Gallium or indium doped s-1 molecular sieve encapsulated metal catalyst, and preparation method and application thereof

Abstract

A gallium or indium doped S-1 molecular sieve encapsulated metal catalyst, its preparation method and application, especially in the application of low carbon alkane dehydrogenation. First, a gallium or indium doped S-1 molecular sieve slurry is prepared by a hydrothermal method, then the above catalyst is prepared through the steps of drying, impregnation, drying, dry gel crystallization reaction, calcination under nitrogen atmosphere, oxidation calcination under air atmosphere, and hydrogen atmosphere reduction. As a specific embodiment of catalyst performance evaluation, the above catalyst is evaluated for its performance in low carbon alkane dehydrogenation by taking propane dehydrogenation reaction as a model reaction. In the reaction process, no hydrogen is added, and a high propane conversion rate and propylene selectivity can be obtained, and the catalyst has good stability and good industrial application prospect. The preparation method is simple, and the dry gel material is crystallized, dried, formed, calcined and reduced to obtain the catalyst. In the preparation process, there is no water washing, filtration and other steps, which reduces the discharge of a large amount of wastewater containing metal and template, and is beneficial to industrial scale production.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of molecular sieve catalysts, and particularly relates to a gallium or indium doped S-1 molecular sieve encapsulated metal catalyst, a preparation method and application thereof. The gallium or indium doped Silicalite-1 molecular sieve is prepared by a one-step hydrothermal method, and then the gallium or indium doped S-1 molecular sieve encapsulated metal catalyst is obtained through steps of impregnation, drying to a required water content, gel crystallization, calcination under a nitrogen atmosphere, oxidation calcination under an air atmosphere, and reduction under a hydrogen atmosphere. BACKGROUND

[0002] Ethylene, propylene and butadiene are representative substances of low-carbon olefins, collectively known as industrial trienes, which are main raw materials and products for producing polymer materials such as plastics, resins and rubbers, and basic organic chemicals. There are many synthesis methods for them, such as dehydrogenation, cracking and dehydration. Among them, the method of directly preparing corresponding olefins from alkanes by dehydrogenation is of great concern because of its high selectivity of olefins, production of hydrogen as a byproduct, good atom economy and other characteristics. However, this technical process is limited by thermodynamic equilibrium. High conversion rate requires high reaction temperature, but high reaction temperature significantly increases side reactions such as C-C cracking, resulting in reduced selectivity of the catalyst, carbon deposition or coking deactivation. Therefore, in order to improve the service life of low-carbon alkane dehydrogenation catalysts, it is often necessary to frequently burn carbon and regenerate the deactivated catalyst.

[0003] At present, the main commercialized catalysts are CrO x / Al2O3 and Pt-Sn / Al2O3 catalysts. These two catalysts cannot maintain high conversion rate and thermal stability of the dehydrogenation catalyst at high temperatures. Considering the toxicity problem of Cr catalysts, platinum-based catalysts have a relatively high market share. The size of platinum metal nanoparticles in platinum-based catalysts is a key factor affecting the dehydrogenation performance. Reducing the particle size is beneficial to exposing more metal active sites, thereby improving the conversion rate of alkanes. Al2O3, SiO2 and other materials are the most commonly used supports for Pt nanoparticles, but in the process of high-temperature conversion of dehydrogenation, small-size Pt nanoparticles will undergo severe sintering and rapidly reduce the activity. Therefore, it is of great significance to develop a metal dehydrogenation catalyst with excellent catalytic performance, high thermal stability and good anti-coking performance.

[0004] In addition to the most commonly used carriers such as Al2O3, SiO2, etc., molecular sieves are also an ideal metal loading carrier due to their regular pore structure, adjustable acidity, excellent hydrothermal stability and chemical stability. At present, the metal loading molecular sieve method can be divided into traditional loading methods mainly including impregnation method and ion exchange method, and one-step synthesis of molecular sieve encapsulated metal method using ligand stabilized metal ions as raw materials. The metal loading molecular sieve prepared by traditional loading method is easy to cause uneven particle size of metal nanoparticles, poor dispersion, and ultimately leads to poor catalytic performance. The molecular sieve encapsulated metal catalyst synthesized by one-step method using ligand stabilized metal ions as raw materials can fully utilize the internal micropore structure of the molecular sieve to effectively inhibit the aggregation of metal particles, reduce the size of metal particles, and at the same time can significantly improve the hydrothermal stability of metal particles, and further improve the catalytic reaction performance. However, the stability of one-step synthesis of molecular sieve encapsulated metal method under the conditions of strong alkalinity, 100-200℃ hydrothermal autogenic pressure reaction of molecular sieve synthesis is also one of the problems to be solved.

[0005] For the dehydrogenation of low carbon alkanes, the aluminum in the molecular sieve framework has a certain acidity, which usually has a negative effect on the selectivity of the corresponding olefins. Therefore, the design of molecular sieve encapsulated metal catalysts usually chooses pure silicon molecular sieves, and the effective synthesis strategy to improve the stability of platinum-based catalysts and the selectivity of olefins is to prepare molecular sieve encapsulated metal catalysts by alloying design with platinum and various auxiliary metal elements (such as tin, gallium, copper, zinc, etc.). Silicalite-1 molecular sieve with MFI topology is a kind of molecular sieve with good adsorption separation characteristics, thermal stability and simple synthesis process, and is considered as an ideal encapsulated metal molecular sieve. Patent CN106669768A discloses a Metal@silicalite-1 molecular sieve catalyst loaded with ultra-small noble metal nanoparticles prepared by one-step hydrothermal synthesis method using noble metal [M(NH2CH2CH2NH2)2]Cl2 (M=Pd, Pt or Au) complex as precursor, which can be applied in formic acid decomposition for hydrogen production and selective catalytic reduction of nitrobenzene. The molecular sieve catalyst is a nano-sized hexagonal prism with an average diameter of 100-200 nm on the top and bottom surfaces and a thickness of 50-100 nm. Patent CN110026230A discloses a catalyst for the dehydrogenation of low carbon alkanes to prepare corresponding olefins and its application. The chemical composition of the catalyst is 0.3-20% noble metal elements, 0.1-50% modification elements and a carrier. Patent CN110479353A discloses a catalyst, its preparation method and application. The catalyst carrier is a pure silicon molecular sieve including silicalite-1 molecular sieve or Beta molecular sieve, and the active elements in the active component include Pt. Among them, Pt is loaded in the form of sub-nanometer Pt clusters in the carrier, and Zn is linked to the carrier in the form of +2 valence Zn ions through Zn-O-Si bond and connected to platinum clusters through Zn-O-Pt bond. In addition, the design of molecular sieve oxide composite dehydrogenation catalysts can also significantly improve the performance of oxide-based dehydrogenation catalysts. Patents CN113509955A, CN110614117A and CN113289671A disclose the preparation methods of a series of Co and Zn oxide molecular sieve composite dehydrogenation catalysts.

[0006] In summary, Pt-based noble metal catalysts are still one of the mainstream propane dehydrogenation catalysts, but the problem of continuous regeneration due to easy coking and deactivation of the catalyst at high temperature still cannot be effectively solved. SUMMARY

[0007] In view of the defects of the prior art in the field of metal-supported molecular sieve catalysts, the present application aims to provide a gallium or indium-doped S-1 molecular sieve encapsulated metal catalyst, a preparation method thereof and an application thereof. The gallium or indium-doped S-1 molecular sieve encapsulated metal catalyst is obtained by first preparing a gallium or indium-doped Silicalite-1 molecular sieve by a one-step hydrothermal method, and then performing the following steps: impregnation, drying to a required water content, gel crystallization, calcination under a nitrogen atmosphere, oxidation calcination under an air atmosphere, and reduction under a hydrogen atmosphere. The present application can significantly improve the utilization rate of metal elements and the catalytic performance of the catalyst in the application of low-carbon alkane dehydrogenation. Moreover, the catalyst of the present application is not prone to coking and deactivation, and does not need continuous regeneration.

[0008] The technical solution of the present application to solve the above technical problems is:

[0009] The present application provides a gallium or indium-doped S-1 molecular sieve encapsulated metal catalyst, which is obtained by doping an active metal into the framework of a Silicalite-1 molecular sieve. The Silicalite-1 molecular sieve is doped with gallium or indium before being doped with the active metal.

[0010] The present application provides a preparation method of a gallium or indium-doped S-1 molecular sieve encapsulated metal catalyst, which comprises the following steps:

[0011] (1) Preparation of gallium or indium-doped Silicalite-1 molecular sieve: weigh deionized water, a gallium or indium compound, a template agent, an alkali metal source, and a silicon source, and mix them uniformly at a temperature of 25-35°C to obtain a mixed sol, and then transfer the mixed sol to a crystallization kettle, and perform crystallization reaction at a stirring speed of 50-200 revolutions / minute and a temperature of 140-180°C for 24-72 hours. After cooling, the crystallization slurry is dried at 70-90°C for 24-48 hours to obtain gallium or indium-doped Silicalite-1 molecular sieve raw powder;

[0012] (2) Preparation of impregnation solution: weigh deionized water, an active metal source, and a chelating agent, and mix them at a temperature of 25-35°C for 1-3 hours to obtain an impregnation solution;

[0013] (3) Impregnate the gallium or indium-doped Silicalite-1 molecular sieve raw powder obtained in step (1) with the impregnation solution obtained in step (2) at a temperature of 30-60°C, and the mass ratio of the impregnation solution to the Silicalite-1 molecular sieve carrier is 2-5:1, and the impregnation time is 3-9 hours. After drying at 70-90°C, dry gel material is obtained, and the mass percentage of water in the dry gel material is controlled to be between 17% and 25%;

[0014] (4) transferring the dry gel material obtained in step (3) into a crystallization kettle, and performing dry gel crystallization reaction at a reaction temperature of 140-180℃ and a reaction time of 24-72 hours;

[0015] (5) obtaining a gallium or indium doped S-1 molecular sieve encapsulated metal catalyst after drying, molding, calcination under nitrogen atmosphere, oxidation calcination under air atmosphere, and reduction under hydrogen atmosphere of the crystallization product obtained in step (4).

[0016] In step (1), the molar ratio of SiO2:(Ga or In):M:ROH:H2O in the mixed sol is 100.0:(0.06-0.40):(0.43-1.43):(17.0-30.0):(1400.0-2100.0), wherein M is an alkali metal in the alkali metal source, ROH is a template agent, and the silicon source is measured in terms of SiO2.

[0017] In step (1), the compound of gallium or indium is selected from one of gallium nitrate, gallium sulfate, indium trichloride, and indium sulfate, the template agent is a tetrapropylammonium hydroxide aqueous solution with a mass concentration of 25-35%, the alkali metal source is sodium hydroxide or potassium hydroxide, and the silicon source is selected from one of tetraethyl orthosilicate and fumed white carbon black.

[0018] In step (1), the stirring and mixing time is preferably 1-6 hours.

[0019] In step (2), the active metal source includes a noble metal source and an auxiliary active metal source, wherein the noble metal in the noble metal source is selected from at least one of Ru, Rh, Pd, Pt, and Au, the auxiliary active metal in the auxiliary active metal source is selected from one of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, W, Ge, Sn, Pb, Sb, Bi, La, and Ce, the chelating agent is selected from one of ethylenediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine, and the molar ratio of the chelating agent to the auxiliary active metal in the active metal source is 5-20:1.

[0020] Further, in the active metal source in step (2), the noble metal in the noble metal source is selected from one of Pt and Pd, and the auxiliary active metal in the auxiliary active metal source is selected from one of Fe, Co, Ni, Cu, Zn, Sn, La, and Ce.

[0021] Further, in the active metal source in step (2), the noble metal source is selected from one of a hexachloroplatinate of a noble metal, ammonium hexachloroplatinate, and palladium chloride dihydrate, and the auxiliary active metal source is selected from one of a hydrochloride, a nitrate, a sulfate, or an acetate of the auxiliary active metal.

[0022] The Silicalite-1 molecular sieve carrier in the dry gel material in step (3) is 0.1-0.7% of the mass of SiO2, the loading of noble metal is 0.1-0.7% of the mass of SiO2, the molar ratio of SiO2, noble metal and auxiliary active metal is 100.0:(0.06-0.40):(0.54-1.89), and the molar ratio of noble metal and gallium or indium is 1:1.

[0023] In the technical solution, in step (3), it is well known to those skilled in the art that the mass percentage of water in the dry gel material is tested by a halogen moisture tester, and the test conditions are: test temperature 120℃, test time 10 minutes.

[0024] In step (5), the drying temperature is 90-120℃, the drying time is 12-24 hours; the nitrogen atmosphere is high-purity nitrogen atmosphere, the calcination temperature is 350-450℃, and the calcination time is 3-9 hours; the oxidation calcination temperature in the air atmosphere is 550-600℃, and the oxidation time is 3-9 hours; the hydrogen atmosphere reduction is high-purity hydrogen atmosphere, the reduction temperature is 550-600℃, and the reduction time is 3-9 hours.

[0025] In step (5), the molding method is processed in a manner well known to those skilled in the art, and the gallium or indium doped S-1 molecular sieve encapsulated metal catalyst crystallization product is mixed with the commonly used carrier (such as diatomite), commonly used adhesive (such as silica sol) and water according to the conventional method in the art, and then molded by the conventional method, and then used, which can directly complete the processes of calcination under nitrogen atmosphere, oxidation calcination under air atmosphere and reduction under hydrogen atmosphere on the industrial device, to obtain the gallium or indium doped S-1 molecular sieve encapsulated metal catalyst.

[0026] The gallium or indium doped Silicalite-1 molecular sieve encapsulated metal catalyst is prepared by the above method, the crystallization product is MFI structure, and the crystal grain size is 0.2-1.0μm.

[0027] The application of the gallium or indium doped Silicalite-1 molecular sieve encapsulated metal catalyst is to use it in low-carbon alkane dehydrogenation, the selectivity of low-carbon alkane dehydrogenation is 89.8%-98% in 1h of reaction, the conversion rate is 41%-45%, the selectivity is 92%-99.6% after 300h of reaction, and the conversion rate is 26%-33.5%.

[0028] As is well known to those skilled in the art, the method for evaluating the activity of dehydrogenation catalysts in a tubular reactor is as follows: Gallium or indium-doped Silicalite-1 molecular sieve-encapsulated metal low-carbon alkane dehydrogenation catalyst powder is pressed into tablets using a tablet press, then pulverized and sieved to a mesh size of 10–20 for activity evaluation. The process involves calcination under nitrogen atmosphere, oxidative calcination under air atmosphere, and reduction under hydrogen atmosphere in a tubular reactor to obtain a gallium or indium-doped Silicalite-1 molecular sieve-encapsulated metal dehydrogenation catalyst with dehydrogenation activity. The low-carbon alkane is selected from ethane, propane, and butane. The evaluation conditions in the tubular reactor are: reaction pressure of 0.05–0.3 MPa, reaction temperature of 500–650 °C, and weight hourly space velocity (WHSV) of the low-carbon alkane feed of 2–100 h⁻¹. -1 The performance of the catalyst in the dehydrogenation reaction was evaluated under the specified conditions.

[0029] Furthermore, as a specific implementation method for catalyst evaluation, the performance of the dehydrogenation catalyst was evaluated using the propane dehydrogenation reaction as a model reaction. The tubular reactor had an inner diameter of 10 mm and a catalyst loading height of approximately 30 mm. The evaluation conditions were: reaction pressure of 0.05 MPa, reaction temperature of 580 °C, and WHSV of propane gas feed of 8 h⁻¹. -1 The performance of the catalyst in the dehydrogenation reaction was evaluated under the specified conditions.

[0030] Furthermore, the specific steps for evaluating the performance of the dehydrogenation catalyst using propane dehydrogenation reaction as a model reaction are as follows: 1. The raw powder of the metal low-carbon alkane dehydrogenation catalyst encapsulated in gallium or indium-doped Silicalite-1 molecular sieve is pressed into tablets using a tablet press, then pulverized and sieved to obtain a 10-20 mesh sample to be evaluated; 2. 1.0 g of the above sample to be evaluated is mixed with 3.0 g of quartz sand, packed into a tubular reactor, heated to 400 °C in a high-purity nitrogen atmosphere at 200 ml / min, calcined for 6 hours, and then switched to 200 ml / min. In an air atmosphere, the temperature was raised to 580℃ and oxidized for 6 hours. Then, the atmosphere was switched to a high-purity nitrogen atmosphere at 200 ml / min and purged at 580℃ for 30 minutes. Finally, the atmosphere was reduced in a high-purity hydrogen atmosphere at 200 ml / min and 580℃ for 6 hours. After the reduction in the high-purity hydrogen atmosphere was completed, the atmosphere was switched to a high-purity nitrogen atmosphere at 200 ml / min and purged for 30 minutes, maintaining the reaction temperature at 580℃. The atmosphere was then switched to propane gas at 72.9 ml / min for the dehydrogenation reaction. The products were analyzed by gas chromatography.

[0031] Furthermore, the method for evaluating catalyst regeneration is as follows:

[0032] 1, after catalyst deactivation, the reaction atmosphere is switched to 200ml / min of high-purity nitrogen gas atmosphere, and the reaction temperature is reduced to 500℃, then switched to 200ml / min of air atmosphere, oxidized for 3 hours, then heated to 550℃, oxidized for 3 hours, and finally heated to 580℃, oxidized for 3 hours;

[0033] 2, switch to 200ml / min of high-purity nitrogen gas atmosphere, purge at 580℃ for 30 minutes, then reduce in 200ml / min of high-purity hydrogen gas atmosphere at 580℃ for 6 hours;

[0034] 3, after high-purity hydrogen gas reduction, switch to 200ml / min of high-purity nitrogen gas atmosphere, maintain the reaction temperature at 580℃, and switch the atmosphere to 72.9ml / min of propane gas for dehydrogenation reaction, and the product is analyzed by gas chromatograph.

[0035] The high-purity gas used in the application represents a mass purity of >99.99%.

[0036] The application is a gallium or indium doped S-1 molecular sieve encapsulated metal catalyst, its preparation method and application, especially in the application of low carbon alkane dehydrogenation, compared with the prior art, the beneficial effects of the application are:

[0037] 1, the gallium or indium doped Silicalite-1 molecular sieve prepared by the hydrothermal method is used as the carrier, the trivalent metal element is easy to be doped into the framework structure of the molecular sieve, the acid sites of the Silicalite-1 molecular sieve are increased, the molecular sieve has better noble metal anchoring and dispersion effect, so that the obtained catalyst has better thermal stability and cycle stability;

[0038] 2, the Silicalite-1 molecular sieve loaded with active metal is subjected to secondary crystallization by dry gel conversion method, the metal coating rate, dispersion and utilization rate are improved, and the loss of metal with the crystallization mother liquor in the process of liquid phase crystallization is avoided;

[0039] 3, the catalyst preparation method is simple, the dry gel material is crystallized, dried, formed, calcined under nitrogen atmosphere, oxidized calcined under air atmosphere, and reduced under hydrogen atmosphere, and the obtained dehydrogenation catalyst can be obtained, and the obtained catalyst does not need water washing, filtering and other steps, a large amount of metal-containing and template agent wastewater is reduced, and the catalyst preparation process technology is relatively mature, which is very beneficial to the industrial scale production of the catalyst. BRIEF DESCRIPTION OF DRAWINGS

[0040] The application will be further described below in combination with the drawings and examples:

[0041] Figure 1is a powder X-ray diffraction pattern of a gallium-doped S-1 molecular sieve encapsulated metal catalyst prepared in Example 1;

[0042] Figure 2 is a scanning electron microscope image of a gallium-doped S-1 molecular sieve encapsulated metal catalyst prepared in Example 1.

[0043] Figure 3 is a powder X-ray diffraction pattern of an indium-doped S-1 molecular sieve encapsulated metal catalyst prepared in Example 2;

[0044] Figure 4 is a scanning electron microscope image of an indium-doped S-1 molecular sieve encapsulated metal catalyst prepared in Example 2. DETAILED DESCRIPTION

[0045] In the description of the present application, it should be noted that, in the examples, no specific conditions are specified, and the conventional conditions or the conditions recommended by the manufacturer are used. The reagents or instruments used are not specified by the manufacturer, and are all conventional products that can be purchased on the market.

[0046] The technical solutions in the embodiments of the present application will be described in detail below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art belong to the scope of protection of the present application.

[0047] The specific implementation of the technical solutions of the present application will be described in detail below through examples, but the present application is not limited to the following description. The performance of the present application is further illustrated by evaluating the dehydrogenation reaction of propane.

[0048] Example 1

[0049] A gallium-doped S-1 molecular sieve encapsulated metal catalyst and a preparation method thereof, comprising the following steps:

[0050] (1) Preparation of gallium-doped Silicalite-1 molecular sieve: 6482.59 g of deionized water, 3.88 g of hydrated gallium nitrate, 3493.94 g of 25% mass fraction of tetrapropylammonium hydroxide aqueous solution, 4.43 g of sodium hydroxide and 5263.72 g of tetraethyl orthosilicate were stirred and mixed at a temperature of 25-35°C for 6 hours to obtain a uniform mixed sol, and then the mixed sol was transferred to a crystallization kettle, and crystallization was carried out at a stirring speed of 50 revolutions / minute and a temperature of 180°C for 24 hours. After cooling, the crystallization slurry was dried at 70°C for 48 hours to obtain gallium-doped Silicalite-1 molecular sieve raw powder. The molar ratio of SiO2: Ga: Na: TPAOH: H2O in the sol is 100.0: 0.06: 0.43: 17.0: 2000.0.

[0051] (2) Impregnation solution preparation: 3323.67 g of deionized water, 3.23 g of palladium chloride dihydrate, 55.12 g of iron nitrate nonahydrate and 164.00 g of chelating agent ethylenediamine were weighed and mixed at a temperature of 25-35°C for 1 hour to obtain an impregnation solution, and the molar ratio of the chelating agent ethylenediamine to Fe was 20:1;

[0052] (3) The impregnation solution obtained in step (2) was used to impregnate the gallium-doped Silicalite-1 molecular sieve raw powder obtained in step (1) at a temperature of 30°C, the mass ratio of the impregnation solution to the Silicalite-1 molecular sieve carrier was 2:1, the impregnation time was 9 hours, and after drying at 70°C, a dry gel material was obtained, and the water content of the dry gel material was controlled to be between 17-25%, the loading amount of the noble metal Pd in the dry gel material was 0.1% of the mass of SiO2 in the Silicalite-1 molecular sieve carrier, and the molar ratio of SiO2, noble metal elements and auxiliary active metal elements was 100.0:0.06:0.54;

[0053] (4) The dry gel material obtained in step (3) was transferred to a crystallization kettle, and a dry gel crystallization reaction was carried out at a reaction temperature of 180°C for 24 hours;

[0054] (5) The crystallization product obtained in step (4) was dried at a drying temperature of 90°C for 24 hours to obtain a Silicalite-1 molecular sieve encapsulated metal low-carbon alkane dehydrogenation catalyst raw powder; and after subsequent molding, calcination in a nitrogen atmosphere, oxidation calcination in an air atmosphere and reduction in a hydrogen atmosphere, a gallium-doped S-1 molecular sieve encapsulated metal catalyst was obtained.

[0055] (6) Propane dehydrogenation performance evaluation: a, the catalyst raw powder obtained in step (5) was tabletted by a tablet press, crushed and sieved to obtain a 10-20 mesh sample to be evaluated; b, 1.0 g of the above sample to be evaluated was mixed with 3.0 g of quartz sand, loaded into a tubular reactor, heated to 400°C in a high-purity nitrogen atmosphere at a flow rate of 200 ml / min, calcined for 6 hours, then switched to an air atmosphere at a flow rate of 200 ml / min, heated to 580°C, and oxidized for 6 hours, then switched to a high-purity nitrogen atmosphere at a flow rate of 200 ml / min, purged at 580°C for 30 minutes, and finally reduced in a high-purity hydrogen atmosphere at a flow rate of 200 ml / min at 580°C for 6 hours; 3, after the high-purity hydrogen atmosphere reduction was completed, the atmosphere was switched to a high-purity nitrogen atmosphere at a flow rate of 200 ml / min for 30 minutes, the reaction temperature was maintained at 580°C, the atmosphere was switched to 72.9 ml / min of propane gas, and the dehydrogenation reaction was carried out, and the products were analyzed by gas chromatography.

[0056] Figure 1The powder X-ray diffraction spectrum of the gallium-doped Silicalite-1 molecular sieve encapsulated metal low-carbon alkane dehydrogenation catalyst shows that the crystallization product still has the MFI structure and no metal peak, indicating that the metal has good dispersity; Figure 2 The scanning electron microscope image shows that the grain size of the obtained catalyst sample ranges from 0.2 to 0.4 microns. The propane dehydrogenation performance of the catalyst prepared in this example is shown in Table 1.

[0057] Example 2

[0058] An indium-doped S-1 molecular sieve encapsulated metal catalyst and a preparation method thereof, comprising the following steps:

[0059] (1) Preparation of the indium-doped Silicalite-1 molecular sieve: 5646.37 g of deionized water, 48.32 g of indium chloride trihydrate, 7182.55 g of 35% tetrapropylammonium hydroxide aqueous solution, 24.05 g of sodium hydroxide and 2526.60 g of fumed white carbon black (Jiangxi Black Cat Co., Ltd., model HM150, 98% dry basis after calcination at 850℃ for 2 h, same below) are mixed at a temperature of 25-35℃ for 1 hour to obtain a uniform mixed sol, which is then transferred to a crystallization kettle for crystallization at a stirring speed of 200 rpm and a temperature of 140℃ for 72 hours. After cooling, the crystallization slurry is dried at 90℃ for 24 hours to obtain indium-doped Silicalite-1 molecular sieve raw powder. The molar ratio of SiO2:In:Na:TPAOH:H2O in the sol is 100.0:0.40:1.43:30.0:1400.0.

[0060] (2) Preparation of the impregnation solution: 12771.54 g of deionized water, 58.55 g of ammonium chloropalladate, 218.92 g of cobalt sulfate heptahydrate and 737.13 g of chelating agent tetraethylenepentamine are mixed at a temperature of 25-35℃ for 3 hours to obtain the impregnation solution, and the molar ratio of the chelating agent tetraethylenepentamine to Co is 5:1;

[0061] (3) The indium-doped Silicalite-1 molecular sieve raw powder obtained in step (1) is impregnated with the impregnation solution obtained in step (2) at a temperature of 60℃, the mass ratio of the impregnation solution to the Silicalite-1 molecular sieve carrier is 5:1, the impregnation time is 3 hours, and after drying at 90℃, a dry gel material is obtained, and the water content of the dry gel material is controlled to be between 17-25%. In the dry gel material, the loading amount of the noble metal Pd is 0.7% of the mass of SiO2, and the molar ratio of SiO2, noble metal elements and auxiliary active metal elements is 100.0:0.40:1.89;

[0062] (4) The dry gel material obtained in step (3) is transferred to a crystallization kettle, and dry gel crystallization is carried out at a reaction temperature of 140°C and a reaction time of 72 hours;

[0063] (5) The crystallization product obtained in step (4) is dried at a drying temperature of 120°C for 12 hours to obtain Silicalite-1 molecular sieve encapsulated metal low-carbon alkane dehydrogenation catalyst powder; after subsequent molding, calcination under a nitrogen atmosphere, oxidation calcination under an air atmosphere, and reduction under a hydrogen atmosphere, an indium-doped S-1 molecular sieve encapsulated metal catalyst can be obtained.

[0064] (6) Propane dehydrogenation performance evaluation: a. The catalyst powder obtained in step (5) is tabletted by a tablet press, crushed, and sieved to obtain 10-20 mesh samples to be evaluated; b. 1.0 g of the above-mentioned sample to be evaluated is mixed with 3.0 g of quartz sand, loaded into a tubular reactor, heated to 400°C under a high-purity nitrogen atmosphere at a flow rate of 200 ml / min, calcined for 6 hours, then switched to an air atmosphere at a flow rate of 200 ml / min, heated to 580°C, and oxidized for 6 hours, then switched to a high-purity nitrogen atmosphere at a flow rate of 200 ml / min, purged at 580°C for 30 minutes, and finally reduced under a high-purity hydrogen atmosphere at a flow rate of 200 ml / min at 580°C for 6 hours; 3. After the high-purity hydrogen reduction is completed, the atmosphere is switched to a high-purity nitrogen atmosphere at a flow rate of 200 ml / min for 30 minutes, the reaction temperature is maintained at 580°C, the atmosphere is switched to 72.9 ml / min of propane gas, and dehydrogenation reaction is carried out, and the product is analyzed by gas chromatography.

[0065] Figure 3 The powder X-ray diffraction spectrum of the indium-doped Silicalite-1 molecular sieve encapsulated metal low-carbon alkane dehydrogenation catalyst shows that the crystallization product still has an MFI structure and no metal peak, indicating that the metal has good dispersity; Figure 4 The scanning electron microscope image shows that the grain size of the obtained catalyst sample ranges from 0.7 to 1.0 microns. The propane dehydrogenation performance of the catalyst prepared in this example is shown in Table 1.

[0066] Example 3

[0067] A gallium-doped S-1 molecular sieve encapsulated metal catalyst and a preparation method thereof, comprising the following steps:

[0068] (1) Preparation of gallium-doped Silicalite-1 molecular sieve: 7775.14 g of deionized water, 10.53 g of gallium sulfate hydrate, 5391.97 g of 30% by mass aqueous tetrapropylammonium hydroxide solution, 19.51 g of potassium hydroxide, and 2322.52 g of fumed silica were mixed at a temperature in the range of 25-35°C for 3 hours to obtain a homogeneous mixed sol, which was then transferred to a crystallization kettle for crystallization at a stirring speed of 120 rpm and a temperature of 160°C for 48 hours. After cooling, the crystallization slurry was dried at 80°C for 36 hours to obtain gallium-doped Silicalite-1 molecular sieve raw powder. The molar ratio of SiO2: Ga: K: TPAOH: H2O in the sol was 100.0: 0.13: 0.90: 21.0: 1700.0.

[0069] (2) Preparation of impregnation solution: 8190.67 g of deionized water, 21.86 g of ammonium hexachloroplatinate, 72.52 g of nickel acetate tetrahydrate, and 262.93 g of chelating agent ethylenediamine were mixed at a temperature in the range of 25-35°C for 2 hours to obtain an impregnation solution, and the molar ratio of chelating agent ethylenediamine to Ni was 15:1.

[0070] (3) The impregnation solution obtained in step (2) was used to impregnate the gallium-doped Silicalite-1 molecular sieve raw powder obtained in step (1) at a temperature of 45°C, and the mass ratio of impregnation solution to Silicalite-1 molecular sieve carrier was 3:1, and the impregnation time was 6 hours. After drying at 80°C, a dry gel material was obtained, and the water content of the dry gel material was controlled to be in the range of 17-25%. In the dry gel material, the loading of noble metal Pt was 0.42% of the mass of SiO2, and the molar ratio of SiO2, noble metal element, and auxiliary active metal element was 100.0: 0.13: 0.77.

[0071] (4) The dry gel material obtained in step (3) was transferred to a crystallization kettle for dry gel crystallization at a reaction temperature of 160°C for 48 hours.

[0072] (5) The crystallization product obtained in step (4) was dried at a temperature of 100°C for 16 hours to obtain Silicalite-1 molecular sieve encapsulated metal low-carbon alkane dehydrogenation catalyst raw powder. After subsequent molding, calcination in a nitrogen atmosphere, oxidation calcination in an air atmosphere, and reduction in a hydrogen atmosphere, a gallium-doped Silicalite-1 molecular sieve encapsulated metal low-carbon alkane dehydrogenation catalyst was obtained.

[0073] (6) Propane dehydrogenation performance evaluation: a, the catalyst powder obtained in step (5) was tabletted by a tablet press, then crushed and sieved to obtain a 10-20 mesh sample for evaluation; b, 1.0 g of the above sample for evaluation was mixed with 3.0 g of quartz sand, and loaded into a tubular reactor, and then heated to 400°C in a high-purity nitrogen atmosphere at a flow rate of 200 ml / min for 6 hours, then switched to an air atmosphere at a flow rate of 200 ml / min, and heated to 580°C for 6 hours, then switched to a high-purity nitrogen atmosphere at a flow rate of 200 ml / min, and purged at 580°C for 30 minutes, and finally reduced in a high-purity hydrogen atmosphere at a flow rate of 200 ml / min at 580°C for 6 hours; 3, after the high-purity hydrogen reduction was completed, the atmosphere was switched to a high-purity nitrogen atmosphere at a flow rate of 200 ml / min for 30 minutes, the reaction temperature was maintained at 580°C, and the atmosphere was switched to 72.9 ml / min of propane gas for dehydrogenation reaction, and the product was analyzed by gas chromatography.

[0074] The propane dehydrogenation performance of the catalyst prepared in this example is shown in Table 1.

[0075] Example 4

[0076] A gallium-doped Silicalite-1 molecular sieve encapsulated metal low-carbon alkane dehydrogenation catalyst and a preparation method thereof, the specific preparation method is the same as that of Example 3, except that the auxiliary active metal source in the impregnation solution of step (2) is 72.82 g of copper sulfate pentahydrate.

[0077] The propane dehydrogenation performance of the catalyst prepared in this example is shown in Table 1.

[0078] Example 5

[0079] A gallium-doped Silicalite-1 molecular sieve encapsulated metal low-carbon alkane dehydrogenation catalyst and a preparation method thereof, the specific preparation method is the same as that of Example 3, except that the auxiliary active metal source in the impregnation solution of step (2) is 86.76 g of zinc nitrate hexahydrate.

[0080] X-ray fluorescence spectroscopy (XRF) tests showed that the Pt content was 0.43% of the mass of silica, the Zn content was 0.86% of the mass of silica, and the Ga content was 0.17% of the mass of silica.

[0081] The propane dehydrogenation performance of the catalyst prepared in this example is shown in Table 1.

[0082] Example 6

[0083] A kind of indium-doped Silicalite-1 molecular sieve encapsulated metal low carbon alkane dehydrogenation catalyst and its preparation method, the specific preparation method is same with embodiment 3, different is that: a, the step (1) is indium-doped Silicalite-1 molecular sieve, and the amount of indium source indium sulfate nine hydrate is 16.73g;B, the auxiliary active metal source in the impregnation solution of the step (2) is 102.14g of tin tetrachloride pentahydrate.

[0084] The propane dehydrogenation performance of the catalyst prepared in this example is shown in Table 1.

[0085] Example 7

[0086] A kind of indium-doped Silicalite-1 molecular sieve encapsulated metal low carbon alkane dehydrogenation catalyst and its preparation method, the specific preparation method is same with embodiment 3, different is that: a, the step (1) is indium-doped Silicalite-1 molecular sieve, and the amount of indium source indium sulfate nine hydrate is 16.73g;B, the auxiliary active metal source in the impregnation solution of the step (2) is 102.90g of lanthanum chloride hexahydrate.

[0087] The propane dehydrogenation performance of the catalyst prepared in this example is shown in Table 1.

[0088] Example 8

[0089] A kind of indium-doped Silicalite-1 molecular sieve encapsulated metal low carbon alkane dehydrogenation catalyst and its preparation method, the specific preparation method is same with embodiment 3, different is that: a, the step (1) is indium-doped Silicalite-1 molecular sieve, and the amount of indium source indium sulfate nine hydrate is 16.73g;B, the auxiliary active metal source in the impregnation solution of the step (2) is 103.30g of cerium chloride hexahydrate.

[0090] The propane dehydrogenation performance of the catalyst prepared in this example is shown in Table 1.

[0091] Comparative Example 1

[0092] A kind of gallium-doped Silicalite-1 molecular sieve encapsulated metal low carbon alkane dehydrogenation catalyst and its preparation method in this comparative example, using two-step hydrothermal synthesis method, and the raw materials used are same with embodiment 5.

[0093] (1) Preparation of gallium-doped Silicalite-1 molecular sieve: 7775.14 g of deionized water, 10.53 g of gallium sulfate hydrate, 5391.97 g of 30% by mass aqueous tetrapropylammonium hydroxide, 19.51 g of potassium hydroxide, and 2322.52 g of fumed silica were stirred and mixed at a temperature in the range of 25-35°C for 3 hours to obtain a uniform mixed sol, which was then transferred to a crystallization kettle for crystallization at a stirring speed of 120 rpm and a temperature of 160°C for 48 hours. After cooling, a gallium-doped Silicalite-1 molecular sieve crystallization slurry was obtained. The molar ratio of SiO2: Ga: K: TPAOH: H2O in the sol was 100.0: 0.13: 0.90: 21.0: 1700.0;

[0094] (2) Metal source preparation: 8190.67 g of deionized water, 21.86 g of ammonium hexachloroplatinate, 86.76 g of zinc nitrate hexahydrate, and 262.93 g of chelating agent ethylenediamine were stirred and mixed at a temperature in the range of 25-35°C for 2 hours to obtain a metal source solution, and the molar ratio of chelating agent ethylenediamine to Zn was 15:1;

[0095] (3) The metal source solution obtained in step (2) was added to the gallium-doped Silicalite-1 molecular sieve crystallization slurry obtained in step (1), and stirred and mixed at a temperature in the range of 25-35°C for 3 hours to obtain a uniform mixed slurry;

[0096] (4) The mixed slurry obtained in step (3) was transferred to a crystallization kettle for crystallization at a stirring speed of 120 rpm and a temperature of 160°C for 48 hours;

[0097] (5) After the crystallization product obtained in step (4) was filtered and washed with water until the pH was 7-8, it was dried at a temperature of 100°C for 16 hours to obtain gallium-doped Silicalite-1 molecular sieve encapsulated metal low-carbon alkane dehydrogenation catalyst powder. After subsequent molding, calcination in a nitrogen atmosphere, oxidation calcination in an air atmosphere, and reduction in a hydrogen atmosphere, a gallium-doped Silicalite-1 molecular sieve encapsulated metal low-carbon alkane dehydrogenation catalyst was obtained.

[0098] X-ray fluorescence spectroscopy (XRF) showed that the Pt content was 0.31% by mass of silica, the Zn content was 0.55% by mass of silica, and the Ga content was 0.10% by mass of silica. Compared with Example 7, it can be seen that, in the product obtained by the hydrothermal crystallization method, the metals were lost to a greater extent in the crystallization mother liquor and the water used for washing.

[0099] The propane dehydrogenation performance of the catalyst prepared in the comparative example was as shown in Table 1.

[0100] Comparative Example 2

[0101] The same as example 1, except that no palladium chloride dihydrate and iron nitrate nonahydrate are added, i.e. no active metal source is added, the selectivity of the catalyst obtained for the dehydrogenation of low carbon alkanes is 88.2%, and the conversion rate is 24.7%.

[0102] Comparative example 3

[0103] The same as example 1, except that no iron nitrate nonahydrate is added, i.e. no auxiliary active metal source is added, the selectivity of the catalyst obtained for the dehydrogenation of low carbon alkanes is 90%, and the conversion rate is 29.3%.

[0104] Comparative example 4

[0105] The same as example 1, except that no gallium nitrate hydrate is added, i.e. no gallium or indium doping is performed, the selectivity of the catalyst obtained for the dehydrogenation of low carbon alkanes is 91.5% after 1h, and the conversion rate is 36.5%, and the conversion rate is reduced compared with example 1.

[0106] Comparative example 5

[0107] The same as example 1, except that the Silicalite-1 molecular sieve raw powder is doped with a metal source first, and then doped with gallium or indium, i.e. the doping order is reversed, such as in step (1), the gallium nitrate hydrate is replaced with palladium chloride dihydrate and iron nitrate nonahydrate, and in step (2), the gallium nitrate hydrate is used to prepare the impregnation solution, then the selectivity of the catalyst obtained for the dehydrogenation of low carbon alkanes is 87%, and the conversion rate is 23.5%.

[0108] The performance of the prepared catalysts for propane dehydrogenation was statistically analyzed, wherein the activity evaluation data of the catalysts prepared in examples 1-8 and comparative examples for propane dehydrogenation catalyst applications are shown in table 1.

[0109] Table 1 Activity evaluation data of the catalysts prepared in examples 1-8 and comparative examples for propane dehydrogenation catalyst applications

[0110]

[0111] Note: The catalyst dehydrogenation reaction performance evaluation was carried out under the conditions of a reaction pressure of 0.05 MPa, a reaction temperature of 580°C, and a WHSV of the propane gas feed of 8h -1

[0112] Comparing the data of comparative example 1 and example 5, the conversion rate of propane is reduced.

[0113] ​The embodiments are only for illustrating the technical concepts and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made according to the spirit and principle of the present application shall be covered within the protection scope of the present application.

Claims

1. A gallium or indium-doped S-1 molecular sieve-encapsulated metal catalyst, characterized in that, The gallium or indium-doped S-1 molecular sieve encapsulated metal catalyst is obtained by doping an active metal into a Silicalite-1 molecular sieve framework, wherein the Silicalite-1 molecular sieve is first doped with gallium or indium before doping with the active metal. The method for preparing the gallium or indium-doped S-1 molecular sieve-encapsulated metal catalyst includes a one-step hydrothermal method to prepare gallium or indium-doped Silicalite-1 molecular sieve, followed by impregnation, drying, and dry gel crystallization reaction to obtain a crystallized product which is then dried, shaped, calcined under a nitrogen atmosphere, oxidized and calcined under an air atmosphere, and reduced under a hydrogen atmosphere to obtain the gallium or indium-doped S-1 molecular sieve-encapsulated metal catalyst. The specific process parameters for the one-step hydrothermal method for preparing gallium or indium-doped Silicalite-1 molecular sieves are as follows: (1) Weigh out deionized water, gallium or indium compound, template agent, alkali metal source and silicon source, stir and mix evenly to obtain mixed sol; (2) Transfer the mixed sol to a crystallization vessel, and crystallize it at 140~180℃ for 24~72 hours with stirring. After cooling, dry it to obtain gallium or indium doped Silicalite-1 molecular sieve powder. The active metal source includes a noble metal source and a co-active metal source, wherein the noble metal in the noble metal source is selected from at least one of Ru, Rh, Pd, Pt, and Au, and the co-active metal in the co-active metal source is selected from one of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, W, Ge, Sn, Pb, Sb, Bi, La, and Ce.

2. The gallium or indium-doped S-1 molecular sieve-encapsulated metal catalyst according to claim 1, characterized in that, In (1), the molar ratio of SiO2:(Ga or In):M:ROH:H2O in the mixed sol is 100.0:(0.06~0.40):(0.43~1.43):(17.0~30.0):(1400.0~2100.0), where M is the alkali metal in the alkali metal source, ROH is the template agent, and the silicon source is measured in SiO2; and / or, the gallium or indium compound is selected from gallium nitrate, gallium sulfate, indium trichloride, and indium sulfate, the template agent is a tetrapropylammonium hydroxide aqueous solution with a mass concentration of 25~35%, the alkali metal source is sodium hydroxide or potassium hydroxide, and the silicon source is selected from tetraethyl orthosilicate and fumed silica; and / or, the stirring and mixing is carried out at room temperature for 1~6 hours; and / or, in (2), the stirring speed is 50~200 rpm, and the drying is carried out at 70~90℃ for 24~48 hours.

3. The gallium or indium-doped S-1 molecular sieve-encapsulated metal catalyst according to claim 1, characterized in that, The impregnation solution used is a mixture of deionized water, an active metal source, and a chelating agent, prepared by stirring evenly. The impregnation and drying process is as follows: the impregnation solution is used to impregnate gallium or indium-doped Silicalite-1 molecular sieve powder at a temperature of 30~60°C. The mass ratio of the impregnation solution to the Silicalite-1 molecular sieve carrier is 2~5:1, the impregnation time is 3~9 hours, and the dry adhesive material is dried while controlling the water content of the dry adhesive material to be between 17~25% by mass to obtain the dry adhesive material.

4. The gallium or indium-doped S-1 molecular sieve-encapsulated metal catalyst according to claim 3, characterized in that, The chelating agent is selected from one of ethylenediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine, and the molar ratio of the chelating agent to the co-active metal in the active metal source is 5~20:

1.

5. The gallium or indium-doped S-1 molecular sieve-encapsulated metal catalyst according to claim 3, characterized in that, In the dry adhesive material, the Silicalite-1 molecular sieve support is based on SiO2, and the loading of noble metals is 0.1~0.7% of the mass of SiO2. The molar ratio of SiO2, noble metals and auxiliary active metals is 100.0:(0.06~0.40):(0.54~1.89), and the molar ratio of noble metals to gallium or indium is 1:

1.

6. The gallium or indium-doped S-1 molecular sieve-encapsulated metal catalyst according to claim 1, characterized in that, The dry adhesive crystallization reaction is as follows: the dry adhesive material is transferred to a crystallization kettle and the dry adhesive crystallization reaction is carried out at a reaction temperature of 140-180℃ and a reaction time of 24-72 hours.

7. The gallium or indium-doped S-1 molecular sieve-encapsulated metal catalyst according to claim 1, characterized in that, The process parameters for drying, shaping, calcination under nitrogen atmosphere, oxidative calcination under air atmosphere, and reduction under hydrogen atmosphere of the crystallized product are as follows: drying temperature is 90~120°C, drying time is 12~24 hours; nitrogen atmosphere is high-purity nitrogen atmosphere, calcination temperature is 350~450°C, calcination time is 3~9 hours; the oxidative calcination temperature under air atmosphere is 550~600°C, oxidation time is 3~9 hours; the reduction under hydrogen atmosphere is high-purity hydrogen atmosphere, reduction temperature is 550~600°C, reduction time is 3~9 hours.

8. The application of the gallium or indium-doped Silicalite-1 molecular sieve-encapsulated metal catalyst of claim 1 in the dehydrogenation of low-carbon alkanes.

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