JP2017144423A - Catalyst for exhaust purification and method for producing the same - Google Patents
Catalyst for exhaust purification and method for producing the same Download PDFInfo
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- 239000003054 catalyst Substances 0.000 title claims abstract description 86
- 238000000746 purification Methods 0.000 title claims abstract description 38
- 238000004519 manufacturing process Methods 0.000 title claims description 5
- 229910052684 Cerium Inorganic materials 0.000 claims abstract description 21
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 20
- 239000002245 particle Substances 0.000 claims description 49
- 239000011572 manganese Substances 0.000 claims description 39
- 239000011164 primary particle Substances 0.000 claims description 15
- QGLKJKCYBOYXKC-UHFFFAOYSA-N nonaoxidotritungsten Chemical compound O=[W]1(=O)O[W](=O)(=O)O[W](=O)(=O)O1 QGLKJKCYBOYXKC-UHFFFAOYSA-N 0.000 claims description 11
- 229910001930 tungsten oxide Inorganic materials 0.000 claims description 11
- 239000007864 aqueous solution Substances 0.000 claims description 9
- 239000003638 chemical reducing agent Substances 0.000 claims description 5
- 239000011163 secondary particle Substances 0.000 claims description 5
- 238000002441 X-ray diffraction Methods 0.000 claims description 4
- 238000002156 mixing Methods 0.000 claims description 4
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 claims description 3
- -1 cerium ions Chemical class 0.000 claims description 3
- 229910001437 manganese ion Inorganic materials 0.000 claims description 3
- 238000001354 calcination Methods 0.000 claims 1
- 239000007789 gas Substances 0.000 description 18
- 230000000052 comparative effect Effects 0.000 description 15
- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitrogen oxide Inorganic materials O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 15
- 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 14
- 230000000694 effects Effects 0.000 description 12
- 239000000446 fuel Substances 0.000 description 10
- NUJOXMJBOLGQSY-UHFFFAOYSA-N manganese dioxide Chemical compound O=[Mn]=O NUJOXMJBOLGQSY-UHFFFAOYSA-N 0.000 description 10
- 238000006243 chemical reaction Methods 0.000 description 9
- 229940082328 manganese acetate tetrahydrate Drugs 0.000 description 7
- CESXSDZNZGSWSP-UHFFFAOYSA-L manganese(2+);diacetate;tetrahydrate Chemical compound O.O.O.O.[Mn+2].CC([O-])=O.CC([O-])=O CESXSDZNZGSWSP-UHFFFAOYSA-L 0.000 description 7
- 239000006069 physical mixture Substances 0.000 description 7
- 229910000420 cerium oxide Inorganic materials 0.000 description 6
- 238000000034 method Methods 0.000 description 6
- BMMGVYCKOGBVEV-UHFFFAOYSA-N oxo(oxoceriooxy)cerium Chemical compound [Ce]=O.O=[Ce]=O BMMGVYCKOGBVEV-UHFFFAOYSA-N 0.000 description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 6
- 238000005259 measurement Methods 0.000 description 5
- 229910000510 noble metal Inorganic materials 0.000 description 5
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- 238000003917 TEM image Methods 0.000 description 4
- 238000011156 evaluation Methods 0.000 description 4
- 239000002244 precipitate Substances 0.000 description 4
- QGZKDVFQNNGYKY-UHFFFAOYSA-O Ammonium Chemical compound [NH4+] QGZKDVFQNNGYKY-UHFFFAOYSA-O 0.000 description 3
- ATRRKUHOCOJYRX-UHFFFAOYSA-N Ammonium bicarbonate Chemical compound [NH4+].OC([O-])=O ATRRKUHOCOJYRX-UHFFFAOYSA-N 0.000 description 3
- 235000012501 ammonium carbonate Nutrition 0.000 description 3
- 239000001099 ammonium carbonate Substances 0.000 description 3
- 238000000975 co-precipitation Methods 0.000 description 3
- 238000002485 combustion reaction Methods 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- 229910052760 oxygen Inorganic materials 0.000 description 3
- 229910052763 palladium Inorganic materials 0.000 description 3
- 229910052697 platinum Inorganic materials 0.000 description 3
- 239000000843 powder Substances 0.000 description 3
- 239000000243 solution Substances 0.000 description 3
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 2
- 230000010718 Oxidation Activity Effects 0.000 description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
- 239000010953 base metal Substances 0.000 description 2
- 230000003197 catalytic effect Effects 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 238000001035 drying Methods 0.000 description 2
- 238000000921 elemental analysis Methods 0.000 description 2
- 150000002696 manganese Chemical class 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 239000001301 oxygen Substances 0.000 description 2
- 238000010405 reoxidation reaction Methods 0.000 description 2
- 229910052703 rhodium Inorganic materials 0.000 description 2
- 238000003756 stirring Methods 0.000 description 2
- DZKDPOPGYFUOGI-UHFFFAOYSA-N tungsten(iv) oxide Chemical compound O=[W]=O DZKDPOPGYFUOGI-UHFFFAOYSA-N 0.000 description 2
- 238000004438 BET method Methods 0.000 description 1
- 229920000049 Carbon (fiber) Polymers 0.000 description 1
- 239000004215 Carbon black (E152) Substances 0.000 description 1
- 150000000703 Cerium Chemical class 0.000 description 1
- PRJCXLZLFQTCLE-UHFFFAOYSA-N [W+]=O Chemical compound [W+]=O PRJCXLZLFQTCLE-UHFFFAOYSA-N 0.000 description 1
- 239000003463 adsorbent Substances 0.000 description 1
- 229910021529 ammonia Inorganic materials 0.000 description 1
- 150000003863 ammonium salts Chemical class 0.000 description 1
- 230000033228 biological regulation Effects 0.000 description 1
- 229910002091 carbon monoxide Inorganic materials 0.000 description 1
- CETPSERCERDGAM-UHFFFAOYSA-N ceric oxide Chemical compound O=[Ce]=O CETPSERCERDGAM-UHFFFAOYSA-N 0.000 description 1
- GWXLDORMOJMVQZ-UHFFFAOYSA-N cerium Chemical compound [Ce] GWXLDORMOJMVQZ-UHFFFAOYSA-N 0.000 description 1
- 229910000422 cerium(IV) oxide Inorganic materials 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 238000010304 firing Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 238000005342 ion exchange Methods 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 229940093474 manganese carbonate Drugs 0.000 description 1
- 235000006748 manganese carbonate Nutrition 0.000 description 1
- 239000011656 manganese carbonate Substances 0.000 description 1
- 229910000016 manganese(II) carbonate Inorganic materials 0.000 description 1
- XMWCXZJXESXBBY-UHFFFAOYSA-L manganese(ii) carbonate Chemical compound [Mn+2].[O-]C([O-])=O XMWCXZJXESXBBY-UHFFFAOYSA-L 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 239000010970 precious metal Substances 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 239000002344 surface layer Substances 0.000 description 1
- 150000003657 tungsten Chemical class 0.000 description 1
- 229910001931 tungsten(III) oxide Inorganic materials 0.000 description 1
Landscapes
- Exhaust Gas After Treatment (AREA)
- Exhaust Gas Treatment By Means Of Catalyst (AREA)
- Catalysts (AREA)
Abstract
Description
本発明は、排ガス浄化用触媒に関し、詳細にはＮＯｘ選択還元触媒に関する。 The present invention relates to an exhaust gas purification catalyst, and more particularly to a NO x selective reduction catalyst.
近年、地球環境保護の観点から、排ガス規制が世界的に年々強化されている。この対応策として、内燃機関においては、排ガス浄化用触媒が用いられる。この排ガス浄化用触媒において、排ガス中のハイドロカーボン（以下、ＨＣと略記することもある。）、ＣＯ及び窒素酸化物（以下、ＮＯｘと略記することもある。）を効率的に除去するために、触媒成分としてＰｔ、Ｐｄ、Ｒｈ等の貴金属などが使用されている。 In recent years, exhaust gas regulations have been strengthened worldwide year by year from the viewpoint of protecting the global environment. As a countermeasure, an exhaust gas purifying catalyst is used in an internal combustion engine. In this exhaust gas purifying catalyst, hydrocarbon (hereinafter also abbreviated as HC), CO and nitrogen oxides (hereinafter also abbreviated as NO x ) in the exhaust gas are efficiently removed. In addition, noble metals such as Pt, Pd, and Rh are used as catalyst components.
この排ガス浄化用触媒を用いた自動車、例えばガソリンエンジン車あるいはジーゼルエンジン車では触媒活性とともに燃費の向上を図るために種々のシステムが用いられている。例えば、燃費を上げるために定常運転中では空燃比（Ａ／Ｆ）がリーン（酸素過剰）の条件で燃焼させ、触媒活性を向上させるために一時的にストイキ（理論空燃比、Ａ／Ｆ＝１４．７）〜リッチ（燃料過剰）の条件で燃焼させている。 Various systems are used to improve fuel efficiency as well as catalyst activity in automobiles using the exhaust gas-purifying catalyst, such as gasoline engine cars or diesel engine cars. For example, in order to improve fuel efficiency, combustion is performed under conditions where the air-fuel ratio (A / F) is lean (excess oxygen) during steady operation, and stoichiometric (theoretical air-fuel ratio, A / F = 14.7) Burning under rich (fuel excess) conditions.
これは、従来公知のＰｔ、Ｐｄ、Ｒｈ等の貴金属などの触媒は酸化条件でのＮＯｘ浄化性能が低く、浄化性能を高めるためにＨＣまたはＣＯ等を加えることによる還元雰囲気を必要とするためである。この触媒活性への影響から、定常運転中でも空燃比（Ａ／Ｆ）を大きくできず、前記貴金属などの触媒では燃費の向上に限界がある。 This is known Pt, Pd, catalysts such as noble metals Rh, etc. have low the NO x purification performance in an oxidizing conditions, it requires a reducing atmosphere by the addition of HC or CO, etc. in order to improve the purification performance It is. Because of this influence on the catalyst activity, the air-fuel ratio (A / F) cannot be increased even during steady operation, and there is a limit to the improvement of fuel consumption with catalysts such as the noble metals.
このように従来公知の貴金属などの触媒では、浄化用触媒を一時的に還元雰囲気にするための燃料と、エンジンでの空燃比（Ａ／Ｆ）を低くすることとが必要であった。そして、自動車用エンジンをはじめ内燃機関の燃費を向上するために、例えば、リーン雰囲気下でＮＯｘ浄化性能を発揮することのできる新たな浄化用触媒が求められていた。 As described above, conventionally known catalysts such as precious metals require a fuel for temporarily setting the purification catalyst in a reducing atmosphere and a low air-fuel ratio (A / F) in the engine. In order to improve the fuel efficiency of internal combustion engines including automobile engines, there has been a demand for new purification catalysts that can exhibit NO x purification performance in a lean atmosphere, for example.
ＮＯｘ浄化用触媒の性能向上について種々の改良の試みがなされている。 Attempts various improvements have been made for the improvement in performance of the NO x purifying catalyst.
特許文献１には、アンモニア等の還元剤の存在下で、比較的低温で窒素酸化物を還元除去する、二酸化マンガンが活性炭素繊維に担持されている低温脱硝触媒が記載されている。 Patent Document 1 describes a low-temperature denitration catalyst in which manganese dioxide is supported on activated carbon fibers, which reduces and removes nitrogen oxides at a relatively low temperature in the presence of a reducing agent such as ammonia.
特許文献２には、酸化セリウムからなる、窒素酸化物用吸着材が記載されている。 Patent Document 2 describes an adsorbent for nitrogen oxide made of cerium oxide.
特許文献３には、酸化セリウムに少量のマンガンを担持した窒素酸化物除去用触媒が記載されている。 Patent Document 3 describes a nitrogen oxide removing catalyst in which a small amount of manganese is supported on cerium oxide.
特許文献４には、マンガンとセリウムの複合酸化物からなる窒素酸化物除去触媒が記載されている。 Patent Document 4 describes a nitrogen oxide removal catalyst comprising a complex oxide of manganese and cerium.
しかし、上記の従来の発明では、低温領域でのＮＯｘ浄化能が不充分であった。こうしたことから、低温においてより優れたＮＯ選択還元能を有し、よりＮＯｘ浄化率の高い触媒が求められている。 However, in the above-described conventional invention, the NO x purification ability in the low temperature region is insufficient. For these reasons, there is a demand for a catalyst having a superior NO selective reduction ability at a low temperature and having a higher NO x purification rate.
本発明者らは、鋭意努力した結果、ＭｎＯ2粒子の表面上にＣｅＯ2粒子を、ＭｎとＣｅの合計量に対してＣｅの量（Ｃｅ／（Ｍｎ＋Ｃｅ））を０モル％超、４０モル％以下として担持させてなる排ガス浄化用触媒が、ＮＯｘ選択還元能において優れた特性を示すことを見いだし、本発明に至ったものである。 As a result of diligent efforts, the inventors have made CeO 2 particles on the surface of MnO 2 particles, and the amount of Ce (Ce / (Mn + Ce)) is more than 0 mol% and 40 mol with respect to the total amount of Mn and Ce. It has been found that an exhaust gas purifying catalyst that is supported in an amount of less than or equal to% exhibits excellent characteristics in NO x selective reduction ability, leading to the present invention.
本発明の態様は、以下のようである。
（１）ＭｎＯ2粒子の表面上にＣｅＯ2粒子を担持した排ガス浄化用触媒であって、この触媒中のＭｎとＣｅの合計量に対するＣｅの量（Ｃｅ／（Ｍｎ＋Ｃｅ））が０モル％超、４０モル％以下である排ガス浄化用触媒。
Aspects of the present invention are as follows.
(1) A catalyst for exhaust gas purification in which CeO 2 particles are supported on the surface of MnO 2 particles, and the amount of Ce (Ce / (Mn + Ce)) with respect to the total amount of Mn and Ce in the catalyst exceeds 0 mol% An exhaust gas purifying catalyst that is 40 mol% or less.
（２）ＣｅＯ2の一次粒子がＭｎＯ2の一次粒子上に担持され、このＭｎＯ2の一次粒子が凝集して二次粒子の形態として存在する、（１）の排ガス浄化用触媒。 (2) primary particles of CeO 2 is supported on the primary particles of MnO 2, the primary particles of the MnO 2 is present in the form of aggregate into secondary particles, the catalyst for purification of exhaust gas (1).
（３）Ｘ線回折により測定し、ＭｎＯ2に起因するピークとＣｅＯ2に起因するピークの両者を有する、（１）又は（２）に記載の排ガス浄化用触媒。 (3) The exhaust gas purifying catalyst according to (1) or (2), which has both a peak due to MnO 2 and a peak due to CeO 2 as measured by X-ray diffraction.
（４）さらにタングステン酸化物粒子が担持されている、（１）〜（３）のいずれかに記載の排ガス浄化用触媒。 (4) The exhaust gas purifying catalyst according to any one of (1) to (3), further supporting tungsten oxide particles.
（５）マンガンイオンとセリウムイオンを、ＭｎとＣｅの合計量に対するＣｅの量（Ｃｅ／（Ｍｎ＋Ｃｅ））が０モル％超、４０モル％以下の比で含む水溶液と、炭酸イオンを含む還元剤を溶解した水溶液とを混合して粒子を析出させた後、焼成することを含む、（１）〜（３）のいずれかに記載の排ガス浄化用触媒の製造方法。 (5) An aqueous solution containing manganese ions and cerium ions with a ratio of Ce (Ce / (Mn + Ce)) of more than 0 mol% and 40 mol% or less with respect to the total amount of Mn and Ce, and a reducing agent containing carbonate ions The method for producing an exhaust gas purifying catalyst according to any one of (1) to (3), which comprises mixing particles with an aqueous solution in which particles are precipitated to deposit particles, followed by firing.
本発明の態様により、より優れたＮＯ選択還元能を有し、よりＮＯｘ浄化率が高く、ＮＯｘ浄化開始温度を低下させた排ガス浄化触媒を提供することが可能となる。 According to the aspect of the present invention, it is possible to provide an exhaust gas purification catalyst having a superior NO selective reduction ability, a higher NO x purification rate, and a reduced NO x purification start temperature.
本発明に係る触媒は、ＭｎＯ2粒子の表面上にＣｅＯ2粒子を担持した排ガス浄化用触媒である。 The catalyst according to the present invention is an exhaust gas purifying catalyst in which CeO 2 particles are supported on the surface of MnO 2 particles.
この触媒中のＣｅの含有量は、ＭｎとＣｅの合計量を基準として（Ｃｅ／（Ｍｎ＋Ｃｅ））、０モル％超、４０モル％以下である。Ｃｅ含有量が４０モル％を超えると、相対的にＭｎＯ2の含有量が少なくなり、ＮＯx浄化能が低下してしまう。 The Ce content in the catalyst is more than 0 mol% and 40 mol% or less based on the total amount of Mn and Ce (Ce / (Mn + Ce)). If the Ce content exceeds 40 mol%, the content of MnO 2 is relatively reduced, and the NOx purification ability is lowered.
本発明に係る触媒においては、１つの結晶格子内にＭｎとＣｅが混在する複合体ではなく、ＭｎＯ2粒子とＣｅＯ2粒子が別個の粒子として存在し、ＭｎＯ2の粒子表層にＣｅＯ2粒子が高分散な状態で担持されている。このことは、本発明に係る触媒をＸ線回折により測定した場合に、ＭｎＯ2に起因するピーク（２θ＝２７．２３６付近）とＣｅＯ2に起因するピーク（２θ＝４７．４７９付近）の両者が観察されることからも裏付けられる。 In the catalyst according to the present invention, rather than the complex Mn and Ce are mixed in a single crystal lattice, present as discrete particles MnO 2 particles and CeO 2 particles, the CeO 2 particles in the particle surface layer of MnO 2 It is supported in a highly dispersed state. This means that when the catalyst according to the present invention is measured by X-ray diffraction, both a peak due to MnO 2 (around 2θ = 27.236) and a peak due to CeO 2 (around 2θ = 47.479). This is supported by the observation.
また、本発明に係る触媒においては、ＣｅＯ2の一次粒子がＭｎＯ2の一次粒子上に担持され、このＭｎＯ2の一次粒子が凝集して二次粒子の形態として存在していると考えられる。このように、ＣｅＯ2の一次粒子がＭｎＯ2の一次粒子上に担持されているため、二次粒子の表面に微細なＣｅＯ2の一次粒子が分散して露出しており、本発明に係る触媒においては、ＭｎＯ2粒子とＣｅＯ2粒子の物理混合物と比較して、比表面積が大きくなっている。 In the catalyst according to the present invention, primary particles of CeO 2 is supported on the primary particles of MnO 2, the primary particles of the MnO 2 is considered to be present in the form of aggregate into secondary particles. Thus, since the primary particles of CeO 2 are supported on the primary particles of MnO 2 , fine primary particles of CeO 2 are dispersedly exposed on the surface of the secondary particles, and the catalyst according to the present invention. , The specific surface area is larger than that of a physical mixture of MnO 2 particles and CeO 2 particles.
ＭｎＯ2粒子とＣｅＯ2粒子の平均粒径は、十分な活性を発揮するため、当該分野において一般的な測定方法により測定し、１〜１００ｎｍであることが好ましい。また、その製造工程において、Ｃｅの使用量を、ＭｎとＣｅの合計量を基準として（Ｃｅ／（Ｍｎ＋Ｃｅ））、０モル％超、４０モル％以下とすることにより、相対的にＭｎの量が多く、結果として得られるＭｎＯ2粒子の大きさ（粒径）はＣｅＯ2粒子の大きさ（粒径）よりも大きくなっていると考えられる。 The average particle diameter of the MnO 2 particles and CeO 2 particles exhibits sufficient activity, and is preferably measured by a general measurement method in the field and is preferably 1 to 100 nm. Further, in the production process, the amount of Ce used is relatively greater than 0 mol% and not more than 40 mol% based on the total amount of Mn and Ce (Ce / (Mn + Ce)). It is considered that the size (particle size) of the resulting MnO 2 particles is larger than the size (particle size) of the CeO 2 particles.
エンジン始動時などの低温においては、下式で示されるFast-ＳＣＲ反応が進行する。
２ＮＨ3＋ＮＯ＋ＮＯ2→２Ｎ2＋３Ｈ2Ｏ
図１に、本発明の触媒が関与する、Fast-ＳＣＲ反応の素反応を示す。図１に示す反応において、ＮＯ2がＭｎの再酸化を担っているが、通常の反応系ではＮＯ2は存在しない。ところが、本発明の触媒においては、微細に分散担持されたＣｅＯ2が存在することにより、下式
２ＣｅＯ2→Ｃｅ2Ｏ3＋Ｏ2
により表されるセリアのレドックスに伴い、移動するＯ2がＮＯを酸化してＮＯ2を供給し、Ｍｎn+→Ｍｎ4+というＭｎの再酸化を促進し、結果として上記のFast-ＳＣＲ反応を促進することになり、低温におけるＮＯx浄化率を向上させることができる。
At a low temperature such as when the engine is started, the Fast-SCR reaction shown by the following formula proceeds.
2NH 3 + NO + NO 2 → 2N 2 + 3H 2 O
FIG. 1 shows an elementary reaction of the Fast-SCR reaction involving the catalyst of the present invention. In the reaction shown in FIG. 1, NO 2 is responsible for reoxidation of Mn, but NO 2 does not exist in a normal reaction system. However, in the catalyst of the present invention, the presence of CeO 2 which is finely dispersed and supported, the following formula 2CeO 2 → Ce 2 O 3 + O 2
With the ceria redox represented by the formula, the moving O 2 oxidizes NO to supply NO 2 , and promotes the Mn n + → Mn 4+ Mn reoxidation, resulting in the above Fast-SCR reaction. Therefore, the NOx purification rate at a low temperature can be improved.
本発明に係る触媒においては、上記のＣｅＯ2の一次粒子とＭｎＯ2の一次粒子からなる二次粒子上にタングステン酸化物が担持されていることが好ましい。触媒中にＣｅＯ2が存在すると、高温において、ＣｅによるＮＨ3の酸化によってＮＯx化が生ずるおそれがあるが、タングステン酸化物を触媒表面に担持させておくことによって、高温におけるＣｅのＮＨ3酸化活性を抑制することができ、高温におけるＮＯx浄化率低下を抑制することができる。タングステン酸化物の担持量は、多すぎるとＣｅＯ2及びＭｎＯ2の相対量が低下し、触媒活性の低下につながるため、ＣｅＯ2及びＭｎＯ2の合計量に対して５〜１０重量％であることが好ましい。このタングステン酸化物としては、酸化タングステン（III）、酸化タングステン（IV）、酸化タングステン（Ｖ）などを用いることができる。 In the catalyst according to the present invention, it is preferable that tungsten oxide is supported on secondary particles composed of the primary particles of CeO 2 and the primary particles of MnO 2 . When CeO 2 is present in the catalyst, there is a possibility that NO x conversion may occur due to the oxidation of NH 3 by Ce at high temperature. However, by supporting tungsten oxide on the catalyst surface, the NH 3 oxidation activity of Ce at high temperature Can be suppressed, and a reduction in the NOx purification rate at high temperatures can be suppressed. If the supported amount of tungsten oxide is too large, the relative amount of CeO 2 and MnO 2 will decrease, leading to a decrease in catalytic activity, so it should be 5 to 10% by weight based on the total amount of CeO 2 and MnO 2. Is preferred. As the tungsten oxide, tungsten (III) oxide, tungsten (IV) oxide, tungsten oxide (V), or the like can be used.
本発明に係る触媒においては、ＭｎＯ2粒子とＣｅＯ2粒子以外の他の成分を含んでいてもよい。この他の成分としては、排ガス浄化用触媒に用いられる公知の成分を制限なく用いることができる。 The catalyst according to the present invention may contain components other than MnO 2 particles and CeO 2 particles. As the other components, known components used for exhaust gas purification catalysts can be used without limitation.
例えば、本発明に係る触媒は、不純物として、触媒中に、Ｍｎ、Ｔｉ以外の貴金属および／または卑金属を、触媒全体に基づいて、約１モル％以下の量含んでいてもよい。また、本発明に係る触媒は、触媒上に、Ｐｔ、Ｒｈ、Ｐｄ、Ｆｅ，Ｃｕなどの貴金属および／または卑金属を、触媒全体の質量に基づいて、約０．０１ｗｔ％〜約１ｗｔ％の量で担持することができる。 For example, the catalyst according to the present invention may contain noble metals and / or base metals other than Mn and Ti as impurities in an amount of about 1 mol% or less based on the whole catalyst. Further, the catalyst according to the present invention contains noble metals such as Pt, Rh, Pd, Fe, Cu and / or base metals on the catalyst in an amount of about 0.01 wt% to about 1 wt% based on the mass of the entire catalyst. Can be supported.
本発明に係る触媒の製造方法としては、一般的な逆共沈法を用いることができる。具体的には、セリウムの塩（例えば硝酸セリウム等）とマンガンの塩（例えば酢酸マンガン４水和物等）を所望の比率となるよう、すなわちマンガンイオンとセリウムイオンが、ＭｎとＣｅの合計量に対するＣｅの量（Ｃｅ／（Ｍｎ＋Ｃｅ））が０モル％超、４０モル％以下の比となる割合で水に加えて水溶液を調製し、この水溶液を、炭酸イオンを含む還元剤（例えば炭酸アンモニウム等）を溶解した水溶液と混合して沈殿を生成させ、乾燥後、得られた粉末を焼成することにより製造することができる。本発明の方法においては、炭酸イオンを含む還元剤を用いることにより、４価のマンガンの塩（炭酸マンガン）を生成し、その後焼成するため、酸素放出能の高いＭｎＯ2を含む触媒材料を製造することができる。 As a method for producing the catalyst according to the present invention, a general reverse coprecipitation method can be used. Specifically, a cerium salt (for example, cerium nitrate) and a manganese salt (for example, manganese acetate tetrahydrate) have a desired ratio, that is, manganese ions and cerium ions are the total amount of Mn and Ce. An aqueous solution was prepared by adding water to the mixture such that the amount of Ce to Ce (Ce / (Mn + Ce)) was in a ratio of more than 0 mol% and 40 mol% or less. Etc.) are mixed with an aqueous solution in which the solution is dissolved to produce a precipitate, and after drying, the obtained powder is fired. In the method of the present invention, by using a reducing agent containing carbonate ions, a tetravalent manganese salt (manganese carbonate) is produced and then calcined, so that a catalyst material containing MnO 2 having a high oxygen releasing ability is produced. can do.
また、こうして得られたＣｅＯ2／ＭｎＯ2触媒を、タングステンの塩（例えばメタタングステン酸アンモニウム水和物）を含む水溶液に分散させ、逆共沈法によりタングステンの酸化物をＣｅＯ2／ＭｎＯ2触媒上に担持させることができる。 The CeO 2 / MnO 2 catalyst thus obtained is dispersed in an aqueous solution containing a tungsten salt (for example, ammonium metatungstate hydrate), and the tungsten oxide is converted into a CeO 2 / MnO 2 catalyst by a reverse coprecipitation method. It can be carried on top.
実施例１
２Ｌのビーカーにイオン交換水を３００ｍｌ加え、プロペラ攪拌機を用いて４００ｒｐｍで撹拌しながら炭酸アンモニウム（０．４ｍｏｌ）を加えて溶解させ、炭酸アンモニウム水溶液を調製した。別の５００ｍｌのビーカーにイオン交換水を３００ｍｌ加え、０．１８モルの酢酸マンガン四水和物と０．０２モルの硝酸セリウムを加え、スターラーで撹拌して溶解させた。この水溶液を、上記の炭酸アンモニウム水溶液中に一気に添加することにより沈殿を生成させた。この沈殿をイオン交換水で洗浄後、１２０℃で蒸発乾固させることによって粉末を得た。得られた粉末を５００℃で２時間昇温、２時間焼成することによって本発明の触媒（90Ｍｎ−10Ｃｅ)を作製した。
Example 1
300 mL of ion exchange water was added to a 2 L beaker, and ammonium carbonate (0.4 mol) was added and dissolved while stirring at 400 rpm using a propeller stirrer to prepare an aqueous ammonium carbonate solution. To another 500 ml beaker, 300 ml of ion-exchanged water was added, 0.18 mol of manganese acetate tetrahydrate and 0.02 mol of cerium nitrate were added and dissolved by stirring with a stirrer. This aqueous solution was added all at once to the above aqueous ammonium carbonate solution to form a precipitate. The precipitate was washed with ion-exchanged water and evaporated to dryness at 120 ° C. to obtain a powder. The obtained powder was heated at 500 ° C. for 2 hours and calcined for 2 hours to prepare a catalyst (90Mn-10Ce) of the present invention.
実施例２
酢酸マンガン四水和物を０．１６モル用い、硝酸セリウムを０．０４モル用いることを除き、実施例１と同様にして触媒を作製した。
Example 2
A catalyst was prepared in the same manner as in Example 1 except that 0.16 mol of manganese acetate tetrahydrate was used and 0.04 mol of cerium nitrate was used.
実施例３
酢酸マンガン四水和物を０．１２モル用い、硝酸セリウムを０．０８モル用いることを除き、実施例１と同様にして触媒を作製した。
Example 3
A catalyst was prepared in the same manner as in Example 1 except that 0.12 mol of manganese acetate tetrahydrate was used and 0.08 mol of cerium nitrate was used.
比較例１
硝酸セリウムを用いることなく、酢酸マンガン四水和物のみを０．２モル用いることを除き、実施例１と同様にして触媒を作製した。
Comparative Example 1
A catalyst was prepared in the same manner as in Example 1 except that 0.2 mol of manganese acetate tetrahydrate alone was used without using cerium nitrate.
比較例２
酢酸マンガン四水和物を０．１モル用い、硝酸セリウムを０．１モル用いることを除き、実施例１と同様にして触媒を作製した。
Comparative Example 2
A catalyst was prepared in the same manner as in Example 1 except that 0.1 mol of manganese acetate tetrahydrate was used and 0.1 mol of cerium nitrate was used.
比較例３
比較例１に記載の方法によって製造した二酸化マンガン粒子及び酸化セリウムを、ＭｎとＣｅの合計量に対するＣｅの量（Ｃｅ／（Ｍｎ＋Ｃｅ））が１０モル％となるような比で混合することにより、二酸化マンガン粒子及び酸化セリウムの物理混合物を作製した。
Comparative Example 3
By mixing the manganese dioxide particles and cerium oxide produced by the method described in Comparative Example 1 at a ratio such that the amount of Ce (Ce / (Mn + Ce)) with respect to the total amount of Mn and Ce is 10 mol%, A physical mixture of manganese dioxide particles and cerium oxide was prepared.
比較例４
比較例１に記載の方法によって製造した二酸化マンガン粒子及び酸化セリウムを、ＭｎとＣｅの合計量に対するＣｅの量（Ｃｅ／（Ｍｎ＋Ｃｅ））が５０モル％となるような比で混合することにより、二酸化マンガン粒子及び酸化セリウムの物理混合物を作製した。
Comparative Example 4
By mixing manganese dioxide particles and cerium oxide produced by the method described in Comparative Example 1 at a ratio such that the amount of Ce (Ce / (Mn + Ce)) with respect to the total amount of Mn and Ce is 50 mol%, A physical mixture of manganese dioxide particles and cerium oxide was prepared.
比較例５
酢酸マンガン四水和物を用いることなく、硝酸セリウムのみを０．２モル用いることを除き、実施例１と同様にして触媒を作製した。
Comparative Example 5
A catalyst was prepared in the same manner as in Example 1 except that 0.2 mol of cerium nitrate alone was used without using manganese acetate tetrahydrate.
評価試験
（ＮＯｘ浄化率評価）
５ｃｃの触媒サンプルについて，ＮＨ３：４００ｐｐｍ、ＮＯ：３００ｐｐｍ，Ｈ２Ｏ：５％，Ｏ２：１０％、ＣＯ2：１０％、残余：窒素（窒素で１００％とした）（体積％）の試験ガスを用いて、毎時空間速度：１８００００ｈ−１、５０℃から２０℃／分の連続昇温しながら１５０℃〜５００℃の温度で、触媒活性評価装置（メーカー名：ベスト測器（株）））を用いてＮＯｘの浄化率を測定することにより行った。
Evaluation test (NO x purification rate evaluation)
For a 5 cc catalyst sample, NH 3 : 400 ppm, NO: 300 ppm, H 2 O: 5%, O 2 : 10%, CO 2 : 10%, the remainder: nitrogen (100% with nitrogen) (volume%) Using test gas, hourly space velocity: 180,000 h −1 , while continuously raising the temperature from 50 ° C. to 20 ° C./min, at a temperature of 150 ° C. to 500 ° C., a catalytic activity evaluation apparatus (manufacturer name: Best Sokki Co., Ltd. )) To measure the NO x purification rate.
実施例１〜３及び比較例１〜５のサンプルを用いて、浄化温度に対する（ＮＯｘ浄化率評価）を行った。この結果を以下の表１に示す。 Using the samples of Examples 1 to 3 and Comparative Examples 1 to 5, (NO x purification rate evaluation) with respect to the purification temperature was performed. The results are shown in Table 1 below.
Ｃｅモル量ｘ（Ｃｅ／（Ｍｎ＋Ｃｅ））に対し浄化率（％）をプロットしたグラフ（図１）に示すように、２００℃において、Ｃｅ非置換のＭｎのみからなる触媒（比較例１）に比して、Ｃｅをわずかでも添加すれば活性が向上し、最大４０モル％のＣｅ添加率まで活性が向上した。また、ＭｎＯ2粒子とＣｅＯ2粒子の単なる物理混合物では、ＣｅとＭｎを所定のモル比としても、活性を向上させることはできなかった。 As shown in the graph (FIG. 1) in which the purification rate (%) is plotted against the Ce molar amount x (Ce / (Mn + Ce)), at 200 ° C., the catalyst composed only of Ce-unsubstituted Mn (Comparative Example 1). On the other hand, the activity was improved by adding even a small amount of Ce, and the activity was improved up to a maximum Ce addition rate of 40 mol%. Moreover, in a simple physical mixture of MnO 2 particles and CeO 2 particles, the activity could not be improved even when Ce and Mn were set to a predetermined molar ratio.
（ＸＲＤ測定）
ＸＲＤ（メーカー名：（株）リガク、型番：ＲＩＮＴ）を用いて、結晶析出相の組成依存性を測定した。そうすると、図２に示すように、実施例１のサンプルでは、ＭｎＯ2に起因するピーク（２θ＝２７．３２９付近）とＣｅＯ2に起因するピーク（２θ＝４７．４７９付近）の両者が観察されることから、ＭｎとＣｅが固溶しておらず、ＭｎＯ2＋ＣｅＯ2として存在していることが観察された。ＭｎＯ2が９０モル％と多い領域で活性が向上していることから、ＭｎＯ2粒子の表面に高分散な状態でＣｅＯ2が担持されており、これにより低温域でのＮＯ酸化活性が向上し、低温域でのＮＯｘ浄化活性が向上したと考えられる。
(XRD measurement)
Using XRD (manufacturer name: Rigaku Corporation, model number: RINT), the composition dependence of the crystal precipitation phase was measured. Then, as shown in FIG. 2, in the sample of Example 1, both a peak due to MnO 2 (near 2θ = 27.329) and a peak due to CeO 2 (near 2θ = 47.479) are observed. Therefore, it was observed that Mn and Ce were not dissolved but existed as MnO 2 + CeO 2 . Since the activity is improved in a region where MnO 2 is as high as 90 mol%, CeO 2 is supported in a highly dispersed state on the surface of MnO 2 particles, thereby improving the NO oxidation activity in a low temperature region. It is considered that the NO x purification activity in the low temperature range has been improved.
参考までに、従来用いられているＮＯx浄化用触媒と、本発明の触媒（実施例１）との１５０℃及び２００℃におけるＮＯx浄化率の測定結果を以下の表に示す。 For reference, the measurement results of the NOx purification rate at 150 ° C. and 200 ° C. of the conventionally used NOx purification catalyst and the catalyst of the present invention (Example 1) are shown in the following table.
この表２に示す結果からも、従来用いられてきたＮＯx浄化用触媒と比較しても、２００℃以下の低温域で非常に高いＮＯｘ浄化活性を示すことから、有望な触媒であると考えられる。 From the results shown in Table 2, thought to be compared with a conventionally used NOx purifying catalyst, since a very high the NO x purification activity in a low temperature range of 200 ° C. or less, is a promising catalyst It is done.
比較例３（ＭｎＯ2粒子とＣｅＯ2粒子の９：１物理混合物）、比較例２（Ｃｅ／（Ｍｎ＋Ｃｅ）＝０．５）及び実施例１（Ｃｅ／（Ｍｎ＋Ｃｅ）＝０．１）のサンプルについてＴＥＭ観察を行い、そのＴＥＭ画像を図４、図５及び図６に示す。また、これらの図中の符号１〜７で示した部位における元素分析を行い、結果を以下の表３及び図７に示す。 Samples of Comparative Example 3 (9: 1 physical mixture of MnO 2 particles and CeO 2 particles), Comparative Example 2 (Ce / (Mn + Ce) = 0.5) and Example 1 (Ce / (Mn + Ce) = 0.1) TEM observation was carried out, and the TEM images are shown in FIG. 4, FIG. 5 and FIG. Moreover, the elemental analysis in the site | part shown with the codes | symbols 1-7 in these figures was performed, and a result is shown in the following Table 3 and FIG.
図４に示すＭｎＯ2粒子とＣｅＯ2粒子の物理混合物では、観察部位によっては、ＣｅのみもしくはＭｎのみが観察され、ＣｅとＭｎが別々の粒子として存在していることが認められた。一方、逆共沈法によって製造したサンプルでは、１つの粒子上にＣｅとＭｎが共存していることが観察された。 In the physical mixture of MnO 2 particles and CeO 2 particles shown in FIG. 4, only Ce or only Mn was observed depending on the observation site, and it was recognized that Ce and Mn existed as separate particles. On the other hand, in the sample manufactured by the reverse coprecipitation method, it was observed that Ce and Mn coexist on one particle.
また、上記実施例１並びに比較例１，２、３及び５のサンプルについて、ＢＥＬ ＪＡＰＡＮ ＩＮＣ．製のＢＥＬsorp maxを用い、一般的なＢＥＴ法により比表面積を測定し、その結果を以下の表４に示す。 For the samples of Example 1 and Comparative Examples 1, 2, 3 and 5, BEL JAPAN INC. The specific surface area was measured by a general BET method using BELsorp max made by the manufacturer, and the results are shown in Table 4 below.
実施例１のサンプルでは、ＭｎＯ2粒子とＣｅＯ2粒子の物理混合物と比較して、比表面積が大きくなっている。これは、粒子の表面に微細なＣｅＯ2の一次粒子が分散して露出しているためであると考えられる。 In the sample of Example 1, the specific surface area is larger than that of the physical mixture of MnO 2 particles and CeO 2 particles. This is considered to be because fine primary particles of CeO 2 are dispersed and exposed on the surface of the particles.
以下の表５及び図８に、実施例１で得たサンプルについて、１５０℃〜５００℃の触媒床温におけるＮＯx浄化率の測定結果を示す。 Table 5 and FIG. 8 below show the measurement results of the NOx purification rate at the catalyst bed temperature of 150 ° C. to 500 ° C. for the sample obtained in Example 1.
この結果から明らかなように、本発明の触媒は、低温において高活性を示すが、昇温に伴い、還元剤であるＮＨ3が酸化してＮＯx化することにより浄化率低下が生ずるようになる。 As is apparent from the results, the catalyst of the present invention exhibits high activity at low temperatures, but as the temperature rises, the reducing agent, NH 3 oxidizes and becomes NOx, resulting in a reduction in purification rate. .
実施例４及び５
実施例１と同様にして触媒を作製し、この触媒に対して酸化タングステン量が５〜１０ｗｔ％となるようにメタタングステン酸アンモニウムを計量し、イオン交換水（２００ｇ程度）に溶解した。例えば、Ｗ＝１０ｗｔ％であれば、ＭｎＣｅ触媒２０．０ｇに対してメタタングステン酸アンモニウムを２．５０ｇ用いた。このメタタングステン酸アンモニウム水溶液にＭｎＣｅ触媒を投入し、８０〜９０℃程度に加熱し、水分を蒸発させた。得られた沈殿を１２０℃の乾燥炉に入れ、完全に乾燥させた後、５００℃×２時間で焼成することによって、上記触媒に酸化タングステンを担持させた。
Examples 4 and 5
A catalyst was produced in the same manner as in Example 1, and ammonium metatungstate was weighed so that the amount of tungsten oxide was 5 to 10 wt% with respect to this catalyst, and dissolved in ion-exchanged water (about 200 g). For example, when W = 10 wt%, 2.50 g of ammonium metatungstate was used with respect to 20.0 g of MnCe catalyst. MnCe catalyst was added to this ammonium metatungstate aqueous solution and heated to about 80 to 90 ° C. to evaporate water. The obtained precipitate was put in a drying furnace at 120 ° C. and completely dried, and then calcined at 500 ° C. for 2 hours, whereby tungsten oxide was supported on the catalyst.
これらのサンプルについて、上記と同様にして、２００℃及び３００℃におけるＮＯx浄化率を測定した。この結果を、以下の表６及び図９に示す。これらの結果より、タングステン酸化物を、触媒に対して５wt％及び１０wt％担持させることにより、低温活性（８０％＠２００℃）を維持しつつ、高温活性（８０％＠３００℃）を達成することができた。 About these samples, the NOx purification rate in 200 degreeC and 300 degreeC was measured like the above. The results are shown in Table 6 below and FIG. From these results, by supporting 5 wt% and 10 wt% of tungsten oxide with respect to the catalyst, high temperature activity (80% @ 300 ° C) is achieved while maintaining low temperature activity (80% @ 200 ° C). I was able to.
上記のように本発明に係る排ガス浄化用触媒によれば、所定の比率でＭｎＯ2粒子の表面上にＣｅＯ2粒子を担持させた酸化物を用いることによって、より高いＮＯｘ浄化率を有し、より低温でＮＯｘを浄化できる。これにより、加熱温度を従来のように高い温度にする必要がなく、幅広い排ガス組成において高いＮＯｘ浄化性能を提供することができる。 As described above, the exhaust gas purifying catalyst according to the present invention has a higher NO x purification rate by using an oxide in which CeO 2 particles are supported on the surface of MnO 2 particles at a predetermined ratio. , NO x can be purified at a lower temperature. Accordingly, the heating temperature as conventionally is not necessary to high temperature, it is possible to provide a high the NO x purification performance in a wide range of exhaust gas composition.
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| CN201710084814.1A CN107088408A (en) | 2016-02-17 | 2017-02-17 | Exhaust gas purification catalyst and its manufacture method |
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