Diesel vehicle multifunctional catalyst and preparation method thereof

Abstract

The invention discloses a multifunctional catalyst for a diesel vehicle and a preparation method, and relates to the field of catalyst preparation, the multifunctional catalyst for the diesel vehicle comprises a precious metal coating and an SCR coating which are arranged in a layered mode, and the SCR coating is located above the precious metal coating; the SCR coating is of a sectional structure and comprises an SCR coating front section and an SCR coating rear section. The problems that an existing catalyst is low in NOx efficiency during cold start, coating regeneration after HC / SO2 poisoning cannot be achieved at the same time, low N2O selectivity cannot be ensured, and unreacted NH3 cannot be treated at the same time are solved, by means of the layered and sectional type coating structure design, diesel oil or other hydrocarbon fuel sprayed backwards by a system can be rapidly oxidized through the bottom layer precious metal coating, reaction heat is generated, and the catalyst can be recycled. The temperature of the whole catalyst is increased, adsorbed HC and sulfide are oxidized and removed, and the SCR activity is recovered. And unreacted NH3 can be treated, so that the arrangement space of a post-treatment catalyst is saved. The upper-layer sectional type coating structure not only can efficiently convert NOx at a low temperature, but also can keep relatively low N2O selectivity.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation technology, specifically to a multifunctional catalyst for diesel vehicles and its preparation method. Background Technology

[0002] Selective catalytic reduction of ammonia (NH3-SCR) is a NO... x Emission reduction technologies can be used to reduce NO emissions from diesel vehicle exhaust. x Emission targets. With the next phase of NO x With increasingly stringent emission limits, traditional after-treatment routes (DOC+cDPF+SCR+ASC) are struggling to meet the requirements. This is because traditional SCR catalytic converters are typically located in the vehicle chassis, far from the engine. Exhaust gas travels a long pipeline from the engine to the SCR, resulting in significant heat loss. Especially during cold starts, the engine exhaust temperature is already low, and after the long distance for heat dissipation, the temperature reaching the SCR is very low, far below the ignition temperature required by the SCR catalyst. Furthermore, cold-start NO... x Emissions account for a large proportion of the entire test cycle.

[0003] In response to the above situation, in order to meet the requirements for ultra-low nitrogen oxide emissions and solve the problem of cold start NO... x The problem is that aftertreatment systems often employ a dual-injection route: cc-SCR + cc-ASC + DOC + cDPF + SCR + ASC, meaning they are equipped with dual SCR catalysts and dual urea injection devices. Depending on the distance between the catalyst and the engine, they are named close-coupled SCR (cc-SCR) and chassis-type SCR. This layout means that the cc-SCR catalyst heats up faster, enabling earlier NO activation. x Conversion. However, this also means that the environment of cc-SCR catalysts differs significantly from that of conventional downstream SCRs. As the first catalyst, cc-SCR is located near the engine outlet and is exposed to leaked HC compounds and sulfur oxides for extended periods. HC compounds and NO x Competitive adsorption occurs, and HC is easily oxidized to form coke deposits, covering active sites and acid sites, leading to decreased activity. Sulfur oxides react with NH3 to form ammonium sulfate, covering active sites and clogging pores, reducing catalyst activity and requiring regeneration at 500℃ for desulfurization. Furthermore, sulfur oxides can react with Cu at active sites to form copper sulfate, further reducing activity and requiring regeneration at 600℃ or even higher. Although HC compounds and sulfur oxides do not affect the molecular sieve structure, they reduce the activity of the cCSCR catalyst, impacting final emissions.

[0004] Based on this, CN201880038081.0 discloses catalytic products and waste gas treatment systems, pointing out that modified SCRs, in addition to reducing NO, also have the ability to reduce NO.x Beyond its functional benefits, it can significantly reduce hydrocarbon escape from upstream oxidation catalyst (DOC) by oxidizing HC compounds, thus raising the SCR outlet temperature to approximately 500°C. However, while the modified SCR prepared by this patent meets the conditions for SCR coating activity recovery after HC poisoning, it does not meet the requirements for deep desulfurization of the SCR coating (>600°C), and further improvements in fuel ignition capability are needed. The SCR layout in this patent is not the first catalyst; upstream of it is a DOC catalyst, which oxidizes some NO to NO2, promoting a fast SCR reaction and improving the low-temperature NO reduction of the SCR coating. x Efficiency. Nevertheless, its 204℃ NO x The conversion rate was only about 71% (approximately 100 Kh⁻¹ space velocity, 1.1 ammonia-to-nitrogen ratio), indicating significantly low activity at low temperatures. Furthermore, this treatment system is designed to oxidize hydrocarbons (HC) but not NH₃, showing no ability to oxidize NH₃; therefore, an ASC catalyst needs to be added later.

[0005] Patent CN202180041983.1 discloses an exhaust gas treatment system including a multifunctional catalyst to treat NO in exhaust gas. x This catalyst effectively prevents HC compounds leaking from DOC from escaping and coking. It comprises a noble metal coating and an SCR coating. The noble metal coating contains platinum group metals, especially palladium, while the SCR coating contains zeolite materials supported on Cu and / or iron. The noble metal coating and SCR coating have a layered structure, forming an MFC catalyst. However, this patent still has the following problems: although the MFC catalyst meets the conditions for SCR coating activity recovery after HC poisoning, it does not meet the requirements for deep desulfurization of the SCR coating (>600℃), and further improvements in fuel ignition capability are needed. This patented MFC layout is not the first catalyst; upstream of it is a DOC catalyst, which oxidizes some NO to NO2, promoting the fast SCR reaction and improving the low-temperature NO reduction of the SCR coating. x Efficiency. This patent does not contain low-temperature NO. x The efficiency results show a minimum test temperature of 290℃. Furthermore, this patent is for oxidizing hydrocarbons; whether it oxidizes NH3 is unknown.

[0006] Therefore, this application is hereby submitted. Summary of the Invention

[0007] This invention provides a multifunctional catalyst for diesel vehicles and its preparation method, which can solve the problem of NO during cold start. x It addresses the issue of low efficiency, enables coating regeneration after HC / SO2 poisoning, ensures low N2O selectivity, and can also handle unreacted NH3.

[0008] This invention is achieved through the following technical solution: In a first aspect, the present invention provides a multifunctional catalyst for diesel vehicles, comprising a layered noble metal coating and an SCR coating, wherein the SCR coating is located above the noble metal coating; wherein the noble metal coating comprises a carrier material and a noble metal loaded on the carrier material; the SCR coating adopts a segmented structure, wherein the front segment of the SCR coating is a first molecular sieve coating and a first active component or a vanadium-based coating loaded on the first molecular sieve coating; and the rear segment of the SCR coating is a second molecular sieve coating and a second active component loaded on the second molecular sieve coating.

[0009] Specifically, in this application, in order to simultaneously achieve NO x To address the issues of reduced emissions, HC / SO2 poisoning, coating regeneration, and NH3 oxidation, a layered structure is employed. The bottom layer, a noble metal coating, possesses excellent fuel ignition capability, primarily rapidly oxidizing diesel or other hydrocarbon fuels (HC) injected after the system, generating heat of reaction to raise the overall catalyst temperature. This, in turn, oxidizes and removes adsorbed HC and sulfides, restoring SCR activity. The upper layer features a segmented coating structure, with the front section preferentially removing some NO... x It is efficiently converted to N2 while maintaining extremely low N2O selectivity, and unreacted NO... x NH3 continues to flow to the later stage. The later stage has excellent low-temperature NO. x Activity ensures high conversion efficiency of the entire system under conditions such as cold start, achieving low-temperature NO x It achieves a combination of high efficiency and low N2O byproduct. Furthermore, the bottom layer, as a precious metal coating, can oxidize unreacted NH3 from the upper SCR coating into N2 and H2O.

[0010] The multifunctional catalyst (MFC) of this invention adds oxidation functionality to CCSCR, thus possessing SCR coating capabilities to remove NO. x Besides reducing it to N2, the SCR coating can also be regenerated by providing heat through oil injection oxidation, thereby restoring its activity. Simultaneously, since MFC has oxidation capabilities, it can also oxidize unreacted NH3 into N2 and water, thus optimizing the aftertreatment route to MFC+DOC+cDPF+SCR+ASC, saving space for the aftertreatment catalyst arrangement.

[0011] As one of the optional implementation methods, the ratio of the front and rear sections of the SCR coating is 1:4 to 4:1.

[0012] Experiments have shown that when the ratio of the front and rear sections of the SCR coating in this invention is 1:1, the catalyst MFC performance is optimal.

[0013] As one of the optional embodiments, the carrier material includes any one of Al2O3, SiO2-Al2O3, and CeO2-Al2O3.

[0014] As one optional implementation, the total content of the precious metal is 3-10 g / ft. 3 The precious metals are Pt and Pd; the mass ratio of Pt and Pd is (5-10):(1-5).

[0015] In this scheme, the underlying precious metal coating is preferably Pt-based.

[0016] Experiments showed that the total precious metal content of this invention is 8 g / ft. 3 When the mass ratio of Pt to Pd is 8:1, the catalyst MFC performance is optimal.

[0017] As one of the optional embodiments, the first molecular sieve coating and the second molecular sieve coating are any one or a combination of at least two of Beta, ZSM-5, CHA, AEI, FAU, LTA, and AFX; wherein the molar ratio of silica to alumina in the first and second molecular sieves in the coating is 5 to 25:1.

[0018] As one of the optional embodiments, the first active component includes at least one of Cu ions and Fe ions, wherein the Cu ions and / or Fe ions account for 2.0 wt% to 5.0 wt% of the mass of the first molecular sieve coating.

[0019] As one of the optional embodiments, the second active component includes Cu ions, wherein the Cu ions account for 3.0 wt% to 6.0 wt% of the mass of the second molecular sieve coating.

[0020] As one of the optional embodiments, the vanadium-based coating comprises TiO2 and vanadium oxide supported on TiO2, wherein vanadium accounts for 2.0 wt% to 5.0 wt% of the total mass of TiO2.

[0021] As one of the optional embodiments, the loading of the precious metal coating is 40-80 g / L, the loading of the front section of the SCR coating is 120-200 g / L, and the loading of the rear section of the SCR coating is 100-180 g / L.

[0022] Secondly, the present invention also provides a method for preparing a multifunctional catalyst for diesel vehicles, comprising the following steps: Preparation of precious metal coating slurry: Mix precious metal solution, carrier material and deionized water, stir evenly and then add binder. After ball milling evenly, the precious metal coating slurry is obtained. Preparation of SCR coating front-end slurry includes two methods: The first method involves loading the first active ingredient onto the first molecular sieve coating material, followed by filtration, washing, drying, and calcination, then adding a binder and deionized water, and ball milling to obtain the SCR coating front-end slurry; The second method involves mixing a vanadium precursor solution, TiO2 support material, and deionized water (containing 2.0 wt% vanadium) using existing methods, stirring until homogeneous, then adding additives and a binder to obtain the front-end vanadium-based coating slurry. Preparation of SCR coating post-stage slurry: The second active ingredient is loaded onto the second molecular sieve coating material, and after filtration, washing, drying and calcination, binder and deionized water are added and mixed. After ball milling, the SCR coating post-stage slurry is obtained. First, a precious metal coating slurry is coated onto a cordierite carrier, and then dried and calcined to obtain a precious metal coating. The SCR coating front-end slurry and the SCR coating back-end slurry were sequentially coated onto the cordierite monolithic carrier according to the segment ratio, and then dried and calcined to obtain the MFC catalyst.

[0023] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. By employing a layered structure, the precious metal coating exhibits excellent fuel ignition capability, primarily by rapidly oxidizing diesel or other hydrocarbon fuels (HC) injected after the system, generating heat of reaction to raise the overall catalyst temperature. This, in turn, oxidizes and removes adsorbed HC and sulfides, restoring SCR activity. This allows the catalyst to simultaneously possess NO... x It can handle reduction function and coating regeneration ability and NH3 oxidation ability after HC / SO2 poisoning.

[0024] 2. The SCR coating adopts a segmented coating structure, with the front segment prioritizing the removal of some NO. x It is efficiently converted to N2 while maintaining extremely low N2O selectivity, and unreacted NO... x NH3 continues to flow to the later stage. The later stage has excellent low-temperature NO. x Activity ensures high conversion efficiency of the entire system under conditions such as cold start, achieving low-temperature NO x It achieves a combination of high efficiency and low N2O byproduct. Furthermore, the bottom layer, as a precious metal coating, can oxidize unreacted NH3 from the upper SCR coating into N2 and H2O. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. The illustrative embodiments and descriptions of this invention are only used to explain this invention and are not intended to limit this invention.

[0026] 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.

[0027] 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.

[0028] 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 article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. Example 1

[0029] This embodiment 1 discloses the preparation of a multifunctional catalyst (MFC) for diesel vehicles, comprising the following steps: Preparation of the underlying precious metal coating slurry: A Pt solution and a Pd solution (with a total Pt and Pd content of 8 g / ft) are applied using an excess impregnation method. 3The mixture of Pt:Pd=3:1, SiO2-Al2O3 material and deionized water is thoroughly mixed. After stirring evenly, the binder is added, and the mixture is ball-milled evenly to obtain the bottom noble metal coating slurry.

[0030] Preparation of the upper SCR coating slurry: Copper nitrate solution (containing 5.0 wt% Cu) was loaded onto SSZ-13 material (molar ratio of silicon oxide to aluminum oxide is 22) by ion exchange method. After filtration and washing, it was dried at 100℃. After drying, it was calcined at 500℃ for 3 hours in air atmosphere to obtain molecular sieve SCR coating. The molecular sieve SCR coating, binder and deionized water were mixed and ball-milled to obtain SCR coating slurry.

[0031] The bottom layer of noble metal coating slurry was applied to a ceramic support with a size of "1in*3in" and a pore density of 400 mesh at a loading of 75 g / L. After drying at 80°C, the top layer of SCR coating slurry was applied to the ceramic support containing the noble metal layer at a loading of 140 g / L. After drying at 80°C, the mixture was calcined at 500°C for 2 hours in a muffle furnace to obtain the MFC catalyst, which was designated as S1.

[0032] The idea behind this embodiment is to cover the underlying coating with an SCR coating.

[0033] Comparative Example 1 This comparative example is modified based on Example 1. The preparation steps of this example are basically the same as those of Example 1, except that the SCR coating slurry of Example 1 is used as the bottom layer and the noble metal slurry of Example 1 is used as the top layer. The resulting MFC catalyst is denoted as B1.

[0034] Comparative Example 2 This comparative example is modified based on Example 1. The preparation steps of this example are basically the same as those of Example 1. The difference is that the SCR coating and noble metal slurry of Example 1 are mixed according to the loading ratio of Example 1 to prepare a single-layer catalyst. The resulting MFC catalyst is denoted as B2.

[0035] Comparative Example 3 This comparative example is a modification of Example 1. The preparation steps of this example are basically the same as those of Example 1, except that: there is no noble metal coating as in Example 1, only an SCR coating, and the resulting SCR catalyst is denoted as B3.

[0036] The catalysts prepared in Example 1 and Comparative Examples 1-3 were subjected to NO treatment in a fixed-bed reactor. x Conversion efficiency test: The simulated gas composition during the test was: [NO x[NH3] = 500ppm, [O2] = 10%, [H2O] = 7%, N2 is used as the balance gas, and the space velocity is 60000h. -1 The reaction temperatures were 175℃, 200℃, 225℃, 250℃, and 300℃. The catalytic activity results for Example 1 and Comparative Examples 1-3 are shown in Table 1 below: Table 1:

[0037] Analysis of the above experimental results shows that: the catalyst with a layered structure design in Example 1 exhibits good low-temperature NO production. x The conversion efficiency is comparable to that of a single SCR catalyst (Comparative Example 3). It is known that the purpose of adding noble metals is to enable the catalyst to have oxidation capabilities, while NO... x The conversion requires a reduction function. Compared to Comparative Examples 1 and 2, the solution in Example 1 (with the addition of precious metals) showed better results regarding NO. x The efficiency impact was minimal and comparable to that of Comparative Example 3. Examples 1 and Comparative Examples 1-3 aimed to determine the catalyst coating structure.

[0038] Therefore, this invention selects a layered structure with a noble metal coating as the bottom layer and an SCR coating as the top layer. Example 2

[0039] Example 2 discloses the preparation of a multifunctional catalyst (MFC) for diesel vehicles, comprising the following steps: The preparation steps for the precious metal coating slurry are the same as those in Example 1.

[0040] Furthermore, the SCR coating has a segmented structure, divided into two sections along the exhaust gas flow direction. The preparation of the SCR coating front section slurry involves loading a copper nitrate solution (containing 4.0 wt% Cu) onto SSZ-13 material (silicon oxide to aluminum oxide molar ratio of 1:2) via ion exchange, filtering, washing, and drying at 100°C. After drying, it is calcined at 500°C for 3 hours in air to obtain the first molecular sieve SCR coating. The first molecular sieve SCR coating, binder, and deionized water are mixed and ball-milled to obtain the upper SCR coating front section slurry. The SCR coating front section employs a low N2O selectivity scheme and is coated at the catalyst inlet end to ensure that NO2O is low within the main operating temperature range. x It is efficiently reduced to N2, thus suppressing the formation of the byproduct N2O to the greatest extent.

[0041] Preparation of the SCR coating post-stage slurry: Copper nitrate solution (containing 5.0 wt% Cu) was loaded onto SSZ-13 material (molar ratio of silicon oxide to aluminum oxide is 2:2) via ion exchange, where SSZ-13 is a type of CHA; after filtration and washing, it was dried at 100℃, and after drying, it was calcined at 500℃ for 3 hours in air atmosphere to obtain the second molecular sieve SCR coating; the second molecular sieve SCR coating, binder and deionized water were mixed and ball-milled to obtain the SCR coating post-stage slurry; The SCR coating section is a low-temperature, high-activity NO. x The conversion efficiency scheme involves coating the catalyst outlet end to reduce unreacted NO in the upstream stage. x Entering this segment, NO can also be effectively captured and reduced, achieving low-temperature NO x Highly efficient conversion.

[0042] A precious metal coating slurry was coated onto a cordierite support (the precious metal coating was located at the bottom layer) with a loading of 75 g / L. After drying and calcination, an SCR coating slurry (the SCR coating was located at the top layer) was then coated onto the cordierite support in a 1:1 ratio between the front and rear sections. The loading of the front section was 140 g / L and the loading of the rear section was 100 g / L. The resulting MFC catalyst was designated as S2. Example 3

[0043] Example 3 discloses the preparation of a multifunctional catalyst (MFC) for diesel vehicles, comprising the following steps: The preparation steps for the precious metal coating slurry are the same as those in Example 1.

[0044] Preparation of SCR coating front-end slurry: Vanadium precursor solution, TiO2 carrier material and deionized water (containing 2.0 wt% vanadium element) are mixed by excess impregnation method, and after stirring evenly, additives and binders are added. After ball milling evenly, the front-end vanadium-based coating slurry is obtained. The preparation steps for the SCR coating post-stage slurry are the same as those in Example 2.

[0045] A precious metal coating slurry was coated onto a cordierite support at a loading of 75 g / L. After drying and calcination, an SCR coating slurry was then coated onto the cordierite support in a 1:1 ratio between the front and rear sections, with a loading of 140 g / L for the front section and 100 g / L for the rear section. The resulting MFC catalyst was designated as S3. Example 4

[0046] Example 4 discloses the preparation of a multifunctional catalyst (MFC) for diesel vehicles, comprising the following steps: The preparation steps for the precious metal coating slurry are the same as those in Example 1.

[0047] Preparation of SCR coating front-end slurry: Ferric nitrate solution (containing 3.0 wt% Cu) was loaded onto Beta material by ion exchange, filtered, washed, and dried at 100℃. After drying, it was calcined at 500℃ for 3 hours in air to obtain molecular sieve SCR coating. The molecular sieve SCR coating, binder, and deionized water were mixed and ball-milled to obtain the upper SCR coating front-end slurry. The preparation steps for the SCR coating post-stage slurry are the same as those in Example 2.

[0048] A precious metal coating slurry was coated onto a cordierite support at a loading of 75 g / L. After drying and calcination, an SCR coating slurry was then coated onto the cordierite support in a 1:1 ratio between the front and rear sections, with a loading of 140 g / L for the front section and 100 g / L for the rear section. The resulting MFC catalyst was designated as S4. Example 5

[0049] This embodiment is a modification of embodiment 4, the difference being that the ratio of the front and rear sections of the SCR coating in embodiment 4 is set to 1:4, and the resulting MFC catalyst is denoted as S5. Example 6

[0050] This embodiment is a modification of embodiment 4, the difference being that the ratio of the front and rear sections of the SCR coating in embodiment 4 is set to 4:1, and the resulting MFC catalyst is denoted as S6.

[0051] The results of each embodiment under the simulated gas test conditions described above are shown in Tables 2-4: Table 2:

[0052] Table 3:

[0053] Table 4:

[0054] The experimental results in Tables 2, 3 and 4 show that Example 1 did not have SCR coating segmentation, and its N2O generation was relatively high. In addition, in Example 4, when the SCR coating front section is an Fe-based molecular sieve catalyst, and the front and rear section ratio is set to 1:1, it exhibits excellent low-temperature NO reduction. x Conversion efficiency and low N2O generation.

[0055] Comparing Examples 1-6, it can be seen that the SCR coating adopts a segmented structure, which allows for high NO content... x While achieving high conversion rates, it also generates relatively low amounts of N2O. Example 7

[0056] This embodiment is a modification of Example 4, and the preparation steps are roughly the same as in Example 4. The difference is that the total content of the noble metals Pt and Pd in ​​Example 4 is changed to 3 g / ft. 3 The resulting MFC catalyst is denoted as S7. Example 8

[0057] This embodiment is a modification of Example 4, and the preparation steps are roughly the same as in Example 4. The difference is that the total content of the precious metals Pt and Pd in ​​Example 4 is changed to 5 g / ft. 3 The resulting MFC catalyst is denoted as S8.

[0058] Comparative Example 4: This embodiment is a modification of Example 4, and the preparation steps are roughly the same as in Example 4. The difference is that the total content of the noble metals Pt and Pd in ​​Example 4 is changed to 12 g / ft. 3 The resulting MFC catalyst is designated as B4.

[0059] The results of each embodiment under the simulated gas test conditions described above are shown in Tables 5-7: Table 5:

[0060] Table 6:

[0061] Table 7:

[0062] Based on the combined experimental results in Tables 5, 6, and 7, it can be concluded that the total content of Pt and Pd in ​​Example 4 is 8 g / ft. 3 At that time, low temperature NO x It has the best overall performance in terms of conversion efficiency, N2O generation, and NH3 leakage.

[0063] The above-described embodiments and comparative examples were prepared using a carrier with dimensions Φ266.7*127 / 400-4, and bench fuel ignition performance was tested at a space velocity of 60,000 h⁻¹. -1 The engine MFC inlet temperature was controlled at 300℃, diesel fuel was injected afterward, and the MFC outlet temperature was recorded. The experimental results are shown in Table 8. Table 8:

[0064] Based on the experimental results in Tables 5-8, it can be seen that the MFC outlet temperature in Example 4 can reach 520℃ after fuel ignition. Comparative Example 4 shows the best performance in terms of NH3 leakage and MFC outlet temperature, indicating that increasing the precious metal content can improve this performance. However, as shown in Tables 5 and 6, Comparative Example 4 shows that NO at 300℃... x Efficiency has decreased significantly, and N2O has increased substantially, posing a considerable risk in practical applications. Example 9

[0065] This embodiment is a modification of Example 4, and the preparation steps are roughly the same as those in Example 4. The difference is that the ratio of noble metals Pt and Pd in ​​Example 4 is changed to 6:1, and the resulting MFC catalyst is denoted as S9.

[0066] This embodiment is a modification of Example 4, and the preparation steps are roughly the same as those in Example 4. The difference is that the ratio of noble metals Pt and Pd in ​​Example 4 is changed to 8:1, and the resulting MFC catalyst is denoted as S10.

[0067] Comparative Example 5: This embodiment is a modification of Example 4, and the preparation steps are roughly the same as those in Example 4. The difference is that the ratio of noble metals Pt and Pd in ​​Example 4 is changed to 1:8, and the resulting MFC catalyst is denoted as B5.

[0068] Based on the above simulated gas test conditions and bench fuel ignition test conditions, the results of each embodiment are shown in Tables 9-12: Table 9:

[0069] Table 10:

[0070] Table 11:

[0071] Table 12:

[0072] Combining Tables 9, 10, 11, and 12, it can be concluded that Example 10 has better NO content. x It exhibits high conversion efficiency, low N2O selectivity, and low NH3 leakage, along with excellent fuel oil ignition capability. The MFC outlet temperature can reach 610℃, meeting the 600℃ requirement for deep desulfurization with SCR coating. Comparative Example 5, on the other hand, shows higher NH3 leakage, posing a safety hazard in practical applications.

[0073] As can be seen from the above embodiments and comparative examples, the coating structure affects NO. xConversion rate; layered coating design can maintain the SCR coating's superior low-temperature NO content. x Performance. The segmented design of the upper SCR coating allows for higher NO content. x While achieving high conversion efficiency, it also exhibits low N2O generation. Furthermore, the content and proportion of precious metals also affect the function of the SCR coating and the fuel ignition capability. When the MFC underlayer is a precious metal coating, the total content of precious metals Pt and Pd is 8 g / ft. 3 Furthermore, when the Pt to Pd ratio is 8:1, the SCR coating consists of an Fe-based molecular sieve coating at the front and a Cu-based molecular sieve coating at the rear, with a 1:1 ratio between the front and rear sections, low-temperature NO x It achieves optimal efficiency, NH3 leakage and N2O selectivity. Meanwhile, through oil injection, the MFC outlet temperature can reach 610℃, meeting the regeneration conditions after catalyst poisoning by HC and sulfur oxides.

[0074] 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 multi-functional catalyst for diesel vehicles, characterized in that, The system comprises a layered noble metal coating and an SCR coating, with the SCR coating located above the noble metal coating. The noble metal coating includes a carrier material and a noble metal loaded on the carrier material, wherein the noble metal in the bottom layer of the noble metal coating is Pt and Pd. The SCR coating adopts a segmented structure, wherein the front section of the SCR coating is a first molecular sieve coating and a first active component or vanadium-based coating loaded on the first molecular sieve coating; and the rear section of the SCR coating is a second molecular sieve coating and a second active component loaded on the second molecular sieve coating.

2. The multi-functional catalyst for diesel vehicles according to claim 1, characterized in that, The ratio of the front and rear sections of the SCR coating is 1:4 to 4:

1.

3. The multi-functional catalyst for diesel vehicles according to claim 1, characterized in that, The carrier material includes any one of Al2O3, SiO2-Al2O3, and CeO2-Al2O3.

4. The multi-functional catalyst for diesel vehicles according to claim 1, characterized in that, The total content of the precious metal is 3-10 g / ft. 3 The precious metals are Pt and Pd; the mass ratio of Pt and Pd is (5-10):(1-5).

5. The multi-functional catalyst for diesel vehicles according to claim 1, characterized in that, The first molecular sieve coating and the second molecular sieve coating are any one or a combination of at least two of Beta, ZSM-5, CHA, AEI, FAU, LTA, and AFX; wherein the molar ratio of silica to alumina in the first and second molecular sieves in the coating is 5 to 25:

1.

6. The multi-functional catalyst for diesel vehicles according to claim 1, characterized in that, The first active component includes at least one of Cu ions and Fe ions, wherein the Cu ions and / or Fe ions account for 2.0 wt% to 5.0 wt% of the mass of the first molecular sieve coating.

7. The multi-functional catalyst for diesel vehicles according to claim 1, characterized in that, The second active component includes Cu ions, wherein the Cu ions account for 3.0 wt% to 6.0 wt% of the mass of the second molecular sieve coating.

8. The multi-functional catalyst for diesel vehicles according to claim 1, characterized in that, The vanadium-based coating comprises TiO2 and vanadium oxide supported on TiO2, wherein vanadium accounts for 2.0 wt% to 5.0 wt% of the total mass of TiO2.

9. The multi-functional catalyst for diesel vehicles according to claim 1, characterized in that, The loading capacity of the precious metal coating is 40-80 g / L, the loading capacity of the front section of the SCR coating is 120-200 g / L, and the loading capacity of the rear section of the SCR coating is 100-180 g / L.

10. A method for preparing a multifunctional catalyst for diesel vehicles, characterized in that, Includes the following steps: Preparation of precious metal coating slurry: Mix precious metal solution, carrier material and deionized water, stir evenly and then add binder. After ball milling evenly, the precious metal coating slurry is obtained. Preparation of SCR coating front-end slurry includes two methods: The first method involves loading the first active ingredient onto the first molecular sieve coating material, followed by filtration, washing, drying, and calcination, then adding a binder and deionized water, and ball milling to obtain the SCR coating front-end slurry; The second method involves mixing the vanadium precursor solution, TiO2 support material, and deionized water using existing methods, stirring until homogeneous, then adding additives and a binder to obtain the front-end vanadium-based coating slurry. Preparation of SCR coating post-stage slurry: The second active ingredient is loaded onto the second molecular sieve coating material, and after filtration, washing, drying and calcination, binder and deionized water are added and mixed. After ball milling, the SCR coating post-stage slurry is obtained. First, a precious metal coating slurry is coated onto a cordierite carrier, and then dried and calcined to obtain a precious metal coating. The SCR coating front-end slurry and the SCR coating back-end slurry were sequentially coated onto the cordierite monolithic carrier according to the segment ratio, and then dried and calcined to obtain the MFC catalyst.

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