JPS6297646A - Catalyst for purifying exhaust gas and its preparation - Google Patents

Abstract

PURPOSE:To obtain a catalyst for purifying exhaust gas reducing CO and hydrocarbon and converting NO2 to NO, by simultaneously supporting palladium and zirconium oxide in a specific mixing ratio by a carrier by the use of a carrier solution having an org. acid added thereto. CONSTITUTION:An org. acid such as citric acid is added to an aqueous solution mixture of a palladium metal precursor such as dinitrodiamine palladium nitrate and a zirconium oxide precursor such as zirconium oxynitrate and a carrier such as a silica/alumina carrier is immersed in said solution mixture. The impregnated carrier is dried and subsequently baked to decompose the precursors to simultaneously support palladium and zirconium oxide. The mixing ratio of palladium and zirconium oxide is set to 1:2-1:50 on a wt. basis and the addition amount of the org. acid to zirconium oxide is set to 1:1-1:5 on a wt. basis. The obtained catalyst converts CO and hydrocarbon in the combustion exhaust gas within a usual oxygen excessive atmosphere to CO2 and H2O and converts NO2 strongest in toxicity in NOx to NO having lower toxicity.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention is directed to converting carbon oxide (hereinafter referred to as Co), which is a harmful combustion product in exhaust gas generated from a combustor or internal combustion engine, into carbon dioxide (Co). (hereinafter referred to as Co2), and nitrogen dioxide (hereinafter referred to as NO2) to -nitrogen oxide (hereinafter referred to as
In an atmosphere with residual oxygen, hydrocarbons (hereinafter referred to as HC), which are incomplete combustion components, are converted into carbon (hereinafter referred to as HC).
The present invention relates to a catalyst for purifying waste gas that simultaneously converts O2 and water (hereinafter referred to as H2O), and a method for manufacturing the same.

BACKGROUND OF THE INVENTION The exhaust gas emitted from combustion equipment and internal combustion engines contains Co, depending on the type of fuel and the type of equipment.

There are HC, NOx (total nitrogen oxides), and even SO (total sulfur oxides), and when these are emitted in large quantities,
It pollutes the air and adversely affects the indoor environment, and has undesirable effects not only on humans but also on animals and plants.

To date, various methods have been taken as countermeasures against these problems. One of them is a method using a catalyst.

Many methods and catalysts have been used to convert CO and HC to CO2 and N20 using oxidation catalysts, and to convert NO to N2 in an oxygen-poor atmosphere using reduction catalysts and decomposition catalysts. It has been proposed and put into practical use.

However, unless the components in the combustion exhaust gas, especially the amount of residual oxygen, are specifically controlled, the residual oxygen in the exhaust gas from ordinary combustion equipment is present in excess of the amount that oxidizes and consumes the oxidizing components. In such an atmosphere, CO and HC are
Although it is possible to convert N08 to H2O, it is impossible to convert N08 to N2 because the reaction partners CO and HC are consumed before the reaction with oxygen. However, neither a method nor a catalyst for converting and removing CO, HC, and NO at the same time in such an atmosphere has been put to practical use. Therefore, the reduction reaction of nitrogen oxides from stationary sources, especially power plants and chemical plants, is
Catalysts and methods for selective catalytic reactions in which a reduction aid such as ammonia is added and reduced in the presence of a catalyst have been put into practical use.

Problems to be solved by the invention: Is the concentration of reducing components such as co or HC as a reduction aid sufficiently high? Or is it necessary to add a reactive substance such as ammonia from outside the system to carry out a selective catalytic reaction? Unless possible, it is completely impossible to reduce NO to N2 in the combustion exhaust gas in a normal excess oxygen atmosphere.

For this reason, among NO, the most toxic is N.
Studies have been conducted to convert O2 to less toxic No and to reduce the No2 component ratio in NOx.

In this case as well, in an excess oxygen atmosphere, although it is not impossible, the conversion efficiency is low and it is difficult to put it into practical use.

The present invention converts Co and HC into Co2 and H2O in combustion exhaust gas in a normal oxygen-rich atmosphere, and also converts N
Convert O2 to No, No! The purpose is to provide a catalyst for greatly reducing the No2 component ratio in the catalyst.

Normally, in the exhaust gas generated from the combustor, No.
and NO coexist, but the coexistence ratio varies depending on the type of combustor and combustion conditions, and generally NO is 2 to 20 times more than No2. Therefore, in a non-selective catalytic reaction in an oxygen-rich atmosphere, N.

The conversion of No2 to NO2 by oxidation is greater than the conversion of No2 to No2 by reduction;
This results in an increase of 2.

The present inventor has determined that the No oxidation ability and the N
We have tested both aspects of O2 reduction ability, and have found a catalyst that, within the range of the previous coexistence ratio of No and No2, reduces NO□ as an overall process and changes the No and No2 ratio in the direction of increasing NO. However, since most of these also reduce the oxidizing ability of other components such as co and HC, they do not result in the reduction of CO and HC at the same time as the reduction of No2, which is the objective of the present invention.

Means to Solve the Problem In order to solve this problem, the present inventor developed several oxidation catalysts based on platinum-based (platinum and radium) catalysts, which are the most effective as oxidation catalysts for CO and HC. As a result of testing the effects of adding zirconium oxide to palladium, it was found that the most effective solution was the addition of zirconium oxide to palladium.

Furthermore, it is desirable that the mixing ratio of palladium metal and zirconium oxide is in the range of 1:2 to 1:50, more preferably in the range of 1:4 to 1:20.

In addition, it is desirable that these palladium metals and zirconium oxide be simultaneously supported on a carrier, and as a result of repeated studies on the types of precursors and auxiliary agents for supporting them, we found that dinitrodiamine palladium An organic acid such as citric acid is added to a mixed aqueous solution of a precursor of palladium gold, such as a nitric acid solution, and a precursor of zirconium oxide, such as zirconium oxynitrate, to form a support solution, and the support is immersed in this solution. Impregnated, dried, decomposed and fired to produce palladium and zirconia (zirconium oxide)
It has been found that the No2 conversion rate becomes higher when both are supported at the same time.

In addition, the amount of organic acid added at this time has little relationship with the amount of palladium metal precursor, but mainly with the amount of zirconium oxide precursor, and the amount of organic acid added in terms of zirconium oxide. The weight ratio of precursor to organic acid is 1:
It is in the range of 0.5 to 1:10, more preferably 1:
It is desirable that the ratio is in the range of 1 to 1:5. In addition, as for the combination of precursor types, the most effective is to use dinitrodiaminol, radium nitric acid solution, zirconium oxynitrate, and citric acid dissolved in ion-exchanged water, as exemplified above. It was also found that the composition of the catalyst of the present invention has an O effect in an oxygen-rich atmosphere.
Although it is not possible to give a clear explanation as to why they are the most effective in reducing Co-HC and No2, platinum-based catalysts such as platinum, rhodium, and palladium alone are naturally effective at reducing Co-HC. Although it is highly effective in reducing No.2, it is hardly effective in reducing No.2. Even more than that, platinum-rhodium has a high ability to convert NO into No2 and increases No2. The reason why only palladium has a lower ability to convert No to NO□ than other platinum-based catalysts is because palladium has a lower oxidation ability than platinum.
This is thought to be due to the supported surface condition. this is,
By adding zirconium oxide, which is the composition of the present invention, it can be considered that the ability of NO to oxidize NO2 is further suppressed, while the conversion of No2 to No2 is promoted. This has become remarkable by blending zirconium oxide precursors, which is a zirconium oxide precursor.The qualitative aspect of zirconium oxide and the effective surface formation caused by the simultaneous support of palladium result in the expression of new active sites. Alternatively, this may be due to a decrease in the No2 oxidation active sites of NO.

Example Examples are shown below.

(Example 1) Boehmite alumina gel 10 prepared in advance using woven fabric and silica cloth spun from high-purity silica fibers.
0 parts and 10 parts of silica sol are uniformly dispersed in 1000 parts of ion-exchanged water. After thoroughly immersing the mixture, remove the excess liquid, dry by a normal method, and heat in an air atmosphere at 50°C to 800°C. The silica-alumina support was wash coated by firing at ℃. This wash coat was adjusted to have a weight ratio of 16 to 45 wt relative to the silica cloth used as the base material.

On the other hand, after dinitrodiamine palladium nitrate solution and zirconium oxynitrate were dissolved in ion-exchanged water in several proportions, citric acid aqueous solution was gradually added, and as soon as the solution became cloudy, it was stirred and further added. Continue stirring, and when the solution does not become clear yellow again and the entire solution becomes cloudy, stop adding citric acid, and stir thoroughly until the white sol substance settles. Immerse the cloth carrier at 100℃ to 150℃
After drying for 1 to 2 hours at 400°C to 7o.

℃ in an electric furnace, the atmosphere was forcibly exchanged with fresh air,
After exhausting the gas generated by decomposition, the mixture was fired for 2 to 6 hours to support a mixture of palladium and zirconium oxide. The ratio of citric acid added at this time was 1:0 relative to the weight of zirconium oxy-nitrate in terms of zirconium oxide.
, 5, it became slightly cloudy, and at 1:1, the degree of white turbidity became sufficiently thick, and when it was more than that, there was not much change, but when it exceeded 1:10, some precipitation started to be seen. Here, the amount of citric acid added was adjusted to 1:1 relative to the equivalent weight of zirconium oxide.The completed catalysts were designated as A and F in Table 1.

(Example 2) Radium and zirconium oxide were supported on silica cloth in exactly the same manner as in Example 1, but the amount of citric acid added to the palladium/zirconium oxide precursor aqueous solution in which the silica cloth support was immersed was changed. , to zirconium oxide in a weight ratio ranging from 1:0.5 to 1:10.This finished catalyst was designated as 1,N in Table 2.

(Example 3) In the same manner as in Example 1, silica cloth was loaded with radium and zirconium oxide (palladium nitrate as a precursor of radium, zirconium nitrate as a precursor of zirconium oxide, and as an organic acid). Butyric acid was used.

(Example 4) Palladium and zirconium oxide were supported on silica cloth in the same manner as in Example 1, but palladium chloride was used as a precursor of palladium, zirconium oxide was used as a precursor, zirconium chloride was used as a precursor, and succinic acid was used as an organic acid. Acid was used.

(Example 6) Palladium and zirconium oxide were supported on silica cloth in the same manner as in Example 1, but dinitrodiammine palladium was used as a palladium precursor, zirconium nitrate was used as a precursor, and zirconium nitrate was used as an organic acid. Butyric acid was used.

(Example 6) A copierite honeycomb structure was prepared by adding 10 parts of boehmite alumina gel to 1 part of ion-exchanged water.
After thoroughly immersing in a solution uniformly dispersed in 000 parts, removing the excess solution, drying in the usual manner,
The alumina support was wash coated by firing at 0°C. This wash coat is 20-30wt% by weight.
It was prepared as follows. A catalyst was prepared by supporting palladium and zirconium oxide on this carrier in the same manner as in Example 1. The composition of the finished catalyst is shown in Table 1 as Catalyst G.

In order to confirm the effects of the present invention, a catalyst AN was attached to the combustion tube of an oil combustor so that the entire amount of exhaust gas passed through the catalyst. The conversion rate of N02 was determined as a percentage of the NO3 concentration when no catalyst was attached. On the other hand, in order to examine the activity of each sample catalyst, the reaction activity was measured using a flow-type reaction tester using a model gas. At this time, the reaction gases were NO2-...-6ppm, NO-...1
00ppm.

Using a model gas with N2 balance at 0...10, the space velocity relative to the catalyst volume was set to 8 x 1oh. The conversion rate was measured at a gas temperature of 600°C.

In addition, as a conventional catalyst, 0.5 wt% palladium was added to the same wash-coated cross carrier as in Example 1.
Conversion rates were compared using supported palladium catalysts.

Tables 1 and 2 show the results for the actual exhaust gas and model gas. Furthermore, when measuring in an oil combustor, the concentrations of CQ during steady state and HC during extinguishing are also measured, and the conversion rates for each component gas with a sample catalyst installed are compared to the concentrations when no catalyst is installed. Calculated as a percentage.

These measurements were carried out using an infrared non-dispersive measuring instrument for CQ and an infrared non-dispersive measuring instrument for HC.
The concentration was measured using a total hydrocarbon measuring device using a hydrogen flame detector, and the concentration was measured using a chemiluminescent nitrogen oxide measuring device for No. Furthermore, for NO2, perform the No. engineering measurement at the same time as the No. measurement, and calculate the value obtained by subtracting the No. value from this No. engineering value.
value.

Here, the surface temperature of the catalyst attached to the oil combustor used for measurement was distributed in the range of 600 to 700'C during steady combustion.

As is clear from Tables 1 and 2, the catalysts according to the examples of the present invention are extremely effective in converting N02 in nitrogen oxides to No. It was found that this conversion of No2 to NO occurs easily even with conventional catalysts when the model gas is in the high temperature range of 800°C or higher, or when the 02 concentration in the reaction gas is as low as 1% or less. However, there is at least 6 to 10% residual oxygen in the exhaust gas of a normal oil combustor, and due to the heat resistance of the catalyst, the catalyst should be installed at a location where the catalyst surface temperature is SOO~850℃ or less. From these points of view, it has been found that the catalysts of the examples of the present invention are extremely effective in reducing No2. At the same time, the purification rate of Co and HC is the same as that of the conventional catalyst, or at least within 1Q. Particularly, by using the catalyst of the present invention,
It was also found that the effectiveness of purification was not reduced to such an extent.

As a result, it was found that the total concentration of nitrogen oxides in the form of NO2 has not changed at all, but the conversion of NO2 to NO has clearly reduced the toxicity of the exhaust gas. It is declining.

Although the results of Examples 1, 2 and 6 have been explained here, the results of Examples 3 and 4.6 show that the Co and HC purification rates are higher than those of Examples 1.2.6. There was no change at all, at 91-93% for CQ and 70-72% for HC, but the No2 conversion rate was slightly lower for both actual exhaust gas and model gas. In other words, the actual exhaust gas is 48 to 5.
6%, and 48-52% for the model gas. However, both of these cases show higher conversion rates than the conventional example.

In addition, in the present invention, the material and shape of the carrier, that is,
A woven fabric of inorganic fibers other than silica cloth, a paper-like ceramic structure, or a normal granular body may be used.Also, in this example, the case where it is supported on a carrier is described.
The catalyst composition of the present invention itself can be mixed and used as an element of the carrier or base material. Also, the precursor of the catalyst material may be other salts or organic acids than those mentioned here. Even a combination of mutually different salts does not impede the effects of the present invention.

Effects of the Invention As described above, the present invention is extremely effective in reducing N02 and can reduce the toxicity of exhaust gas.

Claims (4)

[Claims] (1) A catalyst for exhaust gas purification that supports palladium metal and zirconium oxide on the surface of a carrier. (2) The catalyst for exhaust gas purification according to claim 1, wherein the mixing ratio of palladium metal and zirconium oxide is in the range of 1:4 to 1:20 by weight. (3) A method for producing an exhaust gas purifying catalyst, which comprises adding an organic acid to a solution consisting of these precursors when palladium metal and zirconium oxide are simultaneously supported on the surface of a carrier. (4) The method for producing an exhaust gas purifying catalyst according to claim 3, wherein the amount of the organic acid added is in the range of 1:1 to 1:5 in weight ratio to the equivalent weight of zirconium oxide.