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Applied Catalysis B, Environmental (v.76, #3-4)
Low temperature catalytic oxidation of aldehydes using wood fly ash and molecular oxygen by Praveen Kolar; James R. Kastner; Joby Miller (pp. 203-217).
Aldehydes, such a 2-methylbutanal (2-MB) and 3-methylbutanal (3-MB), are odorous and regulated VOCs generated in the poultry rendering process that are ineffectively removed in chemical wet scrubbers. It was theorized that wood fly ash or selective crystalline phases in the ash could act to catalyze the oxidation of aldehydes at room temperature in the presence of ClO2, resulting in a low-cost/energy air pollution control method. Results indicate that wood fly ash catalyzed the oxidation (i.e., breakdown) of 2-MB and 3-MB both in the presence of ClO2 and with just O2 (i.e., air) itself, potentially via a free radical mechanism. Aldehyde oxidation did not occur at measurable rates without the wood fly ash or activated carbon. The presence of ClO2 did not increase the rate, but altered the end products of oxidation. Wood fly ash also catalyzed the oxidation of 2-MB in the presence of air, leading to the appearance of 2-butanone, compared to acetone from 3-MB. Contact times of 30s reduced 3-MB levels by ∼40% in bench scale, batch reactors. Similar results were found using activated charcoal (i.e., in terms of contact times), except that higher molecular weight compounds appeared to be formed. Continuous catalytic oxidation of 3-MB using wood fly ash was also demonstrated in a fixed-bed reactor at room temperature; the overall oxidation rate appeared to be first order with respect to 3-MB and a representative conversion of 20% at an inlet concentration of 67ppmv and 2s residence time (GHSV 18001/h, 25°C, 1atm) was measured. Results indicate the potential of using inexpensive solid waste materials to breakdown C5 aldehydes in rendering emissions to CO2, H2O, and less odor offensive compounds, but a carbon balance on the reaction and complete identification of end products are required for implementation.
Keywords: Catalytic autoxidation; Room temperature; Activated carbon; Wood fly ash; Aldehydes
Efficient degradation of 4-nitrophenol by using functionalized porphyrin-TiO2 photocatalysts under visible irradiation by Chen Wang; Jun Li; Giuseppe Mele; Gao-Mai Yang; Feng-Xing Zhang; Leonardo Palmisano; Giuseppe Vasapollo (pp. 218-226).
The novel porphyrins 5,10,15,20-tetra-[4-(3-phenoxy)-propoxy]phenyl porphyrin, H2Pp(a) and 5,10,15,20-tetra-[2-(3-phenoxy)-propoxy]phenyl porphyrin, H2Pp(b) and their corresponding copper(II) complexes CuPp(a), CuPp(b) were synthesized and characterized by using various spectroscopic techniques. The photocatalytic activity of polycrystalline TiO2 samples impregnated with H2Pp(a), H2Pp(b), CuPp(a) and CuPp(b) as sensitizers have been investigated by carrying out the photo-degradation of 4-nitrophenol (4-NP) as a probe reaction in aqueous suspension and under visible light. The maximum photocatalytic activity was obtained using TiO2 loaded with a monolayer of the copper porphyrin CuPp(b) in the amount of 18μmol per gram of TiO2.The photocatalytic efficiency decreased in the following order: TiO2-CuPp(b), TiO2-CuPp(a), TiO2-H2Pp(b), TiO2-H2Pp(a). A possible mechanism of the photocatalytic degradation is also proposed.
Keywords: Porphyrin; Cu(II)-porphyrin; Titanium dioxide; Photocatalysis; 4-Nitrophenol; Photo-degradation
Preparation of nanosized Mn3O4/SBA-15 catalyst for complete oxidation of low concentration EtOH in aqueous solution with H2O2 by Yi-Fan Han; Fengxi Chen; Kanaparthi Ramesh; Ziyi Zhong; Effendi Widjaja; Luwei Chen (pp. 227-234).
A new heterogeneous Fenton-like system consisting of nano-composite Mn3O4/SBA-15 catalyst has been developed for the complete oxidation of low concentration ethanol (100ppm) by H2O2 in aqueous solution. A novel preparation method has been developed to synthesize nanoparticles of Mn3O4 by thermolysis of manganese (II) acetylacetonate on SBA-15. Mn3O4/SBA-15 was characterized by various techniques like TEM, XRD, Raman spectroscopy and N2 adsorption isotherms. TEM images demonstrate that Mn3O4 nanocrystals located mainly inside the SBA-15 pores. The reaction rate for ethanol oxidation can be strongly affected by several factors, including reaction temperature, pH value, catalyst/solution ratio and concentration of ethanol. A plausible reaction mechanism has been proposed in order to explain the kinetic data. The rate for the reaction is supposed to associate with the concentration of intermediates (radicals:OH, O2− andHO2) that are derived from the decomposition of H2O2 during reaction. The complete oxidation of ethanol can be remarkably improved only under the circumstances: (i) the intermediates are stabilized, such as stronger acidic conditions and high temperature or (ii) scavenging those radicals is reduced, such as less amount of catalyst and high concentration of reactant. Nevertheless, the reactivity of the presented catalytic system is still lower comparing to the conventional homogenous Fenton process, Fe2+/H2O2. A possible reason is that the concentration of intermediates in the latter is relatively high.
Keywords: Hydrogen peroxide; Fenton catalyst; Complete oxidation of ethanol; Mn; 3; O; 4; /SBA-15
Catalytic effect of platinum on the kinetics of carbon oxidation by NO2 and O2 by M. Jeguirim; V. Tschamber; P. Ehrburger (pp. 235-240).
The effect of a commercial Pt/Al2O3 catalyst on the oxidation by NO2 and O2 of a model soot (carbon black) in conditions close to automotive exhaust gas aftertreatment is investigated. Isothermal oxidations of a physical mixture of carbon black and catalyst in a fixed bed reactor were performed in the temperature range 300–450°C. The experimental results indicate that no significant effect of the Pt catalyst on the direct oxidation of carbon by O2 and NO2 is observed. However, in presence of NO2–O2 mixture, it is found that besides the well established catalytic reoxidation of NO into NO2, Pt also exerts a catalytic effect on the cooperative carbon–NO2–O2 oxidation reaction. An overall mechanism involving the formation of atomic oxygen over Pt sites followed by its transfer to the carbon surface is established. Thus, the presence of Pt catalyst increases the surface concentration of –C(O) complexes which then react with NO2 leading to an enhanced carbon consumption. The resulting kinetic equation allows to model more precisely the catalytic regeneration of soot traps for automotive applications.
Keywords: Soot oxidation; Platinum; NO; 2; O; 2; Reaction mechanism; Activation energy
Effect of hydrogen on reaction intermediates in the selective catalytic reduction of NO x by C3H6 by Xiuli Zhang; Yunbo Yu; Hong He (pp. 241-247).
Selective catalytic reduction of NO x by C3H6 in the presence of H2 over Ag/Al2O3 was investigated using in situ DRIFTS and GC–MS measurements. The addition of H2 promoted the partial oxidation of C3H6 to enolic species, the formation of –NCO and the reactions of enolic species and –NCO with NO x on Ag/Al2O3 surface at low temperatures. Based on the results, we proposed reaction mechanism to explain the promotional effect of H2 on the SCR of NO x by C3H6 over Ag/Al2O3 catalyst.
Keywords: Selective catalytic reduction; NO; x; Ag/Al; 2; O; 3; Enolic species; H; 2; In situ DRIFTS; GC–MS
Influence of preparation conditions of nano-crystalline ceria catalysts on the total oxidation of naphthalene, a model polycyclic aromatic hydrocarbon by Edwin Ntainjua Ndifor; Tomas Garcia; Benjamin Solsona; Stuart H. Taylor (pp. 248-256).
Nano-crystalline ceria catalysts prepared by homogeneous precipitation with urea were tested for the total oxidation of naphthalene, a model polycyclic aromatic hydrocarbon (PAH). Systematic variation of preparation conditions, including calcination temperature, calcination time and aging time, resulted in differences in surface area, reducibility, morphology and crystallite size of the CeO2 catalyst and hence differences in catalytic performance. A combination of high surface area, small crystallite size and high oxygen defect concentration was found to favor the efficiency of the ceria catalysts for the total oxidation of naphthalene. Optimum preparation conditions for this study included: aging time of 12h, calcination temperature of 500°C and a calcination time of 6h.
Keywords: Catalytic oxidation; Ceria; Naphthalene; PAHs
Photocatalytic inactivation of Escherischia coli by A.K. Benabbou; Z. Derriche; C. Felix; P. Lejeune; C. Guillard (pp. 257-263).
The efficiency of photocatalytic disinfection, used to inactivate Escherischia coli K12 under different physico-chemical parameters, was examined. The photocatalyst chosen was the semiconductor TiO2 degussa P25 and the irradiation was produced by an HPK 125 lamp. The effect of titania concentration was investigated using two E. coli concentrations. The photocatalyst concentration ranged from 0.1 to 2.5g/L. The evolution of E. coli inactivation as function of time was discussed depending on the E. coli and TiO2 concentrations. The optimal concentration of the photocatalyst, 0.25g/L, is lower than that necessary to absorb all photons and to degrade the organic compounds. Some hypotheses are presented to explain this behaviour. The effect of the different domains of UV light (UVA, UVB, and UVC) was also studied and modification of the light irradiation intensity is discussed. No bacteria photolysis was obtained with UVA but the use UVC had, on the contrary, a detrimental effect on bacteria survival. The addition of titania at a low concentration, 0.25g/L, improved the inactivation of E. coli in the presence of UVA and UVB, but a detrimental effect was observed under UVC. The disinfection efficiency increases as a function of light intensity, whatever the photocatalytic conditions (different TiO2 concentrations and different UV domains). No bacterial growth was observed after disinfection, whether the system contained titania or not.
Keywords: Photocatalysis; Microorganism; E. coli; Inactivation; Disinfection
Preparation of rough anatase films and the evaluation of their photocatalytic efficiencies by Jorge Medina-Valtierra; Claudio Frausto-Reyes; Jorge Ramírez-Ortíz; Edgar Moctezuma; Facundo Ruiz (pp. 264-274).
Sol–gel derived rough anatase films without controlled particle sizes were prepared by surfactant templating. The coating sol–gel was obtained by hydrolysis of Ti(OC3H7)4 in ethanol/HNO3 solution. The gel films, prepared by dipping glass substrates in surfactant solutions, were dried after immersion under an atmospheric pressure. The rough films of TiO2 anatase were obtained after calcining at 500°C. The resultant films were transparent, semitransparent or opaque and 136–402nm thick. It was found that the TiO2 films prepared from the sol–gel with surfactant showed a granular nanostructure, and they were composed of regular particles, for example; between 50 and 70nm. The roughness of the films was found to depend on the surfactant concentration in the sol–gel solution and can show a roughness between 0.82 and near of 17nm. The photocatalytic activity of the films for the degradation and mineralization of phenol, an industrial pollutant, in water and under 365nm irradiation was improved by the surfactant modification. Kinetic analysis of degradation and mineralization of phenol in water were employed to evaluate the different TiO2 films under the same experimental conditions. The global photonic efficiency for degradation and mineralization of phenol ξg, was calculated to facilitate comparison with a TiO2 standard photocatalyst named Degussa P-25.
Keywords: Sol–gel; Anatase; Films; Roughness; Photocatalyst; Efficiency
Plasma-assisted catalysis total oxidation of trichloroethylene over gold nano-particles embedded in SBA-15 catalysts by Monica Magureanu; Nicolae Bogdan Mandache; Juncheng Hu; Ryan Richards; Mihaela Florea; Vasile I. Parvulescu (pp. 275-281).
The oxidative decomposition of trichloroethylene (TCE) in dry air was investigated in non-thermal plasma at atmospheric pressure and room temperature, both in the absence and in the presence of gold containing mesoporous silica (GMS) catalysts. In the absence of catalyst, TCE removal reached 100% for average powers dissipated in the plasma above 3W, for a TCE concentration of 430ppmv. Carbon monoxide and carbon dioxide were the major reaction products with CO2 selectivity up to 25% and CO selectivity up to 70%. In the presence of gold containing mesoporous catalysts, the concentrations of CO and CO2 increased as compared to those obtained with plasma alone. The GMS catalysts can dissociate ozone produced in plasma to oxygen radicals that decompose TCE. Among these catalysts, the one containing the least amount of Au (0.5% GMS) showed the best catalytic performance. In the presence of ozone generated in the plasma, isolated gold cations might play a critical role for the catalytic behavior.
Keywords: Chlorinated volatile organic compounds; Trichloroethylene; Non-equilibrium plasma; Dielectric barrier discharge; Gold catalysts
Characteristics of Fe-exchanged natural zeolites for the decomposition of N2O and its selective catalytic reduction with NH3 by Ayten Ates (pp. 282-290).
Natural zeolites obtained from various regions of Turkey and their iron-exchanged forms were characterised by XRD, BET, H2-TPR and NH3-TPD methods. Transient experiments with N2O showed that the iron introduced into natural zeolites have appreciable oxygen deposition capacity due to isolated iron species involved. Atomic surface oxygen species in these zeolites are formed at 250°C, which is released through increasing the temperature until 900°C, similar to Fe-containing ZSM-5 zeolite. The steady-state experiments indicate that the iron-containing zeolite of the Yavu-Sivas region, in particular, has high activity in selective catalytic reduction of N2O with NH3 as a consequence of isolated cationic and/or dimeric iron content.
Keywords: Natural zeolite; Step experiment; N; 2; O decomposition; NH; 3; SCR
Promoting effect of electroactive polymer supports on the catalytic performances of palladium-based catalysts for nitrite reduction in water by Ibrahim Dodouche; Florence Epron (pp. 291-299).
Conducting polymers, polypyrrole and polyaniline, were used as supports for Pd in order to obtain catalysts with higher performances than a classical Pd/Al2O3 catalyst for application in water treatment. The supports and the catalysts were characterized by elemental analysis, Fourier transformed infra-red spectroscopy (FTIR), transmission electron microscopy (TEM) coupled with energy dispersive X-ray spectrometry (EDX), X-ray diffraction (XRD) and by their activity in nitrite reduction. It was demonstrated that these conducting polymers can be advantageously used as support for noble metals such as palladium. Indeed, the redox properties of these supports allow the deposition of a part of palladium directly in the reduced state and also a direct reduction of nitrite, even if this reduction is not complete. The Pd/polyaniline and Pd/polypyrrole catalysts are much more active than the classical Pd/Al2O3 catalyst with less ammonium ions. These better performances were explained by the redox and ion-exchange properties of the conducting polymers allowing the exchange between the hydroxides produced and the dopant anion of the conducting polymer. The ion-exchange property of the polymer depends on its oxidation state which is directly linked to the polymerization conditions and then can be easily modulated.
Keywords: Electroactive polymers; Palladium; Catalytic properties; Nitrite reduction
High thermal conductive β-SiC for selective oxidation of H2S: A new support for exothermal reactions by P. Nguyen; D. Edouard; J.-M. Nhut; M.J. Ledoux; Ch. Pham; C. Pham-Huu (pp. 300-310).
Iron supported on a medium surface area silicon carbide (β-SiC) is a high efficiency catalyst for the selective oxidation of hydrogen sulphide into elemental sulphur at reaction temperatures above the sulphur dew point. The strong interaction between the topmost layer of the support and the active phase allows a high dispersion of the iron-based catalyst particles which provide a high active phase-reactants contact surface to maintain the high desulphurization activity even at high space velocity. The high thermal conductivity of the silicon carbide plays an important role in the maintenance of the high selectivity by avoiding the formation of hot spots on the catalyst surface which could favor secondary reactions. On the other hand, insulator supports such as alumina exhibits a poor selectivity due to catalyst surface temperature runaway. The thermal profile of the bed temperature calculated by a simple heterogeneous model was in agreement with the previous hypothesis. The intrinsic chemical inertness and the surface property of the material render the silicon carbide usable in very drastic conditions, i.e. in a corrosive atmosphere (2% H2S) and with a low O2/H2S ratio compared to silica and/or alumina based catalysts. In such conditions, the catalyst remains stable over 1500h on stream with high sulphur yield up to 95%. These performances make silicon carbide based catalysts the most promising catalyst support suitable for the high-temperature selective oxidation process.
Keywords: Silicon carbide; Selective oxidation of H; 2; S; Iron based catalyst; Thermal conductivity; Modelization and simulation
Selective catalytic reduction of NO by ammonia using mesoporous Fe-containing HZSM-5 and HZSM-12 zeolite catalysts: An option for automotive applications by A.L. Kustov; T.W. Hansen; M. Kustova; C.H. Christensen (pp. 311-319).
Mesoporous and conventional Fe-containing ZSM-5 and ZSM-12 catalysts (0.5–8wt% Fe) were prepared using a simple impregnation method and tested in the selective catalytic reduction (SCR) of NO with NH3. It was found that for both Fe/HZSM-5 and Fe/HZSM-12 catalysts with similar Fe contents, the activity of the mesoporous samples in NO SCR with NH3 is significantly higher than for conventional samples. Such a difference in the activity is probably related with the better diffusion of reactants and products in the mesopores and better dispersion of the iron particles in the mesoporous zeolite as was confirmed by SEM analysis. Moreover, the maximum activity for the mesoporous zeolites is found at higher Fe concentrations than for the conventional zeolites. This also illustrates that the mesoporous zeolites allow a better dispersion of the metal component than the conventional zeolites. Finally, the influence of different pretreatment conditions on the catalytic activity was studied and interestingly, it was found that it is possible to increase the SCR performance significantly by preactivation of the catalysts in a 1% NH3/N2 mixture at 500°C for 5h. After preactivation, the activity of mesoporous 6wt% Fe/HZSM-5 and 6wt% Fe/HZSM-12 catalyst is comparable with that of traditional 3wt% V2O5/TiO2 catalyst used as a reference at temperatures below 400°C and even more active at higher temperatures.
Keywords: DeNO; x; catalysts; NO SCR with ammonia; Mesoporous zeolites; Fe/HZSM-5; Fe/HZSM-12; Preactivation
Investigation of a Ba0.5Sr0.5Co0.8Fe0.2O3− δ based cathode SOFC by Aiyu Yan; Vasiliki Maragou; Antonino Arico; Mojie Cheng; Panagiotis Tsiakaras (pp. 320-327).
The effect of carbon dioxide on the chemical stability of a Ba0.5Sr0.5Co0.8Fe0.2O3− δ cathode in the real reaction environment at 450°C was investigated by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), temperature programmed desorption (TPD), X-ray diffraction (XRD) and electrochemical impedance spectra (EIS) techniques. It was found that the presence even of very small quantities of CO2 seriously deteriorates the fuel cell performance at 450°C. XPS, TPD and XRD results strongly evidenced the formation of carbonates involving strontium and possibly barium after the BSCF cathode was operated in 1% CO2/O2 gas mixture at 450°C for 24h. SEM-EDX analysis of the BSCF cathode surface, after treatment in CO2/O2 environment at 450°C, showed small particles on the surface probably associated with a carbonate phase and a segregated phase of the perovskite. The corresponding EDX spectra confirmed the presence of a carbonate layer and also revealed the surface enrichment of strontium and barium elements. EIS results indicated that both ohmic and polarization resistances increased gradually with the introduction of carbon dioxide in the oxidant stream, which could be interpreted by the decreased oxygen reduction kinetics and the formation of carbonate insulating layer.
Keywords: Low and intermediate temperature solid oxide fuel cells; BSCF cathodes; Carbon dioxide effect
Nanocolumnar titania thin films uniquely incorporated with carbon for visible light photocatalysis by Shun-Huei Wang; Ta-Kun Chen; K. Koteswara Rao; Ming-Show Wong (pp. 328-334).
Carbon-doped or carbon-covered titania can enhance photocatalytic performance under visible light. Here we report the first instance of synergistic effect of the carbon incorporation in anatase titania (TiO2− xC x:C) films with both substitutional doping and surface covered characteristics, by reactively co-sputtering Ti metal and graphite targets. The nature of incorporated carbon is characterized by Raman spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. The absorption edge of the carbon incorporated titania thin films shifted from ultraviolet to visible region and directly depended on the carbon content. The photocatalytic performance, e.g., photodegradation of methylene blue (MB), photo-reduction of silver-ions and super hydrophilicity, was greatly enhanced with increasing carbon content. The best photocatalytic activity is obtained in the TiO2− xC x:C film of the most carbon concentration about 9.3at.% with a degradation rate-constant of 0.108h−1 for MB under visible-light illumination.
Keywords: Titanium dioxide; Carbon-doped titania; Carbon-covered titania; Visible-light photocatalyst; Photodegradation; Superhydrophilicity
Synthesis and catalytic properties of Ce0.6Zr0.4O2 solid solutions in the oxidation of soluble organic fraction from diesel engines by Zhaoliang Zhang; Yexin Zhang; Zonggang Mu; Pengfei Yu; Xianzhi Ni; Shilong Wang; Lisheng Zheng (pp. 335-347).
Ce0.6Zr0.4O2 solid solutions were synthesized by co-precipitation, sol–gel like method, solution combustion and surfactant-assistant approaches, respectively. The catalytic properties of bulk and γ-Al2O3 supported Ce0.6Zr0.4O2 solid solutions were studied for the oxidation of soluble organic fractions (SOF) from diesel engines by TG-DTA method. The physicochemical properties were characterized by XRD, BET surface area and pore distribution, SEM, TEM, and particle size distribution techniques. XRD and TEM results show that a Ce0.6Zr0.4O2 solid solution was formed for samples as-prepared and heat-treated at 900°C for 2h in air. The co-precipitation derived Ce0.6Zr0.4O2 has as high BET surface area as 153.71m2/g by controlling preparation conditions. Notable is that the surface area and particle size for fresh Ce0.6Zr0.4O2 ignited at 350°C decreased little after a thermal treatment in air at 900°C for 2h. Furthermore, its bulk density is lowest. The commercial engine oil (SJ5W/40) for FAW-VOLKSWAGEN, which was used by Bora 1.9 TDI diesel cars in China market was substituted for SOF. The catalytic activity was evaluated by normalized peak areas and extrapolated onset temperatures of DTA curves. A computer program was developed by direct non-linear regression model for simulation of TG/DTG curves to determine the thermal processes and kinetic parameters. It is found that lube evaporation/decomposition and thermal decomposition (pyrolysis) were observed under a nitrogen atmosphere. Lube evaporation fractions were inhibited by Ce0.6Zr0.4O2 and γ-Al2O3. While under an air atmosphere, namely, in the process of lube oxidation (combustion), evaporation/decomposition, low-temperature oxidation and high-temperature oxidation were distinguished. Ce0.6Zr0.4O2 solid solutions are active catalysts for lube oxidation, in which the sample prepared by solution combustion has the highest activity, mainly due to the maintenance of the surface area and particle size upon sintering and its lowest bulk density. However, γ-Al2O3 is more like a support. There exists synergism between Ce0.6Zr0.4O2 and γ-Al2O3: γ-Al2O3 adsorbs lube retaining it within its pore structure, whereas, Ce0.6Zr0.4O2 solid solutions initiate oxidation reactions when light-off temperatures reach. The application of CeO2-ZrO2 solid solution prepared by solution combustion at lower temperature would be promising in diesel oxidation catalysts.
Keywords: Cerium/zirconium solid solution; Catalytic oxidation; Soluble organic fractions; Lube; Thermogravimetric analysis; Direct non-linear regression; Catalytic combustion
Influence of transition metal additives and temperature on the rate of organohalide reduction by granular iron: Implications for reaction mechanisms by Stephen J. Bransfield; David M. Cwiertny; Kenneth Livi; D. Howard Fairbrother (pp. 348-356).
This study provides mechanistic insights into the reduction of organohalides by granular iron as well as the origin of the rate enhancements typically observed when transition metals are added to the surface of granular iron. Using step-wise displacement plating of CuCl2, K2PdCl4 and K2PtCl4, different bimetallic and trimetallic reductants were prepared and characterized using a suite of analytical techniques that included energy filtered transmission electron microscopy (EFTEM). Results obtained from batch studies with the trimetals indicate that reactivity enhancements of 1,1,1-trichloroethane (1,1,1-TCA) reduction are controlled by the chemical identity of the transition metal additive at the liquid/solid interface. Temperature-dependent studies involving iron and bimetals revealed that rates of 1,1,1-TCA reduction increased exponentially with increasing temperature. A systematic shift in product distribution towards more fully hydrogenated products was also observed as the overall rate of 1,1,1-TCA reduction increased. Collectively, these results support recent studies, which suggest that atomic hydrogen is involved in the reduction of alkyl polyhalides by granular iron and bimetallic reductants.
Keywords: Bimetallic reductants; Organohalide; 1,1,1-Trichloroethane; Zero-valent iron
Impact of support oxide and Ba loading on the NO x storage properties of Pt/Ba/support catalysts by E.C. Corbos; X. Courtois; N. Bion; P. Marecot; D. Duprez (pp. 357-367).
A series of 1wt.%Pt/ xBa/Support (Support=Al2O3, SiO2, Al2O3-5.5wt.%SiO2 and Ce0.7Zr0.3O2, x=5–30wt.% BaO) catalysts was investigated regarding the influence of the support oxide on Ba properties for the rapid NO x trapping (100s). Catalysts were treated at 700°C under wet oxidizing atmosphere. The nature of the support oxide and the Ba loading influenced the Pt–Ba proximity, the Ba dispersion and then the surface basicity of the catalysts estimated by CO2-TPD. At high temperature (400°C) in the absence of CO2 and H2O, the NO x storage capacity increased with the catalyst basicity: Pt/20Ba/Si2 decreased catalyst performances. The inhibiting effect of CO2 on the NO x uptake increased generally with both the catalyst basicity and the storage temperature. Water negatively affected the NO x storage capacity, this effect being higher on alumina containing catalysts than on ceria–zirconia samples. When both CO2 and H2O were present in the inlet gas, a cumulative effect was observed at low temperatures (200°C and 300°C) whereas mainly CO2 was responsible for the loss of NO x storage capacity at 400°C. Finally, under realistic conditions (H2O and CO2) the Pt/20Ba/Al5.5Si catalyst showed the best performances for the rapid NO x uptake in the 200–400°C temperature range. It resulted mainly from: (i) enhanced dispersions of platinum and barium on the alumina–silica support, (ii) a high Pt–Ba proximity and (iii) a low basicity of the catalyst which limits the CO2 competition for the storage sites.
Keywords: NO; x; storage; Basicity; Barium; Alumina; Silica; Alumina–silica; Ceria–zirconia
Combustion synthesis and electrochemical characterisation of Pt–Ru–Ni anode electrocatalyst for PEMFC by B. Moreno; E. Chinarro; J.C. Pérez; J.R. Jurado (pp. 368-374).
The present work studies the synthesis by the combustion method of an anode catalyst for protonic exchange membrane fuel cell (PEMFC) employing two different fuels, that is, urea and sucrose. The unsupported pure solid solution Pt0.6Ru0.3Ni0.1 was selected from a calculated and empirical ternary phase diagram, which was previously studied. Theoretically, this particular composition exhibited single-phase features without the presence of secondary phases as RuO3 and NiO, regarding the oxygen partial pressure conditions generated during the combustion synthesis. In the X-ray diffraction (XRD) analysis of the nanoparticles synthesized by using two different fuels, a single-phase Pt0.6Ru0.3Ni0.1 alloy was detected. However, the X-ray photoelectron spectroscopy (XPS) studies showed that the nanoparticles prepared could present an onion-shell structure, in the case of the sample synthesized with sucrose as fuel, the external layers are partially constituted by Ni hydroxides, which can exhibit an active role in the hydrogen oxidation reaction. The electrochemical behaviour of this unsupported catalyst was performed by preparing MEAs, which were evaluated using a I– V polarisation curve test. The results obtained indicated that the nanoparticles prepared by sucrose have better performance, 260mW/cm2, than those prepared using urea, 170mW/cm2. These results are discussed in relation with the hydrogen oxidation mechanism. The results obtained reveal combustion synthesis as an appropriate method for preparing PEMFC electrocatalysts, due to its versatility, simplicity and fastness.
Keywords: Combustion synthesis; Electrocatalysts; PEMFC; Anode; Pt–Ru–Ni
The effect of Fe on the catalytic behavior of model Pd-Rh/CeO2-Al2O3 three-way catalyst by Panayiota S. Lambrou; Petros G. Savva; José Luis G. Fierro; Angelos M. Efstathiou (pp. 375-385).
The present work attempts to address the issue whether iron (Fe) which is accumulated on the surface of “three-way” catalysts (TWCs) used in gasoline-driven cars is a true chemical poison of their catalytic activity. This important issue from a scientific and technological point of view is addressed via catalytic activity, temperature-programmed surface reaction (TPSR), and X-ray photoelectron spectroscopy (XPS) measurements over a model TWC (1wt% Pd–Rh/20wt% CeO2–Al2O3). It was found that deposition of Fe up to the level of 0.4wt% (an average concentration found in aged commercial TWCs) on the model TWC does not deteriorate its activity towards CO and C3H6 oxidation, and reduction of NO by H2. Instead it was found that iron improves significantly the T50 parameter in the activity versus temperature profile. Small Fe clusters in contact with the noble metal (Pd and Rh) particles due to the lower work function of Fe compared to Pd and Rh act likely as a source of electron flow towards the noble metals (as evidenced by XPS measurements), thus altering their surface work function and adsorption energetics of reaction intermediates. The latter have increased significantly the activity of the model TWC towards oxidation of CO and propylene, and to a lesser extent the activity towards the reduction of NO by H2. The presence of Fe on the surface of the model TWC provided and/or created also new active catalytic sites for the reactions investigated. According to previous work from this laboratory, iron up to the level of 0.4wt% was shown not to deteriorate the oxygen storage capacity (OSC) of the same model TWC used in the present work. Thus, it could be concluded that Fe when deposited on a commercial TWC at least up to the level of 0.4wt% acts likely as a promoter than a poison of its catalytic activity.
Keywords: TWC deactivation; Iron; XPS; Transient kinetics; TPSR NO; TPSR C; 3; H; 6; NO reduction
Simulation of NO and NO2 sorption–desorption–reduction behaviours on Pt-impregnated HPW supported on TiO2 by M. Labaki; M. Mokhtari; J.F. Brilhac; S. Thomas; V. Pitchon (pp. 386-394).
NO and NO2 (NO x) sorption, desorption and reduction by hydrogen, carbon monoxide and/or propene were investigated on a TiO2-supported heteropolyacid, 12-tungstophosphoric acid hexahydrate (HPW), promoted by platinum. A model taking into account NO x sorption, desorption and reduction was established. Kinetic constants for NO x sorption, desorption and reduction were extracted by modelling for the investigated range of temperature (170–300°C).
Keywords: Kinetic modelling; NO; x; -trap; NO; x; sorption and desorption–reduction; 1% Pt/HPW/TiO; 2
Photocatalytic degradation of ethidium bromide over titania in aqueous solutions by C. Adán; A. Martínez-Arias; M. Fernández-García; A. Bahamonde (pp. 395-402).
The photocatalytic degradation of ethidium bromide (EtBr), a DNA intercalating pollutant, by TiO2-based catalysts has been analyzed. Three different titanium dioxide samples synthesized by sol–gel within reverse microemulsions at different pH and thermal treatments were characterized and studied for the photocatalytic degradation of EtBr by oxygen in aqueous solutions. A commercial titania, Degussa P25, was also examined as a reference material for comparative purposes. Appreciable differences in the final structural and surface properties of these titania samples are observed which include disparities in the anatase/rutile proportions, optical absorption characteristics, EtBr chemisorption and acid–base properties. EtBr photodegradation results suggest that catalytic acid–base properties are the most relevant to explain EtBr chemisorption and play an important role in their final photocatalytic behaviour. It is stressed that photocatalysis can be an interesting alternative to other chemical or biological methods for mineralization of EtBr diluted in aqueous solutions.
Keywords: Photocatalysis; Ethidium bromide; TiO; 2; Photolysis