KR102464146B1 - A catalytic filter having resistance to poisoning for purifying an exhaust gas - Google Patents

Abstract

The present invention relates to a catalyst filter for exhaust gas purification, and relates to a catalyst filter for endothelial exhaust gas purification coated with a lower catalytic active layer and an upper phosphorus poisoning layer. It relates to a catalyst filter for purifying exhaust gas having coating layers in a shape of being coated, the thickness of the coating layers becoming thinner toward the latter part.

Description

A catalytic filter having resistance to poisoning for purifying an exhaust gas

The present invention relates to a catalyst filter for exhaust gas purification, and to a catalyst filter for endothelial exhaust gas purification coated with a lower catalytic active layer and an upper phosphorus poisoning layer. It relates to a catalyst filter for purifying exhaust gas having coating layers coated with a poison layer, and the coating layers have a shape in which the thickness of the coating layers becomes thinner toward the latter part.

A catalyst filter for exhaust gas purification is a filter technology that collects particulate matter (PN) emitted from an internal combustion engine in a filter, burns it, regenerates it, and collects particulate matter again for reuse. A catalyst filter (CSF, Catalyzed soot filter) method may be employed. These catalytic filters effectively remove particulate matter along with HC, CO and NOx in the exhaust gas. The catalyst filter is a porous silicon carbide sintered body, which is a type of ceramic sintered body, or a honeycomb structure formed of cotierite, aluminum titania, etc., and the catalytically active material may be coated on the filter cell wall or supported inside the pores formed on the cell wall.

Continuously strengthening PN regulation requires improvement of PN purification performance, and as the catalyst is poisoned by the phosphorus (P) component emitted from the engine and NOx purification performance deteriorates, it is necessary to develop a technology to lower the performance degradation caused by P poisoning.

An object of the present invention is to provide a filter for exhaust gas purification that maximizes new filtration efficiency (FFE, Fresh Filtration Efficiency) while minimizing the increase in back pressure by applying a porous catalyst active layer to the filter cell wall but thinning the active layer in the longitudinal direction will be. Another object of the present invention is to apply a phosphorus poisoning resistant poisoning layer on the upper portion of the catalytic active layer to prevent phosphorus poisoning, but apply it to become thinner along the longitudinal direction in the same way as the change in the thickness of the active layer to maximize toxicity and improve NOx conversion It is to provide a filter for purifying exhaust gas.

The present invention provides a catalytic filter for exhaust gas purification, specifically, a porous catalytically active layer is applied to the filter cell wall and a phosphorus poisoning layer is applied on the active layer. A catalytic filter is proposed. Without limitation, the thickness of the porous active layer may be 20 to 350 μm, and the thickness may be reduced until reaching the latter part along the longitudinal direction, and the average diameter of the pores distributed in the porous active layer may be adjusted to 1 to 20 μm. In addition, the poison layer has a thickness of 20 to 100 μm, and may be thinned until reaching the second half in the longitudinal direction. Furthermore, the active layer of the filter is formed of a TWC or SCR catalyst material, and the poison layer of the filter is formed of Sr-Al ₂ O ₃ .

A porous catalytically active layer is applied to the filter for purifying exhaust gas according to the present invention, so that the rate of increase in back pressure is increased by about 30% compared to the active layer penetrating inside the conventional cell wall, but the FFE is improved by about 20%, and the catalytically active layer is exposed on the surface of the exhaust gas The purification performance is improved by 10% CO and 20% NOx compared to the permeation active layer. On the other hand, the upper poisoning layer component Sr-Al ₂ O ₃ traps P, thereby lowering P poisoning and improving NOx purification performance.

The drawings are intended to illustrate embodiments of the present invention and are not intended to limit the invention encompassed by the claims.
1 is a schematic perspective view and a partially enlarged cross-sectional view of a catalyst filter.
Figure 2 (a) is a scanning electron microscope (SEM) photograph showing the catalyst material coated on the filter cell wall, Figure 2 (b) is a scanning electron microscope (SEM) photograph showing the catalyst material formed inside the cell wall.
3 is a schematic view of the first half, middle and second half sections of the catalytic filter cell after application of the active layer.
4 is a longitudinal cross-sectional schematic view of filters formed by embodiments.
Figure 5 shows the THC, CO and NOx purification performance for the conventional catalyst for coating the cell wall inside (Comparative Example) and the catalyst for coating the cell wall surface (Example 1).

In the description of the present invention, a 'cross-section' while describing a filter structure is defined as a cross-section perpendicular to the exhaust gas flow direction, unless otherwise specified. On the other hand, the 'half part' or 'outlet side' may be understood as the side through which the exhaust gas is discharged to the outside through the filter, and the 'front part' or 'inlet side' refers to the side where the exhaust gas is discharged from the engine. It is defined as the side where the exhaust gas is introduced. In addition, 'first half' and 'second half' are not necessarily terms that divide the filter in the longitudinal direction, and may be understood as a part of the first half and a part of the second half according to exhaust gas and engine conditions. In the present invention, exhaust gas refers to exhaust gas of a comprehensive concept containing harmful components, including exhaust gas generated from a mobile internal combustion engine such as an automobile or a stationary internal combustion engine such as a power plant. In the present invention, pores means pores formed in the catalytically active layer and pores mean pores formed in the filter cell wall itself, but the two terms may be used interchangeably.

The present invention proposes a catalyst filter for purifying endothelial exhaust gas. First, the filter structure will be described. 1 is a perspective view and a partially enlarged cross-sectional view of a cylindrical catalyst filter.

In the structure of the honeycomb filter 10, a plurality of through-cells or channels 12' and 12" having a substantially square cross section are regularly formed along the axial direction, and each of the through-cells 12', 12" ) are partitioned from each other by thin cell walls 13 . Of the plurality of cells, about half are opened at the inlet end face 9a, and the remaining cells are open at the outlet end face 9b. A catalyst material 30 made of platinum group elements or other metal elements and oxides thereof is coated or supported on the surface or inside the pores of the cell walls 13 inside the cells 12' opened at the inlet end face 9a. The opening of each through-cell 12', 12" is sealed by plugging 15 on either end face 9a, 9b side. Therefore, the entire cross-section of the filter structure exhibits a checkerboard shape. The density is set to around 200 pieces/inch ² , and the thickness of the cell wall 13 is set to around 0.3 mm. As the exhaust gas entering the inside of the cell 12' opened at the inflow end face 9a passes through the cell wall, PN is After being filtered (trap, deposition), only the remaining gas component is discharged to the outside through the cell 12" opened at the outlet end face 9b through the cell wall pores (or pores). At this time, the gas component is converted into a harmless component by promoting the oxidation-reduction reaction by a catalyst coated on the cell wall 13 (FIG. 2a) or supported in the pores inside the cell wall (FIG. 2b) and discharged outside in the direction of the outflow section 9b do.

Various coating methods for the surface of the cell wall 13 or the inside of the pores may be applied. The present invention provides a catalyst filter for exhaust gas purification in which a porous catalytically active layer is applied to the filter cell wall and a phosphorus component poisoning layer is applied on the active layer, and the thickness of the active layer and the poisoning layer becomes thinner toward the latter part of the filter. The active layer according to the present invention includes three-way catalyst components or SCR catalyst components. Polymethylmethacrylate (PMMA) particles may be added to the slurry of catalyst components in order to realize the distribution of pores of a certain size, preferably 1-20 μm in diameter, in the active layer. In the porous slurry layer obtained by coating the slurry to which PMMA is applied, it can be expected to improve the fluidity and reduce the back pressure according to the increase of the specific surface area. Catalyst activated slurry containing PMMA particles is applied to the cell walls by immersion or various coating methods, but most of them are applied to the surface of the cell walls, and within about 10% of the total amount of the slurry permeates into the cell walls. The thickness of the slurry applied to the surface of the cell wall may be applied thinner toward the second half in the longitudinal direction from the first half of the cell wall. The slurry is applied to the entire cell wall, but it may become thinner at a constant slope toward the second half or irregularly in thickness. Preferably, the thickness of the catalytically active layer is about 20 to 350 μm, and the average diameter of the pores distributed in the porous active layer is set to 1 to 20 μm. Without being bound by theory, by applying a small amount of active ingredients to the second half, the PN combustion rate is lower than that in the first half, thereby preventing deterioration of the poisoning layer formed thereon. The poison layer thickness for the phosphorus component is approximately 20-100 μm, and becomes thinner until reaching the latter part along the longitudinal direction in the same manner as the active layer. The thinning of the P poisoning layer along the longitudinal direction, without being bound by theory, is based on the experimental fact that the exhaust gas contact time is large in the first half compared to the second half inside the filter. The material of the catalyst filter to which the present invention is applied is not limited, but may be, for example, a filter made of silicon carbide (SiC), aluminum titania, or cordierite. The active layer includes a TWC (three-way catalyst) material or an SCR catalyst material, and the poison layer component is composed of Sr-Al ₂ O ₃ . After applying the catalyst activated slurry and after applying the Sr-Al ₂ O ₃ slurry, the filter is dried with hot air at a temperature of 140 ° C. in a hot air blower for 20 minutes, and calcined in an electric furnace at 450 to 550 ° C. for 4 hours to complete a double layer filter. . Specifically, two types of washcoats, namely, an activated slurry containing a noble metal and a poisoning slurry without a noble metal, are sequentially applied to the filter cell wall of the present invention. First, an activated slurry containing a noble metal and an oxygen storage component (OSC) is applied over the entire cell wall, dried and calcined. Subsequently, the poisoning slurry is applied over the top of the active layer. Poisoned Slyrie contains strontium oxide to capture P. The noble metal component of the active layer includes a platinum group metal. copy

The catalytic filter of the present invention contains a noble metal component in a sufficient amount to oxidize hydrocarbons and carbon monoxide and reduce nitrogen oxide at the same time as removing PN. The platinum group catalytically active component is supported on a support, preferably on activated alumina and/or ceria-zirconia composite particles so that dispersion of the catalytically active component is achieved. Typically, the at least one noble metal-containing activated slurry comprises OSC. OSCs comprise mixed oxides of one or more rare earth metals, preferably ceria, cerium and zirconium, and mixed oxides of cerium, zirconium, praseodymium, lanthanum and neodymium. The poison slurry is calcined at a high temperature (550° C., 2 h) after impregnating the alumina particles with strontium nitrate. As a precursor of Sr, in addition to nitrate, various precursors such as oxide, acetic acid, and hydroxide may be used. After dispersing the calcined Sr-Al2O3 in water, it is milled to a PSD (D90) of 10 to 20 μm, and a viscosity improver is added to increase coating properties, followed by stirring for at least 1 h to apply to the filter.

Example 1

An activated slurry was prepared by adding PMMA (S50) to the catalyst activated slurry containing noble metals and OSC components in an amount of 40% by weight of the total amount of the slurry, and then a filter (132.1*124, 1.7L, 300 /8) The entire interior of the cell wall was coated. A catalytically active layer was prepared on the filter cell wall by drying and calcining.

3 is a schematic view showing the thickness of the coating layer in the first half, the middle and the second half of the catalytic filter cell after application of the active layer in Example 1, which was carried out three times, and cross-sections thereof.

Example 2

A separately prepared poisoning slurry of Sr-Al ₂ O ₃ component was coated on the catalytic active layer formed in Example 1 over the entire catalytically active layer so that the thickness of the poisoning slurry became thinner from the first half to the second half to complete the catalyst filter.

Table 1 summarizes the thickness of the coating layer in the first half and the second half of the catalytic filter cell after the poisoning layer was applied in Example 2.

first half (wall), um second half (wall), um example (20-100) (1-40)

Coating Length Comparative Example 1

It was coated as in Example 1, but not the entire inside of the cell wall, but 85% of the entire length from the front side, and 15% of the length from the back side was not coated.

Coating Length Comparative Example 2

As in Example 1, the coating was carried out over 70% of the total length from the front side, not the entire inside of the cell wall, so that 30% of the length from the back side was not coated.

4 is a longitudinal cross-sectional schematic view of a filter formed by Example 1 (left) and Example 2 (right). Two pores are exaggeratedly marked on the cell wall, and an active layer (left) and an active layer and poisoned layer (right) appear on the cell wall surface. In particular, pores of a certain size are distributed in the active layer. The back pressure was measured in the filter according to Example 1, and compared with the reference filter without the active layer and the poison layer, the back pressure was increased by 40% for the filter with the active layer, and for the filter having both the active layer and the poison layer, the back pressure was 88% increased.

Table 2 shows the engine evaluation results after P aging for the filters formed by Examples 1 and 2.

Example 1 Example 2 CO conversion rate Before P-poisoning 89.6% 87.0% After P-poisoning 72.9% 78.2% NOx conversion rate Before P-poisoning 82.6% 75.5% After P-poisoning 74.6% 73.6%

Table 3 summarizes the FFE (fresh PN, WLTC) measured for the catalysts according to Example 1 and Comparative Examples 1-2. From this, it was confirmed that the FEE is lowered if not entirely coated inside the cell of the catalyst. FFE values for uncoated catalysts are the standard.

Example 1 Coating Length Comparative Example 1 Coating Length Comparative Example 2 PN(#/km) 92% reduction 75% reduction 72% reduction

Compared with the case where the porous catalytically active layer is coated on the surface of the cell wall (on-wall), the catalyst of the present application increases the back pressure by about 30%p compared to the case where the catalyst is coated on the inside of the cell wall (on-wall). As the gas easily comes into contact with the active ingredient, the emission purification performance is also improved. Table 4 summarizes the FFEs for the cell wall inner coating catalyst and the cell wall surface coating catalyst (Example 1) based on the uncoated catalyst.

Cell wall inner coating catalyst Example 1 PN(#/km) 70% reduction 93% reduction

Figure 5 shows the THC, CO and NOx purification performance for the conventional catalyst for coating the cell wall inside (Comparative Example) and the catalyst for coating the cell wall surface (Example 1). According to this, it was confirmed that the CO and NOx performances were improved by 18% and 27%, respectively, compared to the conventional catalyst.

Claims (6)

A catalytic filter for exhaust gas purification, wherein a lower porous catalytically active layer is applied on the surface of a filter channel wall and a phosphorus poisoning layer is applied on the active layer, and the thickness of each of the active layer and the poisoning layer increases toward the latter part of the filter in the longitudinal direction of the filter. A catalytic filter for exhaust gas purification, characterized in that thin, and the active layer is formed of an SCR catalyst material. The catalyst filter for exhaust gas purification according to claim 1, wherein the active layer has a thickness of 20 to 350 μm and becomes thinner until reaching the latter part of the filter along the longitudinal direction. The catalyst filter for exhaust gas purification according to claim 1, wherein the porous active layer has an average pore diameter of 1 to 20 μm. The catalyst filter for exhaust gas purification according to claim 1, wherein the poison layer has a thickness of 20 to 100 μm and becomes thinner until reaching the latter part of the filter along the longitudinal direction. delete The catalyst filter for exhaust gas purification according to claim 1, wherein the poisoning layer comprises a Sr-Al ₂ O ₃ component.

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