Catalysed diesel particulate filter and its use

Abstract

The application discloses a catalytic diesel particulate filter and application thereof, the catalytic diesel particulate filter takes the cordierite honeycomb ceramic as a carrier, and composite microspheres are loaded on the pore wall of the cordierite honeycomb ceramic through centrifugal action, the composite microspheres take silica microspheres as a core, and active components are shells.The application further improves the filtering efficiency of the diesel particulate filter for carbon smoke particulate matters and catalytic combustion activity while reducing the amount of active components and keeping the normal exhaust back pressure by using the silica composite microspheres and centrifugal self-assembly loading method.The catalytic diesel particulate filter has simple preparation process and good industrial amplification application prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of environmental protection, and particularly relates to a catalytic diesel particulate filter and application thereof. BACKGROUND

[0002] With the growth of economy, the number of automobiles in China increases rapidly, and the problems brought by it are increasingly becoming the focus of attention, among which the environmental problems caused by automobile exhaust are particularly prominent. Diesel engine, as a major branch of automobile power assembly, has more superior fuel economy and power than gasoline engine, and thus becomes the mainstream of medium and heavy automobile power devices. Compared with gasoline engine, diesel engine adopts compression ignition combustion mode, and produces more carbon soot particles (PM) in the high-temperature and oxygen-deficient combustion process, which is 30-60 times higher than that of gasoline engine, and the main component is carbon with a large amount of soluble organic matter (SOF) adsorbed on the surface. Such particles can cause serious harm to human body, and thus a large amount of researches are carried out at home and abroad on how to effectively remove the carbon soot particles in diesel engine exhaust.

[0003] Diesel particulate filter (DPF) is a kind of effective post-processing means for carbon soot particles in diesel engine exhaust that is widely used at present, and the common filter core material is cordierite or silicon carbide ceramic. It can effectively capture the particles in diesel engine exhaust, but cannot automatically remove the captured particles, which will cause the filter to be blocked over time, and thus measures need to be taken to remove the particles in time, mainly by burning the carbon soot particles into carbon dioxide, which generally requires a high temperature. The diesel particulate filter coated with catalyst (CDPF) can effectively reduce the ignition temperature of particles, so that they can be burned at a lower temperature to realize the regeneration of DPF, and is a kind of post-processing technology with low energy consumption and without complex control means. However, it requires the catalyst loaded on the surface to have high catalytic efficiency. The key factors affecting catalytic regeneration include the redox properties of the catalyst itself, the contact ability of the catalyst with the carbon soot, and the stability of the catalyst. In addition, exhaust back pressure is also a major factor for evaluating the performance of DPF. The coating of catalyst on the surface of DPF will increase the exhaust back pressure to a certain extent, and excessive exhaust back pressure will affect the fuel economy and engine performance.

[0004] Most of the existing soot catalysts are in powder or granular form, with most of the size less than 300 nanometers. Such catalysts will significantly increase the exhaust back pressure after being coated on the surface of the DPF, which is not conducive to the operation of the engine, and at the same time greatly reduces the contact area of the catalyst and the soot particles, so that only the surface layer of the catalyst can contact the soot particles to play a catalytic role, greatly reducing the catalytic efficiency and leading to a decrease in practical application value. For example, a supported silver catalyst for reducing the combustion temperature of soot particles is disclosed in Chinese patent CN103212414A. The catalyst includes an active component and a carrier. The active component is silver, and the carrier is cerium dioxide or cerium-based composite oxide. The loading amount of silver is 1% to 20% of the mass of the carrier. The composition of the cerium-based composite oxide has a general formula of Ce 1-x M x O y , wherein M is a rare earth metal. When it is in full contact with soot particles, it has good catalytic performance, but its particle size is about 100 nm, which leads to a significant reduction in the contact area of the catalyst and the soot particles when it is loaded on the cordierite ceramic carrier for practical application, thereby greatly reducing the catalytic efficiency. At the same time, due to the small particle size, when it forms a coating on the surface of the cordierite carrier pore, it will significantly increase the exhaust back pressure, which is not conducive to the operation of the engine; Chinese patent CN108295851A discloses a preparation method of a gasoline vehicle particulate filter catalyst. It uses cordierite honeycomb ceramic as a carrier, and a first coating is coated on the inner pore wall of the inlet gas end of the carrier. The height of the first coating along the axial direction is 50% to 90%. A second coating is coated on the inner pore wall of the outlet gas section of the carrier. The height of the second coating along the axial direction is 50% to 90%. The coating contains noble metals (Pt, Pd) as catalysts. This coating method is too complex and requires multiple steps to complete the coating, which is not conducive to industrial application. In order to effectively increase the contact area of soot particles and catalysts, Chinese patent CN104399480A discloses a method for preparing a monolithic three-dimensional ordered macroporous perovskite catalyst. The method uses a centrifugal method to assemble a polystyrene colloidal crystal template, then uses an immersion method to fill the metal ion nitrate precursor into the template, and finally uses a high-temperature calcination method to remove the template to obtain a three-dimensional ordered macroporous perovskite catalyst. The three-dimensional ordered macroporous catalyst obtained above is a monolithic macroporous integrated body and cannot be applied to the actual cordierite carrier. The existing soot particle catalysts cannot be loaded on the actual DPF carrier, or the loading will greatly reduce the catalytic efficiency and increase the exhaust back pressure, or the coating method is too complex.

[0005] In view of the above technical problems and practical significance, the present application aims to provide a catalytic diesel particulate filter. The diesel particulate filter not only does not contain noble metals such as Pt, Pd, Rh, etc., but also overcomes the shortcomings of disordered morphology of catalysts prepared by traditional dip-coating method, improves the contact efficiency of catalysts with soot particles, to some extent, enhances the capturing capacity of CDPF for soot particles, and reduces the back pressure. SUMMARY

[0006] In view of the above problems, the present application aims to provide a catalytic diesel particulate filter with high catalytic activity for soot particles. In another aspect of the present application, the application also relates to the use of the above catalytic diesel particulate filter.

[0007] In order to solve the technical problems of the present application, the following technical solutions are adopted:

[0008] In one aspect, the present application relates to a catalytic diesel particulate filter, which uses cordierite honeycomb ceramics as a carrier, and loads composite microspheres on the pore walls of the cordierite honeycomb ceramics by centrifugation, wherein the composite microspheres have silica microspheres as a core and active components as a shell.

[0009] The present application can greatly improve the contact area of catalysts with soot particles and the particle capturing efficiency under the premise of ensuring the smooth passage of exhaust gas by using composite microspheres with silica as a core.

[0010] In a preferred embodiment of the present application, the active components are silver nanoparticles. The present application uses silver nanoparticles as active components, which not only improves the catalytic activity, but also helps the composite microspheres to be loaded on the pore walls of the cordierite honeycomb ceramics in a stable form.

[0011] In a preferred embodiment of the present application, the average particle size of the silica microspheres is 0.3-1.5 μm. By setting the average particle size of the silica microspheres in the above range, not only can it be ensured that there are still large pores between the microspheres after they are loaded on the surface of the DPF, so that the exhaust back pressure will not increase significantly, but it is also conducive to the composite microspheres being loaded on the pore walls of the cordierite honeycomb ceramics in a stable form.

[0012] In a preferred embodiment of the present application, the catalytic diesel particulate filter is manufactured by a manufacturing method comprising the following steps:

[0013] The composite microspheres are prepared into a suspension, the cordierite honeycomb ceramics are immersed in the suspension, and ultrasonic is applied under the condition that one pore wall is perpendicular to the centrifugal force.

[0014] In a preferred embodiment of the present application, the immersion, ultrasonic and centrifugation are repeated more than 3 times, and the direction of the pore wall is adjusted each time to assemble the composite microspheres to different walls of the cordierite honeycomb ceramic.

[0015] In a preferred embodiment of the present application, the cordierite honeycomb ceramic is dried after each repeated assembly before being immersed in the suspension.

[0016] In a preferred embodiment of the present application, the composite microspheres are not surface treated when assembled to the walls of the cordierite honeycomb ceramic.

[0017] In addition, the catalytic diesel particulate filter of the present application has a three-dimensional ordered structure compared with the conventional powder type supported catalyst, and can further increase the particulate matter capturing efficiency without substantially increasing the exhaust back pressure. Therefore, the present application also relates to the use of the catalytic diesel particulate filter.

[0018] For the use of the catalytic diesel particulate filter of the present application, it is preferably used for catalytic combustion of soot particulate matter.

[0019] In a preferred embodiment of the present application, the catalytic combustion of soot particulate matter is below 500°C, preferably below 450°C.

[0020] In a preferred embodiment of the present application, the catalytic combustion of soot particulate matter is below 500°C, and the conversion rate of soot particulate matter is more than 80%, preferably more than 90%.

[0021] For the manufacturing method of the present application, it has at least one or more or all of the following advantages:

[0022] (1) The present application selects silica microspheres as the core of the composite microspheres, which can reduce the amount of catalytically active components while effectively increasing the contact area between the surface active components and soot particulate matter, thereby improving the catalytic efficiency. The monodisperse spherical morphology can avoid the significant reduction of contact area caused by agglomeration when loaded onto the surface of the cordierite honeycomb ceramic (DPF) substrate.

[0023] (2) The present application selects larger size composite microspheres rather than nano-sized particles, which can ensure that there are still large pores between the microspheres after being loaded onto the surface of the DPF, so that the exhaust back pressure will not be substantially increased

[0024] (3) Since the composite microspheres used in the present application have a larger density, the method of centrifugal self-assembly can be used to uniformly load them on the surface of the DPF, which is simple and practical.

[0025] (4) Under the action of centrifugal force, the composite microspheres of the present invention can fill the large pores on the DPF and form a three-dimensional ordered structure on the surface of the pores, thereby improving the pore size distribution on the surface of the pores and increasing its collection efficiency for carbon soot particles. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the process for preparing the catalytic diesel particulate filter of the present invention.

[0027] Figures 2-3 SEM images of silica microspheres and silver-coated silica microspheres, respectively.

[0028] Figure 4 XRD image of silver-coated dioxide microspheres.

[0029] Figure 5 The image shows a cross-section and pore plane of the catalytic diesel particulate trap prepared in Example 1.

[0030] Figure 6 SEM images of four different surfaces of the same channel of the catalytic diesel particulate trap prepared in Example 1.

[0031] Figure 7 The images are SEM images of the two ends and the middle of the same channel wall plane of the catalytic diesel particulate trap prepared in Example 1.

[0032] Figure 8 The results show the mechanical stability test results of the catalytic diesel particulate filter prepared in Example 1.

[0033] Figure 9 The results show the test performance of the catalytic diesel particulate trap and blank cordierite honeycomb ceramic prepared in Example 1 on the catalytic combustion of carbon soot particles. Detailed Implementation

[0034] To further illustrate the technical solution of the present invention, the above technical solution will be described in detail below with specific embodiments, but the present invention is not limited to the following embodiments.

[0035] Example 1:

[0036] Reference Figure 1 The schematic diagram shown illustrates the preparation of silver-coated silica microspheres using silver as the active component, following the method described in the reference (Huang Qian. Preparation and surface chemical silver plating of silica microspheres [D]. Kunming University of Science and Technology, 2013). The results are as follows. Figure 2 As shown, Figure 2 This is a SEM image of silica microspheres forming the core. The microspheres have a particle size of 300-400 nm and exhibit a micromonodispersed, uniform spherical structure.Figure 3 The figure shows the silver-coated composite silica microspheres, the surface of which can be seen the presence of obvious silver particles, while maintaining good monodispersity and spherical morphology. Figure 4 The figure is the XRD pattern of the composite microspheres, the characteristic peaks of which can be consistent with the elemental silver standard card, proving the presence of silver.

[0037] Subsequently, the above silver-coated silica microspheres are loaded onto the DPF channel surface by centrifugal self-assembly method, the specific method is as follows: a certain amount of composite microspheres are dispersed in water to prepare a microsphere suspension of 0.1 g / ml, the DPF is washed and then immersed in the suspension, ultrasonic for 1-3 min, then put into the centrifuge, pay attention to keep one of the channel walls perpendicular to the centrifugal force, centrifuge at 6000 r / min for 10 min, then take out the DPF and dry at 100°C for 5 minutes, then immerse it again in the composite microsphere suspension and put it into the centrifuge, pay attention to change the channel wall to keep it perpendicular to the centrifugal force, then repeat the above process, a total of 4 times of centrifugal self-assembly, so that the 4 channel walls are loaded with composite microspheres. The silver-coated silica composite microspheres are uniformly distributed on the surface of the DPF substrate, and a catalytic diesel particulate filter is obtained, as shown in Figure 5 The figure shows the SEM image of the DPF channel wall, the left figure is the DPF channel cross-sectional view, it can be seen that the composite microspheres form a layered structure with a certain thickness on the surface of the channel wall, and fill the larger holes existing on the substrate surface, significantly improving the pore size distribution, which can effectively enhance the filtration efficiency; the right figure is the channel wall plan view, it can be seen that the composite microspheres are uniformly distributed on the channel surface. Further, combined with Figure 6 The figure shows the SEM images of the same channel 4 different wall surfaces and Figure 7 The figure shows the SEM images of the same channel plane at two ends and three different positions in the middle, it can be seen that the composite microspheres are uniformly distributed on the different positions of the entire DPF substrate and form a kind of three-dimensional photonic crystal structure on the surface of the channel wall.

[0038] In order to test the mechanical stability of the composite microspheres loaded on the surface of the DPF, we carried out a simulation experiment, as follows: the prepared catalytic diesel particulate filter is immersed in water, then ultrasonic treatment is carried out, and the mass change at different ultrasonic times is recorded, Figure 7 The test results show that after 30 minutes of ultrasonic treatment, the mass is 99.2% of the original, only 0.8% is lost, which indicates that the prepared catalytic diesel particulate filter has good mechanical stability, and the composite microspheres are stably loaded on the channel wall of the cordierite honeycomb ceramic

[0039] Example 2:

[0040] In order to further evaluate the catalytic activity of the catalyst of the present application, the carbon soot particle catalytic combustion activity evaluation experiment and the carbon soot particle loading experiment are used.

[0041] The carbon soot particle catalytic combustion activity evaluation test is 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 application is packed in the quartz tube, and the quartz tube is placed in a tube furnace, and the temperature is raised from room temperature to 700°C at a rate of 2°C / min. The reaction gas composition (volume fraction) is: 10% O2, 90% N2, the total flow rate is 100 mL / min, and the mass space velocity is 75,000 mL / (gh). The concentrations of CO2 and CO in the final reaction tail gas are analyzed online by a Fuli GC-9790 gas chromatograph.

[0042] The test results of the catalytic combustion performance of hydrogen carbon soot particles are shown in Table 1. Figure 9 Compared with the blank DPF, the catalytic diesel particulate filter prepared in Example 1 of the present application has good catalytic activity, and has obvious catalytic conversion rate on the carbon soot particles below 400°C. Especially below 500°C, the conversion rate of the carbon soot particles is more than 95%.

[0043] The applicant declares that the present application is illustrated by the above examples to explain the detailed implementation of the present application, but the present application is not limited to the above detailed implementation, that is, it does not mean that the present application must rely on the above implementation to be implemented, and the person skilled in the art should understand that any improvement of the present application, equivalent replacement and addition of the product of the present application, and the selection of the specific mode, etc. fall within the protection scope and the disclosure scope of the present application.

Claims

1. A catalytic diesel particulate filter, which is supported by a cordierite honeycomb ceramic, and composite microspheres are loaded on the pore walls of the cordierite honeycomb ceramic by centrifugation to fill the surface existing pores, the composite microspheres are uniform at different positions of the entire cordierite honeycomb ceramic and form a kind of photonic crystal-like three-dimensional structure on the surface of the pore walls, the composite microspheres take silica microspheres as the core and active components as the shell, the active components are nano silver particles; the average particle size of the silica microspheres is 0.3-1.5 μm. The composite microspheres are prepared into a suspension, the cordierite honeycomb ceramic is immersed in the suspension, ultrasonic treatment, and centrifugation under the condition that one pore wall is perpendicular to the centrifugal force.

2. The catalytic diesel particulate filter according to claim 1, wherein the immersion, ultrasonic treatment and centrifugation are repeated more than 3 times, and the direction of the pore wall is adjusted every time to make the composite microspheres assemble to different walls of the cordierite honeycomb ceramic.

3. The catalytic diesel particulate filter according to claim 2, wherein after the assembly of each repetition, the cordierite honeycomb ceramic is dried before entering the suspension.

4. The catalytic diesel particulate filter according to claim 1, wherein the composite microspheres do not perform surface treatment on the cordierite honeycomb ceramic when assembling to the walls of the cordierite honeycomb ceramic.

5. The use of the catalytic diesel particulate filter according to any one of claims 1-4 for catalytic combustion of soot particles.

6. The use according to claim 5, wherein the catalytic combustion of soot particles is below 500℃.

7. The use according to claim 5, wherein the catalytic combustion of soot particles is below 450℃.

8. The use according to claim 5, wherein the catalytic combustion of soot particles is below 500℃, and the conversion rate of soot particles is more than 80%.

9. The use according to claim 5, wherein the catalytic combustion of soot particles is below 500℃, and the conversion rate of soot particles is more than 90%.

Images