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 that has excellent hydrocarbon (HC) adsorption properties; an exhaust gas purification catalyst; an exhaust gas purification device; an exhaust gas purification method; and a method for producing the silver-supported zeolite. The present invention pertains to a silver-supported zeolite. The silver exists as at least one of silver ions, a silver elemental substance, and a silver compound. The contained proportion of silver ions included in the silver is 0.910 or more. The content of the silver is 15.0 mass% or less with respect to the total weight of the silver-supported zeolite.

Description

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

[0001] The present invention relates to a silver-supported zeolite, an exhaust gas purification catalyst, an exhaust gas purification device, an exhaust gas purification method, and a method for producing a silver-supported zeolite.

[0002] Addition of silver to zeolite has been investigated to improve the gas adsorption properties of zeolite. Zeolite with good gas adsorption properties is also effective in absorbing hydrocarbons (HC) and nitrogen oxides (NO) contained in exhaust gases emitted from engines of automobiles, etc. ｘ ), carbon monoxide (CO), and other exhaust gas purification catalysts.

[0003] For example, Patent Document 1 discloses a Si / Al ２ The molar ratio is 2.0 or more and 3.0 or less, the (alkali metal + Ag) / Al molar ratio is 0.9 or more and 1.1 or less, SiO ２ , Al ２ O ３ , Ag ２ Patent Document 1 describes a silver-loaded zeolite shaped body containing 90% by weight or more of a total amount of O and alkali metal oxides, 5% by weight or more of silver ions, and one type of zeolite. According to Patent Document 1, it is possible to provide a zeolite shaped body in which silver aggregation is suppressed and which has excellent silver dispersibility compared to conventional silver-loaded zeolites.

[0004] Patent Document 2 describes a catalyst for purifying exhaust gas, characterized in that the catalyst has an innermost layer provided with a hydrocarbon adsorbent layer mainly composed of Ag-loaded zeolite, an outermost layer provided with a combustion catalyst layer containing at least one catalytic precious metal component selected from palladium, platinum, and rhodium and an oxygen storage-release material, and a layer of oxygen storage-release material alone formed between these layers. According to Patent Document 2, since the layer of oxygen storage-release material alone is formed between the combustion catalyst layer as the outermost layer and the hydrocarbon adsorbent layer as the innermost layer, the reducing property of the treated gas can be alleviated, and H ２It is said that it can efficiently combust and purify HC without compromising its HC retention ability even in a reducing atmosphere containing high concentrations of CO, and can be applied to purify a wide range of exhaust gases without being picky about the atmosphere of the treated gas.

[0005] Patent Document 3 describes a method for treating a radioactive iodine-containing fluid, in which the fluid containing radioactive iodine is passed through an iodine adsorbent made of a silver-containing, binderless zeolite shaped body having a silver content of 50 wt % or less, and the radioactive iodine is adsorbed by the iodine adsorbent. According to Patent Document 3, the iodine adsorbent is made of a silver-containing, binderless zeolite shaped body having a high silver content and supporting silver in a uniformly dispersed state without agglomeration, and is said to have high iodine adsorption performance per unit volume, making it possible to inexpensively adsorb and remove radioactive iodine contained in fluids such as radioactive liquid waste and gas.

[0006] Patent Document 4 describes a hydrocarbon adsorbent that contains Ag and also contains a component that forms an alloy with Ag, or a metal oxide or composite oxide containing Ag, and that has a melting point higher than that of Ag alone. Patent Document 4 states that the deterioration of the adsorption performance of the adsorbent containing Ag can be suppressed.

[0007] Japanese Patent Application Laid-Open No. 2017-154985 Japanese Patent Application Laid-Open No. 2005-144253 International Publication No. 2017 / 146130 Pamphlet Japanese Patent Application Laid-Open No. 2006-21153

[0008] An object of the present invention is to provide a silver-supported zeolite having excellent hydrocarbon (HC) adsorption properties, an exhaust gas purification catalyst, an exhaust gas purification device, an exhaust gas purification method, and a method for producing the silver-supported zeolite.

[0009] The present invention achieves the above object by the following means.

[0010] <Aspect 1> A silver-supported zeolite, wherein the silver is present as at least one of silver ions, elemental silver, and a silver compound, wherein a content ratio of silver ions contained in the silver is 0.910 or more, and the content of the silver is 15.0 mass% or less relative to the total weight of the silver-supported zeolite. <Aspect 2> The silver-supported zeolite according to Aspect 1, wherein the silver-supported zeolite has a BEA-type crystal structure. <Aspect 3> The silver-supported zeolite according to Aspect 1 or 2, wherein the SAR of the silver-supported zeolite is 20 to 40. <Aspect 4> An exhaust gas purification catalyst comprising the silver-supported zeolite according to any one of Aspects 1 to 3. <Aspect 5> An exhaust gas purification device comprising a honeycomb substrate and the exhaust gas purification catalyst according to Aspect 4 supported on the honeycomb substrate. <Aspect 6> A method for purifying exhaust gas, comprising purifying exhaust gas with the exhaust gas purification catalyst according to Aspect 4. <Aspect 7> A method for producing the silver-supported zeolite according to any one of Aspects 1 to 3, comprising: subjecting a zeolite to an ion exchange treatment with a silver-containing aqueous solution; and calcining the ion-exchanged zeolite at a temperature lower than 500°C.

[0011] The silver-supported zeolite, exhaust gas purification catalyst, exhaust gas purification device, and exhaust gas purification method of the present invention can efficiently adsorb HC. Furthermore, the silver-supported zeolite of the present invention can be obtained by the method for producing the silver-supported zeolite of the present invention.

[0012] Figure 1 is a graph showing the HC adsorption amount and silver ion content of silver-loaded zeolites with different silver contents calcined at 400°C. The bar graph shows the HC adsorption amount, and the dots show the silver ion content. Figure 2 is a graph showing the HC adsorption amount and silver ion content of silver-loaded zeolites with a silver content of 8.9 wt% calcined at different temperatures. The bar graph shows the HC adsorption amount, and the dots show the silver ion content.

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the preferred embodiments. However, the present invention is not limited to the following embodiments and can be practiced in various modified forms within the scope of the present invention.

[0014] <<Silver-supported Zeolite>> In the silver-supported zeolite of the present invention, the silver is present as at least one of silver ions, elemental silver, and a silver compound, the content of silver ions 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-supported zeolite.

[0015] The silver-supported zeolite of the present invention can efficiently adsorb HC.

[0016] Silver-loaded zeolites have been investigated to improve the gas adsorption properties of zeolites, but the silver present in silver-loaded zeolites exists in the form of silver ions, elemental silver (metallic silver, silver clusters), silver compounds, etc., and it is believed that the state of the silver affects the gas adsorption properties. When silver exists as metallic silver or silver clusters, the metallic silver or silver clusters clog the pores of the zeolite, which is thought to result in a decrease in the gas adsorption properties of the silver-loaded zeolite.

[0017] The silver-loaded zeolite of the present invention not only loads a certain amount of silver on the zeolite, but also has a large amount of loaded silver present as silver ions, and the amount of silver elemental substance or silver clusters that inhibit HC adsorption is relatively small. Therefore, it is presumed that the silver-loaded zeolite has good HC adsorption properties due to the improvement of HC adsorption properties by loading silver and the suppression of zeolite pore clogging.

[0018] It was also found that the proportion of silver ions in the silver-loaded zeolite of the present invention does not change significantly even when exposed to a high-temperature environment, and 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 automobile exhaust gas purification catalysts.

[0019] <Form of Silver> The silver in the silver-loaded zeolite exists as at least one of silver ions, elemental silver, and a silver compound.

[0020] The silver is not particularly limited, but may be silver ions, metallic silver, silver clusters, etc. Furthermore, the silver is not particularly limited, but may be present on the surface of the zeolite or within the pores of the zeolite.

[0021] The method for supporting silver on zeolite is not particularly limited, and may be electrostatic interaction between zeolite and silver, ionic bonding, covalent bonding, physical adsorption, etc. Silver may also be supported on zeolite by a component other than silver and zeolite, such as an organic binder, an inorganic binder, a coupling agent, or a surface treatment agent.

[0022] <Silver Ion Content> The silver-loaded zeolite has a silver ion content of 0.910 or more in silver.

[0023] From the viewpoint of obtaining a silver-loaded zeolite with higher adsorption properties, the silver ion content of the silver-loaded zeolite of the present invention is not particularly limited, but is preferably 0.910 or more. This is because it is believed that silver ions contribute to the adsorption properties, whereas components other than silver ions (e.g., metallic silver and silver clusters) do not contribute to the adsorption properties.

[0024] The silver ion content may be 0.920 or more, 0.940 or more, 0.960 or more, or 0.980 or more. The silver ion content may be 1.000 or less, 0.995 or less, or 0.990 or less.

[0025] The silver ion content can be determined by UV-vis measurement. Specifically, the UV-vis spectrum of the silver-supported zeolite of the present invention is measured by a diffuse reflectance method using barium sulfate as a standard substance. Next, the powder amount is specified, and the spectrum is output after Kubelka-Munk conversion. The obtained UV-vis spectrum is then subjected to waveform separation, and in the UV-vis spectrum after waveform separation, peaks having peak tops in the wavelength range of 200 nm to 250 nm can be determined as silver ion peaks, and peaks having peak tops in the wavelength range of 250 nm to 600 nm can be determined as peaks other than silver ions. The silver ion content of the silver contained in the silver-supported zeolite can be determined from the peak areas of the obtained peaks.

[0026] The components of silver in silver-loaded zeolite other than silver ions are called inhibitory silver, and are not particularly limited, but may be calculated using the following formula: (Inhibitory silver content) = 1 - (Silver ion content)

[0027] <Silver Content> The silver-supported zeolite has a silver content of 15.0 mass % or less based on the total weight of the silver-supported zeolite.

[0028] From the viewpoint of obtaining a silver-loaded zeolite having a high content of silver ions, the silver content of the silver-loaded zeolite of the present invention is not particularly limited, but is preferably 15.0 mass % or less.

[0029] The silver content may be 13.0% by mass or less, 11.0% by mass or less, or 9.0% by mass or less.

[0030] Furthermore, from the viewpoint that the higher the silver content, the better the adsorption characteristics generally are, the silver content of the silver-supported zeolite of the present invention may be, but is not particularly limited to, 2.0 mass% or more, 4.0 mass% or more, or 6.0 mass% or more.

[0031] The silver content can be determined by X-ray fluorescence analysis (XRF). Specifically, the powder can be measured by quantitative analysis (calibration curve method) using an Axios advanced (manufactured by PANalytical).

[0032] <Zeolite Crystal Structure> The silver-supported zeolite is not particularly limited, but may have a BEA-type crystal structure.

[0033] Examples of the crystal structure of the silver-supported zeolite include, but are not limited to, BEA, LTA, FER, MWW, MFI, MOR, LTL, and FAU types. One or more types of zeolite having the above crystal structure may be included. From the viewpoint of large pore size and ability to adsorb HC contained in automobile exhaust gas, it is preferable to include the BEA type.

[0034] <SAR of Zeolite> The silver-supported zeolite may have an SAR of 20 to 40, although this is not particularly limited.

[0035] Zeolites are generally made of SiO ２ and Al ２ O ３ SAR is a composite oxide of SiO ２ / Al ２ O ３ is the ratio, and Al ２ O３ SiO ２ The content ratio is

[0036] It is believed that by replacing some of the Si in the zeolite framework with Al, a part of the zeolite framework becomes negatively charged, allowing cations to be captured in the zeolite pores. Zeolites with high SAR are mainly composed of SiO ２ It is a composite oxide composed of these, and is said to have high durability and heat resistance, but low ion exchange capacity for ion exchange with cations, although this is not limited to this case.

[0037] The SAR of the silver-supported zeolite is not particularly limited, but is preferably 20 or more from the viewpoint of the durability of the zeolite and use in the temperature range of automobile exhaust gases.

[0038] The lower limit of the SAR may be 22 or more, 24 or more, or 28 or more.

[0039] The SAR of the silver-loaded zeolite is not particularly limited, but is preferably 40 or less from the viewpoint of loading a large amount of silver.

[0040] The upper limit of the SAR may be 38 or less, 36 or less, 34 or less, 32 or less, or 30 or less.

[0041] <<Exhaust Gas Purification Catalyst>> The exhaust gas purification catalyst of the present invention contains the silver-supported zeolite of the present invention.

[0042] The exhaust gas purification catalyst is not particularly limited, but may be one in which a precious metal is supported on an inorganic oxide substrate. The precious metal may be, for example, one or more selected from silver, gold, copper, nickel, palladium, platinum, cobalt, rhodium, iridium, ruthenium, etc., but is not limited to this. In addition, the inorganic oxide substrate may be, for example, zeolite (SiO ２ / Al ２ O ３ composite oxide), alumina (Al ２ O ３ ), zirconia (ZrO ２ ), magnesium oxide (MgO), lanthanum oxide (La ２ O ３ ), cerium oxide (CeO ２), neodymium oxide (Nd ２ O ３ ), yttrium oxide (Y ２ O ３ The catalyst for purifying exhaust gas preferably contains the silver-supported zeolite of the present invention from the viewpoint of high HC adsorption properties.

[0043] The exhaust gas purification catalyst is not particularly limited, but may be used to purify hydrocarbons (HC), nitrogen oxides (NO), etc., exhausted from engines of automobiles, etc. ｘ The silver-supported zeolite of the present invention has high HC adsorption properties, and therefore is preferably used as an HC adsorption catalyst in the exhaust gas purification catalyst of the present invention.

[0044] <<Exhaust Gas Purification Apparatus>> The exhaust gas purification apparatus includes a honeycomb substrate and the silver-supported zeolite of the present invention supported on the honeycomb substrate.

[0045] The substrate may have a honeycomb shape, for example. The substrate may be made of alumina (Al ２ O ３ ), mullite (3Al ２ O ３ -2SiO ２ ), cordierite (2MgO-2Al ２ O ３ -5SiO ２ ), aluminum titanate (Al ２ TiO ５ ), silicon carbide (SiC), or other ceramics can be used.

[0046] The method for producing the exhaust gas purification device is not particularly limited, but examples thereof include a method in which a slurry containing silver-loaded zeolite and, if necessary, a binder is prepared, the slurry is applied to a honeycomb substrate, and then the substrate is dried and fired.

[0047] <<Method for Purifying Exhaust Gas>> The method for purifying exhaust gas of the present invention includes purifying exhaust gas with the silver-supported zeolite of the present invention.

[0048] The method for purifying exhaust gas is not particularly limited, but a method of purifying exhaust gas from an internal combustion engine by contacting the catalyst may be adopted. The internal combustion engine is not particularly limited, but any known internal combustion engine can be used as appropriate, such as a gasoline engine, a diesel engine, or a lean burn engine with a low fuel consumption rate.

[0049] <<Method for Producing Silver-Loaded Zeolite>> The method of the present invention for producing a silver-loaded zeolite comprises: subjecting a zeolite to an ion-exchange treatment with a silver-containing aqueous solution; and calcining the ion-exchanged zeolite at a temperature of less than 500°C.

[0050] According to the method for producing a silver-loaded zeolite of the present invention, a silver-loaded zeolite having a high silver ion content can be obtained.

[0051] The present inventors focused on the silver content and the calcination temperature in order to obtain silver-loaded zeolite having a high silver ion content.

[0052] The present inventors have found that when the silver content is 15.0% by mass or less, a silver-loaded zeolite with a high silver ion content can be obtained. Although the reason why the above silver-loaded zeolite was obtained is not clear, it is presumed that when the silver content is 15.0% by mass or less, the amount of silver present in the zeolite is small, which suppresses aggregation of silver particles, thereby suppressing the generation of metallic silver and silver clusters.

[0053] The present inventors also discovered that calcining zeolite ion-exchanged with silver ions at a low temperature (specifically, for example, below 500°C) yields a silver-loaded zeolite that still contains a high proportion of silver ions after calcination. The reason for this is unclear, but it is presumed that low-temperature calcination suppresses the thermal diffusion of the silver-containing compound (specifically, for example, silver nitrate) contained in the ion-exchanged zeolite, causing the silver-containing compound to decompose while maintaining its dispersed state.

[0054] <Silver-containing aqueous solution> The silver-containing aqueous solution to be subjected to the ion exchange treatment is not particularly limited, but may be any aqueous solution containing a silver compound. For example, the silver-containing aqueous solution may be an aqueous solution in which one or more of silver nitrate, silver sulfate, silver acetate, silver chloride, etc. are dissolved in water, but is not limited to this. The silver concentration of the silver-containing aqueous solution is not particularly limited and may be any.

[0055] <Ion Exchange Treatment> The method for ion-exchanging silver into zeolite is not particularly limited, but examples include a method of stirring the zeolite in a silver-containing aqueous solution so as not to crush it, and a method of passing the silver-containing aqueous solution through zeolite packed in a column. The reaction vessel, mixing time, flow rate, etc. are not particularly limited and are arbitrary. The zeolite that has been ion-exchanged using the silver-containing aqueous solution may be dried to remove moisture, but is not particularly limited. The drying conditions may be, for example, at 80°C for 12 hours or more, or at 250°C for 12 hours or more, but are not limited to these.

[0056] <Caking> The ion-exchanged zeolite is preferably calcined at a temperature of less than 500°C from the viewpoint of increasing the content of silver ions in the silver-loaded zeolite.

[0057] The firing temperature may be less than 450° C. or less than 420° C. Alternatively, the firing temperature may be 360° C. or more, 380° C. or more, or 400° C. or more.

[0058] The present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited to these examples.

[0059] Example 1 Production of Silver-Supported Zeolite A 0.76 g of silver nitrate was added to 40 g of distilled water and mixed until dissolved. ２ / Al ２ O ３ 20 g of BEA-type zeolite powder with a % saturation ratio (Sr) of 28 was added and mixed for 30 minutes. The resulting mixed solution was dried at 80°C for 12 hours or more. The dried powder was then calcined at 400°C for 2 hours to obtain silver-supported zeolite A.

[0060] <Silver Content of Silver-Supported Zeolite A> The silver content of silver-supported zeolite A was determined by XRF analysis using an Axios advanced (manufactured by PANalytical). The silver content was determined by quantitative analysis (calibration curve method) using silver-supported zeolite A crushed to 250 μm or less. It was confirmed that the silver content of silver-supported zeolite A was 2.2 mass%.

[0061] <Silver Ion Content in Silver-Supported Zeolite A> The silver ion content in silver-supported zeolite A was determined by the diffuse reflectance method using a UV-2600 (Shimadzu Corporation). Barium sulfate was used as the standard powder, and measurements were taken at wavelengths from 200 to 600 nm. The obtained measurement values ​​were output after specifying the powder amount and performing Kubelka-Munk conversion. For the output data, the absorption from 200 to 250 nm was considered to be that of silver ions, and the absorption from 250 to 600 nm was considered to be that of other than silver ions, and the absorption up to 250 nm relative to the total absorption was considered to be the silver ion content. The silver ion content in silver-supported zeolite A was confirmed to be 0.962.

[0062] <Content of inhibitory silver in silver-loaded zeolite A> It was assumed that all silver ions in silver-loaded zeolite A existed as inhibitory silver, and was calculated using the following formula. It was confirmed that the content of inhibitory silver in silver-loaded zeolite A was 0.038. Content of inhibitory silver = 1 - content of silver ions

[0063] Example 2 Production of Silver-Supported Zeolite B 1.90 g of silver nitrate was added to 40 g of distilled water and mixed until dissolved. ２ / Al ２ O ３ 20 g of BEA-type zeolite powder having a silver content of 6.4 mass %, a silver ion content of 0.983 mass %, and an inhibitory silver content of 0.017 mass % were added to the mixture and mixed for 30 minutes. The resulting mixed solution was dried at 80°C for 12 hours or more. The resulting dried powder was then calcined at 400°C for 2 hours to obtain silver-supported zeolite B. The silver content, silver ion content, and inhibitory silver content of silver-supported zeolite B were determined in the same manner as for silver-supported zeolite A. Silver-supported zeolite B had a silver content of 6.4 mass %, a silver ion content of 0.983 mass %, and an inhibitory silver content of 0.017 mass %.

[0064] Example 3 Production of Silver-Supported Zeolite C 3.04 g of silver nitrate was added to 40 g of distilled water and mixed until dissolved. ２ / Al ２ O ３ 20 g of BEA-type zeolite powder having a silver content of 8.9 mass %, a silver ion content of 0.942, and an inhibitory silver content of 0.058 were added and mixed for 30 minutes. The resulting mixed solution was dried at 80°C for 12 hours or more. The resulting dried powder was then calcined at 400°C for 2 hours to obtain silver-supported zeolite C. The silver content, silver ion content, and inhibitory silver content of silver-supported zeolite C were determined in the same manner as for silver-supported zeolite A. The silver-supported zeolite C had a silver content of 8.9 mass %, a silver ion content of 0.942, and an inhibitory silver content of 0.058.

[0065] <HC adsorption amount of silver-supported zeolite C> The HC adsorption amount was determined by the HC-TPD method (Hydrocarbon-Temperature Programmed Desorption method). A sample for the HC adsorption test was prepared by compressing and crushing silver-supported zeolite C and molding it into pellets. A gas containing propylene was used as a model gas for the HC adsorption test. The model gas was saturated and adsorbed under the following conditions, and the integrated amount of the difference between the input and output was taken as the adsorption amount. The HC adsorption amount of silver-supported zeolite C was 13.00 mg / g-zeolite. HC adsorption test conditions (1) Pretreatment: Atmosphere: O ２ 1% Temperature: 500°C Time: 5 minutes (2) Saturated adsorption: Atmosphere: Propylene 600 ppm, H ２ O 3% Temperature: 100°C Time: until breakthrough

[0066] Example 4 Production of Silver-Supported Zeolite D 3.78 g of silver nitrate was added to 40 g of distilled water and mixed until dissolved. ２ / Al ２ O ３20 g of BEA-type zeolite powder having a silver content of 12.8 mass %, a silver ion content of 0.949 mass %, and an inhibitory silver content of 0.051 mass % were added to the mixture and mixed for 30 minutes. The resulting mixed solution was dried at 80°C for 12 hours or more. The resulting dried powder was then calcined at 400°C for 2 hours to obtain silver-supported zeolite D. The silver content, silver ion content, and inhibitory silver content of silver-supported zeolite D were determined in the same manner as for silver-supported zeolite A. The silver-supported zeolite D had a silver content of 12.8 mass %, a silver ion content of 0.949 mass %, and an inhibitory silver content of 0.051 mass %.

[0067] <HC adsorption amount of silver-supported zeolite D> The HC adsorption amount of silver-supported zeolite D was determined in the same manner as in Example 3. The HC adsorption amount of silver-supported zeolite D was 11.48 mg / g-zeolite.

[0068] Example 5 Production of Silver-Supported Zeolite E 3.04 g of silver nitrate was added to 40 g of distilled water and mixed until dissolved. ２ / Al ２ O ３ 20 g of BEA-type zeolite powder having a silver content of 8.9 mass %, a silver ion content of 0.967 mass %, and an inhibitory silver content of 0.033 mass % were added to the mixture and mixed for 30 minutes. The resulting mixed solution was dried at 250°C for 12 hours or more. The resulting dried powder was then calcined at 400°C for 2 hours to obtain silver-supported zeolite E. The silver content, silver ion content, and inhibitory silver content of silver-supported zeolite E were determined in the same manner as for silver-supported zeolite A. The silver-supported zeolite E had a silver content of 8.9 mass %, a silver ion content of 0.967 mass %, and an inhibitory silver content of 0.033 mass %.

[0069] <HC adsorption amount of silver-supported zeolite E> The HC adsorption amount of silver-supported zeolite E was determined in the same manner as in Example 3. The HC adsorption amount of silver-supported zeolite E was 12.90 mg / g-zeolite.

[0070] Comparative Example 1: Preparation of Silver-Supported Zeolite a: 5.70 g of silver nitrate was added to 40 g of distilled water and mixed until dissolved. ２ / Al ２ O ３20 g of BEA-type zeolite powder having a silver content of 19.2 mass %, a silver ion content of 0.904 mass %, and an inhibitory silver content of 0.096 mass % were added to the mixture and mixed for 30 minutes. The resulting mixed solution was dried at 80°C for 12 hours or more. The resulting dried powder was then calcined at 400°C for 2 hours to obtain silver-supported zeolite a. The silver content, silver ion content, and inhibitory silver content of silver-supported zeolite a were determined in the same manner as for silver-supported zeolite A. The silver-supported zeolite a had a silver content of 19.2 mass %, a silver ion content of 0.904 mass %, and an inhibitory silver content of 0.096 mass %.

[0071] <HC adsorption amount of silver-supported zeolite a> The HC adsorption amount of silver-supported zeolite a was determined in the same manner as in Example 3. The HC adsorption amount of silver-supported zeolite a was 9.60 mg / g-zeolite.

[0072] Comparative Example 2: Preparation of Silver-Supported Zeolite b: 7.56 g of silver nitrate was added to 40 g of distilled water and mixed until dissolved. ２ / Al ２ O ３ 20 g of BEA-type zeolite powder having a silver content of 28 (ratio) was added and mixed for 30 minutes. The resulting mixed solution was dried at 80°C for 12 hours or more. The resulting dried powder was then calcined at 400°C for 2 hours to obtain silver-supported zeolite b. The silver content, silver ion content, and inhibitory silver content of silver-supported zeolite b were determined in the same manner as for silver-supported zeolite A. Silver-supported zeolite b had a silver content of 25.6 mass%, a silver ion content of 0.813, and an inhibitory silver content of 0.187.

[0073] <HC adsorption amount of silver-supported zeolite b> The HC adsorption amount of silver-supported zeolite b was determined in the same manner as in Example 3. The HC adsorption amount of silver-supported zeolite b was 7.95 mg / g-zeolite.

[0074] Comparative Example 3: Preparation of Silver-Supported Zeolite C: 3.04 g of silver nitrate was added to 40 g of distilled water and mixed until dissolved. ２ / Al ２ O ３20 g of BEA-type zeolite powder having a silver content of 8.9 mass %, a silver ion content of 0.907 mass %, and an inhibitory silver content of 0.093 mass % were added to the mixture and mixed for 30 minutes. The resulting mixed solution was dried at 250°C for 12 hours or more. The resulting dried powder was then calcined at 500°C for 2 hours to obtain silver-supported zeolite c. The silver content, silver ion content, and inhibitory silver content of silver-supported zeolite c were determined in the same manner as for silver-supported zeolite A. The silver-supported zeolite c had a silver content of 8.9 mass %, a silver ion content of 0.907 mass %, and an inhibitory silver content of 0.093 mass %.

[0075] Comparative Example 4: Preparation of Silver-Supported Zeolite D 3.04 g of silver nitrate was added to 40 g of distilled water and mixed until dissolved. ２ / Al ２ O ３ 20 g of BEA-type zeolite powder having a silver content of 8.9 mass %, a silver ion content of 0.770, and an inhibitory silver content of 0.230 were obtained by adding 20 g of BEA-type zeolite powder having a silver content of 8.9 mass %, a silver ion content of 0.770, and an inhibitory silver content of 0.230. The resulting mixed solution was dried at 250°C for 12 hours or more. The resulting dried powder was then calcined at 600°C for 2 hours to obtain silver-supported zeolite d. The silver content, silver ion content, and inhibitory silver content of silver-supported zeolite d were determined in the same manner as for silver-supported zeolite A. The silver-supported zeolite d had a silver content of 8.9 mass %, a silver ion content of 0.770, and an inhibitory silver content of 0.230.

[0076] Comparative Example 5: Preparation of Silver-Supported Zeolite e 3.04 g of silver nitrate was added to 40 g of distilled water and mixed until dissolved. ２ / Al ２ O ３ 20 g of BEA-type zeolite powder having a silver content of 8.9 mass %, a silver ion content of 0.764 mass %, and an inhibitory silver content of 0.236 mass % were added to the mixture and mixed for 30 minutes. The resulting mixed solution was dried at 250°C for 12 hours or more. The resulting dried powder was then calcined at 700°C for 2 hours to obtain silver-supported zeolite e. The silver content, silver ion content, and inhibitory silver content of silver-supported zeolite e were determined in the same manner as for silver-supported zeolite A. The silver-supported zeolite e had a silver content of 8.9 mass %, a silver ion content of 0.764 mass %, and an inhibitory silver content of 0.236 mass %.

[0077] Comparative Example 6: Preparation of Silver-Supported Zeolite f 3.04 g of silver nitrate was added to 40 g of distilled water and mixed until dissolved. ２ / Al ２ O ３ 20 g of BEA-type zeolite powder having a silver content of 8.9 mass%, a silver ion content of 0.725 mass%, and an inhibitory silver content of 0.275 mass% were added to the mixture and mixed for 30 minutes. The resulting mixed solution was dried at 250°C for 12 hours or more. The resulting dried powder was then calcined at 800°C for 2 hours to obtain silver-supported zeolite f. The silver content, silver ion content, and inhibitory silver content of silver-supported zeolite f were determined in the same manner as for silver-supported zeolite A. It was confirmed that the silver content of silver-supported zeolite f was 8.9 mass%, the silver ion content was 0.725 mass%, and the inhibitory silver content was 0.275 mass%.

[0078] <HC adsorption amount of silver-supported zeolite f> The HC adsorption amount of silver-supported zeolite f was determined in the same manner as in Example 3. The HC adsorption amount of silver-supported zeolite f was 7.70 mg / g-zeolite.

[0079] Table 1 shows the production conditions and analytical results of the silver-supported zeolites A to E produced in Examples 1 to 5. Table 2 shows the production conditions and analytical results of the silver-supported zeolites a to f produced in Comparative Examples 1 to 6.

[0080]

[0081]

[0082] In Examples 1 to 5 and Comparative Examples 1 to 6, silver-supported zeolite was produced by: (a) subjecting zeolite to ion exchange treatment with an aqueous silver nitrate solution; and (b) calcining the ion-exchanged zeolite.

[0083] (a) In the ion exchange treatment, when the amount of silver nitrate charged was small, the silver ion content tended to be high. When the calcination temperature was 400°C and the silver content was less than 15.0 mass%, a silver-loaded zeolite with a silver ion content of 0.910 or more could be obtained (Examples 1 to 4, Comparative Examples 1 and 2). It is presumed that when the silver content was less than the above amount, the amount of silver present in the zeolite was small, which prevented aggregation of silver particles and the generation of metallic silver and silver clusters, resulting in a high silver ion content.

[0084] (b) When the calcination temperature was less than 500°C, a silver-loaded zeolite with a high silver ion content was obtained (Examples 3 and 5). On the other hand, when the calcination temperature was 500°C or higher, a silver-loaded zeolite with a low silver ion content was obtained (Comparative Examples 3 to 6). It is presumed that low-temperature calcination suppressed the thermal diffusion of silver nitrate contained in the ion-exchanged zeolite, and the silver nitrate decomposed while maintaining its dispersed state, resulting in a high silver ion content.

[0085] Table 3 shows the results of the HC adsorption test for Examples 3 to 5, Comparative Examples 1 and 2, and Comparative Example 6.

[0086]

[0087] In Examples 3 to 5, Comparative Examples 1 and 2, and Comparative Example 6, the HC adsorption amount was measured for silver-supported zeolites having different silver contents and different silver ion content ratios. Figure 1 is a graph comparing the HC adsorption amount and silver ion content ratio of silver-supported zeolites having the same calcination temperature but different silver contents. In Figure 1, when the silver content was below a certain amount and the silver ion content ratio was high, the HC adsorption amount of the silver-supported zeolite tended to be high.

[0088] 2 is a graph comparing the HC adsorption amount and silver ion content of silver-loaded zeolites with the same silver content but different silver ion content rates depending on the firing temperature. In FIG. 2, the silver-loaded zeolite with a higher silver ion content rate exhibited a higher HC adsorption amount.

[0089] It is believed that the silver-loaded zeolites with high HC adsorption capacity all have a large amount of silver ions and a small amount of inhibitory silver (metallic silver and silver clusters), which prevents the blockage of zeolite pores and shows good adsorption properties. It is believed that silver-loaded zeolites with high HC adsorption capacity can be obtained not only by adding silver to zeolite but also by specifying the state of silver loading.

[0090] Example 6 Production of Silver-Supported Zeolite F (Additional Calcination of Silver-Supported Zeolite C) The silver-supported zeolite C obtained in Example 3 was further calcined at 600°C for 2 hours to obtain silver-supported zeolite F. The silver content, silver ion content, and inhibitory silver content of silver-supported zeolite F were determined in the same manner as for silver-supported zeolite A. The silver-supported zeolite F had a silver content of 8.9 mass%, a silver ion content of 0.910, and an inhibitory silver content of 0.090.

[0091] Table 3 shows the analytical results of the silver-loaded zeolite F of Example 6 in comparison with the silver-loaded zeolite C before calcination and the silver-loaded zeolite d calcined at 600°C.

[0092]

[0093] The zeolite obtained by calcination at 400°C maintained the silver ion content even when further calcined at 600°C (Example 6, Comparative Example 4). It is presumed that the silver ions formed and supported by calcination at 400°C do not aggregate to form metallic silver or silver clusters unless a larger energy is applied, at least a larger energy than that required for calcination at 600°C, and therefore the silver ion content was maintained.

[0094] Although preferred embodiments of the silver-loaded zeolite, exhaust gas purification catalyst, exhaust gas purification apparatus, exhaust gas purification method, and method for producing 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-loaded zeolite, wherein the silver is present as at least one of silver ions, silver alone, and a silver compound, the content of silver ions contained in the silver is 0.910 or more, and the content of silver is 15.0 mass% or less with respect to the total weight of the silver-loaded zeolite.

2. The silver-loaded zeolite according to claim 1, wherein the silver-loaded zeolite has a BEA type crystal structure.

3. The silver-loaded zeolite according to claim 1, wherein the SAR of the silver-loaded zeolite is 20 to 40.

4. An exhaust gas purification catalyst comprising the silver-loaded zeolite according to claim 1.

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

6. A method for purifying exhaust gas, comprising purifying exhaust gas with the exhaust gas purification catalyst according to claim 4.

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

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