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Applied Catalysis B, Environmental (v.82, #3-4)
Highly active deep HDS catalysts prepared using Mo and W heteropolyacids supported on SBA-15 by Lilia Lizama; Tatiana Klimova (pp. 139-150).
A series of Mo (W) catalysts promoted by Ni and supported on pure siliceous SBA-15 was prepared using Keggin-type heteropolyacids (H3PMo12O40 or H3PW12O40) as active phase precursors. These catalysts were compared with corresponding NiMo(W)/SBA-15 catalysts prepared from the traditional precursors (ammonium heptamolybdate, ammonium metatungstate). Prepared catalysts were characterized by N2 physisorption, small- and wide-angle XRD, UV–vis DRS, FT-IR, TPR,31P MAS NMR, HRTEM and evaluated in hydrodesulfurization of 4,6-dimethyldibenzothiophene (4,6-DMDBT). It was found that both Mo and W catalysts prepared from heteropolyacids showed better performance in deep HDS of 4,6-DMDBT than the counterparts prepared from traditionally used Mo (W) ammonium salts. The possible reasons of this phenomenon are discussed.
Keywords: Ultra-deep hydrodesulfurization; 4,6-DMDBT; SBA-15; Keggin-type heteropolyacid
An efficient electron transfer at the Fe0/iron oxide interface for the photoassisted degradation of pollutants with H2O2 by Yulun Nie; Chun Hu; Lei Zhou; Jiuhui Qu (pp. 151-156).
Fe-200 was synthesized through the calcination of iron powder at 200°C for 30min in air. On the basis of characterization by X-ray diffraction and X-ray photoelectron spectroscopy, Fe-200 had a core–shell structure, in which the surface layer was mainly composed of Fe2O3 with some FeOOH and FeO, and the core retained metallic iron. The kinetics and mechanism of the interfacial electron transfer on Fe-200 were investigated in detail for the photoassisted degradation of organic pollutants with H2O2. Under deoxygenated conditions in the dark, the generation of hydroxyl radicals in aqueous Fe-200 dispersion verified that galvanic cells existed at the interface of Fe0/iron oxide, indicating the electron transfer from Fe0 to Fe3+. Furthermore, the effects of hydrogen peroxide and different organic pollutants on the interfacial electron transfer were examined by the change rate of the Fe3+ concentration in the solution. The results indicated that hydrogen peroxide provided a driving force in the electron transfer from Fe2+ to Fe3+, while the degradation of organic pollutants increased the electron transfer at the interface of Fe0/iron oxide due to their reaction withOH.
Keywords: Electron transfer; Galvanic cell-like performance; Iron oxides; Iron metal
Glycerol transformations on polysaccharide derived mesoporous materials by Rafael Luque; Vitaly Budarin; James H. Clark; Duncan J. Macquarrie (pp. 157-162).
New polysaccharide based solid acids are excellent catalysts for selective chemical transformations of glycerol. Reasonable selectivities to mono-, di- and triacetylated glycerols can be obtained by controlled microwave activation of glycerol–acetic and solid acid mixtures. Etherifications of glycerol using a range of alcohols have also been achieved and with a degree of selectivity to both 1- and 2-positions. The use of the Starbon® material as a support for palladium further extends the range of heterogeneous catalysed chemistry to the selective oxidations of glycerol to both glycolic and oxalic acids. In all of the reactions, the catalysts can be easily recovered and reused with only a small loss in activity.
Keywords: Glycerol; Starbon; ®; materials; Esterifications; Etherifications; Oxidations
Catalytic activity and stability of Y zeolite for phenol degradation in the presence of ozone by Yuming Dong; Hongxiao Yang; Kun He; Xuan Wu; Aimin Zhang (pp. 163-168).
As a stable microporous material, de-aluminated Y zeolite has been used for the first time as an ozonation catalyst and showed remarkable activity for the removal of phenol and chemical oxygen demand (COD) in aqueous solution. The Y zeolite exhibited excellent repetitive-use performance even after continuous operation for 10 cycles. The ozone decomposition rate, influence of hydroxyl radical scavenger and influence of reaction temperature were investigated. The results indicate that Y zeolite accelerates the decomposition of ozone and the generation of hydroxyl radicals, consequently enhances the degradation of phenol and the removal of COD.
Keywords: De-aluminated Y zeolite; Catalytic ozonation; Degradation; Phenol
Heterogeneous catalytic activity of NiO-silica composites designated with cubic Pm3 n cage nanostructures by Sherif A. El-Safty; Yoshimichi Kiyozumi; Takaaki Hanaoka; Fujio Mizukami (pp. 169-179).
The fabrication of nanomaterials with the active network sites has led to efficient transport and easier diffusion of guest species in the catalytic application. In this regard, the NiO-supported cage monoliths show evidence to act as effective catalysts toward the oxidation of organic pollutants. Here, the cage-like NiO-silica catalyst with large particle size, cage-like pores, and ordered cubic Pm3 n (HOM-9) structures could be fabricated by a simple, in short period (∼5min), and direct strategy in which microemulsion liquid crystalline phase of Brij 56 (C16EO10) surfactant was used as a template. Our synthetic strategy revealed that the nickel oxide nanoparticles were wrapped onto the pore surface matrices of the cubic Pm3 n monoliths, indicating the simplicity and flexibility to control the geometry, morphology and dispersion of particles. No significant change in the cubic Pm3 n (NiO/HOM-9) phase structures was evident by using this synthetic manipulation; however, high nickel contents up to Si/Ni ratios ∼1 were added to the phase composition domains. Results from the analysis techniques including XRD, N2 isotherms, TEM, XPS, and EDX revealed that the NiO nanoparticles with irregular sizes might be embedded, to some extent, into the pore cavity, particularly with low content of NiO. In turn, with low Si/Ni ratios, The NiO crystallite particles underwent the anisotropic growth to larger sizes (∼15nm) resulted from the aggregation effect, leading to the difficulty to be wrapped into the pore cavity. Practically important results were that the NiO-supported cage monoliths were used as effective catalysts for the oxidation of aminophenols in aqueous solution. However, among all NiO-supported amorphous and ordered silica materials, the NiO/HOM-9 catalyst with open, uniform pore-cage architectures, high surface area and large pore volumes allowed efficient adsorption and diffusion of aminophenols to the active site of NiO clusters, leading to high degree of conversion and reaction rate. On such heterogeneous catalytic systems, the reaction affinity of aminophenols was substantially affected by the structural feature of the catalysts, amount and degree of dispersion NiO particles onto the cubic cage pore surfaces, and the controlled temperature conditions.
Keywords: Monoliths; Cage pores; Organic pollutant; Oxidation reaction; NiO-supported catalysts
Plasma-catalysis destruction of aromatics for environmental clean-up: Effect of temperature and configuration by Alice M. Harling; Vladimir Demidyuk; Stuart J. Fischer; J. Christopher Whitehead (pp. 180-189).
A non-thermal, atmospheric pressure, packed-bed plasma reactor has been used to study the effect of temperature on the plasma-catalytic destruction of toluene and benzene in air using two catalyst positions. TiO2 and γ-Al2O3 supports, and Ag (0.5wt.%) impregnated catalysts of both supports, were used to determine their effects. The reactor (in the one-stage configuration) or the downstream catalyst (in the two-stage arrangement) could be heated to ∼600°C and the destruction efficiencies for toluene and benzene were determined. Plasma catalysis is more effective at destroying benzene and toluene than both conventional thermal-catalysis and plasma alone. Toluene is destroyed much more efficiently than benzene, regardless of the temperature of the system and the reactor configuration. A one-stage, plasma-catalysis configuration is found to be more effective at destroying both toluene and benzene than a two-stage configuration. Plasma catalysis offers no advantage over thermal catalysis for destroying both pollutants in the two-stage configuration.
Keywords: Non-thermal plasma; Plasma-catalysis; Catalysis; Alumina; Titania; Benzene; Toluene
New sulfur adsorbents derived from layered double hydroxides by Dennis E. Sparks; Tonya Morgan; Patricia M. Patterson; S. Adam Tackett; Erin Morris; Mark Crocker (pp. 190-198).
Mixed oxides, prepared via the thermal decomposition of layered double hydroxides (LDHs), were screened gravimetrically for their ability to adsorb carbonyl sulfide (COS). Based on promising results obtained for Ni/Mg/Al, Ni/Mg/Fe and Co/Mg/Al mixed oxides, a study was undertaken to optimize the composition of these materials for COS adsorption. To investigate the effect of the M(II):M(III) ratio, LDHs of the type [M zMg yAl x(OH)2](CO3) x/2·0.5H2O (where M=Ni or Co, and x+ y+ z=1) were prepared at values of x corresponding to 0.33 and 0.20. Simultaneously, the elemental ratio of transition metal to magnesium ( z/ y) was varied. Mixed oxides obtained from the resulting LDHs were tested in fixed bed mode with a feed of 100ppm COS in N2 to determine breakthrough capacity. In general Ni/Mg/Al mixed oxides showed the best performance, a composition with Ni/Mg/Al=0.32/0.48/0.20 showing the best adsorption capacity. Treatment of the spent adsorbent under an atmosphere of 5% H2 in N2 at 450°C was found to provide an effective means of restoring the adsorption capacity over two cycles of adsorption and regeneration, although after three such cycles, adsorption capacity decreased.
Keywords: Adsorption; Carbonyl sulfide; Methyl mercaptan; Layered double hydroxide; Hydrotalcite
New sulfur adsorbents derived from layered double hydroxides by Todd J. Toops; Mark Crocker (pp. 199-207).
H2S and COS adsorption were studied on two calcined layered double hydroxides (LDHs), Mg0.75Al0.25(OH)2(CO3)0.125 and Mg0.65Al0.35(OH)2(CO3)0.175, using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and a chemisorption apparatus. Both demonstrated the ability to irreversibly adsorb H2S, corresponding to uptakes of 1.54 and 1.76μmol/m2, respectively, but Mg0.75Al0.25 had a significantly larger capacity for COS, 1.62μmol/m2 compared to 0.80μmol/m2 for Mg0.65Al0.35. Analysis of the DRIFT spectra suggests the adsorption of H2S proceeds via the substitution of lattice oxygen with sulfur, resulting in the formation of H2O on the surface. COS adsorption is more complicated, although it appears that a similar substitution of lattice oxygen with sulfur occurs. This results in the formation of CO2 and subsequently bicarbonates and carbonates. The formation of hydrogen thiocarbonate is also involved, although this form is generally only observed in the later stages of adsorption and appears to form at the expense of bicarbonate. The Mg0.75Al0.25 LDH retained its ability to adsorb COS in the presence of propene.
Keywords: DRIFTS; Adsorption; Carbonyl sulfide; Layered double hydroxide; Hydrotalcite
Preparation and photocatalytic activity of hierarchically mesoporous-macroporous TiO2− xN x by Gao-Song Shao; Xue-Jun Zhang; Zhong-Yong Yuan (pp. 208-218).
Hierarchically mesoporous-macroporous N-doped titania materials were fabricated by the thermal treatment of spontaneously formed hierarchical mesoporous-macroporous titanias with urea solution, in order to extend their photocatalytic applications from ultraviolet to visible-light range. The resultant meso-macroporous TiO2− xN x exhibited a bicrystalline (anatase and brookite) framework with high surface area and large porosity. The content of the doped nitrogen increased with the urea solution and the nitridation temperature, and the band gaps narrowed from 3.14 to 2.48eV. The formation of OTiN bonds in the meso-macroporous TiO2− xN x was confirmed by the XPS and FT-IR spectra. The photocatalytic activity was evaluated by the photodegradation of methyl orange and rhodamine B under UV and visible-light irradiation, respectively. The significant improvement of photocatalytic activity for water contaminant decomposition under both UV and visible-light irradiation was observed, which is due to the incorporation of nitrogen into the titania lattice and the presence of the hierarchical meso-macroporous structure.
Keywords: Mesoporous-macroporous; Titanium dioxide; N-doping; Photocatalyst; Visible-light
Nb2O5 as efficient and recyclable photocatalyst for indigo carmine degradation by Alexandre G.S. Prado; Lucas B. Bolzon; Carolina P. Pedroso; Aline O. Moura; Leonardo L. Costa (pp. 219-224).
Heterogeneous photocatalysis is a significant green technology for application in water purification. The application of Nb2O5 catalyst for the photodegradation of contaminants is few reported in the literature. Thus, the Nb2O5 catalyst was characterized by SEM, FTIR, surface area and charge surface density. This catalyst was applied to degrade indigo carmine dye, which was compared with degradation catalyzed by TiO2 and ZnO. Almost 100% of dye degradation occurred at 20, 45 and 90min for TiO2, ZnO and Nb2O5, respectively. The effect of Nb2O5 catalyst concentration, pH and ionic strength ( μ) was investigated. The Nb2O5 activity increased at 0.7g/L and for higher catalyst concentrations the degradation was kept constant. Degradation of indigo carmine dye catalyzed by Nb2O5 was improved at pH<4.0 and μ=0.05mol/L. TiO2, ZnO and Nb2O5 were recovered and re-applied in other nine reaction cycles. While TiO2 and ZnO have an abrupt loss of their catalytic activity, Nb2O5 maintained 85% of catalytic activity after 10 reaction cycles.
Keywords: Nb; 2; O; 5; Photodegradation; Dye
Functionalisation versus mineralisation of some N-heterocyclic compounds upon UV-illumination in the presence of un-doped and iron-doped TiO2 photocatalysts by J.A. Navío; M. Macias; M. Garcia-Gómez; M.A. Pradera (pp. 225-232).
Heterogeneous photocatalytic oxidation of some N-heterocyclic compounds (4-picoline, and 6- and 8-methylquinoline) in oxygenated solvents (water or acetonitrile), containing dispersed photocatalyst (un-doped or iron-doped titanium dioxide), was investigated under UV-illumination in a photochemical reactor. This work aimed to correlate experimental parameters such as structural aspects of the substrates, photocatalyst chemical and surface properties, illumination times, and the nature of the solvent with the extent of mineralisation of the substrates and, also, possible selective methyl group functionalisation.Analysis of the products resulting from heterogeneous photocatalytic oxidation of 6- and 8-methylquinoline suspensions in oxygenated acetonitrile with illumination periods of <24h detected, in both cases, the corresponding formyl derivatives quinoline-6- and -8-carbaldehyde, though at low levels. The presence of water appeared to inhibit heterogeneous photocatalytic functionalisation. However, the heterogeneous photocatalytic degradation of such compounds in water proceeds via polyhydroxylated intermediates which consequently undergo mineralisation, which, from a pollution control perspective is beneficial.The physicochemical properties of the photocatalyst were also shown to be influential. Particularly, differences in the affinity to, and mode of adsorption of the substrate compounds studied gave rise to differences in the extent of oxidation.Analysis of photogenerated oxidation products enabled some mechanistic insight into the course of the semiconductor-mediated reaction.The results obtained allow a useful comparison of the functionalisation of N-Heterocyclic compounds via heterogeneous photocatalytic processes in the absence of water, to those carried out in the presence of water, which gave complete mineralisation.
Keywords: Photodegradation; Titanium dioxide; N-bearing compounds; Aromatic heterocycles; Methyl group functionalisation; Iron-doped titanium dioxide
One-pot synthesis of twist-like helix tungsten–nitrogen-codoped titania photocatalysts with highly improved visible light activity in the abatement of phenol by Jingxia Li; Jianhua Xu; Wei-Lin Dai; Hexing Li; Kangnian Fan (pp. 233-243).
The twist-like helix W,N-codoped TiO2 photocatalysts were prepared by a simple one-pot synthesis route to hydrolysis of titania tetrachloride using ammonium tungstate as tungsten and nitrogen sources. The morphology and microstructure characteristics of W,N-codoped titania photocatalysts with different amount of tungsten doping were characterized by means of BET, TEM, SEM, XPS, UV–vis DRS, PLS and XRD. The probable mechanism of codoping effect is proposed. It is presumed that cooperation of nitrogen and tungsten ions leads to produce new states and narrow the band gap between the valence band and conduction band effectively, which will greatly improve the photocatalytic activity in the visible light region. On the other hand, the tungsten ions with changing valences in the W,N-TiO2 samples are considered to act as trapping sites, which will effectively decrease the recombination rate of photo-induced electrons and holes and then increase the photo-oxidation efficiency of the catalysts. The metal and nonmetal codoped 1%-W,N-TiO2 sample shows the best photocatalytic activity, which is much superior to P25 under both visible and ultraviolet light irradiation. The superior activity of W,N-TiO2 photocatalysts can also be ascribed to the special twist-like helix structure with regular holes on the wall, high surface area, large pore volume and well-crystallized anatase phase.
Keywords: Tungsten and nitrogen codoped titania; Mesoporous material; Red shift; Visible light photocatalysis; Phenol abatement
Oxidation pathways of malachite green by Fe3+-catalyzed electro-Fenton process by Mehmet A. Oturan; Elodie Guivarch; Nihal Oturan; Ignasi Sirés (pp. 244-254).
A very detailed scheme for the Fe3+-catalyzed electro-Fenton mineralization of malachite green as a model triarylmethane dye is presented. Bulk electrolyses of 250-mL aqueous solutions of 0.5mM malachite green with 0.2mM Fe3+ as catalyst have been carried out at room temperature and pH 3.0 under constant current in an undivided cell equipped with a graphite-felt cathode and a Pt anode to assess the performance of the electro-Fenton system. In situ electrogeneration of Fe2+ and H2O2 from quick cathodic reduction of Fe3+ and dissolved O2 (from bubbled compressed air), respectively, allows the formation of the very oxidizing species hydroxyl radical (OH) in the medium from Fenton's reaction. A pseudo-first-order decay kinetics with an apparent rate constant of k1,MG=0.244min−1 was obtained for total destruction of malachite green by action ofOH at 200mA, requiring 22min for total decoloration of the solution. In the same experimental conditions, overall mineralization was reached at 540min. Up to 15 aromatic and short-chain carboxylic acid intermediates were identified along the treatment. The evolution of current efficiency was calculated from the chemical oxygen demand (COD) removal. Based on the time course of most of the by-products and the identification of inorganic ions released, some plausible mineralization pathways are proposed and thoroughly discussed. It has been found that the electro-Fenton degradation of malachite green proceeds via parallel pathways, all of them involving primary splitting of the triaryl structure initiated by attack ofOH on the central carbon, thus yielding two different N-dimethylated benzophenones. Successive cleavage of the aromatic intermediates generates oxalic acid as the ultimate short-chain carboxylic acid, whereas N-demethylation of some of them produces formic acid as well. Oxalic acid and its Fe2+ complexes, as well as formic acid, can be slowly but totally mineralized byOH.
Keywords: Malachite green; Electro-Fenton; Mineralization pathway; Water treatment
Direct NO decomposition over La2− xBa xNiO4 catalysts containing BaCO3 phase by Yujun Zhu; Dong Wang; Fulong Yuan; Guo Zhang; Honggang Fu (pp. 255-263).
La2− xBa xNiO4 ( x≤1.2) catalysts have been prepared by citrate method. XRD patterns and IR spectra indicate that with the doping of Ba, more BaCO3 appears and perovskite-like structure is seriously distorted. In directly decomposing 4% NO, the highest N2 yield is achieved with La1.2Ba0.8NiO4 composed of perovskite-like structure phase and BaCO3 in the absence/presence of oxygen. The results of iodometry and H2-TPR reveal that the increase in Ba causes the increase in Ni3+ content. O2-TPD and NO adsorption tests confirm that Ba doping resulted in the increase in oxygen vacancy (Vo). Thus, the redox capability and the amount of Vo are enhanced. It is suggested that the BaCO3 phase, NO x storage component, contributes to the increase in activity by NO-TPD, NO2-TPD and in situ DRIFT. Thus, BaCO3 plays an important role in quickening up the run of catalytic NO decomposition recycle.
Keywords: Nitrogen oxide; Direct decomposition; La; 2−; x; Ba; x; NiO; 4; Perovskite-like oxide
Effect of organosulphur, organonitrogen and organooxygen compounds on the hydrodechlorination of tetrachloroethylene over Pd/Al2O3 by Elena López; Fernando V. Díez; Salvador Ordóñez (pp. 264-272).
The performance of a 0.5wt.% Pd on alumina catalyst used for the hydrodechlorination of tetrachloroethylene, in presence of model organosulphur (thiophene and butanethiol) organonitrogen (quinoline and n-butylamine) and organooxygen (tetrahydrofurane, isobutanol) compounds, was studied in this work. Experiments were carried out in a continuous fixed bed reactor (space time of 1.8ming/mmol of TTCE) at a pressure of 0.5MPa and a temperature range of 200–300°C. Concentrations of heteroatomic molecules in the range 0.5–5% were used in this study.Organosulphur compounds produce strong inhibition on the TTCE hydrodechlorination, decreasing the conversion and increasing the selectivity for partially dechlorinated compounds (trichloroethylene). However, this effect is shown to be highly reversible, the catalyst almost recovering its initial activity when the sulphur source is removed from the feed. Organonitrogen compounds cause a fast and fatal deactivation of the catalysts, being this effect completely irreversible. Different regeneration procedures were tested, being the treatment with hydrogen at 400°C the only way to partially recover catalytic activity. Finally, organooxygen compounds hardly affect catalyst performance.
Keywords: Tetrachloroethylene; Hydrodechlorination; Pd catalyst; Organosulphur compounds; Organonitrogen compounds; Organooxygen compounds; Hydrotreating
Studies on the activation of hydrogen peroxide for color removal in the presence of a new Cu(II)-polyampholyte heterogeneous catalyst by Juan Manuel Lázaro Martínez; María Florencia Leal Denis; Lidia Leonor Piehl; Emilio Rubín de Celis; Graciela Yolanda Buldain; Viviana Campo Dall’ Orto (pp. 273-283).
In this work we describe the application of a new non-soluble and non-porous complex with copper ion based on ethylene glycol diglycidyl ether (EGDE), methacrylic acid (MAA) and 2-methylimidazole (2MI) in the decolorization of an azo dye Methyl Orange (MO) as a model pollutant at room temperature.The complex with copper ion was studied by ESR and SEM and was tested as a heterogeneous catalyst for H2O2 activation. A possible mechanism of interaction involves the production of hydroxyl radicals (confirmed by ESR), dioxygen and water.The Cu(II)-polyampholyte/H2O2 system acted efficiently in the color removal of MO. The adsorption and oxidative degradation of the azo-based dye followed pseudo-first-order kinetic profiles, and the rate constant for degradation had a second-order dependence on copper ion content in the mixture.A removal of MO higher than 90% was achieved in 20min at pH 7.0, combining 0.8mM of complexed copper ions in the mixture with 24mM hydrogen peroxide.The dye adsorbed on the polyampholyte following a L4-type isotherm with 4.9μmolg−1 maximum loading capacity and 3.1μM dissociation constant for the first monolayer.
Keywords: Abbreviations; Cu(II); copper ion; Cu(II)-poly(EGDE-MAA-2MI); complex between copper ion and the polyampholyte obtained by reaction of ethylene glycol diglycidyl ether, methacrylic acid and 2-methylimidazole; MO; Methyl Orange; H; 2; O; 2; hydrogen peroxide; ESR; electron spin resonance; DMPO; 5,5-dimethyl-1-pyrroline-; N; -oxide; FTIR; Fourier transform infra-red; SEM; scanning electron microscopy; R; coefficient of determination; R; ratio of mass of catalyst to volume of MO solution; k; kinetics constant; t; time of reactionHeterogeneous catalyst; Copper ion; Hydrogen peroxide; Azo dyes; ESR