JP2002102700A - Normal temperature catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decompose and remove an environment load substance such as CO, amines, formaldehyde and the like by activating it at a normal temperature of 50 deg.C or less. SOLUTION: The catalyst contains 40 μmol/g or more of an active oxygen active at 50 deg.C or less. The active oxygen is reacted with the environment load substance adsorbed on a surface of the catalyst at a normal temperature of 50 deg.C or less and decomposes the environment load substance by an oxidation. The active oxygen contained in the catalyst is consumed by the reaction with the environment load substance. However, an oxygen gas contained in an air is taken in the catalyst to become an active oxygen and it is further reacted with the environment load substance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for easily decomposing environmentally hazardous substances such as carbon monoxide (CO), hydrocarbons (HC), aldehydes, ethylene and ammonia at room temperature (room temperature) of 50 ° C. or less. It relates to a room temperature catalyst that can be removed.

[0002]

2. Description of the Related Art For example, adhesives for plywood or coatings applied to furniture may contain free formaldehyde, which is gradually released into the atmosphere. In addition, formaldehyde is generated from industrial products using adhesives and paints using formaldehyde as a raw material along with deterioration. This formaldehyde has a pungent odor and is pointed out as one of the causative substances of sick house syndrome. For this reason, house manufacturers are making efforts to reduce the formaldehyde concentration by aging the house before handing it over to the owner after the construction of the house, but aging alone does not necessarily meet the standards of the Ministry of Health and Welfare, There is a need for a further reduction in the formaldehyde concentration in the air.

[0003] Therefore, as a method for removing environmentally hazardous substances from the air, a method using ozone or a method using an adsorbent such as activated carbon or zeolite is widely used.
For example, as a deodorant which is placed in a refrigerator, a closet, a shoe box or the like to deodorize, a product in which an adsorbent is stored in a container through which air can flow is commercially available. Also, an air purifier with a built-in adsorbent or photocatalyst is known.

[0004] In addition, ethylene contained in the air promotes the physiological action of the fruits and vegetables to promote ripening and aging, so that it is thought that the freshness of the fruits and vegetables is reduced by ethylene. Therefore, the removal of ethylene from the atmosphere is effective for maintaining the freshness of fruits and vegetables, and methods of decomposing ethylene by ozone and hydrogen peroxide and adsorbing and removing ethylene have been proposed.

[0005] For example, Japanese Patent Application Laid-Open No. 7-260331 discloses that a photocatalyst and an ultraviolet light source are arranged in a storage container for accommodating fresh vegetables, and a gas harmful to freshness maintenance of fresh vegetables such as ethylene and acetaldehyde is provided by the photocatalytic action. An apparatus for disassembly and removal is disclosed.

For example, Japanese Patent Application Laid-Open No. 10-296087 discloses that
A catalyst in which a noble metal is supported on a support containing zirconia or ceria is disclosed. According to this catalyst, trimethylamine can be oxidatively decomposed at a temperature of about 200 ° C.

A catalyst for oxidizing CO or HC, or NO
_As a catalyst for reducing _x , a catalyst in which a noble metal is supported on a carrier such as alumina is known, and is widely used as an exhaust gas purifying catalyst and the like.

[0008]

However, in the method using ozone, an ozone concentration exceeding a regulated value is required in order to exert the effect of ozone, and there is a possibility that ozone will remain even after removing environmental load substances. is there. Therefore, it is not practical because a catalyst for treating residual ozone is required.

In the method of adsorbing and removing environmentally hazardous substances in the air by the adsorbent, it is difficult to adsorb the adsorbent in excess of the adsorbing capacity of the adsorbent. There is a need.

In the method using a photocatalyst, an artificial light source is required as an excitation source of the photocatalyst. If the light source is constantly irradiated with the light source, an electricity cost for operating the light source is also required, which is expensive. I have.

Further, in the method using a catalyst, the temperature must be raised to the activation temperature of the noble metal, and a catalyst that activates at a normal temperature of 50 ° C. or less has not yet been known.

The present invention has been made in view of such circumstances, and has as its object to provide a catalyst which can be activated at room temperature of 50 ° C. or lower to decompose and remove environmentally harmful substances such as CO, amines and formaldehyde. And

[0013]

The feature of the room temperature catalyst of the present invention that solves the above-mentioned problems is that active oxygen active at 50 ° C. or less
at least μmol / g.

As the room-temperature catalyst, a catalyst in which a noble metal is supported on an oxide in which oxygen vacancies have been introduced by a reduction treatment is desirable. The oxide is preferably at least one selected from transition metal oxides and rare earth oxides, and the transition metal oxides are Zr, Fe, Mn, Co, Ni, Cu, C
It is at least one selected from oxides of r, Mo and Nb, and the rare earth oxide is desirably at least one selected from oxides of Ce, Y, Nd, Pr and Sm. Further, it is preferable that the oxide includes a Ce oxide and a Zr oxide, and at least a part of the Ce oxide exists in a state of oxygen deficiency.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The room temperature catalyst of the present invention contains active oxygen active at 50 ° C. or lower at 40 μmol / g or more. This active oxygen reacts with the environmental load substance adsorbed on the catalyst surface at a room temperature of 50 ° C. or lower, and oxidatively decomposes the environmental load substance. The active oxygen contained in the catalyst is consumed by the reaction with environmentally harmful substances, but the oxygen gas contained in the air is taken into the catalyst to become active oxygen, which further reacts with the environmentally harmful substances . As described above, the oxidation reaction proceeds catalytically, whereby the environmentally hazardous substance can be oxidatively decomposed and removed.

For example, CO is oxidized by active oxygen to form CO.
₂ and formaldehyde (HCHO) or ethylene (C ₂ H ₄ ) is oxidized to CO ₂ and H ₂ O and made harmless.

[0017] The room temperature catalyst of the present invention has an active oxygen content of 40
It contains at least μmol / g. The content of this active oxygen
If it is less than 40 μmol / g, the reaction with the environmental load substance at room temperature of 50 ° C. or less is not sufficient.

As such a catalyst containing active oxygen of 40 μmol / g or more, a catalyst in which a noble metal is supported on an oxide into which oxygen deficiency has been introduced is typically exemplified. Oxygen deficiency refers to a highly active state in which part of oxygen forming an oxide is eliminated, and a state in which the molar amount of oxygen bonded as an oxide is smaller than a specified value. For example, in the case of Ce oxide, CeO ₂ has no oxygen deficiency. Therefore, if the oxygen atom is less than twice the mole of Ce atom, it means that oxygen deficiency has been introduced.

In the room temperature catalyst of the present invention, a noble metal is supported on the oxide into which the oxygen vacancy has been introduced. The activity of the oxide itself is enhanced by the oxygen deficiency, and as a result, the ability of the environmentally hazardous substance to be adsorbed on the noble metal is reduced. As a result, the activity of the noble metal is increased, and the oxidation reaction of the environmentally hazardous substance proceeds using active oxygen activated via the oxygen deficient portion. And, since the amount of active oxygen is as large as 40 μmol / g or more in the ordinary temperature catalyst of the present invention, it is considered that the oxidation reaction of the environmentally harmful substance proceeds quickly, and it is possible to purify the environmentally harmful substance in the ordinary temperature range. Can be Although oxidative purification of environmentally harmful substances is possible even at a high temperature exceeding 50 ° C., it is desirable to use it at 50 ° C. or lower, more preferably 10 to 40 ° C., because oxygen deficiency may be lost.

As the oxide, any oxide can be introduced as long as it can introduce oxygen deficiency, and an oxide of at least one transition metal selected from Zr, Fe, Mn, Co, Ni, Cu, Cr, Mo and Nb;
Alternatively, an oxide of at least one rare earth element selected from Ce, Y, Nd, Pr and Sm is preferable. One of these may be used, or a plurality of them may be used in combination.

Among them, Ce oxide is a particularly preferred oxide because it easily introduces oxygen deficiency and can stably maintain the oxygen deficiency state. If Ce oxide and Zr oxide are used together, the stability of the oxygen deficiency state of Ce oxide is further improved. In this case, it is more desirable that the Ce oxide and the Zr oxide form a composite oxide or a solid solution. By using a composite oxide or a solid solution, more oxygen vacancies can be formed, and the stability of the oxygen deficiency state is further improved.

In order to form oxygen vacancies in the oxide, a method of reducing the oxide is exemplified. For example, the above oxide may be treated in a reducing gas stream at a temperature of 100 ° C. to 800 ° C. for about 1 hour. When the oxide comes in contact with the reducing gas at a high temperature, part of the oxygen of the oxide is combined with the reducing gas and removed, and as a result, part of the oxide becomes an oxygen-deficient state and oxygen deficiency may be introduced. it can. When the temperature of the reduction treatment is lower than 100 ° C., the reduction reaction does not proceed, and it is difficult to form a desired oxygen deficiency state. On the other hand, if the treatment temperature exceeds 800 ° C., the specific surface area of the oxide becomes small, and the catalytic activity is undesirably reduced. Hydrazine,
The reduction treatment can also be performed using a reducing agent represented by aluminum borohydride or the like.

The reducing gas used in the reduction treatment includes:
In addition to reducing gases such as hydrogen and carbon monoxide, hydrocarbons such as methane and aldehydes may be mentioned. The concentration of the reducing gas at the time of the reduction treatment is preferably 0.1% by volume to 100% by volume, more preferably 1% by volume to 100% by volume.

By knowing in advance the relationship between the amount of active oxygen contained and the amount of oxygen deficiency, the amount of oxygen deficiency can be easily adjusted by adjusting the temperature and time of the reduction treatment. The amount of active oxygen contained can be easily increased to 40 μmol / g or more.

As the noble metal supported on the room temperature catalyst of the present invention, at least one selected from Pt, Pd, Rh, Ir, Au and Ru can be used. One of these may be
A plurality of types can be carried. The amount of the noble metal carried is preferably 0.1 to 10% by weight based on the oxide into which oxygen vacancies have been introduced. If the content is less than 0.1% by weight, the catalytic activity at 50 ° C. or less cannot be obtained, which is not preferable. Further, even if the precious metal is supported in an amount exceeding 10% by weight, the purification efficiency is not improved for the addition, and a large amount of expensive precious metal is used, resulting in an increase in cost. The noble metal preferably has a particle size of 5 nm or less, more preferably 2 nm or less.
The smaller the particle size of the supported noble metal, the higher the activity of the catalyst.

For supporting the noble metal, a known supporting method such as an adsorption supporting method, an evaporation to dryness method and a supercritical fluid method can be used. In addition, by carrying a noble metal before reducing the oxide and reducing the noble metal, oxygen vacancies can be more effectively introduced.

Hereinafter, the structure of the room temperature catalyst of the present invention will be described in detail when CeO ₂ -ZrO ₂ which is a solid solution or a composite oxide is used as the oxide.

CeO ₂ -ZrO ₂ was precipitated by a co-precipitation method, an alkoxide method, or the like, using a solution in which at least one of a Ce compound and a Zr compound was dissolved, mixing the other oxide powder as necessary. Thereafter, it can be formed by firing. Further, a mixture of CeO ₂ powder and ZrO ₂ powder may be fired at a high temperature.

The molar ratio of Ce and Zr in CeO ₂ —ZrO ₂ is
e: Zr = 100: 1 to 1: 100 is preferable, and Ce: Zr
= 20: 1 to 1:10, more preferably Ce: Zr = 5:
A range of 1 to 1: 1 is more preferred. By setting it in this range, the oxygen deficiency state can be more stably maintained.
It is desirable that the molar amount of Ce be larger than the molar amount of Zr. This makes it possible to more easily form an oxygen deficiency state and increase the amount of active oxygen.

CeO ₂ -ZrO ₂ has, as a third component, oxides of rare earth elements such as Y, La, Nd, Pr, Fe, Mn, C
1 selected from transition metal oxides such as o, Cr, Ni, and Cu
May contain seeds. By blending these third components, the oxygen-deficient state of CeO ₂ —ZrO ₂ can be more stably maintained. The content of the third component is 1 to
Preferably it is 30 mol%. If the amount is less than this range, the effect of containing the compound cannot be obtained, and if the amount exceeds 30 mol%, it may be difficult to form oxygen vacancies.

The introduction of oxygen deficiency into CeO ₂ —ZrO ₂ can be carried out by a reduction treatment using a reducing gas as described above. As a result, oxygen vacancies are mainly introduced into CeO ₂ . In this case, the composition ratio of _n in CeOn is 1.5 ≦ n
If the oxygen deficiency state is in the range of <2, more preferably 1.5 ≦ n ≦ 1.8, a particularly excellent effect on the purification of formaldehyde is exhibited. A state where the n value is less than 1.5 is considered to be difficult to form by ordinary reduction treatment, and even if it is, it is difficult to identify it under ordinary elemental analysis conditions. The oxygen deficiency state of the oxide can be measured by, for example, X-ray diffraction. From the viewpoint of catalytic activity, it is desirable that the composition ratio in the surface layer of about 100 nm from the surface of the catalyst particles be in the range of 1.5 ≦ n ≦ 1.8 rather than the inside of the catalyst particles.

The noble metals supported on CeO ₂ —ZrO ₂ include:
At least one of Pt, Pd, Rh, Au, and Ru is preferable, and Pt is particularly preferable. The supported amount of the noble metal is 1 of CeO ₂ -ZrO ₂ .
The amount is preferably 0.1 g to 20 g, more preferably 0.5 g to 5 g per 50 g. To support precious metals,
It is carried before the reduction treatment, and the reduction treatment is carried out after the noble metal is carried. When producing CeO ₂ -ZrO ₂ by a coprecipitation method or the like,
After coprecipitation in the coexistence of a noble metal, baking can be carried.

The catalyst of the present invention is prepared as a powder, which can be formed into pellets for use. In addition, a coat layer can be formed from the catalyst powder on the surface of the honeycomb substrate in the same manner as in the usual method.

[0034]

The present invention will be specifically described below with reference to examples and comparative examples.

Example 1 Ce: Zr manufactured by coprecipitation method
= 5: 1 CeO ₂ -ZrO ₂ solid solution powder is impregnated with a predetermined amount of a dinitrodiammine platinum aqueous solution of a predetermined concentration, heated after stirring, evaporated to dryness, and then calcined at 500 ° C for 3 hours in the atmosphere. Pt was loaded. The supported amount of Pt is CeO ₂ -ZrO ₂ solid solution 1
2 g for 50 g.

Next, the obtained Pt-supported CeO ₂ —ZrO ₂ solid solution powder was placed in a nitrogen stream containing 1% by volume of CO, and heated at 500 ° C.
The reduction treatment was performed for 15 minutes to introduce oxygen vacancies, thereby preparing the room temperature catalyst of Example 1.

Example 2 The conditions for the reduction treatment were 400 ° C. and 3
Example 2 was repeated in the same manner as in Example 1 except that
Was prepared at room temperature.

Example 3 The conditions for the reduction treatment were 300 ° C. and 3
Example 3 was performed in the same manner as in Example 1 except that
Was prepared at room temperature.

(Example 4) The conditions of the reduction treatment were 250 ° C. and 3
Example 4 was performed in the same manner as in Example 1 except that the time was changed.
Was prepared at room temperature.

Example 5 The conditions for the reduction treatment were 200 ° C. and 3
Example 5 was performed in the same manner as in Example 1 except that
Was prepared at room temperature.

Example 6 The conditions for the reduction treatment were 100 ° C. and 3
Example 6 was performed in the same manner as in Example 1 except that
Was prepared at room temperature.

Example 7 Example 7 was performed in the same manner as in Example 1 except that Fe ₂ O ₃ powder was used instead of the CeO ₂ —ZrO ₂ solid solution powder, and the reduction temperature was set to 300 ° C. Was prepared.

Example 8 The catalyst of Example 8 was prepared in the same manner as in Example 1 except that MnO ₂ powder was used instead of the CeO ₂ —ZrO ₂ solid solution powder, and the reduction temperature was set to 300 ° C. Was prepared.

Comparative Example 1 A catalyst of Comparative Example 1 was prepared in the same manner as in Example 1 except that Al ₂ O ₃ powder was used instead of the CeO ₂ —ZrO ₂ solid solution powder.

Comparative Example 2 Coconut shell activated carbon (specific surface area: 700 m ² / g), which is generally used as an adsorbent, was used in Comparative Example 2.
And

<Test / Evaluation> (Test Example 1) The active oxygen content of the catalysts of Examples 1 to 8 and Comparative Example 1 was measured. When measuring, first -60 ℃
Until the catalyst was cooled, while raising the temperature in an argon gas stream containing of H ₂ 1% by volume, of H ₂ consumption was detected by TCD detector. The amount of active oxygen was determined from the amount of H ₂ consumed until the temperature reached 50 ° C., and the results are shown in Table 1.

Further, 5 g of each of the catalysts of Examples 1 to 8 and Comparative Example 1 were placed in an evaluation device, and the CO concentration was 250 ppm and the O ₂ concentration was 20.
A model gas consisting of volume% and the balance N ₂ was flowed at a gas flow rate of 10 liter / min, and the CO conversion at room temperature (25 ° C.) was measured. Table 1 shows the results.

The relationship between the amount of active oxygen and the CO conversion in Table 1 was plotted, and the results are shown in FIG.

[0049]

[Table 1]

As shown in Table 1 and FIG. 1, the catalysts of the examples have an active oxygen content of 40 μmol / g or more. And the amount of active oxygen
It is clear that when the concentration is 40 μmol / g or more, the CO purifying activity at room temperature is exhibited, and it is understood that the catalytic activity at room temperature increases as the amount of active oxygen increases.

(Test Example 2) The catalyst of Example 1 and the adsorbent of Comparative Example 2 were selected, and 0.1 g of each was placed in a 5-liter closed container filled with an atmosphere containing 900 ppm of methyl mercaptan. The change over time of the methyl mercaptan concentration in the closed container was measured by gas chromatography. The results are shown in FIG.

From FIG. 2, it is apparent that the catalyst of Example 1 is superior to the adsorbent of Comparative Example 2 in removing methyl mercaptan and has a high normal-temperature purifying activity.

Test Example 3 The procedure of Test Example 2 was repeated except that the catalyst of Example 1 and the adsorbent of Comparative Example 2 were selected, and instead of methyl mercaptan, air containing 900 ppm of triethylamine or ethylene was used. The changes over time in the triethylamine concentration and the ethylene concentration were measured. Fig. 3 shows the results.
And FIG.

From FIGS. 3 and 4, it is clear that the catalyst of Example 1 is superior to the adsorbent of Comparative Example 2 in removing triethylamine and ethylene, and has a high normal-temperature purification activity. I understand.

[0055]

According to the room temperature catalyst of the present invention, 50
Environmentally hazardous substances such as CO, amines and formaldehyde can be efficiently decomposed and removed at room temperature of not more than ℃.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the amount of active oxygen and the CO conversion at room temperature of catalysts of Examples and Comparative Examples of the present invention.

FIG. 2 is a graph showing the change over time of the methyl mercaptan concentration at room temperature in a closed container containing the catalyst of Example 1 and the adsorbent of Comparative Example 2.

FIG. 3 is a graph showing a time-dependent change in the concentration of triethylamine at room temperature in a closed container containing the catalyst of Example 1 and the adsorbent of Comparative Example 2.

FIG. 4 is a graph showing a time-dependent change in ethylene concentration at room temperature in a closed container containing the catalyst of Example 1 and the adsorbent of Comparative Example 2.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B01J 37/16 B01D 53/36 HE B01J 23/64 104A (72) Inventor Kenichiro Suzuki Nagakute, Aichi-gun, Aichi Prefecture 41 in the Toyota Central Research Institute, Inc. (72) Inventor: Satoshi Sasaki 41 in the Ochicho, Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture Toyota Central Research Institute, Inc. (72) Inventor Morikawa Akira 41, Chukku Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture Inside Toyota Central Research Laboratory, Inc. (72) Inventor Masataka Sugiura 41-41, Yokomichi, Nagakute-cho, Aichi-gun, Aichi-gun (Reference) 4C080 AA07 BB02 CC01 HH01 JJ01 KK08 LL02 MM02 QQ03 4D048 AA01 AA05 AA08 AA13 AA18 AA19 AB01 AB03 BA08X BA08Y BA18Y BA19X BA19Y BA28X BA28Y BA30X BA30Y BA31Y BA32A BAA ABABAABABA BAY BAA BC43A BC43B BC44A BC51A BC51B BC55A BC58A BC59A BC62A BC62B BC66A BC66B BC67A BC68A BC69A BC75B CA10 CA11 CA14 CA15 CA17 DA05 FA02 FB14 FB44

Claims (5)

[Claims] An active oxygen which is active at 50 ° C. or less is 40 μmol /
A room temperature catalyst comprising at least g. 2. The room-temperature catalyst according to claim 1, wherein the noble metal is supported on an oxide into which oxygen deficiency has been introduced by the reduction treatment. 3. The room temperature catalyst according to claim 2, wherein the oxide is at least one selected from transition metal oxides and rare earth oxides. 4. The transition metal oxide is zirconium,
Iron, manganese, cobalt, nickel, copper, chromium, at least one selected from oxides of molybdenum and niobium, the rare earth oxide is at least one selected from oxides of cerium, yttrium, neodymium, praseodymium and samarium. The room temperature catalyst according to claim 3. 5. The room temperature catalyst according to claim 2, comprising cerium oxide and zirconium oxide, wherein at least a part of the cerium oxide exists in a state of oxygen deficiency.