Showing papers in "Applied Catalysis B-environmental in 2007"
TL;DR: In this paper, a carbon-doped TiO2 photocatalyst was obtained by using glucose as a carbon source and was characterized by XRD, XPS, TEM, nitrogen adsorption, and UV-vis diffuse reflectance spectroscopy.
Abstract: A visible-light-active TiO2 photocatalyst was prepared through carbon doping by using glucose as carbon source. Different from the previous carbon-doped TiO2 prepared at high temperature, our preparation was performed by a hydrothermal method at temperature as low as 160 °C. The resulting photocatalyst was characterized by XRD, XPS, TEM, nitrogen adsorption, and UV–vis diffuse reflectance spectroscopy. The characterizations found that the photocatalyst possessed a homogeneous pore diameter about 8 nm and a high surface area of 126 m2/g. Comparing to undoped TiO2, the carbon-doped TiO2 showed obvious absorption in the 400–450 nm range with a red shift in the band gap transition. It was found that the resulting carbon-doped TiO2 exhibits significantly higher photocatalytic activity than the undoped counterpart and Degussa P25 on the degradation of rhodamine B (RhB) in water under visible light irradiation (λ > 420 nm). This method can be easily scaled up for industrial production of visible-light driven photocatalyst for pollutants removal because of its convenience and energy-saving.
898 citations
TL;DR: In the early 1970s increased use of cars in some major cities had resulted in serious concerns about urban air quality caused by engine exhaust gas emissions themselves, and by the more harmful species derived from them via photochemical reactions.
Abstract: By the early 1970s increased use of cars in some major cities had resulted in serious concerns about urban air quality caused by engine exhaust gas emissions themselves, and by the more harmful species derived from them via photochemical reactions. The three main exhaust gas pollutants are hydrocarbons (including partially oxidised organic compounds), carbon monoxide and nitrogen oxides. Engine modifications alone were not sufficient to control them, and catalytic systems were introduced to do this. This catalytic chemistry involves activation of small pollutant molecules that is achieved particularly effectively over platinum group metal catalysts. Catalytic emissions control was introduced first in the form of platinum-based oxidation catalysts that lowered hydrocarbon and carbon monoxide emissions. Reduction of nitrogen oxides to nitrogen was initially done over a platinum/rhodium catalyst prior to oxidation, and subsequently simultaneous conversion of all three pollutants over a single three-way catalyst to harmless products became possible when the composition of the exhaust gas could be maintained close to the stoichiometric point. Today modern cars with three-way catalysts can achieve almost complete removal of all three exhaust pollutants over the life of the vehicle. There is now a high level of interest, especially in Europe, in improved fuel-efficient vehicles with reduced carbon dioxide emissions, and “lean-burn” engines, particularly diesels that can provide better fuel economy. Here oxidation of hydrocarbons and carbon monoxide is fairly straightforward, but direct reduction of NO x under lean conditions is practically impossible. Two very different approaches are being developed for lean-NO x control; these are NO x -trapping with periodic reductive regeneration, and selective catalytic reduction (SCR) with ammonia or hydrocarbon. Good progress has been made in developing these technologies and they are gradually being introduced into production. Because of the nature of the diesel engine combustion process they produce more particulate matter (PM) or soot than gasoline engines, and this gives rise to health concerns. The exhaust temperature of heavy-duty diesels is high enough (250–400 °C) for nitric oxide to be converted to nitrogen dioxide over an upstream platinum catalyst, and this smoothly oxidises retained soot in the filter. The exhaust temperature of passenger car diesels is too low for this to take place all the time, so trapped soot is periodically burnt in oxygen above 550 °C. Here a platinum catalyst is used to oxidise higher than normal amounts of hydrocarbon and carbon monoxide upstream of the filter to give sufficient temperature for soot combustion to take place with oxygen. Diesel PM control is discussed in terms of a range of vehicle applications, including very recent results from actual on-road measurements involving a mobile laboratory, and the technical challenges associated with developing ultra-clean diesel-powered cars are discussed.
783 citations
TL;DR: In this article, the role of H 2 O and CO 2 in the degradation of 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 was investigated.
Abstract: 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 H 2 O and CO 2 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 H 2 O and CO 2 . It is demonstrated that the CO 2 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 ≥973 K are required to revert the CO 2 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.
730 citations
TL;DR: The photocatalytic activity of the as-prepared nanocrystalline mesoporous TiO2 powders was evaluated by the degradation of acetone (CH3COCH3) under UV-light irradiation at room temperature in air as mentioned in this paper.
Abstract: Bimodal nanocrystalline mesoporous TiO2 powders with high photocatalytic activity were prepared by a hydrothermal method using tetrabutylorthotitanate (TiO(C4H9)4, TBOT) as precursor. The as-prepared TiO2 powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and N2 adsorption–desorption measurements. The photocatalytic activity of the as-prepared TiO2 powders was evaluated by the photocatalytic degradation of acetone (CH3COCH3) under UV-light irradiation at room temperature in air. The effects of hydrothermal temperature and time on the microstructures and photocatalytic activity of the TiO2 powders were investigated and discussed. It was found that hydrothermal treatment enhanced the phase transformation of the TiO2 powders from amorphous to anatase and crystallization of anatase. All TiO2 powders after hydrothermal treatment showed bimodal pore-size distributions in the mesoporous region: one was intra-aggregated pores with maximum pore diameters of ca. 4–8 nm and the other with inter-aggregated pores with maximum pore diameters of ca. 45–50 nm. With increasing hydrothermal temperature and time, the average crystallite size and average pore size increased, in contrast, the Brunauer-Emmett-Teller (BET) specific surface areas, pore volumes and porosity steadily decreased. An optimal hydrothermal condition (180 °C for 10 h) was determined. The photocatalytic activity of the prepared TiO2 powders under optimal hydrothermal conditions was more than three times higher than that of Degussa P25.
533 citations
TL;DR: In this article, the degradation and mineralization of the non-biodegradable azo dye Orange II (OII) was studied, making use of a heterogeneous Fenton-like oxidation process.
Abstract: In this work, the degradation and mineralization of the non-biodegradable azo dye Orange II (OII) was studied, making use of a heterogeneous Fenton-like oxidation process. For that, hydrogen peroxide activation was achieved by means of two different carbon-based catalysts, which have been impregnated with 7 wt% of iron. The carbon supports employed are quite different, one of them being an activated carbon prepared from agricultural by-products (olive stone), while the other one is a carbon aerogel, prepared by carbonization of an organic resorcinol–formaldehyde polymer. The solids have been characterized using several techniques, namely N2 and CO2 adsorption at −196 and 0 °C, respectively, mercury porosimetry, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS). Then, the catalyst's performance in the Fenton-like oxidation of OII was compared, and the effects of the most relevant operating conditions (pH, catalyst concentration, H2O2 concentration and temperature) analyzed for the most promising one (the carbon aerogel based catalyst). In this catalyst, characterization data point for a very good iron dispersion on the carbon surface. This sample showed very good catalytic performances, with mineralization degrees as high as 90%. However, iron leaching from the support is also considerable leading to a progressive deactivation in consecutive reaction cycles.
492 citations
TL;DR: In this article, a series of TiO 2 supported manganese oxide catalysts were prepared by wet-impregnation method for the low temperature selective catalytic reduction (SCR) of NO with ammonia as a reductant.
Abstract: A series of TiO 2 supported manganese oxide catalysts were prepared by wet-impregnation method for the low temperature selective catalytic reduction (SCR) of NO with ammonia as a reductant. A combination of various physico-chemical techniques such as N 2 physisorption, O 2 chemisorption, TPR, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman were used to characterize the chemical environment of these catalysts. O 2 chemisorption and XRD results suggest that Mn exist in a well-dispersed state at below 16.7 wt.% of Mn on TiO 2 anatase (Hombikat), 7.5 wt.% on TiO 2 rutile (Kemira) and P-25 (80% anatase + 20% rutile), and in microcrystalline phase above these loading levels on respective support materials. These results also reveal that Mn interacts very well with pure anatase phase compared to rutile. XPS results of Mn/TiO 2 anatase (Hombikat) catalysts illustrated the presence of MnO 2 as a major phase (peak at 642.0 eV) along with Mn 2 O 3 as the minor phase at lower loadings. The presence of Mn 2 O 3 disappears at higher loadings. The characterization results indicated that the manganese oxide exists as an isolated species at very low loadings, highly dispersed state probably as two dimensional monolayer species at intermediate loadings, polymeric or microcrystalline form of manganese oxide at higher (above monolayer capacity) loadings was envisaged. The catalytic performance of various amounts of Mn loaded on different TiO 2 supported catalysts for low temperature SCR reaction at catalyst bed temperature 175 °C under power plant conditions using GHSV = 50,000 h −1 was studied. The catalyst with 16.7 wt.% Mn/TiO 2 anatase (Hombikat) was found to be highly active and selective catalyst for this reaction. The Raman studies acted as complimentary tool to XPS in order to characterize the manganese oxides (MnO, Mn 2 O 3 , Mn 3 O 4 , MnO 2 ). Raman data show that there is a strong interaction between the Mn oxides and the support, which is responsible for the impressive catalytic performance in comparison with other systems we investigated.
461 citations
TL;DR: A series of CeO2 promoted cobalt spinel catalysts were prepared by the co-precipitation method and tested for the decomposition of nitrous oxide (N2O) as mentioned in this paper.
Abstract: A series of CeO2 promoted cobalt spinel catalysts were prepared by the co-precipitation method and tested for the decomposition of nitrous oxide (N2O). Addition of CeO2 to Co3O4 led to an improvement in the catalytic activity for N2O decomposition. The catalyst was most active when the molar ratio of Ce/Co was around 0.05. Complete N2O conversion could be attained over the CoCeO.05 catalyst below 400 degrees C even in the presence of O-2, H2O or NO. Methods of XRD, FE-SEM, BET, XPS, H-2-TPR and O-2-TPD were used to characterize these catalysts. The analytical results indicated that the addition of CeO2 could increase the surface area Of Co3O4, and then improve the reduction of Co3+ to Co2+ by facilitating the desorption of adsorbed oxygen species, which is the rate-determining step of the N2O decomposition over cobalt spinel catalyst. We conclude that these effects, caused by the addition of CeO2, are responsible for the enhancement of catalytic activity Of Co3O4. (c) 2007 Elsevier B.V. All rights reserved.
434 citations
TL;DR: In this paper, a Ni/olivine catalyst, previously developed for biomass gasification and tar removal during fluidized bed steam gasification of biomass, was tested in a fixed bed reactor in toluene steam reforming as a tar destruction model reaction.
Abstract: A Ni/olivine catalyst, previously developed for biomass gasification and tar removal during fluidized bed steam gasification of biomass, was tested in a fixed bed reactor in toluene steam reforming as a tar destruction model reaction. The influence of the catalyst preparation parameters (nickel precursor, calcination temperature and nickel content) and operating parameters (reaction temperature, steam to carbon S/C ratio and space-time) on activity and selectivity was examined showing a high toluene conversion and a low carbon formation compared to olivine alone. The steam reforming of toluene was found to be of zero order for water and first order for toluene. Activation energy required for Ni/olivine was determined to be about 196 kJ mol−1 in accordance with literature. Catalyst activity and stability and its resistance against carbon formation were discussed on the basis of X-ray diffraction (XRD), transmission electron microscopy (TEM) and temperature programmed oxidation (TPO) results. Characterization before test (XRD, temperature programmed reduction (TPR), Mossbauer spectroscopy) have shown the presence of NiO–MgO solid solution, formed on the surface of olivine support, which explains the efficiency of the catalyst calcined at 1100 °C. After test, Ni–Fe alloys were observed (TEM, Mossbauer spectroscopy). It was suggested that magnesium oxide enhanced steam adsorption, facilitating the gasification of surface carbon and that Ni–Fe alloys prevented carbon deposition by dilution effect.
408 citations
TL;DR: In this article, the catalytic behavior of the Fe3+/Fe2+ system in the electro-Fenton degradation of the antimicrobial drug chlorophene has been studied considering four undivided electrolytic cells, where a Pt or boron-doped diamond (BDD) anode and a carbon felt or O-2-diffusion cathode have been used.
Abstract: The catalytic behavior of the Fe3+/Fe2+ System in the electro-Fenton degradation of the antimicrobial drug chlorophene has been studied considering four undivided electrolytic cells, where a Pt or boron-doped diamond (BDD) anode and a carbon felt or O-2-diffusion cathode have been used. Chlorophene electrolyses have been carried out at pH 3.0 under current control, with 0.05 M Na2SO4 as supporting electrolyte and Fe3+ as catalyst. In these processes the drug is oxidized with hydroxyl radical ((OH)-O-center dot) formed both at the anode from water oxidation and in the medium from electrochemically generated Fenton's reagent (Fe2+ + H2O2, both of them generated at the cathode). The catalytic behavior of the Fe3+/Fe2+ system mainly depends on the cathode tested. In the cells with an O-2-diffusion cathode, H2O2 is largely accumulated and the Fe3+ content remains practically unchanged. Under these conditions, the chlorophene decay is enhanced by increasing the initial Fe3+ concentration, because this leads to a higher quantity of Fe2+ regenerated at the cathode and, subsequently, to a greater (OH)-O-center dot production from Fenton's reaction. In contrast, when the carbon felt cathode is used, H2O2 is electrogenerated in small extent, whereas Fe2+ is largely accumulated because the regeneration of this ion from Fe3+ reduction at the cathode is much faster than its oxidation to Fe3+ at the anode. In this case, an Fe3+ concentration as low as 0.2 mM is required to obtain the maximum (OH)-O-center dot generation rate, yielding the quickest chlorophene removal. Chlorophene is poorly mineralized in the Pt/O-2 diffusion cell because the final Fe3+-oxalate complexes are difficult to oxidize with (OH)-O-center dot. These complexes are completely destroyed using a BDD anode at high current thanks to the great amount of (OH)-O-center dot generated on its surface. Total mineralization is also achieved in the Pt/carbon felt and BDD/carbon felt cells with 0.2 mM Fe3+, because oxalic acid and its Fe2+ complexes are directly oxidized with (OH)-O-center dot in the medium. Comparing the four cells, the highest oxidizing power regarding total mineralization is attained for the BDD/carbon felt cell at high current due to the simultaneous destruction of oxalic acid at the BDD surface and in the bulk solution. (c) 2006 Elsevier B.V. All rights reserved.
376 citations
TL;DR: In this paper, the efficiency of photocatalytic disinfection, used to inactivate Escherischia coli K12 under different physico-chemical parameters, was examined and the photocatalyst chosen was the semiconductor TiO2 degussa P25 and the irradiation was produced by an HPK 125 lamp.
Abstract: 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 2.5 g/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, 0.25 g/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, 0.25 g/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.
372 citations
TL;DR: In this article, a study on the catalytic properties of palladium for hydrodechlorination using nanoscale zero-valent iron particles is presented. But the results of the study were limited to the case of chlorinated ethylenes.
Abstract: Reported herein is a study on the catalytic properties of palladium for hydrodechlorination using nanoscale zero-valent iron particles. Temperature-dependent experiments and X-ray diffraction (XRD) are conducted to characterize reactions of chlorinated ethylenes with nanoscale Fe and Pd/Fe particles. XRD results suggest bimetallic structures are created as a result of Pd(II) reduction by zero-valent iron and the degree of surface palladium loading is proportional to the initial amount of palladium applied. The optimal content of palladium in the bimetallic particles for dechlorination is in the range of 1–5% by weight. XRD analyses further suggest that oxidation of iron produces mainly iron oxides. No oxidized species of palladium (e.g., PdO) is found before or after the reactions. Activation energies of the dechlorination reactions with the nanoscale Pd/Fe and Fe particles are estimated to be 31.1 and 44.9 kJ/mol, respectively. A conceptual model for the catalytic hydrodechlorination by the nanoscale Pd/Fe particles is presented.
TL;DR: In this article, the NH3-SCR reactivity over a commercial V2O5-WO3/TiO2 catalyst in a wide range of temperatures and NO/NO2 feed ratios was investigated.
Abstract: We present a systematic study of the NH3-SCR reactivity over a commercial V2O5–WO3/TiO2 catalyst in a wide range of temperatures and NO/NO2 feed ratios, which cover (and exceed) those of interest for industrial applications to the aftertreatment of exhaust gases from diesel vehicles. The experiments confirm that the best deNOx efficiency is achieved with a 1/1 NO/NO2 feed ratio. The main reactions prevailing at the different operating conditions have been identified, and an overall reaction scheme is herein proposed. Particular attention has been paid to the role of ammonium nitrate, which forms rapidly at low temperatures and with excess NO2, determining a lower N2 selectivity of the deNOx process. Data are presented which show that the chemistry of the NO/NO2–NH3 reacting system can be fully interpreted according to a mechanism which involves: (i) dimerization/disproportion of NO2 and reaction with NH3 and water to give ammonium nitrite and ammonium nitrate; (ii) reduction of ammonium nitrate by NO to ammonium nitrite; (iii) decomposition of ammonium nitrite to nitrogen. Such a scheme explains the peculiar deNOx reactivity at low temperature in the presence of NO2, the optimal stoichiometry (NO/NO2 = 1/1), and the observed selectivities to all the major N-containing products (N2, NH4NO3, HNO3, N2O). It also provides the basis for the development of a mechanistic kinetic model of the NO/NO2–NH3 SCR reacting system.
TL;DR: In this paper, rare-earth ion doping has been used to increase the surface area of rare earth-modified ceria (CeO 2 ) and rare earth modified ceria(CeReO x with Re-=La, Pr, Sm, Y) catalysts.
Abstract: Ceria (CeO 2 ) and rare-earth modified ceria (CeReO x with Re = La, Pr, Sm, Y) catalysts are prepared by nitrate precursor calcination and are characterised by BET surface area, XRD, H 2 -TPR, and Raman spectroscopy. Potential of the catalysts in the soot oxidation is evaluated in TGA with a feed gas containing O 2 . Seven hundred degree Celsius calcination leads to a decrease in the surface area of the rare-earth modified CeO 2 compared with CeO 2 . However, an increase in the meso/macro pore volume, an important parameter for the soot oxidation with O 2 , is observed. Rare-earth ion doping led to the stabilisation of the CeO 2 surface area when calcined at 1000 °C. XRD, H 2 -TPR, and Raman characterisation show a solid solution formation in most of the mixed oxide catalysts. Surface segregation of dopant and even separate phases, in CeSmO x and CeYO x catalysts, are, however, observed. CePrO x and CeLaO x catalysts show superior soot oxidation activity (100% soot oxidation below 550 °C) compared with CeSmO x , CeYO x , and CeO 2 . The improved soot oxidation activity of rare-earth doped CeO 2 catalysts with O 2 can be correlated with the increased meso/micro pore volume and stabilisation of external surface area. The segregation of the phases and the enrichment of the catalyst surface with unreducible dopant decrease the intrinsic soot oxidation activity of the potential CeO 2 catalytic sites. Doping CeO 2 with a reducible ion such as Pr 4+/3+ shows an increase in the soot oxidation. However, the ease of catalyst reduction and the bulk oxygen-storage capacity is not a critical parameter in the determination of the soot oxidation activity. During the soot oxidation with O 2 , the function of the catalyst is to increase the ‘active oxygen’ transfer to the soot surface, but it does not change the rate-determining step, as evident from the unchanged apparent activation energy (around 150 kJ mol −1 ), for the catalysed and un-catalysed soot oxidation. Spill over of oxygen on the soot surface and its subsequent adsorption at the active carbon sites is an important intermediate step in the soot oxidation mechanism.
TL;DR: In this paper, a novel process for the production of biodegradable lubricant-based stocks from epoxidized vegetable oil with a lower pour point via cationic ion-exchange resins as catalysts was developed.
Abstract: A novel process for the production of biodegradable lubricant-based stocks from epoxidized vegetable oil with a lower pour point via cationic ion-exchange resins as catalysts was developed. This involves two steps, first, ring-opening reactions by alcoholysis followed by esterification of the resultant hydroxy group in the first step. The ring-opening reaction of epoxidized soybean oil with different alcohols such as n-butanol, iso-amyl alcohol and 2-ethylhexanol was carried out in presence of Amberlyst 15 (Dry) as a catalyst; identity of products was confirmed by IR and NMR. Pour points of the products were observed in the range of -5 to - 15 degrees C. The hydroxy group of ring-opening product of n-butanol was further reacted with acetic anhydride in presence of catalyst Amberlyst 15 (Dry), which was previously used to carry out ring-opening reaction by alcoholysis and identity of the resulting product was confirmed by IR. Pour point of the resulting product was observed to be -5 degrees C. (c) 2006 Elsevier B.V. All rights reserved. (Less)
TL;DR: In this paper, the photocatalytic degradation of phenol by nanoTiO2 particles coated on perlite as a new composite nano-catalyst was investigated, and the results showed that the effect of adsorption and degradation on the TiO2/perlite catalysts in the dark conditions were negligible.
Abstract: The photocatalytic degradiation of phenol by nanoTiO2 particles coated on perlite as a new composite nano-catalyst was investigated. Titanium dioxide (Degussa P-25) was immobilized on three different supports (perlite granules, glass plates and steel fiber) by a very simple and inexpensive method. Perlite granules have a porosity of more than 95%, which allows them to stay afloat on water surface. This gives the medium a unique characteristic from the processing point of view, which enables it to get wetted with the polluted solution without requiring any pumping and simultaneously be exposed to the radiation source when coated with the photocatalyst.
The photocatalytic activity of prepared catalysts was tested in appropriate batch reactors. HPLC analyses was used for measuring the concentration of components, XRD and SEM analyses was carried out for characterization including anataze-rotile phase ratio, crystal size and morphology of prepared catalysts.
The XRD results did not reveal any significant changes in the structure of P-25 as a consequence of the applied immobilization process. Also, well and uniform coating of TiO2 on supports were confirmed by SEM method. The obtained results of the photocatalytic treatment experiments of water synthetically polluted with phenol showed a fairly good performance for the three immobilized catalysts. The rate of phenol degradation was positively affected by UV light intensity, according to different intensity of UV lamps, the kinetics of photocatalytic reaction follows a pseudo-first-order model.
Also control experiments confirmed that the effects of adsorption and degradation of phenol onto the TiO2/perlite catalysts in the dark conditions were negligible.
TL;DR: In this article, the evaporation of water from a single droplet of urea water solution is investigated theoretically by a Rapid Mixing model and a Diffusion Limit model, which also considers droplet motion and variable properties of the solution.
Abstract: The evaporation of water from a single droplet of urea water solution is investigated theoretically by a Rapid Mixing model and a Diffusion Limit model, which also considers droplet motion and variable properties of the solution. The Rapid Mixing model is then implemented into the commercial CFD code Fire 8.3 from AVL Corp. Therein, the urea water droplets are treated with Lagrangian particle tracking. The evaporation model is extended for droplet boiling and thermal decomposition of urea. CFD simulations of a SCR DeNO x -system are compared to experimental data to determine the kinetic parameters of the urea decomposition. The numerical model allows to simulate SCR exhaust system configurations to predict conversion and local distribution of the reducing agent.
TL;DR: In this article, the degradation and mineralization of Orange II solutions using catalysts based on pillared saponite impregnated with several iron salts is reported, achieving 99% of dye degradation with 91% of total organic carbon (TOC) reduction (at 70°C) using only ca. 90mg of clay catalyst per litre of solution.
Abstract: In this work, the degradation and mineralization of Orange II solutions (0.1 mM) using catalysts based on pillared saponite impregnated with several iron salts is reported. Oxidation is carried out in a batch reactor, in presence of various hydrogen peroxide concentrations, and in a wide range of temperature and pH values. Twelve samples are prepared, with three iron loads (7.5, 13.0 and 17.0 wt.%) and four iron salts as precursors, namely Fe(II) acetate, Fe(II) oxalate, Fe(II) acetylacetonate and Fe(III) acetylacetonate. The samples are characterized using X-ray diffraction, thermal analysis, infrared spectroscopy, energy dispersive spectroscopy and adsorption of nitrogen at 77 K. The catalytic results show that these solids present good properties for the degradation and mineralization of Orange II solutions, allowing to reach, in the best conditions and after 4 h of oxidation, 99% of dye degradation with 91% of total organic carbon (TOC) reduction (at 70 °C), using only ca. 90 mg of clay catalyst per litre of solution. Nevertheless, 96% of dye removal with 82% of mineralization are also reached at 30 °C. Besides, the amount of iron released into the final solution is lower than 1 ppm, in the worst of the cases, and 0.09 ppm in the best case.
TL;DR: In this paper, a series of nanosized iron-doped anatase TiO 2 catalysts with different iron content (between 0.4 and 5.1% ) were examined with respect to their behavior for UV photocatalytic degradation of aqueous phenol.
Abstract: A series of nanosized iron-doped anatase TiO 2 catalysts with different iron content (between 0.4 and 5.1 wt.%) has been prepared by a microemulsion method and examined with respect to their behaviour for UV photocatalytic degradation of aqueous phenol. The activity results have been correlated with structural, electronic and surface examinations of the catalysts done with XRD, Raman, UV–vis, EPR, N 2 physisorption and NH 3 chemisorption. An enhancement of the photocatalytic activity is observed for doping levels up to ca. 1 wt.% which is attributable to the effective introduction of Fe 3+ cations into the anatase structure along with associated modifications of the surface acid/base properties. Achievement of relatively high levels of surface segregation of oxidic iron-containing amorphous phases for higher doping levels results however detrimental to the photoactivity.
TL;DR: In this article, the degradation of malachite green (MG) in water by means of ultrasound irradiation and its combination with heterogeneous (TiO2) and homogeneous photocatalysis (photo-Fenton) was investigated.
Abstract: The degradation of malachite green (MG) in water by means of ultrasound irradiation and its combination with heterogeneous (TiO2) and homogeneous photocatalysis (photo-Fenton) was investigated. Emphasis was given on the effect of key operating conditions on MG conversion and mineralization rates and the elucidation of major reaction by-products. Eighty-kilohertz of ultrasound irradiation was provided by a horn-type sonicator, while a 9 W lamp was used for UV-A irradiation. The extent of sonolytic degradation increased with increasing ultrasound power (in the range 75–135 W) and decreasing initial concentration (in the range 2.5–12.5 mg L � 1 ), while the presence of TiO2 in the dark generally had little effect on degradation. Sonolysis under argon was substantially faster than under air, oxygen or helium leading to complete MG degradation after 120 min at 10 mg L � 1 initial concentration and 135 W ultrasound power. On the other hand, TiO2 photocatalysis or photo-Fenton led to complete MG degradation in 15–60 min with the rate increasing with increasing catalyst loading (in the range 0.1–0.5 g L � 1 for TiO2 and 7–20 mg L � 1 for Fe 3+ ) and also depending on the gas used. TiO2 sonophotocatalysis was always faster than the respective individual processes due to the enhanced formation of reactive radicals as well as the possible ultrasound-induced increase of the active surface area of the catalyst. For instance, the pseudofirst order rate constant for the sonophotocatalytic degradation at 0.5 mg L � 1 TiO2 under air was 136.7 � 10 � 3 min � 1 with the respective values for photocatalysis and sonolysis being 112.6 � 10 � 3 and 11.6 � 10 � 3 min � 1 . Irrespective of the process employed, mineralization was slower than MG decomposition implying the formation of stable by-products accompanied by the release of nitrates in the solution. GC/MS analysis verified the identity of primary intermediates and a reaction pathway based on them was proposed. Depending on the conditions employed, ecotoxicity of MG to marine bacteria was partly or fully eliminated. # 2007 Published by Elsevier B.V.
TL;DR: In this paper, the authors evaluated photocatalysis as a suitable process to degrade an antibiotic, the sulfamethoxazole, using titania in suspension as catalyst, and UV light.
Abstract: The presence of drugs in the aquatic media has emerged in the last decade as a new environmental risk. The aim of this study is the evaluation of photocatalysis as a suitable process to degrade an antibiotic, the sulfamethoxazole. In this way, sulfamethoxazole in aqueous solution was treated by using titania in suspension as catalyst, and UV light. Sulfamethoxazole degradation and TOC reduction were improved when titania concentration was increased, until an optimum located between 0.5–1.0 g TiO 2 /L. Under the studied conditions, 82% of sulfamethoxazole degradation and 23% of TOC reduction was achieved when working with 0.5 g TiO 2 /L. The initial pH also seemed to influence the process in some extent, although the antibiotic degradation was not affected by this variable, TOC reduction was dramatically decreased when the initial pH was 2, probably due to interferences caused by the sulfate anion. The LC/MS study has been also carried out, and a mechanism has been proposed, through the identification of five intermediates. Sulfate and ammonium ions were also monitored in the solution finding that, as long as the sulfamethoxazole is degraded, the total amount of releasable ions was not reached. The SUVA parameter along the reaction shows a decrease on the aromatic content, but there is still a notable presence of the aromatic compounds after 15 h of reaction. Finally, the experimental data were fitted to different kinetic models. The best results were obtained for a model including the sulfamethoxazole and intermediates concentration.
TL;DR: In this article, the photocatalytic degradation of an azo dye Metanil Yellow was carried out in aqueous solution using TiO2 as photocatalyst under UV irradiation.
Abstract: The photocatalytic degradation of an azo dye Metanil Yellow was carried out in aqueous solution using TiO2 as photocatalyst under UV irradiation. The decolorization and degradation kinetics were investigated and both followed a pseudo first order kinetic according to Langmuir–Hinshelwood model. Using HPLC/DAD and GC/MS analyses, more than 10 major reaction intermediates were identified and a tentative degradation pathway was proposed. Furthermore, ion chromatography (IC) and TOC measurements revealed a complete mineralization of Metanil Yellow into CO2, N2, H2O and inorganic ions (NH4+, NO3− and SO42−).
On the other hand, an experimental design based on the surface response methodology was applied to assess the individual and interaction effects of several operating parameters (dye concentration, TiO2 concentration, pH, light flux, etc.) on the treatment efficiency (dye removal time). Based on the experimental design data, a semi-empirical expression was obtained, permitting to predict and optimize the dye removal time. This model was very consistent with experiment results (correlation factor: 99.5%). Moreover, additional experimental results obtained under near optimal conditions were found to be very close to the predicted values.
This work demonstrates well the utility and benefits of the experimental design approach for screening and modeling the reaction parameters. Furthermore, it contributes significantly to the improvement and better understanding of photocatalytic processes.
TL;DR: In this article, the applicability of humic acid (HA) as an iron chelator in a modified Fenton system with the aim of extending the optimum pH range for this process towards neutral conditions was examined.
Abstract: The suitability of the Fenton process for the remediation of soil and groundwater is limited by the necessity to acidify the reaction medium. This study examines the applicability of humic acid (HA) as an iron chelator in a modified Fenton system with the aim of extending the optimum pH range for this process towards neutral conditions. Addition of HA at a concentration of 50–100 mg L−1 greatly enhances the rate of oxidation of organic compounds in a catalytic Fenton system in the range of pH 5–7. Similar rates at pH 5 in the presence of HA can be achieved as at pH 3 for a typical Fenton process in the absence of HA (k′ = 9 × 10−3 min−1 for benzene degradation at c H 2 O 2 = 0.13 M ). A comparison of the relative reactivities of various model compounds supported the hypothesis that OH radicals are the main reactive species in the HA-modified Fenton system. In contrast, however, another type of chelated Fe-catalyst (Fe-TAML) proved to be more selective than expected for OH radicals. A long-term study revealed that the HA itself is oxidized and thereby loses its ability to enhance the degradation of the pollutant molecules. Therefore, the HA-modified Fenton system is effective for degrading pollutants which are at least as reactive towards OH radicals as the HA itself, such as BTEX, phenols or PAHs. The results obtained indicate that the HA-modified Fenton system is also applicable for compounds with a high sorption tendency towards HA.
TL;DR: In this article, the performance of heterogeneous activation of peroxymonosulfate (PMS) to generate sulfate radicals using cobalt catalyst immobilized on titanium dioxide nanoparticles (Co/TiO2) was evaluated.
Abstract: Recently, sulfate radical-based advanced oxidation technologies have shown significant implications for environmental remediation to decompose water pollutants. In this study, we evaluated the performance of heterogeneous activation of peroxymonosulfate (PMS) to generate sulfate radicals using cobalt catalyst immobilized on titanium dioxide nanoparticles (Co/TiO2). The Co/TiO2 catalyst was prepared via an incipient wetness impregnation method employing Degussa P-25 TiO2 and Co(NO3)·6H2O. The activity of Co/TiO2 system was compared with those of Co(NO3)2 solution for homogeneous PMS activation and neat Co3O4 for heterogeneous PMS activation. More emphasis was given to the effect of cobalt loading and heat treatment on the physicochemical properties of Co/TiO2 and cobalt leaching. The results showed that heat treatment of Co/TiO2 at 500 °C, where cobalt existed as Co3O4, induced negligible Co leaching and enhanced catalytic activity to decompose 2,4-dichlorophenol. The Co/TiO2 catalyst at Co/Ti molar ratio of 0.1 showed the highest activity via heterogeneous PMS activation. On the other hand, Co/TiO2 catalysts with Co/Ti molar ratio of above 0.2 exhibited rather much lower activity which was initiated predominantly via a homogeneous pathway from leached cobalt, although they contained considerable amounts of Co3O4. The formation of Co OH complexes at the surface of Co/TiO2 nanoparticles, due to the ability of TiO2 to dissociate H2O for the formation of surface hydroxyl groups, was proposed to facilitate the heterogeneous PMS activation. However, high cobalt loading covering the TiO2 surface diminished the beneficial role of TiO2 due to the reduction in the concentration of surface hydroxyl groups and thus decreased the heterogeneous PMS activation. The activity of Co3O4 in Co/TiO2 catalysts was much higher than that of neat Co3O4 due to the presence of surface hydroxyl groups and uniform distribution of well-defined 10−15 nm nanocrystalline Co3O4 particles at the surface of 30−40 nm TiO2 nanoparticles.
TL;DR: In this article, the electrocatalytic properties of Ti-Ru-Sn ternary oxide, platinum, lead dioxide and boron-doped diamond anodes for the oxidation of methyl red have been compared by potentiodynamic measurements and bulk electrolysis.
Abstract: The electrocatalytic properties of Ti–Ru–Sn ternary oxide, platinum, lead dioxide and boron-doped diamond anodes for the oxidation of methyl red have been compared by potentiodynamic measurements and bulk electrolysis. The results of the cyclic voltammetries have shown that in the potential region of supporting electrolyte stability polymeric materials, which result in electrode deactivation, are formed on the electrode surfaces. While Ti–Ru–Sn ternary oxide and platinum cannot restore their initial activity by polarization, lead dioxide and boron-doped diamond anodes can be reactivated by electrolysis in the potential region of electrolyte decomposition due to the electrogeneration of hydroxyl radicals. The bulk electrolysis showed that the complete COD and colour removal were only achieved using lead dioxide and boron-doped diamond while Ti–Ru–Sn ternary oxide and platinum only permitted a partial oxidation of methyl red.
TL;DR: In this article, the authors investigated the catalytic properties of nanosized gold catalysts for liquid phase glycerol with carbon supported catalysts and showed that the presence of Pt increases not only the catalyst activity but also the selectivity.
Abstract: As a renewable feedstock and due to its high functionality glycerol is an attractive reactant for the production of a large number of valuable compounds. We report on an environmentally friendly alternative to produce chemicals from the glycerol oxidation, which are currently produced either by stoichiometric oxidation processes or by enzymatic routes. We investigate the heterogeneously catalyzed liquid-phase oxidation of glycerol with carbon supported gold catalysts. The prepared nanosized gold catalysts are highly active, so that the reaction could be performed under atmospheric pressure. The influence of the preparation method of the catalysts has been investigated. Moreover, the support effect on the catalytic process has been studied and discussed in terms of pore structure of the investigated carbon materials. The promotor effect of platinum on Au/C catalysts was examined and it could be shown that the presence of Pt increases not only the catalyst activity but also the selectivity. By promoting the gold catalysts with platinum the selectivity to dihydroxyacetone could be increased from 26% (Au/C) to 36% (Au–Pt/C).
TL;DR: In this paper, the photocatalytic efficiency of pure or doped nanocrystalline titania was tested for discoloration of an aqueous solution of Basic Blue 41.5% for Fe3+ doping.
Abstract: Thin films of pure or doped nanocrystalline titania have been deposited on glass slides by using a sol–gel procedure, in the presence of surfactant Triton X-100, which acts as template of the nanostructure. Fe3+, Cr3+ and Co2+ were used as dopants while the doping extended in a broad domain from very low to very high levels. The photocatalytic efficiency of pure or doped titania was tested for discoloration of an aqueous solution of Basic Blue 41. The presence of dopants resulted in a progressive loss of total crystallinity, some transition from anatase into rutile and, in the case of Co2+, formation of the mixed oxide cobalt titanate. Loss of anatase had dramatic consequences on photocatalytic efficiency by UV–vis excitation, which decreased fast with increasing dopant concentration. Selected visible excitation of the doped titania could lead to photodegradation of the dye but to a far lesser degree than UV–vis excitation. Photosensitization by absorption of light by the dye itself loses its importance in the presence of the dopant. Thus the doped material is a visible-light photocatalyst but substantial photodegradation efficiency is achieved only at very high doping levels, for example, 20 at.% for Fe3+ doping. In any case, direct UV excitation of pure titania is a more efficient photocatalytic process than visible excitation of the doped semiconductor.
Abstract: The stability of methane conversion was studied over a Pd/Al 2 O 3 catalyst and bimetallic Pd–Pt/Al 2 O 3 catalysts. The activity of methane combustion over Pd/Al 2 O 3 gradually decreased with time, whereas the methane conversion over bimetallic Pd–Pt catalysts was significantly more stable. The differences in combustion behavior were further investigated by activity tests where additional water vapor was periodically added to the feed stream. From these tests it was concluded that water speeds up the degradation process of the Pd/Al 2 O 3 catalyst, whereas the catalyst containing Pt was not affected to the same extent. DRIFTS studies in a mixture of oxygen and methane revealed that both catalysts produce surface hydroxyls during combustion, although the steady state concentration on the pure Pd catalyst is higher for a fixed temperature and water partial pressure. The structure of the bimetallic catalyst grains with a PdO domain and a Pd–Pt alloy domain may be the reason for the higher stability, as the PdO domain appears to be more affected by the water generated in the combustion reaction than the alloy. Not all fuels that produce water during combustion will have stability issues. It appears that less strong binding in the fuel molecule will compensate for the degradation.
TL;DR: In this article, a simplified ODS catalytic system composed of Na2WO4, 30% H2O2 and CH3CO2H was found suitable for the deep removal of sulfur in diesel.
Abstract: 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 1100 ppm to 40 ppm. 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 8C in less than 1 h. # 2007 Elsevier B.V. All rights reserved.
TL;DR: In this paper, a Pt/TiO2 photocatalyst was used for hydrogen production by photocatalytic alcohol reforming in the presence of nano-structured titania.
Abstract: Hydrogen production by photocatalytic alcohol reforming has been studied in the presence of a Pt/TiO2 photocatalyst. Nanocrystalline titania was deposited on glass slides by using a sol–gel process in the presence of surfactant template. Band-gap excitation of titania was made by using a low-energy Black-Light source. Water–ethanol mixtures proved the most efficient substrate for hydrogen production. This system demonstrated an impressive efficiency, which reached up to 74% active electron to incident photon ratio and 32% energy conversion efficiency.
TL;DR: In this article, a novel photocatalyst, titanium dioxide (TiO2) doped with neodymium (Nd), was prepared by the sol-gel method and used for the photocatalytic reduction of Cr(VI) under UV illumination, in order to determine its photocatalysis properties.
Abstract: A novel photocatalyst, titanium dioxide (TiO2) doped with neodymium (Nd), was prepared by the sol–gel method and used for the photocatalytic reduction of Cr(VI) under UV illumination, in order to determine its photocatalytic properties. A series of Nd3+–TiO2 catalysts prepared with different Nd3+ dosages were characterized by XRD, Raman spectroscopy, SEM, EDX, TEM, EDS and XPS spectroscopy. In the experiments, formic acid was used as a hole scavenger to enhance the photocatalytic reduction reaction. The experiments demonstrated that Cr(VI) was effectively reduced in aqueous Nd3+–TiO2 suspension by more than 95% within 60 min, while the pH of the solution increased from 3.1 to 3.35 due to the consumption of formic acid. The experimental results indicate that the presence of Nd3+ in TiO2 catalysts substantially enhances the photocatalytic reaction of chromium(VI) reduction. It was found that the optimal dosage of 1–3 wt% Nd3+ in TiO2 achieved the fastest reaction of Cr(VI) reduction under the experimental conditions. The neodymium ions deposited on the TiO2 surface behave as sites at which electrons accumulate. The improved separation of electrons and holes on the modified TiO2 surface allows more efficient channeling of the charge carriers into useful reduction and oxidation reactions rather than recombination reactions. The presence of sacrificial electron donors such as formic acid enhances the photocatalytic reduction of Cr(VI). The Cr(VI) adsorbed on the surface of the TiO2 particles was observed to be almost completely photoreduced to Cr(III).