Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
  • B01J21/02—Boron or aluminium; Oxides or hydroxides thereof
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
  • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
  • B01D53/9404—Removing only nitrogen compounds
  • B01D53/9409—Nitrogen oxides
  • B01D53/9413—Processes characterised by a specific catalyst
  • B01D53/9418—Processes characterised by a specific catalyst for removing nitrogen oxides by selective catalytic reduction [SCR] using a reducing agent in a lean exhaust gas
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
  • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
  • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
  • B01D53/9445—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC]
  • B01D53/945—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC] characterised by a specific catalyst
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
  • B01J23/40—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals of the platinum group metals
  • B01J23/42—Platinum
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J29/00—Catalysts comprising molecular sieves
  • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
  • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
  • B01J29/064—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof containing iron group metals, noble metals or copper
  • B01J29/072—Iron group metals or copper
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J31/00—Catalysts comprising hydrides, coordination complexes or organic compounds
  • B01J31/02—Catalysts comprising hydrides, coordination complexes or organic compounds containing organic compounds or metal hydrides
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J35/00—Catalysts, in general, characterised by their form or physical properties
  • B01J35/19—Catalysts containing parts with different compositions
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J35/00—Catalysts, in general, characterised by their form or physical properties
  • B01J35/50—Catalysts, in general, characterised by their form or physical properties characterised by their shape or configuration
  • B01J35/56—Foraminous structures having flow-through passages or channels, e.g. grids or three-dimensional [3D] monoliths
  • B01J35/57—Honeycombs
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/02—Impregnation, coating or precipitation
  • B01J37/024—Multiple impregnation or coating
  • B01J37/0244—Coatings comprising several layers
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL-COMBUSTION ENGINES
  • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
  • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
  • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
  • F01N3/24—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by constructional aspects of converting apparatus
  • F01N3/28—Construction of catalytic reactors
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/10—Noble metals or compounds thereof
  • B01D2255/102—Platinum group metals
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/20—Metals or compounds thereof
  • B01D2255/207—Transition metals
  • B01D2255/20723—Vanadium
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/20—Metals or compounds thereof
  • B01D2255/207—Transition metals
  • B01D2255/20738—Iron
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/20—Metals or compounds thereof
  • B01D2255/207—Transition metals
  • B01D2255/20761—Copper
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/20—Metals or compounds thereof
  • B01D2255/207—Transition metals
  • B01D2255/20769—Molybdenum
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/20—Metals or compounds thereof
  • B01D2255/207—Transition metals
  • B01D2255/20776—Tungsten
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/50—Zeolites
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/90—Physical characteristics of catalysts
  • B01D2255/902—Multilayered catalyst
  • B01D2255/9022—Two layers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2258/00—Sources of waste gases
  • B01D2258/01—Engine exhaust gases
  • B01D2258/012—Diesel engines and lean burn gasoline engines
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
  • Y02T10/00—Road transport of goods or passengers
  • Y02T10/10—Internal combustion engine [ICE] based vehicles
  • Y02T10/12—Improving ICE efficiencies

Definitions

• the invention relates to the removal of nitrogen-containing noxious gases from the exhaust gas of combustion engines operated with a lean air / fuel mixture (so-called “lean-burn engines”), in particular from the exhaust gas of diesel engines.
• the emissions contained in the exhaust gas of a motor vehicle, which is operated with a lean-burn engine, can be divided into two groups.
• the term primary emissions refers to noxious gases that arise directly from the combustion process of the fuel in the engine and are already present before passing through exhaust gas purification facilities in the so-called raw emissions.
• Secondary emissions refer to such noxious gases which can be produced as by-products in the emission control system.
• the exhaust gas from lean-burn engines contains a relatively high oxygen content of up to 15% by volume. Carbon monoxide and hydrocarbons can easily be neutralized by oxidation. The reduction of nitrogen oxides to nitrogen, however, is much more difficult because of the high oxygen content.
• SCR Selective Catalytic Reduction
• US Pat. No. 6,345,496 B1 describes a method for purifying engine exhaust gases, wherein repeatedly alternately set lean and rich air / fuel ratios and the exhaust gas thus produced is passed through an exhaust system, which contains upstream of a catalyst which converts NO x to NH 3 only under rich exhaust conditions, while downstream there is arranged a further catalyst which adsorbs or stores NO x in the lean, this in the greasing releases so that it can react with NH 3 generated by the upstream catalyst to nitrogen.
• an NH 3 adsorption and oxidation catalyst can be arranged downstream, which stores NH 3 in the fats, desorbs them in the lean and oxidizes them with nitrogen oxides or oxygen to give nitrogen and water.
• a second nachgeordeneten catalyst NH 3 is temporarily stored.
• the nitrogen oxides contained in the exhaust gas in the lean phase are reacted with the stored ammonia.
• the exhaust system also contains a third noble metal-containing catalyst containing at least platinum, palladium or rhodium on support materials, wherein the support materials are capable of storing ammonia in the fatty phase and to desorb it in the lean phase again.
• WO 2005/099873 A1 claims a process for removing nitrogen oxides from the exhaust gas of lean-burn engines in cyclic rich / lean operation, which consists of the substeps of NO x storage in a NO x storage component in the lean exhaust gas, in-situ Conversion of stored NO x to NH 3 in the rich exhaust, storage of NH 3 in at least one NH 3 storage component and implementation of NH 3 with NO x under lean exhaust conditions composed, the first and last partial reaction at least temporarily and / or partially simultaneously and / or run in parallel.
• an integrated catalyst system is claimed which contains at least one NO x storage component, one NH 3 generation component, one NH 3 storage component and one SCR component.
• the reducing agent from an entrained additional tank is metered into the exhaust gas line by means of an injection nozzle, and instead of ammonia it is also possible to use a compound that decomposes easily to ammonia, such as urea Nitrogen oxides are supplied to the exhaust gas.
• ammonia is a gas which already has a pungent odor in low concentrations, the aim in practice is to minimize ammonia slip.
• alpha The molar ratio of ammonia to nitrogen oxides in the exhaust gas is commonly referred to as alpha:
• ammonia blocking catalyst As a measure of the oxidizing power of the Catalyst, the ammonia light-off temperature Ts 0 (NH 3 ) is specified. It indicates at which reaction temperature the ammonia conversion in the oxidation reaction is 50%.
• Ammonia blocking catalysts which are arranged behind an SCR catalyst for the oxidation of breakthrough ammonia, are known in various embodiments.
• DE 3929297 C2 US Pat. No. 5,120,695
• the oxidation catalyst is applied as a coating on a downstream portion of the one-piece honeycomb solid extrudate catalyst, with the oxidation catalyst coated region making up 20 to 50% of the total catalyst volume.
• the oxidation catalyst contains as catalytically active components at least one of the platinum group metals platinum, palladium and rhodium, which are deposited on cerium oxide, zirconium oxide and aluminum oxide as support materials.
• the platinum group metals can also be applied directly to the components of the reduction catalyst as support materials by impregnation with soluble precursors of the platinum group metals.
• the noble metal-containing layer of an ammonia oxidation catalyst can also be introduced under a coating of titanium oxide, zirconium oxide, silicon oxide or aluminum oxide and a transition metal or a rare earth metal.
• ammonia blocking catalysts entails the risk of overoxidation to nitrogen oxides, especially when using highly active oxidation catalysts. This process reduces the conversion rates for nitrogen oxides that can be achieved over the entire SCR and barrier catalytic converter system.
• the selectivity of the ammonia barrier catalyst is therefore an important measure of its quality.
• the selectivity to nitrogen in the sense of this document is a concentration and is calculated from the difference between all measured nitrogen components to the metered amount of ammonia.
• ammonia blocking catalyst can be arranged in the same converter as the SCR catalyst ("integrated ammonia blocking catalyst"), whereby the volume of construction required for the ammonia blocking catalyst is lost to the volume of construction available for the SCR catalyst.
• two different catalysts can be arranged in a converter in succession. Such an arrangement is described in JP 2005-238195.
• the ammonia blocking catalyst occupies about 40% of the construction volume, whereby only about 60% of the construction volume is available to the SCR catalyst.
• US 2004/0206069 shows a method of heat management for a diesel exhaust gas purification system in trucks, wherein a converter for reducing nitrogen oxides by selective catalytic reduction is part of the diesel exhaust gas purification system.
• This converter contains in addition to the SCR main catalyst an upstream hydrolysis catalyst for the release of ammonia from urea and a downstream ammonia barrier catalyst.
• a coating containing the ammonia barrier catalyst is applied to the downstream portion of the SCR catalyst monolithic unsupported catalyst present SCR catalyst is applied, wherein only 1-20% of the length of the SCR catalyst are used as supporting body for the oxidation catalyst.
• EP 0 773 057 A1 proposes a catalyst containing a platinum-copper-exchanged zeolite (Pt-Cu zeolite).
• this Pt-Cu zeolite catalyst is supported on a "common substrate.”
• a second catalyst containing a zeolite exchanged with copper alone is disposed.
• the object is achieved by a catalyst which comprises a honeycomb body and a coating consisting of two superimposed catalytically active layers, the lower layer applied directly to the honeycomb body containing an oxidation catalyst, and the upper layer applied thereto comprising an ammonia storage material contains and has an ammonia storage capacity of at least 20 milliliters of ammonia per gram of catalyst material.
• Ammonia storage materials in the sense of this document are compounds which contain acidic centers to which ammonia can be bound. The person skilled in the art distinguishes these into Lewis acidic centers for the physisorptio ⁇ of ammonia and Bronstedt acid centers for the chemisorption of ammonia.
• An ammonia storage material in an ammonia barrier catalyst according to the invention must have a significant fraction of Brönstedt acidic centers and possibly Lewis acidic centers to ensure adequate ammonia storage capacity.
• the material to be characterized is loaded with a defined amount of ammonia gas after heating of optionally adsorbed components such as water. This is done at room temperature. Then the sample is heated under inert gas at a constant heating rate, so that previously sampled ammonia gas is desorbed and can be detected quantitatively with a suitable analysis.
• the catalyst of the present invention has the ability to store at least 20 milliliters of ammonia per gram of catalyst material in the top layer. Particular preference is given to using ammonia storage materials having an ammonia storage capacity of 40 to 70 milliliters per gram of ammonia storage material, as is typical, for example, for iron-exchanged zeolites, which are also preferably used. These preferably used iron-exchanged zeolites are characterized not only by optimal ammonia storage capacity, but also by good SCR activity.
• the catalyst according to the invention contains only in the upper layer significant amounts of ammonia storage material.
• the lower layer is free of it.
• EP 0 773 057 A1 which comprises, with Pt-Cu zeolite in the lower layer and Cu zeolite in the upper layer, ammonia storage material over the entire layer thickness of the catalyst.
• the total amount of ammonia storage material in the catalyst so large that with temperature fluctuations in dynamic operation, the risk of uncontrolled desorption of ammonia and it surprisingly in turn increased Ammonia breakthroughs in dynamic operation comes.
• the reduction of the ammonia storage material to the upper layer while limiting the amount to the most preferred values, "over-loading" of the catalyst with ammonia and thus uncontrolled desorption is avoided.
• the catalyst according to the invention in its preferred embodiments in the lower layer contains an oxidation catalyst having a strong oxidation action.
• these are oxidation catalysts of a noble metal and an oxidic support material, preferably platinum or palladium or mixtures of platinum and palladium on a support material selected from the group consisting of active alumina, zirconia, titania, silica and mixtures or mixed oxides thereof.
• the inventive catalyst can be used with appropriate dimensioning on the one hand as SCR catalyst, which then has a relation to conventional catalysts reduced ammonia slip.
• the catalyst according to the invention is suitable as a very selective ammonia blocking catalyst.
• the catalyst according to the invention is thus capable of reducing nitrogen oxides (also known as noxious gases with nitrogen in oxidized form) and of oxidatively eliminating ammonia (in other words noxious gases with nitrogen in reduced form).
• Nitrogen oxides and ammonia from the exhaust gas are adsorbed on the top layer (1), which is an SCR-active coating, and react in a selective catalytic reaction to water and nitrogen, which desorb after reaction completion. In this case, ammonia is present in a superstoichiometric amount, that is in excess.
• Unavailable ammonia passes through the upper coating (1) to the underlying layer (2), which is characterized by strong oxidation effect. Here nitrogen and nitrogen oxides are produced. The resulting nitrogen diffuses unchanged through the upper layer (1) and passes into the atmosphere.
• the catalyst of the invention with appropriate dimensioning is ideal for use as SCR catalyst with reduced ammonia slip at temperatures in the range 15O 0 C to 400 0 C, more preferably 200 0 C to 35O 0 C.
• Such temperatures occur in exhaust gas purification in Vehicles with diesel engine typically in converters, which are arranged in subfloor positions at the end of the exhaust line. If an inventive catalyst with sufficient volume is installed in a corresponding exhaust system at the end of the exhaust line in an underfloor converter, then so For example, the nitrogen oxides generated by the diesel engine can be effectively removed while avoiding high ammonia secondary emission.
• ammonia or a compound that is decomposable to ammonia is metered into the exhaust gas line before the catalyst according to the invention which is arranged in the underfloor position.
• the use of an additional ammonia blocking catalyst can be dispensed with in such a process in the rule.
• the catalyst according to the invention can also be used in combination with a conventional SCR catalyst as a highly effective ammonia barrier catalyst.
• a conventional SCR catalyst as a highly effective ammonia barrier catalyst.
• SCR catalysts which contain a zeolite exchanged with copper or iron or a zeolite exchanged with copper and iron or mixtures thereof is preferred.
• SCR catalysts can be used which contain vanadium oxide or tungsten oxide or molybdenum oxide on a support material of titanium oxide.
• Various embodiments of the exhaust system are conceivable.
• SCR catalyst and inventive ammonia barrier catalyst may each be in the form of a coating on an inert honeycomb body, both honeycomb bodies are made of an inert material, preferably of ceramic or metal.
• the two honeycomb bodies can be present in two converters lying one behind the other or in a common converter, the ammonia blocking catalytic converter always being arranged downstream of the SCR catalytic converter.
• the volume of the ammonia trap catalyst typically occupies 5-40% of the available space in the converter. The remaining volume is filled by the SCR catalyst or by the SCR catalyst and an optionally present upstream arranged hydrolysis catalyst.
• an oxidation catalyst can be arranged, which serves for the oxidation of nitrogen monoxide to nitrogen dioxide.
• the two honeycomb bodies of the SCR catalyst and the catalyst according to the invention, used as ammonia blocking catalyst form a unit with a front and a rear part.
• the lower layer of the inventive ammonia blocking catalyst performing oxidation catalyst is disposed only on the rear part of the honeycomb body.
• the upper layer of the ammonia barrier catalyst according to the invention is designed as an SCR catalyst. It may be deposited over the entire length of the honeycomb body, covering the coating containing the oxidation catalyst.
• the SCR catalyst can be embodied in the form of a honeycomb body which consists entirely of the SCR-active material (so-called solid extrudate SCR catalyst).
• the ammonia barrier catalyst according to the invention is then coated on the back of this Vollextrudat- catalyst, so that the rear part of the SCR catalyst serves as a supporting body for the ammonia barrier catalyst.
• Figure 1 Functional principle of the catalyst according to the invention for the removal of nitrogen-containing noxious gases from the exhaust gas of diesel engines containing a honeycomb body and at least two superimposed, catalytically active layers.
• FIG. 3 Concentrations of the nitrogen compounds formed during the oxidation of ammonia in an exhaust-gas purification system consisting of conventional SCR catalyst and unselective ammonia-oxidation catalyst as a function of the temperature
• FIG. 5 Temperature dependence of the selectivity of the ammonia oxidation to N 2 of inventive catalysts (# 2 and # 3) compared to a reference oxidation catalyst (# 1)
• Figure 6 Nitrogen oxide conversion and NH 3 slip of a catalyst (# 5) and of a conventional SCR catalyst of the invention containing iron-exchanged zeolite (# 4), after hydrothermal aging at 65O 0 C.
• FIG. 7 NH 3 desorption, measured on a catalyst according to the invention loaded at 200 ° C. with a starting concentration of 450 ppm NH 3
• SCR catalyst contained on a ceramic honeycomb body a coating of iron exchanged zeolites.
• the volume of the honeycomb body was 12.5 l. It had 62 cells / cm 2 with a cell wall thickness of 0.17 mm.
• the two catalytic converters were tested in a model gas plant.
• the two catalysts had the following composition and were coated onto ceramic honeycombs having a cell density of 62 cm "2:
• Catalyst Conventional SCR catalyst based on V 2 (VTiC) 2 ; Dimension of the honeycomb body: 25.4 mm diameter, 76.2 mm length
• Catalyst Conventional ammonia barrier catalyst consisting of 0.353 g / l Pt
• honeycomb body 25.4 mm diameter, 25.4 mm length
• the model gas had the following composition:
• the concentrations of the measured nitrogen components as a function of the temperature are shown graphically in FIG. At temperatures> 200 ° C ammonia is effectively removed from the exhaust gas mixture. For higher temperatures (T> 300 ° C), however, the formation of undesired by-products can be observed. As the temperature increases, nitrogen components with a higher oxidation state are increasingly formed, from +1 (N 2 O) to +11 (NO) to + IV (NO 2 ).
• Comparative Example 2 The overoxidation to nitrogen oxides shown in Comparative Example 2 can be severely limited by using a catalyst according to the invention as an ammonia barrier catalyst with the same oxidation power.
• the following table shows the formulations according to the invention which have been tested by way of example as ammonia blocking catalysts.
• Figure 4 shows the effectiveness of the ammonia oxidation:
• the course of the ammonia concentration downstream of the catalyst as a function of temperature clearly shows that the ammonia light-off temperatures Ts O (NH 3) for the two catalysts of this invention # 2 and # 3 in the same range (370 ° C to 39O 0 C) as the ammonia light-off temperatures of the non-selective reference NH 3 oxidation catalyzer lysators (about 38O ° C).
• the oxidation activity of all samples tested is equivalent.
• the NH 3 light-off behavior is not affected by the upper layer despite high space velocities.
• the observed NH 3 residual concentration of about 100 ppm at 55O 0 C is due to diffusion limitation due to the very high catalyst loading selected in this experiment.
• the selectivity to N 2 is calculated from the difference between all measured nitrogen components to the metered amount of ammonia. It is shown as a function of the temperature in FIG.
• the ammonia slip shown in Comparative Example 1 can be reduced by using a catalyst according to the invention as an SCR catalyst.
• a catalyst according to the invention as an SCR catalyst.
• Comparison of NO x conversion and ammonia breakthrough concentration of a conventional iron-exchanged zeolite-containing SCR catalyst and a catalyst of the invention demonstrates this.
• the following catalysts were investigated:
• a catalyst according to EP 0 773 057 A1 was produced.
• 35 g / l of a coating consisting of 1% by weight of platinum and a copper-exchanged ZSM-5 zeolite (SiO 2 : Al 2) were applied to a ceramic honeycomb body with 62 cells / cm 2 and a cell wall thickness of 0.17 mm 2 O 3 ratio of 45) containing 2.4 wt .-% copper applied.
• an upper layer consisting of 160 g / l of the copper-exchanged ZSM-5 zeolite (SiO 2 : Al 2 O 3 ratio of 45) containing 2.4% by weight copper was applied. Drying and calcination followed again.
• the honeycomb body finished for testing had a diameter of 25.4 mm and a length of 76.2 mm and contained a total of 0.353 g / l of platinum based on the volume of the honeycomb body.
• the catalyst # 6 obtained in this way was investigated in comparison to the inventive catalyst # 2 from Example 1 (upper layer: 160 g / l) in an ammonia desorption experiment in the model gas plant.
• the catalysts were first exposed in a fresh state at 200 ° C over a period of about one hour of a 450 ppm ammonia-containing gas mixture at a space velocity of 30,000 l / h.
• the gas mixture also contained 5 vol.% Oxygen and 1.3 vol.% Water vapor in nitrogen.
• a complete breakthrough of the metered amount of ammonia through the catalyst was observed.
• the ammonia feed was turned off.
• the catalysts were heated after a holding time of two minutes at a constant temperature at a heating rate of 1 ° per second.
• the desorbing amount of ammonia was measured by means of an FTIR spectrometer.
• FIG. 7 shows the results obtained for catalyst # 2 according to the invention and the comparative catalyst according to EP 0 773 057 A1, # 6.
• the temperatures measured before the catalyst are plotted over the time course of the experiment. Shown is only the desorption phase.
• the ammonia desorption begins at about 210 0 C. It can be clearly seen that significantly more ammonia desorbs from the comparative catalyst # 6 than from the inventive catalyst Wl. This "overcharging" of the catalyst # 6 with ammonia leads, as described, during temperature fluctuations in dynamic operation to uncontrolled ammonia desorption and thus to undesirable ammonia breakthroughs during driving.

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• 2007
  • 2007-02-15 US US12/301,752 patent/US20100166628A1/en not_active Abandoned
  • 2007-05-04 CA CA002652837A patent/CA2652837A1/en not_active Abandoned
  • 2007-05-04 DE DE202007019652.0U patent/DE202007019652U1/de not_active Expired - Lifetime
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