Preparation method of silicon-based composite solid acid catalyst and application thereof

Abstract

The application discloses a preparation method of a silicon-based composite solid acid catalyst and application thereof. SiO2 microsphere powder is added into a certain amount of chloroform solvent and chlorosulfonic acid, and is fully stirred until the solution is uniformly mixed and no gas is emitted, and is refluxed at 60-90 DEG C for 0.5-3h; the reaction is ended, and the SiO2-SO3H powder is prepared after washing and drying; the prepared SiO2-SO3H powder is added into a certain amount of toluene solvent, is uniformly dispersed in the solvent through ultrasonic treatment, and then a certain amount of APTES is added; the reaction system is refluxed at 90-120 DEG C for 4-7h under stirring, then a certain amount of CrCl3.6H2O is added into the mixed solution after reflux reaction, and the reaction is continuously carried out at 90-120 DEG C for 2-5h; after the reaction is ended, separation, washing and drying are carried out, and the composite solid acid Cr-SiO2-SO3H is obtained. 3+ The prepared composite solid acid catalyst Cr-SiO2-SO3H simultaneously loads-SO3H and Cr on the surface of silicon, can efficiently convert cellulose into HMF, and has excellent stability and can be recycled.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation and application technology, specifically relating to a method for preparing a silicon-based composite solid acid catalyst and its application. Background Technology

[0002] Among all renewable resources, cellulose is widely used in the production of various value-added chemicals due to its abundant sources, low price, and renewability. 5-Hydroxymethylfurfural (HMF) is a furan compound composed of a furan ring, aldehyde group, and alcohol group. It is an important platform compound, known as the "sleeping giant," capable of producing various high value-added products through chemical reactions.

[0003] Cellulose, glucose, and fructose are common raw materials for the preparation of HMF (hydrogenated fatty acids). The conversion of cellulose to HMF is generally considered to involve three steps: 1. Under acidic conditions, the β-1,4-glycosidic bonds in cellulose break, hydrolyzing to glucose; 2. Glucose isomerizes to fructose under the catalysis of enzymes, Lewis acids, or bases; 3. Fructose dehydrates under acidic conditions to obtain HMF. Currently, CrCl3 is one of the reported highly efficient catalysts for the conversion of glucose to HMF, but chromium ions pose a significant environmental hazard and do not meet the requirements of "green chemistry." Summary of the Invention

[0004] To achieve the above objectives and solve the problems existing in the prior art, this invention provides a method for preparing a silicon-based composite solid acid catalyst and its application. The composite solid acid catalyst Cr-SiO2-SO3H prepared by this method simultaneously supports -SO3H and Cr on the surface of the silicon substrate. 3+ It can efficiently convert cellulose into HMF and has excellent stability, making it recyclable.

[0005] One objective of this invention is to provide a method for preparing a silicon-based composite solid acid catalyst, the specific steps of which are as follows:

[0006] Step 1: Add SiO2 microspheres to a certain volume of solvent, disperse by ultrasonication, heat the reaction system under reflux at 100-130℃ for 6-10 hours, wash and dry to obtain a powdered product with SiO2 microsphere surface modification.

[0007] Step 2: Add the powdered product obtained after washing and drying in Step 1 to a certain amount of chloroform solvent, add chlorosulfonic acid, stir thoroughly until the solution is uniformly mixed and no gas escapes, reflux at 60-90℃ for 0.5-3h, the reaction is completed, wash and dry to prepare SiO2-SO3H powder.

[0008] Step 3: Add the prepared SiO2-SO3H powder to a certain amount of solvent, and sonicate to disperse the SiO2-SO3H powder evenly in the solvent. Then add a certain amount of APTES to the reaction system and reflux the reaction system at 90-120℃ for 4-7 hours with stirring. Subsequently, add a certain amount of CrCl3·6H2O to the mixture after reflux reaction and continue to react at 90-120℃ for 2-5 hours. After the reaction is completed, separate, wash and dry to obtain the composite solid acid Cr-SiO2-SO3H.

[0009] As a preferred embodiment, in step two, 20 ml of chloroform is added to each gram of powdered product after surface modification of SiO2 microspheres.

[0010] As a preferred embodiment, in step two, the amount of chlorosulfonic acid added is 0.15-0.75 ml per gram of powdered product after surface modification of SiO2 microspheres.

[0011] As a preferred embodiment, in step three, the amount of APTES added is 1-6 mL per gram of SiO2-SO3H powder.

[0012] As a preferred embodiment, in step three, the mass ratio of CrCl3·6H2O to SiO2-SO3H is 0.1-0.3:1.

[0013] As a preferred embodiment, in step three, ultrasonic treatment for 3-15 minutes is performed to ensure that the SiO2-SO3H powder is evenly dispersed in the solvent.

[0014] As a preferred embodiment, the SiO2 microspheres are prepared in step one as follows:

[0015] S11. Select Triton TX-100 as the surfactant and n-hexanol as the co-surfactant. Mix Triton TX-100 and n-hexanol at a certain volume ratio to obtain a mixed surfactant. Then mix cyclohexane with the mixed surfactant at a certain mass ratio, ultrasonically vibrate, and then add a certain amount of deionized water. The molar ratio of deionized water to Triton TX-100 is 4-16:1. Then ultrasonically vibrate again to mix it evenly and prepare a microemulsion. Add ammonia water to adjust its pH to 10-12.

[0016] S12. A certain amount of ethyl silicate is slowly added dropwise to the microemulsion. The amount of ethyl silicate added is 1 / 20 to 1 / 5 of the molar amount of water. The mixture is stirred at room temperature for more than 24 hours. After the reaction is completed, acetone is added to break the microemulsion. Then, the mixture is separated, washed, and dried to prepare SiO2 microspheres.

[0017] A second objective of this invention is to provide applications for silicon-based composite solid acid catalysts.

[0018] Add cellulose to the ionic liquid [BMIM]Cl, the amount of cellulose added is 5-15% of the mass of [BMIM]Cl, and stir in a constant temperature oil bath at 90-120℃ for 0.5-2 hours to completely dissolve the cellulose.

[0019] After adding a certain amount of deionized water, the temperature is raised to 150-190℃. A certain amount of the catalyst composite solid acid Cr-SiO2-SO3H prepared above is added, and tetrahydrofuran is added under reflux. The amount of tetrahydrofuran added is 0-4 times the volume of [BMIM]Cl. The reaction is continued under reflux for 2-6 hours with stirring to obtain 5-hydroxymethylfurfural.

[0020] As a preferred option, the amount of Cr-SiO2-SO3H added is 0.5-2 times the mass of microcrystalline cellulose.

[0021] Compared with the prior art, the present invention has at least the following beneficial effects:

[0022] Firstly, compared with existing technologies, this approach provides a composite solid acid catalyst Cr-SiO2-SO3H by preparing a novel catalyst and optimizing the preparation method. This is achieved by simultaneously loading -SO3H and Cr onto the surface of a silicon-based substrate. 3+ This method can efficiently convert cellulose into HMF and exhibits excellent stability and recyclability. Structural characterization confirmed that -SO3H is supported on SiO2, and further demonstrated that Cr... 3+ It complexes with -NH2 in APTES and is loaded onto SiO2-SO3H, thus giving the prepared Cr-SiO2-SO3H a composite catalytic active site, possessing the catalytic effects of both L acid and Brønsted acid sites.

[0023] Secondly, this scheme provides an application of the composite solid acid catalyst Cr-SiO2-SO3H. Its application in the preparation of HMF from cellulose can effectively and significantly improve the HMF yield. The HMF yield using Cr-SiO2-SO3H as a catalyst is significantly higher than that using SiO2-SO3H or Cr-SiO2 as catalysts. Cr-SiO2-SO3H also contains... The Lewis acidic sites can synergistically catalyze the conversion of cellulose to HMF, improving reaction efficiency. Compared with catalysts using a single active component, the composite solid acid catalyst Cr-SiO2-SO3H exhibits better catalytic performance. Attached Figure Description

[0024] Figure 1 Phase diagrams of ternary microemulsions of Triton TX-100 and n-hexanol at different volume ratios (VTX-100 :V Hexanol =3:1);

[0025] Figure 2 Phase diagrams of ternary microemulsions of Triton TX-100 and n-hexanol at different volume ratios (V TX-100 :V Hexanol =3:2);

[0026] Figure 3 SEM images of SiO2 prepared under conditions with different molar ratios of water and Triton TX-100 (n H2O :n TX-100 =4);

[0027] Figure 4 SEM images of SiO2 prepared under conditions with different molar ratios of water and Triton TX-100 (n H2O :n TX-100 =8);

[0028] Figure 5 SEM images of SiO2 prepared under conditions with different molar ratios of water and Triton TX-100 (n H2O :n TX-100 =12);

[0029] Figure 6 SEM images (n) of SiO2 prepared under conditions with different molar ratios of water and TEOS H2O :n TEOS =6);

[0030] Figure 7 SEM images (n) of SiO2 prepared under conditions with different molar ratios of water and TEOS H2O :n TEOS =12);

[0031] Figure 8 SEM images (n) of SiO2 prepared under conditions with different molar ratios of water and TEOS H2O :n TEOS =20);

[0032] Figure 9 Infrared comparison spectra of SiO2 and Cr-SiO2-SO3H;

[0033] Figure 10 The full spectrum of Cr-SiO2-SO3H is shown.

[0034] Figure 11 The high-resolution C1s spectrum of Cr-SiO2-SO3H is shown.

[0035] Figure 12The high-resolution S2p spectrum of Cr-SiO2-SO3H;

[0036] Figure 13 The high-resolution Cr 2p spectrum of Cr-SiO2-SO3H is shown.

[0037] Figure 14 The Py-IR spectrum of Cr-SiO2-SO3H;

[0038] Figure 15 TG and DTG spectra of Cr-SiO2-SO3H

[0039] Figure 16 Schematic diagram showing the effect of SiO2-SO3H, Cr-SiO2, and Cr-SiO2-SO3H catalysts on HMF yield;

[0040] Figure 17 A schematic diagram of the mechanism for preparing HMF from cellulose using Cr-SiO2-SO3H catalysis;

[0041] Figure 18 Table showing the effect of the number of Cr-SiO2-SO3H cycles on the yield of HMF. Detailed Implementation

[0042] To make the technical means, creative features, objectives, and beneficial effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0043] In addition, to better illustrate the present invention, numerous specific details are given in the following detailed embodiments. Those skilled in the art should understand that the present invention can be implemented even without certain specific details. In other embodiments, methods, means, equipment and steps well known to those skilled in the art are not described in detail in order to highlight the main points of the present invention.

[0044] This scheme provides a method for preparing a silicon-based composite solid acid catalyst, the specific steps of which are as follows:

[0045] Step 1: Preparation of SiO2 microspheres. Triton TX-100 was selected as the surfactant and n-hexanol as the co-surfactant. They were mixed at a volume ratio of 3:2 to obtain a mixed surfactant (MS). Then, cyclohexane and MS were mixed at a mass ratio of 1:1. After ultrasonic vibration, a certain amount of deionized water was added, 4-16 times the molar amount of TX-100. The mixture was ultrasonically vibrated again to ensure homogeneity, thus preparing a microemulsion. Ammonia was added to adjust the pH to 10-12. A certain amount of tetraethyl orthosilicate (TEOS) was dispensed using a peristaltic pump at a rate of 1 mL / min. -1The ester was slowly added dropwise to the microemulsion, with the amount of tetraethyl orthosilicate (TEOS) being 1 / 20 to 1 / 5 of the molar amount of water. The mixture was stirred at room temperature for more than 24 hours. After the reaction was complete, a small amount of acetone was added to break the microemulsion. The mixture was then separated by centrifugation (10,000 r / min, 5 min). The precipitate was repeatedly washed with anhydrous ethanol and dried to prepare SiO2 microspheres.

[0046] Step 2: SiO2 sulfonation. The prepared SiO2 microspheres are added to a solvent containing benzyl alcohol and toluene in a volume ratio of 1:4. After ultrasonic dispersion, the mixture is refluxed at 100-130℃ for 6-10 hours in a constant-temperature oil bath. After the reaction, the mixture is washed approximately ten times with anhydrous ethanol, dried, and set aside to obtain a powdered product with modified SiO2 microsphere surface. The dried powdered product is added to a chloroform solvent, along with chlorosulfonic acid (ClSO3H). The amount of chlorosulfonic acid (ClSO3H) added is 0.15-0.75 ml per gram of the powdered product with modified SiO2 microsphere surface. The mixture is stirred thoroughly until the solution is homogeneous and no gas escapes. The mixture is refluxed at 60-90℃ for 0.5-3 hours. After the reaction, the mixture is washed with anhydrous ethanol and dried under vacuum to obtain sulfonated silica solid acid SiO2-SO3H.

[0047] Step 3: Loading chromium ions. The prepared SiO2-SO3H was added to toluene solvent and sonicated for 3-15 min to ensure uniform dispersion. Then, γ-aminopropyltriethoxysilane (APTES) was added at a volume ratio of 1-6 mL per gram of SiO2-SO3H sample. The mixture was refluxed at 90-120℃ for 4-7 h with magnetic stirring. Subsequently, CrCl3·6H2O was added to the mixture at a mass ratio of 0.1-0.3 times the mass of the SiO2-SO3H sample. The reaction was continued for 2-5 h while maintaining a constant temperature. After the reaction, the mixture was separated by centrifugation (10000 r / min, 5 min), and the precipitate was repeatedly washed and vacuum dried to obtain the composite solid acid Cr-SiO2-SO3H.

[0048] This scheme also provides a method for preparing 5-hydroxymethylfurfural using the above-mentioned silicon-based composite solid acid catalyst. A certain amount of microcrystalline cellulose (MCC) is added to the ionic liquid [BMIM]Cl. The amount of microcrystalline cellulose (MCC) added is 5-15% of the mass of [BMIM]Cl. The mixture is stirred in a constant temperature oil bath at 90-120℃ for 0.5-2 hours to completely dissolve the microcrystalline cellulose. After adding 1% (by mass) of deionized water to the [BMIM]Cl reaction system, the temperature was raised to 150-190℃. The prepared catalyst Cr-SiO2-SO3H was then added, with the amount of Cr-SiO2-SO3H added being 0.5-2 times the mass of the microcrystalline cellulose. Tetrahydrofuran (THF) was also added, with the amount of THF added being 0-4 times the volume of [BMIM]Cl. The mixture was mechanically stirred and reacted at 150-190℃ for 2-6 hours. After standing and separating the layers, the contents of 5-hydroxymethylfurfural and glucose were determined, and the yield of 5-hydroxymethyl and the conversion rate of the raw materials were calculated.

[0049] The mechanism of Cr-SiO2-SO3H catalysis for the preparation of HMF from cellulose is as follows: Figure 17 As shown, in the ionic liquid reaction phase, cellulose is hydrolyzed to glucose under the catalysis of the Brønsted acid active sites in Cr-SiO2-SO3H. Glucose, under the action of the Lewis acid active sites, undergoes a ring-opening-hydrogen transfer-ring-closure pathway to isomerize to fructose. Fructose, under the catalysis of the Brønsted acid sites, loses three water molecules to obtain the target product HMF. HMF in the [BMIM]Cl reaction phase is immediately extracted in situ into THF upon formation, thereby reducing reaction byproducts and increasing the HMF yield.

[0050] Example 1

[0051] Triton TX-100 was selected as the surfactant and n-hexanol as the co-surfactant. They were mixed at a volume ratio of 3:2 to obtain a mixed surfactant (MS). Subsequently, cyclohexane and MS were mixed at a mass ratio of 1:1, ultrasonically vibrated, and then a certain amount of deionized water (12 times the molar amount of TX-100) was added. The mixture was ultrasonically vibrated again to ensure homogeneity, thus preparing a microemulsion. Ammonia was added to adjust the pH to 11. A certain amount of tetraethyl orthosilicate (TEOS) was then pumped using a peristaltic pump at a rate of 1 mL / min. -1 The ester was slowly added dropwise to the microemulsion, with the amount of tetraethyl orthosilicate (TEOS) being 1 / 20 of the molar amount of deionized water. The mixture was stirred at room temperature for more than 24 hours. After the reaction was complete, a small amount of acetone was added until the microemulsion was broken. The mixture was then separated by centrifugation (10,000 r / min, 5 min). The precipitate was repeatedly washed with anhydrous ethanol and dried to prepare SiO2 microspheres with an average particle size of 72 nm.

[0052] Take 2g of the SiO2 microspheres prepared in the previous step and add them to a round-bottom flask containing 5mL benzyl alcohol and 20mL toluene. After ultrasonic dispersion, heat in a constant temperature oil bath at 110℃ under reflux for 8h. After the reaction is complete, wash with anhydrous ethanol about ten times, and then vacuum dry to obtain a powdered product with modified SiO2 microsphere surface. Take 1g of the dried powdered product with modified SiO2 microsphere surface and add it to a round-bottom flask containing 20mL chloroform and 0.6mL chlorosulfonic acid (ClSO3H). Stir thoroughly until the solution is uniformly mixed and no gas escapes. Reflux at 70℃ for 2h. After the reaction is complete, wash with anhydrous ethanol and vacuum dry to prepare SiO2-SO3H.

[0053] Add 1g of SiO2-SO3H powder and 20mL of toluene obtained in the previous step to a round-bottom flask. Sonicate for 5min to disperse the powder evenly. Then add 2mL of APTES and reflux at 110℃ for 5h with magnetic stirring. Then add 0.2g of CrCl3·6H2O to the mixture and continue the reaction for 3h while keeping the temperature constant. After the reaction is completed, separate by centrifugation (10000r / min, 5min), wash repeatedly to obtain the precipitate, and dry under vacuum to obtain 1.12g of Cr-SiO2-SO3H.

[0054] Example 2

[0055] Triton TX-100 was selected as the surfactant and n-hexanol as the co-surfactant. They were mixed at a volume ratio of 3:2 to obtain a mixed surfactant (MS). Subsequently, cyclohexane and MS were mixed at a mass ratio of 1:1, ultrasonically vibrated, and then a certain amount of deionized water was added. The amount of deionized water added was four times the molar amount of TX-100. The mixture was ultrasonically vibrated again to ensure homogeneity, thus preparing a microemulsion. Ammonia was added to adjust the pH to 12. A certain amount of tetraethyl orthosilicate (TEOS) was dispensed using a peristaltic pump at a rate of 1 mL / min. -1 The ester was slowly added dropwise to the microemulsion, with the amount of tetraethyl orthosilicate (TEOS) being 1 / 5 the molar amount of deionized water. The mixture was stirred at room temperature for at least 24 hours. After the reaction was complete, acetone was added to break the microemulsion. The microemulsion was then separated by centrifugation (10000 r / min, 5 min). The precipitate was repeatedly washed with anhydrous ethanol and dried to prepare SiO2 microspheres with an average particle size of 105 nm.

[0056] Take 2g of the SiO2 microspheres obtained in the previous step and add them to a round-bottom flask containing 5mL benzyl alcohol and 20mL toluene. After ultrasonic dispersion, heat in a constant temperature oil bath at 130℃ for reflux for 6h. After the reaction is complete, wash with anhydrous ethanol about ten times, and then vacuum dry to obtain a powdered product with SiO2 microsphere surface modification. Take 1g of the dried powdered product with SiO2 microsphere surface modification and add it to a round-bottom flask containing 20mL chloroform and 0.75mL chlorosulfonic acid (ClSO3H). Stir thoroughly until the solution is uniformly mixed and no gas escapes. Reflux at 60℃ for 3h. After the reaction is complete, wash with anhydrous ethanol and vacuum dry to prepare SiO2-SO3H.

[0057] Add 1g of SiO2-SO3H powder and 20mL of toluene obtained in the previous step to a round-bottom flask. Sonicate for 5min to disperse the powder evenly. Then add 1mL of APTES and reflux at 90℃ for 7h with magnetic stirring. Then add 0.3g of CrCl3·6H2O to the mixture and continue the reaction for 5h while keeping the temperature constant. After the reaction is completed, separate by centrifugation (10000r / min, 5min), wash repeatedly to obtain the precipitate, and dry under vacuum to obtain 1.24g of Cr-SiO2-SO3H.

[0058] Example 3

[0059] Triton TX-100 was selected as the surfactant and n-hexanol as the co-surfactant. They were mixed at a volume ratio of 3:2 to obtain a mixed surfactant (MS). Subsequently, cyclohexane and MS were mixed at a mass ratio of 1:1, ultrasonically vibrated, and then a certain amount of deionized water was added. The amount of deionized water added was 16 times the molar amount of TX-100. The mixture was ultrasonically vibrated again to ensure homogeneity, thus preparing a microemulsion. Ammonia was added to adjust the pH to 10. A certain amount of tetraethyl orthosilicate (TEOS) was dispensed using a peristaltic pump at a rate of 1 mL / min. -1 The ester was slowly added dropwise to the microemulsion, with the amount of tetraethyl orthosilicate (TEOS) being 1 / 12 of the molar amount of deionized water. The mixture was stirred at room temperature for at least 24 hours. After the reaction was complete, acetone was added to break the microemulsion. The microemulsion was then separated by centrifugation (10000 r / min, 5 min). The resulting precipitate was repeatedly washed with anhydrous ethanol and dried to obtain SiO2 microspheres with an average particle size of 91 nm.

[0060] Take 2g of the SiO2 microspheres obtained in the previous step and add them to a round-bottom flask containing 5mL benzyl alcohol and 20mL toluene. After ultrasonic dispersion, heat in a constant temperature oil bath at 100℃ for reflux for 10h. After the reaction is complete, wash with anhydrous ethanol about ten times, and then vacuum dry to obtain a powdered product with SiO2 microsphere surface modification. Take 1g of the dried powdered product with SiO2 microsphere surface modification and add it to a round-bottom flask containing 20mL chloroform and 0.15mL chlorosulfonic acid (ClSO3H). Stir thoroughly until the solution is mixed evenly and no gas escapes. Then add 1g of dried powder and reflux at 90℃ for 0.5h. After the reaction is complete, wash with anhydrous ethanol and vacuum dry to prepare SiO2-SO3H.

[0061] Add 1g of SiO2-SO3H powder and 20mL of toluene obtained in the previous step to a round-bottom flask. Sonicate for 5min to disperse the powder evenly. Then add 6mL of APTES and reflux at 120℃ for 4h with magnetic stirring. Then add 0.1g of CrCl3·6H2O to the mixture and continue the reaction for 5h while keeping the temperature constant. After the reaction is completed, separate by centrifugation (10000r / min, 5min). Wash the precipitate repeatedly and dry it under vacuum to obtain 1.27g of Cr-SiO2-SO3H.

[0062] Example 4

[0063] Triton TX-100 was selected as the surfactant and n-hexanol as the co-surfactant. They were mixed at a volume ratio of 3:2 to obtain a mixed surfactant (MS). Then, cyclohexane and MS were mixed at a mass ratio of 1:1, ultrasonically vibrated, and a certain amount of deionized water (16 times the molar amount of TX-100) was added. The mixture was ultrasonically vibrated again to ensure homogeneity, thus preparing a microemulsion. Ammonia was added to adjust the pH to 10. A certain amount of tetraethyl orthosilicate (TEOS) was slowly added dropwise to the microemulsion at a rate of 1 mL·min⁻¹ using a peristaltic pump, the amount being 1 / 12 of the molar amount of deionized water. The mixture was stirred at room temperature for at least 24 hours. After the reaction was complete, acetone was added to break the microemulsion. The microemulsion was then separated by centrifugation (10000 r / min, 5 min). The precipitate was repeatedly washed with anhydrous ethanol and dried to prepare SiO₂ microspheres with an average particle size of 91 nm.

[0064] 2g of the SiO2 microspheres prepared in the previous step were added to a round-bottom flask containing 5mL benzyl alcohol and 20mL toluene. After ultrasonic dispersion, the mixture was heated under reflux in a constant temperature oil bath at 100℃ for 10h. After the reaction was completed, the mixture was washed approximately ten times with anhydrous ethanol and then vacuum dried to obtain a powdery product with modified SiO2 microsphere surface. 1g of the dried powdery product with modified SiO2 microsphere surface was added to a round-bottom flask containing 20mL chloroform and 0.15mL chlorosulfonic acid (ClSO3H). The mixture was stirred thoroughly until the solution was homogeneous and no gas escaped. The mixture was refluxed at 90℃ for 0.5h. After the reaction was completed, the mixture was washed with anhydrous ethanol and vacuum dried to prepare SiO2-SO3H.

[0065] Add 1g of SiO2-SO3H powder and 20mL of toluene obtained in the previous step to a round-bottom flask. Sonicate for 5min to disperse the powder evenly. Then add 2mL of APTES and reflux at 110℃ for 5h with magnetic stirring. Then add 0.125g of CrCl3·6H2O to the mixture and continue the reaction for 2h while keeping the temperature constant. After the reaction is completed, separate by centrifugation (10000r / min, 5min), wash repeatedly to obtain the precipitate, and dry under vacuum to obtain 1.08g of Cr-SiO2-SO3H.

[0066] This method employs visual titration to construct the ternary microemulsion phase diagram. MS and cyclohexane are mixed thoroughly at mass ratios of 0:10, 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, 9:1, and 10:0. Under magnetic stirring, deionized water is slowly added dropwise to these MS and cyclohexane mixtures at different mass ratios. The phase transition point where the solution changes from clear to turbid is the disappearance of the microemulsion phase. The amount of deionized water used at this point is recorded. The mass fractions of cyclohexane, MS, and deionized water in the system are calculated, and the ternary microemulsion phase diagram is plotted.

[0067] Without the addition of a co-surfactant, the surfactant in its high-concentration liquid crystal state is difficult to bend and cannot interact with cyclohexane and deionized water to form a microemulsion. The co-surfactant hexanol can insert into the cyclohexane / deionized water interface, assisting the surfactant Triton TX-100 (TX-100) in solidifying at the two-phase interface. Figure 1 , 2 The figures show the phase diagrams of ternary microemulsions with volume ratios of Triton TX-100 and n-hexanol of 3:1 and 3:2, respectively. The shaded areas represent the microemulsion regions, indicating a stable microemulsion state, while the blank areas represent the regions where phase separation occurs. The results show that when V... TX-100 :V HexanolWhen the surfactant-to-co-surfactant ratio is 3:2, the microemulsion area is relatively large. An appropriate ratio of surfactant to co-surfactant helps to expand the microemulsion area, form a stable microemulsion, and facilitate experimental operation. Therefore, after research, V was selected in Examples 1-4 above. TX-100 :V Hexanol =3:2 as a mixed surfactant.

[0068] In this embodiment of the scheme, a water-in-oil reverse microemulsion system consisting of deionized water as the aqueous phase and n-hexane as the oil phase is used to form SiO2 microspheres by hydrolysis and condensation reaction of TEOS under alkaline conditions. Figure 3-5 SEM images of SiO2 prepared by water and Triton TX-100 under different molar ratios are shown. The SEM results indicate that the prepared SiO2 has a well-dispersed spherical structure, and the average particle size of SiO2 gradually decreases with increasing molar ratio of water to Triton TX-100. When n... H2O :n TX-100 When n = 4, the average particle size of SiO2 is 127 nm; when n H2O :n TX-100 When n = 8, the average particle size of SiO2 is 99 nm; when n H2O :n TX-100 When n = 12, the average particle size of SiO2 is 72 nm. These results indicate that when n... H2O :n TX-100 When the ratio is 12, SiO2 microspheres with relatively small particle size and good dispersibility can be obtained.

[0069] In this scheme, TEOS is used as the silicon source for preparing SiO2 by the reverse microemulsion method, and its content has a significant impact on the particle size of SiO2 microspheres. Figure 6-8 For n H2O :n TX-100 SEM images of SiO2 prepared under different molar ratios of water and TEOS at a concentration of 12 were obtained. The SEM results showed that the prepared SiO2 had a well-dispersed spherical structure, and the average particle size of SiO2 gradually decreased with increasing molar ratio of water to Triton TX-100. When n... H2O :n TEOS When n = 6, the average particle size of SiO2 is 105 nm; when n H2O :n TEOS When n = 12, the average particle size of SiO2 is 91 nm; when n H2O :n TEOS When the concentration of water to Triton TX-100 is constant, the average particle size of SiO2 is 72 nm. These results indicate that when the molar ratio of water to Triton TX-100 is constant, and n... H2O :n TEOS When the concentration is 20, microspheres with relatively small particle size and good dispersibility can be obtained.

[0070] Figure 9 This is a comparison of the infrared spectra of SiO2 and the modified Cr-SiO2-SO3H. Fourier transform infrared spectroscopy (FTIR) can effectively analyze the functional group composition of materials. The figure shows that the SiO2 microspheres prepared by the reverse microemulsion method exhibit better performance at 1099 cm⁻¹. -1 796cm -1 470cm -1 Characteristic peaks appeared at 1631 cm⁻¹, corresponding to the antisymmetric vibration peak, symmetric vibration peak, and bending vibration peak of the Si-O-Si bond, respectively. -1 The absorption peak at 3201 cm⁻¹ is the HOH bond bending vibration peak. -1 The broad absorption peaks appearing at 1523 cm⁻¹ are stretching vibration peaks of Si-OH, and the appearance of these characteristic peaks indicates the successful preparation of SiO₂. Compared with the infrared spectrum of SiO₂, Cr-SiO₂-SO₃H shows a higher absorption peak at 1523 cm⁻¹. -1 The bending vibration peak of NH appears at 3050 cm⁻¹. -1 and 3436cm -1 The double peaks at 616 cm⁻¹ belong to the stretching vibration peaks of NH, indicating that SiO₂ has been modified by APTES amination. -1 The presence of a characteristic absorption peak of -SO3H at the point confirms that -SO3H is loaded onto SiO2.

[0071] This plan, Figure 10-13 The XPS full-spectrum and high-resolution spectra of Cr-SiO2-SO3H are shown. XPS spectroscopy can analyze the surface composition and elemental valence states of a sample. Figure 10 The signals of elements C, O, N, Si, S, and Cr appeared. Figure 11 The high-resolution spectrum of the contaminating carbon was corrected for binding energy using C1s = 284.8 eV. Figure 12 This is the high-resolution spectrum of S2p. The figure shows that S2p has a binding energy of 168.9 eV (S2p...). 1 / 2 ) and 167.8 eV (S2p 3 / 2 Two characteristic peaks of -SO3H appeared, confirming that -SO3H was loaded on SiO2. Figure 13 This is the high-resolution spectrum of Cr 2p, with Cr(NH3)6 at 578.7 eV. 3+ Characteristic peaks confirm that Cr in CrCl3·6H2O 3+ It complexes with -NH2 in APTES, is loaded onto SiO2-SO3H and exhibits Cr 6+ The valence state; the binding energy is at 577.1 eV (Cr 2p 3 / 2 ) at 586.8 eV (Cr 2p 1 / 2 The characteristic peak at () is attributed to Cr 3+The binding energy is 589.7 eV (Cr 2p 1 / 2 The characteristic peak at () is attributed to Cr 6+ .

[0072] In this plan, Figure 14 The image shows the Py-IR spectrum of Cr-SiO2-SO3H. Py-IR analysis uses pyridine, which has a strong adsorption capacity, as a probe molecule. It can interact with both L and B acids on the catalyst surface at the same time, and the required information is obtained by analyzing the position and intensity of the infrared characteristic peaks. Figure 14 This indicates that Cr-SiO2-SO3H at 1450 cm⁻¹ -1 and 1610cm -1 The absorption peak appearing at 1544 cm⁻¹ is a characteristic peak of L-acid, and is located at 1544 cm⁻¹. -1 The absorption peak at 1490 cm⁻¹ is a characteristic peak of Brønsted acid. -1 The peak at this point is a characteristic peak formed by the interaction of L-acid and Brønsted acid with pyridine.

[0073] To determine the stability of the Cr-SiO2-SO3H prepared in Examples 1-4 during experiments, TG analysis was performed on it at temperatures ranging from 30℃ to 600℃. Figure 15 As shown, between 30℃ and 130℃, the sample lost 6.2% of its weight due to the loss of free water in Cr-SiO2-SO3H; between 130℃ and 290℃, the loss of bound water in the sample caused the weight loss; between 290℃ and 360℃, the weight loss rate in the sample was relatively fast, which was caused by the violent oxidative decomposition reaction of Cr2O3; when the temperature was above 360℃, the decomposition and loss of -SO3H in the sample caused the weight loss.

[0074] Comparative Example 1

[0075] Triton TX-100 was selected as the surfactant and n-hexanol as the co-surfactant. They were mixed at a volume ratio of 3:2 to obtain a mixed surfactant (MS). Then, cyclohexane and MS were mixed at a mass ratio of 1:1, ultrasonically vibrated, and a certain amount of deionized water (12 times the molar amount of TX-100) was added. The mixture was ultrasonically vibrated again to ensure homogeneity, thus preparing a microemulsion. Ammonia was added to adjust the pH to 11. A certain amount of tetraethyl orthosilicate (TEOS) was slowly added dropwise to the microemulsion at a rate of 1 mL·min⁻¹ using a peristaltic pump. The amount of TEOS added was 1 / 20 of the molar amount of water. The mixture was stirred at room temperature for at least 24 hours. After the reaction was complete, acetone was added to break the microemulsion. The microemulsion was then separated by centrifugation (10000 r / min, 5 min). The precipitate was repeatedly washed with anhydrous ethanol and dried to prepare SiO₂ microspheres with an average particle size of 72 nm.

[0076] 1 g of SiO2 powder and 20 mL of toluene were added to a round-bottom flask. The mixture was sonicated for 5 min to disperse the powder evenly. Then, 2 mL of APTES was added and the mixture was refluxed at 110 °C for 5 h with magnetic stirring. Subsequently, 0.2 g of CrCl3·6H2O was added to the mixture and the temperature was kept constant for 3 h. After the reaction was completed, the mixture was separated by centrifugation (10000 r / min, 5 min). The precipitate was repeatedly washed and dried under vacuum to obtain 1.32 g of Cr-SiO2.

[0077] Comparative Example 2

[0078] Triton TX-100 was selected as the surfactant and n-hexanol as the co-surfactant. They were mixed at a volume ratio of 3:2 to obtain a mixed surfactant (MS). Then, cyclohexane and MS were mixed at a mass ratio of 1:1, ultrasonically vibrated, and a certain amount of deionized water (12 times the molar amount of TX-100) was added. The mixture was ultrasonically vibrated again to ensure homogeneity, thus preparing a microemulsion. Ammonia was added to adjust the pH to 11. A certain amount of tetraethyl orthosilicate (TEOS) was slowly added dropwise to the microemulsion at a rate of 1 mL·min⁻¹ using a peristaltic pump. The amount of TEOS added was 1 / 20 of the molar amount of water. The mixture was stirred at room temperature for at least 24 hours. After the reaction was complete, acetone was added to break the microemulsion. The microemulsion was then separated by centrifugation (10000 r / min, 5 min). The precipitate was repeatedly washed with anhydrous ethanol and dried to prepare SiO₂ microspheres with an average particle size of 72 nm.

[0079] 2g of SiO2 microspheres were added to a round-bottom flask containing 5mL benzyl alcohol and 20mL toluene. After ultrasonic dispersion, the mixture was heated under reflux in a constant-temperature oil bath at 110℃ for 8 hours. After the reaction was completed, the mixture was washed approximately ten times with anhydrous ethanol and then vacuum dried to obtain a powdered product of surface-modified SiO2 microspheres. 1g of the dried powdered product was added to a round-bottom flask containing 20mL chloroform and 0.6mL chlorosulfonic acid (ClSO3H). The mixture was stirred thoroughly until the solution was homogeneous and no gas was released. The mixture was refluxed at 70℃ for 2 hours. After the reaction was completed, the mixture was washed with anhydrous ethanol and vacuum dried to prepare 1.48g of SiO2-SO3H.

[0080] Application Example 1

[0081] 2g of ionic liquid [BMIM]Cl and 0.1g of microcrystalline cellulose were added to a round-bottom flask. The mixture was magnetically stirred in a constant-temperature oil bath at 100°C for 0.5 hours until the reaction system became transparent. After adding 0.02g of deionized water, the temperature was raised to 160°C, and 0.1g of the Cr-SiO2-SO3H composite solid acid prepared in Example 1 was added. Tetrahydrofuran (THF) was slowly added dropwise under reflux. The amount of tetrahydrofuran (THF) added was 3 times the volume of [BMIM]Cl. The reaction was continued for 4 hours. The two phases of [BMIM]Cl and THF were separated by standing in a separatory funnel. The total yield of 5-hydroxyfurfural was 54.8%, and the conversion rate of the raw material (cellulose) was 88.1%.

[0082] Application Example 2

[0083] 2g of ionic liquid [BMIM]Cl and 0.2g of microcrystalline cellulose were added to a round-bottom flask. The mixture was magnetically stirred in a constant-temperature oil bath at 90°C for 2 hours until the reaction system became transparent. After adding 0.02g of deionized water, the temperature was raised to 150°C, and 0.1g of the Cr-SiO2-SO3H composite solid acid prepared in Example 2 was added. Tetrahydrofuran (THF) was not added, and the reaction was continued for 2 hours. The total yield of 5-hydroxyfurfural was 44.2%, and the conversion rate of the raw materials was 84.5%.

[0084] Application Example 3

[0085] 2g of ionic liquid [BMIM]Cl and 0.3g of microcrystalline cellulose were added to a round-bottom flask. The mixture was magnetically stirred in a constant-temperature oil bath at 120°C for 1 hour until the reaction system became transparent. After adding 0.02g of deionized water, the temperature was raised to 190°C, and 0.6g of the Cr-SiO2-SO3H composite solid acid prepared in Example 3 was added. Tetrahydrofuran (THF) was slowly added dropwise under reflux. The volume of THF was 4 times that of [BMIM]Cl. The reaction was continued for 6 hours. The two phases of [BMIM]Cl and THF were separated by standing in a separatory funnel. The total yield of 5-hydroxyfurfural was 48.1%, and the conversion rate of the raw materials was 87.3%.

[0086] Application Example 4

[0087] 2g of ionic liquid [BMIM]Cl and 0.1g of microcrystalline cellulose were added to a round-bottom flask. The mixture was magnetically stirred in a constant-temperature oil bath at 100℃ for half an hour until the reaction system became transparent. After adding 0.02g of deionized water, the temperature was raised to 160℃, and 0.1g of the Cr-SiO2 composite solid acid prepared in Comparative Example 1 was added. Tetrahydrofuran (THF) with a volume of 3 times that of [BMIM]Cl was slowly added dropwise under reflux. The reaction was continued for 4 hours. The two phases of [BMIM]Cl and THF were separated by standing in a separatory funnel. The total yield of 5-hydroxyfurfural was 35.2%, and the conversion rate of the raw materials was 47.3%.

[0088] Application Example 5

[0089] 2g of ionic liquid [BMIM]Cl and 0.1g of microcrystalline cellulose were added to a round-bottom flask. The mixture was magnetically stirred in a constant-temperature oil bath at 100℃ for half an hour until the reaction system became transparent. After adding 0.02g of deionized water, the temperature was raised to 160℃, and 0.1g of the SiO2-SO3H composite solid acid prepared in Comparative Example 2 was added. Tetrahydrofuran (THF) with a volume of 3 times that of [BMIM]Cl was slowly added dropwise under reflux. The reaction was continued for 4 hours. The two phases of [BMIM]Cl and THF were separated by standing in a separatory funnel. The total yield of 5-hydroxyfurfural was 32.4%, and the conversion rate of the raw materials was 59.6%.

[0090] Compared with the above application examples 1, 4 and 5, the yield of 5-hydroxymethylfurfural prepared by using the composite catalyst Cr-SiO2-SO3H was increased by 55.7% and 69.1% compared with Cr-SiO2 and SiO2-SO3H, respectively.

[0091] The following analysis, based on comparative examples and application examples, shows that the yield of the reaction product HMF changes with the reaction conditions. To promote efficient conversion of microcrystalline cellulose while achieving a high HMF yield, the application examples of this scheme investigated the effects of reaction temperature, reaction time, catalyst, catalyst dosage, and the volume ratio of the reaction phase to the extraction phase on the HMF yield and MCC conversion rate. Furthermore, the number of catalyst recycling cycles was studied through repeated experiments.

[0092] Figure 16The effects of three catalysts—SiO2-SO3H, Cr-SiO2, and Cr-SiO2-SO3H—on the HMF yield were compared. The figures show that the HMF yield increased with increasing reaction temperature for all three catalysts. At any given temperature, the HMF yield using Cr-SiO2-SO3H as a catalyst was significantly higher than that using SiO2-SO3H or Cr-SiO2 as catalysts. At a reaction temperature of 160℃, the maximum HMF yield of 54.8% was achieved with Cr-SiO2-SO3H as the catalyst. However, with SiO2-SO3H and Cr-SiO2 as catalysts, the reaction temperature needed to be increased to 170℃ to achieve maximum HMF yields of 36.7% and 40.9%, respectively. This phenomenon may be attributed to the poor catalytic effect of catalysts with a single active component, thus requiring an increase in reaction temperature to enhance the effective collision between the catalyst's active sites and the reactants, thereby increasing the reaction rate. Furthermore, Cr-SiO2-SO3H contains... The Lewis acidic sites can synergistically catalyze the conversion of MCC to HMF, improving reaction efficiency. Therefore, compared with catalysts using a single active component, the composite solid acid catalyst Cr-SiO2-SO3H exhibits better catalytic performance.

[0093] This scheme, in n H2O :n TX-100 =12, n H2O :n TEOS SiO2 microspheres with a particle size of 72 nm and good dispersibility were prepared in a reverse microemulsion with a pH of 20. A chemical grafting method was used with ClSO3H as the acid source to load -SO3H onto SiO2, and APTES was used as the -NH2 source to modify the surface of the prepared SiO2 microspheres through amination. Taking advantage of the -NH2 complexation property of metal ions, chromium ions were loaded onto SiO2 to prepare a Cr-SiO2-SO3H catalyst. Compared to the catalysts with acidic sites, SiO2-SO3H or Lewis acidic sites, the composite acid catalyst Cr-SiO2-SO3H exhibits highly efficient catalytic performance. In a reaction system with [BMIM]Cl as the reaction phase and THF as the extraction phase, using microcrystalline cellulose as the substrate and Cr-SiO2-SO3H as the catalyst, the optimal reaction conditions are: a reaction temperature of 160℃, a reaction time of 4 h, a composite solid acid to cellulose acid mass ratio of 1, and a [BMIM]Cl to THF volume ratio of 1:3. Under these conditions, HMF can achieve a maximum yield of 54.8%, with an MCC conversion of 88.1% and an HMF selectivity of 62.2%. Furthermore, the catalyst can be reused without significant loss of catalytic activity, as detailed in Table 1 below.

[0094] Table 1 Effect of Cr-SiO2-SO3H cycle number on HMF yield

[0095] Loop count / time 1 2 3 4 5 HMF Yield / % 54.8 52.9 50.3 49.1 47.5

[0096] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a silicon-based composite solid acid catalyst, characterized in that: Step 1: Add a certain amount of SiO2 microspheres to a certain volume of solvent, disperse by ultrasonication, heat the reaction system under reflux at 100-130℃ for 6-10 hours, and after washing and drying, obtain a powdered product with SiO2 microsphere surface modification. Step 2: Add the powdered product obtained after washing and drying in Step 1 to a certain amount of chloroform solvent, add chlorosulfonic acid, stir thoroughly until the solution is uniformly mixed and no gas escapes, reflux at 60-90℃ for 0.5-3h, the reaction is completed, wash and dry to prepare SiO2-SO3H powder. Step 3: Add the prepared SiO2-SO3H powder to a certain amount of solvent, and sonicate to disperse the SiO2-SO3H powder evenly in the solvent. Then add a certain amount of APTES to the reaction system and reflux the reaction system at 90-120℃ for 4-7 hours with stirring. Then add a certain amount of CrCl3·6H2O to the mixture after reflux reaction and continue to react at 90-120℃ for 2-5 hours. After the reaction is completed, separate, wash and dry to obtain the composite solid acid Cr-SiO2-SO3H. In step one, the SiO2 microspheres are prepared as follows: S11. Select Triton TX-100 as the surfactant and n-hexanol as the co-surfactant. Mix Triton TX-100 and n-hexanol at a certain volume ratio to obtain a mixed surfactant. Then mix cyclohexane with the mixed surfactant at a certain mass ratio, ultrasonically vibrate, and then add a certain amount of deionized water. The molar ratio of deionized water to Triton TX-100 is 4-16:

1. Then ultrasonically vibrate again to mix it evenly and prepare a microemulsion. Add ammonia water to adjust its pH to 10-12. S12. A certain amount of ethyl silicate is slowly added dropwise to the microemulsion. The amount of ethyl silicate added is 1 / 20 to 1 / 5 of the molar amount of water. The mixture is stirred at room temperature for more than 24 hours. After the reaction is completed, acetone is added to break the microemulsion. Then, the mixture is separated, washed, and dried to prepare SiO2 microspheres. In step one, the solvent is a mixture of benzyl alcohol and toluene, and the volume ratio of benzyl alcohol to toluene is 1:

4. In step three, the amount of APTES added is 1-6 mL per gram of SiO2-SO3H powder; the mass ratio of CrCl3·6H2O to SiO2-SO3H is 0.1-0.3:

1.

2. The method for preparing the silicon-based composite solid acid catalyst according to claim 1, characterized in that: In step two, 20 ml of chloroform is added to each gram of powdered product after surface modification of SiO2 microspheres.

3. The method for preparing the silicon-based composite solid acid catalyst according to claim 1, characterized in that: In step two, the amount of chlorosulfonic acid added is 0.15-0.75 ml per gram of powdered product after surface modification of SiO2 microspheres.

4. The method for preparing the silicon-based composite solid acid catalyst according to claim 1, characterized in that: In step three, ultrasonic treatment for 3-15 min is used to ensure that the SiO2-SO3H powder is evenly dispersed in the solvent.

5. The application of silicon-based composite solid acid catalysts, characterized in that: Add cellulose to the ionic liquid [BMIM]Cl, the amount of cellulose added is 5-15% of the mass of [BMIM]Cl, and stir in a constant temperature bath at 90-120℃ for 0.5-2h to completely dissolve the cellulose. After adding a certain amount of deionized water, the temperature is raised to 150-190℃. A certain amount of the catalyst composite solid acid Cr-SiO2-SO3H prepared according to any one of claims 1-4 is added, and tetrahydrofuran is added under reflux. The volume of tetrahydrofuran added is 0-4 times the volume of [BMIM]Cl. The reaction is continued under reflux for 2-6 hours under stirring to obtain 5-hydroxymethylfurfural.

6. The application of the silicon-based composite solid acid catalyst according to claim 5, characterized in that: The amount of Cr-SiO2-SO3H added is 0.5-2 times the mass of microcrystalline cellulose.

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