Application of a PtSn alloy catalyst in propane dehydrogenation to produce propylene

Abstract

The present invention relates to a PtSn disordered alloy sub-nanometer catalyst for propane dehydrogenation. The catalyst uses γ-Al2O3 nanospheres as a carrier, and the active component Pt is diluted to a single-atom dispersion state by excessive Sn. During the high-temperature H2 reduction process, the Sn atoms around Pt are reduced by the hydrogen spillover effect of Pt atoms, and finally a PtSn disordered alloy sub-nanometer catalyst is formed. Among them, the mass percentage of Pt is 0.01-0.1%, the mass percentage of Sn is 0.08-2%, and the mass ratio of Pt to Sn is 1:10-1:12. This PtSn disordered alloy sub-nanometer catalyst has a simple preparation process and excellent catalytic performance, with high reaction activity and strong stability, and has broad application value in reducing the consumption of precious metals and improving reaction activity.

Description

Technical Field

[0001] The present invention belongs to the field of industrial applications, and relates to the preparation of a catalyst and its research on the performance of propane dehydrogenation. Specifically, it relates to the preparation of a PtSn disordered alloy sub-nanometer catalyst and its application research in the reaction of direct dehydrogenation of propane to propylene. Background Art

[0002] Propylene is a chemical raw material for producing polypropylene, various propane oxides, and acrylonitrile, and is known as the second largest petrochemical raw material after ethylene. For a long time, propylene has mainly come from catalytic cracking and steam cracking of petroleum. Since the 20th century, relying on these two traditional production methods has been unable to meet the increasing market demand for propylene. Coupled with the discovery of shale gas and the further development and utilization of coal resources, coal-to-olefins and propane dehydrogenation have gradually developed. Among them, propane dehydrogenation, as a production method dedicated to producing propylene, has received increasing attention. Currently, there are two methods for propane dehydrogenation: direct dehydrogenation and oxidative dehydrogenation. Among them, the direct dehydrogenation method has good dehydrogenation effect and high selectivity, and has been industrially applied. The mainstream processes are the Oleflex process of UOP Company in the United States and the Catofin process of ABB Lummus Company, and the catalysts used are Pt-Sn / Al 2 O 3 and CrO x / Al 2 O 3 . Due to the toxicity and environmental problems of Cr-based catalysts, the research and development of new propane dehydrogenation catalyst systems still mainly focus on Pt-based catalysts, and other Cr-free oxide systems are also constantly being tried.

[0003] From a thermodynamic perspective, direct dehydrogenation of propane is a strongly endothermic and thermodynamically limited reaction. At the same time, the equilibrium constant of this reaction is small, the industrial reaction temperature is generally above 600 °C, and the equilibrium conversion rate is about 50%. Reducing the pressure helps the reaction proceed in the forward direction, but when the pressure is too low, severe carbon deposition will cause the catalyst to deactivate. Therefore, in order to inhibit carbon deposition, a certain hydrogen partial pressure is often required in industry. In addition to the main reaction, too high a reaction temperature will also cause cracking, hydrogenolysis, and isomerization to occur, resulting in a decrease in selectivity. Or, under high-temperature and oxygen-free conditions, it is easy to deeply dehydrogenate and polymerize into polycyclic aromatic hydrocarbons, etc., forming carbon deposition to cover the active centers, resulting in a decrease in activity. For Pt-based catalysts, its advantage is that the C-H bond activity ability is strong and the activity is good. The main problem lies in stability. The main reasons for poor stability are carbon deposition, as well as particle aggregation and sintering during high-temperature reactions and repeated regeneration processes. The current solution ideas mainly focus on developing functional carriers that can confine and stabilize Pt particles or adding a second metal promoter. For Pt-Sn / Al 2 O 3Taking the [system] as an example, on the one hand, the addition of Sn can divide Pt nanoparticles into small Pt atomic clusters, thereby reducing or avoiding the multi-site adsorption of propane molecules on adjacent Pt sites, preventing the cleavage of C-C bonds and deep dehydrogenation, and reducing carbon deposition, which is called the geometric effect of Sn; on the other hand, Sn has an electron-donating effect on Pt, thereby reducing the interaction between Pt and the C=C double bond of propylene, contributing to the desorption of propylene, and preventing its further deep dehydrogenation or cracking, which is called the electronic effect of Sn.

[0004] From the binary phase diagram of PtSn, at high temperatures, Pt and Sn can form intermetallic compounds in various proportions, such as Pt 3 Sn, PtSn, Pt 2 Sn 3 、PtSn 2 and PtSn 4 etc. Intermetallic compounds, as an alloy form with a fixed crystal structure, chemical composition, and ordered structure, have the advantage in the propane dehydrogenation reaction that their structure is relatively stable and not prone to particle aggregation at high temperatures. However, at the same time, the exposed degree of the active metal Pt in the intermetallic compound is low and the coordination structure is relatively stable. On the one hand, this causes most of the Pt to be hidden inside the particles and unable to play a catalytic role. On the other hand, the intrinsic activity of the Pt sites with a stable coordination structure is relatively low. Therefore, in order to achieve a satisfactory yield, the loading amount of Pt needs to be very high, resulting in a decrease in the utilization rate of precious metal atoms and an increase in production costs.

[0005] When the particle size decreases or the content of the metal component changes, the ordered arrangement of atoms in the intermetallic compound will be affected, and the crystal structure will be misaligned, deformed or even collapsed, resulting in an increase in the overall atomic arrangement disorder, forming an amorphous disordered alloy with no fixed composition. Such an alloy often has a high degree of coordination unsaturation of atoms and thus has good catalytic activity. Based on this, seeking an effective synthesis strategy in the PtSn system to reduce the particle size and adjust the composition of PtSn, and then promote the disordering of the PtSn alloy, is of great significance for improving the activity and stability of the catalyst. Summary of the Invention

[0006] The object of the present invention is, in view of the above-mentioned prior art situation, to provide a PtSn disordered alloy sub-nanocatalyst for propane dehydrogenation reaction. This catalyst has the characteristics of high activity, high atomic utilization rate and high stability for propane dehydrogenation reaction.

[0007] To achieve the above object, in the present invention, γ-alumina nano-spheres with a diameter of 10 nm and a relatively large specific surface area are selected as the carrier, and the active component Pt is diluted to a single-atom dispersion state by excessive Sn, and at high temperature H 2During the reduction process, the hydrogen spillover effect of Pt atoms is utilized to reduce the surrounding Sn atoms, and finally a PtSn disordered alloy sub-nanocatalyst is formed. The average particle size of this catalyst is about 0.85 nm, the dispersion degree is close to 100%, and the degree of unsaturation of the active component Pt is relatively high, so it has high activity. On the other hand, this alloy structure also ensures that the catalyst has a certain stability.

[0008] The preparation method of the PtSn disordered alloy sub-nanocatalyst described in the present invention is that a metal precursor solution containing Pt and Sn is impregnated onto alumina nanospheres, and then dried, calcined, and in-situ reduced. The mass percentage content of the active component Pt is 0.01 - 0.1%, and the mass percentage content of Sn is 0.08 - 2%. The Pt precursor solution used is an ethanol solution of H 2 PtCl 6 ·6H 2 O, and the Sn precursor is an ethanol solution of SnCl 2 ·2H 2 O. The impregnation method is equal-volume impregnation or excess impregnation, and the impregnation sequence is co-impregnation or stepwise impregnation. The drying conditions are drying in an oven at 60 - 120 °C for 5 - 30 h, the calcination conditions are calcination in a muffle furnace at 300 - 500 °C for 2 - 10 h, and the reduction conditions are reduction at 600 °C under 5 - 50% H 2 / He for 1 - 10 h.

[0009] The PtSn disordered alloy sub-nanocatalyst prepared by any of the above methods is used in the propane dehydrogenation reaction. The characteristic reaction conditions are that the reaction temperature is 580 - 620 °C, and the volume ratio of the reaction gases is: 5 - 14% C 3 H 8 , 5 - 14% H 2 ; the balance is He, and the WHSV is 1 - 10 h -1 .

[0010] This preparation process of the PtSn disordered alloy sub-nanocatalyst is simple and has excellent catalytic performance, with high reaction activity and strong stability, and has wide application value in reducing the consumption of precious metals and improving the reaction activity.

[0011] The present invention has the following advantages compared with the prior art:

[0012] 1. For the PtSn disordered alloy sub-nanocatalyst prepared in the present invention, the mass percentage content of Pt is 0.01 - 0.1%, the mass percentage content of Sn is 0.08 - 2%, and the mass ratio of Pt to Sn is 1:10 - 1:12. By diluting Pt with a greatly excessive amount of Sn, the consumption of the precious metal Pt is effectively reduced.

[0013] 2. The support used in the present invention is γ-alumina nanospheres with a diameter of 5-20 nm. On the one hand, there is a strong interaction between the support and PtSn, which can achieve atomic-level dispersion of Pt and Sn on the support. After high-temperature reduction, PtSn disordered alloy sub-nanoparticles with a dispersion close to 100% are formed. On the other hand, due to the nano-scale size of the support itself and its three-dimensional spherical structure, PtSn is difficult to aggregate and grow during the reaction, and the particle size is always maintained at about 1 nm. This can effectively increase the exposure degree of the noble metal Pt and inhibit the occurrence of structure-sensitive side reactions, greatly reducing carbon deposition and improving the catalyst stability.

[0014] The present invention will be described in detail below through specific examples. It should be noted that these examples are only for illustration and do not constitute any limitation to the essence and scope of the present invention. As long as the conditions described in the content part of the present invention are met, the present invention can be realized. Therefore, the protection scope of the present invention is subject to the claims of the application. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is the STEM image of the alumina support after calcination at 500 °C and reduction at 600 °C in Example 4.

[0016] Figure 2 It is the particle size distribution and EDX image after reduction at 600 °C in Example 4.

[0017] Figure 3 It is the XAFS image of Example 4.

[0018] Figure 4 It is the XPS image of Example 4.

[0019] Figure 5 It is the correlation diagram of Pt loading and performance of Examples 1, 2, and 4. DETAILED DESCRIPTION OF THE INVENTION

[0020] Example 1.

[0021] 0.01Pt0.1Sn / Al 2 O 3 -nano catalyst preparation:

[0022] Weigh 500 mg of γ-alumina nanosphere support with a particle size of 5-20 nm (denoted as Al 2 O 3 -nano) into a 20 ml glass vial. At room temperature (about 25 °C), use a pipette to measure 0.066 mL (Pt: 0.753 mg / mL) of H 2 PtCl 6 ·6H 2Put the ethanol solution in a 2 ml centrifuge tube, and then add 0.061 mL (Sn: 8.18 mg / mL) of SnCl 2 ·2H 2 ethanol solution and 0.68 mL of absolute ethanol were fully mixed and evenly dispersed. The impregnation solution after mixing was added dropwise to the Al 2 O 3 -nano support with a 1 mL syringe. Then, it was stirred evenly with a glass rod until it became a viscous paste. After standing overnight at room temperature, it was placed in an oven at 60 °C for 12 h of drying. Finally, it was ground and transferred to a muffle furnace for calcination at 500 °C for 4 h to obtain 0.01Pt0.1Sn / Al with a particle size of 0.5 - 1.5 nm 2 O 3 -nano catalyst.

[0023] Example 2.

[0024] 0.05Pt0.5Sn / Al 2 O 3 -nano catalyst preparation:

[0025] Weigh 500 mg of γ-alumina nanosphere support with a particle size of 5 - 20 nm into a 20 ml glass vial. At room temperature (about 25 °C), use a pipette to measure 0.033 mL (Pt: 7.53 mg / mL) of H 2 PtCl 6 ·6H 2 ethanol solution in a 2 ml centrifuge tube, and then add 0.306 mL (Sn: 8.18 mg / mL) of SnCl 2 ·2H 2 ethanol solution and 0.46 mL of absolute ethanol were fully mixed and evenly dispersed. The impregnation solution after mixing was added dropwise to the Al 2 O 3 -nano support with a 1 mL syringe. Then, it was stirred evenly with a glass rod until it became a viscous paste. After standing overnight at room temperature, it was placed in an oven at 60 °C for 12 h of drying. Finally, it was ground and transferred to a muffle furnace for calcination at 500 °C for 4 h to obtain 0.05Pt0.5Sn / Al with a particle size of 0.5 - 1.5 nm 2 O 3 -nano catalyst.

[0026] Example 3.

[0027] Weigh 500 mg of γ-alumina nanosphere support with a particle size of 5 - 20 nm into a 20 ml glass vial. At room temperature (about 25 °C), use a pipette to measure 0.033 mL (Pt: 7.53 mg / mL) of H 2 PtCl 6 ·6H 2Put the anhydrous ethanol solution of O into a 2ml centrifuge tube, and then add 0.367mL (Sn: 8.18mg / mL) SnCl 2 ·2H 2 O anhydrous ethanol solution and 0.40mL anhydrous ethanol are fully mixed evenly. Use a 1mL syringe to dropwise add the evenly mixed impregnation solution to Al 2 O 3 -nano support. Then use a glass rod to stir it evenly until it becomes a viscous paste. Let it stand overnight at room temperature and then dry it in an oven at 60°C for 12h. Finally, grind it and transfer it to a muffle furnace for calcination at 500°C for 4h to obtain 0.05Pt0.6Sn / Al with a particle size of 0.5 - 1.5nm 2 O 3 -nano catalyst.

[0028] Example 4.

[0029] 0.1Pt1Sn / Al 2 O 3 -nano catalyst preparation:

[0030] Weigh 500mg of γ-aluminum oxide nanosphere support with a particle size of 5 - 20nm into a 20ml glass vial. At room temperature (about 25°C), use a pipette to measure 0.066mL (Pt: 7.53mg / mL) H 2 PtCl 6 ·6H 2 O anhydrous ethanol solution into a 2ml centrifuge tube, and then add 0.611mL (Sn: 8.18mg / mL) SnCl 2 ·2H 2 O anhydrous ethanol solution and 0.12mL anhydrous ethanol are fully mixed evenly. Use a 1mL syringe to dropwise add the evenly mixed impregnation solution to Al 2 O 3 -nano support. Then use a glass rod to stir it evenly until it becomes a viscous paste. Let it stand overnight at room temperature and then dry it in an oven at 60°C for 12h. Finally, grind it and transfer it to a muffle furnace for calcination at 500°C for 4h to obtain 0.1Pt1Sn / Al with a particle size of 0.5 - 1.5nm 2 O 3 -nano catalyst.

[0031] Example 5.

[0032] 0.1Pt1.2Sn / Al 2 O 3 -nano catalyst preparation:

[0033] Weigh 500 mg of γ-alumina nanosphere support with a particle size of 5 - 20 nm into a 20 ml glass vial. At room temperature (about 25 °C), use a pipette to measure 0.066 mL (Pt: 7.53 mg / mL) of H 2 PtCl 6 ·6H 2 O absolute ethanol solution into a 2 ml centrifuge tube, then add 0.73 mL (Sn: 8.18 mg / mL) of SnCl 2 ·2H 2 O absolute ethanol solution and mix well. Use a 1 mL syringe to dropwise add the well-mixed impregnation solution to the Al 2 O 3 -nano support. Then use a glass rod to stir it evenly until it becomes a viscous paste. Let it stand overnight at room temperature and then dry it in an oven at 60 °C for 12 h. Finally, grind it and transfer it to a muffle furnace for calcination at 500 °C for 4 h to obtain a 0.1Pt1.2Sn / Al 2 O 3 -nano catalyst with a particle size of 0.5 - 1.5 nm.

[0034] Example 6.

[0035] Preparation of 0.1Pt1Sn / Al 2 O 3 -nano catalyst by the stepwise impregnation method (impregnate Pt first and then Sn):

[0036] Weigh 500 mg of γ-alumina nanosphere support with a particle size of 5 - 20 nm into a 20 ml glass vial. At room temperature (about 25 °C), use a pipette to measure 0.066 mL (Pt: 7.53 mg / mL) of H 2 PtCl 6 ·6H 2 O absolute ethanol solution into a 2 ml centrifuge tube, then add 0.72 mL of absolute ethanol and mix well. Use a 1 mL syringe to dropwise add the well-mixed impregnation solution to the Al 2 O 3 -nano support. Then use a glass rod to stir it evenly until it becomes a viscous paste. Let it stand overnight at room temperature and then dry it in an oven at 60 °C for 12 h. Finally, grind it and transfer it to a muffle furnace for calcination at 500 °C for 4 h; Weigh 500 mg of the obtained catalyst into a 20 ml glass vial. At room temperature (about 25 °C), use a pipette to measure 0.611 mL (Sn: 8.18 mg / mL) of SnCl 2 ·2H 2Place the O anhydrous ethanol solution in a 2 ml centrifuge tube, then add 0.18 mL of anhydrous ethanol and mix well. Use a 1 mL syringe to dropwise add the uniformly mixed impregnation solution onto the catalyst powder, and then use a glass rod to stir it evenly until it becomes a viscous paste. Let it stand overnight at room temperature and then dry it in an oven at 60 °C for 12 h. Finally, grind it and transfer it to a muffle furnace for calcination at 500 °C for 4 h to obtain a 0.1Pt1Sn / Al catalyst with a particle size of 0.5 - 1.5 nm by the stepwise impregnation method (first impregnate Pt and then impregnate Sn). 2 O 3 -nano catalyst.

[0037] Example 7.

[0038] 0.1Pt1Sn / Al 2 O 3 Preparation of 0.1Pt1Sn / Al-nano catalyst by the stepwise impregnation method (first impregnate Sn and then impregnate Pt):

[0039] Weigh 500 mg of γ-alumina nanosphere support with a particle size of 5 - 20 nm into a 20 ml glass vial. At room temperature (about 25 °C), use a pipette to measure 0.611 mL (Sn: 8.18 mg / mL) of SnCl 2 ·2H 2 O anhydrous ethanol solution in a 2 ml centrifuge tube, then add 0.18 mL of anhydrous ethanol and mix well. Use a 1 mL syringe to dropwise add the uniformly mixed impregnation solution onto the Al 2 O 3 -nano support, and then use a glass rod to stir it evenly until it becomes a viscous paste. Let it stand overnight at room temperature and then dry it in an oven at 60 °C for 12 h. Finally, grind it and transfer it to a muffle furnace for calcination at 500 °C for 4 h; Weigh 500 mg of the obtained catalyst into a 20 ml glass vial. At room temperature (about 25 °C), use a pipette to measure 0.066 mL (Pt: 7.53 mg / mL) of H 2 PtCl 6 ·6H 2 O anhydrous ethanol solution in a 2 ml centrifuge tube, then add 0.72 mL of anhydrous ethanol and mix well. Use a 1 mL syringe to dropwise add the uniformly mixed impregnation solution onto the catalyst powder, and then use a glass rod to stir it evenly until it becomes a viscous paste. Let it stand overnight at room temperature and then dry it in an oven at 60 °C for 12 h. Finally, grind it and transfer it to a muffle furnace for calcination at 500 °C for 4 h to obtain a 0.1Pt1Sn / Al 2 O 3 -nano catalyst.

[0040] Example 8.

[0041] 0.1Pt1Sn / Al2 O 3 Preparation by excess impregnation method of -nano catalyst:

[0042] Weigh 500 mg of γ-alumina nanosphere support with a particle size of 5 - 20 nm into a 20 ml glass vial. At room temperature (about 25 °C), use a pipette to measure 0.066 mL (Pt: 7.53 mg / mL) of H 2 PtCl 6 ·6H 2 O absolute ethanol solution into a 2 ml centrifuge tube, and then add 0.611 mL (Sn: 8.18 mg / mL) of SnCl 2 ·2H 2 O absolute ethanol solution and 8 mL of absolute ethanol, mix them evenly. Use a 10 mL syringe to dropwise add the evenly mixed impregnation solution to the Al 2 O 3 -nano support. Then place the mixture in a 50 °C water bath and stir to evaporate the water. Let it stand overnight at room temperature and then dry it in an oven at 60 °C for 12 h. Finally, grind it and transfer it to a muffle furnace for calcination at 500 °C for 4 h to obtain a 0.1Pt1Sn / Al with a particle size of 0.5 - 1.5 nm prepared by the excess impregnation method 2 O 3 -nano catalyst.

[0043] Example 9.

[0044] Activity evaluation of the 0.01Pt0.1Sn / Al 2 O 3 -nano catalyst with a particle size of 0.5 - 1.5 nm prepared in Example 1:

[0045] Pretreatment conditions: 600 °C, a mixture of 20% H 2 and He by volume, 18,000 mL·h -1 ·g -1 , after treatment for 2 hours.

[0046] Catalytic reaction conditions: A quartz reaction tube with an inner diameter of 10 mm in a fixed bed. The volume ratio of the raw material gas composition is 14% C 3 H 8 , 14% H 2 , 72% He as the balance gas, and the space velocity of the raw material gas is 18,000 mL·h -1 ·g -1 . The reaction temperature is 600 °C, and the reaction pressure is atmospheric pressure.

[0047] Example 10.

[0048] The 0.05Pt0.5Sn / Al with a particle size of 0.5 - 1.5 nm prepared in Example 22 O 3 -nano activity evaluation: under the same conditions as in Example 9.

[0049] Example 11.

[0050] 0.05Pt0.6Sn / Al with a particle size of 0.5 - 1.5 nm prepared in Example 3 2 O 3 -nano activity evaluation: under the same conditions as in Example 9.

[0051] Example 12.

[0052] 0.1Pt1Sn / Al with a particle size of 0.5 - 1.5 nm prepared in Example 4 2 O 3 -nano activity evaluation: under the same conditions as in Example 9.

[0053] Example 13.

[0054] 0.1Pt1.2Sn / Al with a particle size of 0.5 - 1.5 nm prepared in Example 5 2 O 3 -nano activity evaluation: under the same conditions as in Example 9.

[0055] Example 14.

[0056] 0.1Pt1Sn / Al with a particle size of 0.5 - 1.5 nm prepared in Example 6 2 O 3 -nano (stepwise impregnation, Pt first then Sn) activity evaluation: under the same conditions as in Example 9.

[0057] Example 15.

[0058] 0.1Pt1Sn / Al with a particle size of 0.5 - 1.5 nm prepared in Example 7 2 O 3 -nano (stepwise impregnation, Sn first then Pt) activity evaluation: under the same conditions as in Example 9.

[0059] Example 16.

[0060] 0.1Pt1Sn / Al with a particle size of 0.5 - 1.5 nm prepared in Example 8 2 O 3 -nano (excessive impregnation) activity evaluation: under the same conditions as in Example 9.

[0061] Example 17.

[0062] 0.1Pt1Sn / Al with a particle size of 0.5 - 1.5 nm prepared in Example 9 2 O3 -nano catalyst activity evaluation:

[0063] Pretreatment conditions: 600 °C, 20% H by volume 2 mixed with He, 18,000 mL·h -1 ·g -1 , after treatment for 8 hours.

[0064] Catalytic reaction conditions: a quartz reaction tube with an inner diameter of 10 mm in a fixed bed, the volume ratio of the raw material gas composition is 14% C 3 H 8 、14% H 2 、72% He as the balance gas, the space velocity of the raw material gas is 18,000 mL·h -1 ·g -1 . The reaction temperature is 600 °C, and the reaction pressure is atmospheric pressure.

[0065] Example 18.

[0066] 0.1Pt1Sn / Al with a particle size of 0.5 - 1.5 nm prepared in Example 1 2 O 3 -nano intrinsic reaction rate evaluation:

[0067] Weigh 20 mg of 0.1Pt1Sn / Al 2 O 3 -nano catalyst and dilute it with 80 mg of pure Al 2 O 3 support, and after mixing evenly, load it into the quartz reaction tube.

[0068] Pretreatment conditions: 600 °C, 20% H by volume 2 mixed with He, 18,000 mL·h -1 ·g -1 , after treatment for 2 hours.

[0069] Catalytic reaction conditions: a quartz reaction tube with an inner diameter of 10 mm in a fixed bed, the volume ratio of the raw material gas composition is 14% C 3 H 8 、14% H 2 、72% He as the balance gas, the space velocity of the raw material gas is 18,000 mL·h -1 ·g -1 . The reaction temperature is 600 °C, and the reaction pressure is atmospheric pressure.

[0070] Comparative Example 1.

[0071] 0.05Pt0.5Sn / Al 2 O 3 -sheet catalyst preparation:

[0072] Weigh 500 mg of Al with the same nanoscale size but in the form of two-dimensional nanosheets (length and width are 5 - 100 nm) 2 O 3- sheet support into a 20-ml glass vial. At room temperature (about 25 °C), use a pipette to measure 0.033 mL (Pt: 7.53 mg / mL) of H 2 PtCl 6 ·6H 2 O absolute ethanol solution into a 2-ml centrifuge tube. Then add 0.306 mL (Sn: 8.18 mg / mL) of SnCl 2 ·2H 2 O absolute ethanol solution and 0.46 mL of absolute ethanol, and mix them thoroughly. Use a 1-ml syringe to dropwise add the well-mixed impregnation solution onto the Al 2 O 3- sheet support. Then use a glass rod to stir it evenly until it becomes a viscous paste. Let it stand overnight at room temperature and then dry it in an oven at 60 °C for 12 h. Finally, grind it and transfer it to a muffle furnace for calcination at 500 °C for 4 h to obtain the 0.05Pt0.5Sn / Al 2 O 3 -sheet catalyst.

[0073] Comparative Example 2.

[0074] 0.1Pt1Sn / normal-Al 2 O 3 Catalyst preparation:

[0075] Weigh 500 mg of normal-Al with a micron-scale size and an irregular three-dimensional structure 2 O 3 support into a 20-ml glass vial. At room temperature (about 25 °C), use a pipette to measure 0.066 mL (Pt: 7.53 mg / mL) of H 2 PtCl 6 ·6H 2 O absolute ethanol solution into a 2-ml centrifuge tube. Then add 0.611 mL (Sn: 8.18 mg / mL) of SnCl 2 ·2H 2 O absolute ethanol solution and 0.12 mL of absolute ethanol, and mix them thoroughly. Use a 1-ml syringe to dropwise add the well-mixed impregnation solution onto the normal-Al 2 O 3 support. Then use a glass rod to stir it evenly until it becomes a viscous paste. Let it stand overnight at room temperature and then dry it in an oven at 60 °C for 12 h. Finally, grind it and transfer it to a muffle furnace for calcination at 500 °C for 4 h to obtain the 0.1Pt1Sn / normal-Al 2O 3 Catalyst.

[0076] Comparative Example 3.

[0077] 0.1Pt0.3Sn / Al 2 O 3 -nano Catalyst Preparation:

[0078] Weigh 500 mg of γ-alumina nanosphere support with a particle size of 5 - 20 nm into a 20 ml glass vial. At room temperature (about 25 °C), use a pipette to measure 0.066 mL (Pt: 7.53 mg / mL) of H 2 PtCl 6 ·6H 2 O absolute ethanol solution into a 2 ml centrifuge tube, then add 0.183 mL (Sn: 8.18 mg / mL) of SnCl 2 ·2H 2 O absolute ethanol solution and 0.55 mL of absolute ethanol, mix well. Use a 1 mL syringe to dropwise add the well-mixed impregnation solution to the Al 2 O 3 -nano support. Then use a glass rod to stir it evenly until it becomes a viscous paste. Let it stand overnight at room temperature and then dry it in an oven at 60 °C for 12 h. Finally, grind it and transfer it to a muffle furnace for calcination at 500 °C for 4 h to obtain 0.1Pt0.3Sn / Al 2 O 3 -nano catalyst.

[0079] Comparative Example 4.

[0080] 0.1Pt2Sn / Al 2 O 3 -nano Catalyst Preparation:

[0081] Weigh 500 mg of γ-alumina nanosphere support with a particle size of 5 - 20 nm into a 20 ml glass vial. At room temperature (about 25 °C), use a pipette to measure 0.066 mL (Pt: 7.53 mg / mL) of H 2 PtCl 6 ·6H 2 O absolute ethanol solution into a 2 ml centrifuge tube, then add 1.22 mL (Sn: 8.18 mg / mL) of SnCl 2 ·2H 2 O absolute ethanol solution and mix well. Use a 2 mL syringe to dropwise add the well-mixed impregnation solution to the Al 2 O 3-nano support, and then stir it evenly with a glass rod until it becomes a viscous paste. After standing overnight at room temperature, place it in an oven at 60 °C for 12 h of drying. Finally, grind it and transfer it to a muffle furnace for calcination at 500 °C for 4 h to obtain 0.1Pt2Sn / Al 2 O 3 -nano catalyst.

[0082] Comparative Example 5.

[0083] 0.5Pt1Sn / Al 2 O 3 -nano catalyst preparation:

[0084] Weigh 500 mg of γ-alumina nanosphere support with a particle size of 5-20 nm into a 20 ml glass vial. At room temperature (about 25 °C), use a pipette to measure 0.33 mL (Pt: 7.53 mg / mL) of H 2 PtCl 6 ·6H 2 O absolute ethanol solution into a 2 ml centrifuge tube, and then add 0.25 mL (Sn: 20 mg / mL) of SnCl 2 ·2H 2 O absolute ethanol solution and 0.28 mL of absolute ethanol and mix them evenly. Use a 1 mL syringe to dropwise add the evenly mixed impregnation solution to the Al 2 O 3 -nano support, and then stir it evenly with a glass rod until it becomes a viscous paste. After standing overnight at room temperature, place it in an oven at 60 °C for 12 h of drying. Finally, grind it and transfer it to a muffle furnace for calcination at 500 °C for 4 h to obtain 0.5Pt1Sn / Al 2 O 3 -nano catalyst. This catalyst is a common loading for industrial catalysts.

[0085] Comparative Example 6.

[0086] Activity evaluation of the 0.05Pt0.5Sn / Al 2 O 3 -sheet catalyst prepared in Comparative Example 1: Under the same conditions as in Example 9

[0087] Comparative Example 7.

[0088] Activity evaluation of the 0.1Pt1Sn / normal-Al 2 O 3 catalyst prepared in Comparative Example 2: Under the same conditions as in Example 9

[0089] Comparative Example 8.

[0090] Activity evaluation of the 0.1Pt0.3Sn / Al 2 O3 Activity evaluation of -nano catalyst: under the same conditions as in Example 9

[0091] Comparative Example 9.

[0092] 0.1Pt2Sn / Al prepared in Comparative Example 4 2 O 3 Activity evaluation of -nano catalyst: under the same conditions as in Example 9

[0093] Comparative Example 10.

[0094] 0.5Pt1Sn / Al prepared in Comparative Example 5 2 O 3 Measurement of -nano intrinsic reaction rate:

[0095] Weigh 8 mg of 0.5Pt1Sn / Al 2 O 3 -nano catalyst and add 92 mg of pure Al 2 O 3 -nano support for dilution, mix evenly and then load into a quartz reaction tube.

[0096] Pretreatment conditions: 600 °C, 20% (volume percentage) H 2 mixed with He, 18,000 mL·h -1 ·g -1 , after treatment for 2 hours.

[0097] Catalytic reaction conditions: a quartz reaction tube with an inner diameter of 10 mm in a fixed bed, the volume ratio of the raw material gas composition is 14% C 3 H 8 、14% H 2 、72% He as the balance gas, the space velocity of the raw material gas is 18,000 mL·h -1 ·g -1 . The reaction temperature is 600 °C and the reaction pressure is atmospheric pressure.

[0098] Comparative Example 11.

[0099] 0.05Pt0.5Sn / Al with a particle size of 0.5 - 1.5 nm prepared in Example 2 2 O 3 Reduction activity evaluation of -nano catalyst at 500 °C:

[0100] Pretreatment conditions: 500 °C, 20% (volume percentage) H 2 mixed with He, 18,000 mL·h -1 ·g -1 , after treatment for 2 hours.

[0101] Catalytic reaction conditions: A quartz reaction tube with an inner diameter of 10 mm in a fixed bed, the volume ratio of the raw material gas components is 14% C 3 H 8 、14% H 2 、72% He as the balance gas, and the space velocity of the raw material gas is 18,000 mL·h -1 ·g -1 . The reaction temperature is 600 °C, and the reaction pressure is atmospheric pressure.

[0102] Comparative Example 12.

[0103] Activity evaluation of the 0.05Pt0.5Sn / Al 2 O 3 -nano catalyst with a particle size of 0.5 - 1.5 nm prepared in Example 2 after reaction atmosphere pretreatment:

[0104] Pretreatment conditions: 600 °C, raw material gas (volume ratio of components is 14% C 3 H 8 、14% H 2 、72% He as the balance gas) 18,000 mL·h -1 ·g -1 , after treatment for 2 hours.

[0105] Catalytic reaction conditions: A quartz reaction tube with an inner diameter of 10 mm in a fixed bed, the volume ratio of the raw material gas components is 14% C 3 H 8 、14% H 2 、72% He as the balance gas, and the space velocity of the raw material gas is 18,000 mL·h -1 ·g -1 . The reaction temperature is 600 °C, and the reaction pressure is atmospheric pressure.

[0106] Comparative Example 13.

[0107] Activity evaluation of the 0.1Pt1Sn / Al 2 O 3 -nano catalyst with a particle size of 0.5 - 1.5 nm prepared in Example 4 after reduction with pure hydrogen at 600 °C:

[0108] Pretreatment conditions: 600 °C, under pure hydrogen, 18,000 mL·h -1 ·g -1 , after treatment for 2 hours.

[0109] Catalytic reaction conditions: A quartz reaction tube with an inner diameter of 10 mm in a fixed bed, the volume ratio of the raw material gas components is 14% C 3 H 8 、14% H 2 、72% He as the balance gas, and the space velocity of the raw material gas is 18,000 mL·h -1 ·g-1 The reaction temperature is 600 °C, and the reaction pressure is atmospheric pressure.

[0110] Comparative Example 14.

[0111] Activity evaluation of the 0.1Pt1Sn / Al 2 O 3 -nano catalyst with a particle size of 0.5 - 1.5 nm prepared in Example 4 after reduction at 700 °C:

[0112] Pretreatment conditions: 700 °C, a mixed gas of 20% H 2 and He, at a flow rate of 18,000 mL·h -1 ·g -1 , after treatment for 2 hours.

[0113] Catalytic reaction conditions: A quartz reaction tube with an inner diameter of 10 mm in a fixed bed. The volume ratio of the raw material gas components is 14% C 3 H 8 、14% H 2 、72% He as the balance gas, and the space velocity of the raw material gas is 18,000 mL·h -1 ·g -1 The reaction temperature is 600 °C, and the reaction pressure is atmospheric pressure.

[0114] Comparative Example 15.

[0115] Activity evaluation of the 0.1Pt1Sn / Al 2 O 3 -nano catalyst with a particle size of 0.5 - 1.5 nm prepared in Example 4 after reduction at 800 °C:

[0116] Pretreatment conditions: 800 °C, a mixed gas of 20% H 2 and He, at a flow rate of 18,000 mL·h -1 ·g -1 , after treatment for 2 hours.

[0117] Catalytic reaction conditions: A quartz reaction tube with an inner diameter of 10 mm in a fixed bed. The volume ratio of the raw material gas components is 14% C 3 H 8 、14% H 2 、72% He as the balance gas, and the space velocity of the raw material gas is 18,000 mL·h -1 ·g -1 The reaction temperature is 600 °C, and the reaction pressure is atmospheric pressure.

[0118] The corresponding conversion rate and selectivity results are shown in the following table:

[0119]

[0120]

[0121] Note: "-" indicates that this data item was not measured under the conditions of this example.

[0122] In Example 10 and Comparative Example 6, the sizes of the carriers are at the nanometer level. However, since the alumina nanospheres in Example 5 have a three-dimensional structure, they have a better dispersion effect on PtSn compared to two-dimensional nanosheets, resulting in higher activity. In Example 12 and Comparative Example 7, the carriers are both three-dimensional structures. However, the alumina nanospheres in Example 12 are smaller in size, so they can effectively prevent the aggregation and growth of PtSn during the reduction process, maintaining the particle size at about 1 nm and a higher Pt exposure degree, thus having better activity. Through the above comparison, the unique advantages of alumina nanospheres as carriers in improving catalyst performance can be seen. From Examples 12, 13 and Comparative Examples 8, 9, it can be seen that the catalyst performance is optimal when the mass ratio of Pt to Sn is 1:10 - 1:12. From Examples 12, 14, 15, 16, it can be seen that the same catalytic effect can be achieved by over-impregnation and stepwise impregnation. From Example 12 and Example 17, it can be seen that the same catalytic effect can be achieved when the reduction time is 2 h or 8 h. From Example 10 and Comparative Examples 11, 12, Example 12 and Comparative Examples 13 - 15, it can be seen that only when pretreated with a mixed gas of 20% H 2 and He at 600 °C can a good catalytic effect be achieved. From Example 18 and Comparative Example 10, it can be seen that our disordered alloy sub-nanometer catalyst has higher intrinsic activity compared to conventional industrial catalysts.

[0123] Figure 1 The provided are electron microscope images of the alumina nanosphere carrier, and after calcination at 500 °C and reduction at 600 °C in Example 4. It can be seen that the carrier is a nanosphere with a diameter of 10 nm. After loading PtSn and calcination, both Pt and Sn are in a monodispersed state. After reduction, they combine to form PtSn alloy sub-nanometer particles, and the excess Sn continues to be in a monodispersed state.

[0124] Figure 2 The provided is the STEM image after reduction at 600 °C in Example 4. It can be seen that the average particle size in Example 4 is 0.85 nm, and each particle is composed of PtSn alloy, but the PtSn content is not fixed. There are particles with a high Sn content, particles with a high Pt content, and particles with an equal content of both, indicating that the PtSn alloy formed in Example 4 is a disordered sub-nanometer alloy.

[0125] Figure 3The XAFS data of Example 4 are given. The presence of Pt-Sn bonds proves the formation of the PtSn alloy, where the Pt-Pt bond length (R) is 2.75, the coordination number (N) is 3.9, the Pt-Sn bond length (R) is 2.66, and the coordination number (N) is 1.4, N Pt-Pt / N Pt-Sn = 3. This does not conform to the standard intermetallic compound data, so it is a disordered alloy structure. Such as in the intermetallic compound Pt 3 Sn, both the Pt-Pt and Pt-Sn bond lengths (R) are 2.82, N Pt-Pt / N Pt-Sn = 2.

[0126] Figure 4 The XPS data of Example 4 are given. Among them, the proportion of zero-valent Sn alloyed with Pt is 13%.

[0127] Figure 5 The initial activity diagrams of Examples 1, 2, and 4 are given. It can be seen that their initial activities show a linear growth trend with the increase of Pt loading, indicating the consistency of the active structures of Examples 1, 2, and 4, all of which are PtSn disordered sub-nanoalloys, proving the universality of the synthesis method within the PtSn loading range.

Claims

1. Application of a PtSn alloy catalyst in the dehydrogenation of propane to propylene, characterized in that: The catalyst is supported on γ-alumina nanosphere carriers with a particle size of 5-20 nm. After loading soluble compounds of Sn and Pt on the carriers, it is calcined in air at 300-500 °C for 2-10 h, and finally reduced in a mixed gas of H 2 and He with a hydrogen volume percentage of 5% - 50% at 550-650 °C for 1-10 h; in the catalyst, Pt and Sn, wherein the mass percentage of Pt is 0.01 - 0.1%, and the mass percentage of Sn is 0.08 - 2%; the ratio range of Pt to Sn is 1:8 - 1:18 by mass; in the catalyst, Pt and part of Sn exist in the form of PtSn sub-nano alloy with a particle size of 0.5 - 1.5 nm, and the Sn forming the alloy is 10 - 20% of the total mass of Sn, and they are uniformly dispersed on the surface of the carrier; the remaining Sn is dispersed on the surface of the carrier in the form of single atoms.

2. The application according to claim 1, characterized in that: the ratio range of Pt to Sn is 1:10 - 1:12 by mass.

3. The application according to claim 1, characterized in that: the preparation process of the catalyst is: impregnating a metal precursor solution containing Pt and Sn onto the carrier nano-alumina, and then drying, calcining, and in-situ reducing; after loading soluble compounds of Sn and Pt on the carrier by the impregnation method and then drying, a calcination operation is carried out, and the drying conditions are drying in an oven at 60 - 120 °C for 5 - 30 h; The Pt precursor solution is an ethanol solution of H 2 PtCl 6 ·6H 2 O, and the Sn precursor is an ethanol solution of SnCl 2 ·2H 2 O; the impregnation method is equal-volume impregnation or excess impregnation, and the impregnation sequence is co-impregnation or stepwise impregnation.

4. The application according to any one of claims 1 - 3, characterized in that: The reaction conditions are 580 - 620 °C, and the volume ratio of the raw material gases is: 5 - 14% C 3 H 8 , 5 - 14% H 2 ; the balance is He, and the WHSV is 1 - 10 h -1 .

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