A solid superacid catalyst, its preparation method and application

Abstract

This invention discloses a solid superacid catalyst, its preparation method, and its application, belonging to the field of catalyst preparation technology. The catalyst comprises a mesoporous support, sulfate ions bound to the mesoporous support, and rare earth ions doped onto the mesoporous support. The mesoporous support is composed of ZrO2 and Al2O3; the rare earth ions are Yb. 3+ and Ce 3+ The solid superacid catalyst provided in this invention has uniformly dispersed active components and high catalytic activity, which can improve the conversion rate of ethyl octanoate in the preparation process of octanoyl hydroxamic acid, and at the same time extend the cycle life of the catalyst.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology, and particularly relates to a solid superacid catalyst, its preparation method and application. Background Technology

[0002] Capryloyl hydroxamic acid, as an ideal organic acid, has excellent antibacterial and bacteriostatic properties at neutral pH. It can be used in formulation systems without chemical preservatives, is compatible with most raw materials, and is not affected by surfactants, proteins, or other raw materials in the system. It can be compounded with preservatives such as alcohols and glycols, making it a safe and efficient preservative.

[0003] There are many methods for synthesizing octanoyl hydroxamic acid, but the two main synthetic routes currently on the market are: hydroxylamine-ester method and hydroxylamine-acyl chloride method. The hydroxylamine-acyl chloride method has drawbacks such as increased viscosity and decreased flowability after fatty acid acyl chloride oxidation, the generation of large amounts of acid gas, easy corrosion of equipment, and severe environmental pollution. The hydroxylamine-ester method is currently the mainstream synthesis method. The hydroxylamine-ester method first uses n-octanoic acid and methanol / ethanol for esterification to produce methyl / ethyl octanoate. The synthesized octanoate ester is then reacted with hydroxylamine salt for hydroxylation to synthesize the final octanoyl hydroxamic acid. The n-octanoate esterification reaction to synthesize ethyl octanoate mainly uses concentrated sulfuric acid as a catalyst. For example, patent CN110845367B uses n-octanoic acid and ethanol under sulfuric acid catalysis via heating and reflux to prepare ethyl octanoate. However, concentrated sulfuric acid cannot be reused, the reaction generates a large amount of wastewater, significantly increasing production costs and causing environmental pollution. Therefore, developing a highly active and stable catalyst to improve catalyst recycling efficiency is of great significance. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes a solid superacid catalyst, its preparation method, and its applications. The solid superacid catalyst provided by this invention exhibits uniformly dispersed active components and high catalytic activity, which can improve the conversion rate of ethyl n-octanoate in the preparation process of octanoyl hydroxamic acid, while also extending the catalyst's cycle life.

[0005] To address the aforementioned technical problem, this invention provides a solid superacid catalyst, comprising a mesoporous support, sulfate ions bound to the mesoporous support, and rare earth ions doped onto the mesoporous support. The mesoporous support is composed of ZrO2 and Al2O3; the rare earth ions are Yb. 3+ and Ce 3+ The molar ratio of ZrO2 to Al2O3 is 2-6:1; the Yb 3+ and Ce 3+ The molar ratio of Al₂O₃ to Yb is 0.8-2.5:1. 3+ The molar ratio is 2.5-8:1.

[0006] This invention provides a method for preparing the above-described solid superacid catalyst, comprising the following steps:

[0007] 1) Prepare a mixed solution of aluminum nitrate, ytterbium nitrate, cerium nitrate and template agent, denoted as solution A; prepare a mixed solution of zirconium propoxide and acetylacetone, denoted as solution B; add the mixture of solution B and deionized water to solution A under stirring to obtain a mixed solution;

[0008] 2) Adjust the pH of the obtained mixed solution to 5-6 and age it to obtain a gel;

[0009] 3) The obtained gel is added to an alkaline solution in sequence for reflux, washing, drying and grinding to obtain powder; the alkaline solution includes NaOH, KOH, ammonia, Na2CO3 and NaHCO3 solutions;

[0010] 4) The obtained powder is calcined to obtain rare earth ion-doped ZrO2-Al2O3 powder;

[0011] 5) The ZrO2-Al2O3 powder doped with rare earth ions was impregnated in sulfuric acid solution, stirred, filtered, and the resulting filter cake was dried and calcined in sequence to obtain a solid superacid catalyst.

[0012] Preferably, the aging temperature in step 2) is 45-80℃ and the aging time is 6-48h.

[0013] Preferably, the calcination temperature in step 4) is 200-800℃ and the time is 3-8h.

[0014] Preferably, the drying temperature in step 5) is 80-130℃ and the time is 12-24h; the calcination temperature is 400-800℃ and the time is 3-8h.

[0015] This invention provides the application of the aforementioned solid superacid catalyst in the synthesis of octanoyl hydroxamic acid, wherein octanoyl hydroxamic acid is synthesized using the following steps:

[0016] (1) Mix octanoic acid, ethanol and solid superacid catalyst, react the resulting mixture, and distill the reaction solution under reduced pressure to obtain ethyl octanoate;

[0017] (2) After adding hydroxylamine salt and solid base to ethanol solvent and mixing them evenly, add the above-mentioned ethyl octanoate to react and obtain octanoyl hydroxamic acid.

[0018] Preferably, the amount of catalyst added in step (1) is 1wt%-10wt% of octanoic acid.

[0019] Preferably, the molar ratio of octanoic acid and ethanol in step (1) is 1:1-1.5.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] The solid superacid catalyst provided by this invention uses ZrO2 and Al2O3 as supports and introduces Yb and Ce, which not only increases the number of Lewis acid centers, but also helps stabilize sulfur species on the catalyst surface due to the presence of rare earth elements. This exhibits a significant synergistic effect, thereby affecting the acid properties of the catalyst surface and the interaction between sulfate species and the support. As a result, the catalyst prepared by the method of this invention has better catalytic activity and stability, effectively reduces catalyst consumption in the preparation step of ethyl octanoate, and maintains the stable production of octanoyl hydroxamic acid. Attached Figure Description

[0022] Figure 1 This is a SEM image of the catalyst prepared in Example 1 of the present invention. Detailed Implementation

[0023] The technical solutions in specific embodiments of the present invention will be described in detail and completely below. Obviously, the described embodiments are only some specific implementations of the overall technical solution of the present invention, and not all implementations. Based on the overall concept of the present invention, all other embodiments obtained by those skilled in the art fall within the protection scope of the present invention.

[0024] This invention provides a solid superacid catalyst, comprising a mesoporous support, sulfate ions bound to the mesoporous support, and rare earth ions doped onto the mesoporous support. The mesoporous support is composed of ZrO2 and Al2O3; the rare earth ions are Yb. 3+ and Ce 3+ In this invention, the molar ratio of ZrO2 to Al2O3 is 2-6:1. The Yb 3+ and Ce 3+ The molar ratio of Al2O3 to Yb is 1-2:1; 3+ The molar ratio is 5-20:1.

[0025] The solid superacid catalyst provided by this invention introduces Yb and Ce, which not only increases the number of Lewis acid centers, but also helps stabilize sulfur species on the catalyst surface due to the presence of rare earth elements. This exhibits a significant synergistic effect, thereby affecting the acid properties of the catalyst surface and the interaction between sulfate species and the support. As a result, the catalyst prepared by the method of this invention has better catalytic activity and stability, effectively reducing catalyst consumption in the preparation step of ethyl octanoate and maintaining the stable production of octanoyl hydroxamic acid.

[0026] This invention provides a method for preparing any of the above-described solid superacid catalysts, comprising the following steps:

[0027] 1) Prepare a mixed solution of aluminum nitrate, ytterbium nitrate, cerium nitrate and template agent, denoted as solution A; prepare a mixed solution of zirconium propoxide and acetylacetone, denoted as solution B; add the mixture of solution B and deionized water to solution A under stirring to obtain a mixed solution;

[0028] 2) Adjust the pH of the obtained mixed solution to 5-6 and age it to obtain a gel;

[0029] 3) The obtained gel was added to an alkaline solution in sequence for reflux, washing, drying and grinding to obtain a powder;

[0030] 4) The obtained powder is calcined to obtain rare earth ion-doped ZrO2-Al2O3 powder;

[0031] 5) The ZrO2-Al2O3 powder doped with rare earth ions was impregnated in sulfuric acid solution, stirred, filtered, and the resulting filter cake was dried and calcined in sequence to obtain a solid superacid catalyst.

[0032] This invention prepares a mixed solution of aluminum nitrate, ytterbium nitrate, cerium nitrate, and a template agent, denoted as solution A; and a mixed solution of zirconium propoxide and acetylacetone, denoted as solution B. A mixture of solution B and deionized water is added to solution A under stirring to obtain a mixed solution. In this invention, the template agent is preferably a surfactant template such as Pluronic F127, Pluronic P123, PEI (polyethyleneimine), CTAB (hexadecyltrimethylammonium bromide), SDS (sodium dodecyl sulfonate), or polyoxyethylene sorbitan ester, as well as glucose, maltose, urea, tartaric acid derivatives, polyethylene glycol, microemulsions, and emulsions.

[0033] After obtaining the mixed solution, the pH value of the mixed solution is adjusted to 5-6 and aged to obtain a gel. In this invention, the aging temperature is preferably 45-80℃, and the aging time is preferably 6-48 hours.

[0034] After obtaining the gel, the present invention sequentially adds the gel to an alkaline solution for reflux, washing, drying, and grinding to obtain a powder. In the present invention, the alkaline solution includes NaOH, KOH, ammonia, Na₂CO₃, and NaHCO₃ solutions; the concentration of the alkaline solution is preferably 0.2-5 mol / L; the reflux time is preferably 24 hours. In the present invention, it is preferred to use 2-5 times the weight of the solids for washing to remove excess metal ions. In the present invention, after washing, it is preferred to use a conductivity meter to measure the conductivity and maintain it at 0-1.0 mS / cm. In the present invention, the drying temperature is preferably 60-120℃, and the drying time is preferably 8-24 hours.

[0035] After obtaining the powder, the present invention calcines the powder to obtain ZrO2-Al2O3 powder doped with rare earth ions. In the present invention, the calcination temperature is preferably 200-800℃, more preferably 300-700℃, and most preferably 450-580℃; the calcination time is preferably 3-8h.

[0036] After obtaining rare-earth ion-doped ZrO2-Al2O3 powder, this invention impregnates the rare-earth ion-doped ZrO2-Al2O3 powder in sulfuric acid solution, stirs, filters, and then sequentially dries and calcines the resulting filter cake to obtain a solid superacid catalyst. In this invention, the impregnation method includes, but is not limited to, excess impregnation, equal-volume impregnation, multiple impregnation, impregnation-precipitation, fluidized bed spray impregnation, and vapor phase impregnation. In this invention, the concentration of the sulfuric acid solution is preferably 0.2-1.0 mol / L, and the stirring time is preferably 6-18 h. The drying temperature is preferably 80-130℃, and the drying time is preferably 12-24 h. In this invention, the calcination temperature is preferably 400-800℃, more preferably 500-600℃; the calcination time is preferably 3-12 h.

[0037] This invention provides a method for preparing a solid superacid catalyst, which employs an integrated synthesis method. Rare earth elements Yb and Ce are added during the preparation of ZrO2-Al2O3, resulting in a rare earth-doped LDH solid solution, i.e., Yb. 3+ Ce 3+ Partially replaced Zr in the layer plate 4+ Or Al 3+ This introduces an imbalance of lattice charges and fundamentally alters the structure, stability, and surface acidity / alkalinity of the catalyst.

[0038] In this invention, five Hammett acid indicators are preferably used to determine the acidity of solid superacid catalysts: (1) the color change reaction of p-nitrotoluene (acid strength (H0=-11.35), (2) m-nitrotoluene (H0=-11.99), (3) p-nitrochlorobenzene (H0=-12.70), (4) 2,4-dinitrotoluene (H0=-13.75) and (5) 2,4-dinitrofluorobenzene (H0=-14.52) to determine the acid strength of the catalyst.

[0039] This invention provides the application of the aforementioned solid superacid catalyst in the synthesis of octanoyl hydroxamic acid, wherein octanoyl hydroxamic acid is synthesized using the following steps:

[0040] (1) Mix octanoic acid, ethanol and solid superacid catalyst, react the resulting mixture, and distill the reaction solution under reduced pressure to obtain ethyl octanoate;

[0041] (2) After adding hydroxylamine salt and solid base to ethanol solvent and mixing them evenly, add the above-mentioned ethyl octanoate to react and obtain octanoyl hydroxamic acid.

[0042] This invention involves mixing octanoic acid, ethanol, and a solid superacid catalyst, reacting the resulting mixture, and then distilling the reaction solution under reduced pressure to obtain ethyl octanoate. In this invention, the molar ratio of octanoic acid to ethanol is preferably 1:1-1.5. In this invention, the amount of catalyst added is preferably 1wt%-10wt% of octanoic acid, more preferably 4wt%-8wt%. In this invention, the reaction temperature is preferably 50-150℃, more preferably 60-100℃, and most preferably 80-90℃; the reaction time is preferably 2-20h, more preferably 5-10h, and most preferably 7-10h. In this invention, the pressure during reduced pressure distillation is preferably 0.003-0.01MPa, and the temperature is preferably 80-120℃.

[0043] After obtaining ethyl n-octanoate, the present invention adds hydroxylamine salt and solid base to ethanol solvent, mixes them evenly, and then adds the above-mentioned ethyl n-octanoate to react and obtain octanoyl hydroxamic acid. In the present invention, the hydroxylamine salt is preferably hydroxylamine hydrochloride or hydroxylamine sulfate; the solid base is preferably sodium carbonate, sodium bicarbonate, sodium hydroxide, or sodium methoxide. In the present invention, the molar ratio of ethyl n-octanoate to hydroxylamine salt and solid base is 1:1-2:1-2. In the present invention, the mass ratio of ethyl n-octanoate to ethanol solvent is preferably 1:4-9. In the present invention, the reaction temperature is preferably 10-50℃, more preferably 10-40℃, and most preferably 20-30℃; the reaction time is preferably 1-5 h. In the present invention, after the reaction is completed, it is preferable to further include filtration, vacuum distillation to remove the solvent, adding water to crystallize and adjusting the pH to 6-7, filtering and drying to obtain octanoyl hydroxamic acid.

[0044] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0045] Example 1

[0046] 20 g of Pluronic F127, 37.5 g of Al(NO3)3·9H2O, 4.49 g of Yb(NO3)3·6H2O, and 4.78 g of Ce(NO3)3·3H2O were dissolved in 500 mL of anhydrous ethanol and stirred for 30 min, and this solution was designated as solution A. 163.8 g of zirconium propoxide (Zr(OPr)4) (containing 60 wt.% n-propanol) and 8.7 g of acetylacetone were mixed and dissolved in 320 mL of anhydrous ethanol, and this solution was designated as solution B. A mixture of solution B and 32 mL of water was slowly added dropwise to solution A under vigorous stirring. The pH was adjusted to 5, and the solution was aged at 60 °C for 24 h. The resulting sol was then refluxed in 1 mol / L NaOH solution for 24 h. Subsequently, excess Na ions were removed with deionized water, and the sol was dried overnight at 80 °C. Then, it was ground into a solid powder and placed in a muffle furnace, heated to 580℃ at a heating rate of 10℃ / min, and held for 8 h to obtain Yb and Ce doped ZrO2-Al2O3.

[0047] 5 g of ZrO2-Al2O3 powder was impregnated in 100 mL of 0.5 mol / L sulfuric acid solution, stirred for 12 h, and then filtered. The resulting filter cake was dried at 120 °C for 12 h and then calcined in a muffle furnace at 500 °C for 5 h to obtain a solid superacid catalyst SO4. 2- The catalyst is a mixture of ZrO2-Al2O3 (Zr / Al = 2:1), denoted as catalyst 1. The SEM image of this catalyst is shown below. Figure 1 As shown. The acidity of the obtained catalyst was determined by the Hammett acid indicator method, and the acid strength H0 of the catalyst was found to be <-12.70, which is at the level of superacid.

[0048] Example 2

[0049] The difference from Example 1 is that the amount of Al(NO3)3·9H2O is added at a molar ratio of Zr / Al = 3:1, while the other steps are the same as in Example 1. The specific operation is as follows:

[0050] 20 g of Pluronic F127, 56.25 g of Al(NO3)3·9H2O, 4.49 g of Yb(NO3)3·6H2O, and 4.78 g of Ce(NO3)3·3H2O were dissolved in 500 mL of anhydrous ethanol and stirred for 30 min, and this solution was designated as solution A. 163.8 g of zirconium propoxide (Zr(OPr)4) (containing 60 wt.% n-propanol) and 8.7 g of acetylacetone were dissolved in 320 mL of anhydrous ethanol, and this solution was designated as solution B. A mixture of solution B and 32 mL of water was slowly added dropwise to solution A under vigorous stirring. The pH was adjusted to 5, and the solution was aged at 60 °C for 24 h. The resulting sol was then refluxed in 1 mol / L NaOH solution for 24 h. Subsequently, excess Na ions were removed with deionized water, and the sol was dried overnight at 80 °C. Then, it was ground into a solid powder and placed in a muffle furnace, heated to 580℃ at a heating rate of 10℃ / min, and held for 8 h to obtain Yb and Ce doped ZrO2-Al2O3.

[0051] 5 g of ZrO2-Al2O3 powder was impregnated in 100 mL of 0.5 mol / L sulfuric acid solution, stirred for 12 h, and then filtered. The resulting filter cake was dried at 120 °C for 12 h and then calcined in a muffle furnace at 500 °C for 5 h to obtain a solid superacid catalyst SO4. 2- The catalyst, denoted as catalyst 2, is a mixture of ZrO2-Al2O3 (Zr / Al = 3:1). The acidity of the catalyst was determined using the Hammett acid indicator method, and the acid strength H0 < -12.70, indicating it has reached the level of a superacid.

[0052] Example 3

[0053] The difference from Example 1 is that the amount of Al(NO3)3·9H2O is added at a molar ratio of Zr / Al = 1:1, while the other steps are the same as in Example 1. The specific operation is as follows:

[0054] 20 g of Pluronic F127, 18.75 g of Al(NO3)3·9H2O, 4.49 g of Yb(NO3)3·6H2O, and 4.78 g of Ce(NO3)3·3H2O were dissolved in 500 mL of anhydrous ethanol and stirred for 30 min, and this solution was designated as solution A. 163.8 g of zirconium propoxide (Zr(OPr)4) (containing 60 wt.% n-propanol) and 8.7 g of acetylacetone were dissolved in 320 mL of anhydrous ethanol, and this solution was designated as solution B. A mixture of solution B and 32 mL of water was slowly added dropwise to solution A under vigorous stirring. The pH was adjusted to 5, and the solution was aged at 60 °C for 24 h. The resulting sol was then refluxed in 1 mol / L NaOH solution for 24 h. Subsequently, excess Na ions were removed with deionized water, and the sol was dried overnight at 80 °C. Then, it was ground into a solid powder and placed in a muffle furnace, heated to 580℃ at a heating rate of 10℃ / min, and held for 8 h to obtain Yb and Ce doped ZrO2-Al2O3.

[0055] 5 g of ZrO2-Al2O3 powder was impregnated in 100 mL of 0.5 mol / L sulfuric acid solution, stirred for 12 h, and then filtered. The resulting filter cake was dried at 120 °C for 12 h and then calcined in a muffle furnace at 500 °C for 5 h to obtain a solid superacid catalyst SO4. 2- The catalyst, denoted as catalyst 3, is a mixture of ZrO2-Al2O3 (Zr / Al = 1:1). The acidity of the catalyst was determined using the Hammett acid indicator method, and the acid strength H0 < -12.70, indicating it has reached the level of a superacid.

[0056] Example 4

[0057] 20 g of Pluronic F127, 37.5 g of Al(NO3)3·9H2O, 6.74 g of Yb(NO3)3·6H2O, and 4.78 g of Ce(NO3)3·3H2O were dissolved in 500 mL of anhydrous ethanol and stirred for 30 min, and this solution was designated as solution A. 163.8 g of zirconium n-propoxide (Zr(OPr)4) (in which n-propanol is 60 wt.%) and 8.7 g of acetylacetone were dissolved in 320 mL of anhydrous ethanol, and this solution was designated as solution B. A mixture of solution B and 32 mL of water was slowly added dropwise to solution A under vigorous stirring. The pH was adjusted to 5, and the solution was aged at 80 °C for 6 h. The resulting sol was then refluxed in 1 mol / L NaOH solution for 24 h. Subsequently, excess Na ions were removed with deionized water, and the sol was dried overnight at 80 °C. Then, it was ground into a solid powder and placed in a muffle furnace, heated to 800℃ at a heating rate of 10℃ / min, and held for 4 h to obtain Yb and Ce doped ZrO2-Al2O3.

[0058] 5 g of ZrO2-Al2O3 powder was impregnated in 100 mL of 0.5 mol / L sulfuric acid solution, stirred for 12 h, and then filtered. The resulting filter cake was dried at 120 °C for 12 h and then calcined in a muffle furnace at 400 °C for 8 h to obtain a solid superacid catalyst SO4. 2- The catalyst, denoted as catalyst 4, is a mixture of ZrO2-Al2O3 (Zr / Al = 2:1). The acidity of the catalyst was determined using the Hammett acid indicator method, and the acid strength H0 < -12.70, indicating it reaches the level of a superacid.

[0059] Example 5

[0060] 20 g of Pluronic F127, 37.5 g of Al(NO3)3·9H2O, 8.98 g of Yb(NO3)3·6H2O, and 3.18 g of Ce(NO3)3·3H2O were dissolved in 500 mL of anhydrous ethanol and stirred for 30 min, and this solution was designated as solution A. 163.8 g of zirconium propoxide (Zr(OPr)4) (in which n-propanol is 60 wt.%) and 8.7 g of acetylacetone were dissolved in 320 mL of anhydrous ethanol, and this solution was designated as solution B. A mixture of solution B and 32 mL of water was slowly added dropwise to solution A under vigorous stirring. The pH was adjusted to 6, and the solution was aged at 45 °C for 48 h. The resulting sol was then refluxed in 1 mol / L NaOH solution for 24 h. Subsequently, excess Na ions were removed with deionized water, and the sol was dried overnight at 80 °C. Then, it was ground into a solid powder and placed in a muffle furnace, heated to 300℃ at a heating rate of 10℃ / min, and held for 8 h to obtain Yb and Ce doped ZrO2-Al2O3.

[0061] 5 g of ZrO2-Al2O3 powder was impregnated in 100 mL of 0.5 mol / L sulfuric acid solution, stirred for 12 h, and then filtered. The resulting filter cake was dried at 120 °C for 12 h and then calcined in a muffle furnace at 800 °C for 3 h to obtain a solid superacid catalyst SO4. 2- The catalyst, denoted as catalyst 5, is a mixture of ZrO2-Al2O3 (Zr / Al = 2:1). The acidity of the catalyst was determined using the Hammett acid indicator method, and the acid strength H0 < -12.70, indicating it reaches the level of a superacid.

[0062] Example 6

[0063] (1) Preparation of ethyl octanoate

[0064] 43.26 g of octanoic acid and 17.97 g of anhydrous ethanol were mixed in a 250 mL three-necked flask, and then 2.2 g of catalyst 1 was added. The mixture was heated under reflux at 85 °C for 5 h. After the reaction was completed, the reaction solution was cooled, and the catalyst was separated from the reaction solution. The reaction solution was then subjected to vacuum distillation (pressure 0.01 MPa, temperature 120 °C) to obtain 48.25 g of a colorless liquid product. Gas chromatography analysis showed that the purity of the liquid product was 99.3%, and the yield was 89.7%.

[0065] (2) Preparation of octanoyl hydroxamic acid

[0066] 120.8 g of ethanol was added to a 250 ml three-necked flask, followed by 7.69 g (0.11 mol, 1.1 eq) of hydroxylamine hydrochloride and 6.8 g of solid base (sodium hydroxide) catalyst. After mixing thoroughly, 17.23 g (0.1 mol, 1.0 eq) of the synthesized ethyl octanoate was added, and the mixture was reacted at 35 °C for 1.5 h. The mixture was filtered, and the ethanol-water solution was removed by vacuum distillation. Then, 80 ml of deionized water was added, and hydrochloric acid was slowly added dropwise at a temperature below 5 °C to adjust the pH to 4. A white solid precipitated, which was filtered, washed with water, and dried to obtain 13.25 g of white solid, which was the octanoyl hydroxamic acid product with a purity of 99.5% and a yield of 87.5%.

[0067] Comparative Example 1

[0068] 20 g of Pluronic F127 and 37.5 g of Al(NO3)3·9H2O were dissolved in 500 mL of anhydrous ethanol and stirred for 30 min, denoted as solution A. 163.8 g of zirconium n-propoxide (Zr(OPr)4) (60 wt.% n-propanol) and 8.7 g of acetylacetone were dissolved in 320 mL of anhydrous ethanol, denoted as solution B. A mixture of solution B and 32 mL of water was slowly added dropwise to solution A under vigorous stirring. The pH was adjusted to 5, and the solution was aged at 60 °C for 24 h. The resulting sol was then refluxed in 1 mol / L NaOH solution for 24 h. Excess Na ions were removed with deionized water, and the sol was dried overnight at 80 °C. The resulting powder was then ground into a solid powder and placed in a muffle furnace. The temperature was increased to 580 °C at a rate of 10 °C / min and maintained for 8 h to obtain ZrO2-Al2O3.

[0069] 5 g of ZrO2-Al2O3 powder was impregnated in 100 mL of 0.5 mol / L sulfuric acid solution, stirred for 12 h, and then filtered. The resulting filter cake was dried at 120 °C for 12 h and then calcined in a muffle furnace at 500 °C for 5 h to obtain a solid superacid catalyst SO4. 2-The catalyst, designated as catalyst 6, is a mixture of ZrO2-Al2O3 (Zr / Al = 2:1). The acidity of the catalyst was determined using the Hammett acid indicator method, showing an acid strength H0 < -12.70, indicating it reaches the level of a superacid.

[0070] Comparative Example 2

[0071] 20 g of Pluronic F127, 37.5 g of Al(NO3)3·9H2O, and 4.78 g of Ce(NO3)3·3H2O were dissolved in 500 mL of anhydrous ethanol and stirred for 30 min, denoted as solution A. 163.8 g of zirconium n-propoxide (Zr(OPr)4) (containing 60 wt.% n-propanol) and 8.7 g of acetylacetone were dissolved in 320 mL of anhydrous ethanol, denoted as solution B. A mixture of solution B and 32 mL of water was slowly added dropwise to solution A under vigorous stirring. The pH was adjusted to 5, and the solution was aged at 60 °C for 24 h. The resulting sol was then refluxed in 1 mol / L NaOH solution for 24 h. Subsequently, excess Na ions were removed with deionized water, and the sol was dried overnight at 80 °C. Then, it was ground into a solid powder and placed in a muffle furnace, heated to 580℃ at a heating rate of 10℃ / min, and held for 8 h to obtain Ce-doped ZrO2-Al2O3.

[0072] 5 g of ZrO2-Al2O3 powder was impregnated in 100 mL of 0.5 mol / L sulfuric acid solution, stirred for 12 h, and then filtered. The resulting filter cake was dried at 120 °C for 12 h and then calcined in a muffle furnace at 500 °C for 5 h to obtain a solid superacid catalyst SO4. 2- The catalyst, designated as catalyst 7, is a mixture of ZrO2-Al2O3 (Zr / Al = 2:1). The acidity of the catalyst was determined using the Hammett acid indicator method, showing an acid strength H0 < -12.70, indicating it reaches the level of a superacid.

[0073] Comparative Example 3

[0074] The difference from Example 1 is that the rare earth elements are directly impregnated onto the support using Yb(NO3)3·6H2O and Ce(NO3)3·3H2O. All other operations are exactly the same as in Example 1, as detailed below:

[0075] 20 g of Pluronic F127 and 37.5 g of Al(NO3)3·9H2O were dissolved in 500 mL of anhydrous ethanol and stirred for 30 min, denoted as solution A. 163.8 g of zirconium n-propoxide (Zr(OPr)4) (60 wt.% n-propanol) and 8.7 g of acetylacetone were dissolved in 320 mL of anhydrous ethanol, denoted as solution B. A mixture of solution B and 32 mL of water was slowly added dropwise to solution A under vigorous stirring. The pH was adjusted to 5, and the solution was aged at 60 °C for 24 h. The resulting sol was then refluxed in 1 mol / L NaOH solution for 24 h. Subsequently, excess Na ions were removed with deionized water, and the sol was dried overnight at 80 °C and then ground into a solid powder. A mixed solution of 4.49 g Yb(NO3)3 and 4.78 g Ce(NO3)3·3H2O was impregnated onto a solid powder using an equal-volume impregnation method. The powder was then placed in a muffle furnace and heated to 580 °C at a rate of 10 °C / min, and held for 8 h to obtain Yb and Ce doped ZrO2-Al2O3.

[0076] 5 g of ZrO2-Al2O3 powder was impregnated in 100 mL of 0.5 mol / L sulfuric acid solution, stirred for 12 h, and then filtered. The resulting filter cake was dried at 120 °C for 12 h and then calcined in a muffle furnace at 500 °C for 5 h to obtain a solid superacid catalyst SO4. 2- The catalyst, designated as catalyst 8, is a ZrO2-Al2O3 (Zr / Al = 2:1) catalyst. The SEM image of this catalyst is shown below. Figure 1 As shown. The acidity of the obtained catalyst was determined by the Hammett acid indicator method, and the acid strength H0 of the catalyst was found to be <-12.70, which is at the level of superacid.

[0077] Example 7

[0078] The catalysts prepared in Examples 1-5 and Comparative Examples 1-3 were used to react octanoic acid and ethanol to synthesize ethyl octanoate. The specific reaction parameters and results are shown in Table 1.

[0079] Table 1

[0080]

[0081] Example 8

[0082] 43.26 g of octanoic acid and 17.97 g of anhydrous ethanol were mixed in a 250 ml three-necked flask, and then 2.2 g of catalyst 1 was added. The mixture was heated to reflux at 85 °C for 5 h. After the reaction was completed, the reaction solution was cooled, and the catalyst was separated from the reaction solution. The reaction solution was treated according to step (1) in Example 7. The catalyst was washed, calcined, and reserved for the second batch. The second batch of reactants was added to the three-necked flask according to the feed ratio of the first batch to start the second batch of reaction, and the subsequent batches were reacted in sequence. The effect of the number of times the catalyst was used on the reaction was investigated, and the results are shown in Table 2.

[0083] Table 2

[0084]

[0085] As can be seen from Table 2, after multiple cycles, the conversion rate of octanoic acid and the yield of ethyl octanoate remained basically stable, indicating that the catalyst prepared by this invention has good stability and long service life.

Claims

1. A solid superacid catalyst, characterized in that, The catalyst comprises a mesoporous support, sulfate ions bound to the mesoporous support, and rare earth ions doped onto the mesoporous support. The mesoporous support is composed of ZrO2 and Al2O3. The rare earth ions are Yb. 3+ and Ce 3+ The molar ratio of ZrO2 to Al2O3 is 2-6:1; the Yb 3+ and Ce 3+ The molar ratio of Al₂O₃ to Yb is 0.8-2.5:

1. 3+ The molar ratio is 2.5-8:1; The solid superacid catalyst is prepared using the following steps: 1) Prepare a mixed solution of aluminum nitrate, ytterbium nitrate, cerium nitrate and template agent, denoted as solution A; prepare a mixed solution of zirconium propoxide and acetylacetone, denoted as solution B; add the mixture of solution B and deionized water to solution A under stirring to obtain a mixed solution; 2) Adjust the pH of the obtained mixed solution to 5-6 and age it to obtain a gel; 3) The obtained gel is added to an alkaline solution in sequence for reflux, washing, drying and grinding to obtain powder; the alkaline solution includes NaOH, KOH, ammonia, Na2CO3 and NaHCO3 solutions; 4) The obtained powder is calcined to obtain rare earth ion-doped ZrO2-Al2O3 powder; 5) The ZrO2-Al2O3 powder doped with rare earth ions was impregnated in sulfuric acid solution, stirred, filtered, and the resulting filter cake was dried and calcined in sequence to obtain a solid superacid catalyst.

2. The method for preparing the solid superacid catalyst according to claim 1, characterized in that, Includes the following steps: 1) Prepare a mixed solution of aluminum nitrate, ytterbium nitrate, cerium nitrate and template agent, denoted as solution A; prepare a mixed solution of zirconium propoxide and acetylacetone, denoted as solution B; add the mixture of solution B and deionized water to solution A under stirring to obtain a mixed solution; 2) Adjust the pH of the obtained mixed solution to 5-6 and age it to obtain a gel; 3) The obtained gel is added to an alkaline solution in sequence for reflux, washing, drying and grinding to obtain powder; the alkaline solution includes NaOH, KOH, ammonia, Na2CO3 and NaHCO3 solutions; 4) The obtained powder is calcined to obtain rare earth ion-doped ZrO2-Al2O3 powder; 5) The ZrO2-Al2O3 powder doped with rare earth ions was impregnated in sulfuric acid solution, stirred, filtered, and the resulting filter cake was dried and calcined in sequence to obtain a solid superacid catalyst.

3. The preparation method according to claim 2, characterized in that, The aging temperature described in step 2) is 45-80℃, and the aging time is 6-48h.

4. The preparation method according to claim 2, characterized in that, The calcination temperature in step 4) is 200-800℃, and the time is 3-8h.

5. The preparation method according to claim 2, characterized in that, The drying temperature in step 5) is 80-130℃ and the time is 12-24h; the calcination temperature is 400-800℃ and the time is 3-8h.

6. The application of the solid superacid catalyst according to claim 1 in the synthesis of octanoyl hydroxamic acid, characterized in that, Octanoyl hydroxamic acid was synthesized using the following steps: (1) Mix octanoic acid, ethanol and solid superacid catalyst, react the resulting mixture, and distill the reaction solution under reduced pressure to obtain ethyl octanoate; (2) After adding hydroxylamine salt and solid base to ethanol solvent and mixing them evenly, add the above-mentioned ethyl octanoate to react and obtain octanoyl hydroxamic acid.

7. The application according to claim 6, characterized in that, The amount of catalyst added in step (1) is 1wt%-10wt% of octanoic acid.

8. The application according to claim 6, characterized in that, The molar ratio of octanoic acid and ethanol in step (1) is 1:1-1.5.

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