A diatomic catalyst with high stability for propane dehydrogenation and its preparation method
By pretreating the γ-Al2O3 support and loading Pt and Sn using electrostatic adsorption, a diatomic catalyst is formed, which solves the problem of easy carbon deposition and deactivation of existing catalysts, realizes efficient and stable propane dehydrogenation reaction, and reduces costs.
Patent Information
- Application Number
- CN202311211428.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-09-20
- Publication Date
- 2026-01-06
- Estimated Expiration
- 2043-09-20
AI Technical Summary
Existing propane dehydrogenation catalysts are prone to carbon buildup and deactivation at high temperatures, have short lifespans, require frequent regeneration, are costly, and are difficult to apply on a large scale.
By calcining and pretreating the γ-Al2O3 support to make its electrokinetic potential negative, Pt and Sn are loaded using electrostatic adsorption to form a diatomic catalyst. Pt and Sn are dispersed in a diatomic form of 0.2~1.5 nm in a ratio of 5:1~1:5, which reduces the amount of precious metals and improves stability.
It achieves high conversion rate and selectivity at lower temperatures, with fewer byproducts, stable catalyst structure, long lifespan, no need for repeated regeneration, and reduced production costs.
Smart Images
Figure CN117181221B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of catalyst technology, and relates to a highly stable diatomic catalyst for propane dehydrogenation, its preparation method, and its application. Background Technology
[0002] my country possesses abundant propane reserves, and its production has further increased in recent years with the development of shale gas. The efficient conversion of propane into high-value-added products holds broad prospects and significant economic benefits. Propylene, a crucial component in the production of polypropylene, acrylic acid, propylene oxide, and acrylonitrile, is primarily obtained as a byproduct of naphtha steam cracking and fluidized catalytic cracking units in oil refineries. The ever-growing demand for propylene makes propane dehydrogenation increasingly important. Currently, two processes for this reaction have been industrialized: the Oleflex process (Pt-Sn based catalyst) and the Catofin process (CrOx / Al2O3 catalyst); however, the high cost of Pt and the toxicity of Cr have prompted the search for alternative, low-cost, and environmentally friendly catalysts.
[0003] In the process of propane dehydrogenation to propylene, although direct propane dehydrogenation is industrialized, this reaction is a thermodynamically constrained, strongly endothermic process requiring high temperatures (>600 °C) to achieve high stability. High temperatures also lead to problems such as catalyst carbonization, causing severe aggregation and loss of activity of the active components. Continuous catalyst regeneration is necessary during the reaction, a cumbersome process that negatively impacts the efficiency of propane dehydrogenation. In recent years, researchers have improved propylene selectivity by adding co-catalysts, typically Group IB elements, to Pt-based catalysts to reduce costs and promote propylene desorption. Furthermore, the choice of support plays a crucial role in catalyst selection; Al₂O₃, being inexpensive and readily available, is commonly used as the support for this reaction. Generally, the composition of the support and the catalyst preparation method determine the particle size and dispersion of the active components. In existing Pt-Sn / ZnAl2O4 catalysts, the Pt content is high, the deactivation is rapid during the reaction, requiring repeated regeneration and resulting in a short catalyst life. Therefore, it is difficult to put them into large-scale industrial application (Bao Khanh VuMyoung BokSongIn Young Ahn. Pt-Sn alloy phases and coke mobility over Pt-Sn / Al2O3 and Pt-Sn / ZnAl2O4 catalysts for propane dehydrogenation[J]. Applied Catalysis, A.General: An International Journal Devoted to Catalytic Science and Its Applications, 2011, 400(1a2).).
[0004] There is an urgent need to develop catalysts and preparation methods with high stability for propane dehydrogenation, which can achieve high conversion and selectivity for propane dehydrogenation to propylene, while maintaining high stability and long-term activity without repeated regeneration. Summary of the Invention
[0005] Through continuous exploration, the inventors of this invention discovered that by calcining and pretreating the catalyst support (γ-Al₂O₃) to achieve a negative electrokinetic potential in aqueous solution, and then loading the active component of the catalyst using electrostatic adsorption, a diatomic catalyst is obtained. Compared to existing bicomponent alloy catalysts, this catalyst requires less Pt, exhibits high stability, is less prone to deactivation, and demonstrates higher propane conversion and propylene selectivity with fewer byproducts, showing promising application prospects for the industrialization of propane dehydrogenation. Furthermore, the diatomic catalyst preparation method of this patent is simple and suitable for large-scale application and promotion.
[0006] The purpose of this invention is to provide a diatomic catalyst with high stability for propane dehydrogenation, its preparation method, and its application. By pretreating the catalyst support γ-Al₂O₃ through calcination to make its electrokinetic potential in aqueous solution negative, and adding a positively charged Pt precursor salt to the negatively charged, high-specific-surface-area γ-Al₂O₃, the active component Pt can be effectively anchored onto the γ-Al₂O₃. Simultaneously, the addition of the promoter Sn effectively disperses the active metal component, resulting in a diatomic catalyst. For the propane dehydrogenation to propylene reaction, the diatomic catalyst obtained by this invention has a much lower Pt loading rate than existing technologies, yet still exhibits excellent conversion rate and selectivity, reducing the amount of precious metals used and lowering production costs; furthermore, it maintains high stability over a long period, eliminating the need for repeated regeneration and improving production efficiency. The purpose of this invention is achieved through the following technical solutions.
[0007] A diatomic catalyst with high stability for propane dehydrogenation is characterized in that the catalyst support is γ-Al2O3 pretreated by calcination, and the electrokinetic potential of the pretreated γ-Al2O3 in aqueous solution is negative; the active components are Pt and Sn, which are dispersed in a diatomic form, and the particle size of Pt and Sn is 0.2~1.5 nm, with an average size of 0.4 nm.
[0008] Furthermore, the mass ratio of Pt to Sn is 5:1 to 1:5, and the total loading of Pt and Sn is 0.05 to 2 wt%, preferably 0.1 to 1 wt%. Adding an appropriate amount of tin can reduce the use of platinum, lower catalyst costs, and prevent excessive aggregation of platinum particles, thereby helping to maintain the activity and stability of the catalyst. Within this ratio range, metallic Pt and metallic Sn can couple well, achieving the expected conversion rate for propane dehydrogenation, reducing operating costs, and maintaining high activity.
[0009] A method for preparing a diatomic catalyst for propane dehydrogenation to propylene, the method comprising the following steps:
[0010] S1 The γ-Al2O3 support was calcined in air for later use, so that its electrokinetic potential in aqueous solution was negative;
[0011] S2 Dissolve the precursor salts of Pt and Sn in water, add the γ-Al2O3 support pretreated in step S1 to the solution, so that the precursor salts of Pt and Sn are impregnated onto the γ-Al2O3 support by electrostatic adsorption, and then stir and heat in an oil bath until the solution evaporates to dryness.
[0012] S3. Dry the product from step S2 by evaporation, and then calcine it in air;
[0013] S4 The calcination product from step S3 is activated in a mixed gas of hydrogen and nitrogen to obtain a diatomic catalyst with high stability for propane dehydrogenation.
[0014] Furthermore, in step S1, the calcination temperature is 200–600℃, and the calcination time is 2–8 h. At lower temperatures, the thermal vibration of the crystal is smaller, the alumina crystal structure is relatively stable, and fewer aluminum vacancies are formed. Within this temperature range, the thermal vibration of the crystal increases, and atoms move more easily. This leads to the loss of aluminum atoms from the crystal lattice, forming aluminum vacancies. At this time, the crystal structure of alumina gradually becomes more ordered. This makes the zeta potential of the calcined γ-Al₂O₃ negative, which is more conducive to the adsorption of Pt positive ions.
[0015] Further, in step S2, the precursor salt of Pt is a positively charged tetraamminenitrate or tetraamminechlorate of Pt, and the precursor salt of Sn includes one or more of oxalate, sulfate or chloride salts. The oil bath temperature is 60~120℃ and the time is 30~120min.
[0016] Furthermore, in step S3, the drying temperature is 80~140℃ and the time is 4~12h. Excessively high drying temperature may affect the dispersion effect of the active metal; the calcination temperature is 300~600℃ and the time is 3~8h. When the calcination temperature exceeds this temperature range, it may affect the crystal structure of the carrier.
[0017] Furthermore, in step S4, the activation temperature is 300~600℃ and the time is 1~5h.
[0018] Another object of the present invention is to provide a catalyst for the dehydrogenation of propane to propylene, wherein the specific reaction conditions are: reaction temperature 400~600℃, and feed space velocity 5000~12000ml / g·h.
[0019] This invention has the following advantages compared to existing catalysts:
[0020] (1) The diatomic catalyst of the present invention is easy to prepare, has good reproducibility, and requires a small amount of precious metal Pt.
[0021] (2) The diatomic catalyst of the present invention has high conversion rate for propane dehydrogenation reaction at lower temperatures, high selectivity for propylene, and low amount of by-products.
[0022] (3) The diatomic catalyst of the present invention has a stable structure, long service life, and is not prone to agglomeration during the reaction process, and does not require repeated regeneration. Attached Figure Description
[0023] Figure 1 This is a scanning transmission electron microscope image of the PtSn / Al2O3 catalyst obtained in Example 1 in a ring dark-field phase with spherical aberration correction.
[0024] Figure 2 The activity diagram of the PtSn / Al2O3 catalyst obtained in Example 1 is shown under the reaction conditions of 500°C and space velocity of 8000 ml / g•h.
[0025] Figure 3 This is a scanning transmission electron microscope image of the PtSn / Al2O3 catalyst obtained in Example 2 in a ring dark-field phase with spherical aberration correction.
[0026] Figure 4 The activity graph of the PtSn / Al2O3 catalyst obtained in Example 2 is shown under the reaction conditions of 550°C and space velocity of 8000 ml / g•h.
[0027] Figure 5 This is a scanning transmission electron microscope image of the PtSn / Al2O3 catalyst obtained in Example 3 in a ring dark-field phase with spherical aberration correction.
[0028] Figure 6 The activity diagram of the PtSn / Al2O3 catalyst obtained in Example 3 is shown under the reaction conditions of 600°C and space velocity of 12000 ml / g•h.
[0029] Figure 7 The images shown are X-ray diffraction (XRD) patterns of Examples 1-3.
[0030] Figure 8 This is an X-ray absorption fine structure (EXAFS) diagram of Examples 1-3. Implementation
[0031] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the protection scope of the present invention. Example 1
[0032] 1 g of commercial γ-Al₂O₃ was calcined in air at 300 °C for 3 h. The electromotive force of the treated γ-Al₂O₃ was measured to be -13.2 in aqueous solution. Then, 2 mg of tetraammineplatinum nitrate and 2 mg of stannous chloride hydrate were dissolved in 10 ml of distilled water and added dropwise to the treated γ-Al₂O₃. The mixture was then heated in an oil bath at 80 °C for 3 h, dried in an oven at 100 °C for 6 h, calcined in air at 500 °C for 4 h in a muffle furnace, and finally treated in 30% H₂ / N₂ at 600 °C for 2 h to obtain a PtSn / γ-Al₂O₃ diatomic catalyst containing only 0.1% Pt. Its dispersion was measured to be 92% by CO chemisorption.
[0033] Then, the performance of the propane dehydrogenation to propylene reaction was evaluated. The catalyst dosage was 100 mg, the reaction temperature was 500 °C, the reaction time was 50 h, the feed gas was a mixture of propane and nitrogen, and the space velocity was 8000 ml / g•h.
[0034] The corresponding biatomic aberration-corrected annular dark-field phase scanning transmission electron microscope images are as follows: Figure 1 As shown, Pt and Sn are uniformly dispersed on the support surface in a diatomic form. The propane dehydrogenation performance evaluation diagram is shown below. Figure 2 As shown, with a Pt content of only 0.1%, the average propane conversion rate is 42.9% at a reaction temperature of 500℃, the selectivity of the target product ethylene is 95.6%, and the stability is as high as 50h without hydrogen, requiring no regeneration. Example 2
[0035] 1 g of commercial γ-Al₂O₃ was calcined in air at 400 °C for 2 h. The electrokinetic potential of the treated γ-Al₂O₃ was measured to be -11.2 in aqueous solution. Then, 3 mg of tetraammineplatinum nitrate and 3 mg of stannous chloride hydrate were dissolved in 10 ml of distilled water and added dropwise to the treated γ-Al₂O₃. The mixture was then heated in an oil bath at 80 °C for 3 h, dried in an oven at 120 °C for 8 h, calcined in air at 500 °C for 4 h in a muffle furnace, and finally treated in 30% H₂ / N₂ at 600 °C for 2 h to obtain a PtSn / γ-Al₂O₃ diatomic catalyst containing only 0.15% Pt. Its dispersion was measured to be 89% by CO chemisorption.
[0036] Then, the performance of the propane dehydrogenation to propylene reaction was evaluated. The catalyst dosage was 100 mg, the reaction temperature was 550 °C, the reaction time was 10 h, the feed gas was a mixture of propane and nitrogen, and the space velocity was 8000 ml / g•h.
[0037] The corresponding biatomic aberration-corrected annular dark-field phase scanning transmission electron microscope images are as follows: Figure 3 As shown. The activity evaluation graph is as follows. Figure 4 As shown, with a Pt content of only 0.15%, the average propane conversion rate can reach 52.2% at a reaction temperature of 550℃, which is close to the thermodynamic equilibrium limit. The selectivity of the target product ethylene is 96.7%, and it can operate stably for 10 hours without the participation of hydrogen, without the need for regeneration. Example 3
[0038] 1 g of commercial γ-Al₂O₃ was calcined in air at 400 °C for 3 h. The electrokinetic potential of the treated γ-Al₂O₃ was measured to be -12.6 in aqueous solution. Then, 6 mg of tetraammineplatinum nitrate and 6 mg of stannous chloride hydrate were dissolved in 10 ml of distilled water and added dropwise to the treated γ-Al₂O₃. The mixture was then heated in an oil bath at 80 °C for 3 h, dried in an oven at 120 °C for 8 h, calcined in air at 500 °C for 4 h in a muffle furnace, and finally treated in 30% H₂ / N₂ at 600 °C for 2 h to obtain a PtSn / γ-Al₂O₃ diatomic catalyst containing only 0.3% Pt. Its dispersion was measured to be 81% by CO chemisorption.
[0039] Then, the performance of the propane dehydrogenation to propylene reaction was evaluated. The catalyst dosage was 200 mg, the reaction temperature was 600 °C, the reaction time was 10 h, the feed gas was a mixture of propane and nitrogen, and the space velocity was 12000 ml / g•h.
[0040] The corresponding biatomic aberration-corrected annular dark-field phase scanning transmission electron microscope images are as follows: Figure 5 As shown. The activity evaluation graph is as follows. Figure 6 As shown, with a Pt content of only 0.3% and a reaction temperature of 600℃, the average propane conversion rate is 61.6%, the selectivity of the target product propylene is 93.3%, and the propylene yield is 57.5%, which is extremely high. Moreover, the yield remains very high even during the 10-hour test, indicating that the catalyst deactivation rate is low.
[0041] In addition, X-ray diffraction (XRD) tests were performed on the catalysts of the above three embodiments, such as... Figure 7 The results showed that all peaks in the figure were characteristic of γ-Al₂O₃, with no characteristic peaks for Pt and Sn. This indicates that Pt and Sn are low in content and uniformly dispersed on the support surface, making them difficult to detect. To further confirm that the active component of the prepared catalyst is a Pt-Sn diatomic pair, synchrotron radiation tests were performed. Figure 8 The corresponding figures are shown. The results indicate that the figures mainly show Pt-O coordination bonds, indicating that Pt exists in atomic form in all three examples. Moreover, compared to elemental Pt, it is not difficult to find that the samples do not contain Pt-Pt bonds, indicating that the samples do not contain metal particles or clusters. This is consistent with the results of aberration-corrected annular dark-field phase scanning transmission electron microscopy.
[0042] Although embodiments of the present invention have been shown and described above, it is understood that these embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions, and alterations to the above embodiments within the scope of the present invention without departing from its principles and spirit. The scope of protection of the present invention is defined by the claims and their equivalents.
Claims
1. Use of a diatomic catalyst having high stability for the dehydrogenation of propane, characterized in that, The diatomic catalyst is used for propane dehydrogenation reaction without hydrogen participation, the carrier of the catalyst is γ-Al2O3 pretreated by calcination, the zeta potential of the pretreated γ-Al2O3 in aqueous solution is negative, the active component is Pt and Sn, Pt and Sn are dispersed and distributed in the form of diatomic, the particle size of Pt and Sn is 0.2-1.5 nm, and the average size is 0.4 nm.
2. Use according to claim 1, characterized in that, The mass ratio of Pt and Sn is 5:1-1:5, and the total loading amount of Pt and Sn is 0.05-2 wt%.
3. Use according to claim 2, characterized in that, The total loading amount of Pt and Sn is 0.1-1 wt%.
4. Use according to claim 1, characterized in that, The preparation method of the diatomic catalyst comprises the following steps: S1, calcining the γ-Al2O3 carrier in air for standby, so that the zeta potential of the carrier in aqueous solution is negative; S2, dissolving the precursor salt of Pt and Sn in water, adding the pretreated γ-Al2O3 carrier in step S1 to the solution, so that the precursor salt of Pt and Sn is impregnated on the γ-Al2O3 carrier by electrostatic adsorption, then oil bath stirring and heating until the solution is evaporated; S3, drying the evaporated product in step S2, and then calcining in air; S4, activating the calcined product in step S3 in a mixed gas of hydrogen and nitrogen to obtain a diatomic catalyst with high stability for propane dehydrogenation.
5. Use according to claim 4, characterized in that, The calcination temperature in step S1 is 200-600 DEG C, and the time is 2-8 h.
6. Use according to claim 4, characterized in that, In step S2, the precursor salt of Pt is a positively charged tetraammine nitrate or tetraammine chlorate, and the precursor salt of Sn includes one or more of oxalate, sulfate or chloride; the oil bath temperature is 60-120 DEG C, and the time is 30-120 min.
7. Use according to claim 4, characterized in that, In step S3, the drying temperature is 80-140 DEG C, and the time is 4-12 h; the calcination temperature is 300-600 DEG C, and the time is 3-8 h.
8. Use according to claim 4, characterized in that, In step S4, the activation temperature is 300-600 DEG C, and the time is 1-5 h.
9. Use according to claim 1, characterized in that, The medium-low temperature is 400-600 DEG C, and the raw material space velocity is 5000-12000 mL / (g.h).