TiO₂–ZrO₂ prevented catalyst deactivation and helped to maintain a high and stable catalytic activity.

Keywords: Carbon dioxide; Oxidative dehydrogenation; Ethylbenzene; Styrene; Vanadium oxide; Cerium oxide; Titania–zirconia; Catalyst characterization

Remarkably enhanced photocatalytic activity by nickel nanoparticle deposition on sulfur-doped titanium dioxide thin film by Masaki Yoshinaga; Katsutoshi Yamamoto; Nobuaki Sato; Koyu Aoki; Takeshi Morikawa; Atsushi Muramatsu (pp. 239-244).

To enhance the photocatalytic performance of titanium dioxide, the structures of both bulk and surface were modified. Doping of sulfur atoms to be substituted for lattice oxygen atoms of titanium dioxide was carried out to extend the light absorption by atmosphere-controlled pulsed laser deposition, which allows direct preparation of impurity-included thin film such as sulfur-doped titanium dioxide. On the other hand, to enhance the surface catalytic reaction, nickel nanoparticles were deposited at the thin film substrate by chemical vapor reductive deposition method, which is a novel preparation technique of metallic nanoparticles on the substrate surface. Obtained sulfur-doped titanium dioxide was found to possess sensitivity to visible light with the wavelength up to 550nm, indicating the photocatalytic activity in visible region. Sulfur doping induced the dye degradation activity under visible light irradiation. When nickel nanoparticles were deposited, a remarkable enhancement of the hydrogen evolution activity through ethanol decomposition of more than 20 times as much as unmodified titanium dioxide thin film was accomplished. In addition, the stability of sulfur atom doped into titanium dioxide structure was investigated.

Keywords: Nickel nanoparticle; Titanium dioxide; Sulfur doping; Thin film; Photocatalyst

Gold/hydroxyapatite catalysts by M.I. Domínguez; F. Romero-Sarria; M.A. Centeno; J.A. Odriozola (pp. 245-251).

This work reports the synthesis, characterization and catalytic activity for CO oxidation of gold catalysts supported on calcium hydroxyapatite. On both, the hydroxyapatite support and the gold-supported hydroxyapatite catalyst, the CO conversion shows a peak near 100% of conversion at room temperature. The generation of structural vacancies by interaction of CO with the solid provokes the formation of peroxide species in the presence of gaseous oxygen, which seems to be responsible of this high conversion of CO at room temperature. Moreover, the influence of the pre-treatment temperature on the activity has been observed and related with the elimination of carbonate species and the generation of structural defects in the apatite structure, which are able to modify the gold oxidation state.

Keywords: Gold; Hydroxyapatite; CO oxidation; Vacancies; Peroxides

Retraction notice to “Ultrasonic irradiation enhanced degradation of azo dye on MnO₂” [Appl. Catal. B: Environ. 47(2) (2004) 133–140] by Jiantuan Ge; Jiuhui Qu (pp. 252-252).

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Applied Catalysis B, Environmental (v.87, #3-4)