Catalyst for preparing 2, 4-dichlorobenzonitrile and preparation process thereof

Abstract

The invention relates to the technical field of catalyst preparation, in particular to a catalyst for preparing 2, 4-dichlorobenzonitrile and a preparation process of the catalyst. The prepared catalyst overcomes the problems that a traditional catalyst for synthesizing 2, 4-dichlorobenzonitrile is poor in catalytic property and poor in catalytic cycle stability. The catalyst is composed of main active metals containing vanadium / molybdenum / tungsten and the like, rare earth metals, acid and alkali metals and other active components and a molecular sieve carrier, and the conversion rate and selectivity of ammoxidation reaction are significantly improved through the synergistic effect of the multi-metal components and through the mechanisms of redox cycle, electron transfer regulation and control, acid site optimization and the like. The carrier adopts a hydrothermal synthesis process, and is subjected to pre-crystallization, crystallization, calcination, ammonium chloride exchange and other steps to form a regular pore channel structure, so that the metal-carrier interaction is enhanced, and the activity stability in recycling is guaranteed; according to the mixing process, through two-stage calcination and accurate proportion regulation and control, uniform loading of active metal is achieved, and the finally prepared catalyst is excellent in catalytic performance and high in stability.

Description

Technical Field

[0001] The present invention relates to the technical field of catalyst preparation, in particular to a catalyst for preparing 2,4-dichlorobenzonitrile and a preparation process thereof. Background Art

[0002] 2,4-Dichlorobenzonitrile is an important organic synthesis intermediate with widespread applications in pesticides, pharmaceuticals, dyes, and other fields. Currently, the preparation of 2,4-dichlorobenzonitrile primarily relies on chemical synthesis, in which catalysts play a crucial role. However, existing catalysts used for the preparation of 2,4-dichlorobenzonitrile suffer from low catalytic activity, poor selectivity, and insufficient stability. This results in low 2,4-dichlorobenzonitrile yields and unstable product quality, while also increasing production costs and energy consumption, making it difficult to meet the needs of industrial large-scale production.

[0003] In the prior art, patent CN101757940B discloses a catalyst for preparing 3,4-dichlorobenzonitrile, which mainly uses silicon dioxide as a carrier and uses metals such as manganese, iron, cobalt, nickel, molybdenum and tungsten as active components. However, the active components are easily lost and the thermal stability still needs to be optimized. Patent CN102909043B discloses a catalyst, synthesis method and application for preparing 2,6-dichlorobenzonitrile, which has the advantages of high product yield and high content, and low cost of raw materials for catalyst preparation. However, its catalytic effect after multiple use cycles remains to be studied. Patent CN116351434B discloses a catalyst for preparing 2,4-dichlorobenzonitrile, preparation method and application, which uses a silicon-aluminum composite oxide as a carrier, and limits the types of multiple carriers, and loads a vanadium-containing iron-titanium composite oxide for catalysis. However, the loading amount of the active component reaches up to 70%, which causes clogging of the pores of the carrier. As the number of uses increases, the clogging effect becomes more obvious and the catalytic effect decreases. In addition, the catalysts prepared by the traditional impregnation method have poor dispersion, which limits the reaction efficiency.

[0004] Therefore, it is of great practical significance to develop a catalyst for preparing 2,4-dichlorobenzonitrile with high catalytic activity, good selectivity and strong stability and a preparation process thereof. To this end, a catalyst for preparing 2,4-dichlorobenzonitrile and a preparation process thereof are proposed. Summary of the Invention

[0005] The present invention aims to provide a catalyst for preparing 2,4-dichlorobenzonitrile and a preparation process thereof. The catalyst comprises active ingredients such as primary active metals containing vanadium, molybdenum, and tungsten, rare earth metals, and acidic and alkali metals, along with a molecular sieve support. The multi-metal components act synergistically to significantly improve the conversion rate and selectivity of ammoxidation reactions through redox cycling, electron transfer regulation, and acid site optimization. The support is synthesized hydrothermally through pre-crystallization, crystallization, calcination, and ammonium chloride exchange to form a regular pore structure, enhancing metal-support interaction and ensuring stable activity during cyclic use. A hybrid process achieves uniform loading of the active metals through two-stage calcination and precise ratio control, resulting in a catalyst with excellent catalytic performance and strong stability.

[0006] To achieve the above object, the present invention provides the following technical solutions: The present invention provides a preparation process of a catalyst for preparing 2,4-dichlorobenzonitrile. The catalyst is composed of an active component and a carrier. The active component of the catalyst is as follows: A a Ti b Fe c Ce d Co e F f G g H h O x ; wherein A is one or two of vanadium, molybdenum and tungsten; F is one of lanthanum, yttrium, neodymium and praseodymium; G is one of magnesium, potassium and sodium; H is one of phosphorus and sulfur; The catalyst is obtained by mixing an active metal mixed liquid and a catalyst precursor, performing two-stage calcination after programmed temperature increase, and drying after exchange; the active metal mixed liquid is calcined and exchanged to obtain an active component; the catalyst precursor is calcined and exchanged to obtain a carrier.

[0007] Preferably, the active metal mixture solution comprises ammonium metavanadate solution, titanium oxalate solution, ferric nitrate solution, cerium nitrate solution, cobalt nitrate solution, lanthanum nitrate solution, phosphoric acid solution, sulfuric acid solution, ammonium molybdate solution, ammonium metatungstate solution, yttrium nitrate solution, neodymium nitrate solution, praseodymium nitrate solution, potassium chloride solution, magnesium chloride solution and sodium chloride solution.

[0008] Preferably, in the active components of the catalyst, a is 1-1.71, b is 0.13-0.34, c is 0.06-0.16, d is 0.04-0.11, e is 0.02-0.06, f is 0.03-0.16, g is 0.03-0.16, h is 0.01-0.05, and x is the number of oxygen atoms required to satisfy the valence of each element in the catalyst.

[0009] Preferably, the preparation method of the catalyst precursor is as follows: adding aluminum sulfate 18hydrate to a sodium hydroxide solution under heating and stirring, adding tetrapropylammonium bromide and polyethylene glycol after complete dissolution, and finally adding silica gel, completely dissolving and adjusting the pH to obtain a precursor solution; the precursor solution is pre-crystallized, crystallized, filtered, washed, dried and calcined to obtain a catalyst precursor.

[0010] Preferably, the catalyst is prepared as follows: adding an active metal mixed solution to a catalyst precursor, performing two-stage heating and two-stage calcination to obtain a catalyst intermediate; and exchanging and drying the catalyst intermediate to obtain the catalyst.

[0011] Preferably, the exchange is carried out using a 1 mol / L ammonium chloride solution and the catalyst intermediate at a volume mass ratio (g / mL) of 1:20 at 80°C for 6 hours.

[0012] The catalyst is prepared by loading the active ingredient on a carrier; the catalyst is prepared by any of the above preparation processes; the specific surface area of the catalyst is 38-45m 2 / g, with a pore size of 30–50nm. The catalyst is mainly used for the preparation of 2,4-dichlorobenzonitrile by the ammonia-oxygen process. The catalyst can be fixed in a fluidized bed for use. The optimum catalytic conditions for the catalyst are an oxygen volume fraction of 8%–15% in the reaction gas. The catalyst loading can account for 30%–55% of the effective volume of the reactor. The catalyst is used to catalyze the synthesis of 2,4-dichlorobenzonitrile, and the conversion rate, selectivity and single-pass yield of 2,4-dichlorobenzonitrile are 95.4%-99.8%, 86.2%-98.1% and 91.2%-97.5%, respectively.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1. Enhanced catalytic activity through the synergistic action of multiple active metal components. Vanadium, molybdenum, and tungsten serve as primary active sites, providing the redox activity required for the ammoxidation reaction. Their ionic valence cycling promotes the dehydrogenation of toluene methyl groups and the ammoxidation reaction. Titanium regulates electron transfer efficiency, enhancing the catalyst's conductivity and intermediate adsorption capacity while also stabilizing the framework structure. Iron accelerates intermediate conversion and inhibits carbon deposition. Phosphorus and sulfur regulate surface acid sites, suppressing excessive oxidation side reactions. Potassium, magnesium, and sodium neutralize strong acid sites, reducing byproduct formation. Cobalt promotes the dissociation of oxygen into reactive oxygen species. Cerium utilizes its redox activity to remove carbon precursors. The synergistic effect of these multiple metal components creates abundant active centers and a suitable reaction environment, significantly enhancing the catalytic effect on the synthesis of 2,4-dichlorobenzonitrile and significantly increasing reaction conversion and selectivity.

[0014] 2. A unique preparation process utilizes sodium hydroxide, aluminum sulfate octahydrate, tetrapropylammonium bromide, polyethylene glycol, and silica gel as raw materials. Through pH control, pre-crystallization, crystallization, and calcination, a molecular sieve support with a regular pore structure and high porosity is formed. Pre-crystallization slowly forms initial nuclei at low temperatures, avoiding structural defects. During crystallization, aluminosilicates grow around the template, forming ordered pores. After calcination, the support is loaded with active metals through physical adsorption or ion exchange, creating a strong interaction between the metal and the support. Ammonium chloride solution is then used to exchange and remove sodium ions, creating acidic sites while preventing excessive alkalinity. This structure prevents active metal loss and pore clogging during catalyst recycling, maintaining a stable skeleton structure and effectively maintaining high conversion, selectivity, and single-pass yield, demonstrating excellent cyclic catalytic stability.

[0015] 3. The active metal mixture is composed of a mixture of various metal salt solutions in specific proportions, including the primary active metal, rare earth metals, alkaline and acidic metals, and an acid solution. By precisely controlling the ratio of each metal, an appropriate amount of metal oxide is loaded onto the molecular sieve support. The catalyst precursor is prepared through a complex process to form a support with a specific pore structure and surface properties. When the two are mixed, a two-stage heating and calcination process is employed: low-temperature calcination fixes the metal precursor, while high-temperature calcination promotes crystallization of the metal oxide and enhances metal-support interaction. An ammonium chloride solution is used in the exchange process to optimize the acid sites and cation composition on the support surface. This production process ensures uniform loading of the active metals and their full interaction with the support, resulting in a catalyst with a well-distributed active center distribution and a stable structure. Ultimately, the catalyst exhibits excellent catalytic performance and demonstrates excellent catalytic activity in the ammonia-oxygen synthesis of 2,4-dichlorobenzonitrile. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a process flow chart for preparing the catalyst of the present invention; Figure 2 These are the catalytic cycle performance test results of the catalysts of Example 2, Example 7, and Example 8. DETAILED DESCRIPTION

[0017] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0018] See also Figures 1 to 2The present invention provides a catalyst for preparing 2,4-dichlorobenzonitrile and a preparation process thereof. The technical scheme is as follows: information on substances used: ammonium metatungstate hydrate CAS: 12333-11-8; ammonium metavanadate CAS: 7803-55-6; ferric nitrate CAS: 7782-61-8; cobalt nitrate CAS: 10026-22-9; lanthanum nitrate CAS: 100587-94-8; ammonium molybdate CAS: 12054-85-2; ammonium metatungstate hydrate CAS: 11120-25-5; yttrium nitrate CAS: 13494-98-9‌; neodymium nitrate CAS: 16454-60-7; praseodymium nitrate CAS: 15878-77-0; cerium nitrate was purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0019] Example 1 Ammonium metavanadate (NH4VO3), titanium oxalate (Ti(C2O4)2), iron nitrate (Fe(NO3)3·9H2O), cerium nitrate (Ce(NO3)3·6H2O), cobalt nitrate (Co(NO2)2·6H2O), lanthanum nitrate (La(NO3)3·H2O), ammonium molybdate ((NH4)6Mo7O 24 4H2O), ammonium metatungstate hydrate ((NH4)6[H2W 12 O 42 ]·xH2O), yttrium nitrate (Y(NO3)3·6H2O), neodymium nitrate (Nd(NO3)3·6H2O), praseodymium nitrate (Pr(NO3)3·6H2O) and the corresponding metal solutions obtained by dissolving them in deionized water at 60°C. The specific solution concentrations, acid solutions and alkali metal solutions are shown below; ; The ammonium metavanadate solution, titanium oxalate solution, ferric nitrate solution, cerium nitrate solution, cobalt nitrate solution, lanthanum nitrate solution, acid solution and alkali metal solution are mixed in a volume ratio of 1:1:1:1:1:1:1:0.2:1 to obtain an active metal mixed solution.

[0020] Sodium hydroxide was dissolved in deionized water to obtain a sodium hydroxide solution, and then aluminum sulfate 18hydrate was added under constant temperature stirring at 50°C. After complete dissolution, tetrapropylammonium bromide (TPABr) and PEG-6000 were added, and finally silica gel was added, completely dissolved and the pH was adjusted to 11 to obtain a precursor solution; the precursor solution was pre-crystallized at 50°C for 12 hours and then transferred to a crystallization kettle, crystallized at 140°C for 2 hours to obtain a crystallized product, filtered, rinsed with deionized water, and completely dried. The temperature was increased from room temperature to 600°C at a rate of 5°C / min, calcined for 5 hours to obtain a catalyst precursor, and cooled to room temperature at a rate of 4°C / min; 1 / 10 of the volume of the active metal mixed solution in the catalyst precursor was added dropwise to the catalyst precursor and mixed evenly, and the temperature was increased from room temperature to 300°C at a rate of 2°C / min, calcined for 1.5 hours, and then increased to 500°C at a rate of 5°C / min. After calcination for 3 hours, the catalyst intermediate was cooled to room temperature; 1 The catalyst intermediate was exchanged with a mol / L ammonium chloride solution at a volume-to-mass ratio of 1:20 at 80°C for 6 hours. The catalyst was then washed, filtered, and dried. Calcination was performed in air. The molar mass ratio of SiO2, Al2O3, TPABr, PEG-6000, Na2O, and H2O in the precursor solution was 3:600:0.1:0.1:0.05:30.

[0021] Examples 2-5 The amount of metal elements in the active metal mixed solution, the amount of acid solution, and the mixed volume with the precursor solution are shown in Table 1.

[0022] Table 1 Preparation method and dosage of active metal mixed solution ; Unless otherwise specified, the following parameters are adjusted in the comparative example, and the rest remain the same as in Example 1.

[0023] Comparative Example 1 No cerium nitrate solution was added.

[0024] Comparative Example 2 No lanthanum nitrate solution was added.

[0025] Comparative Example 3 Ammonium metavanadate solution, titanium oxalate solution, ferric nitrate solution, cerium nitrate solution, cobalt nitrate solution, lanthanum nitrate solution, acid solution and alkali metal solution were mixed in the ratio of 0.2L:0.8L:0.1L:0.8L:0.5L:0.5L:0.2L:0.1L to obtain an active metal mixed solution.

[0026] Comparative Example 4 The mixed volumes of the precursor solution and the active metal mixed solution were 10 L and 3 L, respectively.

[0027] Experimental Example 1 The catalyst prepared by the above method was tested for its catalytic performance in the synthesis of 2,4-dichlorobenzonitrile. 2,4-Dichlorotoluene (DCT) reacted with ammonia and oxygen in the presence of the catalyst to produce 2,4-dichlorobenzonitrile in a single step. The molar ratio of oxygen to ammonia (O2 / NH3) was controlled at 1.2, the volume fraction of oxygen in the reaction gas was 10%, and the reaction temperature was 673K. The catalyst was fixed in a fluidized bed with a superficial gas velocity of 0.5 m / s. The catalyst loading accounted for 40% of the reactor's effective volume. The catalyst was tested for the conversion, selectivity, and single-pass yield of 2,4-dichlorobenzonitrile. Conversion rate of 2,4-dichlorobenzonitrile (%) = (molar amount of 2,4-dichlorobenzonitrile reacted / molar amount of 2,4-dichlorobenzonitrile raw material) × 100%; Selectivity of 2,4-dichlorobenzonitrile (%) = (molar amount of 2,4-dichlorobenzonitrile produced / molar amount of 2,4-dichlorobenzonitrile reacted) × 100%; 2,4-dichlorobenzonitrile single-pass yield (%) = (mol amount of 2,4-dichlorobenzonitrile produced / mol amount of 2,4-dichlorobenzonitrile as raw material) × 100%; The final test results are shown in Table 2.

[0028] Table 2 Catalytic effects of catalysts of Examples 1-6 and Comparative Examples 1-4 ; An active metal mixed solution is prepared by using vanadium, titanium, iron, cerium, cobalt, alkali metals and rare earth metals and an acid as raw materials, and the mixing ratio of the metals is adjusted, as well as the mixing ratio of the active metal mixed solution and the precursor solution, so that an appropriate amount of metal oxide is loaded on the molecular sieve, thereby improving the catalytic effect on the synthesis of 2,4-dichlorobenzonitrile, and improving the conversion rate, selectivity and single-pass yield; wherein under the conditions of Examples 1-6, the molecular formulas of the metal oxides are VTi 0.26 Fe 0.16 Ce 0.11 Co 0.05 La 0.16 Mg 0.16 P 0.05 O x 、VTi 0.13 Fe 0.08 Ce 0.04 Co 0.04 La 0.04 Mg 0.04 SO x 、MoW 1.71 Ti 0.34 Fe 0.14 Ce 0.11 Co 0.06 La 0.03 Na0.06 P 0.03 O x 、MoW 1.71 Ti 0.26 Fe 0.06 Ce 0.05 Co 0.02 Y 0.03 K 0.03 S 0.01 O x 、VTi 0.20 Fe 0.12 Ce 0.07 Co 0.03 Nd 0.03 Mg 0.05 P 0.01 O x and VTi 0.26 Fe 0.11 Ce 0.05 Co 0.04 Pr 0.04 Mg 0.04 S 0.01 O x The conversion rate, selectivity and single-pass yield of 2,4-dichlorobenzonitrile are 97.1%-99.8%, 86.2%-98.1% and 91.5%-97.5% respectively. The vanadium used is the main active site, providing redox activity for the ammoxidation reaction. 5+ / V 4+ Cyclic promotion of toluene methyl dehydrogenation and ammoxidation reaction; titanium through Ti 3+ / Ti 4+ The oxidation state regulates the efficiency of electron transfer, enhances the conductivity of the catalyst and the adsorption capacity of reaction intermediates. In addition, titanium promotes the stabilization of the catalyst skeleton structure and reduces the loss of active components. Iron 2+ / Fe 3+ Electron transfer accelerates the conversion of NH3 adsorbed reaction intermediates and inhibits carbon deposition. The added phosphoric acid and sulfuric acid regulate the distribution of acid sites on the catalyst surface through the phosphorus and sulfur in them, inhibiting excessive oxidation side reactions. The added potassium, magnesium and sodium metals reduce the generation of byproducts CO2 and NH4Cl by neutralizing strong acid sites such as free VO bonds, thereby improving the selectivity of the target product. Cobalt in the oxide accelerates the ammoxidation process of toluene methyl by promoting the dissociation of O2 into active oxygen species. Cerium utilizes Ce to 3+ / Ce 4+The rapid redox ability of the catalyst removes carbon deposit precursors and prolongs the life of the catalyst. The activity of the vanadium-based catalyst decreases due to the volatilization of V2O5. Molybdenum and tungsten are used to replace the vanadium used. After high-temperature calcination, molybdenum and tungsten form a composite oxide MoO3-WO3 heterostructure, which exposes abundant oxygen vacancies and acid sites on its surface. It serves as the adsorption activation center of O2 and NH3 in the ammonia oxidation reaction, promoting the dehydrogenation and cyanation reaction of toluene methyl group. Molybdenum (Mo 6+ / Mo 4+ ) and tungsten (W 6+ / W 4+ ) oxidized state circulates in the reaction, accelerating the dissociation of oxygen molecules to generate active oxygen species (O - or O 2- ), promoting the dehydrogenation of 2,4-dichlorotoluene (DCT) and the oxidation of ammonia; the strong oxidizing property of molybdenum combined with the stability of tungsten can inhibit excessive oxidation side reactions, such as the generation of CO2 or chlorinated byproducts, and improve the selectivity of 2,4-dichlorobenzonitrile; at the same time, the introduction of tungsten can inhibit the formation of carbon deposits and extend the service life of the catalyst. Example 3 replaces vanadium with molybdenum and tungsten, and the effect is lower than that of Example 1; Example 4 uses yttrium instead of lanthanum, and adjusts the amount of other metal elements at the same time to maximize the conversion rate, selectivity and single-pass yield; Examples 5-6 adjust the amount of different metal elements, and replace lanthanum with neodymium and praseodymium, which reduces the element pore size control ability and reduces the mass transfer efficiency; Comparative Example 1 lacks Ce 3+ / Ce 4+ cycles, the carbon deposition rate increased and the selectivity decreased; in Comparative Example 2, the metal oxide did not contain lanthanum, the pore size was out of control, the amount of by-products such as chloroaryl hydrocarbons generated increased, and the yield decreased; in Comparative Example 3, the active metal loading was uneven, and some sites were deactivated; in Comparative Example 4, the excessive active liquid caused the carrier pores to be blocked, the mass transfer was limited, and the single-pass yield was significantly reduced.

[0029] Example 7 Different from Example 2, the pH of the precursor solution is 10, the pre-crystallization temperature is 45°C and the time is 15 h, the crystallization temperature is 130°C and the time is 4 h, the calcination temperature of the catalyst precursor is 550°C and the time is 6 h, the first stage heating rate after the addition of the active metal mixture is 3°C / min, the first stage calcination temperature is 350°C and the time is 1 h, the second stage heating rate after the addition of the active metal mixture is 6°C / min, the second stage calcination temperature is 550°C and the time is 2.5 h, and the molar mass ratio of SiO2, Al2O3, TPABr, PEG-6000, Na2O and H2O is 5:400:0.2:0.1:0.03:30.

[0030] Example 8 Different from Example 2, the pH of the precursor solution is 10, the pre-crystallization temperature is 40°C and the time is 20 h, the crystallization temperature is 150°C and the time is 1 h, the calcination temperature of the catalyst precursor is 500°C and the time is 8 h, the first stage heating rate after the addition of the active metal mixture is 2°C / min, the first stage calcination temperature is 280°C and the time is 1 h, the second stage heating rate after the addition of the active metal mixture is 5°C / min, the second stage calcination temperature is 500°C and the time is 3.5 h, and the molar mass ratio of SiO2, Al2O3, TPABr, PEG-6000, Na2O and H2O is 2:800:0.3:0.1:0.01:30.

[0031] Comparative Example 5 The precursor solution was directly crystallized without undergoing a pre-crystallization process. Other methods remained the same as those in Example 2.

[0032] Comparative Example 6 The precursor solution was not subjected to the pre-crystallization and crystallization processes, but was directly filtered and dried to obtain a catalyst precursor. Other methods were the same as those in Example 2.

[0033] Comparative Example 7 After the active metal mixture was added, only one stage of heating and calcination was performed, with a heating rate of 5° C. / min, a calcination temperature of 500° C., and a calcination time of 5 h. Other methods were consistent with those in Example 2.

[0034] Comparative Example 8 1 mol / L ammonium chloride solution was not used for exchange, and other methods remained the same as in Example 2.

[0035] Comparative Example 9: The order of adding the active metal mixed solution was changed. Specifically, the catalyst precursor was cooled to room temperature and then exchanged with an ammonium chloride solution. The mixture was filtered and dried and then mixed with the active metal mixed solution. The temperature was raised from room temperature to 300°C at a rate of 2°C / min, calcined for 1.5 hours, and then heated to 500°C at a rate of 5°C / min. After calcination for 3 hours, the mixture was cooled to room temperature to obtain the catalyst. The other methods were consistent with those in Example 2.

[0036] Experimental Example 2 The catalysts obtained in Examples 2, 7, 8 and Comparative Examples 1-9 were subjected to catalytic cycle performance tests to test the effects of 10 uses on conversion, selectivity and single-pass yield. The final test results are shown in the figure. Figure 2 and shown in Table 3.

[0037] Table 3 Cyclic performance test results

[0038] After the active metal mixture was prepared, the catalyst was prepared using SiO2, Al2O3, TPABr, PEG-6000, NaOH and H2O as raw materials; NaOH provided OH - , with Al3+ The reaction generates aluminum hydroxide colloid, which serves as the aluminum source of the molecular sieve framework. The pH is controlled to be strongly alkaline to promote the dissolution of Al(OH)3 to form aluminate (AlO 2- ), which lays the foundation for the subsequent formation of the aluminosilicate skeleton; the added tetrapropylammonium bromide organic cation (C3H7)4N + Through electrostatic interaction, it combines with the negatively charged aluminosilicate framework to guide the directional growth of the molecular sieve pore structure MFI topology, and acts as a template to form pores during the calcination process, providing loading sites for active metals. PEG-6000 acts as a template and dispersant to prevent particle agglomeration through steric hindrance, while participating in the formation of mesoporous structure and improving the specific surface area and pore distribution of the molecular sieve. After the SiO2 source dissolves, silicate ions SiO3 are released. 2- , and aluminate forms an aluminosilicate gel network through condensation reaction, controls the strong alkaline conditions to promote the dissolution-recrystallization process of the aluminosilicate gel, forms a uniform molecular sieve precursor structure, and slowly forms the initial crystal nucleus at low temperature during pre-crystallization to avoid structural defects caused by rapid crystallization; under the hydrothermal conditions of crystallization, the aluminosilicate gel further grows around the TPABr template to form ZSM-5 type molecular sieve crystals with regular pores; after calcination, it is mixed with an active metal mixed solution, and the molecular sieve precursor has high porosity and adsorbs metal ions V through capillary action. 5+ 、Ti 4+ 、Fe 3+ etc., and adsorb acid / alkali metal ions. The metal ions react with Na + Exchange or physical adsorption fixed on the pore surface at high temperature accelerates the polycondensation reaction and promotes the orderly arrangement of the skeleton atoms Si and Al; low-temperature calcination evaporates water and fixes the metal precursor on the support surface; nitrate is initially decomposed, Fe(NO3)3→Fe2O3+NO2+O2, forming small particle metal oxide cores; high-temperature calcination promotes further crystallization of metal oxides to form a highly active phase; at the same time, it promotes metal-support interaction (SMSI effect) and improves stability; acid / alkali metal component K + and Na + Migrate to the active metal interface to adjust its electron density or acidic site distribution; ammonium chloride solution ion exchange NH 4+ Replacement of Na in the skeleton + , reduce the basic sites, avoid excessive alkalinity resulting in excessive adsorption of reactants, and introduce NH 4+ After that, it is decomposed into H + , forming acidic site B acid center; promoting the progress of the catalytic process.

[0039] By adjusting the pre-crystallization and crystallization temperatures, calcination time, the order of adding the active metal mixture after the molecular sieve is prepared, and the calcination procedure, the conversion rate, selectivity and single-pass yield of 2,4-dichlorobenzonitrile can be maintained at a high value after the catalyst is recycled. 5+ / Ce 4+ Redox cycle, serious carbon deposition, and a sharp drop in yield after the cycle; Comparative Example 2 molecular sieve pore size is out of control, by-product generation increases, and catalytic performance decreases after the cycle; Comparative Example 3 uneven metal loading leads to local deactivation, Comparative Example 4 carrier pores are blocked, mass transfer is limited, Comparative Example 5 does not pre-crystallize, resulting in loose molecular sieve structure, Comparative Example 6 catalyst structure is disordered, active sites are easily lost, Comparative Example 7 high temperature rapid calcination leads to metal agglomeration, Comparative Example 8 does not use ammonium chloride to remove the template, residual organic matter blocks the pores, Comparative Example 9 and Comparative Example 10 loading order and preparation process are changed, and the catalytic and catalytic cycle properties of the final catalyst are significantly reduced. The embodiment prepares a molecular sieve carrier containing Al and Si by a hydrothermal synthesis method, tetrapropylammonium bromide is used as a template, PEG-6000 assists in molding, NaOH adjusts the alkaline environment to promote silicon-aluminum condensation, and a metal mixture is directly added dropwise to the calcined carrier. Metal components such as V, Ti, Fe, and Ce are loaded by physical adsorption or ion exchange, and finally Na4Cl solution is used to exchange Na in the carrier. + , forming H + Type or NH 4+ Type molecular sieve, enhance the acid site, improve the catalytic property and cyclic catalytic stability; Comparative Example 9 first uses ammonium chloride solution to exchange the Na + , which will lead to the enhancement of the acidity of the support surface, NH 4+ Hydrolysis produces H + , and the cation concentration in the pores is reduced. At this time, when the active metal mixture is loaded, the surface charge density of the carrier is reduced, and the electrostatic adsorption force of the metal ions is weakened, resulting in insufficient loading or uneven distribution. At the same time, the acidic environment causes some metal salts such as ammonium metavanadate to dissolve or hydrolyze and change their form. 5+ Soluble polyvanadates are formed, which are difficult to deposit on the support; and during the calcination process, they are prone to migration and agglomeration to form large particles of metal oxides, which reduce the number of active sites, catalytic activity and cyclic catalytic stability.

[0040] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A process for preparing a catalyst for preparing 2,4-dichlorobenzonitrile, characterized in that: The catalyst is composed of active components and a carrier, and the active components of the catalyst are as follows: AaTibFecCedCoeFfGgHhOx; wherein A is one or two of vanadium, molybdenum and tungsten; F is one of lanthanum, yttrium, neodymium and praseodymium; G is one of magnesium, potassium and sodium; H is one of phosphorus and sulfur; In the active components of the catalyst, a is 1-1.71, b is 0.13-0.34, c is 0.06-0.16, d is 0.04-0.11, e is 0.02-0.06, f is 0.03-0.16, g is 0.03-0.16, h is 0.01-0.05, and x is the number of oxygen atoms required to satisfy the valence of each element in the catalyst; The catalyst is obtained by mixing an active metal mixed liquid and a catalyst precursor, performing two-stage calcination after programmed temperature increase, and drying after exchange; the active metal mixed liquid is calcined and exchanged to obtain the active component; the catalyst precursor is calcined and exchanged to obtain the carrier; The catalyst precursor is obtained by pre-crystallization, crystallization, filtration, washing, drying and calcination of a precursor solution; the exchange is to treat the catalyst intermediate with an ammonium chloride solution; the pre-crystallization temperature is 40-50°C and the time is 12-20 hours; the crystallization temperature is 130-150°C and the time is 1-4 hours.

2. A process for preparing a catalyst for preparing 2,4-dichlorobenzonitrile according to claim 1, characterized in that: The active metal mixed solution comprises ammonium metavanadate solution, titanium oxalate solution, ferric nitrate solution, cerium nitrate solution, cobalt nitrate solution, lanthanum nitrate solution, phosphoric acid solution, sulfuric acid solution, ammonium molybdate solution, ammonium metatungstate solution, yttrium nitrate solution, neodymium nitrate solution, praseodymium nitrate solution, potassium chloride solution, magnesium chloride solution and sodium chloride solution.

3. A process for preparing a catalyst for preparing 2,4-dichlorobenzonitrile according to claim 1, characterized in that: The precursor solution is prepared as follows: aluminum sulfate 18hydrate is added to a sodium hydroxide solution under heating and stirring, and after it is completely dissolved, tetrapropylammonium bromide and polyethylene glycol are added, and finally silica gel is added, and after it is completely dissolved and the pH is adjusted to 10-11, the precursor solution is obtained.

4. A process for preparing a catalyst for preparing 2,4-dichlorobenzonitrile according to claim 1, characterized in that: The preparation method of the catalyst is as follows: adding the active metal mixed solution to the catalyst precursor, performing two-stage heating and two-stage calcination to obtain the catalyst intermediate; and performing the exchange and drying of the catalyst intermediate to obtain the catalyst.

5. A catalyst for preparing 2,4-dichlorobenzonitrile, characterized in that: The catalyst is obtained by loading an active component on a carrier; the catalyst is prepared by the preparation process according to any one of claims 1 to 4.

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