JPH04193348A - Catalyst for purification of exhaust gas - Google Patents

Abstract

PURPOSE:To simultaneously remove hydrocarbon, CO and NOx in exhaust gas by using a catalyst obtd. by supporting Pt and Cu and/or Co on crystalline titanosilicate having a specified compsn. CONSTITUTION:Pt and Cu and/or Co are supported on a crystalline compd. having a silicate skeleton with incorporated Ti ions and represented by formula I (where M is an Na or K ion and(n)< 27) to form a catalyst. In order to support the Pt and Cu and/or Co on the crystalline titanosilicate represented by the formula I, ion exchange may be carried out as usual by stirring an aq. soln. of metallic salts mixed with iron silicate. The titanosilicate can be synthesized by hydrothermally compounding water glass as a prescribed silicate with Ti ions, etc. The formed catalyst accelerates the reaction of hydrocarbon with NOx in exhaust gas in preference to the reaction of the hydrocarbon with oxygen.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a catalyst for purifying nitrogen oxides in exhaust gas discharged from internal combustion engines such as automobiles and chemical plants such as nitric acid manufacturing plants.

[Conventional technology]

Exhaust gas emitted from internal combustion engines such as automobiles and nitric acid manufacturing plants contains nitrogen oxides (NOx), etc. In recent years, various studies have been conducted on purifying nitrogen oxides from exhaust gas. being done.

Conventionally, the purification of nitrogen oxides has mainly been carried out using reducing catalysts made of noble metals or metals in the presence of reducing gases, but there are almost no known catalysts that purify nitrogen oxides in the presence of oxidizing gases. .

Titanosilicate is made by substituting aluminum of pentasil type zeolite ZSM-5 with titanium at the stage of crystal synthesis.
It has been reported that it is useful as a catalyst for aromatizing lower olefins, such as aromatizing olefins (Catalyst Vol.
2B, No. 2.1986), however, there is no description suggesting the application of this catalyst to the purification of NOx, etc. in exhaust gas.

Furthermore, in recent years, gasoline engines have become required to perform lean combustion in order to improve fuel efficiency and reduce carbon dioxide emissions. However, because the exhaust gas from this lean-burn gasoline engine is in an oxygen-rich atmosphere, conventional three-way catalysts (catalysts that remove the three harmful components of nitrogen oxides, carbon oxides, and hydrocarbons in the exhaust gas) cannot be used. ,
No method has been put into practical use to remove harmful components.

There are known methods for removing nitrogen oxides from such oxygen-excess exhaust gas, including adding a reducing agent such as ammonia and removing nitrogen oxides by absorbing them in alkali. However, these methods are not effective for use in moving sources such as automobiles, and their application is limited.

[Problem to be solved by the invention]

Therefore, the present invention solves the problems of the prior art as described above, and provides an exhaust gas purification catalyst that simultaneously removes nitrogen oxides, carbon oxides, and hydrocarbons from exhaust gas discharged from internal combustion engines of automobiles, etc. The purpose is to provide

[Means for Solving the Problems] According to the present invention, first, compositional formula (r): Mn(Tt, ,
5Lb-no+qz) + 16HzO(r) (where M represents sodium or potassium ion, and n<2
There is provided a catalyst which mainly removes nitrogen oxides from exhaust gas, which is made by supporting at least one metal selected from platinum, copper and cobalt on the crystalline titanosilicate shown in item 7). Ru.

As mentioned above, the exhaust gas purification catalyst according to the present invention differs from the known zeolite (aluminosilicate ZSM-5 manufactured by Mobil Oil Co., Ltd.) in that it has the composition formula (1) having a structure in which titanium atoms are incorporated into the silicate skeleton. This is a catalyst made by supporting Pt, Cu and/or Co on a crystalline substance represented by:

An example of a method for supporting Pt, Cu and/or CO on a crystalline titanosilicate catalyst is the usual ion exchange method in which iron silicate is mixed into an aqueous metal salt solution and stirred.

The crystalline titanosilicate catalyst represented by the compositional formula (I) can be easily obtained by hydrothermally synthesizing water glass, which is a predetermined silicate, and titanium ions. The S i /T i atomic ratio in this titanosilicate is preferably 15 or more, more preferably 25
~100. Also supported Pt, Cu and/or C
o is preferably 1.0% by weight or more, more preferably 2 to 7% by weight, based on the weight of titanosilicate.

According to the present invention, nitrogen oxides in the oxidizing exhaust gas can be purified by bringing the oxidizing exhaust gas containing hydrocarbons and nitrogen oxides into contact with the purification catalyst.

Here, ``Oxidizing exhaust gas J'' refers to the amount of oxygen that is greater than the amount of oxygen required to completely oxidize reducing substances such as carbon monoxide, hydrogen, and hydrocarbons contained in exhaust gas and convert them into water and carbon dioxide gas. Refers to exhaust gas that contains an excessive amount of oxygen. For example, in the case of exhaust gas emitted from internal combustion engines such as automobiles, it is the case when the air/fuel ratio (A/F) is high (fuel lean region). This is exhaust gas that is emitted.

The metal-supported titanosilicate catalyst according to the present invention purifies nitrogen oxides by promoting the reaction between hydrocarbons and nitrogen oxides more preferentially than the reaction between hydrocarbons and oxygen in exhaust gas. Therefore, hydrocarbons and nitrogen oxides in the exhaust gas can be purified.

The hydrocarbons present in the exhaust gas to be purified may be the hydrocarbons remaining in normal exhaust gas, but if the hydrocarbons are insufficient to carry out the reaction between the nitrogen oxides and the hydrocarbons, Hydrocarbons can be replenished from the outside. The required amount of hydrocarbons is 100 to 10,000 ppm (
(as the concentration when converted to CHa) is preferable.

The purification method according to the present invention usually involves arranging the metal-supported titanosilicate catalyst in a reactor and introducing exhaust gas into the reactor to bring the metal-supported titanosilicate catalyst into contact with the exhaust gas. This is carried out by reducing and purifying nitrogen oxides and then discharging the purified exhaust gas from the reactor. Further, in the purification method of the present invention, the purification effect can be further enhanced by using a known purification catalyst together.

In the present invention, the reaction temperature of the catalyst layer during purification is as follows:
From the viewpoint of durability and catalytic activity, 200-800'C
A temperature in the range of . The temperature of this catalyst layer is 800°
If it exceeds C, the durability of the catalyst may deteriorate, which is not preferable. Further, if the temperature is less than 200°C, purification will be insufficient, which is not preferable. In addition, in the purification method according to the present invention, the space velocity (SV) at which exhaust gas is introduced into the catalyst layer
There is no particular limit to the value, for example, 1.000 to 500.
A range of 0.000/hour is desirable to maintain activity.

The supported titanosilicate catalyst containing the above-described specific metal (i.e., Pt, Cu and/or Co) according to the present invention is
Because it has a crystalline structure with titanium atoms incorporated in the silicate skeleton, compared to those formed by supporting the above-mentioned specific metal on alumina or supporting titanium on silicate by ion exchange, it has a lower nitrogen content. It has excellent performance in purifying oxides.

When this metal-supported titanosilicate catalyst is brought into contact with oxidizing exhaust gas containing at least hydrocarbons and nitrogen oxides, the nitrogen oxides in the exhaust gas are reduced to nitrogen gas with high efficiency and the exhaust gas is purified. be able to.

In addition, this metal-supported titanosilicate catalyst
Even after a durability test of heating with C for 5 hours, it still has exhaust gas purification performance and can be used as a normal exhaust gas catalyst.

The method for purifying exhaust gas according to the present invention purifies nitrogen oxides by bringing the specific metal-supported titanosilicate catalyst described above into contact with oxidizing exhaust gas containing hydrocarbons and nitrogen oxides. This oxidizing exhaust gas - contains an amount of oxygen in excess of that required to completely oxidize reducing substances such as carbon oxides, hydrogen and hydrocarbons, converting them into water and carbon dioxide. It is.

[Effect]

The Pt5Cu and/or Co-supported titanosilicate catalyst according to the present invention reacts hydrocarbons and nitrogen oxides preferentially to the reaction between hydrocarbons and oxygen, and reduces the nitrogen oxides to produce nitrogen gas. The hydrocarbons then react with oxygen and are converted to carbon dioxide. In this way, nitrogen oxides in the oxidizing exhaust gas can be purified.

〔Example〕

EXAMPLES The present invention will be specifically explained below with reference to Examples, but it goes without saying that the present invention is not limited to the following Examples.

Beard [Catalyst Preparation] A pt-supported titanosilicate catalyst having an atomic ratio of S i /T i of 25 was prepared as follows.

A liquid: Titanium sulfate (IV) (Ti (SOa) z・4HJ) 3.3
9 gHzO85, Og Liquid B: Water glass (Si (h 35-38% by weight) 50.0g
HzO50, Og Solution C: Sulfuric acid (>85% by weight) 15. Og
Solution D: Tetrapropylammonium hydroxide ((
C3H? ), NOF! (20-25% by weight))30.
Four solutions of 0 g were prepared.

The above-mentioned solution A was placed in a 200-mm beaker, the pH was maintained at 2.5 to 3.5 at room temperature, and solutions B and C were added dropwise and mixed while stirring vigorously. Solution D was mixed into this mixed solution and stirred for about 3 hours, and the resulting mixed solution was transferred to an autoclave and heated to 180 °C at a heating rate of 1°C/min without stirring.
The temperature was raised to 210°C by heating at a heating rate of 0.25°C/min, and then held at 210°C for 60 hours. After cooling, the product was washed and heated to 120°C.
It was dried. Next, it was fired at 550°C under nitrogen flow for 15 hours, and then at 550°C under air flow for 5 hours.

Subsequently, this fired body was immersed in an NLNO:+ solution at a concentration of IN for 3 hours to convert it into an ammonium type. After that, after washing with water at room temperature, drying at 100°C, and then 50°C in air.
A titanosilicate was obtained by firing at 0''C for 1 hour.The content of titanium was 2.74% by weight.

This ammonium type titanosilicate was immersed in a 0.2 M/l Pt amine aqueous solution for 3 hours to exchange Pt ions, washed with water at room temperature, dried at 100°C, and then heated in air at 350°C for 3 hours. The Pt1B-bearing titanosilicate catalyst A was obtained by firing.

Regarding ion exchange, the higher the pH and the higher the temperature of the aqueous solution, the higher the amount of exchange.

The Pt content of the Pt-supported titanosilicate catalyst obtained above was 7.44% by weight.

As comparative catalysts, catalyst B in which 1.2% by weight of Pt was supported on activated alumina and ammonium type titanosilicate catalyst C prepared by the method described above were used.

[Purification performance evaluation]

Catalyst performance was compared with the pt-supported titanosilicate catalyst color comparison catalysts B and C obtained above.

After a fresh and 5-hour durability test at 600°C, the purification performance was compared by contacting with a gas having the composition and conditions shown below, which simulates automobile exhaust gas.

Gas composition: HC (hydrocarbon): 0.08%, co: o, i1%, 0
2:4.30%, NO:0.10%, N2:o, 03%
, C02: 11.9%, N20: 2.3%, N2:
8t, 2%, SV (space velocity for introducing gas into the catalyst layer): 420,000/hour, temperature of the catalyst layer: 250°C, 1300°C and 400°C
Table 1 shows the initial purification rate in the test, and Table 2 shows the purification rate after the durability test.

As shown in Tables 1 and 2, Catalyst A according to the present invention purified nitrogen oxides several times to several times as much as Comparative Example Catalysts B and C. It was also excellent in purifying performance for hydrocarbons and carbon oxides.

The following margin is 1 ゛ ° % (I) [Catalyst Preparation] A Cu-supported titanosilicate catalyst having an Si/Ti atomic ratio of 25 was prepared as follows.

The ammonium-type titanosilicate prepared by the method of Example 1 was immersed in a 0.2M #2 copper acetate aqueous solution for 3 hours to exchange Cu ions, washed with water at room temperature, dried at 100°C, and further heated in air for 350°C. It was calcined at °C for 3 hours to obtain a Cu-supported titanosilicate catalyst.

For Cu ion exchange with copper acetate, the pH is high;
The higher the temperature of the aqueous solution, the better the exchange rate.

The Cυ content of the Cu-supported titanosilicate catalyst obtained above was 3.64% by weight.

As comparative catalysts, Catalyst E in which 1.2% by weight of Cu was supported on activated alumina and Ammonium titanosilicate Catalyst F prepared by the method described above were used.

[Evaluation of purification performance] The catalytic performance of the Cu-supported titanosilicate catalyst obtained above and comparative catalysts E and F were compared.

After a fresh and 5-hour durability test at 600'C, each sample was brought into contact with a gas having the following composition and conditions that simulated automobile exhaust gas, and the purification performance was compared.

Gas composition: HC (hydrocarbon): o, o8%, co: o, i1%, 0
□: 4.30%, NO: 0.10%, H2: 0.03
%, COx: 11.9%, H2O: 2.3%, Nz
:81.2%, SV (space velocity for introducing gas into the catalyst layer) = 420,000/hour, temperature of the catalyst layer = 400°C, 1500°C and 600°C
Table 3 shows the initial purification rate, and Table 4 shows the purification rate after the durability test.

As shown in Tables 3 and 4, the catalyst according to the present invention purified nitrogen oxides several times to more than ten times as much as Comparative Example Catalysts E and F. It was also excellent in purifying performance for hydrocarbons and carbon oxides. Furthermore, improved performance at high temperatures was observed compared to the noble metal-supported titanosilicate catalyst.

The following blanks are left out. [Preparation of Catalyst] A Co-supported titanosilicate catalyst having an Si/Ti atomic ratio of 25 was prepared as follows.

Ammonium type titanosilicate prepared by the method of Example 1 was added to 0.2M#! C by immersion in cobalt acetate aqueous solution for 3 hours
After ion exchange, the product was washed with water at room temperature, dried at 100°C, and further calcined in air at 350°C for 3 hours to obtain CO-supported titanosilicate catalyst G.

The CO content of the Co-supported titanosilicate catalyst obtained above was 3.2% by weight.

As a comparative catalyst, ammonium titanosilicate catalyst H prepared by the method described above was used.

[Purification performance evaluation]

The catalyst performance was compared with the Co-supported titanosilicate catalyst color comparison catalyst H obtained above.

After a fresh and 5-hour durability test at 600°C, the samples were brought into contact with a gas having the composition and conditions shown below, which simulates automobile exhaust gas, and their purification performance was compared.

Gas composition: HC:C hydrocarbon): 0.08%, Co: 0.11%,
ORr4.30%, NO:0.10%, H:0.03
%, CO□: 11.9%, H, 0: 2.3%, N,
: 81.2%, SV (space velocity for introducing gas into the catalyst layer): 420,000/hour, Temperature of the catalyst layer: 500°C, 1600°C and 700°C
Table 5 shows the initial purification rate in the test, and Table 6 shows the purification rate after the durability test.

As shown in Tables 5 and 6, Catalyst G according to the present invention purified nitrogen oxides several times to several times as much as Comparative Example Catalyst H. It was also excellent in purifying performance for hydrocarbons and carbon oxides. Furthermore, improved performance at high temperatures was observed compared to the noble metal-supported titanosilicate catalyst.

Blank space below [Effects of the Invention] As explained below, according to the present invention, by using a catalyst in which Pt, Cu and/or Co is supported on crystalline titanosilicate having the above-mentioned specific composition, oxygen excess can be achieved. Hydrocarbons, carbon oxides, and nitrogen oxides in exhaust gas can be removed simultaneously in an atmosphere, and even at 600°C
Even after a 5-hour durability test, it has a purification performance that is practically acceptable.

The Pt, Cu and/or Co-supported titanosilicate catalyst according to the present invention may have any structure during purification, such as granular, pellet, or honeycomb shapes.

In addition to internal combustion engines such as automobiles, nitric acid manufacturing plants,
It can be used to purify exhaust gas containing nitrogen oxides from various combustion equipment.

Claims (1)

[Claims] 1. Composition formula: M_n(Ti_nSi_9_6_-_nO_1_9_2
)・16H_2O(I) (wherein M represents a sodium or potassium ion, and n<27) is added with at least one metal selected from platinum, copper, and cobalt. An exhaust gas purification catalyst that mainly removes nitrogen oxides from exhaust gas, characterized by being supported on the catalyst.