Three-way catalytic converter system for exhaust gas purification of an engine and use thereof

Abstract

A three-way catalytic conversion system for engine exhaust purification treatment includes an oxidation section containing an oxidation catalyst and a three-way conversion section containing a three-way catalyst, the oxidation catalyst is used to catalyze the oxidation reaction of reducing components in engine exhaust with oxygen, the oxidation section is located downstream of the engine, the three-way conversion section is located downstream of the oxidation section, an ultra-high temperature resistant oxidation catalyst is arranged upstream of the three-way catalyst, so that the engine exhaust is first treated by the oxidation catalyst and then treated by the three-way catalyst, which can reduce the performance decay of the three-way catalyst caused by combustion during the treatment process, avoid the adverse effects of high temperature caused by combustion on the three-way conversion reaction and the structure and performance of the three-way catalyst, thereby ensuring the exertion of the three-way conversion function of the system and improving the purification efficiency of engine exhaust emissions.

Description

[0001] This disclosure is a divisional application of the invention patent application filed with the China National Intellectual Property Administration, application number 202180039632.7, application date September 30, 2021, entitled "Three-way catalytic converter system for engine exhaust purification and its application". Technical Field

[0002] This invention relates to the field of engine aftertreatment, specifically to a three-way catalytic converter system for purifying engine exhaust gases and its application. Background Technology

[0003] The exhaust gas emitted by a car engine in operation contains harmful gases such as HC, CO, and NOx, which can usually be eliminated by a three-way catalytic converter (TWC system). The current TWC system is based on the three-way catalytic conversion function of a three-way catalyst (TWC) to convert HC, CO, and NOx in the exhaust into carbon dioxide (CO2), nitrogen (N2), and water, thereby eliminating HC, CO, and NOx. The basic components of a three-way catalyst mainly include a porous matrix material, an oxygen storage material, and noble metals. The noble metals are mainly platinum (Pt), palladium (Pd), and rhodium (Rh). Noble metals are the active components of TWC. The main functions of Pt and Pd are to accelerate the oxidation of hydrocarbons (HC) and carbon monoxide (CO) under lean exhaust conditions (air-fuel ratio λ>1, oxygen-rich exhaust) and to catalyze the steam reforming of HC and the water-gas reaction of CO under rich exhaust conditions (λ<1, oxygen-deficient exhaust) to eliminate HC and CO. The main function of rhodium (Rh) is to convert nitrogen oxides (NOx) under equivalence (λ=1) and slightly rich (λ<1) exhaust conditions. The basic function of the oxygen storage material is to adjust the λ value within a small range and reduce the degree of deviation from λ=1 in order to maintain the three-way reaction under equivalence conditions. The oxygen storage material usually needs to be combined with noble metals to effectively exert its function. The porous matrix material is usually alumina (Al2O3) based material with a loose structure and a large specific surface area. It mainly serves as a supporting material to disperse noble metals and ensure the activity and stability of the catalyst. Rh readily reacts with Al2O3 at high temperatures and becomes ineffective. Therefore, in TWC catalysts, Rh is usually supported on an oxygen storage material, which is then filled on the surface of an alumina-based material to separate Rh from Al2O3 and prevent catalyst failure.

[0004] Under normal circumstances, during the operation of a three-way catalytic converter (TWC), oxygen reacts rapidly with reducing components such as HC and CO, releasing a large amount of heat and causing the TWC temperature to rise sharply. This is especially true when treating exhaust gas with high oxygen content (e.g., exhaust gas from engines with an oxygen volume content greater than 1%, or even greater than 2-3%, in a three-way catalytic converter), where the reaction is even more intense, causing the TWC temperature to rise even higher. On the one hand, a large amount of combustion reaction occupies most of the TWC space at the engine exhaust inlet, leaving only the rear portion of the TWC capable of three-way conversion (i.e., most of the TWC is used to burn reducing components such as HC and CO and consume oxygen, while only a small portion performs three-way conversion, converting NOx), thus limiting the TWC's function. On the other hand, the high temperatures generated by combustion can typically reach over 950℃, exceeding the TWC conversion temperature window (generally 350-700℃), which is detrimental to the three-way conversion reaction and affects the conversion efficiency of harmful gases such as NOx. Furthermore, the high temperatures generated by combustion in the TWC cause it to operate at extremely high temperatures (900-980℃). Working at ultra-high temperatures (such as 950℃) for a long time will accelerate the aging of TWC, causing the function of TWC to be severely degraded. The main manifestations are: (1) the pores of the porous matrix material collapse and the surface area decreases sharply, affecting the overall structure and performance of TWC, especially burying some precious metals and reducing the number of catalytic active sites; (2) the oxygen storage material ages, the combination with precious metals weakens, the regulation function of λ is reduced, and the steam reforming function of CO and HC is reduced. At the same time, the protection function of Rh decreases, Rh is easy to contact Al2O3 and fail, which seriously reduces the catalyst's ability to catalyze the reduction of NOx; (3) the precious metal particles continue to grow, causing the three-way catalytic activity of TWC to decrease. Summary of the Invention

[0005] This invention provides a three-way catalytic converter system for engine exhaust purification and its application, which at least solves the problems in the prior art, such as excessive temperature caused by prolonged catalytic combustion of excessive HC and CO reducing components by TWC, and the resulting serious damage to catalyst performance and limited function.

[0006] In one aspect, the present invention provides a three-way catalytic converter system for purifying engine exhaust, comprising an oxidation section containing a high-temperature resistant oxidation catalyst and a three-way converter section containing a three-way catalyst, wherein the oxidation catalyst is used to catalyze the oxidation reaction between reducing components in the exhaust and oxygen, the oxidation section is located downstream of the engine, and the three-way converter section is located downstream of the oxidation section.

[0007] According to one embodiment of the present invention, the oxidation catalyst comprises a first alumina-based material and palladium supported on the first alumina-based material, and satisfies at least one of the following characteristics: the pore volume of the first alumina-based material is 0.8 cc / g to 1.2 cc / g; the specific surface area of ​​the first alumina-based material is 130 to 180 m². 2 / g; the specific surface area of ​​the first alumina-based material after aging at 1200±100℃ for 4±0.5 hours is not less than 60m². 2 / g.

[0008] According to one embodiment of the present invention, the first alumina-based material comprises γ-alumina.

[0009] According to one embodiment of the present invention, the first alumina-based material contains rare earth elements, and the mass content of rare earth elements in the first alumina-based material is 0-7%.

[0010] According to one embodiment of the present invention, the mass content of palladium in the oxidation catalyst is 0.06 to 1.0%.

[0011] According to one embodiment of the present invention, the number of oxidation segments is at least two, and the distance between any two adjacent oxidation segments is not less than 150 mm.

[0012] According to one embodiment of the present invention, the oxidation section includes a first support and a first active layer located on the surface of the first support, wherein the oxidation catalyst is present in the first active layer.

[0013] According to one embodiment of the present invention, the first active layer further comprises a binder and / or a modifying agent, and satisfies at least one of the following characteristics: the binder comprises aluminum glue and / or silicone; the modifying agent comprises cerium material and / or zirconium material; the mass content of the oxidation catalyst in the first active layer is 85%-98%, and the balance is the binder and / or the modifying agent.

[0014] According to one embodiment of the present invention, the forming material of the first carrier includes at least one of ceramics and metals.

[0015] According to one embodiment of the present invention, the oxidation catalyst comprises a first alumina-based material and palladium supported on the first alumina-based material, wherein the mass ratio of palladium to the volume of the first support in the oxidation catalyst is (3-50) grams: 1 cubic foot.

[0016] According to one embodiment of the present invention, the mass ratio of the first active layer to the volume of the first carrier is (100-200) grams: 1 liter.

[0017] According to one embodiment of the present invention, the three-way conversion section further includes a second support and a second active layer located on the surface of the second support, wherein the three-way catalyst is present in the second active layer.

[0018] According to one embodiment of the present invention, the second active layer further comprises a binder and / or a modifying agent, and satisfies at least one of the following characteristics: the binder comprises aluminum glue and / or silicone; the modifying agent comprises cerium material and / or zirconium material; the mass content of the three-way catalyst in the second active layer is 85%-98%, and the balance is the binder and / or the modifying agent.

[0019] According to one embodiment of the present invention, the three-way catalyst comprises a porous matrix material, an oxygen storage material, and a noble metal, wherein the noble metal includes platinum, rhodium, and palladium, the oxygen storage material is filled in the porous matrix material, the rhodium is supported on the oxygen storage material, and the noble metals other than rhodium are supported on the porous matrix material or on the oxygen storage material.

[0020] According to one embodiment of the present invention, the oxygen storage material comprises CeZrO.

[0021] According to one embodiment of the present invention, the porous matrix material comprises a second alumina-based material and satisfies at least one of the following characteristics: the pore volume of the second alumina-based material is less than 0.8 cc / g;

[0022] The specific surface area of ​​the second alumina-based material is 130 m². 2 / g~240m 2 / g; the specific surface area of ​​the second alumina-based material after aging at 1200±100℃ for 4±0.5 hours is not less than 40m². 2 / g.

[0023] According to one embodiment of the present invention, the pore volume of the second alumina-based material is 0.4 cc / g to 0.8 cc / g.

[0024] According to one embodiment of the present invention, the second alumina-based material comprises γ-alumina and / or θ-alumina.

[0025] According to one embodiment of the present invention, the second alumina-based material contains rare earth elements, and the mass content of rare earth elements in the second alumina-based material is 3% to 7%.

[0026] According to one embodiment of the present invention, the forming material of the second carrier includes at least one of ceramics and metals.

[0027] According to one embodiment of the present invention, the three-way conversion section further includes a second support and a second active layer located on the surface of the second support, wherein the three-way catalyst is present in the second active layer; the mass ratio of the noble metal in the three-way catalyst to the volume of the second support is (3-50) grams: 1 cubic foot.

[0028] According to one embodiment of the present invention, the three-way catalyst further includes platinum, with a mass ratio of rhodium to platinum of 1:0 to 15; and / or, a mass ratio of rhodium to palladium of 1:2 to 15.

[0029] In another aspect, the present invention provides an application of the above-mentioned three-way catalytic converter system in engine exhaust purification treatment.

[0030] According to one embodiment of the present invention, the engine exhaust includes engine exhaust with high oxygen content, wherein the volume content of oxygen in the engine exhaust with high oxygen content is not less than 1%.

[0031] According to one embodiment of the present invention, the engine exhaust includes equivalent operating engine exhaust.

[0032] The three-way catalytic converter system (TWC system) for engine exhaust purification provided by this invention first treats the engine exhaust with an oxidation catalyst, allowing oxygen and reducing components such as HC and CO to burn under the catalytic action of the oxidation catalyst. This eliminates oxygen, reduces the degree of combustion during the three-way catalytic converter treatment process, and avoids the adverse effects of combustion occupying most of the space of the three-way catalytic converter and the high temperature generated by combustion on the three-way conversion reaction and the structure and performance of the three-way catalytic converter. This ensures the proper functioning of the three-way catalytic converter and efficiently eliminates harmful components such as HC, CO, and NOx in the exhaust. The exhaust treated by the TWC system of this invention can meet the target emission standards. Attached Figure Description

[0033] Figure 1 The curve showing the change in oxygen concentration in the exhaust gas as a function of engine output power is shown in the figure.

[0034] Figure 2 The graph shows the temperature of the exhaust inlet of the oxidation section and the catalyst in the oxidation section as a function of engine output power.

[0035] Figure 3 The graph shows the conversion rate of NMHC to CO as a function of catalyst aging time in the oxidation section.

[0036] Figure 4 The graph shows the conversion rate of NMHC to CO as a function of aging time.

[0037] Figure 5The graph shows the change in NOx concentration in engine exhaust after treatment by the catalyst system as a function of the catalyst reaction temperature in the oxidation section.

[0038] Figure 6 The graph shows the NOx conversion rate of the catalyst system as a function of the catalyst reaction temperature in the oxidation section.

[0039] Figure 7 This is a graph showing the changes in exhaust inlet temperature of oxidation section B, temperature of oxidation catalyst in oxidation section B, and exhaust outlet temperature of oxidation section B with engine power in one embodiment of the present invention.

[0040] Figure 8 This is a graph showing the changes in oxygen concentration at the exhaust inlet and exhaust outlet of oxidation section B as a function of engine power in one embodiment of the present invention. Detailed Implementation

[0041] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below.

[0042] The TWC system for engine exhaust purification provided by the present invention includes an oxidation section containing an oxidation catalyst and a three-way conversion section containing a three-way catalyst. The oxidation catalyst is used to catalyze the oxidation reaction between the reducing components in the exhaust and oxygen. The oxidation section is located downstream of the engine, and the three-way conversion section is located downstream of the oxidation section.

[0043] In this invention, the three-way conversion section (three-way catalyst) is located downstream / rear of the oxidation section (oxidation catalyst). That is, the exhaust outlet of the engine, the oxidation section, and the three-way conversion section are arranged in sequence. The oxidation section is located between the engine exhaust outlet and the three-way conversion section, so that the exhaust gas discharged from the engine flows through the oxidation section and the three-way conversion section in sequence. It is first treated by the oxidation catalyst of the oxidation section and then treated by the three-way catalyst of the three-way conversion section to achieve the purification of the exhaust gas. The oxidation catalyst catalyzes the reaction between oxygen and reducing components such as HC and CO, consuming most of the oxygen and reducing components like HC and CO in the exhaust gas. The exhaust gas treated by the oxidation catalyst is then further treated by a three-way catalyst. The three-way catalyst is used for three-way conversion (primarily the simultaneous conversion of HC, CO, and NOx). During the three-way catalyst treatment, less oxygen and reducing components like HC and CO remain in the exhaust gas, reducing combustion and preventing the three-way catalyst from being covered by combustion, thus ensuring its three-way conversion function. It also avoids excessively high temperatures, allowing the three-way catalyst to perform the three-way conversion reaction at a suitable reaction temperature (350–700℃). Furthermore, it prevents high temperatures from adversely affecting the structure and performance of the three-way catalyst (e.g., pore collapse of porous supported materials, reduced activity of precious metals, and functional degradation of oxygen storage materials), thereby improving the efficiency and durability of the three-way conversion reaction.

[0044] In practice, the distance between the oxidation catalyst and the three-way catalyst or their relative positions can be adjusted according to factors such as the composition of the engine exhaust to ensure that the three-way catalyst located at the rear end of the oxidation catalyst operates at 350-700℃ (i.e., the temperature during the three-way catalyst treatment process is controlled to be approximately 350-700℃), while avoiding prolonged exposure of the three-way catalyst to ultra-high temperatures (850-950℃).

[0045] In addition, the exhaust gas is first treated by an oxidation catalyst. During this process, the oxidation catalyst catalyzes the reaction of reducing components such as HC and CO in the exhaust gas with oxygen. The source of this oxygen can be the oxygen contained in the exhaust gas produced by the engine (i.e., the oxygen contained in the exhaust gas produced by the engine), or oxygen can be introduced into the inlet of the oxidation catalyst as needed (two air-injection air-fuel reductant to accelerate the temperature rise of the catalyst during the cold start stage) to consume most of the reducing components such as HC and CO in the exhaust gas, avoiding combustion and high temperature phenomena during the three-way catalyst treatment process, so that the three-way catalyst can carry out the three-way conversion reaction at a suitable reaction temperature (350~700℃). Therefore, in some embodiments, an intake pipe may also be included that communicates with the engine exhaust inlet of the oxidation section. The exhaust gas generated by the engine enters the oxidation section from the exhaust inlet of the oxidation section. The intake pipe is used to introduce air (oxygen) into the exhaust gas entering the oxidation section so that most of the reducing components such as HC and CO are consumed after the exhaust gas entering the oxidation section is treated by the oxidation catalyst. The intake pipe is also equipped with a valve so that when it is not necessary to introduce oxygen into the exhaust gas entering the oxidation section, the air can be stopped, and when it is necessary to introduce oxygen into the exhaust gas entering the oxidation section, air (oxygen) can be introduced into the exhaust gas entering the oxidation section through the intake pipe.

[0046] The temperature during oxidation catalyst treatment is relatively high, but generally does not exceed 1000℃ (the maximum temperature exposed by the catalyst can be controlled by combining different oxidation catalysts). The aforementioned oxidation catalyst can be a high-temperature resistant catalyst, specifically an ultra-high-temperature resistant catalyst resistant to approximately 1000℃ to 1100℃. That is, under conditions of approximately 1000℃ to 1100℃, the structure and performance of the oxidation catalyst remain basically stable; for example, pore collapse is unlikely to occur. Specifically, the oxidation catalyst may include a first alumina-based material and palladium supported on the first alumina-based material. The pore volume of the first alumina-based material is 0.8 cc / g to 1.2 cc / g (i.e., cm³ / g). 3 / g), for example, 0.8cc / g, 0.9cc / g, 1cc / g, 1.1cc / g, 1.2cc / g, or any combination thereof, with a specific surface area of ​​130–180 m². 2 / g, for example 130m2 / g, 140m 2 / g, 150m 2 / g, 160m 2 / g、170m 2 / g、180m 2 The specific surface area of ​​the first alumina-based material after aging at 1200±100℃ for 4±0.5 hours is not less than 60 m² / g or any combination thereof. 2 / g, using this first alumina-based material can improve the high temperature resistance and stability of the oxidation catalyst, further ensuring its catalytic activity and service life.

[0047] Specifically, the first alumina-based material may include γ-alumina, which may be doped alumina and / or undoped alumina. In some embodiments, the first alumina-based material contains rare earth elements, and the mass content of the rare earth elements in the first alumina-based material is 0-7% (i.e., the mass of rare earth element oxides accounts for 0-7% of the first alumina-based material), for example 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%. When the mass content of rare earth elements is 0%, the first alumina-based material is undoped alumina; when the mass content of rare earth elements is not 0%, the first alumina-based material is doped alumina (or rare earth alumina). Relatively speaking, using doped alumina is beneficial for further improving the high-temperature resistance of the alumina-based material. Optionally, the rare earth elements include, for example, lanthanum (La).

[0048] The first alumina-based material can be commercially available or self-made. Generally, high-temperature aging treatment of alumina raw materials can cause the easily collapsible pores to collapse, thereby obtaining a structurally stable high-temperature resistant alumina-based material. This ensures that the alumina-based material will not experience severe collapse when applied under high-temperature conditions, thus improving the high-temperature resistance of the oxidation catalyst using this high-temperature resistant alumina-based material as the matrix. Specifically, in some embodiments, the first alumina-based material can be prepared by a process including the following steps: aging the alumina raw material at 1000℃~1500℃ for at least 2 hours to obtain the first alumina-based material. The first alumina-based material obtained by this aging treatment has good stability below 1000℃, thereby ensuring the high-temperature resistance of the oxidation catalyst. When preparing a first alumina-based material without rare earth elements, the alumina raw material is an alumina raw material without rare earth elements. When preparing a first alumina-based material doped with rare earth elements, the alumina raw material is an alumina raw material doped with rare earth elements. The alumina raw material used in the above process can be commercially purchased or self-made, and the present invention does not impose any special restrictions on this.

[0049] After aging at 1000℃ to 1500℃, the aforementioned alumina-based material can be loaded with palladium using conventional methods in the art, such as impregnation (e.g., equal-volume impregnation), to obtain an oxidation catalyst. Specifically, the palladium precursor can be dissolved in a first solvent to prepare a first impregnation solution. This first impregnation solution is then used to impregnate the first alumina-based material, either by immersing the material in the solution or by spraying the solution onto it. After impregnation, the material is dried to remove the solvent, thus loading palladium onto the alumina-based material and obtaining the oxidation catalyst. The first solvent may include water, and the palladium precursor may include a soluble salt of palladium, such as palladium nitrate. Furthermore, elements with noble metal anchoring functions, such as barium (Ba), can be added to the oxidation catalyst (or the first coating described below) to increase the stability of the noble metal.

[0050] The oxidation section may further include a first support for supporting the oxidation catalyst, i.e., the oxidation catalyst is disposed on the first support. In some preferred embodiments, the oxidation section includes the first support and a first active layer located on the surface of the first support, and the oxidation catalyst is present in the first active layer (i.e., the first active layer contains the oxidation catalyst).

[0051] Typically, the first active layer also includes a binder and / or modifying agents. The binder may include aluminum glue and / or silicone, and the modifying agents may include cerium materials and / or zirconium materials to further improve the stability and other properties of the oxidation section. In some embodiments, based on the total mass of the first active layer, the mass percentage of the oxidation catalyst is 85%-98% (i.e., the mass content of the oxidation catalyst in the first active layer is 85%-98%), for example, a range of 85%, 88%, 90%, 93%, 95%, 98%, or any two of these, with the balance being binder and / or modifying agents.

[0052] In a specific implementation, the oxidation catalyst, binder and / or modifying agent can be mixed with the fourth solvent to form a slurry, and then the slurry can be coated on the surface of the first carrier. After drying and other treatments, the first active material layer is formed on the surface of the first carrier.

[0053] Optionally, the forming material of the first carrier may include at least one of ceramics (such as cordierite), metals, etc., that is, the first carrier may be formed by a mixture of one or more of ceramic materials, metals, etc. The first carrier may be a particulate filter (GPF), a honeycomb carrier, but is not limited thereto.

[0054] According to the research of the present invention, palladium is a metallic active component of catalytic oxidation active material (i.e., oxidation catalyst), and its content is an important factor affecting the performance of oxidation catalyst. In some preferred embodiments, based on the total mass of oxidation catalyst, the mass percentage of palladium is 0.06 to 1.0% (i.e., the mass content of palladium in oxidation catalyst is 0.06 to 1.0%).

[0055] In this invention, the number of oxidation sections containing oxidation catalysts is at least one, that is, it can be one or at least two (i.e., a combination of two or more oxidation catalysts). When the number of oxidation sections is at least two, the distance between two adjacent oxidation sections is generally not less than 150 mm (this distance is the distance along the flow direction of engine exhaust). In the two adjacent oxidation sections, the palladium content in the oxidation catalyst of the upstream oxidation section can be lower than, equal to, or higher than the palladium content in the oxidation catalyst of the downstream oxidation section, and can be set as needed in specific implementations. By combining at least two oxidation sections, each oxidation section can partially oxidize the reducing agent in the exhaust (consuming some oxygen) without generating a very high temperature rise. That is, the heat generated by combustion is distributed to the two oxidation catalysts with a certain distance between them, which can control the maximum temperature exposed by the oxidation catalyst in the oxidation section, thus further improving the efficiency and durability of engine exhaust purification treatment.

[0056] In addition, the ratio of the mass of palladium in the oxidation catalyst to the volume of the first support can be (3-50) g: 1 cubic foot (i.e. (3-50) g / ft3), for example, 3 g: 1 cubic foot, 5 g: 1 cubic foot, 10 g: 1 cubic foot, 20 g: 1 cubic foot, 30 g: 1 cubic foot, 40 g: 1 cubic foot, 50 g: 1 cubic foot or any two of these ratios, which is beneficial to improving the processing efficiency of the above oxidation catalyst.

[0057] Furthermore, the ratio of the mass of the first active layer to the volume of the first carrier can be (100-200) grams: 1 liter (i.e. (100-200) g / L), for example, 100 g: 1 liter, 150 g: 1 liter, 160 g: 1 liter, 170 g: 1 liter, 180 g: 1 liter, 190 g: 1 liter, 200 g: 1 liter, or any two of these ratios.

[0058] This invention can employ conventional three-way catalysts (TWCs) in the art. In some embodiments, the three-way catalyst comprises a porous matrix material, an oxygen storage material, and a noble metal, including palladium and rhodium. The oxygen storage material is filled within the porous matrix material, and rhodium is supported on the oxygen storage material. Other noble metals besides rhodium can be supported on either the porous matrix material or the oxygen storage material, as needed. Palladium can be supported on either the porous matrix material or the oxygen storage material. Supporting rhodium on the oxygen storage material also protects rhodium and reduces its contact reaction with the porous matrix material and other components. Preferably, palladium is supported on the oxygen storage material; more preferably, all of the aforementioned noble metals are supported on the oxygen storage material.

[0059] This invention can employ conventional methods in the art to load the aforementioned noble metals onto oxygen storage materials or porous matrix materials, such as impregnation methods (e.g., equal-volume impregnation). For example, a rhodium precursor can be mixed with a second solvent to prepare a second impregnation solution, which is then used to impregnate the oxygen storage material to load rhodium onto the oxygen storage material. The second solvent may include water, and the rhodium precursor may be a soluble salt of rhodium, such as rhodium nitrate. Alternatively, a platinum precursor can be mixed with a third solvent to prepare a third impregnation solution, which is then used to impregnate the porous matrix material to load platinum onto the porous matrix material. The third solvent may include water, and the platinum precursor may be a soluble salt of platinum, such as platinum nitrate.

[0060] Oxygen storage materials can adjust the air-fuel ratio (λ) of engine exhaust on the catalyst surface, allowing the three-way conversion reaction to proceed at near-equivalent levels, ensuring the efficiency of the three-way conversion reaction and the proper functioning of each component. In some embodiments, the oxygen storage material may include CeZrO, and may also include ZrO2, i.e., a combination of CeO2 and ZrO2, but the invention is not limited thereto. Porous matrix materials are used to disperse components such as noble metals, thereby ensuring the dispersion and catalytic activity of the three-way catalyst. In some embodiments, the porous matrix material may include a second alumina-based material with a pore volume less than 0.8 cc / g, generally preferably 0.4 cc / g to 0.8 cc / g, for example, 0.4 cc / g, 0.5 cc / g, 6 cc / g, 7 cc / g, 8 cc / g, or any combination thereof, and a specific surface area of ​​130 m². 2 / g~240m 2 / g, for example 130m 2 / g, 140m 2 / g, 150m 2 / g, 160m 2 / g、170m 2 / g、180m 2 / g、190m 2 / g、200m 2 / g、210m2 / g、220m 2 / g、230m 2 / g、240m 2 The range of / g or any two of these components facilitates the dispersion of noble metals and other components in the porous matrix material, thereby improving the performance of the three-way catalyst. Furthermore, the specific surface area of ​​this second alumina-based material after aging at 1200±100℃ for 4±0.5 hours is generally not less than 40 m². 2 / g.

[0061] Specifically, the second alumina-based material may include γ-alumina and / or θ-alumina, which may be doped alumina and / or undoped alumina. Doped alumina typically contains rare earth elements. In some embodiments, the second alumina-based material contains rare earth elements, and the mass content of rare earth elements in the second alumina-based material, based on rare earth oxides, may be 3% to 7% (i.e., the mass of rare earth oxides accounts for 3% to 7% of the second alumina-based material), for example, a range of 3%, 4%, 5%, 6%, 7%, or any combination thereof. Optionally, the rare earth elements may include, for example, La. The second alumina-based material may be commercially available or homemade, and the present invention does not impose any particular limitation on this.

[0062] The aforementioned three-way conversion section may further include a second support for supporting the three-way catalyst, i.e., the three-way catalyst is disposed on the second support, and the three-way catalyst may form a coating on the second support, but is not limited thereto. In some preferred embodiments, the three-way conversion section includes a second support and a second active layer located on the surface of the second support, and the three-way catalyst is present in the second active layer (i.e., the second active layer contains the aforementioned three-way catalyst).

[0063] Typically, the second active layer also includes a binder and / or modifying agents. The binder may include aluminum glue and / or silicone, and the modifying agents may include cerium materials and / or zirconium materials to further improve the stability and other properties of the three-way conversion stage. In some embodiments, based on the total mass of the second active layer, the mass percentage of the three-way catalyst is 85%-98% (i.e., the mass content of the three-way catalyst in the second active layer is 85%-98%), for example, a range of 85%, 88%, 90%, 93%, 95%, 98%, or any two of these, with the balance being binder and / or modifying agents.

[0064] In practice, the three-way catalyst, binder and / or modifier can be mixed with the fifth solvent to form a slurry, and then the slurry can be coated on the surface of the second carrier. After drying and other treatments, the second active material layer is formed on the surface of the second carrier.

[0065] Optionally, the forming material of the second carrier may include at least one of ceramics (such as cordierite), metal, etc. The second carrier may be a particulate filter (GPF) or a honeycomb carrier, but is not limited thereto. The second carrier may be the same as or different from the first carrier.

[0066] In some embodiments, the aforementioned precious metal includes platinum, wherein the mass ratio of rhodium to platinum is 1:0 to 15, preferably 1:0.5 to 8, for example, a range consisting of 1:0.5, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, or any two thereof; and the mass ratio of rhodium to palladium can be 1:2 to 15, for example, a range consisting of 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, or any two thereof. Platinum can be supported on a porous matrix material or on an oxygen storage material.

[0067] In some embodiments, the mass ratio of the precious metal to the volume of the second support in the three-way catalyst is (5-50) grams per cubic foot, for example, 5g:1 cubic foot, 10g:1 cubic foot, 20g:1 cubic foot, 30g:1 cubic foot, 40g:1 cubic foot, 50g:1 cubic foot, or any two of these ratios. The mass of the precious metal is the sum of the masses of all types of precious metals in the three-way catalyst. For example, if the precious metals in the three-way catalyst are rhodium, platinum, and palladium, then the mass of the precious metal refers to the sum of the masses of rhodium, platinum, and palladium in the three-way catalyst.

[0068] This invention also provides the application of the above-mentioned TWC system in engine exhaust purification. Specifically, the engine of this invention can be a fuel engine, whose exhaust generally contains hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NOx), etc. During application, the exhaust generated by the engine is discharged from the engine's exhaust outlet, then enters the oxidation section through the exhaust inlet of the oxidation section. In the oxidation section, it comes into contact with an oxidation catalyst. Under the action of the oxidation catalyst, the reducing components such as HC and CO in the exhaust react with oxygen, and then are discharged from the exhaust outlet of the oxidation section. The exhaust then enters the three-way conversion section through the exhaust inlet of the three-way conversion section, where it comes into contact with a three-way catalyst for three-way conversion, converting HC, CO, and NOx in the exhaust into carbon dioxide (CO2), nitrogen (N2), and water, thus obtaining purified exhaust. The purified exhaust is discharged from the exhaust outlet of the three-way conversion section.

[0069] The TWC system of the present invention can be used in particular for the treatment of engine exhaust with high oxygen content. In some embodiments, the engine exhaust includes engine exhaust with high oxygen content, wherein the volume content of oxygen in the engine exhaust is not less than 1%, for example not less than 2%, 2.5%, 3%, 3.5%, etc.

[0070] The exhaust gas from a high-oxygen-content equivalent operating engine contains oxidizing components such as oxygen (O2) and NOx, as well as reducing components such as HC and CO. The content of reducing components is roughly equivalent to that of O2 (both are high). In conventional TWC systems, the reaction of a large amount of O2 with reducing components such as HC and CO on the TWC releases a large amount of heat, generating high temperatures. This affects the three-way catalytic conversion efficiency and aging resistance of the TWC, causing the harmful components in the engine exhaust to fail to meet emission standards. The three-way catalytic conversion system of this invention can effectively solve this problem. In some embodiments, the aforementioned engine exhaust includes equivalent operating engine exhaust, especially high-oxygen equivalent operating engine exhaust with an oxygen volume content greater than 1% (including much greater than 1%).

[0071] Specifically, the exhaust gas from this high-oxygen-content equivalent engine has a high oxygen (O2) content, and the amount of reducing components such as HC and CO is also roughly equivalent to that of O2. It is easier to burn during conventional TWC treatment and generates high temperatures (even higher than 850-980℃). Prolonged operation at high temperatures (>850℃) will cause damage to the TWC structure and affect the function of TWC. The catalytic system of this invention can solve the problem of ultra-high catalyst temperature caused by high-oxygen-content equivalent exhaust gas and can be used in the aftertreatment system of engine exhaust gas that exceeds the high temperature resistance limit of TWC.

[0072] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0073] Example 1

[0074] In this embodiment, the three-way catalytic converter system includes an oxidation section containing an oxidation catalyst and a three-way conversion section containing a three-way catalyst. The oxidation catalyst is used to catalyze the oxidation reaction between reducing components such as HC and CO in the exhaust gas and oxygen. The oxidation section is located downstream of the engine, and the three-way conversion section is located downstream of the oxidation section; wherein:

[0075] The oxidation section consists of a first support and a first active layer on the surface of the first support. The first active layer contains an oxidation catalyst and a binder. The mass content of the oxidation catalyst in the first active layer is 90-98%, and the remainder is the binder, which is aluminum glue and silica gel. The first support is cordierite. The mass ratio of the first active layer to the volume of the first support is 160 grams to 1 liter.

[0076] The oxidation catalyst comprises a first alumina-based material and palladium supported on the first alumina-based material. The oxidation catalyst is prepared by impregnating palladium nitrate onto the first alumina-based material using an equal-volume impregnation method. The first alumina-based material is high-temperature resistant rare-earth alumina (γ-alumina) from Baizhexing Energy Co., Ltd., with a pore volume of approximately 0.94 cc / g and a surface area of ​​approximately 169.4 m². 2 / g, after aging at 1200℃ for 4 hours, has a specific surface area of ​​approximately 61.23m². 2 / g; the rare earth element it contains is La, and the mass content of La in the first alumina-based material is about 4% based on La oxide (La2O3);

[0077] The palladium content in the oxidation catalyst is approximately 0.22% by mass (approximately 0.353 g of palladium per liter of oxidation catalyst); in the oxidation section, the mass ratio of palladium in the oxidation catalyst to the volume of the first support is 10 g: 1 cubic foot.

[0078] The three-way catalyst consists of a second support and a second active layer located on the surface of the second support. The second active layer contains the three-way catalyst and a binder. The mass content of the three-way catalyst in the second active layer is 90-98%, and the remainder is the binder, which is aluminum glue and silica gel. The second support is cordierite.

[0079] The three-way catalyst consists of a second alumina-based material, CeZrO, and noble metals, specifically rhodium and palladium, supported on CeZrO, which is then filled within the second alumina-based material. The second alumina-based material is rare earth alumina (γ-alumina) from Baizhexing Energy Co., Ltd., with a pore volume of approximately 0.49 cc / g and a surface area of ​​approximately 145 m². 2 / g, after aging at 1000℃ for 4 hours, has a specific surface area of ​​approximately 110m². 2 / g; the rare earth element it contains is La, and the mass content of La2O3 in the second alumina-based material is about 4% based on the oxide of La (La2O3);

[0080] In the three-way conversion stage, the mass ratio of the precious metal in the three-way catalyst to the volume of the second support is 10 grams: 1 cubic foot, wherein the mass ratio of rhodium to palladium is 3:7.

[0081] Application Examples

[0082] The performance of the above-mentioned catalytic system was verified through engine bench tests. During the experiment, exhaust gas flowed sequentially through the oxidation section and the three-way conversion section after being discharged from the engine. The process is briefly described as follows: Exhaust gas from the engine enters the oxidation section through the exhaust inlet after exiting the engine's exhaust outlet. In the oxidation section, it comes into contact with the oxidation catalyst, causing the oxygen and reducing components to undergo an oxidation-reduction reaction. Then, it exits from the exhaust outlet of the oxidation section and enters the three-way conversion section through the exhaust inlet. In the three-way conversion section, it comes into contact with the three-way catalyst for three-way conversion and then exits from the exhaust outlet of the three-way conversion section, thus obtaining purified exhaust gas. Experiments 1 to 3, and Comparative Experiment 1 and Comparative Experiment 2 were conducted according to the above process:

[0083] In the following experiments, the conversion rate of NMHC = ((amount of NMHC in simulated exhaust gas - amount of NMHC in exhaust gas discharged from the oxidation section outlet after oxidation section reaction) / amount of NMHC in simulated exhaust gas) × 100%; the conversion rate of CO = ((amount of CO in simulated exhaust gas - amount of CO in exhaust gas discharged from the oxidation section outlet after oxidation section reaction) / amount of CO in simulated exhaust gas) × 100%;

[0084] The curve showing the change in oxygen concentration (volume content) in the exhaust gas of a simulated high-oxygen-content equivalent engine as a function of engine output power is shown below. Figure 1 The contents of NMHC and CO are approximately equivalent to those of oxygen; the temperature variation curves of the exhaust inlet in the oxidation section with engine output power and the temperature variation curves of the oxidation section with engine output power are shown below. Figure 2 (The temperature of the oxidation stage reaches over 800℃ (between 800 and 950℃), exceeding the conversion temperature window of TWC (350-700℃)); among which, Figure 2 The curves showing the temperature variation with engine output power in the oxidation section of Experiment 1 and Comparative Experiment 1 are shown. In the remaining experiments below, unless otherwise specified, the reaction temperature in the oxidation section is similar.

[0085] Comparative Experiment 1: The oxidation catalyst in the oxidation section was conventional TWC (the difference between it and the three-way catalyst in Example 1 is that the mass ratio of the noble metal to the volume of the second support is 40 g: 1 cubic foot, wherein the mass ratio of palladium to rhodium is 7:1). The reaction time (or aging time) of the oxidation catalyst in the oxidation section was controlled as follows: Figure 3The conversion rates of NMHC and CO (atmosphere concentration changes before and after oxidation catalyst were measured at 850℃) in the oxidation section were obtained as a function of the aging time of the oxidation section (at 950℃ on an engine bench) (see curves). Figure 3 The conversion efficiency decreases with increasing aging time, and after 300 hours of aging, the conversion efficiency decreases significantly.

[0086] Experiment 1: The oxidation catalyst of Example 1 was aged at 1050℃, and the aged catalyst was used as the oxidation catalyst in the oxidation section. Following the procedure of Experiment 1, the effect of the aged catalyst at 1050℃ for different times (from 110 to 830 hours) on the conversion rate of NMHC and CO was measured. The curves showing the change in the conversion rate of NMHC and CO (with changes in atmosphere concentration before and after the oxidation catalyst were measured at 850℃) as a function of aging time were obtained (see...). Figure 4 As can be seen, the conversion rate of NMHC to CO is high and tends to stabilize with increasing aging time, indicating that the above-mentioned oxidation catalyst has good aging resistance.

[0087] Experiment 2: After aging the oxidation catalyst from Example 1 at 1050℃ for 830 hours, the aged catalyst was used as the oxidation catalyst in the oxidation stage; the reaction temperature of the oxidation stage was controlled as follows: Figure 5 and Figure 6 The concentration of NOx in the purified exhaust gas and the NOx conversion rate (the ratio of the amount of NOx in the purified exhaust gas to the amount of NOx in the simulated exhaust gas before entering the oxidation section) of the catalyst system (catalyst in the oxidation section + catalyst in the three-way converter section) were measured as a function of reaction temperature. (See the curves below.) Figure 5 and Figure 6 The oxidation catalyst has stable performance after aging at 1050℃ for 830 hours. The NOx concentration in the exhaust gas after purification by the catalyst system (catalyst in the oxidation section + catalyst in the three-way conversion section) is <5ppm, which meets the emission requirements.

[0088] Comparative Experiment 2: The TWC from Comparative Experiment 1 was aged at 950℃ for 300 hours. The aged TWC was used as a catalyst in the oxidation stage. The reaction temperature of the oxidation stage was controlled as follows: Figure 5 and Figure 6 The concentration of NOx in the purified exhaust gas and the NOx conversion rate (the ratio of the change in NOx in the exhaust gas before and after treatment by the catalyst system to the amount of NOx in the simulated exhaust gas before entering the oxidation section) were measured as a function of reaction temperature. (See the curves below.) Figure 5 and Figure 6 Compared with Experiment 1, TWC showed significant performance degradation after aging at 950℃ for 300 hours. The NOx concentration after purification by the catalyst system (catalyst in the oxidation section + catalyst in the three-way conversion section) was >15ppm, which is higher than the emission requirement (<5ppm).

[0089] Experiment 3

[0090] The difference from Experiments 1 and 2 is that there are two oxidation sections in Experiment 3, namely oxidation section A and oxidation section B. Oxidation section B is located upstream of oxidation section A (that is, the engine exhaust is first treated by the oxidation catalyst in oxidation section B and then by the oxidation catalyst in oxidation section A). Oxidation section A is the same as the oxidation section in Experiments 1 or 2 above (that is, it is equivalent to adding an oxidation section B upstream of the oxidation section in Experiments 1 or 2). The ratio of the mass of palladium to the volume of the first carrier in the oxidation catalyst of oxidation section B is 3 grams: 1 cubic foot. The other conditions are the same as those of oxidation section A.

[0091] The experiment was conducted following the procedure of Experiment 2. The exhaust inlet temperature of oxidation section B, the temperature of the oxidation catalyst in oxidation section B, and the exhaust outlet temperature of oxidation section B were measured as a function of engine power. (See the curves for the curves.) Figure 7 The curves showing the changes in oxygen concentration at the exhaust inlet and outlet of oxidation section B with engine power are shown below. Figure 8 The oxidation catalyst in oxidation section B partially oxidizes the reducing agent in the exhaust gas and consumes some of the oxygen in the exhaust gas. This can effectively weaken the redox reaction of the exhaust gas on the oxidation catalyst in downstream oxidation section A and reduce the temperature rise of the catalyst that generates heat due to the redox reaction.

[0092] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A three-way catalytic converter system for exhaust gas purification treatment of equivalent operating engines, characterized in that, It includes an oxidation section containing a high-temperature resistant oxidation catalyst and a three-way conversion section containing a three-way catalyst. The oxidation catalyst is used to catalyze the oxidation reaction between reducing components in the exhaust gas and oxygen. The oxidation section is located downstream of the engine, and the three-way conversion section is located downstream of the oxidation section. The oxidation catalyst comprises a first alumina-based material and a noble metal, wherein the noble metal is supported on the first alumina-based material; The first alumina-based material is prepared according to the following steps: Alumina raw material is aged at 1000℃~1500℃ for at least 2 hours to cause the easily collapsible pores to collapse, thereby obtaining the first alumina-based material. The specific surface area of ​​the first alumina-based material after aging at 1200±100℃ for 4±0.5 hours is not less than 60 m². 2 / g; The three-way catalyst includes a porous matrix material, an oxygen storage material, and a precious metal. The porous matrix material includes a second alumina-based material, and the precious metal includes rhodium. The oxygen storage material can adjust the air-fuel ratio λ within a preset range to reduce the deviation of the actual air-fuel ratio λ from λ=1. The precious metal rhodium is loaded on the oxygen storage material, and the oxygen storage material is spaced between the precious metal rhodium and the porous matrix material.

2. The three-way catalytic conversion system according to claim 1, characterized in that, Satisfying at least one of the following characteristics: The noble metal loaded on the first alumina-based material includes palladium. The specific surface area of ​​the first alumina-based material is 130–180 m². 2 / g; The pore volume of the first alumina-based material is 0.8 cc / g to 1.2 cc / g; The first alumina-based material includes γ-alumina.

3. The three-way catalytic conversion system according to claim 1, characterized in that, The first alumina-based material contains rare earth elements, and the mass content of rare earth elements in the first alumina-based material is 0-7%.

4. The three-way catalytic conversion system according to claim 1, characterized in that, The mass content of the noble metal in the oxidation catalyst is 0.06% to 1.0%.

5. The three-way catalytic conversion system according to claim 1, characterized in that, The number of oxidation segments is at least two, and the distance between any two adjacent oxidation segments is not less than 150 mm.

6. The three-way catalytic conversion system according to any one of claims 1-5, characterized in that, The oxidation section includes a first support and a first active layer located on the surface of the first support, wherein the oxidation catalyst is present in the first active layer.

7. The three-way catalytic conversion system according to claim 6, characterized in that, The first active layer further comprises a binder and / or a modifying agent, and satisfies at least one of the following characteristics: The adhesive includes aluminum glue and / or silicone; The modifying agent includes cerium materials and / or zirconium materials; The oxidation catalyst in the first active layer has a mass content of 85%-98%, with the remainder being the binder and / or modifying agent.

8. The three-way catalytic conversion system according to claim 6, characterized in that, The material forming the first carrier includes at least one of ceramics and metals.

9. The three-way catalytic conversion system according to claim 6, characterized in that, The ratio of the mass of the noble metal in the oxidation catalyst to the volume of the first support is (3-50) grams: 1 cubic foot.

10. The three-way catalytic conversion system according to claim 6, characterized in that, The ratio of the mass of the first active layer to the volume of the first carrier is (100-200) grams: 1 liter.

11. The three-way catalytic conversion system according to claim 1, characterized in that, The three-way conversion section further includes a second support and a second active layer located on the surface of the second support, wherein the three-way catalyst is present in the second active layer.

12. The three-way catalytic conversion system according to claim 11, characterized in that, The second active layer further comprises a binder and / or a modifying agent, and satisfies at least one of the following characteristics: The adhesive includes aluminum glue and / or silicone; The modifying agent includes cerium materials and / or zirconium materials; The mass content of the three-way catalyst in the second active layer is 85%-98%, with the remainder being the binder and / or modifying agent.

13. The three-way catalytic conversion system according to claim 1, characterized in that, The oxygen storage material is filled in the porous matrix material, the rhodium is loaded on the oxygen storage material, and the precious metals other than rhodium are loaded on the porous matrix material or on the oxygen storage material.

14. The three-way catalytic conversion system according to claim 1 or 13, characterized in that, The oxygen storage material includes CeZrO.

15. The three-way catalytic conversion system according to claim 1, characterized in that, Satisfying at least one of the following characteristics: The specific surface area of ​​the second alumina-based material is 130 m². 2 / g~240m 2 / g; The specific surface area of ​​the second alumina-based material after aging at 1200±100℃ for 4±0.5 hours is not less than 40 m². 2 / g; The second alumina-based material includes γ-alumina and / or θ-alumina.

16. The three-way catalytic conversion system according to claim 1 or 15, characterized in that, The pore volume of the second alumina-based material is less than 0.8 cc / g.

17. The three-way catalytic conversion system according to claim 16, characterized in that, The pore volume of the second alumina-based material is 0.4cc / g to 0.8cc / g.

18. The three-way catalytic conversion system according to claim 1 or 15, characterized in that, The second alumina-based material contains rare earth elements, and the mass content of the rare earth elements in the second alumina-based material is 3% to 7%.

19. The three-way catalytic conversion system according to claim 11, characterized in that, The material forming the second carrier includes at least one of ceramics and metals.

20. The three-way catalytic conversion system according to claim 1 or 13, characterized in that, The three-way conversion section further includes a second support and a second active layer located on the surface of the second support, wherein the three-way catalyst is present in the second active layer; the mass ratio of the noble metal in the three-way catalyst to the volume of the second support is (3-50) grams: 1 cubic foot.

21. The three-way catalytic conversion system according to claim 1 or 13, characterized in that, The three-way catalyst further includes platinum and / or palladium, satisfying the following conditions: the mass ratio of rhodium to platinum is 1:0 to 15; and / or, the mass ratio of rhodium to palladium is 1:2 to 15.

22. The application of the three-way catalytic converter system according to any one of claims 1-21 in engine exhaust purification treatment.

23. The application according to claim 22, characterized in that, The engine exhaust includes high-oxygen engine exhaust, wherein the oxygen volume content of the high-oxygen engine exhaust is not less than 1%.

24. The application according to claim 22 or 23, characterized in that, The engine exhaust includes the exhaust from the equivalent operating engine.

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