WO2022030861A1

WO2022030861A1 - Catalyst for purification of exhaust gas provided with thin barrier against catalytically active material on high-porosity substrate

Info

Publication number: WO2022030861A1
Application number: PCT/KR2021/009767
Authority: WO
Inventors: 이귀연; 송진우
Original assignee: 희성촉매 주식회사
Priority date: 2020-08-06
Filing date: 2021-07-28
Publication date: 2022-02-10
Also published as: KR20220018160A; KR102441367B1

Abstract

The present invention relates to a catalyst for purification of exhaust gas, which is provided with a thin barrier against a catalytically active material on a high-porosity substrate, and to a catalyst for purification of exhaust gas and, particularly, to a three-way catalyst, to which a thin barrier is applied in order to minimize the penetration of a catalytically active material from a catalytically active layer coated on a substrate into pores formed in the inner wall of the substrate, wherein improved results in THC, CO, and NOx emissions are exhibited, compared to a thin-barrier-member catalyst, and particularly, the low-temperature activity improvement function of a catalyst according to a reduction in the thermal capacity of a high-porosity substrate, can be realized.

Description

Catalyst for exhaust gas purification provided with a thin layer of blocking catalytically active material on a high pore carrier

The present invention relates to a catalyst for purification of exhaust gas provided with a thin layer for blocking a catalytically active material on a high porosity substrate, wherein the catalytically active material from a catalytically active layer coated on the carrier penetrates into pores formed on the inner wall of the carrier. In order to minimize the phenomenon, it relates to a catalyst for purification of exhaust gas with a thin barrier applied, particularly a three-way catalyst, which shows improved results in THC, CO, and NOx emission compared to a catalyst without a thin barrier layer. It relates to an exhaust gas purification catalyst capable of realizing a function of improving catalyst low-temperature activity according to a reduction in heat capacity.

Recently, as the use of automobiles increases and the amount of traffic increases, the problem of air pollution due to exhaust gas is emerging as a serious social problem. Therefore, governments of each country have set emission standards for pollutants in exhaust gas such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) for exhaust gas regulation, and these exhaust gas regulations are gradually being strengthened and have. In addition, each automobile manufacturer is putting a lot of effort into effectively responding to stricter exhaust gas regulations. In particular, in the cold start section of automobiles, that is, before the catalyst is activated, the performance of purifying exhaust gas emitted from the engine is more required. Ceramics mainly used in automobile catalysts to shorten the time to reach the catalyst activation temperature for the purpose of improving low-temperature catalyst activity A high-pore carrier technology for reducing the heat capacity of a material substrate has been introduced.

However, in the case of a high pore carrier, the porosity in the wall forming the carrier channel is higher than that of a conventional carrier, so that small particulate matter and soluble catalytically active substances in the catalyst layer coated on the carrier wall during the catalyst preparation process are part of the carrier wall surface. It can penetrate or be absorbed into the pores existing in the On the contrary, since the exhaust gas passing through the carrier channel hardly passes into the inside of the wall constituting the carrier channel, the catalyst components that permeate or absorbed into the wall of the carrier channel cannot contact the exhaust gas, resulting in loss of the effective catalyst component. problem arises. In particular, in the case of a high pore carrier, the catalyst purification performance can be improved in the cold-start section because the catalyst has a higher porosity than a conventional carrier, is light in weight, and the temperature rise rate of the catalyst is increased due to the reduction in heat capacity. As some of the components penetrate, the benefits in the cold start section that can be achieved through the application of the high pore carrier cannot be achieved.

The present inventors have studied a way to minimize the penetration of catalytically active materials into the walls of the high pore support, and suggested the possibility of improving the performance of the catalyst to which the high-functional support is applied through the application of a thin layer to prevent penetration of the catalytically active material. Therefore, it is an object of the present invention to apply a thin barrier layer on the wall forming the carrier channel to prevent the catalytically active ingredient from penetrating into the carrier wall during the catalyst preparation and high-temperature deterioration process in a catalyst for exhaust gas purification using a high pore carrier. to improve the catalyst purification performance.

The present invention relates to a catalyst for purifying exhaust gas in which a catalytically active layer is formed on the inner wall of a high pore carrier, wherein a thin layer is formed between the inner wall of the high pore carrier and the catalytically active layer. Without limitation, the thin layer may include heat-resistant inorganic oxide particles, and the diameter of the inorganic oxide particles is larger than the diameter of pores formed on the inner wall surface of the high pore carrier. In addition, the catalytically active layer may be formed as a single layer or multiple layers.

Electron Probe X-ray Micro Analyzer (EPMA) showed that penetration of the catalytically active ingredient into the carrier wall was significantly reduced through the application of a thin layer that prevents penetration of the catalytically active ingredient into the pores forming a part of the high pore carrier wall. was confirmed through this, and accordingly, the exhaust gas purification performance, especially the catalyst purification performance in the cold-start section of automobiles, can be improved.

1 is a schematic cross-sectional view of a three-way catalyst having a two-layer structure according to the present invention, wherein a thin layer is applied to inhibit the penetration of a catalytically active material into pores of a wall of a high pore carrier.

Fig. 2 is a schematic cross-sectional view of a three-way catalyst having a one-layer structure according to the present invention, wherein a thin layer is applied to inhibit penetration of a catalytically active material into pores of a wall of a high pore carrier.

3 is a schematic cross-sectional view of a three-way catalyst having a two-layer structure according to the prior art, in which a catalytically active material is directly coated on a wall of a high pore carrier.

4 is an electron micro-probe analyzer (EPMA) measurement image of catalysts with or without a thin barrier layer.

5 is a graph comparing THC, CO, and NOx reduction performance of catalysts according to the presence or absence of a thin barrier layer.

6 is a graph comparing THC reduction performance in the cold start section of catalysts according to the presence or absence of a thin barrier layer.

Justice

As used herein, the term 'catalyst' refers to a powder form in which an active ingredient such as Pd or Rh is supported on a support such as alumina powder, and the term 'catalyst body' refers to a structure in which the 'catalyst' is applied to a substrate such as cordierite. do. The 'wash coat' refers to a slurry in which the catalyst and other components are mixed. The washcoat is applied to a substrate to form the catalyst body, and thus the substrate may also be referred to as a carrier or carrier. However, as will be understood by one of ordinary skill in the art, the terms catalyst or catalyst body may be used interchangeably. As used herein, catalytically active material penetration refers to a phenomenon in which catalyst powder or catalyst slurry enters the pores or pores of the carrier by physical or chemical factors.

As used herein, the term 'high pore substrate' refers to a substrate having a porosity of about 40 to about 80%. The high pore substrate may preferably have a porosity of at least about 50%. The meat-air material may preferably have a porosity of less than about 75%, more preferably less than about 70%. As used herein, the term porosity refers to the total porosity, preferably as measured by mercury porosimetry. A large number of macropores exist on the surface and inside of the wall forming the passageway or channel of the high pore substrate. Carrier walls are understood to be walls that form a passageway or channel of a carrier or substrate. In the present invention, a honeycomb type monolithic ceramic substrate may be used as the substrate. Preferably the substrate has a plurality of fine, parallel passageways extending from an inlet to an outlet of the substrate, the passageways open to fluid flow. A monolithic substrate may have about 700 or more fluid flow passages (or “cells”) per cubic inch of cross-section, although even fewer may be used. For example, the carrier may have cells per cubic inch (cpsi) of from about 7 to 600, more typically from about 100 to 400. A passageway that is a substantially straight path from the substrate inlet to the outlet is coated with the catalyst slurry as a washcoat thereon and the passageway is defined by interior walls. The fluid flow passages of the monolithic substrate are channels formed by thin walls that may be of any suitable cross-sectional shape, such as trapezoidal, rectangular, square, triangular, sinusoidal, hexagonal, elliptical, circular, and the like. The present invention is not limited to a particular substrate type, material or geometry. The heat-resistant ceramic substrate may be a suitable refractory material such as cordierite, cordierite-α alumina, α-alumina, silicon carbide, silicon nitride, zirconia, alumina-silica magnesia, zirconium silicate, magnesium silicate, aluminosilicate and mixtures thereof. can be made with

The present invention relates to an exhaust gas catalyst to which a thin barrier layer is applied to prevent penetration of a catalytically active ingredient or catalyst slurry into the interior of pores present in walls forming high pore carrier passages. Before applying a washcoat containing a catalytically active material to the inner wall of a carrier, the inner wall of the carrier is treated with a thin barrier layer to prevent penetration of the slurry into the pores existing on and/or on the surface of the carrier wall. Inorganic oxide particles having a particle size greater than or equal to the pore size on the surface and/or inside of the wall forming the passage of the honeycomb-type high pore carrier are coated on the inner wall of the carrier to form a thin layer, and then a catalytically active material is formed on the thin layer. A wash coat is applied to complete the catalyst body. Preferably, the thin layer is free of catalytically active components, in particular noble metals.

Hereinafter, a catalyst to which a thin barrier layer is applied will be described with reference to the drawings, but is not limited thereto.

1 is a schematic diagram of a catalyst according to the present invention; The catalyst to which the thin barrier layer according to the present invention is applied includes a carrier (1), a thin barrier layer (3) formed on the inner wall surface of the carrier, and a catalytically active layer (4, 5) coated on the thin layer, wherein the thin layer comprises the The catalytically active component constituting the catalytically active layer is prevented from penetrating into the pores constituting the inner wall of the carrier. The catalytically active layer may be composed of a single or multiple layers, for example, the active layer is a first catalytically active layer 4 applied directly to a thin layer and a second catalytically active layer applied on top of the first catalytically active layer and having components different from the first catalytically active layer. A catalytically active layer (5) may be included. 2 shows a catalyst in which the catalytically active layer 6 is composed of a single layer.

The carrier (1) is a high pore substrate having a porosity of at least 30% or more, and a number of macropores exist on the surface and inside the wall forming the passage of exhaust gas, and the high pore substrate is made of a heat-resistant inorganic material or metal of cordierite It is a functional substrate designed with a low heat capacity to shorten the time to reach the catalyst activation temperature for the purpose of improving catalyst low temperature activity.

The barrier thin layer 3 formed on part or all of the inner wall forming the passage of the carrier 1 is composed of an inert particulate material that does not contain noble metals and components having catalytic activity, for example, Al ₂ O ₃ , CeZrOx, CeOx, A refractory inorganic oxide of ZrOx is suitable. The size of the inert particulate material is preferably greater than or equal to the pore size of the carrier, for example, 5 µm to 80 µm, preferably 10 µm to 20 µm. In addition, the content of the thin barrier layer is 5 g/L to 100 g/L, preferably 20 to 50 g/L. A method of applying the inert particulate material to form a thin film is not particularly limited, but a method of coating a pulverized slurry by mixing the particulate material in an aqueous solution on a carrier may be exemplified. The slurry is coated on the inner wall of the carrier and dried, but the drying conditions depend on the shape and dimensions of the carrier, but typically 80 ° C. (for example, 100 ° C. for 1 hour to 10 hours. 300 ℃ ℃ (for example, 400 ℃ ℃ 1 hour ~ 4 hours. The barrier thin layer formed on the inner wall of the carrier is to prevent the materials constituting the catalytically active layer from penetrating into the interior through the pores forming the inner wall. , For this purpose, the thickness and composition of the barrier thin layer can be considered.Thin layer can be coated over the entire inner wall, but can only be applied to a portion of it.For example, two catalytically active layers are applied to the inner wall of the carrier. In this case, the thin barrier layer may be coated on the inner wall to which one kind of catalytically active layer is applied, but the thin barrier layer may not be coated on the inner wall to which the other kind of catalytically active layer is applied.

In the catalyst of the present invention, a single layer or multiple catalytically active layers may be applied on the thin barrier layer. The catalytically active layer is made of a particulate material impregnated with a support such as Pd, Rh, Pt, Ir, Ru and the like, and includes aluminum oxide (Al ₂ O ₃ , alumina), cerium oxide (CeO ₂ , ceria), and zirconium oxide. (ZrO ₂ ), silicon oxide (SiO ₂ , silica), yttrium oxide (Y ₂ O ₃ ), and metal oxides such as lanthanum oxide (La ₂ O ₃ ) and neodymium oxide (Nd ₂ O ₃ ), or a solid solution or composite thereof Oxides may be used. Optionally, the active layer may include an enhancer capable of improving catalyst performance, such as Ba, La, Zr, Nd, or the like. The method for applying the catalytically active layer to the thin barrier layer is not particularly limited, but a catalytically active slurry obtained by mixing a particulate material impregnated with a noble metal in an aqueous solution and pulverizing it is coated on the thin layer, preferably, the noble metal impregnated support is applied to the thin layer. A catalytically active slurry is prepared by mixing the particulate matter obtained by calcining at 300° C. in an aqueous solution and pulverizing it, and coating the same. The active catalyst layer may have one or more layers, and the content of the catalyst active layer is 50 g/L to 300 g/L, preferably 150 g/L to 250 g/L. 1 shows a catalyst coated with two catalytically active layers, and FIG. 2 shows a catalyst coated with a single catalytically active layer on a thin barrier layer.

The present invention applies a thin barrier layer that prevents penetration of catalytically active ingredients from the active catalyst layer into the pores of the inner wall constituting the passage of the carrier when a high pore carrier is used among carriers, and through this, the essential advantage of the high pore carrier, namely, heat capacity It is to improve the catalytic activity by implementing the reduction function. Hereinafter, although described in detail through embodiments of the present invention, it is clear that the spirit of the present invention is not limited thereto.

Example 1

1. Formation of a thin barrier layer (3)

Alumina oxide (Al ₂ O ₃ ) powder was dispersed in a solvent to prepare a slurry having a diameter of 13 μm to 15 μm, and an amount of 40 g/L of the slurry was coated on a high pore carrier (1) having a porosity of 40%. Then, a thin barrier layer was formed on the inner wall forming the high pore carrier passage through a drying process at 80°C for 1 hour to 10 hours and a firing process at 300°C for 1 hour to 4 hours.

2. Formation of the first catalytically active layer (4)

A Pd-N (Pd-nitrate) aqueous solution was impregnated into a cerium zirconium oxide (CeZrOx) composite oxide. The zirconium oxide composite oxide powder was dried at 150° C. for 5 hours, and calcined at 400° C. to 650° C. for 2 hours to prepare a pre-catalyst. A slurry was prepared by mixing the obtained pre-catalyst, alumina powder, and barium oxide (BaOx) in a solvent, coated on a thin-layered carrier, and then dried at 80°C for 1 hour to 10 hours, and at 300°C for about 1 hour. A first catalytically active layer was prepared through a 4-hour calcination process.

3. Formation of the second catalytically active layer (5)

An aqueous RhN (Rh-nitrate) solution was impregnated into the mixed powder of alumina oxide and zirconium composite oxide. The powder was dried at 150° C. for 5 hours and calcined at 400° C. to 650° C. for 2 hours to prepare a pre-catalyst. A slurry was prepared by mixing the obtained pre-catalyst, cerium zirconium oxide composite oxide, and zirconium oxide (ZrOx) in a solvent, coated on the first catalyst active layer, and dried at 80° C. for 1 hour to 10 hours, and at 300° C. for 1 hour A second catalytically active layer was formed through a calcination process of ˜4 hours, thereby completing a catalyst having a thin barrier layer and two catalytically active layers, as shown in FIG. 1 .

Example 2

After forming the barrier thin layer of Example 1, mixed with PdN (Pd-nitrate) and RhN (Rh-nitrate) aqueous solution, impregnated with a mixed powder of alumina oxide and cerium zirconium oxide composite oxide, dried at 150° C. for 5 hours, and , and calcined at 400°C to 650°C for 2 hours to prepare a pre-catalyst. A slurry was prepared by mixing the obtained precatalyst and zirconium oxide (ZrOx) in a solvent, coated on a thin barrier layer, dried at 80°C for 1 hour to 10 hours, and calcined at 300°C for 1 hour to 4 hours. By forming the catalytically active layer, a catalyst having a thin barrier layer and a single-layered catalytically active layer 6, shown in FIG. 2, was completed.

Comparative Example 1

A comparative catalyst having two catalytically active layers (4, 5) without a thin barrier layer on a high pore carrier was completed in the same manner as in Example 1, except that the step of forming a thin barrier layer was omitted. The comparative catalyst is shown in FIG. 3 , and particles or solubles constituting the catalytically active layer penetrate into the pores in a plurality of pores on the inner wall forming the passage of the high pore carrier.

Comparative Example 2

Comparison of having two catalytically active layers without a thin barrier layer on the low pore carrier by using the same as in Example 1, but using a low pore carrier having a porosity of 28% instead of a high pore carrier and omitting the step of forming a thin barrier layer The catalyst was completed.

1. Penetration into the inner wall of the carrier: The evaluation of whether the material constituting the catalyst active layer penetrates into the wall of the carrier passage was performed using EPMA after each catalyst was cut to a predetermined size. Figure 4 (a) is the EPMA for the comparative catalyst prepared in Comparative Example 1, Figure 4 (b) is the EPMA for the catalyst according to the present invention prepared in Example 1. Although the components constituting the catalytically active layer permeate into the base of the comparative catalyst, it can be seen that penetration of the components constituting the catalytically active layer is suppressed in the base of the catalyst according to the present invention.

2. Catalyst deterioration: For the deterioration of each catalyst, an actual engine deterioration or a gas composition controllable tubular electric furnace was used. Specifically, in the case of engine deterioration, the catalyst bed temperature was performed under operating conditions in which stoichiometric and lean and rich atmospheres were repeated over 50 hours at 1050°C. Repeated operating conditions were performed.

3. Performance evaluation: The activity of each catalyst was evaluated in an actual vehicle. Specifically, FTP-75 mode evaluation was performed by installing a catalyst that was degraded at the MCC location of a vehicle having a 1.6L T-GDI engine, and the amount of exhaust gas after the catalyst was measured to determine the difference in activity between each catalyst. Specifically, referring to FIG. 5 , when comparing the catalytic performance of the low pore carrier (Comparative Example 2), the high pore carrier (Comparative Example 1) and the high pore carrier (Example 1), the catalyst in which a barrier foil layer is applied to the high pore carrier It can be seen that the catalyst performance is superior to that of the low-pore carrier and the catalyst applied with the high-pore carrier without the barrier thin layer. Therefore, the thin barrier layer proposed by the present invention provides a method for effectively utilizing a high pore carrier with reduced heat capacity sold for the purpose of improving catalyst low-temperature activity.

Meanwhile, referring to FIG. 6 , when the catalyst purification performance of the high pore carrier (Comparative Example 1) and the high pore carrier (Example 1) was compared in the cold-start section, the case of Example 1 showed a lower emission than Comparative Example 1. As can be seen, it can be confirmed that the catalyst performance is excellent in the low-temperature section. Also, comparing the catalyst temperature rise, that is, the slope of the high pore carrier (Comparative Example 1) and the high pore carrier (Example 1), the catalyst increase rate in Example 1 was faster than in Comparative Example 1, which This means that the advantage of reducing the heat capacity of the carrier is further realized in Example 1.

Claims

A catalyst for exhaust gas purification in which a catalytically active layer is formed on an inner wall of a high pore support, wherein a thin layer is formed between the inner wall of the high pore support and the catalytically active layer.
The catalyst for purifying exhaust gas according to claim 1, wherein the thin layer contains heat-resistant inorganic oxide particles.
The catalyst for purifying exhaust gas according to claim 2, wherein a diameter of the inorganic oxide particles is larger than a diameter of pores formed on the inner wall surface of the high pore carrier.
The catalyst for exhaust gas purification according to claim 1, wherein the catalytically active layer is a single layer or multiple layers.