JP5169987B2 - Exhaust gas purification catalyst - Google Patents
Exhaust gas purification catalyst Download PDFInfo
- Publication number
- JP5169987B2 JP5169987B2 JP2009116685A JP2009116685A JP5169987B2 JP 5169987 B2 JP5169987 B2 JP 5169987B2 JP 2009116685 A JP2009116685 A JP 2009116685A JP 2009116685 A JP2009116685 A JP 2009116685A JP 5169987 B2 JP5169987 B2 JP 5169987B2
- Authority
- JP
- Japan
- Prior art keywords
- composite oxide
- catalyst
- bismuth
- exhaust gas
- oxide
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
- 239000003054 catalyst Substances 0.000 title claims description 82
- 238000000746 purification Methods 0.000 title claims description 35
- 239000002131 composite material Substances 0.000 claims description 140
- 229910052797 bismuth Inorganic materials 0.000 claims description 48
- JCXGWMGPZLAOME-UHFFFAOYSA-N bismuth atom Chemical compound [Bi] JCXGWMGPZLAOME-UHFFFAOYSA-N 0.000 claims description 48
- 238000011144 upstream manufacturing Methods 0.000 claims description 30
- 229910044991 metal oxide Inorganic materials 0.000 claims description 20
- 150000004706 metal oxides Chemical class 0.000 claims description 20
- QCWXUUIWCKQGHC-UHFFFAOYSA-N Zirconium Chemical compound [Zr] QCWXUUIWCKQGHC-UHFFFAOYSA-N 0.000 claims description 16
- 229910052726 zirconium Inorganic materials 0.000 claims description 16
- 229910052684 Cerium Inorganic materials 0.000 claims description 11
- GWXLDORMOJMVQZ-UHFFFAOYSA-N cerium Chemical compound [Ce] GWXLDORMOJMVQZ-UHFFFAOYSA-N 0.000 claims 2
- 239000007789 gas Substances 0.000 description 63
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 26
- 229910002091 carbon monoxide Inorganic materials 0.000 description 26
- 239000000203 mixture Substances 0.000 description 26
- 238000000034 method Methods 0.000 description 25
- -1 oxygen ion Chemical class 0.000 description 21
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 21
- 229910052751 metal Inorganic materials 0.000 description 20
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- 238000006722 reduction reaction Methods 0.000 description 17
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- 239000002585 base Substances 0.000 description 9
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- 238000002441 X-ray diffraction Methods 0.000 description 4
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- 230000003197 catalytic effect Effects 0.000 description 4
- 239000003093 cationic surfactant Substances 0.000 description 4
- HSJPMRKMPBAUAU-UHFFFAOYSA-N cerium(3+);trinitrate Chemical compound [Ce+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O HSJPMRKMPBAUAU-UHFFFAOYSA-N 0.000 description 4
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- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
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Description
本発明は、排ガス浄化用触媒に関する。 The present invention relates to an exhaust gas purifying catalyst.
自動車用エンジン等の内燃機関からの排ガス中には、窒素酸化物（ＮＯｘ）、一酸化炭素（ＣＯ）、炭化水素（ＨＣ）等の有害物質が含まれる。そこで一般に、排ガス中のＣＯ及びＨＣを酸化するとともにＮＯｘを還元する排ガス浄化触媒を用い、排ガスを浄化してから大気中に放出している。排ガス浄化触媒の代表的なものとしては、白金（Ｐｔ）、ロジウム（Ｒｈ）、パラジウム（Ｐｄ）等の貴金属を活性アルミナ等の多孔質金属酸化物担体に担持させた三元触媒が知られている。 Exhaust gas from an internal combustion engine such as an automobile engine contains harmful substances such as nitrogen oxides (NO x ), carbon monoxide (CO), and hydrocarbons (HC). Therefore in general, using the exhaust gas purifying catalyst for reducing NO x as well as oxidizing CO and HC in the exhaust gas, it is discharged from the purifying exhaust gas into the atmosphere. As a typical exhaust gas purification catalyst, a three-way catalyst in which a noble metal such as platinum (Pt), rhodium (Rh), palladium (Pd) is supported on a porous metal oxide carrier such as activated alumina is known. Yes.
ここで、三元触媒に関して低温領域での酸化還元能の向上は、早急に解決しなければならない課題である。エンジン始動直後などにおいては触媒が活性温度に達していない低温領域にあり、この状態では未燃焼の炭化水素などが外部へ排出される虞がある。 Here, improvement of the oxidation-reduction ability in the low temperature region with respect to the three-way catalyst is a problem that must be solved immediately. Immediately after the engine is started, the catalyst is in a low temperature region where the activation temperature has not been reached.
特に、アルコール混合燃料を使用する自動車（Flexible-fuel vehicle、以下ＦＦＶと呼ぶ）では、ガソリンと比較してアルコールの発熱量が小さいことから、エンジン始動直後における触媒の温度上昇が緩やかである。そのためＦＦＶに用いる触媒については、低温領域での酸化還元能の向上が特に急務な課題となっている。 In particular, in an automobile using an alcohol-mixed fuel (flexible-fuel vehicle, hereinafter referred to as FFV), since the calorific value of alcohol is smaller than that of gasoline, the temperature rise of the catalyst immediately after engine startup is moderate. Therefore, with regard to the catalyst used for FFV, improvement of redox ability in a low temperature region is a particularly urgent issue.
ＦＦＶ及びガソリンエンジン車用の排ガス浄化触媒としては、酸化セリウムと酸化ジルコニウムとの複合酸化物に白金、パラジウム、ロジウム等の貴金属を担持した触媒が実用化され、一般的に使用されている。酸化セリウムやセリウム−ジルコニウム複合酸化物は、酸化セリウムによる良好な酸素吸収・放出能を示し、触媒温度が３００℃以上で酸化還元能を示す。 As an exhaust gas purification catalyst for FFV and gasoline engine vehicles, a catalyst in which a noble metal such as platinum, palladium or rhodium is supported on a composite oxide of cerium oxide and zirconium oxide has been put into practical use and is generally used. Cerium oxide and cerium-zirconium composite oxide show good oxygen absorption / release ability by cerium oxide, and show redox ability when the catalyst temperature is 300 ° C. or higher.
しかしながら、酸化セリウムやセリウム−ジルコニウムの複合酸化物は、触媒温度が３００℃未満の低温領域で酸化還元能が充分ではない。そこで、セリウム−ジルコニウム複合酸化物に第３成分として複数の酸化数をとる遷移金属を添加した複合酸化物が提案されている（例えば、特許文献１参照。）。特にビスマスを第３成分として添加した複合酸化物を有する排ガス浄化用触媒では、触媒温度が３００℃未満という低温領域で酸化活性が向上するとされている。 However, the complex oxide of cerium oxide or cerium-zirconium does not have sufficient redox ability in a low temperature range where the catalyst temperature is less than 300 ° C. Thus, a composite oxide in which a transition metal having a plurality of oxidation numbers as a third component is added to a cerium-zirconium composite oxide has been proposed (see, for example, Patent Document 1). In particular, in an exhaust gas purifying catalyst having a composite oxide to which bismuth is added as a third component, the oxidation activity is improved in a low temperature region where the catalyst temperature is less than 300 ° C.
また、更に低温領域で酸化還元能を発揮するよう、セリウム−ジルコニウム−ビスマスの複合酸化物に第４成分として銀を添加したセリウム−ジルコニウム−ビスマス−銀の４元系複合酸化物が提案されている（例えば、特許文献２参照。）。 In addition, a cerium-zirconium-bismuth-silver quaternary composite oxide in which silver is added as a fourth component to a cerium-zirconium-bismuth composite oxide so as to exhibit redox ability in a lower temperature region has been proposed. (For example, refer to Patent Document 2).
上記特許文献１に記載のセリウム−ジルコニウム−ビスマス複合酸化物を有する排ガス浄化用触媒は、低温領域においてＣＯやＨＣの酸化性能に優れるものの、Ｎｏｘの還元性能が低下していることが明らかとなった。上記特許文献２に記載のセリウム−ジルコニウム−ビスマス−銀の４元系複合酸化物についても同様であった。 Although the exhaust gas-purifying catalyst having the cerium-zirconium-bismuth composite oxide described in Patent Document 1 is excellent in the oxidation performance of CO and HC in the low temperature region, it is clear that the reduction performance of No x is lowered. became. The same applies to the cerium-zirconium-bismuth-silver quaternary composite oxide described in Patent Document 2.
本発明はこのような従来の事情に鑑みてなされたものであり、低温領域において酸化性能と還元性能の両立が図られた排ガス浄化用触媒を提供することを目的とする。 The present invention has been made in view of such conventional circumstances, and an object of the present invention is to provide an exhaust gas purifying catalyst in which both oxidation performance and reduction performance are achieved in a low temperature region.
請求項１に係る発明は、排ガス流れ方向の上流部は第一の複合酸化物を有し、下流部は第二の複合酸化物を有し、
前記第一の複合酸化物は、セリウム、ジルコニウム及びビスマスを含有する複合酸化物であり、
前記第二の複合酸化物は、少なくともセリウム及びジルコニウムを含有し、更にビスマスを含有する場合には第一の複合酸化物よりもビスマスの含有量が少ない複合酸化物である排ガス浄化用触媒である。
In the invention according to claim 1, the upstream portion in the exhaust gas flow direction has the first composite oxide, the downstream portion has the second composite oxide,
The first composite oxide is a composite oxide containing cerium, zirconium and bismuth,
The second composite oxide is an exhaust gas purifying catalyst which is a composite oxide containing at least cerium and zirconium, and further containing bismuth and having a lower bismuth content than the first composite oxide. .
請求項２に係る発明は、前記第一の複合酸化物及び第二の複合酸化物が、該第一の複合酸化物及び該第二の複合酸化物以外の金属酸化物に担持されてなる請求項１に記載の排ガス浄化用触媒である。 In the invention according to claim 2, the first composite oxide and the second composite oxide are supported on a metal oxide other than the first composite oxide and the second composite oxide. Item 2. An exhaust gas purifying catalyst according to Item 1.
本発明によれば、低温領域において酸化性能と還元性能の両立が図られた排ガス浄化用触媒を提供することができる。 According to the present invention, it is possible to provide an exhaust gas purifying catalyst in which both oxidation performance and reduction performance are achieved in a low temperature region.
本発明の排ガス浄化用触媒は、排ガス流れ方向の上流部は第一の複合酸化物を有し、下流部は第二の複合酸化物を有する。上流部の第一の複合酸化物は、セリウム、ジルコニウム及びビスマスを含有する複合酸化物である。下流部の第二の複合酸化物は、少なくともセリウム及びジルコニウムを含有する複合酸化物である。下流部の第二の複合酸化物が更にビスマスを含有する場合には、第一の複合酸化物よりもビスマスの含有量が少ない複合酸化物とする。 In the exhaust gas purifying catalyst of the present invention, the upstream portion in the exhaust gas flow direction has the first composite oxide, and the downstream portion has the second composite oxide. The first composite oxide in the upstream portion is a composite oxide containing cerium, zirconium, and bismuth. The second complex oxide in the downstream portion is a complex oxide containing at least cerium and zirconium. When the second composite oxide in the downstream portion further contains bismuth, the composite oxide has a smaller bismuth content than the first composite oxide.
本発明者は、セリウム−ジルコニウム−ビスマス複合酸化物、及びセリウム−ジルコニウム−ビスマス−銀複合酸化物について酸化還元能を調べたところ、低温領域での酸化性能は従来の触媒よりも向上しているものの、還元性能が低くなるという問題を見出した。この原因を鋭意研究によって検討したところ、複合酸化物を構成する酸化物のうち、酸化ビスマスの性質に起因しているものと推測した。 The present inventor examined the oxidation-reduction ability of the cerium-zirconium-bismuth composite oxide and the cerium-zirconium-bismuth-silver composite oxide. As a result, the oxidation performance in the low temperature region was improved as compared with the conventional catalyst. However, the problem that reduction performance becomes low was found. As a result of diligent research, the cause was presumed to be due to the properties of bismuth oxide among the oxides constituting the composite oxide.
下記表１に示すように、酸化ビスマスは酸化セリウムや酸化ジルコニウムに比べて酸素イオンの伝導度が高い。ここで、酸素イオンの伝導度とは、固体酸化物中のイオンの伝わり易さ、すなわちイオンの伝わる速さを意味する。 As shown in Table 1 below, bismuth oxide has higher oxygen ion conductivity than cerium oxide or zirconium oxide. Here, the conductivity of oxygen ions means the ease with which ions in a solid oxide are transmitted, that is, the speed with which ions are transmitted.
そのため、酸化ビスマスを含む複合酸化物は、排ガス中の酸素分子を効率良く取り込み、取り込まれた酸素によってＨＣとＣＯの酸化が行なわれているものと考えられる。そのため、排ガス中のＮＯｘ中に存在する酸素原子は、ＨＣとＣＯを酸化するために使用される機会が減り、結果的にＮＯｘの還元が起こり難くなると考えられる。複合酸化物中の酸化ビスマスの有無によるＮＯｘ還元の差異の様子を図１にイメージ図として示すが、このイメージ図によって本発明は限定されない。図１（Ａ）は、ビスマスを含まない又はビスマスの含有量の少ない複合酸化物１を用いたとき、図１（Ｂ）は複合酸化物１よりもビスマスを多く含有する複合酸化物２を用いたときのＮＯｘ還元の様子を説明するイメージ図である。 Therefore, it is considered that the composite oxide containing bismuth oxide efficiently takes in oxygen molecules in the exhaust gas and oxidizes HC and CO with the taken-in oxygen. Therefore, it is considered that the oxygen atoms present in NOx in the exhaust gas have fewer opportunities to be used to oxidize HC and CO, and as a result, reduction of NOx hardly occurs. Although the state of the difference in NOx reduction depending on the presence or absence of bismuth oxide in the composite oxide is shown as an image diagram in FIG. 1, the present invention is not limited by this image diagram. FIG. 1A shows a case where a composite oxide 1 containing no bismuth or having a low bismuth content is used, and FIG. 1B uses a composite oxide 2 containing more bismuth than the composite oxide 1. It is an image figure explaining the mode of NOx reduction when there was.
そこで、本発明の排ガス浄化用触媒では、図２に示すように、排ガス流れ方向の上流部１０と下流部１２で異なる組成の複合酸化物を用い、上流部１０には、セリウム、ジルコニウム及びビスマスを含有する第一の複合酸化物を用いる。セリウム、ジルコニウム及びビスマスを含有する第一の複合酸化物を用いることで、低温領域での酸化性能に優れる排ガス浄化用触媒となる。 Therefore, in the exhaust gas purifying catalyst of the present invention, as shown in FIG. 2, composite oxides having different compositions are used in the upstream portion 10 and the downstream portion 12 in the exhaust gas flow direction, and cerium, zirconium and bismuth are used in the upstream portion 10. A first composite oxide containing is used. By using the first composite oxide containing cerium, zirconium and bismuth, it becomes an exhaust gas purifying catalyst having excellent oxidation performance in a low temperature region.
また、本発明の排ガス浄化用触媒において下流部１２に用いる第二の複合酸化物は、少なくともセリウム及びジルコニウムを含有する複合酸化物であればよく、ビスマスを含有しても含有していなくてもよい。但し、第二の複合酸化物がビスマスを含有する場合には上流部１０の第一の複合酸化物よりもビスマスの含有量が少ない複合酸化物とする。
ビスマスを含有しない又はビスマスの含有量の少ない第二の複合酸化物を用いることで、全体としてＮＯｘの還元性能が損なわれない排ガス浄化用触媒とすることができる。
Further, the second composite oxide used for the downstream portion 12 in the exhaust gas purifying catalyst of the present invention may be a composite oxide containing at least cerium and zirconium, and may or may not contain bismuth. Good. However, when the second composite oxide contains bismuth, the composite oxide has a lower bismuth content than the first composite oxide in the upstream portion 10.
By using the second composite oxide that does not contain bismuth or has a low bismuth content, an exhaust gas purification catalyst that does not impair the NOx reduction performance as a whole can be obtained.
ここで、本発明者は、排ガス流れ方向の上流側にビスマスの含有量の多い複合酸化物を配置した排ガス浄化用触媒とすることが、浄化率の向上に極めて有益であることを明らかにした。このような構成の排ガス浄化用触媒としたときに浄化効率に優れる理由を以下のように推測するが、下記推測によって本発明は限定されない。 Here, the present inventor has clarified that it is extremely beneficial to improve the purification rate by using an exhaust gas purification catalyst in which a composite oxide having a high bismuth content is arranged upstream in the exhaust gas flow direction. . The reason why the exhaust gas purification catalyst having such a configuration is excellent in purification efficiency is estimated as follows, but the present invention is not limited by the following estimation.
ビスマスを含有するセリウム−ジルコニウム−ビスマス複合酸化物を有する排ガス浄化用触媒は、低温領域での酸化活性に優れるため、低温領域であってもＣＯやＨＣの酸化反応が進行する。このＣＯやＨＣの酸化反応は発熱反応であり、発生した熱がガス流によって下流側に運ばれる。そこで、酸化反応によって発生した熱量を触媒の活性化に利用するよう、酸化反応に寄与するビスマス含有量の多い複合酸化物を上流側に配置する。これにより上流側で発生した熱を下流側でのＮＯｘ還元反応のための触媒活性化に効果的に利用でき、ＮＯｘ浄化率が高められる。 Since the exhaust gas purifying catalyst having a cerium-zirconium-bismuth composite oxide containing bismuth is excellent in oxidation activity in a low temperature region, the oxidation reaction of CO and HC proceeds even in the low temperature region. This oxidation reaction of CO and HC is an exothermic reaction, and the generated heat is carried downstream by the gas flow. Therefore, a composite oxide having a high bismuth content that contributes to the oxidation reaction is arranged upstream so that the amount of heat generated by the oxidation reaction is used for the activation of the catalyst. Thereby, the heat generated on the upstream side can be effectively used for catalyst activation for the NOx reduction reaction on the downstream side, and the NOx purification rate is increased.
また、上流側にビスマス含有量の多い複合酸化物を配置して、上流側で発生した熱がガス流によって下流側に運ばれることは、下流側でのＣＯやＨＣの酸化反応を促進させることにもつながり、ＣＯやＨＣの浄化効率が高められる。 In addition, the arrangement of a complex oxide with a high bismuth content on the upstream side, and the heat generated on the upstream side being carried to the downstream side by the gas flow, promotes the oxidation reaction of CO and HC on the downstream side. This also improves CO and HC purification efficiency.
したがって、本発明の排ガス浄化用触媒では、主に上流側でＣＯやＨＣを酸化し、主に下流側でＮＯｘを還元する。上流部１０で酸化反応によって発生した熱は下流部１２の触媒を暖機し、下流部１２でのＮＯｘの還元反応が効果的に行なわれると同時に、ＣＯやＨＣの酸化反応も効果的に行なわれる。 Therefore, in the exhaust gas purifying catalyst of the present invention, CO and HC are mainly oxidized on the upstream side, and NOx is mainly reduced on the downstream side. The heat generated by the oxidation reaction in the upstream section 10 warms up the catalyst in the downstream section 12 and the NOx reduction reaction in the downstream section 12 is effectively performed, and at the same time, the oxidation reaction of CO and HC is also performed effectively. It is.
なお、本発明の効果を損なわない範囲で、第一の複合酸化物及び第二の複合酸化物は他の金属元素を含んでいてもよい。このような他の金属元素としては、例えば、白金、スカンジウム、イットリウム、ランタン、プラセオジウム、ネオジウム、サマリウム、ユーロピウム、ガドリウム、テルビウム、ジスプロシウム、ホルミウム、エルビウム、ツリウム、イッテルビウム、ルテチウム等の希土類金属のほか、チタン、ハフニウム、バナジウム、クロム、マンガン、コバルト、ニッケル、銅、亜鉛、モリブデン、タングステン、インジウム、スズ、アンチモン、タンタル等が挙げられる。これらは１種又は２種以上で用いることができる。
このような他の金属元素は、原料物質であるセリウム化合物、ジルコニウム化合物、ビスマス化合物の中の不純物に由来して含まれているものであってもよい。
In addition, the 1st complex oxide and the 2nd complex oxide may contain the other metal element in the range which does not impair the effect of this invention. Such other metal elements include, for example, rare earth metals such as platinum, scandium, yttrium, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. Examples include titanium, hafnium, vanadium, chromium, manganese, cobalt, nickel, copper, zinc, molybdenum, tungsten, indium, tin, antimony, and tantalum. These can be used alone or in combination of two or more.
Such other metal elements may be derived from impurities in the cerium compound, zirconium compound, and bismuth compound, which are raw material materials.
上記他の金属として白金を含有する第一の複合酸化物及び第二の複合酸化物では、還元雰囲気下における低温領域でのＣＯやＨＣに対する酸化能の低下が抑えられる。これは、酸化ビスマスの還元よりも優先して酸化白金が還元されるため、酸化ビスマスの還元が抑制され、ビスマスは複合酸化物中で酸化物として安定的に存在し、結果、複合酸化物の組成の変動が抑えられ、酸化能の低下が抑制されると考えられる。 In the first composite oxide and the second composite oxide containing platinum as the other metal, a reduction in oxidizing ability with respect to CO and HC in a low temperature region under a reducing atmosphere can be suppressed. This is because platinum oxide is reduced in preference to the reduction of bismuth oxide, so that the reduction of bismuth oxide is suppressed, and bismuth is stably present as an oxide in the composite oxide. It is considered that the variation of the composition is suppressed and the decrease in the oxidation ability is suppressed.
以上から、上流部１０の第一の複合酸化物は、Ｃｅｖ１Ｚｒｗ１Ｂｉｘ１Ｍ１ ｙ１Ｏｚ１で表される化合物である。ここで、Ｍ１は上記他の金属元素を表す。 From the above, the first composite oxide in the upstream portion 10 is a compound represented by Ce v1 Zr w1 Bi x1 M 1 y1 O z1 . Here, M 1 represents the other metal element.
第一の複合酸化物中のセリウムの含有率（上記組成式中のｖ１）は、０．１以上０．９以下であることが好ましく、０．３以上０．８以下であることがより好ましく、０．５以上０．７以下であることが更に好ましい。
第一の複合酸化物中のジルコニウムの含有率（上記組成式中のｗ１）は、０．０１以上０．５以下であることが好ましく、０．０５以上０．３以下であることがより好ましく、０．１以上０．２以下であることが更に好ましい。
The content of cerium in the first composite oxide (v1 in the above composition formula) is preferably 0.1 or more and 0.9 or less, more preferably 0.3 or more and 0.8 or less. And more preferably 0.5 or more and 0.7 or less.
The zirconium content in the first composite oxide (w1 in the composition formula) is preferably 0.01 or more and 0.5 or less, more preferably 0.05 or more and 0.3 or less. More preferably, it is 0.1 or more and 0.2 or less.
第一の複合酸化物中のビスマスの含有率（上記組成式中のｘ１）は、０．０５以上０．４以下であることが好ましく、０．１以上０．３以下であることがより好ましく、０．１５以上０．２５以下であることが更に好ましい。 The content of bismuth in the first composite oxide (x1 in the above composition formula) is preferably 0.05 or more and 0.4 or less, more preferably 0.1 or more and 0.3 or less. And more preferably 0.15 or more and 0.25 or less.
第一の複合酸化物中の酸素の含有率（上記組成式中のｚ１）は、１．５以上２．０以下であることが好ましく、１．６以上１．９５以下であることがより好ましく、１．７以上１．９以下であることが更に好ましい。 The oxygen content in the first composite oxide (z1 in the above composition formula) is preferably 1.5 or more and 2.0 or less, and more preferably 1.6 or more and 1.95 or less. More preferably, it is 1.7 or more and 1.9 or less.
第一の複合酸化物中の他の金属元素Ｍ１の含有率（上記組成式中のｙ１）は、他の金属元素の種類にもよるが、０以上０．５以下であることが好ましく、０以上０．２以下であることがより好ましく、０以上０．１以下であることが更に好ましい。 The content of other metal element M1 in the first composite oxide (y1 in the above composition formula) is preferably 0 or more and 0.5 or less, although it depends on the type of the other metal element, It is more preferably 0 or more and 0.2 or less, and further preferably 0 or more and 0.1 or less.
第一の複合酸化物の上記組成式において、ｖ１、ｗ１、ｘ１、ｙ１及びｚ１の大小関係は、ｚ１＞ｖ１＞ｘ１＞ｗ１＞ｙ１であることが好ましい。 In the above composition formula of the first composite oxide, the magnitude relationship between v1, w1, x1, y1, and z1 is preferably z1> v1> x1> w1> y1.
また下流部１２の第二の複合酸化物は、Ｃｅｖ２Ｚｒｗ２Ｂｉｘ２Ｍ１ ｙ２Ｏｚ２で表される化合物であり、Ｍ１は上記他の金属元素を表す。ここでＸ２は、第一の複合酸化物の組成式におけるＸ１よりも小さく、Ｘ１＞Ｘ２の関係を満たす。 The second composite oxide of the downstream section 12 is a compound represented by Ce v2 Zr w2 Bi x2 M 1 y2 O z2, M 1 represents the other metal element. Here, X2 is smaller than X1 in the composition formula of the first composite oxide and satisfies the relationship of X1> X2.
第二の複合酸化物中のセリウムの含有率（上記組成式中のｖ２）は、０．１以上０．９以下であることが好ましく、０．３以上０．８以下であることがより好ましく、０．５以上０．８以下であることが更に好ましい。
第二の複合酸化物中、ジルコニウムの含有率（上記組成式中のｗ２）は、０．０１以上０．５以下であることが好ましく、０．０５以上０．３以下であることがより好ましく、０．１以上０．２以下であることが更に好ましい。
The content of cerium in the second composite oxide (v2 in the above composition formula) is preferably 0.1 or more and 0.9 or less, and more preferably 0.3 or more and 0.8 or less. And more preferably 0.5 or more and 0.8 or less.
In the second composite oxide, the zirconium content (w2 in the above composition formula) is preferably 0.01 or more and 0.5 or less, more preferably 0.05 or more and 0.3 or less. More preferably, it is 0.1 or more and 0.2 or less.
第二の複合酸化物中のビスマスの含有率（上記組成式中のｘ２）は、０以上０．４以下であることが好ましく、０以上０．３以下であることがより好ましく、０以上０．２以下であることが更に好ましい。 The content of bismuth in the second composite oxide (x2 in the above composition formula) is preferably 0 or more and 0.4 or less, more preferably 0 or more and 0.3 or less, and 0 or more and 0 or less. More preferably, it is 2 or less.
第二の複合酸化物中の酸素の含有率（上記組成式中のｚ２）は、１．５以上２．０以下であることが好ましく、１．６以上２．０以下であることがより好ましく、１．７以上２．０以下であることが更に好ましい。 The oxygen content in the second composite oxide (z2 in the composition formula) is preferably 1.5 or more and 2.0 or less, and more preferably 1.6 or more and 2.0 or less. More preferably, it is 1.7 or more and 2.0 or less.
第二の複合酸化物中の他の金属元素Ｍ１の含有率（上記組成式中のｙ２）は、他の金属元素の種類にもよるが、０以上０．５以下であることが好ましく、０以上０．２以下であることがより好ましく、０以上０．１以下であることが更に好ましい。 Second composite oxide other content of the metallic element M 1 in the (y2 in the composition formula) preferably depending on the kind of other metal elements, is 0 to 0.5, It is more preferably 0 or more and 0.2 or less, and further preferably 0 or more and 0.1 or less.
第二の複合酸化物の上記組成式において、ｖ２、ｗ２、ｘ２、ｙ２及びｚ２の大小関係は、ｚ２＞ｖ２＞ｘ２＞ｗ２＞ｙ２であることが好ましい。 In the above composition formula of the second composite oxide, the magnitude relationship between v2, w2, x2, y2, and z2 is preferably z2> v2> x2> w2> y2.
第一の複合酸化物及び第二の複合酸化物の各構成元素は、全てが複合化している場合に上記作用が最大限に発揮されるが、少なくとも一部が複合体を形成している場合でも上記作用を得ることができる。複合酸化物として存在しているか否かは、例えばＸ線回折やラマンスペクトル測定により確認することができる。 When the constituent elements of the first composite oxide and the second composite oxide are all combined, the above-mentioned action is exerted to the maximum, but at least a part forms a composite. However, the above action can be obtained. Whether or not it exists as a complex oxide can be confirmed, for example, by X-ray diffraction or Raman spectrum measurement.
第一の複合酸化物及び第二の複合酸化物は、当業者に公知の任意の方法によって調製することができる。例えば、固相反応法、沈殿法、共沈法、均一沈殿法、水熱合成法、加水分解法、化学気相輸送法、熱分解法、噴霧乾燥法、スパッタ法、ガス中蒸発法、マイクロエマルジョン法、エマルジョン法、レーザー合成法等を挙げることができる。更に具体的な製造方法の例を以下で説明するが、これらの製造方法に限定されない。 The first composite oxide and the second composite oxide can be prepared by any method known to those skilled in the art. For example, solid phase reaction method, precipitation method, coprecipitation method, homogeneous precipitation method, hydrothermal synthesis method, hydrolysis method, chemical vapor transport method, thermal decomposition method, spray drying method, sputtering method, gas evaporation method, micro Examples thereof include an emulsion method, an emulsion method, and a laser synthesis method. Examples of specific manufacturing methods will be described below, but the present invention is not limited to these manufacturing methods.
共沈法では、セリア、ジルコニウム、ビスマス等のイオンを含む混合溶液に、沈殿剤を加えて共沈させ、それを分離、洗浄、乾燥後、焼成して複合酸化物を得る。
加水分解法では、セリア、ジルコニウム、ビスマス等を含む混合アルコキシド溶液を調製し、この混合アルコキシド溶液に脱イオン水を加えて加水分解し、この加水分解生成物を熱処理する。
固相反応法では、セリア、ジルコニウム、ビスマス等の塩や酸化物をボールミル等により機械的に混合し、得られた混合物を焼成して複合酸化物を製造する。
In the coprecipitation method, a precipitant is added to a mixed solution containing ions such as ceria, zirconium, bismuth and the like to coprecipitate it, separated, washed, dried and then fired to obtain a composite oxide.
In the hydrolysis method, a mixed alkoxide solution containing ceria, zirconium, bismuth and the like is prepared, deionized water is added to the mixed alkoxide solution for hydrolysis, and the hydrolysis product is heat-treated.
In the solid-phase reaction method, a salt or oxide such as ceria, zirconium, or bismuth is mechanically mixed with a ball mill or the like, and the resulting mixture is fired to produce a composite oxide.
第一の複合酸化物及び第二の複合酸化物を構成するセリア、ジルコニウム、ビスマス等の原料物質としては、酸化物、水酸化物、塩化物、硫酸塩、硝酸塩、塩酸塩、リン酸塩、硝酸アンモニウム塩などの無機塩；酢酸塩、炭酸塩、シュウ酸塩、クエン酸塩などの有機塩；アルコキシド；アセチルアセトナト錯体；及び各種有機金属化物を使用することができる。 Examples of raw materials such as ceria, zirconium, and bismuth constituting the first composite oxide and the second composite oxide include oxides, hydroxides, chlorides, sulfates, nitrates, hydrochlorides, phosphates, Inorganic salts such as ammonium nitrate salts; organic salts such as acetates, carbonates, oxalates, and citrates; alkoxides; acetylacetonato complexes; and various organometallic compounds can be used.
沈殿法や共沈法で使用する沈殿剤としては、アルカリ水溶液、有機酸、β−ジケトン、シクロポリエンが用いられる。前記アルカリ水溶液としては、炭酸ナトリウム水溶液、アンモニア水溶液、炭酸アンモニウム水溶液が挙げられ、有機酸としては、有機スルホン酸や、シュウ酸、クエン酸などの有機カルボン酸が挙げられる。 As a precipitant used in the precipitation method or coprecipitation method, an alkaline aqueous solution, an organic acid, a β-diketone, and cyclopolyene are used. Examples of the alkaline aqueous solution include an aqueous sodium carbonate solution, an aqueous ammonia solution, and an aqueous ammonium carbonate solution, and examples of the organic acid include organic sulfonic acids, and organic carboxylic acids such as oxalic acid and citric acid.
なお、沈殿法や共沈法とは、沈殿剤との反応によって溶剤から沈殿する方法のほか、溶液のｐＨを適宜に調節することによって沈殿させる方法や、更には、溶剤を除去することによって反応生成物を得る方法も含むものとする。 The precipitation method and the coprecipitation method are not only a method of precipitating from a solvent by reaction with a precipitant, but also a method of precipitating by appropriately adjusting the pH of the solution, and further by removing the solvent. A method of obtaining the product is also included.
加水分解法で使用するアルコキシドとしては、セリア、ジルコニウム、ビスマス等のメトキシド、エトキシド、プロポキシド、ブトキシドなどやこれらのエチレンオキサイド付加物などが挙げられる。 Examples of the alkoxide used in the hydrolysis method include methoxide such as ceria, zirconium and bismuth, ethoxide, propoxide, butoxide and the like, and ethylene oxide adducts thereof.
溶剤は、原料物質を溶解させるものであり、沈殿法や共沈法では原料物質と沈殿剤との反応によって沈殿物を形成するような溶剤が適宜選ばれる。このような溶剤としては、通常、水が好ましく用いられ、場合によっては、非水溶剤、例えば、アルコールや有機カルボン酸エステル等を用いてもよい。 The solvent dissolves the raw material. In the precipitation method or coprecipitation method, a solvent that forms a precipitate by the reaction between the raw material and the precipitant is appropriately selected. As such a solvent, water is usually preferably used, and in some cases, a non-aqueous solvent such as an alcohol or an organic carboxylic acid ester may be used.
溶媒を用いる製造方法では、得られた共沈物、沈殿物、加水分解生成物等は、濾過洗浄した後、好ましくは約５０〜２００℃で約１〜４８時間乾燥する。
また、溶媒の使用の有無に拘らず、複合酸化物の製造のため焼成を行なう。焼成温度は約３５０〜１２００℃が好ましく、より好ましくは４００〜１０００℃である。焼成の加熱時間は、約０．５〜１２時間の範囲である。
In the production method using a solvent, the obtained coprecipitate, precipitate, hydrolysis product and the like are filtered and washed, and preferably dried at about 50 to 200 ° C. for about 1 to 48 hours.
In addition, firing is performed to produce a composite oxide regardless of whether or not a solvent is used. The firing temperature is preferably about 350 to 1200 ° C, more preferably 400 to 1000 ° C. The heating time for baking ranges from about 0.5 to 12 hours.
更に、上記製造工程において沈殿剤を加える際に、あらかじめ添加剤として界面活性剤を加えてもよい。界面活性剤の添加により沈殿が微細で均一化されるため、その後の焼成工程で各陽イオンの拡散が促され、最終的に得られる複合酸化物の結晶性、均一性が向上し、低温における酸化還元能が著しく向上する場合がある。 Furthermore, when adding a precipitant in the said manufacturing process, you may add surfactant as an additive previously. The addition of the surfactant makes the precipitate fine and uniform, which promotes the diffusion of each cation in the subsequent firing step, and improves the crystallinity and uniformity of the finally obtained composite oxide. The redox ability may be significantly improved.
前記界面活性剤の種類としては、陽イオン性、陰イオン性、非イオン性界面活性剤が挙げられる。陽イオン性界面活性剤としては、アミン塩型及び／又は第４級アンモニウム塩型カチオン界面活性剤が挙げられ、具体的には例えば、ソロミンＡ、アーコベルＡ、ラウリルトリメチルアンモニウムハライド（クロライドまたはブロマイド。以下同様）、セチルトリメチルアンモニウムハライド、ヘキサデシルトリメチルアンモニウムハライド等が用いられる。また陰イオン性界面活性剤としては、石鹸、硫酸エステル塩、スルホン酸塩、リン酸エステル塩、ジチオリン酸エステル塩が挙げられ、具体的には例えば、ラウリン酸ナトリウム、ラウリルアルコール硫酸エステルナトリウム、エアロゾルＯＴ等が用いられる。非イオン界面活性剤としては、多価アルコール型、及び／又はポリエチレングリコール型非イオン界面活性剤が挙げられ、具体的には例えば、Ｔｗｅｅｎ８０、ノニルフェノールエチレンオキサイド１０モル付加物等が挙げられる。 Examples of the surfactant include cationic, anionic, and nonionic surfactants. Examples of the cationic surfactant include amine salt type and / or quaternary ammonium salt type cationic surfactants, and specifically include, for example, Solomine A, Arcobel A, lauryltrimethylammonium halide (chloride or bromide. The same applies hereinafter), cetyltrimethylammonium halide, hexadecyltrimethylammonium halide, and the like. Examples of the anionic surfactant include soap, sulfate ester salt, sulfonate salt, phosphate ester salt and dithiophosphate ester salt. Specifically, for example, sodium laurate, sodium lauryl alcohol sulfate, aerosol OT or the like is used. Examples of nonionic surfactants include polyhydric alcohol type and / or polyethylene glycol type nonionic surfactants, and specific examples include Tween 80, nonylphenol ethylene oxide 10 mol adduct and the like.
前記界面活性剤のなかでも、第４級アンモニウム塩型カチオン界面活性剤が好ましく用いられ、ヘキサデシルトリメチルアンモニウムハライドがより好ましく用いられる。 Among the surfactants, quaternary ammonium salt type cationic surfactants are preferably used, and hexadecyltrimethylammonium halide is more preferably used.
また、上記製造工程の焼成時に表面処理剤を添加することにより、得られる複合酸化物を有する排ガス浄化用触媒の酸化還元能がさらに向上する場合がある。
前記表面処理剤としては、金属ハロゲン化物、ハロゲン化アルカリ、酸、アルカリ、含ハロゲン有機化合物等が用いられ、気体、固体、液体、溶融塩、溶液のうち少なくとも１つ以上の状態で上述の複合酸化物と接触させる。
Moreover, the oxidation-reduction ability of the exhaust gas-purifying catalyst having the composite oxide obtained may be further improved by adding a surface treatment agent during the firing in the production process.
As the surface treatment agent, a metal halide, an alkali halide, an acid, an alkali, a halogen-containing organic compound, or the like is used, and the above-described composite in at least one of a gas, a solid, a liquid, a molten salt, and a solution. Contact with oxide.
表面処理剤として具体的には、例えば、ハロゲン化アンモニウム、ハロゲン化リチウム、ハロゲン化カリウム、ハロゲン化ナトリウム、ハロゲン化カルシウム、ハロゲン化アルミニウム、ハロゲン化鉄、ハロゲン化ガリウム、ハロゲン化リン、ハロゲン化インジウム、炭酸アンモニウム、炭酸ナトリウム、炭酸水素ナトリウム、炭酸リチウム、炭酸水素リチウム、炭酸カリウム、炭酸水素カリウム、塩酸、硫酸、硝酸、酢酸、フッ酸、臭化水素酸、シュウ酸、クエン酸、ハロゲン水、ハロゲン酸、水酸化ナトリウム、水酸化カリウム、アンモニア水、過酸化水素水、四ハロゲン化炭素、ホスゲン、ハロゲン化チオニル、およびこれらの水、アルコール、エーテル、ケトン、炭化水素溶液のうち、少なくとも１つ以上選ばれるものが使用される。 Specific examples of the surface treatment agent include, for example, ammonium halide, lithium halide, potassium halide, sodium halide, calcium halide, aluminum halide, iron halide, gallium halide, phosphorus halide, indium halide. , Ammonium carbonate, sodium carbonate, sodium bicarbonate, lithium carbonate, lithium bicarbonate, potassium carbonate, potassium bicarbonate, hydrochloric acid, sulfuric acid, nitric acid, acetic acid, hydrofluoric acid, hydrobromic acid, oxalic acid, citric acid, halogen water, Halogen acid, sodium hydroxide, potassium hydroxide, ammonia water, hydrogen peroxide solution, carbon tetrahalide, phosgene, thionyl halide, and at least one of these water, alcohol, ether, ketone, and hydrocarbon solution The one selected above is used
前記ハロゲンとしては、フッ素、塩素、臭素、沃素等があげられるが、取り扱いの容易さや得られる表面改質効果を大きくするために、好ましくは塩素を含有する塩、溶液、塩素水、塩素酸、塩酸等が用いられる。 Examples of the halogen include fluorine, chlorine, bromine, iodine, etc. In order to increase the ease of handling and the obtained surface modification effect, a salt containing chlorine, a solution, chlorine water, chloric acid, Hydrochloric acid or the like is used.
上記表面改質は、複合酸化物を、上記表面処理剤に浸漬あるいは混合させ、複合酸化物表面の一部又は表面全体を化学処理した後、余分な表面処理剤を取り除くことが望ましい。余分な表面処理剤の除去は、焼成や溶剤によって洗浄し或いは昇華させるか、または気相錯体を形成する錯化剤を用い、生成した錯体を揮発させることにより行われる。 The surface modification is preferably performed by immersing or mixing the composite oxide in the surface treatment agent and chemically treating a part or the entire surface of the composite oxide, and then removing the excess surface treatment agent. The excess surface treatment agent is removed by washing or sublimation with baking or a solvent, or by volatilizing the formed complex using a complexing agent that forms a gas phase complex.
余分な表面処理剤の除去に用いる溶剤としては、水、メタノール、エタノール、プロパノール、ブタノール、アセトン、ジエチルエーテル、リグロイン、ヘプタン、ヘキサン、シクロヘキサン、ベンゼン、トルエン、キシレン等が用いられる。また、前記錯化剤としては、気相錯体を形成する金属ハロゲン化物、すなわちアルカリ金属ハロゲン化物、アルカリ土類金属ハロゲン化物、遷移金属ハロゲン化物、これらを含む多成分金属ハロゲン化物、およびこれらの混合物のいずれを用いられる。なかでも塩化アルミニウム、塩化カリウム、および塩化ナトリウムが好ましく用いられる。 As a solvent used for removing the surplus surface treating agent, water, methanol, ethanol, propanol, butanol, acetone, diethyl ether, ligroin, heptane, hexane, cyclohexane, benzene, toluene, xylene, and the like are used. The complexing agent includes metal halides that form gas phase complexes, that is, alkali metal halides, alkaline earth metal halides, transition metal halides, multicomponent metal halides containing these, and mixtures thereof. Either of these can be used. Of these, aluminum chloride, potassium chloride, and sodium chloride are preferably used.
更に、表面処理後に得られた複合酸化物を、必要に応じて空気中において焼成処理を行ってもよい。このときの焼成温度は、上記複合酸化物の製造工程での焼成温度と同様である。 Furthermore, the composite oxide obtained after the surface treatment may be fired in air as necessary. The firing temperature at this time is the same as the firing temperature in the manufacturing process of the composite oxide.
第一の複合酸化物及び第二の複合酸化物の組成は、Ｘ線回折やラマンスペクトル測定により同定される。 The composition of the first composite oxide and the second composite oxide is identified by X-ray diffraction or Raman spectrum measurement.
本発明の排ガス浄化用触媒は、上述の複合酸化物（第一の複合酸化物及び第二の複合酸化物）を活性アルミナ等の金属酸化物（以下「金属酸化物担体」と称する）に担持したものでもよい。なお、少なくとも複合酸化物の一部が金属酸化物担体に担持していれば、複合酸化物と金属酸化物担体とが単に混合している部分が存在していてもよい。 The exhaust gas purifying catalyst of the present invention carries the above-mentioned composite oxide (first composite oxide and second composite oxide) on a metal oxide such as activated alumina (hereinafter referred to as “metal oxide support”). You may have done. In addition, as long as at least a part of the composite oxide is supported on the metal oxide support, a part where the composite oxide and the metal oxide support are simply mixed may exist.
金属酸化物担体の比表面積は、５０ｍ２／ｇ以上であることが好ましく、１００ｍ２／ｇ以上３５０ｍ２／ｇ以下であることがより好ましい。担体の比表面積が上記範囲にあると、充分な触媒活性を発揮させるために必要な量の複合酸化物が担持される。なお、比表面積は吸着等温線からＢＥＴ等温吸着式を用いてＢＥＴ比表面積として算出することができる。 The specific surface area of the metal oxide support is preferably 50 m 2 / g or more, and more preferably 100 m 2 / g or more and 350 m 2 / g or less. When the specific surface area of the support is within the above range, an amount of the complex oxide necessary for exhibiting sufficient catalytic activity is supported. The specific surface area can be calculated as a BET specific surface area from the adsorption isotherm using the BET isotherm adsorption formula.
このような金属酸化物担体としては、活性アルミナ、シリカアルミナ及びゼオライト等が挙げられ、活性アルミナの一種であるγ−アルミナが好適である。 Examples of such a metal oxide support include activated alumina, silica alumina, zeolite and the like, and γ-alumina which is a kind of activated alumina is preferable.
複合酸化物と金属酸化物担体とを含む排ガス浄化用触媒は、当業者に公知の任意の方法によって調製することができる。例えば、上記複合酸化物の調製において、原料物質の１つとしてγーアルミナ等の金属酸化物担体も更に添加した混合溶液を準備し、これを沈殿、共沈或いは加水分解させた後、得られた物質を加熱処理して調製することができる。 The exhaust gas-purifying catalyst containing the composite oxide and the metal oxide support can be prepared by any method known to those skilled in the art. For example, in the preparation of the composite oxide, it was obtained after preparing a mixed solution to which a metal oxide carrier such as γ-alumina was further added as one of the raw materials, and precipitating, co-precipitating or hydrolyzing it. The material can be prepared by heat treatment.
複合酸化物と金属酸化物担体とを含む排ガス浄化用触媒において、複合酸化物の含有比率は、第一の複合酸化物及び第二の複合酸化物ともに、５質量％以上８０質量％以下であることが好ましく、１０質量％以上５０質量％以下であることがより好ましく、１５質量％以上３０質量％以下であることが更に好ましい。
排ガス浄化用触媒中の複合酸化物の含有比率が上記範囲内にあると、充分な低温活性を示し、且つ触媒中での複合酸化物の分散性に優れる。
In the exhaust gas purifying catalyst including the composite oxide and the metal oxide support, the content ratio of the composite oxide is 5% by mass or more and 80% by mass or less for both the first composite oxide and the second composite oxide. It is preferably 10% by mass or more and 50% by mass or less, and more preferably 15% by mass or more and 30% by mass or less.
When the content ratio of the composite oxide in the exhaust gas purification catalyst is within the above range, sufficient low-temperature activity is exhibited and the dispersibility of the composite oxide in the catalyst is excellent.
更に、本発明の排ガス浄化用触媒には、白金、パラジウム、ロジウム、金及びイリジウムからなる群より選択される少なくとも１種の貴金属、又は鉄、コバルト、ニッケル、モリブデン、タングステン、バナジウム、チタン及びニオブからなる群より選択される少なくとも１種の金属を担持して用いられる。これらの貴金属又は金属は、酸化還元反応の活性点として機能する。
より高い触媒活性を示すという観点からは、白金、パラジウム、ロジウム、金及びイリジウムからなる群より選択される少なくとも１種の貴金属を担持することが好適である。
Further, the exhaust gas purifying catalyst of the present invention includes at least one noble metal selected from the group consisting of platinum, palladium, rhodium, gold and iridium, or iron, cobalt, nickel, molybdenum, tungsten, vanadium, titanium and niobium. And at least one metal selected from the group consisting of: These noble metals or metals function as active sites for redox reactions.
From the viewpoint of exhibiting higher catalytic activity, it is preferable to support at least one kind of noble metal selected from the group consisting of platinum, palladium, rhodium, gold and iridium.
上記貴金属又は金属は、上記複合酸化物を担体として担持される。また、複合酸化物と金属酸化物担体とを含む排ガス浄化用触媒の場合には、複合酸化物と金属酸化物担体の両者を担体として担持されていてもよい。このときの様子を図３に模式的に示すが、図３によって本発明は限定されない。 The noble metal or metal is supported using the composite oxide as a carrier. In the case of an exhaust gas purifying catalyst containing a composite oxide and a metal oxide support, both the composite oxide and the metal oxide support may be supported as a support. The state at this time is schematically shown in FIG. 3, but the present invention is not limited by FIG.
図３に示す排ガス浄化用触媒３０は、上流部１０と下流部１２を備える。上流部１０は、第一の複合酸化物２０と金属酸化物担体２２とを含有し、貴金属又は金属２４は、第一の複合酸化物２０と金属酸化物担体２２の両者を担体として担持されている。下流部１２は、第二の複合酸化物２１と金属酸化物担体２２とを含有し、貴金属又は金属２４は、第二の複合酸化物２１と金属酸化物担体２２の両者を担体として担持されている。
第一の複合酸化物２０は、第二の複合酸化物２１に比べてビスマスの含有量が多い複合酸化物である。
The exhaust gas purifying catalyst 30 shown in FIG. 3 includes an upstream portion 10 and a downstream portion 12. The upstream portion 10 includes a first composite oxide 20 and a metal oxide support 22, and the noble metal or metal 24 is supported by using both the first composite oxide 20 and the metal oxide support 22 as a support. Yes. The downstream portion 12 includes a second composite oxide 21 and a metal oxide support 22, and the noble metal or metal 24 is supported by using both the second composite oxide 21 and the metal oxide support 22 as a support. Yes.
The first composite oxide 20 is a composite oxide having a higher bismuth content than the second composite oxide 21.
上記貴金属又は金属２４の担持は、当業者に公知の任意の方法によって行うことができる。例えば白金を担持させる場合、白金源として白金の塩又は錯塩を用い、これを所定の濃度で含有する溶液（約１〜２０質量％）に複合酸化物を含む担体を浸漬させ、その後、乾燥（約５０〜２００℃で約１〜４８時間）及び焼成（４００〜７００℃で約１〜１２時間）等することによって行う。 The noble metal or the metal 24 can be supported by any method known to those skilled in the art. For example, when platinum is supported, a platinum salt or complex salt is used as a platinum source, and the support containing the composite oxide is immersed in a solution (about 1 to 20% by mass) containing this at a predetermined concentration, and then dried ( For about 1 to 48 hours at about 50 to 200 ° C.) and firing (about 1 to 12 hours at 400 to 700 ° C.).
上記貴金属又は金属の担持量は、本発明の排ガス浄化用触媒中、０．０５質量％以上１０質量％以下であることが好ましく、０．１質量％以上５質量％以下であることがより好ましい。
上記貴金属又は金属の担持量が上記範囲内にあると、これら貴金属又は金属によっても触媒活性が発揮され、且つ担持した貴金属又は金属の粒成長が抑えられる。
The amount of the noble metal or metal supported is preferably 0.05% by mass or more and 10% by mass or less, and more preferably 0.1% by mass or more and 5% by mass or less in the exhaust gas purifying catalyst of the present invention. .
When the amount of the noble metal or metal supported is within the above range, catalytic activity is exhibited by the noble metal or metal, and grain growth of the supported noble metal or metal is suppressed.
本発明の排ガス浄化用触媒は、得られた複合酸化物（金属酸化物担持体を含有する場合を含む）の粉末を圧縮・粉砕してペレット状にしたものや、該粉末に所定のバインダを加えてスラリー化し、これをコージェライト製ハニカム構造状基材等の触媒基材上に付与したものとして使用される。 The exhaust gas purifying catalyst of the present invention is obtained by compressing and pulverizing a powder of the obtained composite oxide (including a case of containing a metal oxide support) into a pellet, or a predetermined binder on the powder. In addition, it is used as a slurry, which is applied onto a catalyst substrate such as a cordierite honeycomb structure substrate.
ペレット状の排ガス浄化用触媒の場合には、ビスマスの含有量の異なる複合酸化物の粉末を準備し、それぞれを別個にペレット状に成形した上流部１０と下流部１２とを配置してもよい。 In the case of a pellet-shaped exhaust gas purifying catalyst, powders of complex oxides having different bismuth contents may be prepared, and an upstream portion 10 and a downstream portion 12 may be arranged, each formed into a pellet shape. .
前記触媒基材としては、モノリス状基材、ペレット状基材、プレート状基材等が好適に採用される。また、触媒基材の材質は特に制限されないが、コージェライト、炭化ケイ素、ムライト等のセラミックスからなる基材や、クロム及びアルミニウムを含むステンレススチール等の金属からなる基材が好適に採用される。 As said catalyst base material, a monolithic base material, a pellet-shaped base material, a plate-shaped base material etc. are employ | adopted suitably. The material of the catalyst substrate is not particularly limited, but a substrate made of ceramics such as cordierite, silicon carbide, mullite, or a substrate made of metal such as stainless steel including chromium and aluminum is preferably employed.
また触媒基材上に複合酸化物を付与して使用する場合、１つの触媒基材に第一の複合酸化物及び第二の複合酸化物を塗り分けて付与し上流部１０及び下流部１２としてもよいし、第一の複合酸化物を付与した触媒基材と第二の複合酸化物を付与した触媒基材を別個に準備して、これら触媒基材を上流側及び下流側にそれぞれ配置してもよい。 In addition, when the composite oxide is used on the catalyst base, the first composite oxide and the second composite oxide are separately applied to one catalyst base to provide the upstream part 10 and the downstream part 12. Alternatively, a catalyst base material provided with the first composite oxide and a catalyst base material provided with the second composite oxide are separately prepared, and these catalyst base materials are arranged on the upstream side and the downstream side, respectively. May be.
本発明の排ガス浄化用触媒では、ガス流方向の上流側で発熱反応させて触媒の暖機を図ることが望ましいため、図２に示すように、ガス流方向において上流側端部Ｔから５０％（排ガス浄化用触媒のガス流方向の長さをＬとしたときにＬ１／Ｌ×１００で表される数値をいう）までの間の少なくとも一部において、ビスマスを含有する第一の複合酸化物を含有する上流部１０とすることが好ましく、上流側端部Ｔから３０％までの間の少なくとも一部を上流部１０とすることがより好ましい。 In the exhaust gas purifying catalyst of the present invention, it is desirable to warm the catalyst by causing an exothermic reaction on the upstream side in the gas flow direction. Therefore, as shown in FIG. 2, 50% from the upstream end T in the gas flow direction. First composite oxide containing bismuth in at least part of the period up to (refers to a numerical value represented by L1 / L × 100, where L is the length in the gas flow direction of the exhaust gas purification catalyst) It is preferable to set it as the upstream part 10 containing, and it is more preferable to set at least a part between 30% from the upstream end T as the upstream part 10.
ガス流方向において、上流部１０と下流部１２の長さの比は、好適には１０：９０〜５０：５０であり、より好適には１０：９０〜３０：７０である。 In the gas flow direction, the ratio of the length of the upstream portion 10 and the downstream portion 12 is preferably 10:90 to 50:50, and more preferably 10:90 to 30:70.
本発明の排ガス浄化用触媒では、低温領域において優れた酸化性能と還元性能を示し、低温領域での酸化性能と還元性能の両立が図られる。よって、本発明の排ガス浄化用触媒は、ガソリン燃料を使用する自動車は勿論、アルコール混合燃料を使用するＦＦＶにおいても、優れた排ガス浄化作用を示す。 The exhaust gas purifying catalyst of the present invention exhibits excellent oxidation performance and reduction performance in a low temperature region, and achieves both oxidation performance and reduction performance in a low temperature region. Therefore, the exhaust gas purifying catalyst of the present invention exhibits an excellent exhaust gas purifying action not only in automobiles using gasoline fuel but also in FFVs using alcohol mixed fuel.
以下、本発明を実施例に基づいて更に詳細に説明するが、本発明はこれらの実施例に限定されるものではない。 EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited to these Examples.
＜第一の複合酸化物（Ｂｉ含有）を含む触媒の作製＞
硝酸セリウム７．８１ｇ、硝酸ジルコニウム１．２０ｇ、硝酸ビスマス２．７６ｇの水溶液に、γ−アルミナ２０ｇを加え、そこにクエン酸１１．５ｇの水溶液を攪拌しながら滴下した。次いで、８０℃で５時間攪拌した後、更に室温（２０℃）で２時間攪拌した。その後、水分をエバポレータで除去した後、８０℃で１２時間乾燥し、更に１０００℃で１時間焼成した。
得られた粉末に白金の含有率が２質量％となるように硝酸白金の水溶液を加え、室温で１時間攪拌した。次いで、水分をエバポレータで除去した後、１００℃で２時間乾燥し、更に５００℃で２時間焼成した。
<Preparation of catalyst containing first composite oxide (containing Bi)>
20 g of γ-alumina was added to an aqueous solution of 7.81 g of cerium nitrate, 1.20 g of zirconium nitrate, and 2.76 g of bismuth nitrate, and an aqueous solution of 11.5 g of citric acid was added dropwise thereto with stirring. Subsequently, after stirring at 80 degreeC for 5 hours, it stirred at room temperature (20 degreeC) for 2 hours further. Then, after removing water with an evaporator, it was dried at 80 ° C. for 12 hours, and further baked at 1000 ° C. for 1 hour.
An aqueous solution of platinum nitrate was added to the obtained powder so that the platinum content was 2% by mass, and the mixture was stirred at room temperature for 1 hour. Next, after removing water with an evaporator, the film was dried at 100 ° C. for 2 hours and further calcined at 500 ° C. for 2 hours.
得られた複合酸化物の組成をＸ線回折測定によって同定したところ、Ｃｅ０．６４Ｚｒ０．１６Ｂｉ０．２０Ｏ１．９であった。表２に触媒の組成を示す。 When the composition of the obtained composite oxide was identified by X-ray diffraction measurement, it was Ce 0.64 Zr 0.16 Bi 0.20 O 1.9 . Table 2 shows the composition of the catalyst.
＜第二の複合酸化物（Ｂｉ無し）を含む触媒の作製＞
硝酸セリウム９．７６ｇ、硝酸ジルコニウム１．５０ｇの水溶液に、γ−アルミナ２０ｇを加え、そこにクエン酸１１．５ｇの水溶液を攪拌しながら滴下した。次いで、８０℃で５時間攪拌した後、更に室温（２０℃）で２時間攪拌した。その後、水分をエバポレータで除去した後、８０℃で１２時間乾燥し、更に１０００℃で１時間焼成した。
得られた粉末に白金の含有率が２質量％となるように硝酸白金の水溶液を加え、室温で１時間攪拌した。次いで、水分をエバポレータで除去した後、１００℃で２時間乾燥し、更に５００℃で２時間焼成した。
<Preparation of catalyst containing second composite oxide (without Bi)>
20 g of γ-alumina was added to an aqueous solution of 9.76 g of cerium nitrate and 1.50 g of zirconium nitrate, and an aqueous solution of 11.5 g of citric acid was added dropwise thereto with stirring. Subsequently, after stirring at 80 degreeC for 5 hours, it stirred at room temperature (20 degreeC) for 2 hours further. Then, after removing water with an evaporator, it was dried at 80 ° C. for 12 hours, and further baked at 1000 ° C. for 1 hour.
An aqueous solution of platinum nitrate was added to the obtained powder so that the platinum content was 2% by mass, and the mixture was stirred at room temperature for 1 hour. Next, after removing water with an evaporator, the film was dried at 100 ° C. for 2 hours and further calcined at 500 ° C. for 2 hours.
得られた複合酸化物の組成をＸ線回折測定によって同定したところ、Ｃｅ０．８Ｚｒ０．２Ｏ２．０であった。表２に触媒の組成を示す。 When the composition of the obtained composite oxide was identified by X-ray diffraction measurement, it was Ce 0.8 Zr 0.2 O 2.0 . Table 2 shows the composition of the catalyst.
[実施例１、参考例１及び比較例１]
得られた複合酸化物触媒の粉末をペレット状に成形し、下記表３のように配置した。
[Example 1, Reference Example 1 and Comparative Example 1]
The obtained composite oxide catalyst powder was formed into pellets and arranged as shown in Table 3 below.
＜触媒活性の耐久試験＞
得られた触媒をＵ字型の石英管に装填し、下記に示す組成のモデルガスを１０Ｌ／分の流量で流通させながら、モデルガスの温度を室温（２０℃）から５００℃まで連続的に上昇させた。流通後のガス組成を市販の排ガス分析計によって連続的に測定し、その結果から触媒のＣＯ浄化率（％）及びＮＯｘ浄化率（％）を求めて触媒活性を評価した。ＮＯｘ浄化率（％）の結果を図４、５に示し、ＣＯ浄化率（％）の結果を図６、７に示す。なお、図５は、モデルガスの温度が５００℃のときのＮＯｘ浄化率（％）を表し、図７は、モデルガスの温度が１５０℃のときのＣＯ浄化率（％）を表す。
<Catalyst activity durability test>
The obtained catalyst was loaded into a U-shaped quartz tube, and the model gas temperature was continuously changed from room temperature (20 ° C.) to 500 ° C. while a model gas having the following composition was passed at a flow rate of 10 L / min. Raised. The gas composition after distribution was continuously measured with a commercially available exhaust gas analyzer, and the catalytic activity was evaluated by obtaining the CO purification rate (%) and NOx purification rate (%) of the catalyst from the results. The results of NOx purification rate (%) are shown in FIGS. 4 and 5, and the results of CO purification rate (%) are shown in FIGS. FIG. 5 shows the NOx purification rate (%) when the temperature of the model gas is 500 ° C., and FIG. 7 shows the CO purification rate (%) when the temperature of the model gas is 150 ° C.
−モデルガス組成−（容量％）
ＣＯ：１２００ｐｐｍ
Ｃ３Ｈ６：８００ｐｐｍ
ＮＯｘ：２４００ｐｐｍ
Ｏ２：０．３５％
ＣＯ２：１４％
Ｎ２：残部
-Model gas composition-(% by volume)
CO: 1200ppm
C 3 H 6 : 800 ppm
NOx: 2400ppm
O 2 : 0.35%
CO 2 : 14%
N 2 : remainder
図４、５に示すように、実施例１の触媒は、上流部及び下流部の双方にビスマスを含有する複合酸化物を用いた比較例１の触媒に比べて、格段にＮＯｘ浄化率が向上していることが分かる。下流部においてビスマスを含有する複合酸化物を用いた参考例１の触媒に比べても、ＮＯｘ浄化率が向上していた。
また、図６、７に示すように、実施例１の触媒は、比較例１の触媒に比べればＣＯ浄化率が低下しているが、ビスマスを含有する複合酸化物の体積は比較例１の触媒の半分であるにも拘らず、ＣＯ浄化率の低下は４割程度に抑えられていた（図７）。また、実施例１の触媒は参考例１の触媒に比べて、約１．２５倍のＣＯ浄化率を示した（図７）。
As shown in FIGS. 4 and 5, the catalyst of Example 1 has a significantly improved NOx purification rate compared to the catalyst of Comparative Example 1 using a composite oxide containing bismuth in both the upstream and downstream portions. You can see that Compared with the catalyst of Reference Example 1 using a composite oxide containing bismuth in the downstream portion, the NOx purification rate was improved.
6 and 7, the catalyst of Example 1 has a lower CO purification rate than the catalyst of Comparative Example 1, but the volume of the composite oxide containing bismuth is that of Comparative Example 1. Despite being half of the catalyst, the decrease in CO purification rate was suppressed to about 40% (FIG. 7). Moreover, the catalyst of Example 1 showed about 1.25 times the CO purification rate compared with the catalyst of Reference Example 1 (FIG. 7).
つまり、図４、５、６及び７に示されるように、ビスマスを含有する第一の複合酸化物のみを用いる比較例１では、ＣＯ浄化率には優れるがＮＯｘ浄化率が著しく低下していた。また、ビスマスを含有する第一の複合酸化物を下流側に設け、上流側にはビスマスを含有しない第二の複合酸化物を設けた参考例１では、ビスマスを含有する第一の複合酸化物を上流側に設け、下流側にビスマスを含有しない第二の複合酸化物を設けた実施例１に比較して、ＣＯ浄化率及びＮＯｘ浄化率の両者において共に劣っていた。
このように、本発明に該当する実施例１の触媒は、低温領域でのＣＯの酸化性能とＮＯｘの還元性能の両立が図られていた。
That is, as shown in FIGS. 4, 5, 6 and 7, in Comparative Example 1 using only the first composite oxide containing bismuth, the CO purification rate was excellent, but the NOx purification rate was significantly reduced. . Further, in Reference Example 1 in which the first composite oxide containing bismuth is provided on the downstream side and the second composite oxide not containing bismuth is provided on the upstream side, the first composite oxide containing bismuth is provided. Was inferior in both the CO purification rate and the NOx purification rate as compared with Example 1 in which the second composite oxide not containing bismuth was provided on the upstream side.
As described above, the catalyst of Example 1 corresponding to the present invention achieved both CO oxidation performance and NOx reduction performance in a low temperature region.
１ ビスマスを含有しない又は含有量の少ない複合酸化物
２ ビスマス含有量の多い複合酸化物
１０ 上流部
１２ 下流部
２０ 第一の複合酸化物
２１ 第二の複合酸化物
２２ 金属酸化物担体
２４ 貴金属又は金属
３０ 排ガス浄化用触媒
DESCRIPTION OF SYMBOLS 1 Composite oxide which does not contain bismuth or has low content 2 Composite oxide 10 with high bismuth content 10 Upstream portion 12 Downstream portion 20 First composite oxide 21 Second composite oxide 22 Metal oxide support 24 Noble metal or Metal 30 Exhaust gas purification catalyst
Claims (2)
前記第一の複合酸化物は、セリウム、ジルコニウム及びビスマスを含有する複合酸化物であり、
前記第二の複合酸化物は、少なくともセリウム及びジルコニウムを含有し、更にビスマスを含有する場合には第一の複合酸化物よりもビスマスの含有量が少ない複合酸化物である排ガス浄化用触媒。 The upstream portion in the exhaust gas flow direction has the first composite oxide, the downstream portion has the second composite oxide,
The first composite oxide is a composite oxide containing cerium, zirconium and bismuth,
The exhaust gas-purifying catalyst, wherein the second composite oxide contains at least cerium and zirconium, and further contains bismuth, has a lower bismuth content than the first composite oxide.
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