JP4233572B2 - Honeycomb catalyst for exhaust gas purification - Google Patents
Honeycomb catalyst for exhaust gas purification Download PDFInfo
- Publication number
- JP4233572B2 JP4233572B2 JP2006030668A JP2006030668A JP4233572B2 JP 4233572 B2 JP4233572 B2 JP 4233572B2 JP 2006030668 A JP2006030668 A JP 2006030668A JP 2006030668 A JP2006030668 A JP 2006030668A JP 4233572 B2 JP4233572 B2 JP 4233572B2
- Authority
- JP
- Japan
- Prior art keywords
- catalyst
- molded body
- exhaust gas
- honeycomb catalyst
- gas
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
- 239000003054 catalyst Substances 0.000 title claims description 122
- 238000000746 purification Methods 0.000 title claims description 19
- 239000011148 porous material Substances 0.000 claims description 44
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 41
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims description 38
- 239000010409 thin film Substances 0.000 claims description 25
- 238000000034 method Methods 0.000 claims description 17
- 229910052697 platinum Inorganic materials 0.000 claims description 17
- 239000000377 silicon dioxide Substances 0.000 claims description 17
- 239000000463 material Substances 0.000 claims description 14
- 239000004094 surface-active agent Substances 0.000 claims description 13
- 239000002243 precursor Substances 0.000 claims description 11
- 229910052751 metal Inorganic materials 0.000 claims description 6
- 239000002184 metal Substances 0.000 claims description 6
- 238000000576 coating method Methods 0.000 claims description 5
- 238000005342 ion exchange Methods 0.000 claims description 5
- 239000011248 coating agent Substances 0.000 claims description 4
- 238000005470 impregnation Methods 0.000 claims description 4
- 239000003929 acidic solution Substances 0.000 claims description 3
- 150000004703 alkoxides Chemical class 0.000 claims description 3
- 238000010304 firing Methods 0.000 claims description 3
- 239000007789 gas Substances 0.000 description 61
- 239000002245 particle Substances 0.000 description 37
- MWUXSHHQAYIFBG-UHFFFAOYSA-N Nitric oxide Chemical compound O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 34
- 239000013335 mesoporous material Substances 0.000 description 34
- 229910002089 NOx Inorganic materials 0.000 description 33
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 20
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- WSFSSNUMVMOOMR-UHFFFAOYSA-N Formaldehyde Chemical compound O=C WSFSSNUMVMOOMR-UHFFFAOYSA-N 0.000 description 2
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- YRKCREAYFQTBPV-UHFFFAOYSA-N acetylacetone Chemical compound CC(=O)CC(C)=O YRKCREAYFQTBPV-UHFFFAOYSA-N 0.000 description 2
- 150000001336 alkenes Chemical class 0.000 description 2
- -1 alkylamine N-oxides Chemical class 0.000 description 2
- 229910052788 barium Inorganic materials 0.000 description 2
- DSAJWYNOEDNPEQ-UHFFFAOYSA-N barium atom Chemical compound [Ba] DSAJWYNOEDNPEQ-UHFFFAOYSA-N 0.000 description 2
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- 239000012876 carrier material Substances 0.000 description 2
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- 229910017052 cobalt Inorganic materials 0.000 description 2
- 239000010941 cobalt Substances 0.000 description 2
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 2
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- WPBNNNQJVZRUHP-UHFFFAOYSA-L manganese(2+);methyl n-[[2-(methoxycarbonylcarbamothioylamino)phenyl]carbamothioyl]carbamate;n-[2-(sulfidocarbothioylamino)ethyl]carbamodithioate Chemical compound [Mn+2].[S-]C(=S)NCCNC([S-])=S.COC(=O)NC(=S)NC1=CC=CC=C1NC(=S)NC(=O)OC WPBNNNQJVZRUHP-UHFFFAOYSA-L 0.000 description 2
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- 229910052759 nickel Inorganic materials 0.000 description 2
- JCXJVPUVTGWSNB-UHFFFAOYSA-N nitrogen dioxide Inorganic materials O=[N]=O JCXJVPUVTGWSNB-UHFFFAOYSA-N 0.000 description 2
- 229910000510 noble metal Inorganic materials 0.000 description 2
- BMMGVYCKOGBVEV-UHFFFAOYSA-N oxo(oxoceriooxy)cerium Chemical compound [Ce]=O.O=[Ce]=O BMMGVYCKOGBVEV-UHFFFAOYSA-N 0.000 description 2
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- URGAHOPLAPQHLN-UHFFFAOYSA-N sodium aluminosilicate Chemical compound [Na+].[Al+3].[O-][Si]([O-])=O.[O-][Si]([O-])=O URGAHOPLAPQHLN-UHFFFAOYSA-N 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- DLYUQMMRRRQYAE-UHFFFAOYSA-N tetraphosphorus decaoxide Chemical compound O1P(O2)(=O)OP3(=O)OP1(=O)OP2(=O)O3 DLYUQMMRRRQYAE-UHFFFAOYSA-N 0.000 description 2
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- KLFRPGNCEJNEKU-FDGPNNRMSA-L (z)-4-oxopent-2-en-2-olate;platinum(2+) Chemical compound [Pt+2].C\C([O-])=C\C(C)=O.C\C([O-])=C\C(C)=O KLFRPGNCEJNEKU-FDGPNNRMSA-L 0.000 description 1
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- 229910052715 tantalum Inorganic materials 0.000 description 1
- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 description 1
- 238000002076 thermal analysis method Methods 0.000 description 1
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- 239000010936 titanium Substances 0.000 description 1
- 230000001052 transient effect Effects 0.000 description 1
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 1
- 229910052721 tungsten Inorganic materials 0.000 description 1
- 239000010937 tungsten Substances 0.000 description 1
- WTHDKMILWLGDKL-UHFFFAOYSA-N urea;hydrate Chemical compound O.NC(N)=O WTHDKMILWLGDKL-UHFFFAOYSA-N 0.000 description 1
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- VWQVUPCCIRVNHF-UHFFFAOYSA-N yttrium atom Chemical compound [Y] VWQVUPCCIRVNHF-UHFFFAOYSA-N 0.000 description 1
- RUDFQVOCFDJEEF-UHFFFAOYSA-N yttrium(III) oxide Inorganic materials [O-2].[O-2].[O-2].[Y+3].[Y+3] RUDFQVOCFDJEEF-UHFFFAOYSA-N 0.000 description 1
- 229910052725 zinc Inorganic materials 0.000 description 1
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- 229910052726 zirconium Inorganic materials 0.000 description 1
Landscapes
- Exhaust Gas After Treatment (AREA)
- Exhaust Gas Treatment By Means Of Catalyst (AREA)
- Catalysts (AREA)
Description
本発明はモノリス成形体のガス流路内壁に薄膜状のメソポーラス材料を形成させ、これに触媒を担持させて成るハニカム触媒に関するものであり、該ハニカム触媒を用いることによって自動車の排ガスに含まれるNOxを高効率で浄化処理できる。 The present invention relates to a honeycomb catalyst in which a thin film mesoporous material is formed on the inner wall of a gas flow path of a monolith molded body and the catalyst is supported thereon, and NOx contained in the exhaust gas of an automobile by using the honeycomb catalyst. Can be purified with high efficiency.
自動車の排ガス浄化用触媒の主流となっている三元触媒は、触媒支持体としてコージェライト(鉱物名)製のモノリス成形体を用い、該成型体のガス流路内壁に触媒である数100nm〜数μmの大きさの白金-パラジウム-ロジウム粒子を含んだ数μm〜数十μmの大きさの活性アルミナ(=γ-アルミナ)粒子を塗布した構造となっている。塗布層の厚みは一般的に50μmから500μmの範囲にあり、通常、100μm程度である。使用される活性アルミナ粒子は数10nm〜数100nmの微粒子の凝集体であり、微粒子間の間隙に触媒粒子が吸着している。この粒子間の間隙の細孔(間隙型の細孔)は空間的な広がりが少なく(平面的)、本発明における薄膜状のメソポーラス材料に存在するネットワーク状に広がった貫通型の細孔構造(細孔チャンネルという)とは基本的に異なる。すなわち、従来の触媒粒子は3次元的な細孔に触媒粒子が捕捉されている状態ではない。 The three-way catalyst which has become the mainstream of exhaust gas purification catalysts for automobiles uses a monolith molded body made of cordierite (mineral name) as a catalyst support, and the catalyst on the inner wall of the gas flow path of the molded body is several hundred nm to It has a structure in which activated alumina (= γ-alumina) particles having a size of several μm to several tens of μm including platinum-palladium-rhodium particles having a size of several μm are applied. The thickness of the coating layer is generally in the range of 50 μm to 500 μm, and is usually about 100 μm. The activated alumina particles used are agglomerates of fine particles of several tens nm to several hundreds nm, and the catalyst particles are adsorbed in the gaps between the fine particles. The interstitial pores (gap type pores) between these particles have little spatial expansion (planar), and the penetration type pore structure (in the form of a network) present in the thin film mesoporous material in the present invention ( This is basically different from the pore channel). That is, the conventional catalyst particles are not in a state where the catalyst particles are trapped in the three-dimensional pores.
また、この三元触媒はガソリン車の排ガス処理には非常に有効であるが、軽油燃料で走行するディーゼル車の排ガス処理にはほとんど効果がない。特に、過渡走行時に排出される120〜200℃の低温排NOxを浄化するための触媒開発は触媒化学の分野においても未解決である。そして、現在でも、ディーゼル車の排ガス処理のための実用的な触媒は知られていない。その主な理由は、上記三元触媒がディーゼル排ガスにおける比較的高濃度の酸素雰囲気下で著しい活性低下を起こすことからきている。ガソリン車排ガスの酸素濃度は1%以下であるが、軽油の空燃比はガソリンの空燃比の数倍以上であるのでディーゼル排ガスに含まれる酸素濃度は通常5%以上である。ガソリン車の場合は、空気と燃料の理論的重量混合比を示す理論空燃比近傍で燃焼させることで共存酸素を1%以下に制御しているので、この燃焼はリッチバーンとよばれているが、ディーゼル燃料の燃焼は吸気量が理論値よりも大過剰であり、燃料供給量が相対的に少ないのでリーンバーンとよばれている。この燃焼の条件で酸素濃度が5%になると三元触媒の活性がほとんど失活するからである。 This three-way catalyst is very effective for the exhaust gas treatment of gasoline vehicles, but has little effect on the exhaust gas treatment of diesel vehicles running on light oil fuel. In particular, the development of a catalyst for purifying low-temperature exhaust NOx at 120 to 200 ° C. exhausted during transient running has not been solved in the field of catalytic chemistry. Even now, no practical catalyst for treating exhaust gas from diesel vehicles is known. The main reason is that the three-way catalyst causes a significant decrease in activity in a relatively high concentration oxygen atmosphere in diesel exhaust gas. The oxygen concentration of gasoline vehicle exhaust gas is 1% or less, but since the air-fuel ratio of light oil is more than several times that of gasoline, the oxygen concentration contained in diesel exhaust gas is usually 5% or more. In the case of a gasoline vehicle, co-existing oxygen is controlled to 1% or less by burning near the stoichiometric air-fuel ratio indicating the theoretical weight mixing ratio of air and fuel. This combustion is called rich burn. The combustion of diesel fuel is called lean burn because the intake amount is excessively larger than the theoretical value and the fuel supply amount is relatively small. This is because the activity of the three-way catalyst is almost deactivated when the oxygen concentration becomes 5% under these combustion conditions.
一般に、工業的な触媒は多孔性材料に担持した状態で使用されることが多い。多孔性材料の細孔は、IUPAC(国際純正及び応用化学連合)によると、細孔直径が2nm以下のミクロ細孔、2〜50nmのメソ細孔、及び50nm以上のマクロ細孔に分類されている。ミクロからメソの範囲にわたる広い分布をもつような単一の多孔性材料は活性炭以外には知られていない。近年、数nmの位置に細孔ピークをもち、比表面積が400〜1100m2/gという非常に大きな値を有するシリカ、アルミナ、及びシリカアルミナ系メソポーラス分子ふるいが開発された。これらは、例えば、特許文献1、2、及び3等に開示されている。 In general, industrial catalysts are often used in a state where they are supported on a porous material. According to IUPAC (International Pure and Applied Chemical Association), the pores of the porous material are classified into micropores with a pore diameter of 2 nm or less, mesopores with 2 to 50 nm, and macropores with 50 nm or more. Yes. No single porous material other than activated carbon has a wide distribution ranging from the micro to meso range. In recent years, silica, alumina, and silica-alumina mesoporous molecular sieves having a pore peak at a position of several nm and a very large specific surface area of 400 to 1100 m 2 / g have been developed. These are disclosed in, for example, Patent Documents 1, 2, and 3.
触媒反応は表面反応であるので触媒の比表面積が大きいほど触媒活性が高い。また、触媒を担持するための担体は比表面積が大きいほど触媒活性を発現しやすい。自動車用の排ガス浄化用触媒としては、一般的に、モノリス成形体のガス流路内壁に触媒を塗布した構造をもつ所謂ハニカム触媒が用いられている。その理由は、自動車が排出する排ガスは、一般的に、毎時5万リットル〜20万リットルの大流量であり、このような大流量の排ガスを浄化する際の圧損が少なく、しかも効率的に処理するための触媒構造としてハニカム構造が適しているからである。このような観点から自動車用三元触媒をみると、支持体としてのモノリス成形体の比表面積が約0.2m2/g、触媒を担持するための担体としてのアルミ
ナ粒子の比表面積が110〜340m2/g、触媒の比表面積は粒径から推定すると20〜40m2/g程度である。
Since the catalytic reaction is a surface reaction, the larger the specific surface area of the catalyst, the higher the catalytic activity. Further, the carrier for supporting the catalyst is more likely to exhibit the catalytic activity as the specific surface area is larger. As an exhaust gas purification catalyst for automobiles, a so-called honeycomb catalyst having a structure in which a catalyst is applied to the inner wall of a gas flow path of a monolith molded body is generally used. The reason for this is that the exhaust gas discharged from automobiles is generally a large flow rate of 50,000 liters to 200,000 liters per hour, and there is little pressure loss when purifying such a large flow amount of exhaust gas, and it is processed efficiently. This is because a honeycomb structure is suitable as a catalyst structure for this purpose. Looking at the three-way catalyst for automobiles from this point of view, the specific surface area of the monolith molded body as the support is about 0.2 m 2 / g, the specific surface area of the alumina particles as the carrier for supporting the catalyst is 110 to 340 m. 2 / g, specific surface area of the catalyst is 20 to 40 m 2 / g approximately Extrapolating from particle size.
一方、上記したように工業材料として1000m2/g以上の比表面積をもつメソポーラス材料が知られており、触媒粒子は近年の触媒調整法の発達によって数nmの粒子を製造できるようになってきている。数nmの触媒粒子は、それだけで1000m2/g程度の比表面積をもっている。すなわち、従来の自動車用ハニカム触媒は、触媒効率を最大限発揮するのに十分であるとは言い難い。したがって、高比表面積を有するメソポーラス材料に担持したナノ触媒をモノリス成形体に塗布することによってディーゼル排ガスに対する触媒活性の向上を図ることが考えられる。 On the other hand, as described above, mesoporous materials having a specific surface area of 1000 m 2 / g or more are known as industrial materials, and catalyst particles can be produced with a particle size of several nanometers due to the recent development of catalyst preparation methods. Yes. The catalyst particles of several nm alone have a specific surface area of about 1000 m 2 / g. That is, it is difficult to say that the conventional honeycomb catalyst for automobiles is sufficient to maximize the catalyst efficiency. Therefore, it is conceivable to improve the catalytic activity against diesel exhaust gas by applying a nano catalyst supported on a mesoporous material having a high specific surface area to a monolith molded body.
しかしながら、従来方法によるモノリス成形体へのメソポーラス材料の塗布には幾つかの問題がある。従来法では塗布に際しモノリス成形体との密着性を高めるために、通常、バインダーとメソポーラス材料の混合物を塗布することが行われるのであるが、メソポーラス材料の細孔内にバインダー粒子が侵入することによる有効細孔数の減少、メソポーラス材料の細孔表面がバインダー粒子によって被覆されることによる有効比表面積の減少、等の問題が生じる。また、メソポーラス材料に予め担持した触媒をモノリス成形体に塗布する場合でも、バインダーを用いる限り、上記のような問題が生じる。これらの問題は、モノリス成形体のガス流路を高速で通過する排ガスと担持触媒との接触効率の低下を生じるので好ましくない。
本発明の特徴は、上記の問題を解決するために、バインダーを用いることなくモノリス成形体のガス流路内壁に薄膜状のメソポーラス材料を形成させたことにある。
However, there are some problems in applying a mesoporous material to a monolith molded body by a conventional method. In the conventional method, a mixture of a binder and a mesoporous material is usually applied in order to increase the adhesion with the monolith molded body during application, but the binder particles enter the pores of the mesoporous material. Problems such as a decrease in the number of effective pores and a decrease in effective specific surface area due to the pore surfaces of the mesoporous material being covered with binder particles arise. Even when a catalyst previously supported on a mesoporous material is applied to a monolith molded body, the above-described problems occur as long as the binder is used. These problems are not preferable because the contact efficiency between the exhaust gas passing through the gas flow path of the monolith molded body and the supported catalyst is lowered.
A feature of the present invention resides in that a thin film mesoporous material is formed on the inner wall of the gas flow path of the monolith molded body without using a binder in order to solve the above problems.
本発明の目的は、上記の事情に鑑み、自動車の排ガス、特にディーゼル排ガスに含まれるNOxの浄化のための新規なハニカム触媒を提供することである。具体的には、従来困難であったディーゼル排NOxを効率的に浄化するために、リーンバーンの比較的高濃度酸素雰囲気下でもNOxに対して高活性を示す新規のハニカム触媒を提供することである。 In view of the above circumstances, an object of the present invention is to provide a novel honeycomb catalyst for purifying NOx contained in automobile exhaust gas, particularly diesel exhaust gas. Specifically, in order to efficiently purify diesel exhaust NOx, which has been difficult in the past, by providing a novel honeycomb catalyst exhibiting high activity against NOx even in a relatively high concentration oxygen atmosphere of lean burn. is there.
本発明者らは、上記の目的を達成するために鋭意研究を重ねた結果、特定の細孔分布と高比表面積を有する薄膜状のメソポーラス材料をモノリス成形体のガス流路内壁にバインダーを用いることなく特定手段で形成させ、これに特定の貴金属を担持させることによって作成したハニカム触媒がリーンバーン排NOx処理に対して非常に有効であることを見いだし、この知見に基づいて本発明を完成させるに至った。 As a result of intensive studies to achieve the above object, the present inventors use a thin-film mesoporous material having a specific pore distribution and a high specific surface area on the inner wall of the gas flow path of the monolith molded body. The honeycomb catalyst formed by forming the specific means without any specific means and supporting the specific noble metal thereon is found to be very effective for the lean burn exhaust NOx treatment, and the present invention is completed based on this finding. It came to.
すなわち、本発明は、
1.(1)モノリス成形体のガス流路内壁に界面活性剤を溶解した酸性溶液を付着させる工程、(2)モノリス成形体のガス流路内壁に気体状態のメソポーラスシリカ材料の前駆物質を流通させ、メソポーラスシリカ材料の中間体を生成させる工程、(3)該中間体を焼成することによってゲル化させ同時に界面活性剤を分解除去することによって薄膜状のメソポーラスシリカ材料を固着させる工程を、順次、経ることによって、モノリス成形体
のガス流路内壁に比表面積が100〜1400m2/g、細孔径が1 nm〜20 nm、及び厚みが10 nm〜10μmである薄膜状のメソポーラスシリカ材料を被覆して形成させた担持体に、イオン交換法又は含浸法によって白金含有触媒が担持された構造であることを特徴とする排ガス浄化用ハニカム触媒、
2.上記メソポーラスシリカ材料の前駆物質が、金属アルコキシドであることを特徴とする上記1.に記載の排ガス浄化用ハニカム触媒、
3.上記1.又は2.に記載の排ガス浄化用ハニカム触媒を用いた、自動車用の排ガス浄化用ハニカム触媒、に関する。
That is, the present invention
1. (1) A step of attaching an acidic solution in which a surfactant is dissolved to the inner wall of the gas flow path of the monolith molded body, (2) circulating a precursor of the mesoporous silica material in a gaseous state to the inner wall of the gas flow path of the monolith molded body, A step of generating an intermediate of mesoporous silica material, (3) a step of gelling the intermediate by firing and fixing the thin-film mesoporous silica material by simultaneously decomposing and removing the surfactant are sequentially performed. Monolith molded body
A support formed by coating a thin film mesoporous silica material having a specific surface area of 100 to 1400 m 2 / g, a pore diameter of 1 nm to 20 nm, and a thickness of 10 nm to 10 μm on the inner wall of the gas channel , A honeycomb catalyst for purifying exhaust gas, characterized by having a structure in which a platinum-containing catalyst is supported by an ion exchange method or an impregnation method ,
2 . The above-mentioned 1. The precursor of the mesoporous silica material is a metal alkoxide. A honeycomb catalyst for exhaust gas purification as described in
3. Above 1. Or 2. Using an exhaust gas purifying honeycomb catalyst, exhaust gas purification honeycomb catalyst for automobiles, articles described.
本発明のハニカム触媒は、従来達成できなかったリーンバーン排NOx処理を低温領域でも極めて効率よく行うことができる。例えば、三元触媒では酸素濃度14%の雰囲気下における一酸化窒素はほとんど浄化できないが、本発明の白金触媒を担持したハニカム触媒は、酸素濃度14%の雰囲気に存在する一酸化窒素の80%以上を160〜300℃において浄化できる。 The honeycomb catalyst of the present invention can perform lean burn exhaust NOx treatment, which could not be achieved conventionally, very efficiently even in a low temperature region. For example, a three-way catalyst can hardly purify nitrogen monoxide in an atmosphere having an oxygen concentration of 14%, but a honeycomb catalyst carrying the platinum catalyst of the present invention is 80% of nitrogen monoxide present in an atmosphere having an oxygen concentration of 14%. The above can be purified at 160-300 ° C.
以下、本発明を詳細に説明する。
本発明は、薄膜状のメソポーラス材料をモノリス成形体のガス流路内壁に形成させ、これを触媒の担体として用いる。従来方法では担体材料(通常、活性アルミナ)とバインダーの混合分散液にモノリス成形体を浸漬後、乾燥、焼成することによってバインダー粒子を含む担体材料をモノリス成形体のガス流路内壁に塗布した後、触媒を担持することによってハニカム触媒を製造していた。この方法では、触媒は塗布層の最表面に担持されるが内部には侵入しにくいので一回の塗布では所定の触媒量を担持することができず、塗布工程を数回から10回程度繰り返すことを行っていた。そのため、触媒層の厚みが少なくとも100μm以上になっていた。しかし、自動車排ガスの浄化反応は触媒表面での接触によって起きるので塗布層の表面近傍に存在する触媒は有効であるけれども内部に存在する触媒はあまり利用されておらず非効率的であった。これに対して本発明のハニカム触媒における薄膜状のメソポーラス材料は、比表面積が従来使用されている担体の数倍から10倍程度あるので、担体の最表面に触媒を担持させるだけで触媒の担持量を従来の数倍から10倍にすることができる。したがって、従来よりも桁違いの高い効率で排ガス浄化を行うことができる。薄膜状のメソポーラス材料の比表面積は特別な事情がない限り高ければ高いほどよい。本発明に用いることのできる薄膜状のメソポーラス材料の比表面積は100〜1400m2/gであり、好ましくは400〜1200m2/gであり、より好ましくは600m2/g〜1000m2/gである。比表面積が100m2/g未満では、触媒の担持量が少なくなるので担持触媒の触媒性能を引き出す上で100m2/g以上であることが好ましい。一方、材料強度上の面からは比表面積が1400m2/g以下であることが好ましい。
Hereinafter, the present invention will be described in detail.
In the present invention, a thin-film mesoporous material is formed on the inner wall of the gas flow path of a monolith molded body, and this is used as a catalyst carrier. In the conventional method, after the monolith molded body is immersed in a mixed dispersion of a carrier material (usually activated alumina) and a binder, and then dried and fired, the carrier material containing binder particles is applied to the inner wall of the gas flow path of the monolith molded body. The honeycomb catalyst was manufactured by supporting the catalyst. In this method, the catalyst is supported on the outermost surface of the coating layer, but does not easily enter the inside, so a predetermined amount of catalyst cannot be supported by a single coating, and the coating process is repeated several to ten times. Was doing things. Therefore, the thickness of the catalyst layer is at least 100 μm or more. However, since the purification reaction of automobile exhaust gas takes place by contact on the catalyst surface, the catalyst existing in the vicinity of the surface of the coating layer is effective, but the catalyst existing inside is not used so much and is inefficient. In contrast, the mesoporous material in the form of a thin film in the honeycomb catalyst of the present invention has a specific surface area several times to 10 times that of a conventionally used carrier, so that the catalyst is supported only by carrying the catalyst on the outermost surface of the carrier. The amount can be increased from several times to 10 times. Therefore, exhaust gas purification can be performed with efficiency that is orders of magnitude higher than that of the prior art. The specific surface area of the thin film mesoporous material is preferably as high as possible unless there are special circumstances. The specific surface area of a thin film of a mesoporous materials that may be used in the present invention is 100~1400m 2 / g, are preferably 400~1200m 2 / g, more preferably 600m 2 / g~1000m 2 / g . The specific surface area of 100m less than 2 / g, it is preferable since the amount of supported catalyst is reduced in terms of pulling out the catalytic performance of the supported catalyst is 100m 2 / g or more. On the other hand, in terms of material strength, the specific surface area is preferably 1400 m 2 / g or less.
さらに薄膜状のメソポーラス材料は貫通型の細孔をもつので触媒の捕捉が強いこと、細孔チャンネルを通じたガス拡散の効果が期待できること、細孔分布を制御することで触媒活性種の好ましい粒径範囲を維持できること、触媒を細孔内に坦持することで触媒粒子の再凝集を抑制し触媒の均一高分散を図れること、などの優れた効果がある。以下で述べるように、NOxに対して高活性を示す触媒粒子の粒径はナノサイズであるので、担体である薄膜状のメソポーラス材料の細孔径は触媒粒子と同程度でなければならない。通常、メソポーラス材料の細孔内に坦持される触媒の粒径は、細孔径とほぼ同程度であるので、薄膜状のメソポーラス材料の細孔径を制御することによって、好ましい粒径を有するナノ触媒を均一に分散坦持することができる。ナノ触媒を担持するための薄膜状のメソポーラス材料が有する細孔の大部分は、細孔径(直径表示)が1〜20nmの範囲にあり、好ましくは2〜10nmの範囲にあり、より好ましくは2〜6nmにある。ここでいう細孔の大部分とは、1〜20nmの範囲の細孔が占める細孔容積が全細孔容積の60%以上であることをいう。細孔径が2nm未満であってもナノ触媒の坦持は可能であるが不純物等による汚染の影響を考えると2nm以上が好ましい。20nmを越えると分散担持されたナノ触媒が水熱高温条件などによる
シンタリングによって巨大粒子に成長しやすくなるので20nm以下が好ましい。なお、本発明における薄膜状のメソポーラス材料が有する比表面積及び細孔径は、脱吸着の気体として窒素を用いた窒素吸着法によって測定される値である。比表面積はBET法によって測定され、細孔径を与える細孔分布は1〜200nmの範囲を測定し、BJH法で求められる微分分布で示される。
In addition, thin film mesoporous materials have penetrating pores, so that the catalyst is strongly captured, the effect of gas diffusion through the pore channels can be expected, and the preferred particle size of the catalytically active species by controlling the pore distribution There are excellent effects such as that the range can be maintained, and that the catalyst particles are supported in the pores, thereby preventing reaggregation of the catalyst particles and achieving uniform and high dispersion of the catalyst. As described below, since the particle size of the catalyst particles exhibiting high activity with respect to NOx is nano-sized, the pore size of the thin film mesoporous material that is the carrier must be approximately the same as that of the catalyst particles. Usually, the particle size of the catalyst supported in the pores of the mesoporous material is approximately the same as the pore size. Therefore, by controlling the pore size of the mesoporous material in the form of a thin film, the nano catalyst having a preferable particle size Can be dispersed and supported uniformly. Most of the pores of the thin-film mesoporous material for supporting the nanocatalyst have a pore diameter (diameter display) in the range of 1 to 20 nm, preferably in the range of 2 to 10 nm, more preferably 2 ~ 6nm. As used herein, the majority of pores means that the pore volume occupied by pores in the range of 1 to 20 nm is 60% or more of the total pore volume. Even if the pore diameter is less than 2 nm, the nanocatalyst can be supported, but 2 nm or more is preferable in consideration of the influence of contamination by impurities and the like. If it exceeds 20 nm, the nanocatalyst dispersed and supported tends to grow into giant particles by sintering under hydrothermal high temperature conditions and the like, so 20 nm or less is preferable. The specific surface area and pore diameter of the thin film mesoporous material in the present invention are values measured by a nitrogen adsorption method using nitrogen as a desorption gas. The specific surface area is measured by the BET method, and the pore distribution giving the pore diameter is measured in the range of 1 to 200 nm and is indicated by a differential distribution obtained by the BJH method.
本発明で用いる薄膜状のメソポーラス材料としては、例えば、メソポーラスのシリカ、アルミナ、チタニア、ジルコニア、イットリア、セリア、ニオビア、シリカ-アルミナ、及びこれらの複合材料があり、このなかで、シリカ、アルミナ、チタニア、ジルコニア、シリカ-アルミナ及びこれらの複合物は機械物性が比較的高いので好ましい。これらの中でもメソポーラスシリカは比表面積が高く細孔径が数nmの範囲にあり耐熱性も高いので、最も好ましい。 Examples of the thin film mesoporous material used in the present invention include mesoporous silica, alumina, titania, zirconia, yttria, ceria, niobia, silica-alumina, and composite materials thereof. Among these, silica, alumina, Titania, zirconia, silica-alumina and composites thereof are preferred because of their relatively high mechanical properties. Among these, mesoporous silica is most preferable because it has a high specific surface area and a pore diameter in the range of several nanometers and high heat resistance.
前記に説明したように、モノリス成形体のガス流路内壁に形成させる薄膜状のメソポーラス材料の厚みは、薄ければ薄いほど浄化反応には好都合である。反面、薄すぎると機械的な衝撃等によって欠陥が生じる恐れがある。したがって、適度な厚みの範囲が存在する。本発明における薄膜状のメソポーラス材料の厚みは、10nmから10μmの範囲が好ましく、さらに好ましくは100nmから1μmである。10μm以上の厚みにすることは可能であるが、内部への排ガスの拡散が少ないので10μm以下であることが好ましい。 As described above, the thinner the mesoporous material formed on the inner wall of the gas flow path of the monolith molded body, the better the purification reaction. On the other hand, if it is too thin, defects may occur due to mechanical impact or the like. Therefore, there is an appropriate thickness range. The thickness of the thin film mesoporous material in the present invention is preferably in the range of 10 nm to 10 μm, more preferably 100 nm to 1 μm. Although the thickness can be 10 μm or more, it is preferably 10 μm or less because the diffusion of exhaust gas into the interior is small.
本発明のモノリス成形体のガス流路内壁への薄膜状のメソポーラス材料の形成は、通常、化学的蒸着法(CVD法:Chemical Vapor Deposition)によって行うことができる。この方法では、最初にモノリス成形体のガス流路内壁に界面活性剤を溶解した酸性溶液を付着させる。しかる後、モノリス成形体に気体状態のメソポーラス材料の前駆物質を所定時間、所定温度で流通させ、メソポーラス材料の中間体(通常はゾル状物質)を生成させる。必要に応じてアンモニア水又はアンモニアガスを流通させ、反応をクエンチすることもできる。生成した中間体を所定温度で焼成することによってゲル化させ同時に界面活性剤を分解除去することによって薄膜状のメソポーラス材料を固着させる。必要に応じて水洗することによって含有する酸を除去する。界面活性剤としては、従来のメソポーラス分子ふるいの作成に用いられているミセル形成の界面活性剤、例えば、長鎖の4級アンモニウム塩、長鎖のアルキルアミンN−オキシド、長鎖のスルホン酸塩、ポリエチレングリコールアルキルエーテル、ポリエチレングリコール脂肪酸エステル等のいずれであってもよい。上記界面活性剤の他に金属への配位能を有する化合物を少量添加すると反応系の安定性を著しく高めることができる。このような安定剤としては、アセチルアセトン、テトラメチレンジアミン、エチレンジアミン四酢酸、ピリジン、ピコリンなどの金属配位能を有する化合物が好ましい。溶媒としては、通常、水、アルコール類、ジオールの1種以上が用いられるが、水系溶媒が好ましい。酸としては、硝酸、硫酸、塩酸、リン酸、無水リン酸、ポリリン酸、酢酸、シュウ酸、過塩素酸、ホウ酸、ヘテロポリ酸などの通常の酸を用いることができる。酸性水溶液のpHは、通常、5〜0.01の範囲である。メソポーラス材料の前駆物質としては、通常、金属アルコキシドを用いるが、昇華性又は常温・常圧で気体状である金属のハロゲン化物、水素化物、有機金属化合物、等を用いることもできる。反応時間、反応温度は、使用するメソポーラス材料の前駆物質の反応性に応じて適当に設定するのであるが、通常、数秒から数十時間、−20℃から200℃の範囲である。生成した中間体の焼成は、通常、空気中500℃から1000℃の範囲で数10分から数十時間行う。前駆物質、界面活性剤、溶媒及び安定剤からなる反応系の組成は、前駆物質の全組成に対するモル比が0.01〜0.60、好ましくは0.02〜0.50、前駆物質/界面活性剤のモル比が1〜30、好ましくは1〜10、溶媒/界面活性剤のモル比が1〜1000、好ましくは5〜500、安定化剤/前駆物質のモル比が0.01〜1.0、好ましくは0.2〜0.6である。 Formation of a thin film mesoporous material on the inner wall of the gas flow path of the monolith molded article of the present invention can be usually performed by chemical vapor deposition (CVD: Chemical Vapor Deposition). In this method, an acidic solution in which a surfactant is dissolved is first attached to the inner wall of the gas flow path of the monolith molded body. Thereafter, a precursor of the mesoporous material in a gaseous state is passed through the monolith molded body for a predetermined time at a predetermined temperature to generate an intermediate (usually a sol-like substance) of the mesoporous material. If necessary, ammonia water or ammonia gas can be circulated to quench the reaction. The formed intermediate is gelled by firing at a predetermined temperature, and at the same time, the surfactant is decomposed and removed to fix the thin film mesoporous material. The contained acid is removed by washing with water as necessary. Surfactants include micelle-forming surfactants used to make conventional mesoporous molecular sieves, such as long-chain quaternary ammonium salts, long-chain alkylamine N-oxides, long-chain sulfonates , Polyethylene glycol alkyl ether, polyethylene glycol fatty acid ester and the like. The addition of a small amount of a compound capable of coordinating to a metal in addition to the surfactant can significantly increase the stability of the reaction system. As such a stabilizer, a compound having a metal coordination ability such as acetylacetone, tetramethylenediamine, ethylenediaminetetraacetic acid, pyridine, picoline and the like is preferable. As the solvent, one or more of water, alcohols, and diols are usually used, and an aqueous solvent is preferable. Usable as the acid are ordinary acids such as nitric acid, sulfuric acid, hydrochloric acid, phosphoric acid, phosphoric anhydride, polyphosphoric acid, acetic acid, oxalic acid, perchloric acid, boric acid, and heteropolyacid. The pH of the acidic aqueous solution is usually in the range of 5 to 0.01. As the precursor of the mesoporous material, a metal alkoxide is usually used, but metal halides, hydrides, organometallic compounds, etc. that are sublimable or gaseous at normal temperature and normal pressure can also be used. The reaction time and reaction temperature are appropriately set according to the reactivity of the precursor of the mesoporous material to be used, but are usually in the range of −20 ° C. to 200 ° C. for several seconds to several tens of hours. The resulting intermediate is usually baked in the air in the range of 500 ° C. to 1000 ° C. for several tens of minutes to several tens of hours. The composition of the reaction system consisting of the precursor, surfactant, solvent and stabilizer is such that the molar ratio of the precursor to the total composition is 0.01 to 0.60, preferably 0.02 to 0.50, and the precursor / surfactant molar ratio is 1 to 30, preferably 1-10, the solvent / surfactant molar ratio is 1-1000, preferably 5-500, and the stabilizer / precursor molar ratio is 0.01-1.0, preferably 0.2-0.6.
次に本発明で用いる触媒としては、白金含有触媒が好ましい。従来、白金を含有する自
動車の排ガス浄化用触媒としては三元触媒が知られているが、この触媒はディーゼル排NOx浄化処理にはほとんど効果がないことが知られている。その理由は、白金以外の構成元素であるパラジウム及びロジウムが高濃度の酸素によって表面酸化を受けるためである。三元触媒は白金-パラジウム-ロジウムで構成されているので表面酸化を受けるとたちまち失活し易い。本発明で白金含有触媒を用いる理由は、触媒の主成分である白金が排NOxの主成分である一酸化窒素を二酸化窒素に酸化する触媒能力が高く、高濃度の酸素雰囲気中でも化学的に安定であるからである。又、貴金属類の中では白金が比較的低温活性であるからでもある。触媒反応によって生成する二酸化窒素は、炭素数1から6の低級オレフィン及び低級パラフィン(燃料に少量含まれる)又はアンモニア態尿素(トラックなどに搭載できる)などの還元性物質によって容易に窒素と水に分解される。触媒粒子の表面積は粒径の二乗に反比例するので、触媒粒子が小さいほど触媒活性が高くなる。例えば、粒径1nmの触媒粒子の表面積は0.1μmのそれと比べると104倍大きい。また、ナノサイズに微粒化された触媒粒子は、活性を示すエッジ、コーナー、ステップなどの高次数の結晶面を多量にもつので、触媒活性が著しく向上するだけでなく、バルクでは触媒活性を示さないような不活性金属でも予期しなかった触媒活性を発現する場合があることが知られている。したがって、触媒能力の観点からは触媒粒子は細かいほど好ましいのであるが、反面、微粒化による表面酸化、副反応などの好ましくない性質もでてくるので、微粒子の粒子径には最適範囲が存在する。本発明における目的のNOx分解浄化処理に対して効果的な活性を示す触媒粒子の平均粒径は1〜20nmの範囲にあり、特に1〜10nmの範囲が高活性を示すことがわかった。本発明の触媒は薄膜状のメソポーラス材料の細孔に坦持された坦持型触媒である。主触媒としての白金の坦持量は0.01〜20質量%であり、好ましくは0.1〜10質量%であるが、量的な問題がなければ、通常は、1ないし数質量%の担持量で用いる。触媒坦持量は20質量%以上でも可能であるが、坦持量が過剰になると反応にほとんど寄与しない細孔深部の触媒が増えるので20質量%以下が好ましい。0.01質量%未満では活性が十分ではないので0.01質量%以上が好ましい。また、本発明の主触媒である白金触媒に異なる機能をもつ助触媒的成分を添加することによってシナジー効果による触媒性能の向上をはかることもできる。このような成分として、例えば、クロム、マンガン、鉄、コバルト、ニッケル、銅、亜鉛、バリウム、スカンジウム、イットリウム、チタン、ジルコニウム、ハフニウム、ニオブ、タンタル、モリブデン、タングステン、ランタン、セリウム、バリウム、及びこれらの化合物をあげることができる。これらの中で、不動態化膜になるクロム、鉄、コバルト、ニッケル、還元剤の吸着力が比較的高い銅、NOx吸蔵性がある酸化バリウム、中程度の酸化力をもつ酸化セリウムと三二酸化マンガン、SOx被毒防止に有効な銅-亜鉛、鉄-クロム、酸化モリブデン、などは好ましい。これらの助触媒的成分の添加量は、通常、白金重量の0.01倍から100倍程度であるが、必要に応じて100倍以上であってもよい。
Next, the catalyst used in the present invention is preferably a platinum-containing catalyst. Conventionally, a three-way catalyst is known as an exhaust gas purifying catalyst for automobiles containing platinum, but this catalyst is known to have little effect on diesel exhaust NOx purification treatment. The reason is that palladium and rhodium, which are constituent elements other than platinum, are subjected to surface oxidation by a high concentration of oxygen. Since the three-way catalyst is composed of platinum-palladium-rhodium, it is easily deactivated when subjected to surface oxidation. The reason for using the platinum-containing catalyst in the present invention is that platinum, which is the main component of the catalyst, has a high catalytic ability to oxidize nitrogen monoxide, which is the main component of exhaust NOx, into nitrogen dioxide, and is chemically stable even in a high concentration oxygen atmosphere. Because. It is also because platinum is relatively low temperature active among noble metals. Nitrogen dioxide produced by the catalytic reaction can be easily converted into nitrogen and water by reducing substances such as lower olefins having 1 to 6 carbon atoms and lower paraffin (a small amount in fuel) or ammonia urea (which can be mounted on trucks). Disassembled. Since the surface area of the catalyst particles is inversely proportional to the square of the particle diameter, the smaller the catalyst particles, the higher the catalytic activity. For example, the surface area of the catalyst particles having a particle diameter of 1nm to 10 4 times greater than that of 0.1 [mu] m. In addition, catalyst particles atomized into nano-sizes have a large number of high-order crystal planes such as edges, corners, and steps that exhibit activity, so that not only catalytic activity is significantly improved but also catalytic activity is exhibited in bulk. It is known that even an inert metal such as this may exhibit unexpected catalytic activity. Therefore, finer catalyst particles are preferable from the viewpoint of catalytic ability, but on the other hand, there are also undesirable properties such as surface oxidation and side reactions due to atomization, so there is an optimum range for the particle size of the fine particles. . It has been found that the average particle diameter of the catalyst particles exhibiting an effective activity for the target NOx decomposition purification treatment in the present invention is in the range of 1 to 20 nm, and particularly in the range of 1 to 10 nm. The catalyst of the present invention is a supported catalyst supported on pores of a thin film mesoporous material. The supported amount of platinum as the main catalyst is 0.01 to 20% by mass, and preferably 0.1 to 10% by mass. If there is no problem with quantity, the supported amount is usually 1 to several percent by mass. . The supported amount of the catalyst can be 20% by mass or more. However, if the supported amount becomes excessive, the catalyst in the deep part of the pores that hardly contributes to the reaction increases, and therefore it is preferably 20% by mass or less. Since activity is not enough if it is less than 0.01 mass%, 0.01 mass% or more is preferable. Further, by adding a promoter component having a different function to the platinum catalyst which is the main catalyst of the present invention, the catalyst performance can be improved by the synergy effect. Examples of such components include chromium, manganese, iron, cobalt, nickel, copper, zinc, barium, scandium, yttrium, titanium, zirconium, hafnium, niobium, tantalum, molybdenum, tungsten, lanthanum, cerium, barium, and these. Can be mentioned. Among these, chromium, iron, cobalt, nickel, which is a passivating film, copper with a relatively high adsorptive power of reducing agents, barium oxide with NOx storage, cerium oxide and trioxide with moderate oxidizing power Manganese, copper-zinc, iron-chromium, molybdenum oxide and the like effective for preventing SOx poisoning are preferable. The amount of these promoter components is usually about 0.01 to 100 times the weight of platinum, but may be 100 times or more as required.
本発明におけるモノリス成形体とは、成形体の断面が網目状で、軸方向に平行に互いに薄い壁によって仕切られたガス流路を設けている成形体のことである。成形体の外形は、特に限定するものではないが、通常は、円柱形である。本発明のハニカム触媒とは、モノリス成形体のガス流路内壁に薄膜状のメソポーラス材料を形成させ、そこに触媒を担持させたことによって成る触媒を意味している。触媒の担持量はモノリス成形体に対して、0.1から5質量%が好ましい。5%を超える担持量は、担体内部に存在する触媒へのガス拡散が遅いので5%以下が好ましい。また、触媒性能を十分に発揮する上から0.1%以上であることが好ましい。 The monolith molded body in the present invention is a molded body in which a cross section of the molded body is mesh-like and provided with gas flow paths partitioned by thin walls in parallel to the axial direction. Although the external shape of a molded object is not specifically limited, Usually, it is a cylindrical shape. The honeycomb catalyst of the present invention means a catalyst formed by forming a mesoporous material in the form of a thin film on the inner wall of a gas flow path of a monolith molded body and supporting the catalyst thereon. The amount of catalyst supported is preferably 0.1 to 5% by mass relative to the monolith molded article. The supported amount exceeding 5% is preferably 5% or less because gas diffusion to the catalyst existing inside the support is slow. Moreover, it is preferable that it is 0.1% or more from the standpoint of fully exhibiting catalyst performance.
本発明のハニカム触媒は、自動車用三元触媒を付着したモノリス成形体の製造方法に準じて製造することができる。通常、イオン交換法又は含浸法によって製造することができる。これらの二つの方法は、担体への触媒の沈着化について、イオン交換法が担体表面のイオン交換能を利用し、含浸法が担体のもつ毛管作用を利用しているという違いはあるが、基本的なプロセスはほとんど同じである。すなわち、薄膜状のメソポーラス材料をガス
流路内壁に形成させたモノリス成形体を触媒原料の水溶液に浸した後、濾過、乾燥し、必要に応じて水洗を行い、還元剤で還元処理することによって製造することができる。白金の触媒原料としては、例えば、H2PtCl4、(NH4)2PtCl4、H2PtCl6、(NH4)2PtCl6、Pt(NH3)4(NO3)2、Pt(NH3)4(OH)2、PtCl4、白金のアセチルアセトナート、等を用いることができる。必要に応じて主触媒に添加する助触媒的成分の原料としては、例えば、塩化物、硝酸塩、硫酸塩、炭酸塩、酢酸塩などの水溶性塩類を用いることができる。白金に助触媒的成分を添加した触媒についても、その原料を主触媒原料に混合して同様にして製造することができる。還元剤としては、水素、ヒドラジン水溶液、ホルマリン、等を用いることができる。還元は、それぞれの還元剤について知られている通常の条件で行なえばよい。例えば、水素還元は、ヘリウムなどの不活性ガスで希釈した水素ガス気流下にサンプルを置き、通常、300〜500℃で数時間処理することによって行なうことができる。還元後、必要に応じて、不活性ガス気流下500〜1000℃で数時間熱処理してもよい。
The honeycomb catalyst of the present invention can be manufactured according to a method for manufacturing a monolith molded article to which a three-way catalyst for automobiles is attached. Usually, it can be produced by an ion exchange method or an impregnation method. These two methods are different in that the catalyst is deposited on the support, although the ion exchange method uses the ion exchange capacity of the support surface and the impregnation method uses the capillary action of the support. The general process is almost the same. That is, by immersing a monolith molded body in which a thin film mesoporous material is formed on the inner wall of the gas flow path in an aqueous catalyst material solution, filtering, drying, washing with water as necessary, and reducing with a reducing agent Can be manufactured. Examples of platinum catalyst materials include H 2 PtCl 4 , (NH 4 ) 2 PtCl 4 , H 2 PtCl 6 , (NH 4 ) 2 PtCl 6 , Pt (NH 3 ) 4 (NO 3 ) 2 , Pt (NH 3 ) 4 (OH) 2 , PtCl 4 , platinum acetylacetonate, and the like can be used. As a raw material of the co-catalytic component added to the main catalyst as necessary, for example, water-soluble salts such as chloride, nitrate, sulfate, carbonate and acetate can be used. A catalyst obtained by adding a promoter component to platinum can also be produced in the same manner by mixing the raw material with the main catalyst raw material. As the reducing agent, hydrogen, an aqueous hydrazine solution, formalin, or the like can be used. The reduction may be performed under normal conditions known for each reducing agent. For example, hydrogen reduction can be performed by placing a sample in a hydrogen gas stream diluted with an inert gas such as helium and treating the sample at 300 to 500 ° C. for several hours. After reduction, if necessary, heat treatment may be performed at 500 to 1000 ° C. for several hours under an inert gas stream.
本発明のハニカム触媒は、自動車、特にディーゼル自動車に搭載することによって、自動車が排出するリーンバーン排NOxを100〜700℃の広い温度範囲において極めて効果的に浄化することができる。排NOxの処理には還元剤が必要であるが、乗用車などの小型車の場合には、燃料である軽油に少量含まれている炭素数1から6の低級オレフィン及び低級パラフィンが還元剤となるので、燃料を直接又は改質器を通して触媒上に供給すればよい。リッチバーンの時には酸素濃度が低くリーンバーンの時には酸素濃度が高いので、リッチバーンとリーンバーンを交互に行うことができる小型ディーゼルの排ガス浄化処理のために本発明のモノリス触媒を用いると、150〜700℃の広い温度範囲において効率よく排NOxを浄化処理できる。また、トラックなどの大型車の場合には、通常、尿素水を熱分解して還元剤としてのアンモニアを発生させ触媒上に供給するシステムを利用できるので、尿素供給システムを搭載する大型ディーゼル用の排NOx浄化用触媒としても用いることができる。 When the honeycomb catalyst of the present invention is mounted on an automobile, particularly a diesel automobile, the lean burn exhaust NOx discharged by the automobile can be extremely effectively purified in a wide temperature range of 100 to 700 ° C. Although a reducing agent is required for the treatment of exhaust NOx, in the case of small cars such as passenger cars, lower olefins and lower paraffins having 1 to 6 carbon atoms contained in a small amount of light oil as fuel become reducing agents. The fuel may be supplied directly or through the reformer onto the catalyst. Since the oxygen concentration is low at the time of rich burn and the oxygen concentration is high at the time of lean burn, when the monolith catalyst of the present invention is used for exhaust gas purification treatment of a small diesel that can perform rich burn and lean burn alternately, 150 to Exhaust NOx can be purified efficiently over a wide temperature range of 700 ° C. Also, in the case of large vehicles such as trucks, it is usually possible to use a system that thermally decomposes urea water to generate ammonia as a reducing agent and supplies it onto the catalyst. It can also be used as an exhaust NOx purification catalyst.
以下に実施例などを挙げて本発明を具体的に説明する。
実施例中の粉末X線回折パターンは理学電機社製RINT2000型X線回折装置によって測定した。触媒の平均粒径は、透過型電子顕微鏡を用いた直接観察によって決定し、粉末X線回折パターンのメインピークの半値幅をシェラー式に代入して算出した値と一致することを確認した。比表面積及び細孔分布は、脱吸着の気体として窒素を用い、カルロエルバ社製ソープトマチック1800型装置によって測定した。比表面積はBET法によって求めた。細孔分布は1〜200nmの範囲を測定し、BJH法で求められる微分分布で示した。合成した薄膜状のメソポーラス材料の多くは指数関数的に左肩上がりの分布における特定の細孔直径の位置にピークを示した。このピークを、便宜上、細孔ピークと呼ぶ。材料の結晶性と残留界面活性剤を調べるための熱分析は、島津製作所製DTA-50型熱分析装置によって、昇温速度20℃min-1で測定した。自動車排NOxのモデルガスとして、ヘリウム希釈一酸化窒素、酸素、及び還元性ガス(エチレン又はアンモニア)を用いた。一酸化窒素の処理率は、減圧式化学発光法NOx分析計(日本サーモ株式会社製造:モデル42C)によって処理後のガスに含まれるNOxを測定し、以下の式(1)に従って算出した。
The present invention will be specifically described below with reference to examples.
The powder X-ray diffraction patterns in the examples were measured with a RINT2000 type X-ray diffraction apparatus manufactured by Rigaku Corporation. The average particle diameter of the catalyst was determined by direct observation using a transmission electron microscope, and it was confirmed that the average particle diameter of the catalyst coincided with the value calculated by substituting the half width of the main peak of the powder X-ray diffraction pattern into the Scherrer equation. The specific surface area and pore distribution were measured with a Sorpmatic 1800 type apparatus manufactured by Carlo Elba using nitrogen as a desorption gas. The specific surface area was determined by the BET method. The pore distribution was measured in the range of 1 to 200 nm and indicated by a differential distribution obtained by the BJH method. Many of the thin film mesoporous materials synthesized showed a peak at a specific pore diameter in an exponentially increasing distribution. This peak is called a pore peak for convenience. Thermal analysis for investigating the crystallinity of the material and the residual surfactant was measured with a DTA-50 type thermal analyzer manufactured by Shimadzu Corporation at a heating rate of 20 ° C. min −1 . Helium-diluted nitric oxide, oxygen, and reducing gas (ethylene or ammonia) were used as model gases for automobile exhaust NOx. The treatment rate of nitric oxide was calculated according to the following equation (1) by measuring NOx contained in the treated gas with a reduced pressure chemiluminescence NOx analyzer (manufactured by Nippon Thermo Co., Ltd .: model 42C).
「製造例1」比較サンプル[Pt-Pd-Rh/γ-アルミナ/モノリス]の作成
γ-アルミナ(日揮化学株式会社製造:比表面積250m2/g、細孔径6.2nm、粒径2〜3μmの微粒子)10gを10質量%のアルミナゾルの水溶液100gに加え攪拌する。これに市販のコージェライト製モノリス成形体(400セル/in2、直径118mm×長さ50mm、重量243g)から切り出したミニ成形体(21セル、直径8mm×長さ9mm、重量0.15g)を5個入れ10分間静置した後、成形体を取り出し300℃で1時間加熱した。この操作を5回繰り返した後、空気中500℃で3時間焼成した。γ-アルミナの塗布量はミニ成形体の約10質量%であり、塗布層の厚みは約100μmであった。次にこの成形体を0.0215gのPtCl4・5H2O、0.0106gのPdCl2・2H2O、及び0.0162gのRh(NO3)3・2H2Oを溶解した水溶液10gに1時間浸漬した後、成形体を取り出し、100℃で3時間真空乾燥を行った。この試料を石英管に入れヘリウム希釈水素ガス(10%v/v)気流下500℃で3時間熱処理した。貴金属の含有量は約2質量%であった(表1に記載)。
[Production Example 1] Preparation of comparative sample [Pt-Pd-Rh / γ-alumina / monolith] γ-alumina (manufactured by JGC Chemical Co., Ltd .: specific surface area 250 m 2 / g, pore size 6.2 nm, particle size 2 to 3 μm 10 g of (fine particles) is added to 100 g of a 10% by mass aqueous solution of alumina sol and stirred. 5 mini-molded bodies (21 cells, diameter 8 mm × length 9 mm, weight 0.15 g) cut out from a commercially available cordierite monolith molded body (400 cells / in 2 , diameter 118 mm × length 50 mm, weight 243 g) After allowing the container to stand for 10 minutes, the molded body was taken out and heated at 300 ° C. for 1 hour. This operation was repeated 5 times and then calcined in air at 500 ° C. for 3 hours. The coating amount of γ-alumina was about 10% by mass of the mini-molded body, and the thickness of the coating layer was about 100 μm. Next, the compact was immersed in 10 g of an aqueous solution in which 0.0215 g of PtCl 4 .5H 2 O, 0.0106 g of PdCl 2 .2H 2 O, and 0.0162 g of Rh (NO 3 ) 3 .2H 2 O were dissolved for 1 hour. Thereafter, the molded body was taken out and vacuum-dried at 100 ° C. for 3 hours. This sample was put in a quartz tube and heat-treated at 500 ° C. for 3 hours under a helium-diluted hydrogen gas (10% v / v) stream. The precious metal content was about 2% by mass (described in Table 1).
「製造例2」比較サンプル[Pt/γ-アルミナ/モノリス]の作成
製造例1で作成したγ-アルミナを塗布したコージェライト製モノリス成形体のミニ成形体を5個、0.0267gのH2PtCl6・6H2O を溶解した水溶液10gに1時間浸漬した後、成形体を取り出し、100℃で3時間真空乾燥を行った。この試料を石英管に入れヘリウム希釈水素ガス(10%v/v)気流下500℃で3時間熱処理した。白金の含有量は約1質量%であった(表1に記載)。
Production Example 2 Preparation of comparative sample [Pt / γ-alumina / monolith]
5 cordierite monolith compacts coated with γ-alumina prepared in Production Example 1 were immersed in 10 g of an aqueous solution in which 0.0267 g of H 2 PtCl 6 · 6H 2 O was dissolved, and then molded. The body was taken out and vacuum-dried at 100 ° C. for 3 hours. This sample was put in a quartz tube and heat-treated at 500 ° C. for 3 hours under a helium-diluted hydrogen gas (10% v / v) stream. The platinum content was about 1% by mass (described in Table 1).
「製造例3」白金含有ハニカム触媒[Pt/メソポーラスシリカ/モノリス]の作成
容積100mlのビーカーに、蒸留水30g、エタノール24g、ドデシルアミン0.3g、及び硫酸0.5gを入れ、攪拌し、均一な水溶液を調整した。これに、製造例1で使用したものと同じミニ成形体を5個入れ、10分間静置した後、ミニ成形体を取り出し風乾した。これを、2gのテトラエチルオルトシリケート(TEOS)の入ったシャーレを置いた容積200mlのデシケータの中に、TEOSに触れないように水平に置き、乾燥機に入れ、90℃で1時間処理した。試料を取り出し500℃で5時間焼成した。得られた試料の切片を走査型電子顕微鏡で観察した結果、薄膜状のメソポーラスシリカがミニ成形体のガス流路内壁に形成されていることが確認された。該メソポーラスシリカの厚みは約200nmであり、比表面積は980m2/g、細孔径は3.2nmであった。
次に、この成形体を0.0267gのH2PtCl6・6H2O を溶解した水溶液10gに1時間浸漬した後、成形体を取り出し、100℃で3時間真空乾燥を行った。この試料を石英管に入れヘリウム希釈水素ガス(10%v/v)気流下500℃で3時間熱処理した。白金の含有量は約1質量%であった(表1に記載)。
“Production Example 3” Preparation of platinum-containing honeycomb catalyst [Pt / mesoporous silica / monolith] In a beaker with a capacity of 100 ml, 30 g of distilled water, 24 g of ethanol, 0.3 g of dodecylamine and 0.5 g of sulfuric acid were added and stirred to obtain a homogeneous aqueous solution. Adjusted. Into this, 5 pieces of the same mini-molded body as used in Production Example 1 were put, allowed to stand for 10 minutes, and then the mini-molded body was taken out and air-dried. This was placed horizontally in a 200 ml desiccator containing a petri dish containing 2 g of tetraethylorthosilicate (TEOS) so as not to touch TEOS, placed in a dryer, and treated at 90 ° C. for 1 hour. A sample was taken out and baked at 500 ° C. for 5 hours. As a result of observing a section of the obtained sample with a scanning electron microscope, it was confirmed that thin mesoporous silica was formed on the inner wall of the gas channel of the mini-molded product. The mesoporous silica had a thickness of about 200 nm, a specific surface area of 980 m 2 / g, and a pore diameter of 3.2 nm.
Next, the molded body was immersed in 10 g of an aqueous solution in which 0.0267 g of H 2 PtCl 6 .6H 2 O was dissolved for 1 hour, and then the molded body was taken out and vacuum dried at 100 ° C. for 3 hours. This sample was put in a quartz tube and heat-treated at 500 ° C. for 3 hours under a helium-diluted hydrogen gas (10% v / v) stream. The platinum content was about 1% by mass (described in Table 1).
「比較例1、2」還元剤として炭化水素を用いたリーンバーン条件でのNOx処理
石英製の連続流通式反応管に製造例1及び2で作成した触媒担持のミニ成形体をそれぞれ1個入れ、ヘリウムで濃度調整した一酸化窒素を流通処理した。被処理ガスの成分モル濃度は、一酸化窒素0.1%、酸素14%、水蒸気10%、及びエチレン0.3%であった。反応管へ導入した混合ガスの流量を毎分100 ml、処理温度を160〜300℃とした。処理後のガスに含まれるNOxを測定し、一酸化窒素の処理率を求めた。結果を表2に示した。
“Comparative Examples 1 and 2” NOx treatment under lean burn conditions using hydrocarbons as reducing agent 1 each of the catalyst-supported mini-molded bodies prepared in Production Examples 1 and 2 was placed in a continuous flow reaction tube made of quartz. Then, nitrogen monoxide adjusted in concentration with helium was flow-treated. The component molar concentrations of the gas to be treated were 0.1% nitric oxide, 14% oxygen, 10% water vapor, and 0.3% ethylene. The flow rate of the mixed gas introduced into the reaction tube was 100 ml per minute, and the treatment temperature was 160 to 300 ° C. NOx contained in the treated gas was measured to determine the treatment rate of nitric oxide. The results are shown in Table 2.
「実施例1」還元剤として炭化水素を用いたリーンバーン条件でのNOx処理
石英製の連続流通式反応管に製造例3で作成した触媒担持のミニ成形体を1個入れ、ヘリウムで濃度調整した一酸化窒素を流通処理した。被処理ガスの成分モル濃度は、一酸化窒素0.1%、酸素14%、水蒸気10%、及びエチレン0.3%であった。反応管へ導入した混合ガスの流量を毎分100 ml、処理温度を160〜300℃とした。処理後のガスに含まれるNOxを測定し、一酸化窒素の処理率を求めた。結果を表2に示した。
表1から、従来の三元触媒類似の触媒は、高濃度酸素雰囲気にあるNOxは殆ど処理できないが、これに対して、本発明のハニカム触媒は、エチレンなどの炭化水素を還元剤に用いて高濃度酸素共存下でのNOxを160〜300℃の低温領域でも80%以上浄化できること
がわかる。したがって、小型ディーゼル車の排NOx処理に適していることがわかる。
"Example 1" NOx treatment under lean burn conditions using hydrocarbon as a reducing agent Place one catalyst-molded mini-molded body prepared in Production Example 3 into a quartz continuous flow reaction tube and adjust the concentration with helium The treated nitric oxide was flow-treated. The component molar concentrations of the gas to be treated were 0.1% nitric oxide, 14% oxygen, 10% water vapor, and 0.3% ethylene. The flow rate of the mixed gas introduced into the reaction tube was 100 ml per minute, and the treatment temperature was 160 to 300 ° C. NOx contained in the treated gas was measured to determine the treatment rate of nitric oxide. The results are shown in Table 2.
From Table 1, the conventional three-way catalyst-like catalyst can hardly process NOx in a high-concentration oxygen atmosphere, whereas the honeycomb catalyst of the present invention uses a hydrocarbon such as ethylene as a reducing agent. It can be seen that NOx in the presence of high concentration oxygen can be purified by 80% or more even in a low temperature range of 160 to 300 ° C. Therefore, it turns out that it is suitable for the exhaust-NOx process of a small diesel vehicle.
「実施例2」還元剤として炭化水素を用いたリッチバーン条件でのNOx処理
石英製の連続流通式反応管に製造例3で作成した触媒担持のミニ成形体を1個入れ、ヘリウムで濃度調整した一酸化窒素を流通処理した。被処理ガスの成分モル濃度比は、一酸化窒素0.1%、酸素1%、エチレン1%であった。該調整ガスの流量を毎分100 ml、処理温度を300〜600℃とした。処理後のガスに含まれるNOxを測定し一酸化窒素の処理率を求めた。結果を表3に示した。
表3から、本発明のハニカム触媒(製造例3)は、エチレンなどの炭化水素を還元剤に用いてリッチバーンの条件にあるNOxを300℃から600℃にわたって効率よく浄化できることがわかる。したがって、例えば、リーンバーンとリッチバーンを交互に行えば、実施例1のハニカム触媒は、広い温度範囲でNOxを除去できるので、リーンバーンとリッチバーンを交互に行うことのできる小型ディーゼル車の排NOx処理に適していることがわかる。
"Example 2" NOx treatment under rich burn conditions using hydrocarbon as a reducing agent Place one catalyst-molded mini-molded body prepared in Production Example 3 into a quartz continuous flow reaction tube and adjust the concentration with helium The treated nitric oxide was flow-treated. The component molar concentration ratio of the gas to be treated was 0.1% nitric oxide, 1% oxygen, and 1% ethylene. The flow rate of the adjustment gas was 100 ml / min, and the treatment temperature was 300 to 600 ° C. NOx contained in the treated gas was measured to determine the treatment rate of nitric oxide. The results are shown in Table 3.
From Table 3, it can be seen that the honeycomb catalyst of the present invention (Production Example 3) can efficiently purify NOx under rich burn conditions from 300 ° C. to 600 ° C. using a hydrocarbon such as ethylene as a reducing agent. Therefore, for example, if the lean burn and the rich burn are alternately performed, the honeycomb catalyst of Example 1 can remove NOx in a wide temperature range. Therefore, the exhaust of a small diesel vehicle that can perform the lean burn and the rich burn alternately. It turns out that it is suitable for NOx treatment.
「実施例3」還元剤としてアンモニアを用いたNOx処理
石英製の連続流通式反応管に製造例3で作成した触媒担持のミニ成形体を1個入れ、ヘリウムで濃度調整した一酸化窒素を流通処理した。被処理ガスの成分モル濃度比は、一酸化窒素0.1%、酸素14%、水蒸気10%、アンモニア0.3%とした。該調整ガスの流量を毎分100
ml、処理温度を100〜600℃とした。処理後のガスに含まれるNOxを測定し一酸化窒素の浄化処理率を求めた。結果を表4に示した。
表4から、本発明のハニカム触媒は、アンモニアを還元剤として用いても高濃度酸素共存下(リーンバーン条件下)でのNOxを効率よく浄化できることがわかる。したがって、アンモニア源としての尿素供給システムを搭載している大型ディーゼル車の排NOx浄化処理に適していることがわかる。
"Example 3" NOx treatment using ammonia as a reducing agent Place one catalyst-molded mini-molded body prepared in Production Example 3 into a quartz continuous-flow reaction tube, and flow through nitric oxide adjusted in concentration with helium Processed. The component molar concentration ratio of the gas to be treated was 0.1% nitric oxide, 14% oxygen, 10% water vapor, and 0.3% ammonia. The flow rate of the adjustment gas is 100 per minute.
ml, the processing temperature was 100-600 ° C. The NOx contained in the treated gas was measured to determine the nitric oxide purification rate. The results are shown in Table 4.
From Table 4, it can be seen that the honeycomb catalyst of the present invention can efficiently purify NOx in the presence of high-concentration oxygen (lean burn condition) even when ammonia is used as a reducing agent. Therefore, it turns out that it is suitable for the exhaust-NOx purification process of the large-sized diesel vehicle carrying the urea supply system as an ammonia source.
本発明のハニカム触媒は、ディーゼル排NOx浄化用触媒として有用である。 The honeycomb catalyst of the present invention is useful as a diesel exhaust NOx purification catalyst.
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