A high-activity Pt-based molecular sieve catalyst and its preparation method and its application in the catalytic oxidation of light alkanes

Abstract

The present invention discloses a highly active Pt-based molecular sieve catalyst, a preparation method, and its application in the catalytic oxidation of light alkanes. NaAlO2, TEOS, and Cr(NO3)3·9H2O are added to an alkaline solution to obtain a mixed solution; tetrapropylammonium hydroxide is added to the mixed solution, and after a hydrothermal reaction, the mixture is dried and calcined to obtain a Cr-ZSM-5 material, which is hydrogen-modified. The hydrogen-modified Cr-HZSM-5 material dispersion is used to load Pt by a wet impregnation method. In the present invention, the precious metal Pt element is fixed by in-situ introduction of Cr element into the HZSM-5 molecular sieve carrier, so that the active sites are highly dispersed, and due to the low electronegativity of Cr, more electrons are transferred to the Pt site, resulting in more Pt 0 The generation of active sites improves its low-temperature catalytic oxidation activity and also has excellent high-temperature stability.

Description

Technical Field

[0001] The present invention belongs to the field of air pollution control and technology, and in particular relates to a high-activity Pt-based molecular sieve catalyst, a preparation method thereof, and application thereof in the catalytic oxidation of light alkanes. Background Art

[0002] With the continuous development of industry, emissions of volatile organic compounds (VOCs) are increasing, causing significant environmental damage and triggering numerous severe weather events. Low-carbon alkanes, which are among VOCs, are very stable and difficult to destroy due to their large C-H bond energies. Compared to transition metal catalysts, noble metal catalysts offer high activity and selectivity, making them widely used in industrial catalysis. However, their susceptibility to sintering and agglomeration at high temperatures has hindered their development. To address this high-temperature agglomeration of noble metals, the current mainstream approach is to use molecular sieve-supported noble metal catalysts, which utilize the pores of the molecular sieve to prevent high-temperature agglomeration of the noble metals. However, these catalysts also suffer from the disadvantage of poor dispersion of the noble metal active sites, resulting in low catalytic activity. Research has shown that introducing transition metals into the system to manipulate the material's surface physicochemical properties, altering the interaction and connection with the noble metal active phase, is an effective means of improving the dispersion and activity of noble metals.

[0003] For example, patent CN114749203B describes loading Pt and then Ni onto hexagonal mesoporous silica to improve the dispersion and catalytic activity of the active component. Similarly, patent CN110180582A describes modifying a molecular sieve with a non-precious metal and then increasing the activity of the loaded precious metal.

[0004] However, the above methods cannot achieve a high dispersion of transition metals on molecular sieves, and thus cannot further disperse precious metals. As a result, the utilization rate of precious metals cannot be improved, resulting in wasteful use of precious metals. Therefore, exploring the preparation of highly dispersed, high-utilization, and high-temperature stable precious metal catalysts is crucial for the development of industrial catalysis. Summary of the Invention

[0005] In order to overcome the problems in the prior art, the purpose of the present invention is to provide a highly active Pt-based molecular sieve catalyst and a preparation method and its application in the catalytic oxidation of light alkanes. The catalyst prepared by this method has the characteristics of being economical and inexpensive, simple in preparation materials, high in low-temperature reaction activity, and high stability.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for preparing a high-activity Pt-based molecular sieve catalyst comprises the following steps:

[0008] NaAlO2, TEOS, and Cr(NO3)3·9H2O are added to an alkaline solution and stirred to obtain a mixed solution; tetrapropylammonium hydroxide is added to the mixed solution and mixed to obtain a mixed solution; the mixed solution is hydrothermally reacted at 170-220°C for 36-72 hours, dried, and calcined at 450-600°C for 4-8 hours to obtain a Cr-ZSM-5 material;

[0009] The Cr-ZSM-5 material is hydrogen-modified to obtain a hydrogen-modified Cr-HZSM-5 material;

[0010] The hydrogen-modified Cr-HZSM-5 material dispersion was used to load Pt by wet impregnation method to obtain a highly active Pt-based molecular sieve catalyst.

[0011] Furthermore, the alkaline solution is prepared by the following process: adding an inorganic alkaline substance to deionized water to prepare an alkaline solution; wherein the usage ratio of the inorganic alkaline substance to the deionized water is 0.1-2 g: 50-100 mL.

[0012] Furthermore, the inorganic alkaline substance is NaOH, KOH, K2CO3 or Na2CO3;

[0013] The usage ratio of inorganic alkaline substance, NaAlO2, TEOS, Cr(NO3)3·9H2O and tetrapropylammonium hydroxide is 0.1-2g:0.2-1g:NaAlO2:20-60mL:0.2-2g:6-12g.

[0014] Furthermore, the hydrogen-modified Cr-HZSM-5 material is prepared by the following process: adding the Cr-ZSM-5 material to an NH4Cl solution, stirring evenly, washing, drying, and calcining at 450-600°C for 4-8h to obtain the hydrogen-modified Cr-HZSM-5 material.

[0015] Furthermore, the usage ratio of the Cr-ZSM-5 material to the NH4Cl solution is 1-5 g: 220-280 mL, and the concentration of the NH4Cl solution is 0.5-1 mol / L.

[0016] Furthermore, the hydrogen-modified Cr-HZSM-5 material dispersion is prepared by the following process: adding the hydrogen-modified Cr-HZSM-5 material to deionized water and stirring evenly to obtain the hydrogen-modified Cr-HZSM-5 material dispersion; wherein the dosage ratio of the hydrogen-modified Cr-HZSM-5 material to deionized water is 1-2 g: 30-60 mL.

[0017] Furthermore, the highly active Pt-based molecular sieve catalyst is prepared by the following process:

[0018] Pt(NH3)4(NO3)2 solution is added to the hydrogen-modified Cr-HZSM-5 material dispersion, stirred, and evaporated to obtain a mixture. After the mixture is dried, it is calcined at 400-500°C for 3-5h to obtain Pt / Cr-HZSM-5 material.

[0019] Furthermore, the usage ratio of Pt(NH3)4(NO3)2 to hydrogen-modified Cr-HZSM-5 material is 0.04g:1-2g.

[0020] A high-activity Pt-based molecular sieve catalyst prepared according to the preparation method described above.

[0021] The invention discloses an application of a high-activity Pt-based molecular sieve catalyst prepared according to the preparation method described above in the catalytic oxidation of light alkanes.

[0022] Furthermore, at 60000 mL·g·cat -1 ·h -1 Under the condition of space velocity, Pt / HZSM-5 is used as catalyst to catalytically oxidize propane in volatile organic compounds. The catalytic reaction temperature is 25-300℃, the concentration of propane is 1000ppm, the volume concentration of oxygen is 21%, and nitrogen is the balance gas.

[0023] Compared with the prior art, the present invention has the following beneficial results:

[0024] In the present invention, the Cr element is introduced in situ into the HZSM-5 molecular sieve carrier to fix the precious metal Pt element, and the high-activity Pt-based molecular sieve catalyst Pt / Cr-HZSM-5 catalyst is prepared, so that the active sites are highly dispersed, and due to the low electronegativity of Cr, more electrons are transferred to the Pt site, resulting in more Pt 0 The generation of active sites improves its low-temperature catalytic oxidation activity, and it also has excellent high-temperature stability.

[0025] At 60000mL·g·cat -1 ·h -1 Under the space velocity condition of 1000ppm, the balance gas N2, 21% O2 and 1000ppm C3H8 were introduced. At the reaction temperature of 255℃, propane can be completely oxidized, and when the catalyst is calcined at 800℃ for 6h, it still has excellent catalytic oxidation performance. Its excellent activity comes from the in-situ introduction of Cr element into the HZSM-5 molecular sieve carrier to fix the precious metal Pt element, making the active sites highly dispersed. And due to the low electronegativity of Cr, it will transfer more electrons to the Pt site, resulting in more Pt 0The catalyst of the present invention has a simple and environmentally friendly synthesis process. The Pt / Cr-HZSM-5 catalyst prepared by the present invention exhibits excellent catalytic oxidation performance for propane at low temperatures, with a propane degradation rate reaching 100% at 255°C. It also exhibits excellent high-temperature stability, outperforming traditional industrial precious metal catalysts. Therefore, the use of the prepared catalyst for the catalytic oxidation of light alkanes has considerable industrial practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The catalyst is at a C3H8 concentration of 1000ppm and a space velocity of 60000mL·g·cat -1 ·h -1 Graph of propane catalytic oxidation performance under test conditions.

[0027] Figure 2 The catalyst was calcined at 800℃ for 6h and the C3H8 concentration was 1000ppm and the space velocity was 60000mL·g·cat -1 ·h -1 Graph of propane catalytic oxidation performance under test conditions.

[0028] Figure 3 This is the X-ray diffraction test spectrum of the catalyst.

[0029] Figure 4 This is the X-ray photoelectron spectroscopy test spectrum of the catalyst. DETAILED DESCRIPTION

[0030] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to the accompanying drawings. The accompanying drawings illustrate preferred embodiments of the present invention. However, the present invention may be implemented in a variety of different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the disclosure of the present invention.

[0031] The present invention provides a method for preparing a high-activity Pt-based molecular sieve catalyst, comprising the following steps:

[0032] The first step is the preparation of Cr-HZSM-5 carrier:

[0033] Add 0.1-2 g of an inorganic alkaline substance (NaOH, KOH, K2CO3 or Na2CO3) to 50-100 mL of deionized water to prepare an alkaline solution.

[0034] 0.2-1 g of NaAlO2, 20-60 mL of TEOS and 0.2-2 g of Cr(NO3)3·9H2O were added to the alkaline solution and magnetically stirred for 0.5-1 h to obtain a mixed solution.

[0035] Then, 6-12g of tetrapropylammonium hydroxide was added to the mixed solution and stirred at 700rpm for 2h until fully mixed. The mixed solution was then transferred to a 150mL high-pressure reactor, placed in an oven and heated to 170-220°C for 36-72h. After the reaction was completed, the temperature dropped to room temperature, and the solid product was filtered and washed twice with 100ml of a mixture of deionized water and anhydrous ethanol (wherein the volume ratio of deionized water to ethanol was 2:1-6:1), dried in a vacuum oven at 100-150°C for 10-12h, and thoroughly ground. Calcinated in a muffle furnace at 450-600°C for 4-8h to obtain Cr-ZSM-5 material.

[0036] The Cr-ZSM-5 material is then hydrogen modified:

[0037] 1-5 g of the above Cr-ZSM-5 material is added to 220-280 mL of 0.5-1 mol / L NH4Cl solution, magnetically stirred at 700-1000 rpm at room temperature for 3-6 hours, filtered, and washed twice with 100 ml of a mixture of deionized water and anhydrous ethanol (the volume ratio of deionized water to ethanol is 2:1-6:1), dried in a vacuum oven at 100-150°C for 12 hours, and then calcined at 450-600°C for 4-8 hours to obtain a hydrogen-modified Cr-HZSM-5 material.

[0038] Finally, preparation of Pt / Cr-HZSM-5:

[0039] Pt was loaded using the wet impregnation method. 1-2 g of hydrogen-modified Cr-HZSM-5 material was added to 30-60 mL of deionized water and stirred at room temperature for 3-6 h to obtain a Cr-HZSM-5 dispersion.

[0040] Dissolve 0.02-0.04g of Pt(NH3)4(NO3)2 in 10-20mL of deionized water, then slowly add it dropwise to the Cr-HZSM-5 dispersion. Continue stirring at room temperature at 700-900rpm for 1-2h, then heat to 90°C, stir, and evaporate to dryness. After cooling to room temperature, transfer the mixture to an oven and dry it in a vacuum drying oven at 100-150°C for 12-24h. Grind the dried mixture thoroughly and then calcine at 400-500°C for 3-5h to obtain the Pt / Cr-HZSM-5 material.

[0041] The present invention investigates the low-temperature catalytic activity and high-temperature stability of Pt / HZSM-5 and Pt / nCr-HZSM-5 catalysts in propane catalytic oxidation.

[0042] Catalyst usage: 60000mL·g·cat -1 ·h -1Under the conditions of space velocity, Pt / HZSM-5 and Pt / nCr-HZSM-5 (n=0.5, 1.0, 1.5, 2.0) materials are used as catalysts to catalytically oxidize propane in volatile organic compounds. The catalytic reaction temperature is 25-300°C, the propane concentration is 1000ppm, the oxygen volume concentration is 21%, and nitrogen is used as the balance gas.

[0043] Comparative Example 1

[0044] 1 g of commercial HZSM-5 material was added to 50 mL of deionized water and stirred at room temperature for 4 h to obtain a HZSM-5 dispersion.

[0045] Dissolve 0.02 g of Pt(NH₃)₄(NO₃)₂ in 10 mL of deionized water and slowly add it dropwise to the HZSM-5 dispersion. Stir at room temperature for 2 hours at 700 rpm, then raise the temperature to 90°C and evaporate to dryness with stirring. After cooling to room temperature, transfer the mixture to an oven and dry it at 120°C for 24 hours. The dried mixture is thoroughly ground, transferred to a ceramic crucible, placed in a muffle furnace, and calcined at 500°C for 4 hours to obtain the Pt / HZSM-5 material.

[0046] Example 1

[0047] Preparation of hydrogen-modified 0.5Cr-HZSM-5 support:

[0048] 0.2 g of NaOH was added to 60 mL of deionized water to prepare a NaOH solution. To this solution were added 0.4 g of NaAlO₂, 40 mL of tetraethyl orthosilicate, and 0.5 g of Cr(NO₃)₃·9H₂O, and magnetically stirred for 1 h. 10 g of tetrapropylammonium hydroxide was then added to the mixture, and stirring was continued at 700 rpm for 2 h until thoroughly mixed. The mixture was then transferred to a 150 mL autoclave, heated to 180°C in an oven, and reacted for 36 h. After the reaction was complete and the temperature was cooled to room temperature, the solid product was filtered and washed twice with 100 mL of a mixture of deionized water and anhydrous ethanol (the volume ratio of deionized water to ethanol was 4:1). The solid product was then dried in a vacuum oven at 100°C for 12 h, thoroughly ground, and calcined in a muffle furnace at 550°C for 6 h to obtain the Cr-ZSM-5 material.

[0049] The material is then hydrogen modified:

[0050] 2 g of the above Cr-ZSM-5 material was added to 240 mL of 0.5 mol / L NH4Cl solution, magnetically stirred at 800 rpm at room temperature for 4 h, filtered, and washed twice with 100 ml of a mixture of deionized water and anhydrous ethanol (the volume ratio of deionized water to ethanol was 4:1). The material was dried in a vacuum oven at 100 ° C overnight, and then calcined at 550 ° C for 4 h to obtain hydrogen-modified 0.5Cr-HZSM-5 material.

[0051] Pt was loaded using the wet impregnation method. 1 g of Cr-HZSM-5 material was added to 50 mL of deionized water and stirred at room temperature for 4 hours. 0.02 g of Pt(NH3)4(NO3)2 was dissolved in 10 mL of deionized water and then slowly added dropwise to the Cr-HZSM-5 dispersion. Stirring was continued at 700 rpm for 2 hours at room temperature, then the temperature was raised to 90°C and evaporated to dryness with stirring. After cooling to room temperature, the mixture was transferred to an oven and dried in a vacuum drying oven at 120°C for 24 hours. The dried mixture was thoroughly ground and then calcined at 500°C for 4 hours to obtain the Pt / nCr-HZSM-5 (n=0.5) material.

[0052] Example 2

[0053] Preparation of hydrogen-modified 1.0Cr-HZSM-5 support:

[0054] 0.2 g of NaOH was added to 60 mL of deionized water to prepare a NaOH solution. To this solution were added 0.4 g of NaAlO₂, 40 mL of tetraethyl orthosilicate, and 1.0 g of Cr(NO₃)₃·9H₂O, and magnetic stirring was performed for 1 h. Then, 10 g of tetrapropylammonium hydroxide was added to the mixture, and stirring was continued at 700 rpm for 2 h until thoroughly mixed. The mixture was then transferred to a 150 mL autoclave, heated to 180°C in an oven, and reacted for 36 h. After the reaction was complete and the temperature was cooled to room temperature, the solid product was filtered and washed twice with 100 mL of a mixture of deionized water and anhydrous ethanol (the volume ratio of deionized water to ethanol was 4:1). The solid product was then dried in a vacuum oven at 100°C for 12 h, thoroughly ground, and calcined in a muffle furnace at 550°C for 6 h to obtain the Cr-ZSM-5 material.

[0055] The material is then hydrogen modified:

[0056] 2 g of the above Cr-ZSM-5 material was added to 240 mL of 0.5 mol / L NH4Cl solution, magnetically stirred at 800 rpm at room temperature for 4 h, filtered, and washed twice with 100 ml of a mixture of deionized water and anhydrous ethanol (the volume ratio of deionized water to ethanol was 4:1). The material was dried in a vacuum oven at 100 ° C overnight, and then calcined at 550 ° C for 4 h to obtain hydrogen-modified 1.0Cr-HZSM-5 material.

[0057] Pt was loaded using the wet impregnation method. 1 g of Cr-HZSM-5 material was added to 50 mL of deionized water and stirred at room temperature for 4 hours. 0.02 g of Pt(NH3)4(NO3)2 was dissolved in 10 mL of deionized water and then slowly added dropwise to the Cr-HZSM-5 dispersion. Stirring was continued at 700 rpm for 2 hours at room temperature, then the temperature was raised to 90°C and evaporated to dryness with stirring. After cooling to room temperature, the mixture was transferred to an oven and dried in a vacuum drying oven at 120°C for 24 hours. The dried mixture was thoroughly ground and then calcined at 500°C for 4 hours to obtain the Pt / nCr-HZSM-5 (n=1.0) material.

[0058] Example 3

[0059] Preparation of hydrogen-modified 1.5Cr-HZSM-5 support:

[0060] 0.2 g of NaOH was added to 60 mL of deionized water to prepare a NaOH solution. To this solution were added 0.4 g of NaAlO₂, 40 mL of tetraethyl orthosilicate, and 1.5 g of Cr(NO₃)₃·9H₂O, and magnetic stirring was performed for 1 h. 10 g of tetrapropylammonium hydroxide was then added to the mixture, and stirring was continued at 700 rpm for 2 h until thoroughly mixed. The mixture was then transferred to a 150 mL autoclave, heated to 180°C in an oven, and reacted for 36 h. After the reaction was complete and the temperature was cooled to room temperature, the solid product was filtered and washed twice with 100 mL of a mixture of deionized water and anhydrous ethanol (the volume ratio of deionized water to ethanol was 4:1). The solid product was then dried in a vacuum oven at 100°C for 12 h, thoroughly ground, and calcined in a muffle furnace at 550°C for 6 h to obtain the Cr-ZSM-5 material.

[0061] The material is then hydrogen modified:

[0062] 2 g of the above Cr-ZSM-5 material was added to 240 mL of 0.5 mol / L NH4Cl solution, magnetically stirred at 800 rpm at room temperature for 4 h, filtered, and washed twice with 100 ml of a mixture of deionized water and anhydrous ethanol (the volume ratio of deionized water to ethanol was 4:1). The material was dried in a vacuum oven at 100 ° C overnight, and then calcined at 550 ° C for 4 h to obtain hydrogen-modified 1.5Cr-HZSM-5 material.

[0063] Pt was loaded using the wet impregnation method. 1 g of Cr-HZSM-5 material was added to 50 mL of deionized water and stirred at room temperature for 4 hours. 0.02 g of Pt(NH3)4(NO3)2 was dissolved in 10 mL of deionized water and then slowly added dropwise to the Cr-HZSM-5 dispersion. Stirring was continued at 700 rpm for 2 hours at room temperature, then the temperature was raised to 90°C and evaporated to dryness with stirring. After cooling to room temperature, the mixture was transferred to an oven and dried in a vacuum drying oven at 120°C for 24 hours. The dried mixture was thoroughly ground and then calcined at 500°C for 4 hours to obtain the Pt / nCr-HZSM-5 (n=1.5) material.

[0064] Example 4

[0065] Preparation of hydrogen-modified 2.0Cr-HZSM-5 support:

[0066] 0.2 g of NaOH was added to 60 mL of deionized water to prepare a NaOH solution. To this solution were added 0.4 g of NaAlO₂, 40 mL of tetraethyl orthosilicate, and 2.0 g of Cr(NO₃)₃·9H₂O, and magnetically stirred for 1 h. Then, 10 g of tetrapropylammonium hydroxide was added to the mixture, and stirring was continued at 700 rpm for 2 h until thoroughly mixed. The mixture was then transferred to a 150 mL autoclave, heated to 180°C in an oven, and reacted for 36 h. After the reaction was complete and the temperature was cooled to room temperature, the solid product was filtered and washed twice with 100 mL of a mixture of deionized water and anhydrous ethanol (the volume ratio of deionized water to ethanol was 4:1). The solid product was then dried in a vacuum oven at 100°C for 12 h, thoroughly ground, and calcined in a muffle furnace at 550°C for 6 h to obtain the Cr-ZSM-5 material.

[0067] The material is then hydrogen modified:

[0068] 2 g of the above Cr-ZSM-5 material was added to 240 mL of 0.5 mol / L NH4Cl solution, magnetically stirred at 800 rpm at room temperature for 4 h, filtered, and washed twice with 100 ml of a mixture of deionized water and anhydrous ethanol (the volume ratio of deionized water to ethanol was 4:1). The material was dried in a vacuum oven at 100 ° C overnight, and then calcined at 550 ° C for 4 h to obtain hydrogen-modified 2.0Cr-HZSM-5 material.

[0069] Pt was loaded using the wet impregnation method. 1 g of Cr-HZSM-5 material was added to 50 mL of deionized water and stirred at room temperature for 4 hours. 0.02 g of Pt(NH3)4(NO3)2 was dissolved in 10 mL of deionized water and then slowly added dropwise to the Cr-HZSM-5 dispersion. Stirring was continued at 700 rpm for 2 hours at room temperature, then the temperature was raised to 90°C and evaporated to dryness with stirring. After cooling to room temperature, the mixture was transferred to an oven and dried in a vacuum drying oven at 120°C for 24 hours. The dried mixture was thoroughly ground and then calcined at 500°C for 4 hours to obtain the Pt / nCr-HZSM-5 (n=2.0) material.

[0070] Example 5

[0071] 0.1 g of KOH was added to 50 mL of deionized water to prepare a NaOH solution. To this solution were added 0.2 g of NaAlO₂, 20 mL of tetraethyl orthosilicate, and 1.7 g of Cr(NO₃)₃·9H₂O, and magnetic stirring was performed for 0.5 h. 11 g of tetrapropylammonium hydroxide was then added to the mixture, and stirring was continued at 700 rpm for 2 h until thoroughly mixed. The mixture was then transferred to a 150 mL autoclave, heated to 170°C in an oven, and reacted for 72 h. After the reaction was complete and the temperature was lowered to room temperature, the solid product was filtered and washed twice with 100 mL of a mixture of deionized water and anhydrous ethanol (the volume ratio of deionized water to ethanol was 4:1). The solid product was then dried in a vacuum oven at 110°C for 12 h, thoroughly ground, and calcined in a muffle furnace at 450°C for 8 h to obtain the Cr-ZSM-5 material.

[0072] The material is then hydrogen modified:

[0073] 1 g of the above Cr-ZSM-5 material was added to 220 mL of 0.5 mol / L NH4Cl solution, magnetically stirred at 700 rpm at room temperature for 6 h, filtered, and washed twice with 100 ml of a mixture of deionized water and anhydrous ethanol (the volume ratio of deionized water to ethanol was 4:1). The material was dried in a vacuum oven at 100 ° C for 12 h, and then calcined at 450 ° C for 8 h to obtain hydrogen-modified 0.5Cr-HZSM-5 material.

[0074] Pt was loaded using the wet impregnation method. 1 g of Cr-HZSM-5 material was added to 30 mL of deionized water and stirred at room temperature for 3 hours. 0.02 g of Pt(NH3)4(NO3)2 was dissolved in 10 mL of deionized water and then slowly added dropwise to the Cr-HZSM-5 dispersion. Stirring was continued at 700 rpm for 2 hours at room temperature, then the temperature was raised to 90°C and evaporated to dryness with stirring. After cooling to room temperature, the mixture was transferred to an oven and dried in a vacuum drying oven at 100°C for 24 hours. The dried mixture was thoroughly ground and then calcined at 400°C for 5 hours to obtain the Pt / nCr-HZSM-5 (n=0.5) material.

[0075] Example 6

[0076] 2g of K2CO3 was added to 60mL of deionized water to prepare a NaOH solution. To this solution were added 1g of NaAlO2, 30mL of tetraethyl orthosilicate, and 1.2g of Cr(NO3)3·9H2O, and magnetic stirring was performed for 0.8h. Then, 6g of tetrapropylammonium hydroxide was added to the mixture, and stirring was continued at 700rpm for 2h until thoroughly mixed. The mixture was then transferred to a 150mL autoclave, heated to 200°C in an oven, and reacted for 50h. After the reaction was complete and the temperature was cooled to room temperature, the solid product was filtered and washed twice with 100ml of a mixture of deionized water and anhydrous ethanol (the volume ratio of deionized water to ethanol was 4:1). The solid product was then dried in a vacuum oven at 120°C for 12h, thoroughly ground, and calcined in a muffle furnace at 500°C for 7h to obtain the Cr-ZSM-5 material.

[0077] The material is then hydrogen modified:

[0078] 3 g of the above Cr-ZSM-5 material was added to 230 mL of 0.6 mol / L NH4Cl solution, magnetically stirred at 800 rpm at room temperature for 5 h, filtered, and washed twice with 100 ml of a mixture of deionized water and anhydrous ethanol (the volume ratio of deionized water to ethanol was 2:1). The material was dried in a vacuum oven at 150 ° C overnight, and then calcined at 500 ° C for 6 h to obtain hydrogen-modified 0.5Cr-HZSM-5 material.

[0079] Pt was loaded using the wet impregnation method. 2g of Cr-HZSM-5 material was added to 60mL of deionized water and stirred at room temperature for 4h. 0.03g of Pt(NH3)4(NO3)2 was dissolved in 15mL of deionized water and then slowly added dropwise to the Cr-HZSM-5 dispersion. Stirring continued at room temperature for 1.5h at 800rpm, the mixture was then heated to 90°C and evaporated to dryness with stirring. After cooling to room temperature, the mixture was transferred to an oven and dried in a vacuum drying oven at 150°C for 12h. The dried mixture was thoroughly ground and then calcined at 420°C for 5h to obtain Pt / nCr-HZSM-5 (n=0.5) material.

[0080] Example 7

[0081] 1 g of Na₂CO₃ was added to 70 mL of deionized water to prepare a NaOH solution. To this solution were added 1.5 g of NaAlO₂, 40 mL of tetraethyl orthosilicate, and 1 g of Cr(NO₃)₃·9H₂O, and magnetic stirring was performed for 1 hour. 12 g of tetrapropylammonium hydroxide was then added to the mixture, and stirring was continued at 700 rpm for 2 hours until thoroughly mixed. The mixture was then transferred to a 150 mL autoclave, heated to 210°C in an oven, and reacted for 45 hours. After the reaction was complete and the temperature was cooled to room temperature, the solid product was filtered and washed twice with 100 mL of a mixture of deionized water and anhydrous ethanol (the volume ratio of deionized water to ethanol was 2:1). The solid product was then dried in a vacuum oven at 140°C for 10 hours, thoroughly ground, and calcined in a muffle furnace at 600°C for 4 hours to obtain the Cr-ZSM-5 material.

[0082] The material is then hydrogen modified:

[0083] 4 g of the above Cr-ZSM-5 material was added to 260 mL of 0.8 mol / L NH4Cl solution, and magnetically stirred at 1000 rpm at room temperature for 3 h. After filtration, the mixture was washed twice with 100 ml of a mixture of deionized water and anhydrous ethanol (the volume ratio of deionized water to ethanol was 3:1), dried in a vacuum oven at 120 ° C overnight, and then calcined at 550 ° C for 5 h to obtain hydrogen-modified 0.5Cr-HZSM-5 material.

[0084] Pt was loaded using the wet impregnation method. 1.5 g of Cr-HZSM-5 material was added to 60 mL of deionized water and stirred at room temperature for 5 h. 0.04 g of Pt(NH3)4(NO3)2 was dissolved in 20 mL of deionized water and then slowly added dropwise to the Cr-HZSM-5 dispersion. Stirring continued at room temperature for 1 h at 900 rpm, then the temperature was raised to 90°C and evaporated to dryness with stirring. After cooling to room temperature, the mixture was transferred to an oven and dried in a vacuum drying oven at 120°C for 21 h. The dried mixture was thoroughly ground and then calcined at 450°C for 4 h to obtain Pt / nCr-HZSM-5 (n=0.5) material.

[0085] Example 8

[0086] 0.6 g of NaOH was added to 80 mL of deionized water to prepare a NaOH solution. To this solution were added 2 g of NaAlO₂, 50 mL of tetraethyl orthosilicate, and 0.8 g of Cr(NO₃)₃·9H₂O, and magnetically stirred for 1 h. 7 g of tetrapropylammonium hydroxide was then added to the mixture, and stirring was continued at 700 rpm for 2 h until thoroughly mixed. The mixture was then transferred to a 150 mL autoclave, heated to 220°C in an oven, and reacted for 38 h. After the reaction was complete and the temperature was cooled to room temperature, the solid product was filtered and washed twice with 100 mL of a mixture of deionized water and anhydrous ethanol (the volume ratio of deionized water to ethanol was 6:1). The solid product was then dried in a vacuum oven at 130°C for 11 h, thoroughly ground, and calcined in a muffle furnace at 580°C for 5 h to obtain the Cr-ZSM-5 material.

[0087] The material is then hydrogen modified:

[0088] 5 g of the above Cr-ZSM-5 material was added to 280 mL of 1 mol / L NH4Cl solution, magnetically stirred at 900 rpm at room temperature for 4 h, filtered, and washed twice with 100 ml of a mixture of deionized water and anhydrous ethanol (the volume ratio of deionized water to ethanol was 5:1). The material was dried in a vacuum oven at 130 ° C overnight, and then calcined at 600 ° C for 4 h to obtain hydrogen-modified 0.5Cr-HZSM-5 material.

[0089] Pt was loaded using the wet impregnation method. 1 g of Cr-HZSM-5 material was added to 40 mL of deionized water and stirred at room temperature for 6 h. 0.02 g of Pt(NH3)4(NO3)2 was dissolved in 16 mL of deionized water and then slowly added dropwise to the Cr-HZSM-5 dispersion. Stirring was continued at 750 rpm for 2 h at room temperature, then the temperature was raised to 90°C and evaporated to dryness with stirring. After cooling to room temperature, the mixture was transferred to an oven and dried in a vacuum drying oven at 130°C for 18 h. The dried mixture was thoroughly ground and then calcined at 470°C for 4 h to obtain the Pt / nCr-HZSM-5 (n=0.5) material.

[0090] Example 9

[0091] 1.5 g of NaOH was added to 100 mL of deionized water to prepare a NaOH solution. To this solution were added 0.7 g of NaAlO₂, 60 mL of tetraethyl orthosilicate, and 0.2 g of Cr(NO₃)₃·9H₂O, and magnetically stirred for 1 h. 8 g of tetrapropylammonium hydroxide was then added to the mixture, and stirring was continued at 700 rpm for 2 h until thoroughly mixed. The mixture was then transferred to a 150 mL autoclave, heated to 220°C in an oven, and reacted for 36 h. After the reaction was complete and the temperature was cooled to room temperature, the solid product was filtered and washed twice with 100 mL of a mixture of deionized water and anhydrous ethanol (the volume ratio of deionized water to ethanol was 5:1). The solid product was then dried in a vacuum oven at 100°C for 12 h, thoroughly ground, and calcined in a muffle furnace at 550°C for 6 h to obtain the Cr-ZSM-5 material.

[0092] The material is then hydrogen modified:

[0093] 2 g of the above Cr-ZSM-5 material was added to 240 mL of 0.7 mol / L NH4Cl solution, magnetically stirred at 950 rpm at room temperature for 4 h, filtered, and washed twice with 100 ml of a mixture of deionized water and anhydrous ethanol (the volume ratio of deionized water to ethanol was 6:1). The mixture was dried in a vacuum oven at 140 ° C overnight, and then calcined at 480 ° C for 7 h to obtain hydrogen-modified 0.5Cr-HZSM-5 material.

[0094] Pt was loaded using the wet impregnation method. 2 g of Cr-HZSM-5 material was added to 50 mL of deionized water and stirred at room temperature for 3.5 h. 0.03 g of Pt(NH3)4(NO3)2 was dissolved in 18 mL of deionized water and then slowly added dropwise to the Cr-HZSM-5 dispersion. Stirring was continued at 850 rpm for 1.5 h at room temperature, then the temperature was raised to 90°C and evaporated to dryness with stirring. After cooling to room temperature, the mixture was transferred to an oven and dried in a vacuum drying oven at 140°C for 14 h. The dried mixture was thoroughly ground and then calcined at 500°C for 3 h to obtain the Pt / nCr-HZSM-5 (n=0.5) material.

[0095] Example 10

[0096] Activity test of the catalysts in Comparative Example 1, Example 1, Example, Example 3 and Example 4: 0.30 g of the catalysts obtained in Comparative Example 1, Example 1, Example, Example 3 and Example 4 were pressed into pellets and sieved to 40-60 mesh and placed in a fixed bed reactor for catalytic activity evaluation. The experimental conditions were: 1000 ppm C3H8, 21% O2, N2 as the balance gas, and a reaction space velocity of 60000 mL·g·cat -1 ·h -1 The propane concentration was detected by gas chromatography. The catalytic performance results are as follows Figure 1 As shown, from Figure 1 It can be seen that the Pt / 0.5Cr-HZSM-5 catalyst can completely oxidize propane at 255 °C, and its performance is better than other catalysts.

[0097] Example 11

[0098] Performance test of Comparative Example 1, Example 1, Example, Example 3 and Example 4 after calcination at 800°C for 6 h in air atmosphere: 0.30 g of the catalysts in Comparative Example 1, Example 1, Example, Example 3 and Example 4 after calcination at 800°C for 6 h in air atmosphere were placed in a fixed bed reactor for catalytic activity evaluation. The experimental conditions were: 1000 ppm C3H8, 21% O2, N2 as the balance gas, and a reaction space velocity of 60000 mL·g·cat -1 ·h -1 The propane concentration was detected by gas chromatography. The catalytic performance results are as follows Figure 2 As shown, from Figure 2 It can be seen that the Pt / 0.5Cr-HZSM-5 catalyst can still completely oxidize propane at 275°C, and its stability is better than that of the Pt / HZSM-5 catalyst.

[0099] Example 12

[0100] The catalysts in Comparative Example 1, Example 1, Example 3 and Example 4 were subjected to X-ray diffraction tests. The test results are shown in FIG. Figure 3 As shown, from Figure 3 The Pt / HZSM-5 catalyst exhibits a high peak at approximately 40°, indicating the presence of relatively large Pt nanoparticles on its surface. However, the Pt / nCr-HZSM-5 (n=0.5, 1.0, 1.5, 2.0) catalysts exhibit no distinct peak at approximately 40°, demonstrating excellent dispersion of the Pt nanoparticles on the nCr-HZSM-5 (n=0.5, 1.0, 1.5, 2.0) support. This is the primary reason for their excellent catalytic performance in propane oxidation. This difference in dispersion can be attributed to the ability of the Cr species dispersed on the nCr-HZSM-5 (n=0.5, 1.0, 1.5, 2.0) support to bind Pt atoms, resulting in a highly dispersed Pt nanoparticle structure.

[0101] Example 13

[0102] The catalysts in Comparative Example 1, Example 1, Example 3 and Example 4 were tested by X-ray photoelectron spectroscopy. Figure 4 and as shown in Table 1.

[0103] Table 1 Pt element proportion on the surface of different materials

[0104]

[0105]

[0106] from Figure 4 As can be seen from Table 1, the Pt in the Pt / nCr-HZSM-5 (n=0.5, 1.0, 1.5, 2.0) catalyst 0 The content of Pt is higher than that of Pt / HZSM-5 catalyst without Cr. 0 It is the active center for catalytic oxidation of propane, so the activity of Pt / nCr-HZSM-5 (n=0.5, 1.0, 1.5, 2.0) catalyst is better than that of Pt / HZSM-5 catalyst. 0 The increase in valence content is mainly due to the fact that Cr has a lower electronegativity than Pt, so electrons will be transferred to Pt, resulting in a large amount of Pt 0 produce.

[0107] The Pt / Cr-HZSM-5 catalyst prepared in the present invention fixes the precious metal Pt element by in-situ introduction of Cr element into the HZSM-5 molecular sieve carrier, making the active sites highly dispersed. And due to the low electronegativity of Cr, it transfers more electrons to the Pt site, resulting in more Pt 0The generation of active sites improves its low-temperature catalytic oxidation activity, and it also has excellent high-temperature stability.

[0108] The above description is merely a description of the preferred embodiment of the present invention and is not to be construed as limiting the claims. The present invention is not limited to the above embodiment, and variations in the specific structure are permitted. Any variations made within the scope of the independent claims of the present invention are also within the scope of protection of the present invention.

[0109] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

Claims

1. A method for preparing a high-activity Pt-based molecular sieve catalyst for catalytic oxidation of light alkanes, characterized in that: The following steps are involved: NaAlO2, TEOS, and Cr(NO3)3·9H2O are added to an alkaline solution and stirred to obtain a mixed solution; tetrapropylammonium hydroxide is added to the mixed solution and mixed to obtain a mixed solution; the mixed solution is hydrothermally reacted at 170-220°C for 36-72 hours, dried, and calcined at 450-600°C for 4-8 hours to obtain a Cr-ZSM-5 material; The Cr-ZSM-5 material is hydrogen-modified to obtain a hydrogen-modified Cr-HZSM-5 material; The high-activity Pt-based molecular sieve catalyst was obtained by loading Pt onto a hydrogen-modified Cr-HZSM-5 material dispersion using a wet impregnation method. The hydrogen-modified Cr-HZSM-5 material is prepared by the following process: adding the Cr-ZSM-5 material to an NH4Cl solution, stirring evenly, washing, drying, and calcining at 450-600°C for 4-8 hours to obtain the hydrogen-modified Cr-HZSM-5 material; Highly active Pt-based molecular sieve catalysts are prepared by the following process: Pt(NH3)4(NO3)2 solution is added to the hydrogen-modified Cr-HZSM-5 material dispersion, stirred, and evaporated to obtain a mixture. After the mixture is dried, it is calcined at 400-500°C for 3-5h to obtain Pt / Cr-HZSM-5 material.

2. The method for preparing a high-activity Pt-based molecular sieve catalyst for catalytic oxidation of light alkanes according to claim 1, characterized in that: The alkaline solution is prepared by the following process: adding an inorganic alkaline substance into deionized water to prepare an alkaline solution; wherein the usage ratio of the inorganic alkaline substance to the deionized water is 0.1-2g:50-100mL.

3. The method for preparing a high-activity Pt-based molecular sieve catalyst for catalytic oxidation of light alkanes according to claim 2, characterized in that: The inorganic alkaline substance is NaOH, KOH, K2CO3 or Na2CO3; The usage ratio of the inorganic alkaline substance, NaAlO2, TEOS, Cr(NO3)3·9H2O and tetrapropylammonium hydroxide is 0.1-2g:0.2-1g:20-60mL:0.2-2g:6-12g.

4. The method for preparing a high-activity Pt-based molecular sieve catalyst for catalytic oxidation of light alkanes according to claim 1, characterized in that: The usage ratio of the Cr-ZSM-5 material and the NH4Cl solution is 1-5 g: 220-280 mL, and the concentration of the NH4Cl solution is 0.5-1 mol / L.

5. The method for preparing a high-activity Pt-based molecular sieve catalyst for catalytic oxidation of light alkanes according to claim 1, characterized in that: The hydrogen-modified Cr-HZSM-5 material dispersion is prepared by the following process: adding the hydrogen-modified Cr-HZSM-5 material to deionized water and stirring uniformly to obtain the hydrogen-modified Cr-HZSM-5 material dispersion; wherein the dosage ratio of the hydrogen-modified Cr-HZSM-5 material to the deionized water is 1-2 g: 30-60 mL.

6. The method for preparing a high-activity Pt-based molecular sieve catalyst for catalytic oxidation of light alkanes according to claim 1, characterized in that: The usage ratio of Pt(NH3)4(NO3)2 to hydrogen-modified Cr-HZSM-5 material is 0.04g:1-2g.

7. A high-activity Pt-based molecular sieve catalyst prepared according to the preparation method according to any one of claims 1 to 6.

8. Use of a high-activity Pt-based molecular sieve catalyst prepared according to the preparation method according to any one of claims 1 to 6 in the catalytic oxidation of light alkanes.

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