JPH0394818A - Catalytic converter - Google Patents

Abstract

PURPOSE:To improve the purification capacity when the air-to-fuel ratio is high at high temp. by incorporating rhodium, platinum or palladium into a catalyst on the inlet side of exhaust gas and palladium and rhodium into the catalyst on the outlet side and controlling the volume ratio of both catalysts to (8:1)-(1:3). CONSTITUTION:A soln. of platinum nitrate in dinitrodiamine, a rhodium nitrate soln. and activated alumina are mixed to form alumina carrying platinum and rhodium, the alumina and cerium oxide are then wet-crushed to obtain a slurry, and a monolithic carrier is dipped in the slurry to obtain a catalyst on the inlet side of exhaust gas. Meanwhile, alumina carrying palladium and rhodium is formed from a palladium nitrate soln., a rhodium nitrate soln. and activated alumina, the alumina and cerium oxide are wet-pulverized to obtain a slurry, and a monolithic carrier is dipped in the slurry to obtain a catalyst on the outlet side of exhaust gas. The volume ratio of the inlet-side catalyst to outlet- side catalyst packed in the catalytic converter is controlled to (8:1)-(1:3). Consequently, the purification capacity is improved when the air-to-fuel ratio is high at high temp.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a catalytic converter device for purifying exhaust gas from automobiles. Conventional technology> Catalysts used in automobile exhaust gas purification usually remove hydrocarbons (HC), carbon monoxide (Co), and nitrogen oxides (NO.) at the same time (hereinafter referred to as "ternary performance").
A three-way catalyst is used. In recent years, as fuel-saving engines have increased in output, there has been a strong demand for catalysts with excellent purification performance. Additionally, exhaust gas regulations, particularly HC regulations, are being enforced that are even stricter than the current ones. Under these circumstances, conventional three-way catalysts cannot be said to be sufficient in terms of performance. Normally, automobiles are operated near the stoichiometric air-fuel ratio, but when accelerating, a fuel lynch atmosphere (hereinafter referred to as ``rich side'' or ``lynch time'') is created, and a large amount of HC is emitted. It is necessary to improve the HC purification ability with the air-fuel ratio on the side.

As catalysts for more complete combustion of IC and GO, an oxidation catalyst is installed on the inflow side and a reduction catalyst is installed on the outflow side.Furthermore, platinum (Pt) is placed at the front of the outflow side, and rhodium (R) is placed at the rear of the outflow side.
A catalytic converter device is shown (Japanese Patent Application Laid-open No. 164715/1989) that uses Rh') separately, but the catalyst on the inflow side does not contain Rh, but only on the outflow side, and the inflow side catalyst does not contain Rh. It has a diffusion chamber between the catalyst and the catalyst on the outflow side, and is completely different from the present invention.

In addition, a catalytic converter device (unexamined patent application) in which the catalyst is divided into two parts, one on the inflow side and one on the outflow side, supports a high temperature activated catalyst (titanium, chromium, etc.) upstream and a low temperature activated catalyst (responsible metal) downstream. No. 41772/1982>, a catalytic converter device (Japanese Patent Application Laid-Open No. 7935/1983) which specifies the amount of wash coating, amount of responsible metals, cerium content, and cell density of the catalyst on the inflow and outflow sides of a three-way catalyst is disclosed. However, there are few specific descriptions of these catalysts, and further study is required to implement them.In addition, a catalytic converter device using multiple catalysts with different heat capacities (Japanese Utility Model Application No. 565)
071.6), but there are no specific values,
Also, since its purpose is simply to provide a small catalyst for startup, HC. ．． The effect on CO combustion is insufficient.

Problems to be Solved by the Invention In a situation where exhaust gas regulations that are even stricter than the current ones are being enforced, it is possible to improve performance in purifying exhaust gas containing a lot of HC emitted in a fuel-rich atmosphere6. There is a need for an inexpensive catalyst inverter device.

Means for Solving the Problems (l) In a catalytic converter device in which a plurality of exhaust gas purifying catalysts are housed in one catalytic converter device, the catalyst (A) on the exhaust gas inflow side is ( a) contains rhodium and platinum or (bj rhodium, platinum and palladium, the exhaust gas outflow side catalyst (B) contains palladium and rhizium 1, and the exhaust gas inflow side catalyst (A) and the volume ratio of the catalyst (B) on the exhaust gas outflow side (
A catalytic converter device characterized in that (A)H (B) ) is 8=1 to 1:3.

According to the findings of the present inventors, in terms of HC oxidation ability, Pd has an excellent ability to purify unsaturated IC, and Pt has an excellent ability to purify saturated HC.

In order to maximize this characteristic, as a result of combining catalysts as described above, when the catalyst volume ratio is in the range of 8:1 to 1:3 on the exhaust gas inflow side and exhaust gas outflow side, when the air-fuel ratio is rich, It has become possible to improve the purification ability, especially the 00 purification ability.

Another effect of the present invention is that compared to the conventional case where one catalyst containing PT and Rh is housed in a catalytic converter, PT on the outflow side can be replaced with Pd.
Since it is cheaper than PT, it leads to cost reduction. Furthermore, 1.
Remetallic (Pt, Pd, Rh) catalysts also show the above performance improvements and further reduce costs.

Further, the volume ratio of the catalyst on the exhaust inflow side and the catalyst on the exhaust outflow side is 8:J to 1:3.

If this volume ratio becomes smaller than 1=3 on the inflow side, NO. This results in a decrease in the purification ability, and furthermore, there is less improvement in the IC purification ability on the inlet side or on the edge side where the volume ratio is greater than 8:1.

However, palladium, rhodium or platinum is supported on a metal oxide, and this metal oxide contains activated alumina, α
- Aluminum, silica, titania, silica-alkuna, iron oxide, di-nokel oxide, alkali metal oxides, alkaline earth metal oxides, rare earth oxides, and the like.

Further, cerium oxide (hereinafter referred to as "ceria") is contained at least in the catalyst on the exhaust gas inflow side, and preferably in the rain side catalyst on the exhaust gas inflow side and the exhaust gas outflow side.

EXAMPLES The present invention will be explained in more detail with reference to Examples below, but it goes without saying that the invention is not limited to these unless it goes against the spirit of the invention. Example 1 Nitric acid aqueous solution of dinitrodiammine platinum (Pt content: 10
0g/liter) and 41.7ml of rhodium nitrate aqueous solution (
Rh content: 50g/lysotol) 16.7m6 with pure water
O 0m7! activated alumina 500 in an aqueous solution diluted with
After mixing, dry at 150℃ for 3 hours,
Calcining was performed at 0° C. for 2 hours to obtain platinum and rhodium supported alumina. Next, 500 g of alumina supporting platinum and rhodium and 250 g of ceria were wet-pulverized to obtain a slurry. The same 10.85A monolithic carrier was immersed in this slurry, the excess slurry was blown off, and the carrier was dried at 150°C for 3 hours and burned at 400°C for 2 hours to obtain a complete catalyst for the inflow side. The resulting catalyst has a pt of 0.83 g per liter.
Rh is 0. (Hereinafter, the weight per liter of catalyst is expressed as r g / l J.) Next, a palladium nitrate aqueous solution (Pd content = 100 g
/liter) 41.7o+/ and rhodium nitrate aqueous solution (R
h content: 50g/riftle) 16.7n+j! Add 500% active alumina to an aqueous solution diluted to 500IIN with pure water.
After mixing, dry at 150℃ for 3 hours,
Burning was performed at 0°C for 2 hours to obtain palladium and rhodium-supported alumina.

Next, 500 g of alumina supporting palladium and rhodium and 7250 g of seri were wet-pulverized to obtain a slurry.

0.8 for this slurry! M! After immersing the monolithic carrier in the slurry and blowing off the excess slurry, it was dried at 150°C for 3 hours and burned at 400°C for 2 hours to obtain a complete catalyst for the outflow side.

The resulting catalyst contained 0.83 g of Pd per liter.
/1, Rh was supported at 0.17 g/ffi.

Example 2 In place of platinum and rhodium in the catalyst on the exhaust inlet side, platinum, palladium, and rhodium were each added at 0.00%. 4 2 g/lo
．． 42g/l and 0.17g/j! A catalyst was obtained in the same manner as in Example 1 except that. Examples 3 to 5 Catalysts were obtained in the same manner as in Example 1, except that the catalyst capacities on the exhaust gas inflow side and exhaust gas outflow side were varied. The results are shown in Table 1.

However, the amounts of palladium, rhodium, and platinum per liter of catalyst are the same. Comparative Example 1 In Example 1, palladium and rhodium in the catalyst on the exhaust outlet side were replaced with platinum and rhodium, and 0.83 g each was used.
/7! A catalyst was obtained in the same manner as in Example 1, except that 0.11 g/l was maintained. Further, the catalyst on the exhaust gas inflow side was obtained in the same manner as in Example 1.

Comparative Example 2 In Example 1, platinum and rhodium in the catalyst on the exhaust inflow side were replaced with palladium and rhodium, each 0.83 g.
//! A catalyst was obtained in the same manner as in Example 1 except that 0.17 g/It was supported. In addition, the catalyst on the exhaust gas outflow side is
Obtained in the same manner as in Example 1.

Comparative Examples 3 and 4 Catalysts were obtained in the same manner as in Example I, except that the volume of the catalyst on the exhaust gas inflow side and the exhaust gas outflow side was varied. The results are shown in Table 1. ．． However, the amounts of palladium, rhodium, and platinum per liter of catalyst were the same as in Example 1.

Example 6 The catalyst performance of the catalysts obtained in Examples 5 to 5 and Comparative Examples 1 to 4 was investigated with respect to }Ic, CO, and No when the air-fuel ratio was on the Lynch side at high temperatures after engine endurance running. (Durability conditions) Durability running uses a commercially available electronically controlled engine.
Each catalytic converter was installed. Inlet temperature is 850℃
The durability time was 100 hours.

(Performance when the air-fuel ratio is rich at high temperature) Next, the performance of the catalyst when the air-fuel ratio is rich at high temperature was measured at a catalyst inlet temperature of 400° C. under the following conditions. Engine air-fuel ratio (Air/Fu
el or A/F) was continuously varied from 15 to 14 (an IHz sine wave signal was introduced into the engine control section using an external oscillator, and the air-fuel ratio was adjusted to ±1.OA/F).
, vibrated at IHz)′. Table 2 shows the purification rate (Conv.) at A/F of 14.4 when the air-fuel ratio is rich.

Effects of the Invention> Table 2 shows that the catalysts of Examples 1 to 5 according to the present invention are as follows: Comparative Example 1
-4, it has a remarkable effect on the purification ability when the air-fuel ratio is rich at high temperatures, especially the HC purification ability, and furthermore, even within the range of the catalyst capacity ratio on the exhaust gas inflow side and the outflow side according to the present invention. In this case, the catalyst performance is further improved, and even when expensive PT is replaced with Pd, which is cheaper than PT, the above-mentioned high performance is exhibited, and costs can be kept to a low limit.

Table 2 Performance of rich air-fuel ratio after endurance running

Claims (1)

[Claims] (1) In a catalytic converter device in which a plurality of exhaust gas purifying catalysts are housed in one catalytic converter device, the catalyst (A) on the exhaust gas inflow side is made of (a) rhodium and platinum, or (b) rhodium, The catalyst (B) on the exhaust gas outflow side contains platinum and palladium, the catalyst (B) on the exhaust gas outflow side contains palladium and rhodium, and the volume of the catalyst (A) on the exhaust gas inflow side and the catalyst (B) on the exhaust gas outflow side. Ratio ((A)
:(B)) is 8:1 to 1:3.