JPS6117545B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ozone decomposition catalyst, particularly for use in exhaust ozone treatment.

Ozone, which has strong oxidizing ability, can be used to decolorize, deodorize,
It is widely used for purposes such as sterilization and COD removal, but unreacted exhaust ozone is emitted into the atmosphere during the usage process, which may cause secondary pollution, so exhaust ozone treatment is necessary. . This exhaust ozone treatment method is desired to have high ozone decomposition efficiency, safety, maintainability, compact size, and excellent economic efficiency.

Technologies currently used in the field of exhaust ozone treatment include the activated carbon method, thermal decomposition method, and chemical cleaning method.The activated carbon method is used for low concentrations of exhaust ozone, while the For high concentration exhaust ozone, thermal decomposition method is often adopted from the viewpoint of safety, maintainability and ozone decomposition efficiency.

However, the thermal decomposition method requires a residence time of 2 seconds or more at a temperature of 300° C. or more in order to obtain a high ozone decomposition efficiency of 99% or more, and is therefore unfavorable in terms of economy and compactness. In order to eliminate the drawbacks of this thermal decomposition method, the use of ozone decomposition catalysts has recently been considered, and it has been reported that manganese dioxide (MnO ₂ ), for example, has excellent ozone decomposition performance as a catalyst ( Japanese Unexamined Patent Publication 1973-
73323, Special Publication No. 50-80293).

In addition, transition metal oxides are generally known as excellent catalyst materials, and because they are relatively inexpensive, they are widely known as components of industrial catalysts.
Among transition metals, Mn oxide, which has the second Clark number (percentage of elements that make up the earth's crust) after iron, is one of the cheapest transition metal oxides and has almost no resource constraints. It is widely used as a catalytic component because it does not cause oxidation, and as mentioned above, it has also been reported as an excellent ozone decomposition catalyst.

However, as a result of various experiments conducted by the present inventors on the ozone decomposition performance of MnO ₂ catalysts, we found that MnO ₂
It was found that the catalyst has the disadvantage that its ozone decomposition performance gradually decreases when used at temperatures below 100°C.

Therefore, the object of the present invention is to
The object of the present invention is to provide an ozone decomposition catalyst that eliminates the drawbacks of the MnO ₂ catalyst and has better ozone decomposition performance and durability at temperatures below 100°C.

The present inventors conducted various experiments and numerous studies in order to eliminate the above-mentioned drawbacks of conventional MnO ₂ catalysts, and as a result, the present inventors added 5 to 15 atomic percent of Co to MnO _2.
It has been found that if Co oxide is added, an ozone decomposition catalyst with excellent ozone decomposition performance and durability can be obtained.

Therefore, according to the present invention, 5 to 15% Co oxide ( _hereinafter referred to as CoOx
An ozone decomposition catalyst is provided.

The term "atomic % Co" as used herein means the percentage (%) of Co atoms represented by the formula:

Atom% of Co = Number of Co atoms/(Number of Co atoms + Number of Mn atoms) x
100 In the present invention, “Co oxide” refers to CoO,
Collectively refers to _Co2O3 , _{Co3O4 , etc.} The catalyst of the present invention is
As a result of analysis by line diffraction, it was recognized that Co ₃ O ₄ was present as the main component in many cases. However, since it was confirmed that other substances are also active phases, in the present invention, the term CoOx is used to include all of these substances.

The catalyst of the present invention may be a finely divided powder or in the form of granules, pellets or other forms having particle sizes of any size. Preferably, it can take the form of granules that are bound by an inert binder and then crushed. As the binder, silica sol or the like can be used.

The catalyst according to the present invention can be produced by many methods such as kneading method, suspension precipitation method, coprecipitation method, and impregnation method.

For example, in the kneading method, MnO ₂ obtained by thermally decomposing manganese carbonate in an oxygen stream, and CoOx obtained by calcining a precipitate produced by adding a sodium hydroxide aqueous solution to a cobalt nitrate aqueous solution in an air stream. After mixing and kneading an appropriate amount of silica sol, the mixture is calcined in an air stream and crushed.
A MnO ₂ -CoOx catalyst can be obtained.

In the suspension precipitation method, MnO ₂ powder obtained by thermally decomposing manganese carbonate in an oxygen stream is suspended in an aqueous cobalt nitrate solution, and an aqueous sodium hydroxide solution is added to this to obtain a MnO ₂ -cobalt hydroxide mixture. After separating and drying this, it is calcined in an air stream to produce MnO ₂ −
By making a CoOx mixture, adding silica sol and kneading it, then calcining it in an air stream and crushing it.
A MnO ₂ -CoOx catalyst can be obtained.

In the coprecipitation method, potassium permanganate is added to a mixed aqueous solution of manganese sulfate, potassium nitrate, and cobalt nitrate to obtain a MnO ₂ -cobalt hydroxide coprecipitate, which is separated and calcined in an air stream to produce MnO ₂ - CoOx
By obtaining a mixture, mixing an appropriate amount of silica sol with it, and then calcining it in an air stream and crushing it.
A _MnO2 -CoOx catalyst can be produced.

In addition, in the impregnation method, an appropriate amount of silica sol is kneaded with MnO ₂ powder obtained by thermally decomposing manganese carbonate in an oxygen stream, and then calcined in an air stream and crushed.
MnO ₂ catalyst is impregnated with an aqueous cobalt nitrate solution and then calcined in a stream of air.
A CoOx supported _MnO2 catalyst can be obtained.

The catalyst of the present invention has superior ozone decomposition performance and durability compared to conventional MnO ₂ catalysts,
Further, by adopting this, it is possible to achieve improvements in economical efficiency by making the exhaust ozone treatment device more compact and reducing operating temperature.

Although it is not clear why the catalyst of the present invention has superior ozone decomposition performance and durability compared to conventional MnO ₂ catalysts, it is clear that composite oxides with excellent ozone decomposition performance in the CoOx range of 5 to 15 atomic % This seems to be because it is generated.

Although the catalyst of the present invention has been described above as being applicable to treating high-concentration exhaust ozone, it can also be applied to treating low-concentration ozone generated from various devices such as copying machines.

Examples are presented to further illustrate the invention.

Production of catalyst (1) Production of MnO ₂ -CoOx catalyst by kneading method Manganese carbonate (MnCO ₃ ) was heated at 350°C in an oxygen stream.
_{MnO 2 obtained} by thermal decomposition for ₃ hours at After washing with water, in an air stream
CoOx obtained by firing at 250° C. for 3 hours was mixed with MnO ₂ so that the amount of CoOx added was 0, 1, 5, 10, 15 and 20% expressed in atomic % of Co. Furthermore, after adding 20% by weight of silica sol and thoroughly kneading it,
A MnO ₂ -CoOx catalyst was obtained by calcination for a period of time. The performance test of the catalyst was carried out by crushing the catalyst to a particle size of 10 to 12 mesh and filling it into a reaction tube made of pirate glass.

(2) Production of catalyst by suspension precipitation method MnO ₂ powder obtained by thermally decomposing manganese carbonate at 350°C in an oxygen stream for 3 hours is added to a cobalt nitrate aqueous solution of a predetermined concentration, stirred and suspended, and then hydroxylated. Add a sodium aqueous solution, and the amount of cobalt hydroxide added is 1 atomic % of Co relative to MnO ₂ .
MnO ₂ -cobalt hydroxide mixtures of 5, 10, 15 and 20% were obtained. This mixture was thoroughly washed with pure water, dried at 120°C for 3 hours, and then calcined in an air stream at 300°C for 3 hours.
A MnO ₂ .CoOx mixture was obtained. Then add 20 to this
After adding % by weight of silica sol and thoroughly kneading,
Calcinate for 3 hours at 250℃ in air flow to obtain MnO ₂ −CoOx
I got a catalyst. The performance test of the catalyst was carried out by crushing the catalyst to a particle size of 10 to 12 mesh and filling it into a reaction tube made of Pyrex glass.

(3) Production of catalyst by coprecipitation method By adding potassium permanganate to a mixed hot aqueous solution of manganese sulfate, potassium nitrate, and cobalt nitrate, the amount of cobalt hydroxide added to MnO ₂ is 1 atomic % of Co. MnO ₂ -cobalt hydroxide coprecipitates were obtained at concentrations of 5, 10, 15 and 20%. This coprecipitate was thoroughly washed with pure water, dried at 120°C for 3 hours, and further calcined in an air stream at 300°C for 3 hours to obtain a MnO ₂ -CoOx mixture. Next, 20% by weight of silica sol was added to this, and after thorough kneading, it was heated to 250°C in an air stream for 3
A MnO ₂ -CoOx catalyst was obtained by calcination for a period of time. The performance test of the catalyst was carried out using crushed pieces arranged into 10 to 12 meshes.

(4) Production of catalyst by impregnation method 20% by weight of silica sol was added to MnO ₂ powder obtained by thermally decomposing manganese carbonate at 350°C in an oxygen stream for 3 hours, thoroughly kneaded, and then heated at 250°C in an air stream.
The MnO ₂ catalyst obtained by calcination for 3 hours was crushed to give 10
The particle size was adjusted to ~12 mesh. Next, this was added to a cobalt nitrate aqueous solution of a predetermined concentration and treated at room temperature for 5 hours, and the _excess cobalt nitrate aqueous solution was removed by filtration. Cobalt nitrate impregnated MnO ₂ at 1, 5, 10, 15 and 20%
I got it. Furthermore, this was calcined at 300° C. for 6 hours in an air stream to obtain a CoOx-supported MnO ₂ catalyst.

Catalyst Ozone Decomposition Performance Testing Apparatus FIG. 1 is a schematic diagram of a catalyst ozone decomposition performance testing apparatus. Air that has passed through the compressor and dehumidifier is supplied to ozonizer A. This air is converted by ozonizer A into air containing ozone at a predetermined concentration. This ozone-containing air is
After passing through a needle valve B and a flow meter _F1 , the gas is guided to a gas washer G, which simulates a water treatment device, and is humidified. The humidified ozone-containing air is pumped into three directions.
After passing through _C1 , the ozone decomposition device M is supplied to an ozone decomposition device M consisting of an electric furnace E in which an ozone decomposition catalyst D is set. This ozone decomposition apparatus M has a temperature detector (not shown) for detecting the temperature of the catalyst layer of the ozone decomposition catalyst D. After passing through the ozone decomposition device M, the ozone-containing air is disposed of via a three-way tank C ₂ , a dehumidifier H, and a flow meter F ₂ . In order to measure the ozone concentration in the air before it flows into the ozone decomposition device M and the ozone concentration in the air after it passes through the ozone decomposition device M, the three-way cots C1 and C2 are equipped with an ozone concentration measuring device _K1 and an ozone concentration measuring device _K1 and _C2 , respectively. K ₂ is connected. By switching the flow path of the ozone-containing air to the ozone concentration measuring devices _K1 and _K2 , the respective ozone concentrations can be determined.

Ozone decomposition performance of catalyst and its durability test (1) Test 1 The ozone decomposition performance of the MnO ₂ --CoOx catalyst produced by the above-mentioned (1) kneading method was tested using the apparatus shown in FIG. The results are shown in FIG.
The test conditions were as follows.

Catalyst filling amount: 1.5cc, catalyst layer temperature: 50℃, ozone-containing air (exhaust ozone) flow rate: 1.0/min,
Space velocity GHSV: 40000hr ^-1 , catalyst layer inlet ozone concentration: 2000ppm.

Characteristic lines A and B in Figure 2 represent the initial performance of the catalyst (ozone decomposition efficiency) and 150
Shows performance after time use.

(2) Test 2 Similarly, test (2) above was conducted using the apparatus shown in Figure 1.
The ozone decomposition performance of MnO ₂ -CoOx catalyst prepared by suspension precipitation method was tested. The result is the third
As shown in the figure. The test conditions were as follows.

Catalyst filling amount: 1.5cc, catalyst layer temperature: 50℃, ozone-containing air (exhaust ozone) flow rate: 1.0/min,
Space velocity GHSV: 40000hr ^-1 , catalyst layer inlet ozone concentration: 2000ppm.

Characteristic lines A and B in FIG. 3 indicate the initial performance of the catalyst and the performance after 150 hours of use, respectively.

(3) Test 3 Similarly, the above test was carried out using the apparatus shown in Figure 1.
(3) The ozone decomposition performance of the MnO ₂ -CoOx catalyst produced by the coprecipitation method was tested. The results are shown in FIG. The test conditions were as follows.

Catalyst filling amount: 1.5cc, catalyst layer temperature: 50℃, ozone-containing air (exhaust ozone) flow rate: 10/min,
Space velocity GHSV: 40000hr ^-1 , catalyst layer inlet ozone concentration: 2000ppm.

Characteristic lines A and B in FIG. 4 indicate the initial performance of the catalyst and the performance after 150 hours of use, respectively.

(4) Test 4 Similarly, test (4) above was conducted using the apparatus shown in Figure 1.
The ozone decomposition performance of the MnO ₂ -CoOx catalyst prepared by the impregnation method was tested. The results are shown in FIG. The test conditions were as follows.

Catalyst filling amount: 1.5cc, catalyst layer temperature: 50℃, ozone-containing air (exhaust ozone) flow rate: 1.0/min,
Space velocity GHSV: 40000hr ^-1 , catalyst layer inlet ozone concentration: 2000ppm.

Characteristic lines A and B in FIG. 5 indicate the initial performance and performance of the catalyst after 150 hours of use, respectively.

(5) Test 5 Similarly, using the apparatus shown in Figure 1, a conventional MnO ₂ catalyst and an MnO ₂ -CoOx catalyst (indicated as MnO ₂ -10%CoOx) to which 10% Co atom % of CoOx was added were tested. Tested for durability. The result is the 6th
As shown in the figure. The test conditions were as follows.

Catalyst filling amount: 6.0cc, catalyst layer temperature: 90℃, ozone-containing air (exhaust ozone) flow rate: 1.0/min,
Space velocity GHSV: 10000hr ^-1 , catalyst layer inlet ozone concentration: 2000ppm.

Characteristic lines A and B in Figure 5 are respectively
Figure 3 shows the change in ozone decomposition performance of MnO ₂ catalyst and MnO ₂ -10%CoOx catalyst with respect to test time.

In addition, in FIGS. 2 to 6, the ozone decomposition efficiency was determined by the following formula.

Ozone decomposition efficiency (%) = (1 - ozone concentration at the outlet of the catalyst layer / ozone concentration at the inlet of the catalyst layer) x 100 However, as can be understood from Figures 2 to 5, there are some differences depending on the catalyst manufacturing method. However, in all cases, the ozone decomposition performance is higher than that of MnO ₂ alone when the amount of CoOx added is between 1 and 20 atomic percent, and especially when the amount of CoOx added is around 10 atomic percent. There is a peak of ozone decomposition performance. What should be emphasized further is that, as can be seen from the comparison of characteristic lines A and B in Figures 2 to 5 and Figure 6, MnO ₂ -
The CoOx catalyst has superior durability at low temperatures below 100°C compared to the MnO ₂ catalyst.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a catalyst ozone decomposition performance testing apparatus. Figure 2 shows MnO ₂ − obtained by the kneading method.
It is a graph showing the composition and ozone decomposition performance of a CoOx catalyst. Figure 3 shows MnO ₂ − obtained by suspension precipitation method.
It is a graph showing the composition and ozone decomposition performance of a CoOx catalyst. Figure 4 shows MnO ₂ −CoOx obtained by coprecipitation method.
It is a graph showing the composition of a catalyst and ozone decomposition performance. FIG. 5 is a graph showing the composition and ozone decomposition performance of a MnO ₂ -CoOx catalyst obtained by the impregnation method. Figure 6 shows the conventional MnO ₂ catalyst and the MnO ₂ -10 of the present invention.
%CoOx is a graph showing the durability of the catalyst.

Claims (1)

[Claims] 1. An ozone decomposition catalyst made by adding 5 to 15% Co oxide expressed in atomic % of Co to MnO ₂ .