US20120285148A1 - Catalyst device - Google Patents
Catalyst device Download PDFInfo
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- US20120285148A1 US20120285148A1 US13/468,305 US201213468305A US2012285148A1 US 20120285148 A1 US20120285148 A1 US 20120285148A1 US 201213468305 A US201213468305 A US 201213468305A US 2012285148 A1 US2012285148 A1 US 2012285148A1
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- catalyst
- base material
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- oxidation catalyst
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- 239000003054 catalyst Substances 0.000 title claims abstract description 144
- 239000000463 material Substances 0.000 claims abstract description 51
- 230000003647 oxidation Effects 0.000 claims abstract description 50
- 238000007254 oxidation reaction Methods 0.000 claims abstract description 50
- 239000011148 porous material Substances 0.000 claims abstract description 25
- 238000002485 combustion reaction Methods 0.000 claims description 6
- 230000007062 hydrolysis Effects 0.000 claims description 6
- 238000006460 hydrolysis reaction Methods 0.000 claims description 6
- 239000003638 chemical reducing agent Substances 0.000 claims description 2
- 239000000758 substrate Substances 0.000 abstract description 8
- MWUXSHHQAYIFBG-UHFFFAOYSA-N Nitric oxide Chemical compound O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 61
- 230000000052 comparative effect Effects 0.000 description 39
- 239000007789 gas Substances 0.000 description 28
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 description 27
- 239000004202 carbamide Substances 0.000 description 27
- 239000013618 particulate matter Substances 0.000 description 21
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 16
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 15
- 229910052593 corundum Inorganic materials 0.000 description 14
- 238000000746 purification Methods 0.000 description 14
- 239000000243 solution Substances 0.000 description 14
- 229910001845 yogo sapphire Inorganic materials 0.000 description 14
- 239000011248 coating agent Substances 0.000 description 12
- 238000000576 coating method Methods 0.000 description 12
- 229910021529 ammonia Inorganic materials 0.000 description 8
- 230000008021 deposition Effects 0.000 description 6
- 238000002347 injection Methods 0.000 description 5
- 239000007924 injection Substances 0.000 description 5
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- MGWGWNFMUOTEHG-UHFFFAOYSA-N 4-(3,5-dimethylphenyl)-1,3-thiazol-2-amine Chemical compound CC1=CC(C)=CC(C=2N=C(N)SC=2)=C1 MGWGWNFMUOTEHG-UHFFFAOYSA-N 0.000 description 3
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 3
- 229910002091 carbon monoxide Inorganic materials 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 238000011156 evaluation Methods 0.000 description 3
- 229930195733 hydrocarbon Natural products 0.000 description 3
- 150000002430 hydrocarbons Chemical class 0.000 description 3
- JCXJVPUVTGWSNB-UHFFFAOYSA-N nitrogen dioxide Inorganic materials O=[N]=O JCXJVPUVTGWSNB-UHFFFAOYSA-N 0.000 description 3
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 239000000446 fuel Substances 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 230000001590 oxidative effect Effects 0.000 description 2
- 230000008929 regeneration Effects 0.000 description 2
- 238000011069 regeneration method Methods 0.000 description 2
- 230000001629 suppression Effects 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 229910021536 Zeolite Inorganic materials 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 238000010531 catalytic reduction reaction Methods 0.000 description 1
- 229910010293 ceramic material Inorganic materials 0.000 description 1
- 229910052878 cordierite Inorganic materials 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- JSKIRARMQDRGJZ-UHFFFAOYSA-N dimagnesium dioxido-bis[(1-oxido-3-oxo-2,4,6,8,9-pentaoxa-1,3-disila-5,7-dialuminabicyclo[3.3.1]nonan-7-yl)oxy]silane Chemical compound [Mg++].[Mg++].[O-][Si]([O-])(O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2)O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2 JSKIRARMQDRGJZ-UHFFFAOYSA-N 0.000 description 1
- HNPSIPDUKPIQMN-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Al]O[Al]=O HNPSIPDUKPIQMN-UHFFFAOYSA-N 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 238000006722 reduction reaction Methods 0.000 description 1
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 description 1
- 229910010271 silicon carbide Inorganic materials 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 238000005549 size reduction Methods 0.000 description 1
- 239000010457 zeolite Substances 0.000 description 1
Images
Classifications
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- 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
- B01D53/9459—Removing one or more of nitrogen oxides, carbon monoxide, or hydrocarbons by multiple successive catalytic functions; systems with more than one different function, e.g. zone coated catalysts
- B01D53/9463—Removing one or more of nitrogen oxides, carbon monoxide, or hydrocarbons by multiple successive catalytic functions; systems with more than one different function, e.g. zone coated catalysts with catalysts positioned on one brick
- B01D53/9468—Removing one or more of nitrogen oxides, carbon monoxide, or hydrocarbons by multiple successive catalytic functions; systems with more than one different function, e.g. zone coated catalysts with catalysts positioned on one brick in different layers
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- 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
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- 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
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- 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
- B01J29/40—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11, as exemplified by patent documents US3702886, GB1334243 and US3709979, respectively
- B01J29/42—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11, as exemplified by patent documents US3702886, GB1334243 and US3709979, respectively containing iron group metals, noble metals or copper
- B01J29/46—Iron group metals or copper
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- F01N3/02—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust
- F01N3/021—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters
- F01N3/033—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters in combination with other devices
- F01N3/035—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters in combination with other devices with catalytic reactors, e.g. catalysed diesel particulate filters
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- 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
- F01N3/103—Oxidation catalysts for HC and CO only
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- 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
- F01N3/18—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 methods of operation; Control
- F01N3/20—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 methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
- F01N3/2066—Selective catalytic reduction [SCR]
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- B01D53/34—Chemical or biological purification of waste gases
- B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
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- 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
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- 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
- B01D53/944—Simultaneously removing carbon monoxide, hydrocarbons or carbon making use of oxidation catalysts
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
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- F01N2510/00—Surface coverings
- F01N2510/06—Surface coverings for exhaust purification, e.g. catalytic reaction
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
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- F01N2510/00—Surface coverings
- F01N2510/06—Surface coverings for exhaust purification, e.g. catalytic reaction
- F01N2510/068—Surface coverings for exhaust purification, e.g. catalytic reaction characterised by the distribution of the catalytic coatings
- F01N2510/0684—Surface coverings for exhaust purification, e.g. catalytic reaction characterised by the distribution of the catalytic coatings having more than one coating layer, e.g. multi-layered coatings
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- 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 device, and more particularly, to a catalyst device that is used in an exhaust gas purification apparatus that utilizes a urea selective catalytic reduction (SCR) system.
- SCR selective catalytic reduction
- a urea SCR system comprises: an oxidation catalyst for oxidizing nitrogen monoxide (NO) into nitrogen dioxide (NO 2 ); an SCR catalyst, disposed downstream of the oxidation catalyst, for reducing NOx to nitrogen and water through a chemical reaction between NOx and ammonia generated out of the aqueous urea solution; a urea addition system for adding the aqueous urea solution to the SCR catalyst; and an oxidation catalyst, disposed downstream of the SCR catalyst, for oxidizing residual ammonia that is not consumed in the chemical reaction in the SCR catalyst.
- a diesel particulate filter (DPF) for removing particulate matter (PM) can be provided between the SCR catalyst and the oxidation catalyst that oxidizes NO.
- the present invention provides a catalyst device that purifies an exhaust gas discharged by an internal combustion engine, comprising: a porous base material that supports, in the interior thereof, an SCR catalyst that reduces NOx in the exhaust gas; a trapping layer that traps PM in the exhaust gas and is coated on a surface of the base material on the internal combustion engine side; and an oxidation catalyst layer that contains an oxidation catalyst and is coated on a surface of the base material on a side opposite to the internal combustion engine side.
- FIG. 1 is a schematic diagram of the configuration of an exhaust gas purification apparatus provided with a catalyst device according to an embodiment of the present invention.
- FIG. 2 is a cross-sectional diagram of a substrate in the catalyst device according to the embodiment.
- FIG. 1 illustrates a schematic diagram of the configuration of an exhaust gas purification apparatus provided with catalyst device according to an embodiment of the present invention.
- An exhaust pipe 2 through which exhaust gas discharged from a diesel engine 1 flows is provided with an oxidation catalyst device 3 and a catalyst device 4 that purifies the exhaust gas.
- An injection nozzle 7 that injects an aqueous urea solution, as a reductant, is provided between the oxidation catalyst device 3 and the catalyst device 4 .
- the injection nozzle 7 communicates, via piping 8 , with an aqueous urea solution tank 9 that stores an aqueous urea solution.
- the piping 8 is provided with an aqueous urea solution addition system 6 for supplying aqueous urea solution from inside the aqueous urea solution tank 9 to the injection nozzle 7 .
- the aqueous urea solution addition system 6 is electrically connected to an ECU 5 which is a control device.
- the catalyst device 4 has a wall flow-type substrate 14 .
- the substrate 14 includes a porous base material 11 .
- the material used in the base material 11 may be a ceramic material ordinarily used as a filter substrate, for instance cordierite, alumina, silicon carbide or the like.
- An SCR catalyst for reduction of NOx is supported in the pores in the interior of the base material 11 .
- a surface 11 a of the base material 11 on the diesel engine 1 side is coated with a trapping layer 12 that traps PM in the exhaust gas.
- the same material as in the base material 11 can be used as the material of the trapping layer 12 .
- a surface 11 b of the base material 11 on the side opposite to the diesel engine 1 side is coated with an oxidation catalyst layer 13 that is formed of an oxidation catalyst.
- a thickness X 1 of the base material 11 is greater than both a thickness X 2 of the trapping layer 12 and a thickness X 3 of the oxidation catalyst layer 13 .
- the thickness X 1 of the base material 11 ranges from 200 ⁇ m to 400 ⁇ m.
- the thickness X 2 of the trapping layer 12 ranges preferably from 10 ⁇ m to less than 200 ⁇ m, and the thickness X 3 of the oxidation catalyst layer 13 ranges preferably from 0.1 ⁇ m to less than 200 ⁇ m.
- the porosity of the base material 11 is greater than the porosity of the trapping layer 12 , and the porosity of the oxidation catalyst layer 13 is equal to or greater than the porosity of the base material 11 .
- the porosity of the base material 11 and of the oxidation catalyst layer 13 range from 55% to 70%, and the porosity of the trapping layer 12 ranges preferably from 20% to less than 55%.
- the average pore size of the base material 11 is greater than the average pore size of the trapping layer 12 , and the average pore size of the oxidation catalyst layer 13 is equal to or greater than the average pore size of the base material 11 .
- the average pore size of the base material 11 and the oxidation catalyst layer 13 ranges from 15 ⁇ m to 100 ⁇ m, and the average pore size of the trapping layer 12 ranges preferably from 6 ⁇ m to less than 15 ⁇ m.
- exhaust gas discharged by the diesel engine 1 flows through the exhaust pipe 2 .
- the exhaust gas flows into the oxidation catalyst device 3 , whereupon NO in the exhaust gas is oxidized into NO 2 .
- the exhaust gas flows into the catalyst device 4 .
- the ECU 5 operates the aqueous urea solution addition system 6 at an appropriate timing, to supply aqueous urea solution in the aqueous urea solution tank 9 to the injection nozzle 7 via the piping 8 , and cause the aqueous urea solution to be added into the catalyst device 4 from the injection nozzle 7 .
- the PM in the exhaust gas that flows into the catalyst device 4 is captured by the trapping layer 12 as the exhaust gas passes through the trapping layer 12 .
- the exhaust gas diffuses into the pores of the base material 11 .
- the aqueous urea solution added into the catalyst device 4 is hydrolyzed on account of the heat of the exhaust gas, to yield ammonia and carbon dioxide.
- the SCR catalyst supported in the pores in the base material 11 the generated ammonia reacts with NOx in the exhaust gas that has diffused into the pores, and NOx is reduced thereby to nitrogen and water. Residual ammonia that has not been consumed in the base material 11 is oxidized at the oxidation catalyst in the oxidation catalyst layer 13 , and the purified exhaust gas is discharged to the atmosphere.
- the amount of PM captured in the trapping layer 12 increases as time goes by.
- the trapping layer 12 can be regenerated in accordance with known methods, for instance through addition of fuel to the exhaust gas.
- hydrocarbons and carbon monoxide are oxidized by the oxidation catalyst in the oxidation catalyst layer 13 .
- the SCR catalyst is supported in the interior of the porous base material 11 , and hence the coating amount need not be reduced to thereby reduce the pressure loss.
- the trapping layer 12 is coated onto the surface 11 a of the base material 11 on the diesel engine 1 side. Therefore, it is not necessary to reduce the pressure loss by using a high-porosity base material.
- a DPF, an SCR catalyst and an oxidation catalyst can be integrated together while fulfilling a combined DPF function and SCR catalyst function.
- the trapping layer 12 may be coated with, for instance, alumina, titania, a zeolite, silica or the like, as the hydrolysis catalyst for hydrolysis of urea.
- urea can be hydrolyzed on account of the heat of the exhaust gas
- the hydrolysis catalyst allows urea to be hydrolyzed reliably also when the temperature of the exhaust gas is low, for instance immediately after startup of the diesel engine 1 .
- a second SCR catalyst different from the SCR catalyst that is supported in the interior of the base material 11 may be incorporated in the oxidation catalyst layer 13 .
- NOx can be reduced in the oxidation catalyst layer 13 as well, and the NOx purification power can be thus enhanced.
- Table 1 sets forth the features of Examples 1 to 3, which correspond to catalyst devices according to the present invention, and the features of catalyst devices according to Comparative examples 1 to 9 (Comparative example 1 is a conventional urea SCR system wherein a DPF, an SCR catalyst and an oxidation catalyst are separate members).
- Examples 1 to 3 have a three-layer structure explained in the embodiment, comprising a trapping layer coated with Al 2 O 3 as a hydrolysis catalyst, a porous base material in which Fe-ZSM5 as an SCR catalyst is supported in internal pores, and an oxidation catalyst layer that contains Fe-ZSM5 as a second SCR catalyst and PtPd/Al 2 O 3 as an oxidation catalyst.
- Table 1 gives the porosity, average pore size (APS) and thickness for each layer, as well as the coating amount of SCR catalyst in the base material.
- Comparative example 1 is a conventional urea SCR system having a DPF, an SCR catalyst and an oxidation catalyst as separate members.
- Comparative examples 2 to 4 have a one-layer structure in which Fe-ZSM5, as an SCR catalyst, is supported in pores of a porous base material.
- Comparative examples 5 to 9 have a two-layer structure comprising a trapping layer coated with Al 2 O 3 , as a hydrolysis catalyst, and a porous base material in which Fe-ZSM5, as an SCR catalyst, is supported in internal pores.
- Table 1 gives the porosity, average pore size and thickness for each layer, as well as the coating amount of SCR catalyst in the base material.
- Table 2 sets forth evaluation results obtained upon evaluation of the performance of the catalyst devices of Examples 1 to 3 and Comparative examples 2 to 9, using these catalyst devices installed as the catalyst device 4 of the exhaust gas purification apparatus illustrated in FIG. 1 , and using a conventional urea SCR system as Comparative example 1.
- the evaluation results were graded qualitatively into a three-grade ranking in which a double circle denotes excellent results, a single circle denotes good results, and a cross mark denotes problematic results.
- Examples 1 to 3 and Comparative examples 2 to 9 utilize integrated catalyst devices, and hence exhibit superior compactness vis-à-vis Comparative example 1, which is a conventional urea SCR system in which a DPF, an SCR catalyst and an oxidation catalyst are separate members.
- PM trapping ability, pressure loss derived from PM deposition and NOx purification rate are related to compatibility between the DPF function and SCR catalyst function.
- Comparative examples 2 to 4 there is no trapping layer, and PM is trapped in the base material.
- the coating amount of SCR catalyst decreases and the NOx purification rate becomes poorer.
- the pressure loss derived from PM deposition becomes worse when the coating amount of SCR catalyst is increased with respect to that of Comparative example 2, as in Comparative example 3.
- the PM trapping ability becomes worse when adjusting the porosity and average pore size in Comparative example 3 in order to improve the pressure drop, as in Comparative example 4.
- the pressure loss derived from PM deposition is yet worse.
- the pressure loss derived from PM deposition is improved by reducing the coating amount of SCR catalyst, but the NOx purification rate drops in doing so.
- the thickness of the trapping layer is set to 300 ⁇ m and the thickness of the base material is set to 70 ⁇ m. The results of Comparative examples 8 and 9 indicate that it is difficult to achieve, on the basis of such a thickness relationship, both the coating amount of SCR catalyst (NOx purification rate) and pressure loss derived from PM deposition as are required.
- Comparative examples 2 to 9 which lack an oxidation catalyst layer that is formed of an oxidation catalyst that oxidizes ammonia, hydrocarbons and carbon monoxide, yielded problematic results in terms of ammonia slip properties, and slip-through properties of hydrocarbons and carbon monoxide during PM regeneration.
- Examples 1 to 3 which are specific embodiments of the catalyst device according to the present invention, display a satisfactory DPF function, SCR catalyst function and oxidation catalyst function, while integrating those functions with each other. That is, high PM trapping (low pressure loss) and high coating amount of an SCR catalyst (high NOx purification rate) can be realized. It also becomes possible to achieve further size reduction through coating of the oxidation catalyst layer.
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Abstract
A catalyst device has a wall flow-type substrate. The substrate is formed of a porous base material. An SCR catalyst for reduction of NOx is supported in pores in the interior of the base material. The surface of the base material on a diesel engine side is coated with a trapping layer that traps PM in an exhaust gas. The surface of the substrate on a side opposite to the diesel engine side is coated with an oxidation catalyst layer that is formed of an oxidation catalyst.
Description
- The present invention relates to a catalyst device, and more particularly, to a catalyst device that is used in an exhaust gas purification apparatus that utilizes a urea selective catalytic reduction (SCR) system.
- 1. Description of the Related Art
- Urea SCR systems have been developed in order to decrease the amount of nitrogen oxide (NOx) that is present in the exhaust gas of diesel engines. In a basic configuration, a urea SCR system comprises: an oxidation catalyst for oxidizing nitrogen monoxide (NO) into nitrogen dioxide (NO2); an SCR catalyst, disposed downstream of the oxidation catalyst, for reducing NOx to nitrogen and water through a chemical reaction between NOx and ammonia generated out of the aqueous urea solution; a urea addition system for adding the aqueous urea solution to the SCR catalyst; and an oxidation catalyst, disposed downstream of the SCR catalyst, for oxidizing residual ammonia that is not consumed in the chemical reaction in the SCR catalyst. A diesel particulate filter (DPF) for removing particulate matter (PM) can be provided between the SCR catalyst and the oxidation catalyst that oxidizes NO.
- This conventional urea SCR system that is formed of two oxidation catalysts, an SCR catalyst and a DPF, becomes very large as a whole. Also the SCR catalyst is disposed far removed from the engine. As a result, such a system is problematic in that the temperature of the exhaust gas drops before the exhaust gas reaches the SCR catalyst, and the purification performance of the SCR catalyst decreases accordingly. In order to solve this problem, Japanese Patent Application Publication No. 2010-19221 discloses a configuration wherein the size of a urea SCR system as a whole is reduced through the use of a catalyst device in which an SCR catalyst, a DPF and an oxidation catalyst are integrated together, and wherein the catalyst device is disposed as close as possible to the engine.
- In order to integrate the SCR catalyst, the DPF and the oxidation catalyst with each other, the SCR catalyst and the oxidation catalyst were coated onto a filter that corresponds to a DPF in Japanese Patent Application Publication No. 2010-19221. However, this resulted in a higher pressure drop, and loss of fuel mileage, which was problematic. Here, NOx purification performance drops when the coating amount of the SCR catalyst is decreased in order to reduce the pressure drop. Therefore, a high-porosity substrate must be used as the filter. Doing so, however, translates into a lower PM trapping performance. Therefore, it was difficult to combine a DPF function with an SCR catalyst function.
- In order to solve the above problems, it is an object of the present invention to provide a catalyst device in which a DPF, an SCR catalyst and an oxidation catalyst are integrated together, such that the catalyst device combines a DPF function and an SCR catalyst function.
- The present invention provides a catalyst device that purifies an exhaust gas discharged by an internal combustion engine, comprising: a porous base material that supports, in the interior thereof, an SCR catalyst that reduces NOx in the exhaust gas; a trapping layer that traps PM in the exhaust gas and is coated on a surface of the base material on the internal combustion engine side; and an oxidation catalyst layer that contains an oxidation catalyst and is coated on a surface of the base material on a side opposite to the internal combustion engine side.
-
FIG. 1 is a schematic diagram of the configuration of an exhaust gas purification apparatus provided with a catalyst device according to an embodiment of the present invention; and -
FIG. 2 is a cross-sectional diagram of a substrate in the catalyst device according to the embodiment. - Embodiments of the present invention are explained next with reference to the accompanying drawings.
-
FIG. 1 illustrates a schematic diagram of the configuration of an exhaust gas purification apparatus provided with catalyst device according to an embodiment of the present invention. Anexhaust pipe 2 through which exhaust gas discharged from adiesel engine 1 flows is provided with anoxidation catalyst device 3 and a catalyst device 4 that purifies the exhaust gas. An injection nozzle 7 that injects an aqueous urea solution, as a reductant, is provided between theoxidation catalyst device 3 and the catalyst device 4. The injection nozzle 7 communicates, viapiping 8, with an aqueousurea solution tank 9 that stores an aqueous urea solution. Thepiping 8 is provided with an aqueous ureasolution addition system 6 for supplying aqueous urea solution from inside the aqueousurea solution tank 9 to the injection nozzle 7. The aqueous ureasolution addition system 6 is electrically connected to anECU 5 which is a control device. - As illustrated in
FIG. 2 , the catalyst device 4 has a wall flow-type substrate 14. Thesubstrate 14 includes aporous base material 11. The material used in thebase material 11 may be a ceramic material ordinarily used as a filter substrate, for instance cordierite, alumina, silicon carbide or the like. An SCR catalyst for reduction of NOx is supported in the pores in the interior of thebase material 11. A surface 11 a of thebase material 11 on thediesel engine 1 side is coated with atrapping layer 12 that traps PM in the exhaust gas. The same material as in thebase material 11 can be used as the material of thetrapping layer 12. A surface 11 b of thebase material 11 on the side opposite to thediesel engine 1 side is coated with anoxidation catalyst layer 13 that is formed of an oxidation catalyst. - A thickness X1 of the
base material 11 is greater than both a thickness X2 of thetrapping layer 12 and a thickness X3 of theoxidation catalyst layer 13. Preferably, the thickness X1 of thebase material 11 ranges from 200 μm to 400 μm. The thickness X2 of thetrapping layer 12 ranges preferably from 10 μm to less than 200 μm, and the thickness X3 of theoxidation catalyst layer 13 ranges preferably from 0.1 μm to less than 200 μm. - Setting the thickness relationship such as noted above allows suppression of pressure loss in the
trapping layer 12, and allows the base material (coatable surface area inside the porous base material) to be made appropriate for the coating amount of SCR catalyst as required for NOx purification. - The porosity of the
base material 11 is greater than the porosity of thetrapping layer 12, and the porosity of theoxidation catalyst layer 13 is equal to or greater than the porosity of thebase material 11. Preferably, the porosity of thebase material 11 and of theoxidation catalyst layer 13 range from 55% to 70%, and the porosity of thetrapping layer 12 ranges preferably from 20% to less than 55%. - The average pore size of the
base material 11 is greater than the average pore size of thetrapping layer 12, and the average pore size of theoxidation catalyst layer 13 is equal to or greater than the average pore size of thebase material 11. Preferably, the average pore size of thebase material 11 and theoxidation catalyst layer 13 ranges from 15 μm to 100 μm, and the average pore size of thetrapping layer 12 ranges preferably from 6 μm to less than 15 μm. - Setting the relationships of porosity and average pore size such as noted above allows suppression of pressure loss downstream of the
trapping layer 12, while enabling, at the same time, good contact between the exhaust gas and the catalyst. - The operation of the exhaust gas purification apparatus provided with the catalyst device according to the present embodiment will be explained next.
- As illustrated in
FIG. 1 , exhaust gas discharged by thediesel engine 1 flows through theexhaust pipe 2. The exhaust gas flows into theoxidation catalyst device 3, whereupon NO in the exhaust gas is oxidized into NO2. Next, the exhaust gas flows into the catalyst device 4. The ECU 5 operates the aqueous ureasolution addition system 6 at an appropriate timing, to supply aqueous urea solution in the aqueousurea solution tank 9 to the injection nozzle 7 via thepiping 8, and cause the aqueous urea solution to be added into the catalyst device 4 from the injection nozzle 7. - As illustrated in
FIG. 2 , the PM in the exhaust gas that flows into the catalyst device 4 is captured by thetrapping layer 12 as the exhaust gas passes through thetrapping layer 12. Next, the exhaust gas diffuses into the pores of thebase material 11. The aqueous urea solution added into the catalyst device 4 is hydrolyzed on account of the heat of the exhaust gas, to yield ammonia and carbon dioxide. By virtue of the SCR catalyst supported in the pores in thebase material 11, the generated ammonia reacts with NOx in the exhaust gas that has diffused into the pores, and NOx is reduced thereby to nitrogen and water. Residual ammonia that has not been consumed in thebase material 11 is oxidized at the oxidation catalyst in theoxidation catalyst layer 13, and the purified exhaust gas is discharged to the atmosphere. - The amount of PM captured in the
trapping layer 12 increases as time goes by. When the amount of captured PM is determined to be equal to or greater than a prescribed amount, for instance through detection of a pressure difference between the inlet and outlet of the catalyst device 4, thetrapping layer 12 can be regenerated in accordance with known methods, for instance through addition of fuel to the exhaust gas. During regeneration of thetrapping layer 12, hydrocarbons and carbon monoxide are oxidized by the oxidation catalyst in theoxidation catalyst layer 13. - The SCR catalyst is supported in the interior of the
porous base material 11, and hence the coating amount need not be reduced to thereby reduce the pressure loss. Thetrapping layer 12 is coated onto the surface 11 a of thebase material 11 on thediesel engine 1 side. Therefore, it is not necessary to reduce the pressure loss by using a high-porosity base material. As a result, a DPF, an SCR catalyst and an oxidation catalyst can be integrated together while fulfilling a combined DPF function and SCR catalyst function. - In the present embodiment, the
trapping layer 12 may be coated with, for instance, alumina, titania, a zeolite, silica or the like, as the hydrolysis catalyst for hydrolysis of urea. Although urea can be hydrolyzed on account of the heat of the exhaust gas, the hydrolysis catalyst allows urea to be hydrolyzed reliably also when the temperature of the exhaust gas is low, for instance immediately after startup of thediesel engine 1. A second SCR catalyst different from the SCR catalyst that is supported in the interior of thebase material 11 may be incorporated in theoxidation catalyst layer 13. As a result, NOx can be reduced in theoxidation catalyst layer 13 as well, and the NOx purification power can be thus enhanced. - The effect of the catalyst device according to the present invention is explained next based on examples.
- Table 1 sets forth the features of Examples 1 to 3, which correspond to catalyst devices according to the present invention, and the features of catalyst devices according to Comparative examples 1 to 9 (Comparative example 1 is a conventional urea SCR system wherein a DPF, an SCR catalyst and an oxidation catalyst are separate members).
-
TABLE 1 Base material Coating Trapping layer amount Oxidation catalyst layer Thick- Thick- of Thick- Feature of Porosity APS ness Porosity APS ness catalyst Porosity APS ness DPF/SCR [%] [μm] [μm] Catalyst [%] [μm] [μm] Catalyst [g/L] [%] [μm] [μm] Catalyst Example 1 Integral 50 12 10 Al2O3 60 20 300 Fe-ZSM5 150 65 25 70 Fe-ZSM5 + type PtPd/Al2O3 Example 2 Integral 50 12 100 Al2O3 65 25 300 Fe-ZSM5 150 65 25 70 Fe-ZSM5 + type PtPd/Al2O3 Example 3 Integral 50 12 70 Al2O3 65 25 300 Fe-ZSM5 150 65 25 70 Fe-ZSM5 + type PtPd/Al2O3 Comparative Separate — — — — — — — — — — — — — example 1 type Comparative Integral — — — — 50 12 300 Fe-ZSM5 20 — — — — example 2 type Comparative Integral — — — — 50 12 300 Fe-ZSM5 150 — — — — example 3 type Comparative Integral — — — — 65 25 300 Fe-ZSM5 150 — — — — example 4 type Comparative Integral 50 12 70 Al2O3 50 12 300 Fe-ZSM5 150 — — — — example 5 type Comparative Integral 50 12 70 Al2O3 50 12 300 Fe-ZSM5 20 — — — — example 6 type Comparative Integral 50 12 70 Al2O3 65 25 300 Fe-ZSM5 150 — — — — example 7 type Comparative Integral 50 12 300 Al2O3 65 25 70 Fe-ZSM5 20 — — — — example 8 type Comparative Integral 65 25 300 Al2O3 50 12 70 Fe-ZSM5 150 — — — — example 9 type - Examples 1 to 3 have a three-layer structure explained in the embodiment, comprising a trapping layer coated with Al2O3 as a hydrolysis catalyst, a porous base material in which Fe-ZSM5 as an SCR catalyst is supported in internal pores, and an oxidation catalyst layer that contains Fe-ZSM5 as a second SCR catalyst and PtPd/Al2O3 as an oxidation catalyst. Table 1 gives the porosity, average pore size (APS) and thickness for each layer, as well as the coating amount of SCR catalyst in the base material.
- As explained above, Comparative example 1 is a conventional urea SCR system having a DPF, an SCR catalyst and an oxidation catalyst as separate members. Comparative examples 2 to 4 have a one-layer structure in which Fe-ZSM5, as an SCR catalyst, is supported in pores of a porous base material. Comparative examples 5 to 9 have a two-layer structure comprising a trapping layer coated with Al2O3, as a hydrolysis catalyst, and a porous base material in which Fe-ZSM5, as an SCR catalyst, is supported in internal pores. Table 1 gives the porosity, average pore size and thickness for each layer, as well as the coating amount of SCR catalyst in the base material.
- Table 2 sets forth evaluation results obtained upon evaluation of the performance of the catalyst devices of Examples 1 to 3 and Comparative examples 2 to 9, using these catalyst devices installed as the catalyst device 4 of the exhaust gas purification apparatus illustrated in
FIG. 1 , and using a conventional urea SCR system as Comparative example 1. The evaluation results were graded qualitatively into a three-grade ranking in which a double circle denotes excellent results, a single circle denotes good results, and a cross mark denotes problematic results. -
TABLE 2 Slip- NOx through Com- PM purifica- Ammonia property pact- trapping Pressure tion slip of HC ness ability loss rate property and CO Example 1 ⊚ ◯ ◯ ⊚ ⊚ ⊚ Example 2 ⊚ ⊚ ◯ ⊚ ⊚ ⊚ Example 3 ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ Comparative X ⊚ ⊚ X ⊚ ⊚ example 1 Comparative ⊚ ⊚ ⊚ X X X example 2 Comparative ⊚ ⊚ X ⊚ X X example 3 Comparative ⊚ X ⊚ ⊚ X X example 4 Comparative ⊚ ⊚ X ⊚ X X example 5 Comparative ⊚ ⊚ ⊚ X X X example 6 Comparative ⊚ ⊚ ⊚ ⊚ X X example 7 Comparative ⊚ ⊚ ⊚ X X X example 8 Comparative ⊚ ⊚ X ⊚ X X example 9 - Examples 1 to 3 and Comparative examples 2 to 9 utilize integrated catalyst devices, and hence exhibit superior compactness vis-à-vis Comparative example 1, which is a conventional urea SCR system in which a DPF, an SCR catalyst and an oxidation catalyst are separate members. PM trapping ability, pressure loss derived from PM deposition and NOx purification rate are related to compatibility between the DPF function and SCR catalyst function. In Comparative examples 2 to 4 there is no trapping layer, and PM is trapped in the base material. When attempting to improve PM trapping ability and pressure loss derived from PM deposition as in Comparative example 2, however, the coating amount of SCR catalyst decreases and the NOx purification rate becomes poorer. The pressure loss derived from PM deposition becomes worse when the coating amount of SCR catalyst is increased with respect to that of Comparative example 2, as in Comparative example 3. The PM trapping ability becomes worse when adjusting the porosity and average pore size in Comparative example 3 in order to improve the pressure drop, as in Comparative example 4. In Comparative example 5, the pressure loss derived from PM deposition is yet worse. In Comparative example 6, the pressure loss derived from PM deposition is improved by reducing the coating amount of SCR catalyst, but the NOx purification rate drops in doing so. In Comparative examples 8 and 9 the thickness of the trapping layer is set to 300 μm and the thickness of the base material is set to 70 μm. The results of Comparative examples 8 and 9 indicate that it is difficult to achieve, on the basis of such a thickness relationship, both the coating amount of SCR catalyst (NOx purification rate) and pressure loss derived from PM deposition as are required.
- Comparative examples 2 to 9, which lack an oxidation catalyst layer that is formed of an oxidation catalyst that oxidizes ammonia, hydrocarbons and carbon monoxide, yielded problematic results in terms of ammonia slip properties, and slip-through properties of hydrocarbons and carbon monoxide during PM regeneration.
- That is, even though a cross mark appears in at least one given item in all of Comparative examples 1 to 9, in Examples 1 to 3, by contrast, all items are excellent or good. Therefore, the catalyst devices in Examples 1 to 3 are found to combine both a DPF function and an SCR catalyst function. Accordingly, Examples 1 to 3, which are specific embodiments of the catalyst device according to the present invention, display a satisfactory DPF function, SCR catalyst function and oxidation catalyst function, while integrating those functions with each other. That is, high PM trapping (low pressure loss) and high coating amount of an SCR catalyst (high NOx purification rate) can be realized. It also becomes possible to achieve further size reduction through coating of the oxidation catalyst layer.
Claims (7)
1. A catalyst device that purifies an exhaust gas discharged by an internal combustion engine, comprising:
a porous base material that supports, in the interior thereof, an SCR catalyst that reduces NOx in the exhaust gas;
a trapping layer that traps PM in the exhaust gas and is coated on a surface of the base material on the internal combustion engine side; and
an oxidation catalyst layer that contains an oxidation catalyst and is coated on a surface of the base material on a side opposite to the internal combustion engine side.
2. The catalyst device according to claim 1 , wherein porosity of the base material is greater than porosity of the trapping layer, and porosity of the oxidation catalyst layer is equal to or greater than the porosity of the base material,
an average pore size of the base material is greater than an average pore size of the trapping layer, and an average pore size of the oxidation catalyst layer is equal to or greater than the average pore size of the base material, and
thickness of the base material is greater than both thickness of the trapping layer and thickness of the oxidation catalyst layer.
3. The catalyst device according to claim 1 , wherein porosity of the base material and porosity of the oxidation catalyst layer range from 55% to 70%, and porosity of the trapping layer ranges from 20% to less than 55%.
4. The catalyst device according to claim 1 , wherein an average pore size of the base material and an average pore size of the oxidation catalyst layer range from 15 μm to 100 μm, and an average pore size of the trapping layer ranges from 6 μm to less than 15 μm.
5. The catalyst device according to claim 1 , wherein thickness of the base material ranges from 200 μm to 400 μm, thickness of the trapping layer ranges from 10 μm to less than 200 μm, and thickness of the oxidation catalyst layer ranges from 0.1 μm to less than 200 μm.
6. The catalyst device according to claim 1 , wherein the oxidation catalyst layer further contains a second SCR catalyst.
7. The catalyst device according to claim 1 , wherein the trapping layer contains a hydrolysis catalyst that hydrolyzes a reductant that is added to the catalyst device in order for NOx to be reduced by the SCR catalyst.
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Cited By (2)
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US20170284248A1 (en) * | 2014-09-08 | 2017-10-05 | Continental Automotive Gmbh | Particle filter and method for producing a particle filter |
CN109891064A (en) * | 2016-10-26 | 2019-06-14 | 斗山英维高株式会社 | Exhausted gas post-processing system |
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CA2899149C (en) * | 2013-02-14 | 2020-03-24 | Haldor Topsoe A/S | Method and catalyst for the simultaneous removal of carbon monoxide and nitrogen oxides from flue or exhaust gas |
JP6043227B2 (en) * | 2013-03-29 | 2016-12-14 | 日本碍子株式会社 | Honeycomb structure |
JP6074306B2 (en) * | 2013-03-29 | 2017-02-01 | 日本碍子株式会社 | Honeycomb structure |
EP2826971A1 (en) * | 2013-07-17 | 2015-01-21 | DEUTZ Aktiengesellschaft | Method for reducing nitrogen oxides in diesel engine exhaust gases and exhaust gas treatment system for carrying out the method |
JP6028769B2 (en) | 2014-07-15 | 2016-11-16 | トヨタ自動車株式会社 | Exhaust gas purification device for internal combustion engine |
US10279313B2 (en) | 2015-05-19 | 2019-05-07 | Umicore Ag & Co. Kg | Method, multifunctional filter and system for the removal of particulate matter and noxious compounds from engine exhaust gas |
EP4265315A1 (en) * | 2020-12-16 | 2023-10-25 | Umicore Shokubai Japan Co., Ltd. | Fine particle filter, method for removing particulate material from exhaust gas of internal combustion engine, and method for producing fine particle filter |
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JP4638892B2 (en) * | 2007-03-30 | 2011-02-23 | トヨタ自動車株式会社 | Exhaust gas purification device for internal combustion engine |
WO2008122023A1 (en) * | 2007-04-02 | 2008-10-09 | Geo2 Technologies, Inc | A selective catalytic reduction filter and method of using same |
US8105545B2 (en) * | 2007-06-19 | 2012-01-31 | Hino Motors, Ltd. | Engine exhaust gas purifier |
GB0812544D0 (en) * | 2008-07-09 | 2008-08-13 | Johnson Matthey Plc | Exhaust system for a lean burn IC engine |
JP5258426B2 (en) | 2008-07-14 | 2013-08-07 | Udトラックス株式会社 | Engine exhaust purification system |
DE102008055890A1 (en) * | 2008-11-05 | 2010-05-12 | Süd-Chemie AG | Particulate reduction with combined SCR and NH3 slip catalyst |
US8246922B2 (en) * | 2009-10-02 | 2012-08-21 | Basf Corporation | Four-way diesel catalysts and methods of use |
JP5726414B2 (en) * | 2009-11-18 | 2015-06-03 | 日本碍子株式会社 | Catalyst-carrying filter and exhaust gas purification system |
CN102762827B (en) * | 2010-04-14 | 2014-12-24 | 尤米科尔股份公司及两合公司 | Reduction-catalyst-coated diesel particle filter having improved characteristics |
FR2964413B1 (en) * | 2010-09-02 | 2016-07-01 | Peugeot Citroen Automobiles Sa | PARTICLE FILTER HAVING THREE CATALYTIC COATINGS |
-
2011
- 2011-05-13 JP JP2011108165A patent/JP2012237282A/en not_active Withdrawn
-
2012
- 2012-05-02 EP EP12166402A patent/EP2522419A1/en not_active Withdrawn
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Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
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US20170284248A1 (en) * | 2014-09-08 | 2017-10-05 | Continental Automotive Gmbh | Particle filter and method for producing a particle filter |
CN109891064A (en) * | 2016-10-26 | 2019-06-14 | 斗山英维高株式会社 | Exhausted gas post-processing system |
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