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Applied Catalysis B, Environmental (v.73, #3-4)
NO SCR with propane and propene on Co-based alumina catalysts prepared by co-precipitation by Fuxiang Zhang; Shujuan Zhang; Naijia Guan; Ellen Schreier; Manfred Richter; Reinhard Eckelt; Rolf Fricke (pp. 209-219).
Homogeneous dispersions and small size of deposited high-content cobalt on alumina were achieved by the co-precipitation method and were well maintained on the cobalt-based binary alumina catalysts with Zn, Ag, Fe, Cu or Ni as modifiers. The component and concentration of deposited cobalt species were characterized by UV–vis, EDX and XPS spectra and found to be greatly related to the Co loading, calcination temperatures and the type of additive metals. The optimal Co loading of 8wt% and calcination temperatures of 800°C were demonstrated. With respect to the single cobalt-based alumina catalyst, the surface concentration of Co2+ on the binary catalysts with addition of Fe, Cu, Ag or Ni was all reduced and accompanying with part conversion of Co2+ to Co3O4 on the Fe and Ni-modified catalysts. A slight enhanced surface Co2+ concentration was only achieved on the Zn-promoted catalyst. It was also demonstrated that for the case of Cu and Fe the additive metals themselves participated in the activation of propene. The octahedral and tetrahedral Co2+ ions were suggested as the common active sites. A maximum deNOx activity of 96% was observed on the 8Co4ZnA800 catalyst at the reaction temperatures of 450°C, and the catalytic performance on the cobalt-based binary alumina catalysts can be described as fellows: CoZn>CoAg, CoNi>Co Cu>CoFe. Based on the in situ DRIFT spectra, different reaction intermediates R–ONO and –NCO besides –NO2 were formed on the 8Co4ZnA800 and 8Co4FeA800 samples, respectively, demonstrating their dissimilar reaction mechanisms.
Keywords: Co-precipitation method; High cobalt content; Homogeneous dispersion; NO SCR
Acridine yellow as solar photocatalyst for enhancing biodegradability and eliminating ferulic acid as model pollutant by Ana M. Amat; Antonio Arques; Francisco Galindo; Miguel A. Miranda; Lucas Santos-Juanes; Rosa F. Vercher; R. Vicente (pp. 220-226).
The possibility of using acridine yellow G (AYG) as solar photocatalyst for wastewater treatment has been examined in this paper. A phenolic compound, namely ferulic acid, has been employed as target pollutant. The effect of pH, concentration of the substrate and photocatalyst has been investigated. Control of pH is critical in the process, as rate constants obtained at pH 3 ( k=0.020min−1) were one order of magnitude higher than in basic media ( k=0.002min−1 at pH 9), due to differences in the absorption spectrum in the UVA–vis region. Under acidic conditions, 80% removal of the substrate was achieved after 3h irradiation, although TOC decrease was moderate (around 20%). Nevertheless important detoxification of the solution was measured, and the remaining organic matter showed an enhanced biodegradability. For this reason, a combination of AYG-driven solar photocatalysis with biological treatment seems a good approach to deal with these effluents. Experimental data are consistent with an electron transfer mechanism between the excited photocatalyst and the substrate: involvement of hydroxyl radicals can be ruled out, and photophysical measurements indicate a quenching of the fluorescence of AYG in the presence of ferulic acid. The rate constant for this process was obtained from the Stern–Volmer equation ( kq=4.4×109M−1s−1). Finally, based on the Rehm–Weller equation, a Δ G=−22.8kcal/mol was calculated, indicating that the process is thermodynamically favourable.
Keywords: Acridine yellow G; Ferulic acid; Photodegradation; Photocatalysis; Solar light; Oxidation; Fluorescence
Surface nano-aggregation and photocatalytic activity of TiO2 on H-type activated carbons by Tulynan Cordero; Jean-Marc Chovelon; Christian Duchamp; Corinne Ferronato; Juan Matos (pp. 227-235).
The main objective of this work is to detect any associative or synergistic effects between TiO2 and activated carbon in 4-chlorophenol photodegradation. Different activated carbons (AC) were prepared from Tabebuia pentaphyla wood by means of physical activation with CO2 or by extensive carbonization under N2 flow at temperatures from 450°C up to 1000°C during 1h. Results indicate a clear correlation between photocatalytic activities of titania with texture and surface chemistry of AC. Kinetic results of 4-chlorophenol photodegradation indicate that for most of mixed TiO2 and AC solids a synergistic effect between both solids is observed. Surface nano-aggregation of TiO2 on AC was observed by scanning electronic microscopy and dispersion of TiO2 nanoparticles was improved as a function of more basic surface pH of AC. In conclusion, an increase of electronic density in carbon support clearly introduces an enhancement in titania's photoactivity for 4CP photodegradation. This beneficial effect indicates that it is possible to obtain clean water in a much shorter period of time by employing some selected AC in conjunction with TiO2.
Keywords: Photocatalysis; 4-Chlorophenol; Titania; Activated carbon; Synergy
Degradation of olive oil mill effluents by catalytic wet air oxidation: 2-Oxidation of p-hydroxyphenylacetic and p-hydroxybenzoic acids over Pt and Ru supported catalysts by D. Pham Minh; G. Aubert; P. Gallezot; M. Besson (pp. 236-246).
Catalytic wet air oxidation of p-hydroxyphenylacetic acid and p-hydroxybenzoic acid, two important pollutants present in the olive oil mill wastewaters, was studied in a batch reactor using platinum and ruthenium catalysts supported on titanium and zirconium oxides at 140°C and 50bar of total air pressure. Reaction pathways for the oxidation of these two substrates were proposed, with formation of different aromatic compounds and short-chain organic acids through hydroxylation and decarboxylation reactions.It was observed that the conversion and the mineralization of these two substrates were markedly affected by the nature of the ruthenium precursor (RuCl3 or Ru(NO)(NO3)3), with the non-chlorine containing salt giving the best performances. Calcination of the catalyst precursor before reduction was detrimental. The nature of the metallic precursor (H2PtCl6 or Pt(NH3)4(NO3)2) had little influence on the catalytic properties of platinum catalysts, whereas the textural properties of the support were an important factor.
Keywords: Wet air oxidation; Olive oil mill effluents; Platinum catalysts; Ruthenium catalysts; p; -Hydroxyphenylacetic acid; p; -Hydroxybenzoic acid
Effect of Ru on LaCoO3 perovskite-derived catalyst properties tested in oxidative reforming of diesel by R.M. Navarro; M.C. Alvarez-Galvan; J.A. Villoria; I.D. González-Jiménez; F. Rosa; J.L.G. Fierro (pp. 247-258).
The oxidative reforming of diesel over Co/La2O3 and Ru–Co/La2O3 catalysts derived from LaCoO3 perovskite precursors was studied. Physicochemical characterization by XPS, TPR and XRD revealed that the incorporation of Ru to LaCoO3 produces changes in LaCoO3 evidenced by a smaller size of the LaCoO3 particles and cobalt segregation on the LaCoO3 surface. The modifications in the structure of LaCoO3 induced by the addition of Ru directly affect the dispersion and morphology of Co particles developed under the reaction. The active phases derived from pretreatment of perovskites evolve differently with time on stream, being observed that the presence of a greater proportion of perovskite phase in the Ru/LaCoO3 sample produces an increase in catalyst stability. TPD-MS analysis also indicates that bulk oxygen release from the Ru–Co/La2O3 sample could improve its catalytic behaviour. The characterization of used samples reveals that improvements in the cobalt surface concentration and Co–La2O3 interactions contribute to the better catalytic stability of the Ru–Co/La2O3-derived catalyst.
Keywords: LaCoO; 3; perovskite; Ru; Oxidative reforming; Diesel; Hydrogen production
Optimisation of degradation conditions of 1,8-diazabicyclo[5.4.0]undec-7-ene in water and reaction kinetics analysis using a cocurrent downflow contactor photocatalytic reactor by Idoko J. Ochuma; Robert P. Fishwick; Joseph Wood; J. Mike Winterbottom (pp. 259-268).
The photocatalytic degradation of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU, a non-biodegradable nitrogenous organic compound) in water was optimised under UV radiation using titanium dioxide photocatalyst. The reactor used was a pilot scale cocurrent downflow contactor photocatalytic reactor (CDCPR), a system offering very high mass transfer efficiency. The effect of photocatalyst loading, initial substrate concentration, temperature, pH, and different combinations of UV, O2, H2O2 and TiO2 on the photocatalytic oxidation of DBU was investigated. The TiO2 photocatalyst used was Degussa VP Aeroperl P25/20, a granulated form of Degussa P-25, recently developed to ameliorate downstream catalyst separation problems. The CDCPR was fitted with an internally and vertically mounted 1.0kW UV lamp. The reactions were carried out at 40–60°C and 1barg, with the reactor being operated in closed loop recycle mode and suspended photocatalyst being re-circulated. Optimisation of reaction conditions using a combination of TiO2, UV radiation and O2 gave the most rapid degradation and mineralisation of the DBU in comparison with other processes. Under optimised conditions, 100% degradation of DBU was achieved in 45min, with a quantum yield of 7.39, using a 1kW lamp, 0.5g/dm3 TiO2, 100mg/dm3 DBU, 1barg, 50°C and pH of 3.17. Investigating the reaction pathway and its modelling showed a first order dependency, incorporating the effect of first intermediates of degradation. The activation energy was found to be 54.68kJmol−1 showing a significant influence of temperature on the photocatalytic degradation of DBU.
Keywords: Cocurrent downflow contactor; Optimisation; Photocatalysis; Environment; Kinetics
Oxidative gas phase carbonylation of methanol to dimethyl carbonate over chloride-free Cu-impregnated zeolite Y catalysts at elevated pressure by M. Richter; M.J.G. Fait; R. Eckelt; E. Schreier; M. Schneider; M.-M. Pohl; R. Fricke (pp. 269-281).
Incipient wetness impregnation of zeolite Y with copper(II) nitrate solution and inert activation at 650°C led to active catalysts for the oxidative carbonylation of methanol to dimethyl carbonate in the gas phase. Activities were measured under elevated pressure (0.4–1.6MPa) with feed compositions of CO/MeOH/O2=40/20/6–1.5vol.% (balanced by N2) over zeolite Y loaded with 10–17wt.% copper. It could be shown that inert activation at 650°C enhanced the activity, and that Cu loading of 14–17wt.% gave the best performance. By combined XRD, TEM, TPR and DRIFT characterization it was found that the inert activation initiated dispersion of crystalline CuO, auto-reduction of Cu2+ to Cu+ and redistribution of copper ions with enrichment inside the supercages of the zeolite. The O2 content of the feed was found to control the selectivity to dimethyl carbonate. Dimethyl carbonate selectivities of 70–75% were achieved within the temperature range of 140–170°C at an O2 content of 1.5vol.%. This allowed space-time yields of dimethyl carbonate up to 632glcat−1h−1 at methanol conversions of 5–12%. Formation of the main side product, dimethoxymethane, was surprisingly affected by CO, which is not in line with suggested reaction pathways. A mechanism is proposed including formation of surface carbonate structures as common intermediate.
Keywords: Carbonylation; Methanol; Dimethyl carbonate; Impregnated copper faujasite; Inert activation; Chloride-free
Performance and characterization of supported metal catalysts for complete oxidation of formaldehyde at low temperatures by Jiaxi Peng; Shudong Wang (pp. 282-291).
Activities of a series of metals (Pt, Pd, Rh, Cu, Mn) supported on TiO2 were investigated for the catalytic oxidation of formaldehyde. Among them, Pt/TiO2 was found to be the most promising catalyst. Nitrogen adsorption, hydrogen chemisorption, X-ray diffraction (XRD), transmission electron microscopy (TEM) and temperature programmed reduction (TPR) by H2 were used to characterize the platinum catalysts. Using Ce0.8Zr0.2O2, Ce0.2Zr0.8O2, SiO2 as supports instead of TiO2, the activity sequence of 0.6wt.% platinum with respect to the supports is TiO2>SiO2>Ce0.8Zr0.2O2>Ce0.2Zr0.8O2, and this appears to be correlated with the dispersion of platinum on supports rather than the specific surface areas of the catalysts. Platinum loading on TiO2 has a great effect on the catalytic activity, and 0.6wt.% Pt/TiO2 catalyst was observed to be the most active, which could be attributed to the well-dispersed platinum surface phase. The reduction temperature greatly affects the particle size and, consequently, the catalytic activity. The smaller particle size of platinum, due to its high dispersion on support, has a positive effect on catalytic performance. Increasing formaldehyde concentration and space velocity exhibits an inhibiting effect on the catalytic activity.
Keywords: Catalytic oxidation; Formaldehyde; Titania; Supported platinum catalyst
Structure and photocatalytic performance of TiO2/clay nanocomposites for the degradation of dimethachlor by V. Belessi; D. Lambropoulou; I. Konstantinou; A. Katsoulidis; P. Pomonis; D. Petridis; T. Albanis (pp. 292-299).
In the present study TiO2/clay composites were synthesized by dispersion of TiO2 on the surfaces of a natural montmorillonite and a synthetic hectorite in order to increase the sorption ability of TiO2 and therefore its photocatalytic action. Six materials with different loading in TiO2 (15, 30 and 55wt%) were prepared and characterized by several analytical techniques including XRD, BET and SEM analysis. The synthetic procedure allows the development of delaminated layers for hectorite–TiO2 samples, while in the case of montmorillonite–TiO2 composites we have the formation of a more lamellar-like aggregation. It was found that, the greater the percentage of TiO2, the greater the pore volume and the specific surface area of the montmorillonite–TiO2 samples. On the contrary, in the case of hectorite–TiO2 samples, as the content of TiO2 increases, the surface area and pore volume decreases. The photocatalytic efficiency of the nanocomposite catalysts was evaluated using a chloroacetanilide herbicide (dimethachlor) in water as model compound. The primary degradation of dimethachlor followed pseudo-first-order kinetics according to the Langmuir–Hinshelwood model. All supported catalysts exhibit good photodegradation efficiency and their overall removal efficiency per mass of TiO2 was better than that of bare TiO2 produced by the sol–gel method. In conclusion, together with their good sedimentation ability the composite materials could be considered as a promising alternative for the removal of organic water contaminants.
Keywords: TiO; 2; photocatalysts; Nanocomposites; Clays; Organic pollutants
High rates of CO and hydrocarbon oxidation and NO reduction by CO over Ti0.99Pd0.01O1.99 by Sounak Roy; A. Marimuthu; M.S. Hegde; Giridhar Madras (pp. 300-310).
This study aims at synthesizing a new by substituting 1atom% Pd2+ in ionic state in TiO2 in the form of Ti0.99Pd0.01O1.99 with oxide-ion vacancy. The catalyst was synthesized by solution combustion method and was characterized by XRD and XPS. The catalytic activity was investigated by performing CO oxidation, hydrocarbon oxidation and NO reduction. A reaction mechanism for CO oxidation by O2 and NO reduction by CO was proposed. The model based on CO adsorption on Pd2+ and dissociative chemisorption of O2 in the oxide-ion vacancy for CO oxidation reaction fitted the experimental for CO oxidation. For NO reduction in presence of CO, the model based on competitive adsorption of NO and CO on Pd2+, NO chemisorption and dissociation on oxide-ion vacancy fitted the experimental data. The rate parameters obtained from the model indicated that the reactions were much faster over this catalyst compared to other catalysts reported in the literature. The selectivity of N2, defined as the ratio of the formation of N2 and formation of N2 and N2O, was very high compared to other catalysts and 100% selectivity was reached at temperature of 350°C and above. As the N2O+CO reaction is an intermediate reaction for NO+CO reaction, it was also studied as an isolated reaction and the rate of the isolated reaction was less than that of intermediate reaction.
Keywords: Ionic substitution; CO and hydrocarbon oxidation; CO; +; NO reaction; CO; +; N; 2; O reaction; Kinetic models
Desulfurization of diesel via the H2O2 oxidation of aromatic sulfides to sulfones using a tungstate catalyst by Farhan Al-Shahrani; Tiancun Xiao; Simon A. Llewellyn; Sami Barri; Zheng Jiang; Huahong Shi; Gary Martinie; Malcolm L.H. Green (pp. 311-316).
A simplified oxidative desulfurizataion (ODS) catalytic system composed of Na2WO4, 30% H2O2 and CH3CO2H has been found suitable for the deep removal of sulfur in diesel. By combining ODS and methanol extraction, the sulfur level in a commercial diesel has been reduced from 1100ppm to 40ppm. Treatment of model solutions of octane containing dibenzothiophene and 4,6-dimethyl dibenzothiophene with our ODS system shows 100% conversion of the thiophenes to sulfones at 70°C in less than 1h.
Keywords: Sulfur removal; Oxidative desulfurizataion; Deep removal of sulfur; Sodium tungstate; Hydrogen peroxide; Sulfone
Biodiesel from sunflower oil by using activated calcium oxide by M. López Granados; M.D. Zafra Poves; D. Martín Alonso; R. Mariscal; F. Cabello Galisteo; R. Moreno-Tost; J. Santamaría; J.L.G. Fierro (pp. 317-326).
This work studies the activity of activated CaO as a catalyst in the production of biodiesel by transesterification of triglycerides with methanol. Three basic aspects were investigated: the role of H2O and CO2 in the deterioration of the catalytic performance by contact with room air, the stability of the catalyst by reutilization in successive runs and the heterogeneous character of the catalytic reaction. The characterization by X-ray diffraction (XRD), evolved gas analysis by mass spectrometry (EGA-MS) during heating the sample under programmed temperature, X-ray photoelectron (XPS) and Fourier transform-infrared (FT-IR) spectroscopies allowed to concluding that CaO is rapidly hydrated and carbonated by contact with room air. Few minutes are enough to chemisorb significant amount of H2O and CO2. It is demonstrated that the CO2 is the main deactivating agent whereas the negative effect water is less important. As a matter of fact the surface of the activated catalyst is better described as an inner core of CaO particles covered by very few layers of Ca(OH)2. The activation by outgassing at temperatures ≥973K are required to revert the CO2 poisoning. The catalyst can be reused for several runs without significant deactivation. The catalytic reaction is the result of the heterogeneous and homogeneous contributions. Part of the reaction takes place on basic sites at the surface of the catalyst, the rest is due to the dissolution of the activated CaO in methanol that creates homogeneous leached active species.
Keywords: Lime; CaO; Ca(OH); 2; CaCO; 3; Transesterification; Fatty acid methyl esters (FAME); Heterogeneous basic catalyst
Catalytic reduction of NO x with H2/CO/CH4 over PdMOR catalysts by Johannis A.Z. Pieterse; Saskia Booneveld (pp. 327-335).
Conversion of NO x with reducing agents H2, CO and CH4, with and without O2, H2O, and CO2 were studied with catalysts based on MOR zeolite loaded with palladium and cerium. The catalysts reached high NO x to N2 conversion with H2 and CO (>90% conversion and N2 selectivity) range under lean conditions. The formation of N2O is absent in the presence of both H2 and CO together with oxygen in the feed, which will be the case in lean engine exhaust. PdMOR shows synergic co-operation between H2 and CO at 450–500K. The positive effect of cerium is significant in the case of H2 and CH4 reducing agent but is less obvious with H2/CO mixture and under lean conditions. Cerium lowers the reducibility of Pd species in the zeolite micropores. The catalysts showed excellent stability at temperatures up to 673K in a feed with 2500ppm CH4, 500ppm NO, 5% O2, 10% H2O (0–1% H2), N2 balance but deactivation is noticed at higher temperatures. Combining results of the present study with those of previous studies it shows that the PdMOR-based catalysts are good catalysts for NO x reduction with H2, CO, hydrocarbons, alcohols and aldehydes under lean conditions at temperatures up to 673K.
Keywords: NO; x; Palladium; Cerium; Mordenite H; 2; CO; CH; 4; SCR; Stability
Syngas production from butane using a flame-made Rh/Ce0.5Zr0.5O2 catalyst by Nico Hotz; Michael J. Stutz; Stefan Loher; Wendelin J. Stark; Dimos Poulikakos (pp. 336-344).
The capability of flame-made Rh/Ce0.5Zr0.5O2 nanoparticles catalyzing the production of H2- and CO-rich syngas from butane was investigated for different Rh loadings (0–2.0wt% Rh) and two different ceramic fibers (Al2O3/SiO2 and SiO2) as plugging material in a packed bed reactor for a temperature range from 225 to 750°C. The main goal of this study was the efficient processing of butane at temperatures between 500 and 600°C for a micro-intermediate-temperature SOFC system. Our results showed that Rh/Ce0.5Zr0.5O2 nanoparticles offer a very promising material for butane-to-syngas conversion with complete butane conversion and a hydrogen yield of 77% at 600°C. The catalytic performance of packed beds strongly depended on the use of either Al2O3/SiO2 or SiO2 fiber plugs. This astonishing effect could be attributed to the interplay of homogeneous and heterogeneous chemical reactions during the high-temperatures within the reactor.
Keywords: Butane processing; Syngas; Catalytic nanoparticles; Rhodium catalyst; Micro-reactor; Fuel cell; Intermediate-temperature SOFC
Efficient destruction of bacteria with Ti(IV) and antibacterial ions in co-substituted hydroxyapatite films by Chun Hu; Jian Guo; Jiuhui Qu; Xuexiang Hu (pp. 345-353).
Hydroxyapatite (Ca10(PO4)6(OH)2: HAP) was co-substituted with Ti(IV) and antibacterial ions (Ag+, Cu2+ or Zn2+) (HAPTiM), by coprecipitation and ion-exchange methods. Both HAPTiAg and HAPTiCu coated on porous spumous nickel film showed high efficiency for killing Escherichia coli and Staphylococcus aureus in the dark and under weak UVA irradiation, respectively. Moreover, their bactericidal activities were much higher than that of P25-TiO2 film. The studies of ESR revealed that not only O2− was formed on HAPTiM, HAPTi, HAP and P25-TiO2 films under weak UVA irradiation, but also at ambient temperature without light O2− was generated on HAPTiCu, HAPTiAg, and HAPTi. The redox couples of Cu0/Cu2+ and Ag0/Ag+ in the structure of HAPTiCu (Ag) caused the transfer of electron leading to the O2− generation under the above conditions. The higher bactericidal activities of HAPTiM were due to the synergy of the oxidation role of the O2− and the bacteriostatic action of antibacterial ions. The process of the damage of the cell wall and the cell membrane was directly observed by TEM, and further confirmed by the determination of potassium ion (K+) leakage from the killed bacteria.
Keywords: Bacteriostatic action; Bactericidal activity; Hydroxyapatite; Synergistic bactericidal mechanism
Efficient destruction of pathogenic bacteria with AgBr/TiO2 under visible light irradiation by Yongqing Lan; Chun Hu; Xuexiang Hu; Jiuhui Qu (pp. 354-360).
The photocatalytic inactivation of pathogenic bacteria in water was investigated systematically with AgBr/TiO2 under visible light ( λ>420nm) irradiation. The catalyst was found to be highly effective for the killing of Escherichia coli, a Gram-negative bacterium, and Staphylococcus aureus, a Gram-positive bacterium. The decomposition of the cell wall and cell membrane was directly observed by TEM and further confirmed by K+ leakage from the inactivated bacteria. A possible cell damage mechanism by visible light-driven AgBr/TiO2 is proposed. In addition, the effects of pH, inorganic ions on bacterial photocatalytic inactivation were investigated. The electrostatic force interaction of the bacteria–catalyst is crucial for the efficiency of disinfection. Moreover, AgBr/TiO2 supported on porous nickel showed much higher bactericidal activity than fixed P25 TiO2 under visible or near UV light irradiation.
Keywords: Bactericidal mechanism; Interaction of bacteria–catalyst; Pathogenic bacteria; Visible light-driven
Erratum to “The kinetics of phenol decomposition under UV irradiation with and without H2O2 on TiO2, Fe–TiO2 and Fe–C–TiO2 photocatalysts” [Appl. Catal. B: Environ. 65 (2006) 86–92]
by Beata Tryba; Antoni W. Morawski; Michio Inagaki; Masahiro Toyoda (pp. 361-361).