JPS6019036A - Catalyst for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To enhance CO-purifying capacity as a low temp., by a method wherein upper and lower two activated alumina layers are laminated to the surface of a base material and platinum or Pd is supported by the lower layer while Ph and platinum or Rh and Pd are supported by the upper layer. CONSTITUTION:Upper and lower two activated alumina layers are laminated to the surface of a base material comprising cordierite and platinum or Pd is supported by the lower layer while Rh and platinum or Rh and Pd are supported by the upper layer. With respect to the amount of each catalytic metal, Rh is 0.1- 0.3g/l or Pt or Pd is about 0.5g/l in the upper layer while Pt or Pd is about 0.5g/l in the lower layer. Because this catalyst supports not only Rh having strong poisoning resistance to CO, lead or phosphorus only in the upper layer thereof but also platinum or Pd in a proper amount, platinum or Pd in the lower layer is protected. In addition, because CO-oxidation in the lower layer is facilitated by diffusing CO in the upper layer, the ignition temp. of CO is lowered and this catalyst shows excellent purifying capacity even at a lower temp. as compared with a conventional one.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a catalyst for purifying exhaust gas discharged from internal combustion engines such as automobiles.

(Prior Art) Catalysts for purifying exhaust gas in internal combustion engines, especially automobiles, are required to have relatively high purification performance. High purification performance is required over a wide temperature range from around 300°C to around 1000°C, and activity at low temperatures is especially important because the temperature of the bleed gas drops as a recent fuel saving measure. Sexuality is increasing.

However, since conventional exhaust gas purification catalysts are basically high-temperature types, they cannot be said to adequately respond to the recent decline in exhaust gas temperature, and are not always satisfactory in terms of purification performance at low temperatures. It wasn't.

(Objective of the Invention) Does the present invention address the problems in the above-mentioned prior art? /,, The purpose is to investigate the low-temperature activity of honeycomb-shaped monolithic catalysts supporting platinum group elements, which are currently the mainstream of three-way catalysts for automobile exhaust gas purification. An object of the present invention is to provide a catalyst with improved purification characteristics for (CO).

(Structure of the Invention) That is, the bleed gas purification catalyst of the present invention has activated alumina layers laminated in two layers, upper and lower, on the surface of a base material made of cordierite, etc., with platinum or palladium in the lower layer and platinum or palladium in the upper layer. It is characterized by supporting rhodium and platinum, or more specifically rhodium and palladium, to fully enhance carbon monoxide purification performance at low temperatures.

Catalytic gold such as platinum, palladium, or rhodium (1.-5%) usually maintains Ji3 uniformly throughout the activated alumina layer, but the catalyst metal on the light surface absorbs carbon monoxide (CO) and lead (Pb) in the exhaust gas.
), phosphorus (P), etc.

Furthermore, since the degree of poisoning varies depending on the type of catalyst metal, the purification performance of the catalyst as a whole will be improved if the catalyst is used in appropriate stratification.

Particularly at low temperatures, CO has a strong adsorption power for noble metals, so in the CO oxidation reaction, the reaction rate becomes a negative order of CO concentration, and as the COa degree increases, the reaction rate decreases and the ignition angle increases. . For this reason, the purification performance decreases, but if the soil layer contains a metal such as rhodium or platinum or palladium, and the lower layer contains platinum, palladium, or y414, the lower layer has a strong adsorption power for CO. Platinum and palladium are less likely to be poisoned by CO, and the CO concentration in the lower layer decreases due to the diffusion resistance caused by the upper alumina layer, resulting in a decrease in ignition temperature for the above-mentioned reasons.

As for the type of activated alumina, those normally used for this type of purpose, such as α-sized or r-alumina, can be used.The specific surface area and pore diameter are related to activity and pore clogging due to poisoning, so it is appropriate. choose something. If a material with a small specific surface area (large pore size) is used for the upper layer, it will be resistant to poisoning. Two activated alumina layers are usually sufficient, but three or more layers may be provided.

The thickness of the alumina layer is important because it is related to the above-mentioned CO adsorption and diffusion resistance, and the thickness of the upper and lower layers is usually 100 μm in total.
degree. The thickness of each layer can be selected arbitrarily. For example, if the thickness of the upper layer is 60 μm or more, the It fire temperature m can be sufficiently reduced even when the CO concentration is high.

The amount of catalyst metal supported on both the upper and lower layers is usually J (h O, 1 to 0.3 f/l) per unit volume of catalyst for the upper layer.
.

Pi or Pd around 0.5f/, P for the lower layer
It is preferable that t or Pd O,59/ be around. In addition, components added to improve the activity of noble metal catalyst components, such as lanthanum (La), cerium (Ce), and iron (Fe 2 ), can also be appropriately dispensed.

Low-temperature activity is usually below 300°C, especially room temperature to 300°C.
Although the exhaust gas purification performance between the two levels is a problem, the use of the catalyst of the present invention can provide practically sufficient performance regarding CO.

(Example) The present invention will be explained in further detail in the following example. Note that the present invention is not limited to the following examples.

Example 1: Commercially available alumina silua 00y with alumina content of 10y
A slurry was prepared by adding 1000 fi of alumina powder to a mixed turbid solution consisting of 40% by weight aqueous aluminum nitrate solution 15 (1) and 200 f of ion-exchanged water.

Inside this is a cordierite monolith carrier base material (diameter 93 mm).
m Length 76 m) k It was immersed for 2 minutes, then pulled up and removed by blowing it away with the air stream inside the cell. After drying at 200°C for 2 hours, it was calcined at 700 U for 2 hours to form alumina/metal A'fr:. Next, 0.265'/z
It was immersed in 1 t of diaminoplatinum aqueous solution for 1 hour and then dried at 20° C. for 1 hour to support the Pt on the alumina layer. Next, the sample was immersed in the alumina slurry for 2 minutes again and the same operation was performed to form a second alumina If/f13. After this o,
z6y7t thick hemp dinitrosifumi/platinum aqueous solution 1
t, next a? It was immersed in 1 t of rhodium chloride solution of 0.0521 i'//, concentration III, and dried at 200'C for 1 hour to bend the P t /lt h stiffness medium a of the present invention.

Example 2 The pd/lt of the present invention was prepared in exactly the same manner as in Example 1 except that palladium chloride was used instead of dinitrodiaminoplatinum.
A catalyst was obtained.

FIG. 1 shows a perspective view of an exhaust gas purifying catalyst 1 of the present invention. FIG. 2 is a partially enlarged sectional view of the catalyst in FIG.
In the figure, 2e represents the cordierite carrier base material, 3 represents the alumina layer A, and 4 represents the alumina layer 13.

Comparative Example 1: An alumina layer was formed in the same manner as in Example 1. At this time, in order to achieve the same amount of alumina coating as in Example 1, the alumina coating operation was repeated twice. After this, add 1 t of dinitrodiaminoplatinum aqueous solution (0,529/l), then 0.
A comparative example of P L/ )th catalyst C was obtained by immersing it in a rhodium chloride solution of 052'//l.

Comparative Example 2 A Pd/l (h catalyst d) of Comparative Example was obtained in the same manner as in Example 1 using radium chloride instead of dinitroaminoplatinum.

Table 1 shows the amount of noble metal supported on the catalysts of Example 1.2 and Comparative Example 1.2.

// //″' 7-/ , /' ]/ 2// ,,'z / Table 1: Amount of precious metal supported per 1 ton of catalyst (f/l) Durability test: Obtained in Examples and Comparative Examples A total of four types of catalytic converters were loaded and connected to the exhaust system of an engine with a displacement of 2,000 cc, and the exhaust gas purification performance was evaluated after a durability test of 300 hours of normal driving.Results. is shown in Figure 3.

As is clear from the figure, catalyst a of the present invention and catalyst C of the comparative example.
1 and the catalyst of the present invention compared to the catalyst di of the comparative example, the carbon monoxide purification rate is improved over the entire temperature range, and even when the human gas temperature is 250°C or less, the catalyst of the present invention has a sufficient Shows purification rate.

(Effects of the Invention) As described above, the exhaust gas purifying catalyst of the present invention supports rhodium, which is resistant to carbon oxide, lead, and phosphorus, only in the upper layer, and also supports an appropriate amount of platinum and radium. It serves to retain platinum and radium in the lower layer, and also diffuses carbon oxide in the upper layer. This makes it easier to oxidize in the lower layer, lowering the ignition temperature of carbon monoxide, resulting in superior purification performance at lower temperatures than before, and fuel efficiency in recent years has lowered the gas temperature by 1 nod. It does not reduce purification performance even under various conditions, and is compatible with hard water, which is an increasingly strict environmental protection requirement, and has excellent effects.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of the exhaust gas purifying catalyst of the present invention, Fig. 2 is a partially enlarged sectional view of the catalyst of Fig. 1, and Fig. 3 is the individual gas temperature of the catalyst of the present invention and the catalyst of the comparative example. It is a graph of carbon monoxide purification rate +S. In the figure, 1... Exhaust gas purification catalyst 2... Cordierite support 3... Alumina layer A 4... Alumina layer B Patent applicant Toyota Motor Corporation

Claims (1)

[Claims] Activated alumina layers are laminated in two layers, upper and lower, on the surface of a substrate made of cordierite, etc., with platinum or palladium in the lower layer and rhodium and platinum in the upper layer. , Ri is rhodium and 74
An exhaust gas purification catalyst characterized by supporting radium to improve carbon monoxide purification performance at low temperatures.