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CN-121972209-A - Molecular sieve catalyst and preparation method and application thereof

CN121972209ACN 121972209 ACN121972209 ACN 121972209ACN-121972209-A

Abstract

The invention discloses a molecular sieve catalyst and a preparation method and application thereof, and belongs to the technical field of petrochemical catalysts. The preparation method adopts an integrated strategy of etching, modification and limiting, firstly uses a mixed alkali solution of alkali metal hydroxide and ethylenediamine to controllably etch a pure silicon Silicalite-1 (S-1) molecular sieve, constructs silicon hydroxyl nest defects in situ in a framework, retains atomically dispersed alkali metal, and then loads platinum and second metal salt on the etched molecular sieve, and finally obtains a final catalyst through drying, calcining and reduction treatment. According to the invention, through the limited-domain microenvironment created in advance in the etching step, the accurate positioning and strong interaction of the platinum, the second metal and the alkali metal are realized, and the problems of difficult propane initial activation, low propylene selectivity and poor stability of the traditional platinum-based catalyst are effectively solved. The catalyst shows high conversion rate, high selectivity and excellent thermal stability in propane dehydrogenation reaction.

Inventors

  • ZHENG ANMIN
  • Xiang Xiaoge
  • LIU GUOLIANG
  • LIU YI
  • DENG LIDAN

Assignees

  • 武汉科技大学

Dates

Publication Date
20260505
Application Date
20260120

Claims (10)

  1. 1. A method for preparing a molecular sieve catalyst, comprising the steps of: S1, dissolving alkali metal hydroxide and ethylenediamine in deionized water to obtain a mixed alkali solution; S2, dissolving platinum salt and a precursor of a second metal in an aqueous solution to obtain a metal precursor solution; s3, adding the mixed alkali solution obtained in the step S1 into the S-1 molecular sieve under continuous stirring, washing after etching treatment, drying and calcining; And S4, dispersing the S-1 molecular sieve obtained in the step S3 into the metal precursor solution of the step S2, stirring, drying, calcining, and calcining in a reducing atmosphere to obtain the molecular sieve catalyst.
  2. 2. The process according to claim 1, wherein in step S1, the molar ratio of alkali metal hydroxide to ethylenediamine is 1:10 to 10:1.
  3. 3. The method according to claim 1, wherein in the step S2, the platinum salt is one or more of chloroplatinic acid, platinum chloride, platinum nitrate and dinitroso diammineplatinum, and the second metal is one or more of indium, gallium and tin.
  4. 4. The method of claim 3, wherein the molar ratio of platinum to the second metal in step S2 is 1:10 to 10:1.
  5. 5. The method according to claim 3, wherein in the step S2, the second metal is indium, a precursor of which is one or more of indium nitrate hydrate, indium chloride or indium sulfate, or the second metal is gallium, a precursor of which is one or more of gallium nitrate hydrate, gallium chloride or gallium sulfate, or the second metal is tin, a precursor of which is one or more of tin nitrate hydrate, tin chloride or tin sulfate.
  6. 6. The method of claim 1, wherein in step S3, the concentration of the S-1 molecular sieve in the mixed alkali solution is1 to 100 g/L.
  7. 7. The method according to claim 1, wherein in step S3, the etching time is 0.5 to 20 hours and the etching temperature is 20 to 100 ℃.
  8. 8. The method according to claim 1, wherein in the step S4, the reducing atmosphere is a mixed gas of H 2 /Ar having a hydrogen concentration of 1 to 100 vol%.
  9. 9. A molecular sieve catalyst made by the method of any of claims 1-8.
  10. 10. Use of the molecular sieve catalyst of claim 9 in a reaction for the dehydrogenation of propane to propylene.

Description

Molecular sieve catalyst and preparation method and application thereof Technical Field The invention belongs to the technical field of petrochemical catalysts, and particularly relates to a molecular sieve catalyst, a preparation method and application thereof. Background Propane dehydrogenation is an important way to increase the yield of propylene with high added value. Propane dehydrogenation is an important way to increase the yield of propylene with high added value. Currently, noble metal platinum-based catalysts are one of the mainstream catalytic systems for this reaction. However, the existing platinum-based catalyst mainly faces two bottleneck problems in industrial application, namely, firstly, the bond energy of a first carbon-hydrogen bond in a reactant propane molecule is higher, so that the initial activation is difficult, the intrinsic activity of the catalyst under mild conditions and the conversion rate of propane are limited, secondly, the target product propylene is strong in adsorption on an active site, difficult to timely desorb, and easy to generate continuous deep dehydrogenation side reaction, low-carbon byproducts such as ethylene and methane are generated or carbon deposition is caused, and the propylene selectivity and the catalyst stability are seriously reduced. In order to solve the above problems, fine control of electron and geometry of the platinum active center is critical. The prior art mainly introduces platinum and a second metal (such as tin, indium and the like) and an alkali metal (such as sodium, potassium and the like) component into a catalyst system simultaneously by methods of co-impregnation, fractional loading or one-pot hydrothermal synthesis and the like. The alkali metal component can adjust the electron density of platinum and help to reduce the activation energy barrier of propane C-H bond, while the second metal component (such as tin, indium and the like) can form alloy or interface site with platinum, can adjust the electron structure of platinum, effectively weaken the over-strong adsorption of the platinum to propylene, thereby synergistically improving the activity and selectivity of the catalyst. However, the conventional method, especially the one-pot method, has obvious limitations that firstly, platinum, second metal and alkali metal ions may be randomly distributed in a pore canal or a surface of a molecular sieve in a synthesis process, and the interaction site and the tightness between the platinum, the second metal and the alkali metal ions are difficult to precisely control, so that the active site structure is not uniform, secondly, the alkali metal ions are easy to migrate, sinter or run off in a high-temperature treatment or reaction process, the stable modification effect is difficult to maintain for a long time, and furthermore, the direct encapsulation method has weaker 'limited domain' effect on an active center, and metal nano particles are easy to migrate and aggregate under severe reaction conditions, so that the catalytic stability is influenced. Therefore, a novel method capable of constructing stable, limited-domain and active microenvironment rich in hydroxyl defects in situ so as to realize accurate, stable and strong interaction of platinum, second metal and alkali metal components is developed, and the method has important significance for breaking through the performance bottleneck of the existing catalyst. Disclosure of Invention In view of the above, the invention provides a molecular sieve catalyst, a preparation method and application thereof, so as to solve the problems of insufficient propane conversion rate and propylene selectivity of the platinum-based catalyst in the prior art. The technical scheme of the invention is realized as follows: in a first aspect, the present invention provides a method for preparing a molecular sieve catalyst, comprising the steps of: S1, dissolving alkali metal hydroxide and ethylenediamine in deionized water to obtain a mixed alkali solution; S2, dissolving platinum salt and a precursor of a second metal in an aqueous solution to obtain a metal precursor solution; s3, adding the mixed alkali solution obtained in the step S1 into the S-1 molecular sieve under continuous stirring, washing after etching treatment, drying and calcining; And S4, dispersing the S-1 molecular sieve obtained in the step S3 into the metal precursor solution of the step S2, stirring, drying, calcining, and calcining in a reducing atmosphere to obtain the molecular sieve catalyst. Based on the above technical scheme, preferably, in the step S1, the molar ratio of the alkali metal hydroxide to the ethylenediamine is 1:10-10:1. In the present invention, the ethylenediamine is preferably used in the form of its monohydrate. The alkali metal hydroxide provides an alkaline environment, and ethylenediamine is used as an organic alkali regulator, and the alkali metal hydroxide and the ethylenediamine are combined to