Process for the purification of a gas using an electrically heated MnO2 catalyst

Abstract: The catalyst of the invention can be heated directly by electric current supply and used efficiently for a long period of time. The catalyst can be used in various application fields including catalytic oxidation, ozone decomposition, etc.

Description: The present invention concerns a method for the purification of a gas that can be used in various fields including catalytic oxidation, as well as deodorization or ozone decomposition. When a catalyst, e.g, for catalytic oxidation is used, the catalyst is heated generally in view of the reaction temperature. However, heating of the catalyst requires an additional installation of a heating source such as a gas burner or an electric heater. This is not only economically disadvantageous in view of the installation cost but also results in a drawback in view of a heat efficiency since heating by the heating source is usually applied by indirect heating. Further, since a space for the heating source has to be secured, no compact structure can be attained. In addition, indirect heating of the catalyst as described above leads to the loss of heat energy, as well as it inevitably brings about unevenness in the heating. On the other hand, a catalyst for ozone decomposition or a catalyst for ozone deodorization is usually operated at a normal temperature without heating but the catalytic function can not fully be utilized sometimes depending on the working conditions. For instance, the catalyst activity can not fully be attained due to the effect of moisture if an object to be treated is a gas at high humidity. It is considered that the active sites at the surface of the catalyst are covered with moisture to reduce the chance of contact between the gas to be treated and the catalyst. Accordingly, it is difficult to maintain the catalyst set to a reaction device at a high catalytic activity for a long period of time in such a case. For avoiding such a disadvantage, there may be considered to pass a gas at high humidity into the reaction device after previously heating the gas, but this requires installation of an additional heating source to bring about a problem similar to that in the catalyst used for catalytic oxidation. EP-A-0 275 620 discloses a catalyst for the purification of a gas containing ozone or a component of offensive odors comprising an inorganic support comprising TiO₂, SiO₂ and/or ZrO₂ and one or more additional metals selected from Mn, Fe, Co, Ni, Ag, Pt, Pd and Rh. The catalyst can be prepared by molding. It is not disclosed in this document that any of the used catalysts can be electroconductive and the catalysts are usually not heated. US-A-4,350,613 describes a catalyst for purifying an exhaust gas which comprises a carrier substantially composed of calcium aluminate and 5 to 90 weight percent of titanium oxide based on the amount of carrier and a catalytic component of a platinum group metal or a metal oxide capable of oxidizing reductive gases into innoxious ones. If the metal oxide is used, the amount of metal oxide is 0.1 to 10 weight percent. The metal oxide can be an oxide of Fe, Co, Ni, Cr, Mo, Sn, Pb, Mn, Cu, Ag, La, Zn, Cd or V or mixtures thereof. BE-A-881 318 teaches the catalytic decomposition of ozone and the neutralisation of electric current resulting from this process. If the catalyst of the ozone decomposer is conductive, the catalyst itself can ensure the discharge and no separate discharger is necessary. CH-A-332 799 discloses a catalyst characterized by a thin film of a catalytically active inorganic oxide which is coated on an electric resistance. In CH-A-332 799 a metal is used as electrical resistance, usually a wire. The electrical resistance can be heated by electrical current, thereby also heating the catalyst. OBJECT OF INVENTION The present invention has been accomplished in view of the foregoing situations and the object thereof is to provide a useful method of using a catalyst which can be heated easily in a state of use, can provide the catalytic activity effectively and stably for a long period of time in such a way of use, and does not suffer from any particular disadvantage in view of cost and space, irrespective of that the catalyst is used under heating. The method should be useful in various application fields such as catalytic oxidation, deodorization and ozone decomposition. SUMMARY OF THE INVENTION The foregoing object can be attained by a method for purification a gas, comprising: introducing the gas to an electroconductive catalyst being directly heated by applying electric current thereto, said catalyst being a member consisting of (A) MnO₂ and (B) at least one or more of elements selected from the group consisting of Fe, Co, Ni, Cu, Ag, Au, Pt, Pd and Rh, and which is carried on (C) an inorganic support and is molded, and which contains from 25 to 60% by weight of (A), from 0 to 60% by weight, as oxide, in the case of Fe, Co, Ni, Cu and Ag and from 0 to 10% by weight, as metal element, in the case of Au, Pt, Pd and Rh of (B) and from 40 to 75% by weight of (C), and whereby (A), (B) and (C) together are not more than 100%. The catalysts use inorganic supports selected from at least one of Ti - Si binary composite oxide, Ti - Zr binary composite oxide and Ti - Si - Zr ternary composite oxide The catalysts used in the present invention have excellent deodorizing function and effective deodorizing method can be attained by using them. As the deodorizing method, it is proposed such a constitution of introduction a gas containing malodor components to a catalyst while directly heating the catalyst by electric current supply and than removing the malodor components by catalytic oxidation. The heating temperature in this case is preferably set to 100 - 400°C. It is not always necessary that the direct heating by electric current supply is conducted continuously but it may be heated intermittently. By the way, there has also been known a deodorizing method of introducing malodor components contained in a gas into ozone and then removing them by catalytic oxidizing decomposition under the presence of a catalyst, and the catalysts used in the present invention can also be used as such a ozone deodorizing catalyst. As the deodorizing method, it is proposed such a constitution of using the catalysts and conducting deodorization while regenerating the catalyst by directly heating under electric current supply. The heating temperature is preferably about from 100 to 400°C like that in the deodorizing method described previously. On the other hand, the catalysts used in the present invention can also be used as the ozone decomposing catalyst and ozone can effectively be decomposed catalytically by introducing an ozone-containing gas to the catalysts while directly heating the catalysts by electric current supply. The heating temperature is preferably about from 50 to 400°C. Further, the catalysts used in the present invention can also be applied to a method of treating a gas containing components to be adsorbed. For such a method, it is proposed an adsorption-burning decomposition method for treating a gas containing components to be adsorbed which comprises using the catalyst, disposing a catalyst, an adsorbent and a catalyst in this order from the upstream in the flowing direction of the gas, and alternately repeating a step of introducing the gas containing components to be adsorbed into the adsorbent thereby adsorbing the components to be adsorbed to the adsorbent or the adsorbent and the catalyst and a step of elevating the temperature of the adsorbent and the catalyst and applying a catalytic effect to the components to be adsorbed which are desorbed from the adsorbent. In particular, the catalyst also has an adsorbing function, and an adsorption-burning decomposition method as described below can be proposed by utilizing this property. That is, a method of using the catalyst according to the present invention is an adsorption-burning decomposion method of adsorbing components to be adsorbed to a catalyst having an adsorbing function, desorbing the adsorbed components by heating and burning to decomposition them under the catalytic effect, wherein the catalyst is disposed such that the flowing direction of the gas is vertical relative thereto, the gas containing components to be adsorbed is introduced from below to said catalyst by means of a blower when adsorbing step is conducted for the components to be adsorbed, while the temperature of the catalyst is elevated and the operation of the blower is stopped or the blowing is reduced by decreasing the number of rotation for the blower when the components to be adsorbed are desorbed and decomposed by burning, thereby preventing the unburnt components to be adsorbed from being released to the outside. DESCRIPTION OF INVENTION The present inventors have made a study from various approaches in view of developing a catalyst that can be used efficiently for a long period of time. As a result, it has been found that a catalyst prepared by integrally molding MnO₂ and other catalytic ingredients (see below) can provide a stable catalytic treating effect for a long period of time with no requirement for disposing an additional heating source. The present inventors have further made a study for improving the catalytic function of the above catalyst. As a result, it has been found that more excellent catalytic function can be provided by incorporating, in addition to MnO₂, one or more of catalytic ingredients selected from the group consisting of Fe, Co, Ni, Cu, Ag, Au, Pt, Pd and Rh. When MnO₂ and the catalytic ingredients are molded into a catalyst, since molding is difficult with MnO₂ alone or a mixture of MnO₂ and other catalyst ingredient alone, a binder such as a silica sol or alumina sol or other molding aids may usually be used. Further, it has also been found that the moldability upon molding is further improved by integrally molding MnO₂ and the catalyst ingredient as described above while being carried on an inorganic support. While most of metal oxides are non-electroconductive material, MnO₂ is conductive having a specific resistivity of about 0.1 ohm.cm. In addition, MnO₂ is useful as a catalyst having a function of promoting chemical reactions such as catalystic oxidation or ozone decomposition. In the catalyst described above, MnO₂ and the other catalyst ingredients are integrally molded and used as the catalyst while taking notice on the electroconductive property of MnO₂ and with an aim of providing excellent catalytic function. Since the catalyst used in the present invention does not use carbon or graphite as an electroconductive material, it is free from ignition danger and has a merit of excellent ozone resistance. In addition, the present invention provides a catalyst blended with the catalyst ingredients as described above and such a catalyst can improve the catalytic function remarkably as compared with that of MnO₂ alone. The inorganic compound usable as the inorganic support in the present invention includes usual compounds such as alumina, silica, silica-alumina, titania, zirconia, zeolite, diatomaceous earth and magnesium silicate, which may be used optionally alone or as a mixture of two or more of them to make the moldability upon preparation satisfactory. In particular, a binary composite oxide comprising Ti and Si, a binary composite oxide comprising Ti and Zr and a ternary composite oxide comprising Ti, Si and Zr are preferred. That is, these composite oxides have satisfactory moldability and excellent function as a support, as well as they are excellent in (1) adsorbing performance, (2) sulfur resistance, (3) ozone decomposing function, etc. and can provide the catalyst with such performances (catalyst V, V'). The composition ratio for the MnO₂ (A), the catalyst ingredient (B) and the inorganic support (C) can be determined depending on the desired electroconductivity and the catalytic function. It is from 25 to 60 % by weight for (A), up to 60 % by weight, as oxide, in the case of Co, Ni, Cu and Ag and up to 10 % by weight, as metal element, in the case of Au, Pt, Pd and Rh for (B) and from 40 to 75 % by weight of (C). The catalyst used in the present invention has to be molded integrally since direct heating by electric current supply is necessary but there is no particular restriction to the shape. However, in view of the catalytic efficiency between the material and catalyst, pressure loss, etc., a honeycomb shape is optimum having a geometrical surface area which is increased relative to the space for disposition the catalyst. As a specific means for the direct heating of the catalyst by electric current supply, there can be mentioned, typically, such a constitution of coating an electroconductive paste (for instance, silver paste) on both sides of the catalyst, bonding a metal plate to each of the coated sides and then connecting a lead wire to the metal plate for electric current supply. When the catalyst used in the present invention is used, the time for direct heating by electric current supply may be determined depending on the situation of use and it is heated continuously or intermittently in accordance with the situation. For instance, in a case of using the catalyst for the catalytic oxidation, the catalyst is continuously heated by electric current supply. In a case of using under a normal temperature and at high humidity, it is possible to conduct repeating procedures of using the catalyst at a normal temperature without heating for a period in which the activity is not reduced, applying heating by electric current thereby evaporating to remove moisture adsorbed an the surface of the catalyst at a time when the activity is reduced by the adsorbed moisture and then interrupting the heating by electric current supply at the instance when the regeneration of the catalyst is completed and thereafter using it under the normal temperature again. The method of controlling the temperature upon heating by electric current supply for the catalyst may properly be determined depending on the purpose of use for the catalyst. There can be mentioned a method, for example, of heating by electric current supply while setting the voltage or current constant without using a temperature sensor, or a method of acurately controlling the range for the heating temperature by applying ON-OFF control by a temperature sensor, etc. However, since the resistance value of the catalyst is lowered as the temperature is elevated, it is necessary, upon temperature control, that the current supply conditions for voltage, current, etc. have to be set with reference to the resistance value at the working temperature. When the catalyst according to the present invention is integrally molded, it can be molded easily by using a heat resistant inorganic binder. As such an inorganic binder, there can be mentioned, for example, alumina sol or silica sol. As a method of preparing a catalyst in which the catalyst ingredients described above added to MnO₂, there can be mentioned the following method. (1) A method off adding an inorganic binder such as an alumina sol or silica sol and a molding aid to a powder of MnO₂, mixing and kneading them while adding an appropriate amount of water, molding them into a honeycomb-like shape by an extrusion molding machine, drying and sintering the molding product to obtain a MnO₂ molding product, which is then impregnated with an aqueous solution of a metal salt as the catalyst ingredient described above, supporting the catalyst ingredient thereon and then drying and calcining them. (2) A method of adding an aqueous solution of the metal salt of the catalyst ingredient or the oxide of the catalyst ingredient together with a molding aid to a powder of MnO₂ and then kneading and molding them. Further, for the preparation of the catalyst used in the present invention, there can be mentioned the following methods: (A) A method of adding a molding aid to a powder of an inorganic support, mixing and kneading them while adding an appropriate amount of water, molding them into a honeycomb shape by an extrusion molding machine, drying and calcining them to obtain an inorganic support molding product, impregnating the molding product with an aqueous solution of manganese nitrate and then drying and calcining them to support MnO₂ thereon, or further impregnating an aqueous solution of the metal salt as the catalyst ingredient thereby supporting the catalyst ingredient and then drying and calcining them. (B) A method of adding an aqueous solution of manganese nitrate or a powder of MnO₂ to a powder of an inorganic support and then kneading and molding them, or further impregnating the molding product with an aqueous solution of a metal salt for support and then drying and calcining them. (C) A method of adding an aqueous solution of a metal salt or the oxide of the catalyst ingredient together with a molding aid to a powder mixture of MnO₂ and a powder of an inorganic support and then kneading and molding them. In the deodorizing method according to the present invention, a gas containing malodor components is introduced alone or together with ozone into catalyst while heating the catalyst directly by electric current supply thereby catalytically decomposing the malodor components, in which the temperature for the heating is set preferably to 100 - 400°C. If the temperature is lower than 100°C, decomposing function at high efficiency can not be provided and, on the other hand, if it exceeds 400°C, the running cost increases and there is a problem for the durability of the catalyst. In the ozone decomposition method according to the present invention, catalytic decomposition is conducted by the catalyst, in which the heating temperature is set preferably to 50 - 400°C. If the temperature is lower than 50°C, decomposing effect at high efficiency can not be provided and, on the other hand, if it exceeds 400°C, the running cost increased and there is a problem for the durability catalyst. By the way, as a method of removing various components contained in gases (for example, malodor components, triethylamine, methylmercaptan, etc.), adsorption-burning decomposition method by catalyst is known. In the method, steps of adsorbing the components onto an adsorbing catalyst and then heating them to desorb the components and removing them by burning are repeated. Since it has merits that the constitution of the device is relatively simple, regeneration of the adsorbing catalyst and the burning removal can be conducted in parallel and, in addition, the components to be adsorbed can be decomposed efficiently in a condensated state, it has been generally practiced in various fields. However, the adsorption-burning decomposition method has been conducted somewhat at random and it can not always be said that optimum operation conditions have been found. Accordingly, the inherent merit of the method can not sometimes be attained fully depending on the conditions. Under such situations, the present inventors have made a study from various approaches with a view point of effectively utilizing the feature of the catalyst, intending for developing an adsorption burning decomposition method capable of operating efficiently for a long period of time and providing the merit thereof sufficiently. As a result, it has been accomplished an adsorption-burning decomposition method according to the present invention based on the finding that components to be adsorbed can be put to burning decomposition efficiently for a long period of time by using the catalyst, and by adopting such a constitution as disposing a catalyst, an adsorbent and a catalyst in this order from the upstream in the flowing direction of a gas and carrying out operation while skillfully combining an adsorption step by the adsorbent and a burning decomposition step by the catalyst, by which respective merits for both of them can be obtained to the maximum extent and regeneration for the adsorbent can be conducted optionally. For practicing the adsorption-burning decomposition method described above, a gas containing components to be adsorbed is introduced into the adsorbent to adsorb the components thereon and a cleaned gas after removal of the components to be adsorbed is allowed to pass Then, the adsorbent and the catalyst are heated before the adsorbent is saturated, the components to be adsorbed are desorbed from the adsorbent and introduced to the catalyst, thereby subjecting the adsorbed components to the catalytic action and to the burning decomposition. When all the components to be adsorbed are desorbed and entirely decomposed through burning by the catalyst, heating is interrupted and the process is returned to the adsorbing step. The purpose of the present invention can be attained by repeating the steps. There is no particular restriction for the heating means in the above method. The adsorbent and the catalyst may be heated simultaneously or the adsorbent and the catalyst may be closely laminated in which only the catalyst is heated directly by electric current supply and the heat is conducted to the adsorbent. In any of the cases, the temperature for both of the catalyst and the adsorbent have to be elevated together. In the present invention, a gas containing the components to be adsorbed may be introduced (blowing) always through the entire period for each of the steps or may be introduced only during the adsorption step and its introduction may be interrupted during heating (burning step). In the former process, since the adsorbed components desorbed from the adsorbent are mixed into a flowing gas, the concentration of the adsorbed components in the flowing gas is diluted. Accordingly, it is desirable to somewhat reduce the amount of the gas containing the adsorbed components. On the other hand, in the case of using the latter means, since it may be considered that the adsorbed components may be diffused to the upstream in the flowing direction of the gas when desorbed from the adsorbent, the constitution of the present invention, in which the catalyst is disposed also to the upstream in the flowing direction of the gas in the adsorbent, can conduct burning decomposition also by the catalyst on the upstream, which is particularly effective. There is no particular restriction for the adsorbent used in the above method and there can be mentioned, for example, zeolite, alumina, silica - alumina and flame retardant activated carbon. Further, there is no particular restriction also to the shape of the adsorbent and, for example, any of shapes such as honeycomb, pellet, etc. may be used. The catalysts used in the present invention are particularly excellent in view of the adsorbing effect as well as the catalytic effect. In view of the above, the present inventors have made a study from an aspect different from that in the method described above, for developing an adsorption-burning decomposition method capable of effective operation for a long period of time by utilizing the foregoing features and capable of fully developping such features. As a result, it has been found that the foregoing object can be attained by disposing a catalyst such that a gas flows in the vertical direction relative thereto, and adopting such constitution as introducing a gas containing adsorbed components from below to the adsorbing catalyst by means of a blower, and adsorbing the adsorbed components, heating the catalyst upon burning decomposition while interrupting the operation of the blower and conducting burning decomposition for the adsorbed components in the course where the adsorbed components are desorbed and uprise spontaneously by temperature elevation. In this method, it is necessary to introduce the gas containing the adsorbed components from below relative to the adsorbing catalyst, so that once adsorbed components are prevented from being desorbed during temperature elevation step and upwardly releasing in an unburnt state. That is, if the gas containing adsorbed components is introduced from above the catalyst, the adsorbed components are so adsorbed that the adsorbing concentration is gradually reduced from above to below of the catalyst. In such a state, most of the components desorbed during temperature elevation step of the catalyst escape upwardly due to spontaneous uprising by the temperature elevation before they subjected to catalytic effect. On the contrary, if the gas containing adsorbed components is introduced from below the catalyst as in this method, the adsorbed Components are adsorbed such that the concentration of the adsorption is gradually decreased from below to the above of the catalyst. In such a state, the catalyst and the adsorbed components have a sufficient chance of contact before the adsorbed components uprise spontaneously and are discharged from above the catalyst during temperature elevation step of the catalyst, thereby enabling, as much as possible, to avoid that the adsorbed components are discharged externally while being unburnt. Further in this method, it is necessary to interrupt the operation of the blower or reducing the number of rotation of the blower to reduce the stream of the blower during burning decomposition, for preventing the rapid uprising release of the desorbed components by usual operation of the blower thereby sufficiently conducting the reaction of the burning decomposition. That is, in a constitution that the blower is put to usual rotation also during burning decomposition, if the gas is adapted to be introduced from below and the concentration slope for the adsorption is formed as described above, the components desorbed are rapidly released and no sufficient time of contact required for receiving the sufficient catalytic decomposition can be ensured. The present invention will be described more specifically referring to examples but the present invention is not limited only to the examples. Preparatory Example 1 After adding 0.5 kg of silica-sol (30% by weight SiO₂ content) to 10 kg of β-MnO₂ and mixing them thoroughouly in a kneader with an appropriate amount of water, the mixture was sufficiently kneaded in a kneader and the uniform kneading product was extrusion molded to prepare a lattice-like honeycomb product having an outer shape of 50 mm height, 50 mm width and 50 mm length (0.3 mm thickness, 1.4 mm opening), which was dried at 150°C for 5 hours and then calcined at 300°C for 2 hours in an air atmosphere to prepare a catalyst according to the present invention. The resultant catalyst had a specific resistivity of 1.2 ohm.cm. CO oxidizing function of the thus prepared catalyst was examined as described below. 125 cc of the lattice-like honeycomb catalyst described above was charged into a tubular reactor made of SUS and air containing 1% CO at a normal temperature was introduced to the catalyst at a flow rate of 1.25 Nm³/h (space velocity at 10000 hr⁻¹). In this case, voltage was controlled such that the catalyst temperature was 300°C and the CO oxidation removal rate was determined to be 87%. The CO oxidation removal rate was calculated by the following equation: Preparatory Example 2 At first, a composite oxide comprising Ti and Si was prepared in the following procedures. As a Ti source, an aqueous sulfuric acid solution of titanyl sulfate of the following composition was used. TiOSO₄ 250 g/l (converted as TiO₂) Total H₂SO₄ 1100 g/l A solution prepared by adding 280 liter of an aqueous ammonia (NH₃, 25%) to 400 liter of water and further adding 24 kg of Snowtex NCS-30 (silica sol manufactured by Nissan Kagaku Co., containing about 30 % by weight of SiO₂) was previously prepared. Then, a titanium-containing aqueous solution of sulfuric acid prepared by adding 300 liter of water to 153 liter of the aqueous solution of sulfuric acid as described above for dilution was gradually dropped under stirring to form a coprecipitation gel. The thus obtained TiO₂ - SiO₂ gel was filtered, washed with water and then dried at 200°C for 10 hours. Then, it was calcined at 550°C in an air atmosphere for 6 hours. The resultant powder had a composition of TiO₂ : SiO₂ = 4 : 1 (molar ratio) and a BET surface area of 185 m²/g. The resultant powder (hereinafter referred to as TS-1) was used to prepare the catalyst according to the present invention by the procedures described below. After adding an appropriate amount of water to 10 kg of TS-1 powder, mixing them sufficiently in a kneader and then kneading them by the kneader and extrusion molding the uniform kneaded product to prepare a lattice-like honeycomb having an outer shape of 50 mm height, 50 mm width and 50 mm length (0.3 mm wall thickness, 1.4 mm opening), it was dried at 150°C for 5 hours and, subsequently, calcined at 300°C for 2 hours in air to prepare a honeycomb molding product. Subsequently, the molding product was impregnated with an aqueous solution of manganese nitrate, dried and sintered to obtain a catalyst comprising TS-1 : MnO₂ = 70:30 by weight ratio as the oxide. The resultant catalyst had a specific resistivity of 137 ohm.cm. When the CO oxidation function of the thus prepared catalyst was examined in the same manner as in Preparatory Example 1, the CO oxidation removal rate was 94%. Preparatory Example 3 At first, a composite oxide comprising Ti and Zr was prepared by the following procedures. 1.93 kg of zirconium oxychloride (ZrOCl₂.8H₂O) was dissolved into 100 liter of water and 7.8 liter of an aqueous solution of sulfuric acid containing titanyl sulfate having the same composition as that used in Preparatory Example 2 was added and mixed sufficiently. While maintaining the temperature at 30°C and under sufficient stirring, an aqueous ammonia was gradually dropped till pH reached 7 and then stood still for 15 hours to form a coprecipitation gel. The thus obtained TiO₂ - ZrO₂ gel was filtered, washed with water and then dried at 200°C for 10 hours. Than, it was calcined at 550°C in an air atmosphere for 6 hours. The resultant powder had a composition of TiO₂ : ZrO₂ = 4:1 (molar ratio) and a BET surface area of 140 m²/g. Using the thus resultant powder (hereinafter referred to as TZ-1), a MnO₂ carrying support was prepared by the same procedures as in Preparatory Example 2. The catalyst had a composition TZ-1 : MnO₂ = 70 : 30 by weight ratio as oxide and a specific resistivity of 130 ohm.cm. When the CO oxidation function of the thus prepared catalyst was examined in the same manner as in Preparatory Example 1, the CO oxidation removal rate was 90%. Preparatory Example 4 After adding an appropriate amount of water to a γ-alumina powder and sufficiently mixing them in a kneader, the mixture was sufficiently kneaded by a kneader and the uniform kneading product was extrusion molded to prepare a lattice-like honeycomb having an outer shape of 50 mm height, 50 mm width and 50 mm length (wall thickness 0.3 mm, opening 1.4 mm), dried at 150°C for 5 hours and, subsequently, sintered at 300°C for 2 hours in an air atmosphere into a honeycomb molding product. Subsequently, the product was impregnated with an aqueous solution of manganese nitrate, dried and sintered to obtain a catalyst having a composition of γ-Al₂O₃:MnO₂ = 70:30 by weight ratio as an oxide. The resultant catalyst had a specific resistivity of 150 ohm.cm. When the oxidation function of the thus prepared catalyst was examined in the same way as in Preparatory Example 1, the CO removal rate was 81%. Preparatory Example 5 A lattice-like honeycomb catalyst was prepared in the same procedures as those in Preparatory Example 4 except for using a powder mixture of a TS-1 powder and a zeolite powder instead of γ-alumina powder. The resultant catalyst had a composition or zeolite : TS-1 : MnO₂ = 50:20:30 by weight ratio, and a specific resistivity of 145 ohm.cm. When the oxidation function of the thus prepared catalyst was examined in the same way as in Preparatory Example 1, the CO removal rate was 89%. Preparatory Example 6 Using the catalyst prepared in Preparatory Example 2, the deodorizing decomposition function was examined under the following conditions. 125 cc of the lattice-like honeycomb catalyst obtained in Preparatory Example 2 was charged into a tubular reactor made of SUS and air containing 1 ppm of triethylamine and 1 ppm of methylmercaptan was introduced at a flow rate of 2.5 Nm³/hr (space velocity of 20,000 hr⁻¹) at a normal temperature to the catalyst. In this case, the catalyst was heated at 200°C for 30 min once per day and trimethylamine and methylmercaptan adsorbed to the catalyst were removed by catalytic oxidation. The deodorizing rate was measured at a time 20 days after introducing air. The results are shown in Table 1. The deodorizing rate was determined by the following equation: Malodor components Deodorization rate (%) Trimethylamine 95 Methylmercaptan 90 Example 1 The catalyst obtained in Preparatory Example 2 was further impregnated with an aqueous solution of platinum nitrate, dried and calcined to prepare a catalyst also containing platinum as the catalyst ingredient. The thus prepared catalyst contained 2 g of Pt per one liter of the catalyst and had a specific resistivity of 141 ohm.cm. The CO oxidation function of the thus prepared catalyst was examined as described below. 125 cc of the lattice-like honeycomb catalyst was charged into a tubular reactor made of SUS and air containing 1% CO at a normal temperature was introduced at a rate of 3.75 Nm³/hr (space velocity at 30,000 hr⁻¹). When voltage was controlled such that the catalyst temperature was 180°C and, CO oxidation removal rate was determined, it was more than 99%. Example 2 A lattice-like honeycomb catalyst was prepared in the same procedures as in Example 1 except for using an aqueous solution of palladium nitrate instead of an aqueous solution of platinum nitrate. The resultant catalyst contained 2 g of Pd per one liter of the catalyst and had a specific resistivity of 143 ohm.cm. When the CO oxidation function of the thus prepared catalyst was examined in the same way as in Example 1, the CO removal rate showed a high value of 99%. Example 3 A lattice-like honeycomb catalyst was prepared in the same procedures as in Example 1 except for using an aqueous mixed solution of copper nitrate and iron nitrate instead of an aqueous solution of platinum nitrate. The resultant catalyst contained 15 g of CuO and 10 g of Fe₂O₃ per one liter of the catalyst and had a specific resistivity of 153 ohm.cm. When the CO oxidation function of the thus prepared catalyst was examined in the same way as in Preparatory Example 1, the oxidation removal rate was more than 99%. Example 4 The catalyst obtained in Preparatory Example 3 was further impregnated with an aqueous solution of platinum nitrate, dried and calcined to prepare a catalyst also containing platinum as the catalyst ingredient. The resultant catalyst had a composition, as an oxide, at a weight ratio of TZ-1 : MnO₂ = 70:30, contained 2 g of Pt per one liter of the catalyst and had a specific resistivity of 160 ohm.cm. When the CO oxidation function of the thus prepared catalyst was examined in the same way as in Example 1, the CO oxidation removal rate was more than 99%. Example 5 The catalyst obtained in Preparatory Example 6 was further impregnated with an aqueous solution of platinum nitrate, dried and calcined to prepare a catalyst also containing also platinum as the catalyst ingredient. The resultant catalyst contained 2 g of Pt per one liter of the catalyst and had a specific resistivity of 160 ohm.cm. When the CO oxidation function of the thus prepared catalyst was examined in the same way as in Example 1, the CO oxidation removal rate was more than 99%. Example 6 Using the catalyst prepared in Example 1, the trimethylamine oxidation function was examined under the following conditions. 125 cc of the lattice-like honeycomb catalyst obtained in Example 1 was charged into a tubular reactor made of SUS and air containing 50 ppm of triethylamine at a normal temperature was introduced into the catalyst at a flow rate of 2.5 Nm³/hr (space velocity at 20,000 hr⁻¹). When voltage was controlled so that the catalyst temperature was 250°C and the triethylamine oxidation removal rate was determined, it was 98%. Example 7 Using the catalyst prepared in Example 1, when the deodorizing decomposing function was examined under the conditions shown in Preparatory Example 6, the same results as those in Preparatory Example 6 were obtained.

Claims: A method for purification of a gas, comprising: introducing the gas to an electroconductive catalyst being directly heated by applying electric current thereto, said catalyst being molded and consisting of (A) MnO₂ and (B) at least one or more of elements selected from the group consisting of Fe, Co, Ni, Cu, Ag, Au, Pt, Pd and Rh, and carried on (C) an inorganic support, the catalyst containing from 25 to 60% by weight of (A), up to 60% by weight, as oxide, in the case of Fe, Co, Ni, Cu and Ag and up to 10% by weight, as metal element, in the case of Au, Pt, Pd and Rh of (B) and from 40 to 75% by weight of (C), and whereby (A), (B) and (C) together are not more than 100%. A method according to claim 1, wherein the inorganic support is at least one of a binary composite oxide comprising Ti and Si, a binary composite oxide comprising Ti and Zr and a ternary composite oxide comprising Ti, Si, and Zr. A method according to claim 1 or 2, wherein a gas containing malodor components is introduced to the catalyst, thereby catalytically oxidizing and removing the malodor components. A method according to any one of claims 1 to 3, wherein the temperature for directly heating the catalyst by electric current supply is from 100 to 400°C. A method according to any one of claims 1 to 4, wherein the heating for the catalyst is conducted intermittently. A method according to any one of claims 3 to 5, further comprising introducing ozone into a gas containing malodor components, and the catalyst conducts deodorization under regeneration by direct heating of electric current supply. An ozone decomposition method in which an ozone-containing gas is introduced to the catalyst as defined in claim 1 or 2 by directly heating the catalyst by electric current supply, and the ozone is catalytically decomposed. An ozone decomposition method according to claim 7, wherein the temperature for directly heating the catalyst by electric current supply is from 50 to 400°C. An ozone decomposition method according to claim 7 or 8, wherein the direct heating for the catalyst by electric current supply is conducted intermittently. An adsorption-burning decomposition method for treating a gas containing components, which comprises using the catalyst in the way defined in claim 1 or 2, adopting a constitution in which a catalyst, an adsorbent and a catalyst are disposed in this order from the upstream in the flow direction of the gas, alternately repeating a step of introduction of the gas into the adsorbent thereby adsorbing the components on to the adsorbent or to the adsorbent and the catalyst, and a step of elevating the temperature of the adsorbent and the catalyst, and bringing said components desorbed from the adsorbent into contact with the catalyst by elevating the temperature of the adsorbent and the catalyst, thereby applying a catalytic effect to said adsorbed components. An adsorption-burning decomposition method of adsorbing components to a catalyst having an adsorbing function, and desorbing said components by heating, thereby subjecting them to a catalytic effect, which comprises using the catalyst in the way defined in claim 1 or 2, disposing said catalyst such that the flowing direction of the gas is vertical thereto, introducing the gas from below to said catalyst by means of a blower when an adsorption is practiced for the components, while elevating the temperature of said catalyst, and interrupting the operation of said blower or reducing the rotation of said blower, thereby restricting the blowing stream when the components are desorbed and subjected to the burning decomposition so that said adsorbed components are prevented from being discharged externally in an unburnt state.

Inventors: INOUE AKIRA, NISHIKAWA KAZUYOSHI, SANO KUNIO, TERUI SADAO, YOKOTA YOSHIYUKI, INOUE, AKIRA, NISHIKAWA, KAZUYOSHI, SANO, KUNIO, TERUI, SADAO, YOKOTA, YOSHIYUKI
Applicants: NIPPON CATALYTIC CHEM IND, NIPPON SHOKUBAI CO., LTD.
Application year: 1990
Main classification: B01D53
IPC codes: B01J35, B01J23, B01D53