Exhaust gas purifying catalyst
阅读说明：本技术 排气净化催化剂 (Exhaust gas purifying catalyst ) 是由 二桥裕树 于 2019-01-16 设计创作，主要内容包括：一种排气净化催化剂,是在无机氧化物的二次粒子(10)上担载有催化剂金属的粒子(20)的排气净化催化剂(100),从所述二次粒子(10)的表面向中心进行扫描透射型电子显微镜-能量色散型X射线的线分析时,所述二次粒子(10)的表面侧的催化剂金属的担载密度高于所述二次粒子(10)的中心部的催化剂金属的担载密度。(An exhaust gas purification catalyst (100) in which particles (20) of a catalytic metal are supported on secondary particles (10) of an inorganic oxide, wherein when a scanning transmission electron microscope-energy dispersive X-ray line analysis is performed from the surface of the secondary particles (10) to the center, the supporting density of the catalytic metal on the surface side of the secondary particles (10) is higher than the supporting density of the catalytic metal at the center of the secondary particles (10).)
1. An exhaust gas purifying catalyst comprising secondary particles of an inorganic oxide carrying catalytic metal particles,
when a scanning transmission electron microscope-energy dispersive X-ray line analysis is performed from the surface of the secondary particle to the center, the supporting density of the catalytic metal on the surface side of the secondary particle is higher than the supporting density of the catalytic metal at the center of the secondary particle.
2. The exhaust gas purifying catalyst according to claim 1,
the secondary particles have an average particle diameter of more than 1.5 μm,
80% or more of the catalytic metal is supported in a range from the surface of the secondary particle to 600 nm.
3. The exhaust gas purifying catalyst according to claim 1,
the secondary particles have an average particle diameter of more than 1.0 μm,
80% or more of the catalytic metal is supported in a range of 400nm from the surface of the secondary particle.
4. The exhaust gas purifying catalyst according to any one of claims 1 to 3,
the catalyst metal is one or more metals selected from the platinum group, the copper group and the iron group.
5. The exhaust gas purifying catalyst according to any one of claims 1 to 4,
the inorganic oxide is an oxide containing one or more selected from the group consisting of alumina, ceria, and zirconia.
6. An exhaust gas purifying catalyst device comprising a substrate and a catalyst coating layer on the substrate,
the catalyst coating layer contains the exhaust gas purifying catalyst according to any one of claims 1 to 5.
7. A method for producing the exhaust gas purifying catalyst according to any one of claims 1 to 5, comprising the steps of:
impregnating carrier particles in a mixed liquid for metal supporting, and
the carrier particles immersed in the coating liquid are fired,
the carrier particles are composed of secondary particles of an inorganic oxide, and
the metal-supporting mixed liquid contains precursor particles composed of a metal precursor and an organic compound having a mercapto group and a carboxyl group.
8. The method of claim 7, wherein the first and second light sources are selected from the group consisting of,
the organic compound is one or more selected from thioglycolic acid, 2-mercaptopropionic acid, 2-mercaptosuccinic acid, 2, 3-dimercaptosuccinic acid, 3-mercaptopropionic acid, 3-mercaptoisobutyric acid, N-acetylcysteine, penicillamine and 2-mercaptobenzoic acid.
9. The method according to claim 7 or 8,
the amount of the organic compound in the metal-supporting preparation solution is 1 mol or more and 50 mol or less based on 1 mol of the metal precursor.
10. The method according to any one of claims 7 to 9,
the precursor particles are formed by coordinating a sulfur atom in a mercapto group of the organic compound with a metal atom in the metal precursor.
11. The method according to any one of claims 7 to 10,
the average particle diameter of the precursor particles is 0.7nm to 10.0nm, as represented by the median diameter determined by a dynamic light scattering photometer.
Technical Field
The present invention relates to an exhaust gas purifying catalyst.
Background
As a catalyst for exhaust gas purification, a supported catalyst in which catalyst metal fine particles are supported on carrier particles is sometimes used. In particular, exhaust gas purification catalysts using secondary particles of an inorganic oxide as carrier particles are widely known in the industry.
When the exhaust gas is purified by using such an exhaust gas purifying catalyst, the exhaust gas diffuses on the surface and in the pores of the carrier particles, reaches the catalyst metal particles as the reaction active sites, and then undergoes a catalytic reaction.
Patent document 1 describes an exhaust gas purifying catalyst which is a Pd-based composite oxide containing at least one kind selected from alkaline earth metals. Patent document 1 is based on the following technical idea: there is no site on the support where Pd is present in the metallic state, but rather Pd2+The form is properly dispersed, suppressing the particle growth of Pd each other, thereby improving the exhaust gas purification ability. In example 1 of patent document 1, it is described that Sr is obtained by bringing strontium nitrate and palladium nitrate into contact with malic acid and then firing them2PdO3。
Disclosure of Invention
Fig. 2 shows a schematic sectional view for explaining the structure of an exhaust gas purifying catalyst in the related art. In the exhaust gas purifying catalyst (200) of fig. 2, catalytic metal particles (20) are supported on secondary particles (10) formed by the aggregation of a plurality of primary particles (1) of inorganic oxide. The catalytic metal particles (20) are supported not only in a shallow region near the surface of the secondary particles (10) of the inorganic oxide but also in a deep region (central portion of the secondary particles (10)) inside the pores, which are the gaps between the primary particles (1) constituting the secondary particles (10).
In the exhaust gas purification catalyst (200) of fig. 2, when the supply rate of the exhaust gas is relatively slow and/or at the initial stage of the reaction, the exhaust gas can sufficiently diffuse into the pores, which are the gaps between the surfaces of the secondary particles (10) and the primary particles (1) constituting the secondary particles (10), and reach the center portions of the secondary particles (10). Therefore, in this case, in addition to the catalytic metal supported near the surface, the catalytic metal supported at the center of the secondary particle (10) can participate in the reaction, and the supported catalytic metal can be efficiently used.
However, when the supply speed of the exhaust gas to the exhaust purification catalyst (200) is high, the exhaust gas does not reach the center of the secondary particles (10) because it does not diffuse deeply into the pores while contacting the region near the surface of the secondary particles (10). Therefore, in this case, the catalytic metal supported at the center of the secondary particle (10) cannot participate in the reaction, and only a part of the supported catalytic metal can participate in the reaction. When the reaction progresses and the pores of the secondary particles (10) are blocked, the exhaust gas cannot penetrate into the pores of the secondary particles (10) and cannot reach the center, and the catalyst metal in the center cannot participate in the reaction.
Therefore, in the case of an exhaust gas purification catalyst using secondary particles of an inorganic oxide as carrier particles, the selective arrangement of metal particles in the vicinity of the surface of the secondary particles enables effective use of the catalytic metal, which is the active site of the reaction.
An object of the present invention is to provide an exhaust gas purifying catalyst in which catalyst metal particles are selectively arranged in the vicinity of the surface of secondary particles of an inorganic oxide.
The present invention for achieving the above object is as follows.
< embodiment 1>
An exhaust gas purifying catalyst comprising secondary particles of an inorganic oxide carrying catalytic metal particles,
when a scanning transmission electron microscope-energy dispersive X-ray line analysis is performed from the surface of the secondary particle to the center, the supporting density of the catalytic metal on the surface side of the secondary particle is higher than the supporting density of the catalytic metal at the center of the secondary particle.
<
According to the exhaust gas purifying catalyst of < mode 1>,
the secondary particles have an average particle diameter of more than 1.5 μm,
80% or more of the catalytic metal is supported in a range from the surface of the secondary particle to 600 nm.
< mode 3>
According to the exhaust gas purifying catalyst of < mode 1>,
the secondary particles have an average particle diameter of more than 1.0 μm,
80% or more of the catalytic metal is supported in a range of 400nm from the surface of the secondary particle.
< embodiment 4>
The exhaust gas purification catalyst according to any one of < mode 1> to < mode 3>,
the catalyst metal is one or more metals selected from the platinum group, the copper group and the iron group.
< embodiment 5>
The exhaust gas purification catalyst according to any one of < mode 1> to < mode 4>,
the inorganic oxide is an oxide containing one or more selected from the group consisting of alumina, ceria, and zirconia.
<
An exhaust gas purifying catalyst device comprising a substrate and a catalyst coating layer on the substrate,
the catalyst coating layer includes the exhaust gas purification catalyst according to any one of < mode 1> to < mode 5 >.
< embodiment 7>
A method of manufacturing an exhaust gas purification catalyst according to any one of < mode 1> to < mode 5>, comprising the steps of:
impregnating carrier particles in a mixed liquid for metal supporting, and
the carrier particles immersed in the coating liquid are fired,
the carrier particles are composed of secondary particles of an inorganic oxide, and
the metal-supporting mixed liquid contains precursor particles composed of a metal precursor and an organic compound having a mercapto group and a carboxyl group.
<
According to the method described in < means 7>,
the organic compound is one or more selected from thioglycolic acid, 2-mercaptopropionic acid, 2-mercaptosuccinic acid, 2, 3-dimercaptosuccinic acid, 3-mercaptopropionic acid, 3-mercaptoisobutyric acid, N-acetylcysteine, penicillamine and 2-mercaptobenzoic acid.
< mode 9>
According to the method described in < manner 7> or <
the amount of the organic compound in the metal-supporting preparation solution is 1 mol or more and 50 mol or less based on 1 mol of the metal precursor.
<
The method according to any one of < mode 7> to < mode 9>,
the precursor particles are formed by coordinating a sulfur atom in a mercapto group of the organic compound with a metal atom in the metal precursor.
< mode 11>
The method according to any one of < mode 7> to <
the average particle diameter of the precursor particles is 0.7nm to 10.0nm, as represented by the median diameter determined by a dynamic light scattering photometer.
According to the present invention, there is provided an exhaust gas purifying catalyst in which particles of a catalytic metal are selectively arranged in the vicinity of the surface of secondary particles of an inorganic oxide.
Drawings
Fig. 1 is a schematic sectional view for explaining the structure of an exhaust gas purifying catalyst according to the present invention.
Fig. 2 is a schematic sectional view for explaining the structure of an exhaust gas purifying catalyst in the related art.
FIG. 3 is an XPS chart of the metal-supporting preparation solution and DL-mercaptosuccinic acid obtained in preparation example 1 and comparative preparation example 1, respectively.
FIG. 4 is an EDS chart of the Rh-supported alumina catalyst obtained in preparation example 1 before firing.
FIG. 5 is an EDS chart of an Rh-supported alumina catalyst obtained in comparative preparation example 1 before firing.
FIG. 6 is an EDS chart of an Rh-supported alumina catalyst obtained in comparative preparation example 2 before firing.
FIG. 7 is an FE-EPMA image of the Pt supported alumina catalyst before firing obtained in preparation example 2.
Detailed Description
< exhaust gas purifying catalyst >
The exhaust gas purifying catalyst of the present invention,
an exhaust gas purifying catalyst comprising particles of a catalytic metal supported on secondary particles of an inorganic oxide,
when a scanning transmission electron microscope-energy dispersive X-ray line analysis is performed from the surface of the secondary particle to the center, the supporting density of the catalytic metal on the surface side of the secondary particle is higher than the supporting density of the catalytic metal at the center of the secondary particle.
Hereinafter, preferred embodiments of the exhaust gas purifying catalyst of the present invention will be described in detail.
Fig. 1 shows a schematic sectional view for explaining the structure of an exhaust gas purifying catalyst of the present invention.
Similarly to the exhaust gas purification catalyst (200) of fig. 2, the exhaust
Even when the supply rate of the exhaust gas is high and/or the pores of the secondary particles (10) are clogged, the exhaust gas can contact the region near the surface of the secondary particles (10). Therefore, according to the exhaust gas purification catalyst (100) of the present invention in which the catalytic metal is supported in a concentrated manner in a shallow region near the surface of the secondary particle (10), even when the supply rate of the exhaust gas is high and the degree of clogging of the pores is large, most of the catalytic metal can participate in the reaction, and therefore, there is an advantage that the activity can be stably expressed for a long period of time.
< particle diameter of secondary particle and depth of catalyst Metal Supported >
In the exhaust gas purifying catalyst of the present invention, the supporting density of the catalytic metal on the surface side of the secondary particle is higher than the supporting density of the catalytic metal in the central portion of the secondary particle.
From the viewpoint of ensuring, for example, the stability and coatability of the coating liquid for coating when producing the exhaust gas purifying catalyst of the present invention, the particle size of the secondary particles may be, for example, more than 1.0 μm, more than 1.5 μm, 2.0 μm or more, 2.5 μm or more, 3.0 μm or more, 4.0 μm or more, 5.0 μm or more, 10 μm or more, 15 μm or more, or 20 μm or more, and may be, for example, 200 μm or less, 150 μm or less, 100 μm or less, 80 μm or less, 60 μm or less, 50 μm or less, 40 μm or less, 30 μm or less, 20 μm or less, 15 μm or less, 10 μm or less, 5 μm or less, or 3 μm or less.
In the exhaust gas purifying catalyst of the present invention, the supporting density of the catalytic metal on the surface side of the secondary particles is higher than that of the catalytic metal in the central portion of the secondary particles, and specifically, the following two cases can be exemplified.
(1) The secondary particles have an average particle diameter of more than 1.5 μm,
an exhaust gas purification catalyst (1 st exhaust gas purification catalyst) in which 80% or more of the catalytic metals are supported in a range from the surface of the secondary particles to 600 nm; and
(2) the secondary particles have an average particle diameter of more than 1.0. mu.m,
an exhaust gas purifying catalyst (2 nd exhaust gas purifying catalyst) in which 80% or more of the catalytic metal is supported in a range of 400nm from the surface of the secondary particle.
In the 1 st exhaust gas purifying catalyst, the particle diameter of the secondary particles may exceed 1.5 μm, be 2.0 μm or more, 5.0 μm or more, 10 μm or more, 15 μm or more, or 20 μm or more, from the viewpoint of providing a sufficient difference in the supporting density of the catalytic metal between the surface side and the central portion of the secondary particles to reliably exhibit the effect of the present invention. The upper limit of the particle diameter of the secondary particles in this case may be, for example, 200 μm or less, 150 μm or less, 100 μm or less, 80 μm or less, 60 μm or less, 50 μm or less, 40 μm or less, or 30 μm or less.
In the 1 st exhaust gas purifying catalyst, from the viewpoint of further improving the utilization efficiency of the catalytic metal and further improving the catalytic reaction activity, the depth range in which 80% or more of the catalytic metal is supported may be a depth range from the surface of the secondary particle to 600nm, 550nm, 500nm, 450nm, or 400 nm.
In the exhaust gas purifying catalyst of the 2 nd aspect, from the viewpoint of providing a sufficient difference in the supporting density of the catalytic metal between the surface side and the central portion of the secondary particle to thereby reliably exhibit the effect of the present invention, the depth range in which 80% or more of the catalytic metal is supported may be a depth range from the surface of the secondary particle to 400nm, 350nm, 300nm, 250nm or 200 nm.
In the exhaust gas purifying catalyst of the 2 nd, from the viewpoint of sufficiently increasing the surface area of the secondary particles and further improving the exhaust gas purifying ability, the particle diameter of the secondary particles may be as small as exceeding 1.0 μm, and may be, for example, 50 μm or less, 40 μm or less, 30 μm or less, 20 μm or less, 15 μm or less, 10 μm or less, 5 μm or less, or 3 μm or less. The lower limit of the particle size of the secondary particles in this case may be, for example, more than 1.5 μm, 2.0 μm or more, 2.5 μm or more, or 3.0 μm or more.
In both the 1 st and 2 nd exhaust gas purification catalysts, the proportion of the catalytic metal supported in the above depth range from the surface of the secondary particles is 80% or more from the viewpoint of effective use of the catalytic metal. From the viewpoint of further improving the utilization efficiency of the catalytic metal, the proportion of the catalytic metal supported in the above depth range from the surface of the secondary particle may be 85% or more, 90% or more, or 95% or more, or may be 100%.
The depth range of the catalyst metal support was measured by line analysis using a scanning transmission electron microscope and energy dispersive X-ray (STEM-EDX). The measurement can also be carried out by a field emission type electron beam micro analyzer (FE-EPMA) or the like.
< Secondary particles >
In the exhaust gas purifying catalyst of the present invention, secondary particles of an inorganic oxide are used as a carrier.
The inorganic oxide in the present invention may be, for example, one containing a metal selected from the group consisting of alumina (Al)2O3) Silicon dioxide (SiO)2) Zirconium oxide (ZrO)2) Titanium dioxide (TiO)2) And one or more inorganic oxides of rare earth elements. The oxide of the rare earth element may be lanthanum oxide (La)2O3) Cerium oxide (CeO)2) Neodymium oxide (Nd)2O3) Europium oxide (Eu)2O3) Gadolinium oxide (Gd)2O3) And the like. The inorganic oxide may be, for example, an oxide containing one or more selected from alumina, ceria, and zirconia, and may include, for example, an alumina and ceria-zirconia composite oxide.
The secondary particles of the inorganic oxide may be aggregates of the primary particles of the inorganic oxide.
The particle size of the primary particles of the inorganic oxide may be, for example, 1nm or more, 5nm or more, 10nm or more, 15nm or more, or 20nm or more from the viewpoint of facilitating the diffusion of the gaseous reactant into the pores of the secondary particles and ensuring good handling properties, and may be, for example, 200nm or less, 150nm or less, 100nm or less, or 80nm or less from the viewpoint of ensuring a specific surface area necessary as a support.
The particle size of the secondary particles is as described above.
< particles of catalyst Metal >
As the metal constituting the catalyst metal particles, a desired catalyst metal may be selected, and may be either a noble metal or a base metal. Specifically, the noble metal may be one or more metals selected from the platinum group, the copper group, and the like. Platinum groups are, for example, palladium, platinum and rhodium. The copper group is, for example, silver, copper, etc. The base metal may be, for example, a metal of the iron group, and may be selected from, for example, cobalt, nickel, iron, and the like.
The amount of the catalyst metal to be supported and the particle diameter of the catalyst metal may be appropriately set according to the size of the exhaust gas purification catalyst device, the kind of the catalyst metal, and the like to be expected to be applied, and for example, the following is given.
Particle diameter of catalyst metal: 1nm or more, 2nm or more, 3nm or more, 4nm or more, or 5nm or more; 20nm or less, 15nm or less or 10nm or less
Loading of catalyst metal: 0.1 mass% or more, 0.3 mass% or more, 0.5 mass% or more, 1.0 mass% or more, 2.0 mass% or more, or 3.0 mass% or more of the secondary particles of the inorganic oxide based on the mass of the secondary particles; 20% by mass or less, 15% by mass or less, 10% by mass or less, 8% by mass or less, 7% by mass or less, or 5% by mass or less
< method for producing exhaust gas purifying catalyst >
The exhaust gas purifying catalyst of the present invention can be produced, for example, by a method comprising:
immersing the carrier particles in the mixed solution for supporting metal (immersing step), and
the carrier particles immersed in the coating liquid are fired (firing step),
the carrier particles are composed of secondary particles of an inorganic oxide, and
the mixed solution contains precursor particles composed of a metal precursor and an organic compound having a mercapto group and a carboxyl group.
< Carrier particle >
The carrier particles are composed of secondary particles of an inorganic oxide, and reference can be made to the above description of the exhaust gas purifying catalyst of the present invention. The kind of the inorganic oxide may be selected according to the kind of the carrier particle of the desired catalyst.
< preparation solution for Metal Loading >
The metal-supporting mixed liquid used in the method for producing an exhaust gas purifying catalyst of the present invention is a liquid composition in which precursor particles composed of a metal precursor and an organic compound having a mercapto group and a carboxyl group, and optional components used as necessary are dissolved or dispersed in an appropriate solvent.
The precursor particles contained in the mixing liquid in the present invention may be particles in which an organic compound having a mercapto group and a carboxyl group is coordinated to a metal precursor.
The average particle diameter of the precursor particles is represented by a median diameter (D50) determined by a Dynamic Light Scattering (DLS) photometer, and may be, for example, 0.7nm or more, 0.8nm or more, 1.0nm or more, 1.5nm or more, 2.0nm or more, or 1.5nm or more, and may be, for example, 10.0nm or less, 8.0nm or less, 7.0nm or less, 6.0nm or less, 5.0nm or less, or 4.0nm or less.
(Metal precursor)
The metal precursor is a compound of a catalytic metal that is reduced in an arbitrary step (for example, a firing step described later) in the method for producing an exhaust gas purifying catalyst of the present invention to produce secondary particles of an inorganic oxide.
As the metal atom in the metal precursor, a catalyst metal in a desired catalyst may be selected, and the metal atom may be selected with reference to the above description of the exhaust gas purifying catalyst of the present invention. The metal atoms may be noble metals or base metals. Specifically, the noble metal may be a metal of the platinum group, copper group, or the like. Platinum group is for example palladium, platinum and rhodium. The copper family is for example mercury and copper. The base metal may be, for example, a metal of the iron group, and may be selected from, for example, cobalt, nickel, iron, and the like.
The metal precursor may be a nitrate, hydroxide, halide, complex, or the like, containing the selected metal atom. The halide is preferably chloride. Specific examples of the metal precursor include the following, depending on the kind of the metal atom.
The palladium precursor may be, for example, palladium (II) nitrate, palladium (II) chloride, palladium (II) hydroxide, dinitrodiamine palladium (II), dichlorodiamine palladium (II), or the like. Of these, dinitrodiamine palladium (II) and dichlorodiamine palladium (II) which are palladium complexes can be used as nitric acid solutions to prepare mixed solutions.
The platinum precursor may be, for example, platinum (IV) nitrate, platinum (IV) chloride, hexahydroxyplatinic acid, dinitrodiammine platinum (II), or the like. Among them, platinic (IV) chloride acid, hexahydroxyplatinic (IV) acid, and dinitrodiammine platinum (II) which are platinum complexes can be used as nitric acid solutions to prepare mixed solutions.
For example, the rhodium precursor may be rhodium (III) nitrate, rhodium (III) chloride, rhodium (III) hydroxide, hexanitrorhodium (III) acid, or the like.
The base metal precursor may be, for example, cobalt (II) nitrate, cobalt (II) chloride, cobalt (II) hydroxide, nickel (II) nitrate, nickel (II) chloride, nickel (II) hydroxide, copper (II) nitrate, copper (II) chloride, copper (II) hydroxide, iron (II) nitrate, iron (II) chloride, iron (II) hydroxide, or the like.
The metal precursor is preferably selected from palladium (II) hydroxide, hexahydroxyplatinic acid, dinitrodiammine platinum (II) acid, rhodium (III) hydroxide, cobalt (II) hydroxide, nickel (II) hydroxide, copper (II) hydroxide and iron (II) hydroxide among the above, from the viewpoint that anions, catalyst poisoning components and the like in the precursor can be easily removed by washing and the amount of residues in the obtained catalyst can be reduced.
As the catalyst metal of the exhaust gas purifying catalyst of the present invention, a metal of the platinum group, the copper group or the iron group can be selected, and a platinum group metal is particularly preferably used.
(organic Compound having mercapto group and carboxyl group)
The organic compound having a mercapto group and a carboxyl group interacts with the metal precursor and the carrier particles mixed in the mixed liquid for supporting a metal when the exhaust gas purifying catalyst of the present invention is produced, and has a function of retaining the metal precursor in the vicinity of the surfaces of the carrier particles. That is, it is considered that the sulfur atom in the mercapto group of the organic compound coordinates to the metal atom in the metal precursor, and the carboxyl group interacts with the surface of the support particle, whereby the metal precursor is retained in the vicinity of the surface of the support particle. In this way, it is considered that the catalyst metal particles are selectively present in the vicinity of the surface of the support particle by performing the firing in a state where the metal precursor is retained in the vicinity of the surface of the support particle.
The organic compound having a mercapto group and a carboxyl group is preferably a compound having a relatively low molecular weight in order to effectively exhibit the function of retaining the metal precursor in the vicinity of the surface of the carrier particle by interacting with both the metal precursor and the surface of the carrier particle. Specifically, the molecular weight of the organic compound having a mercapto group and a carboxyl group may be 1,000 or less or 500 or less. On the other hand, the molecular weight of the organic compound may be 77 or more, 100 or more, or 120 or more, as required to have both a mercapto group and a carboxyl group.
The number of mercapto groups in the organic compound may be 1 or more, preferably 1 or more and 4 or less, and more preferably 1 or 2.
The number of carboxyl groups in the organic compound may be 1 or more, preferably 1 or more and 4 or less, and more preferably 1 or 2.
Examples of the organic compound having a mercapto group and a carboxyl group include thioglycolic acid, 2-mercaptopropionic acid, 2-mercaptosuccinic acid (also known as thiomalic acid), 2, 3-dimercaptosuccinic acid, 3-mercaptopropionic acid, 3-mercaptoisobutyric acid, N-acetylcysteine, penicillamine, and 2-mercaptobenzoic acid.
As the organic compound having a mercapto group and a carboxyl group, thiomalic acid, 2, 3-dimercaptosuccinic acid, or cysteine is more preferable, and thiomalic acid or cysteine is more preferable.
When the organic compound having a mercapto group and a carboxyl group has optical isomers, all of the D, L and racemic bodies can be used without limitation.
The use ratio of the organic compound having a mercapto group and a carboxyl group may be, for example, 1 mol or more, 3 mol or more, 5 mol or more, 7 mol or more, or 10 mol or more, and for example, 50 mol or less, 40 mol or less, 30 mol or less, 20 mol or less, or 15 mol or less, relative to 1 mol of the metal precursor to be blended in the coating liquid. If the use ratio of the organic compound is 1 mole or more relative to 1 mole of the metal precursor in the coating liquid, the organic compound can effectively interact with the metal precursor and the carrier particles mixed in the coating liquid, and the function of retaining the metal precursor in the vicinity of the surfaces of the carrier particles can be effectively exhibited. On the other hand, if the ratio is 50 mol or less, the generation of a burned residue from the organic compound can be suppressed in the burning step in the production of the catalyst, and a suitable exhaust gas purification ability can be exhibited.
(optional ingredients)
The metal-supporting mixed solution contains precursor particles composed of a metal precursor and an organic compound having a mercapto group and a carboxyl group, and may contain other optional components, as well as a solvent described later. Optional ingredients may be, for example, pH adjusters, surfactants, thickeners, and the like.
(solvent)
The solvent contained in the mixed liquid for supporting metal may be an aqueous solvent, for example, water or a mixed solvent of water and a water-soluble organic solvent. Examples of the water-soluble organic solvent include alcohols such as methanol, ethanol, isopropanol, and ethylene glycol; ethers such as 1, 2-dimethoxyethane, tetrahydrofuran, and 1, 4-dioxane; ketones such as acetone; esters such as ethyl acetate; polar solvents such as dimethylformamide, and the like.
The solvent of the metal-supporting mixed solution is preferably water.
(coordination of a sulfur atom to a Metal atom)
It is considered that in the metal-supporting mixed solution, a sulfur atom in the organic compound having a mercapto group and a carboxyl group coordinates to a metal atom in the metal precursor. Whether or not the sulfur atom is coordinated to the metal atom can be confirmed by, for example, X-ray photoelectron spectroscopy (XPS). When the sulfur atom is coordinated to the metal atom, the binding energy of S2p shifts to the lower energy side. For example, 2-mercaptosuccinic acid has a sulfur atom in the mercapto group having an S2p binding energy of about 163.5eV, and when this sulfur atom is coordinated to rhodium, it shifts to about 162.5eV on the low energy side.
(particle diameter of precursor particle)
In the metal-supporting mixed solution, the metal precursor may form precursor particles together with an organic compound having a mercapto group and a carboxyl group. In order to easily obtain particles of the catalyst metal having an appropriate particle diameter and to ensure handleability of the blended solution by restricting sedimentation of the particles, the particle diameter of the precursor particles may be, for example, 0.1nm or more, 0.3nm or more, 0.5nm or more, 1.0nm or more, 1.5nm or more, or 2.0nm or more, and may be, for example, 50nm or less, 30nm or less, 20nm or less, 15nm or less, 12nm or less, or 10nm or less.
The particle diameter is a particle diameter (D50, median diameter) in which the cumulative volume is 50% of the entire particle diameter distribution measured by a particle diameter distribution measuring apparatus using a dynamic light scattering method (DLS).
(liquid Property of blending liquid for Metal Loading)
The liquid properties of the metal-supporting mixed liquid may be appropriately set within a range in which precursor particles composed of a metal precursor and an organic compound having a mercapto group and a carboxyl group are stably dispersed. The liquid property of the blended liquid may be, for example, 0.0 or more, 0.5 or more, 1.0 or more, 1.5 or more, or 1.0 or more, and may be, for example, 13.0 or less, 10.0 or less, 7.0 or less, 5.0 or 3.0 or less, as the pH value.
(concentration of blending liquid for supporting Metal)
From the viewpoint of the requirement of easily and reliably supporting the catalyst metal on the carrier particles and ensuring the uniformity of the blended liquid, the concentration of the blended liquid for metal support may be, for example, 0.5 mass% or more, 1 mass% or more, 2 mass% or more, or 3 mass% or more, and may be, for example, 30 mass% or less, 20 mass% or less, 10 mass% or less, or 5 mass% or less, as the proportion of the total mass of the total components other than the solvent in the blended liquid in the total mass of the blended liquid.
(preparation of blending solution for Metal Loading)
The metal-supporting mixed solution can be prepared by adding and mixing the metal precursor, the organic compound having a mercapto group and a carboxyl group, and optional components used as needed in a predetermined solvent. The components may be added to the solvent simultaneously or sequentially.
The mixed solution may be heated during mixing. In order to promote the formation of a coordinate bond between the metal precursor and the organic compound having a mercapto group and a carboxyl group, it is preferable to mix the metal precursor and the organic compound while heating. The heating temperature in this case may be, for example, 40 ℃ or higher, 50 ℃ or higher, or 60 ℃ or higher, and may be, for example, 150 ℃ or lower, 120 ℃ or lower, or 100 ℃ or lower. The heating time may be, for example, 30 minutes or more, 1 hour or more, 2 hours or more, or 3 hours or more, and may be, for example, 12 hours or less, 10 hours or less, 8 hours or less, or 5 hours or less.
< immersion step >
In the impregnation step, the support particles are impregnated into the metal-supporting mixed solution.
The use ratio of the carrier particles to the mixed solution in the impregnation step may be appropriately set according to the amount of the metal supported on the carrier particles of the desired catalyst.
The temperature of the mixed solution when the carrier particles are immersed in the mixed solution may be set to, for example, 5 to 90 ℃, preferably 25 to 60 ℃. The immersion time may be, for example, 1 minute to 6 hours, preferably 10 minutes to 1 hour.
Thereafter, a solvent removal step may be performed as necessary. In the solvent removal step, for example, a method of leaving the mixture at room temperature or higher and 120 ℃ or lower, for example, for 5 minutes or longer and 12 hours or shorter, may be employed.
< firing Process >
Next, in the firing step, the exhaust gas purifying catalyst of the present invention can be obtained by firing the carrier particles after being immersed in the coating liquid.
The temperature in the firing step may be, for example, 400 ℃ or higher, 450 ℃ or higher, or 500 ℃ or higher in order to reduce the metal atoms of the metal precursor and sufficiently remove the organic component, and may be, for example, 1500 ℃ or lower, 1200 ℃ or lower, 1000 ℃ or lower, or 800 ℃ or lower in order to avoid sintering of the catalyst metal particles. From the same viewpoint, the firing time may be, for example, 10 minutes or more, 30 minutes or more, 1 hour or more, or 1.5 hours or more, and may be, for example, 24 hours or less, 12 hours or less, 10 hours or less, 8 hours or less, or 5 hours or less.
The ambient atmosphere in the firing step may be any of an oxidizing atmosphere, an inert atmosphere, and a reducing atmosphere. The oxidizing atmosphere is, for example, in air. The inert atmosphere is, for example, in nitrogen, argon, etc. The reducing atmosphere is, for example, a mixed gas of hydrogen and an inert gas (nitrogen, argon, or the like).
< application of exhaust gas purifying catalyst >
The exhaust gas purifying catalyst of the present invention can be used for purification of exhaust gas as a catalyst component contained in a coating layer formed on a substrate.
< exhaust gas purifying catalyst device >
The exhaust gas purifying catalyst of the present invention can be used as an exhaust gas purifying catalyst device having a coating layer containing the exhaust gas purifying catalyst of the present invention on an appropriate substrate.
The substrate used in the exhaust gas purification catalyst device of the present invention may be, for example, a monolithic honeycomb substrate composed of cordierite, SiC, stainless steel, metal oxide particles, or the like.
The coating layer on the substrate contains the catalyst of the present invention, and may contain other optional components as needed. Examples of the optional component include inorganic oxide particles, a binder, an alkali metal compound, and an alkaline earth metal compound.
The inorganic oxide particles may be, for example, a composite oxide containing alumina, silica-alumina, zeolite, titania, silica, ceria, zirconia, and a rare earth element (other than cerium), or the like.
The binder has a function of bonding the catalysts of the present invention to each other, between the catalyst of the present invention and other components, and between them and the surface of the substrate, thereby imparting mechanical strength to the coating layer of the exhaust gas purification catalyst device. Such a binder may be, for example, alumina sol, zirconia sol, silica sol, titania sol, or the like.
Examples of the alkali metal compound include potassium compounds and lithium compounds. Examples of the alkaline earth metal compound include a calcium compound, a barium compound, and a strontium compound. All of them may be oxides, carbonates, and the like of the exemplified metals.
In this exhaust gas purifying catalyst device, the coating layer containing the exhaust gas purifying catalyst of the present invention may be formed over the entire length of the substrate, or may be formed only in a part of the length of the substrate. When the coating layer is formed only on a part of the length of the substrate, the coating layer containing the catalyst of the present invention may or may not be formed on a part of the substrate where the coating layer is not formed.
The coating layer containing the exhaust gas purifying catalyst of the present invention may be formed directly on the substrate, or may be formed on the substrate with another coating layer interposed therebetween. Further, other coating layers may be formed on the coating layer containing the catalyst of the present invention.
The exhaust gas purifying catalyst device of the present invention can be produced by coating, for example, an aqueous slurry containing the exhaust gas purifying catalyst of the present invention and other optional components on a desired substrate, followed by firing.
- 上一篇：一种医用注射器针头装配设备
- 下一篇：用于圆锥破碎机的内部磨损部件的螺母的提升工具