JP7599150B2 - VOC removal catalyst, its manufacturing method, and VOC removal method - Google Patents

Description

The present invention relates to a VOC removal catalyst, a method for producing the catalyst, and a method for removing VOCs.

VOC is an abbreviation for volatile organic compounds, and examples of such compounds include toluene, xylene, benzene, ethyl acetate, methanol, and dichloromethane. While such VOCs are widely used in solvents, adhesives, chemical raw materials, etc., they have been pointed out as causing photochemical oxidants or suspended particulate matter (SPM), and therefore their emissions are strictly regulated by the Air Pollution Control Act. For this reason, there is a need to establish technology to more efficiently remove VOCs in order to further reduce VOC emissions.

A method using catalytic oxidation is known as a technique for removing VOCs. This method is considered to be the most promising because it removes VOCs at relatively low temperatures. Catalytic oxidation methods mainly use transition metal oxides, which are more cost-effective than precious metal catalysts, and from this perspective, research into improving the catalytic performance of transition metal oxides has been widely conducted. For example, Patent Document 1 discloses a technique for efficiently removing VOCs using a material containing manganese (IV) oxide.

JP 2019-147131 A

However, conventional VOC removal catalysts still do not have sufficient VOC removal performance in low-temperature environments, and they also have the problem of taking time to manufacture, so overall there are still challenges to be overcome when considering practical application. From this perspective, there is currently a demand for the development of a catalyst that can be easily manufactured and can efficiently remove VOCs even at low temperatures.

The present invention has been made in view of the above, and aims to provide a VOC removal catalyst that is easy to manufacture, has excellent VOC removal efficiency, and can efficiently remove VOCs even at low temperatures, as well as a method for manufacturing the same and a method for removing VOCs.

As a result of extensive research into achieving the above-mentioned objective, the inventors discovered that the above-mentioned objective could be achieved by using crystalline manganese oxide containing a specific metal, and thus completed the present invention.

That is, the present invention includes, for example, the subject matter described in the following sections.
Item 1
A VOC removal catalyst comprising:
A crystalline manganese oxide containing a metal M,
The VOC removal catalyst, wherein the metal M includes at least one selected from the group consisting of Ce, La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.
Item 2
Item 2. The VOC removal catalyst according to Item 1, wherein the crystalline manganese oxide containing the metal M is a crystalline manganese oxide containing an oxide of Ce.
Item 3
Item 2. The VOC removal catalyst according to item 1, wherein in the crystalline manganese oxide containing the metal M, the molar ratio of the metal M to manganese (metal M:Mn) is 1:0.001 to 1:5.
Item 4
Item 3. The VOC removal catalyst according to item 2, wherein in the crystalline manganese oxide containing an oxide of Ce, the molar ratio of cerium to manganese (Ce:Mn) is 1:0.001 to 1:5.
Item 5
A step 1 of obtaining a product by mixing a raw material liquid A containing a manganese source, a raw material liquid B containing a metal element M source, and a raw material liquid C containing a reducing agent;
Step 2 of calcining the product obtained in step 1;
Equipped with
A method for producing a VOC removal catalyst, wherein the metal element M includes at least one selected from the group consisting of Ce, La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.
Item 6
Item 6. The method for producing a VOC removal catalyst according to Item 5, wherein the reducing agent is a carboxylic acid compound and/or vitamin C.
Item 7
Item 7. The method for producing a VOC removal catalyst according to Item 6, wherein the carboxylic acid compound is at least one selected from the group consisting of citric acid, formic acid, and acetic acid.
Item 8
A method for removing VOCs, comprising a step of decomposing VOCs using the VOC removal catalyst according to any one of items 1 to 4 or the VOC catalyst obtained by the production method according to any one of items 5 to 7.

The VOC removal catalyst of the present invention is easy to manufacture, has excellent VOC removal efficiency, and can efficiently remove VOCs even at low temperatures.

1 is a schematic diagram showing an example of a method for producing a VOC removal catalyst of the present invention. FIG. 2 is a schematic diagram showing a flow of an evaluation test method for a VOC removal catalyst. 1 shows SEM images of the catalysts obtained in Examples 1 to 4 and Comparative Example 1. 1 shows XRD spectra of the catalysts obtained in Examples 1 to 4 and Comparative Example 1. The results of a VOC removal test using the catalysts obtained in the examples and comparative examples are shown below.

The embodiments of the present invention will be described in detail below. In this specification, the expressions "contain" and "include" include the concepts of "contain," "include," "consist essentially of," and "consist only of."

1. VOC Removal Catalyst The VOC removal catalyst of the present invention contains a crystalline manganese oxide containing a metal M, and the metal M contains at least one selected from the group consisting of Ce, La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

The VOC removal catalyst of the present invention has the property of being able to decompose VOCs by oxidation or the like. In particular, the VOC removal catalyst of the present invention is easy to manufacture, has excellent VOC removal efficiency, and can efficiently remove VOCs even at low temperatures. Specific embodiments of the VOC removal catalyst of the present invention are described below.

The crystalline manganese oxide containing metal M contained in the VOC removal catalyst of the present invention is the main component of the VOC removal catalyst of the present invention. Hereinafter, "crystalline manganese oxide containing metal M" may be referred to as "manganese oxide 1."

Manganese oxide 1 can be, for example, crystalline manganese oxide containing an oxide of metal M. More specifically, manganese oxide 1 may be a mixture of an oxide of metal M and crystalline manganese oxide, or a mixture of an oxide of metal M and crystalline manganese oxide. Alternatively, manganese oxide 1 may be a solid solution.

In manganese oxide 1, the presence of metal M reduces the crystallinity of crystalline manganese oxide. As a result, the VOC removal catalyst of the present invention has excellent VOC removal efficiency, and can efficiently remove VOCs, even when the VOCs are decomposed at low temperatures.

The metal M contained in manganese oxide 1 may be one type alone or two or more types.

The metal M is preferably Ce. In this case, the crystallinity of the crystalline manganese oxide in manganese oxide 1 is smaller, so that the VOC removal catalyst of the present invention has excellent VOC removal efficiency and can efficiently remove VOCs even when the VOCs are decomposed at a lower temperature. Among these, the metal M is particularly preferably trivalent Ce3 ⁺ , which further improves the catalytic performance of the VOC removal catalyst.

Therefore, in the VOC removal catalyst of the present invention, manganese oxide 1 is preferably a crystalline manganese oxide containing an oxide of Ce.

In manganese oxide 1, the molar ratio of metal M to manganese (metal M:Mn) is preferably 1:0.001 to 1:5. In this case, the VOC removal catalyst of the present invention has excellent VOC removal efficiency and is also likely to have improved VOC decomposition performance at low temperatures. Metal M:Mn is more preferably 1:0.1 to 1:4.5, even more preferably 1:1 to 1:4, and particularly preferably 1:3 to 1:4.

When manganese oxide 1 is a crystalline manganese oxide containing an oxide of Ce, the molar ratio of cerium to manganese (Ce:Mn) is preferably 1:0.001 to 1:5. In this case, the VOC removal catalyst of the present invention has excellent VOC removal efficiency and is more likely to have improved VOC decomposition performance at low temperatures. Ce:Mn is more preferably 1:0.1 to 1:4.5, even more preferably 1:1 to 1:4, and particularly preferably 1:3 to 1:4.

When the manganese oxide 1 contains a large proportion of manganese, it becomes easier to form a solid solution, and as a result, the VOC removal catalyst of the present invention has even better VOC removal efficiency and can remove VOCs particularly efficiently at low temperatures. This tendency is particularly strong when metal M is Ce, that is, when manganese oxide 1 is a crystalline manganese oxide containing an oxide of Ce. When metal M:Mn or Ce:Mn is 1:3 to 1:4, the VOC removal catalyst has particularly excellent VOC decomposition properties at low temperatures.

In the VOC removal catalyst of the present invention, the metal M may be present in the crystalline manganese oxide, or the metal M may be present not inside the manganese oxide, or may be present on the surface as well as inside. For example, the metal M may be present in the crystal structure of the crystalline manganese oxide. This reduces the crystallinity of the crystalline manganese oxide, resulting in excellent VOC decomposition properties at low temperatures for the VOC removal catalyst.

In manganese oxide 1, manganese can exist as Mn2 ⁺ , Mn3 ⁺ , and Mn4 ⁺ , and two or more of these may coexist. In terms of excellent decomposition performance of the VOC catalyst at low temperatures, it is preferable that Mn3 ⁺ is present in large amounts, and it is more preferable that Mn3 ⁺ is present in large amounts on the surface of the VOC catalyst. In this case, the VOC removal efficiency is excellent and the VOC decomposition characteristics at low temperatures are even more excellent.

As described above, manganese present in manganese oxide 1 can have various valences. For example, in the case of crystalline manganese oxide containing Ce, the following general formula (1)
CeMn _x O _y (1)
It can be expressed as:

Here, x is 0.5≦x≦5, preferably 1≦x≦4, more preferably 2≦x≦4, and particularly preferably 3≦x≦4. Also, y is 2.5≦y≦18. y is preferably 3 or more, more preferably 3.5 or more, and particularly preferably 4 or more. Also, y is preferably 17 or less, even more preferably 16 or less, and particularly preferably 15 or less.

In the VOC removal catalyst of the present invention, the structure of manganese oxide 1 can be analyzed from the XRD spectrum, and the crystallinity of manganese oxide can be determined relatively from the spectrum.

The shape of manganese oxide 1 is not particularly limited, and it can take various shapes such as particles, rods, needles, fibers, and scales. It is also preferable that manganese oxide 1 is porous, in which case the VOC decomposition properties at low temperatures are likely to be improved.

As described above, crystalline manganese oxide containing metal M has a low degree of crystallinity, i.e., low crystallinity. For this reason, the VOC catalyst of the present invention has excellent VOC removal efficiency, can efficiently decompose VOCs even when VOCs are treated at low temperatures, and has excellent catalytic performance.

The VOC removal catalyst of the present invention may contain other components (e.g., other elements, compounds, additives, etc.) other than manganese oxide 1, as long as the effect of the present invention is not impaired. The VOC catalyst of the present invention may also be formed only from manganese oxide 1. In this case, it is acceptable for the VOC catalyst to contain unavoidable elements, components, etc. that may be contained in the VOC catalyst. When the VOC catalyst of the present invention contains other elements or components other than manganese oxide 1, the total content thereof may be, for example, 5 mass% or less, preferably 3 mass% or less, more preferably 1 mass% or less, and particularly preferably 0.5 mass% or less or 0.5 mass% relative to the total mass of the VOC catalyst.

The method for producing the VOC removal catalyst of the present invention is not particularly limited, and it can be produced, for example, by various known methods. Specifically, the VOC removal catalyst of the present invention can be produced by a production method including steps 1 and 2 described below.

2. Method for Producing the VOC Removal Catalyst The method for producing the VOC removal catalyst of the present invention includes the following steps 1 and 2.
Step 1: A step of obtaining a product by mixing a raw material liquid A containing a manganese source, a raw material liquid B containing a metal element M source, and a raw material liquid C containing a reducing agent.
Step 2: Calcining the product obtained in step 1.

In the metal element M source used in step 1, the metal element M includes at least one selected from the group consisting of Ce, La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

(Step 1)
In step 1, a mixing treatment is carried out of a raw material liquid A containing a manganese source, a raw material liquid B containing a metal element M source, and a raw material liquid C containing a reducing agent.

The manganese source-containing raw material liquid A used in step 1 has the manganese source dissolved or dispersed in a solvent. The manganese source may be manganese itself or a compound containing manganese, but a compound containing manganese is preferred.

The type of the compound containing manganese is not particularly limited, and may be, for example, various inorganic compounds containing manganese. Examples of the inorganic compound containing manganese include permanganate, nitrate, sulfate, chloride, hydrochloride, chlorate, perchlorate, carbonate, hydrogencarbonate, phosphate, and hydrogenphosphate of manganese, and among them, the inorganic compound containing manganese is preferably permanganate. A specific example of the permanganate is potassium permanganate (KMnO ₄ ).

Other compounds containing manganese include various organic compounds containing manganese, such as manganese acetate, oxalate, formate, and succinate.

In addition, manganese-containing compounds can also contain two or more different anions (e.g., ammonium manganese sulfate, etc.).

It is particularly preferable to use potassium permanganate (KMnO ₄ ) as the manganese source, since this facilitates the production of the VOC catalyst.

The raw material liquid B containing the metal element M source used in step 1 has the metal element M source dissolved or dispersed in a solvent. The metal element M source may be the metal element M alone or a compound containing the metal element M. The metal element M is preferably Ce. In this case, the obtained VOC catalyst can efficiently remove VOCs.

The type of compound containing the metal element M is not particularly limited, and examples thereof include various inorganic compounds containing the metal element M. Examples of inorganic compounds containing the metal element M include nitrates, sulfates, oxides, chlorides, hydrochlorides, chlorates, perchlorates, carbonates, hydrogencarbonates, phosphates, and hydrogenphosphates of the metal element M.

Compounds containing the metal element M can also include various organic compounds, such as acetates, oxalates, formates, and succinates of the metal element M, and cyclodipentadienyl dichloride salts.

In view of facilitating the production of the VOC catalyst, the source of the metal element M is preferably an inorganic compound containing the metal element M, and in view of excellent reactivity, it is more preferable to use a nitrate of the metal element M, and among these, cerium nitrate (Ce(NO ₃ ) ₃ ) is particularly preferable.

The reducing agent-containing raw material liquid C used in step 1 has the reducing agent dissolved or dispersed in a solvent.

The type of reducing agent is not particularly limited, and for example, a wide variety of known reducing agents can be used. Specifically, the reducing agent can be a carboxylic acid compound and/or vitamin C. The carboxylic acid compound can be various compounds having a reducing action, for example, at least one selected from the group consisting of citric acid, formic acid, and acetic acid. The reducing agent is preferably citric acid, since it has excellent VOC removal efficiency at low temperatures and is easy to exert an etching effect on the catalyst surface.

The reducing agent can be used alone or in combination of two or more types.

Raw material liquid A, raw material liquid B, and raw material liquid C may each contain a solvent. The type of solvent is not particularly limited, and examples that can be used include water; alcohols having 1 to 4 carbon atoms such as methanol and ethanol; and mixed solvents thereof; amide-based solvents such as N,N-dimethylformamide; and pyrrolidone-based solvents such as N-methylpyrrolidone. In terms of facilitating the reaction in step 1, the solvents contained in raw material liquid A, raw material liquid B, and raw material liquid C are preferably water and the alcohols, or mixed solvents thereof, and more preferably water. The solvents contained in raw material liquid A, raw material liquid B, and raw material liquid C may be the same as each other, or may be partially or entirely different, and more preferably all of them are water.

There is no particular limitation on the concentration of the manganese source in raw material liquid A. For example, the concentration of manganese in raw material liquid A can be 1×10 ⁻⁴ to 2M, preferably 1×10 ⁻³ to 1M, and more preferably 1×10 ⁻² to 0.5M.

There is no particular limitation on the concentration of the metal element M source in the raw material liquid B. For example, the concentration of the metal element M source in the raw material liquid B can be 1×10 ⁻⁴ to 2M, preferably 1×10 ⁻³ to 1M, and more preferably 1×10 ⁻² to 0.5M.

There is no particular limitation on the concentration of the reducing agent in the raw material liquid C. For example, the concentration of the reducing agent in the raw material liquid C can be 1×10 ⁻⁴ to 2M, preferably 1×10 ⁻³ to 1M, and more preferably 1×10 ⁻² to 0.5M.

In step 1, the mixing ratio of raw material liquid A and raw material liquid B is not particularly limited. For example, it is preferable to mix the two so that the molar ratio of metal element M to manganese (metal element M:Mn) is 1:0.5 to 1:5. In this case, the obtained VOC removal catalyst is likely to have improved VOC decomposition performance at low temperatures. The metal element M:Mn ratio is more preferably 1:1 to 1:4, even more preferably 1:2 to 1:4, and particularly preferably 1:3 to 1:4.

In step 1, the amount of raw material liquid C used is not particularly limited. For example, the amount of raw material liquid C can be adjusted so that the molar ratio of the reducing agent to manganese in raw material liquid C (reducing agent:manganese) is 1:0.1 to 1:5.

In step 1, the method of mixing raw material liquid A, raw material liquid B, and raw material liquid C is not particularly limited. As an example, the mixing process can be performed by adding raw material liquid A and raw material liquid B to raw material liquid C that is being stirred. In this case, raw material liquid A and raw material liquid B can be added separately to raw material liquid C, or raw material liquid A and raw material liquid B can be mixed in advance and then added to raw material liquid C. When raw material liquid A and raw material liquid B are added separately to raw material liquid C, raw material liquid A and raw material liquid B can also be added to raw material liquid C at the same time.

The rate at which raw material liquid A and raw material liquid B are added to raw material liquid C is not particularly limited, and can be, for example, in the range of 0.1 to 50 mL/min.

When mixing raw material liquid A, raw material liquid B, and raw material liquid C, the temperature during mixing is not particularly limited and can be, for example, 5 to 40°C, and preferably around room temperature (for example, 15 to 30°C). The time for the mixing process is also not particularly limited and can be set appropriately depending on the temperature during mixing.

By mixing raw material liquid A, raw material liquid B, and raw material liquid C, the manganese source, the metal element M source, and the reducing agent may react to produce a precipitate. The resulting precipitate can be separated by an appropriate method such as centrifugation or filtration. The separated precipitate can be washed, dried, etc., as necessary.

The precipitate obtained by the above mixing process is calcined in step 2 described later to become the target VOC removal catalyst. Therefore, the precipitate obtained by the mixing process is, so to speak, a precursor of the VOC removal catalyst. Such a precursor contains, for example, an oxide of manganese (MnO _x , i.e., the valence of manganese is not specified) and an oxide of cerium (e.g., CeO ₂ ), and may also contain the solid solution. The precursor is represented, for example, by the general formula (1). The precursor also contains the reducing agent used in step 1, but this reducing agent can be removed by calcination in step 2 described later.

(Step 2)
Step 2 is a step for calcining the product (precursor) obtained in step 1. The intended VOC removal catalyst is obtained by such calcination.

In step 2, the method of calcination is not particularly limited, and any known calcination method can be widely adopted. For example, the temperature of the calcination can be 250°C or higher. In addition, the calcination temperature is preferably less than 650°C, since the crystallinity of the manganese oxide in the VOC catalyst obtained by calcination tends to be low. The preferred calcination temperature is 250 to 480°C, more preferably 290 to 450°C, and even more preferably 300 to 400°C.

The firing time may be appropriately selected depending on the firing temperature, and may be, for example, 1.5 to 5 hours. In step 2, the heating rate during firing is not particularly limited and may be appropriately set, for example, 1 to 10°C/min.

The calcination process may be carried out in air or in an inert gas atmosphere. It is preferable to carry out the calcination process in air. For example, a known heating device such as a commercially available heating furnace can be used for the calcination process.

The calcination treatment in step 2 removes, for example, any remaining reducing agent, and forms a sintered body of the product (precursor), which can be obtained as the desired VOC removal catalyst. The resulting VOC removal catalyst is a catalyst containing crystalline manganese oxide (manganese oxide 1) containing the aforementioned metal M, for example, crystalline manganese oxide containing Ce.

By using the manufacturing method including steps 1 and 2 described above, the VOC removal catalyst of the present invention can be easily obtained through simple steps, and the obtained VOC removal catalyst can efficiently remove VOCs even at low temperatures.

3. VOC Removal Method The VOC removal method of the present invention comprises a step of combusting VOCs using the above-mentioned VOC removal catalyst or the VOC catalyst obtained by the production method comprising the steps 1 and 2.

For example, a VOC removal catalyst is placed in a container, and VOCs such as toluene are introduced into the container and treated at a specified temperature to combust the VOCs. This allows the VOCs to be removed. If necessary, nitrogen and/or oxygen can be introduced into the container, allowing the VOCs to be combusted in the presence of nitrogen and/or oxygen.

When removing VOCs, there is no particular limit to the type of container used; for example, any known container used in catalytic combustion of VOCs can be used. The treatment temperature of the VOCs in the container is not particularly limited, and can be the same as the treatment temperature set for the removal of known VOCs. In particular, in the present invention, by using the above-mentioned VOC removal catalyst, the VOC removal efficiency is excellent even at low temperatures.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

Example 1
The VOC removal catalyst was synthesized according to the procedure shown in the schematic diagram of FIG. 1. First, an aqueous solution with a concentration of _KMnO4 of 0.1 M (A solution in FIG. 1) was prepared as raw material solution A, and an aqueous solution with a concentration of Ce( _NO3 ) ₃ of 0.1 M (B solution) was prepared as raw material solution B. These were each dropped into a vigorously stirred 0.2 M citric acid aqueous solution (raw material solution C) at a feed rate of 10 mL/min. This resulted in a brown-black suspension. The resulting suspension was centrifuged to separate the solid (product), and the resulting solid was washed several times with deionized water and then dried overnight at 60°C to obtain a precursor of the VOC removal catalyst (step 1). This precursor was heated to 350°C at a heating rate of 5°C/min in an air atmosphere in a muffle furnace, and the product was calcined at this temperature for 3 hours (step 2), thereby obtaining a VOC removal catalyst with a Mn:Ce ratio of 1:1.

Example 2
Steps 1 and 2 were carried out in the same manner as in Example 1, except that the concentration of _KMnO4 in raw material solution A was changed to 0.133 M and the concentration of Ce( _NO3 ) ₃ in raw material solution B was changed to 0.067 M, thereby obtaining a VOC removal catalyst with a Mn:Ce ratio of 2:1.

Example 3
Steps 1 and 2 were carried out in the same manner as in Example 1, except that the concentration of _KMnO4 in raw material solution A was changed to 0.15 M and the concentration of Ce( _NO3 ) ₃ in raw material solution B was changed to 0.05 M, thereby obtaining a VOC removal catalyst with a Mn:Ce ratio of 3:1.

Example 4
Steps 1 and 2 were carried out in the same manner as in Example 1, except that the concentration of _KMnO4 in raw material solution A was changed to 0.16 M and the concentration of Ce( _NO3 ) ₃ in raw material solution B was changed to 0.04 M, thereby obtaining a VOC removal catalyst with a Mn:Ce ratio of 4:1.

(Comparative Example 1)
An aqueous solution with a concentration of 0.1 _M KMnO4 was dropped at a feed rate of 10 mL/min into a vigorously stirred 0.2 M aqueous citric acid solution. This resulted in a brown-black suspension. The resulting suspension was centrifuged to separate the solid (product), which was washed several times with deionized water and then dried at 60°C overnight to obtain a precursor for VOC removal catalyst. This precursor was heated to 350°C in a muffle furnace under an air atmosphere at a heating rate of 5°C/min, and the product was calcined at this temperature for 3 hours (step 2) to obtain a comparative catalyst.

<Evaluation method>
(VOC removal test)
According to the schematic flow shown in FIG. 2, a toluene removal test was performed on the VOC removal catalyst obtained in each Example. In this test, the VOC removal catalyst was packed in a container so as to be sandwiched between quartz wool, and toluene was flowed into the container at a predetermined flow rate to cause a reaction, thereby removing the toluene. As shown in FIG. 2, the container was connected to an oxygen cylinder and a nitrogen cylinder, so that oxygen and nitrogen could be flowed into the container. As conditions for the toluene removal test, a glass reactor with an inner diameter of 8 mm was used, the amount of the VOC removal catalyst packed therein was 50 mg, and the toluene concentration in the container was 1000 ppm by volume. In addition, the flow rate of the nitrogen gas for carrier into the container was 40 cm ³ /min, the flow rate of the nitrogen gas for introducing toluene was 40 mL/min, and the flow rate of the oxygen gas was 10 cm ³ /min. The reaction temperature in the container was adjusted to various temperatures in the range of 130 to 300° C., and the toluene removal characteristics were evaluated. In the range of 130 to 210°C, sampling was performed twice every 10°C, and in the range of 210 to 300°C, sampling was performed twice every 5°C. A Shimadzu GC-2014 gas chromatograph was used to measure the VOC concentration. In addition, a HORIBA FG-120 FT-IR gas analyzer was used to measure the carbon dioxide concentration discharged from the container outlet.

Figure 3 shows SEM images of the catalysts obtained in Examples 1 to 4 and Comparative Example 1. From Figure 3, it can be seen that when the molar ratio of Mn is increased, as in Example 4, the catalyst is formed in a porous form.

Figure 4 shows the XRD spectra of the catalysts obtained in Examples 1 to 4 and Comparative Example 1.

From Figure 4, comparing the XRD spectrum of Comparative Example 1 with the XRD spectra of Examples 1 to 4, it was found that the inclusion of Ce as metal M can suppress the crystallinity of manganese oxide (MnOx). In particular, when the molar ratio of Mn is large as in Examples 3 and 4, the degree of crystallinity is very small, resulting in a structure close to that of amorphous manganese oxide. Metal elements such as Ce are inserted into the lattice structure of manganese oxide to expand the interlayer spacing, which is thought to reduce the crystallinity of manganese oxide.

Fig. 5 shows the results of the VOC removal test using the catalysts obtained in Examples 1 to 4 and Comparative Example 1. Specifically, Fig. 5 is a plot showing the relationship between temperature (X-axis) and toluene removal rate (Y-axis). In addition, the values of the 10% decomposition temperature (T _10% ), 50% decomposition temperature (T _50% ), 90% decomposition temperature (T _90% ), and 100% decomposition temperature (T _100% ) of toluene for each catalyst are inserted in the graph of Fig. 5.

5 and 6, it can be seen that the VOC removal catalysts obtained in each Example have better VOC removal performance than Comparative Example 1. The catalyst obtained in Comparative Example 1 had a toluene decomposition rate of less than 70% even at 300° C., whereas the catalysts obtained in each Example were found to decompose 90% or more of toluene even when VOCs were treated at a temperature lower than 280° C. In particular, the catalysts obtained in Examples 3 and 4 had 100% decomposition temperatures (T _100% ) of 215° C. and 245° C., respectively, and were found to have particularly excellent VOC removal efficiency at low temperatures.

From the above, it was found that the VOC removal catalysts obtained in each example can be suitably used as catalysts for the catalytic combustion of toluene, a typical VOC substance.

Claims (4)

A method for producing a VOC removal catalyst, comprising the steps of:
A step 1 of obtaining a product by mixing a raw material liquid A containing a manganese source, a raw material liquid B containing a cerium source, and a raw material liquid C containing a reducing agent at 5 to 40° C.;
Step 2 of calcining the product obtained in step 1 at 250 to 480° C .;
Equipped with
The VOC removal catalyst comprises crystalline manganese oxide containing Ce, and the molar ratio of cerium to manganese (Ce:Mn) is 1:1 to 1:4 . The method for producing a VOC removal catalyst according to claim 1 , wherein the reducing agent is a carboxylic acid compound and/or vitamin C. The method for producing a VOC removal catalyst according to claim 2 , wherein the carboxylic acid compound is at least one selected from the group consisting of citric acid, formic acid, and acetic acid. A method for removing VOCs, comprising a step of decomposing VOCs using a VOC catalyst obtained by the production method according to any one of claims 1 to 3 .

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