A catalyst, its preparation and use

Abstract

The embodiment of the application provides a catalyst and a preparation method and application thereof. The bimetallic molecular sieve catalyst comprises a molecular sieve carrier and a metal active source; the metal active source loaded on the outer surface of the molecular sieve carrier is M1 active source, and the metal active source loaded in the channel of the molecular sieve carrier is M2 active source, wherein the active metal element in the M1 active source is active metal element M1, the active metal element in the M2 active source is active metal element M2, and the active metal element M1 and the active metal element M2 are different metal elements. The bimetallic molecular sieve catalyst of the application constructs a synergistic catalytic path of efficient dehydrogenation on the catalyst surface and efficient cracking in the channel of the catalyst, realizes high conversion rate of raw materials and high selectivity of low-carbon olefins, and provides a key technical guarantee for efficient industrial application of naphtha catalytic cracking.

Description

Technical Field

[0001] This application relates to the field of molecular sieve catalytic materials technology, and in particular to a catalyst, its preparation method and application. Background Technology

[0002] Naphtha, as an important intermediate distillate in petroleum refining, can be significantly enhanced in its resource utilization value by being converted into bulk basic chemical feedstocks such as ethylene, propylene, and butadiene. Compared with traditional steam cracking processes, catalytic cracking of naphtha has attracted widespread attention and focused research in the industry due to its advantages such as lower reaction temperature, lower energy consumption, and adjustable product distribution. The catalyst system, as the core of the catalytic cracking reaction, plays a decisive role in the conversion efficiency, product selectivity, and reaction stability of naphtha.

[0003] In the traditional silica-alumina molecular sieve catalyst catalyzing naphtha cracking, alkane molecules in naphtha first undergo protonation at the Brønsted acid sites of the molecular sieve, generating a highly reactive carbocation intermediate. This intermediate then cracks, producing a lower-carbon alkane and a smaller carbocation, which is subsequently deprotonated to generate a lower-carbon olefin. This type of catalyst relies on a single acidic site for catalysis, resulting in significant drawbacks: firstly, the protonation reaction requires a high activation energy, leading to low naphtha conversion; secondly, it easily induces side reactions such as hydrogen transfer and deep cracking, resulting in poor yield and selectivity of lower-carbon olefins. To address these issues, existing research generally introduces metal ions into the molecular sieve to optimize the catalyst's performance and overcome the limitations of traditional catalytic systems, but the effects remain limited.

[0004] Therefore, there is an urgent need to develop a high-performance catalyst to achieve high conversion rate of naphtha catalytic cracking and high selectivity of low-carbon olefins, so as to provide key technical support for the efficient industrial application of naphtha catalytic cracking. Summary of the Invention

[0005] This application provides a bimetallic molecular sieve catalyst that constructs a synergistic catalytic pathway of efficient dehydrogenation on the catalyst surface and efficient cracking within the catalyst channels, achieving high conversion rate of naphtha catalytic cracking and high selectivity for low-carbon olefins, providing key technical support for the efficient industrial application of naphtha catalytic cracking.

[0006] This application also provides a preparation method for preparing the above-mentioned bimetallic molecular sieve catalyst.

[0007] This application also provides a catalytic method, which uses the above-described catalyst or the catalyst prepared by the above-described preparation method to achieve efficient catalytic conversion of raw materials.

[0008] In a first aspect, embodiments of this application provide a bimetallic molecular sieve catalyst, the catalyst comprising a molecular sieve support and a metal active source;

[0009] The metal active source loaded on the outer surface of the molecular sieve support is the M1 active source.

[0010] The metal active source loaded inside the pores of the molecular sieve support is the M2 active source.

[0011] Wherein, the active metal element in the M1 active source is active metal element M1, and the active metal element in the M2 active source is active metal element M2, wherein active metal element M1 and active metal element M2 are different metal elements.

[0012] In one specific embodiment, the molecular sieve support includes aluminosilicate molecular sieves; the molecular sieve support has at least one of a ten-membered ring cross-channel structure and a twelve-membered ring cross-channel structure.

[0013] In one specific embodiment, the active metal element M1 includes metal elements from Group VIII of the periodic table.

[0014] In one specific embodiment, the active metal element M2 includes at least one metal element selected from Group VIB, Group VIIB, Group VIII, Group IB, and Group IIB of the periodic table.

[0015] In one specific embodiment, the molecular sieve carrier includes at least one of ZSM-5, ZSM-11, or Beta molecular sieve.

[0016] In one specific embodiment, the active metal element M1 includes at least one of Pt, Fe, Ir, Rh, Co, Ni, and Pd.

[0017] In one specific embodiment, the active metal element M2 includes at least one of Cr, Mo, Zn, Ga, Cu, and Ni.

[0018] In one specific embodiment, the loading of the active metal element M1 is 0.1wt% to 1wt% based on the mass of the bimetallic molecular sieve catalyst, preferably 0.2wt% to 0.6wt%.

[0019] In one specific embodiment, the loading of the active metal element M2 is 0.1wt% to 3wt% based on the mass of the bimetallic molecular sieve catalyst, preferably 0.2wt% to 1.5wt%.

[0020] Secondly, embodiments of this application provide a method for preparing the catalyst, comprising the following steps:

[0021] 1) The template agent and the complex of M2 metal salt and complexing agent are subjected to a first mixing treatment to obtain a first mixture;

[0022] 2) The intermediate solution, including the first mixture and the molecular sieve raw material source, is subjected to a crystallization reaction to obtain an intermediate;

[0023] 3) Prepare an M1 metal salt solution by mixing M1 metal salt, organic compound, and acid solution;

[0024] 4) The intermediate is mixed with a solution containing M1 metal salt, and then subjected to aging and drying treatments in sequence to obtain a catalyst precursor;

[0025] 5) Dissolve the coating agent in anhydrous ethanol to obtain a coating agent solution. Mix the catalyst precursor with the coating agent solution and stir to obtain a mixture. Perform a pre-hydrolysis condensation treatment on the mixture to obtain the coated product.

[0026] 6) The coated product is subjected to drying and calcination treatments in sequence to obtain an intermediate product;

[0027] 7) The intermediate product is subjected to ammonium exchange treatment and ammonium roasting treatment in sequence to obtain the catalyst.

[0028] In one specific embodiment, the anion of the M1 metal salt includes at least one of carbonate, sulfate, nitrate, and chloride ions.

[0029] In one specific embodiment, the anion of the complex of the M2 metal salt-complexing agent includes at least one of ethylene glycol diethyl ether diaminetetraacetic acid combined with M2 anion, ethylenediaminetetraacetic acid combined with M2 anion, 1,2-cyclohexanediaminetetraacetic acid combined with M2 anion, hydroxyethyl ethylenediaminetriacetic acid combined with M2 anion, and ethylenediaminedisuccinic acid combined with M2 anion.

[0030] In one specific embodiment, the temperature of the first mixing treatment is 25~80℃, and the treatment time is 0.5~2 hours; preferably, the temperature is 30~60℃, and the treatment time is 0.5~1 hour.

[0031] In one specific embodiment, the temperature of the crystallization reaction is 150~200℃ and the reaction time is 48~90 hours; preferably, the temperature is 150~180℃ and the reaction time is 60~80 hours.

[0032] In one specific embodiment, the aging treatment temperature is 20~80℃ and the aging time is 4~12 hours; preferably, the temperature is 20~40℃ and the aging time is 4~8 hours.

[0033] In one specific embodiment, the ammonium exchange treatment is carried out at a temperature of 50~120℃ for 1~5 hours and at a stirring speed of 200~800 r / min; preferably, the temperature is 70~100℃ for 1~4 hours and the stirring speed is 300~600 r / min.

[0034] In one specific embodiment, the roasting treatment and the ammonium roasting treatment are performed at a temperature of 300~600℃ for 2~8 hours; preferably, the temperature is 400~600℃ for 2~4 hours.

[0035] In one specific embodiment, the mass ratio of the template agent to the complex of the M2 metal salt-complexing agent is (100~300):1.

[0036] In one specific embodiment, the mass ratio of the first mixture to the molecular sieve raw material source is 1:(1~3).

[0037] In one specific embodiment, the molar ratio of the complex of the M2 metal salt and the complexing agent (based on the molar amount of the active metal element M2) to the M1 metal salt (based on the molar amount of the active metal element M1) is (0.5~4):(0.5~8); and / or,

[0038] The volume ratio of the organic compound to the acid solution is (0.2~5):1, preferably (0.5~2):1.

[0039] Thirdly, embodiments of this application also provide a catalytic method using the catalyst described above, or the catalyst prepared by the preparation method described above.

[0040] In one specific embodiment, the feedstock to be catalyzed in the catalytic method includes at least one of naphtha, hydrogenated gasoline, coking gasoline, and atmospheric gas oil.

[0041] The catalytic method is performed at a temperature of 450~650℃ and a mass hourly space velocity of 2000~5000 h⁻¹. -1 Preferably, the temperature is 500~600℃ and the mass hourly space velocity is 2500~4000 h⁻¹. -1 .

[0042] The bimetallic molecular sieve catalyst of this application constructs a synergistic catalytic pathway of efficient dehydrogenation on the catalyst surface and efficient cracking within the catalyst channels, achieving high conversion rate of catalytic cracking feedstock and high selectivity for low-carbon olefins, providing key technical support for the efficient industrial application of naphtha catalytic cracking. Attached Figure Description

[0043] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0044] Figure 1 A catalytic pathway diagram of the bimetallic molecular sieve catalyst provided in this application;

[0045] Figure 2 This is a catalytic pathway diagram for a traditional catalyst;

[0046] Figure 3 The feed conversion rate diagrams for the bimetallic molecular sieve catalyst of Example 1 and the molecular sieve catalysts of Comparative Examples 2 and 3 provided in this application;

[0047] Figure 4 Low-carbon olefin yield and selectivity graphs for the bimetallic molecular sieve catalyst of Example 1 and the molecular sieve catalysts of Comparative Examples 2 and 3 provided in this application;

[0048] Figure 5 Hydrogen and 1-hexene selectivity plots for the bimetallic molecular sieve catalyst of Example 1 and the molecular sieve catalysts of Comparative Examples 2 and 3 provided in this application;

[0049] Figure 6 XRD patterns of the bimetallic molecular sieve catalyst of Example 1 and the molecular sieve catalysts of Comparative Examples 2 and 3 provided in this application;

[0050] Figure 7 XPS plots of the active metal element M2 in the bimetallic molecular sieve catalyst of Example 1 and the molecular sieve catalyst of Comparative Example 2 provided in this application;

[0051] Figure 8 XPS images of the active metal element M1 in the bimetallic molecular sieve catalyst of Example 1 and the molecular sieve catalyst of Comparative Example 2 provided in this application;

[0052] Figure 9 SEM and mapping spectra of the bimetallic molecular sieve catalyst of Example 1 and the molecular sieve catalysts of Comparative Examples 2 and 3 provided in this application.

[0053] The accompanying drawings have illustrated specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to specific embodiments. Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0055] As mentioned earlier, traditional silica-alumina molecular sieve catalysts suffer from limitations in naphtha cracking, resulting in poor feed conversion and product selectivity, making it difficult to achieve targeted cracking of low-carbon olefins. While existing research has attempted to modify molecular sieve catalysts by introducing metal ions, it has yet to overcome the bottleneck of mutual constraint between conversion and selectivity, hindering a synergistic improvement in both.

[0056] Based on this, embodiments of this application provide a bimetallic molecular sieve catalyst, the catalyst comprising a molecular sieve support and a metal active source;

[0057] The metal active source loaded on the outer surface of the molecular sieve support is the M1 active source.

[0058] The metal active source loaded inside the pores of the molecular sieve support is the M2 active source.

[0059] Among them, the active metal element in the M1 active source is active metal element M1, and the active metal element in the M2 active source is active metal element M2. Active metal element M1 and active metal element M2 are different metal elements.

[0060] The bimetallic molecular sieve catalyst of this invention constructs a reaction pathway of dehydrogenation followed by pyrolysis by introducing bimetals at different positions on the molecular sieve. It should be noted that the M1 active source is an active component containing active metal element M1 in the form of metal oxide, metal cluster, or metal monatomic particles, located on the outer surface of the molecular sieve support; the M2 active source is an active component containing active metal element M2 in the form of metal ions or metal clusters, located inside the pores of the molecular sieve support. It should also be noted that the active metal element M2 can be loaded onto the surface of the framework within the pores of the molecular sieve support, or it can be partially embedded within the molecular sieve framework.

[0061] Specifically, taking the catalysis of n-hexane as an example, the catalytic pathway of the bimetallic molecular sieve catalyst of this application is as follows: Figure 1 As shown, the traditional catalytic pathway of metal-free molecular sieve catalysts is as follows: Figure 2 As shown. In the bimetallic molecular sieve catalyst of the present invention, the active metal element M1, which is loaded on the outer surface of the molecular sieve support, acts as a Lewis acid center and can effectively capture the electron cloud of the CH bond of the alkane molecule, causing the CH bond to become polarized and weakened, thereby promoting the removal of hydrogen atoms and achieving efficient catalytic dehydrogenation of alkanes. By loading the active source M1 on the outer surface of the molecular sieve support, the active metal element M1 forms a high-density dehydrogenation active site on the surface of the molecular sieve support, which can significantly reduce the energy barrier for the catalytic dehydrogenation of the feedstock, enabling high straight-chain alkanes to complete dehydrogenation on the outer surface of the catalyst support and convert them into high straight-chain olefin intermediates (1-hexene) or carbocation intermediates (hexyl carbocations), providing highly active precursors for subsequent cracking located in the pores of the molecular sieve support, thereby effectively improving the overall catalytic cracking efficiency and endowing the catalyst with a high feedstock conversion rate.

[0062] After the highly active precursor enters the molecular sieve channels, the Brønsted acid (B acid) within the channels provides H₂. + The process further converts high-linear-chain olefin intermediates into hexyl carbocations. The active metal element M2 in the M2 active source stabilizes the hexyl carbocation through electrostatic interactions, inhibiting its isomerization and lowering the cleavage energy barrier, thereby causing the hexyl carbocation to directionally cleave into two molecules of low-carbon olefins. Furthermore, the active metal element M2 can undergo ion exchange reactions with acidic protons in the molecular sieve framework, replacing some of the Brønsted acid (B) acid sites. Simultaneously, the active metal element M2 forms coordinate bonds with oxygen atoms in the molecular sieve framework, weakening the polarity of the OH bonds and regulating the proton-donating capacity of the B acid, thus controlling the strength and distribution of the B acid within the pores, further guiding the directional cleavage of the carbocation into low-carbon olefins. Under the synergistic effect of the active metal element M2 and the B acid sites, the high-linear-chain olefin intermediates directionally cleave into two molecules of low-carbon olefins, significantly improving the conversion rate and selectivity for olefins of the bimetallic molecular sieve catalyst.

[0063] It should be noted that some high-linear-chain alkanes that do not undergo dehydrogenation on the catalyst surface diffuse directly into the pores of the molecular sieve. Under the combined effect of the electrostatic field and spatial confinement effect inside the pores, the M2 active source inside the pores can catalyze the dehydrogenation of high-linear-chain alkanes into high-linear-chain olefin intermediates, which are further directionally cracked into low-carbon olefins under the synergistic effect of Brønsted acid.

[0064] In one specific implementation, the dehydrogenation effect of active metal element M1 is stronger than that of active metal element M2.

[0065] This invention designs bimetallic molecular sieve catalysts with different spatial loadings, placing active metal elements M1 and M2 on the outer surface and inside the pores of the molecular sieve support, respectively. This constructs a synergistic catalytic pathway that enables efficient dehydrogenation on the catalyst surface and efficient pyrolysis within the catalyst pores. This pathway can achieve the directional pyrolysis of high-chain alkanes into two molecules of low-carbon olefins, achieving a synergistic improvement in feedstock conversion and low-carbon olefin selectivity, significantly increasing the yield of the target product, low-carbon olefins, and providing key technical support for the efficient industrial application of naphtha catalytic cracking.

[0066] In one specific embodiment, the molecular sieve support includes aluminosilicate molecular sieves; the molecular sieve support has at least one of a ten-membered ring cross-channel structure and a twelve-membered ring cross-channel structure.

[0067] Silicate-aluminate molecular sieves possess high specific surface area and a well-ordered microporous structure. When the molecular sieve support for bimetallic molecular sieve catalysts is of this type, it can provide a large number of anchoring sites. Its framework is a Si-O-Al structure, with aluminum ions (Al...) 3+ ) replace silicon ions (Si 4+ When the molecular sieve generates a negative skeletal charge, electrostatic interactions can strongly adsorb metal cations. The spatial confinement effect of the microporous structure can effectively prevent the migration of metal particles, making the distribution of the M1 active source on the outer surface of the molecular sieve support and the M2 active source within the pores of the molecular sieve support more stable and uniform. When the molecular sieve support has a ten-membered ring cross-channel structure or a twelve-membered ring cross-channel structure, its excellent pore connectivity results in a high mass transfer rate, which can further enable precise control of the feed conversion rate and low-carbon olefin selectivity of the molecular sieve catalyst. The specific pore structure can be selected according to actual application requirements. Taking the ten-membered ring cross-channel structure as an example, its pore size matches the size of high straight-chain alkanes, and this structure can significantly improve the feed conversion rate of the catalyst.

[0068] To further improve the conversion rate of the catalyst, in one specific embodiment, the active metal element M1 includes a metal element from Group VIII of the periodic table.

[0069] Specifically, all Group VIII metals are transition metals with unfilled d orbitals in their valence layers. These orbitals can selectively polarize and activate the CH bonds of alkanes through σ-π coordination, significantly lowering the energy barrier for dehydrogenation reactions. Simultaneously, these elements can adsorb and dissociate hydrogen atoms, thereby shifting the dehydrogenation equilibrium towards olefins and preferentially activating CH bonds while inhibiting C / C bond breaking. When the active metal element M1 is a Group VIII metal, it can form highly dispersed and highly active dehydrogenation centers on the molecular sieve support surface, efficiently converting long-chain alkanes into olefin intermediates. This provides highly active precursors for subsequent cracking, significantly optimizing the catalyst's feedstock conversion rate and selectivity for low-carbon olefins.

[0070] In one specific embodiment, the active metal element M2 includes at least one metal element selected from Group VIB, Group VIIB, Group VIII, Group IB, and Group IIB of the periodic table.

[0071] Specifically, when the active metal element M2 is selected from the aforementioned transition metal elements, it can selectively activate CH and CC bonds through coordination, and stabilize the carbocation intermediates in the pores through both electronic and electrostatic effects, effectively suppressing their isomerization and rearrangement side reactions, and ultimately directionally cracking them into low-carbon olefins, thereby significantly optimizing the catalyst's selectivity for low-carbon olefins.

[0072] To further optimize the application performance of the catalyst, in one specific embodiment, the molecular sieve support includes at least one of ZSM-5, ZSM-11, or Beta molecular sieve.

[0073] Specifically, ZSM-5 and ZSM-11 molecular sieve supports feature a ten-membered ring two-dimensional cross-channel structure, combining high feed conversion rate with low-carbon olefin selectivity; while the Beta molecular sieve support's twelve-membered ring three-dimensional cross-channel structure significantly reduces internal diffusion resistance, allowing long-chain alkane and olefin intermediates to more easily enter the pores and contact active sites. It also offers a wide range of tunable acidity, adaptable to the cracking requirements of different feedstocks. The specific molecular sieve support can be selected based on actual application needs.

[0074] In one specific embodiment, the active metal element M1 includes at least one selected from Pt, Fe, Ir, Rh, Co, Ni, and Pd. All of these active metal elements possess outstanding dehydrogenation performance. When the active metal element M1 is of the above type, the dehydrogenation rate of high-linear-chain alkanes on the catalyst surface can be significantly increased, further enhancing the catalyst's feedstock conversion rate.

[0075] To further enhance the selectivity of the catalyst for low-carbon olefins, in one specific embodiment, the active metal element M2 includes at least one of Cr, Mo, Zn, Ga, Cu, and Ni. When the active metal element M2 is selected from the above types, the acidity distribution and acid strength within the pores can be directionally controlled. Through electrostatic interactions and electronic effects, the carbocation intermediates can be stabilized synergistically, and their isomerization and rearrangement side reactions can be suppressed, thereby improving the selectivity of the catalyst for low-carbon olefins.

[0076] In one specific embodiment, the loading of active metal element M1 is 0.1wt% to 1wt% based on the mass of the bimetallic molecular sieve catalyst, preferably 0.2wt% to 0.6wt%.

[0077] By adjusting the loading of active metal element M1 from 0.1wt% to 1wt%, the number and dispersion of dehydrogenation active sites on the catalyst surface can be optimized, thereby improving the dehydrogenation efficiency of high straight-chain alkanes and increasing the catalyst feedstock conversion rate. When the loading of active metal element M1 is 0.2wt% to 0.6wt%, the catalyst feedstock conversion rate can be further improved.

[0078] In one specific embodiment, the loading of active metal element M2 is 0.1wt% to 3wt% based on the mass of the bimetallic molecular sieve catalyst, preferably 0.2wt% to 1.5wt%.

[0079] By adjusting the loading of active metal element M2 from 0.1wt% to 3wt%, the degree of substitution of Brønsted acid sites within the molecular sieve pores by active metal element M2 can be effectively controlled, thereby optimizing the distribution and intensity of Brønsted acid sites within the pores and thus optimizing the catalyst's selectivity for low-carbon olefins. When the loading of active metal element M2 is 0.2wt% to 1.5wt%, the catalyst's selectivity for low-carbon olefins is further improved.

[0080] Secondly, embodiments of this application provide a method for preparing a catalyst, comprising the following steps:

[0081] 1) The template agent and the complex of M2 metal salt and complexing agent are subjected to a first mixing treatment to obtain a first mixture;

[0082] 2) The intermediate solution, including the first mixture and the molecular sieve raw material source, is subjected to a crystallization reaction to obtain an intermediate;

[0083] 3) Prepare an M1 metal salt solution by mixing M1 metal salt, organic compound, and acid solution;

[0084] 4) After mixing the intermediate with the M1 metal salt solution, the mixture is subjected to aging and drying treatments in sequence to obtain the catalyst precursor;

[0085] 5) Dissolve the coating agent in anhydrous ethanol to obtain a coating agent solution. Mix the catalyst precursor with the coating agent solution and stir to obtain a mixture. Perform a pre-hydrolysis and condensation treatment on the mixture to obtain the coated product.

[0086] 6) The coated product is subjected to drying and calcination treatments in sequence to obtain the intermediate product;

[0087] 7) The intermediate product was subjected to ammonium exchange treatment and ammonium roasting treatment in sequence to obtain the catalyst.

[0088] Specifically, in step 1), the template agent and the complex of M2 metal salt-complexing agent are subjected to a first mixing treatment, so that the complex of M2 metal salt-complexing agent is uniformly dispersed in the mixed system. The complex has a stable structure, so that the active metal element M2 in it remains dispersed in the subsequent molecular sieve framework formation process, providing a stable precursor for the active metal element M2 to enter the molecular sieve framework in the subsequent steps.

[0089] It should be noted that the present invention does not specifically limit the type of template agent, and those skilled in the art can select conventional template agents according to actual needs. Exemplarily, it includes, but is not limited to, at least one of quaternary ammonium bases, organic amines, and alkali metal hydroxides. In a preferred embodiment, the template agent includes at least one of tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetraethylammonium hydroxide, ethylamine, ethylenediamine, polydiallyldimethylammonium chloride, and sucrose.

[0090] Specifically, in step 2), the intermediate solution undergoes a crystallization reaction to promote the formation of the molecular sieve framework, yielding the intermediate. During this process, the amorphous silica-alumina gel undergoes directional reconfiguration of chemical bonds. The disordered silica-alumina structural units rearrange and crosslink to form crystal nuclei with long-range ordered characteristics, completing the phase transition from amorphous to crystalline. The crystal nuclei serve as growth centers, where silica-alumina tetrahedral structural units directionally overlap and extend along the crystal planes. Si-O-Si and Si-O-Al bonds continue to grow in an orderly manner, gradually forming a complete molecular sieve framework with fixed channels and a cage-like structure. Meanwhile, in the process of molecular sieve crystallization, the M2 metal salt-complexing agent complex, through the substitution of Si and Al sites in the Si-O-Si and Si-O-Al covalent bonds by the M2 active source, allows some of the active metal element M2 to be in situ embedded and stably bound to the molecular sieve framework, constructing a molecular sieve framework structure loaded with the M2 active source, which is the intermediate.

[0091] It should be noted that the raw material sources for molecular sieves include silicon sources, aluminum sources, alkaline compounds, and deionized water. In the intermediate solution, the silicon and aluminum sources exist in an amorphous aluminosilicate gel state. Specifically, the alkaline compounds and deionized water form an alkaline medium, in which the silicon and aluminum sources undergo hydrolysis to generate hydroxylated active monomers [Si(OH)4]. - With [Al(OH)4] - They undergo dehydration and condensation to form covalent bonds Si-O-Si and Si-O-Al, generating amorphous aluminosilicate gels.

[0092] It should be noted that the crystallization reaction includes purification and a first drying process. The purification process involves filtering the crystallized product and washing the filter residue with deionized water until the pH of the residue reaches 5-8 (preferably, washing to pH 6-7), yielding a purified crystallized product. The purified crystallized product is then subjected to a first drying process to remove the solvent water, yielding an intermediate.

[0093] This invention does not limit the preparation method of the intermediate solution comprising the first mixture and the molecular sieve raw material source. Exemplarily, it can be prepared by the following process: first, a silicon source is added to the first mixture and stirred at 25-80°C for 0.5-2 hours; then, an aluminum source and an alkaline compound are added and stirred at 25-80°C for 5-30 minutes (preferably 10-20 minutes); subsequently, deionized water is added and stirred at 30-100°C for 2-8 hours to obtain the intermediate solution. The intermediate solution can also be prepared by the following steps: mixing the silicon source, aluminum source, alkaline compound, and deionized water to obtain a molecular sieve raw material source mixture; adding the molecular sieve raw material source mixture to the first mixture; and then stirring at 25-80°C for 2-8 hours to obtain the intermediate solution.

[0094] It should be noted that the silicon source includes, but is not limited to, at least one of silicon-based quaternary ammonium bases, organic amines, and alkali metal hydroxides; in a preferred embodiment, the silicon source includes at least one of tetraethyl orthosilicate and methyl orthosilicate. The aluminum source includes, but is not limited to, at least one of sodium aluminate, boehmite, aluminum hydroxide, aluminum nitrate, aluminum sulfate, and aluminum isopropoxide; in a preferred embodiment, the aluminum source includes at least one of sodium aluminate, aluminum isopropoxide, and aluminum hydroxide. Alkali compounds include, but are not limited to, at least one of sodium hydroxide, potassium hydroxide, calcium hydroxide, and organic bases; in a preferred embodiment, the alkali compound includes at least one of sodium hydroxide and calcium hydroxide.

[0095] It should be noted that the molar ratio of silicon source (calculated as the molar amount of Si element), aluminum source (calculated as the molar amount of Al element), alkali compound (calculated as the molar amount of alkali metal cation therein), and H2O in the molecular sieve raw material source is (0.5~2):(0.01~0.05):(0.01~0.05):(10~40).

[0096] Further, in step 3), an M1 metal salt solution is prepared by mixing the M1 metal salt, organic compound, and acid solution. This step yields an impregnation solution of the M1 metal salt, which is used in the impregnation process of step 4) to make the M1 metal salt spread more uniformly on the surface of the intermediate. Specifically, the synergistic effect of the organic compound and acid solution reduces the surface tension of the impregnation solution, significantly improving the wettability and spreading properties of the metal precursor on the outer surface of the molecular sieve, achieving highly dispersed and uniform loading of the M1 metal salt, while preventing the metal from entering the pores.

[0097] It should be noted that this invention does not specifically limit the type of organic compound, which includes, but is not limited to, at least one of ethanol, isopentyl glycol, and alkyl glycosides. This invention also does not specifically limit the type of acid solution, which includes, but is not limited to, at least one of citric acid, oxalic acid, and tartaric acid. The concentration of the acid solution is 0.1~2 mol / L.

[0098] Subsequently, in step 4), the intermediate is mixed with the M1 metal salt solution to obtain an intermediate mixture. The intermediate mixture is then aged to allow the active metal element M1 to fully diffuse on the surface of the molecular sieve support and coordinate with the Si-OH and Al-OH groups on the surface of the molecular sieve support, resulting in an aged mixture. It should be noted that in this step, the template agent blocks the pores of the molecular sieve support, preventing the M1 metal salt from entering the pores during impregnation, thus precisely controlling the loading of the active metal element M1 onto the outer surface of the molecular sieve support rather than within the pores. It should also be noted that the drying process in step 4) is a second drying process.

[0099] In a preferred embodiment, the M1 metal salt solution is added dropwise to the intermediate to obtain an intermediate mixture, with a dropping rate of 0.1~1 mL / min, preferably 0.2~0.5 mL / min. After the addition, the intermediate mixture is further ground to maintain a powdery state.

[0100] Further, in step 5), a coating agent solution is prepared and mixed with the catalyst precursor. The mixture is stirred to allow the coating agent to adsorb onto the catalyst precursor, resulting in a mixture. The mixture is then subjected to a pre-hydrolysis condensation treatment to coat the catalyst precursor with the coating agent, yielding a coated product. This step 5) ensures the stability of the M1 metal salt loaded on the outer surface of the catalyst precursor, preventing migration and aggregation during calcination. Subsequently, step 6) is performed sequentially, followed by drying (the third drying process) and calcination, to form covalent bonds between the active metal element M1 and the outer surface of the molecular sieve, thus anchoring the active metal element M1 and partially removing the template agent from the system, ultimately yielding an intermediate product.

[0101] It should be noted that the coating agent solution is prepared by dissolving the coating agent in anhydrous ethanol. This invention does not limit the specific type of coating agent, but includes, but is not limited to, at least one of methyltriethoxysilane and ethyl triethoxysilyl ester. It should be noted that the mixing temperature in step 5) is 20~60℃, the time is 0.5~2h, and the stirring speed is 200~800r / min; preferably, the mixing temperature is 20~40℃, the time is 0.5~1h, and the stirring speed is 300~600r / min. The mass / volume ratio of the coating agent to anhydrous ethanol is 0.01~1g / mL, preferably 0.01~0.5g / mL.

[0102] It should be noted that the pre-hydrolysis condensation treatment is carried out at a temperature of 80~140℃ for 0.5~2 hours, with a stirring speed of 200~800 r / min; preferably, the temperature is 80~120℃ for 0.5~1 hour, with a stirring speed of 300~600 r / min. The drying temperature is 100~140℃; preferably, the drying temperature is 110~130℃. The calcination treatment is carried out at a temperature of 300~600℃ for 2~8 hours; preferably, the temperature is 400~600℃ for 2~4 hours.

[0103] Further, in step 7), the intermediate product is subjected to ammonium exchange treatment to replace the alkali metal cations on the outer surface of the molecular sieve, preventing the alkali metal cations from inducing the aggregation or even deactivation of the metal active components, thereby improving the dispersibility and stability of the active metal elements loaded on the molecular sieve. Then, ammonium calcination is performed to remove the template agent inside the molecular sieve, preparing the bimetallic molecular sieve catalyst.

[0104] It should be noted that the ammonium exchange treatment steps include: dissolving the intermediate product in an ammonium salt solution and mechanically stirring to obtain a suspension containing a bimetallic molecular sieve catalyst; centrifuging the suspension; and performing a fourth drying treatment on the precipitate. The dissolution, mechanical stirring, centrifugation, and fourth drying treatment are repeated twice.

[0105] It should be noted that the temperature for the first, second, and fourth drying processes is 90~150℃, and the drying time is 8~15 hours.

[0106] The preparation method of the present invention involves loading an active metal element M1 onto the outer surface of a molecular sieve support and loading an active metal element M2 onto the pores of the molecular sieve support, thereby achieving a synthesis method with different loadings of different metal elements on the molecular sieve and preparing a bimetallic molecular sieve catalyst with high raw material conversion rate and high selectivity for low-carbon olefins.

[0107] In one specific embodiment, the anion of the M1 metal salt includes at least one of carbonate, sulfate, nitrate, and chloride ions.

[0108] When the anions of the M1 metal salt include the types mentioned above, the active metal element M1 can be more evenly distributed on the outer surface of the molecular sieve support, and the binding can be more robust, forming more dispersed and stable metal active sites on the outer surface of the molecular sieve support.

[0109] In one specific embodiment, the anion of the M2 metal salt-complexing agent complex includes at least one of the following: ethylene glycol diethyl ether diaminetetraacetic acid (EDTA)-M2 anion, ethylenediaminetetraacetic acid (EDTA)-M2 anion, 1,2-cyclohexanediaminetetraacetic acid (1,2-cyclohexanediaminetetraacetic acid)-M2 anion, hydroxyethyl ethylenediaminetriacetic acid (EDTA)-M2 anion, and ethylenediaminedisuccinic acid (EDTA)-M2 anion. When the anion in the M2 metal salt-complexing agent complex is selected from the above types, the stability of the complex during catalyst preparation can be further improved, the dispersion of the active metal element M2 during the molecular sieve framework formation process can be significantly optimized, and it can be more uniformly loaded into the pores of the molecular sieve support, thereby improving the stability and long-term activity of the catalyst.

[0110] This invention does not limit the specific source of the complex of the M2 metal salt-complexing agent, which can be commercially available. The complex of the M2 metal salt-complexing agent includes, but is not limited to, at least one of the following: nickel disodium ethylenediaminetetraacetate, cobalt disodium ethylenediaminetetraacetate, ferric disodium ethylenediaminetetraacetate, chromium disodium ethylenediaminetetraacetate, zinc disodium ethylenediaminetetraacetate, nickel disodium ethylenediaminetetraacetate, cobalt disodium ethylenediaminetetraacetate, nickel disodium 1,2-cyclohexanediaminetetraacetate, chromium disodium 1,2-cyclohexanediaminetetraacetate, cobalt disodium hydroxyethyl ethylenediaminetriacetate, ferric disodium hydroxyethyl ethylenediaminetriacetate, zinc disodium ethylenediaminedisuccinate, and chromium disodium ethylenediaminedisuccinate.

[0111] In one specific embodiment, the temperature of the first mixing treatment is 25~80℃, and the treatment time is 0.5~2 hours; preferably, the temperature is 30~60℃, and the treatment time is 0.5~1 hour. By adjusting the temperature and time of the first mixing treatment, the dispersibility and structural stability of the M2 metal salt-complexing agent complex in the mixed system can be significantly optimized, providing a stable precursor for the subsequent entry of the active metal element M2 into the molecular sieve channels.

[0112] In one specific embodiment, the crystallization reaction temperature is 150~200℃ and the reaction time is 48~90 hours; preferably, the temperature is 150~180℃ and the reaction time is 60~80 hours. By controlling the temperature and reaction time of the crystallization reaction, the crystallinity and grain size of the molecular sieve support can be significantly optimized, thereby controlling the pore structure and framework regularity of the molecular sieve support.

[0113] In one specific embodiment, the aging temperature is 20~80℃ and the aging time is 4~12 hours; preferably, the temperature is 20~40℃ and the aging time is 4~8 hours. By controlling the temperature and time of the aging treatment, the active metal element M1 can be more evenly dispersed on the outer surface of the molecular sieve support, and its binding strength with the outer surface of the molecular sieve support can be strengthened, thereby improving the stability of the catalyst dehydrogenation active sites.

[0114] In one specific embodiment, the ammonium exchange treatment is carried out at a temperature of 50-120°C for 1-5 hours, with a stirring speed of 200-800 r / min; preferably, the temperature is 70-100°C for 1-4 hours, with a stirring speed of 300-600 r / min. By controlling the temperature, time, and stirring speed of the ammonium exchange reaction, the removal efficiency and depth of alkali metal cations can be precisely controlled, thereby optimizing the crystallinity, structural integrity, and pore regularity of the molecular sieve framework.

[0115] In one specific embodiment, the calcination treatment and the ammonium calcination treatment are carried out at a temperature of 300~600℃ for 2~8 hours; preferably, the temperature is 400~600℃ for 2~4 hours. By controlling the temperature and time of the calcination treatment and the ammonium calcination treatment, the template agent in the molecular sieve can be removed more completely, while the stable dispersion and anchoring of active metal elements M1 and M2 can be achieved.

[0116] In one specific embodiment, the mass ratio of the template agent to the complex of the M2 metal salt-complexing agent is (100~300):1. By adjusting the mass ratio of the template agent to the complex of the M2 metal salt-complexing agent, the loading of the active metal element M2 can be precisely controlled, thereby optimizing the catalytic cracking efficiency within the molecular sieve channels and optimizing the catalyst's conversion rate and selectivity.

[0117] In one specific embodiment, the mass ratio of the first mixture to the molecular sieve raw material source is 1:(1~3). By adjusting the mass ratio of the first mixture to the molecular sieve raw material source to this range, a molecular sieve framework with more regular channels and a more complete and stable structure can be formed, thereby improving the overall stability of the catalyst.

[0118] In one specific embodiment, the molar ratio of the M2 metal salt-complexing agent complex (based on the molar amount of active metal element M2) to the M1 metal salt (based on the molar amount of active metal element M1) is (0.5~4):(0.5~8). By adjusting the molar ratio of the M2 metal salt-complexing agent complex to the M1 metal salt within this range, the loading of active metal element M1 on the outer surface of the molecular sieve and the loading of active metal element M2 within the pores can be precisely controlled, achieving synergistic optimization of the catalyst surface dehydrogenation efficiency and the pore-level cracking efficiency, thereby improving the catalyst's feed conversion rate and selectivity for low-carbon olefins.

[0119] To further optimize the dispersion and uniformity of M1 metal salt loading on the outer surface of the molecular sieve support, in one specific embodiment, the volume ratio of organic compound to acid solution is (0.2~5):1, preferably (0.5~2):1.

[0120] Thirdly, this application also provides a catalytic method using the above-described catalyst or the catalyst prepared by the above-described preparation method. Therefore, using this catalytic method can achieve highly efficient catalytic conversion of raw materials, featuring high raw material conversion rate and excellent selectivity for low-carbon olefins. Simultaneously, the catalyst exhibits good stability and outstanding long-term operating performance, effectively optimizing the overall catalytic efficiency.

[0121] This invention does not limit the specific steps of the catalytic method. Exemplarily, it may include the following catalytic steps: 1) Loading the catalyst into the reactor and performing high-temperature activation treatment under an inert or reducing atmosphere to remove impurities and residual moisture adsorbed on the catalyst surface, fully activating the acidic sites and metal active centers of the molecular sieve, ensuring full exposure of the catalytic active sites. 2) Heating the feedstock to be catalyzed to a specified temperature via a preheater to vaporize the feedstock, and adjusting the feedstock partial pressure and residence time. 3) Continuously feeding the vaporized feedstock into the reactor, and carrying out the catalytic reaction under the set temperature, pressure, and mass hourly space velocity. 4) Rapidly cooling the reaction products at the reactor outlet, causing the heavy components in the reaction products to condense into a liquid phase, while the light components remain in the gas phase. The products are then distilled to collect the target product. 5) Passing the used catalyst into a regenerator, burning off carbon deposits at high temperature under an oxygen-containing atmosphere, restoring the pore flow of the molecular sieve and the activity of the active centers. The regenerated catalyst can be recycled back to the reactor for reuse.

[0122] In one specific embodiment, the feedstock to be catalyzed in the catalytic method includes at least one of naphtha, hydrogenated gasoline, coking gasoline, and atmospheric gas oil;

[0123] The catalytic method is performed at temperatures of 450–650 °C and mass hourly space velocities of 2000–5000 h⁻¹. -1 Preferably, the temperature is 500~600℃ and the mass hourly space velocity is 2500~4000 h⁻¹. -1 .

[0124] When the catalytic feedstock includes the aforementioned petroleum hydrocarbon feedstock, the catalytic method of the present invention can directionally convert the feedstock into low-carbon olefins. The catalytic process exhibits excellent conversion rates and high selectivity for low-carbon olefins. In one possible embodiment, the temperature of the catalytic method is 450~650°C, and the mass hourly space velocity (HHSV) is 2000~5000 h⁻¹. -1 Preferably, the temperature is 500~600℃ and the mass hourly space velocity is 2500~4000 h⁻¹. -1 .

[0125] The bimetallic molecular sieve catalyst provided in this application achieves highly efficient synergy between dehydrogenation and cracking functions through the spatial partitioning arrangement of active metal elements M1 and M2: active metal element M1 efficiently dehydrogenates olefin intermediates on the catalyst surface, while active metal element M2 activates undehydrogenated alkanes within the catalyst channels to generate carbocations and promotes the directional cracking of carbocations into lower-carbon olefins. This bimetallic molecular sieve catalyst overcomes the bottleneck of mutual constraint between conversion rate and selectivity in traditional catalysts, significantly improving the feedstock conversion efficiency and product distribution controllability of the catalytic cracking reaction.

[0126] The bimetallic molecular sieve catalyst of this application will be further described in detail below through specific embodiments.

[0127] Example 1

[0128] The bimetallic molecular sieve catalyst in this embodiment was prepared through the following steps:

[0129] 1) Weigh out 13g of tetrapropylammonium hydroxide and 0.086g of anhydrous disodium nickel ethylenediaminetetraacetate, place them in a 100ml beaker for the first mixing treatment, and stir continuously at 40℃ for 1h to obtain the first mixture;

[0130] 2) Add tetraethyl orthosilicate (8.32 g) to the first mixture prepared in 1) and stir continuously at 40 °C for 1 h; then add aluminum isopropoxide (0.32 g) and sodium hydroxide (0.08 g) and stir at 40 °C for 15 min; add deionized water (15 g) and stir at 60 °C for 4 h to obtain an intermediate solution;

[0131] 3) The intermediate solution was placed in a crystallization kettle for crystallization reaction at 170℃ for 72 hours. After filtration and washing until the pH of the filter residue was 7, it was dried at 120℃ for 2 hours to obtain the intermediate.

[0132] 4) Basic cobalt carbonate (0.029 g) was mixed with anhydrous ethanol (2 ml) and citric acid solution (1 mol / L, 2 mL), and then added dropwise to the intermediate prepared in step 3) at a rate of 0.5 ml / min. After being ground until uniform and free of fine particles, it was aged for 6 hours at 25 °C. After aging, it was dried at 120 °C for 2 hours to obtain the catalyst precursor.

[0133] 5) Dissolve 0.116 g of methyltriethoxysilane in 5 mL of anhydrous ethanol and stir for 10 min to obtain a uniform coating agent solution;

[0134] 6) Mix the catalyst precursor with the coating agent solution and stir at 25°C for 1 hour at a stirring speed of 400 r / min to obtain a mixture. Then slowly heat the mixture to 100°C and continue stirring for 30 minutes to obtain the coated product. Then dry the coated product at 120°C for 4 hours, and then calcine it at 550°C for 4 hours to obtain the intermediate product.

[0135] 7) The intermediate product (3.3 g) was mixed with an ammonium chloride solution (1 mol / L, 33 mL), and subjected to ammonium exchange treatment by mechanical stirring at a speed of 400 r / min, a temperature of 80 °C, and a time of 2 hours. The mixture was then centrifuged, and the precipitate was dried at 120 °C for 2 hours. This process was repeated twice. Finally, ammonium calcination was performed at 550 °C for 3 hours to obtain bimetallic molecular sieve catalyst 1, denoted as Q3.

[0136] Example 2

[0137] This embodiment is basically the same as Example 1, except that in step 1), tetrapropylammonium hydroxide is replaced with hexadecyltrimethylammonium bromide (23.30 g) and anhydrous ethylenediaminetetraacetic acid disodium nickel salt is replaced with anhydrous ethylenediaminetetraacetic acid disodium ferric salt (0.094 g). This embodiment yields bimetallic molecular sieve catalyst 2.

[0138] Example 3

[0139] This embodiment is basically the same as Embodiment 1, except that in step 2), tetraethyl orthosilicate is replaced with silica sol (8g), aluminum isopropoxide is replaced with sodium aluminate (0.13g), and sodium hydroxide is replaced with potassium hydroxide (0.11g). This embodiment yields bimetallic molecular sieve catalyst 3.

[0140] Example 4

[0141] This embodiment is basically the same as Example 1, except that tetrapropylammonium hydroxide in step 1 is replaced with tetrabutylammonium hydroxide (16.6g). This embodiment yields bimetallic molecular sieve catalyst 4.

[0142] Example 5

[0143] This embodiment is basically the same as Example 1, except that tetrapropylammonium hydroxide in step 1 is replaced with tetraethylammonium hydroxide (9.4g). This embodiment yields bimetallic molecular sieve catalyst 5.

[0144] Example 6

[0145] This embodiment is basically the same as Example 1, except that tetrapropylammonium hydroxide in step 1 is replaced with methyltriethylammonium bromide (3.14 g). This embodiment yields bimetallic molecular sieve catalyst 6.

[0146] Example 7

[0147] This embodiment is basically the same as Embodiment 1, except that in step 4), basic cobalt carbonate is replaced with ferric nitrate (0.10 g). This embodiment yields bimetallic molecular sieve catalyst 7.

[0148] Example 8

[0149] This embodiment is basically the same as Example 1, except that the ammonium chloride solution in step 5) is replaced with ammonium acetate (1 mol / L, 33 mL). This embodiment yields bimetallic molecular sieve catalyst 8.

[0150] Example 9

[0151] This embodiment is basically the same as Embodiment 1, except that the temperature of the first mixing treatment in step 1) is adjusted to 60°C and the time is adjusted to 0.5 h. This embodiment yields bimetallic molecular sieve catalyst 9.

[0152] Example 10

[0153] This embodiment is basically the same as Embodiment 1, except that step 2) is adjusted as follows: add tetraethyl orthosilicate (8.32g) to the first mixture prepared in step 1) and stir continuously at 60°C for 0.5h; then add aluminum isopropoxide (0.32g) and sodium hydroxide (0.08g) and stir at 60°C for 20min; add deionized water (15g) and stir at 80°C for 6h to obtain an intermediate solution.

[0154] This embodiment yields a bimetallic molecular sieve catalyst 10.

[0155] Example 11

[0156] The bimetallic molecular sieve catalyst in this embodiment was prepared through the following steps:

[0157] 1) Weigh out 13g of tetrapropylammonium hydroxide and 0.082g of disodium cobalt ethylenediaminetetraacetate, place them in a 100ml beaker for the first mixing treatment, and stir continuously at 50℃ for 1h to obtain the first mixture;

[0158] 2) Add tetraethyl orthosilicate (8.32 g) to the first mixture prepared in step 1) and stir continuously at 50 °C for 1 h; then add aluminum isopropoxide (0.32 g) and sodium hydroxide (0.08 g) and stir at 50 °C for 15 min; add deionized water (15 g) and stir at 60 °C for 4 h to obtain an intermediate solution;

[0159] 3) The intermediate solution was placed in a crystallization kettle for crystallization reaction at 180℃ for 72 hours. After filtration and washing until the pH of the filter residue was 7, it was dried at 120℃ for 2 hours to obtain the intermediate.

[0160] 4) Basic nickel carbonate (0.087 g) was mixed with anhydrous ethanol (2 ml) and citric acid solution (1 mol / L, 2 mL), and then added dropwise to the intermediate obtained in 3) at a rate of 0.5 ml / min. After being ground until uniform and free of fine particles, it was aged for 6 hours at 25 °C. After aging, it was dried at 120 °C for 2 hours to obtain the catalyst precursor.

[0161] 5) Dissolve 0.116 g of methyltriethoxysilane in 5 mL of anhydrous ethanol and stir for 10 min to obtain a uniform coating agent solution;

[0162] 6) Mix the catalyst precursor with the coating agent solution and stir at 25°C for 1 hour at a stirring speed of 400 r / min to obtain a mixture. Then, slowly heat the mixture to 100°C and continue stirring for 30 minutes to obtain the coated product. The coated product is then dried at 120°C for 4 hours and subsequently calcined at 550°C for 4 hours to obtain the intermediate product.

[0163] 7) The intermediate product (3.3 g) was mixed with ammonium chloride solution (1 mol / L, 33 mL), and ammonium exchange treatment was carried out by mechanical stirring at a stirring speed of 400 r / min, a temperature of 80 °C, and a time of 2 hours. The mixture was then centrifuged, and the precipitate was dried at 120 °C for 2 hours. This process was repeated twice. Finally, ammonium calcination was performed at a temperature of 550 °C for 3 hours to obtain bimetallic molecular sieve catalyst 11.

[0164] Example 12

[0165] The bimetallic molecular sieve catalyst in this embodiment was prepared through the following steps:

[0166] 1) Weigh 13g of tetrapropylammonium hydroxide and 0.08g of sodium chromium ethylenediaminetetraacetate (where the active metal element M2 is chromium), place them in a 100ml beaker for the first mixing treatment, and stir continuously at 30℃ for 1h to obtain the first mixture;

[0167] 2) Add tetraethyl orthosilicate (8.32 g) to the first mixture prepared in step 1) and stir continuously at 30°C for 1 h; then add aluminum isopropoxide (0.32 g) and sodium hydroxide (0.08 g) and stir at 30°C for 15 min; add deionized water (15 g) and stir at 70°C for 4 h to obtain an intermediate solution;

[0168] 3) The intermediate solution was placed in a crystallization kettle for crystallization reaction at 160℃ for 72 hours. After filtration and washing until the pH reached 7, it was dried at 120℃ for 2 hours to obtain the intermediate.

[0169] 4) After mixing ferric nitrate (0.32 g) with anhydrous ethanol (2 ml) and citric acid solution (1 mol / L, 2 mL), the mixture was added dropwise to the intermediate prepared in step 3) at a rate of 0.5 ml / min. After grinding until uniform and free of fine particles, the mixture was aged for 6 hours at 25 °C. After aging, the mixture was dried at 120 °C to obtain the catalyst precursor.

[0170] 5) Dissolve 0.116 g of methyltriethoxysilane in 5 mL of anhydrous ethanol and stir for 10 min to obtain a uniform coating agent solution;

[0171] 6) Mix the catalyst precursor with the coating agent solution and stir at 25°C for 1 hour at a stirring speed of 400 r / min to obtain a mixture. Then slowly heat the mixture to 100°C and continue stirring for 30 minutes to obtain the coated product. The coated product is then dried at 120°C for 4 hours and subsequently calcined at 550°C for 4 hours.

[0172] 7) The intermediate product (3.3 g) was mixed with an ammonium chloride solution (1 mol / L, 33 mL), and subjected to ammonium exchange treatment by mechanical stirring at a speed of 400 r / min, a temperature of 80 °C, and a time of 2 hours. The mixture was then centrifuged, and the precipitate was dried at 120 °C for 2 hours. This process was repeated twice. Finally, ammonium calcination was performed at a temperature of 550 °C for 3 hours to obtain bimetallic molecular sieve catalyst 12.

[0173] Example 13

[0174] This embodiment is basically the same as Example 1, except that in step 4), basic cobalt carbonate is replaced with palladium nitrate (0.45g), and the amounts of anhydrous ethanol and citric acid solution are adjusted so that the total volume of the mixture of anhydrous ethanol and citric acid solution is 9.5mL (the volume ratio of anhydrous ethanol to citric acid solution is 0.8:1). Simultaneously, the aging time is adjusted to 8 hours; the drying temperature is 60℃, and the drying time is 10 hours. Bimetallic molecular sieve catalyst 13 is obtained.

[0175] Example 14

[0176] This embodiment is basically the same as Embodiment 13, except that in step 4), palladium nitrate is replaced with platinum tetrachloride (0.32g), and the amount of anhydrous ethanol and citric acid solution added is adjusted so that the total volume of the mixture of anhydrous ethanol and citric acid solution is 8.5mL (the volume ratio of anhydrous ethanol to citric acid solution is 1.8:1). Bimetallic molecular sieve catalyst 14 is obtained.

[0177] Example 15

[0178] This embodiment is basically the same as Embodiment 13, except that in step 4), palladium nitrate is replaced with cobalt nitrate hexahydrate (0.4g), and anhydrous ethanol is replaced with isopentyl glycol. The total volume of the mixture of isopentyl glycol and citric acid solution is 10mL (the volume ratio of isopentyl glycol to citric acid solution is 1.2:1). Bimetallic molecular sieve catalyst 15 is obtained.

[0179] Example 16

[0180] This embodiment is basically the same as Embodiment 13, except that in step 4), palladium nitrate is replaced with silver nitrate (0.4g), and anhydrous ethanol is replaced with alkyl glycoside. The total volume of the mixture of alkyl glycoside solution and citric acid solution is 9mL (the volume ratio of alkyl glycoside solution to citric acid solution is 0.6:1, and the mass fraction of alkyl glycoside solution is 50%, including 1.2mL of alkyl glycoside). Bimetallic molecular sieve catalyst 16 is obtained.

[0181] Comparative Example 1

[0182] The molecular sieve catalyst of this comparative example was prepared by the following steps:

[0183] 1) Add tetrapropylammonium hydroxide (13g) to tetrapropylammonium hydroxide (8.32g) and stir continuously at 40℃ for 1h; then add aluminum isopropoxide (0.32g) and sodium hydroxide (0.08g) and stir at 40℃ for 15min; add deionized water (15g) and stir at 60℃ for 4h to obtain an intermediate solution;

[0184] 2) The intermediate solution was placed in a crystallization vessel for crystallization reaction at 170℃ for 72 hours. After filtration and washing until the pH reached 7, it was dried at 120℃ for 2 hours to obtain the intermediate. Subsequently, the intermediate was calcined to obtain the molecular sieve framework.

[0185] 3) Basic cobalt carbonate (0.146 g), basic nickel carbonate (0.106 g), anhydrous ethanol (2 ml), and citric acid solution (1 mol / L, 2 mL) were mixed and added dropwise to the molecular sieve framework prepared in step 3) at a dropping rate of 0.5 mL / min. After being ground until uniform and free of fine particles, the mixture was aged for 6 hours at 25 °C. After aging, it was dried at 120 °C for 2 hours to obtain the catalyst precursor.

[0186] 4) Dissolve 0.116 g of methyltriethoxysilane in 5 mL of anhydrous ethanol and stir for 10 min to obtain a uniform coating agent solution;

[0187] 5) Mix the catalyst precursor with the coating agent solution and stir at 25°C for 1 hour at a stirring speed of 400 r / min to obtain a mixture. Then, slowly heat the mixture to 100°C and continue stirring for 30 minutes to obtain the coated product. The coated product is then dried at 120°C for 4 hours and subsequently calcined at 550°C for 4 hours to obtain the intermediate product.

[0188] 6) The intermediate product (3.3 g) was mixed with an ammonium chloride solution (1 mol / L, 33 mL), and subjected to ammonium exchange treatment by mechanical stirring at a speed of 400 r / min, a temperature of 80 °C, and a time of 2 hours. The mixture was then centrifuged, and the precipitate was dried at 120 °C for 2 hours. This process was repeated twice. Finally, ammonium calcination was performed at 550 °C for 4 hours to obtain molecular sieve catalyst 17, denoted as Q2.

[0189] Comparative Example 2

[0190] This comparative example is basically the same as Comparative Example 1, except that step 3 is not performed. This comparative example yields molecular sieve catalyst 18, denoted as Q1.

[0191] Comparative Example 3

[0192] This embodiment is basically the same as Example 1, except that disodium nickel ethylenediaminetetraacetate is not added in step 1). This embodiment yields molecular sieve catalyst 19.

[0193] Comparative Example 4

[0194] This embodiment is basically the same as Example 1, except that basic cobalt carbonate is not added in step 4). This embodiment yields molecular sieve catalyst 20.

[0195] Experimental Example 1

[0196] Inductively coupled plasma atomic emission spectrometry (ICP-AES) was used to analyze the catalysts in all examples and comparative examples, and to determine the loading of active metal elements M1 and M2 on the catalysts. The results are shown in Table 1.

[0197] Table 1

[0198]

[0199] Experimental Example 2

[0200] Catalytic cracking reaction was evaluated using a micro-fixed bed catalyst under catalytic cracking conditions, with n-hexane simulating naphtha feedstock. The catalytic temperature was 600℃ and the mass hourly space velocity (WHSV) was 3106 h⁻¹. -1The catalytic pyrolysis products were in the gas phase. The composition of the products was analyzed using a gas chromatograph (Agilent 7890B). The chromatographic column was a quartz capillary column. The vaporization chamber temperature and detector temperature were both 250°C. The carrier gas was nitrogen. The detector was a flame ionization detector. The fuel gas was hydrogen, and the combustion-supporting gas was air. The sample volume of the gaseous or liquid product was 1 μL.

[0201] The conversion rate and selectivity of the raw materials are calculated using the following formulas.

[0202]

[0203]

[0204] X represents the conversion rate of the raw material; S(C x H y ) indicates that the product C x H y Selectivity; m i (C6) indicates the mass of n-hexane in the feedstock; m o (C6) indicates the mass of n-hexane in the product; m(C x H y ) indicates that C in the product x H y The quality.

[0205] The conversion rates of feedstocks, the selectivity and yield of low-carbon olefins (including the sum of ethylene, propylene, and butene), and the hydrogen yield of Comparative Example 1 (Q3), Comparative Example 1 (Q2), and Comparative Example 2 (Q1) are shown in [reference needed]. Figures 3-5 The conversion rates of feedstocks, selectivity of low-carbon olefins (including the sum of ethylene, propylene, and butene), and hydrogen yields for all examples and comparative examples are shown in Table 2.

[0206] from Figures 3-5 As can be seen, compared with Q1 and Q2, the bimetallic molecular sieve catalyst Q3 prepared by the method of this invention exhibits outstanding low-carbon olefin selectivity and feed conversion rate in the n-hexane cracking reaction, but with lower 1-hexene selectivity. This result strongly confirms the effectiveness of the designed reaction pathway and metal spatial distribution strategy, successfully synergistically improving the reaction conversion rate and low-carbon olefin selectivity.

[0207] Table 2

[0208]

[0209] As shown in Table 2, the bimetallic molecular sieve catalyst of the present invention has high feed conversion rate and high selectivity for low carbon olefins through different metal placement, while improving the yield of the target product low carbon olefins.

[0210] Experimental Example 3

[0211] 1. XRD test

[0212] The crystal structure of the catalyst was analyzed using a full-resolution Xpert 3 powder diffractometer. The test conditions were: Cu Kα radiation (0.154 nm), tube voltage 40 kV, tube current 40 mA; scanning range 2θ 5°–90°, scanning speed 4° / min. Results are shown below. Figure 6 .

[0213] Depend on Figure 6 It can be seen that the catalysts of Example 1 and Comparative Example 1 all show characteristic peaks representing the topological structure of MFI at positions of 2θ=7.7°, 8.9°, 23.4°, 23.9° and 24.3°, which are consistent with the structural characteristics of Comparative Example 2 without metal loading. This indicates that the introduction of active metal elements M1 and M2 does not change the framework structure of the molecular sieve.

[0214] 2. XPS Test

[0215] The catalysts were characterized using XPS with a Thermo ESCALAB 250Xi X-ray photoelectron spectroscopy system. The distribution of modifying elements in different molecular sieve catalyst samples was measured, and the electron binding energy of the samples was calibrated based on the binding energy of the C1s (284.8 eV) peak of carbon. Results are shown below. Figure 3 .

[0216] Figure 7 The 2p spectra of the active metal element M2 (Ni) in the bimetallic molecular sieve catalyst Q3 of Example 1 and the molecular sieve catalyst Q2 of Comparative Example 1 show two characteristic main peaks at binding energies of 873-874 eV and 855-860 eV, respectively, which are attributed to the 2p of M2. 1 / 2 2p 3 / 2 The spin orbital splitting peak. Among them, the 2p peak of the active metal element M2. 3 / 2 The spectrum contains two characteristic peaks: 857–857.2 eV corresponds to nickel aluminate species, and 856.0–856.4 eV corresponds to M2. 2+ This indicates that the active metal element M2 in the catalyst exists as ions (M2 2+ It exists in the form of )

[0217] Figure 8 The 2p spectra of the active metal element M1 (Co) in Q3 and Q2 show two characteristic main peaks at binding energies of 799–800 eV and 778–788 eV, respectively, corresponding to the 2p spectra of the active metal element M1. 1 / 2 2p 3 / 2 The spin orbital peak. M1 2p in the catalyst. 3 / 2The binding energy (BE) is 781.8 eV, which belongs to M1. 2+ Species, and M1 does not appear in the spectrum. 3+ Characteristic peaks indicate that the active metal element M1 in the catalyst is in the form of ions (M1 2+ It exists in the form of )

[0218] 3. SEM testing

[0219] The morphology of the samples was photographed using a Hitachi S 4800 scanning electron microscope, and the results are shown in the figure. Figure 9 .

[0220] like Figure 9 As shown, the prepared bimetallic molecular sieve catalyst Q3 has a blocky morphology, indicating that the introduction of active metal elements M1 and M2 in the preparation method of this bimetallic molecular sieve catalyst did not change the original morphology and structure of the molecular sieve. The elemental distribution of Q3 was characterized by mapping. Ni (active metal element M2) is mainly dispersed in the pores of the bimetallic molecular sieve catalyst, while Co (active metal element M1) is mainly dispersed on the outer surface of the bimetallic molecular sieve catalyst.

[0221] Q2 is a molecular sieve catalyst in which active metal elements are introduced through impregnation, wherein Ni and Co metal elements are irregularly distributed within the pores and on the outer surface of the molecular sieve catalyst; Q1 is a molecular sieve catalyst without introduced active metal elements. As shown in Table 2, the overall performance of the molecular sieve catalyst Q3 is significantly better than that of Q2 and Q1. The bimetallic molecular sieve catalyst of this invention, by introducing active metal element M1 on the outer surface of the molecular sieve support and active metal element M2 within the pores of the molecular sieve support, significantly improves feed conversion rate, low-carbon olefin selectivity, and low-carbon olefin yield, providing key technical support for the efficient industrial application of naphtha catalytic cracking.

[0222] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A bimetallic molecular sieve catalyst characterized in that, The catalyst comprises a molecular sieve support and a metal active source; The metal active source loaded on the outer surface of the molecular sieve support is the M1 active source. The metal active source loaded inside the pores of the molecular sieve support is the M2 active source. Wherein, the active metal element in the M1 active source is active metal element M1, and the active metal element in the M2 active source is active metal element M2, wherein active metal element M1 and active metal element M2 are different metal elements.

2. The bimetallic molecular sieve catalyst of claim 1, wherein, The molecular sieve support comprises aluminosilicate molecular sieves; the molecular sieve support has at least one of a ten-membered ring cross-channel structure and a twelve-membered ring cross-channel structure; and / or The active metal element M1 includes metal elements from Group VIII of the periodic table; and / or, The active metal element M2 includes at least one metal element from Group VIB, Group VIIB, Group VIII, Group IB, and Group IIB of the periodic table.

3. The bimetallic molecular sieve catalyst of either claim 1 or 2, characterized by, The molecular sieve support includes at least one of ZSM-5, ZSM-11, or Beta molecular sieves; and / or, The active metal element M1 includes at least one selected from Pt, Fe, Ir, Rh, Co, Ni, and Pd; and / or, The active metal element M2 includes at least one of Cr, Mo, Zn, Ga, Cu, and Ni.

4. The bimetallic molecular sieve catalyst of any one of claims 1-3, wherein, Based on the mass of the bimetallic molecular sieve catalyst, the loading of the active metal element M1 is 0.1 wt% to 1 wt%, preferably 0.2 wt% to 0.6 wt%; and / or, Based on the mass of the bimetallic molecular sieve catalyst, the loading of the active metal element M2 is 0.1wt% to 3wt%, preferably 0.2wt% to 1.5wt%.

5. A method for preparing the bimetallic molecular sieve catalyst of any one of claims 1-4, characterized in that, Includes the following steps: 1) The template agent and the complex of M2 metal salt and complexing agent are subjected to a first mixing treatment to obtain a first mixture; 2) The intermediate solution, including the first mixture and the molecular sieve raw material source, is subjected to a crystallization reaction to obtain an intermediate; 3) Prepare an M1 metal salt solution by mixing M1 metal salt, organic compound, and acid solution; 4) The intermediate is mixed with the M1 metal salt solution and then subjected to aging and drying treatments in sequence to obtain the catalyst precursor; 5) Dissolve the coating agent in anhydrous ethanol to obtain a coating agent solution. Mix the catalyst precursor with the coating agent solution and stir to obtain a mixture. Perform a pre-hydrolysis condensation treatment on the mixture to obtain the coated product. 6) The coated product is subjected to drying and calcination treatments in sequence to obtain an intermediate product; 7) The intermediate product is subjected to ammonium exchange treatment and ammonium roasting treatment in sequence to obtain the catalyst.

6. The method of making a bimetallic molecular sieve catalyst of claim 5, wherein, The anion of the M1 metal salt includes at least one selected from carbonate, sulfate, nitrate, and chloride ions; and / or, The anion of the complex of the M2 metal salt-complexing agent includes at least one of ethylene glycol diethyl ether diaminetetraacetic acid combined with M2 anion, ethylenediaminetetraacetic acid combined with M2 anion, 1,2-cyclohexanediaminetetraacetic acid combined with M2 anion, hydroxyethyl ethylenediaminetriacetic acid combined with M2 anion, and ethylenediaminedisuccinic acid combined with M2 anion.

7. The method of making a bimetallic molecular sieve catalyst of any one of claims 5-6, wherein, The temperature of the first mixing treatment is 25~80℃, and the treatment time is 0.5~2 hours; preferably, the temperature is 30~60℃, and the treatment time is 0.5~1 hour; and / or, The crystallization reaction is carried out at a temperature of 150-200°C for a reaction time of 48-90 hours; preferably, the temperature is 150-180°C for a reaction time of 60-80 hours; and / or, The aging process is carried out at a temperature of 20-80°C for 4-12 hours; preferably, the temperature is 20-40°C for 4-8 hours; and / or, The ammonium exchange treatment is performed at a temperature of 50-120°C for 1-5 hours, with a stirring speed of 200-800 r / min; preferably, the temperature is 70-100°C for 1-4 hours, with a stirring speed of 300-600 r / min; and / or, The roasting treatment and the ammonium roasting treatment are performed at a temperature of 300~600℃ for 2~8 hours; preferably, the temperature is 400~600℃ for 2~4 hours.

8. The method of making a bimetallic molecular sieve catalyst of any one of claims 5-7, wherein, The mass ratio of the template agent to the complex of the M2 metal salt-complexing agent is (100~300):1; and / or, The mass ratio of the first mixture to the molecular sieve raw material source is 1:(1~3); and / or, The molar ratio of the complex of the M2 metal salt and the complexing agent (based on the molar amount of the active metal element M2) to the M1 metal salt (based on the molar amount of the active metal element M1) is (0.5~4):(0.5~8); and / or, The volume ratio of the organic compound to the acid solution is (0.2~5):1, preferably (0.5~2):

1.

9. A catalytic process characterized by, The bimetallic molecular sieve catalyst prepared by any one of claims 1-4, or by any one of claims 5-8.

10. The catalytic process of claim 9, wherein, The feedstock to be catalyzed in the catalytic method includes at least one of naphtha, hydrogenated gasoline, coking gasoline, and atmospheric gas oil. The catalytic method is performed at a temperature of 450~650℃ and a mass hourly space velocity of 2000~5000 h⁻¹. -1 Preferably, the temperature is 500~600℃ and the mass hourly space velocity is 2500~4000 h⁻¹. -1 .

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