JPH05277373A - Exhaust gas purifying catalyst and purifying system using the catalyst - Google Patents

Abstract

PURPOSE:To simultaneously remove CO, HC and NOx with a smaller amt. of catalyst than before and without using rhodium. CONSTITUTION:A mixture of the catalytic component consisting of 0.5-30g of palladium, 0.1-50g of an alkaline-earth metal oxide, 10-150g of cerium oxide and 0.1-50g of zirconium oxide per liter of catalyst and 100-300g of activated alumina is deposited on a monolithic carrier to constitute the exhaust gas purifying catalyst. The efficiency of the catalyst in removing NO is remarkably improved even if the exhaust gas is in a enriched state in an engine exhaust gas, and the efficiency in removing CO, HC and NOx is improved even when the composition of the gaseous fuel is close to stoichiometry.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying catalyst and an exhaust gas purifying system. More specifically, the present invention relates to carbon monoxide (CO), which is a harmful component contained in exhaust gas from an internal combustion engine such as an automobile,
The present invention relates to an exhaust gas purification catalyst and an exhaust gas purification system that simultaneously remove hydrocarbons (HC) and nitrogen oxides (NOx).

[0002]

2. Description of the Related Art Various catalysts for purifying exhaust gas which remove 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; air / fuel (A / F) is on the fuel side), the NOx purification capacity is low. Therefore, it is used only on the lean side, for example, as a so-called oxidation catalyst, or by combining rhodium having a high NOx purification capacity with the above palladium, it is 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 rhodium used in the catalyst component or not to use it. It is indispensable as an essential component as a component of an exhaust gas purification catalyst that simultaneously removes carbon oxide (CO), hydrocarbon (HC) and nitrogen oxide (NOx).

[0005]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a novel exhaust gas purification catalyst and an exhaust gas purification system.

Another object of the present invention is to provide an exhaust gas purifying catalyst and an exhaust gas purifying system capable of simultaneously removing three components of CO, HC and NOx without using rhodium and in an extremely small amount as compared with the prior art. To provide.

[0007]

These objects are achieved by combining alkaline earth metal oxides, cerium oxides and zirconium oxides with palladium so that engine exhaust gas, which is a problem of palladium catalysts, is rich. N
Not only is the Ox purification performance remarkably improved, but CO, HC and NO are also present even when the fuel gas composition is near the stoichiometric ratio (the amount of air required to completely burn the fuel gas).
It was found that the x purification capacity was improved, and the present invention was completed based on this finding.

That is, various objects of the present invention are as follows: 0.5 to 30 g of palladium, 0.1 to 50 g of alkaline earth metal oxide, and 10 to 15 of cerium oxide per 1 liter of catalyst.
Carbon monoxide, hydrocarbons and nitrogen oxidation from the exhaust gas of an internal combustion engine in which a catalytically active component of 0 g and zirconium oxide of 0.1 to 50 g and activated alumina of 10 to 300 g are supported on a monolith structure carrier. This is achieved by an exhaust gas purifying catalyst for simultaneously removing substances.

Another object of the present invention is to use 0.5 g of palladium as a catalyst on the exhaust gas inflow side for 1 liter of the catalyst.
To 30 g, 0.1 to 50 g of alkaline earth metal oxide, 10 to 150 g of cerium oxide, and 0.1 to 50 g of zirconium oxide, and a mixture of 10 to 250 g of activated alumina and a monolith structure. The catalyst formed on the carrier is used as a catalyst on the exhaust gas outflow side, and a mixture of (a) rhodium and platinum or (b) a catalytically active component of rhodium, platinum and palladium and a refractory inorganic oxide is used as a monolith structure carrier It can also be achieved by an exhaust gas purification system in which a catalyst supported on is disposed.

Another object of the present invention is to use a mixture of (a) rhodium and platinum or (b) a catalytically active component of rhodium, platinum and palladium and a refractory inorganic oxide as a catalyst on the exhaust gas inflow side. The catalyst supported on the monolith structure carrier was used as the catalyst on the exhaust gas outflow side, and 0.5 to 3 of palladium was added to 1 liter of the catalyst.
0 g, alkaline earth metal 0.1 to 50 g, cerium oxide 10 to 150 g and zirconium oxide oxide 0.
1-50 g of catalytically active component and activated alumina 1
It can also be achieved by an exhaust gas purification system in which a catalyst having a carrier having a monolith structure carrying a mixture of 0 to 300 g is arranged.

[0011]

The exhaust gas purifying catalyst according to the present invention is a honeycomb having a monolith structure of a mixture of a catalytically active component of palladium, an alkaline earth metal oxide, cerium oxide and zirconium oxide and a refractory inorganic oxide. It is carried on a carrier.

First, the amount of palladium used in the present invention varies depending on the conditions under which the catalyst is used, but is usually 0.5 to 30 g, preferably 0.5 to 25 g per liter of the catalyst. If the amount of palladium is less than 0.5 g, the purifying ability is low, and if it exceeds 30 g, no improvement in performance commensurate with the amount added is seen.

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, or activated alumina alone or straddling it.

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 the alkaline earth metal oxide used is 0.1 to 50 g, preferably 0.5 to 40 g, per liter of the catalyst. The alkaline earth metal oxide may be supported on any of cerium oxide, zirconium oxide or their composites, solid solution or activated alumina, and therefore the preparation method is not particularly limited.

The alkaline earth metal precursor may be any of oxides, organic salts and inorganic salts,
It is not particularly limited. For example, there are barium acetate, barium oxalate, barium nitrate, barium sulfate, barium hydroxide, barium carbonate and the like. The state may be any of an aqueous solution, a gel, a suspension and a solid.

The relation between the alkaline earth metal oxide and the palladium is 1: 100 to 150: 1, preferably by weight ratio (alkaline earth metal oxide / palladium).
It is 1: 100 to 100: 1. When the amount of the alkaline earth metal oxide is less than 1: 100, the ternary performance is poor, and in particular, the NOx purification rate is poor, and when the amount of the alkaline earth metal oxide is more than 150: 1, the addition effect is improved. However, the loading ratio and loading amount are limited by the relationship between the loading amount of other oxides and the strength of the catalyst.

The cerium oxide is not particularly limited, but it can be used as the cerium oxide as it is or by firing various water-soluble salts or the like. The amount of cerium oxide used is preferably 10 to 150 g, and particularly preferably 20 to 140 g per liter of the catalyst, and when it is less than 10 g, the purifying ability is low, and 1
When the amount exceeds 50 g, no significant effect can be seen even if the amount exceeds 50 g.

The cerium oxide source used in the present invention is not particularly limited as long as it can exist as cerium dioxide (CeO ₂ ) in the catalyst. For example, commercially available CeO ₂ , cerium carbonate, cerium hydroxide and the like can be used. Alternatively, a solution of a cerium salt, for example, a cerium nitrate solution may be impregnated and supported on activated alumina.

Examples of the water-insoluble cerium compound include cerium oxide, cerium hydroxide and cerium carbonate. This water-insoluble cerium compound is used in the form of fine powder.

The zirconium oxide is not particularly limited, but it can be used as the zirconium oxide as it is or by firing various water-soluble salts or the like. The amount of zirconium oxide used is 0.1 to 50 g, especially 1 to 50 g per liter of the catalyst.
If g is less than 0.1 g, the effect is small, and if it exceeds 50 g, the purification performance is deteriorated.

Cerium oxide and zirconium oxide are
At least a part thereof is preferably present as a composite or solid solution. More preferably, the ratio of the cerium oxide and the zirconium oxide (weight ratio in terms of oxide) is 100: 2 to 100: 60, and preferably,
It is 100: 4 to 100: 40. This ratio is 100: 2
More cerium oxide, or 100: 6
When the amount of zirconium oxide is larger than 0, the catalytic performance tends to be low.

A method for preparing a composite or solid solution of cerium oxide and zirconium oxide is shown below, but is not particularly limited as long as at least a part of these oxides exists as a composite or solid solution. However, it is preferably within the above range.

(1) A method of drying and calcining an aqueous solution of cerium salt and zirconium salt which are soluble in water, (2) a method of solid-phase reaction of cerium oxide and zirconium oxide, (3) cerium oxide A method of immersing in an aqueous solution of a water-soluble zirconium salt and drying and firing, (4) a method of impregnating activated alumina with an aqueous solution of water-soluble cerium salt and zirconium salt, and then drying and firing, or (5) an integral structure Various methods can be appropriately used according to the preparation of the catalyst, such as a method in which a body carrier is coated with activated alumina and then an aqueous solution of a cerium salt and a zirconium salt which is soluble in water is dried and calcined.

The cerium oxide used in the present invention preferably has a crystallite size of 250 angstroms or less after firing in air at 900 ° C. for 10 hours, and the cerium oxide in this range has a thermal stability. It has properties and improves the durability of the catalyst. Also, the crystallite size is 250
When it exceeds angstrom, the thermal stability is poor and it is not preferable. The crystallite size is measured by calcination in air at 900 ° C. for 10 hours after preparing a powder of cerium oxide and zirconium oxide, at least a part of which is a composite or solid solution, or in some cases after preparing a catalyst. After that, it was measured and calculated by the half width of the X-ray diffraction chart obtained by the X-ray diffraction method.

Cerium oxide and zirconium oxide, at least a part of which is a composite or a solid solution, are heated at 900 ° C. in air for 10 hours, and after hydrogen reduction at 500 ° C. for 30 minutes at 400 ° C. The oxygen consumption is preferably 5 × 10 ⁻⁵ mol (O ₂ conversion) or more per 1 g of cerium oxide. Oxygen consumption is 1g of cerium oxide
When the amount is less than 5 × 10 ⁻⁵ mol (O ₂ conversion),
The durability of the catalyst is low.

The measurement of oxygen consumption was carried out by using an ordinary flow pulse reactor. After firing cerium oxide and zirconium oxide, at least a part of which is a composite or solid solution, in air at 900 ° C. for 10 hours, the reactor is filled with a predetermined amount of powder, and then an inert gas is added. After passing through it, it was reduced with hydrogen at 500 ° C for 30 minutes, then an inert gas was passed again, the temperature was lowered to 400 ° C, an oxygen pulse was passed, the oxygen consumption at that time was measured, and 1 g of cerium oxide was passed. The oxygen consumption per unit was calculated.

The activated alumina is usually in the form of powder and has a specific surface area of 10 to 400 m ² / g, preferably 50 to 3.
It is 00 m ² / g. The amount used is 10 to 300 g, preferably 10 to 250 g, per liter of the catalyst.
That is, if it is less than 10 g, the purification performance is low, while
If it exceeds 300 g, the back pressure of the catalyst increases, which is not preferable.
Activated alumina has a crystal form of χ, ρ, κ, γ,
It refers to amorphous alumina such as δ, η, and θ.

As a method for preparing the catalyst, for example, (1) the above-mentioned catalytically active component and activated alumina are put together, made into an aqueous slurry using a ball mill or the like, coated on a monolithic support, then dried and, if necessary, calcined. (2) After coating the activated alumina on the monolithic structure carrier in advance, the monolithic structure carrier is immersed in an aqueous solution of a cerium salt or zirconium salt, which is soluble in water, dried, and calcined, Then, a method of supporting the rest of the catalytically active component in the same manner, (3) the above composite oxide and the activated alumina supporting each component are made into an aqueous slurry by a ball mill or the like, coated on a monolithic structure carrier, and then dried. If necessary, there are methods such as firing to obtain a finished catalyst, and these methods are appropriately changed and used depending on the convenience of the work procedure.

The catalytically active component per liter of the monolithic support is 50 to 400 g, preferably 100 to 350 g.
Is. If it is less than 50 g, the purification performance is low and 4
When the amount of more than 00 g is coated on the integrally molded body with the catalytically active component, the back pressure increases, which is not preferable.

The monolithic structure carrier used in the present invention (hereinafter,
(Also referred to simply as a monolith carrier) may be one that is usually called a ceramic honeycomb carrier, and particularly cordierite, mullite, α-alumina, zirconia, titania, titanium phosphate, aluminum titanate, petalite, spodumene, alumino-. Honeycomb carriers made of silicate, magnesium silicate or the like are preferable, and cordierite type is particularly preferable for internal combustion engines. In addition, an integrated structure carrier made of an oxidation resistant heat resistant metal such as stainless steel or Fe—Cr—Al alloy may be used. These monolith carriers are manufactured by an extrusion molding method, a method of winding and solidifying a sheet-shaped element, or the like. The shape of the gas passage (cell type) is a hexagon,
It may be a quadrangle, a triangle or a corrugation type. Cell density (number of cells / unit cross-sectional area) is 150
~ 600 cells / square inch is fully usable,
Give good results.

The monolithic support coated with the catalytically active component and the refractory inorganic support is dried to a temperature of 200 to 800 ° C., preferably 300 to 700 ° C. for 0.1 to 5 hours, preferably 0.2 to It is calcined for 3 hours to obtain a finished catalyst.

The catalyst thus obtained is inserted into a converter and used for purifying exhaust gas from an internal combustion engine of an automobile or the like.

This catalyst is also used as a catalyst on the exhaust gas inflow side, while (a) rhodium and platinum or (b) a catalytically active component of rhodium, platinum and palladium and a mixture of refractory inorganic oxides. An exhaust gas purification system may be constructed by arranging a catalyst supported on a carrier having a monolith structure on the exhaust gas outflow side.

Further, on the contrary, the catalyst prepared by supporting a mixture having a monolith structure with a mixture of (a) rhodium and platinum or (b) rhodium, a catalytically active component of platinum and palladium and a refractory inorganic oxide is exhausted. An exhaust gas purification system may be provided by arranging the catalyst according to the present invention on the gas inflow side and on the exhaust gas outflow side.

The noble metal used in the noble metal catalyst in the above exhaust gas purification system is (a) rhodium and platinum or (b) rhodium, platinum and palladium, and the amount of these used is 0.1 to 1 per liter of catalyst.
It is 0 g, preferably 0.3 to 5 g. If it is less than 0.1 g, the purifying ability is low, and if it exceeds 10 g, the effect corresponding to the added amount is small.

Examples of the refractory inorganic oxide include additives such as activated alumina, silica, titania, cerium oxide, zirconium oxide, alkali metal, alkaline earth metal, rare earth metal, iron, cobalt and nickel. It can be added in the form of an oxide or the like. Of these additives, activated alumina, cerium oxide and zirconium oxide are preferable. The amount of refractory inorganic oxide used is from 10 to 300 g, preferably 1 per liter of catalyst.
It is 0 to 250 g.

The monolithic support used for the exhaust gas inflow side catalyst and the exhaust gas outflow side catalyst may be any one as long as it is a monolithic support commonly used for exhaust gas purifying catalysts. A monolithic carrier such as a honeycomb type or a corrugated type is used, and the material thereof may be any as long as it has a fire resistance, for example, a fire-resistant ceramic such as cordierite or a ferritic stainless steel. A monolithic monolithic carrier is used.

The volume ratio of the exhaust gas inflow side catalyst to the exhaust gas outflow side catalyst is 100: 1 to 1: 100, preferably 50: 1 to 1:50. When it is less than 100: 1 and when it exceeds 1: 100, the performance improvement due to the combination is not shown.

The catalyst on the exhaust gas inflow side and the catalyst on the exhaust gas outflow side can be installed in the same catalytic converter, and depending on the shape of the exhaust pipe, the shape of the catalyst, etc.
Each can be separated and left alone.

The exhaust gas inflow side catalyst and the exhaust gas outflow side catalyst do not have to be one in number, respectively, as long as there is no hindrance to the shape of the exhaust pipe, the place where the catalyst is installed, the back pressure of exhaust gas, etc. The catalyst on the exhaust gas inflow side and the catalyst on the exhaust gas outflow side can each be divided into a plurality of catalysts for use.

[0041]

EXAMPLES The present invention will be specifically described below with reference to examples, but the invention is not limited to these examples unless it goes against the gist of the present invention.

Example 1 Commercially available cerium oxide (CeO ₂ , specific surface area 149 m ² /
g) with an aqueous zirconyl oxynitrate solution in CeO ₂ / ZrO
Total 10/1 (CeO ₂ and ZrO ₂ in ₂ ratio of 100
g), dried, and then calcined at 500 ° C. for 1 hour to obtain 100 g of powder and activated alumina (γ-Al ₂ O).
₃ , average particle diameter 45 μm, specific surface area 155 m ² / g) 20
An aqueous slurry was prepared by adding an aqueous palladium nitrate solution containing 0 g, 16.7 g of barium acetate and 4 g of palladium and wet pulverizing with a ball mill. A cordierite monolithic carrier (outer diameter 33 mm × length 7) having 400 cells per 1 inch square in this slurry was prepared.
(6 mm) was dipped and taken out, and the excess slurry in the cell was blown off with compressed air, followed by drying and firing to obtain a finished catalyst.

Example 2 In Example 1, 16.7 g of barium acetate was added to 50.1
A completed catalyst was obtained in the same manner as in Example 1 except that g was changed.

Example 3 In Example 1, 16.7 g of barium acetate was added to 0.83
A completed catalyst was obtained in the same manner as in Example 1 except that g was changed.

Example 4 A finished catalyst was obtained in the same manner as in Example 1 except that 16.7 g of barium acetate was changed to 28.2 g of calcium acetate.

Example 5 A finished catalyst was obtained in the same manner as in Example 1 except that 16.7 g of barium acetate was changed to 19.8 g of strontium acetate.

Example 6 In Example 1, the CeO ₂ / ZrO ₂ ratio was 10/1.
A completed catalyst was obtained in the same manner as in Example 1 except that the total amount of CeO ₂ and ZrO ₂ was 30 g, and the amount of activated alumina was changed to 270 g.

Example 7 In Example 1, the CeO ₂ / ZrO ₂ ratio was 10/1.
A completed catalyst was obtained in the same manner as in Example 1 except that the total amount of CeO ₂ and ZrO ₂ was 160 g, and the amount of activated alumina was changed to 140 g.

Example 8 In Example 1, the CeO ₂ / ZrO ₂ ratio was set to 10/3.
A completed catalyst was obtained in the same manner as in Example 1 except that the total amount of CeO ₂ and ZrO ₂ was changed to 100 g.

Example 9 In Example 1, the CeO ₂ / ZrO ₂ ratio was 25/1.
A completed catalyst was obtained in the same manner as in Example 1 except that the total amount of CeO ₂ and ZrO ₂ was changed to 100 g.

Example 10 A completed catalyst was obtained in the same manner as in Example 1 except that 16.7 g of barium acetate was changed to 35.3 g of magnesium acetate.

Example 11 A completed catalyst was obtained in the same manner as in Example 1 except that the palladium nitrate aqueous solution containing 4 g of palladium was changed to the palladium nitrate aqueous solution containing 2 g of palladium.

Example 12 A completed catalyst was obtained in the same manner as in Example 1 except that the palladium nitrate aqueous solution containing 4 g of palladium was changed to the palladium nitrate aqueous solution containing 8 g of palladium.

Example 13 A completed catalyst was obtained in the same manner as in Example 1 except that the palladium nitrate aqueous solution containing 4 g of palladium was changed to the palladium nitrate aqueous solution containing 16 g of palladium.

Example 14 A completed catalyst was obtained in the same manner as in Example 1 except that the palladium nitrate aqueous solution containing 4 g of palladium was changed to the palladium nitrate aqueous solution containing 40 g of palladium.

Example 15 In Example 1, 16.7 g of barium acetate was added to 133.
A completed catalyst was obtained in the same manner as in Example 1 except that the amount was changed to 6 g.

Example 16 In Example 1, the CeO ₂ / ZrO ₂ ratio was 10/1.
A finished catalyst was obtained in the same manner as in Example 1 except that the total amount of CeO ₂ and ZrO ₂ was 200 g, and the amount of activated alumina was changed to 100 g.

Example 17 In Example 1, CeO₂/ ZrO₂The ratio of 10/1
(CeO₂And ZrO ₂Total of 260g) and active
Completed in the same manner as in Example 1 except that Lumina 40g was used.
A catalyst was obtained.

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

Comparative Example 2 A finished catalyst was obtained in the same manner as in Example 1 except that zirconyl oxynitrate was omitted.

Comparative Example 3 A completed catalyst was obtained in the same manner as in Example 1 except that zirconyl oxynitrate and barium acetate were omitted.

Comparative Example 4 200 g of activated alumina used in Example 1 was mixed with a solution of a dinitrodiamine platinum aqueous solution containing 2.25 g of platinum and a rhodium nitrate aqueous solution containing 0.22 g of rhodium.
Powder impregnated with and cerium oxide 1 used in Example 1
After wet-milling 00 g with a ball mill, a finished catalyst was obtained in the same manner as in Example 1.

Comparative Example 5 Obtained by impregnating 200 g of activated alumina used in Example 1 with 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, drying and firing. The obtained powder and 100 g of cerium oxide used in Example 1 were wet pulverized with a ball mill, and a finished catalyst was obtained in the same manner as in Example 1.

Comparative Example 6 A solution of a dinitrodiamine platinum aqueous solution containing 2.25 g of platinum and a rhodium nitrate aqueous solution containing 0.22 g of rhodium, and 16.7 g of barium acetate were impregnated with 200 g of the activated alumina used in Example 1. The supported powder and the cerium oxide and the zirconyl oxynitrate aqueous solution used in Example 1 were mixed at a CeO ₂ / ZrO ₂ ratio of 10/1 (CeO ₂
And ZrO ₂ are mixed so that the total is 100 g), dried, and then calcined at 500 ° C. for 1 hour to obtain 100 g of a powder, which is then wet pulverized with a ball mill to prepare a finished catalyst in the same manner as in Example 1. Obtained.

Comparative Example 7 A completed catalyst was obtained in the same manner as in Example 1 except that 100 g of zirconium oxide was used instead of cerium oxide and zirconium oxide.

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

[0067]

[Table 1]

Example 18 Next, the catalyst activity of the catalysts of Examples 1 to 17 and the catalysts of Comparative Examples 1 to 7 after the running of the engine was examined.

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 gas temperature at the catalyst inlet is 850 ° 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 (1800 cc with 4 cylinders) and connecting a multi-converter filled with each catalyst to the exhaust system of the engine. The three-way performance of the catalyst was evaluated under the conditions of a catalyst inlet gas temperature of 400 ° C. and a space velocity of 90,000 hr ⁻¹ . At this time, introduce a 1Hz sine wave type signal from an external oscillator into the control unit of the engine,
While oscillating the air-fuel ratio (A / F) at ± 1.0 A / F and 1 Hz, the average air-fuel ratio is continuously changed, and the catalyst inlet and outlet gas compositions at this time are simultaneously analyzed, and the average air-fuel ratio is The purification rates of CO, HC and NO from A / F 15.1 to 14.1 were obtained.

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

[0072]

[Table 2]

From Table 2, the catalyst disclosed in the present invention contains no palladium as the noble metal, only palladium and no C
It was found that the three components of O, HC and NOx can be removed simultaneously.

As for the purification performance of the catalyst at low temperature, while vibrating under the condition that the air-fuel ratio is ± 0.5 A / F (1 Hz),
The engine is operated with the average air-fuel ratio fixed at 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 50 ° C.
It was evaluated by continuously changing the temperature to 0 ° C., analyzing the catalyst inlet and outlet gas compositions, and determining the purification rates of CO, HC and NO. CO, obtained as described above,
The temperature (light-off temperature) at a purification rate of HC and NO of 50% was measured and is shown in Table 3.

[0075]

[Table 3]

Example 19 CeO ₂ crystallite diameter and oxygen consumption were measured by the following procedure.

Example 19A The zirconyl oxynitrate aqueous solution was added to the cerium oxide used in Example 1 at a CeO ₂ / ZrO ₂ ratio of 100/100, respectively.
4 (sample NO.a), 100/10 (sample NO.b),
100/30 (Sample NO.c), 100/50 (Sample N
O. d), the mixture was dried and then baked at 500 ° C., and then, in air, at 900 ° C. for 10 hours.
The total of CeO ₂ and ZrO ₂ is 20 g.

Example 19B A cerium nitrate aqueous solution and a zirconyl oxynitrate aqueous solution were mixed with C
eO ₂ / ZrO ₂ ratio of 100/10 (sample NO.e)
Were mixed, dried and calcined at 500 ° C. for 1 hour. Then, it baked at 900 degreeC in air for 10 hours.

Example 19C 20 g of the cerium oxide used in Example 1 was mixed with 9% in air.
It was baked at 00 ° C. for 10 hours (Comparative sample f).

Measurement of Crystallite Size X of the samples obtained in Examples 19A, 19B and 19C
The line diffraction was measured to determine the crystallite size of the cerium oxide.
The results are shown in Table 4. The purpose of this measurement of the crystallite size is that the catalyst is usually required to have high temperature durability, but it is difficult to evaluate the presence or absence of high temperature durability only at room temperature treatment, so cerium oxide and zirconium oxide at high temperature cannot be evaluated. This is to evaluate whether or not a compound of things is effective. The condition is that firing is performed in air at 900 ° C. for 10 hours.

Measurement of Oxygen Consumption The samples obtained in Examples 19A, 19B and 19C were filled in a normal flow type pulse reactor, then, after passing helium gas, reduction treatment with hydrogen at 500 ° C. for 30 minutes. After that, helium gas is again passed for 15 minutes, then the temperature is lowered to 400 ° C. in the same atmosphere, and then a pulse of a predetermined amount of oxygen is passed, and the oxygen consumption at that time is measured, and 1 g of cerium oxide is measured. The oxygen consumption per unit was calculated. The results are shown in Table 4.

[0082]

[Table 4]

The catalysts used for measuring the oxygen consumption were Examples 1, 8 and 9 and Comparative Example 2. The catalyst performances of these catalysts were compared, and Tables 2 and 3 show that the present invention was performed. It can be seen that the use of durable cerium oxide shows excellent exhaust gas purification ability.

Further, as can be seen from Table 4, 900 ° C.
It can be seen that the cerium oxide is stabilized by the zirconium oxide in the oxygen atmosphere.

Preparation of catalyst The catalyst obtained in Example 1 was used as a finished catalyst (I).

Next, a powder prepared by impregnating and supporting 200 g of activated alumina used in Example 1 in a solution prepared by mixing an aqueous dinitrodiamine platinum solution containing 1.67 g of platinum and an aqueous rhodium nitrate solution containing 0.33 g of rhodium, and 100 g of the cerium oxide used in Example 1 was added, and after wet grinding with a ball mill, the finished catalyst (I
I) got.

Example 20 Complete catalysts (I) and (II) obtained in the above catalyst preparation
And the catalyst corresponding to the example, that is, the combination of the example (1) of the pre-stage catalyst (I) and the post-stage catalyst (II) and the combination (2) of the pre-stage catalyst (I).
I) and post-catalyst (I) and 3 of pre-catalyst (II) and post-catalyst (II) which are combinations (3) of comparative examples.
Table 5 shows the results of obtaining the purification rates of CO, HC and NO for the combination of types by the same evaluation method as in Example 19.

[0088]

[Table 5]

[0089]

The exhaust gas purifying catalyst according to the present invention has a monolithic support carrying a mixture of a catalytically active component of palladium, an alkaline earth metal oxide, cerium oxide and zirconium oxide and activated alumina. It is presumed that the effect of adding the alkaline earth metal oxide is to directly react with palladium and change its charge state to enhance the reactivity. Furthermore, cerium oxide and zirconium oxide are added. By using, the above-mentioned effect can be further improved.

That is, the exhaust gas purifying catalyst according to the present invention and the purifying shimtem using the same have the problems of the palladium catalyst by combining the alkaline earth metal oxide, the cerium oxide and the zirconium oxide with palladium. Even if the engine exhaust gas is rich, N
Ox purification ability can be remarkably improved, and further CO, HC and NOx purification ability can be improved even when the fuel gas composition is near the stoichiometric ratio (the amount of air required to completely burn the fuel gas). It can be said that it is excellent in.

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

Claims (7)

[Claims] 1. 0.5 to 30 g of palladium and 0.1 to 50 of alkaline earth metal oxide per 1 liter of catalyst.
g, 10 to 150 g of cerium oxide and 0.1 to 50 g of zirconium oxide, and a mixture of 10 to 300 g of activated alumina on a monolithic structure support, and carbon monoxide from exhaust gas of an internal combustion engine. , An exhaust gas purifying catalyst for simultaneously removing hydrocarbons and nitrogen oxides. 2. The exhaust gas purifying 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. 3. The ratio of the cerium oxide to the zirconium oxide (weight ratio in terms of oxide) is 100: 2 to 100: 6.
The exhaust gas purifying catalyst according to claim 1, which is 0. 4. The composite or solid solution of at least a part of the cerium oxide and the zirconium oxide is 900
The exhaust gas purifying catalyst according to claim 2, which has a crystallite size of 250 angstroms or less after calcination in air at a temperature of ℃ for 10 hours. 5. The composite or solid solution of at least a portion of the cerium oxide and the zirconium oxide is 900
After calcination in air at a temperature of 10 ° C. for 10 hours, the oxygen consumption at 400 ° C. after hydrogen reduction at 500 ° C. for 30 minutes is 5 × 10 ⁻⁵ mol (O ₂ conversion) or more per 1 g of the cerium oxide. The exhaust gas purifying catalyst according to claim 2. 6. The catalyst as claimed in claim 1 as an exhaust gas inflow side.
The catalyst according to any one of 5 and a mixture of (a) rhodium and platinum or (b) a catalytically active component consisting of rhodium, platinum and palladium and a refractory inorganic oxide as a catalyst on the exhaust gas outflow side is a monolith structure. An exhaust gas purification system in which a catalyst supported on a carrier is arranged. 7. A monolith structure carrier carrying a mixture of (a) rhodium and platinum or (b) a catalytically active component of rhodium, platinum and palladium and a refractory inorganic oxide as a catalyst on the exhaust gas inflow side. An exhaust gas purification system comprising the catalyst and the catalyst according to any one of claims 1 to 5 as an exhaust gas outflow side catalyst.