A molecular sieve monolithic catalyst, a method for preparing the same, and a method for treating exhaust gas of an internal combustion engine

Abstract

The present application belongs to the technical field of catalysts, and particularly relates to a molecular sieve monolithic catalyst, a preparation method thereof and a method for treating exhaust gas of an internal combustion engine. The molecular sieve monolithic catalyst comprises a honeycomb carrier, a continuous molecular sieve layer crystallized on the surface of the carrier, and a platinum group metal active component loaded on the molecular sieve layer. The catalyst provided by the present application solves at least one of the problems of a small specific surface area of an existing diesel oxidation catalyst, insufficient hydrocarbon adsorption capacity, and poor mechanical stability.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, and particularly relates to a molecular sieve monolithic catalyst, its preparation method, and a method for treating internal combustion engine exhaust gas. Background Technology

[0002] Diesel engines are widely used due to their high torque, fuel economy, and long durability, but their exhaust gases contain a large amount of harmful pollutants, especially hydrocarbons (HC). During the cold start phase, due to the low catalyst temperature, traditional diesel oxidation catalysts (DOC) have extremely low catalytic conversion efficiency for HC, resulting in the direct emission of large amounts of unburned HC, causing serious environmental pollution.

[0003] Existing diesel oxidation catalysts generally suffer from insufficient adsorption capacity when treating hydrocarbon emissions during the cold start phase, and the mechanical stability and long-term operational reliability of the catalyst structure need to be improved. Summary of the Invention

[0004] In view of the above problems, this application provides a molecular sieve monolithic catalyst, its preparation method, and a method for treating internal combustion engine exhaust gas. The catalyst provided by this invention solves at least one of the problems of existing diesel oxidation catalysts, such as small specific surface area, insufficient hydrocarbon adsorption capacity, and poor mechanical stability.

[0005] On one hand, the present invention provides a molecular sieve monolithic catalyst, comprising a honeycomb support, a continuous molecular sieve layer crystallized and bonded to the surface of the support, and a platinum group metal active component supported on the molecular sieve layer.

[0006] The catalyst provided by this invention has a continuous molecular sieve layer crystallized and bonded to the surface of a honeycomb carrier, forming an integrated composite structure with good mechanical strength and thermal stability. The synergistic configuration of the molecular sieve layer and the platinum group metal active components creates a large specific surface area and effective active sites, making it suitable for the adsorption, enrichment, and catalytic conversion of gaseous pollutants.

[0007] It should be noted that the continuous molecular sieve layer has a microporous crystal structure, and its thickness is less than the thickness of the carrier pore wall. This thickness design ensures that the molecular sieve layer has sufficient active sites while avoiding clogging the carrier's through-pores, reducing gas flow resistance while maintaining through-flow channels, and fully exposing the active regions.

[0008] Specifically, the molecular sieves in the continuous molecular sieve layer have an MFI topology, and the silica-to-alumina ratio of the molecular sieve is 20-100. The MFI topology has specific pore sizes (ten-membered rings) and acidic site distribution; the silica-to-alumina ratio of 20-100 gives the molecular sieve suitable acid strength and ion exchange capacity, and good adsorption and retention capacity and catalytic oxidation activity for hydrocarbons.

[0009] Preferably, the molecular sieve is a ZSM-5 molecular sieve. ZSM-5 molecular sieve has high thermal and hydrothermal stability.

[0010] For example, the cellular carrier is selected from one of cordierite cellular carrier, mullite cellular carrier, silicon carbide cellular carrier, quartz cellular carrier or alumina cellular carrier.

[0011] The honeycomb carrier has a through airflow channel and a geometric specific surface area; the thermal expansion coefficients of materials such as cordierite, mullite, and silicon carbide are matched with those of the molecular sieve layer, maintaining the integrity of the interface structure during temperature changes; among them, cordierite has a low thermal expansion rate and high thermal shock stability.

[0012] In one possible implementation, the honeycomb carrier is a cordierite honeycomb carrier.

[0013] Preferably, the platinum group metal is selected from at least one of Pt or Pd. The platinum group metal active component constitutes the catalytic oxidation active center, which can promote the oxidation reaction of hydrocarbons and carbon monoxide. Pt and Pd give the catalyst good low-temperature catalytic ignition activity, and the metal particles form a gas-solid phase catalytic reaction interface on the surface of the molecular sieve layer.

[0014] On the other hand, the present invention also provides a method for preparing a monolithic molecular sieve catalyst, which includes the following steps: (1) Seed preparation: The template agent and silicon source are mixed and crystallized in an ethanol-water solution to obtain a whole silicon molecular sieve seed solution; (2) Seed deposition: The honeycomb carrier is immersed in the seed solution obtained in step (1), and after ultrasonic treatment, drying and calcination, the carrier for seed deposition is obtained; (3) Hydrothermal growth: The carrier of the seed crystal obtained in step (2) is immersed in an alkaline ethanol-water solution containing silicon source, aluminum source, template agent and alkali source for crystallization. After washing, drying and calcination, a continuous aluminosilicate molecular sieve layer is formed on the surface of the carrier. (4) Active loading: The support after step (3) is immersed in a solution containing platinum group metals, and then dried and calcined to obtain a molecular sieve monolithic catalyst loaded with the platinum group metal active components.

[0015] This invention employs a two-stage growth method, involving seed deposition and hydrothermal growth in stages to construct a continuous molecular sieve layer in situ on the carrier surface, forming chemically bonded interfacial bonds. This preparation process achieves control over the nucleation sites of the molecular sieve layer, crystal orientation growth, and layer thickness regulation, ensuring that the final product maintains good structural uniformity and high interfacial bonding strength.

[0016] Specifically, the all-silicon molecular sieve seed crystal in step (1) is an all-silicon MFI type molecular sieve seed crystal; the aluminosilicate molecular sieve layer in step (3) is a ZSM-5 molecular sieve layer.

[0017] Preferably, the all-silicon MFI molecular sieve seed crystal is Silicalite-1 (S-1) seed crystal.

[0018] For example, the silicon source in steps (1) and (3) is independently selected from at least one of sodium silicate, silica hydrogel and tetraethyl orthosilicate; the aluminum source in step (3) is sodium aluminate; and the platinum group metal in step (4) is selected from at least one of Pt or Pd.

[0019] All-silicon MFI seed crystals serve as crystal structure templates, promoting the epitaxial growth of molecular sieves on the support surface. Sodium silicate, silica hydrogel, tetraethyl orthosilicate, and other silicon sources provide silicon monomers, while sodium aluminate provides the framework aluminum. Under hydrothermal condensation conditions, an aluminosilicate molecular sieve framework is formed. The selection of different silicon sources allows for the control of crystallization rate and crystal morphology.

[0020] Preferably, the template agents mentioned in steps (1) and (3) are each independently selected from at least one of tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetrapropylammonium chloride, and tetraethylammonium hydroxide. These template agents, acting as structure-directing agents, can guide the nucleation and growth of silicon-aluminum species along the MFI topology, giving the molecular sieve a regular microporous structure and crystallinity. The template agent molecules are removed during subsequent calcination, forming a continuous microporous channel system.

[0021] Preferably, the alkali source is selected from at least one of sodium hydroxide, potassium hydroxide, or ammonia water.

[0022] It should be noted that, in step (1), the effective components of the all-silicon molecular sieve seed solution, measured by molar ratio, are silicon source: template agent: water: ethanol = 1:(0.1~0.5):(3~10):(3~8). The above molar ratio range controls the reactant concentration and solvent polarity environment in seed synthesis. A lower water-silicon ratio and alcohol-silicon ratio form a supersaturated gel system, achieving homogeneous nucleation and size control of seed nanoparticles.

[0023] Further, the crystallization conditions in step (1) include: a temperature of 90℃-120℃ and a time of 12h-72h; the crystallization conditions in step (3) include: a temperature of 120℃-180℃ and a time of 12h-72h.

[0024] Preferably, the calcination temperature in step (2) is 450℃-650℃, and the holding time is 1h-6h.

[0025] Furthermore, the calcination temperature in step (3) is 450℃-650℃, and the holding time is 1h-6h.

[0026] Step (1) uses low-temperature crystallization conditions of 90℃-120℃ to form seed crystals of uniform size; step (3) uses high-temperature crystallization of 120℃-180℃ to meet the kinetic conditions for molecular sieve crystal growth and promote continuous and dense growth of crystals on the carrier surface. Calcination temperature of 450℃-650℃ can achieve complete decomposition of organic template agent and dehydroxylation stabilization of molecular sieve framework, forming a thermodynamically stable microporous structure.

[0027] It is worth noting that, in step (3), the effective components of the alkaline ethanol-water solution, measured by molar ratio, are: silicon source: template agent: aluminum source: water: alkaline source: ethanol = 1: (0.1~0.5): (0.01~0.1): (50~150): (0.2~0.5): (5~10). The chemical environment for the hydrothermal growth of aluminum-containing molecular sieves constructed within the above ratio range, with the introduction of the aluminum source forming framework aluminum sites and acidic centers; and the high water-to-silicon ratio serving as a dilution medium for crystal growth, is beneficial for forming a continuous molecular sieve layer with high crystallinity.

[0028] Further, the platinum group metal-containing solution in step (4) is selected from at least one of nitrates, ammonia complexes, halides or organometallic compounds.

[0029] Preferably, the platinum group metal-containing solution is a tetraamminenitrate solution.

[0030] Preferably, the platinum group metal-containing solution is a [Pt(NH3)4](NO3)2 solution.

[0031] Precursors such as nitrates, ammonium complexes, and halides provide soluble platinum group metal ions, which, through an impregnation step, achieve ion exchange or adsorption dispersion of the metal species within and on the outer surface of the molecular sieve layer pores. Soluble complexes such as tetraammineplatinum nitrate, after calcination and decomposition, can form highly dispersed metal or metal oxide active sites, thus exerting catalytic oxidation functions.

[0032] On the other hand, the present invention also provides a method for treating exhaust gas from an internal combustion engine, wherein an exhaust gas containing hydrocarbons is contacted with the catalyst to adsorb and oxidize the hydrocarbons.

[0033] The catalyst of this invention exhibits excellent adsorption and retention capacity for hydrocarbons at low temperatures and high catalytic oxidation activity at high temperatures, achieving a seamless temperature window for pollutant capture and conversion. During the cold start-up phase, the microporous structure of the molecular sieve layer retains hydrocarbons through physical and chemical adsorption; during the heating phase, the platinum group metal active components catalytically oxidize the adsorbed hydrocarbons and carbon monoxide in the gas stream, achieving efficient pollutant removal.

[0034] Compared with the prior art, the present invention has at least the following beneficial effects: 1. The monolithic molecular sieve catalyst provided by this invention achieves an integrated structure through the chemical bonding of a continuous molecular sieve layer and a honeycomb carrier, overcoming the technical defects of traditional physical coatings that are prone to pulverization and peeling, and exhibiting excellent mechanical stability and durability. Simultaneously, the in-situ grown continuous molecular sieve layer endows the catalyst with a high specific surface area and a regular microporous structure, enabling low-temperature adsorption and enrichment of gaseous pollutants; the platinum group metal active components supported thereon provide catalytic oxidation active centers, achieving high-temperature catalytic conversion of gaseous pollutants. The synergistic configuration of these two components significantly improves the catalyst's purification performance and service life under complex operating conditions.

[0035] 2. This invention employs a secondary growth method. All-silica molecular sieve seeds are pre-deposited on the surface of a honeycomb carrier, followed by hydrothermal crystallization in an alkaline system containing an aluminum source. This allows the molecular sieve crystals to nucleate and grow in situ on the carrier surface, forming a continuous molecular sieve layer chemically bonded to the carrier. In the monolithic catalyst prepared by this method, the molecular sieve layer and the carrier surface form an integrated structure, giving the catalyst excellent mechanical stability and avoiding the powdering and peeling problems caused by thermal expansion coefficient mismatch in traditional physical coating processes. Simultaneously, the in-situ grown continuous molecular sieve layer has a regular microporous structure and a high specific surface area, which is beneficial for the dispersion and immobilization of platinum group metal active components on the molecular sieve layer surface, improving the catalyst's low-temperature adsorption and enrichment capacity and high-temperature catalytic oxidation activity. The synergistic effect of the low-temperature adsorption and enrichment capacity of the molecular sieve layer and the high-temperature catalytic oxidation activity of the platinum group metals enhances the capture-conversion efficiency of gaseous pollutants and the long-term operational stability. Attached Figure Description

[0036] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 This is a scanning electron microscope image of the monolithic molecular sieve catalyst before Pt loading in Example 1 of the present invention; Figure 2 The X-ray diffraction pattern of the monolithic molecular sieve catalyst before Pt loading in Example 1 of this invention; Figure 3 This is a toluene adsorption breakthrough curve of the monolithic molecular sieve catalyst before Pt loading in Example 1 of the present invention; Figure 4 This is an ignition curve of toluene on the Pt-supported molecular sieve monolithic catalyst in Example 1 of the present invention. Figure 5 This is a graph showing the change in CO2 concentration as a function of temperature during the catalytic oxidation of toluene using a Pt-supported molecular sieve monolithic catalyst in Example 1 of the present invention. Figure 6 The nitrogen adsorption-desorption isotherm curves of the molecular sieve monolithic catalyst before Pt loading in Example 1 of this invention are shown. Detailed Implementation

[0037] The embodiments of the technical solution of this application will be described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion.

[0039] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0040] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0041] The present invention’s molecular sieve monolithic catalyst, its preparation method, and its application are described below with reference to specific embodiments.

[0042] Example 1 This embodiment provides a molecular sieve monolithic catalyst and its preparation method.

[0043] The preparation process includes: (1) Synthesis of Silicalite-1 (S-1) seed crystals: Weigh tetraethyl orthosilicate, tetrapropylammonium hydroxide, deionized water and anhydrous ethanol in a molar ratio of silicon source: template agent: water: ethanol = 1:0.2:9:4. Mix tetrapropylammonium hydroxide, deionized water and anhydrous ethanol evenly, and add tetraethyl orthosilicate dropwise while stirring. After stirring for 2 h, transfer to a hydrothermal reactor and crystallize at 100℃ for 24 h. Cool to room temperature to obtain S-1 seed crystal solution for later use.

[0044] (2) S-1 seed deposition: Take a 2×2×1 cm cordierite honeycomb carrier that has been cleaned and dried, immerse it in an S-1 seed solution diluted 10 times with deionized water and ethanol, sonicate for 10 min, then take it out and blow it with compressed air to remove excess residual solution, dry it and heat treat it at 350℃ for 5 min; repeat the above process 3 times, and finally calcine it at 500℃ for 1 h to obtain the carrier for depositing S-1 seeds.

[0045] (3) ZSM-5 molecular sieve growth: Weigh tetraethyl orthosilicate, tetrapropylammonium hydroxide, sodium aluminate, deionized water, sodium hydroxide and anhydrous ethanol in the molar ratio of silicon source: template agent: aluminum source: water: alkali source: ethanol = 1:0.1:0.05:100:0.35:8. Mix sodium aluminate, sodium hydroxide, deionized water, anhydrous ethanol and tetrapropylammonium hydroxide evenly, add tetraethyl orthosilicate under stirring, and continue stirring for 1 h to obtain the synthesis solution; place the carrier of the seed crystal obtained in step (2) vertically in the synthesis solution in the crystallization kettle, crystallize at 160℃ for 24 h, take it out, wash and dry it, and calcine at 550℃ for 4 h to form a continuous ZSM-5 molecular sieve layer on the surface of the carrier.

[0046] (4) Active loading: The sample obtained in step (3) was immersed in 200 mL of [Pt(NH3)4](NO3)2 solution with a concentration of 0.0001 mol / L for 2 h, dried and then calcined at 500℃ for 2 h to obtain a molecular sieve monolithic catalyst loaded with platinum active components.

[0047] The scanning electron microscope image of the monolithic molecular sieve catalyst prepared in this embodiment before loading active Pt is shown below. Figure 1 As shown, the surface exhibits a honeycomb morphology, indicating that a continuous and uniform molecular sieve layer has been successfully grown on the surface of the monolithic support; the X-ray diffraction pattern of the monolithic molecular sieve catalyst before loading active Pt prepared in this embodiment is shown below. Figure 2 As shown, the pattern is consistent with the standard spectrum of the MFI topology (ZSM-5), indicating that the formed molecular sieve layer has a highly crystalline MFI framework structure; the nitrogen adsorption-desorption isotherm curve of the monolithic catalyst in this embodiment is shown below. Figure 6As shown in the figure, the adsorption amount increases rapidly in the low relative pressure region, indicating that the micropores are filled, that is, the molecular sieve layer has a microporous crystalline structure.

[0048] Example 2 This embodiment provides a molecular sieve monolithic catalyst and its preparation method.

[0049] The preparation process is basically the same as in Example 1, except that the silicon-aluminum ratio is adjusted in step (3). Sodium aluminate is weighed with a molar ratio of silicon source:aluminum source = 1:0.01 (i.e., Si / Al = 100). The other preparation conditions are the same as in Example 1, and a ZSM-5 molecular sieve monolithic catalyst with a high silicon-aluminum ratio is obtained.

[0050] Example 3 This embodiment provides a molecular sieve monolithic catalyst and its preparation method.

[0051] The preparation process is basically the same as in Example 1, except that the support used in step (2) is a silicon carbide honeycomb support (2×2×1 cm), and the solution containing platinum group metals in step (4) is a [Pd(NH3)4]Cl2 solution. The impregnation time is 2 h, and after drying, it is calcined at 500℃ for 2 h to obtain a molecular sieve monolithic catalyst loaded with palladium active components.

[0052] Comparative Example 1 This comparative example provides a physically coated catalyst and its preparation method.

[0053] The preparation process includes: ZSM-5 powder (with the same silicon-to-aluminum ratio as in Example 1, Si / Al=20) was mixed with alumina sol binder at a mass ratio of 7:3, and deionized water was added and ball-milled for 4 h to prepare a slurry with a solid content of 30 wt%. A 2×2×1 cm cordierite honeycomb carrier was immersed in the above slurry for 1 min, and after being removed, excess slurry in the pores was removed by blowing with compressed air. After drying, it was calcined at 550℃ for 4 h to obtain a coated carrier with a coating amount of 150 g / L. The above coated carrier was immersed in 200 mL of a 0.0001 mol / L [Pt(NH3)4](NO3)2 solution for 2 h, and after drying, it was calcined at 500℃ for 2 h to obtain a physically coated monolithic catalyst.

[0054] Comparative Example 2 This comparative example provides a molecular sieve monolithic catalyst and its preparation method.

[0055] The difference between the preparation process and Example 1 is that the seed deposition process in step (2) is omitted, and the cleaned and dried cordierite honeycomb carrier is directly immersed in the synthesis solution in step (3) and crystallized at 160°C for 24 h. The other preparation conditions are the same as in Example 1.

[0056] The crystallization, drying, calcination and other operations described in the above embodiments and comparative examples are all conventional technical means for preparing molecular sieve catalysts in the art. Those skilled in the art can flexibly adjust the process parameters and operating steps according to the actual production conditions and equipment, and do not need to be limited to the specific values ​​mentioned above.

[0057] [Performance Testing] Adsorption test: A 1×1×1 cm molecular sieve monolithic catalyst, before being loaded with active Pt, was placed in a fixed-bed reactor wrapped with quartz wool. After high-temperature pretreatment, the temperature was cooled and maintained at 50 °C. Then, a toluene / air mixture of 200 ppm was introduced for adsorption. The inlet gas flow rate was controlled at 100 mL / min, corresponding to a space velocity of 6,000 h⁻¹. -1 Gas chromatography was used to monitor the concentration of toluene in the inlet gas (denoted as C0) and the concentration of toluene in the tail gas (denoted as C).

[0058] Oxidation test: A 1×1×1 cm molecular sieve monolithic catalyst loaded with Pt was wrapped in quartz wool and placed in a fixed-bed reactor. After the reactor temperature stabilized at 100 °C, a toluene / air mixture of 1000 ppm was introduced (the inlet gas flow rate was controlled at 100 mL / min, corresponding to a space velocity of 6,000 h⁻¹). -1 Simultaneously, the temperature was increased to 400 °C at a rate of 2 °C / min, and the concentrations of toluene and CO2 in the exhaust gas were monitored simultaneously using gas chromatography (equipped with a TCD detector or a mass spectrometer), and the change in CO2 generation with temperature was recorded.

[0059] The results are shown in Table 1 and... Figures 3 to 5 .

[0060] Table 1

[0061] pass Figure 3 The toluene adsorption breakthrough curve of the monolithic molecular sieve catalyst before loading active Pt in Example 1 of this invention shows that the C / CO ratio is close to 0 during the period of 0-126 min, indicating that toluene is effectively adsorbed by the molecular sieve layer; breakthrough begins after about 126 min, and it tends to saturate by 250 min, which confirms that the monolithic molecular sieve catalyst before loading active Pt in Example 1 has a good adsorption and retention capacity for hydrocarbons under low temperature conditions.

[0062] pass Figure 4The ignition curve of the Pt-supported molecular sieve monolithic catalyst for toluene catalytic oxidation in Example 1 of this invention shows that the conversion rate is close to 0 in the 100℃-150℃ range, indicating that toluene is mainly stored in the adsorbed state. From about 150℃, the conversion rate increases rapidly with increasing temperature. The temperature of 50% conversion rate is about 196℃, the temperature of 90% conversion rate is about 236℃, and the conversion rate reaches 95% after 250℃ and slowly increases and gradually tends to stabilize, indicating that the catalyst of Example 1 has good low-temperature catalytic activity and high-temperature stability.

[0063] pass Figure 5 The CO2 generation curves of the Pt-loaded molecular sieve monolithic catalyst in Example 1 of this invention during the programmed temperature rise process show that, in the low-temperature range of 100℃-180℃, the CO2 concentration remains at a low level, indicating that toluene is mainly stored in the molecular sieve micropores in an adsorbed state; a CO2 release peak appears in the range of 180℃-210℃, indicating that the adsorbed toluene is concentratedly desorbed and oxidized; in the high-temperature range of 210℃-400℃, the CO2 concentration stabilizes at approximately 7000 ppm (corresponding to the complete stoichiometric oxidation of 1000 ppm imported toluene), indicating that the catalyst has entered steady-state oxidation conditions. These curves confirm the adsorption and retention capacity of the catalyst in Example 1 for hydrocarbons during the cold start-up phase and its catalytic oxidation capacity after temperature rise.

[0064] As shown in Table 1, in the fixed-bed adsorption test, the toluene breakthrough time of the monolithic molecular sieve catalysts before loading active Pt in Examples 1 to 3 was longer than that in Comparative Examples 1 and 2, indicating that the continuous molecular sieve layer crystallized and bonded to the support surface of the present invention can effectively prolong the adsorption retention time of hydrocarbons. In the oxidation test, the temperature at which the toluene conversion rate of the monolithic molecular sieve catalysts loaded with Pt in Examples 1 to 3 reached 50% was all below 200℃, and lower than that in Comparative Examples 1 and 2, indicating that the catalyst of the present invention has good low-temperature catalytic ignition activity; at 250℃, the toluene conversion rate of Examples 1 to 3 all reached more than 95%, higher than that in Comparative Examples 1 and 2, indicating that the catalyst of the present invention still maintains high catalytic oxidation capacity at typical operating temperatures; the CO2 selectivity of Examples 1 to 3 all reached more than 95%, higher than that in Comparative Examples 1 and 2, indicating that the toluene can effectively reduce the generation of incomplete oxidation byproducts under the action of the catalyst of the present invention. In this embodiment of the invention, a continuous molecular sieve layer is prepared on the surface of a honeycomb carrier by a secondary growth method, and platinum group metal active components are synergistically configured to form a large specific surface area and effective active sites. This achieves the synergistic effect of low-temperature adsorption and enrichment and high-temperature catalytic oxidation, thereby effectively controlling hydrocarbon emissions during the cold start stage and improving the purification efficiency of pollutants.

[0065] In summary, the monolithic molecular sieve catalyst provided by this invention, through the chemical bonding of a continuous molecular sieve layer and a honeycomb carrier to form an integrated structure, solves the technical defects of traditional physical coatings that are prone to pulverization and peeling, exhibiting excellent mechanical stability, thermal shock resistance, and durability. Simultaneously, the in-situ grown continuous molecular sieve layer endows the catalyst with a high specific surface area and a regular microporous structure, enabling low-temperature adsorption and enrichment of gaseous pollutants; the platinum group metal active components supported thereon provide catalytic oxidation active centers, achieving high-temperature catalytic conversion of adsorbed species and gaseous pollutants. The synergistic configuration of these two components enhances the catalyst's purification performance and service life under complex operating conditions.

[0066] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A molecular sieve monolithic catalyst, characterized in that, It includes a cellular carrier, a continuous molecular sieve layer crystallized and bonded to the surface of the carrier, and a platinum group metal active component loaded on the molecular sieve layer.

2. The catalyst according to claim 1, characterized in that, The molecular sieves in the continuous molecular sieve layer have an MFI topology, and the silica-to-alumina ratio of the molecular sieves is 20-100.

3. The catalyst according to claim 2, characterized in that, The molecular sieve is ZSM-5 molecular sieve.

4. The catalyst according to claim 1, characterized in that, The honeycomb carrier is selected from one of cordierite honeycomb carrier, mullite honeycomb carrier, silicon carbide honeycomb carrier, quartz honeycomb carrier or alumina honeycomb carrier.

5. The catalyst according to claim 1, characterized in that, The platinum group metal is selected from at least one of Pt or Pd.

6. A method for preparing a monolithic molecular sieve catalyst, characterized in that, The preparation of the catalyst according to any one of claims 1-5 comprises the following steps: (1) Seed preparation: The template agent and silicon source are mixed and crystallized in an ethanol-water solution to obtain a whole silicon molecular sieve seed solution; (2) Seed deposition: The honeycomb carrier is immersed in the seed solution obtained in step (1), and after ultrasonic treatment, drying and calcination, the carrier for seed deposition is obtained; (3) Hydrothermal growth: The carrier of the seed crystal obtained in step (2) is immersed in an alkaline ethanol-water solution containing silicon source, aluminum source and template agent to crystallize. After washing, drying and calcining, a continuous aluminosilicate molecular sieve layer is formed on the surface of the carrier. (4) Active loading: The support after step (3) is immersed in a solution containing platinum group metals, and then dried and calcined to obtain a molecular sieve monolithic catalyst loaded with the platinum group metal active components.

7. The preparation method according to claim 6, characterized in that, The all-silicon molecular sieve seed crystal in step (1) is an all-silicon MFI type molecular sieve seed crystal; the aluminosilicate molecular sieve layer in step (3) is a ZSM-5 molecular sieve layer.

8. The preparation method according to claim 6, characterized in that, The silicon source in steps (1) and (3) is independently selected from at least one of sodium silicate, silica hydrogel and tetraethyl orthosilicate; the aluminum source in step (3) is sodium aluminate; the platinum group metal in step (4) is selected from at least one of Pt or Pd.

9. The preparation method according to claim 6, characterized in that, The effective components of the all-silicon molecular sieve seed solution in step (1) are calculated in molar ratio as follows: silicon source: template agent: water: ethanol = 1: (0.1~0.5): (3~10): (3~8). The effective components of the alkaline ethanol-water solution in step (3) are in the following molar ratio: silicon source: template agent: aluminum source: water: alkali: ethanol = 1: (0.1~0.5): (0.01~0.1): (50~150): (0.2~0.5): (5~10), wherein the alkali is added in the form of an alkali source, and the alkali source is selected from at least one of sodium hydroxide, potassium hydroxide or ammonia water.

10. A method for treating exhaust gas from an internal combustion engine, characterized in that, The exhaust gas containing hydrocarbons is contacted with the catalyst according to any one of claims 1-5 to adsorb and oxidize the hydrocarbons.

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