JP2007175654A - Catalyst for deoxidizing nitrogen oxide selectively - Google Patents
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本発明は、過剰酸素を含有する排ガス中の窒素酸化物を除去する触媒に関するものである。 The present invention relates to a catalyst for removing nitrogen oxides in exhaust gas containing excess oxygen.
燃焼器や種々のエンジン等の燃焼排ガス中には、酸化性の有害成分である窒素酸化物(NOx)が含まれている。これを、触媒を用いて還元して無害化するためには種々の還元剤が使用されるが、その中では排ガス中に含まれる還元剤と反応させることが、還元剤を別に供給する必要がなく望ましい方法であり、特に、ほとんどの排ガス中に含まれる一酸化炭素（CO）を用いることが実用的に好ましい。
しかしながら、燃焼排ガスのうち、ボイラー、リーンバーンエンジン、ディーゼルエンジン排ガス中のNOxを除去する場合、排ガス中には一酸化炭素（CO）と同時に過剰の酸素が含まれているため、このような条件においても選択的に一酸化炭素（CO）を用いてNOxを還元できる触媒が必要である。
Combustion exhaust gases from combustors and various engines contain nitrogen oxides (NOx) that are oxidative harmful components. Various reducing agents are used to reduce this using a catalyst and render it harmless. Among them, it is necessary to separately supply the reducing agent to react with the reducing agent contained in the exhaust gas. This is a desirable method, and in particular, it is practically preferable to use carbon monoxide (CO) contained in most exhaust gases.
However, when removing NOx from exhaust gas from boilers, lean burn engines, and diesel engines, exhaust gas contains excess oxygen at the same time as carbon monoxide (CO). Need a catalyst that can selectively reduce NOx using carbon monoxide (CO).
すなわち、酸素存在下、窒素酸化物（NOx）として一酸化窒素（NO）、還元剤として一酸化炭素（CO）を用いる場合には、化１に示す反応式（１）、（２）により進行すると推測される。 That is, in the presence of oxygen, when nitrogen monoxide (NO) is used as nitrogen oxide (NOx) and carbon monoxide (CO) is used as a reducing agent, the reaction proceeds according to the reaction formulas (1) and (2) shown in Chemical formula 1. I guess that.
（化１）
２NO＋２CO → N２＋ ２CO2 （１）
O2 ＋ 2CO → ２CO2 （２）
(Chemical formula 1)
2NO + 2CO → N 2 + 2CO 2 (1)
O 2 + 2CO → 2CO 2 (2)
式（１）により、NOを高い割合でＮ２まで還元させるには、ＣＯがＮＯによってCO2まで酸化されることが必要であり、ＣＯの酸化が進行しなければ、ＮＯのN２への還元も進行しない。一方、式（２）でCOの酸素による酸化が進むと、ＣＯは式（１）の反応に関与しなくなり、その結果としてＮＯのN２への還元率も低下する。したがって、ＮＯを高い割合で還元するには、ＮＯの還元剤であるCOが、高濃度で存在する酸素と式（２）により反応するよりも、低濃度で存在するNOと式（１）により選択的に反応する触媒機能が必要となる。 In order to reduce NO to N 2 at a high rate according to the formula (1), it is necessary that CO is oxidized to CO 2 by NO. If the oxidation of CO does not proceed, NO is converted to N 2 . Reduction does not proceed. On the other hand, when the oxidation of CO by oxygen proceeds in Formula (2), CO does not participate in the reaction of Formula (1), and as a result, the reduction rate of NO to N 2 also decreases. Therefore, in order to reduce NO at a high rate, CO, which is a reducing agent for NO, reacts with oxygen present at a high concentration by the formula (2), and by using NO and the formula (1) present at a low concentration. A catalytic function to react selectively is required.
これまで、COによるNOx選択還元にはイリジウムを含む触媒が活性を示すことが知られている。
例えば、ＳＯ２１ｐｐｍ以下の条件下に、NOx転化率が８０％を超す触媒として、Ｉｒ／シリカライトを用いるもの（非特許文献１）が報告されているが、活性は不十分である。
また最近、酸素過剰雰囲気下、ＳＯ２の存在下で良好な還元性能を発揮するイリジウム／シリカ触媒とロジウム／シリカ触媒（特許文献１）が開発されている。
これらの触媒は、いずれも、酸素１．３％の条件でも最大NOx転化率が６５%と比較的高い活性を有するが、高濃度酸素雰囲気下で活性が著しく低下する。またＳＯ２が存在しない場合には活性が発現しないなどの欠点を有する。
Until now, it is known that a catalyst containing iridium exhibits activity for NOx selective reduction by CO.
For example, a catalyst using Ir / silicalite as a catalyst having a NOx conversion rate exceeding 80% under a condition of 1 ppm or less of SO 2 (Non-patent Document 1) has been reported, but the activity is insufficient.
Recently, an iridium / silica catalyst and a rhodium / silica catalyst (Patent Document 1) that exhibit good reduction performance in an oxygen-excess atmosphere and in the presence of SO 2 have been developed.
All of these catalysts have a relatively high activity with a maximum NOx conversion of 65% even under the condition of oxygen 1.3%, but the activity is remarkably reduced in a high concentration oxygen atmosphere. Further, when SO 2 is not present have the disadvantage of such activity is not exhibited.
イリジウム触媒では、他に酸化タングステンおよび酸化亜鉛（非特許文献２、３）などの金属酸化物に担持したものも報告されている。これらの触媒は、酸素２％の酸素過剰雰囲気下でも９０％以上の高いNOx転化率を示すものの、空間速度が非常に低く、SO２による阻害も受けるため（非特許文献２）、実用条件下で性能を発揮するとは言い難い。
その他にも、Ｉｒ／WO３-ＳｉＯ２を用いるもの（非特許文献４）では、空間速度数万h−１以上の条件でNOx転化率は８０％を超すが、高い活性を示す温度域が５０℃未満と狭く、広範囲な温度となる実用条件下では効果的なNOx除去が行えない可能性がある。
In addition, iridium catalysts supported on metal oxides such as tungsten oxide and zinc oxide (Non-patent Documents 2 and 3) have also been reported. Although these catalysts show a high NOx conversion rate of 90% or more even in an oxygen-excess atmosphere of 2% oxygen, the space velocity is very low and they are also inhibited by SO 2 (Non-patent Document 2). It is hard to say that the performance is exhibited.
In addition, in the case of using Ir / WO 3 —SiO 2 (Non-patent Document 4), the NOx conversion rate exceeds 80% under the condition of a space velocity of several tens of thousands h −1 , but the temperature range showing high activity is There is a possibility that effective NOx removal cannot be performed under practical conditions where the temperature is narrow and less than 50 ° C. and a wide range of temperatures.
以上のように、これまで知られている触媒は、すべて実用的な性能を有するとは言い難く、そのため、より高い活性、広い活性温度、実ガス条件下での高い耐久性を有する触媒の開発改良が望まれていた。
本発明の課題は、酸素過剰雰囲気下、排ガス中に含まれるNOxをCOを用いて、幅広い、温度、空間速度等の反応条件において、高い活性を長期間に渡り安定に示す触媒を提供することである。 An object of the present invention is to provide a catalyst that stably exhibits high activity over a long period of time in a wide range of reaction conditions such as temperature and space velocity using CO as the NOx contained in exhaust gas in an oxygen-excess atmosphere. It is.
本発明者らは、従来技術に存在する問題を解決するために鋭意研究を重ねた結果、酸化タングステン(WO３)とシリカ(ＳｉＯ２)からなる担体に、イリジウムと、活性助剤として周期律表第１，２，３，９，１１及び１２族金属のうち1種以上とを担持した触媒が、ＳＯ２含有あるいは存在しないにかかわらず、幅広い温度範囲と空間速度条件で、NOxを酸素過剰雰囲気下でもCOによって効率よく選択的に長期間にわたり還元できることを見出した。
すなわち、ＮＯｘと還元剤としてのＣＯとの、より選択的な反応を促すために、本発明の周期律表第１，２，３，９，１１及び１２族金属から選ばれる1種以上の金属とイリジウムを、酸化タングステンおよびシリカからなる担体に担持した触媒を使用することが重要となるものである。そして、このことは、従来技術であるシリカを担体としてイリジウムと活性助剤を担持した触媒の性能と、酸化タングステンとシリカからなる担体にイリジウムを担持した触媒の性能を、単に組み合わせただけの効果とは明らかに異なるものである。
As a result of intensive studies to solve the problems existing in the prior art, the present inventors have found that a carrier composed of tungsten oxide (WO 3 ) and silica (SiO 2 ) has iridium and a periodic rule as an active assistant. Tables 1, 2 , 3, 9, 11, and 12 or more of the group 12 metal supported catalysts, NOx is oxygen-excessed over a wide temperature range and space velocity conditions, regardless of whether or not SO 2 is contained. We have found that CO can be efficiently and selectively reduced over a long period of time even in an atmosphere.
That is, in order to promote a more selective reaction between NOx and CO as a reducing agent, one or more metals selected from Group 1, 2, 3, 9, 11 and 12 metals of the periodic table of the present invention. It is important to use a catalyst in which iridium and iridium are supported on a support made of tungsten oxide and silica. This is because the performance of a catalyst in which iridium and an active aid are supported using silica as a support, and the performance of a catalyst in which iridium is supported on a support made of tungsten oxide and silica, are simply combined. Is clearly different.
本発明によると、以下の発明が提供される。
（１）酸素存在下で、一酸化炭素により窒素酸化物を選択的に還元する触媒であって、周期律表第１，２，３，９、１１及び１２族金属から選ばれる1種以上の金属とイリジウムを、酸化タングステンおよびシリカからなる担体に担持したことからなることを特徴とする還元触媒。
（２）前記酸化タングステン及びシリカからなる担体において、タングステンの含有量が１〜５０ｗｔ％であることを特徴とする（１）の還元触媒。
（３）前記酸化タングステン及びシリカからなる担体に対する前記イリジウムの担持量が、０．１〜１０ｗｔ％であることを特徴とする（１）又は（２）の還元触媒。
（４）前記周期律表第１，２，３，９，１１及び１２族金属から選ばれる1種以上の金属の担持量が、前記イリジウムの担持量に対して原子比で１／３０〜１０であることを特徴とする（１）ないし（４）のいずれかの還元触媒。
According to the present invention, the following inventions are provided.
(1) A catalyst that selectively reduces nitrogen oxides with carbon monoxide in the presence of oxygen, the catalyst comprising one or more metals selected from Group 1, 2, 3, 9, 11 and 12 metals of the periodic table A reduction catalyst comprising a metal and iridium supported on a carrier made of tungsten oxide and silica.
(2) The reduction catalyst according to (1), wherein the support comprising tungsten oxide and silica has a tungsten content of 1 to 50 wt%.
(3) The reduction catalyst according to (1) or (2), wherein the amount of the iridium supported on the carrier made of tungsten oxide and silica is 0.1 to 10 wt%.
(4) The loading amount of one or more metals selected from Group 1, 2, 3, 9, 11 and 12 metals of the periodic table is 1/30 to 10 in atomic ratio with respect to the loading amount of iridium. The reduction catalyst according to any one of (1) to (4), wherein
本発明により得られる触媒は、COによる窒素酸化物の選択的還元反応において、酸素過剰雰囲気下でＳＯ２を含有するもしくは存在しないに拘わらず、９０％を超えるNOx転化率が得られるとともに、約５０%を超えるNOx転化率が約１００℃の広範な温度範囲にわたり得られ、かつ幅広い空間速度でも高い活性を発揮し、さらに高活性を長時間維持できる。 The catalyst obtained according to the present invention has a NOx conversion rate of more than 90% in a selective reduction reaction of nitrogen oxides with CO, regardless of whether or not SO 2 is contained in an oxygen-excess atmosphere, A NOx conversion rate exceeding 50% can be obtained over a wide temperature range of about 100 ° C., exhibits high activity even at a wide space velocity, and can maintain high activity for a long time.
本発明の触媒は、周期律表第１，２，３，９，１１及び１２族金属のうち1種以上とイリジウムを酸化タングステンおよびシリカからなる担体に担持した触媒である。
本発明触媒の構成主成分であるシリカ（ＳｉＯ２）は、耐熱、耐水性に優れた金属酸化物であり、合成は従来公知の方法により行われる。
The catalyst of the present invention is a catalyst in which one or more of the metals in Groups 1, 2, 3, 9, 11, and 12 of the periodic table and iridium are supported on a carrier made of tungsten oxide and silica.
Silica (SiO 2 ), which is a constituent component of the catalyst of the present invention, is a metal oxide excellent in heat resistance and water resistance, and synthesis is performed by a conventionally known method.
本件発明における担体を構成する1成分であるシリカそのものは、COを還元剤に使用してもNOx還元活性を全く示さない。また、該シリカにイリジウムあるいはイリジウムと活性助剤を担持した触媒では、ＳＯ２存在下でのみNOx還元活性を示すものの、活性温度域が狭い上に活性劣化も著しい。さらに、酸化タングステン(WO３)とシリカからなる担体にイリジウムを担持した触媒も、NOx還元活性は示すものの、活性温度域が狭く、活性の劣化も著しい。
これに対し、本発明の、酸化タングステン(WO３)とシリカ（ＳｉＯ２）を複合化し、イリジウム(Ｉｒ)と、周期律表第１，２，３，９，１１及び１２族金属のうち１種以上を担持した触媒は、幅広い温度及び高い空間速度で、ＳＯ２が含有あるいは存在しない場合でも、長期間にわたり著しく高いNOｘ除去性能を維持する。このような特異的な活性は、酸化タングステンとシリカとからなる担体に、イリジウム及び周期律表第１，２，３，９，１１及び１２族金属のうち1種以上が組み合わさることによって始めて発現するものである。
Silica itself, which is one component constituting the carrier in the present invention, shows no NOx reduction activity even when CO is used as a reducing agent. Further, a catalyst in which iridium or iridium and an active assistant are supported on the silica exhibits NOx reduction activity only in the presence of SO 2 , but the activation temperature range is narrow and the activity deterioration is remarkable. Further, a catalyst in which iridium is supported on a support made of tungsten oxide (WO 3 ) and silica also shows NOx reduction activity, but has a narrow activation temperature range and significant deterioration in activity.
On the other hand, tungsten oxide (WO 3 ) and silica (SiO 2 ) of the present invention are composited, and iridium (Ir) is selected from 1st, 2nd, 3rd, 9th, 11th and 12th metals in the periodic table. Catalysts loaded with more than a species maintain a significantly higher NOx removal performance over a long period of time, over a wide range of temperatures and high space velocities, even when SO 2 is not present or present. Such a specific activity is manifested only when a carrier composed of tungsten oxide and silica is combined with one or more of iridium and Group 1, 2, 3, 9, 11 and 12 metals of the periodic table. To do.
上記の周期律表第１族金属としては、Ｌｉ，Na，Ｋ，Ｃｓ等があげられ、周期律表第２族金属としてはＭｇ，Ｃａ，Ｂａ，Ｓｒ等があげられ、周期律表第３族金属としてはＬａ，Ｓｃ，Ｙ，Ｃｅ，Ｐｒ，Ｅｕ等があげられ、周期律表第９族金属としてはＣｏ，Ｒｈ等があげられ、周期律表第１１族金属としてはＣｕ，Ａｇ，Ａｕがあげられ、周期律表第１２族金属としてはＺｎ等があげられる。 Examples of the Periodic Table Group 1 metal include Li, Na, K, and Cs. Examples of the Periodic Table Group 2 metal include Mg, Ca, Ba, and Sr. Group metals include La, Sc, Y, Ce, Pr, Eu, etc., Group 9 metals of the periodic table include Co, Rh, etc., Group 11 metals of the periodic table include Cu, Ag, Au is exemplified, and the group 12 metal of the periodic table includes Zn and the like.
上記WO３含有量は、WO３-ＳｉＯ２重量に対して1〜５０重量%、好ましくは１０重量%である。上記Ｉｒの含有量は、０．１〜１０ｗｔ％、好ましくは０．５〜５ｗｔ%である。
周期律表第１，２，３，９、１１及び１２族金属のうち1種以上の金属の含有量として、Ｉｒ含有量に対して原子比で１／３０〜１０、好ましくは１／２０〜1の広範囲で効果を示す。
The content of WO 3 is 1 to 50% by weight, preferably 10% by weight, based on 2 % by weight of WO 3 —SiO 2 . The content of Ir is 0.1 to 10 wt%, preferably 0.5 to 5 wt%.
As content of 1 or more types of metals among 1st, 2nd, 3rd, 9th, 11th and 12th group metals of periodic table, 1 / 30-10 by atomic ratio with respect to Ir content, Preferably 1/20 1 shows a wide range of effects.
酸化タングステンとシリカからなる担体を調製する方法は、タングステン化合物の水溶液にシリカを浸漬する含浸法や、シリカ化合物ならびにタングステン化合物の混合溶液を用いるゾルゲル法等で行うことができる。特に、含浸法の場合は、タングステン化合物のクエン酸およびリンゴ酸水溶液を用いることが好ましい。たとえば、タングステン化合物のクエン酸水溶液にシリカを浸漬し、乾燥した後、空気中で焼成することにより、酸化タングステンとシリカの複合担体が得られる。複合担体では、シリカ上にタングステンが酸化物の状態で層状に存在する。 The carrier comprising tungsten oxide and silica can be prepared by an impregnation method in which silica is immersed in an aqueous solution of a tungsten compound, a sol-gel method using a mixed solution of a silica compound and a tungsten compound, or the like. In particular, in the case of the impregnation method, it is preferable to use a citric acid and malic acid aqueous solution of a tungsten compound. For example, a composite carrier of tungsten oxide and silica can be obtained by immersing silica in an aqueous citric acid solution of a tungsten compound, drying it, and firing in air. In the composite carrier, tungsten is present in a layered form on the silica in an oxide state.
イリジウム（Ｉｒ）の担持方法は、前記の手順に従って調製したWO３-ＳｉＯ２担体に、イリジウム（Ｉｒ）の化合物からなる水溶液を含浸する方法等が採用される。担体にイリジウム（Ｉｒ）化合物を含浸させた後、乾燥、焼成する。このときのＩｒ化合物は、水に可溶であればどのようなものでもよいが、通常は、残存陰イオンを空気中の焼成処理により比較的低温で分解できる六塩化イリジウム酸等が用いられる。
周期律表第１，２，３，９，１１及び１２族金属のうち1種以上の金属を担持する際も、イリジウムの場合と同様の方法が採用され、同様に水に可溶な化合物であれば特に限定するものではないが、上記のように残存陰イオンを空気中の焼成処理によって比較的低温で分解除去できる金属硝酸塩化合物が好ましく用いられる。
As a method for supporting iridium (Ir), a method of impregnating an aqueous solution composed of a compound of iridium (Ir) into a WO 3 —SiO 2 carrier prepared according to the above procedure is employed. The carrier is impregnated with an iridium (Ir) compound, and then dried and fired. The Ir compound at this time may be any compound as long as it is soluble in water, but usually hexachloroiridium acid or the like capable of decomposing residual anions at a relatively low temperature by a firing treatment in air is used.
The same method as in the case of iridium is adopted when supporting one or more metals among the metals in Groups 1, 2, 3, 9, 11 and 12 of the periodic table, and it is also a water-soluble compound. Although there is no particular limitation as long as it is present, a metal nitrate compound capable of decomposing and removing residual anions at a relatively low temperature by firing in air as described above is preferably used.
いずれの場合も、含浸は、室温〜１００℃で、１〜２４時間で行い、通常は、室温で１〜３時間行う。含浸後は、通常は、乾燥した後、空気中で焼成する。空気中の焼成は、約３００〜９００℃、好ましくは約４００〜７００℃で、約１〜１０時間で行い、低温、短時間であると、化合物の分解が十分に進行せず、高温、長時間であると、含有成分の凝集やシンタリングが起きて、触媒の活性が低下してしまう。焼成後には、Ｉｒや周期律表第１，２，３，９，１１及び１２族金属のうち1種以上の金属は、主にシリカ上の酸化タングステンの層の上に酸化物として存在すると考えられる。
Ｉｒと、活性助剤として機能する周期律表第１，２，３，９，１１及び１２族金属のうち1種以上の金属の酸化タングステンとシリカの複合担体への担持順序は特に限定するものでなく、Ｉｒを先に担持し、それを焼成した後に活性助剤を追加担持する方法、Ｉｒと活性助剤を同時に担持する方法等があげられる。
In any case, the impregnation is performed at room temperature to 100 ° C. for 1 to 24 hours, and usually at room temperature for 1 to 3 hours. After impregnation, it is usually dried and then fired in air. Firing in air is performed at about 300 to 900 ° C., preferably about 400 to 700 ° C., for about 1 to 10 hours. When the temperature is low and the time is short, the decomposition of the compound does not proceed sufficiently, and the If it is time, aggregation of components and sintering occur, and the activity of the catalyst is reduced. After firing, one or more of Ir and Group 1, 2, 3, 9, 11 and 12 metals are considered to be present mainly as oxides on the tungsten oxide layer on silica. It is done.
The order in which Ir and one or more metals of the periodic table functioning as active aids of metals 1, 2, 3, 9, 11 and 12 are supported on the composite carrier of tungsten oxide and silica is particularly limited. In addition, there are a method in which Ir is supported first, an active assistant is additionally supported after firing it, a method in which Ir and an active assistant are simultaneously supported, and the like.
本発明の触媒は、粉状、粒状、ペレット状、ハニカム状等、種々の形状で使用することができる。
本発明の触媒は、使用前に、約４００〜８００℃、好ましくは約５００〜７００℃で、約５〜２０%の水素を含むガスで約１〜３時間還元処理を行う。
The catalyst of the present invention can be used in various shapes such as powder, granules, pellets, and honeycombs.
Prior to use, the catalyst of the present invention is subjected to reduction treatment at about 400 to 800 ° C., preferably about 500 to 700 ° C., with a gas containing about 5 to 20% hydrogen for about 1 to 3 hours.
本発明において、処理の対象となるNOx含有ガスは、ディーゼル車や定置式ディーゼル機関等のディーゼル排ガス、リーンバーンガソリン車等の排ガスをはじめ、各種燃焼設備等の排ガスをあげることができる。
これら排ガス中のNOxの除去は、上記した本発明の触媒を用いて、該触媒に、酸素を含む酸化雰囲気中、COの存在下で、排ガスを接触させることにより行う。
ここで、酸化雰囲気とは、排ガス中に含まれるCOを、完全に酸化してＣＯ２に変換するのに必要な酸素量よりも過剰な酸素が含まれる雰囲気である。
上記のCOは、排ガス中に残存するものであり、COの量は特に制限されない。ただし、必要な理論量より過剰とした方が還元反応はより進行されるので、一般には、過剰に存在させるのが好ましい。COを還元剤とする場合、NOxの還元除去に必要な理論量の約2倍〜１４倍量（NO５００ppmに対して１０００〜７０００ppm）の過剰、好ましくは約４〜１０倍量の過剰とするのが適している。
In the present invention, the NOx-containing gas to be treated can include diesel exhaust gas from a diesel vehicle or a stationary diesel engine, exhaust gas from a lean burn gasoline vehicle, and exhaust gas from various combustion facilities.
The removal of NOx in the exhaust gas is performed by using the above-described catalyst of the present invention and bringing the exhaust gas into contact with the catalyst in an oxidizing atmosphere containing oxygen in the presence of CO.
Here, the oxidizing atmosphere is an atmosphere that contains oxygen in excess of the amount of oxygen necessary to completely oxidize CO contained in the exhaust gas and convert it into CO 2 .
The above CO remains in the exhaust gas, and the amount of CO is not particularly limited. However, since the reduction reaction proceeds more when the amount is larger than the required theoretical amount, it is generally preferable that the amount be excessive. When CO is used as the reducing agent, the excess is about 2 to 14 times the theoretical amount necessary for NOx reduction and removal (1000 to 7000 ppm relative to NO500 ppm), preferably about 4 to 10 times the excess. Is suitable.
本発明において、ＳＯ２濃度は特に制限されない。本発明の触媒は、ＳＯ２濃度が０ppm〜２０ppmの範囲で、その活性を全く低下させることがない。 このことは、本発明の触媒が、ＳＯ２の含有もしくは存在しないことにかかわらず燃焼排ガスのNOx処理に対応可能であることを意味しており、さらに耐ＳＯ２性を有することを示している。 In the present invention, the SO 2 concentration is not particularly limited. The catalyst of the present invention, SO 2 concentration in the range of 0Ppm～20ppm, not reduced at all its activity. This catalyst of the present invention, it means that the NOx treatment of the combustion exhaust gas regardless of that it does not contain or presence of SO 2 is adaptable, indicating that further has a resistance to SO 2 resistance .
本発明の触媒を用いたNOxの還元除去は、上記の触媒を配置した反応器を用意し、ＳＯ２の含有する、もしくは存在しない酸化雰囲気中で、COを存在させて、NOx含有排ガスを通過させることにより行う。このときの反応温度は、一般には、約１００〜８００℃、好ましくは約２００〜６００℃である。反応圧力は特に制限されず、加圧下でも減圧下でも反応は進行するが、通常の排気圧で排ガスを触媒層へ導入し、反応を進行させるのが簡便である。
空間速度は特に制限しないが、約１０，０００〜５００，０００ｈ−１、好ましくは約４０，０００〜３００，０００ｈ−１である。
以下、本発明の実施例を説明する。
For NOx reduction using the catalyst of the present invention, a reactor equipped with the above catalyst is prepared, and CO is present in an oxidizing atmosphere containing or not containing SO 2 and passes through the NOx-containing exhaust gas. To do. The reaction temperature at this time is generally about 100 to 800 ° C, preferably about 200 to 600 ° C. The reaction pressure is not particularly limited, and the reaction proceeds either under pressure or under reduced pressure, but it is convenient to introduce the exhaust gas into the catalyst layer at a normal exhaust pressure to advance the reaction.
The space velocity is not particularly limited, but is about 10,000 to 500,000 h −1 , preferably about 40,000 to 300,000 h −1 .
Examples of the present invention will be described below.
水５０ｇにクエン酸３ｇを溶かした溶液にパラタングステン酸アンモニウムを１．２４ｇ入れ室温にて溶かし溶液Aを調製した。次に溶液Ａに、WO３とＳｉＯ２重量比が１：９となるように分量を調節してシリカ粒(富士シリシア化学社製商品名“CARIACT G-10”３００ｍ２／g <比表面積>)を混合した。その後、この混合溶液を９０℃以下で蒸発乾固させ、１１０℃、空気中で一晩乾燥し、５００℃で４時間焼成することで、WO３重量が１０重量%のＷＯ３-ＳｉＯ２を得た。
得られた１０重量％ＷＯ３-ＳｉＯ２、２gに対してＩｒ重量が５重量%となるよう濃度を調整した塩化イリジウム酸水溶液４ｇを含浸し、１１０℃空気中で一晩乾燥し、その後、６００℃で６時間焼成することで、Ｉｒ／ＷＯ３-ＳｉＯ２を得た。
得られたＩｒ／ＷＯ３-ＳｉＯ２、１gに対し、Ｂａ／Ｉｒ原子比が１／１０となるように濃度を調整した硝酸バリウム水溶液２gを含浸し、１１０℃空気中で一晩乾燥し、その後、６００℃で６時間焼成することにより、周期律表第２族金属であるバリウムとイリジウムを、酸化タングステン及びシリカからなる担体に担持した触媒（Ｂａ／Ｉｒ／ＷＯ３-ＳｉＯ２）を得た。
A solution A was prepared by adding 1.24 g of ammonium paratungstate to a solution of 3 g of citric acid in 50 g of water and dissolving at room temperature. Next, the amount of silica particles (trade name “CARIACT G-10” manufactured by Fuji Silysia Chemical Co., Ltd., 300 m 2 / g <specific surface area>) was adjusted in the solution A so that the weight ratio of WO 3 and SiO 2 was 1: 9. ) Were mixed. Thereafter, this mixed solution is evaporated to dryness at 90 ° C. or less, dried in air at 110 ° C. overnight, and baked at 500 ° C. for 4 hours, thereby converting WO 3 -SiO 2 having a WO 3 weight of 10% by weight. Obtained.
Impregnated with 4 g of 10% by weight of WO 3 —SiO 2 , 4 g of chloroiridium acid aqueous solution whose concentration was adjusted so that Ir weight was 5% by weight, and dried in air at 110 ° C. overnight. by calcining 6 hours at 600 ° C., to obtain a Ir / WO 3 -SiO 2.
The obtained Ir / WO 3 —SiO 2 , 1 g, was impregnated with 2 g of an aqueous barium nitrate solution adjusted to have a Ba / Ir atomic ratio of 1/10, and dried in air at 110 ° C. overnight. Thereafter, obtained by baking for 6 hours at 600 ° C., barium and iridium are periodic table group 2 metal, supported on a carrier consisting of tungsten oxide and silica in the catalyst (Ba / Ir / WO 3 -SiO 2) It was.
上記のようにして得られた本発明の触媒０．００４gを常圧流通式反応装置に充填した。触媒床温度を測定するための熱電対を触媒床中心付近に配置した。
触媒は反応前に１０％Ｈ２／Ｈｅ気流中、６００℃、2時間還元を施した。５００ppm ＮＯ、３０００ppm CO、５％Ｏ２、６％Ｈ２Ｏ、１ppmＳＯ２を含むHe希釈混合ガスの模擬排ガスを反応ガスとし、流量９０ｍｌ／ｍｉｎ（ＳＶ約７５０００ｈ−１に相当）で触媒床に流通し、その生成ガスを、ガスクロマトグラフ(CO，CO２，Ｎ２，Ｎ２O分析)で分析した。
活性評価は、次式に示すNO転化率により行い、その結果を表１に示した。
NO転化率 = [2×(N２濃度＋N２O濃度)／NO入口濃度]×100 (%)
0.004 g of the catalyst of the present invention obtained as described above was charged into a normal pressure flow reactor. A thermocouple for measuring the catalyst bed temperature was placed near the center of the catalyst bed.
During 10% H 2 / H e stream before the catalytic reaction, 600 ° C., subjected to 2 hours reduction. 500ppm NO, 3000ppm CO, 5% O 2, 6% H 2 O, and the reaction gas simulated exhaust gas of He diluent gas mixture containing 1ppmSO 2, the catalyst bed at a flow rate of 90 ml / min (corresponding to SV about 75000h -1) distribution, and the generated gas was analyzed by gas chromatograph (CO, CO2, N 2, N 2 O analysis).
The activity was evaluated based on the NO conversion rate shown in the following formula, and the results are shown in Table 1.
NO conversion rate = [2 × (N 2 concentration + N 2 O concentration) / NO inlet concentration] × 100 (%)
実施例１において、イリジウム担持量を2重量％とした以外は、実施例１と同様にしてNOの還元反応を行い、その結果を表１に示した。 In Example 1, the NO reduction reaction was performed in the same manner as in Example 1 except that the amount of iridium supported was 2% by weight. The results are shown in Table 1.
実施例１において、イリジウム担持量を０．５重量％とした以外は、実施例１と同様にしてNOの還元反応を行い、その結果を表１に示した。 In Example 1, NO reduction reaction was performed in the same manner as in Example 1 except that the amount of iridium supported was 0.5% by weight. The results are shown in Table 1.
実施例１において、バリウム担持量をイリジウム担持量に対して原子比が１／２０とした以外は、実施例１と同様にしてNOの還元反応を行い、その結果を表１に示した。 In Example 1, the reduction reaction of NO was performed in the same manner as in Example 1 except that the atomic ratio of the barium supported amount was 1/20 with respect to the iridium supported amount. The results are shown in Table 1.
実施例１において、バリウム担持量をイリジウム担持量に対して原子比が１／５とした以外は、実施例１と同様にしてNOの還元反応を行い、その結果を表１に示した。 In Example 1, the NO reduction reaction was performed in the same manner as in Example 1 except that the atomic ratio of the barium supported amount to the iridium supported amount was 1/5. The results are shown in Table 1.
実施例１において、バリウム担持量をイリジウム担持量に対して原子比が１／１とした以外は、実施例１と同様にしてNOの還元反応を行い、その結果を表１に示した。 In Example 1, NO reduction reaction was carried out in the same manner as in Example 1 except that the atomic ratio of the barium supported amount was 1/1 with respect to the iridium supported amount. The results are shown in Table 1.
実施例１において、硝酸バリウムを使用しない以外は、実施例１と同様にしてNOの還元反応を行い、その結果を表１に示した。 In Example 1, a reduction reaction of NO was performed in the same manner as in Example 1 except that barium nitrate was not used. The results are shown in Table 1.
実施例１において、担体としてシリカのみを使用する以外は、実施例１と同様にしてNOの還元反応を行い、その結果を表１に示した。 In Example 1, a NO reduction reaction was performed in the same manner as in Example 1 except that only silica was used as the support. The results are shown in Table 1.
表１から明らかなように、実施例１の本発明の触媒活性は、比較例１ならびに比較例２に示す従来技術の触媒の活性に比べて広い温度範囲にわたって著しく高いことがわかる。このことは、本発明の触媒性能が従来技術である比較例１と比較例２を単に組み合わせただけのものではないことを示している。
本発明の触媒では、Ｉｒ担持量が大きいほど、特に低温にて高い活性を示すことがわかる。また、Ｂａ／Ｉｒ原子比が１／２０〜１／１に至るまで著しく高い活性が得られ、特に実施例５においては最大NOx転化率が９４％に達し、約５０％以上の転化率が得られる温度領域が約１００℃（２６０〜３６０℃）と非常に広く、比較例１の約２０℃(２８０〜３００℃)と比べると約5倍、比較例２と比べても約3倍にまで拡大している。
以上のことから、ＷＯ３-ＳｉＯ２担体とＩｒとＢａが組み合わさることにより、広範な温度域で非常に高い活性を持つこれまでにない触媒性能が現れることがわかった。
As is apparent from Table 1, the catalytic activity of the present invention in Example 1 is remarkably high over a wide temperature range as compared with the activities of the prior art catalysts shown in Comparative Example 1 and Comparative Example 2. This indicates that the catalyst performance of the present invention is not merely a combination of Comparative Example 1 and Comparative Example 2 which are conventional techniques.
In the catalyst of the present invention, it can be seen that the greater the amount of Ir supported, the higher the activity especially at low temperatures. In addition, remarkably high activity was obtained until the Ba / Ir atomic ratio reached 1/20 to 1/1. In particular, in Example 5, the maximum NOx conversion reached 94%, and a conversion of about 50% or more was obtained. The temperature range is as wide as about 100 ° C. (260 to 360 ° C.), about 5 times compared to about 20 ° C. (280 to 300 ° C.) of Comparative Example 1, and about 3 times compared to Comparative Example 2. It is expanding.
From the above, it was found that unprecedented catalytic performance with very high activity in a wide temperature range appears by combining the WO 3 —SiO 2 carrier, Ir and Ba.
硝酸バリウムを硝酸リチウムに代えた以外は、実施例１と同様にしてNOの還元反応を行い、その結果を表２に示した。
このとき触媒に対するイリジウム（Ｉｒ）の担持量は５．０重量％、 周期律表第１族金属であるリチウム（Ｌｉ）の担持量はイリジウム（Ｉｒ）の担持量に対して原子比で１／１０であった。
The NO reduction reaction was carried out in the same manner as in Example 1 except that barium nitrate was replaced with lithium nitrate. The results are shown in Table 2.
At this time, the supported amount of iridium (Ir) with respect to the catalyst is 5.0% by weight, and the supported amount of lithium (Li), which is a Group 1 metal of the periodic table, is 1 / in atomic ratio with respect to the supported amount of iridium (Ir). 10.
硝酸バリウムを硝酸カリウムに代えた以外は、実施例１と同様にしてNOの還元反応を行い、その結果を表２に示した。
このとき触媒に対するイリジウム（Ｉｒ）の担持量は５．０重量％、周期律表第１族金属であるカリウム（ K）の担持量はイリジウム（Ｉｒ）の担持量に対して原子比で１／１０であった。
The NO reduction reaction was performed in the same manner as in Example 1 except that barium nitrate was replaced with potassium nitrate. The results are shown in Table 2.
At this time, the supported amount of iridium (Ir) on the catalyst is 5.0% by weight, and the supported amount of potassium (K) which is a Group 1 metal of the periodic table is 1 / in atomic ratio with respect to the supported amount of iridium (Ir). 10.
硝酸バリウムを硝酸カルシウムに代えた以外は、実施例１と同様にしてNOの還元反応を行い、その結果を表２に示した。
このとき触媒に対するイリジウム（Ｉｒ）の担持量は５．０重量％、周期律表第２族金属であるカルシウム（Ca）の担持量はイリジウム（Ｉｒ）の担持量に対して原子比で１／１０であった。
NO was reduced in the same manner as in Example 1 except that barium nitrate was replaced with calcium nitrate. The results are shown in Table 2.
At this time, the supported amount of iridium (Ir) with respect to the catalyst is 5.0% by weight, and the supported amount of calcium (Ca) which is a Group 2 metal of the periodic table is 1 / in atomic ratio with respect to the supported amount of iridium (Ir). 10.
硝酸バリウムを硝酸ランタンに代えた以外は、実施例１と同様にしてNOの還元反応を行い、その結果を表２に示した。
このとき触媒に対するイリジウム（Ｉｒ）の担持量は５．０重量％、周期律表第３族金属であるランタン（La）の担持量はイリジウム（Ｉｒ）の担持量に対して原子比で１／１０であった。
The NO reduction reaction was carried out in the same manner as in Example 1 except that barium nitrate was replaced with lanthanum nitrate. The results are shown in Table 2.
At this time, the supported amount of iridium (Ir) on the catalyst is 5.0% by weight, and the supported amount of lanthanum (La), which is a Group 3 metal of the periodic table, is 1 / in atomic ratio with respect to the supported amount of iridium (Ir). 10.
硝酸バリウムを酢酸コバルトに代えた以外は、実施例１と同様にしてNOの還元反応を行い、その結果を表２に示した。
このとき触媒に対するイリジウム（Ｉｒ）の担持量は５．０重量％、周期律表第９族金属であるコバルト（Ｃｏ）の担持量はイリジウム（Ｉｒ）の担持量に対して原子比で１／１０であった。
The NO reduction reaction was performed in the same manner as in Example 1 except that barium nitrate was replaced with cobalt acetate. The results are shown in Table 2.
At this time, the supported amount of iridium (Ir) with respect to the catalyst is 5.0% by weight, and the supported amount of cobalt (Co) which is a Group 9 metal of the periodic table is 1 / in atomic ratio with respect to the supported amount of iridium (Ir). 10.
硝酸バリウムを塩化金酸に代えた以外は、実施例１と同様にしてNOの還元反応を行い、その結果を表２に示した。
このとき触媒に対するイリジウム（Ｉｒ）の担持量は５．０重量％、周期律表第１１族金属である金（Au）の担持量はイリジウム（Ｉｒ）の担持量に対して原子比で１／１０であった。
NO was reduced in the same manner as in Example 1 except that barium nitrate was replaced with chloroauric acid, and the results are shown in Table 2.
At this time, the supported amount of iridium (Ir) on the catalyst is 5.0% by weight, and the supported amount of gold (Au) which is a Group 11 metal of the periodic table is 1 / in atomic ratio with respect to the supported amount of iridium (Ir). 10.
硝酸バリウムを硝酸亜鉛に代えた以外は、実施例１と同様にしてNOの還元反応を行い、その結果を表２に示した。
このとき触媒に対するイリジウム（Ｉｒ）の担持量は５．０重量％、周期律表第１２族金属である亜鉛（Ｚｎ）の担持量はイリジウム（Ｉｒ）の担持量に対して原子比で１／１０であった。
The NO reduction reaction was carried out in the same manner as in Example 1 except that barium nitrate was replaced with zinc nitrate. The results are shown in Table 2.
At this time, the supported amount of iridium (Ir) on the catalyst is 5.0% by weight, and the supported amount of zinc (Zn), which is a Group 12 metal of the periodic table, is 1 / at atomic ratio relative to the supported amount of iridium (Ir). 10.
表２から、ＷＯ３-ＳｉＯ２担体にＩｒを担持した触媒にＬｉ，Ｋ，Ｃａ，Ｂａ，Ｌａ，Ｃｏ，Ａｕ，Ｚｎ等の金属を加えることで、加えない場合よりも活性が向上することがわかる。
このことから、高いNOx除去活性を得るためには、周期律表第１，２，３，９，１１及び１２族金属のいずれか１種以上を添加すればよく、特に広い温度範囲で高い触媒性能を発揮するには、周期律表第２族金属の添加が好ましいことがわかる。
From Table 2, the activity is improved by adding a metal such as Li, K, Ca, Ba, La, Co, Au, and Zn to the catalyst having Ir supported on the WO 3 —SiO 2 carrier, compared to the case where it is not added. I understand.
For this reason, in order to obtain a high NOx removal activity, it is only necessary to add one or more of Periodic Table Nos. 1, 2, 3, 9, 11, and Group 12 metals, and a high catalyst particularly in a wide temperature range. It can be seen that the addition of a Group 2 metal of the periodic table is preferable for exhibiting performance.
原料ガスにSO２を使用しない以外は、実施例５と同様にしてNOの還元反応を行い、その結果を表３に示した。 The NO reduction reaction was performed in the same manner as in Example 5 except that SO 2 was not used as the source gas. The results are shown in Table 3.
原料ガスのSO２濃度を２０ppmとした以外は、実施例５と同様にしてNOの還元反応を行い、その結果を表３に示した。 The NO reduction reaction was carried out in the same manner as in Example 5 except that the SO 2 concentration of the source gas was 20 ppm, and the results are shown in Table 3.
原料ガスにＳＯ２を使用しない以外は、比較例１と同様にしてNOの還元反応を行い、その結果を表３に示した。 The NO reduction reaction was performed in the same manner as in Comparative Example 1 except that SO 2 was not used as the source gas. The results are shown in Table 3.
原料ガスにＳＯ２を使用しない以外は、比較例２と同様にしてNOの還元反応を行い、その結果を表３に示した。 The NO reduction reaction was performed in the same manner as in Comparative Example 2 except that SO 2 was not used as the source gas. The results are shown in Table 3.
表３から明らかなように、ＳＯ２が高濃度で存在しても、存在しなくても活性はほとんど変わらず、高い活性を示す。従って、本発明の触媒はＳＯ２が含有する、もしくは存在しないにかかわらず非常に高いNOx除去活性を示すことがわかった。一方、Ｉｒ／ＷＯ３-ＳｉＯ２触媒では、ＳＯ２が存在しない場合でもNOx除去活性は最大でも５０％程度である。またＩｒ／ＳｉＯ２にBaを添加した触媒に至ってはＳＯ２が存在しない場合には活性が発現しない。すなわち、活性助剤の添加は、ＳＯ２共存下でのみ有効である。したがって、本発明のＷＯ３-ＳｉＯ２担体とＩｒとＢａ添加の組み合わせは、従来技術からは予測することのできない触媒性能を生み出すことがわかった。 As apparent from Table 3, even if SO 2 is present in high concentrations, the activity hardly changes even in the absence, exhibits high activity. Therefore, it was found that the catalyst of the present invention exhibits a very high NOx removal activity regardless of whether SO 2 is contained or absent. On the other hand, with the Ir / WO 3 —SiO 2 catalyst, the NOx removal activity is about 50% at the maximum even in the absence of SO 2 . In addition, the catalyst obtained by adding Ba to Ir / SiO 2 exhibits no activity in the absence of SO 2 . That is, the addition of the active auxiliary is effective only in the presence of SO 2 . Thus, it has been found that the combination of the WO 3 —SiO 2 support of the present invention and the addition of Ir and Ba produces catalyst performance that cannot be predicted from the prior art.
触媒量を０．０１ｇ (ＳＶ約３００，０００ｈ−１に相当)とした以外は、実施例１と同様にしてNOの還元反応を行い、その結果を表４に示した。 The NO reduction reaction was performed in the same manner as in Example 1 except that the amount of catalyst was 0.01 g (corresponding to SV of about 300,000 h −1 ). The results are shown in Table 4.
表４から本発明の触媒は、ＳＶが７５，０００〜３００，０００ｈ−１という幅広い処理ガス量の条件下でも効果的に機能することがわかる。 From Table 4, it can be seen that the catalyst of the present invention functions effectively even under a wide range of processing gas amounts of SV of 75,000 to 300,000 h −1 .
ＷＯ３-ＳｉＯ２に塩化イリジウム酸と硝酸バリウムを同時に含浸した以外は、実施例１と同様にしてNOの還元反応を行い、その結果を表５に示した。 The NO reduction reaction was carried out in the same manner as in Example 1 except that WO 3 -SiO 2 was simultaneously impregnated with iridium chloride and barium nitrate. The results are shown in Table 5.
表５の結果から、調製法としては、Ｉｒの化合物を含浸し、乾燥、焼成した後にバリウム化合物を含浸しても、Ｉｒの化合物とバリウム化合物を同時に含浸しても、どちらでも最大NOx転化率が８０％以上と高い活性を示すことがわかる。 From the results shown in Table 5, the maximum NOx conversion rate can be obtained by either impregnating the Ir compound, drying and calcining, then impregnating the barium compound, or impregnating the Ir compound and the barium compound simultaneously. As can be seen from FIG.
原料ガスのCO濃度を１０００ppmとした以外は、実施例５と同様にしてNOの還元反応を行い、その結果を表６に示した。 The NO reduction reaction was performed in the same manner as in Example 5 except that the CO concentration of the source gas was set to 1000 ppm. The results are shown in Table 6.
原料ガスのCO濃度を５０００ppmとした以外は、実施例５と同様にしてNOの還元反応を行い、その結果を表６に示した。 The NO reduction reaction was performed in the same manner as in Example 5 except that the CO concentration of the raw material gas was set to 5000 ppm. The results are shown in Table 6.
表６から、CO濃度が１０００ppmでは活性が著しく低下することから、原料ガス中のCO濃度は少なくとも１０００ppmより高い濃度で使用することが望ましいことが分かった。 From Table 6, it was found that the CO concentration in the raw material gas is desirably higher than at least 1000 ppm because the activity is remarkably lowered when the CO concentration is 1000 ppm.
実施例１で調製した触媒について、活性の安定性を調べるため、反応時間１００時間相当の活性劣化試験を行った。１００時間相当後の触媒活性維持率を（試験終了時のNO転化率）／（試験開始直後のNO転化率）(%)として表７に示す。 The catalyst prepared in Example 1 was subjected to an activity deterioration test corresponding to a reaction time of 100 hours in order to examine the stability of the activity. Table 7 shows the catalyst activity retention ratio after 100 hours, as (NO conversion ratio at the end of the test) / (NO conversion ratio immediately after the start of the test) (%).
比較例１で調製した触媒について、活性の安定性を調べるため、反応時間１００時間相当のaging試験を行った。１００時間相当後の触媒活性維持率を（試験終了時のNO転化率）／（試験開始直後のNO転化率）(%)として表７に示す。 The catalyst prepared in Comparative Example 1 was subjected to an aging test corresponding to a reaction time of 100 hours in order to examine the stability of activity. The catalyst activity retention after 100 hours is shown in Table 7 as (NO conversion at the end of the test) / (NO conversion immediately after the start of the test) (%).
比較例２で調製した触媒について、活性の安定性を調べるため、反応時間１００時間相当のaging試験を行った。１００時間相当後の触媒活性維持率を（試験終了時のNO転化率）／（試験開始直後のNO転化率）(%)として表７に示す。 The catalyst prepared in Comparative Example 2 was subjected to an aging test corresponding to a reaction time of 100 hours in order to examine the stability of activity. Table 7 shows the catalyst activity retention ratio after 100 hours, as (NO conversion ratio at the end of the test) / (NO conversion ratio immediately after the start of the test) (%).
表７から、本発明の触媒は、従来技術のＩｒ／WO３-ＳＯ２触媒、Ｂａ／Ｉｒ／ＳＯ２触媒に比べて明らかに長時間にわたり高い触媒性能を発揮できることがわかる。従って、WO３-ＳＯ２担体とＩｒとＢａ添加を組み合わせることが、触媒活性の高さという点ばかりでなく触媒性能の安定性という点でもこれまでにない効果をもたらすことがわかった。 From Table 7, it can be seen that the catalyst of the present invention can clearly exhibit high catalytic performance over a long period of time as compared with the prior art Ir / WO 3 -SO 2 catalyst and Ba / Ir / SO 2 catalyst. Therefore, it has been found that combining the WO 3 —SO 2 carrier with the addition of Ir and Ba brings about an unprecedented effect not only in terms of high catalyst activity but also in terms of stability of catalyst performance.
本発明の触媒は、過剰酸素を含む排ガス中のNOxの低減に有効な活性を示すものであり、排ガス規制強化が進められつつあるディーゼル車あるいはディーゼル車と同じく排ガス中に酸素が存在しNOxの還元無害化が難しいリーンバーンガソリン車、さらには燃焼器の排ガス処理技術として利用されることが期待される。
The catalyst of the present invention exhibits an effective activity for reducing NOx in exhaust gas containing excess oxygen, and there is oxygen in the exhaust gas as in the case of diesel vehicles or diesel vehicles whose exhaust gas regulations are being strengthened. It is expected to be used as a lean burn gasoline vehicle that is difficult to reduce and detoxify, and as an exhaust gas treatment technology for combustors.
Claims (4)
The loading amount of one or more metals selected from Group 1, 2, 3, 9, 11 and 12 metals of the periodic table is 1/30 to 10 in atomic ratio with respect to the loading amount of iridium. The reduction catalyst according to any one of claims 1 to 3, wherein:
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| JP2011220213A (en) * | 2010-04-08 | 2011-11-04 | Hitachi Constr Mach Co Ltd | Exhaust emission control system in internal combustion engine of construction machine |
| CN115487798A (en) * | 2022-09-14 | 2022-12-20 | 福州大学 | Preparation method and application of assistant-promoted Ru-based nanocluster catalyst |
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