Diatomite supported molybdenum-copper catalyst and method for preparing benzenediol by catalyzing reaction of phenol and hydrogen peroxide by using diatomite supported molybdenum-copper catalyst

Abstract

The invention discloses a diatomite-loaded molybdenum-copper catalyst and a method for preparing benzenediol by catalyzing phenol and hydrogen peroxide to react by using the diatomite-loaded molybdenum-copper catalyst. The catalyst is prepared by the following steps: firstly, pretreating diatomite with hydrochloric acid under the assistance of microwaves so as to enhance the surface acidity and anchor loci of the diatomite; and then loading a mixed salt solution of ammonium molybdate and copper nitrate on the treated diatomite by adopting an equivalent-volume impregnation method, and carrying out aging, drying and high-temperature calcination to prepare the high-dispersion composite metal oxide catalyst. In a phenol hydroxylation reaction, hydrogen peroxide is used as a green oxidant, the catalyst can efficiently catalyze phenol conversion under mild conditions, and the yield and selectivity of benzenediol are remarkably improved. According to the invention, the synergistic effect of molybdenum-copper active components and the structural advantages of diatomite are fully utilized, the unification of low cost, high activity and good stability of the catalyst is realized, the catalyst is easy to separate and recover, and a technical path with application prospects is provided for green synthesis of benzenediol.

Description

Technical Field

[0001] This invention belongs to the field of hydroquinone synthesis technology, specifically relating to a diatomaceous earth-supported molybdenum-copper catalyst, and a method for preparing hydroquinone by catalyzing the reaction of phenol and hydrogen peroxide with the catalyst. Background Technology

[0002] Hydroquinone, mainly including catechol and hydroquinone, is an extremely important fine chemical raw material and intermediate. Catechol is widely used in pesticides, fragrances, pharmaceuticals (such as intermediates for anticancer drugs), and antioxidants; hydroquinone is an important photographic developer, polymer inhibitor, and dye intermediate. With the rapid development of downstream industries, the global demand for hydroquinone continues to grow, making the development of efficient and environmentally friendly hydroquinone synthesis processes of significant economic and social value.

[0003] Traditional processes for preparing hydroquinone all have significant limitations and environmental risks. Specifically: the cumene process, as a co-production process for phenol, is complex, energy-intensive, and causes significant environmental pollution. Furthermore, the ratio of ortho- and para-hydroxyquinone products in this process is fixed and difficult to adjust flexibly according to market demand. The aniline process involves numerous reaction steps, uses toxic substances as raw materials, and generates large amounts of iron sludge solid waste, placing a heavy burden on the environment. The hydrolysis of chlorophenol uses highly toxic chlorine gas as a raw material, causing severe equipment corrosion and posing significant safety and environmental hazards; it has been largely phased out. Clearly, each method has its advantages and disadvantages, making it difficult to simultaneously meet the demands of high efficiency and environmental protection.

[0004] CN119143582A discloses a method for preparing hydroquinone using TS molecular sieves. The method utilizes titanium-silicon molecular sieves to catalyze the oxidation of phenol to prepare hydroquinone and catechol, employing a specially structured reaction system to distribute and mix the raw materials phenol and hydrogen peroxide for the reaction. The reaction system used in this method includes a feeding vessel, multiple tubular reactors, a reaction vessel, a catalyst separator, and a distillation unit. When multiple sets of reaction devices are used, the system becomes even more complex. This complexity leads to high equipment investment and difficult maintenance. Furthermore, the preparation of TS molecular sieves requires the use of specific piperidine quaternary ammonium base ammonium hydroxide as a template agent. These template agents are complex to synthesize and expensive, increasing the catalyst production cost. CN116253619A discloses a method for preparing hydroquinone. The method involves ultrasonically dispersing titanium silicate molecular sieves, diatomaceous earth, and sodium silicate in deionized water to form a slurry. This slurry is then spray-granulated and calcined to obtain product A. Product A is added to a mixed acid solution, stirred, filtered, washed, vacuum dried, and calcined to obtain product B. Product B is then ultrasonically dispersed with copper, cerium, and chromium salts in deionized water, dried, and calcined to obtain a supported catalyst. While this method is technically advanced, it suffers from drawbacks such as complex catalyst preparation (e.g., spray granulation), harsh reaction conditions, high energy consumption, and environmental risks. In practical industrial applications, these factors need to be balanced, and the process optimized to reduce costs and improve stability. Chen Wei et al. (Chen Wei, Wang Shuo, Wu Zhaoji. Diatomaceous earth-supported iron-copper catalyst for the preparation of hydroquinone from phenol and hydrogen peroxide [J]. Journal of Tangshan Normal University, 2019, 41(06):6-8.) reacted treated diatomaceous earth with a 1:1 iron-copper precipitate to obtain a diatomaceous earth-supported Fe-Cu catalyst, which was then used to catalyze the preparation of hydroquinone from phenol and hydrogen peroxide. The hydroquinone yield of this method was low; even under optimal conditions, the highest yield was only 59.81%, with approximately 40% of the raw materials failing to convert into the target product or generating byproducts, indicating that there is still room for improvement in catalyst activity or selectivity. CN112194571A discloses a method for highly selectively preparing hydroquinone compounds by phenol oxidation. Under ambient temperatures up to 80°C, an oxidant hydrogen peroxide solution, a copper-containing catalyst, phenol, and a mixed solvent are mixed and reacted for a period of time under stirring to obtain a mixture of hydroquinones. While this method achieves highly selective preparation of catechols, it is limited by a complex solvent system—a mixture of water-soluble and non-water-soluble solvents—sensitive reaction conditions, and potential economic and operational issues. Further optimization is needed for practical industrial applications. Summary of the Invention

[0005] The purpose of this invention is to provide a copper-molybdenum composite metal oxide catalyst with natural diatomaceous earth as a support, and to apply it to the phenol hydroxylation reaction with hydrogen peroxide as a green oxidant, so as to improve the phenol conversion rate and hydroquinone selectivity.

[0006] To achieve the above objectives, the diatomaceous earth-supported molybdenum-copper catalyst provided by the present invention uses acidified diatomaceous earth as a carrier to support active components Mo and Cu. Based on the mass of the catalyst, the loading of Mo is 3% to 15% and the loading of Cu is 5% to 15%.

[0007] Furthermore, based on the mass of the catalyst, the preferred loading of Mo is 5% to 10% and the loading of Cu is 8% to 10%.

[0008] The diatomaceous earth-supported molybdenum-copper catalyst provided by this invention is prepared by the following steps:

[0009] Step 1: Add diatomaceous earth to 3-5 mol / L hydrochloric acid and soak it for 30-90 minutes under microwave assistance to obtain acidified diatomaceous earth.

[0010] Step 2: Add ammonium molybdate and copper nitrate to deionized water, heat and stir until the solids are completely dissolved to obtain a mixed salt solution.

[0011] Step 3: Under stirring conditions, add the mixed salt solution from Step 2 dropwise to the acidified diatomaceous earth, seal and let stand at room temperature for 36-48 hours, and then put it in an oven to dry.

[0012] Step 4: Calcine the dried solid powder at 400-600℃ in air for 3-6 hours to obtain a diatomaceous earth-supported molybdenum-copper catalyst.

[0013] Furthermore, in step 1 above, the preferred feeding ratio of diatomaceous earth to hydrochloric acid is 10-15g:10mL.

[0014] Furthermore, in step 1 above, it is preferable to immerse the sample for 45 to 90 minutes under microwave assistance with a power of 350 to 500W.

[0015] Furthermore, in step 4 above, it is preferable to calcine the dried solid powder at 500°C for 4 hours.

[0016] The present invention also provides the use of the above-mentioned diatomaceous earth-supported molybdenum-copper catalyst for catalyzing the reaction of phenol and hydrogen peroxide to prepare hydroquinone.

[0017] Furthermore, the present invention provides a method for preparing hydroquinone by reacting phenol and hydrogen peroxide. The method is as follows: phenol and the diatomaceous earth-supported molybdenum-copper catalyst are added to deionized water, heated to 60-90°C, and then hydrogen peroxide is added dropwise, and the reaction is carried out at a constant temperature for 1-2 hours.

[0018] In the above method for preparing hydroquinone by reacting phenol and hydrogen peroxide, the preferred mass ratio of phenol to diatomaceous earth-supported molybdenum-copper catalyst is 1:0.1 to 0.15.

[0019] The beneficial effects of this invention are as follows:

[0020] 1. This invention utilizes diatomaceous earth, a widely available and inexpensive material, as a support. Its large specific surface area, stable structure, and abundant porous structure facilitate the dispersion of active components and the mass transfer of reactants. Microwave-assisted acidification pretreatment effectively increases the acidity and anchoring sites on the support surface, laying the foundation for robust loading of the active components. Furthermore, an equal-volume impregnation method is used to co-load copper and molybdenum, two transition metals, onto the support in a specific manner, forming a composite metal oxide active center with a significant synergistic catalytic effect. This results in a catalyst that exhibits significantly superior catalytic activity and selectivity for the target product, hydroquinone, in the phenol hydroxylation reaction compared to traditional single-metal catalysts.

[0021] 2. The catalyst of this invention uses inexpensive and readily available raw materials, and its preparation process is mature and simple. The active component and the support are firmly bonded, resulting in a stable catalyst structure that is not easily lost or deactivated, and has a long lifespan. Furthermore, the catalyst is a solid powder, which can be easily recovered and reused after the reaction through simple filtration and washing, greatly reducing the cost of catalyst use and the difficulty and cost of product separation. The phenol hydroxylation reaction is carried out under mild conditions of low temperature and normal pressure, requiring minimal equipment, consuming little energy, and operating safely, thus possessing excellent potential for industrial scale-up. In addition, this invention completely eliminates the large amounts of strong acids and bases required by the traditional "sulfonation-alkali fusion method," instead using hydrogen peroxide as the oxidant. Its reaction byproduct is only water, eradicating serious waste pollution at the source, greatly reducing the environmental burden, and perfectly aligning with the principles of green chemistry.

[0022] 3. The entire process of this invention exhibits high atom economy and process efficiency. The conversion from phenol to hydroquinone is completed in one step, with a simple process and high energy utilization efficiency. By optimizing the catalyst composition and reaction conditions (such as controlling the hydrogen peroxide droplet acceleration), not only are side reactions such as excessive oxidation of phenol to quinones effectively suppressed, resulting in high selectivity for ortho / para-hydroxyquinones, but the utilization efficiency of hydrogen peroxide is also significantly improved, further reducing production costs. This provides a novel route for the synthesis of hydroquinone that combines technological advancement, economic feasibility, and environmental friendliness. Attached Figure Description

[0023] Figure 1 This is a scanning electron microscope image of the diatomaceous earth-supported molybdenum-copper catalyst prepared in Example 1, magnified 1000 times.

[0024] Figure 2 This is a scanning electron microscope image of the diatomaceous earth-supported molybdenum-copper catalyst prepared in Example 1, magnified 2500 times. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the scope of protection of the present invention is not limited to these embodiments.

[0026] Example 1

[0027] Step 1: Immerse 5g of diatomaceous earth in 4mL of 4mol / L hydrochloric acid for 60 minutes under microwave assisted power of 385W, filter, wash with water to obtain acidified diatomaceous earth.

[0028] Step 2: Add 0.263g of ammonium molybdate and 1.9g of copper nitrate to 20mL of deionized water, and stir at 70℃ until the solids are completely dissolved to obtain a mixed salt solution.

[0029] Step 3: Under stirring conditions, add the mixed salt solution from Step 2 dropwise to the acidified diatomaceous earth to ensure that the solution is evenly absorbed by the diatomaceous earth without obvious clumping or overly wet areas. Then, seal and let stand at room temperature for 40 hours, centrifuge, and deionize and wash until the pH of the supernatant is 7. Then, put it in an oven and dry at 90°C for 8 hours to completely remove physically adsorbed water.

[0030] Step 4: Grind the dried solid powder, place it in a muffle furnace, and calcine it to 500°C at a rate of 3°C / min under air atmosphere. Maintain this temperature for 4 hours, then grind again to obtain the diatomaceous earth-supported Mo-Cu catalyst. Based on the catalyst's mass of 100%, the Mo loading is 5% and the Cu loading is 8%.

[0031] Depend on Figure 1 , 2 It can be seen that Mo-Cu nanoparticles are uniformly and densely loaded on the surface of diatomaceous earth, and the diatomaceous earth structure is intact. From the center to the edge of the field of view, almost the entire visible surface of diatomaceous earth is covered with Mo-Cu nanoparticles, and no large blank areas or severe agglomerates were observed.

[0032] Example 2

[0033] In step 1 of this embodiment, 5g of diatomaceous earth was acid-impregnated in 4mL of 4mol / L hydrochloric acid for 30 minutes under microwave-assisted conditions at 385W. The mixture was then filtered and washed with water to obtain acidified diatomaceous earth. The other steps were the same as in Example 1, resulting in a diatomaceous earth-supported Mo-Cu catalyst.

[0034] Example 3

[0035] In step 2 of this embodiment, 0.538 g of ammonium molybdate and 1.90 g of copper nitrate were added to 20 mL of deionized water and stirred at 70 °C until the solids were completely dissolved to obtain a mixed salt solution. The other steps were the same as in Example 1, resulting in a diatomaceous earth-supported Mo-Cu catalyst. Based on the mass of the catalyst being 100%, the Mo loading in this catalyst was 10%, and the Cu loading was 8%.

[0036] Example 4

[0037] In step 4 of this embodiment, the dried solid powder is ground, placed in a muffle furnace, and heated to 600°C at a rate of 3°C / min under air atmosphere, and calcined at this temperature for 4 hours. The other steps are the same as in Example 1, resulting in a diatomaceous earth-supported Mo-Cu catalyst.

[0038] Comparative Example 1

[0039] The difference from Example 1 is that the diatomaceous earth is not subjected to the acidification treatment in step 1. In step 3, the mixed salt solution from step 2 is directly added dropwise to the un-acidified diatomaceous earth. The other steps are the same as in Example 1.

[0040] Comparative Example 2

[0041] The difference from Example 1 is that calcination is not performed in step 4; the dried solid powder is directly ground and used. The other steps are the same as in Example 1.

[0042] Application Example 1

[0043] The catalysts obtained in Examples 1-4 and Comparative Examples 1-2 were used to catalyze the preparation of hydroquinone from phenol. The specific method was as follows: 2g of phenol, 0.216g of catalyst, and 50mL of deionized water were added to a 250mL three-necked flask. After stirring and mixing at 60℃ for 30 minutes, 20mL of hydrogen peroxide was added dropwise to the flask through a constant-pressure dropping funnel. The temperature was raised to 70℃ or 90℃ and the reaction was stirred for 2 hours. After the reaction was complete, the mixture was cooled and filtered. The product was subjected to qualitative and quantitative analysis. The catalyst obtained after filtration was recycled according to this method. The reaction results are shown in Table 1.

[0044] Table 1. Reaction results of the catalysts used in Examples 1-4 and Comparative Examples 1-2 for the preparation of hydroquinone from phenol.

[0045]

[0046] Note: In the table, 'a' represents a reaction temperature of 70℃ and 'b' represents a reaction temperature of 90℃.

Claims

1. A diatomaceous earth-supported molybdenum-copper catalyst, characterized in that: The catalyst uses acidified diatomaceous earth as a support, loading active components Mo and Cu, with the Mo loading at 3%–15% and the Cu loading at 5%–15% based on 100% of the catalyst mass. The catalyst is prepared by the following steps: Step 1: Add diatomaceous earth to 3-5 mol / L hydrochloric acid and impregnate for 30-90 minutes under microwave assistance to obtain acidified diatomaceous earth; Step 2: Add ammonium molybdate and copper nitrate to deionized water, heat and stir until the solids are completely dissolved to obtain a mixed salt solution; Step 3: Under stirring conditions, add the mixed salt solution from Step 2 dropwise to the acidified diatomaceous earth, seal and let stand at room temperature for 36-48 hours, and then put it in an oven to dry. Step 4: Calcine the dried solid powder at 400-600℃ in air for 3-6 hours to obtain a diatomaceous earth-supported molybdenum-copper catalyst.

2. The diatomaceous earth-supported molybdenum-copper catalyst according to claim 1, characterized in that: Based on the mass of the catalyst being 100%, the loading of Mo is 5% to 10%, and the loading of Cu is 8% to 10%.

3. The diatomaceous earth-supported molybdenum-copper catalyst according to claim 1, characterized in that: In step 1, the ratio of diatomaceous earth to hydrochloric acid is 10-15g:10mL.

4. The diatomaceous earth-supported molybdenum-copper catalyst according to claim 1, characterized in that: In step 1, the sample is immersed for 45 to 90 minutes under microwave assistance with a power of 350 to 500W.

5. The diatomaceous earth-supported molybdenum-copper catalyst according to claim 1, characterized in that: In step 4, the dried solid powder is calcined at 500°C for 4 hours.

6. Use of the diatomaceous earth-supported molybdenum-copper catalyst according to any one of claims 1 to 5 for the catalytic reaction of phenol and hydrogen peroxide to prepare hydroquinone.

7. A method for preparing hydroquinone by reacting phenol and hydrogen peroxide, characterized in that: Phenol and the diatomaceous earth-supported molybdenum-copper catalyst as described in any one of claims 1 to 5 are added to deionized water, heated to 60 to 90°C, and then hydrogen peroxide is added dropwise. The reaction is carried out at a constant temperature for 1 to 2 hours.

8. The method for preparing hydroquinone by reacting phenol and hydrogen peroxide according to claim 7, characterized in that: The mass ratio of phenol to diatomaceous earth-supported molybdenum-copper catalyst is 1:0.1 to 0.15.

Images