Method for preparing nano palladium or platinum carbon monoxide combustion improver

Abstract

The invention relates to the technical field of combustion improvers, in particular to a method for preparing a nano palladium or platinum carbon monoxide combustion improver, which comprises the following steps: step 1, weighing 1-5 parts by mass of a palladium-containing or platinum-containing precursor, 0.5-3 parts by mass of a composite surfactant, 2-8 parts by mass of a novel reducing agent, 50-80 parts by mass of a special carrier, 0.5-1.5 parts by mass of a benzoin defoaming agent and 0.3-1 part by mass of a silane coupling agent. According to the present invention, the mesoporous alumina and graphene composite carrier is adopted, the composite carrier effectively inhibits the migration and the agglomeration of the metal particles through the physical confinement effect and the chemical synergistic effect, the wear resistance of the carrier is enhanced, the high thermal conductivity of the graphene can rapidly export the reaction heat, the catalyst deactivation caused by local overheating is avoided, and the catalyst performance is improved. Therefore, the service life of the combustion improver is remarkably prolonged, precious metal consumption is reduced, and environmental burden is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of combustion improvers, in particular to a method for preparing a nano palladium or platinum carbon monoxide combustion improver. Background Art

[0002] A combustion aid refers to a substance that cannot burn itself but can produce the oxygen required for combustion. In a broad sense, all additives used to improve combustion conditions are combustion aids.

[0003] In the prior art, ordinary alumina and other carriers with disordered pore structures are usually used in the preparation process of combustion aids, which causes active metal particles to easily agglomerate under high temperature conditions, reducing the number of active sites and having a low thermal conductivity, which will aggravate the sintering of metal particles and the collapse of the carrier structure. However, the service life of the combustion aid in application is difficult to meet the requirements.

[0004] Based on this, the present invention provides a method for preparing a nano palladium or platinum carbon monoxide combustion promoter. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing a nano palladium or platinum carbon monoxide combustion improver to solve the problems raised by the above background technology.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for preparing a nano palladium or platinum carbon monoxide combustion improver, comprising the following steps: Step 1: Weigh 1-5 parts of palladium- or platinum-containing precursor, 0.5-3 parts of composite surfactant, 2-8 parts of novel reducing agent, 50-80 parts of special carrier, 0.5-1.5 parts of benzoin defoaming agent, and 0.3-1 parts of silane coupling agent according to mass proportions; Step 2: dissolving a palladium- or platinum-containing precursor in deionized water to prepare a solution with a concentration of 0.1-0.5 mol / L; Step 3: In a constant temperature water bath at 50-80° C., stirring the solution at a stirring rate of 300-800 r / min and adding a composite surfactant to obtain a sol; Step 4: using a peristaltic pump to dropwise add the novel reducing agent into the sol at a rate of 0.5-2 mL / min and maintaining the pH value of the reaction system at 8-10, reacting for 1-3 h to obtain a reaction solution; Step 5: fully mixing the reaction solution with the special carrier, adding benzoin defoamer and silane coupling agent, and preparing supported nanoparticles with a particle size of 5-50 nm by spray drying; Step six: subjecting the supported nanoparticles to microwave-assisted calcination treatment. During the treatment, under nitrogen protection, the temperature is raised to 300-400° C. at a heating rate of 10° C. / min and kept at this temperature for 2-3 hours to obtain a nano-palladium or platinum carbon monoxide combustion promoter.

[0007] Preferably, the palladium-containing precursor may be selected from at least one of palladium nitrate and palladium acetate, and the platinum-containing precursor may be selected from at least one of chloroplatinic acid and platinum acetylacetonate.

[0008] Preferably, the composite surfactant is a compound of polyethylene glycol-4000 and cetyltrimethylammonium bromide, and the compounding ratio is (2-5):1.

[0009] Preferably, the novel reducing agent is a mixed solution of hydrazine hydrate and sodium borohydride, the mixed volume ratio is (3-5):1, and the reduction potential is controlled at -(0.8-1.2)V.

[0010] Preferably, the special carrier is prepared by compounding mesoporous alumina and graphene in a mass ratio of 7:3, and the mesoporous alumina has a pore size of 8-12 nm and a three-dimensional interconnected structure.

[0011] Preferably, the method for preparing mesoporous alumina comprises the following steps: Step 1: The mesoporous alumina raw materials include aluminum source and template agent; Step 2: Mixing an aluminum source with deionized water at a molar concentration of 0.5-2 mol / L and stirring at a stirring rate of 200-400 r / min for 30-60 min at room temperature to obtain an aluminum source solution, and then mixing a template with deionized water at a molar concentration of 0.1-0.5 mol / L and stirring at a stirring rate of 200-400 r / min for 30-60 min at room temperature to obtain a template solution; Step 3: The aluminum source solution is continuously stirred at a stirring rate of 50-100 r / min, and the template solution is added dropwise during the process, and then continuously stirred for 1-3 hours to obtain a mixed solution; Step 4: Transfer the mixed solution to a hydrothermal reactor and react at 100-150°C for 12-24 hours to obtain a solid precipitate. Then, wash the solid precipitate repeatedly with deionized water and ethanol, dry it at 80-120°C for 6-12 hours, and calcine it at 500-600°C for 3-6 hours to obtain mesoporous alumina.

[0012] Preferably, the aluminum source can be selected from at least one of aluminum nitrate and aluminum isopropoxide, and the template agent is hexadecyltrimethylammonium bromide.

[0013] Preferably, the method for preparing a composite of mesoporous alumina and graphene comprises the following steps: mixing graphene and N-methylpyrrolidone at a mass volume ratio of 0.5-2 mg / mL, dispersing for 1-3 hours under ultrasonic power of 50-200 W and frequency of 40 kHz to obtain a graphene dispersion, weighing mesoporous alumina as needed and adding it to the graphene dispersion, stirring and mixing at a speed of 300-600 r / min for 3-6 hours, transferring to a centrifuge, centrifuging at 5000-8000 r / min for 10-15 minutes, taking the centrifugal precipitate, and then drying it at 80-120°C for 12-24 hours to obtain a special carrier.

[0014] Preferably, a method for preparing a nano palladium or platinum carbon monoxide combustion improver, wherein the combustion improver has a carbon coating layer of 2-5 nm thick on its surface, and the formation method thereof comprises the following steps: S1: pre-treat the microwave calcined combustion improver to 200-300°C in a nitrogen atmosphere for 1h; S2: A mixed gas of methane and argon is introduced; S3: Raise the temperature to 400-600°C at 5°C / min and keep it at this temperature for 1-3h, so that the carbon atoms at the edge of the graphene migrate to the surface of the particles to form a coating layer; S4: After cooling to room temperature, store under nitrogen protection.

[0015] Preferably, the methane volume fraction in the S2 mixed gas is 5-10%, and the mixed gas flow rate is controlled to be 20-50 mL / min.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. In this preparation method, a composite carrier of mesoporous alumina and graphene is used, wherein the three-dimensional interconnected pores of mesoporous alumina provide a high specific surface area and abundant active sites, while the interlaced structure of graphene sheets forms a conductive network to promote electron transfer and heat dispersion. This composite carrier effectively inhibits the migration and agglomeration of metal particles through physical confinement effects and chemical synergy, while enhancing the wear resistance of the carrier. In addition, the high thermal conductivity of graphene can quickly conduct reaction heat and avoid catalyst deactivation caused by local overheating, thereby significantly extending the service life of the combustion aid, reducing the amount of precious metals used, and reducing the environmental burden.

[0017] 2. In this preparation method, a microwave-assisted calcination process is adopted, and the high dielectric loss characteristics of graphene are utilized to form a dynamic temperature gradient inside the carrier. This gradient heating causes atomic-level diffusion between the active metal and the carrier to form a stable interface bond, while inhibiting the sintering and agglomeration of metal particles. In addition, the local plasma effect generated in the microwave field can induce the rearrangement of carbon atoms at the edge of graphene, forming an ultra-thin carbon coating on the surface of the metal particles. This carbon layer further stabilizes the nanostructure through chemical anchoring, so that the combustion aid can still maintain structural integrity in a high-temperature environment.

[0018] 3. In the present preparation method, a composite system of polyethylene glycol and hexadecyltrimethylammonium bromide is used, and a double-layer coating structure is formed on the surface of the nanoparticles through the synergistic effect of nonionic and cationic surfactants. This structure can effectively reduce the surface energy of the particles, inhibit the agglomeration driven by van der Waals forces, and make the active metals uniformly loaded on the carrier surface in a nanoscale monodisperse state. At the same time, the hydrophilic groups of the composite surfactant form hydrogen bonds with the carrier hydroxyl groups, enhancing the interfacial bonding force between the particles and the carrier, thereby significantly improving the exposure and utilization rate of the catalytic active sites. DETAILED DESCRIPTION

[0019] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 made by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] Embodiment 1:

[0021] This embodiment provides a method for preparing a nano-palladium or platinum carbon monoxide combustion promoter, comprising the following steps: Step 1: Weigh 1 part of palladium- or platinum-containing precursor, 0.5 part of composite surfactant, 2 parts of novel reducing agent, 50 parts of special carrier, 0.5 part of benzoin defoaming agent, and 0.3 part of silane coupling agent according to mass proportions; Step 2: dissolving a palladium- or platinum-containing precursor in deionized water to prepare a solution with a concentration of 0.1 mol / L; Step 3: In a constant temperature water bath at 50° C., the solution is stirred at a stirring rate of 300 r / min and a composite surfactant is added to obtain a sol; Step 4: using a peristaltic pump to dropwise add the novel reducing agent into the sol at a rate of 0.5 mL / min and maintaining the pH value of the reaction system at 8, reacting for 1 h to obtain a reaction solution; Step 5: fully mix the reaction solution with the special carrier, add benzoin defoamer and silane coupling agent, and prepare supported nanoparticles with a particle size of 5 nm by spray drying; Step six: subjecting the supported nanoparticles to microwave-assisted calcination treatment. During the treatment, under nitrogen protection, the temperature is raised to 300° C. at a heating rate of 10° C. / min and kept at this temperature for 2 hours to obtain a nano-palladium or platinum carbon monoxide combustion aid.

[0022] Among them, the palladium-containing precursor is palladium nitrate, and the platinum-containing precursor is chloroplatinic acid.

[0023] Among them, the composite surfactant is a compound of polyethylene glycol-4000 and hexadecyltrimethylammonium bromide, and the compounding ratio is 2:1.

[0024] Among them, the new reducing agent is a mixed solution of hydrazine hydrate and sodium borohydride, with a mixing volume ratio of 3:1 and a reduction potential controlled at -0.8V.

[0025] Among them, the special carrier is prepared by combining mesoporous alumina and graphene in a mass ratio of 7:3. The mesoporous alumina has a pore diameter of 8nm and a three-dimensional connected structure.

[0026] The method for preparing mesoporous alumina comprises the following steps: Step 1: The mesoporous alumina raw materials include aluminum source and template agent; Step 2: Mixing an aluminum source with deionized water at a molar concentration of 0.5 mol / L and stirring at a stirring rate of 200 r / min for 30 min at room temperature to obtain an aluminum source solution, and then mixing a template with deionized water at a molar concentration of 0.1 mol / L and stirring at a stirring rate of 200 r / min for 30 min at room temperature to obtain a template solution; Step 3: The aluminum source solution is continuously stirred at a stirring rate of 50 r / min, during which the template solution is added dropwise, and then continuously stirred for 1 hour to obtain a mixed solution; Step 4: Transfer the mixed solution to a hydrothermal reactor and react at 100°C for 12 hours to obtain a solid precipitate. The solid precipitate is then repeatedly washed with deionized water and ethanol, dried at 80°C for 6 hours, and calcined at 500°C for 3 hours to obtain mesoporous alumina.

[0027] Wherein, the aluminum source is aluminum nitrate, and the template agent is hexadecyltrimethylammonium bromide.

[0028] Among them, the preparation method of mesoporous alumina and graphene composite includes the following steps: mixing graphene and N-methylpyrrolidone at a mass volume ratio of 0.5 mg / mL, and then dispersing for 1 hour under ultrasonic power of 50 W and frequency of 40 kHz to obtain a graphene dispersion, and then weighing mesoporous alumina as needed to add the graphene dispersion, stirring and mixing at a speed of 300 r / min for 3 hours, transferring to a centrifuge, centrifuging at 5000 r / min for 10 minutes, taking the centrifugal precipitate, and then drying it at 80°C for 12 hours to obtain a special carrier.

[0029] Among them, a method for preparing a nano palladium or platinum carbon monoxide combustion improver, the combustion improver surface has a 2nm thick carbon coating layer, and the formation method thereof comprises the following steps: S1: pre-treat the microwave calcined combustion enhancer to 200°C in a nitrogen atmosphere for 1 h; S2: A mixed gas of methane and argon is introduced; S3: Raise the temperature to 400°C at 5°C / min and keep it at this temperature for 1h, so that the carbon atoms at the edge of graphene migrate to the surface of the particles to form a coating layer; S4: After cooling to room temperature, store under nitrogen protection.

[0030] The methane volume fraction in the S2 mixed gas is 5%, and the mixed gas flow rate is controlled to be 20 mL / min.

[0031] Embodiment 2:

[0032] A method for preparing a nano palladium or platinum carbon monoxide combustion improver comprises the following steps: Step 1: Weigh 5 parts of palladium- or platinum-containing precursor, 3 parts of composite surfactant, 8 parts of novel reducing agent, 80 parts of special carrier, 1.5 parts of benzoin defoaming agent, and 1 part of silane coupling agent according to mass proportion; Step 2: dissolving a palladium- or platinum-containing precursor in deionized water to prepare a solution with a concentration of 0.5 mol / L; Step 3: In a constant temperature water bath at 80° C., stirring the solution at a stirring rate of 800 r / min and adding a composite surfactant to obtain a sol; Step 4: using a peristaltic pump to dropwise add the new reducing agent into the sol at a rate of 2 mL / min and maintaining the pH value of the reaction system at 10, reacting for 3 h to obtain a reaction solution; Step 5: fully mix the reaction solution with the special carrier, add benzoin defoamer and silane coupling agent, and prepare supported nanoparticles with a particle size of 50 nm by spray drying; Step six: subjecting the supported nanoparticles to microwave-assisted calcination treatment. During the treatment, under nitrogen protection, the temperature is raised to 400° C. at a heating rate of 10° C. / min and kept at this temperature for 3 hours to obtain a nano-palladium or platinum carbon monoxide combustion promoter.

[0033] Among them, the palladium-containing precursor can be palladium acetate, and the platinum-containing precursor can be platinum acetylacetonate.

[0034] Among them, the composite surfactant is a compound of polyethylene glycol-4000 and hexadecyltrimethylammonium bromide, and the compounding ratio is 5:1.

[0035] Among them, the new reducing agent is a mixed solution of hydrazine hydrate and sodium borohydride with a mixing volume ratio of 5:1 and a reduction potential controlled at -1.2V.

[0036] Among them, the special carrier is prepared by combining mesoporous alumina and graphene in a mass ratio of 7:3. The mesoporous alumina has a pore size of 12nm and a three-dimensional connected structure.

[0037] The method for preparing mesoporous alumina comprises the following steps: Step 1: The mesoporous alumina raw materials include aluminum source and template agent; Step 2: Mixing an aluminum source with deionized water at a molar concentration of 2 mol / L and stirring at a stirring rate of 400 r / min for 60 min at room temperature to obtain an aluminum source solution, and then mixing a template with deionized water at a molar concentration of 0.5 mol / L and stirring at a stirring rate of 400 r / min for 60 min at room temperature to obtain a template solution; Step 3: The aluminum source solution is continuously stirred at a stirring rate of 100 r / min, during which the template solution is added dropwise, and then continuously stirred for 3 hours to obtain a mixed solution; Step 4: Transfer the mixed solution to a hydrothermal reactor and react at 150°C for 24 hours to obtain a solid precipitate. The solid precipitate is then repeatedly washed with deionized water and ethanol, dried at 120°C for 12 hours, and calcined at 600°C for 6 hours to obtain mesoporous alumina.

[0038] The aluminum source is aluminum isopropoxide, and the template agent is hexadecyltrimethylammonium bromide.

[0039] Among them, the preparation method of mesoporous alumina and graphene composite includes the following steps: mixing graphene and N-methylpyrrolidone at a mass volume ratio of 2 mg / mL, and then dispersing for 3 hours under ultrasonic power of 200 W and frequency of 40 kHz to obtain a graphene dispersion, and then weighing mesoporous alumina as needed to add the graphene dispersion, stirring and mixing at a speed of 600 r / min for 6 hours, transferring to a centrifuge, centrifuging at 8000 r / min for 15 minutes, taking the centrifugal precipitate, and then drying it at 120°C for 24 hours to obtain a special carrier.

[0040] Among them, a method for preparing a nano palladium or platinum carbon monoxide combustion improver, the combustion improver surface has a 5nm thick carbon coating layer, and the formation method thereof comprises the following steps: S1: pre-treat the microwave calcined combustion enhancer to 300°C in a nitrogen atmosphere for 1 h; S2: A mixed gas of methane and argon is introduced; S3: Raise the temperature to 600°C at 5°C / min and keep it at this temperature for 3h, so that the carbon atoms at the edge of graphene migrate to the surface of the particles to form a coating layer; S4: After cooling to room temperature, store under nitrogen protection.

[0041] The volume fraction of methane in the S2 mixed gas is 10%, and the mixed gas flow rate is controlled to be 50 mL / min.

[0042] Embodiment 3:

[0043] A method for preparing a nano palladium or platinum carbon monoxide combustion improver comprises the following steps: Step 1: Weigh 3 parts of palladium- or platinum-containing precursor, 1.5 parts of composite surfactant, 5 parts of novel reducing agent, 65 parts of special carrier, 1.5 parts of benzoin defoaming agent, and 0.6 parts of silane coupling agent according to mass proportions; Step 2: dissolving a palladium- or platinum-containing precursor in deionized water to prepare a solution with a concentration of 0.3 mol / L; Step 3: In a constant temperature water bath at 65° C., stirring the solution at a stirring rate of 500 r / min and adding a composite surfactant to obtain a sol; Step 4: using a peristaltic pump to dropwise add the new reducing agent into the sol at a rate of 1.2 mL / min and maintaining the pH value of the reaction system at 9, reacting for 2 h to obtain a reaction solution; Step 5: fully mix the reaction solution with the special carrier, add benzoin defoamer and silane coupling agent, and prepare supported nanoparticles with a particle size of 30 nm by spray drying; Step six: subjecting the supported nanoparticles to microwave-assisted calcination treatment. During the treatment, under nitrogen protection, the temperature is raised to 350° C. at a heating rate of 10° C. / min and kept at this temperature for 2.5 hours to obtain a nano-palladium or platinum carbon monoxide combustion promoter.

[0044] Among them, the palladium-containing precursor is palladium nitrate, and the platinum-containing precursor is platinum acetylacetonate.

[0045] Among them, the composite surfactant is a compound of polyethylene glycol-4000 and hexadecyltrimethylammonium bromide, and the compounding ratio is 3:1.

[0046] Among them, the new reducing agent is a mixed solution of hydrazine hydrate and sodium borohydride, with a mixing volume ratio of 4:1 and a reduction potential controlled at -1V.

[0047] Among them, the special carrier is prepared by combining mesoporous alumina and graphene in a mass ratio of 7:3. The mesoporous alumina has a pore size of 10nm and a three-dimensional connected structure.

[0048] The method for preparing mesoporous alumina comprises the following steps: Step 1: The mesoporous alumina raw materials include aluminum source and template agent; Step 2: Mixing an aluminum source with deionized water at a molar concentration of 1 mol / L and stirring at a stirring rate of 300 r / min for 45 min at room temperature to obtain an aluminum source solution, and then mixing a template with deionized water at a molar concentration of 0.3 mol / L and stirring at a stirring rate of 300 r / min for 45 min at room temperature to obtain a template solution; Step 3: The aluminum source solution is continuously stirred at a stirring rate of 80 r / min, during which the template solution is added dropwise, and then continuously stirred for 2 hours to obtain a mixed solution; Step 4: Transfer the mixed solution to a hydrothermal reactor and react at 125°C for 18 hours to obtain a solid precipitate. The solid precipitate is then repeatedly washed with deionized water and ethanol, dried at 100°C for 9 hours, and calcined at 550°C for 4.5 hours to obtain mesoporous alumina.

[0049] Wherein, the aluminum source is aluminum nitrate, and the template agent is hexadecyltrimethylammonium bromide.

[0050] Among them, the preparation method of mesoporous alumina and graphene composite includes the following steps: mixing graphene and N-methylpyrrolidone at a mass volume ratio of 1 mg / mL, and then dispersing for 2 hours under ultrasonic power of 150 W and frequency of 40 kHz to obtain a graphene dispersion, and then weighing mesoporous alumina as needed to add the graphene dispersion, stirring and mixing at a speed of 450 r / min for 4.5 hours, transferring to a centrifuge, centrifuging at 6500 r / min for 12 minutes, taking the centrifugal precipitate, and then drying at 100°C for 18 hours to obtain a special carrier.

[0051] Among them, a method for preparing a nano palladium or platinum carbon monoxide combustion improver, wherein the combustion improver surface has a 3.5 nm thick carbon coating layer, and the formation method thereof comprises the following steps: S1: pre-treat the microwave calcined combustion enhancer to 250°C in a nitrogen atmosphere for 1 h; S2: A mixed gas of methane and argon is introduced; S3: Raise the temperature to 500°C at 5°C / min and keep it at this temperature for 2h, so that the carbon atoms at the edge of graphene migrate to the surface of the particles to form a coating layer; S4: After cooling to room temperature, store under nitrogen protection.

[0052] The volume fraction of methane in the S2 mixed gas is 8%, and the mixed gas flow rate is controlled to be 35 mL / min.

[0053] Comparative Example 1: The difference between this comparative example and Examples 1-3 is that in the process of preparing the nano-palladium or platinum carbon monoxide combustion aid in this comparative example, only a single surfactant, hexadecyltrimethylammonium bromide, is used as the surfactant, and polyethylene glycol-4000 is not introduced.

[0054] Comparative Example 2: The difference between this comparative example and Examples 1-3 is that in the process of preparing the nano-palladium or platinum carbon monoxide combustion aid in this comparative example, traditional muffle furnace calcination is adopted, and microwave-assisted calcination is not used.

[0055] Comparative Example 3: The difference between this comparative example and Examples 1-3 is that in the process of preparing the nano-palladium or platinum carbon monoxide combustion aid in this comparative example, ordinary alumina carrier is used instead of special carrier.

[0056] Test methods and test items: Nanoparticle dispersibility: Evaluate the particle size distribution uniformity and agglomeration degree in accordance with GB / T 29022-2012 standard combined with lens electron microscopy analysis; High temperature sintering resistance: Keep the temperature at 700℃ in air atmosphere for 10 hours, analyze the change of grain size by XRD, and compare the change rate before and after aging; Wear resistance: Use a fluidized bed abrasion tester, set the air velocity to 3m / s, and use quartz sand as the abrasion medium for 24 hours, and record the wear amount.

[0057] The performance tests were conducted on the nano palladium or platinum carbon monoxide combustion improvers prepared in Examples 1-3 and Comparative Examples 1-3, and the test data obtained are recorded in the following table:

[0058] By comparing the data in Examples 1-3 and Comparative Example 1 in the comparison table, it can be seen that the nano palladium or platinum carbon monoxide combustion improver prepared by the preparation method of Comparative Example 1 is compared with the nano palladium or platinum carbon monoxide combustion improver prepared by Examples 1-3. It can be seen that the traditional combustion improver cannot effectively regulate the nucleation kinetics of nanoparticles due to the single action mechanism of a single surfactant. However, by using a composite system of polyethylene glycol-4000 and hexadecyltrimethylammonium bromide, the long-chain ether bond of polyethylene glycol-4000 combines with the hydrophobic tail of hexadecyltrimethylammonium bromide through hydrophobic interaction to form a double-layer micelle structure, and the polyethylene glycol- 4000 provides steric hindrance to inhibit particle collision, and the hexadecyltrimethylammonium bromide cation weakens the van der Waals force through electrostatic repulsion. The two synergistically reduce the surface energy of the particles. At the same time, the dynamic light scattering results show that the PDI of the embodiment is 0.11, indicating that the particles are evenly dispersed, while the PDI of the comparative example 1 is 0.39, indicating that the single hexadecyltrimethylammonium bromide causes an electrostatic shielding effect due to charge overload, and the particles aggregate disorderly, verifying the inhibitory effect of the composite surfactant on Ostwald ripening. This shows that the design of the composite surfactant can significantly increase the active site density, laying the foundation for high catalytic activity; The above analysis shows that the traditional single surfactant has weak adsorption ability on the surface of nanoparticles, which easily leads to particle agglomeration and reduces active sites. The present invention adopts a composite system of polyethylene glycol and hexadecyltrimethylammonium bromide, and forms a double-layer coating structure on the surface of nanoparticles through the synergistic effect of non-ionic and cationic surfactants. This structure can effectively reduce the surface energy of particles, inhibit the agglomeration driven by van der Waals forces, and make the active metal uniformly loaded on the carrier surface in a nanoscale monodisperse state. At the same time, the hydrophilic group of the composite surfactant forms a hydrogen bond with the hydroxyl group of the carrier, which enhances the interfacial bonding force between the particles and the carrier, thereby significantly improving the exposure and utilization rate of catalytic active sites. By comparing the data in Examples 1-3 and Comparative Example 2 in the comparison table, it can be seen that the nano palladium or platinum carbon monoxide combustion aid prepared by the preparation method of Comparative Example 2 is compared with the nano palladium or platinum carbon monoxide combustion aid prepared by Examples 1-3. It can be seen that the traditional calcination relies on heat conduction heating, and the poor temperature uniformity leads to a decrease in the energy barrier for particle surface migration, while the microwave gradient calcination uses the dielectric difference between mesoporous alumina and graphene to form a dynamic temperature gradient inside the carrier. The gradient drives the nanoparticles to migrate directional into the mesopores, and the pore confinement effect inhibits grain boundary diffusion. After high-temperature aging, the particle size growth of Examples 1-3 is ≤8.5%, while that of Comparative Example 2 is >26.0%, which shows that microwave calcination achieves embedded fixation of particles through a non-equilibrium thermodynamic process, effectively delaying high-temperature sintering; From the above analysis, it can be concluded that the traditional muffle furnace calcination relies on heat conduction, which is easy to cause local overheating and abnormal grain growth. The present invention adopts a microwave-assisted calcination process and utilizes the high dielectric loss characteristics of graphene to form a dynamic temperature gradient inside the carrier. This gradient heating causes atomic-level diffusion between the active metal and the carrier to form a stable interface bond, while inhibiting the sintering and agglomeration of metal particles. In addition, the local plasma effect generated in the microwave field can induce the rearrangement of carbon atoms at the edge of graphene to form an ultra-thin carbon coating layer on the surface of the metal particles. This carbon layer further stabilizes the nanostructure through chemical anchoring, so that the combustion aid can still maintain structural integrity in a high-temperature environment; By comparing the data in Examples 1-3 and Comparative Example 3 in the comparison table, it can be seen that the nano palladium or platinum carbon monoxide combustion aid prepared by the preparation method of Comparative Example 3 is compared with the nano palladium or platinum carbon monoxide combustion aid prepared by Examples 1-3. It can be seen that the ordinary alumina carrier has a tortuous diffusion path of the reactants due to its disordered pore size distribution and high closed porosity, while the mesoporous alumina-graphene composite carrier constructs a hierarchical mass transfer network through three-dimensional interconnected channels and interlaced graphene sheets. At the same time, the introduction of graphene enhances the mechanical strength of the carrier and significantly reduces the wear index. This shows that the special carrier can significantly increase the life of the combustion aid.

[0059] From the above analysis, it can be concluded that the pore structure of ordinary alumina carriers is disordered and the specific surface area is low, which limits the catalytic efficiency. The present invention adopts a composite carrier of mesoporous alumina and graphene, wherein the three-dimensional connected pores of mesoporous alumina provide a high specific surface area and abundant active sites, while the interlaced structure of graphene sheets forms a conductive network to promote electron transfer and heat dispersion. This composite carrier effectively inhibits the migration and agglomeration of metal particles through physical confinement effects and chemical synergy, while enhancing the wear resistance of the carrier. In addition, the high thermal conductivity of graphene can quickly remove the reaction heat and avoid catalyst deactivation caused by local overheating, thereby significantly extending the service life of the combustion aid, reducing the amount of precious metals used, and reducing the environmental load.

[0060] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0061] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing a nano palladium or platinum carbon monoxide combustion improver, characterized in that: The following steps are involved: Step 1: Weigh 1-5 parts of palladium- or platinum-containing precursor, 0.5-3 parts of composite surfactant, 2-8 parts of novel reducing agent, 50-80 parts of special carrier, 0.5-1.5 parts of benzoin defoaming agent, and 0.3-1 parts of silane coupling agent according to mass proportions; Step 2: dissolving a palladium- or platinum-containing precursor in deionized water to prepare a solution with a concentration of 0.1-0.5 mol / L; Step 3: In a constant temperature water bath at 50-80° C., stirring the solution at a stirring rate of 300-800 r / min and adding a composite surfactant to obtain a sol; Step 4: using a peristaltic pump to dropwise add the novel reducing agent into the sol at a rate of 0.5-2 mL / min and maintaining the pH value of the reaction system at 8-10, reacting for 1-3 h to obtain a reaction solution; Step 5: fully mixing the reaction solution with the special carrier, adding benzoin defoamer and silane coupling agent, and preparing supported nanoparticles with a particle size of 5-50 nm by spray drying; Step six: subjecting the supported nanoparticles to microwave-assisted calcination treatment. During the treatment, under nitrogen protection, the temperature is raised to 300-400° C. at a heating rate of 10° C. / min and kept at this temperature for 2-3 hours to obtain a nano-palladium or platinum carbon monoxide combustion promoter.

2. The method of nano palladium or platinum carbon monoxide combustion improver according to claim 1, characterized in that, The palladium-containing precursor may be selected from at least one of palladium nitrate and palladium acetate, and the platinum-containing precursor may be selected from at least one of chloroplatinic acid and platinum acetylacetonate.

3. The method of nano palladium or platinum carbon monoxide combustion improver according to claim 1, characterized in that, The composite surfactant is a compound of polyethylene glycol-4000 and hexadecyltrimethylammonium bromide, and the compounding ratio is (2-5):

1.

4. The method of nano palladium or platinum carbon monoxide combustion improver according to claim 1, characterized in that: The novel reducing agent is a mixed solution of hydrazine hydrate and sodium borohydride, the mixed volume ratio is (3-5):1, and the reduction potential is controlled at -(0.8-1.2)V.

5. The method of nano palladium or platinum carbon monoxide combustion improver according to claim 1, characterized in that, The special carrier is prepared by compounding mesoporous alumina and graphene in a mass ratio of 7:

3. The mesoporous alumina has a pore size of 8-12 nm and presents a three-dimensional interconnected structure.

6. The method of preparing nano palladium or platinum carbon monoxide combustion improver according to claim 5, characterized in that: The method for preparing mesoporous alumina comprises the following steps: Step 1: The mesoporous alumina raw materials include aluminum source and template agent; Step 2: Mixing an aluminum source with deionized water at a molar concentration of 0.5-2 mol / L and stirring at a stirring rate of 200-400 r / min for 30-60 min at room temperature to obtain an aluminum source solution, and then mixing a template with deionized water at a molar concentration of 0.1-0.5 mol / L and stirring at a stirring rate of 200-400 r / min for 30-60 min at room temperature to obtain a template solution; Step 3: The aluminum source solution is continuously stirred at a stirring rate of 50-100 r / min, and the template solution is added dropwise during the process, and then continuously stirred for 1-3 hours to obtain a mixed solution; Step 4: Transfer the mixed solution to a hydrothermal reactor and react at 100-150°C for 12-24 hours to obtain a solid precipitate. Then, wash the solid precipitate repeatedly with deionized water and ethanol, dry it at 80-120°C for 6-12 hours, and calcine it at 500-600°C for 3-6 hours to obtain mesoporous alumina.

7. The method of preparing nano palladium or platinum carbon monoxide combustion improver according to claim 6, characterized in that: The aluminum source can be selected from at least one of aluminum nitrate and aluminum isopropoxide, and the template agent is hexadecyltrimethylammonium bromide.

8. The method of nano palladium or platinum carbon monoxide combustion improver according to claim 6, characterized in that: The composite preparation method of mesoporous alumina and graphene comprises the following steps: mixing graphene and N-methylpyrrolidone at a mass volume ratio of 0.5-2 mg / mL, dispersing for 1-3 hours under ultrasonic power of 50-200 W and frequency of 40 kHz to obtain a graphene dispersion, weighing mesoporous alumina as needed and adding it to the graphene dispersion, stirring and mixing for 3-6 hours at a speed of 300-600 r / min, transferring to a centrifuge, centrifugally separating for 10-15 minutes at 5000-8000 r / min, taking a centrifugal precipitate, and drying it at 80-120° C. for 12-24 hours to obtain a special carrier.

9. The method of a nano palladium or platinum carbon monoxide combustion improver according to claim 1, characterized in that: The combustion-supporting agent has a carbon coating layer with a thickness of 2-5 nm on its surface, and the formation method thereof comprises the following steps: S1: pre-treat the microwave calcined combustion improver to 200-300°C in a nitrogen atmosphere for 1h; S2: A mixed gas of methane and argon is introduced; S3: Raise the temperature to 400-600°C at 5°C / min and keep it at this temperature for 1-3h, so that the carbon atoms at the edge of the graphene migrate to the surface of the particles to form a coating layer; S4: After cooling to room temperature, store under nitrogen protection.

10. The method of preparing nano palladium or platinum carbon monoxide combustion improver according to claim 9, characterized in that: The methane volume fraction in the S2 mixed gas is 5-10%, and the mixed gas flow rate is controlled to be 20-50 mL / min.

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