Showing papers on "Selective catalytic reduction published in 2002"
TL;DR: In this paper, the authors investigated the effect of ammonium nitrate on the SCR reaction in the presence of NO and showed that ammonium Nitrate can lead to the formation of NO 2.
369 citations
TL;DR: In this paper, the NO reduction mechanism is studied using combined in situ FTIR and online mass spectrometry (OMS) to analyze reaction products, and it is concluded that both NO and NO2 are involved in the reaction with NH4+ ions to form N2.
290 citations
TL;DR: In this paper, Fe2O3-TiO2 catalysts were used for selective catalytic oxidation (SCO) of ammonia to nitrogen in the presence of excess oxygen, and they showed high selectivity for SCO.
177 citations
TL;DR: In this paper, the authors investigated the role of NO2 on catalysts based on TiO2-WO3-V2O5 and showed that the vanadium species formed during the reduction of NO with ammonia are reoxidized faster by NO2 than by oxygen, resulting in an increased reaction rate of the fast SCR reaction.
170 citations
TL;DR: Fe-Mn based transition metal oxides show nearly 100% NO conversion at 100-180 degrees C for selective catalytic reduction of NO with NH3 under the applied conditions with a space velocity of 15,000 h-1.
167 citations
Patent•
20 Dec 2002TL;DR: In this paper, a method of selectively catalyzing the reduction of NO x in an exhaust gas flowing in an internal combustion engine comprising a filter for particulate matter comprising a catalyst capable of selectively catalysing the reduction with a reducing agent was proposed.
Abstract: A method of selectively catalysing the reduction of NO x in an exhaust gas flowing in an exhaust system of an internal combustion engine comprising a filter ( 40 ) for particulate matter comprising a catalyst capable of selectively catalysing the reduction of NO x with a reducing agent, which method comprising introducing a reducing agent, or a precursor thereof, into the exhaust gas and contacting the resulting gas with the filter ( 40 ).
164 citations
TL;DR: In this paper, the main and side reactions of the three selective catalytic reduction (SCR) reactions with ammonia over TiO2−WO3−V2O5 catalysts have been investigated using synthetic gas mixtures matching the composition of diesel exhaust.
Abstract: The main and side reactions of the three selective catalytic reduction (SCR) reactions with ammonia over TiO2−WO3−V2O5 catalysts have been investigated using synthetic gas mixtures matching the composition of diesel exhaust. The three SCR reactions are standard SCR with pure NO, fast SCR with an equimolar mixture of NO and NO2, and NO2 SCR with pure NO2. At high temperatures the selective catalytic oxidation (SCO) of ammonia and the formation of nitrous oxide compete with the SCR reactions. Water strongly inhibits the SCO of ammonia and the formation of nitrous oxide, thus increasing the selectivity of the SCR reactions. However, water also inhibits SCR activity, most pronounced at low temperatures. NO2 fractions exceeding 50% enhance the formation of nitrous oxide at low temperatures. If the feed of NOx consists of pure NO2, the formation of nitrous oxide may occur by two different reactions having different temperature regimes. The reaction responsible for N2O formation at low temperatures probably invo...
161 citations
TL;DR: In this article, the combined effect of H 2 O and SO 2 on V 2 O 5 /AC was studied for selective catalytic reduction (SCR) of NO with NH 3 at lower temperatures.
Abstract: Combined effect of H 2 O and SO 2 on V 2 O 5 /AC the activity of catalyst for selective catalytic reduction (SCR) of NO with NH 3 at lower temperatures was studied. In the absence of SO 2 , H 2 O inhibits the catalytic activity, which may be attributed to competitive adsorption of H 2 O and reactants (NO and/or NH 3 ). Although SO 2 promotes the SCR activity of the V 2 O 5 /AC catalyst in the absence of H 2 O, it speeds the deactivation of the catalyst in the presence of H 2 O. The dual effect of SO 2 is attributed to the SO 4 2− formed on the catalyst surface, which stays as ammonium-sulfate salts on the catalyst surface. In the absence of H 2 O, a small amount of ammonium-sulfate salts deposits on the surface of the catalyst, which promote the SCR activity; in the presence of H 2 O, however, the deposition rate of ammonium-sulfate salts is much greater, which results in blocking of the catalyst pores and deactivates the catalyst. Decreasing V 2 O 5 loading decreases the deactivation rate of the catalyst. The catalyst can be used stably at a space velocity of 9000 h −1 and temperature of 250 °C.
148 citations
TL;DR: In this paper, the performance of SCR and SCR catalysts was investigated individually and as a combined system for the removal of NOx by ammonia using synthetic gas mixtures matching the composition of diesel exhaust.
Abstract: The performances of oxidation and SCR catalysts were investigated individually and as a combined system for the removal of NOx by ammonia. Experiments were carried out with synthetic gas mixtures matching the composition of diesel exhaust. Introducing an oxidation catalyst upstream of the SCR catalyst enhances the removal of NOx at low temperatures. The beneficial effects of combining the two catalysts are the oxidation of unburned hydrocarbons that inhibit the SCR reaction and the conversion of NO to NO2 on the oxidation catalyst. NO2 fractions up to 50% of total NOx enhance the NOx conversion at temperatures below 300 °C. However, excess NO2 should be avoided because the reaction of NO2 with ammonia is slow, resulting in a decreased NOx conversion. Above 350 °C, the NOx conversion essentially does not depend on the ratio NO2/NOx or on the presence of hydrocarbons in the feed. A simple mathematical prediction of the NOx conversion for the combined system is also possible. The parameters used in this calc...
145 citations
TL;DR: In this article, a low-temperature selective catalytic reduction (SCR) of NO x by NH 3 is described operating at temperatures lower than 470 K in the presence of water with NO conversions of 80-100% at space velocities of 30,000-50,000 h −1.
131 citations
TL;DR: In this paper, the authors studied the kinetics of the selective catalytic reduction (SCR) of NO with vanadia-based catalysts and showed that the SCR mechanism on Fe-ZSM-5 involves NO2 as an intermediate and the formation of NO2 from NO oxidation (NO+(1/2)O2→NO2) is probably the rate-determining step.
Abstract: Fe-exchanged ZSM-5 has been found previously to be much more active than commercial vanadia-based catalysts for selective catalytic reduction (SCR) of NO with NH3. The kinetics of the SCR reaction is studied in this work. The results show that the rate of NO conversion on Fe-ZSM-5 is first-order with respect to NO, zeroth-order w.r.t. NH3 and nearly half-order w.r.t. O2, at 260–300 °C. This is in good agreement with our previous FTIR result that the catalyst surface is nearly completely covered by ammonia adsorbed species (i.e. NH4+ ions) under reaction conditions. The present results further support that the SCR mechanism on Fe-ZSM-5 involves NO2 as an intermediate and the formation of NO2 from NO oxidation (NO+(1/2)O2→NO2) is probably the rate-determining step. The apparent activation energy for the reaction is found to be 54 kJ/mol.
TL;DR: In this paper, the selective catalytic reduction (SCR) of NO with NH3 was investigated using Fe-exchanged zeolites, i.e., mordenite (MOR), clinoptilolite (HEU), beta, ferrierite (FER), and chabazite (CHA).
Patent•
16 Aug 2002TL;DR: In this article, a metal-promoted zeolite beta catalyst is used for selective catalytic reduction of nitrogen oxides with ammonia in which the zeolites beta is pre-treated so as to provide improved hydrothermal stability.
Abstract: The present invention is directed to a metal-promoted zeolite beta catalyst useful in the selective catalytic reduction of nitrogen oxides with ammonia in which the zeolite beta is pre-treated so as to provide the zeolite with improved hydrothermal stability. The stabilized beta zeolite is provided by incorporating into the zeolite structure non-framework aluminum oxide chains. The aluminum oxide chains can be incorporated into the zeolite structure by a unique steaming regimen or by treatment with rare earth metals, such as cerium. The treatment process is unlike well-known methods of dealuminizing zeolites for the purpose of increasing the silica to alumina ratio. In the present invention, the non-framework aluminum oxide is characterized by FT-IR by a peak at 3781+2 cm-1, which when present, stabilizes the zeolite against further dealumination such as under oxidizing and harsh hydrothermal conditions.
TL;DR: In this article, the combination of HC-SCR and cold plasma enhanced the overall reaction rate and allowed an effective removal of NOX at low temperatures, using NH3 as a reducing agent, which resulted in an effective conversion of NO to NO2.
TL;DR: In this article, a reduced Pd/CeO2 catalyst was shown to be active for nitrate reduction in the presence of hydrogen adsorbed on palladium sites.
Patent•
30 Dec 2002TL;DR: In this article, a very high efficiency NO X aftertreatment system is provided for use in lean burn engines, where a lean NO X adsorber is synergistically combined with a selective catalytic reduction catalyst to use the ammonia formed within the NO X adorber, during regeneration of the NOX adsorbers while periodically operating the engine in a fuel-rich combustion mode.
Abstract: A very high efficiency NO X aftertreatment system is provided for use in lean burn engines. A lean NO X adsorber is synergistically combined with a selective catalytic reduction catalyst to use the ammonia formed within the NO X adsorber, during regeneration of the NO X adsorber while periodically operating the engine in a fuel-rich combustion mode, to reduce NO X remaining in the exhaust gas stream after passage through the NO X adsorber during normal operation of the engine in a lean burn combustion mode.
TL;DR: A quaternary catalyst library of 56 samples comprising all combinations of four elements, viz. Ag, Co, Cu, In, with six equally spaced atomic fraction increments from 0 to 1 was prepared by impregnation of a proprietary mesoporous alumina support as discussed by the authors.
Abstract: A quaternary catalyst library of 56 samples comprising all combinations of four elements, viz. Ag, Co, Cu, In, with six equally spaced atomic fraction increments from 0 to 1 was prepared by impregnation of a proprietary mesoporous alumina support. Catalytic properties of the library were tested in the selective catalytic reduction (SCR) of NO x by propane under lean conditions in the temperature range 400–500 °C. The catalytic data acquired by a parallel 64-channel microreactor system with automated time-of-flight mass spectrometric analysis have been evaluated regarding selectivity–compositional relationships, synergistic effects for NO x conversion, and efficiency of propane utilization. Full conversion of NO x is achieved over Ag–Co combinations at 450 °C with N 2 selectivities of more than 90% and reductant utilization of 20% in a feed of 1500 ppm NO, 1500 ppm propane and 5 vol.% O 2 (space velocity of 36,000 cm 3 g cat −1 h −1 ). For the single-component catalysts Ag/Al 2 O 3 , Co/Al 2 O 3 , Cu/Al 2 O 3 , and In/Al 2 O 3 , the state of the elements on the mesoporous alumina was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Cobalt forms a spinel-like cobalt aluminate phase whereas copper and indium are present as oxides with small sizes not detectable by XRD. Silver occurs in both metallic state and as Ag 2 O, and forms Ag n clusters of at least two different sizes, predominantly with diameters of about 30 nm. The conclusions are consistent with the reducibility of the single-component catalysts samples by H 2 . Surface area measurements and pore size distributions revealed reasonable modifications of the textural properties. The main pore size of the alumina support is decreased from 7 to ca. 5 nm after loading of the active components.
TL;DR: In this article, the mechanism of selective catalytic reduction (SCR) of NOx with NH3 over Fe/MFI was studied using in situ FTIR spectroscopy, and the authors rationalized that the consumption ratio of NO and NH3 is close to unity and that the effect of water vapor depends on the reaction temperature.
Abstract: The mechanism of selective catalytic reduction (SCR) of NOx with NH3 over Fe/MFI was studied using in situ FTIR spectroscopy. Exposing Fe/MFI first to NH3 then to flowing NO + O2 or using the reversed sequence, invariably leads to the formation of ammonium nitrite, NH4NO2. In situ FTIR results in flowing NO + NH3 + O2 at different temperatures show that NH3 is strongly adsorbed and reacts with impinging NOx. The intensity of the NH4NO2 bands initially increases with temperature, but passes through a maximum at 120 °C because the nitrite decomposes to N2 + H2O. The mechanistic model rationalizes that the consumption ratio of NO and NH3 is close to unity and that the effect of water vapor depends on the reaction temperature. At high temperature H_2O enhances the rate because it is needed to form NH4NO2. At low temperature, when adsorbed H2O is abundant it lowers the rate because it competes with NOx for adsorption sites.
TL;DR: The addition of copper to alumina-supported silver catalysts, by co-incipient wetness impregnation, increased the selectivity to nitrogen during the catalytic oxidation of ammonia at 250°C without significant decrease in activity relative to that of Ag/alumina alone as mentioned in this paper.
TL;DR: In this article, a small amount of noble metal (Pt, Rh or Pd) was added to the Fe-ZSM-5 catalyst to reduce the reaction temperature to 250-350 °C.
Abstract: We have reported previously the excellent performance of Fe-exchanged ZSM-5 for selective catalytic oxidation (SCO) of ammonia to nitrogen at high temperatures (e.g., 400-500 °C). The present work indicates that the reaction temperature can be decreased to 250-350 °C when a small amount of noble metal (Pt, Rh or Pd) is added (by both doping and ion exchange) to the Fe-ZSM-5. The SCO activity follows the order: Pt/Fe-ZSM-5 > Rh/Fe-ZSM-5 > Pd/Fe-ZSM-5. The noble metal promoted Fe-ZSM-5 catalysts also show higher activity for NH3 oxidation than Ce-exchanged Fe-ZSM-5 at low temperatures. On the Pt promoted Fe-ZSM-5, near 100% of NH3 conversion is obtained at 250 °C at a high space velocity (GHSV = 2.3 × 105 h-1) and nitrogen is the main product. The presence of H2O and SO2 decreases the SCO performance only slightly. This catalyst is a good candidate for solving the ammonia slip problem that plagues the selective catalytic reduction (SCR) of NO with ammonia in power plants.
Patent•
17 Jun 2002
TL;DR: In this article, the authors describe a method for generating ammonia from urea based on the hydrolysis of an aqueous solution of urea and/or biuret by heating under pressure.
Abstract: This patent describes technology for generating ammonia from urea. The method is based on the hydrolysis of an aqueous solution of urea and/or biuret by heating under pressure to form a mixture of ammonia, carbon dioxide and water. The gas mixtures produced are useful for supplying ammonia at controlled pressure and rate of flow for many industrial applications without the risks and hazards associated with the transportation and on-site storage of ammonia, thereby providing a significant safety advantage over present industrial practice.
TL;DR: A series of Pt and Pt,Cu supported catalysts were prepared by wet impregnation of Mg-Al supports obtained from hydrotalcite-type (HT) precursor compounds as mentioned in this paper.
TL;DR: In this paper, a bimetallic Pt-Cu/γAl 2 O 3 catalyst has been prepared by controlled deposition of copper onto platinum particles according to a redox reaction between hydrogen, pre-adsorbed on metallic platinum, and Cu 2+ ions in water.
Abstract: Bimetallic Pt-Cu/γAl 2 O 3 catalyst has been prepared by controlled deposition of copper onto platinum particles according to a redox reaction between hydrogen, pre-adsorbed on metallic platinum, and Cu 2+ ions in water. This catalyst has been submitted to either oxidizing or reducing treatments, at ambient temperature or at 400 °C. The interaction between copper and platinum in the bimetallic catalysts was estimated from temperature-programmed reduction (TPR) profiles, determined after various pre-treatments, and compared to that of a fresh catalyst. It was demonstrated that reducing and oxidizing pre-treatments noticeably affect the interactions between platinum and copper and consequently the catalytic activity for nitrate reduction in water.
TL;DR: In this paper, the combination of SCR and cold plasma enhances the overall reaction and allows an effective removal of NOx at relatively low temperatures, with an energy effort of ca. 30 eV per NO-molecule, a temperature of 300 ǫ c and a space velocity of 20,000 h−1 at the catalyst.
Abstract: The oxidative potential of a non-thermal plasma (NTP) in engine off-gases with excess oxygen results in an effective conversion of NO to NO2 that can be converted synergistically to molecular nitrogen with appropriate catalysts by selective catalytic reduction of NO2 with hydrocarbons (HC-SCR). The hydrocarbon added has two essential functions: first, it assists the gas-phase oxidation of NO to NO2 by the electric discharge in excess oxygen and, secondly, it reacts with NO2 in the hydrocarbon SCR. Besides CO2 and CO, significant amounts of formaldehyde and acetaldehyde are formed in the plasma-initiated gas-phase reaction. These and other by-products are involved together with the remaining propene in the subsequent catalytic reaction. The combination of SCR and cold plasma enhances the overall reaction and allows an effective removal of NOx at relatively low temperatures. Certain modifications of Al2O3 and ZrO2 have been found to be effective as catalysts in this reaction. With an energy effort of ca. 30 eV per NO-molecule, a temperature of 300 °C and a space velocity of 20,000 h−1 at the catalyst, it is possible to reduce 500 ppm NO in excess oxygen by more than half. The synergistic combination of NTP and HC-SCR has been verified under real conditions with exhaust gas from a diesel engine.
Patent•
17 Jul 2002TL;DR: In this paper, the authors proposed an emission abatement system with a source of emissions and a catalyst for receiving the emissions, which includes absorber catalysts and selective catalytic reduction catalysts.
Abstract: Emission abatement system. The system includes a source of emissions and a catalyst for receiving the emissions. Suitable catalysts are absorber catalysts and selective catalytic reduction catalysts. A plasma fuel converter generates a reducing gas from a fuel source and is connected to deliver the reducing gas into contact with the absorber catalyst for regenerating the catalyst. A preferred reducing gas is a hydrogen rich gas and a preferred plasma fuel converter is a plasmatron. It is also preferred that the absorber catalyst be adapted for absorbing NO x .
TL;DR: In this paper, the influence of ammonia and nitric oxide oxidation on the selective catalytic reduction (SCR) of NO by ammonia with copper/nickel and vanadium oxide catalysts, supported on titania or alumina have been investigated, paying special attention to N2O formation.
TL;DR: In this paper, the authors reviewed the non-thermal plasma treatment of lean combustion exhaust gases and found that because of the oxygen concentration of several per cent, oxidation of noxious compounds is the prevailing nonthermal plasmin-induced process.
Abstract: Experiments and numerical model calculations on non-thermal plasma treatment of lean combustion exhaust gases were reviewed. It was found that because of the oxygen concentration of several per cent, oxidation of noxious compounds is the prevailing non-thermal plasma-induced process. Therefore nitric oxides cannot be reduced directly, but hybrid processes combining non-thermal plasma pre-treatment with catalytic reduction using either hydrocarbons or ammonia-based reducing agents have to be applied. Plasma-enhanced selective catalytic reduction (PE-SCR) of the nitric oxides emitted from a modern car's diesel engine for values of more than 60% was demonstrated in test bench experiments. For these experiments, a compact dielectric barrier discharge reactor with a flow cross section of 15 cm2 excited by a semiconductor switched pulse voltage source and a urea-based selective catalytic reduction system were applied. The average fuel penalty for this process under urban driving conditions was estimated to be around 2%. Thus PE-SCR has the potential to reduce the NOx emission of diesel cars to values well below future emission standards to be set in force in 2007. A number of investigations on the non-thermal plasma-induced oxidation of diesel soot showed very encouraging results.
TL;DR: Results have indicated that some commercial SCR catalysts are capable of oxidizing elemental Hg in flue gas obtained from the inlets of SCR or air heater units.
Abstract: The speciation of Hg in coal-fired flue gas can be important in determining the ultimate Hg emissions as well as potential control options for the utility. The effects of NOx control processes, such as selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR), on Hg speciation are not well understood but may impact emissions of Hg. EPRI has investigated the reactions of Hg in flue gas at conditions expected for some NOx control processes. This paper describes the methodology used to investigate these reactions in actual flue gas at several power plants. Results have indicated that some commercial SCR catalysts are capable of oxidizing elemental Hg in flue gas obtained from the inlets of SCR or air heater units. Results are affected by various flue gas and operating parameters. The effect of flue gas composition, including the presence of NH3, has been evaluated. The influence of NH3 on fly ash Hg reactions also is being investigated.
TL;DR: In this paper, the effects of calcium and iron impregnated on coal chars as catalysts on NO-char reaction have been investigated under various atmospheres in a quartz fixed bed reactor.
TL;DR: In this paper, the influence of hydrocarbon structure on selective reduction of NO by hydrocarbons (HC-SCR) over Cu-Al2O3 catalyst was studied by using linear and branched alkanes with different carbon numbers.
Abstract: Influence of hydrocarbon structure on selective reduction of NO by hydrocarbons (HC-SCR) over Cu-Al2O3 catalyst was studied by using linear and branched alkanes with different carbon numbers. As the carbon number of linear alkanes increased, reaction rates of NO and hydrocarbon increased. Reaction rates of NO and hydrocarbon for branched alkanes were lower than for linear alkanes of the same carbon number. Structure of hydrocarbon had no influence on the selectivity. Both reaction rates of NO and hydrocarbon had good correlations with mean bond energy of the alkanes. These correlations were also confirmed for the other catalysts such as Ag-Al2O3, Cu-MFI and so on, indicating that the mean bond energy of a hydrocarbon is a useful parameter to estimate its ability as a NO reductant for HC-SCR in diesel emission containing various hydrocarbons.