A catalyst for preparing a binary fatty nitrile by direct aminolysis nitrilation of a binary carboxylic acid ester, a preparation method and application thereof

Abstract

The application provides a catalyst for preparing a binary fatty nitrile through direct aminolysis nitrilation of a dicarboxylic acid ester, a preparation method and application of the catalyst, the catalyst comprising a carrier full-silicon molecular sieve and a metal oxide active component loaded on the carrier. The application provides a molecular sieve supported metal oxide type solid acid catalyst with dispersed active sites and high space-time yield of binary fatty nitrile and mild reaction conditions, which is applied to catalyze the preparation of a binary fatty nitrile, has mild reaction conditions, reduces production energy consumption, improves the dispersity and utilization rate of the active sites of the catalyst, has high space-time yield of the binary fatty nitrile, and reduces the theoretical design size of a reactor.

Description

Technical Field

[0001] This invention belongs to the field of catalysis technology, and relates to a catalyst for the direct ammonolysis and nitrification of dicarboxylic acid esters to prepare dialiphatic nitrile, its preparation method, and its application. Background Technology

[0002] Nitriles are important raw materials and synthetic intermediates in fine chemicals, especially dialiphatic nitrs such as adiponitrile, glutaronitrile, succinic anhydride, azelaic anhydride, and sebacic anhydride. The dialiphatic amines obtained by hydrogenation of these compounds are key monomer raw materials for the synthesis of nylon and other polyurethane materials. Specifically, hexamethylenediamine can be used in the synthesis of nylon 6 and nylon 66, pentanediamine in the synthesis of nylon 54 and nylon 56, butylenediamine in the synthesis of nylon 46, azelaic anhydride in the synthesis of nylon 9T, and sebacic anhydride in the synthesis of nylon 1010.

[0003] The reported synthetic methods for the nitrification of diacids mainly involve the amination reaction of dicarboxylic acids. In addition, there are three mainstream synthetic methods for adiponitrile: adipic acid amination dehydration method, acrylonitrile electrolytic dimerization method, and butadiene hydrocyanation method. These methods have limitations in application and promotion due to the use of corrosive or highly toxic raw materials and high energy consumption. Therefore, a route based on the direct ammonolysis and nitrification of dimethyl adipate has recently been developed, which is green, safe, and has the potential for large-scale production.

[0004] Currently, various catalysts have been developed for the direct ammonolysis nitrification of dicarboxylic acid esters. CN114160120A discloses a solid acid catalyst with a polyionic liquid-supported heteropolyacid, which provides Lewis acid sites through the heteropolyacid anion and can be used for the ammonolysis nitrification of dimethyl glutarate / dimethyl adipate with ammonia in a batch reaction. For the continuous ammonolysis nitrification of dicarboxylic acid esters in fixed-bed / fluidized-bed reactors, there are few related literature and patent reports. Metal oxide solid acids (CN109912452A), metal-doped / acidified metal oxides (CN110511162A), and pyridine-based ionic liquid-functionalized silicon / aluminum oxide catalysts (CN114160120) are the three types of catalysts reported in the patents. All three catalysts can achieve high dinitrile selectivity (80-90%). However, due to the different particle sizes and densities of the different catalysts, it is difficult to evaluate the catalyst production capacity solely based on space velocity and dinitrile selectivity. The space-time yield (STY) of dionitrile is the dionitrile yield per unit mass / volume of catalyst per unit time. It can be used to compare different catalysts at the capacity level. However, the relevant data is not explicitly disclosed in the aforementioned patent.

[0005] Based on the literature published in the same period on the direct ammonolysis and nitrification of dimethyl adipate to prepare adiponitrile, the optimal production capacity and corresponding operating conditions of different catalysts can be summarized as shown in Table 1 below (Ding, GR, Wang, YF, Duan, GY, et al. Chemoselective nitrilation of dimethyl adipate with ammonia over carbonencapsulated WOx catalysts under continuous flow conditions. Catal. Sci. Technol., 2022, 12, 3982-3991. Xu, XF, Wang, YF, Guo, T., et al. Synthesis of adiponitrile from dimethyl adipate and ammonia in the vapor-phase over niobium oxide. Catal. Sci. Technol., 2022, 12, 3947-3956. He, LJ, Wang, YF, Guan, PX, et al. HZSM-5-Catalyzed vapor-phase conversion of dimethyl adipate to adiponitrile:The influence of the SiO2 / Al2O3 ratio onreactivity.ChemistrySelect,2023,8(12),e202300799.Ding,GR,Wang,YF,Duan,GY,et al.Adjustment of WO-Zr Boundaries Boosts Efficient Nitrilation ofDimethyl Adipate with Ammonia on WO x / ZrO2 Catalysts.ACS Appl.Mater.Interfaces,2023,15(2),3633-3643.Guo,T.,Yan,FY,Wang,YF,et al.Boosted nitrilation ofdimethyl adipate with NH3 to adiponitrile over bimetallic oxide:Synergetic effect between Nb and W. Chem. Eng. Sci., 2023, 281, 119121).

[0006] Table 1. Optimal adiponitrile production and reaction conditions of catalysts reported in the literature.

[0007]

[0008]

[0009] The increased space-time yield of binary aliphatic nitriles is of great significance for their industrial production. How to improve the utilization rate of catalyst active sites, maintain a large space-time yield, and reduce the theoretical design size of the reactor; at the same time, reduce the reaction temperature, reduce energy consumption, and reduce production costs are two urgent problems that need to be solved to determine whether the above methods can be industrialized. Summary of the Invention

[0010] To address the shortcomings of existing technologies, the present invention aims to provide a catalyst and its preparation method for the direct ammonolysis and nitrification of dicarboxylic acid esters to prepare dialiphatic nitriles. The present invention provides a molecular sieve-supported metal oxide solid acid catalyst with dispersed active sites, considerable space-time yield of dialiphatic nitriles, and mild reaction conditions. This catalyst has a weakly acidic surface on its all-silica support, which is unfavorable for carboxylic acid ester conversion and results in fewer side reactions generated by the support. Furthermore, it exhibits good hydrothermal stability, and its hydrophobic surface is beneficial for the dehydration reaction process. The pore structure of the molecular sieve support is tunable; by introducing metal oxides to adjust the location of active sites and their internal / external surfaces, the mass transfer efficiency of reactants at active sites can be enhanced, thereby increasing the reaction activity. By adjusting the interaction between the all-silica support with different surface acidities and the active sites, a supported, highly dispersed metal oxide catalyst with rich interfacial structures is obtained, thereby adjusting the type and amount of surface acid and reducing the activation energy of the reaction.

[0011] To achieve this objective, the present invention employs the following technical solution:

[0012] On one hand, the present invention provides a catalyst for the direct ammonolysis and nitrification of dicarboxylic acid esters to prepare dialiphatic nitrile, the catalyst comprising a supported all-silica molecular sieve and a metal oxide active component supported on the support.

[0013] Preferably, the all-silicon molecules are selected from any one of Silicalite-1, Silicalite-2, SBA-15, MCM-41, MCM-48, MCM-50, or KIT-6.

[0014] Preferably, the pore size distribution of the all-silica molecular sieve is 2 to 15 nm, for example, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 12 nm, 14 nm or 15 nm.

[0015] Preferably, the metal oxide is selected from any one or a combination of at least two of the oxides of Nb, W, Mo, Al, Ti, Zr, V or Ta.

[0016] Preferably, the particle size of the catalyst is 20 to 100 mesh, for example 20 mesh, 30 mesh, 40 mesh, 50 mesh, 60 mesh, 70 mesh, 80 mesh, 90 mesh or 100 mesh, preferably 40 to 80 mesh.

[0017] On the other hand, the present invention provides a method for preparing the catalyst for the direct ammonolysis and nitrification of dicarboxylic acid esters to prepare dialiphatic nitrile as described above, the preparation method comprising the following steps:

[0018] The catalyst is obtained by loading a metal precursor salt onto a silica molecular sieve as a support, followed by calcination and molding.

[0019] Preferably, the metal precursor salt is selected from one or a combination of at least two of niobium nitrate, niobium oxalate, niobium ethoxide, sodium tungstate, ammonium metatungstate, ammonium paratungstate, ammonium phosphotungstate, ammonium molybdate, aluminum nitrate, aluminum trichloride, sodium aluminosilicate, titanium nitrate, zirconium nitrate, zirconium chloride, ammonium metavanadate, sodium metavanadate, tantalum chloride, or tantalum ethoxide.

[0020] Preferably, the loading method is any one of the equal volume impregnation method, sol-gel method, or co-precipitation method, with the equal volume impregnation method or sol-gel method being preferred.

[0021] Preferably, the loading of metal oxide in the catalyst is 1 to 70 wt%, for example, 1 wt%, 3 wt%, 5 wt%, 8 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, or 70 wt%, preferably 1 to 50 wt%.

[0022] Preferably, the catalyst comprises a multi-metal component;

[0023] Preferably, the multi-metal component is NbM, VM, AlM, TiM or ZrM, and the metal oxide with a higher molar fraction is defined as the main metal, with a molar fraction of 60-95%, for example 60%, 65%, 68%, 70%, 74%, 78%, 80%, 83%, 85%, 88%, 90% or 95%.

[0024] Preferably, the calcination temperature is 150–700°C, for example, 150°C, 160°C, 180°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, or 700°C, and more preferably, the calcination temperature is 300–600°C.

[0025] Preferably, the calcination time is 3 to 10 hours, for example, 3 hours, 3.5 hours, 4 hours, 5 hours, 6 hours, 8 hours, or 10 hours, and more preferably, the calcination time is 5 to 8 hours.

[0026] On the other hand, the present invention provides the application of the catalyst described above in the catalytic preparation of dicarboxylic acid esters into diacidic nitrile.

[0027] Preferably, the method for preparing dicarboxylic acid esters into diacid nitrile esters by catalysis includes the following steps: loading the catalyst into the isothermal zone of a fixed bed, verifying good airtightness, raising the temperature to the reaction temperature, pretreating with ammonia, and then introducing the dicarboxylic acid ester raw material. After stable discharge, samples are taken at equal intervals, and the samples are analyzed offline by gas chromatography.

[0028] Preferably, the dicarboxylic acid ester includes one or a combination of at least two of the following: dimethyl glutarate, diethyl glutarate, dimethyl succinate, diethyl succinate, dimethyl adipate, diethyl adipate, dimethyl azelaate, or dimethyl sebacate.

[0029] Preferably, the catalyst is packed at 2% to 80% of the fixed-bed reactor volume, for example, 2%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, or 80%.

[0030] Preferably, the reaction temperature is 280–400°C, for example 280°C, 300°C, 320°C, 350°C, 380°C or 400°C, and more preferably the temperature range is 300–380°C.

[0031] The preparation of dialiphatic nitrile using the catalyst described in this invention offers a milder reaction condition compared to existing catalytic systems for the amination of dicarboxylic acid esters. The reaction temperature during the catalytic amination process can be reduced to 300°C, which is 40°C lower than the lowest reported temperature. Furthermore, the dialiphatic nitrile produced by this invention exhibits a high space-time yield. For the catalytic amination of adipate esters, the space-time yield can reach 45 mmol·g.cat -1 ·h -1 The active site utilization rate of this invention is high. Using all-silica molecular sieves as a carrier achieves effective dispersion of the active sites, thus improving their utilization rate.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] This invention provides a molecular sieve-supported metal oxide type solid acid catalyst with dispersed active sites, considerable space-time yield of binary aliphatic nitrile, and mild reaction conditions. When applied to the preparation of binary aliphatic nitrile, the reaction conditions are mild, the production energy consumption is reduced, and the dispersion and utilization of the catalyst's active sites are improved. The high space-time yield of the binary aliphatic nitrile reduces the theoretical design size of the reactor. Detailed Implementation

[0034] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0035] Example 1:

[0036] Ammonium metatungstate / niobium oxalate were dissolved in 15 mL of deionized water at a molar ratio of 1 / 108, and the total loading of the composite metal oxide was controlled at 45 wt%. 1 g of SBA-15 molecular sieve was added, and the mixture was stirred at 70 °C for 10 h. Excess water was removed by rotary evaporation, and the mixture was dried at 120 °C for 24 h. The resulting solid particles were ground and calcined in a tube furnace at 600 °C for 5 h to obtain the catalyst. The catalyst was granulated and sieved to 40–60 mesh, and 0.2 g of the catalyst was weighed and packed into a fixed bed. Dimethyl adipate was introduced at 0.018 mL / min, and ammonia was introduced at 25 mL / min. The reaction temperature was 300 °C, and the average catalytic performance over a 4 h reaction time was used as the evaluation index. The yield of adiponitrile was 45 mmol·g. cat -1 ·h -1 The selectivity for adiponitrile was 64%.

[0037] Comparative Example 1:

[0038] Niobium oxalate / amine metavanadate was dissolved in 15 mL of deionized water at a molar ratio of 3 / 7, and the total loading of the composite metal oxide was controlled at 45 wt%. 1 g of SBA-15 molecular sieve was added, and the mixture was stirred at 70 °C for 10 h. Excess water was removed by rotary evaporation, and the mixture was dried at 120 °C for 24 h. The resulting solid particles were ground and calcined in a tube furnace at 600 °C for 5 h to obtain the catalyst. The catalyst was granulated and sieved to 40–60 mesh, and 0.2 g of the catalyst was weighed and packed into a fixed bed. Dimethyl adipate was introduced at 0.018 mL / min, and ammonia was introduced at 25 mL / min. The reaction temperature was 300 °C, and the average catalytic performance over a 4 h reaction time was used as the evaluation index. The yield of adiponitrile was 33 mmol·g. cat -1 ·h -1 The selectivity for adiponitrile is 52%.

[0039] Example 2:

[0040] 0.15 g of ammonium molybdate was dissolved in 15 mL of deionized water, and 1 g of MCM-41 was added. The mixture was stirred at 70 °C for 10 h. Excess water was removed by rotary evaporation, and the mixture was dried at 120 °C for 24 h. The resulting solid particles were ground and calcined in a tube furnace at 550 °C for 5 h to obtain the catalyst. The catalyst was granulated and sieved to 40–60 mesh. 0.2 g of the catalyst was weighed and packed into a fixed bed. Dimethyl succinate was introduced at 0.018 mL / min, and ammonia was introduced at 20 mL / min. The reaction temperature was 350 °C, and the average catalytic performance over a 4 h reaction time was used as the evaluation index. The yield of adiponitrile was 40 mmol·g. cat -1 ·h -1 The selectivity for adiponitrile was 46%.

[0041] Comparative Example 2:

[0042] 0.15 g of ammonium molybdate was dissolved in 15 mL of deionized water, and 1 g of Silicalite-2 was added. The mixture was stirred at 70 °C for 10 h. Excess water was removed by rotary evaporation, and the mixture was dried at 120 °C for 24 h. The resulting solid particles were ground and calcined in a tube furnace at 550 °C for 5 h to obtain the catalyst. The catalyst was granulated and sieved to 40–60 mesh. 0.2 g of the catalyst was weighed and packed into a fixed bed. Dimethyl succinate was introduced at 0.018 mL / min, and ammonia was introduced at 20 mL / min. The reaction temperature was 350 °C, and the average catalytic performance over a 4 h reaction time was used as the evaluation index. The yield of adiponitrile was 3 mmol·g. cat -1 ·h -1 The selectivity for adiponitrile was 56%.

[0043] Example 3:

[0044] 170 mg of niobium oxalate and 26 mg of ammonium metatungstate were dissolved in 15 mL of deionized water, 0.4 g of citric acid and 1 g of MCM-41 molecular sieve were added, and the mixture was stirred at 70 °C for 10 h. Excess water was removed by rotary evaporation, and the mixture was dried at 120 °C for 24 h. The resulting solid particles were ground and calcined in a tube furnace at 550 °C for 5 h to obtain the catalyst. The catalyst was granulated and sieved to 40–60 mesh, and 0.2 g of the catalyst was weighed and packed into a fixed bed. Dimethyl sebacate was introduced at 0.010 mL / min, ammonia was introduced at 20 mL / min, and the reaction temperature was 320 °C. The average catalytic performance over a 4 h reaction time was used as the evaluation index. The yield of sebaonitrile was 29 mmol·g. cat -1 ·h -1 The selectivity of sebacate is 72%.

[0045] Comparative Example 3:

[0046] 170 mg of niobium oxalate and 26 mg of ammonium metatungstate were dissolved in 15 mL of deionized water, 0.4 g of citric acid and 1 g of MCM-41 molecular sieve were added, and the mixture was stirred at 70 °C for 10 h. Excess water was removed by rotary evaporation, and the mixture was dried at 120 °C for 24 h. The resulting solid particles were ground and calcined in a tube furnace at 450 °C for 5 h to obtain the catalyst. The catalyst was granulated and sieved to 40–60 mesh, and 0.2 g of the catalyst was weighed and packed into a fixed bed. Dimethyl sebacate was introduced at 0.010 mL / min, ammonia was introduced at 20 mL / min, and the reaction temperature was 320 °C. The average catalytic performance over a 4 h reaction time was used as the evaluation index. The yield of sebaonitrile was 23 mmol·g. cat -1 ·h -1 The selectivity of sebacate is 68%.

[0047] Example 4:

[0048] 170 mg of niobium oxalate and 26 mg of ammonium metatungstate were dissolved in 15 mL of deionized water, 0.4 g of citric acid and 1 g of MCM-41 molecular sieve were added, and the mixture was stirred at 70 °C for 10 h. Excess water was removed by rotary evaporation, and the mixture was dried at 120 °C for 24 h. The resulting solid particles were ground and calcined in a tube furnace at 550 °C for 5 h to obtain the catalyst. The catalyst was granulated and sieved to 60–80 mesh, and 0.2 g of the catalyst was weighed and packed into a fixed bed. Dimethyl adipate was introduced at 0.020 mL / min, ammonia was introduced at 30 mL / min, and the reaction temperature was 350 °C. The average catalytic performance over a 4 h reaction time was used as the evaluation index. The yield of adiponitrile was 28 mmol·g. cat -1 ·h -1 The selectivity for adiponitrile was 53%.

[0049] Comparative Example 4:

[0050] 170 mg of niobium oxalate and 26 mg of ammonium metatungstate were dissolved in 15 mL of deionized water, 0.4 g of citric acid and 1 g of MCM-41 molecular sieve were added, and the mixture was stirred at 70 °C for 10 h. Excess water was removed by rotary evaporation, and the mixture was dried at 120 °C for 24 h. The resulting solid particles were ground and calcined in a tube furnace at 550 °C for 5 h to obtain the catalyst. The catalyst was granulated and sieved to 20–40 mesh, and 0.2 g of the catalyst was weighed and packed into a fixed bed. Dimethyl adipate was introduced at 0.020 mL / min, ammonia was introduced at 30 mL / min, and the reaction temperature was 350 °C. The average catalytic performance over a 4 h reaction time was used as the evaluation index. The yield of adiponitrile was 18 mmol·g. cat -1 ·h -1 The selectivity for adiponitrile is 55%.

[0051] Example 5:

[0052] 170 mg of niobium oxalate and 26 mg of ammonium metatungstate were dissolved in 15 mL of deionized water, 0.4 g of citric acid and 1 g of KIT-6 molecular sieve were added, and the mixture was stirred at 70 °C for 10 h. Excess water was removed by rotary evaporation, and the mixture was dried at 120 °C for 24 h. The resulting solid particles were ground and calcined in a tube furnace at 450 °C for 5 h to obtain the catalyst. The catalyst was granulated and sieved to different sizes, and 0.2 g of the catalyst was weighed and packed into a fixed bed. Dimethyl adipate was introduced at 0.020 mL / min, ammonia was introduced at 30 mL / min, the reaction temperature was 320 °C, and the average catalytic performance over a 4 h reaction time was used as the evaluation index. The yield of glutaronitrile was 31 mmol·g. cat -1 ·h -1 The selectivity for adiponitrile is 55%.

[0053] Comparative Example 5:

[0054] 170 mg of niobium oxalate and 26 mg of ammonium metatungstate were dissolved in 15 mL of deionized water, 0.4 g of citric acid and 1 g of KIT-6 molecular sieve were added, and the mixture was stirred at 70 °C for 10 h. Excess water was removed by rotary evaporation, and the mixture was dried at 120 °C for 24 h. The resulting solid particles were ground and calcined in a tube furnace at 450 °C for 5 h to obtain the catalyst. The catalyst was granulated and sieved to different sizes, and 0.2 g of the catalyst was weighed and packed into a fixed bed. Dimethyl adipate was introduced at 0.020 mL / min, ammonia was introduced at 30 mL / min, the reaction temperature was 360 °C, and the average catalytic performance over a 4 h reaction time was used as the evaluation index. The yield of glutaronitrile was 27 mmol·g. cat -1 ·h-1 The selectivity for adiponitrile was 61%.

[0055] Example 6:

[0056] 0.15 g of ammonium molybdate was dissolved in 15 mL of deionized water, and 1 g of SBA-15 was added. The mixture was stirred at 70 °C for 10 h. Excess water was removed by rotary evaporation, and the mixture was dried at 120 °C for 24 h. The resulting solid particles were ground and calcined in a tube furnace at 550 °C for 5 h to obtain the catalyst. The catalyst was granulated and sieved to 40–60 mesh. 0.2 g of the catalyst was weighed and packed into a fixed bed. Dimethyl azelaate was introduced at 0.018 mL / min, and ammonia was introduced at 20 mL / min. The reaction temperature was 350 °C, and the average catalytic performance over a 4 h reaction time was used as the evaluation index. The yield of azelaic acid was 17 mmol·g. cat -1 ·h -1 The selectivity of azelaonitrile is 29%.

[0057] Comparative Example 6:

[0058] 0.15 g of ammonium molybdate was dissolved in 15 mL of deionized water, and 1 g of SBA-15 was added. The mixture was stirred at 70 °C for 10 h. Excess water was removed by rotary evaporation, and the mixture was dried at 120 °C for 24 h. The resulting solid particles were ground and calcined in a tube furnace at 550 °C for 5 h to obtain the catalyst. The catalyst was granulated and sieved to 40–60 mesh. 0.2 g of the catalyst was weighed and packed into a fixed bed. Dimethyl nonanoic acid was introduced at 0.018 mL / min, and ammonia was introduced at 30 mL / min. The reaction temperature was 350 °C. The average catalytic performance over a 4 h reaction time was used as the evaluation index. The results are shown in Table 7. The yield of azelaic acid was 13 mmol·g. cat -1 ·h -1 The selectivity for azelaic acid was 34%.

[0059] The applicant declares that this invention illustrates the catalyst, its preparation method, and application for the direct ammonolysis and nitrification of dicarboxylic acid esters to prepare dialiphatic nitriles through the above embodiments. However, this invention is not limited to the above embodiments, i.e., it does not mean that this invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvements to this invention, equivalent substitutions of the raw materials used in this invention, additions of auxiliary components, and selection of specific methods all fall within the protection and disclosure scope of this invention.

Claims

1. The application of a catalyst in the catalytic preparation of dicarboxylic acid esters into dialiphatic nitrile, characterized in that, The catalyst comprises a supported all-silica molecular sieve and a metal oxide active component supported on the support; The metal oxide is selected from a combination of Nb and W oxides; The catalyst has a metal oxide loading of 35-50 wt%. The all-silicon molecules are selected from any one of SBA-15, MCM-41, or KIT-6.

2. The application according to claim 1, characterized in that, The pore size distribution of the all-silica molecular sieve is 2 ~ 15 nm.

3. The application according to claim 1, characterized in that, The particle size of the catalyst is 20-100 mesh.

4. The application according to claim 3, characterized in that, The catalyst has a particle size of 40 to 80 mesh.

5. The application according to claim 1, characterized in that, The preparation method of the catalyst for the direct ammonolysis and nitrification of dicarboxylic acid esters to prepare dialiphatic nitrile includes the following steps: The catalyst is obtained by loading a metal precursor salt onto a silica molecular sieve as a support, followed by calcination and molding.

6. The application according to claim 5, characterized in that, The metal precursor salt is selected from a combination of niobium oxalate and amine metatungstate.

7. The application according to claim 5, characterized in that, The loading method is any one of the following: equal volume impregnation method, sol-gel method, or co-precipitation method.

8. The application according to claim 7, characterized in that, The loading method is either the equal-volume impregnation method or the sol-gel method.

9. The application according to claim 5, characterized in that, The calcination temperature is 150~700℃.

10. The application according to claim 9, characterized in that, The calcination temperature is 300~600℃.

11. The application according to claim 5, characterized in that, The calcination time is 3 to 10 hours.

12. The application according to claim 11, characterized in that, The calcination time is 5-8 hours.

13. The application according to claim 1, characterized in that, The method for preparing dicarboxylic acid esters into diacid nitrile esters by catalysis includes the following steps: the catalyst is loaded into the isothermal zone of a fixed bed, and after the airtightness is checked, the temperature is raised to the reaction temperature. After ammonia pretreatment, the dicarboxylic acid ester raw material is introduced. After the material is stably discharged, samples are taken at equal intervals, and the samples are analyzed offline by gas phase.

14. The application according to claim 1, characterized in that, The dicarboxylic acid esters include one or a combination of at least two of the following: dimethyl glutarate, diethyl glutarate, dimethyl succinate, diethyl succinate, dimethyl adipate, diethyl adipate, dimethyl azelaate, or dimethyl sebacate.

15. The application according to claim 13, characterized in that, The catalyst is packed at 2 to 80% of the volume of the fixed-bed reactor.

16. The application according to claim 13, characterized in that, The reaction temperature is 280~400℃.

17. The application according to claim 16, characterized in that, The reaction temperature range is 300~380℃.

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