JP2698302B2 - Exhaust gas purification catalyst - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to carbon monoxide (C) which is a harmful component contained in exhaust gas from internal combustion engines such as automobiles.
O), hydrocarbons (HC) and nitrogen oxides (NOx) at the same time.

[0002]

2. Description of the Related Art Various exhaust gas purifying catalysts for removing harmful components in exhaust gas discharged from an internal combustion engine have been proposed.

Conventionally, palladium catalysts have high heat resistance and have a high C value in an oxidizing atmosphere of engine exhaust gas (so-called lean; air / fuel (A / F) is large on the air side).
It is generally known that O and HC have high purifying ability. On the other hand, as a problem, when the engine exhaust gas is in a reducing atmosphere (so-called rich; (A / F) is large on the fuel side),
NOx purification ability is low. Therefore, use only on the lean side, for example, use as a so-called oxidation catalyst,
Alternatively, rhodium having a high NOx purifying ability is combined with the above-mentioned palladium and used as a three-way catalyst for purifying CO, HC and NOx simultaneously.

However, since rhodium is very expensive, it is desired that the amount of rhodium used in the catalyst component be reduced or not used. However, since rhodium has a characteristic of having a high NOx purification ability, it has one characteristic. As a component of the exhaust gas purifying catalyst for simultaneously removing carbon oxide (CO), hydrocarbon (HC) and nitrogen oxide (NOx), it is indispensable as an essential component.

[0005]

SUMMARY OF THE INVENTION The present invention provides an exhaust gas purifying catalyst which can simultaneously purify CO, HC and NOx without using rhodium and which exhibits a higher catalytic performance than a conventional catalyst system. The task is to provide.

[0006]

The object of the present invention is to use rhodium without using rhodium.
It is another object of the present invention to provide an exhaust gas purifying catalyst capable of simultaneously removing three components of CO, HC and NOx by greatly reducing the amount of use thereof in comparison with the prior art.

[0007]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve this problem, and have found that they contain palladium, alkaline earth metal oxides, refractory inorganic oxides, and cerium and lanthanum. It has been found that a catalyst in which a catalytically active component containing zirconium oxide is coated on an integral structure has an exhaust gas purifying ability equal to or higher than that of a conventional three-way catalyst containing rhodium. It has been reached. The catalyst according to the present invention can improve the NOx purification ability particularly when the exhaust gas is rich.

More specifically, the present invention relates to (A) palladium,
( B) alkaline earth metal oxide, (C) refractory inorganic oxidation
The Mononami beauty (D) a catalytically active component containing zirconium oxide containing cerium and lanthanum, a catalyst coated integrally structure, zirconium oxide containing the cerium and lanthanum (D) is (a ) The weight ratio of cerium to zirconium oxide is 1: 8 to 1: 1 in terms of CeO ₂ : ZrO ₂ , and (b) the weight ratio of lanthanum to zirconium oxide is La ₂ O ₃ : ZrO ₂ converted at 1: 1.5 to 1: 60 der is, 10 at 900 ° C. (c)
Cerium by X-ray diffraction measurement after time aging
The oxide has a crystallite diameter of 250 ° or less, and (d) 5
Oxygen at 400 ° C after hydrogen reduction treatment at 00 ° C for 30 minutes
Consumption capacity is 5 × 10 ^-5 mol- / g of cerium oxide
An exhaust gas purifying catalyst for purifying carbon monoxide, hydrocarbons and nitrogen oxides in exhaust gas of an internal combustion engine, which is characterized by being at least O ₂ .

Preferably, 0.1 to 30 g of palladium and CeO ₂ are contained per liter of the integrated structure.
When converted to 10 to 100 g, the lanthanum is converted to La ₂ O ₃ ,
0.1 to 50 g, zirconium oxide is 10 to 100
g, the alkaline earth metal oxide is 0.1 to 50 g, and the refractory inorganic oxide is 10 to 300 g.

It is preferable that the zirconium oxide containing cerium and lanthanum is present, at least in part, as a composite oxide or solid solution of cerium oxide, lanthanum oxide and zirconium oxide. Hereinafter, the present invention will be described in more detail.

The amount of palladium used in the present invention varies depending on the conditions for using the catalyst, but is usually 0.1 to 30 g, preferably 0.1 to 25 g per liter of the catalyst. When the amount of palladium is less than 0.1, the purification ability is low, and when it exceeds 30 g, the improvement in performance corresponding to the addition is not seen.

Although the position where palladium is supported varies depending on the amount and conditions of use, it is preferable that the palladium be supported on at least a zirconium oxide containing cerium and lanthanum. Can improve the purification ability near the stoichiometric ratio.

Next, examples of the alkaline earth metal include beryllium, magnesium, calcium, strontium and barium, and at least one selected from the group consisting of calcium, strontium and barium is particularly preferable. The amount of alkaline earth metal oxide used is catalyst 1.
0.1 to 50 g per liter. If it is 0.1 g or less, no improvement in NOx purification performance is shown, and if it exceeds 50 g, the effect corresponding to the addition is small. Since the alkaline earth metal may be supported on the zirconium oxide or refractory inorganic oxide containing cerium and lanthanum, or may support palladium, the preparation method is not particularly limited.

The relationship between alkaline earth metal and palladium is
Their weight ratio (alkaline earth metal oxide / palladium) is 1: 100 to 150: 1, preferably 1: 1.
00 to 100: 1. When the amount of the alkaline earth metal is less than 1: 100, the ternary performance deteriorates,
The effect of addition is improved when the NO purification rate is poor and the amount of alkaline earth metal is greater than 150: 1, but the loading ratio and the loading amount are limited by the relationship between the loading amount of other oxides and the strength of the catalyst. .

As the alkaline earth metal oxide source, besides using the oxide as it is, a precursor which becomes an oxide by firing may be used. For example, barium acetate, barium oxalate, etc. Any of organic salts and inorganic salts such as barium nitrate, barium sulfate, barium hydroxide, and barium carbonate may be used, and the state thereof is not limited to an aqueous solution, but may be a gel or a suspension. Well, the above is not particularly limited.

In the zirconium oxide containing cerium and lanthanum, (a) the weight ratio of cerium to zirconium oxide is 1: 8 in terms of CeO ₂ : ZrO _2.
To 1: 1, preferably 1: 7 to 1: 1.
When the amount of cerium (in terms of CeO ₂ ) is less than 1: 8, the performance is low, and the amount of cerium (in terms of CeO ₂ ) is 1: 1.
When it exceeds, the NOx purification ability in a rich atmosphere is reduced.

In the zirconium oxide containing cerium and lanthanum, (b) the weight ratio of lanthanum to zirconium oxide is 1: _{2 in} terms of La ₂ O ₃ : ZrO _2.
1.5 to 1:60, preferably 1: 2 to 1:50. When the lanthanum amount (La ₂ O ₃ conversion) is less than 1:60, the performance is low, and the lanthanum amount (La ₂ O ₃ conversion) is obtained.
However, if the ratio exceeds 2: 3, no improvement in performance corresponding to the added amount of lanthanum can be obtained.

The starting material of cerium and lanthanum used in the zirconium oxide containing cerium and lanthanum is not particularly limited, but water-soluble salts such as nitrates, sulfates, chlorides and acetates are used. Alternatively, a solution of a gel suspension can be used.

As the starting material of the zirconium oxide used in the zirconium oxide containing cerium and lanthanum, when the oxide itself is used, the specific surface area is at least 20 m ² / g, preferably 40 m ² / g. By using the above, on the other hand, when water-soluble is used as the zirconium oxide source, for example, nitrate, sulfate, acetate, chloride or carbonate can be used.

The method for preparing the zirconium oxide containing cerium and lanthanum is shown below, but other methods than those shown below can be used without departing from the spirit of the present invention.

(1) A method in which an aqueous solution of a cerium salt and a lanthanum salt is added to zirconium oxide, mixed, dried and calcined. (2) An aqueous solution of a cerium salt is added to the zirconium oxide, mixed and dried. After firing, a method of adding a lanthanum salt in a similar procedure, (3) zirconium oxide,
A method of adding an aqueous solution of a lanthanum salt, mixing and drying, adding an aqueous solution of a lanthanum salt, mixing, drying and calcining,
(4) mixing aqueous solutions of zirconium salt, cerium salt and lanthanum salt, and co-precipitating by a usual method, for example,
It can be prepared by a method of coprecipitating with ammonia or an organic acid under pH control, drying and baking.

The thus obtained zirconium oxide containing cerium and lanthanum is coated on an integral structure by a conventional method, or is impregnated or mixed with another catalytically active component such as a noble metal. Can be coated on the body.

(5) Further, the integral structure is coated with a refractory inorganic oxide by a usual method, and further, an aqueous solution of a zirconium salt, a cerium salt and a lanthanum salt is mixed or impregnated separately, dried and calcined. , A zirconium oxide containing the cerium and lanthanum can be prepared.
Among the above methods, the methods (1) to (3) are preferable in consideration of production cost, ease of preparation, and the like.

The zirconium oxide containing cerium and lanthanum is preferably present, at least in part, as a composite oxide or a solid solution. Further, when the zirconium oxide containing cerium and lanthanum is prepared, and after aging at 900 ° C. for 10 hours, X-ray diffraction is measured, it is preferable that the crystallite diameter of the cerium oxide is 250 ° or less.

After the aging, the zirconium oxide containing cerium and lanthanum has a reduced oxygen consumption capacity (so-called OSC: oxygen storage capacity) at 400 ° C. after a hydrogen reduction treatment at 500 ° C. for 30 minutes. It is preferably at least 5 × 10 to ⁵ mol-O ₂ (equivalent to oxygen O ₂ mol) per 1 g.

The amount of cerium (in terms of CeO ₂ ) in the zirconium oxide containing cerium and lanthanum per liter of the integrated structure is 10 to 100 g, preferably 1 to 100 g.
0-80 g, lanthanum amount (La ₂ O ₃ conversion) 0.1-5
0 g, 0.5 to 40 g, zirconium oxide (ZrO ₂
(Converted) is 10 to 100 g, preferably 10 to 80 g.

Examples of the refractory inorganic oxide include those having a high surface area such as activated alumina, silica and zirconia, and activated alumina is particularly preferred. This refractory inorganic oxide, per liter of the integrated structure,
50 g to 400 g, preferably 100 g to 350 g. When it is less than 50 g, the purification performance is low, and when it exceeds 400 g, when the integral structure is coated with the catalyst composition, the back pressure increases, which is not preferable.

The integral structure means a structure usually used for purifying exhaust gas, preferably a structure having a honeycomb shape, a ceramic monolith carrier such as cordierite or mullite, and a stainless steel or Fe--Cr alloy. −
A monolithic carrier made of a metal such as an Al alloy may be used. The cell shape, hole diameter, and the like through which these exhaust gases pass can be variously selected depending on the type of exhaust gas and the engine displacement.

[0029]

As described above, the catalyst according to the present invention comprises:
It is possible to provide an exhaust gas purifying catalyst that removes three components of CO, HC and NOx at the same time without using rhodium and by greatly reducing the amount of rhodium used conventionally.

The effect of the addition of the alkaline earth metal oxide is to directly act on palladium and change its charge state, thereby increasing the reactivity and improving the NOx purification ability in a rich atmosphere.

By using the zirconium oxide containing cerium and lanthanum, the stoichiometric ratio of the fuel gas (the amount of air required to completely burn the fuel gas)
CO, HC and NOx purification capacity and rich NOx in the vicinity
Significant improvement in purification capacity is shown.

Further, since the palladium is supported on the zirconium oxide containing at least cerium and lanthanum, the purification ability near the above stoichiometric ratio can be greatly improved.

[0033]

The present invention will be described in more detail with reference to the following examples, which should not be construed as limiting the scope of the present invention.

Example 1 A method for preparing a zirconium oxide containing cerium and lanthanum.

An aqueous solution of cerium nitrate and lanthanum nitrate (30 equivalents of CeO ₂ ) was added to 60 g of commercially available zirconium oxide (ZrO ₂ having a specific surface area of 100 m ² / g).
g, containing 10 g in terms of La ₂ O ₃ ), and after drying,
The powder was fired at 500 ° C. for 1 hour to prepare a zirconium oxide powder containing cerium and lanthanum.

100 g of the above powder and activated alumina (Al
₂ O ₃ with a specific surface area of 155 m ² / g)
Was added to an aqueous solution of palladium nitrate containing 3 g of palladium, mixed, dried and then calcined at 500 ° C. for 1 hour.

This powder and barium acetate (20 g in terms of barium oxide) were added and wet-pulverized with a ball mill.
A water-soluble slurry was prepared. A cordierite monolith carrier (inner diameter 33 mm, length 76 mm) having 400 cells per square inch in cross-sectional area was immersed in the slurry, taken out, and the excess slurry in the cells was blown off with compressed air. Drying and calcination yielded the finished catalyst.

(Example 2) In Example 1, zirconium oxide (ZrO ₂ , specific surface area of 100 m ² /
A completed catalyst was obtained in the same manner as in Example 1, except that g) was changed to a zirconium oxide having a specific surface area of 30 m ² / g.

(Embodiments 3 and 4)
Completed catalysts 3 and 4 were obtained in the same manner as in Example 1 except that the amount of lanthanum nitrate was changed to 10 g in terms of La ₂ O ₃ and 30 g and 1 g, respectively.

(Examples 5 and 6) In Example 1,
Completed catalysts 5 and 6 were obtained in the same manner as in Example 1 except that the amount of cerium nitrate was changed to 60 g and 12 g, respectively, instead of 30 g in terms of CeO ₂ .

Example 7 In Example 1, the amount of zirconium oxide was changed to 60 g, the amount of cerium nitrate was changed to 30 g in terms of CeO ₂ , and the amount of zirconium oxide was changed to 40 g, and the amount of cerium nitrate was changed to 20 g in terms of CeO _2. Except for the replacement
A completed catalyst was obtained in the same manner as in Example 1.

Example 8 In Example 1, the amount of zirconium oxide was changed to 60 g, the amount of cerium nitrate was changed to 30 g in terms of CeO ₂ , the amount of zirconium oxide was changed to 20 g, and the amount of cerium nitrate was changed to 12 g in terms of CeO _2. Except for the replacement
A completed catalyst was obtained in the same manner as in Example 1.

(Examples 9 and 10) In Example 1, the amount of barium acetate was changed to 20 g in terms of BaO,
The amount of barium acetate was 0.25 g,
Except that the catalyst was replaced with 0 g, the same procedure as in Example 1 was carried out to complete catalyst 9
And 10 were obtained.

(Examples 11 to 13) In Example 1,
The amount of barium acetate was changed to 20 g in terms of BaO, strontium nitrate was 20 g in terms of SrO, calcium nitrate was 20 g in terms of CaO, and magnesium nitrate was MgO.
Except that the conversion was 20 g, completed catalysts 11 to 13 were obtained in the same manner as in Example 1.

Example 14 A method for preparing a zirconium oxide containing cerium and lanthanum.

An aqueous solution of zirconium oxynitrate containing 60 g in terms of ZrO ₂ and an aqueous solution of cerium nitrate and lanthanum nitrate (containing 30 g in terms of CeO ₂ and 10 g in terms of La ₂ O ₃ ) were mixed. Was slowly added dropwise to form a precipitate, which was aged. Thereafter, the precipitate was washed with water, filtered, dried, and calcined at 500 ° C. for 1 hour to obtain a zirconium oxide containing cerium and lanthanum.

The procedure of Example 1 was repeated, except that the zirconium oxide containing cerium and lanthanum obtained in Example 14 was used instead of the zirconium oxide containing cerium and lanthanum used. Thus, a completed catalyst was obtained.

Comparative Example 1 A completed catalyst was obtained in the same manner as in Example 1 except that barium acetate was omitted.

Comparative Example 2 In Example 1, cerium nitrate and lanthanum nitrate were replaced with cerium oxide (specific surface area 1).
00 m ² / g) and lanthanum oxide (specific surface area 20 m ² / g)
Except having changed to g), it carried out similarly to Example 1, and obtained the completed catalyst.

Comparative Example 3 A completed catalyst was obtained in the same manner as in Example 1 except that lanthanum nitrate was replaced by lanthanum oxide (specific surface area: 20 m ² / g).

Comparative Example 4 A dinitrodiamine platinum aqueous solution containing 1.125 g of platinum and 0.11 g of rhodium
150 g of the activated alumina used in Example 1 was added to a mixed solution of the contained rhodium nitrate aqueous solution, mixed, dried, and calcined at 500 ° C. for 1 hour to obtain a powder. This powder was mixed with 50 g of the cerium oxide used in Example 15,
The slurry was obtained by wet grinding with a ball mill. This slurry was coated on a monolithic carrier in the same procedure as in Example 1 to obtain a completed catalyst. Table 1 shows each catalyst component and the amount thereof carried per liter of the catalysts of the examples and comparative examples thus obtained.

[0052]

[Table 1]

(Example 15) The catalysts obtained in Examples 1 to 14 and Comparative Examples 1 to 4 were evaluated for catalytic activity after engine durability. The procedure is described below.

A commercially available electronically controlled engine (8 cylinders 4
400 cc), a multi-converter filled with each catalyst was connected to the exhaust system of the engine, and a durability test was performed. The engine was operated in a mode operation of steady operation 60 seconds and deceleration 6 seconds (fuel was cut during deceleration, and the catalyst was exposed to severe conditions of a high-temperature oxidizing atmosphere). The catalyst was aged under the following conditions for 50 hours. Evaluation of catalyst performance after aging was performed using a commercially available electronically controlled engine (4-cylinder 1800c).
Using c), a multi-converter filled with each catalyst was connected to the exhaust system of the engine. The three-way performance of the catalyst is as follows: catalyst inlet gas temperature 400 ° C, space velocity 90,00
The evaluation was performed under the condition of 0 hr- ¹ . At this time, 1
Hz sine wave type signal is introduced into the control unit of the engine, and the air-fuel ratio (A / F) is ± 1.0 A / F,
The average air-fuel ratio was continuously changed while oscillating at 1 Hz, and the catalyst inlet and outlet gas compositions at this time were analyzed simultaneously, and the average air-fuel ratio A / F was increased from 15.1 to 14.1 C
The purification rates of O, HC and NO were determined.

The CO, HC and N determined as described above
The purification rate of O versus the inlet air-fuel ratio is plotted on a graph to create a ternary characteristic curve, the purification rate at the intersection (called a crossover point) of the CO and NO purification rate curves, and the A at the intersection.
The HC purification rate at the / F value Further, the A / F is 14.2
Table 2 shows the NO purification ability when the engine exhaust gas is rich.

The purifying performance of the catalyst at a low temperature is determined by oscillating the air-fuel ratio under the condition of ± 0.5 A / F (1 Hz).
The engine was operated with the average air-fuel ratio fixed to A / F of 14.6, a heat exchanger was installed in front of the catalytic converter in the engine exhaust system, and the temperature of the gas at the catalyst inlet was 200 ° C to 500 ° C.
The temperature was continuously changed to 0 ° C., and the gas composition at the inlet and the outlet of the catalyst was analyzed to evaluate the purification rate of CO, HC and NO. The temperature (light-off temperature) at a CO, HC, and NO purification rate of 50% obtained as described above was measured and shown in Table 2.

As can be seen from Table 2, the catalyst disclosed in the present invention does not contain rhodium as a noble metal and contains
It can be seen that three components of O, HC and NOx can be simultaneously removed with high performance. Further, the exhaust gas of the engine is excellent in NOx purification rate (NOx value when A / F is 14.2) on the rich side, and simultaneously removes three components of HC, CO and NO at extremely low temperature (light-off temperature). Value).

[0058]

[Table 2]

(Preparation of catalyst for physical property test) Preparation of a test catalyst for physical properties of zirconium oxide containing cerium and lanthanum will be described. In the same manner as in Examples 1 and 3 to 6, zirconium oxides containing cerium and lanthanum were prepared, respectively, and used as Examples (a) to (e).

The same zirconium oxide, cerium oxide and lanthanum oxide as those used in Comparative Example 2 were ground and mixed in an agate mortar in the same amount ratio as in Comparative Example 2, and then heated to 500 ° C. under flowing air. And baked for 1 hour
(f).

An oxide similar to the cerium oxide used in Comparative Example 2 was calcined at 500 ° C. for 1 hour in an air stream to obtain Comparative Example (g).

(Example 18) The catalysts of Examples (a) to (e) and Comparative Examples (f) and (g) were calcined at 900 ° C for 10 hours.
A line diffraction measurement was performed. The crystal diameter was measured from the half width of the X-ray diffraction chart, and the results are shown in Table 3.

[0063]

[Table 3]

(Example 19) A catalyst similar to the catalyst used in Example 18 was subjected to a reduction treatment at 500 ° C. for 30 minutes in a flow system of hydrogen under a flow of hydrogen and then to helium gas. The temperature was lowered to 400 ° C. under the same atmosphere, and a predetermined amount of oxygen pulse was introduced into the catalyst bed filled with the catalyst to measure the oxygen consumption. Table 3 shows the results.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Tomohisa Ohata 992, Nishioki, Okihama-shi, Aboshi-ku, Himeji-shi

Claims (4)

(57) [Claims] 1. A (A) palladium, a catalytic active component containing (B) an alkaline earth metal oxides, zirconium oxide containing (D) cerium and lanthanum (C) a refractory inorganic oxide Mononami Beauty, integral a catalyst coated to a structure, the weight ratio of zirconium oxide containing the cerium and lanthanum (D) is (a) cerium and zirconium oxide calculated as CeO _2: ZrO ₂ in terms of 1: 8 to 1: 1
And (b) the weight ratio of lanthanum to zirconium oxide is 1: 1.5 to 1: in terms of La ₂ O ₃ : in terms of ZrO _2.
60 der is, after 10 hours aging at 900 ° C. (c)
Of the crystallite diameter of cerium oxide by X-ray diffraction measurement
Not more than 250 ° and (d) at 500 ° C. for 30 minutes
Cerium oxygen consumption at 400 ° C after hydrogen reduction
An exhaust gas purifying catalyst for simultaneously purifying carbon monoxide, hydrocarbons and nitrogen oxides in an exhaust gas of an internal combustion engine, wherein the catalyst is not less than 5 × 10 ⁻⁵ mol-O ₂ per gram of oxide . 2. Per liter of the integrated structure, 0.1-30 g of palladium and 10-10 cerium in terms of CeO _{2 are} converted.
100 g, lanthanum is 0.1 to 50 in terms of La ₂ O _3.
The catalyst according to claim 1, wherein the amount of the zirconium oxide is 10 to 100 g, the alkaline earth metal oxide is 0.1 to 50 g, and the refractory inorganic oxide is 10 to 300 g. 3. The catalyst according to claim 1, wherein the palladium is supported on at least a zirconium oxide containing cerium and lanthanum. 4. The zirconium oxide containing cerium and lanthanum is present, at least in part, as a composite oxide or solid solution of cerium oxide, lanthanum oxide and zirconium oxide. Catalyst.