Catalyst for photocatalytic oxidation of furfural to prepare furfuroic acid and application thereof

Abstract

The application discloses a kind of catalysts for photocatalytic oxidation of furfural to prepare furfuryl acid and application thereof, belong to renewable energy technology field, by adding noble metal in g-C3N4, when metal and g-C3N4 coordination complex, the addition of noble metal changes the electronic structure and band gap structure of g-C3N4, and then improve its photocatalytic activity;Again through the catalyst prepared under different conditions and the influence of photocatalytic reaction under different conditions, it is known that the conversion rate of furfural and the yield of furfuryl acid are higher under the condition of oxygen photocatalytic reaction at 40 DEG C;The application uses furfural as raw material, and prepares furfuryl acid by adding g-C3N4-based catalyst for photocatalysis, with low cost, raw material is easy to obtain, production process is simple, realizes the efficient use of biomass raw material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of renewable energy, and particularly relates to a catalyst for photocatalytic oxidation of furfural to prepare furfuryl acid and application thereof. BACKGROUND

[0002] Furfural is one of the most competitive biomass-based platform compounds as a common industrial chemical derived from lignocellulosic biomass. Furfural has an aldehyde group and a diene ether functional group, and is very active in chemical properties, and can generate various derivatives through oxidation, hydrogenation and condensation reactions. Furfural has a chemical structure of furan heterocyclic aldehyde, and is also called furfuraldehyde. The furan heterocycle exhibits the characteristics of diene aromatic compounds. Furfural contains an aldehyde group, and thus has high chemical activity and strong reactivity. When furfural is in contact with air, especially when furfural contains acid, furfural is automatically oxidized to become brown, and even black-brown resin-like substances. Therefore, furfural is often used as a basic raw material for synthesizing a large number of industrial chemicals, and is widely used in the fields of medicine, pesticide and synthetic plastic, and is one of the most important derivatives of furan ring.

[0003] Furfuryl acid, also known as a-furfuryl acid, is mainly prepared by oxidation of furfural. Furfuryl acid is an important intermediate for organic synthesis, and is an important raw material for synthesizing tetrahydrofurfuryl acid, furfuryl amide, furfuryl ester and furfuryl chloride. In the plastic industry, furfuryl acid can be used for producing plasticizers and thermosetting resins. In the food industry, furfuryl acid can be used as a mildew inhibitor and a preservative. Furfuryl acid can also be used as an intermediate for synthesizing a new anticancer drug, and is an important organic synthesis raw material, and thus has a wide range of uses.

[0004] Traditional furfuryl acid preparation methods mainly include equivalent oxidant oxidation method, Cannizarro disproportionation method and catalytic oxidation method. The equivalent oxidant has some limitations in use, such as problems of three wastes, low selectivity, low utilization rate of oxidant atoms, and safety of the oxidant itself. Cannizarro disproportionation reaction is simple, and two molecules of glycoside can be converted into one molecule of furfuryl acid and one molecule of furfuryl alcohol under alkaline conditions. However, the equivalent furfuryl alcohol is generated in the reaction, which makes the separation operation cumbersome, and the furfuryl alcohol is unstable in structure and has a high separation cost.

[0005] As a popular non-metal semiconductor photocatalyst, graphite phase carbon nitride has many advantages: adjustable band gap, wide visible light absorption range, high chemical stability and rich nitrogen atom edge structure. At the same time, g-C3N4 is also widely used in the fields of pollutant degradation, hydrogen production by water splitting, oxidation reaction and hydrogenation reaction, etc. It is an environmentally friendly carbon material. However, due to the shortcomings of g-C3N4 such as wide band gap, high recombination rate of photo-generated carriers and pores, low visible light utilization rate, its performance still has a lot of room for improvement, so it is necessary to effectively modify g-C3N4 and develop composite photocatalysts with better performance. It is usually improved by heterostructure construction, morphology adjustment, noble metal modification, metal and non-metal element doping, etc. At present, doping noble metal loaded carbon nitride is to deposit noble metals such as Au, Ag, Pt, Pb, etc. on the surface of g-C3N4 material or doped into the lattice of g-C3N4 crystal to improve its photocatalytic performance. Because Ag has lower preparation cost and simpler preparation among many noble metals, and its chemical properties are stable, so it has been widely used in noble metal modification.

[0006] Chinese invention patent application No. 202110973897.6 discloses a preparation method of a composite catalyst for the oxidation of furfural to produce furfuryl acid. First, copper nitrate, cobalt molybdate and cobalt nitrate are added to a container, then deionized water is added, and it is completely dissolved under stirring at 70°C. The pH is adjusted to 8-9 by adding ammonium oxalate solution dropwise, and it is aged for 12 hours. The precipitate is washed with deionized water for 10 times, dried at 110°C for 5 hours, then transferred to a muffle furnace and calcined at 550°C for 5 hours to obtain the catalyst. Pure water and the catalyst are added to a four-necked flask, and air is introduced as the oxygen source. The reaction temperature is controlled at 60°C, and 35g of furfural is added dropwise and reacted for 30 minutes. The catalyst is filtered out while hot and reused. The mother liquor is added to activated carbon, and decolorization is carried out at 70-80°C for 30-60 minutes. The activated carbon is filtered out, and the temperature is slowly reduced to 0-5°C. The product is obtained by filtration. The wet product is dried in an oven at 50°C for 5 hours to obtain the furfuryl acid product. The preparation process of the catalyst is relatively complex, and the calcination time is relatively long, which may cause energy consumption.

[0007] Chinese invention patent application No. 202011108544.1 discloses a method for preparing furfuryl acid. The preparation method is as follows: 1 mmol of furfural, 10 mL of dimethyl sulfoxide, 10 mol% of Chimassorb 944 and 10 mol% of sodium tungstate are added to a 25 ml high-pressure reaction kettle. After tightening the screw, oxygen is filled, and the oxygen pressure is increased to 2 MPa after three times of replacement. The temperature is increased to 80°C under magnetic stirring for 12 hours. After the reaction is completed, the temperature is cooled to room temperature, N,N-dimethylformamide is added as an internal standard, and methanol is added for dilution. The reaction product is detected by gas chromatography. This method has a long reaction time and low industrial production efficiency.

[0008] Chinese invention patent application No. 201611098903.3 discloses a method for preparing methyl furoate by catalytic oxidation and esterification of furfural, which specifically comprises dissolving cobalt acetate, copper acetate and 2-methyl-phenanthroline in ethanol and stirring, adding a carrier Mg(OH)2, stirring in a water bath at 45 DEG C for 2h, removing the solvent by rotary evaporation, drying, and calcining at 700 DEG C for 3h in an inert atmosphere to obtain a catalyst CoCuNC / MgO; adding the catalyst, furfural and methanol into a high-pressure reaction kettle, and selecting oxygen or air as the oxygen source to catalytically oxidize furfural to methyl furoate under the conditions of a reaction temperature of 60-120 DEG C and a reaction pressure of 0.1-1 MPa for 1-12h; the method uses a plurality of organic reagents in the preparation process, is not environmentally friendly, and the preparation process is relatively complex. SUMMARY

[0009] In view of the problems of complex catalyst preparation process, high price, environmental unfriendliness, poor catalyst stability and low reaction activity in the prior art, the present application is proposed, i.e. a method for preparing furoic acid by photocatalytic oxidation of furfural.

[0010] To solve the above technical problems, the present application provides the following technical solutions:

[0011] The present application provides a catalyst for catalytically oxidizing furfural to prepare furoic acid, which is a metal-nitrogen-containing compound, and the metal-nitrogen-containing compound catalyst is a metal-doped modified nitrogen-containing compound, which is prepared by calcination at high temperature under an inert gas.

[0012] Preferably, the metal is one or two of silver, copper, gold, platinum, palladium and ruthenium.

[0013] Preferably, the nitrogen-containing compound is urea, monocyamide or dicyamide.

[0014] Preferably, the loading amount of silver in the catalyst is 0.5%-10%.

[0015] Preferably, the calcination temperature is 300-800 DEG C.

[0016] Preferably, the inert gas is nitrogen or argon.

[0017] Preferably, the reducing gas is hydrogen, CO or a mixture of the two.

[0018] The present application also provides the use of the above catalyst in the photocatalytic oxidation of furfural to prepare furoic acid, wherein furfural, a metal-nitrogen-containing compound and a solvent are mixed and subjected to photocatalytic oxidation with oxygen to prepare furoic acid.

[0019] Preferably, the solvent is water.

[0020] Preferably, the photocatalytic oxidation is solar light, visible light or ultraviolet light.

[0021] Beneficial effects:

[0022] (1) Compared with the traditional g-C3N4 catalyst, the metal is doped and modified to g-C3N4 in the application, the photocatalytic activity of the catalyst is improved, and the catalyst has excellent stability and catalytic property.

[0023] (2) The application uses oxygen as the oxygen source for catalytic oxidation to prepare furfural, and the only by-product in the whole reaction process is water, which is a green oxidizing agent, cheap and pollution-free.

[0024] (3) The application adopts a new method of photocatalytic oxidation, the reaction conditions are mild, the product selectivity is high, and the catalyst is cheap and easy to obtain. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 X-ray diffraction spectrum of the catalyst prepared in examples 1-3 of the application;

[0026] Figure 2 Reaction result graph of furfural conversion rate catalyzed by the catalyst prepared in examples 1-3 of the application;

[0027] Figure 3 Reaction result graph of furfural acid yield catalyzed by the catalyst prepared in examples 1-3 of the application;

[0028] Figure 4 Reaction result graph of furfural conversion rate catalyzed by the catalyst prepared in examples 1, 4 and 5 of the application;

[0029] Figure 5 Reaction result graph of furfural acid yield catalyzed by the catalyst prepared in examples 1, 4 and 5 of the application. DETAILED DESCRIPTION

[0030] In order to make the above-mentioned purposes, features and advantages of the application more obvious and easy to understand, the specific embodiments of the application will be described in detail below with reference to the embodiments of the specification.

[0031] Example 1

[0032] 0.1575g of silver nitrate and 20g of urea were weighed, dissolved in 50ml of ultrapure water, stirred for 12h, evaporated in an oil bath at 70℃, dried in an oven at 80℃, ground, and then nitrogen was introduced into the horizontal furnace, and the temperature was increased to 500℃ at a rate of 4℃ / min and calcined for 2 hours. After cooling to room temperature, hydrogen was introduced again, the temperature was increased to 500℃ at a rate of 4℃ / min, and calcined for 2 hours again. After grinding, a catalyst with Ag content of 0.5% of the mass of g-C3N4 was obtained, which was recorded as 0.5% Ag-g-C3N4 (N2+H2).

[0033] Example 2

[0034] Take silver nitrate 0.3150 g, urea 20 g, dissolved in 50 ml of ultrapure water, stirring for 12 h, 70 ℃ oil bath evaporation, drying in the oven at 80 ℃, grinding, and then introducing nitrogen into the horizontal furnace, and then increasing the temperature to 500 ℃ at a rate of 4 ℃ / min and calcining for 2 hours. After cooling to room temperature, hydrogen was introduced again at a rate of 4 ℃ / min to 500 ℃ and calcined for 2 hours. After grinding, a catalyst with an Ag content of 1% of the mass of g-C3N4 was obtained, which was recorded as 1% Ag-g-C3N4(N2+H2).

[0035] Example 3

[0036] Take silver nitrate 1.575 g, urea 20 g, dissolved in 50 ml of ultrapure water, stirring for 12 h, 70 ℃ oil bath evaporation, drying in the oven at 80 ℃, grinding, and then introducing nitrogen into the horizontal furnace, and then increasing the temperature to 500 ℃ at a rate of 4 ℃ / min and calcining for 2 hours. After cooling to room temperature, hydrogen was introduced again at a rate of 4 ℃ / min to 500 ℃ and calcined for 2 hours. After grinding, a catalyst with an Ag content of 1% of the mass of g-C3N4 was obtained, which was recorded as 1% Ag-g-C3N4(N2+H2).

[0037] Example 4

[0038] Take silver nitrate 0.1575 g, urea 20 g, dissolved in 50 ml of ultrapure water, stirring for 12 h, 70 ℃ oil bath evaporation, drying in the oven at 80 ℃, grinding, and then introducing nitrogen into the horizontal furnace, and then increasing the temperature to 500 ℃ at a rate of 4 ℃ / min and calcining for 2 hours. After cooling to room temperature, hydrogen was introduced again at a rate of 4 ℃ / min to 500 ℃ and calcined for 2 hours. After grinding, a catalyst with an Ag content of 1% of the mass of g-C3N4 was obtained, which was recorded as 1% Ag-g-C3N4(N2+H2).

[0039] Example 5

[0040] Take silver nitrate 0.1575 g, urea 20 g, dissolved in 50 ml of ultrapure water, stirring for 12 h, 70 ℃ oil bath evaporation, drying in the oven at 80 ℃, grinding, and then introducing nitrogen into the horizontal furnace, and then increasing the temperature to 500 ℃ at a rate of 4 ℃ / min and calcining for 2 hours. After grinding, a catalyst with an Ag content of 1% of the mass of g-C3N4 was obtained, which was recorded as 1% Ag-g-C3N4(N2+H2).

[0041] Performance test

[0042] The X-ray diffraction patterns of the Ag-doped carbon nitride catalysts prepared in Examples 1-3 were tested, and the test results are shown in Figure 1 Figure 1 ​It can be seen that the X-ray diffraction patterns of different proportions of catalysts are shown, and it can be observed that there is a clear diffraction peak at 27.4° which is attributed to carbon nitride. All catalysts appear diffraction peaks corresponding to Ag(111), (200), (220) and (311) crystal faces at about 38.11°, 44.30°, 64.44° and 77.40°, which shows that silver is successfully doped into carbon nitride.

[0043] Table 1 is the reaction conditions of Examples 1-3 and the conversion rate of furfural and the yield of furfuryl acid.

[0044] Table 1

[0045]

[0046] Table 2 is the reaction conditions of Examples 1, 4, 5 and the conversion rate of furfural and the yield of furfuryl acid.

[0047] Table 2

[0048]

[0049] From Figure 2 and Figure 3 It can be seen that the catalytic performance of the catalyst prepared in Examples 1-3, Example 10.5% Ag-g-C3N4(N2+H2), is the best, in which the conversion rate of furfural can reach 58%, and the yield of furfuryl acid can reach 25%, and as the amount of catalyst increases, the conversion rate of furfural can reach 60%, and the yield of furfuryl acid can reach 30%.

[0050] From Figure 4 and Figure 5 It can be seen that among the catalysts prepared in Examples 1, 4, 5, the catalytic performance of the catalyst calcined by only passing nitrogen is lower than that of the catalyst calcined by passing air and hydrogen and nitrogen and hydrogen. It is indicated that it may be due to the fact that the hydrogen atmosphere shortens the band gap of g-C3N4 and reduces Ag in AgNO3, thereby improving its redox ability.

[0051] Among them, the catalyst of Example 4 has the highest conversion rate of furfural, which can reach 60%. And in the case of no oxygen is passed, the yield and conversion rate are also lower than that of the case of passing oxygen for catalysis.

[0052] The Ag-doped carbon nanocatalyst prepared in Examples 1-5 was tested for furfural catalytic activity, and the test method was as follows:

[0053] (1) Take 50ml ultrapure water, add 0.05g NaOH, 83μL furfural, ultrasonic dissolution, take 200μL sample;

[0054] (2) Pour the material in the beaker into the photo-reactor, and add 0.05 g of catalyst, and magnetically stir for 1 h at 40 DEG C, and adsorb in the dark, and take samples every 30 min, and a total of twice;

[0055] (3) Use visible light irradiation, and pass oxygen at a flow rate of 30 mL / min, and keep the reaction temperature at 40 DEG C, and magnetically stir for 8 h, and carry out the reaction, and take samples every 1 h, and a total of 7 times;

[0056] (4) After the reaction is completed, filter 100 muL of the reaction sample liquid, dilute to 1 mL, and use an Agilent 1260 Series high-performance liquid chromatograph to carry out analysis, the mobile phase is 100% acetonitrile: water = 50:50, the column temperature is 30 DEG C, the flow rate is 0.6 mL / min, the detection wavelength is 220 nm, and the sample amount is 10 muL.

[0057] Compared with a traditional carbon nitride photocatalyst, the method realizes efficient utilization of catalytic oxidation of furfural by doping and modifying carbon nitride with a noble metal silver.

[0058] The application obtains an Ag-g-C3N4 catalyst by using metal silver to dope and modify carbon nitride, and the catalyst has good stability and excellent catalytic performance.

[0059] The application uses biomass derivative furfural as a raw material to prepare furfuryl acid, and the catalytic process is simple and suitable for industrial application.

[0060] The application uses oxygen as an oxygen source to catalytically oxidize furfural, and the byproduct in the whole reaction process is water, which is a green oxidant and cheap and pollution-free.

[0061] It should be noted that the above examples are only used to illustrate the technical solutions of the present application and are not limiting, and although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application, and they should be covered in the scope of the claims of the present application.

Claims

1. The application of a catalyst in the photocatalytic oxidation of furfural to prepare furoic acid, characterized in that: The catalyst is a metal-nitrogen compound, which is a metal-doped modified nitrogen compound. It is prepared by high-temperature calcination under an inert gas, cooling to room temperature, then introducing hydrogen gas and heating to 500°C at a rate of 4°C / min, followed by calcination. The metal is silver, and the nitrogen compound is urea, cyanamide, or dicyandiamide.

2. The application of the catalyst according to claim 1 in the photocatalytic oxidation of furfural to prepare furoic acid, characterized in that: The catalyst has a silver loading of 0.5% to 10%.

3. The application of the catalyst according to claim 1 in the photocatalytic oxidation of furfural to prepare furoic acid, characterized in that: The high-temperature calcination temperature is 300–800℃.

4. The application of the catalyst according to claim 1 in the photocatalytic oxidation of furfural to prepare furoic acid, characterized in that: The inert gas is nitrogen or argon.

5. The application of the catalyst according to claim 1 in the photocatalytic oxidation of furfural to prepare furoic acid, characterized in that: Furoic acid is prepared by photocatalytic oxidation of furfural, a metal-nitrogen compound catalyst, and a solvent by passing oxygen through a mixture.

6. The application of the catalyst according to claim 5 in the photocatalytic oxidation of furfural to prepare furoic acid, characterized in that: The solvent is water.

7. The application of the catalyst according to claim 5 in the photocatalytic oxidation of furfural to prepare furoic acid, characterized in that: The photocatalytic oxidation is carried out by sunlight, visible light, or ultraviolet light.

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