A rare earth-based propane dehydrogenation catalyst and its preparation method

Abstract

The present invention belongs to the field of catalyst technology and specifically discloses a rare earth-based propane dehydrogenation catalyst and its preparation method. The synthesis process of the present invention primarily involves dispersing rare earth metals into nanosols and loading them onto a carrier via a hydrothermal synthesis method. The acidic sites are then adjusted using alkaline metals, resulting in a rare earth-based catalyst with controllable acidity. When used in propane dehydrogenation reactions, this rare earth-based catalyst does not sinter or migrate in complex atmospheres, such as those encountered during reaction and regeneration. The catalyst exhibits high stability, excellent weather resistance, and a long lifespan. The catalyst does not use expensive or toxic elements (such as Pt, Cr, and V), making it inexpensive and environmentally friendly.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysts, and particularly relates to a rare earth-based propane dehydrogenation catalyst and a preparation method thereof. Background Art

[0002] Affected by multiple factors such as the electrification of automotive energy, the dual-carbon economy, and shale gas development, the traditional petrochemical landscape is undergoing major changes. As a platform molecule in the carbon three industry chain, the source of propylene is shifting from the traditional oil-head route to the gas-head route, and the technology of producing propylene by dehydrogenating propane has been widely favored by the industry. At present, propane dehydrogenation technology has been successfully industrialized, and commercial catalysts mainly include two types: Pt-based catalysts and Cr-based catalysts. Among them, Pt-based catalysts are relatively expensive because they use precious metal Pt as an active component, and are easily sintered and deactivated during operation; the main active component of Cr-based catalysts is Cr2O3, but the catalyst has a certain amount of Cr during operation. 6+ Therefore, the development of cheap, efficient, stable and environmentally friendly new catalysts remains an urgent problem to be solved in this technical field.

[0003] Currently, researchers are mainly turning to transition metal-based catalysts. The invention patent with publication number CN113967472A discloses a Mn-based catalyst for propane dehydrogenation. 3+ The catalyst has higher dehydrogenation activity, better propylene selectivity, and significantly improved propylene yield, but the catalyst is prone to sintering and agglomeration during the reaction, resulting in reduced catalyst performance. Patent application number CN202411442073.6 discloses a nickel-vanadium oxide catalyst, which primarily addresses the problem of active component loss caused by high reaction temperatures (T>500°C) in transition metal-based catalysts during propane dehydrogenation. The catalyst has high selectivity for propane oxidative dehydrogenation to propylene at low temperatures, but the catalyst conversion rate is low, resulting in a large amount of raw material waste.

[0004] In general, the currently developed propane dehydrogenation catalysts are mainly divided into two categories: (1) metal-based catalysts. These catalysts are in the form of metal nanoparticles during the reaction. Due to the relatively low melting point of metals, they are prone to sintering, agglomeration, and volatilization during use. Their long-term operation in industry is still restricted, resulting in complex reaction and regeneration processes; (2) metal oxide catalysts. These catalysts are in the form of metal oxides during the reaction, generally variable valence metal oxides. However, these metal oxides also have serious loss problems under high temperature conditions in complex environments such as reduction, regeneration oxidation, and water vapor, such as Cr, V, etc., loss in oxidizing atmospheres, Mo, W, Ga, In, etc., loss in water vapor atmospheres, and loss of Sn, Zn, Cu, Co, etc. in reducing atmospheres. The loss problem seriously restricts the stable operation of oxide catalysts in industry and also affects the safety of the reaction equipment and the environment.

[0005] Therefore, developing a propane dehydrogenation catalyst with good stability and low cost is a technical problem that the present invention needs to solve. Summary of the Invention

[0006] In order to solve the above technical problems, the purpose of the present invention is to provide a rare earth-based propane dehydrogenation catalyst and a preparation method thereof. Rare earth metals are dispersed into nanosols and loaded on a carrier through a hydrothermal synthesis method, and the acidic sites are further adjusted by alkaline metals, thereby obtaining a rare earth-based catalyst with controllable acidity. When used in the propane dehydrogenation reaction, the rare earth-based catalyst will not undergo changes such as sintering and migration in complex atmospheres such as reaction and regeneration. The catalyst has high stability, good weather resistance and long service life.

[0007] The purpose of the present invention can be achieved through the following technical solutions:

[0008] In a first aspect, the present invention provides a rare earth-based propane dehydrogenation catalyst, wherein the chemical composition of the catalyst is M2O-ReOx / L, wherein M is an alkali metal element, Re is a rare earth element, and L is a carrier.

[0009] The present invention catalyzes the propane dehydrogenation reaction by loading rare earth on a carrier. The acidic site in the propane dehydrogenation catalyst reaction is the dehydrogenation active center, but the acidic site is also the active center for propane cracking, polymerization and other reactions. Light rare earth materials are abundant in my country and are relatively cheap. At the same time, rare earth oxides easily form defective fluorite structures, have certain Lewis acidity, and have potential dehydrogenation activity. However, rare earth atoms have a large radius, a high coordination number, and relatively complex acidity, which is not conducive to obtaining a more moderate acidic site suitable for dehydrogenation activity. The present invention pre-synthesizes and loads nanoparticles of rare earth and composite rare earth oxides to form controllable acidic sites, and further uses alkali metals to regulate the acidic sites, thereby obtaining an efficient propane dehydrogenation catalyst.

[0010] Preferably, M is at least one of Li, Na, and K.

[0011] Preferably, the Re is at least one of La, Ce, Pr, Nd, and Eu.

[0012] Preferably, L is at least one of Al2O3, SiO2, and kaolin. The carrier should be selected to ensure good dispersion of the metal elements while providing ample dispersion space to prevent loss of the metal elements, thereby ensuring the selectivity and economic efficiency of the catalyst. Furthermore, the carrier should be stable at high temperatures. The selected carriers meet these requirements.

[0013] A second aspect of the present invention provides a method for preparing a rare earth-based propane dehydrogenation catalyst, the preparation method comprising the following steps:

[0014] (1) dissolving a rare earth precursor salt, a surfactant, and a homogeneous precipitant in a first solvent, mixing them uniformly, and synthesizing a rare earth oxide monodisperse nanosol through a hydrothermal reaction;

[0015] (2) dissolving the carrier in a second solvent and dispersing the carrier uniformly, then adding the rare earth oxide monodisperse nanosol to the carrier and stirring, followed by filtering and washing to obtain loaded ReOx / L;

[0016] (3) Dissolving an alkali metal salt in deionized water to obtain an alkali metal salt solution, impregnating ReOx / L in the alkali metal salt solution, and drying and calcining the mixture to obtain a rare earth propane dehydrogenation catalyst.

[0017] Preferably, the rare earth precursor salt is at least one of nitrates or acetates of La, Ce, Pr, Nd, and Eu, and the loading amount of ReOx in the rare earth-based propane dehydrogenation catalyst is 1-40%.

[0018] Rare earth oxides such as La, Ce, and Pr easily form defective fluorite structures, have certain Lewis acidity, have potential dehydrogenation activity, are abundant in my country, are relatively cheap, and pose no environmental hazards.

[0019] Preferably, the alkali metal salt is at least one of the nitrates or acetates of Li, Na, and K, and the mass fraction of MO in the rare earth-based propane dehydrogenation catalyst is 0.1-2%. The dehydrogenation active centers of propane dehydrogenation catalysts are acidic sites, which are also active centers for reactions such as propane cracking and polymerization. Alkali metal salts can precisely control the strength, number, and distribution of acidic sites through ion exchange, electronic effects, and structural modification, thereby improving catalyst performance. However, excessive neutralization can lead to catalyst deactivation.

[0020] Preferably, the surfactant is at least one of polyvinyl pyrrolidone, polyvinyl alcohol, and citric acid. On the one hand, the surfactant adsorbs on the surface of newly formed nanoparticles, slowing the growth of rare earth nanoparticles through steric hindrance or electrostatic repulsion, thereby preventing the dissolution of small particles and the growth of large particles, which can lead to excessively large rare earth particles. On the other hand, the surfactant tends to adsorb on specific crystal faces, changing the surface energy of each crystal face, thereby guiding anisotropic growth and obtaining specific crystal faces that are conducive to the reaction.

[0021] Preferably, the homogeneous precipitant is at least one of urea, hexamethylenetetramine, and dimethyl oxalate. The homogeneous precipitant slowly and evenly releases precipitating ions in the solution, thereby achieving uniform formation of rare earth nanoparticles, thereby avoiding rapid nucleation and particle agglomeration caused by local oversaturation.

[0022] Preferably, the molar ratio of the rare earth precursor salt, surfactant, and homogeneous precipitant in step (1) is 1: (0.1-1.5): (1-10). Excessive surfactant is difficult to completely remove, and the residual carbon after calcination blocks the catalyst pores, reducing the specific surface area and mass transfer efficiency; too little surfactant cannot effectively template the mesoporous structure, resulting in particle agglomeration or disordered pores, and at the same time causing uneven dispersion of the metal precursor particles, forming large-sized agglomerates after calcination. Excessive homogeneous precipitant will introduce impurities and cause particle coarsening, while also causing pH imbalance, forming soluble hydroxyl complexes, and thus reducing the yield; too little homogeneous precipitant will result in incomplete precipitation, uncontrolled precipitation rate, and the formation of amorphous or large rare earth particles.

[0023] Preferably, the first solvent in step (1) is at least one of deionized water and ethanol.

[0024] Preferably, the second solvent in step (2) is at least one of deionized water, ethanol, acetone, and isopropanol.

[0025] Preferably, the temperature of the hydrothermal reaction in step (1) is 40-120°C, and the time of the hydrothermal reaction is 2-80 hours; the stirring time in step (2) is 1-8 hours; the drying temperature in step (3) is 6-120°C, and the drying time is 6-10 hours; the roasting temperature is 500-700°C, and the roasting time is 2-6 hours.

[0026] Preferably, the rare earth-based propane dehydrogenation catalyst is used in a propane dehydrogenation reaction at a temperature of 550-620°C and a reaction space velocity of 0.5-5h -1 .

[0027] The rare earth-based propane dehydrogenation catalyst provided by the present invention combines the structural characteristics of rare earth oxides, namely, the easy formation of defective fluorite structures and a certain Lewis acidity. However, the rare earth atoms have a large radius, a high coordination number, and relatively complex acidity, which is not conducive to obtaining a relatively moderate acid site suitable for dehydrogenation activity. By pre-synthesizing and loading nanoparticles of rare earth and composite rare earth oxides to form controllable acid sites, and further using alkali metals to regulate the acid sites, a high-efficiency propane dehydrogenation catalyst is obtained, which can be used in fixed bed, fluidized bed, and circulating fluidized bed reaction devices.

[0028] The beneficial effects of this application are as follows:

[0029] The catalyst of the present invention does not use expensive or toxic elements (such as Pt, Cr, V, etc.), is inexpensive and environmentally friendly, and the active components of the catalyst are rare earth oxides. It will not undergo sintering, migration, or other changes in complex atmospheres such as reaction and regeneration. The catalyst has high stability, good weather resistance, and long service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the TEM image of catalyst A1 in Example 1.

[0031] Figure 2 This is the TEM image of catalyst B1 in Comparative Example 1.

[0032] Figure 3 This is the TEM image of catalyst B4 in Comparative Example 4. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0034] Example 1: Preparation of Rare Earth Propane Dehydrogenation Catalyst A1

[0035] (1) 0.8 g La(NO3)3·6H2O, 0.0376 g citric acid, and 0.11 g urea were weighed and dissolved in 12 g deionized water. After thorough mixing, the mixture was hydrothermaled at 90 °C for 24 h to obtain a La2O3 monodisperse nanosol.

[0036] (2) 2 g of Al2O3 was dissolved in 10 g of deionized water, and after ultrasonic dispersion, the hydrothermally synthesized La2O3 monodisperse nanosol was added thereto and stirred for 6 h, followed by filtration and washing to obtain La2O3 / Al2O3;

[0037] (3) 0.02 g of KNO3 was dissolved in 2 g of deionized water to obtain a KNO3 solution. La2O3 / Al2O3 was then impregnated in the KNO3 solution. The impregnated sample was dried at 80 °C for 8 h and then calcined at 600 °C for 4 h to obtain the K2O-La2O3 / Al2O3 catalyst, which was designated as A1.

[0038] Transmission electron micrograph of catalyst A1 Figure 1 As shown in the figure, it can be seen that the catalyst obtained by hydrothermal synthesis of rare earth nanoparticle precursors has uniform particle size and a small average particle size, which ensures that the catalyst has good catalytic performance.

[0039] Example 2: Preparation of Rare Earth Propane Dehydrogenation Catalyst A2

[0040] (1) 0.8 g La(NO3)3·6H2O, 0.0376 g citric acid, and 0.11 g urea were weighed and dissolved in 12 g deionized water. After thorough mixing, the mixture was hydrothermaled at 90 °C for 24 h to obtain a La2O3 monodisperse nanosol.

[0041] (2) 2 g of Al2O3 was dissolved in 10 g of deionized water, and after ultrasonic dispersion, the hydrothermally synthesized La2O3 monodisperse nanosol was added thereto and stirred for 6 h, followed by filtration and washing to obtain La2O3 / Al2O3;

[0042] (3) 0.015 g of LiNO3 was dissolved in 2 g of deionized water to obtain a LiNO3 solution. La2O3 / Al2O3 was then impregnated in the LiNO3 solution. The impregnated sample was dried at 80 °C for 8 h and then calcined at 600 °C for 4 h to obtain the Li2O-La2O3 / Al2O3 catalyst, which was designated as A2.

[0043] Example 3: Preparation of Rare Earth Propane Dehydrogenation Catalyst A3

[0044] (1) 0.8 g La(NO3)3·6H2O, 0.0376 g citric acid, and 0.11 g urea were weighed and dissolved in 12 g deionized water. After thorough mixing, the mixture was hydrothermaled at 90 °C for 24 h to obtain a La2O3 monodisperse nanosol.

[0045] (2) 2 g of Al2O3 was dissolved in 10 g of deionized water, and after ultrasonic dispersion, the hydrothermally synthesized La2O3 monodisperse nanosol was added thereto and stirred for 6 h, followed by filtration and washing to obtain La2O3 / Al2O3;

[0046] (3) 0.075 g of NaNO3 was dissolved in 2 g of deionized water to obtain a NaNO3 solution. La2O3 / Al2O3 was then impregnated in the NaNO3 solution. The impregnated sample was dried at 80°C for 8 h and then calcined at 600°C for 4 h to obtain a Na2O-La2O3 / Al2O3 catalyst, which was designated as A3.

[0047] Example 4: Preparation of Rare Earth Propane Dehydrogenation Catalyst A4

[0048] (1) 0.4 g La(NO3)3·6H2O, 0.177 g citric acid, and 0.55 g urea were weighed and dissolved in 6 g deionized water. After thorough mixing, the mixture was hydrothermaled at 75 °C for 35 h to obtain a La2O3 monodisperse nanosol.

[0049] (2) 2 g of SiO2 powder was dissolved in 18 g of deionized water. After ultrasonic dispersion, the hydrothermally synthesized La2O3 monodisperse nanosol was added thereto and stirred for 6 h. The mixture was then filtered and washed to obtain La2O3 / SiO2.

[0050] (3) 0.02 g of KNO3 was dissolved in 2 g of deionized water to obtain a KNO3 solution. La2O3 / SiO2 was then impregnated in the KNO3 solution. The impregnated sample was dried at 80°C for 8 h and then calcined at 600°C for 4 h to obtain a K2O-La2O3 / SiO2 catalyst, which was designated as A4.

[0051] Example 5: Preparation of Rare Earth Propane Dehydrogenation Catalyst A5

[0052] (1) 0.88 g of Ce(NO3)3·6H2O, 0.045 g of citric acid, and 0.12 g of urea were dissolved in 6 g of deionized water, mixed thoroughly, and hydrothermaled at 100 °C for 18 h to obtain a monodisperse Ce2O3 nanosol.

[0053] (2) 2 g of kaolin was dissolved in 10 g of deionized water, and after ultrasonic dispersion, the hydrothermally synthesized Ce2O3 monodisperse nanosol was added thereto and stirred for 6 h. The mixture was then filtered and washed to obtain Ce2O3 / kaolin.

[0054] (3) 0.02 g of KNO3 was dissolved in 2 g of deionized water to obtain a KNO3 solution. The Ce2O3 / kaolin was then impregnated in the KNO3 solution. The impregnated sample was dried at 80°C for 8 h and then calcined at 600°C for 4 h to obtain a K2O-Ce2O3 / kaolin catalyst, which was designated as A5.

[0055] Example 6: Preparation of Rare Earth Propane Dehydrogenation Catalyst A6

[0056] (1) 0.5 g of Pr(NO3)3·6H2O, 0.11 g of citric acid, and 0.14 g of urea were dissolved in 6 g of deionized water, mixed thoroughly, and then hydrothermaled at 90 °C for 24 h to obtain a monodisperse Pr2O3 nanosol.

[0057] (2) 2 g of Al2O3 was dissolved in 10 g of deionized water, and after ultrasonic dispersion, the hydrothermally synthesized Pr2O3 monodisperse nanosol was added thereto and stirred for 6 h, followed by filtration and washing to obtain Pr2O3 / Al2O3;

[0058] (3) 0.02 g of KNO3 was dissolved in 2 g of deionized water to obtain a KNO3 solution. Pr2O3 / Al2O3 was then impregnated in the KNO3 solution. The impregnated sample was dried at 80 °C for 8 h and then calcined at 600 °C for 4 h to obtain a K2O-Pr2O3 / Al2O3 catalyst, which was designated as A6.

[0059] Example 7: Preparation of Rare Earth Propane Dehydrogenation Catalyst A7

[0060] (1) 0.8 g La(NO3)3·6H2O, 1.1 g polyvinylpyrrolidone, and 0.26 g hexamethylenetetramine were weighed and dissolved in 12 g deionized water. After thorough mixing, the mixture was hydrothermaled at 60 °C for 48 h to obtain a La2O3 monodisperse nanosol.

[0061] (2) 2 g of Al2O3 was dissolved in 10 g of deionized water, and after ultrasonic dispersion, the hydrothermally synthesized La2O3 monodisperse nanosol was added thereto and stirred for 6 h, followed by filtration and washing to obtain La2O3 / Al2O3;

[0062] (3) 0.02 g of KNO3 was dissolved in 2 g of deionized water to obtain a KNO3 solution. La2O3 / Al2O3 was then impregnated in the KNO3 solution. The impregnated sample was dried at 80 °C for 8 h and then calcined at 600 °C for 4 h to obtain the K2O-La2O3 / Al2O3 catalyst, which was designated as A7.

[0063] Example 8: Preparation of Rare Earth Propane Dehydrogenation Catalyst A8

[0064] (1) 0.8 g La(NO3)3·6H2O, 4.1 g polyvinyl alcohol, and 1.98 g dimethyl oxalate were dissolved in a mixed solvent of 12 g deionized water and 15 g ethanol. After thorough mixing, the mixture was hydrothermaled at 65 °C for 72 h to obtain a La2O3 monodisperse nanosol.

[0065] (2) 2 g of Al2O3 was dissolved in 10 g of deionized water, and after ultrasonic dispersion, the hydrothermally synthesized La2O3 monodisperse nanosol was added thereto and stirred for 6 h, followed by filtration and washing to obtain La2O3 / Al2O3;

[0066] (3) 0.02 g of KNO3 was dissolved in 2 g of deionized water to obtain a KNO3 solution. La2O3 / Al2O3 was then impregnated in the KNO3 solution. The impregnated sample was dried at 80 °C for 8 h and then calcined at 600 °C for 4 h to obtain the K2O-La2O3 / Al2O3 catalyst, which was designated as A8.

[0067] Comparative Example 1: Preparation of Rare Earth-Based Propane Dehydrogenation Catalyst B1

[0068] 0.8g La(NO₃)₃·6H₂O, 0.0376g citric acid, and 0.11g urea were weighed and dissolved in 12g deionized water, mixed thoroughly, and set aside. 2g Al₂O₃ was dissolved in 10g deionized water, ultrasonically dispersed, and the resulting solution was added and stirred for 6 hours. The mixture was then filtered and washed for later use. 0.02g KNO₃ was dissolved in 2g deionized water and used to impregnate the resulting catalyst. The impregnated sample was dried at 80°C for 8 hours and then calcined at 600°C for 4 hours. The resulting catalyst is designated B1.

[0069] The transmission electron micrograph of catalyst B1 is shown in FIG. Figure 2 As shown, it can be seen that the particle size of the catalyst prepared without the hydrothermal synthesis method is larger, which leads to a decrease in the performance of the catalyst.

[0070] Comparative Example 2: Preparation of Rare Earth Propane Dehydrogenation Catalyst B2

[0071] 0.8g of La(NO₃)₃·6H₂O, 0.0376g of citric acid, and 0.11g of urea were dissolved in 12g of deionized water, thoroughly mixed, and hydrothermally heated at 90°C for 24h to produce a La₂O₃ monodisperse nanosol. 2g of Al₂O₃ was dissolved in 10g of deionized water, ultrasonically dispersed, and the hydrothermally synthesized La₂O₃ monodisperse nanosol was added and stirred for 6h. The mixture was then filtered, washed, and calcined at 600°C for 4h. The resulting catalyst is designated B2.

[0072] Comparative Example 3: Preparation of Rare Earth-Based Propane Dehydrogenation Catalyst B3

[0073] (1) 0.8 g La(NO3)3·6H2O, 0.0376 g citric acid, and 0.11 g urea were weighed and dissolved in 12 g deionized water. After thorough mixing, the mixture was hydrothermaled at 90 °C for 24 h to obtain a La2O3 monodisperse nanosol.

[0074] (2) 2 g of Al2O3 was dissolved in 10 g of deionized water, and after ultrasonic dispersion, the hydrothermally synthesized La2O3 monodisperse nanosol was added thereto and stirred for 6 h, followed by filtration and washing to obtain La2O3 / Al2O3;

[0075] (3) 0.1 g KNO3 was dissolved in 2 g deionized water and then impregnated with La2O3 / Al2O3. The impregnated sample was dried at 80 °C for 8 h and then calcined at 600 °C for 4 h to obtain K2O-La2O3 / Al2O3 catalyst, which was recorded as B3.

[0076] Comparative Example 4: Preparation of Rare Earth-Based Propane Dehydrogenation Catalyst B4

[0077] (1) Weigh 0.8 g of La(NO3)3·6H2O and 0.11 g of urea and dissolve them in 12 g of deionized water. After thorough mixing, heat the mixture at 90 °C for 24 h to obtain a La2O3 monodisperse nanosol.

[0078] (2) 2 g of Al2O3 was dissolved in 10 g of deionized water, and after ultrasonic dispersion, the hydrothermally synthesized La2O3 monodisperse nanosol was added thereto and stirred for 6 h, followed by filtration and washing to obtain La2O3 / Al2O3;

[0079] (3) 0.02 g of KNO3 was dissolved in 2 g of deionized water and then impregnated with La2O3 / Al2O3. The impregnated sample was dried at 80 °C for 8 h and then calcined at 600 °C for 4 h to obtain the K2O-La2O3 / Al2O3 catalyst, which was designated as B4.

[0080] The transmission electron micrograph of catalyst B4 is shown in FIG. Figure 3 As shown, it can be seen that the particle size of the catalyst prepared by the traditional impregnation method is larger, which leads to a decrease in the performance of the catalyst.

[0081] Comparative Example 5: Preparation of Rare Earth-Based Propane Dehydrogenation Catalyst B5

[0082] (1) 0.8 g La(NO3)3·6H2O, 1.1 g citric acid, and 0.11 g urea were weighed and dissolved in 12 g deionized water. After thorough mixing, the mixture was hydrothermaled at 90 °C for 24 h to obtain a La2O3 monodisperse nanosol.

[0083] (2) 2 g of Al2O3 was dissolved in 10 g of deionized water, and after ultrasonic dispersion, the hydrothermally synthesized La2O3 monodisperse nanosol was added thereto and stirred for 6 h, followed by filtration and washing to obtain La2O3 / Al2O3;

[0084] (3) 0.02 g of KNO3 was dissolved in 2 g of deionized water and then impregnated with La2O3 / Al2O3. The impregnated sample was dried at 80 °C for 8 h and then calcined at 600 °C for 4 h to obtain the K2O-La2O3 / Al2O3 catalyst, which was designated as B5.

[0085] Comparative Example 6: Preparation of Rare Earth Propane Dehydrogenation Catalyst B6

[0086] (1) 0.8 g La(NO3)3·6H2O, 0.0376 g citric acid, and 1.85 g urea were weighed and dissolved in 12 g deionized water. After thorough mixing, the mixture was hydrothermaled at 90 °C for 24 h to obtain a La2O3 monodisperse nanosol.

[0087] (2) 2 g of Al2O3 was dissolved in 10 g of deionized water, and after ultrasonic dispersion, the hydrothermally synthesized La2O3 monodisperse nanosol was added thereto and stirred for 6 h, followed by filtration and washing to obtain La2O3 / Al2O3;

[0088] (3) 0.02 g of KNO3 was dissolved in 2 g of deionized water and then impregnated with La2O3 / Al2O3. The impregnated sample was dried at 80 °C for 8 h and then calcined at 600 °C for 4 h to obtain the K2O-La2O3 / Al2O3 catalyst, which was designated as B6.

[0089] Comparative Example 7: Preparation of Rare Earth Propane Dehydrogenation Catalyst B7

[0090] 0.8g of La(NO₃)₃·6H₂O was dissolved in 2g of deionized water. The resulting mixed solution was then impregnated with 2g of Al₂O₃. After ultrasonic dispersion for 30 minutes, the mixture was placed in an 80°C oven for 8h and subsequently calcined at 600°C for 4h to produce La₂O₃ / Al₂O₃. 0.02g of KNO₃ was dissolved in 2g of deionized water and then impregnated with the La₂O₃ / Al₂O₃. The impregnated sample was dried at 80°C for 8h and then calcined at 600°C for 4h. The resulting catalyst was designated B7.

[0091] Application testing:

[0092] The rare earth propane dehydrogenation catalysts A1 to A8 prepared in Examples 1 to 8 and the rare earth propane dehydrogenation catalysts B1 to B7 prepared in Comparative Examples 1 to 7 were used for propane dehydrogenation reaction. The rare earth propane dehydrogenation catalysts prepared in Examples 1 to 6 were heated to 100°C at a reaction temperature of 600°C and a propane space velocity of 1 h -1 The reaction was carried out under the following conditions: the rare earth propane dehydrogenation catalyst obtained in Example 7-8 was subjected to a reaction temperature of 550°C and a propane space velocity of 3.3h -1 The reaction was carried out under the following conditions; the rare earth propane dehydrogenation catalyst obtained in Comparative Example 1-7 was subjected to a reaction temperature of 600°C and a propane space velocity of 1h -1 The reaction was carried out under the following conditions. The evaluation results of the propane dehydrogenation reaction were recorded in Table 1 using pure propane as the raw material and nitrogen as the carrier gas.

[0093] The propane dehydrogenation reaction process is to continuously introduce pure propane gas into the tubular fixed bed filled with catalyst. The outlet gas is the product propylene, by-products and unreacted raw material propane. The product is analyzed and calculated by gas chromatography. Since it is a continuous reaction, the various indicators fluctuate. The initial results of the catalytic reaction are selected for parallel comparison.

[0094]

[0095]

[0096]

[0097] Table 1 Propane dehydrogenation reaction evaluation results

[0098]

[0099] It can be seen from the data in Table 1 that the rare earth-based catalyst prepared in the present invention has a high initial propane conversion rate, initial propylene selectivity and yield when used in a propane dehydrogenation reaction.

[0100] Compared with Example 1, Comparative Example 1 did not use the hydrothermal synthesis method to prepare the La2O3 nanoparticle precursor, so the initial propane conversion rate, initial propylene selectivity and yield of the obtained catalyst when used for the propane dehydrogenation reaction were low. This shows that the hydrothermal synthesis method for synthesizing rare earth nanoparticle precursors is a necessary condition for synthesizing rare earth-based catalysts for propane dehydrogenation reactions.

[0101] Comparing Example 1 with Comparative Examples 2-3, it can be seen that the performance of the catalyst obtained when the modified alkali metal is excessive or no alkali metal is added is poor, which means that the prepared rare earth-based catalyst must be acid-modified, but the neutralization should not be excessive during the modification.

[0102] From the comparison between Example 1 and Comparative Examples 4-5, it can be seen that a surfactant must be used in the preparation of rare earth nanoparticle precursors by the hydrothermal synthesis method to prevent the nanoparticles from growing. However, too much surfactant should not be added, otherwise the performance of the catalyst will be reduced.

[0103] From the comparison between Example 1 and Comparative Example 6, it can be seen that when preparing rare earth nanoparticle precursors by the hydrothermal synthesis method, the amount of homogeneous precipitant cannot be too much, as too much will lead to reduced catalyst performance.

[0104] From the comparison between Example 1 and Comparative Example 7, it can be seen that the supported rare earth-based catalyst prepared by the traditional impregnation method has poor catalytic performance when used in propane dehydrogenation reaction.

[0105] The above is a specific description of the preferred implementation of the present invention, but the invention is not limited to the embodiments. Those skilled in the art can make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A method for preparing a rare earth propane dehydrogenation catalyst, characterized in that: The chemical composition of the catalyst is M2O-ReOx / L, wherein L is a carrier; M is at least one of Li, Na, and K; Re is at least one of La, Ce, Pr, Nd, and Eu; L is at least one of Al2O3, SiO2, and kaolin; the loading amount of ReOx in the rare earth-based propane dehydrogenation catalyst is 1-40%; and the mass fraction of M2O in the rare earth-based propane dehydrogenation catalyst is 0.1-2%. The preparation method comprises the following steps: (1) dissolving a rare earth precursor salt, a surfactant, and a homogeneous precipitant in a first solvent, mixing them uniformly, and synthesizing a rare earth oxide monodisperse nanosol through a hydrothermal reaction; (2) dissolving the carrier in a second solvent and dispersing the carrier uniformly, then adding the rare earth oxide monodisperse nanosol to the carrier and stirring, followed by filtering and washing to obtain loaded ReOx / L; (3) dissolving an alkali metal salt in deionized water to obtain an alkali metal salt solution, impregnating ReOx / L in the alkali metal salt solution, and drying and calcining the mixture to obtain a rare earth propane dehydrogenation catalyst; The molar ratio of the rare earth precursor salt, the surfactant, and the homogeneous precipitant in step (1) is 1: (0.1-1.5): (1-10).

2. The method for preparing a rare earth-based propane dehydrogenation catalyst according to claim 1, wherein: The rare earth precursor salt is at least one of nitrates or acetates of La, Ce, Pr, Nd, and Eu.

3. The method for preparing a rare earth-based propane dehydrogenation catalyst according to claim 1, wherein: The alkali metal salt is at least one of nitrates or acetates of Li, Na, and K.

4. The method for preparing a rare earth-based propane dehydrogenation catalyst according to claim 1, wherein: The surfactant is at least one of polyvinyl pyrrolidone, polyvinyl alcohol, and citric acid, and the homogeneous precipitant is at least one of urea, hexamethylenetetramine, and dimethyl oxalate.

5. The method for preparing a rare earth-based propane dehydrogenation catalyst according to claim 1, characterized in that: The temperature of the hydrothermal reaction in step (1) is 40-120° C., and the time of the hydrothermal reaction is 2-80 hours; the stirring time in step (2) is 1-8 hours; the drying temperature in step (3) is 6-120° C., and the drying time is 6-10 hours; the roasting temperature is 500-700° C., and the roasting time is 2-6 hours.

6. Use of a rare earth-based propane dehydrogenation catalyst prepared by the preparation method according to any one of claims 1 to 5 in a propane dehydrogenation reaction, characterized in that: The propane dehydrogenation reaction temperature is 550-620°C and the reaction space velocity is 0.5-5h -1 .

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