JP2010188302A - Three-way catalyst for cleaning exhaust gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a three-way catalyst for cleaning exhaust gas capable of reducing sulfur poisoning while securing high catalytic activity by suppressing reaction between catalytic noble metal and barium. <P>SOLUTION: The three-way catalyst for cleaning exhaust gas has a catalyst coating layer 10 which comprises a lower layer 2 containing barium sulfate and an upper layer 1 containing no barium sulfate on a base material 3. The three-way catalyst for cleaning exhaust gas is effective even when being applied only to the exhaust gas inflow side of a catalyst device such as honeycomb. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a three-way catalyst for exhaust gas purification with reduced sulfur poisoning.

  Sulfur poisoning is a phenomenon in which sulfur contained in fuel or engine oil adheres to the active site of the catalyst during the combustion process and inhibits the catalytic reaction of the catalyst noble metal.

  As a countermeasure, there is a policy to reduce the sulfur content, such as regulations that limit the sulfur concentration in the fuel, but it is very difficult to completely remove the sulfur content of the fuel or engine oil. This measure is also necessary.

  Conventionally, in order to prevent or reduce sulfur poisoning, means such as addition of alkaline earth metals, rare earth metals, nickel, iron and the like as elements to adsorb the sulfur content of the catalyst have been taken.

  However, the above-described components have a problem that the activity is lowered by reacting with the noble metal to form an alloy or changing the charge of the noble metal.

  In addition, as a method for adding an alkaline earth metal, when carbonate is used, it is water-soluble, so that it is added on the catalyst coat layer after it is formed.

  Patent Document 1 discloses a three-way catalyst containing a cerium-zirconium composite oxide, a catalyst noble metal, and a support material, and the support material is barium sulfate particles. The composite oxide is supported directly on the barium sulfate particles, and the catalyst noble metal is supported directly on the barium sulfate particles or indirectly through the composite oxide. Since barium sulfate has high thermal stability and is difficult to sinter, sintering of the composite oxide is suppressed, and sintering of the catalyst noble metal and embedding in the composite oxide are avoided. However, no consideration is given to the reduction of sulfur poisoning, and neither the formation of an alloy by the reaction of barium in barium sulfate with a catalytic noble metal or the decrease in activity due to a change in the charge of the noble metal is considered.

  Patent Document 2 discloses an exhaust gas purification catalyst in which barium is contained as a sulfur storage layer in a NOx storage layer. However, in this case as well, the formation of an alloy due to the reaction with the catalytic noble metal such as Pt and Pd in the NOx occlusion layer and the decrease in activity due to the change in the charge of the noble metal cannot be avoided.

Japanese Patent No. 4200768 JP 2000-110551 A

  An object of the present invention is to provide a three-way catalyst for purifying exhaust gas that can suppress sulfur poisoning while ensuring a high catalytic activity by suppressing the reaction between catalytic noble metal and barium.

  In order to achieve the above object, according to the present invention, there is provided an exhaust gas purifying device characterized in that a catalyst coat layer comprising a lower layer containing barium sulfate and an upper layer not containing barium sulfate is provided on a substrate. An original catalyst is provided.

  Since the catalyst of the present invention does not react with each other in the upper layer of the catalyst coat layer that does not contain barium, the catalytic activity due to alloying or the change in the charge of the catalyst metal is correspondingly reduced. Without causing a reduction, the sulfur adsorption ability can be reduced by the lower layer of the catalyst coat layer containing barium to reduce sulfur poisoning.

  Moreover, since the lower layer barium is used as a sulfate having low solubility in water, the lower layer of the catalyst coat layer can be formed on the substrate before the upper layer of the catalyst coat layer is formed.

  The catalyst of the present invention is effective even when applied only to the exhaust gas inflow side of a catalyst device (honeycomb or the like).

It is a perspective view of an exhaust gas purification catalyst honeycomb. It is (A) cross-sectional view which shows the cross-section of the catalyst of this invention, (B) longitudinal cross-sectional view, (C) longitudinal cross-sectional view of another aspect. It is a graph which compares and shows the purification rate with respect to HC, NOx, and CO by each catalyst of Examples 1 and 2 and Comparative Examples 1 and 2. It is a graph which shows the relationship between the addition amount of barium sulfate to a lower layer, and the purification rate of (A) HC, (B) NOx, and (C) CO.

  Embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a ceramic honeycomb serving as a base material for an exhaust gas purification catalyst, in which a catalyst coat layer is formed on the inner walls of a large number of through holes provided in a cylindrical shape.

  FIG. 2 shows a state in which the catalyst coat layer of the present invention comprising two upper and lower layers is formed. 2A shows a cross section in the radial direction of the cylindrical honeycomb in FIG. 1, and FIGS. 2B and 2C show longitudinal cross sections in the axial direction of the cylindrical honeycomb in FIG. As shown in FIG. 2A, the catalyst coat layer 10 is composed of an upper layer 1 (not including barium sulfate) exposed in the through-hole and a lower layer 2 (including barium sulfate) located thereunder. A substrate made of ceramic (not shown) surrounds the entire outside of the catalyst coat layer 10 (directly the lower layer 2). 2 (B) shows a case where the catalyst coat layer 10 has an upper and lower two-layer structure over the entire length of the honeycomb. FIG. 2 (C) shows a half length on the exhaust gas inflow side of the entire honeycomb length, and an upper and lower two-layer structure. The case where the catalyst coat layer has a single-layer structure consisting of only the upper layer is shown.

[Example 1]
(1) Formation of lower layer coat layer (1-1) Preparation of slurry for lower layer coat Pd is added to zirconia (manufactured by Daiichi Elemental Chemical Co., Ltd., ZrO ₂ : 90 wt%, Y ₂ O ₃ : 10 wt%). The Pd nitrate chemical solution was impregnated and supported so as to be 1.7 wt%, dried and fired.

26 g of the obtained Pd-supported catalyst and 3γ g of γ-alumina (manufactured by Sasol, Al ₂ O ₃ : 96 wt%, La ₂ O ₃ : 4 wt%) and 9 g of barium sulfate were added and mixed.

  The obtained mixed powder was dispersed in water, an alumina binder was added so that the weight ratio of the alumina binder and the mixed powder was 1:19, and milling was performed to obtain a slurry for the lower layer.

  The amount of barium sulfate in the obtained lower layer slurry is 10 g / L.

(1-2) Formation of lower layer coat layer on substrate The obtained lower layer slurry was applied to a ceramic honeycomb (manufactured by Denso Corporation, cell density 600 cell / inch ² , wall thickness 3 mil, φ103 mm × L105 mm) and dried. The lower coat layer 2 was formed by firing.

(2) Formation of upper layer coating layer (2-1) Preparation of slurry for upper layer coating Ceria-zirconia-yttria-lantana powder (CeO ₂ : 20 wt%, ZrO ₂ : 70 wt%, Y ₂ O ₃ : 5 wt%, La ₂ O ₃ : 5 wt%) was impregnated and supported with a Rh nitric acid chemical solution so that Rh was 0.2 wt%, dried and fired.

44 g of the obtained Rh-supported catalyst and 44 g of γ-alumina (manufactured by Sasol, Al ₂ O ₃ : 96 wt%, La ₂ O ₃ : 4 wt%) were mixed and dispersed in water. Further, the alumina binder and the mixed powder were mixed at a weight ratio of 1: 1.9, and water was added to obtain an upper layer slurry.

(2-2) Formation of upper layer coat layer on base material The obtained upper layer coat slurry is poured into the honeycomb having the lower layer coat layer described above from the upper part and sucked from the lower part to coat the lower layer. The upper coat layer 2 was formed by applying the solution on top, drying and firing.

[Example 2]
(1) Formation of lower layer coat layer (1-1) Preparation of slurry for lower layer coat Pd is added to zirconia (manufactured by Daiichi Elemental Chemical Co., Ltd., ZrO ₂ : 90 wt%, Y ₂ O ₃ : 10 wt%). 3. Pd nitrate Pd chemical solution was impregnated and supported so as to be 3.34 wt%, dried and fired.

13 g of the obtained Pd-supported catalyst and 15 g of γ-alumina (manufactured by Sasol, Al ₂ O ₃ : 96 wt%, La ₂ O ₃ : 4 wt%) and 9 g of barium sulfate were added and mixed.

  The obtained mixed powder was dispersed in water, an alumina binder was added so that the weight ratio of the alumina binder and the mixed powder was 1:19, and milling was performed to obtain a slurry for the lower layer.

(1-2) Formation of lower layer coat layer on substrate The obtained lower layer slurry was applied to a ceramic honeycomb (manufactured by Denso Corporation, cell density 600 cell / inch ² , wall thickness 3 mil, φ103 mm × L105 mm) and dried. The lower coat layer 2 was formed by firing. At that time, the slurry was applied so as to cover up to 50% (52.5 mm) of the total length of the honeycomb (105 mm) when sucked from the opposite side of the slurry charging side, dried and fired.

(2) Formation of upper layer coating layer In the same manner as in Example 1, an upper layer coating slurry was prepared, and an upper layer coating layer applied, dried and fired on a base material on which a lower layer coating layer had been formed was formed.

[Example 3] to [Example 9]
A catalyst was prepared in the same manner as in Example 1 except that the amount of barium sulfate in the lower layer coating slurry was variously changed.

[Comparative Example 1]
A catalyst was prepared in the same manner as in Example 1 except that barium sulfate was not added to the lower coat layer.

[Comparative Example 2]
Barium sulfate was not added to the lower coat layer, and 9 g of barium sulfate was further added when the Rh-supported catalyst and γ-alumina were mixed during the preparation of the upper layer coating slurry. Otherwise, the catalyst was prepared in the same manner as in Example 1.

  In Table 1, the compounding situation of the barium sulfate in the catalyst of Examples 1-9 and Comparative Examples 1-2 is shown collectively.

<Characteristic evaluation>
<Exhaust gas purification rate>
In order to investigate the influence of sulfur poisoning, an endurance test was conducted using gasoline containing 50 ppm of sulfur.

  The test temperature was a catalyst-containing gas temperature of 900 ° C., and the test time was 100 hours.

  The catalyst subjected to the durability test was attached to a gasoline engine with a displacement of 2.4 L, and the purification rate was measured for HC, NOx, and CO at A / F 14.6 and a catalyst-containing gas temperature of 400 ° C. The results for the catalysts of Examples 1 and 2 and Comparative Examples 1 and 2 are shown in FIG.

  As shown in FIG. 3, the catalyst of the example according to the present invention exhibits an excellent purification rate as compared with the catalyst of the comparative example. Example 1 (form of FIG. 2 (B)) which contains barium sulfate in the whole lower layer, and Example 2 (form of FIG. 2 (C)) which contains only the upper half length of a honeycomb among lower layers are substantially equivalent. Excellent purification rate. Comparative Example 2 containing barium sulfate only in the upper layer exhibits a purification rate superior to that of Comparative Example 1 containing no barium sulfate at all. It is inferior to either.

<Effect of barium sulfate content>
FIG. 4 shows the relationship between the amount of barium sulfate added to the lower layer and the purification rate for (A) HC, (B) NOx, and (C) CO.

  As compared with the case where barium sulfate is not contained at all (Comparative Example 1), the purification rate is improved in all cases where Barium sulfate is contained only in the lower layer (Examples 1-9) according to the present invention (Examples 1-9).

  Based on the case where 10 g / L of barium sulfate is contained only in the upper layer (Comparative Example 2), the case where 3 g / L to 50 g / L of barium sulfate is contained only in the lower layer (Examples 1 to 6) exhibits a high purification rate. ing.

  ADVANTAGE OF THE INVENTION According to this invention, the three-way catalyst for exhaust gas purification | cleaning which can reduce sulfur poisoning can be provided, suppressing reaction with a catalyst noble metal and barium, ensuring high catalyst activity.

1 Upper layer of catalyst coat layer not containing barium sulfate 2 Lower layer of catalyst coat layer containing barium sulfate 3 Catalyst base material

Claims (1)

  A three-way catalyst for purifying exhaust gas, comprising a catalyst coat layer comprising a lower layer containing barium sulfate and an upper layer not containing barium sulfate on a substrate.

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