Preparation method of composite catalyst for catalyzing polyol conversion

Abstract

The invention discloses a preparation method of a composite catalyst for catalyzing polyol conversion, which specifically comprises the following steps: soaking foam metal in a salt solution of second metal to be loaded, and loading the second metal component onto the foam metal by using a glow discharge plasma reduction method, a replacement method or an electrodeposition method; and cleaning and drying the reacted product to obtain the composite catalyst. According to the method, an efficient catalytic activity interface can be constructed on the surface of the foam metal, based on the synergistic effect of the two metal components, the polyol is quickly converted into a product with a high additional value under the reaction conditions of normal temperature and normal pressure, and the conversion rate of the polyol (glycerol and glucose) to a target product (such as 1, 2-propylene glycol) is remarkably increased. The conversion rate and the selectivity of 1, 3-propylene glycol, gluconic acid) are improved.

Description

Technical Field

[0001] The present invention relates to a preparation method of a composite catalyst for catalyzing the conversion of polyols. Background Art

[0002] With the increasing demand for the high-value utilization of biomass resources, the efficient conversion of biomass-based polyols (such as glycerol, furfural, 5-hydroxymethylfurfural, sorbitol, glucose, etc.) has become a research hotspot in the field of green chemistry. For the conversion of biomass-based polyols, traditional thermal catalytic methods and industrial routes are relatively mature, but they rely on noble metal catalysts (such as Pt, Ru), and need to react at high temperatures of 150-200 °C and high pressures of 5-10 MPa, with high energy consumption, demanding equipment requirements, and at the same time facing the risk of poor catalyst stability. Although the biological fermentation method has mild reaction conditions, it is limited by problems such as low key enzyme activity, low product concentration, and high separation and purification costs, resulting in a slow industrialization process. Although the photocatalytic method is green and environmentally friendly, it has problems such as slow reaction rate, low product concentration, and great industrialization difficulty. Based on the problems existing in the above traditional processes, using electrocatalytic technology to effectively convert biomass resources into high-value fine chemicals is one of the new energy treatment technologies for realizing sustainable green development. The electrocatalytic technology can selectively convert biomass-based polyols into a variety of high-value chemical products, such as gluconic acid, glucaric acid, 1,3-propanediol, etc., at normal temperature and pressure, and at the same time, the electrocatalytic energy conversion technology has the advantages of mild reaction conditions, environmental friendliness, and high energy utilization rate.

[0003] Existing catalysts for electrocatalytic polyol conversion include single-metal catalysts and multi-metal catalysts. The single-metal catalyst process is mature and does not require complex alloying steps; however, the surface adsorption energy of the single-metal catalyst is single, and it is difficult to optimize multiple-step reactions simultaneously. Currently, the preparation methods of multi-metal catalysts include hydrothermal method, coating method, sol-gel method, etc. The multi-metal catalyst prepared by the hydrothermal method is prone to disadvantages such as uneven loading and easy aggregation of metal particles. The multi-metal catalyst prepared by the coating method has the disadvantage that the active components are easy to fall off, resulting in low catalytic stability. The sol-gel method has disadvantages such as expensive precursors and difficult to accurately control the porosity. Summary of the Invention

[0004] Object of the Invention: The object of the present invention is to provide a preparation method of a composite catalyst for catalyzing the conversion of polyols. The composite catalyst prepared by this method can improve the loading amount of active components, as well as the loading uniformity and loading stability on the carrier, thereby effectively improving the catalytic activity and catalytic stability of the catalyst, and further greatly improving the conversion rate of polyols and the selectivity of target products.

[0005] Technical solution: The preparation method of the composite catalyst for catalyzing the conversion of polyols according to the present invention is specifically as follows: Immerse the porous metal in the salt solution of the second metal to be loaded, and use the glow discharge plasma reduction method, replacement method or electrodeposition method to load the second metal component onto the porous metal; wash and dry the reaction product to obtain the composite catalyst.

[0006] Among them, before the porous metal is immersed, it needs to be pretreated. The pretreatment process is as follows: Immerse the porous metal in a hydrochloric acid solution with a mass fraction of 37% for chemical etching (1-3 min), and then ultrasonically clean it in acetone, absolute ethanol and ultrapure water in sequence (5-15 min each) to remove the surface oxide, and then place it in a drying oven for storage for later use.

[0007] Among them, the porous metal is any one of porous nickel, porous zinc, porous copper, porous aluminum, porous silver, porous cobalt or porous titanium.

[0008] Among them, the second metal salt solution is at least one of HAuCl4 solution, PdCl2 solution, H2PtCl6 solution, RuCl3 solution, H2IrCl6 solution, AgNO3 solution, CuSO4 solution, ZnSO4 solution, CuCl2 solution, FeCl3 solution, Mn(NO3)2 solution, SnCl2 solution, Co(NO3)2 solution or Ni(NO3)2 solution.

[0009] Among them, in the second metal salt solution, the concentration of metal ions is 3 mM to 1.03 M.

[0010] Among them, when the glow discharge plasma reduction method is adopted, the impregnated porous metal is put into a glow discharge plasma reactor, and the reaction parameters are as follows: When the vacuum degree is below 80 Pa, turn on the plasma power supply for glow discharge plasma reduction; the treatment time is 2-2.5 min, the nitrogen flow rate is 150-160 SCCM, and the power is 150-155 W.

[0011] Under normal temperature and pressure, according to the metal activity series: K>Na>Ca>Mg>Al>Zn>Fe>Ni>Sn>Pb>(H)>Cu>Ag>Au. The metal at the front end (strong reducing agent) can displace the cation of the metal at the back end from its salt solution. For example, CuSO4 + Zn → ZnSO4 + Cu. When the metal activity of the second metal to be loaded is lower than the metal activity of the corresponding porous metal, the replacement method can be used to load the second metal on the porous metal, specifically: Immerse the porous metal in the precursor salt solution, and the replacement time is not less than 1 h.

[0012] Among them, when the electrodeposition method is adopted, a foam electrode is used as the working electrode, a platinum sheet electrode is used as the counter electrode, a saturated calomel electrode is used as the reference electrode, and a precursor salt solution is used as the electrolyte; reaction parameters: constant current method, the current value is set to -2 to -2.5 A, and the electrodeposition time is 2 to 3 min.

[0013] Among them, the vacuum drying temperature is 60 to 80 °C, and the drying time is 10 to 12 h.

[0014] Among them, the composite catalyst uses a foam metal as the carrier, and a second metal component is loaded on the carrier (the second metal component is loaded on the foam metal in the form of nanoparticles); the types of metal elements of the foam metal and the second metal component are different.

[0015] Among them, the loading amount of the second metal component on the carrier is 0.05% to 3.0% of the mass of the carrier.

[0016] The method of the present invention can make the surface of the foam metal have uniform pores, thereby effectively increasing the loading amount of the active component and the specific surface area of the catalyst, providing abundant active sites, ensuring the uniform distribution of the current, and further improving the conversion rate of polyols and the selectivity of the target product. At the same time, the multi-metal catalyst improves the catalytic activity and target product selectivity of the multi-metal catalyst through the electronic cooperation and geometric effects between multiple metals.

[0017] Application of the composite catalyst prepared by the above method in the electrocatalytic selective oxidation / reduction reaction of polyols. Using an aqueous polyol solution as the reaction solution, a three-electrode system is adopted; specifically: in the electrocatalytic selective reduction reaction of glycerol, the three-electrode system is: using the foam metal loaded with the second metal component as the working electrode, a carbon felt as the counter electrode, and Ag / AgCl as the reference electrode; in the electrocatalytic selective oxidation reaction of glucose, the three-electrode system is: using the foam metal loaded with the second metal component as the working electrode, Pt as the counter electrode, and Hg / HgO as the reference electrode; in the aqueous polyol solution (reaction solution), the concentration of glycerol or glucose is 0.01 mol / L to 0.25 mol / L.

[0018] Among them, the electrocatalytic selective oxidation of glucose is glucose acid; the electrocatalytic selective reduction of glycerol is 1,3-propanediol.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: The method of the present invention can construct an efficient catalytic active interface on the surface of the foam metal, and based on the synergistic effect of two metal components, quickly convert polyols into high-value-added products under the reaction conditions of normal temperature and normal pressure, and significantly improve the conversion rate and selectivity of polyols (glycerol, glucose) to the target product (such as 1,3-propanediol, glucose acid); at the same time, after continuous cycling more than 5 times, it still has high catalytic activity. Description of the Drawings

[0020] Figure 1 Scanning electron microscopy image of Au / Ni Foam (plasma reduction method) prepared in Example 1;

[0021] Figure 2 Transmission electron microscopy image of Au / Ni Foam (plasma reduction method) prepared in Example 1;

[0022] Figure 3 Scanning electron microscopy image of AuPd / Ni Foam (plasma reduction method) prepared in Example 3;

[0023] Figure 4 Scanning electron microscopy image of Cu / Zn Foam (displacement method) prepared in Example 5;

[0024] Figure 5 Schematic diagram of the device for electrocatalytic oxidation of glucose in Example 1, Example 2, Example 3 and Comparative Example 1; wherein, (a) is the working electrode; (b) is the counter electrode; (c) is the reference electrode;

[0025] Figure 6 Schematic diagram of the device for electrocatalytic reduction of glycerol in Example 4, Example 5, Example 6 and Comparative Example 2; wherein, (a) is the working electrode; (b) is the counter electrode; (c) is the reference electrode;

[0026] Figure 7 Scanning electron microscopy image of Ni Foam in Comparative Example 1;

[0027] Figure 8 Scanning electron microscopy image of Zn Foam in Comparative Example 2. Detailed implementation method

[0028] Example 1

[0029] The preparation method of the composite catalyst (Au / Ni Foam) for catalyzing the conversion of polyols in the present invention includes the following steps:

[0030] (1) Pretreat the nickel foam. The pretreatment process is as follows: Immerse the nickel foam in a hydrochloric acid solution with a mass fraction of 37% for chemical etching (1 - 3 min), then ultrasonically clean it in acetone, absolute ethanol and ultrapure water successively (5 - 15 min each) to remove the surface oxides, and then place it in a drying oven for storage for later use;

[0031] (2) Add 0.0603 g of HAuCl4 to 1 mL of ultrapure water according to the theoretical Au loading of 0.05 wt.%, and stir magnetically until a homogeneous phase is formed to obtain the precursor salt solution;

[0032] (3) Immerse the pretreated nickel foam (57 mg) in the precursor salt solution of step (2), evenly immerse the front and back sides of the nickel foam with the precursor salt solution. After immersion, hold it with tweezers, dry it with a hair dryer and then spray it with water mist. Then place it on a watch glass and put it into a glow discharge plasma reactor. Click the lower pump to open and the nitrogen valve to open in sequence; set the experimental parameters: the treatment time is 2 min, the nitrogen flow rate is 150 SCCM, and the power is 150 W; when the vacuum degree is below 80 Pa, turn on the plasma power supply for glow discharge plasma reduction; rinse the reacted foam metal with ultrapure water for multiple times. After removing the residual precursor salt, place it in a vacuum drying oven and dry it at 60 °C for 10 h. The obtained composite catalyst is denoted as Au / Ni Foam (plasma reduction method).

[0033] Calculation method of the theoretical Au loading: First, weigh the mass of the nickel foam (57 mg), then 0.0603 g * 0.477 (the ratio of Au in HAuCl4) / the mass of nickel foam 57 mg = 0.05%.

[0034] Apply the composite catalyst Au / Ni Foam prepared in Example 1 to the electrocatalytic selective oxidation process of glucose. The electrochemical measurement is carried out on an electrochemical workstation (Auto Lab), using a three-electrode system. The composite catalyst Au / Ni Foam prepared in Example 1 is used as the working electrode, a Pt sheet is used as the counter electrode, and a Hg / HgO electrode is used as the reference electrode; the reaction conditions are at room temperature of 25 °C and normal pressure of 101 kPa. The reaction solution is an aqueous solution containing 0.01 mol / L glucose and 0.1 mol / L K2CO3. The reaction time is 12 h, and the rotation speed of the magnetic stirrer is 500 r / min; the liquid-phase products are detected by HPLC, and a differential refractive index detector (RID-10A) is used to detect the separated compounds. The glucose conversion rate measured by liquid chromatography is 75.8%, and the glucose monoacid selectivity is 87.3%.

[0035] Figure 1 Figure for the scanning electron microscope of Au / Ni Foam (plasma reduction method) loaded with the second metal component in Example 1. From Figure 1 it can be found that after loading the second metal component, Au / Ni Foam shows a uniform porous flake structure, enabling the catalyst to have a large specific surface area and thus abundant active sites.

[0036] Figure 2TEM image of Au / Ni Foam (plasma reduction method) prepared in Example 1. Through high-magnification TEM images, it can be seen that gold is highly dispersed on the surface of nickel foam in the form of nanoparticles, with a high density of active sites, thus significantly improving the performance of electrocatalytic selective oxidation of glucose. After the combination of nickel foam and the second metal component Au, the selectivity of glucose monoacid reaches 87.3%. The synergistic system of carrier electron regulation and metal active site optimization promotes the directional adsorption of glucose C1-OH, leading to a significant increase in the conversion rate of the directional conversion of glucose molecules.

[0037] The composite catalyst Au / Ni Foam prepared in Example 1 was applied to the electrocatalytic selective oxidation process of glucose and continuously cycled five times. Each time, a 12-hour experiment was carried out in the above manner. After the first cycle, the glucose conversion rate was 75.8% and the selectivity of glucose monoacid was 87.3%; after the second cycle, the glucose conversion rate was 75.0% and the selectivity of glucose monoacid was 85.0%; after the third cycle, the glucose conversion rate was 73.5% and the selectivity of glucose monoacid was 83.6%; after the fourth cycle, the glucose conversion rate was 72.8% and the selectivity of glucose monoacid was 81.4%; after the fifth cycle, the glucose conversion rate was 70.9% and the selectivity of glucose monoacid was 80.1%.

[0038] Example 2

[0039] The preparation method of the composite catalyst (Au / Ti Foam) for catalyzing the conversion of polyols in the present invention includes the following steps:

[0040] (1) Pretreat the titanium foam. The pretreatment process is as follows: Immerse the titanium foam in a hydrochloric acid solution with a mass fraction of 37% for chemical etching (1 - 3 min), and then ultrasonically clean it in acetone, absolute ethanol, and ultrapure water (5 - 15 min each) to remove surface oxides, and then place it in a drying oven for storage for later use;

[0041] (2) Add 0.35 g of HAuCl4 to 1 mL of ultrapure water according to the theoretical Au loading of 0.05 wt.%, and stir magnetically until a homogeneous phase is formed to obtain a precursor salt solution;

[0042] (3) Immerse the pretreated titanium foam (334 mg) in the precursor salt solution of step (2). The precursor salt solution is evenly impregnated on the front and back sides of the titanium foam. After drying with a hair dryer, spray water mist (hold it with tweezers and dry it after impregnation), then place it on a watch glass and put it into a glow discharge plasma reactor. Click the lower pump to open and the nitrogen valve to open in sequence; set the experimental parameters: the treatment time is 2 min, the nitrogen flow rate is 150 SCCM, and the power is 150 W; when the vacuum degree is below 80 Pa, turn on the plasma power supply for glow discharge plasma reduction; rinse the reacted foam metal with ultrapure water multiple times. After removing the residual precursor salt, place it in a vacuum drying oven and dry it at 65 °C for 10 h. The obtained composite catalyst is denoted as Au / TiFoam (plasma reduction method).

[0043] Calculation method of the theoretical Au loading: First, weigh the mass of the titanium foam (334 mg), then 0.35 g * 0.477 (ratio of Au in HAuCl4) / mass of titanium foam 334 mg = 0.05%.

[0044] Apply the composite catalyst Au / Ti Foam prepared in Example 2 to the electrocatalytic selective oxidation process of glucose. The electrochemical measurement is carried out on an electrochemical workstation (Auto Lab). A three-electrode system is adopted. The composite catalyst Au / Ti Foam prepared in Example 2 is used as the working electrode, a Pt sheet is used as the counter electrode, and a Hg / HgO electrode is used as the reference electrode; the reaction conditions are at room temperature of 25 °C and normal pressure of 101 kPa. The reaction solution is an aqueous solution containing 0.01 mol / L glucose and 0.1 mol / L K2CO3. The reaction time is 12 h, and the rotation speed of the magnetic stirrer is 500 r / min; the liquid-phase products are detected by HPLC, and a refractive index detector (RID-10A) is used to detect the separated compounds. The glucose conversion rate is measured to be 51.7% and the glucose acid selectivity is 67.8% by liquid chromatography.

[0045] Example 3

[0046] The preparation method of the composite catalyst (AuPd / Ni Foam) for catalyzing the conversion of polyols in the present invention includes the following steps:

[0047] (1) Pretreat the nickel foam. The pretreatment process is as follows: Immerse the nickel foam in a hydrochloric acid solution with a mass fraction of 37% for chemical etching (1 - 3 min), then ultrasonically clean it in acetone, absolute ethanol, and ultrapure water in sequence (5 - 15 min each) to remove the surface oxides, and then place it in a drying oven for storage and standby;

[0048] (2) According to the theoretical loading of Au being 0.025 wt.% and the theoretical loading of Pd being 0.025 wt.%, 0.03 g of HAuCl4 and 0.024 g of PdCl2 were added to 1 mL of ultrapure water, and after magnetic stirring until a homogeneous phase was formed, a precursor salt solution was obtained;

[0049] (3) The pretreated nickel foam (57 mg) in step (1) was immersed in the precursor salt solution in step (2). The precursor salt solution was evenly impregnated on the front and back sides of the nickel foam. After drying with a hair dryer and spraying with water mist (holding it with tweezers and drying after impregnation), it was placed on a watch glass and put into a glow discharge plasma reactor. Then, click to turn on the lower pump and the nitrogen valve in sequence; set the experimental parameters: the treatment time is 2 min, the nitrogen flow rate is 150 SCCM, and the power is 150 W; when the vacuum degree is below 80 Pa, turn on the plasma power supply for glow discharge plasma reduction; the reacted foam metal was rinsed with ultrapure water multiple times, and after removing the residual precursor salt, it was placed in a vacuum drying oven and dried at 60 °C for 10 h. The obtained composite catalyst was denoted as AuPd / NiFoam (plasma reduction method).

[0050] Calculation method for the theoretical loading of Au: 0.03 g * 0.477 (ratio of Au in HAuCl4) / mass of nickel foam 57 mg = 0.025%; Calculation method for the theoretical loading of Pd: 0.024 g * 0.6 (ratio of Pd in PdCl2) * 0.99 (drug purity) / mass of nickel foam 57 mg = 0.025%.

[0051] The composite catalyst AuPd / Ni Foam prepared in Example 3 was applied to the electrocatalytic selective oxidation process of glucose. Electrochemical measurements were carried out on an electrochemical workstation (Auto Lab). A three-electrode system was used, with the composite catalyst AuPd / Ni Foam prepared in Example 3 as the working electrode, a Pt sheet as the counter electrode, and a Hg / HgO electrode as the reference electrode; the reaction conditions were at room temperature of 25 °C and normal pressure of 101 kPa. The reaction solution was an aqueous solution containing 0.01 mol / L glucose and 0.1 mol / L K2CO3, the reaction time was 12 h, and the rotation speed of the magnetic stirrer was 500 r / min; the liquid-phase products were detected by HPLC, and a differential refractive index detector (RID-10A) was used to detect the separated compounds. The glucose conversion rate was measured to be 48.0% by liquid chromatography, the selectivity for gluconic acid was 62.6%, and the selectivity for glucaric acid was 6.3%.

[0052] Figure 3 SEM image of AuPd / Ni Foam (plasma reduction method) loaded with the second metal component for Example 3. From Figure 3It can be found that after loading the second metal component, the nickel foam presents a dense porous flake structure, forming a three-dimensional through porous network. This structure significantly increases the specific surface area, providing rich diffusion channels and active sites for glucose. Compared with Example 1, in Example 3, a more valuable glucaric acid is obtained. The strong oxidizing property of Pd causes the intermediate products (such as gluconic acid) to be further oxidized to glucaric acid, enhancing the tendency of C-C bond cleavage.

[0053] Example 4

[0054] The preparation method of the composite catalyst (Cu / Zn Foam) for catalyzing the conversion of polyols in the present invention includes the following steps:

[0055] (1) Pretreat the zinc foam. The pretreatment process is as follows: Immerse the zinc foam in a hydrochloric acid solution with a mass fraction of 37% for chemical etching (1 - 3 min), then ultrasonically clean it in acetone, absolute ethanol, and ultrapure water successively (each for 5 - 15 min) to remove the surface oxides, and then place it in a drying oven for storage for later use;

[0056] (2) According to the theoretical loading amount of Cu being 0.5 wt.%, add 2.4 mg of CuCl2 to 1 mL of ultrapure water, and stir magnetically until a homogeneous phase is formed to obtain a precursor salt solution;

[0057] (3) Immerse the pretreated zinc foam (220 mg) in the precursor salt solution in step (2), uniformly impregnate the front and back sides of the nickel foam with the precursor salt solution, blow it dry with a hair dryer and then spray it with water mist (hold it with tweezers and blow it dry after impregnation), and then place it on a watch glass and put it into a glow discharge plasma reactor. Click the lower pump to open and the nitrogen valve to open in sequence; Set the experimental parameters: the treatment time is 2 min, the nitrogen flow rate is 150 SCCM, and the power is 150 W; When the vacuum degree is below 80 Pa, turn on the plasma power supply for glow discharge plasma reduction; Rinse the reacted foam metal with ultrapure water multiple times, remove the residual precursor salt, and then place it in a vacuum drying oven and dry it at 70 °C for 12 h. The obtained composite catalyst is denoted as Cu / ZnFoam (plasma reduction method).

[0058] Calculation method of the theoretical loading amount of Cu: 2.4 mg * 0.472 (the ratio of Cu in CuCl2) * 0.98 (drug purity) / the mass of zinc foam 220 mg = 0.5%.

[0059] The composite catalyst Cu / Zn Foam prepared in Example 4 was applied to the electrocatalytic selective reduction of glycerol. The electrochemical measurement was carried out on an electrochemical workstation (CHI 660E). A three-electrode system was used, with the composite catalyst Cu / Zn Foam prepared in Example 4 as the working electrode, a carbon felt as the counter electrode, and a silver-silver chloride electrode as the reference electrode. The reaction conditions were at room temperature of 25 °C and atmospheric pressure of 101 kPa. The reaction solution was an aqueous solution containing 0.25 mol / L glycerol and 0.5 mol / L potassium chloride (the pH of the reaction solution was adjusted to about 1 with hydrochloric acid). The reaction time was 12 h, and the rotation speed of the magnetic stirrer was 500 r / min. The liquid-phase products were detected by HPLC, and the separated compounds were detected with a refractive index detector (RID-10A) and a UV-visible photodetector at 210 nm (SPD-20A). The glycerol conversion was measured to be 53.5% and the selectivity for 1,3-propanediol was 27.4% by liquid chromatography.

[0060] Example 5

[0061] The preparation method of the composite catalyst (Cu / Zn Foam) for catalyzing the conversion of polyols in the present invention includes the following steps:

[0062] (1) Pretreat the zinc foam. The pretreatment process is as follows: Immerse the zinc foam in a hydrochloric acid solution with a mass fraction of 37% for chemical etching (1 - 3 min), then ultrasonically clean it in acetone, absolute ethanol, and ultrapure water in sequence (each for 5 - 15 min) to remove the surface oxides, and then place it in a drying oven for storage for later use;

[0063] (2) According to the theoretical Cu loading of 3.0 wt.%, add 17 mg of copper sulfate to 1 mL of ultrapure water, and stir magnetically until a homogeneous phase is formed to obtain a precursor salt solution;

[0064] (3) Immerse the pretreated zinc foam (220 mg) in the precursor salt solution in step (2) for a displacement reaction. The displacement time is 1 h. After the reaction, rinse it with deionized water multiple times to remove the precursor residues, and the obtained composite catalyst is denoted as Cu / Zn Foam (displacement method), and place it in a vacuum drying oven for later use.

[0065] Calculation method of the theoretical Cu loading: 17 mg * 0.398158 (the proportion of Cu in CuSO4) * 0.98 (drug purity) / the mass of zinc foam is 220 mg = 3.0%.

[0066] The composite catalyst Cu / Zn Foam prepared in Example 5 was applied to the electrocatalytic selective reduction of glycerol. Electrochemical measurements were carried out on an electrochemical workstation (CHI 660E) using a three-electrode system. The composite catalyst Cu / Zn Foam prepared in Example 5 was used as the working electrode, a carbon felt as the counter electrode, and a silver-silver chloride electrode as the reference electrode. The reaction conditions were at room temperature of 25 °C and atmospheric pressure of 101 kPa. The reaction solution was an aqueous solution containing 0.25 mol / L glycerol and 0.5 mol / L potassium chloride (the pH of the reaction solution was adjusted to about 1 with hydrochloric acid). The reaction time was 12 h, and the rotational speed of the magnetic stirrer was 500 r / min. The liquid-phase products were detected by HPLC, and the separated compounds were detected using a refractive index detector (RID-10A) and a UV-visible photodetector (SPD-20A) at 210 nm. The glycerol conversion rate was measured to be 56.6% and the selectivity for 1,3-propanediol was 28.1% by liquid chromatography.

[0067] Figure 4 Figure 4 is a scanning electron microscope image of the Cu / Zn Foam (replacement method) electrode loaded with the second metal component in Example 5. Figure 4 It can be found from the figure that after loading the second metal component, the zinc foam is distributed with densely arranged nanospheres, and each spherical particle presents a flower-like structure, providing abundant active sites, thus significantly improving the performance of electrocatalytic selective reduction of glycerol.

[0068] The composite catalyst Cu / Zn Foam prepared in Example 5 was applied to the electrocatalytic selective reduction of glycerol and continuously cycled five times. Each time, a 12-h experiment was carried out in the above manner. The glycerol conversion rate after the first cycle was 56.6% and the selectivity for 1,3-propanediol was 28.1%; the glycerol conversion rate after the second cycle was 56.5% and the selectivity for 1,3-propanediol was 28.0%; the glycerol conversion rate after the third cycle was 56.2% and the selectivity for 1,3-propanediol was 27.7%; the glycerol conversion rate after the fourth cycle was 55.8% and the selectivity for 1,3-propanediol was 27.4%; the glycerol conversion rate after the fifth cycle was 55.5% and the selectivity for 1,3-propanediol was 26.9%.

[0069] The composite catalyst Cu / Zn Foam prepared in Example 5 was applied to the electrocatalytic selective reduction of glycerol. A 24-h experiment was carried out in the above manner, and the measured glycerol conversion rate was 67.6% and the selectivity for 1,3-propanediol was 30.3%.

[0070] The composite catalyst Cu / Zn Foam prepared in the present invention has good stability.

[0071] The glycerol conversion rate in Example 5 (56.6%) is higher than that in Example 4 (53.5%), indicating that a higher Cu loading provides more active sites. The selectivity of 1,3-propanediol in Example 5 (28.1%) is higher than that in Example 4 (27.4%), which is related to the promotion of C-O bond hydrogenation by high-loading Cu.

[0072] Example 6

[0073] The preparation method of the composite catalyst (Zn / Cu Foam) for catalyzing polyol conversion in the present invention includes the following steps:

[0074] (1) Pretreat the copper foam. The pretreatment process is as follows: Immerse the copper foam in a hydrochloric acid solution with a mass fraction of 37% for chemical etching (1 - 3 min), then ultrasonically clean it in acetone, absolute ethanol, and ultrapure water successively (5 - 15 min each) to remove surface oxides, and then place it in a drying oven for storage and standby;

[0075] (2) According to the theoretical Zn loading of 3.0 wt.%, add 28 mg of ZnSO4·7H2O and 2.11 mL of H2SO4 with a concentration of 1.5 M to 25 mL of ultrapure water, and stir magnetically until a homogeneous phase is formed to obtain a precursor salt solution;

[0076] (3) Perform constant current deposition on the copper foam (200 mg) pretreated in step (1). Use the copper foam as the working electrode, a platinum plate electrode as the counter electrode, and a saturated calomel electrode as the reference electrode. Use the precursor salt solution in step (2) as the electrolyte (reaction solution); Set the experimental parameters: the current value is set to -2 A, and the electrodeposition time is 2 min; After the electrodeposition is completed, wash it with deionized water multiple times to remove the precursor residue. The obtained composite catalyst is denoted as Zn / Cu Foam (electrodeposition method) and placed in a vacuum drying oven for standby.

[0077] Calculation method of the theoretical Zn loading: 28 mg * 0.22 (the proportion of Zn in ZnSO4·7H2O) * 0.99 (drug purity) / the mass of copper foam is 200 mg = 3.0%.

[0078] The composite catalyst Zn / Cu Foam prepared in Example 6 was applied to the electrocatalytic selective reduction of glycerol. Electrochemical measurements were carried out on an electrochemical workstation (CHI 660E) using a three-electrode system. The composite catalyst Zn / Cu Foam prepared in Example 6 was used as the working electrode, a carbon felt as the counter electrode, and a silver-silver chloride electrode as the reference electrode. The reaction conditions were at room temperature of 25 °C and atmospheric pressure of 101 kPa. The reaction solution was an aqueous solution containing 0.25 mol / L glycerol and 0.5 mol / L potassium chloride (the pH of the reaction solution was adjusted to about 1 by hydrochloric acid). The reaction time was 12 h, and the rotation speed of the magnetic stirrer was 500 r / min. The liquid-phase products were detected by HPLC, and the separated compounds were detected using a refractive index detector (RID-10A) and a UV-visible photodetector at 210 nm (SPD-20A). The glycerol conversion rate was measured to be 50.0% and the selectivity for 1,3-propanediol was 31.4% by liquid chromatography.

[0079] Comparative Example 1

[0080] The foam metal electrode used in Comparative Example 1 was a pretreated Ni Foam electrode without loading a second metal component. The specific treatment process was as follows: The nickel foam was immersed in a hydrochloric acid solution with a mass fraction of 37% for chemical etching (1 - 3 min), and then ultrasonically cleaned in acetone, absolute ethanol, and ultrapure water in turn (5 - 15 min each) to remove surface oxides, and then stored in a drying oven for standby.

[0081] The Ni Foam in Comparative Example 1 was applied to the electrocatalytic selective oxidation of glucose. Electrochemical measurements were carried out on an electrochemical workstation (Auto Lab) using a three-electrode system. Ni Foam was used as the working electrode, a Pt sheet as the counter electrode, and a Hg / HgO electrode as the reference electrode. The reaction conditions were at room temperature of 25 °C and atmospheric pressure of 101 kPa. The reaction solution was an aqueous solution containing 0.01 mol / L glucose and 0.1 mol / L K2CO3. The reaction time was 12 h, and the rotation speed of the magnetic stirrer was 500 r / min. The liquid-phase products were detected by HPLC, and the separated compounds were detected using a refractive index detector (RID-10A). The glucose conversion rate was measured to be 30.0% and the selectivity for gluconic acid was 42.2% by liquid chromatography.

[0082] Comparing Comparative Example 1 with Example 1, after loading the second metal component Au, the conversion rate of glucose and the selectivity for gluconic acid can be significantly improved. Figure 7 Figure for the scanning electron microscope of Ni Foam in Comparative Example 1. The morphology of the nickel foam itself presents an uneven porous flake structure, which will reduce the effective active sites and lead to insufficient contact area between the reactant glucose. Figure 1Comparing the SEM images of the Au / Ni Foam prepared in Example 1, the structure of the nickel foam was optimized after loading Au, presenting a uniform and regular porous flake structure, with a flattened surface and an increased specific surface area, providing abundant active sites for glucose oxidation. Therefore, after loading the second metal component, both the glucose conversion rate and the selectivity of gluconic acid were significantly improved.

[0083] Comparative Example 2

[0084] The foam metal electrode used in Comparative Example 2 was the pretreated Zn Foam electrode without loading the second metal component. The specific treatment process was as follows: The zinc foam was immersed in a hydrochloric acid solution with a mass fraction of 37% for chemical etching (1 - 3 min), and then successively ultrasonically cleaned in acetone, absolute ethanol, and ultrapure water (5 - 15 min each) to remove surface oxides, and stored in a drying oven for standby.

[0085] The Zn Foam in Comparative Example 2 was applied to the electrocatalytic selective reduction of glycerol. The electrochemical measurement was carried out on an electrochemical workstation (CHI 660E) using a three - electrode system, with the Zn Foam as the working electrode, the carbon felt as the counter electrode, and the silver - silver chloride electrode as the reference electrode; the reaction conditions were at room temperature of 25 °C and atmospheric pressure of 101 kPa. The reaction solution was an aqueous solution containing 0.25 mol / L glycerol and 0.5 mol / L potassium chloride (the pH of the reaction solution was adjusted to about 1 with hydrochloric acid), the reaction time was 12 h, and the rotation speed of the magnetic stirrer was 500 r / min. The liquid - phase products were detected by HPLC, and the separated compounds were detected with a refractive index detector (RID - 10A) and a UV - visible photodetector (SPD - 20A) at 210 nm. The glycerol conversion rate measured by liquid chromatography was 24.1%, and the selectivity of 1,3 - propanediol was 10.5%.

[0086] Comparing Comparative Example 2 with Example 5, after loading the second metal component Cu, the conversion rate of glycerol and the selectivity of 1,3 - propanediol can be significantly improved.

[0087] Figure 8 SEM image of the Zn Foam in Comparative Example 2. The surface of the Zn foam substrate without loading the second component has smooth and uniform pores, with an average pore diameter of about 100 μm, presenting a typical three - dimensional porous structure. Comparing with Figure 4 the SEM image of the Cu / Zn Foam (replacement method) prepared in Example 5, Figure 4 dense Cu particles are distributed on the pore wall surface of the Zn foam in , and the deposition of copper provides abundant sites for glycerol catalysis.

[0088] Comparative Example 3

[0089] Preparation method of composite catalyst (Cu / Zn Foam) for catalyzing polyol conversion, comprising the following steps:

[0090] (1) Pretreat the zinc foam. The pretreatment process is as follows: Immerse the zinc foam in a hydrochloric acid solution with a mass fraction of 37% for chemical etching (1 - 3 min), then ultrasonically clean it in acetone, absolute ethanol, and ultrapure water successively (5 - 15 min each) to remove surface oxides, and then place it in a drying oven for storage and standby;

[0091] (2) Weigh 20.2 mg of Cu / CNT according to the theoretical Cu loading of 3.0 wt.%, place it in a centrifuge tube, add 1 mL of a 2% volume fraction of naphthol solution, ultrasonicate for 15 min, and evenly drip - coat it on the front and back of the zinc foam (220 mg) in small amounts with a pipette several times, then put it in an oven at 40 °C to dry for standby; The obtained composite catalyst is denoted as Cu / Zn Foam (coating method).

[0092] Calculation method of theoretical Cu loading: 20.2 mg * 0.333 (proportion of Cu in Cu / CNT) / mass of zinc foam 220 mg = 3.0%.

[0093] Apply the composite catalyst Cu / Zn Foam prepared in Comparative Example 3 to the electrocatalytic selective reduction process of glycerol. Electrochemical measurements are carried out on an electrochemical workstation (CHI 660E). A three - electrode system is adopted, using the composite catalyst Zn / Cu Foam prepared in Example 6 as the working electrode, a carbon felt as the counter electrode, and a silver - silver chloride electrode as the reference electrode; The reaction conditions are at room temperature of 25 °C and normal pressure of 101 kPa. The reaction solution is an aqueous solution containing 0.25 mol / L glycerol and 0.5 mol / L potassium chloride (the pH of the reaction solution is adjusted to about 1 by hydrochloric acid), the reaction time is 12 h, and the rotation speed of the magnetic stirrer is 500 r / min. The liquid - phase products are detected by HPLC, and the separated compounds are detected by a refractive index detector (RID - 10A) and a 210 nm ultraviolet - visible photodetector (SPD - 20A). The glycerol conversion rate measured by liquid chromatography is 35.7%, and the selectivity for 1,3 - propanediol is 11.4%.

[0094] The composite catalyst Cu / Zn Foam prepared in Comparative Example 3 was applied to the electrocatalytic selective reduction of glycerol. The experiment was carried out continuously for five cycles, and each cycle was carried out for 12 h in the above-mentioned manner. After one cycle, the glycerol conversion rate was 35.7%, and the selectivity for 1,3-propanediol was 11.4%; after two cycles, the glycerol conversion rate was 32.4%, and the selectivity for 1,3-propanediol was 10.0%; after three cycles, the glycerol conversion rate was 25.8%, and the selectivity for 1,3-propanediol was 7.2%; after four cycles, the glycerol conversion rate was 20.7%, and the selectivity for 1,3-propanediol was 5.4%; after five cycles, the glycerol conversion rate was 15.3%, and the selectivity for 1,3-propanediol was 3.2%.

[0095] The composite catalyst Cu / Zn Foam prepared in Comparative Example 3 was applied to the electrocatalytic selective reduction of glycerol. The experiment was carried out for 24 h in the above-mentioned manner, and the glycerol conversion rate was measured to be 40.3%, and the selectivity for 1,3-propanediol was 10.8%.

[0096] Comparing Comparative Example 3 with Example 5, it can be seen that the catalytic activity and catalytic stability of the composite catalyst prepared by the coating method are both lower than those of the composite catalyst prepared in the present invention. During the experiment, it was found that the problem of shedding of the second metal component copper loaded occurred, resulting in a rapid and significant decrease in the glycerol conversion rate.

Claims

1. A preparation method of a composite catalyst for catalyzing the conversion of polyols, characterized in that, Specifically: Immerse the porous metal in the salt solution of the second metal to be loaded, and use the glow discharge plasma reduction method, displacement method or electrodeposition method to load the second metal component onto the porous metal; clean and dry the reaction product to obtain the composite catalyst.

2. The preparation method of the composite catalyst according to claim 1, characterized in that: Before immersion, the porous metal needs to be pretreated. The pretreatment process is as follows: Immerse the porous metal in hydrochloric acid solution for chemical etching, and then ultrasonically clean it in acetone, absolute ethanol and ultrapure water in sequence to remove surface oxides.

3. The preparation method of the composite catalyst according to claim 1, characterized in that: The porous metal is any one of porous nickel, porous zinc, porous copper, porous aluminum, porous silver, porous cobalt or porous titanium.

4. The preparation method of the composite catalyst according to claim 1, characterized in that: The second metal salt solution is at least one of HAuCl4 solution, PdCl2 solution, H2PtCl6 solution, RuCl3 solution, H2IrCl6 solution, AgNO3 solution, CuSO4 solution, ZnSO4 solution, CuCl2 solution, FeCl3 solution, Mn(NO3)2 solution, SnCl2 solution, Co(NO3)2 solution or Ni(NO3)2 solution.

5. The preparation method of the composite catalyst according to claim 4, characterized in that: In the second metal salt solution, the concentration of metal ions is 3 mM to 1.03 M.

6. The preparation method of the composite catalyst according to claim 1, characterized in that: When using the glow discharge plasma reduction method, put the immersed porous metal into a glow discharge plasma reactor. The reaction parameters are as follows: Turn on the plasma power supply for glow discharge plasma reduction when the vacuum degree is below 80 Pa; the treatment time is 2 to 2.5 min, the nitrogen flow rate is 150 to 160 SCCM, and the power is 150 to 155 W.

7. The preparation method of the composite catalyst according to claim 1, wherein: When the metal activity of the second metal to be loaded is lower than that of the corresponding porous metal, the displacement method can be used to load the second metal onto the porous metal. Specifically: Immerse the porous metal in the precursor salt solution, and the displacement time is not less than 1 h.

8. The preparation method of the composite catalyst according to claim 1, characterized in that: When using the electrodeposition method, use the porous electrode as the working electrode, the platinum sheet electrode as the counter electrode, and the saturated calomel electrode as the reference electrode, and use the precursor salt solution as the electrolyte; The reaction parameters are as follows: constant current method, the current value is set to -2 to -2.5 A, and the electrodeposition time is 2 to 3 min.

9. The preparation method of the composite catalyst according to claim 1, characterized in that: The vacuum drying temperature is 60 to 80 °C, and the drying time is 10 to 12 h.

10. The preparation method of the composite catalyst according to claim 1, characterized in that: The composite catalyst uses the porous metal as the carrier, and the second metal component is loaded on the carrier; the loading amount of the second metal component on the carrier is 0.05 wt.% to 3.0 wt.%.

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