Precious metal catalyst suitable for purifying tail gas of natural gas vehicle and preparation method of noble metal catalyst

Abstract

The invention discloses a noble metal catalyst suitable for purifying tail gas of a natural gas vehicle and a preparation method of the noble metal catalyst. The noble metal catalyst is prepared from noble metal and a carrier material through a double-solvent method, the loading capacity of the noble metal in the noble metal catalyst is 1-3 wt%, and the noble metal is calculated as a simple substance; the carrier material is a cerium-containing oxide oxygen storage material, and the cerium content in the cerium-containing oxide oxygen storage material is greater than or equal to 40wt%. The preparation method is used for preparing the noble metal catalyst. The noble metal in the noble metal catalyst is uniformly dispersed, the dispersity is high, and the noble metal catalyst has good light-off performance and hydrothermal aging resistance.

Description

Technical Field

[0001] The invention relates to the technical field of catalysts, and in particular to a noble metal catalyst suitable for purifying exhaust gas from natural gas vehicles and a preparation method thereof. Background Art

[0002] With the rapid growth of global car ownership, exhaust emissions are becoming more and more serious. Controlling and managing automobile exhaust pollution has become an important issue of concern to countries around the world.

[0003] In order to solve the problem of automobile exhaust emissions, natural gas vehicles that use natural gas as energy are gradually applied and promoted. The pollutant emissions of natural gas vehicles are much lower than those of ordinary gasoline or diesel vehicles. However, incomplete combustion of fuel, especially incomplete combustion of CH4, will still cause pollutant emissions, and this problem is difficult to eliminate. The commonly used method is to install a three-way catalyst on the automobile exhaust system. The three-way catalyst often uses Pt, Pd, and Rh as active components. However, as far as the current catalyst preparation method is concerned, the catalytic performance of the traditional impregnation method still needs to be improved. This is mainly because the impregnation method limits the dispersion of precious metals on the carrier material, which also leads to a more obvious decline in catalytic performance after high-temperature aging.

[0004] Furthermore, if the dispersion of the precious metal on the carrier material is improved, it will be beneficial to improve the ignition performance and hydrothermal aging resistance of the catalyst.

[0005] Based on this, the present invention aims to provide a process method for improving the dispersion of precious metals in catalysts, thereby improving the ignition performance and hydrothermal aging resistance of the catalysts. Summary of the invention

[0006] The object of the present invention is to provide a precious metal catalyst suitable for purifying exhaust gas from natural gas vehicles, wherein the precious metal in the precious metal catalyst is evenly dispersed, has a high degree of dispersion, and has good ignition performance and hydrothermal aging resistance. At the same time, the present invention also provides a preparation method for preparing the precious metal catalyst.

[0007] The first aspect of the present invention provides a precious metal catalyst suitable for purifying exhaust gas from natural gas vehicles, which is prepared from a precious metal and a carrier material by a double solvent method;

[0008] The loading amount of the noble metal in the noble metal catalyst is 1 wt% to 3 wt%, wherein the noble metal is calculated as a single substance;

[0009] The carrier material is a cerium-containing oxide oxygen storage material, and the cerium content in the cerium-containing oxide oxygen storage material is greater than or equal to 40wt%.

[0010] In the noble metal catalyst, the noble metal is platinum or palladium.

[0011] In the noble metal catalyst, the cerium-containing oxide oxygen storage material is ceria and / or zirconium-doped ceria.

[0012] In the noble metal catalyst, the cerium-containing oxide oxygen storage material consists of cerium dioxide and zirconium dioxide, wherein the content of cerium dioxide is 40wt% to 99.9wt%, and the content of zirconium dioxide is 0wt% to 60wt%.

[0013] The second aspect of the present invention provides a method for preparing a noble metal catalyst, which is used to prepare the noble metal catalyst mentioned above, and the preparation method comprises the following steps:

[0014] S1: adding 20-40 g of oxygen storage material into 300 mL-1200 mL of hydrophobic solvent and magnetically stirring for 1.5-3 h to obtain a uniform mixed solution;

[0015] S2 adds 1 to 9 g of a noble metal precursor solution with a content of 14 to 16% to the mixed solution, stirs for 1 to 3 hours, and then dries and calcines to obtain a catalyst powder;

[0016] S3: mixing the catalyst powder, the adhesive and water, and ball milling to obtain a coating slurry; wherein the catalyst powder, the adhesive and the water are mixed in an amount of 90 to 99 parts by weight, 1 to 10 parts by weight and 100 to 200 parts by weight;

[0017] S4: coating the coating slurry on the surface of the cordierite honeycomb ceramic carrier, and drying and calcining the coating slurry to obtain the precious metal catalyst.

[0018] In the preparation method, the hydrophobic solvent is a n-hexane solvent or a cyclohexane solvent.

[0019] In the preparation method, the noble metal precursor in the noble metal precursor solution is one of platinum nitrate, platinum chlorate, palladium nitrate, or a combination of any two groups of substances.

[0020] In the preparation method, the adhesive is one of silica sol, aluminum sol, zirconium sol or a combination of any two groups of substances.

[0021] In the preparation method, in the steps S2 and S4, the drying temperature is 40-60°C, and the calcining temperature is 450-550°C.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The preparation method of the present invention is simple, and the prepared precious metal catalyst has a high degree of precious metal dispersion, so that the prepared precious metal catalyst has good ignition performance and enhanced reducibility, so that the catalytic removal activity of the precious metal catalyst for three pollutants (CH4, NOx, CO) is improved, and after hydrothermal aging, the hydrothermal aging resistance of the precious metal catalyst is also significantly improved, thereby having broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0025] Figure 1 The fresh catalyst prepared in Example 1, Comparative Example 1 and Comparative Example 2 reacted with CH 4 Ignition performance curve diagram;

[0026] Figure 2 It is a graph showing the NOx ignition performance of the fresh catalysts prepared in Example 1, Comparative Example 1 and Comparative Example 2;

[0027] Figure 3 The catalysts prepared in Example 1, Comparative Example 1 and Comparative Example 2 were subjected to hydrothermal aging at 800°C for CH 4 Ignition performance curve diagram;

[0028] Figure 4 The NOx ignition performance curves of the catalysts prepared in Example 1, Comparative Example 1 and Comparative Example 2 after hydrothermal aging at 800° C. are shown;

[0029] Figure 5 The catalysts prepared in Example 1, Comparative Example 1 and Comparative Example 2 were subjected to hydrothermal aging at 900°C for CH 4 Ignition performance curve diagram;

[0030] Figure 6 The NOx ignition performance curves of the catalysts prepared in Example 1, Comparative Example 1 and Comparative Example 2 after hydrothermal aging at 900° C. are shown; DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments. The illustrative embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0032] The first embodiment of the present invention provides a precious metal catalyst suitable for purifying exhaust gas from natural gas vehicles, which is prepared from precious metals and a carrier material by a double solvent method; the loading amount of the precious metal in the precious metal catalyst is 1wt% to 3wt%, wherein the precious metal is calculated as a single substance; the carrier material is a cerium-containing oxide oxygen storage material, and the cerium content in the cerium-containing oxide oxygen storage material is greater than or equal to 40wt%.

[0033] In specific applications, the noble metal is platinum or palladium.

[0034] In specific applications, the cerium-containing oxide oxygen storage material is ceria and / or zirconium-doped ceria.

[0035] In specific applications, the cerium-containing oxide oxygen storage material consists of cerium dioxide and zirconium dioxide, wherein the content of cerium dioxide is 40wt% to 99.9wt%, and the content of zirconium dioxide is 0wt% to 60wt%.

[0036] The second embodiment of the present invention provides a method for preparing a precious metal catalyst, which is used to prepare the precious metal catalyst mentioned above, and the preparation method comprises the following steps:

[0037] S1: adding 20-40 g of oxygen storage material into 300 mL-1200 mL of hydrophobic solvent and magnetically stirring for 1.5-3 h to obtain a uniform mixed solution;

[0038] S2 adds 1 to 9 g of a noble metal precursor solution with a content of 14 to 16% to the mixed solution, stirs for 1 to 3 hours, and then dries and calcines to obtain a catalyst powder;

[0039] S3: mixing the catalyst powder, the adhesive and water, and ball milling to obtain a coating slurry; wherein the catalyst powder, the adhesive and the water are mixed in an amount of 90 to 99 parts by weight, 1 to 10 parts by weight and 100 to 200 parts by weight;

[0040] S4: coating the coating slurry on the surface of the cordierite honeycomb ceramic carrier, and drying and calcining the coating slurry to obtain the precious metal catalyst.

[0041] In a specific implementation, the hydrophobic solvent is a n-hexane solvent or a cyclohexane solvent.

[0042] In a specific implementation, the noble metal precursor in the noble metal precursor solution is one of platinum nitrate, platinum chlorate, palladium nitrate, or a combination of any two groups of substances.

[0043] In a specific implementation, the adhesive is one of silica sol, aluminum sol, zirconium sol, or a combination of any two groups of substances.

[0044] In specific implementation, in the steps S2 and S4, the drying temperature is 40-60°C, and the calcining temperature is 450-550°C.

[0045] For better understanding and implementation of the present invention, the present invention is further explained and illustrated below in conjunction with specific embodiments.

[0046] Example 1

[0047] A precious metal catalyst suitable for purifying exhaust gas from natural gas vehicles, the preparation method of which comprises the following steps:

[0048] S1 25g of oxygen storage material - cerium dioxide (CeO 2 ) was added to 500 mL of a hydrophobic solvent and magnetically stirred for 3 h to obtain a uniform mixed solution;

[0049] S2 added 15% platinum nitrate (Pt(NO 3 ) 2 ) 2.5 g of noble metal precursor solution was added to the mixed solution, stirred for 3 h, dried at 50 ° C and calcined at 500 ° C to obtain a catalyst powder;

[0050] S3: mixing the catalyst powder, the adhesive and water, and ball milling to obtain a coating slurry; wherein the catalyst powder, the adhesive and the water are mixed in the proportions of 93 parts by weight, 7 parts by weight and 150 parts by weight respectively;

[0051] S4: Apply the coating slurry on the surface of the cordierite honeycomb ceramic carrier, dry it at 50°C, and calcine it at 500°C to obtain a Pt content of 1.5wt%, CeO 2 Pt / CeO with a content of 99.9% 2 Monolithic precious metal catalysts.

[0052] Example 2

[0053] A precious metal catalyst suitable for purifying exhaust gas from natural gas vehicles, the preparation method of which comprises the following steps:

[0054] S1 25g oxygen storage material-zirconium doped cerium dioxide (Ce 0.4 Zr 0.6 O 2 ) was added to 500 mL of a hydrophobic solvent and magnetically stirred for 3 h to obtain a uniform mixed solution;

[0055] S2 added 15% palladium nitrate (Pd(NO 3 ) 2) 2.5 g of noble metal precursor solution was added to the mixed solution, stirred for 3 h, dried at 50 ° C and calcined at 500 ° C to obtain a catalyst powder;

[0056] S3: mixing the catalyst powder, the adhesive and water, and ball milling to obtain a coating slurry; wherein the catalyst powder, the adhesive and the water are mixed in the proportions of 93 parts by weight, 7 parts by weight and 150 parts by weight respectively;

[0057] S4: coating the coating slurry on the surface of the cordierite honeycomb ceramic carrier, drying it at 50°C and calcining it at 500°C to obtain a Pd content of 1.5wt%, CeO 2 The content is 40%, ZrO 2 Pd / Ce content of 60% 0.4 Zr 0.6 O 2 Monolithic catalyst.

[0058] Comparative Example 1

[0059] The preparation method of the noble metal catalyst prepared by the equal volume impregnation method comprises the following steps:

[0060] S1 The catalyst was prepared by equal volume impregnation method. First, 2.5 g of precursor solution containing 15% platinum nitrate was weighed, then 9 g of deionized water was added, and 25 g of CeO 2 The carrier is then stirred for a certain period of time, and then dried and calcined at 500°C to obtain catalyst powder;

[0061] S2 slurry preparation: 93 parts by weight of the catalyst powder described in S1, 7 parts by weight of silica sol, and 150 parts by weight of water are mixed and ball-milled to obtain a coating slurry;

[0062] S3 coating: coating the coating slurry on the surface of the cordierite honeycomb ceramic carrier, and then drying and calcining to obtain a Pt content of 1.5wt%, CeO 2 Pt / CeO with a content of 99.9% 2 Monolithic catalyst.

[0063] Comparative Example 2

[0064] The preparation method of the noble metal catalyst based on the sol-gel method comprises the following steps:

[0065] S1: 2.5 g of a precursor solution containing 15% platinum nitrate and 48 g of cerium nitrate hexahydrate were dissolved in 50 mL of deionized water, and citric acid (metal ion (cerium + platinum): citric acid (molar ratio) = 2:1) was added while stirring, and then stirring was continued for 1 hour, followed by drying, calcination at 500° C., etc. to obtain a catalyst powder;

[0066] S2 slurry preparation: 93 parts by weight of the catalyst powder, 7 parts by weight of silica sol and 150 parts by weight of water are mixed and ball-milled to obtain a coating slurry;

[0067] S3 coating: coating the coating slurry on the surface of the cordierite honeycomb ceramic carrier, and then drying and calcining to obtain Pt / CeO 2 Monolithic catalyst.

[0068] Comparative Example 3

[0069] The preparation method of the noble metal catalyst prepared by the equal volume impregnation method comprises the following steps:

[0070] S1 uses the equal volume impregnation method to prepare the catalyst. First, weigh 2.5g of the precursor solution containing 15% palladium nitrate, then add 11g of deionized water, and add 25g of zirconium-doped cerium dioxide (Ce 0.4 Zr 0.6 O 2 ) carrier, stirring for a certain period of time, and then drying, calcining at 500°C, etc. to obtain catalyst powder;

[0071] S2 slurry preparation: 93 parts by weight of the catalyst powder, 7 parts by weight of silica sol and 150 parts by weight of water are mixed and ball-milled to obtain a coating slurry;

[0072] S3 coating: coating the coating slurry on the surface of the cordierite honeycomb ceramic carrier, and then drying and calcining to obtain Pt / Ce 0.4 Zr 0.6 O 2 Monolithic catalyst.

[0073] On this basis, the catalysts obtained in the above Examples 1-2 and Comparative Examples 1-3 were aged, and the activity of the fresh and aged samples was tested. Specifically:

[0074] The aging conditions are: hydrothermal aging, 10 vol% (volume fraction) of vaporized water is brought into the air, and the aging is continued at a temperature of 800° C. or 900° C. for 20 hours.

[0075] The test conditions are as follows: the activity evaluation of the catalyst is carried out in a fixed bed reactor with multiple fixed continuous flows, and the exhaust gas composition of the simulated natural gas vehicle is: NO 1000ppm, CO 4000ppm, CH 4 1000ppm, H 2 O 100000ppm, O 2 3500ppm, CO 2 80000ppm,N 2As carrier gas, the space velocity is 40000h-1.

[0076] The test process is as follows: all catalyst samples were pretreated at 550°C for 1 hour in a reaction atmosphere before the reaction, and then the activity test was carried out at a heating rate of 5°C / min.

[0077] CO, NO, CH during the test 4 The concentration of was tested by Fourier infrared gas analyzer (MKS, USA, MultigGas6030EBG2EZKS13T), the test temperature was 250℃-600℃, and the temperature points at which the conversion rate of pollutants of fresh and aged samples of the catalyst was 50% and 90% were obtained as shown in Table 1, and Figures 1 to 6 The conversion rate curves of fresh and aged catalysts for pollutants are shown. Since CO has been completely converted before 300°C, the T50 and T90 summaries of CO are not listed in Table 1.

[0078]

[0079] Table 1 Summary of T50 and T90 of fresh catalyst and 800℃ aged samples

[0080] According to Table 1, we can conclude that:

[0081] Using the dual solvent method, Pt or Pd is loaded on high Ce or medium Ce oxygen storage materials (Examples 1-2) to reduce the pollutants NOx and CH 4 The catalyst prepared by the dual solvent method showed good catalytic activity for the purification of NOx, CH 4 The conversion temperature is significantly lower, which shows that the catalyst prepared by the dual solvent method has good ignition performance and resistance to hydrothermal aging.

[0082] For Comparative Examples 1 to 3, the Pt or Pd-based catalysts were prepared by the impregnation method (Comparative Example 1, Comparative Example 3) or the sol-gel method (Comparative Example 2). The performance of the fresh samples was slightly different from that of the examples. However, after being hydrothermally aged at 800°C for 20 h, the performance of the samples was significantly different from that of the examples. 4 The conversion temperature increased significantly.

[0083] At the same time, for the test samples, this embodiment also makes statistics on the metal dispersion of some samples, as shown in the following Table 2:

[0084]

[0085] Table 2 Statistical results of metal dispersion of some examples and comparative examples

[0086] Table 2 lists the metal dispersions of some examples and comparative examples. It can be found that the metal dispersion (Pt) of the catalysts prepared by the dual solvent method, whether fresh or aged, is significantly higher than that of the samples prepared by the traditional impregnation method or sol-gel method. This enhancement is mainly due to the change in the preparation method, which improves the metal dispersion and the reducibility of the catalyst, which will also increase the catalyst's resistance to the three pollutants (CH 4 , NOx, CO) is improved.

[0087] like Figure 1-Figure 2 The CH of fresh catalysts prepared in Example 1 and Comparative Example 1 and Comparative Example 2 is shown. 4 , NOx ignition performance curve with temperature; the ordinate represents the conversion rate, unit %, and the abscissa represents the temperature, unit ℃. Figure 3 to Figure 6 The CH of Example 1, Comparative Example 1 and Comparative Example 2 at different aging temperatures 4 , the ignition performance curve of NOx changing with temperature; wherein, the ordinate represents the conversion rate, in %, and the abscissa represents the temperature, in ℃.

[0088] Combination Figure 1-Figure 6 It can be seen that:

[0089] For fresh performance, according to Figure 1-2 It can be seen that Example 1 has a significant effect on CH 4 The conversion efficiency of the two pollutants, NO and NOx, is better than that of comparative examples 1 and 2. This is because the dispersion of Pt in Example 1 is improved, so that Pt is more evenly dispersed on the corresponding carrier compared with the other two methods, thereby improving the catalytic activity against pollutants.

[0090] After hydrothermal aging at 800℃ or 900℃ for 20h, Figure 3-6 It can be seen that the conversion rate of pollutants in Example 1 is significantly higher than that in Comparative Examples 1 and 2. Although the conversion temperatures of pollutants of all catalysts are increased relative to fresh samples, the differences between the catalysts prepared by different methods are also quite obvious. This is because the use of the dual solvent method can significantly improve the dispersion of precious metals on the carrier, thereby improving the ignition performance of pollutants, regardless of whether it is a fresh or aged sample, and still maintains a better processing capacity after high-temperature hydrothermal aging. This also shows that the dual solvent method can improve the hydrothermal aging resistance of the catalyst.

[0091] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A precious metal catalyst suitable for purifying exhaust gas from natural gas vehicles, characterized in that: It is prepared from noble metals and support materials by a double solvent method; The loading amount of the noble metal in the noble metal catalyst is 1 wt% to 3 wt%, wherein the noble metal is calculated as a single substance; The carrier material is a cerium-containing oxide oxygen storage material, and the cerium content in the cerium-containing oxide oxygen storage material is greater than or equal to 40wt%.

2. The noble metal catalyst according to claim 1, characterized in that The noble metal is platinum or palladium.

3. The noble metal catalyst according to claim 1, characterized in that The cerium-containing oxide oxygen storage material is cerium dioxide and / or zirconium-doped cerium dioxide.

4. The noble metal catalyst according to claim 3, characterized in that The cerium-containing oxide oxygen storage material consists of cerium dioxide and zirconium dioxide, wherein the content of cerium dioxide is 40wt% to 99.9wt%, and the content of zirconium dioxide is 0wt% to 60wt%.

5. A method for preparing a noble metal catalyst, for preparing the noble metal catalyst according to any one of claims 1 to 4, characterized in that: The preparation method comprises the following steps: S1: adding 20-40 g of oxygen storage material into 300 mL-1200 mL of hydrophobic solvent and magnetically stirring for 1.5-3 h to obtain a uniform mixed solution; S2 adds 1 to 9 g of a noble metal precursor solution with a content of 14 to 16% to the mixed solution, stirs for 1 to 3 hours, and then dries and calcines to obtain a catalyst powder; S3: mixing the catalyst powder, the adhesive and water, and ball milling to obtain a coating slurry; wherein the catalyst powder, the adhesive and the water are mixed in an amount of 90 to 99 parts by weight, 1 to 10 parts by weight and 100 to 200 parts by weight; S4: coating the coating slurry on the surface of the cordierite honeycomb ceramic carrier, and drying and calcining the coating slurry to obtain the precious metal catalyst.

6. The method for preparing a noble metal catalyst according to claim 5, characterized in that: The hydrophobic solvent is n-hexane solvent or cyclohexane solvent.

7. The method for preparing a noble metal catalyst according to claim 5, characterized in that: The noble metal precursor in the noble metal precursor solution is one of platinum nitrate, platinum chlorate, palladium nitrate, or a combination of any two groups of substances.

8. The method for preparing a noble metal catalyst according to claim 5, characterized in that: The adhesive is one of silica sol, aluminum sol and zirconium sol or a combination of any two groups of substances.

9. The method for preparing a noble metal catalyst according to claim 5, characterized in that: In the steps S2 and S4, the drying temperature is 40-60°C, and the calcining temperature is 450-550°C.

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