WO2011125960A1 - 排気浄化用触媒 - Google Patents

排気浄化用触媒 Download PDF

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Publication number
WO2011125960A1
WO2011125960A1 PCT/JP2011/058482 JP2011058482W WO2011125960A1 WO 2011125960 A1 WO2011125960 A1 WO 2011125960A1 JP 2011058482 W JP2011058482 W JP 2011058482W WO 2011125960 A1 WO2011125960 A1 WO 2011125960A1
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WIPO (PCT)
Prior art keywords
exhaust
adsorbent
oxidation catalyst
ceo
catalyst
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Application number
PCT/JP2011/058482
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English (en)
French (fr)
Inventor
林　孝太郎
諭 長尾
鈴木　秀明
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トヨタ自動車株式会社
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Application filed by トヨタ自動車株式会社 filed Critical トヨタ自動車株式会社
Priority to EP20110765860 priority Critical patent/EP2554255B1/en
Priority to US13/637,798 priority patent/US9138736B2/en
Publication of WO2011125960A1 publication Critical patent/WO2011125960A1/ja

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    • B01J37/0248—Coatings comprising impregnated particles
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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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    • B01D53/9445—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC]
    • B01D53/945—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC] characterised by a specific catalyst
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    • 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
    • B01D2255/2065—Cerium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/40—Nitrogen compounds
    • B01D2257/404—Nitrogen oxides other than dinitrogen oxide
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2258/00—Sources of waste gases
    • B01D2258/01—Engine exhaust gases
    • 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
    • B01J2229/00—Aspects of molecular sieve catalysts not covered by B01J29/00
    • B01J2229/10—After treatment, characterised by the effect to be obtained
    • B01J2229/18—After treatment, characterised by the effect to be obtained to introduce other elements into or onto the molecular sieve itself
    • B01J2229/186—After treatment, characterised by the effect to be obtained to introduce other elements into or onto the molecular sieve itself not in framework positions
    • 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
    • F01N2570/00—Exhaust treating apparatus eliminating, absorbing or adsorbing specific elements or compounds
    • F01N2570/10—Carbon or carbon oxides
    • 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 an exhaust purification catalyst, and more particularly to an exhaust purification catalyst capable of efficiently oxidizing CO at a low temperature by having a specific structure.
  • exhaust purification is an important environmental issue, and regulations have been strengthened from the viewpoint of preventing air pollution.
  • treatment using an exhaust purification catalyst is performed.
  • exhaust discharged from an engine is purified by a catalytic converter and released into the atmosphere.
  • the catalyst in the catalytic converter is in an inactive state, and the exhaust is not sufficiently purified.
  • catalysts that are generally used for exhaust purification are those in which noble metals such as Ag, Pt, and Pd are supported on a carrier, and these noble metals are expensive and have problems in terms of resources. It is necessary to reduce the amount used. For this reason, various studies have been made on catalysts.
  • an HC adsorbent made of zeolite in which at least one of Pd and Ag is ion-exchange-supported, and arranged on the exhaust downstream side of the HC adsorbent are selected from Fe, Cu, and Co.
  • an NO X adsorbent made of zeolite on which at least one kind is ion exchange-supported and an exhaust purification device made of a CO adsorbent arranged on the exhaust downstream side of the NO X adsorbent and carrying Pd on ceria.
  • C 3 H 6 as HC, NO 2 , CO, H 2 O and the balance of N 2 model gas are allowed to flow at room temperature (25 ° C.) for 20 seconds, and the adsorption rate is measured. An example in which is obtained is shown.
  • the CO purification rate when the gas is continuously circulated in the presence of oxygen in a short period of time is not known.
  • an object of the present invention is to provide an exhaust purification catalyst capable of efficiently purifying CO at a wide range of temperatures including low temperatures.
  • the present invention relates to a CO oxidation catalyst that is disposed in an exhaust flow path of an internal combustion engine and oxidizes and purifies CO in exhaust gas, and upstream of the CO oxidation catalyst in the exhaust flow direction.
  • the present invention relates to an exhaust emission control device for an internal combustion engine characterized by being in the range of 0.01 to 5.0 mass%.
  • “a wide range of temperatures including low temperatures” refers to temperatures in the range of 50 to 300 ° C.
  • CO can be efficiently purified means that a CO purification rate equal to or higher than that of a conventionally known CO oxidation catalyst can be exhibited.
  • an exhaust purification catalyst capable of efficiently purifying CO at a wide range of temperatures including low temperatures can be obtained.
  • FIG. 1 is a schematic view of an exhaust purification catalyst according to one embodiment of the present invention.
  • FIG. 2 is a schematic view of an exhaust purification catalyst outside the scope of the present invention.
  • FIG. 3 is a schematic view of another exhaust purification catalyst outside the scope of the present invention.
  • FIG. 4 is a graph showing the performance of the exhaust purification catalyst of one embodiment of the present invention.
  • FIG. 5 is a graph showing the performance of the exhaust purification catalyst outside the scope of the present invention.
  • FIG. 6 is a graph showing the influence of the exhaust composition of the CO oxidation catalyst used in the present invention on the CO purification performance.
  • FIG. 7 is a graph comparing NO X adsorption performance of various NO X adsorbents at a specific gas composition.
  • FIG. 8 is a graph comparing NO X adsorption performance of various NO X adsorbents at other gas compositions.
  • Pd and CeO 2 are provided as a CO oxidation catalyst that is disposed in an exhaust flow path of an internal combustion engine and oxidizes and purifies CO in the exhaust gas, and the amount of Pd supported is 0. 0 relative to CeO 2 .
  • a catalyst of 01 to 5.0 mass%, preferably 0.1 to 2.5 mass% adsorbs HC in the exhaust from upstream to the upstream side in the exhaust flow direction with respect to the CO oxidation catalyst.
  • a HC adsorbent for, it is necessary that an exhaust purification device that includes a NO X adsorbent and adsorbs NO X in the exhaust gas upstream of the CO oxidation catalyst at the downstream side, thereby, the actual It is possible to obtain sufficient CO purification performance by applying it to exhaust gas having an exhaust composition close to that of the above.
  • an exhaust gas purification apparatus 1 for an internal combustion engine has Pd and CeO 2 disposed in an exhaust passage 10 of an internal combustion engine to oxidize and purify CO in exhaust gas.
  • the CO oxidation catalyst 2 with a supported amount of 0.01 to 5.0% by mass with respect to CeO 2 , and the exhaust from the upstream to the upstream side of the exhaust gas flow direction 11 with respect to the CO oxidation catalyst 2 It includes an HC adsorbent 3 that adsorbs HC therein, and a NO X adsorbent 4 that adsorbs NO X in the exhaust.
  • the exhaust gas composition is a model gas composition of CO, O 2 and N 2.
  • curve 1 as shown in FIG. 1, a high CO purification rate is exhibited in a wide range of temperatures including a low temperature of less than 100 ° C., but the actual exhaust composition is CO, O 2 , N 2 , HC, H 2 O, N 2 .
  • the CO purification rate at 100 ° C. or lower is greatly reduced as shown by the curve: 2, whereas the coexistence system also includes a low temperature of less than 100 ° C. as shown by the curve 3. It is confirmed that a high CO purification rate can be exhibited at temperatures in the range.
  • the exhaust gas purification apparatus shown in FIG. 3 in which the positions of the HC adsorbent and the NO x adsorbent are changed even when the CO oxidation catalyst is used, the exhaust composition has CO, O 2 .
  • the CO purification rate at 100 ° C. or lower remains significantly low as shown by curve 4. 4 and 5 described above, the exhaust gas purification apparatus of the present invention uses the CO oxidation catalyst, the HC adsorbent on the upstream side in the exhaust flow direction with respect to the CO oxidation catalyst, and the CO oxidation. it upstream side of the catalyst it is necessary to place a NO X adsorbent on the downstream side of the HC adsorbing material is understood.
  • the CO oxidation catalyst used in the present invention is greatly affected by the CO purification rate depending on the gas composition, has the least influence of the CO + O 2 system of the curve 5, and the CO 2 coexistence system of the curve 6.
  • CO + O 2 + CO 2 C 3 H 6 coexistence system curve 7 (CO + O 2 + C 3 H 6), NO coexistence system of curve 8 (CO + O 2 + NO ), H 2 O coexistence system curve 9 (CO + O 2 + H 2 O) and the all component coexistence system (CO + O 2 + CO 2 + C 3 H 6 + NO + H 2 O) in curve 10 increases in order, and it is understood that the CO purification rate is reduced.
  • the NO X adsorbent used in the present invention is affected by the amount of NO X adsorbed at the low temperature of 50 ° C. depending on the type and gas composition of the substance constituting the adsorbent.
  • the CO 2 coexistence system decreases the NO X adsorption amount of 52 mg / L, the NO X adsorbent Ag / alumina rod 3 H 2 O, NO X adsorption amount of 94 mg / L in CO 2 coexistence system C 3 H 6 , NO x adsorption amount of 0 mg / L in H 2 O, CO 2 coexisting system Drops, in H 2 O, NO X adsorption amount of 15 mg / L in CO 2 coexistence system C 3 H 6, H 2 O , CO 2 coexistence system 106 mg / reduced the NO X adsorption amount of L, the NO X adsorbent Ag / beta zeolite rod 2 H 2 O, NO X adsorption amount of 132 mg / L with CO 2 coexistence system C 3 H 6, H 2 O , the CO 2 coexistence system decreases the NO X adsorption amount of 52 mg / L, the NO X adsorbent Ag / alumina rod 3 H 2
  • the CO oxidation catalyst used in the present invention has a Pd loading of 0.01 to 5.0% by mass of Pd / CeO 2 , particularly 0.1 to 2.5% by mass of Pd / CeO 2.
  • the salt can be obtained by carrying the salt on CeO 2 carrier particles and preferably heat-treating in an oxidizing atmosphere, particularly at a temperature in the range of 850 to 950 ° C.
  • the Pd salt is supported on the CeO 2 carrier particles by, for example, using CeO 2 carrier particles prepared by a method known per se and a Pd salt capable of giving Pd, for example, by impregnating and supporting Pd on the CeO 2 carrier particles. It can be supported.
  • CeO 2 carrier particles are obtained by separating a precipitate from a CeO 2 precursor, for example, an aqueous solution of Ce hydroxide or Ce salt hydrate that gives an oxide, and heat-treating it in a temperature range of 300 to 500 ° C. Can be obtained.
  • a precipitate for example, an aqueous solution of Ce hydroxide or Ce salt hydrate that gives an oxide
  • the oxidizing atmosphere include a gas atmosphere containing 1 to 25% of air or O 2
  • examples of the heat treatment time include a range of 2 to 100 hours.
  • Pd salt Pd chloride, nitrate, sulfate, sulfonate, phosphate, ammine complex (salt), preferably chloride, nitrate, ammine salt can be used.
  • the diameter is roughly in the order of (large) chloride>nitrate> ammine salt (small). Therefore, it is possible to select a salt suitable for the desired Pd particle size.
  • the Pd salt can be used as an aqueous solution, but the concentration of Pd in the aqueous Pd salt solution can be about 1 ⁇ 10 ⁇ 4 mol / L to 1 ⁇ 10 ⁇ 3 mol / L.
  • the heat-treated CeO 2 -supported Pd CO oxidation catalyst can be used by forming a CO oxidation catalyst layer by coating the substrate with a CeO 2 -supported Pd CO oxidation catalyst.
  • the CO oxidation catalyst layer is obtained by obtaining a slurry for coating from powdered CeO 2 -supported Pd and water, coating the slurry by introducing the slurry into a substrate, for example, a honeycomb substrate, and sucking the lower part, and drying. It can form in a catalyst base material by baking.
  • the coating amount of the CO oxidation catalyst layer can be performed by adjusting the viscosity, solid content, and slurry input amount of the slurry.
  • the coating amount of the CO oxidation catalyst layer is suitably 300 g / L or more.
  • the CO oxidation catalyst of the present invention can exhibit CO oxidation activity that oxidizes CO and converts it into harmless CO 2 at a wide range of temperatures from low to high.
  • NO X adsorbent in the present invention those having basicity such as ZrO 2 , ⁇ zeolite, spinel, MgAl 2 O 4 , Al 2 O 3 or those having both acidity and basicity, under low temperature conditions in which desorbs NO X at a high temperature to adsorb the NO X can be used.
  • ZrO 2 has the property of adsorbing NO X at a temperature of room temperature ⁇ 350 ° C., and desorbs NO X at a temperature of 350 °C ⁇ 400 °C.
  • at least one of La, K, and Ca may be added to the NO X adsorbent.
  • transitions such as alkali metal oxides, alkaline earth metal oxides, rare earth element oxides, Co 3 O 4 , NiO 2 , MnO 2 , Fe 2 O 3 , ZrO 2, etc. it can be a NO X adsorbent singly or plural kinds of metal oxide or the like.
  • the alumina, silica, silica - alumina, zirconia, titania, alkali metal on a porous oxide support such as zeolite also a material obtained by supporting a metal element selected from alkaline earth metals and rare earth elements and NO X adsorbent it can.
  • porous oxide if the alkali metal or alkaline earth metal or rare earth element and is supported by ion exchange with NO X adsorbent, the temperature of adsorbed NO X is released is low, medium temperature range from a low temperature repeating the adsorption and release of even the exhaust temperature NO X in becomes possible. Also, those obtained by adding an alkali metal or alkaline earth metal to ZrO 2, show excellent NO X adsorbing capacity. Furthermore, when noble metals such as Ag, Pt, Rh, and Pd or transition metal oxides such as Co 3 O 4 , NiO 2 , MnO 2 , and Fe 2 O 3 are supported on these, the NO X adsorption ability is further improved. .
  • the oxidation activity is expressed by noble metals, Co 3 O 4 , NiO 2 , MnO 2 , Fe 2 O 3, etc., and the NO X adsorption amount increases as NO in the exhaust is oxidized to NO 2. It is considered.
  • Said zeolite has pores comparable to the size of the molecule, contains cations to neutralize the negative charge of the main component Al 2 O 3 , alkali metals, alkaline earth metals and rare earth elements It is possible to carry at least one metal element selected from the above by ion exchange, and the metal element carried by ion exchange is very highly dispersed on the zeolite and thus has very high activity, and oxidation of NO in a low temperature range. It is thought that activity improves.
  • zeolite such as ⁇ zeolite, ferrierite, ZSM-5, mordenite, Y-type zeolite and the like can be used.
  • the NO X adsorbent is preferably a Mn—Zr—O NO X adsorbent or Ag / ⁇ zeolite.
  • HC adsorbent in the present invention any one of mordenite, ZSM-5, Y-type zeolite, ferrierite or ⁇ -zeolite can be mentioned.
  • the HC adsorbent may carry a noble metal, for example, at least one of Ag, Pt, Rh, or Pd.
  • the exhaust purification catalyst of the present invention can efficiently purify CO at a wide range of temperatures including low temperatures by having the above-described configuration. However, as long as the effect is not reduced, a member having any other function that can be applied to the exhaust gas purification catalyst of the internal combustion engine can be added. For example, particulate matter in the exhaust gas can be added to an arbitrary position. A particulate filter (DPF) to collect may be added.
  • the exhaust purification catalyst of the present invention can be applied to all internal combustion engines that can generate CO when operating at low temperatures, including automobile engines.
  • Model gas evaluation apparatus Measurement conditions Model gas composition (vol%) 1) CO: 800 ppm, O 2 : 10%, N 2 : balance 2) CO: 800 ppm, O 2 : 10%, HC (C 3 H 6 ): 400 ppm, NO: 100 ppm, H 2 O: 3%, CO 2 : 10%, N 2 : remainder gas flow rate: 10 mL / min
  • CO oxidation catalyst Pd was supported by an impregnation supporting method using Pd (NO 3 ) 2 on CeO 2 (manufactured by Rhodia, specific surface area of 157 m 2 / g). The amount of Pd supported was 0.4 mass% Pd / CeO 2 . This was calcined at 600 ° C. in air for 3 hours, and further heat-treated at 10 ° C. in H 2 O / 900 ° C. for 25 hours to obtain a CO oxidation catalyst.
  • Example 1 The above-mentioned CO oxidation catalyst, HC adsorbent and NO X adsorbent were mounted on the above-described CO purification rate measuring apparatus so as to have the configuration shown in FIG. 1 to produce an exhaust purification catalyst.
  • the temperature is increased at a constant rate (temperature increase rate: 20 ° C./min) to a temperature of 50 to 350 ° C. or higher by the above model gas composition 2), and the CO purification rate at each temperature ( %).
  • the obtained results are shown together with other results in the curve 3 of FIG.
  • Comparative Example 1 The above-described CO oxidation catalyst was mounted on the above-described CO purification rate measuring apparatus so as to have the configuration shown in FIG. 2 to produce an exhaust purification catalyst.
  • the above-mentioned model gas composition 1) was increased in temperature at a constant rate (temperature increase rate: 20 ° C./min) to a temperature of 50 to 350 ° C. or higher, and the CO purification rate ( %).
  • the obtained results are shown together with other results in the curve 1 of FIGS.
  • the above-mentioned model gas composition 2) is heated at a constant rate (temperature increase rate: 20 ° C./min) to a temperature of 50 to 350 ° C. or higher to purify CO at each temperature. The rate (%) was measured.
  • the obtained results are shown together with other results in the curve 2 of FIGS.
  • Comparative Example 2 The above-mentioned CO oxidation catalyst, HC adsorbent and NO X adsorbent were mounted on the above-described CO purification rate measuring apparatus so as to have the configuration shown in FIG. 3 to produce an exhaust purification catalyst. Using this exhaust purification catalyst, the temperature is increased at a constant rate (temperature increase rate: 20 ° C./min) to a temperature of 50 to 350 ° C. or higher by the above model gas composition 2), and the CO purification rate at each temperature ( %). The obtained results are shown together with other results in the curve 4 of FIG.
  • Reference example 1 The above-described CO oxidation catalyst was mounted on the above-described CO purification rate measuring apparatus so as to have the configuration shown in FIG. 2 to produce an exhaust purification catalyst.
  • this gas purification catalyst the following various model gas compositions were heated at a constant rate to a temperature of 50 to 350 ° C. or higher (temperature increase rate: 20 ° C./min), and the CO purification rate (% ) was measured.
  • Mn—Zr—O composition ratio: 1: 1: 2 (made by coprecipitation from Mn nitrate and Zn nitrate) Ag / ⁇ zeolite (Ag loading: 11% by mass) Ag / alumina (Ag loading: 11% by mass) Pt / alumina (Pt loading: 2% by mass) The measurement results are shown in FIGS.
  • CO can be efficiently purified over a wide range of temperatures including low temperatures, so that CO can be efficiently removed from the exhaust from the internal combustion engine.

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Abstract

課題　低温を含む広い範囲の温度でＣＯを効率的に浄化し得る排気浄化触媒を提供する。 解決手段　内燃機関の排気流路に配置されて排気中のＣＯを酸化して浄化するＣＯ酸化触媒と、該ＣＯ酸化触媒に対して排気の流れ方向の上流側に、上流から排気中のＨＣを吸着するＨＣ吸着材と、排気中のＮＯXを吸着するＮＯX吸着材とを備え、該ＣＯ酸化触媒がＰｄとＣｅＯ2とを有し、該Ｐｄの担持量がＣｅＯ2に対して０．０１～５．０質量％の範囲内であることを特徴とする内燃機関の排気浄化装置。

Description

排気浄化用触媒
　本発明は、排気浄化触媒に関し、さらに詳しくは特定の構造を有することにより低温でＣＯを効率的に酸化し得る排気浄化触媒に関する。
　近年、排気浄化は環境上の重要課題であり、大気汚染防止の観点から規制が強化されている。自動車等の内燃機関その他の燃焼機関から生じる排気中の有害成分を除去するために、排気浄化触媒を用いた処理が行われている。
　例えば、エンジンから排出される排気は触媒コンバーターにより浄化されて大気中に放出される。しかし、エンジン始動直後は低温のため、触媒コンバーター内の触媒が不活性状態であり、排気が十分浄化されない。
　一方、一般に排気浄化に用いられる触媒には担体上にＡｇ、ＰｔやＰｄなどの貴金属を担持したものが用いられており、これらの貴金属が高価であって資源的にも問題があることからその使用量を低減することが必要である。
　このため、触媒について種々の検討がされている。
　例えば、特開２００７−１６０１６８号公報にはＰｄ及びＡｇの少なくとも一方をイオン交換担持したゼオライトよりなるＨＣ吸着材と、該ＨＣ吸着材の排気下流側に配置され、Ｆｅ、Ｃｕ及びＣｏから選ばれる少なくとも一種をイオン交換担持したゼオライトよりなるＮＯＸ吸着材と、該ＮＯＸ吸着材の排気下流側に配置され、セリアにＰｄを担持してなるＣＯ吸着材よりなる排気浄化装置が記載されている。そして、具体例としてＨＣとしてのＣ３Ｈ６、ＮＯ２、ＣＯ、Ｈ２Ｏおよび残部がＮ２のモデルガスを室温（２５℃）で２０秒間流通させて吸着率を測定して高い吸着率が得られた例が示されている。しかし、酸素共存下で短時間ではなく連続的にガスを流通させた場合のＣＯ浄化率は不明である。
特開２００７−１６０１６８号公報
　このように、公知の特許文献に記載された排気浄化装置では、１００℃未満の温度を含む広い範囲の温度で良好なＣＯ浄化率は達成されておらず、低温でＣＯを効率的に浄化し得る排気浄化触媒が求められている。
　このため、本発明者等は、低温を含む広い範囲の温度でＣＯ酸化活性を示し得るＣＯ酸化触媒について特許出願（特願２０１０−００３２２１）を行った。しかし、この出願の発明の、ＣＯ酸化触媒がＰｄとＣｅＯ２とを有し、Ｐｄの担持量がＣｅＯ２に対して０．０１~５．０質量％の範囲内である内燃機関の排気浄化装置によっても、実際の組成に近い排気に適用するとＣＯ浄化性能が十分でないことが明らかになった。
　従って、本発明の目的は、低温を含む広い範囲の温度でＣＯを効率的に浄化し得る排気浄化触媒を提供することである。
　本発明は、内燃機関の排気流路に配置されて排気中のＣＯを酸化して浄化するＣＯ酸化触媒と、該ＣＯ酸化触媒に対して排気の流れ方向の上流側に、上流から排気中のＨＣを吸着するＨＣ吸着材と、排気中のＮＯＸを吸着するＮＯＸ吸着材とを備え、該ＣＯ酸化触媒がＰｄとＣｅＯ２とを有し、該Ｐｄの担持量がＣｅＯ２に対して０．０１~５．０質量％の範囲内であることを特徴とする内燃機関の排気浄化装置に関する。
　本明細書において、「低温を含む広い範囲の温度」とは、５０~３００℃の範囲の温度をいう。また、本発明において「ＣＯを効率的に浄化し得る」とは、従来公知のＣＯ酸化触媒に比べて同等以上のＣＯ浄化率を示し得ることをいう。
　本発明によれば、低温を含む広い範囲の温度でＣＯを効率的に浄化し得る排気浄化触媒を得ることができる。
図１は、本発明の１実施態様の排気浄化触媒の模式図である。 図２は、本発明の範囲外の排気浄化触媒の模式図である。 図３は、本発明の範囲外の他の排気浄化触媒の模式図である。 図４は、本発明の１実施態様の排気浄化触媒の性能を示すグラフである。 図５は、本発明の範囲外の排気浄化触媒の性能を示すグラフである。 図６は、本発明で用いるＣＯ酸化触媒の排気組成によるＣＯ浄化性能への影響を示すグラフである。 図７は、特定のガス組成における各種ＮＯＸ吸着材によるＮＯＸ吸着性能を比較したグラフである。 図８は、他のガス組成における各種ＮＯＸ吸着材によるＮＯＸ吸着性能を比較したグラフである。
　本願においては、内燃機関の排気流路に配置されて排気中のＣＯを酸化して浄化するＣＯ酸化触媒としてＰｄとＣｅＯ２とを有し、該Ｐｄの担持量がＣｅＯ２に対して０．０１~５．０質量％、好適には０．１~２．５質量％である触媒を用い、該ＣＯ酸化触媒に対して排気の流れ方向の上流側に、上流から排気中のＨＣを吸着するＨＣ吸着材と、その下流側で且つ前記ＣＯ酸化触媒の上流側に排気中のＮＯＸを吸着するＮＯＸ吸着材とを備えた排気浄化装置であることが必要であり、これによって、実際の排気組成に近い排気に適用して十分なＣＯ浄化性能を得ることが可能となる。
　以下、本願の発明について、図１~図８を参照して説明する。
　図１に示すように、本発明の内燃機関の排気浄化装置１は、内燃機関の排気流路１０に配置されて排気中のＣＯを酸化して浄化するＰｄとＣｅＯ２とを有し該Ｐｄの担持量がＣｅＯ２に対して０．０１~５．０質量％の範囲内であるＣＯ酸化触媒２と、該ＣＯ酸化触媒２に対して排気の流れ方向１１の上流側に、上流から排気中のＨＣを吸着するＨＣ吸着材３と、排気中のＮＯＸを吸着するＮＯＸ吸着材４とを備えている。
　本発明の実施態様の排気浄化装置によれば、図４に示すように、前記ＣＯ酸化触媒のみからなる図２に示す排気浄化装置では、排気組成がＣＯ、Ｏ２、Ｎ２のモデルガス組成では曲線：１に示すように１００℃未満の低温を含む広い範囲の温度で高いＣＯ浄化率を示すが、排気組成がＣＯ、Ｏ２、Ｎ２、ＨＣ、Ｈ２Ｏ、Ｎ２の実際の排気を模した共存系では曲線：２に示すように１００℃以下でのＣＯ浄化率が大幅に低下するのに対して、前記共存系でも曲線３に示すように１００℃未満の低温を含む広い範囲の温度で高いＣＯ浄化率を示し得ることが確認される。
　しかし、前記ＣＯ酸化触媒を用いてもＨＣ吸着材とＮＯＸ吸着材との位置を変えた図３に示す排気浄化装置によれば、図５に示すように、排気組成がＣＯ、Ｏ２、Ｎ２、ＨＣ、Ｈ２Ｏ、Ｎ２の実際の排気を模した共存系では曲線：４に示すように１００℃以下でのＣＯ浄化率が大幅に低いままである。
　以上の図４と図５とから、本発明の排気浄化装置においては前記ＣＯ酸化触媒を用いることと、このＣＯ酸化触媒に対して排気の流れ方向の上流側にＨＣ吸着材を、そしてＣＯ酸化触媒の上流側でＨＣ吸着材の下流側にＮＯＸ吸着材を配置することが必要であることが理解される。
　本発明において用いられる前記ＣＯ酸化触媒は、図６に示すように、ガスの組成によってＣＯ浄化率が大きく影響を受け、曲線５のＣＯ＋Ｏ２系の影響が最も少なく、曲線６のＣＯ２共存系（ＣＯ＋Ｏ２＋ＣＯ２）、曲線７のＣ３Ｈ６共存系（ＣＯ＋Ｏ２＋Ｃ３Ｈ６）、曲線８のＮＯ共存系（ＣＯ＋Ｏ２＋ＮＯ）、曲線９のＨ２Ｏ共存系（ＣＯ＋Ｏ２＋Ｈ２Ｏ）そして曲線１０の全成分共存系（ＣＯ＋Ｏ２＋ＣＯ２＋Ｃ３Ｈ６＋ＮＯ＋Ｈ２Ｏ）の順に影響が大きくなり、ＣＯ浄化率が低下していることが理解される。
　本発明において用いられるＮＯＸ吸着材は、図７および図８に示すように、５０℃の低温では、吸着材を構成する物質の種類とガス組成によってＮＯＸ吸着量が影響を受け、棒１のＭｎ−Ｚｒ−ＯのＮＯＸ吸着材ではＨ２Ｏ、ＣＯ２共存系で２３５ｍｇ／ＬのＮＯＸ吸着量であったものがＣ３Ｈ６、Ｈ２Ｏ、ＣＯ２共存系では１０６ｍｇ／ＬのＮＯＸ吸着量に低下し、棒２のＡｇ／βゼオライトのＮＯＸ吸着材ではＨ２Ｏ、ＣＯ２共存系で１３２ｍｇ／ＬのＮＯＸ吸着量がＣ３Ｈ６、Ｈ２Ｏ、ＣＯ２共存系では５２ｍｇ／ＬのＮＯＸ吸着量に低下し、棒３のＡｇ／アルミナのＮＯＸ吸着材ではＨ２Ｏ、ＣＯ２共存系で９４ｍｇ／ＬのＮＯＸ吸着量がＣ３Ｈ６、Ｈ２Ｏ、ＣＯ２共存系では０ｍｇ／ＬのＮＯＸ吸着量に低下し、棒４のＰｔ／アルミナのＮＯＸ吸着材ではＨ２Ｏ、ＣＯ２共存系で１５ｍｇ／ＬのＮＯＸ吸着量がＣ３Ｈ６、Ｈ２Ｏ、ＣＯ２共存系では０ｍｇ／ＬのＮＯＸ吸着量に低下していることが理解される。
　図７および図８から、本発明において用いられるＮＯＸ吸着材として、Ｍｎ−Ｚｒ−ＯのＮＯＸ吸着材又はＡｇ／βゼオライトのＮＯＸ吸着材が好適であることが理解される。
　本発明において用いられる前記ＣＯ酸化触媒は、Ｐｄ担持量が０．０１~５．０質量％Ｐｄ／ＣｅＯ２、特に０．１~２．５質量％Ｐｄ／ＣｅＯ２がとなる割合で、Ｐｄ塩をＣｅＯ２担体粒子に担持させ、好適には酸化性雰囲気で加熱処理、特に８５０~９５０℃の範囲の温度で加熱処理することによって得ることができる。
　前記のＰｄ塩のＣｅＯ２担体粒子への担持は、例えば、それ自体公知の方法によって作成したＣｅＯ２担体粒子とＰｄを与え得るＰｄ塩とから、例えば含浸担持法によってＣｅＯ２担体粒子にＰｄを担持し得る。
　また、ＣｅＯ２担体粒子は、ＣｅＯ２の前駆体、例えば酸化物を与えるＣｅ水酸化物又はＣｅ塩の水和物の水溶液から沈殿物を分離取得し、３００~５００℃の温度範囲で加熱処理することによって得ることができる。
　前記の酸化性雰囲気としては空気又はＯ２を１~２５％含むガス雰囲気が挙げられ、前記の加熱処理の時間としては例えば２~１００時間の範囲が挙げられる。
　前記のＰｄ塩としては、Ｐｄの塩化物、硝酸塩、硫酸塩、スルホン酸塩、リン酸塩、アンミン錯体（塩）、好適には塩化物、硝酸塩、アンミン塩を用い得るが、Ｐｄ粒子の粒子径はおおよそ（大）塩化物＞硝酸塩＞アンミン塩（小）の順となる。従って、求めるＰｄ粒子の粒径に対して適した塩を選択し得る。
　前記のＰｄ塩は水溶液にして用いられ得るが、Ｐｄ塩水溶液中のＰｄの濃度で１×１０−４ｍｏｌ／Ｌ~１×１０−３ｍｏｌ／Ｌ程度であり得る。
　前記の加熱処理したＣｅＯ２担持ＰｄのＣＯ酸化触媒は、基材にＣｅＯ２担持ＰｄのＣＯ酸化触媒をコートしてＣＯ酸化触媒層を形成して用いることができる。
　前記のＣＯ酸化触媒層は、粉末状のＣｅＯ２担持Ｐｄと水とからコート用スラリーを得て、スラリーを基材、例えばハニカム基材に投入し、下部を吸引することによってコートし、乾燥、焼成することによって触媒基材に形成し得る。前記のＣＯ酸化触媒層のコート量はスラリーの粘度や固形分量、スラリー投入量を調整することによって行い得る。ＣＯ酸化触媒層のコート量は３００ｇ／Ｌ以上が適当である。
　本発明のＣＯ酸化触媒は、低温~高温の広い範囲の温度でＣＯを酸化して無害なＣＯ２に転換するＣＯ酸化活性を示し得る。
　本発明における前記ＮＯＸ吸着材としては、ＺｒＯ２、βゼオライト、スピネル、ＭｇＡｌ２Ｏ４、Ａｌ２Ｏ３等の塩基性を持つもの又は酸性および塩基性の両性を持つもので、低温条件下でＮＯＸを吸着し高温条件下でＮＯＸを脱離するものが使用できる。例えばＺｒＯ２は、室温~３５０℃の温度条件下でＮＯＸを吸着し、３５０℃~４００℃の温度条件下でＮＯＸを脱離する特性をもつ。
　また、ＮＯＸ吸着材にＬａ、Ｋ、Ｃａの少なくとも一種を添加してもよい。
　また、ＮＯＸ吸着材としては、アルカリ金属の酸化物、アルカリ土類金属の酸化物、希土類元素の酸化物、Ｃｏ３Ｏ４、ＮｉＯ２、ＭｎＯ２、Ｆｅ２Ｏ３、ＺｒＯ２などの遷移金属酸化物などを単独であるいは複数種類組み合わせてＮＯＸ吸着材とすることができる。またアルミナ、シリカ、シリカ−アルミナ、ジルコニア、チタニア、ゼオライトなどの多孔質酸化物担体にアルカリ金属、アルカリ土類金属及び希土類元素から選ばれる金属元素を担持したものをＮＯＸ吸着材とすることもできる。
　特に、多孔質酸化物は、アルカリ金属やアルカリ土類金属あるいは希土類元素をイオン交換担持してＮＯＸ吸着材とすれば、吸着されたＮＯＸが放出される温度が低くなり、低温から中温域の排気温度であってもＮＯＸの吸着・放出の繰り返しが可能となる。また、ＺｒＯ２にアルカリ金属やアルカリ土類金属を添加したものも、優れたＮＯＸ吸着能を示す。
　さらに、これらに、Ａｇ、Ｐｔ、Ｒｈ、Ｐｄなどの貴金属、あるいはＣｏ３Ｏ４、ＮｉＯ２、ＭｎＯ２、Ｆｅ２Ｏ３などの遷移金属酸化物を担持すると、ＮＯＸ吸着能がさらに向上する。これは、貴金属やＣｏ３Ｏ４、ＮｉＯ２、ＭｎＯ２、Ｆｅ２Ｏ３などによって酸化活性が発現し、排気中のＮＯがＮＯ２に酸化されることによってＮＯＸ吸着量が増加するためと考えられている。
　前記のゼオライトは、分子の大きさに匹敵する細孔を有し、主成分であるＡｌ２Ｏ３の負電荷を中和するために陽イオンを含み、アルカリ金属、アルカリ土類金属及び希土類元素から選ばれる少なくとも１種の金属元素をイオン交換担持することができ、イオン交換担持された金属元素は、ゼオライト上にきわめて高分散に担持されているので活性がきわめて高く、低温域におけるＮＯの酸化活性が向上すると考えられる。
　前記ゼオライトとしては、βゼオライト、フェリエライト、ＺＳＭ−５、モルデナイト、Ｙ型ゼオライトなどのゼオライトなどを用いることができる。
　特に、本発明においては、ＮＯＸ吸着材として、Ｍｎ−Ｚｒ−ＯのＮＯＸ吸着材又はＡｇ／βゼオライトが好適である。
　また、本発明における記ＨＣ吸着材としては、モルデナイト、ＺＳＭ−５、Ｙ型ゼオライト、フェリエライト又はβゼオライトのいずれか１つを挙げることができる。
　前記ＨＣ吸着材は、貴金属、例えばＡｇ、Ｐｔ、Ｒｈ又はＰｄの少なくとも１つを担持したものであり得る。
　本発明の排気浄化触媒は、上記の構成を有することによって低温を含む広い範囲の温度でＣＯを効率的に浄化し得る。しかし、前記効果を低減しない限り、内燃機関の排気浄化触媒に適用し得る任意の他の機能を有する部材を加えることが可能であり、例えば任意の位置に排気中の排気中の粒子状物質を捕集する粒子フィルタ（ＤＰＦ）を加え得る。
　本発明の排気浄化触媒によれば、自動車のエンジンを含めて低温での運転時にＣＯを発生し得る全ての内燃機関に適用し得る。
　以下、本発明の実施例を示す。
　以下の実施例は単に説明するためのものであり、本発明を限定するものではない。
　以下の各例で、排気浄化触媒のＣＯ浄化率測定は以下に示す装置を測定した。
１．装置：モデルガス評価装置
２．測定条件
　モデルガス組成（ｖｏｌ％）
　１）ＣＯ：８００ｐｐｍ、Ｏ２：１０％、　Ｎ２：　残部
　２）ＣＯ：８００ｐｐｍ、Ｏ２：１０％、　ＨＣ（Ｃ３Ｈ６）：４００ｐｐｍ、ＮＯ：１００ｐｐｍ、Ｈ２Ｏ：３％、ＣＯ２：１０％、Ｎ２：残部
　ガス流量：１０ｍＬ／分
　以下の各例で用いた以下のＣＯ酸化触媒、ＨＣ吸着材およびＮＯＸ吸着材を用いた。
　１）ＣＯ酸化触媒
　ＣｅＯ２（ローディア製、比表面積１５７ｍ２／ｇ）に対し、Ｐｄ（ＮＯ３）２を用いて含浸担持法によりＰｄを担持した。Ｐｄ担持量は０．４質量％Ｐｄ／ＣｅＯ２であった。これを空気中６００℃で３時間焼成し、さらにこれを１０％Ｈ２Ｏ／空気中９００℃で２５時間加熱処理を行って、ＣＯ酸化触媒を得た。
　２）ＨＣ吸着材
　常法によりＡｇをフェリエライト（東ソー社製）に担持させた、Ａｇ／フェリエライト（Ａｇ担持量：１１質量％）を用いた。
　３）ＮＯＸ吸着材
　Ｍｎ−Ｚｒ−Ｏ（組成比：１：１：２）（硝酸Ｍｎと硝酸Ｚｎより共沈法で作成したもの）に常法によりＡｇをβゼオライト（東ソー社製）に担持させた、Ａｇ／βゼオライト（Ａｇ担持量：１１質量％）を用いた。
実施例１
　上記のＣＯ浄化率測定用装置に、図１に模式図を示す構成となるように上記のＣＯ酸化触媒、ＨＣ吸着材およびＮＯＸ吸着材を装着して、排気浄化触媒を作製した。
　この排気浄化触媒を用いて、上記のモデルガス組成２）によって、５０~３５０℃以上の温度まで一定速度で温度上昇（昇温速度：２０℃／分）させて、各温度におけるＣＯ浄化率（％）を測定した。
　得られた結果を他の結果とまとめて図４の曲線３に示す。
比較例１
　上記のＣＯ浄化率測定用装置に、図２に模式図を示す構成となるように上記のＣＯ酸化触媒を装着して、排気浄化触媒を作製した。
　この排気浄化触媒を用いて、上記のモデルガス組成１）について、５０~３５０℃以上の温度まで一定速度で温度上昇（昇温速度：２０℃／分）させて、各温度におけるＣＯ浄化率（％）を測定した。得られた結果を他の結果とまとめて図４および図５の曲線１に示す。
　また、この排気浄化触媒を用いて、上記のモデルガス組成２）について、５０~３５０℃以上の温度まで一定速度で温度上昇（昇温速度：２０℃／分）させて、各温度におけるＣＯ浄化率（％）を測定した。得られた結果を他の結果とまとめて図４および図５の曲線２に示す。
比較例２
　上記のＣＯ浄化率測定用装置に、図３に模式図を示す構成となるように上記のＣＯ酸化触媒、ＨＣ吸着材およびＮＯＸ吸着材を装着して、排気浄化触媒を作製した。
　この排気浄化触媒を用いて、上記のモデルガス組成２）によって、５０~３５０℃以上の温度まで一定速度で温度上昇（昇温速度：２０℃／分）させて、各温度におけるＣＯ浄化率（％）を測定した。
　得られた結果を他の結果とまとめて図５の曲線４に示す。
参考例１
　上記のＣＯ浄化率測定用装置に、図２に模式図を示す構成となるように上記のＣＯ酸化触媒を装着して、排気浄化触媒を作製した。
　この気浄化触媒を用いて、下記の各種モデルガス組成について、５０~３５０℃以上の温度まで一定速度で温度上昇（昇温速度：２０℃／分）させて、各温度におけるＣＯ浄化率（％）を測定した。
　モデルガス組成（ｖｏｌ％）
　５）ＣＯ：８００ｐｐｍ、Ｏ２：１０％
　６）ＣＯ：８００ｐｐｍ、Ｏ２：１０％、ＣＯ２：１０％
　７）ＣＯ：８００ｐｐｍ、Ｏ２：１０％、Ｃ３Ｈ６：４００ｐｐｍ
　８）ＣＯ：８００ｐｐｍ、Ｏ２：１０％、ＮＯ：１００ｐｐｍ
　９）ＣＯ：８００ｐｐｍ、Ｏ２：１０％、Ｈ２Ｏ：３％
　１０）ＣＯ：８００ｐｐｍ、Ｏ２：１０％、　ＣＯ２：１０％、Ｃ３Ｈ６：４００ｐｐｍ、ＮＯ：１００ｐｐｍ、Ｈ２Ｏ：３％
　ガス流量：１０ｌ／ｍｉｎ
　得られた結果を図６の曲線５~１０（各曲線番号は各ガス組成番号に対応している。）に示す。
参考例２
　下記の各ＮＯ吸着材を用いて、Ｈ２Ｏ、ＣＯ２共存系（組成比＝３：１０）、Ｃ３Ｈ６、Ｈ２Ｏ、ＣＯ２共存系（組成比＝４：３００：１０００）の２種類のモデルガス組成のガスを供給して、各々吸着温度５０℃におけるＮＯＸ吸着量（ｍｇ／１ｌ当り２００ｇコート）を測定した。
　Ｍｎ−Ｚｒ−Ｏ（組成比：１：１：２）（硝酸Ｍｎと硝酸Ｚｎとから共沈法により作成した。）
　Ａｇ／βゼオライト（Ａｇ担持量：１１質量％）
　Ａｇ／アルミナ（Ａｇ担持量：１１質量％）
　Ｐｔ／アルミナ（Ｐｔ担持量：２質量％）
　測定結果を図７および図８に示す。
　以上の図４および図７~８の結果から、本発明においては前記の図１に示すＣＯ酸化触媒とＨＣ吸着材とＮＯＸ吸着材との配置にすることが必要であり、前記の各構成とＮＯＸ吸着材としてのＭｎ−Ｚｒ−Ｏ又はＡｇ／βゼオライトとを組み合わせることが特に好適であることが明らかになった。
　本発明によれば、低温を含む広い範囲の温度でＣＯを効率的に浄化し得るので、内燃機関からの排気から効率よくＣＯを除去し得る。

Claims (5)

  1. 　内燃機関の排気流路に配置されて排気中のＣＯを酸化して浄化するＣＯ酸化触媒と、該ＣＯ酸化触媒に対して排気の流れ方向の上流側に、上流から排気中のＨＣを吸着するＨＣ吸着材と、排気中のＮＯＸを吸着するＮＯＸ吸着材とを備え、該ＣＯ酸化触媒がＰｄとＣｅＯ２とを有し、該Ｐｄの担持量がＣｅＯ２に対して０．０１~５．０質量％の範囲内であることを特徴とする内燃機関の排気浄化装置。
  2. 　前記ＣＯ酸化触媒のＰｄの担持量がＣｅＯ２に対して０．１~２．５質量％の範囲内である請求項１に記載の排気浄化装置。
  3. 　前記ＮＯＸ吸着材が、Ｍｎ−Ｚｒ−ＯのＮＯＸ吸着材又はＡｇ／βゼオライトである請求項１に記載の排気浄化装置。
  4. 　前記ＨＣ吸着材が、モルデナイト、ＺＳＭ−５、Ｙ型ゼオライト、フェリエライト又はβゼオライトのいずれか１つを含む請求項１に記載の排気浄化装置。
  5. 　前記ＨＣ吸着材が、貴金属を担持したものである請求項１又は２に記載の排気浄化装置。
PCT/JP2011/058482 2010-04-01 2011-03-29 排気浄化用触媒 WO2011125960A1 (ja)

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JP2017025758A (ja) * 2015-07-21 2017-02-02 本田技研工業株式会社 内燃機関の排気浄化装置
JP2016217357A (ja) * 2016-09-07 2016-12-22 日立建機株式会社 熱機関の排ガス浄化装置
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