Method for reducing precious metal usage, natural gas vehicle aftertreatment catalyst and method of making

Abstract

The application relates to the technical field of natural gas vehicle tail gas purification catalysts, and particularly discloses a method for reducing the amount of noble metal, a natural gas vehicle aftertreatment catalyst and a preparation method, which comprises an upper layer of catalytic coating and a bottom layer of catalytic coating; the upper layer of catalytic coating comprises noble metal and rare earth composite oxides; the bottom layer of catalytic coating comprises noble metal and modified alumina, the modified alumina is BaSO4 surface grafting-NH2 group doped cerium modified alumina CeAlO x ; the total content of noble metal in the upper layer of catalytic coating and the bottom layer of catalytic coating is 20-50 g / cft. According to the unique modification of the alumina carrier in the bottom layer of catalyst, the freshness and durability of the catalyst can be ensured and improved on the basis that the amount of noble metal is reduced by more than 50% compared with the commercially available catalyst, the durability requirement of regulations is met, and the problem that the cost of the current aftertreatment catalyst is high is solved.

Description

Technical Field

[0001] This invention relates to the field of natural gas vehicle exhaust purification catalyst technology, and more specifically, to a method for reducing the amount of precious metals used, a natural gas vehicle aftertreatment catalyst, and a preparation method thereof. Background Technology

[0002] With the increasing demand for heavy-duty natural gas vehicles, the corresponding increase in exhaust pollutants such as hydrocarbons (mainly methane), carbon monoxide, and nitrogen oxides is also rising. Methane in natural gas vehicle exhaust is the most structurally stable alkane, making it more difficult to process than hydrocarbons from gasoline and diesel vehicles. Therefore, after-treatment catalysts for natural gas vehicles require a higher content of precious metals to ensure their catalytic performance against methane. Since the implementation of the China VI emission standard for heavy-duty natural gas vehicles, although the amount of precious metals used in catalysts has decreased significantly, the mainstream after-treatment catalysts for heavy-duty natural gas vehicles currently on the market still contain more than 30g of precious metals per set, resulting in persistently high costs.

[0003] The durability testing methods for engine-aftertreatment systems required by the China VI emission standards can be conducted on a whole vehicle or engine bench. The durability test mileage must not be less than the minimum mileage. For N3 category heavy-duty vehicles weighing 16 tons or more, the minimum mileage is 233,000 km. According to the standard cycle conditions of GB20890-2007, the bench durability time is 1456 hours (5 hours of bench durability = 800 km of whole vehicle mileage). Such a long durability test requirement places a great strain on the durability performance of the catalyst, especially since the amount of precious metals used in the catalyst has been significantly reduced after multiple rounds of cost reduction iterations. Further reductions would not meet the durability requirements.

[0004] Therefore, how to reduce the amount of precious metals used while ensuring the freshness and performance of the catalyst after 1456 hours of standard bench durability are comparable to or better than mainstream commercially available catalysts is a pressing issue that needs to be addressed in this industry. This patented invention provides a low-precious-metal catalyst, which reduces the amount of precious metals used by more than 50% compared to mainstream commercially available catalysts. This not only solves the problem of high post-processing catalyst costs but also significantly improves catalyst durability, meeting regulatory durability requirements.

[0005] In view of the above, this application is hereby submitted. Summary of the Invention

[0006] The existing technology has problems. Currently, the amount of precious metals used in after-treatment catalysts for natural gas vehicles is still relatively high. However, further reducing the amount of precious metals will lead to the catalyst's freshness and durability failing to meet the requirements. Therefore, this invention provides a method for reducing the amount of precious metals, a natural gas vehicle after-treatment catalyst, and a preparation method. By uniquely modifying the alumina support in the bottom catalyst, it is possible to reduce the amount of precious metals by more than 50% compared to commercially available catalysts, while ensuring and improving the freshness and durability of the catalyst, meeting regulatory durability requirements, and solving the problem of the high cost of current after-treatment catalysts.

[0007] This invention is achieved through the following technical solution:

[0008] In a first aspect, the present invention provides a three-way catalyst for the aftertreatment of natural gas vehicles that reduces the amount of precious metals used, comprising an upper catalytic coating and a lower catalytic coating.

[0009] The upper catalytic coating comprises noble metals and rare earth composite oxides;

[0010] The underlying catalytic coating comprises a noble metal and modified alumina, wherein the modified alumina is CeAlO4 modified alumina with cerium-doped BaSO4 surface grafted with -NH2 groups. x ;

[0011] The total content of precious metals in the upper and lower catalytic coatings is 20~50 g / cmf.

[0012] Currently, there are many ways to modify alumina supports. The most common method is cerium-modified alumina. While cerium-modified alumina can improve oxygen storage capacity, it suffers from poor dispersion processes, leading to easy agglomeration of CeO2. Furthermore, cerium-modified alumina is prone to grain coarsening at high temperatures, failing to generate a reinforcing phase, thus limiting its thermal shock resistance. Barium-modified alumina, on the other hand, when excessive Ba is added or unevenly dispersed, accelerates pore collapse and abnormal grain growth, resulting in a sharp reduction in specific surface area and decreased catalyst performance.

[0013] This invention further modifies existing cerium-modified alumina by grafting -NH2 groups onto the surface of BaSO4. The -NH2 groups grafted onto the surface of BaSO4 enhance the bonding with alumina, improve the dispersion uniformity of alumina and CeO2, and prevent CeO2 agglomeration, thereby increasing the specific surface area retention rate of the alumina material after high-temperature aging. At the same time, it can also increase the electron density of the noble metal Pd, strengthen the Pd-O bond, optimize the electronic structure of the Pd / Al2O3 catalyst, inhibit the high-temperature decomposition of PdO to enhance the stability of PdO, and thus effectively improve the activity of methane combustion.

[0014] Therefore, by adding the special modified alumina material of this invention, the freshness and anti-aging ability of the catalyst can be greatly improved, ensuring that even after the amount of precious metal is reduced by half (total amount of precious metal is 20 g / cft), the performance is still comparable to or better than that of commercially available catalysts. In the catalyst of this invention, the amount of precious metal can be selected to be 20 g / cft, which is lower than that of commercially available catalysts (more than 50 g / cft), and it can still maintain the freshness and anti-aging ability comparable to or better than that of commercially available catalysts.

[0015] In one specific embodiment, the BaSO4 surface grafted with -NH2 groups is obtained by modifying BaSO4 with γ-aminopropyltriethoxysilane (KH-550, A-1100) or γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH-560, A-187).

[0016] In one specific embodiment, the noble metal in the bottom catalytic coating is Pd, or a combination of Pd and Pt; wherein the Pd content is 1~50 g / cft, and the Pt content is 0~50 g / cft; the total noble metal content in the bottom catalytic coating is 1~50 g / cft.

[0017] In one specific embodiment, the noble metals used in the upper catalytic coating are Pt and Rh; wherein the Pt content is 1~50 g / cft, the Rh content is 0.4~10 g / cft, and the total noble metal content in the upper catalytic coating is 1.4~50 g / cft.

[0018] In one specific embodiment, the content of BaSO4 in the modified alumina is cerium-modified alumina (CeAlO). x Content: 0-5 wt%.

[0019] In one specific embodiment, the rare earth composite oxide is a modified rare earth composite oxide obtained by using Y, Sm, Pr, and La doped cerium-based oxides.

[0020] This invention improves the support material in the upper catalytic coating by introducing four rare earth elements (Y, Sm, Pr, and La) to co-dopate CeO2, forming a multi-component composite oxide. This significantly enhances the material's oxygen storage performance, stability, catalytic performance, and anti-aging properties compared to single-doped or traditional Ce-Zr systems. Specifically, Y… 3+ 、Sm 3+ Pr 3+ / Pr 4+ La 3+ All are low-valence / variable-valence ions. Upon entering the CeO2 lattice, they can generate charge-compensating oxygen vacancies and simultaneously cause multi-level lattice distortion, producing more oxygen vacancies and improving the oxygen storage capacity of CeO2. La 3+ Y 3+It can increase surface alkalinity, thereby promoting the anchoring of precious metals such as Pt and Pd, reducing their tendency for high-temperature sintering, and inhibiting carbon deposition; Sm 3+ This invention can promote the full dispersion of precious metals in the support material and improve catalytic performance. The support for the upper catalytic coating of this invention adopts multi-element doped modified rare earth composite oxide, which can further improve the catalytic performance and anti-aging properties of the catalyst. In synergy with modified alumina, it can further ensure that the catalyst performance can meet regulatory requirements even after the amount of precious metal is reduced.

[0021] In a specific embodiment, the rare earth composite oxide contains the following components by mass fraction: CeO2 50~75 wt%, Y2O3 2~5 wt%, Pr2O3 2.5~15 wt%, Sm2O3 0.5~15 wt%, and La2O3 10~15 wt%.

[0022] In one specific embodiment, an intermediate transition layer is provided between the upper catalytic coating and the lower catalytic coating, and the intermediate transition layer is made of cerium-zirconium-aluminum composite oxide.

[0023] In this invention, Ce, as the main component, ensures the cubic fluorite structure, possessing high lattice energy while maintaining structural stability under high temperature, oxidation, or reduction conditions; La can prevent excessive lattice distortion, and an appropriate amount of La... 3+ Doping with Pr can introduce a large number of oxygen vacancies, significantly increasing the oxygen vacancy concentration; Pr provides variable valence Pr 3+ / Pr 4+ It can more efficiently regulate oxygen concentration while inhibiting the migration of CeO2 grains at high temperatures, thus improving the high-temperature stability of the catalyst; trace amounts of Y and Sm doping can promote the anchoring and dispersion of noble metals, reduce their tendency to sinter at high temperatures, and inhibit carbon deposition.

[0024] Because the material composition of the bottom and top catalytic coatings differs significantly, the coefficients of thermal expansion between them also differ considerably. This difference leads to relatively concentrated interfacial stress between the bottom and top layers, causing coating cracking and reducing the catalyst's three-way performance. Furthermore, the layered coating increases porosity, reducing the effective contact area between the reactant gas and the catalyst coating, or causing pore blockage and increased diffusion mass transfer resistance, resulting in the failure of some active sites.

[0025] This invention adds an intermediate transition layer with a thermal expansion coefficient between that of the bottom and top layers. The intermediate layer coating does not undergo a separate calcination process but is calcined together with the top slurry coating after it is applied. This process allows for a balance of the thermal expansion coefficients of the entire catalyst coating, reduces the thermal stress concentration coefficient, and enhances the interaction forces between the intermediate and bottom layers, as well as between the intermediate and top layers, thereby improving the interfacial bonding energy and ensuring the catalyst's durability. Furthermore, the preparation process uses zirconium balls with a wide distribution range to ball mill the slurry, resulting in a intermediate slurry with a large particle size dispersion. This ensures the catalyst's efficient mass transfer capability and maintains high efficiency in treating CH4 and NO over a longer period. x And the ability to generate CO.

[0026] In a specific embodiment, the mass fraction of each component in the cerium-zirconium-aluminum-based composite oxide is as follows: CeO2 is 30-70 wt%, ZrO2 is 30-60 wt%, Al2O3 is 0-20 wt%, and additives (La2O3 or Pr2O3) are 0-5 wt%.

[0027] In one specific embodiment, the coating amount of the upper catalytic coating is 50~150 g / L, the coating amount of the bottom catalytic coating is 50~150 g / L, and the coating amount of the intermediate transition layer is 60~100 g / L.

[0028] In one specific embodiment, the underlying catalytic coating further includes a cerium-zirconium composite oxide, wherein the ratio of modified alumina to cerium-zirconium composite oxide is 1:2 to 2:1. This invention utilizes a mixture of modified alumina and cerium-zirconium composite oxide as the noble metal carrier material for the underlying catalytic coating. The alumina material provides a highly dispersed platform and basic structure, while the cerium-zirconium composite oxide provides dynamic oxygen buffering and thermal stability support. The two are interdependent and complementary: the cerium-zirconium composite oxide relies on the large specific surface area of ​​the alumina material to achieve good dispersion of itself and the noble metal, and stabilizes the alumina material structure; the alumina material, in turn, relies on the oxygen storage function of the cerium-zirconium composite oxide to maintain wide-window high-efficiency operation and to carry the main oxidizing active components, further ensuring the relevant performance of the catalyst.

[0029] In one specific embodiment, the cerium-zirconium composite oxide is doped with La and Pr.

[0030] Secondly, the present invention provides a method for preparing a three-way catalyst for the aftertreatment of natural gas vehicles that reduces the amount of precious metals used, comprising the following steps:

[0031] S1, Preparation of the underlying catalytic coating:

[0032] BaSO4 powder was dissolved in a solvent, and then γ-aminopropyltriethoxysilane was added to graft -NH2 groups onto the surface of BaSO4.

[0033] Grafting -NH2 groups onto the surface of BaSO4 and adding them to CeAlO x The mixture is mixed in a slurry, dried, and calcined to obtain a BaSO4-modified alumina powder carrier;

[0034] Noble metals were loaded onto a BaSO4-modified alumina powder support to prepare a bottom catalyst slurry, which was then coated onto the support surface and dried and calcined to obtain a bottom catalyst coating.

[0035] S2, Preparation of the intermediate transition layer:

[0036] Cerium zirconium aluminum oxide powder was prepared into a slurry, coated onto the underlying catalyst coating, and then dried.

[0037] S3, Preparation of the upper catalytic coating:

[0038] Noble metals are loaded onto a rare earth composite oxide support to prepare an upper catalyst slurry, which is then coated onto a dried intermediate transition layer. After drying and calcination, a co-sintered intermediate transition layer and an upper catalyst coating are obtained.

[0039] Secondly, the present invention provides a method for reducing the amount of noble metals used in a three-way catalyst, by replacing the alumina support material in the three-way catalyst with modified alumina, wherein the modified alumina is CeAlO modified alumina with cerium-doped BaSO4 surface grafted with -NH2 groups. x .

[0040] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0041] 1. The method for reducing the amount of precious metals, the after-treatment catalyst for natural gas vehicles and the preparation method provided in the embodiments of the present invention, by uniquely modifying the alumina support in the bottom catalyst, can reduce the amount of precious metals by more than 50% compared with commercially available catalysts, while ensuring and improving the freshness and durability of the catalyst, meeting the regulatory durability requirements, and solving the problem of the high cost of current after-treatment catalysts.

[0042] 2. The method for reducing the amount of precious metals, the after-treatment catalyst for natural gas vehicles, and the preparation method provided in this invention further modify cerium-modified alumina by grafting -NH2 groups onto the surface of BaSO4. This enhances the bonding with alumina, improves dispersion uniformity, and prevents CeO2 agglomeration, thereby increasing the specific surface area retention rate of the alumina material after high-temperature aging. Simultaneously, it increases the electron density of the precious metal Pd, strengthens the Pd-O bond, optimizes the electronic structure of the Pd / Al2O3 catalyst, and inhibits the high-temperature decomposition of PdO to enhance its stability, thus effectively improving the activity of methane combustion. The addition of this modified alumina material significantly improves the catalyst's freshness and anti-aging ability, ensuring that even with a 50% reduction in precious metal usage, it still maintains performance comparable to or better than commercially available catalysts.

[0043] 3. The method for reducing the amount of precious metals, the after-treatment catalyst for natural gas vehicles and the preparation method provided in the embodiments of the present invention improve the support material in the upper catalytic coating by introducing four rare earth elements, Y, Sm, Pr and La, to co-dope CeO2 to form a multi-component composite oxide. This significantly improves the oxygen storage performance, stability, catalytic performance and anti-aging performance of the material. In synergy with modified alumina, it can further ensure that the catalyst performance can meet regulatory requirements after the amount of precious metals is reduced.

[0044] 4. The method for reducing the amount of precious metals, the natural gas vehicle aftertreatment catalyst, and the preparation method provided in the embodiments of the present invention, by adding an intermediate transition layer between the bottom and top layers, whose coefficient of thermal expansion is between that of the bottom and top layers, and by not undergoing a separate calcination process for the intermediate coating but calcining it together with the top slurry coating after the top layer is coated, can balance the coefficient of thermal expansion of the entire catalyst coating, reduce the thermal stress concentration coefficient, enhance the interaction forces between the middle and bottom layers and between the middle and top layers, and improve the interfacial bonding energy. This can ensure the catalyst's efficient mass transfer capacity and durability, thereby maintaining efficient treatment of CH4 and NO over a longer period of time. x And the ability to generate CO. Attached Figure Description

[0045] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0046] Figure 1 These are comparative images of the coating morphology of the fresh catalysts provided in Examples 1 and 3 of this invention.

[0047] Figure 2 This is a comparison diagram of the coating morphology of the aging catalysts provided in Examples 1 and 3 of the present invention. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0049] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other embodiments, well-known materials or methods have not been specifically described in order to avoid obscuring the invention.

[0050] Throughout this specification, references to "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the present invention. Therefore, the phrases "an embodiment," "an example," "an example," or "an example" appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0051] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is understood that ranges of 60–110 and 80–120 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0" and "5" have been listed in this document; "0-5" is merely a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. Unless otherwise specified, all steps in this application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) can be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0052] Example 1

[0053] This invention provides a method for preparing a three-way catalyst for the aftertreatment of natural gas vehicles that reduces the amount of precious metals used, comprising the following steps:

[0054] (1) Preparation of BaSO4 modified Ce 0.2 Ba 0.05 Al 0.75 O x -S material:

[0055] 1.1 First, BaSO4 powder and solvent (water / ethanol) were mixed at a mass ratio of 1:5. Zirconia ball milling beads (particle size 0.1–0.5 mm) were added and the mixture was ball milled for 4–6 h to obtain a suspension with D50 < 200 nm. Then, 3–5% KH-550 was added and the mixture was stirred at 60 °C for 2 h to graft -NH2 groups onto the surface of BaSO4.

[0056] 1.2 Ce 0.2 Al 0.75 O x The material powder was dispersed in water, and the BaSO4 nano-suspension was slowly added dropwise to Ce. 0.2 Al 0.75 O x In the slurry (of which BaSO4 content accounts for a certain percentage of Ce), 0.2 Al 0.75 O x (5 wt%), and then ball milled the slurry using a sand mill for half an hour to obtain a slurry of BaSO4 modified alumina material;

[0057] 1.3 The above slurry was dried and then calcined at 500℃ for 2-4 h to remove the organic dispersant, finally yielding BaSO4-modified Ce. 0.2 Ba 0.05 Al 0.75 O x -S powder.

[0058] (2) Preparation of the bottom catalytic coating

[0059] Pd was loaded onto Ce, a modified alumina material carrier, using an equal-volume impregnation method. 0.2 Ba 0.05 Al 0.75 O x -S and Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O x (The total loading of Pd in ​​the two carrier materials is 0.4414%), that is, the content of the bottom noble metal Pd is 15 g / cmf. Then, Pd / Ce were obtained through drying, calcination and other processes. 0.2 Ba 0.05 Al 0.75 O x -S powder and Pd / Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O x Powder; the above two catalyst powders Pd / Ce 0.2 Ba 0.05 Al 0.75 O x -S at 62 wt%, Pd / Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O xThe bottom coating slurry was obtained by ball milling 31 wt%, 7 wt% binder, and 200 wt% water for 30 min. The bottom coating slurry was then coated on the surface of cordierite honeycomb ceramic carriers (coated on a small carrier Φ1*1 in with a mesh size of 400 cpsi and a volume of 0.01638 L, and a large carrier Φ12*6 in with a mesh size of 400 cpsi and a volume of 11.12 L), with a coating amount of 129.03 g / L. After drying, the substrate was calcined at 500℃ in air for 2 h to obtain the bottom layer containing Pd catalyst.

[0060] (3) Preparation of intermediate transition layer

[0061] The middle-layer cerium-zirconium-aluminum composite material CeZrAlO was prepared by co-precipitation method. x (CeO2 30~70 wt%, ZrO2 30~60 wt%, Al2O3 0~20 wt%, and auxiliary agent La2O3 or Pr2O3 0~5 wt%), then washed with deionized water until neutral, dried in an oven at 120℃ for 4 h, and finally calcined in a muffle furnace at 400℃ for 4 h to obtain CeZrAlO x Powder; the above CeZrAlO x The zirconia balls were ball-milled with 95 wt%, 5 wt% binder, and 200 wt% water. The size distribution of the selected zirconia balls was Ф5~40 mm. The ball-milling time was 20 min, and a medium-layer coating slurry with a large particle size distribution was finally obtained. The medium-layer coating slurry was coated on the bottom layer with a coating amount of 60 g / L. After coating, the catalyst semi-finished product was dried until the water loss rate of the medium-layer coating was 95%.

[0062] (4) Preparation of upper catalytic coating

[0063] 4.1 Material 1: Preparation of composite oxides with a metal ion molar ratio of Ce:Y:Sm:Pr:La = 70:5:3:12:10

[0064] 36.13 g Ce(NO3)3·6H2O, 2.36 g Y(CH3COO)3·4H2O, 1.60 g Sm(NO3)3·6H2O, 6.2 g Pr(NO3)3·6H2O, and 5.15 g La(NO3)3·6H2O were added in proportion, along with 41.8 g EDTA acid, 300 ml deionized water, and 30 ml 30% H2O2. The solution was formed by stirring in an 80°C water bath. NH3·H2O was added dropwise until the pH reached 8.5, and stirring continued to form a homogeneous sol. The solution was dried at 120°C for 12 h and then ground into powder. The powder was then placed in a muffle furnace and calcined at 500°C for 2 h at a heating rate of 10°C / min.

[0065] The prepared material powder was immersed in a precious metal solution for 4 hours and then evaporated at 90°C. The content of the precious metal was Pt=13 g / cm³.

[0066] 4.2 Material 2: A composite oxide with a metal ion molar ratio of Ce:Zr:Pr:La = 20:70:2:8 was prepared by the same method. After being immersed in a noble metal solution for 4 h, it was evaporated and dried at 90 °C. The noble metal content was Rh = 2 g / cft.

[0067] 4.3 The prepared precious metal loaded powder was added to a ball mill jar at a ratio of material 1: material 2 = 1. Acetic acid was added to adjust the pH of the slurry to 2-7. A binder was added to keep the slurry viscous and then the mixture was placed in a ball mill and stirred rapidly. The prepared slurry was coated on the intermediate transition layer with a coating amount of 80 g / L. After drying at room temperature for 2-4 h, the mixture was calcined at 500℃ for 2 h to obtain the co-sintered intermediate transition layer and the upper catalytic coating.

[0068] Example 2

[0069] This invention provides a method for preparing a three-way catalyst for the aftertreatment of natural gas vehicles that reduces the amount of precious metals used, comprising the following steps:

[0070] (1) Preparation of BaSO4 modified Ce 0.2 Ba 0.05 Al 0.75 O x -S material, same as in Example 1.

[0071] (2) Preparation of the bottom catalytic coating

[0072] Pd and Pt were loaded onto Ce, a modified alumina material carrier, using an equal-volume impregnation method. 0.2 Ba 0.05 Al 0.75 O x -S and Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O x (Pd loading is 0.5886%, Pt loading is 0.2943%), meaning the bottom layer contains 10 g / cm³ of Pd and 5 g / cm³ of Pt. Pd / Ce ratios were then obtained through drying and calcination processes. 0.2 Ba 0.05 Al 0.75 O x -S powder and Pt / Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 Ox Powder; the above two catalyst powders Pd / Ce 0.2 Ba 0.05 Al 0.75 O x -S at 46.5 wt%, Pt / Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O x The bottom coating slurry was obtained by ball milling 46.5 wt%, 7 wt% binder, and 200 wt% water for 30 min. The bottom coating slurry was then coated on the surface of cordierite honeycomb ceramic carriers (coated on a small carrier Φ1*1 in with a mesh size of 400 cpsi and a volume of 0.01638 L, and a large carrier Φ12*6 in with a mesh size of 400 cpsi and a volume of 11.12 L), with a coating amount of 129.03 g / L. After drying, the substrate was calcined at 500℃ in air for 2 h to obtain the bottom layer containing Pd and Pt catalysts.

[0073] (3) Preparation of intermediate transition layer

[0074] The middle-layer cerium-zirconium-aluminum composite material CeZrAlO was prepared by co-precipitation method. x (CeO2 30~70 wt%, ZrO2 30~60 wt%, Al2O3 0~20 wt%, and auxiliary agent La2O3 or Pr2O3 0~5 wt%), then washed with deionized water until neutral, dried in an oven at 120℃ for 4 h, and finally calcined in a muffle furnace at 400℃ for 4 h to obtain CeZrAlO x Powder; the above CeZrAlO x The zirconia balls were ball-milled with 95 wt%, 5 wt% binder, and 200 wt% water. The size distribution of the selected zirconia balls was Ф5~40 mm. The ball-milling time was 20 min, and a medium-layer coating slurry with a large particle size distribution was finally obtained. The medium-layer coating slurry was coated on the bottom layer with a coating amount of 60 g / L. After coating, the catalyst semi-finished product was dried until the water loss rate of the medium-layer coating was 95%.

[0075] (4) Preparation of upper catalytic coating

[0076] 4.1 Material 1: Preparation of composite oxides with a metal ion molar ratio of Ce:Y:Sm:Pr:La = 70:5:3:12:10

[0077] 36.13 g Ce(NO3)3·6H2O, 2.36 g Y(CH3COO)3·4H2O, 1.60 g Sm(NO3)3·6H2O, 6.2 g Pr(NO3)3·6H2O, and 5.15 g La(NO3)3·6H2O were added in proportion, along with 41.8 g EDTA acid, 300 ml deionized water, and 30 ml 30% H2O2. The solution was formed by stirring in an 80°C water bath. NH3·H2O was added dropwise until the pH reached 8.5, and stirring continued to form a homogeneous sol. The solution was dried at 120°C for 12 h and then ground into powder. The powder was then placed in a muffle furnace and calcined at 500°C for 2 h at a heating rate of 10°C / min.

[0078] The prepared material powder was immersed in a precious metal solution for 4 hours and then evaporated at 90°C. The content of the precious metal was Pt=13 g / cm³.

[0079] 4.2 Material 2: A composite oxide with a metal ion molar ratio of Ce:Zr:Pr:La = 20:70:2:8 was prepared by the same method. After being immersed in a noble metal solution for 4 h, it was evaporated and dried at 90 °C. The noble metal content was Rh = 2 g / cft.

[0080] 4.3 The prepared precious metal loaded powder was added to a ball mill jar at a ratio of material 1: material 2 = 1. Acetic acid was added to adjust the pH of the slurry to 2-7. A binder was added to keep the slurry viscous and then the mixture was placed in a ball mill and stirred rapidly. The prepared slurry was coated on the intermediate transition layer with a coating amount of 80 g / L. After drying at room temperature for 2-4 h, the mixture was calcined at 500℃ for 2 h to obtain the co-sintered intermediate transition layer and the upper catalytic coating.

[0081] Example 3

[0082] This invention provides a method for preparing a three-way catalyst for the aftertreatment of natural gas vehicles that reduces the amount of precious metals used, comprising the following steps:

[0083] (1) Preparation of BaSO4 modified Ce 0.2 Ba 0.05 Al 0.75 O x -S material:

[0084] 1.1 First, BaSO4 powder and solvent (water / ethanol) were mixed at a mass ratio of 1:5. Zirconia ball milling beads (particle size 0.1–0.5 mm) were added and the mixture was ball milled for 4–6 h to obtain a suspension with D50 < 200 nm. Then, 3–5% KH-550 was added and the mixture was stirred at 60 °C for 2 h to graft -NH2 groups onto the surface of BaSO4.

[0085] 1.2 Ce0.2 Al 0.75 O x The material powder was dispersed in water, and the BaSO4 nano-suspension was slowly added dropwise to Ce. 0.2 Al 0.75 O x In the slurry (of which BaSO4 content accounts for a certain percentage of Ce), 0.2 Al 0.75 O x (5 wt%), and then ball milled the slurry using a sand mill for half an hour to obtain a slurry of BaSO4 modified alumina material;

[0086] 1.3 The above slurry was dried and then calcined at 500℃ for 2-4 h to remove the organic dispersant, finally yielding BaSO4-modified Ce. 0.2 Ba 0.05 Al 0.75 O x -S powder.

[0087] (2) Preparation of the bottom catalytic coating

[0088] Pd was loaded onto Ce, a modified alumina material carrier, using an equal-volume impregnation method. 0.2 Ba 0.05 Al 0.75 O x -S and Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O x (The total loading of Pd in ​​the two carrier materials is 0.4414%), that is, the content of the bottom noble metal Pd is 15 g / cmf. Then, Pd / Ce were obtained through drying, calcination and other processes. 0.2 Ba 0.05 Al 0.75 O x -S powder and Pd / Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O x Powder; the above two catalyst powders Pd / Ce 0.2 Ba 0.05 Al 0.75 O x -S at 62 wt%, Pd / Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O xThe bottom coating slurry was obtained by ball milling 31 wt%, 7 wt% binder, and 200 wt% water for 30 min. The bottom coating slurry was then coated on the surface of cordierite honeycomb ceramic carriers (coated on a small carrier Φ1*1 in with a mesh size of 400 cpsi and a volume of 0.01638 L, and a large carrier Φ12*6 in with a mesh size of 400 cpsi and a volume of 11.12 L), with a coating amount of 129.03 g / L. After drying, the substrate was calcined at 500℃ in air for 2 h to obtain the bottom layer containing Pd catalyst.

[0089] (3) Preparation of upper catalytic coating

[0090] 3.1 Material 1: Preparation of composite oxides with a metal ion molar ratio of Ce:Y:Sm:Pr:La = 70:5:3:12:10

[0091] 36.13 g Ce(NO3)3·6H2O, 2.36 g Y(CH3COO)3·4H2O, 1.60 g Sm(NO3)3·6H2O, 6.2 g Pr(NO3)3·6H2O, and 5.15 g La(NO3)3·6H2O were added in proportion, along with 41.8 g EDTA acid, 300 ml deionized water, and 30 ml 30% H2O2. The solution was stirred in an 80°C water bath to form a solution. NH3·H2O was added dropwise until the pH reached 8.5, and stirring continued to form a homogeneous sol. The solution was dried at 120°C for 12 h and then ground to obtain a powder. The powder was then placed in a muffle furnace and calcined at 500°C for 2 h at a heating rate of 10°C / min.

[0092] The prepared material powder was immersed in a precious metal solution for 4 hours and then evaporated at 90°C. The content of the precious metal was Pt=13 g / cm³.

[0093] 3.2 Material 2: A composite oxide with a metal ion molar ratio of Ce:Zr:Pr:La = 20:70:2:8 was prepared by the same method. After being immersed in a noble metal solution for 4 h, it was evaporated and dried at 90 °C. The noble metal content was Rh = 2 g / cft.

[0094] 3.3 The prepared precious metal loaded powder was added to a ball mill jar at a ratio of material 1: material 2 = 1. Acetic acid was added to adjust the pH of the slurry to 2-7. A binder was added to keep the slurry viscous. The slurry was then placed in a ball mill and stirred rapidly. The prepared slurry was coated on the bottom layer at a coating amount of 80 g / L. After drying at room temperature for 2-4 h, the top catalytic coating was obtained by calcination at 500℃ for 2 h.

[0095] The difference between this embodiment and Embodiment 1 is that it does not include an intermediate transition layer.

[0096] Example 4

[0097] This invention provides a method for preparing a three-way catalyst for the aftertreatment of natural gas vehicles that reduces the amount of precious metals used, comprising the following steps:

[0098] (1) Preparation of BaSO4 modified Ce 0.2 Ba 0.05 Al 0.75 O x -S material:

[0099] 1.1 First, BaSO4 powder and solvent (water / ethanol) were mixed at a mass ratio of 1:5. Zirconia ball milling beads (particle size 0.1–0.5 mm) were added and the mixture was ball milled for 4–6 h to obtain a suspension with D50 < 200 nm. Then, 3–5% KH-550 was added and the mixture was stirred at 60 °C for 2 h to graft -NH2 groups onto the surface of BaSO4.

[0100] 1.2 Ce 0.2 Al 0.75 O x The material powder was dispersed in water, and the BaSO4 nano-suspension was slowly added dropwise to Ce. 0.2 Al 0.75 O x In the slurry (of which BaSO4 content accounts for a certain percentage of Ce), 0.2 Al 0.75 O x (5 wt%), and then ball milled the slurry using a sand mill for half an hour to obtain a slurry of BaSO4 modified alumina material;

[0101] 1.3 The above slurry was dried and then calcined at 500℃ for 2-4 h to remove the organic dispersant, finally yielding BaSO4-modified Ce. 0.2 Ba 0.05 Al 0.75 O x -S powder.

[0102] (2) Preparation of the bottom catalytic coating

[0103] Pd was loaded onto Ce, a modified alumina material carrier, using an equal-volume impregnation method. 0.2 Ba 0.05 Al 0.75 O x -S and Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O x(The total loading of Pd in ​​the two carrier materials is 0.2943%), that is, the content of the bottom noble metal Pd is 10 g / cmf. Then, Pd / Ce were obtained through drying, calcination and other processes. 0.2 Ba 0.05 Al 0.75 O x -S powder and Pd / Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O x Powder; the above two catalyst powders Pd / Ce 0.2 Ba 0.05 Al 0.75 O x -S at 62 wt%, Pd / Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O x The bottom coating slurry was obtained by ball milling 31 wt%, 7 wt% binder, and 200 wt% water for 30 min. The bottom coating slurry was then coated on the surface of cordierite honeycomb ceramic carriers (coated on a small carrier Φ1*1 in with a mesh size of 400 cpsi and a volume of 0.01638 L, and a large carrier Φ12*6 in with a mesh size of 400 cpsi and a volume of 11.12 L), with a coating amount of 129.03 g / L. After drying, the substrate was calcined at 500℃ in air for 2 h to obtain the bottom layer containing Pd catalyst.

[0104] (3) Preparation of upper catalytic coating

[0105] 3.1 Material 1: Preparation of composite oxides with a metal ion molar ratio of Ce:Y:Sm:Pr:La = 70:5:3:12:10

[0106] 36.13 g Ce(NO3)3·6H2O, 2.36 g Y(CH3COO)3·4H2O, 1.60 g Sm(NO3)3·6H2O, 6.2 g Pr(NO3)3·6H2O, and 5.15 g La(NO3)3·6H2O were added in proportion, along with 41.8 g EDTA acid, 300 ml deionized water, and 30 ml 30% H2O2. The solution was formed by stirring in an 80°C water bath. NH3·H2O was added dropwise until the pH reached 8.5, and stirring continued to form a homogeneous sol. The solution was dried at 120°C for 12 h and then ground into powder. The powder was then placed in a muffle furnace and calcined at 500°C for 2 h at a heating rate of 10°C / min.

[0107] The prepared material powder was immersed in a precious metal solution for 4 hours and then evaporated at 90°C. The content of the precious metal was Pt=8.5 g / cm³.

[0108] 3.2 Material 2: A composite oxide with a metal ion molar ratio of Ce:Zr:Pr:La = 20:70:2:8 was prepared by the same method. After being immersed in a noble metal solution for 4 h, it was evaporated and dried at 90 °C. The noble metal content was Rh = 1.5 g / cft.

[0109] 3.3 The prepared precious metal loaded powder was added to a ball mill jar at a ratio of material 1: material 2 = 1. Acetic acid was added to adjust the pH of the slurry to 2-7. A binder was added to keep the slurry viscous. The slurry was then placed in a ball mill and stirred rapidly. The prepared slurry was coated on the bottom layer at a coating amount of 80 g / L. After drying at room temperature for 2-4 h, the top catalytic coating was obtained by calcination at 500℃ for 2 h.

[0110] The difference between this embodiment and Embodiment 3 is that the total amount of precious metals used is 20 g / cft.

[0111] Comparative Example 1

[0112] This invention provides a method for preparing a three-way catalyst for the aftertreatment of natural gas vehicles that reduces the amount of precious metals used, comprising the following steps:

[0113] (1) Preparation of the bottom catalytic coating

[0114] Pd was loaded onto commercial Ce using an equal-volume impregnation method. 0.2 Al 0.8 O x and Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O x (The total loading of Pd in ​​the two carrier materials is 0.4414%), that is, the content of the bottom noble metal Pd is 15 g / cmf. Then, Pd / Ce were obtained through drying, calcination and other processes. 0.2 Al 0.8 O x Powder and Pd / Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O x Powder; the above two catalyst powders Pd / Ce 0.2 Al 0.8 O x Based on 62 wt%, Pd / Ce 0.4 Zr 0.5 La 0.05 Pr 0.05O x The bottom layer coating slurry was obtained by ball milling 31 wt%, 7 wt% binder, and 200 wt% water for 30 min. The bottom layer coating slurry was coated on the surface of cordierite honeycomb ceramic carrier (coated on a small carrier Φ1*1 in with a mesh size of 400 cpsi and a volume of 0.01638 L, and a large carrier Φ12*6 in with a mesh size of 400 cpsi and a volume of 11.12 L), with a coating amount of 129.03 g / L. After drying, it was calcined at 500℃ in air atmosphere for 2 h to obtain the bottom layer containing Pd catalyst.

[0115] (2) Preparation of upper catalytic coating

[0116] 2.1 Material 1: Preparation of composite oxides with a metal ion molar ratio of Ce:Y:Sm:Pr:La = 70:5:3:12:10

[0117] 36.13 g Ce(NO3)3·6H2O, 2.36 g Y(CH3COO)3·4H2O, 1.60 g Sm(NO3)3·6H2O, 6.2 g Pr(NO3)3·6H2O, and 5.15 g La(NO3)3·6H2O were added in proportion, along with 41.8 g EDTA acid, 300 ml deionized water, and 30 ml 30% H2O2. The solution was stirred in an 80 °C water bath to form a solution. NH3·H2O was added dropwise until the pH reached 8.5, and stirring continued to form a homogeneous sol. The solution was dried at 120 °C for 12 h and then ground to obtain a powder. The powder was then placed in a muffle furnace and calcined at 500 °C for 2 h at a heating rate of 10 °C / min.

[0118] The prepared material powder was immersed in a precious metal solution for 4 hours and then evaporated at 90°C. The content of the precious metal was Pt=13 g / cm³.

[0119] 2.2 Material 2: A composite oxide with a metal ion molar ratio of Ce:Zr:Pr:La = 20:70:2:8 was prepared by the same method. After being immersed in a noble metal solution for 4 hours, it was evaporated and dried at 90℃. The noble metal content was Rh = 2 g / cft.

[0120] 2.3 The prepared precious metal loaded powder was added to a ball mill jar at a ratio of material 1: material 2 = 1. Acetic acid was added to adjust the pH of the slurry to 2-7. A binder was added to keep the slurry viscous. The slurry was then placed in a ball mill and stirred rapidly. The prepared slurry was coated on the bottom layer with a coating amount of 80 g / L. After drying at room temperature for 2-4 h, the top catalytic coating was obtained by calcining at 500℃ for 2 h.

[0121] The difference between this comparative example and Example 3 is that commercial Ce is used. 0.2Al 0.8 O x Replace the modified alumina material carrier Ce of the present invention 0.2 Ba 0.05 Al 0.75 O x -S.

[0122] Comparative Example 2

[0123] This invention provides a method for preparing a three-way catalyst for the aftertreatment of natural gas vehicles that reduces the amount of precious metals used, comprising the following steps:

[0124] (1) Preparation of the bottom catalytic coating

[0125] Pd was loaded onto commercial Ce using an equal-volume impregnation method. 0.2 Al 0.8 O x and Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O x (The total loading of Pd in ​​the two carrier materials is 0.4414%), that is, the content of the bottom noble metal Pd is 15 g / cmf. Then, Pd / Ce were obtained through drying, calcination and other processes. 0.2 Al 0.8 O x Powder and Pd / Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O x Powder; the above two catalyst powders Pd / Ce 0.2 Al 0.8 O x Based on 62wt%, Pd / Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O x The bottom layer coating slurry was obtained by ball milling 31 wt%, 7 wt% binder, and 200 wt% water for 30 min. The bottom layer coating slurry was coated on the surface of cordierite honeycomb ceramic carrier (coated on a small carrier Φ1*1 in with a mesh size of 400 cpsi and a volume of 0.01638 L, and a large carrier Φ12*6 in with a mesh size of 400 cpsi and a volume of 11.12 L), with a coating amount of 129.03 g / L. After drying, it was calcined at 500℃ in air atmosphere for 2 h to obtain the bottom layer containing Pd catalyst.

[0126] (2) Preparation of upper catalytic coating

[0127] 2.1 Material 1: Preparation of Ce 0.68 Zr 0.32 O2

[0128] 37.8 g Ce(NO3)3·6H2O, 16.1 g Zr(NO3)4·5H2O, 44.9 g EDTA acid, 300 ml deionized water, and 30 ml 30% H2O2 were added together; the mixture was stirred in an 80°C water bath to form a homogeneous solution; NH3·H2O was added dropwise until the pH reached 8.5, and stirring was continued to form a homogeneous sol; the mixture was dried at 120°C for 12 h and ground to obtain a powder; the powder was placed in a muffle furnace and calcined at 500°C for 2 h at a heating rate of 10°C / min.

[0129] The prepared material powder was immersed in a precious metal solution for 4 hours and then evaporated at 90°C. The content of the precious metal was Pt=13 g / cm³.

[0130] 2.2 Material 2: A composite oxide with a metal ion molar ratio of Ce:Zr:Pr:La = 20:70:2:8 was prepared by the same method. After being immersed in a noble metal solution for 4 h, it was evaporated and dried at 90 °C. The noble metal content was Rh = 2 g / cft.

[0131] 2.3 The prepared precious metal loaded powder was added to a ball mill jar at a ratio of material 1: material 2 = 1. Acetic acid was added to adjust the pH of the slurry to 2-7. A binder was added to keep the slurry viscous. The slurry was then placed in a ball mill and stirred rapidly. The prepared slurry was coated on the bottom layer with a coating amount of 80 g / L. After drying at room temperature for 2-4 h, the top catalytic coating was obtained by calcining at 500℃ for 2 h.

[0132] The difference between this comparative example and Example 3 is that commercial Ce is used. 0.2 Al 0.8 O x Replace the modified alumina material carrier Ce of the present invention 0.2 Ba 0.05 Al 0.75 O x -S, using Ce 0.68 Zr 0.32 O2 replaces the composite oxide of the present invention with a metal ion molar ratio of Ce:Y:Sm:Pr:La = 70:5:3:12:10. The total amount of catalyst remains unchanged.

[0133] Comparative Example 3

[0134] This invention provides a method for preparing a three-way catalyst for the aftertreatment of natural gas vehicles that reduces the amount of precious metals used, comprising the following steps:

[0135] (1) Preparation of the bottom catalytic coating

[0136] Pd was loaded onto commercial Ce using an equal-volume impregnation method. 0.2 Al 0.8 O x and Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O x (The total loading of Pd in ​​the two carrier materials is 0.8829%), that is, the content of the bottom noble metal Pd is 30 g / cmf. Then, Pd / Ce were obtained through drying, calcination and other processes. 0.2 Al 0.8 O x Powder and Pd / Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O x Powder; the above two catalyst powders Pd / Ce 0.2 Al 0.8 O x Based on 62 wt%, Pd / Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O x The bottom layer coating slurry was obtained by ball milling 31 wt%, 7 wt% binder, and 200 wt% water for 30 min. The bottom layer coating slurry was coated on the surface of cordierite honeycomb ceramic carrier (coated on a small carrier Φ1*1 in with a mesh size of 400 cpsi and a volume of 0.01638 L, and a large carrier Φ12*6 in with a mesh size of 400 cpsi and a volume of 11.12 L), with a coating amount of 129.03 g / L. After drying, it was calcined at 500℃ in air atmosphere for 2 h to obtain the bottom layer containing Pd catalyst.

[0137] (2) Preparation of upper catalytic coating

[0138] 2.1 Material 1: Preparation of Ce 0.68 Zr 0.32 O2

[0139] 37.8 g Ce(NO3)3·6H2O, 16.1 g Zr(NO3)4·5H2O, 44.9 g EDTA acid, 300 ml deionized water, and 30 ml 30% H2O2 were added together; the mixture was stirred in an 80°C water bath to form a homogeneous solution; NH3·H2O was added dropwise until the pH reached 8.5, and stirring was continued to form a homogeneous sol; the mixture was dried at 120°C for 12 h and ground to obtain a powder; the powder was placed in a muffle furnace and calcined at 500°C for 2 h at a heating rate of 10°C / min.

[0140] The prepared material powder was immersed in a precious metal solution for 4 hours and then evaporated at 90°C. The content of the precious metal was Pt=26 g / cm³.

[0141] 2.2 Material 2: A composite oxide with a metal ion molar ratio of Ce:Zr:Pr:La = 20:70:2:8 was prepared by the same method. After being immersed in a noble metal solution for 4 hours, it was evaporated and dried at 90℃. The noble metal content was Rh = 4 g / cft.

[0142] 2.3 The prepared precious metal loaded powder was added to a ball mill jar at a ratio of material 1: material 2 = 1. Acetic acid was added to adjust the pH of the slurry to 2-7. A binder was added to keep the slurry viscous. The slurry was then placed in a ball mill and stirred rapidly. The prepared slurry was coated on the bottom layer with a coating amount of 80 g / L. After drying at room temperature for 2-4 h, the top catalytic coating was obtained by calcining at 500℃ for 2 h.

[0143] The difference between this comparative example and Comparative Example 2 is that the total amount of precious metals used is 60 g / ft. 3 The dosage was twice that of control example 2.

[0144] Comparative Example 4

[0145] This invention provides a method for preparing a three-way catalyst for the aftertreatment of natural gas vehicles that reduces the amount of precious metals used, comprising the following steps:

[0146] (1) Preparation of the bottom catalytic coating

[0147] Pd was loaded onto commercial Ce using an equal-volume impregnation method. 0.2 Al 0.8 O x and Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O x (The total loading of Pd in ​​the two carrier materials is 0.2943%), that is, the content of the bottom noble metal Pd is 10 g / cmf. Then, Pd / Ce were obtained through drying, calcination and other processes. 0.2 Al 0.8 O x Powder and Pd / Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O x Powder; the above two catalyst powders Pd / Ce 0.2 Al 0.8 O x Based on 62 wt%, Pd / Ce 0.4Zr 0.5 La 0.05 Pr 0.05 O x The bottom layer coating slurry was obtained by ball milling 31 wt%, 7 wt% binder, and 200 wt% water for 30 min. The bottom layer coating slurry was coated on the surface of cordierite honeycomb ceramic carrier (coated on a small carrier Φ1*1 in with a mesh size of 400 cpsi and a volume of 0.01638 L, and a large carrier Φ12*6 in with a mesh size of 400 cpsi and a volume of 11.12 L), with a coating amount of 129.03 g / L. After drying, it was calcined at 500℃ in air atmosphere for 2 h to obtain the bottom layer containing Pd catalyst.

[0148] (2) Preparation of upper catalytic coating

[0149] 2.1 Material 1: Preparation of Ce 0.68 Zr 0.32 O2

[0150] 37.8 g Ce(NO3)3·6H2O, 16.1 g Zr(NO3)4·5H2O, 44.9 g EDTA acid, 300 ml deionized water, and 30 ml 30% H2O2 were added together; the mixture was stirred in an 80°C water bath to form a homogeneous solution; NH3·H2O was added dropwise until the pH reached 8.5, and stirring was continued to form a homogeneous sol; the mixture was dried at 120°C for 12 h and then ground to obtain a powder; the powder was placed in a muffle furnace and calcined at 500°C for 2 h at a heating rate of 10°C / min.

[0151] The prepared material powder was immersed in a precious metal solution for 4 hours and then evaporated at 90°C. The content of the precious metal was Pt=8.5 g / cf.

[0152] 2.2 Material 2: A composite oxide with a metal ion molar ratio of Ce:Zr:Pr:La = 20:70:2:8 was prepared by the same method. After being immersed in a noble metal solution for 4 h, it was evaporated and dried at 90 °C. The noble metal content was Rh = 1.5 g / cft.

[0153] 2.3 The prepared precious metal loaded powder was added to a ball mill jar at a ratio of material 1: material 2 = 1. Acetic acid was added to adjust the pH of the slurry to 2-7. A binder was added to keep the slurry viscous. The slurry was then placed in a ball mill and stirred rapidly. The prepared slurry was coated on the bottom layer with a coating amount of 80 g / L. After drying at room temperature for 2-4 h, the top catalytic coating was obtained by calcining at 500℃ for 2 h.

[0154] The difference between this comparative example and comparative example 2 is that the total amount of precious metal used is 20 g / cft, which is 10 g / cft less than that used in comparative example 2.

[0155] Comparative Example 5

[0156] This invention provides a method for preparing a three-way catalyst for the aftertreatment of natural gas vehicles that reduces the amount of precious metals used, comprising the following steps:

[0157] (1) Preparation of the bottom catalytic coating

[0158] Pd and Pt were loaded onto commercial Ce using an equal-volume impregnation method. 0.2 Al 0.8 O x and Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O x (Pd loading is 1.1772%, Pt loading is 0.5886%), meaning the bottom layer contains 20 g / cm³ of Pd and 10 g / cm³ of Pt. Pd / Ce ratios were then obtained through drying and calcination processes. 0.2 Al 0.8 O x Powder and PtCe 0.4 Zr 0.5 La 0.05 Pr 0.05 O x Powder; the above two catalyst powders Pd / Ce 0.2 Al 0.8 O x Based on 46.5 wt%, Pt / Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O x The bottom coating slurry was obtained by ball milling 46.5 wt%, 7 wt% binder, and 200 wt% water for 30 min. The bottom coating slurry was then coated on the surface of cordierite honeycomb ceramic carriers (coated on a small carrier Φ1*1 in with a mesh size of 400 cpsi and a volume of 0.01638 L, and a large carrier Φ12*6 in with a mesh size of 400 cpsi and a volume of 11.12 L), with a coating amount of 129.03 g / L. After drying, the substrate was calcined at 500℃ in air for 2 h to obtain the bottom layer containing Pd and Pt catalysts.

[0159] (2) Preparation of upper catalytic coating

[0160] 2.1 Material 1: Preparation of Ce 0.68 Zr 0.32 O2

[0161] 37.8 g Ce(NO3)3·6H2O, 16.1 g Zr(NO3)4·5H2O, 44.9 g EDTA acid, 300 ml deionized water, and 30 ml 30% H2O2 were added together; the mixture was stirred in an 80°C water bath to form a homogeneous solution; NH3·H2O was added dropwise until the pH reached 8.5, and stirring was continued to form a homogeneous sol; the mixture was dried at 120°C for 12 h and ground to obtain a powder; the powder was placed in a muffle furnace and calcined at 500°C for 2 h at a heating rate of 10°C / min.

[0162] The prepared material powder was immersed in a precious metal solution for 4 hours and then evaporated at 90°C. The content of the precious metal was Pt=26 g / cm³.

[0163] 2.2 Material 2: A composite oxide with a metal ion molar ratio of Ce:Zr:Pr:La = 20:70:2:8 was prepared by the same method. After being immersed in a noble metal solution for 4 hours, it was evaporated and dried at 90℃. The noble metal content was Rh = 4 g / cft.

[0164] 2.3 The prepared precious metal loaded powder was added to a ball mill jar at a ratio of material 1: material 2 = 1. Acetic acid was added to adjust the pH of the slurry to 2-7. A binder was added to keep the slurry viscous. The slurry was then placed in a ball mill and stirred rapidly. The prepared slurry was coated on the bottom layer with a coating amount of 80 g / L. After drying at room temperature for 2-4 h, the top catalytic coating was obtained by calcining at 500℃ for 2 h.

[0165] The difference between this comparative example and comparative example 3 is that the underlying precious metals are: Pd content of 20 g / cmft and Pt content of 10 g / cmft.

[0166] Comparative Example 6

[0167] This invention provides a method for preparing a three-way catalyst for the aftertreatment of natural gas vehicles that reduces the amount of precious metals used, comprising the following steps:

[0168] (1) Preparation of the bottom catalytic coating

[0169] Pd and Pt were loaded onto Ce, a modified alumina material carrier, using an equal-volume impregnation method. 0.2 Al 0.8 O x and Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O x (Pd loading is 0.5886%, Pt loading is 0.2943%), meaning the bottom layer contains 10 g / cm³ of Pd and 5 g / cm³ of Pt. Pd / Ce ratios were then obtained through drying and calcination processes.0.2 Al 0.8 O x Powder and Pt / Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O x Powder; the above two catalyst powders Pd / Ce 0.2 Al 0.8 O x Based on 46.5 wt%, Pt / Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O x The bottom coating slurry was obtained by ball milling 46.5 wt%, 7 wt% binder, and 200 wt% water for 30 min. The bottom coating slurry was then coated on the surface of cordierite honeycomb ceramic carriers (coated on a small carrier Φ1*1 in with a mesh size of 400 cpsi and a volume of 0.01638 L, and a large carrier Φ12*6 in with a mesh size of 400 cpsi and a volume of 11.12 L), with a coating amount of 129.03 g / L. After drying, the substrate was calcined at 500℃ in air for 2 h to obtain the bottom layer containing Pd and Pt catalysts.

[0170] (2) Preparation of intermediate transition layer

[0171] The middle-layer cerium-zirconium-aluminum composite material CeZrAlO was prepared by co-precipitation method. x (CeO2 30~70 wt%, ZrO2 30~60 wt%, Al2O3 0~20 wt%, and auxiliary agent La2O3 or Pr2O3 0~5 wt%), then washed with deionized water until neutral, dried in an oven at 120℃ for 4 h, and finally calcined in a muffle furnace at 400℃ for 4 h to obtain CeZrAlO x Powder; the above CeZrAlO x The zirconia balls were ball-milled with 95 wt%, 5 wt% binder, and 200 wt% water. The size distribution of the selected zirconia balls was Ф5~40 mm. The ball-milling time was 20 min, and a medium-layer coating slurry with a large particle size distribution was finally obtained. The medium-layer coating slurry was coated on the bottom layer with a coating amount of 60 g / L. After coating, the catalyst semi-finished product was dried until the water loss rate of the medium-layer coating was 95%.

[0172] (3) Preparation of upper catalytic coating

[0173] 3.1 Material 1: Preparation of composite oxides with a metal ion molar ratio of Ce:Y:Sm:Pr:La = 70:5:3:12:10

[0174] 36.13 g Ce(NO3)3·6H2O, 2.36 g Y(CH3COO)3·4H2O, 1.60 g Sm(NO3)3·6H2O, 6.2 g Pr(NO3)3·6H2O, and 5.15 g La(NO3)3·6H2O were added in proportion, along with 41.8 g EDTA acid, 300 ml deionized water, and 30 ml 30% H2O2. The solution was stirred in an 80°C water bath to form a solution. NH3·H2O was added dropwise until the pH reached 8.5, and stirring continued to form a homogeneous sol. The solution was dried at 120°C for 12 h and then ground to obtain a powder. The powder was then placed in a muffle furnace and calcined at 500°C for 2 h at a heating rate of 10°C / min.

[0175] The prepared material powder was immersed in a precious metal solution for 4 hours and then evaporated at 90°C. The content of the precious metal was Pt=13 g / cm³.

[0176] 3.2 Material 2: A composite oxide with a metal ion molar ratio of Ce:Zr:Pr:La = 20:70:2:8 was prepared by the same method. After being immersed in a noble metal solution for 4 hours, it was evaporated and dried at 90℃. The noble metal content was Rh = 2 g / cft.

[0177] 3.3 The prepared precious metal loaded powder was added to a ball mill jar at a ratio of material 1: material 2 = 1. Acetic acid was added to adjust the pH of the slurry to 2-7. A binder was added to keep the slurry viscous and the mixture was placed in a ball mill and stirred rapidly. The prepared slurry was coated on the intermediate transition layer with a coating amount of 80 g / L. After drying at room temperature for 2-4 h, it was calcined at 500℃ for 2 h to obtain the co-sintered intermediate transition layer and the upper catalytic coating.

[0178] The difference between this comparative example and Example 2 is that commercial Ce was used. 0.2 Al 0.8 O x Replace the modified alumina material carrier Ce of the present invention 0.2 Ba 0.05 Al 0.75 O x -S.

[0179] Comparative Example 7

[0180] This invention provides a method for preparing a three-way catalyst for the aftertreatment of natural gas vehicles that reduces the amount of precious metals used, comprising the following steps:

[0181] (1) Preparation of the bottom catalytic coating

[0182] Pd and Pt were loaded onto Ce, a modified alumina material carrier, using an equal-volume impregnation method. 0.2 Ba0.05 Al 0.75 O x and Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O x (Pd loading is 0.5886%, Pt loading is 0.2943%), meaning the bottom layer contains 10 g / cm³ of Pd and 5 g / cm³ of Pt. Pd / Ce ratios were then obtained through drying and calcination processes. 0.2 Ba 0.05 Al 0.75 O x Powder and Pt / Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O x Powder; the above two catalyst powders Pd / Ce 0.2 Ba 0.05 Al 0.75 O x Based on 46.5 wt%, Pt / Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O x The bottom coating slurry was obtained by ball milling 46.5 wt%, 7 wt% binder, and 200 wt% water for 30 min. The bottom coating slurry was then coated on the surface of cordierite honeycomb ceramic carriers (coated on a small carrier Φ1*1 in with a mesh size of 400 cpsi and a volume of 0.01638 L, and a large carrier Φ12*6 in with a mesh size of 400 cpsi and a volume of 11.12 L), with a coating amount of 129.03 g / L. After drying, the substrate was calcined at 500℃ in air for 2 h to obtain the bottom layer containing Pd and Pt catalysts.

[0183] (2) Preparation of intermediate transition layer

[0184] The middle-layer cerium-zirconium-aluminum composite material CeZrAlO was prepared by co-precipitation method. x (CeO2 30~70 wt%, ZrO2 30~60 wt%, Al2O3 0~20 wt%, and auxiliary agent La2O3 or Pr2O3 0~5 wt%), then washed with deionized water until neutral, dried in an oven at 120℃ for 4 h, and finally calcined in a muffle furnace at 400℃ for 4 h to obtain CeZrAlO x Powder; the above CeZrAlO xThe zirconia balls were ball-milled with 95 wt%, 5 wt% binder, and 200 wt% water. The size distribution of the selected zirconia balls was Ф5~40 mm. The ball-milling time was 20 min, and a medium-layer coating slurry with a large particle size distribution was finally obtained. The medium-layer coating slurry was coated on the bottom layer with a coating amount of 60 g / L. After coating, the catalyst semi-finished product was dried until the water loss rate of the medium-layer coating was 95%.

[0185] (3) Preparation of upper catalytic coating

[0186] 3.1 Material 1: Preparation of composite oxides with a metal ion molar ratio of Ce:Y:Sm:Pr:La = 70:5:3:12:10

[0187] 36.13 g Ce(NO3)3·6H2O, 2.36 g Y(CH3COO)3·4H2O, 1.60 g Sm(NO3)3·6H2O, 6.2 g Pr(NO3)3·6H2O, and 5.15 g La(NO3)3·6H2O were added in proportion, along with 41.8 g EDTA acid, 300 ml deionized water, and 30 ml 30% H2O2. The solution was stirred in an 80°C water bath to form a solution. NH3·H2O was added dropwise until the pH reached 8.5, and stirring continued to form a homogeneous sol. The solution was dried at 120°C for 12 h and then ground to obtain a powder. The powder was then placed in a muffle furnace and calcined at 500°C for 2 h at a heating rate of 10°C / min.

[0188] The prepared material powder was immersed in a precious metal solution for 4 hours and then evaporated at 90°C. The content of the precious metal was Pt=13 g / cm³.

[0189] 3.2 Material 2: A composite oxide with a metal ion molar ratio of Ce:Zr:Pr:La = 20:70:2:8 was prepared by the same method. After being immersed in a noble metal solution for 4 hours, it was evaporated and dried at 90℃. The noble metal content was Rh = 2 g / cft.

[0190] 3.3 The prepared precious metal loaded powder was added to a ball mill jar at a ratio of material 1: material 2 = 1. Acetic acid was added to adjust the pH of the slurry to 2-7. A binder was added to keep the slurry viscous and the mixture was placed in a ball mill and stirred rapidly. The prepared slurry was coated on the intermediate transition layer with a coating amount of 80 g / L. After drying at room temperature for 2-4 h, it was calcined at 500℃ for 2 h to obtain the co-sintered intermediate transition layer and the upper catalytic coating.

[0191] The difference between this comparative example and Example 2 is that commercial Ce was used. 0.2 Ba 0.05 Al 0.75 O xReplace the modified alumina material carrier Ce of the present invention 0.2 Ba 0.05 Al 0.75 O x -S.

[0192] Comparative Example 8

[0193] This invention provides a method for preparing a three-way catalyst for the aftertreatment of natural gas vehicles that reduces the amount of precious metals used, comprising the following steps:

[0194] (1) Preparation of BaSO4 modified Ce 0.2 Ba 0.05 Al 0.75 O x -S material, same as in Example 1.

[0195] (2) Preparation of the bottom catalytic coating

[0196] Pd was loaded onto Ce, a modified alumina material carrier, using an equal-volume impregnation method. 0.2 Ba 0.05 Al 0.75 O x -S and Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O x (The total loading of Pd in ​​the two carrier materials is 0.4414%), that is, the content of the bottom noble metal Pd is 15 g / cmf. Then, Pd / Ce were obtained through drying, calcination and other processes. 0.2 Ba 0.05 Al 0.75 O x -S powder and Pd / Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O x Powder; the above two catalyst powders Pd / Ce 0.2 Ba 0.05 Al 0.75 O x -S at 62 wt%, Pd / Ce 0.4 Zr 0.5 La 0.05 Pr 0.05 O xThe bottom coating slurry was obtained by ball milling 31 wt%, 7 wt% binder, and 200 wt% water for 30 min. The bottom coating slurry was then coated on the surface of cordierite honeycomb ceramic carriers (coated on a small carrier Φ1*1 in with a mesh size of 400 cpsi and a volume of 0.01638 L, and a large carrier Φ12*6 in with a mesh size of 400 cpsi and a volume of 11.12 L), with a coating amount of 129.03 g / L. After drying, the substrate was calcined at 500℃ in air for 2 h to obtain the bottom layer containing Pd catalyst.

[0197] (3) Preparation of intermediate transition layer

[0198] The middle-layer cerium-zirconium-aluminum composite material CeZrAlO was prepared by co-precipitation method. x (CeO2 30-70 wt%, ZrO2 30-60 wt%, Al2O3 0-20 wt%, and auxiliary agent La2O3 or Pr2O3 0-5 wt%), then washed with deionized water until neutral, dried in an oven at 120℃ for 4 h, and finally calcined in a muffle furnace at 400℃ for 4 h to obtain CeZrAlO x Powder; the above CeZrAlO x The zirconia balls were ball-milled with 95 wt%, 5 wt% binder, and 200 wt% water. The size distribution of the selected zirconia balls was Ф5~40 mm. The ball-milling time was 20 min, and a medium-layer coating slurry with a large particle size distribution was finally obtained. The medium-layer coating slurry was coated on the bottom layer with a coating amount of 60 g / L. After coating, the catalyst semi-finished product was dried until the water loss rate of the medium-layer coating was 95%.

[0199] (4) Preparation of upper catalytic coating

[0200] 4.1 Material 1: Preparation of composite oxides with a metal ion molar ratio of Ce:Y:Sm = 70:18:12

[0201] 36.40 g Ce(NO3)3·6H2O, 7.30 g Y(CH3COO)3·4H2O, and 6.4 g Sm(NO3)3·6H2O were added in proportion, along with 41.9 g EDTA acid, 300 ml deionized water, and 30 ml 30% H2O2. The mixture was stirred in an 80 °C water bath to form a solution. NH3·H2O was added dropwise until the pH reached 8.5, and stirring continued to form a homogeneous sol. The solution was dried at 120 °C for 12 h and then ground to obtain a powder. The powder was then placed in a muffle furnace and calcined at 500 °C for 2 h at a heating rate of 10 °C / min.

[0202] The prepared material powder was immersed in a precious metal solution for 4 hours and then evaporated at 90°C. The content of the precious metal was Pt=13 g / cf.

[0203] 4.2 Material 2: A composite oxide with a metal ion molar ratio of Ce:Zr:Pr:La=20:70:2:8 was prepared by the same method. After being immersed in a noble metal solution for 4 hours, it was evaporated and dried at 90℃. The noble metal content was Rh=2 g / cft.

[0204] 4.3 The prepared precious metal loaded powder was added to a ball mill jar at a ratio of material 1: material 2 = 1. Acetic acid was added to adjust the pH of the slurry to 2-7. A binder was added to keep the slurry viscous and then the mixture was placed in a ball mill and stirred rapidly. The prepared slurry was coated on the intermediate transition layer with a coating amount of 80 g / L. After drying at room temperature for 2-4 h, the mixture was calcined at 500℃ for 2 h to obtain the co-sintered intermediate transition layer and the upper catalytic coating.

[0205] The difference between this comparative example and Example 1 is that a composite oxide with a metal ion molar ratio of Ce:Y:Sm = 70:18:12 is used instead of the composite oxide with a metal ion molar ratio of Ce:Y:Sm:Pr:La = 70:5:3:12:10 in this invention.

[0206] Performance testing

[0207] 1. The 1*1in small-sample catalysts obtained in the above examples and comparative examples were subjected to aging treatment, and activity tests were conducted on fresh and aged samples. Specifically, the aging conditions and atmosphere were: air, 20 vol% H2O catalyst, continuous aging at 850℃ for 50 h. The test conditions were: the catalyst activity evaluation was carried out in a multi-channel fixed-bed reactor with continuous flow, simulating the composition of natural gas vehicle exhaust gas as follows: CH4 1500ppm, NOx 1500ppm, H2 3000ppm, CO 0.3%, CO2 11%, H2O 20%, N2 balance gas, space velocity 40000h. -1 The O2 concentration was adjusted to allow λ to change at a frequency of 2 seconds per test within the range of 0.97-0.99-1.01-0.99. The concentrations of CO, NO, and CH4 were measured using a Fourier transform infrared gas analyzer, and the Tf values ​​of each fresh and aged sample for the pollutants were obtained. 50 T 90 The results are shown in Tables 1 and 2.

[0208] 2. The Φ12*6in catalyst samples obtained from the above examples and comparative examples were subjected to aging treatment. The aging conditions and atmosphere were: air, 20 vol% H2O catalyst, continuous aging at 850℃ for 50 h. Examples 1-4 and comparative examples 1-5 were subjected to a 1456 h standard bench durability test according to the standard cyclic conditions of GB 20890-2007. The performance of the above rapidly aged catalyst samples and bench durable catalyst samples was evaluated according to the WHTC cycle test specified in GB 17691-2018. The emission results of each scheme were obtained, and the results are shown in Tables 3 and 4.

[0209] 3. The catalyst coatings obtained in Examples 1 and 3 were tested for coating peeling rate, and the results are shown in Table 5.

[0210] Table 1 Fresh Sample T 50 T 90 Statistical table

[0211]

[0212] Table 2. Aging Samples at 850℃ for 50 hours (T) 50 T 90 Statistical table

[0213]

[0214] Table 3. Statistical Table of WHTC Cyclic Test on Large Sample Stand at 850℃-50h

[0215]

[0216] Table 4. Statistical Table of GB20890-2007 Standard Bench Cycle 1456h Durability Parts Bench WHTC Cycle Test

[0217]

[0218] Table 5. Comparison of shedding rates of fresh and aged parts in Example 1 and Comparative Example 1.

[0219]

[0220] The results in Tables 1 and 2 show that Example 4 has comparable fresh and aged performance to Comparative Examples 1, 2, and 6-8, indicating that the modified catalyst can maintain its catalytic performance even with a low amount of precious metals. Examples 1 and 2 have only 50% of the precious metal content of Comparative Examples 3 and 5, but their fresh performance is comparable to Comparative Examples 3 and 5, and their aged performance (T4) is similar. 90The temperature was reduced by approximately 15°C, indicating that adding the intermediate layer, modified bottom layer, and top layer can improve the aging performance of the catalyst while reducing costs; Example 2, compared to Comparative Examples 6 and 7, showed improved freshness performance (CH4, NO). x T 90 The temperature was reduced by about 25°C, resulting in a significant improvement in aging performance (CH4, NO). x T 90 The approximately 60°C reduction indicates that the addition of Ba in the upper layer and the modification of the four rare earth elements in the lower layer can effectively improve the catalyst's performance and high-temperature stability. In Comparative Example 8, compared to Example 1, the absence of La and Pr elements resulted in the catalyst's CH4 and NO content being lowered. x The temperature of freshness and aging (T) 90 The increase indicates that the synergistic effect of the four elements can effectively improve catalytic performance.

[0221] As can be seen from the results in Tables 3 and 4, compared with other comparative examples, the gas emissions of Examples 1 and 2 after bench durability testing were significantly lower than the China VI emission limits, especially for CO emissions, while maintaining HC and NO emissions at a lower level. x High purification performance of NH3; Although the amount of precious metals used in Example 4 was relatively low, the catalytic performance still met the China VI emission limits, while except for Comparative Examples 5 and 7, the other comparative examples contained CH4 and NO. x Or, in cases where NH3 emissions exceed the China VI emission limits.

[0222] From Table 5 and Figure 1 , Figure 2 As can be seen from the example, Example 1 also has an intermediate transition layer, so its catalyst surface shedding rate is significantly lower than that of Example 3 without an intermediate transition layer. In particular, after aging, the shedding rate of Example 3 is significantly increased. Therefore, by setting an intermediate transition layer between the bottom layer and the top layer, the present invention can balance the thermal expansion coefficient of the entire catalyst coating, reduce the thermal stress concentration coefficient, and enhance the interaction force between the middle layer and the bottom layer, and between the middle layer and the top layer.

[0223] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment 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 within the scope of protection of the present invention.

Claims

1. A three-way catalyst for aftertreatment in natural gas vehicles that reduces the amount of precious metals used, characterized in that, Including the upper catalytic coating and the lower catalytic coating; The upper catalytic coating comprises noble metals and rare earth composite oxides; The underlying catalytic coating comprises a noble metal and modified alumina, wherein the modified alumina is CeAlO4 modified alumina with cerium-doped BaSO4 surface grafted with -NH2 groups. x ; The total content of precious metals in the upper and lower catalytic coatings is 20~50 g / cmf; The rare earth composite oxide comprises the following components by mass fraction: CeO2 50~75 wt%, Y2O3 2~5 wt%, Pr2O3 2.5~15 wt%, Sm2O3 0.5~15 wt%, and La2O3 10~15 wt%.

2. The three-way catalyst for reducing precious metal usage in natural gas vehicle aftertreatment according to claim 1, characterized in that, The noble metal in the bottom catalytic coating is Pd, or a combination of Pd and Pt; wherein the Pd content is 1~50 g / cft and the Pt content is 0~50 g / cft; the total noble metal content in the bottom catalytic coating is 1~50 g / cft.

3. The three-way catalyst for reducing precious metal usage in natural gas vehicle aftertreatment according to claim 1, characterized in that, The noble metals used in the upper catalytic coating are Pt and Rh; the Pt content is 1~50 g / cft, the Rh content is 0.4~10 g / cft; the total noble metal content in the upper catalytic coating is 1.4~50 g / cft.

4. The three-way catalyst for reducing precious metal usage in natural gas vehicle aftertreatment according to claim 1, characterized in that, The BaSO4 content in modified alumina is cerium-modified alumina (CeAlO). x Content: 0-5 wt%.

5. The three-way catalyst for reducing precious metal usage in natural gas vehicle aftertreatment according to claim 1, characterized in that, An intermediate transition layer is provided between the upper catalytic coating and the lower catalytic coating, and the intermediate transition layer is made of cerium-zirconium-aluminum composite oxide.

6. The three-way catalyst for reducing precious metal usage in natural gas vehicle aftertreatment according to claim 5, characterized in that, The mass fractions of each component in the cerium-zirconium-aluminum-based composite oxide are: CeO2 30~70 wt%, ZrO2 30~60 wt%, Al2O3 0~20 wt%, and La2O3 or Pr2O3 0~5 wt%.

7. The three-way catalyst for reducing precious metal usage in natural gas vehicle aftertreatment according to claim 5, characterized in that, The coating amount of the upper catalytic coating is 50~150 g / L, the coating amount of the bottom catalytic coating is 50~150 g / L, and the coating amount of the intermediate transition layer is 60~100 g / L.

8. The three-way catalyst for reducing precious metal usage in natural gas vehicle aftertreatment according to claim 1, characterized in that, The -NH2 groups grafted onto the surface of BaSO4 were obtained by modifying BaSO4 with γ-aminopropyltriethoxysilane or γ-(2,3-epoxypropoxy)propyltrimethoxysilane.

9. The three-way catalyst for reducing precious metal usage in natural gas vehicle aftertreatment according to claim 1, characterized in that, The underlying catalytic coating also includes cerium-zirconium composite oxide, and the ratio of the modified alumina to the cerium-zirconium composite oxide is 1:2 to 2:

1.

10. The three-way catalyst for reducing precious metal usage in natural gas vehicle aftertreatment according to claim 9, characterized in that, The cerium-zirconium composite oxide is doped with La and Pr.

11. The preparation method of the three-way catalyst for reducing precious metal usage in natural gas vehicle aftertreatment according to any one of claims 1 to 10, characterized in that, Includes the following steps: S1, Preparation of the underlying catalytic coating: BaSO4 powder was dissolved in a solvent, and then γ-aminopropyltriethoxysilane was added to graft -NH2 groups onto the surface of BaSO4. Grafting -NH2 groups onto the surface of BaSO4 and adding them to CeAlO x The mixture is mixed in a slurry, dried, and calcined to obtain a BaSO4-modified alumina powder carrier; Noble metals were loaded onto a BaSO4-modified alumina powder support to prepare a bottom catalyst slurry, which was then coated onto the support surface and dried and calcined to obtain a bottom catalyst coating. S2, Preparation of the intermediate transition layer: Cerium zirconium aluminum oxide powder was prepared into a slurry, coated onto the underlying catalyst coating, and then dried. S3, Preparation of the upper catalytic coating: Noble metals are loaded onto a rare earth composite oxide support to prepare an upper catalyst slurry, which is then coated onto a dried intermediate transition layer. After drying and calcination, a co-sintered intermediate transition layer and an upper catalyst coating are obtained.

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