JPH05212284A - Exhaust gas cleaning catalyst - Google Patents

Abstract

PURPOSE:To simultaneously remove the three components of carbon monoxide, hydrocarbons and nitrogen oxides by a method for simultaneously removing harmful gas components of carbon monoxide, hydrocarbons and nitrogen oxides contained in an exhaust gas from the internal combustion engine of an automobile, in detail, without using rhodium, for an exhaust gas cleaning catalyst. CONSTITUTION:The catalyst is formed by covering catalytically active components containing palladium and an alkaline earth metal oxide, cerium oxide carrying zirconium and lanthanum and a fire resistant inorg. oxide carrying cerium and zirconium on a integrated structural body.

Description

Detailed Description of the Invention

[0001]

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

[0002]

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

Conventional palladium catalysts have high heat resistance and C in the oxidizing atmosphere of engine exhaust gas (so-called lean; air / fuel (A / F) is on the air side).
It was generally known that O and HC have high purification 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),
It can be mentioned that the NOx purification capacity is low. Therefore, use only on the lean side, for example, as a so-called oxidation catalyst,
Alternatively, rhodium, which has a high NOx purification ability, is used in combination with the above palladium to be used as a three-way catalyst for simultaneously purifying CO, HC and NOx.

However, since rhodium is extremely expensive, it is desirable to reduce the amount of the catalyst used in the catalyst component or not to use it. It is indispensable as an essential component as a component of an exhaust gas purifying catalyst that simultaneously removes carbon oxide (CO), hydrocarbon (HC) and nitrogen oxide (NOx).

[0005]

SUMMARY OF THE INVENTION The present invention provides an exhaust gas purifying catalyst that can purify CO, HC, and NOx at the same time without using rhodium, and that exhibits a higher catalytic performance than the conventional catalyst system. The challenge is to provide.

[0006]

OBJECTS OF THE INVENTION The present invention does not use rhodium,
It is another object of the present invention to provide an exhaust gas purifying catalyst that reduces the amount of CO, HC and NOx at the same time by greatly reducing the amount used.

[0007]

Means for Solving the Problems As a result of intensive studies to solve this problem, the present inventors have found that (a) palladium and alkaline earth metal oxides, and (b) zirconium and lanthanum are supported. Cerium oxide,
(c) Having an exhaust gas purifying ability equivalent to that of a conventional rhodium-containing three-way catalyst by coating a monolithic structure with a catalyst component composed of a refractory inorganic oxide having cerium and zirconium supported thereon. That is, the present invention has been completed. According to the present invention, NOx on the rich side of engine exhaust gas, which is a problem of the palladium catalyst,
The purification ability can be improved.

That is, the present invention relates to a catalyst for simultaneously removing carbon monoxide, hydrocarbons and nitrogen oxides in exhaust gas of an internal combustion engine, wherein (a) palladium and alkaline earth metal oxides and (b) zirconium. Exhaust gas characterized in that a monolithic structure is coated with a catalytically active component composed of cerium oxide carrying lanthanum and (c) refractory inorganic oxide carrying cerium and zirconium. It is a purification catalyst. The present invention will be described in detail below.

Among (a) palladium and alkaline earth metal oxides according to the present invention, the amount of palladium used varies depending on the conditions under which the catalyst is used, but is usually 0.5 to 30 g, preferably 0.5 per liter of the catalyst. ~ 25g. When the amount of palladium is less than 0.5, the purifying ability is low, and when it exceeds 30 g, the performance corresponding to the amount added is not improved.

The position on which palladium is supported varies depending on the amount used and the conditions under which it is used, but it may be supported on zirconium oxide, cerium oxide, lanthanum oxide, or refractory inorganic oxide alone or straddling it. Become.

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 0.1 to 50 g per liter of catalyst. If it is 0.1 g or less, no improvement in NOx purification performance is shown, and if it exceeds 50 g, the effect commensurate with the addition is small. The alkaline earth metal may be supported on any of cerium oxide, zirconium oxide, lanthanum oxide, or refractory inorganic oxide, and therefore the preparation method is not particularly limited.

The alkaline earth metal oxide source may be a precursor which becomes an oxide by firing, in addition to the oxide as it is, an organic salt such as barium acetate or barium oxalate, and barium nitrate, Any of inorganic salts such as barium sulfate, barium hydroxide and barium carbonate may be used,
Further, the state thereof may be not only an aqueous solution state, but also a gel state or a suspension state, and the above 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.
It is 00-100: 1. When the amount of alkaline earth metal is less than 1: 100, the ternary performance is deteriorated, and in particular,
The NO purification rate is inferior, and the addition effect is improved when the amount of alkaline earth metal is larger than 150: 1, but the loading ratio and loading amount are limited by the relationship between the loading amount of other oxides and the strength of the catalyst. ..

Among the cerium oxides (b) on which zirconium and lanthanum are supported according to the present invention, the source of cerium oxide is not particularly limited, but as an oxide or as a nitrate, a sulfate or the like. The cerium oxide obtained by baking the water-soluble salt or carbonate of can be used.

As zirconium and lanthanum, water-soluble salts such as nitrates and sulfates, gel-like or suspension-like solutions and the like can be used.

(B) The method for preparing the cerium oxide in which zirconium and lanthanum are supported includes (1) a method in which the cerium oxide is simultaneously impregnated with an aqueous solution of the above-mentioned zirconium salt and lanthanum salt, and then dried and calcined. ) There is a method of impregnating and supporting an aqueous solution of zirconium salt on cerium oxide, and then impregnating and supporting an aqueous solution of lanthanum salt, and (3) a method of impregnating and supporting an aqueous solution of lanthanum salt and then impregnating and supporting an aqueous solution of zirconium salt. In any case, it can be appropriately used.

The zirconium supported on the cerium oxide preferably exists at least partially as a composite or solid solution with the cerium oxide and / or the lanthanum oxide.

The ratio of cerium oxide to zirconium oxide (weight ratio in terms of oxide) is 100: 2 to 100: 60, more preferably 100: 4 to 100: 40. If the ratio of cerium oxide is more than 100: 2, the performance tends to be poor, and if the ratio of zirconium oxide is more than 100: 60, the performance tends to be poor.

The amount of lanthanum oxide used is 0.1 to 50 g per liter of the monolithic structure. If the amount of lanthanum oxide is less than 0.1 g, no improvement in performance is shown. I can't get it.

Among the refractory inorganic oxides (c) supporting cerium and zirconium according to the present invention, cerium and zirconium are water-soluble salts, gels,
There is no particular limitation as long as it is in a suspended state.

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 preferable. This refractory inorganic oxide per 1 liter of the integral structure,
The coating is preferably 10 g to 300 g.

As a method for preparing the catalyst, (1) water-soluble cerium and zirconium salt are simultaneously impregnated in the refractory inorganic oxide and then dried and calcined, and (2) water-soluble cerium salt is impregnated in the refractory inorganic oxide. After loading, there is a method of impregnating and supporting a water-soluble zirconium salt, (3) impregnating and supporting a water-soluble zirconium salt on a refractory inorganic oxide, and then impregnating and supporting a water-soluble cerium salt. It can be used as appropriate. It is preferable that at least a part of the cerium oxide and the zirconium oxide be present as a composite or solid solution. More preferably, the ratio of the cerium oxide to the zirconium oxide (weight ratio in terms of oxide) is 10.
0: 2 to 100: 60, more preferably 10
It is 0: 4 to 100: 40. If this ratio is higher than 100: 2 with cerium oxide, the performance is poor and 100:
When the amount of zirconium oxide is more than 60, the performance tends to be low.

The cerium oxide used in the above (b) and (c) is 10 to 150 per liter of the integrated structure.
g, zirconium oxide is 0.1 to 50 g. When the amount of cerium oxide is less than 10 g, the purification performance is low, and when it exceeds 150 g, the performance improvement commensurate with the addition is not shown. If the amount of zirconium oxide is less than 0.1 g, the purification performance is low, and if it exceeds 50 g, the performance is deteriorated.

The ratio (weight ratio in terms of oxide) of cerium contained in (b) cerium oxide carrying zirconium and lanthanum to (c) cerium contained in the refractory inorganic oxide carrying cerium and zirconium is: , 100: 1 to 1
It is preferably 0: 100. More preferably,
It is 100: 5 to 20: 100. When the amount of cerium oxide (b) is more than 100: 1, NO on the rich side
x performance deterioration is shown, and the performance tends to decrease as the amount of the cerium oxide (c) increases from 10: 100.

The catalyst composition per liter of the monolithic structure is 50 to 400 g, preferably 100 to 350 g. If the amount is less than 50 g, the purification performance is low and 400
When it exceeds g, when the integrally molded body is coated with the catalyst composition, the back pressure thereof is increased, which is not preferable.

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

[0027]

As described above, the catalyst according to the present invention is
It is possible to provide an exhaust gas purifying catalyst which does not use rhodium and whose use amount is greatly reduced compared to the conventional one, and which simultaneously removes three components of CO, HC and NOx.

The effect of adding the alkaline earth metal oxide is that it acts directly on palladium and changes its charge state, thereby increasing the reactivity and improving the NOx purification ability in a rich atmosphere. By mixing and using (b) cerium oxide carrying zirconium and lanthanum and (c) refractory inorganic oxide carrying cerium and zirconium, the fuel gas composition has a stoichiometric ratio (fuel gas A large improvement in the CO, HC and NOx purification capacity and the rich NOx purification capacity in the vicinity of the amount of air required to completely burn the NOx is shown.

When only (b) is used, or (c)
Both of them have lower performances than the cases of mixing (b) and (c). The addition of lanthanum in (b) shows an improvement in the CO, HC and NOx purifying ability in the vicinity of the stoichiometric ratio, but a decrease in the rich NOx purifying ability. On the other hand, when (c) is mixed with (b), the performance improvement due to the addition of lanthanum is further increased, and the decrease in rich NOx purification capacity is not only suppressed but also improved.

[0030]

EXAMPLES The present invention will be specifically described below with reference to examples, but the invention is not limited to these examples as long as the object of the present invention is not impaired.

Example 1 (b) Cerium oxide carrying zirconium and lanthanum Commercially available cerium oxide (CeO ₂ , specific surface area 149 m ² /
g) An aqueous solution of zirconyl oxynitrate and lanthanum nitrate in 50 g (zirconium oxide 5 g, lanthanum oxide 10
g) was mixed, dried, and then calcined at 500 ° C. for 1 hour to obtain (b) powder.

(C) Refractory inorganic oxide on which cerium and zirconium are supported Activated alumina (γ-Al ₂ O ₃ , specific surface area 155 m ² /
g) 60 g of an aqueous solution of cerium nitrate and zirconyl oxynitrate (cerium oxide 50 g, zirconia oxide 5
g) was mixed, dried, and then calcined at 500 ° C. for 1 hour to obtain (c) powder.

An aqueous palladium nitrate solution containing the above powders (b) and (c), barium acetate (20 g as barium oxide) and 3 g of palladium was added and wet pulverized with a ball mill to prepare a water-soluble slurry. A cordierite monolithic carrier (inner diameter: 33 mm x length: 76 mm) having 400 cells per 1 inch square in cross section was immersed in this slurry, taken out, and the excess slurry in the cells was blown off with compressed air, followed by drying. Then, it was calcined to obtain a finished catalyst.

(Examples 2 to 8) In Example 1,
(B) cerium oxide, zirconium oxide in the powder,
A completed catalyst was obtained in the same manner as in Example 1, except that the contents of lanthanum oxide, cerium oxide and zirconium oxide in the powder (c) were changed. The amount of each catalyst component supported per liter of the catalyst obtained in this way is shown in Table 1.
It was shown to.

(Examples 9 and 10) In Example 1, barium acetate (20 g as barium oxide) was replaced with barium acetate (0.5 g and 40 g as barium oxide, respectively).
A completed catalyst was obtained in the same manner as in Example 1 except that

(Embodiments 11 and 12) In Embodiment 1,
A completed catalyst was obtained in the same manner as in Example 1 except that barium acetate (20 g as barium oxide) was changed to calcium acetate and strontium acetate (both were 20 g as oxide), respectively.

(Examples 13 and 14) In Example 1,
(B) cerium oxide, zirconium oxide in the powder,
And the finished catalyst was obtained in the same manner as in Example 1 except that the contents of cerium oxide and zirconium oxide in the powder (c) were changed.

(Examples 15 and 16) In Example 4,
A completed catalyst was obtained in the same manner as in Example 4 except that the palladium nitrate aqueous solution containing 3 g of palladium was changed to 10 g and 20 g, respectively.

Comparative Example 1 A completed catalyst was obtained in the same manner as in Example 4 except that barium acetate was omitted.

Comparative Example 2 A finished catalyst was obtained in the same manner as in Example 4, except that lanthanum nitrate was omitted.

Comparative Example 3 A finished catalyst was obtained in the same manner as in Example 4 except that zirconyl oxynitrate was omitted.

Comparative Example 4 100 g of the cerium oxide used in Example 1 was mixed with an aqueous solution of zirconyl oxynitrate and lanthanum nitrate (10 g of zirconium oxide and 10 g of lanthanum oxide), dried, and then dried at 500 ° C. for 1 hour. The calcined powder, 60 g of activated alumina used in Example 1, barium acetate (20 g as barium oxide) and palladium nitrate containing 3 g of palladium were added to obtain a completed catalyst in the same manner as in Example 1.

(Comparative Example 5) In Example 1, 60 g of activated alumina was mixed with cerium nitrate, zirconyl oxynitrate and lanthanum nitrate (100 g of cerium oxide, 10 g of zirconium oxide, 10 g of lanthanum oxide), dried and dried at 500 ° C. Then, the powder calcined for 1 hour, barium acetate (20 g as barium oxide) and palladium nitrate containing 3 g of palladium were added, and a completed catalyst was obtained in the same manner as in Example 1.

Comparative Example 6 Powder in which 200 g of activated alumina used in Example 1 was impregnated and supported in a solution prepared by mixing an aqueous dinitrodiamine platinum solution containing 2.25 g of platinum and an aqueous rhodium nitrate solution containing 0.22 g of rhodium. Then, 100 g of the cerium oxide used in Example 1 was wet pulverized with a ball mill, and a finished catalyst was obtained in the same manner as in Example 1.

Comparative Example 7 A mixed solution of an aqueous palladium nitrate solution containing 2.25 g of palladium and an aqueous rhodium nitrate solution containing 0.22 g of rhodium was impregnated into 200 g of the activated alumina used in Example 1 and dried, followed by firing. The obtained powder and 100 g of the cerium oxide used in Example 1 were wet pulverized with a ball mill and then a finished catalyst was obtained in the same manner as in Example 1.

Table 1 shows the supported amounts of the respective catalyst components per liter of the catalysts of Examples and Comparative Examples thus obtained.

Example 17 The catalysts obtained in Examples 1 to 16 and Comparative Examples 1 to 7 were evaluated for catalytic activity after engine durability. The procedure is shown below.

Commercially available electronically controlled engine (8 cylinders 4
Using 400 cc), a multi-converter filled with each catalyst was connected to the exhaust system of the engine and a durability test was conducted. The engine operates in a mode operation of 60 seconds of steady operation and 6 seconds of deceleration (fuel is cut during deceleration, and the catalyst is exposed to severe conditions of high temperature oxidizing atmosphere), and the catalyst bed temperature is 950 ° C during steady operation. The catalyst was aged for 50 hours under the following conditions. The catalyst performance after aging was evaluated by 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 such that the catalyst inlet gas temperature is 400 ° C and the space velocity is 90,000.
It was evaluated under the condition of 0 hr- ¹ . At this time, 1 from the external oscillator
Introducing a Hz sine wave type signal into the engine control unit, the air-fuel ratio (A / F) is ± 1.0A / F,
The average air-fuel ratio is continuously changed while oscillating at 1 Hz, and the catalyst inlet and outlet gas compositions at this time are simultaneously analyzed, and the average air-fuel ratio A / F is 15.1 to 14.1 C
The purification rates of O, HC and NO were obtained.

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

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

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

[0052]

[Table 1]

[0053]

[Table 2]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tomohisa Ohata 1 992 Nishikioki, Kamahama, Aboshi-ku, Himeji-shi, Hyogo 1

Claims (5)

[Claims] 1. A (a) palladium and alkaline earth metal oxide, (b) a cerium oxide carrying zirconium and lanthanum, and (c) a refractory inorganic oxide carrying cerium and zirconium. An exhaust gas purifying catalyst, characterized in that the catalytically active component contained therein is coated on an integral structure. 2. Palladium in an amount of 0.5 to 30 g and cerium oxide in an amount of 10 to 1 per liter of the integrated structure.
50 g, zirconium oxide 0.1 to 50 g, lanthanum oxide 0.1 to 50 g, alkaline earth metal oxide 0.1 to 50 g, and refractory inorganic oxide 10 to 300.
The catalyst according to claim 1, which is coated with g. 3. The catalyst according to claim 1, wherein at least a part of the cerium oxide and the zirconium oxide is present as a composite or solid solution. 4. The catalyst according to claim 1, 2 or 3, wherein the ratio of the cerium oxide to the zirconium oxide (oxide conversion weight ratio) is 100: 2 to 100: 60. 5. A ratio of cerium contained in (b) cerium oxide carrying zirconium and lanthanum and (c) refractory inorganic oxide carrying cerium and zirconium (weight ratio in terms of oxide). ) Is from 100: 1
The catalyst according to claim 1, which is 10: 100.