EP2073929A1 - A catalyst for inhibiting the no2 generation - Google Patents

A catalyst for inhibiting the no2 generation

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Publication number
EP2073929A1
EP2073929A1 EP07808305A EP07808305A EP2073929A1 EP 2073929 A1 EP2073929 A1 EP 2073929A1 EP 07808305 A EP07808305 A EP 07808305A EP 07808305 A EP07808305 A EP 07808305A EP 2073929 A1 EP2073929 A1 EP 2073929A1
Authority
EP
European Patent Office
Prior art keywords
generation
inhibiting
catalyst
catalyst composition
module
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP07808305A
Other languages
German (de)
French (fr)
Other versions
EP2073929A4 (en
Inventor
Hyun-Sik Han
Tae-Woo Lee
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Heesung Catalysts Corp
Original Assignee
Heesung Catalysts Corp
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Filing date
Publication date
Application filed by Heesung Catalysts Corp filed Critical Heesung Catalysts Corp
Publication of EP2073929A1 publication Critical patent/EP2073929A1/en
Publication of EP2073929A4 publication Critical patent/EP2073929A4/en
Withdrawn legal-status Critical Current

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    • 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
    • B01J37/0246—Coatings comprising a zeolite
    • 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
    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/74—Iron group metals
    • B01J23/75—Cobalt
    • 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
    • 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
    • B01J21/04—Alumina
    • 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
    • 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
    • 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
    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/89—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals
    • B01J23/8933—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals also combined with metals, or metal oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/8946—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals also combined with metals, or metal oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with alkali or alkaline earth metals
    • 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
    • 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
    • B01J37/0242—Coating followed by impregnation
    • 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
    • B01D2255/1021—Platinum
    • 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
    • B01D2255/1023—Palladium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/204—Alkaline earth 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
    • B01D2255/206—Rare earth 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
    • B01D2255/20746—Cobalt
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/209—Other metals
    • B01D2255/2092—Aluminium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/40—Mixed oxides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/50—Zeolites
    • B01D2255/502—Beta zeolites
    • 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
    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/76—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/83—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with rare earths or actinides
    • 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
    • B01J29/70—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of types characterised by their specific structure not provided for in groups B01J29/08 - B01J29/65
    • B01J29/72—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of types characterised by their specific structure not provided for in groups B01J29/08 - B01J29/65 containing iron group metals, noble metals or copper
    • B01J29/74—Noble metals
    • B01J29/7415—Zeolite Beta
    • 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
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
    • Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
    • 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 present invention relates to a catalyst for inhibiting the generation of NO .
  • HC trap catalysts which are used to remove HC discharged when an engine is cold-started, at which time a catalyst does not fulfill its function, by temporarily collecting the HC using a porous material, such as zeolite, and then purifying the HC using an activated catalyst, have also been put to practical use.
  • the above exhaust gas purification technologies allow HC and CO to be purified at a constant level.
  • NOx which is another cause of photochemical smog, is formed when nitrogen and oxygen in intake air react with each other at high temperatures. Therefore, the amount of NO that is emitted is increased when the engine load is increased due to high speed running. Since NO causes widespread environmental damage, such as smog, acid rain, and the like, NO emission standards have become stricter since ULEV. It has been known that rhodium is very effective in the purification of NO , but the yield of rhodium is low, and the price thereof is very high, compared to platinum or palladium. Accordingly, methods of efficiently purifying NO using a very small amount of rhodium or without using rhodium have been required.
  • the amount of exhaust gas that can be treated using a catalyst increases under high-load combustion conditions, and thus the purification performance of NO depends on the degree of contact of exhaust gas and precious metal. For this reason, in addition to the catalyst composition, whether the dispersion state of precious metal is maintained to some degree has been considered.
  • diesel engines have high thermal efficiency and air-fuel ratios compared to gasoline engines, and they are thus expected to reduce the emission of CO in Europe.
  • vehicles equipped with diesel engines have a problem in that the emission of particulate matter (PM), such as graphite, and NO , required to be purified through reduction, must be decreased.
  • PM particulate matter
  • Such particulate matter (PM) is solid, and cannot be satisfactorily removed using a conventional flow type catalyst. Therefore, a diesel particulate filter (DPF) is used in order to remove the particulate matter (PM). Since DPF physically collects PM, PM can be removed at high efficiency, but DPF cannot always be operated to thus remove PM, and it is necessary to burn and remove the PM collected on the DPF at a certain point.
  • DPF diesel particulate filter
  • diesel engine vehicles are equipped with a catalyzed soot filter (CSF), fabricated by catalyzing DPF. That is, diesel engine vehicles are operated in a state in which they are equipped with an oxidation catalyst housing coated with a diesel oxidation catalyst (DOC) and a catalyzed soot filter (CSF) fabricated by catalyzing DPF.
  • CSF catalyzed soot filter
  • the present inventors have recognized a serious problem in that yellow smog is generated by a diesel engine vehicle in which a DOC and a CSF are serially mounted. As the result of research of the problem, they have found that the yellow smog was derived from NO . That is, they found that NO , which is an oxidation product, was ejected in the form of yellow smog through a tailpipe while NO passes through the DOC and CSF, and they have researched the NO generation mechanism in order to treat NO , thus completing the present invention.
  • the present invention relates to the effects of non-precious metal oxides on the conversion of nitrogen oxides, and industrially to a system for inhibiting the generation of NO , visible as yellow smog, the system being equipped with a module for inhibiting the generation of NO , including a refractory carrier coated with a catalyst containing non-precious oxides for inhibiting the generation of NO .
  • an object of the present invention is to provide a method of inhibiting the generation of NO .
  • Another object of the present invention is to provide a system for inhibiting the generation of NO .
  • a further object of the present invention is to provide a method and system for preventing the formation of a visible pollution source by inhibiting the generation of yellow smog.
  • the present invention provides a catalyst composition for inhibiting the generation of NO , comprising a basic metal oxide catalyst composition combined with ceria-cobalt oxide, active alumina, and zeolite, wherein the basic metal oxide catalyst composition is supported with a precious metal, such as platinum and/or palladium, and a non-precious metal, such as barium or strontium.
  • the present invention provides a module for inhibiting the generation of NO , comprising a refractory carrier coated with the catalyst composition for inhibiting the generation of NO .
  • the present invention provides an af- tertreatment system comprising the module for inhibiting the generation of NO , wherein the module is provided immediately behind a DOC and/or a CSF.
  • the catalyst composition according to the present invention can be applied to an exhaust gas aftertreatment system as a module for inhibiting the generation of NO , including a refractory carrier supported with the catalyst composition through commonly-used methods.
  • the module for inhibiting the generation of NO is disposed at the rear end of a DOC or a CSF, thus inhibiting the generation of NO .
  • the module is more preferably disposed at the rear end of the CSF, so that the generation of NO is prevented, with the result that the emission of visible exhaust gas is prevented, thereby contributing to environmental purification.
  • FIG. 1 is a graph showing HC conversion rates obtained using non-precious metals, according to the present invention
  • FIG. 2 is a graph showing NO/NO conversion rates using non-precious metals, according to the present invention
  • FIG. 3 is a graph showing HC conversion rates obtained using the catalyst compositions of Example 1 and Comparative Example 1 according to the present invention.
  • FIG. 4 is a graph showing NO/NO conversion rates obtained using the catalyst compositions of Example 1 and Comparative Example 1 according to the present invention.
  • active alumina in the present specification means alumina having a high
  • the BET surface area includes gamma- alumina, theta-alumina, and alpha- alumina.
  • the combination of ceria-cobalt oxide, active alumina, and zeolite is achieved through a process of blending or mixing particles.
  • the module for inhibiting the generation of NO according to the present invention includes a refractory carrier coated with the catalyst composition of the present invention.
  • the catalyst composition according to the present invention which is a catalytic material for inhibiting the generation of NO , is coated with a mixture of cerium oxide particles impregnated with cobalt, active alumina particles and Fe/zeolite particles, wherein a precious metal, such as platinum and/or palladium, and a non-precious metal, such as barium or strontium, are dispersed in the mixture.
  • a precious metal such as platinum and/or palladium
  • a non-precious metal such as barium or strontium
  • the carrier of the present invention is formed of ceramic materials, such as cordierite, ⁇ -alumina and mullite, and has a monolithic honeycomb structure.
  • the ceria-cobalt oxide catalytic material is prepared by drying and calcining a slurry of ceria particles and cobalt salt, and specifically, is prepared by mixing the ceria particles and cobalt salt with an acidifier, such as water, acetic acid, nitric acid, or the like, and then milling the mixture to a desired particle size.
  • the basic metal oxide catalyst composition composed of ceria-cobalt oxide, active alumina, and Fe/zeolite, is a constituent of the catalytic material of the present invention, and serves as a support for other constituents thereof, including a precious metal, such as Pt or Pd, and a non- precious metal, such as Ba or Sr.
  • the basic metal oxide catalyst composition is applied on a carrier, and the carrier is impregnated with a precious metal compound solution and a non-precious metal compound solution, dried, and then calcined, thus preparing a catalyst composition for inhibiting the generation of NO .
  • the fixation of the carrier may be conducted by calcination, H2S treatment, and other commonly-known methods.
  • the fixation of the carrier is conducted in order to impart insolubility to a catalyst.
  • platinum (Pt) compound potassium platinum chloride, ammonium platinum thiocyanate, amine-solubilized platinum hydroxide, chloroplatinic acid, or the like may be used.
  • palladium (Pd) compound palladium nitrate, palladium chloride, or the like, which are commonly used in this field, may be used.
  • barium (Ba) compound barium hydroxide, barium nitrate, or barium acetate may be used, and, as the strontium (Sr) compound, strontium hyd roxide, strontium nitrate, or strontium acetate may be used.
  • Step A 205.1 g of Y-alumina powder was mixed with acetic acid having a concentration of about 1.5% based on the weight of the Y-alumina powder to form a mixture, the mixture was sufficiently mixed with 300 g of H O to form slurry, and then the slurry was ball-milled such that 90% by weight of the particles in the slurry had a particle size of 8 ⁇ 10 D.
  • the slurry formed in this step was referred to as slurry A.
  • Step B The preparation of ceria-cobalt oxide: 981.1 g of cerium oxide was sufficiently mixed with 149.8 g of cobalt nitrate and about 170 g of H O to form slurry. Subsequently, the slurry was dried at a temperature of 12O 0 C for about 2 hours, and then calcined at a temperature of 500 0 C for about 2 hours, thus preparing ceria-cobalt oxide.
  • Step C The slurry A was mixed with 101.5 g of the ceria-cobalt oxide, and was then ball-milled such that 90% by weight of the particles in the slurry A had a particle size of 6 ⁇ 8 D to form slurry B. Subsequently, the slurry B was mixed with 444 g of Fe/ ⁇ -zeolite, and was then dispersed for about 30 minutes to form slurry C.
  • Step D A cordierite honeycomb core was coated with the slurry C, dried at a temperature of 15O 0 C for about 20 minutes, and then calcined at a temperature of 500 0 C for about 5 hours.
  • Step E The basic metal oxide catalyst composition applied on the cordierite honeycomb core was impregnated with 0.2 g of Pt and 5 g of Ba using chloroplatinic acid and barium compounds through commonly-known methods, thus completing a catalyst composition for inhibiting the generation of NO according to the present invention.
  • Example 1 Although Y-alumina was used as an active alumina, theta-alumina and alpha- alumina may be each independently used as the active alumina, and combinations thereof may also be used as the active alumina. As described above, in addition to cordierite, ⁇ -alumina or mullite may be used as the carrier. Further, the catalyst composition according to the present invention may be completed by impregnating the catalyst composition with Pd instead of Pt or impregnating it with Sr instead of Ba. Further, in step E, even when the amount of Pt is adjusted to 1.6 or 3.2 gll, or when the amount of Ba is adjusted to 2 or 20 gll, the effect of inhibiting the generation of NO is not reduced.
  • the Pt/Ba/ceria-cobalt oxide/T-alumina/zeolite catalyst was produced as in Example 1, except the process of impregnating the basic metal oxide catalyst composition with Ba.
  • NOx consists of NO and NO , and the NO conversion rate means the rate at which
  • NO was converted into molecules other than NO and NO , that is, the rate of at which x 2
  • Example 1 based on the tests, and then measured the HC conversion rate and the NO/NO conversion rate using the catalysts, and the results thereof are shown in FIGS. 3 and 4. From FIGS. 3 and 4, it can be seen that the catalyst of Example 1 exhibits the effect of considerably inhibiting NO formation (see FIG. 4) while not changing the HC conversion rate (see FIG. 3), and thus the catalyst composition according to the present invention inhibits NO formation, thereby reducing the generation of yellow smog.

Abstract

Disclosed herein is a catalyst composition for inhibiting the generation of NO2, comprising a basic metal oxide catalyst composition combined with ceria-cobalt oxide, active alumina, and zeolite, wherein the basic metal oxide catalyst composition is supported with a precious metal, such as platinum and/or palladium, and a non-precious metal, such as barium or strontium, and a module for inhibiting the generation of NO2 using the catalyst composition. In the exhaust gas aftertreatment system, in which a DOC and a CSF are serially disposed, the module is disposed at the rear end of the CSF, so that the generation of NO2 is prevented, with the result that the emission of visible exhaust gas is prevented, thereby contributing to environmental purification.

Description

Description
A CATALYST FOR INHIBITING THE NO2 GENERATION
Technical Field
[1] The present invention relates to a catalyst for inhibiting the generation of NO .
Background Art
[2] Recently, diesel engine vehicles have been equipped with an oxidation catalyst module coated with a diesel oxidation catalyst (DOC) and a catalyzed soot filter (CSF) fabricated by catalyzing a diesel particulate filter (DPF) in order to meet environmental standards, and thus the oxidation catalyst module and CSF have been used for purifying HC, CO and NO . In particular, since the emission of HC and NO , causing the formation of photochemical smog, are more strictly regulated, various catalytic or mechanical methods of efficiently purifying HC and NO are required.
[3] Photochemical smog is chiefly formed by HC and NO . In ultra low-emission vehicles, the emission of HC is increasingly regulated. HC, which is derived form unburned gasoline, is mostly discharged when an engine is cold-started. Therefore, in order to reduce the amount of HC emissions, it is absolutely necessary to decrease the emission of HC immediately after the engine is started. However, a catalyst (DOC) must be heated to a predetermined temperature or higher in order for the catalyst to fulfill its function. Therefore, the reason why a large amount of HC is discharged immediately after the engine is started is that the catalyst is not heated to a temperature at which the catalyst fulfills its function. For this reason, methods of electrically heating a catalyst have been actively considered, but these methods are problematic in that the battery load is increased, and a large number of parts is required, and thus the methods can only be put to practical use within a limited range. Currently, methods of accelerating the increase in the temperature of a catalyst, such as a method of increasing the temperature of catalyst at an early stage through the operation of an engine control unit, a method of keeping a catalyst warm by improving the structure of an exhaust pipe, a method of decreasing the weight of a ceramic carrier coated with catalytic components, and the like, are being considered. In addition, HC trap catalysts, which are used to remove HC discharged when an engine is cold-started, at which time a catalyst does not fulfill its function, by temporarily collecting the HC using a porous material, such as zeolite, and then purifying the HC using an activated catalyst, have also been put to practical use. The above exhaust gas purification technologies allow HC and CO to be purified at a constant level.
[4] NOx, which is another cause of photochemical smog, is formed when nitrogen and oxygen in intake air react with each other at high temperatures. Therefore, the amount of NO that is emitted is increased when the engine load is increased due to high speed running. Since NO causes widespread environmental damage, such as smog, acid rain, and the like, NO emission standards have become stricter since ULEV. It has been known that rhodium is very effective in the purification of NO , but the yield of rhodium is low, and the price thereof is very high, compared to platinum or palladium. Accordingly, methods of efficiently purifying NO using a very small amount of rhodium or without using rhodium have been required. The amount of exhaust gas that can be treated using a catalyst increases under high-load combustion conditions, and thus the purification performance of NO depends on the degree of contact of exhaust gas and precious metal. For this reason, in addition to the catalyst composition, whether the dispersion state of precious metal is maintained to some degree has been considered.
[5] Meanwhile, diesel engines have high thermal efficiency and air-fuel ratios compared to gasoline engines, and they are thus expected to reduce the emission of CO in Europe. However, vehicles equipped with diesel engines have a problem in that the emission of particulate matter (PM), such as graphite, and NO , required to be purified through reduction, must be decreased. Such particulate matter (PM) is solid, and cannot be satisfactorily removed using a conventional flow type catalyst. Therefore, a diesel particulate filter (DPF) is used in order to remove the particulate matter (PM). Since DPF physically collects PM, PM can be removed at high efficiency, but DPF cannot always be operated to thus remove PM, and it is necessary to burn and remove the PM collected on the DPF at a certain point. The exhaust gas temperature needs to be increased in order to burn and remove PM, but the increase of the exhaust gas temperature causes the deterioration of the air- fuel ratio characteristics of the diesel engine. For this reason, in order to burn the PM collected on the DPF at a lower temperature, diesel engine vehicles are equipped with a catalyzed soot filter (CSF), fabricated by catalyzing DPF. That is, diesel engine vehicles are operated in a state in which they are equipped with an oxidation catalyst housing coated with a diesel oxidation catalyst (DOC) and a catalyzed soot filter (CSF) fabricated by catalyzing DPF.
Disclosure of Invention Technical Problem
[6] The present inventors have recognized a serious problem in that yellow smog is generated by a diesel engine vehicle in which a DOC and a CSF are serially mounted. As the result of research of the problem, they have found that the yellow smog was derived from NO . That is, they found that NO , which is an oxidation product, was ejected in the form of yellow smog through a tailpipe while NO passes through the DOC and CSF, and they have researched the NO generation mechanism in order to treat NO , thus completing the present invention.
[7] The present invention relates to the effects of non-precious metal oxides on the conversion of nitrogen oxides, and industrially to a system for inhibiting the generation of NO , visible as yellow smog, the system being equipped with a module for inhibiting the generation of NO , including a refractory carrier coated with a catalyst containing non-precious oxides for inhibiting the generation of NO .
[8] Accordingly, an object of the present invention is to provide a method of inhibiting the generation of NO .
[9] Another object of the present invention is to provide a system for inhibiting the generation of NO .
[10] A further object of the present invention is to provide a method and system for preventing the formation of a visible pollution source by inhibiting the generation of yellow smog. Technical Solution
[11] In order to accomplish the above objects, the present invention provides a catalyst composition for inhibiting the generation of NO , comprising a basic metal oxide catalyst composition combined with ceria-cobalt oxide, active alumina, and zeolite, wherein the basic metal oxide catalyst composition is supported with a precious metal, such as platinum and/or palladium, and a non-precious metal, such as barium or strontium. Further, the present invention provides a module for inhibiting the generation of NO , comprising a refractory carrier coated with the catalyst composition for inhibiting the generation of NO . Further, the present invention provides an af- tertreatment system comprising the module for inhibiting the generation of NO , wherein the module is provided immediately behind a DOC and/or a CSF.
Advantageous Effects
[12] The catalyst composition according to the present invention can be applied to an exhaust gas aftertreatment system as a module for inhibiting the generation of NO , including a refractory carrier supported with the catalyst composition through commonly-used methods. Further, preferably, the module for inhibiting the generation of NO is disposed at the rear end of a DOC or a CSF, thus inhibiting the generation of NO . Further, in the exhaust gas aftertreatment system in which a DOC and a CSF are serially disposed, the module is more preferably disposed at the rear end of the CSF, so that the generation of NO is prevented, with the result that the emission of visible exhaust gas is prevented, thereby contributing to environmental purification. Brief Description of the Drawings
[13] FIG. 1 is a graph showing HC conversion rates obtained using non-precious metals, according to the present invention; [14] FIG. 2 is a graph showing NO/NO conversion rates using non-precious metals, according to the present invention;
[15] FIG. 3 is a graph showing HC conversion rates obtained using the catalyst compositions of Example 1 and Comparative Example 1 according to the present invention; and
[16] FIG. 4 is a graph showing NO/NO conversion rates obtained using the catalyst compositions of Example 1 and Comparative Example 1 according to the present invention.
Best Mode for Carrying Out the Invention
[17] The term "active alumina" in the present specification means alumina having a high
BET surface area, and includes gamma- alumina, theta-alumina, and alpha- alumina. The combination of ceria-cobalt oxide, active alumina, and zeolite is achieved through a process of blending or mixing particles. The module for inhibiting the generation of NO according to the present invention includes a refractory carrier coated with the catalyst composition of the present invention. The catalyst composition according to the present invention, which is a catalytic material for inhibiting the generation of NO , is coated with a mixture of cerium oxide particles impregnated with cobalt, active alumina particles and Fe/zeolite particles, wherein a precious metal, such as platinum and/or palladium, and a non-precious metal, such as barium or strontium, are dispersed in the mixture.
[18] The carrier of the present invention is formed of ceramic materials, such as cordierite, α-alumina and mullite, and has a monolithic honeycomb structure. The ceria-cobalt oxide catalytic material is prepared by drying and calcining a slurry of ceria particles and cobalt salt, and specifically, is prepared by mixing the ceria particles and cobalt salt with an acidifier, such as water, acetic acid, nitric acid, or the like, and then milling the mixture to a desired particle size. The basic metal oxide catalyst composition, composed of ceria-cobalt oxide, active alumina, and Fe/zeolite, is a constituent of the catalytic material of the present invention, and serves as a support for other constituents thereof, including a precious metal, such as Pt or Pd, and a non- precious metal, such as Ba or Sr. In this case, the basic metal oxide catalyst composition is applied on a carrier, and the carrier is impregnated with a precious metal compound solution and a non-precious metal compound solution, dried, and then calcined, thus preparing a catalyst composition for inhibiting the generation of NO . When the carrier is dried and then fixed, the fixation of the carrier may be conducted by calcination, H2S treatment, and other commonly-known methods. The fixation of the carrier is conducted in order to impart insolubility to a catalyst. [19] As the platinum (Pt) compound, potassium platinum chloride, ammonium platinum thiocyanate, amine-solubilized platinum hydroxide, chloroplatinic acid, or the like may be used. Further, as the palladium (Pd) compound, palladium nitrate, palladium chloride, or the like, which are commonly used in this field, may be used.
[20] Moreover, as the barium (Ba) compound, barium hydroxide, barium nitrate, or barium acetate may be used, and, as the strontium (Sr) compound, strontium hyd roxide, strontium nitrate, or strontium acetate may be used.
[21] Generally, the amount of precious metal component or non-precious metal component is marked with component weight/catalyst volume (gll). Mode for the Invention
[22] A better understanding of the present invention may be obtained through the following examples, which are set forth to illustrate, but are not to be construed as the limit of the present invention.
[23] Example 1
[24] The Pt/Ba/ceria-cobalt oxide/T- alumina/zeolite catalyst according to the present invention was produced through the following steps.
[25] Step A: 205.1 g of Y-alumina powder was mixed with acetic acid having a concentration of about 1.5% based on the weight of the Y-alumina powder to form a mixture, the mixture was sufficiently mixed with 300 g of H O to form slurry, and then the slurry was ball-milled such that 90% by weight of the particles in the slurry had a particle size of 8~10 D. The slurry formed in this step was referred to as slurry A.
[26] Step B : The preparation of ceria-cobalt oxide: 981.1 g of cerium oxide was sufficiently mixed with 149.8 g of cobalt nitrate and about 170 g of H O to form slurry. Subsequently, the slurry was dried at a temperature of 12O0C for about 2 hours, and then calcined at a temperature of 5000C for about 2 hours, thus preparing ceria-cobalt oxide.
[27] Step C: The slurry A was mixed with 101.5 g of the ceria-cobalt oxide, and was then ball-milled such that 90% by weight of the particles in the slurry A had a particle size of 6~8 D to form slurry B. Subsequently, the slurry B was mixed with 444 g of Fe/ β-zeolite, and was then dispersed for about 30 minutes to form slurry C.
[28] Step D: A cordierite honeycomb core was coated with the slurry C, dried at a temperature of 15O0C for about 20 minutes, and then calcined at a temperature of 5000C for about 5 hours.
[29] Step E: The basic metal oxide catalyst composition applied on the cordierite honeycomb core was impregnated with 0.2 g of Pt and 5 g of Ba using chloroplatinic acid and barium compounds through commonly-known methods, thus completing a catalyst composition for inhibiting the generation of NO according to the present invention.
[30] In Example 1, although Y-alumina was used as an active alumina, theta-alumina and alpha- alumina may be each independently used as the active alumina, and combinations thereof may also be used as the active alumina. As described above, in addition to cordierite, α-alumina or mullite may be used as the carrier. Further, the catalyst composition according to the present invention may be completed by impregnating the catalyst composition with Pd instead of Pt or impregnating it with Sr instead of Ba. Further, in step E, even when the amount of Pt is adjusted to 1.6 or 3.2 gll, or when the amount of Ba is adjusted to 2 or 20 gll, the effect of inhibiting the generation of NO is not reduced.
[31] Comparative Example 1
[32] In order to explain the effect of the non-precious metal component according to the present invention, the Pt/Ba/ceria-cobalt oxide/T-alumina/zeolite catalyst was produced as in Example 1, except the process of impregnating the basic metal oxide catalyst composition with Ba.
[33] Hereinafter, the process of designing the catalyst of Example 1 will be described.
[34] First, based on tests of FIGS. 1 and 2, among various candidate materials, Ba and Sr were selected as components for inhibiting the generation of NO . That is, the HC conversion rate of a fresh catalyst (a catalyst containing no Ba or Sr) was similar to that of a catalyst impregnated with Ba or Sr, but the range of the NO/ NO conversion rate, which is an index indicating the NO formation rate, of the fresh catalyst was widest, the range of the NO/ NO conversion rate of a catalyst impregnated with Sr was next to that of the fresh catalyst, and the range of the NO/ NO conversion rate of a catalyst impregnated with Ba was narrow. For this reason, Ba and Sr, and more preferably Ba, were selected as components for inhibiting the generation of NO .
[35] NOx consists of NO and NO , and the NO conversion rate means the rate at which
2 x
NO was converted into molecules other than NO and NO , that is, the rate of at which x 2
NO was converted into N and N O. Meanwhile, since only NO in NO was analyzed x 2 2 J x J
(NO in NO was not analyzed) to determine the NO conversion rate thereof, NO
2 x conversion - NO conversion = NO formation rate, and thus the difference in the range x 2 of the NO/ NO conversion rate can be taken as the NO formation rate.
2 2
[36] The present inventors fabricated catalysts of Example 1 and Comparative Example
1 based on the tests, and then measured the HC conversion rate and the NO/NO conversion rate using the catalysts, and the results thereof are shown in FIGS. 3 and 4. From FIGS. 3 and 4, it can be seen that the catalyst of Example 1 exhibits the effect of considerably inhibiting NO formation (see FIG. 4) while not changing the HC conversion rate (see FIG. 3), and thus the catalyst composition according to the present invention inhibits NO formation, thereby reducing the generation of yellow smog.

Claims

Claims
[1] A catalyst composition for inhibiting the generation of NO , comprising:
A basic metal oxide catalyst composition combined with ceria-cobalt oxide, active alumina, and zeolite, wherein the basic metal oxide catalyst composition is supported with a precious metal, such as platinum and/or palladium, and a non-precious metal, such as barium or strontium. [2] A module for inhibiting the generation of NO , comprising a refractory carrier coated with the catalyst composition for inhibiting the generation of NO according to claim 1. [3] An aftertreatment system comprising the module for inhibiting the generation of
NO according to claim 2, wherein the module is provided immediately behind a
DOC and/or CSF.
EP07808305A 2006-10-04 2007-09-18 A catalyst for inhibiting the no2 generation Withdrawn EP2073929A4 (en)

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KR1020060097585A KR100809661B1 (en) 2006-10-04 2006-10-04 A catalyst for inhibiting the no2 generation
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EP0507590A1 (en) * 1991-04-05 1992-10-07 Nippon Shokubai Co., Ltd. Catalyst for purifying exhaust gas
US5736482A (en) * 1995-02-03 1998-04-07 Institut Francais Du Petrole Catalysts for reducing nitrogen oxides to molecular nitrogen in a superstoichiometric medium of oxidizing compounds, process for preparation, and uses
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