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CN-122006797-A - Core-shell type MFI molecular sieve and preparation method and application thereof

CN122006797ACN 122006797 ACN122006797 ACN 122006797ACN-122006797-A

Abstract

The application discloses a core-shell type MFI molecular sieve, a preparation method and application thereof, and belongs to the technical field of molecular sieve catalysts. The core-shell type MFI molecular sieve comprises a core phase and a shell layer coated on the surface of the core phase, wherein the core phase is Sne-Silicalite-1 loaded by metal, the shell layer is HZSM-5, and Sne-Silicalite-1 is a molecular sieve with a large number of defect anchoring sites formed after boron removal of the borosilicate MFI molecular sieve B-Silicalite-1. The functional boundary domains of the core-shell MFI molecular sieve are obviously distinguished and orderly connected, have gradient acid sites, can inhibit migration and agglomeration of internal metals, and enable the internal weak acid sites and the external strong acid sites to catalyze different reactions on a reaction path respectively, so that the progress of the tandem reaction is promoted, and the aromatization reaction is promoted.

Inventors

  • ZHANG HONGXIANG
  • WANG SENYAN
  • ZHAO LONG
  • XU MINGGAO

Assignees

  • 中国科学技术大学

Dates

Publication Date
20260512
Application Date
20260410

Claims (10)

  1. 1. The core-shell type MFI molecular sieve comprises a core phase and a shell layer coated on the surface of the core phase, and is characterized in that the core phase is Sne-Silicalite-1 loaded by metal, the shell layer is HZSM-5, and Sne-Silicalite-1 is a molecular sieve with a large number of defect anchoring sites formed after boron removal of the borosilicate MFI molecular sieve B-Silicalite-1.
  2. 2. The core-shell MFI molecular sieve according to claim 1, wherein the size of the core phase is 500-700nm and the thickness of the shell layer is 100-200nm; and/or the metal is at least one of molybdenum, iron, gallium and zinc; and/or, the metal loading amount is 3-5 wt% based on the total mass of the core-shell MFI molecular sieve.
  3. 3. A process for preparing a core-shell MFI molecular sieve according to claim 1 or 2, wherein the process is divided into a first or a second process, wherein the first process comprises the steps of: preparing a borosilicate MFI molecular sieve B-Silicalite-1, and performing boron removal treatment on the B-Silicalite-1 to obtain a molecular sieve Sne-Silicalite-1 with a defect anchoring site; Carrying metal on the surface of Sne-Silicalite-1 to obtain M/Sne-Silicalite-1, and carbonizing to obtain MC/Sne-Silicalite-1; Coating an HZSM-5 shell layer on the surface of MC/Sne-Silicalite-1 to obtain a core-shell type MFI molecular sieve M/Sne-Silicalite-1@HZSM-5; The second method comprises the following steps: Preparing seed crystal B-Silicalite-1; Mixing seed crystal B-Silicalite-1 with shell crystallization mother liquor, and performing hydrothermal crystallization to obtain Sne-Silicalite-1/HZSM-5 catalyst; and loading metal on the surface of Sne-Silicalite-1/HZSM-5 catalyst to obtain the core-shell MFI molecular sieve M/Sne-Silicalite-1@HZSM-5.
  4. 4. A method according to claim 3, wherein the preparation of seed B-Silicalite-1 comprises the steps of: mixing a silicon source, a boron source, a template agent and water, fully stirring until ethanol volatilizes to form solid powder, keeping the solid powder at 80-120 ℃ for 18-30h for aging, standing at 175-185 ℃ for 120-192h, washing with water to be neutral, and drying to obtain seed crystal B-Silicalite-1; The borosilicate MFI molecular sieve B-Silicalite-1 is formed by calcining the seed B-Silicalite-1 at 550-560 ℃ for 6-8 hours.
  5. 5. The method of claim 4, wherein the silicon source is one of tetraethyl orthosilicate, sodium silicate and silica sol, the boron source is boric acid, the template agent is one of tetrapropylammonium hydroxide and tetrapropylammonium bromide, and the silicon source and the boron source are proportioned according to a mole ratio of Si to B of 1 (0.01-0.04).
  6. 6. A method according to claim 3, wherein the boron removal treatment is carried out by adding molecular sieves to ammonium chloride or ammonium nitrate solution, stirring and heating, washing with water, drying and calcining.
  7. 7. The method according to claim 3, wherein the carbonization treatment in the first method is carried out by heating the M/Sne-Silicalite-1 catalyst to 680-720 ℃ under a non-reactive atmosphere, introducing a mixed gas of a carbon source and nitrogen, and reacting at a space velocity of 3000-4000 ml.h -1 ·g -1 , wherein the carbon source is one of C1-C5 alkane or alkene.
  8. 8. The method of claim 3, wherein in method one, the HZSM-5 shell is hydrothermally synthesized by adding MC/Sne-Silicalite-1 to the ZSM-5 precursor solution.
  9. 9. The method of claim 8, wherein the ZSM-5 precursor solution is prepared by mixing a silicon source, an aluminum source, a template agent and water, wherein the silicon source is one of tetraethyl orthosilicate, sodium silicate and silica sol, the aluminum source is one of sodium metaaluminate and sodium nitrate, the template agent is one of tetrapropylammonium hydroxide and tetrapropylammonium bromide, and the silicon source and the aluminum source are proportioned according to a mole ratio of Si to Al of 1 (0.02-0.06); And/or the weight ratio of MC/Sne-Silicalite-1 to ZSM-5 precursor solution is 1 (1.2-2.5); And/or the hydrothermal synthesis process is that the hydrothermal synthesis is carried out by firstly keeping at 80-120 ℃ for 18-30h and then standing at 175-185 ℃ for 48-72h.
  10. 10. The use of the core-shell MFI molecular sieve according to claim 1 or 2 or the core-shell MFI molecular sieve prepared by the method according to claims 3-9 as a catalyst in an aromatization reaction.

Description

Core-shell type MFI molecular sieve and preparation method and application thereof Technical Field The application belongs to the technical field of molecular sieve catalysts, and particularly relates to a core-shell type MFI molecular sieve and a preparation method thereof, and application of the core-shell type MFI molecular sieve as a catalyst. Background Aromatization technology is a process in which low molecular weight non-aromatic hydrocarbons (e.g., C1-C5 alkanes or alkenes such as methane, ethane, propane, etc.) are converted to high value-added aromatic hydrocarbons at high temperatures over a catalyst. The technology can effectively improve the economic value of light non-aromatic hydrocarbon resources, and has important application in the fields of petrochemical industry and natural gas processing. In the aromatization technology, the performance of the catalyst is critical. The molecular sieve with the MFI topological structure (such as ZSM-5) has good application prospect, excellent catalytic performance, high specific surface area and rich strong acid sites, and provides necessary active centers for alkane activation and aromatization. However, the strong acidity promotes unnecessary side reactions to cause carbon deposition, so that the activity of the catalyst is rapidly reduced and the service life is shortened. At present, the synthesis of a core-shell structure is one of effective strategies for controlling the acidity of an MFI molecular sieve and inhibiting carbon deposition. For example, micron-sized pure silicon molecular sieve Silicalite-1 is used as a core phase, ZSM-5 molecular sieve nano layer is used as a shell phase, so that the core-shell type MFI molecular sieve with good catalytic performance can be obtained, but the pure silicon molecular sieve lacks anchoring sites inside, so that after the metal is loaded, the metal can migrate and agglomerate to cause sintering in the reaction process, and active sites are reduced. Disclosure of Invention In view of the above, the primary object of the present application is to provide a core-shell type MFI molecular sieve, in which a molecular sieve Sne-Silicalite-1 with a large number of defect anchoring sites formed after the boron removal of borosilicate MFI molecular sieve B-Silicalite-1 is used as an inner core, and after metal loading, the surface of the core-shell type MFI molecular sieve is coated with boroaluminate MFI molecular sieve (HZSM-5), so as to obtain a core-shell type MFI molecular sieve with gradient acid sites, the functional domains of which are obviously distinguished and orderly connected, and to inhibit migration and agglomeration of internal metals, so that the internal weak acid sites and the external strong acid sites respectively catalyze different reactions on the reaction paths, and the reaction is performed in series. In order to achieve the above purpose, the present application adopts the following technical scheme: The application discloses a core-shell type MFI molecular sieve, which comprises a core phase and a shell layer coated on the surface of the core phase, wherein the core phase is Sne-Silicalite-1 loaded by metal, the shell layer is HZSM-5, and Sne-Silicalite-1 is a molecular sieve which forms a large number of defect anchoring sites after boron removal of the borosilicate MFI molecular sieve B-Silicalite-1. In another aspect, the present application discloses a method for preparing the core-shell MFI molecular sieve according to the present application, which is classified into a first method or a second method, wherein the first method comprises the following steps: preparing a borosilicate MFI molecular sieve B-Silicalite-1, and performing boron removal treatment on the B-Silicalite-1 to obtain a molecular sieve Sne-Silicalite-1 with a defect anchoring site; Carrying metal on the surface of Sne-Silicalite-1 to obtain M/Sne-Silicalite-1, and carbonizing to obtain MC/Sne-Silicalite-1; Coating an HZSM-5 shell layer on the surface of MC/Sne-Silicalite-1 to obtain a core-shell type MFI molecular sieve M/Sne-Silicalite-1@HZSM-5; The second method comprises the following steps: Preparing seed crystal B-Silicalite-1; Mixing seed crystal B-Silicalite-1 with shell crystallization mother liquor, and performing hydrothermal crystallization to obtain Sne-Silicalite-1/HZSM-5 catalyst; and loading metal on the surface of Sne-Silicalite-1/HZSM-5 catalyst to obtain the core-shell MFI molecular sieve M/Sne-Silicalite-1@HZSM-5. The application also discloses the application of the core-shell type MFI molecular sieve or the core-shell type MFI molecular sieve prepared by the method as a catalyst in an aromatization reaction. The application has the beneficial effects that: According to the application, a borosilicate MFI molecular sieve B-Silicalite-1 is used as a core phase, and the core phase is treated by boron removal (B) to generate a large number of defect site anchoring metals, so that the core phase m