A noble metal catalyst suitable for natural gas vehicle exhaust purification and a preparation method thereof

Abstract

The application discloses a noble metal catalyst suitable for natural gas vehicle tail gas purification and a preparation method thereof. The noble metal catalyst is prepared from noble metal and carrier material by a double solvent method. The loading amount of the noble metal in the noble metal catalyst is 1wt%-3wt%, wherein the noble metal is calculated by element. The carrier material is a cerium-containing oxide oxygen storage material, and the content of cerium 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 catalyst has the advantages of uniform dispersion, high dispersion degree, good light-off performance and good water and heat aging resistance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalysts, in particular to a noble metal catalyst suitable for natural gas vehicle tail gas purification and a preparation method thereof. BACKGROUND

[0002] With the rapid growth of global automobile ownership, the problem of tail gas emission is becoming more and more serious, and controlling and governing automobile tail gas pollution has become an important issue of concern for countries around the world.

[0003] In order to solve the problem of automobile tail gas emission, natural gas vehicles using natural gas as energy are gradually applied and popularized, and the pollutant emission of natural gas vehicles is much lower than that of ordinary gasoline or diesel vehicles. However, incomplete combustion of fuel, especially incomplete combustion of CH4, still causes pollutant emission problems, 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, according to the current catalyst preparation method, the catalytic performance of the catalyst prepared by the traditional impregnation method still needs to be improved. This is mainly because the dispersion of noble metal on the carrier material is limited, which also leads to a more obvious decline in catalytic performance after high-temperature aging.

[0004] Furthermore, if the dispersion of noble metal on the carrier material is improved, it will be beneficial to improve the light-off performance and water-thermal aging resistance of the catalyst.

[0005] Based on this, the present application aims to provide a process method for improving the dispersion of noble metal in a catalyst, so as to improve the light-off performance and water-thermal aging resistance of the catalyst. SUMMARY

[0006] The present application aims to provide a noble metal catalyst suitable for natural gas vehicle tail gas purification, which has uniform dispersion of noble metal, high dispersion, and good light-off performance and water-thermal aging resistance. At the same time, the present application also provides a preparation method for preparing the noble metal catalyst.

[0007] The present application provides a noble metal catalyst suitable for natural gas vehicle tail gas purification, which is prepared by a double solvent method from noble metal and carrier material.

[0008] The loading amount of the noble metal in the noble metal catalyst is 1wt%-3wt%, wherein the noble metal is calculated as an element.

[0009] The carrier material is a cerium-containing oxide oxygen storage material, and the content of cerium 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 precious metal catalyst, the cerium-containing oxide oxygen storage material is ceria and / or zirconium-doped ceria.

[0012] In the precious metal catalyst, the cerium-containing oxide oxygen storage material is composed of ceria and zirconia, wherein the content of ceria is 40wt%-99.9wt%, and the content of zirconia is 0wt%-60wt%.

[0013] The second aspect of the present application provides a preparation method of a precious metal catalyst, which is used for preparing the precious metal catalyst described above, and the preparation method comprises the following steps:

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

[0015] S2: 1-9g of a precious metal precursor solution with a content of 14-16% is added dropwise into the mixed solution, and stirring is performed for 1-3h, and after completion, drying and calcination are performed to obtain catalyst powder;

[0016] S3: the catalyst powder is mixed with a binder and water, and after ball milling, a coating slurry is obtained; wherein the catalyst powder, the binder and water are mixed in a weight ratio of 90-99:1-10:100-200;

[0017] S4: the coating slurry is coated on the surface of a cordierite honeycomb ceramic carrier, and after drying and calcination, the precious metal catalyst is obtained.

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

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

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

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

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

[0023] The preparation method is simple, the noble metal catalyst prepared has high noble metal dispersion, the noble metal catalyst prepared has good light-off performance, the reducibility is enhanced, the catalytic removal activity of the noble metal catalyst to three pollutants (CH4, NOx and CO) is improved, and the hydrothermal aging resistance of the noble metal catalyst is obviously improved after hydrothermal aging, thereby having wide application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0024] The accompanying drawings, which are included to provide a further understanding of the embodiments of the application and are incorporated in and constitute a part of this application, illustrate embodiments of the application and together with the description serve to explain the principles of the application. In the drawings:

[0025] Figure 1 Light-off performance curve of fresh catalyst prepared for Example 1, Comparative Example 1 and Comparative Example 2 to CH4;

[0026] Figure 2 Light-off performance curve of fresh catalyst prepared for Example 1, Comparative Example 1 and Comparative Example 2 to NOx;

[0027] Figure 3 Light-off performance curve of catalyst prepared for Example 1, Comparative Example 1 and Comparative Example 2 to CH4 after hydrothermal aging at 800 DEG C;

[0028] Figure 4 Light-off performance curve of catalyst prepared for Example 1, Comparative Example 1 and Comparative Example 2 to NOx after hydrothermal aging at 800 DEG C;

[0029] Figure 5 Light-off performance curve of catalyst prepared for Example 1, Comparative Example 1 and Comparative Example 2 to CH4 after hydrothermal aging at 900 DEG C;

[0030] Figure 6 Light-off performance curve of catalyst prepared for Example 1, Comparative Example 1 and Comparative Example 2 to NOx after hydrothermal aging at 900 DEG C; DETAILED DESCRIPTION

[0031] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the embodiments. The schematic embodiments of the present application and the descriptions thereof are only used to explain the present application and do not limit the present application.

[0032] The first embodiment of the present application provides a noble metal catalyst suitable for natural gas vehicle exhaust purification, which is prepared by a double solvent method from noble metal and carrier material; the loading amount of the noble metal in the noble metal catalyst is 1wt%-3wt%, wherein the noble metal is calculated as an element; 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 a specific application, the noble metal is platinum or palladium.

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

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

[0036] The second embodiment of the present application provides a noble metal catalyst preparation method for preparing the above noble metal catalyst, which comprises the following steps:

[0037] S1 20-40g of the oxygen storage material is added to 300mL-1200mL of a hydrophobic solvent, and magnetic stirring is performed for 1.5-3h to obtain a uniform mixed solution;

[0038] S2 1-9g of a noble metal precursor solution with a content of 14-16% is added dropwise to the mixed solution, and stirring is performed for 1-3h, and after completion, drying and calcination are performed to obtain catalyst powder;

[0039] S3 The catalyst powder is mixed with a binder and water, and after ball milling, a coating slurry is obtained; wherein the catalyst powder, the binder and water are mixed in a weight ratio of 90-99, 1-10 and 100-200;

[0040] S4 The coating slurry is coated on the surface of a cordierite honeycomb ceramic carrier, and after drying and calcination, the noble metal catalyst is obtained.

[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 and palladium nitrate, or a combination of any two of the substances.

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

[0044] In the step S2 and S4, the drying temperature is 40-60℃, and the calcination temperature is 450-550℃.

[0045] For better understanding and implementation of the present application, the present application is further explained and described below in combination with specific examples.

[0046] Example 1

[0047] A noble metal catalyst suitable for natural gas vehicle exhaust purification, the preparation method comprising the following steps:

[0048] S1 25g of oxygen storage material-cerium dioxide (CeO2) is added to 500mL of hydrophobic solvent, and magnetic stirring is carried out for 3h to obtain a uniform mixed solution;

[0049] S2 2.5g of 15% platinum nitrate (Pt(NO3)2) noble metal precursor solution is added dropwise to the mixed solution, and stirring is carried out for 3h. After completion, drying is carried out at 50℃, and calcination is carried out at 500℃ to obtain catalyst powder;

[0050] S3 The catalyst powder is mixed with a binder and water, and after ball milling, a coating slurry is obtained; wherein the catalyst powder, the binder and the water are mixed in a weight ratio of 93:7:150;

[0051] S4 The coating slurry is coated on the surface of a cordierite honeycomb ceramic carrier, and dried at 50℃ and calcined at 500℃ to obtain a Pt / CeO2 monolithic noble metal catalyst with a Pt content of 1.5wt% and a CeO2 content of 99.9%.

[0052] Example 2

[0053] A noble metal catalyst suitable for natural gas vehicle exhaust purification, the preparation method comprising the following steps:

[0054] S1 25g of oxygen storage material-zirconium-doped cerium dioxide (Ce 0.4 Zr 0.6 O2) is added to 500mL of hydrophobic solvent, and magnetic stirring is carried out for 3h to obtain a uniform mixed solution;

[0055] S2 2.5g of 15% palladium nitrate (Pd(NO3)2) noble metal precursor solution is added dropwise to the mixed solution, and stirring is carried out for 3h. After completion, drying is carried out at 50℃, and calcination is carried out at 500℃ to obtain catalyst powder;

[0056] S3 The catalyst powder is mixed with a binder and water, and after ball milling, a coating slurry is obtained; wherein the catalyst powder, the binder and the water are mixed in a weight ratio of 93:7:150;

[0057] S4 coating the coating slurry on the surface of the cordierite honeycomb ceramic carrier, drying at 50°C and calcining at 500°C to obtain a Pd / CeO2 / ZrO2 monolithic catalyst with a Pd content of 1.5wt%, a CeO2 content of 40%, and a ZrO2 content of 60%. 0.4 Zr 0.6 O2 monolithic catalyst.

[0058] Comparative Example 1

[0059] The precious metal catalyst prepared based on the equal volume impregnation method includes the following steps:

[0060] S1: Catalyst preparation by equal volume impregnation method. First, 2.5g of precursor solution containing 15% platinum nitrate is weighed, then 9g of deionized water is added, followed by 25g of CeO2 carrier, and stirring for a certain period of time. After drying and calcining at 500°C, catalyst powder is obtained.

[0061] S2: Slurry preparation: Mix the catalyst powder from S1 with 93 parts by weight, 7 parts by weight of silica sol, and 150 parts by weight of water, and ball mill to obtain a coating slurry.

[0062] S3: Coating: Coating the coating slurry on the surface of the cordierite honeycomb ceramic carrier, followed by drying and calcining to obtain a Pt / CeO2 monolithic catalyst with a Pt content of 1.5wt% and a CeO2 content of 99.9%.

[0063] Comparative Example 2

[0064] The precious metal catalyst prepared based on the sol-gel method includes the following steps:

[0065] S1: Dissolve 2.5g of precursor solution containing 15% platinum nitrate and 48g of cerium nitrate hexahydrate in 50mL of deionized water, while stirring, add citric acid (molar ratio of metal ions (cerium + platinum) : citric acid = 2:1), continue stirring for 1h, then dry and calcine at 500°C to obtain catalyst powder.

[0066] S2: Slurry preparation: Mix the catalyst powder with 93 parts by weight, 7 parts by weight of silica sol, and 150 parts by weight of water, and ball mill to obtain a coating slurry.

[0067] S3: Coating: Coating the coating slurry on the surface of the cordierite honeycomb ceramic carrier, followed by drying and calcining to obtain a Pt / CeO2 monolithic catalyst.

[0068] Comparative Example 3

[0069] A noble metal catalyst prepared based on an equal-volume impregnation method, a preparation method thereof comprising the following steps:

[0070] S1. Preparation of the catalyst using an equal-volume impregnation method. First, a precursor solution containing 15% palladium nitrate 2.5 g is weighed, then 11 g of deionized water is added, and then 25 g of zirconium-doped ceria (Ce 0.4 Zr 0.6 O2) support is added, and stirring is performed for a certain period of time, followed by drying, calcination at 500°C, and the like to obtain catalyst powder;

[0071] S2. Slurry preparation: the catalyst powder is mixed with 93 parts by weight of silica sol, 7 parts by weight of water, and ball-milling is performed to obtain a coating slurry;

[0072] S3. Coating: the coating slurry is coated on the surface of a cordierite honeycomb ceramic carrier, and then drying and calcination are performed to obtain a Pt / Ce 0.4 Zr 0.6 O2 monolithic catalyst.

[0073] On this basis, the catalysts obtained in the above Examples 1-2 and Comparative Examples 1-3 are subjected to aging treatment, and the fresh and aged samples are subjected to activity testing, specifically:

[0074] The aging conditions are: hydrothermal aging, 10 vol% (volume fraction) of water vaporized by air is brought in, and continuous aging is performed at a temperature of 800°C or 900°C for 20 h.

[0075] The test conditions are: the activity evaluation of the catalyst is performed in a multi-path fixed continuous flow fixed bed reactor, and the composition of the simulated natural gas tail gas is: NO 1000 ppm, CO 4000 ppm, CH4 1000 ppm, H2O 100000 ppm, O2 3500 ppm, CO2 80000 ppm, N2 as a carrier gas, and the space velocity is 40000 h-1.

[0076] The test process is: all catalyst samples are pretreated at 550°C in the reaction atmosphere for 1 h before reaction. Then, the activity test is performed at a temperature rising rate of 5°C / min.

[0077] The concentrations of CO, NO, and CH4 during the test are tested by a Fourier infrared gas analyzer (MKS, Multigas 6030EBG2EZKS13T, USA), and the test temperature is 250°C-600°C. The temperature points at which the fresh and aged samples of the catalysts achieve 50% and 90% conversion rates of pollutants are obtained, and the temperature points at which the fresh and aged samples of the catalysts achieve 50% and 90% conversion rates of pollutants are obtained Figures 1 to 6Conversion curves of fresh and aged catalysts for pollutants. Since CO has been completely converted before 300°C, T50, T90 summary for CO is not listed in Table 1.

[0078]

[0079] Table 1 T50, T90 summary of fresh and 800°C aged catalysts

[0080] From Table 1, it can be concluded that:

[0081] According to Table 1, it can be concluded that:

[0082] For the comparative examples 1-3, Pt or Pd based catalysts were prepared by impregnation method (comparative example 1, comparative example 3) or sol-gel method (comparative example 2). The performance of fresh samples of comparative examples 1-3 was similar to that of the examples. However, after 800°C hydrothermal aging for 20h, the conversion temperature of NOxand CH4of the samples of comparative examples 1-3 was significantly increased.

[0083] Meanwhile, for the tested samples, the metal dispersion of some samples was also counted, and the results are shown in Table 2.

[0084]

[0085] Table 2 Metal dispersion of some examples and comparative examples

[0086] As shown in Table 2, the metal dispersion of some examples and comparative examples was listed. It can be found that the metal dispersion (Pt) of the fresh and aged samples prepared by the double solvent method was significantly higher than that of the samples prepared by the traditional impregnation method or sol-gel method. This enhancement was mainly due to the change of the preparation method, which improved the metal dispersion and the reducibility of the catalyst, and this also improved the catalytic removal activity of the catalyst for the three pollutants (CH4, NOx, CO).

[0087] As shown in Table 2, the metal dispersion of some examples and comparative examples was listed. It can be found that the metal dispersion (Pt) of the fresh and aged samples prepared by the double solvent method was significantly higher than that of the samples prepared by the traditional impregnation method or sol-gel method. This enhancement was mainly due to the change of the preparation method, which improved the metal dispersion and the reducibility of the catalyst, and this also improved the catalytic removal activity of the catalyst for the three pollutants (CH4, NOx, CO). Figures 1-2 As shown in Table 2, the metal dispersion of some examples and comparative examples was listed. It can be found that the metal dispersion (Pt) of the fresh and aged samples prepared by the double solvent method was significantly higher than that of the samples prepared by the traditional impregnation method or sol-gel method. This enhancement was mainly due to the change of the preparation method, which improved the metal dispersion and the reducibility of the catalyst, and this also improved the catalytic removal activity of the catalyst for the three pollutants (CH4, NOx, CO). Figures 3-6Temperature-dependent light-off performance curves of CH4, NOx at different aging temperatures for Example 1 and Comparative Example 1, Comparative Example 2; wherein, the vertical coordinate represents conversion rate, unit %; the horizontal coordinate represents temperature, unit ℃.

[0088] In combination Figures 1-6 It can be seen that:

[0089] For fresh performance, according to Figures 1-2 It can be seen that the conversion efficiency of Example 1 for CH4, NOx is better than that of Comparative Examples 1 and 2, because the dispersion of Pt in Example 1 is improved, so that Pt is more uniformly dispersed on the corresponding carrier than the other two methods, thereby improving the catalytic activity for pollutants.

[0090] After hydrothermal aging at 800℃ or 900℃ for 20h, according to Figures 3-6 It can be seen that the conversion rate of Example 1 for pollutants is significantly higher than that of Comparative Examples 1 and 2, although the conversion temperature of all catalysts for pollutants increases relative to the fresh sample, the difference between the catalysts prepared by different methods is also obvious, because whether it is a fresh or aged sample, the use of a double solvent method can significantly improve the dispersion of noble metals on the carrier, so that its light-off performance for pollutants is improved, and after high-temperature hydrothermal aging, it still maintains a better treatment capacity, which also shows that the double solvent method can improve the hydrothermal aging resistance of the catalyst.

[0091] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application. It should be understood that the above description is only a specific embodiment of the present application and is not intended to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing a noble metal catalyst, characterized in that, The noble metal catalyst is prepared by a dual-solvent method using a noble metal and a support material; the loading of the noble metal in the noble metal catalyst is 1wt% to 3wt%, wherein the noble metal is calculated as elemental; the support material is a cerium-containing oxide oxygen storage material, wherein the cerium content in the cerium-containing oxide oxygen storage material is greater than or equal to 40wt%; the noble metal is platinum or palladium; the cerium-containing oxide oxygen storage material is cerium dioxide and / or zirconium-doped cerium dioxide; the cerium-containing oxide oxygen storage material is composed of cerium dioxide and zirconium dioxide, wherein the cerium dioxide content is 40wt% to 99.9wt% and the zirconium dioxide content is 0wt% to 60wt%; The preparation method includes the following steps: S1. Add 20-40g of oxygen storage material to 300mL-1200mL of hydrophobic solvent and stir magnetically for 1.5-3h to obtain a homogeneous mixed solution. S2 is added dropwise to a noble metal precursor solution with a content of 14-16% (1-9 g) into a mixed solution, stirred for 1-3 hours, and then dried and calcined to obtain catalyst powder. S3 The catalyst powder is mixed with binder and water, and ball-milled to obtain a coating slurry; wherein the catalyst powder, binder and water are mixed in proportions of 90-99 parts by weight, 1-10 parts by weight and 100-200 parts by weight. S4 The coating slurry is applied to the surface of a cordierite honeycomb ceramic carrier, and then dried and calcined to obtain the noble metal catalyst.

2. The method for preparing a noble metal catalyst according to claim 1, characterized in that, The hydrophobic solvent is n-hexane or cyclohexane.

3. The method for preparing a noble metal catalyst according to claim 1, characterized in that, The noble metal precursor in the noble metal precursor solution is one or a combination of any two of the following: platinum nitrate, platinum chlorate, and palladium nitrate.

4. The method for preparing a noble metal catalyst according to claim 1, characterized in that, The adhesive is one or a combination of any two of the following: silica sol, aluminum sol, and zirconium sol.

5. The method for preparing a noble metal catalyst according to claim 1, characterized in that, In steps S2 and S4, the drying temperature is 40~60℃ and the calcination temperature is 450~550℃.

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