WO2015087781A1 - 排ガス浄化用触媒 - Google Patents
排ガス浄化用触媒 Download PDFInfo
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- WO2015087781A1 WO2015087781A1 PCT/JP2014/082148 JP2014082148W WO2015087781A1 WO 2015087781 A1 WO2015087781 A1 WO 2015087781A1 JP 2014082148 W JP2014082148 W JP 2014082148W WO 2015087781 A1 WO2015087781 A1 WO 2015087781A1
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- Prior art keywords
- crystallite
- oxide
- catalyst
- exhaust gas
- crystallites
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- 239000003054 catalyst Substances 0.000 title claims abstract description 142
- 229910000510 noble metal Inorganic materials 0.000 claims abstract description 59
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- 238000010438 heat treatment Methods 0.000 claims abstract description 5
- VSZWPYCFIRKVQL-UHFFFAOYSA-N selanylidenegallium;selenium Chemical compound [Se].[Se]=[Ga].[Se]=[Ga] VSZWPYCFIRKVQL-UHFFFAOYSA-N 0.000 claims abstract description 3
- 238000000746 purification Methods 0.000 claims description 28
- 238000002485 combustion reaction Methods 0.000 claims description 9
- 229910052727 yttrium Inorganic materials 0.000 claims description 3
- VWQVUPCCIRVNHF-UHFFFAOYSA-N yttrium atom Chemical compound [Y] VWQVUPCCIRVNHF-UHFFFAOYSA-N 0.000 claims description 3
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- 230000033228 biological regulation Effects 0.000 description 2
- ZCCIPPOKBCJFDN-UHFFFAOYSA-N calcium nitrate Chemical compound [Ca+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O ZCCIPPOKBCJFDN-UHFFFAOYSA-N 0.000 description 2
- CETPSERCERDGAM-UHFFFAOYSA-N ceric oxide Chemical compound O=[Ce]=O CETPSERCERDGAM-UHFFFAOYSA-N 0.000 description 2
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- 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
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- B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
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- B01D2255/00—Catalysts
- B01D2255/20—Metals or compounds thereof
- B01D2255/206—Rare earth metals
- B01D2255/2061—Yttrium
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2255/00—Catalysts
- B01D2255/20—Metals or compounds thereof
- B01D2255/206—Rare earth metals
- B01D2255/2063—Lanthanum
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2255/00—Catalysts
- B01D2255/20—Metals or compounds thereof
- B01D2255/206—Rare earth metals
- B01D2255/2065—Cerium
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2255/00—Catalysts
- B01D2255/20—Metals or compounds thereof
- B01D2255/206—Rare earth metals
- B01D2255/2068—Neodymium
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2255/00—Catalysts
- B01D2255/20—Metals or compounds thereof
- B01D2255/207—Transition metals
- B01D2255/20715—Zirconium
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2255/00—Catalysts
- B01D2255/40—Mixed oxides
- B01D2255/407—Zr-Ce mixed oxides
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2255/00—Catalysts
- B01D2255/90—Physical characteristics of catalysts
- B01D2255/908—O2-storage component incorporated in the catalyst
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2255/00—Catalysts
- B01D2255/90—Physical characteristics of catalysts
- B01D2255/92—Dimensions
- B01D2255/9202—Linear dimensions
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2255/00—Catalysts
- B01D2255/90—Physical characteristics of catalysts
- B01D2255/92—Dimensions
- B01D2255/9207—Specific surface
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J2523/00—Constitutive chemical elements of heterogeneous catalysts
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
- F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
- F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
- F01N3/24—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by constructional aspects of converting apparatus
- F01N3/28—Construction of catalytic reactors
- F01N3/2803—Construction of catalytic reactors characterised by structure, by material or by manufacturing of catalyst support
- F01N3/2825—Ceramics
- F01N3/2828—Ceramic multi-channel monoliths, e.g. honeycombs
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/10—Internal combustion engine [ICE] based vehicles
- Y02T10/12—Improving ICE efficiencies
Definitions
- the present invention relates to an exhaust gas purifying catalyst provided in an exhaust system of an internal combustion engine. Note that this international application claims priority based on Japanese Patent Application No. 2013-254479 filed on December 9, 2013, the entire contents of which are incorporated herein by reference. ing.
- a three-way catalyst that can simultaneously reduce x is used.
- a porous support made of a metal oxide such as alumina (Al 2 O 3 ), a noble metal (PGM) belonging to a platinum group such as platinum (Pt), rhodium (Rh), and palladium (Pd). The thing which carried
- supported is used.
- CZ complex oxide a complex oxide mainly composed of ceria (CeO 2 ) and zirconia (ZrO 2 ) has been conventionally used as the OSC material.
- CZ complex oxide a complex oxide mainly composed of ceria (CeO 2 ) and zirconia (ZrO 2 )
- Patent Document 1 discloses a CZ composite oxide in which the solubility of zirconium oxide in cerium oxide is 50% or more, and the average diameter of crystallites constituting the particles of the CZ composite oxide is 100 nm or less.
- An example of a conventional exhaust gas purifying catalyst provided with an OSC material made of a CZ composite oxide characterized by the above is disclosed.
- Patent Document 2 listed below introduces a method for producing CZ composite oxide particles, which are CZ composite oxides used as OSC materials and have a crystallite diameter of about 10 nm.
- one of the weak points of the CZ composite oxide used as the OSC material is low heat resistance. That is, in the particles (primary particles) made of the conventional CZ composite oxide, crystal growth of the crystallites constituting the particles is likely to occur at a high temperature (for example, during an endurance test), and accordingly, the particles are made of the CZ composite oxide. Aggregation of the noble metal supported on the OSC material also proceeds, and as a result, there is a risk of reducing the active sites. Therefore, improving the heat resistance of the CZ composite oxide used as the OSC material, more specifically, suppressing the crystal growth of the crystallites constituting the CZ composite oxide particles, aggregating noble metals and lowering the OSC function. There is a demand for improvement in heat resistance that can suppress the above.
- the present inventor mixed two kinds of crystallites having different crystal structures (more specifically, different lattice constants) in order to suppress crystal growth of the crystallites constituting the CZ composite oxide particles.
- by mixing two kinds of crystallites having different crystal structures from each other different crystallites can serve as a barrier to prevent crystal growth, and noble metal aggregation and OSC function can be prevented. The decrease can be suppressed.
- the present invention aims to further improve the catalyst performance in an exhaust gas purifying catalyst in which two kinds of crystallites having different crystal structures are mixed.
- the inventor supports a noble metal on a crystallite having a lower Ce content, and contains Ce. It has been found that the catalyst performance can be further improved by not supporting the noble metal on the crystallite having a higher rate, and the present invention has been completed.
- the exhaust gas purifying catalyst disclosed herein includes oxide particles in which crystallites A on which noble metals are supported and crystallites B on which noble metals are not supported are mixed.
- the crystallite A on which the noble metal is supported is made of an oxide containing at least one of zirconium (Zr) and cerium (Ce), and the crystallite B on which the noble metal is not supported is cerium (Ce). It is an oxide containing,
- the Ce content rate (mol%) in this oxide consists of an oxide whose content rate (mol%) in the oxide of the said crystallite A is higher.
- the configuration of the present invention by including what consists of oxide particles in which crystallite A and crystallite B are mixed, crystal growth is suppressed even when used under high temperature conditions such as a thermal endurance test, Aggregation of the noble metal composed of PGM supported on the crystallite A can be suppressed.
- the noble metal is supported on the crystallite A having a lower Ce content, and the noble metal is not supported on the crystallite B having a higher Ce content, thereby maintaining a good metal state of the noble metal and having a high OSC function. Can be demonstrated. Therefore, according to the present invention, it is possible to provide a high-performance exhaust gas purification catalyst in which the three-way performance of the three-way catalyst is further improved.
- the specific surface area after heat treatment in air for 5 hours 30 m 2 / g or more. Since crystal growth can be suppressed even when used under high temperature conditions, such a high specific surface area can be maintained, and high catalytic ability (typically ternary performance) can be maintained. Further, by maintaining such a high specific surface area, more crystallites A supporting noble metal are arranged around the crystallites B not supporting the noble metal, and the distance between the crystallite B and the noble metal becomes closer. The OSC function of the crystallite B is better expressed. Therefore, it is possible to provide a high-performance exhaust gas purification catalyst capable of exhibiting a high OSC function even though the noble metal is not supported on the crystallite B.
- the Ce content contained in the oxide constituting the crystallite A is 0 to 30 mol% of the whole oxide in terms of oxide, and the crystal The Ce content contained in the oxide constituting the child B is 35 to 99 mol% of the whole oxide in terms of oxide. According to this configuration, particularly high crystal growth suppressing ability and OSC function (and hence ternary performance) can be exhibited.
- the crystallite A is made of an oxide containing yttrium (Y) together with Zr. According to the crystallite A made of an oxide containing such a metal component, higher crystal growth suppressing ability can be exhibited.
- the crystallite B is made of an oxide containing Zr together with Ce. According to the crystallite B made of an oxide containing such a metal component, higher crystal growth suppressing ability and OSC function can be exhibited.
- the crystallite A and the crystallite B are in a highly dispersed state, typically 10 or more of the same type of crystallite in both A and B under observation with an electron microscope. It is characterized by being mixed in the oxide particles in a highly dispersed state so as not to be in contact with each other.
- “more than ten crystallites of the same kind do not exist in contact with each other” means other crystals existing around the crystallites selected arbitrarily in an electron microscope observation (typically a TEM image).
- TEM image electron microscope observation
- FIG. 1 is a perspective view schematically showing an example of an exhaust gas purifying catalyst.
- FIG. 2 is a diagram schematically illustrating a main part of the catalyst layer according to the embodiment.
- FIG. 3 is a graph showing the relationship between the specific surface area of the powder and the NOx 50% purification temperature.
- FIG. 4 is a graph showing the relationship between the number of continuous contacts and the NOx 50% purification temperature.
- FIG. 5 is a graph showing the relationship between the Ce content and the NOx 50% purification temperature.
- crystallite refers to the largest collection (particles) of basic structures that consist of a series of continuous crystal lattices and can be regarded as a single crystal.
- the properties of the crystallites can be examined by performing, for example, XRD (X-ray diffraction) measurement and Rietveld analysis. Further, the existence state of the crystallite can be clarified by observation with an electron microscope (typically, TEM). Further, elemental analysis and composition analysis of the target crystallite can be performed by combining electron microscope observation and EDX (energy dispersive X-ray spectroscopy) (for example, TEM-EDX).
- EDX energy dispersive X-ray spectroscopy
- the exhaust gas-purifying catalyst disclosed herein is provided with at least a part of the catalyst layer with oxide particles composed of the above-described two different crystallites (A and B) mixed (dispersed).
- the exhaust gas purifying catalyst characterized by the above, and other configurations are not particularly limited.
- the catalyst is used as an exhaust gas purification catalyst disposed in an exhaust pipe of an internal combustion engine as a three-way catalyst, and is a base material and a catalyst layer formed on the base material, and is an oxidation catalyst and / or a reduction catalyst. And a catalyst layer containing the above-mentioned oxide particles.
- the exhaust gas-purifying catalyst disclosed herein is selected from various types of precious metals, oxide particles, and base materials, which will be described later, and formed into a desired shape according to the application, thereby various internal combustion engines, particularly automobile gasoline engines. It can arrange in the exhaust system (exhaust pipe). In the following description, it is assumed that the exhaust gas purifying catalyst of the present invention is mainly applied to a three-way catalyst provided in the exhaust pipe of an automobile gasoline engine. It is not intended to be limited to the embodiments described below.
- the exhaust gas purifying catalyst disclosed herein is installed in the exhaust pipe, various materials and forms conventionally used for this type of application can be adopted as the base material constituting the catalyst skeleton.
- a cordierite having high heat resistance, a ceramic such as silicon carbide (SiC), or a base material made of an alloy (such as stainless steel) can be used.
- the shape may be the same as that of a conventional exhaust gas purification catalyst.
- the exhaust gas purification catalyst 10 shown in FIG. 1 is a honeycomb substrate 1 having a cylindrical outer shape, and through holes (cells) 2 serving as exhaust gas passages are provided in the cylinder axis direction.
- the thing which exhaust gas can contact the partition (rib wall) 4 which divides the cell 2 is mentioned.
- the shape of the substrate 1 can be a foam shape, a pellet shape, or the like in addition to the honeycomb shape. Moreover, about the external shape of the whole base material, it may replace with a cylindrical shape and may employ
- the catalyst layer formed on the substrate is the main component of this type of exhaust gas purification catalyst as a place for purifying exhaust gas, and typically, as shown in FIG. It is comprised from the oxide particle in which the crystallite A with which the noble metal particle is carry
- a catalyst layer having a predetermined thickness and porosity is formed on the rib walls 4 constituting the cells of the substrate 1.
- the catalyst layer as a whole may be composed of a single layer having substantially the same configuration, or may be a layered structure type catalyst layer formed on the substrate 1 and having two or more different upper and lower layers or three or more layers. .
- the noble metal 20 provided in the catalyst layer of the exhaust gas purifying catalyst disclosed herein may employ various metal species that can function as an oxidation catalyst or a reduction catalyst.
- rhodium which is PGM
- Platinum Pt
- palladium Pd
- Ruthenium Ru
- osmium Os
- Ir iridium
- silver Au
- Cu copper
- An alloy of two or more of these noble metals may be used. Alternatively, it may be one containing other metal species (typically an alloy).
- Rh having a high reduction activity and Pd or Pt having a high oxidation activity in order to construct a three-way catalyst.
- Such noble metal is preferably used as fine particles having a sufficiently small particle diameter from the viewpoint of increasing the contact area with the exhaust gas.
- the average particle diameter of the metal particles is about 1 to 15 nm, particularly 10 nm or less, 7 nm or less, and further 5 nm or less. preferable.
- the supporting rate of the noble metal 20 (the noble metal content when the carrier is 100% by mass) is preferably 5% by mass or less, more preferably 3% by mass or less. For example, it is preferably 0.05% by mass or more and 5% by mass or less, and more preferably 0.1% by mass or more and 3% by mass or less.
- the loading rate is too smaller than the above range, the catalytic effect of the metal is difficult to obtain. If the loading rate is too much higher than the above range, there is a risk that the metal grain growth proceeds, which is also disadvantageous in terms of cost.
- the oxide particles disclosed herein are composed of a mixture of a crystallite A carrying the noble metal 20 (that is, used as a carrier) and a crystallite B not carrying the noble metal 20. Oxide particles. Oxide particles containing such different crystallites A and B are provided upstream and / or downstream in the exhaust gas flow direction in the catalyst layer.
- the crystallite A on which the noble metal is supported is composed of an oxide containing at least one of Zr and Ce.
- the crystallite B on which noble metal is not supported is an oxide containing Ce, and the Ce content (mol%) in the oxide is higher than the content (mol%) in the oxide of the crystallite A. Is also composed of a high oxide.
- crystal growth is suppressed even after heat treatment in air at 1150 ° C. for 5 hours, typically 30 m 2 / g or more (particularly preferably A high specific surface area of 35 m 2 / g or more, particularly preferably 40 m 2 / g or more.
- the noble metal is supported on the crystallite A having a lower Ce content, and the noble metal is not supported on the crystallite B having a higher Ce content, thereby maintaining a good metal state of the noble metal and having a high OSC function. Can be demonstrated.
- the crystallite A and the crystallite B have different crystal structures, more specifically, different lattice constants from each other, so that the different crystallites can serve as a barrier to prevent crystal growth at high temperatures.
- ⁇ Crystallite A> when the crystallite A (A and B are only symbols for classification) on which the noble metal 20 is supported is mainly composed of Zr, the other element is Ce, and one or two of the other elements.
- the above rare earth elements such as yttrium (Y), lanthanum (La), neodymium (Nd), praseodymium (Pr), samarium (Sm), europium (Eu), etc.
- alkaline earth elements such as.
- a suitable example is a crystallite A composed of a composite oxide having a Zr content of 75 to 99 mol% in terms of oxide and a small amount of Y (for example, 5 mol% or less, or 10 mol% or less). It is done. Further, it is mainly composed of Zr, and the Ce content is 30 mol% or less (preferably 20 mol% or less, more preferably 10 mol% or less, for example 0 mol% (that is, including Ce) in terms of oxide. There is a preferred example of the crystallite A comprising an oxide.
- the crystallite B on which the noble metal 20 is not supported needs only to contain Ce at a higher rate than the crystallite A, and other elements include Zr and other one or more rare earth elements (La , Y, Nd, Pr, Sm, Eu, etc.).
- a crystallite B made of an oxide having a Ce content of 35 to 99 mol% in terms of oxide and containing a small amount of La is preferable.
- the average size of the crystallites A and B may be the same as that constituting an OSC material (for example, a CZ composite oxide) used for a conventional exhaust gas purification catalyst, and is typically 2 in an electron microscope observation such as TEM.
- the thickness is about 100 to 100 nm, preferably about 5 to 50 nm.
- the oxide particles composed of the crystallite A and the crystallite B having different crystal structures (lattice constants) as described above may contain various compounds (typically constituent metals) so as to include elements constituting the crystallite A in advance.
- a precursor (non-fired product) A prepared from a metal salt containing an element, such as a salt of Zr, Ce, or a rare earth element, such as a nitrate, ammonium salt, or phosphate salt, is similarly composed of a crystallite B in advance.
- a precursor (non-calcined product) B prepared from various compounds (typically various metal salts) so as to contain an element to be mixed with an appropriate oxidizing agent such as various organic acids and hydrogen peroxide. And calcining under oxidizing conditions (typically in the atmosphere).
- an appropriate oxidizing agent such as various organic acids and hydrogen peroxide.
- This manufacturing method includes a step (crystallite A precursor preparation step) in which a coprecipitate is precipitated from an aqueous solution containing a constituent element of crystallite A to obtain a crystallite A precursor.
- the solvent (aqueous solvent) constituting the aqueous solution is typically water, and may be a mixed solvent containing water as a main component.
- an aqueous solution containing a compound capable of supplying Ce ions, Zr ions and the like in an aqueous solvent may be used.
- the aqueous solution is heated to 80 ° C. to 100 ° C. (preferably 90 ° C.
- the crystallite A precursor preparation step may include a process of supporting a noble metal on the crystallite A precursor.
- a noble metal may be added under the condition of pH 12 or higher so that the noble metal is supported on the crystallite A precursor.
- the production method disclosed herein can be preferably carried out in such a manner that a noble metal is supported on the unsintered crystallite A precursor.
- this manufacturing method includes a step (crystallite B precursor preparation step) in which a coprecipitate is precipitated from an aqueous solution containing the constituent element of crystallite B to obtain a crystallite B precursor.
- the solvent (aqueous solvent) constituting the aqueous solution is typically water, and may be a mixed solvent containing water as a main component.
- an aqueous solution containing a compound that can supply Ce ions or the like in an aqueous solvent may be used.
- the aqueous solution is heated to 80 ° C. to 100 ° C. (preferably 90 ° C.
- the pH can be adjusted by supplying an alkaline agent (a compound having a function of tilting liquidity to alkaline, such as urea) to the aqueous solution.
- an alkaline agent a compound having a function of tilting liquidity to alkaline, such as urea
- the crystallite A precursor and the crystallite B precursor thus produced are mixed to prepare a mixed slurry (slurry preparation step).
- a mixed slurry typically, the crystallite A precursor and the crystallite B precursor are added to water, and an organic acid and hydrogen peroxide solution are added and stirred to obtain a mixed slurry.
- the organic acid for example, malonic acid can be preferably used.
- the production method disclosed herein can be preferably implemented in an embodiment using such an organic acid and hydrogen peroxide solution.
- the slurry preparation step may include a process of stirring the mixed slurry and then stirring with a disperser (for example, a homogenizer). The heating temperature can be set to 75 ° C. to 90 ° C.
- the stirring time may be a time until the mixed slurry is uniformly mixed, for example, 5 minutes or more (for example, 5 minutes to 120 minutes), preferably 15 minutes or more, more preferably 30 minutes or more, and further preferably It can be set to 60 minutes or more. Within such a stirring time range, oxide particles having a smaller number of contacts between the crystallites A and B can be obtained.
- ⁇ Baking process> After stirring the mixed slurry as described above, it is washed and dried. And the oxide particle which consists of a crystallite A and a crystallite B is obtained by baking this mixture (baking process).
- This firing step is preferably performed in the atmosphere or in an atmosphere richer in oxygen than in the atmosphere.
- the maximum firing temperature is determined in the range of 700 ° C. or more and 900 ° C. or less in the air atmosphere.
- the firing time can be set to 3 to 8 hours, for example. In this way, oxide particles composed of crystallite A and crystallite B can be obtained.
- the catalyst layer of the exhaust gas-purifying catalyst disclosed herein may include one or more carriers in addition to the oxide particles composed of different crystallites A and B.
- a porous carrier made of an inorganic compound having a specific surface area (referred to as a specific surface area measured by the BET method; hereinafter the same) is suitably used.
- Suitable supports include, for example, alumina (Al 2 O 3 ), ceria (CeO 2 ), zirconia (ZrO 2 ), silica (SiO 2 ), titania (TiO 2 ), and solid solutions thereof (eg, ceria-zirconia composites).
- ceramics such as alumina and zirconia having good heat resistance are supported or non-supported (noble metal). May be included in the catalyst layer as a constituent component of the catalyst layer not supporting the same.
- the carrier or non-supported particles (for example, alumina powder) preferably have a specific surface area of 30 m 2 / g or more.
- the carrier such as alumina is preferably 50 m 2 / g or more, for example, 50 to 500 m 2 / g (for example, 200 to 400 m 2 / g) from the viewpoints of heat resistance and structural stability.
- the average particle size of the carrier particles is not particularly limited, but is preferably about 1 nm to 500 nm (more preferably 10 nm to 200 nm).
- the precious metal content per catalyst unit volume (1 L) is preferably about 0.1 to 10 g / L, and 0.2 to 5 g / L. About L is preferable. If the precious metal content is too large, it is not preferable in terms of cost.
- the catalyst unit volume (1 L) includes the bulk volume (1 L) including the internal void volume (cell) volume (that is, including the catalyst layer formed in the void (cell)) in addition to the pure volume of the base material.
- the exhaust gas-purifying catalyst having the above-described configuration can be manufactured by a manufacturing process similar to the conventional one. For example, first, a desired carrier powder carrying a noble metal such as Pd, Pt, or Rh (which may include a general carrier such as an oxide made of crystallite A, alumina, or zirconia) and a noble metal are carried. A non-supported body (which may include an unsupported body such as oxide composed of crystallite B, alumina, zirconia, etc.) powder is coated on the honeycomb substrate by a known wash coat method or the like. Thereafter, the catalyst layer can be formed on the substrate by firing at a predetermined temperature and time.
- a noble metal such as Pd, Pt, or Rh
- a noble metal which may include a general carrier such as an oxide made of crystallite A, alumina, or zirconia
- a non-supported body which may include an unsupported body such as oxide composed of crystallite B, alumina, zirconia, etc.
- the catalyst layer can be
- the firing conditions of the wash-coated slurry vary depending on the shape and size of the substrate or carrier, and are not particularly limited. Typically, by performing firing at about 400 to 1000 ° C. for about 1 to 4 hours, The target catalyst layer can be formed.
- the drying conditions before firing are not particularly limited, but drying at a temperature of 80 to 300 ° C. (for example, 150 to 250 ° C.) for about 1 to 12 hours is preferable.
- a binder is added to the slurry in order to suitably adhere the upper layer forming slurry to the surface of the base material, and in the case of a laminated catalyst layer, to the lower layer surface. You may make it contain.
- a binder for example, use of alumina sol, silica sol or the like is preferable.
- Example 1 Production of exhaust gas purification catalyst>
- cerium nitrate solution (20 mass% as CeO 2 )
- zirconium oxynitrate solution (10 mass% as ZrO 2 )
- neodymium nitrate solution (10 mass% as Nd 2 O 3 )
- 13.19 g, 13.28 g of yttrium nitrate solution (10% by mass as Y 2 O 3 )
- PVP K-30 polyvinylpyrrolidone
- this mixed solution was heated to 90 to 95 ° C., and urea was added to adjust the pH to 11 to obtain a coprecipitate. Thereafter, 13 g of hydrazine was added and stirred at 90 to 95 ° C. for 12 hours. The obtained coprecipitate was filtered and washed with pure water to obtain a precursor a1.
- the entire amount of the precursor a1 was added and dispersed in 1000 mL of ion-exchanged water, and after adjusting the pH to 12 by adding an aqueous sodium hydroxide solution, 10 g of a rhodium nitrate solution (5% by mass as Rh) was added. Then, Rh was supported on the precursor a1, and the aqueous solution was removed by suction filtration to obtain an Rh-supported precursor a1. When the filtrate was analyzed by ICP emission spectroscopy, the Rh loading efficiency was 100%.
- the whole amount of the Rh-supported precursor a1 and the precursor b1 was added to 1000 mL of ion-exchanged water, and 1 g of malonic acid and 10 g of 3% hydrogen peroxide water were further added and stirred as organic acids.
- the mixed slurry thus prepared was heated to 80 to 85 ° C. and then stirred for 60 minutes with a homogenizer. Then, after filtering and washing
- the obtained powder A1B1 was subjected to TEM-EDX measurement (200,000 to 400,000 times, 50 visual fields), and the properties of the powder were examined.
- the elemental composition of 50 consecutive crystallites on an arbitrary straight line is analyzed by TEM-EDX measurement (200,000 to 400,000 times, 50 visual fields), and crystallite A and crystallite B are analyzed. And the maximum value of the number of crystallites A that are in continuous contact and the maximum value of the number of crystallites B that are in continuous contact were determined for the 50 crystallites analyzed. This was similarly performed in 50 visual fields, and the average value of the maximum values in each visual field was defined as the number of crystallites A or B continuously contacting. The results are shown in the corresponding column of Table 1. As shown in Table 1, in the powder A1B1 according to Example 1, the number of crystallites A that are in continuous contact is two, and the number of crystallites B that are in continuous contact is three.
- the powder A1B1 was compacted and pulverized to obtain a pellet-shaped catalyst I for a catalytic activity evaluation test described later having a particle size of 0.5 to 1.0 mm.
- Example 2 Except that the stirring time in the homogenizer was changed from 60 minutes to 15 minutes, a pellet-like catalyst II for catalytic activity evaluation test was obtained by the same process as in Example 1 described above. Properties of catalyst II such as TEM-EDX measurement results are shown in the corresponding column of Table 1.
- Example 3 Except that the stirring time in the homogenizer was changed from 60 minutes to 5 minutes, a pellet-shaped catalyst III for catalytic activity evaluation test was obtained by the same process as in Example 1 described above. Properties of catalyst III such as TEM-EDX measurement results are shown in the corresponding column of Table 1.
- Example 4 A pellet-like catalyst IV for catalytic activity evaluation test was obtained in the same process as in Example 1 except that the malonic acid and hydrogen peroxide solution were not used. Properties of catalyst IV such as TEM-EDX measurement results are shown in the corresponding column of Table 1.
- Example 1 The catalytic activity was the same as in Example 1 except that the malonic acid and hydrogen peroxide solution were not used, the mixed slurry was not heated, and the homogenizer was not used. A pellet-shaped catalyst V for evaluation test was obtained. Properties of catalyst V such as TEM-EDX measurement results are shown in the corresponding column of Table 1.
- the powder Rh / A1 (25 g) and the powder B1 (25 g) were dispersed in 400 mL of ion exchange water and stirred to prepare a mixed slurry. Next, the mixed slurry was subjected to suction filtration to remove the aqueous solution, then dried at 110 ° C. for 12 hours, and baked at 500 ° C. in the air to obtain powder A1 + B1.
- This catalyst was compacted and pulverized to obtain a pellet-like catalyst VI for a catalytic activity evaluation test described later having a particle size of 0.5 to 1.0 mm.
- the properties of the catalyst VI such as the TEM-EDX measurement results are shown in the corresponding column of Table 1.
- Example 5 The catalyst was prepared in the same process as in Example 1 except that 10 g of dinitrodiamine Pt nitric acid solution (5 mass% as Pt) was used instead of 10 g of the rhodium nitrate solution (5 mass% as Rh) used in Example 1 above. A pellet catalyst VII for activity evaluation test was obtained. Properties of catalyst VII such as TEM-EDX measurement results are shown in the corresponding column of Table 1.
- Example 6 Evaluation of catalytic activity in the same process as in Example 1 except that 10 g of palladium nitrate solution (5% by mass as Pd) was used instead of 10 g of rhodium nitrate solution (5% by mass as Rh) used in Example 1 above. A pellet-like catalyst IX for test was obtained. Properties of catalyst IX such as TEM-EDX measurement results are shown in the corresponding column of Table 1.
- the entire amount of the precursor b1 was added and dispersed in 1000 mL of ion-exchanged water, and after adding a sodium hydroxide aqueous solution to adjust the pH to 12, 10 g of a rhodium nitrate solution (5% by mass as Rh) was added. Then, Rh was supported on the precursor b1, and the aqueous solution was removed by suction filtration to obtain an Rh-supported precursor b1. When the filtrate was analyzed by ICP emission spectroscopy, the Rh loading efficiency was 100%.
- the catalyst powder Rh / A1B1 was compacted and pulverized to obtain a pellet-shaped catalyst XI for a catalytic activity evaluation test described later having a particle size of 0.5 to 1.0 mm.
- the properties of catalyst XI, such as TEM-EDX measurement results, are shown in the corresponding column of Table 1.
- Example 7 In 700 mL of ion-exchanged water, 537.5 g of zirconium oxynitrate solution (10% by mass as ZrO 2 ), 4.98 g of yttrium nitrate solution (10% by mass as Y 2 O 3 ), 0.05 g of PVP K-30 (trade name) A mixed solution was prepared by adding and stirring. Next, this mixed solution was heated to 90 to 95 ° C., and urea was added to adjust the pH to 11 to obtain a coprecipitate. Thereafter, 13 g of hydrazine was added and stirred at 90 to 95 ° C. for 12 hours. The obtained coprecipitate was filtered and washed with pure water to obtain a precursor a2.
- Rh rhodium nitrate solution (5% by mass as Rh) was added. Then, Rh was supported on the precursor a1, and the aqueous solution was removed by suction filtration to obtain an Rh-supported precursor a2. When the filtrate was analyzed by ICP emission spectroscopy, the Rh loading efficiency was 100%.
- Rh-supported precursor a2 and precursor b2 was added to 1000 mL of ion-exchanged water, and 1 g of malonic acid and 10 g of 3% hydrogen peroxide water were further added and stirred as organic acids.
- the mixed slurry thus prepared was heated to 80 to 85 ° C. and then stirred for 60 minutes with a homogenizer. Then, after filtration, washing with pure water, drying at 110 ° C., and firing in the air at 800 ° C. for 5 hours, an exhaust gas purifying catalyst (Rh / A2B2) according to Example 7 was obtained. .
- the catalyst powder Rh / A2B2 was compacted and pulverized to obtain a pellet-like catalyst XII for a catalytic activity evaluation test described later having a particle size of 0.5 to 1.0 mm. Properties of catalyst XII such as TEM-EDX measurement results are shown in the corresponding column of Table 1.
- Example 8 In 700 mL of ion-exchanged water, 36.59 g of cerium nitrate solution (20 mass% as CeO 2 ), 445.3 g of zirconium oxynitrate solution (10 mass% as ZrO 2 ), yttrium nitrate solution (10 mass% as Y 2 O 3 ) 24 0.000 g and 0.05 g of PVP K-30 (trade name) were added and stirred to prepare a mixed solution. Next, this mixed solution was heated to 90 to 95 ° C., and urea was added to adjust the pH to 11 to obtain a coprecipitate. Thereafter, 13 g of hydrazine was added and stirred at 90 to 95 ° C. for 12 hours.
- the obtained coprecipitate was filtered and washed with pure water to obtain a precursor a3.
- a pellet-shaped catalyst XIII for catalytic activity evaluation test was obtained in the same process as in Example 7 except that the powder A3B2 was used instead of the powder A2B2.
- the properties of the catalyst XIII, such as TEM-EDX measurement results, are shown in the corresponding column of Table 1.
- Example 9 70.24 g of cerium nitrate solution (20 mass% as CeO 2 ), 378.4 g of zirconium oxynitrate (10 mass% as ZrO 2 ), 7008.4 g of yttrium nitrate solution (10 mass% as Y 2 O 3 ) in 700 mL of ion-exchanged water 12 g and 0.05 g of PVP K-30 (trade name) were added and stirred to prepare a mixed solution. Next, this mixed solution was heated to 90 to 95 ° C., and urea was added to adjust the pH to 11 to obtain a coprecipitate. Thereafter, 13 g of hydrazine was added and stirred at 90 to 95 ° C. for 12 hours.
- the obtained coprecipitate was filtered and washed with pure water to obtain a precursor a4.
- a pellet catalyst XIV for catalytic activity evaluation test was obtained by the same process as in Example 7 except that the powder A4B2 was used instead of the powder A2B2.
- the properties of catalyst XIV, such as TEM-EDX measurement results, are shown in the corresponding column of Table 1.
- Example 10 10. 700 g of ion-exchanged water, 101.9 g of cerium nitrate solution (20 mass% as CeO 2 ), 316.3 g of zirconium oxynitrate (10 mass% as ZrO 2 ), yttrium nitrate solution (10 mass% as Y 2 O 3 ) 30 g and 0.05 g of PVP K-30 (trade name) were added and stirred to prepare a mixed solution. Next, this mixed solution was heated to 90 to 95 ° C., and urea was added to adjust the pH to 11 to obtain a coprecipitate. Thereafter, 13 g of hydrazine was added and stirred at 90 to 95 ° C. for 12 hours.
- the obtained coprecipitate was filtered and washed with pure water to obtain a precursor a5. And it replaced with the precursor a2 used in the above-mentioned Example 7, and obtained powder A5B2 with the process similar to the above-mentioned Example 7 except having used the said precursor a5.
- a pellet-shaped catalyst XV for catalytic activity evaluation test was obtained by the same process as in Example 7 except that the powder A5B2 was used instead of the powder A2B2.
- the properties of the catalyst XV such as TEM-EDX measurement results are shown in the corresponding column of Table 1.
- the obtained coprecipitate was filtered and washed with pure water to obtain a precursor a6. And it replaced with the precursor a2 used in the above-mentioned Example 7, and obtained powder A6B2 with the process similar to the above-mentioned Example 7 except having used the said precursor a6.
- a pellet catalyst XVI for catalytic activity evaluation test was obtained by the same process as in Example 7 described above except that the powder A6B2 was used instead of the powder A2B2. Properties of catalyst XVI such as TEM-EDX measurement results are shown in the corresponding column of Table 1.
- [Comparative Example 7] 15. 700 g of ion-exchanged water, 158.6 g of cerium nitrate solution (20 mass% as CeO 2 ), 204.4 g of zirconium oxynitrate (10 mass% as ZrO 2 ), yttrium nitrate solution (10 mass% as Y 2 O 3 ) 81 g and PVP K-30 (trade name) 0.05 g were added and stirred to prepare a mixed solution. Next, this mixed solution was heated to 90 to 95 ° C., and urea was added to adjust the pH to 11 to obtain a coprecipitate. Thereafter, 13 g of hydrazine was added and stirred at 90 to 95 ° C. for 12 hours.
- the obtained coprecipitate was filtered and washed with pure water to obtain a precursor a7.
- Example 11 Powder A1B2 was obtained by the same process as in Example 1 except that precursor b2 was used instead of precursor b1 used in Example 1 described above. Further, a pellet catalyst for a catalytic activity evaluation test was obtained by the same process as in Example 1 except that the powder A1B2 was used instead of the powder A1B1. The properties of the catalyst such as TEM-EDX measurement results are shown in the corresponding column of Table 1.
- ⁇ Test Example 2 Degree of crystal growth during high temperature treatment -Measurement of specific surface area-> The BET specific surface area (m 2 / g) after heat-treating each of the catalysts of Examples 1 to 10 and Comparative Examples 1 to 7 obtained in Test Example 1 was examined. Specifically, each catalyst (powder) was heat-treated (fired) at 1150 ° C. for 5 hours in the air (Air atmosphere). Thereafter, the surface area was measured based on a general BET method. The results are shown in Table 1.
- the specific surface areas of the catalyst powders (oxide particles) of each Example were all 30 m 2 / g or more, and some were 40 m 2 / g or more.
- the specific surface areas of the catalyst powders (oxide particles) of Comparative Examples 1 to 4 were all 25 m 2 / g or less. This indicates that in the catalyst of the example in which different kinds of crystallites are mixed in a dispersed state, the different kinds of crystallites serve as a barrier to prevent crystal growth, and as a result, it is possible to effectively prevent a decrease in specific surface area. .
- ⁇ Test Example 3 Evaluation of catalytic activity> The catalyst activity of each of the catalysts of Examples 1 to 10 and Comparative Examples 1 to 7 obtained in Test Example 1 was examined for thermal durability and then evaluated for catalytic activity. Specifically, each catalyst (the above-mentioned pellet-shaped catalyst) is placed in a flow-type thermal durability test apparatus, lean gas obtained by adding 6 mol% of oxygen (O 2 ) to nitrogen gas, and carbon monoxide (CO ) was added to the rich gas with a gas flow rate of 500 mL / min at a catalyst bed temperature of 850 ° C. for 100 hours alternately for 3 hours.
- O 2 oxygen
- CO carbon monoxide
- the treated catalyst is placed in an atmospheric pressure fixed bed flow reactor, and the temperature is increased from 100 ° C. to 500 ° C. at a rate of 12 ° C./min while a stoichiometric model gas is passed through the catalyst in the device.
- the HC purification rate and the NO x purification rate were continuously measured.
- the temperature at which the purification rate was 50% was determined as the 50% purification temperature.
- the results are shown in the corresponding column of Table 1. Part of the results (Examples 1 to 4, 7 to 10 and Comparative Examples 1, 2, 6, and 7) are shown in FIGS.
- the 50% HC purification temperature and 50% NO x purification temperature of the catalyst according to the example are It was lower than the 50% HC purification temperature and 50% NO x purification temperature of the catalyst of the comparative example. This is because, in the catalyst of each Example in which different kinds of crystallites are mixed in a dispersed state, the different kinds of crystallites serve as a barrier to prevent crystal growth, resulting in aggregation of noble metal (here, PGM) and deterioration of OSC function. It shows that it can be prevented to maintain high catalytic activity.
- the catalyst of each Example in which a noble metal was supported on a crystallite A having a low Ce content was a catalyst of Comparative Example 5 in which a noble metal was supported on a crystallite B having a high Ce content.
- the 50% HC purification temperature and the 50% NO x purification temperature were lower than the above. From this, in the aggregate composed of mixed particles of different crystallites having different Ce contents, the noble metal is supported on the crystallite A having a low Ce content, and the noble metal is supported on the crystallite B having a high Ce content. It was confirmed that even higher catalytic activity could be obtained by not using the above.
- the catalyst of Example 2 using the powder A1B1 (that is, the powder having a Ce content of 5 mol% of the crystallite A and the Ce content of 35 mol% of the crystallite B) is the powder A1B2 (that is, the Ce content of 5 mol of the crystallite A).
- the 50% HC purification temperature and 50% the NO x purification temperature showed a downward trend. From this, it can be seen that higher catalytic activity can be obtained by lowering the Ce content of the crystallite B.
- the Ce content of the crystallite B is generally 50% or less (for example, 25% to 50%), preferably 40% or less (for example, 25% to 40%), and more preferably 35%. % Or less (for example, 25% to 35%).
- the Ce content of the crystallite A is approximately 20% or less (for example, 1% to 20%), preferably 10% or less (for example, 1% to 10%).
- the use of the exhaust gas purifying catalyst disclosed herein prevents aggregation of noble metals due to crystal growth and a decrease in OSC ability.
- the catalytic activity (three-way performance) of a three-way catalyst Can be exhibited stably.
- the catalytic performance in the exhaust gas purifying catalyst in which two kinds of crystallites are mixed, the catalytic performance can be further improved.
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Abstract
Description
なお、本国際出願は2013年12月9日に出願された日本国特許出願第2013-254479号に基づく優先権を主張しており、その出願の全内容は本明細書中に参照として組み入れられている。
三元触媒では、OSC材として、セリア(CeO2)とジルコニア(ZrO2)を主体とする複合酸化物(以下「CZ複合酸化物」ともいう。)が従来から使用されている。例えば下記特許文献1には、セリウム酸化物に対するジルコニウム酸化物の固溶度が50%以上であるCZ複合酸化物であって該CZ複合酸化物の粒子を構成する結晶子の平均径が100nm以下であることを特徴とするCZ複合酸化物から成るOSC材を備えた従来の排ガス浄化用触媒の一例が開示されている。また、下記特許文献2には、OSC材として使用されるCZ複合酸化物であって結晶子径が10nm程度のCZ複合酸化物粒子の製造方法が紹介されている。
ここで「同種の結晶子が10個以上互いに接して存在しない」とは、電子顕微鏡観察(典型的にはTEM像)において任意に選択した一つの結晶子からみてその周囲に存在する他の結晶子のうち、最も近い位置にある9個が全て同種の結晶子とはならない、換言すれば、電子顕微鏡観察(典型的にはTEM像)において10個以上の同種の結晶子が偏って存在せず、相互に近接する10個の結晶子を電子顕微鏡観察下で任意にピックアップしたとき、そのうちの少なくとも1個は他の9個の結晶子とは異なる種類の結晶子となる程度の高度な分散状態にあることをいう。電子顕微鏡観察を複数の視野(例えば異なるTEM画像)において行う場合は、各視野における平均値をいう。
このような高度な分散状態を維持した酸化物粒子では、特に高い結晶成長抑制能およびOSC機能を発揮させることができる。さらに同種の結晶子が7個以上(さらには5個以上、特には3個以上)互いに接して存在しない分散状態が特に好ましい。
ここで開示される排ガス浄化用触媒は、後述する貴金属、酸化物粒子、基材の種類を適宜選択し、用途に応じて所望する形状に成形することによって種々の内燃機関、特に自動車のガソリンエンジンの排気系(排気管)に配置することができる。
以下の説明では、主として本発明の排ガス浄化用触媒を自動車のガソリンエンジンの排気管に設けられる三元触媒に適用することを前提として説明しているが、ここで開示される排ガス浄化用触媒を以下に説明する実施形態に限定することを意図したものではない。
ここで開示される排ガス浄化用触媒を排気管に設置する場合において触媒の骨格を構成する基材としては、従来この種の用途に用いられる種々の素材及び形態のものを採用することができる。例えば、高耐熱性を有するコージェライト、炭化ケイ素(SiC)等のセラミックス、或いは合金(ステンレス鋼等)製の基材を使用することができる。
形状についても従来の排ガス浄化用触媒と同様でよい。一例として図1に示す排ガス浄化用触媒10のように、外形が円筒形状であるハニカム基材1であって、その筒軸方向に排ガス流路としての貫通孔(セル)2が設けられ、各セル2を仕切る隔壁(リブ壁)4に排ガスが接触可能となっているものが挙げられる。基材1の形状はハニカム形状の他にフォーム形状、ペレット形状などとすることができる。また基材全体の外形については、円筒形に代えて楕円筒形、多角筒形を採用してもよい。
基材上に形成される触媒層は、排ガスを浄化する場として、この種の排ガス浄化用触媒の主体をなすものであり、図2に示すように、典型的には貴金属粒子20と、該貴金属粒子が担持されている結晶子Aと該貴金属粒子が担持されていない結晶子Bとが混在した酸化物粒子とから構成される。例えば上述した図1に示すハニカム基材1を採用した場合には、当該基材1のセルを構成するリブ壁4上に所定の厚み、気孔率の触媒層が形成される。触媒層は全体がほぼ同一の構成の一層からなるものでもよく、或いは、基材1上に形成された相互に異なる上下二層若しくは三層以上を有する積層構造タイプの触媒層であってもよい。
ここで開示される排ガス浄化用触媒の触媒層に備えられる貴金属20は、種々の酸化触媒や還元触媒として機能し得る金属種が採用され得るが、典型的には、PGMであるロジウム(Rh)、白金(Pt)、パラジウム(Pd)等が挙げられる。ルテニウム(Ru)、オスミウム(Os)、イリジウム(Ir)、銀(Ag)、銅(Cu)等を使用してもよい。これら貴金属の2種以上が合金化したものを用いてもよい。或いは他の金属種を含むもの(典型的には合金)であってもよい。
この中で、還元活性が高いRhと、酸化活性が高いPdやPtとを組み合わせて用いることが三元触媒を構築するうえで特に好ましい。例えば、ここで開示される異種結晶子A及びBから成るOSC材には、Rh或いはPt若しくはPdを担持させることが好ましい。
かかる貴金属は、排ガスとの接触面積を高める観点から十分に小さい粒径の微粒子として使用されることが好ましい。典型的には上記金属粒子の平均粒径(TEM観察により求められる粒径の平均値。以下同じ。)は1~15nm程度であり、10nm以下、7nm以下、更には5nm以下であることが特に好ましい。
かかる貴金属20の担持率(担体を100質量%としたときの貴金属含有率)は、5質量%以下が好ましく、より好ましくは3質量%以下である。例えば、0.05質量%以上5質量%以下であることが好ましく、0.1質量%以上3質量%以下であることがより好ましい。担持率が上記範囲より少なすぎると、金属による触媒効果が得られにくい。かかる担持率が上記範囲より多すぎると、金属の粒成長が進行する虞があり、さらにコスト面でも不利である。
ここで開示される酸化物粒子は、上記貴金属20が担持されている結晶子A(つまり担体として用いられる。)と、上記貴金属20が担持されていない結晶子Bとが混在して構成される酸化物粒子である。かかる異種結晶子AおよびBを含む酸化物粒子を触媒層における排ガス流動方向の上流側及び/又は下流側に備える。貴金属が担持されている結晶子Aは、ZrおよびCeのうちの少なくとも一方を含む酸化物から構成されている。一方、貴金属が担持されていない結晶子Bは、Ceを含む酸化物であって該酸化物中のCeの含有率(mol%)が結晶子Aの酸化物中の含有率(mol%)よりも高い酸化物から構成されている。このような2種の結晶子AおよびBを混在させることにより、例えば1150℃、5時間の大気中での熱処理後においても結晶成長を抑え、典型的には30m2/g以上(特に好ましくは35m2/g以上、特に好ましくは40m2/g以上)であるような高い比表面積を維持することができる。また、Ce含有率がより少ない結晶子Aに貴金属を担持させ、かつ、Ce含有率がより多い結晶子Bに貴金属を担持させないことにより、貴金属のメタル状態を良好に維持し、なおかつ高いOSC機能を発揮させることができる。
例えば、貴金属20が担持されている結晶子A(A、Bは区分のための記号にすぎない。)がZrを主体とするものである場合、その他の元素としてCe、その他1種又は2種以上の希土類元素、例えば、イットリウム(Y)、ランタン(La)、ネオジム(Nd)、プラセオジム(Pr)、サマリウム(Sm)、ユウロピウム(Eu)等のうちの1種又は2種以上、さらにはカルシウムなどのアルカリ土類元素を含むものでもよい。例えばZrの含有率が酸化物換算で酸化物全体の75~99mol%であるとともにYを少量(例えば5mol%以下、或いは10mol%以下)含む複合酸化物から成る結晶子Aが好適な一例として挙げられる。また、Zrを主体とするものであって、Ceの含有率が酸化物換算で酸化物全体の30mol%以下(好ましくは20mol%以下、より好ましくは10mol%以下、例えば0mol%(つまりCeを含まない))である酸化物から成る結晶子Aが好適な一例として挙げられる。
他方、貴金属20が担持されていない結晶子Bは、結晶子AよりもCeを高率に含有するものであればよく、その他の元素としてZr、その他1種又は2種以上の希土類元素(La、Y、Nd、Pr、Sm、Eu等)を含むものでもよい。例えばCeの含有率が酸化物換算で酸化物全体の35~99mol%であるとともにLaを少量(例えば5mol%以下、或いは10mol%以下)含む酸化物から成る結晶子Bが好ましい。
結晶子AおよびBの平均サイズは、従来の排ガス浄化用触媒に使用されるOSC材(例えばCZ複合酸化物)を構成するものと同様でよく、典型的にはTEM等の電子顕微鏡観察において2~100nm、好ましくは5~50nm程度である。
この製造方法は、結晶子Aの構成元素を含む水性溶液から共沈物を析出させて結晶子A前駆体を得る工程(結晶子A前駆体調製工程)を含む。上記水性溶液を構成する溶媒(水性溶媒)は、典型的には水であり、水を主成分とする混合溶媒であってもよい。例えば、水性溶媒中にCeイオン、Zrイオン等を供給し得る化合物を含む水性溶液を使用するとよい。この結晶子A前駆体調製工程は、上記水性溶液を80℃~100℃(好ましくは90℃~95℃)に加熱した後、pH11以上の条件下で上記水性溶液から共沈物を析出させる段階を含み得る。上記pHは、アルカリ剤(液性をアルカリ性に傾ける作用のある化合物、例えば尿素)を上記水性溶液に供給することにより調整することができる。また、この結晶子A前駆体調製工程は、上記結晶子A前駆体に貴金属を担持させる処理を含み得る。例えば、上記結晶子A前駆体を水に分散させた後、pH12以上の条件下で貴金属を添加して結晶子A前駆体に貴金属を担持させるとよい。ここで開示される製造方法は、このように未焼成の結晶子A前駆体に貴金属を担持させる態様で好ましく実施され得る。
また、この製造方法は、結晶子Bの構成元素を含む水性溶液から共沈物を析出させて結晶子B前駆体を得る工程(結晶子B前駆体調製工程)を含む。上記水性溶液を構成する溶媒(水性溶媒)は、典型的には水であり、水を主成分とする混合溶媒であってもよい。例えば、水性溶媒中にCeイオン等を供給し得る化合物を含む水性溶液を使用するとよい。この結晶子B前駆体調製工程は、上記水性溶液を80℃~100℃(好ましくは90℃~95℃)に加熱した後、pH11以上の条件下で上記水性溶液から共沈物を析出させる段階を含み得る。上記pHは、アルカリ剤(液性をアルカリ性に傾ける作用のある化合物、例えば尿素)を上記水性溶液に供給することにより調整することができる。
本実施態様では、このようにして生成した結晶子A前駆体と結晶子B前駆体とを混合して混合スラリーを調製する(スラリー調製工程)。このスラリー調製工程では、典型的には、結晶子A前駆体および結晶子B前駆体を水中に添加し、有機酸および過酸化水素水を添加して攪拌することにより混合スラリーを得る。有機酸としては、例えばマロン酸を好ましく用いることができる。ここで開示される製造方法は、このような有機酸および過酸化水素水を用いる態様で好ましく実施され得る。また、スラリー調製工程は、上記混合スラリーを加熱した後、分散機(例えばホモジナイザー)で攪拌する処理を含み得る。加熱温度としては、75℃~90℃(好ましくは80℃~85℃)に設定され得る。また、攪拌時間としては、混合スラリーが均一に混ざるまでの時間であればよく、例えば5分以上(例えば5分~120分)、好ましくは15分以上、より好ましくは30分以上、さらに好ましくは60分以上に設定され得る。このような攪拌時間の範囲内であると、結晶子Aと結晶子Bとの接触個数がより少ない酸化物粒子が得られうる。
上記のように混合スラリーを攪拌した後、洗浄して乾燥させる。そして、この混合物を焼成することにより結晶子Aおよび結晶子Bから成る酸化物粒子を得る(焼成工程)。この焼成工程は、大気中や大気よりも酸素がリッチな雰囲気中で行うことが望ましい。好ましくは、大気雰囲気中において700℃以上900℃以下の範囲内に最高焼成温度を決定するとよい。焼成時間としては、例えば3時間~8時間に設定され得る。このようにして、結晶子Aおよび結晶子Bから成る酸化物粒子を得ることができる。
担体又は非担持体の粒子(例えばアルミナ粉末)としては、比表面積が30m2/g以上であることが好ましい。アルミナ等の担体としては50m2/g以上、例えば50~500m2/g(例えば200~400m2/g)であることが耐熱性、構造安定性の観点から好ましい。また、担体粒子の平均粒径は特に限定するものではないが、1nm以上500nm以下(より好ましくは10nm以上200nm以下)程度であることが好ましい。
また、このような無機化合物(セラミックス)を担体として使用する場合、好ましくは触媒単位容積(1L)あたりの貴金属含有量が0.1~10g/L程度が適当であり、0.2~5g/L程度が好ましい。貴金属含有量が多すぎるとコスト的に好ましくなく、少なすぎると排ガス浄化能が低いために好ましくない。ここで触媒単位容積(1L)は、基材の純容積に加えて内部の空隙(セル)容積を含む(即ち当該空隙(セル)内に形成された触媒層を含む)嵩容積(1L)をいう。
例えば、先ず、Pd、Pt、Rh等の貴金属を担持した所望の担体粉末(結晶子Aから成る酸化物、アルミナ、ジルコニア等の一般的な担体を含んでもよい。)と、貴金属を担持していない非担持体(結晶子Bから成る酸化物、アルミナ、ジルコニア等の非担持体を含んでもよい。)粉末を含むスラリーを公知のウォッシュコート法等によってハニカム基材にコートする。その後、所定の温度及び時間で焼成することにより、基材上に触媒層を形成することができる。
ウォッシュコートされたスラリーの焼成条件は基材または担体の形状及びサイズによって変動するので、特に限定しないが、典型的には400~1000℃程度で約1~4時間程度の焼成を行うことによって、目的の触媒層を形成することができる。なお、焼成前の乾燥条件については特に限定されるものではないが、80~300℃の温度(例えば150~250℃)で1~12時間程度の乾燥が好ましい。また、触媒層をこのようなウォッシュコート法により形成する場合、基材の表面、さらに積層構造触媒層の場合には下層の表面に上層形成用スラリーを好適に密着させるため、スラリーにはバインダーを含有させてもよい。かかる目的のバインダーとしては、例えばアルミナゾル、シリカゾル等の使用が好ましい。
[実施例1]
イオン交換水700mLに、硝酸セリウム溶液(CeO2として20質量%)16.87g、オキシ硝酸ジルコニウム溶液(ZrO2として10質量%)434.8g、硝酸ネオジム溶液(Nd2O3として10質量%)13.19g、硝酸イットリウム溶液(Y2O3として10質量%)13.28g、ポリビニルピロリドン(PVP K-30(商品名))0.05gを添加し、攪拌して混合溶液を調製した。
次いで、この混合溶液を90~95℃に加熱した後、尿素を添加してpHを11に調整して共沈物を得た。その後、ヒドラジン13gを添加し、90~95℃で12時間攪拌した。得られた共沈物を濾過し、純水で洗浄することにより前駆体a1を得た。
次いで、この混合溶液を90~95℃に加熱した後、尿素を添加してpHを11に調整して共沈物を得た。その後、ヒドラジン13gを添加し、90~95℃で12時間攪拌した。得られた共沈物を濾過し、純水で洗浄することにより前駆体b1を得た。
また、得られた粉末A1B1中では、結晶子A1、結晶子B1の何れについても同種の結晶子が10個以上互いに接して存在しない高度な分散状態で結晶子A1と結晶子B1が混在していることが確認された。具体的には、TEM-EDX測定(20万倍~40万倍、50視野)により、任意の直線上にある連続する50個の結晶子について元素組成を分析し、結晶子Aと結晶子Bを区別するとともに、分析した上記50個の結晶子について、結晶子Aが連続して接触する個数の最大値、及び結晶子Bが連続して接触する個数の最大値を求めた。これを50視野において同様に行い、各視野での最大値の平均値を結晶子A又は結晶子Bが連続して接触する個数とした。結果を表1の該当欄に示す。表1に示すように、本実施例1に係る粉末A1B1では、結晶子Aが連続して接触する個数は2個であり、結晶子Bが連続して接触する個数は3個であった。
上記ホモジナイザーでの攪拌時間を60分から15分に変更した以外は上述した実施例1と同様のプロセスで触媒活性評価試験用のペレット状触媒IIを得た。TEM-EDX測定結果等の触媒IIの性状は、表1の該当欄に示す。
上記ホモジナイザーでの攪拌時間を60分から5分に変更した以外は上述した実施例1と同様のプロセスで触媒活性評価試験用のペレット状触媒IIIを得た。TEM-EDX測定結果等の触媒IIIの性状は、表1の該当欄に示す。
上記マロン酸および過酸化水素水を用いなかったこと以外は上述した実施例1と同様のプロセスで触媒活性評価試験用のペレット状触媒IVを得た。TEM-EDX測定結果等の触媒IVの性状は、表1の該当欄に示す。
上記マロン酸および過酸化水素水を用いなかったことと、上記混合スラリーを加熱しなかったことと、さらに上記ホモジナイザーを使用しなかったこと以外は、上述した実施例1と同様のプロセスで触媒活性評価試験用のペレット状触媒Vを得た。TEM-EDX測定結果等の触媒Vの性状は、表1の該当欄に示す。
イオン交換水700mLに、硝酸セリウム溶液(CeO2として20質量%)16.87g、オキシ硝酸ジルコニウム溶液(ZrO2として10質量%)434.8g、硝酸ネオジム溶液(Nd2O3として10質量%)13.19g、硝酸イットリウム溶液(Y2O3として10質量%)13.28g、PVP K-30(商品名)0.05gを添加し、攪拌して混合溶液を調製した。
次いで、この混合溶液を90~95℃に加熱した後、尿素を添加してpHを11に調整して共沈物を得た。その後、ヒドラジン13gを添加し、90~95℃で12時間攪拌した。得られた共沈物を濾過し、純水で洗浄した後、110℃で乾燥させ、大気中、800℃で5時間の焼成を行うことにより粉末A1を得た。
次に、イオン交換水1000mLに上記粉末A1を全量添加して分散させ、水酸化ナトリウム水溶液を添加してpHを12に調整した後、硝酸ロジウム溶液(Rhとして5質量%)10gを投入して粉末A1にRhを担持させ、吸引濾過により水溶液を除去し、Rh担持粉末A1を得た。濾液をICP発光分光で分析したところRh担持効率は100%であった。
Rh担持粉末A1を110℃で乾燥させ、大気中、800℃で5時間の焼成を行うことにより、本比較例2に係る粉末Rh担持A1(Rh/A1)を得た。
TEM-EDX測定結果から、本比較例3に係る粉末Rh/A1は、酸化物換算で構成金属元素の含有率(mol%)がZr/Ce/Nd/Y/=90/5/2/3であるRh担持結晶子A1が存在することが確認された。
次いで、この混合溶液を90~95℃に加熱した後、尿素を添加してpHを11に調整して共沈物を得た。その後、ヒドラジン13gを添加し、90~95℃で12時間攪拌した。得られた共沈物を濾過し、純水で洗浄した後、110℃で乾燥させ、大気中、800℃で5時間の焼成を行うことにより粉末B1を得た。
TEM-EDX測定結果から、本比較例2に係る粉末B1は、酸化物換算で構成金属元素の含有率(mol%)がCe/Zr/Nd/La=35/60/3/2である結晶子B1が存在することが確認された。
上記実施例1において使用した硝酸ロジウム溶液(Rhとして5質量%)10gに代えてジニトロジアミンPt硝酸溶液(Ptとして5質量%)10gを用いた以外は上述した実施例1と同様のプロセスで触媒活性評価試験用のペレット状触媒VIIを得た。TEM-EDX測定結果等の触媒VIIの性状は、表1の該当欄に示す。
上記比較例2において使用した硝酸ロジウム溶液(Rhとして5質量%)10gに代えてジニトロジアミンPt硝酸溶液(Ptとして5質量%)10gを用いた以外は上述した比較例2と同様のプロセスで触媒活性評価試験用のペレット状触媒VIIIを得た。TEM-EDX測定結果等の触媒VIIIの性状は、表1の該当欄に示す。
上記実施例1において使用した硝酸ロジウム溶液(Rhとして5質量%)10gに代えて硝酸パラジウム溶液(Pdとして5質量%)10gを用いた以外は上述した実施例1と同様のプロセスで触媒活性評価試験用のペレット状触媒IXを得た。TEM-EDX測定結果等の触媒IXの性状は、表1の該当欄に示す。
上記比較例2において使用した硝酸ロジウム溶液(Rhとして5質量%)10gに代えて硝酸パラジウム溶液(Pdとして5質量%)10gを用いた以外は上述した比較例2と同様のプロセスで触媒活性評価試験用のペレット状触媒Xを得た。TEM-EDX測定結果等の触媒Xの性状は、表1の該当欄に示す。
イオン交換水700mLに、硝酸セリウム溶液(CeO2として20質量%)17.04g、オキシ硝酸ジルコニウム溶液(ZrO2として10質量%)439.2g、硝酸ネオジム溶液(Nd2O3として10質量%)13.32g、硝酸イットリウム溶液(Y2O3として10質量%)13.41g、PVP K-30(商品名)0.05gを添加し、攪拌して混合溶液を調製した。次いで、この混合溶液を90~95℃に加熱した後、尿素を添加してpHを11に調整して共沈物を得た。その後、ヒドラジン13gを添加し、90~95℃で12時間攪拌した。得られた共沈物を濾過し、純水で洗浄することにより前駆体a1を得た。
かかる触媒粉末Rh/A1B1を圧粉成型し、粉砕して粒度0.5~1.0mmの後述する触媒活性評価試験用のペレット状触媒XIを得た。TEM-EDX測定結果等の触媒XIの性状は、表1の該当欄に示す。
イオン交換水700mLにオキシ硝酸ジルコニウム溶液(ZrO2として10質量%)537.5g、硝酸イットリウム溶液(Y2O3として10質量%)4.98g、PVP K-30(商品名)0.05gを添加し、攪拌して混合溶液を調製した。次いで、この混合溶液を90~95℃に加熱した後、尿素を添加してpHを11に調整して共沈物を得た。その後、ヒドラジン13gを添加し、90~95℃で12時間攪拌した。得られた共沈物を濾過し、純水で洗浄することにより前駆体a2を得た。
次に、イオン交換水1000mLに上記前駆体a2を全量添加して分散させ、水酸化ナトリウム水溶液を添加してpHを12に調整した後、硝酸ロジウム溶液(Rhとして5質量%)15gを投入して前駆体a1にRhを担持させ、吸引濾過により水溶液を除去し、Rh担持前駆体a2を得た。濾液をICP発光分光で分析したところRh担持効率は100%であった。
一方、イオン交換水700mLに、硝酸セリウム溶液(CeO2として20質量%)151.4g、オキシ硝酸ジルコニウム溶液(ZrO2として10質量%)126.5g、硝酸カルシウム溶液(CaOとして5質量%)3.29g、硝酸ランタン溶液(La2O3として10質量%)19.11g、PVP K-30(商品名)0.05gを添加し、攪拌して混合溶液を調製した。次いで、この混合溶液を90~95℃に加熱した後、尿素を添加してpHを11に調整して共沈物を得た。その後、ヒドラジン13gを添加し、90~95℃で12時間攪拌した。得られた共沈物を濾過し、純水で洗浄することにより前駆体b2を得た。
イオン交換水700mLに硝酸セリウム溶液(CeO2として20質量%)36.59g、オキシ硝酸ジルコニウム溶液(ZrO2として10質量%)445.3g、硝酸イットリウム溶液(Y2O3として10質量%)24.00g、PVP K-30(商品名)0.05gを添加し、攪拌して混合溶液を調製した。次いで、この混合溶液を90~95℃に加熱した後、尿素を添加してpHを11に調整して共沈物を得た。その後、ヒドラジン13gを添加し、90~95℃で12時間攪拌した。得られた共沈物を濾過し、純水で洗浄することにより前駆体a3を得た。
そして、上述の実施例7において使用した前駆体a2に代えて上記前駆体a3を使用した以外は上述した実施例7と同様のプロセスで粉末A3B2を得た。TEM-EDX測定結果から、本実施例8に係る粉末A3B2は、酸化物換算で構成金属元素の含有率(mol%)がZr/Ce/Y=85/10/5であるRh担持結晶子A3と、酸化物換算で構成金属元素の含有率(mol%)がCe/Zr/La/Ca=60/35/4/1である結晶子B2とが存在することが確認された。
さらに、粉末A2B2に代えて上記粉末A3B2を用いた以外は、上述した実施例7と同様のプロセスで触媒活性評価試験用のペレット状触媒XIIIを得た。TEM-EDX測定結果等の触媒XIIIの性状は、表1の該当欄に示す。
イオン交換水700mLに硝酸セリウム溶液(CeO2として20質量%)70.24g、オキシ硝酸ジルコニウム(ZrO2として10質量%)378.4g、硝酸イットリウム溶液(Y2O3として10質量%)23.12g、PVP K-30(商品名)0.05gを添加し、攪拌して混合溶液を調製した。次いで、この混合溶液を90~95℃に加熱した後、尿素を添加してpHを11に調整して共沈物を得た。その後、ヒドラジン13gを添加し、90~95℃で12時間攪拌した。得られた共沈物を濾過し、純水で洗浄することにより前駆体a4を得た。
そして、上述の実施例7において使用した前駆体a2に代えて上記前駆体a4を使用した以外は上述した実施例7と同様のプロセスで粉末A4B2を得た。TEM-EDX測定結果から、本実施例7に係る粉末A4B2は、酸化物換算で構成金属元素の含有率(mol%)がZr/Ce/Y=75/20/5であるRh担持結晶子A4と、酸化物換算で構成金属元素の含有率(mol%)がCe/Zr/La/Ca=60/35/4/1である結晶子B2とが存在することが確認された。
さらに、粉末A2B2に代えて上記粉末A4B2を用いた以外は、上述した実施例7と同様のプロセスで触媒活性評価試験用のペレット状触媒XIVを得た。TEM-EDX測定結果等の触媒XIVの性状は、表1の該当欄に示す。
イオン交換水700mLに硝酸セリウム溶液(CeO2として20質量%)101.9g、オキシ硝酸ジルコニウム(ZrO2として10質量%)316.3g、硝酸イットリウム溶液(Y2O3として10質量%)22.30g、PVP K-30(商品名)0.05gを添加し、攪拌して混合溶液を調製した。次いで、この混合溶液を90~95℃に加熱した後、尿素を添加してpHを11に調整して共沈物を得た。その後、ヒドラジン13gを添加し、90~95℃で12時間攪拌した。得られた共沈物を濾過し、純水で洗浄することにより前駆体a5を得た。
そして、上述の実施例7において使用した前駆体a2に代えて上記前駆体a5を使用した以外は上述した実施例7と同様のプロセスで粉末A5B2を得た。TEM-EDX測定結果から、本実施例10に係る粉末A5B2は、酸化物換算で構成金属元素の含有率(mol%)がZr/Ce/Y=65/30/5であるRh担持結晶子A5と、酸化物換算で構成金属元素の含有率(mol%)がCe/Zr/La/Ca=60/35/4/1である結晶子B2とが存在することが確認された。
さらに、粉末A2B2に代えて上記粉末A5B2を用いた以外は、上述した実施例7と同様のプロセスで触媒活性評価試験用のペレット状触媒XVを得た。TEM-EDX測定結果等の触媒XVの性状は、表1の該当欄に示す。
イオン交換水700mLに硝酸セリウム溶液(CeO2として20質量%)131.3g、オキシ硝酸ジルコニウム(ZrO2として10質量%)258.4g、硝酸イットリウム溶液(Y2O3として10質量%)21.53g、PVP K-30(商品名)0.05gを添加し、攪拌して混合溶液を調製した。次いで、この混合溶液を90~95℃に加熱した後、尿素を添加してpHを11に調整して共沈物を得た。その後、ヒドラジン13gを添加し、90~95℃で12時間攪拌した。得られた共沈物を濾過し、純水で洗浄することにより前駆体a6を得た。
そして、上述の実施例7において使用した前駆体a2に代えて上記前駆体a6を使用した以外は上述した実施例7と同様のプロセスで粉末A6B2を得た。TEM-EDX測定結果から、本比較例6に係る粉末A6B2は、酸化物換算で構成金属元素の含有率(mol%)がZr/Ce/Y=55/40/5であるRh担持結晶子A6と、酸化物換算で構成金属元素の含有率(mol%)がCe/Zr/La/Ca=60/35/4/1である結晶子B2とが存在することが確認された。
さらに、粉末A2B2に代えて上記粉末A6B2を用いた以外は、上述した実施例7と同様のプロセスで触媒活性評価試験用のペレット状触媒XVIを得た。TEM-EDX測定結果等の触媒XVIの性状は、表1の該当欄に示す。
イオン交換水700mLに硝酸セリウム溶液(CeO2として20質量%)158.6g、オキシ硝酸ジルコニウム(ZrO2として10質量%)204.4g、硝酸イットリウム溶液(Y2O3として10質量%)20.81g、PVP K-30(商品名)0.05gを添加し、攪拌して混合溶液を調製した。次いで、この混合溶液を90~95℃に加熱した後、尿素を添加してpHを11に調整して共沈物を得た。その後、ヒドラジン13gを添加し、90~95℃で12時間攪拌した。得られた共沈物を濾過し、純水で洗浄することにより前駆体a7を得た。
そして、上述の実施例7において使用した前駆体a2に代えて上記前駆体a7を使用したこと以外は上述した実施例7と同様のプロセスで粉末A7B2を得た。TEM-EDX測定結果から、本比較例7に係る粉末A7B2は、酸化物換算で構成金属元素の含有率(mol%)がZr/Ce/Y=45/50/5であるRh担持結晶子A7と、酸化物換算で構成金属元素の含有率(mol%)がCe/Zr/La/Ca=60/35/4/1である結晶子B2とが存在することが確認された。
さらに、粉末A2B2に代えて上記粉末A7B2を用いた以外は、上述した実施例7と同様のプロセスで触媒活性評価試験用のペレット状触媒XVIIを得た。TEM-EDX測定結果等の触媒XVIIの性状は、表1の該当欄に示す。
上述した実施例1において使用した前駆体b1に代えて前駆体b2を使用したこと以外は上述した実施例1と同様のプロセスで粉末A1B2を得た。さらに、粉末A1B1に代えて上記粉末A1B2を用いた以外は、上述した実施例1と同様のプロセスで触媒活性評価試験用のペレット状触媒を得た。TEM-EDX測定結果等の触媒の性状は、表1の該当欄に示す。
A1:Zr/Ce/Nd/Y Oxide
=90/5/2/3
A2:Zr/Y Oxide
=99/1
A3:Zr/Ce/Y Oxide
=85/10/5
A4:Zr/Ce/Y Oxide
=75/20/5
A5:Zr/Ce/Y Oxide
=65/30/5
A6:Zr/Ce/Y Oxide
=55/40/5
A7:Zr/Ce/Y Oxide
=45/50/5
結晶子Bの組成(mol%)
B1:Ce/Zr/Nd/La Oxide
=35/60/3/2
B2:Ce/Zr/La/Ca Oxide
=60/35/4/1
試験例1で得られた実施例1~10および比較例1~7の各触媒を熱処理した後のBET比表面積(m2/g)を調べた。
具体的には、各触媒(粉末)について大気(Air雰囲気)中で1150℃、5時間の熱処理(焼成)を行った。その後、一般的なBET法に基づいて表面積を測定した。結果を表1に示す。
試験例1で得られた実施例1~10および比較例1~7の各触媒を熱耐久試験に供試した後の触媒活性の評価を調べた。
具体的には、各触媒(上記ペレット状触媒)を、流通式の熱耐久試験装置に配置し、窒素ガスに酸素(O2)を6mol%加えたリーンガスと、窒素ガスに一酸化炭素(CO)を6mol%加えたリッチガスを、触媒床温度850℃において500mL/分のガス流で3分周期で交互に100時間流通させる熱耐久処理を行った。
Claims (5)
- 内燃機関の排気管に配置されて該内燃機関から排出される排ガスの浄化を行う排ガス浄化用触媒であって、
貴金属が担持されている結晶子Aと、貴金属が担持されていない結晶子Bとが混在した酸化物粒子を含んでおり、
前記貴金属が担持されている結晶子Aは、ジルコニウム(Zr)およびセリウム(Ce)のうちの少なくとも一方を含む酸化物からなり、
前記貴金属が担持されていない結晶子Bは、セリウム(Ce)を含む酸化物であって、該酸化物中のCeの含有率(mol%)が前記結晶子Aの酸化物中の含有率(mol%)よりも高い酸化物からなり、
ここで前記酸化物粒子の1150℃、5時間の大気中での熱処理後における比表面積が30m2/g以上であり、
前記結晶子Aおよび前記結晶子Bのいずれについても電子顕微鏡観察下で同種の結晶子が10個以上互いに接して存在しないように高度に分散した状態で前記酸化物粒子中に混在している、排ガス浄化用触媒。 - 前記結晶子Aを構成する酸化物に含まれるCeの含有率は酸化物換算で該酸化物全体の0~30mol%であり、
前記結晶子Bを構成する酸化物に含まれるCeの含有率は酸化物換算で該酸化物全体の35~99mol%である、請求項1に記載の排ガス浄化用触媒。 - 前記結晶子Aは、Zrとともにイットリウム(Y)を含む酸化物からなる、請求項1または2に記載の排ガス浄化用触媒。
- 前記結晶子Bは、CeとともにZrを含む酸化物からなる、請求項1~3の何れか一つに記載の排ガス浄化用触媒。
- 前記結晶子Aおよび前記結晶子Bのいずれについても電子顕微鏡観察下で同種の結晶子が7個以上互いに接して存在しないように高度に分散した状態で前記酸化物粒子中に混在している、請求項1~4の何れか一つに記載の排ガス浄化用触媒。
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