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Showing papers on "Selective catalytic reduction published in 2006"


Journal ArticleDOI
TL;DR: It is proposed that future research in this area should focus on determining the reaction mechanism and kinetics and searching for more cost-effective catalyst and support materials.
Abstract: Methods for removing mercury from flue gas have received increased attention because of recent limitations placed on mercury emissions from coal-fired utility boilers by the U. S. Environmental Protection Agency and various states. A promising method for mercury removal is catalytic oxidation of elemental mercury (Hg0) to oxidized mercury (Hg2+), followed by wet flue gas desulfurization (FGD). FGD cannot remove Hg0, but easily removes Hg2+ because of its solubility in water. To date, research has focused on three broad catalyst areas: selective catalytic reduction catalysts, carbon-based materials, and metals and metal oxides. We review published results for each type of catalyst and also present a discussion on the possible reaction mechanisms in each case. One of the major sources of uncertainty in understanding catalytic mercury oxidation is a lack of knowledge of the reaction mechanisms and kinetics. Thus, we propose that future research in this area should focus on two major aspects: determining the reaction mechanism and kinetics and searching for more cost-effective catalyst and support materials.

492 citations


Journal ArticleDOI
Zhiming Liu1, Seong Ihl Woo1
TL;DR: In this paper, the authors classified the selective catalytic reduction (SCR) of NOx by hydrocarbon into two categories: one is the adsorption/dissociation mechanism, and the other is the oxidation reduction mechanism.
Abstract: The catalytic removal of nitrogen oxide (NOx) under lean‐burn conditions is one of the most important targets in catalysis research. Some lean‐NOx control technologies such as the direct decomposition of NOx, NOx storage‐reduction (NSR), and selective catalytic reduction (SCR) using different reducing agents (diesel soot, NH3, or hydrocarbon) are described. The reaction mechanism of NSR, which is the most promising technology, together with some novel NSR catalysts is discussed. Some mechanisms of SCR of NOx by hydrocarbon (HC‐SCR) were classified into two categories: one is the adsorption/dissociation mechanism, and the other is the oxidation‐reduction mechanism. Based on the discussion of the reaction mechanism, the influence of some factors (catalyst support, metal loading, calcination temperature, catalyst preparation method, oxygen, reducing agents, water, and sulfur) on the activity of HC‐SCR catalyst is discussed. It seems that Ag/Al2O3 catalyst offers the most promising for SCR of NOx by hydrocarb...

484 citations


Journal ArticleDOI
TL;DR: In this article, the influence of NO2 on the selective catalytic reduction (SCR) of NO with ammonia was studied over Fe-ZSM5 coated on cordierite monolith.
Abstract: The influence of NO2 on the selective catalytic reduction (SCR) of NO with ammonia was studied over Fe-ZSM5 coated on cordierite monolith. NO2 in the feed drastically enhanced the NOx removal efficiency (DeNOx) up to 600 °C, whereas the promoting effect was most pronounced at the low temperature end. The maximum activity was found for NO2/NOx = 50%, which is explained by the stoichiometry of the actual SCR reaction over Fe-ZSM5, requiring a NH3:NO:NO2 ratio of 2:1:1. In this context, it is a special feature of Fe-ZSM5 to keep this activity level almost up to NO2/NOx = 100%. The addition of NO2 to the feed gas was always accompanied by the production of N2O at lower and intermediate temperatures. The absence of N2O at the high temperature end is explained by the N2O decomposition and N2O-SCR reaction. Water and oxygen influence the SCR reaction indirectly. Oxygen enhances the oxidation of NO to NO2 and water suppresses the oxidation of NO to NO2, which is an essential preceding step of the actual SCR reaction for NO2/NOx

283 citations


Journal ArticleDOI
TL;DR: In this article, the selective catalytic reduction of nitrogen oxides (NOx) with ammonia over ZSM-5 catalysts was studied with and without water vapor, and the results showed that the activity was greatly enhanced by the introduction of copper ions.
Abstract: The selective catalytic reduction of nitrogen oxides (NOx) with ammonia over ZSM-5 catalysts was studied with and without water vapor. The activity of H-, Na- and Cu-ZSM-5 was compared and the result showed that the activity was greatly enhanced by the introduction of copper ions. A comparison between Cu-ZSM-5 of different silica to alumina ratios was also performed. The highest NO conversion was observed over the sample with the lowest silica to alumina ratio and the highest copper content. Further studies were performed with the Cu-ZSM-5-27 (silica/alumina = 27) sample to investigate the effect of changes in the feed gas. Oxygen improves the activity at temperatures below 250 °C, but at higher temperatures O2 decreases the activity. The presence of water enhances the NO reduction, especially at high temperature. It is important to use about equal amounts of nitrogen oxides and ammonia at 175 °C to avoid ammonia slip and a blocking effect, but also to have high enough concentration to reduce the NOx. At high temperature higher NH3 concentrations result in additional NOx reduction since more NH3 becomes available for the NO reduction. At these higher temperatures ammonia oxidation increases so that there is no ammonia slip. Exposing the catalyst to equimolecular amounts of NO and NO2 increases the conversion of NOx, but causes an increased formation of N2O.

243 citations


Journal ArticleDOI
TL;DR: In this article, new Fe 2 O 3 based materials are developed for the selective catalytic reduction (SCR) of NO x by NH 3 in diesel exhaust, and the highest catalytic activity is observed for ZrO 2 that is coated with 1.4Fe/7.0W/Zr catalyst.
Abstract: In this study, new Fe 2 O 3 based materials are developed for the selective catalytic reduction (SCR) of NO x by NH 3 in diesel exhaust. As a result of the catalyst screening, performed in a synthetic model exhaust, ZrO 2 is considered to be the most effective carrier for Fe 2 O 3 . The modification of the Fe 2 O 3 /ZrO 2 system with tungsten leads to drastic increase of SCR performance as well as pronounced thermal stability. These results show that tungsten acts as bifunctional component. The highest catalytic activity is observed for ZrO 2 that is coated with 1.4 mol% Fe 2 O 3 and 7.0 mol% WO 3 (1.4Fe/7.0W/Zr). By the use of this catalyst quantitative conversion of NO x is obtained between 285 and 430 °C with selective formation of N 2 . Here, the turnover frequency of NO x per Fe atom is found to be 35 × 10 −5 s −1 that indicates a high catalytic performance. The SCR activity of the 1.4Fe/7.0W/Zr material is decreased in the presence of H 2 O and CO 2 , whereas it is increased by NO 2 . Temperature programmed reduction by H 2 (HTPR) analyses show that the Fe sites of the 1.4Fe/7.0W/Zr catalyst are mainly in the form of crystalline Fe 2 O 3 , whereby relatively small oxide entities are also present. The strongly aggregated Fe 2 O 3 species are associated with the presence of the promoter tungsten. Based upon stationary catalytic examinations as well as diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) studies we postulate an Eley Rideal type mechanism for SCR on 1.4Fe/7.0W/Zr catalyst. The mechanistic model includes a redox cycle of the active Fe sites. As first reaction step, we assume dissociative adsorption of NH 3 that leads to partial reduction of the iron as well as to production of very reactive amide surface species. These amide intermediates are supposed to react with gaseous NO to form N 2 and H 2 O. In the final step, the reduced Fe sites be regenerated by oxidation with O 2 . As a side reaction of SCR, imide species, originated from decomposition of amide, are oxidized by NO 2 or O 2 into NO.

228 citations


Journal ArticleDOI
TL;DR: In this article, the performance of the CuZSM5 catalyst in the urea selective catalytic reduction (SCR) process was examined under a simulated feed gas stream containing 10% water at a temperature range of 600-800°C.

203 citations


Journal ArticleDOI
TL;DR: A series of TiO2-, Al2O3-, and SiO2-supported manganese oxide catalysts were prepared, characterized, and catalytically tested for selective catalytic reduction (SCR) of NO with NH3 in the presence of excess oxygen at low temperatures (373−523 K) as discussed by the authors.
Abstract: A series of TiO2-, Al2O3-, and SiO2-supported manganese oxide catalysts were prepared, characterized, and catalytically tested for selective catalytic reduction (SCR) of NO with NH3 in the presence of excess oxygen at low temperatures (373−523 K). Various commercial supports were used in this study to find out the influence of surface area, support nature (acidic, basic), and crystalline phase on SCR activity. XRD studies reveal the presence of anatase and rutile phases for titania supports and the existence of γ-alumina in the case of alumina support. Silica support was amorphous. No independent lines corresponding to the crystalline MnO2 were observed on pure anatase and rutile samples. However, the presence of MnO2 was confirmed on other supports by XRD. BET surface area values suggest that specific surface area of the supports was decreased after impregnating with MnO2. The FT-IR and ammonia TPD studies indicate the presence of two types of acid sites on these catalysts, and the acidic strength of the...

202 citations


Journal ArticleDOI
TL;DR: A series of Fe-ZSM-5 catalysts prepared by improved liquid ion exchange (see part I [J. Catal. 231 (2005) 314]) containing 0.2-1.2 wt% Fe, with a systematically changing nature of Fe sites, was studied during the selective catalytic reduction (SCR) of NO with NH 3 or isobutane or during the interaction with feed components by various in situ methods (EPR, UV-vis, and FTIR spectroscopy) as discussed by the authors.

196 citations


Proceedings ArticleDOI
03 Apr 2006
TL;DR: In this article, a 3D numerical computer model of the injection of urea-water-solution and their interaction with the exhaust gas flow and exhaust tubing is developed to evaluate different configurations during the development process of such a DeNOxsystem.
Abstract: The selective catalytic reduction (SCR) based on ureawater-solution is an effective technique to reduce nitrogen oxides (NOx) emitted from diesel engines. A 3D numerical computer model of the injection of urea-water-solution and their interaction with the exhaust gas flow and exhaust tubing is developed to evaluate different configurations during the development process of such a DeNOxsystem. The model accounts for all relevant processes appearing from the injection point to the entrance of the SCR-catalyst:

187 citations


Journal ArticleDOI
TL;DR: In this paper, the performance of Fe-ZSM5 was investigated in the selective catalytic reduction of NO with ammonia over a broad temperature range, applying simulated diesel exhaust gas conditions.
Abstract: Fe-ZSM5 coated on cordierite monolith was investigated in the selective catalytic reduction (SCR) of NO with ammonia over a broad temperature range, applying simulated diesel exhaust gas conditions. The catalyst exhibited over 80% NOx reduction (DeNOx) from 400 to 650 °C at very good selectivity. The dosage of variable amounts of ammonia in the catalytic tests revealed that the SCR reaction is inhibited by ammonia. At very high temperatures DeNOx is reduced due to the selective catalytic oxidation (SCO) of ammonia to nitrogen and the oxidation to NO. Water-free experiments resulted in generally higher DeNOx values, which are explained by the inhibiting effect of water on the NO oxidation capability of Fe-ZSM5. The catalyst was stable upon thermal ageing and only 5–15% loss in DeNOx activity was observed after hydrothermal treatment. This loss in DeNOx is in parallel with a loss of ammonia storage capacity of the aged catalyst. Characterization by NH3 TPD and MAS 27Al NMR spectroscopy revealed dealumination of the zeolite by hydrothermal ageing, which reduces the Bronsted acidity of the catalyst.

185 citations


Journal ArticleDOI
TL;DR: In this article, the role of silver and alumina in Ag-alumina catalysts for the selective catalytic reduction (SCR) of NO x by methane in gas streams containing excess oxygen was examined.

Journal ArticleDOI
TL;DR: In this paper, the optimal proportions of Pt-Cu and Pd-Cu in bimetallic catalysts on activated carbon, obtained by wetness impregnation, have been found.
Abstract: The increasing pollution of natural sources of drinking water encourages the development of new emerging technologies and processes for water remediation. This work deals with the study of catalytic reduction of contaminated waters containing nitrates (60 ppm) in a continuous reactor working at room temperature and atmospheric pressure and using hydrogen as reducing agent. Optimal proportions of Pt-Cu and Pd-Cu in bimetallic catalysts on activated carbon, obtained by wetness impregnation, have been found. Besides, novel catalysts obtained from copper nanoparticles doped with Pd or Pt and supported on activated carbon, have also been studied. For all catalysts the Pt-Cu pair seems to be more selective in the transformation of the nitrates ions to nitrogen compared to Pd-Cu pair. Furthermore, considering the noble metal amount, the bimetallic nanosphere catalysts are more active (between 20 and 50) than the impregnated ones. The catalysts have been characterized by hydrogen chemisorption, BET, X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analysis. During the reaction, a considerable amount of the noble metal in its oxidised form has been detected. Based on this result an additional step to the generally accepted reaction mechanism of the nitrate reduction has been proposed.

Journal ArticleDOI
TL;DR: The current research of supported Ag catalysts is reviewed from the viewpoints of practical use and the reaction mechanism, i.e., the reaction scheme, the role of surface adsorbed species, and the structure of active Ag species.
Abstract: Selective catalytic reduction of NO by hydrocarbons (HC-SCR) is one of the promising technologies for removal of NO in exhausts containing excess oxygen, such as diesel and lean burn gasoline engines. Supported Ag catalysts, especially Ag/Al2O3, are thought to be the promising candidates for use in diesel exhausts, as confirmed by several reports on engine bench tests. The HC-SCR performance of supported Ag catalysts is very sensitive to the reaction conditions, especially the type of hydrocarbons and the addition of H2. The control of reaction conditions would be key for practical use. The current research of supported Ag catalysts is reviewed from the viewpoints of practical use and the reaction mechanism, i.e., the reaction scheme, the role of surface adsorbed species, and the structure of active Ag species.

Journal ArticleDOI
TL;DR: In this article, the authors reported on the efficiency of the catalytic reduction of nitrogen monoxide (NO) and the selectivity towards NH 3. Chemical ionization mass spectrometry (CIMS) has been applied to monitor NH 3 and NO emissions at a time resolution of 2.

Journal ArticleDOI
TL;DR: In this article, transient kinetic data demonstrate an inhibiting effect of ammonia on the NH3-selective catalytic reduction (SCR) of nitric oxide (NO) at low temperatures over a V2O5-WO3/TiO2 commercial catalyst for vehicles.
Abstract: We present transient kinetic data that demonstrate an inhibiting effect of ammonia on the NH3-selective catalytic reduction (SCR) of nitric oxide (NO) at low temperatures over a V2O5-WO3/TiO2 commercial catalyst for vehicles. This effect has significant mechanistic as well as practical implications. It cannot be reproduced by conventional or modified Eley–Rideal approaches used in the past for SCR-deNOx stationary applications, but is well described by a novel dual-site redox rate expression assuming that ammonia may block the vanadium-related catalyst sites for NO + NH3 activation. The same rate model also successfully represents the kinetic influence of the oxygen concentration. It is shown that account of ammonia inhibition at low temperatures is critical for simulating the highly transient operation of onboard SCR converters for diesel exhaust aftertreatment. © 2006 American Institute of Chemical Engineers AIChE J, 2006

Journal ArticleDOI
TL;DR: In this paper, a series of Fe-based perovskites with high specific surface area was prepared by a new method, reactive grinding, and characterized by N 2 adsorption, XRD, SEM, H 2 -TPR, TPD of O 2, TPDP of NO+O 2,TPD of C 3 H 6, and TPSR of NO−O 2 under C 3H 6 /He flow.

Journal ArticleDOI
TL;DR: The catalytic conversion of NO to NO2 and the catalytic decomposition of NOx were observed on the tertiary catalysts during NOx adsorption at 300 degrees C, which was highly related to the loading of cobalt.
Abstract: CoxMg3-x/Al hydrotalcite-like compounds (where x=0.0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0) were synthesized by the coprecipitation method and characterized by the XRD and TGA techniques. Incorporation of Co for x=0.0-3.0 gradually decreased the transformation temperature of the hydrotalcites to the corresponding oxides from 444 to 246 degrees C and also decreased the surface area from 162.7 to 21.6 m2/g upon calcination at 800 degrees C for 4 h in air. The resultant oxide was generally composed of a poor MgO phase and a spinel phase, with more spinel phase at higher Co incorporation. The derived oxides were tested as the storage/reduction catalysts for NOx adsorption/desorption. The storage capacity for NOx was highly dependent on the catalyst composition and storage temperature. In general, more NOx was stored at lower temperature (100 degrees C) than that at higher temperature (300 degrees C), and tertiary catalysts (x=0.5-2.5) stored more NOx than binary catalyst (x=0.0 or 3.0). The catalytic conversion of NO to NO2 and the catalytic decomposition of NOx were observed on the tertiary catalysts during NOx adsorption at 300 degrees C, which was highly related to the loading of cobalt. The reducibility of catalysts was determined by TPR experiments, and the reduction of cobalt cations started at 150-200 degrees C in H2. In situ IR spectra of catalysts adsorbing NOx revealed that the major NOx species formed on the catalysts were various kinds of nitrites and nitrates, together with some forms of dimers, such as N2O2(2-) and N2O4 (or NO+NO3-). The storage/reduction mechanism and the function of Co in the mixed oxides are proposed and discussed on the basis of these observations.

Journal ArticleDOI
TL;DR: A kinetic model for predicting the amount of mercury (Hg) oxidation across selective catalytic reduction (SCR) systems in coal–fired power plants was developed and tested and can be used to predict the impact of coal properties, catalyst design, and operating conditions on Hg oxidation across SCRs.
Abstract: A kinetic model for predicting the amount of mercury (Hg) oxidation across selective catalytic reduction (SCR) systems in coal–fired power plants was developed and tested. The model incorporated the effects of diffusion within the porous SCR catalyst and the competition between ammonia and Hg for active sites on the catalyst. Laboratory data on Hg oxidation in simulated flue gas and slipstream data on Hg oxidation in flue gas from power plants were modeled. The model provided good fits to the data for eight different catalysts, both plate and monolith, across a temperature range of 280–420 °C, with space velocities varying from 1900 to 5000 hr–1. Space velocity, temperature, hydrochloric acid content of the flue gas, ratio of ammonia to nitric oxide, and catalyst design all affected Hg oxidation across the SCR catalyst. The model can be used to predict the impact of coal properties, catalyst design, and operating conditions on Hg oxidation across SCRs.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the performance of mixed oxide catalysts in selective catalytic reduction of NO x by NH 3 and showed a clear correlation between the dependence of these properties and the mixed oxide composition.
Abstract: Manganese–cerium mixed oxide catalysts with different molar ratio Mn/(Mn + Ce) (0, 0.25, 0.50, 0.75, 1) were prepared by citric acid method and investigated concerning their adsorption behavior, redox properties and behavior in the selective catalytic reduction of NO x by NH 3 . The studies based on pulse thermal analysis combined with mass spectroscopy and FT-IR spectroscopy uncovered a clear correlation between the dependence of these properties and the mixed oxide composition. Highest activity to nitrogen formation was found for catalysts with a molar ratio Mn/(Mn + Ce) of 0.25, whereas the activity was much lower for the pure constituent oxides. Measurements of adsorption uptake of reactants, NO x (NO, NO 2 ) and NH 3 , and reducibility showed similar dependence on the mixed oxide composition indicating a clear correlation of these properties with catalytic activity. The adsorption studies indicated that NO x and NH 3 are adsorbed on separate sites. Consecutive adsorption measurements of the reactants showed similar uptakes as separate measurements indicating that there was no interference between adsorbed reactants. Mechanistic investigations by changing the sequence of admittance of reactants (NO x , NH 3 ) indicated that at 100–150 °C nitrogen formation follows an Eley–Rideal type mechanism, where adsorbed ammonia reacts with NO x in the gas phase, whereas adsorbed NO x showed no significant reactivity under conditions used.

Journal ArticleDOI
TL;DR: In this article, the selective catalytic reduction of NOx in the typical operation temperatures and oxygen concentrations of diesel engines has been studied in the presence of V3W9Ti in a tubular flow reactor.

Journal ArticleDOI
TL;DR: Variations of the terphenyl substituents in the triamidoamine ligand demonstrate that the original ligand is not unique in its ability to yield successful catalysts, but complexes that contain sterically less demanding ligands fail to catalyze formation of ammonia from dinitrogen.
Abstract: Since our discovery of the catalytic reduction of dinitrogen to ammonia at a single molybdenum center, we have embarked on a variety of studies designed to further understand this complex reaction cycle. These include studies of both individual reaction steps and of ligand variations. An important step in the reaction sequence is exchange of ammonia for dinitrogen in neutral molybdenum(III) compounds. We have found that this exchange reaction is first order in dinitrogen and relatively fast (complete in <1 h) at 1 atm of dinitrogen. Variations of the terphenyl substituents in the triamidoamine ligand demonstrate that the original ligand is not unique in its ability to yield successful catalysts. However, complexes that contain sterically less demanding ligands fail to catalyze formation of ammonia from dinitrogen; it is proposed as a consequence of a base-catalyzed decomposition of a diazenido (MoNNH) intermediate.

Journal ArticleDOI
TL;DR: A review of the work in this area can be found in this article, where the authors use in situ UV-Vis spectroscopy to monitor the form of Ag in the catalyst and appear to indicate that the addition of hydrogen promotes the formation of small Ag clusters which are highly reactive for NO − 1 − 3 conversion.
Abstract: Research is progressing fast in the field of the hydrogen assisted hydrocarbon selective catalytic reduction (HC-SCR) over Ag-based catalysts: this paper is a review of the work to date in this area. The addition of hydrogen to the HC-SCR reaction feed over Ag/Al2O3 results in a remarkable improvement in NO x conversion using a variety of different hydrocarbon feeds. There is some debate concerning the role that hydrogen has to play in the reaction mechanism and its effect on the form of Ag present during the reaction. Many of the studies use in situ UV–Vis spectroscopy to monitor the form of Ag in the catalyst and appear to indicate that the addition of hydrogen promotes the formation of small Ag clusters which are highly reactive for NO x conversion. However, some authors have expressed concern about the use of this technique for these materials and further work is required to address these issues before this technique can be used to give an accurate assessment of the state of Ag during the SCR reaction. A study using in situ EXAFS to probe the H2 assisted octane-SCR reaction has shown that small Ag particles (containing on average 3 silver atoms) are formed during the SCR reaction but that the addition of H2 to the feed does not result in any further change in the Ag particle size. This points to the direct involvement of H2 in the reaction mechanism. Clearly the addition of hydrogen results in a large increase in the number and variety of adsorbed species on the surface of the catalyst during the reaction. Some authors have suggested that conversion of cyanide to isocyanate is the rate-determining step and that hydrogen promotes this conversion. Others have suggested that hydrogen reduces nitrates to more reactive nitrite species which can then activate the hydrocarbon; activation of the hydrocarbon to form acetates has been proposed as the key step. It is probable that all these promotional effects can take place and that it very much depends on the reaction temperature and feed conditions as to which one is most important.

Journal ArticleDOI
TL;DR: In this paper, the authors presented a new benchmark for the automobile selective catalytic reduction of NOx : Mg(NH3)6Cl2, which has a high volumetric ammonia density of up to 93% of that of liquid ammonia.

Journal ArticleDOI
TL;DR: In this paper, the authors used 1%Pd/TiO2/Al2O3 as the catalyst and at temperatures ranging from 140 to 180°C, the V2O5-containing catalyst not only increases NO conversion but also widens the reaction temperature window to 250°C.

Journal ArticleDOI
TL;DR: In this paper, the selective catalytic reduction (SCR) of nitric oxide by ammonia on V 2 O 9 H 8 cluster was simulated by means of density functional theory (DFT) calculations performed at B3LYP/6-31G * level.

Journal ArticleDOI
TL;DR: In this article, the V2O5-WO3 catalysts loaded on the Ti-rich TiO 2-SiO2-SO42− prepared by the coprecipitation method were investigated for the influences of the active components and the supports on the activities in SCR of NO by NH3 and in the oxidation of SO2 in comparison with a commercial V 2O5 WO3/TiO2 -SO42 − catalyst.
Abstract: The V2O5-WO3 catalysts loaded on the Ti-rich TiO2-SiO2-SO42− prepared by the coprecipitation method were investigated for the influences of the active components and the supports on the activities in SCR of NO by NH3 and in the oxidation of SO2 in comparison with a commercial V2O5-WO3/TiO2-SO42− catalyst. The physico-chemical properties of the catalysts were characterized by BET, XRD, IR, Raman, NH3-TPD, XPS and acidity measurements. The incorporation of sulfate to TiO2-SiO2 considerably increases the acidity of TiO2-SiO2, especially Bronsted acidity of the corresponding catalyst, resulting in the remarkable increase of the SCR activity and simultaneously, the addition of WO3 significantly enhances the SCR activity. The SCR activity changes depending on the calcination temperature of TiO2-SiO2-SO42−, which influences its acidity, surface area and titania crystallinity. The higher SCR activity was observed at high vanadia loadings above 2 wt.% as compared with the V2O5-WO3/TiO2-SO42− catalyst. This seems to be due to the fact that polymeric vanadates on the catalyst, which cause the oxidation of NH3 to N2O, are almost absent as evidenced by Raman analysis. The SO2 oxidation activity is increased by elevating the calcination temperature of TiO2-SiO2-SO42−, which shifts the oxidation state of vanadium species to the higher state, and the activity is slightly enhanced by WO3 but not changed by sulfate. The tendency of the increase in the SO2 oxidation activity with increasing V2O5 loadings is significantly smaller than the V2O5-WO3/TiO2-SO42− catalyst. This was attributed to the lower oxidation state of vanadium species, almost the absence of polymeric vanadates responsible for the SO2 oxidation and also a more strongly inhibiting effect of ammonia on the oxidation of SO2.

Journal ArticleDOI
TL;DR: In this article, the authors studied the inhibition effect of H2O on V2O5/AC catalyst for NO reduction with NH3 at temperatures up to 250°C through TPD, elemental analyses, temperature-programmed surface reaction (TPSR) and FT-IR analyses.
Abstract: The inhibition effect of H2O on V2O5/AC catalyst for NO reduction with NH3 is studied at temperatures up to 250 °C through TPD, elemental analyses, temperature-programmed surface reaction (TPSR) and FT-IR analyses. The results show that H2O does not reduce NO and NH3 adsorption on V2O5/AC catalyst surface, but promotes NH3 adsorption due to increases in Bronsted acid sites. Many kinds of NH3 forms present on the catalyst surface, but only NH4+ on Bronsted acid sites and a small portion of NH3 on Lewis acid sites are reactive with NO at 250 °C or below, and most of the NH3 on Lewis acid sites does not react with NO, regardless the presence of H2O in the feed gas. H2O inhibits the SCR reaction between the NH3 on the Lewis acid sites and NO, and the inhibition effect increases with increasing H2O content. The inhibition effect is reversible and H2O does not poison the V2O5/AC catalyst.

Journal ArticleDOI
TL;DR: In this article, the authors show that high temperature FeCl3 sublimation leads to isolated and hydroxylated iron species (Fe(OH)2) attached to the ion exchange positions of ZSM-5.

Journal ArticleDOI
TL;DR: The key role of acid treatment on carbon surface chemistry and pore structure, which are closely related to catalyst dispersion and adsorption capacity, is examined and found that under the NO/NH(3)=1 the NO could be selective catalytic reduction with NH(3), which catalyzed by fresh and spent AC-supported catalyst.

Journal ArticleDOI
TL;DR: In this paper, the performance of the LaMnO 3 perovskites with high specific surface areas was characterized by N 2 adsorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), H 2 -temperature programmed reduction (TPR), O 2 -, NO+O 2 - and C 3 H 6 -temper programmed desorption (TPD) under C 3H 6 /He flow.
Abstract: Nanoscale LaMn 1− x Cu x O 3 perovskites with high specific surface areas were prepared by reactive grinding and characterized by N 2 adsorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), H 2 -temperature programmed reduction (TPR), O 2 -, NO + O 2 - and C 3 H 6 -temperature programmed desorption (TPD) and NO + O 2 -temperature programmed surface reduction (TPSR) under C 3 H 6 /He flow. The samples were then submitted to activity tests in the selective catalytic reduction (SCR) of NO by C 3 H 6 with or without O 2 . The catalytic performances over unsubstituted LaMnO 3 is observed with maximum N 2 yield of 62% and a C 3 H 6 conversion of 80% at 550 °C at a space velocity of 50,000 h −1 (3000 ppm NO, 3000 ppm C 3 H 6 , 1% O 2 in helium). The N 2 yield is however significantly improved by Cu incorporation into the lattice, achieving a remarkable N 2 yield of 86% at 500 °C at 20% Mn substitution by Cu. The content of α-oxygen over lanthanum manganite is enhanced by Cu substitution, but the opposite occurs for excess oxygen. The better performance of Cu-substituted samples is likely to correspond to the facility in the formation of adsorbed nitrate species via the oxidation of NO by α-oxygen in addition to the intrinsic effect of Cu in NO transformation. However, the excessive α-oxygen content observed over LaCo 0.8 Cu 0.2 O 3 accelerated the unselective hydrocarbon oxidation and suppressed the formation of organo nitrogen compounds, which led to a poor N 2 yield with respect to Mn-based perovskites. A mechanism involving the formation of an organic nitrogen intermediate, which further converts into N 2 , CO 2 and H 2 O via isocyanate, was proposed. The gas phase oxygen acts as a promoter when its concentration is lower than 1000 ppm because of the promotion of nitrate formation and organo nitrogen compounds transformation. O 2 acts however as an inhibitor when its concentration is higher than 5000 ppm due to the heavily unselective combustion of C 3 H 6 by O 2 , in the reaction of NO and C 3 H 6 over LaMn 0.8 Cu 0.2 O 3 at 400 °C.