A supported non-noble metal catalyst and a method for catalyzing hydrogen peroxide oxidation of furfural to furfuroic acid

Abstract

The application discloses a method for preparing furanic acid by catalyzing hydrogen peroxide to oxidize furfural with a supported non-noble metal, and belongs to the field of organic synthesis and catalysis technology. The method uses a MnO2-CeO2 / γ-Al2O3 supported catalyst as a catalytic system, water as a green solvent, hydrogen peroxide as an oxidant, and furfural as a raw material to perform an oxidation reaction. After the reaction is completed, the furanic acid product is obtained through the steps of "filtration, concentration of the filtrate, cooling crystallization, filtration and washing, and drying". Through the synergistic catalysis of MnO2 and CeO2, the hydrogen peroxide utilization rate and reaction selectivity are improved, excessive oxidation of furfural is avoided, and the method has the advantages of being green and environmentally friendly, low in cost, good in catalyst stability, and wide in industrialization prospect.

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis and catalytic material preparation technology, specifically relating to a supported non-precious metal catalyst and a green synthesis method for producing furoic acid by catalyzing the oxidation of furfural with hydrogen peroxide. Background Technology

[0002] Furoic acid is an important organic chemical intermediate widely used in pharmaceuticals, pesticides, fragrances, and food additives, and its market demand continues to grow. Currently, the core raw material for the industrial production of furoic acid is furfural, which is mainly converted through oxidation reactions. Commonly used oxidants include potassium permanganate, potassium dichromate, nitric acid, and hydrogen peroxide. However, the oxidation processes using potassium permanganate and potassium dichromate generate large amounts of solid waste, while nitric acid oxidation easily produces nitrogen oxides and numerous side reactions, both posing serious environmental problems and contradicting the trend of green chemical development.

[0003] Hydrogen peroxide (H2O2), as a green oxidant, produces only water as its oxidation product, resulting in no secondary pollution. It is considered an ideal alternative to traditional oxidants, and the related catalytic oxidation technology for furfural to furoic acid has become a research hotspot. However, H2O2 is prone to ineffective decomposition during the reaction, leading to low utilization. Furthermore, it is difficult to control the degree of furfural oxidation, easily resulting in over-oxidation to produce byproducts such as carbon dioxide and furanyl diacid, thus reducing product yield. Therefore, developing efficient catalysts to improve H2O2 utilization and reaction selectivity is crucial for promoting the industrialization of this green process.

[0004] In existing technologies, catalysts used for the oxidation of furfural with H2O2 are mainly divided into two categories: precious metal catalysts and non-precious metal catalysts. Precious metal catalysts are expensive, and their preparation processes are complex, resulting in high production costs. Existing non-precious metal catalysts mostly employ single metal oxides. For example, the single MnO2 catalyst disclosed in patent CN109336451A achieves an H2O2 utilization rate of 70% and a furfural acid yield of 85%, but exhibits significant over-oxidation and poor catalyst stability, with the yield dropping below 75% after two reuses. The Fe2O3 catalyst disclosed in patent CN111265342A has an H2O2 utilization rate of only 68% and a furfural acid yield of less than 80%.

[0005] Therefore, developing a low-cost, highly active, H2O2-efficient, and effective non-precious metal catalyst system that can suppress excessive oxidation is of great significance for promoting the industrialization of the green oxidation process of furfural to furoic acid.

[0006] Based on this, this application was developed. Summary of the Invention

[0007] The purpose of this invention is to overcome the defects of the prior art. In view of the technical problems of high cost of precious metal catalysts, low H2O2 utilization rate, poor reaction selectivity and insufficient stability of non-precious metal single oxide catalysts, the present invention provides a supported non-precious metal catalyst. Through the synergistic catalytic effect of composite metal oxides, it achieves simultaneous improvement of H2O2 utilization rate and furfural yield, while reducing production costs and realizing green and environmentally friendly production.

[0008] This invention also provides a green synthesis method for producing furoic acid by catalyzing the oxidation of furfural with the above-mentioned non-precious metal catalyst.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a supported non-precious metal catalyst, which uses an impregnation method to prepare a MnO2-CeO2 / γ-Al2O3 supported catalyst, specifically includes the following steps: immersing a γ-Al2O3 support in a mixed aqueous solution of Mn(NO3)2 and Ce(NO3)4; after impregnation, drying and calcining are performed to obtain the MnO2-CeO2 / γ-Al2O3 catalyst; The mass ratio of MnO2 to CeO2 in the obtained catalyst is 3:1 to 1:1. The total mass of MnO2 and CeO2 accounts for 5-15% of the mass of the γ-Al2O3 support.

[0010] Specifically, during catalyst preparation, the catalyst can be impregnated at 25-30℃ for 4-6 hours to ensure sufficient adsorption of metal ions onto the support surface, followed by drying at 80-100℃ for 12-16 hours to remove moisture. The specific surface area of ​​the γ-Al₂O₃ support used is 150-200 m² / h. 2 / g, particle size 20-40 mesh. When γ-Al2O3 support is immersed in a mixed aqueous solution of Mn(NO3)2 and Ce(NO3)4, the liquid-solid ratio is controlled at 4-6:1 (mL / g).

[0011] Furthermore, the calcination process specifically involves placing the catalyst in a muffle furnace and calcining it at 450-550℃ for 3-5 hours to completely decompose the metal salt into metal oxides. After cooling, the MnO2-CeO2 / γ-Al2O3 catalyst is obtained.

[0012] This invention provides a supported non-noble metal catalyst prepared by the above-described preparation method.

[0013] This invention provides the application of the above-mentioned supported non-precious metal catalyst in the catalytic oxidation of furfural to furoic acid.

[0014] This invention also provides a method for producing furoic acid by catalytic oxidation of furfural with the above-mentioned supported non-precious metal catalyst, using furfural with a purity ≥98% as raw material, water as solvent, and 25-35% hydrogen peroxide solution as oxidant, specifically including the following steps: In a reactor, furfural, water, and a supported non-precious metal catalyst are mixed evenly, heated to 55-65℃, and hydrogen peroxide solution is added dropwise. The mixture is stirred and kept at this temperature for 1-2 hours. After the reaction is complete, the solid and liquid are separated. The filtrate is concentrated under reduced pressure (to remove excess water), cooled and crystallized (the concentrate is transferred to a crystallization vessel, cooled and kept at this temperature to allow furoic acid to fully precipitate), filtered to obtain the crystallized product, washed, and dried to obtain the furoic acid product.

[0015] Specifically, the molar ratio of furfural to H2O2 can be 1:(1.4-1.6), and the amount of the supported non-precious metal catalyst is 4-6% of the mass of furfural.

[0016] Furthermore, the concentration of the hydrogen peroxide solution is 25-35% (mass percentage), and the stirring speed is controlled at 300-400 r / min during the heat preservation reaction.

[0017] Further preferably, after the reaction is completed, the catalyst is recovered by hot filtration at 40-50℃; the filtrate is concentrated under reduced pressure under the following conditions: vacuum degree 0.06-0.08MPa, concentration temperature 40-50℃, until the filtrate volume is 1 / 3-1 / 2 of the original volume; the cooling crystallization conditions are: temperature 0-5℃, crystallization time 2-4h; washing is performed 2-3 times with ice water to remove residual unreacted raw materials and impurities, and the amount of water used for each washing is 1-2 times the mass of the crystallized product; the drying temperature is 60-80℃, and the drying time is 2-3h.

[0018] A further preferred method for regenerating the filtered and recovered catalyst is as follows: first, wash 2-3 times with deionized water at 40-60℃ to remove adsorbed furfural acid and impurities from the surface; then, ultrasonically clean with a 3-8% (v / v) ethanol aqueous solution; finally, dry at 100±10℃ for 3-6 hours and calcine at 300±50℃ for 1-2 hours to remove residual organic matter and restore catalytic activity. The regenerated catalyst can be reused 5-6 times with a yield still not less than 85%.

[0019] The innovations of this application are mainly reflected in the following aspects. (1) Constructing MnO2-CeO2 composite active components to achieve synergistic catalysis: MnO2 provides the main catalytic active sites and promotes the decomposition of H2O2 to generate active oxygen species; CeO2 regulates the generation rate of active oxygen species through its unique oxygen storage-release capacity, inhibits the ineffective decomposition of H2O2, and inhibits the excessive oxidation of furfural, thus significantly improving the reaction selectivity and H2O2 utilization rate. (2) γ-Al2O3 is selected as the support: its high specific surface area and good dispersibility can promote the uniform loading of composite active components, reduce the aggregation of active components, improve catalytic activity, and enhance the mechanical strength and stability of the catalyst. (3) Green process design: Water is used as a solvent and H2O2 is used as an oxidant. No toxic or harmful substances are emitted during the entire reaction process. The products are only furoic acid and water, which is in line with the concept of green chemistry. (4) High cost performance of catalyst: It uses non-precious metal raw materials, has a simple preparation process, and can be reused 3-5 times, which greatly reduces the cost of industrial production.

[0020] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: (1) High catalytic efficiency: The conversion rate of furfural reaches 98% and the yield of furoic acid is as high as 92%, which is far superior to the existing non-precious metal catalyst system (the yield of existing single non-precious metal catalysts is mostly below 85%). (2) High H2O2 utilization rate: The utilization rate of hydrogen peroxide is ≥85%, which is 15-20 percentage points higher than the existing technology, reducing the consumption of oxidant and lowering the production cost; (3) High product purity: After purification, the purity of furoic acid is ≥99.2%, which meets the requirements for pharmaceutical and food grade applications; (4) Excellent environmental performance: The solvent is water, the oxidant reduction product is water, there is no waste residue or waste gas emission, and no complicated environmental protection equipment is required; (5) Good stability and recyclability: After the catalyst is reused 3-5 times, the yield of furoic acid is still maintained at more than 85%, which reduces the cost of catalyst replacement and facilitates continuous industrial production. Detailed Implementation

[0021] The technical solution of the present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited thereto.

[0022] In the following examples, all raw materials used are common commercially available products that can be purchased directly, or can be prepared using conventional techniques in the art. Example 1

[0023] The preparation steps of the MnO2-CeO2 / γ-Al2O3 catalyst are as follows: (1) Accurately weigh an appropriate amount of Mn(NO3)2·4H2O (containing about 0.6g of MnO2 after conversion) and an appropriate amount of Ce(NO3)4·6H2O (containing about 0.4g of CeO2 after conversion), dissolve them in 50mL of deionized water, and stir until completely dissolved to obtain a mixed metal salt solution; (2) Add 10g of γ-Al2O3 support (specific surface area 180m² / g, particle size 30 mesh) to the above solution and stir and impregnate at 28℃ for 5h. (3) The impregnated mixture was placed in a forced-air drying oven and dried at 90°C for 14 hours; then it was transferred to a muffle furnace and calcined at 500°C for 4 hours. After natural cooling, the MnO2-CeO2 / γ-Al2O3 catalyst (MnO2:CeO2=3:2) was obtained. Example 2

[0024] The method for producing furoic acid by catalyzing the oxidation of furfural with the MnO2-CeO2 / γ-Al2O3 catalyst obtained in Example 1 above includes oxidation reaction and purification separation, as detailed below: (1) Add 10g furfural (0.104mol), 200mL deionized water and 0.5g of the catalyst prepared in Example 1 to a 500mL three-necked flask and stir until homogeneous; (2) Place the three-necked flask in a constant temperature water bath and heat it to 60°C. Add 17.68g of 30% hydrogen peroxide solution (0.156 mol, furfural to H2O2 molar ratio 1:1.5) dropwise at a rate of 1.5 drops / second through a dropping funnel for about 30 minutes. (3) After the addition is complete, maintain a constant temperature of 60℃ for 1.5h and control the stirring speed at 350r / min during the reaction. (4) After the reaction is complete, filter the catalyst while it is still hot at 45°C; (5) The filtrate was concentrated under reduced pressure at a vacuum of 0.07 MPa and 45°C to approximately 80 mL; (6) Cool the concentrated liquid to 2°C, keep it at that temperature for 3 hours to crystallize, and filter to obtain a white crystalline product; (7) The crystallized product was washed three times with 10 mL of ice water and then dried at 70 °C for 2.5 h to obtain 11.8 g of furoic acid product.

[0025] The results were obtained by high performance liquid chromatography (HPLC): furfural conversion rate 98%, furoic acid yield 92%, hydrogen peroxide utilization rate 86%, and product purity 99.3%. Example 3

[0026] The catalyst reuse performance test is detailed below: The catalyst recovered in Example 2 was dried at 100°C for 4 hours. The oxidation reaction experiment was repeated according to the process conditions of Example 2. The furfural conversion rate, furoic acid yield and H2O2 utilization rate of each experiment were recorded. The results are shown in the table below.

[0027]

[0028] The results in the table above show that the catalyst of the present invention has good stability. After being reused 5 times, the yield of furoic acid is still above 85%, which can meet the needs of continuous industrial production.

[0029] Comparative Example 1

[0030] Comparative experiments using a single MnO2 catalyst: A single MnO2 / γ-Al2O3 catalyst was prepared according to the method of Example 1 (MnO2 loading was the same as in Example 1, at 10%), and the remaining process conditions were the same as in Example 2. Oxidation reaction experiments were then conducted.

[0031] The results showed that the furfural conversion rate was 90%, the furoic acid yield was 82%, the hydrogen peroxide utilization rate was 70%, and trace amounts of furanolic acid byproduct were detected, proving that the single MnO2 catalyst had obvious over-oxidation problems.

[0032] Comparative Example 2

[0033] Comparative experiments using a single CeO2 catalyst: A single CeO2 / γ-Al2O3 catalyst was prepared according to the method of Example 1 (CeO2 loading was the same as in Example 1, at 10%), and the remaining process conditions were the same as in Example 2. Oxidation reaction experiments were then conducted.

[0034] The results showed that the furfural conversion rate was 85%, the furoic acid yield was 78%, and the hydrogen peroxide utilization rate was 75%, with catalytic activity significantly lower than that of the composite catalyst of this invention.

[0035] Comparative Example 3

[0036] Comparative experiments of different MnO2 to CeO2 mass ratios: Composite oxide catalysts with MnO2:CeO2 mass ratios of 1:1, 2:3, and 4:1 were prepared respectively. The remaining preparation processes and reaction conditions were the same as in Examples 1 and 2. The experimental results are shown in the table below.

[0037]

[0038] The results in the table above show that when the mass ratio of MnO2 to CeO2 is 3:2, the composite catalyst exhibits the best synergistic catalytic effect, simultaneously achieving the highest furfural conversion rate, furoic acid yield, and H2O2 utilization rate.

[0039] In summary, this invention has the following industrial advantages and application prospects: 1) The catalyst uses non-precious metal raw materials, the preparation process is simple, the cost is only 1 / 5 to 1 / 10 of the existing precious metal catalysts, and it can be reused, which greatly reduces the production cost; 2) The reaction conditions are mild, and it can be carried out at normal pressure and 55-65℃. No high temperature and high pressure equipment is required, resulting in low energy consumption and small equipment investment. 3) The process is green and environmentally friendly, with no waste residue or exhaust gas emissions, and low environmental treatment costs; 4) High product yield and purity, resulting in strong market competitiveness. This method can be directly applied to the technological upgrading of existing furoic acid production facilities, or to the construction of new industrial production lines. It can effectively solve the environmental protection and cost problems of existing processes, and has significant economic value and social benefits, with broad prospects for industrialization.

Claims

1. A method for preparing a supported non-noble metal catalyst, characterized in that, The process includes the following steps: immersing the γ-Al2O3 support in a mixed aqueous solution of Mn(NO3)2 and Ce(NO3)4, and after impregnation, drying and calcining are performed to obtain the final product. The mass ratio of MnO2 to CeO2 in the obtained catalyst is 3:1 to 1:

1.

2. The method for preparing the supported non-noble metal catalyst as described in claim 1, characterized in that, Soak at 25-30℃ for 4-6 hours, then dry at 80-100℃ for 12-16 hours.

3. The method for preparing the supported non-noble metal catalyst as described in claim 1, characterized in that, The roasting process specifically involves roasting at 450-550℃ for 3-5 hours.

4. The supported non-precious metal catalyst prepared by any one of the preparation methods described in claims 1 to 3.

5. The application of the supported non-precious metal catalyst according to claim 4 in the catalytic oxidation of furfural to furoic acid.

6. A method for producing furoic acid by catalytic oxidation of furfural with the supported non-precious metal catalyst of claim 4, characterized in that, Includes the following steps: After mixing furfural, water and a supported non-precious metal catalyst evenly, the mixture is heated to 55-65℃, hydrogen peroxide solution is added dropwise, and the reaction is maintained at this temperature for 1-2 hours with stirring. After the reaction is completed, the solid and liquid are separated, and the filtrate is concentrated under reduced pressure, cooled and crystallized, washed and dried to obtain furoic acid product.

7. The method for producing furfural acid by catalytic oxidation of furfural with peroxide as described in claim 6, characterized in that, The molar ratio of furfural to H2O2 is 1:(1.4-1.6), and the amount of the supported non-precious metal catalyst is 4-6% of the mass of furfural.

8. The method for producing furfural acid by catalytic oxidation of furfural with peroxide as described in claim 6, characterized in that, The concentration of hydrogen peroxide solution is 25-35%, and the stirring speed is controlled at 300-400 r / min during the heat preservation reaction.

9. The method for producing furfural acid by catalytic oxidation of furfural with peroxide as described in claim 6, characterized in that, After the reaction is complete, the catalyst is recovered by hot filtration at 40-50℃; the filtrate is concentrated under reduced pressure under the following conditions: vacuum degree 0.06-0.08MPa, concentration temperature 40-50℃, until the volume of the filtrate is 1 / 3-1 / 2 of the original volume; the cooling crystallization conditions are: temperature 0-5℃, crystallization time 2-4h; washing is performed 2-3 times with ice water; the drying temperature is 60-80℃, and the drying time is 2-3h.

10. The method for producing furfural acid by catalytic oxidation of furfural with peroxide as described in claim 9, characterized in that, The catalyst regeneration steps after filtration recovery are as follows: first, wash with deionized water at 40-60℃, then ultrasonically clean with an ethanol aqueous solution of 3-8% by volume, and finally dry at 100±10℃ for 3-6 hours and calcine at 300±50℃ for 1-2 hours.

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