Search

CN-121988384-A - Catalyst with core-shell structure and preparation method and application thereof

CN121988384ACN 121988384 ACN121988384 ACN 121988384ACN-121988384-A

Abstract

The invention discloses a catalyst with a core-shell structure, a preparation method and application thereof, and belongs to the technical field of catalysts. The invention successfully synthesizes the catalyst with the core-shell structure by regulating and controlling the chemical composition and crystallization condition of the core-shell. The use of seed crystals in the preparation method suppresses the influence of core skeleton characteristics on the shell layer, and subsequent secondary growth is induced to form a shell structure which grows mutually. The catalyst prepared by the invention takes ZSM-5 zeolite with an acid nuclear position as a main part and MCM-22 zeolite with a super cage structure as a structural basis, and the synergistic effect of the ZSM-5 zeolite and the MCM-22 zeolite respectively shows excellent performances in dehydrogenation, oligomerization, cyclization reaction and carbon deposit resistance of methane. The core-shell catalyst prepared by the invention not only serves MDA, but also can be expanded to other high-temperature acid catalytic reactions, and promotes industrialization and process integration.

Inventors

  • WANG SENYAN
  • PENG LI
  • ZHANG HONGXIANG
  • ZHAO LONG

Assignees

  • 中国科学技术大学

Dates

Publication Date
20260508
Application Date
20260410

Claims (10)

  1. 1. The preparation method of the core-shell structure catalyst is characterized by comprising the following steps of: (1) Dissolving an aluminum source, a template agent and a silicon source in an alkaline aqueous solution to obtain an MCM-22 precursor solution; (2) Adding crystal nucleus HZSM-5 into MCM-22 precursor solution for dynamic crystallization, washing the obtained product to be neutral after the dynamic crystallization is finished, and drying to obtain core-shell molecular sieve raw powder; (3) Roasting the core-shell molecular sieve raw powder to remove a template agent, adding the template agent into an ammonium salt solution for proton exchange, and sequentially drying and calcining to obtain an H-type core-shell structure molecular sieve, namely HZSM-5@MCM-22; (4) Adding HZSM-5@MCM-22 into the metal precursor solution, stirring under heating until the solution is completely evaporated, and calcining and granulating to obtain a target product.
  2. 2. The method of claim 1, wherein in step (1), the aluminum source is Al 2 O 3 , the templating agent is HMI, and the silicon source is SiO 2 sol.
  3. 3. The method of claim 1, wherein in step (1), the MCM-22 precursor solution has a molar ratio of silicon to aluminum of 30:1.
  4. 4. The method according to claim 1, wherein in the step (2), the silicon to aluminum molar ratio of the crystal nucleus HZSM-5 is 36:1, and the mass ratio of the MCM-22 synthesized by the MCM-22 precursor solution to the crystal nucleus HZSM-5 is (0.3-0.7): 1.
  5. 5. The method according to claim 1, wherein in the step (2), the dynamic crystallization is performed under a dynamic hydrothermal condition of 165-175 ℃ for 48-72 hours.
  6. 6. The method according to claim 1, wherein the temperature of the calcination in step (3) and the calcination in step (4) is 550 ℃.
  7. 7. The core-shell catalyst is characterized by being prepared by adopting the preparation method according to any one of claims 1 to 6, and comprises an inner core and a shell layer coating the inner core, wherein the inner core is HZSM-5, the shell layer is MCM-22, and the core-shell catalyst is loaded with metallic Mo.
  8. 8. The catalyst of claim 7, wherein the metal Mo is supported in an amount of 2 to 8% based on the total mass of the catalyst of the core-shell structure.
  9. 9. Use of a core-shell structured catalyst according to claim 7 or 8 in the dehydroaromatization of methane, comprising the steps of: The core-shell structured catalyst according to claim 7 or 8 is placed in a reaction device, heated to 700 ℃, and subjected to methane dehydrogenation aromatization reaction in an atmospheric pressure environment under the condition of reaction gas consisting of CH 4 and Ar.
  10. 10. Use of the core-shell structured catalyst according to claim 7 or 8 in light hydrocarbon aromatization reactions or dehydrogenation-aromatization coupling reactions.

Description

Catalyst with core-shell structure and preparation method and application thereof Technical Field The invention belongs to the technical field of catalysts, and particularly relates to a core-shell structure catalyst and a preparation method and application thereof. Background Natural gas, consisting primarily of methane (about 95%), has been attractive as an energy source and chemical feedstock that can replace conventional crude oil. Methane Dehydroaromatization (MDA) is a very promising non-oxidative process that does not form oxidized carbon species (e.g., CO or CO 2) and can produce aromatic hydrogen carbon bonds (mainly benzene, toluene, and xylenes). Since Xu et al reported MDA on molybdenum-loaded ZSM-5 (Socony Mobil-5) molecular sieves for the first time in 1993, it is widely believed that methane is first activated on Mo species in zeolite channels, and then intermediate C2 hydrocarbons are aromatized on Bronsted acid sites in the channels. Thus, research on supported molybdenum zeolite catalysts has focused mainly on determining the active molybdenum species for methane activation and elucidating the effect of the molybdic acid sites. However, the catalytic performance of these catalysts remains uncertain in terms of their activity, since the heavy carbon deposited in the pores of zeolite catalysts causes rapid deactivation of the catalyst. During aromatization, polyaromatic and aliphatic carbon deposits are often formed in large amounts in side reactions, plugging the interfaces or pores of the zeolite, leading to severe catalyst deactivation. These problems lead to difficulties in the industrialization of the light hydrocarbon aromatization process. Although many attempts have been made to reduce carbon deposition (e.g., synthesis of small particle zeolites or synthesis of zeolites having a hierarchical structure), rapid deactivation of the catalyst has been considered one of the greatest challenges affecting the stability of the aromatization reaction. Therefore, it is necessary to redesign the structure of the catalyst to facilitate the diffusion of the product and prevent further polymerization or carbonization of the product, resulting in the formation of polyaromatics or coke, which is the cause of catalyst deactivation. Core-shell catalysts are widely used in the catalytic field due to their unique core-shell reaction pathways and rich active sites. The prior art discloses a core-shell catalyst as follows: CN103861637A prepares a core-shell type composite molecular sieve with ZSM-5 as a core and MCM-41 as a shell layer, and realizes interface regulation and spatial position regulation of a microporous molecular sieve and a mesoporous molecular sieve. But the MCM-41 has larger pore diameter, uncontrollable MDA reaction path, poorer stability at high temperature and easy collapse. CN113830778B prepares ZSM-5/beta core-shell molecular sieve, while beta molecular sieve has bigger pore size, bigger molecular reactant can enter, and increases accessibility of active center, but has no shape selecting function to small molecular low carbon olefin such as ethylene, propylene, etc., is suitable for transalkylation reaction and heavy aromatic hydrocarbon lightening reaction, and is not suitable for MDA reaction. CN118356968A is used for preparing Co/SiO 2 @HZSM-5 with a core-shell structure, and can be used for preparing hydrogen by gasifying waste plastics and synthesizing gas. The Co/SiO 2 core-shell catalyst protected by the HZSM-5 shell has good stability and activity, but the pure silicon of the inner core has no acid site, which is unfavorable for the MDA reaction. CN103418429B prepares a core-shell molecular sieve carrier Z5S1 or Z11S1 with a shell layer of Silicalite-1 and a core phase of ZSM-5 or ZSM-11, mainly solves the problems of lower benzene selectivity and higher carbon deposition selectivity of a target product in the prior art, and improves the catalytic stability of the catalyst. However, the preparation process is complex, the acid sites on the outer surface must be completely removed, and the process requirement is high. In the prior art, the methane anaerobic aromatization reaction catalyst mainly depends on a single molecular sieve simple modification and a composite system, and the following obvious defects exist in the methods: The simple modification of the single molecular sieve has the defects that the catalyst is deactivated rapidly due to the shape selective effect and more carbon deposition at the same time due to the single pore diameter of the single molecular sieve, the problem that mesoporous framework collapse and the like can be caused by alkaline etching due to the simple modification, the acid sites are fixed, too many, carbon deposition is easy, the acid sites are fewer, the activity is poor, and the benzene yield and the conversion rate are lower. Although the single molecular sieve and the simple modification method thereof can regulate and control the acid