Catalyst for automobile tail gas treatment or volatile organic compound oxidation as well as preparation method and application of catalyst

Abstract

The invention belongs to the technical field of organic matter oxidation catalytic materials, and relates to a catalyst for automobile exhaust treatment or volatile organic matter oxidation and a preparation method and application thereof, the catalyst comprises 30-60 wt% of a regular carrier, 20-50 wt% of a porous alumina material, 10-30 wt% of a cerium-zirconium solid solution material and 0.3-2 wt% of noble metal, the average particle size of the noble metal is greater than 2 nm and less than 4.5 nm, and the distribution uniformity of the noble metal is 10-30. The preparation method comprises the following steps: forming the carrier comprising the coating, impregnating the noble metal under specific supercritical conditions, drying and roasting. The catalyst has higher low-temperature oxidation activity of volatile organic compounds.

Description

Technical Field

[0001] The invention belongs to the technical field of organic oxidation catalytic materials. Technical background:

[0002] China is currently experiencing rapid growth in its vehicle population, having been the world's largest auto producer and new car market for ten consecutive years. With the rapid development of the auto industry, the environmental pollution caused by automobiles has received increasing attention from both the government and society. While domestic sales and ownership of new energy vehicles have continued to rise in recent years, overall, gasoline-powered vehicles will remain the dominant force in the future auto market.

[0003] To mitigate the environmental impact of automobile exhaust, pollutant emissions must be minimized. Post-process control measures involving exhaust purification, filtration, and catalytic conversion are effective methods for reducing harmful exhaust emissions, with exhaust catalysts playing a key role. These catalysts, typically placed within vehicle exhaust purifiers, convert harmful exhaust gases into harmless substances before releasing them into the atmosphere. They are currently widely used and promoted worldwide.

[0004] While automotive exhaust catalysts have made significant contributions to environmental protection, they also face certain development challenges. Currently, automotive exhaust catalysts have become the leading application for precious metals, with strong demand. However, precious metal production has remained stable, leading to a continuous upward trend in the prices of metals used in automotive exhaust catalysts, such as Pd, and placing greater cost pressure on the automotive exhaust catalyst industry. Therefore, further reducing the amount of precious metals used in automotive exhaust catalysts is a necessary step for future research and development. This requires catalysts to exhibit significantly higher activity with lower precious metal usage, or even higher activity with the same amount of precious metal.

[0005] Current automotive exhaust catalysts generally exhibit excellent high-temperature catalytic performance but insufficient low-temperature performance. The approximately two-minute transition time between cold and hot internal combustion engines means the exhaust gas temperature does not reach the required catalyst temperature, resulting in suboptimal catalytic performance. Studies have shown that 60% to 80% of toxic gases in automotive exhaust are produced within two minutes of a cold start. To further improve catalytic efficiency, the catalyst's low-temperature performance must be maximized to enhance the low-temperature conversion of exhaust gas.

[0006] Volatile organic compounds (VOCs) are organic compounds with a saturated vapor pressure greater than 70 Pa at room temperature and a boiling point below 260°C at normal pressure, or any volatile organic compound with a vapor pressure greater than or equal to 10 Pa at 20°C. VOCs are diverse and classified into eight categories based on their chemical structure: alkanes, aromatic hydrocarbons, halogenated hydrocarbons, esters, aldehydes, ketones, and other compounds. VOCs are categorized by their boiling point as very volatile organic compounds (VVOCs), volatile organic compounds (VOCs), and semi-volatile organic compounds (SVOCs). VOCs have a small molecular weight, easily vaporize, and are highly reactive. They can exist as primary volatiles in the gaseous state or undergo chemical reactions under ultraviolet light to form more complex mixtures of gaseous and solid states, posing direct or indirect risks to the environment and human health.

[0007] At present, the main VOCs treatment technologies in industry are as follows:

[0008] Adsorption recovery technology is suitable for the treatment of VOCs with high concentration, single components and certain recovery value.

[0009] Thermal storage combustion technology is suitable for the treatment of VOCs that are high in concentration, complex in composition, toxic and harmful, and can poison catalysts.

[0010] Catalytic oxidation technology can be applied to different air volumes, different concentrations and a variety of VOCs treatment, and has good adaptability and flexibility.

[0011] Catalytic oxidation technology for treating VOCs is gaining increasing attention from researchers and industry. Among them, VOCs catalytic oxidation catalyst is the core of the technology, and its treatment efficiency and treatment volume directly affect the treatment effect of VOCs catalytic oxidation.

[0012] Currently, industrial VOCs catalytic oxidation catalysts often use precious metals as active components, resulting in relatively high costs. Reducing catalyst manufacturing costs is a key factor influencing the widespread adoption of these technologies. Furthermore, researchers are also focusing on the low-temperature conversion performance of VOC catalytic oxidation catalysts. Lower conversion temperatures broaden industrial application ranges and reduce energy consumption. Summary of the Invention

[0013] The first technical problem to be solved by the present invention is to provide a volatile organic compound oxidation conversion catalyst with a low precious metal content, which has a good organic compound oxidation conversion effect under the condition of low precious metal content.

[0014] The second technical problem to be solved by the present invention is to provide a method for preparing a VOCs oxidation catalyst. The catalyst prepared by this method has a better distribution of precious metals on the surface of the catalyst carrier and has a certain degree of dispersibility, which can achieve a better VOCs organic matter oxidation conversion effect under the premise of a low amount of precious metals.

[0015] The third technical problem to be solved by the present invention is to provide a method for applying the VOCs oxidation catalyst in automobile exhaust purification or VOCs catalytic oxidation.

[0016] In the present invention, the dispersion of the precious metal is expressed as the average particle size of the precious metal. The precious metal particle size in the carrier (coating) is measured by transmission electron microscopy. The metal particle size is the minimum circumscribed circle diameter of the precious metal particle projection. The average particle size of 20 randomly measured metal particles is calculated as the arithmetic mean of their particle sizes to obtain the average particle size as the dispersion. The smaller the average particle size, the higher the precious metal dispersion.

[0017] The distribution of precious metals refers to the distribution of precious metal particles in different locations of the coating. Precious metal particles do not aggregate significantly in the coating and are relatively evenly distributed. The uniformity of precious metal distribution (also known as distribution uniformity or dispersion) is determined by making a cross-section of the product and then scanning it with an electron probe (EPMA) to examine the distribution of precious metals in the coating of the catalyst system. An indicator of distribution uniformity is to use a computer to calculate the concentration of precious metals in 200 to 1000 tiny areas (expressed as the intensity of the EPMA signal) and calculate the standard deviation of the concentration values. The larger the standard deviation, the worse the uniformity of the precious metal distribution.

[0018] Pore ​​distribution can be measured using nitrogen adsorption capacity. For calculations of pore volume and pore size distribution, refer to RIPP 151-90, "Determination of Pore Volume and Pore Size Distribution of Catalysts by Nitrogen Adsorption Capacity," in Petrochemical Analytical Methods (RIPP Test Method) (edited by Yang Cuiding et al., Science Press, 1990). Specific surface area is calculated using the BET formula.

[0019] The isoelectric point is measured using zeta potential analysis. Particles with an average particle size of 5 to 30 μm are dispersed into a slurry with a solids content of 0.3% by weight. The zeta potential of the material is measured using electrophoretic light scattering. Adjusting the pH of the slurry changes the zeta potential. When the zeta potential is 0, the corresponding pH is the isoelectric point of the material.

[0020] The present invention provides a volatile organic compound oxidation catalyst, which includes 30 to 60 weight percent of a structured carrier, 20 to 50 weight percent of a porous alumina material, 10 to 30 weight percent of a cerium-zirconium solid solution material, and 0.3 to 2 weight percent of a noble metal, wherein the average particle size of the noble metal is greater than 2 nm and less than 4.5 nm, and the distribution uniformity of the noble metal is 10 to 30.

[0021] Preferably, the cerium-zirconium solid solution and the porous alumina material form a coating that adheres to the pore surface and / or outer surface of the structured support.

[0022] Preferably, in the volatile organic compound oxidation catalyst or the coating, the weight ratio of the cerium-zirconium solid solution to the porous alumina material is 1:5 to 3:2, for example, 0.8:1 to 1.2:1.

[0023] Preferably, the weight ratio of the noble metal to the cerium-zirconium solid solution in the volatile organic compound oxidation catalyst or the coating is 0.01:1 to 0.2:1. The cerium-zirconium solid solution and the porous alumina material are calculated on a dry basis.

[0024] Preferably, in the volatile organic compound oxidation catalyst provided by the present invention, the distribution uniformity of the metal is 12-23, preferably 12-16.

[0025] Preferably, in the volatile organic compound oxidation catalyst provided by the present invention, the average particle size of the noble metal is, for example, 2.2 to 4.3 nm.

[0026] The present invention also provides a method for preparing a structured supported catalyst for automobile exhaust treatment or volatile organic compound oxidation, comprising the following steps:

[0027] (1) forming a coating comprising a porous alumina material and a cerium-zirconium solid solution on a structured support to obtain a coated support;

[0028] (2) impregnating the product of step (1) with a supercritical fluid solution of a noble metal salt; the supercritical fluid is a supercritical fluid with a specific polarity and a dipole moment greater than 1.0D; obtaining an impregnated catalyst;

[0029] (3) Optional drying and roasting.

[0030] According to the preparation method of the structured supported catalyst provided by the present invention, in one embodiment, the method of forming a coating comprising a porous alumina material and a cerium-zirconium solid solution on a structured support in step (1) is as follows: a mixture of the porous alumina material, the cerium-zirconium solid solution and water is formed, ground to obtain a first slurry, and the structured support is coated with the first slurry, the coating process is carried out once or multiple times, dried, and calcined to obtain a coated support; wherein the solid content of the first slurry can be 10 to 25% by mass, preferably 15 to 20% by mass, and the content of the coating in the coated support can be 20 to 55% by mass (based on the support), preferably 25 to 50% by mass of the support.

[0031] According to the method for preparing the structured supported catalyst provided by the present invention, the dipole moment of the supercritical fluid is greater than 1.0D, and the supercritical fluid is, for example, ammonia or methanol, and preferably ammonia. In the catalyst preparation method provided by the present invention, the noble metal is dissolved in the supercritical fluid having a high dipole moment in the form of a nitrate. The supercritical fluid molecules and the noble metal ions undergo polarization, so that when the noble metal ions are precipitated on the support, the ions are relatively far apart from each other, making it easier to form noble metal particles with good distribution uniformity.

[0032] According to the method for preparing the structured supported catalyst provided by the present invention, preferably, the temperature of the supercritical fluid solution immersion in step (2) is higher than 132.3° C. and not more than 160° C., and the pressure is higher than 11.3 MPa and not more than 18 MPa.

[0033] According to the method for preparing the structured supported catalyst provided by the present invention, the supercritical fluid solution preferably further includes a cosolvent, such as one or more of ethylene glycol and methyl oxalate. In one embodiment, the weight ratio of the cosolvent to the supercritical fluid in the supercritical fluid solution is 0.02:1 to 0.08:1. Under the preparation conditions described herein, the catalyst prepared with the addition of the cosolvent exhibits higher low-temperature activity.

[0034] The drying and calcining methods in step (3) can be conventional methods, which are well known to those skilled in the art. For example, the calcination temperature can be 450-550° C., and the calcination time can be 1-6 hours. Drying can be performed by air drying, oven drying, or airflow drying.

[0035] According to the method for preparing the structured supported catalyst provided by the present invention, the molar ratio of cerium to zirconium in the cerium-zirconium solid solution may be 30:70 to 60:40.

[0036] According to the method for preparing the structured supported catalyst provided by the present invention, the isoelectric point of the cerium-zirconium solid solution is preferably 8.0-8.5.

[0037] According to the method for preparing the structured supported catalyst provided by the present invention, the specific surface area of ​​the porous alumina material can be 200 to 350 m 2 / gFor example, 220~300m 2 / g, the pore volume can be 0.45~0.6cm 3 In one embodiment, the porous alumina material has a unimodal pore structure distribution.

[0038] The porous alumina material, for example, includes one or more of pseudo-boehmite, γ-alumina, and aluminum sol.

[0039] According to the method for preparing the structured supported catalyst provided by the present invention, the isoelectric point of the porous alumina material is preferably 8.0 to 8.5.

[0040] The porous alumina and cerium oxide-zirconium oxide solid solution (cerium-zirconium solid solution) are preferably neutral to alkaline materials. Measurement of their surface potentials indicates that the isoelectric points of the alumina and cerium oxide-zirconium oxide solid solution are each preferably 8.0 to 8.5. When noble metal salts are dissolved in the supercritical fluid and combined with suitable isoelectric porous alumina and cerium-zirconium solid solution supports, they can better penetrate the micropores of the support and be better dispersed and distributed. This can also effectively reduce aggregation of the noble metals during drying and calcining, achieving a more uniform distribution.

[0041] According to the method for preparing the structured supported catalyst provided by the present invention, in one embodiment, the structured support is a porous cordierite ceramic material, preferably a support having honeycomb channels.

[0042] According to the method for preparing the structured supported catalyst provided by the present invention, the precious metal is preferably one or more of platinum, palladium, and rhodium.

[0043] The present invention further provides the use of the volatile organic compound oxidation catalyst in automobile exhaust purification or catalytic oxidation of volatile organic compounds (VOCs).

[0044] In one embodiment, the catalytic oxidation of volatile organic compounds comprises contacting the exhaust gas containing VOCs with the volatile organic compound oxidation catalyst at a temperature of 220 to 420°C. The VOC content in the exhaust gas containing VOCs may be 50 to 10,000 ppmV, and the flow rate of the VOCs may be 500 to 10,000 Nm 3 / (h×m 3 The VOCs include, for example, one or more of ethane, ethylene, propane, propylene, butane, butene, benzene, toluene, xylene, and heterocyclic organic compounds.

[0045] In one embodiment, the volatile organic compound catalytic oxidation catalyst is used for automobile exhaust purification, and its application method includes the step of contacting exhaust gas generated by an automobile engine with the volatile organic compound oxidation catalyst provided by the present invention. The exhaust gas generated by the automobile engine is, for example, exhaust gas generated by a gasoline engine.

[0046] The volatile organic compound (VOC) catalytic oxidation catalyst provided by the present invention has a low precious metal content, a certain degree of dispersion, and a high degree of distribution uniformity. For the catalytic oxidation of VOCs, the catalyst achieves improved low-temperature conversion efficiency compared to existing organic oxidation catalysts at the same precious metal content. For example, the organic oxidation catalyst provided by the present invention achieves a 50% organic conversion rate at a lower reaction temperature, demonstrating high low-temperature conversion activity and the ability to achieve a lower organic conversion temperature. Furthermore, due to the low precious metal content, the cost of the organic oxidation catalyst can be reduced.

[0047] The method for preparing a structured carrier catalyst provided by the present invention can reduce the uneven distribution phenomenon during the noble metal loading process, reduce the obvious high-density distribution, and make the noble metal more evenly distributed in the carrier coating with a certain degree of dispersibility.

[0048] The catalyst provided by the present invention is used for catalytic oxidation of VOCs, so that the volatile organic compounds therein are oxidized to form carbon oxides such as CO2, and has high conversion activity, especially high low-temperature conversion activity. For example, the catalyst prepared in Example 3 of the present invention is compared with the catalyst provided in Comparative Example 3 under the same amount of precious metal under the total volume space velocity of 3000h -1 When the propane concentration is 2.5%, the 50% conversion temperature of propane (the temperature at which hydrocarbons are converted to 50%) is reduced by 29°C, and the low-temperature oxidation activity is significantly improved.

[0049] The organic oxidation catalyst provided by the present invention can also be used to treat automobile exhaust, simultaneously removing CO, NO, and hydrocarbon pollutants from automobile exhaust at relatively low temperatures. For example, when the catalyst provided in Example 2 of the present invention is used as an automobile exhaust catalyst, compared to Comparative Example 2 based on the prior art, at the same precious metal dosage, the 50% conversion temperature for CO is reduced by 8°C, the 50% conversion temperature for NOx is reduced by 10°C, and the 50% conversion temperature for hydrocarbons is reduced by 8°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 Cross-sectional view (left) and precious metal distribution (right) of the coating (coating 1) prepared by conventional method. Cross-sectional EPMA analysis of the catalyst prepared in Comparative Example 2.

[0051] Figure 21 is a cross-sectional view of the coating (coating 2) prepared by the method of the present invention and the distribution of precious metals. 2 is a cross-sectional EPMA analysis of the catalyst prepared in Example 2.

[0052] EPMA analysis of cross sections of coating 1 and coating 2 Figure 1 and Figure 2 It can be seen that coating 1 forms obvious precious metal aggregation on the surface or in the bulk; coating 2 has a more uniform distribution of precious metals, and no obvious precious metal aggregation is formed on the surface or in the bulk.

[0053] Figure 3 This is a simplified diagram of the sample evaluation device. 1 is the air feed line, 2 is the CO gas feed line, 3 is the NO gas feed line, 4 is the hydrocarbon gas feed line, 5 is the catalyst, 6 is the thermocouple, 7 is the heating jacket, and 8 is the detection equipment.

[0054] Figure 4 Cross-sectional EPMA analysis diagram and precious metal distribution of the catalyst prepared in Comparative Example 6. DETAILED DESCRIPTION

[0055] In one embodiment, the present invention provides a method for preparing a catalyst, comprising:

[0056] (1) preparing a slurry of suitable concentration from raw materials including porous alumina material and cerium-zirconium solid solution material, and coating the slurry on the cordierite carrier to obtain a coated cordierite carrier; wherein the cordierite carrier is a honeycomb carrier with a pore density of, for example, 300 to 600 pores / inch; 2 The porous alumina material preferably has a specific surface area of ​​200 to 350 m 2 / g is, for example, 220 to 300 m 2 / g, the solid content of the slurry of suitable concentration is, for example, 10 to 25 wt % and preferably 15 to 20 wt %;

[0057] (2) calcining the coated cordierite support, for example, at 450-550° C. for 1-6 hours to obtain a calcined support;

[0058] (3) Using a supercritical fluid with or without a cosolvent to dissolve a precious metal salt to obtain a supercritical fluid solution of the precious metal salt. The concentration of the precious metal salt in the supercritical fluid solution of the precious metal salt can be 0.5 to 10% by weight, and the precious metal is one or more of Pt, Pd, and Rh. In one embodiment, the calcined support is immersed in a supercritical fluid solution with or without a cosolvent for a certain period of time, and then removed to obtain an impregnated catalyst; the certain period of time is, for example, 5 to 60 minutes or 5 to 30 minutes.

[0059] (4) The impregnated catalyst is dried and then calcined, for example, at 450-550° C. for 1-6 hours to obtain a finished catalyst.

[0060] The following examples and comparative examples further illustrate the present invention:

[0061] Comparative Examples and Examples:

[0062] Alumina material, crystal form is γ-Al2O3, specific surface area 300m 2 / g, pore volume 0.55cm 3 / g, isoelectric point is 8.5. It was purchased from Zibo Zhengxuan Catalyst Co., Ltd.

[0063] Cerium-zirconium solid solution, manufacturer: Northern Rare Earth Co., Ltd., specific surface area 65m 2 / g, pore volume 0.30cm 3 / g. The isoelectric point is 8.0. The molar ratio of zirconium to cerium is 50:40;

[0064] Pt salt was platinum nitrate, purchased from J&K Company.

[0065] The Pd salt was palladium nitrate, purchased from J&K Company.

[0066] Rh salt was rhodium nitrate, purchased from J&K Company.

[0067] EPMA analysis Electron probe microanalysis (EPMA) was measured using an electron probe microanalyzer (JEOL Ltd., JXA-8530F PLUS).

[0068] Example 1

[0069] A cylindrical cordierite carrier with a pore density of 600 mesh, a diameter of 25 mm, a length of 40 mm, and a volume of 19.6 mL was used.

[0070] 60g of alumina material and 60g of cerium-zirconium solid solution were prepared into a slurry with a solid content of 15 wt%. The slurry was coated on a cordierite carrier in multiple times. After drying and calcining at 500°C for 4 hours, a calcined coated carrier was obtained with a coating content of 50 wt%.

[0071] 1.3 g of Pt salt and 0.25 g of Rh salt were dissolved in supercritical fluid ammonia (supercritical ammonia contained 5% by mass (based on the mass of ammonia) of methyl oxalate). The salt content in the solution was 5 wt%. The calcined coated support was immersed in the supercritical fluid at a temperature of 138°C and a pressure of 11.3 MPa. After 30 minutes, the support was taken out, dried, and calcined at 500°C for 4 hours to obtain the finished catalyst, which was recorded as C1.

[0072] Example 2

[0073] A cylindrical cordierite carrier with a pore density of 600 mesh, a diameter of 25 mm, a length of 40 mm, and a volume of 19.6 mL was used.

[0074] 60g of alumina material and 60g of cerium-zirconium solid solution were prepared into a slurry with a solid content of 15 wt%. The slurry was coated on a cordierite carrier in multiple times. After drying and calcining at 500°C for 4 hours, a calcined coated carrier was obtained with a coating content of 50 wt%.

[0075] 1.5 g of Pd salt and 0.25 g of Rh salt were dissolved in supercritical fluid ammonia (supercritical ammonia contained 5% by mass (based on the mass of ammonia) of methyl oxalate) to form a supercritical fluid solution with a salt content of 5 wt%. The calcined coated carrier was immersed in the supercritical fluid solution at a temperature of 138°C and a pressure of 11.3 MPa. After 30 minutes, the carrier was taken out and dried and calcined at 500°C for 4 hours to obtain a finished catalyst, which was recorded as C2.

[0076] Example 3

[0077] A rectangular cordierite carrier with a pore density of 300 mesh, dimensions of 20*20*40 mm, and a volume of 16 mL was used.

[0078] 60g of alumina material and 60g of cerium-zirconium solid solution were prepared into a slurry with a solid content of 15 wt%. The slurry was coated on a cordierite carrier in multiple times. After drying and calcining at 500°C for 4 hours, a calcined coated carrier was obtained with a coating content of 25 wt%.

[0079] 0.3 g of Pt salt was dissolved in supercritical fluid ammonia (supercritical ammonia contained 5% by mass (based on the mass of ammonia) of methyl oxalate), and the calcined catalyst was immersed in supercritical fluid ammonia to form a supercritical fluid solution with a salt content of 2 wt%. The calcined coated carrier was immersed in the supercritical fluid solution at a temperature of 138°C and a pressure of 11.3 MPa. After 30 minutes, the catalyst was taken out and dried and calcined at 500°C for 4 hours to obtain the finished catalyst, which was recorded as C3.

[0080] Example 4

[0081] A rectangular cordierite carrier with a pore density of 300 mesh, dimensions of 20*20*40 mm, and a volume of 16 mL was used.

[0082] 60g of alumina material (specific surface area 300m 2 / L), 60g of cerium-zirconium solid solution was prepared into a slurry with a solid content of 15 wt%, and the slurry was coated on a cordierite carrier in multiple times. After drying and calcining at 500°C for 4 hours, a calcined coated carrier was obtained with a coating content of 25 wt%.

[0083] 0.3 g of Pd salt was dissolved in supercritical fluid ammonia (supercritical ammonia containing 5% by mass (based on the mass of ammonia) of methyl oxalate) to form a supercritical fluid solution with a salt content of 2 wt%. The calcined coated carrier was immersed in the supercritical fluid solution at a temperature of 138°C and a pressure of 11.3 MPa. After 30 minutes, the carrier was taken out and dried and calcined at 500°C for 4 hours to obtain a finished catalyst, which was recorded as C4.

[0084] Example 5

[0085] A rectangular cordierite carrier with a pore density of 300 mesh, dimensions of 20*20*40 mm, and a volume of 16 mL was used.

[0086] 60g of alumina material (specific surface area 300m 2 / L), 60g of cerium-zirconium solid solution was prepared into a slurry with a solid content of 15 wt%, and the slurry was coated on a cordierite carrier in multiple times. After drying and calcining at 500°C for 4 hours, a calcined coated carrier was obtained with a coating content of 25 wt%.

[0087] 0.1 g of Pt salt and 0.2 g of Pd salt were dissolved in supercritical fluid ammonia (supercritical ammonia contained 5% by mass (based on the mass of ammonia) of methyl oxalate) to form a supercritical fluid solution with a salt content of 2 wt%. The calcined coated carrier was immersed in the supercritical fluid solution at a temperature of 138°C and a pressure of 11.3 MPa. After 30 minutes, the carrier was taken out and dried and calcined at 500°C for 4 hours to obtain a finished catalyst, which was recorded as C5.

[0088] Example 6

[0089] A rectangular cordierite carrier with a pore density of 300 mesh, dimensions of 20*20*40 mm, and a volume of 16 mL was used.

[0090] 60g of alumina material and 60g of cerium-zirconium solid solution were prepared into a slurry with a solid content of 15 wt%. The slurry was coated on a cordierite carrier in multiple times. After drying and calcining at 500°C for 4 hours, a calcined coated carrier was obtained with a coating content of 25 wt%.

[0091] 0.3 g of Pt salt was dissolved in supercritical fluid ammonia (supercritical ammonia does not contain a cosolvent), and the calcined catalyst was immersed in supercritical fluid ammonia to form a supercritical fluid solution with a salt content of 2 wt%. The calcined coated carrier was immersed in the supercritical fluid solution at a temperature of 138°C and a pressure of 11.3 MPa. After 30 minutes, the catalyst was taken out and dried and calcined at 500°C for 4 hours to obtain a finished catalyst, which was recorded as C6.

[0092] Comparative Example 1

[0093] A cylindrical cordierite carrier with a pore density of 600 mesh (square pores, the same below) was used, with a diameter of 25 mm, a length of 40 mm, and a volume of 19.6 mL.

[0094] 60 g of alumina material, 60 g of cerium-zirconium solid solution, 1.3 g of Pt salt and 0.25 g of Rh salt were prepared into a slurry with a solid content of 15 wt%. The slurry was coated on a cordierite carrier in multiple times. After drying and calcining at 500°C for 4 hours, a finished catalyst was obtained, which was recorded as D1, wherein the coating content was 50 wt%.

[0095] Comparative Example 2

[0096] A cylindrical cordierite carrier with a pore density of 600 mesh, a diameter of 25 mm, a length of 40 mm, and a volume of 19.6 mL was used.

[0097] 60 g of alumina material, 60 g of cerium-zirconium solid solution, 1.5 g of Pd salt and 0.25 g of Rh salt were prepared into a slurry with a solid content of 15 wt%. The slurry was coated on a cordierite carrier in multiple times. After drying and calcining at 500°C, a finished catalyst was obtained, recorded as D2, with a coating content of 50 wt%.

[0098] Comparative Example 3

[0099] A rectangular cordierite carrier with a pore density of 300 mesh, dimensions of 20*20*40 mm, and a volume of 16 mL was used.

[0100] 60g of alumina material, 60g of cerium-zirconium solid solution and 0.3g of Pt salt were prepared into a slurry with a solid content of 15 wt%. The slurry was coated on a cordierite carrier in multiple times. After drying and calcining at 500°C, a finished catalyst was obtained, denoted as D3, with a coating content of 25 wt%.

[0101] Comparative Example 4

[0102] A rectangular cordierite carrier with a pore density of 300 mesh, dimensions of 20*20*40 mm, and a volume of 16 mL was used.

[0103] 60 g of alumina material, 60 g of cerium-zirconium solid solution and 0.3 g of Pd salt were prepared into a coating slurry with a solid content of 15 wt%. The slurry was coated on a cordierite carrier in multiple times. After drying and calcining at 500°C, a finished catalyst was obtained, denoted as D4, with a coating content of 25 wt%.

[0104] Comparative Example 5

[0105] A rectangular cordierite carrier with a pore density of 300 mesh, dimensions of 20*20*40 mm, and a volume of 16 mL was used.

[0106] 60g of alumina material, 60g of cerium-zirconium solid solution, 0.1g of Pt salt and 0.2g of Pd salt were prepared into a slurry with a solid content of 15 wt%. The slurry was coated on a cordierite carrier in multiple times. After drying and calcining at 500°C, a finished catalyst was obtained, denoted as D5, with a coating content of 25 wt%.

[0107] Comparative Example 6

[0108] A rectangular cordierite carrier with a pore density of 300 mesh, dimensions of 20*20*40 mm, and a volume of 16 mL was used.

[0109] 60g of alumina material (specific surface area 300m 2 / L), 60g of cerium-zirconium solid solution was prepared into a slurry with a solid content of 15 wt%, and the slurry was coated on a cordierite carrier in multiple times. After drying and calcining at 500°C for 4 hours, a calcined coated carrier was obtained with a coating content of 25 wt%.

[0110] 0.1 g of Pt salt and 0.2 g of Pd salt were dissolved in supercritical fluid CO2 (supercritical CO2 contained 5% by mass of methyl oxalate) to form a supercritical fluid solution with a salt content of 0.8 wt%. The calcined coated carrier was immersed in the supercritical fluid solution at a temperature of 40°C and a pressure of 8.0 MPa. After 30 minutes, the carrier was taken out and dried and calcined at 500°C for 4 hours to obtain the finished catalyst, which was recorded as D6.

[0111] The cross section of Example 6 was prepared and subjected to EPMA analysis. Figure 4 As shown in the figure, it can be seen that the impregnation effect of supercritical CO2 is not as good as that of supercritical ammonia. (The sample prepared by supercritical CO2 still has a relatively obvious banded precious metal distribution area, and the precious metal content in this area is very high.)

[0112] Comparative Example 7

[0113] A rectangular cordierite carrier with a pore density of 300 mesh, dimensions of 20*20*40 mm, and a volume of 16 mL was used.

[0114] 60g of alumina material (specific surface area 300m 2 / L), 60g of cerium-zirconium solid solution was prepared into a slurry with a solid content of 15 wt%, and the slurry was coated on a cordierite carrier in multiple times. After drying and calcining at 500°C for 4 hours, a calcined coated carrier was obtained with a coating content of 25 wt%.

[0115] 0.1 g of Pt salt and 0.2 g of Pd salt were dissolved in supercritical fluid CO2 to form a supercritical fluid solution with a salt content of 0.8 wt%. The calcined coated carrier was immersed in the supercritical fluid solution at a temperature of 40°C and a pressure of 8.0 MPa. The carrier was taken out after 30 minutes, dried, and calcined at 500°C for 4 hours to obtain a finished catalyst, which was recorded as D7.

[0116] The above comparative examples and embodiments were characterized by TEM, and their average particle sizes of precious metals were obtained as shown in Table 1, where the average particle size is obtained by randomly selecting 20 metal particles, taking the minimum circumscribed circle diameter of each particle's projection as the particle size of the metal particle, and taking the arithmetic mean as the average particle size of the precious metal.

[0117] Table 1 Composition, average particle size and distribution uniformity of catalysts in comparative examples and examples

[0118]

[0119] Pollutant conversion efficiency of automobile exhaust catalysts

[0120] The schematic diagram of the evaluation device is as follows: Figure 3 As shown, CO gas, NO, hydrocarbon gas, and air are introduced into the reaction tube at fixed flow rates to simulate the exhaust composition of a car engine. The volume ratio of CO gas, NO, hydrocarbon gas, and air is 6:1:2:60, the hydrocarbon gas is propylene, and the total volume space velocity of all gases is 3000 h -1 (The volume of the gas is calculated based on the volume under standard conditions).

[0121] The catalyst is placed in the reaction tube and heated by an external heater. At the same time, a thermocouple is placed at the bottom of the catalyst to measure the inlet temperature at the bottom of the catalyst.

[0122] The tail gas pollutant conversion temperatures of the catalysts prepared in Comparative Example 1, Comparative Example 2, Example 1 and Example 2 were measured, and the results are shown in Table 2.

[0123] Table 2 Conversion efficiency of automobile exhaust pollutants in comparative examples and examples

[0124]

[0125] Pollutant conversion efficiency of volatile organic compound catalytic oxidation catalyst

[0126] The schematic diagram of the evaluation device is as follows: Figure 3 As shown, CO and NO gases are not introduced at this time, and hydrocarbon gas and air are introduced into the reaction tube at fixed flow rates to simulate the exhaust composition of the volatile organic compound catalytic oxidation device. The volume ratio of hydrocarbon gas to air is 1:40, and the total volume space velocity of all gases is 3000h -1 In order to be more representative, propane, propylene and toluene were selected as hydrocarbon gas model reactants and their conversion temperatures were investigated.

[0127] The catalyst was placed in a reaction tube and heated by an external heater. A thermocouple was placed at the bottom of the catalyst to measure the inlet air temperature. The organic matter conversion temperatures of the catalysts prepared in Comparative Examples 3, 4, 5, 6, 7, Examples 3, 4, 5, and 6 were measured, and the results are shown in Table 3.

[0128] Table 3 Volatile organic compound conversion efficiency of comparative examples and examples

[0129] Catalyst type Propane 50% conversion temperature / ℃ Propylene 50% conversion temperature / ℃ Toluene 50% conversion temperature / ℃ D3 390 251 262 D4 405 263 267 D5 401 258 263 D6 396 253 259 D7 398 251 260 C3 361 231 237 C4 372 240 245 C5 369 236 239 C6 386 246 252

[0130] As can be seen from Tables 2 and 3, the catalyst provided by the present invention has significantly higher low-temperature CO conversion activity and NOx conversion activity, and has significantly better low-temperature oxidation activity for volatile organic compounds.

Claims

1. A volatile organic compound oxidation catalyst comprising 30-60 wt% of a structured support, 20-50 wt% of a porous alumina material, 10-30 wt% of a cerium-zirconium solid solution material, and 0.3-2 wt% of a noble metal, wherein: The average particle size of the noble metal is greater than 2 nm and less than 4.5 nm, and the distribution uniformity of the noble metal is 10-30.

2. The volatile organic compound oxidation catalyst according to claim 1, characterized in that In the volatile organic compound oxidation catalyst, the weight ratio of the cerium-zirconium solid solution to the porous alumina material is 1:5 to 3:2, and the weight ratio of the noble metal to the cerium-zirconium solid solution is 0.01:1 to 0.2:

1.

3. The volatile organic compound oxidation catalyst according to claim 1 or 2, characterized in that: The distribution uniformity of the noble metal is 12-23, and the average particle size of the noble metal is 2.2-4.3 nm.

4. A method for preparing a structured supported catalyst, comprising the following steps: (1) forming a coating comprising a porous alumina material and a cerium-zirconium solid solution on a structured support to obtain a coated support; (2) impregnating the product of step (1) with a supercritical fluid solution of a noble metal salt; the supercritical fluid is a supercritical fluid having a specific polarity and a dipole moment greater than 1.0D; (3) Optional drying and roasting.

5. The method according to claim 4, wherein The method for forming a coating comprising a porous alumina material and a cerium-zirconium solid solution on a structured support is as follows: a mixture of the porous alumina material, the cerium-zirconium solid solution and water is formed, ground to obtain a first slurry, and the structured support is coated with the first slurry. The coating process is performed once or multiple times, followed by drying and calcination to obtain a coated support. The solid content of the first slurry is preferably 15 to 20% by weight, and the content of the coating in the coated support is preferably 25 to 50% of the mass of the structured support.

6. The method according to claim 4, wherein: The supercritical fluid is ammonia or methanol; wherein the supercritical fluid is preferably ammonia, the temperature of the supercritical fluid solution immersion in step (2) is preferably higher than 132.3°C and not more than 160°C, and the pressure is preferably higher than 11.3MPa and not more than 18MPa.

7. The method according to claim 4 or 6, wherein: The supercritical fluid solution further contains a cosolvent, such as one or more of ethylene glycol and methyl oxalate; the weight ratio of the cosolvent to the supercritical fluid is preferably 0.02:1 to 0.08:

1.

8. The method according to claim 4, wherein: The molar ratio of cerium to zirconium in the cerium-zirconium solid solution is 30:70 to 60:40; the specific surface area of ​​the porous alumina material is preferably 220 to 300 m 2 / g, and the pore volume is preferably 0.45 to 0.6 cm 3 / g; the porous alumina material is, for example, one or more of pseudo-boehmite, γ-alumina, and aluminum sol; the precious metal is preferably one or more of platinum, palladium, and rhodium; the regular structure carrier is, for example, a honeycomb carrier.

9. The method according to claim 4 or 8, wherein The isoelectric point of the porous alumina material is 8.0-8.5, and the isoelectric point of the cerium-zirconium solid solution is 8.0-8.

5.

10. Use of the catalyst according to any one of claims 1 to 3 in automobile exhaust treatment or volatile organic compound treatment.

Images