Diesel oxidation catalyst and preparation method thereof

Abstract

The invention provides a diesel oxidation catalyst and a preparation method thereof. The diesel oil oxidation catalyst comprises a cordierite honeycomb ceramic carrier and an active coating attached to the surface of the cordierite honeycomb ceramic carrier, the active coating comprises hydroxyapatite, precious metals are loaded on the hydroxyapatite, and the precious metals comprise Pt metals and Pd metals. According to the present invention, the excellent hydrothermal aging resistance can be represented without the doping modification. On one hand, hydroxyl (OH <->) and phosphate radical (PO43 <->) rich in the surface of hydroxyapatite can form stable chemical bonds with the noble metal, so that the stability of the diesel oil oxidation catalyst is improved, and the interaction between the carrier and the noble metal is enhanced. On the other hand, the ion exchange property of hydroxyapatite is beneficial for improving the dispersing performance of the diesel oil oxidation catalyst. And the precious metals Pt and Pd are used, so that the conversion efficiency of the diesel oxidation catalyst on nitric oxide and the like in diesel engine tail gas is improved, and harmful substances in tail gas emission are reduced.

Description

Technical Field

[0001] The invention relates to the technical field of diesel oxidation catalysts, and in particular to a diesel oxidation catalyst and a preparation method thereof. Background Art

[0002] Motor vehicle exhaust is one of the main sources of air pollutants, including carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NO x ) and particulate matter (PM). Motor vehicle exhaust not only causes serious environmental pollution, but also seriously endangers human health. Diesel vehicles have been widely used due to their fuel economy and high thermal efficiency. Diesel oxidation catalysts (DOC) mainly purify carbon monoxide (CO), hydrocarbon compounds (HC), nitrogen oxides (NO x ) and the soluble organic matter components (SOF) on the surface of particulate matter (PM), oxidizing the above pollutants in the exhaust gas into H2O, CO2 and NO2.

[0003] Traditional commercial DOC catalysts for diesel engine exhaust are mainly based on alumina as a carrier to load Pt and Pd, doped with a small amount of silica, zirconium oxide, titanium oxide, cerium oxide or a combination thereof. In order to improve the anti-aging performance of the catalyst, different amounts of rare earth elements such as Ce, Nd, Y, Pr, Zr, La or a combination thereof are selected to be doped on the above oxide carriers.

[0004] A Chinese patent application with patent authorization publication number CN112246276A discloses a manganese-containing diesel oxidation catalyst, specifically, an oxidation catalyst composite material for treating exhaust emissions from a diesel engine, the oxidation catalyst composite material comprising: a first carrier coating containing zeolite, Pt and a first refractory metal oxide carrier containing manganese; a second carrier coating containing a second refractory metal oxide carrier, a Pt component and a Pd component; and a third carrier coating containing palladium and a rare earth oxide component; selectively doping elements such as Si and Mn to improve the anti-aging properties of the alumina carrier, but the above modification of the carrier material will undoubtedly increase the raw material cost.

[0005] Therefore, developing a diesel oxidation catalyst with low raw material cost and excellent resistance to high-temperature hydrothermal aging is of great significance for the development of diesel engine exhaust purification systems. Summary of the invention

[0006] The main purpose of the present invention is to provide a diesel oxidation catalyst and a preparation method thereof, so as to solve the problems of poor resistance to high temperature hydrothermal aging and high raw material cost of the diesel oxidation catalyst in the prior art.

[0007] In order to achieve the above-mentioned purpose, according to one aspect of the present invention, a diesel oxidation catalyst is provided, which includes a cordierite honeycomb ceramic carrier and an active coating attached to the surface of the cordierite honeycomb ceramic carrier, the active coating includes hydroxyapatite, and the hydroxyapatite is loaded with precious metals, and the precious metals include Pt metal and Pd metal.

[0008] Furthermore, the cordierite honeycomb ceramic carrier has an air outlet and an air inlet, the active coating corresponding to the air inlet is a first active coating, and the active coating corresponding to the air outlet is a second active coating; and / or the concentration of the precious metal in the first active coating is 15 to 30 g / ft 3 , preferably 18 to 30 g / ft 3 , and / or the mass of the precious metal accounts for 0.1-1.5% of the total mass of the first active coating, and / or the mass ratio of Pt metal to Pd metal in the first active coating is 1-6:1.

[0009] Furthermore, the concentration of the precious metal in the second active coating is 5 to 30 g / ft 3 , and / or the mass of the precious metal accounts for 0.1-1.5% of the total mass of the second active coating, and / or the mass ratio of Pt metal to Pd metal in the second active coating is 6-12:1.

[0010] Furthermore, the cordierite honeycomb ceramic carrier is a cylinder, and along the axial direction of the cylinder, the length ratio of the first active coating layer to the second active coating layer is 1:2 to 2:1.

[0011] According to another aspect of the present invention, a method for preparing the above-mentioned diesel oxidation catalyst is provided, and the method comprises: step S1, mixing raw materials including hydroxyapatite and water to obtain slurry, adjusting the pH value of the slurry with glacial acetic acid and performing a first stirring to obtain an acidic slurry; step S2, performing a second stirring on raw materials including the acidic slurry, a platinum salt solution, a palladium salt solution and a bonding aid to obtain a mixture, adjusting the pH value of the mixture with glacial acetic acid to obtain an acidic mixture; step S3, performing a third stirring on the acidic mixture and a thickener to obtain slurry A; step S4, adjusting the amount of the platinum salt solution and the palladium salt solution, repeating steps S1 to S3 to obtain slurry B; step S5, coating slurry A and slurry B on the air inlet end and the air outlet end of a cordierite honeycomb ceramic carrier, respectively, and then drying and calcining in sequence to obtain a diesel oxidation catalyst.

[0012] Furthermore, the pH value of the acidic slurry is 3-5; and / or the rotation speed of the first stirring is 450-650 rpm, and the time of the first stirring is 0.5-2 hours.

[0013] Furthermore, the pH value of the above-mentioned acidic mixture is 3-5; and / or the second stirring speed is 450-650 rpm, and the second stirring time is 0.5-2 hours; and / or the third stirring speed is 450-650 rpm, and the third stirring time is 0.5-2 hours; and / or in slurry A, the amount of bonding aid is 3-6% of the total mass of hydroxyapatite; and / or in slurry B, the amount of bonding aid is 3-6% of the total mass of hydroxyapatite.

[0014] Further, the platinum salt solution is selected from any one or more of an aqueous solution of platinum nitrate, an aqueous solution of platinum chloride, an aqueous solution of chloroplatinic acid, an aqueous solution of platinum acetylacetonate, a platinum acetate solution and a tetraaminoplatinum-platinum tetrachloride solution; and / or, the palladium salt solution is selected from any one or more of an aqueous solution of palladium nitrate, an aqueous solution of palladium chloride, an aqueous solution of chloropalladic acid, an aqueous solution of palladium acetylacetonate, a palladium acetate solution and a tetraaminopalladium-palladium tetrachloride solution; and / or, in slurry A, the mass ratio of the platinum metal element in the platinum salt solution to the palladium metal element in the palladium salt solution is 1 to 6:1; and / or, in slurry B, the mass ratio of the platinum metal element in the platinum salt solution to the palladium metal element in the palladium salt solution is 6 to 12:1.

[0015] Furthermore, the solid content of the above-mentioned slurry A and slurry B is independently 20% to 35%; and / or, in slurry A, the mass proportion of the thickener in slurry A is 0.5% to 1%; and / or, in slurry B, the mass proportion of the thickener in slurry B is 0.5% to 1%.

[0016] Furthermore, the drying temperature is 100-150° C., and the drying time is 0.5-1 hour; and / or the calcination temperature is 500-650° C., and the calcination time is 2-4 hours.

[0017] By applying the technical solution of the present invention, the present invention discloses a diesel oxidation catalyst with excellent hydrothermal aging resistance, and can show excellent hydrothermal aging resistance without doping modification. Specifically, the present application uses hydroxyapatite as a carrier of precious metals Pt and Pd. Hydroxyapatite, as a new type of carrier material, contains only four elements: Ca, P, O and H. On the one hand, the hydroxyl groups (OH - ) and phosphate (PO4 3- ) can form stable chemical bonds with precious metals, which helps to evenly disperse the precious metals on the carrier, thereby improving the stability of the diesel oxidation catalyst and enhancing the interaction between the carrier and the precious metals. In particular, after high-temperature hydrothermal aging, the diesel oxidation catalyst can still maintain good stability and catalytic activity. Specifically, under conditions below 400°C, PO4 3- Play a stabilizing role, while at temperatures above 600°C, the surface OH -The hydroxyapatite has a stabilizing effect to improve the stability of the diesel oxidation catalyst. On the other hand, the ion exchangeability of hydroxyapatite helps to improve the dispersion performance of the diesel oxidation catalyst. At the same time, the use of precious metals Pt and Pd improves the conversion efficiency of the diesel oxidation catalyst to hydrocarbons, carbon monoxide and nitrogen monoxide in diesel engine exhaust, and reduces harmful substances in exhaust emissions. In addition, the raw materials of the diesel oxidation catalyst are simple to prepare, the cost is low, and it has a wide range of application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0019] Figure 1 A comparison chart of the ignition performance of the diesel oxidation catalyst in Example 1 of the present application and Comparative Example 1 is shown;

[0020] Figure 2 A comparison chart of the ignition performance of the diesel oxidation catalyst in Example 1 of the present application and Comparative Example 2 is shown. DETAILED DESCRIPTION

[0021] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0022] As analyzed in the background technology of this application, the prior art has the problem that the diesel oxidation catalyst has poor resistance to high-temperature hydrothermal aging and high raw material costs. In order to solve the above problems, this application provides a diesel oxidation catalyst and a preparation method thereof.

[0023] In a typical embodiment of the present application, a diesel oxidation catalyst is provided, which includes a cordierite honeycomb ceramic carrier and an active coating attached to the surface of the cordierite honeycomb ceramic carrier, the active coating includes hydroxyapatite, and the hydroxyapatite is loaded with precious metals, and the precious metals include Pt metal and Pd metal.

[0024] The present invention discloses a diesel oxidation catalyst with excellent hydrothermal aging resistance, and can exhibit excellent hydrothermal aging resistance without doping modification. Specifically, the present application uses hydroxyapatite as a carrier of precious metals Pt and Pd. Hydroxyapatite, as a new type of carrier material, contains only four elements: Ca, P, O and H. On the one hand, the hydroxyl groups (OH - ) and phosphate (PO4 3-) can form stable chemical bonds with precious metals, which helps to evenly disperse the precious metals on the carrier, thereby improving the stability of the diesel oxidation catalyst and enhancing the interaction between the carrier and the precious metals. In particular, after high-temperature hydrothermal aging, the diesel oxidation catalyst can still maintain good stability and catalytic activity. Specifically, under conditions below 400°C, PO4 3- Play a stabilizing role, while at temperatures above 600°C, the surface OH - The hydroxyapatite has a stabilizing effect to improve the stability of the diesel oxidation catalyst. On the other hand, the ion exchangeability of hydroxyapatite helps to improve the dispersion performance of the diesel oxidation catalyst. At the same time, the use of precious metals Pt and Pd improves the conversion efficiency of the diesel oxidation catalyst to hydrocarbons, carbon monoxide and nitrogen monoxide in diesel engine exhaust, and reduces harmful substances in exhaust emissions. In addition, the raw materials of the diesel oxidation catalyst are simple to prepare, the cost is low, and it has a wide range of application prospects.

[0025] In addition, it should be noted that the molecular formula of hydroxyapatite is Ca 10 (PO4)6(OH)2, belonging to the hexagonal crystal system, is also known as hydroxyapatite and basic calcium phosphate. It is a natural mineralization of calcium apatite (Ca5(PO4)3(OH)). It is the main inorganic component of human and animal bones. It can form chemical bonds with body tissues, participate in body metabolism, and has good biocompatibility. Nano-hydroxyapatite has excellent high thermal stability and a sintering temperature of up to 1200-1300℃.

[0026] In one embodiment of the present application, the cordierite honeycomb ceramic carrier has an air outlet and an air inlet, the active coating corresponding to the air inlet is a first active coating, and the active coating corresponding to the air outlet is a second active coating; and / or the concentration of the precious metal in the first active coating is 15 to 30 g / ft 3 , preferably 18 to 30 g / ft 3 , and / or the mass of the precious metal accounts for 0.1-1.5% of the total mass of the first active coating, and / or the mass ratio of Pt metal to Pd metal in the first active coating is 1-6:1.

[0027] By using different active coatings at both ends of the cordierite honeycomb ceramic carrier, the tail gas purification capacity can be improved in a targeted manner. After the initial catalysis, the types and concentrations of pollutants in the tail gas at the outlet end will change. A higher concentration of precious metals can increase the catalyst at the outlet end to have a higher conversion ability for the remaining pollutants. Therefore, it is preferred to control the range of the above conditions, which can further improve the conversion efficiency, especially for pollutants in the tail gas that are difficult to convert. This partition design helps to optimize the use efficiency of precious metals, reduce production costs, and improve the overall purification effect of the catalyst.

[0028] In one embodiment of the present application, the concentration of the precious metal in the second active coating is 5 to 30 g / ft 3 , and / or the mass of the precious metal accounts for 0.1-1.5% of the total mass of the second active coating, and / or the mass ratio of Pt metal to Pd metal in the second active coating is 6-12:1.

[0029] Since the exhaust gas temperature at the inlet end is relatively low and there are many types of pollutants, a coating with a higher concentration of precious metals can make the catalyst more active at low temperatures. It is preferred to control the concentration and ratio of the precious metals in the second active coating within the above range, which helps to form a more efficient catalytic environment at the outlet end, further improve the conversion rate of pollutants, and especially has a stronger catalytic effect on difficult-to-treat hydrocarbons, which helps to improve the overall performance of the catalyst.

[0030] In one embodiment of the present application, the cordierite honeycomb ceramic carrier is a cylinder, and along the axial direction of the cylinder, the length ratio of the first active coating layer to the second active coating layer is 1:2 to 2:1.

[0031] The first active coating layer and the second active coating layer with different length ratios can adjust the catalytic activity according to the change of the exhaust gas from the inlet end to the outlet end. The longer first active coating layer can process more initial pollutants, while the longer second active coating layer can process residual pollutants that are difficult to convert. Therefore, it is preferred to control the length ratio of the first active coating layer to the second active coating layer within the above range, which helps to improve the overall conversion rate of the catalyst while controlling the cost.

[0032] In another typical embodiment of the present application, a method for preparing the above-mentioned diesel oxidation catalyst is provided, and the preparation method comprises: step S1, mixing raw materials including hydroxyapatite and water to obtain slurry, adjusting the pH value of the slurry with glacial acetic acid and performing a first stirring to obtain an acidic slurry; step S2, performing a second stirring on raw materials including the acidic slurry, a platinum salt solution, a palladium salt solution and a bonding aid to obtain a mixture, adjusting the pH value of the mixture with glacial acetic acid to obtain an acidic mixture; step S3, performing a third stirring on the acidic mixture and a thickener to obtain slurry A; step S4, repeating steps S1 to S3 to obtain slurry B; step S5, respectively coating slurry A and slurry B on the air inlet end and the air outlet end of a cordierite honeycomb ceramic carrier, and then drying and calcining in sequence to obtain a diesel oxidation catalyst.

[0033] The present application discloses a method for preparing the above diesel oxidation catalyst, with the focus on optimizing the slurry preparation process, wherein glacial acetic acid is added in advance to adjust the pH value of the slurry, and the acidic environment can promote the dispersion of hydroxyapatite and precious metals, reduce particle agglomeration, and at the same time, by adjusting the pH value, the dispersibility of the precious metals and the carrier material and the strong interaction between the two are improved, especially after high-temperature hydrothermal aging, the diesel oxidation catalyst can still maintain good stability and catalytic activity, thereby improving the catalytic efficiency and anti-aging ability of the catalyst. This optimized preparation process helps to uniformly load the precious metals and improve the utilization efficiency of the active components of the catalyst, thereby realizing a catalyst with high-temperature hydrothermal aging resistance at a relatively low cost.

[0034] In one embodiment of the present application, the pH value of the acidic slurry is 3-5; and / or the rotation speed of the first stirring is 450-650 rpm, and the time of the first stirring is 0.5-2 hours.

[0035] A specific pH value is conducive to the formation of a more suitable chemical bonding state between the precious metal and the carrier material, promoting the uniform dispersion of the precious metal and the strong interaction with the carrier, and improving the anti-aging activity of the catalyst. The control of the stirring conditions helps to form a slurry with a moderate particle size, which is convenient for the subsequent coating and drying steps, reduces coating defects, and improves the activity and life of the catalyst. Therefore, by controlling the pH value and stirring conditions of the acidic slurry within the above range, the interaction between the precious metal and the carrier material can be further optimized, and the high temperature aging resistance of the catalyst can be improved.

[0036] In one embodiment of the present application, the pH value of the above-mentioned acidic mixture is 3-5; and / or the second stirring speed is 450-650 rpm, and the second stirring time is 0.5-2 hours; and / or the third stirring speed is 450-650 rpm, and the third stirring time is 0.5-2 hours; and / or in slurry A, the amount of bonding aid is 3-6% of the total mass of hydroxyapatite; and / or in slurry B, the amount of bonding aid is 3-6% of the total mass of hydroxyapatite.

[0037] The pH value, stirring time and rotation speed of the slurry are all key factors affecting the structural stability and activity of the catalyst. Further optimization of these parameters is conducive to promoting a better bonding state between the precious metal and the carrier. At the same time, controlling the amount of bonding aid helps to form a uniform and stable coating, thereby improving the overall performance of the catalyst.

[0038] In one embodiment of the present application, the platinum salt solution is selected from any one or more of an aqueous solution of platinum nitrate, an aqueous solution of platinum chloride, an aqueous solution of chloroplatinic acid, an aqueous solution of platinum acetylacetonate, a platinum acetate solution or a tetraaminoplatinum-platinum tetrachloride solution; and / or, the palladium salt solution is selected from any one or more of an aqueous solution of palladium nitrate, an aqueous solution of palladium chloride, an aqueous solution of chloropalladic acid, an aqueous solution of palladium acetylacetonate, a palladium acetate solution or a tetraaminopalladium-palladium tetrachloride solution; and / or, in slurry A, the mass ratio of the platinum metal element in the platinum salt solution to the palladium metal element in the palladium salt solution is 1 to 6:1; and / or, in slurry B, the mass ratio of the platinum metal element in the platinum salt solution to the palladium metal element in the palladium salt solution is 6 to 12:1.

[0039] The selection and ratio of the noble metal salt solution directly affect the loading mode of the noble metals Pt and Pd on the carrier. The specific ratio helps to evenly disperse the noble metals in the first active coating and the second active coating, reduces the risk of sintering and aggregation caused by excessive local concentration, and improves the activity and stability of the catalyst. Therefore, by controlling the selection and ratio of the noble metal salt solution within the above range, it is more conducive to the uniform distribution and stable loading of the noble metals on the carrier, thereby improving the activity and anti-aging performance of the catalyst.

[0040] In one embodiment of the present application, the solid content of the above-mentioned slurry A and slurry B is independently 20% to 35%; and / or, in slurry A, the mass proportion of the thickener in slurry A is 0.5% to 1%; and / or, in slurry B, the mass proportion of the thickener in slurry B is 0.5% to 1%.

[0041] The solid content of the slurry and the amount of thickener added directly affect the thickness and stability of the coating. Appropriate solid content helps to evenly distribute the coating on the carrier and reduce uneven catalytic activity caused by too thick or too thin coating. The addition of thickener helps to control the fluidity and viscosity of the slurry, improve the uniformity and stability of the coating, and thus improve the performance of the catalyst. Therefore, by controlling the solid content of slurry A and slurry B and the amount of thickener added within the above range, the coating performance of the catalyst can be optimized, the uniformity and stability of the coating can be improved, and the conversion efficiency and anti-aging ability of the catalyst can be improved.

[0042] In one embodiment of the present application, the drying temperature is 100-150° C., and the drying time is 0.5-1 hour; and / or the calcining temperature is 500-650° C., and the calcining time is 2-4 hours.

[0043] Drying and calcining are key steps in the catalyst preparation process. The appropriate drying temperature can remove moisture from the coating and reduce the cracking of the coating caused by water evaporation at high temperatures. The selection of calcining temperature and time helps to form a stable catalyst structure, promote the chemical bonding of precious metals and carriers, and improve the activity and anti-aging ability of the catalyst. At the same time, lower drying temperature and appropriate calcining temperature can also reduce thermal damage to the carrier and active components and maintain the high performance of the catalyst. Therefore, by controlling the temperature and time of drying and calcining within the above range, it helps to improve the stability of the internal structure of the catalyst and the stability of the active components, thereby improving the anti-aging performance and conversion efficiency of the catalyst.

[0044] The beneficial effects of the present application will be further illustrated below in conjunction with embodiments.

[0045] Example 1

[0046] The specific steps for preparing the diesel oxidation catalyst are as follows:

[0047] 7.4762 g of hydroxyapatite was added to deionized water and stirred to obtain a slurry, and glacial acetic acid was slowly added to the slurry to adjust the pH value of the slurry to 3.5, and then stirred for 0.5 hour to obtain an acidic slurry; 0.5451 g of a platinum nitrate aqueous solution, 0.1817 g of a palladium nitrate aqueous solution and 0.3894 g of a bonding aid were sequentially added to the acidic slurry, and the mass ratio of the platinum metal element in the platinum salt solution to the palladium metal element in the palladium salt solution was controlled to be 2:1, and then stirred for 1 hour to obtain a mixed solution, and glacial acetic acid was slowly added to the mixed solution to adjust the pH value of the mixed solution to 3 to obtain an acidic mixture; 0.24 g of a thickener was added to the acidic mixture, and stirred for 2 hours to obtain a slurry A;

[0048] 7.4762 g of hydroxyapatite was added to deionized water and stirred to obtain a slurry, and glacial acetic acid was slowly added to the slurry to adjust the pH value of the slurry to 3.5, and then stirred for 0.5 hours to obtain an acidic slurry; 0.2499 g of a platinum nitrate aqueous solution, 0.0151 g of a palladium nitrate aqueous solution and 0.3894 g of a bonding aid were sequentially added to the acidic slurry, and the mass ratio of the platinum metal element in the platinum salt solution to the palladium metal element in the palladium salt solution was controlled to be 11:1, and then stirred for 1 hour to obtain a mixed solution, and glacial acetic acid was slowly added to the mixed solution to adjust the pH value of the mixed solution to 3 to obtain an acidic mixture; 0.24 g of a thickener was added to the acidic mixture, and stirred for 2 hours to obtain a slurry B;

[0049] Slurry A is applied to the air inlet end of the cordierite honeycomb ceramic carrier, and the coating amount is controlled at 100 g / L to obtain a first active coating; slurry B is applied to the air outlet end of the cordierite honeycomb ceramic carrier, and the coating amount is controlled at 100 g / L to obtain a second active coating; wherein the concentration of the precious metal in the first active coating is 30 g / ft 3 The mass of precious metals accounts for 1.05% of the total mass of the first active coating, and the concentration of precious metals in the second active coating is 10g / ft 3 The mass of precious metal accounts for 0.35% of the total mass of the second active coating; the total concentration of precious metal in the first active coating and the second active coating is controlled to be 20g / ft 3 , controlling the length ratio of the first active coating layer to the second active coating layer to be 1:1, and obtaining a coated cordierite honeycomb ceramic carrier.

[0050] When the temperature is raised to 150°C, the coated cordierite honeycomb ceramic carrier is dried for 1 hour; when the temperature is further raised to 550°C, the dried cordierite honeycomb ceramic carrier is calcined for 2 hours; finally, a diesel oxidation catalyst is obtained.

[0051] The diesel oxidation catalyst was placed in a high-temperature tubular furnace for hydrothermal aging, and the heating program was set as follows: starting from room temperature, the temperature was increased by 5°C / min to 750°C, and the temperature was kept for 16 hours and then naturally cooled; the reaction atmosphere was set as follows: the total flow rate was 1L / min, of which compressed air accounted for 90%, i.e. 0.9L / min, and the water vapor flow rate accounted for 10%. The flow rate of H2O in the water vapor generator was set to 80.36μL / min, and the total flux was 86.79mL. After the hydrothermal aging was completed, the diesel oxidation catalyst aging parts were obtained.

[0052] Example 2

[0053] The difference from Example 1 is that the total concentration of precious metals in the first active coating and the second active coating is controlled to be 18 g / ft 3 When preparing slurry A, the mass of platinum nitrate aqueous solution and palladium nitrate aqueous solution added was controlled so that the concentration of precious metals in the first active coating was 18g / ft 3 The mass of the precious metal accounts for 0.63% of the total mass of the first active coating. When preparing slurry B, the mass of the platinum nitrate aqueous solution and the palladium nitrate aqueous solution added is controlled so that the concentration of the precious metal in the second active coating is 18g / ft 3 , the mass of the precious metal accounts for 0.63% of the total mass of the second active coating, and finally a diesel oxidation catalyst is obtained.

[0054] Example 3

[0055] The difference from Example 1 is that the total concentration of precious metals in the first active coating and the second active coating is controlled to be 15 g / ft 3 When preparing slurry A, the mass of the platinum nitrate aqueous solution and the palladium nitrate aqueous solution added was controlled so that the concentration of the precious metal in the first active coating was 22.5 g / ft 3 , the mass of the precious metal accounts for 0.7875% of the total mass of the first active coating; when preparing slurry B, the mass of the platinum nitrate aqueous solution and the palladium nitrate aqueous solution added is controlled so that the concentration of the precious metal in the second active coating is 7.5g / ft 3 , the mass of the precious metal accounts for 0.525% of the total mass of the second active coating, and finally a diesel oxidation catalyst is obtained.

[0056] Example 4

[0057] The difference from Example 1 is that when preparing slurry A, the mass of the platinum nitrate aqueous solution and the palladium nitrate aqueous solution added is controlled so that the concentration of the precious metal in the first active coating is 20 g / ft 3 , the mass of the precious metal accounts for 0.7% of the total mass of the first active coating; when preparing slurry B, the mass of the platinum nitrate aqueous solution and the palladium nitrate aqueous solution added is controlled so that the concentration of the precious metal in the second active coating is 20g / ft 3 , the mass of the precious metal accounts for 0.7% of the total mass of the second active coating, and finally a diesel oxidation catalyst is obtained.

[0058] Example 5

[0059] The difference from Example 1 is that when preparing slurry A, the mass of the platinum nitrate aqueous solution and the palladium nitrate aqueous solution added is controlled so that the concentration of the precious metal in the first active coating is 10 g / ft 3 The mass of the precious metal accounts for 1.8% of the total mass of the first active coating. When preparing slurry B, the mass of the platinum nitrate aqueous solution and the palladium nitrate aqueous solution added is controlled so that the concentration of the precious metal in the second active coating is 30g / ft 3 , the mass of the precious metal accounts for 1.8% of the total mass of the first active coating, and finally a diesel oxidation catalyst is obtained.

[0060] Example 6

[0061] The difference from Example 1 is that when preparing slurry A, the mass ratio of the platinum metal element in the platinum salt solution to the palladium metal element in the palladium salt solution is controlled to be 1:1, and finally a diesel oxidation catalyst is obtained.

[0062] Example 7

[0063] The difference from Example 1 is that when preparing slurry A, the mass ratio of the platinum metal element in the platinum salt solution to the palladium metal element in the palladium salt solution is controlled to be 6:1, and finally a diesel oxidation catalyst is obtained.

[0064] Example 8

[0065] The difference from Example 1 is that when preparing slurry A, the mass ratio of the platinum metal element in the platinum salt solution to the palladium metal element in the palladium salt solution is controlled to be 2:3, and finally a diesel oxidation catalyst is obtained.

[0066] Example 9

[0067] The difference from Example 1 is that when preparing slurry B, the mass ratio of the platinum metal element in the platinum salt solution to the palladium metal element in the palladium salt solution is controlled to be 9:1, and finally a diesel oxidation catalyst is obtained.

[0068] Example 10

[0069] The difference from Example 1 is that when preparing slurry B, the mass ratio of the platinum metal element in the platinum salt solution to the palladium metal element in the palladium salt solution is controlled to be 12:1, and finally a diesel oxidation catalyst is obtained.

[0070] Embodiment 11

[0071] The difference from Example 1 is that when preparing slurry B, the mass ratio of the platinum metal element in the platinum salt solution to the palladium metal element in the palladium salt solution is controlled to be 13:1, and finally a diesel oxidation catalyst is obtained.

[0072] Example 12

[0073] The difference from Example 1 is that when preparing slurry A and slurry B, the amount of glacial acetic acid added is controlled, and the pH value of the mixed solution is adjusted to 3.5, and finally a diesel oxidation catalyst is obtained.

[0074] Embodiment 13

[0075] The difference from Example 1 is that when preparing slurry A and slurry B, the amount of glacial acetic acid added is controlled, and the pH value of the mixed solution is adjusted to 5, so as to finally obtain a diesel oxidation catalyst.

[0076] Embodiment 14

[0077] The difference from Example 1 is that when preparing slurry A and slurry B, the amount of glacial acetic acid added is controlled, and the pH value of the mixed solution is adjusted to 5.5, so as to finally obtain a diesel oxidation catalyst.

[0078] Embodiment 15

[0079] The difference from Example 1 is that the length ratio of the first active coating layer to the second active coating layer is controlled to be 1:2. When preparing slurry A, the mass of the platinum nitrate aqueous solution and the palladium nitrate aqueous solution added is controlled so that the concentration of the precious metal in the first active coating layer is 30 g / ft 3, the mass of the precious metal accounts for 0.7% of the total mass of the first active coating; when preparing slurry B, the mass of the platinum nitrate aqueous solution and the palladium nitrate aqueous solution added is controlled so that the concentration of the precious metal in the second active coating is 15g / ft 3 , the mass of the precious metal accounts for 0.525% of the total mass of the second active coating, and finally a diesel oxidation catalyst is obtained.

[0080] Example 16

[0081] The difference from Example 1 is that the length ratio of the first active coating layer to the second active coating layer is controlled to be 2:3. When preparing slurry A, the mass of the added platinum nitrate aqueous solution and palladium nitrate aqueous solution is controlled so that the concentration of the precious metal in the first active coating layer is 30 g / ft 3 , the mass of the precious metal accounts for 1.05% of the total mass of the first active coating; when preparing slurry B, the mass of the platinum nitrate aqueous solution and the palladium nitrate aqueous solution added is controlled so that the concentration of the precious metal in the second active coating is 13.33 g / ft 3 , the mass of the precious metal accounts for 0.467% of the total mass of the second active coating, and finally a diesel oxidation catalyst is obtained.

[0082] Embodiment 17

[0083] The difference from Example 1 is that the length ratio of the first active coating layer to the second active coating layer is controlled to be 1:3. When preparing slurry A, the mass of the platinum nitrate aqueous solution and the palladium nitrate aqueous solution added is controlled so that the concentration of the precious metal in the first active coating layer is 30 g / ft 3 , the mass of the precious metal accounts for 1.05% of the total mass of the first active coating; when preparing slurry B, the mass of the platinum nitrate aqueous solution and the palladium nitrate aqueous solution added is controlled so that the concentration of the precious metal in the second active coating is 13.33 g / ft 3 , the mass of the precious metal accounts for 0.467% of the total mass of the second active coating, and finally a diesel oxidation catalyst is obtained.

[0084] Embodiment 18

[0085] The difference from Example 1 is that when preparing slurry A and slurry B, the platinum solution selected is platinum acetate solution, and the palladium solution selected is palladium acetate solution, and finally a diesel oxidation catalyst is obtained.

[0086] Embodiment 19

[0087] The difference from Example 1 is that when preparing slurry A and slurry B, the platinum solution selected is a tetraaminoplatinum-platinum tetrachloride solution, and the palladium solution selected is a tetraaminopalladium-palladium tetrachloride solution, and finally a diesel oxidation catalyst is obtained.

[0088] Comparative Example 1

[0089] 7.4762 g of hydroxyapatite, 0.5451 g of platinum nitrate aqueous solution, 0.1817 g of palladium nitrate aqueous solution, 0.3894 g of a bonding aid and 0.24 g of a thickener were added to deionized water and stirred to obtain a mixed slurry, glacial acetic acid was slowly added to the mixed slurry to adjust the pH value of the mixed slurry to 3, and stirred for 2 hours to obtain slurry A;

[0090] 7.4762 g of hydroxyapatite, 0.2499 g of platinum nitrate aqueous solution, 0.0151 g of palladium nitrate aqueous solution, 0.3894 g of a bonding aid and 0.24 g of a thickener were added to deionized water and stirred to obtain a mixed slurry, glacial acetic acid was slowly added to the mixed slurry to adjust the pH value of the mixed slurry to 3, and stirred for 2 hours to obtain slurry B;

[0091] Applying slurry A to the air inlet end of the cordierite honeycomb ceramic carrier, and controlling the coating amount to 100 g / L, to obtain a second active coating; applying slurry B to the air outlet end of the cordierite honeycomb ceramic carrier, and controlling the coating amount to 100 g / L, to obtain a first active coating; controlling the length ratio of the first active coating to the second active coating to be 1:1, to obtain a coated cordierite honeycomb ceramic carrier;

[0092] When the temperature is raised to 150°C, the coated cordierite honeycomb ceramic carrier is dried for 1 hour; when the temperature is further raised to 550°C, the dried cordierite honeycomb ceramic carrier is calcined for 2 hours; finally, a diesel oxidation catalyst is obtained.

[0093] The diesel oxidation catalyst is placed in a high-temperature tubular furnace for hydrothermal aging. The heating program is set as follows: starting from room temperature, the temperature is raised to 750°C at 5°C / min, and the temperature is kept for 16 hours and then naturally cooled; the reaction atmosphere is set as follows: the total flow rate is 1L / min, of which compressed air accounts for 90%, i.e. 0.9L / min, and the water vapor flow rate accounts for 10%. The flow rate of H2O in the water vapor generator is set to 80.36μL / min, and the total flux is 86.79mL. After the hydrothermal aging is completed, the diesel oxidation catalyst aging part can be obtained. Among them, the ignition performance comparison diagram of the diesel oxidation catalyst in Example 1 and Comparative Example 1 is as follows: Figure 1 shown.

[0094] Comparative Example 2

[0095] The difference from Example 1 is that commercial alumina is selected for pulping, and finally a diesel oxidation catalyst is obtained. The comparison of the ignition performance of the diesel oxidation catalyst in Example 1 and Comparative Example 2 is shown in the figure below: Figure 2 shown.

[0096] Performance Test:

[0097] The sample needs to be activated before testing. The activation atmosphere is: 8% O2, 8% H2O, 500ppm CO, 500ppm NO, 200ppm C3H6, 100ppm C3H8, and the rest is N2. The air velocity is 80000·h -1 , starting from room temperature, heating up to 600℃ at 10℃ / min, and keeping warm for 10min. The test conditions of the DOC sample are the same as the activation conditions, and the changes in the gas components at the outlet of the DOC sample are recorded. THC, total hydrocarbons. T50, the reaction temperature corresponding to a conversion rate of 50%; T90, the reaction temperature corresponding to a conversion rate of 90%. The performance test results of the aged catalysts of the above embodiments and comparative examples are shown in Table 1.

[0098] Table 1

[0099]

[0100]

[0101] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0102] The present invention discloses a diesel oxidation catalyst with excellent hydrothermal aging resistance, and can exhibit excellent hydrothermal aging resistance without doping modification. Specifically, the present application uses hydroxyapatite as a carrier of precious metals Pt and Pd. Hydroxyapatite, as a new type of carrier material, contains only four elements: Ca, P, O and H. On the one hand, the hydroxyl groups (OH - ) and phosphate (PO4 3- ) can form stable chemical bonds with precious metals, which helps to evenly disperse the precious metals on the carrier, thereby improving the stability of the diesel oxidation catalyst and enhancing the interaction between the carrier and the precious metals. In particular, after high-temperature hydrothermal aging, the diesel oxidation catalyst can still maintain good stability and catalytic activity. Specifically, under conditions below 400°C, PO4 3- Play a stabilizing role, while at temperatures above 600°C, the surface OH - The hydroxyapatite has a stabilizing effect to improve the stability of the diesel oxidation catalyst. On the other hand, the ion exchangeability of hydroxyapatite helps to improve the dispersion performance of the diesel oxidation catalyst. At the same time, the use of precious metals Pt and Pd improves the conversion efficiency of the diesel oxidation catalyst to hydrocarbons, carbon monoxide and nitrogen monoxide in diesel engine exhaust, and reduces harmful substances in exhaust emissions. In addition, the raw materials of the diesel oxidation catalyst are simple to prepare, the cost is low, and it has a wide range of application prospects.

[0103] The above are only embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A diesel oxidation catalyst, characterized in that: The diesel oxidation catalyst comprises a cordierite honeycomb ceramic carrier and an active coating attached to the surface of the cordierite honeycomb ceramic carrier, wherein the active coating comprises hydroxyapatite, and the hydroxyapatite is loaded with precious metals, wherein the precious metals comprise Pt metal and Pd metal.

2. The diesel oxidation catalyst according to claim 1, characterized in that The cordierite honeycomb ceramic carrier has an air outlet and an air inlet, the active coating corresponding to the air inlet is a first active coating, and the active coating corresponding to the air outlet is a second active coating; and / or the concentration of the precious metal in the first active coating is 15 to 30 g / ft 3 , preferably 18 to 30 g / ft 3 , and / or the mass of the precious metal accounts for 0.1-1.5% of the total mass of the first active coating, and / or the mass ratio of Pt metal to Pd metal in the first active coating is 1-6:

1.

3. The diesel oxidation catalyst according to claim 2, characterized in that: The concentration of the precious metal in the second active coating is 5 to 30 g / ft 3 , and / or the mass of the precious metal accounts for 0.1-1.5% of the total mass of the second active coating, and / or the mass ratio of Pt metal to Pd metal in the second active coating is 6-12:

1.

4. The diesel oxidation catalyst according to claim 2, characterized in that: The cordierite honeycomb ceramic carrier is a cylinder, and along the axial direction of the cylinder, the length ratio of the first active coating layer to the second active coating layer is 1:2 to 2:

1.

5. A method for preparing the diesel oxidation catalyst according to any one of claims 1 to 4, characterized in that: The preparation method comprises: Step S1, mixing raw materials including hydroxyapatite and water to obtain slurry, adjusting the pH value of the slurry with glacial acetic acid and performing a first stirring to obtain an acidic slurry; Step S2, subjecting the raw materials including the acidic slurry, the platinum salt solution, the palladium salt solution and the bonding aid to a second stirring to obtain a mixture, and adjusting the pH value of the mixture with glacial acetic acid to obtain an acidic mixture; Step S3, stirring the acidic mixture and the thickener for a third time to obtain slurry A; Step S4, adjusting the dosage of the platinum salt solution and the palladium salt solution, repeating the steps S1 to S3 to obtain slurry B; Step S5, after coating the slurry A and the slurry B on the air inlet end and the air outlet end of the cordierite honeycomb ceramic carrier respectively, drying and calcining them in sequence to obtain the diesel oxidation catalyst.

6. The preparation method according to claim 5, characterized in that: The pH value of the acidic slurry is 3-5; and / or the rotation speed of the first stirring is 450-650 rpm, and the time of the first stirring is 0.5-2 hours.

7. The preparation method according to claim 5, characterized in that: The pH value of the acidic mixture is 3 to 5; and / or the rotation speed of the second stirring is 450 to 650 rpm, and the time of the second stirring is 0.5 to 2 hours; and / or, the rotation speed of the third stirring is 450-650 rpm, and the time of the third stirring is 0.5-2 hours; and / or in the slurry A, the amount of the bonding aid is 3-6% of the total mass of the hydroxyapatite; And / or, in the slurry B, the amount of the bonding aid is 3-6% of the total mass of the hydroxyapatite.

8. The preparation method according to claim 5, characterized in that: The platinum salt solution is selected from any one or more of an aqueous solution of platinum nitrate, an aqueous solution of platinum chloride, an aqueous solution of chloroplatinic acid, an aqueous solution of platinum acetylacetonate, a platinum acetate solution and a tetraaminoplatinum-platinum tetrachloride solution; and / or, the palladium salt solution is selected from any one or more of an aqueous solution of palladium nitrate, an aqueous solution of palladium chloride, an aqueous solution of chloropalladic acid, an aqueous solution of palladium acetylacetonate, a palladium acetate solution and a tetraaminopalladium-palladium tetrachloride solution; and / or, in the slurry A, the mass ratio of the platinum metal element in the platinum salt solution to the palladium metal element in the palladium salt solution is 1 to 6:1; and / or, in the slurry B, the mass ratio of the platinum metal element in the platinum salt solution to the palladium metal element in the palladium salt solution is 6 to 12:

1.

9. The preparation method according to claim 5, characterized in that: The solid content of the slurry A and the slurry B is independently 20% to 35%; and / or, in the slurry A, the mass proportion of the thickener in the slurry A is 0.5% to 1%; and / or, in the slurry B, the mass proportion of the thickener in the slurry B is 0.5% to 1%.

10. The preparation method according to claim 5, characterized in that: The drying temperature is 100-150° C., and the drying time is 0.5-1 hour; and / or the calcining temperature is 500-650° C., and the calcining time is 2-4 hours.

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