JP6639309B2 - Exhaust gas purification catalyst - Google Patents
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- JP6639309B2 JP6639309B2 JP2016075339A JP2016075339A JP6639309B2 JP 6639309 B2 JP6639309 B2 JP 6639309B2 JP 2016075339 A JP2016075339 A JP 2016075339A JP 2016075339 A JP2016075339 A JP 2016075339A JP 6639309 B2 JP6639309 B2 JP 6639309B2
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- 239000003054 catalyst Substances 0.000 title claims description 163
- 238000000746 purification Methods 0.000 title claims description 8
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 claims description 151
- 229910052763 palladium Inorganic materials 0.000 claims description 74
- 239000006104 solid solution Substances 0.000 claims description 18
- 239000007789 gas Substances 0.000 description 53
- 239000012298 atmosphere Substances 0.000 description 29
- 238000002441 X-ray diffraction Methods 0.000 description 17
- 238000004519 manufacturing process Methods 0.000 description 17
- 229910052751 metal Inorganic materials 0.000 description 17
- 239000002184 metal Substances 0.000 description 17
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 15
- 239000001301 oxygen Substances 0.000 description 15
- 229910052760 oxygen Inorganic materials 0.000 description 15
- 239000000843 powder Substances 0.000 description 15
- 238000001228 spectrum Methods 0.000 description 15
- 229910052777 Praseodymium Inorganic materials 0.000 description 11
- 239000002245 particle Substances 0.000 description 11
- PUDIUYLPXJFUGB-UHFFFAOYSA-N praseodymium atom Chemical compound [Pr] PUDIUYLPXJFUGB-UHFFFAOYSA-N 0.000 description 10
- 238000005245 sintering Methods 0.000 description 10
- 239000010410 layer Substances 0.000 description 9
- 230000001590 oxidative effect Effects 0.000 description 9
- 238000001354 calcination Methods 0.000 description 8
- 238000000034 method Methods 0.000 description 8
- 239000000243 solution Substances 0.000 description 8
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 6
- 238000004993 emission spectroscopy Methods 0.000 description 6
- 238000009616 inductively coupled plasma Methods 0.000 description 6
- 229910000510 noble metal Inorganic materials 0.000 description 6
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 5
- 239000007864 aqueous solution Substances 0.000 description 5
- 229910002091 carbon monoxide Inorganic materials 0.000 description 5
- 239000002131 composite material Substances 0.000 description 5
- 238000011156 evaluation Methods 0.000 description 5
- 239000000446 fuel Substances 0.000 description 5
- 238000010438 heat treatment Methods 0.000 description 5
- GPNDARIEYHPYAY-UHFFFAOYSA-N palladium(ii) nitrate Chemical compound [Pd+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O GPNDARIEYHPYAY-UHFFFAOYSA-N 0.000 description 5
- 239000011232 storage material Substances 0.000 description 5
- 239000000758 substrate Substances 0.000 description 5
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 4
- CETPSERCERDGAM-UHFFFAOYSA-N ceric oxide Chemical compound O=[Ce]=O CETPSERCERDGAM-UHFFFAOYSA-N 0.000 description 4
- 229910000422 cerium(IV) oxide Inorganic materials 0.000 description 4
- 230000008859 change Effects 0.000 description 4
- 239000013078 crystal Substances 0.000 description 4
- 239000000203 mixture Substances 0.000 description 4
- 238000012360 testing method Methods 0.000 description 4
- 239000000706 filtrate Substances 0.000 description 3
- 229910052757 nitrogen Inorganic materials 0.000 description 3
- 239000012299 nitrogen atmosphere Substances 0.000 description 3
- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitrogen oxide Inorganic materials O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 3
- 238000007254 oxidation reaction Methods 0.000 description 3
- 238000006722 reduction reaction Methods 0.000 description 3
- 238000001878 scanning electron micrograph Methods 0.000 description 3
- 239000002002 slurry Substances 0.000 description 3
- TWRXJAOTZQYOKJ-UHFFFAOYSA-L Magnesium chloride Chemical compound [Mg+2].[Cl-].[Cl-] TWRXJAOTZQYOKJ-UHFFFAOYSA-L 0.000 description 2
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
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- 239000006185 dispersion Substances 0.000 description 2
- 238000010304 firing Methods 0.000 description 2
- 229910052809 inorganic oxide Inorganic materials 0.000 description 2
- 239000011259 mixed solution Substances 0.000 description 2
- 150000002940 palladium Chemical class 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 230000002441 reversible effect Effects 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- 230000002776 aggregation Effects 0.000 description 1
- 238000004220 aggregation Methods 0.000 description 1
- 238000003915 air pollution Methods 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- QZPSXPBJTPJTSZ-UHFFFAOYSA-N aqua regia Chemical compound Cl.O[N+]([O-])=O QZPSXPBJTPJTSZ-UHFFFAOYSA-N 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 230000033228 biological regulation Effects 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 238000000975 co-precipitation Methods 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 229910052878 cordierite Inorganic materials 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 239000008367 deionised water Substances 0.000 description 1
- 229910021641 deionized water Inorganic materials 0.000 description 1
- JSKIRARMQDRGJZ-UHFFFAOYSA-N dimagnesium dioxido-bis[(1-oxido-3-oxo-2,4,6,8,9-pentaoxa-1,3-disila-5,7-dialuminabicyclo[3.3.1]nonan-7-yl)oxy]silane Chemical compound [Mg++].[Mg++].[O-][Si]([O-])(O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2)O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2 JSKIRARMQDRGJZ-UHFFFAOYSA-N 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 238000011068 loading method Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
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Classifications
-
- 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
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
- Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
Landscapes
- Exhaust Gas After Treatment (AREA)
- Exhaust Gas Treatment By Means Of Catalyst (AREA)
- Catalysts (AREA)
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.
従来から、自動車の排ガスを処理する排ガス浄化用触媒としては、セリアやアルミナ等の無機酸化物にパラジウム等の貴金属を担持させてなる三元触媒が広く使用されている。この三元触媒では、貴金属は、窒素酸化物の還元反応並びに一酸化炭素及び炭化水素の酸化反応を促進する役割を担っている。また、無機酸化物は、貴金属の比表面積を増大させると共に、反応による発熱を消散させて貴金属のシンタリングを抑制する役割を担っている。 2. Description of the Related Art Conventionally, a three-way catalyst in which a noble metal such as palladium is supported on an inorganic oxide such as ceria or alumina has been widely used as an exhaust gas purifying catalyst for treating automobile exhaust gas. In this three-way catalyst, the noble metal plays a role in promoting the reduction reaction of nitrogen oxides and the oxidation reaction of carbon monoxide and hydrocarbons. In addition, the inorganic oxide has a role of increasing the specific surface area of the noble metal, dissipating heat generated by the reaction, and suppressing sintering of the noble metal.
ところで、近年、自動車等の自動推進車両は、そのエンジン性能向上に伴い、高速で走行する機会が増えている。これに加え、大気汚染を防止すべく、排ガス規制の強化が進められている。このような背景のもと、自動推進車両の排ガス温度は益々高くなる傾向にある。従って、このような使用環境下でも十分な性能を発揮する排ガス浄化用触媒を実現すべく、研究開発が盛んに行われている。 By the way, in recent years, the opportunity of running at high speeds has increased in an auto-propelled vehicle such as an automobile with the improvement of the engine performance. In addition, regulations on exhaust gas are being strengthened to prevent air pollution. Against this background, the temperature of exhaust gas from self-propelled vehicles tends to increase. Therefore, research and development are being actively conducted to realize an exhaust gas purifying catalyst that exhibits sufficient performance even in such a use environment.
例えば、特許文献１は、パラジウム含有率が０．０５〜７重量％であり、Ｐｒ／（Ｚｒ＋Ｐｒ）原子比が０．０５〜０．６の範囲であるＺｒαＰｒβＰｄγＯ2-δ固溶体（α＋β＋γ＝１．０００であり、δは電荷中性条件を満たすように定まる値である）からなる排ガス浄化用触媒を開示する。この触媒は、以下のとおり製造される。ＺｒＯ2−Ｐｒ6Ｏ11の固溶体結晶上にＰｄＯ及び／又はＰｄＯ2を担持させ、その後、ＰｄＯ及び／又はＰｄＯ2の金属パラジウムへの還元が進行しない条件で熱処理する。これにより、Ｐｄ4+がＺｒＯ2−Ｐｒ6Ｏ11の固溶体結晶中に取り込まれ、ＺｒαＰｒβＰｄγＯ2-δ固溶体が形成される。 For example, Patent Document 1, palladium content of from 0.05 to 7 wt%, Pr / (Zr + Pr ) atomic ratio is in the range of 0.05~0.6 Zr α Pr β Pd γ O 2-δ Disclosed is an exhaust gas purifying catalyst comprising a solid solution (α + β + γ = 1.000, and δ is a value determined so as to satisfy a charge neutrality condition). This catalyst is produced as follows. PdO and / or PdO 2 is supported on the solid solution crystal of ZrO 2 —Pr 6 O 11 , and then heat-treated under the condition that reduction of PdO and / or PdO 2 to palladium metal does not proceed. As a result, Pd 4+ is incorporated into the solid solution crystal of ZrO 2 —Pr 6 O 11 , and a Zr α Pr β Pd γ O 2-δ solid solution is formed.
パラジウムなどの貴金属を含んだ排ガス浄化用触媒は、高温であり且つ燃料リッチの排ガスが供給された場合に、貴金属のシンタリングを生じ易い。 Exhaust gas purifying catalysts containing a noble metal such as palladium tend to cause sintering of the noble metal when a high temperature and fuel-rich exhaust gas is supplied.
そこで、本発明は、パラジウムのシンタリングに起因した性能の劣化を生じ難い排ガス浄化用触媒を提供することを目的とする。 Therefore, an object of the present invention is to provide an exhaust gas purifying catalyst that is unlikely to cause performance deterioration due to palladium sintering.
本発明の一側面によると、Ｐｒ6Ｏ11からなる担体と、前記担体に担持されたパラジウムとを含む排ガス浄化用触媒であって、前記排ガス浄化用触媒は、前記パラジウムの前記担体への固溶率が８０％以上である排ガス浄化用触媒が提供される。 According to one aspect of the present invention, there is provided an exhaust gas purifying catalyst including a carrier made of Pr 6 O 11 and palladium supported on the carrier, wherein the exhaust gas purifying catalyst is a catalyst for fixing the palladium to the carrier. An exhaust gas purifying catalyst having a solubility of 80% or more is provided.
本発明によると、パラジウムのシンタリングに起因した性能の劣化を生じ難い排ガス浄化用触媒が提供される According to the present invention, there is provided an exhaust gas purifying catalyst which is unlikely to cause performance deterioration due to palladium sintering.
以下、本発明の態様について、図面を参照しながら詳細に説明する。なお、同様又は類似した機能を発揮する構成要素には全ての図面を通じて同一の参照符号を付し、重複する説明は省略する。 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that components that perform the same or similar functions are denoted by the same reference numerals throughout all the drawings, and redundant description will be omitted.
図１は、本発明の一態様に係る排ガス浄化用触媒を概略的に示す斜視図である。図２は、図１に示す排ガス浄化用触媒の一部を拡大して示す断面図である。図３は、図１に示す排ガス浄化用触媒に含まれる担持触媒が燃料リーンな高温雰囲気（酸化性雰囲気）中で呈する状態を概略的に示す断面図である。図４は、図１に示す排ガス浄化用触媒に含まれる担持触媒が燃料リッチな高温雰囲気（還元性雰囲気）中で呈する状態を概略的に示す断面図である。 FIG. 1 is a perspective view schematically showing an exhaust gas purifying catalyst according to one embodiment of the present invention. FIG. 2 is an enlarged sectional view showing a part of the exhaust gas purifying catalyst shown in FIG. FIG. 3 is a cross-sectional view schematically showing a state in which a supported catalyst included in the exhaust gas purifying catalyst shown in FIG. 1 is presented in a fuel-lean high-temperature atmosphere (oxidizing atmosphere). FIG. 4 is a cross-sectional view schematically showing a state in which a supported catalyst included in the exhaust gas purifying catalyst shown in FIG. 1 is presented in a fuel-rich high-temperature atmosphere (reducing atmosphere).
図１及び図２に示す排ガス浄化用触媒１は、モノリス触媒である。この排ガス浄化用触媒１は、モノリスハニカム基材などの基材２を含んでいる。基材２は、典型的には、コージェライトなどのセラミックス製である。 The exhaust gas purifying catalyst 1 shown in FIGS. 1 and 2 is a monolithic catalyst. The exhaust gas purifying catalyst 1 includes a substrate 2 such as a monolith honeycomb substrate. The substrate 2 is typically made of a ceramic such as cordierite.
基材２の隔壁上には、触媒層３が形成されている。触媒層３は、担持触媒３０を含み、担持触媒３０は、図３及び図４に示す担体３１及び触媒金属３２を含んでいる。担体３１は、Ｐｒ6Ｏ11からなり、触媒金属３２は、パラジウムである。 The catalyst layer 3 is formed on the partition wall of the substrate 2. The catalyst layer 3 includes a supported catalyst 30, and the supported catalyst 30 includes a support 31 and a catalyst metal 32 illustrated in FIGS. The support 31 is made of Pr 6 O 11 , and the catalyst metal 32 is palladium.
担体３１は、例えば、粒子の形態で存在している。この場合、担体３１の平均粒径は、例えば０．５乃至１００μｍの範囲内にあり、典型的には、１乃至２０μｍの範囲内にある。なお、この「平均粒径」は、以下の方法によって得られる値を意味している。 The carrier 31 exists, for example, in the form of particles. In this case, the average particle size of the carrier 31 is, for example, in the range of 0.5 to 100 μm, and typically in the range of 1 to 20 μm. The "average particle size" means a value obtained by the following method.
まず、排ガス浄化用触媒１から触媒層３の一部を除去する。次に、走査電子顕微鏡（ＳＥＭ）を用いて、この試料のＳＥＭ像を、２５００倍乃至５００００倍の範囲内の倍率で撮影する。ＳＥＭ像の撮影は、２５視野について行う。次いで、各ＳＥＭ像に写っている担体３１の中から、全体が見えている粒子を無作為に４つ選択し、選択した各粒子の面積を求める。これら面積と等しい面積を有している円の直径をそれぞれ算出し、更に、これら直径の算術平均を求める。この算術平均を平均粒径とする。なお、この平均粒径の標準偏差は１５μｍ以下である。 First, a part of the catalyst layer 3 is removed from the exhaust gas-purifying catalyst 1. Next, using a scanning electron microscope (SEM), an SEM image of this sample is taken at a magnification in the range of 2500 to 50,000 times. SEM images are taken for 25 fields of view. Next, from the carrier 31 shown in each SEM image, four particles which are entirely visible are randomly selected, and the area of each selected particle is obtained. The diameters of the circles having the same area are calculated, and the arithmetic average of these diameters is obtained. The arithmetic average is defined as the average particle size. The standard deviation of the average particle size is 15 μm or less.
担体３１は、触媒金属３２の比表面積を増大させると共に、反応による発熱を消散させて触媒金属３２のシンタリングを抑制する役割を担っている。なお、担体３１が果たす他の役割については、後で詳しく説明する。 The carrier 31 has a role of increasing the specific surface area of the catalyst metal 32 and dissipating heat generated by the reaction to suppress sintering of the catalyst metal 32. The other role played by the carrier 31 will be described later in detail.
排ガス浄化用触媒１は、触媒金属３２であるパラジウムの担体３１への固溶率が８０％以上であり、典型的には８０％乃至１００％であり、好ましくは９０％乃至１００％であり、更に好ましくは９５乃至１００％である。 The exhaust gas purifying catalyst 1 has a solid solution rate of the catalyst metal 32 of palladium in the carrier 31 of 80% or more, typically 80% to 100%, and preferably 90% to 100%. More preferably, it is 95 to 100%.
排ガス浄化用触媒１を、酸化性雰囲気中（例えば、大気雰囲気中）において高温（例えば、１０５０℃で１時間）で加熱すると、加熱処理直後の触媒において、触媒金属３２であるパラジウムの少なくとも一部は、担体３１に固溶している（図３参照）。このとき、パラジウムの少なくとも一部は酸化されている（酸化数が増大している）可能性がある。 When the exhaust gas-purifying catalyst 1 is heated at a high temperature (for example, at 1050 ° C. for 1 hour) in an oxidizing atmosphere (for example, in an air atmosphere), at least a part of the catalyst metal 32, palladium, Is dissolved in the carrier 31 (see FIG. 3). At this time, at least a part of the palladium may have been oxidized (the oxidation number has increased).
一方、排ガス浄化用触媒１を、還元性雰囲気中（例えば、１０体積％の一酸化炭素を含む窒素雰囲気中）において高温（例えば、１０００℃で１０時間）で加熱すると、加熱処理直後の触媒において、触媒金属３２であるパラジウムの少なくとも一部は、担体３１に担持されている（図４参照）。 On the other hand, when the exhaust gas purifying catalyst 1 is heated at a high temperature (for example, at 1000 ° C. for 10 hours) in a reducing atmosphere (for example, in a nitrogen atmosphere containing 10% by volume of carbon monoxide), At least a part of the palladium as the catalyst metal 32 is supported on the carrier 31 (see FIG. 4).
パラジウムが担体３１に固溶しているとは、パラジウムが、担体３１を構成しているＰｒ6Ｏ11の結晶格子中に侵入または置換することにより、パラジウムとＰｒ6Ｏ11とが固溶体を形成していることを意味する。また、パラジウムが担体３１に担持されているとは、パラジウムが担体３１に固溶することなく、その表面に保持されていること、例えば、パラジウムが担体３１に物理的に担持されていることを意味する。なお、物理的担持とは、Ｐｒ6Ｏ11をパラジウム塩水溶液に分散させた後、分散液を加熱すること（後述の乾燥や焼成など）によりＰｒ6Ｏ11にパラジウムを保持させることである。 The fact that palladium is dissolved in the carrier 31 means that palladium penetrates or substitutes in the crystal lattice of Pr 6 O 11 constituting the carrier 31, whereby palladium and Pr 6 O 11 form a solid solution. Means you are. Further, that palladium is supported on the carrier 31 means that palladium is not dissolved in the carrier 31 and is held on the surface thereof, for example, that palladium is physically supported on the carrier 31. means. The physical loading means that after dispersing Pr 6 O 11 in an aqueous solution of palladium salt, the dispersion is heated (drying or baking described later, etc.) so that the palladium is retained on Pr 6 O 11 .
本明細書において、パラジウムの担体３１への固溶率は、パラジウムの総質量（すなわち、担体３１に担持されているパラジウムと担体３１に固溶しているパラジウムとの合計質量）に対する、担体３１に固溶しているパラジウムの質量％を意味する。また、本明細書において、パラジウムの担体３１への固溶率は、製造直後の排ガス浄化用触媒１について得られる値である。製造直後の排ガス浄化用触媒１は、上述のとおり、８０％以上の固溶率、好ましくは９０％以上の固溶率、更に好ましくは９５％以上の固溶率を有する。固溶率が８０％より低いと、担持されているパラジウムの凝集（シンタリング）が生じ易くなる。 In the present specification, the solid solution rate of palladium in the carrier 31 is expressed by the total mass of palladium (that is, the total mass of palladium carried on the carrier 31 and palladium dissolved in the carrier 31). % Of palladium dissolved in the solid solution. In this specification, the solid solution rate of palladium in the carrier 31 is a value obtained for the exhaust gas-purifying catalyst 1 immediately after production. As described above, the exhaust gas purifying catalyst 1 immediately after production has a solid solution rate of 80% or more, preferably 90% or more, and more preferably 95% or more. When the solid solution rate is lower than 80%, aggregation (sintering) of the supported palladium tends to occur.
パラジウムの担体３１への固溶率は、ＩＣＰ発光分光分析法（高周波誘導結合プラズマ発光分光分析法）を用いて求めることができる。具体的には、所定の質量の担持触媒３０を、触媒中の全パラジウムが可溶である溶液に浸漬し、得られた溶液をＩＣＰ発光分光分析法により測定する。これにより、触媒に含まれる全パラジウムの質量を算出する。一方、所定の質量の担持触媒３０を、パラジウムが不溶であり、かつ担体３１を構成するＰｒ6Ｏ11が可溶である溶液に浸漬し、この溶液を濾過し、濾液をＩＣＰ発光分光分析法により測定する。これにより、濾液に含有されるパラジウムの質量を算出する。得られた２つの算出値から、パラジウムの固溶率を算出する。 The solid solution rate of palladium in the carrier 31 can be determined using ICP emission spectroscopy (high-frequency inductively coupled plasma emission spectroscopy). Specifically, a supported catalyst 30 having a predetermined mass is immersed in a solution in which all palladium in the catalyst is soluble, and the obtained solution is measured by ICP emission spectroscopy. Thus, the mass of all palladium contained in the catalyst is calculated. On the other hand, a supported catalyst 30 having a predetermined mass is immersed in a solution in which palladium is insoluble and Pr 6 O 11 constituting the carrier 31 is soluble, the solution is filtered, and the filtrate is subjected to ICP emission spectroscopy. Measured by Thereby, the mass of palladium contained in the filtrate is calculated. From the two calculated values obtained, the solid solution rate of palladium is calculated.
また、排ガス浄化用触媒１は、Ｘ線回折スペクトルについて以下の特性を有する。 Further, the exhaust gas purifying catalyst 1 has the following characteristics with respect to the X-ray diffraction spectrum.
排ガス浄化用触媒１を、還元性雰囲気中（即ち、１０体積％の一酸化炭素を含む窒素雰囲気中）、１０００℃で１０時間に亘って加熱し、加熱処理直後の排ガス浄化用触媒１についてＸ線回折スペクトル１を得る。また、排ガス浄化用触媒１を、酸化性雰囲気中（即ち、大気雰囲気中）、１０５０℃で１時間に亘って加熱し、加熱処理直後の排ガス浄化用触媒１についてＸ線回折スペクトル２を得る。Ｘ線回折スペクトル１では、Ｐｒ6Ｏ11に対応するピーク（２θ＝２８．２５°）が存在する。Ｘ線回折スペクトル２では、Ｐｒ6Ｏ11の結晶格子中に含まれるパラジウムの量に応じて、Ｐｒ6Ｏ11に対応するピーク（２θ＝２８．２５°）が高角度側にシフトする。典型的には、Ｘ線回折スペクトル２では、Ｐｒ6Ｏ11に対応するピーク（２θ＝２８．２５°）が高角度側に０．４°〜３．８°シフトし、結果として、２８．６５°〜３２．０５°の範囲にピークが存在する。Ｘ線回折スペクトル２で、Ｐｒ6Ｏ11に対応するピーク（２θ＝２８．２５°）が高角度側に０．４°〜３．８°シフトするということは、パラジウムが、担体３１を構成するＰｒ6Ｏ11に対して０．８８〜８質量％の量で担体３１に固溶していることを示す。 The exhaust gas-purifying catalyst 1 was heated at 1000 ° C. for 10 hours in a reducing atmosphere (ie, in a nitrogen atmosphere containing 10% by volume of carbon monoxide). A line diffraction spectrum 1 is obtained. Further, the exhaust gas-purifying catalyst 1 is heated in an oxidizing atmosphere (that is, in an air atmosphere) at 1050 ° C. for 1 hour, and an X-ray diffraction spectrum 2 is obtained for the exhaust gas-purifying catalyst 1 immediately after the heat treatment. In X-ray diffraction spectrum 1, there is a peak (2θ = 28.25 °) corresponding to Pr 6 O 11 . In the X-ray diffraction spectrum 2, depending on the amount of palladium contained in the crystal lattice of Pr 6 O 11, peaks corresponding to Pr 6 O 11 (2θ = 28.25 °) are shifted to a higher angle side. Typically, in X-ray diffraction spectrum 2, the peak corresponding to Pr 6 O 11 (2θ = 28.25 °) is shifted to the higher angle side by 0.4 ° to 3.8 °, and as a result, 28. There is a peak in the range of 65 ° to 32.05 °. In the X-ray diffraction spectrum 2, the peak (2θ = 28.25 °) corresponding to Pr 6 O 11 is shifted to the higher angle side by 0.4 ° to 3.8 °, which means that palladium constitutes the carrier 31. It shows that it is dissolved in the carrier 31 in an amount of 0.88 to 8% by mass with respect to Pr 6 O 11 .
担体３１の質量と触媒金属３２の質量との合計に占める触媒金属３２の質量の割合は、例えば１乃至１０質量％の範囲内にあり、典型的には１乃至３質量％の範囲内にある。この質量比を小さくすると、高い排ガス浄化性能を達成するためには、より多量の担体３１が必要となり、それ故、排ガス浄化用触媒１の熱容量が増大する。この質量比を大きくすると、触媒金属３２のシンタリングを生じ易くなる。 The ratio of the mass of the catalyst metal 32 to the sum of the mass of the carrier 31 and the mass of the catalyst metal 32 is, for example, in the range of 1 to 10% by mass, and typically in the range of 1 to 3% by mass. . If this mass ratio is reduced, a larger amount of the carrier 31 is required to achieve high exhaust gas purification performance, and therefore, the heat capacity of the exhaust gas purification catalyst 1 increases. When this mass ratio is increased, sintering of the catalyst metal 32 is likely to occur.
触媒金属３２の質量と排ガス浄化用触媒１の容積との比は、例えば０．１乃至２０ｇ／Ｌの範囲内にあり、典型的には１乃至１０ｇ／Ｌの範囲内にある。この比が小さい場合、高い排ガス浄化性能を達成することが難しい。この比を大きくすると、排ガス浄化用触媒１の原料コストが増大する。 The ratio of the mass of the catalyst metal 32 to the volume of the exhaust gas purifying catalyst 1 is, for example, in the range of 0.1 to 20 g / L, and typically in the range of 1 to 10 g / L. If this ratio is small, it is difficult to achieve high exhaust gas purification performance. When this ratio is increased, the raw material cost of the exhaust gas purifying catalyst 1 increases.
なお、ここで触媒金属３２について言及した数値は、酸化性雰囲気中で高温に加熱した直後の排ガス浄化用触媒１について得られる値である。 Here, the numerical values mentioned for the catalytic metal 32 are values obtained for the exhaust gas purifying catalyst 1 immediately after being heated to a high temperature in an oxidizing atmosphere.
触媒層３は、他の成分を更に含むことができる。例えば、触媒層３は、酸素貯蔵材料を更に含んでいてもよい。 The catalyst layer 3 can further include other components. For example, the catalyst layer 3 may further include an oxygen storage material.
酸素貯蔵材料は、酸素過剰条件下で酸素を吸蔵し、酸素希薄条件下で酸素を放出して、ＨＣ及びＣＯの酸化反応並びにＮＯxの還元反応を最適化する。酸素貯蔵材料は、例えば粒子の形態にある。 Oxygen storage material, the oxygen storing oxygen in excess conditions, and releases oxygen in an oxygen lean conditions, to optimize the reduction reaction of the oxidation reactions and NO x of HC and CO. The oxygen storage material is, for example, in the form of particles.
酸素貯蔵材料は、例えば、セリア、セリアと他の金属酸化物との複合酸化物、又はそれらの混合物である。複合酸化物としては、例えば、セリアとジルコニアとの複合酸化物を使用することができる。 The oxygen storage material is, for example, ceria, a composite oxide of ceria and another metal oxide, or a mixture thereof. As the composite oxide, for example, a composite oxide of ceria and zirconia can be used.
この排ガス浄化用触媒１は、高温条件下で以下に説明する状態変化を生じる。
図３は、高温条件下で高酸素濃度雰囲気に晒した場合、例えばエンジンへの燃料供給を停止した場合に排ガス浄化用触媒１に含まれる担持触媒３０が呈する状態を示している。他方、図４は、高温条件下で低酸素濃度雰囲気に晒した場合、例えばエンジンに多量の燃料を供給し続けている場合に排ガス浄化用触媒１に含まれる担持触媒３０が呈する状態を示している。なお、以下の説明において、触媒金属３２はパラジウムであるとする。
The exhaust gas purifying catalyst 1 undergoes a state change described below under a high temperature condition.
FIG. 3 shows a state where the supported catalyst 30 included in the exhaust gas purifying catalyst 1 exhibits when exposed to a high oxygen concentration atmosphere under a high temperature condition, for example, when fuel supply to the engine is stopped. On the other hand, FIG. 4 shows a state where the supported catalyst 30 included in the exhaust gas purifying catalyst 1 exhibits when exposed to a low oxygen concentration atmosphere under high temperature conditions, for example, when a large amount of fuel is continuously supplied to the engine. I have. In the following description, it is assumed that the catalyst metal 32 is palladium.
図３に示す状態において、パラジウムは、主に、担体３１に固溶している。なお、図３では、図示されるパラジウムの全てが担体３１に固溶しているが、パラジウムの一部が担体３１に担持されていてもよい。また、この状態において、パラジウムの少なくとも一部は酸化されている可能性がある。 In the state shown in FIG. 3, palladium is mainly dissolved in the carrier 31. In FIG. 3, all of the illustrated palladium is dissolved in the carrier 31, but a part of the palladium may be supported on the carrier 31. In this state, at least a part of palladium may be oxidized.
高温条件下で雰囲気中の酸素濃度が低くなると、排ガス浄化用触媒１に含まれる担持触媒層３０は、図３に示す状態から図４に示す状態へと変化する。具体的には、担体３１からパラジウムが析出し、析出したパラジウムは担体３１に担持される。なお、図４では、図示されるパラジウムの全てが担体３１に担持されているが、パラジウムの一部が担体３１に固溶していてもよい。 When the oxygen concentration in the atmosphere decreases under high temperature conditions, the supported catalyst layer 30 included in the exhaust gas purifying catalyst 1 changes from the state shown in FIG. 3 to the state shown in FIG. Specifically, palladium is precipitated from the carrier 31, and the deposited palladium is supported on the carrier 31. In FIG. 4, all of the illustrated palladium is supported on the carrier 31, but a part of the palladium may be dissolved in the carrier 31.
そして、高温条件下で雰囲気中の酸素濃度が再び高くなると、排ガス浄化用触媒１に含まれる担持触媒３０は、図４に示す状態から図３に示す状態へと変化する。具体的には、担体３１に担持されているパラジウムの少なくとも一部は担体３１へと固溶する。 Then, when the oxygen concentration in the atmosphere increases again under high temperature conditions, the supported catalyst 30 included in the exhaust gas purifying catalyst 1 changes from the state shown in FIG. 4 to the state shown in FIG. Specifically, at least a part of the palladium supported on the carrier 31 is dissolved in the carrier 31.
このように、排ガス浄化用触媒１に含まれる担持触媒３０は、高温条件下において、雰囲気中の酸素濃度の変化に伴って可逆的な変化を生じる。 As described above, the supported catalyst 30 included in the exhaust gas-purifying catalyst 1 undergoes a reversible change with a change in the oxygen concentration in the atmosphere under a high temperature condition.
このような可逆的な変化が起こることにより、触媒金属３２であるパラジウムのシンタリングを長期間に亘って抑制することができる。即ち、排ガス浄化用触媒１は、パラジウムのシンタリングに起因した性能の劣化を生じ難い。 When such a reversible change occurs, sintering of palladium as the catalyst metal 32 can be suppressed for a long period of time. That is, the exhaust gas purifying catalyst 1 is unlikely to cause performance degradation due to palladium sintering.
排ガス浄化用触媒１は、例えば、以下の方法により製造する。
まず、担体３１を準備する。担体３１は、市販品を購入してもよいし、共沈法等の公知の方法により調製してもよい。
The exhaust gas purifying catalyst 1 is manufactured, for example, by the following method.
First, the carrier 31 is prepared. The carrier 31 may be purchased commercially or may be prepared by a known method such as a coprecipitation method.
担体３１を構成するＰｒ6Ｏ11は、複合酸化物と比べて単純な組成を有している。このため、担体３１の準備に関する煩雑さがなく、担体３１の組成が原子レベルで均一であるという利点を有する。 Pr 6 O 11 constituting the carrier 31 has a simpler composition than the composite oxide. Therefore, there is an advantage that the preparation of the carrier 31 is not complicated and the composition of the carrier 31 is uniform at the atomic level.
準備された担体３１を脱イオン水中に分散させる。続いて、この分散液に、パラジウム塩溶液を添加して、担体３１にパラジウムを吸着させる。その後、これを乾燥させ、更に酸化性雰囲気中で焼成する。焼成は、例えば約１０００℃乃至約１１００℃の範囲内の温度で、例えば１〜５時間で行うことができる。焼成温度が１０００℃より低いと、製造直後におけるパラジウムの担体３１への固溶率が低下する傾向がある。また、焼成温度が１１００℃より高いと、パラジウムが、担体３１に担持されず、担体３１を構成するＰｒ6Ｏ11と複合酸化物（Ｐｒ4ＰｄＯ7）を形成し易くなる。以上のようにして、担体３１とこれに担持された触媒金属３２とを含んだ担持触媒３０を得る。 The prepared carrier 31 is dispersed in deionized water. Subsequently, a palladium salt solution is added to the dispersion to allow the carrier 31 to adsorb palladium. Thereafter, it is dried and further fired in an oxidizing atmosphere. The calcination can be performed, for example, at a temperature in the range of about 1000 ° C. to about 1100 ° C., for example, for 1 to 5 hours. If the firing temperature is lower than 1000 ° C., the solid solution rate of palladium in the carrier 31 immediately after production tends to decrease. On the other hand, if the firing temperature is higher than 1100 ° C., palladium is not supported on the carrier 31 and it is easy to form a composite oxide (Pr 4 PdO 7 ) with Pr 6 O 11 constituting the carrier 31. As described above, the supported catalyst 30 including the carrier 31 and the catalyst metal 32 supported on the carrier 31 is obtained.
その後、この担持触媒３０を含んだスラリーを調製する。このスラリーには、必要に応じて、他の成分、例えば酸素貯蔵材料を添加する。次いで、このスラリーを基材２にコートし、更に塗膜の乾燥及び焼成を行う。以上のようにして、排ガス浄化用触媒１を完成する。 Thereafter, a slurry containing the supported catalyst 30 is prepared. If necessary, other components such as an oxygen storage material are added to the slurry. Next, this slurry is coated on the substrate 2, and the coating film is further dried and fired. As described above, the exhaust gas purifying catalyst 1 is completed.
なお、ここで説明した排ガス浄化用触媒１において、触媒層３は単層構造を有しているが、触媒層３は多層構造を有していてもよい。また、ここでは、モノリス触媒について説明したが、上述した技術はペレット触媒に適用することも可能である。 In the exhaust gas purifying catalyst 1 described here, the catalyst layer 3 has a single layer structure, but the catalyst layer 3 may have a multilayer structure. Further, here, the monolith catalyst has been described, but the above-described technique can be applied to a pellet catalyst.
以下に、本発明の例を記載する。
排ガス浄化用触媒を、以下の方法により製造した。
Hereinafter, examples of the present invention will be described.
An exhaust gas purifying catalyst was produced by the following method.
＜触媒Ａの製造＞
４８．５ｇのプラセオジム系酸化物Ｉ（Ｐｒ6Ｏ11＝１００（質量％））と、３０ｇの硝酸パラジウム水溶液（５質量％のパラジウムを含む）とを、２００ｍＬのイオン交換水に添加し、この混合液を６０分間撹拌した。次いで、この混合液を１１０℃で乾燥させ、大気雰囲気中、１０００℃で１時間に亘って焼成して、５０ｇ（パラジウム含量：１．５ｇ）の粉末を得た。このようにして得られた粉末を「触媒Ａ」と呼ぶ。
<Production of catalyst A>
48.5 g of praseodymium-based oxide I (Pr 6 O 11 = 100 (% by mass)) and 30 g of palladium nitrate aqueous solution (containing 5% by mass of palladium) were added to 200 mL of ion-exchanged water. The mixture was stirred for 60 minutes. Next, this mixed solution was dried at 110 ° C., and calcined at 1000 ° C. for 1 hour in an air atmosphere to obtain 50 g (palladium content: 1.5 g) of powder. The powder thus obtained is referred to as "catalyst A".
＜触媒Ｂの製造＞
焼成を１０００℃で行う代わりに８００℃で行ったこと以外は、触媒Ａについて上述したのと同様の方法により粉末を得た。以下、この触媒を「触媒Ｂ」と呼ぶ。
<Production of catalyst B>
A powder was obtained in the same manner as described above for Catalyst A, except that calcination was performed at 800 ° C instead of at 1000 ° C. Hereinafter, this catalyst is referred to as “catalyst B”.
＜触媒Ｃの製造＞
焼成を１０００℃で行う代わりに９００℃で行ったこと以外は、触媒Ａについて上述したのと同様の方法により粉末を得た。以下、この触媒を「触媒Ｃ」と呼ぶ。
<Production of catalyst C>
A powder was obtained in the same manner as described above for Catalyst A, except that calcination was performed at 900 ° C. instead of at 1000 ° C. Hereinafter, this catalyst is referred to as “catalyst C”.
＜触媒Ｄの製造＞
焼成を１０００℃で行う代わりに１１００℃で行ったこと以外は、触媒Ａについて上述したのと同様の方法により粉末を得た。以下、この触媒を「触媒Ｄ」と呼ぶ。
<Production of catalyst D>
A powder was obtained in the same manner as described above for Catalyst A, except that calcination was performed at 1100 ° C instead of at 1000 ° C. Hereinafter, this catalyst is referred to as “catalyst D”.
＜触媒Ｅの製造＞
焼成を１０００℃で行う代わりに１２００℃で行ったこと以外は、触媒Ａについて上述したのと同様の方法により粉末を得た。以下、この触媒を「触媒Ｅ」と呼ぶ。
<Production of catalyst E>
A powder was obtained in the same manner as described above for Catalyst A, except that calcination was performed at 1200 ° C. instead of at 1000 ° C. Hereinafter, this catalyst is referred to as “catalyst E”.
＜触媒Ｆの製造＞
焼成を１０００℃で行う代わりに１０５０℃で行ったこと以外は、触媒Ａについて上述したのと同様の方法により粉末を得た。以下、この触媒を「触媒Ｆ」と呼ぶ。
<Production of catalyst F>
A powder was obtained in the same manner as described above for Catalyst A, except that calcination was performed at 1050 ° C instead of at 1000 ° C. Hereinafter, this catalyst is referred to as “catalyst F”.
＜触媒Ｇの製造＞
プラセオジム系酸化物Ｉ（Ｐｒ6Ｏ11＝１００（質量％））の代わりにプラセオジム系酸化物II（Ｐｒ6Ｏ11／ＺｒＯ2＝８０／２０（質量％））を使用したこと以外は、触媒Ａについて上述したのと同様の方法により粉末を得た。以下、この触媒を「触媒Ｇ」と呼ぶ。
<Production of catalyst G>
Except that the praseodymium-based oxide I (Pr 6 O 11 = 100 (% by mass)) was replaced by the praseodymium-based oxide II (Pr 6 O 11 / ZrO 2 = 80/20 (% by mass)), A powder was obtained in the same manner as described above for A. Hereinafter, this catalyst is referred to as “catalyst G”.
＜触媒Ｈの製造＞
プラセオジム系酸化物Ｉ（Ｐｒ6Ｏ11＝１００（質量％））の代わりにプラセオジム系酸化物III（Ｐｒ6Ｏ11／Ａｌ2Ｏ3＝７０／３０（質量％））を使用したこと以外は、触媒Ａについて上述したのと同様の方法により粉末を得た。以下、この触媒を「触媒Ｈ」と呼ぶ。
<Production of catalyst H>
Except that praseodymium-based oxide III (Pr 6 O 11 / Al 2 O 3 = 70/30 (% by mass)) was used instead of praseodymium-based oxide I (Pr 6 O 11 = 100 (% by mass)) A powder was obtained in the same manner as described above for Catalyst A. Hereinafter, this catalyst is referred to as “catalyst H”.
＜触媒Ｉの製造＞
３０ｇの硝酸パラジウム溶液（５質量％のパラジウムを含む）の代わりに１０ｇの硝酸パラジウム水溶液（５質量％のパラジウムを含む）を使用したこと以外は、触媒Ａについて上述したのと同様の方法により粉末を得た。以下、この触媒を「触媒Ｉ」と呼ぶ。
<Production of catalyst I>
The powder was prepared in the same manner as described above for Catalyst A, except that an aqueous solution of 10 g of palladium nitrate (containing 5% by mass of palladium) was used instead of the solution of 30 g of palladium nitrate (containing 5% by mass of palladium). I got Hereinafter, this catalyst is referred to as “catalyst I”.
＜触媒Ｊの製造＞
３０ｇの硝酸パラジウム溶液（５質量％のパラジウムを含む）の代わりに１００ｇの硝酸パラジウム水溶液（５質量％のパラジウムを含む）を使用したこと以外は、触媒Ａについて上述したのと同様の方法により粉末を得た。以下、この触媒を「触媒Ｊ」と呼ぶ。
<Production of catalyst J>
The powder was prepared in the same manner as described above for Catalyst A, except that 100 g of an aqueous solution of palladium nitrate (containing 5% by mass of palladium) was used instead of 30 g of palladium nitrate solution (containing 5% by mass of palladium). I got Hereinafter, this catalyst is referred to as “catalyst J”.
＜触媒Ｋの製造＞
焼成を１０００℃で行う代わりに５００℃で行ったこと以外は、触媒Ａについて上述したのと同様の方法により粉末を得た。以下、この触媒を「触媒Ｋ」と呼ぶ。
<Production of catalyst K>
A powder was obtained in the same manner as described above for Catalyst A, except that calcination was performed at 500 ° C instead of at 1000 ° C. Hereinafter, this catalyst is referred to as “catalyst K”.
＜評価１：固溶率＞
触媒Ａ乃至Ｋについて、パラジウムのプラセオジム系酸化物への固溶率を以下の方法により調べた。
<Evaluation 1: Solid solution rate>
For the catalysts A to K, the solid solubility of palladium in the praseodymium-based oxide was examined by the following method.
製造直後の各触媒について、触媒に含まれる全パラジウムの質量を以下のとおり求めた。
触媒の一部を、フッ化水素酸、王水の混合液に溶解した。なお、この条件は、触媒（粉末）の全量が溶解する条件である。得られた溶液中のパラジウムを、高周波誘導結合プラズマ（ＩＣＰ）発光分析法により定量分析した。この分析結果から触媒（粉末）に含まれる全パラジウムの質量を算出した。
For each catalyst immediately after the production, the mass of all palladium contained in the catalyst was determined as follows.
A part of the catalyst was dissolved in a mixed solution of hydrofluoric acid and aqua regia. This condition is a condition under which the entire amount of the catalyst (powder) is dissolved. Palladium in the obtained solution was quantitatively analyzed by high frequency inductively coupled plasma (ICP) emission spectrometry. From this analysis result, the mass of all palladium contained in the catalyst (powder) was calculated.
また、製造直後の各触媒について、プラセオジム系酸化物に固溶しているパラジウムの質量を以下のとおり求めた。
触媒の一部を、７質量％のフッ酸水溶液に溶解し、室温で２０時間放置した。その後、得られた溶液を０．１μφのフィルターで濾過した。なお、この条件は、プラセオジム系酸化物のみが溶解する条件である。濾液に溶解したパラジウムを、高周波誘導結合プラズマ（ＩＣＰ）発光分析法により定量分析した。この分析結果からプラセオジム系酸化物に固溶しているパラジウムの質量を算出した。
Further, for each catalyst immediately after production, the mass of palladium dissolved in the praseodymium-based oxide was determined as follows.
A part of the catalyst was dissolved in a 7% by mass aqueous solution of hydrofluoric acid and left at room temperature for 20 hours. Thereafter, the obtained solution was filtered with a 0.1 μφ filter. Note that this condition is a condition under which only the praseodymium-based oxide dissolves. Palladium dissolved in the filtrate was quantitatively analyzed by high frequency inductively coupled plasma (ICP) emission spectrometry. From this analysis result, the mass of palladium dissolved in the praseodymium-based oxide was calculated.
これらの結果から、パラジウムのプラセオジム系酸化物への固溶率を算出した。 From these results, the solid solubility of palladium in the praseodymium-based oxide was calculated.
＜評価２：パラジウム粒径＞
触媒Ａ乃至Ｋの耐久性を以下の方法により調べた。
まず、触媒Ａ乃至Ｋの各々を流通式の耐久試験装置内に設置し、触媒床に窒素を主成分としたガスを１００ｍＬ／分の流量で２０時間流通させた。この間、触媒床温度は１０００℃に維持した。また、触媒床に流通させるガスとしては、窒素に酸素を５％加えてなるリーンガスと、窒素に一酸化炭素を１０％加えてなるリッチガスとを使用し、これらガスは５分毎に切り替えた。この耐久試験は、触媒床に最後に流通させるガスがリッチガスとなるように行った。
<Evaluation 2: Palladium particle size>
The durability of the catalysts A to K was examined by the following method.
First, each of the catalysts A to K was placed in a flow-type durability test apparatus, and a gas containing nitrogen as a main component was passed through the catalyst bed at a flow rate of 100 mL / min for 20 hours. During this time, the catalyst bed temperature was maintained at 1000 ° C. Further, as a gas to be passed through the catalyst bed, a lean gas obtained by adding 5% of oxygen to nitrogen and a rich gas obtained by adding 10% of carbon monoxide to nitrogen were used, and these gases were switched every 5 minutes. This durability test was performed so that the gas finally passed through the catalyst bed was a rich gas.
耐久試験後の触媒（粉末）に対し、Ｘ線回折測定（Rigaku RINT-2500）を行った。得られたＸ線回折スペクトルより、２θ＝８２°付近のピークに基づいてパラジウム粒径を算出した。 The catalyst (powder) after the durability test was subjected to X-ray diffraction measurement (Rigaku RINT-2500). From the obtained X-ray diffraction spectrum, the palladium particle size was calculated based on the peak near 2θ = 82 °.
＜評価３：Ｘ線回折スペクトル＞
触媒Ａの一部を、還元性雰囲気中で熱処理した。具体的には、１０体積％の一酸化炭素を含む窒素雰囲気中、１０００℃で１０時間に亘って熱処理を行った。還元性雰囲気中で熱処理した直後の触媒Ａに対し、Ｘ線回折測定（Rigaku RINT-2500）を行い、Ｘ線回折スペクトル１を得た。
<Evaluation 3: X-ray diffraction spectrum>
A portion of Catalyst A was heat treated in a reducing atmosphere. Specifically, heat treatment was performed at 1000 ° C. for 10 hours in a nitrogen atmosphere containing 10% by volume of carbon monoxide. An X-ray diffraction measurement (Rigaku RINT-2500) was performed on the catalyst A immediately after the heat treatment in a reducing atmosphere, and an X-ray diffraction spectrum 1 was obtained.
また、触媒Ａの一部を、酸化性雰囲気中で熱処理した。具体的には、大気雰囲気中、１０５０℃で１時間に亘って熱処理を行った。酸化性雰囲気中で熱処理した直後の触媒Ａに対し、Ｘ線回折測定（Rigaku RINT-2500）を行い、Ｘ線回折スペクトル２を得た。 A part of the catalyst A was heat-treated in an oxidizing atmosphere. Specifically, heat treatment was performed at 1050 ° C. for one hour in an air atmosphere. An X-ray diffraction measurement (Rigaku RINT-2500) was performed on the catalyst A immediately after the heat treatment in an oxidizing atmosphere, and an X-ray diffraction spectrum 2 was obtained.
＜結果＞
評価１及び２の結果を以下の表１に示し、評価３の結果を図５に示す。
<Result>
The results of Evaluations 1 and 2 are shown in Table 1 below, and the results of Evaluation 3 are shown in FIG.
表１に示されるとおり、担体としてＰｒ6Ｏ11を使用し、かつ、パラジウムの担体への固溶率が８０％以上である場合に、耐久試験後のパラジウム粒径がとりわけ小さかった。したがって、かかる触媒（触媒Ａ、Ｄ、Ｆ、Ｉ及びＪ）は、パラジウムのシンタリングに起因した性能の劣化を生じ難いという効果を奏する。また、表１より、かかる触媒は、触媒製造時の焼成を、１０００℃〜１１００℃の温度で１時間行うことにより得られることが分かる。 As shown in Table 1, when Pr 6 O 11 was used as the carrier and the solid solution ratio of palladium to the carrier was 80% or more, the particle size of palladium after the durability test was particularly small. Therefore, such catalysts (catalysts A, D, F, I and J) have an effect that the performance is hardly deteriorated due to the sintering of palladium. Also, from Table 1, it can be seen that such a catalyst can be obtained by performing calcination during the production of the catalyst at a temperature of 1000 ° C to 1100 ° C for 1 hour.
図５より、Ｘ線回折スペクトル１では、Ｐｒ6Ｏ11に対応するピーク（２θ＝２８．２５°）が見られた。Ｘ線回折スペクトル２では、２９．４０°にピークが見られ、Ｘ線回折スペクトル１で見られたＰｒ6Ｏ11に対応するピーク（２θ＝２８．２５°）が、高角度側に１．１５°シフトしていた。この結果は、パラジウムが、Ｐｒ6Ｏ11に対して２．４３質量％の量でＰｒ6Ｏ11に固溶していることを示す。 5, in X-ray diffraction spectrum 1, a peak (2θ = 28.25 °) corresponding to Pr 6 O 11 was observed. In the X-ray diffraction spectrum 2, a peak is observed at 29.40 °, and the peak (2θ = 28.25 °) corresponding to Pr 6 O 11 observed in the X-ray diffraction spectrum 1 is 1.10 on the high angle side. Had been shifted by 15 °. This result indicates that the palladium is in solid solution in the Pr 6 O 11 in an amount of 2.43 wt% relative to the Pr 6 O 11.
１…排ガス浄化用触媒、２…基材、３…触媒層、３０…担持触媒、３１…担体、３２…触媒金属。 DESCRIPTION OF SYMBOLS 1 ... Exhaust gas purification catalyst, 2 ... Base material, 3 ... Catalyst layer, 30 ... Supported catalyst, 31 ... Carrier, 32 ... Catalyst metal.
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