A microorganism-sodium alginate-based porous composite palladium-carbon catalyst and its preparation method

Abstract

The invention discloses a microorganism-sodium alginate-based porous composite palladium-carbon catalyst and a preparation method thereof, and belongs to the technical field of fuel cells. A solution containing calcium ions is added to a mixed solution containing sodium alginate, calcium carbonate and microorganisms for cross-linking reaction to form composite gel microspheres; the composite gel microspheres are placed in an acidic solution for leaching to obtain porous composite gel microspheres; after the porous composite gel microspheres are placed in water, a palladium source is added for adsorption; palladium-loaded composite gel microspheres are obtained; the palladium-loaded composite gel microspheres are freeze-dried, carbonized and reduced and roasted in sequence to obtain a microorganism-sodium alginate-based porous composite palladium-carbon catalyst having a porous structure, good stability, and a high and uniform nano-palladium loading, showing high catalytic activity, which can be applied to fuel cells.

Description

Technical Field

[0001] The present invention relates to an electrocatalytic material, in particular to a microorganism-sodium alginate-based porous composite palladium-carbon catalyst, and also relates to a preparation method thereof, belonging to the technical field of fuel cells. Background Art

[0002] With the increasing reduction of fossil energy and the worldwide energy crisis, it is urgent to develop new, efficient, widely applicable and environmentally friendly power devices. The Proton Exchange Membrane Fuel Cell (PEMFC) has the advantages of environmental friendliness, high energy density and high energy conversion rate, meeting the future requirements for energy. Therefore, it is one of the most promising future batteries. However, due to the high cost of catalysts, the complex bipolar plate process and the high manufacturing cost of the diffusion layer, the commercialization and practical application of the proton exchange membrane fuel cell have progressed slowly.

[0003] As one of the important component structures of PEMFC, the catalyst catalyzes the formation of protons from hydrogen at the anode and the reduction of oxygen at the cathode to generate oxygen ions, and the combination of oxygen ions and hydrogen protons to form water can generate energy. The noble metals platinum (Pt) and palladium (Pd) are currently relatively common and ideal catalyst materials, but their global reserves are limited. Therefore, developing catalysts with low cost, high activity and high stability is an urgent problem to be solved for the current proton exchange membrane fuel cell.

[0004] In the existing methods for preparing fuel cell catalysts, compared with physical and chemical methods, the microbial synthesis of metal nanocatalysts has incomparable advantages, mainly manifested in: (1) Heredity: Obtaining a porous and heteroatom-doped catalyst carbon carrier through biological genetic effects; (2) Self-assembly: Spontaneously assembling multi-component and hierarchical functional materials; (3) High dispersibility: Microorganisms have excellent hydrophilicity, and highly dispersed nanocatalyst materials can be in-situ synthesized using microorganisms as templates; (4) Green environmental protection: No additional dispersant is required, and the surface of the synthesized nanomaterials is clean; (5) Compatibility: It is easy to combine with chemical synthesis methods to synergistically construct the distribution of catalyst components, structures, etc., and improve the designability of materials. However, the current process for synthesizing nano-metal materials using microorganisms has deficiencies such as unstable particle size, low adsorption capacity, and low specific surface area. For example, the particle size of bio-nano metals is usually in the range of 1 - 50 nm, and the proportion of precious metals in the catalyst is about 10%. Shewanella is widely distributed in natural environments such as fresh water, the ocean, and sediments, and has excellent ability to deposit metal nanoparticles and is a typical dissimilatory metal-reducing bacterium. Currently, studies have explored the effects of different Shewanella strains (such as MR-1, CN-32, W-3181), hydrogen reduction processes, microorganism-different carbon material composite matrices, different cells and extracellular components, hydrogenase / reductase, etc. in the synthesis of metal nanomaterials. By controlling these technical conditions, the size of nano-metals can be adjusted within 10 nm, thus achieving uniform distribution of nano-metals. Although some adjustment methods and mechanisms have been elaborated, the implementation still has certain difficulties and is not suitable for large-scale production. Summary of the Invention

[0005] Aiming at the technical problems such as insufficient metal adsorption amount and difficult distribution regulation in the process of synthesizing metal nanomaterials by the existing biological method, the first object of the present invention is to provide a microorganism-sodium alginate-based porous composite palladium-carbon catalyst, which catalyst has a porous structure, good stability, high nano-palladium loading amount, and uniform distribution, and exhibits high catalytic activity.

[0006] The second object of the present invention is to provide a preparation method of a microorganism-sodium alginate-based porous composite palladium-carbon catalyst, which preparation method is simple to operate, the raw materials are easy to obtain, the cost is low, and it is beneficial to expand production.

[0007] In order to achieve the above technical objects, the present invention provides a preparation method of a microorganism-sodium alginate-based porous composite palladium-carbon catalyst, which method comprises the following steps:

[0008] 1) Adding a mixed solution containing sodium alginate, calcium carbonate, and microorganisms into a solution containing calcium ions for cross-linking reaction to form composite gel microspheres;

[0009] 2) Immerse the composite gel microspheres in an acidic solution for leaching to obtain porous composite gel microspheres;

[0010] 3) After placing the porous composite gel microspheres in water, add a palladium source for adsorption to obtain palladium-loaded composite gel microspheres;

[0011] 4) Subject the palladium-loaded composite gel microspheres to freeze-drying, carbonization, and reduction roasting in sequence to obtain the product.

[0012] The technical solution of the present invention uses a co-embedding technique to construct a carrier for a catalytic material. Specifically, sodium alginate forms gel microspheres under the cross-linking action of calcium ions, and microorganisms are embedded in the gel microspheres. More specifically, after cross-linking, sodium alginate provides a stable skeleton support for the gel microspheres, and the embedded microorganisms are stably and dispersedly filled in the skeleton of the gel microspheres and are not easily lost. Sodium alginate and microorganisms make full use of their relatively abundant oxygen-containing functional groups to enhance the adsorption of the palladium source in the solution system, greatly improving the adsorption efficiency and adsorption capacity of the palladium source, and can improve the dispersion of the palladium source, avoid agglomeration, and is conducive to obtaining nano-sized metallic palladium particles subsequently. On this basis, the technical solution of the present invention further adopts a template pore-forming technique. Using calcium carbonate as a pore-forming template, rich pores are formed in the gel microspheres, which can increase the connection channels between the inside of the gel spheres and the external medium, better expose the internal palladium source adsorption sites, not only provide more active sites to bind the palladium source, but also are more conducive to the diffusion of the palladium source into the inside of the gel microspheres and the uniform distribution of the palladium source inside the gel microspheres. The technical solution of the present invention carbonizes and reduces the gel microspheres adsorbed with the palladium source, and the gel microspheres form a stable porous structure carrier, and nano-sized metallic palladium is in-situ generated on the surface and in the pores of the carrier, realizing stable and dispersed loading, and the particle size is more uniform and smaller, so that the overall catalytic material exhibits high catalytic activity.

[0013] As a preferred solution, the mass percentage concentration of sodium alginate in the mixed solution containing sodium alginate, calcium carbonate, and microorganisms is 1.5-2.5%, the mass percentage concentration of calcium carbonate is 1-2%, and the content of microorganisms is measured by the mass of microorganisms collected from a culture solution with 60-80 L OD 600 =1.0-1.2. Calcium carbonate is used as a pore-forming template. If the content of calcium carbonate is too low, rich pore channels cannot be formed in the gel microspheres, which is not conducive to the palladium source entering the inside of the gel microspheres and contacting its adsorption sites. If the proportion of calcium carbonate is too high, the stability of the porous carrier formed after carbonization of the gel microspheres will be affected. If the proportion of sodium alginate relative to microorganisms is too low, it is difficult to fully embed the microorganisms, and if the proportion of sodium alginate relative to microorganisms is too high, there are fewer microorganisms filled in the gel microspheres, making it difficult to increase the adsorption amount and dispersion of the palladium source.

[0014] As a preferred embodiment, the calcium ion concentration in the calcium ion-containing solution is 1 to 3 mol / L. The calcium ion-containing solution mainly uses calcium ions to perform ion exchange on sodium alginate to achieve crosslinking. The calcium ion-containing solution is provided by a water-soluble calcium salt, more specifically calcium chloride, calcium nitrate, etc.

[0015] As a preferred embodiment, the volume ratio of the calcium ion-containing solution to the mixed solution containing sodium alginate, calcium carbonate and microorganisms is 3:1 to 5:1. If the proportion of the calcium ion-containing solution is too low, the crosslinking degree of sodium alginate will be reduced and stable gel microspheres cannot be formed. If the calcium ion proportion is too high, some adsorption active sites will be occupied, reducing the adsorption capacity of the gel microspheres.

[0016] As a preferred embodiment, the microorganism is Shewanella. A more specific microorganism is Shewanella strain Shewanella onedensis MR-1 (purchased from the American Type Culture Collection, catalog number ATCC700550). The preferred Shewanella has a good adsorption effect on the palladium source, contains rich hydrogenase, has a high tolerance to noble metals, and has 2+ excellent adsorption capacity for Pd, and under certain conditions, it also has a certain reducing ability for metal ions. Therefore, using Shewanella can achieve a good purpose of depositing metal nanoparticles. Selecting Shewanella for the adsorption characteristics of Pd 2+ and the subsequent carbonization process can synthesize a carbonized bacteria-supported noble metal catalyst with good stability and high catalytic activity. Moreover, the obtained carbon material after carbonization has a nitrogen doping effect, which can not only improve the loading stability of palladium, but also synergistically improve the catalytic activity of palladium. Shewanella can well adsorb palladium ions, and after carbonization, the palladium ions can be evenly and stably loaded in the carbonized Shewanella.

[0017] As a preferred embodiment, the leaching conditions are as follows: using a hydrochloric acid solution with a concentration of 0.1 to 0.3 mol / L, leaching at room temperature for 15 to 30 min. Using a dilute acid with an appropriate concentration can decompose and remove the calcium carbonate template agent without damaging the structure of the gel microspheres. If the concentration is too low, it is difficult to efficiently remove the calcium carbonate. If the concentration is too high, it is easy to damage the gel microspheres.

[0018] As a preferred embodiment, the palladium source is sodium tetrachloropalladate; the palladium source is added in the form of a solution with a concentration of 6 to 8 mmol / L.

[0019] As a preferred solution, the carbonization and reduction roasting process is as follows: First, under a protective atmosphere, the temperature is raised to 750 - 850 °C at a rate of 3 - 4 °C / min, held for 2.5 - 3.5 h, then cooled to 180 - 220 °C, and under a reducing atmosphere, held for 1.5 - 2.5 h. The reducing atmosphere is, for example, hydrogen. At the preferred carbonization temperature, sufficient carbonization of organic matter and decomposition of the palladium source can be achieved. If the temperature is too high, the porous structure of the carbonized material is easily damaged and metal agglomeration is likely to occur. If the temperature is too low, carbonization and decomposition of the palladium source are incomplete.

[0020] The present invention also provides a microorganism-sodium alginate-based porous composite palladium-carbon catalyst obtained by the preparation method.

[0021] The microorganism-sodium alginate-based porous composite palladium-carbon catalyst of the present invention uses a porous carbon material as a carrier, and nano-sized metal palladium particles are uniformly dispersed and loaded on the surface and pores of the carrier. The average particle size of the nano-sized metal palladium particles is about 7 nm, and the particle distribution is uniform.

[0022] Compared with the prior art, the technical solution of the present invention has the following advantages and beneficial effects:

[0023] In the preparation process of the microorganism-sodium alginate-based porous composite palladium-carbon catalyst of the present invention, the co-embedding technology is adopted to construct the carrier of the catalytic material. Sodium alginate forms gel microspheres under the cross-linking action of calcium ions, and microorganisms are stably and dispersedly filled in the framework of the gel microspheres without easy loss. The relatively rich oxygen-containing functional groups of sodium alginate and microorganisms can strengthen the adsorption of the palladium source in the solution system, greatly improving the adsorption efficiency and adsorption capacity of the palladium source, and can also improve the dispersibility of the palladium source, avoiding agglomeration, which is beneficial to obtaining nano-sized metal palladium particles subsequently.

[0024] In the preparation process of the microorganism-sodium alginate-based porous composite palladium-carbon catalyst of the present invention, the template pore-forming technology is adopted. Calcium carbonate is used as a pore-forming template to form rich pores in the gel microspheres, which can increase the connection channels between the inside of the gel spheres and the external medium, making the internal palladium source adsorption sites better exposed. It can not only provide more active sites to bind the palladium source, but also is more conducive to the diffusion of the palladium source into the inside of the gel microspheres and the uniform distribution of the palladium source inside the gel microspheres.

[0025] In the preparation process of the microorganism-sodium alginate-based porous composite palladium-carbon catalyst of the present invention, calcium carbonate template pore-forming and sodium alginate cross-linking are used to form porous gel microspheres, and further carbonization is carried out to form a stable porous structure carrier. The microorganisms that adsorb the palladium source are embedded and filled in the gel microspheres, and highly dispersed and uniformly sized nano-sized metal palladium is formed in situ through carbonization and reduction, and is loaded on the surface and pores of the carrier, making the overall catalytic material exhibit high catalytic activity.

[0026] The preparation method of the microorganism-sodium alginate-based porous composite palladium-carbon catalyst of the present invention is simple in operation, easy to obtain raw materials, and low in cost, which is conducive to expanding production.

[0027] The microorganism-sodium alginate-based porous composite palladium-carbon catalyst of the present invention has a porous structure, a large specific surface area, small particle size of palladium nanoparticles, narrow distribution (average particle size is about 7 nanometers), and is uniformly and stably loaded in the carrier, improving the comprehensive performance of the catalytic material. Description of the Drawings

[0028] Figure 1 It is a physical picture before and after Pd adsorption of Shewanella-alginate-based porous composite gel microspheres in Example 1; the left picture is the gel microspheres formed by co-embedding Shewanella and sodium alginate, and the right picture is after the co-embedded gel microspheres complete Pd adsorption.

[0029] Figure 2 It is a transmission electron microscope (TEM) and particle size statistical chart of different treated samples in Example 1. In the figure, a and b are Shewanella-based palladium-carbon catalysts (Pd / MR1), c and d are Shewanella-alginate-based palladium-carbon catalysts (Pd / MR1-SA), and e and f are Shewanella-alginate-calcium carbonate pore-forming-based palladium-carbon catalysts (Pd / MR1-SA-CaCO 3 )

[0030] Figure 3 It is a TEM image of Shewanella-alginate-calcium carbonate pore-forming-based palladium-carbon catalyst (Pd / MR1-SA-CaCO 3 ) at different magnifications and scales in Example 1.

[0031] Figure 4 It is the electrochemical test results of different treated samples in Example 1; in the figure, a and b are Shewanella-based palladium-carbon catalysts (Pd / MR1), c and d are Shewanella-alginate-based palladium-carbon catalysts (Pd / MR1-SA), and e and f are Shewanella-alginate-calcium carbonate pore-forming-based palladium-carbon catalysts (Pd / MR1-SA-CaCO 3 ) Detailed Embodiments

[0032] The following specific examples are intended to further illustrate the content of the present invention, rather than limiting the protection scope of the claims.

[0033] In the following examples, if there is no special description, the chemical raw materials are all conventional commercially available products. The calcium carbonate powder is the analytical pure calcium carbonate of Sinopharm Chemical Reagent Co., Ltd., and the product model is 10005760.

[0034] Example 1

[0035] 1) Activation and expansion of microbial strains: The microorganism used is Shewanella onedensis MR-1. When activating, take the bacteria out of the -80℃ refrigerator, streak on the LB solid culture medium, and then culture at 30℃ for 20 hours. Inoculate the cultured single colony into 100mL LB culture medium, and culture it in a shaking incubator at 170rpm and 30℃ for 18 hours. Inoculate the activated bacterial liquid into 1500ml LB liquid culture medium at a 2% inoculation rate, and culture it in a shaking incubator at 170rpm and 30℃ for 15 hours. Measure the OD 600 = 1.1. The bacteria after expansion culture were collected by centrifugation, and the centrifugation parameters were set to 8000 rpm for 8 min.

[0036] 2) Preparation of composite gel microspheres: Prepare 25 ml of a mixed solution containing 2% sodium alginate and 1.5% calcium carbonate powder, add the bacteria collected in the previous step to the prepared mixed solution until fully mixed, and then drop 2 mol / L CaCl 2 The solution (100 ml) was cross-linked to form gel microspheres.

[0037] 3) Calcium carbonate pore formation: After the gel microspheres are stable, they are removed and placed in a 0.2 mol / L HCl solution for reaction for 20 min. The gel microspheres can be seen floating, indicating that the pore formation is successful.

[0038] 4) Palladium ion adsorption: The collected bacteria, composite gel microspheres (without calcium carbonate) and composite gel microspheres after calcium carbonate pores were placed in 25 mL of deionized water, respectively. In addition, 75 mL of a 6.89 mmol / L sodium tetrachloropalladate solution was prepared, and the pH was adjusted to 3 with hydrochloric acid. A peristaltic pump was used to drop the sodium tetrachloropalladate solution into the collected bacteria, composite gel microspheres and composite gel microspheres after calcium carbonate pores, and a magnetic stirrer was used to fully stir and adsorb. The peristaltic pump dropwise speed was 0.5 mL / min, the magnetic stirring speed was 400 rpm, and the reaction time was 24 h.

[0039] 5) Freeze drying, high temperature reduction carbonization, the bacterial cells adsorbed with palladium, the composite gel microspheres and the composite gel microspheres after calcium carbonate pore formation were placed in a -80°C refrigerator for freezing overnight, and then freeze dried using a vacuum freeze dryer for the next step of carbonization reduction. The carbonization reduction was carried out in a tubular furnace, argon was introduced, and the temperature of the tubular furnace was raised to 800°C at a rate of 3°C / min and kept warm for 3h. When the temperature dropped to 200°C, hydrogen was introduced and kept warm for 2h. The hydrogen was turned off and the sample was taken out after the tubular furnace dropped to room temperature, and the Shewanella-based palladium carbon catalyst (Pd / MR1), Shewanella-sodium alginate-based palladium carbon catalyst (Pd / MR1-SA), Shewanella-sodium alginate-calcium carbonate pore-forming palladium carbon catalyst (Pd / MR1-SA-CaCO 3 ).

[0040] Figure 2 Transmission electron microscope (TEM) and particle size statistical charts of different processed samples. In the figure, a and b are Pd / MR1, c and d are Pd / MR1-SA, and e and f are Pd / MR1-SA-CaCO 3 . It can be seen from the TEM images that obvious metal agglomeration occurred in the Pd / MR1 catalyst, with the worst uniformity. The dispersion of palladium particles in Pd / MR1-SA and Pd / MR1-SA-CaCO 3 was better, and it was visible to the naked eye that after pore formation with CaCO 3 the palladium nanoparticles in the Pd / MR1-SA-CaCO 3 catalyst sample were more finely and uniformly distributed. Statistical analysis using software showed that the average particle sizes of the three groups were 15.97 nm, 11.26 nm, and 6.99 nm, respectively. This result was basically consistent with the TEM observation results, and it could also be roughly inferred that pore formation was helpful for particle distribution and thus improved the catalyst performance.

[0041] Figure 3 TEM images of Pd / MR1-SA-CaCO 3 at different magnifications and scales. After pore formation with CaCO 3 in the Shewanella gel microspheres, the distribution of palladium particles was improved. After magnifying the TEM images, a series of light-colored, circular pore-like structures could be observed, indicating that CaCO 3 successfully formed pores in the catalytic material and the final catalyst presented the expected porous structure. Pd / MR1-SA-CaCO 3 could also benefit from its porous structure, which increased the connection channels between the inside of the gel sphere and the external medium, better exposed the internal adsorption sites to the external adsorbates, and made the distribution of palladium more uniform.

[0042] Catalytic performance test:

[0043] 1) Preparation of catalyst ink:

[0044] Weigh 4 mg of palladium-carbon catalyst, add 200 μL of ethanol, gently shake, and then add 760 μL of distilled water and 40 μL of Nafion (5% wt) in sequence, and sonicate for 30 min.

[0045] 2) Cleaning and spotting drying of the working electrode:

[0046] The working electrode was polished and cleaned with 0.05 μm polishing powder. After the electrode was dried, 15 μL of the prepared catalyst ink was pipetted and dropped on the sample application area of the glassy carbon electrode, and then the sample was allowed to dry completely.

[0047] 3) Preparation for electrochemical detection:

[0048] Add an appropriate amount of freshly prepared 0.1 M KOH electrolyte to the electrolyte container, and introduce oxygen for 30 min to form an oxygen-saturated electrolyte. Before the formal test, first activate the working electrode, that is, within the test voltage range, perform cyclic voltammetry scanning at a scanning rate of 0.05 V / s for 20 cycles. After the working electrode is fully activated, perform cyclic voltammetry detection and linear sweep voltammetry detection.

[0049] Cyclic voltammetry: Voltage range: -1 V - 0.2 V, Scanning rate: 0.01 V / s

[0050] Linear sweep voltammetry: Voltage range: -0.8 V - 0.4 V, Scanning rate: 0.01 V / s

[0051] 4) Calculation of catalytic activity index

[0052] The calculation of electrochemical activity indexes mainly includes the electrochemical surface area (ECSA), mass activity (MA), and specific surface area (SA) of the catalyst. The formulas are as follows:

[0053] ECSA = Q / (424 × Pd load );

[0054] 1 / j = 1 / j d + 1 / j k ;

[0055] MA = j k / Pd load ;

[0056] SA = MA / ECSA;

[0057] Among them, Q represents the integrated area of the oxygen reduction peak, j represents the instantaneous current at 0.1 V of the voltage at 1600 rpm. j d is the limiting current. Pd load is the loading of palladium, which is calculated based on the ICP detection results.

[0058] Figure 4 are the electrochemical test results of three groups of treated samples. Figures (a, b) are Shewanella-based palladium-carbon catalysts (Pd / MR1), Figures (c, d) are Shewanella-alginate-based palladium-carbon catalysts (Pd / MR1-SA), and Figures (e, f) are Shewanella-alginate-calcium carbonate pore-forming-based palladium-carbon catalysts (Pd / MR1-SA-CaCO 3 ).

[0059] Table 1 summarizes the main activity indicators of the above test results. It can be seen that Pd / MR1-SA-CaCO 3 has higher ECSA and MA compared to the other two groups, reaching 32.32 m 2 ·g- 1 and 53.77 A·g- 1 respectively. ECSA represents the electrochemically active surface area. For some nanomaterials, a larger surface area can expose more abundant active sites, thus enhancing the electrochemical performance. MA depends to a large extent on the size of the electrocatalyst particles. Smaller-sized catalysts exhibit higher mass activity because smaller-sized particles have a larger ratio of surface atoms to total atoms per unit mass and have a large number of electrocatalytic active sites. Therefore, the electrochemical results are basically consistent with the characterization results in Example 1, and it is also verified that the surface area and metal distribution of the catalyst are improved after pore-forming treatment, which is conducive to the catalyst to exert better performance.

[0060] Calculation results of the activity index parameters of the electrochemical test in Table 1

[0061]

[0062] Example 2

[0063] Set the sodium alginate concentration in step 2) of Example 1 to 1.5%, and the calcium carbonate powder concentration to 1.5%. The other conditions are the same as those in Example 1.

[0064] The average particle size of the palladium nanoparticles in the prepared Pd / MR1-SA-CaCO 3 is 8.89 nm, and its ECSA, MA, and SA are 28.67 m 2 ·g -1 , 43.25 A·g -1 and 1.63 A·m -2 .

[0065] Example 3

[0066] Set the sodium alginate concentration in step 2) of Example 1 to 2.5%, and the calcium carbonate powder concentration to 1.5%. The other conditions are the same as those in Example 1.

[0067] The average particle size of the palladium nanoparticles in the prepared Pd / MR1-SA-CaCO 3 is 7.45 nm, and its ECSA, MA, and SA are 30.78 m 2 ·g -1 , 47.68 A·g -1 and 1.67 A·m -2, the uniformity and catalytic performance of palladium nanoparticles under this treatment condition are slightly lower than those of the sample treated in Example 1 and slightly higher than those of the sample treated in Example 2. It can be seen that when the calcium carbonate concentration is kept constant, an appropriate sodium alginate content will improve the performance of the catalyst. When the content is too low or too high, it will aggravate the agglomeration of metal particles, thus affecting the catalyst activity.

[0068] Example 4

[0069] Set the sodium alginate concentration in step 2) of Example 1 to 2% and the calcium carbonate concentration to 2%, and the other conditions are the same as those in Example 1.

[0070] The average particle size of the prepared Pd / MR1-SA-CaCO 3 is 7.61 nm, and its ECSA, MA, and SA are 31.06 m 2 ·g -1 , 48.35 A·g -1 and 1.72 A·m -2 , the metal uniformity and catalytic performance under this treatment condition are similar to those in Example 3, slightly lower than those of the sample treated in Example 1, and higher than those of the sample treated in Example 2. It can be seen that under the optimal sodium alginate content condition in the above cases, continuing to increase the calcium carbonate concentration to create a porous environment is not suitable for the preparation of the catalyst. This may be because too many pore structures weaken the fixation of metal particles, thus increasing the agglomeration.

Claims

1. Preparation method of a microbial-sodium alginate-based porous composite palladium-carbon catalyst, Characterized in that: Comprising the following steps: 1) Add a solution containing calcium ions to a mixed solution containing sodium alginate, calcium carbonate, and microorganisms for a cross-linking reaction to form composite gel microspheres; the mass percentage concentration of sodium alginate in the mixed solution containing sodium alginate, calcium carbonate, and microorganisms is 1.5 - 2.5%, the mass percentage concentration of calcium carbonate is 1 - 2%, and the content of microorganisms is measured by the mass of microorganisms collected from a culture solution with an OD 600 = 1.0 - 1.2 per liter of the mixed solution; 2) Immerse the composite gel microspheres in an acidic solution to obtain porous composite gel microspheres; 3) After placing the porous composite gel microspheres in water, add a palladium source for adsorption; Obtain palladium-loaded composite gel microspheres; 4) Subject the palladium-loaded composite gel microspheres to freeze-drying, carbonization and reduction roasting in sequence to obtain the product.

2. The preparation method of a microbial-sodium alginate-based porous composite palladium-carbon catalyst according to claim 1, Characterized in that: The calcium ion concentration in the calcium ion-containing solution is 1-3 mol / L.

3. The preparation method of a microbial-sodium alginate-based porous composite palladium-carbon catalyst according to any one of claims 1-2, Characterized in that: The volume ratio of the calcium ion-containing solution to the mixed solution containing sodium alginate, calcium carbonate and microorganisms is 3:1-5:

1.

4. The preparation method of a microbial-sodium alginate-based porous composite palladium-carbon catalyst according to claim 3, Characterized in that: The microorganism is Shewanella.

5. The preparation method of a microbial-sodium alginate-based porous composite palladium-carbon catalyst according to claim 1, Characterized in that: The conditions for the leaching are: using a hydrochloric acid solution with a concentration of 0.1-0.3 mol / L, and leaching at room temperature for 15-30 min.

6. The preparation method of a microbial-sodium alginate-based porous composite palladium-carbon catalyst according to claim 1, Characterized in that: The palladium source is sodium tetrachloropalladate; the palladium source is added in the form of a solution with a concentration of 6-8 mmol / L.

7. The preparation method of a microbial-sodium alginate-based porous composite palladium-carbon catalyst according to claim 1, Characterized in that: The process of the carbonization and reduction roasting is: first, under a protective atmosphere, heat up to 750-850 °C at a rate of 3-4 °C / min, keep warm for 2.5-3.5 h, then cool down to 180-220 °C, and keep warm for 1.5-2.5 h under a reducing atmosphere.

8. A microbial-sodium alginate-based porous composite palladium-carbon catalyst, Characterized in that: Obtained by the preparation method according to any one of claims 1-7.

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