A neodymium-praseodymium-doped magnesium aluminum oxide catalyst, its preparation method and its application
By loading neodymium-praseodymium-doped magnesium aluminum oxide catalysts onto a modified γ-Al2O3 support, the problems of poor reaction selectivity and insufficient catalytic activity in the synthesis of methyl acetophenone were solved, achieving efficient, green, and low-cost synthesis of methyl acetophenone.
Patent Information
- Application Number
- CN202610636106.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-05-10
- Publication Date
- 2026-06-30
AI Technical Summary
Existing methyl acetophenone synthesis processes suffer from problems such as poor reaction selectivity, numerous byproducts, low raw material conversion rate, high energy consumption, insufficient catalytic activity, poor stability, and complex post-processing.
A neodymium-praseodymium-doped magnesium aluminum oxide catalyst was used. This catalyst was prepared by impregnation of rare earth oxides on a modified support. The support was modified γ-Al2O3. The acid-base properties were adjusted to improve the dispersibility of the rare earth active components. The catalyst was used for the synthesis reaction of methylbenzoic acid and acetic acid.
This method enables the efficient and green synthesis of methyl acetophenone, resulting in high product purity, few byproducts, simple equipment, suitability for industrial production, reduced production costs, and improved catalyst stability and selectivity.
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Figure CN122298391A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of industrial catalyst preparation technology, and in particular to a neodymium-praseodymium-doped magnesium aluminum oxide catalyst, its preparation method, and its application. Background Technology
[0002] Methyl acetophenone is a class of aromatic organic compounds containing a benzene ring, a methyl group, and an acetyl group. Based on the different substitution positions of the methyl group on the benzene ring, it mainly includes three isomers: 2-methylacetophenone (o-methylacetophenone), 3-methylacetophenone (m-methylacetophenone), and 4-methylacetophenone (p-methylacetophenone). These are important aromatic derivatives widely used in the fine chemical industry. Their basic physicochemical properties and applications are as follows: 1. Basic physical and chemical properties All three isomers of methyl acetophenone are colorless to pale yellow transparent liquids or low-melting-point solids, naturally possessing a sweet aroma reminiscent of hawthorn and almond. They exhibit significant hydrophobicity, are poorly soluble in water, but are well miscible with common organic solvents such as ethanol, ether, and esters. Among them, p-methyl acetophenone has the largest industrial production capacity and the widest market application, with a melting point of 28℃ and a boiling point of 226℃. At room temperature, it exists as a flaky solid or liquid, with a rich and mellow aroma. o-methyl acetophenone and m-methyl acetophenone are both liquids at room temperature, with slightly lower boiling points than p-methyl acetophenone. Their aromas lean towards a strong, sharp, spicy style, exhibiting distinct differences in aroma characteristics.
[0003] 2. Main uses The fragrance and flavor industry can use it to formulate daily chemical floral fragrances such as acacia, lilac, and hawthorn, and it can also be used to formulate edible fragrances such as cherry and nut flavors. It is commonly added to soaps, detergents, cosmetics and fragrance products, and is a key raw material in the daily chemical fragrance system.
[0004] Organic synthesis intermediates are core intermediates in the synthesis of pharmaceuticals, pesticides, photosensitive materials, and dyes. They are commonly used in industry to prepare adrenaline-like pharmaceutical compounds, selective herbicides, and fine dye auxiliaries, etc., and their synthesis industry chain has outstanding value.
[0005] Other industrial applications include use as a plasticizer for functional plastics, a high-boiling-point organic solvent, and as a standard reagent for chromatographic analysis, used for organic detection and qualitative and quantitative analysis of substances.
[0006] Currently, traditional synthetic processes for methyl acetophenone (MAP) generally suffer from drawbacks such as poor reaction selectivity, numerous byproducts, low feed conversion rates, harsh reaction conditions, high energy consumption, and significant environmental impact. Furthermore, existing catalytic systems often exhibit insufficient activity, poor stability, equipment corrosion, and complex post-processing, severely restricting product purity and industrial production cost control. Therefore, developing novel, green, efficient, highly selective, and low-cost synthetic processes is of significant practical importance, and the screening and optimization of catalyst systems are crucial for improving synthetic processes and enhancing production efficiency. Summary of the Invention
[0007] This invention addresses the problems of poor reaction selectivity, numerous byproducts, low raw material conversion rate, and high energy consumption in the existing methyl acetophenone synthesis process, as well as the insufficient activity, poor stability, and complex post-processing of existing catalytic systems. It provides a neodymium-praseodymium-doped magnesium aluminum oxide catalyst, along with a method for preparing the catalyst and its application in the synthesis of methyl acetophenone, to achieve green, efficient, and continuous industrial production of methyl acetophenone.
[0008] To achieve the above objectives, the technical solution of the present invention is implemented as follows: This invention provides a neodymium-praseodymium-doped magnesium aluminum oxide catalyst, characterized in that the catalyst is a composite oxide of magnesium, aluminum, neodymium, and praseodymium, composed of rare earth oxides. and Loaded on Modified The structure on the carrier is represented as / ,in, The mass fraction of the carrier is 70%–80%. The mass fraction is 3.3% to 20%. The mass fraction is 4% to 25%. In the carrier The mass fraction is 1% to 5%.
[0009] Preferably, It ranges from 4% to 20%. It ranges from 4% to 20%. The carrier content is 76%–80%.
[0010] This invention provides a method for preparing a neodymium-praseodymium-doped magnesium aluminum oxide catalyst, comprising the following steps: using neodymium nitrate... and praseodymium nitrate As a raw material for rare earth active components, it is loaded onto [material] using an impregnation method. After drying and calcination on the catalyst support, the resulting product is... Composite oxide catalyst.
[0011] Furthermore, the catalyst support It is through alkaline oxides Modified ,pass Modification can adjust the acid-base properties of the support, improve the dispersibility of rare earth active components, and thus enhance the catalytic performance and stability of the catalyst. (Included in the instruction manual) Furthermore, the aforementioned The catalyst support is prepared by: using magnesium nitrate With aluminum nitrate Prepare a mixed solution, add NaOH solution dropwise to the mixed solution to initiate a precipitation reaction. After precipitation is complete, wash the precipitate repeatedly until neutral, dry it, and then calcine it to obtain... Carrier.
[0012] The present invention also provides an application of the above-mentioned neodymium-praseodymium-doped magnesium aluminum oxide catalyst, characterized in that the catalyst is used in the production of methylbenzoic acid (… Using acetic acid as a raw material, methyl acetophenone (Methyl acetophenone) was synthesized by catalysis. ).
[0013] The beneficial effects of this invention are as follows: 1. The neodymium-praseodymium-doped magnesium aluminum oxide catalyst provided by this invention uses neodymium-praseodymium mixed rare earth oxides as the active component, supported on... Modified The preparation process is simple and convenient, requiring no complex equipment, making it suitable for large-scale industrial production. Meanwhile, the catalyst has a high specific surface area and uniformly dispersed active centers, exhibiting high catalytic activity, good selectivity, and strong stability, which can effectively reduce the formation of by-products and improve the purity of methyl acetophenone.
[0014] 2. The catalyst of this invention is specifically adapted to the process route for synthesizing methyl acetophenone using acetic acid and methyl benzoic acid as raw materials, and successfully realizes the efficient synthesis of methyl acetophenone under this raw material system. The raw materials (methyl benzoic acid and acetic acid) used in this process route are widely available, readily available and inexpensive. Methyl benzoic acid can be obtained from xylene (a high-yield product of petrochemical enterprises) through existing mature processes, or it can be prepared by the carbonylation reaction of toluene. Acetic acid can be obtained in large quantities and cheaply through the carbonylation reaction of methanol. The supply of raw materials is stable and conducive to industrial promotion.
[0015] 3. This synthesis process involves a reduction in the number of carbon atoms, with water and carbon dioxide as byproducts. No harmful pollutants are generated, making it a green and environmentally friendly process. At the same time, the reaction device has a simple process flow, stable product quality, and low equipment investment costs. It is suitable for small and medium-scale continuous production, which can effectively reduce the industrial production cost of methyl acetophenone and enhance the product's market competitiveness. Attached Figure Description
[0016] Figure 1 is a gas chromatogram of methyl acetophenone prepared in Example 1 of the present invention.
[0017] Figure 2 is a gas chromatogram of methyl acetophenone prepared in Comparative Example 1 of the present invention. Detailed Implementation
[0018] The principles and features of the present invention are described below. The embodiments given are only for explaining the present invention and are not intended to limit the scope of the present invention.
[0019] Example 1 The neodymium-praseodymium-doped magnesium aluminum oxide catalyst of this embodiment was prepared according to the following steps: S1. Preparation of catalyst support γ-Al₂O₃ modified with basic oxide MgO was prepared by precipitation method. 2.6 g of magnesium nitrate hydrate (Mg(NO₃)₂·6H₂O) and 149 g of aluminum nitrate hydrate (AL(NO₃)₃·9H₂O) were dissolved in 100 ml of deionized water. While stirring, 10% NaOH solution was added dropwise until the pH reached 8. The resulting precipitate was filtered and washed with deionized water to remove Na₂O. + Ions. After drying at 110℃ and calcining at 500℃ for 4 hours, approximately 41 g of a composite support containing 1 wt% MgO and 99 wt% Al2O3 was obtained, denoted as 1%MgO-Al2O3, with a measured specific surface area of 200 m². 2 / g, water absorption rate 100%.
[0020] S2, Preparation of catalyst 5g of Nd(NO3)3·6H2O was dissolved in 10ml of deionized water to obtain solution one, and 25g of Pr(NO3)3·6H2O was dissolved in 50ml of deionized water to obtain solution two. Solutions one and two were mixed, and 40g of the above-mentioned substance with a specific surface area of approximately 200m² was impregnated. 2 / g of 1% MgO-Al2O3 support was impregnated for 12 hours. Then it was dried in an oven at 110℃. After drying, it was calcined in a muffle furnace at 590℃ for 5 hours to obtain 51g of Nd2O3-Pr6O3-doped magnesium aluminum oxide catalyst. 11 / MgO-Al2O3, wherein Nd2O3 is 4wt% and Pr6O 11 The content is 20 wt%, and 1 wt% MgO-Al2O3 is 76 wt%.
[0021] Characterization by X-ray diffraction (XRD) and Beta-Earth Expansion Test (BET) confirmed that the catalyst possesses a high specific surface area, ranging from 185 to 210 m². 2 The catalyst contains uniformly dispersed rare earth active centers, which can effectively enhance the activity and selectivity of the catalytic reaction.
[0022] S3, Application of catalysts 50g of the above catalyst was loaded into a single-tube reactor, and inert coarse quartz sand was filled at both ends of the reactor to fix the catalyst bed; the reactor temperature was precisely controlled by a temperature controller.
[0023] The raw materials are mixed according to a molar ratio of acetic acid to methyl benzoic acid of 1.5, heated to 70°C to completely dissolve the methyl benzoic acid and form a homogeneous mixed raw material liquid. The mixed raw material liquid is quantitatively delivered by a metering pump, and then preheated to about 350°C by a preheater before being introduced into the reactor for catalytic reaction.
[0024] The reaction process conditions are: feed liquid mass hourly space velocity 0.5 h⁻¹, reaction temperature 350 °C, and reaction pressure 0.12 MPa.
[0025] After the reaction was completed, the reaction liquid was collected and purified by two-step distillation. The first step was atmospheric distillation. The first distillation column was operated at atmospheric pressure, with the top temperature controlled at about 56 °C and the bottom temperature at about 100 °C. The byproduct acetone was separated at the top of the column. The bottom material after the acetone was removed was sent to the second distillation column for vacuum distillation, with the vacuum level controlled at about 90 kPa, the top temperature at about 140 °C, and the bottom temperature at about 150 °C. The target product methyl acetophenone was obtained by distillation.
[0026] The product was quantitatively detected using a GC9890-ES gas chromatograph paired with a BP-1 column. The gas chromatogram is shown below. Figure 1 As shown in Table 1, the test results indicate that this process can stably prepare methyl acetophenone with a purity of up to 99.94%. Detailed product properties and reaction data are shown in Table 1.
[0027] Example 2 The preparation and application steps of the neodymium-praseodymium-doped magnesium aluminum oxide catalyst in this embodiment are basically the same as those in Example 1, except that the liquid hourly space velocity of the raw material is 0.2 h⁻¹. -1 The results are shown in Table 1.
[0028] Example 3 The preparation and application steps of the neodymium-praseodymium-doped magnesium aluminum oxide catalyst in this embodiment are basically the same as those in Example 1, except that the liquid hourly space velocity (LHSV) of the raw material is 3.0 h⁻¹. -1 The results are shown in Table 1.
[0029] Example 4 The preparation and application steps of the neodymium-praseodymium-doped magnesium aluminum oxide catalyst in this embodiment are basically the same as those in Example 1, and the reaction conditions are the same as in Example 1. The catalyst was continuously used in the reactor for 3600 hours, and the cycle life of the catalyst was observed. The results are shown in Table 1.
[0030] Example 5 The preparation and application of the neodymium-praseodymium-doped magnesium aluminum oxide catalyst in this embodiment are carried out according to the following steps: S1. Preparation of catalyst support γ-Al₂O₃ modified with basic oxide MgO was prepared by precipitation method. 13g of magnesium nitrate hydrate (Mg(NO₃)₂·6H₂O) and 150g of aluminum nitrate hydrate (Al(NO₃)₃·9H₂O) were dissolved in 100ml of deionized water. While stirring, 10% NaOH solution was added dropwise until the pH reached 8. The resulting precipitate was filtered and washed with deionized water to remove Na₂O. + Ions. After drying at 110℃ and calcining at 500℃ for 4 hours, approximately 43.5 g of a support containing 5% MgO and 95% Al2O3 was obtained, denoted as 5%MgO-Al2O3, with a measured specific surface area of 180 m². 2 / g, water absorption rate 95%.
[0031] S2, Preparation of catalyst Dissolve 25g of Nd(NO3)3·6H2O in 50ml of deionized water, and dissolve 5g of Pr(NO3)3·6H2O in 50ml of deionized water. After mixing, impregnate 40g of the above-mentioned material with a specific surface area of approximately 180m². 2 The catalyst was impregnated with a 5% MgO-Al2O3 support for 12 hours. It was then dried in an oven at 110℃ and finally calcined in a muffle furnace at 590℃ for 5 hours. Approximately 51 g of catalyst was obtained, with an oxide weight composition of 20% Nd2O3 and 10% Pr6O3. 11 4%, 5% MgO-Al2O3 76%.
[0032] S3. The application of the catalyst is the same as in Example 1. The results are shown in Table 1.
[0033] Example 6 The preparation and application steps of the neodymium-praseodymium-doped magnesium aluminum oxide catalyst in this embodiment are basically the same as those in Example 1. The difference is that water is added to the mixture of raw materials acetic acid and methyl benzoic acid in the catalytic synthesis of methyl acetophenone, wherein the weight of the added water is 20% of the weight of methyl benzoic acid. The results are shown in Table 1.
[0034] Example 7 The preparation and application steps of the neodymium-praseodymium-doped magnesium aluminum oxide catalyst in this embodiment are basically the same as those in Example 1, and the reaction conditions are the same as those in Example 6. The catalyst was continuously used in the reactor for 3600 hours, and the cycle life of the catalyst was observed. The results are shown in Table 1.
[0035] Example 8 The preparation and application steps of the Nd2O3-doped magnesium aluminum oxide catalyst in this embodiment are basically the same as those in Example 1. The difference is that the weight composition of the prepared oxide is Nd2O3 5% and Pr6O3 5%.11 25%, 1% MgO-Al2O3 70%. The results are shown in Table 1.
[0036] Example 9 The preparation and application steps of the Nd2O3-doped magnesium aluminum oxide catalyst in this embodiment are basically the same as those in Example 1. The difference is that the weight composition of the prepared oxide is Nd2O3 3.3% and Pr6O3 3.3%. 11 16.7%, 1%MgO-Al2O3 80%. The results are shown in Table 1.
[0037] Example 10 The preparation and application steps of the neodymium-praseodymium-doped magnesium aluminum oxide catalyst in this embodiment are basically the same as those in Example 1. The difference is that the reaction conditions in step S3 are: liquid hourly space velocity of raw material 0.5 h⁻¹. -1 The reaction temperature was 450℃ and the reaction pressure was 0.1MPa. The results are shown in Table 1.
[0038] Example 11 The preparation and application steps of the neodymium-praseodymium-doped magnesium aluminum oxide catalyst in this embodiment are basically the same as those in Example 1. The difference is that the reaction conditions in step S3 are: liquid hourly space velocity of the raw material is 0.2 h⁻¹. -1 The reaction temperature was 450℃ and the reaction pressure was 0.1MPa. The results are shown in Table 1.
[0039] Example 12 The preparation and application steps of the neodymium-praseodymium-doped magnesium aluminum oxide catalyst in this embodiment are basically the same as those in Example 1, except that the reaction conditions in step S3 are: liquid hourly space velocity (LHSV) of the raw material is 3.0 h⁻¹. -1 The reaction temperature was 450℃ and the reaction pressure was 0.1MPa. The results are shown in Table 1.
[0040] Example 13 The preparation and application steps of the neodymium-praseodymium-doped magnesium aluminum oxide catalyst in this embodiment are basically the same as those in Example 1. The difference is that the reaction conditions in step S3 are: liquid hourly space velocity of raw material 0.5 h⁻¹. -1 The reaction temperature was 450℃ and the reaction pressure was 1.0MPa. The results are shown in Table 1.
[0041] Example 14 The preparation and application steps of the neodymium-praseodymium-doped magnesium aluminum oxide catalyst in this embodiment are basically the same as those in Example 1. The difference is that the reaction conditions in step S3 are: liquid hourly space velocity of the raw material is 0.2 h⁻¹. -1 The reaction temperature was 450℃ and the reaction pressure was 1.0MPa. The results are shown in Table 1.
[0042] Example 15 The preparation and application steps of the neodymium-praseodymium-doped magnesium aluminum oxide catalyst in this embodiment are basically the same as those in Example 1. The difference is that the reaction conditions in step S3 are: liquid hourly space velocity of the raw material is 3 h⁻¹. -1 The reaction temperature was 450℃ and the reaction pressure was 1.0MPa. The results are shown in Table 1.
[0043] Comparative Example 1 The catalyst preparation method of this comparative example is the same as steps S1 and S2 of Example 1, except that the catalyst support is replaced with γ-Al2O3 without MgO modification. The application method of the catalyst is also the same as step S3 of Example 1. The results are shown in Table 1. Chromatographic analysis was performed on the methyl acetophenone product obtained in this comparative example, and the chromatogram is shown in Table 1. Figure 2 It can be seen that the purity of the obtained methyl acetophenone is 99.73%.
[0044] Comparative Example 2 The catalyst in this comparative example was prepared using the same steps S1 and S2 as in Example 1, except that the catalyst support 1% MgO-Al2O3 was replaced with MgO. The application method of the catalyst was also the same as step S3 in Example 1. The results are shown in Table 1.
[0045] Comparative Example 3 The catalyst in this comparative example was prepared using the same steps S1 and S2 as in Example 1, except that Pr(NO3)3·6H2O was not used in the catalyst preparation process; that is, the catalyst was a neodymium-doped magnesium-aluminum composite oxide. The application method of the catalyst was also the same as step S3 in Example 1. The results are shown in Table 1.
[0046] Comparative Example 4 The catalyst in this comparative example was prepared using the same steps S1 and S2 as in Example 1, except that Nd(NO3)3·6H2O was not used in the catalyst preparation process; that is, the catalyst was a praseodymium-doped magnesium-aluminum composite oxide. The application method of the catalyst was also the same as step S3 in Example 1. The results are shown in Table 1.
[0047] Comparative Example 5 The catalyst used in this comparative example was a commercially available copper-zinc-aluminum TH309 catalyst, and the application method was the same as step S3 in Example 1. The results are shown in Table 1.
[0048] Comparative Example 6 The catalyst used in this comparative example was the commercially available existing molecular sieve catalyst H-ZSM-5, and the application method of the catalyst was the same as step S3 in Example 1. The results are shown in Table 1.
[0049] The gas chromatograms of the methyl acetophenone products obtained in Examples 2-9 above show the same pattern as... Figure 1The purity of the obtained methyl acetophenone was all above 99.9%, which will not be elaborated here. The purity of the methyl acetophenone obtained in Comparative Examples 2-4 was all below 99.9%, which will not be elaborated here.
[0050] The yield data of the product methyl acetophenone in the above examples and comparative examples are shown in Table 1, wherein the yield of methyl acetophenone = conversion of methyl benzoic acid * selectivity of methyl acetophenone.
[0051] Table 1
[0052] As shown in Table 1, the Nd2O3-Pr6O3 neodymium-praseodymium-doped magnesium aluminum oxide catalyst prepared by the process of this invention... 11 / MgO-Al2O3 exhibits excellent specific catalytic performance in the synthesis of methyl acetophenone from acetic acid and methylbenzoic acid. The product after the catalytic reaction, after conventional distillation, yields methyl acetophenone with a purity of over 99.9%, and the yield is consistently above 70%. This opens a new route for the synthesis of methyl acetophenone, and the catalyst preparation method is simple and suitable for industrial production. A comparison of Examples 1, 4, 6, and 7 shows that the catalyst prepared in this invention can be used to synthesize methyl acetophenone without the addition of water during the reaction, but its recyclability is poor. Adding water during the reaction significantly improves the catalyst's lifespan and ensures the quality of the synthesized product. Comparative Examples 1-4 characterize the synergistic effect between the components in the catalyst prepared in this invention, i.e., the absence of Nd2O3 and Pr6O3. 11 When composite oxides formed from any of the elements selected from MgO and Al2O3 are used for the catalytic synthesis of methyl acetophenone, the results are not ideal. The extremely low yield of methyl acetophenone obtained in Comparative Examples 5-6 indicates that the catalytic synthesis has extremely low reactivity, characterizing the reaction specificity of the catalyst prepared in this invention. The specificity of its effect is unmatched by conventional catalysts in the prior art.
[0053] The reaction mechanism is as follows: methylbenzoic acid ( The molecule first removes the carboxyl group. ), to generate methylphenyl ( -), the removed carboxyl group is converted into Excretion; H atoms produced during decarboxylation react with acetic acid ( ) hydroxyl group in the molecule The acetic acid molecules combine to form water and are expelled; the acetic acid molecule that loses its hydroxyl group is converted into an acetyl group. ), acetyl ( ) and methylphenyl ( A coupling (condensation) reaction occurs, ultimately producing methyl acetophenone. Furthermore, there may also be a pathway where acetic acid undergoes decarboxylation first, followed by a coupling reaction with methylbenzoic acid. The core function of the neodymium-praseodymium-doped magnesium aluminum oxide catalyst provided by this invention is to lower the activation energy of the above reactions, thereby facilitating the synthesis of methyl acetophenone from methylbenzoic acid and acetic acid, and improving the selectivity and conversion rate of the reaction.
Claims
1. A neodymium-praseodymium-doped magnesium aluminum oxide catalyst, characterized in that, The catalyst is a composite oxide of magnesium, aluminum, neodymium, and praseodymium, composed of rare earth oxides. and Loaded on Modified The structure on the carrier is represented as / ,in, The mass fraction of the carrier is 70%–80%. The mass fraction is 3.3% to 20%. The mass fraction is 4% to 25%. In the carrier The mass fraction is 1% to 5%.
2. The neodymium-praseodymium-doped magnesium aluminum oxide catalyst as described in claim 1, characterized in that, It ranges from 4% to 20%. It ranges from 4% to 20%. The carrier content is 76%–80%.
3. A method for preparing a neodymium-praseodymium-doped magnesium aluminum oxide catalyst as described in claim 1, characterized in that, With neodymium nitrate and praseodymium nitrate As a raw material for rare earth active components, it is loaded onto [material] using an impregnation method. After drying and calcination on the catalyst support, the resulting product is... Composite oxide catalyst.
4. The method for preparing a neodymium-praseodymium-doped magnesium aluminum oxide catalyst as described in claim 3, characterized in that, The catalyst support It is through alkaline oxides Modified .
5. The method for preparing a neodymium-praseodymium-doped magnesium aluminum oxide catalyst as described in claim 4, characterized in that, Magnesium nitrate With aluminum nitrate Prepare a mixed solution, add NaOH solution dropwise to the mixed solution to initiate a precipitation reaction. After precipitation is complete, wash the precipitate repeatedly until neutral, dry it, and then calcine it to obtain... Carrier.
6. An application of the neodymium-praseodymium-doped magnesium aluminum oxide catalyst as described in claim 1, characterized in that, This catalyst is used to catalyze the synthesis of methyl acetophenone from methylbenzoic acid and acetic acid.