High-temperature-resistant diesel oxidation catalyst and preparation method thereof

Abstract

The invention provides a high-temperature-resistant diesel oxidation catalyst and a preparation method thereof. The diesel oil oxidation catalyst comprises silicon-modified hydroxyapatite and noble metals loaded on the surface of the silicon-modified hydroxyapatite, wherein the noble metals comprise Pt metal and Pd metal. According to the diesel oil oxidation catalyst disclosed by the invention, silicon-modified hydroxyapatite is adopted as a carrier, and Pt and Pd noble metals are loaded, so that the high-temperature resistance of the catalyst is remarkably improved. In addition, the catalyst is simple in raw material preparation and relatively low in cost, provides reference for development of a high-thermal-stability diesel engine oxidation catalyst, and has a wide application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of diesel oxidation catalysts, and in particular to a high temperature resistant 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 diesel oxidation catalysts DOC mainly use oxides (such as alumina or a mixture of alumina with silica, zirconium oxide and cerium oxide, etc.) as carriers to load Pt and Pd, but the catalyst has poor thermal stability, the metal active components are easily sintered at high temperatures, and the catalytic activity decreases significantly after high-temperature aging.

[0004] Therefore, developing an oxidation catalyst with better CO, HC and NO conversion performance and high-temperature thermal stability is of great significance to meet the development of diesel engine exhaust purification systems. Summary of the invention

[0005] The main purpose of the present invention is to provide a high temperature resistant diesel oxidation catalyst and a preparation method thereof, so as to solve the problem of poor high temperature stability of diesel oxidation catalysts in the prior art.

[0006] To achieve the above objective, according to one aspect of the present invention, a diesel oxidation catalyst is provided. The diesel oxidation catalyst comprises silicon-modified hydroxyapatite and a noble metal supported on the surface of the silicon-modified hydroxyapatite, wherein the noble metal comprises Pt metal and Pd metal.

[0007] Furthermore, the mass ratio of the silicon-modified hydroxyapatite to the noble metal is 10 to 200:1, and / or the mass ratio of the Pt metal to the Pd metal is 1 to 6:1.

[0008] Furthermore, the content of silicon in the silicon-modified hydroxyapatite is 0.5-30%.

[0009] Furthermore, the molar ratio of B acid sites to L acid sites in the diesel oxidation catalyst is 0.5 to 2.5:1.

[0010] Furthermore, the calcium-phosphorus ratio in the silicon-modified hydroxyapatite is 1.67:1.

[0011] According to another aspect of the present invention, a method for preparing the above-mentioned diesel oxidation catalyst is provided, and the preparation method comprises: step S1, modifying hydroxyapatite with a silicon source to obtain silicon-modified hydroxyapatite; step S2, impregnating the silicon-modified hydroxyapatite in a mixture of a Pt metal salt solution and a Pd metal salt solution to obtain impregnated silicon-modified hydroxyapatite; step S3, sequentially performing a first drying and a first sintering on the impregnated silicon-modified hydroxyapatite to obtain a diesel oxidation catalyst.

[0012] Further, in the above step S1, the silicon-modified hydroxyapatite is prepared by a hydrolysis polycondensation method, and the process includes: step S11, mixing raw materials including anhydrous ethanol and silicate and performing a first heating to obtain a first mixed solution; step S12, mixing raw materials including hydroxyapatite and water and performing a second heating to obtain a second mixed solution; step S13, adding the second mixed solution to the first mixed solution, continuing heating and stirring to obtain a third mixed solution; step S14, filtering, second drying and second sintering the third mixed solution in sequence to obtain silicon-modified hydroxyapatite; wherein the ratio of the mass of hydroxyapatite to the volume of silicate is (0.1 ~10) g:1 mL, the silicate is selected from any one or more of ethyl silicate, methyl silicate and orthopropyl orthosilicate; the volume of anhydrous ethanol to silicate in the first mixed solution is 0.5-2:1; the temperatures of the first mixed solution, the second mixed solution and the third mixed solution are independently 60-90°C; the ratio of the mass of hydroxyapatite to the mass of water in the second mixed solution is 2-4:1; the temperature of the second drying is 80-100°C, and the time of the second drying is 10-12h; the temperature of the second sintering is 400-600°C, and the time of the second sintering is 2-4h; the volume ratio of the first mixed solution to the second mixed solution is 1:0.5-2.

[0013] Furthermore, in the above step S1, silicon-modified hydroxyapatite is prepared by an impregnation method, and the process includes: step S11', mixing raw materials including water and hydroxyapatite to obtain a fourth mixed solution; step S12', adding silica sol to the fourth mixed solution and impregnating and stirring to obtain a fifth mixed solution; step S13', subjecting the fourth mixed solution to a third drying and a third sintering in sequence to obtain silicon-modified hydroxyapatite; wherein the solid content of the silica sol is 29-31%; the ratio of the mass of water to the mass of hydroxyapatite in the fourth mixed solution is 2-4; the ratio of the mass of hydroxyapatite to the mass of the silica sol is 1-50:1; the time for impregnation and stirring is 6-10h; the temperature of the third drying is 80-100°C, and the time of the third drying is 10-12h; the temperature of the third sintering is 400-600°C, and the time of the third sintering is 2-4h.

[0014] Furthermore, in the above step S2, the mass ratio of Pt ions in the Pt metal salt solution to Pd ions in the Pd metal salt solution is 1 to 6:1, the Pt metal salt solution is selected from any one or more of platinum nitrate solution, platinum chloride solution, chloroplatinic acid solution, platinum acetate solution, acetylacetonate platinum solution and tetraamineplatinum tetrachloride solution; the Pd metal salt solution is selected from any one or more of palladium nitrate solution, palladium chloride solution, chloropalladic acid solution, platinum acetate solution, acetylacetonate palladium solution and tetraaminepalladium tetrachloride solution; and / or the immersion time is 6 to 12 hours.

[0015] Furthermore, in the above step S3, the temperature of the first drying is 80-100° C., and the time of the first drying is 10-12 hours; and / or the temperature of the first sintering is 500-650° C., and the time of the first sintering is 3-5 hours.

[0016] By applying the technical solution of the present invention, the present application discloses a diesel oxidation catalyst, which significantly improves the high temperature resistance of the catalyst by using silicon-modified hydroxyapatite as a carrier and loading Pt and Pd precious metals. Specifically, the surface of the hydroxyapatite carrier is rich in hydroxyl groups, and the acidity of the surface of the hydroxyapatite (Si / HAP) carrier after silicon modification is further improved, which significantly enhances the interaction between the carrier and Pt and Pd, reduces the agglomeration of precious metal particles during high temperature aging, and improves the anti-sintering ability of the active components Pt and Pd of the catalyst, thereby improving the high temperature aging performance of the catalyst. At the same time, the optimized modification of the carrier improves the stable dispersion of the precious metal on the carrier, and the catalyst can maintain a high catalytic activity even under high temperature conditions above 800°C. In addition, the raw materials of the catalyst are simple to prepare and the cost is low, which provides a reference for the development of high thermal stability diesel engine oxidation catalysts and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] 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:

[0018] Figure 1 A comparison chart of the ignition performance of different catalyst aged parts in Example 1, Comparative Example 1 and Comparative Example 2 of the present application is shown;

[0019] Figure 2 NH3-TPD diagrams of the silicon-modified hydroxyapatite in Example 2 of the present application and the commercial hydroxyapatite in Comparative Example 1 are shown;

[0020] Figure 3 The TEM image of the aged diesel oxidation catalyst using commercial hydroxyapatite as a carrier in Comparative Example 1 of the present application is shown;

[0021] Figure 4 The TEM image of the aged diesel oxidation catalyst using silicon-modified hydroxyapatite as a carrier in Example 1 of the present application is shown;

[0022] Figure 5 The figure shows the particle size distribution of precious metals in the aged diesel oxidation catalyst with commercial hydroxyapatite as the carrier in Comparative Example 1 of the present application;

[0023] Figure 6 The graph showing the particle size distribution of precious metals in the aged diesel oxidation catalyst using silicon-modified hydroxyapatite as a carrier according to Example 1 of the present application is shown. DETAILED DESCRIPTION

[0024] 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.

[0025] As analyzed in the background technology of this application, there is a problem in the prior art that diesel oxidation catalysts have poor high-temperature stability. In order to solve the above problem, this application provides a high-temperature resistant diesel oxidation catalyst and a preparation method thereof.

[0026] In a typical embodiment of the present application, a diesel oxidation catalyst is provided. The diesel oxidation catalyst includes silicon-modified hydroxyapatite and a noble metal supported on the surface of the silicon-modified hydroxyapatite, wherein the noble metal includes Pt metal and Pd metal.

[0027] The present application discloses a diesel oxidation catalyst, which significantly improves the high temperature resistance of the catalyst by using silicon-modified hydroxyapatite as a carrier and loading Pt and Pd precious metals. Specifically, the surface of the hydroxyapatite carrier is rich in hydroxyl groups, and the acidity of the surface of the hydroxyapatite (Si / HAP) carrier after silicon modification is further improved, which significantly enhances the interaction between the carrier and Pt and Pd, reduces the agglomeration of precious metal particles during high temperature aging, and improves the anti-sintering ability of the active components Pt and Pd of the catalyst, thereby improving the high temperature aging performance of the catalyst. At the same time, the optimized modification of the carrier improves the stable dispersion of the precious metal on the carrier, and the catalyst can maintain a high catalytic activity even under high temperature conditions above 800°C. In addition, the raw materials of the catalyst are simple to prepare and the cost is low, which provides a reference for the development of high thermal stability diesel engine oxidation catalysts and has broad application prospects.

[0028] In one embodiment of the present application, the mass ratio of the silicon-modified hydroxyapatite to the noble metal is 10-200:1, and / or the mass ratio of Pt metal to Pd metal is 1-6:1.

[0029] The loading amount and ratio of precious metals directly affect the catalytic activity and stability of the catalyst. The combination of an appropriate amount of silicon-modified hydroxyapatite and precious metals, as well as a reasonable ratio between Pt and Pd, helps the catalyst to have the best catalytic activity and anti-aging performance when treating a variety of pollutants in diesel exhaust. Therefore, by controlling the mass ratio of silicon-modified hydroxyapatite to precious metals, as well as the mass ratio between Pt and Pd within the above range, the catalytic efficiency of the catalyst can be further improved and the catalyst life can be extended.

[0030] In one embodiment of the present application, the content of silicon in the silicon-modified hydroxyapatite is 0.5-30%.

[0031] The introduction of silicon can adjust the surface acidity of hydroxyapatite. A moderate silicon content can enhance the adsorption of precious metals by the carrier and reduce the agglomeration and sintering of precious metals under high temperature conditions. At the same time, the silicon content affects the crystal structure and stability of the carrier. The above silicon content helps to better balance the catalytic performance and carrier stability. Therefore, by controlling the content of silicon in silicon-modified hydroxyapatite within the above range, it helps to promote the carrier to have sufficient surface acidity to enhance the interaction with precious metals. It also helps to control the stability of the carrier and reduce the risk of carrier performance degradation due to excessive silicon content.

[0032] In one embodiment of the present application, the molar ratio of B acid sites to L acid sites in the diesel oxidation catalyst is 0.5-2.5:1.

[0033] The presence of B acid sites and L acid sites on the catalyst surface will affect the activity and selectivity of the catalyst. A suitable B acid site / L acid site molar ratio is conducive to providing acid sites that are more conducive to the catalytic reaction, promoting the conversion of organic matter such as CO, C3H6, C3H8, while improving the oxidation efficiency of NO and reducing the emission of harmful substances in diesel exhaust. Therefore, by controlling the B acid site / L acid site molar ratio in diesel oxidation catalysis within the above range, it is helpful to optimize the acid sites of the catalytic reaction, thereby improving the oxidation conversion efficiency of the catalyst to harmful substances in diesel exhaust.

[0034] In one embodiment of the present application, the calcium-phosphorus ratio in the silicon-modified hydroxyapatite is 1.67:1.

[0035] The calcium-phosphorus ratio directly affects the crystal structure and porosity of hydroxyapatite. Changing the calcium-phosphorus ratio can adjust the physical and chemical properties of the carrier, such as increasing the surface acidity and optimizing the pore size distribution, thereby enhancing the carrier's support for precious metals, reducing sintering and agglomeration under high temperature conditions, and maintaining the high efficiency and activity of the catalyst. Therefore, by controlling the calcium-phosphorus ratio in silicon-modified hydroxyapatite within the above range, it is helpful to optimize the pore structure and stability of the carrier, and further improve the thermal stability and catalytic activity of the catalyst.

[0036] 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, modifying hydroxyapatite with a silicon source to obtain silicon-modified hydroxyapatite; step S2, impregnating the silicon-modified hydroxyapatite in a mixed solution of a Pt metal salt solution and a Pd metal salt solution to obtain impregnated silicon-modified hydroxyapatite; step S3, sequentially performing a first drying and a first sintering on the impregnated silicon-modified hydroxyapatite to obtain a diesel oxidation catalyst.

[0037] The present application adopts a silicon source to modify hydroxyapatite, and the obtained silicon-modified hydroxyapatite helps to enhance the thermal stability and acid properties of the silicon-modified hydroxyapatite carrier, provides a stable support structure for the precious metals, significantly enhances the interaction between the carrier and Pt and Pd, and reduces the agglomeration of precious metal particles during high-temperature aging, thereby not only helping the precious metals to be evenly dispersed on the carrier surface, but also improving the sintering resistance of the active components Pt and Pd of the catalyst, which is conducive to the preparation of catalysts with high thermal stability and excellent catalytic performance.

[0038] In one embodiment of the present application, in the above step S1, silicon-modified hydroxyapatite is prepared by a hydrolysis and condensation method, and the process includes: step S11, mixing raw materials including anhydrous ethanol and silicate and performing a first heating to obtain a first mixed solution; step S12, mixing raw materials including hydroxyapatite and water and performing a second heating to obtain a second mixed solution; step S13, adding the second mixed solution to the first mixed solution, continuing heating and stirring to obtain a third mixed solution; step S14, filtering, second drying and second sintering the third mixed solution in sequence to obtain silicon-modified hydroxyapatite; wherein the ratio of the mass of hydroxyapatite to the volume of silicate is (0.1~10)g: 1mL, preferably (0.4-6.15)g:1mL; silicate is selected from any one or more of ethyl silicate, methyl silicate and orthopropyl orthosilicate; the volume of anhydrous ethanol to silicate in the first mixed solution is 0.5-2:1; the temperature of the first mixed solution, the second mixed solution and the third mixed solution are each independently 60-90°C; the ratio of the mass of hydroxyapatite to the mass of water in the second mixed solution is 2-4:1; the temperature of the second drying is 80-100°C, and the time of the second drying is 10-12h; the temperature of the second sintering is 400-600°C, and the time of the second sintering is 2-4h; the volume ratio of the first mixed solution to the second mixed solution is 1:0.5-2.

[0039] The silica sol prepared by the hydrolysis and condensation method can form a uniform silicon-modified layer on the hydroxyapatite carrier. By controlling the ratio of silicate to hydroxyapatite and the reaction conditions, it helps to precisely control the deposition of silica on the hydroxyapatite carrier, thereby affecting the surface acidity of the carrier and the dispersibility of the metal active components, and enhancing the interaction between the carrier and the precious metal.

[0040] In one embodiment of the present application, in the above-mentioned step S1, silicon-modified hydroxyapatite is prepared by an impregnation method, and the process includes: step S11', mixing raw materials including water and hydroxyapatite to obtain a fourth mixed liquid; step S12', adding silica sol to the fourth mixed liquid for impregnation and stirring to obtain a fifth mixed liquid; step S13', subjecting the fourth mixed liquid to a third drying and a third sintering in sequence to obtain silicon-modified hydroxyapatite; wherein the solid content of the silica sol is 29-31%; the ratio of the mass of water to the mass of hydroxyapatite in the fourth mixed liquid is 2-4; the ratio of the mass of hydroxyapatite to the mass of the silica sol is 1-50:1; the time for impregnation and stirring is 6-10h; the temperature of the third drying is 80-100°C, and the time of the third drying is 10-12h; the temperature of the third sintering is 400-600°C, and the time of the third sintering is 2-4h.

[0041] Silicon-modified hydroxyapatite can also be prepared by the impregnation method. Further optimization of the above reaction conditions is beneficial to improving the preparation efficiency of the catalyst, and is also beneficial to improving the performance and stability of the catalyst.

[0042] However, compared with the hydrolysis and condensation method, the particle size of silicon-modified hydroxyapatite prepared by the impregnation method is relatively coarse and the performance is slightly worse.

[0043] In one embodiment of the present application, in the above step S2, the mass ratio of Pt ions in the Pt metal salt solution to Pd ions in the Pd metal salt solution is 1 to 6:1, and the Pt metal salt solution is selected from any one or more of platinum nitrate solution, platinum chloride solution, chloroplatinic acid solution, platinum acetate solution, acetylacetonate platinum solution and tetraamineplatinum tetrachloride solution; the Pd metal salt solution is selected from any one or more of palladium nitrate solution, palladium chloride solution, chloropalladic acid solution, platinum acetate solution, acetylacetonate palladium solution and tetraaminepalladium tetrachloride solution; and / or the immersion time is 6 to 12 hours.

[0044] The ratio of noble metal ions and the impregnation time directly affect the loading amount and distribution uniformity of the noble metal ions on the carrier. Therefore, by controlling the ratio of metal ions in the Pt and Pd metal salt solutions and the impregnation time within the above range, it is helpful to evenly distribute the noble metal particles on the carrier surface, reduce alloying and sintering under high temperature conditions, and help improve the high temperature resistance and catalytic activity of the catalyst. In addition, it is preferred that the process of impregnating the silicon-modified hydroxyapatite in the mixed solution of the Pt metal salt solution and the Pd metal salt solution is an equal volume impregnation method.

[0045] In one embodiment of the present application, in the above step S3, the first drying temperature is 80-100° C., and the first drying time is 10-12 hours; and / or, the first sintering temperature is 500-650° C., and the first sintering time is 3-5 hours.

[0046] The conditions of the first drying and the first sintering are directly related to the structural integrity of the catalyst and the stability of the metal active components. It is preferred to control the temperature and time of the first drying within the above ranges to help remove moisture from the catalyst. It is preferred to control the temperature and time of the first sintering within the above ranges to help promote the close bonding of the metal and the carrier, prevent the particles from being too large or sintered, and thus improve the activity and stability of the catalyst under high temperature aging conditions.

[0047] The beneficial effects of the present application will be further illustrated below in conjunction with embodiments.

[0048] Example 1

[0049] 8.13 mL of anhydrous ethanol and 8.13 mL of silicate raw material were mixed, and the mixture was heated to 80° C. to obtain a first mixed solution; 150 g of water and 50 g of hydroxyapatite were mixed, and the mixture was heated to 80° C. to obtain a second mixed solution; the second mixed solution was slowly added to the first mixed solution, and the mixture was stirred at 80° C. for 6 hours to obtain a third mixed solution; the third mixed solution was filtered in sequence, dried at 80° C. for 12 hours, and sintered at 550° C. for 3 hours to obtain silicon-modified hydroxyapatite in which the content of silicon element in the silicon-modified hydroxyapatite was 2.5%;

[0050] 2 g of silicon-modified hydroxyapatite was placed in 3.6 mL of a mixed solution of platinum nitrate and palladium nitrate with mass concentrations of 5.56 g / L and 2.78 g / L of platinum and palladium elements, respectively, for equal volume impregnation to obtain impregnated silicon-modified hydroxyapatite; then the impregnated silicon-modified hydroxyapatite was dried when the temperature was raised to 80°C, and after drying for 12 hours, it was sintered, and after sintering at 550°C for 3 hours, a diesel oxidation catalyst was obtained.

[0051] The diesel oxidation catalyst was placed in a muffle furnace for thermal aging. The heating program was set as follows: starting from room temperature, the temperature was increased to 850°C at 5°C / min, and the temperature was kept for 10 hours and then naturally cooled. After the thermal aging was completed, the diesel oxidation catalyst aging parts were obtained.

[0052] Example 2

[0053] The difference from Example 1 is that the ratio of the mass of hydroxyapatite to the volume of silicate is adjusted to 4.91 g:1 mL, so that the content of silicon in the silicon-modified hydroxyapatite is 2.5%, and finally a diesel oxidation catalyst aging part is obtained.

[0054] Example 3

[0055] 150 g of water and 50 g of hydroxyapatite are mixed to obtain a fourth mixed solution; 25.23 g of silica sol is added to the fourth mixed solution, and the mixture is immersed and stirred for 6 hours to obtain a fifth mixed solution; the fourth mixed solution is dried at 80° C. for 12 hours, and then sintered at 550° C. for 3 hours to obtain silicon-modified hydroxyapatite in which the content of silicon element in the silicon-modified hydroxyapatite is 2%;

[0056] The preparation method of the diesel oxidation catalyst aged part is the same as that in Example 1.

[0057] Example 4

[0058] The difference from Example 1 is that the added masses of platinum nitrate solution and palladium nitrate solution are controlled so that the mass ratio of silicon-modified hydroxyapatite to precious metal is 100:1, and finally a diesel oxidation catalyst aging part is obtained.

[0059] Example 5

[0060] The difference from Example 1 is that the added masses of platinum nitrate solution and palladium nitrate solution are controlled so that the mass ratio of silicon-modified hydroxyapatite to precious metal is 50:1, and finally a diesel oxidation catalyst aging part is obtained.

[0061] Example 6

[0062] The difference from Example 1 is that the added masses of platinum nitrate solution and palladium nitrate solution are controlled so that the mass ratio of silicon-modified hydroxyapatite to precious metal is 200:1, and finally a diesel oxidation catalyst aging part is obtained.

[0063] Example 7

[0064] The difference from Example 1 is that the added masses of the platinum nitrate solution and the palladium nitrate solution are controlled so that the mass ratio of the platinum element to the palladium element is 1:1, and finally an aged diesel oxidation catalyst part is obtained.

[0065] Example 8

[0066] The difference from Example 1 is that the added volumes of platinum nitrate solution and palladium nitrate solution are controlled so that the mass ratio of platinum element to palladium element is 6:1, and finally a diesel oxidation catalyst aging part is obtained.

[0067] Example 9

[0068] The difference from Example 1 is that the added volumes of platinum nitrate solution and palladium nitrate solution are controlled so that the mass ratio of platinum element to palladium element is 7:1, and finally a diesel oxidation catalyst aging part is obtained.

[0069] Example 10

[0070] The difference from Example 1 is that the selected platinum solution is a platinum acetate solution, and the selected palladium solution is a palladium acetate solution, so that the mass ratio of silicon-modified hydroxyapatite to the precious metal is 66.67:1, and finally a diesel oxidation catalyst aging part is obtained.

[0071] Embodiment 11

[0072] The difference from Example 1 is that the ratio of the mass of the added hydroxyapatite to the volume of ethyl silicate is adjusted to 0.6 g:1 mL, so that the content of silicon in the silicon-modified hydroxyapatite is 15%, and finally a diesel oxidation catalyst is obtained.

[0073] Example 12

[0074] The difference from Example 1 is that the ratio of the mass of the added hydroxyapatite to the volume of ethyl silicate is adjusted to 0.47 g:1 mL, so that the content of silicon in the silicon-modified hydroxyapatite is 18%, and finally a diesel oxidation catalyst is obtained.

[0075] Example 13

[0076] The difference from Example 1 is that the ratio of the mass of the added hydroxyapatite to the volume of ethyl silicate is adjusted to 0.4 g:1 mL, so that the content of silicon in the silicon-modified hydroxyapatite is 20%, and finally a diesel oxidation catalyst is obtained.

[0077] Comparative Example 1

[0078] The difference from Example 1 is that commercial alumina is selected for slurrying, and finally the diesel oxidation catalyst aging part is obtained.

[0079] Comparative Example 2

[0080] The difference from Example 1 is that unmodified hydroxyapatite is selected for pulping, and finally a diesel oxidation catalyst aging part is obtained.

[0081] Performance Test:

[0082] 0.1 g of the diesel oxidation catalyst of the embodiment and the comparative example were respectively tested, and the test conditions were: 8% O2, 10% H2O, 500 ppm CO, 500 ppm NO, 200 ppm C3H6, 100 ppm C3H8, and the rest N2, with a space velocity of 300000 h -1 , starting from room temperature, heating up to 550℃ at 10℃ / min, keeping warm for 60min, and recording the changes in the outlet gas composition. T50: the reaction temperature corresponding to 50% conversion rate; T90: the reaction temperature corresponding to 90% conversion rate.

[0083] Catalyst test conditions: The activated diesel oxidation catalysts were placed in a muffle furnace for thermal aging. The heating program was set as follows: starting from room temperature, the temperature was raised to 850°C at 5°C / min, and the temperature was kept for 10 hours and then naturally cooled. After the thermal aging was completed, the diesel oxidation catalyst aging parts were obtained. The ignition performance comparison of different catalyst aging parts in Example 1, Comparative Example 1 and Comparative Example 2 of the present application is shown in the figure. Figure 1 As shown; the NH3-TPD diagram of the silicon-modified hydroxyapatite in Example 2 of the present application and the commercial hydroxyapatite in Comparative Example 1 is as shown Figure 2 As shown; the TEM image of the diesel oxidation catalyst aging part with commercial hydroxyapatite as the carrier in Comparative Example 1 of the present application is as follows Figure 3 As shown; the TEM image of the diesel oxidation catalyst aging part with silicon-modified hydroxyapatite as the carrier in Example 1 of the present application is as shown Figure 4 As shown; the precious metal particle size distribution diagram of the diesel oxidation catalyst aging part with commercial hydroxyapatite as the carrier in Comparative Example 1 of this application is as shown Figure 5As shown; the precious metal particle size distribution diagram of the diesel oxidation catalyst aging part with silicon-modified hydroxyapatite as the carrier in Example 1 of this application is as shown Figure 6 shown.

[0084] Table 1

[0085]

[0086]

[0087] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0088] The present application discloses a diesel oxidation catalyst, which significantly improves the high temperature resistance of the catalyst by using silicon-modified hydroxyapatite as a carrier and loading Pt and Pd precious metals. Specifically, the surface of the hydroxyapatite carrier is rich in hydroxyl groups, and the acidity of the surface of the hydroxyapatite (Si / HAP) carrier after silicon modification is further improved, which significantly enhances the interaction between the carrier and Pt and Pd, reduces the agglomeration of precious metal particles during high temperature aging, and improves the anti-sintering ability of the active components Pt and Pd of the catalyst, thereby improving the high temperature aging performance of the catalyst. At the same time, the optimized modification of the carrier improves the stable dispersion of the precious metal on the carrier, and the catalyst can maintain a high catalytic activity even under high temperature conditions above 800°C. In addition, the raw materials of the catalyst are simple to prepare and the cost is low, which provides a reference for the development of high thermal stability diesel engine oxidation catalysts and has broad application prospects.

[0089] 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 silicon-modified hydroxyapatite and a noble metal supported on the surface of the silicon-modified hydroxyapatite, wherein the noble metal comprises Pt metal and Pd metal.

2. The diesel oxidation catalyst according to claim 1, characterized in that The mass ratio of the silicon-modified hydroxyapatite to the noble metal is 10 to 200:1, and / or the mass ratio of the Pt metal to the Pd metal is 1 to 6:

1.

3. The diesel oxidation catalyst according to claim 1 or 2, characterized in that: The content of silicon in the silicon-modified hydroxyapatite is 0.5-30%.

4. The diesel oxidation catalyst according to claim 1 or 2, characterized in that: The molar ratio of the B acid site to the L acid site in the diesel oxidation catalyst is 0.5 to 2.5:

1.

5. The diesel oxidation catalyst according to claim 1 or 2, characterized in that: The calcium-phosphorus ratio in the silicon-modified hydroxyapatite is 1.67:

1.

6. A method for preparing a diesel oxidation catalyst according to any one of claims 1 to 5, characterized in that: The preparation method comprises: Step S1, modifying hydroxyapatite with a silicon source to obtain silicon-modified hydroxyapatite; Step S2, immersing the silicon-modified hydroxyapatite in a mixture of a Pt metal salt solution and a Pd metal salt solution to obtain impregnated silicon-modified hydroxyapatite; Step S3, performing a first drying and a first sintering on the impregnated silicon-modified hydroxyapatite in sequence to obtain the diesel oxidation catalyst.

7. The preparation method according to claim 6, characterized in that: In the step S1, the silicon-modified hydroxyapatite is prepared by a hydrolysis and condensation method, and the process includes: Step S11, mixing the raw materials including anhydrous ethanol and silicate and performing a first heating to obtain a first mixed liquid; Step S12, mixing the raw materials including hydroxyapatite and water and performing a second heating to obtain a second mixed solution; Step S13, adding the second mixed liquid to the first mixed liquid, continuing heating and stirring to obtain a third mixed liquid; Step S14, filtering, second drying and second sintering the third mixed solution in sequence to obtain the silicon-modified hydroxyapatite; The ratio of the mass of the hydroxyapatite to the volume of the silicate is (0.1-10) g:1 mL, and the silicate is selected from any one or more of ethyl silicate, methyl silicate and orthopropyl orthosilicate; The volume ratio of the anhydrous ethanol to the silicate in the first mixed solution is 0.5 to 2:1; The temperatures of the first mixed liquid, the second mixed liquid and the third mixed liquid are independently 60 to 90° C.; The ratio of the mass of the hydroxyapatite to the mass of the water in the second mixed solution is 2 to 4:1; The second drying temperature is 80-100° C., and the second drying time is 10-12 hours; The temperature of the second sintering is 400-600° C., and the time of the second sintering is 2-4 hours; The volume ratio of the first mixed liquid to the second mixed liquid is 1:0.5-2.

8. The preparation method according to claim 7, characterized in that: In the step S1, the silicon-modified hydroxyapatite is prepared by an impregnation method, and the process includes: Step S11', mixing raw materials including water and hydroxyapatite to obtain a fourth mixed solution; Step S12', adding silica sol into the fourth mixed liquid, immersing and stirring, to obtain a fifth mixed liquid; Step S13', subjecting the fourth mixed solution to a third drying and a third sintering in sequence to obtain the silicon-modified hydroxyapatite; Wherein, the solid content of the silica sol is 29-31%; The ratio of the mass of the water to the mass of the hydroxyapatite in the fourth mixed solution is 2 to 4; The ratio of the mass of the hydroxyapatite to the mass of the silica sol is 1 to 50:1; The dipping and stirring time is 6 to 10 hours; The temperature of the third drying is 80-100° C., and the time of the third drying is 10-12 hours; The temperature of the third sintering is 400-600° C., and the time of the third sintering is 2-4 hours.

9. The preparation method according to claim 6, characterized in that: In the step S2, the mass ratio of Pt ions in the Pt metal salt solution to Pd ions in the Pd metal salt solution is 1 to 6:1, and the Pt metal salt solution is selected from any one or more of a platinum nitrate solution, a platinum chloride solution, a chloroplatinic acid solution, a platinum acetate solution, a platinum acetylacetonate solution, and a tetraamine platinum tetrachloride solution; the Pd metal salt solution is selected from any one or more of a palladium nitrate solution, a palladium chloride solution, a chloropalladic acid solution, a platinum acetate solution, a palladium acetylacetonate solution, and a tetraamine palladium tetrachloride solution; And / or, the immersion time is 6 to 12 hours.

10. The preparation method according to claim 6, characterized in that: In the step S3, the first drying temperature is 80-100° C., and the first drying time is 10-12 hours; and / or the first sintering temperature is 500-650° C., and the first sintering time is 3-5 hours.

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