Modified tin-silicon molecular sieve as well as preparation method and application thereof

Abstract

The modified tin-silicon molecular sieve is characterized by containing tin, silicon, oxygen and alkali metal elements, the modified tin-silicon molecular sieve is characterized by XPS, the central value of the Sn 3d5 / 2 spectral peak binding energy is 487.1 + / -0.4 eV, and the ratio of the spectral peak area of hexa-coordinated tin to the spectral peak area of tetra-coordinated tin is greater than 1: 1.

Description

Technical Field

[0001] The present invention belongs to the technical field of molecular sieves, and more specifically relates to tin silicon molecular sieves, methods for modifying molecular sieves, and applications of molecular sieves as catalysts. Background Art

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

[0003] The preparation of methyl methacrylate by direct aldol condensation of methyl propionate and formaldehyde does not use highly toxic raw materials. The raw materials are cheap and widely available, which is an important production method for methyl methacrylate in the future. It is known that the most effective aldol condensation catalyst for methyl propionate and formaldehyde is a supported catalyst with silicon dioxide as the main carrier and cesium as the main active component. The supported catalyst has low activity, the raw materials cannot be fully converted, and because the catalyst is supported by amorphous silicon dioxide, the specific surface area gradually decreases and the strength gradually weakens in the reaction system as time goes by.

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

[0005] CN112675830A discloses an aldol condensation catalyst, which uses foam porous silicon dioxide as a carrier to load metal elements, so that the catalyst has excellent water resistance, anti-carbon deposition performance and long-term activity stability, and is suitable for industrial application of preparing methyl methacrylate through aldol condensation of methyl propionate and formaldehyde.

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

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

[0008] In order to achieve one of the above objectives, the present invention provides a modified tin silicon molecular sieve in the first aspect, 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 central value of the spectral peak binding energy is located at 487.1±0.4eV, and the ratio of the spectral peak area between hexacoordinated tin and tetracoordinated tin is greater than 1:1.

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

[0010] In order to achieve the third purpose of the present invention, the third aspect of the present invention provides a catalyst containing modified tin silicon molecular sieve, characterized in that it contains the modified tin silicon molecular sieve provided by the first aspect of the present invention or the modified tin silicon molecular sieve prepared by the method provided by the second aspect of the present invention, and the weight ratio of the modified tin silicon molecular sieve to the modified tin silicon molecular sieve catalyst is preferably 5%-100%.

[0011] In order to achieve the fourth purpose of the present invention, the fourth aspect of the present invention provides a method for aldol condensation, in which a carbonyl-containing compound having an α-H undergoes a carbon-carbon bond coupling reaction with another carbonyl-containing compound under aldol condensation reaction conditions and in the presence of a catalyst containing a modified tin silicon molecular sieve to generate a carbonyl-containing compound having a β-hydroxyl group or a carbonyl-containing compound having an α,β-unsaturated bond.

[0012] The modified tin silicon molecular sieve of the present invention has alkali metal and tin as main active components, alkali metal provides alkaline active center, and tin provides acidic active center. The modified tin silicon molecular sieve generates appropriate catalytic active center through the interaction between alkali metal and tin, and has good product selectivity while ensuring high conversion rate in aldol condensation reaction. The preparation method of the modified tin silicon molecular sieve is simple, the steps are short, the raw material source is wide, it is suitable for large-scale industrial application, and it is environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[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 This is the infrared spectrum of pyridine in Comparative Example 2.

[0016] Figure 4 This is the infrared spectrum of pyridine in Example 1. DETAILED DESCRIPTION

[0017] The present invention is described in detail below by way of examples. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0018] The 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 central value of the peak binding energy is located at 487.1±0.4 eV, and the ratio of the peak area of ​​hexacoordinated tin to that of tetracoordinated tin is greater than 1:1.

[0019] According to the present invention, the Sn 3d 5 / 2 The central value of the peak binding energy 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 central value of the binding energy is the binding energy corresponding to the highest point of the peak.

[0020] According to the present invention, X-ray photoelectron spectroscopy (XPS) can give the composition and valence state of atoms with a thickness of 4 to 5 nm on the surface of the molecular sieve based on the principle of photoelectron migration of atomic orbitals such as Sn (3d) and Si (2p) (Spectroscopy and Spectral Analysis, 2015, 35 (12): 3514-3518). For tin silicon molecular sieve, taking the MFI structure as an example, there are skeleton tin atoms (four-coordinated) and non-skeleton tin atoms (six-coordinated). The central value of the binding energy of the four-coordinated tin spectrum peak is located at 488.2 ± 0.2 eV, and the central value of the binding energy of the six-coordinated tin spectrum peak is located at 487.3 ± 0.2 eV. Its Sn 3d 5 / 2 The center value of the peak binding energy varies with the ratio of tetra- / hexa-coordinated tin. Generally speaking, the existing technology pursues a high tetra-coordinated tin content. 5 / 2 The central value of the spectral peak binding energy is between 487.5 and 488.2 eV, and the higher the tetracoordinated tin content, the higher the central value of the binding energy. The modified tin silicon molecular sieve provided by the present invention has a tin species spectral peak binding energy central value significantly lower than the binding energy of the tin species in the conventional tin silicon molecular sieve, and thus, its performance is better than the conventional tin silicon molecular sieve. The XPS spectrum test of the modified tin silicon molecular sieve of the present invention is a conventional method in the art.

[0021] According to the present invention, the XPS characterization results of the modified tin silicon molecular sieve can be used to perform peak fitting to determine the ratio of hexacoordinated tin to tetracoordinated tin. Preferably, the ratio of the peak areas of the hexacoordinated tin to the tetracoordinated tin titanium spectrum is greater than 1:1, preferably greater than 2:1, more preferably greater than 5:1, further preferably greater than 10:1, further 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, 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 spectrometer analysis method (XRF).

[0024] According to the present invention, the molar ratio of tin to silicon in the tin silicon molecular sieve is (0.001-0.05): 1, preferably (0.004-0.03): 1, further preferably (0.006-0.02): 1, and more preferably (0.008-0.015): 1. The molar ratio of tin to silicon in the modified tin silicon molecular sieve of the present invention is obtained by X-ray fluorescence spectrometer analysis.

[0025] According to the present invention, the modified tin silicon molecular sieve has a framework structure type that in principle includes any suitable structure type or any suitable combination of structure types. Therefore, the available molecular sieve crystal structure types in principle include the following structural crystal types: 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 structure types.Or it is an amorphous structure, wherein the amorphous structure includes MCM-41, MCM-48, SBA-15. Further preferred are MFI, MEL, BEA, MWW, MOR, SVR structures.

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

[0027] According to the present invention, the modified tin silicon molecular sieve is characterized by pyridine infrared acidity, and the molecular sieve has no obvious B acid, and is mainly L acid. The acid amount at 150°C is less than 150μmol / g, preferably the acid amount is less than 110μmol / g, further preferably the acid amount is less than 80μmol / g, more preferably the acid amount is less than 40μmol / g, and further preferably the acid amount is less than 20μmol / g, for example, the acid amount is less than 10μmol / g, the acid amount is less than 5μmol / g, and most preferably, the acid amount at 150°C is 0μmol / g; the acid amount at 50°C is less than 280μmol / g, preferably the acid amount is less than 250μmol / g, further preferably the acid amount is less than 220μmol / g, more preferably the acid amount is less than 200μmol / g, further preferably the acid amount is less than 180μmol / g, and most preferably the acid amount is less than 160μmol / g. The pyridine infrared method is a conventional method for characterizing the acid content of catalysts. The adsorption of pyridine on the catalyst B acid and L acid produces different vibrations under the infrared spectrum, which can be used for quantitative characterization of the acid content. Conventional pyridine infrared characterization measures the acid content of the sample at 200°C and above. Since the acid content of the modified tin silicon molecular sieve of the present invention is small, it needs to be measured at a lower temperature.

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

[0029] The second aspect of the present invention provides a method for preparing a modified tin silicon molecular sieve, which comprises mixing a tin silicon molecular sieve as a starting modified raw material with an alkali metal hydroxide or salt and a solvent, and then drying and calcining the mixture to obtain the modified tin silicon molecular sieve.

[0030] According to the preparation method of the present invention, in the preparation method of the alkali metal modified tin silicon molecular sieve, the mixing treatment method can be one or more of the following methods: impregnation method, ion exchange method, spraying method, solid phase ion exchange method, grinding method, and can be reused multiple times. Since the grinding method can make the alkali metal and the tin silicon molecular sieve contact better than other methods, a grinding chemical reaction occurs, which is more conducive to the formation of the catalytic active center of the modified tin silicon molecular sieve of the present invention, the grinding method is preferably used.

[0031] According to the preparation method of the present invention, the tin silicon molecular sieve as the starting modified raw material can be obtained by a hydrothermal synthesis method or a post-synthesis method. The post-synthesis method can be a rearrangement method, a silicon aluminum molecular sieve dealumination tin insertion method, a silicon boron molecular sieve deboronation tin insertion method, a silicon germanium molecular sieve degermanium 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 limitation, and preferably uses a tin silicon molecular sieve obtained by a hydrothermal synthesis method as the starting modified raw material.

[0032] According to the preparation method of the present invention, the molar ratio of tin element to silicon element in the tin silicon molecular sieve used as the starting modified raw material is preferably (0.001-0.05):1, further preferably (0.004-0.03):1, more preferably (0.006-0.02):1, and most preferably (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 a tin species mainly in a tetracoordinated form, for example, the tetracoordinated tin / hexacoordinated tin ratio is greater than 1:1, preferably greater than 2:1, further preferably greater than 5:1, more preferably greater than 10:1, further preferably greater than 20:1, and most preferably all tetracoordinated tin. Characterization by XPS or UV-Vis can be performed to confirm the coordination state of tin, and the judgment of the coordination state and content of tin belongs to conventional methods, which will not be repeated in the present invention.

[0034] According to the preparation method of the present invention, the skeleton structure of the tin silicon molecular sieve used as the starting modified raw material is preferably selected from the crystal structures of MFI, MEL, MWW, BEA, MOR, SVR, or amorphous structures such as MCM-41, MCM-48, SBA-15, preferably one or more crystal structures of MFI, MEL, BEA, and further preferably one or more crystal structures of MFI and MEL with multi-level 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, preferably one or more of sodium, potassium and cesium, more preferably potassium and / or cesium, and most preferably cesium.

[0036] The alkali metal salts include alkali metal hydrochlorides, hypochlorites, chlorites, metachlorites, perchlorates, nitrates, sulfates, bisulfates, sulfites, bisulfites, phosphates, hydrogen phosphates, dihydrogen phosphates, high phosphates, metaphosphates, phosphites, hypophosphites, carboxylates, pyrophosphates, ammonium salts, C1-C 20 The preferred alkali metal salts are nitrates and carbonates. The alkali metal hydroxide or salts are exemplified by but 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 as the starting modified raw material is (0.001-0.1):1, preferably (0.005-0.08):1, further preferably (0.005-0.06):1, further 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 can be selected from C1-C 10 Alcohol, C3-C 10 Ketone, C2-C 10 The ester may be an aliphatic solvent or an aromatic solvent, or a chlorinated solvent, such as one or more of methyl chloride, dichloromethane, chloroform, carbon tetrachloride, ethyl chloride, dichloroethane, trichloroethane, and tetrachloroethane. 10The alcohol is a C1-C6 alkanol, such as methanol, ethanol, propanol and isopropanol, preferably methanol. The amount of the inorganic solvent or organic solvent added is calculated according to the carrier. Preferably, the solvent is preferably at least one of water, methanol, ethanol, propanol, chloroform, dichloromethane and chloroform. Wherein, the molar ratio of the tin silicon molecular sieve (calculated as SiO2) as the starting modified raw material 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 preferably has a pressure (absolute pressure) of 10-100 KPa, preferably 20-80 KPa, and more preferably 30-50 KPa. The treatment is more conducive to the dispersion of alkali metals in the tin silicon molecular sieve under a certain vacuum degree, forming a better interaction between tin and alkali metals. The treatment process can be carried out on a vacuum glove box or a vacuum ball mill or other equipment that meets the treatment requirements.

[0041] According to the preparation method of the present invention, after the solvent mixing treatment, the solvent needs to be removed. The method of removing the solvent can be pressure evaporation, normal pressure evaporation, reduced pressure evaporation, filtration, centrifugation, sedimentation, etc., and the present invention has no particular limitation.

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

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

[0044] The fourth aspect of the present invention provides a tin silicon molecular sieve catalyst, which contains the modified tin silicon molecular sieve of the first aspect of the present invention or the modified tin silicon molecular sieve prepared by the preparation method of 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-containing compound having α-H undergoes a carbon-carbon bond coupling reaction with another carbonyl-containing compound to generate a carbonyl-containing compound having a β-hydroxyl group or a carbonyl-containing compound having an α,β-unsaturated bond, using the tin silicon molecular sieve catalyst provided in the fourth aspect as a catalyst.

[0046] The α and β positions refer to the functional groups of hydrocarbon molecules, such as carbonyl, hydroxyl, carboxyl, etc., and the carbon atoms of the first ortho and second ortho positions. The carbonyl-containing compound includes the first carbonyl compound and the second carbonyl compound, and the carbon number of the carbonyl compound is preferably C1-C 20 The carbonyl compound may include the following structure:

[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, isohexyl, 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 Arylalkyl, preferably C7-C 12Phenylalkyl, such as benzyl, 1-phenylethyl, 2-phenylethyl, 1-phenylpropyl, 2-phenylpropyl, 3-phenylpropyl, 1-phenylbutyl, 2-phenylbutyl, 3-phenylbutyl and 4-phenylbutyl, particularly preferably benzyl;

[0051] C6-C 14 Aryl, for example phenyl, 1-naphthyl, 2-naphthyl, 1-anthryl, 2-anthryl, 9-anthryl, 1-phenanthrenyl, 2-phenanthrenyl, 3-phenanthrenyl, 4-phenanthrenyl, 9-phenanthrenyl, preferably phenyl, which is 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, isohexyl, sec-butyl and tert-butyl.

[0053] Halogen, such as fluorine, chlorine, bromine, iodine, preferably chlorine.

[0054] C1-C 12 Alkoxy, preferably C1-C6 alkoxy, such as methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy, tert-butoxy, n-pentoxy, isopentylpropoxy, n-hexyloxy and isohexyloxy, particularly preferably methoxy, ethoxy, n-propoxy, n-butoxy.

[0055] Preferably, the first carbonyl compound contains α-H, and the second carbonyl compound contains α-H or does not contain α-H. More preferably, the carbonyl compound that does not contain α-H is preferably formaldehyde, benzaldehyde, furfural, 5-hydroxyfurfural, 5-methylfurfural or a derivative thereof, and formaldehyde is further preferred; the carbonyl compound containing α-H is preferably acetaldehyde, propionaldehyde, acetone, butyraldehyde, butanone, valeraldehyde, 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 at least one of 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), further preferably 1:(0.2-6), more preferably 1:(0.4-4), more preferably 1:(0.8-3) and more preferably 1:(1-2).

[0057] According to the method for aldol condensation of the present invention, one or more diluents may also be included in the mixed stream of the carbonyl compound. The diluent includes at least one of alcohols, ethers, alkanes, halogenated alkanes, and toluene, and the preferred diluents are methanol, cycloalkane, ether, and toluene. The molar ratio of the diluent to the 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 the group consisting of N2, He, Ar, CH4, C2H6, H2, CO, and CO2, preferably N2.

[0059] According to the aldol condensation method of the present invention, the aldol condensation reaction temperature is 200-500°C, preferably 250-480°C, more preferably 300-400°C. Before the reaction, the temperature of the mixed solution is preferably raised to between 250-400°C, more preferably between 300-400°C; the reaction pressure (gauge pressure) is 0-2.5MPa, preferably 0.2-1.5MPa, more preferably 0.5-1.0MPa; based on the total mass of the carbonyl compound and the diluent, the reaction liquid hourly space velocity is 0.05-5h -1 , further preferably 0.08-3h -1 , more preferably 0.1-2h -1 The space velocity is understood to be the mass space velocity, which means the ratio of the mass flow rate of the sum of the mass of the carbonyl compound and the diluent (in units of (mass / time)) to the mass of the catalyst. Therefore, the unit of the space velocity is h -1 .

[0060] The inventors have found that the catalysts of the present invention are surprisingly capable of greatly improving the activity and selectivity for the condensation of a methylene source such as formaldehyde with a carboxylic acid or a hydrocarbyl ester such as methyl acetate to form an olefinically unsaturated carboxylic acid ester. The formaldehyde source is an anhydrous formaldehyde source, preferably methylal, trioxymethylene and paraformaldehyde.

[0061] In a 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 reaction liquid hourly space velocity of 0.1 to 2 h -1 .

[0062] In another specific embodiment, the conditions for the aldol condensation reaction of formaldehyde and methyl propionate include: a molar ratio of methyl propionate: formaldehyde of 1:2 to 1:0.2, a molar ratio of methanol: 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 reaction liquid hourly space velocity of 0.1 to 2 h -1 .

[0063] The method for aldol condensation according to the present invention can be carried out in a fixed bed reactor, a fluidized bed reactor, a microchannel reactor or a kettle reactor. It will be appreciated by those skilled in the art that, depending on the different reactors used, the catalyst of the present invention can be the original powder of the modified tin silicon molecular sieve, or it can be a shaped catalyst after the modified tin silicon molecular sieve is shaped. The separation of the reaction product and the catalyst can be achieved in a variety of ways. For example, when the original powder is used as the catalyst, the separation of the product and the recycling of the catalyst can be achieved by sedimentation, filtration, centrifugation, evaporation, membrane separation and the like; the shaped catalyst is loaded in a fixed bed reactor, and the catalyst is recovered after the reaction is completed. The separation and recovery methods of various catalysts are widely involved in the existing literature and will not be described here.

[0064] The present invention is described in detail below by way of examples.

[0065] The XPS characterization experimental instrument of the sample is an ESCALAB 250 X-ray photoelectron spectrometer produced by Thermo Fisher Scientific. The test conditions are monochromatic Al Kα X-ray, energy 1486.6 eV, power 150 W, and the C1s peak (284.8 eV) of contaminated carbon is used to correct the charge shift.

[0066] Sample 29 Si MAS NMR characterization instrument is AVANCEⅢ600WB nuclear magnetic resonance spectrometer, using 7mm double resonance probe, Ф4mm SnO2 rotor, produced by Bruker. Tested under room temperature, the resonance frequency is 99.3MHz, the magic angle speed is 5kHz, the pulse width is 2.73μs, the cycle delay time is 5.0s, the number of scans is about 500 times, and the heavy water is locked.

[0067] The pyridine infrared adsorption spectrum (Py-IR) of the sample was tested on the FTS3000 Fourier transform infrared spectrometer produced by BIO-RAD, USA. The sample was pressed into a tablet and sealed in the in-situ cell of the infrared spectrometer. It was evacuated to 10-3Pa at 350℃ and kept for 1 hour to desorb the gas molecules on the surface of the sample. After cooling to room temperature, pyridine vapor with a pressure of 2.67Pa was introduced into the in-situ cell. After balancing for 30 minutes, the temperature was raised to 50℃, and it was evacuated to 10-3Pa again, kept for 30 minutes, cooled to room temperature, and the sample was observed at 1400-1700cm -1 Scan within the wavenumber range and record the infrared absorption spectrum of pyridine adsorption at 50℃; then move the sample in the infrared absorption cell to the heat treatment area, heat it to 150℃, evacuate it to 10-3Pa, keep it for 30min, cool it to room temperature, and record the infrared spectrum of pyridine adsorption at 150℃. -1 The peak at 1540 cm is generated by the reaction between the L acid center and pyridine. -1 The peak at is produced by the reaction of B acid and pyridine.

[0068] The method of aldol condensation is described by taking the aldol condensation of methyl propionate and formaldehyde to synthesize methyl acrylate as an example. A fixed bed reactor is used at normal pressure, the molar ratio of methyl propionate to formaldehyde is 1:1, methanol is used as solvent, the molar ratio of methyl propionate to solvent methanol is 1:2, and the raw material mixed liquid feed space velocity is 1h -1 ; The amount of catalyst is 5g; During the reaction, the carrier gas (N2) flow rate is maintained at 50mL / min, and the reaction temperature is 350°C. The product is condensed and subjected to chromatographic analysis. Unless otherwise specified, the raw materials in the embodiments of the present application are purchased through commercial channels. The composition of the reaction product is analyzed by gas chromatography, and the analysis results are quantified by the external standard method. Among them, the analysis conditions of the chromatography are: Agilent-6890 chromatograph, HP-5 capillary chromatographic column, injection volume 0.5μL, injection port temperature 280°C. The column temperature is maintained at 100°C for 2min, and then increased to 200°C at a rate of 15°C / min and maintained for 3min. FID detector, detector temperature 300°C.

[0069] The conversion rate and selectivity in the embodiment are calculated as follows:

[0070]

[0071]

[0072] Comparative Example 1

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

[0074] The specific steps of Cs / SiO2 catalyst are as follows: weigh a certain amount of cesium hydroxide and dissolve it in deionized water, and then immerse SiO2 in the cesium hydroxide solution. Among them, the molar ratio of cesium to silicon is 0.02, and the molar ratio of SiO2 (calculated as silicon dioxide) to solvent is 1:50. The immersion treatment is carried out at an absolute pressure of 100kPa and 30°C for 30 minutes to make the cesium ions evenly distributed on the silicon dioxide. Then evaporate the solvent, dry it in a drying oven at 110°C for 6 hours, and calcine it in a muffle furnace at 400°C for 6 hours to obtain the catalyst. The catalyst was characterized and evaluated, and the characterization and evaluation 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, 25wt%) solution are mixed according to the molar ratio of SiO2: 0.015SnO2: 0.3TPAOH: 30H2O, and then stirred for 15 minutes, water is added to the liquid, and stirred at 348-353K for about 3 hours to obtain a clear sol, and then crystallized at 170°C for 3 days, and then the obtained solid is filtered, washed with distilled water, dried at 120°C for 5 hours, and then calcined at 550°C for 5h to obtain the molecular sieve Sn-MFI. The XPS spectrum and pyridine infrared spectrum are shown in Figure 1 and Figure 3 The characterization and evaluation results are shown in Table 1. Among them, the center value of the spectrum peak of tin in XPS is 488eV, 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, 40wt%) solution are mixed according to the molar ratio of SiO2: 0.01SnO2: 0.3TBAOH: 30H2O, then stirred for 15 minutes and then water is added to the liquid, stirred at 348-353K for about 3 hours to obtain a clear sol, then crystallized at 443K for 3 days, then the obtained solid is filtered, washed with distilled water, dried at 373K for 5 hours, and then calcined at 823K for 5 hours to obtain the molecular sieve Sn-MEL. The results are shown in Table 1, wherein the peak center value of tin in XPS is 487.7eV, and the hexacoordinated tin / tetracoordinated tin is less than 1.

[0079] Example 1

[0080] The specific steps of Cs / Sn-MFI catalyst are as follows: weigh a certain amount of cesium hydroxide and dissolve it in deionized water, and then mix the Sn-MFI of comparative example 2 with the cesium hydroxide solution. Among them, the molar ratio of cesium to silicon is 0.02, and the molar ratio of Sn-MFI (calculated as silicon dioxide) to solvent is 1:3. Grind the mixture for 30 minutes at an absolute pressure of 50 kPa and 30°C to make the cesium ions evenly distributed on the Sn-MFI. Then evaporate the solvent, dry it in a drying oven at 110°C for 6 hours, and calcine it in a muffle furnace at 400°C for 6 hours to obtain the catalyst. The catalyst was characterized and evaluated, and the XPS spectrum and pyridine infrared spectrum are shown respectively. Figure 2 and Figure 4 ,The characterization and evaluation results are shown in Table 1.

[0081] Example 2

[0082] The specific steps of the Cs / Sn-MFI catalyst are as follows: weigh a certain amount of cesium nitrate and dissolve it in deionized water, then mix the Sn-MFI of Comparative Example 2 with the cesium nitrate solution. Among them, the molar ratio of cesium to silicon is 0.04, and the molar ratio of Sn-MFI (calculated as silicon dioxide) to the solvent is 1:8. Grind the mixture for 50 minutes at an absolute pressure of 100 kPa and 25°C to uniformly distribute the cesium ions on the Sn-MFI. Then evaporate the solvent, dry it in a drying oven at 110°C for 3 hours, and calcine it in a muffle furnace at 450°C for 6 hours to obtain the catalyst. The catalyst was characterized and evaluated, and the characterization and evaluation results are shown in Table 1.

[0083] Example 3

[0084] The specific steps of the Cs / Sn-MFI catalyst are as follows: weigh a certain amount of cesium hydroxide and dissolve it in isopropanol, and then mix the Sn-MFI of Comparative Example 2 with the cesium hydroxide solution. Among them, the molar ratio of cesium to silicon is 0.035, and the molar ratio of Sn-MFI (calculated as silicon dioxide) to the solvent is 1:6. Grind the mixture for 60 minutes at an absolute pressure of 80kPa and 70°C to make the cesium ions evenly distributed on the Sn-MFI. Then evaporate to remove the solvent, dry it in a drying oven at 110°C for 6h, and calcine it in a muffle furnace at 400°C for 6h to obtain the catalyst. The catalyst was characterized and evaluated, and the characterization and evaluation results are shown in Table 1.

[0085] Example 4

[0086] The specific steps of the Cs / Sn-MFI catalyst are as follows: weigh a certain amount of cesium acetate and dissolve it in deionized water, then mix the Sn-MFI of Comparative Example 2 with the cesium acetate solution. Among them, the molar ratio of cesium to silicon is 0.015, and the molar ratio of Sn-MFI (calculated as silicon dioxide) to the solvent is 1:2. Grind the mixture for 30 minutes at an absolute pressure of 30 kPa and 40°C to make the cesium ions evenly distributed on the Sn-MFI. Then evaporate the solvent, dry it in a drying oven at 110°C for 6 hours, and calcine it in a muffle furnace at 430°C for 6 hours to obtain the catalyst. The catalyst was characterized and evaluated, and the characterization and evaluation results are shown in Table 1.

[0087] Example 5

[0088] The specific steps of the Cs / Sn-MFI catalyst are as follows: weigh a certain amount of cesium nitrate and dissolve it in deionized water, then mix the Sn-MFI of Comparative Example 2 with the cesium acetate solution. Among them, the molar ratio of cesium to silicon is 0.02, and the molar ratio of Sn-MFI (calculated as silicon dioxide) to the solvent is 1:4. Grind the mixture for 10 minutes at an absolute pressure of 40kPa and 60°C to uniformly distribute the cesium ions on the Sn-MFI. Then evaporate the solvent, dry it in a drying oven at 110°C for 6 hours, and calcine it in a muffle furnace at 400°C for 6 hours to obtain the catalyst. The catalyst was characterized and evaluated, and the characterization and evaluation results are shown in Table 1.

[0089] Example 6

[0090] The specific steps of the Cs / Sn-MEL catalyst are as follows: weigh a certain amount of cesium hydroxide and dissolve it in deionized water, then mix the Sn-MEL of Comparative Example 3 with the cesium hydroxide solution. Among them, the molar ratio of cesium to silicon is 0.02, and the molar ratio of Sn-MEL (calculated as silicon dioxide) to the solvent is 1:5. Grind the mixture for 30 minutes at an absolute pressure of 80kPa and 30°C to make the cesium ions evenly distributed on the Sn-MEL. Then evaporate the solvent, dry it in a drying oven at 120°C for 6h, and calcine it in a muffle furnace at 400°C for 6h to obtain the catalyst. The catalyst was characterized and evaluated, and the characterization and evaluation results are shown in Table 1.

[0091] Comparative Example 4

[0092] Referring to the method described in Example 1 of the specification of Chinese patent CN1301599A, the Sn-MFI molecular sieve of comparative example 2 was rearranged and pore-enlarged to prepare the Sn-MFI-R molecular sieve, and the preparation steps were as follows: Sn-MFI, tetrapropylammonium hydroxide, and water were mixed in a weight ratio of 1:0.4:15, and then treated at 170°C autogenous pressure for 24h. After that, the obtained solid was filtered, washed with distilled water, dried at 120°C for 5 hours, and then calcined at 550°C for 5h to obtain the molecular sieve Sn-MFI-R. The catalyst was subjected to standard evaluation, and the characterization and evaluation results are shown in Table 1, wherein the XPS measured the tin species spectrum peak binding energy center value of 487.7eV, and the six-coordinated tin: four-coordinated tin was 0.55:1.

[0093] Comparative Example 5

[0094] The specific steps of Cs / SBA-15 catalyst are as follows: weigh a certain amount of cesium hydroxide and dissolve it in deionized water, and then immerse the SBA-15 molecular sieve in the cesium hydroxide solution. Among them, the molar ratio of cesium to silicon is 0.02, and the molar ratio of SBA-15 (calculated as silicon dioxide) to solvent is 1:50. The immersion treatment is carried out at an absolute pressure of 100kPa and 30°C for 30 minutes to make the cesium ions evenly distributed on SBA-15. Then evaporate the solvent, dry it in a drying oven at 110°C for 6 hours, and calcine it in a muffle furnace at 400°C for 6 hours to obtain the catalyst. The catalyst was characterized and evaluated, and the characterization and evaluation results are shown in Table 1.

[0095] Example 7

[0096] The preparation steps of Cs / Sn-MFI-R catalyst are as follows: weigh a certain amount of cesium hydroxide and dissolve it in deionized water, and then mix Sn-MFI-R with the cesium hydroxide solution. Among them, the molar ratio of cesium to silicon is 0.02, and the molar ratio of Sn-MFI-R (calculated as silicon dioxide) to the solvent is 1:3. Grind the mixture for 30 minutes at an absolute pressure of 50kPa and 30°C to make the cesium ions evenly distributed on Sn-MFI-R. Then evaporate the solvent, dry it in a drying oven at 110°C for 6 hours, and calcine it in a muffle furnace at 400°C for 6 hours to obtain the catalyst. The catalyst was characterized and evaluated, and the characterization and evaluation results are shown in Table 1.

[0097] Example 8

[0098] The preparation steps of Cs / Sn-MFI-R catalyst are as follows: weigh a certain amount of cesium hydroxide and dissolve it in deionized water, and then mix Sn-MFI-R with the cesium hydroxide solution. Among them, the molar ratio of cesium to silicon is 0.03, and the molar ratio of Sn-MFI-R (calculated as silicon dioxide) to the solvent is 1:4. Grind the mixture for 20 minutes at an absolute pressure of 50 kPa and 50°C to make the cesium ions evenly distributed on Sn-MFI-R. Then evaporate the solvent, dry it in a drying oven at 110°C for 6 hours, and calcine it in a muffle furnace at 450°C for 6 hours to obtain the catalyst. The catalyst was characterized and evaluated, and the characterization and evaluation results are shown in Table 1.

[0099] Example 9

[0100] The preparation steps of Cs / Sn-MFI-R catalyst are as follows: weigh a certain amount of cesium nitrate and dissolve it in deionized water, then mix Sn-MFI-R with the cesium nitrate solution. Among them, the molar ratio of cesium to silicon is 0.03, and the molar ratio of Sn-MFI-R (calculated as silicon dioxide) to the solvent is 1:3. Grind the mixture for 30 minutes at an absolute pressure of 40kPa and 60°C to make the cesium ions evenly distributed on Sn-MFI-R. Then evaporate the solvent, dry it in a drying oven at 110°C for 6 hours, and calcine it in a muffle furnace at 400°C for 6 hours to obtain the catalyst. The catalyst was characterized and evaluated, and the characterization and evaluation results are shown in Table 1.

[0101] Example 10

[0102] The preparation steps of Cs / Sn-MFI-R catalyst are as follows: weigh a certain amount of cesium acetate and dissolve it in ethanol, and then mix Sn-MFI-R with the cesium acetate solution. Among them, the molar ratio of cesium to silicon is 0.02, and the molar ratio of Sn-MFI-R (calculated as silicon dioxide) to the solvent is 1:2. Grind the mixture for 10 minutes at an absolute pressure of 30kPa and 70°C to make the cesium ions evenly distributed on Sn-MFI-R. Then evaporate the solvent, dry it in a drying oven at 110°C for 3h, and calcine it in a muffle furnace at 400°C for 6h to obtain the catalyst. The catalyst was characterized and evaluated, and the characterization and evaluation results are shown in Table 1.

[0103] Table 1

[0104]

[0105] According to GC-MS characterization and analysis, the main product of the embodiment of the present invention is methyl methacrylate, and the main by-products are methacrolein, methyl dimethylpentenoate, etc., while the main product of the comparative example is methyl methacrylate, and the main by-products are propionic acid, methyl isobutyrate, methyl methylbutyrate, methyl methylhexenoate, etc.

[0106] From the comparison between Examples 1-10 and Comparative Examples 1-5, it can be seen that the center value of the Sn element binding energy of the modified tin silicon molecular sieve of the present invention is significantly lower than that of the conventional tin silicon molecular sieve, and the molecular sieve has only L acid, and the acid content at 50°C and 150°C is significantly lower than that of the conventional tin silicon molecular sieve, and there is no significant Q 3 Silicon nuclear magnetic spectrum peak. The modified tin silicon molecular sieve is used as a catalyst for the aldol condensation reaction of formaldehyde and methyl propionate, which has a good methyl propionate conversion rate and selectivity for the target product methyl methacrylate. Moreover, after the molecular sieve is expanded to have multi-level pores, the catalytic performance is further improved.

Claims

1. A modified tin silicon molecular sieve, characterized in that: 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 central value of the spectral peak binding energy is located at 487.1±0.4eV, and the ratio of the spectral peak area between hexacoordinated tin and tetracoordinated tin is greater than 1:

1.

2. The modified tin-silicon molecular sieve according to claim 1, characterized in that: 3d 5 / 2 The central value of the spectral peak binding energy is located at 487.1±0.3 eV, preferably 487.1±0.2 eV, and more preferably 487.1±0.1 eV.

3. The modified tin-silicon molecular sieve according to claim 1, characterized in that: The ratio of the peak areas of hexacoordinated tin to tetracoordinated tin is greater than 2:1, preferably greater than 5:1, more preferably greater than 10:1, further preferably greater than 50:1, and most preferably greater than 100:

1.

4. The modified tin-silicon molecular sieve according to claim 1, characterized in that: 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.

5. The modified tin-silicon molecular sieve according to claim 1 or 4, characterized in that: 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.

6. The modified tin-silicon molecular sieve according to claim 1, characterized in that: The molar ratio of tin element to silicon element is (0.001-0.05):1, preferably (0.004-0.03):1, more preferably (0.006-0.02):1, and more preferably (0.008-0.015):

1.

7. The modified tin-silicon molecular sieve according to claim 1, characterized in that: It has a crystalline structure of at least one selected from MFI, MEL, MWW, BEA, MOR, and SVR, or an amorphous structure of at least one selected from MCM-41, MCM-48, and SBA-15.

8. The modified tin-silicon molecular sieve according to claim 1, characterized in that: A molecular sieve containing micropores and at least one mesopore and / or macropore, wherein the micropores have a pore diameter less than 2 nm; the mesopores have a pore diameter of 2-50 nm; and the macropores have a pore diameter greater than 50 nm.

9. The modified tin-silicon molecular sieve according to claim 1, characterized in that: Characterized by pyridine infrared acidity, the acid content at 150°C is less than 150 μmol / g, and the acid content at 50°C is less than 280 μmol / g.

10. The modified tin-silicon molecular sieve according to claim 1, characterized in that: Characterized by pyridine infrared acidity, the acid amount at 150°C is less than 110 μmol / g, preferably less than 80 μmol / g, further preferably less than 40 μmol / g, more preferably less than 20 μmol / g, further more preferably less than 10 μmol / g, and most preferably less than 5 μmol / g.

11. The modified tin-silicon molecular sieve according to claim 10, characterized in that: Characterized by pyridine infrared acidity, the acid content at 150°C was 0 μmol / g.

12. The modified tin-silicon molecular sieve according to claim 1, characterized in that: Characterized by pyridine infrared acidity, the acid content at 50°C is less than 250 μmol / g, preferably less than 220 μmol / g, further preferably less than 200 μmol / g, more preferably less than 180 μmol / g, and most preferably less than 160 μmol / g.

13. The modified tin-silicon molecular sieve according to claim 1, characterized in that: Characterized by NMR silicon spectrum, Q 4 With Q 3 The ratio of signal peak height is greater than 100:1, Q 4 represents Si(OSi)4 species, Q 3 Representative: Si(OSi)3(OH) species.

14. The modified tin-silicon molecular sieve according to claim 13, characterized in that: Characterized by NMR silicon spectrum, Q 4 With Q 3 The ratio of the signal peak heights is greater than 150:1, preferably greater than 200:1, further preferably 250:1, and even more preferably 300:

1.

15. The modified tin-silicon molecular sieve according to claim 13, characterized in that: Characterized by NMR silicon spectrum, no Q 3 Signal peak.

16. The method for preparing the modified tin-silicon molecular sieve according to any one of claims 1 to 15, characterized in that: The tin silicon molecular sieve as the starting modified raw material is mixed with the hydroxide or salt of the alkali metal and the solvent, and then dried and calcined to obtain the modified tin silicon molecular sieve; the mixing treatment is carried out at 20-150° C. and an absolute pressure of 10-100 KPa for 5-120 minutes.

17. The preparation method according to claim 16, wherein the mixing treatment is carried out by immersion, ion exchange, spraying, solid phase ion exchange, or grinding, wherein the grinding method is preferred.

18. The preparation method according to claim 16, wherein: The tin silicon molecular sieve used as the starting modified raw material is one or more selected from molecular sieves having MFI, MEL, MWW, BEA, MOR, and SVR framework structures, or one or more selected from molecular sieves with amorphous structures such as MCM-41, MCM-48, and SBA-15.

19. The preparation method according to claim 16, wherein: The tin silicon molecular sieve used as the starting modified raw material is obtained by a hydrothermal synthesis method.

20. The preparation method according to claim 16, wherein: The molar ratio of the tin element to the silicon element in the tin silicon molecular sieve used as the starting modified raw material is (0.001-0.05):

1.

21. The preparation method according to claim 16, wherein: The alkali metal is selected from one or more of lithium, sodium, potassium, rubidium and cesium.

22. The preparation method according to claim 16, wherein: The alkali metal salt is an alkali metal hydrochloride, hypochlorite, chlorite, metachlorate, perchlorate, nitrate, sulfate, hydrogen sulfate, sulfite, bisulfite, phosphate, hydrogen phosphate, dihydrogen phosphate, high phosphate, metaphosphate, phosphite, hypophosphite, carboxylate, pyrophosphate, C1-C 20 One or more of carboxylates and inorganic salts.

23. The preparation method according to claim 16, wherein: The hydroxide of the alkali metal is cesium hydroxide, and the salt of the alkali metal is selected from one or more of cesium nitrate, cesium carbonate, cesium bicarbonate, and cesium acetate.

24. The preparation method according to claim 16, wherein: The molar ratio of the tin silicon molecular sieve as the starting modified raw material, calculated as SiO2, the hydroxide or salt of the alkali metal, and the solvent is 1: (0.001-0.1): (0-10).

25. The preparation method according to claim 16, wherein: The mixing treatment is carried out at 25-100° C., preferably 30-70° C., 20-80 KPa, preferably 30-50 KPa for 5-60 min, preferably 10-30 min.

26. The modified tin silicon molecular sieve obtained by the preparation method according to any one of claims 16 to 25.

27. A catalyst, characterized in that Contains the modified tin silicon molecular sieve according to claims 1-15 or contains the modified tin silicon molecular sieve according to claim 26.

28. The catalyst according to claim 27, characterized in that The modified tin silicon molecular sieve accounts for 5% to 100% of the weight of the catalyst.

29. A method for aldol condensation, wherein a carbonyl-containing compound having α-H undergoes a carbon-carbon bond coupling reaction with another carbonyl-containing compound to generate a carbonyl-containing compound having β-hydroxyl or a carbonyl-containing compound having α,β-unsaturated bonds, characterized in that: Carried out in the presence of a catalyst according to claim 27 or 28.

30. The method according to claim 29, characterized in that It is the aldol condensation reaction of formaldehyde and methyl acetate.

31. The method according to claim 30, characterized in that The aldol condensation 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 to 400°C, a reaction gauge pressure of 0 to 1 MPa, a nitrogen flow rate of 30 to 100 mL / min, and a reaction liquid hourly space velocity of 0.1 to 2 h -1 .

32. The method according to claim 29, characterized in that It is the aldol condensation reaction between formaldehyde and methyl propionate.

33. The method according to claim 32, characterized in that The aldol condensation reaction conditions 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 reaction liquid hourly space velocity of 0.1 to 2 h -1 .

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