A zero-gas generator catalyst and a method for preparing the same

Abstract

This invention belongs to the field of catalysis technology, specifically relating to a zero-gas generator catalyst and its preparation method. The preparation method includes the following steps: 1) Adding urea, a metal salt additive, and boehmite powder sequentially to water, followed by an acid solution. After mixing evenly, a sol slurry modified with the metal additive is obtained; a gelling agent is further added to obtain a mixed sol; 2) Dropping the mixed sol into a hot oil column to form spheres, followed by washing, drying, and calcination to obtain γ-Al₂O₃ microspheres modified with the metal oxide additive; 3) Preheating a noble metal precursor solution and adding it to a coating machine, then adding the γ-Al₂O₃ microspheres modified with the metal oxide additive, drying the solution under rotating conditions at 60-90°C to obtain an impregnated sample, which is further dried and calcined to obtain the final product. This zero-gas generator catalyst has advantages such as high catalytic activity, good thermal stability, and long service life, and can eliminate total hydrocarbons (based on methane) to below 10 ppb.

Description

Technical Field

[0001] This invention belongs to the field of catalysis technology, specifically relating to a zero-gas generator catalyst and its preparation method. Background Technology

[0002] Zero gas generators effectively filter out moisture, SO2, nitrogen oxides, and hydrocarbon gases such as alkanes, aromatics, alkenes, alkynes, alcohols, aldehydes, ethers, and esters from the air. They are a crucial component in air quality monitoring systems, providing sufficiently stable and dry zero gas for various systems and are widely used in environmental monitoring stations and gas analyzers. According to the "Technical Regulations for Continuous Automatic Monitoring of Non-Methane Total Hydrocarbons in Ambient Air" (Document No. 61 of 2021 issued by the National Ecological and Environmental Monitoring Center), a hydrocarbon removal device must be installed before the gas source enters the analysis unit, requiring a total hydrocarbon (methane) concentration ≤10 ppb. Therefore, extremely high requirements are placed on zero gas generators.

[0003] Among many hydrocarbons, methane (CH4) is the most stable hydrocarbon and is usually difficult to activate or oxidize. Therefore, the catalyst in the zero gas generator must have high activity and stability. The catalyst module is often small in size but has a large gas flow rate, especially in portable models. Generally, the catalyst particle size is required to be less than 2 mm and about 20 grams are required. Therefore, the catalyst module needs to be as small as possible while meeting the requirements, and the catalyst should have high strength and not be easily pulverized, otherwise it will easily clog the pipeline and affect the normal operation of the equipment.

[0004] Alumina is widely used as a catalyst support due to its excellent properties such as high specific surface area, good adsorption, thermal stability, and surface acidity. Currently, patented catalysts and their preparation methods for low-concentration methane catalytic combustion are all monolithic catalysts or alumina supports made of powder or spherical shapes using a rolling method. These materials are prone to powder loss and have poor strength. In contrast, alumina spheres prepared by the oil column forming method have good sphericity, smooth surfaces, high crushing strength, and are less prone to powder loss, making them most suitable for use as catalyst supports in zero-gas generators. Patent CN201110388703.2 reports a catalyst for low-concentration methane catalytic combustion, but the powder support is unsuitable for use as a catalyst support in zero-gas generators, and the reaction temperature is relatively high at 600℃. Patent CN201110388703.2 also reports a palladium-based catalyst treated with high-temperature aging, but the support is powder, and a large amount of precious metals is used, resulting in high operating costs for the user. Therefore, developing a zero-gas generator catalyst with low precious metal content and high activity is of great significance. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a zero-gas generator catalyst and its preparation method. This catalyst has the advantages of high catalytic activity, good thermal stability, and long service life, and can eliminate methane to below 10 ppb.

[0006] To achieve the objectives of this invention, the following technical solution is specifically adopted:

[0007] A method for preparing a zero-gas generator catalyst includes the following steps:

[0008] 1) Add urea, auxiliary metal salt and pseudoboehmite powder to water in sequence and mix evenly. Then add acid solution and mix evenly to obtain auxiliary metal modified sol slurry. The alumina content in the sol slurry is 15-25 wt%. Further add gelling agent to obtain mixed sol.

[0009] The auxiliary metal salt is selected from one or more of the soluble salts of cerium, lanthanum, potassium, sodium, magnesium and barium;

[0010] 2) The mixed sol obtained in step 1) is dropped into a hot oil column at 90-110℃ to form spheres. The formed spheres are then removed, washed, dried and calcined to obtain γ-Al2O3 spheres modified with auxiliary metal oxides, wherein the content of auxiliary metal oxides is 5-30wt%.

[0011] 3) After preheating the aqueous solution of the precious metal precursor, add it to the coating machine, then add the γ-Al2O3 microspheres modified with metal oxide as an auxiliary agent, and dry the solution under rotation at 60-90℃ to obtain the impregnated sample. Further drying and calcination will yield the zero gas generator catalyst, in which the content of precious metal elements is 0.1-2wt%.

[0012] Preferably, in step 1), the mass fraction of the solute in the acid solution is 15-25%.

[0013] Preferably, in step 1), the acid solution is selected from one or more of hydrochloric acid, nitric acid, citric acid, formic acid, and acetic acid.

[0014] Preferably, in step 1), the mass ratio of urea to alumina in the pseudoboehmite powder is 40-70:100.

[0015] Preferably, in step 1), the auxiliary metal salt is selected from one or more of soluble salts of cerium and soluble salts of lanthanum; more preferably, the soluble salt includes at least one of nitrates and chlorides.

[0016] Preferably, in step 1), the gelling agent is hexamethylenetetramine, and the amount of gelling agent added is 6-10% based on the mass of alumina in the pseudoboehmite powder.

[0017] Preferably, in step 2), the oil phase in the hot oil column is selected from at least one of medical lubricating oil, liquid paraffin oil, and white oil.

[0018] Preferably, in step 2), the drying temperature is 90-120℃ and the time is 2-4h.

[0019] Preferably, in step 2), the calcination temperature is 550-650℃ and the time is 2-4h.

[0020] Preferably, in step 2), the particle size of the γ-Al2O3 microspheres modified with the auxiliary metal oxide is 1.6-2 mm.

[0021] Preferably, in step 3), the noble metal precursor is a palladium precursor or a mixture of palladium and platinum precursors.

[0022] More preferably, the platinum precursor is selected from one or more of chloroplatinic acid, platinum nitrate, and dinitrodiamineplatinum;

[0023] The palladium precursor is selected from one or more of palladium chloride, palladium nitrate, and palladium acetate.

[0024] Preferably, in step 3), the preheating is to preheat to 60-90°C.

[0025] Preferably, in step 3), the calcination temperature is 450-600℃ and the time is 2-4h.

[0026] Preferably, the step of aging the zero gas generator catalyst obtained in step 3) is also included:

[0027] The zero-gas generator catalyst is placed in a methane-containing gas environment and aged at 400-600℃ for 2-6 hours.

[0028] The present invention also provides a zero gas generator catalyst, which is prepared by the above preparation method.

[0029] Compared with the prior art, the present invention has the following advantages and effects:

[0030] (1) This invention provides a method for preparing a zero-gas generator catalyst, wherein the prepared catalyst comprises a spherical support, an active component, and auxiliary components. The noble metal element in the active component can play a role in the decomposition and elimination of hydrocarbons.

[0031] The spherical support is composed of γ-Al₂O₃ microspheres modified with auxiliary metal oxides, prepared using the oil droplet method, which significantly improves the strength and stability of the support. The auxiliary metal oxides help enhance the catalyst's ability to store and release oxygen and activate oxygen, thereby improving the catalyst's catalytic activity and maintaining the stability of the catalyst's active structure during the reaction process.

[0032] (2) The present invention provides a method for preparing a zero gas generator catalyst. The precious metal solution is preheated and poured into a coating machine. The solution is dried by heating and rotating the coating machine, which can quickly dry the carrier, so that the active components remain on the surface of the carrier to the maximum extent, which is beneficial to the dispersion of precious metals and improves the mechanical properties of the catalyst after impregnation.

[0033] (3) The present invention provides a method for preparing a catalyst for a zero gas generator. The catalyst obtained is used in a zero gas generator and has the advantages of high strength, no powder shedding, high catalytic activity, good thermal stability and long service life. It can not only achieve efficient purification of hydrocarbons, but also maintain the stability of the physicochemical properties of the catalyst after 1000 hours.

[0034] (4) This invention provides a method for preparing a catalyst for a zero-gas generator. The method involves preparing an additive-modified support, impregnating the catalyst, and calcining and aging it using an oil-drop method. The resulting catalyst exhibits better stability and catalytic activity, making it highly suitable for use in zero-gas generator equipment. Furthermore, the method includes a molding process, facilitating direct industrial application. Detailed Implementation

[0035] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to specific embodiments. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in the art, or in accordance with the product manual.

[0036] Example 1

[0037] (1) Carrier preparation

[0038] Aluminum sol was prepared using the sol-gel method. 37.3 g of urea and 17.4 g of cerium nitrate hexahydrate were added to 160 g of distilled water. After stirring evenly on a magnetic stirrer, 90 g of boehmite powder (specific surface area 254 m²) was slowly added. 2 / g (alumina dry basis weight 69%), stirred at 100 rpm for 30 min, then 23.0 mL of 20% nitric acid solution was added, and stirring was continued for 2 h to form a stable aluminum sol with Ce additive, at which point the alumina content in the sol slurry was about 20 wt%; then 24.8 g of 20% hexamethylenetetramine solution was added, and stirring was continued for 10 min to obtain a mixed sol;

[0039] The hot oil column bath temperature was set to 98℃ and the oil phase thickness was 2 meters. The mixed sol was dropped into the hot oil column to form spheres, which were then directly removed from the bottom of the device. At this point, the spheres had a diameter of 1.6-2 mm. They were washed with water, dried at 120℃ for 2 hours, and calcined at 600℃ for 4 hours to obtain Ce-modified γ-Al2O3 microspheres with a CeO2 weight content of 10%.

[0040] (2) Catalyst preparation

[0041] Take 3.3g of palladium nitrate solution with a mass fraction of 10% and 1.1g of platinum nitrate solution with a mass fraction of 15%, add them to 90g of deionized water to obtain a noble metal precursor solution. Preheat the solution to about 80℃, then pour it into a coating machine (Nanjing Huaiteng Machinery Design Co., Ltd., BY-300). Then pour 100g of alumina microspheres obtained in step (1) into the noble metal precursor solution. Dry the solution at 70℃ and 15 rpm. Finally, dry it in an oven at 120℃ for 4h. Then, calcine it at 500℃ for 2h at a heating rate of 3 / min to obtain a catalyst with a noble metal element content of 0.5wt% and a platinum-palladium ratio of 1:2.

[0042] (3) Catalyst aging

[0043] The catalyst was placed in a tube furnace, and 0.5% CH4 gas was introduced into the catalyst. The background atmosphere was air, the temperature was 400℃, and the time was 2h.

[0044] Example 2

[0045] Based on Example 1, in step (1), 17.4 g of cerium nitrate hexahydrate was added instead of 17.5 g of lanthanum nitrate hexahydrate. Other operations were the same as in Example 1.

[0046] Example 3

[0047] Based on Example 1, the 3.3g palladium nitrate solution with a mass fraction of 10% and the 1.1g platinum nitrate solution with a mass fraction of 15% in step (2) were replaced with 6.6g palladium nitrate solution with a mass fraction of 10% and the 2.2g platinum nitrate solution with a mass fraction of 15%. Other operations were the same as in Example 1.

[0048] Example 4

[0049] Based on Example 1, the 0.5% CH4 gas in step (3) is changed to 3.5% CH4 gas, and the other operations are the same as in Example 3.

[0050] Example 5

[0051] Based on Example 1, the temperature of 400°C and time of 2h in step (3) are changed to 600°C and time of 6h, and other operations are the same as in Example 3.

[0052] Comparative Example 1

[0053] Compared with Example 1, the only difference is that the auxiliary metal salt cerium nitrate hexahydrate is not added in step (1).

[0054] Comparative Example 2

[0055] Compared with Example 1, the only difference is that in step (2), 3.3g of palladium nitrate solution with a mass fraction of 10% and 1.1g of platinum nitrate solution with a mass fraction of 15% are replaced with 5.0g of palladium nitrate solution with a mass fraction of 10%.

[0056] Comparative Example 3

[0057] Compared with Example 1, the only difference is that step (2) does not use a coating machine. The specific steps are as follows: take 3.3g of palladium nitrate solution with a mass fraction of 10% and 1.1g of platinum nitrate solution with a mass fraction of 15%, add them to 90g of deionized water to obtain a noble metal precursor solution. Pour 100g of alumina microspheres obtained in step (1) into the above noble metal precursor solution, mix evenly, and then put them in an oven to dry at 120℃ for 4h. After that, heat the oven to 500℃ at a heating rate of 3 / min and calcine for 2h to obtain the catalyst.

[0058] Comparative Example 4

[0059] Compared with Example 1, the only difference is that step (3) is omitted.

[0060] Comparative Example 5

[0061] Compared with Example 1, the only difference is that commercially available alumina microspheres are used in step (1). Specifically, 25.2g of cerium nitrate hexahydrate is added to 54mL of water, and then 90g of commercially available γ-Al2O3 microspheres (1.6-2mm) prepared by the rolling ball method are added. After mixing evenly, the mixture is placed in an oven and dried at 120℃ for 4h. Then, the temperature is increased to 600℃ at a heating rate of 3 / min and calcined for 4h to obtain Ce-modified γ-Al2O3 microspheres with a CeO2 weight content of 10%.

[0062] Test case

[0063] The test gas was an HC hydrocarbon, with methane as a representative substance, at a concentration of 50 ppm, and the gas hourly space velocity (GHSV) was 10,000 h⁻¹. -1 A commercially available zero-gas generator catalyst module device was used. The reaction tube was cylindrical with an inner diameter of 12 mm and a height of 300 mm. Stainless steel mesh sheets with a diameter of 12 mm and an aperture of 1 mm were placed at both ends inside the reaction tube. The stainless steel inlet and outlet pipes at both ends had an inner diameter of 3 mm. 20 grams of catalyst were placed in the reaction tube, and the temperature of the reaction tube was controlled at 400℃ using a tube furnace. The concentration of methane after elimination by the catalyst was measured using gas chromatography. The physical parameters of the prepared catalyst are shown in Table 1, and the test results are shown in Table 2.

[0064] Table 1 Physical parameters of each catalyst

[0065] serial number Particle size (mm) Crushing strength (N / particle) Wear rate (%) Example 1 1.6-2 45.3 0.56 Example 2 1.6-2 43.6 0.53 Example 3 1.6-2 41.5 0.60 Example 4 1.6-2 43.1 0.52 Example 5 1.6-2 44.9 0.54 Comparative Example 1 1.6-2 42.6 0.55 Comparative Example 2 1.6-2 42.8 0.56 Comparative Example 3 1.6-2 35.2 1.35 Comparative Example 4 1.6-2 42.4 0.57 Comparative Example 5 1.6-2 27.6 4.74

[0066] Table 2 Results of Elimination Capacity Tests for Each Catalyst

[0067]

[0068] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method of preparing a zero-gas generator catalyst, characterized by, Includes the following steps: 1) Add urea, auxiliary metal salt and pseudoboehmite powder to water in sequence and mix evenly. Then add acid solution and mix evenly to obtain auxiliary metal modified sol slurry. The alumina content in the sol slurry is 15-25 wt%. Further add gelling agent to obtain mixed sol. In step 1), the mass ratio of urea to alumina in the pseudoboehmite powder is 40-70:100; In step 1), the auxiliary metal salt is selected from one or more of the soluble salts of cerium and soluble salts of lanthanum. In step 1), the gelling agent is hexamethylenetetramine; based on the mass of alumina in the pseudoboehmite powder, the amount of gelling agent added is 6-10%; 2) The mixed sol obtained in step 1) is dropped into a hot oil column at 90-110℃ to form spheres. The formed spheres are then removed, washed, dried and calcined to obtain γ-Al2O3 spheres modified with auxiliary metal oxides, wherein the content of auxiliary metal oxides is 5-30wt%. 3) After preheating the aqueous solution of the precious metal precursor, add it to the coating machine, then add the γ-Al2O3 microspheres modified with metal oxide as an auxiliary agent, and dry the solution under rotation at 60-90℃ to obtain the impregnated sample. Further drying and calcination will yield the zero gas generator catalyst, in which the content of precious metal elements is 0.1-2wt%. In step 3), the noble metal precursor is a mixture of palladium precursor and platinum precursor; It also includes the step of aging the zero gas generator catalyst obtained in step 3): The zero-gas generator catalyst is placed in a methane-containing gas environment and aged at 400-600℃ for 2-6 hours.

2. The preparation method according to claim 1, characterized in that, In step 1), the acid solution is selected from one or more of hydrochloric acid, nitric acid, citric acid, formic acid, and acetic acid.

3. The preparation method according to claim 1 or 2, characterized in that, In step 2), the drying temperature is 90-120℃ and the time is 2-4 hours; And / or, the calcination temperature is 550-650℃, and the time is 2-4h; And / or, the particle size of the γ-Al2O3 microspheres modified with the auxiliary metal oxide is 1.6-2 mm.

4. The preparation method according to claim 1 or 2, characterized in that, The platinum precursor is selected from one or more of chloroplatinic acid, platinum nitrate, and dinitrodiamine platinum. The palladium precursor is selected from one or more of palladium chloride, palladium nitrate, and palladium acetate.

5. A zero-gas generator catalyst, characterized in that, It is prepared by the preparation method according to any one of claims 1-4.

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