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Applied Catalysis B, Environmental (v.96, #1-2)
Partial oxidation of ethanol over cobalt oxide based cordierite monolith catalyst by Clarissa Perdomo Rodrigues; Victor Teixeira da Silva; Martin Schmal (pp. 1-9).
Ethanol partial oxidation was studied on Co3O4/γ–Al2O3/cordierite honeycomb structured catalyst. Honeycomb structure consists of parallel channels that favor the gas phase reactions, which in some temperature and flow rate conditions could be limited by mass transfer effects in gas phase. The catalytic activity and products selectivity were evaluated at different temperatures and O2:ethanol ratios. Also, it evaluated the effect of space velocity (h−1) and presence of H2O in the feed. Overall, the results showed that the partial oxidation reaction occurs in a way that the ethanol is first decomposed in gas phase and then formed in the presence of oxygen radicals that decomposed on the catalyst surface. The CO2:CO low ratio observed in most experiments indicates that shift reaction occurs in gas phase and its equilibrium limits the hydrogen formation. Although this catalyst has not presented any significant deactivation, some carbon formation was observed after 30h on reaction.
Keywords: Monolithic catalysts; Structured catalysts; Ethanol partial oxidation
Inhibition of nZVI reactivity by magnetite during the reductive degradation of 1,1,1-TCA in nZVI/magnetite suspension by Sungjun Bae; Woojin Lee (pp. 10-17).
We demonstrated that the reactivity of nano-sized zero-valent iron (nZVI) can be inhibited by magnetite for the reductive degradation of 1,1,1-trichloroethane (1,1,1-TCA) in nZVI/magnetite suspension under low content of nZVI. A remarkable reductive degradation of 1,1,1-TCA (0.289h−1) was observed in nZVI (0.01g/24mL) suspension in 5h, while no significant degradation was observed in nZVI (0.01g)/magnetite (0.5g) suspension in 80h. The reductive dechlorination of 1,1,1-TCA in the nZVI/magnetite suspension started as the content of nZVI increased to 0.02g. The slope of rate constant increase with respect to the nZVI content for nZVI suspension (17.67g−1h−1) was greater than that for nZVI/magnetite suspension (14.89g−1h−1) at the nZVI content between 0 and 0.1g/24mL. No significant difference in the inhibition of nZVI reactivity by magnetite was observed in the pH range of 6–9. Surface analyses using transmission electron microscopy and X-ray photoelectron spectroscopy revealed that the significant increase of Fe(II) on the magnetite surface was due to an electron transfer from nZVI on its surface resulting in the inhibition of nZVI reactivity for the reductive degradation of 1,1,1-TCA in the nZVI/magnetite suspension.
Keywords: Nano-sized zero-valent iron (nZVI); Magnetite; Reductive degradation; 1,1,1-Trichloroethane; nZVI inhibition
Low temperature catalytic steam reforming of ethanol. 1. The effect of the support on the activity and stability of Pt catalysts by P. Ciambelli; V. Palma; A. Ruggiero (pp. 18-27).
The effects of the support (alumina or ceria) on the activity, selectivity and stability of 1wt% Pt catalyst for the low temperature ethanol steam reforming reaction have been investigated. Experimental results in the range 300–450°C showed a better performance of ceria supported catalyst, especially with reference to deactivation rate. The characterizations of catalysts reveal the presence of very well dispersed PtO x in the ceria that, during the calcination step, is stabilized in the highest oxidation state, in contrast with Al2O3. Moreover, H2 TPR, and TPD showed that the better performances of the ceria supported catalyst are strictly linked to the greater ability of CeO2 to release and store oxygen, resulting in higher stability with respect to alumina supported catalysts. Coke formation, investigated by TPO experiments, occurred on supports and catalysts. However, more stable carbonaceous species were found on Al2O3 and Pt/Al2O3, likely responsible for the higher deactivation rate with respect to CeO2 supported Pt catalyst.Finally, catalytic activity, selectivity and stability of Pt/CeO2 catalyst increase by increasing the Pt load in the range 1–5wt%. The best catalyst formulation (5wt% Pt on CeO2) was selected for further studies. It is worthwhile that this catalyst is also active for the water gas shift conversion of CO to CO2, resulting in the absence of CO in the reformate product.
Keywords: Fuel cell; Hydrogen production; Low temperature ethanol steam reforming; Pt/CeO; 2; catalyst; Pt/Al; 2; O; 3; catalyst; Ethanol pre-reforming; Catalyst deactivation
Au/ZrO2 catalysts for LT-WGSR: Active role of sulfates during gold deposition by Maela Manzoli; Flora Boccuzzi; Valentina Trevisan; Federica Menegazzo; Michela Signoretto; Francesco Pinna (pp. 28-33).
The effect of the addition of various amounts of sulfates to a zirconia support and its possible role during the Au deposition–precipitation step was examined. The high activity showed by the Au/ZrO2 catalysts in the WGS reaction was enhanced by the action of sulfates on the support. SO42− addition to zirconia brings a higher gold dispersion due to (i) the larger surface area and (ii) the positive role of SO42− groups that determine the deposition of Au in the form of highly dispersed non-metallic gold clusters in close contact with the support.
Keywords: Dispersion; Gold; Sulfated zirconia; WGS reaction; Sulfates
Ruthenium and platinum catalyzed carbon oxidation: A comparative kinetic study by M. Jeguirim; K. Villani; J.F. Brilhac; J.A. Martens (pp. 34-40).
Carbon oxidation catalyzed by Ru/Na-Y zeolite under conditions relevant to automotive exhaust gas after treatment was experimentally investigated. In the presence of Ru/Na-Y zeolite catalyst carbon oxidation can be described by three mechanisms, viz. (i) reaction between carbon and NO2; (ii) reaction between carbon and O2 and (iii) cooperative reaction of carbon involving O2 and NO2 simultaneously. The kinetic analysis suggested that the direct C–O2 and the cooperative C–NO2–O2 reaction in the presence of Ru/Na-Y catalyst proceeded according to the adsorption of oxygen on carbon surface followed by a decomposition of these oxygenate surface complexes. The kinetic description of the Ru/Na-Y zeolite catalyst is compared with kinetic models of platinum based carbon oxidation from literature. The catalytic properties of ruthenium and platinum based catalysts were found to be fundamentally different. On the ruthenium catalyst the activation energy for the cooperative C–O2–NO2 reaction and the direct C–O2 reaction is similar, whereas on platinum, the direct C–O2 reaction is slower. In the presence of platinum catalyst NO2 molecules intervene in the decomposition of surface oxygenated carbon complexes, formed by the oxygen adsorption on carbon surface. The kinetic models based on the occurring of direct and cooperative reactions may be applied for the catalytic oxidation of soot in the regenerative particle trap conditions.
Keywords: Carbon oxidation; Ruthenium catalyst; NO; 2; O; 2; Kinetic modeling; Activation energy
The effect of the crystalline phase of alumina on the selective CO oxidation in a hydrogen-rich stream over Ru/Al2O3 by Yun Ha Kim; Eun Duck Park (pp. 41-50).
We prepared Ru catalysts supported on various aluminum oxides with different crystalline phases, viz. α-Al2O3, κ-Al2O3, γ-Al2O3, η-Al2O3, δ-Al2O3 and θ-Al2O3, by the incipient wetness method and applied them to the selective CO oxidation in a hydrogen-rich stream. For comparison, the complete CO oxidation in the absence of H2 was also carried out over the same catalysts. Ru/α-Al2O3 showed the highest CO conversion among the tested catalysts, especially at low temperatures, irrespective of the presence of H2. For all of the catalysts, the catalytic activity for CO oxidation was much suppressed in the absence of H2 compared with that in the presence of H2. Several techniques: N2 physisorption, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), X-ray diffraction (XRD), CO chemisorption, temperature-programmed oxidation (TPO), temperature-programmed reduction (TPR), temperature-programmed desorption (TPD) of CO2 with mass spectroscopy and transmission electron microscopy (TEM) were employed to characterize the catalysts. The least amount of chemisorbed CO and CO2 was obtained at room temperature over Ru/α-Al2O3. The least amount of O2 was chemisorbed during TPO and the oxidized Ru species could be fully reduced in the presence of hydrogen at the lowest temperature over Ru/α-Al2O3 among the Ru/Al2O3 catalysts. Ru/α-Al2O3 can reduce a high inlet concentration of CO to less than 10ppm even in the presence of H2O and CO2 over a wide temperature range.
Keywords: Selective CO oxidation; PROX; Ru catalysts; PEMFC; Fuel cell
Heterogeneous catalytic 2,4,6-trichlorophenol degradation at hemin–acrylic copolymer by Goretti Díaz-Díaz; María Celis-García; M. Carmen Blanco-López; M. Jesús Lobo-Castañón; Arturo J. Miranda-Ordieres; Paulino Tuñón-Blanco (pp. 51-56).
The synthesis, characterization and evaluation of the catalytic properties of a hemin–methacrylamide–ethylene glycol dimethacrylate copolymer are described. This polymer catalyzes the oxidative dechlorination of 2,4,6-trichlorophenol (TCP) in the presence of hydrogen peroxide, yielding 2,6-dichloro-1,4-benzoquinone as the main reaction product. This low-cost material allows the complete removal of TCP from water at concentration level of 20mgL−1 in less than 30min.
Keywords: Abbreviations; MA; methacrylamide; EGDMA; ethileneglycoldimethacrylate; AIBN; 2,2′-azo-bis-(isobutyronitrile); DMSO; dimethylsulfoxide; 2-CP; 2-chlorophenol; 3-CP; 3-chlorophenol; 4-CP; 4-chlorophenol; 2,4-DCP; 2,4-dichlorophenol; 2,6-DCP; 2,6-dichlorophenol; TCP; 2,4,6-trichlorophenol; 2,3,5,6-TeCP; 2,3,5,6-tetrachlorophenol; PCP; pentachlorophenol; 4-FP; 4-fluorophenol; DCQ; 2,6-dichloro-1,4-benzoquinone2,4,6-Trichlorophenol; Degradation; Heme-catalyst; Acrylic polymer
Production of advanced biofuels: Co-processing of upgraded pyrolysis oil in standard refinery units by F. de Miguel Mercader; M.J. Groeneveld; S.R.A. Kersten; N.W.J. Way; C.J. Schaverien; J.A. Hogendoorn (pp. 57-66).
One of the possible process options for the production of advanced biofuels is the co-processing of upgraded pyrolysis oil in standard refineries. The applicability of hydrodeoxygenation (HDO) was studied as a pyrolysis oil upgrading step to allow FCC co-processing. Different HDO reaction end temperatures (230–340°C) were evaluated in a 5L autoclave, keeping the other process conditions constant (total 290bar, 5wt.% Ru/C catalyst), in order to find the required oil product properties necessary for successful FCC co-processing (miscibility with FCC feed and good yield structure: little gas/coke make and good boiling range liquid yields). After HDO, the upgraded pyrolysis oil underwent phase separation resulting in an aqueous phase, some gases (mainly CO2 and CH4), and an oil phase that was further processed in a Micro-Activity Test (MAT) reactor (simulated FCC reactor). Although the oil and aqueous phase yields remained approximately constant when the HDO reaction temperature was increased, a net transfer of organic components (probably hydrodeoxygenated sugars) from the aqueous phase to the oil phase was observed, increasing the carbon recovery in the oil product (up to 70wt.% of the carbon in pyrolysis oil).The upgraded oils were subsequently tested in a lab scale catalytic cracking unit (MAT reactor), assessing the suitability of HDO oils to be used as FCC feed. In spite of the relatively high oxygen content (from 17 to 28wt.%, on dry basis) and the different properties of the HDO oils, they all could be successfully dissolved in and co-processed (20wt.%) with a Long Residue, yielding near normal FCC gasoline (44–46wt.%) and Light Cycle Oil (23–25wt.%) products without an excessive increase of undesired coke and dry gas, as compared to the base feed only. Near oxygenate-free bio-hydrocarbons were obtained, probably via hydrogen transfer from the Long Residue. In this way, we have demonstrated on a laboratory scale that it is possible to produce hydrocarbons from ligno-cellulosic biomass via a pyrolysis oil upgrading route. The much higher coke yields obtained from the catalytic cracking of undiluted HDO oil showed the importance of co-processing using a refinery feed as a diluent and hydrogen transfer source.
Keywords: Pyrolysis oil; Bio-oil; Upgrading; Hydrodeoxygenation; Co-processing; Fluid catalytic cracking; Biofuels
New materials for photocatalytic degradation of Indigo Carmine—Synthesis, characterization and catalytic experiments of nanometric tin dioxide-based composites by M.G. Coelho; G.M. de Lima; R. Augusti; D.A. Maria; J.D. Ardisson (pp. 67-71).
Herein we describe experiments of photocatalytic degradation of Indigo Carmine dye, carried out by new composites containing nanometric SnO2 supported on Al2O3. The composites were prepared in a sequence of procedures which involved reactions of SnBuCl3, aluminium hydroxide with NH4OH in ethanol in order to impregnate organotin oxide in Al2O3 in different stoichiometry. Hence, the obtained materials were employed in experiments of thermal decomposition in O2 at different temperatures, yielding nanoparticles of SnO2 supported on Al2O3, with ratios of Sn/Al2O3 of 30% (1), 40% (2) and 60% (3) in weight, respectively. XRD experiments revealed diffraction patterns of SnO2, and those of Al2O3 were not observed due to their low crystallinity.119Sn Mössbauer experiments suggested the formation of SnO2 in all experiments. Studies of scanning electron microscopies (SEM) showed the formation of tin(IV) oxide on the surface of Al2O3 in composites (1)–(3). The crystallite average size ( D) was calculated employing Scherrer equation, revealing the presence of nanometric SnO2 in all samples. Photocatalytic degradation of Indigo Carmine in aqueous medium, induced by composites (1)–(3), was monitored by electronic spectroscopy, and composite (3) displayed the higher activity. In addition, results from electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (ESI-MS/MS) allowed us to propose a degradation route for the dye.
Keywords: Pyrolysis; Organotin derivatives; Tin oxide; Photocatalysis; Environment contaminants
Effect of sulfur as a growth promoter for CN x nanostructures as PEM and DMFC ORR catalysts by Elizabeth J. Biddinger; Douglas S. Knapke; Dieter von Deak; Umit S. Ozkan (pp. 72-82).
The impact of thiophene, a carbon growth promoter, was investigated when added to acetonitrile during pyrolysis over 2wt%Fe/MgO to form nitrogen-containing carbon nanostructured (CN x) oxygen reduction reaction (ORR) catalysts. ORR activity and selectivity were studied using rotating ring disk electrode (RRDE) electrochemical testing. Catalysts were characterized using XPS, TEM, hydrophobicity testing and BET surface area. It was found that thiophene did increase CN x yield, but did not affect the ORR activity of the resulting catalysts. Characterization results revealed that sulfur was incorporated into the CN x catalyst. Viability of catalysts for use in a PEM or direct methanol fuel cell environment was further investigated using temperature programmed oxidation and desorption (TPO, TPD) techniques to determine the stability of sulfur in CN x, catalyst. Post-synthesis treatment to prevent sulfur desorption during long-term use in a fuel cell was found to be feasible.
Keywords: Nitrogen-containing carbon; ORR catalysts; Fuel cell; Nanostructured carbon; Carbon growth promoters; Sulfur; CN; x
Pd and Pt ions as highly active sites for the water–gas shift reaction over combustion synthesized zirconia and zirconia-modified ceria by Parag A. Deshpande; M.S. Hegde; Giridhar Madras (pp. 83-93).
Noble metal substituted ionic catalysts were synthesized by solution combustion technique. The compounds were characterized by X-ray diffraction, FT-Raman spectroscopy, and X-ray photoelectron spectroscopy. Zirconia supported compounds crystallized in tetragonal phase. The solid solutions of ceria with zirconia crystallized in fluorite structure. The noble metals were substituted in ionic form. The water–gas shift reaction was carried out over the catalysts. Negligible conversions were observed with unsubstituted compounds. The substitution of a noble metal ion was found to enhance the reaction rate. Equilibrium conversion was obtained below 250°C in the presence of Pt ion substituted compounds. The formation of Bronsted acid–Bronsted base pairs was proposed to explain the activity of zirconia catalysts. The effect of oxide ion vacancies on the reactions over substituted ceria–zirconia solid solutions was established.
Keywords: Heterogeneous catalysis; Solid solutions; Oxide ion vacancy; Redox mechanism; Surface processes; Acid–base pairs
FeOOH catalytic ozonation of oxalic acid and the effect of phosphate binding on its catalytic activity by Minghao Sui; Li Sheng; Kexiang Lu; Feng Tian (pp. 94-100).
The catalytic activity of FeOOH on ozonation of oxalic acid at pH 4.0 and 7.0 conditions was investigated in a semi-continuous experimental mode. The results indicate that FeOOH can effectively promote the generation of hydroxyl radicals (OH) under acidic and neutral pH conditions, resulting in the enhancement of the degradation efficiency of oxalic acid by ozone. It is deduced that the hydroxyl groups both of in neutral state (Me-OH) and positive charge state (Me-OH2+) can perform as the active sites for ozone decomposition into hydroxyl radicals generation. The ligand exchange of hydroxyl groups by phosphate adsorption deteriorates the catalytic activity of FeOOH on ozonation, but the phosphate is found to desorb from FeOOH during the catalytic ozonation process, resulting in the reactivation of the catalytic activity of FeOOH.
Keywords: Catalytic ozonation; FeOOH; Hydroxyl groups; Oxalic acid; Phosphate
Effects of adsorbed and gaseous NO x species on catalytic oxidation of diesel soot with MnO x–CeO2 mixed oxides by Xiaodong Wu; Fan Lin; Haibo Xu; Duan Weng (pp. 101-109).
MnO x–CeO2, MnO x and CeO2 catalysts were synthesized by the sol–gel method. The structural, redox and adsorption properties of the individual and mixed oxides were investigated by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), CO temperature-programmed reduction (TPR), NO temperature-programmed oxidation (TPO), NO x temperature-programmed desorption (TPD) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The TPO tests were performed with the soot–catalyst mixture under loose contact conditions to evaluate the catalytic activity of the oxide catalysts for soot oxidation. The MnO x–CeO2 mixed oxide catalyst presents the lowest soot oxidation temperature among the catalysts investigated in the presence of NO and O2. The synergetic effect between manganese oxide and ceria restrains the growth of oxide crystallites, increases the specific surface area and improves the low-temperature redox property. Especially, the activity of MnO x–CeO2 mixed oxides for NO oxidation and its capacity for NO2 storage in the form of surface nitrates are greatly enhanced. Not only the NO2 released from decomposition of surface nitrates but also that formed by catalytic oxidation of gaseous or adsorbed NO on the catalyst is confirmed important for soot oxidation. It is found by the in situ DRIFTS tests with the soot–catalyst mixture that the generation of surface oxygen complexes (SOCs), such as carboxylic anhydrides, lactones, quinine, ceto-enol groups, ethers and phenols, occurs at about 100°C lower temperature with exposure to NO than in the absence of NO, which is an important step for soot oxidation.
Keywords: MnO; x; –CeO; 2; mixed oxides; Soot oxidation; NO oxidation; Nitrate storage; Surface oxygen complexes
NO x removal by rhodium catalysts supported on carbon nanotubes: Evidence for the stoichiometric reduction of NO2 and NO by the carbon support by Hans Beyer; Klaus Köhler (pp. 110-116).
The catalytic removal of NO and NO2 over rhodium particles supported on carbon nanotubes (Rh/CNT) was studied in the absence and presence of oxygen. It was found that the stoichiometric oxidation of the carbon support by adsorbed oxygen deriving from the rhodium-catalyzed scission of NO is crucial to achieve steady-state conversion of NO x. The proposed reaction pathway is verified by complete nitrogen and oxygen balances. In the absence of excess oxygen, Rh/CNT catalysts exhibit high activities in the catalytic reduction of NO and NO2 with the carbon support acting as the reducing agent. Oxidative pretreatment of the CNT support enhances the catalytic activity. The lifetime of the catalysts is limited by the stoichiometric oxidation of the support material. The structural degradation during the time on stream is evidenced by transmission electron microscopy.
Keywords: NO; NO; 2; NO; x; Decomposition; Reduction; Rhodium catalyst; CNT
Total oxidation of propene over Au/ xCeO2-Al2O3 catalysts: Influence of the CeO2 loading and the activation treatment by Pandian Lakshmanan; Laurent Delannoy; Vincent Richard; Christophe Méthivier; Claude Potvin; Catherine Louis (pp. 117-125).
This study explores the reaction of oxidation of propene (1200ppm) under excess oxygen (9%) over Au/ xCeO2/Al2O3 catalysts ( x=1.5, 3, 5, and 10wt% CeO2) to mimic the conditions of VOC decomposition. The present study reveals the influence of several factors that affect the oxidative performance of the Au/ xCeO2/Al2O3 catalysts, such as the ceria loading, the catalyst activation method, i.e., the gold oxidation state, the gold particle size and the distribution of gold on ceria and alumina. The Au/ xCeO2/Al2O3 catalysts were found 100% selective to CO2. Their activity was intermediate between that of Au/Al2O3 (poorly active) and Au/CeO2 (active). Interestingly, the activity increased with the ceria loading when the samples were activated under H2 at 300°C, but decreased when they were activated under O2 at 500°C. Characterization of the Au/ xCeO2/Al2O3 catalysts after both types of activation was performed by TEM, EFTEM, XPS and CO oxidation reaction. The results show that whatever the mode of activation, as the CeO2 loading increased, the proportion of gold particles on alumina decreased while that on ceria increased, but gold remained unreduced on ceria after calcination under O2 whereas it was metallic after reduction under H2. Gold on ceria being more active when it is metallic than when it is unreduced, this explained the evolution of the catalytic results of propene oxidation as the ceria loading varied.
Keywords: Au/CeO; 2; Au/Al; 2; O; 3; Au/CeO; 2; -Al; 2; O; 3; Gold catalyst; VOC oxidation; Propene oxidation; EFTEM; XPS
The effect of Fe2+, Fe3+, H2O2 and the photo-Fenton reagent at near neutral pH on the solar disinfection (SODIS) at low temperatures of water containing Escherichia coli K12 by Dorothee Spuhler; Julian Andrés Rengifo-Herrera; César Pulgarin (pp. 126-141).
The effect of Fe2+, Fe3+, H2O2 and the photo-Fenton system (Fe2+ or 3+/H2O2/ hv) on solar water disinfection (SODIS) at low temperature and at near neutral pH are discussed in detail. We focus on Escherichia coli K12 suspended in either MilliQ water, water containing mineral ions and in MilliQ water enriched with resorcinol, a model for natural organic matter (NOM).Recently, the photo-Fenton reagent at near neutral pH and at millimolar concentrations (0.6mg−1 Fe2+ or 3+ and 10mgL−1 H2O2), was demonstrated to be highly efficient not only for the acceleration of solar disinfection of river water, but also for the elimination of NOM, which is a known precursor for halogenated disinfection byproducts.In this work, these effects were systematically assessed at laboratory scale and in well controlled conditions excluding thermal inactivation. Besides the highly bactericidal properties of the photo-Fenton system at near neutral pH, a bactericidal effect of Fe2+ alone and of Fe3+ under irradiation (Fe3+/ hv) were also observed. This was associated with diffusion and intracellular dark Fenton reactions for Fe2+, while the effect of Fe3+/ hv was attributed to the adsorption of Fe3+ on the bacterial cell wall and subsequent photosensitization of these iron-bacteria exciplexes, leading to the direct oxidation of the cell membrane and the generation of ROS close to the target microorganism.In MilliQ water, photo-inactivation rates for E. coli were increased by 200% in the presence of Fe2+/ hv compared to the basic SODIS system ( hv) and up to 250% in the presence of Fe2+/H2O2/ hv. When Fe3+ was added, photo-inactivation was enhanced up to 135% for Fe3+/ hv and 145% for Fe3+/H2O2/ hv.Inorganic ions contained in mineral water did generally inhibit the beneficial effect of Fe2+ or 3+ and H2O2 on bacterial inactivation. In contrast, the systems containing model NOM (resorcinol in MilliQ water, corresponding to 30mgTOCL−1) resulted in a higher iron-photo-assisted bacterial inactivation. This was associated with the formation of Fe3+-organo bounds, which are stable at near neutral pH and undergo photosensitization under solar radiation leading to the generation of ROS and the oxidation of the organic compounds. Photo-inactivation in the presence of the photo-Fenton reagent was enhanced up to 320% for Fe2+/H2O2/ hv and 355% for Fe3+/H2O2/ hv, with a simultaneous mineralization of 90% TOC within 4h.Based on these experimental results and supported by literature, a mechanistic interpretation of iron-catalyzed solar water disinfection is proposed, which illustrates the possible pathways involved in photo-inactivation of E. coli in the presence of Fe2+, Fe3+ and H2O2.
Keywords: SODIS; Iron; photo-Fenton; Escherichia coli; K12; Photo-oxidative stress
Characterization of Cr(III)-grafted TiO2 for photocatalytic reaction under visible light by Hiroshi Irie; Toshihiko Shibanuma; Kazuhide Kamiya; Shuhei Miura; Toshihiko Yokoyama; Kazuhito Hashimoto (pp. 142-147).
We investigated the chemical state and environment of Cr ions in a Cr ion-grafted TiO2 photocatalyst by means of X-ray absorption fine structure (XAFS) measurements. The XAFS results indicated that the Cr ions exist on TiO2 as Cr(III) in an amorphous Cr2O3-like structure. The Cr2O3-like structure formed clusters and attached to the TiO2 surface. The activity (CO2 generation rate and QE value) was evaluated by 2-propanol decomposition under visible light (1mWcm−2, 450–580nm) and was highest with a weight fraction of Cr/TiO2 equaling 1.0×10−3. In addition, the activity of the Cr(III)-grafted TiO2 photocatalyst was highly reproducible.
Keywords: Photocatalysis; Visible light; Cr(III) ion; TiO; 2; Oxidative decomposition
Hydrodechlorination of chloromethanes with Pd on activated carbon catalysts for the treatment of residual gas streams by M.A. Álvarez-Montero; L.M. Gómez-Sainero; M. Martín-Martínez; F. Heras; J.J. Rodriguez (pp. 148-156).
Laboratory-prepared Pd/C catalysts have been investigated in the deep gas-phase hydrodechlorination (HDC) of monochloromethane (CH3Cl), dichloromethane (CH2Cl2) and trichloromethane (CHCl3). The catalysts were found to be active in HDC, the reactivity following the order CHCl3>CH2Cl2>CH3Cl. Selectivities to non-chlorinated compounds were found to be higher than 90% in most cases. The results obtained with the catalyst prepared from PdCl2 suggest that all the reaction products are primary products. The CH4, CH3Cl and CH2Cl2 come from the hydrogenation of the corresponding adsorbed chloride radical, while hydrocarbons of more than one carbon atoms are formed by reaction and subsequent hydrodechlorination of two radicals adsorbed in neighbouring active centers. The catalyst undergoes a significant deactivation which appears to be due to the poisoning of active centers with chlorinated hydrocarbons. The use of Pd(NO3)2 as Pd precursor leads to a decrease in the activity due to its lower Pd dispersion and a lower proportion of electrodeficient Pd species.
Keywords: Hydrodechlorination; Residual gases; Dichloromethane; Chloroform; Monochloromethane; Pd/activated carbon catalysts
Low temperature selective catalytic reduction of NO by activated carbon fiber loading lanthanum oxide and ceria by Pei Lu; Caiting Li; Guangming Zeng; Linjin He; Dunliang Peng; Huafei Cui; Shanhong Li; Yunbo Zhai (pp. 157-161).
Due to the contribution to air pollution, the controlling of NO discharge needs further studies. In this paper, loaded catalysts of 10–40% (w/w) CeO2/ACF were prepared by impregnation method and used for the selective catalytic reduction of NO with ammonia in the presence of O2. Such catalysts were characterized by surface area measurement (BET), thermo gravimetric (TG) analysis and Fourier transform infrared (FTIR) spectroscopy. The catalytic activity of 10–40% CeO2/ACF at different temperatures, and the catalytic stability at 200°C were studied. Moreover, the experimental results were compared with those of previous studied catalysts. The results show that the 10% CeO2/ACF and 20% La2O3/ACF can yield higher NO conversion and maintain higher catalytic activity at higher temperature than others. 10% CeO2/ACF yields about 70% NO conversion in the SCR of NO at 150°C, and meanwhile 20% La2O3/ACF and 10% CeO2/ACF yield over 90% NO conversion when the temperatures are higher than 350°C. The catalytic activity and the catalyst stability of 10% CeO2/ACF and 20% La2O3/ACF are both higher than those of many reported catalysts.Based on the catalytic and characterizing results, such as BET, TG and FTIR, it can be found that the SCR of NO mechanism of loaded catalysts is different from those of ACF and HNO3/ACF. ACF-C is the catalyst and reducing agent in the SCR of NO of ACF and HNO3/ACF, while the metal oxides loaded by ACF are the catalytic centers, NH3 is the main reducing agent in the SCR of loaded catalysts.
Keywords: Selective catalytic reduction; Nitrogen oxide; Activated carbon fiber; Lanthanum oxide; Ceria
S-doped α-Fe2O3 as a highly active heterogeneous Fenton-like catalyst towards the degradation of acid orange 7 and phenol by Liqin Guo; Feng Chen; Xiangqun Fan; Wandong Cai; Jinlong Zhang (pp. 162-168).
S-doped α-Fe2O3 (α-Fe2O3/S) was synthesized with ferrous sulfate and Na2S2O3 via a hybrid hydrothermal-calcination treatment. The crystal phase, special surface area, morphology of the α-Fe2O3/S as well as the chemical state of the sulfur were studied by X-ray diffraction (XRD), scanning electro microscopy (SEM), Raman spectrum and X-ray photoelectron spectroscopy (XPS). The Fenton and photo-Fenton reactivities of the α-Fe2O3/S were tested by degrading acid orange 7 (AO7) and phenol. Although α-Fe2O3/S showed little Fenton reactivity in the dark, it had an excellent heterogeneous Fenton reaction under either UV or visible irradiation, while other α-Fe2O3s were still kept inactive. S element was found to dope into α-Fe2O3 in the forms of FeS or FeS2 in α-Fe2O3/S. The doped S element promotes the photo-Fenton reaction of α-Fe2O3/S via two roles: retarding the recombination of photogenerated charge carriers and promoting the electron transfer between the peroxide species and iron ions at the interface.
Keywords: α-Fe; 2; O; 3; /S; Heterogeneous Fenton reaction; Doping; Acid orange 7; Phenol
Study of active sites and mechanism for soot oxidation by silver-loaded ceria catalyst by Ken-ichi Shimizu; Hiroshi Kawachi; Atsushi Satsuma (pp. 169-175).
The catalytic behaviors of metal oxides and Ag-loaded CeO2 have been studied for soot oxidation by O2 in tight contact condition. Ag2O, as the most active oxide among 30 kinds of metal oxides tested, showed high activity even under inert atmosphere. However, Ag2O completely deactivated after the first catalytic run because of its conversion to Ag metal particle, indicating that Ag2O does not act as a catalyst but as a strong oxidant for soot combustion. Ag(20wt%)-loaded CeO2 (Ag20Ce), consisted of silver metal nanoparticles on CeO2, showed higher activity than CeO2, and the catalyst showed high durability. Kinetic studies for soot oxidation under O2 and He showed that the activation energy changed in the order CeO2>Ag2O≈Ag20Ce, and activation energy under O2 was close to those under He, indicating that surface oxygen plays an important role in catalytic soot oxidation in the presence of O2 and active oxygen species of Ag20Ce and Ag2O have similar nature. Time-resolved UV–vis analysis of Ce4+/Ce3+ redox kinetics under reducing (H2) and oxidizing (O2) atmosphere showed that the presence of Ag on CeO2 enhanced the reduction of Ce4+ to Ce3+ but did not enhance the re-oxidation of Ce3+. It is concluded that a strong interaction between supported silver nanoparticle and CeO2 surface results in the formation of highly reducible surface oxygen at silver-ceria interface, whose reactivity for soot oxidation is similar to the surface oxygen of Ag2O.
Keywords: Ceria; Diesel soot; Oxidation; Silver
Uniform dispersion of Au nanoparticles on TiO2 film via electrostatic self-assembly for photocatalytic degradation of bisphenol A by Pingfeng Fu; Pengyi Zhang (pp. 176-184).
A simple electrostatic self-assembly method was developed to uniformly disperse ultra-fine Au nanoparticles (NPs) on TiO2 film to improve the photocatalytic activity. Without any modification of TiO2 surface with functional groups, negatively charged Au NPs could be spontaneously adsorbed on TiO2 films with electrostatic attraction when the pH of Au colloids was lower than or close to the isoelectric point of TiO2. Ultra high-resolution FESEM observation showed that Au NPs with diameter of 3–5nm were physically separated and uniformly dispersed on TiO2 film. The pH of Au colloids remarkably influenced the Au loading that was decreased at high pH. The average size of deposited Au NPs increased from 3.1±1.3nm at −5°C to 10.5±3.1nm at 40°C, indicating that growth of Au NPs was retarded at low temperature. The dispersed Au NPs on TiO2 film enhanced the photocurrent generation with ∼five folds and increased the photovoltage of ∼115mV, revealing that the recombination of electron–hole pairs was significantly reduced. The photocatalytic activity of the Au–TiO2 nanocomposite film was improved with ∼2.5 folds for degradation of bisphenol A, and no deactivation was observed during 10 cyclic tests. The key characteristics of deposited Au NPs, such as ultra-fine size, uniform dispersion, physical separation and high loading, were responsible for improved photocatalytic activity of the Au–TiO2 film.
Keywords: Au–TiO; 2; film; Photocatalysis; Nanoparticles; Electrostatic self-assembly; Uniform dispersion; Bisphenol A; Water purification
Electric-agitation-enhanced photodegradation of rhodamine B over planar photoelectrocatalytic devices using a TiO2 nanosized layer by Jing Shang; Fengwei Zhao; Tong Zhu; Qing Wang; Han Song; Yuchao Zhang (pp. 185-189).
The photocatalytic (PC) and photoelectrocatalytic (PEC) degradations of liquid-phase rhodamine B (RhB) were investigated over titanium dioxide (TiO2) coated patterned indium tin oxide (ITO) substrate, denoted as planar ITO/TiO2/ITO device. It is found that over planar ITO/TiO2/ITO device, the PEC degradation of RhB by a bias of 1.5V is significantly increased than the PC degradation of RhB, mainly because the horizontal electric field can not only suppress the hole-electron recombination, but also act as an electric agitator to enhance the competitive adsorption of RhB onto the TiO2 surface. The results show that the planar ITO/TiO2/ITO device is an alternative way to achieve efficient degradation of dyes with simple configuration.
Keywords: Photoelectrocatalysis; Photocatalysis; ITO/TiO; 2; /ITO device; TiO; 2; film
Low temperature catalytic steam reforming of ethanol. 2. Preliminary kinetic investigation of Pt/CeO2 catalysts by P. Ciambelli; V. Palma; A. Ruggiero (pp. 190-197).
Catalytic activity, selectivity and stability of a Pt/CeO2 (5wt% Pt) catalyst were investigated in the low temperature ethanol steam reforming reaction for hydrogen production.Experimental results showed that the catalyst is very active and selective, with negligible CO production and complete ethanol conversion already at 300°C. The main promoted reactions are ethanol decomposition, ethanol steam reforming and CO water gas shift, and a preliminary kinetic investigation showed that the apparent reaction orders are 0.5 and 0 for ethanol and steam respectively, with an apparent activation energy of 18kJmol−1 evaluated in the range 300–450°C.Kinetic evaluations and temperature programmed desorption experiments suggest a surface reaction mechanism involving the following step: (i) ethanol dissociative adsorption on catalyst surface to form acetaldehyde intermediate, (ii) decarbonylation to produce mainly H2, CH4 and CO, and (iii) WGS reaction of CO adsorbed on Pt sites to produce H2 and CO2.
Keywords: Fuel cell; Hydrogen production; Low temperature ethanol steam reforming; Pt/CeO; 2; catalyst; Kinetics of ethanol reforming
Investigation of coke formation on Ni-Mg-Al catalyst for hydrogen production from the catalytic steam pyrolysis-gasification of polypropylene by Chunfei Wu; Paul T. Williams (pp. 198-207).
Co-precipitated Ni-Mg-Al catalyst was prepared and investigated in relation to the production of hydrogen from the catalytic steam pyrolysis-gasification of polypropylene using a two-stage reaction system. Coke formation on the Ni-Mg-Al catalyst was investigated by using temperature-programmed oxidation (TPO), X-ray diffraction (XRD), scanning electron microscopy (SEM)/energy dispersive X-ray spectroscopy (EDXS), transmission electron microscopy (TEM) and focused ion beam (FIB)/scanning electron microscopy (SEM). The coke formation mechanism on the Ni-Mg-Al catalyst is proposed. It is suggested that the Ni-Mg-Al catalyst is initially reduced during the gasification process, the reactions of decomposition/reforming of hydrocarbons gases occur on the surface and inside the catalyst; this resulted in partial fragmentation of the catalyst into small particles. Layered carbons, perhaps containing monoatomic carbon, metal carbides, etc., are suggested to be a transition layer for the formation of filamentous carbons. The addition of Mg into the Ni-Al catalyst was found to increase the catalytic activity and the physical stability of catalyst. In addition, increasing the calcination temperature from 750 to 850°C reduced the surface area of the fresh Ni-Mg-Al catalyst, increased the NiO crystal size, and resulted in a decrease of catalytic activity in the pyrolysis-gasification of polypropylene; however, a more stable catalyst was obtained with higher calcination temperature.
Keywords: Polypropylene; Nickel; Coke; Gasification; Magnesium; Catalyst
Photo-Fenton-like treatment of the commercially important H-acid: Process optimization by factorial design and effects of photocatalytic treatment on activated sludge inhibition by Idil Arslan-Alaton; Nuray Ayten; Tugba Olmez-Hanci (pp. 208-217).
H-acid is a biologically inert, photochemically stable napthalene sulphonate derivative (1-amino-8-hydroxynaphthalene-3,6-disulphonic acid) being frequently produced as an essential raw material of many commercially available textile azo dyes. Treatability reports dealing with the advanced chemical oxidation of H-acid are limited to a few case studies that do not provide a deep insight into single as well as combinative effects of the main process variables influencing the treatment performance. In the present study, the degradation of aqueous H-acid and its organic carbon (COD, TOC) content with the Photo-Fenton-like advanced oxidation process was optimized in terms of selected major process variables (ferric iron concentration, hydrogen peroxide concentration, initial COD value and reaction time) by employing response surface methodology and central composite design. For this purpose, two main targets were set in the optimization approach, namely (i) the achievement of complete/highest possible oxidation (mineralization) and a (ii) partial oxidation option under relatively mild reaction conditions. The photocatalytic treatment performance was examined by the analysis of the process outputs H-acid, COD and TOC removals. Statistical evaluation of the established polynomial regression models as well as validation experiments run under locally (initial COD-based) optimized reaction conditions to test the reliability of the obtained models revealed that Photo-Fenton-like oxidation of aqueous H-acid is highly efficient and the proposed reaction model successfully predicts organic carbon abatement rates for both treatment targets. From the empirical regression models derived for organic carbon removal it was also evident that the photocatalytic treatment system was mainly affected by the initial COD content (negative effect) closely followed by the parameter initial hydrogen peroxide concentration (positive effect). Activated sludge inhibition experiments conducted with heterotrophic biomass indicated that during the application of Photo-Fenton treatment under optimized reaction conditions, no toxic oxidation products were formed.
Keywords: H-acid; Response surface methodology; Central composite design; Photo-Fenton-like oxidation process; Activated sludge inhibition
Effect of H2O vapor addition on the photocatalytic oxidation of ethanol, acetaldehyde and acetic acid in the gas phase on TiO2 semiconductor powders by Masato Takeuchi; Junichi Deguchi; Shiro Sakai; Masakazu Anpo (pp. 218-223).
The effect of H2O vapor addition on the photocatalytic oxidation of ethanol, acetaldehyde and acetic acid on TiO2 semiconductor powders under UV light irradiation were investigated. The photocatalytic oxidation of acetaldehyde and acetic acid on TiO2 surfaces was enhanced by the addition of H2O vapor, its extent depending on the pressure while, on the other hand, the photocatalytic oxidation of ethanol was depressed by its coexistence with the H2O vapor. Since the Ti4+ sites on the TiO2 surfaces work as trap sites for the photo-formed electrons, the carbonyl compounds strongly adsorbed on the Ti4+ sites are not directly oxidized by the holes. However, when optimal amounts of H2O molecules exist in the reaction system, the OH radicals formed by the photo-oxidation of H2O molecules indirectly oxidize such organic species on the Ti4+ sites. In contrast, although ethanol molecules promptly interact with the photo-formed holes on the hydroxyl groups, the coexistence of H2O molecules in the reaction system lessens the efficient interaction between ethanol and the hydroxyl groups on TiO2 surfaces, resulting in a suppression of photocatalytic reactivity. In this way, the correlation of the different surface sites, such as Ti4+ or the hydroxyl groups, on which organic compounds adsorb and the photo-formed carriers are trapped, is not clearly understood but is observed to play an important role in the efficient photocatalytic oxidation of various organic compounds on TiO2 semiconductor in the presence or the absence of an H2O vapor.
Keywords: TiO; 2; Photocatalytic oxidation; Water vapor addition; Adsorption sites
Electrocatalytic activity and stability of niobium-doped titanium oxide supported platinum catalyst for polymer electrolyte membrane fuel cells by Sheng-Yang Huang; Prabhu Ganesan; Branko N. Popov (pp. 224-231).
Rutile phase niobium-doped titanium oxide [Nb xTi(1− x)O2, x=0.25] with a high electrical conductivity (1.11Scm−1) was synthesized and investigated as a cathode catalyst support material for polymer electrolyte membrane fuel cells (PEMFCs). The TEM image of the Pt/Nb xTi(1− x)O2 catalyst revealed that Pt particles ( dPt=3–4nm) were deposited on the Nb xTi(1− x)O2 support using a borohydride reduction method. The Pt/Nb xTi(1− x)O2 catalyst showed comparable oxygen reduction reaction (ORR) activity to that of a commercial Pt/C catalyst (E-TEK) when tested in rotating ring-disk electrode (RRDE). The results of an accelerated durability test (ADT, continuous cycling between 0.6 and 1.4V) in RRDE indicated high stability for the Pt/Nb xTi(1− x)O2 electrocatalysts at high potentials in terms of minimum loss in Pt electrochemical surface area (ECSA). Furthermore, the Pt/Nb xTi(1− x)O2 showed nearly 10-fold higher ORR activity after potential cycling tests when compared to the Pt/C catalyst (1.19 and 0.13mAcm−2 for Pt/Nb xTi(1− x)O2 and Pt/C, respectively). The Pt/C catalyst showed no activity in fuel cell testing after 1000 cycles due to severe carbon corrosion and subsequent disintegration of the catalyst layer. Conversely, the Pt/Nb xTi(1− x)O2 catalyst showed only a small voltage loss (0.11V at 0.6Acm−2) even after 3000 cycles. Based on the ADT results, the Pt/Nb xTi(1− x)O2 electrocatalyst synthesized in this investigation offers a new approach to improve the reliability and durability of PEM-based fuel cell cathode catalysts.
Keywords: Niobium-doped titanium oxide; Metal oxide; Cathode catalyst support; Corrosion resistance; Oxygen reduction reaction; Proton exchange membrane fuel cell
Catalytic conversion of tar from hot coke oven gas using 1-methylnaphthalene as a tar model compound by Jun Yang; Xueguang Wang; Lin Li; Kui Shen; Xionggang Lu; Weizhong Ding (pp. 232-237).
High concentration (1.3vol.%) of 1-methylnaphthalene was selected as a tar model compound to investigate the catalytic conversion of tar from hot coke oven gas (COG) with lower steam content under atmospheric pressure over the Ni/MgO/Al2O3 catalysts. The catalysts were prepared by impregnating boehmite (AlOOH) with an aqueous solution of magnesium nitrate and nickel nitrate. The effects of Ni loading, reaction temperature, steam/carbon (S/C) molar ratio on the catalytic performance of the catalysts were discussed in detail. The catalysts exhibited excellent activity, stability and resistance to carbon deposition. Tar compounds could be completely converted into light fuel gases over 10% Ni/MgO/Al2O3 at 775°C and S/C=0.7. The effect experiments of sulphur were performed by adding 1000 and 2500ppm H2S in the feed. The used catalysts were characterized by XRD and TG analyses. It was first found that addition of H2S in the feed could greatly inhibit the carbon formation on the catalyst surface and lead to significant improvement in the activity and stability of the catalyst. This phenomenon has never been reported previously in the tar steam reforming.
Keywords: Ni catalyst; Coke oven gas; Tar; 1-Methylnaphthalene; Catalytic conversion