Method for producing formic acid

Abstract

To provide a method for easily and efficiently producing formic acid from saccharides, a type of renewable resource.SOLUTION: A method for producing formic acid according to the present invention includes a step of applying light to a saccharide aqueous solution containing a cerium oxide catalyst in the presence of oxygen, wherein the cerium oxide catalyst contains cerium oxide (IV), cerium oxide (III), and cerium hydroxide.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for easily and efficiently producing formic acid from sugars, which are also renewable resources. [Background technology]

[0002] Formic acid has unique properties, such as being both acidic and reducing due to the presence of both a carboxyl group and an aldehyde group in the molecule, and its acidity is much stronger than that of acetic acid, and it has been used in various fields since ancient times. For example, because formic acid has antibacterial properties, it is used as a preservative and antibacterial agent in livestock feed (silage). In the poultry industry, it is sometimes added to feed to remove Salmonella bacteria, and in the beekeeping industry, it is used as an insecticide against mites. It is also used in the pickling process to make it easier for tanning agents such as chromium and tannin to penetrate the leather. Ethyl formate is also found in pineapples and other fruits, and is used as a flavoring agent.

[0003] Formic acid is also used in organic synthesis as a reagent for N-methylation and as a reducing agent for reductive amination reactions. Formic acid fuel cells that use formic acid as fuel are also being considered. In particular, since a technology has been developed recently to efficiently extract hydrogen by decomposing formic acid at room temperature and pressure, its use as a safe hydrogen source for storage and transportation is also being considered.

[0004] Generally, formic acid is industrially produced by hydrolyzing methyl formate, which is obtained from methanol and carbon monoxide in the presence of a strong base. However, carbon monoxide is a dangerous substance that can bind to hemoglobin and cause carbon monoxide poisoning. In addition, the raw materials, methanol and carbon monoxide, are generally derived from fossil resources. Therefore, technologies to produce formic acid using renewable resources as raw materials are being investigated.

[0005] For example, Patent Document 1 describes a method for catalytically producing formic acid by contacting a specific polyoxometalate ion with a hydrocarbon or glycoside. Patent Document 2 describes a method for producing formic acid by reacting a monosaccharide with an oxidizing agent in the presence of a specific copper-supported catalyst. Non-Patent Document 1 describes the conversion of glucose to formic acid on nano-titanium oxide. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2013-540735 [Patent Document 2] JP 2015-134324 A [Non-patent literature]

[0007] [Non-Patent Document 1] Binbin Jin et al.,ACS Sustainable Eng.,2017,5,6377-6381 Summary of the Invention [Problem to be solved by the invention]

[0008] As described above, methods for producing formic acid from renewable resources have been developed in the past, but none of them have been very efficient. For example, in the method of Patent Document 1, a salt containing a specific polyoxometalate ion is used as a catalyst, but the polymetalate ion is easily dissolved in a solvent, and even if formic acid is produced from a renewable resource, it is difficult to separate the polymetalate ion from the formic acid, and it is also difficult to separate the polymetalate ion from the solvent and reuse it. Furthermore, heating at a temperature below 120°C, such as 80°C, is required. The method of Patent Document 2 requires an oxidizing agent such as hydrogen peroxide, otherwise lactic acid will be produced, and requires a reaction temperature of over 100°C, such as 120°C. In addition, according to the method described in Non-Patent Document 1, formic acid is obtained from glucose, but it is believed that a considerable amount of formic acid is further decomposed into carbonate ions or hydrogen carbonate ions and dissolved in the aqueous sodium hydroxide solution, which is the solvent. In fact, Figure 4(b) shows that inorganic carbon (IC) increases over time. Therefore, an object of the present invention is to provide a method for easily and efficiently producing formic acid from sugars, which are also renewable resources. [Means for solving the problem]

[0009] The present inventors have conducted extensive research to solve the above problems, and as a result, have found that by using a specific cerium oxide catalyst, formic acid produced from saccharides is not further decomposed, and formic acid can be efficiently produced, thereby completing the present invention. The present invention will now be described.

[0010] [1] A method for producing formic acid, comprising: The method includes a step of irradiating an aqueous saccharide solution containing a cerium oxide catalyst with light in the presence of oxygen, The method, wherein the cerium oxide catalyst comprises cerium (IV) oxide, cerium (III) oxide, and cerium hydroxide. [2] The method according to [1], wherein the peak wavelength of the light is within the visible light range. [3] The method according to [1], further comprising the step of obtaining the cerium oxide catalyst by adding a cerium salt to a basic aqueous solution. [4] The method according to [3] above, in which the cerium salt is added to the basic aqueous solution to produce a precipitate, which is then dried or calcined at 500°C or less to obtain the cerium oxide catalyst. [5] The concentration of sugar in the sugar solution is 1×10 -4 g / mL or more, 1×10 -2 The method according to claim 1, wherein the concentration is 0.01 g / mL or less. [6] The method according to [1], wherein the ratio of the cerium oxide catalyst to the aqueous saccharide solution is 0.1 mg / mL or more and 10 mg / mL or less. Effect of the Invention

[0011] According to the method of the present invention, it is possible to decompose sugars, which are renewable resources, into formic acid at room temperature without heating. In addition, the light required for the reaction to proceed may be not only ultraviolet light but also visible light. Furthermore, according to the method of the present invention, the target compound formic acid is not decomposed further or is hardly decomposed further. Therefore, the present invention is industrially very excellent as a technology that can easily and efficiently produce useful formic acid from sugars, which are renewable resources. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 shows the IR spectra of various catalyst samples. [Diagram 2] FIG. 2 is a graph showing the formic acid yield after 4 hours of reaction when catalysts having different calcination temperatures are used. [Diagram 3] FIG. 3 is a graph showing the change in composition over time of the aqueous glucose solution and the gas phase when a titanium oxide catalyst (1) and a cerium oxide catalyst according to the present invention (2) are used. [Figure 4] FIG. 4 is a graph showing the change in composition over time of an aqueous glucose solution and a gas phase when the cerium oxide catalyst according to the present invention is used and visible light is used as irradiation light. [Diagram 5] FIG. 5 is a graph showing the yield of formic acid when the cerium oxide catalyst according to the present invention is used and sunlight, ultraviolet light or blue light is used as the irradiation light. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The method for producing formic acid (HC(=O)OH) according to the present invention includes a step of irradiating an aqueous saccharide solution containing a cerium oxide catalyst with light in the presence of oxygen.

[0014] Cerium oxide catalysts are cerium(IV) oxide (CeO2), cerium(III) oxide (Ce2O3) and cerium hydroxide (Ce(OH) x(wherein x represents 3 or 4). According to the experimental findings of the present inventors, when titanium oxide (TiO2), a representative photocatalyst, is used, glucose is decomposed not only to formic acid but also to carbon dioxide. The reason for this is that titanium oxide has a relatively large band gap of 3.2 eV, requires a relatively large energy for excitation, and has strong reducing and oxidizing power, so that glucose is oxidatively decomposed from formic acid to carbon dioxide. In contrast, cerium oxide (IV) has a relatively small band gap of 3.0 eV, and the band gap is further reduced by oxygen defects due to cerium oxide (III) and cerium hydroxide. As a result, the cerium oxide catalyst according to the present invention is excited not only by high-energy light such as ultraviolet light but also by visible light, and it is considered that due to its relatively weak oxidizing power, the generated target compound, formic acid, is not decomposed further or is hardly decomposed at all.

[0015] When the cerium oxide catalyst according to the present invention is analyzed by infrared absorption spectroscopy, absorption probably due to OH species on the catalyst surface is observed in the range of 1700 to 700 cm -1 The absorption by O-Ce is at 700cm -1 In addition, the absorption due to the stretching vibration of OH species on the catalyst surface is ~3600 cm -1 In addition, since cerium oxide (IV) is white to pale yellow, cerium oxide (III) is golden yellow, and cerium hydroxide is pale yellow, the cerium oxide catalyst according to the present invention is pale yellow to yellow.

[0016] The cerium oxide catalyst according to the present invention can be produced, for example, by a reverse homogeneous precipitation method, which is a method in which an aqueous solution of a metal salt is added to an aqueous basic solution to rapidly and uniformly form a hydroxide or the like.

[0017] Specifically, the base that can be used may be ammonia, sodium hydroxide, potassium hydroxide, etc. The concentration of the basic aqueous solution may be appropriately adjusted, for example, 10% by mass or more and 30% by mass or less for ammonia water, and 0.5 mol / L or more and 5 mol / L or less for sodium hydroxide or potassium hydroxide.

[0018] The cerium salt is not particularly limited, but for example, nitrate, sulfate, carbonate, acetate, chloride, etc. can be used, and nitrate is preferred. The cerium salt may be added directly to the basic aqueous solution, but is preferably added in the form of an aqueous solution from the viewpoint of uniformity. The concentration of the aqueous solution may be appropriately adjusted depending on the water solubility of the cerium salt used, and is not particularly limited, but can be prepared to be, for example, 0.1M or more and 20M or less.

[0019] The amount of the cerium salt added to the basic aqueous solution may be appropriately adjusted within the range in which a precipitate is obtained. For example, the concentration of the cerium salt in the basic aqueous solution after the addition of the cerium salt or the cerium salt aqueous solution may be set to 0.5 mol / L or more and 10 mol / L or less.

[0020] When the cerium salt or the aqueous solution of the cerium salt is added to the basic aqueous solution, the basic aqueous solution may be added continuously or intermittently in small amounts while stirring, or the entire amount may be added at once. After the cerium salt is added to the basic aqueous solution, the mixture may be stirred. The mixture may be allowed to stand to promote precipitation, for example. For example, the mixture may be stirred for 1 hour or more and 48 hours or less, and then allowed to stand for 1 hour or more and 24 hours or less. All of the above operations may be performed at room temperature, except for the case of preparing an aqueous solution of a cerium salt with relatively low water solubility.

[0021] After the cerium oxide catalyst precipitates, it is separated from the liquid phase by centrifugation, filtration, or the like, and is thoroughly washed with water, for example, until the color of the washing liquid disappears. The cerium oxide catalyst may then be dried. The drying method is not particularly limited, but examples thereof include heat drying, reduced pressure drying, and freeze drying.

[0022] The dried cerium oxide catalyst may be further calcined, but according to the experimental findings of the present inventors, it has become clear that the higher the calcination temperature, the lower the glucose decomposition activity. Therefore, the calcination temperature is preferably 500°C or less, more preferably 400°C or less, 300°C or less, or 200°C or less. It is also preferable not to calcinate at a temperature higher than 100°C, and the catalyst may be simply dried at a temperature between room temperature and 100°C or less. The calcination time is preferably 10 hours or less, more preferably 5 hours or less, and even more preferably 2 hours or less.

[0023] It is believed that the larger the specific surface area of ​​a cerium oxide catalyst, the more active it is. The BET specific surface area of ​​a cerium oxide catalyst is 60 m 2 / g or more is preferable, and 70m 2 / g or more or 80m 2 / g or more is more preferable, and 90m 2 / g or more is even more preferable.

[0024] The concentration of the aqueous solution of the saccharide may be appropriately adjusted within a range in which the saccharide is satisfactorily decomposed into formic acid. For example, -4 g / mL or more, 1×10 -2 g / mL or less, or 0.01% by mass or more and 5% by mass or less.

[0025] Sugars, also known as carbohydrates, are generally classified as C m (H2O) n However, in the present invention, glycolaldehyde (HO-CH2-CHO), which is a disaccharide that is not technically included in the sugars, is also included in the sugars.

[0026] The sugars used in the present invention are preferably water-soluble. In the present disclosure, water-soluble does not only mean that the sugars can be dissolved in water without limit, but also means that, for example, when 1 g or 1 mL of the target sugar powder is placed in water and vigorously shaken for 30 seconds every 5 minutes at 20±5°C, the amount of water required to dissolve the sugar within 30 minutes is less than 100 mL. The amount of water is preferably less than 30 mL, more preferably less than 10 mL, and even more preferably less than 1 mL. Note that, since it is considered that the reaction will proceed sequentially if even a part of the sugar is dissolved, the aqueous solution may contain some insoluble sugar.

[0027] Examples of sugars include glycolaldehyde, which is a dicarbonose; glyceraldehyde and dihydroxyacetone, which are tricarbonoses; tetracarbonoses such as erythrose and threose; pentoses such as ribose, arabinose, xylose, lyxose, ribulose, and xylulose; hexoses such as allose, altrose, glucose, mannose, gulose, idose, galactose, talose, psicose, fructose, sorbose, and tagatose; sucrose, lactulose, lactose, and maltose. disaccharides such as starch, guar gum, locust bean gum, tara gum, konjac mannan, pectin, gum arabic, xylan, tamarind gum, alginic acid and its salts, carrageenan, agar, xanthan gum, gellan gum, veran gum, rhamsan gum, pullulan, curdlan, chitin, chitosan, hyaluronic acid, and other polysaccharides; glucose derivatives such as 2-deoxyglucose, N-acetyl-D-glucosamine, 2-S-ethyl-2-thio-D-glucose, and other water-soluble cellulose derivatives such as carboxymethylcellulose, methylcellulose, hydroxypropylmethylcellulose, hydroxyethylcellulose, and hydroxypropylcellulose.

[0028] The amount of cerium oxide catalyst added to the aqueous saccharide solution may be appropriately adjusted within the range in which the saccharide is satisfactorily decomposed into formic acid, and may be, for example, 0.1 mg / mL or more and 10 mg / mL or less.

[0029] In the method of the present invention, an aqueous saccharide solution containing a cerium oxide catalyst is irradiated with light in the presence of oxygen. In this disclosure, irradiating with light does not mean performing a reaction under normal room light, but means irradiating the reaction solution with light directly from a lamp or the like, or approximately directly through only a transparent reaction vessel, in order to promote the reaction.

[0030] In the present disclosure, "in the presence of oxygen" refers to the presence of sufficient oxygen in the reaction system for the reaction from saccharide to formic acid. For example, if a sufficient amount of oxygen is dissolved in the saccharide aqueous solution, the reaction may be carried out as is. If a sufficient amount of oxygen is not dissolved in the saccharide aqueous solution, for example, the gas phase in contact with the saccharide aqueous solution may be replaced with oxygen gas, or an oxygen-containing gas such as oxygen gas or air may be blown into the saccharide aqueous solution.

[0031] The light to be irradiated to the saccharide aqueous solution may be appropriately selected within a range in which the saccharide is effectively decomposed into formic acid. For example, it is considered that the reaction will proceed more efficiently if short-wavelength, high-energy light is used. As the high-energy light, light with a peak wavelength in the range of 180 nm or more and 360 nm or less can be used. In addition, light containing UV-B with a wavelength of 280 nm or more and 315 nm or less and / or UV-C with a wavelength of 180 nm or more and 280 nm or less can be used, and light containing UV-C with a wavelength of 180 nm or more and 280 nm or less can be used, and light with a peak wavelength in these ranges can also be used.

[0032] On the other hand, in the method of the present invention, since the cerium oxide catalyst is excited even with a relatively low energy, visible light may be used. For example, light having a peak wavelength in the range of 360 nm to 830 nm may be used. The lower limit of the peak wavelength range is preferably 380 nm, more preferably 450 nm, and the upper limit is preferably 780 nm, more preferably 625 nm, 590 nm, 565 nm or 500 nm, and even more preferably 485 nm.

[0033] The means of light irradiation is not particularly limited as long as it can irradiate light of the above wavelength, but examples of light sources that include light in this wavelength range include low-pressure mercury lamps, medium-pressure mercury lamps, high-pressure mercury lamps such as "HELIOS-24(120)" manufactured by Koike Precision Machinery Manufacturing Co., Ltd., ultra-high-pressure mercury lamps, chemical lamps, black light lamps, metal halide lamps, and LED lamps such as "TKG-3029-6000" manufactured by Hayashi Lepic Co., Ltd. From the viewpoint of reaction efficiency and cost, low-pressure mercury lamps and LED lamps are preferred, and LED lamps are more preferred. In addition, sunlight may be irradiated directly to the reaction solution, or approximately directly through only a transparent reaction vessel or the like.

[0034] The conditions such as the intensity of the irradiated light may be set appropriately. For example, the intensity of the light at the shortest distance from the light source to the saccharide aqueous solution is 1 mW / cm, although this depends on the scale of implementation and the wavelength of the irradiated light. 2 More than 500mW / cm 2 For example, when the wavelength of the irradiated light is relatively short, the light intensity is preferably 100 mW / cm 2 Less than or equal to 50mW / cm 2 Less than 20 mW / cm is more preferable. 2 Less than or equal to 10mW / cm 2 It is even more preferable that the wavelength of the irradiated light is 10 mW / cm or less. 2 or more than 20mW / cm 2 More preferably, 50 mW / cm 2 or more than 100mW / cm 2 or more, and 400 mW / cm 2 Less than or equal to 300mW / cm 2 Less than 200 mW / cm is more preferable. 2The following is even more preferred. The shortest distance between the light source and the aqueous saccharide solution is preferably 1 m or less, more preferably 50 cm or less, and even more preferably 10 cm or less or 5 cm or less. The lower limit of the shortest distance is not particularly limited, but may be 0 cm, i.e., the light source may be immersed in the aqueous saccharide solution. When sunlight is used, it is impossible to adjust the distance between the light source and the aqueous saccharide solution within the above range, but it is preferable to at least adjust the position of the reaction system so that sunlight can be irradiated directly to the reaction solution or approximately directly through only a transparent reaction vessel or the like.

[0035] The light irradiation time may be appropriately determined within a range in which the sugar is sufficiently decomposed into formic acid. For example, it may be 10 hours or more and 200 hours or less. The time is preferably 20 hours or more or 30 hours or more, more preferably 40 hours or more or 50 hours or more, and preferably 150 hours or less or 120 hours or less, more preferably 100 hours or less or 80 hours or less, and more preferably 70 hours or less or 60 hours or less. A more specific light irradiation time may be, for example, the time when the concentration or amount of the sugar does not decrease any more or becomes difficult to decrease, or the concentration or amount of the formic acid does not increase any more or becomes difficult to increase.

[0036] After the reaction is completed, a general post-treatment may be carried out. For example, the cerium oxide catalyst may be separated from the reaction solution by filtration or centrifugation. The separated cerium oxide catalyst may be dried and reused. Alternatively, the reaction solution from which the cerium oxide catalyst has been separated may be acidified by adding an acid such as hydrochloric acid, and then formic acid may be extracted. Examples of the extraction solvent include ether solvents such as diethyl ether, methyl ethyl ether, diisopropyl ether, ethyl t-butyl ether, and ethyl isobutyl ether. The extract may be dried over anhydrous sodium sulfate or anhydrous magnesium sulfate, concentrated, and further purified by distillation. EXAMPLES

[0037] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples, and it is possible to carry out the present invention by making appropriate modifications within the scope of the above and below-mentioned aims, and all of these modifications are included in the technical scope of the present invention.

[0038] Example 1 (1) Preparation of catalyst 5M cerium nitrate hexahydrate solution (300mL) was added to 28% ammonia water (750mL), stirred for 11 hours, and then allowed to stand for 6 hours. The resulting precipitate was centrifuged at 5000rpm and washed with ultrapure water until the phenolphthalein solution no longer showed color. Next, the mixture was suction filtered while being washed with ultrapure water (2L), then placed in a dryer and dried at 100℃ for one day. The mixture was then baked in an electric furnace at 100-900℃ for two hours. Even when 0.5M cerium nitrate hexahydrate was used, a cerium oxide catalyst was successfully obtained. Figure 1 shows the IR spectra of the sample that was dried only, the sample that was calcined at 900°C, commercial cerium oxide (IV) (Kanto Chemical), and the Reference Catalyst Committee reference catalyst cerium oxide ("JRC-CEO-1").

[0039] 700~1300cm -1 The broad peak at 3700 cm is probably attributable to OH species on the catalyst surface. -1 The peak in the vicinity is thought to be due to stretching vibrations such as -OH. Furthermore, when the firing temperature was 400 to 500°C or higher, the pale yellow changed to white. Since cerium oxide (IV) is white and cerium oxide (III) is golden yellow, it is believed that the higher the firing temperature, the fewer oxygen defects there are and the higher the purity of the cerium oxide (IV). Therefore, the higher the calcination temperature, the closer the sample came to pure cerium(IV) oxide, and the sample that was only dried was considered to be a mixture of cerium(IV) oxide, cerium(III) oxide, and cerium hydroxide.

[0040] (2) Measurement of specific surface area The BET specific surface area of ​​the obtained cerium oxide sample was measured using a high-precision gas adsorption measurement device ("BELSORP MAX" manufactured by Bel Japan Co., Ltd.) The results are shown in Table 1.

[0041] [Table 1]

[0042] As shown in the results in Table 1, there was a tendency for the specific surface area to increase as the sintering temperature decreased. The reason for this is thought to be that the higher the sintering temperature, the more the crystal particles bonded together, resulting in a denser material.

[0043] (3) Photocatalytic reaction Ultrapure water (5 mL), glucose (28 μmol, 1000 ppm), the prepared catalyst (50 mg), and a stirrer were placed in a test tube, the gas phase was filled with oxygen, and the tube was sealed with a W stopper. While stirring the reaction solution, it was irradiated with ultraviolet light of λ>300 nm from a mercury lamp at room temperature for 4 hours. Liquid and gas phase samples were obtained before the start of the reaction and every hour after the start of the reaction. The liquid phase samples were analyzed by HPLC under the following conditions, and the gas phase samples were analyzed by GC-TCD under the following conditions. [HPLC conditions] Column: Column for simultaneous analysis of sugars and organic acids ("SUGAR SH1821" manufactured by Resonac) Detector: Refractive Index Detector (RID) Column temperature: 50℃ Mobile phase: 5mM sulfuric acid Flow rate: 0.5mL / min [GC-TCD conditions] Column: "Porapak QS" manufactured by GL Sciences Detector: Thermal Conductivity Detector (TCD) Mobile phase: He

[0044] In addition, from the measurement results, the formic acid yield and conversion rate were calculated according to the following formulas. Formic acid yield (%) = {[FA] / ([Glu0] × 6)} × 100 Conversion rate (%) = {([Glu0]-[Glu]) / [Glu0]} x 100 [In the formula, [FA] represents the peak intensity of formic acid after the reaction, [Glu0] represents the peak intensity of glucose before the reaction, and [Glu] represents the peak intensity of glucose after the reaction.]

[0045] For comparison, a similar experiment was carried out using commercially available titanium oxide ("P25 (JRC-TIO-15)" manufactured by Japan Aerosil Co., Ltd.).

[0046] FIG. 2 shows the formic acid yield after 4 hours of reaction when each catalyst was used. As shown in the results in FIG. 2, the lower the calcination temperature, the higher the formic acid yield tended to be, and it became clear that the catalyst that was only dried but not calcined had the highest activity.

[0047] FIG. 3 shows the change in composition of the liquid phase and the gas phase when a titanium oxide catalyst and a cerium oxide catalyst according to the present invention (only dried and not calcined) are used. As shown in Figure 3(1), in the case of the titanium oxide catalyst, the glucose concentration in the liquid phase decreased over time, and the formic acid concentration increased only slightly, but the carbon dioxide concentration in the gas phase continued to increase clearly. From these results, it is believed that glucose was decomposed to produce formic acid, but that the produced formic acid was further decomposed to produce carbon dioxide. In contrast, as shown in Figure 3 (2), in the case of the cerium oxide catalyst of the present invention, the carbon dioxide in the gas phase hardly increased and the formic acid concentration in the liquid phase increased over time as the glucose concentration in the liquid phase decreased. This demonstrates that the cerium oxide catalyst of the present invention promotes the decomposition reaction of glucose but does not catalyze the decomposition reaction of formic acid.

[0048] Example 2: Photocatalytic activity evaluation using visible light The mercury lamp is replaced by a blue LED (λ max The formic acid yield was determined in the same manner as in Example 1 (3), except that the wavelength was changed to 470 nm and the reaction was carried out for 24 hours. The formic acid selectivity was calculated by the following formula. The results are shown in Table 2. Selectivity (%) = (formic acid yield / conversion rate) x 100

[0049] [Table 2]

[0050] As shown in the results in Table 2, when titanium oxide was used and visible light was irradiated, no formic acid was obtained at all. When ultraviolet light was used, a small amount of formic acid was detected, which suggests that glucose was not decomposed in the first place. In contrast, when the cerium oxide catalyst according to the present invention was used, formic acid was detected. These results demonstrate that the cerium oxide catalyst according to the present invention can promote the reaction of decomposing glucose to obtain formic acid not only by using high-energy ultraviolet light but also by using safe visible light.

[0051] Example 3: Photocatalytic activity evaluation using visible light Replace the mercury lamp with a blue LED (approx. 1000 mW, λ max The reaction was carried out for 120 hours, with the temperature being changed to 470 nm (=470 nm) and only the cerium oxide catalyst according to the present invention (dried but not calcined) being used as the catalyst. Samples were taken from the liquid phase and the gas phase at the start of the reaction and every 24 hours from the start of the reaction and analyzed, but the concentration of each product was determined in the same manner as in Example 1(3). The results are shown in Figure 4. As shown in the results in FIG. 4, when the cerium oxide catalyst of the present invention was used, even when visible light was irradiated, the glucose concentration in the liquid phase decreased over time, the carbon dioxide in the gas phase showed almost no increase, and the formic acid concentration in the liquid phase increased over time. This demonstrates that the cerium oxide catalyst of the present invention promotes the decomposition reaction of glucose but does not promote the decomposition reaction of formic acid.

[0052] Example 4: Photocatalytic activity evaluation using sunlight On August 22, 2023, the reaction system was installed on the roof of the Kochi University Faculty of Science and Technology Building (Kochi City, Kochi Prefecture) (weather: sunny to cloudy), and the concentration of each product was determined in the same manner as in Example 1 (3), except that the reaction system was exposed to direct sunlight. The results are shown in Table 3 and FIG. 5 together with the results of Example 1 (3) and the results of Example 3 6 hours after the start of the reaction.

[0053] [Table 3]

[0054] As shown in the results in Table 3 and Figure 5, when the enzyme was irradiated with sunlight for 4 hours, the yield of formic acid from glucose was intermediate between that when the enzyme was irradiated with ultraviolet light for 4 hours and blue light for 6 hours. Therefore, it may be possible to produce large amounts of formic acid from sugars outdoors without using lamps or other devices. As shown in the results of Figures 3 and 4, it is believed that if the light irradiation time is extended, formic acid can be obtained from glucose in a higher yield.

[0055] Example 5: Sugar studies The mercury lamp is replaced by a blue LED (λ max The yield and amount of formic acid were determined in the same manner as in Example 1(3), except that the reaction was carried out for 24 hours by changing the wavelength of reaction mixture to 470 nm (470 nm), using only the cerium oxide catalyst according to the present invention (dried but not calcined), and changing glucose to the saccharides shown in Table 4. The results are shown in Table 4.

[0056] [Table 4]

[0057] As shown in the results in Table 4, the method of the present invention makes it possible to produce formic acid from various sugars, and in some cases, formic acid was obtained in a higher yield than from glucose.

Claims

1. 1. A process for producing formic acid, comprising: The method includes a step of irradiating an aqueous saccharide solution containing a cerium oxide catalyst with light in the presence of oxygen, The method according to claim 1, wherein the cerium oxide catalyst comprises cerium (IV) oxide, cerium (III) oxide and cerium hydroxide.

2. The method of claim 1 , wherein the peak wavelength of the light is in the visible light range.

3. 2. The method of claim 1, further comprising the step of obtaining the cerium oxide catalyst by adding a cerium salt to a basic aqueous solution.

4. 4. The method according to claim 3, wherein the precipitate formed by adding the cerium salt to the basic aqueous solution is dried or calcined at a temperature of 500° C. or less to obtain the cerium oxide catalyst.

5. The concentration of the sugar in the aqueous sugar solution is 1×10 -4 g / mL or more, 1×10 -2 The method of claim 1, wherein the concentration is less than or equal to 100 mg / mL.

6. The method according to claim 1, wherein the ratio of the cerium oxide catalyst to the aqueous saccharide solution is 0.1 mg / mL or more and 10 mg / mL or less.

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