A molybdenum trioxide-loaded reduced graphene oxide catalyst and a preparation method and application thereof

Abstract

The present application relates to the technical field of biodiesel synthesis, and particularly relates to a molybdenum trioxide loaded reduced graphene oxide catalyst and a preparation method and application thereof, the preparation method comprising the following steps: mixing graphite powder, concentrated sulfuric acid and potassium permanganate to perform oxidation treatment, adding hydrogen peroxide to continue the reaction after the reaction is completed, and performing calcination on the graphene oxide product under the protection of a nitrogen atmosphere to obtain reduced graphene oxide; ammonium molybdate is calcined in a muffle furnace to obtain molybdenum trioxide, the obtained molybdenum trioxide and the reduced graphene oxide are compounded through a coprecipitation method, and are subjected to ultrasonic dispersion, stirring and mixing and drying treatment to obtain the molybdenum trioxide loaded reduced graphene oxide catalyst. The catalyst prepared by the present application is a solid catalyst, can be used for catalyzing the transesterification reaction of waste soybean oil to synthesize biodiesel, has no equipment corrosion, the product is easy to separate, the process is environmentally friendly, can be recycled, has a lower cost, and has a good industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of biodiesel synthesis technology, specifically to a molybdenum trioxide-supported reduced graphene oxide catalyst, its preparation method, and its application. Background Technology

[0002] Biodiesel refers to fatty acid monoalkyl esters produced by transesterification of animal and vegetable oils with short-chain alcohols such as methanol or ethanol. It is an environmentally friendly renewable energy source. Compared to traditional petrochemical diesel, biodiesel has a higher cetane number, lower sulfur content, excellent lubrication properties, and biodegradability, and can effectively reduce emissions of unburned hydrocarbons and polycyclic aromatic hydrocarbons. The large amounts of waste cooking oil generated by the catering industry, if not properly managed, pose a safety risk by returning to the food chain. Converting such waste cooking oil into biodiesel through catalytic transesterification not only achieves the resource utilization of low-value waste but also cuts off the illegal recycling chain at its source, resulting in significant environmental and social benefits. Therefore, synthesizing biodiesel from waste soybean oil using catalytic technology has important theoretical exploration significance and practical application value.

[0003] The key to synthesizing biodiesel from waste soybean oil lies in the development of high-performance catalysts. Currently, commonly used catalysts are mainly divided into acid catalysts and base catalysts. However, liquid acid / base catalysts form a homogeneous catalytic process in the reaction system, which suffers from technical drawbacks such as difficulty in separating reaction products, challenges in catalyst recovery and reuse, and strong corrosiveness to equipment. At present, research on efficient heterogeneous solid catalysts for the catalytic synthesis of biodiesel from waste soybean oil is still relatively weak, limiting the application of green and efficient catalytic systems in this field. Therefore, developing a novel high-performance solid catalyst to achieve the efficient and clean conversion of waste soybean oil into biodiesel has become a critical technical challenge that urgently needs to be overcome. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a reduced graphene oxide catalyst supported on molybdenum trioxide, its preparation method, and its application. The prepared catalyst is a solid catalyst that can be used to catalyze the transesterification reaction of waste soybean oil to synthesize biodiesel. It is non-corrosive to equipment, the products are easy to separate, the process is environmentally friendly, it can be recycled, and the cost is lower.

[0005] The purpose of this invention is to provide a method for preparing a molybdenum trioxide-supported reduced graphene oxide catalyst, comprising the following steps: Step 1: Oxidation treatment is carried out using graphite powder as carbon source, concentrated sulfuric acid as intercalating agent, and potassium permanganate as oxidant. After the reaction is completed, hydrogen peroxide is added to continue the reaction. The resulting graphene oxide product is placed in a tube furnace and calcined under nitrogen atmosphere to obtain reduced graphene oxide. Step 2: Using ammonium molybdate as the molybdenum source, molybdenum trioxide is obtained by calcination in a muffle furnace. Subsequently, the obtained molybdenum trioxide is combined with reduced graphene oxide by co-precipitation, followed by ultrasonic dispersion, stirring and mixing and drying to obtain a molybdenum trioxide-supported reduced graphene oxide catalyst.

[0006] This invention first uses a thermal reduction process to prepare reduced graphene oxide. The resulting reduced graphene oxide has a relatively smooth surface with minimal damage and no defects, and a large relative surface area, which is beneficial for loading. At the same time, it generates virtually no waste liquid, making it safe and environmentally friendly. Then, the reduced graphene oxide is combined with a molybdenum source using a co-precipitation method, uniformly loading the molybdenum source into the solid crystal structure of the graphene to form a solid catalyst. This catalyst has more stable mesopores, can be used for the preparation of biodiesel, is convenient to use, easy to separate, and can be recycled multiple times.

[0007] The co-precipitation method of this invention refers to the method of preparing a supported catalyst by adding a precipitant to a solution containing metal cations, forming a uniform precipitate, and then preparing the catalyst through steps such as drying and calcination.

[0008] Furthermore, the loading of molybdenum in the reduced graphene oxide support is 1% to 10%, preferably 3% to 8%, and more preferably 7.5%.

[0009] Furthermore, in step one, the mass-to-volume ratio of graphite powder, concentrated sulfuric acid, potassium permanganate, and hydrogen peroxide is 1g:18-23mL:3-10g:1-4mL, preferably 1g:20mL:4g:2mL; the concentration of hydrogen peroxide is 30%. In this technical solution, hydrogen peroxide is used as a manganese removal agent to reduce the remaining potassium permanganate and manganese oxides.

[0010] Furthermore, in step one, graphite is first mixed with concentrated sulfuric acid for 0.2-0.8 hours, then potassium permanganate is added and stirred to carry out a three-stage gradient temperature reaction. After the reaction is completed, hydrogen peroxide is added and mixed evenly after the temperature drops to 50°C. The mixture is then allowed to stand for 12 hours, washed until neutral, and dried at 60°C for 12 hours to obtain graphene oxide product.

[0011] Furthermore, the three-stage gradient temperature reaction is as follows: the first stage is stirred at an ice bath temperature of -5℃ to -15℃ for 0.5-1.5h, the second stage is stirred at 30-40℃ for 1.5-3.5h, and the third stage is stirred at 60-80℃ for 0.2-0.8h; preferably, the first stage is stirred at an ice bath temperature of 0℃ for 1h, the second stage is stirred at 35℃ for 2h, and the third stage is stirred at 70℃ for 0.5h.

[0012] Furthermore, in step one, the calcination temperature is 150-500℃ and the calcination time is 3-6h; preferably, the calcination temperature is 200-400℃ and the calcination time is 4.5-5.5h; more preferably, the calcination temperature is 250℃ and the calcination time is 5h.

[0013] Furthermore, in step two, the ultrasonic time is 1-6 hours, preferably 3 hours; the stirring time is 1-4 hours.

[0014] Furthermore, the specific method for step one is as follows: Graphite powder was added to a 500 mL three-necked flask, followed by concentrated H2SO4. The mixture was cooled to 0 °C using an ice bath and stirred for 30 min. KMnO4 powder was then slowly added and stirred for 1 h. The reaction mixture was then heated to 35 °C and stirred for 2 h. Ultrapure water was then slowly added, and the reaction mixture was stirred at 70 °C for 30 min. The mixture was then cooled to 50 °C, and 30% H2O2 was added until no gas was produced. The mixture was allowed to stand for 12 h, washed until neutral, and sonicated. The reaction product was dried at 60 °C for 24 h. The dried product was then placed in a tube furnace and calcined at 250 °C for 5 h in a nitrogen atmosphere to obtain reduced graphene oxide, denoted as rGO.

[0015] The present invention also provides a reduced graphene oxide catalyst supported on molybdenum trioxide prepared by the above preparation method.

[0016] This invention also provides an application of the above-mentioned molybdenum trioxide-loaded reduced graphene oxide catalyst in the catalytic transesterification reaction of waste soybean oil to synthesize biodiesel. Specifically, in the catalytic transesterification reaction of waste soybean oil to synthesize biodiesel, waste soybean oil and methanol are used as raw materials, and molybdenum trioxide-loaded reduced graphene oxide is added. The mixture is placed in a high-pressure sealed container and stirred at 80–160°C for 6–16 hours. After the reaction is completed, the mixture is centrifuged and separated to obtain biodiesel.

[0017] Compared with the prior art, the present invention has the following advantages: 1. The reduced graphene oxide supported on molybdenum trioxide provided by this invention is a solid catalyst. Using graphite powder as the carbon source, reduced graphene oxide is prepared by oxidation followed by thermal reduction, and then mixed with a molybdenum source using a co-precipitation method. Experiments have confirmed that the reduced graphene oxide catalyst supported on molybdenum trioxide prepared by this invention exhibits a highly dispersed state of molybdenum trioxide on the surface of the reduced graphene oxide, with good adsorption and binding between molybdenum trioxide and the reduced graphene oxide. Molybdenum trioxide can be uniformly and densely distributed on the catalyst surface. This structural advantage and the interaction of chemical properties enable the MoO3 / rGO solid catalyst to exhibit excellent catalytic performance and good catalytic stability in the catalytic transesterification reaction of waste soybean oil to synthesize biodiesel, with a conversion rate reaching 90.13%. 2. The solid catalyst prepared by this invention has no obvious equipment corrosion when used to catalyze the transesterification reaction of waste soybean oil to synthesize biodiesel. The catalyst is highly safe to use and is insoluble in the reaction raw materials and products, making it easy to separate. It can be reused after simple treatment. The reaction products can be separated by stratification, without complicated post-processing. The process generates almost no wastewater and has green and environmentally friendly characteristics. The catalyst provided by this invention also has the advantage of simple and easy preparation process and has good prospects for industrial application. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. The drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without exceeding the scope of protection claimed by the present invention.

[0019] Figure 1 The images show scanning electron microscope (SEM) and transmission electron microscope (TEM) images (a, b) of the reduced graphene oxide prepared in Example 1 of this invention and scanning electron microscope (SEM) and transmission electron microscope (TEM) images (c, d) of the 7.5% MoO3 / rGO catalyst. Figure 2 X-ray diffraction patterns of the reduced graphene oxide (rGO) and 7.5% MoO3 / rGO catalyst prepared in Example 1 of this invention; Figure 3 The attached diagram shows the N2 physisorption and desorption of the reduced graphene oxide (rGO) and the 7.5% MoO3 / rGO catalyst prepared in Example 1 of this invention. Detailed Implementation

[0020] The above-described technical features of the present invention and the technical features specifically described below (such as in the embodiments) can be combined with each other to form new or preferred technical solutions. However, the present invention is not limited to these embodiments, nor are these embodiments limited in any way.

[0021] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the formulations involved in the following examples are all commercially available products that can be purchased from the market.

[0022] Reagents and raw materials: Graphite powder (2000 mesh) (AR, Shanghai Maclean Biochemical Technology Co., Ltd.), potassium permanganate (KMnO4, AR, Chengdu Kelong Chemical Co., Ltd.), sulfuric acid (H2SO4, AR, Chengdu Kelong Chemical Co., Ltd.), ammonium molybdate ((NH4)6Mo7O 24• 4H2O (AR, Tianjin Yongda Chemical Reagent Co., Ltd.), methanol (CH3OH, AR, Xilong Chemical Co., Ltd.), hydrogen peroxide (H2O2, AR, Xilong Chemical Co., Ltd.), waste soybean oil (laboratory-made).

[0023] Example 1 A method for preparing a molybdenum trioxide-supported reduced graphene oxide catalyst includes the following steps: (1) Preparation of reduced graphene oxide (rGO): Add 4g of graphite powder (2000 mesh) to a 500mL three-necked flask, followed by 80mL of concentrated H2SO4 (AR). Cool the mixture to 0°C in an ice bath and stir at 500 rpm for 30 minutes. Then, slowly add 16g of KMnO4 powder to maintain the reaction temperature below 0°C for 1 hour. Subsequently, heat the reaction mixture to 35°C and stir for 2 hours. Then, slowly add ultrapure water, which produces a significant external heating effect, reaching a maximum temperature of 70°C. Stir the reaction mixture at 70°C for 30 minutes, then cool it to 50°C, and then add 8mL of... 30% H2O2 was added until no gas was produced, and the mixture was allowed to stand for 12 hours. The supernatant was then poured off, and the remaining solid material was washed repeatedly with ultrapure water until neutral. The mixture was then sonicated for 2 hours, and the reaction product was dried at 60°C for 24 hours. The resulting powder was ground to obtain graphene oxide (GO). An appropriate amount of graphene oxide was placed in a tube furnace and calcined at 250°C for 5 hours under a nitrogen atmosphere to obtain reduced graphene oxide (rGO). (2) Using ammonium molybdate as the molybdenum source, molybdenum trioxide was prepared by calcining it in a muffle furnace at 550°C for 3 hours in an air atmosphere. Subsequently, a certain amount of molybdenum trioxide (equivalent to 7.5 wt% of the theoretical molybdenum loading in the support) was dissolved in 400 mL of distilled water (50 mL of distilled water was used for 0.5 g of support), sonicated for 1 hour, and then 4 g of reduced graphene oxide was added. The mixture was sonicated for 2 hours, stirred at 30°C for 2 hours, and dried at 60°C for 24 hours to obtain the reduced graphene oxide catalyst supported on molybdenum trioxide, labeled as 7.5%MoO3 / rGO.

[0024] Example 2 A method for preparing a molybdenum trioxide-supported reduced graphene oxide catalyst includes the following steps: (1) Preparation of reduced graphene oxide (rGO): Add 4g of graphite powder (2000 mesh) to a 500mL three-necked flask, followed by 72mL of concentrated H2SO4 (AR). Cool the mixture to -5°C in an ice bath and stir at 500 rpm for 60min. Then, slowly add 12g of KMnO4 powder to maintain the reaction temperature below 0°C for 1h. Subsequently, heat the reaction mixture to 30°C and stir for 3.5h. Then, slowly add ultrapure water, which produces a significant external heating effect, reaching a maximum temperature of 70°C. Stir the reaction mixture at 60°C for 48min, then cool to 50°C, and then add 5mL of... 30% H2O2 was added until no gas was produced, and the mixture was allowed to stand for 12 hours. The supernatant was then poured off, and the remaining solid material was washed repeatedly with ultrapure water until neutral. The mixture was then sonicated for 2 hours, and the reaction product was dried at 60°C for 24 hours. The resulting powder was ground to obtain graphene oxide (GO). An appropriate amount of graphene oxide was placed in a tube furnace and calcined at 250°C for 5 hours under a nitrogen atmosphere to obtain reduced graphene oxide (rGO). (2) Using ammonium molybdate as the molybdenum source, molybdenum trioxide was prepared by calcining it in a muffle furnace at 550°C for 3 hours in an air atmosphere. Subsequently, a certain amount of molybdenum trioxide (equivalent to 7.5 wt% of the theoretical molybdenum loading in the support) was dissolved in 400 mL of distilled water (50 mL of distilled water was used for 0.5 g of support), sonicated for 1 hour, and then 4 g of reduced graphene oxide was added. The mixture was sonicated for 3 hours, stirred at 30°C for 1 hour, and dried at 60°C for 24 hours to obtain the reduced graphene oxide catalyst supported on molybdenum trioxide, labeled as 7.5%MoO3 / rGO.

[0025] Example 3 A method for preparing a molybdenum trioxide-supported reduced graphene oxide catalyst includes the following steps: (1) Preparation of reduced graphene oxide (rGO): Add 4g of graphite powder (2000 mesh) to a 500mL three-necked flask, followed by 92mL of concentrated H2SO4 (AR). Cool the mixture to 15°C in an ice bath and stir at 500 rpm for 90 min. Then, slowly add 20g of KMnO4 powder to maintain the reaction temperature below 0°C for 1 h. Subsequently, heat the reaction mixture to 40°C and stir for 3.5 h. Then, slowly add ultrapure water, which produces a significant external heating effect, reaching a maximum temperature of 70°C. Stir the reaction mixture at 70°C for 15 min, then cool to 50°C, and then add 16mL of... 30% H2O2 was added until no gas was produced, and the mixture was allowed to stand for 12 hours. The supernatant was then poured off, and the remaining solid material was washed repeatedly with ultrapure water until neutral. The mixture was then sonicated for 2 hours, and the reaction product was dried at 60°C for 24 hours. The resulting powder was ground to obtain graphene oxide (GO). An appropriate amount of graphene oxide was placed in a tube furnace and calcined at 250°C for 5 hours under a nitrogen atmosphere to obtain reduced graphene oxide (rGO). (2) Using ammonium molybdate as the molybdenum source, molybdenum trioxide was prepared by calcining it in a muffle furnace at 550°C for 3 hours in an air atmosphere. Then, a certain amount of molybdenum trioxide (equivalent to 7.5 wt% of the theoretical molybdenum loading in the support) was dissolved in 400 mL of distilled water (50 mL of distilled water was used for 0.5 g of support), sonicated for 1 hour, and then 4 g of reduced graphene oxide was added. The mixture was sonicated for 6 hours, stirred at 30°C for 4 hours, and dried at 60°C for 24 hours to obtain the reduced graphene oxide catalyst loaded with molybdenum trioxide, labeled as 7.5%MoO3 / rGO.

[0026] Examples 4-7 The difference from Example 1 is that the calcination temperature during the preparation of reduced graphene oxide in step (1) is different, namely: Example 4 (150℃), Example 5 (200℃), Example 6 (300℃), and Example 7 (350℃).

[0027] Examples 8-11 The difference from Example 1 is that the molybdenum loading in step (2) is different, namely: the molybdenum loading in Example 8 is 1wt%, the molybdenum loading in Example 9 is 2.5wt%, the molybdenum loading in Example 10 is 5wt%, and the molybdenum loading in Example 11 is 10wt%.

[0028] Comparative Example 1 A method for preparing a carbon nanotube-supported molybdenum trioxide (7.5% MoO3 / CNT) solid catalyst includes the following steps: (1) Preparation of carbon nanotubes (CNTs) Purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., with a purity of AR. (2) Preparation of carbon nanotube supported molybdenum trioxide solid catalyst A certain amount of molybdenum trioxide (equivalent to 7.5 wt% of the theoretical molybdenum loading in the support) was dissolved in 400 mL of distilled water (50 mL of distilled water was used for 0.5 g of support) to obtain a molybdenum trioxide aqueous solution of a certain concentration. The solution was sonicated for 1 h, and then 4 g of carbon nanotube powder was added. The solution was sonicated for 2 h, stirred at 30 °C for 2 h, and dried at 60 °C for 24 h to obtain a carbon nanotube-supported molybdenum trioxide solid catalyst, labeled as 7.5%MoO3 / CNT.

[0029] Experimental Example 1: Catalyst Structure Analysis 1. Characterization and analysis of solid catalysts for the reduction of graphene oxide supported on molybdenum trioxide (1) The reduced graphene oxide (rGO) prepared in Example 1 and the reduced graphene oxide catalyst supported on molybdenum trioxide (7.5% MoO3 / rGO) were used as test samples. They were characterized using a scanning electron microscope (SUPRA55, Carl Zeiss GmbH, Germany) under high vacuum conditions and an accelerating voltage of 5 kV to facilitate observation and analysis of the microstructure of the samples. The images from the scanning electron microscope are shown below. Figure 1 As shown in a and c.

[0030] (2) Using the reduced graphene oxide (rGO) prepared in Example 1 and the reduced graphene oxide catalyst supported on molybdenum trioxide (7.5% MoO3 / rGO) as test samples, the samples were characterized and analyzed using a transmission electron microscope (JEM-2100, NEC Corporation) at an accelerating voltage of 200 kV, a point resolution of 0.23 nm, and a line resolution of 0.14 nm. The transmission electron microscope images are shown below. Figure 1 As shown in b and d.

[0031] pass Figure 1 Scanning electron microscope images show that the molybdenum trioxide-loaded reduced graphene oxide solid catalyst and the reduced graphene oxide have similar wrinkles and morphologies, both exhibiting a thin sheet-like and wrinkled appearance. Transmission electron microscopy images further illustrate the above phenomenon, indicating that the introduction of metallic Mo did not destroy the size and morphology of the reduced graphene oxide.

[0032] Furthermore, it should be noted that the morphology and structure of the molybdenum trioxide-supported reduced graphene oxide solid catalysts synthesized at different calcination temperatures (150, 200, 300, 350) and the MoO3 with different loading amounts (1%, 2.5%, 5%, 10%) are basically the same as those of the molybdenum trioxide-supported reduced graphene oxide solid catalysts obtained in Example 1.

[0033] 2. Crystal structure of the molybdenum trioxide-supported reduced graphene oxide solid catalyst The reduced graphene oxide (rGO) prepared in Example 1 and the reduced graphene oxide catalyst supported on molybdenum trioxide (7.5% MoO3 / rGO) were used as test samples, with MoO3 as a control. X-ray diffraction (XRD) was used to study the microstructure of all catalysts. The instrument was a RIGAKUUltima IV diffractometer (Rigaku, Japan) with a scan step of 0.02°, CuKα as the source, a scan range of 5-70°, and a scan rate of 10° / min. -1 The obtained X-ray diffraction pattern is as follows Figure 2 As shown.

[0034] from Figure 2The X-ray diffraction patterns clearly show a large diffraction peak at 20°-26° for both samples, corresponding to the (002) crystal plane of graphene. This indicates that the crystal structure of the reduced graphene oxide was not destroyed after the introduction of MoO3 species. Furthermore, the presence of MoO3 species was observed in the X-ray diffraction patterns. The 7.5% MoO3 / rGO sample showed five diffraction peaks at 12.6°, 23.8°, 26.1°, 34.8°, and 39.2°, consistent with the peak positions of the MoO3 sample, indicating that the metallic MoO3 was highly dispersed on the rGO surface. This demonstrates that the molybdenum trioxide-supported reduced graphene oxide synthesized in this experiment is a solid catalyst with good metal dispersion.

[0035] Furthermore, it should be noted that the microstructure of the reduced graphene oxide solid catalysts supported on molybdenum trioxide synthesized at different calcination temperatures (150, 200, 300, 350) and the reduced graphene oxide solid catalysts supported on molybdenum trioxide with different MoO3 loadings (1%, 2.5%, 5%, 10%) are basically the same as those obtained in Example 1.

[0036] 3. Surface structure of the molybdenum trioxide-supported reduced graphene oxide solid catalyst Using the reduced graphene oxide (rGO) prepared in Example 1 and the reduced graphene oxide catalyst supported on molybdenum trioxide (7.5% MoO3 / rGO) as test samples, the specific surface area and pore structure of the catalyst samples were characterized by N2 physical adsorption-desorption using a Micromeritics ASAP2020M instrument (Micron Instruments, Inc., USA). The samples were pretreated with liquid nitrogen at -196℃ and degassed at 200℃ for 10 h. The specific surface area and pore size distribution of the samples were calculated according to the Brunauer-Emmett-Teller (BET) equation and the Barrett-Joyner-Halenda (BJH) model. The results are as follows: Figure 3 As shown.

[0037] Depend on Figure 3It can be seen that the nitrogen adsorption-desorption isotherms of both samples conform to Type IV characteristics, and a clear H3-type hysteresis loop appears in the range where the relative pressure P / P0 is greater than 0.4. This characteristic indicates that both rGO and 7.5%MoO3 / rGO have mesoporous pores as the main pore type, and their channels are mainly composed of slit-like pores formed by the stacking of rGO sheets and interparticle fissures. Compared with the pure rGO sample, 7.5%MoO3 / rGO shows a significant advantage in nitrogen adsorption capacity across the entire relative pressure range. In the low-to-medium pressure stage where P / P0 < 0.8, the increase in adsorption volume of the composite material directly reflects its significantly increased specific surface area compared to pure rGO; while when P / P0 > 0.8, nitrogen undergoes capillary condensation in the channels, and the sharp increase in adsorption capacity further confirms that the total pore volume of 7.5%MoO3 / rGO is significantly improved. The above-mentioned optimization effect of pore structure is mainly due to the loading effect of MoO3 nanoparticles between rGO sheets. MoO3 particles can act as "spacer support units" between the layers, effectively preventing the aggregation and recombination of rGO layers, thereby forming a looser and more interconnected network of channels.

[0038] Experimental Example 2: Synthetic Biodiesel 1. The reduced graphene oxide solid catalyst supported on molybdenum trioxide prepared in Examples 1-11, the reduced graphene oxide catalyst prepared in Example 1, and the 7.5% MoO3 / CNT catalyst prepared in Comparative Example 1 were used to catalyze the transesterification reaction of waste soybean oil to synthesize biodiesel. The specific methods are as follows: Weigh out 3g of waste soybean oil and 1.64g of methanol according to a molar ratio of waste soybean oil to methanol of 1:15. Then weigh out 0.06g of catalyst and add them to a 25mL hydrothermal reactor. After sealing, place the reactor in a 140℃ oil bath and stir for 12 hours. Centrifuge at 10000rpm for 8 minutes to obtain three phases: a mixed product phase, a glycerol phase, and a solid catalyst phase. The mixed product phase was analyzed using an Agilent-7890B gas chromatograph (Agilent Technologies, Inc.) with a flame ionization detector (FID) and an FFAP capillary column (30m × 0.32mm × 0.50μm). The waste soybean oil conversion rate (X) was calculated according to the following formula. WCSO ) and biodiesel selective (S Biodiesel The calculation results are shown in Table 1. The formulas for calculating the waste soybean oil conversion rate and biodiesel selectivity are as follows: The calculation formula is as follows: (1) (2) in and This refers to the initial and final molar amounts of WCSO in the reaction.n MP , n MS , n MO , n ML ,n GLAME and n Other It represents the molar amounts of methyl palmitate, methyl stearate, methyl oleate, methyl linoleate, methyl linolenate, and other products.

[0039] Table 1 Conversion Rate and Selectivity Results

[0040] As shown in Table 1, in Examples 4, 5, 1, 6, and 7, the catalytic activity of the molybdenum trioxide-loaded reduced graphene oxide solid catalyst initially increased slightly and then remained constant with minimal change as the calcination temperature of the support increased. The maximum conversion rate of waste soybean oil reached 90.13% at a calcination temperature of 250°C. Subsequently, the loading of MoO3 was investigated. In Examples 8, 9, 10, 1, and 11, the catalytic activity of the molybdenum trioxide-loaded reduced graphene oxide solid catalyst continued to increase with the increase of MoO3 loading. However, after the loading reached 7.5%, further increases in MoO3 content resulted in a stable catalytic activity. Therefore, a comparative analysis was conducted between the 7.5% MoO3-loaded molybdenum trioxide-loaded reduced graphene oxide solid catalyst and reduced graphene oxide. The molybdenum trioxide-loaded reduced graphene oxide solid catalyst showed a catalytic activity nearly 31 times that of reduced graphene oxide, indicating that the introduction of metallic MoO3 can significantly improve the performance of the catalyst in catalyzing esterification reactions. Meanwhile, by comparing the reduced graphene oxide solid catalyst supported on molybdenum trioxide with the 7.5% MoO3 / CNT solid catalyst in Comparative Example 1, it can be found that the catalytic activity of metal MoO3 supported on CNT is lower than that supported on rGO. This indicates that MoO3 can better exhibit its metal activity on the reduced graphene oxide prepared in this invention.

[0041] The above experimental results show that the molybdenum trioxide-supported reduced graphene oxide solid catalyst prepared in this invention significantly improves the conversion rate of waste soybean oil transesterification to biodiesel, especially the 7.5% MoO3 / rGO solid catalyst. Furthermore, the selectivity of this series of catalysts for catalyzing waste soybean oil transesterification to biodiesel is all above 99.9%. Since 99.9% of the reaction products are the target products, and the target products and by-products exhibit stratification, this further indicates that the subsequent separation process of the target products is simple and more conducive to industrial promotion and application.

[0042] 2. Stability testing of biodiesel synthesis from waste soybean oil transesterification catalyzed by a molybdenum trioxide-supported reduced graphene oxide solid catalyst. Taking the 7.5% MoO3 / rGO solid catalyst obtained in Example 1 as an example of catalyzing the transesterification reaction of waste soybean oil to synthesize biodiesel, the stability of the reduced graphene oxide solid catalyst supported on metal MoO3 in catalyzing the transesterification reaction of waste soybean oil to synthesize biodiesel was tested. During the test, the reduced graphene oxide solid catalyst with a loading of 7.5 wt% MoO3 was simply washed with n-hexane and anhydrous ethanol and reused five times. The specific operation method for each reaction is as follows: 3g of waste soybean oil and 1.64g of methanol were weighed according to a molar ratio of waste soybean oil to methanol of 1:15. Then, 0.06g of catalyst was added to a 25mL hydrothermal reactor. After sealing, the reactor was placed in a 140℃ oil bath and stirred for 12 hours. Centrifugation was then performed at 10000 rpm for 8 minutes, yielding three phases: a mixed product phase, a glycerol phase, and a solid catalyst phase. The mixed product phase was analyzed using an Agilent-7890B gas chromatograph (Agilent Technologies, Inc.) with a flame ionization detector (FID) and an FFAP capillary column (30m × 0.32mm × 0.50μm). The waste soybean oil conversion rate (X) was calculated according to the following formula. WCSO ) and biodiesel selective (S Biodiesel The results are shown in Table 2.

[0043] Table 2 Cyclic stability results

[0044] As can be seen from the data in Table 2, in the reaction of waste soybean oil transesterification to biodiesel catalyzed by the reduced graphene oxide solid catalyst with a loading of 7.5 wt% MoO3 obtained in Example 1, after simple washing with n-hexane and anhydrous ethanol, the conversion rate of waste soybean oil decreased by only 10.17% after five repeated reactions. This is completely acceptable in macromolecular catalytic reactions, indicating that the reduced graphene oxide solid catalyst with molybdenum trioxide loaded by the method of the present invention has good catalytic stability and a wide range of applications.

[0045] Finally, it should be emphasized that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a molybdenum trioxide-supported reduced graphene oxide catalyst, characterized in that, Includes the following steps: Step 1: Oxidation treatment is carried out using graphite powder as carbon source, concentrated sulfuric acid as intercalating agent, and potassium permanganate as oxidant. After the reaction is completed, hydrogen peroxide is added to continue the reaction. The resulting graphene oxide product is placed in a tube furnace and calcined under nitrogen atmosphere to obtain reduced graphene oxide. Step 2: Using ammonium molybdate as the molybdenum source, molybdenum trioxide is obtained by calcination in a muffle furnace. Subsequently, the obtained molybdenum trioxide is combined with reduced graphene oxide by co-precipitation, followed by ultrasonic dispersion, stirring and mixing and drying to obtain a molybdenum trioxide-supported reduced graphene oxide catalyst.

2. The method for preparing a molybdenum trioxide-supported reduced graphene oxide catalyst according to claim 1, characterized in that, The loading of molybdenum in the reduced graphene oxide support is 1% to 10%, preferably 3% to 8%, and more preferably 7.5%.

3. The method for preparing a molybdenum trioxide-supported reduced graphene oxide catalyst according to claim 1, characterized in that, In step one, the mass-to-volume ratio of graphite powder, concentrated sulfuric acid, potassium permanganate, and hydrogen peroxide is 1g:18-23mL:3-10g:1-4mL, preferably 1g:20mL:4g:2mL; the concentration of hydrogen peroxide is 30%.

4. The method for preparing a molybdenum trioxide-supported reduced graphene oxide catalyst according to claim 1, characterized in that, In step one, graphite is first mixed with concentrated sulfuric acid for 0.2-0.8 hours, then potassium permanganate is added and stirred to carry out a three-stage gradient temperature reaction. After the reaction is completed, hydrogen peroxide is added after the temperature drops to 50°C and mixed evenly. After standing for 12 hours, it is washed until neutral and then dried at 60°C for 12 hours to obtain graphene oxide product.

5. The method for preparing a molybdenum trioxide-supported reduced graphene oxide catalyst according to claim 4, characterized in that, The three-stage gradient temperature reaction is as follows: the first stage is stirred at an ice bath temperature of -5℃ to -15℃ for 0.5-1.5h, the second stage is stirred at 30-40℃ for 1.5-3.5h, and the third stage is stirred at 60-80℃ for 0.2-0.8h; preferably, the first stage is stirred at an ice bath temperature of 0℃ for 1h, the second stage is stirred at 35℃ for 2h, and the third stage is stirred at 70℃ for 0.5h.

6. The method for preparing a molybdenum trioxide-supported reduced graphene oxide catalyst according to claim 1, characterized in that, In step one, the calcination temperature is 150-500℃ and the calcination time is 3-6h; preferably, the calcination temperature is 200-400℃ and the calcination time is 4.5-5.5h; more preferably, the calcination temperature is 250℃ and the calcination time is 5h.

7. The method for preparing a molybdenum trioxide-supported reduced graphene oxide catalyst according to claim 1, characterized in that, In step two, the ultrasonic time is 1-6 hours, preferably 3 hours; the stirring time is 1-4 hours.

8. A method for preparing a molybdenum trioxide-supported reduced graphene oxide catalyst according to any one of claims 1-7, characterized in that, The specific method for step one is as follows: Graphite powder was added to a 500 mL three-necked flask, followed by concentrated H2SO4. The mixture was cooled to 0 °C using an ice bath and stirred for 30 min. KMnO4 powder was then slowly added and stirred for 1 h. The reaction mixture was then heated to 35 °C and stirred for 2 h. Ultrapure water was then slowly added, and the reaction mixture was stirred at 70 °C for 30 min. The mixture was then cooled to 50 °C, and 30% H2O2 was added until no gas was produced. The mixture was allowed to stand for 12 h, washed until neutral, and sonicated. The reaction product was dried at 60 °C for 24 h. The dried product was then placed in a tube furnace and calcined at 250 °C for 5 h in a nitrogen atmosphere to obtain reduced graphene oxide, denoted as rGO.

9. A reduced graphene oxide catalyst supported on molybdenum trioxide, prepared by the method according to any one of claims 1-8.

10. The application of a molybdenum trioxide-supported reduced graphene oxide catalyst prepared by the preparation method according to any one of claims 1-8, or the molybdenum trioxide-supported reduced graphene oxide catalyst according to claim 9, in the catalytic transesterification reaction of waste soybean oil to synthesize biodiesel, characterized in that, In the synthesis of biodiesel through catalytic transesterification of waste soybean oil, waste soybean oil and methanol are used as raw materials. Reduced graphene oxide loaded with molybdenum trioxide is added, and the mixture is placed in a high-pressure sealed container and stirred at 80–160°C for 6–16 hours. After the reaction is completed, the mixture is centrifuged and separated into layers to obtain biodiesel.

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