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CN-122010695-A - Method for preparing surface methoxy species based on H-ZSM-5 molecular sieve catalytic dimethyl ether conversion

CN122010695ACN 122010695 ACN122010695 ACN 122010695ACN-122010695-A

Abstract

The invention belongs to the field of catalysis, and discloses a method for preparing surface methoxy species based on H-ZSM-5 molecular sieve catalytic dimethyl ether conversion. The method comprises the step of reacting mixed gas of dimethyl ether and nitromethane under the mild condition of 90-120 ℃ by taking an H-ZSM-5 molecular sieve as a catalyst, so that the dimethyl ether can be efficiently decomposed into surface methoxy species and methanol. The method has the remarkable advantages of simple and convenient operation, mild reaction conditions and the like, provides an innovative solution for the controllable preparation and industrial application of the surface methoxy species, and has important scientific research value and wide industrial application prospect.

Inventors

  • LIU FENGQING
  • YI XIANFENG
  • ZHENG ANMIN

Assignees

  • 中国科学院精密测量科学与技术创新研究院

Dates

Publication Date
20260512
Application Date
20260112

Claims (8)

  1. 1. A method for preparing a surface methoxy species based on the catalysis of dimethyl ether conversion by an H-ZSM-5 molecular sieve, which is characterized by comprising the following steps: Dehydrating H-ZSM-5 molecular sieve; Respectively adsorbing 13 C marked dimethyl ether gas and nitromethane gas into the dehydrated H-ZSM-5 molecular sieve in a vacuum environment; vacuum sealing the adsorbed H-ZSM-5 molecular sieve sample, and transferring the sample to an incubator for heating reaction; The samples were subjected to solid nuclear magnetic resonance analysis.
  2. 2. The method for preparing surface methoxy species based on the conversion of dimethyl ether catalyzed by an H-ZSM-5 molecular sieve according to claim 1, wherein the molar ratio point of adsorption molecular dimethyl ether/nitromethane/bronsted acid sites is 2/2/1.
  3. 3. The method for preparing surface methoxy species based on the conversion of dimethyl ether catalyzed by an H-ZSM-5 molecular sieve according to claim 1, wherein the method for dehydration treatment of the H-ZSM-5 molecular sieve comprises: Respectively placing H-ZSM-5 molecular sieve samples in glass tubes, tightly connecting the glass tubes to a vacuum system, placing the glass tubes in the center of a heating furnace, and carrying out heating dehydration treatment; Gradually increasing the temperature from room temperature to a target temperature 673: 673K at a ramp rate of 1K/min; Continuously dehydrating 10 h under the conditions of temperature 673K and pressure < 10 -3 Pa, and naturally cooling to room temperature to obtain dehydrated sample.
  4. 4. The method for preparing a surface methoxy species based on the catalysis of dimethyl ether conversion by an H-ZSM-5 molecular sieve according to claim 1, wherein the method for adsorbing the reaction molecules comprises: Opening a valve above the sample tube, adsorbing quantitative 13 C marked dimethyl ether gas and nitromethane gas into a dehydrated activated H-ZSM-5 molecular sieve sample, and freezing the sample tube by liquid nitrogen to accelerate the adsorption process; After the adsorption is finished, the sample tube is sealed by a flame gun.
  5. 5. The method for preparing surface methoxy species based on the catalysis of dimethyl ether conversion by H-ZSM-5 molecular sieve according to claim 1, wherein the temperature of the heating reaction is 80-120 ℃.
  6. 6. The method for preparing surface methoxy species based on the conversion of dimethyl ether catalyzed by H-ZSM-5 molecular sieve according to claim 1, wherein the heating reaction time is 0.5 to 2 hours.
  7. 7. The method for preparing a surface methoxy species based on the conversion of dimethyl ether catalyzed by an H-ZSM-5 molecular sieve according to claim 1, wherein the subjecting the sample to solid state nmr analysis comprises: And collecting 13 C CP/MAS NMR spectrum of the sample after the reaction of adsorbing dimethyl ether and/or nitromethane by using a solid nuclear magnetic resonance spectrometer, and judging whether to generate surface methoxy species by chemical shift.
  8. 8. The method for preparing surface methoxy species based on the conversion of dimethyl ether catalyzed by an H-ZSM-5 molecular sieve according to claim 1, further comprising a comparative experiment; The comparative experiment shows that only adsorption reaction molecules are different, the molar ratio point of dimethyl ether/Bronsted acid sites of the adsorption molecules is 2/1, and other processes are the same.

Description

Method for preparing surface methoxy species based on H-ZSM-5 molecular sieve catalytic dimethyl ether conversion Technical Field The invention belongs to the field of catalysis, and particularly relates to a method for preparing surface methoxy species based on H-ZSM-5 molecular sieve catalytic dimethyl ether conversion. Background The molecular sieve catalyzed methanol/dimethyl ether conversion reaction can efficiently convert methanol into high-value hydrocarbon chemicals such as olefin, aromatic hydrocarbon and the like, and provides a sustainable path for producing basic petrochemical raw materials by utilizing non-petroleum resources (coal, natural gas, biomass and the like). This chemistry is always a research hotspot in industry and academia. The surface methoxy species is used as a key active intermediate, and not only participates in methanol activation and formation of a first C-C bond, but also promotes methylation reaction of olefin and aromatic hydrocarbon, thereby driving the whole methanol conversion process. Therefore, the deep understanding of the generation and evolution mechanism of the surface methoxy species has important scientific significance for elucidating the methanol conversion reaction mechanism, and can provide theoretical guidance for industrial process optimization. At present, although research has been reported to report that Lewis acid sites catalyze methanol to generate surface methoxy species at room temperature, bronsted acid sites (Bronsted NSTED ACID SITES) as main active centers of molecular sieves still face a great challenge in catalyzing the process under mild conditions, and related research has been reported. This results mainly from the fact that the reaction needs to overcome an activation energy barrier of up to 150 kJ/mol, which usually needs to be carried out at high temperatures above 200 ℃. In addition, methanol, dimethyl ether and surface methoxy species are interconverted at high temperatures, further increasing the complexity of the system. Aiming at the key scientific problem, the breakthrough difficulty is how to design mild conditions to realize the controllable generation of surface methoxy species. Disclosure of Invention In order to solve the technical problem of high surface methoxy species generation temperature and complex reaction at high temperature, the invention aims to provide a method for preparing surface methoxy species based on H-ZSM-5 molecular sieve catalytic dimethyl ether conversion, the method creatively adopts dimethyl ether and nitromethane as mixed reactants, and regulates and controls the reaction microenvironment through the nitromethane, so that surface methoxy species can be controllably generated at the mild reaction temperature of 90-120 ℃, and the reaction temperature of the dimethyl ether generated by the dehydration of the methanol can be effectively reduced. In order to achieve the above purpose, the present invention provides the following technical solutions: a method for preparing a surface methoxy species based on H-ZSM-5 molecular sieve catalyzed dimethyl ether conversion, the method comprising: Dehydrating H-ZSM-5 molecular sieve; Respectively adsorbing 13 C marked dimethyl ether gas and nitromethane gas into the H-ZSM-5 molecular sieve after dehydration treatment in a vacuum environment, wherein the molar ratio point of adsorption molecule dimethyl ether/nitromethane/Bronsted acid site is 2/2/1; vacuum sealing the adsorbed H-ZSM-5 molecular sieve sample, and transferring the sample to an incubator for heating reaction; The samples were subjected to solid nuclear magnetic resonance analysis. Optionally, the method for dehydrating the H-ZSM-5 molecular sieve comprises the following steps: Respectively placing H-ZSM-5 molecular sieve samples in glass tubes, tightly connecting the glass tubes to a vacuum system, placing the glass tubes in the center of a heating furnace, and carrying out heating dehydration treatment; Gradually increasing the temperature from room temperature to a target temperature 673: 673K at a ramp rate of 1K/min; continuously dehydrating 10 h under the conditions of temperature 673K and pressure < 10 -3 Pa, and naturally cooling to room temperature to obtain dehydrated sample. The dehydration treatment is used to activate the molecular sieve. Optionally, the method for adsorbing the reactive molecules comprises: Opening a valve above the sample tube, adsorbing quantitative 13 C marked dimethyl ether gas and nitromethane gas into a dehydrated activated H-ZSM-5 molecular sieve sample, and freezing the sample tube by liquid nitrogen to accelerate the adsorption process; After the adsorption is finished, the sample tube is sealed by a flame gun. Preferably, the temperature of the heating reaction is 80-120 ℃. Preferably, the heating reaction is carried out for a period of 0.5 to 2 hours. Optionally, the subjecting the sample to solid state nuclear magnetic resonance analysis comprises: And colle