ZSM-5 molecular sieve, noble metal catalyst and preparation method thereof

Abstract

The invention discloses a ZSM-5 molecular sieve, a noble metal catalyst and a preparation method thereof, and belongs to the technical field of VOCs catalysts. The aluminum coordination in the ZSM-5 molecular sieve is penta-coordination aluminum; the structural formula of the penta-coordinated aluminum is shown in the specification; or. In the synthesis process of the ZSM-5 molecular sieve, urea and thiourea are added to form abundant defective aluminum sites on the surface of the molecular sieve, and important guarantee is provided for formation of atomic-scale precious metal such as Pt sites. The preparation process of the catalyst is simple, the preparation process is easy to amplify, the catalyst is rich in pore structure, sufficient metal active sites are exposed on the surface, the noble metal content is low, the catalyst has excellent low-temperature oxidation activity, meanwhile, the rich aluminum hydroxyl on the surface of the catalyst effectively inhibits adsorption of water molecules, the water resistance of the catalyst is remarkably improved, and the catalyst is suitable for industrial production. The problems of high cost and poor hydrothermal stability of a noble metal catalyst are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of molecular sieves, and in particular to a ZSM-5 molecular sieve, a noble metal catalyst and a preparation method thereof. Background Art

[0002] ZSM-5 molecular sieve, a zeolite with an MFI topology, was developed by Mobil Corporation in the United States in 1972. This zeolite exhibits a typical three-dimensional pore structure, consisting of intersecting straight 10-membered ring channels (0.53 nm × 0.56 nm) and sinusoidal zigzag 10-membered ring channels (0.51 nm × 0.55 nm). Since the 1970s, ZSM-5 has been widely used in key industries such as oil refining, petrochemicals, and coal chemical industry due to its unique pore structure, tunable acidity, and excellent thermal and hydrothermal stability.

[0003] As an important type of solid acid catalyst, the catalytic performance of ZSM-5 zeolite is closely related to the distribution of defective aluminum sites.

[0004] How to form abundant defective aluminum sites on the surface of ZSM-5 zeolite is a technical problem that needs to be solved urgently. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a ZSM-5 molecular sieve. The surface of this ZSM-5 has abundant aluminum hydroxyl groups and defective aluminum sites, which can provide important guarantees for the subsequent loading of other elements.

[0006] A further technical problem to be solved by the present invention is to provide a method for preparing the above-mentioned ZSM-5 molecular formula.

[0007] The present invention also provides a noble metal catalyst using the ZSM-5, and a preparation method and application thereof.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A ZSM-5 molecular sieve, wherein the aluminum coordination in the ZSM-5 molecular sieve is penta-coordinate aluminum; the structural formula of the penta-coordinate aluminum is as follows:

[0010] ;or .

[0011] Pentacoordinate aluminum is an amorphous structure with very weak crystal phase peaks in XRD and can usually only be formed under special conditions.

[0012] The formation process of pentacoordinate aluminum in the present invention is as follows:

[0013] ;or .

[0014] The ZSM-5 molecular sieve is loaded with rare earth metals and transition metals, and the loading amount of the rare earth metals and transition metals is 5.0 to 20.0 wt.%.

[0015] The preparation method of the above-mentioned ZSM-5 molecular sieve comprises the following steps:

[0016] Mix the silicon source, template, urea, and thiourea in deionized water and stir to form solution A;

[0017] Add aluminum source to deionized water, mix and stir to completely dissolve to form solution B;

[0018] After mixing and stirring solution A and solution B uniformly, the mixture is placed in a reaction vessel, and reacted at 100-200° C. for 12-60 hours to obtain a reaction product. The reaction product is then filtered, washed, dried, and calcined to obtain the ZSM-5 molecular sieve.

[0019] The template agent can be n-butylamine, methyltriethylammonium hydroxide, tetrapropylammonium bromide, ethylenediamine, n-butanol, etc.

[0020] Preferably, the molar ratio of the urea to the silicon in the silicon source is (0.01-0.3):1; the molar ratio of the thiourea to the silicon in the silicon source is (0.05-0.2):1; the molar ratio of the template to the silicon in the silicon source is (0.09-0.5):1; and the aluminum-silicon ratio of the aluminum source to the silicon source is (0.005-0.02):1.

[0021] More preferably, the molar ratio of the urea to the silicon in the silicon source is (0.02~0.25):1; the molar ratio of the thiourea to the silicon in the silicon source is (0.05~0.1):1; the molar ratio of the template to the silicon in the silicon source is (0.1~0.3):1; and the aluminum-silicon ratio (molar ratio) of the aluminum source to the silicon source is (0.005~0.01):1.

[0022] Preferably, the silicon source is at least one of sodium silicate, silica sol, ethyl orthosilicate, etc., and the aluminum source is at least one of aluminum sulfate 18hydrate, aluminum chloride, sodium metaaluminate, etc.

[0023] Preferably, a rare earth metal source and a transition metal source are further added to the B solution; wherein the rare earth metal in the rare earth metal source is at least one of cerium, lanthanum, samarium, neodymium, and holmium, and the transition metal in the transition metal is at least one of cobalt, manganese, niobium, nickel, and iron; the molar ratio of the rare earth metal to the silicon in the silicon source is (0.015-0.028):0.33, and the molar ratio of the transition metal to the silicon in the silicon source is (0.029-0.014):0.33.

[0024] Preferably, the drying treatment is carried out at 60-120° C. for 12-36 hours, and the calcination treatment is carried out at 300-550° C. in an air atmosphere for 1-5 hours.

[0025] A noble metal catalyst, comprising the aforementioned ZSM-5 molecular sieve, wherein the noble metal catalyst is a ZSM-5 molecular sieve loaded with a noble metal, wherein the noble metal may be at least one of Pt, Pd, Ru, and the like.

[0026] The preparation method of the above-mentioned noble metal catalyst comprises the following steps:

[0027] The ZSM-5 molecular sieve is added to the noble metal solution for adsorption treatment. After adsorption saturation, the noble metal catalyst is obtained by filtering, washing, drying and calcining.

[0028] The adsorption treatment temperature is 20-60° C., the drying treatment is specifically drying at 60-120° C. for 12-48 hours, and the calcination treatment is treating in an air atmosphere at 250-400° C. for 1-5 hours.

[0029] Preferably, the concentration of the noble metal element in the noble metal solution is (0.0002-0.002) mol / L, preferably 0.0001-0.001 mol / L, and the solvent in the noble metal solution can be anhydrous ethanol, deionized water, etc.

[0030] Application of the above-mentioned noble metal catalyst in the treatment of volatile organic gases.

[0031] Preferably, the volatile organic gas treatment is a catalytic combustion treatment, and the reaction conditions of the catalytic combustion treatment are a reaction space velocity of 1000 to 200000 mL·g -1 ·h -1 .

[0032] The beneficial effects of the present invention are as follows:

[0033] (1) In the process of synthesizing ZSM-5 molecular sieves, the present invention adds urea and thiourea to form abundant defective aluminum sites on the surface of the molecular sieve, which provides an important guarantee for the formation of atomic-level noble metal sites such as Pt sites.

[0034] (2) Furthermore, the present invention significantly improves the concentration of oxygen vacancies on the catalyst surface by regulating the ratio of rare earth metal elements and transition metal elements during the synthesis of molecular sieves, enhances the redox performance of the catalyst and the surface acid strength and concentration, realizes the synergistic effect between surface oxygen vacancies, acid sites and noble metal active sites, and significantly improves the activity, stability and water resistance of the catalyst.

[0035] (3) The preparation method of the precious metal catalyst of the present invention is simple, the preparation process is easy to scale up, and the content of precious metal Pt in the catalyst used is low, which significantly reduces the catalyst cost.

[0036] (4) The surface of the noble metal catalyst prepared by the present invention has abundant aluminum hydroxyl groups and defect sites, which can inhibit the adsorption of water molecules on the active sites of the catalyst surface, so that the prepared catalyst has excellent water resistance, which has important research significance and application value for the catalytic oxidation and elimination of industrial multi-component VOCs. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Characterization diagram of the samples prepared in Example 1 (Cat-0) and Comparative Example 1 (DB-0); wherein, Figure 1 a in the figure is the XRD pattern of the sample. Figure 1 b in the figure is the NMR spectrum of the sample.

[0038] Figure 2 VOCs catalytic combustion activity diagram - benzene conversion rate of the precious metal catalysts prepared in Examples 1-10 of the present invention and the catalysts prepared in Comparative Examples 1-4.

[0039] Figure 3 VOCs catalytic combustion activity diagram - toluene conversion rate of the precious metal catalysts prepared in Examples 1-10 of the present invention and the catalysts prepared in Comparative Examples 1-4.

[0040] Figure 4 VOCs catalytic combustion activity diagram - propane conversion rate of the precious metal catalysts prepared in Examples 1-10 of the present invention and the catalysts prepared in Comparative Examples 1-4.

[0041] Figure 5 Thermal stability diagrams of the noble metal catalysts prepared in Examples 1-10 of the present invention and the catalysts prepared in Comparative Examples 2-4.

[0042] Figure 6 This is a graph showing the water resistance of the noble metal catalysts prepared in Examples 1-10 of the present invention and the catalysts prepared in Comparative Examples 2-4. DETAILED DESCRIPTION

[0043] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only intended to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0044] Unless otherwise specified, the raw materials and equipment used in the examples of the present invention are commercially available.

[0045] Example 1

[0046] Part 1: Synthesis of ZSM-5 molecular sieve.

[0047] (1) Sodium silicate (molecular weight 122.06) (66.8 g), n-butylamine (3.69 g), urea (0.92 g), and thiourea (4.56 g) were mixed in 80 mL of deionized water and stirred to form solution A.

[0048] (2) Add aluminum sulfate 18hydrate (2.20 g) to 80 mL of deionized water and stir until completely dissolved to form solution B.

[0049] (3) After mixing and stirring solution A and solution B evenly, place them in a stainless steel reaction vessel lined with polytetrafluoroethylene, perform crystallization reaction at 100°C for 36 hours, filter, wash with water, dry at 60°C for 24 hours, and calcined at 450°C in air atmosphere for 3 hours to obtain defect-rich ZSM-5 molecular sieve.

[0050] Part II: Synthesis of precious metal catalysts.

[0051] Chloroplatinic acid (0.0187 g) was added to 50 ml of anhydrous ethanol and stirred until completely dissolved. Then, 3.0 g of the ZSM-5 molecular sieve prepared above was added to the platinum mixed solution. After adsorption saturation at 20°C, the solution was filtered, washed with water, dried at 60°C for 24 hours, and calcined at 250°C in an air atmosphere for 5 hours to obtain a precious metal catalyst with catalytic activity, which was marked as Cat-0.

[0052] Comparative Example 1

[0053] First, sodium silicate (molecular weight 122.06) (66.8 g) and n-butylamine (8.78 g) were mixed in 80 mL of deionized water and stirred to form Solution A. Then, aluminum sulfate 18hydrate (2.20 g) was added to 80 mL of deionized water and stirred until completely dissolved, forming Solution B. Subsequently, Solutions A and B were mixed and stirred evenly before being placed in a stainless steel reaction vessel lined with polytetrafluoroethylene. Crystallization reaction was carried out at 180°C for 36 hours, followed by filtration, washing with water, drying at 80°C for 24 hours, and calcination at 400°C in air for 3 hours to obtain a defect-rich ZSM-5 molecular sieve support. Next, chloroplatinic acid (0.0187 g) was added to 50 mL of anhydrous ethanol and stirred until completely dissolved. Then, 3.0 g of defect-rich ZSM-5 molecular sieve was added to the platinum mixed solution. After adsorption saturation at 40°C, the mixture was filtered, washed with water, dried at 80°C for 24 h, and calcined at 350°C in an air atmosphere for 2 h to obtain a precious metal catalyst with catalytic activity, which was marked as DB-0.

[0054] See also Figure 1 , Figure 1 a in the figure is the XRD pattern of the catalysts prepared in Example 1 and Comparative Example 1, Figure 1 b in the figure is the NMR image of the catalyst prepared in Example 1 and Comparative Example 1. Figure 1 As can be seen from a in the figure, the precious metal catalyst prepared in Example 1 was added with urea and thiourea, and its crystal structure changed to form amorphous five-coordinate aluminum; the catalyst prepared in Comparative Example 1 had a strong diffraction peak, which mainly formed four-coordinate aluminum and six-coordinate aluminum.

[0055] from Figure 1 As can be seen from b in Example 1, compared with Comparative Example 1, the proportion of penta-coordinated aluminum in the precious metal catalyst prepared in Example 1 increased from 3% to 31%, while the proportion of tetra-coordinated aluminum in the precious metal catalyst prepared in Example 1 decreased from 85% to 66%, and the proportion of hexa-coordinated aluminum decreased from 12% to 3%.

[0056] Example 2

[0057] Part 1: Synthesis of ZSM-5 molecular sieve.

[0058] (1) Sodium silicate (66.8 g), n-butylamine (3.69 g), urea (0.92 g), and thiourea (4.56 g) were mixed in 80 mL of deionized water and stirred to form solution A.

[0059] (2) Aluminum sulfate 18hydrate (2.20 g), cobalt nitrate hexahydrate (0.54 g), and hydrated manganese nitrate (2.27 g) were added to 80 mL of deionized water in sequence, and the mixture was stirred until completely dissolved to form solution B.

[0060] (3) After mixing and stirring solution A and solution B evenly, the mixture was placed in a stainless steel reaction vessel lined with polytetrafluoroethylene, and crystallized at 100°C for 36 hours. The mixture was filtered, washed with water, dried at 60°C for 24 hours, and calcined at 450°C in an air atmosphere for 3 hours to obtain a defect-rich ZSM-5 molecular sieve carrier.

[0061] Part II: Synthesis of precious metal catalysts.

[0062] Chloroplatinic acid (0.0187 g) was added to 50 mL of anhydrous ethanol and stirred until completely dissolved. Then, 3.0 g of the ZSM-5 molecular sieve prepared above was added to the platinum mixed solution. After adsorption saturation at 20°C, the mixture was filtered, washed with water, dried at 60°C for 24 hours, and calcined at 250°C in an air atmosphere for 5 hours to obtain a precious metal catalyst with catalytic activity, which was marked as Cat-1.

[0063] Example 3

[0064] Part 1: Synthesis of ZSM-5 molecular sieve.

[0065] (1) Sodium silicate (66.8 g), n-butylamine (5.74 g), urea (1.89 g), and thiourea (4.25 g) were mixed in 80 mL of deionized water and stirred to form solution A.

[0066] (2) Aluminum sulfate 18hydrate (2.20 g), cerium nitrate hexahydrate (0.38 g), lanthanum nitrate hexahydrate (0.40 g), cobalt nitrate hexahydrate (1.09 g), and niobium oxalate (0.61 g) were added to 80 mL of deionized water in sequence, mixed and stirred until completely dissolved to form solution B.

[0067] (3) After mixing and stirring solution A and solution B evenly, place them in a stainless steel reaction vessel lined with polytetrafluoroethylene, crystallize them at 120°C for 24 hours, filter, wash with water, dry at 80°C for 20 hours, and calcine at 300°C in air atmosphere for 5 hours to obtain defect-rich ZSM-5 molecular sieve.

[0068] Part II: Synthesis of precious metal catalysts.

[0069] Platinum acetylacetonate (0.0030 g) was added to 50 ml of anhydrous ethanol and stirred until completely dissolved. Subsequently, 3.0 g of the ZSM-5 molecular sieve prepared in the first part was added to the platinum mixed solution. After adsorption saturation at 30°C, the mixture was filtered, washed with water, dried at 80°C for 20 hours, and calcined at 300°C in an air atmosphere for 4 hours to obtain a precious metal catalyst with catalytic activity, which was marked as Cat-2.

[0070] Example 4

[0071] Part 1: Synthesis of ZSM-5 molecular sieve.

[0072] (1) Sodium silicate (66.8 g), n-butylamine (6.58 g), urea (3.15 g), and thiourea (3.95 g) were mixed in 80 mL of deionized water and stirred to form solution A.

[0073] (2) Aluminum sulfate 18hydrate (2.20 g), cerium nitrate hexahydrate (0.63 g), samarium nitrate hexahydrate (0.38 g), hydrated manganese nitrate (0.91 g), and niobium oxalate (0.61 g) were added to 80 mL of deionized water in sequence, mixed and stirred until completely dissolved to form solution B.

[0074] (3) After mixing and stirring solution A and solution B evenly, the mixture was placed in a stainless steel reaction vessel lined with polytetrafluoroethylene, and crystallized at 140°C for 12 hours. The mixture was filtered, washed with water, dried at 100°C for 18 hours, and calcined at 350°C in an air atmosphere for 2 hours to obtain a defect-rich ZSM-5 molecular sieve carrier.

[0075] Part II: Synthesis of precious metal catalysts.

[0076] Chloroplatinic acid (0.005 g) was added to 50 ml of anhydrous ethanol and stirred until completely dissolved. Then, 3.0 g of the ZSM-5 molecular sieve prepared in the first part was added to the platinum mixed solution. After adsorption saturation at 50°C, the solution was filtered, washed with water, dried at 100°C for 18 hours, and calcined at 350°C in an air atmosphere for 3 hours to obtain a precious metal catalyst with catalytic activity, which was marked as Cat-3.

[0077] Example 5

[0078] Part 1: Synthesis of ZSM-5 molecular sieve.

[0079] (1) Sodium silicate (66.8 g), n-butylamine (7.69 g), urea (4.39 g), and thiourea (3.76 g) were mixed in 80 mL of deionized water and stirred to form solution A.

[0080] (2) Aluminum sulfate 18hydrate (2.20 g), lanthanum nitrate hexahydrate (0.27 g), samarium nitrate hexahydrate (0.43 g), cobalt nitrate hexahydrate (0.54 g), hydrated manganese nitrate (0.54 g), and niobium oxalate (0.85 g) were added to 80 mL of deionized water in sequence, mixed and stirred until completely dissolved to form solution B.

[0081] (3) After mixing and stirring solution A and solution B evenly, the mixture was placed in a stainless steel reaction vessel lined with polytetrafluoroethylene, and crystallized at 160°C for 60 hours. The mixture was filtered, washed with water, dried at 120°C for 36 hours, and calcined at 400°C in an air atmosphere for 1 hour to obtain a defect-rich ZSM-5 molecular sieve carrier.

[0082] Part II: Synthesis of precious metal catalysts.

[0083] Platinum nitrate (0.0049 g) was added to 50 ml of anhydrous ethanol and stirred until completely dissolved. Then, 3.0 g of the ZSM-5 molecular sieve prepared in the first part was added to the platinum mixed solution. After adsorption saturation at 60°C, the mixture was filtered, washed with water, dried at 120°C for 16 hours, and calcined at 400°C in an air atmosphere for 2 hours to obtain a catalytically active precious metal catalyst, which was labeled Cat-4.

[0084] Example 6

[0085] Part 1: Synthesis of ZSM-5 molecular sieve.

[0086] (1) Sodium silicate (66.8 g), n-butylamine (8.78 g), urea (5.12 g), and thiourea (3.52 g) were mixed in 80 mL of deionized water and stirred to form solution A.

[0087] (2) Aluminum sulfate 18hydrate (2.20 g), cerium nitrate hexahydrate (0.38 g), lanthanum nitrate hexahydrate (0.40 g), samarium nitrate hexahydrate (0.38 g), cobalt nitrate hexahydrate (0.54 g), and niobium oxalate (0.61 g) were added to 80 mL of deionized water in sequence and stirred to completely dissolve to form solution B.

[0088] (3) After mixing and stirring solution A and solution B evenly, place them in a stainless steel reaction vessel lined with polytetrafluoroethylene, crystallize them at 180°C for 48 hours, filter, wash with water, dry at 80°C for 24 hours, and calcine at 450°C in air atmosphere for 4 hours to obtain defect-rich ZSM-5 molecular sieve.

[0089] Part II: Synthesis of precious metal catalysts.

[0090] Chloroplatinic acid (0.0125 g) was added to 50 ml of anhydrous ethanol and stirred until completely dissolved. Then, 3.0 g of the ZSM-5 molecular sieve prepared in the first part was added to the platinum mixed solution. After adsorption saturation at 40°C, the solution was filtered, washed with water, dried at 70°C for 48 hours, and calcined at 350°C in an air atmosphere for 3 hours to obtain a precious metal catalyst with catalytic activity, which was marked as Cat-5.

[0091] Example 7

[0092] Part 1: Synthesis of ZSM-5 molecular sieve.

[0093] (1) Sodium silicate (66.8 g), n-butylamine (9.15 g), urea (5.96 g), and thiourea (3.32 g) were mixed in 80 mL of deionized water and stirred to form solution A.

[0094] (2) Aluminum sulfate 18hydrate (2.20 g), cerium nitrate hexahydrate (0.25 g), lanthanum nitrate hexahydrate (0.35 g), samarium nitrate hexahydrate (0.46 g), hydrated manganese nitrate (0.77 g), and niobium oxalate (0.69 g) were added to 80 mL of deionized water in sequence and stirred to completely dissolve to form solution B.

[0095] (3) After mixing and stirring solution A and solution B evenly, the mixture was placed in a stainless steel reaction vessel lined with polytetrafluoroethylene, and crystallized at 200°C for 24 hours. The mixture was filtered, washed with water, dried at 90°C for 18 hours, and calcined at 350°C in an air atmosphere for 3 hours to obtain a defect-rich ZSM-5 molecular sieve carrier.

[0096] Part II: Synthesis of precious metal catalysts.

[0097] Platinum nitrate (0.0097 g) was added to 50 ml of anhydrous ethanol and stirred until completely dissolved. Then, 3.0 g of the ZSM-5 molecular sieve prepared in the first part was added to the platinum mixed solution. After adsorption saturation at 50°C, the mixture was filtered, washed with water, dried at 80°C for 20 hours, and calcined at 300°C in an air atmosphere for 1 hour to obtain a precious metal catalyst with catalytic activity, which was marked as Cat-6.

[0098] Example 8

[0099] Part 1: Synthesis of ZSM-5 molecular sieve.

[0100] (1) Sodium silicate (66.8 g), n-butylamine (9.69 g), urea (6.53 g), and thiourea (3.16 g) were mixed in 80 mL of deionized water and stirred to form solution A.

[0101] (2) Aluminum sulfate 18hydrate (2.20 g), lanthanum nitrate hexahydrate (0.40 g), samarium nitrate hexahydrate (0.46 g), cobalt nitrate hexahydrate (0.62 g), hydrated manganese nitrate (0.45 g), and niobium oxalate (0.61 g) were added to 80 mL of deionized water in sequence, mixed and stirred until completely dissolved to form solution B.

[0102] (3) After mixing and stirring solution A and solution B evenly, place them in a stainless steel reaction vessel lined with polytetrafluoroethylene, crystallize them at 120°C for 48 hours, filter, wash with water, dry at 100°C for 36 hours, and calcine at 400°C in air atmosphere for 5 hours to obtain defect-rich ZSM-5 molecular sieve.

[0103] Part II: Synthesis of precious metal catalysts.

[0104] Platinum acetylacetonate (0.0150 g) was added to 50 ml of anhydrous ethanol and stirred until completely dissolved. Subsequently, 3.0 g of the ZSM-5 molecular sieve prepared in the first part was added to the platinum mixed solution. After adsorption saturation at 20°C, the mixture was filtered, washed with water, dried at 90°C for 18 hours, and calcined at 250°C in an air atmosphere for 5 hours to obtain a precious metal catalyst with catalytic activity, which was marked as Cat-7.

[0105] Example 9

[0106] Part 1: Synthesis of ZSM-5 molecular sieve.

[0107] (1) Sodium silicate (66.8 g), n-butylamine (10.25 g), urea (7.12 g), and thiourea (2.92 g) were mixed in 80 mL of deionized water and stirred to form solution A.

[0108] (2) Aluminum sulfate 18hydrate (2.20 g), cerium nitrate hexahydrate (0.43 g), lanthanum nitrate hexahydrate (0.40 g), samarium nitrate hexahydrate (0.43 g), and hydrated manganese nitrate (0.60 g) were added to 80 mL of deionized water in sequence, mixed and stirred until completely dissolved to form solution B.

[0109] (3) After mixing and stirring solution A and solution B evenly, place them in a stainless steel reaction vessel lined with polytetrafluoroethylene, crystallize them at 180°C for 24 hours, filter, wash with water, dry at 120°C for 20 hours, and calcine at 300°C in air atmosphere for 2 hours to obtain defect-rich ZSM-5 molecular sieve.

[0110] Part II: Synthesis of precious metal catalysts.

[0111] Platinum nitrate (0.0097 g) was added to 50 ml of anhydrous ethanol and stirred until completely dissolved. Then, 3.0 g of the ZSM-5 molecular sieve prepared in the first part was added to the platinum mixed solution. After adsorption saturation at 60°C, the mixture was filtered, washed with water, dried at 100°C for 24 hours, and calcined at 450°C in an air atmosphere for 2 hours to obtain a catalytically active precious metal catalyst, which was labeled Cat-8.

[0112] Example 10

[0113] Part 1: Synthesis of ZSM-5 molecular sieve.

[0114] (1) Silica sol (110.15 g, SiO2 content 30%, from Macklin), methyltriethylammonium hydroxide (10.65 g), urea (7.12 g), and thiourea (2.92 g) were mixed in 80 mL of deionized water and stirred to form solution A.

[0115] (2) Aluminum chloride (0.40 g), cerium nitrate hexahydrate (0.43 g), lanthanum nitrate hexahydrate (0.40 g), samarium nitrate hexahydrate (0.43 g), and hydrated manganese nitrate (0.60 g) were added to 80 mL of deionized water in sequence, mixed and stirred until completely dissolved to form solution B.

[0116] (3) After mixing and stirring solution A and solution B evenly, place them in a stainless steel reaction vessel lined with polytetrafluoroethylene, crystallize them at 180°C for 24 hours, filter, wash with water, dry at 120°C for 20 hours, and calcine at 300°C in air atmosphere for 2 hours to obtain defect-rich ZSM-5 molecular sieve.

[0117] Part II: Synthesis of precious metal catalysts.

[0118] Palladium nitrate (0.007 g) was added to 50 ml of anhydrous ethanol and stirred until completely dissolved. Then, 3.0 g of the ZSM-5 molecular sieve prepared in the first part was added to the platinum mixed solution. After adsorption saturation at 60°C, the mixture was filtered, washed with water, dried at 100°C for 24 hours, and calcined at 450°C in an air atmosphere for 2 hours to obtain a catalytically active precious metal catalyst, which was labeled Cat-9.

[0119] Example 11

[0120] Part 1: Synthesis of ZSM-5 molecular sieve.

[0121] (1) Sodium silicate (56.90 g), n-butylamine (10.25 g), urea (7.12 g), and thiourea (2.92 g) were mixed in 80 mL of deionized water and stirred to form solution A.

[0122] (2) Aluminum sulfate 18hydrate (1.80 g), cerium nitrate hexahydrate (0.43 g), lanthanum nitrate hexahydrate (0.40 g), samarium nitrate hexahydrate (0.43 g), and hydrated manganese nitrate (0.60 g) were added to 80 mL of deionized water in sequence, mixed and stirred until completely dissolved to form solution B.

[0123] (3) After mixing and stirring solution A and solution B evenly, place them in a stainless steel reaction vessel lined with polytetrafluoroethylene, crystallize them at 180°C for 24 hours, filter, wash with water, dry at 120°C for 20 hours, and calcine at 300°C in air atmosphere for 2 hours to obtain defect-rich ZSM-5 molecular sieve.

[0124] Part II: Synthesis of precious metal catalysts.

[0125] Platinum nitrate (0.0097 g) was added to 50 ml of anhydrous ethanol and stirred until completely dissolved. Then, 3.0 g of the ZSM-5 molecular sieve prepared in the first part was added to the platinum mixed solution. After adsorption saturation at 60°C, the mixture was filtered, washed with water, dried at 120°C for 12 hours, and calcined at 450°C in an air atmosphere for 2 hours to obtain a precious metal catalyst with catalytic activity, which was marked as Cat-10.

[0126] Example 12

[0127] Part 1: Synthesis of ZSM-5 molecular sieve.

[0128] (1) Sodium silicate (86.90 g), n-butylamine (10.25 g), urea (7.12 g), and thiourea (2.92 g) were mixed in 80 mL of deionized water and stirred to form solution A.

[0129] (2) Aluminum sulfate 18hydrate (4.90 g), cerium nitrate hexahydrate (0.43 g), lanthanum nitrate hexahydrate (0.40 g), samarium nitrate hexahydrate (0.43 g), and hydrated manganese nitrate (0.60 g) were added to 80 mL of deionized water in sequence and stirred to completely dissolve to form solution B.

[0130] (3) After mixing and stirring solution A and solution B evenly, place them in a stainless steel reaction vessel lined with polytetrafluoroethylene, crystallize them at 180°C for 24 hours, filter, wash with water, dry at 120°C for 12 hours, and calcine at 550°C in air atmosphere for 1 hour to obtain defect-rich ZSM-5 molecular sieve.

[0131] Part II: Synthesis of precious metal catalysts.

[0132] Platinum nitrate (0.0097 g) was added to 50 ml of anhydrous ethanol and stirred until completely dissolved. Then, 3.0 g of the ZSM-5 molecular sieve prepared in the first part was added to the platinum mixed solution. After adsorption saturation at 60°C, the mixture was filtered, washed with water, dried at 100°C for 24 hours, and calcined at 450°C in an air atmosphere for 2 hours to obtain a catalytically active precious metal catalyst, which was labeled Cat-11.

[0133] Comparative Example 2

[0134] First, sodium silicate (66.8 g) and n-butylamine (8.78 g) were mixed in 80 mL of deionized water and stirred to form Solution A. Then, aluminum sulfate 18hydrate (2.20 g), cerium nitrate hexahydrate (0.38 g), lanthanum nitrate hexahydrate (0.40 g), samarium nitrate hexahydrate (0.38 g), cobalt nitrate hexahydrate (0.54 g), and niobium oxalate (0.61 g) were added sequentially to 80 mL of deionized water and stirred until completely dissolved, forming Solution B. Subsequently, Solutions A and B were mixed and stirred uniformly before being placed in a polytetrafluoroethylene-lined stainless steel reaction vessel and crystallized at 180°C for 36 hours. The resulting product was filtered, washed with water, dried at 80°C for 24 hours, and calcined at 400°C in air for 3 hours to obtain a defect-rich ZSM-5 molecular sieve support. Next, chloroplatinic acid (0.0187 g) was added to 50 mL of anhydrous ethanol and stirred until completely dissolved. Then, 3.0 g of defect-rich ZSM-5 molecular sieve was added to the platinum mixed solution. After adsorption saturation at 40°C, the mixture was filtered, washed with water, dried at 80°C for 24 hours, and calcined at 350°C in an air atmosphere for 2 hours to obtain a precious metal catalyst with catalytic activity, which was marked as DB-1.

[0135] Comparative Example 3

[0136] First, sodium silicate (66.80 g), n-butylamine (7.69 g), and urea (5.12 g) were mixed in 80 mL of deionized water and stirred to form Solution A. Then, aluminum sulfate 18hydrate (2.20 g), cerium nitrate hexahydrate (0.38 g), lanthanum nitrate hexahydrate (0.40 g), samarium nitrate hexahydrate (0.38 g), cobalt nitrate hexahydrate (0.54 g), and niobium oxalate (0.61 g) were added sequentially to 80 mL of deionized water and stirred until completely dissolved, forming Solution B. Subsequently, Solutions A and B were mixed and stirred thoroughly before being placed in a polytetrafluoroethylene-lined stainless steel reaction vessel and crystallized at 180°C for 48 hours. The mixture was filtered, washed with water, dried at 80°C for 24 hours, and calcined at 350°C in air for 3 hours to obtain a defect-rich ZSM-5 molecular sieve support. Next, platinum acetylacetonate (0.0120 g) was added to 50 mL of anhydrous ethanol and stirred until completely dissolved. Then, 3.0 g of defect-rich ZSM-5 molecular sieve was added to the platinum mixed solution. After adsorption saturation at 40°C, the mixture was filtered, washed with water, dried at 70°C for 48 hours, and calcined at 350°C in an air atmosphere for 2 hours to obtain a precious metal catalyst with catalytic activity, which was labeled DB-2.

[0137] Comparative Example 4

[0138] First, sodium silicate (66.8 g), n-butylamine (9.15 g), and thiourea (3.52 g) were mixed in 80 mL of deionized water and stirred to form Solution A. Then, aluminum sulfate 18hydrate (2.20 g), cerium nitrate hexahydrate (0.38 g), lanthanum nitrate hexahydrate (0.40 g), samarium nitrate hexahydrate (0.38 g), cobalt nitrate hexahydrate (0.54 g), and niobium oxalate (0.61 g) were added sequentially to 80 mL of deionized water and stirred until completely dissolved, forming Solution B. Subsequently, Solutions A and B were mixed and stirred uniformly before being placed in a polytetrafluoroethylene-lined stainless steel reaction vessel and crystallized at 200°C for 24 hours. The resulting solution was then filtered, washed with water, dried at 80°C for 24 hours, and calcined at 450°C in air for 3 hours to obtain a defect-rich ZSM-5 molecular sieve support. Next, chloroplatinic acid (0.0156 g) was added to 50 mL of anhydrous ethanol and stirred until completely dissolved. Then, 3.0 g of defect-rich ZSM-5 molecular sieve was added to the platinum mixed solution. After adsorption saturation at 40°C, the mixture was filtered, washed with water, dried at 70°C for 48 hours, and calcined at 350°C in an air atmosphere for 2 hours to obtain a precious metal catalyst with catalytic activity, which was marked as DB-3.

[0139] Test Example 1: Catalytic Performance Test

[0140] The performance test method is as follows: 400 mg of noble metal catalyst was loaded into a quartz fixed bed microreactor, and the evaluation parameters included a gas flow rate of 200 ml·min -1The initial concentrations of the reactant benzene gas were 2000 ppm, the initial concentrations of the reactant toluene gas were 3000 ppm, and the initial concentrations of the reactant propane were 2000 ppm. The rest was 80% N2 + 20% O2 balance gas. The concentration of the tail gas after the reaction was detected using a Fuli GC-9790 gas chromatograph. The performance evaluation space velocity was 30000 mL·g -1 ·h -1 .

[0141] In this embodiment, the benzene / toluene / propane conversion rate = ((benzene / toluene / propane) initial concentration - (benzene / toluene / propane) concentration in the tail gas) / (benzene / toluene / propane) initial concentration × 100%.

[0142] The test results are as follows Figures 2 to 4 As shown, from Figures 2 to 4 It can be seen that the activity of the catalyst prepared in the embodiment of the present invention is significantly better than that of the comparative example, and the benzene conversion rate of the catalyst is greater than 99% at 180°C, the toluene conversion rate is greater than 99% at 200°C, and the propane conversion rate is greater than 99% at 240°C.

[0143] Test Example 2: Thermal stability test

[0144] Thermal stability test method: 400 mg of catalyst was loaded into a quartz fixed bed microreactor. The evaluation parameters included a gas flow rate of 200 ml min -1 The initial concentration of benzene gas was 2000 ppm, and the rest was 80% N2 + 20% O2 balance gas. The concentration of tail gas after reaction was detected by Fuli GC-9790 gas chromatograph. The stability test space velocity was 30000 mL g -1 ·h -1 , the test temperature is 200℃, and the test time is 0~600 min.

[0145] like Figure 5 As shown, compared with the comparative example, the catalyst prepared in this example has excellent thermal stability at 200°C and no deactivation occurs during long-term testing.

[0146] Test Example 3: Water resistance test

[0147] Water resistance test method: 400 mg of catalyst was loaded into a quartz fixed bed microreactor, and the evaluation parameters included a gas flow rate of 200 ml·min -1 The initial concentration of benzene gas was 2000 ppm, and the rest was 80% N2 + 20% O2 balance gas. The concentration of the reaction tail gas was detected by Fuli GC-9790 gas chromatograph. The air velocity of the water resistance stability test was 30000 mL g -1 ·h -1, the water vapor content is 5 vol.%, the test temperatures are 160℃, 180℃, 200℃ and 220℃, and the test time is 0~600 min.

[0148] like Figure 6 As shown, compared with the comparative example, the catalyst prepared in this example has excellent water resistance under the test conditions and no deactivation phenomenon occurs during long-term testing.

[0149] The present invention forms abundant aluminum defect sites (penta-coordinated aluminum) by adding urea, thiourea, rare earth metal elements, and transition metal elements during the synthesis of ZSM-5 molecular sieves. The precious metal is then precisely localized to the aluminum defect sites through electrostatic adsorption, achieving near-atomic-level dispersion and ultra-low loading of the precious metal Pt. The catalyst preparation process is simple and easily scalable. The catalyst has a rich pore structure, abundant metal active sites exposed on the surface, a low precious metal content, and excellent low-temperature oxidation activity. It can completely convert VOCs molecules in industrial waste gas into non-toxic CO2 and H2O. The abundant aluminum hydroxyl groups on the catalyst surface effectively inhibit the adsorption of water molecules, significantly improving the catalyst's water resistance and addressing the high cost and poor hydrothermal stability of precious metal catalysts.

[0150] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

[0151] Any portions not described in detail in this specification are known in the art. The above embodiments are provided for illustrative purposes only and are not intended to limit the scope of the present invention. The scope of the present invention is defined by the appended claims. Various equivalent substitutions and modifications that do not depart from the spirit and principles of the present invention are intended to be encompassed within the scope of the present invention.

Claims

1. A ZSM-5 molecular sieve, characterized in that The aluminum coordination in the ZSM-5 molecular sieve is penta-coordinate aluminum; the structural formula of the penta-coordinate aluminum is as follows: ;or .

2. The ZSM-5 molecular sieve according to claim 1, characterized in that The ZSM-5 molecular sieve is loaded with rare earth metals and transition metals, and the loading amount of the rare earth metals and transition metals is 5.0 to 20.0 wt.%.

3. The method for preparing the ZSM-5 molecular sieve according to claim 1 or 2, characterized in that: The steps include: Mix the silicon source, template, urea, and thiourea in deionized water and stir to form solution A; Add aluminum source to deionized water, mix and stir to completely dissolve to form solution B; Solution A and solution B are mixed and stirred evenly, placed in a reaction vessel, and reacted at 100-200° C. for 12-60 hours to obtain a reaction product, which is then filtered, washed, dried, and calcined to obtain the ZSM-5 molecular sieve.

4. The method for preparing the ZSM-5 molecular sieve according to claim 3, wherein The molar ratio of the urea to the silicon in the silicon source is (0.01-0.3):1; the molar ratio of the thiourea to the silicon in the silicon source is (0.05-0.2):1; the molar ratio of the template to the silicon in the silicon source is (0.09-0.5):1; and the aluminum-silicon ratio of the aluminum source to the silicon source is (0.005-0.02):

1.

5. The method for preparing the ZSM-5 molecular sieve according to claim 3, wherein The silicon source is at least one of sodium silicate, silica sol, ethyl orthosilicate, etc., and the aluminum source is at least one of aluminum sulfate 18hydrate, aluminum chloride, sodium metaaluminate, etc.

6. The method for preparing the ZSM-5 molecular sieve according to claim 3, wherein A rare earth metal source and a transition metal source are also added to the B solution; The molar ratio of the rare earth metal to the silicon in the silicon source is (0.002-0.0006):1, and the molar ratio of the transition metal to the silicon in the silicon source is (0.004-0.02):

1.

7. The method for preparing the ZSM-5 molecular sieve according to any one of claims 3 to 6, characterized in that: The drying process is carried out at 60-120° C. for 12-36 hours, and the calcination process is carried out at 300-550° C. in an air atmosphere for 1-5 hours.

8. A noble metal catalyst, characterized in that The noble metal catalyst comprises the ZSM-5 molecular sieve according to claim 1 or 2, and the noble metal catalyst is a ZSM-5 molecular sieve loaded with noble metal.

9. The method for preparing the noble metal catalyst according to claim 8, characterized in that: The steps include: The ZSM-5 molecular sieve is added to the noble metal solution for adsorption treatment. After adsorption saturation, the noble metal catalyst is obtained by filtering, washing, drying and calcining. The adsorption treatment temperature is 20-60°C, the drying treatment is specifically drying at 60-120°C for 12-48 hours, and the calcination treatment is carried out in an air atmosphere at 250-400°C for 1-5 hours. The concentration of the precious metal element in the precious metal solution is (0.0002-0.002) mol / L.

10. Use of the noble metal catalyst according to claim 8 in the treatment of volatile organic gases, characterized in that: The volatile organic gas treatment is a catalytic combustion treatment, and the reaction conditions of the catalytic combustion treatment are a reaction space velocity of 1000 to 200000 mL·g -1 ·h -1 .

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