Catalyst for reverse water-gas shift reaction and method for producing carbon monoxide using the same

Abstract

To provide a catalyst for inverse water gas shift reaction excellent in catalytic activity and having high reactivity even under a reaction condition of low temperature and a production method of carbon monoxide using the same.SOLUTION: A catalyst for inverse water gas shift reaction is used to produce carbon monoxide from carbon dioxide and hydrogen. The catalyst for inverse water gas shift reaction includes a metal oxide carrier, a complex oxide carried by the metal oxide carrier, and a metal catalyst. The complex oxide contains an oxide of at least one metal element selected from the group consisting of the group 4 elements, the group 5 elements, and the group 6 elements of the periodic table as a first metal oxide and an oxide of at least one metal element selected from the group consisting of the group 1 elements and the group 2 elements of the periodic table as a second metal oxide.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a catalyst for reverse water-gas shift reactions and a method for producing carbon monoxide using the same. [Background technology]

[0002] In recent years, research has been conducted on converting carbon dioxide (CO2) into basic chemicals by reducing it with hydrogen (H2), a renewable energy source, with the aim of creating a sustainable low-carbon society based on green and sustainable chemistry. For example, carbon monoxide (CO), obtained by reducing CO2 with H2, is a useful chemical raw material as a carbonyl raw material in organic synthesis and as a raw material for liquid hydrocarbons such as alcohol, jet fuel, and gasoline.

[0003] One known method for reducing CO2 with H2 is the reverse water-gas shift reaction shown in equation (1) below. CO2 + H2 → CO + H2O ... (1)

[0004] The reverse water-gas shift reaction is an equilibrium reaction, an endothermic reaction, and is favored at high temperatures. Catalysts for the reverse water-gas shift reaction have been reported, for example, those containing alkaline earth metal carbonates consisting of Ca, Sr, or Ba, and composite oxides of Ca, Sr, or Ba with Ti, Al, Zr, Fe, W, or Mo (see Patent Document 1). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2010-194534 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, the catalyst described in Patent Document 1 does not have sufficient catalytic activity, requiring the reaction temperature of the reverse water-gas shift reaction to be 700°C or higher, and energy conservation was desired. Furthermore, because a high reaction temperature is required, special manufacturing equipment such as materials with high heat resistance and multi-stage heat exchangers is necessary, which leads to an increase in the production cost of CO. Moreover, prolonged exposure of the catalyst under high temperature conditions accelerates catalyst degradation, leading to a further increase in manufacturing costs. On the other hand, under low-temperature reaction conditions, the reactivity decreases due to equilibrium constraints, making it difficult to efficiently produce CO by the reverse water-gas shift reaction.

[0007] The present invention aims to provide a catalyst for reverse water-gas shift reactions that exhibits high reactivity even under low-temperature reaction conditions and has excellent catalytic activity, and a method for producing carbon monoxide using the same. [Means for solving the problem]

[0008] The inventors conducted extensive research to solve the above problems and, as a result, discovered that the above problems can be solved by using a catalyst comprising a metal oxide support, a composite oxide containing an oxide of a specific metal element supported on the metal oxide support, and a metal catalyst, thus completing the present invention.

[0009] In other words, the present invention encompasses the following embodiments. [1] A catalyst for a reverse water-gas shift reaction used to produce carbon monoxide from carbon dioxide and hydrogen, the catalyst comprising a metal oxide support, a composite oxide supported on the metal oxide support, and a metal catalyst, The composite oxide comprises, as the first metal oxide, an oxide of at least one metal element selected from the group consisting of Group 4 elements, Group 5 elements, and Group 6 elements, As the second metal oxide, an oxide of at least one metal element selected from the group consisting of Group 1 elements and Group 2 elements, A catalyst for reverse water-gas shift reactions, including the following: [2] The catalyst for the reverse water-gas shift reaction according to [1], wherein the metal oxide support is TiO2. [3] The catalyst for the reverse water-gas shift reaction according to [1] or [2], wherein the metal catalyst is Pt. [4] The catalyst for a reverse water-gas shift reaction according to any one of [1] to [3], wherein the first metal oxide is an oxide of at least one metal element selected from the group consisting of Mo, V, Nb, and W. [5] The catalyst for the reverse water-gas shift reaction according to any one of [1] to [4], wherein the second metal oxide is an oxide of at least one metal element selected from the group consisting of Rb, Cs, Ca, Sr, and Ba. [6] The catalyst for the reverse water-gas shift reaction according to any one of [1] to [5], wherein the first metal oxide is an oxide of Mo. [7] The catalyst for the reverse water-gas shift reaction according to [6], wherein the content of the Mo oxide is 0.2 to 3.0% by mass as the Mo metal element, based on the total amount of the catalyst for the reverse water-gas shift reaction. [8] The catalyst for a reverse water-gas shift reaction according to any one of [1] to [7], wherein the composite oxide further comprises a lanthanide oxide as a third metal oxide. [9] The catalyst for the reverse water-gas shift reaction according to [8], wherein the third metal oxide is an oxide of at least one metal element selected from the group consisting of La, Ce, Pr, Nd, Eu, Gd, Dy, Er, and Lu.

[10] A reverse water-gas shift reaction step is provided, in which a raw material gas containing carbon dioxide and hydrogen is brought into contact with a reverse water-gas shift reaction catalyst described in any of [1] to [9] to obtain a product gas containing carbon monoxide. A method for producing carbon monoxide.

[11] The method for producing carbon monoxide according to

[10] , wherein the reaction temperature of the reverse water-gas shift reaction step is 100 to 400°C. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a catalyst for the reverse water gas shift reaction having excellent catalytic activity with high reactivity even under low-temperature reaction conditions, and a method for producing carbon monoxide using the same.

Mode for Carrying Out the Invention

[0011] Hereinafter, the present invention will be described in detail. The description of the constituent elements described below is an exemplification for explaining the present invention, and the present invention is not limited to these contents.

[0012] (Catalyst for Reverse Water Gas Shift Reaction) The catalyst for the reverse water gas shift reaction according to the present embodiment is used for producing CO from CO2 and H2, and includes a metal oxide carrier, a composite oxide supported on the metal oxide carrier, and a metal catalyst.

[0013] Although the mechanism of action of the catalyst for the reverse water gas shift reaction according to the present embodiment has not been fully clarified, an example of the presumed mechanism of action is shown below. In the reverse water gas shift reaction catalyst according to the present embodiment, a composite oxide containing, for example, an oxide of molybdenum is supported on a metal oxide carrier, and a metal catalyst is further supported on the metal oxide carrier and / or the composite oxide. It is presumed that the catalyst for the reverse water gas shift reaction according to the present embodiment has excellent reactivity even under low-temperature reaction conditions because the oxygen deficiency of the oxide constituting the composite oxide is responsible for the adsorption and activation of CO2, and the metal catalyst is responsible for the dissociation of H2, due to the cooperative catalytic action of the composite oxide and the metal catalyst. In addition, since the metal oxide carrier supporting the composite oxide and / or the metal catalyst has a porous structure, it has a large specific surface area and many reaction active sites. Therefore, it is presumed that the reverse water gas shift reaction catalyst according to the present embodiment has high reactivity for the reverse water gas shift reaction even under low-temperature reaction conditions.

[0014] <Metal Oxide Carrier> The main role of the metal oxide carrier is to support a composite oxide and / or a metal catalyst having activity as a catalyst.

[0015] From the perspective of being able to further promote the reverse water gas shift reaction, the metal oxide carrier of this embodiment has a porous structure. Note that a catalyst without a carrier such as that in Patent Document 1 is usually formed at a firing temperature of 1000 °C or higher. In this case, the catalyst cannot form a porous structure and tends to be inferior in reactivity to the reverse water gas shift reaction. On the other hand, since the catalyst for the reverse water gas shift reaction of this embodiment includes a metal oxide carrier having a porous structure, it has a large specific surface area and many reactive sites, and is excellent in catalytic activity.

[0016] The metal oxide carrier is not limited as long as it can form a porous structure. For example, titanium oxide (TiO2), zirconium oxide (ZrO2), aluminum oxide (Al2O3), or silicon oxide (SiO2), etc. can be mentioned. Among these, TiO2 is preferred from the perspective of being able to further promote the reverse water gas shift reaction.

[0017] The catalyst for the reverse water gas shift reaction may be in powder form. On the other hand, from the perspective of densely filling the reaction system, the metal oxide carrier is preferably a molded body such as a spherical or cylindrical shape.

[0018] The particle size of the primary particles of the particles as the metal oxide carrier is preferably 10 nm or more, more preferably 50 nm or more. Also, as the particle size, it is preferably 1000 nm or less, more preferably 800 nm or less. If the particle size is 10 nm or more, the production efficiency of CO can be increased without deteriorating the contact efficiency in the reaction system. Also, if the particle size is 1000 nm or less, it is easy to obtain a sufficient specific surface area and tends to be able to further promote the reverse water gas shift reaction. The particle size of the primary particles of the particles can be determined by X-ray diffraction method.

[0019] The specific surface area of the particles as the metal oxide carrier is preferably 10 m 2 / g or more, more preferably 20 m 2 / g or more, and even more preferably 30 m 2A value of 1,000 m² or more is even more preferable. On the other hand, the specific surface area should be 1,000 m² from the viewpoint of maintaining catalyst strength. 2 Preferably less than / g, 500m 2 Less than / g is more preferable, 400m 2 A value of less than / g is even more preferable. The specific surface area of ​​particles used as metal oxide supports can be determined by the Brunauer-Emmett-Teller (BET) single-point method.

[0020] <Complex Oxides> The composite oxide is supported on a metal oxide support. The composite oxide serves both as a support for the metal catalyst (described later) and as a catalyst to promote the reverse water-gas shift reaction. Furthermore, the composite oxide has the function of improving the mechanical strength of the catalyst for the reverse water-gas shift reaction.

[0021] The composite oxide is thought to develop oxygen vacancies upon reduction. These oxygen-vacuated sites can function as active sites in a reaction that extracts oxygen atoms from CO2 to produce CO. Therefore, the composite oxide according to this embodiment serves both as a support for the metal catalyst described later and as a catalyst that promotes the reverse water-gas shift reaction.

[0022] The composite oxide includes, as a first metal oxide, an oxide of at least one metal element selected from the group consisting of Group 4 elements, Group 5 elements, and Group 6 elements, and as a second metal oxide, an oxide of at least one metal element selected from the group consisting of Group 1 elements and Group 2 elements. By combining the first metal oxide with the second metal oxide, the reactivity of the reverse water-gas shift reaction can be further improved.

[0023] <<First Metal Oxide>> The first metal oxide is not particularly limited as long as it is an oxide of a metal element belonging to Group 4, Group 5, or Group 6 of the periodic table of long-period elements as defined by IUPAC (International Union of Pure and Applied Chemistry). Specifically, the first metal oxide can be an oxide of titanium (Ti), zirconium (Zr), hafnium (Hf), rutherfordium (Rf), vanadium (V), niobium (Nb), tantalum (Ta), dubnium (Db), chromium (Cr), molybdenum (Mo), tungsten (W), or seaborgium (Sg). The first metal oxide may be a single type or two or more types may be used.

[0024] Among the above, from the viewpoint of excellent reactivity in the reverse water-gas shift reaction, the first metal oxide is preferably an oxide of at least one metal element selected from the group consisting of V, Nb, Mo, and W, and is particularly preferably an oxide of Mo.

[0025] Mo is known to be able to take on at least eight oxidation states: 6, 5, 4, 3, 2, 1, -1, and -2. At least two molybdenum oxides of Mo are known, for example, molybdenum(IV) oxide (MoO2) and molybdenum(VI) oxide (MoO3). Of these molybdenum oxides, molybdenum(VI) oxide (MoO3) is more preferred from the viewpoint of exhibiting excellent reactivity in the reverse water-gas shift reaction after appropriate reduction treatment. However, it is thought that molybdenum oxide can take on different oxidation states through reduction and reverse shift reactions.

[0026] <<Second Metal Oxide>> The second metal oxide is not particularly limited as long as it is an oxide of a metal element belonging to Group 1 or Group 2 of the periodic table of long-period elements as defined by IUPAC (International Union of Pure and Applied Chemistry). Specifically, the second metal oxide can be an oxide of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), or radium (Ra). The second metal oxide may be a single element or two or more elements may be used.

[0027] Among the above, from the viewpoint of excellent reactivity in the reverse water-gas shift reaction, the second metal oxide is preferably an oxide of at least one metal element selected from the group consisting of Rb, Cs, Ca, Sr, and Ba.

[0028] <<The third metal oxide>> The composite oxide may optionally further contain a third metal oxide. The third metal oxide is preferably an oxide of at least one metal element selected from the group consisting of Group 3, Group 14, and Group 15 elements in the long-period periodic table as defined by IUPAC (International Union of Pure and Applied Chemistry), and more preferably an oxide of a lanthanide. A lanthanide refers to any metal element with atomic numbers 57 to 71, including atomic numbers 57 and 71. The third metal oxide may be a single element or two or more elements may be used.

[0029] Among lanthanides, from the viewpoint of excellent reactivity in the reverse water-gas shift reaction, the third metal element is preferably an oxide of at least one metal element selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), europium (Eu), gadolinium (Gd), dysprosium (Dy), erbium (Er), and lutetium (Lu).

[0030] In addition to the lanthanide oxides mentioned above, other metal oxides that can be used as a third metal oxide include scandium (Sc), which belongs to Group 3 of the periodic table; tin (Sn), which belongs to Group 14 of the periodic table; or bismuth (Bi), which belongs to Group 15 of the periodic table.

[0031] From the viewpoint of excellent reactivity in the reverse water-gas shift reaction, the content of metal oxides in the composite oxide is preferably 0.5% by mass or more, more preferably 0.7% by mass or more, and even more preferably 1.0% by mass or more, based on the total amount of catalyst for the reverse water-gas shift reaction. On the other hand, from the viewpoint of balancing oxygen abstraction and hydrogenation, the content is preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 7% by mass or less, based on the total amount of catalyst for the reverse water-gas shift reaction. Note that the content of metal oxides in the composite oxide is the sum of the content of two or more metal elements, including the first metal oxide, the second metal oxide, and an arbitrary third metal oxide.

[0032] When the first metal oxide contains molybdenum oxide (MoO3), which is an oxide of Mo, the content of Mo as a metal element is preferably 0.2% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more, based on the total amount of catalyst for the reverse water-gas shift reaction, from the viewpoint of excellent reactivity in the reverse water-gas shift reaction. On the other hand, from the viewpoint of economic process, the content is preferably 3.0% by mass or less, more preferably 2.0% by mass or less, and even more preferably 1.0% by mass or less, based on the total amount of catalyst for the reverse water-gas shift reaction. In conventional catalysts, the Mo content is typically 10% by mass or more, based on the total catalyst amount. The inventors have for the first time discovered that catalysts containing molybdenum oxide within the above range as a composite oxide exhibit excellent reactivity in the reverse water-gas shift reaction.

[0033] As described above, the composite oxide may be used as a metal oxide and may be oxidized after being supported on a carrier as a metal, or it may be supported on a carrier as a metal oxide as is.

[0034] <Metal catalyst> The metal catalyst is supported on a metal oxide support and / or a composite oxide. The metal catalyst functions as a catalyst that promotes the reverse water-gas shift reaction.

[0035] The metal catalyst is not particularly limited as long as it promotes the reverse water-gas shift reaction, but it is preferably a metal element belonging to Group 8, Group 9, or Group 10 of the periodic table of long-period elements as defined by IUPAC (International Union of Pure and Applied Chemistry). Among these, nickel (Ni), iron (Fe), cobalt (Co), ruthenium (Ru), rhodium (Rh), palladium (Pd), or platinum (Pt) are preferred as metal catalysts, with Pt being particularly preferred. The metal catalyst may be used alone or in combination of two or more types.

[0036] From the viewpoint of excellent reactivity in the reverse water-gas shift reaction, the metal catalyst content is preferably 0.1% by mass or more, and more preferably 0.5% by mass or more, based on the total amount of catalyst for the reverse water-gas shift reaction. On the other hand, from an economic viewpoint, the content is preferably 10.0% by mass or less, and more preferably 5.0% by mass or less, based on the total amount of catalyst for the reverse water-gas shift reaction.

[0037] <Other ingredients> The catalyst for the reverse water-gas shift reaction may optionally contain other components, such as molding aids, as long as they do not impair the objectives of the present invention, from the viewpoint of improving moldability. The molding aid may be at least one selected from the group consisting of, for example, thickeners, surfactants, water-retaining agents, plasticizers, binder raw materials, etc. Furthermore, the catalyst for the reverse water-gas shift reaction may contain other useful components as long as they do not impair the objectives of the present invention.

[0038] (Method for preparing a catalyst for a reverse water-gas shift reaction) The catalyst for the reverse water-gas shift reaction is not particularly limited and can be prepared by conventionally known methods. For example, a catalyst for a reverse water-gas shift reaction can be obtained by a method that includes the steps of: mixing an aqueous solution of a metal oxide support and a composite oxide precursor, removing the solvent, and then calcining a solid containing the remaining metal oxide support and composite oxide; and contacting the solid with an aqueous solution of a metal catalyst precursor, removing the solvent, and then calcining a solid containing the remaining metal oxide support, composite oxide, and metal catalyst.

[0039] There are no particular restrictions on the firing temperature when firing solid materials, but 300 to 600°C is preferred. If the firing temperature is 300°C or higher, it is easier to obtain thermal stability that can withstand long-term use, and catalysts with high catalytic activity tend to be obtained. Also, if the firing temperature is 600°C or lower, the metal oxide support tends to form a porous structure. There are no particular restrictions on the firing time, but 0.1 to 24 hours is preferred.

[0040] Catalysts for reverse water-gas shift reactions are usually reduced before being used as reaction catalysts. The method of reduction is not particularly limited. For example, the catalyst for the reverse water-gas shift reaction can be reduced by heating it in an atmosphere containing hydrogen gas. The heating temperature for the reduction is, for example, 150 to 450°C. The reduction time is, for example, 0.1 to 5 hours.

[0041] (Method for producing carbon monoxide) The carbon monoxide production method according to this embodiment comprises a reverse water-gas shift reaction step, in which a raw material gas containing CO2 and H2 is brought into contact with the reverse water-gas shift reaction catalyst according to this embodiment described above to obtain a product gas containing CO, as shown in formula (2) below. CO2 + H2 → CO + H2O ... (2)

[0042] <Raw material gas> The raw material gas only needs to contain at least CO2 and H2. The source of CO2 and H2 is not particularly restricted. For example, CO2 can be used as is from a mixed gas generated in processes where hydrocarbons are burned as fuel or unreacted hydrocarbons are burned in petroleum refining, petrochemicals, power generation, steelmaking, boilers, etc., or it can be used after being purified. Alternatively, CO2 from the atmosphere may be concentrated and used.

[0043] The volume ratio of CO2 to H2 in the raw material gas (H2 / CO2) is not particularly limited, but 7:1 to 1:2 is preferred, and 5:1 to 1:1 is more preferred. A higher H2 / CO2 ratio in the raw material gas tends to facilitate the reverse water-gas shift reaction, but if it is too high, the side reaction of methane reaction tends to occur more easily.

[0044] The raw material gas may further contain other compounds besides CO2 and H2, as long as they do not inhibit the reverse water-gas shift reaction. For example, it may further contain inert gases such as nitrogen or argon.

[0045] <Reverse water-gas shift reaction process> In the reverse water-gas shift reaction process, for example, the reaction may be carried out by using a reactor filled with a catalyst for the reverse water-gas shift reaction and flowing the raw material gas through the reactor. Various reactors used for gas-phase reactions with solid catalysts can be used as the reactor. Examples of reactors include fixed-bed reactors, radial-flow reactors, and tubular reactors.

[0046] When the raw material gas is brought into contact with the catalyst for the reverse water gas shift reaction (which can also be referred to as the reaction temperature of the reverse water gas shift reaction or the temperature in the reactor), from the viewpoints of energy conservation and production cost, it is preferably 400 °C or lower, and more preferably 300 °C or lower. Since the catalyst for the reverse water gas shift reaction according to this embodiment is excellent in catalytic activity as described above, CO can be efficiently produced even at a low temperature of 400 °C or lower. On the other hand, from the viewpoint of further improving the yield and production rate of CO, the temperature is preferably 100 °C or higher, and more preferably 150 °C or higher.

[0047] The pressure when the raw material gas is brought into contact with the catalyst for the reverse water gas shift reaction (which can also be referred to as the reaction pressure of the reverse water gas shift reaction or the pressure in the reactor) is not particularly limited, and for example, it may be 0 to 4.0 MPaG.

[0048] When the reverse water gas shift reaction step is carried out in a continuous reaction mode in which raw materials are continuously supplied, the gas hourly space velocity (hereinafter sometimes referred to as "GHSV") is preferably 10 h -1 or higher, and more preferably 100 h -1 or higher. If the GHSV is 10 h -1 or higher, the reactor size can be made smaller. On the other hand, the GHSV is preferably 100,000 h -1 or lower, and preferably 50,000 h -1 or lower. If the GHSV is 100,000 h -1 or lower, the yield of CO tends to be higher. Here, the GHSV is the ratio (F / V) of the supply rate (supply amount / hour) F of the raw material gas to the capacity V of the catalyst for the reverse water gas shift reaction in a continuous reaction apparatus. The amounts of the raw material gas and the catalyst used may be appropriately selected within a more preferable range according to the reaction conditions, the activity of the catalyst, etc., and the GHSV is not limited to the above range.

Examples

[0049] The present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited to these examples.

[0050] <Example 1> (Preparation of catalyst for reverse water-gas shift reaction) A mixture of 3.67 mg of pentakis(hydrogen oxalate)niobium(V)(n-hydrate) (Mitsuwa Chemical Co., Ltd.) as a complex oxide precursor, 4.42 mg of hexaammonium heptamolybdate tetrahydrate (Fujifilm Wako Pure Chemical Industries, Ltd.), 2.28 mg of barium nitrate (Kanto Chemical Co., Ltd.), 286.6 mg of titanium dioxide (P-25, Nippon Aerosil) as a metal oxide support, and 100 mL of water was stirred at room temperature for 30 minutes. The solvent was removed by distillation under reduced pressure while heating the mixture to 50°C, and the residue was dried at 110°C for 1 hour. The dried solid was ground using an agate mortar and pestle. The resulting powder was calcined at 500°C for 3 hours in an air atmosphere to obtain particles containing titanium dioxide, supported niobium oxide, molybdenum oxide, and barium oxide. 150 mg of the obtained particles were mixed with 0.1 g of dinitrodiammineplatinum(II) nitric acid solution (Furuya Metal, Pt purity 4.60 wt%) as a metal catalyst precursor and 20 mL of water, and stirred at room temperature for 30 minutes. The solvent was removed by distillation under reduced pressure while heating the mixture to 50°C, and the residue was dried at 110°C for 1 hour. The dried solid was ground in an agate mortar and pestle to obtain the catalyst for the reverse water-gas shift reaction of Example 1, which contains titanium dioxide, niobium oxide (0.2 mass as Nb), molybdenum oxide (0.8 mass as Mo), barium oxide (0.4 mass as Ba), and platinum (3.0 mass as Pt) supported thereon.

[0051] (Production of carbon monoxide) Ten mg of the reverse water-gas shift catalyst was reduced at 300°C for 0.5 hours under atmospheric pressure with a hydrogen flow of 40 mL / min. The entire reduced volume of the reverse water-gas shift catalyst was loaded into a fixed-bed reactor. Subsequently, 60 mL / min of hydrogen, 20 mL / min of carbon dioxide, and 5 mL / min of nitrogen were introduced into the fixed-bed reactor at atmospheric pressure. The reaction was carried out at 250°C.

[0052] Forty hours after the start of the reaction, the product gas was collected from the fixed-bed reactor. The start of the reaction refers to the time when the supply of the raw material gas began. The collected product gas was analyzed using a gas chromatograph (TCD-GC) equipped with a thermal conductivity detector. Based on the gas chromatography data, each component of the collected product gas was quantified, and the carbon monoxide yield was calculated. The reaction rate of carbon monoxide per amount of catalyst was also calculated. The results are shown in Table 1.

[0053] The reaction rate of carbon monoxide per catalyst was determined as follows. The CO2 supply rate was calculated from the CO2 concentration and flow rate, and the CO production rate (mmol / min) was determined by multiplying the CO supply rate by the CO yield. Furthermore, the CO production rate per unit amount of catalyst (mmol / min / gcat) was calculated by dividing the CO production rate by the amount of catalyst (g) for the reverse water-gas shift reaction.

[0054] <Example 2> Except for using 3.67 mg of pentakis(hydrogen oxalate)niobium(V)(n-hydrate) (Mitsuwa Chemical Co., Ltd.), 4.42 mg of hexaammonium heptamolybdate tetrahydrate (Fujifilm Wako Pure Chemical Industries, Ltd.), 0.81 mg of rubidium carbonate (Fujifilm Wako Pure Chemical Industries, Ltd.), and 1.24 mg of lutetium nitrate (Fujifilm Wako Pure Chemical Industries, Ltd.) instead of the composite oxide precursor of Example 1, the catalyst for the reverse water-gas shift reaction of Example 2 was obtained by the same procedure as in Example 1. The catalyst for the reverse water-gas shift reaction of Example 2 comprises titanium dioxide, niobium oxide (0.2 mass as Nb), molybdenum oxide (0.8 mass as Mo), rubidium oxide (0.2 mass as Rb), lutetium oxide (0.2 mass as Lu), and platinum (3.0 mass as Pt) supported thereon. The carbon monoxide yield and the reaction rate of carbon monoxide per catalyst were calculated using the same procedure as in Example 1. The results are shown in Table 1.

[0055] <Example 3> Except for using 18.34 mg of pentakis(hydrogen oxalate)niobium(V)(n-hydrate) (Mitsuwa Chemical Co., Ltd.), 5.52 mg of hexaammonium heptamolybdate tetrahydrate (Fujifilm Wako Pure Chemical Industries, Ltd.), 4.05 mg of rubidium carbonate (Fujifilm Wako Pure Chemical Industries, Ltd.), and 17.22 mg of gadolinium nitrate (Fujifilm Wako Pure Chemical Industries, Ltd.) instead of the composite oxide precursor of Example 1, the catalyst for the reverse water-gas shift reaction of Example 3 was obtained by the same procedure as in Example 1. The catalyst for the reverse water-gas shift reaction of Example 3 comprises titanium dioxide, niobium oxide (1.0% by mass as Nb), molybdenum oxide (1.0% by mass as Mo), rubidium oxide (1.0% by mass as Rb), gadolinium oxide (2.0% by mass as Gd), and platinum (3.0% by mass as Pt) supported thereon. The yield of carbon monoxide and the reaction rate of carbon monoxide per amount of catalyst for the reverse water-gas shift reaction were calculated using the same procedure as in Example 1. The results are shown in Table 1.

[0056] <Example 4> The catalyst for the reverse water-gas shift reaction of Example 4 was obtained by the same procedure as in Example 1, except that 4.42 mg of hexaammonium heptamolybdate tetrahydrate (Fujifilm Wako Pure Chemical Industries), 3.43 mg of barium nitrate (Kanto Chemical), 1.27 mg of erbium nitrate n hydrate (Fujifilm Wako Pure Chemical Industries), and 4.18 mg of bismuth nitrate pentahydrate (Fujifilm Wako Pure Chemical Industries) were used instead of the composite oxide precursor of Example 1. The catalyst for the reverse water-gas shift reaction of Example 4 has titanium dioxide, supported thereon molybdenum oxide (0.8 mass%), barium oxide (0.6 mass%), erbium oxide (0.2 mass%), bismuth oxide (0.6 mass%), and platinum (3.0 mass%). The yield of carbon monoxide and the reaction rate of carbon monoxide per amount of catalyst for the reverse water-gas shift reaction were calculated using the same procedure as in Example 1. The results are shown in Table 1.

[0057] <Example 5> Except for using 4.42 mg of hexaammonium heptamolybdate tetrahydrate (Fujifilm Wako Pure Chemical Industries), 2.28 mg of barium nitrate (Kanto Chemical), and 2.88 mg of anhydrous tin(II) chloride (Fujifilm Wako Pure Chemical Industries) instead of the composite oxide precursor of Example 1, the catalyst for the reverse water-gas shift reaction of Example 5 was obtained by the same procedure as in Example 1. The catalyst for the reverse water-gas shift reaction of Example 5 comprises titanium dioxide, molybdenum oxide (0.8 mass as Mo), barium oxide (0.4 mass as Ba), tin oxide (0.6 mass as Sn), and platinum (3.0 mass as Pt) supported thereon. The yield of carbon monoxide and the reaction rate of carbon monoxide per amount of catalyst for the reverse water-gas shift reaction were calculated using the same procedure as in Example 1. The results are shown in Table 1.

[0058] <Example 6> The catalyst for the reverse water-gas shift reaction of Example 6 was obtained by following the same procedure as in Example 1, except that ammonium vanadinate (V) (Fujifilm Wako Pure Chemical Industries) 3.44 mg, pentakis(hydrogen oxalate)niobium(V) (n-hydrate) (Mitsuwa Chemical Co., Ltd.) 18.34 mg, hexaammonium heptamolybdate tetrahydrate (Fujifilm Wako Pure Chemical Industries, Ltd.) 2.76 mg, strontium nitrate (Kanto Chemical) 7.25 mg, and barium nitrate (Kanto Chemical) 4.57 mg were used instead of the complex oxide precursor of Example 1. The catalyst for the reverse water-gas shift reaction in Example 6 comprises titanium oxide, vanadium oxide (0.5% by mass as V), niobium oxide (1.0% by mass as Nb), molybdenum oxide (0.5% by mass as Mo), strontium oxide (1.0% by mass as Sr), barium oxide (0.8% by mass as Ba), and platinum (3.0% by mass as Pt), supported thereon. The yield of carbon monoxide and the reaction rate of carbon monoxide per amount of catalyst for the reverse water-gas shift reaction were calculated using the same procedure as in Example 1. The results are shown in Table 1.

[0059] <Example 7> The catalyst for the reverse water-gas shift reaction of Example 7 was obtained by following the same procedure as in Example 1, except that instead of the complex oxide precursor of Example 1, 3.67 mg of pentakis(hydrogen oxalate) niobium(V) (n-hydrate) (Mitsuwa Chemical Co., Ltd.), 3.31 mg of hexaammonium heptamolybdate tetrahydrate (Fujifilm Wako Pure Chemical Industries, Ltd.), 0.43 mg of ammonium tungstate-para pentahydrate (Fujifilm Wako Pure Chemical Industries, Ltd.), 0.44 mg of cesium nitrate (Kanto Chemical Co., Ltd.), and 2.96 mg of scandium(III) acetate hydrate (Tokyo Chemical Industries, Ltd.) were used. The catalyst for the reverse water-gas shift reaction in Example 7 comprises titanium oxide, supported thereon niobium oxide (0.2% by mass as Nb), molybdenum oxide (0.6% by mass as Mo), tungsten oxide (0.1% by mass as W), cesium oxide (0.1% by mass as Cs), scandium oxide (0.2% by mass as Sc), and platinum (3.0% by mass as Pt). The yield of carbon monoxide and the reaction rate of carbon monoxide per amount of catalyst for the reverse water-gas shift reaction were calculated using the same procedure as in Example 1. The results are shown in Table 1.

[0060] <Example 8> The catalyst for the reverse water-gas shift reaction of Example 8 was obtained by following the same procedure as in Example 1, except that 8.28 mg of ammonium heptamolybdate tetrahydrate (Fujifilm Wako Pure Chemical Industries), 3.62 mg of strontium nitrate (Kanto Chemical), 18.70 mg of lanthanum(III) nitrate hexahydrate (Fujifilm Wako Pure Chemical Industries), 4.40 mg of europium nitrate hexahydrate (Alfa Aesar), and 6.19 mg of lutetium nitrate (Fujifilm Wako Pure Chemical Industries) were used instead of the complex oxide precursor of Example 1. The catalyst for the reverse water-gas shift reaction in Example 8 comprises titanium oxide, supported thereon molybdenum oxide (1.5% by mass as Mo), strontium oxide (0.5% by mass as Sr), lanthanum oxide (2.0% by mass as La), europium oxide (0.5% by mass as Eu), lutetium oxide (1.0% by mass as Lu), and platinum (3.0% by mass as Pt). The yield of carbon monoxide and the reaction rate of carbon monoxide per amount of catalyst for the reverse water-gas shift reaction were calculated using the same procedure as in Example 1. The results are shown in Table 1.

[0061] <Example 9> The catalyst for the reverse water-gas shift reaction of Example 9 was obtained by following the same procedure as in Example 1, except that ammonium vanadinate (V) (Fujifilm Wako Pure Chemical Industries) 3.44 mg, pentakis(hydrogen oxalate)niobium(V) (n-hydrate) (Mitsuwa Chemical Co., Ltd.) 18.34 mg, hexaammonium heptamolybdate tetrahydrate (Fujifilm Wako Pure Chemical Industries, Ltd.) 2.76 mg, calcium nitrate tetrahydrate (Fujifilm Wako Pure Chemical Industries, Ltd.) 8.84 mg, and lanthanum(III) nitrate hexahydrate (Fujifilm Wako Pure Chemical Industries, Ltd.) 4.68 mg were used instead of the complex oxide precursor of Example 1. The catalyst for the reverse water-gas shift reaction in Example 9 comprises titanium oxide, vanadium oxide (0.5% by mass as V), niobium oxide (1.0% by mass as Nb), molybdenum oxide (0.5% by mass as Mo), calcium oxide (0.5% by mass as Ca), lanthanum oxide (0.5% by mass as La), and platinum (3.0% by mass as Pt). The yield of carbon monoxide and the reaction rate of carbon monoxide per amount of catalyst for the reverse water-gas shift reaction were calculated using the same procedure as in Example 1. The results are shown in Table 1.

[0062] <Example 10> The catalyst for the reverse water-gas shift reaction of Example 10 was obtained by the same procedure as in Example 1, except that instead of the complex oxide precursor of Example 1, 18.34 mg of pentakis(hydrogen oxalate) niobium(V) (n-hydrate) (Mitsuwa Chemical Co., Ltd.), 2.76 mg of ammonium heptamolybdate tetrahydrate (Fujifilm Wako Pure Chemical Industries, Ltd.), 3.62 mg of strontium nitrate (Kanto Chemical Co., Ltd.), 13.95 mg of cerium(III) nitrate hexahydrate (Fujifilm Wako Pure Chemical Industries, Ltd.), and 16.86 mg of dysprosium nitrate hexahydrate (Fujifilm Wako Pure Chemical Industries, Ltd.) were used. The catalyst for the reverse water-gas shift reaction in Example 10 comprises titanium oxide, supported thereon niobium oxide (1.0 mass as Nb), molybdenum oxide (0.5 mass as Mo), strontium oxide (0.5 mass as Sr), cerium oxide (1.5 mass as Ce), dysprosium oxide (2.0 mass as Dy), and platinum (3.0 mass as Pt). The yield of carbon monoxide and the reaction rate of carbon monoxide per amount of catalyst for the reverse water-gas shift reaction were calculated using the same procedure as in Example 1. The results are shown in Table 1.

[0063] <Example 11> Except for substituting the composite oxide precursor of Example 1, 3.67 mg of pentakis(hydrogen oxalate)niobium(V)(n-hydrate) (Mitsuwa Chemical Co., Ltd.), 3.31 mg of hexaammonium heptamolybdate tetrahydrate (Fujifilm Wako Pure Chemical Industries, Ltd.), 6.16 mg of cesium nitrate (Kanto Chemical Co., Ltd.), and 5.71 mg of barium nitrate (Kanto Chemical Co., Ltd.) were used, and the catalyst for the reverse water-gas shift reaction of Example 11 was obtained by the same procedure as in Example 1. The catalyst for the reverse water-gas shift reaction of Example 11 comprises titanium dioxide, niobium oxide (0.2 mass as Nb), molybdenum oxide (0.6 mass as Mo), cesium oxide (1.4 mass as Cs), barium oxide (1.0 mass as Ba), and platinum (3.0 mass as Pt) supported thereon. The yield of carbon monoxide and the reaction rate of carbon monoxide per amount of catalyst for the reverse water-gas shift reaction were calculated using the same procedure as in Example 1. The results are shown in Table 1.

[0064] <Example 12> Except for using 3.67 mg of pentakis(hydrogen oxalate)niobium(V)(n-hydrate) (Mitsuwa Chemical Co., Ltd.), 3.31 mg of hexaammonium heptamolybdate tetrahydrate (Fujifilm Wako Pure Chemical Industries, Ltd.), 4.05 mg of rubidium carbonate (Fujifilm Wako Pure Chemical Industries, Ltd.), and 5.71 mg of barium nitrate (Kanto Chemical Co., Ltd.) instead of the composite oxide precursor of Example 1, the catalyst for the reverse water-gas shift reaction of Example 12 was obtained by the same procedure as in Example 1. The catalyst for the reverse water-gas shift reaction of Example 12 comprises titanium dioxide, niobium oxide (0.2 mass as Nb), molybdenum oxide (0.6 mass as Mo), rubidium oxide (1.0 mass as Rb), barium oxide (1.0 mass as Ba), and platinum (3.0 mass as Pt) supported thereon. The yield of carbon monoxide and the reaction rate of carbon monoxide per amount of catalyst for the reverse water-gas shift reaction were calculated using the same procedure as in Example 1. The results are shown in Table 1.

[0065] <Comparative Example 1> Comparative Example 1's catalyst for the reverse water-gas shift reaction was obtained by the same procedure as in Example 1, except that 27.60 mg of ammonium heptamolybdate tetrahydrate (Fujifilm Wako Pure Chemical Industries) was used instead of the composite oxide precursor of Example 1. The catalyst for the reverse water-gas shift reaction of Comparative Example 1 comprises titanium oxide, molybdenum oxide (5.0% by mass as Mo) supported thereon, and platinum (3.0% by mass as Pt). The yield of carbon monoxide and the reaction rate of carbon monoxide per amount of catalyst for the reverse water-gas shift reaction were calculated using the same procedure as in Example 1. The results are shown in Table 1.

[0066] <Comparative Example 2> A catalyst for the reverse water-gas shift reaction of Comparative Example 2 was obtained by the same procedure as in Example 1, except that 0.55 mg of ammonium heptamolybdate tetrahydrate (Fujifilm Wako Pure Chemical Industries) was used instead of the composite oxide precursor of Example 1. The catalyst for the reverse water-gas shift reaction of Comparative Example 2 comprises titanium oxide, molybdenum oxide (0.1% by mass as Mo) supported thereon, and platinum (3.0% by mass as Pt). The yield of carbon monoxide and the reaction rate of carbon monoxide per amount of catalyst for the reverse water-gas shift reaction were calculated using the same procedure as in Example 1. The results are shown in Table 1.

[0067] [Table 1]

[0068] As shown in Table 1, when the catalysts of Examples 1 to 12 according to this embodiment were used under low-temperature conditions of a reaction temperature of 250°C, no methane by-product was detected, and only CO was produced. The CO production rate in Examples 1 to 12 was 2.5 mmol / min / gcat or higher in all cases, indicating that the catalysts of Examples 1 to 12 have high catalytic activity. Furthermore, the catalysts of Examples 1 to 12 showed excellent CO yields. On the other hand, while the catalysts of Comparative Examples 1 and 2 were capable of generating CO even under low-temperature conditions of 250°C, their CO generation rate and yield were inferior to those of the catalysts of Examples 1 to 12.

Claims

1. A catalyst for a reverse water-gas shift reaction used to produce carbon monoxide from carbon dioxide and hydrogen, wherein the catalyst comprises a metal oxide support, a composite oxide supported on the metal oxide support, and a metal catalyst. The aforementioned metal oxide support is TiO₂, The aforementioned metal catalyst is Pt, The aforementioned composite oxide comprises, as the first metal oxide, a metal oxide containing at least Mo, As the second metal oxide, an oxide of at least one metal element selected from the group consisting of Rb, Cs, Ca, Sr, and Ba, A catalyst for reverse water-gas shift reactions, including the following:

2. The catalyst for a reverse water-gas shift reaction according to claim 1, wherein the first metal oxide further comprises at least one metal element selected from the group consisting of V, Nb, and W.

3. The catalyst for a reverse water-gas shift reaction according to claim 1 or 2, wherein the content of the Mo oxide is 0.2 to 3.0% by mass as Mo metal element, based on the total amount of the catalyst for the reverse water-gas shift reaction.

4. The catalyst for a reverse water-gas shift reaction according to any one of claims 1 to 3, wherein the content of the Mo oxide is 0.2 to 1.0% by mass as Mo metal element, based on the total amount of the catalyst for the reverse water-gas shift reaction.

5. The catalyst for a reverse water-gas shift reaction according to any one of claims 1 to 4, wherein the composite oxide further comprises a lanthanide oxide as a third metal oxide.

6. The catalyst for a reverse water-gas shift reaction according to claim 5, wherein the third metal oxide is an oxide of at least one metal element selected from the group consisting of La, Ce, Pr, Nd, Eu, Gd, Dy, Er, and Lu.

7. The method comprises a reverse water-gas shift reaction step in which a raw material gas containing carbon dioxide and hydrogen is brought into contact with a reverse water-gas shift reaction catalyst according to any one of claims 1 to 6 to obtain a product gas containing carbon monoxide. A method for producing carbon monoxide.

8. The method for producing carbon monoxide according to claim 7, wherein the reaction temperature of the reverse water-gas shift reaction step is 100 to 400°C.

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