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CN-118270800-B - Independent preparation method of pure silicon or heteroatom STT molecular sieve

CN118270800BCN 118270800 BCN118270800 BCN 118270800BCN-118270800-B

Abstract

The invention belongs to the field of molecular sieve preparation, and provides an independent preparation method of a pure silicon or heteroatom STT molecular sieve, which comprises the following steps of (1) uniformly mixing a silicon source, a structure directing agent and water to obtain a precursor, carrying out hydrothermal crystallization on the precursor, filtering, washing, drying and calcining to obtain a Si-MWW molecular sieve, (2) adopting a crystal transformation method, taking the Si-MWW molecular sieve as the silicon source, respectively adding different heteroatom sources, the structure directing agent and the water, uniformly mixing, carrying out hydrothermal crystallization, centrifuging, washing, drying and calcining to obtain the Si-STT, al-STT, B-STT and Zr-STT molecular sieves. The invention breaks through the problems of long synthesis period, need of assistance of fluorine medium and easy generation of hetero-equality in the traditional synthesis method of STT molecular sieve, and can efficiently realize synthesis of pure-phase STT and introduction of hetero-atoms.

Inventors

  • REN LIMIN
  • HUANG WEI
  • YAN XIN

Assignees

  • 大连理工大学

Dates

Publication Date
20260512
Application Date
20240407

Claims (7)

  1. 1. An independent preparation method of a pure silicon or heteroatom STT molecular sieve is characterized by comprising the following steps: (1) The synthesis of the parent molecular sieve comprises the steps of uniformly stirring an aqueous solution of a structure directing agent 1 and a structure directing agent 2 to form a first mixed solution, adding a silicon source into the first mixed solution, and stirring for 12 hours to form a second mixed solution; Crystallizing the second mixed solution by a dynamic crystallization method at 150 ℃ for 5 days, cooling at room temperature, filtering and separating to obtain a sample, washing with water until PH=7, drying at 80 ℃ for 12 hours, drying at 600 ℃ and calcining at a heating rate of 1 ℃ per min for 10 hours to obtain the Si-MWW molecular sieve; The structure directing agent 1 is N, N, N-trimethyl-1-adamantyl ammonium hydroxide; the structure directing agent 2 is cyclohexylimine; (2) Synthesis of pure silicon and heteroatom STT molecular sieves: Taking Si-MWW molecular sieve as a silicon source, adding the structure directing agent 1 and water, and stirring for 12 hours to obtain a third mixed solution; taking Si-MWW molecular sieve as a silicon source, adding an aluminum source, a structure directing agent 1 and water, and stirring for 12 hours to obtain a fourth mixed solution; Taking Si-MWW molecular sieve as a silicon source, adding a boron source, a structure directing agent 1 and water, and stirring for 12 hours to obtain a fifth mixed solution; Taking Si-MWW molecular sieve as a silicon source, adding a zirconium source, a structure directing agent 1 and water, and stirring for 12 hours to obtain a sixth mixed solution; the method comprises the steps of adopting a crystal transformation method to respectively carry out static crystallization on a third mixed solution, a fourth mixed solution, a fifth mixed solution and a sixth mixed solution at the temperature of 170,200,170,170 ℃ for 10 hours, cooling at room temperature, carrying out centrifugal separation to obtain a sample, washing with water to PH=7, then drying at the temperature of 80 ℃ for 12 hours, heating to 600 ℃ at the temperature of 1 ℃ per minute during calcination after drying, and calcining at 600 ℃ for 10 hours to respectively obtain a Si-STT molecular sieve, an Al-STT molecular sieve, a B-STT molecular sieve and a Zr-STT molecular sieve.
  2. 2. The method for preparing pure silicon or heteroatom STT molecular sieve according to claim 1, wherein, In the step (1), the step of (a), The silicon source is white carbon black; the dynamic crystallization method is carried out under the condition of rotation, wherein the rotation speed is 15-30 rpm; in the second mixed solution, the molar ratio of the silicon source to the structure directing agent 1 to the structure directing agent 2 to the water is 1:0.25:0.31:44 calculated by SiO 2 .
  3. 3. The method for preparing pure silicon or heteroatom STT molecular sieve according to claim 1, wherein, In the step (2), the step of (C), The aluminum source is sodium metaaluminate; the boron source is boric acid; the zirconium source is zirconium sulfate.
  4. 4. The method for preparing pure silicon or heteroatom STT molecular sieve according to claim 1, wherein, In the step (2), the step of (C), In the third mixed solution, the molar ratio of the silicon source to the structure directing agent 1 to water is 1:0.5:20 based on SiO 2 .
  5. 5. The method for preparing pure silicon or heteroatom STT molecular sieve according to claim 1, wherein, In the step (2), the step of (C), In the fourth mixed solution, the silicon source is calculated by SiO 2 , the aluminum source is calculated by Al 2 O 3 , and the molar ratio of the structure directing agent 1 to water is 1:0.02:0.2:20 or 1:0.01:0.2-0.4:20 or 1:0.005:0.3-0.5:20.
  6. 6. The method for preparing pure silicon or heteroatom STT molecular sieve according to claim 1, wherein, In the step (2), the step of (C), In the fifth mixed solution, the silicon source is calculated by SiO 2 , the boron source is calculated by B 2 O 3 , and the molar ratio of the structure directing agent 1 to water is 1:0.01-0.1:0.5-0.65:20-23.
  7. 7. The method for preparing pure silicon or heteroatom STT molecular sieve according to claim 1, wherein, In the step (2), the step of (C), In the sixth mixed solution, the silicon source is calculated by SiO 2 , the zirconium source is calculated by ZrO 2 , and the mol ratio of the structure directing agent 1 to water is 1:0.005-0.01:0.5:20.

Description

Independent preparation method of pure silicon or heteroatom STT molecular sieve Technical Field The invention belongs to the field of molecular sieve preparation, and particularly relates to an independent preparation method of a pure silicon or heteroatom STT molecular sieve. Background STT molecular sieves are a common small pore molecular sieve having a unique odd number of ring structures, including seven-membered ring channels parallel to the [001] crystal plane and nine-membered ring channels （Miguel A. Camblor, et al.SSZ-23: An Odd Zeolite with Pore Openings of Seven and Nine Tetrahedral Atoms [J]. Angew. Chem. Int. Ed., 1998, 37(15):2122-2126.）.SSZ-23 parallel to the [101] crystal plane, are synthesized in the presence of N, N, N-trimethyl-1-adamantylammonium hydroxide (TMAdaOH) as a Structure Directing Agent (SDA), which is not characteristic of SSZ-23 formation and in the presence of which other molecular sieves can also be formed, which results in the synthesis system of STT molecular sieves that tend to exhibit other molecular sieve impurity phases, such as CHA. In addition, F-ions are also needed to serve as mineralizer for the synthesis of the STT molecular sieve, and the synthesis of the pure-silicon STT molecular sieve in the traditional hydrothermal synthesis method is up to 30 days （Miguel A. Camblor, et al. A Synthesis, MAS NMR, Synchrotron X-ray Powder Diffraction, and Computational Study of Zeolite SSZ-23 [J]. Chem. Mater., 1999, 11:2878-2885.）., and the pure-silicon STT molecular sieve has no framework aluminum atoms, so that the catalytic activity is weak and is rarely applied to the field of catalysis. Researchers have made full use of the special nine-membered ring and seven-membered ring channels of STT molecular sieves to synthesize STT molecular sieve membranes and applied the STT molecular sieve membranes to separation （Koji Kida, et al. Synthesis of pure silica STT-type zeolite membrane [J]. Mater. Lett.,2017, 209:36-38.）. of gas molecules, and besides pure silicon STT molecular sieves, researchers have made many efforts on synthesis of heteroatom STT molecular sieves. Einar et al used hydrothermal synthesis to synthesize Ti-STT with Si/Ti=106 with the aid of TMAdaOH and hydrofluoric acid, and performed ethylene epoxidation reaction with hydrogen peroxide as a model reaction, demonstrating that the material has shape selectivity to the reactant （Einar André Eilertsen, et al. Ti-STT: a new zeotype shape selective oxidation catalyst [J]. Chem. Commun., 2011, 47:11867-11869.）.I. Zones et al replaced hydrofluoric acid with ammonium fluoride, boric acid as boron source, successfully synthesized boron-containing SSZ-23 molecular sieve （S.I. Zones, et al. A novel approach to borosilicate zeolite synthesis in the presence of fluoride [J]. Microporous Mesoporous Mater., 2011, 146:48-56.）.Jason et al synthesized Sn-STT under TMAdaOH guidance with Si-STT added as seed crystal in the synthesis system, and the synthesis period was up to 31 days （Jason S. Bates, et al. Distinct Catalytic Reactivity of Sn Substituted in Framework Locations and at Defect Grain Boundaries in Sn-Zeolites [J]. ACS Catal., 2019, 9:6146-6168.）. It follows that the synthesis of heteroatom STT molecular sieves also requires a long synthesis period and needs to be carried out under a fluorine system, and this difficulty in synthesis makes its use in the catalytic field limited. Disclosure of Invention The invention provides an independent preparation method of pure silicon or heteroatom STT molecular sieve, which overcomes the defects of the prior synthesis means. The technical scheme of the invention is as follows: An independent preparation method of pure silicon or heteroatom STT molecular sieve comprises the following steps: (1) The synthesis of the parent molecular sieve comprises the steps of uniformly stirring an aqueous solution of a structure directing agent 1 and a structure directing agent 2 to form a first mixed solution, adding a silicon source into the first mixed solution, and stirring for 12 hours to form a second mixed solution; Crystallizing the second mixed solution at 150 ℃ for 5 days by adopting a dynamic crystallization method, cooling at room temperature, filtering and separating to obtain a sample, washing the sample with water until PH=7, drying the sample at 80 ℃ for 12 hours, and calcining the dried sample at 600 ℃ for 10 hours at a heating rate of 1 ℃ per minute to obtain the Si-MWW molecular sieve; the dynamic crystallization method is carried out under the condition of rotation, wherein the rotation speed is 15-30 rpm; the structure directing agent 1 is N, N, N-trimethyl-1-adamantyl ammonium hydroxide, the structure directing agent 2 is cyclohexylimine, and the silicon source is white carbon black; The addition ratio of the silicon source, the structure directing agent and the water in the second mixed solution is that the molar ratio of SiO 2, the structure directing agent 1, the struct