JP2021065837A - Catalyst for cleaning exhaust gas - Google Patents

Abstract

To provide a catalyst for cleaning an exhaust gas that can be used even in a severe heat environment and has catalytic activity and heat resistance further improved.SOLUTION: A catalyst for cleaning an exhaust gas contains a noble metal, an alkali metal, and mesoporous silica. The catalyst has one or more peaks in each range of pore size of 1 nm or more and 5 nm or less, and 10 nm or more and 50 nm or less in a pore size distribution curve of the catalyst for cleaning an exhaust gas obtained by analyzing an isothermal curve of the adsorption side of a nitrogen adsorption isothermal curve by a DH method. The catalyst has a ratio A/B of a content (A mol%) of the alkali metal to a content (B mol%) of the mesoporous silica in the range of 1.0×10-4 or more and 5.0×10-3 or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to an exhaust gas purification catalyst.

Exhaust gas emitted from gasoline engines such as motorcycles and motorcycles (also called saddle-type vehicles) and internal combustion engines such as diesel engines contains hydrocarbons (HC) from unburned fuel and one due to incomplete combustion. It contains harmful components such as carbon oxide (CO) and nitrogen oxides (NOx) due to excessive combustion temperature. In order to treat the exhaust gas from such an internal combustion engine, an exhaust gas purification catalyst is used. For example, hydrocarbons (HC) in the exhaust gas are oxidized and converted into water and carbon dioxide for purification. Carbon monoxide (CO) is oxidized and converted to carbon dioxide for purification. In addition, nitrogen oxides (NOx) are reduced and converted to nitrogen for purification. The exhaust gas purification catalyst is used in a state where, for example, a noble metal such as platinum, palladium, or rhodium having a catalytic function is supported on a carrier. Since the catalyst reacts on the surface of the carrier, the catalyst activity increases as the catalyst is supported on a carrier having a large specific surface area.

For example, Patent Document 1 discloses a catalyst carrier obtained by crystallizing the pore surface of mesoporous silica having ^{a pore diameter of 2 to 20 nm and a specific surface area of 400 to 1400 m 2 / g.}

JP-A-2007-69095

However, mesoporous silica has low thermal stability, pores tend to disappear in a high temperature range, and the temperature range in which high catalytic activity can be maintained is narrow. Purification of hydrocarbons (HC) in exhaust gas with a catalyst is strongly affected by the exhaust gas temperature, and generally requires a high temperature of 300 ° C or higher. Depending on the running condition of the vehicle, the temperature may reach 800 ° C or higher. There is also. Therefore, a carrier that supports a noble metal having a catalytic function is also required to have improved heat resistance.

Therefore, an object of the present invention is to provide an exhaust gas purification catalyst that can be used even in a harsh thermal environment and has improved catalytic activity and heat resistance.

The present invention
With precious metals
Alkali metal and
An exhaust gas purification catalyst containing mesoporous silica.
In the pore diameter distribution curve of the exhaust gas purification catalyst obtained by analyzing the isotherm on the adsorption side of the nitrogen adsorption isotherm by the DH method, the pore diameter is 1 nm or more and 5 nm or less and 10 nm or more and 50 nm or less, respectively. Has one or more peaks
The ratio A / B of the alkali metal content (Amol%) to the mesoporous silica content (Bmol%) is in the range of ^{1.0 × 10 -4} or more and 5.0 × 10 ^{-3 or less.} It is a catalyst for purifying exhaust gas.

The exhaust gas purification catalyst proposed by the present invention can provide an exhaust gas purification catalyst that maintains a pore structure even in a harsh thermal environment and has further improved heat resistance.

The pore size distribution curve obtained by analyzing the isotherm on the adsorption side of the nitrogen adsorption isotherm of the exhaust gas purification catalyst of Example 2 and Comparative Examples 1 and 2 by the DH method is shown.

Next, the present invention will be described based on examples of embodiments. However, the present invention is not limited to the embodiments described below.

An example of the embodiment of the present invention is an exhaust gas purification catalyst containing a noble metal, an alkali metal, and mesoporous silica, and the isotherm on the adsorption side of the nitrogen adsorption isotherm is DH (Dollimore-Heal: DH). In the pore diameter distribution curve of the exhaust gas purification catalyst obtained by analysis by the method, the pore diameter has one or more peaks in the range of 1 nm or more and 5 nm or less and the range of 10 nm or more and 50 nm or less, respectively, and the mesoporous silica has one or more peaks. For exhaust gas purification, the ratio A / B of the alkali metal content (Amol%) to the content (Bmol%) is in ^{the range of 1.0 × 10 -4} or more and 5.0 × 10 ^{-3 or less.} It is a catalyst.

Precious metals Precious metals are at least selected from the group consisting of gold (Au), silver (Ag), platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru) and osmium (Os). It is one kind. Among the noble metals, at least one selected from the platinum group consisting of Rh, Pd, Pt, Ir, Ru, and Os may be used. The noble metal is preferably at least one selected from the group consisting of Pt, Pd and Rh in order to further promote the catalytic purification of hydrocarbons (HC) in the exhaust gas even at high temperatures.

The mesoporous silica exhaust gas purification catalyst is also referred to as a pore size distribution curve (hereinafter, also referred to as “pore size distribution curve”) of the exhaust gas purification catalyst obtained by analyzing the isotherm on the adsorption side of the nitrogen adsorption isotherm by the DH method. ) Includes mesoporous silica (also referred to as "BMS") having binary pores having one peak in the range of 1 nm or more and 5 nm or less and one peak in the range of 10 nm or more and 50 nm or less. In the exhaust gas purification catalyst, BMS is a carrier that supports the catalyst and the alkali metal. In the pore size distribution curve, BMS has a peak in the range of 1 nm or more and 5 nm or less, a first pore having a pore diameter in the range of 1 nm or more and 5 nm or less, and a peak in the range of 10 nm or more and 50 nm or less. It has a second pore with a pore diameter in the range of 10 nm or more and 50 nm or less. It is presumed that the first pores having a pore size in the range of 1 nm or more and 5 nm or less are pores derived from the structure defining agent formed in the individual particles of mesoporous silica. Further, unlike ordinary mesoporous silica (hereinafter, also referred to as “MS”), BMS has a second pore having a pore diameter in the range of 10 nm or more and 50 nm or less. The second pore diameter having a pore diameter in the range of 10 nm or more and 50 nm or less is presumed to be pores derived from the particle gaps of mesoporous silica. In BMS, the specific surface area is expanded by the first pores derived from the structure-defining agent to enhance the catalytic activity, and the second pores having a relatively large pore size derived from the particle gaps are the exhaust gas in the particle gaps. Diffusibility can be improved and catalytic activity can be enhanced. In addition, since the second pores can be maintained even at a high temperature of, for example, 800 ° C. or higher, the heat resistance of BMS can be enhanced, which can contribute to the improvement of catalytic activity, and also the effect of suppressing aggregation and burial of the supported precious metal. It is presumed that there is.

Alkali metal The alkali metal is preferably at least one selected from the group consisting of Li, Na, K and Rb, and more preferably at least one selected from the group consisting of Li, Na and K.

In the exhaust gas purification catalyst, the ratio A / B of the alkali metal content (Amol%) to the mesoporous silica content (Bmol%) is 1.0 × 10 ^-4 or more and 5.0 × 10 ^-3 or less. It is within the range. The ratio A / B of the exhaust gas purification catalyst is preferably in ^{the range of 2.0 × 10 -4} or more and 4.5 × 10 ^-3 or less, and more preferably 3.0 × 10 ^-4 or more. It is within the range of 0 × 10 ^{-3 or less.} The exhaust gas purification catalyst contains an alkali metal whose ratio A / B is within the above range, so that the catalytic activity is improved. When an alkali metal is contained in the exhaust gas purification catalyst, the specific surface area of BMS tends to decrease, as will be described later, when the catalyst is placed at a high temperature of, for example, 800 ° C. or higher. However, if the catalyst for purifying exhaust gas contains an alkali metal, the electron density of oxygen atoms on the BMS increases, and the increase in electron density makes it easier to bond with a noble metal that becomes a cation, so that the catalyst becomes hot. The precious metal can remain dispersed even when exposed. Therefore, when the exhaust gas purification catalyst contains a noble metal, an alkali metal, and BMS _{, the contact frequency between the highly dispersed noble metal and the hydrocarbon (for example, C 3} H ₆ ) which is a reaction substrate increases, and the catalyst It is presumed that the activity can be improved. If the ratio A / B of the alkali metal in the exhaust gas purification catalyst is ^{less than 1.0 × 10 -4} , the amount of the alkali metal is too small, and it is difficult to improve the dispersion of the noble metal and the catalytic activity. When the ratio A / B of the alkali metal in the exhaust gas purification catalyst ^{exceeds 5.0 × 10 -3} , the Si—O—Si network constituting the mesoporous silica is easily cut, and 800. At high temperatures of ° C. or higher, the pores of mesoporous silica are condensed and recombined, the pores are easily broken, the specific surface area is reduced, and the catalytic activity is reduced.

In the exhaust gas purification catalyst, the ratio A / P of the alkali metal content (Amol%) to the noble metal content (Pmol%) is preferably in the range of 0.03 or more and 2.00 or less, more preferably. Is in the range of 0.05 or more and 1.80 or less, and more preferably in the range of 0.10 or more and 1.50 or less. In the exhaust gas purification catalyst, if the ratio A / P of the content of the alkali metal to the content of the noble metal is within the range of 0.03 or more and 2.00 or less, a sufficient amount of oxygen on the BMS with respect to the noble metal Since the effect of increasing the electron density of the atom can be obtained, it is presumed that the noble metal can maintain a highly dispersed state even after being exposed to a high temperature of, for example, 800 ° C. or higher, and the catalytic activity can be improved.

The exhaust gas purification catalyst has one or more peaks in the pore diameter distribution curve of 1 nm or more and 5 nm or less and 10 nm or more and 50 nm or less, respectively.
In the pore diameter distribution curve of the exhaust gas purification catalyst, the peak having a pore diameter in the range of 1 nm or more and 5 nm or less is derived from the first pore in the pore diameter range of 1 nm or more and 5 nm or less of mesoporous silica.
In the pore diameter distribution curve of the exhaust gas purification catalyst, the peak having a pore diameter in the range of 10 nm or more and 50 nm or less is derived from the second pore in the pore diameter range of 10 nm or more and 50 nm or less of mesoporous silica.
The exhaust gas purification catalyst has one or more peaks in the pore size distribution curve in the range of 1 nm or more and 5 nm or less and the range of 10 nm or more and 50 nm or less before the heat resistance test. In the present specification, the heat resistance test means to heat-treat an exhaust gas purification catalyst containing a noble metal, an alkali metal, and mesoporous silica in a range of 800 ° C. or higher and 1000 ° C. or lower for 1 hour or more and 10 hours or less.

The exhaust gas purification catalyst has an integrated pore volume V1 (mL / g) in the range of 1 nm or more and 5 nm or less with respect to the total integrated pore volume Va (mL / g) in the range of 1 nm or more and 100 nm or less in the pore diameter distribution curve. The pore volume ratio V1 / Va is preferably in the range of 0.300 or more and 0.600 or less, more preferably in the range of 0.400 or more and 0.580 or less, and further preferably 0.420 or more. It is in the range of 0.550 or less. In the present specification, the pore volume ratio V1 / Va is obtained from the pore diameter distribution curve of the exhaust gas purification catalyst before the heat resistance test. In the pore size distribution curve of the exhaust gas purification catalyst before the heat resistance test, if the pore volume ratio V1 / Va is in the range of 0.300 or more and 0.600 or less, the range of 1 nm or more and 5 nm or less formed in the particles. The first pores derived from the structural defining agent of No. 1 are sufficiently present, and the specific surface area can be increased to improve the catalytic activity. Here, the total integrated pore volume Va (mL / g) is obtained by integrating the range of 1 nm or more and 100 nm or less of the pore diameter distribution curve obtained by analyzing the isotherm on the adsorption side of the nitrogen adsorption isotherm by the DH method. The value obtained by The integrated pore volume V1 (mL / g) refers to a value obtained by integrating the range of 1 nm or more and 5 nm or less of the pore diameter distribution curve.

The exhaust gas purification catalyst has an integrated pore volume V2 (mL / g) in the range of 10 nm or more and 50 nm or less with respect to the total integrated pore volume Va (mL / g) in the range of 1 nm or more and 100 nm or less in the pore diameter distribution curve. The pore volume ratio V2 / Va is preferably in the range of 0.300 or more and 0.600 or less, more preferably in the range of 0.400 or more and 0.550 or less, and further preferably 0.450 or more. It is within the range of 0.520 or less. In the present specification, the pore volume ratio V2 / Va is obtained from the pore diameter distribution curve of the exhaust gas purification catalyst before the heat resistance test. In the pore size distribution curve of the exhaust gas purification catalyst before the heat resistance test, if the pore volume ratio V2 / Va is within the range of 0.300 or more and 0.600 or less, the gap between particles in the range of 10 nm or more and 50 nm or less. The second pores derived from the above are sufficiently present, and the aggregation of the noble metal can be suppressed, the heat resistance can be enhanced, and the diffusivity of the exhaust gas in the particle gap can be improved. Here, the integrated pore volume V2 (mL / g) is obtained by integrating the range of 10 nm or more and 50 nm or less of the pore diameter distribution curve obtained by analyzing the isotherm on the adsorption side of the nitrogen adsorption isotherm by the DH method. The obtained value.

The exhaust gas purification catalyst has an integrated pore volume V1 (mL / g) in the range of 1 nm or more and 100 nm or less, preferably in the range of 0.300 or more and 0.600 or less in the pore diameter distribution curve of the exhaust gas purification catalyst. Of the above, more preferably in the range of 0.320 or more and 0.580 or less, further preferably in the range of 0.350 or more and 0.550 or less, and particularly preferably in the range of 0.380 or more and 0.540 or less. It is within the range. In the exhaust gas purification catalyst, the specific surface area increases when the integrated pore volume V1 (mL / g) in the range of 1 nm or more and 10 nm or less in the pore diameter distribution curve of the exhaust gas purification catalyst is within the above range. , The catalytic activity can be improved.

The exhaust gas purification catalyst has an integrated pore volume V2 (mL / g) in the range of 10 nm or more and 50 nm or less, preferably in the range of 0.400 or more and 0.600 or less in the pore diameter distribution curve of the exhaust gas purification catalyst. It is more preferably in the range of 0.42 or more and 0.580 or less, and further preferably in the range of 0.450 or more and 0.570 or less. In the exhaust gas purification catalyst, if the integrated pore volume V2 (mL / g) in the range of 10 nm or more and 50 m or less is within the above range in the pore diameter distribution curve of the exhaust gas purification catalyst, the gap between the particles is formed. The second pores from which the gas is derived are sufficiently present, and the aggregation of the noble metal can be suppressed, the heat resistance can be enhanced, and the diffusivity of the exhaust gas in the particle gap can be improved.

Method for producing exhaust gas purification catalyst Next, an example of a method for producing an exhaust gas purification catalyst composition will be described. The method for producing the exhaust gas purification catalyst composition is not limited to the examples described below.

A method for producing a catalyst for purifying exhaust gas is a mesoporous silica having binary pores having one or more peaks in a pore diameter range of 1 nm or more and 5 nm or less and a pore diameter of 10 nm or more and 50 nm or less in a pore diameter distribution curve. The step of preparing BMS), the step of bringing the BMS into contact with the precious metal or the compound containing the noble metal, and the compound containing the alkali metal or the alkali metal to attach the noble metal and the alkali metal to the BMS, and the noble metal and This includes a step of heat-treating the BMS to which the alkali metal is attached to obtain a catalyst for purifying exhaust gas containing the noble metal, the alkali metal, and the BMS.

Step of Preparing Mesoporous Silica (BMS) Next, as a step of preparing mesoporous silica, an example of a method for producing mesoporous silica will be described. The method for producing mesoporous silica is not limited to the examples described below. Mesoporous silica can generally be formed by the sol-gel method. First, as a structure-determining agent, a surfactant having a concentration equal to or higher than the critical micelle concentration is dissolved in water to form rod-shaped micelle particles, and when the particles are allowed to stand for a while, they become colloidal particles. Here, when a silica source is added to the solution and a predetermined acid or base is added as a catalyst so as to have a predetermined pH, the sol-gel reaction proceeds in the gaps between the colloidal particles to form a gel having a silica gel skeleton. After that, mesoporous silica can be produced by heat-treating the gel at a temperature of 500 ° C. or higher. Examples of the surfactant include cetyltrimethylammonium chloride (CH ₃ (CH ₂ ) ₁₅ N (CH ₃ ) ₃ Cl: CTAC). Examples of the silica source include tetraethoxysilane (Si (OC ₂ H ₅ ) ₄ : TEOS). The obtained mesoporous silica has pores in which the positions where the rod-shaped micelle particles were present are voids. By adjusting the pH value when forming the mesoporous silica, the degree of aggregation of the mesoporous silica is changed, and the first pores derived from the structure-defining agent and the second pores derived from the particle gaps are formed. , Mesoporous silica (BMS) having binary pores can be formed. BMS is preferably adjusted by adding a basic compound so that the pH of the solution containing, for example, a surfactant and tetraethoxysilane is 9 to 10.5. In the method for producing BMS, after obtaining a gel, it may be dried at a temperature of, for example, 50 ° C. or higher to obtain a mesoporous silica precursor, and the mesoporous silica precursor may be heat-treated to obtain BMS. In the present specification, the heat treatment performed on the gel or mesoporous silica precursor may be referred to as the first heat treatment. The temperature at which the obtained gel or mesoporous silica precursor is first heat-treated is preferably 500 ° C. or higher, and may be in the range of 550 ° C. or higher and 800 ° C. or lower, or 700 ° C. or lower. Good. The atmosphere in which the first heat treatment is performed may be an atmospheric atmosphere or an atmosphere of an inert gas such as nitrogen. The atmospheric pressure at which the first heat treatment is performed may be under atmospheric pressure.

Step of Adhering Noble Metal and Alkali Metal As a method of contacting and adhering a compound containing a noble metal or a noble metal and a compound containing an alkali metal or an alkali metal to mesoporous silica, an impregnation method, a precipitation method, an ion exchange method, etc. Can be mentioned. Examples of the impregnation method include an impingient wetness method, an evaporative drying method, a pore-filling method, a spray method, an equilibrium adsorption method, and the like. Examples of the precipitation method include a kneading method and a deposition method.

When the noble metal and the alkali metal are attached to the mesoporous silica by the impregnation method, a method of immersing the mesoporous silica in a mixed solution containing the noble metal and the alkali metal and impregnating the mesoporous silica can be mentioned. The mesoporous silica is immersed in a solution containing a noble metal or a solution containing a compound containing a noble metal, the noble metal is attached to the mesoporous silica, and then the mesoporous silica to which the noble metal is attached is dried. Next, the mesoporous silica to which the noble metal is attached is immersed in a solution containing an alkali metal, and the mesoporous silica to which the noble metal and the alkali metal are attached is dried to obtain the mesoporous silica to which the noble metal and the alkali metal are attached. .. The time for immersing the mesoporous silica in the solution containing the noble metal or alkali metal can be 0.5 hours or more and 5 hours or less, preferably 1 hour or more and 4 hours or less. After the immersion, the mesoporous silica to which the noble metal is attached or the mesoporous silica to which the noble metal and the alkali metal are attached may be dried. The drying temperature can be 50 ° C. or higher and 100 ° C. or lower, and 50 ° C. or higher and 80 ° C. or higher. It may be below ° C. The drying time can be 0.5 hours or more and 5 hours or less, and may be 1 hour or more and 4 hours or less. The pressure at the time of drying is not particularly limited, and may be atmospheric pressure (0.1 MPa) or under reduced pressure of 0.1 MPa or less.

The ratio A / B of the alkali metal content (Amol%) to the mesoporous silica content (Bmol%) in the obtained exhaust gas purification catalyst is 1.0 × 10 ^-4 or more. It is preferable to adhere to mesoporous silica so as to have a range of 5.0 × 10 ^{-3 or less.} It is more preferable that the alkali metal is attached to the obtained exhaust gas purification catalyst so that the ratio A / B is in ^{the range of 2.0 × 10 -4} or more and 4.5 × 10 ^{-3 or less.} It is more preferable to attach the mixture so as to have a range of 0.0 × 10 ^-4 or more and 4.0 × 10 ^{-3 or less.} By adhering the alkali metal so that the ratio A / B is within the above range, the catalytic activity can be improved and the heat resistance can be improved.

The alkali metal has a ratio A / P of the alkali metal content (Amol%) of 0.03 or more and 2.00 or less with respect to the noble metal content (Pmol%) in the obtained exhaust gas purification catalyst. It is preferable to attach it so as to be within the range. It is more preferable that the alkali metal is attached to the obtained exhaust gas purification catalyst so that the ratio A / P is in the range of 0.10 or more and 1.50 or less. By adhering the alkali metal so that the ratio A / P is within the above range, the dispersibility of the noble metal can be improved and the catalytic activity can be improved.

Heat treatment step For example, a noble metal and an alkali metal are attached to mesoporous silica by an impregnation method, and then heat treatment is performed to obtain an exhaust gas purification catalyst containing the noble metal, the alkali metal, and the mesoporous silica. In the present specification, the heat treatment performed on the mesoporous silica to which the noble metal and the alkali metal are attached may be referred to as a second heat treatment. The second heat treatment temperature is preferably in the range of 200 ° C. or higher and 800 ° C. or lower, more preferably 400 ° C. or higher and 700, in order to maintain the silica gel skeleton of mesoporous silica, support the noble metal, and attach the alkali metal. It is within the range of ° C or lower. The atmosphere in which the second heat treatment is performed may be an atmospheric atmosphere or an inert gas atmosphere such as nitrogen. The atmospheric pressure at which the second heat treatment is performed may be under atmospheric pressure.

The exhaust gas purification catalyst containing the noble metal, alkali metal and mesoporous silica obtained as described above is an exhaust gas purification catalyst obtained by analyzing the isotherm on the adsorption side of the nitrogen adsorption isotherm by the DH method. In the pore size distribution curve, the pore size has one or more peaks in the range of 1 nm or more and 5 nm or less and the range of 10 nm or more and 50 nm or less, respectively, and the content of alkali metal (Amol) with respect to the content of mesoporous silica (Bmol%). %) Ratio A / B is in the range of ^{1.0 × 10 -4} or more and 5.0 × 10 ^{-3 or less.}

The exhaust gas purification catalyst obtained as described above exhibits catalytic activity even when exposed to a high temperature in a temperature range of 800 ° C. or higher and 1100 ° C. or lower, for example, a temperature range of 800 ° C. or higher and 1000 ° C. or lower. It maintains and exhibits stable and high purification performance of hydrocarbons (HC). Such an exhaust gas purification catalyst can exhibit stable and high exhaust gas purification performance as an exhaust gas purification catalyst for an internal combustion engine powered by fossil fuels such as a gasoline engine and a diesel engine. In particular, the exhaust gas purification catalyst of the present embodiment can be suitably used for purifying exhaust gas discharged from an internal combustion engine such as a motorcycle or a motorcycle because of its high heat resistance. The exhaust gas purification composition of the present embodiment is effectively used for purifying hydrocarbons (HC) in the exhaust gas.

Hereinafter, the present invention will be described in more detail based on Examples and Comparative Examples. The present invention is not limited to these examples.

Production of Mesoporous Silica (BMS) Mesoporous silica (BMS) having binary pores was produced by the sol-gel method. _{Cetyltrimethylammonium chloride (CH 3} (CH ₂ ) ₁₅ N (CH ₃ ) ₃ Cl: CTAC) is used as the raw material surfactant, and _{tetraethoxysilane (Si (OC 2} H ₅ ) ₄ : TEOS) is used as the silica source. ) Was used. Weighed so that the molar ratio of CTAC: TEOS: water (H ₂ O) was 0.19: 1.0: 75. Specifically, 3.88 g of CTAC was added to 80 mL of distilled water and stirred with a stirrer to completely dissolve CTAC. 14 mL of TEOS was added to this solution, and the mixture was stirred with a stirrer for 1 hour. _{A 2 mol / L aqueous ammonia (NH 3} ) solution was added to the solution containing CTAC and TEOS at once with continuous stirring so that the pH became 10. After confirming the gelation of the solution, stirring was stopped, the solution was allowed to stand at room temperature (20 ° C. to 25 ° C.) for 5 hours, and the solution was filtered. The obtained gel was washed with distilled water, and then the gel was dried at 60 ° C. for 12 hours to obtain a mesoporous silica precursor. This mesoporous silica precursor was first heat-treated in an electric furnace at 550 ° C. for 3 hours in the air to obtain mesoporous silica. The obtained mesoporous silica has a pore diameter in the range of 1 nm or more and 5 nm or less in the pore size distribution curve of the mesoporous silica obtained by analyzing the adsorption side isotherm of the nitrogen adsorption isotherm measured by the method described later by the DH method. It was confirmed that the mesoporous silica (BMS) had one or more peaks in the range of 10 nm or more and 50 nm or less and had binary pores.

Examples 1 to 3
Using the produced BMS as a carrier, platinum (Pt) was supported by an impregnation method so that the amount of platinum (Pt) supported was 1% by mass. Specifically, BMS is immersed in an aqueous solution of diaminedinitroplatinum (II) (Pt (NH ₃ ) ₂ (NO ₂ ) ₂ ), platinum is attached to BMS so as to be 1% by mass, and platinum is removed from the aqueous solution. The attached BMS was taken out and dried at 60 ° C. for 3 hours. After drying, BMS to which platinum is attached is immersed in an aqueous solution of potassium nitrate (KNO ₃ ) so that the amount of potassium (% by mass) shown in Table 1 of each example is obtained, and platinum and potassium are attached to BMS. , BMS to which platinum and potassium were attached was taken out from the aqueous solution and dried at 60 ° C. for 3 hours. After drying, a second heat treatment was performed in an electric furnace at 600 ° C. for 3 hours in the air to obtain an exhaust gas purification catalyst containing platinum (Pt), potassium (K), and BMS.

Comparative Example 1
An exhaust gas purification catalyst containing no potassium was obtained in the same manner as in Example 1 except that the BMS to which platinum was attached was _{not immersed in a potassium nitrate (KNO 3) solution.}

Comparative Example 2: Production of catalyst for purifying exhaust gas As shown in Table 1, for purifying exhaust gas in the same manner as in Examples 1 to 3 except that potassium was attached so as to be 0.500% by mass. Obtained a catalyst.

Ratio A / B and ratio A / P
For each of the exhaust gas purification catalysts of Examples and Comparative Examples, the amount of the raw material noble metal (Pt) (Pmol%), the amount of the alkali metal (K) (Amol%), and the amount of mesoporous silica (BMS) (Bmol%). Therefore, the ratio A / B of the alkali metal content (Amol%) to the mesoporous silica content (Bmol%) and the ratio A / B of the alkali metal content (Amol%) to the noble metal content (Pmol%). I asked for P.

Measurement of Nitrogen Adsorption Isotherm The nitrogen adsorption isotherm was measured for each exhaust gas purification catalyst before the heat resistance test of Examples and Comparative Examples. A high-precision gas adsorption device (product name: BELSORP mini, manufactured by Microtrack Bell Co., Ltd.) was used for the measurement. The measurement conditions are as follows. The sample was measured after being heated at 10 Pa and 300 ° C. for 2 hours as a pretreatment. It was confirmed whether or not each of the nitrogen adsorption isotherms had one peak in the range of 1 nm or more and 5 nm or less and the range of 10 nm or more and 50 nm or less. Further, the pore diameter of the peak top existing in the range of 1 nm or more and 5 nm or less was defined as the representative pore diameter D1, and the pore diameter of the peak top existing in the range of 10 nm or more and 50 nm or less was defined as the representative pore diameter D2. Further, in the pore diameter distribution curve obtained by analyzing the isotherm on the adsorption side of the nitrogen adsorption isotherm by the DH method, the total integrated pore volume Va (mL / g) obtained by integrating the range of 1 nm or more and 100 nm. Measure the integrated pore volume V1 (mL / g) obtained by integrating the range of 1 nm or more and 5 nm or less, and the integrated pore volume V2 (mL / g) obtained by integrating the range of 10 nm or more and 50 nm or less. did.
Measurement method: Constant-capacity gas adsorption method Adsorption gas: Pretreatment condition of nitrogen device: 300 ° C for 2 hours at pressure 10 Pa or less Vacuum exhaust analysis program: Adsorption / desorption isothermal measurement
: Measurement of pore size distribution curve by DH method Measurement relative pressure range: P / P0 = 0.13 to 0.99
Measured amount: 0.05 g

Heat resistance test Each exhaust gas purification catalyst of Examples and Comparative Examples was heat-treated in the air at 800 ° C. for 3 hours to perform a heat resistance test.

Evaluation of catalytic activity The catalytic activity of each exhaust gas purification catalyst after the heat resistance test of Examples and Comparative Examples was measured as follows. In the measurement test of the catalyst activity, 0.1 g of a catalyst sample having a particle size of 355 μm to 600 μm was filled in a quartz glass reaction tube and fixed with quartz wool using a pressure-fixed bed flow reactor. As a pretreatment, a helium (He) gas containing 1.5% by volume of oxygen (O ₂ ) was circulated through the reaction tube, the temperature was raised to 600 ° C. at 10 ° C./min, and the temperature was maintained at 600 ° C. for 10 minutes. Next, _{a test gas having C 3} H ₆ at 1500 ppm, O ₂ at 9000 ppm, and the balance of He was circulated at a total flow rate of 500 cm ³ / min, and the catalytic performance at each temperature from 100 ° C. to 600 ° C. was evaluated. _{From the time when the introduction of the test gas into the reaction tube was started, the measurement of the CO 2} concentration in the exhaust gas after the test gas came into contact with the exhaust gas purification catalyst (after passing through the catalyst) was started, and all the CO 2 concentration in the test gas was started. The time (T50) required for the amount of _{C 3} H ₆ to be halved when converted to CO ₂ and H _{2 O was measured.} When T50 is less than 220 ° C, it is excellent (Excellent: E), when it is 220 ° C or more and less than 250 ° C, it is good (Good: G), when it is 250 ° C or more and less than 260 ° C, it is possible (Average: A), and when it is 260 ° C or more, it is not possible (Power: It was evaluated as P). _{For the analysis of C 3} H ₆ , CO and CO _{2 in} the gas emitted after the reaction, a gas chromatograph (product number GC-14B (FID detector), manufactured by Shimadzu Corporation) and a methane reduction device (product number: MTN-1) , Shimadzu Corporation) was used.
Measurement conditions for gas chromatograph Column type: Column 1: Activated carbon
Column 2: Unibeds 1S
Carrier gas:
He: Column 1 75 kPa
Column 2 120 kPa
H2: Column 1 80 kPa
Column 2 70 kPa
Air: Column 1 55 kPa
Column 2 47.5 kPa
Injection port temperature: 200 ° C
Detector temperature: 250 ° C
Column temperature: 100 ° C

As shown in Table 1, all of the exhaust gas purification catalysts after the heat resistance test of Examples 1 to 3 have a T50 of 250 ° C. or lower and maintain the pore structure even in a harsh thermal environment of 800 ° C. or higher. It was confirmed that the heat resistance was improved.

The exhaust gas purification catalyst of Comparative Example 1 has a larger integrated pore volume diameter V1 and integrated pore volume diameter V2 before the heat resistance test than the exhaust gas purification catalyst before the heat resistance test of Examples 1 to 3. However, since it does not contain an alkali metal, T50 after the heat resistance test is not possible, and the catalytic activity is lowered.

The exhaust gas purification catalyst of Comparative Example 2 is smaller than the exhaust gas purification catalysts of Examples 1 to 3 before the heat resistance test in both the integrated pore volume diameter V1 and the integrated pore volume diameter V2 before the heat resistance test, and is alkaline. Since it contains a large amount of metal, T50 after the heat resistance test is not possible, the pores of the mesoporous silica are broken, and the catalytic activity is lowered.

As shown in FIG. 1, the exhaust gas purification catalysts of Example 2 and Comparative Examples 1 and 2 are all exhaust gas purification catalysts obtained by analyzing the isotherm on the adsorption side of the nitrogen adsorption isotherm by the DH method. In the pore size distribution curve of No. 1, the pore size had one peak in the range of 1 nm or more and 5 nm or less and the range of 10 nm or more and 50 nm or less.

The exhaust gas purification catalyst according to the present disclosure can maintain the pore structure, improve the catalytic activity, and further improve the heat resistance even when placed in a harsh thermal environment. Therefore, the exhaust gas purification catalyst according to the present disclosure can be suitably used for purifying the exhaust gas discharged from an internal combustion engine such as a motorcycle or a motorcycle.

Claims (4)

With precious metals
Alkali metal and
An exhaust gas purification catalyst containing mesoporous silica.
In the pore diameter distribution curve of the exhaust gas purification catalyst obtained by analyzing the isotherm on the adsorption side of the nitrogen adsorption isotherm by the DH method, the pore diameter is 1 nm or more and 5 nm or less and 10 nm or more and 50 nm or less, respectively. Has one or more peaks
The ratio A / B of the alkali metal content (Amol%) to the mesoporous silica content (Bmol%) is in the range of ^{1.0 × 10 -4} or more and 5.0 × 10 ^{-3 or less.} Exhaust gas purification catalyst. The exhaust gas purification according to claim 1, wherein the ratio A / P of the alkali metal content (Amol%) to the noble metal content (Pmol%) is in the range of 0.03 or more and 2.00 or less. For catalyst. In the pore size distribution curve, the pore volume ratio V1 of the integrated pore volume V1 (mL / g) in the range of 1 nm or more and 5 nm or less with respect to the total integrated pore volume Va (mL / g) in the range of 1 nm or more and 100 nm or less. The exhaust gas purification catalyst according to claim 1 or 2, wherein / Va is in the range of 0.300 or more and 0.600 or less. In the pore size distribution curve, the pore volume ratio V2 of the integrated pore volume V2 (mL / g) in the range of 10 nm or more and 50 nm or less with respect to the total integrated pore volume Va (mL / g) in the range of 1 nm or more and 100 nm or less. The exhaust gas purification catalyst according to any one of claims 1 to 3, wherein / Va is in the range of 0.300 or more and 0.600 or less.

Images