JP2015120116A - Sulfur trioxide decomposition catalyst, method for producing the same, and method for generating hydrogen using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sulfur trioxide decomposition catalyst improved in catalytic activity as compared with a conventional catalyst, and a method for producing the same.SOLUTION: The sulfur trioxide decomposition catalyst is provided, in which a complex oxide containing an alkali metal and vanadium is carried on a catalyst carrier. The method for producing the sulfur trioxide decomposition catalyst is also provided, which includes: (a) a step of impregnating a catalyst carrier with one of an alkali metal compound solution and a vanadium compound solution, and then drying and temporarily firing the catalyst carrier; and (b) a step of impregnating the catalyst carrier obtained in the step (a) with the other of the alkali metal compound solution and the vanadium compound solution, and then drying and firing the catalyst carrier.

Description

The present invention relates to a sulfur trioxide (SO ₃ ) decomposition catalyst and a method for producing the same. Furthermore, the present invention relates to a hydrogen generation method including a step of decomposing sulfur trioxide using the sulfur trioxide decomposition catalyst.

  Hydrogen attracts attention as a clean fuel because it does not generate carbon dioxide when burned. However, industrial hydrogen production relies on fossil fuels, and carbon dioxide is emitted during the production process. Therefore, even if hydrogen is used as a fuel, the problems of fossil fuel depletion and global warming due to carbon dioxide are not necessarily solved.

  In relation to this, as a method for generating hydrogen without using fossil fuel, it has been proposed to use solar thermal energy, nuclear thermal energy, or the like (for example, Patent Document 1, Non-Patent Document 1, etc.). .

As a method for generating hydrogen from water using thermal energy, a method called an IS (iodine-sulfur) cycle method represented by the following formulas (1) to (3) has been proposed.
(1) H ₂ SO ₄ (Liquid)
→ H ₂ O (gas) + SO ₂ (gas) + 1 / 2O ₂ (gas)
(Reaction temperature = about 950 ° C., ΔH = 188.8 kJ / mol-H ₂ )
(2) I ₂ (Liquid) + SO ₂ (Gas) + 2H ₂ O (Liquid)
→ 2HI (liquid) + H ₂ SO ₄ (a liquid)
(Reaction temperature = about 130 ° C., ΔH = −31.8 kJ / mol-H ₂ )
(3) 2HI (liquid) → H ₂ (gas) + I ₂ (gas)
(Reaction temperature = about 400 ° C., ΔH = 146.3 kJ / mol-H ₂ )

The overall reaction of the IS (iodine-sulfur) cycle method represented by the above formulas (1) to (3) is as follows.
H ₂ O → H ₂ + 1 / 2O ₂
(ΔH = 286.5 kJ / mol-H ₂ (based on higher heating value)
(ΔH = 241.5 kJ / mol-H ₂ (low calorific value standard)

Here, the reaction of the above formula (1) can be divided into two elementary reactions of the following formulas (1-1) and (1-2).
(1-1) H ₂ SO ₄ (liquid) → H ₂ O (gas) + SO ₃ (gas)
(Reaction temperature = about 300 ° C., ΔH = 90.9 kJ / mol-H ₂ )
(1-2) SO ₃ (gas) → SO ₂ (gas) + 1 / 2O ₂ (gas)
(Reaction temperature = about 950 ° C., ΔH = 97.9 kJ / mol-H ₂ )

That is, when hydrogen is generated in the IS cycle method, the highest temperature is required in the decomposition reaction of sulfur trioxide (SO ₃ ) of the above formula (1-2). However, conventionally, it has been very difficult to obtain a high temperature as required in the decomposition reaction.

  Therefore, it has been proposed to use a platinum catalyst in order to reduce the temperature required in the decomposition reaction. However, although the platinum catalyst generally exhibits a high catalytic activity at the start of its use, when used at a temperature of 650 ° C. or more, in particular, in the decomposition reaction of sulfur trioxide as shown in the above formula (1-2). Platinum is oxidized by the generated oxygen, and sintering occurs relatively easily. When such sintering occurs, the platinum particles become coarse, and the initial activity of the platinum catalyst is lost. Further, since the platinum catalyst is relatively expensive, it is difficult to use the platinum catalyst on an industrial scale from the viewpoint of material cost.

  Patent Document 2 describes a sulfur trioxide decomposition catalyst in which a composite oxide of vanadium and at least one metal selected from the group consisting of transition metals and rare earth elements is supported on a support, specifically copper-vanadium. A catalyst in which a composite oxide, a cerium-vanadium composite oxide or the like is supported on a porous silica carrier is disclosed. Similarly, Patent Document 3 describes a sulfur trioxide decomposition catalyst in which a composite oxide of copper and vanadium is supported on a porous silica carrier. Patent Documents 2 and 3 describe that these sulfur trioxide decomposition catalysts can reduce the temperature required for the sulfur trioxide decomposition reaction.

Non-Patent Document 2 describes a catalyst in which copper pyrovanadate (Cu ₂ V ₂ O ₇ ) is supported on a porous silica carrier as an alternative to a platinum catalyst. According to Non-Patent Document 2, uniform thin layers of Cu ₂ V ₂ O ₇ are formed on the pores and the outer surface of the porous silica support by thermal aging at 800 ° C., and such a catalyst is used. For example, it is described that high catalytic activity can be achieved in the decomposition reaction of sulfur trioxide.

  In addition to the IS cycle method, the Westinghouse cycle, the Ispra-Mark 13 cycle method, the Los Alamos Science Laboratory cycle method, etc. are generally known as methods for generating hydrogen using thermal energy. Yes. In these methods, as in the IS cycle method, it is necessary to decompose sulfur trioxide into sulfur dioxide and oxygen.

JP 2007-218604 A JP 2012-148268 A JP 2013-111542 A

A. Giaconia, et al. , “Hydrogen / ethanol production by sulfur-iodine thermal chemical powered by combined solar / fossil energy 4”, International Journal 9 M.M. Macida, et al. , “Macroporous Supported Cu-V Oxide as a Promising Substitut of the Pt Catalyst for Sulfuric Acid Decomposition in Solar Thermochemistry”

  In Patent Document 2, for example, a sulfur trioxide decomposition reaction proceeds at a temperature of 700 ° C. or 650 ° C. in a sulfur trioxide decomposition catalyst in which a copper-vanadium composite oxide or a cerium-vanadium composite oxide is supported on a porous silica carrier. It is described that it can be made. However, with these sulfur trioxide decomposition catalysts, the reaction may not proceed sufficiently at high space velocity conditions in a compact reactor at temperatures lower than 700 ° C. or 650 ° C. Therefore, the sulfur trioxide decomposition catalyst described in Patent Document 2 still has room for improvement with respect to its catalytic activity, particularly the catalytic activity at low temperatures.

  In the sulfur trioxide decomposition catalyst described in Patent Document 3, in order to obtain high catalytic activity, it is necessary to calcinate at a high temperature of 700 ° C. or higher or once to use at a high temperature of about 800 ° C. in the catalyst preparation stage. is there. In addition, in the sulfur trioxide decomposition catalyst described in Patent Document 3, even when such activation treatment is performed, the catalytic activity is not always sufficient in the decomposition reaction of sulfur trioxide, particularly at a low temperature of about 600 ° C. There was a case that could not be achieved.

  In the catalyst described in Non-Patent Document 2, in order to obtain high catalyst activity, it is necessary to perform a heat aging treatment at a high temperature of about 800 ° C. in the catalyst preparation stage. Further, in the catalyst described in Non-Patent Document 2, even when such a heat aging treatment is performed at a high temperature, the catalyst is not always sufficient in the decomposition reaction of sulfur trioxide particularly at a low temperature of about 600 ° C. In some cases, activity could not be achieved.

  Therefore, the present invention is a novel sulfur trioxide decomposition catalyst, a sulfur trioxide decomposition catalyst having improved catalytic activity, in particular, catalytic activity at low temperatures, compared to conventional catalysts, a method for producing the same, and a method for producing the same. An object of the present invention is to provide a hydrogen production method.

The present invention for solving the above problems is as follows.
(1) A sulfur trioxide decomposition catalyst obtained by supporting a composite oxide containing an alkali metal and vanadium on a catalyst carrier.
(2) The sulfur trioxide decomposition catalyst according to (1), wherein the alkali metal is selected from the group consisting of sodium, potassium, rubidium, cesium, and combinations thereof.
(3) The sulfur trioxide decomposition catalyst according to (2), wherein the alkali metal is selected from the group consisting of potassium, cesium, and combinations thereof.
(4) The trioxide according to any one of (1) to (3), wherein an atomic ratio of alkali metal to vanadium (alkali metal: vanadium) in the composite oxide is 1: 1 to 1: 8. Sulfur decomposition catalyst.
(5) The composite oxide described above, wherein the composite oxide comprises an alkali metal vanadate represented by the formula A _1-x VO _3-0.5x (wherein A is an alkali metal and 0 ≦ x <1) The sulfur trioxide decomposition catalyst according to any one of 1) to (4).
(6) The sulfur trioxide decomposition catalyst according to (5), wherein the composite oxide includes an alkali metal metavanadate represented by the formula AVO ₃ (wherein A is an alkali metal).
(7) Any of the above (3) to (5), wherein the alkali metal is cesium and the composite oxide includes CsVO ₃ , Cs ₂ V ₄ O ₁₁ , CsV ₃ O ₈ , or a combination thereof. 2. The sulfur trioxide decomposition catalyst according to item 1.
(8) The sulfur trioxide decomposition catalyst according to any one of (1) to (7), wherein the catalyst carrier is selected from the group consisting of silica, alumina, zirconia, titania, and combinations thereof.
(9) The sulfur trioxide decomposition catalyst according to (8), wherein the catalyst support has mesopores and / or macropores.
(10) The sulfur trioxide decomposition catalyst according to (8) or (9), wherein the catalyst carrier is silica.
(11) (a) a step of impregnating a catalyst carrier with one of an alkali metal compound solution and a vanadium compound solution, drying and pre-baking; and (b) an alkali metal compound solution and a vanadium compound solution. Decomposition of sulfur trioxide obtained by supporting a composite oxide containing an alkali metal and vanadium on a catalyst carrier, which includes impregnating the other solution of the catalyst into the catalyst carrier obtained in step (a), drying and calcining. A method for producing a catalyst.
(12) Sulfur trioxide decomposition comprising impregnating a catalyst carrier with a solution containing an alkali metal compound and a vanadium compound, drying and firing the composite oxide containing an alkali metal and vanadium on the catalyst carrier A method for producing a catalyst.
(13) The method according to (11) or (12), wherein the firing is performed at a temperature of 400 ° C. or higher and 650 ° C. or lower.
(14) The method according to (13), wherein the baking is performed at a temperature of 500 ° C. or higher and 600 ° C. or lower.
(15) A method for producing sulfur dioxide, comprising a decomposition reaction in which sulfur trioxide is decomposed into sulfur dioxide and oxygen using the sulfur trioxide decomposition catalyst according to any one of (1) to (10) above.
(16) The method according to (15), wherein the decomposition reaction is performed at a temperature of 600 ° C. or lower.
(17) A hydrogen generation method comprising decomposing water into hydrogen and oxygen, the method comprising decomposing sulfuric acid into water, sulfur dioxide and oxygen in the reaction represented by the following formula (X1): Of the elementary reactions of the formulas (X1-1) and (X1-2) that are elementary reactions of the reaction represented by (X1), the elementary reaction of the formula (X1-2) is described in the above (15) or (16) Hydrogen production method carried out by the method of:
(X1) H ₂ SO ₄ → H ₂ O + SO ₂ + 1 / 2O ₂
(X1-1) H ₂ SO ₄ → H ₂ O + SO ₃
(X1-2) SO ₃ → SO ₂ + 1 / 2O ₂
(18) The hydrogen generation method according to the above (17), which is an IS cycle method, a Westinghouse cycle method, an Ispra-Mark 13 cycle method, or a Los Alamos Science Laboratory cycle method.

According to the present invention, a composite oxide in which vanadium is combined with an alkali metal is supported on a catalyst carrier, thereby comparing with a conventional catalyst, for example, a catalyst in which a composite oxide of copper and vanadium is supported on a catalyst carrier. Thus, even under high space velocity (SV) conditions, the catalytic activity of the resulting sulfur trioxide decomposition catalyst, particularly the sulfur trioxide (SO ₃ ) decomposition activity at a temperature of about 600 ° C. or lower, is remarkable. Can be improved. Furthermore, according to the method of the present invention, sulfur trioxide (SO ₃ ) decomposition activity under such low temperature is remarkably improved without the need for firing or use at a high temperature of 700 ° C. or higher. It is possible to produce a sulfur decomposition catalyst.

It is a conceptual diagram which shows the mechanism of the sulfur trioxide decomposition reaction in the sulfur trioxide decomposition catalyst of this invention. Cs ₂ O-V ₂ O ₅ system is a state diagram of. The fixed bed flow reactor used for the activity evaluation of the sulfur trioxide decomposition catalyst of Examples 1-4 and Comparative Examples 1-3 is shown. The X-ray-diffraction pattern regarding the sulfur trioxide decomposition catalyst of Example 4 and Comparative Examples 1 and 3 is shown. The analysis result by the Raman spectroscopy of the sulfur trioxide decomposition catalyst of Example 4 is shown.

<Sulfur trioxide decomposition catalyst>
The sulfur trioxide decomposition catalyst of the present invention is characterized in that a composite oxide containing an alkali metal and vanadium is supported on a catalyst carrier.

  As described above, when a platinum catalyst is used in the decomposition reaction of sulfur trioxide, platinum is oxidized by oxygen generated in the decomposition reaction of sulfur trioxide and sintering is relatively easily caused. Therefore, the platinum catalyst has deteriorated relatively early and it has been difficult to use it stably over a long period of time.

This time, the present inventors examined the composite oxide which combined vanadium with the alkali metal. Then, the present inventors support the conventional oxide such as copper described in JP 2012-148268 A and JP 2013-111542 A by supporting the composite oxide on a catalyst carrier. The catalytic activity of the resulting sulfur trioxide decomposition catalyst, especially about 600 ° C. or higher, even under high space velocity (SV) conditions, compared to a catalyst comprising a vanadium composite oxide supported on a catalyst support. It was also found that the sulfur trioxide (SO ₃ ) decomposition activity at a low temperature can be remarkably improved.

  As described above, when hydrogen is produced in the IS (iodine-sulfur) cycle method, a temperature close to 1000 ° C. is generally required to decompose sulfur trioxide into sulfur dioxide and oxygen. Therefore, conventionally, in the I-S cycle method, a method for efficiently producing hydrogen by taking out and using such high-temperature heat from a high temperature gas-cooled reactor (HTGR) is particularly researched. Has been done.

  For this reason, it has been generally considered that it is difficult to use solar heat in the IS cycle method. For example, as a condensing device for obtaining solar thermal energy, a parabolic dish concentrating device, a solar tower concentrating device, a parabolic trough concentrating device, and the like are generally known. However, among these concentrators, the parabolic trough concentrator, which has a relatively simple structure, is inexpensive and suitable for large-scale plants, is a balance between solar thermal energy collection and radiation energy dissipation. Therefore, it is technically very difficult to collect solar thermal energy at 700 ° C. or higher, particularly at a high temperature close to 1000 ° C., and it is difficult to realize it in terms of cost.

  Therefore, by using the sulfur trioxide decomposition catalyst of the present invention, the temperature required for the sulfur trioxide decomposition reaction is lowered, for example, at a temperature of about 600 ° C. or lower and under a high SV condition. The ability to proceed with the decomposition reaction of sulfur trioxide is very important from an industrial point of view.

[Alkali metal]
According to the present invention, the alkali metal may preferably include sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), or combinations thereof, more preferably potassium (K). , Cesium (Cs), or a combination thereof, and most preferably cesium (Cs).

  Although not intended to be bound by any particular theory, it is considered that the sulfur trioxide decomposition catalyst of the present invention proceeds with a sulfur trioxide decomposition reaction by a reaction mechanism as described below, for example.

FIG. 1 is a conceptual diagram showing the mechanism of sulfur trioxide decomposition reaction in the sulfur trioxide decomposition catalyst of the present invention. For ease of understanding, FIG. 1 illustrates a case where a composite oxide (that is, AVO ₃ ) having an atomic ratio of alkali metal (A) to vanadium (alkali metal: vanadium) of 1: 1 is used.

First, it is generally known that an alkali metal is an element that relatively easily forms a peroxide. Therefore, in the composite oxide (AVO ₃ ) in which the alkali metal is combined with vanadium, at least a part of vanadium in the AVO _{3 on} the catalyst surface is not as VO ₃ due to the action of the alkali metal (A) but in the gas phase. It is considered that oxygen exists in the peroxidized state, ie, VO ₄ (see FIG. 1A). Next, since such adsorbed oxygen has higher reactivity than oxygen in other vanadium-oxygen (VO) bonds, as shown in FIG. It is thought that (SO ₃ ) is further adsorbed on the adsorbed oxygen and separated to produce sulfur dioxide (SO ₂ ) (see FIG. 1 (c)). Here, since oxygen remaining on VO ₄ in FIG. 1 (c) is very highly active, as shown in FIG. 1 (d), sulfur trioxide in the gas phase is easily added to the oxygen. Adsorbed and finally, sulfur dioxide (SO ₂ ) and oxygen molecules (O ₂ ) are considered to be separated (see FIG. 1 (e)).

According to the sulfur trioxide decomposition catalyst of the present invention, by combining an alkali metal with vanadium, for example, in the oxygen adsorption or oxygen addition mechanism as described above, the adsorptivity and reactivity of the composite oxide to sulfur trioxide are enhanced. it is conceivable that. As a result, according to the sulfur trioxide decomposition catalyst of the present invention, compared with the conventional catalyst, even under high space velocity (SV) conditions, from a relatively low temperature range, for example, a temperature range of 600 ° C. or less. It is considered that high sulfur trioxide (SO ₃ ) decomposition activity could be achieved.

  In addition, although not intending to be bound by any particular theory, in the sulfur trioxide decomposition catalyst of the present invention, the composite oxide containing alkali metal and vanadium is present as a uniform thin layer on the catalyst support. Or is supported on the catalyst support in a highly dispersed form as fine crystals.

With reference to FIG. 2, the case where cesium (Cs) is used as an alkali metal will be described in more detail below. FIG. 2 is a phase diagram of the Cs ₂ O—V ₂ O ₅ system. As shown in FIG. 2, the melting point is 642 ° C. in a composite oxide having a cesium / vanadium atomic ratio (Cs: V) of 1: 1, that is, cesium metavanadate (CsVO ₃ ). However, as can be seen from FIG. 2, for example, when this composition is slightly shifted to the vanadium (V) rich side, the melting point is greatly reduced to about 400 ° C. Here, since there is a concentration distribution in the actual composition, even if the atomic ratio of cesium to vanadium (Cs: V) is 1: 1 as a whole, a V-rich region exists partially, Therefore, it is considered that there is a region where the melting point is partially reduced.

Therefore, even in a relatively low temperature calcination operation at the time of catalyst preparation, for example, a calcination operation of about 400 ° C. to about 600 ° C., the composite oxide precursor containing cesium and vanadium is finally melted while partially melting. It is considered that a complex oxide composed of a uniform thin layer is formed on the support, or is supported on the catalyst support in a highly dispersed form as a microcrystalline complex oxide. According to the sulfur trioxide decomposition catalyst of the present invention, since there is an active catalyst layer composed of such a uniform thin layer or microcrystal, the space velocity (SV) condition is higher than that of the conventional catalyst. Originally, it is considered that high sulfur trioxide (SO ₃ ) decomposition activity could be achieved from a relatively low temperature range, for example, a temperature range of 600 ° C. or lower.

  In particular, when a metal oxide such as silica is used for the catalyst support, a part of cesium (as well as other alkali metals) reacts with the silica, so the composition of the composite oxide precursor at the time of catalyst preparation is Partially V-rich. Therefore, even in a firing operation in a relatively low temperature region of about 600 ° C. or less, the composite oxide precursor containing cesium and vanadium is melted to form a composite oxide composed of a uniform thin layer on silica, or It is considered that it is supported on silica in a highly dispersed form as a microcrystalline composite oxide.

The high SO ₃ decomposition activity at a low temperature in the sulfur trioxide decomposition catalyst of the present invention is improved in the adsorptivity and reactivity of the composite oxide to sulfur trioxide by addition of alkali metal as described above, and / or alkali metal. This is thought to be due to the formation of an active catalyst layer based on the lowering of the melting point of the alkali metal vanadate by the combination of vanadium and vanadium.

[Composite oxide]
According to the present invention, the atomic ratio of alkali metal to vanadium (alkali metal: vanadium) in the composite oxide is generally 1: 0.8 to 1: 9.

  If the atomic ratio of alkali metal to vanadium is less than 1: 0.8, the amount of alkali metal is so large that the alkali metal may precipitate on the catalyst surface and be strongly bound to oxygen. In such a case, there may be a case where an adsorbed oxygen species having a relatively high reactivity as described with reference to FIG. 1 cannot be formed. In addition, since the melting point of the alkali metal vanadate cannot be sufficiently lowered with such a larger amount of alkali metal added, the active catalyst is constituted by a uniform thin layer or microcrystal of the composite oxide. The layer may not be formed.

  On the other hand, when the atomic ratio of alkali metal to vanadium is more than 1: 9, the addition amount of the alkali metal is small, so that the adsorption property and reactivity of the composite oxide to the sulfur trioxide by the addition of the alkali metal are improved. The effect may not be obtained sufficiently. In addition, when such a small amount of alkali metal is added, the melting point of the alkali metal vanadate becomes relatively high, so that an active catalyst layer composed of a uniform thin layer or microcrystal of the composite oxide is formed. It may not be possible to form.

Therefore, according to the present invention, the atomic ratio of alkali metal to vanadium (alkali metal: vanadium) in the composite oxide is generally 1: 0.8 or more, preferably 1: 1 or more, and generally Is 1: 9 or less, preferably 1: 8 or less, 1: 6 or less, 1: 4 or less, 1: 3 or less, or 1: 2 or less. More preferably, the atomic ratio of alkali metal to vanadium (alkali metal: vanadium) in the composite oxide is 1: 1 to 1: 8, and most preferably 1: 1. By controlling the atomic ratio of the alkali metal and vanadium within such a range, the above-described effect due to the composite of the alkali metal and vanadium can be sufficiently exhibited. As a result, SO ₃ decomposition activity, in particular it is possible to obtain a sulfur trioxide decomposition catalyst SO ₃ decomposing activity at low temperatures is significantly improved.

In the sulfur trioxide decomposition catalyst of the present invention, the composite oxide may contain various alkali metal vanadates. The composite oxide generally contains an alkali metal vanadate represented by the formula A _1-x VO _3-0.5x (wherein A is an alkali metal and 0 ≦ x <1). Preferably, an alkali metal metavanadate represented by the formula AVO ₃ (wherein A is an alkali metal) can be included. When the alkali metal is cesium, the composite oxide can contain, for example, CsVO ₃ , Cs ₂ V ₄ O ₁₁ , CsV ₃ O ₈ , or a combination thereof, preferably CsVO ₃ Can be included. These various alkali metal vanadates can be easily produced by appropriately selecting the charging ratio of the alkali metal compound and vanadium compound introduced when preparing the composite oxide in the present invention. Is possible.

[Catalyst support]
In the sulfur trioxide decomposition catalyst of the present invention, the composite oxide is supported on a catalyst support described later in any appropriate amount. Although not particularly limited, for example, in the composite oxide, the amount of vanadium contained in the composite oxide is generally 0.01 wt% or more, 0.1 wt% or more, 0.5 wt% with respect to the catalyst support. 1 wt% or more, or 2 wt% or more, and / or 20 wt% or less, 15 wt% or less, 10 wt% or less, 8 wt% or less, 7 wt% or less, or 5 wt% or less. can do.

According to the present invention, the catalyst carrier on which the composite oxide is supported is not particularly limited, but any metal oxide generally known as a catalyst carrier in this technical field can be used. Examples of such a catalyst carrier include silica (SiO ₂ ), alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ), titania (TiO ₂ ), or combinations thereof. In the sulfur trioxide decomposition reaction, since the reaction is performed in the presence of sulfur trioxide and moisture, it is generally preferable to use a sulfuric acid resistant material as the catalyst carrier. Therefore, from the viewpoint of sulfuric acid resistance, it is preferable to use silica (SiO ₂ ), zirconia (ZrO ₂ ), or a combination thereof as the catalyst carrier.

  According to the present invention, the catalyst carrier is preferably a porous material having a pore structure.

  However, when a porous material having so-called micropores such as zeolite is used as a catalyst support and a composite oxide of alkali metal and vanadium is supported in such pores, the fine particles of sulfur trioxide are concerned. Since diffusion into the pores is extremely restricted, there is a possibility that the decomposition reaction of sulfur trioxide is hindered as a result. Such a tendency is particularly remarkable when a metal element having a large ionic radius such as cesium is used as the alkali metal. Therefore, in the sulfur trioxide decomposition catalyst of the present invention, the catalyst support preferably has mesopores and / or macropores.

  The term “mesopore” used in the present invention generally refers to a pore having a diameter of 2 to 50 nm. The term “macropore” used in the present invention generally refers to a pore having a diameter of more than 50 nm.

  From the standpoint of sulfuric acid resistance and further the pore size of the catalyst carrier, silica can be preferably used as the catalyst carrier in the present invention, more preferably porous silica such as mesoporous silica. Can be used. Although it does not specifically limit as mesoporous silica, For example, cubic mesoporous silica like KIT-6 can be mentioned. Examples of other mesoporous silica include SBA-15, SBA-16, MCM-41, MCM-48, FMS-16, and the like. These mesoporous silicas can be produced by any method known to those skilled in the art, and generally can be produced by a sol-gel method using a surfactant as a template.

<Method for producing sulfur trioxide decomposition catalyst>
In the present invention, a method for producing a sulfur trioxide decomposition catalyst is further provided, and the production method for producing the sulfur trioxide decomposition catalyst of the present invention, wherein the composite oxide having the above-mentioned various characteristics is supported on a catalyst carrier. be able to.

  Specifically, the sulfur trioxide decomposition catalyst of the present invention is first impregnated with a solution of an alkali metal compound in a catalyst carrier, dried and calcined, and then impregnated with the solution of a vanadium compound in the catalyst carrier and dried. And it can manufacture by baking. On the other hand, the sulfur trioxide decomposition catalyst of the present invention is first impregnated with a vanadium compound solution, dried and calcined, and then impregnated with the alkali metal compound solution. It is also possible to manufacture by drying and baking.

  Alternatively, for example, when a specific alkali metal compound and a vanadium compound are selected and a solvent capable of dissolving both of them is used, the sulfur trioxide decomposition catalyst of the present invention is used for the alkali metal compound and the vanadium compound. It is also possible to produce a solution containing both by impregnating the catalyst support, drying and calcining.

  In a conventional catalyst using a vanadium-containing composite oxide, for example, a catalyst in which a composite oxide of copper and vanadium is supported on a catalyst carrier, the sulfur trioxide decomposition reaction is not always sufficient at a temperature lower than 700 ° C or 650 ° C. May not be able to proceed. Alternatively, in order to achieve high catalytic activity in such a catalyst, it was necessary to calcinate at a high temperature of 700 ° C. or higher or once use it at a high temperature of about 800 ° C. in the catalyst preparation stage.

The present inventors combine vanadium with an alkali metal instead of a transition metal such as copper, more specifically, a composite oxide containing an alkali metal and vanadium by an impregnation support method using an alkali metal compound and a vanadium compound. Compared with a conventional catalyst, for example, a catalyst in which a composite oxide of copper and vanadium is supported on a catalyst support, without the necessity of calcining or using it at a high temperature of 700 ° C. or higher. The present inventors have found that a sulfur trioxide decomposition catalyst having significantly improved sulfur trioxide (SO ₃ ) decomposition activity at low temperatures can be produced. Furthermore, the present inventors have found that the sulfur trioxide decomposition catalyst produced by the method of the present invention has such a low temperature under a very high space velocity (SV) condition compared to the conventional catalyst. It has been found that lower sulfur trioxide (SO ₃ ) decomposition activity can be achieved.

[Alkali metal compounds and vanadium compounds]
Although it does not specifically limit as an alkali metal compound, For example, the nitrate, acetate, sulfate, hydroxide, etc. of the said alkali metal can be mentioned. On the other hand, the vanadium compound is not particularly limited, and examples thereof include vanadate such as ammonium metavanadate.

  In the method of the present invention, the alkali metal compound and the vanadium compound generally have an atomic ratio of alkali metal to vanadium (alkali metal: vanadium) of 1: 0.8 to 1: 9, preferably 1: 1 to 1: In the range of 8, the solution containing an alkali metal compound and / or a vanadium compound is prepared by dissolving separately or together in a solvent such as water. In order to improve the solubility, the vanadium compound may be dissolved in a solvent such as water together with a small amount of acid such as oxalic acid as necessary. In addition, the vanadium compound can be dissolved in a solvent in a range such that the amount of vanadium is generally 0.01 wt% to 20 wt% with respect to the catalyst carrier.

[Catalyst support]
According to the method of the present invention, any metal oxide generally known as a catalyst support in the art can be used as the catalyst support in the same manner as described for the sulfur trioxide decomposition catalyst of the present invention. . Examples of such a catalyst carrier include silica (SiO ₂ ), alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ), titania (TiO ₂ ), or combinations thereof, preferably silica. More preferably, mention may be made of porous silica such as mesoporous silica.

[Drying and pre-baking or baking]
In the method of the present invention, in the case of producing the sulfur trioxide decomposition catalyst of the present invention by the sequential impregnation method, after impregnating the catalyst support with the alkali metal compound solution, the catalyst support is dried and pre-calcined, After impregnating the catalyst carrier with the vanadium compound solution, the catalyst carrier is dried and calcined. Alternatively, after impregnating the catalyst support with the vanadium compound solution, the catalyst support is dried and pre-calcined, and after impregnating the catalyst support with the alkali metal compound solution, the catalyst support is then dried and calcined. The On the other hand, when the sulfur trioxide decomposition catalyst of the present invention is produced by the co-impregnation method, the catalyst carrier is dried and calcined after impregnating the catalyst carrier with a solution containing an alkali metal compound and a vanadium compound.

  Such drying and pre-firing or firing may be performed at a temperature and time sufficient to decompose and remove impurities and volatile components and / or to form a composite oxide containing alkali metal and vanadium. it can. Although not particularly limited, for example, the drying can be performed at a temperature of about 80 ° C. to about 250 ° C. for about 1 hour to about 24 hours under reduced pressure or normal pressure. On the other hand, calcination or calcination is generally about 400 ° C. or more and less than about 700 ° C., preferably about 400 ° C. or more and about 650 ° C. or less in an inert atmosphere such as nitrogen or argon or in an oxidizing atmosphere such as air. Alternatively, it can be carried out at a temperature of about 500 ° C. or more and about 600 ° C. or less, particularly 600 ° C. for about 1 hour to about 10 hours.

According to the method of the present invention, the melting point of these composite oxide precursors can be lowered by combining an alkali metal and vanadium. As a result, according to the method of the present invention, the composite oxide containing alkali metal and vanadium is supported in a highly dispersed state on the catalyst support at a lower calcination temperature compared with the conventional catalyst, and therefore at a low temperature. It is possible to easily produce a sulfur trioxide decomposition catalyst with significantly improved sulfur trioxide (SO ₃ ) decomposition activity.

<Method for producing sulfur dioxide>
The method of the present invention for producing sulfur dioxide includes a decomposition reaction in which sulfur trioxide is decomposed into sulfur dioxide and oxygen using the sulfur trioxide decomposition catalyst of the present invention. According to this method, by using the sulfur trioxide decomposition catalyst of the present invention, the sulfur trioxide decomposition reaction is carried out at a temperature lower than that of the conventional method, for example, less than 650 ° C., particularly 600 ° C. Can do.

  For example, at a temperature of 650 ° C. or higher, glass may be formed by reacting alkali metal, particularly sodium, with silica or the like as a catalyst carrier. In such a case, the catalyst may deteriorate and sufficient sulfur trioxide decomposition activity may not be achieved. Therefore, the fact that the sulfur trioxide decomposition reaction can be carried out in a relatively low temperature region of less than 650 ° C., particularly 600 ° C. or less, means that the sulfur trioxide decomposition catalyst of the present invention can be used stably over a long period of time. Is very advantageous.

<Hydrogen generation method>
The method of the present invention for producing hydrogen can be achieved by decomposing water into hydrogen and oxygen, for example by the IS cycle method, Westinghouse cycle method, Ispra-Mark 13 cycle method, or Los Alamos Science Laboratory cycle method. Includes cracking water into hydrogen and oxygen. Here, the method of the present invention for producing hydrogen includes decomposing sulfuric acid into water, sulfur dioxide and oxygen in the reaction represented by the following formula (X1), and of the reaction represented by the following formula (X1). Of the elementary reactions of the formulas (X1-1) and (X1-2) which are elementary reactions, the elementary reaction of the formula (X1-2) is carried out by the method of the present invention in which sulfur dioxide is generated.
(X1) H ₂ SO ₄ → H ₂ O + SO ₂ + 1 / 2O ₂
(X1-1) H ₂ SO ₄ → H ₂ O + SO ₃
(X1-2) SO ₃ → SO ₂ + 1 / 2O ₂

(I-S cycle method)
For example, the method of the present invention for producing hydrogen is represented by the formula (X1) which is an elementary reaction of the reaction of the formula (X1) in the IS (iodine-sulfur) cycle method represented by the following formulas (X1) to (X3). Among the elementary reactions of -1) and (X1-2), the elementary reaction of the formula (X1-2) is carried out by the method of the present invention for producing sulfur dioxide.
(X1) H ₂ SO ₄ → H ₂ O + SO ₂ + 1 / 2O ₂
(X1-1) H ₂ SO ₄ → H ₂ O + SO ₃
(X1-2) SO ₃ → SO ₂ + 1 / 2O ₂
(X2) I ₂ + SO ₂ + 2H ₂ O → 2HI + H ₂ SO ₄
(X3) 2HI → H ₂ + I ₂
Total reaction: H ₂ O → H ₂ + 1 / 2O ₂

(Westinghouse cycle method)
In addition, for example, the method of the present invention for generating hydrogen is a formula (X1), (X4) and a Westinghouse cycle method represented by the following formula (X1): Among the elementary reactions of (X1-1) and (X1-2), the elementary reaction of the formula (X1-2) is carried out by the method of the present invention for producing sulfur dioxide.
(X1) H ₂ SO ₄ → H ₂ O + SO ₂ + 1 / 2O ₂
(X1-1) H ₂ SO ₄ → H ₂ O + SO ₃
(X1-2) SO ₃ → SO ₂ + 1 / 2O ₂
(X4) SO ₂ + 2H ₂ O → H ₂ SO ₃
(X5) H ₂ SO ₃ + H ₂ O + → H ₂ + H ₂ SO ₄ (electrolysis)
Total reaction: H ₂ O → H ₂ + 1 / 2O ₂

(Ispra-Mark 13 cycle method)
Further, for example, the method of the present invention for generating hydrogen is a formula that is an elementary reaction of the reaction of the formula (X1) in the Ispra-Mark 13 cycle method represented by the following formulas (X1), (X6), and (X7). Among the elementary reactions of (X1-1) and (X1-2), the elementary reaction of the formula (X1-2) is carried out by the method of the present invention for producing sulfur dioxide.
(X1) H ₂ SO ₄ → H ₂ O + SO ₂ + 1 / 2O ₂
(X1-1) H ₂ SO ₄ → H ₂ O + SO ₃
(X1-2) SO ₃ → SO ₂ + 1 / 2O ₂
(X6) 2HBr → Br ₂ + H ₂
(X7) Br ₂ + SO ₂ + 2H ₂ O + → 2HBr + H ₂ SO ₄
Total reaction: H ₂ O → H ₂ + 1 / 2O ₂

(Los Alamos Science Laboratory Cycle Method)
Further, for example, the method of the present invention for producing hydrogen is an elementary reaction of the reaction of the formula (X1) in the Los Alamos Science Laboratory cycle method represented by the following formulas (X1) and (X8) to (X10). Among the elementary reactions of the formulas (X1-1) and (X1-2), the elementary reaction of the formula (X1-2) is performed by the method of the present invention for producing sulfur dioxide.
(X1) H ₂ SO ₄ → H ₂ O + SO ₂ + 1 / 2O ₂
(X1-1) H ₂ SO ₄ → H ₂ O + SO ₃
(X1-2) SO ₃ → SO ₂ + 1 / 2O ₂
(X8) Br ₂ + SO ₂ + 2H ₂ O + → 2HBr + H ₂ SO ₄
(X9) 2CrBr ₃ → 2CrBr ₂ + Br ₂
(X10) 2HBr + 2CrBr ₂ → 2CrBr ₃ + H ₂
Total reaction: H ₂ O → H ₂ + 1 / 2O ₂

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these Examples at all.

In the following examples, various sulfur trioxide decomposition catalysts prepared by supporting a composite oxide containing an alkali metal and vanadium on a catalyst support were prepared, and their sulfur trioxide (SO ₃ ) decomposition activity and characteristics were examined. .

[Example 1]
In Example 1, a sulfur trioxide decomposition catalyst in which a composite metal oxide of sodium (Na) and vanadium (V) was supported on a catalyst support (SiO ₂ : KIT-6) was produced.

[Preparation of catalyst support (SiO ₂ : KIT-6)]
The catalyst support was cubic mesoporous silica (KIT-6) and was prepared as follows.
(1) To 144 mL of distilled water, 7.9 g of 35% by mass hydrochloric acid (HCl) and 4.0 g of nonionic surfactant (Pluronic ™ P-123) are added, and the resulting aqueous solution is 35 ° C. Stir at the temperature of to dissolve the ingredients.
(2) Add 4.0 g of 1-butanol to the resulting mixture and stir at a temperature of 35 ° C. until the mixture is clear, thereby self-aligning the nonionic surfactant.
(3) Add 8.6 g of tetraethoxysilane (TEOS) as a silica source to the obtained mixture, vigorously stir for 24 hours at a temperature of 35 ° C., and use a self-aligned nonionic surfactant as a template. As described above, tetraethoxysilane (TEOS) is hydrolyzed.
(4) It is allowed to stand at a temperature of 100 ° C. for 24 hours, and then dried at a temperature of 110 ° C. for 24 hours without washing.
(5) Washing by stirring for 1.5 hours in a mixture of 8 ml of 35% by mass hydrochloric acid and 120 mL of ethanol.
(6) Drying at a temperature of 110 ° C. for 24 hours and heating to 550 ° C. at a temperature increase rate of 3 ° C./min, followed by firing at this temperature for 5 hours to obtain cubic mesoporous silica (KIT-6) Get.

[Production of NaVO ₃ / SiO ₂ ]
First, 1.0 g of the catalyst support (SiO ₂ : KIT-6) prepared above was impregnated with a solution obtained by diluting a predetermined amount of sodium nitrate (NaNO ₃ ) with 3 mL of ultrapure water, and then dried at 110 ° C. overnight. Thereafter, it was calcined in air at 500 ° C. for 2 hours in a decomposition furnace. Next, a predetermined amount of ammonium metavanadate (NH ₄ VO ₃ ) was dissolved in 1M oxalic acid aqueous solution, and this aqueous solution was then impregnated on the catalyst support. Finally, the catalyst support is dried at 110 ° C. overnight and then calcined in a cracking furnace at 600 ° C. for 5 hours to be composed of NaVO ₃ / SiO ₂ (Na: V: Si = 1: 1: 12). A sulfur trioxide decomposition catalyst was obtained.

[Example 2]
[Production of KVO ₃ / SiO ₂ ]
Trioxide made of KVO ₃ / SiO ₂ (K: V: Si = 1: 1: 12) in the same manner as in Example 1 except that potassium nitrate (KNO ₃ ) was used instead of sodium nitrate (NaNO ₃ ). A sulfur decomposition catalyst was obtained.

[Example 3]
[Production of RbVO ₃ / SiO ₂ ]
_Three samples of RbVO ₃ / SiO ₂ (Rb: V: Si = 1: 1: 12) were used in the same manner as in Example 1 except that rubidium nitrate (RbNO ₃ ) was used instead of sodium nitrate (NaNO ₃ ). A sulfur oxide decomposition catalyst was obtained.

[Example 4]
[Production of CsVO ₃ / SiO ₂ ]
_Three samples of CsVO ₃ / SiO ₂ (Cs: V: Si = 1: 1: 12) were used in the same manner as in Example 1 except that cesium nitrate (CsNO ₃ ) was used instead of sodium nitrate (NaNO ₃ ). A sulfur oxide decomposition catalyst was obtained.

[Comparative Example 1]
[Production of CuV ₂ O ₆ / SiO ₂ ]
In this comparative example, a conventional sulfur trioxide decomposition catalyst obtained by supporting a composite oxide of copper (Cu) and vanadium (V) on a catalyst carrier (SiO ₂ : KIT-6) was produced.

Specifically, first, a catalyst carrier (SiO ₂ : KIT-6) prepared above is impregnated with a solution of a predetermined amount of copper nitrate (Cu (NO ₃ ) ₂ ) in water, and then dried at 150 ° C. And calcined at 350 ° C. for 1 hour. Next, a predetermined amount of ammonium metavanadate (NH ₄ VO ₃ ) was dissolved in water, the aqueous solution was impregnated with the above catalyst support, dried at 150 ° C., and calcined at 350 ° C. for 1 hour. Finally, the obtained catalyst support was calcined at 600 ° C. for 2 hours to obtain a sulfur trioxide decomposition catalyst composed of CuV ₂ O ₆ / SiO ₂ (Cu: V: Si = 1: 2: 17).

[Comparative Example 2]
[Production of K-added CuV ₂ O ₆ / SiO ₂ ]
First, a catalyst carrier (SiO ₂ : KIT-6) 0.6 g prepared above is impregnated with a solution obtained by diluting a predetermined amount of potassium nitrate (KNO ₃ ) and copper nitrate (Cu (NO ₃ ) ₂ ) with 3 mL of ultrapure water. Then, after drying overnight at 110 ° C., it was calcined in air at 500 ° C. for 2 hours in a decomposition furnace. Next, a predetermined amount of ammonium metavanadate (NH ₄ VO ₃ ) was dissolved in 1M oxalic acid aqueous solution, and this aqueous solution was then impregnated on the catalyst support. Finally, the catalyst support was dried at 110 ° C. overnight and then calcined in a cracking furnace at 600 ° C. for 5 hours in the presence of K-added CuV ₂ O ₆ / SiO ₂ (Cu: V: K: Si = 1: A sulfur trioxide decomposition catalyst consisting of 2: 1: 17) was obtained.

[Comparative Example 3]
[Production of Cs-added CuV ₂ O ₆ / SiO ₂ ]
Cs-added CuV ₂ O ₆ / SiO ₂ (Cu: V: K: Si = 1: 2) in the same manner as Comparative Example 2 except that cesium nitrate (CsNO ₃ ) was used instead of potassium nitrate (KNO ₃ ). A sulfur trioxide decomposition catalyst consisting of 1:17) was obtained.

[Evaluation of catalyst activity]
Regarding the sulfur trioxide decomposition catalysts of Examples 1 to 4 and Comparative Examples 1 to 3, the sulfur trioxide decomposition reaction of the following formula (X1-2):
(X1-2) SO ₃ → SO ₂ + 1 / 2O ₂
Were evaluated for their sulfur trioxide (SO ₃ ) decomposition activity. Specifically, the sulfur trioxide decomposition reaction was performed as described below using a fixed bed flow reaction apparatus shown in FIG.

First, 0.5 g of a sulfur trioxide decomposition catalyst adjusted to 14 to 20 mesh was packed as a catalyst bed 10 into a quartz reaction tube 4 (inner diameter 10 mm). Next, nitrogen (N ₂ ) and sulfuric acid (H ₂ SO ₄ ) aqueous solutions were supplied to the lower stage of the quartz reaction tube 4 from the nitrogen supply unit 1 and the sulfuric acid supply unit 3, respectively. The weight space velocity (WHSV) was 110 g-H ₂ SO ₄ / g-cat / h corresponding to a relatively high space velocity (SV) condition.

The sulfuric acid (H ₂ SO ₄ ) supplied to the lower stage of the quartz reaction tube 4 is heated in the lower and middle stages of the quartz reaction tube 4 and decomposed into sulfur trioxide (SO ₃ ) and oxygen (O ₂ ), Then, it flows into the catalyst bed 10. Here, in the quartz reaction tube 4, the lower stage was heated to about 400 ° C. by the heater 4a, and the middle stage and the upper stage were heated to about 600 ° C. by the heaters 4b and 4c. The effluent gas from the quartz reaction tube 4 was air-cooled and then bubbled into a 0.05 M iodine (I ₂ ) solution to absorb sulfur dioxide (SO ₂ ) in the iodine solution. Iodometric titration was performed on an iodine solution that had absorbed sulfur dioxide using a 0.025 M sodium thiosulfate (Na ₂ S ₂ O ₃ ) solution to determine the amount of absorbed sulfur dioxide.

The effluent gas after bubbling into the iodine solution is cooled with a dry ice / ethanol mixture, and the remaining sulfur dioxide and sulfur trioxide are completely removed with a mistabsorber and silica gel. The amount of oxygen (O ₂ ) was determined using a MPA3000 (Horiba, Ltd.) and a gas chromatograph (GC8A, molecular sieve 5A, TCD detector, Shimadzu). The arrival rate with respect to the equilibrium conversion rate from sulfur trioxide (SO ₃ ) to sulfur dioxide (SO ₂ ) was calculated from the amounts of sulfur dioxide and oxygen determined as described above. The results are shown in Table 1.

Referring to Table 1, the sulfur trioxide decomposition catalysts of Examples 1 to 4 are the conventional sulfur trioxide decomposition catalyst (CuV ₂ O ₆ / SiO ₂ ) of Comparative Example 1 and Comparative Example 2 in which an alkali metal is added thereto. Compared to 3 sulfur trioxide cracking catalyst, it exhibits a significantly higher equilibrium conversion at a relatively low temperature of 600 ° C. and therefore has significantly higher sulfur trioxide (SO ₃ ) cracking activity. It is understood that Further, in Comparative Examples 2 and 3 of the sulfur trioxide decomposition catalyst with the addition of alkali metal to CuV ₂ O ₆ / SiO ₂ of Comparative Example 1, but showed a high SO ₃ decomposition activity than the catalyst of Comparative Example 1, performed Compared with the sulfur trioxide decomposition catalyst of Examples 1-4, the activity fell significantly. From this result, it was found that the alkali metal vanadate itself has a high SO ₃ decomposition activity.

  Next, for the sulfur trioxide decomposition catalysts of Examples 1 to 4 and Comparative Examples 1 to 4, first, the upper stage of the quartz reaction tube 4 was heated to 750 ° C. by the heater 4c, and then at this temperature for about 1 hour. After carrying out the sulfur trioxide decomposition reaction, the arrival rate with respect to the equilibrium conversion rate of each sulfur trioxide decomposition catalyst when the temperature was lowered to 600 ° C. was examined. The results are shown in Table 2.

Referring to Table 2, in the sulfur trioxide decomposition catalyst of Comparative Example 1, when the reaction temperature was once increased to 750 ° C. and then decreased again to 600 ° C., the reach to the equilibrium conversion rate was 5.5% of Table 1. It can be seen that there is a significant improvement from 34.0%. This is considered to be due to the fact that the composite oxide composed of CuV ₂ O ₆ spreads in a thin layer on the catalyst support by using it at a high temperature such as 750 ° C., and its dispersibility is improved. On the other hand, in the sulfur trioxide decomposition catalysts of Examples 1 to 4, the reach to the equilibrium conversion rate is somewhat lowered by once raising the reaction temperature to 750 ° C., and three of Example 1 using sodium as the alkali metal. Such a decrease was particularly remarkable in the sulfur oxide decomposition catalyst.

  In the sulfur trioxide decomposition catalyst of the present invention, it is considered that a complex oxide composed of a uniform thin layer has already been formed on the catalyst support by firing at about 600 ° C. during catalyst preparation. Therefore, even if it is used at a high temperature such as 750 ° C., the catalyst activity is not improved, and conversely, it is considered that the catalyst is somewhat deteriorated due to the reaction between the alkali metal and the catalyst carrier. However, nonetheless, in all of the sulfur trioxide decomposition catalysts of Examples 1 to 4, a high attainment rate is maintained as compared with the sulfur trioxide decomposition catalyst of Comparative Example 1, and therefore high sulfur trioxide decomposition activity is maintained. Could be achieved. In addition, in the sulfur trioxide decomposition catalyst of Comparative Examples 2 and 3 in which an alkali metal was added to the sulfur trioxide decomposition catalyst of Comparative Example 1, the arrival rate with respect to the equilibrium conversion rate was decreased, and therefore, the trioxide as in Comparative Example 1 was reduced. No improvement in sulfur decomposition activity was observed. Although not shown in Tables 1 and 2, although the sulfur trioxide decomposition catalyst of Example 4 having the highest performance was subjected to a sulfur trioxide decomposition reaction over a long period of time, no significant deterioration of the catalyst was observed. Therefore, it was confirmed that the catalyst exhibits high durability even under severe conditions such as in a concentrated sulfuric acid stream.

[Structural analysis of catalyst by X-ray diffraction (XRD)]
Next, the sulfur trioxide decomposition catalyst of Example 4 and Comparative Examples 1 and 3 in which the highest sulfur trioxide decomposition activity was obtained were measured by X-ray diffraction (XRD). The result is shown in FIG.

  FIG. 4 shows the X-ray diffraction patterns for the sulfur trioxide decomposition catalyst of Example 4 and Comparative Examples 1 and 3. FIG. 4 shows an X-ray diffraction pattern after firing at 600 ° C. and after reaction at 750 ° C. for each catalyst. Referring to FIG. 4, although a small diffraction peak due to CuO was observed in the catalysts of Comparative Examples 1 and 3, no significant peak was observed in any of the catalysts except for some impurities. This suggests that there are no crystals as large as observed by X-ray diffraction in each catalyst, especially the catalyst of Example 4.

[Analysis of catalysts by Raman scattering]
The sulfur trioxide decomposition catalyst of Example 4 was measured using a Raman spectrometer. The result is shown in FIG. FIG. 5 shows the analysis result of the sulfur trioxide decomposition catalyst of Example 4 by Raman spectroscopy. FIG. 5 shows, for reference, analysis results obtained by measuring samples of CsVO ₃ and CsV ₃ O ₈ alone that are not supported on the catalyst carrier.

Referring to FIG. 5, the peak near 940 cm ⁻¹ attributed to the symmetric stretching of VO ₃ of CsVO ₃ is higher than the peak of CsVO ₃ shown as a reference in the sulfur trioxide decomposition catalyst of Example 1. It can be seen that it has shifted to several sides and is broad. This shift toward the high wave number suggests that the VO bond in VO ₃ is strengthened, and therefore, the contribution to the improvement of sulfur trioxide decomposition activity is considered to be small. On the other hand, the broadening of the peak is attributed to the fact that the composite oxide composed of CsVO ₃ spreads thinly on the catalyst support (silica) or to the microcrystallization of the composite oxide. It is done.

DESCRIPTION OF SYMBOLS 1 Nitrogen supply part 3 Sulfuric acid supply part 4 Quartz reaction tube 4a, 4b, 4c Heater 10 Catalyst bed

Claims (18)

  A sulfur trioxide decomposition catalyst obtained by supporting a composite oxide containing an alkali metal and vanadium on a catalyst carrier.   The sulfur trioxide decomposition catalyst according to claim 1, wherein the alkali metal is selected from the group consisting of sodium, potassium, rubidium, cesium, and combinations thereof.   The sulfur trioxide decomposition catalyst according to claim 2, wherein the alkali metal is selected from the group consisting of potassium, cesium, and combinations thereof.   The sulfur trioxide decomposition catalyst according to any one of claims 1 to 3, wherein an atomic ratio of alkali metal to vanadium (alkali metal: vanadium) in the composite oxide is 1: 1 to 1: 8. The composite oxide comprises an alkali metal vanadate represented by the formula A _1-x VO _3-0.5x (wherein A is an alkali metal and 0 ≦ x <1). The sulfur trioxide decomposition catalyst according to any one of the above. The sulfur trioxide decomposition catalyst according to claim 5, wherein the composite oxide includes an alkali metal metavanadate represented by the formula AVO ₃ (wherein A is an alkali metal). Wherein the alkali metal is cesium, the composite _{oxide, CsVO 3, Cs 2 V 4} O 11, CsV 3 O 8, or combinations thereof, according to any one of claims 3 to 5 three Sulfur oxide decomposition catalyst.   The sulfur trioxide decomposition catalyst according to any one of claims 1 to 7, wherein the catalyst support is selected from the group consisting of silica, alumina, zirconia, titania, and combinations thereof.   The sulfur trioxide decomposition catalyst according to claim 8, wherein the catalyst support has mesopores and / or macropores.   The sulfur trioxide decomposition catalyst according to claim 8 or 9, wherein the catalyst support is silica. (A) impregnating a catalyst carrier with one solution of an alkali metal compound solution and a vanadium compound solution, drying and pre-baking, and (b) the other of an alkali metal compound solution and a vanadium compound solution. The catalyst support obtained in step (a) is impregnated with the above solution, dried and calcined, and the catalyst is supported on a composite oxide containing alkali metal and vanadium. Method.   Production of a sulfur trioxide decomposition catalyst comprising a catalyst carrier carrying a composite oxide containing an alkali metal and vanadium, comprising impregnating a catalyst carrier with a solution containing an alkali metal compound and a vanadium compound, followed by drying and firing. Method.   The method of Claim 11 or 12 with which the said baking is implemented at the temperature of 400 to 650 degreeC.   The method according to claim 13, wherein the baking is performed at a temperature of 500 ° C. or higher and 600 ° C. or lower.   The production | generation method of sulfur dioxide including the decomposition | disassembly reaction which decomposes | disassembles sulfur trioxide into sulfur dioxide and oxygen using the sulfur trioxide decomposition catalyst of any one of Claims 1-10.   The method according to claim 15, wherein the decomposition reaction is performed at a temperature of 600 ° C. or less. A method for producing hydrogen comprising decomposing water into hydrogen and oxygen, the method comprising decomposing sulfuric acid into water, sulfur dioxide and oxygen in the reaction represented by the following formula (X1): The elementary reaction of the formula (X1-2) among the elementary reactions of the formulas (X1-1) and (X1-2), which is an elementary reaction of the reaction represented by formula (X1-2), is carried out by the method according to claim 15 or 16. , Hydrogen generation method:
(X1) H ₂ SO ₄ → H ₂ O + SO ₂ + 1 / 2O ₂
(X1-1) H ₂ SO ₄ → H ₂ O + SO ₃
(X1-2) SO ₃ → SO ₂ + 1 / 2O ₂   The hydrogen generation method according to claim 17, which is an IS cycle method, a Westinghouse cycle method, an Ispra-Mark 13 cycle method, or a Los Alamos Science Laboratory cycle method.

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