Carbon Dioxide Reduction Catalyst

Abstract

To provide a carbon dioxide reduction catalyst that can form a hydrocarbon having 5 or more carbon atoms with high efficiency even at a high flow rate.SOLUTION: A carbon dioxide reduction catalyst hydrogenates carbon dioxide to reduce carbon dioxide, producing a hydrocarbon. The carbon dioxide reduction catalyst comprises Fe and Ga as catalyst metals. In the catalyst metals, the Ga content is 10-30 mass%. Preferably, the Ga content should be 20-30 mass%. Preferably, the catalyst metals comprise an Fe-Ga complex oxide composed of Fe and Ga.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a carbon dioxide reduction catalyst. [Background technology]

[0002] Conventionally, there are known technologies for producing fuel by subjecting carbon dioxide to a hydrogenation reaction. For example, a catalyst made of Cu, Zn, and alumina has been proposed as a catalyst for synthesizing methanol from a mixed gas of carbon dioxide and hydrogen (see Patent Document 1).

[0003] However, it is required to produce hydrocarbons with a carbon number of, for example, 5 or more that can be used as liquid fuels as fuels obtained by hydrogenating carbon dioxide. As such a technology, a method has been proposed in which potassium is used as a promoter for an Fe catalyst in the Fischer-Tropsch (FT) synthesis reaction to prepare highly branched products with C5 or more carbon atoms (see Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 45-16682 [Patent Document 2] Special Publication No. 2005-537340 Summary of the Invention [Problem to be solved by the invention]

[0005] The potassium used as a promoter in the technology disclosed in Patent Document 2 is thought to have the function of capturing carbon dioxide in the FT synthesis reaction. However, it is thought that the potassium used as a promoter does not directly contribute to increasing the carbon number of the produced hydrocarbons. For this reason, it has been impossible to produce hydrocarbons with a carbon number of, for example, 5 or more in high yield under high flow rates such as exhaust gas from an internal combustion engine.

[0006] The present invention has been made in consideration of the above problems, and has an object to provide a carbon dioxide reduction catalyst that can produce hydrocarbons having a carbon number of 5 or more with high efficiency even under a high flow rate. [Means for solving the problem]

[0007] (1) The present invention relates to a carbon dioxide reduction catalyst for producing hydrocarbons by reducing carbon dioxide through a hydrogenation reaction of carbon dioxide, the carbon dioxide reduction catalyst comprising Fe and Ga as catalytic metals, and wherein the Ga content in the catalytic metal is 10 to 30 mass %.

[0008] (2) The carbon dioxide reduction catalyst according to (1), wherein the catalytic metal contains 20 to 30 mass % of Ga.

[0009] (3) The carbon dioxide reduction catalyst according to (1) or (2), wherein the catalytic metal includes an Fe—Ga composite oxide formed by the Fe and the Ga.

[0010] (4) The carbon dioxide reduction catalyst according to any one of (1) to (3), further comprising Na as the catalytic metal.

[0011] (5) The present invention also relates to a method for producing the carbon dioxide reduction catalyst according to any one of (1) to (4), comprising a coprecipitation step of extracting a precipitate from an aqueous solution in which a predetermined amount of the nitrate of Fe and the nitrate of Ga are dissolved in distilled water, by a coprecipitation method.

[0012] (6) The method for producing a carbon dioxide reduction catalyst according to (5), comprising, subsequent to the coprecipitation step, an impregnation step of dropping an aqueous solution containing Na onto the precipitate, drying the precipitate for a predetermined period of time, and calcining the obtained powder at a predetermined temperature.

[0013] (7) In the coprecipitation step, NaCO 3 The method for producing a carbon dioxide reduction catalyst according to (5) or (6), wherein the aqueous solution is dropped to obtain a precipitate solution. Effect of the Invention

[0014] According to the present invention, it is possible to provide a carbon dioxide reduction catalyst capable of efficiently producing hydrocarbons having 5 or more carbon atoms even under a high flow rate.

Brief Description of the Drawings

[0015] [Figure 1] It is a graph showing the CO2 conversion rate according to the examples and comparative examples. [Diagram 2] It is a graph showing the hydrocarbon selectivity according to the examples and comparative examples. [Diagram 3] It is a graph showing the C5+ production rate according to the examples and comparative examples. [Figure 4] It is a graph showing the relationship between the CO2 conversion rate and the Ga content. [Diagram 5] It is a graph showing the relationship between the C5+ selectivity and the Ga content. [Figure 6] It is a graph showing the relationship between the C5+ production rate and the Ga content. [Figure 7] It is a graph showing the relationship between the catalyst metal particle size and the Ga content. [Figure 8] It is a graph showing the relationship between the CO2 conversion rate and the Na content. [Figure 9] It is a graph showing the relationship between the C5+ selectivity and the Na content. [Figure 10] It is a graph showing the relationship between the C5+ production rate and the Na content.

Modes for Carrying Out the Invention

[0016] An embodiment of the present invention will be described below. The carbon dioxide reduction catalyst according to this embodiment is a catalyst that can reduce carbon dioxide by a hydrogenation reaction and generate hydrocarbons. In particular, the carbon dioxide reduction catalyst according to this embodiment has a higher production ratio and production rate of hydrocarbons having a carbon number of 5 or more than conventional catalysts. There are no particular limitations on the carbon dioxide supply source, but the carbon dioxide reduction catalyst according to this embodiment can preferably generate hydrocarbons having a carbon number of 5 or more even from a supply source that supplies carbon dioxide at a high flow rate, such as exhaust gas from an internal combustion engine.

[0017] <Carbon dioxide reduction catalyst> The carbon dioxide reduction catalyst according to this embodiment (hereinafter, sometimes simply referred to as "catalyst") contains Fe (iron) and Ga (gallium) as catalytic metals. It is also preferable that it contains Na (sodium). The carbon dioxide reduction reaction using the catalyst according to this embodiment is carried out by H 2 (hydrogen) and CO 2 (carbon dioxide) mixed gas as the raw material, 2 This is a reaction to produce hydrocarbons by carrying out, in a single stage, a reverse shift reaction in which CO is reduced to CO (carbon monoxide) and an FT synthesis reaction in which CO is converted to hydrocarbons. The catalyst according to this embodiment contributes to both the reverse shift reaction and the FT synthesis reaction. The carbon dioxide reduction reaction using the catalyst according to this embodiment has a space velocity (SV) of, for example, 50,000 h compared to the conventional FT synthesis reaction. -1 Even under high flow rates, hydrocarbons with carbon numbers of 5 or more can be produced with high efficiency.

[0018] The Fe contained in the catalyst metal according to this embodiment may be a compound such as an oxide, a carbonate compound, a nitrate compound, or a sulfate compound, and is preferably an oxide. Two or more of these compounds may be contained. In addition, it is more preferable that Fe is contained in the catalyst metal as an Fe-Ga composite oxide formed by Fe and Ga. Since the Fe-Ga composite oxide is finely divided compared with compounds such as iron oxide, the reaction site of the Fe catalyst is increased, and the reaction time of the FT synthesis reaction, that is, the time for the carbon chain of the generated hydrocarbon to grow, can be secured. Therefore, the yield of hydrocarbons having a carbon number of 5 or more can be improved even under high flow rate.

[0019] The Ga contained in the catalytic metal according to the present embodiment may be a compound such as an oxide, a carbonate compound, a nitrate compound, or a sulfate compound, similar to Fe, and is preferably an oxide. Two or more of these compounds may be contained. It is more preferable that Ga is contained in the catalytic metal as an Fe-Ga composite oxide formed by Fe and Ga.

[0020] The content of Ga in the catalyst metal according to this embodiment is 10 to 30 mass % in terms of metal atoms. The content of Ga is preferably 20 to 30 mass %. If the content of Ga is less than 10 mass %, the catalyst metal may not be sufficiently finely divided. If the content of Ga exceeds 30 mass %, Ga may cover the reactive sites of Fe, resulting in a decrease in catalytic activity.

[0021] The catalytic metal according to this embodiment preferably further contains Na. Na functions as a promoter in the catalytic metal containing Fe and Ga, and reduces CO 2 Na 2 CO 3 By capturing it as H 2 and CO 2 The reverse shift reaction occurs, producing CO from CO 2The conversion rate can be improved. It is preferable that Na is present on the surface of the Fe-Ga composite oxide in the form of an oxide or the like, separately from the Fe-Ga composite oxide. The catalyst metal may contain an alkali metal such as Li, K, Rb, or Cs instead of or together with Na.

[0022] The content of Na in the catalyst metal according to this embodiment is preferably 0.5 to 1.5 mass%, and more preferably 1.0 mass%. If the Na content is less than 0.5 mass%, sufficient production efficiency of hydrocarbons having 5 or more carbon atoms cannot be obtained. If the Na content exceeds 1.5 mass%, Na covers the reaction sites of Fe, thereby reducing the catalytic activity.

[0023] The carbon dioxide reduction catalyst according to this embodiment may be, for example, a powder of a catalytic metal, or a pellet-shaped molded body formed by pressure molding a catalytic metal. Alternatively, the catalytic metal may be supported on a known catalyst carrier such as silica. In addition to the above, the carbon dioxide reduction catalyst according to this embodiment may contain unavoidable impurities that are mixed in during the catalyst production process, etc., but it is preferable that the catalyst contains as few impurities as possible.

[0024] <Method of manufacturing carbon dioxide reduction catalyst> The method for producing a carbon dioxide reduction catalyst according to this embodiment includes a coprecipitation step. It is preferable that the method includes an impregnation step subsequent to the coprecipitation step.

[0025] (co-precipitation process) The coprecipitation step is a step of extracting a catalyst precursor precipitate by coprecipitation from an aqueous solution in which a predetermined amount of Fe nitrate and Ga nitrate are dissolved in distilled water. Fe-Ga composite oxide is formed by the coprecipitation step. In the coprecipitation step, Na 2 CO 3 A precipitate solution is obtained by dropping the aqueous solution. The precipitate is then separated from the precipitate solution by filtration, washing, etc., and dried to obtain a precipitate (Fe-Ga composite oxide) that is a catalyst precursor.

[0026] (impregnation process) The impregnation step is a step of dropping an aqueous solution containing Na onto the precipitate obtained by the coprecipitation step, drying for a predetermined time, and firing the obtained powder at a predetermined temperature. The impregnation step allows the Na compound to be unevenly distributed near the surface of the Fe-Ga composite oxide. The aqueous solution containing Na is, for example, NaNO 3 Examples include aqueous solutions of NaNO 3 The aqueous solution can be dropped under ultrasonic vibration. This allows the Na compound to be distributed uniformly near the surface of the Fe-Ga composite oxide. The firing temperature can be, for example, 550°C, and the firing time can be 4 hours.

[0027] The present invention is not limited to the above-described embodiment, and the present invention includes modifications and improvements within the scope that can achieve the object of the present invention. EXAMPLES

[0028] Next, an embodiment of the present invention will be described, but the present invention is not limited to this embodiment.

[0029] [Example 1] The nitrate of Fe (Fe(NO 3 ) 3 9H 2 O) and Ga nitrate (Ga(NO 3 ) 3 6H 2 The Fe:Ga mass ratio was 8:2 in terms of metal atoms, and the solution was dissolved in distilled water. 3 The aqueous solution was dripped at 2 ml / min and the pH was fixed at 8.5 to obtain a precipitation solution containing Fe and Ga as precipitates. The precipitation solution was then aged at room temperature for 24 hours, after which the precipitate was separated by repeated filtration and washing. The separated precipitate was dried at 60°C for 12 hours to obtain an Fe-Ga catalyst precursor.

[0030] The Fe-Ga catalyst precursor was treated with NaNO 3The aqueous solution was dropped under ultrasonic vibration at 92 kHz so that the Na content was 1.0 mass%. The mixture was then dried under a vacuum of 5000 Pa for 1 hour, and further dried at normal pressure at 60°C for 12 hours to obtain a powder. The obtained powder was calcined at 550°C for 4 hours to obtain a catalyst according to Example 1.

[0031] [Examples 2 to 3, Comparative Examples 1 to 9] Catalysts according to Examples 2 to 3 and Comparative Examples 1 to 9 were obtained in the same manner as in Example 1, except that the types and amounts of catalytic metal 1 (Fe) and catalytic metal 2 were respectively as shown in Table 1. Comparative Example 1 used only Fe nitrate without using catalytic metal 2. Note that while Table 1 shows the parts by mass of catalytic metal 1 and catalytic metal 2, the catalytic metal according to each Example and Comparative Example contains 1.0 mass % Na in addition to catalytic metal 1 and catalytic metal 2 shown in Table 1.

[0032] [Table 1]

[0033] [evaluation] The carbon dioxide reduction catalysts of Examples 1 to 3 and Comparative Examples 1 to 9 were used to carry out a carbon dioxide reduction reaction in the following manner. 2 2.8NL / h, H 2 8.4NL / h(CO 2 / H 2 = 1 / 3). 0.25 g of the carbon dioxide catalyst in each of the examples and comparative examples was prepared in the form of pellets measuring 0.4 to 0.8 mm square. The pellets were packed in a reaction tube (inner diameter 6 mm) to a length of 5 cm. W / F (catalyst weight / gas flow rate) was 0.5 g·h / mol, and SV (space velocity) = 50,000 h -1The reaction conditions were a temperature of 380°C, a pressure of 3 MPa, and a reaction time of 4 hours. The gas components after the catalytic reaction were qualitatively and quantitatively analyzed by online gas chromatography (Shimadzu, GC-2014AT, detector: thermal conductivity detector (TCD)) and a flame ionization detector (FID) (Shimadzu, GC-2014AF). The liquid components after the catalytic reaction were also qualitatively and quantitatively analyzed by offline gas chromatography (Shimadzu, GC-2014AF, detector: flame ionization detector (FID)).

[0034] (CO 2 Conversion rate) CO from the above carbon dioxide reduction reaction 2 The conversion rate was calculated by the following formula (1). The results are shown in Figure 1. CO 2 Conversion rate (%) = (CO before reaction 2 concentration)-(CO after reaction 2 (concentration) / (CO before reaction 2 Concentration)×100…(1)

[0035] (hydrocarbon selectivity) The hydrocarbons (CO, CH) produced by the carbon dioxide reduction reaction 4 , C 2-4 , C 5+ The selectivity of C was calculated by the following formula (2). 2-4 indicates a hydrocarbon having 2 to 4 carbon atoms, and C 5+ indicates hydrocarbons with 5 or more carbon atoms. The results are shown in Figure 2. Hydrocarbon selectivity (%) = (hydrocarbon concentration) / ((CO before reaction 2 concentration)-(CO after reaction 2 Concentration))×100 …(2)

[0036] (C 5+ generation rate) C produced by the above carbon dioxide reduction reaction 5+ The production rate of (hydrocarbons having 5 or more carbon atoms) was calculated by the following formula (3). The results are shown in FIG. C 5+ Generation rate (%)=CO 2 Conversion rate × C5+ Selection rate / 100 …(3)

[0037] (Ga content and CO 2 (Relationship with conversion rate) Next, the mass ratio of Fe and Ga in the catalytic metal was changed as shown in Table 1 in Examples 1 to 3, and the Ga content was set to 40 mass%, 50 mass%, and 60 mass%, respectively (Fe content: about 60 mass%, about 50 mass%, and about 40 mass%), and the Ga content was set to 1.0 mass%, and the Ga content was set to 1.0 mass%, respectively (Fe content: about 1.0 mass%, about 1.0 mass%, and about 1.0 mass%) in Comparative Example 1. 2 The relationship between the conversion rate and the CO concentration was investigated. The results are shown in Figure 4. The vertical axis of Figure 4 is the CO concentration calculated by the above formula (1). 2 4 shows the conversion rate (%), and the horizontal axis of Fig. 4 shows the Ga content (mass%). Each catalyst contains 1.0 mass% Na, but the mass ratio of Ga to the total of Fe and Ga in the catalyst metal can be used as an approximation for the Ga content (same below).

[0038] (Ga content and C 5+ (Relationship with selection rate) Next, the relationship between the Ga content and the C content in the carbon dioxide reduction reaction using the catalysts of Examples 1 to 3 and Comparative Example 1 was compared in the same manner as in FIG. 5+ The relationship between the selectivity and the saturation rate was investigated. The results are shown in Figure 5. The vertical axis of Figure 5 is the C 5+ 5 indicates the selectivity (%), and the horizontal axis of FIG. 5 indicates the Ga content (mass %).

[0039] (Ga content and C 5+ (Relationship with generation rate) Next, the relationship between the Ga content and the C content in the carbon dioxide reduction reaction using the catalysts of Examples 1 to 3 and Comparative Example 1 was compared in the same manner as in FIG. 5+ The relationship between the generation rate and the C 5+ 5 indicates the production rate (%), and the horizontal axis of FIG. 5 indicates the Ga content (mass %).

[0040] (Relationship between Ga content and catalytic metal particle size) Next, the relationship between the Ga content and the catalyst metal particle size (nm) of the catalysts of Examples 1 to 3 and Comparative Example 1 was examined in the same manner as in FIG. 4. The results are shown in FIG. 7. The vertical axis of FIG. 7 indicates the catalyst metal particle size (nm), and the horizontal axis of FIG. 7 indicates the Ga content (mass%). The catalyst metal particle size (nm) was calculated using the Scherrer formula shown in the following formula (4) for a peak obtained near 2θ=35.6° using an X-ray diffraction intensity measurement device with an X-ray source of CuKα radiation and an output of 40 kV and 50 mA. In addition, in formula (4), K indicates the Scherrer constant, λ indicates the X-ray wavelength (nm), β indicates the half-width of the peak, and θ indicates the diffraction angle, respectively. Particle diameter (nm)=K=K×λ / (β×cosθ) …(4)

[0041] (Na content and CO 2 Conversion rate, C 5+ Selectivity, C 5+ (Relationship with generation rate) Next, catalysts in which the Ga content in the catalytic metal was 30 mass% were changed to 0 mass%, 0.5 mass%, 1.0 mass%, 1.5 mass%, and 2.0 mass% Na, with the remaining catalytic metal component being Fe, were prepared, and the catalysts were subjected to CO 2 Conversion rate, C 5+ Selectivity, C 5+ The production rates were measured and calculated, and the relationship with the Na content was examined. The results are shown in Figures 8 to 10, respectively.

[0042] [Consideration] 1 to 3, the catalyst of Example 1 has a higher selectivity and production rate for hydrocarbons having 5 or more carbon atoms, and a higher CO 2 The results also revealed a relatively high conversion rate.

[0043] 4 to 6, it is clear that the content of Ga as a catalytic metal is preferably in the range of 10 to 30 mass %, and more preferably in the range of 20 to 30 mass %. 5+However, when the Ga content exceeds 30 mass %, Ga covers the reaction sites of Fe, which is considered to result in a decrease in catalytic activity.

[0044] In addition, from FIG. 7, it is clear that when the Ga content is within the range of 10 to 30 mass %, the catalyst metal is finely divided. Considering the results of FIGS. 4 to 6 together, the C 5+ The improvement in catalytic activity, such as production rate, is presumably due to the catalytic metal being made into fine particles.

[0045] 8 to 10, when the content of Ga as a catalytic metal is within the range of 10 to 30 mass%, the content of Na as a catalytic metal is preferably within the range of 0.5 to 1.5 mass%, and more preferably within the range of 1.0 mass%. 5+ Although the production activity is improved, if the Na content exceeds 1.0 mass %, Na covers the reaction sites of the Fe catalyst, presumably resulting in a decrease in catalytic activity.

Claims

1. A carbon dioxide reduction catalyst for reducing carbon dioxide by a hydrogenation reaction to produce hydrocarbons, The catalytic metal includes Fe, Ga, and Na; the Fe and the Ga are contained in the catalytic metal as an Fe-Ga composite oxide; The Na is unevenly distributed near the surface of the Fe—Ga composite oxide, A carbon dioxide reduction catalyst, wherein the catalytic metal contains 10 to 30 mass % of Ga.

2. A carbon dioxide reduction catalyst as described in claim 1, wherein the mass ratio of Fe to Ga in the catalytic metal, Fe:Ga, is 7:3 to 9:

1.

3. A carbon dioxide reduction catalyst as described in claim 1 or 2, wherein the Na content in the catalytic metal is 0.5 to 1.5 mass %.

4. 2. The carbon dioxide reduction catalyst according to claim 1, wherein the catalytic metal contains 20 to 30 mass % of Ga.

5. A method for producing a carbon dioxide reduction catalyst according to any one of claims 1 to 4, A method for producing a carbon dioxide reduction catalyst, comprising a coprecipitation step of extracting a precipitate by a coprecipitation method from an aqueous solution in which a predetermined amount of the Fe nitrate and the Ga nitrate are dissolved in distilled water.

6. 6. The method for producing a carbon dioxide reduction catalyst according to claim 5, further comprising, following the coprecipitation step, an impregnation step of dropping an aqueous solution containing Na onto the precipitate, drying the precipitate for a predetermined period of time, and calcining the obtained powder at a predetermined temperature.

7. In the coprecipitation step, NaCO ３ The method for producing a carbon dioxide reduction catalyst according to claim 5 or 6, wherein the precipitate solution is obtained by dropping an aqueous solution.

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