Silver-supported zeolite, exhaust gas purification catalyst, exhaust gas purification device, exhaust gas purification method, and method for producing silver-supported zeolite

Abstract

The purpose of the present invention is to provide a silver-supported zeolite having excellent hydrocarbon (HC) adsorption characteristics, an exhaust gas purification catalyst, an exhaust gas purification device, an exhaust gas purification method, and a method for producing a silver-supported zeolite. In the silver-loaded zeolite, the silver is present in the form of at least one of a silver ion, a silver elementary substance, and a silver compound, the content ratio of the silver ion contained in the silver is 0.910 or more, and the content of the silver is 15.0 mass% or less with respect to the total weight of the silver-loaded zeolite.

Description

Technical Field

[0001] This invention relates to silver-loaded zeolite, exhaust gas purification catalyst, exhaust gas purification device, exhaust gas purification method, and method for manufacturing silver-loaded zeolite. Background Technology

[0002] To improve the adsorption properties of zeolites for gases, the addition of silver to zeolites is being investigated. Furthermore, zeolites with excellent gas adsorption properties are being used to purify hydrocarbons (HC) and nitrogen oxides (NOx) contained in exhaust gases from automobile engines. x Catalysts for exhaust purification, such as carbon monoxide (CO).

[0003] For example, Patent Document 1 describes a silver-loaded zeolite profile containing a Si / Al2 molar ratio of 2.0 or higher and 3.0 or lower, an (alkali metal + Ag) / Al molar ratio of 0.9 or higher and 1.1 or lower, a total content of SiO2, Al2O3, Ag2O, and alkali metal oxides of 90% by weight or higher, and containing 5% by weight or higher of silver ions, wherein the zeolite is one type. According to Patent Document 1, a zeolite profile can be provided that exhibits superior silver dispersion and reduced silver agglomeration compared to conventional silver-loaded zeolites.

[0004] Patent Document 2 discloses a catalyst for exhaust gas purification, characterized in that the innermost layer of the catalyst is a hydrocarbon adsorbent material layer mainly composed of zeolite loaded with Ag, and the outermost layer is a combustion catalyst layer containing at least one of palladium, platinum, and rhodium as a catalyst noble metal component and an oxygen storage material, and a separate layer of oxygen storage material is formed between these layers. According to Patent Document 2, the separate layer of oxygen storage material between the outermost combustion catalyst layer and the innermost hydrocarbon adsorbent material layer can mitigate the reducing properties of the treated gas, enabling efficient combustion purification even in reducing atmospheres containing high concentrations of H2 and CO without compromising HC retention capacity, and making it suitable for a wide range of exhaust gas purification applications without needing to select the atmosphere of the treated gas.

[0005] Patent Document 3 describes a method for treating a fluid containing radioactive iodine. The method involves passing the fluid through an iodine adsorbent composed of a silver-containing, binderless zeolite molded body with a silver content of 50% by weight or less, allowing the adsorbent to adsorb the radioactive iodine. According to Patent Document 3, the silver-containing, binderless zeolite molded body, composed of a high-silver-content material uniformly dispersed rather than agglomerated state, exhibits high iodine adsorption capacity per unit volume, enabling the inexpensive adsorption and removal of radioactive iodine contained in fluids such as radioactive waste liquids and gases.

[0006] Patent Document 4 discloses a hydrocarbon adsorbent material containing Ag, which simultaneously forms an alloy with Ag, or a metal oxide or composite oxide containing Ag, and further contains components that, compared to the case of Ag alone, form an alloy with Ag or a metal oxide or composite oxide containing Ag with an increased melting point. According to Patent Document 4, it is possible to suppress the decline in adsorption performance of the Ag-containing adsorbent material.

[0007] Existing technical documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2017-154985

[0009] Patent Document 2: Japanese Patent Application Publication No. 2005-144253

[0010] Patent Document 3: International Publication No. 2017 / 146130

[0011] Patent Document 4: Japanese Patent Application Publication No. 2006-21153 Summary of the Invention

[0012] The purpose of this invention is to provide silver-loaded zeolite with excellent hydrocarbon (HC) adsorption properties, exhaust gas purification catalyst, exhaust gas purification device, exhaust gas purification method, and method for manufacturing silver-loaded zeolite.

[0013] The present invention achieves the above objectives through the following means.

[0014] <Method 1> A silver-loaded zeolite, wherein the silver exists in the form of at least one of silver ions, elemental silver, and silver compounds.

[0015] The silver content of the aforementioned silver is 0.910 or higher, and

[0016] The silver content is less than 15.0% by mass relative to the total weight of the silver-loaded zeolite.

[0017] <Method 2> The silver-loaded zeolite according to Method 1 has a BEA-type crystal structure.

[0018] <Method 3> The silver-loaded zeolite according to Method 1 or 2 has an SAR of 20~40.

[0019] <Method 4> An exhaust gas purification catalyst comprising any one of Methods 1 to 3 silver-loaded zeolite.

[0020] <Method 5> An exhaust purification device having a honeycomb substrate and an exhaust purification catalyst as described in Method 4 supported on the honeycomb substrate.

[0021] <Method 6> An exhaust gas purification method, comprising the step of purifying exhaust gas with the exhaust gas purification catalyst described in Method 4.

[0022] <Method 7> A method for manufacturing silver-loaded zeolite according to any one of Methods 1 to 3, comprising the following steps:

[0023] Ion exchange treatment of zeolite with silver-containing aqueous solution; and

[0024] The zeolite after the above ion exchange treatment was calcined at a temperature below 500°C.

[0025] The silver-loaded zeolite, exhaust gas purification catalyst, exhaust gas purification device, and exhaust gas purification method according to the present invention can efficiently adsorb HC. Furthermore, the silver-loaded zeolite of the present invention can be obtained through the manufacturing method of the silver-loaded zeolite according to the present invention. Attached Figure Description

[0026] Figure 1 This is a graph showing the HC adsorption amount and the ratio of silver ion content in silver-loaded zeolites with different silver contents after calcination at 400℃. The bars represent the HC adsorption amount, and the dots represent the proportion of silver ions.

[0027] Figure 2 This is a graph showing the HC adsorption amount and silver ion content ratio of silver-loaded zeolite with a silver content of 8.9% by weight after calcination at different temperatures. The bars represent the HC adsorption amount, and the dots represent the silver ion content ratio. Detailed Implementation

[0028] The embodiments of the present invention will now be described in detail. Furthermore, the present invention is not limited to the following embodiments, and various modifications can be made within the scope of the present invention.

[0029] [Silver-loaded zeolite]

[0030] In the silver-loaded zeolite of the present invention

[0031] The aforementioned silver exists in at least one of the following forms: silver ions, elemental silver, and silver compounds.

[0032] The silver content of the aforementioned silver is 0.910 or higher, and

[0033] The silver content is less than 15.0% by mass relative to the total weight of the silver-loaded zeolite.

[0034] The silver-loaded zeolite according to the present invention can efficiently adsorb HC.

[0035] To improve the gas adsorption properties of zeolites, silver-loaded zeolites are being studied. However, the silver in silver-loaded zeolites exists in various states, including silver ions, elemental silver (metallic silver, silver clusters), and silver compounds. The state of the silver affects the gas adsorption properties. It is believed that if the silver exists in the form of metallic silver or silver clusters, the metallic silver or silver clusters will block the pores of the zeolite, resulting in a decrease in the gas adsorption properties of the silver-loaded zeolite.

[0036] The silver-loaded zeolite of this invention not only supports a certain amount of silver on the zeolite, but also the silver is mostly in the form of silver ions, resulting in a relatively small amount of elemental silver and silver clusters that hinder HC adsorption. Therefore, it is speculated that the above-mentioned silver-loaded zeolite achieves good HC adsorption characteristics through the improved HC adsorption properties brought about by silver loading and the suppression of zeolite pore blockage.

[0037] Furthermore, it was found that the proportion of silver ions in the silver-loaded zeolite of the present invention does not change significantly even when exposed to high-temperature environments. Therefore, the silver-loaded zeolite of the present invention is expected to be used as a gas adsorption material in high-temperature environments, such as in automotive exhaust purification catalysts.

[0038] <The Forms of Silver>

[0039] The silver in silver-loaded zeolites exists in the form of at least one of silver ions, elemental silver, and silver compounds.

[0040] The silver mentioned above is not particularly limited and can be silver ions, metallic silver, silver clusters, etc. Furthermore, the silver mentioned above is not particularly limited and can exist on the surface of zeolite or within the pores of zeolite.

[0041] There are no particular limitations on the loading of silver onto zeolite; it can be achieved through electrostatic interactions, ionic bonds, covalent bonds, physical adsorption, etc., between zeolite and silver. Alternatively, silver can be loaded onto zeolite using components other than silver and zeolite, such as organic binders, inorganic binders, coupling agents, and surface treatment agents.

[0042] <Proportion of silver ions>

[0043] The silver content of silver ions in silver-loaded zeolite is above 0.910.

[0044] From the viewpoint of obtaining silver-loaded zeolites with higher adsorption properties, the content ratio of silver ions in the silver-loaded zeolites of the present invention is not particularly limited, but is preferably 0.910 or higher. This is because silver ions are considered to contribute to adsorption properties, while components other than silver ions (such as metallic silver or silver clusters) do not contribute to adsorption properties.

[0045] The silver ion content can also be 0.920 or higher, 0.940 or higher, 0.960 or higher, or 0.980 or higher. Alternatively, the silver ion content can be 1.000 or lower, 0.995 or lower, or 0.990 or lower.

[0046] The proportion of silver ions can be determined by UV-vis measurement. Specifically, barium sulfate is used as a standard substance, and the UV-vis spectrum of the silver-loaded zeolite of this invention is measured by diffusion reflectance method. Next, the powder amount is specified, and a Kubelka-Munk transform is performed before output. Then, the obtained UV-vis spectrum is subjected to waveform separation. In the waveform-separated UV-vis spectrum, peaks with apexes at wavelengths above 200 nm and below 250 nm are identified as silver ion peaks, while peaks with apexes at wavelengths above 250 nm and below 600 nm are identified as non-silver ion peaks. The proportion of silver ions in the silver-loaded zeolite can be determined based on the peak areas.

[0047] The components of silver in silver-loaded zeolites other than silver ions act as barrier silver, without particular limitation, and can be calculated by the following formula.

[0048] (Proportion of silver content) = 1 - (Proportion of silver ions)

[0049] <Silver content>

[0050] In silver-loaded zeolite, the silver content is less than 15.0% by mass relative to the total weight of the silver-loaded zeolite.

[0051] From the viewpoint of obtaining silver-loaded zeolite with a high proportion of silver ions, there is no particular limitation, but the silver content of the silver-loaded zeolite of the present invention is 15.0% by mass or less.

[0052] The silver content can also be below 13.0% by mass, below 11.0% by mass, or below 9.0% by mass.

[0053] Furthermore, based on the general view that the higher the silver content, the higher the adsorption properties, there is no particular limitation. The silver content of the silver-loaded zeolite of the present invention can be 2.0% by mass or more, 4.0% by mass or more, or 6.0% by mass or more.

[0054] The silver content can be determined using X-ray fluorescence (XRF) analysis. Specifically, Axiosadvanced (manufactured by PANalytical) can be used to determine the powder content through quantitative analysis (calibration curve method).

[0055] <Crystal Structure of Zeolites>

[0056] There are no particular limitations on silver-loaded zeolites; they can also have a BEA-type crystal structure.

[0057] The crystal structures of silver-loaded zeolites can include BEA, LTA, FER, MWW, MFI, MOR, LTL, and FAU types, but are not limited to these. They may also contain one or more zeolites with the above-mentioned crystal structures. From the viewpoint of large pore size and effective adsorption of HC contained in automobile exhaust, the BEA type is preferred.

[0058] <SAR of Zeolites>

[0059] There are no particular limitations on silver-loaded zeolites, and the SAR can be 20~40.

[0060] Zeolites are generally composite oxides of SiO2 and Al2O3. SAR is the SiO2 / Al2O3 ratio, which is the proportion of SiO2 relative to Al2O3.

[0061] By replacing some of the Si in the zeolite framework with Al, and by making part of the zeolite framework negatively charged, cations can be introduced into the zeolite pores. Zeolites with high SAR are composite oxides mainly composed of SiO2. Although they have high durability and heat resistance, their ion exchange capacity for cation exchange is low, but this is not the only limitation.

[0062] There is no particular limitation on the SAR of silver-loaded zeolite, but from the viewpoint of zeolite durability and use in the automotive exhaust temperature range, it is preferred to be 20 or higher.

[0063] The lower limit of SAR can also be above 22, above 24, or above 28.

[0064] In addition, the SAR of silver-loaded zeolite is not particularly limited, but from the viewpoint of large-scale silver loading, it is preferred to be 40 or less.

[0065] The upper limit of SAR can also be below 38, below 36, below 34, below 32, or below 30.

[0066] [Exhaust gas purification catalyst]

[0067] The exhaust gas purification catalyst of the present invention comprises the silver-loaded zeolite of the present invention.

[0068] The exhaust gas purification catalyst is not particularly limited, and a catalyst supported on an inorganic oxide substrate with a precious metal can be used. As a precious metal, one or more selected from silver, gold, copper, nickel, palladium, platinum, cobalt, rhodium, iridium, ruthenium, etc., can be used, but it is not limited to this. As an inorganic oxide substrate, one or more selected from zeolite (SiO2 / Al2O3 composite oxide), alumina (Al2O3), zirconium oxide (ZrO2), magnesium oxide (MgO), lanthanum oxide (La2O3), cerium oxide (CeO2), neodymium oxide (Nd2O3), yttrium oxide (Y2O3), etc., can be used, but it is not limited to this. From the viewpoint of high HC adsorption characteristics, the exhaust gas purification catalyst preferably includes the silver-supported zeolite of the present invention.

[0069] There are no particular limitations on exhaust purification catalysts; they can also be used to purify hydrocarbons (HC) and nitrogen oxides (NOx) emitted from engines of automobiles and other vehicles. x ), carbon monoxide (CO). The silver-loaded zeolite of the present invention is preferred as an HC adsorption catalyst in the exhaust gas purification catalyst of the present invention due to its high HC adsorption characteristics.

[0070] [Exhaust gas purification device]

[0071] The exhaust purification device comprises a honeycomb substrate and the silver-loaded zeolite of the present invention supported on the honeycomb substrate.

[0072] The shape of the substrate can be, for example, a honeycomb shape. The material of the substrate can be, for example, ceramics such as alumina (Al2O3), mullite (3Al2O3-2SiO2), cordierite (2MgO-2Al2O3-5SiO2), aluminum titanate (Al2TiO5), and silicon carbide (SiC).

[0073] There is no particular limitation on the method for manufacturing exhaust purification devices. The following methods can be listed: adjust the slurry containing silver-loaded zeolite and binder added as needed, apply it to the honeycomb substrate, and then dry and fire it.

[0074] [Exhaust gas purification methods]

[0075] The exhaust gas purification method of the present invention includes the step of purifying exhaust gas with the silver-loaded zeolite of the present invention.

[0076] There are no particular limitations on exhaust purification methods; methods such as purifying exhaust by contacting it with exhaust from an internal combustion engine can also be used. There are no particular limitations on the internal combustion engine; any known internal combustion engine can be used, such as gasoline engines, diesel engines, or lean-burn engines with low fuel consumption.

[0077] [Preparation method of silver-loaded zeolite]

[0078] The method of the present invention for manufacturing silver-containing zeolite comprises the following steps:

[0079] Ion exchange treatment of zeolite with silver-containing aqueous solution; and

[0080] The zeolite that has undergone the above ion exchange treatment is calcined at a temperature below 500°C.

[0081] According to the method for manufacturing silver-loaded zeolite of the present invention, silver-loaded zeolite with a high proportion of silver ions can be obtained.

[0082] In order to obtain silver-loaded zeolite with a high proportion of silver ions, the inventors focused on the silver content and firing temperature.

[0083] The inventors have discovered that silver-loaded zeolites with a high proportion of silver ions can be obtained when the silver content is below 15.0% by mass. The main reason for obtaining these silver-loaded zeolites is not yet fully clear, but it is speculated that when the silver content is below 15.0% by mass, the amount of silver present in the zeolite is low, and the aggregation of silver particles is suppressed, thus inhibiting the formation of metallic silver and silver clusters.

[0084] Furthermore, the inventors have discovered that if zeolite that has undergone ion exchange treatment with silver ions is calcined at a low temperature (specifically, for example, below 500°C), silver-loaded zeolite with a high proportion of silver ions after calcination can be obtained. The main reason for obtaining the aforementioned silver-loaded zeolite is not entirely clear, but it is speculated that during low-temperature calcination, the thermal diffusion of the silver-containing compounds (specifically, for example, silver nitrate) contained in the ion-exchange treated zeolite is suppressed, causing these silver-containing compounds to decompose while maintaining their dispersed state.

[0085] <Silver-containing aqueous solution>

[0086] There are no particular limitations on the silver-containing aqueous solutions used for ion exchange treatment; any aqueous solution containing a silver compound is acceptable. Examples of silver-containing aqueous solutions include aqueous solutions obtained by dissolving one or more of silver nitrate, silver sulfate, silver acetate, and silver chloride in water, but this is not a limitation. The silver concentration in the silver-containing aqueous solution is not particularly limited and is arbitrary.

[0087] <Ion Exchange Treatment>

[0088] There are no particular limitations on the method for treating zeolite with silver ion exchange. Examples include stirring the zeolite in a silver-containing aqueous solution without pulverizing it, or allowing the silver-containing aqueous solution to flow through the zeolite packed in the column. The reaction vessel, mixing time, and flow rate are arbitrary and not particularly limited. There are no particular limitations on the zeolite treated with the silver-containing aqueous solution for ion exchange; it can be dried to remove moisture. Drying conditions can be, for example, at 80°C for more than 12 hours, or at 250°C for more than 12 hours, but are not limited to these conditions.

[0089] <Firing>

[0090] From the viewpoint of increasing the silver ion content of silver-loaded zeolite, the firing temperature of the ion-exchanged zeolite is preferably carried out at a temperature below 500°C.

[0091] The firing temperature can also be below 450℃ or below 420℃. Alternatively, the firing temperature can be above 360℃, above 380℃, or above 400℃.

[0092] Example

[0093] The invention will be described in more detail with reference to the embodiments shown below, but the scope of the invention is not limited by these embodiments.

[0094] [Example 1]

[0095] <Preparation of Silver-Loaded Zeolite A>

[0096] Add 0.76 g of silver nitrate to 40 g of distilled water and mix until dissolved. Then, add 20 g of BEA-type zeolite powder with a SAR (SiO2 / Al2O3 ratio) of 28 and mix for 30 minutes. Dry the resulting solution at 80°C for at least 12 hours. Next, calcine the dried powder at 400°C for 2 hours to obtain silver-loaded zeolite A.

[0097] <Silver content of silver-loaded zeolite A>

[0098] The silver content of silver-loaded zeolite A was determined by XRF analysis using Axios Advanced (PANalytical). The silver content was further determined by quantitative analysis (standard curve method) using material pulverized to below 250 μm. The silver content of silver-loaded zeolite A was confirmed to be 2.2% by mass.

[0099] <Proportion of silver ions in silver-loaded zeolite A>

[0100] The silver ion content of silver-loaded zeolite A was determined using a UV-2600 (manufactured by Shimadzu Corporation) via diffusion-reflectance method. Barium sulfate was used as the standard powder, and the measurement wavelength was measured from 200 to 600 nm. The obtained values, specifying the powder content, were then converted using the Kubelka-Munk method before output.

[0101] For the output data, 200-250 nm was considered as the absorption of silver ions, and 250-600 nm was considered as the absorption of substances other than silver ions. The absorption up to 250 nm, relative to the overall absorption, was taken as the proportion of silver ions. The proportion of silver ions in silver-loaded zeolite A was confirmed to be 0.962.

[0102] <Proportion of silver-impregnating zeolite A>

[0103] Assuming that silver ions, other than silver ions, exist as hindering silver in silver-loaded zeolite A, the following formula can be used to calculate the content of hindering silver in silver-loaded zeolite A. The content of hindering silver in silver-loaded zeolite A is confirmed to be 0.038.

[0104] The proportion of silver hindering its formation = 1 - the proportion of silver ions.

[0105] [Example 2]

[0106] <Manufacturing of Silver-Loaded Zeolite B>

[0107] 1.90 g of silver nitrate was added to 40 g of distilled water and mixed until dissolved. Then, 20 g of BEA-type zeolite powder with a SAR (SiO2 / Al2O3 ratio) of 28 was added and mixed for 30 minutes. The resulting solution was dried at 80°C for at least 12 hours. Next, the dried powder was calcined at 400°C for 2 hours to obtain silver-loaded zeolite B. The silver content, silver ion content, and silver-blocking content of silver-loaded zeolite B were determined using the same method as for silver-loaded zeolite A. The silver content of silver-loaded zeolite B was 6.4% by mass, the silver ion content was 0.983, and the silver-blocking content was 0.017.

[0108] [Example 3]

[0109] <Preparation of Silver-Loaded Zeolite C>

[0110] Add 3.04 g of silver nitrate to 40 g of distilled water and mix until dissolved. Then, add 20 g of BEA-type zeolite powder with a SAR (SiO2 / Al2O3 ratio) of 28 and mix for 30 minutes. Dry the resulting solution at 80°C for at least 12 hours. Next, calcine the dried powder at 400°C for 2 hours to obtain silver-loaded zeolite C. The silver content, silver ion content, and silver-blocking content of silver-loaded zeolite C were determined using the same method as for silver-loaded zeolite A. The silver content of silver-loaded zeolite C is 8.9% by mass, the silver ion content is 0.942%, and the silver-blocking content is 0.058%.

[0111] <HC adsorption capacity of silver-loaded zeolite C>

[0112] HC adsorption capacity was determined using the HC-TPD method (Hydrocarbon-Temperature Programmed Desorption). The sample used in the HC adsorption test was prepared by pressing and crushing silver-loaded zeolite C into granules. A gas containing propylene was used as the model gas in the HC adsorption test. Under the following conditions, the model gas was saturated with adsorption, and the cumulative difference between the inflow and outflow was taken as the adsorption capacity. The HC adsorption capacity of silver-loaded zeolite C was 13.00 mg / g zeolite.

[0113] HC adsorption test conditions

[0114] (1) Pretreatment: Atmosphere: O2 1%

[0115] Temperature: 500℃

[0116] Time: 5 minutes

[0117] (2) Saturated adsorption: Atmosphere: 600 ppm propylene, 3% H2O

[0118] Temperature: 100℃

[0119] Time: Until it takes effect

[0120] [Example 4]

[0121] <Manufacturing of Silver-Loaded Zeolite D>

[0122] Add 3.78 g of silver nitrate to 40 g of distilled water and mix until dissolved. Then, add 20 g of BEA-type zeolite powder with a SAR (SiO2 / Al2O3 ratio) of 28 and mix for 30 minutes. Dry the resulting solution at 80°C for at least 12 hours. Next, calcine the dried powder at 400°C for 2 hours to obtain silver-loaded zeolite D. The silver content, silver ion content, and silver-blocking content of silver-loaded zeolite D were determined using the same method as for silver-loaded zeolite A. The silver content of silver-loaded zeolite D is 12.8% by mass, the silver ion content is 0.949%, and the silver-blocking content is 0.051.

[0123] <HC adsorption capacity of silver-loaded zeolite D>

[0124] The HC adsorption capacity of silver-loaded zeolite D was determined using the same method as in Example 3. The HC adsorption capacity of silver-loaded zeolite D was 11.48 mg / g-zeolite.

[0125] [Example 5]

[0126] <Manufacturing of Silver-Loaded Zeolite E>

[0127] Add 3.04 g of silver nitrate to 40 g of distilled water and mix until dissolved. Then, add 20 g of BEA-type zeolite powder with a SAR (SiO2 / Al2O3 ratio) of 28 and mix for 30 minutes. Dry the resulting solution at 250°C for at least 12 hours. Next, calcine the dried powder at 400°C for 2 hours to obtain silver-loaded zeolite E. The silver content, silver ion content, and silver-blocking content of silver-loaded zeolite E were determined using the same method as for silver-loaded zeolite A. The silver content of silver-loaded zeolite E is 8.9% by mass, the silver ion content is 0.967%, and the silver-blocking content is 0.033.

[0128] <HC adsorption capacity of silver-loaded zeolite E>

[0129] The HC adsorption capacity of silver-loaded zeolite E was determined using the same method as in Example 3. The HC adsorption capacity of silver-loaded zeolite E was 12.90 mg / g-zeolite.

[0130] [Comparative Example 1]

[0131] <Manufacturing of silver-loaded zeolite A>

[0132] Add 5.70 g of silver nitrate to 40 g of distilled water and mix until dissolved. Then, add 20 g of BEA-type zeolite powder with a SAR (SiO2 / Al2O3 ratio) of 28 and mix for 30 minutes. Dry the resulting solution at 80°C for at least 12 hours. Next, calcine the dried powder at 400°C for 2 hours to obtain silver-loaded zeolite a. The silver content, silver ion content, and silver-blocking content of silver-loaded zeolite a were determined using the same method as for silver-loaded zeolite A. The silver content of silver-loaded zeolite a is 19.2% by mass, the silver ion content is 0.904%, and the silver-blocking content is 0.096.

[0133] <HC adsorption capacity of silver-loaded zeolite a>

[0134] The HC adsorption capacity of silver-loaded zeolite a was determined using the same method as in Example 3. The HC adsorption capacity of silver-loaded zeolite a was 9.60 mg / g-zeolite.

[0135] [Comparative Example 2]

[0136] <Manufacturing of silver-loaded zeolite B>

[0137] 7.56 g of silver nitrate was added to 40 g of distilled water and mixed until dissolved. Then, 20 g of BEA-type zeolite powder with a SAR (SiO2 / Al2O3 ratio) of 28 was added and mixed for 30 minutes. The resulting solution was dried at 80°C for at least 12 hours. Next, the dried powder was calcined at 400°C for 2 hours to obtain silver-loaded zeolite b. The silver content, silver ion content, and silver-blocking content of silver-loaded zeolite b were determined using the same method as for silver-loaded zeolite A. The silver content of silver-loaded zeolite b was 25.6% by mass, the silver ion content was 0.813, and the silver-blocking content was 0.187.

[0138] <HC adsorption capacity of silver-loaded zeolite b>

[0139] The HC adsorption capacity of silver-loaded zeolite b was determined using the same method as in Example 3. The HC adsorption capacity of silver-loaded zeolite b was 7.95 mg / g-zeolite.

[0140] [Comparative Example 3]

[0141] <Manufacturing of Silver-Loaded Zeolite C>

[0142] Add 3.04 g of silver nitrate to 40 g of distilled water and mix until dissolved. Then, add 20 g of BEA-type zeolite powder with a SAR (SiO2 / Al2O3 ratio) of 28 and mix for 30 minutes. Dry the resulting solution at 250°C for at least 12 hours. Next, calcine the dried powder at 500°C for 2 hours to obtain silver-loaded zeolite c. The silver content, silver ion content, and silver-blocking content of silver-loaded zeolite c were determined using the same method as for silver-loaded zeolite A. The silver content of silver-loaded zeolite c is 8.9% by mass, the silver ion content is 0.907%, and the silver-blocking content is 0.093.

[0143] [Comparative Example 4]

[0144] <Manufacturing of silver-loaded zeolite D>

[0145] Add 3.04 g of silver nitrate to 40 g of distilled water and mix until dissolved. Then, add 20 g of BEA-type zeolite powder with a SAR (SiO2 / Al2O3 ratio) of 28 and mix for 30 minutes. Dry the resulting solution at 250°C for at least 12 hours. Next, calcine the dried powder at 600°C for 2 hours to obtain silver-loaded zeolite d. The silver content, silver ion content, and silver-blocking content of silver-loaded zeolite d were determined using the same method as for silver-loaded zeolite A. The silver content of silver-loaded zeolite d is 8.9% by mass, the silver ion content is 0.770%, and the silver-blocking content is 0.230.

[0146] [Comparative Example 5]

[0147] <Manufacturing of silver-loaded zeolite e>

[0148] Add 3.04 g of silver nitrate to 40 g of distilled water and mix until dissolved. Then, add 20 g of BEA-type zeolite powder with a SAR (SiO2 / Al2O3 ratio) of 28 and mix for 30 minutes. Dry the resulting solution at 250°C for at least 12 hours. Next, calcine the dried powder at 700°C for 2 hours to obtain silver-loaded zeolite e. The silver content, silver ion content, and silver-blocking content of silver-loaded zeolite e were determined using the same method as for silver-loaded zeolite A. The silver content of silver-loaded zeolite e is 8.9% by mass, the silver ion content is 0.764%, and the silver-blocking content is 0.236.

[0149] [Comparative Example 6]

[0150] <Manufacturing of silver-loaded zeolite f>

[0151] Add 3.04 g of silver nitrate to 40 g of distilled water and mix until dissolved. Then, add 20 g of BEA-type zeolite powder with a SAR (SiO2 / Al2O3 ratio) of 28 and mix for 30 minutes. Dry the resulting solution at 250°C for at least 12 hours. Next, calcine the dried powder at 800°C for 2 hours to obtain silver-loaded zeolite f. The silver content, silver ion content, and silver-blocking content of silver-loaded zeolite f were determined using the same method as for silver-loaded zeolite A. The silver content of silver-loaded zeolite f was confirmed to be 8.9% by mass, the silver ion content to be 0.725%, and the silver-blocking content to be 0.275%.

[0152] <HC adsorption capacity of silver-loaded zeolite f>

[0153] The HC adsorption capacity of silver-loaded zeolite f was determined using the same method as in Example 3. The HC adsorption capacity of silver-loaded zeolite f was 7.70 mg / g-zeolite.

[0154] Table 1 shows the manufacturing conditions and analytical results of the silver-loaded zeolites A to E produced in Examples 1 to 5. Table 2 shows the manufacturing conditions and analytical results of the silver-loaded zeolites a to f produced in Comparative Examples 1 to 6.

[0155]

[0156]

[0157] Examples 1-5 and Comparative Examples 1-6 were manufactured using the following steps:

[0158] Step (a): Ion exchange treatment of zeolite with silver nitrate aqueous solution;

[0159] Step (b): Calcining the zeolite that has undergone the above ion exchange treatment.

[0160] In the ion exchange treatment of step (a), there is a tendency for a high proportion of silver ions when the amount of silver nitrate added is small. When the calcination temperature is 400°C and the silver content is less than 15.0% by mass, silver-loaded zeolite with a silver ion content of 0.910 or more can be obtained (Examples 1-4, Comparative Examples 1 and 2). It is speculated that when the silver content is below the above amount, the amount of silver present in the zeolite is small, therefore, the aggregation of silver is suppressed, the formation of metallic silver and silver clusters can be suppressed, and thus the proportion of silver ions becomes higher.

[0161] In the firing process of step (b), when the firing temperature is below 500°C, silver-loaded zeolites with a high proportion of silver ions can be obtained (Examples 3 and 5). On the other hand, when the firing temperature is above 500°C, silver-loaded zeolites with a low proportion of silver ions are obtained (Comparative Examples 3 to 6). It is speculated that during low-temperature firing, the thermal diffusion of silver nitrate contained in the ion-exchange treated zeolite is suppressed, and the silver nitrate decomposes while maintaining its dispersed state, thus increasing the proportion of silver ions.

[0162] Table 3 shows the results of HC adsorption tests for Examples 3-5, Comparative Examples 1-2, and Comparative Example 6.

[0163]

[0164] In Examples 3-5, Comparative Examples 1-2 and Comparative Example 6, the HC adsorption capacity of silver-loaded zeolites with different silver contents and silver ion content ratios was determined. Figure 1 It is a graph comparing the HC adsorption capacity and the silver ion content ratio of silver-loaded zeolites with the same firing temperature but different silver contents. Figure 1 When the silver content is below a certain level and the proportion of silver ions is high, there is a tendency for the HC adsorption capacity of silver-loaded zeolite to increase.

[0165] in addition, Figure 2 This is a graph comparing the HC adsorption capacity and silver ion content of silver-loaded zeolites with the same silver content but different silver ion content ratios due to firing temperature. Figure 2 Among them, silver-loaded zeolites with a high proportion of silver ions showed high HC adsorption capacity.

[0166] It is believed that silver-loaded zeolites with high HC adsorption capacity all contain a large number of silver ions, which minimize the amount of silver (metallic silver or silver clusters) that can be absorbed, thus inhibiting the clogging of zeolite pores and exhibiting good adsorption characteristics. It is also believed that by not only adding silver to the zeolite but also specifying the silver's loading state, silver-loaded zeolites with high HC adsorption capacity can be obtained.

[0167] [Example 6]

[0168] <Preparation of silver-loaded zeolite F (additional calcination of silver-loaded zeolite C)>

[0169] The silver-loaded zeolite C obtained in Example 3 was further calcined at 600°C for 2 hours to obtain silver-loaded zeolite F. The silver content, silver ion content, and silver-blocking content of silver-loaded zeolite F were determined using the same method as for silver-loaded zeolite A. The silver content of silver-loaded zeolite F was 8.9% by mass, the silver ion content was 0.910, and the silver-blocking content was 0.090.

[0170] Table 3 shows a comparison of the analytical results of silver-loaded zeolite F in Example 6 with those of silver-loaded zeolite C before calcination and silver-loaded zeolite d after calcination at 600°C.

[0171]

[0172] The zeolite obtained by firing at 400°C maintained the silver ion content even after additional firing at 600°C (Example 6, Comparative Example 4). It is speculated that the silver ions formed and supported by firing at 400°C will not condense to form metallic silver and silver clusters unless there is greater energy, at least greater than that required for firing at 600°C, thus maintaining the silver ion content.

[0173] Although preferred embodiments of the silver-loaded zeolite, exhaust gas purification catalyst, exhaust gas purification device, exhaust gas purification method, and method for manufacturing silver-loaded zeolite of the present invention have been described in detail, those skilled in the art will understand that modifications can be made without departing from the scope of the claims.

Claims

1. A silver-supported zeolite, the silver being present in the form of at least one of silver ions, elemental silver, and silver compounds, the silver-supported zeolite containing the silver ions at a proportion of 0.910 or more, and the silver being contained at a content of 15.0 mass% or less with respect to the total weight of the silver-supported zeolite.

2. The silver-supported zeolite according to claim 1, having a crystal structure of BEA type.

3. The silver-supported zeolite according to claim 1, having a SAR of 20 to 40.

4. An exhaust gas purification catalyst having the silver-supported zeolite according to claim 1.

5. An exhaust gas purification device having a honeycomb substrate and the exhaust gas purification catalyst according to claim 4 supported on the honeycomb substrate.

6. An exhaust gas purification method comprising a step of purifying exhaust gas with the exhaust gas purification catalyst according to claim 4.

7. A method of producing the silver-supported zeolite according to any one of claims 1 to 3, comprising the steps of: ion-exchanging a zeolite with an aqueous silver-containing solution; and firing the zeolite after the ion-exchange treatment at a temperature of less than 500°C. ​ ​

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