JPS5950378B2 - Catalyst for internal combustion engine exhaust gas purification - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention aims to eliminate nitrogen oxides (NO) and combustible carbonaceous substances such as carbon monoxide (CO) and hydrocarbons contained in gases emitted from vehicles, particularly automobiles with internal combustion engines. (HC
), etc., at the same time.

Many catalysts have been announced that are effective in simultaneously removing NOx, CO, HC, etc. from vehicle exhaust gas.

Generally, under conditions where there are many oxidizing components in the exhaust gas, CO
, HC, but under such conditions the ability to reduce NOx is significantly reduced; conversely, under conditions where there are many reducing components, it is suitable for removing NOx, but CO, HC
Therefore, it is desired to develop a highly effective three-component simultaneous treatment catalyst (3-way catalyst) that efficiently converts CO, HC, and NOx at the same time using the same catalyst. .

As you can see from the above explanation (3-way catalyst is more efficient <CO.

In order to convert HC and NOx into harmless substances at the same time, it is desirable that the oxidizing and reducing components in the exhaust gas be in an almost equal amount, that is, the value of 1/R shown in Figure 1 should be around 1.0. Become.

Here, l/R is expressed by the following formula.

1/R=Oo10R OO: Amount of oxygen required for all of the reducing components to become N20 and CO2 OR: Amount of oxygen that can be supplied in the oxidizing components Here, representative examples of reducing components include C09H2°HC, etc. , 02. as an oxidizing component. There are NOx etc., and C
O2, N20. The N2 isoneutralizing component is not involved in the calculation of l/R.

1/R<1, that is, a state in which the reducing component is present in excess compared to the oxidizing component is called rich, and 1/R>1
That is, a state in which oxidizing components are present in excess compared to reducing components is called lean.

As mentioned above, <1/1 to make the 3-way catalyst work effectively.
It is desirable for the R value to be around 1.0, but in reality it is very difficult to always control exhaust gas to 1/R = 1.0, so it is used even under somewhat rich or lean conditions. It turns out.

Therefore, it is desirable to have a catalyst that has as high a conversion rate of CO and HC as possible even under rich conditions and as high a conversion rate of NOx as possible even under lean conditions.

In this way, in the 3-way catalyst, there is a characteristic called a window that indicates the permissible range of the value of 1/R.

Now, if NOx, CO, and HC in the exhaust gas are all 70
If a conversion rate (purification rate) of % or more is required, 3W
For a 3-way catalyst having the purification characteristics shown in Fig. 1, the l/R value of the exhaust gas supplied to the ay catalyst is determined by line segment ab in Fig. 1.
This line segment ab is called a window in which the NOx, HC, and CO purification rates are all 70% or more.

Therefore, the wider the window, the more desirable it is; if the window is narrow, the 1/R value must be controlled more strictly, and if it is even narrower, it becomes practically unusable.

Therefore, the previously developed Co and HC oxidation catalysts and NOx reduction catalysts are used in either a lean or rich state, respectively, and the window is too narrow to be used as a 3-way catalyst. , or the window itself does not exist, and does not function as a 3-way catalyst.

What is more important is that HC near 1/R=1 due to use,
C.O.

The 3Ws are that the NOx purification ability does not deteriorate and that the aforementioned window does not become narrower, that is, it has durability.
This is an important characteristic required for ay catalysts.

Many conventional 3-way catalysts that combine rhodium (Rh) and other platinum group metals have been reported.
These produce NOx during actual use.

The active ability to purify CO, HC, etc. decreases with use at around 1/R = 1, and the decrease is particularly noticeable when used for a long time, and the window is not wide enough and it is also used for a long time. In this case, there was a drawback that the window became narrower.

The present invention aims to solve the above-mentioned problems, and includes Rh and Rh in an inorganic porous carrier such as alumina.
After containing at least one of platinum group metals other than Pt and Pd, molybdenum (Mo) or iron (F
We have discovered that excellent results can be obtained by adding e) and forming a layer mainly composed of MO or Fe on the surface of the catalyst and on the inner surface of the pores, rather than the platinum group metal-containing layer. Completed the invention.

Here, Mo on the apparent surface and the inner surface of the pores of the catalyst
It is important to form the Fe-containing layer on the surface rather than the platinum group metal-containing layer.If MO or Fe is added first, then the platinum group metal is supported and the Mo- or Fe-containing layer is formed in the middle. If it is made into a layer, it is hardly possible to expect the storage effect described later, and the main part of Mo or Fe tends to react with the alumina layer, which reduces the window expansion effect and storage effect of the 3-way catalyst. This impairs the usefulness of Mo or Fe that has this.

Next, the window enlargement effect will be explained.

Mo as an oxide is MoO9Mo2039MoO29M
o205゜MoO2, and Fe as an oxide Fed
, Fe0z.

Fe2O3 exists in a stable form.

Now, when the exhaust gas controlled at around 1/R21□ passes through the 3-way catalyst, the 1/R value is not a constant value, but 1/R<1(
It is a state in which 1/R>1 (rich) is repeatedly fluctuated, and the average value is 1/R, which is 1 in the middle.

When rich and lean conditions are repeated in this way, Mo or Fe oxides are reduced in the rich state and release 02. For example, MOO3→1/2M020o+1/40
2゜Fe2O3 → 2FeO+1/202), and conversely in a lean state, the oxide is oxidized and takes in 02 (for example, MoO+1/402 → 1/2M0203.FeO+1
/20□→Fe02) occurs, and this phenomenon is called the 02 Strade effect, and MO and Fe are elements that have a particularly large 02 Strade effect.

In a catalyst in which a Mo or Fe containing layer forms a surface layer as in the present invention, when the gas is in a rich state, Mo or F is removed in the process of passing through the Mo or Fe containing layer.
02 is released from the e layer and reaches the Shinkin group metal containing layer with a 1/R value close to 1, creating a more favorable state for the activation of the catalyst. Conversely, the gas becomes lean. If it is in such a state, 02 is absorbed during the process of passing through the MO or Fe-containing layer, resulting in a favorable state in which the 1/R value approaches 1, resulting in the effect of expanding the window. It is something that can be done.

Here, if a Mo or Fe-containing layer forms an intermediate layer and a platinum group metal-containing layer is formed on the surface, the above-mentioned window enlargement effect can hardly be expected.

As described above, in order to obtain the catalyst of the present invention, a layer containing Mo or Fe must exist in a form covering at least a layer containing rhodium and other platinum group metals.

Therefore, in completing the present invention, rhodium and other platinum group metals are impregnated into an inorganic porous carrier such as alumina or an integral structure whose surface portion is mainly made of alumina, and then molybdenum or iron is supported. Must.

In the present invention, as shown in the following examples, the content of each component necessary to maintain sufficient performance is determined per filling volume of the finished catalyst (11) in the case of a granular catalyst in the invention in which a Mo-containing layer is formed. 0.2 g or more of RhO, 0.2 g or more of platinum group metals other than Rh.

It is necessary that Mo is 2.0 g or more, and furthermore, considering practical costs, etc., Rho is 02 to 2.0 g.

Platinum group metals other than Rh 0.2-10. Og, Mo2
．． A range of 0 to 100 g is preferred.

On the other hand, in the case of a catalyst having an integral structure, Rh0.01 to 2.0 per apparent volume If of the completed catalyst. Og
, 0.2 to 10.0 g of platinum group metals other than Rh, Mo2.
A range of 0 to 100 g is preferred.

Further, in the invention in which a Fe-containing layer is formed next, in the case of a granular catalyst, RhO, Olg
, 0.2g or more of platinum group metals other than Rh, Fe2.0
g or more, and considering practical costs, etc., Rho, 01 to 2. Og.

0.2g to 10.0g of platinum group metals other than Bh, Fe2.
A range of 0 to 6°g is optimal.

The present invention will be explained in detail below according to examples.

Reference Examples 1 to 7 describe methods for producing catalysts as comparisons of the present invention, and Example 1 to Example 5. Examples 9 to 13 describe the method for producing the catalyst of the present invention, and Examples 6 to 8 describe the method for producing the catalyst of the present invention. Examples 14 and 15 show the test results of these catalysts.

[Reference example 1] In this reference example, commercially available carrier A is used.

This carrier A is manufactured by Rhone-Poulenc and is a spherical carrier consisting of 99% or more γ-alumina and having a specific surface area of 75 to 120 m''/gV2 average pore diameter of about 100 to 200.

Each carrier A II was impregnated with the solution shown in Table 1 as a carrier strengthening solution for impregnation for about 10 minutes to incorporate the entire amount, and then dried at 120° C. for 3 hours.

Next, the carrier B was baked at 600°C for 1 hour in Air.
C, D, E, F were obtained.

Table 1 shows the specifications of the solutions used to produce the obtained antibodies and their respective carriers.

11 each of the obtained carriers B, C, D, E, F and raw material carrier A were each impregnated with 380 ml of a Pt-Rh mixed solution for about 10 minutes.

Then, after drying at 120°C for 3 hours, it was dried at 600°C in Air.
℃ for 1 hour to obtain catalyst 1b.

le, ld, le, If and 1a were obtained.

The Pt-Rh mixed solution used at this time was contained in 380ml.
Concentrated nitric acid 0.4ml, Ptl, Og, RhO, Ig
HPt2C1o-Rh(NO3) 3 mixed nitric acid acidic aqueous solution.

In addition, the amount of each component contained in the obtained catalyst is calculated as follows:
By quantitatively analyzing each part by weight relative to 0 parts by weight and multiplying it by 10 times the bulk density (unit: g/cc), the amount of each component contained per 11 filled volumes of the finished catalyst (unit: g ) are shown in Table 2.

The bulk density of these catalysts is 0.66 to 0.68 g/
It was between cc.

W: 100c of sample after drying at 150℃ for 2 hours
Weight (g) when filled into measuring cylinder c [Example 1] Catalysts 1a, lb, prepared in exactly the same manner as Reference Example 1
Mob in 380 ml of solution to 11 each of IC, ld, le,
The sample was impregnated with 380 ml of aqueous ammonium molybdate solution containing 2 moles for about 10 minutes.

Next, the mixture was calcined at 120°C for 3 hours and then at 600°C for 1 hour to obtain catalysts IA, IB, IC, ID, and IE.

Table 3 shows the amount of each component contained in the catalysts 1A to 1E in terms of the amount contained per 11 completed catalysts (unit: g).

BaCl was added to the same carrier AIO1 as used in Example 1.
After impregnating the carrier with an aqueous solution 3.81 containing 5 moles of 2 for 10 minutes to incorporate the entire amount, it was dried at 120°C for 3 hours, and then calcined in Air at 1,100°C for 2 hours to obtain carrier G.

Pd containing 5 g of Pd and 15 g of Pt in the total amount of the obtained carrier G
(NO3)2-Pt(NH3)2(NO2)2 Mixed nitric acid acidic aqueous solution 3.81 was impregnated for 10 minutes to incorporate the entire amount, dried at 120°C for 3 hours, and then heated to 50°C in Air.
It was baked at 0°C for 1 hour.

Next, the RhCl3 aqueous solution containing 2 g of Rh was impregnated with 3.81 g of RhCl3 aqueous solution for 10 hours to absorb the entire amount, and then dried at 120°C for 3 hours, and then calcined in air at 500°C for 1 hour to produce a catalyst 2A.
I got it.

After separating 11 pieces of each catalyst 2A, 380 ml of a solution containing 380 ml of an aqueous molybdic acid solution containing MO as shown in Table 4 was impregnated for about 10 minutes, calcined at 120°C for 3 hours, and then heated to 600°C. The catalysts 2B to 2H were fired for 1 hour.
I got it.

The Mo content of the obtained catalyst is shown in Table 4 as the amount contained per 11 finished catalysts (unit: g).

In addition, the contents of Ph, Pt, and Pd in these catalysts are as follows: Rho, 2 g, Ptl, 5 g per 11 completed catalysts.
, Pd0.5g, Ba68g [Example 3
] After supporting Ba in exactly the same manner as in Example 2, 11 pieces each were separated to obtain 11 pieces each of Ba-attached carriers 2a to 2h.

2a to 2h Each 11 was impregnated with 380 ml of Pt(NH3)2(N02)2 aqueous solution containing Pt as shown in Table 5 for about 10 minutes to absorb the entire amount, and then dried at 120°C for 3 hours. Then, it was baked in air at 500° C. for 1 hour.

Next, 380 ml of RhCl 3 aqueous solution containing 0.2 g of Rh
After soaking for 10 minutes to absorb the entire amount, soak at 120℃ for 3 minutes.
It was dried for 1 hour and calcined at 500° C. for 1 hour in N2 gas.

Furthermore, after impregnating 380 ml of ammonium molybutate aqueous solution containing 0.2 mole Mo for 10 minutes to absorb the entire amount, drying at 120°C for 3 hours, and drying in Air for 6 minutes.
Catalysts 3A to 3H were obtained by firing at 00°C for 2 hours.

The Pt content of these catalysts is shown in Table 5 as the amount of pt (unit: g) contained per 11 finished catalysts.

Furthermore, these catalysts have KhQ per 11 finished catalysts, 2
It contained 19g of Mo, 68g of Ba.

[Example 4] After supporting Ba in exactly the same manner as in Example 3, Pt1
380m of Pt (NHa) 6C14 aqueous solution containing 5g
1 was impregnated for about 10 minutes to incorporate the entire amount, and then 11 portions were each taken out to obtain catalysts 3A to 3E.

Next, Rh contained in each 380 ml of RhCl3 aqueous solution
Rh,
M.

were supported to obtain catalysts 4A to 4G.

The Rh content of these catalysts is shown in Table 6 as the amount of Rh contained per finished catalyst II (unit: g).

These catalysts contained 1) 0.5 g of Pd per 11 finished catalysts.

It contained 5 g of Ptl, 68 g of Ba, and 9.5 g of Mo.

[Example 5] Catalyst 1a prepared in exactly the same manner as in Reference Example 1 was charged with the amount (unit: mole) of Fe as shown in Table 7.
After impregnating 380 ml of Fe (NO3) a aqueous solution containing Fe (NO3) a for about 10 minutes and drying at 120°C for 3 hours,
Catalysts 5A to 5H were obtained by calcining at 600° C. for 2 hours in r.

The amount of Fe (unit: g) contained in each of these catalysts is shown in Table 7.

Incidentally, these catalysts are also Rho, Ig, Ptl,
Contains Og.

In the preparation of catalyst 5H (7), the Fe (NO3) 3 aqueous solution was impregnated at about 70°C, and all other impregnations were carried out at room temperature.

[Example 6] Catalysts 6a to 6h were obtained in exactly the same manner as catalyst 1a in Reference Example 1, except that the amount of Rh contained in 380 ml of Rh-Pt mixed aqueous solution was changed as shown in Table 8.

These catalysts 6a to 6h were impregnated with 380 ml of FeCl aqueous solution containing 2 moles of Fed for about 10 minutes, dried at 120°C for 3 hours, and then calcined in N2 at 600°C for 2 hours to obtain catalysts 6A to 6H. .

The amounts of Rh contained in these catalysts 11 are also shown in Table 8.

Incidentally, these catalysts 11 contain Pt1. Qg. Fe1l
, contained Ig.

[Example 7] The carrier All was PdOoIg, 0.2 ml of concentrated hydrochloric acid, and PdC12 containing each amount of Pt as shown in Table 9.
-H2PtC16 Hydrochloric acid acidic mixed aqueous solution 380ml 10
After being impregnated for a minute, 500 ml of aqueous Hatani containing NaBH at a ratio of 43 g/l was added and left to stand for 10 minutes with stirring. Excess liquid was drained off, and washing with water and hot water were repeated.

Next, it was impregnated with 380 ml of Rh(NO3)3 aqueous solution containing 2 g of Rho for 10 minutes, dried at 120° C. for 3 hours, and then fired in air at 600° C. for 1 hour.

Next, it was impregnated in 380 ml of Mohr salt water solution containing 2 moles of FeQ for 10 minutes, dried at 120°C for 3 hours, and then calcined in air at 600°C for 1 hour to prepare catalysts 7A to 7.
I got H.

The amounts of Pt contained in these catalysts 11 are also shown in Table 9.

In addition, these catalysts contain Rho, 2g, and Pd.
Contains 001g, Fe1l, and Ig.

Table 9 [Reference Example 2] Support All was impregnated with 380 ml of RhCl3-H3PtC1e mixed aqueous solution containing 2 g of Ptl, Og, and Rho for 10 minutes, and dried at 120°C for 3 hours.
The catalyst was calcined at 9500° C. for 1 hour to obtain catalyst 8a.

[Reference Example 3] 380 m of FeCl 30.3 mole solution on carrier All
After impregnating 1 for 10 minutes and baking at 120°C for 3 hours,
It was fired at 829,500°C for 1 hour.

Next, pt and Rh were supported in the same manner as in Reference Example 2 to obtain catalyst 8b.

[Reference Example 4] FeC1aO, 3 mole, Ptl, on carrier Al
RhCl3-H2P containing Og and Rho, 2g
After impregnating 380ml of tCl3-FeC13 mixed aqueous solution for 10 minutes and drying at 120°C for 3 hours,
C. for 1 hour to obtain catalyst 8C.

[Example 8] Catalyst 8A was obtained by supporting Fe on catalyst 8al 1 obtained in exactly the same manner as in Reference Example 2 in exactly the same manner as in Reference Example 3.

These catalysts 8a, 8b, 8C, and 8A contain Ptl, Og, 0.2 g of Rh, and 16.7 g of Fe in the catalyst 11.

[Reference Example 5] This reference example uses an integral structure carrier B in which a honeycomb-like integral structure made of copillite is coated with alumina.

The weight and apparent volume of this carrier is 583 g per segment, approximately 517 cc.

Contains carrier B in a proportion of H2PtCl60.1m01e and Rhc in a proportion of 130.05mole.
The sample was immersed in 500 cc of a t-Rh mixed aqueous solution for about 5 minutes, excess solution was removed, and then dried at 120°C for 3 hours.

Then, it was calcined at 829,500° C. for 1 hour to obtain catalyst 9a.

[Example 9] Catalyst 9a prepared in the same manner as Reference Example 5 was designated as M.

The sample was immersed for about 10 minutes in 500 cc of an aqueous ammonium molybdate solution containing 0.2 mole of ammonium molybdate, and the excess solution was washed away.

Then, after drying at 120°C for 3 hours, drying at 600°C in Air.
The catalyst was calcined for 2 hours to obtain catalyst 9A.

[Example 10] Catalyst 9a prepared in exactly the same manner as Reference Example 5 was
1 per 500cc of aqueous solution containing 40.5 moles per month
After soaking for 0 minutes, excess solution was poured off.

Next, after drying at 120°C for 5 hours, it was dried at 600°C in Air.
C. for 1 hour to obtain catalyst 10A.

For catalysts 9a, 9A, and 10A, the amount of each component contained in the finished catalyst was determined by chemical analysis (unit: weight %) and multiplied by 5837517 x 10. Contained per apparent volume of the finished catalyst 11 The amount of each component is Pt5,
8g, Rhl, 5g, and catalyst 9A is further M
Catalyst 10A also contains 8.3 g of Fe.

[Example 11] Reference catalysts 1a to 1f obtained in Reference Example 1 and Examples 1 to 1
Catalysts 1A-IE, 2A-2H, 3A-3 obtained in Example 4
For G, 4A to 4G, the 1/R value controlled around 1.0 is substantially 1/R≧l and l/R≦
A 300-hour durability test was conducted in exhaust gas varying between 1 and 1.

At this time, the catalyst bed temperature was approximately 800°C, and the space velocity (Spac
e Velocity (hereinafter referred to as S and V) was approximately 50,000 hr'.

Furthermore, we conducted a laboratory activity evaluation test (hereinafter referred to as the test) to evaluate the activity of the catalyst.

This D test is CO2, 5-0.5%. NOx500~2
, 500 pPm, C2H61,20 as HC
0~700pJ)m, 020.2~1.2%, H20
,8~0.15%, H2020%, CO22,5~4%
, the l/R value is set to 0.0 with the remaining H2 component range.
To the steady gas changed between 4 and 2.0, further 1 to 1
．． A fluctuating gas introduced alternately at 1/2 H2 to give a 5% excess 02, 2-3% excess CO was heated to about 500 °C,
The purification rate of HC, Co and NO was measured by passing through the catalyst to reduce NO and oxidize CO and HC at a rate of about 30,000 hr, and the results were shown in the graph shown in Figure 1. After that, as mentioned above, the window was determined by reading Δl/R, which shows a purification rate of 70% or more for both NO, HC, and CO, from the graph, and the 17R value of the steady gas before introducing 02 and CO was adjusted to around 1 in particular. This is an attempt to evaluate the activity of the catalyst, mainly including the 02 Strade effect, from the purification rate at the specified time (even in this case, 02 and CO are also alternately introduced into the gas supplied to the catalyst as described above). It is.

Note that 1/R in this D test is expressed as 1/R of the steady gas before 02 and CO are introduced alternately, and 02.
It is not the average 17R value after alternating introduction of CO.

Therefore, the window display also becomes a value read based on this l/R.

Needless to say, the higher the values of Δ1/R, NO purification rate, CO purification rate, and HC purification rate, the better the 3-way catalyst is.

The results of the D test on the catalysts prepared in Example 1 and Reference Example 1 and the samples after the durability test are shown in the first example.
It is shown in Table 0.

Further, the results of the D test conducted on the samples after testing the catalysts prepared in Examples 2 to 4 for durability are shown in FIGS. 2, 3, and 4, respectively.

In addition, the 1/R value in the above-mentioned steady gas is 0.4 to 2.0.
As a representative example of the HC, CO, and NO purification rate curves when changing between the levels, catalyst A is shown in Fig. 1.

From the results in Table 10, the catalysts 1A to 1E of the present invention are the reference catalysts 1a to 1e without MO added, respectively.
Window, HC, Co, before and after durability compared to catalyst.
It can be seen that all of the NO purification rates are excellent.

This is particularly noticeable in the CO and NO purification rate after durability and in the window, and it can be seen that the durability performance is excellent.

Further, Mo is added before containing the platinum group metal to form a Mo
It can be seen that the catalyst 1f in which the containing layer is an intermediate layer is somewhat better than the reference catalyst 1a to which Mo is not added, but is considerably inferior to the catalyst of the present invention.

FIG. 2 shows the relationship between Mo content and window for catalysts 2A to 2H.

Figure 3 shows the pt content and NO, for catalysts 3A to 3H.
It shows the relationship between the purification rates of CO and HC, and curve 6
is a curve showing the purification characteristics of HC, curve 5 is a CO9, and curve 4 is a curve showing the purification characteristics of NO.

From these figures, the content of each component per 11 finished catalysts is:
Rho, 02g, P as a platinum group component other than Rh
It can be seen that tQ: 2 g or more and Mo2: 0 g or more are preferable.

[Example 12] The l/R value of exhaust gas for catalysts 9a and 9A prepared in Reference Example 5 and Example 9 was approximately 0.995. Catalyst bed temperature approx. 76
A 200-hour durability test was conducted at 0°C, S, V, and approximately 90,000 hr'.

About catalysts before and after durability test A/F14 mainly for internal combustion engines
,6. A/F fluctuation width 0.25 frequency IHz, S, V
An activity test was conducted by passing exhaust gas through the catalyst for approximately 34,000 hr' and an average exhaust gas temperature of approximately 500° C. at 50 mm in front of the catalyst bed.

The results are shown in Table 11 in terms of purification rates (%) of HC, CO, and NOx.

These results show that the catalyst 9A of the present invention is superior to the reference catalyst 9a to which Mo is not added, especially in terms of purification rate after durability.

[Example 13] 20 cc of each catalyst IA-IE was subjected to a heat resistance test in air at 800°C for 5 hours and at 1,100°C for 5 hours.

The crushing strength of these samples was measured using a Honya type hardness tester.

The measured value of the crushing strength is expressed as the arithmetic average of 16 points, excluding the two upper and lower points among the measured values of each 20 particles, after standardizing the size of the catalyst particles to 5 to 6 meshes.

The results are shown in Table 12.

As is clear from these results, especially when used at high temperatures, it is preferable to add alkaline earth metals, rare earth metals, etc. for the purpose of preventing a decrease in the crushing strength of the catalyst.

[Example 14] Reference Examples 2 to 4. A durability test was conducted on the catalysts prepared in Examples 5 to 8 under the conditions shown in Table 13, and a D test was conducted on these samples before and after durability.

Table 14 shows the results of the D test for catalysts 8a to 8e and 8A before and after durability testing, and the D test for catalysts 5a to 5H96A to 6H and 7A to 7H after durability testing. The results are shown in Figure 5.
It is shown in FIGS. 6 and 7.

From the results in Table 14, it can be seen that catalyst 8A, which is a catalyst of the present invention, is superior to catalysts 8a to 8C, which are reference catalysts, in terms of window, CO, HC, and NO purification rates both before and after durability.

This is particularly noticeable in the purification rate of CO and NO after durability, and it can be seen that the durability is excellent.

FIG. 5 shows the relationship between the Fe content and the window for the catalyst 5a and catalysts 5A to 5H, and the straight line a indicates the window for the catalyst 5a.

Figure 6 shows Rh content and NO, C for catalysts 6A to 6H.
It shows the relationship between the purification rates of O and HC, and curve 12
is a curve showing the purification characteristics of HC, curve 11 is a CO5, and curve 10 is a curve showing the purification characteristics of NO.

Figure 7 shows the pt content and HC, C for catalysts 7A to 7H.
O,N.

This shows the relationship between purification rates.

From the results shown in Figures 5, 6, and 7, the content of each component is
It can be seen that 0.2 g or more of Rho, 0.2 g or more of platinum group metals other than Rh, and 2 g or more of Fe are preferable per 11 catalysts.

[Example 15] A durability test was conducted under the same conditions as the catalyst 9a in Example 12, and the catalyst 9a and IOA before and after the durability test were
An activity test was conducted by passing exhaust gas through the catalyst when an internal combustion engine was operated with the air-fuel ratio varied in the range of 13.0 to 15.0.

S of this test, ■ is about 34.0OOhr1, 5 before the catalyst bed
The exhaust gas temperature at 0mm is approximately 50 when the air-fuel ratio is 14.6.
It was 0°C.

Instead of the above-mentioned l/R value, a relationship curve between A/F and the purification rate of each gas was drawn, and a window showing a purification rate of 70% or more for HC, Co, and NOx was determined. The results are shown in Table 15. .

This result shows that the catalyst 10A of the present invention is superior to the catalyst 9a to which Fe is not added.

[Brief explanation of drawings]

FIG. 1 shows HC1 when catalyst 1A is used and the 1/R value in steady gas is varied between 0.4 and 2.0. A CO2, NO3O3 conversion rate curve is shown. FIG. 2 shows the relationship between Mo content and window in catalysts 2A to 2H. Figure 3 shows the pt content and NO4 in catalysts 3A to 3H.
The relationship between the purification rates of CO5 and HC6 is shown. Figure 4 shows the Rh content and NO7 in catalysts 4A to 4G.
The relationship between the purification rates of CO8 and HC9 is shown. FIG. 5 shows the relationship between Fe content and window in catalysts 5A to 5H. Figure 6 shows the Rh content and N0IO in catalysts 6A to 6H.
, C011, and HCl2. Figure 7 shows the pt content and N013 in catalysts 7A to 7H.
゜COI 4. The relationship between each purification rate of HCI 5 is shown.

Claims (1)

[Claims] 1 The inorganic porous substance contains at least one of rhodium and platinum and palladium, which are platinum group metals other than rhodium.
Nitrogen oxides, carbon monoxide and A catalyst for purifying internal combustion engine exhaust gas that simultaneously removes hydrocarbons.