Patent Application
20120220451
The present invention relates to an oxidation catalyst, an adsorbent, and a material for purging harmful substances.
A variety of catalysts and adsorbents are used in order to remove harmful substances. For example, in Patent Literature 1, it is described that ammonia, which is a bad smell compound having a strong pungent odor, can be decomposed by a photocatalyst carrying a platinum compound.
As described above, the catalyst that oxidizes harmful substances to remove the harmful substances often carries Pt in order to keep the oxidation activity of the catalyst high. However, Pt is very expensive, deposits of Pt are small, and resource is limited; accordingly, its stable supply for a long period of time may not be achieved.
Moreover, examples of an adsorbent that adsorbs and removes harmful substances include activated carbon; however, in order to produce activated carbon, an activating step to form a larger surface area is necessary after a carbonizing step.
Then, an object of the present invention is to provide an oxidation catalyst that can oxidize harmful substances without using Pt. Another object of the present invention is to provide an adsorbent that can adsorb harmful substances without being subjected to an activating step as in the case of activated carbon, and a material for purging harmful substances that can purge harmful substances.
The present invention provides an oxidation catalyst comprising a carbon material prepared by calcining the following (i) or
(ii), the oxidation catalyst oxidizing at least one of target substances (compounds to be oxidized) selected from the group consisting of NO, CO, NH3, and aromatic hydrocarbons:
(i) a transition metal compound and a nitrogen-containing organic substance
(ii) a transition metal compound, a nitrogen-containing organic substance, and a carbon compound not containing nitrogen.
As the carbon material, in Japanese Patent Application Laid-Open Publication No. 2004-362802, it is shown that carbon alloy fine particles prepared by heat treating and grinding a phthalocyanine-containing furan resin can be used as a base material for an electrode for a fuel cell; however, it has newly been found that a carbon material prepared by calcining (i) or (ii) above has an oxidation action and is useful as an oxidation catalyst for NO, CO, NH3, or an aromatic hydrocarbon.
It is preferable that the oxidation catalyst oxidizes the target substance at a temperature of not less than 10° C.
In the oxidation catalyst, an activity at a low temperature is high, and even in a low temperature environment of not less than 10° C., the oxidation catalyst can oxidize NO, CO, NH3, or an aromatic hydrocarbon as the target substance.
Moreover, it is preferable that the oxidation catalyst oxidizes the aromatic hydrocarbons of the target substances above at a temperature of not less than 200° C.
At a temperature of not less than 200° C., the activity of the oxidation catalyst is improved, and the ability to oxidize the aromatic hydrocarbons becomes significantly higher.
In the oxidation catalyst, at least one load material selected from the group consisting of Pd, Rh, Ru, Ni, Co, Fe, Ce, Cu, Ti, Zr, Sn, V, Nb, Ta, Cr, Mo, W, Bi, Mn, and compounds thereof may be supported on the carbon material.
By carrying the load material, the activity of the oxidation catalyst is further improved, and the oxidation ability particularly for the aromatic hydrocarbons or the like is extremely good.
Moreover, the present invention provides an adsorbent comprising a carbon material prepared by calcining the following (i) or
(ii), the adsorbent adsorbing at least one target substance (compound to be adsorbed) selected from the group consisting of NO, NO2, formaldehyde, and acetaldehyde:
(i) a transition metal compound and a nitrogen-containing organic substance
(ii) a transition metal compound, a nitrogen-containing organic substance, and a carbon compound not containing nitrogen.
As described above, the carbon material has not only an oxidation action but also an adsorbing action, and is useful as an adsorbent for NO, NO2, formaldehyde, or acetaldehyde.
It is preferable that the adsorbent adsorbs the target substance at a temperature of not less than 10° C.
In the adsorbent, the adsorbing ability at a low temperature is high, and even in a low temperature environment of not less than 10° C., the adsorbent can adsorb NO, NO2, formaldehyde, or acetaldehyde as the target substance.
The present invention also provides a material for purging harmful substances comprising at least one of the oxidation catalyst and the adsorbent described above. In the present invention, the harmful substances include bad smell compounds. The oxidation catalyst and adsorbent according to the present invention are used as the material for purging harmful substances; thereby, the harmful substances can be purged with high efficiency.
According to the present invention, an oxidation catalyst that can oxidize harmful substances without using Pt can be provided. Moreover, an adsorbent that can adsorb harmful substances without being subjected to an activating step as in the case of activated carbon. Thereby, a purging material that can remove harmful substances can be provided.
Hereinafter, an embodiment of the present invention will be described. A carbon material that forms the oxidation catalyst or adsorbent according to the present embodiment is prepared by calcining the following (i) or (ii). Such a carbon material is a carbon alloy material in which the carbon skeleton is doped with nitrogen atoms, and a transition metal element is contained, and the activity is high.
(i) A transition metal compound and a nitrogen-containing organic substance
(ii) A transition metal compound, a nitrogen-containing organic substance, and a carbon compound not containing nitrogen
In production of the carbon material, calcining is performed using the (i) as a raw material in the case where the nitrogen-containing organic substance is not only a nitrogen source, but also sufficiently contains carbon as a carbon source; in the case where the carbon source is further needed, the (ii) is used as a raw material.
Here, the carbon compounds not containing nitrogen are not particularly limited; for example, celluloses, carboxymethyl celluloses, polyvinyl alcohol, polyacrylic acid, polyfurfuryl alcohol, furan resins, phenol resins, phenol formaldehyde resins, epoxy resins, pitch, general-purpose plastics such as polyvinylidene chloride and polymethacrylic acid, engineering plastics, super engineering plastics such as polysulfones, ionomer resins, or the like can be used. Inorganic substances such as coal can also be used. These compounds can be used alone, or two or more thereof can be used in combination. Among them, polymethacrylic acid is preferable from the viewpoint of cost and carbonization yield.
Moreover, as the nitrogen-containing organic substance, for example, pyrrole compounds such as polypyrrole, imide compounds such as a phthalocyanine complex, polyimides, and polycarbodiimide, amide compounds such as polyamides, imidazole compounds such as polyimidazole, lignin, biomass, poly(vinylpyridine), melamine resins, urea resins, chelate resins, humic acid, polyaniline, polyacrylonitrile, ε-caprolactam, protein, and the like can be used; among them, ε-caprolactam is preferable.
As a transition metal, elements that belong to the 4th Row of Group 3 to Group 12 on the periodic table can be used, and for example, cobalt (Co), iron (Fe), manganese (Mn), nickel (Ni), copper (Cu), titanium (Ti), chromium (Cr), and zinc (Zn) are preferable; as the transition metal compound, salts, hydroxides, oxides, nitrides, sulfides, carbides, complexes, and polymer complexes of the transition metals can be used, and among these, particularly, cobalt chloride, cobalt oxide, cobalt phthalocyanine, iron chloride, iron oxide, and iron phthalocyanine are preferable. Co, Fe, Mn, Ni, Cu, Ti, Cr, Zn, and compounds thereof improve the catalyst activity of the carbon catalyst.
The (i) or (ii) may be dissolved in a solvent and mixed to prepare a precursor composition. The solvent is not particularly limited as long as the solvent can dissolve these carbon compound not containing nitrogen, nitrogen-containing organic substance, and transition metal compound; for example, dimethylformamide, dimethylacetamide, dimethylsulfoxide, N-methylpyrrolidone, cyclohexanone, methyl ethyl ketone, and the like can be used.
It is also preferable that a carbon additive such as carbon black is added to the mixture of the (i) or (ii). By adding the carbon additive, the activity of the carbon material can be improved.
When the (i) or (ii) is calcined, in order to prevent contamination with impurities of the carbon material to be produced, it is preferable that calcination is performed in an inert atmosphere purged by nitrogen or the like.
Moreover, the produced carbon material can be powdered by a ball mill or the like, and formed into fine particles. Further, using sieves having different sizes of opening, coarse products are removed to provide uniform fine particles; thereby, the surface area of the carbon material is increased, and the activities as the oxidation catalyst, the adsorbent, and the material for purging harmful substances are improved.
It is preferable that the proportion of the carbon compound not containing nitrogen with respect to the nitrogen-containing organic substance to be blended is such that the amount of nitrogen atoms in the carbon material after calcining is not less than 0.5% by mass and not more than 20% by mass, and more preferably not less than 5% by mass and not more than 20% by mass based on the total mass of the carbon material.
The carbonization treatment of the (i), (ii), or precursor composition prepared by dissolving and mixing these in the solvent is performed preferably at 800 to 1000° C. for 0.5 to 5 hours, and particularly preferably at 900° C. to 1000° C. for 0.5 to 2 hours.
Moreover, the carbon material may be doped with boron atoms and/or a chalcogen compound. In the carbon material doped with boron atoms and/or a chalcogen compound, the activity is improved compared to the carbon material doped with nitrogen atoms. In order for the carbon material to be doped with boron atoms and/or a chalcogen compound, for example, boric acid, boric acid salt, halogenated boric acid salt, or the like as a boron-containing organic substance and an oxide, a sulfide or the like as the chalcogen compound may be added to the mixture of the (i) or (ii).
The oxidation catalyst can oxidize NO even at room temperature. The temperature for oxidizing NO is preferably not less than 10° C., and if the temperature is not less than 10° C. and not more than 25° C., the conversion rate is improved.
Moreover, at a temperature around 10° C., the oxidation catalyst can oxidize CO. The temperature to oxidize CO is preferably not less than 10° C.; at a temperature of not less than 100° C., the activity is improved to improve the conversion rate of CO to CO2; at a temperature of not less than 150° C., the conversion rate is further improved; at a temperature of not less than 200° C., the conversion rate reaches approximately 100%, and CO can be purged almost completely.
The oxidation catalyst can also oxidize NH3 at around 10° C. The temperature to oxidize NH3 is preferably not less than 10° C.; at a temperature of not less than 100° C., the activity is improved to improve the conversion rate of NH3; at a temperature of not less than 200° C., the conversion rate is further improved; at a temperature of not less than 400° C., the conversion rate reaches approximately 100%, and NH3 can be purged almost completely.
Moreover, the oxidation catalyst can oxidize aromatic hydrocarbons such as benzene, toluene, and xylene in an oxidation atmosphere of preferably not less than 10° C., and more preferably not less than 200° C. At a temperature of not less than 250° C., the conversion rate of the aromatic hydrocarbon is improved; at a temperature of not less than 300° C., the conversion rate is further improved. At a temperature of not less than 350° C., the conversion rate reaches approximately 100%, and the hydrocarbon can be purged almost completely.
The relationship between the temperature and the conversion rate in oxidation of NO, CO, NH3, or an aromatic hydrocarbon described above changes depending on the amount of the catalyst. Namely, by adjusting the amount of the catalyst, the oxidation ability can be improved, and the conversion rate can be improved at a lower temperature. For example, about CO, by adjusting the amount of the oxidation catalyst including the carbon material, CO can be oxidized and removed at normal temperature almost completely.
Moreover, the oxidation catalyst can oxidize and purge harmful substances other than NO, CO, NH3, or an aromatic hydrocarbon described above, and also can oxidize hydrogen sulfide (H2S) and mercaptan compounds, for example. About hydrogen sulfide, it is thought that sulfur produced after oxidation adsorbs to the surface of the carbon material; however, for example, by replacing the carbon material after a predetermined period of time, the carbon material can be used as the oxidation catalyst.
Further, the catalyst is not used not only for purging of the harmful substances, and also can purge NO, CO, NH3, an aromatic hydrocarbon, or the like contained in other gas. For example, the catalyst is suitable for application as an oxidation catalyst that oxidizes a small amount of CO contained in hydrogen obtained by reforming natural gas or the like as a fuel for a fuel cell while the relevant oxygen is supplied; the oxidation catalyst is disposed in a CO removing apparatus for supplying gas to the fuel electrode of the fuel cell, or the oxidation catalyst is mixed with a fuel electrode catalyst of the fuel cell and used for the fuel electrode portion, thereby to be able to oxidize CO in hydrogen to CO2 and prevent poisoning of an electrode catalyst.
In the oxidation catalyst, at least one load material selected from the group consisting of Pd, Rh, Ru, Ni, Co, Fe, Ce, Cu, Ti, Zr, Sn, V, Nb, Ta, Cr, Mo, W, Bi, Mn, and compounds thereof is supported on the carbon material; thereby, the oxidation activity of the target substance (particularly, aromatic hydrocarbons) can be improved. Particularly, if the load material is Pd or Rh, the oxidation activity becomes high; accordingly, Pd or Rh is preferable. Based on the mass of the carbon material, Pd or Rh is supported on the carbon material in a proportion of preferably 0.01 to 15% by mass, more preferably 0.1 to 10% by mass, and particularly preferably 0.5 to 2% by mass.
Here, in the case where Pd or Rh is supported on the carbon material, first, an aqueous solution of PdCl2 containing Pd in a desired amount to be supported or Rh(NO3)3 containing Rh in a desired amount to be supported is prepared. The carbon material is mixed with the aqueous solution at room temperature, and the resultant is stirred for 1 to 5 hours. The aqueous solution is kept at 70 to 100° C. for 10 to 20 hours, and the moisture content is vaporized. The carbon material thus obtained is sufficiently polished; thereby, a carbon material carrying Pd or Rh can be obtained. Moreover, in the case of the metal atom other than Pd and Rh, i.e., Ni or the like, an aqueous solution is prepared and mixed with the carbon material in the same manner; thereby, the metal atom can be supported on the carbon material. The amount of the metal atom or the like to be supported can be determined by simple calculation from the amount of a charged sample; in the case of analyzing with high accuracy, an ICP optical emission spectrometer or the like can be used.
Moreover, as described above, the carbon material also functions as the adsorbent that adsorbs harmful substances, and can adsorb, for example, NOx (NO, NO2), formaldehyde, and acetaldehyde to purge the harmful substances. Particularly, the carbon material can adsorb aldehyde compounds such as formaldehyde and acetaldehyde in a higher concentration even at room temperature not less than 10° C.; at a temperature of not less than 10° C. and not more than 25° C., the adsorbing properties are further improved. In order to check that formaldehyde and acetaldehyde are adsorbed by the carbon material, for example, the carbon material and gas of formaldehyde or acetaldehyde are sealed within a commercially available Tedlar Bag, and after a predetermined period of time passes, the concentration of the gas is measured by a gas detecting tube; thereby, quantitative analysis can be performed.
Further, the material for purging harmful substances in the present embodiment includes at least one of the oxidation catalyst and the adsorbent, and can oxidize NO, CO, NH3, or an aromatic hydrocarbon or adsorb NOx (NO, NO2), formaldehyde, acetaldehyde, and the like to purge the harmful substances.
The ability of the oxidation catalyst can be evaluated as a conversion rate of each gas by the following calculation expressions.
Conversion rate of NO=(NO mol flow rate at inlet —NO mol flow rate at outlet)/(NO mol flow rate at inlet)×100%
Conversion rate of CO=(CO mol flow rate at inlet —CO mol flow rate at outlet)/(CO mol flow rate at inlet)×100% Conversion rate of NH3═(NH3 mol flow rate at inlet —NH3 mol flow rate at outlet)/(NH3 mol flow rate at inlet)×100%
Conversion rate of aromatic hydrocarbon=(mol flow rate of aromatic hydrocarbon at inlet−mol flow rate of aromatic hydrocarbon at outlet)/(mol flow rate of aromatic hydrocarbon at inlet)×100% Carbon balance=(total mol flow rate of carbon at outlet−total mol flow rate of carbon at inlet)/(total mol flow rate of carbon at inlet)×100%
Yield of NO2=(NO2 mol flow rate at outlet)/(NO mol flow rate at inlet+NO2 mol flow rate at inlet)×100%
The conversion rate indicates how much NO, CO, NH3, or an aromatic hydrocarbon is oxidized by the oxidation catalyst; a higher conversion rate indicates that NO, CO, NH3, or an aromatic hydrocarbon is more oxidized; if the conversion rate is 100%, it indicates that NO, CO, NH3, or an aromatic hydrocarbon is completely oxidized.
Hereinafter, the present invention will be described according to Examples, but the present invention will not be limited to these Examples.
The carbon material used as the oxidation catalyst or adsorbent in the present Examples was prepared as follows.
First, 1.5 g of polymethacrylic acid was dissolved in 20 g of dimethylformamide. Subsequently, 1.5 g of cobalt oxide (made by Nisshinbo Holdings Inc.), 1.5 g of g-caprolactam (made by Tokyo Chemical Industry Co., Ltd.), and 1.5 g of an n-butylated melamine resin (product name: U-VAN 21R, Mitsui Chemicals, Inc.) were stirred for 6 hours to obtain a mixed solution. Thus, a precursor composition was obtained. Cobalt oxide was produced according to the method described in WO 2007/049549 by electrodialysis treatment.
Next, the carbonization treatment on the precursor composition was performed. Namely, the precursor composition was placed in a quartz tube, and the quartz tube was nitrogen purged for 50 minutes by a paraboloidal reflection type infrared gold image furnace. Then, heating was started, and the temperature of the gold image furnace was raised at a temperature rising rate of 1° C./min from room temperature to 900° C. Subsequently, the quartz tube was kept at 900° C. for 1 hour. Thus, a carbon material produced by carbonizing the precursor composition was obtained.
Further, the powdering treatment of the carbon material was performed. Namely, silicon nitride balls having a diameter of 1.5 cm was set within a planetary ball mill (product name: P-7, Fritsch Japan Co., Ltd.), and the carbon material obtained by the carbonization treatment was powdered at a rotational speed of 800 rpm for 60 minutes. The powdered carbon material was extracted, and classified by a sieve having an opening of 46 μm.
The obtained carbon material was filled into the center of the quartz reaction tube having an inner diameter of 6 mm, and 0.5 g of quartz sand was filled into each side of the carbon material layer for distribution of the gas.
In the analysis of the gas, quantitative analysis of O2, CO, N2O, CO2, a hydrocarbon, an aromatic hydrocarbon such as toluene, and the like was performed by a gas chromatograph (product name: GC-14B, made by Shimadzu Corporation). Moreover, in NOR, NO, NO2, CO, SO2, and the like, quantitative analysis was performed by an NO analyzer (product name: PG-250, made by HORIBA, Ltd.). Moreover, in NH3, quantitative analysis was performed by an UV-visible spectrophotometer (product name: V-530, made by JASCO Corporation).
100 mg of the carbon material was placed in the reaction tube, the gas containing NO at 1000 ppm, O2 at 15%, and He was flowed into the reaction tube at 150 mL/min for 3 hours under an environment of room temperature of 25° C., and the concentrations of NO, NO2, and the like were measured. Subsequently, He was flowed at 150 mL/min at 25° C. until the concentration of NO returned to a level of zero, thereby to clean the reaction tube. Subsequently, the temperature was raised at 10° C./min from 30° C. to 600° C., and He was flowed at 150 ml/min. The result is shown in
As shown in
100 mg of the carbon material was placed in the reaction tube, the gas containing CO at 2500 ppm, O2 at 15%, and He was flowed into the reaction tube (150 mL/min, space velocity (F/w): 90000 mL/(g·h)), and the conversion rate of CO was measured. The result is shown in
As shown in
0.1 g of the carbon material was placed in the reaction tube, the gas containing NH3 at 2000 ppm/air was flowed into the reaction tube (200 mL/min, F/w: 120000 mL/(g·h)), and the conversion rate of NH3 was measured. The result is shown in
As shown in
50 mg of the carbon material was placed in the reaction tube, the gas comprising toluene of 500 ppm/air was flowed into the reaction tube (30 mL/min, F/w: 36000 mL/(g·h)), and the conversion rate of toluene was measured. The result is shown in
As shown in
30 mg of the carbon material was accommodated in a 3-L Tedlar Bag under an environment of 27° C., and the air in which the concentration of acetaldehyde was 20 ppm was injected into the Tedlar Bag. After 24 hours, the concentration of acetaldehyde within the Tedlar Bag was measured using a gas detecting tube (made by GASTEC Corporation); the concentration of acetaldehyde was 0 ppm, and it was recognized that acetaldehyde within the Tedlar Bag was adsorbed by the carbon material, and removed.
Measurement was performed in the same manner as in Example 5 except that the air in which the concentration of acetaldehyde was 20 ppm was replaced by the air in which the concentration of formaldehyde was 50 ppm; the concentration of formaldehyde was 0 ppm after 24 hours, and it was recognized that formaldehyde within the Tedlar Bag was adsorbed by the carbon material, and removed.
In the same manner as in Example 1, using a commercially available alumina material (made by Soekawa Chemical Co., Ltd.), the concentrations of NO, NO2, and the like and adsorption and desorption behaviors of NOx were measured. As shown in
In the same manner as in Example 1, using a Pt/alumina material carrying 2.5% by mass of platinum, the concentrations of NO, NO2, and the like and adsorption and desorption behaviors of NOx were measured. As shown in
In the same manner as in Example 1, using an Ag/alumina material carrying 1.7% by mass of Ag, the concentrations of NO, NO2, and the like and adsorption and desorption behaviors of NOx were measured. In the Ag/alumina material, NO2 was only slightly oxidized. Moreover, as shown in
In the same manner as in Example 1, the concentrations of NO, NO2, and the like and adsorption and desorption behaviors of NOx in the case where the purging material was not used were measured. In the case where the purging material was not used, NO2 was only slightly oxidized. The yield of NO2 was 5.0% (
In the same manner as in Example 2, using a Pt/alumina material carrying 2.5% by mass of platinum, the conversion rate of CO was measured. As shown in
In the same manner as in Example 3, using a Pt/alumina material carrying 1.8% by mass of platinum, the conversion rate of NH3 was measured. As shown in
Measurement was performed in the same manner as in Example 5 except that instead of the carbon material, steam activated carbon (product name: Shirasagi TC, made by Japan EnviroChemicals, Ltd.) was used; the amount of residual acetaldehyde was 10 ppm, and acetaldehyde could not be completely removed.
Measurement was performed in the same manner as in Example 6 except that instead of the carbon material, steam activated carbon (product name: Shirasagi TC, made by Japan EnviroChemicals, Ltd.) was used; the amount of residual formaldehyde was 30 ppm, and formaldehyde could not be completely removed.
According to the present invention, an oxidation catalyst that can oxidize harmful substances without using Pt can be provided. Moreover, an adsorbent that can adsorb harmful substances without being subjected to an activating step as in the case of activated carbon can be provided. Thereby, a purging material that can remove harmful substances can be provided.
1 . . . reference gas cylinder, 2 . . . mass flow controller, 3 . . . reaction tube, 4 . . . electric heating furnace, 5 . . . cooler, 6 . . . gas analyzing apparatus, 10 . . . oxidation catalyst, 11 . . . quartz sand, 12 . . . quartz wool, 13 . . . thermocouple.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-158819 | Jul 2009 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/059125 | 5/28/2010 | WO | 00 | 4/23/2012 |
