JPH04210241A - Catalyst for cleaning exhaust gas - Google Patents

Abstract

PURPOSE:To obtain a catalyst having excellent cleaning ability of hydrocarbon (HC), CO and NOx even in an excess oxygen atmosphere by using a solid super strong acid with a transition metal or a transition metal oxide. CONSTITUTION:The solid super strong acid such as SO4/TiO2 or WO3/ZrO2 is used jointly with the transition metal or the transition metal oxide of Mn, Fe, Co or the like. The catalyst obtained in such a way has excellent cleaning ability of HC, CO and NOx in the exhaust gas of the diesel engine or even in the case of lean burn under a dilute condition of gasoline conc. in an excess oxygen atmosphere. Of course, it has excellent cleaning ability of the exhaust gas in the case of not containing excessive oxygen.

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying catalyst that is installed, for example, in the exhaust system of an internal combustion engine to purify exhaust gas. [0002]

2. Description of the Related Art Monolithic catalysts and pellet catalysts have been widely used as exhaust purifying catalysts for automobile internal combustion engines. These exhaust purification catalysts include a carrier base material,
It is composed of a catalyst support layer such as activated alumina coated on the surface of a carrier base material, and a catalyst metal supported on the catalyst support layer. Here, the catalytic metals include Pt, Pd,
One or more types of Rh and the like are used. It is called a three-way catalyst because it simultaneously purifies these three components by oxidizing HC, CO and reducing NOx in the exhaust gas. [0003]

[Problem to be solved by the invention] However, in such a three-way catalyst, the oxygen concentration in the exhaust gas is lower than the theoretical value (the minimum oxygen concentration necessary to completely oxidize the unburned components in the exhaust gas). When it becomes large (this is called lean burn), there is a drawback that NOx in the exhaust cannot be reduced and removed. That is, it has been difficult to purify NOx in diesel engine exhaust gas that contains a large amount of oxygen. In addition, in recent years, there has been a trend in gasoline engines to burn fuel under conditions with a dilute gasoline concentration (lean region) for the purpose of improving fuel efficiency and reducing carbon dioxide emissions, but in this case as well, oxygen becomes excessive and NO
There is a problem that the purification rate of x decreases. [0004] Methods for purifying NOx in oxygen-excess gas include adding a reducing agent such as ammonia and absorbing it in an alkali, but these methods are not suitable for purifying automobile exhaust gas. The present invention was made in view of the above circumstances, and it is possible to remove HC and CO from exhaust gas in an oxygen-rich atmosphere discharged from internal combustion engines such as automobiles.
The purpose is to purify NOx at the same time. [00051

[Means for Solving the Problems] The exhaust gas purification catalyst of the present invention that solves the above problems is characterized by containing a solid super strong acid and at least one selected from transition metals and transition metal oxides. shall be. The term "solid super strong acid" refers to a solid acid having stronger acidity than 100% sulfuric acid (HO≦-11,9). This solid super strong acid needs to have acidic properties to the extent that it causes skeletal isomerization of saturated hydrocarbons at temperatures from room temperature to about 200°C, for example, S 04 / Hf 02 ,
S O4/5n02, S○4/Fe2O3, 504
/Z rOz, S. 4/T iO2, WO3/Z r 02 , MOO3
/Z roz etc. can be used. [00061 As the transition metal, Mn as the main transition element
, Fe, Co, Ni, Cu, Ag, Pt, Au, etc., and at least one of these metals and oxides thereof is used. The amount added is preferably 0.5 to 20% by weight of the total amount including the solid super strong acid.
Particularly preferred is 2 to 7% by weight. The exhaust gas purification catalyst of the present invention has a solid superacid supporting a transition metal or a transition metal oxide, and if necessary, Si02. Ah 03,
After adding other components such as TiO2 and zeolite, it can be formed into granules and used as a pellet catalyst. When using copper oxide powder, which is transition metal oxide powder, fine particles with a particle size of 1 μm or less are preferable. Furthermore, a monolithic catalyst can be obtained by attaching a slurry containing at least a solid super strong acid and a transition metal or a transition metal oxide to a monolithic ceramic carrier substrate or metal carrier substrate. In order to support a transition metal or a transition metal oxide on a solid superacid, a mixing method, a kneading method, an impregnation method, an ion exchange method, etc. can be used. [0007] Functions and Effects of the Invention The exhaust gas purification catalyst of the present invention contains a solid super strong acid and at least one of a transition metal and a transition metal oxide. Excellent purification performance of HC, CO and NOx under atmosphere. Of course, it also has excellent purification performance for exhaust gas that does not contain excess oxygen. [0008]t, Therefore, according to the exhaust gas purification catalyst of the present invention, the exhaust gas of a diesel engine containing excess oxygen,
It is possible to simultaneously purify HC, CO, and NOx contained in the exhaust gas of a gasoline engine operated in a lean region. [0009]

[Examples] Hereinafter, the present invention will be explained in detail using examples. (Example 1) TiCL 237.5 was dissolved in 21 g of water-cooled deionized water, and aqueous ammonia was added to this aqueous solution with stirring to adjust the pH to 9. Water cooling was also performed during the addition of ammonia water. Thereafter, the mixture was kept in a water bath at 80° C. for 3 hours to ripen the resulting precipitate. The precipitate was filtered and washed with deionized water until no chloride ions were detected. and 100℃
After drying for a day and night, it was fired at 500° C. for 3 hours to obtain TiO2. [00101st Ni, Knee (7) T i 02 100
g was immersed in 200 ml of an aqueous solution containing 4.1 g of (NH4)2SO4, and the water was evaporated in a water bath. After drying at 100°C, the mixture was calcined at 500°C for 3 hours to obtain a powdery solid superacid SO4/Ti0z. This solid super strong acid 5
0 g and 4 g of CuO powder were mixed in a dry ball mill for 1 hour and calcined at 500° C. for 3 hours to prepare the catalyst of this example. (00111 (Example 2) 180.2 g of T i instead of T i Cl 4
A precipitate was formed in the same manner as in the example above except that (SO4) 2 was used, and the obtained precipitate was washed, dried at 100°C, and calcined at 500°C for 3 hours to form a powdery solid superacid S.
O4/T'=O: was obtained. Next, 100g of this solid super strong acid
was dissolved in 200 ml of an aqueous solution containing 19.2 g of Cu(NCh)L, -3H20, and dried at 100°C.
The catalyst of Example 2 was prepared by calcining at 0° C. for 3 hours. (0012) (Example 3) 216.9 g of Zr○(
NO3)! -ZrO2 was formed in the same manner as in Example 1 except that 2H20 was used, and solid superacid SO4/ZrO2 was obtained in the same manner. 50g of this solid super strong acid and Cu
Mixed with 3g of O powder in a dry ball mill for 1 hour,
The catalyst of Example 3 was prepared by calcining at ℃ for 3 hours. (0013) (Example 4) 252.9 g of Fe instead of T i Cl 4
FezO,+ was formed in the same manner as in Example 1 except that (NO3) 3.9H20 was used. This Fe
z O:l log 0゜5N sulfuric acid aqueous solution 500
ml for 3 hours, filtered and dried at 100°C.
The solid superacid S04/F e 203 was obtained by calcining at ℃. (0014) 50 g of this solid superstrong acid and 1 g of CuO powder were mixed in a dry ball mill for 1 hour and calcined at 500°C for 3 hours to prepare the catalyst of Example 4. (Example 5) The catalyst obtained in Example 2 solid super acid SO4/T t 02 50
g and commercially available C03043g for 1 hour, and
The catalyst of Example 5 was prepared by calcining at . [0015] (Example 6) Solid super strong acid SO4/T ioz obtained in Example 2
50 g, 0. IN(P t (NH3) 4
) Immersed in 100 ml of C12 aqueous solution and evaporated water on a water bath. After drying at 100°C, the catalyst was calcined at 500°C to prepare the catalyst of Example 6. (Example 7) Z r (OH) 4 obtained in the same manner as Example 3
The precipitate was dried at 100°C overnight. This Zr (O
H) 50 g of 4 and 47 g of commercially available 82 WO were mixed in a wet ball mill for 2 hours and calcined at 800°C to obtain a solid superacid WO3/Z rO2. [0016] 50 g of this solid super strong acid and 3 g of CuO powder were mixed for 1 hour and calcined at 500° C. to prepare the catalyst of Example 7. (Comparative Example 1) 19.2 g of Cu (No:l) 2 ・3H20
100 g of alumina was immersed in 200 ml of the dissolved aqueous solution, and the water was evaporated on a water bath. The catalyst of Comparative Example 1 was prepared by drying at 100°C and calcining at 500°C. (0017) (Comparative Example 2) 0.05N of (P t (NH3) 4 ) CI2
50 g of alumina was immersed in 100 ml of aqueous solution and the water was evaporated in a water bath. Then, the catalyst of Comparative Example 2 was prepared by drying at 100°C and calcining at 500°C. (Comparative Example 3) 50g of 5iOzA1203 and 0.3g of CuO were mixed into 1
The catalyst of Comparative Example 3 was prepared by mixing for a time and calcining at 500°C. [0018] (Comparative Example 4) The solid super strength SO4/Ti0z prepared in Example 2 was designated as Comparative Example 4. (Test Example) Each of the above catalysts was pressed and pulverized to form granules of 10 to 30 meshes. Put this into a quartz tube with a diameter of 10 mm,
Using an atmospheric fixed bed flow reactor, the N of each catalyst was
01CO and HC purification rates were measured. For the reaction, a model gas having the composition shown in Table 1 and corresponding to A/F=18 was used, the catalyst weight was 0.7 g, the reaction gas flow rate was 717 min, and the reaction test was conducted in a steady state at a constant temperature. The results are shown in Table 2. In addition, the purification rate of No is defined by the following formula. [0019] From Table 2, it is clear that the catalyst of the present invention has excellent No purification performance in a lean atmosphere compared to the comparative example. It is also clear that the coexistence of a transition metal or a transition metal oxide and a solid superacid is essential for the expression of this property. inventor

Claims (1)

[Claims] 1. An exhaust gas purification catalyst comprising a solid super strong acid and at least one selected from transition metals and transition metal oxides.