A method for preparing a nano-palladium or platinum carbon monoxide combustion promoter

Abstract

The present invention relates to the technical field of combustion aids, and specifically to a method for preparing a nano-palladium or platinum carbon monoxide combustion aid, which includes the following steps: Step 1: Weigh 1-5 parts by mass of a palladium-containing or platinum-containing precursor, 0.5-3 parts of a composite surfactant, 2-8 parts of a reducing agent, 50-80 parts of a special carrier, 0.5-1.5 parts of a benzoin defoamer, and 0.3-1 part of a silane coupling agent. In the present invention, a mesoporous alumina and graphene composite carrier is used. This composite carrier effectively inhibits the migration and agglomeration of metal particles through physical confinement effects and chemical synergistic effects, while enhancing the anti-wear performance of the carrier. In addition, the high thermal conductivity of graphene can quickly conduct out the reaction heat, avoiding catalyst deactivation caused by local overheating, thus significantly extending the service life of the combustion aid, reducing the consumption of precious metals, and reducing the environmental burden.

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 improver 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 improvers.

[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:

[0007] Step 1: Weigh 1-5 parts of palladium- or platinum-containing precursor, 0.5-3 parts of composite surfactant, 2-8 parts of 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;

[0008] 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;

[0009] 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;

[0010] Step 4: using a peristaltic pump to drop a 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 hours to obtain a reaction solution;

[0011] 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;

[0012] Step 6: Perform microwave-assisted calcination on the supported nanoparticles. During the process, under nitrogen protection, heat at a heating rate of 10 °C / min to 300-400 °C, and keep the temperature for 2-3 h to obtain the nano-palladium or platinum carbon monoxide combustion promoter.

[0013] Preferably, the palladium-containing precursor is selected from at least one of palladium nitrate and palladium acetate, and the platinum-containing precursor is selected from at least one of chloroplatinic acid and platinum acetylacetonate.

[0014] Preferably, the composite surfactant is a compound of polyethylene glycol-4000 and cetyltrimethylammonium bromide, and the compounding ratio is (2-5):1.

[0015] Preferably, the reducing agent is a mixed solution of hydrazine hydrate and sodium borohydride, and the mixing volume ratio is (3-5):1, and the reduction potential is controlled at -(0.8-1.2) V.

[0016] Preferably, the special carrier is prepared by compounding mesoporous alumina and graphene with a mass ratio of 7:3. The mesoporous alumina has a pore diameter of 8-12 nm and a three-dimensional interconnected structure.

[0017] Preferably, the preparation method of the mesoporous alumina includes the following steps:

[0018] Step 1: Select an aluminum source and a template agent as the raw materials for the mesoporous alumina;

[0019] Step 2: Mix the aluminum source and deionized water at a molar concentration of 0.5-2 mol / L and stir at a stirring rate of 200-400 r / min at room temperature for 30-60 min to obtain an aluminum source solution. Then mix the template agent and deionized water at a molar concentration of 0.1-0.5 mol / L and stir at a stirring rate of 200-400 r / min at room temperature for 30-60 min to obtain a template agent solution;

[0020] Step 3: Continuously stir the aluminum source solution at a stirring rate of 50-100 r / min. During the process, add the template agent solution dropwise, and then continuously stir for 1-3 h to obtain a mixed solution;

[0021] Step 4: Transfer the mixed solution to a hydrothermal reaction kettle, react at 100-150 °C for 12-24 h 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 h, and then calcine it at 500-600 °C for 3-6 h to obtain the mesoporous alumina.

[0022] Preferably, the aluminum source is selected from at least one of aluminum nitrate and aluminum isopropoxide, and the template agent is cetyltrimethylammonium bromide.

[0023] Preferably, the method for preparing the composite of mesoporous alumina and graphene comprises the following steps: mixing graphene with N-methylpyrrolidone at a mass-to-volume ratio of 0.5-2 mg / mL, and then dispersing for 1-3 hours under the conditions of an ultrasonic power of 50-200 W and a frequency of 40 kHz to obtain a graphene dispersion. Then, weigh mesoporous alumina as needed and add it to the graphene dispersion, stir and mix at a rotation speed of 300-600 r / min for 3-6 h, transfer it to a centrifuge, and centrifuge and separate at 5000-8000 r / min for 10-15 min. Take the centrifugal precipitate, and then dry it at 80-120 °C for 12-24 h to prepare a special carrier.

[0024] Preferably, for a method of a nano-palladium or platinum carbon monoxide combustion promoter, the surface of the combustion promoter has a carbon coating layer with a thickness of 2-5 nm, and its formation method comprises the following steps:

[0025] S1: Heat the combustion promoter after microwave calcination to 200-300 °C in a nitrogen atmosphere and pretreat for 1 h;

[0026] S2: Introduce a mixed gas of methane and argon;

[0027] S3: Heat up to 400-600 °C at a rate of 5 °C / min and hold for 1-3 h to enable the migration of carbon atoms at the edges of graphene to the particle surface to form a coating layer;

[0028] S4: Store under nitrogen protection after cooling to room temperature.

[0029] Preferably, the volume fraction of methane in the mixed gas in S2 is 5-10%, and the flow rate of the mixed gas is controlled at 20-50 mL / min.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] 1. In this preparation method, a composite carrier of mesoporous alumina and graphene is used. Among them, the three-dimensional interconnected pores of mesoporous alumina provide a high specific surface area and abundant active sites, while the sheet interpenetrating structure of graphene forms a conductive network, promoting electron transfer and heat dispersion. This composite carrier effectively inhibits the migration and aggregation of metal particles through physical confinement effects and chemical synergistic effects, while enhancing the anti-wear performance of the carrier. In addition, the high thermal conductivity of graphene can quickly conduct out the reaction heat, avoiding catalyst deactivation caused by local overheating, thus significantly extending the service life of the combustion promoter, reducing the usage of precious metals, and reducing the environmental burden.

[0032] 2. In this preparation method, a microwave-assisted calcination process is adopted. Utilizing the high dielectric loss characteristics of graphene, a dynamic temperature gradient is formed inside the carrier. This gradient heating enables atomic-level diffusion between the active metal and the carrier, forming a stable interfacial bonding, 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 edges of graphene, forming an ultrathin carbon coating layer on the surface of metal particles. This carbon layer further stabilizes the nanostructure through chemical anchoring, enabling the combustion promoter to maintain its structural integrity even in a high-temperature environment.

[0033] 3. In this preparation method, a compound system of polyethylene glycol and cetyltrimethylammonium bromide is adopted. Through the synergistic effect of non-ionic and cationic surfactants, a bilayer coating structure is formed on the surface of nanoparticles. This structure can effectively reduce the surface energy of the particles, inhibit the agglomeration driven by van der Waals forces, and enable the active metal to be uniformly loaded on the surface of the carrier in a nanoscale monodispersed state. At the same time, the hydrophilic groups of the composite surfactant form hydrogen bonds with the hydroxyl groups of the carrier, enhancing the interfacial binding force between the particles and the carrier, thereby significantly increasing the exposure amount and utilization rate of catalytic active sites. Detailed implementation mode

[0034] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0035] Example 1:

[0036] This example provides a method for preparing a nano-palladium or platinum carbon monoxide combustion promoter, including the following steps:

[0037] Step 1: Weigh 1 part of a palladium- or platinum-containing precursor, 0.5 part of a composite surfactant, 2 parts of a reducing agent, 50 parts of a special carrier, 0.5 part of a benzoin defoamer, and 0.3 part of a silane coupling agent by mass.

[0038] Step 2: Dissolve the palladium- or platinum-containing precursor in deionized water to prepare a solution with a concentration of 0.1 mol / L.

[0039] Step 3: In a constant temperature water bath at 50 °C, stir the solution at a stirring rate of 300 r / min and add the composite surfactant to obtain a sol.

[0040] Step 4: Use a peristaltic pump to drop the reducing agent into the sol at a rate of 0.5 mL / min and maintain the pH value of the reaction system at 8, and react for 1 h to obtain a reaction solution.

[0041] Step 5: Thoroughly 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 through a spray dryer;

[0042] Step 6: Conduct microwave-assisted calcination treatment on the supported nanoparticles. During the treatment process, under nitrogen protection, heat up to 300 °C at a heating rate of 10 °C / min, and keep the temperature for 2 h to obtain a nano-palladium or platinum carbon monoxide combustion promoter.

[0043] Among them, the palladium-containing precursor is selected from palladium nitrate, and the platinum-containing precursor is selected from chloroplatinic acid.

[0044] Among them, the composite surfactant is a compound of polyethylene glycol-4000 and cetyltrimethylammonium bromide, and the compounding ratio is 2:1.

[0045] Among them, the reducing agent is a mixed solution of hydrazine hydrate and sodium borohydride, and the mixing volume ratio is 3:1, and the reduction potential is controlled at -0.8 V.

[0046] Among them, the special carrier is prepared by compounding mesoporous alumina and graphene with a mass ratio of 7:3. The mesoporous alumina has a pore diameter of 8 nm and a three-dimensional connected structure.

[0047] Among them, the preparation method of mesoporous alumina includes the following steps:

[0048] Step 1: Select an aluminum source and a template agent as raw materials for mesoporous alumina;

[0049] Step 2: Mix the aluminum source and deionized water at a molar concentration of 0.5 mol / L and stir at a stirring rate of 200 r / min at room temperature for 30 min to obtain an aluminum source solution. Then mix the template agent and deionized water at a molar concentration of 0.1 mol / L and stir at a stirring rate of 200 r / min at room temperature for 30 min to obtain a template agent solution;

[0050] Step 3: Continuously stir the aluminum source solution at a stirring rate of 50 r / min. During the process, add the template agent solution dropwise, and then continue to stir for 1 h to obtain a mixed solution;

[0051] Step 4: Transfer the mixed solution to a hydrothermal reaction kettle, react at 100 °C for 12 h to obtain a solid precipitate. Then repeatedly wash the solid precipitate with deionized water and ethanol, dry it at 80 °C for 6 h, and then calcine it at 500 °C for 3 h to obtain mesoporous alumina.

[0052] Among them, the aluminum source is selected from aluminum nitrate, and the template agent is cetyltrimethylammonium bromide.

[0053] Among them, the preparation method of mesoporous alumina-graphene composite includes the following steps: Mix graphene with N-methylpyrrolidone at a mass-volume ratio of 0.5 mg / mL, and then disperse it for 1 hour under the conditions of ultrasonic power of 50 W and frequency of 40 kHz to obtain a graphene dispersion. Then, weigh mesoporous alumina as needed and add it to the graphene dispersion, stir and mix for 3 h under the condition of a rotation speed of 300 r / min, transfer it to a centrifuge, centrifuge and separate for 10 min under the condition of 5000 r / min, take the centrifuged precipitate, and then dry it at 80 °C for 12 h to obtain a special carrier.

[0054] Among them, a method for preparing a nano-palladium or platinum carbon monoxide combustion promoter, the surface of the combustion promoter has a 2-nm-thick carbon coating layer, and its formation method includes the following steps:

[0055] S1: Heat the combustion promoter after microwave calcination to 200 °C in a nitrogen atmosphere and pretreat it for 1 h;

[0056] S2: Introduce a mixed gas of methane and argon;

[0057] S3: Raise the temperature to 400 °C at a rate of 5 °C / min and keep it warm for 1 h to make the carbon atoms at the edge of graphene migrate to the particle surface to form a coating layer;

[0058] S4: Cool to room temperature and store under nitrogen protection.

[0059] Among them, the volume fraction of methane in the mixed gas in S2 is 5%, and the flow rate of the mixed gas is controlled at 20 mL / min.

[0060] Example 2:

[0061] A method for preparing a nano-palladium or platinum carbon monoxide combustion promoter includes the following steps:

[0062] Step 1: Weigh 5 parts of a palladium- or platinum-containing precursor, 3 parts of a composite surfactant, 8 parts of a reducing agent, 80 parts of a special carrier, 1.5 parts of a benzoin defoamer, and 1 part of a silane coupling agent by mass;

[0063] Step 2: Dissolve the palladium- or platinum-containing precursor in deionized water to prepare a solution with a concentration of 0.5 mol / L;

[0064] Step 3: In a constant temperature water bath at 80 °C, stir the solution at a stirring rate of 800 r / min and add the composite surfactant to obtain a sol;

[0065] Step 4: Use a peristaltic pump to drop the reducing agent into the sol at a rate of 2 mL / min and maintain the pH value of the reaction system at 10, and react for 3 h to obtain a reaction solution;

[0066] Step 5: Thoroughly 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 through a spray dryer;

[0067] Step 6: Perform microwave-assisted calcination treatment on the supported nanoparticles. During the treatment process, under nitrogen protection, heat up to 400 °C at a heating rate of 10 °C / min, and keep the temperature for 3 h to obtain a nano-palladium or platinum carbon monoxide combustion promoter.

[0068] Among them, the palladium-containing precursor is selected from palladium acetate, and the platinum-containing precursor is selected from platinum acetylacetonate.

[0069] Among them, the composite surfactant is a compound of polyethylene glycol-4000 and cetyltrimethylammonium bromide, and the compounding ratio is 5:1.

[0070] Among them, the reducing agent is a mixed solution of hydrazine hydrate and sodium borohydride, and the mixing volume ratio is 5:1, and the reduction potential is controlled at -1.2 V.

[0071] Among them, the special carrier is prepared by compounding mesoporous alumina and graphene with a mass ratio of 7:3. The mesoporous alumina has a pore diameter of 12 nm and a three-dimensional interconnected structure.

[0072] Among them, the preparation method of mesoporous alumina includes the following steps:

[0073] Step 1: Select an aluminum source and a template agent as the raw materials for mesoporous alumina;

[0074] Step 2: Mix the aluminum source with deionized water at a molar concentration of 2 mol / L and stir at a stirring rate of 400 r / min at room temperature for 60 min to obtain an aluminum source solution. Then mix the template agent with deionized water at a molar concentration of 0.5 mol / L and stir at a stirring rate of 400 r / min at room temperature for 60 min to obtain a template agent solution;

[0075] Step 3: Continuously stir the aluminum source solution at a stirring rate of 100 r / min. During the process, dropwise add the template agent solution, and then continuously stir for 3 h to obtain a mixed solution;

[0076] Step 4: Transfer the mixed solution to a hydrothermal reaction kettle, react at 150 °C for 24 h to obtain a solid precipitate. Then repeatedly wash the solid precipitate with deionized water and ethanol, dry it at 120 °C for 12 h, and then calcine it at 600 °C for 6 h to obtain mesoporous alumina.

[0077] Among them, the aluminum source is selected from aluminum isopropoxide, and the template agent is cetyltrimethylammonium bromide.

[0078] Among them, the method for preparing the composite of mesoporous alumina and graphene includes the following steps: Mix graphene and N-methylpyrrolidone at a mass-volume ratio of 2 mg / mL, and then disperse it for 3 hours under the conditions of an ultrasonic power of 200 W and a frequency of 40 kHz to obtain a graphene dispersion. Then, weigh mesoporous alumina as needed and add it to the graphene dispersion, stir and mix at a rotation speed of 600 r / min for 6 h, transfer it to a centrifuge, centrifuge and separate at 8000 r / min for 15 min, take the centrifuged precipitate, and then dry it at 120 °C for 24 h to prepare a special carrier.

[0079] Among them, a method for preparing a nano-palladium or platinum carbon monoxide combustion promoter, the surface of the combustion promoter has a 5-nm-thick carbon coating layer, and its formation method includes the following steps:

[0080] S1: Heat the combustion promoter after microwave calcination to 300 °C in a nitrogen atmosphere and pretreat it for 1 h;

[0081] S2: Introduce a mixed gas of methane and argon;

[0082] S3: Raise the temperature to 600 °C at a rate of 5 °C / min and keep it warm for 3 h to make the carbon atoms at the edges of graphene migrate to the particle surface to form a coating layer;

[0083] S4: Cool to room temperature and store it under nitrogen protection.

[0084] Among them, the volume fraction of methane in the mixed gas in S2 is 10%, and the flow rate of the mixed gas is controlled at 50 mL / min.

[0085] Example 3:

[0086] A method for preparing a nano-palladium or platinum carbon monoxide combustion promoter includes the following steps:

[0087] Step 1: Weigh 3 parts of a palladium- or platinum-containing precursor, 1.5 parts of a composite surfactant, 5 parts of a reducing agent, 65 parts of a special carrier, 1.5 parts of a benzoin defoamer, and 0.6 parts of a silane coupling agent by mass;

[0088] Step 2: Dissolve the palladium- or platinum-containing precursor in deionized water to prepare a solution with a concentration of 0.3 mol / L;

[0089] Step 3: In a constant temperature water bath at 65 °C, stir the solution at a stirring rate of 500 r / min and add the composite surfactant to obtain a sol;

[0090] Step 4: Use a peristaltic pump to drop the reducing agent into the sol at a rate of 1.2 mL / min and maintain the pH value of the reaction system at 9, and react for 2 h to obtain a reaction solution;

[0091] Step 5: Thoroughly 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 through a spray dryer;

[0092] Step 6: Conduct microwave-assisted calcination treatment on the supported nanoparticles. During the treatment process, under nitrogen protection, heat up to 350 °C at a heating rate of 10 °C / min, and keep the temperature for 2.5 h to obtain a nano-palladium or platinum carbon monoxide combustion promoter.

[0093] Among them, the palladium-containing precursor is selected from palladium nitrate, and the platinum-containing precursor is selected from platinum acetylacetonate.

[0094] Among them, the composite surfactant is a compound of polyethylene glycol-4000 and cetyltrimethylammonium bromide, and the compounding ratio is 3:1.

[0095] Among them, the reducing agent is a mixed solution of hydrazine hydrate and sodium borohydride, and the mixing volume ratio is 4:1, and the reduction potential is controlled at -1 V.

[0096] Among them, the special carrier is prepared by compounding mesoporous alumina and graphene with a mass ratio of 7:3. The mesoporous alumina has a pore diameter of 10 nm and a three-dimensional interconnected structure.

[0097] Among them, the preparation method of mesoporous alumina includes the following steps:

[0098] Step 1: Select an aluminum source and a template agent as the raw materials for mesoporous alumina;

[0099] Step 2: Mix the aluminum source with deionized water at a molar concentration of 1 mol / L and stir at a stirring rate of 300 r / min at room temperature for 45 min to obtain an aluminum source solution. Then mix the template agent with deionized water at a molar concentration of 0.3 mol / L and stir at a stirring rate of 300 r / min at room temperature for 45 min to obtain a template agent solution;

[0100] Step 3: Continuously stir the aluminum source solution at a stirring rate of 80 r / min. During the process, dropwise add the template agent solution, and then continuously stir for 2 h to obtain a mixed solution;

[0101] Step 4: Transfer the mixed solution to a hydrothermal reaction kettle, react at 125 °C for 18 h to obtain a solid precipitate. Then repeatedly wash the solid precipitate with deionized water and ethanol, dry it at 100 °C for 9 h, and then calcine it at 550 °C for 4.5 h to obtain mesoporous alumina.

[0102] Among them, the aluminum source is selected from aluminum nitrate, and the template agent is cetyltrimethylammonium bromide.

[0103] Among them, the method for preparing the composite of mesoporous alumina and graphene comprises the following steps: mixing graphene and N-methylpyrrolidone at a mass-to-volume ratio of 1 mg / mL, and then dispersing for 2 hours under the conditions of an ultrasonic power of 150 W and a frequency of 40 kHz to obtain a graphene dispersion liquid. Then, weigh mesoporous alumina as needed and add it to the graphene dispersion liquid, stir and mix at a rotation speed of 450 r / min for 4.5 h, transfer it to a centrifuge, centrifuge and separate at 6500 r / min for 12 min, take the centrifuged precipitate, and then dry it at 100 °C for 18 h to prepare a special carrier.

[0104] Among them, a method for a nano-palladium or platinum carbon monoxide combustion promoter, the surface of the combustion promoter has a 3.5-nm-thick carbon coating layer, and its formation method comprises the following steps:

[0105] S1: Heating the combustion promoter after microwave calcination to 250 °C in a nitrogen atmosphere for pretreatment for 1 h;

[0106] S2: Introducing a mixed gas of methane and argon;

[0107] S3: Heating to 500 °C at a rate of 5 °C / min and holding for 2 h to enable the migration of carbon atoms at the edge of graphene to the particle surface to form a coating layer;

[0108] S4: Cooling to room temperature and storing under nitrogen protection.

[0109] Among them, in the mixed gas of S2, the volume fraction of methane is 8%, and the flow rate of the mixed gas is controlled at 35 mL / min.

[0110] 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 promoter in this comparative example, only a single surfactant, cetyltrimethylammonium bromide, is used as the surfactant, and polyethylene glycol-4000 is not introduced.

[0111] 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 promoter in this comparative example, traditional muffle furnace calcination is used, and microwave-assisted calcination is not used.

[0112] 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 promoter in this comparative example, an ordinary alumina carrier is used to replace the special carrier.

[0113] Testing methods and testing items:

[0114] Dispersibility of nanoparticles: Evaluating the particle size distribution uniformity and agglomeration degree according to the GB / T 29022-2012 standard in combination with lens electron microscopy analysis;

[0115] High-temperature anti-sintering performance: Constant temperature for 10 hours in an air atmosphere at 700 °C, analyze the change in grain size by XRD, and compare the change rate before and after aging;

[0116] Wear resistance: Use a fluidized bed wear tester, set the gas velocity at 3 m / s, use quartz sand as the wear medium, and continue for 24 h, record the wear amount.

[0117] Perform performance tests on the nano-palladium or platinum carbon monoxide combustion promoters prepared in Examples 1-3 and Comparative Examples 1-3, and record the test data in the following table:

[0118]

[0119] By comparing the data in Examples 1-3 and Comparative Example 1 in the table, it can be seen that compared with the nano-palladium or platinum carbon monoxide combustion promoters prepared in Examples 1-3, the traditional combustion promoter has a single action mechanism due to a single surfactant and cannot effectively regulate the nucleation kinetics of nanoparticles. However, when using a compound system of polyethylene glycol-4000 and cetyltrimethylammonium bromide, the long-chain ether bond of polyethylene glycol-4000 combines with the hydrophobic tail of cetyltrimethylammonium bromide through hydrophobic interaction to form a double-layer micelle structure. Polyethylene glycol-4000 provides steric hindrance to inhibit particle collision, and the cation of cetyltrimethylammonium bromide weakens the van der Waals force through electrostatic repulsion. The two work together to reduce the surface energy of the particles. At the same time, the dynamic light scattering results show that the PDI of Example is 0.11, indicating that the particles are evenly dispersed, while the PDI of Comparative Example 1 reaches 0.39, indicating that a single cetyltrimethylammonium 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 density of active sites and lay a foundation for high catalytic activity;

[0120] From the above analysis, it can be concluded that the traditional single surfactant has a weak adsorption ability on the surface of nanoparticles, which easily leads to particle aggregation and reduces the active sites. The present invention uses a compound system of polyethylene glycol and cetyltrimethylammonium bromide. Through the synergistic effect of non-ionic and cationic surfactants, a bilayer coating structure is formed on the surface of the nanoparticles. This structure can effectively reduce the surface energy of the particles, inhibit the aggregation driven by the van der Waals force, and enable the active metal to be evenly loaded on the surface of the carrier in a nano-scale monodispersed state. At the same time, the hydrophilic groups of the composite surfactant form hydrogen bonds with the hydroxyl groups of the carrier, enhancing the interfacial binding force between the particles and the carrier, thereby significantly increasing the exposure amount and utilization rate of catalytic active sites;

[0121] It can be seen from the data comparison between Examples 1-3 and Comparative Example 2 in the table that compared with the nano-palladium or platinum carbon monoxide combustion promoters prepared by the preparation method of Comparative Example 2 and those prepared in Examples 1-3, traditional calcination relies on heat conduction heating, and the poor temperature uniformity leads to a decrease in the surface migration energy barrier of the particles. In contrast, microwave gradient calcination utilizes the dielectric difference between mesoporous alumina and graphene to form a dynamic temperature gradient inside the carrier. This gradient drives the nano-particles to migrate directionally into the mesopores, and the pore confinement effect inhibits grain boundary diffusion. After high-temperature aging, the particle size growth in Examples 1-3 is ≤8.5%, while that in Comparative Example 2 is >26.0%. This shows that microwave calcination realizes the embedded fixation of particles through a non-equilibrium thermodynamic process, effectively delaying high-temperature sintering.

[0122] From the above analysis, it can be concluded that traditional muffle furnace calcination relies on heat conduction, which easily leads to local overheating and abnormal grain growth. The present invention adopts a microwave-assisted calcination process. Utilizing the high dielectric loss property of graphene, a dynamic temperature gradient is formed inside the carrier. This gradient heating enables atomic-level diffusion between the active metal and the carrier, forming a stable interfacial bonding. At the same time, it inhibits 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 edges of graphene, forming an ultrathin carbon coating layer on the surface of the metal particles. This carbon layer further stabilizes the nanostructure through chemical anchoring, enabling the combustion promoter to maintain its structural integrity even in a high-temperature environment.

[0123] It can be seen from the data comparison between Examples 1-3 and Comparative Example 3 in the table that compared with the nano-palladium or platinum carbon monoxide combustion promoters prepared by the preparation method of Comparative Example 3 and those prepared in Examples 1-3, due to the disordered pore size distribution and high closed pore rate of the ordinary alumina carrier, the diffusion path of the reactants is tortuous. In contrast, the mesoporous alumina-graphene composite carrier constructs a hierarchical mass transfer network through the three-dimensional interconnected pores and the interpenetration of graphene sheets. At the same time, the introduction of graphene enhances the mechanical strength of the carrier and significantly reduces the attrition index. This shows that the special carrier can significantly improve the service life of the combustion promoter.

[0124] From the above analysis, it can be concluded that the pore structure of the ordinary alumina carrier is disordered and its specific surface area is relatively low, which limits the catalytic efficiency. The present invention adopts a composite carrier of mesoporous alumina and graphene. The three-dimensional interconnected pores of mesoporous alumina provide a high specific surface area and abundant active sites, while the sheet interpenetration structure of graphene forms a conductive network, promoting electron transfer and heat dispersion. This composite carrier effectively inhibits the migration and agglomeration of metal particles through physical confinement effects and chemical synergistic effects, while enhancing the anti-wear performance of the carrier. In addition, the high thermal conductivity of graphene can quickly conduct out the reaction heat, avoiding catalyst deactivation caused by local overheating, thereby significantly extending the service life of the combustion promoter, reducing the consumption of precious metals, and reducing the environmental load.

[0125] In the description of this specification, the descriptions referring to the terms "one embodiment", "example", "specific example", etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0126] 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 embodiments described. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can well understand and utilize the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A method for preparing a nano-palladium or platinum carbon monoxide combustion promoter, 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 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; The composite surfactant is a compound of polyethylene glycol-4000 and hexadecyltrimethylammonium bromide, and the compounding ratio is (2-5):1; The 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; 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 presents a three-dimensional interconnected structure; 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, react at 100-150° C. for 12-24 hours to obtain a solid precipitate, then repeatedly wash the solid precipitate 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; 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 drop a 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 hours 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 the nano-palladium or platinum carbon monoxide combustion promoter according to claim 1, characterized in that, The palladium-containing precursor is selected from at least one of palladium nitrate and palladium acetate, and the platinum-containing precursor is selected from at least one of chloroplatinic acid and platinum acetylacetonate.

3. The method of the nano-palladium or platinum carbon monoxide combustion promoter according to claim 1, characterized in that, The aluminum source is selected from at least one of aluminum nitrate and aluminum isopropoxide, and the template agent is hexadecyltrimethylammonium bromide.

4. The method of the nano-palladium or platinum carbon monoxide combustion promoter according to claim 1, characterized in that, The preparation method of the mesoporous alumina-graphene composite 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 the conditions of an ultrasonic power of 50-200 W and a frequency of 40 kHz to obtain a graphene dispersion liquid, then weighing mesoporous alumina as required and adding it to the graphene dispersion liquid, stirring and mixing for 3-6 h under the conditions of a rotation speed of 300-600 r / min, transferring to a centrifuge, centrifugally separating for 10-15 min under the conditions of 5000-8000 r / min, taking the centrifugal precipitate, and then drying at 80-120 °C for 12-24 h to prepare a special carrier.

5. A method for a nano-palladium or platinum carbon monoxide combustion promoter according to claim 1, characterized in that, The surface of the combustion promoter has a carbon coating layer with a thickness of 2-5 nm, and its formation method comprises the following steps: S1: Heating the combustion promoter after microwave-assisted calcination to 200-300 °C in a nitrogen atmosphere for pretreatment for 1 h; S2: Introducing a mixed gas of methane and argon; S3: Heating to 400-600 °C at a rate of 5 °C / min and holding for 1-3 h to enable the migration of carbon atoms at the edges of graphene to the particle surface to form a coating layer; S4: Storing under nitrogen protection after cooling to room temperature.

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

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