A supported propylene aldehyde selective oxidation catalyst and a method for preparing the same

Abstract

This invention discloses a supported acrolein selective oxidation catalyst and its preparation method, relating to the field of acrolein oxidation technology. The catalyst comprises: an inert porous inorganic support and a mixed metal oxide active component supported on the surface of the inert porous inorganic support; the mixed metal oxide active component includes oxides of molybdenum, vanadium, and tungsten. This invention achieves strong anchoring of the active component on the support surface through chemical bonding, effectively resisting airflow erosion and extending its service life. Simultaneously, it utilizes the spatial confinement effect to inhibit metal particle agglomeration, forming abundant nanopores in situ, improving the dispersion of active sites and reaction mass transfer efficiency, making it suitable for various operating conditions.

Description

Technical Field

[0001] This invention relates to the field of acrolein oxidation technology, specifically to a supported acrolein selective oxidation catalyst and its preparation method. Background Technology

[0002] The selective oxidation of acrolein to acrylic acid is a core process technology in the petrochemical industry. It typically employs a fixed-bed reactor and utilizes supported metal oxide catalysts to convert gaseous acrolein into acrylic acid through a heterogeneous catalytic reaction under specific temperature and pressure conditions. The basic principle is to support the active components with an inert support, allowing reactant molecules to adsorb, react, and desorb at active sites on the catalyst surface as the feed gas flows through the catalyst bed. This enables the continuous production of the target product. It relies on the stability of the catalyst in the reaction environment and the effective utilization rate of the active sites, making it a crucial link in the modern chemical industry chain.

[0003] To ensure production efficiency and safe operation of the equipment, sufficient active metal oxides are typically loaded onto the surface of a support using physical or chemical methods, and these oxides must maintain good dispersion on the support. However, in actual industrial production processes, catalysts are subjected to high-speed scouring by high-temperature gas flows and complex chemical environments for extended periods. Existing supported catalysts are prone to insufficient bonding between the active components and the support. Due to the lack of a stable microscopic bonding mechanism, active substances are prone to migration, aggregation, and even detachment during long-term reactions. This not only leads to a gradual decrease in the catalyst's reactivity and selectivity, shortening its lifespan, but also causes detached dust particles to deposit in downstream pipelines, resulting in pipeline blockage or increased back pressure, making product separation difficult and posing significant safety hazards and economic losses to the continuous and stable operation of the production equipment. Summary of the Invention

[0004] The purpose of this invention is to provide a supported acrolein selective oxidation catalyst and its preparation method, thereby solving the problems existing in the background art.

[0005] To address the aforementioned technical problems, this invention provides a supported acrolein selective oxidation catalyst, comprising an inert porous inorganic support and a mixed metal oxide active component supported on the surface of the inert porous inorganic support; the mixed metal oxide active component comprises oxides of molybdenum, vanadium, and tungsten.

[0006] The supported acrolein selective oxidation catalyst is prepared by the following method: synthesizing hyperbranched polymers modified with alkoxysilane functional groups as molecular bridging agents, and utilizing the amino groups on the molecular chain of the molecular bridging agent to chemically combine with molybdenum, vanadium and tungsten metal precursor ions to form organic-inorganic hybrid precursors.

[0007] The organic-inorganic hybrid precursor is chemically bonded and anchored to the surface of an inert porous inorganic support by hydrolysis of the alkoxysilane functional group and condensation reaction with the hydroxyl groups on the support surface.

[0008] The organic polymer skeleton is removed by programmed heating and calcination, resulting in the formation of highly dispersed mixed metal oxide active components in situ.

[0009] Preferably, the inert porous inorganic carrier is selected from one or a mixture of several of silica, alumina or silicon carbide;

[0010] The specific surface area of ​​the inert porous inorganic carrier is 10. 50 The aperture distribution is 10 100nm;

[0011] In the active component of the mixed metal oxide, the molar ratio of metal elements is Mo:V:W = 12:(2). 6):(0.5 3).

[0012] Preferably, the preparation method of the molecular bridging agent is as follows: dissolving hyperbranched polyethyleneimine in anhydrous ethanol and preparing it to a mass concentration of 5% under ultrasonic dispersion conditions. 10% polymer solution;

[0013] While stirring, 3-(2,3-epoxypropoxy)propyltrimethoxysilane was added dropwise to the polymer solution. After the addition was complete, the temperature was raised to 50°C. 70℃, maintain reflux and stirring for 4 days 6 hours;

[0014] During the reaction, the epoxy group of 3-(2,3-epoxypropoxy)propyltrimethoxysilane undergoes a ring-opening addition reaction with some of the terminal amino groups of hyperbranched polyethyleneimine to obtain a silanized hyperbranched polymer solution that contains both trimethoxysilane anchoring groups and retains free amino binding sites, which is the molecular bridge aid.

[0015] The mass ratio of hyperbranched polyethyleneimine to 3-(2,3-epoxypropoxy)propyltrimethoxysilane is 1:(0.2). 0.8).

[0016] Preferably, the formation process of the organic-inorganic hybrid precursor is as follows:

[0017] Ammonium heptamolybdate, ammonium metavanadate, and ammonium metatungstate were dissolved in deionized water at 60 °C. Stirring at 80℃ in a water bath until completely dissolved to obtain a mixed metal salt aqueous solution;

[0018] The molecular bridging agent was slowly added dropwise to the mixed metal salt aqueous solution, with the dropping rate controlled at 2. 5 mL / min, with vigorous mechanical stirring maintained during the dropwise addition process;

[0019] After the dripping is finished, continue at 40 Stirring at 50℃ for 2 hours After 4 hours, the polyoxometalate ions and the free amino groups of the hyperbranched polymer are fully contacted and chemically bonded. After standing and degassing, a homogeneous and transparent organic-inorganic hybrid precursor solution is obtained.

[0020] Preferably, the chemical bonding anchoring process is as follows:

[0021] The pre-treated, dry, inert porous inorganic support was immersed in the organic-inorganic hybrid precursor solution;

[0022] Ultrasonic oscillation impregnation was performed in a closed system for 30 minutes. 60 minutes to expel air from the carrier pores;

[0023] The system was then heated to 70 degrees Celsius. At 90℃, the solvent is slowly evaporated, which initiates the hydrolysis of methoxysilane on the molecular bridge agent and causes a de-alcoholization condensation reaction with the silanol or aluminum hydroxyl groups on the surface of the support to form covalent bonds.

[0024] After the solvent has evaporated to dryness, place the solid product in a vacuum drying oven at 100°C. Dry at 120℃ for 10 minutes After 12 hours, a modified carrier grafted with a metal complex was obtained.

[0025] A method for preparing a supported acrolein selective oxidation catalyst is also provided, comprising the following steps:

[0026] Step 1: Construction of molecular bridge aid: The amino-rich hyperbranched polymer is modified by using an epoxy-containing silane coupling agent. By controlling the mass ratio of the reactants, the product can simultaneously possess the residual amino groups for binding metals and the alkoxysilane groups for anchoring the carrier.

[0027] Step 2, Pre-assembly of active components: The metal salt solutions of molybdenum, vanadium and tungsten are mixed with the molecular bridging agent prepared in Step 1. Through liquid-phase chemical bonding reaction, the amino groups in the hyperbranched polymer are combined with metal ions to prepare a homogeneous hybrid precursor liquid.

[0028] Step 3, In-situ Grafting and Curing: The inert carrier is placed in the hybrid precursor liquid, and the alkoxysilane is hydrolyzed and condensed with the hydroxyl groups on the carrier surface by heating. The polymer segments loaded with metal are chemically grafted onto the carrier surface, and the solvent is removed by drying.

[0029] Step 4, High-temperature calcination activation: The dried solid obtained in step 3 is subjected to multi-stage programmed heating calcination in an oxygen-containing atmosphere. The organic polymer skeleton is removed by oxidative decomposition, and mixed metal oxide nanoclusters are generated in situ at the anchoring sites on the carrier surface.

[0030] Preferably, the specific process for the multi-stage programmed heating and calcination in step four is as follows:

[0031] Phase 1: Starting with 1 A heating rate of 2℃ / min was used to raise the temperature from room temperature to 150℃. 180℃, heat preservation 1 2 hours to remove physically adsorbed water and residual solvent;

[0032] Phase Two: with 0.5 The heating rate increased to 300℃ / min. 320℃, heat preservation 2 Three hours later, thermal decomposition and carbonization of the hyperbranched polymer backbone were initiated.

[0033] Phase Three: Using 2 The heating rate was increased to 400℃ at a rate of 5℃ / min. 450℃, heat preservation 4 The organic residues were completely removed by oxidation and combustion over 6 hours, and the metal oxides were allowed to form a crystalline structure.

[0034] An airflow is introduced throughout the calcination process, with the air velocity controlled at 500. 1000 .

[0035] Preferably, in step two, the total molar amount of metal ions in the molybdenum, vanadium, and tungsten metal salt solution to the molar ratio of the remaining amino groups in the hyperbranched polymer of step one is 1:(2). 4).

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] By constructing a stable chemical bond between the active component and the inert support, the problem of weak binding force of active materials in traditional catalysts is solved. By using specific chemical methods, the metal precursor is firmly anchored on the surface and inside the pores of the support, which can effectively resist the continuous scouring and mechanical wear of industrial reaction gas flow. It exhibits excellent mechanical stability under harsh reaction conditions, and the shedding rate of the active component is extremely low, thereby extending the service life of the catalyst and ensuring the safety and stability of the long-term operation of the reaction device.

[0038] By utilizing the unique spatial confinement effect, the uniform dispersion of active metal oxides at the microscale is achieved. Through the physical encapsulation and isolation of metal ions, the sintering and agglomeration of active particles during high-temperature calcination are effectively suppressed, ensuring that the final catalyst surface has a high density of active sites. After removing the organic framework, a rich nanoporous structure can be formed in situ on the support surface, which is conducive to the rapid diffusion of reactant molecules and the timely desorption of products, thereby improving the mass transfer efficiency of the catalytic reaction and the selectivity of the target product.

[0039] It has good versatility for various types of support materials. It can achieve uniform loading of active components regardless of the specific surface area or material of the support. By flexibly adjusting the process parameters, the preparation cost can be optimized while ensuring high performance. The heat treatment process is reasonably designed to avoid structural damage caused by violent exothermic reaction. This makes the prepared catalyst have both good thermal conductivity and thermal shock resistance, and it is particularly suitable for complex industrial reaction systems with high flow rate and strong exothermic reaction. Detailed Implementation

[0040] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0041] Before formal preparation, a dynamic correlation model between the amino density of the hyperbranched polymer and the coordination saturation of metal ions was established to determine the optimal molecular bridge auxiliaries construction parameters and metal loading.

[0042] The specific method is as follows: in alcohol-water mixed solvent systems with different pH values, the isothermal adsorption curves of hyperbranched polyethyleneimine for Mo, V, and W polyoxometalate ions are determined by conductivity titration.

[0043] Regression analysis data showed that when the pH of the system was controlled in the range of 4.5–5.5, the primary amines at the ends of the hyperbranched polyethyleneimine exhibited a significant synergistic effect of electrostatic attraction and coordination chelation with the polyoxometalate ions, and the Langmuir adsorption model showed a good fit. ;

[0044] Specifically, this manifests as follows: Low loading region: When the metal / amino molar ratio is <1:4, metal ions mainly bind to the outer layer of the polymer through monodentate coordination, resulting in a small steric hindrance effect, but insufficient loading of active components; Saturated region: When the metal / amino molar ratio is in the range of 1:2 to 1:4, metal ions can penetrate deep into the internal cavity of the polymer, forming a stable core-shell hybrid structure. At this time, the hyperbranched topology effectively isolates the metal clusters and prevents them from agglomerating; Overload region: When the metal / amino molar ratio is >1:2, excessive metal salts cause the polymer molecular chains to coil and precipitate, destroying the stability of the homogeneous system.

[0045] Based on the above correlation model, the molar ratio of the total molar amount of metal ions to the molar ratio of the remaining amino groups in the hyperbranched polymer is set as 1:(2~4) as the key control index to ensure the formation of a homogeneous, transparent and structurally stable organic-inorganic hybrid precursor.

[0046] Example 1

[0047] This embodiment provides a supported acrolein selective oxidation catalyst and its preparation method, which is used to prepare a molecular bridging agent: Hyperbranched polyethyleneimine with a weight-average molecular weight of 25000 g / mol is dissolved in anhydrous ethanol and prepared into a polymer solution with a mass concentration of 8% under ultrasonic dispersion conditions. Specifically, 4.0 g of hyperbranched polyethyleneimine is weighed and dissolved in 46.0 g of anhydrous ethanol; under stirring, 3-(2,3-epoxypropoxy)propyltrimethoxysilane is added dropwise to the polymer solution, wherein the mass ratio of hyperbranched polyethyleneimine to 3-(2,3-epoxypropoxy)propyltrimethoxysilane is set to 1:0. 0.5, that is, 2.0g of the silane coupling agent is added; after the addition is complete, the temperature is raised to 60℃ and the reaction is carried out under reflux and stirring for 5 hours; during this process, the epoxy group of 3-(2,3-epoxypropoxy)propyltrimethoxysilane undergoes a ring-opening addition reaction with some of the terminal amino groups of hyperbranched polyethyleneimine to obtain a silanized hyperbranched polymer solution that contains both trimethoxysilane anchoring groups and retains free amino binding sites, which is the molecular bridge aid; in this step, the reaction temperature and time are strictly controlled to ensure the complete ring opening of the epoxy group, while retaining an appropriate amount of primary amino groups for subsequent metal coordination, thus constructing a bifunctional molecular bridge with both anchoring and grasping functions;

[0048] In this embodiment, silica is selected as an inert porous inorganic carrier, with a specific surface area of ​​[missing information]. The pore size distribution is 50 nm, and this specific pore structure facilitates the diffusion and mass transfer of acrolein molecules within the catalyst; in the mixed metal oxide active components, the molar ratio of metal elements is controlled to be... This ratio is designed to balance redox potential and acidic sites to achieve optimal selectivity;

[0049] In the specific operation of this embodiment, ammonium heptamolybdate is used. Ammonium metavanadate and ammonium metatungstate The following ingredients were dissolved in deionized water: 3.64 g ammonium heptamolybdate, 0.80 g ammonium metavanadate, and 0.74 g ammonium metatungstate were dissolved in 50 mL of deionized water and stirred in a 70°C water bath until completely dissolved. The molecular bridging agent prepared above was slowly added dropwise to the mixed metal salt aqueous solution at a rate of 3 mL / min, with strong mechanical stirring maintained during the addition. At this point, the molar ratio of the total molar amount of metal ions to the molar ratio of the remaining amino groups in the hyperbranched polymer was controlled at 1:3. After the addition was completed, the mixture was stirred at a constant temperature of 45°C for 3 hours to allow the polyoxometalate ions to fully contact and chemically combine with the free amino groups of the hyperbranched polymer. After standing and degassing, a homogeneous and transparent organic-inorganic hybrid precursor solution was obtained. This step utilizes the nanocavities inside the hyperbranched polymer to physically encapsulate and chemically coordinate the metal ions, forming a molecular-level pre-assembled structure, which effectively prevents the crystallization and precipitation of metal salts during the subsequent drying process.

[0050] In this specific embodiment, 10.0 g of pre-treated silica support was immersed in the above-mentioned organic-inorganic hybrid precursor solution and subjected to ultrasonic vibration for 45 minutes in a closed system to remove air from the pores of the support and ensure that the precursor liquid could fully fill the pores. Subsequently, the system was heated to 80°C and the solvent was slowly evaporated, which triggered the hydrolysis of methoxysilane on the molecular bridging agent and a de-alcoholization condensation reaction with the silanol groups on the surface of the support to form covalent bonds. After the solvent evaporated to dryness, the solid product was placed in a vacuum drying oven and dried at 110°C for 12 hours to obtain a modified support grafted with metal complexes. This step, through the formation of covalent bonds, firmly anchors the active components to the surface of the support, solving the problem of weak bonding in the traditional impregnation method.

[0051] In this embodiment, the organic polymer skeleton is finally removed by programmed temperature calcination: the dried solid is subjected to multi-stage programmed temperature calcination in air; the first stage raises the temperature from room temperature to 160°C at a rate of 2°C / min and holds for 1.5 hours to gently remove the solvent and prevent the coating from cracking; the second stage raises the temperature to 310°C at a rate of 1°C / min and holds for 2.5 hours, during which the polymer skeleton begins to carbonize, acting as a separator for metal particles; the third stage raises the temperature to 420°C at a rate of 3°C / min and holds for 5 hours to completely burn off the carbon deposits and form an active crystalline phase; the space velocity is controlled throughout the calcination process. This multi-stage calcination process utilizes the in-situ occupancy effect of polymers, leaving abundant nanopores after calcination, thus achieving high dispersion of active components.

[0052] Example 2

[0053] This embodiment provides a supported acrolein selective oxidation catalyst and its preparation method, focusing on adjusting the support type and the grafting density of the molecular bridge agent. In the preparation of the molecular bridge agent: hyperbranched polyethyleneimine with a weight-average molecular weight of 10000 g / mol is selected, 5.0 g is weighed and dissolved in ethanol, and its mass ratio with 3-(2,3-epoxypropoxy)propyltrimethoxysilane is set at 1:0.2, i.e., 1.0 g of silane is added; the reaction is refluxed and stirred at 50°C for 4 hours. At this ratio, more free amino groups are retained on the polymer chain for metal binding, suitable for high metal loading requirements. In the formation of the organic-inorganic hybrid precursor: the molar ratio of the metal element is controlled as follows: The molecular bridging agent was added dropwise at a rate of 2 mL / min to a mixed metal salt aqueous solution (containing 8.38 g ammonium heptamolybdate, 0.93 g ammonium metavanadate, and 0.49 g ammonium metatungstate); the total molar ratio of metal ions to the remaining amino groups in the hyperbranched polymer was controlled at 1:2; the mixture was stirred at 40 °C for 2 hours; in the chemical bonding anchoring process: 10.0 g alumina was selected as an inert porous inorganic carrier with a specific surface area of ​​[missing information]. The pore size distribution is 10 nm; the support is immersed in the precursor solution and ultrasonically vibrated for 30 minutes; then the temperature is raised to 70 °C and the solvent is slowly evaporated; the solid product is vacuum dried at 100 °C for 10 hours; during the calcination process: in the first stage, the temperature is raised to 150 °C at 1 °C / min and held for 1 hour; in the second stage, the temperature is raised to 300 °C at 0.5 °C / min and held for 2 hours; in the third stage, the temperature is raised to 400 °C at 2 °C / min and held for 4 hours; the space velocity is controlled at... In this embodiment, the combination of a low silane ratio and alumina support verifies the applicability of this method on different support surfaces. Through chemical bonding, the active components can be uniformly spread even on supports with low specific surface area, and the low-W formulation helps to reduce catalyst costs.

[0054] Example 3

[0055] This embodiment provides a supported acrolein selective oxidation catalyst and its preparation method, focusing on a high tungsten content formulation and high anchoring density to improve the catalyst's heat resistance and lifespan. In the preparation of the molecular bridge agent: hyperbranched polyethyleneimine with a weight-average molecular weight of 70,000 g / mol is prepared into a 10% (w / w) polymer solution; 3.0 g of hyperbranched polyethyleneimine is weighed; 3-(2,3-epoxypropoxy)propyltrimethoxysilane is added dropwise at a mass ratio of 1:0.8, i.e., 2.4 g of silane is added; the reaction is refluxed and stirred at 70°C for 6 hours; the high proportion of silane coupling agent significantly increases the anchoring site density and strengthens the binding force between the polymer and the support; in the formation of the organic-inorganic hybrid precursor: the molar ratio of metal elements is controlled to... Dissolved in an 80℃ water bath (containing 1.74g ammonium heptamolybdate, 0.58g ammonium metavanadate, and 0.61g ammonium metatungstate); the molecular bridging agent was added dropwise at a rate of 5mL / min; the molar ratio of the total molar amount of metal ions to the remaining amino groups in the hyperbranched polymer was controlled at 1:4; the mixture was stirred at 50℃ for 4 hours to ensure that the high concentration of metal ions was fully chelated; in the chemical bonding anchoring: 10.0g silicon carbide was selected as an inert porous inorganic carrier with a specific surface area of... The pore size distribution is 100 nm; the impregnation process involves ultrasonic vibration for 60 minutes; followed by heating to 90 °C to evaporate the solvent; the solid product is then vacuum dried at 120 °C for 12 hours; during calcination: in the first stage, the temperature is increased to 180 °C at 2 °C / min and held for 2 hours; in the second stage, the temperature is increased to 320 °C at 1 °C / min and held for 3 hours; in the third stage, the temperature is increased to 450 °C at 5 °C / min and held for 6 hours; the space velocity is controlled at... The catalyst prepared in this embodiment is particularly suitable for high-flow-rate, highly exothermic reaction conditions due to its high-density chemical bonding anchoring and the excellent thermal conductivity of the silicon carbide support. The active components have extremely strong resistance to loss.

[0056] Example 4

[0057] This embodiment provides a supported acrolein selective oxidation catalyst and its preparation method, employing a mixed support system. In the preparation of the molecular bridging agent: 4.0 g of hyperbranched polyethyleneimine with a weight-average molecular weight of 25000 g / mol was weighed, and the mass ratio of 4.0 g of the catalyst to 3-(2,3-epoxypropoxy)propyltrimethoxysilane was set to 1:0.4, i.e., 1.6 g of silane was added. The reaction temperature was 55℃, and the reaction time was 4.5 hours. In the formation of the organic-inorganic hybrid precursor: the molar ratio of the metal elements was controlled to... The total molar ratio of metal ions to the remaining amino groups in the hyperbranched polymer was controlled at 1:2.5; the mixed metal salt solution contained 4.87 g ammonium heptamolybdate, 0.81 g ammonium metavanadate, and 0.57 g ammonium metatungstate; the dropping rate was 4 mL / min; in chemical bonding anchoring: a mixture of silica and silicon carbide, with a mass ratio of 1:1 and a total mass of 10.0 g, was selected as an inert porous inorganic carrier with a specific surface area of ​​approximately Ultrasonic impregnation for 50 minutes, solvent evaporation at 85℃; vacuum drying at 115℃ for 11 hours; during calcination: first stage heating to 170℃, holding for 1.5 hours; second stage heating to 315℃, holding for 2.5 hours; third stage heating to 430℃, holding for 4.5 hours; space velocity... This embodiment demonstrates that the molecular bridging agent can adapt to the complex hydroxyl distribution on the surface of the mixed support, and can still form a stable organic-inorganic hybrid layer by adjusting the reaction parameters, exhibiting excellent process compatibility.

[0058] Example 5

[0059] This embodiment provides a supported acrolein selective oxidation catalyst and its preparation method, exploring intermediate parameter ranges to balance activity and cost. In the preparation of the molecular bridging agent: 4.0 g of hyperbranched polyethyleneimine with a weight-average molecular weight of 25000 g / mol was weighed and its mass ratio to 3-(2,3-epoxypropoxy)propyltrimethoxysilane was set to 1:0.6, i.e., 2.4 g of silane was added; the reaction temperature was 65℃, and the reaction time was 5.5 hours. In the formation of the organic-inorganic hybrid precursor: the molar ratio of the metal elements was controlled to... The total molar ratio of metal ions to the remaining amino groups in the hyperbranched polymer was controlled at 1:3.5; the mixed metal salt solution contained 2.86 g ammonium heptamolybdate, 0.79 g ammonium metavanadate, and 0.83 g ammonium metatungstate; in chemical bonding anchoring: 10.0 g alumina was selected as an inert porous inorganic carrier; ultrasonic impregnation for 40 minutes, solvent evaporation at 75°C; vacuum drying at 105°C for 11 hours; during calcination: the first stage temperature was increased to 165°C; the second stage temperature was increased to 305°C; the third stage temperature was increased to 440°C; space velocity... This embodiment further verifies the controllability of process parameters. The prepared catalyst maintains high dispersibility while promoting the diffusion of the reactant acrolein through optimized pore structure, thereby achieving optimal catalytic efficiency.

[0060] Comparative Example 1

[0061] This comparative example uses the conventional equal-volume impregnation method to prepare the catalyst, without using the molecular bridging agent of this invention. Ammonium heptamolybdate, ammonium metavanadate, and ammonium metatungstate, in equal amounts as in Example 1, are dissolved in deionized water without adding any polymers. This mixed metal salt solution is directly impregnated onto a 10.0 g silica support, identical to that in Example 1. The same drying and calcination procedures are followed. This comparative example serves as a blank control to verify the core role of the molecular bridging agent in the dispersion and anchoring of the active components. Due to the lack of chemical bonding anchoring and the dispersion effect of hyperbranched polymers, the active components mainly adhere to the support through physical adsorption and are prone to aggregation during calcination.

[0062] Comparative Example 2

[0063] This comparative example employs a physical mixing method, using unmodified hyperbranched polyethyleneimine without introducing silane functional groups. During preparation, pure hyperbranched polyethyleneimine that has not reacted with 3-(2,3-epoxypropoxy)propyltrimethoxysilane is mixed with the metal salt. Although the hyperbranched polymer can play a certain role in dispersing metal ions, due to the lack of alkoxysilane functional groups, the organic-inorganic hybrid precursor cannot chemically bond and anchor to the surface of the inert porous inorganic support. During subsequent solvent evaporation and calcination, the active component is prone to phase separation and migration on the support surface. This comparative example is used to verify the necessity of alkoxysilane functional groups in achieving chemical anchoring.

[0064] Comparative Example 3

[0065] In this comparative example, a linear polymer was used instead of a hyperbranched polymer; linear polyethyleneimine was used instead of the hyperbranched polyethyleneimine in Example 1, and silanization modification and catalyst preparation were carried out according to the method of Example 1; since the linear polymer lacks the unique three-dimensional cavity structure of the hyperbranched polymer, its ability to encapsulate and disperse metal ions is weak, and it is difficult to form a nanoporous structure similar to that generated in situ in Example 1 after calcination to remove the organic framework; this comparative example aims to verify the unique advantages of hyperbranched topology in constructing highly dispersed active sites.

[0066] Comparative Example 4

[0067] This comparative example modifies the calcination process, abandoning programmed temperature calcination and instead employing a one-step direct heating method. After obtaining the dried solid according to the pretreatment steps of Example 1, the temperature was directly increased to 420°C at a rate of 5°C / min and held for 5 hours, without setting intermediate low-temperature drying and medium-temperature carbonization stages. This comparative example is used to verify the effect of multi-stage programmed temperature calcination on maintaining the dispersion state of active components and the integrity of the pore structure. Rapid heating can easily lead to violent combustion of the organic framework, causing local overheating and coating cracking.

[0068] Verification test

[0069] Structural characterization and performance testing were performed on the supported acrolein selective oxidation catalysts prepared in Examples 1-5 and Comparative Examples 1-4. The test results are shown below:

[0070] Catalytic performance evaluation test method: Each catalyst sample was loaded into a fixed-bed reactor for performance evaluation; the inner diameter of the reaction tube was 25 mm, and the catalyst loading was 10 mL; the reaction conditions were set as follows: reaction temperature 260℃, atmospheric pressure, feed gas composition of acrolein:oxygen:nitrogen:water vapor = 5:7:50:38 (molar ratio), and space velocity of [missing information]. The reaction products were analyzed online by gas chromatography to calculate the acrolein conversion rate, acrylic acid selectivity, and acrylic acid yield; the data were the average values ​​after the reaction had been running stably for 48 hours.

[0071] Mechanical stability test (active component shedding rate) test procedure: To evaluate the mechanical stability of the catalyst and the binding strength of the active component, an ultrasonic shedding test was performed on each catalyst sample; 5.00g of catalyst sample was accurately weighed and placed in a beaker containing 50mL of deionized water; the beaker was placed in an ultrasonic cleaner (100W power, 40kHz frequency) and ultrasonically vibrated for 30 minutes; after ultrasonication, the solid was filtered and collected, dried at 120℃ to constant weight, and the mass of the remaining solid was weighed; the active component shedding rate was calculated using the formula: shedding rate (%) = [(mass before treatment - mass after treatment) / theoretical mass of the loaded active component] × 100%. This test simulates the fluid erosion and mechanical wear environment that the catalyst may suffer in industrial plants;

[0072] Surface dispersibility characterization (XPS surface atomic ratio) test method description: X-ray photoelectron spectroscopy is used to analyze the elemental composition of the catalyst surface; the atomic ratio of Mo, V, W elements to the support elements is calculated by integration. The higher the ratio, the better the spreading and coverage of the active component on the support surface and the higher the dispersibility.

[0073] Table 1 Catalyst performance test data for each embodiment and comparative example

[0074]

[0075] Results Analysis: As shown in Table 1, the supported acrolein selective oxidation catalyst prepared by the method of the present invention has significantly better overall performance than the comparative examples.

[0076] The key role of the chemical anchoring mechanism: Comparing Example 1 with Comparative Examples 1 and 2, it can be seen that the sample with the introduction of molecular bridge aid and chemical bonding anchoring shows an order-of-magnitude decrease in the detachment rate of the active component; Comparative Examples 1 and 2, due to the lack of covalent bond connection, rely solely on physical adsorption for the active component, which is easily detached under ultrasonic oscillation; This strongly confirms that the alkoxysilane hydrolysis and condensation step in this invention is the decisive factor in achieving the stability of the catalyst structure and effectively inhibits the loss of components during the reaction process;

[0077] Microscopic regulation effect of hyperbranched structure: Compared with Comparative Example 3, Example 1 showed a higher conversion rate and a higher XPS surface atomic ratio; this indicates that the unique spherical three-dimensional topology and internal cavity of the hyperbranched polymer can more effectively disperse and isolate metal ions, prevent sintering and agglomeration during calcination, and thus construct a higher density of active sites in situ on the support surface; linear polymers have relatively limited dispersion ability due to chain segment entanglement.

[0078] Effect of calcination process: Compared with Comparative Example 4, Example 1 showed significantly higher selectivity for acrylic acid; this is because multi-stage programmed temperature calcination allows for the orderly decomposition of the organic framework, leaving abundant mesoporous channels in situ, which is conducive to the timely desorption of acrylic acid and reduces the occurrence of deep oxidation side reactions; while the violent combustion in Comparative Example 4 destroyed the microstructure of the coating, resulting in a decrease in the atomic ratio of XPS surface and insufficient exposure of active sites.

[0079] In summary, this invention, through the design of molecular bridge additives, cleverly combines chemical anchoring and hyperbranching dispersion technologies, along with an optimized calcination process, successfully solving the problems of easy aggregation and loss of active components in existing technologies. The prepared catalyst possesses high activity, high selectivity, and excellent mechanical stability.

[0080] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments that can be applied to other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A supported acrolein selective oxidation catalyst, characterized in that, It includes an inert porous inorganic support and a mixed metal oxide active component loaded on the surface of the inert porous inorganic support; the mixed metal oxide active component includes oxides of molybdenum, vanadium and tungsten; The supported acrolein selective oxidation catalyst is prepared by the following method: synthesizing hyperbranched polymers modified with alkoxysilane functional groups as molecular bridging agents, and utilizing the amino groups on the molecular chain of the molecular bridging agent to chemically combine with molybdenum, vanadium and tungsten metal precursor ions to form organic-inorganic hybrid precursors. The organic-inorganic hybrid precursor is chemically bonded and anchored to the surface of an inert porous inorganic support by hydrolysis of the alkoxysilane functional group and condensation reaction with the hydroxyl groups on the support surface. The organic polymer skeleton is removed by multi-stage temperature calcination, and highly dispersed mixed metal oxide active components are formed in situ. In the active component of the mixed metal oxide, the molar ratio of metal elements is Mo:V:W = 12:(2~6):(0.5~3); Construction of molecular bridging agents: Modification of amino-rich hyperbranched polymers using epoxy-containing silane coupling agents.

2. The supported acrolein selective oxidation catalyst according to claim 1, characterized in that, The inert porous inorganic carrier is selected from one or a mixture of several of silicon dioxide, alumina, or silicon carbide; The specific surface area of ​​inert porous inorganic carriers is 10~50m². 2 / g, with a pore size distribution of 10~100nm.

3. The supported acrolein selective oxidation catalyst according to claim 1, characterized in that, The specific preparation method of the molecular bridging agent is as follows: dissolve hyperbranched polyethyleneimine in anhydrous ethanol and prepare a polymer solution with a mass concentration of 5%~10% under ultrasonic dispersion conditions; Under stirring, 3-(2,3-epoxypropoxy)propyltrimethoxysilane was added dropwise to the polymer solution. After the addition was complete, the temperature was raised to 50-70°C and the mixture was stirred under reflux for 4-6 hours. During the reaction, the epoxy group of 3-(2,3-epoxypropoxy)propyltrimethoxysilane undergoes a ring-opening addition reaction with some of the terminal amino groups of hyperbranched polyethyleneimine to obtain a silanized hyperbranched polymer solution that contains both trimethoxysilane anchoring groups and retains free amino binding sites, which is the molecular bridge aid. The mass ratio of hyperbranched polyethyleneimine to 3-(2,3-epoxypropoxy)propyltrimethoxysilane is 1:(0.2~0.8).

4. The supported acrolein selective oxidation catalyst according to claim 3, characterized in that, The formation process of organic-inorganic hybrid precursors is as follows: Ammonium heptamolybdate, ammonium metavanadate and ammonium metatungstate were dissolved in deionized water and stirred in a water bath at 60-80°C until completely dissolved to obtain a mixed metal salt aqueous solution. The molecular bridging agent was slowly added dropwise to the mixed metal salt aqueous solution, with the adding rate controlled at 2-5 mL / min, and strong mechanical stirring was maintained during the adding process. After the addition is complete, continue stirring at a constant temperature of 40~50℃ for 2~4 hours to allow the polymetallic oxoacid ions to fully contact and chemically combine with the free amino groups of the hyperbranched polymer. After standing and degassing, a homogeneous and transparent organic-inorganic hybrid precursor solution is obtained.

5. The supported acrolein selective oxidation catalyst according to claim 4, characterized in that, The specific process of chemical bonding anchoring is as follows: The pre-treated, dry, inert porous inorganic support was immersed in the organic-inorganic hybrid precursor solution; The carrier is immersed in ultrasonic vibration for 30-60 minutes in a closed system to expel air from the carrier pores. The system was then heated to 70-90°C and the solvent was slowly evaporated, which triggered the hydrolysis of the methoxysilane on the molecular bridge agent and caused a de-alcoholization condensation reaction with the silanol or aluminol on the surface of the support to form a covalent bond. After the solvent has evaporated to dryness, the solid product is placed in a vacuum drying oven and dried at 100~120℃ for 10~12 hours to obtain the modified support grafted with metal complex.

6. A method for preparing a supported acrolein selective oxidation catalyst as described in any one of claims 1 to 5, characterized in that, Includes the following steps: Step 1: Construction of molecular bridge aid: The amino-rich hyperbranched polymer is modified by using an epoxy-containing silane coupling agent. By controlling the mass ratio of the reactants, the product can simultaneously possess the residual amino groups for binding metals and the alkoxysilane groups for anchoring the carrier. Step 2, Pre-assembly of active components: The metal salt solutions of molybdenum, vanadium and tungsten are mixed with the molecular bridging agent prepared in Step 1. Through liquid-phase chemical bonding reaction, the amino groups in the hyperbranched polymer are combined with metal ions to prepare a homogeneous hybrid precursor liquid. Step 3, In-situ Grafting and Curing: The inert carrier is placed in the hybrid precursor liquid, and the alkoxysilane is hydrolyzed and condensed with the hydroxyl groups on the carrier surface by heating. The polymer segments loaded with metal are chemically grafted onto the carrier surface, and the solvent is removed by drying. Step 4, High-temperature calcination activation: The dried solid obtained in step 3 is subjected to multi-stage programmed heating calcination in an oxygen-containing atmosphere. The organic polymer skeleton is removed by oxidative decomposition, and mixed metal oxide nanoclusters are generated in situ at the anchoring sites on the carrier surface.

7. The method for preparing a supported acrolein selective oxidation catalyst according to claim 6, characterized in that, The specific process for the multi-stage programmed heating and calcination in step four is as follows: First stage: Increase the temperature from room temperature to 150-180℃ at a rate of 1-2℃ / min, and keep it at that temperature for 1-2 hours to remove physically adsorbed water and residual solvent; Second stage: Increase the temperature to 300-320℃ at a heating rate of 0.5-1℃ / min, and hold for 2-3 hours to induce thermal decomposition and carbonization of the hyperbranched polymer skeleton; The third stage: the temperature is raised to 400-450℃ at a rate of 2-5℃ / min and held for 4-6 hours to completely remove organic residues through oxidation and combustion, and to form a crystalline structure of metal oxides. An airflow is introduced throughout the calcination process, with the air velocity controlled at 500~1000 h⁻¹. -1 .

8. The method for preparing a supported acrolein selective oxidation catalyst according to claim 6, characterized in that, In step two, the total molar amount of metal ions in the molybdenum, vanadium, and tungsten metal salt solution is 1:(2~4) compared with the molar ratio of the remaining amino groups in the hyperbranched polymer in step one.

Images