JP2007084391A - Exhaust gas purifying device for automobile and hydrogen producing catalyst - Google Patents

Exhaust gas purifying device for automobile and hydrogen producing catalyst Download PDF

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JP2007084391A
JP2007084391A JP2005277034A JP2005277034A JP2007084391A JP 2007084391 A JP2007084391 A JP 2007084391A JP 2005277034 A JP2005277034 A JP 2005277034A JP 2005277034 A JP2005277034 A JP 2005277034A JP 2007084391 A JP2007084391 A JP 2007084391A
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hydrogen production
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Toshiaki Nagayama
敏明 長山
Hidehiro Iizuka
秀宏 飯塚
Masayuki Kamikawa
将行 上川
Masahito Kanae
雅人 金枝
Yuichi Kitahara
雄一 北原
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Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas purifying device having high NOx purifying performance at a low temperature, particularly at 150 to 250°C, and to provide a hydrogen producing catalyst that improves exhaust gas purifying performance at switching of lean/rich. <P>SOLUTION: The hydrogen producing catalyst is a catalyst for producing hydrogen from carbon monoxide in the exhaust gas of an internal-combustion engine and water, and includes one or more noble metals selected from Pt, Pd and Rh and a cerium oxide or a compound oxide of cerium, wherein the cerium oxide is one that has a ratio of the (111) plane diffraction peak intensity to the background of 4.3 or larger. And the exhaust gas purifying device has an above mentioned hydrogen producing catalyst and a catalyst that has a function for adsorbing or occluding nitrogen oxides. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

本発明は、特に低温での窒素酸化物（以下ＮＯｘ）を効率良く浄化する自動車用排ガス浄化装置と、自動車排ガス中で水素を製造する水素製造触媒に関するものである。   The present invention relates to an automobile exhaust gas purification device that efficiently purifies nitrogen oxides (hereinafter referred to as NOx) particularly at low temperatures, and a hydrogen production catalyst that produces hydrogen in automobile exhaust gas.

地球温暖化防止，環境改善を目的に、自動車排ガス中の有害物質であるＣＯ（一酸化炭素），ＮＯｘ（窒素酸化物），ＨＣ（炭化水素）低減、そして温室ガスである二酸化炭素の削減が求められている。自動車排ガスから二酸化炭素を削減するには、燃費を向上させなければならない。そのため、エンジンを希薄燃料雰囲気で運転する必要がある。理論空燃比（Ａ／Ｆ＝約１４.６ ）で運転するガソリンエンジンの排ガス浄化には、三元触媒が用いられ、排ガス成分を利用してＣＯ，ＨＣの酸化とＮＯｘの還元を同時に行う。それより希薄な燃料雰囲気になる空気燃料比（以下リーン）で運転するエンジン（リーンバーンエンジン）では、排ガスに三元触媒で利用できる以上の酸素が含まれるため、還元反応が進行しにくく、ＮＯｘが浄化しにくい。これらを解決するため、リーン時に排ガス中の
ＮＯｘを触媒上に吸着し、一時的に理論空燃比より燃料が過剰な空気燃料比(以下リッチ)にするリーン・リッチ制御を行い、吸着したＮＯｘをリッチガス中のＨＣ，ＣＯ，Ｈ2 などで還元するリーンＮＯｘ触媒が実用化されている。 Reduction of CO (carbon monoxide), NOx (nitrogen oxide) and HC (hydrocarbon), which are harmful substances in automobile exhaust gas, and reduction of carbon dioxide, which is a greenhouse gas, for the purpose of preventing global warming and improving the environment It has been demanded. In order to reduce carbon dioxide from automobile exhaust, fuel efficiency must be improved. Therefore, it is necessary to operate the engine in a lean fuel atmosphere. A three-way catalyst is used for exhaust gas purification of a gasoline engine operating at a theoretical air fuel ratio (A / F = about 14.6), and CO and HC oxidation and NOx reduction are simultaneously performed using exhaust gas components. In an engine (lean burn engine) that operates at an air fuel ratio (hereinafter referred to as lean) that produces a leaner fuel atmosphere, the exhaust gas contains more oxygen than can be used in the three-way catalyst, so the reduction reaction does not proceed easily, and NOx Is difficult to purify. In order to solve these problems, NOx in the exhaust gas is adsorbed on the catalyst during lean, and lean-rich control is performed to temporarily make the air fuel ratio (hereinafter rich) of the fuel excessive from the stoichiometric air-fuel ratio. A lean NOx catalyst that reduces with HC, CO, H 2 or the like in a rich gas has been put into practical use.

ディーゼルエンジンは定常的にリーンで運転するため、排ガスのＮＯｘの浄化が困難である。しかし、ガソリンのリーンバーンエンジンと同様にリーンＮＯｘ触媒を使用しリーン・リッチ制御を行うことによりＮＯｘの浄化が可能になる。   Since the diesel engine is constantly operated lean, it is difficult to purify NOx in the exhaust gas. However, as with the lean burn engine of gasoline, NOx purification can be achieved by performing lean rich control using a lean NOx catalyst.

ディーゼルエンジンの排ガス処理に吸着型リーンＮＯｘ触媒を適用するに当たっての課題は、排ガス温度である。現状のディーゼルエンジンの排ガス温度は、ガソリンリーンバーンエンジンと比較して１００℃程度低い、１５０から２５０℃である。そのため、排ガスによって昇温される触媒の温度も１００℃程度低くなり、触媒活性が十分でない。特にリーン・リッチ制御を行う際に、リーンからリッチの切替え時は、触媒活性が十分でないため、吸着したＮＯｘの還元が不十分でＮＯｘ浄化率の低下が問題となる。   A problem in applying an adsorption type lean NOx catalyst to exhaust gas treatment of a diesel engine is exhaust gas temperature. The exhaust gas temperature of the current diesel engine is 150 to 250 ° C., which is lower by about 100 ° C. than the gasoline lean burn engine. Therefore, the temperature of the catalyst heated by the exhaust gas is also lowered by about 100 ° C., and the catalytic activity is not sufficient. In particular, when performing lean / rich control, the catalytic activity is not sufficient when switching from lean to rich, so that the reduction of the adsorbed NOx is insufficient and the NOx purification rate decreases.

リッチガスにはＨＣ，ＣＯ，Ｈ2 などの還元成分が含まれている。この還元成分を利用してＮＯｘを還元する方法が提案されている。１５０℃から２５０℃の低温での反応性は、ＣＯよりＨ2が高い。そこでＣＯと排ガス中のＨ2ＯからＨ2を製造し、そのＨ2でＮＯｘを還元する方法が考えられている（特開２００１−３００２６２号公報(特許文献１)等）。水素製造触媒は活性成分を貴金属とし、貴金属は、酸化ジルコニウム（ＺｒＯ2 ），酸化マグネシウム（ＭｇＯ）,アルミナ（Ａｌ2Ｏ3）−ＭｇＯ複合酸化物，ＴｉＢａＯ3，スピネルなどに担持して用いられる。ＣＯとＨ2ＯからＨ2を製造する反応は、水性ガスシフト反応と呼ばれ（１）式で表される。 The rich gas contains reducing components such as HC, CO, and H 2 . A method for reducing NOx using this reducing component has been proposed. Reactivity at a low temperature of 250 ° C. from 0.99 ° C. has a higher H 2 than CO. Therefore, a method has been considered in which H 2 is produced from CO and H 2 O in exhaust gas, and NOx is reduced with the H 2 (Japanese Patent Laid-Open No. 2001-300262 (Patent Document 1), etc.). The hydrogen production catalyst uses a noble metal as an active component, and the noble metal is supported on zirconium oxide (ZrO 2 ), magnesium oxide (MgO), alumina (Al 2 O 3 ) -MgO composite oxide, TiBaO 3 , spinel, etc. . The reaction for producing H 2 from CO and H 2 O is called a water gas shift reaction and is represented by the formula (1).

ＣＯ＋Ｈ2Ｏ→ＣＯ2＋Ｈ2 （１）
水性ガスシフト反応が進行しやすい触媒（以下水素製造触媒）と吸着型リーンＮＯｘ触媒を組み合わせることで、低温におけるリッチでのＮＯｘの還元性能を向上させ、リーン・リッチ制御を行ってディーゼルエンジン排ガスを高効率で浄化することが可能になる。 CO + H 2 O → CO 2 + H 2 (1)
A combination of a catalyst that facilitates water gas shift reaction (hereinafter referred to as hydrogen production catalyst) and an adsorption-type lean NOx catalyst improves the reduction performance of rich NOx at low temperatures and performs lean / rich control to increase diesel engine exhaust gas. It becomes possible to purify with efficiency.

特開２００１−３００２６２号公報Japanese Patent Laid-Open No. 2001-300262

本発明の課題は、さらに水性ガスシフト反応が進行しやすく、Ｈ2 製造能力を向上させた水素製造触媒と、それを用いた浄化性能の高い排ガス浄化装置とを提供することにある。 An object of the present invention is to provide a hydrogen production catalyst in which the water gas shift reaction is more likely to proceed and the H 2 production capacity is improved, and an exhaust gas purification apparatus having high purification performance using the hydrogen production catalyst.

上記課題を解決する本発明の特徴は、Ｐｔ，Ｐｄ，Ｒｈから選ばれる貴金属を１つ以上含み、一酸化炭素と水とから水素を生成する水素製造触媒であって、酸化セリウムまたはセリウムを含む複合酸化物を担体とすることにある。   A feature of the present invention that solves the above problems is a hydrogen production catalyst that contains one or more precious metals selected from Pt, Pd, and Rh and generates hydrogen from carbon monoxide and water, and includes cerium oxide or cerium. It is to use a composite oxide as a support.

使用した酸化セリウムは、結晶性が高いものであって、具体的にはＸ線回折パターンが（１１１）面回折ピーク強度とバックグランドの比が４.３ 以上あるものである。また、上記酸化セリウムの担体に、Ｔｉ酸化物を添加した担体を用いることが好ましい。酸化セリウムは、Ｔｉ酸化物との合計量のうち２８％以上含むことが好ましい。   The used cerium oxide has high crystallinity, and specifically, the X-ray diffraction pattern has a (111) plane diffraction peak intensity / background ratio of 4.3 or more. Further, it is preferable to use a carrier obtained by adding a Ti oxide to the cerium oxide carrier. It is preferable that cerium oxide contains 28% or more of the total amount with Ti oxide.

水素製造触媒は、窒素酸化物を吸着又は吸蔵する機能を有する触媒層(ＮＯｘ浄化触媒)との二層構造になっていることが好ましい。特に、前記ＮＯｘ浄化触媒を触媒支持材（例えばコージェライトやメタル，ハニカム等）上にコートし、そのＮＯｘ触媒層と接して水素製造触媒を配置することが好ましい。   The hydrogen production catalyst preferably has a two-layer structure with a catalyst layer (NOx purification catalyst) having a function of adsorbing or occluding nitrogen oxides. In particular, it is preferable to coat the NOx purification catalyst on a catalyst support material (for example, cordierite, metal, honeycomb, etc.), and place the hydrogen production catalyst in contact with the NOx catalyst layer.

また、ディーゼルエンジン自動車用の排ガス浄化装置であって、上記の水素製造触媒と、リーン条件下でＮＯｘを浄化するＮＯｘ浄化触媒とを有するものである。各触媒は混合してもよいが、水素製造触媒の後段にリーンＮＯｘ触媒を配置することが浄化性能の点より好ましい。また、水素製造触媒と、リーンＮＯｘ触媒とを二層構造とすることが効率の点から好ましい。   Moreover, it is an exhaust gas purification apparatus for diesel engine automobiles, and includes the above-described hydrogen production catalyst and a NOx purification catalyst that purifies NOx under lean conditions. Although the respective catalysts may be mixed, it is preferable from the viewpoint of purification performance that a lean NOx catalyst is disposed after the hydrogen production catalyst. In addition, it is preferable in terms of efficiency that the hydrogen production catalyst and the lean NOx catalyst have a two-layer structure.

上記本発明の水素製造触媒によれば、水素製造能力の高い水素製造触媒を提供可能である。また、リーン・リッチ制御を行うディーゼルエンジンの排ガスの浄化装置に、上記の水素製造触媒とリーンＮＯｘ触媒を組み合わせることで、低温におけるリッチでのＮＯｘの還元が効率よく行われる浄化装置が提供できる。また、高ＮＯｘ浄化性能を実現できるリーン・リッチ制御を行うディーゼルエンジン排ガスの浄化方法を提供できる。   According to the hydrogen production catalyst of the present invention, it is possible to provide a hydrogen production catalyst having a high hydrogen production capacity. Further, by combining the above-described hydrogen production catalyst and lean NOx catalyst with the exhaust gas purification device of a diesel engine that performs lean / rich control, it is possible to provide a purification device that efficiently performs rich NOx reduction at low temperatures. Further, it is possible to provide a diesel engine exhaust gas purification method that performs lean / rich control that can achieve high NOx purification performance.

その結果、低燃費かつ排ガス中の有害物質の少ない自動車を提供可能となる。   As a result, it is possible to provide a vehicle with low fuel consumption and less harmful substances in the exhaust gas.

発明者らはディーゼルエンジンの排ガス処理に適したリーンＮＯｘ触媒の開発を行ってきた。リーンＮＯｘ触媒の開発評価では、リーン・リッチ制御を模擬したリーンガスとリッチガスを切替えてＮＯｘ浄化性能を評価する。耐久試験後のＮＯｘ浄化性能は、リーンからリッチに切替わる時に大きく低下する。その原因として、貴金属の劣化が考えられる。   The inventors have developed a lean NOx catalyst suitable for exhaust gas treatment of a diesel engine. In the development evaluation of the lean NOx catalyst, the lean gas and rich gas simulating lean / rich control are switched to evaluate the NOx purification performance. The NOx purification performance after the durability test is greatly reduced when switching from lean to rich. The cause is considered to be deterioration of noble metals.

触媒の活性は温度と共に高まるので、低温での活性は貴金属の劣化の影響を受けやすい。そこで、劣化した貴金属でも十分なＮＯｘ浄化性能が得られるように、ガス中のリッチガスに含まれる還元成分を活用して気相中もしくはリーンＮＯｘ触媒から脱離するＮＯｘを浄化し貴金属への負担を軽減することとした。そのため、リッチガス中のＣＯとＨ2ＯからＨ2 を生成する能力の高い水素製造触媒を用いることとした。その結果、耐久試験後のリーンからリッチに切替わる時のＮＯｘ浄化性能を改善することができた。 Since the activity of the catalyst increases with temperature, the activity at a low temperature is susceptible to the deterioration of the noble metal. Therefore, in order to obtain sufficient NOx purification performance even with deteriorated noble metals, the reducing components contained in the rich gas in the gas are utilized to purify NOx desorbed in the gas phase or from the lean NOx catalyst, thereby burdening the noble metals. I decided to reduce it. Therefore, a hydrogen production catalyst having a high ability to generate H 2 from CO and H 2 O in the rich gas is used. As a result, it was possible to improve the NOx purification performance when switching from lean to rich after the durability test.

酸化セリウム上での水性シフト反応は式（２）から（４）と報告されている。   The aqueous shift reaction on cerium oxide is reported as equations (2) to (4).

ＣＯ＋σ＝ＣＯａｄ （２）
Ｈ2Ｏ＋Ｃｅ2Ｏ3＝２ＣｅＯ2＋Ｈ2 （３）
ＣＯａｄ＋２ＣｅＯ2＝ＣＯ2＋Ｃｅ2Ｏ3＋σ （４）
ａｄ：吸着、σ：金属の吸着サイト
Ｈ2の生成は、（Ａ）ＣＯの金属への吸着（式（２））、（Ｂ）Ｃｅ2Ｏ3へのＨ2Ｏの吸着と、ＣｅＯ2とＨ2の生成（式（３））、（Ｃ）ＣｅＯ2 による金属上のＣＯの酸化（式（４））、の順で進行する。 CO + σ = COad (2)
H 2 O + Ce 2 O 3 = 2CeO 2 + H 2 (3)
COad + 2CeO 2 = CO 2 + Ce 2 O 3 + σ (4)
ad: Adsorption, σ: Adsorption site of metal H 2 is generated by (A) adsorption of CO to metal (formula (2)), (B) adsorption of H 2 O on Ce 2 O 3 , and CeO 2 And H 2 (formula (3)), (C) oxidation of CO on the metal with CeO 2 (formula (4)).

本発明では、（１１１）面のピーク高さとバックグランドの比が高い酸化セリウムを担体にし、Ｐｔ，Ｐｄ，Ｒｈから選ばれた貴金属を１種以上担持することとした。特に、Ｘ線回折パターンにおいて（１１１）面回折ピーク強度とバックグランドの比が４.３ 以上である酸化セリウム、もしくはセリウムを含む酸化物とＴｉ酸化物からなり、酸化セリウムを含む酸化物とＴｉ酸化物に占める酸化セリウムの割合が２８％以上である材料を使用した。回折パターンにおいて回折ピークとバックグランドの比が高いことは、結晶性が高いことを示す。式（３），（４）中の酸化セリウムの状態変化は、酸化セリウム中の酸素をＰｔ上でＣＯと反応させることで継続する。結晶性が高い場合は、この酸化セリウム内の酸素の移動が容易になるため、水素製造能力が高くなっていると思われる。   In the present invention, cerium oxide having a high (111) plane peak height and background ratio is used as a support, and one or more precious metals selected from Pt, Pd, and Rh are supported. In particular, in the X-ray diffraction pattern, the ratio of the (111) plane diffraction peak intensity to the background is 4.3 or more, which is made of cerium oxide, or an oxide containing cerium and Ti oxide, and an oxide containing cerium oxide and Ti. A material in which the ratio of cerium oxide in the oxide was 28% or more was used. A high ratio between the diffraction peak and the background in the diffraction pattern indicates that the crystallinity is high. The state change of cerium oxide in the formulas (3) and (4) is continued by reacting oxygen in cerium oxide with CO on Pt. When the crystallinity is high, the movement of oxygen in the cerium oxide becomes easy, so the hydrogen production capacity seems to be high.

貴金属としては、Ｐｄ，Ｐｔ，Ｒｈを酸化セリウムに担持した場合に、水素製造能力があることを確認した。これらの貴金属は自動車触媒に使用しても安定である。貴金属の量は、要求される性能，コストに応じ決定される。本発明では、同一貴金属で同一量担持した場合に、より水素製造能力が高い酸化セリウムを組み合わせた。もちろんＰｄ，Ｐｔ，Ｒｈを複数あるいはすべてを担持してもかまわない。   As the noble metal, it was confirmed that when Pd, Pt, Rh is supported on cerium oxide, it has hydrogen production capability. These noble metals are stable even when used in automobile catalysts. The amount of precious metal is determined according to the required performance and cost. In the present invention, cerium oxide having a higher hydrogen production capacity when combined with the same amount of the same noble metal is combined. Of course, plural or all of Pd, Pt, and Rh may be supported.

通常、リーンＮＯｘ触媒は、高比表面積のアルミナを担体とし、燃焼活性成分である貴金属，ＮＯｘ吸着材であるアルカリ金属，酸化セリウム等を担持している。高比表面積のアルミナに貴金属を高分散させることで担体の焼結収縮，貴金属の凝集を抑制できる。また、酸化セリウムは、酸素過剰状態ではガス中から酸化セリウム中に酸素を取り込み、酸素不足状態ではガスに酸素を放出することで、ガス組成を平準化し、貴金属上での酸化・還元を助ける。   Usually, a lean NOx catalyst uses alumina having a high specific surface area as a carrier and carries a noble metal as a combustion active component, an alkali metal as a NOx adsorbent, cerium oxide, and the like. Sintering shrinkage of the carrier and aggregation of the noble metal can be suppressed by highly dispersing the noble metal in the alumina having a high specific surface area. In addition, cerium oxide takes oxygen from gas into cerium oxide in an oxygen-excess state and releases oxygen into the gas in an oxygen-deficient state, thereby leveling the gas composition and assisting oxidation / reduction on the noble metal.

請求項２では酸化セリウムを含む酸化物とＴｉ酸化物からなり、酸化セリウムを含む酸化物とＴｉ酸化物に占める酸化セリウムの割合が２８％以上である担体にＰｄｔ，Ｐｄ，Ｒｈから選ばれた貴金属を１種以上担持することとした。同一酸化セリウムでもＴｉを含むと低温での水素製造能力は向上することを発見した。Ｔｉ添加による水素製造能力の向上は、酸化セリウムに他の酸化物を含む場合でも見られ、担体中の酸化セリウムの割合が２８％以上の場合に認められた。後述するようにＴｉＯ2 担体にＰｔを担持した触媒では水素製造能力がほとんど見られないことから、Ｔｉにはシフト反応時の酸素の移動を補助する役割があると推測している。酸化セリウムに他の酸化物を含む場合の代表例として
Ｃｅ−Ｚｒ複合酸化物がある。その他の構成酸化物としてＬａ，Ｐｒ，Ｍｇ，Ｂａなどを含んでも構わない。貴金属の量は要求される性能，コストに応じ決定される。本発明では、同一貴金属で同一量担持した場合に、より水素製造能力が高くなる材料組成を記載したもちろんＰｄ，Ｐｔ，Ｒｈを複数あるいは、すべてを担持してもかまわない。 In claim 2, the carrier is composed of an oxide containing cerium oxide and a Ti oxide, and a carrier having a ratio of cerium oxide in the oxide containing cerium oxide and Ti oxide of 28% or more is selected from Pdt, Pd, and Rh. It was decided to carry one or more precious metals. It has been found that even if the same cerium oxide contains Ti, the hydrogen production capability at low temperatures is improved. An improvement in hydrogen production capacity by addition of Ti was observed even when other oxides were included in cerium oxide, and was observed when the proportion of cerium oxide in the support was 28% or more. As will be described later, a catalyst in which Pt is supported on a TiO 2 carrier has almost no hydrogen production capability. Therefore, it is presumed that Ti has a role of assisting the movement of oxygen during the shift reaction. A typical example of the case where cerium oxide contains another oxide is a Ce-Zr composite oxide. Other constituent oxides may include La, Pr, Mg, Ba and the like. The amount of precious metal is determined according to the required performance and cost. In the present invention, when the same amount is supported by the same noble metal, a material composition that increases the hydrogen production capability is described. Of course, a plurality or all of Pd, Pt, and Rh may be supported.

請求項３では、水素製造触媒とリーンＮＯｘ触媒を組み合わせた触媒について記載した。リーンＮＯｘ触媒のＮＯｘ浄化性能への水素の効果を、図２に示す。あるリーンＮＯｘ触媒に、水素製造触媒をオーバーコートした二層形触媒のＣＯ転化率とＮＯｘ浄化率の関係である。試験は２００℃でリーンガスを３分、リッチガスを３分流通させたときのリッチの平均ＮＯｘ浄化率である。ＣＯ転化率は、リッチガス中のＣＯをＨ2 に転化した割合を示す。図２より、ＣＯ転化率が高くなるとＮＯｘ浄化率が高くなることがわかる。このように触媒上で製造した水素は、リーンＮＯｘ触媒のＮＯｘ浄化に寄与し、その効果は
ＣＯ転化率が高いほど高くなる。 In Claim 3, the catalyst which combined the hydrogen production catalyst and the lean NOx catalyst was described. FIG. 2 shows the effect of hydrogen on the NOx purification performance of the lean NOx catalyst. This is the relationship between the CO conversion rate and the NOx purification rate of a two-layer catalyst in which a hydrogen production catalyst is overcoated on a certain lean NOx catalyst. The test is a rich average NOx purification rate when lean gas is circulated at 200 ° C. for 3 minutes and rich gas for 3 minutes. CO conversion is the ratio obtained by the conversion of CO in the rich gas to H 2. FIG. 2 shows that the NOx purification rate increases as the CO conversion rate increases. The hydrogen thus produced on the catalyst contributes to NOx purification of the lean NOx catalyst, and the effect becomes higher as the CO conversion rate is higher.

窒素酸化物吸着・吸蔵機能一体化水素製造触媒は、ハニカムにリーンＮＯｘ触媒と水素製造触媒を多層に形成、ハニカムにリーンＮＯｘ吸着材と水素製造触媒を混合、吸着材を担持したハニカムと燃焼材を担持したハニカムを組み合わせて使うことができる。特にリーンＮＯｘ触媒と水素製造触媒の位置は、二層型が好ましく、ガス流路側に水素製造触媒を配置することでリッチガス中のＣＯを効率的にＨ2 に転化し、リーンＮＯｘ触媒から脱離するＮＯｘを効率よく浄化させることができる。 Nitrogen oxide adsorption / storage integrated hydrogen production catalyst is composed of a lean NOx catalyst and a hydrogen production catalyst in multiple layers in a honeycomb, a lean NOx adsorbent and a hydrogen production catalyst are mixed in a honeycomb, and a honeycomb and combustion material carrying the adsorbent Can be used in combination. In particular, the position of the lean NOx catalyst and the hydrogen production catalyst is preferably a two-layer type. By arranging the hydrogen production catalyst on the gas flow path side, CO in the rich gas is efficiently converted to H 2 and desorbed from the lean NOx catalyst NOx to be purified can be efficiently purified.

前記、高結晶性の酸化セリウムを担体とする、もしくは酸化セリウムが触媒の２８モル％以上になる範囲のＴｉを添加したＣｅ複合酸化物（ＺｒＯ2 に限らない）への貴金属の担持方法としては、含浸、及び混練方法を用いることができる。 As a method for supporting a noble metal on a Ce composite oxide (not limited to ZrO 2 ) using the above-mentioned highly crystalline cerium oxide as a support or adding Ti in a range where cerium oxide is 28 mol% or more of the catalyst. , Impregnation and kneading methods can be used.

排ガス浄化触媒の形状は、通常の粒状，押出し成型した柱状，プレス成型したペレット型，蜂の巣状のハニカム型等、いずれも使用することができるが、圧損等の観点からハニカム型が好ましい。   As the shape of the exhaust gas purification catalyst, any of normal granular shape, extruded columnar shape, press-molded pellet shape, honeycomb-shaped honeycomb shape and the like can be used, but the honeycomb type is preferable from the viewpoint of pressure loss and the like.

水素製造触媒と共に使用するリーンＮＯｘ触媒は、吸着型，吸蔵型いずれでも構わない。水素製造触媒の水素製造効果はいずれのリーンＮＯｘ触媒でも、低温でのＮＯｘ浄化性能向上に役立つ。   The lean NOx catalyst used together with the hydrogen production catalyst may be either an adsorption type or an occlusion type. The hydrogen production effect of the hydrogen production catalyst is useful for improving the NOx purification performance at low temperatures in any lean NOx catalyst.

二層型の窒素酸化物吸着・吸蔵機能一体化水素製造触媒の作製例を示す。コージェライトハニカムにリーンＮＯｘ触媒層を形成後、水素製造触媒層を形成する。まず、リーン
ＮＯｘ触媒層の作製方法を示す。アルミナ，アルミナゾル、そして精製水を混合したスラリーをコージェライトハニカムに流し込み、乾燥・焼成を行いアルミナ層を形成した。
Ｎａ，Ｋなどのアルカリ成分を水溶液にし、含浸法でアルミナ層に担持した。酸化セリウムなどのＯＳＣ（酸素貯蔵能）を有する酸化物を担持する場合は、硝酸塩など用い水溶液にしてアルミナ層に含浸した。そしてＰｄ，Ｐｔ，Ｒｈの貴金属水溶液をアルミナ層に含浸し、リーンＮＯｘ触媒層を作製した。また、上述の含浸法の他に、混練法でも作製できる。混練法では、リーンＮＯｘ触媒層を形成するアルカリ成分，ＯＳＣを有する酸化物、そして貴金属を混合したスラリーを、コージェライトハニカムに流し込み、リーンＮＯｘ触媒層を形成する。水素製造触媒は、酸化セリウムにＰｄ，Ｐｔ，Ｒｈなどの水溶液を含浸させた後、空気中６００℃で焼成して、水素製造触媒粉末を得た。水素製造触媒粉末にシリカゾルと精製水を加えたスラリーを、リーンＮＯｘ触媒層を形成したハニカムに流し込み水素製造触媒層を形成した。また、水素製造触媒の担体が酸化セリウムを含む酸化物とＴｉ酸化物の場合は、酸化セリウムを含む酸化物にＴｉＯ2 ゾルを含浸し、空気中で
６００℃で焼成した後、貴金属を含浸し、焼成して水素製造触媒粉末を得た。その際、
ＴｉＯ2 ゾルに変えてあらかじめ、ＴｉＯ2 粉末混合する手法でも良い。 An example of the production of a two-layer hydrogen oxide catalyst with integrated nitrogen oxide adsorption and storage function is shown. After forming a lean NOx catalyst layer on the cordierite honeycomb, a hydrogen production catalyst layer is formed. First, a method for producing a lean NOx catalyst layer will be described. A slurry in which alumina, alumina sol, and purified water were mixed was poured into a cordierite honeycomb and dried and fired to form an alumina layer.
An alkaline component such as Na and K was made into an aqueous solution and supported on the alumina layer by an impregnation method. When supporting an oxide having OSC (oxygen storage ability) such as cerium oxide, the alumina layer was impregnated into an aqueous solution using nitrate or the like. Then, an alumina layer was impregnated with an aqueous noble metal solution of Pd, Pt, and Rh to produce a lean NOx catalyst layer. In addition to the above impregnation method, it can also be produced by a kneading method. In the kneading method, a slurry in which an alkali component forming a lean NOx catalyst layer, an oxide containing OSC, and a noble metal are mixed is poured into a cordierite honeycomb to form a lean NOx catalyst layer. The hydrogen production catalyst was impregnated with cerium oxide with an aqueous solution of Pd, Pt, Rh, etc., and then calcined in air at 600 ° C. to obtain a hydrogen production catalyst powder. A slurry obtained by adding silica sol and purified water to a hydrogen production catalyst powder was poured into a honeycomb having a lean NOx catalyst layer to form a hydrogen production catalyst layer. In the case where the carrier of the hydrogen production catalyst is an oxide containing cerium oxide and a Ti oxide, the oxide containing cerium oxide is impregnated with TiO 2 sol, calcined in air at 600 ° C., and then impregnated with a noble metal. And calcined to obtain a hydrogen production catalyst powder. that time,
Instead of the TiO 2 sol, a method of mixing TiO 2 powder in advance may be used.

図１は自動車用ディーゼルエンジン排ガスの後処理システムの一例である。構成としては、エンジンの排ガス流路に三元触媒または酸化触媒を置く、その後段にススなどを除去するためにディーゼルパティキュレートフィルタ（ＤＰＦ）を設置し、そのさらに後段に本発明の窒素酸化物吸着・吸蔵機能一体化水素製造触媒を置く。   FIG. 1 shows an example of an aftertreatment system for automobile diesel engine exhaust gas. As a configuration, a three-way catalyst or an oxidation catalyst is placed in the exhaust gas passage of the engine, a diesel particulate filter (DPF) is installed in the subsequent stage to remove soot, and the nitrogen oxide of the present invention is further installed in the subsequent stage. Put hydrogen adsorption catalyst with integrated adsorption and storage function.

本発明の触媒を用いた排ガス浄化方法は、窒素酸化物吸着・吸蔵機能一体化水素製造触媒に排ガスを通し、エンジンから排出されるＮＯｘを浄化させることである。窒素酸化物吸着・吸蔵機能一体化水素製造触媒を通った排ガスは、該排ガス浄化触媒の上流側に配置される三元触媒または酸化触媒、そしてＤＰＦを既に通った排ガスであることを特徴としている。   The exhaust gas purification method using the catalyst of the present invention is to purify NOx discharged from the engine by passing the exhaust gas through the nitrogen oxide adsorption / occlusion function integrated hydrogen production catalyst. The exhaust gas that has passed through the hydrogen production catalyst integrated with the nitrogen oxide adsorption / storage function is characterized by being a three-way catalyst or an oxidation catalyst disposed upstream of the exhaust gas purification catalyst, and an exhaust gas that has already passed through the DPF. .

（実施例）
以下に本発明の実施例を示す。なお、本発明はこの例に限定されるものではない。 (Example)
Examples of the present invention are shown below. Note that the present invention is not limited to this example.

窒素酸化物吸着・吸蔵機能一体化水素製造触媒では、リーンＮＯｘ触媒，水素製造触媒の両者の機能が合わさって、ＮＯｘを浄化する。リーンＮＯｘ性能が同一性能の場合、水素製造触媒の性能が高いほど、ＮＯｘの浄化性能が高いといえる。本実施例では、水素製造触媒の性能を比較した。   In the hydrogen production catalyst integrated with the nitrogen oxide adsorption / storage function, the functions of both the lean NOx catalyst and the hydrogen production catalyst are combined to purify NOx. When the lean NOx performance is the same, it can be said that the higher the performance of the hydrogen production catalyst, the higher the NOx purification performance. In this example, the performance of the hydrogen production catalyst was compared.

実施例及び比較例の組成は後述の表２に示す。実施例触媒１は次の手順で作製した。酸化セリウムは、ＸＲＤの回折パターンにおいて、（１１１）面のピーク高さとバックグランドの比が９.５ を得られていた粉末（第一稀元素製）を使用した。酸化セリウム粉末に、ジニトロジアンミンＰｔ水溶液を用いてＰｔ担持し、水素製造触媒粉末を得た。水素製造触媒粉末はハニカムに酸化セリウムを１３０ｇ／Ｌ担持した時にＰｔが２.７ｇ／Ｌ になるように調製した。ハニカムに、Ｐｔ担持水素製造触媒粉末をウオッシュコートで酸化セリウムとして１３０ｇ／Ｌ担持した。   The compositions of Examples and Comparative Examples are shown in Table 2 below. Example catalyst 1 was prepared by the following procedure. As the cerium oxide, powder (manufactured by the first rare element) in which the ratio of the peak height of the (111) plane to the background was 9.5 in the XRD diffraction pattern was used. The cerium oxide powder was supported by Pt using a dinitrodiammine Pt aqueous solution to obtain a hydrogen production catalyst powder. The hydrogen production catalyst powder was prepared so that Pt was 2.7 g / L when 130 g / L of cerium oxide was supported on the honeycomb. 130 g / L of Pt-supported hydrogen production catalyst powder as cerium oxide was supported on the honeycomb by wash coating.

実施例触媒２は、酸化セリウム粉末のＸＲＤの回折パターンにおいて、（１１１）面のピーク高さとバックグランドの比が９.５ を得られていた酸化セリウム（第一稀元素製）を使用した。ＣｅＯ2 粉末に、ＴｉＯ2 ゾル水溶液を用いＴｉを担持した。乾燥，焼成後、酸化セリウム粉末に、ジニトロジアンミンＰｔ水溶液を用いＰｔ担持し水素製造触媒粉末を得た。水素製造触媒粉末はハニカムに酸化セリウムを１３０ｇ／Ｌ担持した時に元素換算のＴｉが１８.５ｇ／Ｌ、Ｐｔが２.７ｇ／Ｌになるように調製した。ハニカムに、
Ｐｔ担持水素製造触媒粉末をウオッシュコートで酸化セリウムとして１３０ｇ／Ｌ担持した。 Example catalyst 2 used was cerium oxide (manufactured by 1st rare element) in which the ratio of the peak height of the (111) plane to the background was 9.5 in the XRD diffraction pattern of the cerium oxide powder. Ti was supported on CeO 2 powder using a TiO 2 sol aqueous solution. After drying and calcination, the cerium oxide powder was supported with Pt using a dinitrodiammine Pt aqueous solution to obtain a hydrogen production catalyst powder. The hydrogen production catalyst powder was prepared so that Ti in terms of element was 18.5 g / L and Pt was 2.7 g / L when 130 g / L of cerium oxide was supported on the honeycomb. On the honeycomb,
130 g / L of Pt-supported hydrogen production catalyst powder as cerium oxide was supported by a washcoat.

実施例触媒３は、Ｔｉ量を３２.７ｇ／Ｌ とし実施例触媒２と同様の工程で作製した。実施例触媒４は、Ｔｉ量を４３.３ｇ／Ｌ とし実施例触媒２と同様の工程で作製した。   Example catalyst 3 was produced in the same process as Example catalyst 2 with a Ti content of 32.7 g / L. Example catalyst 4 was produced in the same process as example catalyst 2 with the Ti content of 43.3 g / L.

実施例５は、Ｃｅ−Ｚｒ複合酸化物は市販品（ローディア製）を使用した。Ｃｅ−Ｚｒ複合酸化物粉末に、ＴｉＯ2 ゾル水溶液を用いＴｉを担持した。乾燥，焼成後、Ｃｅ−
Ｚｒ複合酸化物粉末に、ジニトロジアンミンＰｔ水溶液を用い、Ｐｔを担持し水素製造触媒粉末を得た。水素製造触媒粉末はハニカムにＣｅ−Ｚｒ複合酸化物を１３０ｇ／Ｌ担持した時に元素換算のＴｉが５.６ｇ／Ｌ、Ｐｔが２.７ｇ／Ｌになるように調製した。ハニカムに、水素製造触媒粉末をウオッシュコートでＣｅ−Ｚｒ複合酸化物として１３０ｇ／Ｌ担持した。 In Example 5, a commercially available product (manufactured by Rhodia) was used as the Ce—Zr composite oxide. Ti was supported on the Ce—Zr composite oxide powder using an aqueous TiO 2 sol solution. After drying and firing, Ce-
A dinitrodiammine Pt aqueous solution was used as the Zr composite oxide powder, and Pt was supported to obtain a hydrogen production catalyst powder. The hydrogen production catalyst powder was prepared so that Ti in terms of element was 5.6 g / L and Pt was 2.7 g / L when 130 g / L of Ce-Zr composite oxide was supported on the honeycomb. 130 g / L of a hydrogen production catalyst powder as a Ce—Zr composite oxide was supported on the honeycomb by wash coating.

実施例触媒６は、Ｔｉ量を２８.０ｇ／Ｌとし実施例触媒５と同様の工程で作製した。実施例触媒７は、Ｔｉ量を１００ｇ／Ｌとし実施例５と同様の工程で作製した。   Example catalyst 6 was produced in the same process as example catalyst 5 with the Ti amount of 28.0 g / L. Example catalyst 7 was produced in the same process as in Example 5 with the Ti amount being 100 g / L.

比較例触媒１は、ＸＲＤの回折パターンにおいて、（１１１）面のピーク高さとバックグランドの比が４.２ の市販の酸化セリウム粉末を使用し、実施例触媒１と同様に作成した。比較例３，４はそれぞれＴｉＯ2 ，ＺｒＯ2 を担体とした場合である。そして、比較例５はリーンＮＯｘ触媒である。 Comparative Example Catalyst 1 was prepared in the same manner as Example Catalyst 1 using a commercially available cerium oxide powder having an XRD diffraction pattern with a (111) plane peak height to background ratio of 4.2. Comparative Examples 3 and 4 are cases where TiO 2 and ZrO 2 were used as carriers, respectively. Comparative Example 5 is a lean NOx catalyst.

各水素製造触媒の水素製造能力（水性ガスシフト反応の反応性）を耐久処理(劣化処理)後に以下の試験で検証・評価した。水素製造触媒評価試験のガス組成を表１に、評価パターンを図３に、評価装置を図４に示す。   The hydrogen production capacity (reactivity of water gas shift reaction) of each hydrogen production catalyst was verified and evaluated in the following tests after endurance treatment (deterioration treatment). The gas composition of the hydrogen production catalyst evaluation test is shown in Table 1, the evaluation pattern is shown in FIG. 3, and the evaluation apparatus is shown in FIG.

Figure 2007084391
Figure 2007084391

評価では、固定床流通式反応管を用いた。触媒（１７mm×１７mm×長さ２１mm）は６mlとした。評価は以下の手順で実施した。
（１）ストイキ昇温（前処理）
表１（ａ）のストイキガスを流通させ、触媒入口温度で室温から５５０℃まで２０℃／min にて昇温した。１００℃からはポンプで送液した水を反応管内に滴下し水蒸気として加えた。ＳＶは３００００ｈ-1とした。
（２）シフト反応評価
５５０℃に到達後、表１（ｂ）の水素製造触媒評価ガスに切替え、降温しながら３００℃，２５０℃，２００℃，１５０℃でそれぞれ５分間保持した。ＳＶは５００００ｈ-1とした。触媒出口でガス中の水蒸気を水トラップで除去した後、ＣＯ，ＣＯ2 分析計（堀場製作所，ＶＩＡ−５１０）へ導いた。 In the evaluation, a fixed bed flow type reaction tube was used. The catalyst (17 mm × 17 mm × length 21 mm) was 6 ml. The evaluation was performed according to the following procedure.
(1) Stoichi temperature rise (pretreatment)
The stoichiometric gas shown in Table 1 (a) was circulated, and the temperature was increased from room temperature to 550 ° C. at a catalyst inlet temperature of 20 ° C./min. From 100 ° C., water fed by a pump was dropped into the reaction tube and added as water vapor. The SV was 30000 h −1 .
(2) Shift reaction evaluation After reaching 550 ° C., the hydrogen production catalyst evaluation gas shown in Table 1 (b) was switched to and maintained at 300 ° C., 250 ° C., 200 ° C., and 150 ° C. for 5 minutes while cooling down. The SV was set to 50000h- 1 . After removing water vapor in the gas with a water trap at the catalyst outlet, it was led to a CO, CO 2 analyzer (Horiba, VIA-510).

実施例触媒及び比較例触媒のＣＯ転化率を表２に示す。すべて、７００℃×２０ｈの熱処理を実施した。ディーゼル排ガス温度の代表値として２００℃で試験した結果である。   Table 2 shows the CO conversion rates of the example catalyst and the comparative example catalyst. All were heat-treated at 700 ° C. for 20 hours. It is the result of having tested at 200 degreeC as a typical value of diesel exhaust gas temperature.

Figure 2007084391
Figure 2007084391

ここで、ＣＯ転化率は、ガス中のＣＯがＨ2 に転化された割合である。ガスには２％のＣＯを含むため、例えば、ＣＯ転化率１％は、２％ＣＯの１％を転化し、０.０２％ の水素を得たことを示す。ＴｉＯ2，ＺｒＯ2担体を用いると、少なくとも２００℃の低温では水性ガスシフト反応はほとんど見られなかった。リーンＮＯｘ触媒のＣＯ転化率は０.７％であった。 Here, the CO conversion rate is a ratio of CO in the gas converted to H 2 . Since the gas contains 2% CO, for example, a CO conversion of 1% indicates that 1% of 2% CO has been converted to give 0.02% hydrogen. When a TiO 2 or ZrO 2 support was used, almost no water gas shift reaction was observed at a low temperature of at least 200 ° C. The CO conversion of the lean NOx catalyst was 0.7%.

実施例１と比較例１のＣＯ転化率は、それぞれ、６.２，１.０％であった。比較例１はリーンＮＯｘ触媒（比較例５）の０.７％ と近い値にとどまった。これらより、ＸＲＤの回折パターンにおいて、（１１１）面のピーク高さとバックグランドの比が高い酸化セリウムを担体とした場合に、ＣＯ転化率が高くなる。   The CO conversion rates of Example 1 and Comparative Example 1 were 6.2 and 1.0%, respectively. Comparative Example 1 remained close to 0.7% of the lean NOx catalyst (Comparative Example 5). From these, in the XRD diffraction pattern, when cerium oxide having a high ratio of the (111) plane peak height to the background is used as the carrier, the CO conversion rate becomes high.

実施例２から７の転化率について説明する。酸化セリウムまたは、Ｃｅ−Ｚｒ複合酸化物にＴｉを添加するとＣＯ転化率が高くなった。ＣＯ転化率は、実施例１では６.２％ であるのに対し、酸化セリウム担体にＴｉを添加した場合の実施例２から４では６.７〜7.6％と、０.５〜１.４％高くなった。また比較例２の１.１％ に対し、Ｃｅ−Ｚｒ複合酸化物にＴｉを添加した場合は、実施例５から７の１.２〜２.４％となり、０.１〜１.３％高くなった。つまり、触媒中の酸化セリウムの割合が２８％以上の場合、Ｔｉを添加することによってＣＯ転化率が高くなる効果が認められた。   The conversion rate of Examples 2 to 7 will be described. When Ti was added to cerium oxide or Ce—Zr composite oxide, the CO conversion increased. The CO conversion rate is 6.2% in Example 1, whereas 6.7 to 7.6% in Examples 2 to 4 when Ti is added to the cerium oxide support, 0.5 to 1.4. % Higher. Moreover, when adding Ti to Ce-Zr composite oxide with respect to 1.1% of Comparative Example 2, it becomes 1.2 to 2.4% of Examples 5 to 7, and 0.1 to 1.3%. It became high. That is, when the ratio of cerium oxide in the catalyst was 28% or more, the effect of increasing the CO conversion rate by adding Ti was recognized.

ディーゼルエンジンを含むリーンバーン車の排ガス浄化用装置に利用できる。   It can be used for exhaust gas purification equipment for lean-burn vehicles including diesel engines.

ディーゼル排ガス処理のシステム図。The system diagram of diesel exhaust gas treatment. 水素製造能力とＮＯｘ浄化性能の関係。Relationship between hydrogen production capacity and NOx purification performance. 水素製造触媒の評価パターン。Evaluation pattern of hydrogen production catalyst. 水素製造触媒の評価装置。Evaluation equipment for hydrogen production catalysts.

Claims (5)

内燃機関排ガス中の一酸化炭素と水とから水素を生成する水素製造触媒であって、
前記触媒は、Ｘ線回折パターンにおいて（１１１）面回折ピーク強度とバックグランドの比が４.３ 以上である酸化セリウムを担体とし、Ｐｔ，Ｐｄ，Ｒｈから選ばれる貴金属の少なくともいずれかを含むことを特徴とする水素製造触媒。 A hydrogen production catalyst for producing hydrogen from carbon monoxide and water in an exhaust gas of an internal combustion engine,
The catalyst contains cerium oxide having a ratio of (111) plane diffraction peak intensity to background of 4.3 or more in an X-ray diffraction pattern as a support, and contains at least one of noble metals selected from Pt, Pd, and Rh. A hydrogen production catalyst. 請求項１に記載された水素製造触媒であって、
前記セリウム酸化物を複合酸化物として含有することを特徴とする水素製造触媒。 The hydrogen production catalyst according to claim 1,
A hydrogen production catalyst comprising the cerium oxide as a composite oxide. 請求項１または２に記載された水素製造触媒であって、
前記担体にはＴｉ酸化物が含まれることを特徴とする水素製造触媒。 The hydrogen production catalyst according to claim 1 or 2,
A hydrogen production catalyst, wherein the support contains Ti oxide. 内燃機関排ガス中の一酸化炭素と水とから水素を生成する水素製造触媒であって、
前記触媒は、酸化セリウムを含む酸化物とＴｉ酸化物とを含む担体と、前記担体上に担持されたＰｔ，Ｐｄ，Ｒｈの少なくともいずれかの貴金属を有し、
前記酸化セリウムを含む酸化物とＴｉ酸化物の合計量に占める酸化セリウムの割合が
２８％以上であることを特徴とする水素製造触媒。 A hydrogen production catalyst for producing hydrogen from carbon monoxide and water in an exhaust gas of an internal combustion engine,
The catalyst has a support containing an oxide containing cerium oxide and a Ti oxide, and a noble metal of at least one of Pt, Pd, and Rh supported on the support,
A hydrogen production catalyst, wherein a ratio of cerium oxide in a total amount of the oxide containing cerium oxide and Ti oxide is 28% or more. 請求項１ないし４のいずれかに記載された水素製造触媒であって、
前記水素製造触媒の排気ガス流路の後流側に窒素酸化物を吸着又は吸蔵する機能を有する窒素酸化物吸着・吸蔵機能触媒が二層構造で付されていることを特徴とする水素製造触媒。

A hydrogen production catalyst according to any one of claims 1 to 4,
A hydrogen production catalyst characterized in that a nitrogen oxide adsorption / occlusion function catalyst having a function of adsorbing or occluding nitrogen oxides is attached to the downstream side of the exhaust gas flow path of the hydrogen production catalyst in a two-layer structure. .

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2010240533A (en) * 2009-04-02 2010-10-28 Honda Motor Co Ltd Method of cleaning nitrogen oxide
CN108883398A (en) * 2016-04-13 2018-11-23 丰田自动车株式会社 Exhaust emission control catalyst, exhaust gas-cleaning method and emission control system

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2010240533A (en) * 2009-04-02 2010-10-28 Honda Motor Co Ltd Method of cleaning nitrogen oxide
CN108883398A (en) * 2016-04-13 2018-11-23 丰田自动车株式会社 Exhaust emission control catalyst, exhaust gas-cleaning method and emission control system
CN108883398B (en) * 2016-04-13 2021-10-12 丰田自动车株式会社 Exhaust gas purification catalyst, exhaust gas purification method, and exhaust gas purification system

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