Modified tin-silicon molecular sieve, preparation method and application thereof

Abstract

A modified tin-silicon molecular sieve, characterized in that it contains tin, silicon, oxygen and an alkali metal element; the modified tin-silicon molecular sieve is characterized by XPS, the center value of the Sn 3d 5 / 2 spectral peak binding energy is located at 487.1±0.4eV, and the ratio of the spectral peak area of six-coordinated tin to four-coordinated tin is greater than 1:1.

Description

Technical Field

[0001] This invention belongs to the field of molecular sieve technology, and more specifically to tin-silicon molecular sieves, methods for modifying molecular sieves, and applications of molecular sieves as catalysts. Background Technology

[0002] Methyl methacrylate (MMA) is an important organic chemical raw material, mainly used to produce polymethyl methacrylate (PMMA) and acrylic resin materials. It is also widely used in the manufacture of other resins, plastics, coatings, adhesives, lubricants, wetting agents, varnishes, printing and dyeing auxiliaries, and insulating filling materials.

[0003] The direct aldol condensation of methyl propionate and formaldehyde to produce methyl methacrylate (MMA) avoids the use of highly toxic raw materials, which are inexpensive and widely available, making it an important future production method for MMA. Currently, the most effective aldol condensation catalyst for methyl propionate and formaldehyde is a supported catalyst with silica as the main support and cesium as the main active component. However, this supported catalyst suffers from low activity, incomplete conversion of the raw materials, and a gradual decrease in specific surface area and weakening of activity over time due to the use of amorphous silica as the support.

[0004] CN103551148B discloses a water-resistant catalyst for aldol condensation, wherein the main active component includes one or more of the oxides or salts of Cs, the active auxiliary agent is one or more of the oxides or salts of Sb, Nb, Ag, Al, and Zr, and the support includes SiO2 and a support auxiliary agent.

[0005] CN112675830A discloses an aldol condensation catalyst, which uses porous silica as a support to load metal elements, giving the catalyst excellent water resistance, anti-carbon deposition performance and long-term activity stability. It is suitable for the industrial application of methyl propionate and formaldehyde to produce methyl methacrylate via aldol condensation.

[0006] The catalysts used in existing literature on aldol condensation reactions are mostly alkaline catalysts with alkali metals supported on amorphous silica. These catalysts have poor support stability, a single active center, low activity, and low selectivity, which cannot meet the requirements of large-scale industrial production. Summary of the Invention

[0007] The purpose of this invention is to provide a catalytic material that is different from the prior art and suitable for aldol condensation reaction, and to provide its preparation method and application in aldol condensation reaction.

[0008] To achieve one of the above objectives, a first aspect of the present invention provides a modified tin-silicon molecular sieve, characterized in that it contains tin, silicon, oxygen, and alkali metal elements; the modified tin-silicon molecular sieve is characterized by XPS, and its Sn 3d 5 / 2 The center value of the spectral binding energy is located at 487.1±0.4eV, and the ratio of the peak areas of hexacoordinate tin to tetracoordinate tin is greater than 1:1.

[0009] To achieve the second objective of this invention, a second aspect of this invention provides a method for preparing modified tin-silicon molecular sieves, characterized in that the tin-silicon molecular sieve, as the starting material for modification, is mixed with an alkali metal hydroxide or salt and a solvent, and then dried and calcined to obtain modified titanium-silicon molecular sieves.

[0010] To achieve the third objective of this invention, a third aspect of this invention provides a catalyst containing modified tin-silicon molecular sieves, characterized in that it contains the modified tin-silicon molecular sieves provided in the first aspect of this invention or the modified tin-silicon molecular sieves prepared by the method provided in the second aspect of this invention, wherein the modified tin-silicon molecular sieves preferably account for 5%-100% of the weight of the catalyst containing the modified tin-silicon molecular sieves.

[0011] To achieve the fourth objective of this invention, a fourth aspect of this invention provides a method for aldol condensation, wherein a carbonyl compound having α-H undergoes a carbon-carbon bond coupling reaction with another carbonyl compound under aldol condensation reaction conditions and in the presence of a catalyst containing modified tin-silicon molecular sieves to generate a carbonyl compound having β-hydroxyl groups or a carbonyl compound having α,β-unsaturated bonds.

[0012] The modified tin-silicon molecular sieve of this invention uses alkali metals and tin as the main active components, with the alkali metals providing basic active centers and tin providing acidic active centers. The modified tin-silicon molecular sieve generates suitable catalytic active centers through the interaction between the alkali metal and tin, ensuring high conversion rates and good product selectivity in aldol condensation reactions. The preparation method of this modified tin-silicon molecular sieve is simple, involves few steps, and uses widely available raw materials, making it suitable for large-scale industrial applications while also being environmentally friendly. Attached Figure Description

[0013] Figure 1 This is the XPS spectrum of Comparative Example 2.

[0014] Figure 2 This is the XPS spectrum of Example 1.

[0015] Figure 3 The image shows the infrared spectrum of pyridine in Comparative Example 2.

[0016] Figure 4 The image shows the infrared spectrum of pyridine from Example 1. Detailed Implementation

[0017] The present invention will be described in detail below through embodiments. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the present invention.

[0018] The first aspect of this invention provides a modified tin-silicon molecular sieve, characterized in that it contains tin, silicon, oxygen, and alkali metal elements; the modified tin-silicon molecular sieve is characterized by XPS, and its Sn 3d 5 / 2 The center value of the spectral binding energy is located at 487.1±0.4 eV, and the ratio of the peak areas of hexacoordinate tin to tetracoordinate tin is greater than 1:1.

[0019] According to the present invention, its Sn 3d 5 / 2 The center value of the binding energy of the spectral peak is located at 487.1±0.4 eV, preferably 487.1±0.3 eV, further preferably 487.1±0.2 eV, and more preferably 487.1±0.1 eV. The center value of the binding energy is the binding energy corresponding to the highest point of the spectral peak.

[0020] According to the present invention, X-ray photoelectron spectroscopy (XPS) can provide the composition and valence state of atoms with a thickness of 4-5 nm on the surface of molecular sieves based on the photoelectron migration principle of atomic orbitals such as Sn(3d) and Si(2p) (Spectroscopy and Spectral Analysis, 2015, 35(12):3514-3518). For tin-silicon molecular sieves, taking the MFI structure as an example, there are framework tin atoms (tetracoordinate) and non-framework tin atoms (hexacoordinate). The center value of the binding energy of the tetracoordinate tin peak is located at 488.2±0.2 eV, and the center value of the binding energy of the hexacoordinate tin peak is located at 487.3±0.2 eV. Its Sn 3d 5 / 2 The central value of the spectral peak binding energy varies with the ratio of tetra- / hexa-coordinated tin. Generally speaking, current technologies aim for a high tetra-coordinated tin content, which is crucial for Sn 3d... 5 / 2 The center values ​​of the binding energies of the spectral peaks are between 487.5 and 488.2 eV. The higher the tetracoordinate tin content, the higher the center value of the binding energy. The modified tin-silicon molecular sieve provided by this invention has a significantly lower center value of the binding energy of the tin species peaks than that of conventional tin-silicon molecular sieves, thus its performance is superior to that of conventional tin-silicon molecular sieves. The XPS spectra of the modified tin-silicon molecular sieve of this invention are tested using conventional methods in the art.

[0021] According to the present invention, the XPS characterization results of the modified tin-silicon molecular sieve can be used to determine the ratio of hexacoordinate tin to tetracoordinate tin by peak fitting. Preferably, the ratio of the peak areas of hexacoordinate tin to tetracoordinate tin-titanium spectra is greater than 1:1, more preferably greater than 2:1, more preferably greater than 5:1, even more preferably greater than 10:1, even more preferably greater than 50:1, and most preferably greater than 100:1.

[0022] According to the present invention, the alkali metal element is selected from one or more of lithium, sodium, potassium, rubidium, and cesium, preferably potassium and / or cesium, and more preferably cesium. Preferably, the alkali metal element is uniformly dispersed in the modified tin-silicon molecular sieve.

[0023] According to the present invention, the molar ratio of the alkali metal element to the silicon element in the tin-silicon molecular sieve is (0.001-0.1):1, preferably (0.005-0.08):1, further preferably (0.006-0.06):1, more preferably (0.008-0.05):1, and most preferably (0.01-0.03):1. The molar ratio of each element in the modified tin-silicon molecular sieve of the present invention is obtained by X-ray fluorescence spectrometry (XRF).

[0024] According to the present invention, the tin-silicon molecular sieve has a tin to silicon molar ratio of (0.001-0.05):1, preferably (0.004-0.03):1, more preferably (0.006-0.02):1, and even more preferably (0.008-0.015):1. The modified tin-silicon molecular sieve of the present invention has its tin to silicon molar ratio determined by X-ray fluorescence spectrometry.

[0025] According to the present invention, the modified tin-silicon molecular sieve's framework structure type generally includes any suitable structural type or any suitable combination of structural types. Therefore, the available molecular sieve crystal structure types generally include the following crystal structures: ABW, ACO, AEI, AEL, AEN, AET, AFG, AFI, AFN, AFO, AFR, AFS, AFT, AFY, AHT, ANA, APC, APD, AST, ASV, AFX, ATN, ATO, ATS, ATT, ATV, AWO, AWW, BCT, BEA, BEC, BIK, BOF, BOG, BOZ, BPH, BRE, BSV, CAN, CAS, CDO, CFI, CGF, SCO, CFI, SGF, CGS, CHA, CHI, CLO, CON , CZP, DAC, DDR, DFO, DFT, DOH, DON, EAB, EDI, EWT, EON, EPI, ERI, ESV, ETR, EUO, FAU, FER, FRA, GIS, GIU, GME, GON, GOO, HEU, IFR, IHW, ISV, ITE , ITH, ITW, IWR, IWW, IWV, JBW, JNT, JOZ, JRY, JSN, JSR, JST, JSW, KFI, LAU, LEV, LIO, LIT, LOS, LOV, LTA, LTF, LTJ, LTL, LTN, MAR, MAZ, MEI, MEL , MEP, MER, MFI, MFS, MON, MOR, MOZ, MRT, MSE, MSO, MTF, MTN, MTT, MTW, MVY, MWF, MWW, NAB, NAT, NES, NON, NPO, NPT, NSI, OBW, OFF, OKO, OSI, OSO , OWE, PAR, PAU, PCR, PHI, PON, POR, POS, PSI, PTY, PUN, PWN, PWO, PWW, RHO, RON, RRO, RSN, RTE, RTH, RUT, RWR, RWY, SAF, SAO, SAS, SAT, SAV, SBE SBN, SBS, SBT, SFE, SFF, SFG, SFH, SFN, SFO, SFS, SFW, SGT, SIV, SOD, SOF, SOR, SOS, SOV, SSF, SSY, STF, STI, STT, STW, SVR, SVV, SWY, SYT, SSN, TER, THO, TOL, TON, TSC, TUN, UEI, UFI, UOS, UOV, UOZ, USI, UTL, UWY, VET, VFI, VNI, VSV, WEI, WEN, YFI, YUG, ZON, and hybrid structures consisting of two or more of these structural types.Alternatively, it can be an amorphous structure, including MCM-41, MCM-48, and SBA-15. More preferably, it comprises MFI, MEL, BEA, MWW, MOR, and SVR structures.

[0026] According to the present invention, the modified tin-silicon molecular sieve preferably has an MFI, MEL, or BEA crystal structure and possesses hierarchical pore characteristics. The hierarchical pore structure can be obtained through direct synthesis or post-processing of the tin-silicon molecular sieve. For example, it can be synthesized using soft or hard template agents (silanization, cellulose, carbon black, etc.), or expanded by acid or alkali treatment (e.g., by treatment with hydrochloric acid, hydrofluoric acid, ammonium bifluoride, ammonium fluoride, sodium hydroxide, potassium hydroxide, ammonia, ammonium carbonate, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, etc.). The hierarchical pore structure tin-silicon molecular sieve can be a molecular sieve containing micropores and at least one mesopore and / or macropore, wherein the micropores have a pore size less than 2 nm; the mesopores have a pore size of 2-50 nm; and the macropores have a pore size greater than 50 nm.

[0027] According to the present invention, the modified tin-silicon molecular sieve, as characterized by pyridine infrared acidity, shows that the molecular sieve has no obvious Brønsted acid and is mainly composed of Lewis acid. Its acid content at 150°C is less than 150 μmol / g, preferably less than 110 μmol / g, more preferably less than 80 μmol / g, more preferably less than 40 μmol / g, even more preferably less than 20 μmol / g, for example, less than 10 μmol / g, less than 5 μmol / g, and most preferably, 0 μmol / g at 150°C; its acid content at 50°C is less than 280 μmol / g, preferably less than 250 μmol / g, more preferably less than 220 μmol / g, more preferably less than 200 μmol / g, even more preferably less than 180 μmol / g, and most preferably less than 160 μmol / g. The pyridine infrared method is a conventional method for characterizing the acidity of catalysts. Pyridine adsorbs onto Brønsted (B) and Lewis (L) acids in the catalyst, generating different vibrations in the infrared spectrum, which can then be used for quantitative characterization of acidity. Conventional pyridine infrared characterization measures the acidity of samples at 200°C and above. Since the modified tin-silicon molecular sieve of this invention has a relatively low acidity, it needs to be measured at a lower temperature.

[0028] According to the present invention, the modified tin-silicon molecular sieve, characterized by NMR silicon spectroscopy, can reveal Q. 4 With Q 3 The ratio of signal peak height is greater than 100:1, preferably 150:1, further preferably 200:1, even more preferably 250:1, more preferably 300:1, and most preferably no Q. 3 Signal peak. In NMR silicon spectra, Q 4(-113ppm) represents the Si(OSi)4 species, Q 3 (-103ppm) represents Si(OSi)3(OH) species. The modified tin-silicon molecular sieve provided by this invention has a low Q 3 The signal intensity of silicon species indicates that it has fewer defect sites and more uniformly dispersed active centers, which is more conducive to catalytic reactions.

[0029] The second aspect of the present invention provides a method for preparing modified tin-silicon molecular sieves, which involves mixing tin-silicon molecular sieves, which are used as starting materials for modification, with alkali metal hydroxides or salts and solvents, and then drying and calcining them to obtain modified tin-silicon molecular sieves.

[0030] According to the preparation method of the present invention, the mixing treatment method in the preparation method of the alkali metal modified tin-silicon molecular sieve can be one or more of the following methods: impregnation, ion exchange, spraying, solid-phase ion exchange, and grinding, and can be reused multiple times. Since grinding allows for better contact between the alkali metal and the tin-silicon molecular sieve compared to other methods, resulting in a grinding chemical reaction, it is more conducive to the formation of catalytic active centers in the modified tin-silicon molecular sieve of the present invention; therefore, grinding is preferred.

[0031] According to the preparation method of the present invention, the tin-silicon molecular sieve used as the starting modified raw material can be obtained by hydrothermal synthesis or post-synthesis. The post-synthesis method can be a rearrangement method, a silicon-aluminum molecular sieve dealuminization and tin insertion method, a silicon-boron molecular sieve deboronization and tin insertion method, a silicon-germanium molecular sieve degermaniumization and tin insertion method, etc., and can be a liquid-phase tin insertion method or a gas-phase tin insertion method. The present invention has no particular limitations, but preferably uses the tin-silicon molecular sieve obtained by hydrothermal synthesis as the starting modified raw material.

[0032] According to the preparation method of the present invention, the tin-silicon molecular sieve used as the starting modified raw material has a preferred molar ratio of tin to silicon of (0.001-0.05):1, a more preferred ratio of (0.004-0.03):1, a more preferred ratio of (0.006-0.02):1, and a most preferred ratio of (0.008-0.015):1.

[0033] According to the preparation method of the present invention, the tin-silicon molecular sieve used as the starting modified raw material preferably has tin species mainly existing in a four-coordinate form, for example, a four-coordinate tin / six-coordinate tin ratio greater than 1:1, preferably greater than 2:1, further preferably greater than 5:1, more preferably greater than 10:1, even more preferably greater than 20:1, and most preferably entirely four-coordinate tin. The coordination state of tin can be confirmed by XPS or UV-Vis. The determination of the tin coordination state and content is a conventional method and will not be elaborated further in this invention.

[0034] According to the preparation method of the present invention, the tin-silicon molecular sieve used as the starting modified raw material preferably has a framework structure of crystal structures such as MFI, MEL, MWW, BEA, MOR, and SVR, or amorphous structures such as MCM-41, MCM-48, and SBA-15. It is more preferably one or more crystal structures of MFI, MEL, and BEA, and even more preferably one or more crystal structures of MFI and MEL with hierarchical pores.

[0035] According to the preparation method of the present invention, the alkali metal is selected from one or more of lithium, sodium, potassium, rubidium, and cesium. Sodium, potassium, and cesium are preferred, potassium and / or cesium are more preferred, and cesium is most preferred.

[0036] The alkali metal salts mentioned include alkali metal hydrochlorides, hypochlorites, chlorites, metachlorites, perchlorates, nitrates, sulfates, bisulfates, sulfites, bisulfites, phosphates, hydrogen phosphates, dihydrogen phosphates, high phosphates, metaphosphates, phosphites, hypophosphates, carboxylates, pyrophosphates, ammonium salts, and C1-C... 20 It is one or more of the carboxylates. Preferred alkali metal salts are nitrates and carbonates. Examples of the alkali metal hydroxides or salts include, but are not limited to, one or more of cesium hydroxide, cesium nitrate, cesium carbonate, cesium bicarbonate, and cesium acetate.

[0037] According to the preparation method of the present invention, the molar ratio of the alkali metal element to the silicon element in the tin-silicon molecular sieve used as the starting modified raw material is (0.001-0.1):1, preferably (0.005-0.08):1, more preferably (0.005-0.06):1, even more preferably (0.008-0.05):1, and more preferably (0.01-0.03):1.

[0038] According to the preparation method of the present invention, the solvent is an inorganic solvent or an organic solvent. The inorganic solvent includes water; the organic solvent may be selected from C1-C6. 10 alcohols, C3-C 10 Ketones, C2-C 10 The ester can be an aliphatic or aromatic solvent, or a chlorinated solvent, such as one or more of chloromethane, dichloromethane, trichloromethane, carbon tetrachloride, chloroethane, dichloroethane, trichloroethane, and tetrachloroethane. Preferred C1-C... 10The alcohol is a C1-C6 alkanol, such as methanol, ethanol, propanol, and isopropanol, preferably methanol. The amount of inorganic or organic solvent added depends on the carrier. Preferably, the solvent is at least one selected from water, methanol, ethanol, propanol, chloromethane, dichloromethane, and trichloromethane. The molar ratio of the tin-silicon molecular sieve (based on SiO2) used as the starting material for modification to the solvent is 1:(0-10), preferably 1:(1-8), more preferably 1:(1.5-6), and most preferably 1:(1.5-4).

[0039] According to the preparation method of the present invention, the mixing treatment is carried out at 20-150°C for 5-120 min, preferably at 25-100°C for 5-60 min, and more preferably at 30-70°C for 10-30 min.

[0040] According to the preparation method of the present invention, the mixing treatment is preferably carried out at a pressure (absolute pressure) of 10-100 kPa, more preferably 20-80 kPa, and even more preferably 30-50 kPa. Performing the treatment under a certain vacuum degree is more conducive to the dispersion of alkali metals in tin-silicon molecular sieves, forming a better interaction between tin and alkali metals. The treatment process can be carried out on equipment that meets the processing requirements, such as a vacuum glove box or a ball mill with vacuum.

[0041] According to the preparation method of the present invention, after solvent mixing, the solvent needs to be removed. Methods for removing the solvent include pressurized evaporation, atmospheric pressure evaporation, reduced pressure evaporation, filtration, centrifugation, sedimentation, etc., and the present invention does not have any particular limitations.

[0042] According to the preparation method of the present invention, the drying is preferably carried out at a temperature range of 60-150℃, more preferably 90-140℃, and more preferably 100-130℃; the drying time is preferably 0.5-24h, more preferably 1-12h, and more preferably 2-6h. The calcination is preferably carried out at 250-700℃ for 0.5-24h, and more preferably at 350-550℃ for 1-12h. The calcination atmosphere is preferably an oxygen-containing atmosphere, and more preferably an air atmosphere; the calcination temperature is determined according to the decomposition temperature of the alkali element precursor of the modifier. Calcination is preferably carried out at a temperature below 550℃, and a more preferred calcination temperature is 400-500℃ to prevent decomposition of the alkali element precursor. To prevent significant changes in the carrier structure or specific surface area, the calcination time is further preferably 3-8h.

[0043] A third aspect of the present invention provides a modified tin-silicon molecular sieve obtained by the above preparation method.

[0044] A fourth aspect of the present invention provides a tin-silicon molecular sieve catalyst, which contains either the modified tin-silicon molecular sieve of the first aspect of the present invention or the modified tin-silicon molecular sieve obtained by the preparation method described in the third aspect of the present invention. Further, the modified tin-silicon molecular sieve accounts for 5%-100% of the weight of the tin-silicon molecular sieve catalyst.

[0045] The fifth aspect of the present invention provides a method for aldol condensation, characterized in that a carbonyl compound having α-H undergoes a carbon-carbon coupling reaction with another carbonyl compound to generate a carbonyl compound having β-hydroxyl groups or a carbonyl compound having α,β-unsaturated bonds, using the tin-silicon molecular sieve catalyst provided in the fourth aspect above as a catalyst.

[0046] The α and β positions refer to the carbon atoms at the first and second adjacent positions of functional groups in hydrocarbon molecules, such as carbonyl, hydroxyl, and carboxyl groups. The carbonyl-containing compounds include first carbonyl compounds and second carbonyl compounds, preferably with a C1-C2 carbon atom number. 20 Carbonyl compounds may include the following structures:

[0047] C1-C 12 Alkyl groups, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, sec-pentyl, neopentyl, 1,2-dimethylpropyl, isopentyl, n-hexyl, isohexyl, sec-hexyl, n-heptyl, isoheptyl, n-octyl, n-nonyl, n-decyl, and n-dodecyl; preferably C1-C6 alkyl groups, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, sec-pentyl, neopentyl, 1,2-dimethylpropyl, isopentyl, n-hexyl, isohexyl, sec-hexyl, and particularly preferably C1-C4 alkyl groups, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, and tert-butyl.

[0048] C3-C 12 Cycloalkyl groups, such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl, cycloundecyl, and cyclododecyl; preferably cyclopentyl, cyclohexyl, and cycloheptyl.

[0049] Examples of substituted cycloalkyl groups are: 2-methylcyclopentyl, 3-methylcyclopentyl, 2-methylcyclohexyl, 3-methylcyclohexyl, 4-methylcyclohexyl, 2-methoxycyclopentyl, 2-chlorocyclopentyl, 2-methylthiocyclohexyl and other derivatives.

[0050] C7-C 13 Aryl alkyl group, preferably C7-C 12Phenylalkyl groups, such as benzyl, 1-phenylethyl, 2-phenylethyl, 1-phenylpropyl, 2-phenylpropyl, 3-phenylpropyl, 1-phenylbutyl, 2-phenylbutyl, 3-phenylbutyl and 4-phenylbutyl, with benzyl being particularly preferred;

[0051] C6-C 14 Aryl groups, such as phenyl, 1-naphthyl, 2-naphthyl, 1-anthrayl, 2-anthrayl, 9-anthrayl, 1-phenanthyl, 2-phenanthyl, 3-phenanthyl, 4-phenanthyl, 9-phenanthyl, preferably phenyl, are either unsubstituted or substituted with one or more of the following groups:

[0052] C1-C 12 Alkyl groups, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, sec-pentyl, neopentyl, 1,2-dimethylpropyl, isopentyl, n-hexyl, isohexyl, sec-hexyl, n-heptyl, isoheptyl, n-octyl, n-nonyl, n-decyl, and n-dodecyl; preferably C1-C6 alkyl groups, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, sec-pentyl, neopentyl, 1,2-dimethylpropyl, isopentyl, n-hexyl, isohexyl, sec-hexyl, and particularly preferably C1-C4 alkyl groups, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, and tert-butyl.

[0053] Halogens, such as fluorine, chlorine, bromine, and iodine, with chlorine being preferred.

[0054] C1-C 12 Alkoxy groups, preferably C1-C6 alkoxy groups, such as methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy, tert-butoxy, n-pentoxy, isopentoxy, n-hexoxy, and isohexoxy, with methoxy, ethoxy, n-propoxy, and n-butoxy being particularly preferred.

[0055] Preferably, the first carbonyl compound contains α-H, and the second carbonyl compound may or may not contain α-H. More preferably, the carbonyl compound without α-H is formaldehyde, benzaldehyde, furfural, 5-hydroxyfurfural, 5-methylfurfural, or a derivative thereof, with formaldehyde being even more preferred; the carbonyl compound containing α-H is preferably at least one of acetaldehyde, propionaldehyde, acetone, butyraldehyde, butanone, pentanal, pentanone, hexanal, hexanone, cyclohexanone, cyclopentanone, acetic acid, propionic acid, malonic acid, butyric acid, succinic acid, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, cyclohexyl acetate, methyl propionate, ethyl propionate, butyl propionate, dimethyl malonate, methyl butyrate, dimethyl succinate, ethyl butyrate, or a derivative thereof.

[0056] According to the aldol condensation method of the present invention, the molar ratio of the first carbonyl compound to the second carbonyl compound is preferably 1:(0.1-10), more preferably 1:(0.2-6), more preferably 1:(0.4-4), more preferably 1:(0.8-3), and even more preferably 1:(1-2).

[0057] According to the aldol condensation method of the present invention, the carbonyl compound mixture stream may further contain one or more diluents. The diluent includes at least one selected from alcohols, ethers, alkanes, haloalkanes, and toluene; preferred diluents are methanol, cycloalkanes, diethyl ether, and toluene. The molar ratio of diluent to carbonyl compound is (30-0.5):1, preferably (20-0.7):1, further preferably (10-0.8):1, more preferably (5-0.9):1, and most preferably (3-1):1.

[0058] According to the aldol condensation method of the present invention, the aldol condensation reaction can be carried out in an atmosphere containing at least one gas selected from N2, He, Ar, CH4, C2H6, H2, CO, and CO2, with N2 being the preferred atmosphere.

[0059] According to the aldol condensation method of the present invention, the aldol condensation reaction temperature is 200-500°C, preferably 250-480°C, and more preferably 300-400°C. Before the reaction, it is preferable to raise the temperature of the mixture to between 250-400°C, more preferably between 300-400°C; the reaction pressure (gauge pressure) is 0-2.5 MPa, preferably 0.2-1.5 MPa, and more preferably 0.5-1.0 MPa; and the reaction liquid hourly space velocity (HLS) is 0.05-5 h⁻¹, based on the total mass of the carbonyl compound and the diluent. -1 Further optimization of 0.08-3h -1 More preferably 0.1-2h -1 Space velocity should be understood as mass space velocity, which refers to the ratio of the total mass flow rate (unit: mass / time) of the carbonyl compound and diluent to the mass of the catalyst. Therefore, the unit of space velocity is h. -1 .

[0060] The inventors have discovered that the catalyst of this invention can surprisingly and significantly improve the activity and selectivity for the condensation of methylene sources such as formaldehyde with carboxylic acids or hydrocarbon esters such as methyl acetate to form olefinically unsaturated carboxylic acid esters. The formaldehyde source is anhydrous formaldehyde, preferably methylal, trioxymethylene, or oligooxymethylene.

[0061] In one specific embodiment, the conditions for the aldol condensation reaction of formaldehyde and methyl acetate include: a molar ratio of methyl acetate to formaldehyde of 1:2 to 1:1, a molar ratio of methanol to methyl acetate of 1:1 to 2:1, a reaction temperature of 320 to 400°C, a reaction pressure (gauge pressure) of 0 to 1 MPa, a nitrogen flow rate of 30 to 100 mL / min, and a liquid hourly space velocity of 0.1 to 2 h⁻¹. -1 .

[0062] In another specific embodiment, the aldol condensation reaction conditions for formaldehyde and methyl propionate include: a molar ratio of methyl propionate to formaldehyde of 1:2 to 1:0.2, a molar ratio of methanol to methyl propionate of 1:1 to 5:1, a reaction temperature of 320 to 400°C, a reaction pressure (gauge pressure) of 0 to 1 MPa, a nitrogen flow rate of 30 to 100 mL / min, and a liquid hourly space velocity of 0.1 to 2 h⁻¹. -1 .

[0063] The aldol condensation method according to the present invention can be carried out in a fixed-bed reactor, a fluidized-bed reactor, a microchannel reactor, or a batch reactor. Those skilled in the art will understand that, depending on the reactor used, the catalyst of the present invention can be modified tin-silicon molecular sieve powder or a shaped catalyst formed from modified tin-silicon molecular sieve. The separation of reaction products from the catalyst can be achieved in various ways. For example, when using powder as the catalyst, product separation and catalyst recovery and reuse can be achieved through sedimentation, filtration, centrifugation, evaporation, membrane separation, etc.; shaped catalysts are loaded into a fixed-bed reactor, and the catalyst is recovered after the reaction is completed. Various methods for catalyst separation and recovery are widely discussed in existing literature and will not be elaborated upon here.

[0064] The present invention will be described in detail below through examples.

[0065] The XPS characterization of the samples was performed using an ESCALAB 250 X-ray photoelectron spectrometer manufactured by Thermo Fisher Scientific. The testing conditions were monochromatic Al Kα X-rays at an energy of 1486.6 eV and a power of 150 W, with the C1s peak (284.8 eV) of contaminated carbon used to correct for charge shift.

[0066] The sample 29 The Si MAS NMR characterization instrument was an AVANCEⅢ 600WB nuclear magnetic resonance spectrometer, employing a 7mm dual-resonance probe, a Ф4mm SnO2 rotor, and manufactured by Bruker. Tests were conducted at room temperature, with a resonance frequency of 99.3MHz, a magic angle rotation speed of 5kHz, a pulse width of 2.73μs, a cycle delay of 5.0s, approximately 500 scans, and heavy water field locking.

[0067] The pyridine infrared adsorption spectrum (Py-IR) of the sample was obtained using an FTS3000 Fourier transform infrared spectrometer manufactured by Bio-Rad Systems, Inc., USA. The sample was compressed into a pellet and sealed in the in-situ cell of the infrared spectrometer. A vacuum of 10⁻³ Pa was applied at 350 °C and maintained for 1 hour to allow complete desorption of gas molecules from the sample surface. After cooling to room temperature, pyridine vapor at a pressure of 2.67 Pa was introduced into the in-situ cell. After equilibration for 30 minutes, the temperature was raised to 50 °C, and a vacuum of 10⁻³ Pa was applied again and maintained for 30 minutes. The sample was then cooled to room temperature and analyzed at 1400–1700 cm⁻¹. -1 The infrared absorption spectrum of pyridine adsorption at 50℃ was recorded by scanning within the wavenumber range. The sample was then transferred from the infrared absorption cell to the heat treatment zone, heated to 150℃, evacuated to 10⁻³ Pa, held for 30 min, cooled to room temperature, and the infrared spectrum of pyridine adsorption at 150℃ was recorded. The wavelength range was 1450±5 cm⁻¹. -1 The peak at 1540 cm⁻¹ is produced by the reaction of the L acid center with pyridine. -1 The peak at that point is produced by the reaction of Brønsted acid and pyridine.

[0068] The aldol condensation method is illustrated using the aldol condensation of methyl propionate and formaldehyde to synthesize methyl acrylate as an example. An atmospheric pressure fixed-bed reactor is used, with a molar ratio of methyl propionate to formaldehyde of 1:1, methanol as the solvent, and a molar ratio of methyl propionate to methanol of 1:2. The feed space velocity of the feed mixture is 1 h⁻¹. -1 The catalyst dosage was 5g; the carrier gas (N2) flow rate was maintained at 50mL / min during the reaction, and the reaction temperature was 350℃. The product was condensed and then subjected to chromatographic analysis. Unless otherwise specified, the raw materials used in the examples of this application were all purchased commercially. The composition of the reaction product was analyzed by gas chromatography, and the results were quantified using the external standard method. The chromatographic analysis conditions were as follows: Agilent-6890 chromatograph, HP-5 capillary column, injection volume 0.5μL, injection port temperature 280℃. The column temperature was maintained at 100℃ for 2min, then increased to 200℃ at a rate of 15℃ / min and held for 3min. An FID detector was used, with a detector temperature of 300℃.

[0069] The conversion rate and selectivity were calculated as follows in the example:

[0070]

[0071]

[0072] Comparative Example 1

[0073] Preparation of SiO2: Mix 100 mL of water with tetraethyl silicate at room temperature, add ammonia dropwise to the mixture until pH = 13, stir at 50 °C for 30 min, filter the hydrolyzed silica, dry in a drying oven at 110 °C overnight, cool to room temperature and grind to obtain carrier amorphous silica.

[0074] The specific steps for the Cs / SiO2 catalyst are as follows: A certain amount of cesium hydroxide was weighed and dissolved in deionized water, and then SiO2 was impregnated in the cesium hydroxide solution. The molar ratio of cesium to silicon was 0.02, and the molar ratio of SiO2 (based on silicon dioxide) to solvent was 1:50. The impregnation was performed at 100 kPa absolute pressure and 30°C for 30 min to ensure uniform distribution of cesium ions on the silicon dioxide. The solvent was then evaporated, and the catalyst was dried in a drying oven at 110°C for 6 h, followed by calcination in a muffle furnace at 400°C for 6 h to obtain the catalyst. The catalyst was characterized and evaluated, and the results are shown in Table 1.

[0075] Comparative Example 2

[0076] The preparation steps of Sn-MFI molecular sieve are as follows: Tetraethyl orthosilicate (TEOS), stannous chloride, and tetrapropylammonium hydroxide (TPAOH, 25 wt%) solution were mixed at a molar ratio of SiO2:0.015SnO2:0.3TPAOH:30H2O, and stirred for 15 minutes. Water was then added to the liquid, and the mixture was stirred at 348-353 K for about 3 hours to obtain a clear sol. The sol was then crystallized at 170 °C for 3 days. The resulting solid was filtered, washed with distilled water, dried at 120 °C for 5 hours, and then calcined at 550 °C for 5 hours to obtain the Sn-MFI molecular sieve. The XPS spectrum and pyridine infrared spectrum are shown below. Figure 1 and Figure 3 The characterization and evaluation results are shown in Table 1. Among them, the peak center value of tin in XPS is 488 eV, and all of them are tetracoordinated tin species.

[0077] Comparative Example 3

[0078] The preparation steps of Sn-MEL molecular sieve are as follows: Tetraethyl orthosilicate (TEOS), tin tetrachloride, and tetrabutylammonium hydroxide (TBAOH, 40 wt%) solution were mixed at a molar ratio of SiO2:0.01SnO2:0.3TBAOH:30H2O. After stirring for 15 minutes, water was added to the liquid, and the mixture was stirred at 348-353 K for about 3 hours to obtain a clear sol. The sol was then crystallized at 443 K for 3 days. The resulting solid was filtered, washed with distilled water, dried at 373 K for 5 hours, and then calcined at 823 K for 5 hours to obtain the Sn-MEL molecular sieve. The results are shown in Table 1. The XPS peak center value of tin was 487.7 eV, and the ratio of hexacoordinate tin to tetracoordinate tin was less than 1.

[0079] Example 1

[0080] The specific steps for the Cs / Sn-MFI catalyst are as follows: A certain amount of cesium hydroxide was weighed and dissolved in deionized water. Then, Sn-MFI from Comparative Example 2 was mixed with the cesium hydroxide solution. The molar ratio of cesium to silicon was 0.02, and the molar ratio of Sn-MFI (based on silica) to solvent was 1:3. The mixture was ground for 30 min under absolute pressure of 50 kPa and 30 °C to ensure uniform distribution of cesium ions on the Sn-MFI. The solvent was then evaporated, and the mixture was dried in a drying oven at 110 °C for 6 h. Finally, it was calcined in a muffle furnace at 400 °C for 6 h to obtain the catalyst. The catalyst was characterized and evaluated; the XPS spectrum and pyridine infrared spectrum are shown below. Figure 2 and Figure 4 The characterization and evaluation results are shown in Table 1.

[0081] Example 2

[0082] The specific steps for the Cs / Sn-MFI catalyst are as follows: A certain amount of cesium nitrate was weighed and dissolved in deionized water. Then, Sn-MFI from Comparative Example 2 was mixed with the cesium nitrate solution. The molar ratio of cesium to silicon was 0.04, and the molar ratio of Sn-MFI (based on silica) to solvent was 1:8. The mixture was ground for 50 min at an absolute pressure of 100 kPa and 25 °C to ensure uniform distribution of cesium ions on the Sn-MFI. The solvent was then evaporated, and the mixture was dried in a drying oven at 110 °C for 3 h. Finally, it was calcined in a muffle furnace at 450 °C for 6 h to obtain the catalyst. The catalyst was characterized and evaluated, and the results are shown in Table 1.

[0083] Example 3

[0084] The specific steps for the Cs / Sn-MFI catalyst are as follows: A certain amount of cesium hydroxide was weighed and dissolved in isopropanol, and then Sn-MFI from Comparative Example 2 was mixed with the cesium hydroxide solution. The molar ratio of cesium to silicon was 0.035, and the molar ratio of Sn-MFI (based on silica) to solvent was 1:6. The mixture was ground for 60 min at absolute pressure of 80 kPa and 70 °C to ensure uniform distribution of cesium ions on the Sn-MFI. The solvent was then evaporated, and the mixture was dried in a drying oven at 110 °C for 6 h, followed by calcination in a muffle furnace at 400 °C for 6 h to obtain the catalyst. The catalyst was characterized and evaluated, and the results are shown in Table 1.

[0085] Example 4

[0086] The specific steps for the Cs / Sn-MFI catalyst are as follows: A certain amount of cesium acetate was weighed and dissolved in deionized water, and then Sn-MFI from Comparative Example 2 was mixed with the cesium acetate solution. The molar ratio of cesium to silicon was 0.015, and the molar ratio of Sn-MFI (based on silica) to solvent was 1:2. The mixture was ground for 30 min under absolute pressure of 30 kPa and 40 °C to ensure uniform distribution of cesium ions on the Sn-MFI. The solvent was then evaporated, and the mixture was dried in a drying oven at 110 °C for 6 h, followed by calcination in a muffle furnace at 430 °C for 6 h to obtain the catalyst. The catalyst was characterized and evaluated, and the results are shown in Table 1.

[0087] Example 5

[0088] The specific steps for the Cs / Sn-MFI catalyst are as follows: A certain amount of cesium nitrate was weighed and dissolved in deionized water. Then, Sn-MFI from Comparative Example 2 was mixed with a cesium acetate solution. The molar ratio of cesium to silicon was 0.02, and the molar ratio of Sn-MFI (based on silica) to solvent was 1:4. The mixture was ground for 10 min at an absolute pressure of 40 kPa and 60 °C to ensure uniform distribution of cesium ions on the Sn-MFI. The solvent was then evaporated, and the mixture was dried in a drying oven at 110 °C for 6 h. Finally, it was calcined in a muffle furnace at 400 °C for 6 h to obtain the catalyst. The catalyst was characterized and evaluated; the results are shown in Table 1.

[0089] Example 6

[0090] The specific steps for the Cs / Sn-MEL catalyst are as follows: A certain amount of cesium hydroxide was weighed and dissolved in deionized water, and then Sn-MEL from Comparative Example 3 was mixed with the cesium hydroxide solution. The molar ratio of cesium to silicon was 0.02, and the molar ratio of Sn-MEL (based on silicon dioxide) to solvent was 1:5. The mixture was ground for 30 min at an absolute pressure of 80 kPa and 30 °C to ensure uniform distribution of cesium ions on the Sn-MEL. The solvent was then evaporated, and the mixture was dried in a drying oven at 120 °C for 6 h, followed by calcination in a muffle furnace at 400 °C for 6 h to obtain the catalyst. The catalyst was characterized and evaluated, and the results are shown in Table 1.

[0091] Comparative Example 4

[0092] Following the method described in Example 1 of Chinese Patent CN1301599A, the Sn-MFI molecular sieve of Comparative Example 2 was rearranged and expanded to prepare Sn-MFI-R molecular sieve. The preparation steps are as follows: Sn-MFI, tetrapropylammonium hydroxide, and water were mixed at a weight ratio of 1:0.4:15, and then treated at 170°C under autogenous pressure for 24 hours. The resulting solid was then filtered, washed with distilled water, dried at 120°C for 5 hours, and then calcined at 550°C for 5 hours to obtain the Sn-MFI-R molecular sieve. The catalyst was subjected to standard evaluation, and the characterization and evaluation results are shown in Table 1. XPS analysis showed that the binding energy center value of the tin species peak was 487.7 eV, and the ratio of hexacoordinate tin to tetracoordinate tin was 0.55:1.

[0093] Comparative Example 5

[0094] The specific steps for obtaining the Cs / SBA-15 catalyst are as follows: A certain amount of cesium hydroxide was weighed and dissolved in deionized water, and then SBA-15 molecular sieves were impregnated in the cesium hydroxide solution. The molar ratio of cesium to silicon was 0.02, and the molar ratio of SBA-15 (based on silica) to solvent was 1:50. The impregnation was performed at 100 kPa absolute pressure and 30°C for 30 min to ensure uniform distribution of cesium ions on the SBA-15. The solvent was then evaporated, and the catalyst was dried at 110°C for 6 h in a drying oven, followed by calcination at 400°C in a muffle furnace for 6 h to obtain the catalyst. The catalyst was characterized and evaluated, and the results are shown in Table 1.

[0095] Example 7

[0096] The preparation steps of the Cs / Sn-MFI-R catalyst are as follows: A certain amount of cesium hydroxide was weighed and dissolved in deionized water, and then Sn-MFI-R was mixed with the cesium hydroxide solution. The molar ratio of cesium to silicon was 0.02, and the molar ratio of Sn-MFI-R (based on silicon dioxide) to solvent was 1:3. The mixture was ground for 30 min at an absolute pressure of 50 kPa and 30 °C to ensure uniform distribution of cesium ions on Sn-MFI-R. The solvent was then evaporated, and the mixture was dried in a drying oven at 110 °C for 6 h, followed by calcination in a muffle furnace at 400 °C for 6 h to obtain the catalyst. The catalyst was characterized and evaluated, and the results are shown in Table 1.

[0097] Example 8

[0098] The preparation steps of the Cs / Sn-MFI-R catalyst are as follows: A certain amount of cesium hydroxide was weighed and dissolved in deionized water, and then Sn-MFI-R was mixed with the cesium hydroxide solution. The molar ratio of cesium to silicon was 0.03, and the molar ratio of Sn-MFI-R (based on silicon dioxide) to solvent was 1:4. The mixture was ground for 20 min at an absolute pressure of 50 kPa and 50 °C to ensure uniform distribution of cesium ions on Sn-MFI-R. The solvent was then evaporated, and the mixture was dried in a drying oven at 110 °C for 6 h, followed by calcination in a muffle furnace at 450 °C for 6 h to obtain the catalyst. The catalyst was characterized and evaluated, and the results are shown in Table 1.

[0099] Example 9

[0100] The preparation steps of the Cs / Sn-MFI-R catalyst are as follows: A certain amount of cesium nitrate was weighed and dissolved in deionized water, and then Sn-MFI-R was mixed with the cesium nitrate solution. The molar ratio of cesium to silicon was 0.03, and the molar ratio of Sn-MFI-R (based on silicon dioxide) to solvent was 1:3. The mixture was ground for 30 min under absolute pressure of 40 kPa and 60 °C to ensure uniform distribution of cesium ions on Sn-MFI-R. The solvent was then evaporated, and the mixture was dried in a drying oven at 110 °C for 6 h, followed by calcination in a muffle furnace at 400 °C for 6 h to obtain the catalyst. The catalyst was characterized and evaluated, and the results are shown in Table 1.

[0101] Example 10

[0102] The preparation steps of the Cs / Sn-MFI-R catalyst are as follows: A certain amount of cesium acetate was weighed and dissolved in ethanol, and then Sn-MFI-R was mixed with the cesium acetate solution. The molar ratio of cesium to silicon was 0.02, and the molar ratio of Sn-MFI-R (based on silicon dioxide) to solvent was 1:2. The mixture was ground for 10 min at an absolute pressure of 30 kPa and 70 °C to ensure uniform distribution of cesium ions on Sn-MFI-R. The solvent was then evaporated, and the mixture was dried in a drying oven at 110 °C for 3 h, followed by calcination in a muffle furnace at 400 °C for 6 h to obtain the catalyst. The catalyst was characterized and evaluated, and the results are shown in Table 1.

[0103] Table 1

[0104]

[0105] GC-MS characterization analysis showed that the main product of the embodiments of the present invention was methyl methacrylate, and the main byproducts were methacrolein, methyl dimethylpentenoate, etc., while the main product of the comparative example was methyl methacrylate, and the main byproducts were propionic acid, methyl isobutyrate, methyl methylbutyrate, methyl hexanoate, etc.

[0106] A comparison of Examples 1-10 with Comparative Examples 1-5 shows that the Sn element binding energy center value of the modified tin-silicon molecular sieve of the present invention is significantly lower than that of conventional tin-silicon molecular sieves. Furthermore, the molecular sieve contains only L-acid, and the acid content at 50℃ and 150℃ is significantly lower than that of conventional tin-silicon molecular sieves, with no significant Q-value. 3 Silicon NMR peaks. Using this modified tin-silicon molecular sieve as a catalyst for the aldol condensation reaction of formaldehyde and methyl propionate, it exhibits good methyl propionate conversion and selectivity for the target product methyl methacrylate. Moreover, the catalytic performance is further improved after the molecular sieve is expanded to have a hierarchical pore structure.

Claims

1. A method for aldol condensation, comprising reacting a carbonyl-containing compound having α-H with another carbonyl-containing compound in the presence of a catalyst via a carbon-carbon coupling reaction to generate a carbonyl-containing compound having β-hydroxyl groups or a carbonyl-containing compound having α,β-unsaturated bonds, characterized in that, The catalyst is a modified tin-silicon molecular sieve; the modified tin-silicon molecular sieve contains tin, silicon, oxygen, and an alkali metal element, wherein the alkali metal element is cesium, the molar ratio of tin to silicon is (0.008-0.015):1, and the molar ratio of the alkali metal element to silicon in the tin-silicon molecular sieve is (0.008-0.05):1; the modified tin-silicon molecular sieve is characterized by XPS, and its Sn 3d 5 / 2 The central value of the binding energy of the spectral peaks is located at 487.1±0.2 eV, and the ratio of the peak areas of hexacoordinate tin to tetracoordinate tin is greater than 50:1; acidity characterization by pyridine infrared spectroscopy shows that the acidity at 150℃ is less than 10 μmol / g, and the acidity at 50℃ is less than 180 μmol / g; NMR silicon spectroscopy characterization shows that Q... 4 With Q 3 The ratio of signal peak height to peak height is greater than 200:1, Q 4 Representing the Si(OSi)4 species, Q 3 Represents the Si(OSi)3(OH) species; the modified tin-silicon molecular sieve has a crystal structure selected from at least one of MFI and MEL.

2. The method according to claim 1, characterized in that, The reaction involves the aldol condensation reaction of formaldehyde and methyl acetate. The reaction conditions include: a molar ratio of methyl acetate to formaldehyde of 1:2 to 1:1, a molar ratio of methanol to methyl acetate of 1:1 to 2:1, a reaction temperature of 320–400℃, a reaction gauge pressure of 0–1 MPa, a nitrogen flow rate of 30–100 mL / min, and a liquid hourly space velocity of 0.1–2 h⁻¹. -1 .

3. The method according to claim 1, characterized in that, The reaction conditions for the aldol condensation reaction between formaldehyde and methyl propionate include: a molar ratio of methyl propionate to formaldehyde of 1:2 to 1:0.2, a molar ratio of methanol to methyl propionate of 1:1 to 5:1, a reaction temperature of 320 to 400°C, a reaction gauge pressure of 0 to 1 MPa, a nitrogen flow rate of 30 to 100 mL / min, and a liquid hourly space velocity of 0.1 to 2 h⁻¹. -1 .

4. The method according to claim 1, characterized in that, The modified tin-silicon molecular sieve, Sn 3d 5 / 2 The center value of the spectral peak binding energy is located at 487.1±0.1eV.

5. The method according to claim 1, characterized in that, The modified tin-silicon molecular sieve has a peak area ratio of hexacoordinate tin to tetracoordinate tin greater than 100:

1.

6. The method according to claim 1, characterized in that, The modified tin-silicon molecular sieve has a molar ratio of alkali metal element to silicon element in the tin-silicon molecular sieve of (0.01-0.03):

1.

7. The method according to claim 1, characterized in that, The modified tin-silicon molecular sieve, after being characterized by pyridine infrared acidity, showed an acid content of less than 5 μmol / g at 150 °C.

8. The method according to claim 1, characterized in that, The modified tin-silicon molecular sieve, after being characterized by pyridine infrared acidity, showed an acidity of 0 μmol / g at 150°C.

9. The method according to claim 1, characterized in that, The modified tin-silicon molecular sieve, after being characterized by pyridine infrared acidity, showed an acidity of less than 160 μmol / g at 50°C.

10. The method according to claim 1, characterized in that, The modified tin-silicon molecular sieve was characterized by NMR silicon spectroscopy, Q 4 With Q 3 The ratio of signal peak height is greater than 250:

1.

11. The method according to claim 10, characterized in that, The Q 4 With Q 3 The ratio of signal peak height is greater than 300:

1.

12. The method according to claim 1, characterized in that, The modified tin-silicon molecular sieve, characterized by NMR silicon spectroscopy, did not exhibit Q. 3 Signal peak.

13. The method according to claim 1, characterized in that, The modified tin-silicon molecular sieve is prepared by mixing the tin-silicon molecular sieve, which is used as the starting material for modification, with alkali metal cesium hydroxide or salt and solvent, and then drying and calcining to obtain the modified tin-silicon molecular sieve; the mixing treatment is carried out at 30-70℃ and 30-50 KPa for 10-30 min; the mixing treatment is a grinding method.

14. The method according to claim 13, characterized in that, The tin-silicon molecular sieve used as the starting material for modification was obtained by hydrothermal synthesis.

15. The method according to claim 13, characterized in that, The alkali metal cesium salts are cesium hydrochloride, hypochlorite, chlorite, metachlorite, perchlorate, nitrate, sulfate, bisulfate, sulfite, bisulfite, phosphate, hydrogen phosphate, dihydrogen phosphate, high phosphate, metaphosphate, phosphite, hypophosphate, carboxylate, pyrophosphate, and C1-C cesium salts. 20 One or more of the carboxylates.

16. The method according to claim 13, characterized in that, The alkali metal cesium hydroxide is cesium hydroxide, and the alkali metal cesium salt is selected from one or more of cesium nitrate, cesium carbonate, cesium bicarbonate, and cesium acetate.

17. The method according to claim 13, characterized in that, The molar ratio of the tin-silicon molecular sieve (calculated as SiO2), the hydroxide or salt of alkali metal cesium (calculated as alkali metal cesium), and the solvent used as the starting modified raw material is 1:(0.001-0.1):(0-10).

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