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Showing papers in "Applied Catalysis B-environmental in 2012"


Journal ArticleDOI
TL;DR: In this paper, the development of different strategies to modify TiO2 for the utilization of visible light, including non metal and/or metal doping, dye sensitization and coupling semiconductors are discussed.
Abstract: Fujishima and Honda (1972) demonstrated the potential of titanium dioxide (TiO2) semiconductor materials to split water into hydrogen and oxygen in a photo-electrochemical cell. Their work triggered the development of semiconductor photocatalysis for a wide range of environmental and energy applications. One of the most significant scientific and commercial advances to date has been the development of visible light active (VLA) TiO2 photocatalytic materials. In this review, a background on TiO2 structure, properties and electronic properties in photocatalysis is presented. The development of different strategies to modify TiO2 for the utilization of visible light, including non metal and/or metal doping, dye sensitization and coupling semiconductors are discussed. Emphasis is given to the origin of visible light absorption and the reactive oxygen species generated, deduced by physicochemical and photoelectrochemical methods. Various applications of VLA TiO2, in terms of environmental remediation and in particular water treatment, disinfection and air purification, are illustrated. Comprehensive studies on the photocatalytic degradation of contaminants of emerging concern, including endocrine disrupting compounds, pharmaceuticals, pesticides, cyanotoxins and volatile organic compounds, with VLA TiO2 are discussed and compared to conventional UV-activated TiO2 nanomaterials. Recent advances in bacterial disinfection using VLA TiO2 are also reviewed. Issues concerning test protocols for real visible light activity and photocatalytic efficiencies with different light sources have been highlighted.

3,305 citations


Journal ArticleDOI
TL;DR: In this article, a superior Ce-W-Ti mixed oxide catalyst prepared by a facile homogeneous precipitation method showed excellent NH3-SCR activity and 100% N2 selectivity with broad operation temperature window and extremely high resistance to space velocity, which is a very promising catalyst for NOx abatement from diesel engine exhaust.
Abstract: A superior Ce-W-Ti mixed oxide catalyst prepared by a facile homogeneous precipitation method showed excellent NH3-SCR activity and 100% N2 selectivity with broad operation temperature window and extremely high resistance to space velocity, which is a very promising catalyst for NOx abatement from diesel engine exhaust. The excellent catalytic performance is associated with the highly dispersed active Ce and promotive W species on TiO2. The introduction of W species could increase the amount of active sites, oxygen vacancies, and Bronsted and Lewis acid sites over the catalyst, which is also beneficial to improve the low temperature activity by facilitating “fast SCR” reaction and enhance both of the high temperature activity and N2 selectivity simultaneously by inhibiting the unselective oxidation of NH3 at high temperatures.

563 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of different reaction parameters such as initial pH, H2O2 dosage, Fe3O4 nanoparticles addition, initial concentration of 2,4-DCP and temperature on two-stage first-order kinetics of degradation was studied.
Abstract: Fenton-like degradation of 2,4-dichlorophenol (2,4-DCP) in aqueous solution was investigated over Fe3O4 magnetic nanoparticles (MNPs) as catalyst. The obtained samples were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption–desorption isotherms, and physical property measurement system (PPMS). The catalytic results showed that Fe3O4 MNPs presented good properties for the degradation and mineralization of 2,4-DCP, achieving complete decomposition of 2,4-DCP and 51% of TOC removal after 180 min at reaction conditions of H2O2 12 mM, Fe3O4 MNPs 1.0 g/L, 2,4-DCP 100 mg/L, pH 3.0 and T 30 °C. The effect of different reaction parameters such as initial pH, H2O2 dosage, Fe3O4 MNPs addition, initial concentration of 2,4-DCP and temperature on two-stage first-order kinetics of 2,4-DCP degradation was studied. A high utilization efficiency of H2O2 calculated as 73% was observed. According to the analyses of iron leaching, reactive oxidizing species and degradation intermediates, a possible mechanistic steps of 2,4-DCP degradation dominated by OH reactions (especially by free OH in the bulk solution) were proposed. Besides, stability and reusability of Fe3O4 MNPs were tested.

506 citations


Journal ArticleDOI
TL;DR: In this article, multi-walled carbon nanotubes (MWNTs) and graphitic carbon nitride (g-C3N4) composite photocatalysts were synthesized via a facile heating method.
Abstract: Novel multi-walled carbon nanotubes (MWNTs) and graphitic carbon nitride (g-C3N4) composite photocatalysts were synthesized via a facile heating method. The resulting MWNTs/g-C3N4 composite photocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet–visible diffuse reflection spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectroscopy. The photoelectrochemical I–t curves were tested using several on–off cycles of visible light irradiation. The visible light photocatalytic hydrogen evolution was investigated for MWNTs/g-C3N4 in methanol aqueous solutions. The optimal MWNTs content is determined to be 2.0 wt%; and corresponding H2 evolution rate is 7.58 μmol h−1, about 3.7 folds that of pure g-C3N4. A possible mechanism of MWNTs on the enhancement of visible light performance is proposed. It suggests that MWNTs play key roles, which may lead to efficiently separation of the photo-generated charge carriers and, consequently, enhance the visible light photocatalytic H2 production activity.

484 citations


Journal ArticleDOI
TL;DR: In this paper, three different packing methods are introduced into the single-stage plasma-catalysis system to investigate the influence of catalysts packed into the plasma area on the physical properties of the DBD and determine consequent synergistic effects in the plasmacatalytic dry reforming reactions.
Abstract: A coaxial dielectric barrier discharge (DBD) reactor has been developed for plasma-catalytic dry reforming of CH 4 into syngas over different Ni/γ-Al 2 O 3 catalysts. Three different packing methods are introduced into the single-stage plasma-catalysis system to investigate the influence of catalysts packed into the plasma area on the physical properties of the DBD and determine consequent synergistic effects in the plasma-catalytic dry reforming reactions. Compared to the fully packed reactor, which strongly changes the discharge mode due to a significant reduction in the discharge volume, partially packing the Ni/γ-Al 2 O 3 catalyst either in a radial or axial direction into the discharge gap still shows strong filamentary discharge and significantly enhances the physical and chemical interactions between the plasma and catalyst. Optical emission spectra of the discharge demonstrate the presence of reactive species (CO, CH, C 2 , CO 2 + and N 2 + ) in the plasma dry reforming of methane. We also find the presence of the Ni/γ-Al 2 O 3 catalyst in the plasma has a weak effect on the gas temperature of the CH 4 /CO 2 discharge. The synergistic effect resulting from the integration of the plasma and catalyst is clearly observed when the 10 wt% Ni/γ-Al 2 O 3 catalyst in flake form calcined at 300 °C is partially packed in the plasma, showing both the CH 4 conversion (56.4%) and H 2 yield (17.5%) are almost doubled. The synergy of plasma-catalysis also contributes to a significant enhancement in the energy efficiency for greenhouse gas conversion. This synergistic effect from the combination of low temperature plasma and solid catalyst can be attributed to both strong plasma–catalyst interactions and high activity of the Ni/γ-Al 2 O 3 catalyst calcined at a low temperature.

462 citations


Journal ArticleDOI
TL;DR: In this paper, an equilibrium, commercial diluted ZSM-5 catalyst was used as the base case, in comparison with a series of nickel (Ni) and cobalt (Co) modified variants at varying metal loading.
Abstract: The main objective of the present work was the study of different ZSM-5 catalytic formulations for the in situ upgrading of biomass pyrolysis vapors. An equilibrium, commercial diluted ZSM-5 catalyst was used as the base case, in comparison with a series of nickel (Ni) and cobalt (Co) modified variants at varying metal loading (1–10 wt.%). The product yields and the composition of the produced bio-oil were significantly affected by the use of all ZSM-5 catalytic materials, compared to the non-catalytic flash pyrolysis, producing less bio-oil but of better quality. Incorporation of transition metals (Ni or Co) in the commercial equilibrium/diluted ZSM-5 catalyst had an additional effect on the performance of the parent ZSM-5 catalyst, with respect to product yields and bio-oil composition, with the NiO modified catalysts being more reactive towards decreasing the organic phase and increasing the gaseous products, compared to the Co 3 O 4 supported catalysts. However, all the metal-modified catalysts exhibited limited reactivity towards water production, while simultaneously enhancing the production of aromatics and phenols. An interesting observation was the in situ reduction of the supported metal oxides during the pyrolysis reaction that eventually led to the formation of metallic Ni and Co species on the catalysts after reaction, which was verified by detailed XRD and HRTEM analysis of the used catalysts. The Co 3 O 4 supported ZSM-5 catalysts exhibited also a promising performance in lowering the oxygen content of the organic phase of bio-oil.

446 citations


Journal ArticleDOI
TL;DR: Hierarchical flower-like BiOBr microspheres assembled with nanosheets were synthesized via solvothermal method with both two-component solvent (ethylene glycol and isopropanol) and CTAB surfactant as mentioned in this paper.
Abstract: Hierarchical flower-like BiOBr microspheres assembled with nanosheets were synthesized via solvothermal method with both two-component solvent (ethylene glycol and isopropanol) and CTAB surfactant. The growth of BiOBr crystal was significantly influenced by the concentration of ethylene glycol and isopropanol in two-component solvent, the amount of CTAB surfactant and the solvothermal time. According to the photodegradation of rhodamine B (RhB) under visible-light irradiations, the high photocatalytic activity of hierarchical flower-like BiOBr microspheres could be ascribed to the enhanced visible-light absorbance via the light multi-reflections, the efficient separation of photo-generated electrons and holes, the high crystallization and the large surface area. The main active species during the photocatalytic reaction was determined as O2− radical by additionally dissolving the trapping agent in the solution. Meanwhile, BiOBr microspheres also exhibited the excellent durability owing to the stable crystal phase and microsphere morphology.

421 citations


Journal ArticleDOI
TL;DR: In this paper, a new polyaniline (PANI) homopolymer and PANI/ZnO nanocomposite have been successfully synthesized in aqueous diethylene glycol solution medium via the chemical oxidative polymerization of aniline.
Abstract: A new polyaniline (PANI) homopolymer and PANI/ZnO nanocomposite have been successfully synthesized in aqueous diethylene glycol solution medium via the chemical oxidative polymerization of aniline. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, FTIR spectra, UV–vis spectroscopy measurements were used to characterize the resulting PANI homopolymer and PANI/ZnO nanocomposite photocatalysts. The photocatalytic activities of PANI homopolymer and PANI/ZnO nanocomposites were investigated by the degradation of methylene blue (MB) and malachite green (MG) dyes in aqueous medium under natural sunlight and UV light irradiation and the efficiency of the catalysts have been discussed in detail. Results indicate that the addition of the ZnO nanoparticles to the PANI homopolymer enhance the photocatalytic efficiency under natural sunlight irradiation and a little amount of PANI/ZnO nanocomposite photocatalyst (0.4 g/L) degrades both of the dye solutions (MB or MG) with 99% efficiency after 5 h of irradiation under natural sunlight.

384 citations


Journal ArticleDOI
TL;DR: In this article, an overview of the catalytic activity and durability of catalysts supported on graphene is compared with those of carbon blacks and on carbon nanotubes, that is, on rolled graphene.
Abstract: Highly dispersed catalysts on a conductive support, commonly platinum and platinum-based catalysts, are used as electrode materials in low-temperature fuel cells. Carbon blacks are commonly used as fuel cell catalysts supports, but their properties are not completely satisfactory. Thus, in the last years carbon black alternative materials such as nanostructured carbons, ceramic and polymer materials have been proposed as fuel cell catalyst supports. Very recently, in consideration of their high surface area, high conductivity, unique graphitized basal plane structure and potential low manufacturing cost, graphene nanosheets have been investigated as a support for low-temperature fuel cell catalysts. This paper presents an overview of graphene nanosheets used as supports for fuel cell catalysts. In particular, the catalytic activity and durability of catalysts supported on graphene are compared with those of catalysts supported on the commonly used carbon blacks and on carbon nanotubes, that is, on rolled graphene.

380 citations


Journal ArticleDOI
TL;DR: In this article, a visible-light photocatalysis of graphene@TiO2 "dyade"-like structure was synthesized, and photocatalytic degradation of organic compounds over the UV and visible light spectrum regions was investigated.
Abstract: Electron-hole recombination limits the efficiency of TiO2. We have investigated the efficacy with which the graphene@TiO2 "dyade"-like structure reduced charge recombination and enhanced reactivity. A visible-light photocatalysis of graphene@TiO2 "dyade"-like structure was synthesized, and photocatalytic degradation of organic compounds over the UV and visible-light spectrum regions was investigated. The graphene@TiO2 had anatase phase and was able to absorb a high amount of photo energy in the visible-light region, driving effectively photochemical degradation reactions. There were more (OH)-O-center dot radicals produced by the graphene@TiO2 (1:3) than by pure TiO2 under UV and visible-light irradiation. Graphene can enhance the photocatalytic activity of TiO2 in two aspects, namely, e(-) transportation and adsorption. This work provides new insight into the fabrication of graphene@TiO2 as a high performance visible-light photocatalyst and facilitates its application in photocatalytic degradation of organic compounds. (C) 2011 Elsevier B.V. All rights reserved.

370 citations


Journal ArticleDOI
TL;DR: In this paper, hierarchical macro/mesoporpous TiO2-graphene composites with low loadings were first produced by a simple one-step hydrothermal method using tetrabutyl titanate as the titanium precursor.
Abstract: Graphene, a single layer of graphite, possesses a unique two-dimensional structure, high conductivity, superior electron mobility and extremely high specific surface area, and can be obtained on a large scale at low cost. Thus, it has been regarded as an excellent catalyst support. Recently, graphene-based semiconductor photocatalysts have attracted more attention due to their enhanced photocatalytic activity. In this work, hierarchical macro/mesoporpous TiO2–graphene composites with low loadings (0–0.2 wt.%) of graphene were first produced by a simple one-step hydrothermal method using tetrabutyl titanate as the titanium precursor. The prepared composite samples presented enhanced photocatalytic activity in photodegradation of acetone in air. Graphene content exhibited an obvious influence on photocatalytic activity and the optimal graphene addition content was determined. At the optimal graphene concentration (0.05 wt.%), the prepared composites showed the highest photocatalytic activity, exceeding that of pure TiO2 and Degussa P-25 by a factor of 1.7 and 1.6, respectively. The enhanced photocatalytic activity is due to graphene as an excellent electron acceptor and transporter, thus reducing the recombination of charge carriers and enhancing the photocatalytic activity. The transient photocurrent response experiment further confirmed the transfer of photogenerated electrons from TiO2 to graphene and the suggested mechanism.

Journal ArticleDOI
TL;DR: In this article, a series of Ni-based catalysts with different stabilizing components has been tested in the hydrodeoxygenation (HDO) of guaiacol (2-methoxyphenol), bio-oil model compound.
Abstract: Catalytic hydrotreatment or hydrodeoxygenation (HDO) has been researched extensively with the crude bio-oil and its model compounds over conventional sulfided Ni(Mo), Co(Mo) catalysts and supported noble metal catalysts. These types of catalysts showed themselves unsuitable for the target HDO process, which resulted in an urgent need to search for a new catalytic system meeting such requirements as low cost, stability against coke formation and leaching of active components due to adverse effect of the acidic medium (bio-oil). In the present work a series of Ni-based catalysts with different stabilizing components has been tested in the hydrodeoxygenation (HDO) of guaiacol (2-methoxyphenol), bio-oil model compound. The process has been carried out in an autoclave at 320 °C and 17 MPa H2. The main products were cyclohexane, 1-methylcyclohexane-1,2-diol, and cyclohexanone. The reaction scheme of guaiacol conversion explaining the formation of main products has been suggested. The catalyst activity was found to rise with an increase in the active component loading and depend on the catalyst preparation method. The most active catalysts in HDO of guaiacol were Ni-based catalysts prepared by a sol–gel method and stabilized with SiO2 and ZrO2. According to TPR, XRD, XPS, and HRTEM, the high activity of these catalysts correlates with the high nickel loading and the high specific area of active component provided by the formation of nickel oxide–silicate species. The effect of temperature on the product distribution and catalyst activity in the target process (HDO) has been investigated as well. The catalysts were shown to be very promising systems for the production of hydrocarbon fuels by the catalytic upgrading of bio-oil.

Journal ArticleDOI
TL;DR: In this article, a straightforward strategy was designed for the fabrication of magnetically separable CoFe2O4-graphene photocatalysts with differing graphene content, and the significant enhancement in photoactivity under visible-light irradiation can be ascribed to reduction of graphene oxide, because the photogenerated electrons of CoFeO4 can transfer easily from the conduction band to the reduced graphene oxide effectively preventing a direct recombination of electrons and holes.
Abstract: A straightforward strategy was designed for the fabrication of magnetically separable CoFe2O4-graphene photocatalysts with differing graphene content. It is very interesting that the combination of CoFe2O4 nanoparticles with graphene results in a dramatic conversion of the inert CoFe2O4 into a highly active catalyst for the degradation of methylene blue (MB), Rhodamine B (RhB), methyl orange (MO), active black BL-G and active red RGB under visible-light irradiation. The significant enhancement in photoactivity under visible-light irradiation can be ascribed to reduction of graphene oxide, because the photogenerated electrons of CoFe2O4 can transfer easily from the conduction band to the reduced graphene oxide, effectively preventing a direct recombination of electrons and holes. Hydroxyl radicals play the role of main oxidant in the CoFe2O4-graphene system and the radicals’ oxidation reaction is obviously dominant. CoFe2O4 nanoparticles themselves have a strong magnetic property, which can be used for magnetic separation in a suspension system, and therefore the introduction of additional magnetic supports is no longer necessary.

Journal ArticleDOI
Lei Qi1, Qiang Yu1, Yue Dai1, Changjin Tang1, Lianjun Liu1, Hongliang Zhang1, Fei Gao1, Lin Dong1, Yi Chen1 
TL;DR: In this paper, the effects of cerium precursors on the structure, surface state, reducibility and CO oxidation activity of mesoporous CuO-CeO2 catalysts were investigated.
Abstract: This work investigated the effects of cerium precursors [Ce(NO3)3 and (NH4)2Ce(NO3)6] on the structure, surface state, reducibility and CO oxidation activity of mesoporous CuO-CeO2 catalysts. The catalysts were characterized by TG–DTA, XRD, LRS, N2 adsorption–desorption, HRTEM, XPS, H2-TPR and in situ FT-IR. The obtained results suggested that the precursors exerted a great influence on the properties of CuO-CeO2 catalysts: (1) compared with the catalysts from Ce(III) precursor, the derived Ce(IV) precursor catalysts showed smaller grain size, higher BET surface area, narrower pore size distribution, whereas their reducibility and activities were not enhanced. (2) In contrast, the catalysts from Ce(III) precursor without excellent texture displayed high reducibility and activities for CO oxidation due to the high content of Ce3+, following the redox equilibrium of Cu2+ + Ce3+ ↔ Cu+ + Ce4+ shifting to right to form more stable Cu+ species, which was the origin of synergistic effect. The synergistic effect between copper and cerium was the predominant contributor to the improved catalytic activities of CuO-CeO2 catalysts, instead of structural properties.

Journal ArticleDOI
TL;DR: In this article, the state-of-the-art of low Pt and non-Pt electrocatalysts for H2-O2 PEMFCs, Direct Methanol Fuel Cells (DMFCs), and Direct Ethanol Fuel Cell (DEFCs) were provided.
Abstract: Platinum-based nanomaterials are the most commonly adopted electrocatalysts for both anode and cathode reactions in polymer electrolyte membrane fuel cells (PEMFCs) fed with hydrogen or low molecular alcohols. However, the scarce world reserves of Pt and its high price increases the total cost of the system and thus limits the feasibility of PEMFCs. Based on this problem, for PEMFCs to have wide practical applications and become commercially viable, the challenging issue of the high catalyst cost resulting from the exclusive adoption of Pt or Pt-based catalysts should be addressed. One of the targets of the scientific community is to reduce the Pt loading in membrane electrode assemblies (MEAs) to ca. 150 μ g c m MEA − 2 , simultaneously maintaining high PEMFCs performances. The present paper aims at providing the state-of-the-art of low Pt and non-Pt electrocatalysts for: (a) H2-O2 PEMFCs, (b) Direct Methanol Fuel Cells (DMFCs) and (c) Direct Ethanol Fuel Cells (DEFCs). The detailed analysis of a big number of recent investigations has shown that the highest mass specific power density (MSPD) value obtained for H2-O2 PEMFCs has far exceeded the 2015 target ( 5 mW μ g Pt total - 1 ) set by the USA department of energy, while a several number of investigations reported values between 1 and 5 mW μgPt−1. However, the highest values measured under DMFCs and DEFCs working conditions are still relatively low and close to 0.15 and 0.05 mW μgPt−1 respectively. Moreover, the last years, promising results have been reported concerning the design, fabrication, characterization, and testing of novel non-Pt (Pt-free) anodes and cathodes for PEMFCs applications.

Journal ArticleDOI
TL;DR: In this article, the performance of catalytic catalytic hydrodeoxygenation of guaiacol was studied over Fe/SiO2 as a model reaction of lignin pyrolysis vapours hydrotreatment.
Abstract: Lignin could be an important green source for aromatic hydrocarbon production (benzene, toluene and xylenes, BTX). Catalytic hydrodeoxygenation (HDO) of guaiacol was studied over Fe/SiO2 as a model reaction of lignin pyrolysis vapours hydrotreatment. The catalytic conditions were chosen to match with the temperature of never-condensed lignin pyrolysis vapours. The catalyst was characterised by XRD, Mossbauer spectroscopy, N2 sorption and temperature programmed oxidation. A comparison is made with a commercial cobalt-based catalyst. Cobalt-based catalyst shows a too high production of methane. Fe/SiO2 exhibits a good selectivity for BT production. It does not catalyse the aromatic ring hydrogenation. Temperature (623–723 K) and space time (0.1–1.5 gcat h/gGUA) influence the aromatic carbon–oxygen bond hydrogenolysis reaction whereas H2 partial pressure (0.2–0.9 bar) has a minor influence. 38% of BT yield was achieved under the best investigated conditions. Reaction mechanisms for guaiacol conversion over Fe/SiO2 are discussed.

Journal ArticleDOI
TL;DR: In this paper, WS2 nanosheets were prepared through a simple and highly reproducible approach, namely, a mechanical activation strategy by using WO3 and S as the starting materials, and were explored as electrocatalyst for hydrogen evolution reaction (HER).
Abstract: Novel nanostructured material WS2 nanosheets (NSs) were prepared through a simple and highly reproducible approach, namely, a mechanical activation strategy by using WO3 and S as the starting materials, and were explored as electrocatalyst for hydrogen evolution reaction (HER). The as-prepared WS2 NSs reveal separate NSs nanostructure with a sheet thickness of less than 10 nm. On the basis of experimental results obtained under various synthesis conditions, a reasonable reaction process and formation mechanism is proposed, in which the pre-treatment of ball milling is assumed to play a key role for the formation of WS2 NSs. Due to its large active sites originating from its unique structural characteristics such as loosely stacked layers, providing highly exposed rims particularly edges, WS2 NSs catalyst has demonstrated high electrocatalytic activity toward HER, which considerably outperforms the commonly used MoS2 (JDC) catalyst.

Journal ArticleDOI
TL;DR: In this article, the authors describe and critically analyze the literature dealing with the use of supported gold catalysts in the catalytic deep oxidation of volatile organic compounds (VOCs).
Abstract: This review intends to describe and critically analyze the growing literature dealing with the use of supported gold catalysts in the catalytic deep oxidation of volatile organic compounds (VOC). Among the wide family of VOC, attention has been given to the oxidation of saturated (methane, ethane, propane, isobutane, n-hexane) and unsaturated (acetylene, ethylene, propene) aliphatic compounds, aromatic hydrocarbons (benzene, toluene, xylenes, naphthalene), alcohols (methanol, ethanol, n- and iso-propanol), aldehydes (formaldehyde), ketones (acetone), esters (ethylacetate). Moreover, the oxidation of chlorinated VOC (dichloromethane, o-dichlorobenzene, o-chlorobenzene), as well as of nitrogen- (trimethylamine) and sulphur-containing (dimethyldisulfide) compounds has been addressed. The reaction mechanism and the influence of different factors, such as the nature and the properties of the support, the Au particle size and shape, the electronic state of gold, the preparation method and the pretreatment conditions of catalysts, the nature and the concentration of the organic molecule, are discussed in detail.

Journal ArticleDOI
TL;DR: In this article, the reduced graphene oxide-TiO 2 composites (GOT) were evaluated as photocatalysts for the degradation of an important pharmaceutical water pollutant, diphenhydramine (DP), and an azo-dye, methyl orange (MO), under both near-UV/Vis and visible light irradiation as a function of the graphene oxide (GO) content.
Abstract: Reduced graphene oxide–TiO 2 composites (GOT) were prepared by liquid phase deposition followed by post-thermal reduction at different temperatures. The composite materials were systematically evaluated as photocatalysts for the degradation of an important pharmaceutical water pollutant, diphenhydramine (DP), and an azo-dye, methyl orange (MO), under both near-UV/Vis and visible light irradiation as a function of the graphene oxide (GO) content. A marked compositional dependence of the photocatalytic activity was evidenced for DP and MO pollutants degradation and mineralization under both UV/Vis and visible light. Especially under visible light, optimum photocatalytic performance was obtained for the composites treated at 200 °C comprising 3.3–4.0 wt.% GO, exceeding that of the benchmark P25 (Evonik) catalyst. According to scanning electron microscopy, Raman spectroscopy, and porosimetry analysis data, this was attributed to the optimal assembly and interfacial coupling between the reduced GO sheets and TiO 2 nanoparticles. Almost total degradation and significant mineralization of DP and MO pollutants (in less than 60 min) was achieved under near-UV/Vis irradiation for the optimum GOT composites. However, higher GO content and calcination temperatures (350 °C) led to detrimental effects due to the GO excess and the disruption of the GO–TiO 2 binding. Photocatalytic experiments employing sacrificial hole and radical scavenging agents revealed that photogenerated holes are the primary active species in DP degradation for both bare TiO 2 and GOT under UV/Vis irradiation, while an enhanced contribution of radical mediated DP oxidation was evidenced under visible light. These results combined with the distinct quenching of the GO photoluminescence under visible and NIR laser excitation, indicate that reduced GO acts either as electron acceptor or electron donor (sensitizer) of TiO 2 under UV and visible light, respectively. Fine-tuning of the reduced GO–TiO 2 interface is concluded as a very promising route to alleviate electron–hole recombination and circumvent the inherently poor light harvesting ability of TiO 2 in the visible range.

Journal ArticleDOI
TL;DR: In this paper, two different techniques (precipitation with ammonia and hydrothermal synthesis with ethylene glycol, both followed by autoclave aging) were employed for the synthesis of CeO2-ZrO2 mixed oxides on a 80-20-wt.% basis.
Abstract: Two different techniques (precipitation with ammonia and hydrothermal synthesis with ethylene glycol, both followed by autoclave aging) were employed for the synthesis of CeO2–ZrO2 mixed oxides on a 80–20 wt.% basis. Aging parameters, such as time and temperature, were systematically investigated in order to determine the optimal conditions to maintain high surface area and oxygen mobility of the prepared solids. Different loadings of nickel and cobalt (3, 6, 12 and 18 wt.%) were subsequently deposited via homogeneous deposition precipitation method. Calcined bimetallic catalysts were characterized by N2 adsorption–desorption, XRD, H2-TPR, TPO-TGA and FE-SEM methods, and tested for activity, selectivity and stability in the reforming of equimolar CH4–CO2 gas streams. During temperature programmed methane reforming tests, syngas with a H2/CO ratio between 0.3 and 0.79 was produced. Growth of carbon nanofilaments over the catalyst does not lead to deactivation, but can cause reactor plugging. Two conditions are vital and must be fulfilled simultaneously to avoid excessive carbon deposition: strong interaction between the NiCo bimetallic particles and CeZr support, which exists only at NiCo loadings up to 6 wt.%, as well as high oxygen mobility within the highly defective CeO2–ZrO2 crystalline lattice for timely carbon oxidation.

Journal ArticleDOI
TL;DR: In this article, an ultrasound-assisted impregnation method was used to synthesize Mn-Ce mixed oxides (MnCe/Ti) to oxidize elemental mercury (Hg 0 ) at low temperatures in simulated low-rank (sub-bituminous and lignite) coal combustion flue gas and corresponding selective catalytic reduction (SCR) flue gases.
Abstract: TiO 2 supported Mn-Ce mixed oxides (Mn-Ce/Ti) synthesized by an ultrasound-assisted impregnation method were employed to oxidize elemental mercury (Hg 0 ) at low temperatures in simulated low-rank (sub-bituminous and lignite) coal combustion flue gas and corresponding selective catalytic reduction (SCR) flue gas. The catalysts were characterized by BET surface area analysis, X-ray diffraction (XRD) measurement and X-ray photoelectron spectroscopy (XPS) analysis. The combination of MnO x and CeO 2 resulted in significant synergy for Hg 0 oxidation. The Mn-Ce/Ti catalyst was highly active for Hg 0 oxidation at low temperatures (150–250 °C) under both simulated flue gas and SCR flue gas. The dominance of Mn 4+ and the presence of Ce 3+ on the Mn-Ce/Ti catalyst were responsible for its excellent catalytic performance. Hg 0 oxidation on the Mn-Ce/Ti catalyst likely followed the Langmuir–Hinshelwood mechanism, where reactive species on catalyst surface react with adjacently adsorbed Hg 0 to form Hg 2+ . NH 3 consumed the surface oxygen and limited the adsorption of Hg 0 , hence inhibiting Hg 0 oxidation over Mn-Ce/Ti catalyst. However, once NH 3 was cut off, the inhibited mercury oxidation activity could be completely recovered in the presence of O 2 . This study revealed the possibility of simultaneously oxidizing Hg 0 and reducing NO x at low flue gas temperatures. Such knowledge is of fundamental importance in developing effective and economical mercury and NO x control technologies for coal-fired power plants.

Journal ArticleDOI
Hongying Zhao1, Yujing Wang1, Yanbin Wang1, Tongcheng Cao1, Guohua Zhao1 
TL;DR: In this article, a novel electro-Fenton system with the Fe3O4@Fe2O3/activated carbon aerogel (ACA) composite cathode was firstly constructed in this study, which exhibited highly catalytic efficiency over a wide applicable pH range from 3 to 9.
Abstract: A novel electro-Fenton (E-Fenton) system with the Fe3O4@Fe2O3/activated carbon aerogel (ACA) composite cathode was firstly constructed in this study. Its application on degrading imidacloprid exhibited highly catalytic efficiency over a wide applicable pH range from 3 to 9. The removal of imidacloprid and TOC achieved to 90% within 30 and 60 min, respectively. The nature of composite cathode was examined by BJH, XRD, SEM, TEM, XPS and FTIR techniques. ACA with high surface area of 2410 m2 g−1 and multiplicated porosities composed of micropores and mesopores worked not only as cathode but also as Fenton catalyst support, enhancing oxidation activity. We proposed reasonable E-Fenton oxidation mechanisms with Fe3O4@Fe2O3/ACA cathode at acidic and basic conditions. At pH 3, it followed a Haber–Weiss mechanism that the dissolved iron ions and surface Fe(II) sites catalyzed the decomposition of H2O2 to generate hydroxyl radicals ( OH). While at pH 9, it was expected the formation and deactivation of H2O2 complex as well as the catalytic decomposition of H2O2 with surface Fe(III) and Fe(II) sites to produce both superoxide anion ( O2−/HO2 ) and hydroxyl radicals ( OH), involving an in situ recycling of iron oxide (FeO·Fe2O3 → Fe2O3).

Journal ArticleDOI
Huogen Yu1, Rui Liu1, Xuefei Wang1, Ping Wang1, Jiaguo Yu1 
TL;DR: In this paper, an Ag 2 O cocatalyst was applied on the surface of Bi 2 WO 6 nanoparticles by an impregnation method followed by a low-temperature treatment (100-350°C) and their performance was evaluated by the photocatalytic decolorization of methyl orange solution under visible light irradiation.
Abstract: Cocatalyst modification is an efficient strategy to improve the photocatalytic efficiency of photocatalysts by promoting the effective separation of photogenerated electrons and holes. However, most of the cocatalysts are restricted to noble metals (e.g., Ag, Au, Pt) and seldom investigation has been focused on their oxides. In this study, Ag 2 O cocatalyst was coated on the surface of Bi 2 WO 6 nanoparticles by an impregnation method followed by a low-temperature treatment (100–350 °C) and their photocatalytic performance was evaluated by the photocatalytic decolorization of methyl orange solution under visible-light irradiation. It was found that after the surface coating of Ag 2 O, the obtained Ag 2 O/Bi 2 WO 6 composites exhibited an obvious higher photocatalytic activity than the unmodified Bi 2 WO 6 nanoparticles and N-doped TiO 2 . Owing to the photosensitive property of pure Ag 2 O phase, the Ag–Ag 2 O composite easily formed during the decomposition process of organic substances under visible-light irradiation. On the bases of experimental result and band structure analysis, an Ag–Ag 2 O cocatalyst-enhanced photocatalytic mechanism is proposed; namely, the Ag–Ag 2 O cocatalyst possibly reduces oxygen via a multi-electron transfer mechanism. The present results suggest that Ag–Ag 2 O can act as a new and effective cocatalyst for the enhanced photocatalytic performance of photocatalysts, which provides a new approach for the design and development of high-performance visible-light photocatalysts.

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TL;DR: In this paper, a novel property of red phosphorus for visible light driven photocatalytic H 2 formation from water by photogenerated electrons has been discovered, and the detection of hydroxyl radicals and results from photoconductivity measurements confirmed the photogenization of electrons and holes.
Abstract: A novel property of red phosphorus for visible light driven photocatalytic H 2 formation from water by photogenerated electrons has been discovered. The detection of hydroxyl radicals and results from photoconductivity measurements confirmed the photogeneration of electrons and holes. Theoretical calculations also indicated that the reduction of water by photogenerated electrons would be energetically possible. A P-type semiconductor behavior of red phosphorus was observed. Our findings may provide insights for developing phosphorus-based photocatalysts.

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TL;DR: In this article, the formation of methane by hydrogenation of CO2 and CO is carried out with 100% selectivity on a Rh/γ-Al2O3 catalyst at temperatures between 50 and 150 °C at 2 bar of pressure in a pulse reactor.
Abstract: The methanation of CO2 was performed on Rh/γ-Al2O3 catalyst at temperatures between 50 and 150 °C at 2 bar of pressure in a pulse reactor. Experiments confirm the formation of methane at low temperature and pressure. The formation of formiate species during the adsorption of CO2 can be excluded. After reaction with CO2, the catalyst is oxidized. Oxidation is not observed in the presence of CO. The CO2 is adsorbed dissociatively, forming CO (ads) and O (ads). Gem-dicarbonyl Rh(CO)2 species are more reactive than the Rh–CO linear species. The type of adsorbed species depends on the Rh oxidation state. The formation of methane by hydrogenation of CO2 and CO is carried out with 100% selectivity. The activation energy for the hydrogenation of CO2 and CO is lower than values presented in the literature which have been obtained at higher temperature. In the presence of CO2 and CO, the reaction of methanation of CO2 seems to be inhibited by CO. When oxygen is added in low amount in the reactant gas feed, a positive effect on methanation is observed. When the amount of oxygen is too high, oxygen has a negative effect. These results are in agreement with thermodynamics equilibrium calculations, except when O2 is present, confirming the importance of kinetic effects in the reaction. These results open new perspectives of application of catalysis, in order to recycle CO2 in the presence of H2.

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Hong Liu1, Weiran Cao1, Yun Su1, Yong Wang1, Xiaohong Wang1 
TL;DR: In this article, a series of Ag/BiOI photocatalysts with different Ag contents have been synthesized by a hydrothermal combinated with photodeposition method.
Abstract: For the first time, a series of Ag/BiOI photocatalysts with different Ag contents have been synthesized by a hydrothermal combinated with photodeposition method. The as-prepared products were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), high-resolution transmission electron micrographs (HRTEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectra (DRS), and photoluminescence (PL) emission spectroscopy. The photocatalytic activities of these Ag/BiOI composites under visible-light irradiation (λ > 420 nm) were evaluated by the degradation of acid orange II, methyl orange (MO) and rhodamine B (RB). The results revealed that the Ag/BiOI composites exhibited much higher photocatalytic activities than pure BiOI. The Ag amount in the Ag/BiOI composites played an important role in the corresponding photocatalytic properties and the optimized ratio was obtained at 0.6%. The significant enhancement in the Ag/BiOI photoactivity could be ascribed to both the effect of Ag deposits by acting as electron traps and the surface plasma resonance effect of Ag.

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Jing Cao1, Bangde Luo1, Haili Lin1, Benyan Xu1, Shifu Chen1 
TL;DR: In this article, WO 3 /H 2 WO 4 heterostructures with different contents of WO3 were synthesized through a simple thermodecomposition method.
Abstract: Novel WO 3 /H 2 WO 4 heterostructures with different contents of WO 3 were synthesized through a simple thermodecomposition method. Thermogravimetry and differential thermal analysis (TG–DTA), X-ray powder diffraction (XRD), Fourier transform infrared spectrometry (FT-IR), UV–vis diffuse reflectance spectroscopy (DRS) and N 2 adsorption and desorption isotherms were employed to study the structures, morphologies, optical properties and specific surface area of the as-prepared samples. Degradation of rhodamine B (RhB) was carried out to evaluate the photocatalytic activity of samples under visible light irradiation ( λ > 420 nm). WO 3 /H 2 WO 4 heterostructure with 51.04 wt% WO 3 presented the highest photocatalytic activity with apparent k app of 0.0330 min −1 . The increased photocatalytic activity of WO 3 /H 2 WO 4 could be attributed to the formation of the heterojunction between WO 3 and H 2 WO 4 , which suppresses the recombination of photoinduced electron–hole pairs. Moreover, the tests of radical scavengers confirmed that O 2 − and h + were the main reactive species for the degradation of RhB.

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TL;DR: In this article, the as-synthesized SnS 2 /TiO 2 nanocomposite with adjustable TiO 2 contents was synthesized directly via the solvothermal reactions of SnCl 4 ·5H 2 O, thioacetamide and different amounts of tetrabutyl titanate in the mixed solvents of ethanol and acetic acid at 180°C for 12h.
Abstract: SnS 2 /TiO 2 nanocomposites with adjustable TiO 2 contents were synthesized directly via the solvothermal reactions of SnCl 4 ·5H 2 O, thioacetamide and different amounts of tetrabutyl titanate in the mixed solvents of ethanol and acetic acid at 180 °C for 12 h. The structures, compositions, Brunauer–Emmett–Teller (BET) specific surface areas and optical properties of the as-synthesized products were characterized by X-ray diffraction, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, high resolution transmission electron microscopy, N 2 adsorption and UV–vis diffuse reflectance spectra, and their photocatalytic properties were tested for the reduction of aqueous Cr(VI) under visible light ( λ > 420 nm) irradiation. Furthermore, contrast photocatalytic experiments were also conducted for different doses of the as-synthesized SnS 2 /TiO 2 nanocomposite, SnS 2 and physical mixture of SnS 2 and TiO 2 . It was found that the as-synthesized SnS 2 /TiO 2 nanocomposite with a suitable TiO 2 content (e.g., 44.5 mass% TiO 2 ) not only exhibited extraordinary superior photocatalytic activity to SnS 2 , TiO 2 and physical mixture of SnS 2 and TiO 2 (44.5 mass%) at different catalyst doses, but also had good photocatalytic stability. Moreover, Cr(VI) can be reduced to Cr(III) by SnS 2 /TiO 2 -mediated photocatalysis. The tight heterojunction structure of the as-synthesized SnS 2 /TiO 2 nanocomposite, which can facilitate interfacial electron transfer and reduce the separation and self-agglomeration of two components, was considered to play an important role in achieving its greatly improved photocatalytic performance.

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TL;DR: In this paper, the effect of Si content in SAPO-34 on NO selective catalytic reduction over Cu/SAPO34 catalyst was investigated, and three fresh catalysts with different Si contents, prepared by the same procedure, showed different NO conversions from 120°C to 600°C.
Abstract: The effect of Si content in SAPO-34 on NO selective catalytic reduction over Cu/SAPO-34 catalyst was investigated. Three fresh catalysts with different Si contents, prepared by the same procedure, showed different NO conversions from 120 °C to 600 °C. These catalysts were characterized in detail by various techniques (ICP, XRD, SEM, NMR, NH 3 -TPD, H 2 -TPR and EPR). The NH 3 -TPD results indicate that the number of acid sites in Cu/SAPO-34 catalyst increases with increasing Si contents and the SCR activities of the samples correlate well with the number of acidic sites at low temperatures (200 °C). The EPR and H 2 -TPR results show that both the Si and the Al contents affect the number of isolated Cu 2+ ions in Cu/SAPO-34 catalysts. The catalysts aged at 750 °C for 12 h showed higher SCR activities than those of the untreated samples, consistent with the higher numbers of the isolated Cu 2+ ions.

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TL;DR: In this paper, the performance of Ni-based catalysts for the decomposition of urea to benign nitrogen and fuel cell grade hydrogen was investigated through cyclic voltammetry (CV) and polarization techniques.
Abstract: Nickel based catalysts (Ni, Ni-Zn, and Ni-Zn-Co) synthesized through electrodeposition and alkaline leaching processes were used as electrocatalysts for the electrochemical decomposition of urea to benign nitrogen and fuel cell grade hydrogen. The performances of the Ni-based catalysts for the urea decomposition were investigated through cyclic voltammetry (CV) and polarization techniques. The results of the CVs show that the Ni-Zn catalysts and the Ni-Zn-Co catalysts decreased the onset potential of urea oxidation by 40 mV and 80 mV, respectively when compared to Ni catalysts. The highest efficiency for the oxidation of urea was observed with the Ni-Zn-Co catalysts. The Ni-Zn and Ni-Zn-Co catalysts are promising materials for large-scale urea removal/decomposition from urea-rich wastewater, as well as for hydrogen production.