A catalyst for preparing 2,4-dichlorophenyl cyanide and a preparation process thereof

Abstract

The present application relates to the technical field of catalyst preparation, in particular to a kind of catalyst for 2,4-dichloronitrile preparation and its preparation process.The catalyst prepared by the present application overcomes the problems of poor catalytic activity and poor catalytic cycle stability of traditional catalysts used for synthesizing 2,4-dichloronitrile.The catalyst is composed of active components such as vanadium / molybdenum / tungsten, rare earth metals, acid and alkali metals and molecular sieve carrier, and the multiple metal components synergistically act through mechanisms such as oxidation-reduction cycle, electron transfer regulation and optimization of acidic sites, significantly improving the conversion rate and selectivity of ammoxidation reaction.The carrier adopts hydrothermal synthesis process, and through pre-crystallization, crystallization, calcination and ammonium chloride exchange steps, a regular pore structure is formed, the metal-carrier interaction is enhanced, and the activity stability is ensured during cyclic use;The mixed process realizes uniform loading of active metals through two-stage calcination and precise proportion control, and finally the catalyst with excellent catalytic performance and strong stability is obtained.

Description

TECHNICAL FIELD

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

[0002] 2,4-dichlorobenzonitrile is an important organic synthesis intermediate and is widely used in the fields of pesticides, medicines and dyes. At present, the preparation method of 2,4-dichlorobenzonitrile mainly adopts chemical synthesis, and in the synthesis process, the catalyst plays a crucial role. However, the existing catalysts for preparing 2,4-dichlorobenzonitrile have the problems of low catalytic activity, poor selectivity and insufficient stability, which leads to low yield of 2,4-dichlorobenzonitrile, unstable product quality, and increases the production cost and energy consumption, and cannot 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 manganese, iron, cobalt, nickel, molybdenum and tungsten as active components, but the active components are easy to lose and the thermal stability still needs to be optimized; patent CN102909043B discloses a catalyst for preparing 2,6-dichlorobenzonitrile, a synthesis method and application, which has the advantages of high product yield and high content, and the catalyst preparation raw material cost is low, but after multiple use cycles, the catalytic effect needs to be investigated; patent CN116351434B discloses a catalyst for preparing 2,4-dichlorobenzonitrile and a preparation method and use, which uses silicon-aluminum composite oxide as a carrier and limits the types of the carrier, and loads vanadium-iron-titanium composite oxide for catalysis, but the loading amount of the active component is up to 70%, which blocks the pores of the carrier and the blocking effect is more obvious with the increase of the use times, and the catalytic effect decreases. In addition, the catalyst prepared by the traditional impregnation method has poor dispersibility, 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. For this purpose, a catalyst for preparing 2,4-dichlorobenzonitrile and a preparation process thereof are provided. SUMMARY

[0005] The application aims to provide a catalyst for preparing 2,4-dichlorobenzene cyanide and a preparation process thereof, the catalyst is composed of main active metals such as vanadium, molybdenum and tungsten, rare earth metals, active components such as acid and alkali metals and a molecular sieve carrier, the synergistic effect of multiple metal components, through mechanisms such as oxidation-reduction cycle, electron transfer regulation and optimization of acidic sites, significantly improves the conversion rate and selectivity of the ammoxidation reaction. The carrier adopts a hydrothermal synthesis process, and is formed into a regular pore structure through steps such as pre-crystallization, crystallization, calcination and ammonium chloride exchange, thereby enhancing the metal-carrier interaction and ensuring the activity stability in the recycling process; the mixed process realizes uniform loading of the active metals through two-stage calcination and accurate proportion control, and finally the catalyst prepared has excellent catalytic performance and strong stability.

[0006] To achieve the above-mentioned purpose, the application provides the following technical solutions:

[0007] The application provides a preparation process of a catalyst for preparing 2,4-dichlorobenzene cyanide, the catalyst is composed of active components and a carrier, and the active components of the catalyst are as follows: A a Ti b Fe c Ce d Co e F f G g H h O x ;

[0008] 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;

[0009] The catalyst is obtained by mixing an active metal mixed solution and a catalyst precursor, two-stage calcination after programmed temperature rising and drying after exchange; the active metal mixed solution is subjected to calcination and exchange to obtain the active components; and the catalyst precursor is subjected to calcination and exchange to obtain the carrier.

[0010] Preferably, 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.

[0011] 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.

[0012] Preferably, the preparation method of the catalyst precursor is as follows: aluminum sulfate octadecahydrate is added to a sodium hydroxide solution under heating and stirring, tetrapropylammonium bromide and polyethylene glycol are added after complete dissolution, and silica gel is finally added, and the precursor solution is obtained after complete dissolution and pH adjustment; the precursor solution is pre-crystallized, crystallized, filtered, washed, dried and calcined to obtain the catalyst precursor.

[0013] Preferably, the preparation method of the catalyst is as follows: an active metal mixed solution is added to the catalyst precursor, and a catalyst intermediate is obtained after two-stage heating and two-stage calcination; the catalyst intermediate is exchanged and dried to obtain the catalyst.

[0014] Preferably, the exchange is performed at 80°C for 6h using 1mol / L ammonium chloride solution and the catalyst intermediate in a volume-to-mass ratio (g / mL) of 1:20.

[0015] The catalyst is obtained by loading an active component on a carrier; the catalyst is prepared by any one of the preparation processes described above; the specific surface area of the catalyst is 38-45m 2 / g, and the pore size is 30-50nm; the catalyst is mainly used for preparing 2,4-dichloronitrile by the ammoximation method, the catalyst can be fixed in a fluidized bed for use, and the suitable catalytic conditions of the catalyst are that the volume fraction of oxygen in the reaction gas is 8%-15%; the loading amount of the catalyst can account for 30%-55% of the effective volume of the reactor;

[0016] The catalyst is used for catalyzing the synthesis of 2,4-dichloronitrile, and the conversion rate, selectivity and single-pass yield of 2,4-dichloronitrile are 95.4%-99.8%, 86.2%-98.1% and 91.2%-97.5%, respectively.

[0017] Compared with the prior art, the beneficial effects of the present application are:

[0018] 1. The catalytic activity is improved by the synergistic effect of multiple active metal components. Vanadium, molybdenum, tungsten, etc. are used as main active sites to provide the redox activity required for ammoximation reaction, and the ion valence cycle promotes toluene methyl dehydrogenation and ammoximation reaction; titanium regulates the electron transfer efficiency, enhances the conductivity of the catalyst and the adsorption capacity of the intermediate, and stabilizes the skeleton structure; iron accelerates the conversion of the intermediate and inhibits the generation of carbon deposition; phosphorus and sulfur adjust the surface acid sites to inhibit the over-oxidation side reaction; potassium, magnesium and sodium neutralize strong acid sites to reduce the generation of by-products; cobalt promotes the dissociation of oxygen into active oxygen species; cerium uses the redox capacity to remove carbon deposition precursors. The multiple metal components cooperate with each other to form rich active centers and suitable reaction environment, which significantly improves the catalytic effect on the synthesis of 2,4-dichloronitrile and greatly improves the reaction conversion rate and selectivity.

[0019] 2, with special preparation process, with sodium hydroxide, aluminum sulfate octadecahydrate, tetrapropyl ammonium bromide, polyethylene glycol and silica gel as raw materials, by controlling pH, pre-crystallization, crystallization, calcination and other steps, form a molecular sieve carrier with regular pore structure and high porosity. Pre-crystallization slowly forms initial crystal nucleus at low temperature to avoid structural defects; during the crystallization process, silicate grows around the template to form ordered pores; after calcination, the carrier is loaded with active metal by physical adsorption or ion exchange, and strong interaction is formed between the metal and the carrier. Ammonium chloride solution is used to exchange sodium ions, forming acid sites while avoiding excessive alkalinity. This structure makes the catalyst less likely to lose active metal and block the pores during recycling, and the skeleton structure is stable, which can effectively maintain high conversion rate, selectivity and single-pass yield, and exhibits good recycling catalytic stability.

[0020] 3, the active metal mixed solution is mixed by a plurality of metal salt solutions in a specific proportion, covering main active metals, rare earth metals, acid and base metals and acid solutions, etc. By accurately controlling the proportion of each metal, an appropriate amount of metal oxide is loaded on the molecular sieve carrier. The catalyst precursor is prepared by a complex process to form a carrier with specific pore structure and surface properties. When mixed, two-stage heating and two-stage calcination process is used, low-temperature calcination to fix the metal precursor, and high-temperature calcination to promote metal oxide crystallization and enhance metal-support interaction. The exchange process uses ammonium chloride solution to optimize the surface acidity of the carrier and the composition of cations. This production process ensures uniform loading of active metals and full interaction with the carrier, forming a catalyst with reasonable active center distribution and stable structure, which ultimately makes the catalyst have excellent catalytic performance and good catalytic effect in the synthesis of 2,4-dichloronitrile by ammonia oxygen method. BRIEF DESCRIPTION OF DRAWINGS

[0021] Fig. 1 The catalyst preparation process flowchart of the present application;

[0022] Fig. 2 The catalyst recycling performance test results of Example 2, Example 7 and Example 8 catalysts. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0024] Please refer to Figs. 1-2The application provides a catalyst for preparing 2,4-dichlorophenyl cyanide and a preparation process thereof, and the technical scheme is as follows: the used substances are as follows: 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; and cerium nitrate is purchased from Shanghai Maikelin Biochemical Technology Co., Ltd.

[0025] Example 1

[0026] Ammonium metavanadate (NH4VO3), titanium oxalate (Ti(C2O4)2), ferric 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 corresponding metal solutions obtained by dissolving the above substances in deionized water at 60 DEG C respectively, and the specific solution concentration and the acid solution and alkali metal solution are shown as follows:

[0027] ;

[0028] The ammonium metavanadate solution, the titanium oxalate solution, the ferric nitrate solution, the cerium nitrate solution, the cobalt nitrate solution, the lanthanum nitrate solution, the acid solution and the alkali metal solution are mixed according to a volume ratio of 1:1:1:1:1:1:0.2:1 to obtain an active metal mixed solution.

[0029] Sodium hydroxide was dissolved in deionized water to obtain a sodium hydroxide solution, and then aluminum sulfate octadecahydrate 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. After complete dissolution and adjustment of the pH to 11, a precursor solution was obtained. The precursor solution was pre-crystallized at 50°C for 12 h, and then transferred to a crystallization kettle. Crystallization was carried out at 140°C for 2 h to obtain a crystallization product. The product was suction filtered and washed with deionized water, and then completely dried. The temperature was increased from room temperature to 600°C at a rate of 5°C / min, and calcination was carried out for 5 h. After cooling to room temperature at a rate of 4°C / min, a catalyst precursor was obtained. The catalyst precursor was mixed with a volume of 1 / 10 of the active metal mixed solution in the precursor solution, and then mixed uniformly. The temperature was increased from room temperature to 300°C at a rate of 2°C / min, and calcination was carried out for 1.5 h. The temperature was then increased to 500°C at a rate of 5°C / min, and calcination was carried out for 3 h. After cooling to room temperature, a catalyst intermediate was obtained. The catalyst intermediate was exchanged with a 1 mol / L ammonium chloride solution at a volume-to-mass ratio of 1:20 at 80°C for 6 h. Finally, the catalyst was washed, filtered, and dried. The calcination was carried out 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.

[0030] Examples 2-5

[0031] The amounts of metal elements in the active metal mixed solution, the amount of acid solution, and the mixing volume with the precursor solution were changed, as shown in Table 1.

[0032] Table 1 Preparation method and amount of active metal mixed solution

[0033]

[0034] Unless otherwise specified, the comparative examples were consistent with Example 1, except for the following parameters.

[0035] Comparative Example 1 No cerium nitrate solution was added.

[0036] Comparative Example 2 No lanthanum nitrate solution was added.

[0037] Comparative Example 3 The ammonium metavanadate solution, titanium oxalate solution, iron nitrate solution, cerium nitrate solution, cobalt nitrate solution, lanthanum nitrate solution, acid solution, and alkali metal solution were mixed at a volume of 0.2 L:0.8 L:0.1 L:0.8 L:0.5 L:0.5 L:0.2 L:0.1 L to obtain an active metal mixed solution.

[0038] Comparative Example 4 The mixing volumes of the precursor solution and the active metal mixed solution were 10 L and 3 L, respectively.

[0039] Experimental Example 1 ​

[0040] The catalyst prepared by the above method was tested for its effect on the catalytic synthesis of 2,4-dichloronitrile. 2,4-dichlorotoluene (DCT) was used as the raw material, and reacted with ammonia and oxygen under the action of the catalyst to produce 2,4-dichloronitrile in one 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%, the reaction temperature was 673 K, the catalyst was fixed in a fluidized bed, the empty tower gas velocity of the fluidized bed was controlled at 0.5 m / s, and the catalyst loading accounted for 40% of the effective volume of the reactor. The conversion rate, selectivity and single-pass yield of 2,4-dichloronitrile catalyzed by the catalyst were tested.

[0041] The conversion rate of 2,4-dichloronitrile (%) = (molar amount of reacted 2,4-dichloronitrile / molar amount of raw material 2,4-dichloronitrile) x 100%;

[0042] The selectivity of 2,4-dichloronitrile (%) = (molar amount of generated 2,4-dichloronitrile / molar amount of reacted 2,4-dichloronitrile) x 100%;

[0043] The single-pass yield of 2,4-dichloronitrile (%) = (molar amount of generated 2,4-dichloronitrile / molar amount of raw material 2,4-dichloronitrile) x 100%;

[0044] The final test results are shown in Table 2.

[0045] Table 2 Catalytic effect of catalysts of Examples 1-6 and Comparative Examples 1-4

[0046] ;

[0047] By using vanadium, titanium, iron, cerium, cobalt, alkali metal and rare earth metal and acid as raw materials to prepare an active metal mixed solution, adjusting the mixing ratio of the metals, and adjusting the mixing ratio of the active metal mixed solution and the precursor solution, so that a suitable amount of metal oxide is loaded on the molecular sieve, the catalytic effect on the synthesis of 2,4-dichloronitrile is improved, and the conversion rate, selectivity and single-pass yield are improved; under the conditions of Examples 1-6, the molecular formula of the metal oxide is 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 , MoW1.71 Ti 0.34 Fe 0.14 Ce 0.11 Co 0.06 La 0.03 Na 0.06 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, selectivity and single-pass yield of 2,4-dichlorobenzonitrile were 97.1%-99.8%, 86.2%-98.1% and 91.5%-97.5%, respectively. Among them, vanadium was the main active site, providing the redox activity of the ammoxidation reaction, and the dehydrogenation of toluyl and the ammoxidation reaction were promoted by V 5+ / V 4+ cycle in the reaction; titanium regulated the electron transfer efficiency through Ti 3+ / Ti 4+ oxidation state, enhanced the electrical conductivity of the catalyst and the adsorption capacity of the reaction intermediate, in addition, titanium promoted the stability of the catalyst skeleton structure and reduced the loss of active components; iron accelerated the conversion of NH3 adsorbed state reaction intermediates through Fe 2+ / Fe 3+ electron transfer, while inhibiting the generation of carbon deposition; the added phosphoric acid and sulfuric acid regulated the distribution of the acid sites on the catalyst surface through phosphorus and sulfur, inhibiting the over-oxidation side reaction; the added potassium, magnesium and sodium metals reduced the generation of by-products CO2 and NH4Cl by neutralizing the strong acid sites such as free V-O bonds, and improved the selectivity of the target product; cobalt promoted the dissociation of O2 into active oxygen species in the oxide, accelerating the ammoxidation process of toluyl; cerium utilized Ce 3+ / Ce 4+the fast redox ability of the catalyst to remove the carbon deposition precursor and prolong the catalyst life; the activity of the vanadium-based catalyst is decreased due to the volatilization of V2O5, and the vanadium is replaced by molybdenum and tungsten, and the composite oxide MoO3-WO3 heterostructure is formed after calcination at high temperature, and the surface of the composite oxide exposes a large number of oxygen vacancies and acid sites, which are used as the adsorption and activation centers of O2 and NH3 in the ammonia oxidation reaction, and promote the dehydrogenation and cyanation of the methyl group of toluene; the oxidation states of molybdenum (Mo 6+ / Mo 4+ ) and tungsten (W 6+ / W 4+ ) are cycled in the reaction, accelerate the dissociation of oxygen molecules to generate active oxygen (O - or O 2- ), and promote the dehydrogenation and oxidation of ammonia of 2,4-dichlorotoluene (DCT); the strong oxidizing property of molybdenum combined with the stability of tungsten can inhibit the excessive oxidation side reaction, such as the generation of CO2 or chlorinated by-products, and improve the selectivity of 2,4-dichlorobenzonitrile; at the same time, the introduction of tungsten can inhibit the generation of carbon deposition and prolong the service life of the catalyst. 3+ / Ce 4+ is not cycled, the carbon deposition rate increases, and the selectivity decreases; in Comparative Example 2, the metal oxide does not contain lanthanum, the pore size is out of control, the amount of by-products such as chlorinated aromatic hydrocarbons increases, and the yield decreases; in Comparative Example 3, the active metal is unevenly loaded, and part of the sites are deactivated; in Comparative Example 4, the excess of the active liquid causes the blockage of the pore channels of the carrier, the mass transfer is limited, and the single-pass yield decreases significantly.

[0048] Example 7

[0049] Different from Example 2, the pH of the precursor solution is 10, the pre-crystallization temperature is 45℃, the pre-crystallization time is 15h, the crystallization temperature is 130℃, the crystallization time is 4h, the calcination temperature of the catalyst precursor is 550℃, the calcination time is 6h, the first-stage heating rate after the addition of the active metal mixed solution is 3℃ / min, the first-stage calcination temperature is 350℃, the first-stage calcination time is 1h, the second-stage heating rate after the addition of the active metal mixed solution is 6℃ / min, the second-stage calcination temperature is 550℃, the second-stage calcination time is 2.5h, and the molar mass ratio of SiO2, Al2O3, TPABr, PEG-6000, Na2O and H2O is 5:400:0.2:0.1:0.03:30.

[0050] Example 8

[0051] The precursor solution pH is 10, the pre-crystallization temperature is 40°C, the pre-crystallization time is 20h, the crystallization temperature is 150°C, the crystallization time is 1h, the calcination temperature of the catalyst precursor is 500°C, the calcination time is 8h, the first temperature increasing rate after adding the active metal mixed solution is 2°C / min, the first calcination temperature is 280°C, the first calcination time is 1h, the second temperature increasing rate after adding the active metal mixed solution is 5°C / min, the second calcination temperature is 500°C, the second calcination time is 3.5h, and the molar mass ratio of SiO2, Al2O3, TPABr, PEG-6000, Na2O and H2O is 2:800:0.3:0.1:0.01:30.

[0052] In Comparative Example 5, the precursor solution does not undergo the pre-crystallization process, and directly undergoes the crystallization process, and the other processes are the same as those in Example 2.

[0053] In Comparative Example 6, the precursor solution does not undergo the pre-crystallization and crystallization processes, and directly undergoes the filtration and drying to obtain the catalyst precursor, and the other processes are the same as those in Example 2.

[0054] In Comparative Example 7, only the first temperature increasing and calcination are performed after adding the active metal mixed solution, the temperature increasing rate is 5°C / min, the calcination temperature is 500°C, and the calcination time is 5h, and the other processes are the same as those in Example 2.

[0055] In Comparative Example 8, the 1 mol / L ammonium chloride solution is not used for the exchange, and the other processes are the same as those in Example 2.

[0056] In Comparative Example 9, the adding sequence of the active metal mixed solution is changed, specifically, the catalyst precursor is cooled to room temperature, the exchange is performed using the ammonium chloride solution, the filtration and drying are performed, then the active metal mixed solution is mixed, the temperature is increased from room temperature to 300°C at a rate of 2°C / min, the calcination is performed for 1.5h, then the temperature is increased to 500°C at a rate of 5°C / min, the calcination is performed for 3h, and then the catalyst is obtained by cooling to room temperature; and the other processes are the same as those in Example 2.

[0057] Experimental Example 2

[0058] The catalysts obtained in Example 2, Example 7 and Example 8 and Comparative Examples 1-9 are subjected to the catalytic cycle performance test, the influence of 10 times of use on the conversion rate, the selectivity and the single-pass yield is tested, and the final test results are shown in Table 2 and Table 3. Fig. 2

[0059] Table 3 Cycle performance test results

[0060]

[0061] ​After preparing the active metal mixture, a catalyst was prepared using SiO2, Al2O3, TPABr, PEG-6000, NaOH, and H2O as raw materials; NaOH provided OH-. - , with Al 3+ The reaction produces aluminum hydroxide colloid, which serves as the aluminum source for the molecular sieve framework. By controlling the pH to a strongly alkaline state, Al(OH)3 dissolves to form aluminate (AlO). 2- This lays the foundation for the subsequent formation of the aluminosilicate framework; the added tetrapropylammonium bromide organic cation (C3H7)4N + Electrostatic interactions with the negatively charged aluminosilicate framework guide the directional growth of the molecular sieve (MFI) topology and act as a template during calcination, providing loading sites for active metals. PEG-6000, acting as a template and dispersant, prevents particle aggregation through steric hindrance while participating in the formation of mesoporous structures, improving the specific surface area and pore distribution of the molecular sieve. The SiO2 source releases silicate ions (SiO3) upon dissolution. 2- The aluminosilicate gel network is formed through a condensation reaction with aluminates. Controlling strongly alkaline conditions promotes the dissolution-recrystallization process of the aluminosilicate gel, forming a uniform molecular sieve precursor structure. Pre-crystallization at low temperatures slowly forms initial crystal nuclei, avoiding structural defects caused by rapid crystallization. Under hydrothermal crystallization conditions, the aluminosilicate gel further grows around the TPABr template agent, forming ZSM-5 type molecular sieve crystals with regular channels. After calcination, it is mixed with an active metal mixture. The molecular sieve precursor has high porosity and adsorbs metal ions (V) through capillary action. 5+ Ti 4+ Fe 3+ And so on, as well as adsorbing acid / alkali metal ions, the metal ions reacting with Na in the molecular sieve framework + Exchange or physical adsorption fixes the metal precursor onto the pore surface, accelerating the condensation reaction at high temperature and promoting the ordered arrangement of Si and Al framework atoms; low-temperature calcination evaporates moisture, fixing the metal precursor onto the support surface; nitrates undergo initial decomposition, Fe(NO3)3→Fe2O3+NO2+O2, forming small-particle metal oxide nuclei; high-temperature calcination further promotes the crystallization of the metal oxide, forming a highly active phase; simultaneously, it promotes metal-support interaction (SMSI effect), improving stability; acid / alkali metal component K + and Na + Migrating to the active metal interface, it modulates the electron density or acidic site distribution; ammonium chloride solution ion exchange NH4+ 4+ Replace Na in the skeleton + To reduce alkaline sites and avoid excessive reactant adsorption due to over-alkalinity, NH4+ is introduced. 4+ Subsequently, it decomposes into H through calcination. + This forms acidic sites (B-acid centers) and promotes the catalytic process.

[0062] By adjusting the temperature of pre-crystallization and crystallization, the calcination time, the order of adding the active metal mixed solution after the molecular sieve is prepared, and adjusting the calcination process, the conversion rate, selectivity and single-pass yield of 2,4-dichloronitrile can still maintain a high value after the catalyst is recycled. Comparative Example 1 lacks Ce 5+ / Ce 4+ redox cycle, serious carbon deposition, yield drops sharply after recycling; Comparative Example 2 molecular sieve pore size is out of control, by-product generation increases, catalytic performance decreases after recycling; Comparative Example 3 uneven metal loading leads to local deactivation, Comparative Example 4 carrier channel plugging, mass transfer limited, Comparative Example 5 no pre-crystallization leads to loose molecular sieve structure, Comparative Example 6 catalyst structure is disordered, active sites are easy to lose, Comparative Example 7 high temperature rapid calcination leads to metal agglomeration, Comparative Example 8 no use of ammonium chloride to remove the template, residual organic matter plugging the channel, Comparative Example 9 and Comparative Example 10 change the order of loading and the preparation process, the catalytic activity and catalytic recyclability of the final catalyst are significantly reduced. The molecular sieve carrier containing Al and Si is prepared by hydrothermal synthesis method in the embodiment, tetrapropylammonium bromide is used as a template agent, PEG-6000 is used for auxiliary molding, NaOH is used to adjust the alkaline environment to promote the condensation of silicon and aluminum, and the metal mixed solution is directly added on the calcined carrier. The metal components such as V, Ti, Fe and Ce are loaded by physical adsorption or ion exchange, and finally the Na in the carrier is exchanged with NH4Cl solution + , forming H + type or NH 4+ type molecular sieve, enhancing the acid sites, improving the catalytic activity and recycling catalytic stability; Comparative Example 9 first uses the ammonium chloride solution to exchange the Na + in the carrier, which will lead to the enhancement of the surface acidity of the carrier, the hydrolysis of NH 4+ to produce H + , and the reduction of the cation concentration in the channel. At this time, when the active metal mixed solution is loaded, the surface charge density of the carrier is reduced, the electrostatic adsorption force of the metal ions is weakened, which leads to insufficient loading or uneven distribution, and the acid environment makes part of the metal salt such as ammonium metavanadate dissolve or change in the form of hydrolysis, V 5+ forms soluble polyvanadate, which is difficult to deposit on the carrier; and during the calcination process, migration and agglomeration are easy to occur, forming large particle metal oxides, reducing the number of active sites, and reducing the catalytic activity and recycling catalytic stability.

[0063] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A process for preparing a catalyst for the preparation of 2,4-dichlorobenzonitrile, characterized in that: The catalyst is composed of an active component and a support. The active component of the catalyst is as follows: AaTibFecCedCoeFfGgHhOx; Where 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; and H is one of phosphorus and sulfur. In the active component of the catalyst, a takes a value of 1-1.71, b takes a value of 0.13-0.34, c takes a value of 0.06-0.16, d takes a value of 0.04-0.11, e takes a value of 0.02-0.06, f takes a value of 0.03-0.16, g takes a value of 0.03-0.16, h takes a value of 0.01-0.05, and x is the number of oxygen atoms required to satisfy the oxidation states of each element in the catalyst; The catalyst is obtained by mixing an active metal mixture with a catalyst support precursor, followed by two stages of programmed temperature increase, calcination, and exchange followed by drying; the active metal mixture is calcined and exchanged to obtain the active component; the catalyst support precursor is calcined and exchanged to obtain the support; the two-stage calcination is first low-temperature calcination followed by high-temperature calcination; the low-temperature calcination fixes the metal precursor, and the high-temperature calcination promotes the crystallization of metal oxides and enhances the metal-support interaction; The catalyst support precursor is prepared as follows: aluminum sulfate octadecylhydrate is added to sodium hydroxide solution under heating and stirring. After complete dissolution, tetrapropylammonium bromide and polyethylene glycol are added, and finally silica gel is added. After complete dissolution, the pH is adjusted to 10-11 to obtain the precursor solution. The precursor solution is then subjected to pre-crystallization, crystallization, filtration, washing, drying, and calcination to obtain the catalyst support precursor. The exchange is performed using an ammonium chloride solution; the pre-crystallization temperature during the preparation of the catalyst support precursor is 40-50℃ for 12-20h; the crystallization temperature is 130-150℃ for 1-4h.

2. The preparation process of a catalyst for the preparation of 2,4-dichlorobenzonitrile according to claim 1, characterized in that: The precursor solution for preparing A is selected from one or two of ammonium metavanadate solution, ammonium molybdate solution, and ammonium metatungstate solution; the precursor solution for preparing F is selected from one of lanthanum nitrate solution, yttrium nitrate solution, neodymium nitrate solution, and praseodymium nitrate solution; the precursor solution for preparing G is selected from one of potassium chloride solution, magnesium chloride solution, and sodium chloride solution; and the precursor solution for preparing H is selected from one of phosphoric acid solution and sulfuric acid solution.

3. The preparation process of a catalyst for the preparation of 2,4-dichlorobenzonitrile according to claim 1, characterized in that: The catalyst is prepared as follows: the active metal mixture is added to the catalyst support precursor, and a catalyst intermediate is obtained by first heating and first calcination, second heating and second calcination; the catalyst intermediate is then exchanged and dried to obtain the catalyst.

4. A catalyst for the preparation of 2,4-dichlorobenzonitrile, characterized in that: The catalyst is obtained by supporting the active ingredient on a support; the catalyst is prepared by the preparation process described in any one of claims 1-3.

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