WO2014141903A1 - 酸化触媒及びそれを用いた排気ガス浄化装置 - Google Patents
酸化触媒及びそれを用いた排気ガス浄化装置 Download PDFInfo
- Publication number
- WO2014141903A1 WO2014141903A1 PCT/JP2014/055046 JP2014055046W WO2014141903A1 WO 2014141903 A1 WO2014141903 A1 WO 2014141903A1 JP 2014055046 W JP2014055046 W JP 2014055046W WO 2014141903 A1 WO2014141903 A1 WO 2014141903A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- oxidation catalyst
- alumina
- exhaust gas
- light oil
- catalyst
- Prior art date
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- 239000003054 catalyst Substances 0.000 title claims abstract description 213
- 238000007254 oxidation reaction Methods 0.000 title claims abstract description 132
- 230000003647 oxidation Effects 0.000 title claims abstract description 129
- 238000000746 purification Methods 0.000 title claims abstract description 26
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 claims abstract description 155
- 238000002485 combustion reaction Methods 0.000 claims abstract description 103
- 239000000463 material Substances 0.000 claims abstract description 62
- 229910052809 inorganic oxide Inorganic materials 0.000 claims abstract description 58
- 229910000510 noble metal Inorganic materials 0.000 claims abstract description 57
- 230000004913 activation Effects 0.000 claims abstract description 43
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 claims abstract description 37
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 claims abstract description 34
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 33
- 239000000377 silicon dioxide Substances 0.000 claims abstract description 16
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical group [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims description 68
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 claims description 58
- 150000007529 inorganic bases Chemical class 0.000 claims description 32
- 229910052697 platinum Inorganic materials 0.000 claims description 25
- 238000000034 method Methods 0.000 claims description 20
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- 229910001404 rare earth metal oxide Inorganic materials 0.000 claims description 15
- 238000005507 spraying Methods 0.000 claims description 14
- 238000011144 upstream manufacturing Methods 0.000 claims description 13
- 238000000576 coating method Methods 0.000 claims description 12
- 239000011248 coating agent Substances 0.000 claims description 11
- MRELNEQAGSRDBK-UHFFFAOYSA-N lanthanum(3+);oxygen(2-) Chemical group [O-2].[O-2].[O-2].[La+3].[La+3] MRELNEQAGSRDBK-UHFFFAOYSA-N 0.000 claims description 10
- 229910052751 metal Inorganic materials 0.000 claims description 9
- 239000002184 metal Substances 0.000 claims description 9
- 239000004071 soot Substances 0.000 abstract description 8
- 239000011159 matrix material Substances 0.000 abstract 2
- 239000003921 oil Substances 0.000 description 131
- 239000007789 gas Substances 0.000 description 88
- 239000011148 porous material Substances 0.000 description 53
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- 239000002283 diesel fuel Substances 0.000 description 18
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- 230000008859 change Effects 0.000 description 13
- 230000000052 comparative effect Effects 0.000 description 13
- 239000010419 fine particle Substances 0.000 description 13
- 238000010438 heat treatment Methods 0.000 description 13
- NFOHLBHARAZXFQ-UHFFFAOYSA-L platinum(2+);dihydroxide Chemical compound O[Pt]O NFOHLBHARAZXFQ-UHFFFAOYSA-L 0.000 description 12
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- 238000004519 manufacturing process Methods 0.000 description 11
- 238000012360 testing method Methods 0.000 description 11
- 229910018879 Pt—Pd Inorganic materials 0.000 description 10
- 210000004027 cell Anatomy 0.000 description 10
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- 238000011156 evaluation Methods 0.000 description 7
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- 239000011259 mixed solution Substances 0.000 description 7
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- 229910052746 lanthanum Inorganic materials 0.000 description 6
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- 238000006243 chemical reaction Methods 0.000 description 5
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- 239000013078 crystal Substances 0.000 description 5
- 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 5
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- 239000000047 product Substances 0.000 description 5
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- GPNDARIEYHPYAY-UHFFFAOYSA-N palladium(ii) nitrate Chemical compound [Pd+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O GPNDARIEYHPYAY-UHFFFAOYSA-N 0.000 description 3
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- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 2
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- 150000001242 acetic acid derivatives Chemical class 0.000 description 2
- 230000002378 acidificating effect Effects 0.000 description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
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- 229910002091 carbon monoxide Inorganic materials 0.000 description 2
- 150000004649 carbonic acid derivatives Chemical class 0.000 description 2
- 150000001805 chlorine compounds Chemical class 0.000 description 2
- RKTYLMNFRDHKIL-UHFFFAOYSA-N copper;5,10,15,20-tetraphenylporphyrin-22,24-diide Chemical compound [Cu+2].C1=CC(C(=C2C=CC([N-]2)=C(C=2C=CC=CC=2)C=2C=CC(N=2)=C(C=2C=CC=CC=2)C2=CC=C3[N-]2)C=2C=CC=CC=2)=NC1=C3C1=CC=CC=C1 RKTYLMNFRDHKIL-UHFFFAOYSA-N 0.000 description 2
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- 238000010586 diagram Methods 0.000 description 2
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- 150000002823 nitrates Chemical class 0.000 description 2
- 229910017604 nitric acid Inorganic materials 0.000 description 2
- 230000001590 oxidative effect Effects 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
- 239000001301 oxygen Substances 0.000 description 2
- PIBWKRNGBLPSSY-UHFFFAOYSA-L palladium(II) chloride Chemical compound Cl[Pd]Cl PIBWKRNGBLPSSY-UHFFFAOYSA-L 0.000 description 2
- CLSUSRZJUQMOHH-UHFFFAOYSA-L platinum dichloride Chemical compound Cl[Pt]Cl CLSUSRZJUQMOHH-UHFFFAOYSA-L 0.000 description 2
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- 150000002940 palladium Chemical class 0.000 description 1
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- 229910002077 partially stabilized zirconia Inorganic materials 0.000 description 1
- JUFNXAFOTZCFOK-UHFFFAOYSA-M platinum(4+);chloride Chemical compound [Pt+3]Cl JUFNXAFOTZCFOK-UHFFFAOYSA-M 0.000 description 1
- JTAFSELAEYLDJR-UHFFFAOYSA-J platinum(4+);tetrahydroxide Chemical compound [OH-].[OH-].[OH-].[OH-].[Pt+4] JTAFSELAEYLDJR-UHFFFAOYSA-J 0.000 description 1
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- 229910001220 stainless steel Inorganic materials 0.000 description 1
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Images
Classifications
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- 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
- B01J37/03—Precipitation; Co-precipitation
- B01J37/038—Precipitation; Co-precipitation to form slurries or suspensions, e.g. a washcoat
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
- F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
- F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
- F01N3/105—General auxiliary catalysts, e.g. upstream or downstream of the main catalyst
- F01N3/106—Auxiliary oxidation catalysts
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- 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
- B01D53/944—Simultaneously removing carbon monoxide, hydrocarbons or carbon making use of oxidation catalysts
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- 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
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- B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
- B01J23/56—Platinum group metals
- B01J23/63—Platinum group metals with rare earths or actinides
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- B01J35/647—2-50 nm
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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
- B01J37/0201—Impregnation
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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
- B01J37/0244—Coatings comprising several layers
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
- F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
- F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
- F01N3/0821—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents combined with particulate filters
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- 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
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- 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
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- 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
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- 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
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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
- B01J35/00—Catalysts, in general, characterised by their form or physical properties
- B01J35/19—Catalysts containing parts with different compositions
Definitions
- the present invention relates to an oxidation catalyst and an exhaust gas purification apparatus using the same, and more specifically, a collection filter (DPF) or a catalytic combustion filter (CSF) that collects particulate components in exhaust gas from a diesel engine.
- the present invention relates to an oxidation catalyst that is incorporated in an exhaust gas purification device having an excellent combustion ability of light oil sprayed intermittently from a nozzle installed in an exhaust pipe, and an exhaust gas purification device using the same.
- DPF Diesel Particulate Filter
- NO contained in diesel exhaust gas is oxidized to NO 2 by an upstream oxidation catalyst (hereinafter referred to as “DOC”) and then downstream DPF or catalyzed DPF (Catalyzed Soot Filter).
- DOC upstream oxidation catalyst
- CSF catalyzed DPF
- DOC oxidation catalyst
- spraying and supplying fuel such as light oil into the exhaust gas a method of spraying fuel such as light oil by arranging a nozzle in the exhaust pipe between the exhaust port of the engine and the oxidation catalyst (exhaust pipe spraying), and a combustion stroke
- post spray a method for performing additional spraying to the combustion chamber of the internal combustion engine later, which is used depending on the size of the engine and the mechanism of the exhaust gas purification device.
- the above method requires a considerable amount of electric power for an electric heater for heating a large amount of exhaust gas, and also complicates the structure and control of the apparatus.
- it cannot be said that it is an effective method for a diesel engine mounted on a vehicle, and an improvement in the low temperature activity of the light oil combustion performance of the oxidation catalyst itself has been demanded.
- the present applicant has mixed platinum with ⁇ -Al 2 O 3 / La 2 O 3.
- a catalyst supported on a carrier is proposed (see Patent Document 10), and subsequently, palladium is supported on a platinum-supported ⁇ -Al 2 O 3 / La 2 O 3 mixed carrier and contains cerium ion-exchanged ⁇ -type zeolite.
- a catalyst was proposed (see Patent Document 11).
- a base material made of an inorganic oxide or the like that supports an active component such as a noble metal plays an important role in determining the superiority or inferiority of catalyst performance.
- This is an additive that has the function of assisting the material in addition to various physical properties such as the surface area (for example, BET specific surface area), pore diameter, pore volume, etc. This is because it is strongly influenced by the type, number, amount, etc., and in order to search for a catalyst that exhibits excellent catalytic performance, what has brought about good results with respect to the catalytic performance among these factors, It is very important to determine what causes the negative effects.
- Japanese Patent No. 3012249 JP 2001-263051 A Japanese Patent Laid-Open No. 2002-30924 JP 2002-35587 A JP-A-8-42325 Japanese Patent Laid-Open No. 9-222009 JP-A-9-317440 JP-A-10-272324 JP 2002-97930 A Japanese Patent Application Laid-Open No. 2004-290827 JP 2006-281127 A
- An object of the present invention is to provide an exhaust gas purification device having a collection filter (DPF) or a catalytic combustion filter (CSF) that collects particulate components in exhaust gas from a diesel engine in view of the above-mentioned problems of the prior art. It is an object of the present invention to provide an oxidation catalyst excellent in the ability to burn light oil intermittently sprayed from a nozzle installed in an exhaust pipe and an exhaust gas purification apparatus using the same.
- DPF collection filter
- CSF catalytic combustion filter
- the present inventors have found that in an oxidation catalyst in which a noble metal is supported on an inorganic oxide, the BET specific surface area, average pore diameter, Generally known physical property values such as pore volume are not directly related to the light oil combustion performance of the oxidation catalyst, and when an inorganic oxide having an activation energy of light oil combustion performance of 72 kJ / mol or less is used.
- the present invention was completed by elucidating that the diesel oil combustion performance of a diesel engine can be reliably improved.
- the present inventors satisfy the above-mentioned conditions while the slurry is abnormal in properties. It has also been confirmed that the addition of another inorganic oxide with a different bulk density that relaxes the gas oil further improves the light oil combustion performance.
- the inorganic base material is alumina, titania, zirconia, silica, or silica-alumina.
- an oxidation catalyst characterized by using a material that is one or more inorganic oxides selected from above and has an activation energy for light oil combustion performance of 72 kJ / mol or less.
- the mixing ratio of the inorganic oxide having an activation energy of light oil combustion performance to the inorganic base material exceeding 72 kJ / mol is 15% by weight or less.
- An oxidation catalyst is provided.
- an oxidation catalyst characterized in that, in the first or second invention, the inorganic oxide comprises two or more kinds having different bulk densities.
- the noble metal component is platinum (Pt) and / or palladium (Pd).
- the oxidation catalyst according to the first aspect is characterized in that the kind of alumina is one or more selected from ⁇ -alumina, ⁇ -alumina, and ⁇ -alumina. Is provided.
- the oxidation catalyst according to the first aspect wherein the inorganic oxide further contains a rare earth oxide.
- the oxidation catalyst according to the sixth aspect wherein the rare earth oxide is lanthanum oxide.
- the oxidation catalyst according to the first aspect wherein the content of silica in the alumina is 1 to 20% by weight.
- the oxidation catalyst is coated on the monolithic support as one or more catalyst layers. Is provided.
- the oxidation catalyst according to the tenth aspect wherein the coating amount of the catalyst layer is 50 to 300 g / L.
- the oxidation catalyst according to the tenth or eleventh aspect wherein the total supported amount of noble metal is 0.5 to 4.0 g / L in terms of metal. Is done.
- the oxidation catalyst according to any one of the first to twelfth aspects of the present invention includes a diesel particulate filter (DPF) or a noble metal component in the exhaust gas path of the diesel engine.
- DPF diesel particulate filter
- CSF catalytic combustion filter
- the exhaust gas purification device of the thirteenth aspect is used, and intermittently from a nozzle installed in an exhaust pipe installed upstream of the combustion filter (DPF or CSF).
- An exhaust gas purification method characterized in that diesel particulates are combusted and removed by spraying light oil or spraying light oil to the combustion chamber of the internal combustion engine after the combustion stroke.
- the oxidation catalyst of the present invention is a combustion of light oil sprayed intermittently from a nozzle in order to raise the exhaust gas temperature when processing particulate components such as HC, CO, NOx and soot in exhaust gas discharged from a diesel engine. Excellent performance. Furthermore, according to the present invention, since the superiority or inferiority of light oil combustibility as an oxidation catalyst can be easily determined based on the superiority or inferiority of the activation energy required for the light oil combustion performance of the inorganic base material itself, a large-capacity catalyst is produced. In addition, it is not necessary to evaluate with a diesel engine having a large displacement, and the time required for catalyst search can be greatly reduced with low equipment and low cost.
- FIG. 1 is an explanatory diagram showing the degree of change in temperature rise and DTA in a simple light oil combustibility test when alumina powder A is used as the material of the oxidation catalyst (DOC) of the present invention.
- FIG. 2 is an explanatory diagram showing a Kissinger plot for calculating the activation energy of light combustion of the alumina powder A based on the data obtained from FIG.
- FIG. 3 is a graph showing activation energies of light oil combustibility of alumina powders A to G, which are catalyst materials.
- FIG. 4 is a graph showing the BET specific surface areas of alumina powders A to G, which are catalyst materials.
- FIG. 5 is a graph showing average pore diameters of alumina powders A to G, which are catalyst materials.
- FIG. 1 is an explanatory diagram showing the degree of change in temperature rise and DTA in a simple light oil combustibility test when alumina powder A is used as the material of the oxidation catalyst (DOC) of the present invention.
- FIG. 2 is
- FIG. 6 is a graph showing the pore volumes of alumina powders A to G that are catalyst materials.
- FIG. 7 is a graph showing a change in the exhaust gas temperature at the catalyst outlet before and after the diesel oil (displacement 2L) exhaust gas purification apparatus is assembled with the diesel oil combustion oxidation catalyst (DOC) and sprayed with diesel oil.
- FIG. 8 is a graph showing changes in the exhaust gas temperature at the catalyst outlet before and after the diesel oil (displacement amount 5 L) exhaust gas purification apparatus is assembled with the diesel oil combustion oxidation catalyst (DOC) and sprayed with diesel oil.
- FIG. 9 is a graph showing changes in the exhaust gas temperature at the catalyst outlet before and after the diesel oil (displacement 3L) exhaust gas purification apparatus is assembled with the diesel oil combustion oxidation catalyst (DOC) and sprayed with diesel oil.
- the oxidation catalyst and the exhaust gas purifying apparatus of the present invention are applied to diesel automobiles will be mainly described in detail, but the present invention is also effective for diesel engines used for various stationary power sources such as generators. Needless to say.
- the oxidation catalyst (DOC) of the present invention is an oxidation catalyst in which a noble metal component that oxidizes unburned fuel such as NO, HC, CO, and light oil in exhaust gas is supported on a specific inorganic base material.
- a noble metal component that oxidizes unburned fuel such as NO, HC, CO, and light oil in exhaust gas
- Inorganic oxidation containing at least a platinum component excellent in oxidation activity, selected from alumina, titania, zirconia, silica, or silica-alumina as an inorganic base material, and having an activation energy for light oil combustion performance of 72 kJ / mol or less Use things.
- a diesel particulate filter (DPF) or a catalytic combustion filter containing a noble metal component In order for (CSF) to stably collect and remove particulate components such as soot over a long period of time, the oxidation catalyst in the preceding stage exhibits excellent light oil combustion performance at low temperatures. It is much more important than oxidation of HC, etc.
- a platinum component is generally used as a noble metal component, and a palladium component may also be used.
- a palladium component may also be used.
- Pd has such problems, the price is considerably lower than that of Pt, and depending on the HC species and the atmosphere of the exhaust gas, it may show higher oxidation activity than Pt.
- the ratio of Pt and Pd is preferably 1: 1 to 11: 2, more preferably 3: 2 to 11: 2.
- the ratio is less than 1: 1, the decrease in the heat generation capacity of exhaust gas due to the oxidation activity of HC, CO, NO, etc. and the combustion of unburned light oil, etc. accompanying the decrease in the platinum content increases. There is a risk that the merit in price will be lost as the platinum content increases.
- the oxidation catalyst can obtain sufficient low-temperature activity with respect to light oil combustion performance.
- the oxidation catalyst has an oxidation function of oxidizing and removing CO and HC in exhaust gas and oxidizing NO to NO 2 at a lower temperature. It has been demanded.
- the catalyst of the present invention is excellent in low-temperature oxidation reactions such as CO, HC and NO, but further promotes its function, and as a promoter component, ceria, ceria-zirconia, various zeolites, neodymium, lanthanum oxide, etc. Rare earth oxides, zirconia and the like can be used.
- Ceria, ceria-zirconia, etc. contribute to the promotion of oxidation reactions at low temperatures such as CO, HC, NO such as platinum and palladium by receiving supply of oxygen, and various zeolites occlude HC at low temperatures and at high temperatures. It contributes to the purification reaction of HC at a low temperature by releasing and supporting the oxidation reaction by platinum or palladium.
- rare earth oxides such as neodymium and lanthanum oxide and zirconia are considered to be fine particles that are supported around platinum and palladium, thereby preventing platinum and palladium from moving and aggregating on the base material due to heat. .
- ceria, ceria-zirconia and the like are preferably 70% by weight or less, more preferably 50% by weight or less of the weight of the inorganic oxide forming the base material supporting the noble metal.
- various zeolites are preferably 100% by weight or less, more preferably 70% by weight or less of the weight of the inorganic oxide.
- rare earth oxides such as neodymium and lanthanum oxide and zirconia are preferably 500% by weight or less, more preferably 300% by weight or less of the content of noble metals such as platinum.
- cocatalysts have too low a content of ceria and the like, the heat resistance of the catalyst is lowered, and if the content of various zeolites is too high, the pressure loss increases with a decrease in the opening ratio in the cell, and rare earth oxides and the like If the content of is too large, the activity is reduced as the pores of the base material are blocked, and the performance of the oxidation catalyst is lowered.
- the noble metal component and the promoter component are supported on an inorganic oxide (inorganic base material), mixed with other catalyst components as necessary, and coated on a monolithic support as a catalyst composition.
- an inorganic oxide as the inorganic base material supporting the noble metal component as described above, a catalyst material known in the field of exhaust gas purification catalysts can be used.
- Such an inorganic oxide is preferably a porous inorganic oxide that has high heat resistance and has a large BET specific surface area value so that the noble metal component can be stably highly dispersed.
- the activation energy (Ea) in the light oil combustion performance of the inorganic oxide itself is 72 kJ / mol or less.
- the activation energy in the light oil combustion performance of the inorganic oxide itself is calculated from the Kissinger plot shown below.
- Ea is calculated from the slope ( ⁇ Ea / R) obtained from the plot with ln ( ⁇ / T 2 ) at the point (T) where the change rate of the DTA curve is maximum on the vertical axis and 1 / T on the horizontal axis. .
- the plot at the point where the rate of change is maximum is called a Kissinger plot.
- the heating rate ( ⁇ ) 5 to 30 K / min) with a TG-DTA measuring device.
- ⁇ 5 to 30 K / min
- ln ( ⁇ / T 2 ) and 1 / T are plotted (Kissinger plot) at the apex ⁇ the point (T) at which the change rate is the maximum (T) ⁇ of the obtained temperature rise curve (see FIG. 2), and the slope thereof
- the activation energy (Ea) is obtained from The activation energy (Ea) is obtained in the same manner for other samples, and these results are compared later.
- the activation energy for the light oil combustion performance of the inorganic oxide itself must be 72 kJ / mol or less, more preferably 71 kJ / mol or less, and particularly preferably 70 kJ / mol or less.
- the activation energy of the light oil combustion performance of the inorganic oxide itself exceeds 72 kJ / mol, as will be described later, the light oil combustion performance at low temperatures as an oxidation catalyst supporting a noble metal using the inorganic oxide as a base material is lowered. Therefore, it is not preferable.
- the inorganic oxide examples include alumina, titania, zirconia, silica, and silica-alumina. These may be used alone or in combination of two or more inorganic oxides.
- alumina as an inorganic oxide (inorganic base material) for supporting a noble metal or a promoter is described below, but the same applies to other inorganic oxides.
- examples of the alumina material include ⁇ -alumina, ⁇ -alumina, and ⁇ -alumina having a large BET specific surface area value. Note that there is no clear correlation between the alumina type ( ⁇ -, ⁇ -, or ⁇ -) listed here and the light oil combustion performance.
- the main point of the present invention is to determine the superiority or inferiority of light oil combustion performance at low temperature as an oxidation catalyst supporting a noble metal with the inorganic oxide as a base material, only the activation energy of the light oxide combustion performance of the inorganic oxide itself. It is to get.
- lanthanum and other rare earth oxides silica, zirconia and the like to these aluminas.
- alumina added with lanthanum is known to have excellent heat resistance and maintain high catalytic activity even at high temperatures when a noble metal component such as a platinum component or a palladium component is supported (see Japanese Patent Application Laid-Open No. 2004-2004). -290827). Therefore, when the sprayed light oil burns, the spray of the light oil becomes non-uniform due to an abnormality such as a sprayer, and even if a part of the oxidation catalyst is exposed to an abnormally high temperature, the crystal structure of alumina is maintained. It is desirable to add rare earth oxides such as lanthanum, silica, zirconia, etc., which enhance the durability of alumina, to alumina.
- the content of rare earth oxides such as lanthanum, silica, and zirconia in alumina is preferably 1 to 20% by weight, more preferably 2 to 15% by weight.
- the content of rare earth oxides such as lanthanum, silica, zirconia, etc. is less than 1% by weight, the effect of these additives on the durability performance of alumina is too small, and conversely the content is 20% by weight. If exceeded, these additives will adversely affect the physical properties of alumina (BET specific surface area, pore diameter, pore volume, etc.), and the interaction between these additives and noble metals will become too strong, and at low temperatures of light oil. May adversely affect the combustion performance of the battery.
- titania includes anatase type, rutile type, brookite type, etc., but it is preferable to use anatase type titania having a high BET specific surface area capable of highly dispersing noble metals.
- Anatase-type titania turns to rutile-type titania when heated to 900 ° C or higher
- brookite-type titania turns to rutile-type titania when heated to 650 ° C or higher.
- use condition of the catalyst is 800 ° C. or less
- use of a rutile type having a low BET specific surface area or a brookite type having a risk of thermal phase transition is not preferable.
- zirconia has a monoclinic crystal structure at room temperature, and phase transitions to tetragonal and cubic crystals as the temperature is raised. This phase transition is accompanied by a volume change, and the sintered body of zirconia may be destroyed by repeatedly raising and lowering the temperature. Therefore, when zirconia is dissolved in a rare earth oxide such as calcium oxide, magnesium oxide, or yttrium oxide, oxygen vacancies are formed in the structure, cubic and tetragonal crystals are stabilized at room temperature, and destruction due to elevated temperature is prevented. It is suppressed. Such oxides are called stabilized zirconia or partially stabilized zirconia, and their use is preferred in the present invention.
- a rare earth oxide such as calcium oxide, magnesium oxide, or yttrium oxide
- Silica is classified into amorphous, glassy or colloidal in addition to crystalline silica having various different phase transformations, and is generally known to have a higher BET specific surface area than alumina. High dispersion can be expected. Furthermore, silica-alumina is crystalline and non-crystalline, and Si / Al ratios are various. Silica-alumina having an appropriate Si / Al ratio can be selected according to the application. it can. Various types of crystalline zeolites are known depending on the pore structure, but ZSM and ⁇ types are frequently used as denitration catalysts.
- the denitration catalyst include a titania surface coated with silica.
- inorganic oxides and their composite inorganic oxides are not particularly limited depending on the composition, structure and production method.
- starting materials having the above-described elements in the form of nitrates, sulfates, carbonates, acetates, chlorides, etc. are dissolved in an aqueous solution and then mixed and precipitated as precipitates by pH adjustment or evaporated to dryness.
- the solid material obtained by solidifying may be fired, or when mixing or complexing, the plurality of metal salts may be solubilized at once and the above treatment may be performed. After forming the oxide by performing the above treatment on one or more metal salts, the remaining metal salts may be supported at once or sequentially.
- the activation energy in the light oil combustion performance of the inorganic oxide itself is 72 kJ / mol or less. If the noble metal component and the promoter component can be sufficiently dispersed, inorganic oxidation is possible. It is not limited by the BET specific surface area, pore diameter, pore volume, etc. of the product. However, in the oxidation catalyst of the present invention, the low-temperature activity of the light oil combustion performance is most important, and it is desirable that the oxidation performance of NO, CO, HC, etc. is excellent, so the BET specific surface area of the inorganic oxide, It is preferable that the pore diameter and the pore volume are within a range in which the noble metal component and the promoter component can be sufficiently dispersed.
- Alumina preferably has a BET specific surface area value (according to the BET method, the same shall apply hereinafter) of 50 to 300 m 2 / g, more preferably 80 to 250 m 2 / g.
- BET specific surface area value of alumina is larger than 300 m 2 / g, the pore diameter becomes relatively small, and there is a concern about deterioration of gas diffusion and pore clogging.
- the BET specific surface area is smaller than 50 m 2 / g, there is a concern that the dispersibility of the noble metal or the promoter may be deteriorated.
- the pore diameter of the alumina is preferably 10 to 60 nm, more preferably 12 to 50 nm, and further preferably 15 to 40 nm. If the pore diameter of alumina is smaller than 10 nm, the diffusion of gas in the pores becomes slow, and the pores may be blocked by soot or the like. On the other hand, if the pore diameter is larger than 60 nm, the BET specific surface area becomes relatively small, and the dispersibility of noble metals, promoters and the like deteriorates.
- the pore volume of the alumina is preferably 0.3 ⁇ 2.0cm 3 / g, further more preferably those which are 0.5 ⁇ 1.5cm 3 / g.
- the pore volume of alumina is larger than 2.0 cm 3 / g, the pore diameter becomes relatively small, and there is a concern about deterioration of gas diffusion and pore clogging.
- the pore volume is smaller than 0.3 cm 3 / g, there is a concern that the dispersibility of the noble metal and the promoter may be deteriorated.
- At least one inorganic oxide having an activation energy (Ea) of 72 kJ / mol or less in light oil combustion performance is selected and used.
- the activation energy (Ea) of all inorganic oxides is desirably 72 kJ / mol or less.
- platinum starting salts are ethanolamine solution of platinum hydroxide (IV) acid, platinum nitrate, dinitrodiamine platinum nitrate, tetraammineplatinum (II) nitrate, etc.
- Components other than noble metals can be easily treated by heat treatment during catalyst preparation. Those which volatilize in the water are preferred.
- chloride is used as a starting salt, chlorine may remain depending on the production method, which may adversely affect catalyst activity.
- drying and baking can be appropriately performed by a known method.
- the starting salt may be supported separately, but in the present invention, the synergistic effect of platinum and palladium is expected, and in order to bring platinum and palladium as close as possible, the properties of the starting salt aqueous solution of each of platinum and palladium It is preferable to combine (acidic and alkaline).
- platinum nitrate-palladium nitrate (Acidic) combinations of dinitrodiamineplatinum nitrate-palladium nitrate (same as left), platinum chloride (IV) acid-palladium chloride (same as left), and the like.
- a carrier having an integral structure that is, a honeycomb structure (hereinafter also referred to as a honeycomb carrier) is used in order to carry a noble metal component and a promoter component with good dispersibility.
- the honeycomb structure is a honeycomb-shaped structure in which a large number of through holes are concentrated. Examples of the material of such a honeycomb structure include stainless steel, silica, alumina, silicon carbide, cordierite, and the like, and any structure of the honeycomb structure can be used in the present invention.
- the overall shape of such a honeycomb carrier includes a cylindrical shape, a quadrangular prism shape, a hexagonal prism shape, and the like, and can be appropriately selected depending on the structure of the exhaust system to be applied. Furthermore, the number of holes in the opening is determined in consideration of the type of exhaust gas to be processed, gas flow rate, pressure loss, removal efficiency, and the like.
- the exhaust gas purification application for diesel automobiles is preferably about 50 to 900 per 1 inch 2 (6.45 cm 2 ), more preferably 100 to 600. If 1inch 2 (6.45cm 2) Cell density per 50 or more, it is possible to secure a contact area of the exhaust gas and the catalyst, purification function of sufficient exhaust gas is obtained, 1inch 2 (6.
- the thickness of the cell wall of the honeycomb carrier is preferably 2 to 15 mil (milli inch) (0.05 to 0.4 mm), more preferably 3 to 12 mil (0.076 to 0.3 mm).
- the amount of the noble metal component supported is preferably 0.5 to 4.0 g / L in terms of metal per volume of the monolithic structure type carrier, More preferably, it is 3.0 g / L. If the amount of the precious metal component is too small, the oxidation removal performance of HC and CO, the oxidation performance of NO, and the combustibility of unburned fuel such as light oil cannot be obtained sufficiently. There is a risk that the benefits of.
- the coating amount of the oxidation catalyst (DOC) catalyst layer is preferably 50 to 300 g / L, more preferably 70 to 250 g / L.
- the coating amount of the catalyst layer is less than 50 g / L, the dispersibility of the noble metal such as platinum that is supported deteriorates, and the oxidation activity decreases. If it exceeds 300 g / L, the inside of the cell becomes narrow. Since pressure loss increases, it is not preferable.
- a wash coat method is generally used to prepare an oxidation catalyst (DOC) from a honeycomb carrier and a catalyst material.
- DOC oxidation catalyst
- a catalyst material containing an inorganic oxide having a specific activation energy (Ea) and a honeycomb carrier are prepared.
- the catalyst material is mixed with water or a solvent obtained by adding a water-soluble organic solvent to water as necessary to make a slurry mixture, and then applied to the honeycomb carrier and then dried. It is manufactured by firing. That is, a slurry mixture is obtained by mixing the catalyst material and water or a solvent obtained by adding a water-soluble organic solvent (aqueous medium) to water at a predetermined ratio.
- the aqueous medium may be used in such an amount that each catalyst component can be uniformly dispersed in the slurry.
- the catalyst material contains a noble metal component containing at least platinum as an inorganic base material.
- the noble metal component can also be supported on an inorganic base material in advance.
- the metal catalyst component and the inorganic base material are mixed in an aqueous medium to prepare a slurry.
- a known method can be used as appropriate, and an example thereof is as follows.
- compounds such as nitrates, carbonates, acetates and chlorides, specifically, ethanolamine solutions of platinum hydroxide (IV) acid, tetraammineplatinum (II) acetate, tetraammineplatinum (II) Carbonate, tetraammineplatinum (II) nitrate, nitric acid solution of platinum hydroxide (IV) acid, platinum nitrate, dinitrodiamineplatinum nitrate, chloroplatinum (IV) acid, etc.
- platinum hydroxide (IV) acid tetraammineplatinum (II) acetate
- tetraammineplatinum (II) Carbonate tetraammineplatinum (II) nitrate
- nitric acid solution of platinum hydroxide (IV) acid platinum nitrate, dinitrodiamineplatinum nitrate, chloroplatinum (IV) acid, etc.
- tetraamminepalladium (II) acetic acid Prepare a salt, tetraamminepalladium (II) carbonate, tetraamminepalladium (II) nitrate, dinitrodiammine palladium, palladium nitrate, palladium chloride, and the like.
- a solution of the noble metal component raw material is prepared by selecting from these and dissolving in water or an organic solvent.
- this noble metal component raw material solution is mixed with an inorganic base material together with an aqueous medium, dried at 50 to 200 ° C. to remove the solvent, and then fired at 300 to 1,200 ° C.
- a known catalyst material may be blended as a binder or the like.
- known catalyst materials include alumina, silica, titania, zirconia, silica-alumina, ceria, alkali metal materials, alkaline earth metal materials, transition metal materials, rare earth metal materials, and the like.
- An agent and a pH adjuster can be used in combination.
- the viscosity is preferably 100 to 10,000 mPa ⁇ s.
- the viscosity of the slurry is 100 mPa ⁇ s or less, the catalyst material settles quickly in the slurry, and it becomes difficult to apply a predetermined amount to the honeycomb carrier at one time. It may be a problem in terms.
- the viscosity exceeds 10,000 mPa ⁇ s, the slurry may be clogged in the cells of the honeycomb carrier to cause clogging, and the catalyst material may be easily peeled off from the honeycomb after application.
- a preferred viscosity is 500 to 2000 mPa ⁇ s.
- Factors that are likely to affect the properties of the slurry include the bulk density of the inorganic oxide. If the bulk density is too large or too small, the properties of the slurry are deteriorated, and as a result, the slurry becomes an oxidation catalyst after coating. May cause various problems such as clogging, peeling, unevenness of the catalyst layer in the cell, and an increase in the number of coatings.
- the bulk density of the inorganic oxide is very important to set to an appropriate specification.
- alumina will be taken up and described, but the same applies to other inorganic oxides.
- the bulk density is preferably 0.25 to 0.40 g / cm 3 .
- the bulk density is larger than 0.40 g / cm 3 , the sedimentation property in the slurry is fast and the water is separated from the water.
- the bulk density is less than 0.25 g / cm 3 , the water absorption is high. Therefore, in order to obtain a normal slurry, the ratio of the solid content has to be greatly reduced, and the honeycomb carrier can be obtained by a single application. It becomes difficult to apply a fixed amount, and it is applied many times, which is problematic in terms of cost.
- an inorganic oxide having an activation energy of its own light oil combustion performance found in the present invention of 72 kJ / mol or less can be slurried if the bulk density is within the above range.
- both inorganic oxides having different bulk densities have an activation energy of light oil combustion performance of 72 kJ / mol or less.
- the mixing ratio is 15% by weight or less. It is preferably 10% by weight or less, more preferably 5% by weight or less.
- the catalyst composition is applied and coated on the honeycomb carrier as a slurry mixture.
- drying and firing are performed.
- the drying temperature is preferably from 100 to 300 ° C, more preferably from 100 to 200 ° C.
- the firing temperature is preferably 300 to 600 ° C., particularly preferably 400 to 600 ° C.
- the drying time is preferably 0.5 to 2 hours, and the firing time is preferably 1 to 3 hours.
- a heating means it can carry out by well-known heating means, such as an electric furnace and a gas furnace.
- the catalyst composition may be coated as a single layer on the honeycomb carrier, or may be configured to have two or more layers.
- the coating amount of the catalyst layer is preferably 50 to 300 g / L.
- the total amount of noble metal supported is preferably 0.5 to 4.0 g / L in terms of metal.
- the loading ratio of the noble metal is changed between the upper layer and the lower layer, and the upper layer carries 50% by weight or more of the total noble metal amount, more preferably 60% by weight or more of the total noble metal amount is supported on the upper layer.
- the coating amount of the catalyst layer is also preferably changed by changing the coating ratio between the upper layer and the lower layer so that the upper layer is less than 50% by weight, more preferably less than 40% by weight. By doing so, the sprayed gas oil fine particles are easily brought into contact with the noble metal, and a combustion reaction is likely to occur.
- the upper layer may be covered only on the upstream side of the exhaust gas.
- the range covering the upper layer is preferably 75% or less on the upstream side of the honeycomb carrier, more preferably 50% or less, and further preferably 25% or less.
- the range in which the noble metal is supported is preferably 75% or less on the upstream side of the honeycomb carrier, more preferably 50% or less, and further preferably 25% or less. Within this range, the sprayed light oil fine particles are likely to come into contact with the precious metal, and a combustion reaction is likely to occur. As described above, various layers can be used as the oxidation catalyst.
- the layer is composed of one layer, two upper and lower layers, or two upper and lower layers, a simple two-layer or upper layer Whether the precious metal loading area is biased to the upstream side or the precious metal loading area is biased to the upstream side, the exhaust gas regulation values, the type and quality of fuel such as light oil used, and diesel engines These factors are determined in consideration of various factors such as the engine displacement, the location of the oxidation catalyst, the cost allowed for the exhaust gas purification system, and the like.
- the oxidation catalyst (DOC) is accommodated in a diesel engine exhaust gas path together with a diesel particulate filter (DPF) or a catalytic combustion filter (CSF) containing a noble metal component.
- DPF diesel particulate filter
- CSF catalytic combustion filter
- a diesel particulate filter (DPF) collects particulate (diesel particulate) components such as soot in exhaust gas discharged from a diesel engine.
- a catalyzed combustion filter (CSF) It is a combustion filter in which a noble metal component is supported on a DPF and catalyzed.
- the nozzle which sprays light oil intermittently can be installed in the exhaust pipe before DPF or CSF.
- the exhaust gas purification method of the present invention uses the above device to intermittently spray light oil from a nozzle installed in the exhaust pipe before the oxidation catalyst, or add light oil to the combustion chamber of the internal combustion engine after the combustion stroke. It is a method of spraying.
- the light oil is burned on the oxidation catalyst by the light oil spray to generate high-temperature exhaust gas, and at least a part of the particulate component deposited on the combustion filter (DPF or CSF) is forced by the high-temperature exhaust gas. Burned away.
- alumina used for an oxidation catalyst (DOC) in a present Example and a comparative example shows the activation energy of the light oil combustion performance, a BET specific surface area, a pore diameter, a pore volume, and a bulk density below, respectively. Measured by method.
- ⁇ Activation energy for light oil combustion performance After weighing 10 g of various alumina powders, they are fired in an electric furnace at 700 ° C. for 20 hours. After cooling, it is taken out from the electric furnace, 10 mg is taken therefrom, and 1 mg of commercially available light oil is added to the heat-treated alumina powder. After that, it is packed in the sample tube of the TG-DTA measuring device, the temperature increase rate ( ⁇ ) is changed to 5 levels at 5, 10, 15, 20, and 30 K / min, and the Rigaku Thermo Plas TG-8120 is used. Then, DTA measurement was performed. Based on this DTA curve, ln ( ⁇ / T 2 ) at the point of maximum DTA change rate (T) is plotted on the vertical axis and 1 / T is plotted on the horizontal axis (Kissinger plot). Asked.
- the obtained light oil combustible oxidation catalyst (1) is fired in an electric furnace at 650 ° C.
- Example 2 ⁇ Manufacture of light oil combustible oxidation catalyst (2)> BET specific shows the ⁇ - alumina powder B in FIGS. 3-6 surface area 110m 2 / g, average pore diameter 30 nm, pore volume 1.00 cm 3 / g, a bulk density of 0.20 g / cm 3, light oil combustion activation energy
- Example 2 except that the honeycomb flow-through cordierite carrier was replaced with a 300 cell / inch 2 (465 k / m 2 ), 8 mil (0.2 mm) thickness, 190.5 mm diameter ⁇ 76.2 mm length, 2.172 L product.
- the obtained light oil combustible oxidation catalyst (3) is calcined in an electric furnace at 600 ° C.
- Example 3 ⁇ Manufacture of light oil combustion oxidation catalyst (4)> BET specific surface area shows the ⁇ - alumina powder B in FIG. 3 ⁇ 6 166m 2 / g, average pore diameter 20 nm, pore volume 0.82 cm 3 / g, bulk density 0.19 g / cm 3, light oil combustion activation energy
- Example 4 ⁇ Manufacture of light oil combustion oxidation catalyst (5)> BET specific surface area shows the ⁇ - alumina powder B in FIG. 3 ⁇ 6 114m 2 / g, average pore diameter 25 nm, pore volume 0.90cm 3 / g, bulk density 0.23 g / cm 3, light oil combustion activation energy
- the honeycomb flow-through cordierite support was replaced with 65.6 kJ / mol ⁇ -alumina powder E (containing 10 wt% SiO 2 ) and 300 cell / inch 2 (465 k / m 2 ) / 8 mil (0.2 mm), 190.
- an integral carrier that is, a honeycomb flow-through cordierite carrier ⁇ 400 cell / inch 2 (620 k / m 2 ) / 6 mil (0.15 mm), 143.8 mm diameter ⁇ 118 mm length, 1. 917L ⁇ was dipped and applied by a wash coat method so that the supported amount of Pt—Pd supported alumina per unit volume was 112 g / L. Then, it was dried at 150 ° C. for 1 hour, and calcined at 500 ° C.
- Example 1 in which two types of alumina having an activation energy of light oil combustion performance of 72 KJ / mol or less as an inorganic base material was combined ⁇ Alumina A (69.2 KJ / mol) + Alumina B (69.5 KJ / mol) ⁇ , Example 2 ⁇ Alumina A (69.2 KJ / mol) + Alumina C (62.3 KJ / mol) ⁇ , and Example 3 ⁇ Alumina A (69.2 KJ / mol) ) + Alumina D (69.7 KJ / mol) ⁇ is a comparative example 1 ⁇ Alumina A (69.
- FIG. 8 table 2 and various physical properties (FIG. 3) of the alumina powders A to G used as the inorganic base material of the oxidation catalyst, the following can be understood.
- Table 2 and FIG. 3 even when the exhaust gas temperature at the catalyst inlet is further lowered by 20 ° C., alumina having an activation energy for light oil combustion performance of 72 KJ / mol or less is used as an inorganic base material.
- Example 4 ⁇ Alumina A (69.2 KJ / mol) + Alumina E (65.6 KJ / mol) ⁇ in combination with Example 2 was also used in Example 2 ⁇ Alumina A (69.2 KJ / mol) + Alumina C (62.3 KJ / mol). ) ⁇ Exhibited the same level of diesel oil combustion performance.
- FIGS. 7 to 9 and Tables 1 to 3 showing the quality of light oil combustion performance and FIGS. 4 to 6 showing various physical properties (BET specific surface area, pore diameter, pore volume) of alumina the following is clear. is there.
- various physical properties (BET specific surface area, pore diameter) generally said to be closely related to the quality of the activity.
- Pore volume) and the quality of light oil combustion performance are not correlated with each other in terms of their size and quality of light oil combustion performance.
- the activation energy of the light oil combustion performance is 72 KJ / mol or less as an inorganic base material.
- ⁇ -type used for Alumina A, D, F, G
- ⁇ -type used for Alumina B, C, E
- La 2 O 3 content: 4% by weight, used for alumina B, C, D, F
- SiO 2 content: 10% by weight, used for alumina E
- a material having a small bulk density such as alumina B to E
- a material having a small bulk density such as alumina B to E
- the viscosity of the slurry is improved to 600 to 1,400 mPa ⁇ S, and the specification suitable for the application of the catalyst can be achieved. From these results, the quality of diesel oil combustion performance of the oxidation catalyst when spraying light oil using an actual diesel engine is only the magnitude of the activation energy of the diesel oil combustion performance of alumina itself used as the inorganic base material of the oxidation catalyst.
- the oxidation catalyst and exhaust gas purifying apparatus of the present invention can be used for, for example, diesel vehicles, mobile applications such as ships, stationary applications such as generators, etc., and is particularly useful for diesel vehicles.
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Abstract
Description
2NO + C → N2 + CO2
しかし、従来の酸化触媒では排気ガス温度が低い場合には、前記酸化触媒が活性化しておらず、軽油の酸化及び燃焼が生じないため、そのまま排気され、フィルターの再生が行われない。このため、酸化触媒の上流側に電気ヒーター等による加熱手段を設けて、酸化触媒に供給される排気ガス温度を高めることが提案されている(特許文献5~特許文献9参照)。
そこで、上記加熱手段を用いず、低い排気ガス温度領域においても、十分に軽油の酸化および燃焼性能を発揮する手段として、本出願人は、白金をγ-Al2O3/La2O3混合担体に担持させてなる触媒を提案し(特許文献10参照)、続いて、白金担持γ-Al2O3/La2O3混合担体にパラジウムを担持し、セリウムイオン交換β型ゼオライトを含有する触媒を提案した(特許文献11参照)。
また、本発明者らは、無機酸化物が上記条件を満たしていながら、嵩密度の関係でスラリーにした際、粘度異常や沈降異常が生じる場合には、上記条件を満たしつつ、スラリーの性状異常を緩和する嵩密度の異なる別の無機酸化物を加えると、さらに軽油燃焼性能を向上できることも確認している。
また、本発明の第3の発明によれば、第1又は2の発明において、無機酸化物が、嵩密度の異なる二種類以上からなることを特徴とする酸化触媒が提供される。
また、本発明の第4の発明によれば、第1の発明において、貴金属成分が、白金(Pt)及び/又はパラジウム(Pd)であることを特徴とする酸化触媒が提供される。
また、本発明の第5の発明によれば、第1の発明において、アルミナの種類が、γ-アルミナ、δ-アルミナ、θ-アルミナから選ばれる1種以上からなることを特徴とする酸化触媒が提供される。
また、本発明の第6の発明によれば、第1の発明において、無機酸化物が、さらに希土類酸化物を含有することを特徴とする酸化触媒が提供される。
また、本発明の第7の発明によれば、第6の発明において、希土類酸化物が酸化ランタンであることを特徴とする酸化触媒が提供される。
また、本発明の第8の発明によれば、第6又は7の発明において、無機酸化物中の希土類酸化物の含有量が、1~20重量%であることを特徴とする酸化触媒が提供される。
また、本発明の第9の発明によれば、第1の発明において、アルミナ中のシリカの含有量が、1~20重量%であることを特徴とする酸化触媒が提供される。
また、本発明の第10の発明によれば、第1~9のいずれかの発明において、前記酸化触媒が、一体構造型担体に一層以上の触媒層として被覆されることを特徴とする酸化触媒が提供される。
また、本発明の第12の発明によれば、第10又は11の発明において、貴金属の総担持量が金属換算で0.5~4.0g/Lであることを特徴とする酸化触媒が提供される。
さらに、本発明によれば、無機母材自体の軽油燃焼性能に要する活性化エネルギーの優劣を基に、酸化触媒としての軽油燃焼性の優劣も容易に判定できる為、大容量の触媒を製造することも、大排気量のディーゼルエンジンで評価することも必要がなくなり、低設備・低コストで、触媒探索に要する時間も大幅に低減できる。
本発明の酸化触媒(DOC)は、排気ガス中のNO、HC、CO、及び軽油等の未燃の燃料を酸化する貴金属成分を特定の無機母材に担持した酸化触媒であり、貴金属成分として、少なくとも酸化活性に優れた白金成分を含有し、無機母材として、アルミナ、チタニア、ジルコニア、シリカ、又はシリカ-アルミナから選ばれ、かつ軽油燃焼性能の活性化エネルギーが72kJ/mol以下の無機酸化物を使用する。
酸化触媒では、前記のとおり、貴金属成分として一般に白金成分が使用され、パラジウム成分も使用されることがある。但し、Pd成分のみでは充分なNO酸化活性を得ることは難しく、また、ディーゼルエンジンの燃料である軽油や重油中の硫黄成分により被毒し易く、長期間の使用で失活してしまうことがある。
Pdはこの様な問題点はあるものの、価格がPtに比べかなり安価なこと、HC種や排気ガスの雰囲気によっては、Ptより高い酸化活性を示す場合があるため、PtとPdの担持比率を適切に配分することにより、性能面、価格面で最適な条件を見出すことができる。
本発明により、酸化触媒は軽油燃焼性能に関して、十分な低温活性が得られるが、その他に、より低温において、排気ガス中のCO、HCを酸化除去し、NOをNO2に酸化する酸化機能が求められている。
本発明の触媒は、CO、HC、NOなどの低温酸化反応にも優れているが、さらにその機能を促進するため、助触媒成分として、セリア、セリア-ジルコニア、各種ゼオライト、ネオジム、酸化ランタンなどの希土類酸化物、ジルコニアなどが使用できる。
これらの助触媒の含有量は、各々機能により異なり、セリア、セリア-ジルコニアなどは貴金属を担持する母材を形成する無機酸化物の重量の70重量%以下が好ましく、50重量%以下がより好ましい。また、各種ゼオライトは無機酸化物の重量の100重量%以下が好ましく、70重量%以下がより好ましい。その他、ネオジム、酸化ランタンなどの希土類酸化物及びジルコニアは白金などの貴金属含有量の500重量%以下が好ましく、300重量%以下がより好ましい。
これらの助触媒は、セリア等の含有量が多すぎると触媒の耐熱性が低下し、各種ゼオライトの含有量が多すぎるとセル内の開口率の減少に伴い圧損が上昇し、希土類酸化物等の含有量が多すぎると母材の細孔の閉塞に伴い活性低下を引き起こし、酸化触媒の性能が低下するため、好ましくない。
上記貴金属成分や助触媒成分は、無機酸化物(無機母材)に担持され、必要に応じ他の触媒成分と混合し、触媒組成物として一体構造型担体に被覆される。このように貴金属成分を担持する無機母材としての無機酸化物は、排気ガス浄化用触媒の分野で公知の触媒材料が使用できる。このような無機酸化物は、耐熱性が高く、そのBET比表面積値が大きいことで貴金属成分を安定に高分散できる多孔質の無機酸化物が好ましい。
無機酸化物自体の軽油燃焼性能における活性化エネルギーは、以下に示すKissingerプロットから算出される。
無機酸化物自体の軽油燃焼性能の活性化エネルギーは72kJ/mol以下でなければならず、71kJ/mol以下がより好ましく、70kJ/mol以下が特に好ましい。無機酸化物自体の軽油燃焼性能の活性化エネルギーが72kJ/molを超えると、後述するように、当該無機酸化物を母材として貴金属を担持した酸化触媒としての低温時の軽油燃焼性能が低下するので好ましくない。
一例として、貴金属や助触媒を担持するための無機酸化物(無機母材)としてアルミナの場合を以下に述べるが、他の無機酸化物も同様である。
例えば、アルミナの素材としては、BET比表面積値の大きなγ-アルミナ、δ-アルミナ、θ-アルミナなどが挙げられる。
なお、ここに挙げたアルミナのタイプ(γ-、δ-、又はθ-)と軽油燃焼性能との間に明確な相関性があるというわけではない。これは、後述するように、アルミナの諸物性(BET比表面積、平均細孔径、細孔容積)と軽油燃焼性能との間に明確な相関性がないことと同様である。本発明の主眼は、無機酸化物自体の軽油燃焼性能の活性化エネルギーの大小のみが、当該無機酸化物を母材として貴金属を担持した酸化触媒としての低温時の軽油燃焼性能の優劣を判定し得るということにある。
さらに、シリカ-アルミナは、結晶性のものと非結晶性のものがあり、Si/Al比も様々であり、用途に合わせて、適切なSi/Al比を有するシリカ-アルミナを選択することができる。結晶性のゼオライトには、細孔構造によって多種のタイプが知られているが、脱硝触媒ではZSMやβ型などが多用されている。
但し、本発明の酸化触媒においては、軽油燃焼性能の低温活性が最も重要であって、NO、CO、HC等の酸化性能にも優れていることが望ましいため、無機酸化物のBET比表面積、細孔径、細孔容積も貴金属成分や助触媒成分を十分に分散させることができる範囲内にあることが好ましい。
上記の無機母材に貴金属の白金とパラジウムを担持させるため、白金の出発塩として、水酸化白金(IV)酸のエタノールアミン溶液、テトラアンミン白金(II)酢酸塩、テトラアンミン白金(II)炭酸塩、テトラアンミン白金(II)硝酸塩、水酸化白金(IV)酸の硝酸溶液、硝酸白金、ジニトロジアミン白金硝酸、塩化白金(IV)酸などを用いることができる。
また、パラジウムの出発塩として、テトラアンミンパラジウム(II)酢酸塩、テトラアンミンパラジウム(II)炭酸塩、テトラアンミンパラジウム(II)硝酸塩、ジニトロジアンミンパラジウム、硝酸パラジウム、塩化パラジウムなどを用いることができる。白金の出発塩として好ましいのは、水酸化白金(IV)酸のエタノールアミン溶液、硝酸白金、ジニトロジアミン白金硝酸、テトラアンミン白金(II)硝酸塩などで、貴金属以外の成分が触媒調製時の熱処理により容易に揮発する物が好ましい。
なお、塩化物を出発塩とする場合、製法によっては塩素が残留して触媒活性に悪影響を及ぼす恐れがある。
これらの金属塩との水溶液と、無機母材とを混合した後は、適宜公知の方法により乾燥、焼成を行うことができる。
白金とパラジウムの出発塩水溶液の性質を同じにすることにより、両方の水溶液を混合させても沈殿を生じることなく、均一溶液のままで存在するので、無機母材に担持させた後も、白金粒子とパラジウム粒子は各々混合した状態で存在し、それぞれが近接し易い。
本発明において、酸化触媒(DOC)には、貴金属成分や助触媒成分を分散性よく担持するために一体型構造を有する担体、すなわちハニカム構造体(以下、ハニカム担体ともいう)が使用される。ハニカム構造体とは、多数の通孔が集中したハニカム形状の構造体である。このようなハニカム構造体の材質には、ステンレス、シリカ、アルミナ、炭化珪素、コーディエライトなどがあり、本発明には、いずれの材質のハニカム構造体も使用できる。
また、ハニカム担体のセル壁の厚みは、2~15mil(ミリインチ)(0.05~0.4mm)が好ましく、3~12mil(0.076~0.3mm)がより好ましい。
さらに、本発明では酸化触媒(DOC)の触媒層の被覆量が、50~300g/Lであることが好ましく、70~250g/Lであることがより好ましい。触媒層の被覆量が、50g/L未満であると、担持される白金等の貴金属の分散性が悪化することにより酸化活性が低下し、300g/Lを超えると、セル内が狭くなることで圧損が増大するので好ましくない。
本発明において、ハニカム担体と触媒材料から酸化触媒(DOC)を調製するには、一般にウォッシュコート法が用いられる。
まず、特定の活性化エネルギー(Ea)を有する無機酸化物を含む触媒材料、ハニカム担体を用意する。触媒材料は、必要に応じてバインダーや界面活性剤などの添加剤を水または水に水溶性有機溶媒を加えた溶媒と混合してスラリー状混合物にしてから、ハニカム担体へ塗工した後、乾燥、焼成する事により製造される。すなわち、触媒材料と水または水に水溶性有機溶媒(水系媒体)を加えた溶媒と所定の比率で混合してスラリー状混合物を得る。本発明においては、水系媒体は、スラリー中で各触媒成分が均一に分散できる量を用いれば良い。
触媒材料を調製するにあたり、貴金属を、予め無機母材に担持させておく場合、適宜公知の方法を採用できるが、その一例を示すと以下のとおりである。
まず、貴金属成分の原料として硝酸塩、炭酸塩、酢酸塩、塩化物などの化合物、具体的には水酸化白金(IV)酸のエタノールアミン溶液、テトラアンミン白金(II)酢酸塩、テトラアンミン白金(II)炭酸塩、テトラアンミン白金(II)硝酸塩、水酸化白金(IV)酸の硝酸溶液、硝酸白金、ジニトロジアミン白金硝酸、塩化白金(IV)酸などを、パラジウムの出発塩として、テトラアンミンパラジウム(II)酢酸塩、テトラアンミンパラジウム(II)炭酸塩、テトラアンミンパラジウム(II)硝酸塩、ジニトロジアンミンパラジウム、硝酸パラジウム、塩化パラジウムなどを用意する。これらから選択して水、有機溶媒に溶解して貴金属成分原料の溶液を用意する。
スラリーの性状に影響を及ぼし易い要因として、無機酸化物の嵩密度が挙げられ、嵩密度が大き過ぎても、小さ過ぎても、スラリーの性状を悪化させ、ひいてはスラリーを塗布後の酸化触媒にも目詰まり、剥離、セル内の触媒層の偏り、コート回数の増大等々様々な問題を生じかねない。
アルミナの場合、嵩密度は0.25~0.40g/cm3が好ましい。嵩密度が0.40g/cm3より大きいとスラリー中での沈降性が早く、水と分離してしまう。一方、嵩密度が0.25g/cm3より小さいと吸水性が高いので、正常なスラリーにするために、固形分の割合を大幅に下げざるを得ず、一回の塗布でハニカム担体に所定量を塗布することが困難になり、何度も塗布することになり、コスト面で問題がある。
具体的には、無機酸化物の嵩密度が上限を超えた場合は、嵩密度の小さな無機酸化物を混合し、無機酸化物の嵩密度が下限値より小さくなった場合は、嵩密度の大きな無機酸化物を混合して使用することにより混合後の嵩密度を適正にすることで、スラリーの性状を適正にすることが可能になる。その場合、嵩密度の異なる無機酸化物が両方共、軽油燃焼性能の活性化エネルギーが72kJ/mol以下であることが望ましい。しかし、嵩密度が異なる無機酸化物を選ぶ際、止むを得ず、軽油燃焼性能の活性化エネルギーが72kJ/molを超える無機酸化物を使用する場合は、その混合比率を15重量%以下とすることが好ましく、10重量%以下がより好ましく、5重量%以下が特に好ましい。
触媒組成物は、ハニカム担体上に一層として被覆してもよいし、二層以上になる構成としてもよい。
上下二層になる構成の場合は、上層、下層で貴金属の担持比率を変え、上層に総貴金属量の50重量%以上、より好ましくは、上層に総貴金属量の60重量%以上を担持することが好ましい。また、触媒層の被覆量についても、上層、下層で被覆比率を変え、上層を総被覆量の50重量%未満にすることが好ましく、40重量%未満にすることがより好ましい。そうすることで噴霧された軽油の微粒子が貴金属と接触し易くなり、燃焼反応が起こり易くなる。
その他、触媒組成物をハニカム担体上に一層、または二層以上に塗布した後、貴金属のみを排気ガスの上流側にのみ担持してもよい。その場合、貴金属を担持する範囲はハニカム担体の上流側の75%以下が好ましく、50%以下がより好ましく、25%以下がさらに好ましい。この範囲であれば噴霧された軽油の微粒子が貴金属と接触し易くなり、燃焼反応が起こり易くなる。
以上、酸化触媒として様々な層の構成が考えられるが、層の構成を一層にするか、上下二層にするか、また、上下二層にする場合も、単純な二層とするか、上層を被覆する範囲を上流側に偏らせるか、その他、貴金属の担持領域を上流側に偏らせるかは、その地域の排気ガスの規制値、使用される軽油等の燃料の種類と品質、ディーゼルエンジン等のエンジンの排気量、酸化触媒の設置位置、排気ガス浄化システムに許容されるコスト等々、様々な要因を加味して決められる。
本発明の排気ガス浄化装置は、前記酸化触媒(DOC)が、ディーゼルエンジンの排気ガス経路内に、ディーゼル微粒子捕集フィルター(DPF)、又は貴金属成分を含む触媒化燃焼フィルター(CSF)と共に収容され、前記燃焼フィルター(DPF又はCSF)よりも上流側に設置されている。
ディーゼル微粒子捕集フィルター(DPF)は、ディーゼルエンジンから排出される排気ガス中の煤(スート)などの微粒子(ディーゼルパティキュレート)成分を捕集するものであり、触媒化燃焼フィルター(CSF)は、DPFに貴金属成分を担持させ触媒化した燃焼フィルターである。また、間欠的に軽油を噴霧するノズルをDPF又はCSFよりも前の排気管に設置することができる。
本発明の排気ガス浄化方法は、前記装置を用いて、酸化触媒より前の排気管に設置されたノズルから間欠的に軽油が噴霧するか、又は燃焼行程後に内燃機関の燃焼室に軽油を追加噴霧する方法である。
この軽油噴霧により軽油が酸化触媒上で燃焼することで高温の排気ガスが生成し、その高温の排気ガスにより燃焼フィルター(DPF又はCSF)に堆積していた微粒子成分の少なくとも一部が強制的に燃焼除去される。
各種アルミナ粉末を10g計量した後、電気炉内で700℃、20時間、焼成する。冷却した後、電気炉から取り出し、そこから10mgを分取し、熱処理済みアルミナ粉末に市販の軽油を1mg添加する。その後、TG-DTA測定装置のサンプル管の中に詰め、昇温速度(φ)を5、10、15、20、30K/minに5水準に振って、Rigaku社製Thermo Plas TG-8120を使用してDTA測定を行った。このDTA曲線を基に、DTAの変化速度最大の点(T)におけるln(φ/T2)を縦軸に、1/Tを横軸にプロットし(Kissingerプロット)、その傾きから活性化エネルギーを求めた。
各種アルミナ粉末のBET比表面積は、Micromeritcs社製のTristar3000にて吸着分子としてN2を使用し、BET法により算出した。
<細孔分布(細孔径、細孔容積)測定>
各種アルミナ粉末の細孔径{モード径(直径)}及び細孔容積は、Micromeritcs社製のTristar3000にて吸着分子としてN2を使用し、BJH法により算出した。
<嵩密度>
各種アルミナ粉末の嵩密度は、日本粉体工業技術協会規格SAP 01-79に従い測定した。
<粘度>
各種スラリーの粘度は、TOKIMEC社製B型粘度計(Model BII DIGTAL VISCOMETER)にて測定した。
軽油燃焼性酸化触媒をコンバーターに格納後、ディーゼルエンジンの排気口にコンバーターを装着して、以下の要領で軽油噴霧試験を実施し、触媒のエンジン評価を行った。
下記実施例1~4、比較例1及び2の軽油燃焼性酸化触媒では、650℃、50時間(排気量2L ディーゼルエンジン用)の電気炉による熱処理を実施し、実施例2、4は600℃、50時間(排気量5L ディーゼルエンジン用)の電気炉による熱処理を実施し、また、実施例5及び比較例3では、650℃、50時間(排気量3L ディーゼルエンジン用)の電気炉による熱処理を実施した。
1-1.排気量2L ディーゼルエンジンでの軽油噴霧試験
ディーゼルエンジンの回転数を2,000rpmとし、触媒入口の手前に設置した熱電対で排気ガス温度を220℃に固定し、さらにその手前に設置した噴霧管から市販の軽油を10mL/分、3分間隔でON/OFF噴霧し、触媒出口の後ろに設置した熱電対で排気ガスの温度を計測した。軽油噴霧中の触媒出口の排気ガス温度の最高到達温度と軽油噴霧停止中の触媒出口の排気ガス温度の最低到達温度の差異を排気ガス温度の上昇分{下記のΔT(℃)}とし、ΔTが高いほど軽油がより燃焼して発熱していることを示しているので、燃焼性能に優れているとした。
ΔT(℃)=(軽油噴霧中の触媒出口の最高排気ガス温度)-(軽油噴霧停止中の触媒出口の最低排気ガス温度)
ディーゼルエンジンの回転数を2,000rpmとし、触媒入口の手前に設置した熱電対で排気ガス温度を200℃に固定した以外は、上記排気量2L ディーゼルエンジンでの軽油噴霧試験と同様に行った。
ディーゼルエンジンの回転数を1,500rpmとし、触媒入口の手前に設置した熱電対で排気ガス温度を210℃に固定し、軽油を20mL/分とした以外は、上記排気量2L ディーゼルエンジンでの軽油噴霧試験と同様に行った。
<軽油燃焼用酸化触媒(1)の製造>
=下層=
貴金属成分原料として硝酸白金水溶液と硝酸パラジウム水溶液とを、白金とパラジウムの割合が重量比で3:1となるように混合し、Pt-Pd混合溶液を得た。
次に、図3~6に示すBET比表面積125m2/g、平均細孔径20nm、細孔容積0.83cm3/g、嵩密度0.42g/cm3、軽油燃焼性活性化エネルギー69.2kJ/molのγ-アルミナ粉末A 1000gに、前記Pt-Pd混合溶液を貴金属換算で0.407重量%(Pt/Pd=3/1)になるよう含浸させた後、500℃、1時間電気炉にて焼成することで、Pt-Pd担持γ-アルミナ粉末aを得た。
同様に、BET比表面積195m2/g、平均細孔径18nm、細孔容積1.15cm3/g、嵩密度0.22g/cm3、軽油燃焼性活性化エネルギー69.5kJ/molのθ-アルミナ粉末B(4重量%La2O3含有)1000gに、前記Pt-Pd混合溶液を貴金属換算で2.0重量%(Pt/Pd=3/1)になるよう含浸させた後、500℃、1時間電気炉にて焼成することで、Pt-Pd担持θ-アルミナ粉末bを得た。
このPt-Pd担持γ-アルミナ粉末a 920.75g、Pt-Pd担持θ-アルミナ粉末b 186.75g、及び水をボールミルに投入し、所定の粒度になるまでミリングしてスラリーαを得た。このスラリーの粘度を測定し、表1にまとめた。
続いて、このスラリーαに一体型担体、すなわち、ハニカムフロースルー型コージェライト担体{300cell/inch2(465k/m2)、8mil(0.2mm)厚み、143.8mm径×76.2mm長さ、1.238L}を浸漬させ、単位体積あたりのPt-Pd担持アルミナの担持量が110.75g/Lとなるようにウォッシュコート法で塗布した。その後、150℃で1時間乾燥させ、大気雰囲気下、500℃で2時間焼成して軽油燃焼性酸化触媒(1)の下地層を得た。
=上層=
γ-アルミナ粉末A 1000gに、前記Pt-Pd混合溶液を貴金属換算で0.826重量%(Pt/Pd=3/1)になるように含浸させた後、500℃、1時間電気炉にて焼成することで、Pt-Pd担持γ-アルミナ粉末cを得た。同様に、θ-アルミナ粉末B 1000gに、前記Pt-Pd混合溶液を貴金属換算で4.0重量%(Pt/Pd=3/1)になるように含浸させた後、500℃、1時間電気炉にて焼成することで、Pt-Pd担持θ-アルミナ粉末dを得た。
このPt-Pd担持γ-アルミナ粉末c 756.25g、Pt-Pd担持θ-アルミナ粉末d 156.25g、及び水をボールミルに投入し、所定の粒度になるまでミリングしてスラリーβを得た。このスラリーの粘度を測定し、表1にまとめた。
続いて、このスラリーβに前記の下層塗布済み品を浸漬させ、単位体積あたりの触媒担持量が91.25g/Lとなるようにウォッシュコート法で塗布した。その後、150℃で1時間乾燥させ、大気雰囲気下、500℃で2時間焼成して軽油燃焼性酸化触媒(1)(Pt=1.5g/L、Pd=0.5g/L、触媒量:202g/L、アルミナA:アルミナB=83.3:16.7)を得た。
得られた軽油燃焼性酸化触媒(1)を電気炉内で650℃、50時間、空気雰囲気下で焼成し、その後、触媒をコンバーターに詰め、ディーゼルエンジン(排気量:2L)の排気口に接続して、軽油をパルス噴霧しながら、触媒出口の排気ガス温度の時間変化を計測し、表1、図7にまとめた。
<軽油燃焼性酸化触媒(2)の製造>
θ-アルミナ粉末Bを図3~6に示すBET比表面積110m2/g、平均細孔径30nm、細孔容積1.00cm3/g、嵩密度0.20g/cm3、軽油燃焼性活性化エネルギー62.3kJ/molのθ-アルミナ粉末C(4重量%La2O3含有)に置き換えた以外は実施例1と同様の方法で、軽油燃焼性酸化触媒(2)(Pt=1.5g/L、Pd=0.5g/L、触媒量:202g/L、アルミナA:アルミナC=83.3:16.7)を得た。また、下層及び上層用のスラリーの粘度を測定し、表1にまとめた。
得られた軽油燃焼性酸化触媒(2)を電気炉内で650℃、50時間、空気雰囲気下で焼成し、その後、触媒をコンバーターに詰め、2L ディーゼルエンジン(排気量:2L)の排気口に接続して、軽油をパルス噴霧しながら、触媒出口の排気ガス温度の時間変化を計測し、表1、図7にまとめた。
<軽油燃焼性酸化触媒(3)の製造>
ハニカムフロースルー型コージェライト担体を300cell/inch2(465k/m2)、8mil(0.2mm)厚み、190.5mm径×76.2mm長さ、2.172L品に置き換えた以外は実施例2と同様の方法で、軽油燃焼性酸化触媒(3)(Pt=1.5g/L、Pd=0.5g/L、触媒量:202g/L、アルミナA:アルミナC=83.3:16.7)を得た。
得られた軽油燃焼性酸化触媒(3)を電気炉内で600℃、50時間、空気雰囲気下で焼成し、その後、触媒をコンバーターに詰め、5L ディーゼルエンジン(排気量:5L)の排気口に接続して、軽油をパルス噴霧しながら、触媒出口の排気ガス温度の時間変化を計測し、表2、図8にまとめた。
<軽油燃焼性酸化触媒(4)の製造>
θ-アルミナ粉末Bを図3~6に示すBET比表面積166m2/g、平均細孔径20nm、細孔容積0.82cm3/g、嵩密度0.19g/cm3、軽油燃焼性活性化エネルギー69.7kJ/molのγ-アルミナ粉末D(4重量%La2O3含有)に置き換えた以外は実施例1と同様の方法で、軽油燃焼性酸化触媒(4)(Pt=1.5g/L、Pd=0.5g/L、触媒量:202g/L、アルミナA:アルミナD=83.3:16.7)を得た。また、下層及び上層用のスラリーの粘度を測定し、表1にまとめた。
得られた軽油燃焼性酸化触媒(4)を電気炉内で650℃、50時間、空気雰囲気下で焼成し、その後、触媒をコンバーターに詰め、2L ディーゼルエンジン(排気量:2L)の排気口に接続して、軽油をパルス噴霧しながら、触媒出口の排気ガス温度の時間変化を計測し、表1、図7にまとめた。
<軽油燃焼性酸化触媒(5)の製造>
θ-アルミナ粉末Bを図3~6に示すBET比表面積114m2/g、平均細孔径25nm、細孔容積0.90cm3/g、嵩密度0.23g/cm3、軽油燃焼性活性化エネルギー65.6kJ/molのθ-アルミナ粉末E(10重量%SiO2含有)に置き換え、ハニカムフロースルー型コージェライト担体を300cell/inch2(465k/m2)/8mil(0.2mm)、190.5mm径×76.2mm長さ、2.172L品に置き換えた以外は実施例1と同様の方法で、軽油燃焼性酸化触媒(5)(Pt=1.5g/L、Pd=0.5g/L、触媒量:202g/L、アルミナA:アルミナE=83.3:16.7)を得た。また、下層及び上層用のスラリーの粘度を測定し、表2にまとめた。
得られた軽油燃焼性酸化触媒(5)を電気炉内で600℃、50時間、空気雰囲気下で焼成し、その後、触媒をコンバーターに詰め、5L ディーゼルエンジン(排気量:5L)の排気口に接続して、軽油をパルス噴霧しながら、触媒出口の排気ガス温度の時間変化を計測し、表2、図8にまとめた。
<軽油燃焼性酸化触媒(6)の製造>
γ-アルミナ粉末A 1000gに、前記Pt-Pd混合溶液を貴金属換算で1.08重量%(Pt/Pd=3/1)になるよう含浸させた後、500℃、1時間電気炉にて焼成することで、Pt-Pd担持γ-アルミナ粉末eを得た。
同様に、θ-アルミナ粉末C(4重量%La2O3含有)1000gに、前記Pt-Pd混合溶液を貴金属換算で5.18重量%(Pt/Pd=3/1)になるよう含浸させた後、500℃、1時間電気炉にて焼成することで、Pt-Pd担持θ-アルミナ粉末fを得た。
このPt-Pd担持γ-アルミナ粉末e 927g、Pt-Pd担持θ-アルミナ粉末f 193g、及び水をボールミルに投入し、所定の粒度になるまでミリングしてスラリーγを得た。このスラリーの粘度を測定し、表1にまとめた。
続いて、このスラリーγに一体型担体、すなわち、ハニカムフロースルー型コージェライト担体{400cell/inch2(620k/m2)/6mil(0.15mm)、143.8mm径×118mm長さ、1.917L}を浸漬させ、単位体積あたりのPt-Pd担持アルミナの担持量が112g/Lとなるようにウォッシュコート法で塗布した。その後、150℃で1時間乾燥させ、大気雰囲気下、500℃で2時間焼成して軽油燃焼性酸化触媒(6)(Pt=1.5g/L、Pd=0.5g/L、触媒量:112g/L、アルミナA:アルミナC=91.7:18.3)を得た。
得られた軽油燃焼性酸化触媒(6)を電気炉内で650℃、50時間、空気雰囲気下で焼成し、その後、触媒をコンバーターに詰め、3L ディーゼルエンジン(排気量:3L)の排気口に接続して、軽油をパルス噴霧しながら、触媒出口の排気ガス温度の時間変化を計測し、表3、図9にまとめた。
<軽油燃焼性酸化触媒(7)の製造>
θ-アルミナ粉末Bを図3~6に示すBET比表面積179m2/g、平均細孔径15nm、細孔容積0.91cm3/g、嵩密度0.28g/cm3、軽油燃焼性活性化エネルギー73.3kJ/molのγ-アルミナ粉末F(4重量%La2O3含有)に置き換えた以外は実施例1と同様の方法で、軽油燃焼性酸化触媒(7)(Pt=1.5g/L、Pd=0.5g/L、触媒量:202g/L、アルミナA:アルミナF=83.3:16.7)を得た。また、下層及び上層用のスラリーの粘度を測定し、表1にまとめた。
得られた軽油燃焼性酸化触媒(7)を電気炉内で650℃、50時間、空気雰囲気下で焼成し、その後、触媒をコンバーターに詰め、2L ディーゼルエンジン(排気量:2L)の排気口に接続して、軽油をパルス噴霧しながら、触媒出口の排気ガス温度の時間変化を計測し、表1、図7にまとめた。
<軽油燃焼性酸化触媒(8)の製造>
θ-アルミナ粉末Bを図3~6に示すBET比表面積136m2/g、平均細孔径19nm、細孔容積0.89cm3/g、嵩密度0.21g/cm3、軽油燃焼性活性化エネルギー74.3kJ/molのγ-アルミナ粉末Gに置き換えた以外は実施例1と同様の方法で、軽油燃焼性酸化触媒(8)(Pt=1.5g/L、Pd=0.5g/L、触媒量:202g/L、アルミナA:アルミナG=83.3:16.7)を得た。また、下層及び上層用のスラリーの粘度を測定し、表1にまとめた。
得られた軽油燃焼性酸化触媒(8)を電気炉内で650℃、50時間、空気雰囲気下で焼成し、その後、触媒をコンバーターに詰め、2L ディーゼルエンジン(排気量:2L)の排気口に接続して、軽油をパルス噴霧しながら、触媒出口の排気ガス温度の時間変化を計測し、表1、図7にまとめた。
<軽油燃焼性酸化触媒(9)の製造>
θ-アルミナ粉末Cをγ-アルミナ粉末Gに置き換えた以外は実施例5と同様の方法で、軽油燃焼性酸化触媒(9)(Pt=1.5g/L、Pd=0.5g/L、触媒量:112g/L、アルミナA:アルミナG=91.7:18.3)を得た。また、スラリーの粘度を測定し、表3にまとめた。
得られた軽油燃焼性酸化触媒(9)を電気炉内で650℃、50時間、空気雰囲気下で焼成し、その後、触媒をコンバーターに詰め、3L ディーゼルエンジン(排気量:3L)の排気口に接続して、軽油をパルス噴霧しながら、触媒出口の排気ガス温度の時間変化を計測し、表3、図9にまとめた。
上記の結果、図7に示す650℃、50時間の熱処理後の実施例1~3、及び比較例1、2(いずれも触媒容量:1.238L)を用いた2Lディーゼルエンジンによる220℃での軽油燃焼性能の評価試験、および表1と図3に示した酸化触媒の無機母材として使用されたアルミナ粉末A~Gの軽油燃焼性能の活性化エネルギーから次のことがわかる。
同様に、600℃、50時間の熱処理後の実施例2及び4(いずれも触媒容量:2.172L)を用いた5Lディーゼルエンジンによる200℃での軽油燃焼性能の評価試験(図8)、表2と酸化触媒の無機母材として使用されたアルミナ粉末A~Gの諸物性(図3)から次のことがわかる。
図8、表2及び図3から明らかなように、触媒入口の排気ガス温度をさらに20℃下げた200℃においても無機母材として軽油燃焼性能の活性化エネルギーが72KJ/mol以下のアルミナを2種組み合わせた実施例4{アルミナA(69.2KJ/mol)+アルミナE(65.6KJ/mol)}も実施例2{アルミナA(69.2KJ/mol)+アルミナC(62.3KJ/mol)}と同レベルの軽油燃焼性能を発揮した。
例えば、650℃、50時間の熱処理後の実施例5及び比較例3(いずれも触媒容量:1.917L)を用いた3Lディーゼルエンジンによる210℃での軽油燃焼性能の評価結果(図9)と、表3及び図3から本発明の顕著な作用効果が明らかである。すなわち、無機母材として軽油燃焼性能の活性化エネルギーが72KJ/mol以下のアルミナを2種組み合わせた実施例5{アルミナA(69.2KJ/mol、91.7重量%)+アルミナC(62.3KJ/mol、18.3重量%)}は、軽油燃焼性能の活性化エネルギーが72KJ/molを超えるアルミナを無機母材として15重量%を超えて含有する比較例3{アルミナA(69.2KJ/mol、91.7重量%)+アルミナF(74.3KJ/mol、18.3重量%)}に比べ、優れた軽油燃焼性能を発揮している。
また、アルミナとしては、γ-タイプ(アルミナA、D、F、Gに使用)の他、θ-タイプ(アルミナB、C、Eに使用)なども使用可能であり、添加物も希土類に代表されるLa2O3(含有量:4重量%、アルミナB、C、D、Fに使用)やSiO2(含有量:10重量%、アルミナEに使用)なども20重量%以下であれば使用可能である。
しかし、この結果を見る限りは、噴霧された軽油の燃焼時、噴霧器等の異常により、軽油の噴霧が不均一になり、酸化触媒の一部が異常高温下に曝されてもアルミナの結晶構造を保持するためには、γ-アルミナより高温処理されたθ-アルミナやδ-アルミナの使用、アルミナの耐久性を高めるランタン、シリカ、ジルコニアなどのアルミナへの添加が非常に有用といえる。
また、スラリー化に際し、アルミナAの様に嵩密度が大きく、単独で使用すると粘度が計測できないほど粘度異常を起こす場合でも、アルミナB~Eの様に嵩密度の小さい物を添加することが好ましい。それは、表1~3から明らかであり、嵩密度の小さいアルミナを添加するとスラリーの粘度は600~1,400mPa・Sにまで改善され、触媒の塗布に適した仕様にすることが可能になる。
これらの結果から、実際のディーゼルエンジンを用いた軽油噴霧時における酸化触媒の軽油燃焼性能の良否は、酸化触媒の無機母材として使用されるアルミナ自体の軽油燃焼性能の活性化エネルギーの大小にのみ左右されることがわかる。
即ち、大容量のディーゼルエンジンを用い、大容量の酸化触媒を実際に製造し、軽油燃焼性能を評価しなくても、酸化触媒に使用する無機母材自体の軽油燃焼性能の活性化エネルギーを測定し、その値が72KJ/mol以下であれば、この無機酸化物を無機母材として90重量%以上使用することで、高性能の軽油燃焼用酸化触媒を得ることができる。
また、アルミナを単独で使用すると粘度異常・沈降異常を生じるスラリーとなる場合でも、嵩密度が異なる二種類以上のアルミナを使用することで、スラリーの性状が改善され、安定的な触媒の塗布が可能になっていることがわかる。
Claims (14)
- 無機母材に貴金属成分が担持されている排気ガス浄化用の酸化触媒において、無機母材は、アルミナ、チタニア、ジルコニア、シリカ、又はシリカ-アルミナから選ばれる1種以上の無機酸化物であり、かつ軽油燃焼性能の活性化エネルギーが72kJ/mol以下である材料を使用することを特徴とする酸化触媒。
- 無機母材が、軽油燃焼性能の活性化エネルギー72kJ/molを超える無機酸化物を15重量%以下含有することを特徴とする請求項1に記載の酸化触媒。
- 無機酸化物が、嵩密度の異なる二種類以上からなることを特徴とする請求項1又は2に記載の酸化触媒。
- 貴金属成分が、白金(Pt)及び/又はパラジウム(Pd)であることを特徴とする請求項1~3のいずれかに記載の酸化触媒。
- アルミナの種類が、γ-アルミナ、δ-アルミナ、又はθ-アルミナから選ばれる1種以上であることを特徴とする請求項1に記載の酸化触媒。
- 無機酸化物が、さらに希土類酸化物を含有することを特徴とする請求項1に記載の酸化触媒。
- 希土類酸化物が、酸化ランタンであることを特徴とする請求項6に記載の酸化触媒。
- 無機酸化物中の希土類酸化物の含有量が、1~20重量%であることを特徴とする請求項6または7に記載の酸化触媒。
- 無機酸化物中のシリカの含有量が、1~20重量%であることを特徴とする請求項1に記載の酸化触媒。
- 前記酸化触媒が、一体構造型担体に一層以上の触媒層として被覆されることを特徴とする請求項1~9のいずれかに記載の酸化触媒。
- 触媒層の被覆量が、50~300g/Lであることを特徴とする請求項10に記載の酸化触媒。
- 貴金属の総担持量が、金属換算で0.5~4.0g/Lであることを特徴とする請求項10又は11に記載の酸化触媒。
- 請求項1~12のいずれかに記載の酸化触媒が、ディーゼルエンジンの排気ガス経路内に、ディーゼル微粒子捕集フィルター(DPF)、又は貴金属成分を含む触媒化燃焼フィルター(CSF)と共に収容され、前記燃焼フィルター(DPF又はCSF)よりも上流側に設置されていることを特徴とする排気ガス浄化装置。
- 請求項13に記載の排気ガス浄化装置を用い、前記燃焼フィルター(DPF又はCSF)よりも上流側に設置された排気管に設置されたノズルから間欠的に軽油を噴霧するか、又は、燃焼行程後に内燃機関の燃焼室に軽油を追加噴霧することで、ディーゼル微粒子が燃焼除去されることを特徴とする排気ガス浄化方法。
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JP6378169B2 (ja) | 2018-08-22 |
US10030559B2 (en) | 2018-07-24 |
EP2974791A1 (en) | 2016-01-20 |
JPWO2014141903A1 (ja) | 2017-02-16 |
US20160003118A1 (en) | 2016-01-07 |
EP2974791A4 (en) | 2016-12-14 |
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