JP4103407B2 - NOx storage reduction catalyst - Google Patents
NOx storage reduction catalyst Download PDFInfo
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- JP4103407B2 JP4103407B2 JP2002045124A JP2002045124A JP4103407B2 JP 4103407 B2 JP4103407 B2 JP 4103407B2 JP 2002045124 A JP2002045124 A JP 2002045124A JP 2002045124 A JP2002045124 A JP 2002045124A JP 4103407 B2 JP4103407 B2 JP 4103407B2
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- 239000003054 catalyst Substances 0.000 title claims description 95
- 238000003860 storage Methods 0.000 title claims description 16
- 238000000746 purification Methods 0.000 claims description 41
- 239000011232 storage material Substances 0.000 claims description 24
- 150000001875 compounds Chemical class 0.000 claims description 12
- 229910052763 palladium Inorganic materials 0.000 claims description 12
- 229910052697 platinum Inorganic materials 0.000 claims description 11
- 229910052744 lithium Inorganic materials 0.000 claims description 5
- 239000000463 material Substances 0.000 claims description 5
- 238000004519 manufacturing process Methods 0.000 claims description 4
- 229910052700 potassium Inorganic materials 0.000 claims description 4
- 229910052751 metal Inorganic materials 0.000 claims description 2
- 239000002184 metal Substances 0.000 claims description 2
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 description 58
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 45
- PNEYBMLMFCGWSK-UHFFFAOYSA-N Alumina Chemical compound [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 20
- 239000000843 powder Substances 0.000 description 14
- 239000007789 gas Substances 0.000 description 10
- 239000002245 particle Substances 0.000 description 10
- 238000005245 sintering Methods 0.000 description 10
- 239000000243 solution Substances 0.000 description 10
- 230000000052 comparative effect Effects 0.000 description 6
- 238000010304 firing Methods 0.000 description 6
- GPNDARIEYHPYAY-UHFFFAOYSA-N palladium(ii) nitrate Chemical compound [Pd+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O GPNDARIEYHPYAY-UHFFFAOYSA-N 0.000 description 6
- 239000002002 slurry Substances 0.000 description 6
- 239000000758 substrate Substances 0.000 description 6
- 239000007864 aqueous solution Substances 0.000 description 5
- 239000002585 base Substances 0.000 description 4
- 230000003197 catalytic effect Effects 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 4
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 3
- 229910052783 alkali metal Inorganic materials 0.000 description 3
- 150000001340 alkali metals Chemical class 0.000 description 3
- 229910052784 alkaline earth metal Inorganic materials 0.000 description 3
- 150000001342 alkaline earth metals Chemical class 0.000 description 3
- IXSUHTFXKKBBJP-UHFFFAOYSA-L azanide;platinum(2+);dinitrite Chemical compound [NH2-].[NH2-].[Pt+2].[O-]N=O.[O-]N=O IXSUHTFXKKBBJP-UHFFFAOYSA-L 0.000 description 3
- 229910052788 barium Inorganic materials 0.000 description 3
- 238000010438 heat treatment Methods 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitrogen oxide Inorganic materials O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 3
- 230000001590 oxidative effect Effects 0.000 description 3
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- 101150003085 Pdcl gene Proteins 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 239000011575 calcium Substances 0.000 description 2
- 229910002091 carbon monoxide Inorganic materials 0.000 description 2
- 239000011247 coating layer Substances 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000001035 drying Methods 0.000 description 2
- 238000009616 inductively coupled plasma Methods 0.000 description 2
- 238000005342 ion exchange Methods 0.000 description 2
- 238000011068 loading method Methods 0.000 description 2
- 239000011777 magnesium Substances 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
- 150000002941 palladium compounds Chemical class 0.000 description 2
- PIBWKRNGBLPSSY-UHFFFAOYSA-L palladium(II) chloride Chemical compound Cl[Pd]Cl PIBWKRNGBLPSSY-UHFFFAOYSA-L 0.000 description 2
- SCVFZCLFOSHCOH-UHFFFAOYSA-M potassium acetate Chemical compound [K+].CC([O-])=O SCVFZCLFOSHCOH-UHFFFAOYSA-M 0.000 description 2
- 230000002829 reductive effect Effects 0.000 description 2
- 239000011734 sodium Substances 0.000 description 2
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 1
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 1
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 1
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 1
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 description 1
- 238000002441 X-ray diffraction Methods 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- ITHZDDVSAWDQPZ-UHFFFAOYSA-L barium acetate Chemical compound [Ba+2].CC([O-])=O.CC([O-])=O ITHZDDVSAWDQPZ-UHFFFAOYSA-L 0.000 description 1
- DSAJWYNOEDNPEQ-UHFFFAOYSA-N barium atom Chemical compound [Ba] DSAJWYNOEDNPEQ-UHFFFAOYSA-N 0.000 description 1
- 238000001354 calcination Methods 0.000 description 1
- 229910052791 calcium Inorganic materials 0.000 description 1
- 239000000292 calcium oxide Substances 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 229910000422 cerium(IV) oxide Inorganic materials 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 229910052878 cordierite Inorganic materials 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- JSKIRARMQDRGJZ-UHFFFAOYSA-N dimagnesium dioxido-bis[(1-oxido-3-oxo-2,4,6,8,9-pentaoxa-1,3-disila-5,7-dialuminabicyclo[3.3.1]nonan-7-yl)oxy]silane Chemical compound [Mg++].[Mg++].[O-][Si]([O-])(O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2)O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2 JSKIRARMQDRGJZ-UHFFFAOYSA-N 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000004993 emission spectroscopy Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- XIXADJRWDQXREU-UHFFFAOYSA-M lithium acetate Chemical compound [Li+].CC([O-])=O XIXADJRWDQXREU-UHFFFAOYSA-M 0.000 description 1
- 229910052749 magnesium Inorganic materials 0.000 description 1
- 229910000510 noble metal Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 150000003058 platinum compounds Chemical class 0.000 description 1
- 239000011591 potassium Substances 0.000 description 1
- 235000011056 potassium acetate Nutrition 0.000 description 1
- 238000000634 powder X-ray diffraction Methods 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 229910052701 rubidium Inorganic materials 0.000 description 1
- IGLNJRXAVVLDKE-UHFFFAOYSA-N rubidium atom Chemical compound [Rb] IGLNJRXAVVLDKE-UHFFFAOYSA-N 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 229910052708 sodium Inorganic materials 0.000 description 1
- 229910052712 strontium Inorganic materials 0.000 description 1
- CIOAGBVUUVVLOB-UHFFFAOYSA-N strontium atom Chemical compound [Sr] CIOAGBVUUVVLOB-UHFFFAOYSA-N 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- RUDFQVOCFDJEEF-UHFFFAOYSA-N yttrium(III) oxide Inorganic materials [O-2].[O-2].[O-2].[Y+3].[Y+3] RUDFQVOCFDJEEF-UHFFFAOYSA-N 0.000 description 1
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- B01J35/00—Catalysts, in general, characterised by their form or physical properties
- B01J35/19—Catalysts containing parts with different compositions
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
- B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
- B01D53/9404—Removing only nitrogen compounds
- B01D53/9409—Nitrogen oxides
- B01D53/9413—Processes characterised by a specific catalyst
- B01D53/9422—Processes characterised by a specific catalyst for removing nitrogen oxides by NOx storage or reduction by cyclic switching between lean and rich exhaust gases (LNT, NSC, NSR)
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
- B01J23/40—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals of the platinum group metals
- B01J23/44—Palladium
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- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
- 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
- B01J23/58—Platinum group metals with alkali- or alkaline earth metals
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- B01J35/00—Catalysts, in general, characterised by their form or physical properties
- B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
- B01J35/396—Distribution of the active metal ingredient
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- 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
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Description
【０００１】
【発明の属する技術分野】
本発明は、高温雰囲気下での触媒成分のシンタリングが顕著に抑制され、高い耐久性能を有する吸蔵還元型ＮＯx浄化用触媒に関する。
【０００２】
【従来の技術】
地球環境保護のため、自動車用エンジン等の内燃機関から排出される二酸化炭素(ＣＯ2)の発生量を抑え、かつ窒素酸化物(ＮＯx)の発生量を抑えることが世界的課題となっている。
こうした課題に対し、燃費の高いリーンバーンエンジンと、その排気ガスを浄化する触媒としての吸蔵還元型ＮＯx浄化用触媒が開発されている。
【０００３】
この吸蔵還元型ＮＯx浄化用触媒は、一般に、白金(Ｐｔ)、パラジウム(Ｐｄ)等の触媒成分に加え、ＮＯx吸蔵材としてアルカリ金属又はアルカリ土類金属をγ-アルミナ等の担体に担持して構成される。ＮＯxは、リーン条件下でアルカリ金属又はアルカリ土類金属によって吸蔵され、その吸蔵したＮＯxを一時的なストイキ〜リッチ条件下で放出させ、白金等の触媒作用と一時的な還元性雰囲気によって、その放出させたＮＯxを還元浄化する。
【０００４】
しかるに、こうした触媒が、排気ガスの浄化反応を効率的に促進するためには、触媒成分が排気ガスと大きい面積で接触するように、担体上に触媒成分が高分散に担持され、そして、この高分散の担持状態が、排気ガス雰囲気下で経時的に維持されることが必要である。
【０００５】
ここで、自動車用エンジンの排気ガスは、常温と高くは約１０００℃の間で温度の変化を繰り返し、かつ比較的ＨＣとＣＯの濃度が高くてＯ2濃度が低い還元性雰囲気と、比較的ＨＣとＣＯの濃度が低くてＯ2濃度が高い酸化性雰囲気を繰り返す。
【０００６】
【発明が解決しようとする課題】
しかしながら、白金等の貴金属の触媒成分には、こうした雰囲気に長期間曝されると、特に高温の酸化性雰囲気において、触媒成分が移動して肥大化した粒子を形成する、いわゆるシンタリングを生じる性質がある。
このため、触媒成分は、排気ガスとの高い接触面積を維持することができず、排気ガスの浄化性能が経時的に低下するという問題がある。
【０００７】
ところで、本出願人等は、特開平１１−３００２０３号公報、特開平７−２５１０７３号公報等において、ＰｔとＰｄを含み、シンタリングが抑制された排気ガス浄化用触媒を提案している。
本発明は、このような先行技術とは異なる触媒構成により、触媒成分のシンタリングが抑制され、広い温度範囲で経時的に安定して高いＮＯx浄化性能を発揮する吸蔵還元型ＮＯx浄化用触媒を提供することを目的とする。
【０００８】
【課題を解決するための手段】
上記の目的は、酸化物担体上にＰｔ、Ｐｄ、及びＮＯx吸蔵材が担持された第１触媒、並びに酸化物担体上にＰｄ、及びＮＯx吸蔵材が担持された第２触媒を含んでなり、且つ第１触媒におけるＰｄ／ ( Ｐｔ＋Ｐｄ ) のモル比が０ . ０２〜０ . ２である吸蔵還元型ＮＯx浄化用触媒によって達成される。
即ち、本発明の触媒は、第１触媒と第２触媒を含んでなる吸蔵還元型ＮＯx浄化用触媒であって、Ｐｔが第１触媒のみに担持され、Ｐｄが第１触媒と第２触媒の双方に担され、且つ第１触媒におけるＰｄ／ ( Ｐｔ＋Ｐｄ ) のモル比が０ . ０２〜０ . ２であることにより、Ｐｔのシンタリングが抑制され、経時的に安定して高いＮＯx浄化性能を発揮する触媒である。
【０００９】
図１は、かかる触媒のモデル図であり、酸化物担体上でＰｔ粒子を取り囲んでＰｄが存在し、それらの周りにＮＯx吸蔵材が存在する状態の第１触媒と、酸化物担体にＰｄが存在し、その周りにＮＯx吸蔵材が存在する状態の第２触媒が、混在して共存する状態を示す。こうした触媒においてシンタリングが抑制され、広い温度範囲で経時的に安定して高いＮＯx浄化性能を発揮することができる理由は、次のように考えられる。
【００１０】
第１触媒に関し、Ｐｔは、高温酸化性雰囲気において比較的シンタリングを生じやすい性質を有するが、Ｐｄは、比較的シンタリングを生じにくいという性質を有する。したがって、Ｐｔ粒子の周囲にＰｄが存在することで、Ｐｔ移動の抑制作用が生じることができる。
【００１１】
そして、とりわけ、Ｐｄ／(Ｐｔ＋Ｐｄ)のモル比が０.０２〜０.２であるときにかかる状態が発現することができ、また、Ｐｔ化合物とＰｄ化合物を溶解させた溶液を酸化物担体に含浸させ、次いで焼成することにより、かかる状態が、微細な形態で発現することができ、それによって、触媒成分の担体上での高分散性と、この高分散の安定性が得られるものと考えられる。
【００１２】
一方、上記のリーン条件と一時的なストイキ〜リッチ条件の繰り返しによるＮＯxの浄化において、Ｐｔは比較的高い温度でＮＯx浄化作用を奏するが、Ｐｔ粒子は殆どが表出しているため、このＮＯx浄化作用は維持される。したがって、第１触媒は、主として、比較的高い温度で高いＮＯx浄化作用を提供することができる。
【００１３】
次に、第２触媒に関し、Ｐｄは、比較的シンタリングを生じにくいという性質を有する一方で、比較的高い温度では、酸素貯蔵能のためにそれ程ＮＯx浄化作用を奏しないが、比較的低い温度では高いＮＯx浄化作用を奏する。したがって、第２触媒は、主として、比較的低い温度で高いＮＯx浄化作用を提供することができる。
【００１４】
このため、第１触媒と第２触媒が共存することで、広範囲な温度にわたって高いＮＯx浄化性能を発揮する触媒を提供することができ、とりわけ、第１触媒に含まれる(Ｐｔ＋Ｐｄ)のモル量に対する第２触媒に含まれるＰｄのモル量が、Ｐｄ／(Ｐｔ＋Ｐｄ)のモル比として０.９〜１.０であるときに、このＮＯx浄化性能が最適化されるものと考えられる。
また、上記の目的は、酸化物担体上にＰｔ、Ｐｄ、及びＮＯ x 吸蔵材が担持された触媒の製造方法であって、Ｐｔ化合物とＰｄ化合物を溶解させた溶液を酸化物担体に含浸させた後で焼成し、次いでＮＯ x 吸蔵材を担持する触媒の製造方法によって達成される。この本発明の方法では好ましくは、この触媒におけるＰｄ／ ( Ｐｔ＋Ｐｄ ) のモル比が０ . ０２〜０ . ２である。
【００１５】
【発明の実施の形態】
本発明の吸蔵還元型ＮＯx浄化用触媒は、酸化物担体上にＰｔ、Ｐｄ、及びＮＯx吸蔵材が担持された第１触媒、並びに酸化物担体上にＰｄ、及びＮＯx吸蔵材が担持された第２触媒を含んで構成され、且つ第１触媒におけるＰｄ／ ( Ｐｔ＋Ｐｄ ) のモル比が０ . ０２〜０ . ２である。
【００１６】
これら第１触媒と第２触媒の酸化物担体は、アルミナ、シリカ、ジルコニアのような酸化物のほか、シリカ-アルミナ、ジルコニア-セリア、アルミナ-セリア-ジルコニア、セリア-ジルコニア-イットリア、ジルコニア-カルシアのような複合酸化物からなるもので、平均粒子径が１μｍ以下の微粒子からなるものが好適に使用可能であり、第１触媒と第２触媒の酸化物担体は、同じ種類の酸化物又は異なる種類の酸化物からなることができる。
【００１７】
第１触媒の調製に関し、このような酸化物担体にＰｔとＰｄを担持するのは、好ましくは、ジニトロジアンミン白金錯体Ｐｔ(ＮＨ3)2(ＮＯ2)2、塩化白金酸Ｈ2ＰｔＣｌ6・６Ｈ2Ｏ等の白金化合物と、硝酸パラジウムＰｄ(ＮＯ3)2、塩化パラジウムＰｄＣｌ2等のパラジウム化合物を用い、これらの化合物を、所定のＰｄ／(Ｐｔ＋Ｐｄ)のモル比となる量で溶解させた溶液を調製し、この溶液を上記の酸化物担体に含浸し、次いで乾燥・焼成することによって行う。
焼成は、例えば、大気雰囲気の４５０〜６５０℃の温度で数時間加熱することによって行うことができる。
【００１８】
酸化物担体に担持されるＮＯx吸蔵材としては、リチウム(Ｌｉ)、ナトリウム(Ｎａ)、カリウム(Ｋ)、ルビジウム(Ｒｂ)のアルカリ金属、及びマグネシウム(Ｍｇ)、カルシウム(Ｃａ)、ストロンチウム(Ｓｒ)、バリウム(Ｂａ)のアルカリ土類金属の少なくとも１種が例示され、好ましくは、Ｌｉ、Ｋ、及びＢａから選択された少なくとも１種の金属を含む。
【００１９】
好ましくは、ＮＯx吸蔵材は、ＰｔとＰｄを担持した後に担持する。この担持の仕方としては、これらＮＯx吸蔵材の溶液を調製し、この溶液を上記の酸化物担体に含浸し、次いで乾燥・焼成することによって行うことができる。
【００２０】
第２触媒は、第１触媒と同様に、好ましくは、硝酸パラジウムＰｄ(ＮＯ3)2、塩化パラジウムＰｄＣｌ2等のパラジウム化合物を用い、これらの化合物を、所定の量で溶解させた溶液を調製し、この溶液を上記の酸化物担体に含浸し、次いで乾燥・焼成することによってＰｄを担持し、さらに、好ましくは、Ｌｉ、Ｋ、及びＢａから選択された少なくとも１種のＮＯx吸蔵材を担持して調製することができる。
【００２１】
このようにして調製された第１触媒と第２触媒は、例えば、水を媒体にしてボールミル等で湿式混合した後、乾燥して、あるいは、粉末状の第１触媒と第２触媒をヘンシェルミキサー等で乾式混合して、本発明の吸蔵還元型ＮＯx浄化用触媒を得ることができる。
【００２２】
また、本発明の吸蔵還元型ＮＯx浄化用触媒が、通常のハニカム基材にコートされる場合、第１触媒と第２触媒のＮＯx吸蔵材の担持は、ＮＯx吸蔵材が担持される前の、ＰｔとＰｄが担持された第１触媒と第２触媒をハニカム基材にコートした後、そのハニカム基材上のコート層にＮＯx吸蔵材の溶液を含浸し、次いで乾燥・焼成することによって同時に行うこともできる。
酸化物担体上にＰｔ、Ｐｄ、及びＮＯ x 吸蔵材が担持された触媒を製造する本発明の方法では、Ｐｔ化合物とＰｄ化合物を溶解させた溶液を酸化物担体に含浸させた後で焼成し、次いでＮＯ x 吸蔵材を担持する。ここで用いられるＮＯ ｘ 吸蔵材、Ｐｔ化合物、Ｐｄ化合物、酸化物担体については、本発明の吸蔵還元型ＮＯ x 浄化用触媒についての上記の説明を参照することができる。
以下、実施例によって本発明をより具体的に説明する。
【００２３】
【実施例】
実施例１
γ-アルミナ粉末(比表面積約１８０ｍ2／ｇ)に、ジニトロジアンミン白金錯体と硝酸パラジウムを溶解した水溶液(Ｐｔ濃度４.６１質量％、Ｐｄ濃度４.３３質量％)を用いて、γ-アルミナ粉末１２０ｇあたり５.７５ｇのＰｔと０.１５ｇのＰｄとなるように含浸し、乾燥の後、３００℃の大気雰囲気中で１時間焼成した。
別に、γ-アルミナ粉末に、硝酸パラジウムの水溶液(Ｐｄ濃度４.３３質量％)を用いて、γ-アルミナ粉末１２０ｇあたり３.２５ｇのＰｄとなるように含浸し、乾燥の後、４００℃の大気雰囲気中で１時間焼成した。
【００２４】
これらのＰｔＰｄ／γ-アルミナ粉末とＰｄ／γ-アルミナ粉末を１：１の質量比で混合し、さらに１００ｇのアルミナゾル(日産化学製Ａ-２００)と２００ｃｃのイオン交換水を加えてボールミル中で２時間混合し、スラリーを作成した。
得られたスラリーを、直径３０ｍｍ×長さ５０ｍｍのコージェライト製ハニカム基材にウォッシュコートし、１２０℃で２時間乾燥した後、５００℃の大気雰囲気中で１時間焼成して、ハニカム基材１リットルあたり５.７５ｇのＰｔと３.４ｇのＰｄを担持した。
【００２５】
次いでこのコート層に、酢酸バリウム、酢酸カリウム、及び酢酸リチウムを溶解した水溶液を吸水させ、乾燥の後、５００℃の大気雰囲気中で１時間焼成して、ハニカム基材１リットルあたり０.２モルのＢａ、０.１モルのＫ、０.１モルのＬｉを担持し、本発明の触媒を調製した。
【００２６】
比較例１
γ-アルミナ粉末に、ジニトロジアンミン白金錯体と硝酸パラジウムを溶解した水溶液(Ｐｔ濃度４.６１質量％、Ｐｄ濃度４.３３質量％)を用いて、γ-アルミナ粉末１２０ｇあたり５.７５ｇのＰｔと０.１５ｇのＰｄとなるように含浸し、乾燥の後、４００℃の大気雰囲気中で１時間焼成した。
【００２７】
このＰｔＰｄ／γ-アルミナ粉末に１００ｇのアルミナゾルと２００ｃｃのイオン交換水を加えてボールミル中で２時間混合し、スラリーを作成した。
次いで、実施例１と同様にして、得られたスラリーをハニカム基材にウォッシュコートした後、さらに、実施例１と同様にして、ハニカム基材１リットルあたり０.２モルのＢａ、０.１モルのＫ、０.１モルのＬｉを担持し、比較例の触媒を調製した。
【００２８】
比較例２
γ-アルミナ粉末に、硝酸パラジウムを溶解した水溶液(Ｐｄ濃度４.３３質量％)を用いて、γ-アルミナ粉末１２０ｇあたり３．２５ｇのＰｄとなるように含浸し、乾燥の後、４００℃の大気雰囲気中で１時間焼成した。
【００２９】
このＰｄ／γ-アルミナ粉末に１００ｇのアルミナゾルと２００ｃｃのイオン交換水を加えてボールミル中で２時間混合し、スラリーを作成した。
次いで、実施例１と同様にして、得られたスラリーをハニカム基材にウォッシュコートし、乾燥・焼成した後、実施例１と同様にして、ハニカム基材１リットルあたり０.２モルのＢａ、０.１モルのＫ、０.１モルのＬｉを担持し、比較例の触媒を調製した。
【００３０】
−ＮＯx浄化性能の評価−
上記の得られた各触媒を大気雰囲気中の８５０℃×２時間の熱処理に供した後、下記のモデルガスで３００℃、４００℃、及び５００℃におけるＮＯx浄化率を測定した。この結果を図２にまとめて示す。
モデルガス組成：
５００ｐｐｍＮＯ＋２０００ｐｐｍＨＣ＋０.６％ＣＯ＋１０％ＣＯ2 ＋０.３％Ｏ2＋５％Ｈ2Ｏ（残余：Ｎ2）
【００３１】
−触媒成分の粒子径−
ハニカム基材を用いない以外は実施例１と同様にして、γ-アルミナ粉末に、表１に示す量の触媒成分のＰｔとＰｄ、及びＮＯx吸蔵材のＢａ、Ｋ、Ｌｉを担持し、それぞれのγ-アルミナ粉末を、大気雰囲気中で７５０℃×５時間の焼成に供した後、誘導結合プラズマ発光分析(ＩＣＰ)によるＰｔとＰｄの組成分析、及び粉末Ｘ線回折(ＸＲＤ)による触媒成分の粒子径の測定を行った。この結果を図３にまとめて示す。なお、図３に示した粒子径は、触媒成分がＰｔのみの粒子径を基準にした相対値で示す。
【００３２】
−結果より−
図２に示したＮＯx浄化率から、比較例１は、低温側のＮＯx浄化率は比較的低いが、高温側のＮＯx浄化率は比較的高く、比較例２は、低温側のＮＯx浄化率は比較的高いが、高温側のＮＯx浄化率は比較的低いといった結果であるのに対し、実施例１は、全温度範囲で高いＮＯx浄化率を示している。
このことは、第１触媒と第２触媒を含むことによって、双方のＮＯx浄化性能の総和として本発明の触媒のＮＯx浄化性能が発現し、それによって、全温度範囲で高いＮＯx浄化率が得られることを示すものと理解される。
【００３３】
また、図３に示した結果から、第１触媒のＰｄ／(Ｐｔ＋Ｐｄ)のモル比に、触媒成分の粒子径の成長が抑えられる特定の範囲が存在することが分かる。したがって、その範囲であれば第１触媒のＮＯx浄化性能がより効果的に維持されるものと考えられる。
【００３４】
【発明の効果】
触媒成分のシンタリングが抑制され、広い温度範囲で経時的に安定して高いＮＯx浄化性能を発揮する吸蔵還元型ＮＯx浄化用触媒を提供することができる。
【００３５】
【表１】
【図面の簡単な説明】
【図１】本発明の触媒の想定される形態を示すモデル図である。
【図２】ＮＯx浄化率を比較したグラフである。
【図３】熱処理後の触媒成分の粒子径を示すグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a storage reduction type NO x purification catalyst which has a high durability performance in which sintering of catalyst components in a high temperature atmosphere is remarkably suppressed.
[0002]
[Prior art]
In order to protect the global environment, it is a global challenge to reduce the amount of carbon dioxide (CO 2 ) emitted from internal combustion engines such as automobile engines and the amount of nitrogen oxides (NO x ). Yes.
These issues to a high fuel efficiency lean-burn engine, the storage reduction the NO x purification catalyst as a catalyst for purifying an exhaust gas have been developed.
[0003]
The storage reduction the NO x purification catalyst is generally, platinum (Pt), added to the catalyst component such as palladium (Pd), supported alkali metals or alkaline earth metals on a carrier γ- alumina, as the NO x storage material Configured. NO x is occluded by alkali metal or alkaline earth metal under lean conditions, and the occluded NO x is released under temporary stoichiometric to rich conditions, and by catalytic action such as platinum and a temporary reducing atmosphere. Then, the released NO x is reduced and purified.
[0004]
However, in order for such a catalyst to efficiently promote the exhaust gas purification reaction, the catalyst component is supported in a highly dispersed manner on the support so that the catalyst component contacts the exhaust gas in a large area, and this It is necessary that the highly dispersed support state be maintained over time in an exhaust gas atmosphere.
[0005]
Here, the exhaust gas of the automobile engine has a reductive atmosphere in which the temperature changes repeatedly between room temperature and about 1000 ° C., and the concentration of HC and CO is relatively high and the O 2 concentration is low. The oxidizing atmosphere with low HC and CO concentrations and high O 2 concentration is repeated.
[0006]
[Problems to be solved by the invention]
However, the catalytic components of noble metals such as platinum, when exposed to such an atmosphere for a long period of time, in particular in a high-temperature oxidizing atmosphere, the catalytic components move to form enlarged particles, so-called sintering. There is.
For this reason, the catalyst component cannot maintain a high contact area with the exhaust gas, and there is a problem that the exhaust gas purification performance decreases with time.
[0007]
By the way, the present applicants have proposed an exhaust gas purifying catalyst containing Pt and Pd and suppressed sintering in JP-A-11-300203, JP-A-7-255103 and the like.
The present invention, by catalytic structure which is different from such prior art, sintering of the catalyst component is suppressed, for storage reduction the NO x purification to exhibit stable over time with higher the NO x purification performance over a wide temperature range An object is to provide a catalyst.
[0008]
[Means for Solving the Problems]
The above objects, comprises Pt on an oxide support, Pd, and NO first catalyst x storage material is supported, Pd on oxides carrier as well, and the second catalyst NO x storage material is supported in Ri Na, and the molar ratio of Pd / (Pt + Pd) in the first catalyst from 0.02 to 0. it is achieved by storage reduction the NO x purification catalyst is 2.
That is, the catalyst of the present invention is a storage reduction the NO x purification catalyst comprising a first catalyst and a second catalyst, Pt is carried only to the first catalyst, Pd is the first catalyst and the second catalyst both are responsible to a, and the molar ratio of Pd / (Pt + Pd) in the first catalyst from 0.02 to 0. by a 2, sintering of Pt is suppressed, stable over time with a high NO x It is a catalyst that exhibits purification performance.
[0009]
Figure 1 is a model diagram of such catalysts, the oxide surrounding the Pt particles on the support there is Pd, a first catalyst in the state where the NO x storage material around them is present, Pd on the oxide support Is present, and the second catalyst in the state where the NO x storage material is present around it is present in a mixed state. The reason why sintering is suppressed in such a catalyst and the high NO x purification performance can be stably exhibited over time in a wide temperature range is considered as follows.
[0010]
Regarding the first catalyst, Pt has a property that is relatively easy to cause sintering in a high-temperature oxidizing atmosphere, while Pd has a property that is relatively difficult to cause sintering. Therefore, the presence of Pd around the Pt particles can produce an effect of suppressing Pt movement.
[0011]
In particular, such a state can be exhibited when the molar ratio of Pd / (Pt + Pd) is 0.02 to 0.2, and a solution in which a Pt compound and a Pd compound are dissolved is used as an oxide carrier. By impregnating and then firing, such a state can be expressed in a fine form, and it is considered that high dispersibility of the catalyst component on the carrier and stability of this high dispersion can be obtained. It is done.
[0012]
On the other hand, in the purification of NO x by repeating the above lean condition and temporary stoichiometric to rich condition, Pt performs the NO x purification action at a relatively high temperature, but most of the Pt particles are exposed. The NO x purification action is maintained. Accordingly, the first catalyst is mainly capable of providing high the NO x purification action at relatively high temperatures.
[0013]
Next, with respect to the second catalyst, Pd has a property that it is relatively difficult to cause sintering. On the other hand, at a relatively high temperature, Pd does not have a NO x purification effect due to its oxygen storage capacity, but is relatively low. High NO x purification effect at temperature. Therefore, the second catalyst can mainly provide a high NO x purification action at a relatively low temperature.
[0014]
Therefore, the coexistence of the first catalyst and the second catalyst can provide a catalyst that exhibits high NO x purification performance over a wide range of temperatures, and in particular, the molar amount of (Pt + Pd) contained in the first catalyst. It is considered that this NO x purification performance is optimized when the molar amount of Pd contained in the second catalyst with respect to the above is 0.9 to 1.0 as the molar ratio of Pd / (Pt + Pd).
Another object of the present invention is a method for producing a catalyst in which Pt, Pd, and NO x storage material are supported on an oxide carrier, wherein the oxide carrier is impregnated with a solution in which a Pt compound and a Pd compound are dissolved. This is achieved by a method for producing a catalyst which is calcined afterwards and then carries a NO x storage material. Preferably, in the method of the present invention, the molar ratio of Pd / (Pt + Pd) in the catalyst is from 0.02 to 0.2.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Storage reduction NO x purifying catalyst of the present invention, Pt on an oxide support, Pd, and NO first catalyst x storage material is supported, Pd on oxides carrier as well, and NO x storage material is is configured to include a supported second catalyst, and the molar ratio of Pd / (Pt + Pd) in the first catalyst is from 0.02 to 0.2.
[0016]
The oxide supports of these first and second catalysts include oxides such as alumina, silica and zirconia, as well as silica-alumina, zirconia-ceria, alumina-ceria-zirconia, ceria-zirconia-yttria, zirconia-calcia. Can be suitably used, and the oxide support of the first catalyst and the second catalyst can be the same type of oxide or different from each other. It can consist of different types of oxides.
[0017]
Regarding the preparation of the first catalyst, Pt and Pd supported on such an oxide support are preferably dinitrodiammine platinum complex Pt (NH 3 ) 2 (NO 2 ) 2 , chloroplatinic acid H 2 PtCl 6. Using a platinum compound such as 6H 2 O and a palladium compound such as palladium nitrate Pd (NO 3 ) 2 and palladium chloride PdCl 2 , these compounds are dissolved in an amount to give a predetermined Pd / (Pt + Pd) molar ratio. This solution is prepared by impregnating the above-mentioned oxide carrier with this solution, followed by drying and baking.
Firing can be performed, for example, by heating at a temperature of 450 to 650 ° C. in an air atmosphere for several hours.
[0018]
Examples of the NO x storage material supported on the oxide carrier include lithium (Li), sodium (Na), potassium (K), rubidium (Rb) alkali metals, magnesium (Mg), calcium (Ca), strontium ( Sr), at least one of alkaline earth metals of barium (Ba) is exemplified, and preferably contains at least one metal selected from Li, K, and Ba.
[0019]
Preferably, the NO x storage material is supported after supporting Pt and Pd. This loading method can be performed by preparing a solution of these NO x storage materials, impregnating the solution into the above oxide carrier, and then drying and firing.
[0020]
As with the first catalyst, the second catalyst is preferably a palladium compound such as palladium nitrate Pd (NO 3 ) 2 or palladium chloride PdCl 2 , and a solution in which these compounds are dissolved in a predetermined amount is prepared. Then, the above oxide carrier is impregnated with this solution, and then dried and calcined to support Pd, and more preferably, at least one NOx storage material selected from Li, K, and Ba is supported. Can be prepared.
[0021]
The first catalyst and the second catalyst thus prepared are, for example, wet mixed with a ball mill or the like using water as a medium and then dried, or the powdered first catalyst and the second catalyst are combined with a Henschel mixer. it can be dry-mixed to obtain a storage reduction the NO x purification catalyst of the present invention the like.
[0022]
Also, storage reduction the NO x purification catalyst of the present invention, when coated on conventional honeycomb substrate, carrying of the NO x storage material of the first catalyst and the second catalyst, the NO x storage material is supported After the first catalyst and the second catalyst supporting Pt and Pd are coated on the honeycomb base material, the coating layer on the honeycomb base material is impregnated with the NO x storage material solution, and then dried and fired. Can be done simultaneously.
In the method of the present invention Pt on an oxide support, Pd, and the the NO x storage material to produce a supported catalyst, and calcining the solution of a Pt compound and Pd compound was impregnated in the oxide support Then, the NO x storage material is supported. Regarding the NO x storage material, Pt compound, Pd compound, and oxide support used here, the above description of the storage reduction type NO x purification catalyst of the present invention can be referred to.
Hereinafter, the present invention will be described more specifically with reference to examples.
[0023]
【Example】
Example 1
Using an aqueous solution (Pt concentration 4.61% by mass, Pd concentration 4.33% by mass) in which dinitrodiammine platinum complex and palladium nitrate are dissolved in γ-alumina powder (specific surface area about 180 m 2 / g), γ-alumina is used. It was impregnated so as to be 5.75 g of Pt and 0.15 g of Pd per 120 g of powder, dried and then fired in an air atmosphere at 300 ° C. for 1 hour.
Separately, γ-alumina powder was impregnated with an aqueous solution of palladium nitrate (Pd concentration 4.33 mass%) to give 3.25 g of Pd per 120 g of γ-alumina powder. Firing was performed for 1 hour in an air atmosphere.
[0024]
These PtPd / γ-alumina powder and Pd / γ-alumina powder were mixed at a mass ratio of 1: 1, and 100 g of alumina sol (Nissan Chemical A-200) and 200 cc of ion-exchanged water were added in a ball mill. Mix for 2 hours to make a slurry.
The obtained slurry was wash-coated on a cordierite honeycomb substrate having a diameter of 30 mm and a length of 50 mm, dried at 120 ° C. for 2 hours, and then fired in an air atmosphere at 500 ° C. for 1 hour. 5.75 g Pt and 3.4 g Pd were loaded per liter.
[0025]
Next, an aqueous solution in which barium acetate, potassium acetate, and lithium acetate are dissolved is absorbed in this coating layer, dried, and then fired in an air atmosphere at 500 ° C. for 1 hour to give 0.2 mol per liter of honeycomb substrate. The catalyst of the present invention was prepared by loading 0.1 mol of Ba, 0.1 mol of K, and 0.1 mol of Li.
[0026]
Comparative Example 1
Using an aqueous solution (Pt concentration 4.61% by mass, Pd concentration 4.33% by mass) obtained by dissolving dinitrodiammine platinum complex and palladium nitrate in γ-alumina powder, 5.75 g of Pt per 120 g of γ-alumina powder It was impregnated to 0.15 g of Pd, dried and then fired in an air atmosphere at 400 ° C. for 1 hour.
[0027]
To this PtPd / γ-alumina powder, 100 g of alumina sol and 200 cc of ion exchange water were added and mixed in a ball mill for 2 hours to prepare a slurry.
Subsequently, after the obtained slurry was wash-coated on the honeycomb base material in the same manner as in Example 1, and further in the same manner as in Example 1, 0.2 mol of Ba, 0.1 per liter of the honeycomb base material was used. A catalyst of a comparative example was prepared by supporting 1 mol of K and 0.1 mol of Li.
[0028]
Comparative Example 2
γ-alumina powder was impregnated with an aqueous solution of palladium nitrate (Pd concentration 4.33 mass%) to give 3.25 g of Pd per 120 g of γ-alumina powder. Firing was performed for 1 hour in an air atmosphere.
[0029]
To this Pd / γ-alumina powder, 100 g of alumina sol and 200 cc of ion exchange water were added and mixed in a ball mill for 2 hours to prepare a slurry.
Next, the obtained slurry was wash-coated on the honeycomb substrate in the same manner as in Example 1, dried and fired, and then 0.2 mol of Ba per liter of the honeycomb substrate, as in Example 1, A catalyst of a comparative example was prepared by supporting 0.1 mol of K and 0.1 mol of Li.
[0030]
Evaluation of -NO x purification performance -
Each of the obtained catalysts was subjected to a heat treatment at 850 ° C. for 2 hours in an air atmosphere, and the NO x purification rates at 300 ° C., 400 ° C., and 500 ° C. were measured with the following model gas. The results are summarized in FIG.
Model gas composition:
500ppmNO + 2000ppmHC + 0.6% CO + 10
[0031]
-Particle size of catalyst component-
Except for not using a honeycomb substrate, in the same manner as in Example 1, γ-alumina powder was loaded with Pt and Pd as catalyst components in amounts shown in Table 1, and Ba, K, and Li as NO x storage materials, Each γ-alumina powder was subjected to firing at 750 ° C. for 5 hours in an air atmosphere, then Pt and Pd composition analysis by inductively coupled plasma emission spectrometry (ICP), and catalyst by powder X-ray diffraction (XRD) The particle size of the component was measured. The results are summarized in FIG. The particle size shown in FIG. 3 is a relative value based on the particle size of the catalyst component only Pt.
[0032]
-From the results-
From the NO x purification rate shown in FIG. 2, Comparative Example 1, but the NO x purification rate of the low temperature side is relatively low, the NO x purification rate of the high temperature side is relatively high, Comparative Example 2, the low-temperature-side NO Although the x purification rate is relatively high, the high temperature side NO x purification rate is relatively low, whereas Example 1 shows a high NO x purification rate in the entire temperature range.
This can be achieved by including a first catalyst and a second catalyst, the NO x purification performance of the catalyst is expressed in the present invention as the sum of both of the NO x purifying performance, thereby high the NO x purification rate over temperature Is understood to indicate that is obtained.
[0033]
Further, from the results shown in FIG. 3, it can be seen that there is a specific range in which the growth of the particle diameter of the catalyst component can be suppressed in the Pd / (Pt + Pd) molar ratio of the first catalyst. Therefore, it is considered that the NO x purification performance of the first catalyst if the range is maintained more effectively.
[0034]
【The invention's effect】
It is possible to provide a storage-reduction type NO x purification catalyst that suppresses sintering of catalyst components and exhibits high NO x purification performance stably over time in a wide temperature range.
[0035]
[Table 1]
[Brief description of the drawings]
FIG. 1 is a model diagram showing an assumed form of a catalyst of the present invention.
FIG. 2 is a graph comparing NO x purification rates.
FIG. 3 is a graph showing the particle diameter of the catalyst component after heat treatment.
Claims (4)
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| JP5676679B2 (en) | 2013-04-19 | 2015-02-25 | 株式会社キャタラー | Exhaust gas purification catalyst |
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