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Showing papers on "Selective catalytic reduction published in 2007"


Journal ArticleDOI
Martyn V. Twigg1
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


Journal ArticleDOI
TL;DR: In this article, the authors investigated the low temperature selective catalytic reduction (SCR) of NOx with NH 3 in the presence of excess O 2, and the active MnOx catalysts, precipitated with sodium carbonate and calcined in air at moderate temperatures such as 523 K and 623 K, have the high surface area, the abundant Mn 4+ species, and the high concentration of surface oxygen on the surface.
Abstract: Manganese oxide catalysts prepared by a precipitation method with various precipitants were investigated for the low temperature selective catalytic reduction (SCR) of NOx with NH 3 in the presence of excess O 2 . Various characterization methods such as N 2 adsorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis (TGA) and X-ray absorption near edge structure (XANES) were conducted to probe the physical and chemical properties of MnOx catalysts. The active MnOx catalysts, precipitated with sodium carbonate and calcined in air at moderate temperatures such as 523 K and 623 K, have the high surface area, the abundant Mn 4+ species, and the high concentration of surface oxygen on the surface. The amorphous Mn 3 O 4 and Mn 2 O 3 were mainly present in this active catalyst. The carbonate species appeared to help adsorb NH 3 on the catalyst surface, which resulted in the high catalytic activity at low temperatures.

730 citations


Journal ArticleDOI
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


Journal ArticleDOI
Zhongbiao Wu1, Boqiong Jiang1, Yue Liu1, Haiqiang Wang1, Ruiben Jin1 
TL;DR: The DRIFT spectroscopy for the adsorption of NH3 indicated the presence of coordinated NH3 and NH4+ on both of the two catalysts, indicating these species could react with NO effectively.
Abstract: Manganese oxides and iron-manganese oxides supported on TiO2 were prepared by the sol−gel method and used for low-temperature selective catalytic reduction (SCR) of NO with NH3. Base on the previous study, Mn(0.4)/TiO2 and Fe(0.1)−Mn(0.4)/TiO2 were then selected to carry out the in situ diffuse reflectance infrared transform spectroscopy (DRIFT) investigation for revealing the reaction mechanism. The DRIFT spectroscopy for the adsorption of NH3 indicated the presence of coordinated NH3 and NH4+ on both of the two catalysts. When NO was introduced, the coordinated NH3 on the catalyst surface was consumed rapidly, indicating these species could react with NO effectively. When NH3 was introduced into the sample preadsorbed with NO + O2, SCR reaction would not proceed on Mn(0.4)/TiO2. However, for Fe(0.1)−Mn(0.4)/TiO2 the bands due to coordinated NH3 on Fe2O3 were formed. Simultaneously, the bidentate nitrates were transformed to monodentate nitrates and NH4+ was detected. And NO2 from the oxidation of NO on ...

456 citations


Journal ArticleDOI
TL;DR: In this article, a unifying redox approach is proposed to interpret the overall NO/NO2−NH3 SCR chemistry over V-based catalysts, in which vanadium sites are reduced by the reaction between NO and NH3 and are reoxidized either by oxygen (standard SCR) or by nitrates (fast SCR), with the latter formed via NO2 disproportion over other nonreducible oxide catalyst components.

254 citations


Journal ArticleDOI
TL;DR: In this article, an unsupported manganese oxide catalysts with amorphous phase were prepared by three methods, and their activities for SCR of NOx with ammonia were investigated in the presence of O2.

225 citations


Journal ArticleDOI
Zhongbiao Wu1, Boqiong Jiang1, Yue Liu1, Weirong Zhao1, Baohong Guan1 
TL;DR: A catalyst based on MnO(x)/TiO(2) was prepared by sol-gel method for low-temperature selective catalytic reduction (SCR) of NO with NH(3) and the efficiency of NO removal could exceed 90% at temperature of 423K.

180 citations


Journal ArticleDOI
TL;DR: Mn-Ce/ZSM-5 catalyst prepared in an aqueous phase at 423 K exhibits a broad temperature window for high NO conversion (75-100%) in the process of selective catalytic reduction (SCR) by NH3 even in the presence of H2O and SO2 as discussed by the authors.
Abstract: Mn–Ce/ZSM-5 catalyst prepared in an aqueous phase at 423 K exhibits a broad temperature window (517–823 K) for high NO conversions (75–100%) in the process of selective catalytic reduction (SCR) by NH3 even in the presence of H2O and SO2. Both the zeolite matrix and the over-exchanged amounts of manganese and cerium contribute to obtain a complex structure that owns microporous–mesoporous characteristics and specific surface properties.

170 citations


Journal ArticleDOI
TL;DR: In this paper, metal oxide/active carbon/ceramic (MO x /AC/C) monolithic catalysts were prepared by impregnation method for selective catalytic reduction (SCR) of NO x with NH 3 at low-temperature.

155 citations


Journal ArticleDOI
TL;DR: In this article, the selective catalytic reduction of NO by H 2 under strongly oxidizing conditions (H 2 -SCR) has been studied over Pt supported on a series of metal oxides.
Abstract: The selective catalytic reduction of NO by H 2 under strongly oxidizing conditions (H 2 -SCR) in the low-temperature range of 100–200 °C has been studied over Pt supported on a series of metal oxides (e.g., La 2 O 3 , MgO, Y 2 O 3 , CaO, CeO 2 , TiO 2 , SiO 2 and MgO-CeO 2 ). The Pt/MgO and Pt/CeO 2 solids showed the best catalytic behavior with respect to N 2 yield and the widest temperature window of operation compared with the other single metal oxide-supported Pt solids. An optimum 50 wt% MgO-50wt% CeO 2 support composition and 0.3 wt% Pt loading (in the 0.1–2.0 wt% range) were found in terms of specific reaction rate of N 2 production (mols N 2 /g cat s). High NO conversions (70–95%) and N 2 selectivities (80–85%) were also obtained in the 100–200 °C range at a GHSV of 80,000 h −1 with the lowest 0.1 wt% Pt loading and using a feed stream of 0.25 vol% NO, 1 vol% H 2 , 5 vol% O 2 and He as balance gas. Addition of 5 vol% H 2 O in the latter feed stream had a positive influence on the catalytic performance and practically no effect on the stability of the 0.1 wt% Pt/MgO-CeO 2 during 24 h on reaction stream. Moreover, the latter catalytic system exhibited a high stability in the presence of 25–40 ppm SO 2 in the feed stream following a given support pretreatment. N 2 selectivity values in the 80–85% range were obtained over the 0.1 wt% Pt/MgO-CeO 2 catalyst in the 100–200 °C range in the presence of water and SO 2 in the feed stream. The above-mentioned results led to the obtainment of patents for the commercial exploitation of Pt/MgO-CeO 2 catalyst towards a new NO x control technology in the low-temperature range of 100–200 °C using H 2 as reducing agent. Temperature-programmed desorption (TPD) of NO, and transient titration of the adsorbed surface intermediate NO x species with H 2 experiments, following reaction, have revealed important information towards the understanding of basic mechanistic issues of the present catalytic system (e.g., surface coverage, number and location of active NO x intermediate species, NO x spillover).

146 citations


Journal ArticleDOI
TL;DR: In this paper, a multiwalled carbon nanotube (CNTs) supported vanadium catalyst was prepared for selective catalytic reduction (SCR) of NO with NH 3 at low temperatures.

Journal ArticleDOI
TL;DR: In its current form the catalyst might be best applied to destroy perchlorate in the acidic regeneration stream from selective ion exchange columns, and both the rate and extent of reaction decreased at higher values of pH.
Abstract: A new heterogeneous catalyst that promotes the reduction by hydrogen of perchlorate ion in water under mild conditions has been developed. The catalyst is prepared by adsorption of a rhenium(VII) precursor (either ammonium perrhenate or methylrhenium trioxide) onto carbon powder containing 5% palladium by weight. Under standard batch conditions of room temperature, 1 bar of hydrogen, and 200 ppm perchlorate (as HClO4), reduction proceeded to less than 1 ppm in as little as 5 h. Extended reaction times led to residual perchlorate at low parts per billion levels. Chloride was the only observed product, with good material balance. Catalytic materials ranging from 3% to 13% Re showed (pseudo) first-order rates linearly dependent on the Re content. Representative normalized rate constants for catalysts with 5−9% Re were in the range 0.1−0.3 L h-1 (g of cat.)-1. Inhibition by chloride was not significant, with little change in perchlorate reduction rate in the presence of excess chloride to 1000 ppm. However, o...

Journal ArticleDOI
TL;DR: In this article, a series of bench-scale experiments were completed to evaluate acid gases of HCl, SO2, and SO3 on mercury oxidation across a commercial selective catalytic reduction (SCR) catalyst.

Journal ArticleDOI
TL;DR: In this article, the Institute for Combustion Science and Environmental Technology at Western Kentucky University set up a pilot-scale selective catalytic reduction (SCR) slipstream facility at a selected utility boiler burning bituminous coal.
Abstract: One of the cost-effective mercury control technologies in coal-fired power plants is the enhanced oxidation of elemental mercury in selective catalytic reduction (SCR) followed by the capture of the oxidized mercury in the wet scrubber. To better understand Hg oxidation chemistry within a SCR, the Institute for Combustion Science and Environmental Technology at Western Kentucky University set up a pilot-scale SCR slipstream facility at a selected utility boiler burning bituminous coal. The greatest benefit of this scaled-down SCR slipstream test is the ability to investigate the effects of Hg oxidation in a SCR using actual flue gas with fly ash included and to isolate and control specific flue-gas compositions with spike gas additions. The average sulfur, chlorine, and mercury contents in the burned coal were 1.67% and 731 and 0.13 ppm, respectively. CaO and Fe2O3 and loss on ignition of the fly ash, which are reported to possibly affect Hg speciation, are approximately 1.65, 14.6, and 2.6% on average, r...

Journal ArticleDOI
TL;DR: In this article, the mechanistic cause of the dramatic activity improvement of alumina-supported silver (Ag/Al2O3) by H2 addition for the selective catalytic reduction of NO with propane (C3H8-SCR) was investigated by catalytic and spectroscopic studies.
Abstract: The mechanistic cause of the dramatic activity improvement of alumina-supported silver (Ag/Al2O3) by H2 addition for the selective catalytic reduction of NO with propane (C3H8-SCR) was investigated by catalytic and spectroscopic studies. In situ UV−vis, in situ EXAFS, IR, and microcalorimetric experiments show that H2 reduction of Ag+ ions on Ag/Al2O3 at 573 K yields protons on alumina and partially reduced Agnδ+ clusters, which are subsequently aggregated to larger Ag clusters. During H2 + O2 and H2-assisted C3H8-SCR reactions, Ag+ ions and Agnδ+ coexist. Reoxidation with O2 results in the redispersion of the cluster to Ag+ ion, accompanying a reaction of protons. The relationship between cluster size, redox properties, and catalytic activity is examined using Ag/Al2O3 of different Ag loadings. The steady-state NO reduction rate correlates fairly well with the amount of Agnδ+ during the H2-assisted C3H8-SCR reaction. It is shown that Agnδ+ is the active species, whereas monomeric Ag+ ion and metallic Ag ...

Journal ArticleDOI
TL;DR: In this paper, vanadium-titanium deNO x SCR (selective catalytic reduction) catalysts in high-dust position have been investigated in three 100MW-scale boilers during biofuel and peat combustion.
Abstract: Deactivation of vanadium–titanium deNO x SCR (selective catalytic reduction) catalysts in high-dust position have been investigated in three 100 MW-scale boilers during biofuel and peat combustion. The deactivation of the catalyst samples has been correlated to the corresponding flue gas composition in the boilers. Too investigate the effect on catalyst deactivation a sulphate-containing additive was sprayed into one of the furnaces. Increased alkali content on the SCR catalyst samples decreased the catalytic deNO x activity. The study has shown a linear correlation between exposure time in the boilers and alkali concentration (mainly potassium) on the samples. The results imply that mainly alkali in ultra fine particles (

Journal ArticleDOI
TL;DR: In this paper, the nitrogen paths of reaction from NO to N2 and N2O gas products were probed by following the 14NO/H2/O2 → 15 NO/H 2 /O2 switch at 1 bar total pressure.
Abstract: Steady State Isotopic Transient Kinetic Analysis (SSITKA) coupled with Temperature-Programmed Surface Reaction (TPSR) experiments, using on line Mass Spectroscopy (MS) and in situ DRIFTS have been performed to study essential mechanistic aspects of the selective catalytic reduction of NO by H2 under strongly oxidizing conditions (H2-SCR) at 140 °C over a novel 0.1 wt % Pt/MgO−CeO2 catalyst for which patents have been recently obtained. The nitrogen paths of reaction from NO to N2 and N2O gas products were probed by following the 14NO/H2/O2 → 15NO/H2/O2 switch (SSITKA-MS and SSITKA-DRIFTS) at 1 bar total pressure. It was found that the N-pathways of reaction involve two different in structure active chemisorbed NOx species, one present on the MgO and the other one on the CeO2 support surface. The amount of these active NOx intermediate species formed was found to be 14.4 μmol/g, corresponding to a surface coverage of θ = 3.1 (based on Pt metal surface) in agreement with the SSITKA-DRIFTS results. A large f...

Journal ArticleDOI
TL;DR: In this paper, the catalytic activity of silica-free and silica modified rare earth (Ce, Tb, Er) containing V2O5-WO3 -TiO2 catalysts in the selective catalytic reduction of NO by ammonia has been investigated as a function of ageing temperatures.
Abstract: The catalytic activity of silica-free and silica-modified rare earth (Ce, Tb, Er) containing V2O5-WO3 -TiO2 catalysts in the selective catalytic reduction of NO by ammonia has been investigated as a function of ageing temperatures. The adsorption of ammonia on the catalysts and the behavior of their surface hydroxy groups and of bulk vibrations has also been studied by IR spectroscopy. Rare earths slightly decrease the catalytic activity of catalysts in a fresh state, and this has been attributed to the perturbation, observed by IR, of the vanadyl groups with a likely lowering of their Lewis acidity. However, rare earths (in particular Tb and Er) increase strongly the catalytic activity of catalysts after ageing. Silica only does not seem to have a positive effect on thermal stability and activity when vanadium is present. It has been concluded that rare earths strongly increase the thermal resistance of the catalysts and inhibit rutilization and surface area loss because they do not penetrate the anatase bulk while tend to cover the external surface. In addition the negative action of free vanadium on phase stability is decreased due to formation of rare earth vanadates.

Book ChapterDOI
TL;DR: In this paper, the authors present a methodology for developing a combination of different catalytic technologies and particulate filters for exhaust aftertreatment systems, which can contribute considerably in reducing development time and cost.
Abstract: Decreasing emission limits lead to the development of combined aftertreatment systems, consisting of combinations of different catalyst technologies and particulate filters. Modeling such systems can contribute considerably in reducing development time and cost. The methodology for developing catalyst models is reviewed and models for the diesel oxidation catalyst (DOC) with hydrocarbon (HC) adsorption, the NOx storage and reduction catalyst (NSRC) and the urea–selective catalytic reduction system (urea–SCR) are developed. Applications for exhaust aftertreatment system modeling are shown.

Journal ArticleDOI
TL;DR: In this paper, the effect of Co content on the catalytic activity of CoSiBEA zeolites in the selective catalytic reduction (SCR) of NO with ethanol is investigated.
Abstract: The effect of Co content on the catalytic activity of CoSiBEA zeolites in the selective catalytic reduction (SCR) of NO with ethanol is investigated. The CoxSiBEA zeolites (x = 0.3, 0.7, 3.6 and 6.75 Co wt.%) are prepared by a two-step postsynthesis method which allows to control the introduction of cobalt into zeolite and thus to obtain catalysts with specific Co sites. The nature of the active sites is characterized by XRD, diffuse reflectance UV–vis, H2-TPR and XPS. The catalytic activity of CoxSiBEA strongly depends on the nature and environment of Co species. Zeolites with isolated lattice tetrahedral Co(II) (Co0.3SiBEA and Co0.7SiBEA samples) are active in SCR of NO with ethanol with selectivity toward N2 exceeding 85% for NO conversion from 20 to 70%. When additional isolated extra-lattice octahedral Co(II) species appear (Co3.6SiBEA sample), the full oxidation of ethanol by dioxygen becomes a very important reaction pathway. In presence of additional cobalt oxides (Co6.75SiBEA sample), the activity and selectivity toward N2 substantially change and full oxidation of ethanol to CO2 is the main reaction pathway and full NO oxidation also takes place in the temperature range 550–775 K. The lack of correlation between the activity in SCR of NO with ethanol and NO oxidation to NO2 suggests that the two reactions are more competitive than sequential.

Journal ArticleDOI
TL;DR: In this article, a catalytic coating based on a TiO2-V2O5-WO3 catalyst system was developed on a ceramic filter element for combined particle separation and NOx removal or VOC total oxidation.
Abstract: The development of a catalytically active filter element for combined particle separation and NOx removal or VOC total oxidation, respectively, is presented. For NOx removal by selective catalytic reduction (SCR) a catalytic coating based on a TiO2–V2O5–WO3 catalyst system was developed on a ceramic filter element. Different TiO2 sols of tailor-made mean particle size between 40 and 190 nm were prepared by the sol–gel process and used for the impregnation of filter element cylinders by the incipient wetness technique. The obtained TiO2-impregnated sintered filter element cylinders exhibit BET surface areas in the range between 0.5 and 1.3 m2/g. Selected TiO2-impregnated filter element cylinders of high BET surface area were catalytically activated by impregnation with a V2O5 and WO3 precursor solution. The obtained catalytic filter element cylinders show high SCR activity leading to 96% NO conversion at 300 °C, a filtration velocity of 2 cm/s and an NO inlet concentration of 500 vol.-ppm. The corresponding differential pressures fulfill the requirements for typical hot gas filtration applications. For VOC total oxidation, a TiO2-impregnated filter element support was catalytically activated with a Pt/V2O5 system. Complete oxidation of propene with 100% selectivity to CO2 was achieved at 300 °C, a filtration velocity of 2 cm/s and a propene inlet concentration of 300 vol.-ppm.

Patent
18 Jul 2007
TL;DR: In this paper, a method of controlling a rate of introduction of a NOx reducing substance or precursor to a catalyst component is proposed, which is based on obtaining the amount of NOx entering the catalyst component and modelling the amount in the catalytic component.
Abstract: A method of controlling a rate of introduction of a NOx reducing substance or precursor to a catalyst component (1). The method comprises obtaining the amount of NOx entering the catalyst component (1), modelling the amount of NOx reducing substance or precursor in the catalyst component (1) and controlling the rate of introduction of the NOx reducing substance or precursor to reduce NOx.

Patent
16 Aug 2007
TL;DR: In this article, an exhaust gas post treatment system for nitrogen oxide and particle reduction of an internal combustion engines operated with excess air is described. And the reduction agent is ammonia or a material that releases ammonia downstream of the supply location due to the hot exhaust gas.
Abstract: Exhaust gas post treatment system for nitrogen oxide and particle reduction of an internal combustion engines operated with excess air. An oxidation catalytic converter is disposed in the exhaust gas stream of the engine for converting at least a portion of the nitric oxide of the exhaust gas into nitrogen dioxide. A metering device adds reduction agent to the exhaust gas stream downstream of the oxidation catalytic converter and/or to a partial exhaust gas stream branched off upstream of the oxidation catalytic converter and returned to the exhaust gas stream downstream thereof. The reduction agent is ammonia or a material that releases ammonia downstream of the supply location due to the hot exhaust gas. A particle separator or filter is disposed in the exhaust gas stream downstream of the oxidation catalytic converter and of the supply location, and converts carbon particles accumulated in the separator or filter into carbon monoxide, carbon dioxide, nitrogen and nitric oxide with the aid of nitrogen dioxide in the exhaust gas stream. An SCR catalytic converter is disposed downstream of the separator or filter for reducing nitrogen oxides in the exhaust gas stream into nitrogen and water vapor with the aid of ammonia or released ammonia by selective catalytic reduction.

Journal ArticleDOI
TL;DR: In this paper, the selective catalytic reduction of nitrogen oxides with ammonia as the reducing agent was studied using Fourier transform infrared (FTIR) spectroscopy, and the results indicated that the formation of nitrites or nitrates decreased as surface coverage of ammonia increased.
Abstract: The selective catalytic reduction of nitrogen oxides with ammonia as the reducing agent was studied using Fourier transform infrared (FTIR) spectroscopy. The adsorbed species found on a Cu-ZSM-5 powder during exposure to NO, NO2 or NH3 was compared to the adsorbed species identified during SCR conditions. A blocking effect caused by ammonia at 175 °C was investigated by a stepwise increase of the ammonia concentration, and the spectra indicated that the formation of nitrites or nitrates decreased as surface coverage of ammonia increased. No such effect was observed at 350 °C, since the oxidation of ammonia results in very low ammonia coverage. The effect of changes in the NO to NO2 ratio was also studied at 350 °C, and the species identified during SCR reaction indicated that the enhanced activity at equimolecular amounts of NO and NO2 possibly involves gas phase components as well as adsorbed species.

Journal ArticleDOI
TL;DR: The selective catalytic reduction (SCR) characteristics of NO and NO(2) over V (2)O(5)-WO(3)-MnO(2)/TiO( 2) catalyst using ammonia as a reducing agent have been determined in a fixed-bed reactor at 200-400 degrees C.

Journal ArticleDOI
TL;DR: In this article, the additive 0.5% H2 in the selective catalytic reduction of NO by urea (urea-SCR) caused a drastic improvement of NO reduction activity of Ag/Al2O3.
Abstract: Addition of 0.5% H2 in the selective catalytic reduction of NO by urea (urea-SCR) caused a drastic improvement of NO reduction activity of Ag/Al2O3. Among various silver-based catalysts Ag/Al2O3 showed highest activity for H2 assisted urea-SCR, and high NO conversion (above 84%) and no formation of N2O were achieved over wide temperature range (200–500 °C) at GHSV of 75,000 h−1. After H2 assisted urea-SCR at 250 °C with 10% H2O and 50 ppm SO2 under GHSV of 380,000 h−1 for 24 h, NO conversion over Ag/Al2O3 decreased from 48 to 30%, though original activity was recovered when the deactivated catalyst was heated at 500 °C in the urea-SCR condition for 1 h. The catalyst also showed high SO2-tolerance in H2 assisted NH3-SCR at 200 °C.

Journal ArticleDOI
TL;DR: In this article, the effect of electrochemical promotion for the selective catalytic reduction of NO by propene was investigated, for the first time, on a Pt impregnated catalyst film directly deposited onto a Na-β″-Al 2 O 3 solid electrolyte.
Abstract: The effect of electrochemical promotion for the selective catalytic reduction of NO by propene was investigated, for the first time, on a Pt impregnated catalyst film directly deposited onto a Na–β″-Al 2 O 3 solid electrolyte. The effect of sodium promoters on the activity and N 2 selectivity was evaluated at 240 °C under different oxygen concentrations (0.5, 1 and 5%). The presence of promoters still enhanced the selectivity to N 2 , even under large excess of oxygen (5%), where the N 2 reaction rate was increased by a factor of 1.8. Nevertheless, the promotional effect of sodium on the overall catalytic activity for NO removal was progressively lowered with increasing oxygen concentrations, as a result of a strong inhibition of propene adsorption and a relative increase of the oxygen coverage. Characterization by cyclic voltammetry supported these results, providing useful information about the chemisorption of reactant species under the different reaction conditions.

Journal ArticleDOI
TL;DR: In this paper, a chemically consistent dynamic kinetic model of the NH3−NO/NO2NH3-NO2 reacting system was developed on the basis of an extensive fundamental research carried out over a commercial V2O5-WO3/TiO2 selective catalytic reduction (SCR) catalyst for automotive applications.


Journal ArticleDOI
TL;DR: In this article, the effect of sulfation of vanadia-titania binary solid prepared by sol-gel process on its activity for the selective catalytic reduction (SCR) of NO with NH3 was examined.
Abstract: This paper examines the effect of sulfation of vanadia-titania binary solid prepared by sol-gel process on its activity for the selective catalytic reduction (SCR) of NO with NH3. Sulfated and unsulfated vanadia titania have been characterized by means of N-2 adsorption-desorption at 77 K, XRD, TGA, propan-2-ol conversion as acid test, H-2-TPR measurements, EPR, XPS and Raman spectroscopies. The main results of this study highlight the interaction of sulfate ions with vanadia species. The ternary catalyst VTiS exhibits a high activity compared to binary TiS or VTi samples. It is concluded that sulfate species improve the superficial acidity of solid and interact with vanadia leading to a better reducibility of VTiS oxide. (c) 2006 Elsevier B.V. All rights reserved.