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Applied Catalysis B, Environmental (v.104, #1-2)
Catalytic nitrate removal from water, past, present and future perspectives by Noelia Barrabés; Jacinto Sá (pp. 1-5).
Display Omitted► Overview of past and present literature. ► Future opportunities. ► Perspective and recommendations.Catalytic hydrogenation of nitrates has been studied since the beginning of the nineties. Despite the encouraging initial results the problematic of ammonium by-product formation is yet to be solved. This manuscript aims to be an overview of past and present research in the field and propose some key areas, which should be addressed to improve current and newly developed systems.
Keywords: Denitration; Hydrogenation; Photocatalysis
Photocatalytic effect of thermal atomic layer deposition of TiO2 on stainless steel by Hyemin Kang; Chang-Soo Lee; Do-Young Kim; Jungwon Kim; Wonyong Choi; Hyungjun Kim (pp. 6-11).
.Display Omitted► Preparation of thermal-ALD TiO2 films as a photocatalyst. ► Comparative study of chemical and photocatalyst ability on thermal-ALD and plasma enhanced ALD TiO2 films as a photocatalyst. ► Investigation of the difference and advantage of each ALD process.The thermal atomic layer deposition (Th-ALD) of TiO2 films on stainless steel for use as a photocatalyst was investigated and compared to plasma-enhanced ALD (PE-ALD) using the same precursor. Th-ALD TiO2 films were deposited on stainless steel using a Ti(NMe2)4 [tetrakis(dimethylamido) Ti, TDMAT] precursor. The microstructure of the Th-ALD TiO2 films was greatly dependent on the growth temperature as an amorphous structure was obtained at 200°C and a polycrystalline structure was achieved at temperatures above 300°C. From the contact angle measurement of water, the crystalline TiO2 films exhibited super-hydrophilicity after UV irradiation. The anatase phase of both the Th- and PE-ALD TiO2 films grown on stainless steel showed higher photocatalytic abilities than the rutile phase grown at 400°C. In addition, the anatase PE-ALD TiO2 film demonstrated a higher photocatalytic efficiency than the Th-ALD films. The photocatalytic efficiency of the Th-ALD TiO2 films was investigated as a function of film thickness and it was found that the efficiency was saturated above a film thickness of 120nm.
Keywords: Atomic layer deposition; Photocatalyst; TiO; 2
Superparamagnetic γ-Fe2O3@SiO2@TiO2 composite microspheres with superior photocatalytic properties by Xiaoxiao Yu; Shengwei Liu; Jiaguo Yu (pp. 12-20).
.Display Omitted► Hierarchical porous γ-Fe2O3@SiO2@TiO2 composite microspheres with sandwich-like structures are fabricated. ► SiO2 middle layer is crucial for retention of photocatalytic active of TiO2. ► SiO2 middle layer is a good adsorbent towards dye molecules in water. ► Composite photocatalyst can effectively degrade organic pollutants and easily recovered by a magnet.Hierarchical porous γ-Fe2O3@SiO2@TiO2 ( FST) composite microspheres with sandwich-like structure were fabricated by an effective three-step approach. Specifically, the preformed monodisperse Fe3O4 spheres were used as templates for directing the sequential deposition of SiO2 layer by modified Stöber method and subsequent TiO2 layer by vapor–thermal route. Notably, the interior black Fe3O4 templates are converted into dark-brown γ-Fe2O3 during the vapor–thermal assisted TiO2 deposition. By introducing a SiO2 layer between the γ-Fe2O3 core and TiO2 shell, while the superparamagnetic properties was remained to great extent, the photocatalytic activity towards degradation of rhodamine B (RhB) dye molecules was also significantly improved, as compared to that of the Fe3O4@TiO2 ( FT) counterparts. This enhancement in photoactivity is mainly attributed to two positive effects of the interbedded SiO2 layer between the γ-Fe2O3 core and TiO2 shell. Firstly, a direct contact and electron injection from TiO2 to γ-Fe2O3 is blocked by this wide bandgap SiO2 electronic barrier, which avoids charge recombination at the interface. Secondly, a SiO2 middle layer is a good adsorbent towards dye molecules, which enhances the enrichment of pollutant dye molecules around the porous titania photoactive layer and thus the photocatalytic efficiency. Such a novel multifunctional photocatalytic integrated microspheres can effectively degrade organic pollutants and can be easily recovered by a magnet, which was reused at least five times without any appreciable reduction in photocatalytic efficiency.
Keywords: TiO; 2; Fe; 2; O; 3; SiO; 2; Composite microspheres; Superparamagnetic
The influence of physico-chemical properties of TiO2 on photocatalytic generation of C1–C3 hydrocarbons and hydrogen from aqueous solution of acetic acid by Sylwia Mozia; Aleksandra Heciak; Antoni W. Morawski (pp. 21-29).
.Display Omitted► The gaseous products of photocatalytic decomposition of CH3COOH were CH4, CO2, C2H6, C3H8 and H2. ► The most active photocatalyst was P700 obtained by calcination of crude TiO2 at 700°C in air. ► Ratio CH4/CO2<1 was due to mineralization of CH3COOH to H2O and CO2 in which OH radicals were involved. ► Crucial TiO2 parameters were phase composition, crystallite size and activity forOH radicals formation.The present study was focused on the influence of physico-chemical properties of TiO2 on a photocatalytic generation of useful C1–C3 hydrocarbons (mainly methane) and hydrogen from aqueous solution of acetic acid under N2 atmosphere. The photocatalysts applied in the study were prepared from a crude TiO2 obtained by the sulphate technology. The crude TiO2 was calcined at the temperatures of 600, 700 or 800°C in air atmosphere. Moreover, two commercially available photocatalysts, Aeroxide® P25 and VP TiO2 P90 (Evonik, Germany) were also used in the experiments. The photocatalysts were characterized by UV–vis/DR and FTIR spectroscopy, N2 adsorption–desorption at 77K and XRD measurements. The main gaseous products of CH3COOH decomposition were CH4 and CO2. Moreover, small amounts of ethane, propane and hydrogen were detected in the gaseous phase. The main by-products identified in the liquid phase were methanol, ethanol, acetone, acetaldehyde and methyl acetate. The most active photocatalyst towards hydrocarbons and H2 generation was TiO2 calcined at 700°C. The catalyst was composed mainly of anatase (94%) with crystallite size of 32nm and exhibited BET surface area of 30m2/g. After 27h of the process conducted with this catalyst the concentrations of CH4, CO2, C2H6, C3H8 and H2 amounted to 2.92, 2.68, 0.25, 0.08 and 0.22mmol/g of photocatalyst, respectively. It was found that the main parameters responsible for the photoactivity of the photocatalysts were crystallite size of anatase, phase composition and activity towards hydroxyl radicals formation.
Keywords: Photocatalysis; Hydrocarbons; Methane; Acetic acid; TiO; 2
BiVO4/TiO2 nanocrystalline heterostructure: A wide spectrum responsive photocatalyst towards the highly efficient decomposition of gaseous benzene by Yin Hu; Danzhen Li; Yi Zheng; Wei Chen; Yunhui He; Yu Shao; Xianzhi Fu; Guangcan Xiao (pp. 30-36).
. The excellent wide spectrum responsive BiVO4/TiO2 heterostructure photocatalyst was prepared by a simple coupling method. In the experiment, strong photocatalytic activities towards the removal of gaseous benzene under various light sources irradiation were demonstrated. Compared with TiO2− xN x (nitrogen-doped TiO2), its efficiency of removing gaseous benzene and producing CO2 under visible light irradiation (450nm<λ<900nm) was demonstrated more than 3 and 4 times, respectively. Such high conversion and mineralization ratio could be maintained for more than 50h. Furthermore, the catalyst also presented notably high photocatalytic activities under simulated solar light and UV light irradiation. This improved wide spectrum responsive photocatalyst would be needed, which are of importance to the potential application in the photocatalytic field.Display Omitted► A simple sol–gel method can synthesize the BiVO4/TiO2 heterostructure. ► Particular attention is given to its application of gaseous benzene degradation. ► The catalyst performs high activity under different light sources irradiation. ► It paves the road for the extensive industrial application of the behind.A low-cost, time-saving coupling method was developed to prepare a novel BiVO4/TiO2 heterostructure photocatalyst. Benzene was selected as a target pollutant to evaluate the enhanced heterogenous photocatalytic oxidation process of this photocatalyst. The results clearly indicated that the addition of BiVO4 accelerated the degradation of benzene, and the optimum composition was recognized as BiVO4: TiO2 with ratio of 1:200 (mass ratio). Compared with TiO2− xN x (nitrogen-doped TiO2), its efficiency of removing gaseous benzene and producing CO2 under visible light irradiation ( λ>450nm) was demonstrated more than 3 and 4 times, respectively. Such high conversion and mineralization ratio could be maintained for more than 50h. Applications were also given for the photocatalytic elimination of gaseous benzene under simulated solar light and UV light irradiation. The benzene conversion reached 92% and 11%, corresponding to extremely high mineralization ratios of about 80% and 84%, respectively. Hence, this improved wide spectrum responsive photocatalyst would be needed, which were of importance to the potential application in the photocatalytic field.
Keywords: TiO; 2; Photocatalysis; Benzene; Visible light; Heterostructure
Solar transformation and photocatalytic treatment of cocaine in water: Kinetics, characterization of major intermediate products and toxicity evaluation by Cristina Postigo; Carla Sirtori; Isabel Oller; Sixto Malato; Manuel Ignacio Maldonado; Miren López de Alda; Damià Barceló (pp. 37-48).
Display Omitted► Study of the photolytic and photocatalytic transformation of cocaine in water. ► Transformation efficiency: photo-Fenton>TiO2 photocatalysis>solar irradiation ► Most phototransformation products coincide with known cocaine metabolites. ► Main phototransformation routes: ester bond cleavage, hydroxylation, and demethylation. ► Photointermediates were slightly more toxic than cocaine. Overall, low toxic effects.The present manuscript describes for the first time the transformation and mineralization of cocaine (COC) in water (distilled water (DW) and synthetic municipal wastewater effluent (SWeff)) by natural solar irradiation and two solar photocatalytic processes: heterogeneous photocatalysis with titanium dioxide (TiO2) and homogeneous photocatalysis by photo-Fenton. The solar photocatalytic processes were run at equivalent pilot-plant scale by means of compound parabolic collectors, which allowed for comparison of solar transformation kinetics and compound mineralization. Direct photolysis resulted in almost complete and partial disappearance of COC in SWeff and DW, respectively, after 33h of normalized irradiation time, and negligible mineralization. Solar transformation of COC by heterogeneous photocatalysis with TiO2 was completed after 28 and 50min of illumination in DW and SWeff, respectively, whereas about half of the irradiation time was needed with photo-Fenton, which was also proved to be more effective in compound mineralization. Kinetics parameters were calculated for process comparison. Additionally, the phototransformation intermediates generated during each treatment were investigated and characterized by means of ultra-performance liquid chromatography coupled to quadrupole-time of flight tandem mass spectrometry (UPLC-QqTOF-MS/MS). Identity confirmation was possible for some of them with the analysis of commercially available analytical standards. The main COC phototransformation pathways were observed to be ester bond cleavage, hydroxylation, and demethylation. Finally, the application of an acute toxicity test ( Vibrio fischeri) to selected water samples resulted in inhibition percentages of bacterial bioluminescence in most cases below 20% after 30min of sample contact, which indicates low acute toxicity of the photointermediates generated during the different treatments.
Keywords: Cocaine; Solar photo-Fenton; Solar photocatalysis with TiO; 2; Solar photolysis; Phototransformation products
Origin of performance degradation of palladium-based direct formic acid fuel cells by Mingjun Ren; Yongyin Kang; Wei He; Zhiqing Zou; Xinzhong Xue; Daniel L. Akins; Hui Yang; Songlin Feng (pp. 49-53).
Display Omitted► Pd oxide/hydrous oxides (POHOs) have been identified to play a crucial role in determining better performance and degradation of the Pd-based direct formic acid fuel cells (DFAFCs). ► POHOs suffer from a significant decrease under the DFAFC conditions. ► The introduction of POHOs significantly improves the performance of the DFAFCs.The very limited durability of Pd-based anode for direct formic acid fuel cells (DFAFCs) has seriously restricted their practical application. However, the mechanistic clarification on how to remove the poisoning species and to reactivate the Pd-based anode still remains a big challenge. In this work, we have found that Pd oxides/hydrous oxides (POHOs) play a crucial role in promoting better performance and minimizing performance degradation of the Pd-based DFAFCs. The POHOs are unstable under DFAFC conditions. The intrinsic presence or introduction of Pd oxides/hydrous oxides during electrocatalysis of formic acid oxidation is found to promote elimination of poisoning species, thereby leading to a better performance of DFAFCs. The consumption of Pd oxides/hydrous oxides under DFAFC conditions leads to formation of adsorbed CO-like intermediates that are non-removable, and contribute to the irreversible performance degradation. The present study provides new insights into the degradation mechanism of Pd-based DFAFCs and suggests design features for new durable Pd-based nanostructured catalysts.
Keywords: Direct formic acid fuel cell; Pd nanoparticle; Performance degradation; Pd surface oxide
Effect of the acid–base properties of Zr,Al-pillared clays on the catalytic performances in the reaction of propylene oxide with methanol by M.N. Timofeeva; V.N. Panchenko; A. Gil; V.P. Doronin; A.V. Golovin; A.S. Andreev; V.A. Likholobov (pp. 54-63).
Display Omitted► Textural and physicochemical properties of Zr,Al-pillared clays depend on the Zr content. ► Zr content affects the activity of Zr,Al-PILCs in the synthesis of propylene glycol methyl ether. ► The Zr content decreases the reaction rate and the selectivity for 1-methoxy-2-propanol.A series of Zr,Al-pillared interlayered clays (Zr,Al-PILCs) have been prepared and characterized by X-ray diffraction, elemental analysis, FT-IR and N2-adsorption/desorption analyses, 27Al NMR(MAS), FT-IR spectroscopy using pyridine, PhCN and CDCl3 as probe molecules. It was found that textural and physicochemical properties of Zr,Al-PILCs depend on Zr content in clay. The relationship between the acid–base properties and catalytic performances of Zr,Al-PILCs was revealed in the synthesis of propylene glycol methyl ether from methanol and propylene oxide. The results show that the conversion of propylene oxide and the selectivity to 1-methoxy-2-propanol decrease with increasing the amount of zirconium in Zr,Al-PILCs due to the change in acid–base properties.
Keywords: Zr,Al-pillared clays; Propylene glycol methyl ether; Methanol; Propylene oxide
Hydrogen production by methane tri-reforming process over Ni–ceria catalysts: Effect of La-doping by Lidia Pino; Antonio Vita; Francesco Cipitì; Massimo Laganà; Vincenzo Recupero (pp. 64-73).
Display Omitted► Synthesis gas production by CH4-tri-reforming with Ni–CeO2 catalysts doped with La ( x=0.05–0.50). ► Partial formation of solid solution with negative ( x=0) and positive expansion (0.05< x<0.50) of the ceria lattice emerges. ► Superior performance of Ni–La–CeO2 ( x=0.10) sample were related to a synergic effect of nickel–lanthana–surface oxygen vacancies, nickel dispersion and basic sites distribution on the surface.The objective of the present work is the study of CH4 tri-reforming process (simultaneous carbon dioxide reforming, steam reforming and oxygen reforming) that can contribute to the CO2 abatement producing synthesis gas with the desiderate H2/CO ratio.A series of Ni–CeO2 catalysts with different La loadings is prepared by combustion synthesis and tested as catalysts in CH4 Tri-reforming reaction at 800°C under atmospheric pressure with a GHSV of 30,000h−1.It has been found that during tri-reforming reaction the activity of Ni–ceria catalysts can be enhanced by an appropriate amount of La doping (10at.%), the CH4 and CO2 conversion increases from 93% and 83% to 96% and 86.5%, respectively. The activity enhancement appears to be related to synergic effect of nickel–lanthana–surface oxygen vacancies of ceria via interfacial active sites that contribute to increase the nickel dispersion and create a basic site distribution on the surface able to interact with CO2.
Keywords: CO; 2; abatement; Tri-reforming of methane; Ni–CeO; 2; , Ni–La–CeO; 2; catalysts
Efficient low temperature lean NO x reduction over Ag/Al2O3—A system approach by H. Kannisto; X. Karatzas; J. Edvardsson; L.J. Pettersson; H.H. Ingelsten (pp. 74-83).
Display Omitted► A system approach for a possible on-board system, combining ATR and LNR. ► High NO x conversion at low temperatures using Ag/Al2O3. ► Pt doping of a 2%Ag sample increases the NO x conversion at high C/N ratios. ► NH3 formation over high loaded Ag samples may decrease fuel penalty. ► Fuel penalty is considered.This study focuses on lean NO x reduction (LNR) by n-octane using silver–alumina based catalysts, with the addition of hydrogen. The work takes a system approach, where parameters such as temperature, reformate gas composition, fuel penalty and realistic monolith samples are considered. The LNR catalyst samples were prepared by impregnation and sol–gel methods and the NO x reduction performance was characterized by flow-reactor experiments, where realistic engine-out gas compositions were used. The hydrogen feed over the LNR catalyst samples was determined via data achieved by autothermal reforming experiments over a rhodium based catalyst, using real diesel as feedstock. The LNR catalyst samples generally show an enhanced NO x reduction when hydrogen is added to the gas feed. In particular, a 2wt% silver–alumina sample with the addition of minute amounts of platinum, shows a high increase in NO x reduction when hydrogen is added to the feed. The addition of CO, a potential poison in the reaction and a by-product from the reforming, did not show any significant effect on the LNR catalyst performance at the conditions used. This is beneficial, since it renders a CO clean-up step in the reformer system unneeded. Ammonia formation is discussed in terms of a possible dual-SCR system. Finally, the fuel penalty for hydrogen production and hydrocarbon addition is taken into consideration. It is found that an addition of 1000ppm H2 leads to unacceptable fuel penalties.
Keywords: Lean NO; x; reduction; Ag/Al; 2; O; 3; Pt; Fuel reforming; Fuel economy
In situ study of ozone and hybrid plasma Ag–Al catalysts for the oxidation of toluene: Evidence of the nature of the active sites by Monica Magureanu; Daniela Piroi; Nicolae Bogdan Mandache; Vasile I. Pârvulescu; Viorica Pârvulescu; Bogdan Cojocaru; Chris Cadigan; Ryan Richards; Helen Daly; Christopher Hardacre (pp. 84-90).
Display Omitted► Silver colloids embedded in alumina following a sol–gel procedure in the presence of Pluronic 84 are stable catalysts in the presence of ozone. ► Plasma-catalytic experiments in the total oxidation of toluene showed a significantly increased selectivity to CO2 in the presence of Ag embedded colloids. ► In situ studies of the ozone interaction with catalysts provide an insight into the nature of the active sites of supported silver colloids for total oxidation reactions.Silver colloids have been prepared by reducing AgNO3 in aqueous solution and embeded in alumina following a sol–gel procedure in the presence of Pluronic 84 ((EO)19(PO)39(EO)19), as surfactant. Plasma-catalytic experiments aimed at the mineralization of toluene showed that the selectivity to CO2 was significantly increased in the presence of Ag catalysts compared with results obtained using the plasma alone. In- situ studies of the ozone interaction with catalysts provide an insight into the nature of the active sites of supported silver colloids for mineralization reactions. It is noticeable that when ozone is chemisorbed on embedded Ag colloidal catalysts no change in the silver oxidation state or size is found. The population of the chemisorbed species is higher at lower temperatures, where the non-selective decomposition of ozone is smaller. The catalysts exhibit high stability, preserving the structural and textural properties after the catalytic tests, that is indeed very important in the presence of ozone.
Keywords: Colloid; Silver; Oxidation; Hydrocarbon; Plasma; Catalyst
Insights into the coke deposited on HZSM-5, Hβ and HY zeolites during the cracking of polyethylene by Pedro Castaño; Gorka Elordi; Martin Olazar; Andres T. Aguayo; Bárbara Pawelec; Javier Bilbao (pp. 91-100).
Display Omitted► We studied the principles of coke deposition on zeolites in the pyrolysis of HDPE. ► Two stages of coke development: (1) aromatic and (2) aliphatic growth. ► The number of aromatic rings in the coke follows the trend HY>Hβ>HZSM-5. ► The high flow of N2 for the pyrolysis helps by prolonging the life of the catalyst.The effect of the zeolite structure (HZSM-5, Hβ and HY) on coke deposition during the cracking of high-density polyethylene has been studied by combining the results of multiple spectroscopic and analytical techniques: FTIR, Raman, UV–vis,13C NMR and coke extraction, followed by GC-MS and1H NMR analysis. In addition, by combining FTIR and temperature programmed oxidation (TPO) analysis we obtained information on the coke: properties, burn-off, and changes in composition during catalyst regeneration. Samples of the spent catalysts were obtained in a state-of-the-art pilot plant (conical spouted bed reactor) after the continuous treatment of 900g (1gmin−1, 15h) of high-density polyethylene at 500°C, using 30g of catalyst. The results show that as the pore diameter of the zeolite is increased, bimolecular reactions (hydrogen transfer and oligomerizations), condensations and cyclizations are enhanced, yielding more aromatic coke. Furthermore, the pore topology of the HZSM-5 zeolite improves the flow of coke precursors (also favored by the high flow rate of N2) to the outside of the catalyst; viz. HZSM-5 catalyst preserves its activity for longer.
Keywords: Zeolite MFI; BEA; FAU; Coke; Deactivation; Catalyst; HDPE; Polyolefin; Catalytic pyrolysis; Cracking
Carbon nanostrutured materials as direct catalysts for phenol oxidation in aqueous phase by M. Soria-Sánchez; A. Maroto-Valiente; J. Álvarez-Rodríguez; V. Muñoz-Andrés; I. Rodríguez-Ramos; A. Guerrero-Ruíz (pp. 101-109).
Display Omitted► The oxidation treatment with HNO3 of the CNFs gives place to a homogeneous incorporation of oxygen groups. ► The oxidation treatment of HSAG material does not have any significant effect on its catalytic activity. ► The higher relative concentration of COOH functional groups originates an improved elimination of short chain carboxylic acids from the reaction mixture.The catalytic oxidation of phenol in aqueous phase (CWAO) over different carbon nanostrutured materials, nanofibres (CNFs), carbon nanotubes (CNTs) and high surface area graphite (HSAG), and the derivative materials prepared by surface oxidation, has been comparatively studied. Furthermore, in order to determine the effect of the oxidation treatment the samples were characterized by thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and BET measurements. Important differences among these carbon materials were found in terms of catalytic activity. The oxidized CNFs (ox/CNFs), which probably exhibits the most homogeneous surface after introduction of carboxylic groups by oxidation were the most catalytically active. Particular emphasis has been paid to understand the role of different surface chemistry on the produced oxidation intermediates during the phenol CWAO reaction. Samples with higher concentration of carboxylic surface groups, ox/CNFs and ox/CNTs, show less accumulation of refractory short chain acids, like formic, malonic and oxalic acid during the reaction.
Keywords: Catalytic wet air oxidation; Degradation of phenol; Graphite; Nanofibres; Nanotubes; Carbocatalysis
Selective catalytic reduction of NO with NH3 on iron zeolite monolithic catalysts: Steady-state and transient kinetics by Pranit S. Metkar; Nelson Salazar; Rachel Muncrief; Vemuri Balakotaiah; Michael P. Harold (pp. 110-126).
Display Omitted► Lean catalytic reduction of NO by NH3 selective to N2 on Fe-ZSM-5. ► NO oxidation to NO2 is rate limiting step. ► Water inhibition of NO oxidation significant, negligible for SCR. ► Competitive adsorption of NH3 on active sites inhibits NO reduction. ► Washcoat diffusion limitations emerge above 300°C.An experimental study of steady-state and transient selective catalytic reduction (SCR) of NO with NH3 on both commercial and in-house synthesized Fe-ZSM-5 (MFI type) monolith catalysts is presented. The reaction system was studied in a bench-flow reactor spanning a range of temperature, space velocity and washcoat thickness, affording an assessment of activity and selectivity, reaction pathways, temperature window, mass transport and pore diffusion effects. Experiments included NH3 uptake and temperature-programmed desorption, steady-state and transient NO and NH3 oxidation and standard SCR (NO+NH3+O2) reaction studies. Differential kinetics studies were performed for the standard SCR reaction and NO oxidation reaction systems to determine reaction orders and activation energies. In the temperature range of 200–300°C the standard SCR reaction was found to be nearly first-order and half-order with respect to NO and O2, respectively, but moderately negative-order (−0.3) with respect to NH3. Agreement in the kinetics for both reaction systems suggests that the oxidation of NO is the rate determining step, in line with recent literature studies. Rate inhibition by ammonia appears to be the result of blockage of NO oxidation reaction sites; a necessary step for the standard SCR reaction. Water is shown to inhibit the oxidation of NO significantly and of NH3 to a moderate extent, while having only a negligible effect on the standard SCR reaction. A mechanistic-based kinetic model is proposed in which NH3 reacts with surface bound NO2 and nitrous acid via a NH4NO2 intermediate. A mechanism in which gaseous NO reacts with adsorbed oxygen (Eley Rideal like reaction) cannot be ruled out. In the absence of NH3 these surface species inhibit the adsorption of NO and/or O2 during NO oxidation. Both external mass transfer limitations and washcoat diffusion limitations were ruled out for moderate temperature conditions (≤300°C). However, experiments on monoliths with different washcoat thicknesses conclusively show the appearance of washcoat diffusion limitations at higher temperatures.
Keywords: Selective catalytic reduction; Standard SCR; Fast SCR; Ammonia oxidation; NO oxidation; Washcoat diffusion; Mass transfer
Composite template-free TiO2 photocatalyst: Synthesis, characteristics and photocatalytic activity by Adrián A. Vega; Mehrdad Keshmiri; Madjid Mohseni (pp. 127-135).
Display Omitted► Novel approach to the synthesis of mechanically stable composite TiO2 photocatalyst spheres with very low attrition during fluidization. ► Examines thoroughly the effect of various parameters influencing the attrition resistance of the photocatalyst. ► Evaluates and presents the efficacy of the composite photocatalyst spheres through well controlled experiments and through comparison with the standard P-25 titania photocatalyst.Novel template-free millimetre-size TiO2 photocatalyst spheres with a considerable degree of consistency in their shape and size were developed using sol–gel route. The photocatalyst was prepared by developing a bond between the pre-calcined TiO2 particles in suspension of TiO2 nanoparticles (composite sol–gel) formed by the assistance of a polymeric compound structure. Synthesis variables such as reactant concentrations, pH, drying process and calcination temperature were studied in order to improve the attrition resistance, while maintaining the photoefficiency of the catalyst. X-ray diffraction (XRD), scanning electron microscope (SEM), BET specific surface area and thermo gravimetric analyses (TGA) were used to characterize the photocatalyst. The photocatalytic activities of this mechanically robust photocatalyst was assessed in a laboratory scale fluidized bed photocatalytic reactor using UV irradiation at 254nm and formic acid (FA) as a model organic compound.
Keywords: Photocatalytic spheres; Titanium dioxide; Composite sol–gel; Fluidized bed photoreactor
Catalytic hydrotreatment of crude algal bio-oil in supercritical water by Peigao Duan; Phillip E. Savage (pp. 136-143).
Display Omitted► Bio-oils derived from the hydrothermal liquefaction of microalgae show much promise. ► Processing the crude algal oil in SCW with Pd/C is an effective upgrading strategy. ► Higher H content in the treated oil benefited from the presence of high-pressure H2. ► Many of the properties of the treated oil are very similar to those of hydrocarbon fuels.We report herein on the catalytic hydrotreatment of crude bio-oil, produced from the hydrothermal liquefaction of a microalga ( Nannochloropsis sp.) over palladium on carbon (5% Pd/C) in supercritical water (SCW) at 400°C and 3.4MPa high-pressure H2. Influences of wide ranges of reaction time (varied from 1 to 8h) and catalyst loading (varied from 5 to 80wt%) on treated oil composition and yield, gas products composition and yield, and hydrogen consumption were explored. The C, H and energy recoveries were determined. The results demonstrated that longer reaction times and higher catalyst loadings did not favor the treated oil yield due to the increasing amount of gas and coke products formation but did lead to treated bio-oil with higher higher-heating-value (HHV) (41–44MJ/kg) than that of the crude feed. Highest HHV of treated oil (∼44MJ/kg) was obtained after 4h using an 80wt% intake of catalyst on crude bio-oil. The product oil produced at longer reaction times and higher catalyst loadings, which was a freely flowing liquid as opposed to being the viscous, sticky, tar-like crude bio-oil material, was higher in H and lower in O and N than the crude feed, and it was essentially free of sulfur (below detection limits). Typical H/C and O/C molar ratios ranges for the bio-oils treated at different reaction times and catalyst loadings were 1.65–1.79 and 0.028–0.067, respectively. The main gas-phase products were unreacted H2, CH4, CO2, C2H6, C3H8 and C4H10. Overall, many of the properties of the treated oil obtained from catalytic hydrotreatment in SCW in the presence of Pd/C are very similar to those of hydrocarbon fuels derived from fossil fuel resources.
Keywords: Catalytic hydrotreatment; Algal bio-oil; Treated bio-oil; Palladium on carbon; Supercritical water
Cu–Mn and Co–Mn catalysts synthesized from hydrotalcites and their use in the oxidation of VOCs by Daniel Antonio Aguilera; Alejandro Perez; Rafael Molina; Sonia Moreno (pp. 144-150).
Display Omitted► The solids were evaluated in the total oxidation of three different VOCs. ► The structural composition play a determining role in the catalytic behavior. ► The transition metals avoid the formation of intermediaries (more selective to CO2). ► Cu or Co with Mn promotes low crystalline phases and optimizes the redox properties.Mixed oxides of the Cu/Mn/Mg/Al and Co/Mn/Mg/Al type were obtained by means of the thermal decomposition of hydrotalcites, with manganese as the main active phase and with variations in their content by means of the addition of Cu or Co (molar ratio Cu/Mn or Co/Mn between 0.05 and 0.5). The effect of a second active phase on the material was evaluated in the total oxidation of three volatile organic compounds, VOCs (toluene, ethanol and butanol). The catalysts were characterized by means of X-ray fluorescence (XRF), X-ray diffraction (XRD), temperature-programmed reduction with hydrogen (TPR-H2) and physisorption of nitrogen at 77K. All the solids were active in the oxidation reaction of the VOCs, where the scale of difficulty to oxidize the different organic compounds evaluated was: butanol
Keywords: Hydrotalcites; Mixed oxides; Catalytic oxidation; VOCs
Effects of temperature and reductant type on the process of NO x storage reduction over Pt/Ba/CeO2 catalysts by Xiaoying Wang; Yunbo Yu; Hong He (pp. 151-160).
Display Omitted► NO x can be stored as nitrates on both Ba and Ce sites by replacing carbonates species during the lean phase. ► H2 regenerated Ba storage sites more effectively than CO and C3H6 did. ► The deteriorated reduction efficiency of CO at 200°C was due to a serious poisoning of Pt sites. ► The least reactivity of C3H6 was due to its lowest activation ability by the catalysts. ► Water addition had a positive effect on CO reduction ability at 200°C but little influence at elevated temperatures.The influences of temperature and reductant type on NO x storage and reduction behavior were studied by transient lean/rich cycles and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments over Pt/Ba/CeO2 catalysts. It is found that the reducing ability of H2 is more predominant than that of CO and C3H6 especially at low temperatures. DRIFTS results showed that NO x can be stored as nitrates on both Ba and Ce sites by replacing carbonates species during the lean phase. During the rich phase, however, H2 regenerated Ba storage sites more effectively than did CO and C3H6, and Ba(NO3)2 could be easier reduced than Ce(NO3)4. The relatively low reduction performance of CO was attributed to Pt sites being poisoned by CO, which affected low temperature performance, and by carbonates formation, which affected high temperature conversions. The least reactivity of C3H6 was due to its lowest activation ability by the catalysts. Furthermore, water addition had a positive effect on CO reduction ability at 200°C but little influence at elevated temperatures. It was assumed that H2O improved the low temperature NO x reduction process by alleviating CO poisoning of Pt.
Keywords: NO; x; storage reduction; NO; x; removal efficiency; Temperature; Reductants; H; 2; CO; C; 3; H; 6; Pt/Ba/CeO; 2
Chlorophenol degradation using a one-pot reduction–oxidation process by Mohammad S. Yalfani; Anett Georgi; Sandra Contreras; Francesc Medina; Frank-Dieter Kopinke (pp. 161-168).
Display Omitted► Chlorophenol degradation performed using a combination of reduction and oxidation. ► Better DCP degradation obtained using simultaneous reduction–oxidation. ► Consecutive reduction–oxidation process showed better PCP degradation. ► Promising stability of the Pd–Fe catalyst based on the Pd and Fe leaching results.Chlorophenol degradation was achieved using a combination of hydrodechlorination and heterogeneous Fenton-like oxidation. The process was conducted at ambient conditions (25±2°C, atmospheric pressure) as a one-pot reaction involving formic acid as H2 source for both hydrodechlorination of chlorophenols and H2O2 formation. An alumina-supported Pd–Fe catalyst was applied, which is able to decompose formic acid at the Pd sites, forming H2 and CO2, and additionally H2O2 in the presence of O2. At the same time, due to presence of iron sites on the catalyst, the H2O2 formed can be utilized for a Fenton-like oxidation reaction. Three different reaction protocols were tested, including: (i) consecutive reduction–oxidation with an initial oxygen-free phase adjusted by He purging (CRO–He), (ii) consecutive reduction–oxidation with initially oxygen-limited conditions (CRO) and (iii) simultaneous reduction–oxidation where O2 flowing was started at the beginning of the reaction (SRO). 2,4-Dichlorophenol (DCP) and pentachlorophenol (PCP) were selected as representatives for the group of chlorophenols. For DCP degradation, CRO–He and SRO showed similar efficiencies with respect to the mineralization degree (up to 70%), whereas SRO achieved a better detoxification as observed in bioluminescence tests. The CRO–He reaction over the catalyst used showed only a small decrease in its activity during the oxidation stage, with no further change after the catalyst had been recovered twice. For PCP degradation, a self-inhibition effect was observed for the SRO process, indicating that PCP is hardly degradable by catalytic oxidation. In this case, the CRO–He process, which was facilitated by initial transformation of PCP into phenol and its subsequent oxidation, clearly produced a cleaner medium. This was also confirmed by the results of the toxicity measurements. The catalyst indicated a promising stability based upon the Pd and Fe leaching results measured at the end of each run.
Keywords: Chlorophenol; Hydrodechlorination; Fenton-like; Pd–Fe catalyst; Formic acid
Electro-Fenton removal of TNT: Evidences of the electro-chemical reduction contribution by Kaidar Ayoub; Sylvie Nélieu; Eric D. van Hullebusch; Jérôme Labanowski; Isabelle Schmitz-Afonso; Alain Bermond; Michel Cassir (pp. 169-176).
Display OmittedAccording to TNT degradation pathways the majority of the by-products found by electro-Fenton treatment are obtained by cathodic reduction. ► These results are evidenced through high resolution LC–MS/MS. ► These are in contrast with the previous studies, where a dominant hydroxyl oxidation of nitro moieties was found and no cathode reduction process was reported. ► The proposed reaction scheme shows a complex alternation of oxidation and reduction mechanisms. ► This reaction scheme drastically differs from that obtained under Fenton's conditions.This study aims in analyzing, at laboratory scale, the mechanisms and performances of 2,4,6-Trinitrotoluene (TNT) removal from contaminated water using electro-Fenton process. This treatment belongs to the group of advanced oxidation processes (AOPs), regarded as the most effective approach to decontaminate wastewater from persistent and toxic organic pollutants. In this study, the TNT degradation was investigated through high resolution LC–ESI–MS/MS to tentatively identify the aromatic by-products. The proposed degradation scheme shows a complex alternation of oxidation and reduction mechanisms, evidencing the importance of the electrochemical reduction in the whole process. Furthermore, oxidative opening of the highly reduced/oxidized TNT aromatic ring occurred rapidly during the treatment, leading to the transient accumulation of short chain carboxylic acids such as malonic, glyoxylic, oxalic and formic acids. Mineralization occurred but was delayed in front of TNT and carboxylic acids, showing the persistence of some recalcitrant by-products.
Keywords: TNT; Electro-Fenton; Degradation pathways; Mineralization; LC–ESI–MS–MS
Enhancement of the catalytic activity of TiO2 by using activated carbon in the photocatalytic degradation of cytarabine by R. Ocampo-Pérez; M. Sánchez-Polo; J. Rivera-Utrilla; R. Leyva-Ramos (pp. 177-184).
. Adding activated carbon to the system considerably increased the photocatalytic cytarabine removal; the percentage removal was highest with theUV/TiO2/WO3-120 system and decreased in the order:UV/TiO2/WO3-120>UV/TiO2/WO3-30>UV/TiO2/S>UV/TiO2/M>UV/TiO2/W>UV/TiO2/WH2O2>UV/TiO2/WHNO3>UV/TiO2. It is important to note that in the absence of TiO2 those activated carbons samples did not increased the cytarabine photodegradation rate.Display Omitted► This study analyzed the photocatalytic degradation of cytarabine in the presence of both TiO2 and activated carbon. ► The improvement with activated carbonsWH2O2,WHNO3,WO3-30, andWO3-120 was mainly due to interactions between acid sites of the carbons and the radical species generated from the TiO2 photoactivation. ► The presence of radical scavengers demonstrated that the interactions of HO and eaq− radicals with acid sites of the activated carbons. ► The interaction between eaq− and superficial carboxylic acids present on oxidized carbons produced the reduction of carboxylic acids to cetones.This study analyzed the photocatalytic degradation of cytarabine in the presence of both TiO2 and activated carbon. Three commercial activated carbons denominated as S, M, and W were used in this study. Activated carbon W was oxidized with H2O2, HNO3, or O3. The presence of non-oxidized (S, M, and W) and oxidized (WH2O2,WHNO3,WO3-30,WO3-120) activated carbon enhanced the degradation of cytarabine. The improvement with activated carbons S, M, and W was mainly attributable to their high adsorption capacity of cytarabine, whereas the improvement with activated carbonsWH2O2,WHNO3,WO3-30, andWO3-120 was mainly due to interactions between acid sites of the carbons and the radical species generated from the TiO2 photoactivation. Activated carbon samples oxidized with ozone (WO3-30 andWO3-120) had more acid groups on their surface and yielded 20% and 32% additional degradation percentage of cytarabine, respectively. The presence of radical scavengers such as thiourea, t-butanol, and nitrate ions demonstrated that the interactions of HO and eaq− radicals with acid sites of the activated carbons are responsible for the increased photocatalytic activity of TiO2. The interaction between eaq− and superficial carboxylic acids present on oxidized carbons produced the reduction of carboxylic acids to ketones generating H2O2 which can be decomposed into HO radicals and, subsequently, the ketones generated can be transformed into an alcoholic superficial group generating additional HO radicals.
Keywords: Activated carbon; Titanium dioxide; Photodegradation; Catalytic activity; Cytarabine
Reduction and adsorption mechanisms of selenate by zero-valent iron and related iron corrosion by In-Ho Yoon; Kyoung-Woong Kim; Sunbaek Bang; Min Gyu Kim (pp. 185-192).
Display Omitted► The mechanisms of Se(VI) removal by zero-valent iron (ZVI) was investigated. ► At high Se(VI), Se(VI) was not completely reduced to Se(0)/Se(-II) by ZVI. ► Lepidocrocite is the principle ZVI corrosion product at high Se(VI). ► Se(VI) was completely reduced and ZVI was transformed to magnetite at low Se(VI). ► The reduction capacity and iron corrosion depend on Se(VI) concentration.The mechanisms of selenate [Se(VI)] removal by zero-valent iron (ZVI) were investigated using X-ray absorption spectroscopy (XAS) including X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Batch experiments were performed to measure the ZVI removal of Se(VI) as a function of Se(VI) concentration, pH, and dissolved oxygen (DO) concentration; these experiments demonstrated that low Se(VI) concentration, low pH, and the presence of DO increased the kinetics of Se(VI) removal. XAS showed that the main factor affecting Se(VI) reduction and adsorption as well as ZVI corrosion was the ratio between Se(VI) concentration and ZVI. At high Se(VI) concentrations (>50mg/L), lepidocrocite (γ-FeOOH) was the principal ZVI corrosion product. During ZVI corrosion, Se(VI) was not completely reduced to Se metal [Se(0)]/selenide [Se(-II)] with 1g/L ZVI, although Se(VI)/selenite [Se(IV)] was adsorbed onto the surface of the lepidocrocite. At a low Se(VI) concentration (10mg/L), Se(VI) was reduced to Se(0)/Se(-II) with 1g/L ZVI, which indicated that reduction by ZVI was the principal mechanism of Se(VI) removal, with magnetite (Fe3O4) being the primary corrosion product in the absence of absorbed Se(VI) ions. Therefore, the reduction capacity and iron corrosion coating of ZVI depended on Se(VI) concentration (i.e., the Se(VI)/ZVI ratio) and less extensively on pH and DO.
Keywords: Selenate; ZVI; XANES and EXAFS spectroscopy; XRD; Magnetite; Lepidocrocite
TiO2-encapsulating PVC capable of catalytic self-suppression of dioxin emission in waste incineration as an eco-friendly alternative to conventional PVC by Hyonggoo Yoo; Seung-Yeop Kwak (pp. 193-200).
Display Omitted► Incorporation of nanosized catalyst within PVC via typical suspension polymerization. ► Minimized PVC deterioration owing to high dispersity of TiO2 nanoparticles. ► Self-suppression of dioxin emission by catalytic activity of TiO2 incorporated in PVC.► Halved dioxin emission by 0.93wt% of incorporated TiO2 during incineration at 700°C.► PVC–catalyst nanocomposite as an eco-friendly alternative to conventional PVC.Here, we describe the preparation of TiO2-encapsulating poly(vinyl chloride) (TEPVC), and demonstrate the potential applicability of the material as an eco-friendly alternative to conventional PVC. In particular, TEPVC shows lower emission of toxic chemicals upon waste incineration compared to PVC, owing to the catalytic oxidation and decomposition of such chemicals by the encapsulated TiO2 nanoparticles. Surface-modified TiO2 nanoparticles (M-TiO2) are used for the preparation of TEPVC to facilitate the uniform dispersion of monomeric TiO2 in the initial reaction mixture, which is the key to the preparation of a final TEPVC showing a high dispersion of functional TiO2 nanoparticles in the PVC matrix, without significant agglomeration. The content of encapsulated M-TiO2 in TEPVC was determined to be approximately 0.93wt%, and the high dispersity of M-TiO2 minimizes PVC deterioration, as determined by examinations of morphology, and thermal and mechanical properties. The emission levels of toxic chemicals upon incineration of TEPVC and unmodified PVC samples were analyzed by gas chromatography with high-resolution mass spectrometric detection, using internal standards composed of13C-labeled congeners of polychlorinated dibenzo- p-dioxins, polychlorinated dibenzofurans, and polychlorinated biphenyls. The levels of toxic chemicals produced by incineration of TEPVC were 50% of those seen after unmodified PVC incineration; the sum of toxic equivalent values of all toxic chemicals generated from the incineration of TEPVC was thus only half that seen after incineration of unmodified PVC.
Keywords: Titanium dioxide; Dioxin; Incineration; Poly(vinyl chloride); Chlorinated aromatic compounds; Encapsulation
Fe-exchanged zeolites as materials for catalytic wet peroxide oxidation. Degradation of Rodamine G dye by Roman Prihod’ko; Irina Stolyarova; Gönül Gündüz; Oxana Taran; Svetlana Yashnik; Valentin Parmon; Vladislav Goncharuk (pp. 201-210).
Catalytic wet peroxide oxidation decomposition of dyes.Display Omitted► MFI framework is controlling factor in enhancing dye degradation efficiency. ► Surface properties, acidity, dispersion Fe species affect dye degradation efficiency. ► Crystal structure, surface properties of the zeolite influence on CWPO of Rodamine G.The effect of surface acidity, nature, and dispersion of iron species, controlled by the catalyst preparation techniques and parent zeolite Si/Al ratio, on the catalytic wet peroxide oxidation of Rodamine G dye over the Fe-ZSM-5 materials has been studied.Fe-ZSM-5 and Fe-USY have been prepared using two techniques: improved aqueous ion exchange (IE) and conventional aqueous ion exchange (CE). The former procedure causes some rearrangement of the coordination sphere of four-fold coordinated Al3+, accompanied by formation of a small amount of octahedrally coordinated non-framework aluminium species. In case of Fe-ZSM-5(IE), iron is predominantly present in the form of well-dispersed Fe2+ ions, while Fe-ZSM-5(CE) and Fe-USY(CE) contain small aggregated oligonuclear (FeO) n clusters formed by Fe3+. In both cases, iron species are mainly located inside the zeolite pore system. The contribution of the zeolite is a controlling factor in enhancing the Rhodamine G dye degradation activity of the Fe-ZSM-5 catalysts, which is influenced by the specific procedure used for preparation of these materials.The catalytic wet peroxide oxidation (CWPO) behaviours of the materials prepared via the (IE) and (CE) procedures differ due to different nature of the iron species involved. The non-framework Al3+ species present in both the Fe-exchanged ZSM-5 and USY zeolites may participate in formation of the active sites responsible for CWPO of Rhodamine G dye over these catalysts.At near ambient temperature (323K), quasi-neutral pH (4.9), short reaction time (around 150min), catalyst concentration of 1.0gL−1, and H2O2 addition rate of 41.2–82.3mmolh−1, the (IE)-prepared Fe-ZSM-5 catalyst enables the total degradation of the dye, accompanied by removal of ca. 80% of TOC without notable leaching of the Fe ions.
Keywords: Hydrogen peroxide; Catalytic wet peroxide oxidation; Fe-exchanged zeolites; Iron; Dyes; Rodamine G