JP5024656B2 - COMPOSITE MATERIAL, COMPOSITE MATERIAL BASE, COMPOSITE MATERIAL DISPERSION AND METHOD FOR PRODUCING THEM - Google Patents

Description

  The present invention relates to a composite material and a method for producing the same, a composite material substrate using the composite material, a composite material dispersion, and a method for producing a composite material substrate using the same.

  As for gasoline engines, harmful components in the exhaust are steadily reduced due to strict regulations on exhaust and technological advances that can cope with it. However, diesel engines contain particulates (particulate matter: soot made of carbon fine particles, soluble organic components (SOF), etc., hereinafter referred to as “PM”) for exhaust purification. Many technical issues remain.

Therefore, in recent years, an oxidation catalyst that can oxidize PM, particularly a soot component, from a low temperature has been developed. For example, in Japanese Patent Application Laid-Open No. 2004-42021 (Patent Document 1), a catalyst composition having ceria (CeO ₂ ) stabilized with silver (Ag) and / or cobalt (Co) is oxidized by soot oxidation during regeneration of DPF. The molar ratio of Ag to ceria is preferably 4: 1 to 1: 4 (the Ag content (mol%) relative to the total amount of Ce and Ag is equivalent to 20 mol% to 80 mol%), It is described that 3: 1 to 1: 3 (Ag content (mol%) with respect to the total amount of Ce and Ag is equivalent to 33 mol% to 67 mol%) is more preferable. The activity of the mixture having an Ag content of 75 mol% and a Ce content of 25 mol% is said to be maximum. In addition, a mixture having an Ag content of 25 mol% and a Ce content of 75 mol% is active with respect to soot oxidation even if oxygen is used as the only oxidant. In this case, active oxygen species are generated in the gas phase. It is shown that you can. In addition, the manufacturing method of the catalyst described in Patent Document 1 is obtained by impregnating a cellulose material (Whatman (registered trademark) filter paper 540) with a nitrate precursor and drying it overnight at room temperature. This is a method for obtaining a catalyst composition having a porosity concentrated to about 70 to 200 m2 and a high specific surface area of 14 to 150 m ² / g by burning cellulose under conditions.

There are mainly two evaluation methods in Patent Document 1, and one is a method of measuring the decomposition rate by TGA in a 10% oxygen atmosphere or the like in which diesel soot and the catalyst composition are loose-contacted with a spatula, The other is a method of performing a pressure loss balance test using a DPF. For example, in the TGA evaluation for the catalyst composition having an Ag content of 75 mol%, the oxidation rate at 323 ° C. is 0. 0 even under the best catalyst composition of NO ₂ : 1010 ppm and O ₂ : 10%. 117 hr ⁻¹ . That is, even under the condition that a strong oxidizer of NO ₂ is sufficiently present, the ratio of soot oxidized in one hour is only 11.7%. On the other hand, in the pressure loss balance test, CPF-15, which is an Ag-Ce system, can oxidize PM at around 325 ° C, but this test result is inconsistent with the previous test result. Therefore, the present inventors consider that the soot component slipped out in the actual pressure loss balance test, and the catalyst composition described in Document 1, ie, simply Ag and CeO ₂ or Co and CeO ₂ exist. However, it was not possible to sufficiently oxidize carbon-containing components such as soot and components such as HC, CO or NO at low temperatures.
JP 2004-42021 A

  The present invention has been made in view of the above-described problems of the prior art. As an oxidation catalyst that can sufficiently oxidize carbon-containing components such as soot, components such as HC, CO, or NO at a lower temperature. It is an object of the present invention to provide a very useful composite material and a composite material substrate using the same, and a production method capable of efficiently and reliably obtaining such a composite material and composite material substrate.

  As a result of intensive studies to achieve the above object, the inventors of the present invention have an average primary particle size of 0.3 to 30 nm and a metal oxide fine particle composed of a metal oxide capable of changing valence, and at least Oxidation that can sufficiently oxidize carbon-containing components such as soot, components such as HC, CO, or NO at a lower temperature by adopting a structure in which Ag ultrafine particles that are partially +2 are supported. The inventors have found that the composite material is very useful as a catalyst or the like, and have completed the present invention.

  That is, the composite material of the present invention is composed of metal oxide fine particles made of a metal oxide capable of changing the valence, Ag having an average primary particle size of 0.3 to 30 nm and at least a part of +2 Ag. It is characterized by comprising ultrafine particles.

The second metal oxide constituting the Kikin genus oxide fine particles before according to the present invention, La, Ce, Pr, Nd , Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb , Lu, Y, Zr, Fe, Ti, Al, Mg, Co, Ni, Mn, Cr, Mo, W and V oxides, solid solutions thereof, and at least selected from the group consisting of these complex oxides One type is preferred.

The metal oxide fine particles according to the present invention are preferably oxygen active species transfer material particles made of an oxygen active species transfer material capable of transferring oxygen active species generated by the Ag ultrafine particles. In particular, the oxygen active species transfer material is a composite oxide containing CeO ₂ or Ce, and at least one selected from the group consisting of La, Nd, Pr, Sm, Y, Ca, Ti, Fe, Zr, and Al. It is particularly preferable to further contain as an additive metal.

In such a composite material of the present invention, it is preferable that an average primary particle size of the metal oxide fine particles after firing for 5 hours at 500 ° C. in the air is 1 to 75 nm. Further, such a composite material of the present invention is very useful as an oxidation catalyst for oxidizing carbon-containing components .

The first production method of the composite material of the present invention is:
A step of producing an aggregate in which Ag particles are covered with metal compound fine particles derived from a metal salt capable of changing the valence, from a solution containing an Ag salt and a metal salt capable of changing the valence;
A part of Ag is eluted from the obtained aggregate with an acid and then baked to form metal oxide fine particles made of a metal oxide capable of changing the valence, and an average primary particle size of 0.3 to 30 nm. And a step of obtaining a composite material composed of Ag ultrafine particles having at least a part of +2;
It is the method characterized by including.

  In the first method for producing a composite material of the present invention, it is preferable to stop the elution by adding an alkali when eluting a part of the Ag from the aggregate with an acid.

In addition, the second production method of the composite material of the present invention includes:
A step of producing an aggregate in which Ag particles are covered with metal compound fine particles derived from a metal salt capable of changing the valence, from a solution containing an Ag salt and a metal salt capable of changing the valence;
Eluting at least a part of the Ag from the obtained aggregate with an acid;
A metal oxide fine particle composed of an oxide of a metal whose valence can be varied by carrying Ag ultrafine particles on the surface of the metal compound fine particles in the presence of an alkali and then firing, and an average primary particle size of 0.3. Obtaining a composite material composed of Ag ultrafine particles having a diameter of ˜30 nm and at least a part of which is +2;
It is the method characterized by including.

Furthermore, the third method for producing the composite material of the present invention includes:
A step of dissolving the surface of metal oxide fine particles comprising a metal oxide capable of changing valence with an acid;
By supporting Ag ultrafine particles in the presence of alkali on the surface of the metal oxide fine particles, metal oxide fine particles made of a metal oxide capable of changing the valence, and an average primary particle size of 0.3 to 30 nm. A step of obtaining a composite material comprising Ag ultrafine particles that are present and at least a part of which is +2;
It is the method characterized by including.

  In the first to third production methods of the composite material of the present invention, the alkali is particularly preferably ammonia.

  The composite material base material of the present invention comprises a base material and the composite material of the present invention. Such a composite material substrate of the present invention is very useful as an exhaust purification substrate and the like.

  The first composite material dispersion of the present invention contains the composite material of the present invention and a dispersion medium. The first composite material dispersion of the present invention may further contain a binder.

  The second composite material dispersion of the present invention contains a composite material before firing obtained in the first or second production method of the composite material of the present invention and a dispersion medium. It is characterized by this.

  Furthermore, the method for producing a composite material substrate of the present invention is characterized in that a composite material substrate is obtained by firing the first or second composite material dispersion of the present invention after contacting the substrate. It is a method to do.

  The reason why the composite material of the present invention can be obtained by the method for producing the composite material of the present invention is not necessarily clear, but the present inventors speculate as follows. That is, in the first and second production methods of the composite material of the present invention, first, metal compound fine particles (solid metal oxide precursor) derived from a metal salt capable of changing the valence in the reaction solution. It is produced and acts as a reducing agent on Ag ions or Ag compounds derived from Ag salts, and a reduction reaction similar to the so-called silver mirror reaction proceeds. Thus, when the reducing agent is a solid in the electroless plating reaction by the reduction method, the precipitated Ag is a solid reducing agent (metal compound fine particles) while the metal precipitation reaction proceeds on the surface of the solid. It becomes the form covered with. Therefore, the reaction proceeds in such a way that the metal compound fine particles wrap around the core Ag particles, and when the metal compound fine particles aggregate around the Ag particles, the zeta potential of the aggregates changes, thereby generating repulsive forces between the aggregates. In addition, since this state is thermodynamically stable, the present inventors infer that nano-level aggregates with uniform particle sizes are produced.

  And in the 1st manufacturing method of the composite material of this invention, when eluting one part of Ag from the obtained aggregate by an acid treatment, the Ag ultrafine particle which can give / receive a metal oxide and an electron is Since it is difficult to elute even by dissolution treatment with an acid, the core Ag particles are preferentially dissolved and the Ag ultrafine particles remain, and further, the Ag ultrafine particles are caused by the etching action by the acid in the process of dissolving the Ag particles. Is easily formed. Therefore, by firing the acid-treated material in this way, the metal oxide fine particles made of a metal oxide capable of changing the valence have an average primary particle size of 0.3 to 30 nm and at least a part thereof. A composite material in which Ag fine particles having +2 valence are supported can be obtained.

  Further, in the second method for producing a composite material of the present invention, when at least a part of Ag is eluted from the obtained aggregate by acid treatment, Ag ultrafine particles are easily formed by an etching action with an acid. Hydroxyl groups are formed on the surface of the metal compound fine particles by alkali treatment, and Ag super fine particles are formed by reacting the hydroxyl groups with Ag at the atomic level. Therefore, by firing the material that has been subjected to acid treatment in this manner and then reacted with Ag ions in the presence of alkali, the average primary particle size of the metal oxide fine particles composed of metal oxides that can vary in valence can be increased. A composite material carrying Ag ultrafine particles of 0.3 to 30 nm and at least a part of which is +2 is supported.

  Furthermore, in the third production method of the composite material of the present invention, when the surface of the metal oxide fine particles made of a metal oxide capable of changing the valence is dissolved by acid treatment, the Ag ultrafine particles are formed by an etching action with an acid. It becomes easy to form, and furthermore, a hydroxyl group is formed on the surface of the metal compound fine particle by an alkali treatment, and the hydroxyl group and Ag react at the atomic level, thereby forming an Ag ultrafine particle. Therefore, by firing the material that has been subjected to acid treatment in this manner and then reacted with Ag ions in the presence of alkali, the average primary particle size of the metal oxide fine particles composed of metal oxides that can vary in valence can be increased. A composite material carrying Ag ultrafine particles of 0.3 to 30 nm and at least a part of which is +2 is supported.

  In addition, when the composite material of the present invention is used as an oxidation catalyst, it is possible to sufficiently oxidize carbon-containing components such as soot and components such as HC, CO, and NO at a lower temperature in an atmosphere containing oxygen-containing substances. The reason for this is not necessarily clear, but the present inventors infer as follows. Hereinafter, the case where the carbon-containing component is oxidized using oxygen active species transfer material particles as the metal oxide fine particles and oxygen as the oxygen-containing substance will be described as an example.

In the oxidation catalyst of the present invention, the present inventors speculate that Ag ultrafine particles play a role as oxygen-releasing material particles that liberate oxygen from oxygen-containing substances and generate oxygen active species. The Ag ultrafine particles according to the present invention are at least partially detected as Ag ²⁺ . By arranging Ag on metal oxide fine particles made of a metal oxide capable of changing valence, Ag ²⁺ is easily generated by exchange of electrons between the metal element capable of changing valence and Ag. Ag ²⁺ thus generated can be detected by electron spin resonance (ESR). Further, Ag atoms that are detected as Ag ²⁺ are isolated. Note that it is not necessary for all of the Ag ultrafine particles to be atomic, and if Ag is supported so that the average primary particle size is as small as possible, some of them can be isolated and exist as Ag ^2+. It becomes.

Although the mechanism by which oxygen active species are generated from such Ag ultrafine particles is not necessarily clear, the present inventors infer as follows. That is, as described above, at least a part of the Ag ultrafine particles exists as Ag ²⁺ by exchange of electrons with a metal element capable of changing the valence. In addition, although Ag ion can take +1, +2, +3 valence, +1 valence is the most stable. However, when Ag is present as ultrafine particles, Ag ⁺ and a metal element capable of changing the valence can further exchange electrons, so that it is possible to take Ag ²⁺ , and oxygen active species are generated during such electron transfer. The present inventors speculate that this will be done.

In the oxidation catalyst of the present invention, oxygen is released from the oxygen-containing substance even at a relatively low temperature by the Ag ultrafine particles, and the oxygen active species (O ^* : for example, oxygen ions) generated by the release are oxygen active species transfer material particles. It is moved to the surface of the carbon-containing component by (metal oxide fine particles), where a surface oxide is formed. In addition, it is known that the bond of C and O in such a surface oxide can be classified mainly into C═O, C═C, and C—O (Applied Catalysis B, 50, 185-194 (2004)). ). Next, the surface oxide formed in this way is oxidized by gas-phase oxygen or oxygen active species moving through oxygen active species transfer material particles. In this way, the oxidized portion is removed from the periphery of the carbon-containing component, the carbon-containing component shrinks, and finally, it is completely oxidized and the carbon-containing component disappears.

  Thus, the present inventors speculate that in the oxidation catalyst of the present invention, carbon-containing components such as soot can be sufficiently oxidized at a low temperature by the oxidizing action of the oxygen active species. In addition, even in the case of oxidizing other than carbon-containing components such as soot using the oxidation catalyst of the present invention, and even when the oxygen-containing substance is other than oxygen, oxygen active species are generated, and soot or the like is generated by a similar mechanism. Components such as carbon-containing components, HC, CO, or NO can be oxidized.

In the present invention, as such oxygen-containing substances, in addition to O ₂ , NO _X , SO _X , O ₃ , peroxides, superoxides, carbonyl compounds, alcohol compounds, ether compounds, nitro compounds, etc. Examples of the compound containing oxygen atoms in the form of a gas in an atmosphere that oxidizes carbon-containing components such as soot and components such as HC, CO, and NO can be given.

Examples of the oxygen active species include O ₂ ⁻ , O ⁻ and O ²⁻ . It is known that oxygen molecules are activated to oxygen species such as O ₂ → O ₂ ⁻ → 2O ⁻ → 2O ²⁻ as electrons are given on the catalyst.

  According to the present invention, a composite material very useful as an oxidation catalyst capable of sufficiently oxidizing a carbon-containing component such as soot and a component such as HC, CO or NO at a lower temperature, and a composite material using the same It becomes possible to provide a substrate, and a production method capable of efficiently and reliably obtaining such a composite material and a composite material substrate.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments thereof.

  First, the composite material of the present invention will be described. That is, the composite material of the present invention is composed of metal oxide fine particles made of a metal oxide capable of changing the valence, Ag having an average primary particle size of 0.3 to 30 nm and at least a part of +2 Ag. It is characterized by comprising ultrafine particles.

  The Ag ultrafine particles and metal oxide fine particles themselves according to the present invention are primary particles. Secondary particles formed by the former being covered by the latter and secondary particles formed by aggregating the latter are referred to as “aggregates (or primary aggregates). Aggregation) ”and tertiary particles formed by aggregation of such aggregates are referred to as“ aggregates (or secondary aggregates) ”.

  In the composite material of the present invention, Ag ultrafine particles are used as an essential component. Such Ag has a good balance between the liberation of oxygen from the oxygen-containing substance and the binding properties of oxygen atoms, and functions as an oxygen-releasing material that liberates oxygen from the oxygen-containing substance and generates oxygen active species. . Such Ag ultrafine particles can incorporate oxygen atoms into a reaction system that efficiently oxidizes PM and the like. In addition, such Ag ultrafine particles (oxygen release material) may function as an oxygen-containing substance capturing material. Therefore, with such Ag ultrafine particles, it is possible to supply a large amount of oxygen active species from a lower temperature to components such as carbon-containing components, HC, CO, or NO to promote oxidation.

In the Ag ultrafine particles according to the present invention, it is necessary that at least a part of the Ag ultrafine particles is detected as Ag ²⁺ having +2. In the absence of Ag ²⁺ , the release of oxygen from the oxygen-containing substance is not sufficiently achieved, and the ability to oxidize components such as carbon-containing components, HC, CO, or NO decreases.

In addition, the abundance ratio of Ag ²⁺ in the Ag ultrafine particles according to the present invention is not particularly limited, but is preferably included to some extent so as to be detectable by ESR.

  The Ag constituting the Ag ultrafine particles according to the present invention is preferably Ag alone, but may be an alloy composed of Ag and another metal other than Ag. In addition, part of the Ag ultrafine particles may form an oxide or may form a compound with another element. When a part of the Ag ultrafine particles forms an oxide or a compound, the Ag content is preferably 0.3% by mass or more.

In addition, the Ag ultrafine particles according to the present invention are required to have an average primary particle size of 0.3 to 30 nm, and more preferably 0.3 to 20 nm. Since the size of Ag atoms is about 0.3 nm, Ag ultrafine particles having an average primary particle size of less than 0.3 nm cannot theoretically exist. On the other hand, when the average primary particle size of Ag ultrafine particles exceeds 30 nm, , Ag ²⁺ is isolated and difficult to exist.

The metal constituting the metal oxide fine particles according to the present invention is preferably an oxygen active species transfer material capable of transferring the oxygen active species, and a metal capable of changing the valence is used from such a viewpoint. It is done. Such second metal oxides include La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, Zr, Fe, At least one selected from the group consisting of oxides of Ti, Al, Mg, Co, Ni, Mn, Cr, Mo, W, and V, solid solutions thereof, and composite oxides thereof is preferable. CeO ₂ , Fe ₂ From the group consisting of O ₃ , ZrO ₂ , Y ₂ O ₃ , TiO ₂ , Al ₂ O ₃ , MgO, Co ₃ O ₄ , Pr ₂ O ₃ , Nd ₂ O ₃ , solid solutions thereof, and complex oxides thereof It is more preferable that it is at least one selected, and among these, composite oxides containing CeO ₂ and Ce are particularly preferable. In addition, the metal oxide according to the present invention preferably has a certain amount of defects in order to move oxygen active species.

When the metal oxide according to the present invention is a complex oxide containing CeO ₂ or Ce, the mobility of oxygen active species is increased and the coarsening of the complex oxide particles containing CeO ₂ particles or Ce is more reliably prevented. Therefore, at least one selected from the group consisting of La, Nd, Pr, Sm, Y, Ca, Ti, Fe, Zr and Al (particularly preferably La and / or Nd) is further contained as an additive metal. More preferably. In addition, when such an additive component is contained, the content of the additive component is preferably about 1 to 30 mol%, and more preferably about 5 to 20 mol% with respect to the total amount of Ce and the additive component.

  The particle size of the metal oxide fine particles according to the present invention is not particularly limited, but the average particle size after firing for 5 hours at 500 ° C. in the atmosphere is 1 to 75 nm (more preferably 8 to 20 nm, still more preferably). The average particle size after firing for 5 hours at 800 ° C. in an atmosphere consisting of 10 volume% oxygen and 90 volume% nitrogen is preferably 8 to 100 nm (more preferably 8 to 60 nm, further It is preferably 8 to 40 nm. If the average particle size of the metal oxide fine particles is less than the lower limit, contact with a carbon-containing component such as soot tends to be inhibited. On the other hand, if the upper limit exceeds the upper limit, the oxygen active species hardly move on the metal oxide. Tend to be.

  The composite material of the present invention comprises the metal oxide fine particles and the Ag ultrafine particles, and the ratio of the metal oxide fine particles to the Ag ultrafine particles is not particularly limited. The ratio (molar ratio) of Ag constituting the Ag ultrafine particles to the total amount of Ag and the main metal constituting the metal oxide fine particles is preferably 1 to 40 mol%, and more preferably 1 to 30 mol%. . If the amount of Ag constituting the Ag ultrafine particles is less than the above lower limit, the amount of oxygen active species released from the gas phase is reduced, and the ability to oxidize components such as carbon-containing components, HC, CO, or NO is reduced. On the other hand, if the amount of the main metal constituting the metal oxide fine particles is less than the above lower limit, the amount of oxygen-active species that can move to components such as carbon-containing components, HC, CO, or NO decreases, and carbon content The ability to oxidize components tends to decrease.

  The average particle size of the composite material of the present invention is not particularly limited, but is preferably 0.005 to 0.5 μm, and more preferably 0.005 to 0.2 μm. In the composite material of the present invention, it tends to be difficult to obtain a material having an average particle size less than the lower limit. On the other hand, if the average particle size exceeds the upper limit, metal oxide fine particles (oxygen-activated species transfer material) There is a tendency that contact between the particles) and the carbon-containing component is inhibited.

  In addition, the composite material of the present invention preferably has high dispersibility, and 60% by volume or more of all aggregates may have a particle size in the range of the average particle size ± 50%. preferable. When the composite material of the present invention has such a high dispersibility, the ability to oxidize a carbon-containing component is further improved, and the composite material tends to be uniformly supported by a carrier such as DPF.

  Further, in the composite material of the present invention, in addition to the above-mentioned Ag ultrafine particles, Ag particles larger than Ag ultrafine particles may be present. When such Ag particles are present, such Ag particles serve as nuclei. It is preferable that the metal oxide fine particles cover the periphery of the metal oxide fine particles, and the Ag ultrafine particles are supported on the surface of the metal oxide fine particles. When such Ag particles are present, oxygen active species are also generated by such Ag particles, and the amount of oxygen active species that can be transferred to components such as carbon-containing components, HC, CO, or NO is increased, and the carbon-containing components are reduced. The ability to oxidize tends to improve.

  The particle size of such Ag particles should just be larger than the particle size of the above-mentioned Ag ultrafine particles (preferably 1.1 times or more), and although not particularly limited, the average particle size after firing at 500 ° C. in the atmosphere for 5 hours The diameter is preferably 10 to 100 nm (more preferably 10 to 50 nm), and the average particle diameter after baking at 800 ° C. for 5 hours in an atmosphere consisting of 10% oxygen and 90% nitrogen by volume is 10 to 400 nm. (More preferably, it is 10 to 80 nm). When the average particle diameter of the Ag particles exceeds the above upper limit, the Ag particles tend to be difficult to be covered with the metal oxide fine particles.

Next, the 1st manufacturing method of the composite material of this invention is demonstrated. That is, the first manufacturing method of the composite material of the present invention is:
A step of producing an aggregate in which Ag particles are covered with metal compound fine particles derived from a metal salt capable of changing the valence, from a solution containing an Ag salt and a metal salt capable of changing the valence;
A part of Ag is eluted from the obtained aggregate with an acid and then baked to form metal oxide fine particles made of a metal oxide capable of changing the valence, and an average primary particle size of 0.3 to 30 nm. And a step of obtaining a composite material composed of Ag ultrafine particles having at least a part of +2;
It is a method including.

  Examples of the Ag salt according to the present invention include water-soluble salts such as Ag nitrate, acetate, sulfate, sulfite, and inorganic complex salt. Among them, nitrate (for example, silver nitrate) is preferably used. Examples of the metal salt capable of changing the valence according to the present invention include water-soluble salts such as nitrates, acetates, sulfates, sulfites, and inorganic complex salts of the aforementioned metals. Cerium) is preferably used.

  Further, the solvent for preparing the solution containing the Ag salt and the metal salt is not particularly limited, and water, alcohol (for example, methanol, ethanol, ethylene glycol or the like alone or mixed solvent), etc. Among them, water is particularly preferable.

  Note that the blending amount (preparation amount) of the Ag salt and the metal salt does not need to completely match the ratio of the obtained Ag particles to the metal oxide fine particles, and Ag in the composite material to be obtained. The combination of the Ag salt and the metal salt and the condition of the blending amount are appropriately set according to suitable conditions for the combination and ratio of the particles and the metal oxide fine particles. Further, if an excessive amount of Ag salt is present with respect to the metal salt, all the metal oxide fine particles generated in the solution tend to be part of the aggregate, and components other than the aggregate Is preferred because it does not form in solution.

  In the first method for producing a composite material of the present invention, in the step of forming the aggregate, the metal compound fine particles are generated in the presence of a pH adjuster, and the Ag particles are reduced by the reducing action of the metal compound fine particles. It is preferable to form the aggregates by precipitation.

The requirement for the oxidation-reduction reaction can be explained by the potential of Ag to be used and the metal whose valence can be varied, but the potential is pH-dependent. In general, the potential decreases as the pH increases. Therefore, in the method for producing a composite material of the present invention, it is preferable to control the oxidation-reduction reaction by adding a pH adjuster as appropriate. Further, since the activation energy is changed by adding the pH adjuster, the oxidation-reduction reaction can be made the optimum condition. Examples of such a pH adjuster include NaOH, KOH, NH ₃ , HNO ₃ , and H ₂ SO _4, but it is sufficient to use a general acid or alkali.

  In addition, since Ag has a high potential on the acidic side and the reaction proceeds too quickly, there is a tendency that coarse Ag is likely to precipitate, so that it is preferable to make it alkaline in the presence of a base. At that time, if NaOH is used as a pH adjuster, precipitation occurs, and therefore it is preferable to make it alkaline with ammonia. In this case, ammonia also functions as a complexing agent described later. Further, the concentration of such a base is not particularly limited, but when ammonia is used as the base, it is generally preferable to use a solution having an ammonia concentration of about 1 to 50%. Furthermore, the metal compound fine particles in this case are considered to be the hydroxide of the metal used.

  In the first method for producing the composite material of the present invention, in the step of forming the aggregate, an Ag compound is formed in the presence of a complexing agent, and the Ag compound is reduced by the reducing action of the metal compound fine particles. More preferably, the compound is reduced to precipitate Ag particles.

In order to optimize the oxidation-reduction reaction, it is preferable to add a pH adjusting agent as described above. In this case, however, the metal salt may cause a precipitate depending on the pH. Therefore, even when the precipitate is generated when the complexing agent is not used, the metal salt can be obtained by adding the complexing agent. By doing so, the potential and the activation energy also change, so that the conditions can be appropriately adjusted. For example, in the case of a CeO ₂ —Ag system, Ag is preferably [Ag (NH ₃ ) ₂ ] ⁺ . Examples of such a complexing agent include ammonia, alkali salts of organic acids (such as glycolic acid, citric acid, and tartaric acid), thioglycolic acid, hydrazine, triethanolamine, ethylenediamine, glycine, pyridine, and cyanide.

Furthermore, in the first method for producing a composite material of the present invention, it is preferable to adjust the temperature in the step of forming the aggregate. The temperature condition of the reaction solution is an important factor governing the redox reaction. It is preferable to appropriately adjust the temperature of the solution within a range in which the solvent functions as a liquid. For example, in the case of a CeO ₂ -Ag system, it is preferably 30 ° C. or higher, and more preferably 60 ° C. or higher. As in the examples described later, when the conditions are about 1 to 3 atmospheres and about 100 to 150 ° C., the reaction tends to surely occur, and the reaction time can be shortened.

  Even in the so-called “precipitation method” in which the pH adjusting agent-containing solution (for example, basic solution) is added to and mixed with the metal salt solution in the step of forming the aggregate, the pH adjusting agent-containing solution (for example, The so-called “reverse precipitation method” in which the above metal salt solution is added to and mixed with the basic solution) may be used. In this case, you may add and mix sequentially in the order of the salt of Ag, the said salt of the metal, or the reverse order. The reaction time is not particularly limited, but it is preferably about 0.1 to 24 hours, more preferably about 0.1 to 3 hours for aggregation. Moreover, when using a complexing agent, you may perform the said operation, after previously making a metal salt with a complexing agent.

  Further, the solid content concentration in the reaction solution in the step of forming such an aggregate is not particularly limited, but is preferably 1% by mass to 50% by mass, and preferably 10% by mass to 40% by mass. More preferably, it is 15-30 mass%. If the solid content concentration is less than the lower limit, the accelerating effect of the aggregation treatment tends to be lowered. On the other hand, if the solid content concentration exceeds the upper limit, it tends to be difficult to obtain an aggregate having Ag particles as nuclei.

  By performing the aggregation treatment in this way, an aggregate in which the Ag particles are covered with the metal compound fine particles as described above can be obtained efficiently and reliably.

  Next, in the first method for producing a composite material of the present invention, the aggregate obtained in this way is centrifuged as necessary, and then dispersed in an acid solution to form a part of Ag from the aggregate. Is eluted with acid. Examples of the acid used in the acid treatment include nitric acid, sulfuric acid, hydrofluoric acid, and hydrochloric acid. Although hydrochloric acid is not preferable because it easily forms chloride with Ag, it can be used if chloride ions can be appropriately removed after the acid treatment.

  The pH of the acid solution used for the acid treatment is not particularly limited, but is preferably 2 or less, and more preferably 1 or less. When the pH of the acid solution exceeds the above upper limit, the acid treatment tends to take a long time or the acid treatment tends to be insufficient. Further, the temperature during the acid treatment is not particularly limited, but a range of about 0 to 100 ° C is preferable.

  Furthermore, the time for performing the acid treatment is appropriately set according to the size of the core Ag particles, the target Ag elution amount, the acid solution to be used, and the like. It is preferable to elute a part of Ag with acid over time.

  The amount of Ag eluted by acid treatment in the first method for producing a composite material of the present invention is not particularly limited, but is about 1 to 90% by mass of Ag contained in the aggregate and is a core Ag. It is preferable that it is about 1-100 mass% of Ag which comprises particle | grains.

  Next, in the first method for producing the composite material of the present invention, the aggregate treated in this manner is subjected to centrifugation or washing as necessary, and then fired, whereby the composite of the present invention described above is obtained. Material can be obtained. The conditions for such firing are not particularly limited, but in general, firing in an oxidizing atmosphere (for example, air) at 300 to 600 ° C. for about 1 to 5 hours is preferable.

  In the first method for producing a composite material of the present invention, it is preferable to stop the elution of Ag by adding an alkali at the end of the acid treatment. Thus, by adding an alkali, a hydroxyl group is formed on the surface of the metal oxide fine particles, and the reaction between the hydroxyl group and Ag ions tends to make the Ag ultrafine particles easily supported on the surface of the metal oxide fine particles. .

Examples of the alkali used here include NaOH, KOH, NH _{3 and the} like, among which ammonia is preferable. When ammonia is added, Ag forms an ammine complex, and Ag ultrafine particles tend to be more easily formed by reaction with hydroxyl groups on the surface of the metal oxide fine particles. Furthermore, since the ammine complex is formed in this manner, hydroxyl groups and unreacted Ag ions can be removed from the system, and thus the generation of coarse Ag particles tends to be more reliably suppressed. The amount of alkali to be added is not particularly limited as long as it is an amount that can make the acid treatment solution alkaline, and when ammonia is used, it is at least an amount that makes the eluted Ag completely an ammine complex. Preferably there is.

Next, the 2nd manufacturing method of the composite material of this invention is demonstrated. That is, the second manufacturing method of the composite material of the present invention is:
A step of producing an aggregate in which Ag particles are covered with metal compound fine particles derived from a metal salt capable of changing the valence, from a solution containing an Ag salt and a metal salt capable of changing the valence;
Eluting at least a part of the Ag from the obtained aggregate with an acid;
A metal oxide fine particle composed of an oxide of a metal whose valence can be varied by carrying Ag ultrafine particles on the surface of the metal compound fine particles in the presence of an alkali and then firing, and an average primary particle size of 0.3. Obtaining a composite material composed of Ag ultrafine particles having a diameter of ˜30 nm and at least a part of which is +2;
It is a method including.

  The step of generating aggregates in the second production method of the composite material of the present invention is the same as the step of generating aggregates in the first production method. In the second production method of the composite material of the present invention, the step of eluting at least a part of Ag from the aggregate with an acid (acid treatment step) is the same as the acid treatment step in the first production method.

  However, in the second method for producing a composite material of the present invention, in the acid treatment step, at least a part of Ag contained in the aggregate may be eluted, and Ag contained in the aggregate may be completely eluted. The amount of Ag eluted in the acid treatment step is preferably about 1% by mass or more of Ag contained in the aggregate. In the second method for producing a composite material of the present invention, it is generally preferable to elute Ag with an acid over about 0.1 to 24 hours.

  Next, in the second production method of the composite material of the present invention, the acid-treated aggregate is centrifuged or washed as necessary, and then the presence of alkali on the surface of the metal compound fine particles is obtained. The Ag ultrafine particles are supported below. In this way, the presence of an alkali stops elution of Ag, and a hydroxyl group is formed on the surface of the metal oxide fine particles. By reacting the hydroxyl group with Ag ions, the Ag ultrafine particles are formed on the surface of the metal oxide fine particles. Supported.

The alkali used here and the addition amount thereof are the same as the alkali and the addition amount suitably used for stopping the acid treatment in the first production method. Moreover, as Ag ion used here, it can be made to exist in a solution by adding Ag salt (for example, silver nitrate, silver sulfate, silver carbonate, silver acetate). In addition, although the density | concentration of Ag ion in a solution is not specifically limited, It is preferable that it is about 1.0 * 10 < ^-4 > -5 mol%. Moreover, you may heat in order to accelerate | stimulate reaction in this process, and the processing temperature of about 30-150 degreeC is preferable.

  In addition, when the solution from which Ag is eluted in the previous acid treatment step is used as it is as the reaction solution, Ag ions are contained in the reaction solution, and therefore it is not always necessary to newly add a salt of Ag.

  Next, in the second production method of the composite material of the present invention, the aggregates supporting the Ag ultrafine particles in the presence of alkali in this way are subjected to centrifuging or washing as necessary, followed by firing. Thus, the composite material of the present invention described above can be obtained. The conditions for the firing are the same as the conditions for the firing in the first manufacturing method.

Next, the 3rd manufacturing method of the composite material of this invention is demonstrated. That is, the third production method of the composite material of the present invention is:
A step of dissolving the surface of metal oxide fine particles comprising a metal oxide capable of changing valence with an acid;
By supporting Ag ultrafine particles in the presence of alkali on the surface of the metal oxide fine particles, metal oxide fine particles made of a metal oxide capable of changing the valence, and an average primary particle size of 0.3 to 30 nm. A step of obtaining a composite material comprising Ag ultrafine particles that are present and at least a part of which is +2;
It is a method including.

The metal oxide fine particles comprising a metal oxide capable of changing the valence used in the third production method of the composite material of the present invention are not particularly limited, and commercially available metal oxide fine particles (for example, CeO ₂ powder) are used. Can be used.

  In the third method for producing a composite material of the present invention, the step of dissolving the surface of the metal oxide fine particles with an acid (acid treatment step) is the same as the acid treatment step in the first production method.

  However, in the third method for producing a composite material of the present invention, the surface of the metal oxide fine particles is dissolved in the acid treatment step. The amount of the metal oxide dissolved in the acid treatment step is not particularly limited, and is preferably about 1 to 50% by mass of the metal oxide constituting the metal oxide fine particles. In the third method for producing the composite material of the present invention, it is generally preferable to dissolve the surface of the metal oxide fine particles over about 0.1 to 24 hours.

  Next, in the third method for producing the composite material of the present invention, the acid-treated metal oxide fine particles are centrifuged or washed as necessary, and then the surface of the metal compound fine particles is alkalinized. Ag ultrafine particles are supported in the presence of. In this way, dissolution of the metal oxide is stopped by the presence of the alkali, and a hydroxyl group is formed on the surface of the metal oxide fine particle. By reacting the hydroxyl group with Ag ions, the Ag ultrafine particle becomes a metal oxide fine particle. Supported on the surface.

  The alkali used here and the addition amount thereof are the same as the alkali and the addition amount suitably used for stopping the acid treatment in the first production method. The Ag ions, their ion concentration, and the treatment temperature used here are the same as the Ag ions, their ion concentration, and the treatment temperature used in the second production method.

  In the third production method of the composite material of the present invention, the metal oxide fine particles supporting the Ag ultrafine particles in the presence of alkali in this way are centrifuged, washed or fired as necessary. The composite material of the present invention described above can be obtained.

  Next, the composite material substrate of the present invention will be described. That is, the composite material base material of the present invention comprises a base material and the composite material of the present invention.

  The base material used here is not particularly limited, and is appropriately selected according to the use of the obtained composite material base material. However, the DPF base material, monolithic base material, pellet base material, plate base material, foamed material A ceramic substrate or the like is preferably employed. Further, the material of such a base material is not particularly limited, but a base material made of a ceramic such as cordierite, silicon carbide, mullite, or a base material made of a metal such as stainless steel including chromium and aluminum is suitably employed. .

  The amount of the composite material to be applied to the base material in the composite material base material of the present invention is not particularly limited and is appropriately adjusted according to the use of the composite material base material to be obtained. The amount that the amount of the material is about 10 to 300 g is preferable. The composite material itself of the present invention can be used by pelletizing it. Moreover, in the composite material base material of the present invention, the base material has 1 to 300 μm pores, and an average of 0.5 to 50 times the average particle size of the aggregates in the pores. It is preferable that the coating layer having a thickness is formed of the composite material. Such a composite material substrate of the present invention is very useful as an exhaust purification substrate and the like.

Next, the composite material dispersion of the present invention and the production method thereof will be described. That is, the first composite material dispersion of the present invention contains the composite material of the present invention and a dispersion medium. The first composite material dispersion preferably further contains a binder. The binder used here is not particularly limited, and for example, ceria sol is preferably used. Further, the mixing ratio of the composite material and the binder is not particularly limited, and the mixing ratio of the composite material and the binder is preferably about 99: 1 to 80:20 by weight ratio. For example, in the case of CeO ₂ -Ag system, even when a binder is used, a highly dispersible dispersion (slurry) can be easily obtained by ultrasonic treatment.

  The second composite material dispersion of the present invention contains a composite material before firing obtained in the first or second production method of the composite material of the present invention and a dispersion medium. Is. In such a second composite material dispersion, 50 ions remaining in the system are obtained from the solution containing the composite material before firing obtained in the first or second production method of the composite material of the present invention. It is preferable that the composite material is contained in a state obtained by separating 99.9%. By removing residual ions caused by the salt or complexing agent, a dispersion with very high dispersibility can be obtained.

  Next, the manufacturing method of the composite material base material of this invention is demonstrated. That is, the first method for producing a composite material substrate of the present invention is a method for obtaining a composite material substrate by firing the first composite material dispersion of the present invention after contacting the substrate. Moreover, the 2nd manufacturing method of the composite material base material of this invention is a method of obtaining a composite material base material by baking after making the said 2nd composite material dispersion liquid of this invention contact a base material.

  Here, the method for bringing the first or second composite material dispersion into contact with the base material is not particularly limited. For example, when entering the pores of the filter base material such as DPF, contact is made while applying ultrasonic waves. It is preferable to make it. In addition, the firing conditions in this case are preferably the same conditions as the aforementioned firing conditions.

  Further, according to the second method for producing a composite material base material of the present invention, the carbon-containing component such as soot and the component capable of oxidizing HC, CO, NO, etc. are aggregates themselves. Therefore, a more effective composite material substrate can be provided. The method of obtaining the base material by baking the second composite material dispersion liquid after contacting the base material is not limited to the composite material obtained in the process of obtaining the composite material. It can also be applied when obtaining a substrate. That is, if the composite material itself plays the role of a binder, it may be an aggregate of particles of the same species. In this case, in order to obtain a uniform coat layer, it is preferable that the dispersibility of the composite material is high. In order to perform thin layer coating, it is preferable that the particle diameter is small. Furthermore, in order to obtain a better coating layer, it is preferable to suppress decomposition of by-products (for example, ammonium nitrate) derived from the residual ions by removing the residual ions in the system.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

  In addition, cerium nitrate hexahydrate was used as the Ce material, silver nitrate was used as the Ag material, and lanthanum nitrate hexahydrate was used as the La material.

  Moreover, the aggregate obtained by using mol% of the additional component with respect to the total amount of Ce and an additional component of a nitrate solution preparation stage was expressed. For example, an agglomerate prepared with a preparation ratio of Ce: Ag = 40: 60, Ce: La = 90: 10 (Ce: Ag: La = 90: 135: 10) is expressed as “CeAg-La10”. did.

Example 1
<Preparation of aggregate>
A nitrate solution containing Ce, Ag, and an additive component was prepared so that the content (mol%) of the additive component (La) with respect to the total amount of Ce and the additive component was La 10 mol%. A CeO ₂ -Ag-La aggregate “CeAg-La10” was obtained. That is, first, a solution in which 50.46 g of Ce (NO ₃ ) ₃ .6H ₂ O, 5.59 g of La (NO ₃ ) ₃ and 29.62 g of AgNO ₃ were dissolved in 120 mL of water was prepared. Next, ammonia water was prepared by diluting 38.21 g of 25% aqueous ammonia into 100 g of water. Then, the solution prepared as described above is put into the place where the aqueous ammonia is being stirred (reverse precipitation), and the stirring is continued for 10 minutes, and then under the condition of 2 atm in the closed system in the presence of water. Then, the mixture was heated to 120 ° C. and subjected to an aggregation treatment for 2 hours to prepare an aggregate.

<Evaluation 1 of Ag content rate>
The content of Ag in the obtained CeAg-La10 was analyzed by ICP emission spectrometry. As a result, it was 47.82 mol% on the basis of Ce + Ag + La and 49.96 mol% on the basis of Ce + Ag.

<Evaluation of CeO ₂ particle diameter and Ag particle diameter>
When the CeO ₂ particle diameter (average primary particle diameter) and the Ag particle diameter (average primary particle diameter) in the obtained CeAg-La10 were determined by XRD, the CeO ₂ particle diameter was 12 nm and the Ag particle diameter was 28 nm.

<TEM observation 1>
The form of the obtained CeAg-La10 after the aggregation treatment (before firing) was observed by TEM. The obtained results are shown in FIG. Moreover, the spectrum was calculated | required by the energy dispersive X-ray spectroscopy in the measurement point in the TEM photograph shown in FIG. 1, and the count number about the component (Ce and Ag) contained was calculated | required. The obtained results are shown in FIG. Furthermore, the surface state of the same composition (before firing) was observed by SEM. The obtained results are shown in FIG. As is clear from the results shown in FIGS. 1 to 3, it was confirmed that an aggregate in which the periphery of the Ag particles was covered with CeO ₂ particles was sufficiently formed after the aggregation treatment.

<Evaluation of pore volume and pore size distribution>
The pore volume and pore size distribution in the obtained CeAg-La10 were measured with a mercury porosimeter. As a result, the volume of all pores was 0.17 cc / g, and the volume of pores having a pore diameter of 0.01 to 1.0 μm was 0.16 cc / g. The range of void pores formed by the aggregates was 0.05 to 0.15 μm, and the average void pore diameter was 0.1 μm. Therefore, it was confirmed that the volume of void pores having a pore diameter of 0.05 to 0.15 μm in the range of average void pore diameter ± 50% occupies 80% of the total volume of the void pores. It was. It was also confirmed that the volume of pores having a pore diameter of 0.05 to 0.5 μm accounted for 85% of the total pore volume.

<Acid treatment>
Next, after the obtained aggregate (CeAg-La10) was separated by centrifugation, the aggregate was dispersed in 150 ml of water, and then nitric acid (made by Wako Pure Chemical Industries, specific gravity: 1.40, product number) with stirring. 147-01346) 30 ml was added, and stirring was continued at 15 ° C. for 12 hours to carry out elution treatment (acid treatment) of Ag. In addition, the operation of stopping the elution treatment of Ag in this example was performed by adding NH ₃ water having a concentration of 25% until pH = 11 until the eluted Ag was completely an ammine complex.

  After the aggregate subjected to the acid treatment was separated again by centrifugation in this way, the composite material of the present invention was obtained by firing at 500 ° C. in the atmosphere for 5 hours.

<Evaluation 2 of Ag content rate>
When the content rate of Ag in the obtained composite material was analyzed by the ICP emission spectrometry, it was 16 mol% on the basis of Ce + Ag.

<TEM observation 2>
Furthermore, the obtained composite material was observed by TEM with high resolution. The obtained results are shown in FIG. The spectrum was obtained by energy dispersive X-ray spectroscopy at the measurement points (1 to 4) shown in FIG. 4, and the count number for the contained components (Ce and Ag) was obtained to calculate the elemental composition at each measurement point. The content of Ag was 1: 14.15 mol%, 2: 16.52 mol%, 3: 7.93 mol%, 4: 11.73 mol%, 5: 14.51 mol%, 6: 13.58 mol%, 7: It was 13.04 mol%. Although Ag particles could not be confirmed in the CeO ₂ portion by TEM, Ag was also contained in that portion, and it was confirmed that Ag ultrafine particles were present on CeO ₂ .

<ESR measurement 1>
For the purpose of detecting Ag ²⁺ , the obtained composite material (CeAg-La10 HNO ₃ 12h) was subjected to ESR measurement in the air at room temperature using an ESR measurement device (ESP300E, manufactured by Bruker). The obtained ESR spectrum is shown in FIG. From the results shown in FIG. 5, the presence of Ag ²⁺ in the obtained composite material was confirmed.

(Example 2)
Except that the aggregate (CeAg-La10) obtained in the same manner as in Example 1 was used, the temperature in the acid treatment was 25 ° C., the mixture was stirred for 8 hours and then allowed to stand for 16 hours after addition of nitric acid. Obtained a composite material of the present invention in the same manner as in Example 1.

When the content ratio of Ag in the obtained composite material was analyzed in the same manner as in <Evaluation 2 of Ag content ratio>, it was 7.0 mol% based on Ce + Ag. Moreover, the amount of exposed Ag is measured by performing oxidation-reduction titration with O ₂ and H ₂ at 170 ° C., and the Ag particle size (average primary particle size) is obtained based on the composition analysis and the obtained amount of exposed Ag. As a result, it was 3.8 nm. On the other hand, when XRD measurement was performed on the obtained composite material, an Ag peak could not be confirmed.

  Moreover, when ESR measurement was performed about the obtained composite material, the obtained ESR spectrum was the same as the ESR spectrum shown in FIG.

  Furthermore, the pore size distribution in the obtained composite material was measured with a mercury porosimeter. The obtained result is shown in FIG. As is clear from the results shown in FIG. 6, it was confirmed that the composite material obtained in Example 2 had pores centered at 0.05 μm and the uniformity of the pore size distribution was also high. It was.

(Example 3)
After the aggregate (CeAg-La10) obtained in the same manner as in Example 1 was separated by centrifugation, the aggregate (solid content) was dispersed in 150 ml of water, and then nitric acid (manufactured by Wako Pure Chemical Industries, Ltd.) with stirring. , Specific gravity: 1.40, product number: 147-01346) 25 ml was added, and stirring was continued at 25 ° C. for 24 hours to carry out elution treatment (acid treatment) of Ag.

  A part of the aggregate subjected to the acid treatment in this way was taken out, separated by centrifugation and sufficiently washed, and then analyzed for the content ratio of Ag by ICP emission spectrometry. It was confirmed that the acid treatment was carried out until Ag was eluted.

In this example, the operation of stopping the elution process of Ag was performed after stopping the stirring and allowing to stand, and after removing only the supernatant Ag-containing solution, the concentration was 25 until the solution became alkaline (pH = 11). % NH ₃ water was added. Therefore, dissolved Ag remains in the solution, and [Ag (NH ₃ ) ₂ )] ⁺ generated from the Ag reacts with Ce (OH) ₃ formed on the surface of the CeO ₂ particles. As a result, Ag (Ag complex) was supported on the surface of the CeO ₂ particles.

  Thus, after aggregating the aggregate carrying Ag in the presence of alkali again by centrifugation, firing was performed in the atmosphere at 500 ° C. for 5 hours to obtain the composite material of the present invention.

  When the content rate of Ag in the obtained composite material was analyzed in the same manner as in <Evaluation 2 of Ag content rate>, it was 9.7 mol% on the basis of Ce + Ag. Moreover, when ESR measurement was performed about the obtained composite material, the obtained ESR spectrum was the same as the ESR spectrum shown in FIG.

(Comparative Example 1)
AgNO ₃ and CeO ₂ powder (manufactured by Wako Pure Chemical Industries, Ltd., product number: 034-101885) were weighed so that the molar ratio was 15:85, and water was added to the mixture of both to dissolve AgNO ₃ . Next, the obtained dispersion was heated and stirred with a stirrer, evaporated to dryness, and further calcined in the atmosphere at 500 ° C. for 5 hours. The Ag content (mol%) with respect to the total amount of Ce and Ag was 15 mol%. An Ag-supported CeO ₂ powder “Ag / CeO ₂ ” was obtained.

(Comparative Example 2)
AgNO ₃ and α-Al ₂ O ₃ powder (manufactured by Showa Denko KK, trade name: UA-5205) are weighed so that the molar ratio is 50:50, and water is added to the mixture of both to dissolve AgNO ₃ . I let you. Next, the obtained dispersion was heated and stirred with a stirrer, evaporated to dryness, and further calcined in the atmosphere at 500 ° C. for 5 hours. The Ag content (mol%) with respect to the total amount of Al and Ag was 50 mol%. An Ag-supported α-Al ₂ O ₃ powder “Ag / α-Al ₂ O ₃ ” was obtained.

<Measurement of Ag particle diameter>
For the Ag-supported CeO ₂ powder obtained in Comparative Example 1 and the Ag-supported α-Al ₂ O ₃ powder obtained in Comparative Example 2, the Ag particle size (average primary particle size) was determined in the same manner as in Example 2. However, they were 40 nm (Comparative Example 1) and 124 nm (Comparative Example 2), respectively.

<ESR measurement 2>
For the purpose of detecting Ag ²⁺ , the following measurement temperatures were used for the Ag-supported CeO ₂ powder obtained in Comparative Example 1 and the Ag-supported α-Al ₂ O ₃ powder obtained in Comparative Example 2 using the following ESR measurement apparatus. And ESR measurement was performed under pretreatment conditions.
Measuring device: ESP350E, Bruker measuring temperature: 20K
Pre-processing conditions:
(i) A 20 mg sample was weighed, placed in an ESR sample tube, and treated at 600 ° C. under O ₂ flow (30 ml / min). Thereafter, the sample was taken out of the electric furnace while flowing O ₂ and allowed to cool to room temperature.
(ii) The gas was then switched to He (30 ml / min) and purged at room temperature for 30 minutes.

The obtained ESR spectrum is shown in FIG. 7 (Comparative Example 1) and FIG. 8 (Comparative Example 2). From the results shown in FIG. 7 and FIG. 8, Ag ²⁺ was not detected although the obtained materials both carry Ag.

<Evaluation 1 of Soot Oxidation Performance by CO ₂ Generation Strength>
Samples 1 were prepared by mixing the composite materials obtained in Examples 1 to 3 with soot (carbon composition 99.9% or more) by the following mixing method (Sample 1). Further, soot in the method of mixing the following respective Ag supported _alpha-Al 2 _{O 3} powder obtained in Comparative Example 2 Ag-supported CeO ₂ powder obtained in Comparative Example 1 (Sample 1) and (Sample 2) ( Sample 1 and Sample 2 were prepared by mixing with a carbon composition of 99.9% or more. Note that the mixing ratio of the composite material (or powder) and the soot was set to 2: 0.1 by weight ratio (g).

  (Sample 1) Using a stirrer (manufactured by AS ONE, MMPS-M1) and a magnetic mortar (manufactured by AS ONE, MP-02), mix for 3 minutes by electric mixing with a speed scale of “3”. A mixed homogeneous mixture was obtained.

  (Sample 2) The uniform mixture of Sample 1 was further mixed with an agate mortar, and the mixing was repeated until no further improvement in soot oxidation activity was observed by mixing, thereby mixing the uniform mixture by the “strong mixing method” Got. In the drawings attached to this specification, a sample corresponding to the sample 2 is denoted as “tight”.

  In the case where the catalyst and the soot are brought into contact with each other in the pores using the DPF, the so-called “loose-” in which the catalyst and the soot are simply mixed by being pressed by the exhaust pressure or by the multiple collisions in the DPF pores. The contact is better than the mixed state called “contact”. Sample 1 corresponds to a mixed state in which the catalyst and soot are brought into contact with each other in the pores using DPF.

  On the other hand, in the mixed state called “strong mixing method” in which mixing is performed to the limit with a mortar, the contact property is the best, but the influence of the form factor is eliminated and the evaluation is focused on only the chemical properties. Sample 2 corresponds to a mixed state called “strong mixing method”.

Next, with respect to Sample 1 and Sample 2, the CO ₂ generation intensity at the time of temperature rise was measured by the TG-mass method. As the thermogravimetric analyzer, “TG8120” (manufactured by Rigaku Corporation) was used. “GC-MS5972A” (manufactured by Hewlett Packard) was connected to the thermogravimetric analyzer, and the mass spectrum of gas components generated by the thermogravimetric analyzer was measured. Measurement conditions were as follows. In an O ₂ 10% / He balance atmosphere, the temperature was increased to 800 ° C. at a temperature increase rate of 20 K / min, and m / e = 44 component was measured as a CO ₂ component generated by soot oxidation. The obtained results are shown in FIG. 9 (Examples 1 to 3), FIG. 10 (Comparative Example 1), and FIG. 11 (Comparative Example 2).

As is apparent from the results shown in FIGS. 9 to 11, the soot oxidation temperature is relatively high even when the comparative powder without Ag ultrafine particles is used, but the soot oxidation temperature is lowered when the composite material of the present invention is used. Confirmed to do. The present inventors speculate that this phenomenon is caused by the soot oxidation temperature being lowered by the oxygen active species generated from the Ag ultrafine particles and CeO ₂ .

Example 4
After the aggregate (CeAg-La10) obtained in the same manner as in Example 1 was separated by centrifugation, the aggregate (solid content) was dispersed in 150 ml of water, and then nitric acid (manufactured by Wako Pure Chemical Industries, Ltd.) with stirring. , Specific gravity: 1.40, product number: 147-01346) 25 ml was added, and stirring was continued at 25 ° C. for 9 hours to carry out elution treatment (acid treatment) of Ag.

The operation for stopping the elution treatment of Ag in this example was performed by adding NH ₃ water with a concentration of 25% until the solution became alkaline (pH = 11) with the Ag-containing solution removed by centrifugation. It was.

  After the acid-treated aggregate was separated again by centrifugation, the aggregate (solid content) was dispersed with 150 ml of water to obtain a slurry. Next, the slurry was brought into contact with a test piece size (35 ml) DPF (manufactured by Cordierite, porosity: 65%, average pore diameter: 30 μm). The composite material substrate of the present invention in which the composite material of the present invention is coated is obtained by sucking in that state and then repeatedly firing it in the atmosphere at 500 ° C. for 1 hour until the carrying amount (coating amount) reaches 70 g / L. (Test piece) was obtained. When the particle size distribution of the slurry was measured, the aggregate of about 0.1 μm was stably dispersed, so that it was confirmed that coating with DPF was easy.

<Peel test>
The obtained test piece was immersed in ion-exchanged water and irradiated with ultrasonic waves for 2 hours, but peeling of the composite material of the present invention was not confirmed.

<Evaluation 2 of Soot Oxidation Performance by CO ₂ Generation Strength>
Using the obtained test piece, about 2 g / L of PM is deposited at 200 ° C. in the exhaust of the diesel engine, and then the unburned hydrocarbon component is removed by maintaining the N ₂ atmosphere at 500 ° C. for 15 minutes. I did it. For such test piece was attached actual PM in the flow rate 30L / _min, the O 2 10% atmosphere, the temperature was raised at a heating rate of 20 ° C. / min. The soot oxidation performance was evaluated based on the CO ₂ peak at this time. The obtained result is shown in FIG.

  Further, the soot oxidation performance is similarly evaluated for a test piece for comparison in which the actual machine PM is adhered to the DPF of only the base material, and the obtained results are also shown in FIG.

As is apparent from the results shown in FIG. 12, the test piece coated with the composite material of the present invention has a PM oxidation temperature higher than that of the test piece for comparison not coated with the composite material of the present invention. descend. Therefore, it was confirmed that the composite material of the present invention comprising Ag ultrafine particles and CeO ₂ functions as an oxidation catalyst.

  As described above, according to the present invention, a composite material that is very useful as an oxidation catalyst that can sufficiently oxidize a carbon-containing component such as soot, a component such as HC, CO, or NO at a lower temperature, In addition, a composite material substrate using the same can be provided. Furthermore, according to the present invention, such a composite material and a composite material substrate using the composite material can be obtained efficiently and reliably.

  Therefore, the present invention provides a means for removing PM components in exhaust gas, a means for preventing dielectric breakdown due to adhesion of carbon in insulators, a means for preventing coking in reforming catalysts, a process for carbon materials such as fullerene and carbon nanotubes, and ethylene. The present invention is very useful as a technique relating to an oxidation catalyst that can be applied to partial oxidation of hydrocarbons such as partial oxidation to ethylene epoxy.

In addition, the composite material of the present invention includes an ozone decomposition catalyst capable of decomposing O ₃ from around room temperature, an exhaust purification material utilizing the property of taking in oxygen in the gas phase, and a conductive material such as Pt, Au, and Ag. It is also useful as a catalyst for an air electrode of a fuel cell using high properties.

It is a TEM photograph which shows the measurement point of the form after the aggregation process (before baking) of CeAg-La10 obtained in Example 1. FIG. It is a graph which shows the count number about Ce and Ag in the measurement point shown in FIG. It is a SEM photograph which shows the form after the aggregation process (before baking) of CeAg-La10 obtained in Example 1. FIG. 2 is a TEM photograph showing measurement points of the composite material obtained in Example 1. FIG. 4 is a graph showing the results of ESR measurement performed on the composite material obtained in Example 1. 4 is a graph showing the results of measuring the pore size distribution in the composite material obtained in Example 2. 6 is a graph showing the results of ESR measurement performed on the Ag-supported CeO ₂ powder obtained in Comparative Example 1. 6 is a graph showing the results of ESR measurement performed on Ag-supported α-Al ₂ O ₃ powder obtained in Comparative Example 2. It is a graph showing the results of measurement of the CO ₂ generation strength for the composite material obtained in Example 1-3. 6 is a graph showing the results of measuring the CO ₂ generation strength of the Ag-supported CeO ₂ powder obtained in Comparative Example 1. 6 is a graph showing the results of measuring the CO ₂ generation strength of the Ag-supported α-Al ₂ O ₃ powder obtained in Comparative Example 2. Is a graph showing the results of measurement of the CO ₂ generation strength for the test piece was attached actual PM.

Claims (17)

  It is characterized by comprising metal oxide fine particles made of a metal oxide capable of changing the valence, and Ag ultrafine particles having an average primary particle size of 0.3 to 30 nm and at least a part of which is +2 valent. Composite material. Before the second metal oxide constituting the Kikin genus oxide fine particles, La, Ce, Pr, Nd , Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, It is at least one selected from the group consisting of oxides of Zr, Fe, Ti, Al, Mg, Co, Ni, Mn, Cr, Mo, W and V, solid solutions thereof, and composite oxides thereof. The composite material according to claim 1.   The metal oxide fine particles are oxygen active species transfer material particles made of an oxygen active species transfer material capable of transferring oxygen active species generated by the Ag ultrafine particles. The composite material described in 1. The oxygen active species transfer material is a composite oxide containing CeO ₂ or Ce, and at least one selected from the group consisting of La, Nd, Pr, Sm, Y, Ca, Ti, Fe, Zr and Al is added to the metal The composite material according to claim 3, further comprising:   The composite material according to any one of claims 1 to 4, wherein an average primary particle size of the metal oxide fine particles after firing at 500 ° C for 5 hours in the air is 1 to 75 nm. The composite material according to any one of claims 3 to 5, wherein the composite material is an oxidation catalyst for oxidizing a carbon-containing component . A step of producing an aggregate in which Ag particles are covered with metal compound fine particles derived from a metal salt capable of changing the valence, from a solution containing an Ag salt and a metal salt capable of changing the valence;
A part of Ag is eluted from the obtained aggregate with an acid and then baked to form metal oxide fine particles made of a metal oxide capable of changing the valence, and an average primary particle size of 0.3 to 30 nm. And a step of obtaining a composite material composed of Ag ultrafine particles having at least a part of +2;
A method for producing a composite material, comprising:   The method for producing a composite material according to claim 7, wherein when a part of the Ag is eluted from the aggregate with an acid, an alkali is added to stop the elution. A step of producing an aggregate in which Ag particles are covered with metal compound fine particles derived from a metal salt capable of changing the valence, from a solution containing an Ag salt and a metal salt capable of changing the valence;
Eluting at least a part of the Ag from the obtained aggregate with an acid;
A metal oxide fine particle composed of an oxide of a metal whose valence can be varied by carrying Ag ultrafine particles on the surface of the metal compound fine particles in the presence of an alkali and then firing, and an average primary particle size of 0.3. Obtaining a composite material composed of Ag ultrafine particles having a diameter of ˜30 nm and at least a part of which is +2;
A method for producing a composite material, comprising: A step of dissolving the surface of metal oxide fine particles comprising a metal oxide capable of changing valence with an acid;
By supporting Ag ultrafine particles in the presence of alkali on the surface of the metal oxide fine particles, metal oxide fine particles made of a metal oxide capable of changing the valence, and an average primary particle size of 0.3 to 30 nm. A step of obtaining a composite material comprising Ag ultrafine particles that are present and at least a part of which is +2;
A method for producing a composite material, comprising:   The said alkali is ammonia, The manufacturing method of the composite material as described in any one of Claims 8-10 characterized by the above-mentioned.   A composite material base material comprising a base material and the composite material according to any one of claims 1 to 6.   The composite material substrate according to claim 12, wherein the composite material substrate is used as an exhaust purification substrate.   A composite material dispersion liquid comprising the composite material according to any one of claims 1 to 6 and a dispersion medium.   The composite material dispersion according to claim 14, further comprising a binder.   A composite material dispersion, comprising: a composite material before firing obtained in the process of the method for producing a composite material according to any one of claims 7 to 10; and a dispersion medium. .   A method for producing a composite material base material, wherein the composite material base material is obtained by firing the composite material dispersion liquid according to any one of claims 14 to 16 after contacting the base material.