CN111485976A - Diesel particulate trap loaded with macroporous perovskite oxide and application thereof - Google Patents

Abstract

The invention discloses a catalytic diesel particulate trap and application thereof, wherein the catalytic diesel particulate trap takes cordierite honeycomb ceramics as a carrier, composite microspheres are loaded on the channel walls of the cordierite honeycomb ceramics through centrifugal action, the composite microspheres take silica microspheres as cores, and active components are shells. According to the invention, by using the silicon dioxide composite microspheres and a centrifugal self-assembly loading method, the dosage of active components is reduced, the exhaust back pressure is kept normal, and the filtering efficiency and catalytic combustion activity of the diesel particulate filter on soot particulate matters are further improved. The catalytic diesel particulate filter has simple preparation process and good industrial amplification application prospect.

Description

Diesel particulate filter loaded with macroporous perovskite oxide and its application

technical field

The invention belongs to the field of environmental protection, in particular to a catalytic diesel particle trap loaded with macroporous perovskite oxides and applications thereof, in particular to a novel catalytic diesel fuel supported by in-situ grown macroporous perovskite oxides Particle traps and their applications.

Background technique

With the growth of the economy, the number of automobiles in our country has increased sharply, and various problems brought about by it have become the focus of people's attention, among which the environmental problems caused by automobile exhaust gas are particularly prominent. As a major branch of automobile powertrain, diesel engine has superior fuel economy and power performance compared with gasoline engine, so it has become the mainstream of medium and heavy-duty automobile powerplant. Compared with gasoline engine, because diesel engine adopts compression ignition type combustion method, it will generate a larger amount of soot particulate matter (PM) in the process of high temperature anoxic combustion, which is 30-60 times higher than that of gasoline engine. A large amount of soluble organic matter (SOF). This kind of particulate matter can cause serious harm to the human body. Therefore, a lot of research has been carried out at home and abroad on how to effectively remove soot particulate matter from diesel exhaust.

Diesel Particulate Filters (DPF) is a widely used and effective post-processing method for soot particles emitted by diesel engines. Currently, the commonly used filter material is cordierite or silicon carbide ceramics. It can effectively capture the particulate matter in diesel exhaust, but cannot automatically remove the captured particulate matter, which will cause the filter to block after a long time, so it is necessary to take measures to remove the particulate matter in time, mainly by burning soot particulate matter into carbon dioxide. To discharge, this process generally requires higher temperatures. The catalyst-coated diesel particulate filter (Catalytic Diesel Particulate Filters, CDPF) can effectively reduce the ignition temperature of particulate matter, so that it can be burned at a lower temperature to achieve DPF regeneration. control means of post-processing technology. But this requires its surface-supported catalyst to have high catalytic efficiency. The key factors affecting catalytic regeneration include the redox characteristics of the catalyst itself, the contact ability of the catalyst with soot, and the stability of the catalyst. In addition, exhaust back pressure is also a major factor in evaluating DPF performance. After the catalyst is coated on the surface of the DPF, the exhaust back pressure will be increased to a certain extent. Excessive exhaust back pressure will affect the fuel economy and engine performance.

Existing soot catalysts are mostly powder or granular, most of which are smaller than 300 nanometers in size. Such catalysts will significantly increase the exhaust back pressure after coating on the surface of the DPF, which is not conducive to the operation of the engine, and greatly reduces the amount of catalyst. The contact area with the soot particles allows only the surface layer of the catalyst to contact the soot particles to play a catalytic role, which greatly reduces the catalytic efficiency and reduces the practical application value. For example, Chinese patent CN103212414A discloses a supported silver catalyst for reducing the combustion temperature of soot particles. The catalyst includes an active component and a carrier. The active component is silver, and the carrier is ceria or cerium-based composite oxide. The amount is 1% to 20% of the mass of the carrier. The general formula of the cerium-based composite oxide is Ce _1-x M _x O _y , where M is a rare earth metal. It has good catalytic performance when it is in full contact with soot particles, but its particle size is about 100 nm, which leads to a positive contact surface between the catalyst and soot particles when it is supported on a cordierite ceramic carrier for practical application. A large reduction will lead to a significant reduction in catalytic efficiency, and at the same time, due to the small particle size, when it forms a coating on the surface of the cordierite carrier pores, it will significantly increase the exhaust back pressure, which is not conducive to the operation of the engine; Chinese patent CN108295851A A preparation method of a catalyst for a particulate trap for gasoline vehicles is disclosed, which adopts cordierite honeycomb ceramics as a carrier, and a first coating is applied on the inner pore wall of the intake end of the carrier, and the height of the first coating along the axial direction is is 50%-90%; a second coating is coated on the inner channel wall of the carrier gas outlet section, and the height of the second coating along the axial direction is 50%-90%, and the coating contains precious metals (Pt, Pd) as For catalysts, the coating method is too complicated and requires multiple steps to complete the coating, which is not conducive to industrial application. In order to effectively increase the contact area between the soot particles and the catalyst, Chinese patent CN104399480A discloses a method for preparing a monolithic three-dimensional ordered macroporous structure perovskite catalyst, which adopts a centrifugal method to assemble the polystyrene colloidal crystal template, Then, the precursor of metal ion nitrate is filled into the template by the method of impregnation, and finally the template is removed by high temperature calcination to obtain a three-dimensional ordered macroporous structure perovskite catalyst; the three-dimensional ordered macroporous catalyst obtained above is a whole The macroporous integration of the block cannot be applied to the actual cordierite support. Existing soot catalysts may not be able to be loaded on the actual DPF carrier, or after loading, the catalytic efficiency will be greatly reduced and the exhaust back pressure will be increased, or the coating method is too complicated.

In view of the above technical problems and practical significance, the aim is to provide a catalytic diesel particulate filter. The diesel particulate trap not only does not contain precious metals such as Pt, Pd, Rh, etc., but also can overcome the shortcomings of the disordered morphology of the catalyst in the traditional dip coating method, improve the contact efficiency between the catalyst and soot particles, and to a certain extent, enhance the effect of CDPF on carbon The ability to capture smoke particles and reduce back pressure.

SUMMARY OF THE INVENTION

In view of the above-mentioned problems, an object of the present invention is to provide a catalytic diesel particulate trap with high catalytic activity for soot particulate matter. In another aspect of the present invention, it also relates to the application of the above-mentioned catalytic diesel particulate filter.

In order to solve the technical problem of the present invention, the following technical solutions are proposed:

One aspect of the present invention relates to a catalyzed diesel particle trap, wherein the catalyzed diesel particulate trap uses cordierite honeycomb ceramics as a carrier, and loads composite microspheres on the pore walls of the cordierite honeycomb ceramics through centrifugal action, The composite microspheres use silica microspheres as cores and active components as shells.

The invention can greatly improve the contact area between the catalyst and the soot particles and the capture efficiency of the particles by using the composite microspheres with silica as the core on the premise of ensuring the smooth passage of the exhaust gas.

In a preferred embodiment of the present invention, the active component is nano-silver particles. By using silver nanoparticles as active components, the invention can not only improve the catalytic activity, but also help the composite microspheres to be loaded on the pore walls of the cordierite honeycomb ceramics in a stable form.

In a preferred embodiment of the present invention, the silica microspheres have an average particle size of 0.3-1.5 μm. By setting the average particle size of the silica microspheres in the above range, it can not only ensure that after the silica microspheres are loaded on the surface of the DPF, there are still large pores between the microspheres, so that the exhaust back pressure will not be greatly increased. It is also beneficial for the composite microspheres to be loaded on the pore walls of the cordierite honeycomb ceramic in a stable form.

In a preferred embodiment of the present invention, the catalytic diesel particulate filter is manufactured by a manufacturing method comprising the following steps:

The composite microspheres are prepared into a suspension, the cordierite honeycomb ceramics are immersed in the suspension, sonicated, and centrifuged under the condition that a channel wall is perpendicular to the centrifugal force.

In a preferred embodiment of the present invention, the immersion, ultrasonication and centrifugation are repeated more than three times, and the direction of the channel walls is adjusted during each centrifugation so that the composite microspheres are assembled on different walls of the cordierite honeycomb ceramic.

In a preferred embodiment of the present invention, after each repeated assembly, the cordierite honeycomb ceramic is dried before entering the suspension.

In a preferred embodiment of the present invention, the cordierite ceramic honeycomb ceramic is not surface-treated when the composite microspheres are assembled on the cordierite ceramic honeycomb ceramic wall.

In addition, compared with the traditional powder-type supported catalyst, the catalytic diesel particulate filter of the present invention has a three-dimensional ordered structure, which can further increase the particulate matter without greatly increasing the exhaust back pressure. capture efficiency. Accordingly, another aspect of the present invention also relates to the use of the above-described catalytic diesel particulate filter.

For the application of the catalytic diesel particulate filter of the present invention, it is preferably used for catalytic combustion of soot particulate matter.

In a preferred embodiment of the present invention, the catalytic combustion of soot particles is below 500°C, preferably below 450°C.

In a preferred embodiment of the present invention, the catalytic combustion of soot is below 500°C and the conversion of soot exceeds 80%, preferably exceeds 90%.

For the manufacturing method of the present invention, it has at least one or more or all of the following advantages:

(1) The present invention selects silica microspheres as the core of the composite microspheres, which can reduce the amount of catalytically active components and effectively increase the contact area between the surface active components and soot particles, thereby improving the catalytic efficiency. The monodisperse spheroid morphology can avoid a large reduction in contact area caused by agglomeration when it is loaded onto a cordierite honeycomb ceramic surface (DPF) substrate.

(2) In the present invention, larger-sized composite microspheres are selected instead of nano-scale particles, which can ensure that there are still large pores between the microspheres and the microspheres after they are loaded on the surface of the DPF, which makes the exhaust back pressure will not increase significantly

(3) Since the density of the composite microspheres used in the present invention is relatively high, the centrifugal self-assembly method can be used to uniformly load them on the surface of the DPF, and the loading method is simple and practical.

(4) Under the action of centrifugal force in the present invention, the composite microspheres can fill the larger pores existing on the DPF, and at the same time form a three-dimensional ordered structure on the surface of the pore, improve the pore size distribution on the surface of the pore, and increase its capacity for carbon The capture efficiency of smoke particulate matter.

Description of drawings

FIG. 1 is a schematic flow chart of the preparation of a catalytic diesel particulate filter according to the present invention.

Figures 2-3 are SEM images of silica microspheres and silver-coated silica microspheres, respectively.

Figure 4 is an XRD image of silver-coated dioxide microspheres.

FIG. 5 is an SEM image of the cross-section and the pore plane of the catalytic diesel particulate filter prepared in Example 1. FIG.

FIG. 6 is the SEM images of four different surfaces of the same channel of the catalytic diesel particulate filter prepared in Example 1. FIG.

FIG. 7 is the SEM images of the two ends and three different positions in the middle of the same channel wall plane of the catalytic diesel particulate trap prepared in Example 1. FIG.

FIG. 8 is the test result of the mechanical stability of the catalytic diesel particulate filter prepared in Example 1. FIG.

9 is the test result of the catalytic combustion performance of the catalytic diesel particulate filter prepared in Example 1 and the blank cordierite honeycomb ceramic on soot particulate matter.

Detailed ways

In order to further illustrate the technical solutions of the present invention, the above-mentioned technical solutions are described in detail below with specific examples, but the present invention is not limited to the following embodiments.

Example 1:

Referring to the schematic diagram shown in FIG. 1, silver is selected as the active component, and the silver package is prepared by referring to the method described in the reference (Huang Qian. Preparation of Silica Microspheres and Surface Electroless Silver Plating [D]. Kunming University of Science and Technology, 2013.). The results are shown in Figure 2, Figure 2 is the SEM picture of the silica microspheres as the core, the particle size is 300-400nm, and the micro-monodisperse uniform spherical structure, as shown in Figure 3: The silver-coated composite silica microspheres have obvious silver particles on the surface, while maintaining good monodispersity and spherical morphology. Figure 4 is the XRD pattern of the composite microspheres, and its characteristic peaks can be consistent with the standard card of elemental silver, which proves the existence of silver.

Subsequently, the above-mentioned silver-coated silica microspheres were loaded onto the surface of the DPF pores by the centrifugal self-assembly method. The specific method is as follows: take a certain amount of composite microspheres and disperse them in water, prepare a 0.1g/ml microsphere suspension, wash the DPF After cleaning, immerse it in the suspension, sonicate for 1-3 minutes, and then put it into a centrifuge. Pay attention to keeping one of the channel walls perpendicular to the centrifugal force. Centrifuge at a centrifugal speed of 6000 r/min for 10 minutes, then take out the DPF and dry it at 100 °C for 5 minutes. , immerse it in the composite microsphere suspension again and put it into the centrifuge. Be careful to change a channel wall to keep it perpendicular to the centrifugal force and then repeat the above process. A total of 4 times of centrifugal self-assembly are carried out, so that the composite microspheres are loaded on the 4 channel walls. The silver-coated silica composite microspheres are evenly distributed on the surface of the DPF substrate to obtain a catalytic diesel particle trap. The composite microspheres form a layered structure with a certain thickness on the surface of the channel wall, and at the same time fill the larger pores on the surface of the substrate, which significantly improves the pore size distribution and effectively enhances the filtration efficiency; the right picture is the plan view of the channel wall. , it can be seen that the composite microspheres are distributed evenly on the surface of the channel, and further, combined with the SEM images of 4 different wall surfaces of the same channel shown in Figure 6 and the SEM images of the two ends and 3 different positions in the middle of the same channel plane in Figure 7 , it can be seen that the composite microspheres are uniform at different positions of the entire DPF substrate and form a three-dimensional structure of a kind of photonic crystal on the surface of the channel wall.

In order to test the mechanical stability of the composite microspheres loaded on the surface of DPF, we carried out simulation experiments as follows, the prepared catalytic diesel particulate trap was immersed in water, and then ultrasonically treated, and the quality of different ultrasonic time was recorded. Figure 7 shows the test results. It can be seen that after 30 minutes of ultrasonic treatment, the mass is 99.2% of the original, and only 0.8% is lost, indicating that the prepared catalytic diesel particulate filter has good mechanical stability. , the composite microspheres are supported on the pore walls of the cordierite honeycomb ceramic in a stable form

Example 2:

In order to further evaluate the catalytic activity of the catalyst of the present invention, the present invention adopts the soot particulate matter catalytic combustion activity evaluation experiment and the soot particulate matter loading experiment for evaluation.

The catalytic combustion activity evaluation test of soot was carried out in a fixed bed reactor simulated by a quartz tube with a diameter of 23 mm. 800 mg of the monolithic catalyst manufactured in Example 1 of the present invention was loaded into a quartz tube, the quartz tube was placed in a tube furnace, and the temperature was programmed to rise from room temperature to 700° C. with a heating rate of 2° C./min. The reaction gas composition (volume fraction) was: 10% O ₂ , 90% N ₂ , the total flow was 100 mL/min, and the mass space velocity was 75000 mL/(gh). Finally, the concentrations of _CO and CO in the reaction tail gas were analyzed online by a Furui GC-9790 gas chromatograph.

The test results of the catalytic combustion performance of hydrogen soot particulate matter are shown in Figure 9. Compared with the blank DPF, the catalytic diesel particulate filter prepared in Example 1 of the present invention has good catalytic activity, and can reduce the soot particulate matter below 400 ℃. There is a significant catalytic conversion rate. Especially below 500°C, the conversion rate of soot particles is more than 95%.

The applicant declares that the present invention is described in detail by the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed embodiments. Personnel should understand that any improvement of the present invention, equivalent replacement and addition of the product of the present invention, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims (10)

1. A catalytic diesel particulate trap takes cordierite honeycomb ceramic as a carrier, composite microspheres are loaded on channel walls of the cordierite honeycomb ceramic through centrifugal action, the composite microspheres take silicon dioxide microspheres as cores, and active components are shells.

2. The catalyzed diesel particulate trap of claim 1, wherein the active component is nano-silver particles. According to the invention, the silver nanoparticles are used as active ingredients, so that the catalytic activity can be improved, and the composite microspheres can be supported on the channel walls of cordierite honeycomb ceramic in a stable manner.

3. The catalyzed diesel particulate trap of claim 1, wherein the silica microspheres have an average particle size of 0.3 to 1.5 μm.

4. The catalyzed diesel particulate trap of claim 1, manufactured by a manufacturing method comprising the steps of:

preparing composite microspheres into suspension, immersing cordierite honeycomb ceramic into the suspension, performing ultrasonic treatment, and centrifuging under the condition that one pore channel wall is vertical to centrifugal force.

5. The catalyzed diesel particulate trap of claim 4, wherein the immersing, sonicating, and centrifuging are repeated more than 3 times, each time the centrifuging operation adjusts the orientation of the cell walls such that the composite microspheres are assembled onto different walls of the cordierite honeycomb ceramic.

6. The catalyzed diesel particulate trap of claim 5, wherein the cordierite honeycomb ceramic is dried and placed in suspension after each repeated assembly.

7. The catalyzed diesel particulate trap of claim 4, wherein the composite microspheres do not surface treat the cordierite honeycomb ceramic when assembled to the cordierite honeycomb ceramic walls.

8. Use of a catalysed diesel particulate trap according to any one of claims 1 to 7 for the catalytic combustion of soot particulates.

9. Use according to claim 8, the catalytic combustion of soot particles being below 500 ℃, preferably below 450 ℃.

10. Use according to claim 8, the catalytic combustion of soot particles being below 500 ℃ and the conversion of soot particles being over 80%, preferably over 90%.

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