Molecular sieve catalyst, method of making and use thereof

Abstract

The present application relates to a kind of molecular sieve catalyst and preparation method and application, the preparation method of the molecular sieve catalyst, comprising the following steps: (1) obtaining full-silicon Silicate-1 molecular sieve;(2) preparation of molecular sieve catalyst: S1: full-silicon Silicate-1 molecular sieve is uniformly mixed with silicon source, alkali, template agent, water, Pt source, adjuvant, under negative pressure condition is carried out aging;S2: under the condition of microwave induction, heating is carried out crystallization, then washing, drying, calcination, and the molecular sieve catalyst is prepared.The catalyst prepared in the present application shows excellent stability, anti-carbon deposition performance and higher propylene product selectivity in the reaction of propane dehydrogenation to propylene, which is beneficial to prolong the running cycle of the device and reduce the reaction unit consumption.

Description

Technical Field

[0001] This invention belongs to the field of propane catalytic dehydrogenation to propylene technology, and relates to a novel catalyst, its preparation method and application, specifically a method for preparing the catalyst by negative pressure-microwave induced stepwise crystallization. Background Technology

[0002] With rapid socio-economic development, the market demand for propylene has been increasing year by year. Propane dehydrogenation, due to its unique technological advantages and high propylene selectivity, has attracted much attention. Currently, only two propane dehydrogenation processes have achieved large-scale industrial application worldwide: the Catofin process developed by ABB Lummus and the Oleflex process developed by UOP. The Catofin process uses a chromium-based catalyst, which is somewhat toxic to the environment. The Oleflex process uses a platinum-based catalyst prepared by the traditional impregnation method. Due to its preparation characteristics, the active precious metal gradually agglomerates during the reaction, thus losing its high selectivity and activity for propylene. Therefore, this catalyst requires oxychlorination regeneration after a period of use, and the introduction of chlorine increases the risk of the process and the complexity of the regeneration operation.

[0003] Molecular sieve-based catalysts exhibit significant advantages in the field of catalysis due to their unique molecular framework structure, pore size, and interactions with relevant active metals. Through rational synthesis methods and control of synthetic components, it is expected that high-performance catalyst products can be prepared.

[0004] Chinese patent CN1602997A discloses a microwave-assisted synthesis method for perovskite catalysts, exhibiting good electrocatalytic activity. However, this catalyst is not suitable for propane dehydrogenation. Chinese patent CN104556131A discloses a method for preparing a Pt-grain-controlled propane dehydrogenation catalyst. This patent uses Sn-containing alumina as a support and prepares a highly dispersed Pt propane dehydrogenation catalyst with controllable particle size through a vacuum heating and reflux method. However, while this patent's method represents an optimization of a traditional supported method, the resulting catalyst is essentially still a supported catalyst, and it is difficult to overcome the agglomeration of active metals during the reaction process.

[0005] Therefore, it is necessary to develop a new type of catalyst that can overcome problems such as migration and agglomeration of active metals during the high-temperature reaction process when applied to the field of propane catalytic dehydrogenation to propylene. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide a novel molecular sieve catalyst and its preparation method, which has high resistance to carbon deposition, stability and selectivity, simplifies the regeneration process of traditional propane dehydrogenation catalysts, effectively extends the operating cycle of the unit, and improves the economic benefits of propane dehydrogenation to propylene production.

[0007] To achieve the above objectives, this invention employs an in-situ synthesis method for catalyst preparation. By rationally utilizing negative pressure, microwaves, and other techniques, a molecular sieve catalyst with a core-shell structure and uniformly dispersed active metals on its outer surface is obtained. Due to the strong interaction between the molecular sieve framework structure and the active components, as well as the confined characteristics of the pore structure, the migration and aggregation of active metals during the high-temperature reaction process can be effectively overcome. This simplifies the regeneration process of traditional propane dehydrogenation catalysts (regeneration does not require chlorine injection) and exhibits excellent stability, anti-carbon deposition performance, and higher selectivity for propylene products. This catalyst is beneficial for extending the operating cycle of the unit and reducing the unit consumption of the reaction.

[0008] On one hand, the present invention provides a method for preparing a molecular sieve catalyst, comprising the following steps:

[0009] (1) Obtaining Silicate-1 molecular sieve;

[0010] (2) Preparation of molecular sieve catalysts:

[0011] S1: Mix the all-silicon Silicate-1 molecular sieve with silicon source, alkali, template agent, water, Pt source and additives evenly, and age it under negative pressure;

[0012] S2: Crystallization is carried out by heating under microwave-induced conditions, followed by washing, drying, and calcination to obtain the molecular sieve catalyst.

[0013] Step (1) of this invention is a method for obtaining Silicate-1 molecular sieve. The Silicate-1 molecular sieve described in this invention is a publicly available product that can be purchased through ordinary commercial channels or prepared using conventional processes. This method does not have specific requirements regarding its source. For example, in one embodiment, the Silicate-1 molecular sieve can be prepared according to the following method, including the following steps:

[0014] The silicon source, alkali, template agent and water are mixed, and then crystallized, washed, dried and calcined to obtain the all-silicon Silicate-1 molecular sieve.

[0015] The mixing mass ratio of the silicon source, alkali, template agent, and water is 1.0:(0.05-5):(0.2-0.5):(2-5). Specifically, based on the silicon source value of 1.0, the alkali can be 0.05, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, or any combination thereof; the template agent can be 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or any combination thereof; and the water can be 2, 2.5, 3, 3.5, 4, 4.5, 5, or any combination thereof.

[0016] The silicon source is selected from one or more of organosilicon and inorganic silicon sources, preferably one or more of sodium silicate, silica, tetraethyl orthosilicate, and silica sol.

[0017] The alkali is selected from one or more of ammonia water and metal hydroxides, preferably one or more of ammonia water, barium hydroxide, sodium hydroxide, potassium hydroxide, and calcium hydroxide;

[0018] The template agent is selected from one or more of amine compounds, preferably one or more of butylamine, ethylamine, tetrabutylammonium bromide, tetraethylammonium bromide, tetrapropylammonium hydroxide, and tetrapropylammonium bromide;

[0019] The mixing, crystallization, washing, drying, and calcination processes are standard operations in the field, and specific parameters can be selected based on actual conditions. Preferably, the mixing process controls the stirring speed at 50-700 r / min and the stirring time at 30-240 min. Preferably, the crystallization process controls the temperature at 160-190℃ and the time at 16-72 h. Specifically, the stirring speed includes, but is not limited to, 50 r / min, 100 r / min, 200 r / min, 300 r / min, 400 r / min, 500 r / min, 600 r / min, 700 r / min, or any two of these. The stirring time can be within a range consisting of, but is not limited to, 30 min, 50 min, 80 min, 100 min, 130 min, 150 min, 180 min, 200 min, 220 min, 240 min, or any two of these ranges; the crystallization process temperature can be 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, 190℃, or any two of these ranges; and the time can be 16h, 20h, 30h, 40h, 50h, 60h, 70h, 72h, or any two of these ranges.

[0020] Step (2) of this invention is to prepare a molecular sieve catalyst based on the obtained Silicate-1 molecular sieve. The Silicate-1 molecular sieve obtained by the crystallization method is fully mixed and stirred with the other raw materials in a certain proportion, and then vacuumed and aged under negative pressure for a period of time. The aged sample is then microwave-heated to induce secondary crystallization to obtain the catalyst.

[0021] In one embodiment, the silicon source in step S1 is selected from one or more of organosilicon and inorganic silicon sources, preferably one or more of sodium silicate, silica, tetraethyl orthosilicate, and silica sol.

[0022] In one embodiment, the alkali in step S1 is selected from one or more of ammonia water and metal hydroxides, preferably one or more of ammonia water, barium hydroxide, sodium hydroxide, potassium hydroxide, and calcium hydroxide;

[0023] In one embodiment, the template agent in step S1 includes one or more selected from amine compounds, preferably one or more selected from tetraethylammonium bromide, tetrapropylammonium bromide, tetrabutylammonium bromide, tetrapropylammonium hydroxide, ethylamine, and butylamine.

[0024] In one embodiment, the Pt source in step S1 is selected from one or more of H2PtCl6·6H2O and [Pt(NH3)2(NO2)2].

[0025] In one embodiment, the adjuvant in step S1 is selected from C 10 H 12 MgN2Na2O8·4H2O, C 10 H 12 ZnN2Na2O8·4H2O, C 10 H 12 One or more of the following: FeN2Na2O8, MgSO4, MgCl2, KCl, K2SO4, La(NO3)3, InCl3, LaCl3, YCl3, and CeCl3.

[0026] In one embodiment, the mixing mass ratio of the all-silica Silicate-1 molecular sieve, silicon source, alkali, template agent, and water in step S1 is 1.0:(0.1-0.5):(0.03-0.16):(0.08-0.4):(1.2-5.5). Specifically, in this mass ratio, based on the value of the all-silica Silicate-1 molecular sieve being 1.0, the silicon source can be 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or any two of them. The concentrations of the base can be in the range of 0.03, 0.05, 0.07, 0.09, 0.11, 0.13, 0.15, 0.16 or any two of these ranges; the template agent can be in the range of 0.08, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4 or any two of these ranges; and the water can be in the range of 1.2, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5 or any two of these ranges.

[0027] In one embodiment, the amount of Pt source used in step S1 is 0.05-0.5 wt% of the mass of Silicate-1 molecular sieve, including but not limited to 0.05 wt%, 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt%, 0.3 wt%, 0.35 wt%, 0.4 wt%, 0.45 wt%, 0.5 wt%, or any range thereof.

[0028] In one embodiment, the amount of the additive in step S1 is 0.02-0.5 wt% of the mass of Silicate-1 molecular sieve, including but not limited to 0.02 wt%, 0.05 wt%, 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt%, 0.3 wt%, 0.35 wt%, 0.4 wt%, 0.45 wt%, 0.5 wt%, or any range thereof.

[0029] In one embodiment, the uniform mixing in step S1 is achieved by thorough stirring. The stirring speed is controlled at 50-600 r / min, and the stirring time is 30-240 min. Specifically, the stirring speed includes, but is not limited to, 50 r / min, 100 r / min, 200 r / min, 300 r / min, 400 r / min, 500 r / min, 600 r / min, or any range thereof. The stirring time includes, but is not limited to, 30 min, 50 min, 80 min, 100 min, 130 min, 150 min, 180 min, 200 min, 220 min, 240 min, or any range thereof.

[0030] In one embodiment, the aging process described in step S1 is carried out under negative pressure by transferring the material into a reaction tube and evacuating it. The aging process does not have specific temperature requirements; for example, it can be carried out at room temperature. The pressure is -(0.5-0.01) MPa, and the time is 0.5-62 h. Specifically, the pressure can be -0.5 MPa, -0.45 MPa, -0.4 MPa, -0.35 MPa, -0.3 MPa, -0.25 MPa, -0.2 MPa, -0.15 MPa, -0.1 MPa, -0.05 MPa, -0.01 MPa, or a range thereof. The time can be 0.5 h, 1 h, 10 h, 20 h, 30 h, 40 h, 50 h, 60 h, 62 h, or a range thereof.

[0031] In one embodiment, step S2 involves crystallization under microwave-induced heating. This is achieved by transferring the material aged under negative pressure into a microwave heating furnace for microwave-induced heating. The crystallization process involves heating at a temperature of 90°C to 195°C for a time of 0.5 to 32 hours. Specifically, the temperature can be 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 195°C, or any combination thereof, and the time can be 0.5 hours, 1 hour, 5 hours, 10 hours, 15 hours, 20 hours, 25 hours, 30 hours, 32 hours, or any combination thereof.

[0032] In one embodiment, the microwave induction in step S2 has a microwave power of 0.2-10 kW, including but not limited to 0.2 kW, 0.5 kW, 1 kW, 2 kW, 3 kW, 4 kW, 5 kW, 7 kW, 9 kW, 10 kW, or any range thereof.

[0033] After microwave-induced crystallization in step S2 of this invention, the process further includes washing, drying, and calcination. The washing, drying, and calcination are conventional operations in the field, and specific parameters can be selected based on actual conditions; this invention does not have special requirements. Preferably, the washing uses deionized water until neutral. Preferably, the drying temperature is 60-120℃, and the time is 12-24 hours. Preferably, the calcination temperature is 450-590℃, and the time is 3-8 hours. Specifically, the drying temperature can be 60℃, 70℃, 80℃, etc. The temperature can be 90℃, 100℃, 110℃, 120℃ or any combination thereof, and the time can be 12h, 15h, 18h, 20h, 24h or any combination thereof; the roasting temperature can be 450℃, 470℃, 490℃, 500℃, 520℃, 550℃, 570℃, 590℃ or any combination thereof, and the time can be 3h, 4h, 5h, 6h, 7h, 8h or any combination thereof.

[0034] On the other hand, the present invention provides a molecular sieve catalyst prepared by the above method, which has a core-shell structure and uniformly dispersed active metals on the outer surface;

[0035] Specifically, the catalyst has active noble metals mainly distributed in the shallow surface region above 20 nm. Characterization results show that when the depth exceeds 30 nm, Pt metal can no longer be detected, indicating that the active noble metal Pt in the catalyst prepared by the present invention is mainly distributed on the outer surface of the catalyst sample. In addition, the Pt dispersion characterization results show that the dispersion of active metals in the catalyst can reach more than 90%.

[0036] Furthermore, the present invention also provides the application of the molecular sieve catalyst described above as a dehydrogenation catalyst.

[0037] The catalyst described in this invention can be used in the preparation of C3 dehydrogenation, C4 dehydrogenation, methanol to olefins and other fields, and is especially suitable for the catalytic dehydrogenation of propane to propylene.

[0038] In one embodiment, the method for catalytic dehydrogenation of propane to propylene as described above can be carried out using a conventional reactor in the art, such as a fluidized bed reactor or a fixed bed reactor.

[0039] Specifically, a method for the catalytic dehydrogenation of propane to propylene involves passing propane / hydrogen gas into a fixed bed packed with the molecular sieve catalyst described in this invention for reaction. The relevant operations and process conditions in the preparation method of this invention, as well as the apparatus used, can all be carried out using conventional methods in the art, and there are no particular limitations. Those skilled in the art can optimize the process based on existing technology and known processes according to actual needs. Specifically, for example, the conditions listed in the following embodiments of this invention can be used:

[0040] The molar ratio of the raw material gas to hydrogen (propane / hydrogen) is 0.1-0.5, including but not limited to 0.1, 0.2, 0.3, 0.4, 0.5 or any combination thereof;

[0041] The reaction space velocity is 400-1500 hr. -1 Calculated based on catalyst volume and total reaction feed, including but not limited to 400hr -1 600hr -1 800hr -1 1000hr -1 1200hr -1 1400hr -1 1500hr -1 Or a range consisting of any two of them;

[0042] The reaction is carried out at a pressure of 0.101-0.15 MPa and a temperature of 560-620°C. Specifically, the pressure can be 0.101 MPa, 0.11 MPa, 0.12 MPa, 0.13 MPa, 0.14 MPa, 0.15 MPa, or a range thereof, and the temperature can be 560°C, 570°C, 580°C, 590°C, 600°C, 610°C, 620°C, or a range thereof.

[0043] The molecular sieve catalyst of this invention can maintain its performance through regeneration during the production process. Specifically, the catalyst regeneration method involves introducing a gas at 480-620°C with a space velocity of 1200-4500 h⁻¹. -1 The air is regenerated over a period of 0.5-3.5 hours; specifically, the temperature can be 480℃, 500℃, 520℃, 540℃, 560℃, 580℃, 600℃, 620℃, or a range thereof, and the air velocity can be 1200hr. -1 1500hr -1 2000hr -1 2500hr -1 3000hr -1 3500hr-1 4000hr -1 4500hr -1 Or a range consisting of any two of these, wherein the time can be 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h or a range consisting of any two of these.

[0044] In practical applications, this regeneration process is performed online after the reaction is complete, and the completion of the regeneration process constitutes one cycle. The catalyst of this invention maintains high reactivity even after multiple cycles of regeneration, and the amount of carbon deposited on the catalyst remains essentially stable.

[0045] Compared with the prior art, the beneficial effects of the technical solution of the present invention are as follows:

[0046] This invention provides a novel molecular sieve catalyst and its preparation method. This catalyst effectively overcomes the migration and agglomeration of active metals during high-temperature reactions. It simplifies the regeneration process of traditional propane dehydrogenation catalysts, eliminating the need for chlorine injection during regeneration, reducing carbon buildup, extending catalyst lifespan and equipment operating cycles, and enabling low-cost continuous operation of the propane dehydrogenation process. Attached Figure Description

[0047] Figure 1 The curves show the changes in the conversion rate and selectivity of propane dehydrogenation reaction over time under the same experimental conditions for the three catalysts prepared in Example 1, Comparative Example 1, and Comparative Example 2. Detailed Implementation

[0048] The present invention will be illustrated below with reference to specific embodiments, but it should be understood that the protection of the present invention is not limited to the specific embodiments.

[0049] Unless otherwise specified, all raw materials and reagents used in the embodiments and comparative examples of this invention were purchased through commercial channels.

[0050] Preparation of Silicate-1 molecular sieve: First, weigh 263.4 g of deionized water and 64 g of tetraethyl orthosilicate, pour them into a beaker and stir evenly at a speed of 250-700 r / min. Weigh 3.72 g of NaOH and 13.64 g of TPAOH (tetrapropylammonium bromide) and add them to the beaker, stirring at room temperature for 30 min. Then, transfer the mixture to a stainless steel autoclave and place it in an oven for crystallization at 170℃ for 36 h. After crystallization, wash, dry, and calcine the sample to obtain the final product.

[0051]

Example 1

[0052] The steps for preparing molecular sieve catalysts are as follows:

[0053] S1: Weigh 100g of Silicate-1 molecular sieve, 238.2g of deionized water, and 17.5g of tetraethyl orthosilicate, pour them into a 500mL beaker, and stir evenly at a speed of 150-600r / min. Weigh 0.4g of H2PtCl6·6H2O, 0.32g of MgCl2, and 0.15g of InCl3, add them to the beaker, mix, and stir evenly. Weigh 3.98g of NaOH and 9.67g of tetrapropylammonium bromide, add them to the beaker, and continue stirring for 90min. Then transfer the mixture to a reaction tube and perform vacuum treatment, drawing the negative pressure to -0.2MPa, and maintain the negative pressure for static aging for 48h.

[0054] S2: The sample aged under negative pressure was transferred to a microwave oven. The microwave induction power was set to 1.5 kW, and the microwave heating temperature was controlled at 175 °C. The sample was held at this temperature for 16 hours to complete secondary crystallization. After the sample cooled to room temperature, the slurry was removed, washed with deionized water, and filtered until the pH was neutral. The filtered sample was then dried in an oven at 60-120 °C for 12 hours, followed by calcination in a muffle furnace at 550 °C for 6 hours to obtain the molecular sieve catalyst.

[0055] The catalyst has a distinct core-shell structure and a uniform distribution of active metals on its outer surface. The active noble metals are mainly distributed in the shallow layer region of 20-30 nm. Characterization results show that Pt metals can no longer be detected at depths exceeding 30 nm, indicating that the active noble metal Pt in the catalyst prepared by this invention is mainly distributed on the outer surface of the catalyst sample. In addition, the Pt dispersion characterization results show that the dispersion of active metals in the catalyst reaches 93.2%.

[0056]

Example 2

[0057] The steps for preparing molecular sieve catalysts are as follows:

[0058] S1: Weigh 90g of Silicate-1 molecular sieve, 396.5g of deionized water, and 35g of silica sol, pour them into a 500mL beaker, and stir evenly at a speed of 150-600r / min. Weigh 0.28g of [Pt(NH3)2(NO2)2] and 0.12g of C. 10 H 12 ZnN2Na2O8·4H2O was added to a beaker and mixed thoroughly. 5g of potassium hydroxide and 12g of tetrabutylammonium bromide were weighed and added to the beaker, and stirring was continued for 90 minutes. The mixture was then transferred to a reaction tube and subjected to vacuum treatment, with the negative pressure reduced to -0.15MPa. The mixture was then allowed to stand and age for 36 hours under negative pressure.

[0059] S2: The sample aged under negative pressure was transferred to a microwave oven. The microwave induction power was set to 2.2 kW, and the microwave heating temperature was controlled at 160 °C. The sample was held at this temperature for 24 hours to complete secondary crystallization. After the sample cooled to room temperature, the slurry was removed, washed with deionized water, and filtered until the pH was neutral. The filtered sample was then dried in an oven at 60-120 °C for 12 hours, followed by calcination in a muffle furnace at 550 °C for 6 hours to obtain the molecular sieve catalyst.

[0060] The catalyst has a distinct core-shell structure and a uniform distribution of active metals on its outer surface. The active noble metals are mainly distributed in the shallow surface region of 20-30 nm. Characterization results show that Pt metals can no longer be detected at depths exceeding 30 nm, indicating that the active noble metal Pt in the catalyst prepared by this invention is mainly distributed on the outer surface of the catalyst sample. In addition, the Pt dispersion characterization results show that the dispersion of active metals in the catalyst reaches 92.1%.

[0061]

Example 3

[0062] The steps for preparing molecular sieve catalysts are as follows:

[0063] S1: Weigh 110g of Silicate-1 molecular sieve, 245g of deionized water, and 20g of sodium silicate, pour them into a 500mL beaker, and stir evenly at a speed of 150-600r / min. Weigh 0.39g of H2PtCl6·6H2O and 0.35g of La(NO3)3, add them to the beaker, mix, and stir evenly. Weigh 15g of ammonia water and 25g of tetrapropylammonium hydroxide, add them to the beaker, and continue stirring for 90min. Then transfer the mixture to a reaction tube and perform vacuum treatment, drawing the negative pressure to -0.05MPa, and maintain the negative pressure for static aging for 48h.

[0064] S2: The sample aged under negative pressure was transferred to a microwave oven. The microwave induction power was set to 5 kW, and the microwave heating temperature was controlled at 195℃. The sample was held at this temperature for 12 hours to complete secondary crystallization. After the sample cooled to room temperature, the slurry was removed, washed with deionized water, and filtered until the pH was neutral. The filtered sample was then dried in an oven at 60-120℃ for 12 hours, followed by calcination in a muffle furnace at 550℃ for 6 hours to obtain the molecular sieve catalyst.

[0065] The catalyst has a distinct core-shell structure and a uniform distribution of active metals on its outer surface. The active noble metals are mainly distributed in the shallow layer region of 30-40 nm. Characterization results show that Pt metals can no longer be detected at depths exceeding 40 nm, indicating that the active noble metal Pt in the catalyst prepared by this invention is mainly distributed on the outer surface of the catalyst sample. In addition, the Pt dispersion characterization results show that the dispersion of active metals in the catalyst reaches 90.7%.

[0066]

Example 4

[0067] The steps for preparing molecular sieve catalysts are as follows:

[0068] S1: Weigh 100g of Silicate-1 molecular sieve, 329g of deionized water, and 21g of silica, pour them into a 500mL beaker, and stir well at a speed of 150-600r / min. Weigh 0.12g of H2PtCl6·6H2O and 0.2g of C 10 H 12 MgN2Na2O8·4H2O and 0.1g La(NO3)3 were added to a beaker, mixed, and stirred until homogeneous. 7.5g barium hydroxide and 19g tetrapropylammonium bromide were weighed and added to the beaker, and stirring was continued for 90 minutes. The mixture was then transferred to a reaction tube and subjected to vacuum treatment, with the negative pressure reduced to -0.2MPa. The mixture was then allowed to stand and age for 62 hours under negative pressure.

[0069] S2: The sample aged under negative pressure was transferred to a microwave oven. The microwave induction power was set to 1.0 kW, and the microwave heating temperature was controlled at 170℃. The sample was held at this temperature for 18 hours to complete secondary crystallization. After the sample cooled to room temperature, the slurry was removed, washed with deionized water, and filtered until the pH was neutral. The filtered sample was then dried in an oven at 60-120℃ for 12 hours, followed by calcination in a muffle furnace at 550℃ for 6 hours to obtain the molecular sieve catalyst.

[0070] The catalyst has a distinct core-shell structure and a uniform distribution of active metals on its outer surface. The active noble metals are mainly distributed in the shallow layer region of 20-30 nm. Characterization results show that Pt metals can no longer be detected at depths exceeding 30 nm, indicating that the active noble metal Pt in the catalyst prepared by this invention is mainly distributed on the outer surface of the catalyst sample. In addition, the Pt dispersion characterization results show that the dispersion of active metals in the catalyst is above 92.6%.

[0071] Comparative Example 1

[0072] The catalyst in this comparative example was prepared using essentially the same raw materials and processes as in Example 1. The only difference was that the aging process pressure was 0 MPa (atmospheric pressure), and the secondary crystallization process was not induced by microwave but was heated in a conventional oven. Other operations and conditions remained unchanged, and the catalyst was obtained.

[0073] The active metals in this catalyst are randomly dispersed inside the catalyst, and the distribution of surface active metals is poor. Furthermore, the Pt dispersion characterization results show that the dispersion of active metals in the catalyst is 76.4%.

[0074] Comparative Example 2

[0075] This comparative example uses essentially the same raw materials and processes as Example 1 to prepare the catalyst, the only difference being that the aging process pressure is 0 MPa (atmospheric pressure), while other operations and conditions remain unchanged, and the catalyst is obtained.

[0076] The catalyst has a moderate distribution of active metals on its surface. Furthermore, the Pt dispersion characterization results show that the dispersion of active metals in the catalyst is 80.5%.

[0077] Comparative Example 3

[0078] This comparative example uses essentially the same raw materials and processes as Example 1 to prepare the catalyst, the only difference being that the secondary crystallization is not induced by microwave but by conventional oven heating, while other operations and conditions remain unchanged, and the catalyst is obtained.

[0079] The catalyst has a preliminary core-shell structure and a relatively uniform distribution of surface active metals. Furthermore, the Pt dispersion characterization results show that the active metal dispersion of the catalyst is 86.9%.

[0080]

Example 5

[0081] The metal dispersion performance of the catalysts prepared in each embodiment and comparative example was analyzed and compared.

[0082] The platinum dispersion of the catalyst samples in Examples 1-4 and Comparative Examples 1-3 was characterized using the CO-pulse adsorption method, employing a Micromeritics AutoChemⅡ2920 chemisorption analyzer. The characterization results are shown in Table 2.

[0083] Table 1. Test results of Pt dispersion in catalyst samples of Examples 1-4 and Comparative Examples 1-3

[0084] catalyst Aging process pressure Microwave induced power <![CDATA[Pt dispersion ① > Example 1 -0.20MPa 1.5kW 93.2％ Example 2 -0.15MPa 2.2kW 92.1％ Example 3 -0.05MPa 5.0kW 90.7％ Example 4 -0.20MPa 1.0kW 92.6％ Comparative Example 1 0MPa (atmospheric pressure) - 76.4％ Comparative Example 2 0MPa (atmospheric pressure) 1.5kW 80.5％ Comparative Example 3 -0.20MPa - 86.9％

[0085] Note ①: Pt dispersion is calculated based on the amount of CO adsorbed in the sample as detected by TCD.

[0086] As shown in Table 1, the molecular sieve catalyst prepared by the method of this invention exhibits excellent active metal dispersion, with Pt dispersion exceeding 90% in all tests. In contrast, the catalyst sample of Comparative Example 1, prepared using a conventional hydrothermal synthesis method, showed a Pt dispersion of only 76.4%. Based on previous research, higher Pt active metal dispersion helps reduce side reactions such as thermal cracking during propane dehydrogenation. Therefore, in the catalytic performance evaluation process (see...),... Figure 1The catalyst samples of this invention exhibit higher propylene selectivity. Furthermore, a comprehensive comparison of the analysis results of various embodiments and comparative sample samples shows that, compared to the microwave-induced power in the secondary crystallization process, the vacuum negative pressure treatment process in the aging process plays a decisive role in the difference in Pt dispersion in the samples, having a relatively lower aging process pressure, which is beneficial for promoting Pt dispersion in the catalyst samples.

[0087] The distribution of active metals at different depths in the catalysts prepared in Example 1 and Comparative Example 1 was analyzed and compared.

[0088] The XPS sputtering method was used (the selected instrument was a Thermo Fisher K-Alpha photoelectron spectrometer manufactured in the United States). The sputtering depth in this experiment was 0–50 nm, and the experimental results are shown in Table 2.

[0089] Table 2 Results of active metal distribution test within the catalyst

[0090]

[0091] As shown in Table 2, the Pt metal content distribution data within the catalyst at different sputtering depths indicates that the active noble metal in Example 1 is mainly distributed in the shallow surface region above 20 nm. When the sputtering depth exceeds 30 nm, Pt metal is essentially undetectable. This suggests that the active noble metal Pt in the catalyst prepared in this invention is mainly distributed on the outer surface of the catalyst sample, which facilitates rapid adsorption and diffusion-desorption reactions, avoids deep reactions, and ultimately exhibits higher propylene selectivity in the propane dehydrogenation reaction (see Table 2). Figure 1 However, in contrast, Comparative Example 1 showed a relatively small Pt distribution of 0.374–0.481 wt% in the sputtering depth range of 0–50 nm, without a significant gradient difference. This made it difficult to control side reactions such as deep cracking during the reaction process, thus affecting the catalyst's dehydrogenation performance.

[0092]

Example 6

[0093] The catalytic activity, propylene selectivity, reaction stability, and anti-coking properties of the catalysts prepared in Examples 1-4 and Comparative Examples 1-3 in the propane dehydrogenation reaction were evaluated using a conventional fixed-bed pilot-scale experimental setup. The specific experimental conditions are as follows:

[0094] Inert ceramic balls and the catalyst to be tested were packed in layers from top to bottom in the reaction tube, with packing volumes of 8 mL and 4 mL respectively. The reaction space velocity was set to 1200 hr. -1 The molar ratio of the raw material gas to hydrogen (propane / hydrogen) is 0.5, the reaction pressure is set at 0.05 MPa, and the reaction temperature is 605℃.

[0095] Under the same experimental conditions described above, the carbon deposition content (measured by a carbon-sulfur analyzer) of each catalyst after 50 hours of continuous reaction is shown in Table 3. Furthermore, the catalytic performance curves of the catalysts prepared in Example 1, Comparative Examples 1 and 2 as a function of time are shown in Table 3. Figure 1 As shown.

[0096] Table 3. Long-cycle reaction test results of the catalyst

[0097] sample Catalyst carbon deposition content Propylene selectivity / % Example 1 1.87wt% 95.6 Example 2 2.05wt% 94.5 Example 3 2.39wt% 93.1 Example 4 2.16wt% 93.8 Comparative Example 1 9.47wt% 79.5 Comparative Example 2 6.32wt% 84.9 Comparative Example 3 5.85wt% 88.9

[0098] To further verify the stability of the catalyst of this invention during multiple regeneration cycles and to simplify the regeneration process, the molecular sieve catalyst of Example 1 was selected for multi-cycle regeneration performance testing. Each reaction cycle lasted 50 hours, followed by a regeneration process. The completion of the regeneration process constituted one cycle. The regeneration process was conducted at 520°C with a space velocity of 2400 h⁻¹. -1 The air was used for regeneration, and the regeneration time was 2 hours. The results are shown in Table 4.

[0099] Table 4. Results of Multi-cycle Regeneration Performance Tests

[0100] propylene yield carbon deposits One cycle of regeneration 42.5％ 1.92wt% Secondary regeneration cycle 42.4％ 1.95wt% Three-wheel regeneration cycle 42.2％ 1.98wt% Four-wheel regeneration cycle 42.1％ 2.01wt% Five-cycle regeneration 42.1％ 2.02wt%

[0101] As can be seen from the data in Table 3, under the same experimental conditions, the molecular sieve catalyst prepared in this invention has stronger anti-coking performance. After 50 h of continuous propane dehydrogenation reaction, the coking content of the catalyst remained below 2.5 wt%, showing good reaction stability. However, when only one of negative pressure, microwave-induced crystallization or traditional hydrothermal synthesis method was used, the coking content of the catalyst increased significantly after the reaction. Among them, the sample prepared by the traditional hydrothermal synthesis method in Comparative Example 1 had a coking content as high as 9.47 wt%.

[0102] As can be seen from the results in Table 4, this invention does not use the industrial Pt-based catalyst oxychlorination reduction regeneration method that requires the injection of chlorine. Under multiple rounds of air regeneration, Example 1 still maintains high reaction performance, the amount of catalyst carbon deposit remains basically stable, and the propylene yield remains above 40%, demonstrating excellent regeneration stability.

[0103] In addition, by Figure 1The reaction performance curves of the catalyst over time also show that the catalyst prepared according to this invention has higher propylene selectivity and reaction stability. After 50 hours of continuous reaction, the catalyst activity remained basically unchanged (propane conversion rate decreased by less than 1%), and the propylene selectivity was higher than that of the comparative sample. In contrast, the catalyst activity of Comparative Sample 1 decreased significantly after a long period of continuous reaction, indicating that most of the active components on the catalyst were covered by carbon deposits and could not exert a catalytic effect, leaving very little active component available for the reaction. The reaction test results show that under the same experimental conditions, the catalyst prepared by the method of this invention can achieve a higher propylene selectivity of 95.6%, which is 4.1 percentage points higher than the traditional hydrothermal synthesis method. This translates to a reduction of 47 kg of propane consumption, equivalent to 235 yuan / t of propylene.

[0104] Therefore, the negative pressure-microwave induced hierarchical crystallization method of the present invention can obtain a molecular sieve catalyst with good anti-carbon deposition performance and higher propylene selectivity, which is of great significance for extending the reaction cycle and reducing propane consumption in the propane dehydrogenation to propylene process.

Claims

1. A process for the preparation of a molecular sieve catalyst for dehydrogenation, characterized by, The method comprises the following steps: (1) obtaining full-silicon Silicate-1 molecular sieve; (2) preparing the molecular sieve catalyst: S1: uniformly mixing the full-silicon Silicate-1 molecular sieve with a silicon source, a base, a template agent, water, a Pt source, and an additive, and performing aging under negative pressure; S2: performing crystallization under microwave induction, and then washing, drying, and calcining to obtain the molecular sieve catalyst; The aging process in step S1 is performed at a pressure of-(0.5-0.01) MPa for 0.5-62 h; the microwave induction in step S2 is performed at a microwave power of 0.2-10 kW.

2. The production method according to claim 1, characterized by, The full-silicon Silicate-1 molecular sieve in step (1) is prepared by the following method, and the steps include: mixing a silicon source, a base, a template agent, and water, and then performing crystallization, washing, drying, and calcining to obtain the full-silicon Silicate-1 molecular sieve.

3. The preparation method according to claim 2, characterized in that, The mixing mass ratio of the silicon source, the base, the template agent, and the water is 1.0:(0.05-5):(0.2-0.5):(2-5).

4. The preparation method according to claim 2, characterized in that, The silicon source is selected from one or more of organic silicon and inorganic silicon sources.

5. The preparation method according to claim 4, characterized in that, The silicon source is selected from one or more of sodium silicate, white carbon black, tetraethyl orthosilicate, and silica sol.

6. The preparation method according to claim 2, characterized in that, The base is selected from one or more of ammonia water and metal hydroxides.

7. The production method according to claim 6, wherein The base is selected from one or more of ammonia water, barium hydroxide, sodium hydroxide, potassium hydroxide, and calcium hydroxide.

8. The preparation method according to claim 2, characterized in that, The template agent is selected from one or more of ammonia compounds.

9. The production method according to claim 8, characterized by, The template agent is selected from one or more of butylamine, ethylamine, tetrabutylammonium bromide, tetraethylammonium bromide, tetrapropylammonium hydroxide, and tetrapropylammonium bromide.

10. The method of claim 2, wherein, The mixing process is performed at a stirring speed of 50-350 r / min for 30-240 min.

11. The method of claim 2, wherein, The crystallization process is controlled at a temperature of 160-190 ℃ for 16-72 h.

12. The method of claim 1, wherein, In step S1, the silicon source is selected from one or more of organic silicon and inorganic silicon; and / or In step S1, the base is selected from one or more of ammonia water and metal hydroxides; and / or In step S1, the template agent is selected from one or more of ammonia compounds; and / or In step S1, the Pt source is selected from one or more of H2PtCl6·6H2O and [Pt(NH3)2(NO2)2]; and / or The adjuvant of step S1 is selected from C 10 H 12 MgN2Na2O8·4H2O, C 10 H 12 ZnN2Na2O8·4H2O, C 10 H 12 FeN2Na2O8, MgSO4, MgCl2, KCl, K2SO4, La(NO3)3, InCl3, LaCl3, YCl3, CeCl3.

13. The method of claim 12, wherein, The silicon source is selected from one or more of sodium silicate, white carbon black, tetraethyl orthosilicate, and silica sol.

14. The method of claim 12, wherein, The base is selected from one or more of ammonia water, barium hydroxide, sodium hydroxide, potassium hydroxide, and calcium hydroxide.

15. The preparation method according to claim 12, characterized in that, The template agent is selected from one or more of tetrabutylammonium bromide, tetraethylammonium bromide, tetrapropylammonium bromide, tetrapropylammonium hydroxide, ethylamine, and butylamine.

16. The method of claim 1, wherein, In step S1, the mixing mass ratio of the full-silicon Silicate-1 molecular sieve, the silicon source, the base, the template agent, and the water is 1.0:(0.1-0.5):(0.03-0.16):(0.08-0.4):(1.2-5.5); and / or In step S1, the amount of the Pt source is 0.05-0.5 wt% of the mass of the full-silicon Silicate-1 molecular sieve; and / or The amount of the aid in step S1 is 0.02-0.5wt% of the total mass of Silicate-1 molecular sieve.

17. The method of claim 1, wherein, The mixing in step S1 is performed at a stirring speed of 50-350r / min for 30-240min.

18. The method of claim 1, wherein, The crystallization in step S2 is performed at a temperature of 90-195℃ for 0.5-32h; and / or The drying in step S2 is performed at a temperature of 60-120℃ for 12-24h; and / or The calcination in step S2 is performed at a temperature of 450-590℃ for 3-8h.

19. A molecular sieve catalyst for dehydrogenation prepared by the preparation method of any one of claims 1-18.

20. Use of the molecular sieve catalyst for dehydrogenation prepared by the preparation method of any one of claims 1-18 in the preparation of one or more of C3 dehydrogenation, C4 dehydrogenation, methanol to olefins.

21. The use according to claim 20, characterized in that, The reaction is catalytic dehydrogenation of propane to propylene.

22. A process for the catalytic dehydrogenation of propane to propylene, characterized in that, The reaction is performed by feeding propane / hydrogen into a fixed bed filled with the molecular sieve catalyst for dehydrogenation of claim 19.

23. The method of claim 22, wherein, The molar ratio of propane / hydrogen is 0.1-0.

5.

24. The method of claim 22, wherein, The reaction was carried out at a space velocity of 400-1500 hr -1 based on the volume of catalyst and the total reaction feed.

25. The method of claim 22, wherein, The reaction is performed at a pressure of 0.101-0.15MPa and a temperature of 560-620℃.

26. The method of claim 22, wherein, The molecular sieve catalyst maintains its performance by a regeneration operation, the regeneration method being to pass air at a space velocity of 1200-4500 h -1 at 480-620°C for 0.5-3.5 h.

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