JP2010115600A - Oxidation catalyst and apparatus for treating exhaust gas by using the same - Google Patents
Oxidation catalyst and apparatus for treating exhaust gas by using the same Download PDFInfo
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- 239000003054 catalyst Substances 0.000 title claims abstract description 124
- 230000003647 oxidation Effects 0.000 title claims abstract description 116
- 238000007254 oxidation reaction Methods 0.000 title claims abstract description 116
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Substances [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims abstract description 95
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 claims abstract description 61
- 238000011144 upstream manufacturing Methods 0.000 claims abstract description 8
- 229910052763 palladium Inorganic materials 0.000 claims abstract description 6
- 229910052697 platinum Inorganic materials 0.000 claims abstract description 6
- 238000010531 catalytic reduction reaction Methods 0.000 claims abstract 2
- 239000010410 layer Substances 0.000 claims description 12
- 239000002344 surface layer Substances 0.000 claims description 10
- 230000001590 oxidative effect Effects 0.000 abstract description 12
- 230000006866 deterioration Effects 0.000 abstract description 7
- 238000006722 reduction reaction Methods 0.000 abstract 1
- 238000000746 purification Methods 0.000 description 30
- 238000011156 evaluation Methods 0.000 description 18
- 238000006243 chemical reaction Methods 0.000 description 13
- 238000005245 sintering Methods 0.000 description 10
- 230000007423 decrease Effects 0.000 description 9
- 239000013618 particulate matter Substances 0.000 description 8
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 description 3
- 239000004202 carbamide Substances 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 230000008929 regeneration Effects 0.000 description 3
- 238000011069 regeneration method Methods 0.000 description 3
- 230000015556 catabolic process Effects 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- 238000006731 degradation reaction Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 239000000446 fuel Substances 0.000 description 2
- 230000003197 catalytic effect Effects 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000012803 optimization experiment Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/10—Internal combustion engine [ICE] based vehicles
- Y02T10/12—Improving ICE efficiencies
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Abstract
Description
本発明は、酸化触媒及びそれを用いたエンジンの排気処理装置に関するものである。 The present invention relates to an oxidation catalyst and an engine exhaust treatment apparatus using the oxidation catalyst.
エンジンの排気ガスを処理する装置として、ＤＰＦとＳＣＲを組み合わせた排ガス処理装置が用いられることがある。これは、図６に示したように前段酸化触媒１０２及びフィルタ１０４からなるＤＰＦシステム１１０と、ＳＣＲ触媒１０６及び後段酸化触媒１０８からなるＳＣＲシステム１１２とから構成される。
An exhaust gas treatment device combining DPF and SCR may be used as a device for treating engine exhaust gas. As shown in FIG. 6, this is composed of a
このようなＤＰＦとＳＣＲを組み合わせた排ガス処理装置においては、エンジン（不図示）で発生した排ガスは、まず前段酸化触媒１０２及びフィルタ１０４からなるＤＰＦシステム１１０に送り込まれ、フィルタ１０４でＰＭ（Ｐａｒｔｉｃｕｌａｔｅ Ｍａｔｔｅｒ）を捕集されて排出される。
また、前記フィルタ１０４の再生時には、前段酸化触媒１０２が活性化されて燃料供給ライン１１４より供給された燃料が前段酸化触媒１０２で酸化される際に発生する酸化熱によって排気が６００℃以上に昇温され、該昇温された排気によってフィルタ１０４に捕集されたＰＭを燃焼させる。このとき、ＰＭの燃焼によって発生するＣＯは、フィルタ１０４に触媒がコートされていない場合には、後述する後段酸化触媒１０８で無害なＣＯ２に転化される。
In such an exhaust gas treatment apparatus that combines DPF and SCR, exhaust gas generated by an engine (not shown) is first sent to a
Further, when the filter 104 is regenerated, the exhaust gas rises to 600 ° C. or higher due to the oxidation heat generated when the front-stage oxidation catalyst 102 is activated and the fuel supplied from the
前記フィルタ１０４でＰＭを捕集された後の排ガスは、ＳＣＲ触媒１０６に送り込まれる。また、ＳＣＲ触媒１０６の上流側で尿素添加ライン１１６より尿素を添加し、該尿素が分解することによってＮＨ３が生成される。
The exhaust gas after PM is collected by the filter 104 is sent to the SCR catalyst 106. Further, urea is added from the
前記ＮＨ３は一旦ＳＣＲ触媒上に吸着した後、排ガス中のＮＯｘと以下の（１）〜（３）の反応式によって反応し、有害なＮＯｘを無害なＮ２へと転換させる。
ＮＯ＋ＮＯ２＋２ＮＨ３→２Ｎ２＋３Ｈ２Ｏ ・・・（１）
４ＮＯ＋４ＮＨ３＋Ｏ２→４Ｎ２＋６Ｈ２Ｏ ・・・（２）
６ＮＯ２＋８ＮＨ３→７Ｎ２＋１２Ｈ２Ｏ ・・・（３）
The NH 3 is once adsorbed on the SCR catalyst, and then reacts with NO x in the exhaust gas according to the following reaction formulas (1) to (3) to convert harmful NO x into harmless N 2 .
NO + NO 2 + 2NH 3 → 2N 2 + 3H 2 O (1)
4NO + 4NH 3 + O 2 → 4N 2 + 6H 2 O (2)
6NO 2 + 8NH 3 → 7N 2 + 12H 2 O (3)
さらに、ＳＣＲ触媒１０６で反応できなかったＮＨ３は、同様にＳＣＲ触媒１０６で反応できなかったＮＯｘと後段酸化触媒１０８でＳＣＲ触媒１０６と同様に（１）〜（３）の反応式によって反応し、ＮＯｘを無害なＮ２へと転換させる。また、ＳＣＲ触媒１０６上に吸着したＮＨ３は、温度上昇によりＳＣＲ触媒１０６より脱離し、後段酸化触媒で（４）の反応式によりＮ２へと転化される。
１２ＮＨ３＋９Ｏ２→６Ｎ２＋１８Ｈ２Ｏ ・・・（４）
ところで、ＮＨ３は刺激臭のある物質であり、数ｐｐｍという低濃度でも悪臭として感知されることが知られている。そのため、ＮＨ３の環境への排出を防止するために、ＮＨ３を酸化し、ＮＯｘ又はＮ２へと転化させる後段酸化触媒１０８は不可欠なものである。
Further, NH 3 that could not be reacted with the SCR catalyst 106 is reacted with NO x that could not be reacted with the SCR catalyst 106 in the same way as the SCR catalyst 106 with the reaction formulas (1) to (3). And convert NO x to harmless N 2 . Further, NH 3 adsorbed on the SCR catalyst 106 is desorbed from the SCR catalyst 106 due to the temperature rise, and is converted into N 2 by the reaction equation (4) at the subsequent oxidation catalyst.
12NH 3 + 9O 2 → 6N 2 + 18H 2 O (4)
By the way, NH 3 is a substance having an irritating odor and is known to be perceived as a bad odor even at a low concentration of several ppm. Therefore, in order to prevent the discharge of NH 3 into the environment, the post-stage oxidation catalyst 108 that oxidizes NH 3 and converts it into NO x or N 2 is indispensable.
前述のように、ＮＨ３の酸化機能を確保するためには、前記後段酸化触媒１０８にＰｔを担持させることが有用であり、Ｐｔを担持させた触媒は例えば特許文献１に開示されている。
As described above, in order to ensure the oxidation function of NH 3 , it is useful to support Pt on the post-stage oxidation catalyst 108, and a catalyst supporting Pt is disclosed in
しかしながら、後段酸化触媒１０８は、通常運転時及び前記フィルタ１０４の強制再生時の高温に晒されるため性能が低下しやすいという問題がある。該性能の低下を抑制するためには多量のＰｔを担持する必要があるが、その場合Ｐｔは高価であるためコスト高に繋がる。さらにフィルタ１０４が触媒でコートされていない場合は、前述の通り、後段酸化触媒でＣＯも酸化されるため、その反応熱による後段酸化触媒１０８の「触媒劣化」が大きいという問題もある。
前記「触媒劣化」の主な要因は高温環境でのシンタリングによる有効表面積の減少である。この問題を解消するためには高濃度のＰｔ担持が必要であった。
However, since the post-stage oxidation catalyst 108 is exposed to a high temperature during normal operation and during forced regeneration of the filter 104, there is a problem in that the performance is likely to deteriorate. In order to suppress the deterioration of the performance, it is necessary to carry a large amount of Pt. In this case, since Pt is expensive, the cost is increased. Further, when the filter 104 is not coated with a catalyst, as described above, since CO is also oxidized by the post-stage oxidation catalyst, there is a problem that “catalyst deterioration” of the post-stage oxidation catalyst 108 due to the reaction heat is large.
The main factor of the “catalyst deterioration” is a reduction in effective surface area due to sintering in a high temperature environment. In order to solve this problem, it was necessary to carry a high concentration of Pt.
従って、本発明はかかる従来技術の問題に鑑み、劣化によるＮＨ３酸化性能低下を抑制することでＰｔ担持量を低限し、さらにはＮＯｘ浄化性能を向上させることができる酸化触媒及びそれを用いた排気処理装置を提供することを目的とする。 Therefore, in view of the problems of the prior art, the present invention uses an oxidation catalyst capable of limiting the amount of Pt supported by suppressing a decrease in NH 3 oxidation performance due to deterioration, and further improving NOx purification performance, and the same. An object of the present invention is to provide an exhaust treatment device.
上記課題を解決するため本発明においては、エンジンの排気通路に連なり、選択還元型触媒（ＳＣＲ：Ｓｅｌｅｃｔｉｖｅ Ｃａｔａｌｙｔｉｃ Ｒｕｄｕｃｔｉｏｎ）の下流側に位置する酸化触媒において、前記酸化触媒は、担体に白金（Ｐｔ）を担持して構成するとともに、前記酸化触媒にパラジウム（Ｐｄ）を添加したことを特徴とする。 In order to solve the above-mentioned problems, in the present invention, an oxidation catalyst that is connected to an exhaust passage of an engine and is located downstream of a selective catalytic catalyst (SCR), the oxidation catalyst is platinum (Pt) as a carrier. And palladium (Pd) is added to the oxidation catalyst.
Ｐｄは酸化力ではＰｔと比べると劣るが、Ｐｔのシンタリングを抑制する性質を有する。そのため、Ｐｔが担持された酸化触媒（後段酸化触媒）にＰｄを添加することにより、Ｐｔ担持量を低減してもシンタリングによる酸化効率の低下は発生しにくくなり、Ｐｔ担持量を従来よりも低減しても従来以上のＮＨ３、ＮＯｘの浄化作用を有することができる。 Pd is inferior to Pt in oxidizing power, but has the property of suppressing sintering of Pt. Therefore, by adding Pd to the oxidation catalyst (post-stage oxidation catalyst) on which Pt is supported, the reduction in oxidation efficiency due to sintering is less likely to occur even if the amount of Pt supported is reduced. be reduced may have the purifying effect of conventional or more NH 3, NOx.
また、前記エンジンの排気通路に連なり、前記ＳＣＲの上流側、又は前記ＳＣＲの下流側であり前記酸化触媒の上流側にＤＰＦ（Ｄｉｅｓｅｌ Ｐａｒｔｉｃｕｌａｔｅ Ｆｉｌｔｅｒ）を設けたことを特徴とする。
ＤＰＦを設けることでＰＭ（Ｐａｒｔｉｃｕｌａｔｅ Ｍａｔｔｅｒ）の捕集を行う。ＤＰＦに捕集されたＰＭを強制再生によって酸化除去する場合、通常運転時よりも排ガス温度を高温とするが、ＤＰＦの強制再生における排ガスの高温時においても、Ｐｔが担持された酸化触媒にＰｄを添加することにより高温による「触媒劣化」を防止し、Ｐｔ担持量を従来よりも低減しても従来以上のＮＨ３、ＮＯｘの浄化作用を有することができる。
Further, a DPF (Diesel Particulate Filter) is provided on the upstream side of the SCR or on the downstream side of the SCR and on the upstream side of the oxidation catalyst.
PM (Particulate Matter) is collected by providing a DPF. When the PM collected in the DPF is oxidized and removed by forced regeneration, the exhaust gas temperature is set higher than that during normal operation. However, even when the exhaust gas is hot during the forced regeneration of the DPF, Pd is supported on the oxidation catalyst carrying Pt. Is added to prevent “catalyst degradation” due to high temperature, and even if the amount of Pt supported is reduced as compared with the conventional amount, it can have a purifying action of NH 3 and NOx more than conventional.
また、前記酸化触媒におけるＰｔとＰｄの重量比が、Ｐｄ／Ｐｔ＝１／２０〜１／１０であることを特徴とする。
前述の通り、Ｐｄは酸化力ではＰｔと比べると劣るため、Ｐｄの添加量が多すぎると酸化触媒全体として酸化力の面で劣る。そのため、酸化触媒として充分な機能を有するためにはＰｄ／Ｐｔを１／１０以下とすることが適切である。
また、Ｐｄの添加量が少なすぎると、Ｐｔのシンタリングを充分に抑制することができない。そのため、Ｐｔのシンタリングを抑制するためにはＰｄ／Ｐｔを１／２０以上とすることが適切である。
従ってＰｔとＰｄの重量比をＰｄ／Ｐｔ＝１／２０〜１／１０とすることで、酸化触媒として充分な機能を有し、さらにＰｔのシンタリングを抑制することができる。
The weight ratio of Pt to Pd in the oxidation catalyst is Pd / Pt = 1/20 to 1/10.
As described above, Pd is inferior in oxidation power to Pt, so if the amount of Pd added is too large, the oxidation catalyst as a whole is inferior in oxidation power. Therefore, in order to have a sufficient function as an oxidation catalyst, it is appropriate that Pd / Pt is 1/10 or less.
If the amount of Pd added is too small, sintering of Pt cannot be sufficiently suppressed. Therefore, in order to suppress Pt sintering, it is appropriate to set Pd / Pt to 1/20 or more.
Therefore, by setting the weight ratio of Pt and Pd to Pd / Pt = 1/20 to 1/10, it has a sufficient function as an oxidation catalyst and can suppress Pt sintering.
また、前記酸化触媒におけるＰｔ担持量が、０．６ｇ／ｌから０．９ｇ／ｌであることを特徴とする。
Ｐｔ担持量が０．９ｇ／ｌを超えると、酸化触媒の酸化力が強すぎ、特に高温環境においては、ＮＯｘと反応して浄化するためのＮＨ３が酸化されてＮ２やＮＯｘとなってしまうため、結果としてＮＯｘ浄化率が低下する。
Ｐｔ担持量が０．６ｇ／ｌより少ないと、酸化触媒の酸化力が弱く、前記（４）式の反応によって酸化触媒中の全量のＮＨ３を酸化することが困難となり、ＮＨ３が外部に排出されてしまう。
従って、Ｐｔ担持量が、０．６ｇ／ｌから０．９ｇ／ｌとすることで、ＮＨ３を外部に排出することなく、高いＮＯｘ浄化率を保持することができる。
この技術によって従来のＰｔ触媒よりもＰｔ担持量を削減し、低コスト化が可能である。
Further, the amount of Pt supported in the oxidation catalyst is from 0.6 g / l to 0.9 g / l.
If the amount of Pt supported exceeds 0.9 g / l, the oxidizing power of the oxidation catalyst is too strong, and particularly in a high temperature environment, NH 3 that reacts with NO x to purify is oxidized, and N 2 or NO x since thus made, the results as the NO x purification rate decreases.
When the supported amount of Pt is less than 0.6 g / l, oxidizing power of the oxidizing catalyst is weak, the (4) reacting by it becomes difficult to oxidize NH 3 in the total amount in the oxidation catalyst, it is NH 3 to the outside It will be discharged.
Therefore, when the amount of Pt supported is 0.6 g / l to 0.9 g / l, a high NOx purification rate can be maintained without discharging NH 3 to the outside.
With this technology, the amount of Pt supported can be reduced as compared with conventional Pt catalysts, and the cost can be reduced.
また、前記酸化触媒は、表面層がＳＣＲであり、内面層がＰｔが担持されＰｄが添加された酸化触媒である二重層によって構成されることを特徴とする。
本発明は、Ｐｔで担持された層のみの一層で構成された酸化触媒のみならず、前記二重層によって構成される酸化触媒にも適用することができ、汎用性が高いものである。
Further, the oxidation catalyst is characterized in that the surface layer is SCR and the inner surface layer is constituted by a double layer which is an oxidation catalyst in which Pt is supported and Pd is added.
The present invention can be applied not only to an oxidation catalyst composed of only one layer supported by Pt but also to an oxidation catalyst composed of the double layer, and is highly versatile.
以上記載のごとく本発明によれば、劣化による酸化性能低下を抑制することによりＰｔ担持量を削減し、さらにはＮＯｘ浄化性能を向上させることができる酸化触媒及びそれを用いた排気処理装置を提供することができる。 As described above, according to the present invention, there is provided an oxidation catalyst capable of reducing the amount of Pt supported by suppressing deterioration in oxidation performance due to deterioration and further improving NOx purification performance, and an exhaust treatment apparatus using the same. can do.
以下、図面を参照して本発明の好適な実施例を例示的に詳しく説明する。但しこの実施例に記載されている構成部品の寸法、材質、形状、その相対的配置等は特に特定的な記載がない限りは、この発明の範囲をそれに限定する趣旨ではなく、単なる説明例に過ぎない。 Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Not too much.
本発明の実施形態における排気処理装置全体構成は従来と同じであるため、従来図である図６を代用し排気処理装置全体構成の説明は省略する。
本実施例においては、後段酸化触媒１０８を、内面層としてＰｔが担持されＰｄが添加された層であるＤＯＣ層と、表面層であるＳＣＲ層とによって構成される二重層からなる酸化触媒とした。
Since the overall configuration of the exhaust treatment apparatus in the embodiment of the present invention is the same as the conventional one, the explanation of the overall configuration of the exhaust treatment apparatus is omitted by using FIG.
In this embodiment, the post-stage oxidation catalyst 108 is an oxidation catalyst composed of a double layer composed of a DOC layer that is a layer to which Pt is supported and Pd is added as an inner surface layer, and an SCR layer that is a surface layer. .
前記Ｐｔ担持量を変化させ、前記Ｐｄの添加量をＰｄ／Ｐｔ＝１／１０とした複数の後段酸化触媒１０８用の酸化触媒サンプルを用意し、それぞれのサンプルについて２００℃におけるＮＨ３の酸化性能について評価を行った。結果を図１に示す。 A plurality of oxidation catalyst samples for the second-stage oxidation catalyst 108 in which the amount of Pt supported was changed and the amount of Pd added was Pd / Pt = 1/10, and the oxidation performance of NH 3 at 200 ° C. for each sample was prepared. Was evaluated. The results are shown in FIG.
図１において、縦軸はＮＨ３の酸化性能、横軸は前記内面層におけるＰｔの担持量（ｇ／Ｌ）である。また、図１には参考として従来のＰｄを添加しない酸化触媒におけるＮＨ３の酸化性能の評価の結果も示した。図中▲が本発明の酸化触媒における評価、●が従来の酸化触媒の評価の結果である。 In FIG. 1, the vertical axis represents the oxidation performance of NH 3 , and the horizontal axis represents the amount of Pt supported (g / L) on the inner surface layer. FIG. 1 also shows the results of evaluation of the oxidation performance of NH 3 in a conventional oxidation catalyst to which Pd is not added for reference. In the figure, ▲ is the evaluation result of the oxidation catalyst of the present invention, and ● is the result of evaluation of the conventional oxidation catalyst.
図１から明らかであるように、Ｐｔを担持しただけである従来の酸化触媒においては、Ｐｔ添加量の低下に伴いＮＨ３酸化性能が大きく低下したが、本発明のＰｔを担持しＰｄを添加した酸化触媒においては、Ｐｔ添加量が低下してもＮＨ３酸化性能の大きな低下は見られなかった。
従って、要求されるＮＨ３の酸化性能Ｃを満たすためには、従来はＢｇ／ＬのＰｔを担持する必要があったが、本発明においてはＡｇ／ＬのＰｔを担持すればよくＰｔ担持量をａｇ／Ｌだけ削減することができる。Ａは０．６ｇ／ｌ、Ｂは０．９ｇ／ｌである。
As is clear from FIG. 1, in the conventional oxidation catalyst that only supported Pt, the NH 3 oxidation performance greatly decreased with the decrease in the amount of Pt added, but the present invention supported Pt and added Pd. In the oxidized catalyst, even when the Pt addition amount was reduced, no significant reduction in NH 3 oxidation performance was observed.
Therefore, in order to satisfy the required NH 3 oxidation performance C, conventionally, it was necessary to support Bg / L of Pt, but in the present invention, it is sufficient to support Ag / L of Pt. Can be reduced by ag / L. A is 0.6 g / l and B is 0.9 g / l.
さらに、前記Ｐｔ担持量を変化させ、前記Ｐｄの添加量をＰｄ／Ｐｔ＝１／１０とした複数の後段酸化触媒１０８用の酸化触媒サンプルを用意し、それぞれのサンプルについて１８０℃におけるＮＯｘの浄化性能について評価を行った。結果を図２に示す。 Further, an oxidation catalyst sample for a plurality of subsequent oxidation catalysts 108 in which the amount of Pt supported was changed and the amount of Pd added was Pd / Pt = 1/10 was prepared, and NO x at 180 ° C. was measured for each sample. The purification performance was evaluated. The results are shown in FIG.
図２において、縦軸はＮＯｘの酸化性能、横軸は前記内面層におけるＰｔの担持量（ｇ／Ｌ）である。また、図２には参考として従来のＰｄを添加しない酸化触媒におけるＮＨ３の酸化性能の評価の結果も示した。図中▲が本発明の酸化触媒における評価、●が従来の酸化触媒の評価の結果である。 In FIG. 2, the vertical axis represents NOx oxidation performance, and the horizontal axis represents the amount of Pt supported (g / L) on the inner surface layer. FIG. 2 also shows the results of evaluation of the oxidation performance of NH 3 in a conventional oxidation catalyst not added with Pd for reference. In the figure, ▲ is the evaluation result of the oxidation catalyst of the present invention, and ● is the result of evaluation of the conventional oxidation catalyst.
図２から明らかであるように、Ｐｔを担持しただけである従来の酸化触媒においては、Ｐｔ添加量の低下に伴いＮＯｘ浄化性能が大きく低下したが、本発明のＰｔを担持しＰｄを添加した酸化触媒においては、Ｐｔ添加量が低下してもＮＯｘ浄化性能の大きな低下は見られなかった。
従って、要求されるＮＯｘの浄化性能Ｆを満たすためには、従来はＥｇ／ＬのＰｔを担持する必要があったが、本発明においてはＤｇ／ＬのＰｔを担持すればよくＰｔ担持量をｄｇ／Ｌだけ削減することができる。Ｄは０．６ｇ／ｌ、Ｅは０．９ｇ／ｌである。
As is clear from FIG. 2, in the conventional oxidation catalyst that only supported Pt, the NOx purification performance was greatly reduced as the amount of Pt added decreased. However, the present invention supported Pt and added Pd. In the oxidation catalyst, the NOx purification performance was not significantly reduced even when the Pt addition amount was reduced.
Therefore, in order to satisfy the required NOx purification performance F, conventionally, it has been necessary to carry Pt of Eg / L. However, in the present invention, it is sufficient to carry Pt of Dg / L. It can be reduced by dg / L. D is 0.6 g / l and E is 0.9 g / l.
図２にグラフで示した評価結果について更に説明する。
図３は後段酸化触媒におけるＮＯｘとＮＨ３の反応のイメージ図であり、図４はＮＯが酸化されてＮＯ２となるイメージ図である。
ＮＯｘがＮＨ３と反応してＮ２として排出されるためには、従来技術において説明した（１）（２）（３）式による反応を後段酸化触媒で起こさせる必要がある。（１）（２）（３）のうち（１）式に示した反応が最も速い。効率的に該反応を起こさせるためには、ＮＯとＮＯ２が略同モル必要である。
ＮＯとＮＯ２が略同モル存在して後段酸化触媒に送り込まれた場合、図３（Ｂ）に示したように、ＮＯとＮＯ２は何れも表面層であるＳＣＲ層でＮＨ３と反応して無害なＮ２となって排出される。
The evaluation results shown in the graph in FIG. 2 will be further described.
FIG. 3 is an image diagram of the reaction of NO x and NH 3 in the post-stage oxidation catalyst, and FIG. 4 is an image diagram of NO being oxidized to NO 2 .
In order for NO x to react with NH 3 and be discharged as N 2 , it is necessary to cause the reaction according to the formulas (1), (2) and (3) described in the prior art to occur in the post-stage oxidation catalyst. (1) Among the (2) and (3), the reaction shown in the formula (1) is the fastest. In order to efficiently cause the reaction, NO and NO 2 must have approximately the same mole.
When NO and NO 2 exist in substantially the same mole and are fed into the subsequent oxidation catalyst, as shown in FIG. 3B, both NO and NO 2 react with NH 3 in the SCR layer which is the surface layer. And harmless N 2 is discharged.
しかし、後段酸化触媒１０８は、ＮＯ２よりもＮＯの方が圧倒的に多量に送り込まれる。これは、エンジンにおいてＮＯ２よりもＮＯの方が発生しやすいことに加え、後段酸化触媒１０８より上流側のＳＣＲ触媒１０６でも前記（１）（２）（３）の反応が起こるためＮＯ２の大半がＳＣＲ触媒１０６でＮ２に転換されてしまうためである。
そのため、後段酸化触媒１０８では、図３（Ａ）に示したように酸化力のあるＤＯＣ層でＮＯの一部をＮＯ２に転換することでＮＯとＮＯ２を略同モルとし、ＮＯとＮＯ２をＳＣＲ層でＮＨ３と反応させて無害なＮ２となって排出する必要がある。
However, the latter-stage oxidation catalyst 108 is fed with an overwhelmingly larger amount of NO than NO 2 . This is because NO is more likely to be generated than NO 2 in the engine, and the reactions (1), (2), and (3) also occur in the SCR catalyst upstream of the post-stage oxidation catalyst 108, so that the NO 2 This is because most of the SCR catalyst 106 is converted to N 2 .
Therefore, in the post-stage oxidation catalyst 108, as shown in FIG. 3A, a part of NO is converted to NO 2 in the DOC layer having oxidizing power, so that NO and NO 2 are made substantially the same mole, and NO and NO. 2 needs to react with NH 3 in the SCR layer to be harmless N 2 and be discharged.
しかし、前記ＤＯＣ層にＰｔが均等に存在していれば問題ないが、従来のＰｄを添加しない後段酸化触媒においては熱負荷がかかった場合にＰｔがシンタリングを起こし、Ｐｔの表面積が小さくなるためその酸化力は低下する。そのため、充分な量のＮＯからＮＯ２への転換が行われず、その結果最も反応速度の速い（１）式の反応が充分に行われなくなりＮＯｘ浄化率が小さくなる。特にその傾向はＰｔ担持量が少なくなるほど顕著に現れる。 However, there is no problem if Pt is uniformly present in the DOC layer. However, in the latter-stage oxidation catalyst in which conventional Pd is not added, Pt causes sintering when a thermal load is applied, and the surface area of Pt is reduced. Therefore, the oxidizing power decreases. Therefore, a sufficient amount of NO to NO 2 is not converted, and as a result, the reaction of the formula (1) having the fastest reaction rate is not sufficiently performed, and the NO x purification rate is reduced. In particular, this tendency becomes more prominent as the amount of Pt supported decreases.
一方、本発明のＰｄを添加した後段酸化触媒においては、Ｐｄ添加効果によりＰｔのシンタリングは発生しにくい。そのため、充分な量のＮＯからＮＯ２への転換が行われ、その結果（１）（２）（３）の反応が充分に行われて、充分なＮＯｘ浄化率を保持することができる
そのため、前述したように、Ｐｔを担持しただけである従来の酸化触媒においては、Ｐｔ添加量の低下に伴いＮＯｘ浄化性能が大きく低下したが、本発明のＰｔを担持しＰｄを添加した酸化触媒においては、Ｐｔ添加量が低下してもＮＯｘ浄化性能の大きな低下は見られなくなる。
On the other hand, in the post-stage oxidation catalyst to which Pd of the present invention is added, Pt sintering is unlikely to occur due to the Pd addition effect. Therefore, a sufficient amount of NO is converted to NO 2, and as a result, the reactions (1), (2), and (3) are sufficiently performed, and a sufficient NO x purification rate can be maintained. As described above, in the conventional oxidation catalyst that only supports Pt, the NOx purification performance greatly decreases as the amount of Pt added decreases, but in the oxidation catalyst that supports Pt and added Pd of the present invention. No significant decrease in NOx purification performance is observed even when the Pt addition amount is reduced.
さらに、前記Ｐｔ担持量を変化させ、前記Ｐｄの添加量をＰｄ／Ｐｔ＝１／１０とした複数の後段酸化触媒１０８用の酸化触媒サンプルを用意し、それぞれのサンプルについて５００℃におけるＮＯｘの浄化性能について評価を行った。結果を図４に示す。 Further, an oxidation catalyst sample for a plurality of subsequent oxidation catalysts 108 in which the amount of Pt supported was changed and the addition amount of Pd was Pd / Pt = 1/10 was prepared, and NO x at 500 ° C. was prepared for each sample. The purification performance was evaluated. The results are shown in FIG.
図４において、縦軸はＮＯｘの浄化性能、横軸は前記内面層におけるＰｔの担持量（ｇ／Ｌ）である。また、図４には参考として従来のＰｄを添加しない酸化触媒におけるＮＯｘの酸化性能の評価の結果も示した。図中▲が本発明の酸化触媒における評価、●が従来の酸化触媒の評価の結果である。 In FIG. 4, the vertical axis represents the NO x purification performance, and the horizontal axis represents the amount of Pt supported (g / L) in the inner surface layer. FIG. 4 also shows the results of evaluation of the oxidation performance of NOx in a conventional oxidation catalyst not added with Pd for reference. In the figure, ▲ is the evaluation result of the oxidation catalyst of the present invention, and ● is the result of evaluation of the conventional oxidation catalyst.
図４から明らかであるように、Ｐｔを担持しただけである従来の酸化触媒においては、Ｐｔ添加量の上昇に伴いＮＯｘ浄化性能が大きく低下した。これは、５００℃という高温環境でＰｔ担持量が増えると酸化力が強くなり、ＮＯｘと反応して浄化するためのＮＨ３が酸化されてＮ２やＮＯｘとなってしまうことにより、ＮＯｘ浄化率が低下するためである。
一方、本発明のＰｔを担持しＰｄを添加した酸化触媒においては、Ｐｔ担持量：０．６ｇ／ｌ〜０．９ｇ／ｌにてＮＯ２浄化性能の大きな低下は見られなかった。
図４におけるＥは、図２におけるＥと同じＰｔ担持量である。即ち従来のＰｄを添加しない後段酸化触媒においては、１８０℃で必要なＮＯｘ浄化率を満たすようにＰｔ担持量を決定すると５００℃においてはＦのＮＯｘ浄化率が得られるが、本発明によるＰｄを添加した後段酸化触媒においてはＧのＮＯｘ浄化率が得られ、本発明においてはＮＯｘ浄化率が従来よりも向上しているといえる。
As is clear from FIG. 4, in the conventional oxidation catalyst that only supports Pt, the NOx purification performance is greatly reduced as the Pt addition amount increases. This is because when the amount of Pt supported increases in a high-temperature environment of 500 ° C., the oxidizing power becomes stronger, and NH 3 for reacting with NO x to be purified is oxidized to N 2 or NO x , so that NO This is because the x purification rate decreases.
On the other hand, in the oxidation catalyst supporting Pt and adding Pd of the present invention, no significant reduction in NO 2 purification performance was observed when the amount of Pt supported was 0.6 g / l to 0.9 g / l.
E in FIG. 4 is the same amount of Pt supported as E in FIG. Specifically, in the conventional post-stage oxidation catalyst without the addition of Pd, but the NO x purification rate of F is obtained in determining the 500 ° C. The amount of supported Pt to meet the NO x purification rate required at 180 ° C., according to the invention in the downstream side oxidation catalyst added with Pd obtained the NO x purification rate of G, in the present invention it can be said that the NO x purification rate is improved than before.
次に、Ｐｄ添加量の最適化実験を行った。
前記Ｐｄ添加量を重量比でＰｄ／Ｐｔ＝０〜１／４の範囲で変化させ、低温におけるＮＨ３の酸化性能、低温及び高温におけるＮＯｘの浄化作用について評価を行った。なおここでいう低温とは約２００℃、高温とは約５００℃である。
Next, an optimization experiment on the amount of Pd added was performed.
The Pd addition amount was changed in the range of Pd / Pt = 0 to 1/4 by weight ratio, and the oxidation performance of NH 3 at low temperature and the NO x purification action at low temperature and high temperature were evaluated. The low temperature here is about 200 ° C., and the high temperature is about 500 ° C.
前記評価の結果を図５に示す。図５（Ａ）はＰｄ添加量を変化させたときの低温におけるＮＯｘの浄化作用について評価結果、図５（Ｂ）はＰｄ添加量を変化させたときの高温におけるＮＯｘの浄化作用について評価結果、図５（Ｃ）はＰｄ添加量を変化させたときの低温におけるＮＨ３の酸化作用について評価結果である。
図５（Ａ）（Ｂ）（Ｃ）に共通してＰｄ／Ｐｔ＝１／２０〜１／１０が適切であるといえる。これは、Ｐｄは酸化力ではＰｔと比べると劣るため、Ｐｄの添加量が多すぎると酸化触媒全体として酸化力の面で劣るので酸化触媒として充分な機能を有するためにはＰｄ／Ｐｔを１／１０以下とすることが適切であり、Ｐｄの添加量が少なすぎると、Ｐｔのシンタリングを充分に抑制することができないので、Ｐｔのシンタリングを抑制するためにはＰｄ／Ｐｔを１／２０以上とすることが適切であるためであるといえる。
The result of the evaluation is shown in FIG. FIG. 5 (A) shows the evaluation results of the NO x purification action at low temperatures when the amount of Pd addition is changed, and FIG. 5 (B) shows the NO x purification action at high temperatures when the amount of Pd addition is changed. As a result, FIG. 5C shows the evaluation result of the oxidizing action of NH 3 at a low temperature when the amount of Pd addition is changed.
It can be said that Pd / Pt = 1/20 to 1/10 is appropriate in common with FIGS. This is because Pd is inferior to Pt in oxidizing power. Therefore, if the amount of Pd added is too large, the oxidizing catalyst as a whole is inferior in terms of oxidizing power. / 10 or less is appropriate, and if the amount of Pd added is too small, sintering of Pt cannot be sufficiently suppressed. Therefore, in order to suppress sintering of Pt, Pd / Pt is reduced to 1 / It can be said that it is appropriate to set it to 20 or more.
以上のことから、担持量が０．６ｇ／ｌから０．９ｇ／ｌでＰｔが担持された後段酸化触媒に、重量比でＰｄ／Ｐｔ＝１／２０〜１／１０となるようにＰｄを添加することで、低温、高温いずれにおいても高いＮＨ３酸化性能及びＮＯｘ浄化作用を有し、さらに従来よりもＰｔ使用量を削減することができるため低コストで製作することができる排気処理装置が得られるといえる。 From the above, Pd is added to the post-stage oxidation catalyst in which Pt is supported at a supported amount of 0.6 g / l to 0.9 g / l so that Pd / Pt = 1/20 to 1/10 by weight ratio. By adding, it has high NH 3 oxidation performance and NO x purification action at both low temperature and high temperature, and furthermore, the amount of Pt used can be reduced as compared with the conventional exhaust treatment device that can be manufactured at low cost. It can be said that
Ｐｔ担持量を増加させることなく、後段酸化触媒の性能低下を抑制し、さらには後段酸化触媒のＮＯｘ浄化性能を向上させることができる排気処理装置として利用することができる。 Without increasing the amount of Pt supported, it can be used as an exhaust treatment device that can suppress the performance degradation of the post-stage oxidation catalyst and further improve the NOx purification performance of the post-stage oxidation catalyst.
１０４ フィルタ（ＤＰＦ）
１０６ ＳＣＲ触媒
１０８ 後段酸化触媒（酸化触媒）
104 Filter (DPF)
106 SCR catalyst 108 Subsequent oxidation catalyst (oxidation catalyst)
Claims (5)
前記酸化触媒は、担体に白金（Ｐｔ）を担持して構成するとともに、
前記酸化触媒にパラジウム（Ｐｄ）を添加したことを特徴とする酸化触媒。 In the oxidation catalyst that is connected to the exhaust passage of the engine and is located downstream of the selective catalytic reduction (SCR),
The oxidation catalyst is configured by supporting platinum (Pt) on a carrier,
An oxidation catalyst comprising palladium (Pd) added to the oxidation catalyst.
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