JP2016140809A - Catalyst for purifying exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst for purifying exhaust gas, having an excellent effect of removing carbon monoxide (CO) and hydrocarbon (HC).SOLUTION: A catalyst for purifying exhaust gas including silver and manganese and/or an alloy thereof supported on a heat-resistant oxide has a mass ratio of the silver content to the manganese content (Ag/Mn) of 0.16 or more. The catalyst for purifying exhaust gas can have an excellent effect of removing carbon monoxide (CO) and hydrocarbon (HC).SELECTED DRAWING: Figure 1

Description

  The present invention relates to an exhaust gas purifying catalyst, and more particularly to an exhaust gas purifying catalyst for efficiently purifying carbon monoxide (CO) and hydrocarbons (HC) contained in exhaust gas such as automobile engines.

An exhaust gas purification catalyst consisting of a three-way catalyst that can simultaneously purify carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NO _x ) contained in exhaust gas activates noble metals such as Pt, Rh, and Pd. It is a substance.

  Such precious metals, especially Pt and Rh, are expensive, and the price fluctuates severely, so there are various catalysts that can be produced at low cost, such as using relatively inexpensive silver even with the same precious metal. It is being considered.

  As a catalyst for such an exhaust gas purifying catalyst, for example, silver is supported on alumina, and the alumina and silver are calcined at 900 to 1100 ° C. in the atmosphere and then reduced at 100 to 500 ° C. A catalyst has been proposed (see, for example, Patent Document 1).

JP 2010-125373 A

  However, in recent years, further improvement in purification performance of carbon monoxide (CO) and hydrocarbon (HC) in exhaust gas has been desired.

  An object of the present invention is to provide an exhaust gas purification catalyst capable of exhibiting excellent carbon monoxide (CO) and hydrocarbon (HC) purification performance.

  In the exhaust gas purifying catalyst of the present invention, silver and manganese and / or an alloy thereof are supported on a heat-resistant oxide, and the mass ratio of the copper content to the silver content (Ag / Mn) is , 0.16 or more.

  In the exhaust gas purifying catalyst of the present invention, silver and manganese and / or an alloy thereof are supported on a heat-resistant oxide, and the mass ratio of the copper content to the silver content (Ag / Mn) is , 0.16 or more.

  Therefore, excellent carbon monoxide (CO) and hydrocarbon (HC) purification performance can be expressed.

FIG. 1 shows the active metal dependence of the 50% purification temperature of carbon monoxide (CO) and hydrocarbon (HC) of an exhaust gas purification catalyst when lanthanum-containing alumina is a support. FIG. 2 shows the active metal dependence of the 50% purification temperature of carbon monoxide (CO) and hydrocarbon (HC) of the exhaust gas purification catalyst when CZY is a carrier. FIG. 3 shows the carrier dependency of the 50% purification temperature of carbon monoxide (CO) and hydrocarbon (HC) for the exhaust gas purification catalyst. FIG. 4 shows the silver content dependence of the 50% purification temperature of carbon monoxide (CO) and hydrocarbon (HC) for exhaust gas purification catalysts. FIG. 5 shows the dependence of the 50% purification temperature of hydrocarbons (HC) on the exhaust gas purification catalyst on the loading method. FIG. 6 shows the silver content dependency of the specific surface area of the exhaust gas purifying catalyst.

  In the exhaust gas purifying catalyst of the present invention, silver (Ag) and manganese (Mn) and / or their alloys are supported on a heat-resistant oxide (support). That is, the heat-resistant oxide carries either silver and manganese, an alloy of silver and manganese, or silver, manganese, and an alloy of silver and manganese.

  Although it does not restrict | limit especially as a heat resistant oxide, For example, a zirconia type oxide, a ceria type oxide, an alumina, and a titanium type oxide are mentioned.

Examples of the zirconia-based oxide include zirconium dioxide (ZrO ₂ ) and, for example, a zirconia-based composite oxide represented by the following general formula (1).

Zr _{1- (a + b)} Ce _a R _b O _2-c (1)
(Wherein R represents a rare earth element (excluding Ce) and / or alkaline earth metal, a represents the atomic ratio of Ce, b represents the atomic ratio of R, and 1- ( a + b) indicates the atomic ratio of Zr, and c indicates the amount of oxygen defects.)
In the general formula (1), examples of the rare earth element represented by R include Sc (scandium), Y (yttrium), La (lanthanum), Pr (praseodymium), Nd (neodymium), Pm (promethium), and Sm (promethium). Samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Yb (ytterbium), Lu (lutetium) and the like It is done.

  Examples of the alkaline earth metal represented by R include Be (beryllium), Mg (magnesium), Ca (calcium), Sr (strontium), Ba (barium), and Ra (radium).

  These rare earth elements and alkaline earth metals can be used alone or in combination of two or more.

  Moreover, the atomic ratio of Ce shown by a is in the range of 0.1 to 0.65, and preferably in the range of 0.4 to 0.6.

  In addition, the atomic ratio of R represented by b is in the range of 0 to 0.55 (that is, R is an optional component that is optionally included rather than an essential component, and if included, 0.55 or less) (Atomic ratio), preferably in the range of 0 to 0.2, more preferably in the range of 0.03 to 0.06. If it exceeds 0.55, phase separation or other complex oxide phases may be generated.

  Moreover, the atomic ratio of Zr shown by 1- (a + b) is in the range of 0.35 to 0.9, and preferably in the range of 0.4 to 0.6.

  Further, c represents the amount of oxygen defects, which means the ratio of vacancies formed in the crystal lattice of the fluorite-type crystal lattice normally formed by the oxides of Zr, Ce and R.

  Such a zirconia-based composite oxide is not particularly limited, and for example, for preparing a composite oxide in accordance with the description of paragraph numbers [0090] to [0102] of JP-A-2004-243305. It can be produced by an appropriate method, for example, a production method such as a coprecipitation method, a citric acid complex method, or an alkoxide method.

Examples of the ceria-based oxide include cerium oxide (CeO ₂ ) and, for example, a ceria-based complex oxide represented by the following general formula (2).

Ce _{1- (d + e)} Zr _d L _e O _2-f (2)
(In the formula, L represents a rare earth element (excluding Ce) and / or alkaline earth metal, d represents an atomic ratio of Zr, e represents an atomic ratio of L, and 1- ( d + e) indicates the atomic ratio of Ce, and f indicates the amount of oxygen defects.)
In the general formula (2), the rare earth element represented by L includes the rare earth element represented by the general formula (1) (excluding Ce). Moreover, as an alkaline-earth metal shown by L, the alkaline-earth metal shown by General formula (1) is mentioned. These rare earth elements and alkaline earth metals can be used alone or in combination of two or more.

  Moreover, the atomic ratio of Zr shown by d is in the range of 0.2 to 0.7, and preferably in the range of 0.2 to 0.5.

  In addition, the atomic ratio of L represented by e is in the range of 0 to 0.2 (that is, L is an optional component that is optionally included rather than an essential component, and if included, 0.2 or less) Atomic ratio). If it exceeds 0.2, phase separation or other complex oxide phases may be generated.

  Moreover, the atomic ratio of Ce shown by 1- (d + e) is in the range of 0.3 to 0.8, and preferably in the range of 0.4 to 0.6. Moreover, it is suitable that the atomic ratio of Ce represented by 1- (d + e) is larger than the atomic ratio of Ce represented by a in the general formula (1).

  Further, f represents the amount of oxygen defects, which means the proportion of vacancies formed in the crystal lattice in the fluorite-type crystal lattice that is normally formed by Ce, Zr and L oxides.

  Such a ceria-based composite oxide can be manufactured by a manufacturing method similar to the above-described manufacturing method of the zirconia-based composite oxide.

  In addition, when the atomic ratio of Ce in the ceria-based composite oxide overlaps with the atomic ratio of Ce in the zirconia-based composite oxide, in the present invention, the overlapping ceria-based composite oxide is the zirconia-based composite oxide. It belongs to a thing.

  Examples of alumina include α-alumina, θ-alumina, and γ-alumina, and preferably θ-alumina.

  α-alumina has an α-phase as a crystal phase, and examples thereof include AKP-53 (trade name, high-purity alumina, manufactured by Sumitomo Chemical Co., Ltd.). Such α-alumina can be obtained by a method such as an alkoxide method, a sol-gel method, or a coprecipitation method.

  θ-alumina is a kind of intermediate (transition) alumina that has a θ-phase as a crystal phase and transitions to α-alumina, and includes, for example, SPHERALITE 531P (trade name, γ-alumina, manufactured by Procatalyze). . Such θ-alumina can be obtained, for example, by subjecting commercially available activated alumina (γ-alumina) to heat treatment at 900 to 1100 ° C. for 1 to 10 hours in the air.

  γ-alumina has a γ-phase as a crystal phase and is not particularly limited, and examples thereof include known ones used for exhaust gas purification catalysts.

  In addition, alumina containing La and / or Ba can also be used. Alumina containing La and / or Ba can be produced according to the description of paragraph number [0073] of JP-A No. 2004-243305.

Examples of the titanium-based oxide include titanium oxide (TiO ₂ ).

  These heat-resistant oxides can be used alone or in combination of two or more.

  Preferred examples of the heat-resistant oxide include zirconia-based oxides and ceria-based oxides, and more preferably zirconia-based oxides. More preferably, a zirconia-based composite oxide represented by the above general formula (1), particularly preferably a ceria-zirconia-yttrium composite oxide is used.

  In the exhaust gas purifying catalyst, the silver content is, for example, 0.5% by mass or more, preferably 1.0% by mass or more, with respect to the total amount of the heat-resistant oxide, silver and manganese. , 12 mass% or less, preferably 6.0 mass% or less.

  If the silver content is within the above range, the purification performance of carbon monoxide (CO) and hydrocarbon (HC) can be improved.

  In the exhaust gas purifying catalyst, the manganese content is, for example, 1.5% by mass or more, preferably 3.0% by mass or more, with respect to the total amount of the heat-resistant oxide, silver and manganese. For example, it is 9.0 mass% or less, Preferably, it is 6.0 mass% or less.

  If the manganese content is within the above range, the purification performance of carbon monoxide (CO) and hydrocarbon (HC) can be improved.

  In this exhaust gas purifying catalyst, the mass ratio (Ag / Mn) of the silver content to the manganese content is 0.16 or more, preferably 0.33 or more. Hereinafter, it is preferably 2.0 or less.

  If the mass ratio of the silver content to the manganese content (Ag / Mn) is within the above range, the purification performance of carbon monoxide (CO) and hydrocarbons (HC) can be improved.

  In order to obtain an exhaust gas purifying catalyst, for example, silver and manganese are supported on the same heat-resistant oxide simultaneously or sequentially, preferably simultaneously. As a method of supporting silver and manganese on the same heat-resistant oxide, for example, except for the firing temperature and firing time, in accordance with the description in paragraphs [0122] to [0127] of JP-A-2004-243305, Silver and manganese are supported on the above heat-resistant oxide in the above-described ratio.

  Specifically, for example, a salt solution containing silver (silver salt solution) and a salt solution containing manganese (manganese salt solution) are prepared, and the salt solution is converted into a heat-resistant oxide. After impregnation, it may be fired. Preferably, a heat-resistant oxide is impregnated with a mixed solution of a silver salt solution and a manganese salt solution and then fired.

  Examples of the salt-containing solution include nitrate aqueous solution, chloride aqueous solution, hexaammine chloride aqueous solution, dinitrodiammine nitric acid aqueous solution, hexachloro acid hydrate, and practically, nitrate aqueous solution, dinitrodiammine nitric acid solution, Examples include aqueous chloride solutions. The silver salt solution is preferably an aqueous silver nitrate solution, and the manganese salt solution is preferably an aqueous manganese nitrate solution.

  After impregnating the heat-resistant oxide with the silver salt solution and the manganese salt solution, the firing temperature is, for example, 350 to 1000 ° C., preferably 400 to 800 ° C., and the firing time is, for example, 0 .5 to 5 hours, preferably 0.5 to 3 hours.

  If the firing temperature and firing time are within the above ranges, the purification performance of carbon monoxide (CO) and hydrocarbon (HC) can be improved.

  Further, as another method of supporting silver and manganese on a heat-resistant oxide, for example, when the heat-resistant oxide is a zirconia-based composite oxide or a ceria-based composite oxide, zirconium, cerium, and alkaline earth When coprecipitating or hydrolyzing a salt solution or mixed alkoxide solution containing a metal and / or rare earth element, a silver salt or manganese salt solution is added to each component of the zirconia-based complex oxide or ceria-based complex oxide. Moreover, silver and manganese are co-precipitated and then fired.

  Further, when the heat-resistant oxide is θ alumina, α alumina, or γ alumina, silver is precipitated when precipitated from an aqueous aluminum salt solution using ammonia or the like in the manufacturing process of the θ alumina, α alumina, or γ alumina. An example is a method in which a solution of salt and manganese salt is added to coprecipitate silver and manganese together with θ alumina, α alumina, or γ alumina, and then calcined.

  Further, silver and manganese may be supported at a time, or may be supported sequentially in a plurality of times.

  Thereby, silver and manganese can be carried on the heat-resistant oxide, and an exhaust gas purifying catalyst can be obtained as the heat-resistant oxide carrying silver and manganese.

  In addition to the above-described method, for example, a heat-resistant oxide supporting silver and a heat-resistant oxide supporting manganese are prepared and mixed to obtain an exhaust gas purification catalyst.

  More specifically, the heat-resistant oxide supporting silver is obtained by, for example, supporting silver on the above-mentioned heat-resistant oxide in accordance with the above-described method of supporting silver and manganese on the same heat-resistant oxide. Can be manufactured.

  In the heat-resistant oxide supporting silver, the silver content (supported amount) is, for example, 1.0% by mass or more, preferably 2.0% by mass or more with respect to the total amount of the heat-resistant oxide and silver. For example, it is 20% by mass or less, preferably 15% by mass or less.

  The heat-resistant oxide supporting manganese can be produced, for example, by supporting manganese on the above heat-resistant oxide in accordance with the above-described method of supporting silver and manganese on the same heat-resistant oxide. it can.

  In the heat-resistant oxide supporting manganese, the manganese content (supported amount) is, for example, 3.0% by mass or more, preferably 6.0% by mass or more with respect to the total amount of the heat-resistant oxide and manganese. For example, it is 20% by mass or less, preferably 15% by mass or less.

  Next, in this method, a heat-resistant oxide supporting silver and a heat-resistant oxide supporting manganese are mixed.

  The mixing method is not particularly limited, and examples thereof include known physical mixing methods such as dry mixing and wet mixing.

  The mixing ratio is appropriately adjusted so that the content ratio of silver and manganese in the mixture (exhaust gas purification catalyst) is within the above range.

  Thereby, silver and manganese can be carried on the heat-resistant oxide, and an exhaust gas purifying catalyst can be obtained as the heat-resistant oxide carrying silver and manganese.

  The exhaust gas purification catalyst is preferably an exhaust gas purification catalyst obtained by supporting silver and manganese on the same heat-resistant oxide.

  If the exhaust gas purifying catalyst is an exhaust gas purifying catalyst obtained by supporting it on the same heat-resistant oxide, the purification performance of hydrocarbons (HC) present in the exhaust gas can be improved.

  Further, in this method, if necessary, a heat-resistant oxide supporting silver and manganese is reduced under a reducing atmosphere (for example, a hydrogen-nitrogen mixed gas atmosphere) or an oxidizing atmosphere (for example, a model gas atmosphere used in the examples described later). Etc.) All or part of silver and manganese can be alloyed by heat treatment under the above.

  As heat treatment conditions, the heating temperature is, for example, 500 ° C. or higher, preferably 600 ° C. or higher, for example, 1000 ° C. or lower, preferably 900 ° C. or lower. The heating time is, for example, 0.5 hours or more, preferably 1.0 hours or more, for example, 10.0 hours or less, preferably 5.0 hours or less.

  As a result, silver and manganese can be alloyed on the heat-resistant oxide, and the exhaust gas can be used as a heat-resistant oxide carrying an alloy of silver and manganese (further, unalloyed silver and / or manganese). A purification catalyst can be obtained.

The specific surface area (BET specific surface area) of the exhaust gas-purifying catalyst before the heat treatment is, for example, 40 m ² / g or more, preferably 45 m ² / g or more, more preferably 50 m ² / g or more. 110 m ² / g or less.

The specific surface area (BET specific surface area) of the exhaust gas purifying catalyst after the heat treatment is, for example, 25 m ² / g or more, preferably 28 m ² / g or more, more preferably 30 m ² / g or more. 50 m ² / g or less.

  If the specific surface area of the exhaust gas purifying catalyst after the heat treatment is in the above range, the purification performance of carbon monoxide (CO) and hydrocarbon (HC) can be improved.

  Further, for example, a heat-resistant oxide carrying silver and manganese is used as an exhaust gas purifying catalyst without heat treatment in a reducing atmosphere or an oxidizing atmosphere as described above, and exhaust gas at a high temperature (for example, 500 to 1000 ° C.) Silver and manganese can also be alloyed by exposure to.

  Further, for example, an exhaust gas purification catalyst can be obtained by directly supporting a pre-manufactured alloy of silver and manganese on a heat-resistant oxide according to the above-described method.

  The exhaust gas purifying catalyst is not particularly limited, and may be used, for example, as the above powder, or may be used after being molded into an arbitrary predetermined shape by a known method, for example.

  The exhaust gas-purifying catalyst thus obtained can be used as it is, but it can also be prepared as a catalyst compound by a known method such as being supported on a catalyst carrier.

  The catalyst carrier is not particularly limited, and examples thereof include known catalyst carriers such as a honeycomb monolith carrier made of cordierite.

  For carrying on the catalyst carrier, for example, first, water is added to the obtained exhaust gas-purifying catalyst to form a slurry, which is then coated on the catalyst carrier, dried, and then about 300 to 800 ° C., preferably Is heat-treated at about 300-600 ° C.

  In such a case, the heat-resistant oxide supporting silver and manganese may be a known heat-resistant oxide such as alumina or composite oxide (for example, perovskite-type composite oxide, fluorite-type composite oxide). It can be used in combination with a heat-resistant oxide. In such a case, the heat-resistant oxide used in combination contains a noble metal (for example, platinum (Pt), rhodium (Rh), palladium (Pd)) as a support and / or composition as necessary. Can do.

  In the exhaust gas purifying catalyst thus obtained, silver and manganese and / or alloys thereof are supported on the heat-resistant oxide, and the mass ratio of the silver content to the manganese content ( Ag / Mn) is 0.16 or more.

  Therefore, excellent carbon monoxide (CO) and hydrocarbon (HC) purification performance can be achieved even when fired at a relatively low temperature.

  Accordingly, the exhaust gas purifying catalyst is used to purify exhaust gas discharged from, for example, an internal combustion engine such as a gasoline engine or a diesel engine, or a boiler. As a three-way catalyst).

  Specific numerical values such as blending ratio (content ratio), physical property values, and parameters used in the following description are described in the above-mentioned “Mode for Carrying Out the Invention”, and the corresponding blending ratio (content ratio) ), Physical property values, parameters, etc. The upper limit value (numerical value defined as “less than” or “less than”) or lower limit value (number defined as “greater than” or “exceeded”) may be substituted. it can.

Production Example 1
Cerium methoxypropylate [Ce (OCH (CH ₃ ) CH ₂ OCH ₃ ) ₃ ] is 0.1 mol in terms of Ce and zirconium methoxypropylate [Zr (OCH (CH ₃ ) CH ₂ OCH ₃ ) ₃ ] in terms of Zr 0.09 mol, yttrium methoxypropylate [Y (OCH (CH ₃ ) CH ₂ OCH ₃ ) ₃ ] in 0.01 mol in terms of Y and 200 mL of toluene were mixed and stirred to dissolve, A mixed alkoxide solution was prepared.

Further, 80 mL of deionized water was added dropwise to the mixed alkoxide solution for hydrolysis. From the hydrolyzed solution, toluene and deionized water were distilled off and evaporated to obtain a dry solid. The obtained solid was air-dried at 60 ° C. for 24 hours and then heat-treated (fired) at 450 ° C. for 3 hours in an electric furnace, whereby Ce _0.50 Zr _0.45 Y _0.05 O _2. The powder of the zirconia-type oxide (henceforth CZY) shown by this was obtained.

Example 1
Into 4.78 parts by mass of powder of lanthanum-containing θ-alumina (hereinafter abbreviated as La-Al) (lanthanum content: 4.0% by mass), an aqueous silver (I) nitrate solution (specifically, the silver content is 63.43 mass). 60.12 parts by weight of an aqueous solution prepared by dissolving 0.12 parts by weight of silver nitrate (I) salt in 60.000 parts by weight of water and an aqueous manganese (II) nitrate solution (specifically, a manganese content of 18.75). Impregnated with an aqueous solution mixed with 60.80 parts by mass of an aqueous solution prepared by dissolving 0.80 parts by mass of manganese nitrate (II) hexahydrate salt in 60.00 parts by mass of water at 110 ° C. After drying for one day and night, heat treatment (firing) is performed at 650 ° C. for 1 hour in the air in an electric furnace, whereby La—Al powder supporting silver and manganese simultaneously (hereinafter abbreviated as Ag and Mn supporting La—Al). Exhaust gas purification The catalyst was obtained 5.00 parts by weight.

The specific surface area of the exhaust gas purifying catalyst (measured according to the BET method, the same applies hereinafter) was 94 m ² / g. In the exhaust gas purifying catalyst, the supporting ratio of silver (converted to metal) is 1.5% by mass, the supporting ratio of manganese (converted to metal) is 3.0% by mass, and silver with respect to the manganese content The mass ratio (Ag / Mn) of the content of was 0.5.

Example 2
Exhaust gas purifying catalyst was prepared in the same manner as in Example 1 except that La-Al powder was changed to 4.78 parts by mass of CZY powder obtained in Production Example 1. The specific surface area of the exhaust gas purifying catalyst was 56 m ² / g. In the exhaust gas purifying catalyst, the supporting ratio of silver (converted to metal) is 1.5% by mass, the supporting ratio of manganese (converted to metal) is 3.0% by mass, and silver with respect to the manganese content The mass ratio (Ag / Mn) of the content of was 0.5.

Example 3
An exhaust gas purification catalyst was prepared in the same manner as in Example 1 except that the La—Al powder was changed to 4.78 parts by mass of cerium oxide (CeO ₂ ) powder. The specific surface area of the exhaust gas purifying catalyst was 32 m ² / g. In the exhaust gas purifying catalyst, the supporting ratio of silver (converted to metal) is 1.5% by mass, the supporting ratio of manganese (converted to metal) is 3.0% by mass, and silver with respect to the manganese content The mass ratio (Ag / Mn) of the content of was 0.5.

Example 4
An exhaust gas purification catalyst was prepared in the same manner as in Example 1 except that the La-Al powder was changed to 4.78 parts by mass of zirconium oxide (ZrO ₂ ) powder. The specific surface area of the exhaust gas-purifying catalyst was 71 m ² / g. In the exhaust gas purifying catalyst, the supporting ratio of silver (converted to metal) is 1.5% by mass, the supporting ratio of manganese (converted to metal) is 3.0% by mass, and silver with respect to the manganese content The mass ratio (Ag / Mn) of the content of was 0.5.

Example 5
An exhaust gas purification catalyst was prepared in the same manner as in Example 1 except that the La—Al powder was changed to 4.78 parts by mass of titanium oxide (TiO ₂ ) powder. The specific surface area of the exhaust gas purifying catalyst was 2 m ² / g. In the exhaust gas purifying catalyst, the supporting ratio of silver (converted to metal) is 1.5% by mass, the supporting ratio of manganese (converted to metal) is 3.0% by mass, and silver with respect to the manganese content The mass ratio (Ag / Mn) of the content of was 0.5.

Comparative Example 1
To a powder of 4.93 parts by mass of La-Al (lanthanum-containing θ-alumina, lanthanum content: 4.0% by mass), a silver nitrate (I) aqueous solution (specifically, silver nitrate (I) having a silver content of 63.44% by mass) An aqueous solution prepared by dissolving 0.12 parts by mass of salt in 60.00 parts by mass of water) impregnated with 60.12 parts by mass, dried at 110 ° C. for one day and night, and then in an electric furnace at 1 at 650 ° C. in the atmosphere. By performing heat treatment (calcination) for a period of time, 5.0 parts by mass of an exhaust gas purifying catalyst that was Ag-supported La-Al was obtained. The specific surface area of the exhaust gas purifying catalyst was 100.13 m ² / g. Further, in the exhaust gas purifying catalyst, the supporting ratio of silver (in metal conversion) was 1.5% by mass, and manganese was not supported.

Comparative Example 2
To 4.85 parts by mass of a powder of La-Al (lanthanum-containing θ-alumina, lanthanum content: 4.0% by mass), an aqueous manganese (II) nitrate solution (specifically, manganese nitrate having a manganese content of 18.76% by mass ( II) .Aqueous solution prepared by dissolving 0.80 parts by mass of hexahydrate salt in 60.00 parts by mass of water) impregnated with 60.80 parts by mass, dried at 110 ° C. for one day, and then in an electric furnace. By heat treatment (calcination) at 650 ° C. for 1 hour in the air, 5.0 parts by mass of an exhaust gas purifying catalyst that was Mn-supported La—Al was obtained. The specific surface area of the exhaust gas-purifying catalyst was 99.15 m ² / g. Further, in the exhaust gas purifying catalyst, the loading ratio of manganese (in metal conversion) was 3.0% by mass, and silver was not supported.

Comparative Example 3
Exhaust gas purifying catalyst was prepared in the same manner as in Comparative Example 1 except that La-Al powder was changed to 4.93 parts by mass of CZY powder obtained in Production Example 1. The specific surface area of the exhaust gas-purifying catalyst was 59 m ² / g. Further, in the exhaust gas purifying catalyst, the supporting ratio of silver (in metal conversion) was 1.5% by mass, and manganese was not supported.

Comparative Example 4
An exhaust gas purifying catalyst was prepared in the same manner as in Comparative Example 2 except that the La-Al powder was changed to 4.85 parts by mass of the CZY powder obtained in Production Example 1. The specific surface area of the exhaust gas purifying catalyst was 74 m ² / g. Further, in the exhaust gas purifying catalyst, the loading ratio of manganese (in metal conversion) was 3.0% by mass, and silver was not supported.

Example 6
An exhaust gas purifying catalyst was prepared in the same manner as in Example 2 except that an aqueous solution of silver nitrate (I) was prepared by dissolving 0.039 parts by mass of silver nitrate salt (I) in 60.00 parts by mass of water. The specific surface area of the exhaust gas-purifying catalyst was 68 m ² / g. Further, in the exhaust gas purifying catalyst, the supporting ratio of silver (metal conversion) is 0.5% by mass, the supporting ratio of manganese (metal conversion) is 3.0% by mass, and silver with respect to the manganese content The mass ratio of the content of (Ag / Mn) was 0.167.

Example 7
An exhaust gas purification catalyst was prepared in the same manner as in Example 2 except that an aqueous solution of silver nitrate (I) was prepared by dissolving 0.079 parts by mass of silver nitrate salt (I) in 60.00 parts by mass of water. The specific surface area of the exhaust gas-purifying catalyst was 67 m ² / g. In the exhaust gas purifying catalyst, the supporting ratio of silver (converted to metal) is 1.0% by mass, the supporting ratio of manganese (converted to metal) is 3.0% by weight, and silver with respect to the manganese content The mass ratio (Ag / Mn) of the content of was 0.33.

Example 8
An exhaust gas purifying catalyst was prepared in the same manner as in Example 2, except that an aqueous silver (I) nitrate solution was prepared by dissolving 0.24 parts by mass of silver nitrate (I) salt in 60.00 parts by mass of water. The specific surface area of the exhaust gas-purifying catalyst was 49 m ² / g. In the exhaust gas purifying catalyst, the supporting ratio of silver (metal conversion) is 3.0% by mass, the supporting ratio of manganese (metal conversion) is 3.0% by mass, and silver with respect to the manganese content. The mass ratio (Ag / Mn) of the content of was 1.0.

Example 9
An exhaust gas purifying catalyst was prepared in the same manner as in Example 2 except that an aqueous silver (I) nitrate solution was prepared by dissolving 0.47 parts by mass of silver (I) nitrate salt in 60.00 parts by mass of water. The specific surface area of the exhaust gas-purifying catalyst was 47 m ² / g. In the exhaust gas purifying catalyst, the supporting ratio of silver (converted to metal) is 6.0% by mass, the supporting ratio of manganese (converted to metal) is 3.0% by mass, and silver with respect to the manganese content. The mass ratio (Ag / Mn) of the content of was 2.0.

Example 10
An exhaust gas purification catalyst was prepared in the same manner as in Example 2 except that an aqueous solution of silver nitrate (I) was prepared by dissolving 0.95 parts by mass of silver nitrate (I) salt in 60.00 parts by mass of water. The specific surface area of the exhaust gas-purifying catalyst was 44 m ² / g. In the exhaust gas purifying catalyst, the supporting ratio of silver (metal conversion) is 12% by mass, the supporting ratio of manganese (metal conversion) is 3.0% by mass, and the silver content relative to the manganese content The mass ratio of the amount (Ag / Mn) was 4.0.

Example 11
To 4.85 parts by mass of the CZY powder obtained in Production Example 1, an aqueous solution of silver nitrate (I) (specifically, 0.24 parts by mass of silver nitrate (I) salt having a silver content of 64.44% by mass was added to 60.00 water). (Aqueous solution prepared by dissolving in mass parts) impregnated with 60.24 parts by mass, dried at 110 ° C for one day and night, and then heat-treated (fired) at 650 ° C for 1 hour in the air in an electric furnace. 5.00 parts by mass of supported CZY powder (hereinafter abbreviated as Ag-supported CZY) was obtained. In Ag-supported CZY, the support ratio of Ag (in metal conversion) was 3.0% by mass.

  Next, an aqueous manganese (II) nitrate solution (specifically, a manganese (II) nitrate hexahydrate salt having a manganese content of 18.76% by mass) was added to 4.70 parts by mass of the CZY powder obtained in Production Example 1. 1. An aqueous solution prepared by dissolving 1.60 parts by mass in 60.00 parts by mass of water) impregnated with 61.60 parts by mass, dried at 110 ° C. for one day and night, and then in an electric furnace at 650 ° C. for 1 hour in the atmosphere. By heat treatment (firing), 5.00 parts by mass of CZY powder supporting manganese (hereinafter abbreviated as Mn-supporting CZY) was obtained. In the Mn-supported CZY, the support ratio of manganese (in metal conversion) was 6.0% by mass.

  Then, an exhaust gas purification catalyst 10.00 which is a mixed powder of Ag-supported CZY and Mn-supported CZY by pulverizing and mixing Ag-supported CZY5.00 parts by weight and Mn-supported CZY5.00 parts by weight in a mortar for 10 minutes. A mass part was obtained.

The specific surface area of the exhaust gas-purifying catalyst was 67 m ² / g. In the exhaust gas purifying catalyst, the supporting ratio of Ag (metal conversion) is 1.5% by mass, the supporting ratio of manganese (metal conversion) is 3.0% by mass, and silver with respect to the manganese content The mass ratio (Ag / Mn) of the content of was 0.5.

<Evaluation>
1) Endurance treatment (Air 750 ° C, 5h)
The exhaust gas purifying catalysts obtained in each Example and each Comparative Example were subjected to high temperature durability treatment under the following conditions.

In this high-temperature endurance treatment, the exhaust gas purifying catalyst obtained in each example and each comparative example was subjected to an atmospheric condition of 10% water-containing air (O ₂ : 20%, H ₂ O: 10%, N ₂ : Balance). For 5 hours at 750 ° C. and cooled to room temperature.
2) Purification rate evaluation (T50)
The exhaust gas purifying catalysts of the respective examples and comparative examples after the durability treatment were molded into pellets having a size of 0.5 mm to 1.0 mm to prepare test pieces.

  As a model gas of exhaust gas discharged from the diesel engine, a gas having the composition shown in Table 1 below (air-fuel ratio A / F = 14.6) was used. Then, the model gas is supplied to each test piece while increasing the temperature of the exhaust gas discharged by the combustion of the model gas from room temperature to 750 ° C. at a rate of 30 ° C./min. The temperature at which carbon (CO) is purified by 50% (CO50% purification temperature (T50): ° C) and hydrocarbons (HC) (propylene and propane in the case of model gas in Table 1) are purified by 50%. Temperature (HC50 purification temperature (T50): ° C) was measured.

  The results are shown in FIGS.

  Specifically, the CO 50% purification temperature and the HC 50% purification temperature of Example 1, Comparative Example 1 and Comparative Example 2 are shown in FIG. In addition, FIG. 2 shows the CO 50% purification temperature and the HC 50% purification temperature of Example 2, Comparative Example 3 and Comparative Example 4. Further, FIG. 3 shows the CO 50% purification temperature and the HC 50% purification temperature of Examples 1 to 5.

  FIG. 4 shows the CO 50% purification temperature and the HC 50% purification temperature of Example 2, Examples 6 to 10 and Comparative Example 4. Further, the CO 50% purification temperature and the HC 50% purification temperature of Example 2 and Example 11 are shown in FIG.

In addition, the symbol of the support | carrier in FIGS. 1-3 is as follows. In addition, carriers (CZY, ZrO ₂ , La—Al, CeO ₂ , TiO ₂ ) for which the supported metal is not shown include silver (1.5% by mass) and manganese (3.0% by mass). It is supported.

CZY: Ceria-zirconia-yttrium composite oxide ZrO ₂ : Zirconium oxide (IV)
La-Al: lanthanum-containing alumina CeO _2: cerium (IV)
TiO ₂ : Titanium oxide (IV)
Cu / CZY: Copper-supported ceria-zirconia-yttrium composite oxide Mn / CZY: Manganese-supported ceria-zirconia-yttrium composite oxide Further, the exhaust gas purification catalysts (Example 2 and Example 11) used in FIG. The silver content is 1.5% by mass and the manganese content is 3.0% by mass.
3) Specific surface area The specific surface area (m ² / g) of the exhaust gas-purifying catalysts of Example 2 and Examples 6 to 10 before and after the durability treatment was measured according to the BET method. The result is shown in FIG.

<Discussion>
As shown in FIG. 1, in an exhaust gas purification catalyst whose carrier is lanthanum-containing alumina, Example 1 in which silver and manganese are supported relative to the exhaust gas purification catalyst of Comparative Example 1 in which only silver is supported. In the exhaust gas purification catalyst, the CO 50% purification temperature and the HC 50% purification temperature are lowered, and the CO purification performance and the HC purification performance are improved.

  Further, in the exhaust gas purification catalyst in which the carrier is lanthanum-containing alumina, the exhaust gas purification catalyst of Example 1 in which silver and manganese are supported relative to the exhaust gas purification catalyst in Comparative Example 2 in which only manganese is supported. Although the HC50% purification temperature is the same, the CO50% purification temperature is lowered, and the CO purification performance is improved.

  In addition, as shown in FIG. 2, even when the carrier is CZY, the exhaust gas purifying catalyst of Example 2 in which silver and manganese are supported is the exhaust gas purifying catalyst of Comparative Example 3 in which only silver is supported. Compared to the catalyst, the CO 50% purification temperature and the HC 50% purification temperature are reduced, the CO purification performance and the HC purification performance are improved, and the exhaust gas purification catalyst of Comparative Example 4 in which only manganese is supported is provided. On the other hand, the CO 50% purification temperature is lowered, and the CO purification performance is improved.

  From the above, regardless of the type of support, it is possible to improve CO purification performance and HC purification performance by supporting both metals for silver and manganese rather than supporting each metal alone. I understand.

Claims (1)

Silver and manganese and / or their alloys are supported on the heat-resistant oxide,
A catalyst for exhaust gas purification, wherein a mass ratio of silver content to manganese content (Ag / Mn) is 0.16 or more.

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