JP3576471B2 - Exhaust gas treatment method - Google Patents

Description

＊１）炭化水素（ＨＣ）の例としてＣ_３ Ｈ_６ を代表として示した。
＊２）含酸素炭化水素の例としてＣＨ_２ Ｏを代表として示した。
上記反応式において、（１）はＨＣの活性化、（２）はＨＣの燃焼、（３）は脱硝反応、（４）はＣＯの燃焼を意味している。
【００１６】
本発明で排気流入側に配置するイリジウムを有した触媒の好ましい脱硝温度は３００〜５００℃、一方排気流出側に配置する酸化触媒はいずれも３００℃以下が好ましい脱硝温度である。脱硝反応は上式で示すように、ＨＣ，ＣＯの燃焼反応と併発して生じているため、排気流入側のイリジウムを担持した触媒で未燃として残るＨＣが排気流出側の酸化触媒の脱硝反応への有効な還元剤として作用する。
【００１７】
本発明において用いる触媒は、貴金属触媒のため７００℃以上の高温リーン又はリッチ雰囲気に長時間さらされても上記ｋ１ ，ｋ_２ ，ｋ_３ 及びｋ_４ の反応速度定数はほとんど変化せず、耐久性を有する触媒であることを見い出している。
【００１８】
【参考例】
○触媒１〜１７の調製
組成式で、γ−Ａｌ₂ Ｏ₃ 、Ａｌ₂ Ｏ₃ ・ＺｒＯ₂ 、ＴｉＯ₂ 、ＺｒＯ₂ 、ＳｉＯ₂ ・Ａｌ₂ Ｏ₃ 、Ａｌ₂ Ｏ₃ ・ＴｉＯ₂ 、ＴｉＯ₂ ・ＺｒＯ₂ 、ＳＯ₄ ／ＺｒＯ₂ 、ＳＯ₄ ／ＺｒＯ₂ ・Ａｌ₂ Ｏ₃ 、ＳＯ₄ ／ＺｒＯ₂ ・ＴｉＯ₂ 、６Ａｌ₂ Ｏ₃ ・ＢａＯ、１１Ａｌ₂ Ｏ₃ ・Ｌａ₂ Ｏ₃ 、Ｙ型ゼオライト、Ａ型ゼオライト、シリカライト、モルデナイト及びＸ型ゼオライトを担体に用い、各担体１００部に対して、バインダとしてアルミナゾル：３部、シリカゾル：５５部（ＳｉＯ₂ ：２０％）及び水：２００部加え、充分攪拌を行いウォッシュコート用スラリとした。次にコージェライト用モノリス基材（４００セルの格子目）を上記スラリに浸漬し、取り出した後余分なスラリを吹きはらい２００℃で乾燥させた。コート量は基材１リットルあたり２００ｇ担持し、このコート物をハニカムコート物１〜１７とする。次に、塩化イリジウム（ＩｒＣｌ₄ ・Ｈ₂ Ｏ：２．８８ｇ／Ｈ₂ Ｏ：２００ｃｃ）に上記ハニカムコート物１を浸漬し１時間含浸した後、基材の壁の付着した液をふきとり２００℃で乾燥させた。次で５００℃で窒素雰囲気で１２時間パージ処理を行い、ハニカム触媒１〜１７を得た。
【００１９】
○触媒１８〜２１の調製
ハニカム触媒３と同様の方法でＴｉＯ_２ （アナターゼ型）をコージェライトモノリス基材にコートしたハニカムコート物３を、塩化白金酸（Ｈ_２ ＰｔＣｌ_６ ・６Ｈ_２ Ｏ：４．２ｇ／Ｈ_２ Ｏ：２００ｃｃ）、硝酸パラジウム（Ｐｄ（ＮＯ_３ ）_３ ：１．９ｇ／Ｈ_２ Ｏ：２００ｃｃ）、塩化ロジウム（ＲｈＣｌ_３ ：１．７ｇ／Ｈ_２ Ｏ：２００ｃｃ）、塩化ルテニウム（ＲｕＣｌ_３ ・５Ｈ_２ Ｏ：２．７ｇ／Ｈ_２ Ｏ：２００ｃｃ）の各水溶液に各々浸漬し触媒１と同様の方法でハニカム触媒１８〜２１を得た。
以上の触媒１〜２１の触媒の性状を表Ａにまとめて示す。
【００２０】
【表１】

【００２１】
（実験例１）
実施例にて調製したハニカム触媒１〜１７を排気流入側に、白金を担持したハニカム触媒１８を排気流出側に設置し、活性評価試験Ｒｕｎ１〜Ｒｕｎ１７を実施した。活性評価条件は下記のとおり。
【００２２】
○（ガス組成）
ＮＯ：５００ｐｐｍ、ＣＯ：１０００ｐｐｍ、Ｃ_２ Ｈ_４ ：１５００ｐｐｍ、Ｏ_２ ：８％、ＣＯ_２ ：１０％、Ｈ_２ Ｏ：１０％、残：Ｎ_２
○ガス量：４０５Ｎｌ／ｍｉｎ、ＧＨＳＶ１５，０００ｈ^−１
○触媒形状：１５ｍｍ×１５ｍｍ×６０ｍｍ（１４４セル数）１３５ｃｃを２個直列に配置（計２７ｃｃ）
○反応温度：２５０，３５０，４５０℃
初期状態の触媒の脱硝率を後記表Ｂに示す。
【００２３】
（実験例２）
ＲｕｎＮｏ．１〜１７で配置した触媒をリッチ雰囲気（還元雰囲気）で強制劣化試験を実施した。強制劣化試験は下記の通り。
○（ガス条件）
Ｈ_２ ：５％、Ｈ_２ Ｏ：１０％、残：Ｎ_２
ＧＨＳＶ：５０００ｈ^−１、温度：７５０℃、ガス供給時間：６時間
触媒形状：１５ｍｍ×１５ｍｍ×６０ｍｍ（１４４セル）
【００２４】
上記強制劣化条件にて処理したＲｕｎ Ｎｏ．１〜１７の組み合わせ触媒を実験例１の活性評価条件において活性評価試験を実施した。反応温度２５０℃、３５０、４５０℃における強制劣化試験後の触媒の脱硝率を表Ｂに併せて示す。表Ｂに示すように本組み合わせ触媒であるＲｕｎ Ｎｏ．１〜１７は高温還元雰囲気においても触媒の活性を高く維持することを確認した。
なお、ＣＯ及びＨＣの除去率は本反応温度では全て１００％であることを確認している。
【００２５】
【表２】

【００２６】
【発明の効果】
以上、説明したように、本発明による排気ガス浄化に際して使用する触媒は耐久性に富む安定な触媒であり、本発明はガソリン車のリーンバーンエンジン排ガス用やディーゼルエンジン排ガス浄化に極めて有利に利用し得る。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for treating exhaust gas containing nitrogen oxides (hereinafter abbreviated as NOx), carbon monoxide (CO), and hydrocarbons (hereinafter abbreviated as HC).
[0002]
[Prior art]
In exhaust gas treatment of automobiles and the like, it is common to use CO and HC in exhaust gas to purify NOx in an extremely narrow range near the stoichiometric air-fuel ratio. 2. Description of the Related Art In recent years, as global environmental problems have increased, the demand for lower fuel consumption of automobiles has been strongly demanded, and a lean burn engine that burns at a stoichiometric air-fuel ratio or more has attracted attention as a key technology. However, taking into consideration the traveling performance and acceleration of the vehicle, the engine only in the lean region has many disadvantages, and it is actually necessary to perform combustion in both the vicinity of the stoichiometric air-fuel ratio (stoichio) and the lean region. Recently, regarding the purification of NOx in the lean region, a crystalline silicate catalyst containing cobalt or copper has been spotlighted as a catalyst having high performance.
[0003]
However, when accelerating using these catalysts, the gas temperature instantaneously rises and the gas composition at this time becomes a rich atmosphere in which a reducing agent such as hydrogen is excessively present. Under these conditions, the deterioration of the catalyst cannot be prevented even when the crystalline silicate containing cobalt or copper is applied. Therefore, the improvement of the durability of the catalyst in a high-temperature rich atmosphere is a major problem in practical use of these catalysts. It has become.
[0004]
[Problems to be solved by the invention]
In order to overcome the above disadvantages, the present inventors have conducted intensive studies and found that a catalyst supporting iridium is a durable catalyst (see Japanese Patent Application No. 5-26369). Further, the present inventors have found that oxidation catalysts such as Pt and Rh have a denitrifying action in a low temperature range of 200 to 350 ° C. in addition to the combustion of CO and HC (Japanese Patent Application No. 4-230700, Japanese Patent Application No. 5-13575, Japanese Patent Application No. 5-13576).
[0005]
Exhaust gas conditions (gas composition, gas amount, temperature, etc.) of lean burn engines and diesel engines are wider than those of boiler exhaust gas. A method of applying in combination is desired. The present invention seeks to provide a method for purifying exhaust gas containing NOx, CO and CH which can meet this demand.
[0006]
[Means for Solving the Problems]
In view of the above situation, the present inventors have eagerly studied a preferable exhaust gas treatment method, and found that the method is suitable for the above purpose by disposing a catalyst containing iridium on the exhaust inflow side and a specific oxidation catalyst on the exhaust outflow side. They have found and completed the present invention.
[0007]
That is, the present invention has the following configurations (1) to ( 2 ).
(1) In a method for treating exhaust gas containing nitrogen oxides, which is present in a wide temperature range of 200 to 600 ° C. and is discharged from a lean burn engine or a diesel engine as needed, in the presence of hydrocarbons, A catalyst containing iridium is arranged on the side, and platinum, palladium, rhodium and ruthenium are formed on the exhaust outlet side of at least one active metal, and rhodium is provided on the upstream side of the exhaust outlet side. An exhaust gas treatment method comprising: arranging an oxidation catalyst obtained by combining a catalyst containing platinum in series with a catalyst containing platinum on the downstream side of the exhaust gas outflow side .
(2) The carrier of the catalyst containing iridium disposed on the exhaust inflow side is represented by a composition formula of γ-Al ₂ O ₃ , Al ₂ O ₃ .ZrO ₂ , TiO ₂ , ZrO ₂ , SiO ₂ .Al ₂ O ₃ , Al ₂ O ₃ · TiO ₂ , TiO ₂ · ZrO ₂ , SO ₄ / ZrO ₂ , SO ₄ / ZrO ₂ · Al ₂ O ₃ , SO ₄ / ZrO ₂ · TiO ₂ , 6Al ₂ O ₃ · BaO, 11Al ₂ O ₃ · La ₂ O _3, Y-type zeolite, a-type zeolite, the exhaust gas of silicalite, mordenite, the which is a one or more porous material selected from the group consisting of X-type zeolite (1) Processing method .
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
As the carrier in the catalyst to be disposed in the exhaust inflow side of the present invention, alone an oxide _{γ-Al 2 O 3, TiO} 2, ZrO 2, a composite oxide _{Al 2 O 3 · ZrO 2,} SiO 2 · Al _{2 O 3, Al 2 O 3} · TiO 2, TiO 2 · ZrO 2, 6Al 2 O 3 · BaO, 11Al 2 O 3 · La 2 O 3, SO 4 / ZrO 2 is a solid strong acid, SO 4 / ZrO ₂ · Al ₂ O ₃ , SO ₄ / ZrO ₂ · TiO ₂ (These solid strong acids are immersed in 1N H ₂ SO ₄ at room temperature for about 1 hour at room temperature, and the hydroxide and complex hydroxide of each element are filtered, Obtained by drying and calcining) and a zeolite group, Y-type zeolite, A-type zeolite, silicalite (one of zeolites having a pentasil-type structure, which is composed of only Si and O), Rudenaito, X-type zeolite is used.
[0009]
As a method of supporting iridium on the carrier, a porous substance as a carrier can be immersed in an iridium salt solution and supported by an ion exchange method or an impregnation method. The supported iridium exhibits sufficient activity at 0.002 wt% or more, and preferably has high activity at 0.02 wt% or more.
[0010]
The support of the oxidation catalyst containing at least one active metal selected from the group consisting of platinum, palladium, rhodium and ruthenium disposed on the exhaust outlet side of the present invention is generally Al ₂ O ₃ , ZrO ₂ , A material having a high specific surface area such as SiO ₂ or TiO ₂ is used. When treating diesel exhaust gas, it is preferable to use TiO ₂ as a carrier in consideration of SOx durability. Note that the amount of the active metal supported by the oxidation catalyst is in the same range as the above-mentioned catalyst.
[0011]
As the oxidation catalyst disposed on the exhaust outlet side of the present invention, a three-way catalyst (a catalyst capable of simultaneously removing NOx, CO, and HC near the stoichiometric air-fuel ratio) used for purifying exhaust gas of a gasoline engine is used. Can also be used.
[0012]
As oxidation catalyst disposed in exhaust outlet side, by arranging a combination in series by dividing the catalyst containing platinum catalyst containing rhodium on the upstream side of the exhaust on the downstream side of the exhaust, wider temperature range in it is possible to perform the denitration. The reason for combining a rhodium-containing catalyst and a platinum-containing catalyst is that in a normal lean burn engine or diesel engine exhaust gas, a platinum-containing catalyst has a high denitration activity at about 200 ° C., while about 300 ° C. This is because a rhodium-containing catalyst has a high denitrification activity around ℃, and by combining these, a wide denitration activity can be maintained in a low temperature range of 200 to 300 ℃.
[0013]
The oxidation catalyst disposed on the exhaust outlet side of the present invention not only promotes denitration in a low-temperature region, but also enables low-temperature combustion of combustible gases such as CO and HC, as a matter of course.
[0014]
Generally, a purification reaction formula for purifying exhaust gas containing NOx, CO, and HC using a catalyst supporting iridium and an oxidation catalyst supporting platinum, palladium, rhodium, and ruthenium is as follows.
[0015]
Embedded image

* 1) C ₃ H ₆ is shown as a representative example of hydrocarbon (HC).
* 2) CH ₂ O is shown as a representative example of the oxygen-containing hydrocarbon.
In the above reaction formula, (1) means activation of HC, (2) means combustion of HC, (3) means denitration reaction, and (4) means combustion of CO.
[0016]
In the present invention, the preferred denitration temperature of the catalyst having iridium disposed on the exhaust inflow side is 300 to 500 ° C., while the oxidation catalyst disposed on the exhaust outflow side is preferably 300 ° C. or less. As shown in the above equation, the denitration reaction occurs simultaneously with the combustion reaction of HC and CO, so that HC remaining unburned by the catalyst supporting iridium on the exhaust inflow side is denitrification reaction of the oxidation catalyst on the exhaust outflow side. Acts as an effective reducing agent to
[0017]
The catalyst used in the present invention, the reaction rate constant of the precious metal to a high temperature for a long time a lean or rich atmosphere above 700 ° C. for the catalyst exposed even above k1, k _2, k ₃ and k ₄ hardly changes, durability Has been found to be a catalyst having
[0018]
[ Reference example]
○ Preparation formulas of catalysts 1 to 17 are represented by γ-Al ₂ O ₃ , Al ₂ O ₃ .ZrO ₂ , TiO ₂ , ZrO ₂ , SiO ₂ .Al ₂ O ₃ , Al ₂ O ₃ .TiO ₂ , TiO ₂ · ZrO ₂ , SO ₄ / ZrO ₂ , SO ₄ / ZrO ₂ · Al ₂ O ₃ , SO ₄ / ZrO ₂ · TiO ₂ , 6Al ₂ O ₃ · BaO, 11Al ₂ O ₃ · La ₂ O ₃ , Y-type zeolite , using a-type zeolite, silicalite, mordenite and X-type zeolite carrier, relative to 100 parts of each carrier, alumina sol as a binder: 3 parts, silica sol: 55 parts (SiO _2: 20%), and water: 200 parts of added After sufficiently stirring, a slurry for wash coating was obtained. Next, a monolith substrate for cordierite (400-cell grid) was immersed in the above slurry, taken out, and then sprayed with excess slurry and dried at 200 ° C. The coating amount is 200 g per liter of the base material, and the coated products are referred to as honeycomb coated products 1 to 17. Next, the honeycomb coated article 1 was immersed in iridium chloride (IrCl ₄ .H ₂ O: 2.88 g / H ₂ O: 200 cc) and impregnated for 1 hour, and the liquid adhering to the substrate wall was wiped off at 200 ° C. And dried. Next, purging treatment was performed at 500 ° C. in a nitrogen atmosphere for 12 hours to obtain honeycomb catalysts 1 to 17.
[0019]
○ in the same manner as in Preparation honeycomb catalyst 3 catalysts 18-21 the TiO ₂ honeycomb coating material 3 coated with (anatase) cordierite monolith substrate, chloroplatinic acid _{(H 2 PtCl 6 · 6H 2} O: 4 0.2 g / H ₂ O: 200 cc), palladium nitrate (Pd (NO ₃ ) ₃ : 1.9 g / H ₂ O: 200 cc), rhodium chloride (RhCl ₃ : 1.7 g / H ₂ O: 200 cc), ruthenium chloride _{(RuCl 3 · 5H 2 O:} 2.7g / H 2 O: 200cc) was obtained each immersed honeycomb catalyst 18 to 21 in the same way as catalyst 1 to the aqueous solution.
The properties of the above catalysts 1 to 21 are summarized in Table A.
[0020]
[Table 1]

[0021]
(Experimental example 1)
The honeycomb catalysts 1 to 17 prepared in the examples were installed on the exhaust inflow side, and the honeycomb catalyst 18 carrying platinum was installed on the exhaust outflow side, and the activity evaluation tests Run1 to Run17 were performed. The activity evaluation conditions are as follows.
[0022]
○ (gas composition)
_{NO: 500ppm, CO: 1000ppm,} C 2 H 4: 1500ppm, O 2: 8%, CO 2: 10%, H 2 O: 10%, remaining: _{N 2}
○ Gas volume: 405 Nl / min, GHSV 15,000 h ^-1
○ Catalyst shape: 15mm × 15mm × 60mm (144 cells) 135cc arranged in series (total 27cc)
○ Reaction temperature: 250, 350, 450 ° C
The denitration rate of the catalyst in the initial state is shown in Table B below.
[0023]
(Experimental example 2)
RunNo. The catalysts arranged in Nos. 1 to 17 were subjected to a forced deterioration test in a rich atmosphere (reducing atmosphere). The forced deterioration test is as follows.
○ (gas conditions)
H ₂ : 5%, H ₂ O: 10%, balance: N ₂
GHSV: 5000 h ⁻¹ , temperature: 750 ° C., gas supply time: 6 hours Catalyst shape: 15 mm × 15 mm × 60 mm (144 cells)
[0024]
Run No. processed under the above forced deterioration conditions An activity evaluation test was performed on the combination catalysts 1 to 17 under the activity evaluation conditions of Experimental Example 1. Table B also shows the denitration ratio of the catalyst after the forced deterioration test at reaction temperatures of 250 ° C, 350 ° C, and 450 ° C. As shown in Table B, Run No. Nos. 1 to 17 confirmed that the activity of the catalyst was maintained high even in a high-temperature reducing atmosphere.
It has been confirmed that the removal rates of CO and HC are all 100% at the reaction temperature.
[0025]
[Table 2]

[0026]
【The invention's effect】
As described above, the catalyst used for purifying the exhaust gas according to the present invention is a stable catalyst with high durability, and the present invention is extremely advantageously used for purifying lean burn exhaust gas from gasoline vehicles and purifying diesel engine exhaust gas. obtain.

Claims (2)

A method for treating exhaust gas containing nitrogen oxides, which is present in a wide temperature range of 200 to 600 ° C. and is discharged from a lean burn engine or a diesel engine, in the presence of a hydrocarbon, is provided with iridium on an exhaust inlet side. place a catalyst containing platinum on the exhaust outlet side, palladium, consist of one or more active metal selected from the group consisting of rhodium and ruthenium, and containing rhodium in the upstream side of the exhaust outlet-side catalyst Wherein an oxidation catalyst comprising a combination of platinum-containing catalysts arranged in series is disposed downstream of the exhaust gas outlet side . The carrier of the catalyst containing iridium disposed on the exhaust gas inflow side is composed of γ-Al ₂ O ₃ , Al ₂ O ₃ .ZrO ₂ , TiO ₂ , ZrO ₂ , SiO ₂ .Al ₂ O ₃ , Al ₂ O _{3 · TiO 2, TiO 2 · ZrO} 2, SO 4 / ZrO 2, SO 4 / ZrO 2 · Al 2 O 3, SO 4 / ZrO 2 · TiO 2, 6Al 2 O 3 · BaO, 11Al 2 O 3 · La 2 O _3, Y-type zeolite, a-type zeolite, silicalite, mordenite, exhaust gas treatment method according to claim 1, wherein a from the group consisting of X-type zeolite is at least one porous material selected.