Zero gas generator catalyst and preparation method thereof

Abstract

The invention belongs to the technical field of catalysis, and particularly relates to a zero gas generator catalyst and a preparation method thereof. The preparation method comprises the following steps: 1) sequentially adding urea, an assistant metal salt and pseudo-boehmite powder into water, then adding an acid solution, and uniformly mixing to obtain assistant metal modified sol slurry; further adding a gelling agent to obtain mixed sol; (2) dropwise adding the mixed sol into a hot oil column to form balls, washing, drying and roasting to obtain auxiliary agent metal oxide modified gamma-Al2O3 balls; and 3) preheating a precious metal precursor solution, adding the preheated precious metal precursor solution into a coating machine, then adding the auxiliary agent metal oxide modified gamma-Al2O3 pellets, drying the solution under the condition of rotation at 60-90 DEG C to obtain an impregnated sample, and further drying and calcining the impregnated sample to obtain the catalyst. The zero gas generator catalyst has the advantages of high catalytic activity, good thermal stability, long service life and the like, and can eliminate total hydrocarbons (based on methane) to 10 ppb or below.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysis, and in particular relates to a zero gas generator catalyst and a preparation method thereof. Background Art

[0002] The zero gas generator can effectively filter out moisture, SO2, nitrogen oxides and hydrocarbon gases such as alkanes, aromatic hydrocarbons, alkenes, alkynes, alcohols, aldehydes, ethers, and esters in the air. It is a key component of the air quality monitoring system. It can provide sufficiently stable and dry zero gas for a variety of air quality monitoring systems. It is widely used in environmental monitoring stations and gas analyzers. According to the requirements for gas sources in the "Technical Regulations for Continuous Automatic Monitoring of Non-Methane Total Hydrocarbons in Ambient Air" (Document No. 61 of the General Station Gas (2021)) issued by the General Station for Ecological Environment Monitoring, a hydrocarbon removal device must be installed before the gas source enters the analysis unit, and the total hydrocarbon (in terms of methane) concentration is required to be ≤10ppb, so there are also extremely high requirements for 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 for portable ones. Generally, the catalyst particle size is required to be less than 2mm and the loading is about 20 grams. Therefore, the module that needs to be loaded with the catalyst should be as small as possible while meeting the requirements. The catalyst is also required to be strong and not easy to pulverize, otherwise it will easily clog the pipeline and affect the normal operation of the equipment.

[0004] Alumina is widely used as a catalyst carrier due to its excellent properties such as high specific surface area, good adsorption, thermal stability and surface acidity. The catalysts and preparation methods suitable for low-concentration methane catalytic combustion reported in the current patents are all monolithic catalysts or alumina carriers are powdered or spherical by rolling ball method, which are easy to lose powder and have poor strength. The alumina spheres prepared by the oil column molding method have good sphericity, smooth surface, high crushing strength, and are not easy to lose powder. They are most suitable for use as carriers of zero gas generator catalysts. Patent CN201110388703.2 reports a catalyst for low-concentration methane catalytic combustion. The carrier is a powder that is not suitable for use as a zero gas generator catalyst carrier, and the reaction temperature is relatively high, at 600°C. Patent CN201110388703.2 reports a palladium-based catalyst treated with high-temperature aging. The carrier is a powder and uses a large amount of precious metals, resulting in high cost of use for the owner. Therefore, it is of great significance to develop a zero gas generator catalyst with low precious metal content and high activity. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a zero gas generator catalyst and a preparation method thereof. The catalyst has the advantages of high catalytic activity, good thermal stability and long service life, and can eliminate methane to below 10 ppb.

[0006] In order to achieve the purpose of the present invention, the following technical solutions are specifically adopted:

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

[0008] 1) adding urea, auxiliary metal salt and pseudo-boehmite powder to water in sequence and mixing them evenly, then adding acid solution and mixing evenly to obtain auxiliary metal modified sol slurry, wherein the content of aluminum oxide in the sol slurry is 15-25wt%; further adding a gelling agent to obtain a mixed sol;

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

[0010] 2) dripping the mixed sol obtained in step 1) into a hot oil column at 90-110° C. to form balls, then taking out the formed balls, washing, drying and calcining to obtain auxiliary metal oxide-modified γ-Al2O3 balls, wherein the auxiliary metal oxide content is 5-30wt%;

[0011] 3) Preheat the aqueous solution of the precious metal precursor and add it to the coating machine, then add the auxiliary metal oxide modified γ-Al2O3 beads, bake the solution to dryness under 60-90°C rotating conditions to obtain an impregnated sample, further dry and calcine to obtain a zero gas generator catalyst, wherein the content of the precious metal element 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 pseudo-boehmite 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 comprises at least one of nitrate and chloride.

[0016] Preferably, in step 1), the gelling agent is hexamethylenetetramine, and the amount of the gelling agent added is 6-10% based on the mass of alumina in the pseudo-boehmite 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° C. and the drying time is 2-4 hours.

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

[0020] Preferably, in step 2), the particle size of the γ-Al2O3 spheres 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 a palladium precursor and a platinum precursor.

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

[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 preheating to 60-90°C.

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

[0026] Preferably, the method further comprises the step of aging the zero gas generator catalyst obtained in step 3):

[0027] The zero gas generator catalyst is placed in a methane-containing gas environment and aged at 400-600°C 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) The present invention provides a method for preparing a zero gas generator catalyst, wherein the prepared catalyst comprises a spherical carrier, an active component and an auxiliary component, wherein the noble metal element in the active component can decompose and eliminate hydrocarbons.

[0031] The spherical carrier is a γ-Al2O3 ball modified with an additive metal oxide, which is prepared by an oil drop method, and can significantly improve the strength and stability of the carrier. The additive metal oxide helps to improve the catalyst's ability to store and release oxygen and activate oxygen, thereby improving the catalyst's catalytic ability and maintaining the stability of the catalyst's active structure during the reaction.

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

[0033] (3) The present invention provides a method for preparing a zero gas generator catalyst. The obtained catalyst is used in the zero gas generator and has the advantages of high strength, no powder falling, 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 catalyst's physical and chemical properties after withstanding 1000 hours.

[0034] (4) The present invention provides a method for preparing a zero gas generator catalyst, wherein the catalyst is prepared by an oil drop method to modify the carrier, impregnate the catalyst, and then calcine and age it. The catalyst finally prepared has better stability and catalytic ability, and is very suitable for use in zero gas generator equipment. In addition, the method of the present invention includes a molding process, which is convenient for direct industrial application. DETAILED DESCRIPTION

[0035] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with specific embodiments. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention. If no specific technology or conditions are specified in the examples, the technology or conditions described in the literature in this area or the product instructions are used.

[0036] Example 1

[0037] (1) Vector preparation

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

[0039] The oil bath temperature of the hot oil column was set to 98°C, and the thickness of the oil phase was set to 2 meters. The mixed sol was dripped into the hot oil column to form balls, which were directly taken out from the lower end of the device. At this time, the ball diameter was 1.6-2mm. The balls were washed with water, dried at 120°C for 2h, and calcined at 600°C for 4h to obtain Ce-modified γ-Al2O3 balls with a CeO2 weight content of 10%.

[0040] (2) Catalyst preparation

[0041] Take 3.3g of 10% palladium nitrate solution and 1.1g of 15% platinum nitrate solution, add them to 90g of deionized water to obtain a precious metal precursor solution, preheat the solution to about 80°C, and then pour it into a coating machine (Nanjing Huai Teng Machinery Design Co., Ltd., BY-300), then pour 100g of the alumina balls obtained in step (1) into the precious metal precursor solution, bake the solution at 70°C and a speed of 15 rpm, and finally put it in an oven at 120°C for 4h, then heat it to 500°C at a heating rate of 3 / min and calcine it for 2h to obtain a catalyst with a precious 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 tubular furnace, 0.5% CH4 gas was introduced into the catalyst, the background atmosphere was air, the temperature was 400°C, and the time was 2h.

[0044] Example 2

[0045] On the basis of Example 1, 17.4 g of cerium nitrate hexahydrate was added in step (1), and 17.5 g of lanthanum nitrate hexahydrate was added instead. The other operations were the same as in Example 1.

[0046] Example 3

[0047] On the basis of Example 1, the steps of taking 3.3 g of 10% palladium nitrate solution and 1.1 g of 15% platinum nitrate solution in step (2) are replaced by taking 6.6 g of 10% palladium nitrate solution and 2.2 g of 15% platinum nitrate solution, and the other operations are the same as those in Example 1.

[0048] Example 4

[0049] On the basis of 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 Example 3.

[0050] Example 5

[0051] On the basis of Example 1, the temperature of 400° C. and the time of 2 h in step (3) were changed to the temperature of 600° C. and the time of 6 h, and the other operations were the same as those 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: instead of taking 3.3 g of 10% palladium nitrate solution and 1.1 g of 15% platinum nitrate solution by mass fraction in step (2), 5.0 g of 10% palladium nitrate solution by mass fraction is taken.

[0056] Comparative Example 3

[0057] Compared with Example 1, the only difference is that step (2) does not use a coating machine, and the specific steps are: take 3.3g of a 10% palladium nitrate solution and 1.1g of a 15% platinum nitrate solution, add them to 90g of deionized water to obtain a precious metal precursor solution, pour 100g of the alumina balls obtained in step (1) into the above-mentioned precious metal precursor solution, mix well, put into an oven at 120°C and dry for 4h, then heat to 500°C at a heating rate of 3 / min and calcine for 2h to obtain a 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 balls are used in step (1). The specific method is to take 25.2g of cerium nitrate hexahydrate and add it to 54mL of water, then add 90g of commercially available γ-Al2O3 balls (1.6-2mm) prepared by the rolling ball method, mix them evenly and put them in an oven to dry at 120°C for 4h, then heat them to 600°C at a heating rate of 3 / min and calcine them for 4h to obtain Ce-modified γ-Al2O3 balls with a CeO2 weight content of 10%.

[0062] Test example

[0063] The test gas is HC hydrocarbons, with methane as the representative substance, the concentration is 50ppm, and the reaction gas space velocity is 10000h -1 . Simulate the commercially available zero gas generator catalyst module device, the reaction tube is cylindrical, with an inner diameter of 12mm and a height of 300mm. Stainless steel mesh with a diameter of 12mm and an aperture of 1mm is placed at the upper and lower ends of the reaction tube. The inner diameter of the stainless steel pipes for inlet and outlet gas at both ends is 3mm. Take 20 grams of catalyst and put it into the reaction tube. The temperature of the reaction tube is controlled at 400℃ by a tubular furnace. The concentration of methane after elimination by the above catalyst is tested by gas chromatograph. 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 / grain) 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 Test results of the elimination ability of each catalyst

[0067]

[0068] Although the present invention has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements may be made thereto based on the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a zero gas generator catalyst, characterized in that: The following steps are involved: 1) adding urea, auxiliary metal salt and pseudo-boehmite powder to water in sequence and mixing them evenly, then adding acid solution and mixing evenly to obtain auxiliary metal modified sol slurry, wherein the content of aluminum oxide in the sol slurry is 15-25wt%; further adding a gelling agent to obtain a mixed sol; The auxiliary metal salt is selected from one or more soluble salts of cerium, lanthanum, potassium, sodium, magnesium and barium; 2) dripping the mixed sol obtained in step 1) into a hot oil column at 90-110° C. to form balls, then taking out the formed balls, washing, drying and calcining to obtain auxiliary metal oxide-modified γ-Al2O3 balls, wherein the auxiliary metal oxide content is 5-30wt%; 3) Preheat the aqueous solution of the precious metal precursor and add it to the coating machine, then add the auxiliary metal oxide modified γ-Al2O3 beads, bake the solution to dryness under 60-90°C rotating conditions to obtain an impregnated sample, further dry and calcine to obtain a zero gas generator catalyst, wherein the content of the precious metal element is 0.1-2wt%.

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 1), the mass ratio of urea to alumina in pseudo-boehmite powder is 40-70:

100.

4. The preparation method according to claim 1 or 2, characterized in that: In step 1), the auxiliary metal salt is selected from one or more of soluble salts of cerium and soluble salts of lanthanum.

5. The preparation method according to claim 1 or 2, characterized in that: In step 1), the gelling agent is hexamethylenetetramine; based on the mass of alumina in the pseudo-boehmite powder, the amount of the gelling agent added is 6-10%.

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

7. The preparation method according to claim 1 or 2, characterized in that: In step 3), the noble metal precursor is a palladium precursor, or a mixture of a palladium precursor and a platinum precursor; Preferably, the platinum precursor is selected from one or more of chloroplatinic acid, platinum nitrate, and dinitrodiammine platinum; The palladium precursor is selected from one or more of palladium chloride, palladium nitrate and palladium acetate.

8. The preparation method according to claim 1 or 2, characterized in that: The step of aging the zero gas generator catalyst obtained in step 3) is also included: The zero gas generator catalyst is placed in a methane-containing gas environment and aged at 400-600°C for 2-6 hours.

9. A zero gas generator catalyst, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 8.

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