JP4779271B2 - catalyst - Google Patents
catalyst Download PDFInfo
- Publication number
- JP4779271B2 JP4779271B2 JP2001285597A JP2001285597A JP4779271B2 JP 4779271 B2 JP4779271 B2 JP 4779271B2 JP 2001285597 A JP2001285597 A JP 2001285597A JP 2001285597 A JP2001285597 A JP 2001285597A JP 4779271 B2 JP4779271 B2 JP 4779271B2
- Authority
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- Prior art keywords
- catalyst
- supported
- exhaust gas
- sintering
- mass
- Prior art date
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- 239000003054 catalyst Substances 0.000 title claims description 184
- 238000000746 purification Methods 0.000 claims description 18
- 239000010931 gold Substances 0.000 description 55
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 50
- 239000010948 rhodium Substances 0.000 description 47
- 239000007789 gas Substances 0.000 description 33
- 229910052697 platinum Inorganic materials 0.000 description 32
- 229910052703 rhodium Inorganic materials 0.000 description 31
- 239000002245 particle Substances 0.000 description 24
- 229910052737 gold Inorganic materials 0.000 description 22
- 238000005245 sintering Methods 0.000 description 22
- 239000000843 powder Substances 0.000 description 19
- 238000003917 TEM image Methods 0.000 description 13
- 239000000956 alloy Substances 0.000 description 13
- 229910045601 alloy Inorganic materials 0.000 description 13
- 230000000052 comparative effect Effects 0.000 description 12
- 238000000034 method Methods 0.000 description 11
- 238000001556 precipitation Methods 0.000 description 11
- 239000002131 composite material Substances 0.000 description 10
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 8
- 229910002091 carbon monoxide Inorganic materials 0.000 description 8
- 238000001704 evaporation Methods 0.000 description 8
- 239000002923 metal particle Substances 0.000 description 8
- 239000002002 slurry Substances 0.000 description 8
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 7
- 239000000969 carrier Substances 0.000 description 7
- 238000002149 energy-dispersive X-ray emission spectroscopy Methods 0.000 description 7
- 239000011734 sodium Substances 0.000 description 7
- 230000008020 evaporation Effects 0.000 description 6
- 229910000510 noble metal Inorganic materials 0.000 description 6
- OERNJTNJEZOPIA-UHFFFAOYSA-N zirconium nitrate Chemical compound [Zr+4].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O OERNJTNJEZOPIA-UHFFFAOYSA-N 0.000 description 6
- 238000002360 preparation method Methods 0.000 description 5
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 4
- 239000002253 acid Substances 0.000 description 4
- 239000000292 calcium oxide Substances 0.000 description 4
- HSJPMRKMPBAUAU-UHFFFAOYSA-N cerium(3+);trinitrate Chemical compound [Ce+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O HSJPMRKMPBAUAU-UHFFFAOYSA-N 0.000 description 4
- 238000000921 elemental analysis Methods 0.000 description 4
- 229930195733 hydrocarbon Natural products 0.000 description 4
- 150000002430 hydrocarbons Chemical class 0.000 description 4
- 239000002994 raw material Substances 0.000 description 4
- VXNYVYJABGOSBX-UHFFFAOYSA-N rhodium(3+);trinitrate Chemical compound [Rh+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O VXNYVYJABGOSBX-UHFFFAOYSA-N 0.000 description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 4
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 description 3
- 239000007864 aqueous solution Substances 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
- 238000001354 calcination Methods 0.000 description 3
- 238000000975 co-precipitation Methods 0.000 description 3
- 238000011156 evaluation Methods 0.000 description 3
- 238000010438 heat treatment Methods 0.000 description 3
- 230000000977 initiatory effect Effects 0.000 description 3
- 238000005342 ion exchange Methods 0.000 description 3
- 150000002500 ions Chemical class 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
- 230000001376 precipitating effect Effects 0.000 description 3
- 238000001179 sorption measurement Methods 0.000 description 3
- BNGXYYYYKUGPPF-UHFFFAOYSA-M (3-methylphenyl)methyl-triphenylphosphanium;chloride Chemical compound [Cl-].CC1=CC=CC(C[P+](C=2C=CC=CC=2)(C=2C=CC=CC=2)C=2C=CC=CC=2)=C1 BNGXYYYYKUGPPF-UHFFFAOYSA-M 0.000 description 2
- OAKJQQAXSVQMHS-UHFFFAOYSA-N Hydrazine Chemical compound NN OAKJQQAXSVQMHS-UHFFFAOYSA-N 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 2
- ZCCIPPOKBCJFDN-UHFFFAOYSA-N calcium nitrate Chemical compound [Ca+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O ZCCIPPOKBCJFDN-UHFFFAOYSA-N 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 239000003638 chemical reducing agent Substances 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 239000010419 fine particle Substances 0.000 description 2
- 150000002344 gold compounds Chemical class 0.000 description 2
- FDWREHZXQUYJFJ-UHFFFAOYSA-M gold monochloride Chemical compound [Cl-].[Au+] FDWREHZXQUYJFJ-UHFFFAOYSA-M 0.000 description 2
- 238000011068 loading method Methods 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 230000000877 morphologic effect Effects 0.000 description 2
- 239000008188 pellet Substances 0.000 description 2
- GEHJYWRUCIMESM-UHFFFAOYSA-L sodium sulfite Chemical compound [Na+].[Na+].[O-]S([O-])=O GEHJYWRUCIMESM-UHFFFAOYSA-L 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 230000001629 suppression Effects 0.000 description 2
- 230000007704 transition Effects 0.000 description 2
- NGDQQLAVJWUYSF-UHFFFAOYSA-N 4-methyl-2-phenyl-1,3-thiazole-5-sulfonyl chloride Chemical compound S1C(S(Cl)(=O)=O)=C(C)N=C1C1=CC=CC=C1 NGDQQLAVJWUYSF-UHFFFAOYSA-N 0.000 description 1
- 229910001020 Au alloy Inorganic materials 0.000 description 1
- ODINCKMPIJJUCX-UHFFFAOYSA-N Calcium oxide Chemical compound [Ca]=O ODINCKMPIJJUCX-UHFFFAOYSA-N 0.000 description 1
- KRKNYBCHXYNGOX-UHFFFAOYSA-K Citrate Chemical compound [O-]C(=O)CC(O)(CC([O-])=O)C([O-])=O KRKNYBCHXYNGOX-UHFFFAOYSA-K 0.000 description 1
- KCXVZYZYPLLWCC-UHFFFAOYSA-N EDTA Chemical compound OC(=O)CN(CC(O)=O)CCN(CC(O)=O)CC(O)=O KCXVZYZYPLLWCC-UHFFFAOYSA-N 0.000 description 1
- 229910003771 Gold(I) chloride Inorganic materials 0.000 description 1
- KJTLSVCANCCWHF-UHFFFAOYSA-N Ruthenium Chemical compound [Ru] KJTLSVCANCCWHF-UHFFFAOYSA-N 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- XYXNTHIYBIDHGM-UHFFFAOYSA-N ammonium thiosulfate Chemical compound [NH4+].[NH4+].[O-]S([O-])(=O)=S XYXNTHIYBIDHGM-UHFFFAOYSA-N 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 229910001593 boehmite Inorganic materials 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- 229910000422 cerium(IV) oxide Inorganic materials 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 230000003111 delayed effect Effects 0.000 description 1
- 230000008021 deposition Effects 0.000 description 1
- FGRVOLIFQGXPCT-UHFFFAOYSA-L dipotassium;dioxido-oxo-sulfanylidene-$l^{6}-sulfane Chemical compound [K+].[K+].[O-]S([O-])(=O)=S FGRVOLIFQGXPCT-UHFFFAOYSA-L 0.000 description 1
- PCAXGMRPPOMODZ-UHFFFAOYSA-N disulfurous acid, diammonium salt Chemical compound [NH4+].[NH4+].[O-]S(=O)S([O-])(=O)=O PCAXGMRPPOMODZ-UHFFFAOYSA-N 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 229940071106 ethylenediaminetetraacetate Drugs 0.000 description 1
- 238000010304 firing Methods 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 1
- FAHBNUUHRFUEAI-UHFFFAOYSA-M hydroxidooxidoaluminium Chemical compound O[Al]=O FAHBNUUHRFUEAI-UHFFFAOYSA-M 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 150000002736 metal compounds Chemical class 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- 238000001000 micrograph Methods 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 239000004570 mortar (masonry) Substances 0.000 description 1
- 229910052763 palladium Inorganic materials 0.000 description 1
- 238000011056 performance test Methods 0.000 description 1
- 239000012071 phase Substances 0.000 description 1
- ACVYVLVWPXVTIT-UHFFFAOYSA-N phosphinic acid Chemical compound O[PH2]=O ACVYVLVWPXVTIT-UHFFFAOYSA-N 0.000 description 1
- 150000003058 platinum compounds Chemical class 0.000 description 1
- KIDPOJWGQRZHFM-UHFFFAOYSA-N platinum;hydrate Chemical compound O.[Pt] KIDPOJWGQRZHFM-UHFFFAOYSA-N 0.000 description 1
- RWPGFSMJFRPDDP-UHFFFAOYSA-L potassium metabisulfite Chemical compound [K+].[K+].[O-]S(=O)S([O-])(=O)=O RWPGFSMJFRPDDP-UHFFFAOYSA-L 0.000 description 1
- 229940043349 potassium metabisulfite Drugs 0.000 description 1
- 235000010263 potassium metabisulphite Nutrition 0.000 description 1
- 239000010970 precious metal Substances 0.000 description 1
- 238000006722 reduction reaction Methods 0.000 description 1
- MHOVAHRLVXNVSD-UHFFFAOYSA-N rhodium atom Chemical compound [Rh] MHOVAHRLVXNVSD-UHFFFAOYSA-N 0.000 description 1
- 150000003284 rhodium compounds Chemical class 0.000 description 1
- SONJTKJMTWTJCT-UHFFFAOYSA-K rhodium(iii) chloride Chemical compound [Cl-].[Cl-].[Cl-].[Rh+3] SONJTKJMTWTJCT-UHFFFAOYSA-K 0.000 description 1
- 229910052707 ruthenium Inorganic materials 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 239000012279 sodium borohydride Substances 0.000 description 1
- 229910000033 sodium borohydride Inorganic materials 0.000 description 1
- HRZFUMHJMZEROT-UHFFFAOYSA-L sodium disulfite Chemical compound [Na+].[Na+].[O-]S(=O)S([O-])(=O)=O HRZFUMHJMZEROT-UHFFFAOYSA-L 0.000 description 1
- 229940001584 sodium metabisulfite Drugs 0.000 description 1
- 235000010262 sodium metabisulphite Nutrition 0.000 description 1
- 235000010265 sodium sulphite Nutrition 0.000 description 1
- AKHNMLFCWUSKQB-UHFFFAOYSA-L sodium thiosulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=S AKHNMLFCWUSKQB-UHFFFAOYSA-L 0.000 description 1
- 235000019345 sodium thiosulphate Nutrition 0.000 description 1
- PPASLZSBLFJQEF-RXSVEWSESA-M sodium-L-ascorbate Chemical compound [Na+].OC[C@H](O)[C@H]1OC(=O)C(O)=C1[O-] PPASLZSBLFJQEF-RXSVEWSESA-M 0.000 description 1
- 235000019187 sodium-L-ascorbate Nutrition 0.000 description 1
- 239000011755 sodium-L-ascorbate Substances 0.000 description 1
- PVGBHEUCHKGFQP-UHFFFAOYSA-N sodium;n-[5-amino-2-(4-aminophenyl)sulfonylphenyl]sulfonylacetamide Chemical compound [Na+].CC(=O)NS(=O)(=O)C1=CC(N)=CC=C1S(=O)(=O)C1=CC=C(N)C=C1 PVGBHEUCHKGFQP-UHFFFAOYSA-N 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 238000012546 transfer Methods 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
Images
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触媒に関する。
【０００２】
【従来の技術】
自動車用エンジン等の内燃機関から排出される排気ガスには、一酸化炭素(ＣＯ)、炭化水素(ＨＣ)、窒素酸化物(ＮＯX)等が含まれ、これらの有害物質は、一般に、白金(Ｐｔ)、金(Ａｕ)、パラジウム(Ｐｄ)、ルテニウム(Ｒｕ)、ロジウム(Ｒｈ)等の貴金属を触媒成分とする排気ガス浄化用触媒によって浄化される。
【０００３】
この排気ガス浄化用触媒は、通常、金属酸化物の担体に上記の触媒成分を担持して構成されるが、これらの有害物質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の高い接触面積を呈するように、担体上に触媒成分が高分散に担持されることが必要である。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。
【０００４】
例えば、自動車用エンジンの排気ガス浄化用触媒の場合、常温と約１０００℃の間で温度が繰り返して変動し、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が繰り返される条件下で、この高分散の担持状態が維持される必要がある。
【０００５】
しかしながら、上記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、触媒成分が担体上を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り、このシンタリングは、特に高温の酸化性雰囲気下において促進されやすい。
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。
【０００６】
ところで、本出願人は、先に、触媒成分の金属を合金化することにより触媒活性を高めるといった着想に基づき、特開平１１−１５６１９３号公報において、貴金属を含む合金触媒を提案している。しかし、この公報においては、合金触媒のシンタリング抑制に関する特段の開示はしていない。
【０００７】
【発明が解決しようとする課題】
したがって、本発明は、かかるシンタリングが抑制され、経時的に安定して高い触媒性能を発揮する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、担体上にＰｔが担持された第１触媒、及び担体上にＲｈが担持された第２触媒を含んでなり、第１触媒と第２触媒の少なくとも一方にＡｕがさらに担持されたことを特徴とする触媒によって達成される。
即ち、本発明の触媒は、第１の態様において、Ｐｔ、Ｒｈ、及びＡｕが担体上に担持されてなる触媒であって、ＰｔとＲｈが、それぞれ別々の担体に担持されて構成される触媒である。
【０００９】
また、上記の目的は、担体上に、Ｐｔ、Ｒｈ、及びＡｕが共存する合金粒子が担持されてなることを特徴とする触媒によって達成される。
即ち、本発明の触媒は、第２の態様において、Ｐｔ、Ｒｈ、及びＡｕが、担体上で１つの合金粒子を形成した触媒である。
【００１０】
こうした本発明の触媒において、シンタリングが抑制され、高い排気ガス浄化性能を継続して発揮することができるメカニズムは、以下のように考えられる。
第１の態様の触媒は、Ｐｔ、Ｒｈ、及びＡｕの触媒成分を、例えば、溶解性の貴金属化合物の溶液を用いて担体上に担持して調製することで、触媒成分は、担体の表面全体に、極めて微細な高分散の状態で担持されることができる。
【００１１】
このようにして調製された触媒は、シンタリングが有意には進行していない使用開始後の一定期間は、高分散の担持状態の触媒成分により、高い初期活性の触媒性能を発揮することができる。
次いで、高温の排気ガスに長期間曝されることにより、触媒成分のシンタリングが生じるが、ここで、第１の態様の触媒は、シンタリングによって、第２の態様の触媒に移行し、この第２の態様の触媒においては、実質的にシンタリングが停止する。
【００１２】
即ち、Ｐｔ、Ｒｈ、及びＡｕが担体上に担持され、ＰｔとＲｈが、それぞれ別々の担体に高分散の状態で担持されたこれらの触媒成分は、高温の排気ガスに曝されることにより担体上を移動し、もしくは揮発性の酸化物を形成することにより気相を介した物質移動が生じ、Ｐｔ、Ｒｈ、及びＡｕが、担体上で合金粒子を形成する。この合金粒子は、高温の排気ガスにさらに曝されても、粒子径のそれ以上の肥大化が実質的に起こらず、触媒成分の高分散の担持状態が維持され、高い触媒性能を継続して発揮することができる。
また、この第２の態様の触媒への移行は、ＰｔとＲｈを別々の担体に担持することで遅延され、それにより、初期活性の期間をより長くすることができる。
【００１３】
こうした第１の態様の触媒から第２の態様の触媒に移行し、第２の態様の触媒においては実質的にシンタリングが停止することは、後述の実施例に記載するように、透過型電子顕微鏡(ＴＥＭ)による形態観察によって実証されている。
このように、本発明は、Ｐｔ、Ｒｈ、及びＡｕが、シンタリングによって合金粒子を形成し、それによって以降のシンタリングが実質的に停止するといった特異な現象に基づくものである。
【００１４】
このような現象が起きる理由は、必ずしも明らかではないが、ＡｕとＰｔ、ＡｕとＲｈがそれぞれ合金を形成し、これらの合金は担体上を移動するが、この移動によりＰｔとＲｈとＡｕが合体すると高融点のＰｔ-Ｒｈ-Ａｕ合金を形成するため、以降の移動が抑制されるものと推測される。
【００１５】
【発明の実施の形態】
本発明の第１の態様は、担体上にＰｔが担持された第１触媒、及び担体上にＲｈが担持された第２触媒を含んでなり、第１触媒と第２触媒の少なくとも一方にＡｕがさらに担持されたことを特徴とする触媒である。
第１触媒は、担体上にＰｔが担持されて構成され、この担体は、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が好適に使用可能である。
【００１６】
このような担体にＰｔを担持するのは、例えば、白金ジニトロジアンミンＰｔ(ＮＨ3)2(ＮＯ2)2、塩化白金酸Ｈ2ＰｔＣｌ6・６Ｈ2Ｏ等の白金化合物を用い、蒸発乾固法、沈殿法、イオン交換法、吸着法、還元析出法等によって行うことができる。次いで、好ましくは、大気中で３００〜７００℃の温度に数時間加熱することにより、Ｐｔの担持をより強固にすることができる。
【００１７】
第２触媒は、担体上にＲｈが担持されて構成され、同様に、上記の酸化物又は複合酸化物の担体上に、硝酸ロジウムＲｈ(ＮＯ3)3、塩化ロジウムＲｈＣｌ3等のロジウム化合物を用いて蒸発乾固法、沈殿法、イオン交換法、吸着法、還元析出法等によってＲｈを担持することにより得ることができる。
なお、第１触媒の担体と第２触媒の担体は、第１触媒と第２触媒が別々に調製されるならば、同じ種類のものであることができる。
【００１８】
Ａｕは、第１触媒と第２触媒の少なくとも一方に担持され、上記のＰｔ又はＲｈの担持の前又は後に、第１触媒と第２触媒の一方、あるいは第１触媒と第２触媒の双方に、蒸発乾固法、沈殿法、イオン交換法、吸着法、還元析出法等によって担持させることができる。
好ましくは、このＡｕの担持は、水溶液中でＡｕイオンを生成する金化合物の水溶液に還元剤を添加し、Ａｕイオンを還元することによって不溶性にし、Ａｕ粒子を析出させることにより行う。
【００１９】
具体的には、塩化金酸ＨＡｕＣｌ4・４Ｈ2Ｏ、塩化金ＡｕＣｌ3等の金化合物を、第１触媒、第２触媒、又は第１触媒と第２触媒を分散させた水系スラリーに溶解させ、このスラリーに、チオ硫酸ナトリウムＮａ2Ｓ2Ｏ3、チオ硫酸カリウムＫ2Ｓ2Ｏ3、チオ硫酸アンモニウム(ＮＨ4)2Ｓ2Ｏ3、亜硫酸ナトリウムＮａ2ＳＯ3、メタ重亜硫酸ナトリウムＮａ2Ｓ2Ｏ5、メタ重亜硫酸カリウムＫ2Ｓ2Ｏ5、メタ重亜硫酸アンモニウム(ＮＨ4)2Ｓ2Ｏ5、ヒドラジンＮ2Ｈ4、テトラヒドロホウ酸ナトリウムＮａＢＨ4、ホウ水素化物、次亜リン酸塩、クエン酸塩等の還元剤と、L-アスコルビン酸ナトリウムＣ6Ｈ7Ｏ6Ｎａ、エチレンジアミン四酢酸塩等の緩衝剤を添加してＡｕイオンを還元し、Ａｕ微粒子を第１触媒、第２触媒、又は第１触媒と第２触媒の上に析出させる。
【００２０】
こうした還元析出によれば、直径約１ｎｍ(ナノメートル)のレベルのＡｕ微粒子を、実質的に全てＰｔ又はＲｈの上に析出させることが比較的容易である。
第１触媒のみにＡｕを担持させた第１の態様の触媒は、このようにしてＡｕを担持させた第１触媒を調製し、次いで、第２触媒と、例えば、ボールミル、ヘンシェルミキサー等によって混合して得ることができ、第２触媒のみにＡｕを担持させた第１の態様の触媒は、同様に、Ａｕを担持させた第２触媒と第１触媒を混合して得ることができる。
また、第１触媒と第２触媒の双方にＡｕを担持させた第１の態様の触媒は、第１触媒と第２触媒を、例えば、ボールミル、ヘンシェルミキサー等によって混合した後にＡｕを担持して得ることができる。
【００２１】
このようにして得られる第１の態様の触媒は、好ましくは、Ｐｔ／Ａｕのモル比が２００／１〜１／１で、かつＲｈ／Ａｕのモル比が２００／１〜１／１であり、より好ましくは、Ｐｔ／Ａｕのモル比が２００／１〜４／１で、かつＲｈ／Ａｕのモル比が２００／１〜７／３となるように原料比を調節して調製される。
なお、Ｐｔ、Ｒｈ、及びＡｕ以外の金属成分が、Ｐｔ、Ｒｈ、及びＡｕの合計質量を基準に数質量％以下の量で含まれていても、本発明の目的において許容されることができる。
【００２２】
第２の態様の触媒は、第１の態様の触媒を高温雰囲気に長期間曝すことにより発現し、即ち、第１の態様の触媒に含まれる触媒成分のＰｔ、Ｒｈ、及びＡｕは、移動してこれらが１つの粒子の中に共存する合金粒子を形成し、この合金粒子が第１触媒と第２触媒の双方の担体に担持された状態の第２の態様の触媒が形成される。
この第２の態様の触媒において、触媒成分のＰｔ、Ｒｈ、及びＡｕは、これらの合計質量を基準に少なくとも５０質量％、より好ましくは、少なくとも７５質量％が、直径約５〜４０ｎｍの粒子径の粒子として存在し、Ｐｔ／Ａｕのモル比とＲｈ／Ａｕのモル比は、第１の態様の触媒と同等である。
【００２３】
この第２の態様の触媒は、第１の態様の触媒の初期活性に比較すると若干の触媒性能の低下を示すものの、通常シンタリングが促進される高温の酸化性雰囲気に曝した後でも、一定の粒子径を維持し、高い排気ガス浄化性能を持続することができる。
【００２４】
本発明の触媒が適用された通常のハニカム型排気ガス浄化用触媒は、第１の態様の触媒をモノリス担体にウォッシュコート等により担持して調製することができ、排気ガス浄化用触媒として使用される過程で、又は場合によりこの調製時の焼成工程で、第２の態様の触媒が発現する。
以下、実施例によって本発明をより具体的に説明する。
【００２５】
【実施例】
実施例１
硝酸アルミニウム、硝酸セリウム、及び硝酸ジルコニウムを原料として共沈・焼成によって調製したＡｌ2Ｏ3-ＣｅＯ2-ＺｒＯ2複合酸化物粉末(比表面積約１００ｍ2／ｇ、Ａｌ2Ｏ3／ＣｅＯ2／ＺｒＯ2モル比＝２／１／１、表２中「ＡＣＺ」と示す。)を担体として用い、この複合酸化物粉末をイオン交換水に分散させ、得られたスラリーにジニトロジアンミン白金を溶解させ、次いで、蒸発乾固と大気中で５００℃×２時間の熱処理を行い、Ａｌ2Ｏ3-ＣｅＯ2-ＺｒＯ2複合酸化物粉末の上に５.０質量％のＰｔが担持された第１触媒を得た。
【００２６】
別に、ＺｒＯ2粉末(比表面積約７０ｍ2／ｇ)を担体として用い、このＺｒＯ2粉末をイオン交換水に分散させ、得られたスラリーに硝酸ロジウムを溶解させ、次いで、蒸発乾固させることにより、ＺｒＯ2粉末の上に１.０質量％のＲｈを担持させた。
【００２７】
このＲｈ担持ＺｒＯ2粉末の１００ｇを５００ｃｃの６０℃のイオン交換水に分散させたスラリーに、下記の濃度となる量で試薬を順次に添加し、穏やかな攪拌下に２４時間置くことで塩化金酸からＡｕを還元析出させた。
ＨＡｕＣｌ4・４Ｈ2Ｏ ２.００×１０-2質量％
Ｎａ2Ｓ2Ｏ3・５Ｈ2Ｏ １.００×１０-1質量％
Ｎａ2ＳＯ3 ３.００×１０-1質量％
Ｃ6Ｈ7Ｏ6Ｎａ １.００質量％
【００２８】
この還元析出の後、スラリーを濾過・洗浄し、大気中で１２０℃×２時間の乾燥を行い、次いで、大気中で５００℃×２時間の熱処理を行った。これにより、ＺｒＯ2粉末の上に０.９９質量％のＲｈと０.０１質量％のＡｕが高分散で担持された第２触媒を得た。
上記の第１触媒と第２触媒を等質量で乳鉢を用いて混合し、圧縮・解砕して、直径約１〜３ｍｍのペレット状の本発明の触媒Ａを得た。
【００２９】
比較例１
実施例１で調製した５.０質量％のＰｔを担持したＡｌ2Ｏ3-ＣｅＯ2-ＺｒＯ2複合酸化物粉末と、１.０質量％のＲｈを担持したＺｒＯ2粉末を、実施例１と同様にして、等質量で混合し、圧縮・解砕して、ＰｔとＲｈを含む直径約１〜３ｍｍのペレット状の比較例の触媒ａを得た。
【００３０】
−触媒性能評価(１)−
上記の実施例の触媒Ａと比較例の触媒ａの各２.０ｇを、実験室用の排気ガス浄化性能評価装置の反応管内部に設置した。次いで、表１に示す組成のＡ／Ｆ＝１４.４、１４.７、又は２０.０のモデル雰囲気ガスを流通させ、触媒床温度を２０℃／分の速度で昇温させながら、７００℃、８００℃、又は９００℃の温度に高め、それらの温度に３時間曝す耐久処理に供した。
次いで、Ａ／Ｆ＝１４.６(ストイキ)のモデル雰囲気ガスを流通させ、触媒床温度を１０℃／分の速度で降温させながら、Ｃ3Ｈ6の５０％浄化温度(Ｔ50)を測定した。ストイキのモデル雰囲気ガスの流量は６.０リットル／分／０.０３ｇ貴金属とした。
【００３１】
図１に、この耐久処理温度とモデル雰囲気ガスに対するＴ50の関係を示す。図１に示した結果より、比較例の触媒ａでは、８００℃の耐久処理により、特にＡ／Ｆ＝１４.７のスライトリーンと、Ａ／Ｆ＝２０.０のリーンの雰囲気においてＴ50が顕著に高くなり、排気ガス浄化性能が大きく低下するのに対し、実施例の触媒Ａでは、この低下が顕著に軽減されることが明らかに分かる。
【００３２】
−合金触媒の形態観察−
上記の実施例の触媒Ａと比較例の触媒ａについて、透過型電子顕微鏡(ＴＥＭ)による形態観察と、エネルギー分散型Ｘ線分光分析(ＥＤＸ)による電子顕微鏡像のスポット領域における元素分析を行った。結果を図２〜４に示す。
図２(ａ)は、触媒Ａの耐久処理前のＴＥＭ像であり、図２(ｂ)は、触媒ａの耐久処理前のＴＥＭ像である。金属粒子は、これらのＴＥＭ像からは観察されず、極めて微細な状態で担体上に担持されているものと判断される。
【００３３】
図３(ａ)は、触媒ＡをＡ／Ｆ＝１４.７の条件で８００℃×３時間の耐久処理に供した後のＴＥＭ像であり、シンタリングによって成長した直径約２０ｎｍの金属粒子が観察される。この金属粒子をＥＤＸによって元素分析したところ、Ｐｔ、Ｒｈ、及びＡｕの３成分が分析され、１つの粒子の中にこれらの３成分が共存することが確認された。
図３(ｂ)は、比較例１の触媒ａをＡ／Ｆ＝１４.７の条件で８００℃×３時間の耐久処理に供した後のＴＥＭ像であり、同様に、シンタリングによって成長した直径約１００ｎｍの金属粒子が観察される。この金属粒子をＥＤＸによって元素分析したところＰｔのみが分析された。
【００３４】
図４(ａ)は、触媒Ａをより厳しいＡ／Ｆ＝２０.０の条件で８００℃×３時間の耐久処理に供した後のＴＥＭ像であり、シンタリングによって成長した直径約２０ｎｍ金属粒子が観察されるが、Ａ／Ｆ＝１４.７での耐久処理後と同等の粒子径であることが分かる。この金属粒子をＥＤＸによって元素分析したところ、同様に１つの粒子の中にＰｔ、Ｒｈ、及びＡｕの３成分が共存することが確認された。
【００３５】
図４(ｂ)は、触媒ａをより厳しいＡ／Ｆ＝２０.０の条件で８００℃×３時間の耐久処理に供した後のＴＥＭ像であり、シンタリングによってさらに大きく成長した直径約４００ｎｍの金属粒子が観察される。この粒子をＥＤＸによって元素分析したところＰｔのみが分析された。
【００３６】
これらのＴＥＭ像とＥＤＸ分析より、触媒Ａと触媒ａは、いずれも、耐久処理前は触媒成分がＴＥＭ像によっては観察されない微細な状態で存在するが、耐久処理によって触媒成分がシンタリングし、ＴＥＭ像によって観察される直径の粒子に成長することが分かる。しかしながら、触媒Ａでは、直径約２０ｎｍを上回る粒子は観察されず、シンタリングは一定の粒子径になると停止するのに対し、触媒ａでは、直径約４００ｎｍもの大粒子が観察され、シンタリングが継続することが分かる。
【００３７】
また、ＰｔとＲｈが別な担体に担持されて調製された第１の態様の触媒から、１つの粒子の中にＰｔ、Ｒｈ、及びＡｕの３成分が共存する第２の態様の触媒が発現することが分かる。そして、この３成分の共存状態が、シンタリングの抑制作用を奏するものと推定され、図１に示すような、耐久処理によって顕著には排気ガス浄化性能が低下しない効果をもたらすものと考えられる。
【００３８】
実施例２〜５
実施例１と同様にして、表２に摘要を示す実施例２〜５の第１の態様の触媒Ｂ〜Ｅを調製した。
第１触媒の調製として、実施例２〜５は、いずれもジニトロジアンミン白金の蒸発乾固によって、Ａｌ2Ｏ3-ＣｅＯ2-ＺｒＯ2複合酸化物粉末の上にＰｔを担持させ、次いで、実施例２、３、５では、実施例１と同様にしてＨＡｕＣｌ4・４Ｈ2ＯからＡｕを還元析出させて第１触媒を調製し、実施例４では、この還元析出を行わずに、そのまま第１触媒とした。
【００３９】
第２触媒の調製として、実施例２〜３では、担体にＡｌ2Ｏ3粉末(比表面積約１８０ｍ2／ｇ)を用い、実施例４〜５では、実施例１で用いたものと同じＺｒＯ2粉末を用い、これらの担体に、実施例１と同様にして、硝酸ロジウムの蒸発乾固によってＲｈを担持させた。次いで、実施例１と同様にしてＨＡｕＣｌ4・４Ｈ2ＯからＡｕを還元析出させ、実施例２、４、５の第２触媒を調製した。実施例３ではＡｌ2Ｏ3粉末の上にＲｈを担持させたものをそのまま第２触媒とした。
【００４０】
得られた第１触媒と第２触媒をそれぞれ等質量で混合して、ＰｔとＲｈとＡｕの３成分を含む第１の態様の触媒Ｂ〜Ｅを得た。
表２に示した摘要において、「担持量」は担体と貴金属の合計質量を基準にした貴金属の質量％であり、「比率」はＰｔ又はＲｈ／Ａｕの質量比を示す。
【００４１】
比較例２
実施例５におけるＡｕ還元析出を行わない以外は実施例４と同様にして、表２に摘要を示すＰｔとＲｈの２成分を含む比較例の触媒ｂを得た。
【００４２】
実施例６〜９
実施例１と同様にして、表３に摘要を示す実施例６〜９の第１の態様の触媒Ｆ〜Ｉを調製した。
第１触媒の調製として、担体はいずれも、硝酸セリウム、硝酸ジルコニウム、及び硝酸イットリウムを原料として共沈・焼成によって調製したＣｅＯ2-ＺｒＯ2-Ｙ2Ｏ3複合酸化物粉末(比表面積約７０ｍ2／ｇ、ＣｅＯ2／ＺｒＯ2／Ｙ2Ｏ3モル比＝５０／４７／３、表３中「ＣＺＹ」と示す。)とし、いずれもジニトロジアンミン白金の蒸発乾固によって、この複合酸化物粉末の上にＰｔを担持させた。
次いで、実施例６、７、９では、実施例１と同様にしてＨＡｕＣｌ4・４Ｈ2ＯからＡｕを還元析出させて第１触媒を調製し、実施例８では、この還元析出を行わずに、そのまま第１触媒とした。
【００４３】
第２触媒の調製として、実施例６〜８では、担体として、硝酸ジルコニウム、及び硝酸カルシウムを原料として共沈・焼成によって調製しＺｒＯ2-ＣａＯ複合酸化物粉末(比表面積約８０ｍ2／ｇ、ＺｒＯ2／ＣａＯモル比＝２４／１、表３中「ＺＣＯ」と示す。)を用い、実施例９では、実施例１で用いたものと同じＺｒＯ2粉末を用い、これらの担体に、実施例１と同様にして、硝酸ロジウムの蒸発乾固によってＲｈを担持させた。
【００４４】
次いで、実施例１と同様にしてＨＡｕＣｌ4・４Ｈ2ＯからＡｕを還元析出させ、実施例６、８、９の第２触媒を調製した。実施例７ではＺｒＯ2-ＣａＯ複合酸化物粉末の上にＲｈを担持させたものをそのまま第２触媒とした。
得られた第１触媒と第２触媒をそれぞれ等質量で混合して、ＰｔとＲｈとＡｕの３成分を含む触媒Ｆ〜Ｉを得た。
比較例３
実施例９におけるＡｕ還元析出を行わない以外は実施例９と同様にして、表２に摘要を示すＰｔとＲｈの２成分を含む比較例の触媒ｃを得た。
【００４５】
−触媒性能評価(２)−
上記の実施例２〜９、比較例２〜３の各合金触媒の各１００ｇに、４０質量％硝酸アルミニウム水溶液を３０ｇ、ベーマイトを１.５ｇ、イオン交換水を６０ｃｃ加えてスラリーを作成した。
【００４６】
このスラリーを直径３０ｍｍ×長さ５０ｍｍのモノリス担体（壁厚７５μｍ、セル密度９３セル／ｃｍ2、六角セル）にウォッシュコートし、大気中で、１００℃×２時間の仮乾燥と２５０℃×３時間の乾燥の後、５５０℃で２時間焼成し、モノリス担体に上記の各触媒がコートされた排気ガス浄化用触媒を得た。
これらの各排気ガス浄化用触媒を、常圧流通式の耐久処理装置に配置し、空気／燃料（Ａ／Ｆ）の比が１４.６／１のモデル排気ガス雰囲気下で９００℃×５時間の加熱を行う耐久処理に供した。
【００４７】
耐久処理後の各排気ガス浄化用触媒を、固定床流通反応装置に配置し、下記のリーン雰囲気とリッチ雰囲気が１秒間ごとに切り替わるモデル排気ガスを流通させ、触媒温度を高めながらＣ3Ｈ6の浄化率を測定した。
リッチ雰囲気のガス組成：
０.１５％Ｃ3Ｈ6＋１.０５％ＣＯ＋０.３３％Ｏ2＋０.３％ＮＯ
＋０.３５％Ｈ2＋１４.１９％ＣＯ2＋１０％Ｈ2Ｏ （残余Ｎ2）
リーン雰囲気のガス組成：
０.０５％Ｃ3Ｈ6＋０.１４％ＣＯ＋０.９４％Ｏ2＋０.３４％ＮＯ
＋１４.２７％ＣＯ2＋１０％Ｈ2Ｏ （残余Ｎ2）
この排気ガス浄化性能試験において、モデル排気ガスの流量は３０リットル／分、昇温速度は２５℃／分とした。
【００４８】
各触媒のＣ3Ｈ6の５０％浄化率(Ｔ50)を図５〜６にまとめて示す。この結果より、ＰｔとＲｈとＡｕの３成分を含む本発明の触媒は、ＰｔとＲｈの２成分を含む比較例の触媒よりも、顕著に排気ガス浄化性能が高いことが分かり、この理由は、実施例１の触媒Ａと同様に、触媒成分のシンタリングが抑制されたためと考えられる。また、このシンタリング抑制の効果は、第１触媒と第２触媒のいずれか一方又は双方にＡｕが担持されたときに得られることが分かる。
【００４９】
【発明の効果】
触媒成分のシンタリングが抑制され、経時的に安定して触媒性能を発揮する触媒を提供することができる。
【００５０】
【表１】
【表２】
【表３】
【図面の簡単な説明】
【図１】耐久処理条件と触媒浄化性能の関係を示すグラフである。
【図２】触媒成分の粒子構造を示す透過型電子顕微鏡写真である。
【図３】触媒成分の粒子構造を示す透過型電子顕微鏡写真である。
【図４】触媒成分の粒子構造を示す透過型電子顕微鏡写真である。
【図５】触媒浄化性能を比較したグラフである。
【図６】触媒浄化性能を比較したグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a catalyst having a high durability performance in which sintering of a catalyst component under a high temperature atmosphere is remarkably suppressed.
[0002]
[Prior art]
Exhaust gas discharged from internal combustion engines such as automobile engines includes carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NO x ), etc. These harmful substances are generally platinum. It is purified by an exhaust gas purifying catalyst using a noble metal such as (Pt), gold (Au), palladium (Pd), ruthenium (Ru), rhodium (Rh) as a catalyst component.
[0003]
This exhaust gas purifying catalyst is usually configured by supporting the above catalyst component on a metal oxide support. However, in order to efficiently promote the purification reaction of these harmful substances, the catalyst component is exhausted. It is necessary that the catalyst component be supported in a highly dispersed manner on the support so as to exhibit a high contact area with the gas. This highly dispersed support state needs to be maintained over time in an exhaust gas atmosphere.
[0004]
For example, in the case of an exhaust gas purifying catalyst for an automobile engine, a reducing atmosphere in which the temperature repeatedly fluctuates between room temperature and about 1000 ° C., the HC and CO concentrations are relatively high, and the O 2 concentration is low, This highly dispersed support state needs to be maintained under conditions in which an oxidizing atmosphere having relatively low HC and CO concentrations and high O 2 concentration is repeated.
[0005]
However, the above-mentioned precious metal catalyst component has the property of causing so-called sintering, when the catalyst component is exposed to such an atmosphere for a long period of time, forming particles that are enlarged by moving on the support. Is easily promoted particularly in a high-temperature oxidizing atmosphere.
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.
[0006]
By the way, the present applicant has previously proposed an alloy catalyst containing a noble metal in Japanese Patent Application Laid-Open No. 11-156193, based on the idea of increasing the catalytic activity by alloying the metal of the catalyst component. However, this publication does not disclose any particulars regarding suppression of sintering of the alloy catalyst.
[0007]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a catalyst in which such sintering is suppressed and which stably exhibits high catalyst performance over time.
[0008]
[Means for Solving the Problems]
The above object includes a first catalyst in which Pt is supported on a support and a second catalyst in which Rh is supported on a support, and Au is further supported on at least one of the first catalyst and the second catalyst. This is achieved by a catalyst characterized in that.
That is, the catalyst according to the present invention is a catalyst in which Pt, Rh, and Au are supported on a carrier in the first embodiment, and each of Pt and Rh is supported on separate carriers. It is.
[0009]
Further, the above object is achieved by a catalyst characterized in that alloy particles in which Pt, Rh, and Au coexist are supported on a support.
That is, in the second aspect, the catalyst of the present invention is a catalyst in which Pt, Rh, and Au form one alloy particle on the support.
[0010]
In such a catalyst of the present invention, the mechanism by which sintering is suppressed and high exhaust gas purification performance can be continuously exhibited is considered as follows.
The catalyst of the first aspect is prepared by supporting Pt, Rh, and Au catalyst components on a support using, for example, a solution of a soluble noble metal compound. Furthermore, it can be supported in a very fine and highly dispersed state.
[0011]
The catalyst prepared in this way can exhibit high initial activity catalyst performance due to the highly dispersed supported catalyst component for a certain period after the start of use in which sintering has not progressed significantly. .
Subsequently, sintering of the catalyst component occurs due to long-term exposure to high-temperature exhaust gas. Here, the catalyst of the first aspect is transferred to the catalyst of the second aspect by sintering. In the catalyst of the second aspect, sintering substantially stops.
[0012]
That is, Pt, Rh, and Au are supported on a carrier, and Pt and Rh, each of which is supported in a highly dispersed state on separate carriers, are exposed to a high-temperature exhaust gas. By moving up or forming volatile oxides, mass transfer occurs through the gas phase, and Pt, Rh, and Au form alloy particles on the support. Even if the alloy particles are further exposed to high-temperature exhaust gas, no further enlargement of the particle size occurs, the highly dispersed support state of the catalyst components is maintained, and high catalyst performance is maintained. It can be demonstrated.
In addition, the transition to the catalyst of the second aspect is delayed by loading Pt and Rh on separate carriers, thereby allowing a longer period of initial activity.
[0013]
The transition from the catalyst of the first aspect to the catalyst of the second aspect, and the sintering substantially stops in the catalyst of the second aspect, as described in Examples below. This is demonstrated by morphological observation with a microscope (TEM).
As described above, the present invention is based on a unique phenomenon in which Pt, Rh, and Au form alloy particles by sintering, thereby substantially stopping the subsequent sintering.
[0014]
The reason why such a phenomenon occurs is not necessarily clear, but Au and Pt, Au and Rh each form an alloy, and these alloys move on the carrier, but this movement causes Pt, Rh, and Au to coalesce. Then, since a high melting point Pt—Rh—Au alloy is formed, it is presumed that subsequent movement is suppressed.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
The first aspect of the present invention includes a first catalyst in which Pt is supported on a support, and a second catalyst in which Rh is supported on a support, and Au is provided on at least one of the first catalyst and the second catalyst. Is a catalyst further supported.
The first catalyst is formed by supporting Pt on a support, and this support includes oxides such as alumina, silica and zirconia, silica-alumina, zirconia-ceria, alumina-ceria-zirconia, and ceria-zirconia. A composite oxide such as yttria and zirconia-calcia can be preferably used.
[0016]
Pt is supported on such a carrier, for example, by using a platinum compound such as platinum dinitrodiammine Pt (NH 3 ) 2 (NO 2 ) 2 or chloroplatinic acid H 2 PtCl 6 .6H 2 O, and evaporating to dryness. It can be carried out by the method, precipitation method, ion exchange method, adsorption method, reduction precipitation method and the like. Next, it is preferable that the support of Pt be further strengthened by heating to a temperature of 300 to 700 ° C. for several hours in the atmosphere.
[0017]
The second catalyst is configured such that Rh is supported on a support. Similarly, a rhodium compound such as rhodium nitrate Rh (NO 3 ) 3 or rhodium chloride RhCl 3 is formed on the above oxide or composite oxide support. And can be obtained by carrying Rh by evaporation to dryness, precipitation, ion exchange, adsorption, reduction precipitation or the like.
Note that the carrier for the first catalyst and the carrier for the second catalyst can be of the same type as long as the first catalyst and the second catalyst are prepared separately.
[0018]
Au is supported on at least one of the first catalyst and the second catalyst. Before or after the above-described support of Pt or Rh, Au is applied to one of the first catalyst and the second catalyst, or both the first catalyst and the second catalyst. It can be supported by the evaporation to dryness method, precipitation method, ion exchange method, adsorption method, reduction precipitation method and the like.
Preferably, the loading of Au is performed by adding a reducing agent to an aqueous solution of a gold compound that generates Au ions in an aqueous solution, reducing the Au ions to insolubilize, and precipitating Au particles.
[0019]
Specifically, a gold compound such as chloroauric acid HAuCl 4 .4H 2 O and gold chloride AuCl 3 is dissolved in the first catalyst, the second catalyst, or an aqueous slurry in which the first catalyst and the second catalyst are dispersed. In this slurry, sodium thiosulfate Na 2 S 2 O 3 , potassium thiosulfate K 2 S 2 O 3 , ammonium thiosulfate (NH 4 ) 2 S 2 O 3 , sodium sulfite Na 2 SO 3 , sodium metabisulfite Na 2 S 2 O 5 , potassium metabisulfite K 2 S 2 O 5 , ammonium metabisulfite (NH 4 ) 2 S 2 O 5 , hydrazine N 2 H 4 , sodium tetrahydroborate NaBH 4 , borohydride, hypophosphorous acid A reducing agent such as acid salt and citrate and a buffer such as sodium L-ascorbate C 6 H 7 O 6 Na and ethylenediaminetetraacetate are added to reduce Au ions, and Au fine particles are converted into the first catalyst, Second catalyst Or deposited on the first catalyst and the second catalyst.
[0020]
According to such reduction deposition, it is relatively easy to deposit substantially all Au fine particles having a diameter of about 1 nm (nanometer) on Pt or Rh.
For the catalyst of the first mode in which Au is supported only on the first catalyst, the first catalyst supporting Au is prepared in this way, and then mixed with the second catalyst by, for example, a ball mill, a Henschel mixer, or the like. Similarly, the catalyst of the first aspect in which Au is supported only on the second catalyst can be obtained by mixing the second catalyst supporting Au and the first catalyst.
In addition, the catalyst of the first aspect in which Au is supported on both the first catalyst and the second catalyst, the Au catalyst is supported after the first catalyst and the second catalyst are mixed by, for example, a ball mill, a Henschel mixer or the like. Obtainable.
[0021]
The catalyst of the first aspect thus obtained preferably has a Pt / Au molar ratio of 200/1 to 1/1 and a Rh / Au molar ratio of 200/1 to 1/1. More preferably, the raw material ratio is adjusted so that the molar ratio of Pt / Au is 200/1 to 4/1 and the molar ratio of Rh / Au is 200/1 to 7/3.
In addition, even if a metal component other than Pt, Rh, and Au is contained in an amount of several mass% or less based on the total mass of Pt, Rh, and Au, it can be allowed for the purpose of the present invention. .
[0022]
The catalyst of the second aspect is expressed by exposing the catalyst of the first aspect to a high temperature atmosphere for a long period of time, that is, the catalyst components Pt, Rh, and Au contained in the catalyst of the first aspect move. Thus, the alloy particles coexisting in one particle are formed, and the catalyst of the second mode is formed in a state where the alloy particles are supported on both carriers of the first catalyst and the second catalyst.
In this second aspect of the catalyst, the catalyst components Pt, Rh, and Au are at least 50% by weight, more preferably at least 75% by weight, based on their total weight, with a particle size of about 5-40 nm in diameter. The Pt / Au molar ratio and the Rh / Au molar ratio are equivalent to those of the catalyst of the first aspect.
[0023]
Although the catalyst of the second aspect shows a slight decrease in the catalyst performance as compared with the initial activity of the catalyst of the first aspect, it remains constant even after exposure to a high-temperature oxidizing atmosphere in which sintering is usually promoted. Thus, the exhaust gas purification performance can be maintained.
[0024]
A normal honeycomb type exhaust gas purification catalyst to which the catalyst of the present invention is applied can be prepared by carrying the catalyst of the first aspect on a monolith support by a wash coat or the like, and is used as an exhaust gas purification catalyst. In this process, or in some cases, in the calcination step during the preparation, the catalyst of the second aspect is developed.
Hereinafter, the present invention will be described more specifically with reference to examples.
[0025]
【Example】
Example 1
Al 2 O 3 —CeO 2 —ZrO 2 composite oxide powder prepared by coprecipitation / firing using aluminum nitrate, cerium nitrate and zirconium nitrate as raw materials (specific surface area of about 100 m 2 / g, Al 2 O 3 / CeO 2 / ZrO 2 molar ratio = 2/1/1, indicated as “ACZ” in Table 2), this composite oxide powder was dispersed in ion-exchanged water, and dinitrodiammine platinum was dissolved in the resulting slurry. Next, evaporation to dryness and heat treatment at 500 ° C. for 2 hours in the atmosphere were performed, and a first mass in which 5.0 mass% of Pt was supported on the Al 2 O 3 —CeO 2 —ZrO 2 composite oxide powder. A catalyst was obtained.
[0026]
Separately, ZrO 2 powder (specific surface area of about 70 m 2 / g) was used as a carrier, this ZrO 2 powder was dispersed in ion-exchanged water, rhodium nitrate was dissolved in the resulting slurry, and then evaporated to dryness. Further, 1.0% by mass of Rh was supported on the ZrO 2 powder.
[0027]
Reagents were sequentially added in an amount of the following concentration to a slurry in which 100 g of this Rh-supported ZrO 2 powder was dispersed in 500 cc of ion-exchanged water at 60 ° C., and placed under gentle stirring for 24 hours. Au was reduced and precipitated from the acid.
HAuCl 4 · 4H 2 O 2.00 × 10 -2 mass%
Na 2 S 2 O 3 .5H 2 O 1.00 × 10 −1 mass%
Na 2 SO 3 3.00 × 10 −1 mass%
C 6 H 7 O 6 Na 1.00% by mass
[0028]
After this reduction precipitation, the slurry was filtered and washed, dried in air at 120 ° C. for 2 hours, and then heat-treated in air at 500 ° C. for 2 hours. As a result, a second catalyst in which 0.99% by mass of Rh and 0.01% by mass of Au were supported in a highly dispersed manner on the ZrO 2 powder was obtained.
Said 1st catalyst and 2nd catalyst were mixed with an equal mass using a mortar, and it compressed and crushed, and obtained the catalyst A of this invention of the pellet form of a diameter of about 1-3 mm.
[0029]
Comparative Example 1
The Al 2 O 3 —CeO 2 —ZrO 2 composite oxide powder supporting 5.0% by mass of Pt and the ZrO 2 powder supporting 1.0% by mass of Rh prepared in Example 1 were used in Example 1. In the same manner as above, they were mixed at an equal mass, and compressed and crushed to obtain pellets of comparative catalyst a having a diameter of about 1 to 3 mm containing Pt and Rh.
[0030]
-Catalyst performance evaluation (1)-
2.0 g of each of the catalyst A of the above example and the catalyst a of the comparative example was installed inside the reaction tube of the laboratory exhaust gas purification performance evaluation apparatus. Next, a model atmosphere gas of A / F = 14.4, 14.7, or 20.0 having the composition shown in Table 1 was circulated, and the catalyst bed temperature was raised at a rate of 20 ° C./min. , 800 ° C. or 900 ° C., and subjected to an endurance treatment by exposing to those temperatures for 3 hours.
Next, a 50% purification temperature (T50) of C 3 H 6 was measured while flowing a model atmosphere gas of A / F = 14.6 (Stoichi) and lowering the catalyst bed temperature at a rate of 10 ° C./min. . The Stiki model atmosphere gas flow rate was 6.0 liters / minute / 0.03 g noble metal.
[0031]
FIG. 1 shows the relationship between the endurance treatment temperature and T50 for the model atmosphere gas. From the results shown in FIG. 1, in the catalyst a of the comparative example, T50 is remarkable by the endurance treatment at 800 ° C., particularly in the atmosphere of light lean with A / F = 14.7 and lean with A / F = 20.0. It can be clearly seen that the exhaust gas purification performance is greatly reduced and the catalyst A of the embodiment is significantly reduced.
[0032]
-Morphological observation of alloy catalyst-
For the catalyst A of the above example and the catalyst a of the comparative example, morphological observation by transmission electron microscope (TEM) and elemental analysis in the spot region of the electron microscope image by energy dispersive X-ray spectroscopy (EDX) were performed. . The results are shown in FIGS.
2A is a TEM image before the endurance treatment of the catalyst A, and FIG. 2B is a TEM image before the endurance treatment of the catalyst a. The metal particles are not observed from these TEM images, and are judged to be supported on the carrier in a very fine state.
[0033]
FIG. 3 (a) is a TEM image after subjecting the catalyst A to an endurance treatment at 800 ° C. for 3 hours under the condition of A / F = 14.7, and metal particles having a diameter of about 20 nm grown by sintering. Observed. When this metal particle was subjected to elemental analysis by EDX, three components of Pt, Rh, and Au were analyzed, and it was confirmed that these three components coexist in one particle.
FIG. 3B is a TEM image after subjecting the catalyst a of Comparative Example 1 to an endurance treatment at 800 ° C. for 3 hours under the condition of A / F = 14.7. Similarly, the catalyst a grew by sintering. Metal particles with a diameter of about 100 nm are observed. When this metal particle was elementally analyzed by EDX, only Pt was analyzed.
[0034]
FIG. 4 (a) is a TEM image after subjecting the catalyst A to an endurance treatment at 800 ° C. for 3 hours under a more severe condition of A / F = 20.0, and a metal particle having a diameter of about 20 nm grown by sintering. However, it can be seen that the particle diameter is the same as that after the durability treatment at A / F = 14.7. Elemental analysis of the metal particles by EDX confirmed that three components of Pt, Rh, and Au coexist in one particle.
[0035]
FIG. 4 (b) is a TEM image after subjecting the catalyst a to endurance treatment at 800 ° C. for 3 hours under more severe A / F = 20.0 conditions. Metal particles are observed. When this particle was subjected to elemental analysis by EDX, only Pt was analyzed.
[0036]
From these TEM images and EDX analysis, both catalyst A and catalyst a exist in a fine state where the catalyst component is not observed by the TEM image before the durability treatment, but the catalyst component is sintered by the durability treatment, From the TEM image, it can be seen that the particles grow to the diameters observed. However, in Catalyst A, particles having a diameter of more than about 20 nm are not observed, and sintering stops when the particle diameter becomes constant, whereas in Catalyst a, large particles having a diameter of about 400 nm are observed and sintering continues. I understand that
[0037]
In addition, from the catalyst of the first aspect prepared by supporting Pt and Rh on different carriers, the catalyst of the second aspect in which three components of Pt, Rh, and Au coexist in one particle is expressed. I understand that The coexistence state of these three components is presumed to have a sintering suppressing effect, and it is considered that the exhaust gas purification performance is not significantly reduced by the durability treatment as shown in FIG.
[0038]
Examples 2-5
In the same manner as in Example 1, Catalysts B to E of the first embodiment of Examples 2 to 5 which are summarized in Table 2 were prepared.
As the preparation of the first catalyst, Examples 2 to 5 were all carried out by supporting Pt on the Al 2 O 3 —CeO 2 —ZrO 2 composite oxide powder by evaporation to dryness of dinitrodiammine platinum. In Examples 2, 3, and 5, the first catalyst was prepared by reducing and precipitating Au from HAuCl 4 · 4H 2 O in the same manner as in Example 1. In Example 4, the first catalyst was used as it was without performing this reduction and precipitation. One catalyst was used.
[0039]
As the preparation of the second catalyst, in Examples 2 to 3, Al 2 O 3 powder (specific surface area of about 180 m 2 / g) was used as the carrier, and in Examples 4 to 5, the same ZrO as that used in Example 1 was used. Using these two powders, Rh was supported on these carriers by evaporation to dryness of rhodium nitrate in the same manner as in Example 1. Subsequently, Au was reduced and precipitated from HAuCl 4 .4H 2 O in the same manner as in Example 1 to prepare second catalysts of Examples 2, 4, and 5. In Example 3, a material in which Rh was supported on Al 2 O 3 powder was used as the second catalyst as it was.
[0040]
The obtained first catalyst and second catalyst were mixed in equal masses to obtain first to fifth catalysts B to E containing three components of Pt, Rh and Au.
In the summary shown in Table 2, “supported amount” is the mass% of the noble metal based on the total mass of the support and the noble metal, and “ratio” indicates the mass ratio of Pt or Rh / Au.
[0041]
Comparative Example 2
Except not performing Au reduction precipitation in Example 5, it carried out similarly to Example 4, and obtained the catalyst b of the comparative example containing 2 components of Pt and Rh which are summary in Table 2.
[0042]
Examples 6-9
In the same manner as in Example 1, Catalysts F to I of the first embodiment of Examples 6 to 9 which are summarized in Table 3 were prepared.
As for the preparation of the first catalyst, CeO 2 —ZrO 2 —Y 2 O 3 composite oxide powder (specific surface area of about 70 m) prepared by coprecipitation and calcination using cerium nitrate, zirconium nitrate, and yttrium nitrate as raw materials. 2 / g, CeO 2 / ZrO 2 / Y 2 O 3 molar ratio = 50/47/3, indicated as “CZY” in Table 3.), both of which were obtained by evaporating to dryness of dinitrodiammine platinum. Pt was supported on the powder.
Next, in Examples 6, 7, and 9, the first catalyst was prepared by reducing and precipitating Au from HAuCl 4 · 4H 2 O in the same manner as in Example 1. In Example 8, this reduction and precipitation was not performed. The first catalyst was used as it was.
[0043]
As the preparation of the second catalyst, in Examples 6 to 8, ZrO 2 —CaO composite oxide powder (specific surface area of about 80 m 2 / g, prepared by coprecipitation / calcination using zirconium nitrate as a carrier and calcium nitrate as raw materials) ZrO 2 / CaO molar ratio = 24/1, indicated as “ZCO” in Table 3.) In Example 9, the same ZrO 2 powder as used in Example 1 was used, and these carriers were used. In the same manner as in Example 1, Rh was supported by evaporation to dryness of rhodium nitrate.
[0044]
Subsequently, Au was reduced and precipitated from HAuCl 4 .4H 2 O in the same manner as in Example 1 to prepare second catalysts of Examples 6, 8, and 9. In Example 7, Rh supported on ZrO 2 —CaO composite oxide powder was used as the second catalyst as it was.
The obtained first catalyst and second catalyst were mixed in equal masses to obtain catalysts F to I containing three components of Pt, Rh, and Au.
Comparative Example 3
Except not performing Au reduction precipitation in Example 9, it carried out similarly to Example 9, and obtained the catalyst c of the comparative example containing 2 components of Pt and Rh which are shown in Table 2.
[0045]
-Catalyst performance evaluation (2)-
30 g of 40 mass% aluminum nitrate aqueous solution, 1.5 g of boehmite, and 60 cc of ion-exchanged water were added to 100 g of each of the alloy catalysts of Examples 2 to 9 and Comparative Examples 2 to 3 to prepare slurry.
[0046]
This slurry was wash-coated on a monolith carrier (diameter 30 mm × length 50 mm) (wall thickness 75 μm, cell density 93 cells / cm 2 , hexagonal cell), pre-dried at 100 ° C. × 2 hours and 250 ° C. × 3 in air. After drying for a period of time, it was calcined at 550 ° C. for 2 hours to obtain an exhaust gas purifying catalyst in which the above-mentioned catalyst was coated on a monolith support.
Each of these exhaust gas purifying catalysts is placed in a normal pressure flow type endurance treatment apparatus, and is 900 ° C. × 5 hours in a model exhaust gas atmosphere having an air / fuel (A / F) ratio of 14.6 / 1. This was subjected to an endurance treatment for heating.
[0047]
Each exhaust gas purifying catalyst after the durability treatment was placed in a fixed bed flow reactor, was circulated model exhaust gas lean atmosphere and the rich atmosphere of the following is changed every one second, C 3 H 6 while increasing the catalyst temperature The purification rate was measured.
Rich atmosphere gas composition:
0.15% C 3 H 6 + 1.05% CO + 0.33% O 2 + 0.3% NO
+ 0.35% H 2 + 14.19% CO 2 + 10% H 2 O (residual N 2 )
Lean atmosphere gas composition:
0.05% C 3 H 6 + 0.14% CO + 0.94% O 2 + 0.34% NO
+ 14.27% CO 2 + 10% H 2 O (residual N 2 )
In this exhaust gas purification performance test, the flow rate of the model exhaust gas was 30 liters / minute, and the temperature increase rate was 25 ° C./minute.
[0048]
The 50% purification rate (T50) of C 3 H 6 of each catalyst is summarized in FIGS. From this result, it can be seen that the catalyst of the present invention containing three components of Pt, Rh and Au has significantly higher exhaust gas purification performance than the catalyst of the comparative example containing two components of Pt and Rh. This is considered to be because the sintering of the catalyst component was suppressed as in the catalyst A of Example 1. It can also be seen that this sintering suppression effect is obtained when Au is supported on one or both of the first catalyst and the second catalyst.
[0049]
【The invention's effect】
It is possible to provide a catalyst in which sintering of the catalyst component is suppressed and the catalyst performance is stably exhibited over time.
[0050]
[Table 1]
[Table 2]
[Table 3]
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between durability treatment conditions and catalyst purification performance.
FIG. 2 is a transmission electron micrograph showing the particle structure of a catalyst component.
FIG. 3 is a transmission electron micrograph showing the particle structure of a catalyst component.
FIG. 4 is a transmission electron micrograph showing the particle structure of a catalyst component.
FIG. 5 is a graph comparing catalyst purification performance.
FIG. 6 is a graph comparing catalyst purification performance.
Claims (2)
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| JP4971918B2 (en) * | 2007-01-25 | 2012-07-11 | 日産自動車株式会社 | Exhaust gas purification catalyst and method for producing the same |
| JP2008270180A (en) * | 2007-03-28 | 2008-11-06 | Univ Nagoya | Electrode catalyst composition, electrode and fuel cell |
| JP2012179573A (en) * | 2011-03-02 | 2012-09-20 | Toyota Motor Corp | Catalyst for purifying exhaust gas, and method for producing the same |
| US9115621B2 (en) | 2011-03-04 | 2015-08-25 | Toyota Jidosha Kabushiki Kaisha | Metal particles, exhaust gas purifying catalyst comprising metal particles, and methods for producing them |
| US9114384B2 (en) | 2011-08-23 | 2015-08-25 | Toyota Jidosha Kabushiki Kaisha | Exhaust gas purification catalyst and method for producing it |
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| JPH0733342B2 (en) * | 1989-02-21 | 1995-04-12 | 旭硝子株式会社 | Method for producing 1,1,1,2-tetrafluoroethane |
| JP3872153B2 (en) * | 1997-02-05 | 2007-01-24 | トヨタ自動車株式会社 | Exhaust gas purification catalyst |
| JP3903598B2 (en) * | 1997-09-24 | 2007-04-11 | トヨタ自動車株式会社 | Exhaust gas purification catalyst and method for producing the same |
| JP3861489B2 (en) * | 1998-01-30 | 2006-12-20 | マツダ株式会社 | Exhaust gas purification catalyst and method for producing the same |
| JP2001205087A (en) * | 2000-01-25 | 2001-07-31 | Toyota Motor Corp | Catalyst for cleaning exhaust gas |
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