JPS6047449B2 - Exhaust gas purification method - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an exhaust gas purification method that can simultaneously purify carbon monoxide, hydrocarbons, and nitrogen oxides in the exhaust gas of an internal combustion engine with high efficiency. .

[Conventional technology]

Various studies have been conducted on methods for purifying harmful components (carbon monoxide, hydrocarbons, nitrogen oxides) in exhaust gas emitted from internal combustion engines such as automobiles.

Among these methods, one that is considered to be relatively superior is a purification method in which exhaust gas is brought into contact with a platinum-rhodium catalyst or a palladium-rhodium catalyst. However, this conventional purification method, as shown in Figure 1,
Narrow air-fuel ratio (mixture ratio of fuel and air delivered to the internal combustion engine;
It is only in the range of air/fuel ratios that it is possible to simultaneously purify all of the above-mentioned harmful components.

The present invention has been made in an attempt to solve the problems of the conventional method (conventional catalyst).

This will be explained in detail below. That is, as can be seen from FIG. 1, carbon monoxide (curve 1) and hydrocarbons (curve 2) are oxidized to carbon dioxide and water, so that the stoichiometric air-fuel ratio (approximately 14.6) Also on the oxidation side (air fuel ratio 14.6
(above)) and is efficiently purified.

On the other hand, since nitrogen oxides are reduced to nitrogen, they are efficiently purified on the reduction side of the stoichiometric air-fuel ratio (air-fuel ratio of 14.6 or less). In this way, when the above conventional method is used, the operation of the internal combustion engine is controlled at 1 stoichiometric air-fuel ratio ±0.1 J (air-fuel ratio approximately 14
．． Unless it is carried out within an extremely narrow range of 5 to 14.7), the above harmful components cannot be efficiently purified at the same time. However, in order to perform the above operation within such a very narrow air-fuel ratio range, the oxygen concentration in the exhaust gas is measured by an oxygen sensor, and the electronic fuel injection system is activated based on the signal from the oxygen sensor. It is necessary to operate the air-fuel ratio and control the air-fuel ratio.

However, when adopting such an operating method, the above-mentioned oxygen sensor and electronic fuel injection device are required, which makes the operating device and method complicated. In addition, it is difficult to maintain this operating method for a long period of time because oxygen sensors tend to change slightly over time, and electronic fuel injection devices are expensive. . On the other hand, carburetors are currently widely used for air-fuel ratio control, and are considerably cheaper than the electronic fuel injection devices described above.

However, this carburetor can only control the air-fuel ratio over a relatively wide range of 1.0 or more, and it is difficult to control the air-fuel ratio within such a narrow range. Furthermore, automobile engines are generally used with an air-fuel ratio in the range of 12 to 18.

In this case, the air-fuel ratio is 15. The fuel efficiency is the best near
On the other hand, the air fuel ratio is 13. There is a tendency for the engine's output to increase near the end of the range, but for fuel consumption to be somewhat low. From this perspective, Inter-1 industryEmis
s10nC0ntr01Pr0gram2 (IIEC-
2), PrOgramRepOrtNO. 2, SP-4
0yo pages 55-66, paper name RLalx) RatOry
EValLlatiOnOfThreeWay,. C
atalystsJ (February 1967 SOCIETYYO
FAUTOMOTIVE ENGINEERS,. INC.
As a catalyst (so-called three-way catalyst) for simultaneously purifying the three types of harmful components, WindOwgate
It is argued that a catalyst with a wide range of air-fuel ratios, that is, a catalyst that exhibits high purification efficiency over a wide range of air-fuel ratios, should be developed. In addition, currently proposed three-way catalysts include, for example, Pt-Rh catalyst in JP-A-52-56217, CuO-■20, CUO-V2O5 in JP-A-49-77023. -Pd catalysts have been proposed.

However, none of these conventional catalysts can exhibit a satisfactory purification ability as a three-way catalyst over a wide air-fuel ratio range.

As is known from the above, the engine operates at an air/fuel ratio of 1.
It is desirable to perform this in a wide range of 3.5 to 15.5.

However, on the other hand, no method has been found that can simultaneously purify the three types of harmful components with high efficiency over such a wide air-fuel ratio range.

[Problems to be solved by the present invention]

The present invention aims to solve a method that can simultaneously purify the harmful components in exhaust gas from an engine with high efficiency even when the engine is operated in a wide range of air-fuel ratios from 13.5 to 15.5. There is something to do.

[Means for solving problems]

That is, the present invention uses a catalyst (hereinafter referred to as Pt- Rh-■0x catalyst), palladium, rhodium and vanadium oxide (hereinafter referred to as Pd-Rh-■0x catalyst), catalyst consisting of platinum, palladium, rhodium and vanadium oxide (hereinafter referred to as Pt-Pd-Rh-VOx carbon monoxide (hereinafter referred to as CO) in the exhaust gas.
, an exhaust gas purification method characterized by simultaneously purifying hydrocarbons (hereinafter referred to as HC) and nitrogen oxides (hereinafter referred to as NOx).

[Effects of the present invention]

Therefore, in the present invention, to the above Pt-Rh
Since one or more catalysts of Pd-Rh-VOx or Pt-Pd-Rh-VOx are used, CO. H.C. NOx can be purified simultaneously with high efficiency.

Further, for this purpose, the carburetor that is currently widely used for controlling the air-fuel ratio of engines can be used as is. [Detailed Description of the Present Invention] In the present invention, the exhaust gas to be purified is the exhaust gas from an engine operated at an air-fuel ratio within the range of 13.5 to 15.5.

This air-fuel ratio range means that the maximum upper limit is 15.5 and the minimum lower limit is 13.5, but this reciprocating movement does not always need to reciprocate within this air-fuel ratio range of 2.0. do not have. For example, if the air-fuel ratio is 13.8-15.01 or 14
．． It may be 3 to 15.4. However, it is preferable that this fluctuation be made to reciprocate in the vertical direction around the stoichiometric air-fuel ratio (approximately 14.6). If the air-fuel ratio is operated only at a higher or lower ratio than the stoichiometric air-fuel ratio, even if the ratio fluctuates back and forth, if this continues for a long time, excellent purification ability will be exhibited. I can't. From this point of view, the reciprocating fluctuations in the direction of increase and decrease around the stoichiometric air-fuel ratio are at least 20 to 200 times per minute.
It is preferable to carry out the cycle within a range of cycles. Next, the method for controlling the engine as described above, for example, as shown in the outline in FIG. The controller 6 is operated in response to the signal to control the air-fuel ratio in the carburetor 7.

That is, the oxygen sensor 61 detects the oxygen concentration in the exhaust gas, sends a signal corresponding to the concentration to the carburetor 7, and the engine 4 adjusts the air-fuel ratio to 13.5 to 1 as described above.
The carburetor 7 is controlled so that it is operated in step 5.5. In the figure, reference numeral 62 indicates an electrical signal lead wire, and 71 indicates a fuel supply port. 72 is an air supply vibe,
73 is a fuel/air mixture supplying vibe. Although not directly related to the present invention, when adding air to the exhaust gas from the engine 4, air is added into the exhaust gas vibrator 41 by the air pump 8. send.

81 and 82 are air-inhaling vibes.

Regarding each of the above-mentioned catalysts, the amount of catalyst components (Pt.Rh..Pd..VOx) supported on the carrier is preferably within the following range in terms of weight ratio.

That is, Pt and Pd are each 0.02 to 2%, R
h is in the range of 0.002 to 0.2%, and ■0x is in the range of 0.3 to 10%. Note that ■0x here is an oxide of vanadium, and these are V2O5, V2O4, and V2O5.
Some exist in a state such as 2O3 or a mixture thereof. In addition, as shown in the examples, the above catalyst can be prepared by first preparing an aqueous solution in which chloroplatinic acid as a Pt raw material, rhodium chloride as a Rh raw material, palladium chloride as a Pd raw material, etc. are dissolved. A carrier such as δ-alumina is immersed in this, and then taken out, dried, and fired to form a Pt-Rh catalyst, a Pd-Rh catalyst, and a Pt-Rh catalyst.
The catalyst is prepared as a t-Pd-Rh catalyst, and then immersed in an aqueous solution of ammonium metavanadate or the like as a vanadium source, dried, and calcined in air. Vanadium oxide VOx is formed by this firing in air. Note that the above-mentioned carrier can have various structures such as granular and honeycomb shapes. Furthermore, a commonly used converter is used for filling the catalyst. Example 1 (a) Measurement of purification rate Model gases (R gas, S gas, and L
CO. H.C. The purification status of NO was investigated.

That is, assuming that the stoichiometric air-fuel ratio is 14.6, S gas corresponds to 14.55, which is slightly on the reducing side, R gas corresponds to 13.75, which is on the lower side (reducing side) than the stoichiometric air-fuel ratio, and L gas corresponding to 15.35 on the higher side (oxidation side) was used.

The above three types of gas are supplied in the order of S gas → R gas → S gas → L gas → S gas → R gas, and this S →
One cycle of R→S→L was performed in 2 seconds.

Therefore, each gas has 0. It will be sent one by one. Switching between each gas was performed using a solenoid valve. As is known from the above, the above gas supply is carried out by operating the engine with a stoichiometric air-fuel ratio of 14.55, which is centered around the air-fuel ratio range of ±0.8, and reciprocating for 2 seconds per cycle. This corresponds to the case of feeding into a catalyst-filled converter.

The catalyst was prepared as described below and filled into a quartz tube as a converter. The above gas was heated to 500'C in a tube furnace before being introduced into the quartz tube. The gas was passed through the catalyst bed at a space velocity (S.V) of 3.01/hr. CO in the above gas. ．． The purification rate of HC and NO was calculated by first introducing the gas coming out of the catalyst layer into a trapper to remove water droplets, then passing it through a dehumidifier, and then analyzing each of these components in the gas. .

The compositions of the above R gas, S gas, and L gas are shown in Table 1.

In Table 2, the components and supported amounts of one catalyst are shown in ( )
The numbers in the box indicate the amount of each component supported on the carrier.

The supported amount is the value of the metal in each catalyst component.
As is known from Table 2, according to the method of the present invention, NO,
．． CO and HC can be purified simultaneously with extremely high efficiency.

In particular, it is found that a high purification rate can be achieved for NO and CO, which are important in air pollution.
(b) Preparation of catalyst Each catalyst was prepared as follows.

Catalyst C1; 0.7q1 platinum r + [ in distilled water 1e
;1,12Ete110/. :In FOZ Mi Table 1,
H2 is hydrogen, 02 is oxygen, C3F[8 is propane as a hydrocarbon, H2O is water vapor, and N2 is nitrogen.

The above purification rate measurements were performed on eight types of catalysts used in the method of the present invention.

Further, for comparison, similar measurements were performed on three types of catalysts used in the conventional method. Table 2 shows the measurement results of each of the catalysts used above and their purification rates.

A δ-alumina carrier 1f having a particle size of about 4 W$t was immersed at room temperature for 1 hour in an aqueous solution containing chloroplatinic acid and rhodium chloride so as to contain 0.07y of rhodium. The mixture was dried at 600° C. for (a) hours and calcined at 600° C. for 3 hours while a small amount of clean air was passed through to prepare a Pt-Rh catalyst.

Catalyst C2; Prepare an aqueous solution in which palladium chloride and rhodium chloride are dissolved so that it contains 0.7 g of palladium and 0.07 y of rhodium in 1f of distilled water, and in the same manner as in the case of catalyst C1, prepare a Pd-Rh catalyst. Prepared.

Catalyst C3: Distilled water 1e, platinum 0.35 da, palladium r+
Mouth 12E1) 0/. ; Prepare an aqueous solution in which chloroplatinic acid, palladium chloride, and rhodium chloride are dissolved so that it contains 0.35 da of ζium and 0.07 y of rhodium, and in the same manner as in the case of catalyst C1, Pt-Pd-Rh. A catalyst was prepared.

Catalyst 1 The catalyst CllOOml was immersed at room temperature for 1 hour in a vanadium aqueous solution in which ammonium metavanadate was dissolved to contain 0.44y of vanadium in 100mt of distilled water, and after draining the immersion liquid, it was heated at 110°C for 4 hours. Dry. After repeating the above-mentioned impregnation and drying operations four times, the temperature was heated to 600°C while flowing a small amount of clean air.
The mixture was calcined for 3 hours to prepare a Pt-Rh-VOx catalyst.
Catalyst 2: Impregnation in vanadium aqueous solution and drying operations 5
It was prepared in the same manner as Catalyst 1 except that the steps were repeated.

Catalyst 3: An aqueous solution was prepared by dissolving ammonium metavanadate so that 100 mL of distilled water contained 0.88 y of vanadium, but otherwise it was prepared in the same manner as Catalyst 1 above.

Catalyst 4: It was prepared in the same manner as Catalyst 3 above, except that the operations of impregnation with an aqueous vanadium solution and drying were repeated five times.

Catalyst 5: Prepared in the same manner as Catalyst 1, except that an aqueous solution of ammonium metavanadate containing 0.22 q of vanadium was prepared in 100 ml of distilled water, and the impregnation and drying operations were repeated four times.

Catalyst 6; Prepared in the same manner as Catalyst 5 except that the impregnation and drying operations were repeated twice.

Catalyst 7: The catalyst C2lOOmt was immersed at room temperature for 1 hour in an aqueous solution in which ammonium metavanadate was dissolved so that 100ml of distilled water contained 0.44y of vanadium,
After separating the Pd from the immersion liquid, it was dried at 110'C for 4 hours, and in the same manner as Catalyst 1, a Pd-Rh--Ox catalyst was prepared.

Catalyst 8: A Pt-Pd-Rh-10x catalyst was prepared in the same manner as in the case of Catalyst 7 except that the Catalyst C3 was used.

Comparative Example As mentioned above, the catalyst used in the method of the present invention is Pt-
Rh-■0x. ．． Pd-Rh-VOx,. Pt-Pd-
There are three types of catalysts, Rh-10x, and the catalyst that can achieve the purpose of the present invention was developed through many experimental studies.

The inventors have developed Ptl:d. Catalysts based on Rh and various additives shown in Table 3 were prepared, and the purification efficiency was determined by varying the gas composition under the same conditions as shown in the example above. Measurement was carried out.
The results are shown in Tables 2 and 3. In addition, the results of two examples of the method of the present invention are also listed in the same table. Each catalyst in the above is
Pt.
It has an amount of Rh supported.

Further, each of the above additives was supported on the carrier in the same manner as in Catalyst 1 above. As can be seen from Table 3, the method of the present invention was born out of many studies, and is the No. 1 method superior to other methods. ．． C.O. ．． It can be seen that a method for simultaneous HC purification is provided.

That is, when using the comparative catalyst shown in Table 3 above, it is possible to achieve a purification rate that is almost the same or inferior to that of the Pt-Rh catalyst, which is the basic catalyst, but when using the method of the present invention, the above three It can be seen that the components can be simultaneously purified with high efficiency. In addition, apart from the above embodiment, the inventors implemented the method of the present invention by employing the purification method shown in FIG. 2, and found that CO1HC and . NO
were able to be purified at the same time.

[Brief explanation of the drawing]

FIG. 1 shows CO in exhaust gas when a platinum-rhodium catalyst is used. H.C. ．． A diagram showing the NO purification rate in comparison with the air-fuel ratio, and FIG. 2 is a flow sheet showing the method of controlling the engine and the method of introducing air into the exhaust gas. 1...COl2...HCl3...
・・NOl4・・・・・Engine, 5・・・・Converter, 6・o・Controller, 7・・Carburetor, 8・・・・Air pump.

Claims (1)

[Scope of Claims] 1. Exhaust gas discharged from an internal combustion engine operated in an air-fuel ratio range of 13.5 to 15.5 is controlled by a catalyst comprising platinum, rhodium and vanadium oxides, palladium, rhodium and vanadium oxides. carbon monoxide, hydrocarbons and the like in the exhaust gas. An exhaust gas purification method characterized by purifying nitrogen oxides at the same time. 2 The amount of catalyst components supported on the carrier in each catalyst is
Based on the carrier, platinum and palladium are each 0.02 to 2% (weight ratio, the same applies below), rhodium is 0.002 to 0.2%, and vanadium oxide is 0.3 to 10%.
The exhaust gas purification method according to claim 1, wherein the exhaust gas purification method is within the range of .