Modified titanium silicalite molecular sieve as well as preparation method and application thereof

Abstract

The modified titanium silicalite molecular sieve is characterized by containing titanium, silicon, oxygen and cesium elements, the MAS NMR spectrogram of the 133Cs at least has resonance absorption peaks of-94 + / -15 ppm,-73 + / -15 ppm and-36 + / -15 ppm. The modified titanium silicalite molecular sieve can be used in aldol condensation reaction.

Description

Technical Field

[0001] The present invention belongs to the technical field of molecular sieves. More specifically, the present invention relates to a modified titanium silicalite molecular sieve, a preparation method thereof, and an application of the modified titanium silicalite molecular sieve as a catalyst. Background Art

[0002] Aldol condensation, also known as aldol addition, refers to the nucleophilic addition of an aldehyde or ketone with an α-H to another molecule of aldehyde or ketone under acid or base catalysis to form β-hydroxyaldehyde or β-hydroxyketone. β-Hydroxyaldehyde or β-hydroxyketone can be dehydrated by heating to form α,β-unsaturated aldehyde or ketone. Through aldol condensation, new carbon-carbon bonds can be formed in the molecule and the carbon chain can be extended.

[0003] The aldol condensation reaction can be used to prepare a variety of high-value chemicals, such as β-hydroxy compounds like 1,3-propanediol, 1,3-butanediol, neopentyl glycol, and octenal, which are used as monomers for the further production of high polymers such as fragrances, drugs, plasticizers, polymers, or polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polytrimethylene terephthalate (PTT).

[0004] The dehydration product of aldol condensation, α,β-unsaturated aldehyde, is oxidized to the corresponding carboxylic acid, which can be widely used as a raw material for fine chemical production. For example, 2,2-dimethylolpropionic acid can be used as a chain extender for waterborne polyurethane and for the preparation of polyester, photosensitive resin, and liquid crystal; 2-methyl-2-pentenoic acid is an edible flavor with a fruity aroma and can be widely used in the food processing industry and other daily chemical flavor industries; methyl methacrylate (MMA) is mainly used to produce polymethyl methacrylate and acrylic resin materials and is also widely used in the manufacture of other resins, plastics, coatings, adhesives, lubricants, wetting agents, glazing agents, printing aids, and insulation filling materials, etc.; methyl acrylate (MA) is an important organic intermediate widely used in industries such as rubber, leather, medicine, and coatings. In addition, when α,β-unsaturated aldehyde is fully hydrogenated, saturated primary aldehyde is obtained, which can be used as a solvent or for the manufacture of detergents and plasticizers.

[0005] Generally, the aldol condensation reaction can occur under the catalysis of either an acid or a base, but their reaction mechanisms are different. In the case of an acidic catalyst, at the cationic active center (Bronsted center or Lewis center) of the acidic catalyst, the aldehyde carbonyl group is activated to form an enol carbocation, thus undergoing the condensation reaction. Common acidic catalysts include (VO)2P2O7, niobic acid, and MFI zeolite, etc. Basic catalysts are often used in the aldol condensation reaction. Basic catalysts include basic compounds (oxides, hydroxides, bicarbonates, carbonates, and carboxylates of alkali metals or alkaline earth metals), organic amine compounds, and anion exchange resins, etc. In actual industrial applications, the basic catalyst selected for the aldol condensation reaction can be a weak base (such as sodium carbonate, sodium bicarbonate, sodium acetate), or a strong base (such as sodium hydroxide, calcium hydroxide, sodium hydride, sodium alkoxide, etc.). The former is generally used for the condensation between aldehydes with greater activity, and the products are mostly β-hydroxy compounds. The latter is used for the condensation between aldehydes or ketones with less activity and large steric hindrance, and the reaction is mostly carried out in an aprotic polar solvent.

[0006] The direct aldol condensation of methyl propionate and formaldehyde to prepare methyl methacrylate does not use highly toxic raw materials, and the raw materials are cheap and widely available, which is an important production method for methyl methacrylate in the future. Currently, the most effective aldol condensation catalyst for methyl propionate and formaldehyde is a supported catalyst with silica as the main carrier and cesium as the main active component. This supported catalyst has low activity, the raw materials cannot be fully converted completely, and since this catalyst uses amorphous silica as the carrier, there is a phenomenon that the specific surface area gradually decreases and the strength gradually weakens with the extension of time in the reaction system.

[0007] CN103551148B discloses a water-resistant catalyst for aldol condensation. The main active components include one or more of oxides or salts of Cs, and the active promoters are one or more of oxides or salts of Sb, Nb, Ag, Al, Zr. The carrier includes SiO2 and a carrier promoter.

[0008] CN112675830A discloses an aldol condensation catalyst. This catalyst loads metal elements on a foamed porous silica carrier, making the catalyst have excellent water resistance, anti-coking performance, and long-cycle activity stability, and is suitable for the industrial application of preparing methyl methacrylate by the aldol condensation of methyl propionate and formaldehyde.

[0009] Most of the catalysts used in the aldol condensation reaction studied in the existing literature are basic catalysts with alkali metals supported on amorphous silica. Their carriers have poor stability, single active centers, low activity and low selectivity, and cannot meet the requirements of large-scale industrial production.

[0010] At present, there are mainly the following methods for producing methyl acrylate, including propylene oxidation method, acrylonitrile hydrolysis method and propane oxidation method. The propylene oxidation method has technical and economic advantages but low efficiency, and industrial production mainly relies on this method. The acrylonitrile hydrolysis method has a small output and sulfuric acid cannot be recycled. The propane oxidation method is inexpensive but has a low product yield.

[0011] The preparation of methyl acrylate by the condensation reaction of coal-based methyl acetate (or acetic acid) and formaldehyde is a very important and valuable process synthesis route. It not only has low production costs but also effectively controls the discharge of polluted waste liquid, making it a synthesis method with great application prospects.

[0012] "Chemical Industry and Engineering Progress, 2021, 40(4): 2005-2015" reported on the research progress of the condensation of acetic acid (ester)-formaldehyde to acrylic acid (ester). Currently, the main catalysts used in this route include VPO catalysts, alkali metal / alkaline earth metal catalysts and ionic liquid catalysts. Among them, the VPO catalyst has high catalytic efficiency but many side reactions and is prone to deactivation. Compared with VPO, the alkali metal catalyst has no oxidative by-products and higher selectivity, but its catalytic efficiency is slightly lower. The ionic liquid catalyst has mild reaction conditions and high selectivity, but the product separation is difficult and the catalyst is difficult to reuse. In comparison, the preparation process of the alkali metal catalyst is simpler, has a larger adjustable space, high product selectivity, and is easier to achieve industrial application.

[0013] CN 108097290A discloses a catalyst for preparing acrylic acid / methyl acrylate from raw materials containing carbon monoxide and formaldehyde compounds. The catalyst is mainly obtained by metal modification of commercially available MOR configuration molecular sieves with different silicon-aluminum ratios by at least one selected from copper, silver, iron, cobalt, nickel and gallium through impregnation method, ion exchange method and in-situ synthesis method, etc. The highest selectivity of acrylic acid of this catalyst reaches 88.2%, and the selectivity of methyl acrylate is 5.3%.

[0014] The catalyst disclosed in CN 106693941A uses Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba as active components and Al2O3 prepared by the co-precipitation method as the carrier. When the molar ratio of methyl acetate: formaldehyde: methanol is 1:2:2, the conversion rate of methyl acetate is 34.4%, and the selectivity of methyl acrylate is 93.4%.

[0015] CN 104258901A discloses a Cs-loaded pure silica molecular sieve catalyst with KIT-6 as the carrier and Cs as the active component, which is applied to the reaction of aldol condensation of methyl acetate and formaldehyde to prepare methyl acrylate. The molar ratio of methyl acetate, formaldehyde and methanol is 1:2:2. The highest conversion rate of methyl acetate can reach 35%, and the highest selectivity of methyl acrylate can reach 94%.

[0016] Teng He et al. reported in "Catalysis Letters, 2019, 149(2): 373-389" that cesium-loaded SiO2 was used as a catalyst in the aldol condensation reaction of methyl acetate and formaldehyde to prepare methyl acrylate. When the molar ratio of methyl acetate, formaldehyde, and methanol was 1:2:2 and the reaction temperature was 390 °C, the conversion rate of methyl acetate was about 35%, and the selectivity of methyl acrylate was 85-90%.

[0017] Among various catalysts for the aldol condensation reaction of methyl acetate and formaldehyde to prepare MA, although the silica-supported Cs alkali metal catalyst has the best performance, its activity is not ideal, and the yield of the target product is low. Summary of the Invention

[0018] The purpose of the present invention is to provide a catalytic material different from the prior art, a preparation method thereof, a catalyst containing the catalytic material, and the application of the catalyst in the aldol condensation reaction.

[0019] To achieve one of the purposes of the present invention, the first aspect of the present invention provides a modified titanium silicalite molecular sieve, which is characterized by containing titanium, silicon, oxygen, and cesium elements; its 133 The Cs MAS NMR spectrum has at least resonance absorption peaks at -94±15 ppm, -73±15 ppm, and -36±15 ppm.

[0020] To achieve the second purpose of the present invention, the second aspect of the present invention provides a preparation method of the modified titanium silicalite molecular sieve, which is characterized in that the method includes mixing the titanium silicalite molecular sieve as the starting modification raw material with a cesium hydroxide or cesium salt, then treating under steam conditions, and drying and calcining the treated solid to obtain the modified titanium silicalite molecular sieve.

[0021] To achieve the third purpose of the present invention, the third aspect of the present invention provides a catalyst containing the modified titanium silicalite molecular sieve described in the first aspect of the present invention or the modified titanium silicalite molecular sieve obtained by the preparation method described in the second aspect of the present invention, which is characterized by containing the titanium silicalite molecular sieve provided in the first aspect of the present invention or the titanium silicalite molecular sieve prepared by the method provided in the second aspect of the present invention. The weight ratio of the titanium silicalite molecular sieve to the titanium silicalite molecular sieve catalyst is preferably 5%-100%.

[0022] 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 carbon-carbon bond coupling reaction occurs between a carbonyl compound with an α-H and another carbonyl compound in the presence of the titanium silicalite molecular sieve catalyst provided in the third aspect of the present invention to generate a carbonyl compound with a β-hydroxy group or a carbonyl compound with an α,β-unsaturated bond.

[0023] The modified titanium silicalite molecular sieve of the present invention uses cesium and titanium as the main active components. Appropriate catalytic active centers are generated through the interaction between cesium and titanium, ensuring high conversion rate and good product selectivity in the aldol condensation reaction. The preparation method of this modified titanium silicalite molecular sieve is simple, has short steps, and wide raw material sources, is suitable for large-scale industrial applications, and is environmentally friendly at the same time. Description of the Drawings

[0024] The drawings are used to provide a further understanding of the present disclosure and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present disclosure, but do not constitute a limitation to the present disclosure. In the drawings:

[0025] Figure 1 The Cs MAS NMR spectrum of the comparative catalyst Cs / SiO2 for Comparative Example 1. 133 Cs MAS NMR spectrum.

[0026] Figure 2 The Cs MAS NMR spectrum of the comparative catalyst Cs / S-1 for Comparative Example 2. 133 Cs MAS NMR spectrum.

[0027] Figure 3 The XRD spectrum of the TS-1-0.02 titanium silicalite molecular sieve for Preparation Example 1.

[0028] Figure 4 The hydroxyl infrared spectrum of the TS-1-0.02 titanium silicalite molecular sieve for Preparation Example 1.

[0029] Figure 5 The UV-Vis spectrum of the TS-1-0.02 titanium silicalite molecular sieve for Preparation Example 1.

[0030] Figure 6 The XRD spectrum of the catalyst Cs / TS-1-A for Example 1.

[0031] Figure 7 The 133 Cs MAS NMR spectrum of the catalyst Cs / TS-1-A for Example 1.

[0032] Figure 8 The hydroxyl infrared spectrum of the catalyst Cs / TS-1-A for Example 1.

[0033] Figure 9 The UV-Vis spectrum of the catalyst Cs / TS-1-A for Example 1. Specific Embodiments

[0034] The present invention will be described in detail below through examples. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0035] A modified titanium silicalite molecular sieve provided by the first aspect of the present invention is characterized in that it contains titanium, silicon, oxygen, and cesium elements; its 133 Cs MAS NMR spectrum has at least resonance absorption peaks at -94 ± 15 ppm, -73 ± 15 ppm, and -36 ± 15 ppm.

[0036] 133 The resonance absorption peaks in the Cs MAS NMR spectrum are specific spectral peaks generated by cesium in different chemical environments. The number of peaks represents the number of different chemical environments, and the chemical shift of the peaks indicates the degree of influence of the chemical environment on the cesium element. The more negative the chemical shift, the stronger the effect of the environment on it and the stronger the nuclear shielding effect on the cesium nucleus. The presence of characteristic peaks at -94 ± 15 ppm, -73 ± 15 ppm, and -36 ± 15 ppm in the modified titanium silicalite molecular sieve of the present invention indicates that the cesium element exists in a specific chemical environment, which will inevitably bring specific catalytic performance. Since the nuclear magnetic resonance spectroscopy is very complex, under the existing knowledge and research conditions of the present invention, the physical and chemical meanings of each spectral peak cannot be completely confirmed, and only the characteristics and effects are confirmed by comparison. However, since the present invention generates new signal peaks through the action of cesium and titanium silicalite molecular sieve, the new characteristics and effects generated mainly come from the action of cesium and titanium.

[0037] In the modified titanium silicalite molecular sieve of the present invention, there is no limitation on the magnitude relationship of the spectral peak intensities (peak heights) of the resonance absorption peaks at -94 ± 15 ppm, -73 ± 15 ppm, and -36 ± 15 ppm. When the spectral peak intensities of the resonance absorption peaks at -94 ± 15 ppm, -73 ± 15 ppm, and -36 ± 15 ppm are I1, I2, and I3 respectively, they can be in any magnitude order of I1, I2, and I3. Preferably, the spectral peak intensities have the following relationship: I2 > I1 > I3; more preferably, the spectral peak intensities have the following relationship: I1 / I2 = 0.3 - 1, I3 / I2 = 0.2 - 0.9. Further preferably, the spectral peak intensities have the following relationship: I1 / I2 = 0.5 - 0.95, I3 / I2 = 0.4 - 0.8. Most preferably, the spectral peak intensities have the following relationship: I1 / I2 = 0.7 - 0.9, I3 / I2 = 0.65 - 0.8.

[0038] When the modified titanium silicalite molecular sieve of the present invention is characterized by infrared spectroscopy, it can be found that there is no hydroxyl signal peak in its infrared hydroxyl spectrum at 3200 - 3720 cm -1 The infrared hydroxyl characterization method is usually used to characterize the hydroxyl state in solid catalytic materials such as molecular sieves. It is generally considered that the broad peak near 3520 cm -1 represents nest hydroxyl groups, that is, the four silicon hydroxyl group structures left after the framework atoms are removed; the wavelength at 3690 cm -1The signal peak nearby is the adjacent hydroxyl group, that is, the silicon atoms of two silanol groups are connected by oxygen; 3720 cm -1 The signal peak nearby is the titanium hydroxyl group; 3740 cm -1 The signal peak nearby is the terminal silanol group. In the modified titanium silicalite molecular sieve of the present invention, there is no hydroxyl signal peak other than 3740 cm -1 Moreover, the 3740 cm -1 signal peak is very weak or difficult to distinguish.

[0039] When the modified titanium silicalite molecular sieve of the present invention is characterized by ultraviolet-visible spectroscopy (UV-Vis), it can be found that its UV-Vis spectrum has a tetracoordinated titanium signal peak at 210±10 nm and a hexacoordinated titanium signal peak at 270±15 nm; further in the UV-Vis spectrum, there may also be anatase signal peak at 330±15 nm. In the UV-Vis spectrum, based on the total area of the spectral peaks in the range of 200-800 nm in the spectrum, among them, the area ratio of the tetracoordinated titanium signal peak at 210±10 nm is preferably 50%-95%, more preferably 55%-85%, and further preferably 60%-75%; the area ratio of the hexacoordinated titanium signal peak at 270±15 nm is preferably 10%-45%, more preferably 20%-40%, and further preferably 25%-35%; the area ratio of the anatase signal peak at 330±15 nm is preferably 0-40%, more preferably 0-20%, and further preferably 0-10%.

[0040] In the modified titanium silicalite molecular sieve of the present invention, the molar ratio of cesium element to silicon element is (0.0001-0.1):1, preferably (0.001-0.08):1, further preferably (0.005-0.06):1, more preferably (0.008-0.04):1, and most preferably (0.01-0.03):1. The molar ratio of titanium element to silicon element is (0.0001-0.1):1, preferably (0.001-0.08):1, further preferably (0.004-0.06):1, more preferably (0.008-0.04):1, and most preferably (0.01-0.03):1. The molar ratio of each element is obtained by the X-ray fluorescence spectrometer analysis method (XRF).

[0041] The modified titanium silicalite molecular sieve of the present invention, in principle, has a framework structure type including any suitable structure type or any suitable combination of structure types. Therefore, the available molecular sieve crystal structure types in principle include the following structure 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 mixed structures composed of two or more of these structure types.Or it is an amorphous structure, where the amorphous structure includes MCM-41, MCM-48, and SBA-15. Preferably, the crystal type of the structure is MFI, MEL, BEA, MWW, MOR, SVR structure, or an amorphous structure selected from at least one of MCM-41, MCM-48, and SBA-15.

[0042] The modified titanium silicalite molecular sieve of the present invention is more preferably one having at least one crystal structure of MFI, MEL, and BEA. Optionally, the modified titanium silicalite molecular sieve may have hierarchical pore characteristics or mesoporous structure characteristics within a pore distribution range of 2-50 nm. The hierarchical pores or mesoporous structure can be obtained by direct synthesis or post-treatment of the titanium silicalite molecular sieve. For example, it can be synthesized by methods of soft and hard template synthesis (such as silanization method, cellulose method, carbon black method, etc.), and the pores can be enlarged by acid or alkali treatment (such as 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. to enlarge the pores). The hierarchical pores or mesoporous structure can contain micropores and at least one type of mesopores and / or macropores. The micropores have a pore diameter of 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.

[0043] The preparation method of the modified titanium silicalite molecular sieve provided in the second aspect of the present invention is characterized in that the method includes mixing the titanium silicalite molecular sieve as the starting modified raw material with cesium hydroxide or cesium salt, then treating it under steam conditions, and drying and calcining the treated solid to obtain the modified titanium silicalite molecular sieve.

[0044] In the preparation method of the modified titanium silicalite molecular sieve provided by the present invention, the mixing can be carried out in one or more ways of impregnation method, ion exchange method, spraying method, solid-phase ion exchange method, and grinding method, and these methods can be used repeatedly. Since the grinding method can make cesium element contact with the titanium silicalite molecular sieve better and cause grinding chemical reactions, which is more conducive to the formation of the catalytic active center of the titanium silicalite molecular sieve of the present invention, the grinding method is preferably used. The mixing is preferably carried out in the presence of a solvent.

[0045] In the preparation method of the modified titanium silicalite molecular sieve provided by the present invention, the titanium silicalite molecular sieve used as the starting modified raw material can be obtained by hydrothermal synthesis method or post-synthesis method. Among them, the post-synthesis method can be rearrangement method, dealumination and titanium insertion method of silica-alumina molecular sieve, dealumination and titanium insertion method of silica-boron molecular sieve, dealumination and titanium insertion method of silica-germanium molecular sieve, etc.; it can be liquid-phase titanium insertion method or gas-phase titanium insertion method. The present invention has no special limitation, and preferably, the titanium silicalite molecular sieve obtained by hydrothermal synthesis method is used as the titanium silicalite molecular sieve of the starting modified raw material.

[0046] In the preparation method of the modified titanium silicalite provided by the present invention, there is no restriction on the framework structure of the titanium silicalite used as the starting modification raw material. In principle, it includes the following crystal structure 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 mixed structures composed of two or more of these structure types. Or it is an amorphous structure including MCM-41, MCM-48, SBA-15, etc.Preferably, the titanium silicalite used as the starting modification raw material has one or more crystal structures of MFI, MEL, MWW, BEA, MOR, SVR, or an amorphous structure of MCM-41, MCM-48, SBA-15. More preferably, it has one or more crystal structures of MFI, MEL, BEA. The titanium silicalite used as the starting modification raw material optionally contains a hierarchical pore or mesoporous structure.

[0047] In the preparation method of the modified titanium silicalite provided by the present invention, for the titanium silicalite used as the starting modification raw material, the molar ratio of titanium element to silicon element is (0.0001 - 0.1):1, preferably (0.001 - 0.08):1, more preferably (0.004 - 0.06):1, still more preferably (0.008 - 0.04):1, and most preferably (0.01 - 0.03):1.

[0048] In the preparation method of the modified titanium silicalite provided by the present invention, the cesium salt is selected from one or more of cesium hydrochloride, hypochlorite, chlorite, metachlorite, perchlorate, nitrate, sulfate, bisulfate, sulfite, bisulfite, phosphate, hydrogen phosphate, dihydrogen phosphate, perphosphate, metaphosphate, phosphite, hypophosphite, carbonate, bicarbonate, pyrophosphate, C1-C 20 carboxylates. The cesium salt is preferably nitrate, carbonate. Examples of the cesium hydroxide or cesium salt include but are not limited to one or more of cesium hydroxide, cesium nitrate, cesium carbonate, cesium bicarbonate, cesium acetate.

[0049] In the preparation method of the modified titanium silicalite provided by the present invention, the molar ratio of the cesium element to the silicon element in the titanium silicalite used as the starting raw material is (0.0001 - 0.1):1, preferably (0.001 - 0.08):1, more preferably (0.005 - 0.06):1, still more preferably (0.008 - 0.04):1, and most preferably (0.01 - 0.03):1.

[0050] In the preparation method of the modified titanium silicalite provided by the present invention, a solvent can be optionally added. The solvent can be an inorganic solvent or an organic solvent. The inorganic solvent is water, such as distilled water or deionized water; the organic solvents include C1-C 10 alcohols, C3-C 10 ketones, C2-C 10 esters, C6-C 10Alkanes and aromatic hydrocarbons. The solvent can also be a chlorinated solvent, such as one or more of methyl chloride, methylene chloride, chloroform, carbon tetrachloride, chloroethane, dichloroethane, trichloroethane, and tetrachloroethane. The solvent is an aliphatic alcohol, typically a C1-C6 alkanol, such as methanol, ethanol, propanol, isopropanol, butanol, pentanol, and hexanol, preferably methanol, ethanol, or propanol. The addition amount of the solvent is based on the carrier. In the preparation method, the solvent is preferably at least one of water, methanol, ethanol, propanol, methyl chloride, methylene chloride, and chloroform, and the further preferred solvent is at least one of water, methanol, ethanol, and propanol. Among them, the molar ratio of the titanium silicalite (calculated as SiO2) as the starting 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).

[0051] In the preparation method of the modified titanium silicalite provided by the present invention, the mixing is carried out at 20-150°C and an absolute pressure of 10-100 KPa for 5-120 min; the mixing is preferably carried out at 25-100°C, more preferably at 30-70°C, and an absolute pressure of 20-80 KPa, more preferably 30-50 KPa for 5-60 min, more preferably for 10-30 min. The mixing carried out under a certain vacuum is more conducive to the dispersion of cesium in the titanium silicalite and the formation of a good interaction between cesium and titanium. The mixing can be carried out in a vacuum glove box or on a ball mill with a vacuum on equipment that meets the processing requirements.

[0052] In the preparation method of the modified titanium silicalite provided by the present invention, if the mixing is carried out in the presence of a solvent, the solvent needs to be removed. The method for removing the solvent can be pressure evaporation, atmospheric evaporation, vacuum evaporation, filtration, centrifugation, sedimentation, or natural evaporation during the mixing process, etc., and the present invention has no special limitation.

[0053] In the preparation method of the modified titanium silicalite provided by the present invention, the treatment under steam conditions is carried out with water vapor at 100 - 200 °C, preferably 120 - 180 °C, more preferably 130 - 160 °C, and at a gauge pressure of 0 - 1 MPa, preferably 0.1 - 0.8 MPa, more preferably 0.3 - 0.6 MPa for 0.1 - 24 h, preferably 1 - 12 h, further preferably 2 - 8 h. The steam can be superheated steam or saturated steam. The pressure can be adjusted by supplementing gases such as nitrogen, argon, air, etc. The inventors found that cesium mainly exists in three forms on the surface of titanium silicalite, namely cesium oxide, active centers formed by reacting with silicon, and active centers formed by reacting with titanium. Among them, cesium oxide exists in an aggregated state with low dispersion, and its catalytic activity and selectivity for aldol condensation are relatively low. Increasing its content to a certain extent does not significantly improve the catalytic reaction. When the cesium content is relatively high, cesium mainly exists in the form of cesium oxide on the carrier surface. The active centers formed by reacting with silicon and the active centers formed by reacting with titanium have high dispersion and better catalytic performance, and the active centers formed by reacting with titanium have the best catalytic performance. Through treatment under steam conditions, the mesopore volume can be increased, the distribution of cesium elements can be promoted and interact with titanium to form efficient active centers.

[0054] In the preparation method of the modified titanium silicalite provided by the present invention, the drying is preferably carried out in the temperature range of 60 - 150 °C, further preferably 90 - 140 °C, more preferably 100 - 130 °C; the drying time is preferably from 0.5 to 24 h, further preferably 1 to 12 h, more preferably 2 to 6 h. The calcination is preferably carried out at 250 - 800 °C for 0.5 - 24 h, more preferably at 350 - 550 °C for 1 - 12 h. For the calcination, the atmosphere is preferably an oxygen-containing atmosphere, further preferably 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 a temperature lower than 550 °C, and the further preferred calcination temperature is 400 - 500 °C to prevent the decomposition of the alkali element precursor. In order to prevent a large change in the carrier structure or specific surface area, the calcination time is further preferably 3 - 8 h. The calcination atmosphere is preferably an oxygen-containing atmosphere, further preferably an air atmosphere.

[0055] The third aspect of the present invention provides a titanium silicalite catalyst, characterized in that the catalyst contains the titanium silicalite of the first aspect of the present invention or the titanium silicalite obtained by the preparation method described in the second aspect of the present invention. Further, the titanium silicalite accounts for 5% - 100% by weight of the titanium silicalite catalyst.

[0056] The fourth aspect of the present invention provides a method for aldol condensation, which is characterized in that in the presence of the titanium silicalite catalyst provided in the above-mentioned third aspect, a carbonyl compound having an α-H reacts with another carbonyl compound to undergo a carbon-carbon bond coupling reaction to generate a carbonyl compound having a β-hydroxy group or a carbonyl compound having an α,β-unsaturated bond.

[0057] The α and β positions refer to the carbon atoms at the first and second adjacent positions of the functional groups of hydrocarbon molecules, such as carbonyl, hydroxyl, carboxyl, etc. Among them, the carbonyl compound includes a first carbonyl compound and a second carbonyl compound, and the number of carbon atoms thereof is preferably C1-C 20 . Among them, the carbonyl compound may include the following structures:

[0058] 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, tert-butyl.

[0059] C3-C 12 cycloalkyl groups, such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl, cycloundecyl and cyclododecyl; preferably cyclopentyl, cyclohexyl and cycloheptyl.

[0060] 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.

[0061] C7-C 13 arylalkyl groups, preferably C7-C 12 phenylalkyl groups, such as benzyl, 1-phenylethyl, 2-phenylethyl, 1-phenylpropyl, 2-phenylpropyl, 3-phenylpropyl, 1-phenylbutyl, 2-phenylbutyl, 3-phenylbutyl and 4-phenylbutyl, and particularly preferably benzyl;

[0062] C6-C 14An aryl group, such as phenyl, 1-naphthyl, 2-naphthyl, 1-anthryl, 2-anthryl, 9-anthryl, 1-phenanthryl, 2-phenanthryl, 3-phenanthryl, 4-phenanthryl, 9-phenanthryl, preferably phenyl, which is unsubstituted or substituted by one or more of the following groups:

[0063] C1-C 12 An alkyl group, 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 a C1-C6 alkyl group, 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 a C1-C4 alkyl group, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl.

[0064] A halogen, such as fluorine, chlorine, bromine, iodine, preferably chlorine.

[0065] C1-C 12 An alkoxy group, preferably a C1-C6 alkoxy group, such as methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy, tert-butoxy, n-pentyloxy, isopentylpropoxy, n-hexyloxy, and isohexyloxy, and particularly preferably methoxy, ethoxy, n-propoxy, and n-butoxy.

[0066] Preferably, the first carbonyl compound contains α-H, and the second carbonyl compound contains α-H or does not contain α-H. Further preferably, the carbonyl compound that does not contain α-H is preferably formaldehyde, benzaldehyde, furfural, 5-hydroxymethylfurfural, 5-methylfurfural, or a derivative thereof, and further preferably formaldehyde; the carbonyl compound that contains α-H is preferably at least one of 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 a derivative thereof.

[0067] In the aldol condensation method provided by 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 even more preferably 1:(1-2).

[0068] In the aldol condensation method provided by the present invention, the mixture stream of carbonyl compounds may further contain one or more diluents. The diluents include at least one of alcohols, ethers, alkanes, haloalkanes, and toluene. Preferred diluents are methanol, cycloalkanes, diethyl ether, and toluene. The molar ratio of the diluent to the carbonyl compound is (30 - 0.5):1, preferably (20 - 0.7):1, more preferably (10 - 0.8):1, still more preferably (5 - 0.9):1, and most preferably (3 - 1):1.

[0069] In the aldol condensation method provided by the present invention, the aldol condensation reaction can be carried out in an atmosphere containing at least one gas among N2, He, Ar, CH4, C2H6, H2, CO, and CO2. The preferred atmosphere is N2.

[0070] In the aldol condensation method provided by 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 preferred to raise the temperature of the mixed solution 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; based on the total mass of the carbonyl compound and the diluent, the space velocity of the reaction solution is 0.05 - 5 h -1 、further preferably 0.08 - 3 h -1 、more preferably 0.1 - 2 h -1 。The space velocity should be understood as the mass space velocity, which means the mass flow rate (unit: (mass / time)) of the total mass of the carbonyl compound and the diluent divided by the mass of the catalyst. Therefore, the unit of the space velocity is h -1 。

[0071] The inventors of the present invention have found that the catalyst of the present invention can surprisingly greatly improve the activity and selectivity for the condensation of a methylene source such as formaldehyde with a carboxylic acid or a hydrocarbon ester such as methyl acetate to form an olefinically unsaturated carboxylic acid ester. The formaldehyde source is an anhydrous formaldehyde source, preferably methylal, trioxane, and paraformaldehyde.

[0072] In a specific embodiment of the present invention, the conditions for the aldol condensation reaction between formaldehyde and methyl acetate include: the molar ratio of methyl acetate to formaldehyde is 1:2 to 1:1, the molar ratio of methanol to methyl acetate is 1:1 to 2:1, the reaction temperature is 320 - 400 °C, the reaction pressure (gauge pressure) is 0 - 1 MPa, the nitrogen flow rate is 30 - 100 mL / min, and the space velocity of the reaction solution is 0.1 - 2 h -1 。

[0073] In a specific embodiment of the present invention, the conditions for the aldol condensation reaction between formaldehyde and methyl propionate include: the molar ratio of methyl propionate to formaldehyde is 1:2 to 1:0.2, the molar ratio of methanol to methyl propionate is 1:1 to 5:1, the reaction temperature is 320 to 400 °C, the reaction pressure (gauge pressure) is 0 to 1 MPa, the nitrogen flow rate is 30 to 100 mL / min, and the space velocity of the reaction liquid is 0.1 to 2 h -1 .

[0074] In another specific embodiment of the present invention, the reaction conditions for the preparation of octenal by the aldol condensation reaction of butyraldehyde include: the molar ratio of methanol to n-butyraldehyde is 0:1 to 10:1, the reaction temperature is 300 to 380 °C, the reaction pressure (gauge pressure) is 0 to 1 MPa, the nitrogen flow rate is 30 to 100 mL / min, and the space velocity of the reaction liquid is 0.1 to 2 h -1 .

[0075] The aldol condensation method provided by 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 can understand that, depending on the reactor used, the catalyst of the present invention can be the modified titanium silicalite zeolite raw powder or the shaped catalyst after the modification of titanium silicalite zeolite. The separation of the aldol condensation reaction product from the catalyst can be achieved in various ways. For example, when the raw 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 other methods; the shaped catalyst is loaded into the fixed-bed reactor, and the catalyst is recovered after the reaction ends. The separation and recovery methods of various catalysts are involved in many existing literatures and will not be elaborated here.

[0076] The present invention will be described in detail below by way of examples.

[0077] For the sample 133 The Cs MAS NMR characterization instrument is an AVANCEⅢ500WB nuclear magnetic resonance spectrometer, using a 7 mm dual resonance probe, a Ф4 mm SnO2 rotor, and calibrated with cesium chloride.

[0078] The hydroxyl infrared spectrum of the sample was tested on a NICOLET 6700. The sample was placed on a self-supporting film and tested after being treated at 473 K for 2 h.

[0079] The ultraviolet-visible spectrum (UV-Vis) of the sample was detected by a Cary 300 Agilent ultraviolet-visible spectrometer, and the signal in the range of 190 - 800 nm was measured under ambient conditions.

[0080] The chemical composition of the sample was detected by a Rigaku 3721E spectrometer X-ray fluorescence spectrometer, and the measurement voltage was 40 kV.

[0081] The XRD pattern of the sample was obtained on a Philips Panalytical X’pert X-ray diffractometer equipped with a Cu Kα light source, with a scanning step of 0.04° and a scanning range of 5–35°.

[0082] The prepared modified titanium silicalite molecular sieve catalyst was used to catalyze the aldol condensation reaction of methyl acetate and formaldehyde to synthesize methyl acrylate. The catalytic performance of the aldol condensation reaction was tested in an atmospheric pressure fixed bed reactor. Among them, the molar ratio of methyl acetate to formaldehyde was 1:1.8, methanol was used as the solvent, and the molar ratio of methyl acetate to methanol was 1:3. The feed space velocity of the raw material mixture was 1.5 h -1 ; the catalyst dosage was 5 g; during the reaction process, the flow rate of the carrier gas (N2) was maintained at 30 mL / min, and the reaction temperature was 350 °C. After the product was condensed, chromatographic analysis was carried out. Unless otherwise specified, the raw materials in the examples of this application were all purchased through commercial channels.

[0083] The composition of the aldol condensation reaction product was analyzed by gas chromatography, and the analysis results were quantified by the external standard method. Among them, the analysis conditions of the chromatograph were: Agilent-6890 chromatograph, HP-5 capillary chromatographic column, injection volume of 0.5 μL, injection port temperature of 280 °C. The column temperature was maintained at 100 °C for 2 min, and then increased to 200 °C at a rate of 15 °C / min and maintained for 3 min. FID detector, detector temperature of 300 °C.

[0084] The calculation methods of conversion rate, selectivity and yield in the examples are as follows:

[0085]

[0086]

[0087] Y 丙烯酸甲酯 =C 醋酸甲酯 ×S 丙烯酸甲酯

[0088] Comparative Example 1

[0089] This comparative example was used to illustrate the preparation of a comparative catalyst Cs / SiO2 with amorphous silica as the carrier loaded with cesium.

[0090] Preparation of SiO2: 100 mL of water was mixed with 50 g of tetraethyl orthosilicate at room temperature, and ammonia water was added dropwise to the mixed solution until pH = 13. Then, it was stirred at 40 °C for 60 min. The hydrolyzed silica was filtered, dried overnight in an oven at 110 °C, and ground to room temperature to obtain the carrier amorphous silica. XRD analysis was performed on SiO2, and it was found that it had an amorphous structure.

[0091] Preparation of Cs / SiO2 catalyst: Weigh a certain amount of cesium nitrate and dissolve it in deionized water, then immerse SiO2 in the cesium nitrate solution. Among them, the molar ratio of cesium to silicon is 0.03:1, and the molar ratio of SiO2 (calculated as silicon dioxide) to the solvent is 1:40. Immerse and treat at an absolute pressure of 101 kPa and 40 °C for 30 min to make cesium ions evenly distributed on silicon dioxide. Then evaporate to remove the solvent, place it in a drying oven and dry at 120 °C for 6 h, and calcine in a muffle furnace at 400 °C for 6 h to obtain the Cs / SiO2 catalyst.

[0092] Perform XRF characterization, UV-Vis characterization on the Cs / SiO2 catalyst, 133 Cs MAS NMR characterization and the aldol condensation reaction evaluation of methyl acetate and formaldehyde. The characterization and evaluation results are shown in Table 1 and Table 2.

[0093] 133 Two signal peaks at -12 ppm and -36 ppm were found in the Cs MAS NMR characterization spectrum ( Figure 1 ).

[0094] Comparative Example 2

[0095] This comparative example is used to illustrate the preparation of the comparative catalyst Cs / S-1 by loading cesium on the MFI-type all-silica molecular sieve S-1.

[0096] Preparation of MFI-type all-silica molecular sieve S-1: Mix tetraethyl orthosilicate (TEOS), tetrapropylammonium hydroxide (TPAOH, 25 wt%) solution and water according to the molar ratio of SiO2∶0.2TPAOH∶30H2O, then stir for 60 minutes, and then stir at 80 °C for about 3 hours to obtain a clear sol. Then crystallize at 170 °C for 72 h. After that, filter the obtained solid, wash it with distilled water, dry it at 120 °C for 5 h, and then calcine it at 550 °C for 5 h to obtain the molecular sieve S-1. Perform XRD analysis on S-1, and it has an MFI structure.

[0097] Preparation of catalyst Cs / S-1: Weigh a certain amount of cesium nitrate and dissolve it in deionized water, then immerse S-1 in the cesium nitrate solution. Among them, the molar ratio of cesium to silicon is 0.03:1, and the molar ratio of S-1 (calculated as silicon dioxide) to the solvent is 1:40. Immerse and treat at an absolute pressure of 101 kPa and 40 °C for 30 min to make cesium ions evenly distributed on S-1. Then evaporate to remove the solvent, place it in a drying oven and dry at 120 °C for 6 h, and calcine in a muffle furnace at 400 °C for 6 h to obtain the comparative catalyst Cs / S-1.

[0098] Perform XRF characterization, UV-Vis characterization on the catalyst Cs / S-1, 133Cs MAS NMR characterization and evaluation of the aldol condensation reaction of methyl acetate and formaldehyde. The characterization and evaluation results are shown in Table 1 and Table 2.

[0099] 133 Two signal peaks at -19 ppm and -36 ppm were found in the Cs MAS NMR characterization spectrum ( Figure 2 ).

[0100] Preparation Example 1

[0101] Preparation Example 1 illustrates the preparation of TS-1-0.02 titanium silicalite molecular sieve.

[0102] The preparation steps of TS-1-0.02 titanium silicalite molecular sieve are as follows: Tetraethyl orthosilicate (TEOS), tetrabutyl titanate (TBOT), tetrapropylammonium hydroxide (TPAOH, 25 wt%) solution and water were mixed according to the molar ratio of SiO2∶0.02TiO2∶0.2TPAOH∶30H2O, then stirred for 60 minutes, then stirred at 80 °C for about 5 h to obtain a clear sol, then crystallized at 170 °C for 72 h. After that, the obtained solid was filtered, washed with distilled water, dried at 120 °C for 6 h, and then calcined at 550 °C for 6 h to obtain titanium silicalite molecular sieve, numbered TS-1-0.02.

[0103] XRD analysis was performed on TS-1-0.02, and it was found that it has an MFI structure ( Figure 3 ).

[0104] Hydroxyl infrared analysis was performed on TS-1-0.02, and hydroxyl peaks at 3520 cm -1 , 3690 cm -1 , 3720 cm -1 and 3740 cm -1 were found ( Figure 4 ).

[0105] UV-Vis analysis was performed on TS-1-0.02, and a signal peak at 210 nm was found ( Figure 5 ).

[0106] Example 1

[0107] This example illustrates the preparation of a cesium-loaded catalyst Cs / TS-1-A with titanium silicalite molecular sieve TS-1-0.02.

[0108] The specific steps for the Cs / TS-1-A catalyst are as follows: Weigh a certain amount of cesium nitrate and dissolve it in deionized water, and then immerse TS-1-0.02 in the cesium nitrate solution. Among them, the molar ratio of cesium to silicon is 0.03:1, and the molar ratio of TS-1-0.02 (calculated as silicon dioxide) to the solvent is 1:2. In the glove box, grind it at an absolute pressure of 50 kPa and 40 °C for 30 min to make the cesium ions evenly distributed on TS-1-0.02. Then treat the solid with steam at a temperature of 120 °C and a gauge pressure of 0.4 MPa for 3 h. Further evaporate to remove the solvent, place it in a drying oven and dry at 120 °C for 6 h, and calcine it in a muffle furnace at 400 °C for 6 h to obtain the catalyst Cs / TS-1-A.

[0109] Perform XRF characterization, UV-Vis characterization on the catalyst Cs / TS-1-A, 133 Cs MAS NMR characterization and the evaluation of the aldol condensation reaction of methyl acetate and formaldehyde. The characterization and evaluation results are shown in Table 1 and Table 2.

[0110] Perform XRD analysis on Cs / TS-1-A and find that it has an MFI structure ( Figure 6 ).

[0111] Perform nuclear magnetic cesium spectrum analysis on Cs / TS-1-A and find that there are signal peaks at -36 ppm, -73 ppm and -94 ppm ( Figure 7 ).

[0112] Perform hydroxyl infrared analysis on Cs / TS-1-A and find that there is only a hydroxyl peak at 3740 cm -1 ( Figure 8 ).

[0113] Perform UV-Vis analysis on Cs / TS-1-A and find that it has signal peaks at 210 nm, 270 nm and 330 nm ( Figure 9 ).

[0114] Example 2

[0115] This example illustrates the preparation of the cesium-loaded catalyst Cs / TS-1-B on TS-1-0.02.

[0116] The specific steps for preparing the Cs / TS-1-B catalyst are as follows: Weigh a certain amount of cesium carbonate and dissolve it in deionized water, then immerse TS-1-0.02 in the cesium carbonate solution. Among them, the molar ratio of cesium to silicon is 0.02:1, and the molar ratio of TS-1-0.02 (calculated by silicon dioxide) to the solvent is 1:4. In the glove box, grind at an absolute pressure of 30 kPa and 60 °C for 60 min to make the cesium ions evenly distributed on TS-1-0.02. Then, treat the solid with steam at a temperature of 180 °C and a gauge pressure of 0.3 MPa for 2 h. Further evaporate to remove the solvent, dry in an oven at 100 °C for 3 h, and calcine in a muffle furnace at 500 °C for 3 h to obtain the catalyst Cs / TS-1-B.

[0117] The catalyst Cs / TS-1-B was characterized by XRF, UV-Vis, 133 Cs MAS NMR, and evaluated for the aldol condensation reaction of methyl acetate and formaldehyde. The characterization and evaluation results are shown in Table 1 and Table 2.

[0118] XRD analysis of Cs / TS-1-B found that it has an MFI structure.

[0119] Nuclear magnetic cesium spectrum analysis of Cs / TS-1-B found signal peaks at -36 ppm, -73 ppm, and -94 ppm.

[0120] Hydroxyl infrared analysis of Cs / TS-1-B found that only the hydroxyl peak at 3740 cm -1 was present. UV-Vis analysis of Cs / TS-1-B found signal peaks at 210 nm, 270 nm, and 330 nm.

[0121] Preparation Example 2

[0122] This preparation example illustrates the preparation of TS-1-0.04 titanium silicalite molecular sieve.

[0123] The preparation steps of TS-1-0.04 molecular sieve are as follows: Mix tetraethyl orthosilicate (TEOS), tetrabutyl titanate (TBOT), tetrapropylammonium hydroxide (TPAOH, 25 wt%) solution, and water according to the molar ratio of SiO2∶0.04TiO2∶0.25TPAOH∶35H2O, then stir for 60 minutes, then stir at 80 °C for about 6 h to obtain a clear sol, then crystallize at 170 °C for 72 h, then filter the obtained solid, wash it with distilled water, dry it at 120 °C for 6 h, and then calcine it at 550 °C for 6 h to obtain the molecular sieve TS-1-0.04.

[0124] XRD analysis of TS-1-0.04 found that it has an MFI structure.

[0125] Hydroxyl infrared analysis was performed on TS-1-0.04, and hydroxyl peaks at 3520 cm -1 , 3690 cm -1 , 3720 cm -1 and 3740 cm -1 were found.

[0126] UV-Vis analysis was performed on TS-1-0.04, and signal peaks at 210 nm, 270 nm and 330 nm were found.

[0127] Example 3

[0128] This example illustrates the preparation of a cesium-loaded TS-1-0.04 catalyst Cs / TS-1-C.

[0129] The specific steps of the Cs / TS-1-C catalyst are as follows: Weigh a certain amount of cesium nitrate and dissolve it in isopropanol, and then immerse TS-1-0.04 in the cesium nitrate solution. Among them, the molar ratio of cesium to silicon is 0.04:1, and the molar ratio of TS-1-0.04 (calculated as silica) to the solvent is 1:8. In the glove box, stir at an absolute pressure of 100 kPa and 40 °C for 30 min to make the cesium ions evenly distributed on TS-1-0.04. Then use steam at a temperature of 120 °C and a gauge pressure of 0 MPa to treat the solid for 3 h. Further evaporate to remove the solvent, dry in an oven at 120 °C for 6 h, and calcine in a muffle furnace at 400 °C for 6 h to obtain the catalyst Cs / TS-1-C.

[0130] XRF characterization, UV-Vis characterization, 133 Cs MAS NMR characterization and evaluation of the aldol condensation reaction of methyl acetate and formaldehyde were performed on the catalyst Cs / TS-1-C, and the characterization and evaluation results are shown in Table 1 and Table 2.

[0131] XRD analysis was performed on Cs / TS-1-C, and it has an MFI structure.

[0132] Nuclear magnetic cesium spectrum analysis was performed on Cs / TS-1-C, and signal peaks at -36 ppm, -73 ppm and -94 ppm were found.

[0133] Hydroxyl infrared analysis was performed on Cs / TS-1-C, and only a hydroxyl peak at 3740 cm -1 was found.

[0134] UV-Vis analysis was performed on Cs / TS-1-C, and it has signal peaks at 210 nm, 270 nm and 330 nm.

[0135] Example 4

[0136] This example illustrates the preparation of the catalyst Cs / TS-1-D with TS-1-0.04 loaded with cesium.

[0137] The specific steps for the Cs / TS-1-D catalyst are as follows: Weigh a certain amount of cesium carbonate and dissolve it in deionized water, and then immerse TS-1-0.04 in the cesium carbonate solution. Among them, the molar ratio of cesium to silicon is 0.03:1, and the molar ratio of TS-1-0.04 (calculated by silicon dioxide) to the solvent is 1:6. In the glove box, grind it at an absolute pressure of 80 kPa and 50 °C for 15 min to make the cesium ions evenly distributed on TS-1-0.04. Then, use steam at a temperature of 180 °C and a gauge pressure of 0.8 MPa to treat the solid for 5 h. Further evaporate to remove the solvent, dry it in an oven at 130 °C for 2 h, and calcine it in a muffle furnace at 450 °C for 8 h to obtain the catalyst Cs / TS-1-D.

[0138] Perform XRF characterization, UV-Vis characterization, 133 Cs MAS NMR characterization, and the aldol condensation reaction evaluation of methyl acetate and formaldehyde on the catalyst Cs / TS-1-D. The characterization and evaluation results are shown in Table 1 and Table 2.

[0139] Perform XRD analysis on Cs / TS-1-D, and it has an MFI structure.

[0140] Perform nuclear magnetic cesium spectrum analysis on Cs / TS-1-D, and there are signal peaks at -36 ppm, -73 ppm, and -94 ppm.

[0141] Perform hydroxyl infrared analysis on Cs / TS-1-D, and there is only a hydroxyl peak at 3740 cm -1 -1.

[0142] Perform UV-Vis analysis on Cs / TS-1-D, and it has signal peaks at 210 nm, 270 nm, and 330 nm.

[0143] Preparation Example 3

[0144] This preparation example illustrates the synthesis of the mesoporous titanium silicalite HTS-0.02 (referring to the method of Chinese Patent CN1260241A).

[0145] The preparation method of HTS-0.02 is as follows: According to the molar ratio of silicon source (calculated as SiO2): titanium source (calculated as TiO2): template agent: water of 1:0.02:0.2:25, tetraethyl orthosilicate, tetrabutyl titanate, tetrapropylammonium hydroxide (25 wt%) solution and deionized water are mixed, stirred at 30 °C for about 2 h, and then stirred at 80 °C for about 8 h to obtain a sol. The obtained sol is treated at 170 °C for 72 h, and then the resulting slurry is filtered, washed with deionized water until the pH of the filtrate is lower than 9, dried at 120 °C for 6 h, and calcined at 550 °C for 6 h to obtain the intermediate TS-1 product. Then, TS-1, tetrapropylammonium hydroxide and water are mixed according to the weight ratio of 1:0.4:5, and then treated at 170 °C for 24 h. Then, the resulting slurry is filtered, dried and calcined according to the aforementioned method to obtain the titanium silicalite HTS-0.02.

[0146] XRD analysis was performed on HTS-0.02, and it has an MFI structure.

[0147] Hydroxyl infrared analysis was performed on HTS-0.02, and there are hydroxyl peaks at 3520 cm -1 , 3690 cm -1 , 3720 cm -1 and 3740 cm -1 .

[0148] UV-Vis analysis was performed on HTS-0.02, and it has signal peaks at 210 nm and 330 nm.

[0149] Example 5

[0150] This example illustrates the preparation of a cesium-loaded catalyst Cs / HTS-A of HTS-0.02.

[0151] The specific steps of the Cs / HTS-A catalyst are as follows: Weigh a certain amount of cesium nitrate and dissolve it in ethanol, and then mix HTS-A with the cesium nitrate solution. Among them, the molar ratio of cesium to silicon is 0.02:1, and the molar ratio of HTS-A (calculated as silicon dioxide) to the solvent is 1:4. In the glove box, grind and process at an absolute pressure of 40 kPa and 60 °C for 30 min to make the cesium ions evenly distributed on HTS-A. Then, the solid is treated with steam at a temperature of 150 °C and a gauge pressure of 0.3 MPa for 8 h. Further evaporate to remove the solvent, place it in a drying oven and dry at 120 °C for 3 h, and calcine in a muffle furnace at 400 °C for 5 h to obtain the catalyst Cs / HTS-A.

[0152] XRF characterization, UV-Vis characterization and 133 Cs MAS NMR characterization and the aldol condensation reaction evaluation of methyl acetate and formaldehyde were performed on the catalyst Cs / HTS-A, and the characterization and evaluation results are shown in Table 1 and Table 2.

[0153] XRD analysis was performed on Cs / HTS-A, and it has an MFI structure.

[0154] Nuclear magnetic cesium spectrum analysis was performed on Cs / HTS-A, and signal peaks at -36 ppm, -73 ppm, and -94 ppm were present.

[0155] Hydroxyl infrared analysis was performed on Cs / HTS-A, and only the hydroxyl peak at 3740 cm -1 was present.

[0156] UV-Vis analysis was performed on Cs / HTS-A, and it has signal peaks at 210 nm, 270 nm, and 330 nm.

[0157] Example 6

[0158] This example illustrates the preparation of the catalyst Cs / HTS-B with HTS-0.02 loaded with cesium.

[0159] The specific steps of the Cs / HTS-B catalyst are as follows: Weigh a certain amount of cesium hydroxide and dissolve it in deionized water, and then immerse HTS-0.02 in the cesium hydroxide solution. Among them, the molar ratio of cesium to silicon is 0.03:1, and the molar ratio of HTS-0.02 (calculated as silicon dioxide) to the solvent is 1:3. In the glove box, grind at an absolute pressure of 50 kPa and 70 °C for 30 min to make the cesium ions evenly distributed on HTS-0.02. Then, use steam at a temperature of 130 °C and a gauge pressure of 0.5 MPa to treat the solid for 4 h. Further evaporate to remove the solvent, place it in a drying oven at 110 °C for 5 h, and calcine in a muffle furnace at 500 °C for 8 h to obtain the catalyst Cs / HTS-B.

[0160] XRF characterization, UV-Vis characterization, 133 Cs MAS NMR characterization, and the evaluation of the aldol condensation reaction of methyl acetate and formaldehyde were carried out on the catalyst Cs / HTS-B, and the characterization and evaluation results are shown in Table 1 and Table 2.

[0161] XRD analysis was performed on Cs / HTS-B, and it has an MFI structure.

[0162] Nuclear magnetic cesium spectrum analysis was performed on Cs / HTS-B, and signal peaks at -36 ppm, -73 ppm, and -94 ppm were present.

[0163] Hydroxyl infrared analysis was performed on Cs / HTS-B, and only the hydroxyl peak at 3740 cm -1 was present.

[0164] UV-Vis analysis was performed on Cs / HTS-B, and it has signal peaks at 210 nm, 270 nm, and 330 nm.

[0165] Preparation Example 4

[0166] This preparation example illustrates the preparation of TS-2-0.02 titanium silicalite molecular sieve.

[0167] The preparation steps of TS-2-0.02 molecular sieve are as follows: Tetraethyl orthosilicate (TEOS), tetrabutyl titanate (TBOT), tetrabutylammonium hydroxide (TBAOH, 40 wt%) solution and water were mixed according to the molar ratio of SiO2∶0.02TiO2∶0.2TPAOH∶30H2O, then stirred for 120 min, and then stirred at 70 °C for about 4 h to obtain a clear sol, which was then crystallized at 170 °C for 72 h. After that, the obtained solid was filtered, washed with distilled water, dried at 120 °C for 6 h, and then calcined at 550 °C for 6 h to obtain the titanium silicalite molecular sieve TS-2-0.02.

[0168] XRD analysis was performed on TS-2-0.02, and it has a MEL structure.

[0169] Hydroxyl infrared analysis was performed on TS-2-0.02, and there are hydroxyl peaks at 3520 cm -1 、3690 cm -1 、3720 cm -1 and 3740 cm -1 .

[0170] UV-Vis analysis was performed on TS-2-0.02, and it has a signal peak at 210 nm.

[0171] Example 7

[0172] This example illustrates the preparation of a cesium-loaded catalyst Cs / TS-2-A of TS-2-0.02.

[0173] The specific steps of the Cs / TS-2-A catalyst are as follows: Weigh a certain amount of cesium nitrate and dissolve it in ethanol, and then immerse TS-2-0.02 in the cesium nitrate solution. Among them, the molar ratio of cesium to silicon is 0.02:1, and the molar ratio of TS-2-0.02 (calculated as silica) to the solvent is 1:2. In the glove box, it was ground at an absolute pressure of 40 kPa and 40 °C for 20 min to make the cesium ions evenly distributed on TS-2-0.02. Then the solid was treated with steam at a temperature of 140 °C and a gauge pressure of 0.4 MPa for 3 h. The solvent was further evaporated off, dried in a drying oven at 120 °C for 6 h, and calcined in a muffle furnace at 400 °C for 6 h to obtain the catalyst Cs / TS-2-A.

[0174] XRF characterization, UV-Vis characterization were performed on the catalyst Cs / TS-2-A, 133Cs MAS NMR characterization and evaluation of the aldol condensation reaction of methyl acetate and formaldehyde. The characterization and evaluation results are shown in Table 1 and Table 2.

[0175] XRD analysis was performed on Cs / TS-2-A, and it has a MEL structure.

[0176] Nuclear magnetic cesium spectrum analysis was performed on Cs / TS-2-A, and signal peaks at -36 ppm, -73 ppm, and -94 ppm were present.

[0177] Hydroxyl infrared analysis was performed on Cs / TS-2-A, and only the hydroxyl peak at 3740 cm -1 was present.

[0178] UV-Vis analysis was performed on Cs / TS-2-A, and signal peaks at 210 nm, 270 nm, and 330 nm were present.

[0179] Example 8

[0180] This example is used to prepare the catalyst Cs / TS-2-B with 0.02 loading of cesium on TS-2.

[0181] The specific steps for the Cs / TS-2-B catalyst are as follows: Weigh a certain amount of cesium hydroxide and dissolve it in deionized water, then immerse TS-2-0.02 in the cesium hydroxide solution. Among them, the molar ratio of cesium to silicon is 0.015:1, and the molar ratio of TS-2-0.02 (calculated as silicon dioxide) to the solvent is 1:3. In the glove box, grind at an absolute pressure of 30 kPa and 70 °C for 30 min to make the cesium ions evenly distributed on TS-2-0.02. Then use steam at a temperature of 160 °C and a gauge pressure of 0.6 MPa to treat the solid for 5 h. Further evaporate to remove the solvent, place it in a drying oven at 130 °C for 5 h, and calcine in a muffle furnace at 400 °C for 3 h to obtain the catalyst Cs / TS-2-B.

[0182] XRF characterization, UV-Vis characterization, 133 Cs MAS NMR characterization and evaluation of the aldol condensation reaction of methyl acetate and formaldehyde were performed on the catalyst Cs / TS-2-B. The characterization and evaluation results are shown in Table 1 and Table 2.

[0183] XRD analysis was performed on Cs / TS-2-B, and it has a MEL structure.

[0184] Nuclear magnetic cesium spectrum analysis was performed on Cs / TS-2-B, and signal peaks at -36 ppm, -73 ppm, and -94 ppm were present.

[0185] Hydroxyl infrared analysis was performed on Cs / TS-2-B, and only the hydroxyl peak at 3740 cm -1 was present.

[0186] UV-Vis analysis was performed on Cs / TS-2-B, which has signal peaks at 210 nm, 270 nm, and 330 nm.

[0187] Table 1

[0188]

[0189] From the comparison between Examples 1-8 and Comparative Examples 1-2, it can be seen that the modified titanium silicalite molecular sieve catalyst of the present invention has obvious characteristic peaks of -93 ppm and -73 ppm, and there is no hydroxyl signal peak in the hydroxyl infrared spectrum in the range of 3200 - 3720 cm -1 In the UV-Vis spectrum, the area ratio of the signal peak at 210 ± 10 nm is 50% - 95%, and the area ratio of the signal peak at 270 ± 15 nm is 10% - 45%.

[0190] Table 2

[0191] Conversion rate of methyl acetate / % Selectivity of methyl acrylate / % Yield of methyl acrylate / % Comparative Example 1 31 73 23 Comparative Example 2 43 81 35 Example 1 86 94 81 Example 2 85 95 81 Example 3 80 92 74 Example 4 79 93 73 Example 5 93 96 89 Example 6 91 96 87 Example 7 84 94 79 Example 8 85 94 80

[0192] By GC-MS characterization analysis, using this modified titanium silicalite molecular sieve catalyst for the aldol condensation reaction of methyl acetate and formaldehyde, the main product of the examples of the present invention is methyl acrylate, and the main by-products are isobutyraldehyde, methacrolein, and methyl methacrylate, while the by-products of the aldol condensation in the comparative examples contain acetone, acetic acid, etc.

[0193] From the data in Table 2, it can be seen that the aldol condensation method provided by the present invention has good conversion of methyl acetate and selectivity for the target product methyl acrylate.

[0194] Example 9

[0195] This example illustrates the reaction of the prepared catalyst for the aldol condensation reaction of methyl propionate and formaldehyde to prepare methyl methacrylate.

[0196] The catalysts prepared in Comparative Examples 1-2 and Examples 1-8 were used to catalyze the aldol condensation of methyl propionate and formaldehyde to synthesize methyl methacrylate. Using an atmospheric fixed-bed as the reactor, wherein, the molar ratio of methyl propionate to formaldehyde is 1:0.5, methanol is the solvent, and the molar ratio of methyl propionate to methanol is 1:2, and the feed space velocity of the raw material mixture is 0.3 h -1; The catalyst dosage was 5 g; During the reaction process, the flow rate of the carrier gas (N2) was maintained at 30 mL / min, and the reaction temperature was 360 °C. After the product was condensed, chromatographic analysis was carried out, and the external standard method was used for quantification. Among them, the analysis conditions of the chromatograph were: Agilent-6890 chromatograph, HP-5 capillary chromatographic column, injection volume 0.5 μL, injection port temperature 300 °C. The column temperature was maintained at 100 °C for 2 min, and then increased to 260 °C at a rate of 15 °C / min and maintained for 5 min. FID detector, detector temperature 380 °C.

[0197] The calculation of conversion, selectivity and yield is as follows:

[0198]

[0199]

[0200] Y 甲基丙烯酸甲酯 =C 丙酸甲酯 ×S 甲基丙烯酸甲酯

[0201] The reaction results are shown in Table 3.

[0202] Table 3

[0203] Catalyst Conversion rate of methyl propionate / % Selectivity of methyl methacrylate / % Yield of methyl methacrylate / % Comparative Example 1 13 71 9 Comparative Example 2 17 78 13 Example 1 44 97 43 Example 2 45 96 43 Example 3 42 95 40 Example 4 41 95 39 Example 5 47 98 46 Example 6 48 98 47 Example 7 46 96 44 Example 8 45 97 44

[0204] Characterized by GC-MS analysis, using this modified titanium silicalite molecular sieve catalyst for the aldol condensation reaction of methyl propionate and formaldehyde, the main product of the examples of the present invention is methyl methacrylate, and the main by-products are methyl isobutyrate, α-methyl-γ-butyrolactone, dimethyl 2,4-dimethylglutarate, etc., while the by-products of the aldol condensation of the comparative example mainly contain acetone, 3,4-dimethyl-2-cyclopentenone, methyl isobutyrate, propionic acid, etc.

[0205] It can be seen from the data in Table 3 that the aldol condensation method provided by the present invention has good conversion of methyl propionate and selectivity of the target product methyl methacrylate.

[0206] Example 10

[0207] This example illustrates the reaction of the prepared catalyst for catalyzing the aldol condensation reaction of butyraldehyde to prepare octenal.

[0208] The catalysts prepared in Comparative Examples 1-2 and Examples 1-8 were used to catalyze the aldol condensation of n-butyraldehyde to synthesize octenal. Using an atmospheric fixed bed as the reactor, n-butyraldehyde was introduced into the fixed bed reaction, and the feed space velocity was 2 h -1; The catalyst dosage was 5 g; during the reaction, the flow rate of the carrier gas (N2) was maintained at 30 mL / min, and the reaction temperature was 330 °C. After the product was condensed, chromatographic analysis was carried out, and the external standard method was used for quantification. Among them, the analysis conditions of the chromatograph were: Agilent-6890 chromatograph, HP-5 capillary chromatographic column, injection volume 0.5 μL, injection port temperature 300 °C. The column temperature was maintained at 100 °C for 2 min, and then increased to 260 °C at a rate of 15 °C / min and maintained for 5 min. FID detector, detector temperature 380 °C.

[0209] The calculations of conversion rate, selectivity and yield are as follows:

[0210]

[0211]

[0212] Y 辛烯醛 = C 正丁醛 × S 辛烯醛

[0213] The reaction results are shown in Table 4.

[0214] Table 4

[0215] Catalyst Conversion rate of n-butanal / % Selectivity of octenal / % Yield of octenal / % Comparative Example 1 55 78 43 Comparative Example 2 67 82 55 Example 1 98 99 97 Example 2 97 99 96 Example 3 95 98 93 Example 4 96 98 94 Example 5 99 99 98 Example 6 99 99 98 Example 7 97 99 96 Example 8 98 99 97

[0216] Characterized by GC-MS analysis, using this modified titanium silicalite molecular sieve catalyst for the aldol condensation reaction of n-butyraldehyde, the main product of the examples of the present invention is octenal, and the main by-product is hydroxyoctanal.

[0217] It can be seen from the data in Table 4 that the aldol condensation method provided by the present invention has good conversion rate of n-butyraldehyde and selectivity of the target product octenal.

Claims

1. A modified titanium silicalite molecular sieve, characterized in that, Contains titanium, silicon, oxygen, and cesium elements; its 133 The Cs MAS NMR spectrum has at least resonance absorption peaks at -94 ± 15 ppm, -73 ± 15 ppm, and -36 ± 15 ppm.

2. The modified titanium silicalite molecular sieve according to claim 1, wherein When the peak intensities of the resonance absorption peaks at -94 ± 15 ppm, -73 ± 15 ppm, and -36 ± 15 ppm are I1, I2, and I3 respectively, I2 > I1 > I3.

3. The modified titanium silicalite molecular sieve according to claim 2, wherein, The following relationships exist for their peak intensities: I1 / I2 = 0.3 - 1, and I3 / I2 = 0.2 - 0.

9.

4. The modified titanium silicalite molecular sieve according to claim 1, characterized in that, In its infrared hydroxyl spectrum, 3200 - 3720 cm -1 There is no hydroxyl signal peak.

5. The modified titanium silicalite molecular sieve according to claim 1, wherein its UV-Vis spectrum has a tetracoordinated titanium signal peak at 210 ± 10 nm and a hexacoordinated titanium signal peak at 270 ± 15 nm.

6. The modified titanium silicalite molecular sieve according to claim 5, wherein, Based on the total area of the peaks in the 200 - 800 nm range of the UV-Vis spectrum, the peak area ratio of the tetracoordinated titanium signal peak at 210 ± 10 nm is 50% - 95%, and the peak area ratio of the hexacoordinated titanium signal peak at 270 ± 15 nm is 10% - 45%.

7. The modified titanium silicalite molecular sieve according to claim 1, wherein 8. For this, the molar ratio of cesium element to silicon element is (0.0001 - 0.1):1, preferably (0.001 - 0.08):1, further preferably (0.005 - 0.06):1, more preferably (0.008 - 0.04):1, and most preferably (0.01 - 0.03):

1.

8. The modified titanium silicalite molecular sieve according to claim 1, wherein, The molar ratio of titanium element to silicon element is (0.0001 - 0.1):1, preferably (0.001 - 0.08):1, further preferably (0.004 - 0.06):1, more preferably (0.008 - 0.04):1, and most preferably (0.01 - 0.03):

1.

9. The modified titanium silicalite molecular sieve according to claim 1, characterized in that, It has a crystal structure selected from at least one of MFI, MEL, MWW, BEA, MOR, SVR, or an amorphous structure selected from at least one of MCM-41, MCM-48, SBA-15.

10. The preparation method of the modified titanium silicalite molecular sieve according to any one of claims 1-9, characterized in that, This method includes the steps of mixing a titanium silicalite as the starting modification raw material with a cesium hydroxide or cesium salt, then treating it under steam conditions, and drying and calcining the treated solid to obtain the modified titanium silicalite.

11. The preparation method according to claim 10, wherein, The mixing is carried out by impregnation, ion exchange, spraying, solid-phase ion exchange, or grinding methods, with grinding method being preferred.

12. The preparation method according to claim 10, characterized in that, The mixing is carried out in the presence of a solvent.

13. The preparation method according to claim 10, wherein The titanium silicalite as the starting modification raw material is one or more of the molecular sieves with MFI, MEL, MWW, BEA, MOR, SVR crystal structures, or one or more of MCM-41, MCM-48, SBA-15 amorphous structures.

14. The preparation method according to claim 10 or 13, characterized in that, The titanium silicalite as the starting modification raw material is obtained by hydrothermal synthesis or post-synthesis methods.

15. The preparation method according to claim 10, characterized in that, The titanium silicalite as the starting modification raw material has a molar ratio of titanium element to silicon element of (0.0001 - 0.1):1, preferably (0.001 - 0.08):1, further preferably (0.004 - 0.06):1, more preferably (0.008 - 0.04):1, and most preferably (0.01 - 0.03):

1.

16. The preparation method according to claim 10, characterized in that, The cesium salt is selected from one or more of cesium hydrochloride, hypochlorite, chlorite, metachlorite, perchlorate, nitrate, sulfate, bisulfate, sulfite, bisulfite, phosphate, hydrogen phosphate, dihydrogen phosphate, metaphosphate, hypophosphite, carboxylate, pyrophosphate, and carboxylates of C1-C 20 of one or more.

17. The preparation method according to claim 10, characterized in that, The molar ratio of the titanium silicalite as the starting modification raw material based on silicon element and the cesium hydroxide or cesium salt based on cesium is 1: (0.0001-0.1)。 18. The preparation method according to claim 10, characterized in that, The mixing is carried out under the conditions of 20 - 150 °C and an absolute pressure of 10 - 100 KPa for 5 - 120 min; preferably, the mixing is carried out under the conditions of 25 - 100 °C, more preferably 30 - 70 °C, an absolute pressure of 20 - 80 KPa, more preferably 30 - 50 KPa for 5 - 60 min, and more preferably 10 - 30 min.

19. The preparation method according to claim 10, characterized in that, The treatment under the steam condition is carried out with water vapor at 100 - 200 °C, preferably 120 - 180 °C, more preferably 130 - 160 °C, and a gauge pressure of 0 - 1 MPa, preferably 0.1 - 0.8 MPa, more preferably 0.3 - 0.6 MPa for 0.1 - 24 h, preferably 1 - 12 h, and further preferably 2 - 8 h.

20. A titanium-silicate molecular sieve catalyst, characterized in that, Containing the modified titanium silicalite molecular sieve described in claims 1 - 9 or the modified titanium silicalite molecular sieve obtained by the preparation method of any one of claims 10 - 19.

21. The titanium silicalite molecular sieve catalyst according to claim 20, wherein, The weight ratio of the modified titanium silicalite molecular sieve is 5% - 100%.

22. A method for aldol condensation, characterized in that, In the presence of the titanium silicalite molecular sieve catalyst of claim 20, a carbonyl compound having α-H undergoes a carbon-carbon bond coupling reaction with another carbonyl compound to form a carbonyl compound having β-hydroxy or a carbonyl compound having α,β-unsaturated bonds.

23. The aldol condensation method according to claim 22, characterized in that, The reaction temperature is 200 - 500 °C, preferably 250 - 480 °C, more preferably 300 - 400 °C, and the reaction pressure is 0 - 2.5 MPa, preferably 0.2 - 1.5 MPa, more preferably 0.5 - 1.0 MPa. Based on the total mass of the carbonyl compound and the diluent, the space velocity of the reaction liquid is 0.05 - 5 h -1 , preferably 0.08 - 3 h -1 , more preferably 0.1 - 2 h -1 .

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