JP5533783B2 - Catalyst for exhaust gas purification of internal combustion engine - Google Patents
Catalyst for exhaust gas purification of internal combustion engine Download PDFInfo
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- JP5533783B2 JP5533783B2 JP2011112668A JP2011112668A JP5533783B2 JP 5533783 B2 JP5533783 B2 JP 5533783B2 JP 2011112668 A JP2011112668 A JP 2011112668A JP 2011112668 A JP2011112668 A JP 2011112668A JP 5533783 B2 JP5533783 B2 JP 5533783B2
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- 238000000746 purification Methods 0.000 title claims description 150
- 239000003054 catalyst Substances 0.000 title claims description 125
- 238000002485 combustion reaction Methods 0.000 title claims description 34
- 239000010949 copper Substances 0.000 claims description 55
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 53
- 229910052802 copper Inorganic materials 0.000 claims description 53
- 239000010953 base metal Substances 0.000 claims description 43
- 229910044991 metal oxide Inorganic materials 0.000 claims description 42
- 150000004706 metal oxides Chemical class 0.000 claims description 42
- 229910052684 Cerium Inorganic materials 0.000 claims description 13
- 229910052726 zirconium Inorganic materials 0.000 claims description 12
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims description 10
- QCWXUUIWCKQGHC-UHFFFAOYSA-N Zirconium Chemical compound [Zr] QCWXUUIWCKQGHC-UHFFFAOYSA-N 0.000 claims description 9
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 8
- 229910052782 aluminium Inorganic materials 0.000 claims description 8
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 8
- 229910052777 Praseodymium Inorganic materials 0.000 claims description 5
- 229910052746 lanthanum Inorganic materials 0.000 claims description 5
- FZLIPJUXYLNCLC-UHFFFAOYSA-N lanthanum atom Chemical compound [La] FZLIPJUXYLNCLC-UHFFFAOYSA-N 0.000 claims description 5
- 229910052759 nickel Inorganic materials 0.000 claims description 5
- PUDIUYLPXJFUGB-UHFFFAOYSA-N praseodymium atom Chemical compound [Pr] PUDIUYLPXJFUGB-UHFFFAOYSA-N 0.000 claims description 5
- 229910052727 yttrium Inorganic materials 0.000 claims description 5
- VWQVUPCCIRVNHF-UHFFFAOYSA-N yttrium atom Chemical compound [Y] VWQVUPCCIRVNHF-UHFFFAOYSA-N 0.000 claims description 5
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 claims description 4
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 claims description 4
- 229910052779 Neodymium Inorganic materials 0.000 claims description 4
- 229910052788 barium Inorganic materials 0.000 claims description 4
- DSAJWYNOEDNPEQ-UHFFFAOYSA-N barium atom Chemical compound [Ba] DSAJWYNOEDNPEQ-UHFFFAOYSA-N 0.000 claims description 4
- 229910052791 calcium Inorganic materials 0.000 claims description 4
- 239000011575 calcium Substances 0.000 claims description 4
- 229910017052 cobalt Inorganic materials 0.000 claims description 4
- 239000010941 cobalt Substances 0.000 claims description 4
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 claims description 4
- 229910052742 iron Inorganic materials 0.000 claims description 4
- 229910052749 magnesium Inorganic materials 0.000 claims description 4
- 239000011777 magnesium Substances 0.000 claims description 4
- QEFYFXOXNSNQGX-UHFFFAOYSA-N neodymium atom Chemical compound [Nd] QEFYFXOXNSNQGX-UHFFFAOYSA-N 0.000 claims description 4
- 229910052706 scandium Inorganic materials 0.000 claims description 4
- SIXSYDAISGFNSX-UHFFFAOYSA-N scandium atom Chemical compound [Sc] SIXSYDAISGFNSX-UHFFFAOYSA-N 0.000 claims description 4
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 3
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 claims description 3
- 229910052710 silicon Inorganic materials 0.000 claims description 3
- 239000010703 silicon Substances 0.000 claims description 3
- 229910052719 titanium Inorganic materials 0.000 claims description 3
- 239000010936 titanium Substances 0.000 claims description 3
- GWXLDORMOJMVQZ-UHFFFAOYSA-N cerium Chemical compound [Ce] GWXLDORMOJMVQZ-UHFFFAOYSA-N 0.000 claims 2
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 165
- 229910000422 cerium(IV) oxide Inorganic materials 0.000 description 82
- CETPSERCERDGAM-UHFFFAOYSA-N ceric oxide Chemical compound O=[Ce]=O CETPSERCERDGAM-UHFFFAOYSA-N 0.000 description 79
- 230000000052 comparative effect Effects 0.000 description 71
- 229910052760 oxygen Inorganic materials 0.000 description 63
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 59
- 239000001301 oxygen Substances 0.000 description 59
- 239000000843 powder Substances 0.000 description 55
- 239000007789 gas Substances 0.000 description 54
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- 239000000463 material Substances 0.000 description 28
- 230000000694 effects Effects 0.000 description 23
- 238000003860 storage Methods 0.000 description 20
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 19
- 238000012360 testing method Methods 0.000 description 14
- 238000006243 chemical reaction Methods 0.000 description 13
- XTVVROIMIGLXTD-UHFFFAOYSA-N copper(II) nitrate Chemical compound [Cu+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O XTVVROIMIGLXTD-UHFFFAOYSA-N 0.000 description 10
- 238000011156 evaluation Methods 0.000 description 9
- 238000010438 heat treatment Methods 0.000 description 9
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 8
- ZMIGMASIKSOYAM-UHFFFAOYSA-N cerium Chemical compound [Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce] ZMIGMASIKSOYAM-UHFFFAOYSA-N 0.000 description 8
- 239000000243 solution Substances 0.000 description 8
- 229910002091 carbon monoxide Inorganic materials 0.000 description 7
- 239000002131 composite material Substances 0.000 description 7
- 238000004519 manufacturing process Methods 0.000 description 7
- 238000000034 method Methods 0.000 description 7
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- 229910000510 noble metal Inorganic materials 0.000 description 7
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- QPLDLSVMHZLSFG-UHFFFAOYSA-N Copper oxide Chemical compound [Cu]=O QPLDLSVMHZLSFG-UHFFFAOYSA-N 0.000 description 5
- NIPNSKYNPDTRPC-UHFFFAOYSA-N N-[2-oxo-2-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)ethyl]-2-[[3-(trifluoromethoxy)phenyl]methylamino]pyrimidine-5-carboxamide Chemical compound O=C(CNC(=O)C=1C=NC(=NC=1)NCC1=CC(=CC=C1)OC(F)(F)F)N1CC2=C(CC1)NN=N2 NIPNSKYNPDTRPC-UHFFFAOYSA-N 0.000 description 5
- 229910052751 metal Inorganic materials 0.000 description 5
- -1 Group 3 elements Inorganic materials 0.000 description 4
- 230000010757 Reduction Activity Effects 0.000 description 4
- 239000002184 metal Substances 0.000 description 4
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 4
- 239000000126 substance Substances 0.000 description 4
- 229910021193 La 2 O 3 Inorganic materials 0.000 description 3
- 230000003197 catalytic effect Effects 0.000 description 3
- 239000013078 crystal Substances 0.000 description 3
- 229910052747 lanthanoid Inorganic materials 0.000 description 3
- 150000002602 lanthanoids Chemical class 0.000 description 3
- 238000005259 measurement Methods 0.000 description 3
- 230000001590 oxidative effect Effects 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- OVSKIKFHRZPJSS-UHFFFAOYSA-N 2,4-D Chemical compound OC(=O)COC1=CC=C(Cl)C=C1Cl OVSKIKFHRZPJSS-UHFFFAOYSA-N 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- AFCARXCZXQIEQB-UHFFFAOYSA-N N-[3-oxo-3-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)propyl]-2-[[3-(trifluoromethoxy)phenyl]methylamino]pyrimidine-5-carboxamide Chemical compound O=C(CCNC(=O)C=1C=NC(=NC=1)NCC1=CC(=CC=C1)OC(F)(F)F)N1CC2=C(CC1)NN=N2 AFCARXCZXQIEQB-UHFFFAOYSA-N 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 2
- 229910052784 alkaline earth metal Inorganic materials 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
- 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 2
- SXTLQDJHRPXDSB-UHFFFAOYSA-N copper;dinitrate;trihydrate Chemical compound O.O.O.[Cu+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O SXTLQDJHRPXDSB-UHFFFAOYSA-N 0.000 description 2
- 229960004643 cupric oxide Drugs 0.000 description 2
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- 229910002804 graphite Inorganic materials 0.000 description 2
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- 229910052697 platinum Inorganic materials 0.000 description 2
- 230000000630 rising effect Effects 0.000 description 2
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 1
- 239000005751 Copper oxide Substances 0.000 description 1
- 238000005033 Fourier transform infrared spectroscopy Methods 0.000 description 1
- 229910002651 NO3 Inorganic materials 0.000 description 1
- 241000282320 Panthera leo Species 0.000 description 1
- 239000004698 Polyethylene Substances 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- QGZKDVFQNNGYKY-UHFFFAOYSA-N ammonia Natural products N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 1
- 150000001450 anions Chemical class 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 229910052796 boron Inorganic materials 0.000 description 1
- 238000001354 calcination Methods 0.000 description 1
- 239000000969 carrier Substances 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 239000012050 conventional carrier Substances 0.000 description 1
- 229910000431 copper oxide Inorganic materials 0.000 description 1
- BERDEBHAJNAUOM-UHFFFAOYSA-N copper(I) oxide Inorganic materials [Cu]O[Cu] BERDEBHAJNAUOM-UHFFFAOYSA-N 0.000 description 1
- KRFJLUBVMFXRPN-UHFFFAOYSA-N cuprous oxide Chemical compound [O-2].[Cu+].[Cu+] KRFJLUBVMFXRPN-UHFFFAOYSA-N 0.000 description 1
- 229940112669 cuprous oxide Drugs 0.000 description 1
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- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- 229910000311 lanthanide oxide Inorganic materials 0.000 description 1
- UJVRJBAUJYZFIX-UHFFFAOYSA-N nitric acid;oxozirconium Chemical compound [Zr]=O.O[N+]([O-])=O.O[N+]([O-])=O UJVRJBAUJYZFIX-UHFFFAOYSA-N 0.000 description 1
- 239000002736 nonionic surfactant Substances 0.000 description 1
- 125000004430 oxygen atom Chemical group O* 0.000 description 1
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Description
本発明は、主にストイキからリッチ環境下で発生した排ガスを効率よく浄化する触媒に関する。 The present invention relates to a catalyst that efficiently purifies exhaust gas generated mainly in a rich environment from stoichiometry.
車両等に用いられる内燃機関の排ガスは、一酸化炭素や、未燃焼炭化水素等の、人体にとって有害な成分を含む。このため、一般的な車両の排気部分には、有害な成分を分解除去する排気浄化装置が設けられている。従来の排気浄化装置には、アルミナ等の金属酸化物に担持された白金等の貴金属を主成分とする排気浄化用触媒が備えられている。 An exhaust gas of an internal combustion engine used for a vehicle or the like includes components harmful to the human body such as carbon monoxide and unburned hydrocarbons. For this reason, an exhaust purification device that decomposes and removes harmful components is provided in an exhaust portion of a general vehicle. A conventional exhaust purification device includes an exhaust purification catalyst mainly composed of a noble metal such as platinum supported on a metal oxide such as alumina.
近年、白金等の希少で高価な貴金属を含まない、排気浄化用触媒の研究が盛んに行われている。
特許文献１には、（Ａ）酸化第一銅と酸化第二銅を含有する銅成分、並びに（Ｂ）（１）ランタノイド酸化物の１種以上、（２）メンデレーフ周期律表のＩＩ族元素の酸化物の１種以上、（３）ＩＩＩｂ族元素の酸化物の１種以上、及び（４）ＩＶ族元素の酸化物の１種以上を含む混合担体を含んでなり、（Ａ）の銅成分が（Ｂ）の担体の上に分散された触媒に関する技術が記載されている。
In recent years, research on exhaust purification catalysts that do not contain rare and expensive noble metals such as platinum has been actively conducted.
Patent Document 1 includes (A) a copper component containing cuprous oxide and cupric oxide, and (B) (1) one or more lanthanoid oxides, and (2) a group II element in the Mendeleev periodic table. (3) a mixed carrier containing one or more of the oxides of group IIIb elements, and (4) one or more of the oxides of group IV elements, Techniques relating to catalysts in which the components are dispersed on the support (B) are described.
本発明者らが検討した結果、後述する実施例において示すように、上記特許文献１に記載された様な従来の銅触媒は、リッチ環境下で発生した排ガスに対する触媒活性が低い。これは、上記特許文献１に記載された様な従来の担体が酸素吸蔵能に劣るため、排ガス中に残存する酸素等により銅が酸化され、排気浄化能に劣る酸化銅となることによる。したがって、リッチ環境下で発生した排ガスに残存する酸素を吸蔵する材料の開発が強く望まれる。
本発明は、上記実状を鑑みて成し遂げられたものであり、主にストイキからリッチ環境下で発生した排ガスを効率よく浄化する触媒を提供することを目的とする。
As a result of the study by the present inventors, as shown in Examples described later, the conventional copper catalyst as described in Patent Document 1 has low catalytic activity against exhaust gas generated in a rich environment. This is because the conventional carrier as described in Patent Document 1 is inferior in oxygen storage capacity, so that copper is oxidized by oxygen remaining in the exhaust gas and becomes copper oxide inferior in exhaust purification ability. Therefore, development of a material that stores oxygen remaining in exhaust gas generated in a rich environment is strongly desired.
The present invention has been accomplished in view of the above circumstances, and an object of the present invention is to provide a catalyst that efficiently purifies exhaust gas generated mainly under stoichiometric conditions in a rich environment.
本発明の内燃機関の排気浄化用触媒は、ストイキ燃焼乃至リッチ燃焼により生じた排気を浄化する、内燃機関の排気浄化用触媒であって、マグネシウム、カルシウム、バリウム、スカンジウム、イットリウム、ランタン、セリウム、プラセオジム、ネオジム、アルミニウム、及びジルコニウムからなる群より選ばれる２以上の元素を含有し、且つ、パイロクロア構造を一部又は全部に有する金属酸化物、並びに、銅、鉄、コバルト、及びニッケルからなる群より選ばれる１又は２以上の卑金属を含有することを特徴とする。
An exhaust gas purification catalyst for an internal combustion engine of the present invention is an exhaust gas purification catalyst for an internal combustion engine that purifies exhaust gas generated by stoichiometric combustion or rich combustion, and includes magnesium, calcium, barium, scandium, yttrium, lanthanum, cerium, A metal oxide containing two or more elements selected from the group consisting of praseodymium, neodymium, aluminum, and zirconium, and having a pyrochlore structure in part or all, and a group consisting of copper, iron, cobalt, and
本発明においては、前記卑金属が、前記金属酸化物に担持されていてもよい。 In the present invention, the base metal may be supported on the metal oxide.
本発明においては、前記金属酸化物の総含有量を１００質量％としたときの、パイロクロア構造を有する前記金属酸化物の含有割合が２０〜１００質量％であることが好ましい。 In this invention, it is preferable that the content rate of the said metal oxide which has a pyrochlore structure when the total content of the said metal oxide is 100 mass% is 20-100 mass%.
本発明においては、前記排気浄化用触媒全体の質量を１００質量％としたときの、前記卑金属の含有割合が０．５〜１０質量％であることが好ましい。 In this invention, it is preferable that the content rate of the said base metal is 0.5-10 mass% when the mass of the whole exhaust gas purification catalyst is 100 mass%.
本発明においては、さらに、アルミニウム、ケイ素、セリウム、チタン、及びジルコニウムからなる群より選ばれる１又は２以上の元素を含有する酸化物を含んでいてもよい。 In the present invention, it may further contain an oxide containing one or more elements selected from the group consisting of aluminum, silicon, cerium, titanium, and zirconium.
本発明においては、前記卑金属が、前記金属酸化物及び前記酸化物に担持されていてもよい。 In the present invention, the base metal may be supported on the metal oxide and the oxide.
本発明によれば、前記金属酸化物が、ストイキからリッチ環境下で発生した排ガスに対しても酸素を吸蔵するため、前記卑金属が酸化し難くなる結果、低温時の浄化性能を従来よりも向上させることができる。 According to the present invention, since the metal oxide occludes oxygen even in exhaust gas generated in a rich environment due to stoichiometry, the base metal becomes difficult to oxidize, resulting in improved purification performance at a low temperature as compared with the prior art. Can be made.
本発明の内燃機関の排気浄化用触媒は、ストイキ燃焼乃至リッチ燃焼により生じた排気を浄化する、内燃機関の排気浄化用触媒であって、マグネシウム、カルシウム、バリウム、スカンジウム、イットリウム、ランタン、セリウム、プラセオジム、ネオジム、アルミニウム、及びジルコニウムからなる群より選ばれる２以上の元素を含有し、且つ、パイロクロア構造を一部又は全部に有する金属酸化物、並びに、銅、鉄、コバルト、及びニッケルからなる群より選ばれる１又は２以上の卑金属を含有することを特徴とする。
An exhaust gas purification catalyst for an internal combustion engine of the present invention is an exhaust gas purification catalyst for an internal combustion engine that purifies exhaust gas generated by stoichiometric combustion or rich combustion, and includes magnesium, calcium, barium, scandium, yttrium, lanthanum, cerium, A metal oxide containing two or more elements selected from the group consisting of praseodymium, neodymium, aluminum, and zirconium, and having a pyrochlore structure in part or all, and a group consisting of copper, iron, cobalt, and
一般に、内燃機関の燃焼により生じる排気には酸素が残存する。特に、燃焼が不安定な内燃機関始動時等においては、排気中に残存する酸素の量は多い。
以下、排気中に残存する酸素がもたらす悪影響について、担体に担持された銅触媒を排気浄化に用いた場合について検討する。酸化物材料等の担体に担持された銅触媒は、通常、ＣｕＯの様なＩＩ価の酸化物である。このような銅触媒は、還元され、Ｃｕ２Ｏの様なＩ価の酸化物、又はＣｕの様な０価の金属状態となることにより、ＮＯｘ還元活性が発現する。しかし、銅はＩＩ価の酸化物状態が安定である。したがって、排気浄化に銅触媒を用いる際、浄化しようとする排気中に微量の酸素が混在していると、当該酸素により銅が酸化される結果、ＮＯｘの浄化活性、特に、比較的低温条件下におけるＮＯｘの還元活性が低下するという問題が生じる。
In general, oxygen remains in exhaust generated by combustion of an internal combustion engine. In particular, when starting an internal combustion engine where combustion is unstable, the amount of oxygen remaining in the exhaust gas is large.
Hereinafter, the adverse effect of oxygen remaining in the exhaust gas will be examined in the case where a copper catalyst supported on a carrier is used for exhaust gas purification. The copper catalyst supported on a support such as an oxide material is usually a divalent oxide such as CuO. Such a copper catalyst is reduced and becomes an I-valent oxide such as Cu 2 O or a zero-valent metal state such as Cu, thereby exhibiting NOx reduction activity. However, copper has a stable II-valent oxide state. Therefore, when a copper catalyst is used for exhaust purification, if a small amount of oxygen is mixed in the exhaust to be purified, copper is oxidized by the oxygen, resulting in NOx purification activity, particularly under relatively low temperature conditions. This causes a problem that the reduction activity of NOx is reduced.
排気中の酸素を除去する技術として、例えば、（１）貴金属を使用して酸素を除去する触媒や、（２）酸素吸蔵能（Ｏｘｙｇｅｎ Ｓｔｏｒａｇｅ Ｃａｐａｃｉｔｙ；以下、ＯＳＣと称する場合がある）を発現する材料、（３）銅と貴金属触媒をタンデム配置した触媒システム等が知られている。
しかし、（１）高価な貴金属を使用する触媒は、酸素除去のコストが高く、また、ストイキ雰囲気乃至リッチ雰囲気における排気浄化能に劣るという問題がある。また、（２）ストイキ雰囲気下や、リッチ雰囲気下で酸素を吸蔵するＯＳＣ材料は未だ知られていない。これは、少なくともリッチ雰囲気下においてＯＳＣを有する従来の酸化物材料を用いたとしても、酸素を吸蔵する反応よりも、酸素を放出する反応が優先して起こるためである。さらに、（３）銅と貴金属触媒を単にタンデム配置しても、燃焼条件や温度領域により浄化性能に差が生じるという問題がある。
As a technique for removing oxygen in exhaust gas, for example, (1) a catalyst that removes oxygen using a noble metal, and (2) oxygen storage capacity (hereinafter sometimes referred to as OSC) are developed. Materials, (3) a catalyst system in which copper and a noble metal catalyst are arranged in tandem are known.
However, (1) a catalyst using an expensive noble metal has a problem that the cost for removing oxygen is high and the exhaust purification ability in a stoichiometric or rich atmosphere is inferior. Further, (2) an OSC material that occludes oxygen in a stoichiometric atmosphere or a rich atmosphere has not been known yet. This is because even when a conventional oxide material having OSC is used at least in a rich atmosphere, a reaction for releasing oxygen takes precedence over a reaction for storing oxygen. Furthermore, (3) even if the copper and the noble metal catalyst are simply arranged in tandem, there is a problem that the purification performance varies depending on the combustion conditions and temperature range.
銅等の卑金属活性種は、ストイキ雰囲気やリッチ雰囲気においても酸素により酸化される。したがって、ストイキ雰囲気やリッチ雰囲気において、銅等の卑金属活性種は、比較的高い温度条件において還元され０価の金属状態となるまでは、排気浄化能を十分に発揮しない。
本発明者らは、鋭意検討の結果、ストイキ雰囲気からリッチ雰囲気で制御する内燃機関の排気浄化用触媒として、酸素吸蔵能の高い材料を見出した。また、本発明者らは、当該材料を銅等の卑金属活性種と組み合わせることにより、ストイキ燃焼乃至リッチ燃焼により生じた排気に含まれる残存酸素濃度が低減でき、且つ、比較的低い温度領域におけるＮＯｘ還元活性が向上することを見出し、本発明を完成させた。
Base metal active species such as copper are oxidized by oxygen even in a stoichiometric atmosphere or a rich atmosphere. Therefore, in a stoichiometric atmosphere or a rich atmosphere, base metal active species such as copper do not sufficiently exhibit exhaust purification ability until they are reduced to a zero-valent metal state under relatively high temperature conditions.
As a result of intensive studies, the present inventors have found a material having a high oxygen storage capacity as an exhaust purification catalyst for an internal combustion engine controlled from a stoichiometric atmosphere to a rich atmosphere. Further, the present inventors can reduce the residual oxygen concentration contained in the exhaust gas generated by stoichiometric combustion or rich combustion by combining the material with a base metal active species such as copper, and NOx in a relatively low temperature range. The inventors have found that the reduction activity is improved and completed the present invention.
本発明の内燃機関の排気浄化用触媒は、燃費の悪化が１％以内であるリッチ燃焼乃至ストイキ燃焼を前提とした排気システムに使用することを主な目的とする。当該排気システムは、例えば、内燃機関から排気口への流れに沿って前段と後段の少なくとも２段階に分かれ、前段においてＮＯｘを還元浄化し、後段において、導入された空気により、未燃焼の炭化水素（ＨＣ）及び一酸化炭素（ＣＯ）等を酸化するシステムである。本発明の内燃機関の排気浄化用触媒は、このうち、主に前段の触媒として使用することを目的とする。 The main purpose of the exhaust gas purification catalyst for an internal combustion engine of the present invention is to be used in an exhaust system premised on rich combustion or stoichiometric combustion in which deterioration of fuel consumption is within 1%. The exhaust system, for example, is divided into at least two stages, a front stage and a rear stage, along the flow from the internal combustion engine to the exhaust port. This is a system that oxidizes (HC) and carbon monoxide (CO). The exhaust purification catalyst for an internal combustion engine of the present invention is mainly intended to be used as a pre-stage catalyst.
本発明の内燃機関の排気浄化用触媒は、少なくとも、リッチ雰囲気からストイキ雰囲気において酸素を吸蔵する金属酸化物、及びＮＯｘの分解除去に優れた卑金属を含有する。以下、金属酸化物、卑金属、及びその他の成分、並びに触媒の製造方法について、順に説明する。 The exhaust gas purification catalyst for an internal combustion engine of the present invention contains at least a metal oxide that stores oxygen in a rich atmosphere to a stoichiometric atmosphere, and a base metal that is excellent in decomposing and removing NOx. Hereinafter, the metal oxide, the base metal, other components, and the method for producing the catalyst will be described in order.
１．金属酸化物
本発明に使用される金属酸化物は、第２族元素、第３族元素、アルミニウム、及びジルコニウムからなる群より選ばれる２以上の元素を含み、且つ、パイロクロア構造を一部又は全部に有する金属酸化物である。以下、本発明に使用される金属酸化物を、当該金属酸化物と称する場合がある。
ここでいう第２族元素とは、具体的には、マグネシウム、カルシウム、バリウムである。
ここでいう第３族元素とは、具体的には、スカンジウム、イットリウム、及びランタノイドである。ここでいうランタノイドとは、具体的には、ランタン、セリウム、プラセオジム、ネオジムである。
1. Metal oxide The metal oxide used in the present invention contains two or more elements selected from the group consisting of
Specifically, the
The group 3 elements here are specifically scandium, yttrium, and lanthanoids. The lanthanoid here is specifically lanthanum, cerium, praseodymium and neodymium.
パイロクロア構造とは、一般組成式Ａ２Ｂ２Ｏ７で表され、且つ、当該組成式をＡ２Ｂ２Ｏ６Ｏ’と書き直したとき、Ａ、Ｂ、Ｏ、Ｏ’原子が、それぞれ１６ｄ、１６ｃ、４８ｆ、８ｂサイトを占める構造のことである。具体的には、金属原子Ｂは６個の酸素原子Ｏに囲まれた八面体をなし、当該八面体の頂点を共有して三次元ネットワークを形成する。パイロクロア構造は、Ｂ原子を頂点として形成される正四面体が頂点を共有しながら繋がった、いわゆるパイロクロア格子を有する。一方、パイロクロア構造は、Ａ原子からなるパイロクロア格子をも有し、Ａ原子を頂点として形成される各正四面体の中心にＯ’原子が位置する。
本発明のパイロクロア構造の例としては、ＣｅとＺｒの複合酸化物（Ｃｅ２Ｚｒ２Ｏ７）であり、ＣｅとＺｒが酸素を挟んで交互に規則配列した構造が挙げられる。この複合酸化物は、還元状態においては、Ｃｅの価数が３＋であり、パイロクロア相であるが、酸化状態においては、Ｃｅの価数が４＋となり、化学式ＣｅＺｒＯ４で表されるκ構造となる。すなわち、酸化雰囲気下において、パイロクロア構造中のＣｅ３＋がＣｅ４＋に酸化され、化学式ＣｅＺｒＯ４で表されるκ構造に変化する。一方、還元雰囲気下において、κ構造中のＣｅ４＋がＣｅ３＋に還元され、化学式Ｃｅ２Ｚｒ２Ｏ７で表されるパイロクロア構造となる。このように、この複合酸化物は、酸化還元条件により、パイロクロア構造とκ構造との間を可逆的に変化するＣｅとＺｒの複合酸化物であり、パイロクロア構造とκ構造との間の変化に伴い、酸素が吸蔵又は放出される。この複合酸化物においては、Ｃｅ２Ｚｒ２Ｏ７中のＣｅのほぼ１００％が酸素の吸蔵に利用され、高い酸素吸蔵能を示す。
The pyrochlore structure is represented by a general composition formula A 2 B 2 O 7 , and when the composition formula is rewritten as A 2 B 2 O 6 O ′, A, B, O, and O ′ atoms are each 16d. , 16c, 48f, and 8b sites. Specifically, the metal atom B forms an octahedron surrounded by six oxygen atoms O, and forms a three-dimensional network by sharing the vertices of the octahedron. The pyrochlore structure has a so-called pyrochlore lattice in which regular tetrahedrons formed with B atoms as vertices are connected while sharing the vertices. On the other hand, the pyrochlore structure also has a pyrochlore lattice composed of A atoms, and an O ′ atom is located at the center of each tetrahedron formed with the A atom as a vertex.
An example of the pyrochlore structure of the present invention is a complex oxide of Ce and Zr (Ce 2 Zr 2 O 7 ), and a structure in which Ce and Zr are regularly arranged alternately with oxygen in between. In the reduced state, this composite oxide has a valence of Ce of 3+ and is a pyrochlore phase. However, in the oxidized state, the valence of Ce is 4+ and has a κ structure represented by the chemical formula CeZrO 4. . That is, in an oxidizing atmosphere, Ce 3+ in the pyrochlore structure is oxidized to Ce 4+ and changes to a κ structure represented by the chemical formula CeZrO 4 . On the other hand, in a reducing atmosphere, Ce 4+ in the κ structure is reduced to Ce 3+ to form a pyrochlore structure represented by the chemical formula Ce 2 Zr 2 O 7 . Thus, this composite oxide is a composite oxide of Ce and Zr that reversibly changes between the pyrochlore structure and the κ structure depending on the redox conditions. Accompanying this, oxygen is occluded or released. In this composite oxide, almost 100% of Ce in Ce 2 Zr 2 O 7 is used for oxygen storage and exhibits high oxygen storage capacity.
一般的に、セリアジルコニア材料は、還元性のガス成分が多いリッチ雰囲気では酸素を放出し、酸化性のガス成分が多いリーン雰囲気では、酸素を吸蔵する。
後述する実施例において示すように、パイロクロア構造を有しないセリアジルコニア材料は、触媒が浄化活性を発現できる温度条件下（２００〜５００℃）において、リッチ雰囲気下で酸素を放出し、還元された状態になる。一方、パイロクロア構造を有するセリアジルコニア材料は、触媒が浄化活性を発現できる温度条件下（２００〜５００℃）において、リッチ雰囲気下でも酸素を吸蔵できる。
結晶構造が異なると、酸素の吸蔵反応／放出反応の反応速度や、酸素の吸蔵反応／放出反応が生じる温度領域が異なる。バイロクロア構造は、金属元素及び酸素が規則配列した構造のために、還元状態でも結晶構造が安定に存在できる。よって酸素の吸蔵反応が生じる温度領域は、パイロクロア構造を有さないセリアジルコニア材料よりも高くなる。したがって、例えば、卑金属触媒として銅を用いた場合には、銅触媒が浄化活性を発現できる温度領域において、酸素吸蔵反応が生じる。また、セリウムのほぼ１００％が酸素吸蔵に利用できるため、酸素吸蔵反応が長時間継続できる。そのため、排ガス中に含まれる酸素を長時間吸蔵でき、銅活性種の還元を長時間促進できる。
Generally, the ceria zirconia material releases oxygen in a rich atmosphere with a large amount of reducing gas components, and occludes oxygen in a lean atmosphere with a large amount of oxidizing gas components.
As shown in Examples described later, the ceria zirconia material having no pyrochlore structure is in a reduced state by releasing oxygen under a rich atmosphere under a temperature condition (200 to 500 ° C.) in which the catalyst can exhibit purification activity. become. On the other hand, the ceria zirconia material having a pyrochlore structure can occlude oxygen even in a rich atmosphere under temperature conditions (200 to 500 ° C.) at which the catalyst can exhibit purification activity.
When the crystal structures are different, the reaction rate of the oxygen storage / release reaction and the temperature range where the oxygen storage / release reaction occurs are different. Since the birochlore structure is a structure in which metal elements and oxygen are regularly arranged, a crystal structure can exist stably even in a reduced state. Therefore, the temperature range where the oxygen occlusion reaction occurs is higher than that of the ceria zirconia material having no pyrochlore structure. Therefore, for example, when copper is used as the base metal catalyst, an oxygen storage reaction occurs in a temperature range where the copper catalyst can exhibit purification activity. Further, since almost 100% of cerium can be used for oxygen storage, the oxygen storage reaction can be continued for a long time. Therefore, oxygen contained in the exhaust gas can be occluded for a long time, and reduction of the copper active species can be promoted for a long time.
当該金属酸化物は、後述する卑金属がＮＯｘを浄化できる温度領域の全域又は一部において、酸素を吸蔵する性質を有することが好ましい。すなわち、当該金属酸化物が酸素を吸蔵できる温度領域と、後述する卑金属がＮＯｘを浄化できる温度領域とが、重複することが好ましい。例えば、セリアジルコニア材料は、銅がＮＯｘ浄化活性を示す２００〜４００℃の温度領域において酸素を吸蔵できるため、当該金属酸化物がセリアジルコニア材料であり、卑金属が銅である組み合わせは好ましい。
その他にも、当該金属酸化物がセリアジルコニア材料であり、卑金属がニッケルである組み合わせや、当該金属酸化物がアルミナ−セリアジルコニア材料であり、卑金属が銅である組み合わせ等も、当該金属酸化物が酸素を吸蔵できる温度領域と、卑金属がＮＯｘを浄化できる温度領域とが重複するため、好ましい。
It is preferable that the metal oxide has a property of occluding oxygen in the whole or part of a temperature range where a base metal described later can purify NOx. That is, it is preferable that a temperature range in which the metal oxide can store oxygen overlaps a temperature range in which a base metal described later can purify NOx. For example, since the ceria zirconia material can occlude oxygen in a temperature range of 200 to 400 ° C. in which copper exhibits NOx purification activity, a combination in which the metal oxide is a ceria zirconia material and the base metal is copper is preferable.
In addition, the metal oxide is a ceria zirconia material and the base metal is nickel, or the metal oxide is an alumina-ceria zirconia material and the base metal is copper. This is preferable because the temperature range in which oxygen can be occluded overlaps with the temperature range in which the base metal can purify NOx.
当該金属酸化物の総含有量を１００質量％としたときの、パイロクロア構造を有する当該金属酸化物の含有割合は、２０〜１００質量％であることが好ましい。当該含有割合が２０質量％未満である場合には、本願発明の効果の１つである、ストイキからリッチ環境下で発生した排気中の残存酸素を吸蔵する効果が低減するおそれがある。
当該金属酸化物の総含有量を１００質量％としたときの、パイロクロア構造を有する当該金属酸化物の含有割合は、４０〜１００質量％であることがより好ましく、６０〜１００質量％であることがさらに好ましい。
When the total content of the metal oxide is 100% by mass, the content ratio of the metal oxide having a pyrochlore structure is preferably 20 to 100% by mass. When the said content rate is less than 20 mass%, there exists a possibility that the effect which occludes the residual oxygen in the exhaust_gas | exhaustion which generate | occur | produced in the rich environment from stoichiometry which is one of the effects of this invention may be reduced.
When the total content of the metal oxide is 100% by mass, the content ratio of the metal oxide having a pyrochlore structure is more preferably 40 to 100% by mass, and 60 to 100% by mass. Is more preferable.
排気浄化用触媒全体の質量を１００質量％としたときの、当該金属酸化物の含有割合は、２〜８５質量％であることが好ましい。当該含有割合が２質量％未満であるとすると、本願発明の効果の１つである、酸素吸蔵の効果が低減するおそれがある。一方、当該含有割合が８５質量％を超えるとすると、相対的に、排気浄化用触媒全体に対する卑金属等の含有割合が減る結果、上述したＮＯｘ浄化の効果が十分に享受できないおそれがある。
排気浄化用触媒全体の質量を１００質量％としたときの、当該金属酸化物の含有割合は、５〜７０質量％であることがより好ましく、１０〜５０質量％であることがさらに好ましい。
The content ratio of the metal oxide is preferably 2 to 85% by mass when the mass of the entire exhaust gas purification catalyst is 100% by mass. If the content is less than 2% by mass, the effect of oxygen storage, which is one of the effects of the present invention, may be reduced. On the other hand, if the content ratio exceeds 85% by mass, the content ratio of the base metal or the like relative to the entire exhaust gas purification catalyst is relatively reduced, and thus the above-described effect of NOx purification may not be sufficiently enjoyed.
The content ratio of the metal oxide is more preferably 5 to 70% by mass and even more preferably 10 to 50% by mass when the mass of the entire exhaust gas purification catalyst is 100% by mass.
当該金属酸化物に含まれる元素としては、セリウム、ジルコニウム、イットリウム、ランタン、プラセオジム、アルミニウムが好ましい。
当該金属酸化物は、セリウム及びジルコニウムを含む、セリアジルコニア材料であることがより好ましい。
セリアジルコニア材料において、セリア（ＣｅＯ２）とジルコニア（ＺｒＯ２）の含有割合は、モル比にして、ＣｅＯ２：ＺｒＯ２＝４０：６０〜６０：４０であることが好ましい。セリアの含有割合が少なすぎる場合には、複合酸化物の製造時にジルコニアが遊離し、複合酸化物全体に占めるパイロクロア構造の割合が減少するおそれがある。一方、ジルコニアの含有割合が少なすぎる場合には、複合酸化物の製造時に、酸素吸収・放出に寄与しない遊離したセリアが増加するおそれがある。
As an element contained in the metal oxide, cerium, zirconium, yttrium, lanthanum, praseodymium, and aluminum are preferable.
More preferably, the metal oxide is a ceria zirconia material containing cerium and zirconium.
In the ceria zirconia material, the content ratio of ceria (CeO 2 ) and zirconia (ZrO 2 ) is preferably CeO 2 : ZrO 2 = 40: 60 to 60:40 in terms of molar ratio. When the content ratio of ceria is too small, zirconia is liberated during the production of the composite oxide, which may reduce the proportion of the pyrochlore structure in the entire composite oxide. On the other hand, when the content ratio of zirconia is too small, free ceria that does not contribute to oxygen absorption / release may increase during the production of the composite oxide.
２．卑金属
本発明に使用される卑金属は、具体的には、銅、鉄、コバルト、又はニッケルである。これらの卑金属は、１種類のみを単独で用いてもよいし、２種類以上を組み合わせて用いてもよい。また、卑金属は０価の金属であってもよいし、酸化物等の化合物であってもよい。
これらの卑金属のうち、ＮＯｘを吸着し、且つ、ＮＯｘ中のＮ−Ｏ結合を切断するのに優れた特性を有するという観点から、銅を使用することが好ましい。
2. Base metal The base metal used in the present invention is specifically copper, iron, cobalt, or nickel. These base metals may be used alone or in combination of two or more. The base metal may be a zero-valent metal or a compound such as an oxide.
Of these base metals, it is preferable to use copper from the viewpoint of adsorbing NOx and having excellent characteristics for breaking the NO bond in NOx.
銅等の卑金属触媒は、特にリッチ雰囲気下においては、ロジウム等の貴金属触媒に匹敵するほどＮＯｘ還元活性が高い。したがって、銅等の卑金属触媒を用いた貴金属フリー触媒は、リッチ雰囲気下において特に有効であると考えられる。
卑金属近傍の排ガス中に含まれる酸素濃度を、当該金属酸化物によって効果的に低減できるという観点から、卑金属は当該金属酸化物に担持されていてもよい。
Base metal catalysts such as copper have high NOx reduction activity comparable to noble metal catalysts such as rhodium, particularly in a rich atmosphere. Therefore, a noble metal-free catalyst using a base metal catalyst such as copper is considered to be particularly effective in a rich atmosphere.
From the viewpoint that the oxygen concentration contained in the exhaust gas near the base metal can be effectively reduced by the metal oxide, the base metal may be supported on the metal oxide.
排気浄化用触媒全体の質量を１００質量％としたときの、卑金属の含有割合は、０．５〜１０質量％であることが好ましい。当該含有割合が０．５質量％未満であるとすると、本願発明の効果の１つである、ＮＯｘ浄化の効果が低減するおそれがある。一方、当該含有割合が１０質量％を超えるとすると、相対的に、排気浄化用触媒全体に対する当該金属酸化物等の含有割合が減る結果、上述した酸素吸蔵の効果が十分に享受できないおそれがある。
排気浄化用触媒全体の質量を１００質量％としたときの、卑金属の含有割合は、１〜８質量％であることがより好ましく、３〜７質量％であることがさらに好ましい。
The content ratio of the base metal is preferably 0.5 to 10% by mass when the mass of the entire exhaust gas purification catalyst is 100% by mass. If the content is less than 0.5% by mass, the effect of NOx purification, which is one of the effects of the present invention, may be reduced. On the other hand, if the content ratio exceeds 10% by mass, the content ratio of the metal oxide or the like with respect to the entire exhaust gas purification catalyst is relatively reduced, so that the above-described oxygen storage effect may not be sufficiently enjoyed. .
The content ratio of the base metal is more preferably 1 to 8% by mass and further preferably 3 to 7% by mass when the mass of the entire exhaust purification catalyst is 100% by mass.
３．その他の材料
本発明の排気浄化用触媒は、上述した当該金属酸化物及び卑金属の他に、例えば、酸化物（以下、当該酸化物と称する場合がある。）を含有してもよい。
当該酸化物は、上述した卑金属のＮＯｘ浄化の効果、及び、当該金属酸化物の酸素吸蔵効果を損なうものでなければ特に限定されない。当該酸化物としては、例えば、アルミニウム、ケイ素、セリウム、チタン、又はジルコニウムを含む酸化物が挙げられる。これらの元素は、１種類のみを単独で含んでもよいし、２種類以上を組み合わせて含んでいてもよい。
当該酸化物は、アルミナ、シリカ、セリア、チタニア、又はジルコニアであってもよく、これらの中ではアルミナが好ましい。
卑金属が当該酸化物上に高分散に担持されることにより、卑金属のＮＯｘ浄化の活性が増加し、ＮＯｘ浄化能が飛躍的に向上するという観点から、卑金属が、当該酸化物に担持されていてもよい。
なお、卑金属が、当該金属酸化物及び当該酸化物の両方に担持されていてもよい。
3. Other Materials The exhaust purification catalyst of the present invention may contain, for example, an oxide (hereinafter sometimes referred to as the oxide) in addition to the metal oxide and the base metal described above.
The oxide is not particularly limited as long as it does not impair the NOx purification effect of the base metal and the oxygen storage effect of the metal oxide. Examples of the oxide include an oxide containing aluminum, silicon, cerium, titanium, or zirconium. These elements may contain only 1 type independently, and may contain it in combination of 2 or more types.
The oxide may be alumina, silica, ceria, titania, or zirconia, and among these, alumina is preferable.
From the viewpoint that the base metal is supported on the oxide in a highly dispersed manner, the NOx purification activity of the base metal is increased, and the NOx purification performance is dramatically improved, so that the base metal is supported on the oxide. Also good.
Note that the base metal may be supported on both the metal oxide and the oxide.
排気浄化用触媒全体の質量を１００質量％としたときの、当該酸化物の含有割合は、１０〜９３質量％であることが好ましい。当該含有割合が１０質量％未満であるとすると、当該酸化物が少なすぎるため、例えば当該酸化物を担体として用いる場合、担体の嵩が少なくなりすぎるおそれがある。一方、当該含有割合が９３質量％を超えるとすると、相対的に、排気浄化用触媒全体に対する卑金属や当該金属酸化物等の含有割合が減る結果、上述したＮＯｘ浄化の効果、及び酸素吸蔵の効果が十分に享受できないおそれがある。
排気浄化用触媒全体の質量を１００質量％としたときの、当該酸化物の含有割合は、２０〜９０質量％であることがより好ましく、４５〜８５質量％であることがさらに好ましい。
The content ratio of the oxide is preferably 10 to 93% by mass when the mass of the entire exhaust gas purification catalyst is 100% by mass. If the content is less than 10% by mass, the amount of the oxide is too small. For example, when the oxide is used as a carrier, the volume of the carrier may be too small. On the other hand, when the content ratio exceeds 93% by mass, the content ratio of the base metal, the metal oxide, and the like relative to the entire exhaust purification catalyst is relatively reduced. As a result, the NOx purification effect and the oxygen storage effect described above are achieved. May not be fully enjoyed.
The content ratio of the oxide is more preferably 20 to 90% by mass, and further preferably 45 to 85% by mass when the mass of the entire exhaust purification catalyst is 100% by mass.
４．本発明の排気浄化用触媒の製造方法
本発明の排気浄化用触媒の製造方法は、卑金属によるＮＯｘ浄化の効果、及び、当該金属酸化物による酸素吸蔵の効果を損なわない方法であれば、特に限定されない。
以下、卑金属として銅、当該金属酸化物としてセリアジルコニア材料、当該酸化物としてアルミナを含む本発明の排気浄化用触媒の製造方法の典型例について述べる。なお、本発明の排気浄化用触媒の製造方法は、当該典型例に限定されるものではない。
まず、セリアジルコニア材料を準備する。セリアジルコニア材料は、市販のものを用いてもよいし、予め調製したものを用いてもよい。セリアジルコニア材料の調製方法は、セリアとジルコニアが均質に混合した混合物が得られる方法であれば、特に限定されない。
次に、セリアジルコニア材料を適宜加熱し、パイロクロア構造を形成する。加熱条件は特に限定されないが、１０００〜１８００℃、１〜１０時間の条件で加熱することが好ましい。なお、加熱する前に、セリアジルコニア材料を予めプレス成型してもよい。
続いて、パイロクロア構造を有するセリアジルコニア材料に、アルミナ粉末及び銅を混合することにより、本発明の排気浄化用触媒が得られる。混合方法は特に限定されない。パイロクロア構造を有するセリアジルコニア材料、及びアルミナ粉末をそれぞれ担体として、銅を担持させてもよい。銅の担持方法は特に限定されず、公知の方法を用いることができる。得られた排気浄化用触媒は、焼成等の後処理を適宜施してもよい。
4). Production method of exhaust purification catalyst of the present invention The production method of exhaust purification catalyst of the present invention is not particularly limited as long as it does not impair the effect of NOx purification by base metal and the effect of oxygen storage by the metal oxide. Not.
Hereinafter, a typical example of the method for producing an exhaust purification catalyst of the present invention including copper as a base metal, ceria zirconia material as the metal oxide, and alumina as the oxide will be described. In addition, the manufacturing method of the exhaust gas purification catalyst of the present invention is not limited to the typical example.
First, a ceria zirconia material is prepared. As the ceria zirconia material, a commercially available material may be used, or a material prepared in advance may be used. The method for preparing the ceria zirconia material is not particularly limited as long as it is a method capable of obtaining a mixture in which ceria and zirconia are homogeneously mixed.
Next, the ceria zirconia material is appropriately heated to form a pyrochlore structure. Although heating conditions are not specifically limited, It is preferable to heat on 1000-1800 degreeC and the conditions for 1 to 10 hours. Note that the ceria zirconia material may be press-molded in advance before heating.
Subsequently, the catalyst for exhaust gas purification according to the present invention is obtained by mixing alumina powder and copper into a ceria zirconia material having a pyrochlore structure. The mixing method is not particularly limited. Copper may be supported using a ceria zirconia material having a pyrochlore structure and alumina powder as carriers. The method for supporting copper is not particularly limited, and a known method can be used. The obtained exhaust purification catalyst may be appropriately subjected to post-treatment such as calcination.
本発明の排気浄化用触媒は、内燃機関を備える自動車等に応用できる。 The exhaust purification catalyst of the present invention can be applied to automobiles equipped with an internal combustion engine.
以下に、実施例及び比較例を挙げて、本発明をさらに具体的に説明するが、本発明は、これらの実施例のみに限定されるものではない。 Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to these examples.
１．セリアジルコニア固溶体粉末の調製
［実施例１］
セリアとジルコニアの含有モル比（ＣｅＯ２：ＺｒＯ２）が５０：５０のセリアジルコニア固溶体を調製した。まず、ＣｅＯ２換算で２８質量％の硝酸セリウム水溶液４９．１ｇ、ＺｒＯ２換算で１８質量％のオキシ硝酸ジルコニウム水溶液５４．７ｇ、及び界面活性剤（ノニオン系界面活性剤、ライオン社製、商品名：レオコン）をイオン交換水９０ｍＬに溶解させた。次に、当該水溶液中に、アンモニア水（ＮＨ３濃度：２５質量％）を、当該水溶液に溶解している硝酸イオン等の陰イオンに対して１．２倍当量添加し、共沈殿を生成させた。その後得られた共沈物を濾過、洗浄し、さらに１１０℃で乾燥した後、５００℃で５時間大気中にて焼成して、セリアとジルコニアの含有モル比（ＣｅＯ２：ＺｒＯ２）が５０：５０のセリアジルコニア固溶体を得た。
続いて、当該セリアジルコニア固溶体を粉砕後、ポリエチレン製のバッグに充填し、内部を脱気した後、前記バッグの口を加熱して密封した。次に静水圧プレス装置を用いて、１９６ｋｇｆ／ｃｍ２の圧力で１分間プレス成型し、セリアジルコニア固溶体粉末の固形状原料を得た。次に、得られた固形状原料を、黒鉛製のルツボに入れ、黒鉛製のフタをしてＡｒガス中で１７００℃、５時間の温度条件下で加熱し、セリアジルコニアを還元した。得られたセリアジルコニアを、平均粒子径が約５μｍとなるまで粉砕機で粉砕し、実施例１のセリアジルコニア固溶体粉末を得た。実施例１のセリアジルコニア固溶体粉末の結晶構造を解析した結果、パイロクロア構造を有することが分かった。
1. Preparation of ceria zirconia solid solution powder [Example 1]
A ceria zirconia solid solution having a ceria and zirconia content molar ratio (CeO 2 : ZrO 2 ) of 50:50 was prepared. First, 49.1 g of 28 mass% cerium nitrate aqueous solution in terms of CeO 2 , 54.7 g of 18 mass% zirconium oxynitrate aqueous solution in terms of ZrO 2 , and a surfactant (nonionic surfactant, manufactured by Lion Corporation, trade name) : Leocon) was dissolved in 90 mL of ion-exchanged water. Next, 1.2 times equivalent amount of aqueous ammonia (NH 3 concentration: 25% by mass) is added to the aqueous solution with respect to anions such as nitrate ions dissolved in the aqueous solution to form a coprecipitate. It was. Thereafter, the coprecipitate obtained was filtered, washed, and further dried at 110 ° C., and then calcined at 500 ° C. for 5 hours in the atmosphere, so that the molar ratio of ceria to zirconia (CeO 2 : ZrO 2 ) was 50. : 50 ceria zirconia solid solution was obtained.
Subsequently, the ceria zirconia solid solution was pulverized, filled into a polyethylene bag, degassed inside, and then the mouth of the bag was heated and sealed. Next, it was press-molded for 1 minute at a pressure of 196 kgf / cm 2 using an isostatic press, to obtain a solid material of ceria zirconia solid solution powder. Next, the obtained solid raw material was put into a graphite crucible, covered with a graphite lid, and heated in Ar gas at 1700 ° C. for 5 hours to reduce ceria zirconia. The obtained ceria zirconia was pulverized with a pulverizer until the average particle size became about 5 μm, and the ceria zirconia solid solution powder of Example 1 was obtained. As a result of analyzing the crystal structure of the ceria zirconia solid solution powder of Example 1, it was found to have a pyrochlore structure.
［実施例２］
上記実施例１のセリアジルコニア固溶体粉末を１１００℃で５時間焼成し、実施例２のセリアジルコニア固溶体粉末を得た。
[Example 2]
The ceria zirconia solid solution powder of Example 1 was fired at 1100 ° C. for 5 hours to obtain the ceria zirconia solid solution powder of Example 2.
［実施例３］
上記実施例１のセリアジルコニア固溶体粉末を１２００℃で５時間焼成し、実施例３のセリアジルコニア固溶体粉末を得た。
[Example 3]
The ceria zirconia solid solution powder of Example 1 was fired at 1200 ° C. for 5 hours to obtain the ceria zirconia solid solution powder of Example 3.
［比較例１］
上記実施例１のセリアジルコニア固溶体粉末を１２００℃で１０時間焼成し、比較例１のセリアジルコニア固溶体粉末を得た。
[Comparative Example 1]
The ceria zirconia solid solution powder of Example 1 was fired at 1200 ° C. for 10 hours to obtain the ceria zirconia solid solution powder of Comparative Example 1.
２．セリアジルコニア固溶体粉末の評価
２−１．リッチ雰囲気下の酸素吸蔵試験
上記実施例１のセリアジルコニア固溶体粉末、並びに、下記比較例２及び比較例３のセリアジルコニア固溶体粉末について、リッチ雰囲気下の酸素吸蔵試験を行った。なお、比較例２及び比較例３のセリアジルコニア固溶体粉末は、Ｌａ２Ｏ３等の他のランタノイド酸化物も計１０質量％含む。
・比較例２のセリアジルコニア固溶体粉末（ローディア製、ＣｅＯ２：ＺｒＯ２：Ｌａ２Ｏ３：Ｐｒ７Ｏ１１＝６０質量％：３０質量％：３質量％：７質量％）
・比較例３のセリアジルコニア固溶体粉末（ローディア製、ＣｅＯ２：ＺｒＯ２：Ｌａ２Ｏ３：Ｙ２Ｏ３＝３０質量％：６０質量％：５質量％：５質量％）
2. 2. Evaluation of ceria zirconia solid solution powder 2-1. Oxygen storage test under rich atmosphere The ceria zirconia solid solution powder of Example 1 and the ceria zirconia solid solution powders of Comparative Examples 2 and 3 below were subjected to an oxygen storage test under a rich atmosphere. Incidentally, ceria-zirconia solid solution powder of Comparative Examples 2 and 3, other lanthanide oxides such as La 2 O 3 also includes a total of 10 mass%.
-Ceria zirconia solid solution powder of Comparative Example 2 (manufactured by Rhodia, CeO 2 : ZrO 2 : La 2 O 3 : Pr 7 O 11 = 60% by mass: 30% by mass: 3% by mass: 7% by mass)
-Ceria zirconia solid solution powder of Comparative Example 3 (manufactured by Rhodia, CeO 2 : ZrO 2 : La 2 O 3 : Y 2 O 3 = 30% by mass: 60% by mass: 5% by mass: 5% by mass)
試験には、熱重量測定装置（リガク社製、Ｔｈｅｒｍｏ ｐｌｕｓ ＴＧ８１２０）を使用した。サンプル量は２０ｍｇとした。前処理として１％Ｈ２を流通させながら、７００℃の温度条件下３０分間熱処理し、サンプルを還元させた。その後、５０℃の温度条件下で１％Ｈ２＋０．２％Ｏ２の混合ガスを流通させ、サンプルの質量が安定するまで２０分間保持した。その後、１％Ｈ２＋０．２％Ｏ２の混合ガスを流通させた状態で、７００℃まで、２５Ｋ／分の速度で昇温し、昇温前後の質量変化を測定した。なお、サンプル量と組成から、質量変化は、サンプルの酸素吸蔵又は放出を示すことを確認した。 For the test, a thermogravimetric measuring device (Rigaku Corporation, Thermo plus TG8120) was used. The sample amount was 20 mg. As a pretreatment, heat treatment was performed for 30 minutes at a temperature of 700 ° C. while circulating 1% H 2 to reduce the sample. Thereafter, a mixed gas of 1% H 2 + 0.2% O 2 was circulated under a temperature condition of 50 ° C. and held for 20 minutes until the mass of the sample was stabilized. Thereafter, in a state where a mixed gas of 1% H 2 + 0.2% O 2 was circulated, the temperature was increased to 700 ° C. at a rate of 25 K / min, and the mass change before and after the temperature increase was measured. From the sample amount and composition, it was confirmed that the mass change indicates oxygen storage or release of the sample.
図１は、実施例１、比較例２、及び比較例３のセリアジルコニア固溶体粉末について、リッチ雰囲気下における酸素吸蔵量を示したグラフである。
図１から分かるように、比較例２、及び比較例３の様な従来のセリアジルコニア固溶体粉末は、室温〜５０℃の温度領域において酸素を吸蔵する。しかし、比較例２、及び比較例３のセリアジルコニア固溶体粉末は、銅の活性温度領域である２００〜４００℃の温度領域において、室温付近で吸蔵した酸素を放出してしまい、酸素を吸蔵できない。
一方、図１から分かるように、実施例１のセリアジルコニア固溶体粉末は、１５０〜５００℃の広い温度領域において、リッチ雰囲気下においても酸素を吸蔵できる。この結果は、実施例１のセリアジルコニア固溶体粉末が、銅がＮＯｘ浄化活性を示す温度領域において、リッチ雰囲気下においても酸素を吸蔵する結果、銅の活性を向上できることを示唆する。
FIG. 1 is a graph showing the oxygen storage amount in a rich atmosphere for the ceria zirconia solid solution powders of Example 1, Comparative Example 2, and Comparative Example 3.
As can be seen from FIG. 1, conventional ceria zirconia solid solution powders such as Comparative Example 2 and Comparative Example 3 occlude oxygen in a temperature range of room temperature to 50 ° C. However, the ceria zirconia solid solution powders of Comparative Example 2 and Comparative Example 3 release oxygen stored near room temperature in the temperature range of 200 to 400 ° C., which is the active temperature range of copper, and cannot store oxygen.
On the other hand, as can be seen from FIG. 1, the ceria zirconia solid solution powder of Example 1 can occlude oxygen even in a rich atmosphere in a wide temperature range of 150 to 500 ° C. This result suggests that the ceria zirconia solid solution powder of Example 1 can improve the activity of copper as a result of occluding oxygen even in a rich atmosphere in a temperature range where copper exhibits NOx purification activity.
２−２．ＸＲＤ測定
上記実施例１−３、及び比較例１−２のセリアジルコニア固溶体粉末について、Ｘ線回折装置（リガク社製、ＲＩＮＴ２５００）を用いてＸＲＤ測定を行った。
当該ＸＲＤ測定により得られたＸ線回折パターンを用いて、セリアジルコニア固溶体粉末中のパイロクロア構造の含有割合を以下の通り算出した。
まず、熱処理前のセリアジルコニア固溶体粉末のＸ線回折パターンにおいて、２θ角が１４°、２８°、３７°、４４．５°及び５１°におけるベースラインからのピークの高さをそれぞれ求めた。次に、熱処理後のセリアジルコニア固溶体粉末のＸ線回折パターンにおいて、上記２θ角におけるベースラインからのピークの高さをそれぞれ求めた。続いて、上記熱処理前の各ピークの高さを１００％としたときの、対応する上記熱処理後のピークの高さの割合（％）をそれぞれ求めた。最後に、上記５つの２θ角に関する熱処理後のピークの高さの割合の平均を算出し、当該算出した値を、セリアジルコニア固溶体粉末中のパイロクロア構造の含有割合とした。
実施例２−３、及び比較例１のＸ線回折パターンは、それぞれ、熱処理前のセリアジルコニア固溶体粉末である実施例１のＸ線回折パターンと比較した。結果は後述する表２に示す。
2-2. XRD measurement About the ceria zirconia solid solution powder of the said Example 1-3 and the comparative example 1-2, the XRD measurement was performed using the X-ray-diffraction apparatus (the Rigaku company make, RINT2500).
Using the X-ray diffraction pattern obtained by the XRD measurement, the content ratio of the pyrochlore structure in the ceria zirconia solid solution powder was calculated as follows.
First, in the X-ray diffraction pattern of the ceria zirconia solid solution powder before heat treatment, the peak heights from the baseline at 2θ angles of 14 °, 28 °, 37 °, 44.5 °, and 51 ° were determined. Next, in the X-ray diffraction pattern of the ceria zirconia solid solution powder after heat treatment, the peak height from the baseline at the 2θ angle was determined. Subsequently, when the height of each peak before the heat treatment was set to 100%, the corresponding peak height ratio (%) after the heat treatment was determined. Finally, the average ratio of the peak height after the heat treatment for the five 2θ angles was calculated, and the calculated value was used as the content ratio of the pyrochlore structure in the ceria zirconia solid solution powder.
The X-ray diffraction patterns of Example 2-3 and Comparative Example 1 were each compared with the X-ray diffraction pattern of Example 1, which is a ceria zirconia solid solution powder before heat treatment. The results are shown in Table 2 below.
３．排気浄化用触媒の合成
［実施例４］
上記実施例１のセリアジルコニア固溶体粉末３ｇ、及び、アルミナ粉末（サソール社製）６．５ｇの混合粉末を調製した。次に、硝酸銅三水和物１．９ｇ（銅換算で０．５質量％相当）を１００ｍＬのイオン交換水で溶解させ、硝酸銅水溶液を調製した。上記混合粉末に硝酸銅水溶液を含浸させ、セリアジルコニア担体及びアルミナ担体に銅を担持させた。含浸担持後の触媒を、電気炉で６００℃の温度条件下、２時間焼成して、実施例４の排気浄化用触媒１０ｇを得た。なお、排気浄化用触媒全体の質量を１００質量％としたときの銅の担持量は、５質量％であった。
3. Synthesis of exhaust purification catalyst [Example 4]
A mixed powder of 3 g of ceria zirconia solid solution powder of Example 1 and 6.5 g of alumina powder (manufactured by Sasol) was prepared. Next, 1.9 g of copper nitrate trihydrate (corresponding to 0.5% by mass in terms of copper) was dissolved in 100 mL of ion-exchanged water to prepare a copper nitrate aqueous solution. The mixed powder was impregnated with an aqueous copper nitrate solution, and copper was supported on a ceria zirconia support and an alumina support. The impregnated catalyst was calcined in an electric furnace at 600 ° C. for 2 hours to obtain 10 g of an exhaust purification catalyst of Example 4. The amount of copper supported was 5% by mass when the total mass of the exhaust purification catalyst was 100% by mass.
［実施例５］
上記実施例１のセリアジルコニア固溶体粉末５ｇ、及び、アルミナ粉末（サソール社製）４．５ｇの混合粉末を調製した。あとは、実施例４と同様に硝酸銅水溶液の調製、含浸担持及び焼成を行い、実施例５の排気浄化用触媒１０ｇを得た。なお、排気浄化用触媒全体の質量を１００質量％としたときの銅の担持量は、５質量％であった。
[Example 5]
A mixed powder of 5 g of ceria zirconia solid solution powder of Example 1 and 4.5 g of alumina powder (manufactured by Sasol) was prepared. After that, preparation of an aqueous copper nitrate solution, impregnation support and firing were carried out in the same manner as in Example 4 to obtain 10 g of an exhaust purification catalyst of Example 5. The amount of copper supported was 5% by mass when the total mass of the exhaust purification catalyst was 100% by mass.
［実施例６］
上記実施例１のセリアジルコニア固溶体粉末１ｇ、及び、アルミナ粉末（サソール社製）８．５ｇの混合粉末を調製した。あとは、実施例４と同様に硝酸銅水溶液の調製、含浸担持及び焼成を行い、実施例６の排気浄化用触媒１０ｇを得た。なお、排気浄化用触媒全体の質量を１００質量％としたときの銅の担持量は、５質量％であった。
[Example 6]
A mixed powder of 1 g of ceria zirconia solid solution powder of Example 1 and 8.5 g of alumina powder (manufactured by Sasol) was prepared. After that, preparation of an aqueous copper nitrate solution, impregnation support and firing were carried out in the same manner as in Example 4 to obtain 10 g of an exhaust purification catalyst of Example 6. The amount of copper supported was 5% by mass when the total mass of the exhaust purification catalyst was 100% by mass.
［実施例７］
上記実施例２のセリアジルコニア固溶体粉末３ｇ、及び、アルミナ粉末（サソール社製）６．５ｇの混合粉末を調製した。あとは、実施例４と同様に硝酸銅水溶液の調製、含浸担持及び焼成を行い、実施例７の排気浄化用触媒１０ｇを得た。なお、排気浄化用触媒全体の質量を１００質量％としたときの銅の担持量は、５質量％であった。
[Example 7]
A mixed powder of 3 g of ceria zirconia solid solution powder of Example 2 and 6.5 g of alumina powder (manufactured by Sasol) was prepared. After that, preparation of an aqueous copper nitrate solution, impregnation support and firing were carried out in the same manner as in Example 4 to obtain 10 g of an exhaust purification catalyst of Example 7. The amount of copper supported was 5% by mass when the total mass of the exhaust purification catalyst was 100% by mass.
［実施例８］
上記実施例３のセリアジルコニア固溶体粉末３ｇ、及び、アルミナ粉末（サソール社製）６．５ｇの混合粉末を調製した。あとは、実施例４と同様に硝酸銅水溶液の調製、含浸担持及び焼成を行い、実施例８の排気浄化用触媒１０ｇを得た。なお、排気浄化用触媒全体の質量を１００質量％としたときの銅の担持量は、５質量％であった。
[Example 8]
A mixed powder of 3 g of ceria zirconia solid solution powder of Example 3 and 6.5 g of alumina powder (manufactured by Sasol) was prepared. Thereafter, preparation of an aqueous copper nitrate solution, impregnation support and firing were carried out in the same manner as in Example 4 to obtain 10 g of an exhaust purification catalyst of Example 8. The amount of copper supported was 5% by mass when the total mass of the exhaust purification catalyst was 100% by mass.
［比較例４］
硝酸銅三水和物１．９ｇ（銅換算で０．５質量％相当）を１００ｍＬのイオン交換水で溶解させ、硝酸銅水溶液を調製した。上記比較例２のセリアジルコニア固溶体粉末９．５ｇに硝酸銅水溶液を含浸させ、セリアジルコニア担体に銅を担持させた。含浸担持後の触媒を、電気炉で６００℃の温度条件下、２時間焼成して、比較例４の排気浄化用触媒１０ｇを得た。なお、排気浄化用触媒全体の質量を１００質量％としたときの銅の担持量は、５質量％であった。
[Comparative Example 4]
A copper nitrate aqueous solution was prepared by dissolving 1.9 g of copper nitrate trihydrate (corresponding to 0.5% by mass in terms of copper) with 100 mL of ion-exchanged water. 9.5 g of the ceria zirconia solid solution powder of Comparative Example 2 was impregnated with an aqueous copper nitrate solution, and copper was supported on the ceria zirconia support. The impregnated and supported catalyst was calcined in an electric furnace at a temperature of 600 ° C. for 2 hours to obtain 10 g of an exhaust purification catalyst of Comparative Example 4. The amount of copper supported was 5% by mass when the total mass of the exhaust purification catalyst was 100% by mass.
［比較例５］
比較例４において、比較例２のセリアジルコニア固溶体粉末９．５ｇを、アルミナ粉末（サソール社製）９．５ｇに替えたこと以外は、比較例４と同様に硝酸銅水溶液の調製、含浸担持及び焼成を行い、アルミナ担体に銅を担持させた、比較例５の排気浄化用触媒１０ｇを得た。なお、排気浄化用触媒全体の質量を１００質量％としたときの銅の担持量は、５質量％であった。
[Comparative Example 5]
In Comparative Example 4, preparation of an aqueous copper nitrate solution, impregnation support, and the like, as in Comparative Example 4, except that 9.5 g of the ceria zirconia solid solution powder of Comparative Example 2 was replaced with 9.5 g of alumina powder (manufactured by Sasol). Firing was performed to obtain 10 g of an exhaust purification catalyst of Comparative Example 5 in which copper was supported on an alumina carrier. The amount of copper supported was 5% by mass when the total mass of the exhaust purification catalyst was 100% by mass.
［比較例６］
上記比較例１のセリアジルコニア固溶体粉末３ｇ、及び、アルミナ粉末（サソール社製）６．５ｇの混合粉末を調製した。あとは、実施例４と同様に硝酸銅水溶液の調製、含浸担持及び焼成を行い、比較例６の排気浄化用触媒１０ｇを得た。なお、排気浄化用触媒全体の質量を１００質量％としたときの銅の担持量は、５質量％であった。
[Comparative Example 6]
A mixed powder of 3 g of ceria zirconia solid solution powder of Comparative Example 1 and 6.5 g of alumina powder (manufactured by Sasol) was prepared. Thereafter, preparation of an aqueous copper nitrate solution, impregnation support and firing were carried out in the same manner as in Example 4 to obtain 10 g of an exhaust purification catalyst of Comparative Example 6. The amount of copper supported was 5% by mass when the total mass of the exhaust purification catalyst was 100% by mass.
４．排気浄化用触媒の評価
固定床流通式モデルガス反応装置（反応装置：（株）日本ケミカルプラントコンサルタント、分析計：堀場製作所社製、ＭＥＸＡ−６０００ＦＴ、ＭＥＸＡ−７１００Ｈ）により、実施例４−８、及び比較例４−６の排気浄化用触媒の評価を行った。
図３は、触媒評価に用いた固定床流通式モデルガス反応装置の概略模式図である。なお、図１中のガスボンベ（ｇａｓ ｃａｎｉｓｔｅｒ）及びＭＦＣ（Ｍａｓｓ Ｆｌｏｗ Ｃｏｎｔｒｏｌｅｒ）の数は、評価に用いた装置とは必ずしも同じ数とは限らない。
まず、反応管１１の中に、評価に用いる触媒サンプル１２、及びサンプル固定用のグラスウール１３を詰めた後、反応管１１を装置内に設置した。後述する試験ガスをガスボンベから反応管に供給し、反応管から出た成分を、ＦＴ−ＩＲやＧＣ−ＭＳ等の分析機器で分析した。
4). Evaluation of Exhaust Gas Purification Catalyst Example 4-8 using a fixed bed flow model gas reactor (reactor: Nippon Chemical Plant Consultant Co., Ltd., analyzer: manufactured by Horiba, MEXA-6000FT, MEXA-7100H) And the exhaust purification catalyst of Comparative Example 4-6 was evaluated.
FIG. 3 is a schematic diagram of a fixed bed flow type model gas reactor used for catalyst evaluation. Note that the numbers of gas cylinders and MFCs (Mass Flow Controllers) in FIG. 1 are not necessarily the same as the number of apparatuses used for evaluation.
First, the
４−１．リッチ雰囲気下における評価
まず、実施例４−８、及び比較例４−６の排気浄化用触媒の、リッチ雰囲気下における評価を行った。触媒量は３ｇとした。装置の昇温速度は５０Ｋ／ｍｉｎとした。試験ガスの詳細は以下の通りである。
・試験ガス濃度（Ａ／Ｆ＝１４．６相当）
・試験ガス組成：ＮＯｘ（０．３％）、Ｃ３Ｈ６（０．３％Ｃ）、ＣＯ（０．４５％）、Ｏ２（０．５２％）、ＣＯ２（１０％）、Ｈ２Ｏ（３％）（残りはＮ２）
・試験ガス流量：１０Ｌ／ｍｉｎ
下記表１は、実施例４−６、及び比較例４−５の排気浄化用触媒の、リッチ雰囲気下におけるＮＯｘ浄化率（％）の値をまとめた表である。なお、ＮＯｘ浄化率は、以下の式より求めた。
ＮＯｘ浄化率（％）＝｛（触媒の入りＮＯｘ量−触媒の出ＮＯｘ量）／触媒の入りＮＯｘ量｝ｘ１００
また、図２は、２５０℃の温度条件下における、実施例４−６、及び比較例４−５の排気浄化用触媒の、リッチ雰囲気下におけるＮＯｘ浄化率（％）を示した棒グラフである。
4-1. Evaluation under rich atmosphere First, the exhaust purification catalysts of Example 4-8 and Comparative Example 4-6 were evaluated under a rich atmosphere. The amount of catalyst was 3 g. The temperature rising rate of the apparatus was 50 K / min. Details of the test gas are as follows.
・ Test gas concentration (A / F = 14.6 equivalent)
Test gas composition: NOx (0.3%), C 3 H 6 (0.3% C), CO (0.45%), O 2 (0.52%), CO 2 (10%), H 2 O (3%) (the rest is N 2 )
Test gas flow rate: 10 L / min
Table 1 below is a table summarizing the NOx purification rate (%) values in the rich atmosphere of the exhaust purification catalysts of Examples 4-6 and Comparative Example 4-5. The NOx purification rate was obtained from the following formula.
NOx purification rate (%) = {(NOx amount entering catalyst−NOx amount coming out of catalyst) / NOx amount entering catalyst} × 100
FIG. 2 is a bar graph showing the NOx purification rate (%) in a rich atmosphere of the exhaust purification catalysts of Example 4-6 and Comparative Example 4-5 under a temperature condition of 250 ° C.
上記表１より、実施例４−６、及び比較例４−５の排気浄化用触媒の、リッチ雰囲気下における触媒活性について検討する。
まず、比較例４について検討する。比較例４の排気浄化用触媒は、特に３５０〜５００℃の比較的高い温度領域において、実施例４−６、及び比較例４−５の排気浄化用触媒中、最も低いＮＯｘ浄化率を示す。したがって、セリアジルコニア担体に銅を担持させた比較例４の排気浄化用触媒は、リッチ雰囲気下、且つ、３５０〜５００℃の比較的高い温度条件下におけるＮＯｘ浄化能に劣ることが分かる。
From Table 1 above, the catalytic activity of the exhaust purification catalysts of Example 4-6 and Comparative Example 4-5 in a rich atmosphere is examined.
First, Comparative Example 4 is examined. The exhaust purification catalyst of Comparative Example 4 shows the lowest NOx purification rate among the exhaust purification catalysts of Example 4-6 and Comparative Example 4-5, particularly in a relatively high temperature range of 350 to 500 ° C. Therefore, it can be seen that the exhaust purification catalyst of Comparative Example 4 in which copper is supported on a ceria zirconia support is inferior in NOx purification ability under a rich atmosphere and at a relatively high temperature condition of 350 to 500 ° C.
次に、比較例５について検討する。比較例５の排気浄化用触媒は、４５０〜５００℃の温度領域においては、後述する実施例４−６の排気浄化用触媒と同程度のＮＯｘ浄化能を示す。しかし、比較例５の排気浄化用触媒は、４００℃の温度条件下のＮＯｘ浄化率が６０％未満であり、２５０℃以下の温度条件下ではＮＯｘ浄化能を全く示さない。したがって、アルミナ担体に銅を担持させた比較例５の排気浄化用触媒は、リッチ雰囲気下、且つ、特に４００℃以下の温度条件下におけるＮＯｘ浄化能に劣ることが分かる。 Next, Comparative Example 5 will be examined. The exhaust purification catalyst of Comparative Example 5 exhibits the same NOx purification ability as the exhaust purification catalyst of Example 4-6 described later in the temperature range of 450 to 500 ° C. However, the exhaust purification catalyst of Comparative Example 5 has a NOx purification rate of less than 60% under a temperature condition of 400 ° C., and does not show any NOx purification ability under a temperature condition of 250 ° C. or less. Therefore, it can be seen that the exhaust purification catalyst of Comparative Example 5 in which copper is supported on an alumina support is inferior in NOx purification ability under a rich atmosphere and particularly at a temperature of 400 ° C. or lower.
一方、実施例４−６の排気浄化用触媒においては、４５０℃以上のＮＯｘ浄化率は約８０％、４００℃のＮＯｘ浄化率は６０％以上、３５０℃のＮＯｘ浄化率は４０％以上である。また、比較例５の排気浄化用触媒がＮＯｘ浄化能を全く示さない２５０℃の温度条件下においても、実施例４−６の排気浄化用触媒のＮＯｘ浄化率は１０％を超える。さらに、比較例４及び比較例５の排気浄化用触媒がＮＯｘ浄化能を全く示さない２００℃の温度条件下においても、実施例４−６の排気浄化用触媒はＮＯｘ浄化能を発揮する。
以上より、パイロクロア構造を有するセリアジルコニア担体、及びアルミナ担体に銅を担持させた実施例４−６の排気浄化用触媒は、リッチ雰囲気下、且つ、特に２００〜４００℃の比較的低い温度領域において、比較例４及び比較例５の排気浄化用触媒よりも優れたＮＯｘ浄化能を発揮することが分かる。この結果は、パイロクロア構造を有するセリアジルコニア固溶体により、リッチ雰囲気下、且つ、特に２００〜４００℃の比較的低い温度領域において、試験ガス中に微量に存在する酸素が除去された結果、活性点近傍において、試験ガス中に含まれるリッチガス量の割合が増加したことを示唆する。
On the other hand, in the exhaust purification catalyst of Example 4-6, the NOx purification rate at 450 ° C. or higher is about 80%, the NOx purification rate at 400 ° C. is 60% or higher, and the NOx purification rate at 350 ° C. is 40% or higher. . Further, the NOx purification rate of the exhaust purification catalyst of Example 4-6 exceeds 10% even under the temperature condition of 250 ° C. at which the exhaust purification catalyst of Comparative Example 5 does not exhibit any NOx purification ability. Further, the exhaust purification catalyst of Example 4-6 exhibits the NOx purification ability even under a temperature condition of 200 ° C. at which the exhaust purification catalysts of Comparative Example 4 and Comparative Example 5 do not exhibit any NOx purification ability.
From the above, the ceria zirconia support having a pyrochlore structure and the exhaust purification catalyst of Example 4-6 in which copper is supported on an alumina support are in a rich atmosphere and particularly in a relatively low temperature range of 200 to 400 ° C. It can be seen that the NOx purification ability superior to the exhaust purification catalysts of Comparative Example 4 and Comparative Example 5 is exhibited. This result shows that the ceria zirconia solid solution having a pyrochlore structure removes a small amount of oxygen in the test gas in a rich atmosphere and particularly in a relatively low temperature range of 200 to 400 ° C. This suggests that the ratio of the amount of rich gas contained in the test gas has increased.
下記表２は、実施例１−３、及び比較例１−２のセリアジルコニア固溶体粉末中のパイロクロア構造の含有割合（％）、並びに、対応する排気浄化用触媒である実施例４、実施例７−８、比較例６、及び比較例４のリッチ雰囲気下におけるＮＯｘ浄化率（％）の値をまとめた表である。なお、ＮＯｘ浄化率は、上述した式より求めた。 Table 2 below shows the content ratio (%) of the pyrochlore structure in the ceria zirconia solid solution powder of Example 1-3 and Comparative Example 1-2, and Examples 4 and 7 which are the corresponding exhaust purification catalysts. 10 is a table summarizing values of NOx purification rate (%) in a rich atmosphere of −8, Comparative Example 6, and Comparative Example 4; The NOx purification rate was obtained from the above-described formula.
まず、比較例２のセリアジルコニア固溶体粉末について検討する。比較例２は、市販のセリアジルコニア固溶体粉末であり、パイロクロア構造を有しない。したがって、比較例２のセリアジルコニア固溶体粉末を使用した比較例４の排気浄化用触媒は、リッチ雰囲気下、且つ、２５０℃の温度条件下におけるＮＯｘ浄化能に劣る。 First, the ceria zirconia solid solution powder of Comparative Example 2 will be examined. Comparative Example 2 is a commercially available ceria zirconia solid solution powder and does not have a pyrochlore structure. Therefore, the exhaust purification catalyst of Comparative Example 4 using the ceria zirconia solid solution powder of Comparative Example 2 is inferior in NOx purification ability under a rich atmosphere and at a temperature of 250 ° C.
一方、実施例１−３のセリアジルコニア固溶体粉末中のパイロクロア構造の含有割合は２０％以上である。したがって、実施例１−３のセリアジルコニア固溶体粉末をそれぞれ使用した実施例４、７、及び８の排気浄化用触媒は、リッチ雰囲気下、且つ、２５０℃の温度条件下においても９％以上のＮＯｘ浄化率を示す。
実施例１−３のセリアジルコニア固溶体粉末を互いに比較すると、より高温で加熱するほどパイロクロア構造の割合が低くなることが分かる。これは、高温条件下且つ酸化雰囲気下においては、パイロクロア構造が不安定となることを示唆している。
なお、比較例１のように、１２００℃で１０時間焼成した場合には、セリアジルコニア固溶体粉末中のパイロクロア構造の含有割合は１割未満になる。したがって、比較例１のセリアジルコニア固溶体粉末を使用した比較例６の排気浄化用触媒は、比較例２と同程度のＮＯｘ浄化率しか示さない。
表２から、セリアジルコニア固溶体粉末中のパイロクロア構造の含有割合が高いと、ＮＯｘ浄化率の割合も高くなることが分かる。
On the other hand, the content ratio of the pyrochlore structure in the ceria zirconia solid solution powder of Example 1-3 is 20% or more. Therefore, the exhaust purification catalysts of Examples 4, 7, and 8 using the ceria zirconia solid solution powder of Example 1-3 are each 9% or more of NOx under a rich atmosphere and at a temperature of 250 ° C. Indicates the purification rate.
When the ceria zirconia solid solution powders of Example 1-3 are compared with each other, it can be seen that the proportion of the pyrochlore structure decreases as the temperature is higher. This suggests that the pyrochlore structure becomes unstable under high temperature conditions and in an oxidizing atmosphere.
In addition, when it bakes at 1200 degreeC for 10 hours like the comparative example 1, the content rate of the pyrochlore structure in a ceria zirconia solid solution powder will be less than 10%. Therefore, the exhaust purification catalyst of Comparative Example 6 using the ceria zirconia solid solution powder of Comparative Example 1 shows only the same NOx purification rate as Comparative Example 2.
From Table 2, it can be seen that when the content ratio of the pyrochlore structure in the ceria zirconia solid solution powder is high, the ratio of the NOx purification rate is also increased.
４−２．ストイキ雰囲気下における評価
次に、ストイキ雰囲気下における評価を行った。触媒量は３ｇとした。装置の昇温速度は５０Ｋ／ｍｉｎとした。試験ガスの詳細は以下の通りである。
・試験ガス濃度（Ａ／Ｆ＝１４．２相当）
・試験ガス組成：ＮＯｘ（０．３％）、Ｃ３Ｈ６（０．３％Ｃ）、ＣＯ（０．９％）、Ｏ２（０．３５％）、ＣＯ２（１０％）、Ｈ２Ｏ（３％）（残りはＮ２）
・試験ガス流量：１０Ｌ／ｍｉｎ
下記表３は、実施例４、及び比較例４−５の排気浄化用触媒の、ストイキ雰囲気下におけるＮＯｘ浄化率（％）の値をまとめた表である。なお、ＮＯｘ浄化率は、上述した式より求めた。
4-2. Evaluation under stoichiometric atmosphere Next, evaluation under a stoichiometric atmosphere was performed. The amount of catalyst was 3 g. The temperature rising rate of the apparatus was 50 K / min. Details of the test gas are as follows.
Test gas concentration (A / F = 14.2 equivalent)
Test gas composition: NOx (0.3%), C 3 H 6 (0.3% C), CO (0.9%), O 2 (0.35%), CO 2 (10%), H 2 O (3%) (the rest is N 2 )
Test gas flow rate: 10 L / min
Table 3 below is a table summarizing the NOx purification rate (%) values in the stoichiometric atmosphere of the exhaust purification catalysts of Example 4 and Comparative Example 4-5. The NOx purification rate was obtained from the above-described formula.
上記表３より、実施例４、及び比較例４−５の排気浄化用触媒の、ストイキ雰囲気下における触媒活性について検討する。
まず、比較例４について検討する。比較例４の排気浄化用触媒は、特に４００〜５００℃の比較的高い温度領域において、実施例４、及び比較例４−５の排気浄化用触媒中、最も低いＮＯｘ浄化率を示す。したがって、セリアジルコニア担体に銅を担持させた比較例４の排気浄化用触媒は、ストイキ雰囲気下、且つ、４００〜５００℃の比較的高い温度条件下におけるＮＯｘ浄化能に劣ることが分かる。
From Table 3 above, the catalytic activity of the exhaust purification catalysts of Example 4 and Comparative Example 4-5 in a stoichiometric atmosphere is examined.
First, Comparative Example 4 is examined. The exhaust purification catalyst of Comparative Example 4 shows the lowest NOx purification rate among the exhaust purification catalysts of Example 4 and Comparative Example 4-5, particularly in a relatively high temperature range of 400 to 500 ° C. Therefore, it can be seen that the exhaust purification catalyst of Comparative Example 4 in which copper is supported on a ceria zirconia support is inferior in NOx purification ability under a stoichiometric atmosphere and at a relatively high temperature condition of 400 to 500 ° C.
次に、比較例５について検討する。比較例５の排気浄化用触媒は、特に２５０〜３５０℃の比較的低い温度領域において、実施例４、及び比較例４−５の排気浄化用触媒中、最も低いＮＯｘ浄化率を示す。したがって、アルミナ担体に銅を担持させた比較例５の排気浄化用触媒は、ストイキ雰囲気下、且つ、特に２５０〜３５０℃の比較的低い温度条件下におけるＮＯｘ浄化能に劣ることが分かる。 Next, Comparative Example 5 will be examined. The exhaust purification catalyst of Comparative Example 5 exhibits the lowest NOx purification rate among the exhaust purification catalysts of Example 4 and Comparative Example 4-5, particularly in a relatively low temperature range of 250 to 350 ° C. Therefore, it can be seen that the exhaust purification catalyst of Comparative Example 5 in which copper is supported on an alumina carrier is inferior in NOx purification ability under a stoichiometric atmosphere and particularly under a relatively low temperature condition of 250 to 350 ° C.
一方、実施例４の排気浄化用触媒においては、４５０℃以上のＮＯｘ浄化率は４３％以上、４００℃のＮＯｘ浄化率は３０％、３５０℃のＮＯｘ浄化率は１５％である。また、比較例５の排気浄化用触媒がＮＯｘ浄化能を全く示さない２５０〜３００℃の温度領域においても、実施例４の排気浄化用触媒はＮＯｘ浄化能を発揮する。
以上より、パイロクロア構造を有するセリアジルコニア担体、及びアルミナ担体に銅を担持させた実施例４の排気浄化用触媒は、ストイキ雰囲気下、且つ、特に２５０〜５００℃の温度領域において、比較例４及び比較例５の排気浄化用触媒よりも優れたＮＯｘ浄化能を発揮することが分かる。
On the other hand, in the exhaust purification catalyst of Example 4, the NOx purification rate at 450 ° C. or higher is 43% or higher, the NOx purification rate at 400 ° C. is 30%, and the NOx purification rate at 350 ° C. is 15%. Further, the exhaust purification catalyst of Example 4 exhibits the NOx purification ability even in a temperature range of 250 to 300 ° C. at which the exhaust purification catalyst of Comparative Example 5 does not exhibit any NOx purification ability.
From the above, the ceria zirconia support having a pyrochlore structure and the exhaust purification catalyst of Example 4 in which copper was supported on an alumina support were compared with those in Comparative Example 4 and in a stoichiometric atmosphere, particularly in the temperature range of 250 to 500 ° C. It can be seen that the NOx purification ability superior to that of the exhaust purification catalyst of Comparative Example 5 is exhibited.
１１ 反応管
１２ 触媒サンプル
１３ サンプル固定用のグラスウール
11
Claims (6)
マグネシウム、カルシウム、バリウム、スカンジウム、イットリウム、ランタン、セリウム、プラセオジム、ネオジム、アルミニウム、及びジルコニウムからなる群より選ばれる２以上の元素を含有し、且つ、パイロクロア構造を一部又は全部に有する金属酸化物、並びに、
銅、鉄、コバルト、及びニッケルからなる群より選ばれる１又は２以上の卑金属を含有することを特徴とする、内燃機関の排気浄化用触媒。 An exhaust gas purification catalyst for an internal combustion engine that purifies exhaust gas generated by stoichiometric combustion or rich combustion,
Metal oxide containing two or more elements selected from the group consisting of magnesium, calcium, barium, scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, aluminum, and zirconium, and having a pyrochlore structure in part or in whole As well as
An exhaust gas purifying catalyst for an internal combustion engine, comprising one or more base metals selected from the group consisting of copper, iron, cobalt, and nickel.
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| CN103638919B (en) * | 2013-12-20 | 2016-08-17 | 湖南稀土金属材料研究院 | Auto-exhaust catalyst scandium stablizes cerium zirconium composite powder, its preparation method and auto-exhaust catalyst |
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