Self-pillared all-silicon molecular sieve supported catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the field of catalysts, and particularly relates to a self-pillared all-silicon molecular sieve supported catalyst as well as a preparation method and application thereof. The catalyst mainly comprises a nanoscale Silicalite-2 molecular sieve rich in silicon hydroxyl defect sites, an active metal component and an auxiliary agent metal component, wherein the carrier presents a self-pillared morphology formed by splicing and assembling rod-like microcrystals with the particle size of 10-40 nm, after the active metal is loaded by rich silicon hydroxyl defect sites on the surface of the carrier, the interaction between the metal and the carrier can be remarkably enhanced, and the obtained highly-dispersed active metal nanoparticles with the particle size of 1-5 nm are obtained. When the catalyst is applied to propane dehydrogenation reaction, the catalyst shows excellent catalytic activity, the propane conversion rate is 41% or above, the propylene selectivity is up to 97% or above, and good stability provides a new technical approach for developing a propane dehydrogenation fixed bed process which is low in operation cost, low in energy consumption and free of frequent regeneration.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of catalysts, and particularly relates to a self-pillared all-silicon molecular sieve supported catalyst and a preparation method thereof and application of the catalyst in preparation of propylene from propane dehydrogenation. BACKGROUND

[0002] Propylene is the second largest petroleum chemical intermediate in the world, and is widely used in the synthesis of important bulk chemicals such as polypropylene, acrylonitrile, acrylic acid, acetone and propylene oxide. With the increasing demand for downstream derivative chemicals year by year, the traditional propylene production process cannot meet the demand of the chemical industry. In recent years, with the reform of global energy structure and the development of light and diversified raw materials, shale gas, natural gas and coal bed gas rich in propane are used as raw materials to prepare propylene, which can greatly alleviate the contradiction between supply and demand in the propylene market. Compared with traditional catalytic cracking and steam cracking technologies, the propane direct dehydrogenation to propylene (PDH) technology has the advantages of short process flow, high propylene yield, low investment cost and high economic efficiency, and is the main development direction of future propylene capacity expansion.

[0003] The core technology of propane dehydrogenation is to develop a catalyst with high activity, high selectivity and high stability. At present, more than 80% of the propane dehydrogenation devices in the world use the PtSn / Al2O3 catalyst system developed by UOP Company. This type of catalyst has high catalytic activity and good propylene selectivity. However, it still faces two major problems: first, the catalyst is prone to Ostwald ripening and migration and agglomeration during long-term operation at high temperature, and the sintering of the catalyst causes its activity to decrease; second, the large particles formed by agglomeration and the strong acidity of the carrier can promote the occurrence of hydrogenolysis, cracking and other carbon deposition side reactions, leading to catalyst coking and deactivation and reduction of the selectivity of the target product propylene. In addition, the actual industrial moving bed process still needs frequent regeneration (average 5-7 days), which has high energy consumption and the performance cannot be completely restored. Therefore, developing a propane dehydrogenation catalyst with excellent performance, high propylene selectivity and good stability is a key problem to be solved for the existing propane dehydrogenation technology.

[0004] In recent years, a lot of research work has been done to develop a good performance propane dehydrogenation catalyst. Chinese patent CN115430423A discloses a spherical alumina-based PtSn propane dehydrogenation catalyst doped with rare earth elements, which uses oil column forming method to introduce rare earth elements into aluminum sol, and gets uniform dispersion in spherical alumina carrier, then uses the side chain functional groups (-CH2OH) of cross-linking template to occur in-situ addition condensation reaction with formaldehyde to construct S-Al2O3 carrier with three-dimensional cross-linked network pore structure, and the average pore size of mesoporous is 18-50 nm. Finally, the metal Pt and Sn components are impregnated into the carrier channel by one-step vacuum spraying method. After gas phase reduction, high dispersion active metal nanoparticles (1-3 nm) are obtained, which are applied to propane dehydrogenation reaction, the propane conversion rate is 42.9%, and the propylene selectivity is 95.8%, but the stability of the catalyst needs to be investigated. Patent CN109746028A discloses a propane dehydrogenation supported catalyst and a preparation method thereof, and a spherical aluminum-containing mesoporous molecular sieve silica gel composite material is prepared as a carrier, which includes a ball milling aluminum component, a mesoporous molecular sieve material and a silica gel. The carrier material has a special three-dimensional cubic ordered mesoporous pore distribution structure and the pore structure of silica gel, and the specific surface area is 100-180 m 2 / g, so that the metal components are well dispersed inside the pores thereof. After loading the Pt, Sn, and Na components, the catalyst exhibits good propane dehydrogenation performance, with a propane conversion of 28%-30% and a propylene selectivity of about 80%. Patent CN117463391A uses a porous all-silica molecular sieve MFI, MWW, and Beta with weak surface acidity as a carrier, and after loading active metal Pt and transition metal element additives and calcination, the M-O-Si bond formed by the metal species can highly disperse the active sites, so that the active components of the catalyst are not easy to be lost, have good stability, and are not easy to catalyze side reactions. The catalyst has a propane conversion of 17% at 400°C without co-feeding hydrogen, a propylene selectivity of more than 99%, and good stability. Other carrier materials such as composite carrier materials (patent CN109746028A) and carbon materials (patent CN109745978A) construct alumina and mesoporous silica composite materials with special three-dimensional cubic ordered mesoporous pore distribution structures and mesoporous carbon materials with cubic and hexagonal coexisting pore structures with a cubic structure, respectively. The most probable pore size distribution of the former is 4-8 nm and 30-40 nm, and the most probable pore size of the latter is 2-5 nm. After loading the Pt, Sn, and Na components, the propane conversion is 28%-31%, and the propylene selectivity is maintained at 80%-87%. Patent CN116212861A discloses a preparation method of a propane dehydrogenation catalyst, uses an excess of Sn additives to dilute Pt to a single atomic dispersion state, constructs a PtSn disordered alloy sub-nanometer catalyst, and although the stability of the catalyst is improved to a certain extent, the selectivity of propylene is maintained at 80-90%.

[0005] Based on the analysis of the above literature, although the related research on propane dehydrogenation catalysts has made certain progress at the present stage, it is still basically in the basic research stage, and there are problems such as high synthesis cost, poor repeatability, structure stability, and catalyst selectivity to be improved. In particular, the propylene selectivity of the alumina-containing supported catalyst is relatively low compared to the all-silica molecular sieve, and there is still a large space for improvement of the propane dehydrogenation catalyst and the carrier. Therefore, it is crucial to develop a molecular sieve carrier with excellent performance for improving the performance of the propane dehydrogenation catalyst. SUMMARY

[0006] The present application aims at overcoming the problems existing in the prior art, and provides a self-pillared full-silica molecular sieve supported catalyst, a preparation method and application thereof. The present application utilizes the synthesis mechanism of low-temperature nucleation and high-temperature rapid growth of the molecular sieve, and adopts a simple and efficient two-stage crystallization method to rapidly synthesize a nanoscale Silicalite-2 molecular sieve supported catalyst with a self-pillared morphology, so as to effectively shorten the synthesis time of the molecular sieve and improve the synthesis efficiency. Meanwhile, the silicon hydroxyl defect sites rich on the surface of the synthesized molecular sieve carrier can be bonded with the active metal components through Si-O-metal (for example, Si-O-Pt) after loading the active metal, so as to strengthen the interaction between the metal and the carrier, and obtain the active metal component nanoparticles with a size of 1-5 nm. When the catalyst of the present application is applied to a propane dehydrogenation catalytic reaction, the catalytic activity and stability are significantly improved compared with the traditional synthesis method.

[0007] In order to achieve the above-mentioned application purposes, the present application adopts the following technical solutions.

[0008] The first aspect of the present application is to provide a self-pillared full-silica molecular sieve supported catalyst, which comprises a carrier, and an active component and an optional auxiliary component loaded on the carrier, the carrier is rich in silicon hydroxyl defect sites, the active component is selected from at least one of Group VIII metals, and the auxiliary component is selected from at least one of Sn, Zn, Ga and Cu.

[0009] According to the present application, in the self-pillared full-silica molecular sieve supported catalyst:

[0010] The carrier is a nanoscale full-silica molecular sieve with MEL structure, preferably, the carrier presents a self-pillared morphology assembled by rod-like microcrystals with a cross-sectional diameter of 10-40 nm;

[0011] The ratio of the peak area Q3 of the silicon hydroxyl defect sites in the carrier to the peak area Q4 of the silicon oxygen tetrahedron is 1:(3-10) by testing with a nuclear magnetic resonance spectrometer;

[0012] The active component is selected from at least one of Pt, Ir, Au, Pd and Rh, and is preferably Pt;

[0013] In the catalyst, the particle size of the active component metal particles is 1-5 nm;

[0014] The auxiliary component optionally comprises at least one of an alkali metal element and an alkaline earth metal element, for example, at least one of Li, Na, K, Rb, Cs, Mg, Ca and Sr.

[0015] According to the application, the nanoscale full-silica molecular sieve in the self-pillared full-silica molecular sieve supported catalyst has at least one of the following characteristics:

[0016] The particle size of the nanoscale full-silica molecular sieve is 200-500 nm, preferably 200-400 nm;

[0017] The external specific surface area of the nanoscale full-silica molecular sieve is 200-500 m 2 / g, preferably 200-400 m 2 / g;

[0018] The mesopore volume of the nanoscale full-silica molecular sieve is 0.5-1.5 cm 3 / g, preferably 0.5-1.2 cm 3 / g;

[0019] The nanoscale full-silica molecular sieve has a multi-level pore distribution characteristic, with micropore size distribution of 0.5-2 nm and intercrystalline mesopore distribution of 2-50 nm; preferably, the micropore size distribution is 0.5-1 nm and the intercrystalline mesopore distribution is 2-40 nm.

[0020] The content of the active component is 0.1-2 wt%, preferably 0.1-1 wt%, based on 100 wt% of the total weight of the self-pillared full-silica molecular sieve supported catalyst; the content of the auxiliary component is 0.1-10 wt%, preferably 0.1-5 wt%; the content of the alkali metal element is 0-2 wt%, preferably 0-1 wt%; and the content of the alkaline earth metal element is 0-2 wt%, preferably 0-1 wt%.

[0021] The second aspect of the application provides a preparation method of the self-pillared full-silica molecular sieve supported catalyst according to the first aspect of the application, which comprises: immersing a carrier rich in silicon hydroxyl defect sites in a precursor aqueous solution containing an active component precursor compound and an auxiliary component precursor compound, and then obtaining the self-pillared full-silica molecular sieve supported catalyst after removing the solvent, drying and calcining; preferably, the carrier rich in silicon hydroxyl defect sites is a nanoscale Silicalite-2 molecular sieve.

[0022] According to the application, the preparation method of the self-pillared full-silica molecular sieve supported catalyst comprises:

[0023] The active component precursor compound is selected from at least one of a chlorine-containing compound and a nitrate of a metal in Group VIII, preferably at least one of a chlorine-containing compound and / or a nitrate of at least one metal selected from Pt, Ir, Au, Pd and Rh; more preferably at least one of chloroplatinic acid, dichloroplatinum, tetraammineplatinum nitrate and platinum tetrachloride.

[0024] The auxiliary component precursor compound is selected from at least one metal of Sn, Zn, Ga, Cu, and at least one of a chloride and / or nitrate, and optionally at least one of an alkali metal salt and an alkaline earth metal salt; when Sn is used as the auxiliary metal, the Sn source is selected from one or more of crystalline SnCl4.5H2O and SnCl2.2H2O; when Zn or Cu is used as the auxiliary metal, the Zn source is selected from one or more of ZnCl2 and Zn(NO3)2.6H2O; the Cu source is selected from one or more of CuCl4, CuCl2.2H2O and Cu(NO3)2.3H2O; when Ga is used as the auxiliary metal, the Ga source is selected from one or more of GaCl3 and Ga(NO3)2.xH2O; when an alkali metal or alkaline earth metal is used as the auxiliary metal, at least one metal of Li, Na, K, Rb, Cs, Mg, Ca and Sr can be used in the form of a chloride and / or nitrate;

[0025] The impregnation conditions can be selected within a wide range, for example, the impregnation conditions are 20-40℃ and 6-12h;

[0026] The solvent removal is preferably performed by rotary evaporation, and the rotary evaporation conditions are preferably 70-80℃, 120-150rpm and 65-75mbar;

[0027] The drying is not particularly limited, and a commonly used drying device and drying conditions can be used, for example, the drying conditions are 80-120℃ and 6-12h;

[0028] The calcination conditions are preferably 1-2℃ / min to 500-600℃, and the calcination time is 4-6h; preferably, the calcination is performed at 550-580℃.

[0029] According to the present application, the preparation method of the self-pillared all-silicon molecular sieve supported catalyst, the preparation method of the nanoscale Silicalite-2 molecular sieve comprises:

[0030] (1) mixing a silicon source, an organic template agent and water, and stirring to form a mixed gel;

[0031] (2) transferring the mixed gel into an autoclave, and statically crystallizing at different temperatures step by step; preferably, a two-stage crystallization process is used;

[0032] (3) after the crystallization is completed, separating, washing, drying and calcining after cooling to obtain the nanoscale Silicalite-2 molecular sieve.

[0033] According to the present aspect, the preparation method of the nanoscale Silicalite-2 molecular sieve comprises the following steps:

[0034] The mixing conditions can be selected in a wide range, for example, the temperature is 20-40℃, and the time is 2-12h; the stirring speed is 400-600rpm relative to 10g of the mixture system;

[0035] The silicon source is selected from at least one of tetraethyl orthosilicate, silica gel and silica sol, and is preferably tetraethyl orthosilicate; wherein the tetraethyl orthosilicate can be a common commercially available product, for example, tetraethyl orthosilicate, tetraethyl orthosilicate-28, tetraethyl orthosilicate-40, etc.

[0036] The organic template agent is selected from at least one of organic ammonium compounds, and is preferably at least one of tetraethylammonium hydroxide, tetraethylammonium bromide, tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetrapropylammonium chloride, tetrapropylammonium fluoride, tetrabutylammonium hydroxide, tetrabutylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium fluoride;

[0037] The molar ratio of the silicon source, the organic template agent and water is 1:(0.1-1):(10-100), and is preferably 1:(0.1-0.5):(10-80), wherein the silicon source is calculated based on SiO2 contained therein, and the water is preferably deionized water;

[0038] The stirring conditions are as follows: the temperature is 20-40℃, and the time is 2-12h.

[0039] According to the present aspect, the preparation method of the nanoscale Silicalite-2 molecular sieve comprises the following steps:

[0040] The two-stage crystallization comprises a first-stage low-temperature crystallization and a second-stage high-temperature crystallization, and the first-stage low-temperature crystallization and the second-stage high-temperature crystallization adopt different temperature conditions;

[0041] Preferably, the first-stage crystallization conditions are as follows: the crystallization temperature is 50-120℃, and the crystallization time is 24-120h; and the molecular sieve is nucleated at a low temperature in this stage;

[0042] Preferably, the second-stage crystallization conditions are as follows: the crystallization temperature is 120-180℃, and the crystallization time is 24-120h; and the molecular sieve crystal grains complete rapid growth in this stage.

[0043] According to the present aspect, the preparation method of the nanoscale Silicalite-2 molecular sieve comprises the following steps:

[0044] After the two-stage crystallization process is completed, the generated suspension is naturally cooled to room temperature and then centrifuged; the centrifugation is not particularly limited and can be performed by using common centrifugation equipment and operation conditions; preferably, the centrifugation conditions include a rotation speed of 3000-5000 rpm and a time of 0.5-2.0 h;

[0045] After centrifugation, the product is washed with deionized water until the pH value is 7-8; the amount and number of times of washing are not particularly limited, and the product is only required to be washed clean of free ions and precursor solution, and the final pH value is 7-8;

[0046] The drying in step (3) is not particularly limited and can be performed by using common drying equipment and drying conditions, for example, the drying conditions include a temperature of 80-120℃ and a time of 6-12 h;

[0047] The calcination conditions include a temperature rising rate of 1-2℃ / min, a temperature of 500-600℃, and a time of 4-6 h; preferably, the calcination is performed at 550-580℃.

[0048] A third aspect of the present application provides a use of the self-pillared full-silica molecular sieve supported catalyst according to the first aspect of the present application or the self-pillared full-silica molecular sieve supported catalyst obtained by the preparation method according to the second aspect of the present application in a reaction of dehydrogenation of propane to prepare propylene.

[0049] Specifically, the use includes: loading the self-pillared full-silica molecular sieve supported catalyst into a reactor, fixing the upper and lower beds by using quartz sand, diluting the propane gas by using H2, and performing a dehydrogenation reaction with the catalyst to obtain propylene.

[0050] Preferably, in the dehydrogenation reaction, the mass space velocity of the propane gas is 1-50 h -1 , the pressure ratio of H2 to propane is 1:(1-8), and the temperature of the dehydrogenation reaction is 550-620℃.

[0051] Compared with the prior art, the present application has the following beneficial effects:

[0052] (1) The catalyst provided by the present application is synthesized by using a two-stage crystallization method, and the growth mechanism of low-temperature nucleation and high-temperature rapid crystallization is used to significantly improve the crystallization rate and synthesis efficiency of the Silicalite-2 molecular sieve with MEL structure, thereby saving time and cost.

[0053] (2) The Silicalite-2 molecular sieve provided by the present application has a self-pillared morphology assembled by nanorod-shaped microcrystals, and the silicon hydroxyl defect sites on the outer surface are more conducive to the dispersion of the active component and the enhancement of the interaction force between the active component and the carrier, thereby significantly improving the activity and propylene selectivity of the catalyst and helping to prolong the service life of the catalyst.

[0054] (3) The preparation method of the supported catalyst provided by the application is stable, and when used for propane dehydrogenation reaction, the supported catalyst exhibits excellent dehydrogenation activity and propylene selectivity, specifically, the propane conversion rate is 42%, the propylene selectivity can reach more than 97%, and the supported catalyst exhibits good stability and has good industrial application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0055] Figure 1 X-ray diffraction spectrum (XRD) of the nanoscale Silicalite-2 molecular sieve supported catalyst prepared in Example 1, wherein the reference molecular sieve is a commercially available Silicalite-2 molecular sieve;

[0056] Figure 2 Scanning electron microscope (SEM) image of the nanoscale Silicalite-2 molecular sieve supported catalyst prepared in Example 1;

[0057] Figure 3 N2-physical adsorption and desorption curve of the nanoscale Silicalite-2 molecular sieve prepared in Example 1;

[0058] Figure 4 Si nuclear magnetic resonance spectrum of the nanoscale Silicalite-2 molecular sieve prepared in Example 1; 29 Si nuclear magnetic spectrum results;

[0059] Figure 5 High-resolution transmission electron microscope (TEM) image of the nanoscale Silicalite-2 molecular sieve supported catalyst prepared in Example 1. DETAILED DESCRIPTION

[0060] The application will be described in detail below with specific examples. It is necessary to point out here that the following examples are only used to further illustrate the application and cannot be understood as limiting the protection scope of the application. Some non-essential improvements and adjustments to the application made by those skilled in the art based on the content of the application still fall within the protection scope of the application.

[0061] The specific embodiments of the application will be explained and described below. It should be understood that the following specific embodiments are only used to explain and describe the application and are not used to limit the application.

[0062] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not critical to the properties. The endpoints of the ranges and the individual points within the ranges can be combined with one another to recite new ranges and new points, which are also expressly disclosed herein.

[0063] Example 1:

[0064] Preparation of nano Silicalite-2 molecular sieve:

[0065] Weigh 21.89 g of tetrabutylammonium hydroxide (TPAOH) aqueous solution (the concentration of TPAOH is 25 wt%), mix with 8.54 g of deionized water and stir uniformly, then slowly drop 20.05 g of tetraethyl orthosilicate (TEOS) into the above mixed solution, seal and continue stirring at room temperature overnight to make the tetraethyl orthosilicate completely hydrolyzed. Transfer the above gel solution into an autoclave, first crystallize at low temperature 120℃ for 48h, then directly heat to 170℃ for 24h, cool to room temperature, then high-speed centrifugal separation of the crystallization product, and wash with deionized water until pH = 7.5, dry in an oven at 120℃ overnight, finally heat to 580℃ at a heating rate of 1-2℃ / min, and calcine at 580℃ for 6 hours to obtain nano Silicalite-2 molecular sieve.

[0066] Preparation of supported catalyst:

[0067] Weigh 0.0845 g of chloroplatinic acid hexahydrate and 0.1720 g of crystalline tin tetrachloride respectively, dissolve in 2 g of deionized water, stir uniformly until completely dissolved, to prepare a metal precursor aqueous solution.

[0068] Immerse the above prepared nano Silicalite-2 molecular sieve into the metal aqueous solution, immerse at room temperature overnight, then remove the immersed sample from the solution, and vacuumize (vacuum degree 72 mbar) at a water bath temperature of 70℃ and a rotation speed of 120 rpm in a rotary evaporator, then place it in a drying oven at 100℃ for 8h, and finally calcine it in a muffle furnace at 580℃ for 6h to obtain a self-pillared nano Silicate-2 molecular sieve supported catalyst, which is recorded as catalyst A1. The metal content is determined by inductively coupled plasma emission spectrometry, and the mass percentage of each metal component in the total mass of the catalyst is Pt: 0.5 wt%, Sn: 1.0 wt%.

[0069] The phase structure characterization results of catalyst A1 are shown in Figure 1 As can be seen from the figure, the catalyst has high crystallinity and shows a significant MEL structure characteristic peak. From the Figure 2The SEM scanning electron microscope results can be seen that the catalyst presents a self-pillared morphology assembled by nanorod-like microcrystals, and the grain size is between 200-250 nm; and Figure 3 The N2-physical adsorption desorption results show that the catalyst has a multi-stage pore distribution characteristic, and the mesopore size distribution is between 2-30 nm; Figure 4 The nuclear magnetic spectrum results of the silicon coordination environment show that the Q3 / Q4 ratio is 1:8.0, which is higher than the 1:12 of the conventional molecular sieve; this is consistent with the TEM results( Figure 5 ) that the PtSn alloy nanoparticles are well dispersed on the catalyst surface, and the particle size distribution is between 1-5 nm.

[0070] Example 2:

[0071] The preparation method of the catalyst is the same as that of Example 1. The difference is that, on the basis of impregnating the Pt component and the Sn component, a stepwise impregnation method is adopted to continue to load the alkali metal K adjuvant. 0.1102 g of potassium chloride is weighed and dissolved in 1 g of deionized water, and then impregnated on the catalyst precursor containing the Pt and Sn metal components prepared. The impregnated sample is also subjected to solvent removal under vacuum (vacuum degree 72 mbar) on a rotary evaporator with a water bath temperature of 70 ℃ and a rotation speed of 120 rpm, dried in a drying box at 100 ℃ for 8 h, and finally calcined in a muffle furnace at 580 ℃ for 6 h to obtain catalyst A2. The metal content is determined by inductively coupled plasma emission spectrometry. The mass percentage of each metal component in the total mass of the catalyst is Pt: 0.5 wt%, Sn: 1.0 wt%, and K: 1.0 wt%.

[0072] Example 3:

[0073] The preparation method of the catalyst is the same as that of Example 1. The difference is that the crystallization process of the molecular sieve is 48 h at a low temperature of 120 ℃ and 24 h at a high temperature of 180 ℃, respectively, and the nanoscale Silicalite-2 molecular sieve is prepared. The metal precursor solution is impregnated by weighing 0.0634 g of chloroplatinic acid hexahydrate and 0.1557 g of crystalline tin tetrachloride, dissolving them in 2 g of deionized water, and impregnating them on the prepared nanoscale Silicalite-2 molecular sieve overnight. After solvent removal, drying, and calcination, the corresponding catalyst is prepared and is recorded as catalyst A3. The metal content is determined by inductively coupled plasma emission spectrometry. The mass percentage of each metal component in the total mass of the catalyst is Pt: 0.375 wt%, and Sn: 1.0 wt%.

[0074] Example 4:

[0075] The catalyst was prepared in the same way as in Example 3. The difference is that the crystallization was carried out at low temperature 110°C for 72h and at high temperature 170°C for 24h, Zn was selected as the promoter, 0.0634g of chloroplatinic acid hexahydrate and 0.1758g of zinc nitrate hexahydrate were weighed and dissolved in 2g of deionized water to prepare a mixed aqueous solution of metal precursors, which was mixed with the molecular sieve prepared above, impregnated overnight, and then subjected to the same steps of desolventizing, drying and calcining to prepare a catalyst loaded with PtZn components, which is recorded as catalyst A4. The metal content was determined by inductively coupled plasma emission spectrometry. The mass percentage of each metal component in the total mass of the catalyst was Pt: 0.375wt%, Zn: 1.6wt%.

[0076] Example 5:

[0077] The catalyst was prepared in the same way as in Example 3. The difference is that the crystallization was carried out at low temperature 110°C for 72h and at high temperature 170°C for 24h, Zn was selected as the promoter, 0.0634g of chloroplatinic acid hexahydrate and 0.1758g of zinc nitrate hexahydrate were weighed and dissolved in 2g of deionized water to prepare a mixed aqueous solution of metal precursors, which was mixed with the molecular sieve prepared above, impregnated overnight, and then subjected to the same steps of desolventizing, drying and calcining to prepare a catalyst loaded with PtZn components, which is recorded as catalyst A4. The metal content was determined by inductively coupled plasma emission spectrometry. The mass percentage of each metal component in the total mass of the catalyst was Pt: 0.375wt%, Zn: 1.6wt%.

[0078] Example 6:

[0079] The catalyst was prepared in the same way as in Example 3. The difference is that the crystallization was carried out at low temperature 110°C for 72h and at high temperature 170°C for 24h, Zn was selected as the promoter, 0.0634g of chloroplatinic acid hexahydrate and 0.1758g of zinc nitrate hexahydrate were weighed and dissolved in 2g of deionized water to prepare a mixed aqueous solution of metal precursors, which was mixed with the molecular sieve prepared above, impregnated overnight, and then subjected to the same steps of desolventizing, drying and calcining to prepare a catalyst loaded with PtZn components, which is recorded as catalyst A4. The metal content was determined by inductively coupled plasma emission spectrometry. The mass percentage of each metal component in the total mass of the catalyst was Pt: 0.375wt%, Zn: 1.6wt%.

[0080] Comparative Example 1:

[0081] The catalyst was prepared according to the method of Example 1. The difference is that the molecular sieve was prepared by one-step synthesis method (using different crystallization conditions), and other conditions were the same as those of Example 1. The crystallization conditions included: the hydrothermal temperature was 160°C, the hydrothermal time was 120h, and the conventional hexagonal prism Silicalite-2 molecular sieve was prepared after centrifugation, washing, drying and calcination. The same Pt and Sn metal components as in Example 1 were weighed and impregnated with the above prepared conventional molecular sieve overnight. After desolventizing, washing, drying and calcination, the corresponding supported catalyst was obtained, which was recorded as catalyst D1. The metal content was determined by inductively coupled plasma emission spectrometry. The mass percentage of each metal component was 0.5wt% of Pt and 1.0wt% of Sn, based on the total mass of the catalyst.

[0082] Comparative Example 2

[0083] According to the catalyst preparation method in Example 1, the difference is that a commercially purchased γ-Al2O3 carrier was used. Specifically, the same mass of active metal and additive metal components were weighed and dissolved in deionized water, stirred and mixed uniformly, and then co-impregnated on a commercially purchased γ-Al2O3 carrier. The impregnated sample was desolventized in a rotary evaporator at a water bath temperature of 70°C and a rotation speed of 120rpm under vacuum (vacuum degree 72mbar), dried in a drying oven at 100°C for 8h, and calcined in a muffle furnace at 580°C for 6h to obtain a γ-Al2O3 supported catalyst, which was recorded as catalyst D2. The metal content was determined by inductively coupled plasma emission spectrometry. The mass percentage of each metal component was 0.5wt% of Pt and 1.0wt% of Sn, based on the total mass of the catalyst.

[0084] Test Example 1

[0085] The catalysts prepared in Examples 1-6 above were subjected to crystal phase scanning by an X-ray diffractometer of D8 Advance type from Germany Bruker AXS Company. For example, see Figure 1 It can be seen that the catalyst has good crystallinity and shows standard crystal phase of MEL structure, and no Pt and Sn metal components are found, indicating that the active component has very high dispersion.

[0086] Test Example 2

[0087] The catalysts in Examples 1-6 were subjected to scanning electron microscope analysis on a Hitachi S-4800 type cold field emission scanning electron microscope. For example, see Figure 3 The high-resolution transmission electron microscope analysis of the catalysts was carried out on a Thermal Fisher ball aberration electron microscope. For example, see Figure 5 According to the statistics, the particle size distribution of the metal PtSn alloy nanoparticles is 1.0-5.0nm.

[0088] Test Example 3

[0089] The N2 physical adsorption-desorption curves of the catalysts prepared in Examples 1-6 and Comparative Examples 1-2 were determined on a full-automatic adsorption instrument of Autosorb iQ model of Quantachrome in the United States, and the specific surface area and pore volume of the carrier corresponding to each catalyst sample in Examples 1-6 and Comparative Examples 1-2 were calculated, for example, as shown in Figure 3 , and the results are shown in Table 1.

[0090] Test Example 4

[0091] The test method of the peak area of the surface silicon hydroxyl defect (the peak area of the chemical shift-102 ppm represents the silicon-oxygen tetrahedron Q4 (Si(SiO)4) species) of the full-silicon molecular sieve, and the peak area of the chemical shift-112 ppm represents the peak area of the hydroxyl defect Q3 (Si(SiO3)3OH) is as follows: 29 The surface silicon hydroxyl content is determined by Si-NMR solid nuclear magnetic measurement. 29 The Si MAS NMR is performed on a Bruker 400MHz Avance III nuclear magnetic resonance spectrometer, the resonance frequency is 79.5MHz, the high-power proton decoupling sequence is used, the rotation speed is 8kHz, the sampling number is 1024-4096 times, the π / 4 pulse width is 3.2μs, the sampling delay is 10s, for example, as shown in Figure 4 , and the results of the defect site content of the molecular sieve carrier corresponding to each catalyst are shown in Table 1 below.

[0092] Table 1

[0093]

[0094] In Table 1, S Micro refers to the micropore specific surface area of each catalyst; S Ext refers to the external specific surface area; S BET refers to the total specific surface area; V Micro refers to the micropore volume; V meso refers to the mesopore volume; V Total refers to the total pore volume of the catalyst.

[0095] Test Example 5

[0096] The catalysts of the present application were tested and evaluated in a constant-temperature micro fixed bed reactor, and the evaluation conditions were as follows: about 0.5g of catalyst was mixed with 10g of quartz sand in sections, and was packed into a quartz tube reactor with an inner diameter of Φ=10mm, the reaction pressure was atmospheric pressure, the reaction gas was diluted with H2, the mass space velocity of the propane gas was 3h -1, the feed pressure ratio of H2 to propane is 1:4, and the reaction temperature is 550-600℃; the product is analyzed by Agilent 7890A gas chromatography.

[0097]

[0098] The results of the evaluation of the dehydrogenation performance of the catalysts in Examples 1-6 and Comparative Examples 1-2 are shown in Table 2. Shown in Table 2 are the corresponding propane conversion and propylene selectivity at the beginning of the catalytic reaction (after 10 minutes of reaction) and after 12 hours of reaction. It can be seen that the catalysts exhibit excellent propane conversion and propylene selectivity, and after 12 hours of continuous reaction, the propane conversion remains at about 90% of the initial value, and the propylene selectivity is as high as 97.5%, indicating that the good dispersion and strong interaction of the noble metal on the surface of the catalyst are conducive to the stability of the catalyst. In sharp contrast, the lower external surface area of Comparative Example D1 causes the propane conversion to decrease by 10% after 12 hours of reaction.

[0099] It was detected that the catalysts obtained in Examples 2-6 also have similar catalytic stability to Example 1. The catalytic performance of the catalysts obtained in Examples 1-6 and Comparative Examples 1-2 is shown in Table 2.

[0100] Table 2

[0101]

[0102] The above describes the preferred embodiments of the present application, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the present application and fall within the protection scope of the present application.

[0103] It should be noted that the above-described examples are only used to explain the present application and do not constitute any limitation on the present application. The present application is described by referring to typical examples, but it should be understood that the words used therein are descriptive and explanatory words, rather than limiting words. The present application can be modified as specified within the scope of the claims of the present application, and the present application can be revised within the scope and spirit of the present application. Although the present application described therein relates to specific methods, materials and examples, it does not mean that the present application is limited to the specific examples disclosed therein, on the contrary, the present application can be extended to all other methods and applications having the same function.

[0104] All publications, patent applications, patents, and other references mentioned in this specification are herein incorporated by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art. In case of conflict, the present specification, including definitions, will control.

[0105] When the specification states that a material, substance, composition, process, step, apparatus or component etc. is "known to those of ordinary skill in the art", it is intended that the disclosure be interpreted to cover those items which are currently known as well as those which become known in the future.

[0106] The endpoints of the ranges and any values described in this application document are not limited to the precise values stated. The ranges and values should be construed to be approximations that are also meant to cover or range customarily known equivalents. For numeric values, the endpoints of the ranges are not to be understood as being mutually exclusive whereas individual points are to be understood as being mutually exclusive. The various numeric ranges can be combined to form one or more new numeric ranges, which should be considered as being specifically disclosed herein. In the following, the various technical solutions can be combined with each other to form new technical solutions, which should also be considered as being specifically disclosed herein.

[0107] In the context of the present specification, unless specifically stated otherwise, any reference to any prior art is not, and should not be taken as, an acknowledgement or admission that the prior art is commonly known, or forms part of common general knowledge, in any jurisdiction.

[0108] Furthermore, any embodiment described herein can be freely combined with one or more other embodiments described herein, and the technical solutions or technical ideas thus formed are considered as part of the original disclosure or original description of the present application, and should not be considered as new content which has not been disclosed or anticipated herein, unless the combination is considered as being obviously unreasonable by the person skilled in the art.

Claims

1. A self-pillared full-silica molecular sieve supported catalyst, comprising a support, and an active component and an optional auxiliary component supported on the support, wherein the support is rich in silicon hydroxyl defect sites, the active component is at least one selected from the group consisting of Group VIII metals, and the auxiliary component is at least one selected from the group consisting of Sn, Zn, Ga and Cu.

2. The self-pillared full-silica molecular sieve supported catalyst according to claim 1, wherein the support is a nanoscale full-silica molecular sieve with MEL structure, preferably, the support exhibits a self-pillared morphology assembled by rod-like crystallites with a cross-sectional diameter of 10-40 nm; and / or the ratio of the peak area Q3 of silicon hydroxyl defect sites to the peak area Q4 of silicon-oxygen tetrahedra in the support is 1:(3-10) as tested by a nuclear magnetic resonance spectrometer; and / or the active component is at least one selected from the group consisting of Pt, Ir, Au, Pd and Rh, preferably Pt; and / or the particle size of the active component metal particles in the catalyst is 1-5 nm; and / or the auxiliary component optionally comprises at least one of alkali metal elements and alkaline earth metal elements.

3. The self-pillared full-silica molecular sieve supported catalyst according to claim 2, wherein the nanoscale full-silica molecular sieve is Silicalite-2, and has at least one of the following characteristics: the particle size of the nanoscale full-silica molecular sieve is 200-500 nm, preferably 200-400 nm; and / or the nanoscale full-silica molecular sieve exhibits a multi-level pore distribution characteristic, wherein the micropore size distribution is 0.5-2 nm, and the intercrystalline mesopore distribution is 2-50 nm; preferably, the micropore size distribution is 0.5-1 nm, and the intercrystalline mesopore distribution is 2-40 nm.

4. The self-pillared full-silica molecular sieve supported catalyst according to claim 2, wherein the content of the active component is 0.1-2 wt%, preferably 0.1-1 wt%, based on 100 wt% of the total weight of the self-pillared full-silica molecular sieve supported catalyst; the content of the auxiliary component is 0.1-10 wt%, preferably 0.1-5 wt%; and / or the content of the alkali metal elements is 0-2 wt%, preferably 0-1 wt%; and / or the content of the alkaline earth metal elements is 0-2 wt%, preferably 0-1 wt%.

5. A preparation method of the self-pillared full-silica molecular sieve supported catalyst according to claim 1, comprising the following steps: impregnating a support rich in silicon hydroxyl defect sites in a precursor aqueous solution containing an active component precursor compound and an auxiliary component precursor compound, and then removing the solvent, drying and calcining to obtain the self-pillared full-silica molecular sieve supported catalyst; preferably, the support rich in silicon hydroxyl defect sites is a nanoscale Silicalite-2 molecular sieve.

6. The preparation method according to claim 5, wherein the active component precursor compound is at least one selected from the group consisting of chloride compounds and nitrate salts of Group VIII metals, preferably at least one selected from the group consisting of chloride compounds and / or nitrate salts of at least one metal selected from the group consisting of Pt, Ir, Au, Pd and Rh; and / or the auxiliary component precursor compound is at least one selected from the group consisting of chloride compounds and nitrate salts of Sn, Zn, Ga and Cu, preferably at least one selected from the group consisting of chloride compounds and / or nitrate salts of at least one metal selected from the group consisting of Sn, Zn, Ga and Cu. ​ ​ ​ ​ The nanoscale all-silica molecular sieve has an external specific surface area of 200 to 500 m 2 / g, preferably 200 to 400 m 2 / g; and / or, The mesopore volume of the nanoscale all-silica molecular sieve is 0.5 to 1.5 cm 3 / g, preferably 0.5 to 1.2 cm 3 / g; and / or, ​ ​ ​ 5. A process for the preparation of the supported catalyst of self-pillared all-silica molecular sieve according to any one of claims 1 to 4, comprising: ​ ​ ​ The auxiliary component precursor compound is at least one of a chlorine-containing compound and / or nitrate of at least one metal selected from Sn, Zn, Ga, Cu, and optionally at least one of an alkali metal salt and an alkaline earth metal salt; and / or, The impregnation condition is 20-40℃ and 6-12h; and / or, The solvent removal is performed by rotary evaporation, preferably under the following conditions: 70-80℃, 120-150rpm, and 65-75mbar; and / or, The drying condition is 80-120℃ and 6-12h; and / or, The calcination condition is 1-2℃ / min to 500-600℃, and 4-6h; preferably at 550-580℃.

7. The production method according to claim 4 or 5, characterized by, The preparation method of the nanoscale Silicalite-2 molecular sieve comprises: (1) mixing a silicon source, an organic template agent, and deionized water to form a mixed gel by stirring; (2) transferring the mixed gel into an autoclave, and performing static crystallization at different temperatures in steps; preferably, two-step crystallization is adopted; (3) after crystallization is completed, the nanoscale Silicalite-2 molecular sieve is obtained after cooling, separation, washing, drying, and calcination.

8. The preparation method according to claim 7, characterized in that, In step (1): The silicon source is at least one selected from tetraethyl orthosilicate, silica gel, and silica sol, preferably tetraethyl orthosilicate; and / or, The organic template agent is at least one selected from organic ammonium compounds, preferably at least one selected from tetraethylammonium hydroxide, tetraethylammonium bromide, tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetrapropylammonium chloride, tetrapropylammonium fluoride, tetrabutylammonium hydroxide, tetrabutylammonium bromide, tetrabutylammonium chloride, and tetrabutylammonium fluoride; and / or, The molar ratio of the silicon source, the organic template agent, and the deionized water is 1:(0.1-1):(10-100), preferably 1:(0.1-0.5):(10-80), wherein the silicon source is calculated based on SiO2 contained therein; and / or, The stirring condition is 20-40℃ and 2-12h.

9. The preparation method according to claim 7, characterized in that, In step (2): The two-step crystallization comprises first-step low-temperature crystallization and second-step high-temperature crystallization, and the first-step low-temperature crystallization and the second-step high-temperature crystallization adopt different temperature conditions; Preferably, the first-step crystallization condition is 50-120℃ and 24-120h; Preferably, the second-step crystallization condition is 120-180℃ and 24-120h.

10. The preparation method according to claim 7, characterized in that, In step (3): The drying condition is 80-120℃ and 6-12h; and / or, The calcination condition is 1-2℃ / min to 500-600℃, and 4-6h; preferably at 550-580℃.

11. The use of the self-pillared all-silicon molecular sieve supported catalyst according to any one of claims 1 to 4 or the self-pillared all-silicon molecular sieve supported catalyst prepared by the method according to any one of claims 5 to 10 in the reaction of propane dehydrogenation to prepare propylene.

12. The use according to claim 11, wherein the self-pillared all-silicon molecular sieve supported catalyst is loaded into a reactor, quartz sand is used to fix the upper and lower beds, and propane gas is diluted with H2 to contact the catalyst to perform the dehydrogenation reaction to obtain propylene. ​ Preferably, in the dehydrogenation reaction, the propane gas mass space velocity is 1-50 h -1 -1, and / or the H2 / propane feed pressure ratio is 1:(1-8), and / or the dehydrogenation reaction temperature is 550-620°C.

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