A molecular sieve confined noble metal dehydrogenation catalyst and its preparation method and application

Abstract

The present invention relates to the field of nuclear power safety technology, and the present invention discloses a molecular sieve confined noble metal dehydrogenation catalyst and its preparation method and application. The catalyst of the present application has an MFI molecular sieve structure, the content of the noble metal component is less than 0.7wt.%, and the average particle size of the noble metal component is less than 3nm. The preparation method comprises the following steps: A. mixing the noble metal salt and the organic amine compound to obtain a noble metal solution after complexing with the organic amine compound; B. mixing the silicon source, the template, the deionized water and the noble metal solution configured in step A, stirring to obtain a precursor solution of a synthetic pure silicon molecular sieve confined nano noble metal catalyst; C. reacting the precursor solution obtained in step B at a constant temperature, washing and drying after the reaction is completed; D. thermally reducing the material. The prepared catalyst has a small demand for noble metals, a high metal dispersion, a small particle size, and is applied to catalytic oxidation dehydrogenation reactions with high catalytic efficiency.

Description

Technical Field

[0001] The present invention relates to the field of nuclear power safety technology, and in particular to a molecular sieve confined noble metal dehydrogenation catalyst and a preparation method and application thereof. Background Art

[0002] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

[0003] The hydrogen produced during nuclear power plant accidents comes from the reaction of metal zirconium with water vapor and the radiolysis of water. How to quickly and efficiently process the produced hydrogen has become a hot topic of research. Hydrogen isotopes (deuterium and tritium) are the main fuels for future fusion reactors. During the operation of fusion reactors, it is crucial to prevent tritium from leaking into the environment. Catalytic oxidation dehydrogenation technology has the advantages of high efficiency, low pollution, and high safety factor. It is often used in the atmosphere dehydrogenation system of nuclear facilities. The key factor for its removal efficiency is the performance of the catalyst. Al2O3 loaded with precious metals (Pt, Pd, etc.) by impregnation is a common catalyst in the hydrogen oxidation process. However, to achieve excellent removal efficiency, the catalyst usually needs to increase the temperature conditions to 100-200℃. However, higher temperatures will lead to an increase in the size of metal particles, and the catalytic efficiency will usually decrease. In addition, since the exothermic reaction will release a lot of heat, the catalytic efficiency of existing catalysts is limited and it is difficult to reach more than 90%. In addition, the competitive adsorption of hydrogen and oxidation products (water) at metal sites is another factor that has a side effect on catalytic performance. The key to solving these problems is to improve the metal dispersion, stability and hydrophobicity of the catalyst.

[0004] Molecular sieves are crystalline aluminosilicates with uniform pore structures. They contain a large amount of crystal water, which can be vaporized and removed when heated, so they are also called zeolites. Zeolites exist in nature, while those synthesized are called molecular sieves. Commonly used molecular sieves are a type of three-dimensional network structure, belonging to crystalline aluminosilicates, and their chemical formula is: x / n [(Al2O3) x (SiO2)y]·mH2O, where M is a metal cation, n is its valence number; x is the number of Al2O3 molecules, y is the number of SiO2 molecules; and m is the number of crystal water molecules.

[0005] The traditional preparation method of precious metal molecular sieve catalyst adopts the method of preparing the molecular sieve first and then attaching the precious metal to the molecular sieve by impregnation or the like. For example, the prior art CN110560149A discloses a zeolite-loaded metal-type dehydrogenation and detritium removal catalyst and its application. The catalyst comprises zeolite and precious metal, the zeolite is a carrier, the precious metal is an active component, the components of the zeolite are [SiO2]x[AlO4]yMz, M is a metal cation or a proton, X:Y=(100~∞):1, Z=Y / V, V is the valence state of the metal cation M; the precious metal comprises one or any combination of Pt, Pd, Ag or Au. The impregnation method will not only cause the dealumination of the molecular sieve carrier, resulting in a decrease in acidity and affecting the catalytic efficiency of the catalyst, but also the following problems exist in the existing preparation method: (1) High cost and low catalytic efficiency: The precious metals loaded in the molecular sieve are a large number of clusters, resulting in large precious metal particles, low dispersion, and limited catalytic efficiency. To achieve a higher catalytic rate, it is necessary to increase the loading amount of precious metal particles, and the precious metals themselves are expensive. Therefore, the cost and price of existing catalysts are relatively high; (2) Poor heat resistance. During the catalytic exothermic reaction, the metal particles agglomerate, resulting in a sharp decrease in the catalytic efficiency of the catalyst. Summary of the invention

[0006] The purpose of the present invention is to provide a molecular sieve confined precious metal dehydrogenation catalyst and its preparation method and application in view of the deficiencies of the prior art, so as to solve the problems of low content of active components, poor dispersibility and poor heat resistance of the existing catalysts, and obtain a highly dispersed precious metal cluster molecular sieve catalyst, which exhibits efficient dehydrogenation performance. Compared with Pt@Al2O3 prepared by the traditional impregnation method, it has less precious metal content, smaller particle size and higher dispersibility, and can still obtain high dehydrogenation efficiency at temperatures below 100°C and high space velocity. The catalyst has good thermal stability, and the catalytic performance has hardly decreased after multiple cycles. It is an excellent dehydrogenation catalyst in the field of nuclear power safety.

[0007] The technical solution of the present invention is as follows:

[0008] A molecular sieve confined noble metal dehydrogenation catalyst has an MFI molecular sieve structure, the noble metal component content is lower than 0.7wt.%, and the average particle size of the noble metal component is less than 3nm.

[0009] The precious metal catalyst of the present application has a lower precious metal content than the existing precious metal catalysts, but has higher dispersion and smaller average particle size. It can still exert better catalytic efficiency than the existing ones under low temperature conditions of 100 degrees Celsius, and has good application prospects in the field of rapid hydrogen removal.

[0010] The present application also provides a method for preparing the aforementioned molecular sieve confined noble metal dehydrogenation catalyst, comprising the following steps:

[0011] A. Add noble metal salt and organic amine compound in a molar ratio of 1:15-25 into a certain amount of water to prepare a noble metal solution. The amount of water is appropriate for dissolving the noble metal salt. Stir evenly at room temperature to obtain a noble metal complex solution.

[0012] The noble metal salt includes any one of PtCl2, NaPtCl6, and PdCl2.

[0013] The organic amine compound is any one of ethylenediamine and diethylenetriamine.

[0014] B. The silicon source, template, deionized water and the noble metal complex solution obtained in step A are prepared into a solution in proportion, wherein the molar ratio of the silicon source, template, deionized water, noble metal and organic amine compound in the prepared solution is: 1: 0.3-0.56: 33.5-65.5: 0.002-0.011: 0.03-0.28; the mixture is fully mixed and stirred at room temperature to obtain a synthetic molecular sieve precursor solution.

[0015] The silicon source is tetraethoxysilane.

[0016] The template agent is tetrapropylammonium hydroxide.

[0017] C. Place the precursor solution obtained in step B in a polytetrafluoroethylene liner, and place the polytetrafluoroethylene liner in a reactor, and react for a certain time under the constant temperature condition of a drying oven. After the reaction is completed, wash the obtained molecular sieve material with deionized water until it is neutral and dry it. The constant temperature of the drying oven is 150-200°C, preferably 160-180°C; the reaction time is 24-96h, preferably 48h-96h.

[0018] D. The molecular sieve material obtained in step C is subjected to thermal reduction treatment in a 1%-10% hydrogen-argon mixed gas atmosphere at a temperature of 400-600° C. to obtain a pure silicon molecular sieve confined nanometer noble metal catalyst. Preferably, the thermal reduction treatment hydrogen atmosphere is a 5%-10% hydrogen-argon mixed gas.

[0019] The hydrophobicity of the catalyst prepared using pure silicon source is better than that of the catalyst prepared using the method of silicon source plus aluminum source.

[0020] The present application also provides the use of the aforementioned molecular sieve confined noble metal dehydrogenation catalyst in catalytic oxidation dehydrogenation reaction.

[0021] In the process of using the existing Pt@Al2O3 catalyst, the reaction temperature needs to be increased to improve the catalytic efficiency. After the reaction temperature is increased, the size of the metal particles in the catalyst will increase. As time goes by, the catalytic efficiency of the catalyst will gradually decrease, so its dehydrogenation efficiency is limited. The catalyst of the present application is a typical MFI (silicalite-1) molecular sieve structure, the average particle size of the precious metal component is less than 3nm, and the temperature condition of the catalytic reaction is lower than 100°C. It has been proved by experiments that it can achieve 99.9% hydrogen removal efficiency at 75°C, and it has very good thermal stability. It has been verified by experiments that it can be continuously cycled for 6 times at 75°C, and the total reaction time is 7200min, during which its catalytic efficiency is always maintained at 99.9%. Applying it in the catalytic oxidation dehydrogenation reaction can reduce the reaction conditions and improve the removal efficiency on the one hand, and save costs on the other hand. The price of precious metals is very expensive, and the utilization rate of precious metals in the existing Pt@Al2O3 prepared by the impregnation method is low, while the present application can achieve better catalytic efficiency with a lower precious metal content, which can greatly improve the utilization rate of precious metals.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. High catalytic efficiency. The prepared catalyst material shows a good conversion rate in the catalytic oxidation dehydrogenation reaction in the field of nuclear energy safety, and a high hydrogen recovery rate can be achieved under relatively mild reaction process conditions. Pure silicon molecular sieve is used as a carrier loaded with precious metals. By changing the post-treatment conditions of the catalyst material, the dispersion of the active components of the catalyst material can be improved, and the obvious clustering of the active components can be prevented. Nanoclusters (particle size less than 3nm) are obtained, and the control of the particle size, distribution and stable loading of the active components is achieved. The prepared catalyst has good hydrophobicity, and the active sites in the catalyst are highly dispersed, and the catalytic efficiency is high;

[0024] 2. Save costs. Use common products such as ethylenediamine as organic amine compounds to protect precious metal salts to achieve better protection effects. When achieving a better hydrogen conversion rate, the content of precious metals in the catalyst used is less than 0.7wt.%, the cost of each catalyst is reduced, and the prepared catalyst has good thermal stability, high material recovery rate and repetition rate, and reduced catalyst consumption costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the XRD spectrum of the molecular sieve confined nano-Pt noble metal catalyst prepared in Example 1;

[0026] Figure 2 This is the BET result of the molecular sieve confined nano Pd noble metal catalyst prepared in Example 2;

[0027] Figure 3This is the TEM result of the molecular sieve confined nano Pt noble metal catalyst prepared in Example 1.

[0028] Figure 4 This is a TEM result of the molecular sieve confined nano Pt noble metal catalyst prepared in Example 3;

[0029] Figure 5 This is a TEM result of the molecular sieve confined nano-Pt noble metal catalyst prepared in Example 4;

[0030] Figure 6 This is a graph showing the multi-round hydrogen removal performance of the molecular sieve confined nano-Pt precious metal catalyst prepared in Example 1. DETAILED DESCRIPTION

[0031] It should be noted that relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0032] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0033] Embodiment 1

[0034] This embodiment provides a molecular sieve confined noble metal dehydrogenation catalyst and a preparation method and application thereof, and the preparation method comprises the following steps:

[0035] A. Precious metal salt PtCl2 and ethylenediamine are mixed at a molar ratio of 1:15 to prepare a precious metal salt solution; the solution is placed on a magnetic stirrer and stirred at room temperature for 30 minutes to obtain a precious metal solution complexed with an organic amine compound;

[0036] B. Further prepare the silicon source tetraethoxysilane, the template agent tetrapropylammonium hydroxide, deionized water and the noble metal solution prepared in step A into a mixed solution 1 in a certain proportion, wherein the molar ratio of the silicon source tetraethoxysilane: the template agent tetrapropylammonium hydroxide: the deionized water: the noble metal salt: the ethylenediamine is 1:0.4:35:0.0023:0.035, and the mixture is fully mixed and stirred at room temperature for 3 hours to obtain a precursor solution for synthesizing a pure silicon molecular sieve confined nano noble metal catalyst;

[0037] C. The precursor solution obtained in step B is placed in a polytetrafluoroethylene liner, and then placed in a reactor, and reacted for 72 hours in a drying oven at a constant temperature of 170°C. After the reaction is completed, the obtained material is washed with deionized water until it is neutral, and dried in a drying oven at 80°C for 4 hours to obtain an unreduced material.

[0038] D. The material is subjected to thermal reduction treatment at 600°C in an 8% hydrogen-argon mixed gas atmosphere for 10 hours to obtain the catalyst.

[0039] The Pt content was measured to be 0.58wt.%, and the Pt dispersion was 45.5%. Figure 1 The XRD spectrum of the molecular sieve confined nano Pt noble metal catalyst prepared in this embodiment is shown in FIG. According to the figure, the catalyst prepared by the preparation method of this embodiment is a typical MFI (silicalite-1) molecular sieve structure. Figure 3 This is a TEM image of the molecular sieve confined nano-Pt noble metal catalyst prepared in this example. As shown in the figure, the average particle size of the Pt particles is 1.65 nm.

[0040] Embodiment 2

[0041] This embodiment provides a molecular sieve confined noble metal dehydrogenation catalyst and a preparation method and application thereof, and the preparation method comprises the following steps:

[0042] A. Mix soluble precious metal salt PdCl2 and diethylenetriamine at a molar ratio of 1:17 to prepare a precious metal salt solution; place the solution on a magnetic stirrer and stir at room temperature for 30 minutes to obtain a precious metal solution complexed with an organic amine compound.

[0043] B. Further prepare the silicon source tetraethoxysilane, the template agent tetrapropylammonium hydroxide, deionized water and the precious metal solution prepared in step A into a mixed solution 1 in a certain proportion, wherein the molar ratio of silicon source tetraethoxysilane: template agent tetrapropylammonium bromide: deionized water: precious metal salt: diethylenetriamine is 1:0.56:65.5:0.011:0.28, and the mixture is fully mixed and stirred at room temperature for 3 hours to obtain a precursor solution for synthesizing pure silicon molecular sieve confined nano precious metal catalyst.

[0044] C. The precursor solution obtained in step B is placed in a polytetrafluoroethylene liner, and then placed in a reactor, and reacted for 48 hours in a drying oven at a constant temperature of 180°C. After the reaction is completed, the obtained material is washed with deionized water until it is neutral, and dried in a drying oven at 80°C for 4 hours to obtain an unreduced material.

[0045] D. The material is subjected to thermal reduction treatment at 600°C for 10 h in a 10% hydrogen-argon mixed gas atmosphere to obtain a catalyst.

[0046] like Figure 2 The figure shows the N2 adsorption-desorption curve of the molecular sieve confined nano Pd noble metal catalyst prepared in this example. The calculated BET specific surface area is 480 m 2 / g, it can be seen from the figure that the molecular sieve confined nano Pd precious metal catalyst prepared in this embodiment has a large specific surface area, which proves that it is a porous structure. The XRD spectrum of the catalyst is the same as that of Example 1, which proves that it is a typical MFI (silicalite-1) molecular sieve structure. The Pd content is measured to be 0.65wt.%, and the average particle size of the Pd particles is 2.62nm.

[0047] Embodiment 3

[0048] This embodiment provides a molecular sieve confined noble metal dehydrogenation catalyst and a preparation method and application thereof, and the preparation method comprises the following steps:

[0049] A. Mix soluble precious metal salt PtCl2 and ethylenediamine at a molar ratio of 1:15 to prepare a precious metal salt solution; place the solution on a magnetic stirrer and stir at room temperature for 30 minutes to obtain a precious metal solution complexed with an organic amine compound.

[0050] B. Further prepare the silicon source tetraethoxysilane, the template agent tetrapropylammonium hydroxide, deionized water and the precious metal solution prepared in step A into a mixed solution 1 in a certain proportion, wherein the molar ratio of silicon source tetraethoxysilane: template agent tetrapropylammonium hydroxide: deionized water: precious metal salt: ethylenediamine is 1:0.4:35:0.0023:0.035, and the mixture is fully mixed and stirred at room temperature for 3 hours to obtain a precursor solution for synthesizing pure silicon molecular sieve confined nano precious metal catalyst.

[0051] C. The precursor solution obtained in step B is placed in a polytetrafluoroethylene liner, and then placed in a reactor, and reacted for 72 hours in a drying oven at a constant temperature of 170°C. After the reaction is completed, the obtained material is washed with deionized water until it is neutral, and dried in a drying oven at 80°C for 4 hours to obtain an unreduced material.

[0052] D. The material is subjected to thermal reduction treatment at 400°C in a 5% hydrogen-argon mixed gas atmosphere for 10 hours to obtain the catalyst.

[0053] The Pt content was measured to be 0.53 wt.%, and the prepared catalyst had a typical MFI structure. Figure 4 This is a TEM image of the molecular sieve confined nano-Pt precious metal catalyst prepared in this example. As shown in the figure, the average particle size of the Pt particles is 1.56 nm.

[0054] Embodiment 4

[0055] A molecular sieve confined noble metal dehydrogenation catalyst and a preparation method and application thereof, comprising the following steps:

[0056] A. Mix soluble precious metal salt PtCl2 and ethylenediamine at a molar ratio of 1:25 to prepare a precious metal salt solution; place the solution on a magnetic stirrer and stir at room temperature for 30 minutes to obtain a precious metal solution complexed with an organic amine compound.

[0057] B. Further prepare a solution with a molar ratio of silicon source tetraethoxysilane, template agent tetrapropylammonium hydroxide, deionized water, noble metal and organic amine compound ethylenediamine of 1:0.56:35:0.0011:0.035, and fully mix and stir at room temperature for 3 hours to obtain a precursor solution for synthesizing pure silicon molecular sieve confined nano-noble metal catalyst.

[0058] C. The precursor solution obtained in step B is placed in a polytetrafluoroethylene liner, and then placed in a reactor, and reacted for 72 hours in a drying oven at a constant temperature of 170°C. After the reaction is completed, the obtained material is washed with deionized water until it is neutral, and dried in a drying oven at 80°C for 4 hours to obtain an unreduced material.

[0059] D. The material is subjected to a thermal reduction treatment at 500°C in a 5% hydrogen-argon mixed gas atmosphere for 10 hours to obtain a catalyst.

[0060] The Pt content was measured to be 0.58 wt.%, and the prepared catalyst had a typical MFI structure. Figure 5 This is a TEM image of the molecular sieve confined nano-Pt noble metal catalyst prepared in this example. As shown in the figure, the average particle size of the Pt particles is 1.61 nm.

[0061] Application Example 1

[0062] The catalysts prepared in Example 1, Example 2, Example 3, and Example 4 and the commercially available Pt@Al2O3 catalyst were evaluated for their dehydrogenation reaction performance.

[0063] First, 50 mg of catalyst material was placed in a reaction tube, and then hydrogen-containing air with a hydrogen concentration of 2000 ppm was introduced at a reaction temperature of 75 °C, and the air velocity was controlled to be 24000 mL·g -1 ·h -1 The results of the hydrogen removal efficiency (hydrogen conversion rate) after stabilization are shown in Table 1:

[0064] Table 1

[0065]

[0066] The above-mentioned Pt@Al2O3 catalyst was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0067] It can be seen from Table 1 that under the same processing conditions, the hydrogen conversion rate of the catalyst prepared in the present application is at least 10% higher than the conversion rate of the Pt@Al2O3 catalyst prepared by the existing zeolite loading method.

[0068] Comparative analysis of the dehydrogenation efficiency of Example 1, Example 3 and Example 4 shows that, within the temperature range of 400°C-600°C, as the temperature of the thermal reduction treatment increases, the dehydrogenation efficiency of the prepared catalyst increases, with 600°C being the best.

[0069] Application Example 2

[0070] The catalyst prepared in Example 1 was subjected to a cyclic dehydrogenation reaction performance evaluation.

[0071] First, 50 mg of catalyst material was placed in a reaction tube, and then hydrogen-containing air with a hydrogen concentration of 2000 ppm was introduced at a reaction temperature of 75 °C, and the air velocity was controlled to be 24000 mL·g -1 ·h -1 After one round of test, the temperature was lowered to room temperature. A total of 6 rounds of tests were conducted. The total reaction time of the cyclic application test was 7200 min. The results of the hydrogen conversion rate of the catalyst are shown in Figure 6 .

[0072] from Figure 6 It can be seen that the catalytic dehydrogenation performance of the catalyst of the present application has not decreased after multiple cycles of use, which shows that the catalyst prepared by the preparation method of the present application has good thermal stability.

[0073] The above-mentioned embodiments only express the specific implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the protection scope of the present application. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the technical solution concept of the present application, and these all belong to the protection scope of the present application.

[0074] This background section is provided to generally present the context of the invention, and the work of the presently named inventors, the work to the extent described in this background section, and aspects of this section that did not constitute prior art at the time of application are neither explicitly nor implicitly admitted to be prior art to the present invention.

Claims

1. Application of a molecular sieve confined noble metal dehydrogenation catalyst in catalytic oxidation dehydrogenation reaction, characterized in that: The molecular sieve confined noble metal dehydrogenation catalyst has an MFI molecular sieve structure, the noble metal component content is less than 0.7wt.%, and the average particle size of the noble metal component is less than 3nm; The preparation method of the molecular sieve confined noble metal dehydrogenation catalyst comprises the following steps: A. Add the noble metal salt and the organic amine compound into water at a molar ratio of 1:15-25, stir evenly, and obtain a noble metal complex solution; B. Prepare a solution of silicon source, template, deionized water and the noble metal complex obtained in step A in proportion, mix and stir well at room temperature to obtain a synthetic molecular sieve precursor solution; C. The precursor solution obtained in step B is reacted at a constant temperature of 150-200°C for 24-96 hours; after the reaction is completed, the obtained molecular sieve material is washed and dried; D. subjecting the molecular sieve material obtained in step C to thermal reduction treatment at a temperature of 400-600° C. in a 1%-10% hydrogen-argon mixed gas atmosphere to obtain a pure silicon molecular sieve confined nano-precious metal catalyst; The noble metal salt in step A is a salt of Pt or Pd.

2. The use according to claim 1, characterized in that: The conditions of the thermal reduction treatment in step D are: in a 5%-10% hydrogen-argon mixed gas atmosphere, the reaction temperature is 400-600°C.

3. The use according to claim 1, characterized in that: The isothermal reaction condition in step C is 160-180° C., and the reaction time is 48-96 hours.

4. The use according to claim 1, characterized in that: The molar ratio of the synthetic molecular sieve precursor solution in step B is: silicon source: template: deionized water: noble metal salt: organic amine compound: 1: 0.3-0.56: 33.5-65.5: 0.002-0.011: 0.03-0.28, and the molar ratio of the noble metal salt to the organic amine compound is 1: 15-25.

5. The use according to claim 1, characterized in that: The organic amine compound in step A is ethylenediamine or diethylenetriamine.

6. The use according to claim 1, characterized in that: The noble metal salt in step A is any one of PtCl2, PdCl2, and Na2PdCl4.

7. The use according to claim 1, characterized in that: The template in step B is tetrapropylammonium hydroxide.

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