JP2014158992A - Exhaust gas purification catalyst and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new exhaust gas purification catalyst which contains nickel as catalyst component, and a manufacturing method thereof.SOLUTION: An exhaust gas purification catalyst is provided, including a plurality of binary metal particles consisting of silver and nickel with an average particle diameter of more than 0 nm and less than 100 nm supported on a catalyst carrier. The manufacturing method of an exhaust gas purification catalyst is further provided, including the steps of: depositing binary metal particles consisting of silver and nickel in an ionic liquid by sputtering target material which contains silver and nickel; and supporting the produced binary metal particles on a catalyst carrier.

Description

  The present invention relates to an exhaust gas purifying catalyst and a method for producing the same, and more particularly to an exhaust gas purifying catalyst containing nickel as a catalyst component and a method for producing the same.

The exhaust gas discharged from automobile internal combustion engines such as gasoline engines and diesel engines contains harmful components such as carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NOx). For this reason, in general, an exhaust gas purification device for decomposing and removing these harmful components is provided in the vehicle, and these harmful components are rendered harmless by the exhaust gas purification catalyst provided in the exhaust gas purification device. Has been. Conventionally, as such an exhaust gas purification catalyst, a three-way catalyst that simultaneously performs oxidation of CO and HC and reduction of NOx in exhaust gas has been used. Specifically, alumina (Al ₂ O ₃ ) or the like is used. A porous oxide carrier in which a noble metal, in particular, a platinum group element such as platinum (Pt), rhodium (Rh), palladium (Pd) is supported is widely known.

  However, these platinum group elements are very expensive rare metals because they are produced in few regions and their production is biased to specific regions such as South Africa and Russia. In addition, these platinum group elements are used in an increased amount with the tightening of exhaust gas regulations for automobiles, and therefore there is a concern about the depletion of resources. For this reason, while reducing the usage-amount of a platinum group element, it is required to substitute the role of the said platinum group element with another metal etc. in the future. Thus, much research has been conducted on catalyst components for reducing or replacing the amount of platinum group elements used.

  Patent Document 1 describes a NOx purification catalyst in which Au and Fe are supported on a catalyst carrier, and in which at least a part of Au and Fe are present in close proximity to each other. In Patent Document 1, as a method for producing the NOx purification catalyst, a reducing agent such as sodium borohydride is added to a solution containing a protective agent such as Au salt, Fe salt, or polyvinylpyrrolidone (PVP). A method is described in which Au ions and Fe ions contained in the solution are reduced, and metal particles composed of Au and Fe thus obtained are supported on a catalyst carrier powder.

JP 2012-163059 A

  As catalyst components that can be substituted for platinum group elements, in addition to Fe (iron) and the like described in Patent Document 1 above, several metals, particularly some base metals, have been proposed in other documents and the like. Yes. However, it is known that base metals such as iron are generally more easily oxidized than platinum group elements. Therefore, even if such a base metal is used as a catalyst component of the exhaust gas purifying catalyst, the base metal is relatively easily oxidized by an oxidizing component such as oxygen contained in the exhaust gas. In this case, metalization of the base metal becomes insufficient, and as a result, sufficient catalytic activity cannot be achieved for exhaust gas purification, particularly NOx reduction purification.

  Therefore, in order to maintain the base metal in the metal state instead of the oxide state and achieve high catalytic activity for exhaust gas purification, the exhaust gas air-fuel ratio is sufficiently richer than the stoichiometric air-fuel ratio (stoichiometric), for example. It is typically required to control to a good air / fuel ratio. However, such driving in a fuel-rich atmosphere is generally not preferable because it causes a significant deterioration in fuel consumption.

  In the present invention, as a catalyst component in place of the platinum group element, investigations have been made with particular attention to Ni (nickel) among various base metals. Accordingly, an object of the present invention is to provide a novel exhaust gas purifying catalyst containing nickel as a catalyst component, and an exhaust gas purifying catalyst having improved exhaust gas purifying activity, particularly NOx reducing activity, and a method for producing the same. That is.

The present invention for solving the above problems is as follows.
(1) An exhaust gas purifying catalyst characterized in that a plurality of binary metal particles made of silver and nickel and having an average particle diameter of more than 0 nm and less than 100 nm are supported on a catalyst carrier.
(2) The exhaust gas purifying catalyst as described in (1) above, wherein the average content of silver in the binary metal particles is more than 5 atomic% and not more than 90 atomic%.
(3) The exhaust gas purifying catalyst as described in (2) above, wherein an average content of silver in the binary metal particles is 10 atomic% or more and 70 atomic% or less.
(4) The exhaust gas purifying catalyst as described in (3) above, wherein the average content of silver in the binary metal particles is 50 atomic% or more and 70 atomic% or less.
(5) The exhaust gas purifying catalyst as described in any one of (1) to (4) above, wherein the average particle size of the binary metal particles is more than 0 nm and not more than 20 nm.
(6) The exhaust gas purifying catalyst as described in (5) above, wherein the average particle size of the binary metal particles is more than 0 nm and not more than 10 nm.
(7) The exhaust gas purifying catalyst as described in any one of (1) to (6) above, which is a catalyst for purifying NOx.
(8) A deposition step of depositing binary metal particles composed of silver and nickel in an ionic liquid by sputtering a target material containing silver and nickel, and a support for supporting the obtained binary metal particles on a catalyst carrier A method for producing an exhaust gas purifying catalyst according to any one of the above (1) to (7), comprising a step.
(9) The method according to (8), further comprising a calcining step in which the exhaust gas-purifying catalyst is heat-treated in an oxidizing atmosphere at a temperature higher than 300 ° C. and lower than 800 ° C. after the supporting step.
(10) The method according to (8) or (9) above, further comprising a reduction step after the supporting step or the baking step.
(11) The method according to any one of (8) to (10) above, wherein the target material is a disk-shaped material in which silver plates and nickel plates are alternately arranged in a radial pattern.
(12) The above (8) to (11), wherein the ionic liquid is selected from the group consisting of an aliphatic ionic liquid, an imidazolium ionic liquid, a pyridinium ionic liquid, and combinations thereof. The method as described in any one of these.
(13) The aliphatic ionic liquid comprises N, N, N-trimethyl-N-propylammonium bis (trifluoromethanesulfonyl) amide, N-methyl-N-propylpiperidinium bis (trifluoromethanesulfonyl) imide, N , N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium bis (trifluoromethanesulfonyl) imide, N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium tetrafluoroborate And the method according to (12) above, which is selected from the group consisting of combinations thereof.
(14) The imidazolium-based ionic liquid is 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methyl-imidazolium chloride, 1-ethyl-3-methylimidazolium (L) -lactate, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium Hexafluorophosphate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-butyl-3-methylimidazolium (L) -lactic acid Salt, 1-hexyl-3-methylimidazolium bromide, 1-hexyl-3 Methylimidazolium chloride, 1-hexyl-3-methylimidazolium hexafluorophosphate, 1-hexyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium trifluoromethanesulfonate, 1-octyl-3-methylimidazolium chloride, 1-octyl-3-methylimidazolium hexafluorophosphate, 1-decyl-3-methylimidazolium chloride, 1-dodecyl-3-methylimidazolium chloride, 1- Tetradecyl-3-methylimidazolium chloride, 1-hexadecyl-3-methylimidazolium chloride, 1-octadecyl-3-methylimidazolium chloride, 1-ethyl-2,3-dimethylimidazolium bromide, 1-ethyl- , 3-Dimethylimidazolium chloride, 1-butyl-2,3-dimethylimidazolium bromide, 1-butyl-2,3-dimethylimidazolium chloride, 1-butyl-2,3-dimethylimidazolium tetrafluoroborate 1-butyl-2,3-dimethylimidazolium trifluoromethanesulfonate, 1-hexyl-2,3-dimethylimidazolium bromide, 1-hexyl-2,3-dimethylimidazolium chloride, 1-hexyl-2, (12) characterized in that it is selected from the group consisting of 3-dimethylimidazolium trifluoroborate, 1-hexyl-2,3-dimethylimidazolium trifluoromethanesulfonate, and combinations thereof The method described.
(15) The pyridinium-based ionic liquid comprises 1-ethylpyridinium bromide, 1-ethylpyridinium chloride, 1-butylpyridinium bromide, 1-butylpyridinium chloride, 1-butylpyridinium hexafluorophosphate, 1-butylpyridinium tetrafluoro Borate, 1-butylpyridinium trifluoromethanesulfonate, 1-hexylpyridinium bromide, 1-hexylpyridinium chloride, 1-hexylpyridinium hexafluorophosphate, 1-hexylpyridinium tetrafluoroborate, 1-hexylpyridinium The method according to (12) above, which is selected from the group consisting of trifluoromethanesulfonate and combinations thereof.

  ADVANTAGE OF THE INVENTION According to this invention, the catalyst for exhaust gas purification containing the binary metal particle which consists of silver and nickel in which silver and nickel coexisted by nano level can be obtained. Further, according to such an exhaust gas purifying catalyst, silver and nickel coexist in the same metal particle at a nano level, so that, for example, compared with an exhaust gas purifying catalyst containing metal particles of nickel alone, Oxidation can be remarkably suppressed. As a result, according to the present invention, the catalytic activity of nickel can be maintained at a high level, so that the exhaust gas purification activity, particularly the NOx reduction activity, of the obtained exhaust gas purification catalyst can be remarkably improved. is there.

It is the figure which showed typically the manufacturing method of the catalyst for exhaust gas purification of this invention. It is the figure which showed typically the target material containing silver and nickel used in one embodiment of the method of this invention. (A) And (b) shows the photograph by the transmission electron microscope (TEM) of the Ag-Ni binary metal particle (Ag average content 62 atomic%) in Example 1 synthesize | combined in BMI-PF6, (c ) Shows a histogram prepared by measuring the particle diameter of a number of Ag-Ni binary metal particles in (a). (A) And (b) shows the photograph by the transmission electron microscope (TEM) of the Ag-Ni binary metal particle (Ag average content 55 atomic%) in Example 2 synthesize | combined in BMI-PF6, (c ) Shows a histogram prepared by measuring the particle diameter of a number of Ag-Ni binary metal particles in (a). (A) And (b) shows the photograph by the transmission electron microscope (TEM) of the Ag-Ni binary metal particle (Ag average content 10 atomic%) in Example 3 synthesize | combined in BMI-PF6, (c ) Shows a histogram prepared by measuring the particle diameter of a number of Ag-Ni binary metal particles in (a). (A) And (b) shows the photograph by the transmission electron microscope (TEM) of the Ag-Ni binary metal particle (Ag average content 5 atomic%) in Example 4 synthesize | combined in BMI-PF6, (c ) Shows a histogram prepared by measuring the particle diameter of a number of Ag-Ni binary metal particles in (a). (A) shows the photograph by the transmission electron microscope (TEM) of the Ag-Ni bimetallic particle (Ag average content 68 atomic%) in Example 5 synthesize | combined in TMPA-TFSA, (b) shows (a ) Shows a histogram prepared by measuring the particle diameters of a number of Ag-Ni binary metal particles. (A) And (b) shows the photograph by the transmission electron microscope (TEM) of the Ag metal particle in the comparative example 1 synthesize | combined in BMI-PF6, (c) is many Ag metal particles in (a). The histogram created by measuring the particle size is shown. (A) shows the photograph by the transmission electron microscope (TEM) of the Ni metal particle in the comparative example 2 synthesize | combined in BMI-PF6, (b) measured the particle size of many Ni metal particles in (a). A histogram created as shown in FIG. The analysis result by the scanning transmission electron microscope (STEM-EDX) with an energy dispersive X-ray analyzer of the exhaust gas purification catalyst of Example 2 is shown. The analysis result by STEM-EDX of the exhaust gas purification catalyst of Example 3 is shown. The analysis result by STEM-EDX of the catalyst for exhaust gas purification of Example 5 is shown. The photograph by the scanning transmission electron microscope (STEM) of the catalyst for exhaust gas purification of the comparative example 1 is shown. The photograph by the STEM of the catalyst for exhaust gas purification of the comparative example 2 is shown. (A) is a graph which shows NO conversion rate (%) regarding each exhaust gas purification catalyst of Examples 1-4 and Comparative Examples 1 and 2, (b) is each exhaust gas of Example 5 and Comparative Examples 3-5. It is a graph which shows NO conversion rate (%) regarding the catalyst for purification | cleaning.

<Exhaust gas purification catalyst>
The exhaust gas purifying catalyst of the present invention is characterized in that a plurality of binary metal particles made of silver and nickel and having an average particle diameter of more than 0 nm and less than 100 nm are supported on a catalyst carrier.

  As described above in connection with iron, base metals such as nickel, for example, are relatively easily oxidized by oxidizing components contained in exhaust gas, resulting in insufficient metallization, resulting in purification of exhaust gas, In particular, there is a problem that sufficient catalytic activity for NOx reduction purification cannot be achieved.

  Therefore, the present inventors have studied focusing on silver (Ag) having a relatively low affinity for oxygen, synthesized bimetallic particles in which nickel (Ni) and nano-level coexisted, and Exhaust gas finally obtained by supporting binary metal particles on a catalyst carrier, compared to a single metal particle of nickel or metal particles of silver alone supported on a catalyst carrier, or a simple physical mixture thereof. It has been found that the exhaust gas purification activity, particularly the NOx reduction activity of the purification catalyst can be significantly improved.

  As for nickel, although it has been proposed for use as a promoter component in exhaust gas purification catalysts for automobiles and the like, since nickel is a metal that is relatively easily oxidized as described above, The applicability as a catalyst component in a purification catalyst is not generally recognized. Therefore, as in the present invention, it is possible to achieve high activity against reduction of harmful components in exhaust gas, particularly NOx, by adding silver to nickel as a catalyst component and coexisting them at the nano level. Is quite surprising and surprising.

  Although not intended to be bound by any particular theory, the coexistence of silver and nickel at the nano level suppresses the oxidation of nickel present in close proximity to silver, which has a relatively low affinity for oxygen. It is thought that. As a result, it is possible to maintain nickel in a highly active metal state, and it is considered that the exhaust gas purification activity, particularly the NOx reduction activity, of the obtained exhaust gas purification catalyst could be remarkably improved.

[Binary metal particles]
According to the present invention, the binary metal particles made of silver and nickel supported on the catalyst carrier have an average particle size of more than 0 nm and less than 100 nm.

  If the average particle diameter of the metal particles made of silver and nickel is 100 nm or larger, it becomes impossible to form binary metal particles in which silver and nickel coexist at the nano level, and as a result, the effect of suppressing oxidation of nickel by silver is sufficient. You may not be able to get into. Further, when the metal particles made of silver and nickel have such a large average particle diameter, the surface area of the metal particles is reduced, the number of nickel active points is reduced, and the exhaust gas purifying catalyst finally obtained In some cases, sufficient NOx reduction ability cannot be achieved. Therefore, in the exhaust gas purifying catalyst of the present invention, the binary metal particles composed of silver and nickel have an average particle diameter of more than 0 nm and less than 100 nm, preferably more than 0 nm and less than 90 nm, more than 0 nm and less than 80 nm, more than 0 nm and more than 70 nm. Hereinafter, it has an average particle size of more than 0 nm to 60 nm, more than 0 nm to 50 nm, more than 0 nm to 40 nm, more than 0 nm to 30 nm, more than 0 nm to 20 nm, more than 0 nm to 15 nm, more than 0 nm to 10 nm, or more than 0 nm to 5 nm. By using binary metal particles composed of silver and nickel having such an average particle size as a catalyst component, silver and nickel can be surely coexisted at the nano level and the effect of suppressing oxidation of nickel by silver can be sufficiently exerted. As a result, it is possible to obtain an exhaust gas purifying catalyst having a significantly improved NOx reducing ability.

  In the present invention, the “average particle diameter” is 100 or more randomly selected using an electron microscope such as a transmission electron microscope (TEM) and a scanning electron microscope (SEM) unless otherwise specified. The arithmetic average value of the measured values when the unidirectional diameter (Feret diameter) of the particles is measured.

  In the exhaust gas purifying catalyst of the present invention, for example, instead of silver, it is also possible to use bimetallic particles in which gold (Au) having a low affinity for oxygen is combined with nickel in the same manner as silver. is there. However, since gold is an element in which the zero-valent metal state is stable, the interaction with the catalyst support is small, and therefore the particles on the catalyst support are relatively low even at a temperature as low as 300 ° C. or higher. There is a problem that it is easy to grow. Moreover, gold is a very expensive noble metal compared to silver. Therefore, in consideration of the relatively high temperature use conditions in the exhaust gas purification catalyst for purifying the exhaust gas of automobiles, for example, the use conditions where the temperature may reach 1000 ° C. or higher, the material cost, etc., the combination of gold and nickel Rather, it is more advantageous to use binary metal particles combining silver and nickel as in the present invention.

  According to the present invention, the average content of silver in the binary metal particles composed of silver and nickel is preferably more than 5 atomic% and not more than 90 atomic%.

  When the average content of silver in the binary metal particles is 5 atomic% or lower, it may not be possible to sufficiently obtain the oxidation inhibition effect of nickel by silver. Therefore, in such a case, as a matter of course, a sufficient NOx reduction ability cannot be achieved in the exhaust gas purification catalyst. On the other hand, when the average content of silver in the binary metal particles is larger than 90 atomic%, the number of nickel active sites in the binary metal particles is reduced. In addition, in this case, since the active sites may be covered with silver present in a relatively large amount in the binary metal particles, the exhaust gas purifying catalyst finally obtained has a sufficient NOx reduction ability. Sometimes it cannot be achieved. Therefore, it is considered that the ratio of silver and nickel contained in the binary metal particles has an optimum value in consideration of the oxidation inhibition effect of nickel by silver and the number of active points of nickel.

  According to the present invention, the average content of silver in the binary metal particles is more than 5 atomic%, particularly 10 atomic% or more, 20 atomic% or more, 30 atomic% or more, 40 atomic% or more, 50 atomic% or more. Or 55 atom% or more and 90 atom% or less, particularly 85 atom% or less, 80 atom% or less, 75 atom% or less, 70 atom% or less, or 65 atom% or less, for example, more than 5 atom% and 90 atom% or less 10 atomic percent or more and 80 atomic percent or less, 10 atomic percent or more and 70 atomic percent or less, 20 atomic percent or more and 70 atomic percent or less, 50 atomic percent or more and 70 atomic percent or less, or 55 atomic percent or more and 65 atomic percent or less. Further, it is possible to obtain a catalyst for exhaust gas purification in which the effect of suppressing the oxidation of nickel by silver is sufficiently exhibited while maintaining the number of active points of nickel, and as a result, the NOx reduction ability is remarkably improved.

  In the present invention, “average silver content” refers to the ratio of the number of silver atoms to the total number of silver atoms and nickel atoms contained in the binary metal particles. For example, the “average content of silver” in the present invention can be calculated based on the amounts of silver precursor and nickel precursor introduced when synthesizing the bimetallic particles, or alternatively It is also possible to calculate by analyzing the binary metal particles using an optical method before or after loading on the catalyst carrier.

  In the exhaust gas purifying catalyst of the present invention, the binary metal particles can be supported on the catalyst carrier described later in any appropriate amount. Although not particularly limited, for example, the amount of silver and / or nickel contained in the binary metal particles is generally 0.01 wt% or more and 0.1 wt% with respect to the catalyst support. Or more, 0.5 wt% or more, 1 wt% or more, or 2 wt% or more, and / or 10 wt% or less, 8 wt% or less, 7 wt% or less, or 5 wt% or less. Can do.

[Catalyst support]
According to the present invention, the catalyst carrier on which the binary metal particles composed of silver and nickel are supported is not particularly limited, but any metal oxide generally used as a catalyst carrier in the technical field of exhaust gas purification catalysts. Can be used. Examples of such a catalyst carrier include silica (SiO ₂ ), zirconia (ZrO ₂ ), ceria (CeO ₂ ), alumina (Al ₂ O ₃ ), titania (TiO ₂ ), and combinations thereof. As the catalyst carrier, alumina (Al ₂ O ₃ ) can be used as described above, but alumina may react with nickel as a catalyst component to form a solid solution. In such a case, there is a possibility that sufficient exhaust gas purification activity, particularly sufficient NOx reduction activity, cannot be achieved for the exhaust gas purification catalyst finally obtained. Therefore, it is more preferable to use a material containing no alumina as the catalyst carrier.

<Method for producing exhaust gas purifying catalyst>
In the present invention, there is further provided a method for producing an exhaust gas purification catalyst comprising a plurality of binary metal particles comprising silver and nickel supported on a catalyst carrier. The production method comprises a target material containing silver and nickel. It includes a deposition step of depositing binary metal particles composed of silver and nickel in an ionic liquid by sputtering, and a supporting step of supporting the obtained binary metal particles on a catalyst carrier.

  First of all, silver and nickel are systems that do not dissolve in bulk with a larger volume, so it is not possible to produce bimetallic particles in which silver and nickel coexist at the atomic or nano level. Generally very difficult.

  Here, as a method for producing an exhaust gas purifying catalyst in which a plurality of metal elements are supported on a catalyst carrier, for example, a so-called impregnated catalyst catalyst carrier is simply impregnated and supported using a mixed solution containing their salts. Co-impregnation methods are generally known. However, in such a conventional co-impregnation method, it is not possible to form binary metal particles in which those metal elements coexist at a nano level in a specific combination of silver and nickel. Further, in the exhaust gas purifying catalyst obtained by such a method, silver and nickel are separately present on the catalyst carrier as silver particles and nickel particles, respectively, and therefore, an effect of suppressing oxidation of nickel by silver, etc. can be obtained. It is considered impossible. Therefore, an exhaust gas purifying catalyst in which silver and nickel are supported on a catalyst carrier by a conventional co-impregnation method cannot achieve a sufficient NOx reduction ability.

  In addition, for example, a so-called physical mixed catalyst obtained by simply mixing each of a silver-supported catalyst and a nickel-supported catalyst prepared by an impregnation method in a powder state, as in the case of the co-impregnation method, silver and nickel are respectively silver particles and Since nickel particles are separately present on the catalyst carrier, it is not possible to obtain an effect of suppressing oxidation of nickel by silver.

  On the other hand, as one method for producing metal particles containing a plurality of metal elements, a reducing agent such as alcohol is added to a mixed solution containing a salt of each metal element constituting the metal particles, and heating or the like is performed as necessary. There is known a method of simultaneously reducing ions of each metal element contained in a mixed solution while performing the above. For example, J. et al. Phys. Chem. 1933, 97, 5103-5114 describes a method for producing metal particles containing gold and palladium by alcohol reduction. In JP 2012-163059 A, as described above, sodium borohydride is added as a reducing agent to a solution containing a protective agent such as Au salt, Fe salt, and polyvinylpyrrolidone (PVP). A method is described in which Au ions and Fe ions contained in the solution are reduced, and metal particles composed of Au and Fe thus obtained are supported on a catalyst carrier powder.

  However, since the method for producing metal particles using the reducing agent as described above includes a step of reducing the salt or ion of each metal element dissolved in the solution, the reduction of the salt or ion of each metal element. When there is a difference in the ease with which it is performed, it is very difficult to form metal particles in which each metal element coexists at the nano level. More specifically, for example, when a reducing agent such as alcohol is added to a mixed solution containing silver ions and nickel ions, the silver ions and nickel ions are not simultaneously reduced by the reducing agent, but nickel. It is considered that silver ions that are more easily reduced than ions are preferentially reduced and grain growth occurs. As a result, it is considered that the binary metal particles in which silver and nickel coexist at the nano level are not generated, but the silver and nickel phases are separated to generate silver particles and nickel particles, respectively.

  Therefore, even if such a conventionally known method is applied to a combination of specific metal elements of silver and nickel, it is extremely difficult to produce binary metal particles in which these metal elements coexist at the nano level. High degree. Moreover, even if metal particles containing silver and nickel are produced by such a method, if these metal elements do not coexist at the nano level, a unique effect by combining silver and nickel, that is, silver It is considered that there is a low possibility that the nickel oxidation inhibiting effect is obtained.

  In addition, in the method for producing metal particles using the above reducing agent, particularly when sodium borohydride or the like is used as the reducing agent, the solution containing the generated metal particles naturally has hydrogen as the reducing agent. Sodium borohydride remains. The sodium borohydride cannot be sufficiently decomposed and removed by simply drying the solution. Therefore, when the metal particles are supported on the catalyst carrier, it is necessary to remove the sodium borohydride from the solution by subjecting the solution containing the metal particles and sodium borohydride to a purification treatment or the like. It is complicated.

  In contrast to the conventionally known co-impregnation method and the method using a reducing agent, the present inventors use a target material containing silver and nickel, and sputter it into the ionic liquid. It has been found that binary metal particles composed of silver and nickel can be deposited. In addition, the present inventors introduced a catalyst carrier or a dispersion containing the catalyst carrier into the dispersion containing the binary metal particles thus obtained, and then subjected to an appropriate heat treatment, whereby silver and nickel. Is a catalyst for exhaust gas purification, in which binary metal particles coexisting at a nano level, in particular, binary metal particles made of silver and nickel and having an average particle diameter of more than 0 nm and less than 100 nm are supported on a catalyst carrier, It has further been found that an exhaust gas purifying catalyst having a remarkably improved reducing ability can be obtained.

  FIG. 1 is a diagram schematically showing a method for producing an exhaust gas purifying catalyst of the present invention. The method of the present invention will be specifically described with reference to FIG. 1. For example, first, a target material 3 containing silver 1 and nickel 2 is placed on a cathode in a sputtering apparatus, and an ionic liquid 4 is placed thereon. A glass substrate 5 or the like is placed on the anode. Next, a high voltage is applied to the cathode in a state where the inside of the chamber of the sputtering apparatus is in a reduced pressure atmosphere containing an inert gas such as a rare gas or nitrogen, particularly argon (Ar) gas. Then, a glow discharge is generated between the cathode and the anode, and Ar ions or the like generated by the glow discharge collide with the target material 3. By this collision, silver atoms 6 and nickel atoms 7 in the target material 3 are repelled, and these atoms are deposited in the ionic liquid 4 as shown in FIG. .

Here, since the binary metal particle 8 is made of metal, the surface thereof has a charge of δ ⁺ . Therefore, it is considered that the ionic liquid 4 having an ionic property adheres to the surface of the binary metal particle 8 having the δ ⁺ charge, whereby the ionic liquid 4 acts as a protective agent on the binary metal particle 8. It is considered that the agglomeration and grain growth of the binary metal particles 8 can be suppressed and stabilized.

  Next, the ionic liquid 4 on which the binary metal particles 8 are deposited is taken out from the sputtering apparatus, and the catalyst carrier 9 is introduced into the ionic liquid 4 alone or in a dispersion state (FIG. 1B). Next, the resulting dispersion is heated at an appropriate temperature to carry the binary metal particles 8 on the catalyst carrier 9 (FIG. 1 (c)). Finally, the powder is separated from the dispersion by filtration or the like, and then the ionic liquid is sufficiently removed by washing or the like as necessary, followed by drying or the like, whereby a plurality of binary metal particles 8 are supported on the catalyst carrier 9. As a result, the exhaust gas-purifying catalyst 10 can be obtained (FIG. 1D).

[Target material]
According to the method of the present invention, as a target material containing silver and nickel, any suitable material can be used, and is not particularly limited. For example, a target material in which silver and nickel are alternately arranged, A micro-mixed target obtained by mixing silver powder and nickel powder and molding and sintering can be used. According to one preferred embodiment of the method of the present invention, as the target material containing silver and nickel, for example, as shown in FIG. 2, a disk-shaped material in which silver plates and nickel plates are alternately arranged radially is used. Can be used. According to such a disk-shaped target material, it is relatively easy to synthesize binary metal particles having a desired silver or nickel content by appropriately changing the area or area ratio of the silver plate and the nickel plate. Is possible. However, comparing silver and nickel, silver is generally a metal that is more easily repelled by sputtering, and nickel is a metal that is less likely to be repelled.Therefore, considering such characteristics, the composition ratio of silver and nickel in the target material, etc. It is preferable to determine.

[Ionic liquid]
According to the method of the present invention, as the ionic liquid on which the binary metal particles are deposited, any compound that is liquid at room temperature despite being a salt composed only of cations and anions is used. Can do.

  Here, the ionic liquid is stable at high temperature, has a wide liquid temperature range, has a vapor pressure of substantially zero, has ionic properties, low viscosity, high oxidation / reduction resistance, and the like. It can exist stably as a liquid without evaporating even under sputtering conditions under vacuum or reduced pressure as in. In addition, the ionic liquid may become a high temperature during sputtering, but even in such a case, the ionic liquid can exist stably without being decomposed due to its high temperature stability.

Furthermore, since such an ionic liquid has ionicity, as described above, the ionic liquid adheres to the surface of the binary metal particles having a charge of δ ⁺ and aggregates the binary metal particles. It is considered that grain growth can be suppressed and stabilized. Therefore, by appropriately selecting the ionic liquid used in the method of the present invention, it is possible to control the average particle diameter and the like of the synthesized binary metal particles within a desired range. In addition, the ionic liquid applied in the method of the present invention may be hydrophilic or hydrophobic, and the type thereof is not particularly limited. For example, an aliphatic ionic liquid, An imidazolium-based ionic liquid, a pyridinium-based ionic liquid, or a combination thereof can be given.

  Examples of the aliphatic ionic liquid include N, N, N-trimethyl-N-propylammonium bis (trifluoromethanesulfonyl) amide (hereinafter also referred to as “TMPA-TFSA”), N-methyl-N-propylpiperidi. Ni-bis (trifluoromethanesulfonyl) imide, N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium bis (trifluoromethanesulfonyl) imide, N, N-diethyl-N-methyl-N- (2 -Methoxyethyl) ammonium tetrafluoroborate or a combination thereof can be mentioned, and preferably TMPA-TFSA or the like can be used.

  Examples of imidazolium-based ionic liquids include 1,3-dialkylimidazolium salts, 1,2,3-trialkylimidazolium salts, or combinations thereof. Examples of 1,3-dialkylimidazolium salts include 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methyl-imidazolium chloride, and 1-ethyl-3-methylimidazolium (L). -Lactate, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium tetrafluoroborate (hereinafter also referred to as "EMI-BF4"), 1-butyl-3 -Methylimidazolium chloride, 1-butyl-3-methylimidazolium hexafluorophosphate (hereinafter also referred to as “BMI-PF6”), 1-butyl-3-methylimidazolium tetrafluoroborate (hereinafter referred to as “BMI-PF6”) BMI-BF4 "), 1-butyl-3-methylimidazolium trifluoromethanesulfo Acid salt, 1-butyl-3-methylimidazolium (L) -lactate, 1-hexyl-3-methylimidazolium bromide, 1-hexyl-3-methylimidazolium chloride, 1-hexyl-3-methylimidazolium Hexafluorophosphate, 1-hexyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium trifluoromethanesulfonate, 1-octyl-3-methylimidazolium chloride, 1-octyl -3-methylimidazolium hexafluorophosphate, 1-decyl-3-methylimidazolium chloride, 1-dodecyl-3-methylimidazolium chloride, 1-tetradecyl-3-methylimidazolium chloride, 1-hexadecyl-3 -Methylimidazolium chlora De, 1-octadecyl-3-methylimidazolium chloride, or a combination thereof can be mentioned. Examples of the 1,2,3-trialkylimidazolium salt include 1-ethyl-2,3-dimethylimidazolium bromide, 1-ethyl-2,3-dimethylimidazolium chloride, 1-butyl-2, 3-dimethylimidazolium bromide, 1-butyl-2,3-dimethylimidazolium chloride, 1-butyl-2,3-dimethylimidazolium tetrafluoroborate, 1-butyl-2,3-dimethylimidazolium trifluoromethane Sulfonate, 1-hexyl-2,3-dimethylimidazolium bromide, 1-hexyl-2,3-dimethylimidazolium chloride, 1-hexyl-2,3-dimethylimidazolium trifluoroborate, 1-hexyl -2,3-Dimethylimidazolium trifluoromethanesulfo Salt, or a combination thereof can be mentioned. Of these, EMI-BF4, BMI-PF6, BMI-BF4 and the like can be preferably used.

  Examples of the pyridinium-based ionic liquid include an ethyl pyridinium salt, a butyl pyridinium salt, a hexyl pyridinium salt, or a combination thereof. Examples of the ethylpyridinium salt include 1-ethylpyridinium bromide, 1-ethylpyridinium chloride, or a combination thereof. Examples of the butylpyridinium salt include 1-butylpyridinium bromide, 1-butylpyridinium chloride, 1-butylpyridinium hexafluorophosphate, 1-butylpyridinium tetrafluoroborate, 1-butylpyridinium trifluoromethanesulfonic acid. Examples thereof include a salt or a combination thereof. On the other hand, as hexylpyridinium salts, for example, 1-hexylpyridinium bromide, 1-hexylpyridinium chloride, 1-hexylpyridinium hexafluorophosphate, 1-hexylpyridinium tetrafluoroborate, 1-hexylpyridinium trifluoromethanesulfonic acid Examples thereof include a salt or a combination thereof.

  In addition, when using said ionic liquid in the method of this invention, it is preferable to remove a water | moisture content fully, for example by heating over a predetermined time under reduced pressure as a pre-drying process.

[Deposition process]
According to the method of the present invention, in the deposition step, binary metal particles made of silver and nickel are deposited in the ionic liquid by sputtering a target material containing silver and nickel. Such sputtering can be performed under any suitable conditions. Although not particularly limited, for example, the gas used is preferably an inert gas such as a rare gas, particularly argon (Ar) gas, and the pressure is preferably 20 Pa or less. Further, the magnitude of the sputtering current may be appropriately set according to the composition of the target material, the sputtering apparatus, and the like. Furthermore, the sputtering time may be appropriately set in consideration of the desired amount of binary metal particles deposited and other parameters, and is not particularly limited. For example, the sputtering time is between several tens of minutes to several tens of hours. Can be set appropriately. In addition, in order to prevent the temperature of the ionic liquid from rising excessively in a case where a long-time sputtering operation is required to achieve a desired deposition amount of binary metal particles composed of silver and nickel, For example, the sputtering operation may be performed in several times every several hours.

[Supporting process]
According to the method of the present invention, the binary metal particles obtained in the above deposition step are supported on the catalyst carrier in the next supporting step. Here, the catalyst carrier to be introduced in the supporting step is not particularly limited, and any metal oxide generally used as a catalyst carrier in the technical field of exhaust gas purification catalyst can be used. Examples of such a catalyst carrier include silica (SiO ₂ ), zirconia (ZrO ₂ ), ceria (CeO ₂ ), alumina (Al ₂ O ₃ ), titania (TiO ₂ ), or those as described above. A combination etc. are mentioned.

  In the supporting step, a dispersion containing binary metal particles composed of silver and nickel synthesized in the previous deposition step is, for example, a metal oxide (catalyst support) powder dispersed in a predetermined amount of solvent. The amount of silver and / or nickel is generally added in an amount ranging from 0.01 to 10 wt% with respect to the catalyst support. Next, this mixed dispersion is heated at a temperature and for a time sufficient to support the binary metal particles on the catalyst carrier, and stirred as necessary. In general, the heating is performed under an inert atmosphere, such as a nitrogen atmosphere, at a temperature of about 80 ° C. to about 250 ° C. for about 5 minutes to about 5 hours, preferably about 10 minutes to about 1 hour. be able to.

  Next, the powder is separated from the dispersion containing the catalyst carrier on which the binary metal particles are supported by filtration or the like, and then, if necessary, the powder is washed with a solvent such as acetonitrile to sufficiently remove the ionic liquid. After removal, drying and the like can provide an exhaust gas purification catalyst in which a plurality of binary metal particles are supported on a catalyst carrier. In general, such drying can be performed at a temperature of about 80 ° C. to about 250 ° C. for about 1 hour to about 24 hours under reduced pressure or normal pressure.

  Note that the ionic liquid used in the deposition step in the method of the present invention may not be sufficiently removed by a separation operation or a drying process in the subsequent supporting step. Therefore, in order to reliably decompose and remove the ionic liquid, the method of the present invention preferably further includes a baking step after the above-described supporting step. Specifically, it is preferable to heat-treat the exhaust gas-purifying catalyst obtained in the above-mentioned supporting step at a relatively high temperature in an oxidizing atmosphere, for example, air, particularly at a temperature higher than 300 ° C. and not higher than 800 ° C. . Since the ionic liquid that may remain as impurities on the catalyst can be reliably decomposed and removed by such heat treatment, the exhaust gas purification catalyst finally obtained has higher exhaust gas purification activity, particularly higher NOx reduction. It is possible to achieve activity.

  Moreover, in the method of this invention, you may further implement a reduction process optionally after the said carrying | support process or a baking process. By reducing the exhaust gas purifying catalyst obtained by the method of the present invention in the reduction step, nickel in the binary metal particles can be reliably reduced to a highly active metal state. Such reduction treatment can be performed by any method known to those skilled in the art. For example, the exhaust gas-purifying catalyst powder obtained by the method of the present invention can be carried out in a reducing atmosphere, particularly in a hydrogen-containing atmosphere at a temperature of 300 to 800 ° C. for 5 minutes to 3 hours. Alternatively, the above reduction treatment is performed after the powder of the exhaust gas purifying catalyst obtained by the method of the present invention is applied on a catalyst substrate such as a cordierite honeycomb substrate with a predetermined binder or the like added. May be.

  The exhaust gas purifying catalyst obtained by the method of the present invention may be formed into pellets by pressing under high pressure, if necessary, or slurried by adding a predetermined binder or the like, which is made of cordierite. It can be used by coating on a catalyst substrate such as a honeycomb substrate.

  In this specification, the exhaust gas purification catalyst for purifying automobile exhaust gas has been described in detail. However, the exhaust gas purification catalyst of the present invention is not limited to such a specific technical field, The present invention can be widely applied in any technical field that requires purification of factory exhaust gas, particularly NOx purification.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these Examples at all.

  In the following examples, an exhaust gas purification catalyst containing Ag-Ni binary metal particles as a catalyst component was prepared, and its characteristics and NOx purification performance were examined.

[Example 1]
[Synthesis of Ag-Ni binary metal particles (Ag average content 62 atom%)]
First, as an ionic liquid, the following formula:
1-butyl-3-methylimidazolium hexafluorophosphate (BMI-PF6) 2.40 cm ³ represented by the above formula was used, and this was dried under reduced pressure at 120 ° C. for 3 hours as a pretreatment for drying to sufficiently remove moisture. Removed. Next, in a sputtering apparatus (SC-701HMCII No. 4 manufactured by Sanyu Electron), a disk-like alternating array target in which Ag plates and Ni plates are alternately arranged radially as shown in FIG. A tape attached, area ratio Ag: Ni = 2: 1) was installed. Next, after the inside of the chamber of the sputtering apparatus was replaced twice with Ar gas, pre-sputtering was performed for 30 minutes under conditions of a pressure of 3.0 Pa and a sputtering current of 20 mA, so that sputtering could be performed stably.

  Next, the above-mentioned BMI-PF6 that had been subjected to the pre-drying treatment was uniformly spread on a petri dish (diameter: 70 mm), placed in a sputtering apparatus, and then dried under reduced pressure for 30 minutes. Next, sputtering was performed for 150 minutes at a pressure of 3.0 Pa, a sputtering current of 20 mA, and a distance between the target material and the ionic liquid BMI-PF6 of 6.7 cm. Once the atmosphere was released to the atmosphere, the sputter target was replaced with a new Ag—Ni alternating target (Ag: Ni ratio was the same), and sputtering was performed for 150 minutes under the same conditions. The total sputtering time was 300 minutes. Thereafter, the ionic liquid in the petri dish was collected to obtain a dispersion containing Ag—Ni binary metal particles. As a result of the fluorescent X-ray analysis, the concentrations of Ag and Ni in the dispersion were 33.6 mM for Ag and 20.6 mM for Ni. From this analysis result, the Ag average content in the Ag—Ni binary metal particles was calculated to be 62 atomic%.

[Preparation of Ag-Ni / SiO ₂ (Ag average content 62 atom%)]
Next, 3.6 mL of the dispersion liquid containing Ag—Ni binary metal particles obtained above (Ag average content of 62 atom%) was placed in a 50 mL flask, and then dispersed in 4 mL of acetone. 1.3 g (spherical silica manufactured by Nanotech) was added. Next, this mixed dispersion was heated and stirred at 150 ° C. for 30 minutes in a nitrogen stream. After cooling the obtained dispersion, the powder was separated from the dispersion by filtration, and washed with acetonitrile three times to sufficiently remove BMI-PF6. Next, the obtained powder is dried in air at 110 ° C. for 5 hours, and then calcined in air at 500 ° C. for 2 hours to purify exhaust gas composed of Ag—Ni / SiO ₂ (Ag average content 62 atomic%). A catalyst was obtained. The Ag loading was 1.00 wt% and the Ni loading was 0.33 wt%.

[Example 2]
[Preparation of Ag-Ni / SiO ₂ (Ag average content 55 atomic%)]
A dispersion containing Ag—Ni binary metal particles was obtained in the same manner as in Example 1 except that sputtering was continuously performed for 300 minutes without changing the alternating target during the sputtering. As a result of the fluorescent X-ray analysis, the concentrations of Ag and Ni in the dispersion were 21.3 mM for Ag and 17.8 mM for Ni. From this analysis result, the average Ag content in the Ag—Ni binary metal particles was calculated as 55 atomic%. Further, this sample synthesis operation was repeated a plurality of times to obtain a solution amount necessary for the subsequent experiments. Next, 3.6 mL of a dispersion liquid containing the obtained Ag—Ni binary metal particles (Ag average content of 55 atomic%) was placed in a 50 mL flask, and then silica (Nanotech) dispersed in 4 mL of acetone was added thereto. 0.9 g of spherical silica produced by the company was added. Next, this mixed dispersion was heated and stirred at 150 ° C. for 30 minutes in a nitrogen stream. After cooling the obtained dispersion, the powder was separated from the dispersion by filtration, and washed with acetonitrile three times to sufficiently remove BMI-PF6. Next, the obtained powder was dried in air at 110 ° C. for 5 hours, and then calcined in air at 500 ° C. for 2 hours, thereby purifying exhaust gas composed of Ag—Ni / SiO ₂ (Ag average content 55 atomic%). A catalyst was obtained. The Ag loading was 0.90 wt%, and the Ni loading was 0.39 wt%.

[Example 3]
[Synthesis of Ag-Ni binary metal particles (Ag average content of 10 atomic%)]
This was installed in the sputtering apparatus in the same manner as in Example 2 except that an alternately arranged target having an area ratio of Ag: Ni = 1: 1 was used. Next, the inside of the chamber of the sputtering apparatus was replaced with Ar gas twice, and then pre-sputtering was performed for 30 minutes under conditions of a pressure of 3.0 Pa and a sputtering current of 20 mA. Next, the BMI-PF6 that had been subjected to the pre-drying treatment was evenly spread on a petri dish, placed in a sputtering apparatus, and then dried under reduced pressure for 30 minutes. Next, sputtering was performed for 300 minutes at a pressure of 3.0 Pa, a sputtering current of 20 mA, and a distance between the target material and the ionic liquid BMI-PF6 of 6.7 cm. This sample synthesis operation was performed four times in total. Thereafter, the ionic liquid in the petri dish was collected to obtain a dispersion containing Ag—Ni binary metal particles. As a result of fluorescent X-ray analysis, the Ag and Ni concentrations in the dispersion were 11.1 mM for Ag and 105.0 mM for Ni. From this analysis result, the Ag average content in the Ag—Ni binary metal particles was calculated to be 10 atomic%.

[Preparation of Ag-Ni / SiO ₂ (Ag average content 10 atomic%)]
Next, 6.8 mL of the dispersion liquid containing Ag-Ni bimetallic particles (Ag average content of 10 atomic%) obtained above was placed in a 50 mL flask, and then dispersed in 8 mL of acetone. 3.7 g (Nanotech spherical silica) was added. Next, this mixed dispersion was heated and stirred at 150 ° C. for 30 minutes in a nitrogen stream. After cooling the obtained dispersion, the powder was separated from the dispersion by filtration, and washed with acetonitrile three times to sufficiently remove BMI-PF6. Next, the obtained powder is dried in air at 110 ° C. for 5 hours, and then calcined in air at 500 ° C. for 2 hours, thereby purifying exhaust gas composed of Ag—Ni / SiO ₂ (Ag average content 10 atomic%). A catalyst was obtained. The Ag loading was 0.20 wt% and the Ni loading was 1.11 wt%.

[Example 4]
[Synthesis of Ag-Ni binary metal particles (Ag average content 5 atom%)]
This was installed in the sputtering apparatus in the same manner as in Example 2 except that an alternately arranged target having an area ratio of Ag: Ni = 1: 2 was used. Next, the inside of the chamber of the sputtering apparatus was replaced with Ar gas twice, and then pre-sputtering was performed for 30 minutes under conditions of a pressure of 3.0 Pa and a sputtering current of 20 mA. Next, the BMI-PF6 that had been subjected to the pre-drying treatment was evenly spread on a petri dish, placed in a sputtering apparatus, and then dried under reduced pressure for 30 minutes. Next, sputtering was performed for 300 minutes at a pressure of 3.0 Pa, a sputtering current of 20 mA, and a distance between the target material and the ionic liquid BMI-PF6 of 6.7 cm. Thereafter, the ionic liquid in the petri dish was collected to obtain a dispersion containing Ag—Ni binary metal particles. As a result of the fluorescent X-ray analysis, the concentration of Ag and Ni in the dispersion liquid was 8.3 mM for Ag and 142.3 mM for Ni. From this analysis result, the Ag average content in the Ag—Ni binary metal particles was calculated as 5 atomic%.

[Preparation of Ag-Ni / SiO ₂ (Ag average content 5 atom%)]
Next, 15 mL of the dispersion liquid containing Ag-Ni binary metal particles (Ag average content of 5 atom%) obtained above was placed in a 100 mL flask, and then silica (Nanotech) dispersed in 10 mL of acetone was added thereto. 10.5 g of spherical silica (made by company) was added. Next, this mixed dispersion was heated and stirred at 150 ° C. for 30 minutes in a nitrogen stream. After cooling the obtained dispersion, the powder was separated from the dispersion by filtration, and washed with acetonitrile three times to sufficiently remove BMI-PF6. Subsequently, the obtained powder is dried in air at 110 ° C. for 5 hours, and then calcined in air at 500 ° C. for 2 hours, thereby purifying exhaust gas composed of Ag—Ni / SiO ₂ (Ag average content 5 atomic%). A catalyst was obtained. The Ag loading was 0.11 wt%, and the Ni loading was 1.20 wt%.

[Example 5]
[Synthesis of Ag-Ni binary metal particles (Ag average content 68 atom%)]
As an ionic liquid, instead of BMI-PF6, the following formula:
N, N, N-trimethyl-N-propylammonium bis (trifluoromethanesulfonyl) amide (TMPA-TFSA) 2.40 cm ³ is used, and silver powder and nickel powder are mixed as a target material. Using the molded and sintered micro mixed target, the micro mixed target was placed in the sputtering apparatus so that the distance from the TMPA-TFSA was 30 mm, and sputtering was performed in the same manner as in Example 1. Sputtering was performed for 150 minutes after pre-sputtering for 600 seconds under conditions of a pressure of 5.0 Pa and a sputtering current of 40 mA.

Thereafter, the ionic liquid in the petri dish was recovered, another TMPA-TFSA 2.40 cm ³ was again placed in the sputtering apparatus under the same conditions, and sputtering was similarly performed for 150 minutes. Such sputtering operation was performed 6 times in total. Thereafter, the ionic liquid in the petri dish was collected, and the ionic liquid for six times was used as one sample, and further diluted 1.5 times with TMPA-TFSA to obtain a dispersion containing Ag-Ni binary metal particles. As a result of fluorescent X-ray analysis, the Ag and Ni concentrations in the dispersion were 30.7 mM for Ag and 14.4 mM for Ni. From this analysis result, the Ag average content in the Ag—Ni binary metal particles was calculated as 68 atomic%.

[Preparation of Ag-Ni / SiO ₂ (Ag average content 68 atomic%)]
Next, 15 mL of the dispersion liquid containing Ag—Ni binary metal particles (Ag average content of 68 atom%) obtained above was placed in a 100 mL flask, and then silica (Nanotech) dispersed in 15 mL of acetone was added thereto. 4.6 g of spherical silica (made by company) was added. Next, this mixed dispersion was heated and stirred at 150 ° C. for 30 minutes in a nitrogen stream. After cooling the obtained dispersion, the powder was separated from the dispersion by filtration, and washed with acetonitrile three times to sufficiently remove TMPA-TFSA. Next, the obtained powder was dried in air at 110 ° C. for 5 hours and then calcined in air at 500 ° C. for 2 hours, thereby purifying exhaust gas composed of Ag—Ni / SiO ₂ (Ag average content 68 atomic%). A catalyst was obtained. The Ag loading was 1.05 wt% and the Ni loading was 0.27 wt%.

[Comparative Example 1]
[Preparation of Ag / SiO ₂ (Ag average content: 100 atomic%)]
A dispersion containing Ag metal particles was obtained in the same manner as in Example 1 except that an Ag target containing no Ni was used. As a result of fluorescent X-ray analysis, the Ag concentration in the dispersion was 55.5 mM. Next, 5.2 mL of the resulting dispersion containing Ag metal particles was placed in a 50 mL flask, and then 2.3 g of silica (Nanotech spherical silica) dispersed in 5 mL of acetone was added thereto. Next, this mixed dispersion was heated and stirred at 150 ° C. for 30 minutes in a nitrogen stream. After cooling the obtained dispersion, the powder was separated from the dispersion by filtration, and washed with acetonitrile three times to sufficiently remove BMI-PF6. Next, after the obtained powder is dried in air at 110 ° C. for 5 hours and then calcined in air at 500 ° C. for 2 hours, an exhaust gas purifying catalyst composed of Ag / SiO ₂ (Ag average content of 100 atomic%) is obtained. Obtained. The amount of Ag supported was 1.28 wt%.

[Comparative Example 2]
[Preparation of Ni / SiO ₂ (Ag average content 0 atomic%)]
Example 1 except that a Ni target containing no Ag was used and one 60-minute sputtering operation was performed a total of 5 times to make one sample and finally mixed them. Thus, a dispersion containing Ni metal particles was obtained. As a result of fluorescent X-ray analysis, the Ni concentration in the dispersion was 46.2 mM. Next, 8.2 mL of the resulting dispersion containing Ni metal particles was placed in a 50 mL flask, and then 1.7 g of silica (Nanotech spherical silica) dispersed in 8 mL of acetone was added thereto. Next, this mixed dispersion was heated and stirred at 150 ° C. for 30 minutes in a nitrogen stream. After cooling the obtained dispersion, the powder was separated from the dispersion by filtration, and washed with acetonitrile three times to sufficiently remove BMI-PF6. Next, after the obtained powder was dried in air at 110 ° C. for 5 hours and then calcined in air at 500 ° C. for 2 hours, an exhaust gas purification catalyst composed of Ni / SiO ₂ (Ag average content 0 atom%) was obtained. Obtained. Note that the Ni loading was 1.26 wt%.

[Comparative Example 3]
[Preparation of Ag / SiO ₂ (Ag average content 100 atomic%) by impregnation method]
In this comparative example, Ag / SiO ₂ (Ag average content of 100 atomic%) in which only Ag was supported on silica was prepared by a conventional impregnation method. Specifically, first, 50 mL of distilled water was put in a 300 mL beaker, 0.32 g of silver nitrate (I) (AgNO ₃ ) was added thereto, and the mixture was stirred at room temperature. After these were completely dissolved, 15 g of silica (Nanotech spherical silica) was added and heated to remove the dispersion medium. Next, after drying at 120 ° C. for 1 hour, this was pulverized in a mortar to form a uniform powder, and the obtained powder was fired in air at 500 ° C. for 2 hours to obtain Ag / SiO ₂ (Ag average content). A catalyst for exhaust gas purification comprising 100 atomic%) was obtained. The amount of Ag supported was 1.35 wt%.

[Comparative Example 4]
[Preparation of Ni / SiO ₂ (Ag average content 0 atomic%) by impregnation method]
In this comparative example, Ni / SiO ₂ (Ag average content 0 atomic%) in which only Ni was supported on silica was prepared by a conventional impregnation method. Specifically, first, 50 mL of distilled water was put into a 300 mL beaker, and 1.00 g of nickel nitrate (II) hexahydrate (Ni (NO ₃ ) ₂ .6H ₂ O) was added thereto and stirred at room temperature. . After these were completely dissolved, 15 g of silica (Nanotech spherical silica) was added and heated to remove the dispersion medium. Next, after drying at 120 ° C. for 1 hour, this was pulverized in a mortar to form a uniform powder, and the obtained powder was fired in air at 500 ° C. for 2 hours to obtain Ni / SiO ₂ (Ag average content). A catalyst for exhaust gas purification comprising 0 atomic%) was obtained. Note that the Ni loading was 1.35 wt%.

[Comparative Example 5]
[Preparation of physical mixed catalyst of Ag / SiO ₂ and Ni / SiO ₂ by the impregnation method (Ag: Ni ratio (atomic ratio) = 52: 48)]
In this comparative example, was prepared an exhaust gas purifying catalyst comprising Ag / SiO ₂ and Ni / SiO ₂ by simply physically mixing Ag / SiO ₂ and Ni / SiO _2. Specifically, first, a catalyst made of Ag / SiO ₂ was obtained in the same manner as in Comparative Example 3, except that silver nitrate (I) (AgNO ₃ ) was changed to 0.27 g. Next, a catalyst made of Ni / SiO ₂ was obtained in the same manner as in Comparative Example 4 except that nickel nitrate (II) hexahydrate (Ni (NO ₃ ) ₂ .6H ₂ O) was changed to 0.14 g. . Finally, both catalysts were mixed and pulverized in a mortar to obtain an exhaust gas purifying catalyst (Ag: Ni ratio (atomic ratio) = 52: 48) composed of Ag / SiO ₂ and Ni / SiO ₂ . The amount of Ag supported was 0.90 wt% and the amount of Ni supported was 0.45 wt%.

[Analysis of metal particles]
About each metal particle obtained in Examples 1-5 and Comparative Examples 1 and 2, those measurements were performed with the transmission electron microscope (TEM) (Hitachi H-7650). In addition, as a measurement sample, each dispersion liquid containing Ag-Ni binary metal particles, Ag metal particles, or Ni metal particles in Examples 1 to 5 and Comparative Examples 1 and 2 before being supported on the catalyst carrier was used. And the particle size of many particle | grains was measured, the histogram was created, and the average particle diameter ( _dav ) and standard deviation ((sigma)) of each metal particle in Examples 1-5 and Comparative Examples 1 and 2 were computed. These results are shown in FIGS. Table 1 below also shows the catalyst configuration and the amount of each metal supported on the exhaust gas purifying catalysts of Examples 1 to 5 and Comparative Examples 1 to 5.

  FIGS. 3-9 shows the analysis result by the transmission electron microscope (TEM) of each metal particle in Examples 1-5 and Comparative Examples 1 and 2, specifically, the photograph by TEM of each metal particle, 1 shows a histogram created by measuring the particle diameters of a number of metal particles.

  First, referring to the TEM photographs and histograms of FIGS. 3 to 5 and 7 relating to Examples 1 to 3 and 5, although some of the primary particles are aggregated (for example, FIG. 3B and FIG. 4A). It can be seen that very fine primary particles having an average particle size of about 3 nm or smaller are formed.

  Next, referring to the TEM photograph of FIG. 6 relating to the Ag—Ni binary metal particles of Example 4 (Ag average content 5 atom%), it is assumed that the particles are amorphous nickel oxides that do not necessarily show the form of the particles. The average particle size tended to be slightly higher than those of other examples. This result shows that, in the Ag—Ni binary metal particles of Example 4, the average content of Ag is relatively low, so that the effect of suppressing Ni oxidation by Ag is smaller than that of the other examples. It seems to suggest.

  On the other hand, the metal particle which consists only of Ag which does not contain Ni of the comparative example 1 has a large average particle diameter of 6.6 nm compared with other things (FIG. 8), and does not contain Ag of the comparative example 2. About the metal particle which consists only of Ni, the image estimated to be an amorphous nickel oxide was observed (FIG. 9 (a)).

[Analysis of catalyst]
About each exhaust gas purifying catalyst obtained in Examples 2, 3 and 5 and Comparative Examples 1 and 2, they were measured by a scanning transmission electron microscope with an energy dispersive X-ray analyzer (STEM-EDX) (JEM1000 manufactured by JEOL). Measurements were made. These results are shown in FIGS.

  FIGS. 10-12 has shown the analysis result by STEM-EDX of each exhaust-gas purification catalyst of Example 2, 3 and 5. FIG. 10-12, (a) shows the photograph by STEM-EDX of each exhaust gas purification catalyst of Example 2, 3 and 5, (b) is each about the metal particle in (a). The composition ratio (atomic%) of Ag and Ni at the measurement point is shown.

  Referring to FIGS. 10 (a) and 11 (a), in each of the exhaust gas purifying catalysts of Examples 2 and 3 in which Ag-Ni binary metal particles were synthesized using BMI-PF6 as the ionic liquid, the average particle diameter However, it can be confirmed that very fine metal particles of 10 nm or less are present on the silica support. In addition, the big white image other than the metal particle in a figure is a silica. Moreover, the particle size of many metal particles in the figure was 5 nm or less.

  On the other hand, referring to FIG. 12 (a), in the exhaust gas purifying catalyst of Example 5 in which Ag-Ni binary metal particles were synthesized using TMPA-TFSA as the ionic liquid, the exhaust gas of Examples 2 and 3 was used. Compared to the purification catalyst (FIGS. 10 (a) and 11 (a)), a tendency for the particle size of the metal particles to be somewhat larger was observed. On the other hand, in the TEM photograph (FIGS. 4, 5 and 7) immediately after the binary metal particles are deposited in the ionic liquid, there is a large difference in the particle diameters of the Ag—Ni binary metal particles of Examples 2, 3 and 5. Was not observed.

  Therefore, for ionic liquids, BMI-PF6 is considered to have a higher protective power against Ag-Ni binary metal particles than TMPA-TFSA, that is, an ability to suppress aggregation and grain growth of Ag-Ni binary metal particles. It is done. In other words, in the exhaust gas purifying catalyst of Example 5 using TMPA-TFSA as the ionic liquid, one Ag-Ni binary metal is deposited between the Ag-Ni binary metal particle deposition process and the supporting process. It is thought that the part has aggregated. However, in any case, in each of the exhaust gas purifying catalysts of Examples 2, 3 and 5, the Ag—Ni bimetallic particles were not supported even after the supporting operation on the catalyst carrier and further after the firing treatment at 500 ° C. in the air. It was confirmed that a very fine particle size was maintained.

  Next, referring to FIG. 10 (b), in the exhaust gas purifying catalyst of Example 2, both Ag and Ni elements are detected at all measurement points among the measurement points 1 to 6 regarding the metal particles. I understand. Also in FIG. 11 (b), both Ag and Ni elements are detected at nine measurement points excluding the measurement point 4 out of the measurement points 1 to 10 relating to the metal particles. Similarly, FIG. 12 (b) However, both Ag and Ni elements were detected at all measurement points except measurement point 10. These results suggest that Ag and Ni coexist at the nano level in the same metal particles in the exhaust gas purifying catalysts of Examples 2, 3 and 5.

Next, referring to the STEM photograph of FIG. 13 relating to the exhaust gas purifying catalyst (Ag / SiO ₂ ) of Comparative Example 1, fine Ag metal particles are observed on the silica which is the catalyst carrier, and even after loading, before loading. It was confirmed that the same particle size was maintained. On the other hand, referring to the STEM photograph of FIG. 14 regarding the exhaust gas purifying catalyst (Ni / SiO ₂ ) of Comparative Example 2, the presence of metal particles could not be confirmed clearly, but the presence of Ni from the analysis by EDX. It was confirmed.

[Evaluation of catalyst activity]
Next, regarding the exhaust gas purifying catalysts of Examples 1 to 5 and Comparative Examples 1 to 5, the NO—CO reaction of the following formula (1):
NO + CO → 1 / 2N ₂ + CO ₂ (1)
Were evaluated for their NOx reducing ability. Specifically, each exhaust gas-purifying catalyst powder prepared above was compacted at a pressure of 196 MPa and then sieved to obtain a 1.0 to 1.7 mm pellet catalyst. Next, 0.2 g of this pellet catalyst was placed in a flow reactor and subjected to reduction treatment at 600 ° C. for 30 minutes under the flow of reducing gas consisting of 1 vol% H ₂ / N ₂ balance. Then, it cooled to 100 degrees C or less under the same atmosphere. Next, the model gas for evaluation (NO: 3000 ppm, CO: 3000 ppm, N ₂ balance) is flowed through the catalyst bed at a flow rate of 1 L / min, and the temperature of the catalyst bed is increased from 100 ° C. at a rate of 20 ° C./min. Warm and NO conversion up to 600 ° C. was measured using FT-IR analyzer. The result is shown in FIG.

  FIG. 15A is a graph showing the NO conversion rate (%) for the exhaust gas purifying catalysts of Examples 1 to 4 and Comparative Examples 1 and 2, and FIG. 15B is the graph of Example 5 and Comparative Example. It is a graph which shows NO conversion rate (%) regarding each 3-5 exhaust gas purification catalyst. In FIGS. 15A and 15B, the horizontal axis indicates the temperature (° C.) of the catalyst bed, and the vertical axis indicates the NO conversion rate (%).

The peak in the vicinity of about 220 ° C. in FIG. 15 (a), it was confirmed that relate generated primarily nitrous oxide from the results of FT-IR spectrometer (N ₂ O). That is, in this part, rather than the reaction of the above formula (1), the following formula (2):
2NO + CO → N ₂ O + CO ₂ (2)
The reaction of the above formula (1) mainly proceeds at a temperature higher than that, particularly at a temperature higher than 300 ° C., and NO is reduced and purified to N ₂ .

  Here, as is clear from the results in FIGS. 15 (a) and 15 (b), particularly in the temperature range exceeding 300 ° C., the exhaust gas purifying catalysts of Comparative Examples 1 and 3 supporting only Ag are among all the catalysts. The lowest NOx conversion rate, particularly NOx reduction ability was exhibited. From this, it can be seen that Ag shows almost no activity for the reduction of NOx. On the other hand, in the exhaust gas purifying catalysts of Comparative Examples 2 and 4 in which only Ni is supported, and further in the exhaust gas purifying catalyst of Comparative Example 5 in which an Ag supported catalyst and a Ni supported catalyst are physically mixed, the exhaust gases of Comparative Examples 1 and 3 above are used. Although the NOx conversion rate was higher than that of the purification catalyst, sufficient catalytic activity could not be achieved.

  On the other hand, according to the present invention, the exhaust gas purification catalyst of Example 4 (Ag average content of 5 atom%) of Example 4 having a relatively low average Ag content was subjected to exhaust gas purification of Comparative Example 2 in which only Ni was supported. The NOx conversion rate was almost the same as that of the exhaust gas catalyst, but the exhaust gas purification catalysts of the other Examples 1 to 3 and 5 were very high at all temperatures compared to the exhaust gas purification catalyst of Comparative Example 2. A NOx conversion could be achieved. This is observed with respect to the metal particles of Comparative Example 2 in the TEM photograph of FIG. 9A by making Ag and Ni coexist in the same metal particles at the nano level as shown in FIGS. This is thought to be due to the fact that the oxidation of Ni was suppressed.

  Similarly, in the exhaust gas purification catalysts of Examples 1 to 3 and 5, the exhaust gas purification catalyst of Comparative Example 1 in which only Ag was supported, the exhaust gas purification catalyst of Comparative Example 3 in which Ag was impregnated and supported, and Ni were impregnated and supported. Compared with the exhaust gas purification catalyst of Comparative Example 4 and the exhaust gas purification catalyst of Comparative Example 5 in which Ag-supported catalyst and Ni-supported catalyst are physically mixed, a very high NOx conversion can be achieved at all temperatures. did it. The exhaust gas purifying catalyst of Example 5 using TMPA-TFSA as the ionic liquid is compared with the exhaust gas purifying catalyst of Example 1 that uses BMI-PF6 as the ionic liquid and has a relatively close Ag average content. Slightly lower NOx conversion. As described with reference to FIG. 12 and the like, this is because the protective power of TMPA-TFSA against Ag-Ni bimetallic particles is lower than that of BMI-PF6. This is considered to be due to the fact that some of the Ag-Ni binary metal particles have aggregated.

1 Silver 2 Nickel 3 Target material 4 Ionic liquid 5 Glass substrate 6 Silver atom 7 Nickel atom 8 Binary metal particle 9 Catalyst carrier 10 Exhaust gas purification catalyst

Claims (15)

  An exhaust gas purifying catalyst, comprising a catalyst carrier comprising a plurality of binary metal particles made of silver and nickel and having an average particle diameter of more than 0 nm and less than 100 nm.   2. The exhaust gas purifying catalyst according to claim 1, wherein an average content of silver in the binary metal particles is more than 5 atomic% and not more than 90 atomic%.   The exhaust gas purifying catalyst according to claim 2, wherein an average content of silver in the binary metal particles is 10 atomic% or more and 70 atomic% or less.   4. The exhaust gas purifying catalyst according to claim 3, wherein an average content of silver in the binary metal particles is 50 atomic% or more and 70 atomic% or less.   The exhaust gas purifying catalyst according to any one of claims 1 to 4, wherein an average particle diameter of the binary metal particles is more than 0 nm and not more than 20 nm.   6. The exhaust gas purifying catalyst according to claim 5, wherein the average particle size of the binary metal particles is more than 0 nm and not more than 10 nm.   The exhaust gas-purifying catalyst according to any one of claims 1 to 6, wherein the exhaust gas-purifying catalyst is a catalyst for purifying NOx. Including a deposition step of depositing binary metal particles composed of silver and nickel in an ionic liquid by sputtering a target material containing silver and nickel, and a supporting step of supporting the obtained binary metal particles on a catalyst carrier The method for producing an exhaust gas purifying catalyst according to any one of claims 1 to 7, wherein   The method according to claim 8, further comprising a calcination step of heat-treating the exhaust gas-purifying catalyst in an oxidizing atmosphere at a temperature of more than 300 ° C and not more than 800 ° C after the supporting step.   The method according to claim 8 or 9, further comprising a reduction step after the supporting step or the baking step.   The method according to claim 8, wherein the target material is a disk-shaped material in which silver plates and nickel plates are alternately arranged in a radial pattern.   The ionic liquid according to any one of claims 8 to 11, wherein the ionic liquid is selected from the group consisting of an aliphatic ionic liquid, an imidazolium ionic liquid, a pyridinium ionic liquid, and a combination thereof. The method described.   The aliphatic ionic liquid is N, N, N-trimethyl-N-propylammonium bis (trifluoromethanesulfonyl) amide, N-methyl-N-propylpiperidinium bis (trifluoromethanesulfonyl) imide, N, N- Diethyl-N-methyl-N- (2-methoxyethyl) ammonium bis (trifluoromethanesulfonyl) imide, N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium tetrafluoroborate, and them The method according to claim 12, wherein the method is selected from the group consisting of:   The imidazolium-based ionic liquid is 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methyl-imidazolium chloride, 1-ethyl-3-methylimidazolium (L) -lactate, 1-ethyl. -3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium hexafluoroline 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-butyl-3-methylimidazolium (L) -lactate, 1 -Hexyl-3-methylimidazolium bromide, 1-hexyl-3-methyl Imidazolium chloride, 1-hexyl-3-methylimidazolium hexafluorophosphate, 1-hexyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium trifluoromethanesulfonate, 1-octyl-3-methylimidazolium chloride, 1-octyl-3-methylimidazolium hexafluorophosphate, 1-decyl-3-methylimidazolium chloride, 1-dodecyl-3-methylimidazolium chloride, 1- Tetradecyl-3-methylimidazolium chloride, 1-hexadecyl-3-methylimidazolium chloride, 1-octadecyl-3-methylimidazolium chloride, 1-ethyl-2,3-dimethylimidazolium bromide, 1-ethyl-2, 3- Methyl imidazolium chloride, 1-butyl-2,3-dimethylimidazolium bromide, 1-butyl-2,3-dimethylimidazolium chloride, 1-butyl-2,3-dimethylimidazolium tetrafluoroborate, 1-butyl-2,3-dimethylimidazolium chloride Butyl-2,3-dimethylimidazolium trifluoromethanesulfonate, 1-hexyl-2,3-dimethylimidazolium bromide, 1-hexyl-2,3-dimethylimidazolium chloride, 1-hexyl-2,3-dimethyl 13. The method of claim 12, wherein the method is selected from the group consisting of imidazolium trifluoroborate, 1-hexyl-2,3-dimethylimidazolium trifluoromethanesulfonate, and combinations thereof.   The pyridinium-based ionic liquid is 1-ethylpyridinium bromide, 1-ethylpyridinium chloride, 1-butylpyridinium bromide, 1-butylpyridinium chloride, 1-butylpyridinium hexafluorophosphate, 1-butylpyridinium tetrafluoroborate 1-butylpyridinium trifluoromethanesulfonate, 1-hexylpyridinium bromide, 1-hexylpyridinium chloride, 1-hexylpyridinium hexafluorophosphate, 1-hexylpyridinium tetrafluoroborate, 1-hexylpyridinium trifluoromethanesulfone 13. The method of claim 12, wherein the method is selected from the group consisting of acid salts and combinations thereof.