Diesel vehicle cold start stage hydrocarbon adsorption material as well as preparation method and application thereof

Abstract

The invention relates to a hydrocarbon adsorption material in a cold start stage of a diesel vehicle and a preparation method and application of the hydrocarbon adsorption material in the technical field of environmental catalysis and tail gas purification, the adsorption material comprises an active component and a carrier material, the active component is Ag, the carrier material is ZSM-5 zeolite with an MFI topological structure, and the mass fraction of the active component Ag is 2.0 wt%. The carrier ZSM-5 is loaded with Ag species through a two-step ion exchange method, ammonium salt pretreatment and silver ion exchange are included, and after centrifugation, drying and air atmosphere calcination, the high-performance material for hydrocarbon adsorption in the cold start stage of the diesel vehicle is finally prepared. The prepared adsorption material has the advantages of being high in silver species dispersity, large in low-temperature adsorption capacity and good in matching of a high-temperature desorption window and DOC activation temperature, compared with traditional silver modified zeolite, the adsorption capacity is increased by 125.7% and 79.6% respectively, desorption peaks are concentrated and matched in temperature, the HCs rejection rate in the cold start-up stage is larger than or equal to 90%, and the adsorption material has the remarkable application value and is suitable for popularization and application. And upgrading and optimization of a diesel vehicle tail gas purification technology can be promoted.

Description

Technical Field

[0001] This invention relates to the field of environmental catalysis and exhaust gas purification technology, and in particular to a hydrocarbon adsorption material for diesel vehicles during the cold start phase, suitable for controlling the emission of harmful pollutants such as C2H4 and C7H8 in untreated exhaust gas during the cold start phase, as well as its preparation method and application. Background Technology

[0002] Diesel engines are widely used in transportation and other fields due to their high thermal efficiency, high torque, and excellent fuel economy. However, exhaust emissions during the cold start phase pose a significant environmental challenge. In the initial stage of engine startup (within the first few minutes), the exhaust temperature is below 150-200℃. Mainstream aftertreatment devices such as diesel oxidation catalyst (DOC) and selective catalytic reduction (SCR) have not yet reached their activation temperature, resulting in the direct emission of large amounts of carbon monoxide, nitrogen oxides, particulate matter, and hydrocarbons.

[0003] Light olefins (such as C2H4) and aromatic hydrocarbons (such as C7H8) in hydrocarbons are key precursors to photochemical smog and secondary organic aerosols, and pose potential carcinogenic risks. To address this issue, the "passive adsorption-catalysis" synergistic technology has become the mainstream strategy. The core of this technology is to add a hydrocarbon adsorber (HC Trap) before the catalytic unit, which adsorbs HCs at low temperature, desorbs them at high temperature, and then catalytically oxidizes them.

[0004] Ideal adsorbent materials need to possess both high and low temperature adsorption capacity and precise high-temperature desorption characteristics. Microporous zeolite molecular sieves, due to their regular pore structure, large specific surface area, and excellent hydrothermal stability, have become a preferred carrier. Silver (Ag) modified zeolite is used to... + π-complexation with hydrocarbons enables efficient adsorption and reversible desorption, but existing technologies face three major bottlenecks: the state of silver species (Ag) + / Ag n δ+ / The structure-activity relationship between zeolite and adsorption performance is unclear; the synergistic effect of zeolite framework structure on adsorption performance has not been fully explored; traditional preparation methods tend to lead to silver species agglomeration, reducing adsorption efficiency.

[0005] Existing research on the preparation of silver-modified zeolites mostly employs a single ion exchange method, which struggles to balance silver species dispersion and stability. Furthermore, a systematic study of the compatibility of zeolites with different topologies is lacking, failing to meet the broad-spectrum capture requirements of multi-component hydrocarbons. Therefore, developing novel preparation processes and clarifying structure-performance relationships are crucial for enhancing the practical value of adsorption materials. Thus, developing a silver-modified zeolite with a simple preparation process, strong silver species dispersion and stability, and excellent performance in HCs adsorption-desorption has significant practical application value. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a silver-modified zeolite adsorbent material that uses a two-step ion exchange method to regulate the state of silver species, thereby solving the problem of silver species aggregation and achieving efficient capture and precise desorption of multi-component hydrocarbons during the cold start phase.

[0007] This invention is achieved through the following technical solution: This invention provides a hydrocarbon adsorbent material for the cold start phase of diesel vehicles, using microporous zeolite as a carrier, on which silver species are loaded; the silver species include isolated... Ions and / or Ag n δ+ Clusters, Ag n δ+ The cluster size is less than 5 nm; the microporous zeolite is ZSM-5 zeolite with an MFI topology. The adsorbent material is an Ag / ZSM-5 material with high silver species dispersion, which consists of an active component and a support material, wherein the active component is Ag and the support material is ZSM-5 zeolite. ZSM-5 zeolite has a suitable micropore size and abundant Al sites, and the charge imbalance generated by Al substitution allows it to coordinate with Ag.

[0008] Furthermore, in this invention, the mass fraction of the active component Ag is 2 wt.%.

[0009] This invention also provides a method for preparing a hydrocarbon adsorbent material for the cold start phase of a diesel vehicle, comprising the following steps: Step S1, First Ion Exchange: The zeolite support is added to an ammonium salt solution of a specific concentration and stirred for a specific time in a water bath at a specific temperature.

[0010] Step S2, First solid-liquid separation and drying: The mixture obtained in step S1 is subjected to solid-liquid separation and dried at a specific temperature for a specific time to obtain NH4 type zeolite; Step S3, Second Ion Exchange: The NH4-type zeolite obtained in step S2 is added to a silver precursor solution of a specific concentration and stirred for a specific time in a water bath at a specific temperature.

[0011] Step S4, Second solid-liquid separation and drying: The mixture obtained in step S3 is subjected to solid-liquid separation and dried at a specific temperature for a specific time to obtain an intermediate; Step S5: Calcine the intermediate obtained in step S4 in an air atmosphere at a specific temperature and for a specific time to obtain the silver-modified zeolite material.

[0012] Furthermore, in step S1 above, the ammonium salt solution is an aqueous solution of NH4NO3 with a concentration of 2 mol / L; the water bath temperature is 80 °C; and the stirring time is 12 hours.

[0013] Furthermore, in step S2 above, the drying temperature is 80 °C and the drying time is 12 hours.

[0014] Furthermore, in step S3 above, the silver precursor solution is an aqueous solution of AgNO3 with a concentration of 0.5 mol / L; the water bath temperature is 80 °C; and the stirring time is 2 hours.

[0015] Furthermore, in step S4 above, the drying temperature is 80 °C and the drying time is 12 hours.

[0016] Furthermore, in step S5 above, the calcination atmosphere is air, the pressure is atmospheric pressure, the calcination temperature is 500 °C, and the calcination time is 4 hours.

[0017] The present invention also provides an application of the above-mentioned material, wherein the catalyst is used for the adsorption of hydrocarbons during the cold start phase of a diesel vehicle.

[0018] Furthermore, in the application of the above materials, the adsorption of hydrocarbons during the cold start phase of diesel vehicles includes C2H4 adsorption and C7H8 adsorption; the materials can be directly loaded into a fixed-bed reactor, and their performance is evaluated by isothermal adsorption test and programmed temperature desorption test.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention fully utilizes the characteristics of ZSM-5 carrier with suitable micropore size and rich Al sites. By immobilizing Ag ions through Al sites, the dispersibility of Ag active components is effectively improved, while its stability is increased, and aggregation during the reaction is avoided, thereby increasing the number of adsorption active sites and improving intrinsic adsorption performance.

[0020] This invention employs a simple ion exchange method to prepare Ag / ZSM-5 material in two steps: centrifugation, drying, and air calcination. The process is concise, requiring no complex equipment or harsh reaction conditions, facilitating industrial scale-up. Test results show that the prepared Ag / ZSM-5 material exhibits an adsorption capacity of 316 μmol / g for C2H4 and 325 μmol / g for C7H8, representing improvements of 125.7% and 79.6% respectively compared to traditional silver-modified zeolite materials. Furthermore, the prepared Ag / ZSM-5 material exhibits concentrated desorption peaks (without broadened impurities), and the desorption temperatures for C2H4 and C7H8 are 337℃ and 418℃, respectively, perfectly matching the DOC activation window. During the cold start phase, the HCs rejection rate is ≥90%, making it a highly efficient, stable, and reliable hydrocarbon adsorbent for diesel vehicles during the cold start phase. Attached Figure Description

[0021] Figure 1 C2H4 adsorption curves of silver-modified zeolite materials; Figure 2 C7H8 adsorption curve of silver-modified zeolite material; Figure 3 C2H4 temperature-programmed desorption curve of silver-modified zeolite material; Figure 4 Desorption curves of silver-modified zeolite material under C7H8 temperature-programmed conditions. Detailed Implementation

[0022] To make the technical solution of this invention clearer and easier to understand, the invention will be described in detail below with reference to specific embodiments. It should be emphasized that these embodiments are only used to illustrate the implementation of this invention and do not constitute a limitation on the scope of protection of this invention. In the following embodiments, for steps where operating conditions are not specifically described, they should be performed according to conventional conditions well known to those skilled in the art, or according to the instructions of the relevant product. As for chemical reagents whose specific manufacturers are not specified in the embodiments, they should be understood as general-purpose chemicals that meet national quality standards, and these chemicals can all be obtained through conventional market channels.

[0023] Example Prepare a 40 mL 2M NH4NO3 solution using (NH4)2CO3 and nitric acid. Add H / ZSM-5 to the prepared NH4NO3 solution and stir in an 80 °C water bath for 12 hours. Centrifuge the resulting suspension at 6000 rpm for 5 minutes to obtain the precipitate. Repeat the washing and centrifugation process twice with deionized water to obtain the precipitate again. Dry the precipitate in air at 80 °C to obtain NH4 / ZSM-5. Dissolve 0.063 g of AgNO3 in 40 mL of deionized water to obtain an AgNO3 solution. Add the prepared NH4 / ZSM-5 to the prepared AgNO3 solution and stir in an 80 °C water bath for 2 hours. Separate, wash, and dry in the same manner to obtain the Ag / ZSM-5 intermediate. Calcinate the obtained Ag / ZSM-5 intermediate in a muffle furnace at 550 °C for 4 hours to obtain the final Ag / ZSM-5 material from the example.

[0024] Comparative Example 0.063 g of AgNO3 was dissolved in 20 mL of deionized water to obtain an AgNO3 solution. 2 g of H / ZSM-5 was placed in deionized water and stirred for 30 minutes to obtain a carrier suspension. The AgNO3 solution was gradually added dropwise to the continuously stirred carrier suspension, and stirring was continued for 2 hours. Next, the resulting suspension was placed in a flask of a rotary evaporator and subjected to vacuum rotary evaporation at 60 °C for 2 hours with stirring. The precipitate was separated from the inner wall of the flask to obtain Ag / zeolite. The obtained Ag / zeolite was calcined in a muffle furnace at 550 °C for 4 hours to obtain the Ag / ZSM-5 material comparative sample.

[0025] Application examples To better illustrate the catalytic effect of this invention, an experimental bench testing system was built to test the catalytic activity of the ammonia decomposition catalytic materials prepared in the examples and comparative examples. The testing process is as follows: 1. Before starting the experiment, pre-treat the experimental sample in an N2 atmosphere at 550 °C for 1 hour to desorb other gases other than N2 that have been adsorbed from the test sample.

[0026] 2. After pretreatment, adsorption testing was performed first. The tube furnace temperature was controlled at 30 ℃, and the valve was opened to introduce experimental gas containing a certain concentration of HCs for 80 min. During this period, an infrared spectrometer measured one data point every 2 minutes. The experimental gas flow rate was set to 50 mL / min, and the sample volume was controlled to ensure an experimental space velocity of 10000 h⁻¹. -1 For the C2H4 adsorption performance test, the experimental input gas was 600 ppm C2H4, with N2 as the balance gas; for the C7H8 adsorption performance test, the experimental input gas was 300 ppm C7H8, with N2 as the balance gas.

[0027] 3. After completing the adsorption test, the sample was saturated with HCs gas at 30 ℃, and then a desorption test was performed. The valve was opened to introduce N2 for purging, with the N2 flow rate set to 50 mL / min. The tube furnace was then heated from 30 ℃ to 550 ℃ at a rate of 2.5 ℃ / min. During this process, an infrared spectrometer measured one data point every 2 minutes. Multiple data recordings were used to average the results, minimizing experimental error.

[0028]

[0029] The test results of the embodiments and comparative sample samples of the present invention are shown in Table 1 and Figures 1 to 4 As shown in the figure, the examples exhibit excellent overall performance, with higher adsorption capacity and desorption temperature for both C2H4 and C7H8, and their performance is compatible with the activation window of DOC catalysts.

[0030] This invention successfully prepared high-performance silver-modified zeolite adsorbent materials through a simple and controllable preparation method, solving the problem of hydrocarbon emissions during the cold start phase of diesel vehicles. The preparation process is low-cost, easy to scale up, and the material has stable and reliable performance, making it of significant industrial application value.

[0031] The above description is only a preferred embodiment of the present invention. Any equivalent changes and modifications made by those skilled in the art within the scope of the patent application of the present invention shall also fall within the scope covered by the appended claims.

Claims

1. A hydrocarbon adsorbent material for the cold start phase of a diesel vehicle, characterized in that, Microporous zeolite was used as a carrier, and silver species were loaded onto the carrier. The silver species include isolated Ions and / or Ag n δ+ Clusters, Ag n δ+ The cluster size is less than 5 nm.

2. The hydrocarbon adsorption material for the cold start phase of a diesel vehicle according to claim 1, characterized in that, The microporous zeolite is ZSM-5 zeolite with an MFI topology.

3. The hydrocarbon adsorption material for the cold start phase of a diesel vehicle according to claim 1 or 2, characterized in that, Based on the total mass of the material, the mass fraction of Ag is 2.0 wt.%.

4. A method for preparing a hydrocarbon adsorbent material for the cold start phase of a diesel vehicle as described in claims 1 to 3, characterized in that, Includes the following steps: Step S1: Add the zeolite carrier to an ammonium salt solution of a specific concentration and stir for a specific time in a water bath at a specific temperature. Step S2: The mixture obtained in step S1 is subjected to solid-liquid separation and dried at a specific temperature for a specific time to obtain NH4 type zeolite; Step S3: Add the NH4 type zeolite obtained in step S2 to a silver precursor solution of a specific concentration and stir for a specific time in a water bath at a specific temperature. Step S4: The mixture obtained in step S3 is subjected to solid-liquid separation and dried at a specific temperature for a specific time to obtain an intermediate. Step S5: Calcine the intermediate obtained in step S4 in an air atmosphere at a specific temperature and for a specific time to obtain the silver-modified zeolite material.

5. The method for preparing the hydrocarbon adsorbent material for the cold start phase of a diesel vehicle according to claim 4, characterized in that... In step S1, the ammonium salt solution is an aqueous solution of NH4NO3 with a concentration of 2 mol / L; the water bath temperature is 80 °C; and the stirring time is 12 hours.

6. The method for preparing the hydrocarbon adsorbent material for the cold start phase of a diesel vehicle according to claim 4, characterized in that... In step S2, the drying temperature is 80 °C and the drying time is 12 hours.

7. The method for preparing the hydrocarbon adsorbent material for the cold start phase of a diesel vehicle according to claim 4, characterized in that... In step S3, the silver precursor solution is an aqueous solution of AgNO3 with a concentration of 0.5 mol / L; the water bath temperature is 80 °C; and the stirring time is 2 hours.

8. The method for preparing the hydrocarbon adsorbent material for the cold start phase of a diesel vehicle according to claim 4, characterized in that... In step S4, the drying temperature is 80 °C and the drying time is 12 hours; In step S5, the calcination temperature is 500 °C and the calcination time is 4 hours.

9. The application of a hydrocarbon adsorbent material for the cold start phase of a diesel vehicle as described in any one of claims 1 to 4, or a hydrocarbon adsorbent material for the cold start phase of a diesel vehicle prepared by the method described in any one of claims 5 to 8, characterized in that... The hydrocarbon adsorption material used during the cold start phase of a diesel vehicle is used to adsorb hydrocarbons in the diesel vehicle exhaust.

10. The application according to claim 9, characterized in that, The hydrocarbon adsorbent material for the cold start phase of the diesel vehicle is deployed in the diesel vehicle exhaust aftertreatment system, located upstream of the diesel vehicle oxidation catalyst.

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