JPH04161230A - Decomposition and removal of nox - Google Patents

Abstract

PURPOSE:To stably maintain decomposing and removing functions for a long duration by reproducing an NOx decomposition activity of a specified NOx decomposition catalyst by bringing the catalyst into contact with a reducing agent in the case that the NOx decomposition activity of the catalyst is lowered. CONSTITUTION:This NOx decomposition catalyst is so formed as to have the distribution maxima of fine pore diameters at 50-100Angstrom and 500-1000Angstrom and is composed of a porous support consisting of either one or a plurality of gamma-alumina, zirconia, and titanium oxide and either one or a plurality of iridium, platinum, and rhodium carried on the porous support. A combustion discharge gas is processed at an NOx removing part and as the reaction proceeds, the function of the NOx decomposition catalyst A is lowered. This state is detected by an NOx sensor 9 and hydrogen gas g2 is supplied to the NOx decomposition catalyst A from a hydrogen storage part 8. As a result, the NOx decomposition function of the NOx decomposition catalyst A is reproduced and the catalyst exhibits high removal function again.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention has a pore size distribution of 50 to 100 and 500 to 1.
, formed to have a distribution maximum at ,000 people,
In addition, NOx in the gas to be treated is decomposed by a NOx decomposition catalyst in which one or more of iridium, platinum, and rhodium is supported on a porous carrier made of one or more of γ-alumina, zirconia, and titanium oxide. removeN
This invention relates to a method for decomposing and removing Ox.

[Conventional technology]

Conventionally, various methods have been proposed as means for removing NOx contained in combustion exhaust gas and the like. Among them, the above NOx decomposition and removal method is used in a relatively low temperature range (10
This method has been proposed as a method that can be used at temperatures below 0°C and can decompose and remove NOx using relatively small equipment. In this method, it has been found that the pore size distribution of the carrier is an important factor for the decomposition and removal of NOx.

[Problem to be solved by the invention]

Now, with this method, it is possible to decompose and remove, for example, NOx in exhaust gas in a relatively low temperature range, but the NOx decomposition catalyst used in the second method (with a pore size distribution of 50 to 100 people and 500~I,
formed to have a distribution maximum in 000 people,
In addition, the removal performance of iridium, platinum, or rhodium supported on a porous carrier made of one or more of γ-alumina, zirconia, and titanium oxide increases with the passage of reaction time. The present inventor discovered that there is a tendency for the temperature to decrease gradually. (See Figure 3.5.6) Therefore, in the NOx decomposition and removal method using this NOx decomposition catalyst, the object of the present invention is to provide a method that maintains decomposition and removal performance stably over a long period of time. At the point.

[Means to solve the problem]

Therefore, the characteristic structure of the present invention is that the above-mentioned NOx decomposition catalyst has a step of regenerating its NOx decomposition activity by bringing it into contact with a reducing product when its NOx decomposition activity decreases. The actions and effects are as follows.

[For production]

This NOx decomposition catalyst releases NOx as the reaction time progresses.
The decomposition performance of As a result, the activity of the NOx decomposition catalyst can be regenerated.

〔Effect of the invention〕

As a result, even if the removal performance deteriorates, it can be repeatedly restored to its initial state, making it possible to supply a practical device that can be used for a long period of time. Due to the properties of this NOx decomposition catalyst (temperature in use, conditions in use, etc.), it is possible to reduce NOx in combustion exhaust gas with higher performance, which is advantageous and has high practical value in terms of economy and miniaturization of the equipment in which it is used.
It is now possible to provide a method for decomposing and removing NOx using a decomposition catalyst.

That is, this NOx decomposition catalyst can now be used in small-sized combustion appliances, such as those for household use, by adapting the NOx decomposition and removal method.

〔Example〕

An embodiment of the method for decomposing and removing NOx according to the present invention will be described. FIG. 1 shows that the method of the present application is applied to N in combustion exhaust gas (gl).
A schematic diagram of an exhaust gas treatment device (1) used for removing Ox is shown. This device (1) is installed, for example, in the exhaust path (not shown) of a domestic water heater. Now, in this device (1), combustion exhaust gas (g
l) is the NOx decomposition catalyst (
A) (Specific surface area 100 to 170 rn"/g made of one or more of γ-alumina, zirconia, and titanium oxide)
One or more of iridium, platinum, and rhodium is supported on a porous carrier at a content of 0.01 to 10% by weight. For 50 to 100 people and 500 to 1,000 people as shown in Figure 2, preferably 70λ
700 people. ) or NOx removal unit (3)
It flows into. And in this part (3), NO
The processed gas is decomposed into N2.02 and discharged from the processing gas outlet (4). Here, a hydrogen gas supply path (5) is connected to the aforementioned processing gas inflow path (2), and a hydrogen permeable membrane (6) is connected to the hydrogen permeable membrane (6).
) are connected through. And this hydrogen permeable membrane (
A hydrogen storage section (8) containing a hydrogen storage alloy (7) is provided on the opposite side of the processing gas inflow path (2) in 6), and the hydrogen storage section (8) is supplied with hydrogen. A configuration is adopted in which the hydrogen gas (g2) is supplied to the above-mentioned processing gas inflow path (2).

On the other hand, a NOx sensor (9) is located in the processing gas outlet path (4).
) is provided, and based on the detection information of this NOx sensor (9), the heating mechanism (lO) provided in the hydrogen storage section (8) is activated, thereby heating the hydrogen storage alloy (7). The structure is such that hydrogen is desorbed from the The desorbed hydrogen passes through the process gas inflow path (2) and is sent to the NOx reaction section (3) to regenerate the NOx decomposition catalyst (A).

The processing status of combustion exhaust gas will be briefly explained below. NO
The combustion exhaust gas treated in the x removal section (3) is sent out as clean gas to the treated gas outlet path (4).
Along with this reaction, the performance of the NOx decomposition catalyst (A>) decreases. This state is detected by the NOx sensor (9), and hydrogen gas (g2) is released from the hydrogen storage section (8).
It is supplied to the Ox decomposition catalyst (A). here,
The NOx decomposition catalyst (A) has its NOx decomposition performance regenerated and once again exhibits high removal performance.

[Experiment example]

The results of experiments conducted by the inventors in connection with the NOx decomposition and removal method of the present application will be described below. Experimental example 1~
3 relates to the removal performance of the NOx decomposition catalyst of the present application, and Experimental Examples 4 to 6 show experimental results regarding regeneration of the NOx decomposition catalyst.

(1) Experimental Examples 1 to 3 will be explained. In these experiments, by appropriately setting the pore size distribution of the carrier of the catalyst for NOx decomposition, the presence of 0□ in the atmosphere, which is often a problem when these catalysts work (Experiment Example 1, the oxygen concentration 3
I am experimenting with examples. ), the catalyst was confirmed to work without deteriorating its removal performance, and furthermore,
In relatively low temperature regions (Experimental Example 1 (reaction temperature 30°C), Experimental Example 2 (reaction temperature less than 100°C), Experimental Example 3 (reaction temperature 30°C)), this method was applied similarly to NOx. This is an experiment to confirm that the catalyst works effectively.

Experimental example 1, N by this catalyst when changing oxygen concentration
Change in Oxygen reduction rate (see Figure 3) The oxygen concentration of the NOx-containing gas with a NOx concentration of 5.000 ppm was changed, and the reaction temperature was 30°C, SVl, 0OO (h
-'), NOx-containing gases were treated with the conventional and present NOx removal catalysts, and temporal changes in the NOx reduction rate were investigated.

As a result, conventional catalysts (those that do not adjust the pore size distribution)
was deactivated within 1 hour at the lowest oxygen concentration (1.2%), but the catalyst of the present invention exhibited sufficient NOx decomposition performance for a relatively long time even at high oxygen concentrations.

Experimental example 2, N by this catalyst when changing the reaction temperature
Change in Ox reduction rate (see Figure 4) NOx concentration 5. 0ppm of NOx-containing gas is
I, 000 (h-') was treated with the NOx removal catalyst of the present invention, and changes in the NOx reduction rate with temperature changes were investigated.

As a result, sufficient NOx is produced at around room temperature (30 to 70°C).
Decomposition performance was obtained.

Experimental Example 3: Change in NOx removal rate of this catalyst when nitrogen gas is mixed (no drawing) NOx 11 degrees 5.00 ppm, N2 concentration 50%,
Targeting the remaining amount of He gas, the reaction temperature was 30°C, S.
Vl, 000 (h-'') and treated with the conventional and present NOx removal catalysts (surface area 120 m/g).

As a result, the NOx removal rate with the conventional catalyst was 10%, but the NOx removal rate with the catalyst of the present invention was 99.9%.
Met.

(2) Next, Experimental Examples 4 to 6 will be explained. These experiments were conducted when the NOx decomposition catalyst described above loses its activity over time and the NOx reduction rate in the gas to be treated decreases. , to make sure that it is active or regenerated.

Experimental Example 4 is to confirm that regeneration is possible in any case when the reduced product is changed (CH, H2 gas), and Experimental Example 5 is to confirm that regeneration is possible in different states of decreased activity. This is to confirm the case of regenerating a certain catalyst, and furthermore, Experimental Example 6 is to confirm whether a similar regeneration phenomenon can be obtained with a catalyst having a pore size distribution (conventional catalyst) different from that of the present application. It is for the purpose of

Experimental Example 4 Regeneration change in the NOx reduction rate of the catalyst due to reducing gas (see Figure 5) NOx concentration], 000 ppm NOx containing gas
l, 000 (h-'), treated with the NOx removal catalyst of the present invention at a reaction temperature of 30°C, and for a long time (100 and 130
If the NOx reduction rate decreased after 30 minutes (hours) had elapsed, reducing gas was brought into contact and changes in the reduction rate were observed.

As a result, sufficient removal performance recovery effect (recovery to 100%) was obtained by the reducing gas (CH and H2 gas).

Experimental Example 5 Regeneration effect with different NOx reduction rates (see Figure 6) NOx-containing gas with NOx concentration of 500 ppm was
00(h-'), reaction temperature 30°C, NOx of the present invention
After treatment with a removal catalyst and after a long period of time (4,] 3.21.
60 hours), when the NOx reduction rate decreased, hydrogen was brought into contact as a reducing gas and changes in removal performance were investigated. Then, this operation was repeated. As a result, a sufficient recovery effect of removal performance was obtained by repeatedly bringing the material into contact with reducing gas.

Experimental Example 6 IrAl2O3 regeneration experiment without adjusting the pore size distribution (see Figure 7) In order to make a comparison with Experimental Example 5, a catalyst was prepared using a support (IrA1203) with a pore size distribution different from that of the present invention. ,
Combustion exhaust gas with a NOx concentration of 1100pp is SVl, 00
0(h-'), treated at a reaction temperature of 80°C and 130°C,
Hydrogen was contacted as a reducing gas to examine changes in removal performance. In comparison with FIG. 6, the experimental data at each regeneration stage is divided and shown in FIG. That is, in the regeneration stage,
The reaction time is expressed as 0 o'clock, and the order of each NOx removal stage is RUN1, RUN2, RUN3 . RUN4
It was divided and described as follows.

Here, the experiment was conducted in this order over time. Further, each regeneration was performed for 60 minutes using 11,000 pp of hydrogen gas. Furthermore, RUNl, R
The reaction temperature at each stage of UN2 removal was 80°C;
The reaction temperature in each removal stage of RUN3°RUN4 is 3
The temperature was set to 0°C.

To explain the results, looking at the reduction rate of NOx, R
It was found that the initial stage removal performance indicated by UNI began to decline after about one hour, and that the activity could only be maintained even with subsequent reduction treatment. That is, for those that do not satisfy the pore size distribution conditions, the regeneration effect is very low even if the regeneration treatment is performed using a reducing gas.

Incidentally, the steps for obtaining the catalyst of the present application will be explained. The pore size distribution of the carrier is 50-100 and 500-1.00.
In order to have a distribution maximum in 0 people, an example of the case of an alumina carrier is shown in FIG. 8.

In other words, an aluminum salt aqueous solution such as aluminum nitrate is gelled by adding ammonia, and the water content is 10 to 15.
%, mix an appropriate amount of additives into the dehydrated product, dry the mixture at 100°C or less, and dry the dried product to 400-700°C.
C. to form pores by evaporation of the additives.

Here, the key points are selection of the type and amount of additives and adjustment of the pore size distribution. The pore size distribution was confirmed using a mercury injection porosimeter, etc., which injects mercury into the pores and calculates the pore size from the pressure of the mercury.

[Another example]

Another embodiment of the present application will be described below.

(b) In the above embodiment, H2 as the reducing gas,
Although the example of CH4 gas is shown, in addition to these gases, COl
It is also possible to bring other reducing gases such as hydrocarbons or reducing fluids into contact, and these are collectively referred to as reduced products.

(b) The reducing gas may be supplied by any method such as supplying by cylinder, supplying by natural gas or other city gas, supplying by exhaust gas generated by combustion of fossil fuels, etc.

(C) Furthermore, the method of the present application is applicable to NOx of combustion exhaust gas in household and commercial combustion equipment such as water heaters, cooking appliances, space heaters, dryers, boilers, engines, heating furnaces, power plants, etc. Removal or anything else is fine.

[Brief explanation of the drawing]

The drawings show examples and experimental examples of the method for decomposing and removing NOx according to the present invention, and FIG. 1 is a schematic diagram of an exhaust gas treatment device to which this method is applied, and FIG. 2 shows the pore size distribution of the carrier in the catalyst for NOx decomposition. Figures 3 and 4 are diagrams showing the removal performance of the NOx decomposition catalyst, Figures 5 and 6 are diagrams showing the regeneration state of the NOx decomposition catalyst, and Figure 7 is a diagram showing the fineness of the carrier. Figure 8 shows the regeneration state when the pore size distribution is different.
It is a process diagram which illustrates the manufacturing process of the x decomposition catalyst.

Claims (1)

[Claims] 1. Pore size distribution is 50 to 100 Å and 500 to 1,00 Å.
formed to have a distribution maximum at 0 Å, and
NOx in the gas to be treated is decomposed and removed using a NOx decomposition catalyst in which one or more of iridium, platinum, and rhodium is supported on a porous carrier made of one or more of γ-alumina, zirconia, and titanium oxide. A method for decomposing and removing NOx, the method comprising the step of regenerating the NOx decomposing activity of the NOx decomposing catalyst by bringing it into contact with a reducing product when its NOx decomposing activity decreases. . 2. The reduced product is H_2, CH_4, CO
NO according to claim 1, comprising one or more gases.
How to decompose and remove x. 3. The NOx decomposition and removal method according to claim 1, wherein the reduced product is H_2 gas, which is supplied from a hydrogen storage alloy to the NOx decomposition catalyst and brought into contact with it.