Green oxidation esterification process of benzyl alcohol catalyzed by nano-gold

Abstract

The present application relates to the technical field of benzyl alcohol oxidation esterification preparation, in particular to a kind of green oxidation esterification process of nano gold catalysis benzyl alcohol, including carrier and gold active component supported on the carrier;The carrier is zirconium dioxide-silicon dioxide composite oxide with 30% zirconium dioxide by mass fraction, and the carrier particle size is 50-100 mesh;The loading capacity of gold is 0.5wt%-2.0wt%, and the particle size of gold nanoparticles is 1nm-6nm.In terms of catalytic performance, the process optimizes the loading capacity of nano gold, expands the types of multi-component carriers, and introduces a promoter to construct a three-dimensional synergistic catalytic system, which significantly improves the activity and stability of the catalyst, effectively solves the problems of low activity, difficult recovery and poor reusability of traditional catalysts, and prolongs the service life of the catalyst.

Description

Technical Field

[0001] This invention relates to the field of benzyl alcohol oxidative esterification preparation technology, specifically to a green oxidative esterification process of benzyl alcohol catalyzed by nano-gold. Background Technology

[0002] The oxidative esterification of benzyl alcohol to produce methyl benzoate is an important process in the fine chemical industry, with the product widely used in fragrances, pharmaceuticals, coatings, and other industries, resulting in consistently stable market demand. However, existing processes suffer from numerous technical bottlenecks, failing to meet the demands of modern industry for high efficiency, green practices, and low costs. Traditional processes primarily utilize precious metal catalysts, which generally suffer from insufficient catalytic activity and poor stability. Some catalysts are difficult to recover, and their performance rapidly declines after repeated use, increasing energy consumption and costs. Furthermore, the limited selection of support types and poor adaptability prevent flexible adjustments based on reaction requirements, further restricting improvements in catalytic efficiency.

[0003] Regarding the reaction system, existing processes often rely on toxic and harmful oxidants and solvents, which not only cause serious environmental pollution but may also affect product purity and pose safety hazards to production operations. In terms of raw material application, existing processes have stringent requirements for raw material ratios; the fixed ratio range greatly limits the applicable scenarios of the process, and the requirements for raw material purity are extremely high, requiring only high-purity benzyl alcohol, resulting in high raw material procurement costs and making it difficult to achieve large-scale, low-cost production. Furthermore, the benzyl alcohol conversion rate and methyl benzoate selectivity of existing processes are generally low, and the pollutant emissions from the post-reaction system exceed standards, which is inconsistent with the development trend of green chemistry. These problems collectively restrict the industrial application and upgrading of the benzyl alcohol oxidative esterification process. Summary of the Invention

[0004] The primary objective of this invention is to provide a green oxidative esterification process for benzyl alcohol catalyzed by nano-gold.

[0005] A further objective of the present invention is to provide a nano-gold catalyst, characterized in that it comprises a support and a gold active component loaded on the support; the support is a zirconium dioxide-silica composite oxide with a zirconium dioxide mass fraction of 30% and a support particle size of 50-100 mesh; the gold loading is 0.5%-2.0% by weight and the gold nanoparticles have a particle size of 1 nm-6 nm.

[0006] Preferably, the gold loading is 1.0 wt%, and the gold nanoparticles have a particle size of 3 nm.

[0007] A nano-gold composite catalyst containing a co-catalyst includes a support, a gold active component, and a cerium oxide co-catalyst; the support is silica with a particle size of 50-100 mesh; the gold loading is 1.0 wt%, the cerium oxide loading is 1.0 wt%, and the mass ratio of cerium oxide to gold is 1:1; the gold nanoparticles have a particle size of 3 nm.

[0008] A method for preparing a nano-gold catalyst includes the following steps: (1) Take a zirconium dioxide-silica composite oxide carrier with a particle size of 50-100 mesh and a zirconium dioxide mass fraction of 30%, soak it in 1 mol / L hydrochloric acid solution for 2 hours, filter it, wash it with deionized water until neutral, and dry it at 110℃ for 4 hours to obtain a pretreated carrier. (2) Dissolve chloroauric acid in deionized water, add the pretreated carrier, stir for 30 min, add 0.5 mol / L sodium carbonate solution to adjust the pH of the system to 8-9, continue stirring for 1 h, and let it stand to precipitate for 2 h; (3) After filtration, the precipitate was dried at 110℃ for 6 hours, and then calcined in air at 380℃-420℃ for 2 hours to obtain nano gold catalyst.

[0009] Preferably, in step (2), the pH of the system is adjusted to 8.5; and in step (3), the calcination temperature is 400℃.

[0010] A green oxidative esterification process for benzyl alcohol includes the following steps: adding benzyl alcohol, methanol, and the catalyst to a reaction vessel, sealing it, replacing the air inside the vessel with oxygen three times, introducing oxygen until the pressure inside the vessel is 0.2 MPa-0.4 MPa, heating to 50℃-70℃, and stirring the reaction at 500 r / min for 3-5 hours; after the reaction is completed, cooling, depressurizing, filtering, and separating the catalyst to obtain methyl benzoate; the reaction system is a solvent-free system, and the amount of catalyst used is 0.2 g.

[0011] Preferably, the molar ratio of benzyl alcohol to methanol is 1:1 to 1:5.

[0012] Preferably, the oxygen pressure inside the reactor is 0.3 MPa, the reaction temperature is 60°C, and the reaction time is 4 h.

[0013] Preferably, the purity of benzyl alcohol is 90%-99.9%.

[0014] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention comprehensively addresses many shortcomings of existing technologies through multi-dimensional synergistic optimization, possessing significant technical advantages and practical value. Regarding catalytic performance, the process scientifically optimizes the loading of gold nanoparticles, expands the types of diverse supports, and introduces co-catalysts to construct a three-dimensional synergistic catalytic system, significantly improving the activity and stability of the catalyst. This effectively solves the problems of low activity, difficult recovery, and poor reusability of traditional catalysts, extending the catalyst's lifespan.

[0015] 2. This invention utilizes a green oxidant to replace traditional toxic reagents, constructing a solvent-free and green solvent reaction system. This eliminates the pollution of the environment by toxic and harmful substances at its source, reduces pollutant emissions from the reaction system, meets the requirements of modern green chemical development, and improves the safety and environmental friendliness of the production process. Regarding cost control and application scope, the process significantly broadens the range of raw material ratios and improves adaptability to crude benzyl alcohol. It eliminates the need for high-purity raw materials, greatly reducing raw material procurement costs, expanding the application scenarios of the process, and enhancing its practicality and economy.

[0016] 3. The process of this invention has comprehensively improved the conversion rate of benzyl alcohol, the selectivity of methyl benzoate, and the catalyst recovery rate, achieving synergistic optimization of catalytic performance, environmental protection, and production cost. The overall process is simple to operate and highly stable, providing an efficient and feasible solution for the industrial production of benzyl alcohol oxidation esterification, and has broad prospects for promotion and application. Detailed Implementation

[0017] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Example 1: Catalyst preparation: Take 10 g of silica support with a particle size of 80 mesh, soak it in hydrochloric acid solution with a concentration of 1 mol / L for 2 hours, filter it, wash it with deionized water until neutral, and dry it at 110 degrees Celsius for 4 hours to obtain pretreated silica support.

[0019] 0.1 g of chloroauric acid was dissolved in 50 mL of deionized water. Pretreated silica support was added and stirred for 30 minutes. Then, sodium carbonate solution with a concentration of 0.5 mol / L was slowly added dropwise to adjust the pH of the system to 8.5. Stirring was continued for 1 hour, and the mixture was allowed to stand for 2 hours to precipitate. After filtration, the precipitate was dried at 110°C for 6 hours and then calcined in air at 400°C for 2 hours to obtain a gold silica catalyst with a loading of 1.0 wt%.

[0020] The gold nanoparticles in this catalyst have a diameter of 3 nanometers, exhibit excellent dispersibility, and show no agglomeration.

[0021] Oxidative esterification process: 10 mmol benzyl alcohol, 20 mmol methanol, and 0.2 g of the above-mentioned gold silica catalyst were added to a 250 mL high-pressure reactor. After sealing the reactor, the air inside was replaced with oxygen three times. Subsequently, oxygen was introduced until the pressure inside the reactor reached 0.3 MPa. The temperature was raised to 60 °C, and the stirring rate was controlled at 500 rpm. The reaction was continued for 4 hours. After the reaction was completed, the mixture was cooled to room temperature, the pressure was released, and the catalyst was separated by filtration to obtain methyl benzoate.

[0022] Example 2: Catalyst preparation: Take 10 g of silica support with a particle size of 80 mesh, soak it in hydrochloric acid solution with a concentration of 1 mol / L for 2 hours, filter it, wash it with deionized water until neutral, and dry it at 110 degrees Celsius for 4 hours to obtain pretreated silica support.

[0023] 0.15 g of chloroauric acid was dissolved in 50 mL of deionized water. Pretreated silica support was added and stirred for 30 minutes. Then, sodium carbonate solution with a concentration of 0.5 mol / L was slowly added dropwise to adjust the pH of the system to 8.5. Stirring was continued for 1 hour, and the mixture was allowed to stand for 2 hours to precipitate. After filtration, the precipitate was dried at 110°C for 6 hours and then calcined in air at 400°C for 2 hours to obtain a gold silica catalyst with a loading of 1.5% by weight.

[0024] The gold nanoparticles in this catalyst have a diameter of 3 nanometers, exhibit excellent dispersibility, and show no agglomeration.

[0025] Oxidative esterification process: 10 mmol benzyl alcohol, 20 mmol methanol, and 0.2 g of the above-mentioned gold silica catalyst were added to a 250 mL high-pressure reactor. After sealing the reactor, the air inside was replaced with oxygen three times. Subsequently, oxygen was introduced until the pressure inside the reactor reached 0.3 MPa. The temperature was raised to 60 °C, and the stirring rate was controlled at 500 rpm. The reaction was continued for 4 hours. After the reaction was completed, the mixture was cooled to room temperature, the pressure was released, and the catalyst was separated by filtration to obtain methyl benzoate.

[0026] Example 3: Catalyst preparation: 10 g of zirconium dioxide-silica composite oxide with a particle size of 80 mesh was used as a support. The mass fraction of zirconium dioxide in the composite support was 30%. It was soaked in a hydrochloric acid solution with a concentration of 1 mol / L for 2 hours, filtered, washed with deionized water until neutral, and dried at 110 degrees Celsius for 4 hours to obtain the pretreated composite support.

[0027] 0.1 g of chloroauric acid was dissolved in 50 mL of deionized water, and the pretreated composite support was added. After stirring for 30 minutes, sodium carbonate solution with a concentration of 0.5 mol / L was slowly added dropwise to adjust the pH of the system to 8.5. Stirring was continued for 1 hour, and the mixture was allowed to stand for 2 hours to precipitate. After filtration, the precipitate was dried at 110°C for 6 hours and then calcined in air at 400°C for 2 hours to obtain a gold zirconium dioxide silica catalyst with a loading of 1.0 wt%.

[0028] The gold nanoparticles in this catalyst have a diameter of 3 nanometers, exhibit excellent dispersibility, and show no agglomeration.

[0029] Oxidative esterification process: 10 mmol benzyl alcohol, 20 mmol methanol, and 0.2 g of the above-mentioned gold zirconium dioxide silica catalyst were added to a 250 mL high-pressure reactor. After sealing the reactor, the air inside was replaced with oxygen three times. Subsequently, oxygen was introduced until the pressure inside the reactor reached 0.3 MPa. The temperature was raised to 60 °C, and the stirring rate was controlled at 500 rpm. The reaction was continued for 4 hours. After the reaction was completed, the mixture was cooled to room temperature, the pressure was released, and the catalyst was separated by filtration to obtain methyl benzoate.

[0030] Example 4: Catalyst preparation: Take 10 g of silica support with a particle size of 80 mesh, soak it in hydrochloric acid solution with a concentration of 1 mol / L for 2 hours, filter it, wash it with deionized water until neutral, and dry it at 110 degrees Celsius for 4 hours to obtain pretreated silica support.

[0031] 0.1 g of chloroauric acid was dissolved in 50 mL of deionized water, and 0.1 g of cerium oxide powder was added. After ultrasonic dispersion for 30 minutes, pretreated silica support was added, and stirring was continued for 30 minutes. Sodium carbonate solution with a concentration of 0.5 mol / L was slowly added dropwise to adjust the pH of the system to 8.5. Stirring was continued for 1 hour, and the mixture was allowed to stand for 2 hours to precipitate. After filtration, the precipitate was dried at 110 degrees Celsius for 6 hours, and then calcined in air at 400 degrees Celsius for 2 hours to obtain a gold-cerium oxide-silica composite catalyst with a gold and cerium oxide loading of 1.0 wt%.

[0032] The gold nanoparticles in this catalyst have a diameter of 3 nanometers, exhibit excellent dispersibility, and show no agglomeration.

[0033] Oxidative esterification process: 10 mmol benzyl alcohol, 30 mmol methanol, and 0.2 g of the above-mentioned gold cerium oxide-silica composite catalyst were added to a 250 mL high-pressure reactor. After sealing the reactor, the air inside was replaced with oxygen three times. Subsequently, oxygen was introduced until the pressure inside the reactor reached 0.3 MPa. The temperature was raised to 60 °C, and the stirring rate was controlled at 500 rpm. The reaction was continued for 4 hours. After the reaction was completed, the mixture was cooled to room temperature, the pressure was released, and the catalyst was separated by filtration to obtain methyl benzoate.

[0034] Example 5: Catalyst preparation: Take 10 g of silica support with a particle size of 80 mesh, soak it in hydrochloric acid solution with a concentration of 1 mol / L for 2 hours, filter it, wash it with deionized water until neutral, and dry it at 110 degrees Celsius for 4 hours to obtain pretreated silica support.

[0035] 0.1 g of chloroauric acid was dissolved in 50 mL of deionized water, and 0.1 g of cerium oxide powder was added. After ultrasonic dispersion for 30 minutes, pretreated silica support was added, and stirring was continued for 30 minutes. Sodium carbonate solution with a concentration of 0.5 mol / L was slowly added dropwise to adjust the pH of the system to 8.5. Stirring was continued for 1 hour, and the mixture was allowed to stand for 2 hours to precipitate. After filtration, the precipitate was dried at 110 degrees Celsius for 6 hours, and then calcined in air at 400 degrees Celsius for 2 hours to obtain a gold-cerium oxide-silica composite catalyst with a gold and cerium oxide loading of 1.0 wt%.

[0036] The gold nanoparticles in this catalyst have a diameter of 3 nanometers, exhibit excellent dispersibility, and show no agglomeration.

[0037] Oxidative esterification process: 10 mmol benzyl alcohol, 20 mmol methanol, and 0.2 g of the above-mentioned gold cerium oxide-silica composite catalyst were added to a 250 mL high-pressure reactor. After sealing the reactor, the air inside was replaced with oxygen three times. Subsequently, oxygen was introduced until the pressure inside the reactor reached 0.3 MPa. The temperature was raised to 60 °C, and the stirring rate was controlled at 500 rpm. The reaction was carried out for 4 hours. After the reaction was completed, the mixture was cooled to room temperature, the pressure was released, and the catalyst was separated by filtration to obtain methyl benzoate.

[0038] Example 6: Catalyst preparation: Take 10 g of silica support with a particle size of 80 mesh, soak it in hydrochloric acid solution with a concentration of 1 mol / L for 2 hours, filter it, wash it with deionized water until neutral, and dry it at 110 degrees Celsius for 4 hours to obtain pretreated silica support.

[0039] 0.1 g of chloroauric acid was dissolved in 50 mL of deionized water, and 0.1 g of cerium oxide powder was added. After ultrasonic dispersion for 30 minutes, pretreated silica support was added, and stirring was continued for 30 minutes. Sodium carbonate solution with a concentration of 0.5 mol / L was slowly added dropwise to adjust the pH of the system to 8.5. Stirring was continued for 1 hour, and the mixture was allowed to stand for 2 hours to precipitate. After filtration, the precipitate was dried at 110 degrees Celsius for 6 hours, and then calcined in air at 400 degrees Celsius for 2 hours to obtain a gold-cerium oxide-silica composite catalyst with a gold and cerium oxide loading of 1.0 wt%.

[0040] The gold nanoparticles in this catalyst have a diameter of 3 nanometers, exhibit excellent dispersibility, and show no agglomeration.

[0041] Oxidative esterification process: 10 mmol benzyl alcohol, 50 mmol methanol, and 0.2 g of the above-mentioned gold cerium oxide-silica composite catalyst were added to a 250 mL high-pressure reactor. After sealing the reactor, the air inside was replaced with oxygen three times. Subsequently, oxygen was introduced until the pressure inside the reactor reached 0.3 MPa. The temperature was raised to 60 °C, and the stirring rate was controlled at 500 rpm. The reaction was continued for 4 hours. After the reaction was completed, the mixture was cooled to room temperature, the pressure was released, and the catalyst was separated by filtration to obtain methyl benzoate.

[0042] Example 7: Catalyst preparation: Take 10 g of silica support with a particle size of 80 mesh, soak it in hydrochloric acid solution with a concentration of 1 mol / L for 2 hours, filter it, wash it with deionized water until neutral, and dry it at 110 degrees Celsius for 4 hours to obtain pretreated silica support.

[0043] 0.1 g of chloroauric acid was dissolved in 50 mL of deionized water, and 0.1 g of cerium oxide powder was added. After ultrasonic dispersion for 30 minutes, pretreated silica support was added, and stirring was continued for 30 minutes. Sodium carbonate solution with a concentration of 0.5 mol / L was slowly added dropwise to adjust the pH of the system to 8.5. Stirring was continued for 1 hour, and the mixture was allowed to stand for 2 hours to precipitate. After filtration, the precipitate was dried at 110 degrees Celsius for 6 hours, and then calcined in air at 400 degrees Celsius for 2 hours to obtain a gold-cerium oxide-silica composite catalyst with a gold and cerium oxide loading of 1.0 wt%.

[0044] The gold nanoparticles in this catalyst have a diameter of 3 nanometers, exhibit excellent dispersibility, and show no agglomeration.

[0045] Oxidative esterification process: 10 mmol of 90% pure benzyl alcohol, 20 mmol of methanol, and 0.2 g of the above-mentioned gold cerium oxide-silica composite catalyst were added to a 250 mL high-pressure reactor. After sealing the reactor, the air inside was replaced with oxygen three times. Subsequently, oxygen was introduced until the pressure inside the reactor reached 0.3 MPa. The temperature was raised to 60°C, and the stirring rate was controlled at 500 rpm. The reaction was carried out for 4 hours. After the reaction was completed, the mixture was cooled to room temperature, the pressure was released, and the catalyst was separated by filtration to obtain methyl benzoate.

[0046] Comparative Example 1: No catalyst was added, and the remaining oxidative esterification process parameters were the same as in Example 1.

[0047] Comparative Example 2: A commercially available 5% palladium on carbon catalyst was used, in an amount of 0.2 g, and the remaining reaction parameters were the same as in Example 1.

[0048] Comparative Example 3: A gold silica catalyst with a loading of 3.0 wt% was prepared, which is outside the optimized loading range of this invention. The remaining preparation and reaction parameters were the same as in Example 1.

[0049] Comparative Example 4: Potassium permanganate was used as the oxidant, acetone as the solvent, and the gold silica catalyst of Example 1 was used as the catalyst. The remaining reaction parameters were the same as those of Example 1.

[0050] Comparative Example 5: Carrier-free gold nanoparticles were used, with the gold content being the same as in Example 1, and the remaining reaction parameters being the same as in Example 1.

[0051] Comparative Example 6: The gold silica catalyst of Example 1 was used, acetone was used as solvent, and the other reaction parameters were the same as those of Example 1.

[0052] Comparative Example 7: A gold cerium oxide silica catalyst was prepared with a cerium oxide to gold mass ratio of 3:1. The remaining preparation and reaction parameters were the same as in Example 4.

[0053] The zirconium dioxide-silica composite oxide support with a zirconium dioxide mass fraction of 30% described in this invention is prepared by a co-precipitation method, the specific steps of which are as follows: Zirconium nitrate and tetraethyl orthosilicate were weighed at a zirconium dioxide to silicon dioxide mass ratio of 3:7. The tetraethyl orthosilicate was completely dissolved in anhydrous ethanol and stirred until the solution was clear and homogeneous. Zirconium nitrate was dissolved in deionized water and slowly added dropwise to the above tetraethyl orthosilicate ethanol solution while stirring continuously for 30 minutes. Ammonia water with a concentration of 1 mol / L was added dropwise to the mixed solution to adjust the pH value of the system to 9-10. After stirring continuously for 2 hours, the mixture was allowed to stand at room temperature for 12 hours for aging. The aged mixture was filtered, and the filter cake was washed with deionized water until the washing liquid was neutral. It was then dried at 110 degrees Celsius for 12 hours and calcined in air at 550 degrees Celsius for 4 hours. After cooling, it was ground and passed through a 50-100 mesh sieve to obtain a zirconium dioxide-silica composite oxide carrier with a zirconium dioxide mass fraction of 30%.

[0054] The cerium oxide cocatalyst of this invention is chemically impregnated and loaded onto the surface of the support simultaneously with the gold active component. After precipitation, drying, and calcination, a stable supported composite catalytic component is formed. It is not added by physical mixing. Those skilled in the art can achieve uniform loading of cerium oxide by referring to the preparation process described in the specification.

[0055] Performance testing and results analysis: The core performance indicators include benzyl alcohol conversion rate, methyl benzoate selectivity, catalyst recovery rate, and chemical oxygen demand (COD) of the reaction system. All tests are conducted strictly in accordance with industry standards to ensure accurate, comparable, and authoritative results, and to guarantee the repeatability of the technical solution.

[0056] (1) The conversion rate of benzyl alcohol and the selectivity of methyl benzoate were detected by a GC7890 gas chromatograph equipped with an HP5 capillary column with a length of 30 meters, an inner diameter of 0.32 mm, and a film thickness of 0.25 micrometers. Heptane was used as the internal standard. The injection port temperature was 250 degrees Celsius, the detector temperature was 280 degrees Celsius, and the column temperature program was as follows: initial temperature of 80 degrees Celsius, hold for 2 minutes, increase to 200 degrees Celsius at a rate of 10 degrees Celsius per minute, hold for 5 minutes, and calculate the conversion rate and selectivity by area normalization method.

[0057] (2) The catalyst recovery rate was calculated by separating the catalyst by filtration, washing it three times with methanol (10 ml each time), drying it at 110 degrees Celsius for 4 hours, cooling it to room temperature, weighing it, and calculating the recovery rate.

[0058] (3) The chemical oxygen demand of the reaction system was determined by potassium dichromate digestion method and measured by DR1900 COD detector. The digestion temperature was 150 degrees Celsius and the digestion time was 2 hours. The detection standard followed the industry standard HJ828-2017.

[0059] The test results are shown in Table 1 below: Table 1:

[0060] Results analysis: Example 1 serves as the basic scheme, successfully replacing traditional toxic oxidants by constructing a silica-supported gold nanoparticle catalyst. This achieved a benzyl alcohol conversion rate of 98.2%, a methyl benzoate selectivity of 99.1%, a catalyst recovery rate of 92.5%, and a COD value of only 85 mg / L. This lays the core foundation for an efficient and green process, while also clarifying the rationality of each preparation step and process parameter, ensuring that those skilled in the art can repeatedly prepare the catalyst and complete the oxidative esterification reaction according to this scheme.

[0061] Based on this, Example 2 further improved the conversion rate to 99.0% and the selectivity to 99.3% by optimizing the gold nanoparticle loading to 1.5% by weight. While ensuring performance, it achieved reasonable control of preparation cost, proving that the optimization of loading in this invention is not a simple adjustment of the value, but a synergistic balance between performance and cost through precise control.

[0062] Example 3 uses a zirconium dioxide-silica composite support with a zirconium dioxide mass fraction of 30%, which enhances the stability of the catalyst. The conversion rate and selectivity reach 99.2% and 99.5%, respectively, and the COD value is reduced to 80 mg / L, highlighting the synergistic effect of the composite support and gold nanoparticles. The technical effect of this specific ratio of composite support can be achieved without the generalized silica-based support of the prior art.

[0063] Example 4 introduces cerium oxide co-catalyst, strictly controlling the mass ratio of co-catalyst to gold to be 1:1, constructing a three-dimensional synergistic catalytic system. Under suitable process parameters, the conversion rate and selectivity reach 99.5% and 99.6%, respectively, and the catalyst recovery rate is increased to 93.5%. Moreover, the range of process parameter adaptability is significantly broadened, achieving a breakthrough improvement in catalytic efficiency. This synergistic effect far exceeds the technical effect of arbitrarily adding co-catalysts in the prior art, resulting in unexpected technological progress.

[0064] The solvent-free system in Example 5 further enhances the green attributes of the process, reducing the COD value to 75 mg / L while maintaining a high conversion rate of 99.3% and a high selectivity of 99.4%. It fundamentally solves the problem of solvent pollution in traditional processes, demonstrating the innovation and practicality of the green reaction system of this invention.

[0065] Examples 6 and 7 respectively verified the adaptability of the process to a wide range of raw material ratios and low-purity crude raw materials. Under the condition of a benzyl alcohol to methanol molar ratio of 1:5, the conversion rate is still above 98.5%. Even when using crude benzyl alcohol with a purity of 90%, the conversion rate reaches 91.8% and the selectivity is 98.5%, which fully meets the needs of industrial-scale application and solves the technical bottleneck of narrow raw material adaptability and high cost of existing technologies.

[0066] The conversion rate of the catalyst-free system in Comparative Example 1 was only 5.3% and the selectivity was 60.2%, which fully demonstrates that the catalyst system of the present invention is the core guarantee for the efficient reaction and also highlights the necessity of the catalyst preparation process of the present invention.

[0067] Comparative Example 2 uses a traditional palladium-on-carbon catalyst, and all its core performance characteristics are lower than those of Example 1. This demonstrates the superior performance of the nano-gold catalytic system of this invention compared to traditional noble metal catalysts, which cannot be achieved simply by replacing the catalyst.

[0068] Comparative Example 3 (high loading), Comparative Example 4 (toxic oxidant system), Comparative Example 5 (no support), Comparative Example 6 (toxic solvent system), and Comparative Example 7 (improper co-catalyst ratio) all have performance shortcomings or environmental defects and cannot achieve the synergistic technical effect of this invention. Comparative Example 3, due to its loading exceeding the optimization range of this invention, not only had lower selectivity and catalyst recovery rate than Example 2, but also resulted in a significant increase in catalyst preparation cost, proving the rationality of the optimized loading range of this invention. Comparative Example 4 used toxic oxidants and solvents, resulting in a COD value as high as 520 mg / L, with extremely poor environmental performance, in stark contrast to the green process of this invention. Comparative Example 5, the supportless scheme, had a catalyst recovery rate of only 75.2%, and its catalytic activity and selectivity were significantly lower than Example 1, proving the innovation of the support loading technology of this invention. The synergistic effect formed by the support and nano-gold significantly improved the stability and catalytic performance of the catalyst. Comparative Example 7 had an improper co-catalyst-to-gold mass ratio, failing to form an effective synergistic catalytic system, and its performance was far lower than Example 4, proving the criticality of controlling the co-catalyst ratio in this invention.

[0069] This invention, through multi-dimensional collaborative optimization, forms a non-obvious technical solution, solves many defects of the prior art, and has outstanding substantive features and significant technological progress.

[0070] Furthermore, it should be noted that the carrier pretreatment employs a proprietary acidification process, immersing the carrier in 1 mol / L hydrochloric acid. This differs from existing technologies that do not use acidification pretreatment, effectively cleaning the carrier surface and improving the uniformity of gold particle loading. Precipitation adjustment uses a 0.5 mol / L sodium carbonate solution, precisely controlling the pH at 8.5. This differs from existing technologies that use ammonia to adjust pH, preventing gold particle agglomeration and enabling the controllable synthesis of 3-nanometer gold particles. Catalyst activation employs single-air calcination at a temperature controlled at 400 degrees Celsius. This differs from the complex process of stepwise calcination involving hydrogen reduction and oxygen oxidation in existing technologies, simplifying the preparation process and improving catalyst stability. A zirconium dioxide-silica composite carrier with a zirconium dioxide mass fraction of 30% is used. This specific ratio composite carrier differs from the generalized silica-based carriers in existing technologies, possessing a unique loading and catalytic synergistic effect. The mass ratio of the co-catalyst to gold is strictly controlled at 1:1, forming a three-dimensional synergistic catalytic system with the composite carrier. This differs from the arbitrary addition of co-catalysts in existing technologies, and the synergistic effect cannot be derived using conventional techniques in this field. Oxidative esterification employs a solvent-free, green system with a low-temperature reaction at 60 degrees Celsius. It is suitable for a wide molar ratio of benzyl alcohol to methanol from 1:1 to 1:5 and is compatible with 90% pure crude benzyl alcohol. This process differs from existing technologies that rely on solvents, have fixed ratios, and require high-purity raw materials.

[0071] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention.

Claims

1. A nano-gold catalyst, characterized in that, The invention includes a carrier and a gold active component loaded on the carrier; the carrier is a zirconium dioxide-silica composite oxide with a zirconium dioxide mass fraction of 30% and a carrier particle size of 50-100 mesh; the gold loading is 0.5%-2.0% by weight and the gold nanoparticles have a particle size of 1nm-6nm.

2. The nano-gold catalyst according to claim 1, characterized in that, The gold loading is 1.0 wt%, and the gold nanoparticles have a particle size of 3 nm.

3. A nano-gold composite catalyst containing a co-catalyst, characterized in that, It includes a support, a gold active component, and a cerium oxide cocatalyst; the support is silicon dioxide with a particle size of 50-100 mesh; the gold loading is 1.0 wt%, the cerium oxide loading is 1.0 wt%, and the mass ratio of cerium oxide to gold is 1:1; the gold nanoparticles have a particle size of 3 nm.

4. A method for preparing a nano-gold catalyst, used to prepare the nano-gold catalyst according to claim 1 or 2, characterized in that, Includes the following steps: (1) Take a zirconium dioxide-silica composite oxide carrier with a particle size of 50-100 mesh and a zirconium dioxide mass fraction of 30%, soak it in 1 mol / L hydrochloric acid solution for 2 hours, filter it, wash it with deionized water until neutral, and dry it at 110℃ for 4 hours to obtain a pretreated carrier. (2) Dissolve chloroauric acid in deionized water, add the pretreated carrier, stir for 30 min, add 0.5 mol / L sodium carbonate solution to adjust the pH of the system to 8-9, continue stirring for 1 h, and let it stand to precipitate for 2 h; (3) After filtration, the precipitate was dried at 110℃ for 6 hours, and then calcined in air at 380℃-420℃ for 2 hours to obtain nano gold catalyst.

5. The preparation method according to claim 4, characterized in that, In step (2), the pH of the system is adjusted to 8.5; in step (3), the calcination temperature is 400℃.

6. A green oxidative esterification process for benzyl alcohol, characterized in that, Using the catalyst according to any one of claims 1-3, the reaction comprises the following steps: adding benzyl alcohol, methanol, and the catalyst to a reaction vessel, sealing it, replacing the air inside the vessel with oxygen three times, introducing oxygen until the pressure inside the vessel is 0.2 MPa-0.4 MPa, heating to 50℃-70℃, and stirring the reaction at 500 r / min for 3-5 h; after the reaction is completed, cooling, depressurizing, filtering, and separating the catalyst to obtain methyl benzoate; the reaction system is a solvent-free system, and the amount of catalyst used is 0.2 g.

7. The oxidative esterification process according to claim 6, characterized in that, The molar ratio of benzyl alcohol to methanol is 1:1 to 1:

5.

8. The oxidative esterification process according to claim 6, characterized in that, The oxygen pressure inside the reactor was 0.3 MPa, the reaction temperature was 60℃, and the reaction time was 4 hours.

9. The oxidative esterification process according to claim 6, characterized in that, The purity of benzyl alcohol is 90%-99.9%.

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