JP2007244934A - Catalyst for exhaust gas treatment - Google Patents
Catalyst for exhaust gas treatment Download PDFInfo
- Publication number
- JP2007244934A JP2007244934A JP2006068205A JP2006068205A JP2007244934A JP 2007244934 A JP2007244934 A JP 2007244934A JP 2006068205 A JP2006068205 A JP 2006068205A JP 2006068205 A JP2006068205 A JP 2006068205A JP 2007244934 A JP2007244934 A JP 2007244934A
- Authority
- JP
- Japan
- Prior art keywords
- catalyst
- mesoporous
- monolith
- mesoporous silica
- nox
- 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.)
- Granted
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- 239000003054 catalyst Substances 0.000 title claims abstract description 179
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- 239000011148 porous material Substances 0.000 claims abstract description 75
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims abstract description 65
- 239000000377 silicon dioxide Substances 0.000 claims abstract description 58
- 239000002245 particle Substances 0.000 claims abstract description 39
- 229910052697 platinum Inorganic materials 0.000 claims abstract description 29
- 238000000746 purification Methods 0.000 claims description 21
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 abstract description 20
- 229910052760 oxygen Inorganic materials 0.000 abstract description 20
- 239000001301 oxygen Substances 0.000 abstract description 20
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- 229910002089 NOx Inorganic materials 0.000 description 55
- 239000007789 gas Substances 0.000 description 41
- MWUXSHHQAYIFBG-UHFFFAOYSA-N Nitric oxide Chemical compound O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 32
- 238000000034 method Methods 0.000 description 22
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- MGWGWNFMUOTEHG-UHFFFAOYSA-N 4-(3,5-dimethylphenyl)-1,3-thiazol-2-amine Chemical compound CC1=CC(C)=CC(C=2N=C(N)SC=2)=C1 MGWGWNFMUOTEHG-UHFFFAOYSA-N 0.000 description 2
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- JSKIRARMQDRGJZ-UHFFFAOYSA-N dimagnesium dioxido-bis[(1-oxido-3-oxo-2,4,6,8,9-pentaoxa-1,3-disila-5,7-dialuminabicyclo[3.3.1]nonan-7-yl)oxy]silane Chemical compound [Mg++].[Mg++].[O-][Si]([O-])(O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2)O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2 JSKIRARMQDRGJZ-UHFFFAOYSA-N 0.000 description 2
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Abstract
Description
本発明は高比表面積のメソポーラス触媒及びこの触媒をモノリス成形体のガス流路内壁に付着させたモノリス触媒に関するものであり、モノリス触媒を用いることによってリーンバーン自動車排ガスに含まれるNOxを高効率で浄化処理できる。 The present invention relates to a mesoporous catalyst having a high specific surface area and a monolith catalyst in which this catalyst is attached to the inner wall of a gas flow path of a monolith molded body. By using the monolith catalyst, NOx contained in lean burn automobile exhaust gas can be efficiently produced. It can be purified.
従来、ガソリン車の排ガスに含まれるNOx、一酸化炭素、及び炭化水素は、白金族元素から成る三元触媒によって浄化されている(特許文献1参照)。三元触媒は、通常、触媒支持体としてコージェライト製のモノリス成形体を用い、該成形体のガス流路内壁に数μm〜数十μmの大きさの活性アルミナ粒子を塗布し、該塗布層に数100nm〜数μmの大きさの白金−パラジウム−ロジウム粒子を担持させた構造となっている。
三元触媒による浄化方法は、空気:燃料の重量混合比である空燃比を理論空燃比(=14.7)近傍に制御することで(この燃焼はリッチバーンと呼ばれている)排ガスに含まれる酸素濃度を1%以下に維持できるので、排ガスに含まれる一酸化炭素及び炭化水素をNOxの還元剤として利用できるという利点を持つが、排ガス中の酸素濃度が数%以上になると触媒の著しい酸化劣化が生じるという問題がある。
Conventionally, NOx, carbon monoxide, and hydrocarbons contained in exhaust gas from gasoline vehicles have been purified by a three-way catalyst composed of a platinum group element (see Patent Document 1). The three-way catalyst usually uses a cordierite monolith molded body as the catalyst support, and the activated alumina particles having a size of several μm to several tens of μm are applied to the inner wall of the gas flow path of the molded body. In this structure, platinum-palladium-rhodium particles having a size of several hundred nm to several μm are supported.
The purification method with a three-way catalyst is included in the exhaust gas by controlling the air-fuel ratio, which is the air: fuel weight mixing ratio, close to the theoretical air-fuel ratio (= 14.7) (this combustion is called rich burn). Since the oxygen concentration can be maintained at 1% or less, carbon monoxide and hydrocarbons contained in the exhaust gas can be used as a reducing agent for NOx. However, when the oxygen concentration in the exhaust gas exceeds several percent, the catalyst There is a problem that oxidation deterioration occurs.
また、軽油燃料で走行するトラック、バス等の大型ディーゼル車の排ガス処理は、触媒として遷移金属化合物又は白金族元素を用い還元剤として尿素水を用いる、所謂尿素SCR法が検討されている(特許文献2参照)。この方法は、100℃付近の比較的低温領域から600℃付近の比較的高温領域に渡ってNOxを効率的に浄化できるという利点を持つが、還元剤として高価な尿素水の搭載が必要であるという問題がある。
一方、ディーゼル乗用車等の小型ディーゼル車の排NOx処理には三元触媒が使用できない。それは、空燃比がガソリンの空燃比の数倍以上であるので(ディーゼル燃料の燃焼はリーンバーンとよばれている)ディーゼル排ガス中の酸素濃度が通常5%以上であり還元性物質がほとんど含まれていないためである。同様の理由でリーンバーンガソリン車の排ガスも三元触媒では浄化が難しい。
In addition, a so-called urea SCR method using a transition metal compound or a platinum group element as a catalyst and urea water as a reducing agent has been studied for exhaust gas treatment of large diesel vehicles such as trucks and buses that run on light oil fuel (patents). Reference 2). This method has the advantage of being able to efficiently purify NOx from a relatively low temperature region near 100 ° C. to a relatively high temperature region near 600 ° C., but it requires the mounting of expensive urea water as a reducing agent. There is a problem.
On the other hand, a three-way catalyst cannot be used for exhaust NOx treatment of small diesel vehicles such as diesel passenger cars. Because the air-fuel ratio is more than several times that of gasoline (combustion of diesel fuel is called lean burn), the oxygen concentration in diesel exhaust gas is usually over 5% and contains almost no reducing substances. Because it is not. For the same reason, it is difficult to purify the exhaust gas from lean burn gasoline vehicles with a three-way catalyst.
小型ディーゼル車の排NOx処理には、触媒として白金族触媒にNOx吸蔵剤を添加した所謂NOx吸蔵還元触媒が検討されている(特許文献3参照)。この方法は、リーンバーンとリッチバーンのサイクル燃焼を行い、リーンバーン排NOxをNOx吸蔵剤で吸収し、吸収NOxをリッチバーン雰囲気下で放出させ、放出NOxをリッチバーン排ガス中の一酸化炭素、水素、炭化水素等の還元性物質で還元処理するという考えに立脚している。
NOx吸蔵還元触媒を用いた浄化方法は、ガソリン乗用車の排ガス処理に用いられている三元触媒が使用できないような高濃度の酸素雰囲気中でも250℃付近から600℃付近に渡ってNOxを浄化できるという利点を持つが、200℃付近以下でのNOx浄化は非常に困難であるという問題と排ガス中の水分及び少量のSOxによってNOx吸蔵剤が著しく劣化するという問題がある。
A so-called NOx occlusion reduction catalyst in which a NOx occlusion agent is added to a platinum group catalyst as a catalyst has been studied for the exhaust NOx treatment of small diesel vehicles (see Patent Document 3). In this method, lean burn and rich burn cycle combustion is performed, lean burn exhaust NOx is absorbed by the NOx storage agent, absorbed NOx is released in a rich burn atmosphere, and the released NOx is released from the carbon monoxide in the rich burn exhaust gas. It is based on the idea of reducing with a reducing substance such as hydrogen or hydrocarbon.
The purification method using the NOx occlusion reduction catalyst can purify NOx from about 250 ° C. to about 600 ° C. even in a high-concentration oxygen atmosphere in which a three-way catalyst used for exhaust gas treatment of gasoline passenger cars cannot be used. Although there is an advantage, there is a problem that NOx purification at about 200 ° C. or lower is very difficult and a problem that the NOx storage agent is remarkably deteriorated by moisture in the exhaust gas and a small amount of SOx.
また、ディーゼル排ガス等の排NOx浄化用に研究されているゼオライト担持触媒は、水熱条件下での水分及び酸素によって著しく活性が低下するという問題がある。
ところで、国内ではディーゼル乗用車の排出する排ガスの温度は過渡走行時でおよそ120℃〜200℃であり安定走行時でおよそ200℃〜400℃であるが、排出されるNOxの約80%が過渡走行時に排出されている。したがって、ディーゼル乗用車の排NOx処理に要求される触媒は、上記120℃〜200℃の低温領域で高活性を有する触媒であることが望まれている。
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。
Further, the zeolite-supported catalyst that has been studied for purifying exhaust NOx such as diesel exhaust gas has a problem that the activity is remarkably lowered by moisture and oxygen under hydrothermal conditions.
By the way, in Japan, the temperature of exhaust gas discharged from diesel passenger cars is approximately 120 ° C. to 200 ° C. during transient travel and approximately 200 ° C. to 400 ° C. during stable travel, but about 80% of the NOx discharged is transient travel. Sometimes discharged. Therefore, the catalyst required for the exhaust NOx treatment of diesel passenger cars is desired to be a catalyst having high activity in the low temperature range of 120 ° C to 200 ° C.
In general, industrial catalysts are often used in a state where they are supported on a porous material. The pores of the porous material are classified into micropores with a pore diameter of 2 nm or less, mesopores of 2 to 50 nm, and macropores of 50 nm or more according to IUPAC (International Pure and Applied Chemical Association). Yes. No single porous material other than activated carbon has a wide distribution ranging from the micro to meso range.
近年、細孔径が数nmの細孔が規則的に配列し、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のメソポーラス分子篩が開発された。これらは、例えば、特許文献1、2、及び3等に開示されており、細孔の細孔配列があたかも結晶性物質の原子配列に類似していることから結晶性メソポーラス分子篩と命名されている。
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。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であり、その比表面積が約0.2m2/g、担体としてのアルミナ粒子の比表面積が110〜340m2/gであり、触媒の比表面積は粒径から20〜40m2/g程度であると推定される。したがって、従来の触媒粒子の粒径よりも一桁から二桁小さいナノサイズの触媒粒子を上記結晶性のメソポーラス材料の細孔内に担持することによって触媒の表面積は従来の三元触媒の102〜104倍大きくなるので、これをモノリス成形体に塗布することによって自動車排ガスに対する触媒活性の向上を図ることが考えられ、この考えは、例えば、特許文献4〜9に開示されている。しかし、ディーゼル乗用車等が排出する120℃〜200℃付近の低温排NOxを効果的に除去することはできなかった。
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. From this point of view, when looking at a three-way catalyst for automobiles, the monolith molded body as a support has a mesh-shaped cross section and is provided with gas flow paths partitioned by thin walls parallel to each other in the axial direction. It is a molded body, the specific surface area is about 0.2 m 2 / g, the specific surface area of alumina particles as a support is 110 to 340 m 2 / g, and the specific surface area of the catalyst is about 20 to 40 m 2 / g from the particle size. It is estimated that. Therefore, the surface area of the catalyst is 10 2 of that of the conventional three-way catalyst by supporting the nano-sized catalyst particles smaller by one to two digits than the particle diameter of the conventional catalyst particles in the pores of the crystalline mesoporous material. since 10 becomes 4 times larger, which is believed to enhance the catalytic activity for automotive exhaust by applying monolith forming body, this idea, for example, disclosed in Patent Document 4-9. However, it has not been possible to effectively remove low-temperature exhaust NOx around 120 ° C. to 200 ° C. discharged by diesel passenger cars and the like.
本発明の目的は、上記の事情に鑑み、リーンバーン排ガスに含まれるNOxの浄化のための新規な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排NOxに対して活性を示す新規のメソポーラス触媒及びこの触媒を付着させたモノリス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 catalyst for purifying NOx contained in lean burn exhaust gas. Specifically, in order to efficiently purify diesel exhaust NOx, which has been difficult in the past, a novel mesoporous catalyst that exhibits activity against exhaust NOx even in a relatively high concentration oxygen atmosphere of lean burn and this catalyst are attached. To provide a monolithic catalyst.
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非晶性メソポーラスシリカ担体に白金を担持した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。
すなわち、本発明は、
(1)細孔径が2〜50nmの細孔と100〜1400m2/gの比表面積とを有する非晶性メソポーラスシリカ担体に平均粒径が1〜20nmの白金粒子を0.01〜20質量%坦持した触媒であることを特徴とするリーンバーン排NOx浄化用メソポーラス触媒。
(2)上記(1)のメソポーラス触媒をモノリス成形体のガス流路内壁に付着させたことを特徴とするリーンバーン排NOx浄化用モノリス触媒。
(3)モノリス触媒におけるメソポーラス触媒の付着量がモノリス触媒の3〜30質量%、メソポーラス触媒における白金の坦持量が0.1〜10質量%、及びモノリス触媒当たりに換算した白金の坦持量が0.03〜3質量%であることを特徴とする上記(2)に記載のリーンバーン排NOx浄化用モノリス触媒。
(4)上記(2)又は(3)のリーンバーン排NOx浄化用モノリス触媒を用いた、リッチバーンとリーンバーンを交互に行う小型ディーゼル用の排NOx浄化用触媒。
(5)上記(2)又は(3)のリーンバーン排NOx浄化用モノリス触媒を用いた大型ディーゼル用の排NOx浄化用触媒、に関する。
As a result of intensive studies to achieve the above object, the present inventors have found that a catalyst in which platinum is supported on an amorphous mesoporous silica support having a specific pore distribution and a high specific surface area is subjected to lean burn NOx treatment. As a result, the present invention has been completed based on this finding.
That is, the present invention
(1) 0.01 to 20% by mass of platinum particles having an average particle diameter of 1 to 20 nm on an amorphous mesoporous silica support having pores having a pore diameter of 2 to 50 nm and a specific surface area of 100 to 1400 m 2 / g A mesoporous catalyst for purifying lean burn exhaust NOx, which is a supported catalyst.
(2) A lean burn NOx purifying monolith catalyst characterized in that the mesoporous catalyst of (1) is attached to the inner wall of the gas flow path of the monolith molded body.
(3) The amount of mesoporous catalyst attached to the monolith catalyst is 3 to 30% by mass of the monolith catalyst, the amount of platinum supported on the mesoporous catalyst is 0.1 to 10% by mass, and the amount of platinum supported per monolith catalyst The lean-burn exhaust NOx purification monolith catalyst according to the above (2), characterized in that is 0.03 to 3% by mass.
(4) An exhaust NOx purification catalyst for small diesel that performs rich burn and lean burn alternately, using the lean burn exhaust NOx purification monolith catalyst of (2) or (3) above.
(5) The present invention relates to an exhaust NOx purification catalyst for large diesel using the lean burn exhaust NOx purification monolith catalyst of the above (2) or (3).
本発明のメソポーラス触媒は、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、本発明の非晶性のメソポーラスシリカに担持した白金触媒は、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 mesoporous catalyst of the present invention can perform lean burn exhaust NOx treatment, which could not be achieved in the past, extremely efficiently even in a low temperature region. For example, although a three-way catalyst can hardly purify nitric oxide in an atmosphere with an oxygen concentration of 14%, the platinum catalyst supported on the amorphous mesoporous silica of the present invention has a monoxide that exists in an atmosphere with an oxygen concentration of 14%. 80% or more of nitrogen can be purified at 160 ° C to 300 ° C.
以下、本発明を詳細に説明する。
本発明の特徴の一つは、非晶性メソポーラスシリカをNOx浄化用触媒の担体として用いることである。その理由は、非晶性メソポーラスシリカの細孔に触媒を担持できること、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、触媒を細孔内に担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からである。
本発明における非晶性メソポーラスシリカとは、細孔(=空孔)に起因する1本の小角X線回折ピークを持ちTEM観察によって細孔配列の秩序性がまったく観測されないメソポーラスシリカのことである。
Hereinafter, the present invention will be described in detail.
One of the features of the present invention is that amorphous mesoporous silica is used as a carrier for a NOx purification catalyst. The reason is that the catalyst can be supported in the pores of the amorphous mesoporous silica, the effect of gas diffusion through the pore channel can be expected, and the preferable particle size range of the catalytically active species can be maintained by controlling the pore distribution. This is because, by supporting the catalyst in the pores, there are excellent effects such as suppressing reaggregation of the catalyst particles and achieving uniform and high dispersion of the catalyst.
The amorphous mesoporous silica in the present invention is mesoporous silica having one small-angle X-ray diffraction peak due to pores (= vacancies) and no ordering of pore arrangement observed by TEM observation. .
一般に、多孔性材料に存在する空孔は小角X線回折法によって観測することができ、また、TEMによって直接観察することができる。メソ領域の大きさ(2nm〜50nm)の空孔は、横軸に回折角2θ、縦軸にX線回折強度をとったとき、通常、回折角2θが数度以内の領域でブロードな回折ピークを示す。空孔が多孔性材料の細孔であり、それがある程度の長距離範囲において規則正しく配列している場合には、上記回折角の領域において、一般に、結晶性物質に観測されるような複数本の回折ピークが観測され、そのパターンから、細孔配列の帰属ができる。また、この材料をTEM(=透過型電子顕微鏡)観察すると細孔が秩序よく配列している像を観測することができる。このような規則配列した細孔を有するメソポーラス材料がモービルオイル社によって発明され、結晶性のメソポーラス分子篩と命名された(特許第3443428号公報)。 In general, vacancies present in a porous material can be observed by a small-angle X-ray diffraction method, or directly by a TEM. Voids with a meso-region size (2 nm to 50 nm) generally have a broad diffraction peak when the horizontal axis represents the diffraction angle 2θ and the vertical axis represents the X-ray diffraction intensity. Indicates. When the vacancies are pores of a porous material and are regularly arranged in a certain long distance range, in the region of the diffraction angle, a plurality of cavities generally observed in a crystalline substance are used. A diffraction peak is observed, and the pore array can be assigned from the pattern. Further, when this material is observed by TEM (= transmission electron microscope), an image in which pores are arranged in an orderly manner can be observed. A mesoporous material having such regularly arranged pores was invented by Mobil Oil, and named as a crystalline mesoporous molecular sieve (Japanese Patent No. 3444328).
回折ピークが1本しか観測されないときには、パターンの帰属ができないので結晶性であるとは断定できない。このような場合、結晶性なのか非晶性なのかを決定するためにはTEM観察が有効である。本願発明のメソポーラスシリカは、細孔に起因する小角X線回折ピークを1本しか持たない。さらに、TEM観察によって細孔配列の長距離秩序性がまったく観測されないことから結晶性ではなく、所謂、非晶性であることが確認された。結晶性メソポーラスシリカと本願発明の非晶性メソポーラスシリカは、小角X線回折測定及びTEM観察によって明確に区別することができる。
次に、触媒の担体としてメソポーラス材料を考える時には、細孔の形態、細孔分布、比表面積、等の細孔特性のパラメーターが重要である。細孔の形態は、細孔内における触媒粒子の捕捉状態に影響し、細孔分布は触媒粒子の粒径に影響し、比表面積は触媒の分散状態に影響するからである。前記に述べたモービルオイル社発明の結晶性メソポーラス分子篩は細孔配列が六方晶系に属しているので、細孔を有する面が層状に積層しており、各層の面内において繊維状の細長い円筒形状の細孔がそれぞれ平行に配列した蜂の巣状の形態をしている。一方、本願発明の非晶性メソポーラスシリカは、小角X線回折測定及びTEM観察によって、無定型の浅い細孔が所々連結して無秩序に分散した構造をしている。
When only one diffraction peak is observed, it cannot be determined that it is crystalline because the pattern cannot be assigned. In such a case, TEM observation is effective for determining whether it is crystalline or amorphous. The mesoporous silica of the present invention has only one small-angle X-ray diffraction peak due to pores. Furthermore, since the long-range order of the pore arrangement was not observed at all by TEM observation, it was confirmed that it was not crystalline but so-called amorphous. Crystalline mesoporous silica and amorphous mesoporous silica of the present invention can be clearly distinguished by small-angle X-ray diffraction measurement and TEM observation.
Next, when considering a mesoporous material as a catalyst support, parameters of pore characteristics such as pore morphology, pore distribution, specific surface area and the like are important. This is because the morphology of the pores affects the trapping state of the catalyst particles in the pores, the pore distribution affects the particle size of the catalyst particles, and the specific surface area affects the dispersion state of the catalyst. Since the crystalline mesoporous molecular sieve according to the invention of Mobil Oil described above belongs to the hexagonal system in the pore arrangement, the surfaces having pores are laminated in layers, and a fibrous elongated cylinder in the plane of each layer It has a honeycomb-like shape in which the fine pores are arranged in parallel. On the other hand, the amorphous mesoporous silica of the present invention has a structure in which amorphous shallow pores are connected in some places and dispersed randomly by small-angle X-ray diffraction measurement and TEM observation.
これら2種類のメソポーラスシリカに触媒を担持してNOx浄化反応の触媒活性を比較すると、本願発明のメソポーラス触媒のほうがはるかに優れた低温活性を有することが見出された。この意外な触媒活性の違いは、次のように説明することができる。すなわち、六方晶系メソポーラスシリカであるメソポーラスシリカMCM−41に担持された触媒は細孔の表面張力によって細長い細孔内の奥深くに捕捉され、本願発明の非晶性メソポーラスシリカに担持された触媒は細孔の入り口近くの浅い所に捕捉されており、触媒表面での気相反応である排NOx浄化反応に対しては、物質移動が速やかに達成される本発明の非晶性メソポーラスシリカのほうが結晶性メソポーラスシリカよりも触媒担体として優れているからであろう。 When a catalyst was supported on these two types of mesoporous silica and the catalytic activity of the NOx purification reaction was compared, it was found that the mesoporous catalyst of the present invention has a far superior low temperature activity. This unexpected difference in catalytic activity can be explained as follows. That is, the catalyst supported on the mesoporous silica MCM-41, which is a hexagonal mesoporous silica, is captured deep inside the elongated pores by the surface tension of the pores, and the catalyst supported on the amorphous mesoporous silica of the present invention is The amorphous mesoporous silica of the present invention, which is trapped in a shallow place near the entrance of the pores and can achieve mass transfer more quickly, is effective for the exhaust NOx purification reaction that is a gas phase reaction on the catalyst surface. This is because it is superior to crystalline mesoporous silica as a catalyst carrier.
本発明担体の細孔径と細孔に担持される触媒の粒径は密接に関係している。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、担体であるメソポーラスシリカの細孔径は触媒粒子と同程度でなければならない。通常、メソポーラスシリカ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、メソポーラスシリカ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触媒を均一分散坦持することができる。したがって、メソポーラスシリカの細孔径は重要な設計要素である。
本発明非晶性メソポーラスシリカの細孔の大部分は、細孔径(直径表示)が2〜50nmの範囲にあり、好ましくは2〜20nmの範囲にあり、より好ましくは2〜10nmの範囲にある。ここでいう細孔の大部分とは2〜50nm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未満であっても触媒の担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。50nmを越えると分散担持された触媒が水熱高温条件などによるシンタリング(=燒結)によって巨大粒子に成長しやすくなるので50nm以下が好ましい。なお、本発明における細孔径は、吸脱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りBJH法によって求められる1〜200nmの範囲の細孔分布(微分分布表示)で示される。
The pore diameter of the support of the present invention and the particle diameter of the catalyst supported on the pores are closely related. As will be 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 mesoporous silica that is the carrier must be about the same as that of the catalyst particles. Usually, the particle size of the catalyst supported in the pores of the mesoporous silica is approximately the same as the pore size. Therefore, by controlling the pore size of the mesoporous silica, a catalyst having a preferable particle size can be dispersed uniformly. Can have. Therefore, the pore size of mesoporous silica is an important design factor.
Most of the pores of the amorphous mesoporous silica of the present invention have a pore diameter (diameter display) in the range of 2 to 50 nm, preferably in the range of 2 to 20 nm, more preferably in the range of 2 to 10 nm. . As used herein, the majority of pores means that the pore volume occupied by pores of 2 to 50 nm is 60% or more of the total pore volume. The catalyst can be supported even if the pore diameter is less than 2 nm, but 2 nm or more is preferable in consideration of the influence of contamination by impurities and the like. If it exceeds 50 nm, the dispersion-supported catalyst tends to grow into giant particles by sintering (= sintering) under hydrothermal high temperature conditions and the like. In addition, the pore diameter in the present invention is a value measured by a nitrogen adsorption method using nitrogen as an adsorption / desorption gas, and is represented by a pore distribution (differential distribution display) in a range of 1 to 200 nm obtained by the BJH method. .
次に、担体の比表面積は触媒の均一な分散性を図るために重要な設計要素である。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メソポーラスシリカの比表面積は100〜1400m2/gであり、好ましくは100〜1200m2/g、さらに好ましくは、400〜1200m2/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。なお、本発明における比表面積は、吸脱着の気体として窒素を用いたBET窒素吸着法によって測定される値である。 Next, the specific surface area of the support is an important design factor for achieving uniform dispersibility of the catalyst. The specific surface area should be as high as possible unless there are special circumstances. The specific surface area of the mesoporous silica can be used in the present invention is 100~1400m 2 / g, preferably 100~1200m 2 / g, and more preferably from 400~1200m 2 / g. When the specific surface area is less than 100 m 2 / g, the supported amount of the catalyst is reduced. Therefore, it is preferably 100 m 2 / g or more in order to bring out the catalyst performance of the supported catalyst. On the other hand, in terms of material strength, the specific surface area is preferably 1400 m 2 / g or less. The specific surface area in the present invention is a value measured by a BET nitrogen adsorption method using nitrogen as an adsorption / desorption gas.
なお、本発明で用いるメソポーラスシリカは、メソポーラスシリカを構成するケイ素の一部としてランタノイド族を含む3A族元素、3B族元素、4A族元素、5A族元素、及び6A族元素からなる群から選ばれた少なくとも一種類の元素を導入したメソポーラスシリカ複合体とした場合は、意外にも、触媒に低温活性を付与することがわかったので好ましい。
3A族元素では、スカンジウム、イットリウム、ランタン、セリウム、サマリウム、ガドリニウムが好ましく、3B族元素ではホウ素が好ましく、4A族元素ではチタン、及びジルコニウムが好ましく、5A族ではニオブ、及びタンタルが好ましく、6A族ではクロム、モリブデン、及びタングステンが好ましい。
The mesoporous silica used in the present invention is selected from the group consisting of a 3A group element, a 3B group element, a 4A group element, a 5A group element, and a 6A group element including a lanthanoid group as a part of silicon constituting the mesoporous silica. Furthermore, it is preferable to use a mesoporous silica composite in which at least one element is introduced because it has been surprisingly found that the catalyst is imparted with low temperature activity.
Of the group 3A elements, scandium, yttrium, lanthanum, cerium, samarium, and gadolinium are preferred, boron is preferred for group 3B elements, titanium and zirconium are preferred for group 4A elements, niobium and tantalum are preferred for group 5A, and group 6A In this case, chromium, molybdenum, and tungsten are preferable.
中でも、ホウ素、タングステン、ニオブ、及びセリウムが更に好ましく、持続性の面からはタングステン、及びセリウムが特に好ましい。
これらの元素の導入量はメソポーラスシリカを構成する主金属に対して1−20モル%が好ましく、より好ましくは1−10モル%である。
なお、上記の3A族元素等を導入したメソポーラスシリカ複合体とは、メソポーラスシリカを構成するケイ素の一部が上記の3A族元素等の元素で置換された複合体構造のものを言う。
次に、本発明で用いる触媒は、白金触媒である。従来、白金を含有する自動車排ガス処理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低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。
Among these, boron, tungsten, niobium, and cerium are more preferable, and tungsten and cerium are particularly preferable from the viewpoint of sustainability.
The amount of these elements introduced is preferably 1-20 mol%, more preferably 1-10 mol%, relative to the main metal constituting the mesoporous silica.
The mesoporous silica composite introduced with the group 3A element or the like refers to a composite structure in which a part of silicon constituting the mesoporous silica is substituted with an element such as the group 3A element.
Next, the catalyst used in the present invention is a platinum catalyst. Conventionally, a three-way catalyst is known as an automobile exhaust gas treatment catalyst 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, undergo surface oxidation by a low concentration of oxygen. Since the three-way catalyst is composed of platinum-palladium-rhodium, it is easily deactivated when subjected to surface oxidation.
本発明で白金触媒を用いる理由は、白金が排NOxの主成分である一酸化窒素を共存酸素によって二酸化窒素に酸化する触媒能力が高く、高温の酸素雰囲気中でも化学的に安定であるからである。又、白金は低温活性であることがわかったからである。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、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。 The reason why the platinum catalyst is used in the present invention is that platinum has a high catalytic ability to oxidize nitrogen monoxide, which is the main component of exhaust NOx, into nitrogen dioxide by coexisting oxygen, and is chemically stable even in a high-temperature oxygen atmosphere. . Also, platinum was found to be low temperature active. Nitrogen dioxide produced by the catalytic reaction is easily converted into nitrogen and water by reducing substances such as lower olefins having 1 to 6 carbon atoms and lower paraffin (which is contained in 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 of 1nm is 10 4 times greater than that of 0.1 [mu] m.
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白金粒子の平均粒径は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。 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 platinum particles exhibiting an effective activity for the target NOx decomposition and purification treatment in the present invention is in the range of 1 to 20 nm, particularly in the range of 1 to 10 nm.
本発明の触媒はメソポーラスシリカの細孔に担持された担持型触媒である。主触媒としての白金の担持量は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、数%の担持量で用いる。メソポーラスシリカの触媒坦持量は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。また、十分な触媒活性を得るには0.01質量%以上が好ましい。
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、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。この成分の添加量は、通常、白金重量の0.01倍から100倍程度から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。
The catalyst of the present invention is a supported catalyst supported on pores of mesoporous silica. The supported amount of platinum as the main catalyst is 0.01 to 20% by mass, preferably 0.1 to 10% by mass. If there is no quantitative problem, the supported amount is usually several percent. . The supported amount of catalyst of mesoporous silica can be 20% by mass or more. However, when the supported amount is excessive, the catalyst in the deep pores that hardly contributes to the reaction increases, so 20% by mass or less is preferable. Moreover, 0.01 mass% or more is preferable in order to obtain sufficient catalyst activity.
By adding a co-catalytic 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, cerium oxide and manganese dioxide with moderate oxidizing power, effective in preventing SOx poisoning Copper-zinc, iron-chromium, molybdenum oxide, and the like are preferable. The addition amount of this component is usually about 0.01 to 100 times to about 100 times the weight of platinum, but may be 100 times or more as necessary.
本発明の非晶性メソポーラスシリカの製造法は特に限定するものでなく、従来の方法である界面活性剤のミセルをテンプレートとして用いるゾル−ゲル法を応用することによって所用の材料を製造することができる。メソポーラスシリカの前駆物質には、通常、テトラメトキシシラン、テトラエトキシシラン、テトラ−i−プロポキシシラン、テトラ−n−プロポキシシラン、テトラ−i−ブトキシシラン、テトラ−n−ブトキシシラン、テトラ−sec−ブトキシシラン、テトラ−t−ブトキシシラン等のアルコキシドを用いる。
ミセル形成の界面活性剤は、例えば、長鎖のアルキルアミン、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。溶媒として、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。反応系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。
The method for producing the amorphous mesoporous silica of the present invention is not particularly limited, and a desired material can be produced by applying a conventional sol-gel method using a surfactant micelle as a template. it can. The precursors of mesoporous silica are usually tetramethoxysilane, tetraethoxysilane, tetra-i-propoxysilane, tetra-n-propoxysilane, tetra-i-butoxysilane, tetra-n-butoxysilane, tetra-sec- Alkoxides such as butoxysilane and tetra-t-butoxysilane are used.
Examples of micelle-forming surfactants include long-chain alkylamines, long-chain quaternary ammonium salts, long-chain alkylamine N-oxides, long-chain sulfonates, polyethylene glycol alkyl ethers, polyethylene glycol fatty acid esters, etc. Any of these may be used. As the solvent, one or more of water, alcohols, and diols are usually used, and an aqueous solvent is preferable. When a small amount of a compound having a coordination ability to metal is added to the reaction system, the stability of the reaction system can be remarkably enhanced. As such a stabilizer, compounds having metal coordination ability such as acetylacetone, tetramethylenediamine, ethylenediaminetetraacetic acid, pyridine, and picoline are preferable.
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/主剤のモル比が0.01〜1.0、好ましくは0.2〜0.6である。反応温度は、20〜180℃、好ましくは20〜100℃の範囲である。反応時間は5〜100時間、好ましくは10〜50時間の範囲である。反応生成物は通常、濾過により分離し、十分に水洗、乾燥後、500〜1000℃の高温焼成によってテンプレートを熱分解除去し、メソポーラスシリカを得ることができる。必要に応じて、焼成前に界面活性剤をアルコールなどで抽出することもできる。 The composition of the reaction system comprising the precursor, surfactant, solvent and stabilizer is such that the molar ratio of the precursor is 0.01 to 0.60, preferably 0.02 to 0.50, and the precursor / surfactant The molar ratio is 1-30, preferably 1-10, the solvent / surfactant molar ratio is 1-1000, preferably 5-500, and the stabilizer / main agent molar ratio is 0.01-1.0, preferably Is 0.2 to 0.6. The reaction temperature is in the range of 20 to 180 ° C, preferably 20 to 100 ° C. The reaction time is 5 to 100 hours, preferably 10 to 50 hours. The reaction product is usually separated by filtration, sufficiently washed with water and dried, and then the template is thermally decomposed and removed by high-temperature baking at 500 to 1000 ° C. to obtain mesoporous silica. If necessary, the surfactant can be extracted with alcohol or the like before firing.
本発明のメソポーラス触媒は、例えば、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、メソポーラスシリカ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 mesoporous catalyst of the present invention can be produced, for example, 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, it can be produced by immersing mesoporous silica in an aqueous solution of a catalyst raw material, followed by filtration, drying, washing with water as necessary, and reduction treatment with a reducing agent.
Examples of the platinum catalyst material 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.
なお、3A族元素、3B族元素、4A族元素、5A族元素、及び/又は6A族元素をメソポーラスシリカのケイ素の変わりに導入するメソポーラスシリカ複合体は、メソポーラス材料の前駆物質にこれらの元素のアルコキシド、アセチルアセトナート等を適当量加えて、上記メソポーラス材料の製造法と同様の方法によって製造することができる。
本発明の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。本発明のモノリス触媒とは、メソポーラス触媒をモノリス成形体のガス流路内壁に付着させた触媒を意味している。メソポーラス触媒の付着量は、3〜30質量%が好ましい。担体内部に存在する触媒へのガス拡散の面から30%未満が好ましい。また、十分な触媒性能を引き出す上で3%以上が好ましい。モノリス成形体への触媒の塗布量相当の付着量は、成形体の0.03〜3質量%が好ましい。
Note that a mesoporous silica composite in which a group 3A element, a group 3B element, a group 4A element, a group 5A element, and / or a group 6A element is introduced instead of silicon of mesoporous silica is used as a precursor of a mesoporous material. An appropriate amount of alkoxide, acetylacetonate or the like can be added to produce the mesoporous material by the same method as described above.
The monolith molded body of 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 monolith catalyst of the present invention means a catalyst in which a mesoporous catalyst is adhered to the inner wall of the gas flow path of the monolith molded body. The adhesion amount of the mesoporous catalyst is preferably 3 to 30% by mass. It is preferably less than 30% from the viewpoint of gas diffusion to the catalyst existing inside the support. Moreover, 3% or more is preferable in order to draw out sufficient catalyst performance. The adhesion amount corresponding to the coating amount of the catalyst on the monolith molded body is preferably 0.03 to 3% by mass of the molded body.
本発明のモノリス触媒は、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。例えば、メソポーラス触媒とバインダーとしてのコロイダルシリカを、通常、1:(0.01〜0.2)の質量割合で混合した混合物をつくり、これを水分散することによって通常10〜50質量%のスラリーを調整した後、該スラリーにモノリス成形体を浸漬してモノリス成形体のガス流路の内壁にスラリーを付着させ、乾燥後、窒素、ヘリウム、アルゴンなどの不活性雰囲気下500〜1000℃で数時間熱処理することによって製造することがきる。
コロイダルシリカ以外のバインダーとしては、メチルセルロース、アクリル樹脂、ポリエチレングリコールなどを適宜用いることもできる。あるいは、モノリス成形体に非晶性メソポーラスシリカを塗布したのち、触媒原料を該メソポーラスシリカに含浸し、還元処理、熱処理を行う方法によっても製造することができる。
The monolith catalyst of this invention can be manufactured according to the manufacturing method of the monolith molded object which adhered the three-way catalyst for motor vehicles. For example, a mixture in which a mesoporous catalyst and colloidal silica as a binder are usually mixed at a mass ratio of 1: (0.01 to 0.2) is prepared, and this is usually dispersed in water to form a slurry of 10 to 50% by mass. After the monolith molded body is immersed in the slurry, the slurry is attached to the inner wall of the gas flow path of the monolith molded body, dried, and then dried at a temperature of 500 to 1000 ° C. under an inert atmosphere such as nitrogen, helium or argon. It can be manufactured by heat treatment for a long time.
As a binder other than colloidal silica, methyl cellulose, acrylic resin, polyethylene glycol, or the like can be used as appropriate. Alternatively, it can also be produced by a method in which amorphous mesoporous silica is applied to a monolith molded article, and then the mesoporous silica is impregnated with the catalyst raw material, followed by reduction treatment and heat treatment.
また、他の製法としては、スラリーを付着させる代わりに、気体状のメソポーラスシリカの前駆物質を用いて薄膜状のメソポーラスシリカを直接付着させる化学的蒸着法によって行うこともできる。そして、蒸着によって薄膜状のメソポーラスシリカを付着したモノリス成形体への白金触媒の担持は、通常、触媒原料の水溶液を含浸、乾燥後、還元処理、熱処理を行う方法によって行うことができる。
モノリス成形体に付着させるメソポーラス触媒層の厚みは、付着方法によって異なり、前記のスラリーを付着させる方法では、通常、1μm〜100μmであるのが好ましく、10μm〜50μmの範囲が特に好ましい。100μmを超えると反応ガスの拡散が遅くなるので100μm以下が好ましい。触媒性能の劣化を抑制するためには1μm以上が好ましい。また、前記の化学的蒸着法では、通常、10nm〜10μmの範囲が好ましく、さらに好ましくは100nm〜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。
Further, as another production method, instead of attaching the slurry, a chemical vapor deposition method in which a thin film mesoporous silica is directly attached using a gaseous mesoporous silica precursor. The platinum catalyst supported on the monolith molded body to which thin film mesoporous silica is adhered by vapor deposition can be usually performed by a method of impregnating an aqueous solution of a catalyst raw material and drying, followed by reduction treatment and heat treatment.
The thickness of the mesoporous catalyst layer deposited on the monolith molded body varies depending on the deposition method, and in the above-described method of depositing the slurry, it is usually preferably 1 μm to 100 μm, and particularly preferably 10 μm to 50 μm. If it exceeds 100 μm, the diffusion of the reaction gas becomes slow, so that it is preferably 100 μm or less. In order to suppress deterioration of catalyst performance, 1 μm or more is preferable. Moreover, in the said chemical vapor deposition method, the range of 10 nm-10 micrometers is preferable normally, More preferably, it is 100 nm-1 micrometer. Although it is possible to make the
本発明のモノリス触媒は、自動車、特にディーゼル自動車及びリーンバーンガソリン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160〜300℃の低温領域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高くリーンバーンの時には酸素濃度が低いので、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、160〜600℃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。 By mounting the monolith catalyst of the present invention on automobiles, particularly diesel automobiles and lean burn gasoline automobiles, lean burn exhaust NOx discharged by automobiles can be extremely effectively purified in a low temperature range of 160 to 300 ° 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 high at the time of rich burn and the oxygen concentration is low at the time of lean burn, if the monolith catalyst of the present invention is used for exhaust gas purification treatment of a small diesel capable of alternately performing rich burn and lean burn, 160 to Exhaust NOx can be efficiently purified over a wide temperature range of 600 ° 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。
実施例中の小角X線回折パターン及び粉末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。
担体の細孔及び触媒は日立製作所製H−9000UHR型透過型電子顕微鏡を用いて直接観察した。透過型電子顕微鏡によって観察した触媒の粒径は、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。製造したメソポーラスシリカ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。このピークを与える細孔直径が細孔径である。
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42i−HL及び46C−H)によって処理後のガスに含まれる一酸化窒素を測定し、以下の式(1)によって算出した。
The present invention will be specifically described below with reference to examples.
Small-angle X-ray diffraction patterns and powder X-ray diffraction patterns in the examples were measured with a RINT2000 X-ray diffraction apparatus manufactured by Rigaku Corporation.
The pores of the support and the catalyst were directly observed using an H-9000UHR transmission electron microscope manufactured by Hitachi, Ltd. It was confirmed that the particle diameter of the catalyst observed with a transmission electron microscope 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 produced mesoporous silicas showed a peak at a specific pore diameter in an exponentially increasing distribution. The pore diameter that gives this peak is the pore diameter.
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 measured by measuring nitrogen monoxide contained in the treated gas with a reduced pressure chemiluminescence NOx analyzer (manufactured by Nippon Thermo Co., Ltd .: models 42i-HL and 46C-H). Calculated according to (1).
0.215gのPtCl4・5H2O、0.106gのPdCl2・2H2O、及び0.162gのRh(NO3)3・2H2Oを20mlの蒸留水に溶解した水溶液を蒸発皿に入れ、これに10gのγ−アルミナ(粒径2〜3μmの微粒子)を加え、スチームバスで蒸発乾固した後、真空乾燥機に入れ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時間還元し、貴金属の含有量が約2重量%の触媒を合成した。これを、三元触媒を模した貴金属触媒として比較実験に用いた。
「製造例2」Pt/結晶性メソポーラスシリカ触媒の合成
米国特許第5,143,707号明細書における実施例21の方法に従ってMCM−41タイプのメソポーラスシリカを合成した。すなわち、29質量%濃度のドデシルトリメチルアンモニウムブロマイドの水溶液300gをハライド交換樹脂用ハイドロオキサイド10gを充填したカラムを通して、セチルトリメチルアンモニウムハイドロオキサイドの水溶液を得た。これを29質量%濃度のドデシルトリメチルアンモニウムブロマイドの水溶液306gと混合し、これにテトラエチルオルトシリケートを30g加え、40℃で1時間攪拌した。この溶液をポリプロピレン製容器に移し、加湿器に入れ100℃で48時間放置した。
Production Example 2 Synthesis of Pt / Crystalline Mesoporous Silica Catalyst MCM-41 type mesoporous silica was synthesized according to the method of Example 21 in US Pat. No. 5,143,707. That is, an aqueous solution of cetyltrimethylammonium hydroxide was obtained through a column packed with 300 g of an aqueous solution of 29% by mass of dodecyltrimethylammonium bromide and 10 g of hydroxide for halide exchange resin. This was mixed with 306 g of a 29% strength by weight aqueous solution of dodecyltrimethylammonium bromide, 30 g of tetraethylorthosilicate was added thereto, and the mixture was stirred at 40 ° C. for 1 hour. This solution was transferred to a polypropylene container, placed in a humidifier and allowed to stand at 100 ° C. for 48 hours.
生成した沈殿を減圧濾過、水洗後、窒素気流中540℃で1時間仮焼成した後、さらに空気中540℃で6時間焼成した。得られた材料の比表面積は1450m2/g、細孔径は2.5nmであった。小角X線回折パターンは4本の回折ピークを示し、それぞれの面間隔(d値)は3.2nm(strong)、1.8nm(weak)、1.6nm(weak)、及び、1.2nm(very weak)であった。
上記の小角X線回折パターンは、米国特許第5,143,707号明細書における実施例21に記載のMCM−41のデータと一致することから、MCM−41タイプのメソポーラスシリカであることが確認された。
次に、蒸留水20gにH2PtCl6・6H2Oを0.267g溶解した水溶液を蒸発皿に入れ、これに上記のMCM−41タイプのメソポーラスシリカ材料5gを加え、スチームバスで蒸発乾固した後、真空乾燥機に入れ、100℃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(10v/v%)気流下、500℃で3時間還元し、白金の含有量が約2質量%のメソポーラス触媒を合成した。担持された白金触媒の粒径は約2.5nmであった。
The resulting precipitate was filtered under reduced pressure, washed with water, calcined at 540 ° C. for 1 hour in a nitrogen stream, and then further calcined at 540 ° C. in air for 6 hours. The specific surface area of the obtained material was 1450 m 2 / g, and the pore diameter was 2.5 nm. The small-angle X-ray diffraction pattern shows four diffraction peaks, and the interplanar spacing (d value) is 3.2 nm (strong), 1.8 nm (weak), 1.6 nm (weak), and 1.2 nm ( very weak).
The above small-angle X-ray diffraction pattern agrees with the data of MCM-41 described in Example 21 in US Pat. No. 5,143,707, and thus it is confirmed that it is MCM-41 type mesoporous silica. It was done.
Next, put the aqueous solution 0.267g dissolved H 2 PtCl 6 · 6H 2 O in distilled water 20g evaporation dish, to which the above MCM-41 type mesoporous silica material 5g added, evaporated to dryness in a steam bath Then, it put into the vacuum dryer and vacuum-dried at 100 degreeC for 3 hours. This sample was put in a quartz tube and reduced at 500 ° C. for 3 hours under a stream of helium diluted hydrogen gas (10 v / v%) to synthesize a mesoporous catalyst having a platinum content of about 2% by mass. The particle size of the supported platinum catalyst was about 2.5 nm.
「製造例3」白金/非晶性メソポーラスシリカ触媒の合成
1リットルのビーカーに、蒸留水300g、エタノール240g、及びドデシルアミン30gを入れ、溶解させた。攪拌下でテトラエトキシシラン125gを加えて室温で22時間攪拌した。生成物を濾過、水洗し、110℃で5時間温風乾燥した後、空気中で550℃5時間焼成して含有するドデシルアミンを分解除去し、メソポーラスシリカを得た。
該メソポーラスシリカを小角X線回折測定した結果、図1に示すように2θ角が2.72度(d=3.25nm)の所に1本のブロードな回折ピークを示した。
また、透過型電気顕微鏡観察の結果、図2に示すように細孔の配列には規則的な配列が観測されず無秩序に分散している状態が観測された。
Production Example 3 Synthesis of Platinum / Amorphous Mesoporous Silica Catalyst 300 g of distilled water, 240 g of ethanol, and 30 g of dodecylamine were placed in a 1 liter beaker and dissolved. While stirring, 125 g of tetraethoxysilane was added and stirred at room temperature for 22 hours. The product was filtered, washed with water, dried in warm air at 110 ° C. for 5 hours, and then calcined in air at 550 ° C. for 5 hours to decompose and remove contained dodecylamine to obtain mesoporous silica.
As a result of small-angle X-ray diffraction measurement of the mesoporous silica, one broad diffraction peak was observed at a 2θ angle of 2.72 degrees (d = 3.25 nm) as shown in FIG.
Further, as a result of observation with a transmission electric microscope, as shown in FIG. 2, a regular arrangement was not observed in the arrangement of the pores, and a state where the pores were randomly distributed was observed.
これらの結果から、製造したメソポーラスシリカは非晶性であることが確認された。また、細孔分布及び比表面積測定の結果、約3.2nmの位置に細孔ピークがあり、比表面積が933m2/g、細孔容積が1.35cm3/g、2〜50nmの細孔が占める容積は1.34cm3/gであった。
蒸留水20gにH2PtCl6・6H2Oを0.267g溶解した水溶液を蒸発皿に入れ、これに上記のメソポーラスシリカ材料5gを加え、スチームバスで蒸発乾固した後、真空乾燥機に入れ100℃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(10v/v%)気流下500℃で3時間還元し、白金の含有量が約2質量%のメソポーラス触媒を合成した。メソポーラス触媒に坦持された白金粒子の平均粒径は約3.0nmであった。
From these results, it was confirmed that the produced mesoporous silica was amorphous. Moreover, as a result of pore distribution and specific surface area measurement, there was a pore peak at a position of about 3.2 nm, a specific surface area of 933 m 2 / g, a pore volume of 1.35 cm 3 / g, and a pore of 2 to 50 nm. The volume occupied by was 1.34 cm 3 / g.
Put an aqueous solution prepared by 0.267g dissolved H 2 PtCl 6 · 6H 2 O in distilled water 20g evaporation dish, to which the mesoporous silica material 5g was added and after evaporation to dryness on a steam bath, placed in a vacuum dryer Vacuum drying was performed at 100 ° C. for 3 hours. This sample was put in a quartz tube and reduced at 500 ° C. for 3 hours under a helium-diluted hydrogen gas (10 v / v%) stream to synthesize a mesoporous catalyst having a platinum content of about 2 mass%. The average particle size of the platinum particles supported on the mesoporous catalyst was about 3.0 nm.
「製造例4」Pt/非晶性メソポーラスシリカ/モノリス触媒の合成
製造例3の触媒1gとコロイダルシリカ0.1gを蒸留水10mlに加え、攪拌して、スラリーを調整した。これに、市販のコージェライトモノリス成形体(400 cells/in2、直径118mm×長さ50mm、重量243g)から切り出したミニ成形体(21cells、直径8mm×長さ9mm、重量0.15g)を5個浸漬し、試料をとりだし風乾した後、窒素気流下で500℃−3時間熱処理した。メソポーラス触媒の付着量は、ミニ成形体の約10質量%であり、ミニ成形体当たりの白金の坦持量は約0.2質量%であった。
“Production Example 4” Synthesis of Pt / Amorphous Mesoporous Silica / Monolith Catalyst 1 g of the catalyst of Production Example 3 and 0.1 g of colloidal silica were added to 10 ml of distilled water and stirred to prepare a slurry. 5 mini-molded bodies (21 cells,
「実施例1」還元剤としてエチレンを用いたリーンバーンNOx処理
製造例1及び2の触媒サンプルをそれぞれ石英製の連続流通式反応管に0.3g充填し、製造例3のモノリス触媒は触媒担持のミニ成形体を1個充填し、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を、一酸化窒素0.1%、酸素14%、水蒸気10%、及びエチレン0.3%とした。反応管へ導入した混合ガスの流量を毎分100ml、処理温度を160〜300℃とした。排ガスをサンプリングし、一酸化窒素の処理率を求めた。結果を表1に示した。
表1から、本発明のメソポーラス触媒は、エチレンなどの炭化水素を還元剤に用い高濃度酸素共存下でのNOxを低温領域でも効率よく浄化できることがわかる。また、結晶性メソポーラスシリカMCM−41に担持した白金触媒は、一酸化窒素の最大反応率を与える温度が200℃であるのに対して、本発明のメソポーラス触媒は、170℃で一酸化窒素の最大反応率を与える。したがって、本発明のメソポーラス触媒は低温活性が格段に優れていることがわかる。
[Example 1] Lean burn NOx treatment using ethylene as a reducing agent Each of the catalyst samples of Production Examples 1 and 2 was filled in 0.3 g in a continuous flow reaction tube made of quartz, and the monolith catalyst of Production Example 3 was loaded with a catalyst. One mini-molded body was filled, and nitrogen monoxide whose concentration was adjusted with helium was circulated.
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. The exhaust gas was sampled and the treatment rate of nitric oxide was determined. The results are shown in Table 1.
From Table 1, it can be seen that the mesoporous catalyst of the present invention can efficiently purify NOx in the coexistence of high-concentration oxygen using a hydrocarbon such as ethylene as a reducing agent. Further, the platinum catalyst supported on the crystalline mesoporous silica MCM-41 has a temperature that gives the maximum reaction rate of nitric oxide at 200 ° C., whereas the mesoporous catalyst of the present invention has a nitrogen monoxide concentration at 170 ° C. Gives maximum response rate. Therefore, it can be seen that the mesoporous catalyst of the present invention is remarkably excellent in low temperature activity.
「実施例2」還元剤としてエチレンを用いたリッチバーンNOx処理
製造例3及び4の触媒をそれぞれ0.3g用いて一酸化窒素を処理した。被処理ガスの成分モル濃度比を、一酸化窒素0.1%、酸素1%、エチレン1%とした。該調整ガスの流量を毎分100ml、処理温度を160〜600℃とした。排ガスをサンプリングし、一酸化窒素の処理率を求めた。結果を表2に示した。
表2から、本発明のメソポーラス触媒は、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を中温領域から高温領域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、本発明のメソポーラス触媒は、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] Rich burn NOx treatment using ethylene as a reducing agent Nitric oxide was treated using 0.3 g of each of the catalysts of Production Examples 3 and 4. 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 processing temperature was 160 to 600 ° C. The exhaust gas was sampled and the treatment rate of nitric oxide was determined. The results are shown in Table 2.
From Table 2, it can be seen that the mesoporous catalyst of the present invention can efficiently purify NOx under rich burn conditions from a medium temperature region to a high temperature region using hydrocarbon as a reducing agent. Therefore, for example, if the lean burn and the rich burn are alternately performed, the mesoporous catalyst of the present invention can remove NOx in a wide temperature range. Therefore, the exhaust NOx of a small diesel vehicle capable of performing the lean burn and the rich burn alternately. It turns out that it is suitable for processing.
「実施例3」還元剤としてアンモニアを用いたNOx処理
製造例3及び4の触媒をそれぞれ0.3g用いて一酸化窒素を処理した。被処理ガスの成分モル濃度比を、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100ml、処理温度を150〜600℃とした。排ガスをサンプリングし、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、本発明のメソポーラス触媒は、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 Nitric oxide was treated using 0.3 g of each of the catalysts of Production Examples 3 and 4. 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 was 100 ml / min, and the processing temperature was 150 to 600 ° C. The exhaust gas was sampled and the treatment rate of nitric oxide was determined. The results are shown in Table 3.
Table 3 shows that the mesoporous catalyst of the present invention can efficiently purify NOx in the presence of high-concentration oxygen 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.
本発明のメソポーラス触媒及びモノリス触媒は、ディーゼル排NOx浄化用触媒として有用である。 The mesoporous catalyst and monolith catalyst of the present invention are useful as a diesel exhaust NOx purification catalyst.
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JP2011016091A (en) * | 2009-07-09 | 2011-01-27 | Toyota Motor Corp | Exhaust gas purifying catalyst |
JP2011092852A (en) * | 2009-10-29 | 2011-05-12 | Asahi Kasei Corp | Composite monolithic catalyst for cleaning exhaust gas |
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JPH0663400A (en) * | 1992-08-21 | 1994-03-08 | Toyota Motor Corp | Exhaust gas cleaning catalyst |
JP2005169333A (en) * | 2003-12-15 | 2005-06-30 | Nippon Sheet Glass Co Ltd | Metal nano-colloid liquid, carrier material, manufacturing method for metal carrier and metal carrier |
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JP2011016091A (en) * | 2009-07-09 | 2011-01-27 | Toyota Motor Corp | Exhaust gas purifying catalyst |
JP2011092852A (en) * | 2009-10-29 | 2011-05-12 | Asahi Kasei Corp | Composite monolithic catalyst for cleaning exhaust gas |
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