PROCESS FOR PRODUCING SUPPORTED RUTHENIUM OXIDES, AND

PROCESS FOR PRODUCING CHLORINE

[0001]

Technical Field

The present application claims the Paris Convention priorities based on Japanese Patent Application Nos. 2010- 158481 filed on July 13, 2010 and 2010-247226 filed on November 4, 2010, the entire contents of which are incorporated herein by reference.

The present invention relates to a process for producing a supported ruthenium oxide in which ruthenium oxide is supported on a carrier. The present invention also pertains to a process for producing chlorine by oxidizing hydrogen chloride with oxygen by using, as a catalyst, the supported ruthenium oxide produced by the above-described process.

[0002]

Background Art

A supported ruthenium oxide is useful as a catalyst for use in production of chlorine by oxidizing hydrogen chloride with oxygen. For example, Patent Documents 1 and 2 disclose a process comprising the following steps: adding an aqueous acetic acid solution dropwise to a solution of a mixture of tetraethyl orthosilicate with titanium tetraisopropoxide to form a white precipitate, drying the white precipitate at 60°C in air, calcining the same at 550°C to obtain titania silica powder, supporting a ruthenium compound on the titania silica powder, and calcining the same in air; and a process comprising the following steps: supporting a ruthenium compound on molded titania, calcining the same, supporting a silicon compound such as an alkoxysilane compound and a siloxane compound, on the calcined product, and calcining the same in air. Patent Document 3 discloses a process which comprises the steps of supporting an alkoxysilane compound on molded titania, calcining the same in air to thereby support silica on the molded titania, supporting a ruthenium compound on the same, and then, calcining the same in air. This Document also discloses a process which comprises the steps of molding powdery titania having silica supported thereon, supporting a ruthenium compound on the molded titania, and calcining the same in air, wherein a ratio of rutile type titania to total of the rutile type titania and anatase type titania in the powdery titania is 38%, when measured by the X-ray diffraction method.

[0003]

Prior Art Literature

Patent Documents

Patent Document 1: JP-A-2002-292279 Patent Document 2: JP-A-2004-074073

Patent Document 3: JP-A-2008-155199

[0004]

Disclosure of Invention

However, the supported ruthenium oxides obtained by the conventional processes described above are unsatisfactory in view of thermal stability and catalyst lifetime .

[0005]

An object of the present invention is therefore to provide a process for producing a supported ruthenium oxide excellent in thermal stability and catalyst lifetime. Another object of the present invention is to provide a process for stably producing chlorine for a longer time, by using the supported ruthenium oxide obtained by the above- described process. Thus, the present invention has been accomplished.

[0006]

The present inventors have made extensive studies on the production of supported ruthenium oxide catalysts and found out that the following process is effective to achieve the above-described objects: that is, the process comprising the steps of supporting a ruthenium compound on a powdery titania carrier, and calcining the same carrier with the ruthenium compound thereon under an atmosphere of an oxidizing gas, wherein the powdery titania carrier comprises titania and silica supported on the titania, and wherein a ratio of rutile type titania to total of the rutile type titania and anatase type titania is 50% or more, when measured by the X-ray diffraction method.

[0007]

That is, the present invention provides the following.

[1] A process for producing a supported ruthenium oxide, comprising the steps of supporting a ruthenium compound on a powdery titania carrier, and calcining the powdery

titania carrier with the ruthenium compound thereon, under an atmosphere of an oxidizing gas, wherein said powdery titania carrier comprises titania and silica supported on the titania, and wherein a ratio of rutile type titania to total of the rutile type titania and anatase type titania in the powdery titania carrier is 50% or more, when

measured by the X-ray diffraction method.

[2] The process of [1], wherein the supporting of said ruthenium compound is carried out after molding of said titania carrier.

[3] The process of [2], wherein said molding is carried out after a heat treatment of said titania carrier.

[4] The process of [3], wherein said heat treatment is carried out under an atmosphere of an oxidizing gas. [5] The process of [3] or [4], wherein said heat treatment is carried out at a temperature of from 500 to 900°C.

6. The process of any one of Claims 2 to 5, wherein the calcination is carried out after the molding, and then, the supporting of said ruthenium compound is carried out.

7. The process of Claim 6, wherein said calcination after the molding is carried out under an atmosphere of an oxidizing gas.

[8] The process of [6] or [7], wherein said calcination after the molding is carried out at a temperature of from 500 to 800°C.

[9] The process of any one of [1] to [8], wherein a ratio of said titania carrier and said ruthenium compound to be used is controlled so that a weight ratio of ruthenium oxide/titania carrier in said supported ruthenium oxide is from 0.1/99.9 to 20.0/80.0.

[10] The process of any one of [1] to [9], wherein a ratio of said titania carrier and said ruthenium compound to be used is controlled so that a content of ruthenium oxide in said supported ruthenium oxide is from 0.10 to 20 mol per one mol of silica in said titania carrier.

[11] A process for producing chlorine, wherein hydrogen chloride is oxidized with oxygen in the presence of a supported ruthenium oxide produced by the process defined in any of [1] to [10] . [0008]

In addition, according to the present invention, there is provided a process for producing chlorine by oxidizing hydrogen chloride with oxygen in the presence of the supported ruthenium oxide produced by the above-described process .

[0009]

Effect of the Invention

According to the present invention, a supported ruthenium oxide excellent in thermal stability and catalyst lifetime can be produced, and chlorine can be produced by oxidizing hydrogen chloride with oxygen by the use of the above-obtained supported ruthenium oxide as a catalyst.

[0010]

Best Modes for Carrying Out the Invention

Hereinafter, the present invention will be described in detail. In the present invention, powdery titania carrier comprising titania and silica supported on the titania is used. The titnia of such a titania carrier may be rutile type titania (i.e., titania having a rutile type crystalline structure), anatase type titania (i.e., titania having an anatase type crystalline structure) or amorphous titania, or a mixture thereof. In the present invention, a titania carrier which comprises rutile type titania as a main component is preferably used. Preferable is a titania carrier in which a ratio of rutile type titania (hereinafter optionally referred to as a rutile type titania ratio) to total of the rutile type titania and anatase type titania in the titania carrier is 50% or more. More preferable is a titania carrier in which a ratio of rutile type titania to total of the rutile type titania and anatase type titania in the titania carrier is 70% or more. Still more preferable is a titania carrier in which a ratio of rutile type titania to total of the rutile type titania and anatase type titania in the titania carrier is 90% or more. As the rutile type titania ratio becomes higher and higher, the thermal stability and catalyst lifetime of the resultant supported ruthenium oxide are more and more improved. The rutile type titania ratio can be measured by the X-ray diffraction method (hereinafter referred to as the XRD method) and can be calculated by the following equation (1) :

[0011]

Rutile type titania ratio [%] = [I _R /(I _A + I _R ] X 100 (1) [0012]

I _R : an intensity of a diffraction line indicating plane

(110) of rutile type titania

I _A : an intensity of a diffraction line indicating plane

(101) of anatase type titania

[0013] The titania carrier to be used in the present invention is powdery, and it comprises titania and silica previously supported thereon, wherein a ratio of rutile type titania is 50% or more. Such a titania carrier may be a commercially available one or may be prepared by a known method. As the commercially available titania carrier, there are exemplified silica-supporting titania powder (STR-100W®) manufactured by Sakai Chemical Industry Co., Ltd., silica-supporting titania powder ( T-100WP®) manufactured by TAYCA CORPORATION, etc. This titania carrier may be prepared, for example, according to the method disclosed in JP-A-2006-182896.

[0014]

A content of the silica in the above-described titania carrier is preferably from 0.01 to 10% by weight, more preferably from 0.1 to 5% by weight, which however varies depending on the physical properties of the titania or a content of ruthenium oxide in the resultant supported ruthenium oxide.

[0015]

The above-described titania carrier may contain an alkali metal element. As the alkali metal element, there are exemplified sodium, potassium, cesium, etc., while two or more kinds selected therefrom may be used. Above all, sodium is preferably used. This alkali metal element may be such one that is contained in any of the above-mentioned commercially available titania carriers, or may be one which is likely to be contained in the titania carrier during the above-described preparation of the titania carrier with the use of a salt of an alkali metal with silicic acid as a raw material for silica, or may be one which is likely to be contained in the titania carrier during the above-described preparation of the titania carrier, by addition of an alkali metal compound separately from a raw material for silica. As the alkali metal compound, halides of alkali metals are preferable. Among them, sodium chloride and potassium chloride are preferable, and sodium chloride is more preferable. A content of the alkali metal element is preferably 5% by weight or less, more preferably 2% by weight or less, based on the weight of the titania carrier. When two or more kinds of alkali metal elements are contained in the titania carrier, a total content of these elements is adjusted to fall within the above-specified range based on the weight of the titania carrier. A content of the alkali metal element in the titania carrier can be determined, for example, by the inductively-coupled high-frequency plasma atomic emission spectrometry (hereinafter referred to as "ICP analyzing method" ) .

[0016] The titania carrier may be subjected to a heat treatment which may be carried out under an atmosphere of an oxidizing gas, a reducing gas or an inert gas. Preferably, this heat treatment is carried out under an atmosphere of an oxidizing gas. Herein, the oxidizing gas means a gas which contains an oxidizing substance, e.g., an oxygen-containing gas or the like, of which an oxygen concentration is usually from about 1 to about 30% by volume. As an oxygen source therefor, generally, air or pure oxygen is used, and may be optionally diluted with an inert gas or water vapor. The use of air as the oxidizing gas is particularly preferable. The above-described reducing gas means a gas which contains a reducing substance, e.g., a hydrogen-containing gas, a carbon monoxide-containing gas, a hydrocarbon-containing gas or the like. A concentration of the reducing substance is usually from about 1 to about 30% by volume, and this concentraion is controlled with, for example, an inert gas or water vapor. The use of the hydrogen-containing gas or the carbon monoxide-containing gas as the reducing gas is particularly preferable. As the above-described inert gas, there are exemplified nitrogen, carbon dioxide, helium, argon and the like. Such an inert gas may be optionally diluted with water vapor. The use of nitrogen or carbon dioxide as the inert gas is particularly preferable. A temperature for the above-described heat treatment, if carried out, is usually from 300 to 1,000°C, preferably from 500 to 900°C.

[0017]

To support a ruthenium oxide on the titania carrier thus obtained, there is exemplified a process in which a ruthenium compound is supported on the titania carrier, and then, the titania carrier with the ruthenium compound thereon are calcined under an atmosphere of an oxidizing gas.

[0018]

Examples of the above-described ruthenium compound include halides such as RuCl ₃ and RuBr ₃ ; halogeno acid salts such as K ₃ RuCl6 and K ₂ RuCl6/ oxo acid salts such as K ₂ Ru0 ₄ ; oxyhalides such as Ru ₂ OCl ₄ , Ru ₂ OCl ₅ and Ru ₂ OCl ₆ ; halogeno complexes such as K ₂ [RuCls (H ₂ 0) ₄ ] , [RuCl ₂ (H ₂ 0) ₄ ] CI, K ₂ [Ru ₂ OClio] and Cs ₂ [Ru ₂ OCl ₄ ] ; ammine complexes such as [Ru(NH ₃ ) ₅ H ₂ 0]C1 ₂ , [Ru(NH ₃ ) ₅ Cl]Cl ₂ , [Ru (NH ₃ ) ₆ ] Cl ₂ , [Ru (NH ₃ ) ₆ ] Cl ₃ and [Ru (NH ₃ ) ε] Br ₃ ; carbonyl complexes such as Ru(CO)s and Ru ₃ (CO)i ₂ ; carboxylate complexes such as

[Ru ₃ 0 (OCOCH ₃ ) 6 (H ₂ 0) ₃ ] OCOCH ₃ and [Ru ₂ (OCOR) ₄ ] CI (R = a Ci_ ₃ alkyl group); nitrosyl complexes such as K ₂ [RuCl ₅ (NO) ] , [Ru(NH ₃ ) ₅ (NO) ]C1 ₃ , [Ru(OH) (NH ₃ ) 4 (NO) ] (N0 ₃ ) ₂ and

[Ru (NO) ] (N0 ₃ ) ₃ ; phosphine complexes; amine complexes; acetylacetonato complexes; and the like. Among them, the halides are preferably used, and the chlorides are more preferably used. As the ruthenium compound, a hydrate of the ruthenium compound may be optionally used, or two or more kinds selected from the above compounds may be used.

[0019]

A ratio of the ruthenium compound to the titania carrier to be used may be appropriately selected so that a weight ratio of the ruthenium oxide/the titania carrier in the resultant supported ruthenium oxide obtained after calcination, as will be described later, will be preferably 0.1/99.9 to 20.0/80.0, more preferably 0.3/99.7 to 10.0/90.0, still more preferably 0.5/99.5 to 5.0/95.0. Too small an amount of the ruthenium oxide is likely to lead to an insufficient catalytic activity, while too large an amount of the ruthenium oxide is likely to be disadvantageous in view of cost-effectiveness. In addition, a ratio of the ruthenium compound to the titania carrier to be used is so selected that a content of the ruthenium oxide can be preferably from 0.10 to 20 mol, more preferably from 0.20 to 10 mol, per one mole of the silica supported on the titania carrier. When a molar number of the ruthenium oxide per one mol of the silica is too large, the thermal stability of the supported ruthenium oxide is likely to lower. On the other hand, when it is too small, the catalytic activity of the same is likely to lower. [0020]

To support the ruthenium compound on the titania carrier, there may be employed a method of bringing the titania carrier into contact with an aqueous solution which contains the ruthenium compound. In this contact treatment, a temperature for the treatment is usually from 0 to 100°C, preferably from 0 to 50°C; and a pressure for the treatment is usually from 0.1 to 1 MPa, preferably an atmospheric pressure. This contact treatment may be carried out under an atmosphere of air or an inert gas such as nitrogen, helium, argon or carbon dioxide, which may contain water vapor .

[0021]

As the contact treatment, an impregnation or immersion method may be employed. For example, the following methods are exemplified as the method for the contact treatment with the use of the above-described aqueous solution: (A) a method of impregnating the titania carrier with the aqueous solution containing the ruthenium compound; and (B) a method of immersing the titania carrier in the aqueous solution containing the ruthenium compound, while the former method (A) is preferable. In this regard, the aqueous solution may contain an acid.

[0022]

As the water to be contained in the aqueous solution, water with a high purity such as distilled water, ion- exchange water or super-pure water is preferably used. If the water to be used contains a lot of impurities, such impurities tend to adhere to the resultant catalyst, which may lead to a decrease in the catalytic activity thereof. An amount of the water to be used is usually from 1.5 to 8,000 mol, preferably from 3 to 2,500 mol, more preferably from 7 to 1,500 mol, per one mol of the ruthenium compound in the aqueous solution. A lower limit of the amount of the water, required to support the ruthenium compound on the titania carrier, can be found by subtracting the volume of the ruthenium compound in the aqueous solution for use in the supporting, from the total pore volume of the titania carrier to be used.

[0023]

The ruthenium compound may be thus supported on the titania carrier, and then, may be optionally subjected to a reduction treatment as disclosed in, for example, JP-A- 2000-229239, JP-A-2000-254502 , JP-A-2000-281314 or JP-A- 2002-79093.

[0024]

After being supported on the titania carrier, the ruthenium compound is then calcined under an atmosphere of an oxidizing gas. This calcination converts the supported ruthenium compound into a ruthenium oxide. The oxidizing gas is a gas which contains an oxidizing substance, e.g., an oxygen-containing gas. A concentration of oxygen in such a gas is usually from about 1 to about 30% by volume. As an oxygen source therefor, air or pure oxygen is generally used, which may be optionally diluted with an inert gas. In particular, the use of air as the oxidizing gas is preferable. A calcining temperature is usually from

100 to 500°C, preferably from 200 to 400°C.

[0025]

After being supported on the titania carrier, the ruthenium compound may then be dried and calcined under an atmosphere of an oxidizing gas. This drying method may be a known method, wherein a temperature for the drying is usually from a room temperature to about 100°C, and a pressure therefor, usually from 0.001 to 1 MPa, preferably an atmospheric pressure. This drying may be carried out under an atmosphere of air or an inert gas such as nitrogen, helium, argon or carbon dioxide, which may contain water vapor .

[0026]

By way of the above-described calcination, the supported ruthenium oxide can be produced. An oxidation number of ruthenium in the supported ruthenium oxide is usually +4, which indicates ruthenium dioxide (Ru0 ₂ ) as the ruthenium oxide, while ruthenium with other oxidation number or a ruthenium oxide in other form may be contained in the supported ruthenium oxide.

[0027]

The supported ruthenium oxide of the present invention is used preferably as molded articles. For example, the following methods are given as a method of obtaining the supported ruthenium oxide in the form of molded articles:

(A) a method comprising the steps of molding the above- described titania carrier, supporting the ruthenium compound on the molded titania carrier, and calcining the titania carrier with the ruthenium compound thereon under an atmosphere of an oxidizing gas;

(B) a method comprising the steps of subjecting the titania carrier to the above-described heat treatment, molding the heat-treated titania carrier, supporting the ruthenium compound on the molded titania carrier, and calcining the molded titania carrier with the ruthenium compound thereon under an atmosphere of an oxidizing gas;

(C) a method comprising the steps of molding the titania carrier, subjecting the molded titania carrier to the heat treatment, supporting the ruthenium compound on the molded titania carrier, and calcining the titania carrier with the ruthenium compound thereon under an atmosphere of an oxidizing gas;

(D) a method comprising the steps of supporting the ruthenium compound on the titania carrier, molding the titania carrier with the ruthenium compound thereon, and calcining the same under an atmosphere of an oxidizing gas;

(E) a method comprising the steps of subjecting the titania carrier to the heat treatment, supporting the ruthenium compound on the titania carrier, molding the titania carrier with the ruthenium compound thereon, and calcining the same under an atmosphere of an oxidizing gas;

(F) a method comprising the steps of supporting the ruthenium compound on the titania carrier, calcining the titania carrier with the ruthenium compound thereon under an atmosphere of an oxidizing gas, and molding the same; and

(G) a method comprising the steps of subjecting the titania carrier to the heat treatment, supporting the ruthenium compound on the titania carrier, calcining the titania carrier with the ruthenium compound thereon under an atmosphere of an oxidizing gas, and molding the calcined product .

Among those methods, the method (A) or (B) is preferable, and the method (B) is more preferable. The molding step is carried out as follows: for example, titania sol, a molding assistant such as an organic binder, and water are kneaded with the titania carrier, the heat-treated titania carrier, the titania carrier with the ruthenium compound thereon, the heat-treated titania carrier with the ruthenium compound thereon, the titania carrier with the ruthenium compound thereon, having undergone the calcining under the atmosphere of the oxidizing gas, or the heat-treated titania carrier with the ruthenium compound thereon, having undergone the calcining under the atmosphere of the oxidizing gas; and the resulting knead mixture is noodlelike extruded, and is then dried and crushed, to thereby obtain the supported ruthenium oxide as molded articles. After the molding step, preferably, the calcination is subsequently carried out under an oxidizing gas atmosphere. The oxidizing gas is a gas which contains an oxidizing substance, e.g., an oxygen-containing gas, of which a concentration of oxygen is usually from about 1 to about 30% by volume. As an oxygen source therefor, air or pure oxygen is usually used, and may be optionally diluted with an inert gas. The use of air as the oxidizing gas is particularly preferable. A temperature for the calcining step subsequent to the molding step is usually from 400 to 900°C, preferably from 500 to 800°C.

[0028]

A specific surface area of the molded titania carrier in the method (A) or a specific surface area of the heat- treated-and-molded titania carrier in the method (B) is usually from 5 to 300 m ² /g, preferably from 5 to 60 m ² /g. In case where the calcining step is sequentially carried out after the molding step, a specific surface area of the calcined titania carrier is allowed to fall within the above-specified range. When a specific surface area of the titania carrier is too large, the titania and the ruthenium oxide in the resultant supported ruthenium oxide are easily calcined, with the result that thermal stability of the resultant supported ruthenium oxide tends to lower. On the other hand, when a specific surface area of the titania carrier is too small, the ruthenium oxide in the resultant supported ruthenium oxide is hard to be dispersed, with the result that catlytic activity of the resultant supported ruthenium oxide tends to lower. This specific surface area can be measured by the nitrogen adsorption method (or the BET method) , and usually, it is measured by the single point BET method.

[0029]

The supported ruthenium oxide thus produced is used as a catalyst, and chlorine can be efficiently produced by oxidizing hydrogen chloride with oxygen in the presence of this catalyst. A reaction system with the use of a fluidized bed, a fixed bed or a movable bed can be employed as a reaction system therefor, and the use of a fixed-bed reactor of heat insulation type or heat-exchange type is preferred. When a fixed-bed reactor of heat insulation type is used, either a monotubular fixed-bed reactor or a multitubular fixed-bed reactor may be used, of which the monotubular fixed-bed reactor is preferably used. When a fixed-bed reactor of heat-exchange type is used, either a monotubular fixed-bed reactor or a multitubular fixed-bed reactor may be used, of which the multitubular fixed-bed reactor is preferably used.

[0030]

This oxidation reaction is an equilibrium reaction. When this reaction is carried out at too high a temperature, an equilibrium conversion tends to lower. The reaction is therefore carried out at a relatively low temperature. A temperature for the reaction is usually from 100 to 500°C, preferably from 200 to 450°C. A pressure for the reaction is usually from about 0.1 to about 5 Pa. As an oxygen source for the reaction, air or pure oxygen may be used. While a theoretical molar amount of oxygen relative to hydrogen chloride is 1/4 mol, an amount of oxygen to be practically used is 0.1 to 10 times larger than this theoretical amount. A rate of feeding hydrogen chloride is usually from about 10 to about 20, 000 h ^"1 , in terms of a gas-feeding rate per one L of a catalyst (L/h at 0°C under one atmospheric pressure), i.e., in terms of GHSV.

[0031]

Having described the preferred modes of the present invention, the scope of the present invention is not limited to the details of those modes in any way.

[0032]

Examples

While Examples of the present invention will be described below, the scope of the present invention is not limited to the details of Examples in any way. In each of Examples, the content of sodium in the silica-supporting titania powder was analyzed with an ICP emission analyzer (IRIS Advantage manufactured by Nippon Jarrel-Ash Co., Ltd. ) .

[0033]

Example 1

(Molding of Carrier)

Silica-supporting titania powder [STR-100W manufactured by Sakai Chemical Industry Co., Ltd.; a silica (Si0 ₂ ) content = 0.5% by weight; a rutile type titania ratio = 90% or more; and a sodium content = 0.14% by weight] was raised in temperature from a room temperature to 800°C in air over 3 hours, and was then maintained at the same temperature for 3 hours for a heat treatment thereof. The resultant heat-treated product (100 parts by weight) was mixed with an organic binder [65SH-400, manufactured by Shin-Etsu Chemical Co., Ltd.] (2 parts by weight) . This mixture was admixed and kneaded with pure water (30 parts by weight) and titania sol [CSB manufactured by Sakai Chemical Industry Co., Ltd.; a titania content = 40% by weight] (12.5 parts by weight). This knead-mixture was extruded into a noodle with a diameter of 3.0 πτιηφ, which was then dried at 60°C for 2 hours and was then crushed into pieces with lengths of from about 3 to about 5 mm as molded articles. The molded articles were heated from a room temperature to 600°C in air over 1.7 hours and were then maintained at the same temperature for 3 hours for calcination thereof. Thus, there were obtained molded articles of white silica- supporting titania having a silica content of 0.5% by weight [a rutile type titania ratio = 90% or more; and a specific surface area = 25 m ² /g] .

[0034]

(Production of Supported Ruthenium Oxide)

The molded articles (20.0 g) of the silica-supporting titania, thus obtained, were impregnated with an aqueous solution of a hydrate of ruthenium chloride [RuCl ₃ .nH ₂ 0 having a Ru content of 40.0% by weight, manufactured by N.E. CHEMCAT CORPORATION] (0.486 g) in pure water (4.56 g) and were then dried at a room temperature under an atmosphere of air for 2 days, to obtain brown solids (20.6 g) . The solids (20.6 g) were raised in temperature from a room temperature to 300°C over 1.3 hours under a stream of air and were then maintained at the same temperature for 2 hours for calcination thereof. Thus, supported ruthenium oxide (20.1 g) having a ruthenium oxide content of 1.25% by weight was obtained.

[0035]

(Evaluation of Initial Activity of

Supported Ruthenium Oxide)

The molded articles of the supported ruthenium oxide

(1.0 g) obtained as above were diluted with a-alumina balls with a diameter of 2 mm [SSA995 manufactured by NIKKATO CORPORATION] (12 g) . This dilution mixture was charged in a nickel reaction tube with an inner diameter of 14 mm, and the same a-alumina balls (12 g) were further charged in the gas inlet side of the reaction tube to form a pre-heating layer. A hydrogen chloride gas and an oxygen gas were fed into the reaction tube at rates of 0.214 mol/hr. (converted into 4.8 L/hr. at 0°C under one atmospheric pressure) and 0.107 mol/hr. (converted into 2.4 L/hr. at 0°C under one atmospheric pressure) under a normal pressure, respectively Then, the catalyst layer was heated to a temperature of from 282 to 283°C for the reaction. At a point of time when 1.5 hours had passed since the initiation of the reaction, a gas from the outlet of the reaction tube was allowed to pass through an aqueous solution of 30% potassium iodide for sampling for 20 minutes. An amount of produced chlorine was measured by the iodine titration method, to determine a production rate of chlorine (mol/hr.). A conversion of hydrogen chloride was calculated by the following equation, from this chlorine- production rate and the above-described hydrogen chloride- feeding rate. The results is shown in Table 1.

[0036]

Conversion of hydrogen chloride (%) =

[chlorine-production rate (mol/hr.) X 2 ÷

hydrogen chloride-feeding rate (mol/hr.)] X 100

[0037]

(Thermal Stability Test of Supported Ruthenium Oxide)

The molded articles of the supported ruthenium oxide (1.2 g) obtained as above were charged in a quartz reaction tube with an inner diameter of 21 mm. A hydrogen chloride gas, an oxygen gas, a chlorine gas and water vapor were fed into the reaction tube at rates of 0.086 mol/hr. (converted into 1.9 L/hr. at 0°C under one atmospheric pressure), 0.075 mol/hr. (converted into 1.7 L/hr. at 0°C under one atmospheric pressure), 0.064 mol/hr. (converted into 1.4 L/hr. at 0°C under one atmospheric pressure) and 0.064 mol/hr. (converted into 1.4 L/hr. at 0°C under one atmospheric pressure) , under a normal pressure, respectively. Then, the catalyst layer was heated to a temperature of from 435 to 440°C to carry out the reaction. At a point of time when 50 hours had passed since the initiation of the reaction, the reaction was stopped, and the molded articles of the supported ruthenium oxide were cooled, while a nitrogen gas was being fed at a rate of 0.214 mol/hr. (converted into 4.8 L/hr. at 0°C under one atmospheric pressure) .

[0038]

(Evaluation of Activity of Supported Ruthenium Oxide after Thermal Stability Test)

Out of 1.2 g of the molded articles of the supported ruthenium oxide subjected to the above-described thermal stability test, 1.0 g of the same was taken and was used to determine a conversion of hydrogen chloride by the same method as in the above-described evaluation of initial performance. The result is shown in Table 1.

[0039]

Example 2

(Molding of Carrier)

The molding of the carrier was carried out by the same method as in Example 1, except for the use of silica- supporting titania powder [STR-100W manufactured by Sakai Chemical Industry Co., Ltd.; a silica (Si0 ₂ ) content = 2.0% by weight; a rutile type titania ratio = 90% or more; and a sodium content = 26% by weight], instead of the silica- supporting titania powder [STR-100W manufactured by Sakai Chemical Industry Co., Ltd.; a silica (Si0 ₂ ) content = 0.5% by weight; a rutile type titania ratio = 90% or more; and a sodium content = 0.14% by weight], to obtain molded articles of white silica-supporting titania which had a silica content of 2.0% by weight [a rutile type titania ratio = 90% or more; and a specific surface area = 51 m ² /g] [0040]

(Production and Evaluation of Supported Ruthenium Oxide)

The production of the supported ruthenium oxide, the evaluation of the initial activity of the same supported ruthenium oxide, the thermal stability test of the same supported ruthenium oxide, and the evaluation of the activity of the same supported ruthenium oxide after the thermal stability test were conducted in the same manners as in Example 1. The results are shown in Table 1.

[0041]

Comparative Example 1

(Molding of Carrier)

Powder [F-IS manufactured by Showa Titanium Co., Ltd.; a silica content = 0.3% by weight; a rutile type titania ratio = 38%; and a specific surface area = 20 m ² /g] was prepared by subjecting titanium chloride (279 parts by weight) and silicon chloride (1.0 part by weight) to a heat treatment according to the method described in JP-A-2004- 210586. This powder (100 parts by weight) was mixed with an organic binder (YB-152 manufactured by YUKEN INDUSTRY CO., LTD.] (2 parts by weight); and the mixture was then admixed and kneaded with pure water (29 parts by weight) and titania sol [CSB manufactured by Sakai Chemical Industry Co., Ltd.; and a titania content = 40% by weight] (12.5 parts by weight). This knead mixture was extruded into a noodle with a diameter of 3.0 ιηιηφ, which was then dried at 60°C for 2 hours and was then crushed into pieces with lengths of from 3 to 5 mm as molded articles. The molded articles were raised in temperature from a room temperature to 600°C in air over 1.7 hours, and were then maintained at the same temperature for 3 hours for calcination thereof. Thus, there were obtained molded articles of white silica-supporting titania having a silica content of 0.3% by weight [a rutile type titania ratio = 35%; and a specific surface area = 22 m ² /g] .

[0042]

(Production and Evaluation of Supported Ruthenium Oxide)

The production of the supported ruthenium oxide, the evaluation of the initial activity of the same supported ruthenium oxide, the thermal stability test of the same supported ruthenium oxide, and the evaluation of the activity of the same supported ruthenium oxide after the thermal stability test were conducted in the same manners as in Example 1. The results are shown in Table 1. [0043]

Comparative Example 2

(Molding of Titania)

Titania powder [F-1R manufactured by Showa Titanium Co., Ltd.; and a rutile type titania ratio = 93%] (100 parts by weight) was mixed with an organic binder (YB-152A manufactured by YUKEN INDUSTRY CO., LTD.] (2 parts by weight) ; and the mixture was then admixed and kneaded with pure water (29 parts by weight) and titania sol [CSB manufactured by Sakai Chemical Industry Co., Ltd.; and a titania content = 40% by weight] (12.5 parts by weight). This knead mixture was extruded into a noodle with a diameter of 3.0 mm<t> , which was then dried at 60°C for 2 hours and was then crushed into pieces with lengths of from 3 to 5 mm as molded articles. The molded articles were raised in temperature from a room temperature to 600°C in air over 1.7 hours, and were then maintained at the same temperature for 3 hours for calcination thereof.

[0044]

(Supporting of Silica on Titania Molded Articles)

The calcined products (20.0 g) obtained as above were impregnated with a solution of tetraethyl orthosilicate [Si(OC ₂ H ₅ ) ₄ manufactured by Wako Pure Chemical Industries, Ltd.] (0.36 g) in ethanol (2.90 g) and was then dried at 24°C for 15 hours under an atmosphere of air. The resultant solids (20.1 g) were raised in temperature from a room temperature to 300°C over 0.8 hour under a stream of air and were then maintained at the same temperature for calcination thereof. Thus, molded articles of white silica-supporting titania having a silica content of 0.5% by weight [a rutile type titania ratio = 90% or more; and a specific surface area = 17 m ² /g] (20.0 g) were obtained.

[0045]

(Production and Evaluation of Supported Ruthenium Oxide)

The production of the supported ruthenium oxide, the evaluation of the initial activity of the same supported ruthenium oxide, the thermal stability test of the same supported ruthenium oxide, and the evaluation of the activity of the same supported ruthenium oxide after the thermal stability test were conducted in the same manners as in Example 1. The results are shown in Table 1.

[0046]

Table 1