A silver-based NH3-SCO catalyst, its preparation method and application

Abstract

The application relates to a silver-based NH3-SCO catalyst and a preparation method and application thereof, and provides the silver-based NH3-SCO catalyst, which comprises a carrier and an active substance, the carrier is a mixture of silicates, aluminates and silico-aluminates, and the active substance is nano silver particles; the carrier is in a particle accumulation morphology and is accumulated by 2-5 nm particles, the specific surface area of the carrier is 500-700 m 2 ·g ‑1 , and the particle size of the nano silver particles is 1-10 nm. The low-temperature catalytic activity of the silver-based NH3-SCO catalyst can reach 100 DEG C, one-pot method is adopted during preparation, a plurality of steps are continuously carried out without separation of intermediates starting from simple and easily obtained raw materials, and the synthesis time and cost are reduced.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation technology, and in particular to a silver-based NH3-SCO catalyst, its preparation method, and its application. Background Technology

[0002] In order to control nitrogen oxides (NOx) in vehicle exhaust x Generally, selective catalytic reduction (SCR) technology is used for exhaust gas treatment, which involves injecting automotive urea to generate NH3 as NO. x The reducing agent to achieve NO x The conversion is possible, but in the actual reaction, some of the excess NH3 will escape without reacting.

[0003] Currently, the main technical means to prevent ammonia escape from diesel vehicle exhaust is to selectively catalytically oxidize NH3 into N2 and H2O under the action of a catalyst, while producing as little or no NO as possible. x This refers to selective catalytic oxidation (NH3-SCO) technology. The key to this technology is the NH3-SCO catalyst, such as noble metal catalysts, transition metal and composite oxide catalysts, and molecular sieve oxidants. The active components of noble metal catalysts mainly include gold, silver, and platinum group metals. Supported metal catalysts are generally prepared using traditional impregnation methods, with supports primarily consisting of γ-alumina, silica, titanium dioxide, and molecular sieves.

[0004] In recent years, research on noble metal-based NH3-SCO catalysts has mainly focused on Pt-based, Pd-based, Ru-based, and Ag-based catalysts. Selecting appropriate preparation methods, catalyst supports, and pretreatment techniques is crucial for improving the catalytic performance of noble metal-based NH3-SCO catalysts. Although most noble metal-based NH3-SCO catalysts exhibit excellent catalytic activity, they produce a large amount of nitrogen oxide byproducts, leading to secondary pollution. For example, Pt-supported catalysts have high noble metal content and are expensive. Furthermore, these catalysts have low selectivity for N2 and exhibit side reactions, easily generating byproducts such as NO, N2O, and NO2. These problems and challenges limit their widespread application in the future China VII emission standards.

[0005] Most of the Ag-based NH3-SCO catalysts reported so far have been prepared by impregnation method, with alumina, titanium dioxide, Ti-Si and other materials selected as supports. Among the reported methods, Ag-based NH3-SCO catalysts with nano-alumina as the support have excellent low-temperature SCO catalytic performance, with low-temperature catalytic activity reaching 120℃ and N2 selectivity reaching 90%. However, the low-temperature catalytic activity is still not ideal. Summary of the Invention

[0006] To further reduce the low-temperature catalytic activity of silver-based NH3-SCO catalysts, this invention provides a silver-based NH3-SCO catalyst, its preparation method, and its application.

[0007] The technical solution provided by this invention is as follows:

[0008] In a first aspect, the present invention provides a silver-based NH3-SCO catalyst, comprising a support and an active material, wherein the support is a mixture of silicates, aluminates, and aluminosilicates, and the active material is silver nanoparticles; the support exhibits a particle packing morphology, consisting of particles of 2-5 nm in size, and the specific surface area of ​​the support is 500-700 m². 2 ·g -1 The particle size of the silver nanoparticles is 1-10 nm.

[0009] In some embodiments of the present invention, the silver-based NH3-SCO catalyst contains 1 wt% to 10 wt% of Ag, 1 wt% to 10 wt% of Al, and 40 wt% to 50 wt% of Si.

[0010] In some preferred embodiments of the present invention, the particle size of the silver nanoparticles is 2-8 nm.

[0011] In some preferred embodiments of the present invention, the specific surface area of ​​the carrier is 510-660 m². 2 ·g -1 .

[0012] In some preferred embodiments of the present invention, the silver-based NH3-SCO catalyst contains 1 wt% to 10 wt% of Ag, 1 wt% to 6 wt% of Al, and 43 wt% to 46 wt% of Si.

[0013] In some embodiments of the present invention, the silver-based NH3-SCO catalyst further includes an additive, which includes at least one of Re, Sn, Na, and K, where Re represents rhenium.

[0014] In some embodiments of the present invention, the average particle size of the carrier is 10 to 100 nm.

[0015] In some preferred embodiments of the present invention, the average particle size of the carrier is 40-60 nm.

[0016] In some more preferred embodiments of the present invention, the average particle size of the carrier is 45-55 nm.

[0017] Secondly, the present invention provides a method for preparing a silver-based NH3-SCO catalyst, comprising:

[0018] A precursor mixture is provided; the precursor mixture comprises a silicon source, an aluminum source, a silver source, an organic amine, and a strong base;

[0019] The precursor mixture was aged and crystallized, and the crystallization product was filtered out.

[0020] The crystallized product was calcined at 300-600℃ to obtain a silver-based silicate precursor.

[0021] Silver-based silicate precursors were activated to obtain silver-based NH3-SCO catalysts.

[0022] In some embodiments of the present invention, the organic amine is at least one of tetrapropylammonium hydroxide, tetraethylammonium hydroxide, and N,N,N-trimethyl-1-adamantylammonium hydroxide; the silicon source is at least one of tetraethyl orthosilicate, silicon dioxide, and silica sol; the aluminum source is at least one of alumina, aluminum hydroxide, and aluminum isopropoxide; and the silver source is at least one of silver nitrate, silver chloride, and silver sulfate.

[0023] In some preferred embodiments of the present invention, the organic amine is N,N,N-trimethyl-1-adamantyl ammonium hydroxide.

[0024] In some embodiments of the present invention, the aging temperature is 10-40°C and the time is 1-6 hours.

[0025] In some preferred embodiments of the present invention, the aging temperature is 20-30°C and the time is 1-3 hours.

[0026] In some more preferred embodiments of the present invention, the aging temperature is room temperature and the time is 2 hours.

[0027] In some embodiments of the present invention, the crystallization temperature is 50-200°C and the time is 0.1-96h.

[0028] In some preferred embodiments of the present invention, the crystallization temperature is 100-200°C and the time is 20-96 hours.

[0029] In some more preferred embodiments of the present invention, the crystallization temperature is 160-180°C and the time is 24-96 hours.

[0030] In some embodiments of the present invention, the calcination temperature is 500-600°C, the time is 5-6 hours, and the atmosphere is air.

[0031] In some embodiments of the present invention, the activation temperature is 400-700°C, the time is 5-10 hours, and the atmosphere is a hydrogen-containing atmosphere.

[0032] In some preferred embodiments of the present invention, the activation temperature is 400-500°C, the time is 5-7 hours, and the atmosphere is a hydrogen-containing atmosphere.

[0033] Thirdly, the present invention provides a method for treating NH3-containing waste gas, wherein the NH3-containing waste gas is passed through the above-mentioned silver-based NH3-SCO catalyst at 150-200°C under O2 conditions.

[0034] In some embodiments of the present invention, the NH3-containing exhaust gas is automobile exhaust gas.

[0035] Fourthly, the present invention provides an automotive exhaust purification device, comprising the aforementioned silver-based NH3-SCO catalyst.

[0036] Compared with the prior art, the beneficial effects of the present invention include:

[0037] 1. The silver-based NH3-SCO catalyst provided by this invention exhibits excellent low-temperature activity (T before and after hydrothermal aging). 90 The temperature ranges from 150 to 200°C, and this silver-based NH3-SCO catalyst also exhibits excellent N2 selectivity (>80%). Furthermore, silver, as a semi-precious metal, is much cheaper than other precious metals, and the high dispersion and low loading of metallic silver on the catalyst support result in low overall catalyst cost.

[0038] 2. The silver-based NH3-SCO catalyst preparation method provided by the present invention adopts a one-pot method. This preparation method starts from simple and readily available raw materials, does not go through the separation of intermediates, and carries out multiple steps of reaction continuously, which reduces the synthesis time and cost. The preparation method is simple in steps and easy to operate, and has dual benefits of being economical and environmentally friendly. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 The images are scanning electron microscope images of the sample morphology; where: (a) Ag / silicate-1; (b) Ag / silicate-2; (c) Ag / silicate-3; (d) Ag / silicate-4.

[0041] Figure 2 Transmission electron micrographs showing the dispersion and size of metallic silver; where: (a) Ag / silicate-1; (b) Ag / silicate-2; (c) Ag / silicate-3; (d) Ag / silicate-4.

[0042] Figure 3 STEM-EDS elemental distribution and analysis diagram of Ag / silicate-4.

[0043] Figure 4 The graph shows the selective oxidation activity of ammonia by the silver-based NH3-SCO catalyst; where: (a) ammonia conversion rate; (b) nitrogen selectivity; test conditions: ammonia 400 ppm, oxygen 10%, nitrogen balance, total flow rate = 500 mL / min, space velocity 300000 mL·g -1 ·h -1 .

[0044] Figure 5 To determine the NH3-SCO conversion rate of a silver-based NH3-SCO catalyst at low space velocities; test conditions: ammonia 400 ppm, oxygen 10%, nitrogen balance, total flow rate = 50 mL / min, space velocity 30000 mL·g -1 ·h -1 . Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0046] To improve the low-temperature activity of silver-based NH3-SCO catalysts, this invention provides a silver-based NH3-SCO catalyst comprising a support and an active material. The support is a mixture of silicates, aluminates, and aluminosilicates, and the active material is silver nanoparticles. The support exhibits a particle packing morphology, consisting of particles with a size of 2-5 nm, and has a specific surface area of ​​500-700 m². 2 ·g -1 The particle size of the silver nanoparticles is 1-10 nm.

[0047] This silver-based NH3-SCO catalyst can selectively oxidize NH3 to N2 and H2O, while producing as little or no NO as possible. x That is, to selectively react according to equation (1), while avoiding the reactions shown in equations (2) to (4) as much as possible:

[0048] 4 NH3 + 3 O2 → 2 N2 + 6 H2O (1)

[0049] 4 NH3 + 5 O2 → 4 NO + 6 H2O (2)

[0050] 2 NH3 + 2 O2 → N2O + 3 H2O (3)

[0051] 4 NH3 + 7 O2 → 4 NO2 + 6 H2O (4)

[0052] Because the support is composed of 2-5 nm particles, it has a large specific surface area and a strong adsorption capacity for NH3. After NH3 is adsorbed onto the support, the nano-silver particles selectively catalyze the oxidation of NH3, converting it into N2. Compared with existing silver-based NH3-SCO catalysts, the silver-based NH3-SCO catalyst provided by this invention has a larger specific surface area and higher silver particle dispersion, thus exhibiting higher low-temperature activity.

[0053] In some embodiments of the present invention, the silver-based NH3-SCO catalyst contains 1 wt% to 10 wt% of Ag, 1 wt% to 10 wt% of Al, and 40 wt% to 50 wt% of Si.

[0054] In some preferred embodiments of the present invention, the particle size of the silver nanoparticles is 2-8 nm.

[0055] In some preferred embodiments of the present invention, the specific surface area of ​​the carrier is 510-660 m². 2 ·g -1 .

[0056] In some preferred embodiments of the present invention, the silver-based NH3-SCO catalyst contains 1 wt% to 10 wt% of Ag, 1 wt% to 6 wt% of Al, and 43 wt% to 46 wt% of Si.

[0057] In some embodiments of the present invention, the silver-based NH3-SCO catalyst further includes an additive, which includes at least one of Re, Sn, Na, and K, where Re represents rhenium.

[0058] In some embodiments of the present invention, the average particle size of the carrier is 10 to 100 nm.

[0059] In some preferred embodiments of the present invention, the average particle size of the carrier is 40-60 nm.

[0060] In some more preferred embodiments of the present invention, the average particle size of the carrier is 45-55 nm.

[0061] The method for preparing the silver-based NH3-SCO catalyst provided by this invention includes:

[0062] A precursor mixture is provided; the precursor mixture comprises a silicon source, an aluminum source, a silver source, an organic amine, and a strong base;

[0063] The precursor mixture was aged and crystallized, and the crystallization product was filtered out.

[0064] The crystallized product was calcined at 300-600℃ to obtain a silver-based silicate precursor.

[0065] Silver-based silicate precursors were activated to obtain silver-based NH3-SCO catalysts.

[0066] In some embodiments of the present invention, the organic amine is at least one of tetrapropylammonium hydroxide, tetraethylammonium hydroxide, and N,N,N-trimethyl-1-adamantylammonium hydroxide; the silicon source is at least one of tetraethyl orthosilicate, silicon dioxide, and silica sol; the aluminum source is at least one of alumina, aluminum hydroxide, and aluminum isopropoxide; and the silver source is at least one of silver nitrate, silver chloride, and silver sulfate.

[0067] In some preferred embodiments of the present invention, the organic amine is N,N,N-trimethyl-1-adamantyl ammonium hydroxide.

[0068] In some embodiments of the present invention, the aging temperature is 10-40°C and the time is 1-6 hours. During the aging process, the material can be stirred or left to stand.

[0069] In some preferred embodiments of the present invention, the aging temperature is 20-30°C, the time is 1-3 hours, and the aging is carried out by static aging.

[0070] In some more preferred embodiments of the present invention, the aging temperature is room temperature and the time is 2 hours.

[0071] In some embodiments of the present invention, the crystallization temperature is 50-200°C and the time is 0.1-96h.

[0072] In some preferred embodiments of the present invention, the crystallization temperature is 100-200°C and the time is 20-96 hours.

[0073] In some more preferred embodiments of the present invention, the crystallization temperature is 160-180°C and the time is 24-96 hours.

[0074] In some embodiments of the present invention, the calcination temperature is 500-600°C, the time is 5-6 hours, and the atmosphere is air.

[0075] In some embodiments of the present invention, the activation temperature is 400-700°C, the time is 5-10 hours, and the atmosphere is a hydrogen-containing atmosphere. The hydrogen-containing atmosphere is hydrogen, or any volume ratio of hydrogen to oxygen, or any volume ratio of hydrogen to nitrogen.

[0076] In some preferred embodiments of the present invention, the activation temperature is 400-500°C, the time is 5-7 hours, and the atmosphere is hydrogen.

[0077] The present invention provides a method for treating NH3-containing waste gas, wherein the NH3-containing waste gas is passed through the above-mentioned silver-based NH3-SCO catalyst at 150-200°C under O2 conditions.

[0078] In some embodiments of the present invention, the NH3-containing exhaust gas is automobile exhaust gas, and the O2 in the O2-containing condition comes from the O2 in automobile exhaust gas or O2 in the air.

[0079] The automotive exhaust purification device provided by the present invention includes the above-mentioned silver-based NH3-SCO catalyst.

[0080] The technical solution of the present invention will be described in detail below through specific embodiments:

[0081] Example 1

[0082] This embodiment provides a method for preparing a silver-based NH3-SCO catalyst, the specific steps of which are as follows:

[0083] (1) Providing a precursor mixture: An aluminum source, a silicon source, sodium hydroxide and a silver source are added to an organic amine aqueous solution in sequence; the precursor mixture contains 3.7g silica sol (25wt.%), 0.02g silver nitrate, 1.0g N,N,N-trimethyl-1-adamantyl ammonium hydroxide, 1.7g tetraethyl ammonium hydroxide, 0.8g sodium hydroxide and 3g water;

[0084] (2) Stir the precursor mixture at room temperature for 2 hours, then crystallize it in a rotary oven at 160°C for 76 hours, and filter out the solid product.

[0085] (3) The solid product was calcined at 600°C in air for 6 hours to obtain a silver-based silicate precursor.

[0086] (4) The silver-based silicate precursor was activated at 400°C in a hydrogen atmosphere for 5 hours to obtain the silver-based NH3-SCO catalyst, denoted as Ag / silicate-1.

[0087] Example 2

[0088] This embodiment provides a method for preparing a silver-based NH3-SCO catalyst, the specific steps of which are as follows:

[0089] (1) Provide a precursor mixture: Add aluminum source, silicon source, sodium hydroxide and silver source to the organic amine aqueous solution in sequence; the precursor mixture contains 3.7g silica sol (25wt.%), 0.02g silver nitrate, 1.7g tetraethylammonium hydroxide, 1.0g N,N,N-trimethyl-1-adamantylammonium hydroxide, 0.08g sodium hydroxide, 0.7g water; and 0.1g aluminum hydroxide.

[0090] (2) Stir the precursor mixture at room temperature for 2 hours, then crystallize it in a rotary oven at 160°C for 96 hours, and filter out the solid product.

[0091] (3) The solid product was calcined at 500°C in air for 6 hours to obtain the silver-based silicate precursor.

[0092] (4) The silver-based silicate precursor was activated at 400°C in a hydrogen atmosphere for 5 hours to obtain the silver-based NH3-SCO catalyst, denoted as Ag / silicate-2.

[0093] Example 3

[0094] This embodiment provides a method for preparing a silver-based NH3-SCO catalyst, the specific steps of which are as follows:

[0095] (1) Providing a precursor mixture: adding an aluminum source, a silicon source, sodium hydroxide and a silver source to an organic amine aqueous solution in sequence; the precursor mixture contains 3.7 g silica sol (25 wt.%), 0.2 g aluminum hydroxide, 0.1 g silver nitrate, 2.0 g N,N,N-trimethyl-1-adamantyl ammonium hydroxide, 0.8 g sodium hydroxide and 7 g water;

[0096] (2) Stir the precursor mixture at room temperature for 2 hours, then crystallize it in a rotary oven at 120°C for 48 hours, and filter out the solid product.

[0097] (3) The solid product was calcined at 600°C in air for 6 hours to obtain a silver-based silicate precursor.

[0098] (4) The silver-based silicate precursor was activated at 400°C in a hydrogen atmosphere for 5 hours to obtain the silver-based NH3-SCO catalyst, denoted as Ag / silicate-3.

[0099] Example 4

[0100] This embodiment provides a method for preparing a silver-based NH3-SCO catalyst, the specific steps of which are as follows:

[0101] (1) Providing a precursor mixture: An aluminum source, a silicon source, sodium hydroxide, and a silver source are added to an organic amine aqueous solution in sequence; the precursor mixture contains 3.7 g silica sol (25 wt.%), 0.5 g aluminum hydroxide, 0.15 g silver nitrate, 1.7 g N,N,N-trimethyl-1-adamantyl ammonium hydroxide, 0.8 g sodium hydroxide, 0.05 g NH4ReO4, and 3 g water;

[0102] (2) Stir the precursor mixture at room temperature for 2 hours, then crystallize it in a rotary oven at 170°C for 24 hours, and filter out the solid product.

[0103] (3) The solid product was calcined at 600°C in air for 6 hours to obtain a silver-based silicate precursor.

[0104] (4) The silver-based silicate precursor was activated at 400°C in a hydrogen atmosphere for 5 hours to obtain the silver-based NH3-SCO catalyst, denoted as Ag / silicate-4.

[0105] Comparative Example 1

[0106] This embodiment provides a method for preparing a silver-based NH3-SCO catalyst, the specific steps of which are as follows:

[0107] (1) Providing a precursor mixture: An aluminum source, a silicon source, sodium hydroxide and a silver source are added to an organic amine aqueous solution in sequence; the precursor mixture contains 3.7 g silica sol (25 wt.%), 0.3 g aluminum hydroxide, 0.15 g silver nitrate, 1.0 g N,N,N-trimethyl-1-adamantyl ammonium hydroxide, 0.1 g sodium hydroxide and 6 g water;

[0108] (2) Stir the precursor mixture at room temperature for 2 hours, then crystallize it in a rotary oven at 160°C for 76 hours, and filter out the solid product.

[0109] (3) The solid product was calcined at 600°C in air for 6 hours to obtain a silver-based silicate precursor.

[0110] (4) The silver-based silicate precursor was activated at 400°C in a hydrogen atmosphere for 5 hours to obtain a silver-based NH3-SCO catalyst, denoted as Ag / silicate-5.

[0111] The silver-based NH3-SCO catalyst sample obtained in this example has poor activity and very low solid yield.

[0112] Comparative Example 2

[0113] This embodiment provides a method for preparing a silver-based NH3-SCO catalyst, the specific steps of which are as follows:

[0114] (1) Providing a precursor mixture: adding an aluminum source, a silicon source, sodium hydroxide and a silver source to an organic amine aqueous solution in sequence; the precursor mixture contains 3.7g silica sol (25wt.%), 0.3g aluminum hydroxide, 0.15g silver nitrate, 3.0g N,N,N-trimethyl-1-adamantyl ammonium hydroxide, 0.5g sodium hydroxide and 1g water.

[0115] (2) Stir the precursor mixture at room temperature for 2 hours, then crystallize it in a rotary oven at 160°C for 76 hours, and filter out the solid product.

[0116] (3) The solid product was calcined at 600°C in air for 6 hours to obtain the silver-based silicate precursor.

[0117] (4) The silver-based silicate precursor was activated at 400°C in a hydrogen atmosphere for 5 hours to obtain the silver-based NH3-SCO catalyst, denoted as Ag / silicate-6.

[0118] The silver-based NH3-SCO catalyst sample obtained in this comparative example has a high solid yield, but the NH3-SCO activity is poor.

[0119] Example 5 Sample Testing

[0120] Figure 1 Scanning electron microscope (SEM) images of the silver-based NH3-SCO catalysts prepared in Examples 1-4, as shown below. Figure 1 As shown, the silver-based NH3-SCO catalyst exhibits a particle-stacking morphology, consisting of 2-5 nm nanoparticles. The average particle size of the Ag / silicate-1 sample is 200-300 nm, while the average particle size of the Ag / silicate-2, Ag / silicate-3, and Ag / silicate-4 samples is around 50 nm, which is much smaller than the average particle size of the Ag / silicate-1 sample. This indicates that the increased Al content promotes the dispersion of Ag particles.

[0121] Transmission electron microscopy (TEM) images of Ag / silicate samples and particle size distribution of Ag species, as shown in... Figure 2 As shown, Ag was highly dispersed in Ag / silicate-1, Ag / silicate-2, Ag / silicate-3, and Ag / silicate-4 samples. The sizes of Ag particles in silicate-1 to silicate-4 were 2.1 nm, 3.2 nm, 5.5 nm, and 7.4 nm, respectively.

[0122] The elements Ag, Si, Al, O, and Na in Ag / silicate-4 samples were detected using scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDS). Figure 3 As shown, the Si, Al, O and Na elements in the Ag / silicate-4 sample are uniformly distributed, and highly dispersed and uniformly loaded Ag clusters can be seen on the sample surface.

[0123] The performance of the silver-based NH3-SCO catalysts prepared in Examples 1-4 was tested, such as... Figure 4 As shown. Among them, the T values ​​of Ag / silicate-1 and Ag / silicate-2 are... 90 (The temperature at which NH3 conversion reaches 90%) is approximately 175℃, and the T for Ag / silicate-3 and Ag / silicate-4... 90 At approximately 150℃, the low-temperature activity is further improved. Furthermore, all four silver-based NH3-SCO catalyst samples exhibited excellent N2 selectivity, exceeding 80%. Among them, Ag / silicate-4 demonstrated exceptionally excellent low-temperature activity and nitrogen selectivity.

[0124] Table 1 Physicochemical properties of various silver-based NH3-SCO catalyst samples

[0125]

[0126] The total surface area of ​​the silver-based NH3-SCO catalyst was measured using nitrogen adsorption-desorption, and the mass percentages (wt%) of Si, Al, and Ag in the silver-based NH3-SCO catalyst were determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The relevant properties are shown in Table 1. Each silver-based NH3-SCO catalyst sample had different Si and Al contents, with Ag / silicate-1 containing no aluminum. Ag / silicate-1 and Ag / silicate-4 had the same silicon content (1.1 wt%) and similar Ag particle size (2.1 nm). The mass percentage of Ag gradually increased in Ag / silicate-3 (5.5 wt%) and Ag / silicate-4 (7.4 wt%). Ag particle size increased with increasing Ag content. Overall, the total specific surface area of ​​the silver-based NH3-SCO catalyst samples decreased with increasing Ag loading, as Ag particles occupied the micropores and outer surface of the silver-based NH3-SCO catalyst support.

[0127] The NH3-SCO conversion of Ag / silicate-2 was determined at low space velocities. Test conditions: ammonia 400 ppm, oxygen 10%, nitrogen balance, total flow rate = 50 mL / min, space velocity 30000 mL·g⁻¹. -1 ·h -1 ,like Figure 5 As shown, the T of Ag / silicate-2 90 The temperature at which NH3 conversion reaches 90% is approximately 100℃, and its low-temperature activity is outstanding.

[0128] In the description of this specification, the references to terms such as "one embodiment / mode," "some embodiments / modes," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment / mode or example is included in at least one embodiment / mode or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment / mode or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments / modes or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments / modes or examples described in this specification, as well as the features of different embodiments / modes or examples.

[0129] It should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. In this application, "a plurality of" means at least two, such as two, three, etc., unless otherwise expressly specified.

[0130] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. An application of a silver-based NH3-SCO catalyst for the selective oxidation of NH3 to N2 and H2O, characterized in that: The silver-based NH3-SCO catalyst comprises a support and an active material. The support is a mixture of silicates, aluminates, and aluminosilicates, and the active material is silver nanoparticles. The support exhibits a particle packing morphology, consisting of particles with a size of 2-5 nm, and has a specific surface area of ​​500-700 m². 2 ·g -1 The particle size of the silver nanoparticles is 1-10 nm; The preparation method of the silver-based NH3-SCO catalyst includes: A precursor mixture is provided; the precursor mixture comprises a silicon source, an aluminum source, a silver source, an organic amine, and a strong base; The precursor mixture was aged and crystallized, and the crystallization product was filtered out. The crystallized product was calcined at 300-600℃ to obtain a silver-based silicate precursor. Silver-based silicate precursors were activated to obtain silver-based NH3-SCO catalysts.

2. The application according to claim 1, characterized in that: In the silver-based NH3-SCO catalyst, the proportion of Ag element is 1wt%~10wt%, the proportion of Al element is 1wt%~10wt%, and the proportion of Si element is 40wt%~50wt%.

3. The application according to claim 1, characterized in that: The average particle size of the carrier is 10~100nm.

4. The application according to claim 1, characterized in that: The silver-based NH3-SCO catalyst further includes an auxiliary agent, which includes at least one of Re, Sn, Na, and K.

5. The application according to claim 1, characterized in that: The organic amine is at least one of tetrapropylammonium hydroxide, tetraethylammonium hydroxide, and N,N,N-trimethyl-1-adamantylammonium hydroxide; the silicon source is at least one of tetraethyl orthosilicate, silicon dioxide, and silica sol; the aluminum source is at least one of alumina, aluminum hydroxide, and aluminum isopropoxide; and the silver source is at least one of silver nitrate, silver chloride, and silver sulfate.

6. The application according to claim 1, characterized in that: The crystallization temperature is 50-200℃ and the time is 0.1-96h.

7. The application according to claim 1, characterized in that: The activation temperature is 500-700℃, the time is 5-10h, and the atmosphere is a hydrogen-containing atmosphere.

8. The application according to claim 1, characterized in that: At 150~200℃, the NH3-containing waste gas is passed through the silver-based NH3-SCO catalyst under O2 conditions.

Images