Cobalt-based microgel material and preparation method and application thereof

Abstract

The invention provides a cobalt-based microgel material as well as a preparation method and application thereof. The catalytic oxidation activity, stability and universality of the cobalt-based material to sulfite are effectively improved on the basis of the synergistic effect of constructing a microgel structure through reduction of sodium borohydride and regulating and controlling the boron loading amount to optimize catalytic active sites. The specific boron loading amount induced electron interaction between Co-O-B changes the electron cloud distribution and bonding environment of Co, so that the number and distribution of catalytic active sites are effectively regulated and controlled, and the pore structure of the microgel is stabilized, thereby promoting efficient contact between sulfite and the active sites; a stable microgel structure is formed through a liquid phase reduction-gelation process, agglomeration or loss of active components can be avoided, a proper amount of boron loading can prevent pore channel blockage, the problem of catalytic activity attenuation under high loading capacity can be effectively relieved, meanwhile, catalytic requirements of different sulfites are met, and the application range of the material is widened.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of functional materials and environmental catalysis, and particularly relates to a cobalt-based microgel material and a preparation method and application thereof. BACKGROUND

[0002] At present, the zinc desulfurization technology is widely used in the industrial desulfurization field due to the advantages of high desulfurization efficiency, recyclable by-products and the like. The core link of the technology is to use a zinc salt solution to absorb sulfur dioxide in flue gas to generate zinc sulfite (ZnSO3), and then the zinc sulfite needs to be further oxidized into zinc sulfate (ZnSO4) so as to be recycled or discharged up to the standard.

[0003] However, the natural oxidation rate of the zinc sulfite is slow, which is difficult to meet the efficient treatment needs of industrial production. In the prior art, the aeration oxidation or the addition of a catalyst is usually used to accelerate the oxidation reaction, but the traditional catalyst has many limitations: on the one hand, some catalysts (such as manganese-based and iron-based catalysts) need to be used at a high temperature (above 60℃) or under specific pH conditions (such as strong acidity or strong alkalinity) to play a catalytic activity, which increases the industrial operation energy consumption and process control difficulty; on the other hand, the stability of some catalysts is poor, and the active components are easy to lose in the high-concentration sulfite slurry, which leads to rapid attenuation of the catalytic performance and short service life. In addition, the traditional catalyst has poor universality for the catalysis of sulfite, and can only act on specific types of sulfite (such as calcium sulfite), which is difficult to meet the efficient oxidation needs of zinc sulfite in the zinc desulfurization process.

[0004] Therefore, it is of great practical significance to develop a new catalyst with simple preparation process, high catalytic activity, mild application conditions and universal catalysis for sulfite, which is the key to solving the efficient oxidation problem of zinc sulfite in the zinc desulfurization slurry, and promotes the green and efficient development of the industrial desulfurization technology. SUMMARY

[0005] In order to solve the defects in the prior art, the present application provides a cobalt-based microgel material and a preparation method and application thereof.

[0006] The present application adopts the following technical solutions:

[0007] In a first aspect, the present application provides a preparation method of a cobalt-based microgel material, comprising the following steps:

[0008] adding a cobalt salt into water to obtain solution A;

[0009] adding sodium borohydride into water to obtain solution B;

[0010] The solution A is added dropwise into the solution B to perform a co-reduction reaction, and after the reaction is completed, the cobalt-based microgel material is obtained through the steps of aging, centrifugation, washing and drying.

[0011] The molar ratio of the sodium borohydride to cobalt in the cobalt salt is (0.5-3.0):1.

[0012] In some embodiments, the molar ratio of the sodium borohydride to cobalt in the cobalt salt is 1.25:1.

[0013] In some embodiments, the cobalt salt comprises at least one of cobalt nitrate, cobalt sulfate and cobalt chloride.

[0014] In some embodiments, the solution A is added dropwise into the solution B to perform a co-reduction reaction at 1-5 mL / min at 20-25℃.

[0015] In some embodiments, the solution A is added dropwise into the solution B to perform a co-reduction reaction, and after the reaction is completed, the cobalt-based microgel material is obtained through the step of aging, wherein the aging temperature is 20-25℃ and the aging time is 4-8h.

[0016] In some embodiments, in the step of adding the sodium borohydride into water to obtain the solution B, the molar volume ratio of the sodium borohydride to water is (2-12) mmol:(30-40) mL.

[0017] The volume ratio of the solution A to the solution B is (50-60):(30-40).

[0018] In some embodiments, the solution A is added dropwise into the solution B to perform a co-reduction reaction, and after the reaction is completed, the cobalt-based microgel material is obtained through the steps of aging, centrifugation, washing with ethanol and / or water and drying, wherein the drying temperature is 50-80℃ and the drying time is 8-12h.

[0019] In a second aspect, the present application further provides a cobalt-based microgel material prepared by the preparation method.

[0020] In a third aspect, the present application further provides the cobalt-based microgel material prepared by the preparation method or the application of the cobalt-based microgel material in catalyzing the oxidation of sulfite.

[0021] Preferably, the sulfite comprises at least one of zinc sulfite, sodium sulfite, ammonium sulfite and magnesium sulfite.

[0022] The application conditions are as follows: the pH value during the reaction is 7.0-9.0, the reaction temperature is 45-60℃, air is used as the oxidation gas source, and the air flow rate is 0.5-1.5 L / min.

[0023] The cobalt-based microgel material preparation method and application of the application have the following effects compared with the prior art.

[0024] The cobalt-based microgel material preparation method of the application can be carried out at normal temperature and pressure by using one-step liquid-phase chemical reduction method, without the need for complex equipment or post-processing, and has green process and low cost, and is easy to scale up production; the method of the application can effectively control the chemical state, loading amount and microstructure of boron in the final material by accurately adjusting the molar ratio of the reducing agent (NaBH4) to the metal precursor (Co 2+ The advantages of the material are derived from its unique microgel structure and adjustable chemical composition: the three-dimensional network structure provides a large specific surface area and abundant mesopores, greatly promoting the mass transfer of reactants and the exposure of active sites; the amorphous state and the electronic interaction between Co-O-B optimize the electronic structure of the material surface, enhancing the adsorption and activation capacity of oxygen molecules and sulfite ions; the material obtained by the application is a microgel with a three-dimensional network structure rather than a dense particle, significantly improving the dispersibility and effective specific surface area in a liquid reaction system; by simply adjusting the amount of reducing agent, the composition and microstructure of the material can be controlled, providing a flexible means for performance optimization. Especially under simulated actual desulfurization slurry conditions, the optimized catalyst can greatly improve the oxidation rate, shorten the oxidation time and reduce the energy consumption of air blowing; the cobalt-based microgel material of the application can maintain high activity at a near-neutral pH range (7.0-9.0) and moderate temperature (45-60 DEG C), which is highly matched with the working conditions of most industrial desulfurization slurries. The use of the cobalt-based microgel material of the application can accelerate the stabilization and resource utilization process of desulfurization by-products, improve the product quality of zinc sulfate, reduce the land area occupied by oxidation equipment and operation cost, and meet the development requirements of green chemical industry and circular economy. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative effort on the basis of these drawings.

[0026] Figure 1 X-ray diffraction (XRD) patterns of the cobalt-based microgel materials prepared in Examples 1-3;

[0027] Figure 2 Scanning electron microscope (SEM) images of the cobalt-based microgel materials prepared in Examples 1-3;

[0028] Figure 3Effect of different dosing concentrations of CoB-1.25 on the oxidation rate of zinc sulfite;

[0029] Figure 4 Effect of different concentrations of aqueous zinc sulfite solution on the oxidation rate of zinc sulfite;

[0030] Figure 5 Effect of different air aeration rates on the oxidation rate of zinc sulfite;

[0031] Figure 6 Effect of different reaction temperatures on the oxidation rate of zinc sulfite;

[0032] Figure 7 Effect of different reaction pHs on the oxidation rate of zinc sulfite;

[0033] Figure 8 Effect of CoB-1.25 on the oxidation rate constant (K value) of different sulfites (zinc sulfite, sodium sulfite, magnesium sulfite);

[0034] Figure 9 Effect of different catalysts (CoB-0.5, CoB-0.75, CoB-1.25, CoB-2.25, CoB-3.0) on the oxidation rate constant (K value) of zinc sulfite oxidation;

[0035] Figure 10 Effect of the absence of catalyst on the concentration of sulfates generated by the oxidation of zinc sulfite. DETAILED DESCRIPTION

[0036] In order to facilitate the understanding of the present application, the present application will be described more fully below in conjunction with specific embodiments. The preferred embodiments of the present application are given in the specific embodiments. However, the present application can be realized in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided so that the disclosure of the present application can be more thoroughly and completely understood.

[0037] The order of description of the following embodiments is not intended to imply a preferred order of embodiments. Additionally, in the description of the application, the term "including" means "including but not limited to". Various embodiments of the application can exist in a range of forms; it should be understood that the description of a range is merely used for the sake of convenience and brevity, and should not be construed as a rigid limitation on the scope of the application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single values within the range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single values within the range, such as 1, 2, 3, 4, 5 and 6, regardless of the range. In addition, whenever a numerical range is indicated in this document, it refers to any cited number (fraction or integer) within the indicated range.

[0038] The application provides a preparation method of a cobalt-based microgel material, comprising the following steps:

[0039] S1, adding a cobalt salt into water to obtain solution A;

[0040] S2, adding sodium borohydride into water to obtain solution B;

[0041] S3, dropwise adding solution A into solution B to perform a co-reduction reaction, and after the reaction is completed, performing aging, centrifugation, washing and drying to obtain the cobalt-based microgel material;

[0042] The molar ratio of sodium borohydride to cobalt in the cobalt salt is (0.5-3.0):1.

[0043] The preparation method of the cobalt-based microgel material of the application dropwise adds solution A into solution B to perform a co-reduction reaction, and after the dropwise addition is completed, performs aging to obtain a uniform and stable black or dark suspension; the obtained suspension is subjected to centrifugal separation, the obtained solid precipitate is washed with deionized water and ethanol alternately for several times, and finally the washed product is dried to obtain the cobalt-based microgel material.

[0044] The preparation method of the cobalt-based microgel material of the application is characterized in that through a controllable liquid-phase chemical reduction and self-assembly process, an amorphous B-doped Co(OH)2 microgel with a three-dimensional network structure is constructed. The preparation principle is that the hydrolysis of sodium borohydride provides OH - ions, which combine with Co 2+ to form Co(OH)2, and the hydrogen gas released during the hydrolysis of sodium borohydride serves as a bubble template to control the morphology of Co(OH)2, so that the gel network with open pores is formed. This method precisely controls the reducing agent (NaBH4) and the metal precursor (Co 2+The molar ratio of the boron hydride sodium and cobalt ion precursor can effectively control the chemical state, loading amount of boron in the final material and the microstructure of the material. The advantages of the material are derived from the unique microgel structure and the adjustable chemical composition: the three-dimensional network structure provides a large specific surface area and abundant mesopores, greatly promoting the mass transfer of reactants and the exposure of active sites; and the amorphous state and the electronic interaction between Co-O-B optimize the electronic structure of the material surface, enhancing the adsorption and activation capacity of oxygen molecules and sulfite ions.

[0045] The present application effectively improves the catalytic oxidation performance of the material on sulfite based on the synergistic strategy of "composition regulation optimizing electronic structure" and "microgel construction strengthening mass transfer". The reason is that the appropriate boron loading amount (regulated by n(NaBH4) / n(Co 2+ ) can modify the electron cloud density of cobalt, optimize the adsorption strength of cobalt active centers to reactant molecules, and the defects and dangling bonds rich in amorphous structure help to activate oxygen molecules. In addition, the three-dimensional through microgel network ensures good dispersibility and stability in the slurry reaction system, avoids the agglomeration and deactivation of nanoparticles, and provides efficient mass transfer channels for gas-liquid-solid three-phase reactions.

[0046] The present application successfully prepares a cobalt-based microgel catalyst by a simple one-step liquid phase reduction method. The preparation method has the advantages of mild reaction conditions (room temperature), simple operation, short cycle, no need for complex templates or post-treatment steps, low cost and easy to scale up. Compared with the traditional co-precipitation method, thermal decomposition method or preparation process of supported catalysts, the present application can more directly and effectively construct an amorphous microgel structure with high specific surface area and abundant pores, realize the synchronous optimization of the intrinsic activity and macroscopic morphology of the catalyst. The material can significantly alleviate the problems of easy agglomeration and limited mass transfer of traditional catalysts in the slurry reaction.

[0047] Specifically, the present application controls the molar ratio (n(NaBH4) / n(Co 2 + ) of the reducing agent sodium borohydride and the cobalt ion precursor in the range of (0.5~3.0):1; by regulating the molar ratio, the chemical state and loading amount of boron in the material can be accurately changed, thereby optimizing the microstructure and electronic properties thereof. The cobalt-based microgel material prepared by the present application is an amorphous microgel with cobalt as the active metal and boron as the structure additive, which has a three-dimensional network structure and exhibits good dispersibility and abundant mesoporous structure in aqueous and slurry systems, which is beneficial to the mass transfer of reactants and products. By adjusting the n(NaBH4) / n(Co 2+The molar ratio of sodium borohydride to cobalt in the cobalt salt can be accurately controlled, so as to accurately control the chemical state and loading amount of boron in the material, and further optimize the electronic structure and catalytic performance of the material. The cobalt-based microgel material as a catalyst in catalyzing oxidation of sulfite is particularly suitable for catalyzing ZnSO3 in the slurry discharged from the absorption tower in the zinc-based flue gas desulfurization process to ZnSO4.

[0048] In some embodiments, the molar ratio of sodium borohydride to cobalt in the cobalt salt is 1.25:1, and when the molar ratio of n(NaBH4) / n(Co 2+ When the molar ratio of n(NaBH4) / n(Co) is 1.25, the cobalt-based microgel material prepared has the most excellent comprehensive catalytic performance.

[0049] In some embodiments, the cobalt salt comprises at least one of cobalt nitrate, cobalt sulfate and cobalt chloride.

[0050] In some embodiments, the co-reduction reaction is performed by adding solution A into solution B at a flow rate of 1-5 mL / min at 20-25℃.

[0051] In some embodiments, the co-reduction reaction is performed by adding solution A into solution B, and after the reaction is completed, the aging temperature in the aging step is 20-25℃, and the aging time is 4-8h.

[0052] In some embodiments, in the step of adding sodium borohydride into water to obtain solution B, the molar volume ratio of sodium borohydride to water is (2-12) mmol:(30-40) mL.

[0053] The volume ratio of solution A to solution B is (50-60):(30-40).

[0054] In some embodiments, the co-reduction reaction is performed by adding solution A into solution B, and after the reaction is completed, the cobalt-based microgel material is obtained by aging, centrifugation, washing with ethanol and / or water and drying; the drying temperature is 50-80℃, and the drying time is 8-12h.

[0055] In some embodiments, the co-reduction reaction is performed by adding solution A into solution B, and after the reaction is completed, the solid obtained by aging and centrifugation is washed with deionized water and ethanol alternately, and then dried; the drying temperature is 50-80℃, preferably 60℃, and the drying time is 8-12h.

[0056] Based on the same inventive concept, the present application also provides a cobalt-based microgel material prepared by the above preparation method.

[0057] Based on the same inventive concept, the present application also provides the application of the cobalt-based microgel material prepared by the above preparation method or the above cobalt-based microgel material as a catalyst in catalyzing oxidation of sulfite.

[0058] The present application is based on the synergistic effect of sodium borohydride reduction to build microgel structure and regulation of boron loading to optimize catalytic active sites, which effectively improves the catalytic oxidation activity, stability and universality of cobalt-based materials for sulfite. The reason is that the electronic interaction between Co-O-B induced by a specific boron loading changes the electron cloud distribution and bonding environment of Co, which not only effectively regulates the number and distribution of catalytic active sites, but also stabilizes the pore structure of the microgel, thereby promoting efficient contact between sulfite and active sites; in addition, the stable microgel structure formed by the liquid reduction-gelation process can avoid agglomeration or loss of active components, and appropriate boron loading can prevent pore blockage, effectively alleviate the problem of catalytic activity decay under high loading, and adapt to the catalytic needs of different sulfites, thereby widening the application range of the material.

[0059] In some embodiments, the sulfite includes at least one of zinc sulfite, sodium sulfite, ammonium sulfite, and magnesium sulfite; preferably zinc sulfite.

[0060] Specifically, the cobalt-based microgel material of the present application is added as a catalyst to an aqueous sulfite solution, and air is blown in to oxidize the sulfite to sulfate; for example, zinc sulfite, sodium sulfite, ammonium sulfite, and magnesium sulfite are oxidized to zinc sulfate, sodium sulfate, ammonium sulfate, and magnesium sulfate, respectively.

[0061] In some embodiments, the application conditions are as follows: the pH value during the reaction is 7.0-9.0, the reaction temperature is 45-60°C, air is used as the oxidation gas source, and the air flow rate is 0.5-1.5 L / min, preferably 1.0-1.5 L / min.

[0062] In some embodiments, the concentration of the aqueous sulfite solution is 25-100 g / L, and the dosage concentration of the cobalt-based microgel material is 0.25-0.75 mmol / L.

[0063] Specifically, the cobalt-based microgel material of the present application is particularly suitable for use in the zinc-based flue gas desulfurization process, and can efficiently catalyze the oxidation of zinc sulfite (ZnSO3) in the desulfurization slurry to zinc sulfate (ZnSO4). It can operate stably under near-neutral pH (7.0-9.0), moderate temperature (45-60°C), and conventional air blowing intensity, significantly improving the oxidation efficiency and reducing energy consumption.

[0064] In some embodiments, a series of cobalt-based microgel materials CoB-x (x represents the molar ratio) are synthesized by adjusting the molar ratio of n(NaBH4) / n(Co 2+ ) to study the effect of boron loading on the catalytic activity of the cobalt-based microgel material. 2+) The cobalt-based microgel material CoB-1.25 obtained when the molar ratio is 1.25 has the optimal catalytic oxidation performance on zinc sulfite in a simulated zinc desulfurization slurry environment; under the conditions of a ZnSO3 concentration of 50 g / L, a pH of 8.0, a temperature of 45 DEG C, and an air flow rate of 1 L / min, the oxidation rate is as high as 0.122 mmol / L / s, which is more than 3 times higher than that of a non-catalytic system. The catalyst can maintain high activity under wide conditions of a pH of 7.0-9.0 and a temperature of 45-60 DEG C, and has good cycle stability. Compared with commercial Co3O4 powder or a cobalt-based material without a gel structure, the cobalt-based microgel catalyst provided by the application has higher intrinsic activity, better mass transfer efficiency and stronger working condition adaptability, and is suitable for efficient and stable oxidation of sulfite in a wet desulfurization process. The application provides a new material system and preparation idea for developing high-performance and low-cost industrial desulfurization oxidation catalysts.

[0065] The cobalt-based microgel material, the preparation method and the application thereof are further illustrated by specific examples below. This part further illustrates the content of the application in combination with specific examples, but should not be understood as a limitation on the application. If not specifically stated, the technical means adopted in the examples are conventional means familiar to those skilled in the art. Unless specifically stated, the reagents, methods and equipment adopted in the application are conventional reagents, methods and equipment in the art.

[0066] Example 1

[0067] The example provides a preparation method of a cobalt-based microgel material (denoted as CoB-1.25), comprising the following steps:

[0068] S1, 1.164 g (about 4.0 mmol) of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) is accurately weighed and dissolved in 50 mL of deionized water, and is magnetically stirred at room temperature (25 DEG C) until completely dissolved to obtain a uniform pink transparent solution, denoted as solution A;

[0069] S2, 0.1892 g (about 5.0 mmol) of sodium borohydride (NaBH4) is accurately weighed and dissolved in 30 mL of deionized water to obtain a colorless transparent solution, denoted as solution B;

[0070] S3, solution A is added dropwise to solution B at room temperature (25 DEG C) using a constant flow pump at a rate of 3 mL / min. During the dropwise addition process, the mixture quickly turns black and generates a large amount of bubbles, indicating that the reduction reaction occurs rapidly. After the dropwise addition is completed, the aging is continued at room temperature for 6 h to obtain a uniform and stable black suspension;

[0071] S4, centrifugal separation was performed on the suspension obtained in step S3 to collect the solid precipitate; the precipitate was washed with deionized water and anhydrous ethanol alternately for 3 times respectively to completely remove impurity ions and byproducts; the washed wet gel was transferred to an oven and dried at 60°C for 12 hours to obtain a dried cobalt-based microgel material in the form of black powder, namely CoB-1.25 (1.25 in the number represents n(NaBH4) / n(Co 2+ ) molar ratio).

[0072] Example 2

[0073] The present example provides a method for preparing a cobalt-based microgel material (denoted as CoB-0.5), comprising the following steps:

[0074] S1, 1.164 g (about 4.0 mmol) of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) was accurately weighed and dissolved in 50 mL of deionized water, and magnetic stirring was performed at room temperature (25°C) until complete dissolution to obtain a uniform pink transparent solution, denoted as solution A;

[0075] S2, 0.07566 g (about 2.0 mmol) of NaBH4 was accurately weighed and dissolved in 30 mL of deionized water as solution B;

[0076] S3, solution A was added dropwise to solution B at room temperature (25°C) using a constant flow pump at a rate of 3 mL / min; during the dropwise addition process, the mixture quickly turned black and generated a large amount of bubbles, indicating that the reduction reaction occurred rapidly; after the dropwise addition was completed, aging was continued at room temperature for 6 hours to obtain a uniform and stable black suspension;

[0077] S4, centrifugal separation was performed on the suspension obtained in step S3 to collect the solid precipitate; the precipitate was washed with deionized water and anhydrous ethanol alternately for 3 times respectively to completely remove impurity ions and byproducts; the washed wet gel was transferred to an oven and dried at 60°C for 12 hours to obtain a dried cobalt-based microgel material in the form of black powder, namely CoB-0.5 (0.5 in the number represents n(NaBH4) / n(Co 2+ ) molar ratio).

[0078] Example 3

[0079] The present example provides a method for preparing a cobalt-based microgel material (denoted as CoB-3.0), comprising the following steps:

[0080] S1, 1.164 g (about 4.0 mmol) of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) was accurately weighed and dissolved in 50 mL of deionized water, and magnetic stirring was performed at room temperature (25°C) until complete dissolution to obtain a uniform pink transparent solution, denoted as solution A;

[0081] S2, accurately weigh 0.454 g (about 12.0 mmol) NaBH4, dissolve in 30 mL deionized water as solution B;

[0082] S3, at room temperature (25°C), use a constant flow pump to add solution A to solution B at 3 mL / min, during the dropwise addition process, the mixture quickly turns black and produces a large amount of bubbles, indicating that the reduction reaction occurs rapidly; after the dropwise addition is completed, continue to age at room temperature for 6 h, to obtain a uniform and stable black suspension;

[0083] S4, centrifuge the suspension obtained in step S3, collect the solid precipitate; the precipitate is washed with deionized water and anhydrous ethanol alternately for 3 times respectively, to completely remove impurity ions and by-products; transfer the washed wet gel to an oven, dry at 60°C for 12 hours, to obtain a dry black powdery cobalt-based microgel material, namely CoB-3.0 (the number 3.0 in the code represents n(NaBH4) / n(Co 2+ ) molar ratio).

[0084] Example 4

[0085] The present embodiment provides a preparation method of a cobalt-based microgel material (denoted as CoB-0.75), comprising the following steps:

[0086] S1, accurately weigh 1.164 g (about 4.0 mmol) cobalt nitrate hexahydrate (Co(NO3)2·6H2O), dissolve it in 50 mL deionized water, and magnetically stir at room temperature (25°C) until completely dissolved, to obtain a uniform pink transparent solution, denoted as solution A;

[0087] S2, accurately weigh 0.1135 g (about 3.0 mmol) sodium borohydride (NaBH4), dissolve in 30 mL deionized water as solution B;

[0088] S3, at room temperature (25°C), use a constant flow pump to add solution A to solution B at 3 mL / min, during the dropwise addition process, the mixture quickly turns black and produces a large amount of bubbles, indicating that the reduction reaction occurs rapidly; after the dropwise addition is completed, continue to age at room temperature for 6 h, to obtain a uniform and stable black suspension;

[0089] S4, centrifuge the suspension obtained in step S3, collect the solid precipitate; the precipitate is washed with deionized water and anhydrous ethanol alternately for 3 times respectively, to completely remove impurity ions and by-products; transfer the washed wet gel to an oven, dry at 60°C for 12 hours, to obtain a dry black powdery cobalt-based microgel material, namely CoB-0.75 (the number 0.75 in the code represents n(NaBH4) / n(Co 2+ ) molar ratio).

[0090] Example 5

[0091] This embodiment provides a method for preparing a cobalt-based microgel material (denoted as CoB-2.25), including the following steps:

[0092] S1. Accurately weigh 1.164 g (about 4.0 mmol) of cobalt nitrate hexahydrate (Co(NO3)2·6H2O), dissolve it in 50 mL of deionized water, and stir magnetically at room temperature (25℃) until completely dissolved to obtain a homogeneous pink transparent solution, denoted as solution A.

[0093] S2. Accurately weigh 0.3405 g (approximately 9.0 mmol) of sodium borohydride (NaBH4) and dissolve it in 30 mL of deionized water to obtain solution B.

[0094] S3. At room temperature (25℃), solution A was added dropwise to solution B at a constant flow pump at a rate of 3 mL / min. During the addition, the mixture quickly turned black and produced a large number of bubbles, indicating that the reduction reaction occurred rapidly. After the addition was completed, the mixture was aged at room temperature for 6 hours to obtain a uniform and stable black suspension.

[0095] S4. Centrifuge the suspension obtained in step S3 to collect the solid precipitate; wash the precipitate alternately with deionized water and anhydrous ethanol three times each to thoroughly remove impurity ions and byproducts; transfer the washed wet gel to an oven and dry it at 60°C for 12 hours to obtain a dry, black powdery cobalt-based microgel material, namely CoB-2.25 (the 2.25 in the designation represents n(NaBH4) / n(Co)). 2+ (molar ratio).

[0096] Performance testing

[0097] Figure 1 The X-ray diffraction (XRD) patterns of the cobalt-based microgel materials prepared in Examples 1-3 are shown.

[0098] from Figure 1 As can be seen, none of the cobalt-based microgel materials exhibited sharp crystallization diffraction peaks; instead, they displayed broadened diffuse peaks only in the range of approximately 20° to 50°, indicating that the prepared materials have a typical amorphous structure. Comparison with the sharp diffraction peaks of standard Co(OH)₂ (PDF#51-1731) further confirms that the method of this invention successfully suppressed the crystallization process of cobalt species. With increasing boron loading (n(NaBH₄) / n(Co…)… 2+The diffraction patterns always remained amorphous and diffuse from 0.5 to 3.0, indicating that the introduction of boron effectively hindered the growth and ordered arrangement of Co(OH)2crystals, and promoted the formation of short-range ordered and long-range disordered microgel networks. Among them, the diffuse peak shape of CoB-1.25 was the most widened and uniform, indicating that the structural uniformity of the material was best at this ratio, which may be conducive to the formation of more active sites and mesoporous structures, which is consistent with its optimal performance in subsequent catalytic tests. This result confirms from the crystallographic level that the structure of cobalt-based materials can be transformed from crystalline to amorphous by adjusting the boron content, thereby regulating its physical and chemical properties.

[0099] Figure 2 Scanning electron microscope images (SEM) of the cobalt-based microgel materials prepared in Examples 1-3; wherein (a) is the SEM image of CoB-0.5 prepared in Example 2, (b) is the SEM image of CoB-1.25 prepared in Example 1, and (c) is the SEM image of CoB-3.0 prepared in Example 3.

[0100] By comparing Figure 2 It can be seen that the CoB-1.25 material prepared in Example 1 presents a three-dimensional porous network-like microgel morphology, and rich micro-pore structures can be seen on the net wall. The morphology of CoB-0.5 in Example 2 and CoB-3.0 in Example 3 is mainly layered structure. The morphology characteristics of the three materials are related to the n(NaBH4) / n(Co 2+ ) molar ratio, and the concentration of NaBH4 determines the concentration of -OH ions and the H2 release rate in the solution, thereby determining the Co(OH)2crystallization rate and the H2 bubble template concentration, and then affecting the micro-morphology of the cobalt-based microgel product.

[0101] The zinc sulfite catalytic oxidation performance test was conducted on the cobalt-based microgel materials prepared in Examples 1-5. The zinc sulfite (ZnSO3) catalytic oxidation performance evaluation of the catalyst was conducted in a bubbling reactor. Specifically, the catalyst (i.e., the cobalt-based microgel material prepared by the present application) was added to a zinc sulfite aqueous solution, and air was blown in to oxidize the zinc sulfite into zinc sulfate. The basic reaction parameters were as follows: the initial concentration of the zinc sulfite aqueous solution (ZnSO3) was 50 g / L, the catalyst (i.e., the cobalt-based microgel material prepared by the present application) was added at a concentration of 0.5 mmol / L, the reaction temperature was 45°C, the initial pH was 8.0 (adjusted with a NaOH solution), air was used as the oxidant, the air aeration rate was 1.0 L / min, and samples were taken at regular intervals during the reaction. After acidification and constant volume, the sulfuric acid ion concentration in the solution was determined by the barium sulfate turbidimetry method, and the zinc sulfite oxidation reaction rate was calculated accordingly. The calculation method of the oxidation reaction rate was as follows: the sulfuric acid salt concentration generated at different times was counted to obtain a time-sulfate concentration curve, and the oxidation reaction rate (i.e., the sulfuric acid salt concentration generated per unit time) was obtained by fitting the curve.

[0102] Figure 3 The effect of different concentrations (0.25-0.75 mmol / L) of CoB-1.25 on the oxidation rate of zinc sulfite was investigated. The other process parameters were as follows: the initial concentration of zinc sulfite (ZnSO3) was 50 g / L, the reaction temperature was 45°C, the initial pH was 8.0, and air was used as the oxidant at a flow rate of 1.0 L / min.

[0103] As can be seen from Figure 3 , with the increase of the concentration of CoB-1.25, it can be seen that the concentration of CoB-1.25 has a significant effect on the oxidation reaction of ZnSO3. When the concentration of CoB-1.25 is less than 0.5 mmol / L, the oxidation rate of ZnSO3 increases with the increase of the concentration. When the concentration of the catalyst continues to increase, the oxidation rate of ZnSO3 does not increase any more after the concentration reaches 0.75 mmol / L. At this time, the concentration of the catalyst is too high, causing the consumption rate of ZnSO3 in the reaction solution to be too fast, and even all of the ZnSO3 is oxidized to zinc sulfate, resulting in insufficient substrate and thus the oxidation rate of ZnSO3 no longer continues to increase.

[0104] Figure 4 The effect of different concentrations (25-100 g / L) of zinc sulfite aqueous solution on the oxidation reaction rate of zinc sulfite using CoB-1.25 as the catalyst was investigated. The other process parameters were as follows: the CoB-1.25 addition concentration was 0.5 mmol / L, the reaction temperature was 45°C, the initial pH was 8.0, and air was used as the oxidant at a flow rate of 1.0 L / min. As can be seen from Figure 4It can be seen that in the range of 25-75 g / L of zinc sulfite aqueous solution concentration, the oxidation reaction rate of zinc sulfite is basically linearly positively correlated with the substrate concentration, indicating that the reaction is approximately first-order reaction kinetics in this concentration interval, and the reaction rate steadily increases with the increase of substrate concentration, and there is no substrate inhibition phenomenon, which is conducive to maintaining stable oxidation efficiency in the actual high-concentration desulfurization slurry environment.

[0105] Figure 5 In order to use CoB-1.25 as a catalyst, the effect of different air aeration rates (0.5-1.5 L / min) on the oxidation reaction rate of zinc sulfite; wherein the remaining process parameters are: initial concentration of zinc sulfite (ZnSO3) aqueous solution 50 g / L, CoB-1.25 dosage concentration 0.5 mmol / L, reaction temperature 45°C, initial pH 8.0.

[0106] From Figure 5 It can be seen that with the increase of aeration rate from 0.5 L / min to 1.5 L / min, the oxidation reaction rate of zinc sulfite increases significantly, indicating that oxygen mass transfer is one of the key factors affecting the reaction rate. In practical application, the aeration rate of 1.0-1.5 L / min can be selected to balance the oxidation efficiency and energy consumption.

[0107] Figure 6 In order to use CoB-1.25 as a catalyst, the effect of different reaction temperatures (30-60°C) on the oxidation reaction rate of zinc sulfite; wherein the remaining process parameters are: initial concentration of zinc sulfite (ZnSO3) aqueous solution 50 g / L, CoB-1.25 dosage concentration 0.5 mmol / L, initial pH 8.0, air as oxidant, flow rate 1.0 L / min.

[0108] From Figure 6 It can be seen from the above table that with the increase of reaction temperature from 30°C to 60°C, the oxidation reaction rate of zinc sulfite gradually increases, indicating that the increase of temperature is conducive to the acceleration of reaction kinetics. Especially in the interval of 45-60°C, the catalytic activity is maintained at a high level, indicating that CoB-1.25 catalyst has good medium-temperature activity and thermal stability, and is suitable for common desulfurization process temperature window.

[0109] Figure 7 In order to use CoB-1.25 as a catalyst, the effect of different reaction pH (pH 6-9, using H2SO4 or NaOH to adjust pH) on the oxidation rate of zinc sulfite; wherein the remaining process parameters are: initial concentration of zinc sulfite (ZnSO3) 50 g / L, CoB-1.25 dosage concentration 0.5 mmol / L, reaction temperature 45°C, air as oxidant, flow rate 1.0 L / min.

[0110] It can be seen from Figure 7 that the pH has a significant effect on the oxidation rate, reaching a peak near pH 8.0, and decreasing below or above this value. This indicates that a near-neutral environment is most conducive to the stability of active sites on the catalyst surface and the formation of reaction intermediates. This pH characteristic is highly consistent with the common pH range (7.0-9.0) of actual desulfurization slurry, which is conducive to engineering applications.

[0111] Figure 8 The effect of CoB-1.25 on the oxidation rate constant (K value) of different sulfites (zinc sulfite, sodium sulfite, magnesium sulfite); the specific test method is: CoB-1.25 is added to different sulfite (zinc sulfite, sodium sulfite, magnesium sulfite) aqueous solutions, and air is blown in to oxidize the sulfite to sulfate; wherein the reaction parameters are: initial concentration of sulfite aqueous solution 50 g / L, CoB-1.25 dosage concentration 0.5 mmol / L, reaction temperature 45°C, initial pH 8.0 (adjusted with NaOH solution), air as oxidant, air aeration rate 1.0 L / min. The concentration of generated sulfate at different times is calculated, and the oxidation rate constant (K value) is fitted to obtain the results as shown in Figure 8 .

[0112] It can be seen from Figure 8 that the oxidation rate constant of CoB-1.25 on zinc sulfite is 0.122, the oxidation rate constant of CoB-1.25 on magnesium sulfite is 0.263, and the oxidation rate constant of CoB-1.25 on sodium sulfite is 0.310.

[0113] Figure 9 The effect of different catalysts (CoB-0.5, CoB-0.75, CoB-1.25, CoB-2.25, CoB-3.0) on the oxidation rate constant (K value) of zinc sulfite oxidation; the specific test method is: different catalysts (CoB-0.5, CoB-0.75, CoB-1.25, CoB-2.25, CoB-3.0) are added to zinc sulfite aqueous solution, and air is blown in to oxidize the sulfite to sulfate; wherein the reaction parameters are: initial concentration of sulfite aqueous solution 50 g / L, catalyst (CoB-0.5, CoB-0.75, CoB-1.25, CoB-2.25, CoB-3.0) dosage concentration 0.5 mmol / L, reaction temperature 45°C, initial pH 8.0 (adjusted with NaOH solution), air as oxidant, air aeration rate 1.0 L / min. The concentration of generated sulfate at different times is calculated, and the oxidation rate constant (K value) is fitted to obtain the results as shown in Figure 9 .

[0114] From Figure 9It can be seen from the comparison of the sulfate generation kinetics curves and the corresponding reaction rate constants (K values) of different CoB catalysts with different boron loadings with reaction time that, as the boron loading (represented by n(NaBH4) / n(Co 2+ ) increases from 0.5 to 3.0, the oxidation performance of the catalysts shows a trend of first increasing and then decreasing. Specifically, the CoB-1.25 catalyst has the highest reaction rate constant (K = 0.122), and its kinetic curve has the steepest slope, indicating that the amount of sulfate generated is the largest and the catalytic efficiency is the best in the same time. When the boron loading is reduced (CoB-0.5, K = 0.105) or increased (CoB-2.25, K = 0.099; CoB-3.0, K = 0.077), the K value decreases, and the activity decay of CoB-3.0 is particularly significant. The K value of CoB-1.25 is the highest, which is significantly better than that of other CoB materials with different boron loadings. This shows that the amorphous microgel structure obtained by adjusting n(NaBH4) / n(Co 2+ ) = 1.25 has the optimal distribution of active sites and electronic structure, thereby achieving the highest zinc sulfite oxidation efficiency.

[0115] This result further confirms that by precisely adjusting the n(NaBH4) / n(Co 2+ ) molar ratio during the synthesis process, the composition, structure, and performance of the catalyst can be optimized. CoB-1.25, as the optimal composition, achieves the best balance between the number of active sites, intrinsic activity, and mass transfer efficiency in the catalytic oxidation of sulfite, providing a key material basis for its high-performance in desulfurization and other applications.

[0116] Figure 10 To investigate the effect of the oxidation of zinc sulfite to sulfate without adding a catalyst, air was blown into an aqueous zinc sulfite solution to oxidize the sulfite to sulfate. The reaction parameters were an initial concentration of the aqueous sulfite solution of 50 g / L, a reaction temperature of 45°C, an initial pH of 8.0 (adjusted with NaOH solution), air as the oxidant, and an air aeration rate of 1.0 L / min. The concentrations of the generated sulfate at different times were calculated, and the results are shown in Table 1. Figure 10 Table 1 Figure 10 The ordinate in Figure 1 represents the concentration of the generated sulfate.

[0117] Figure 10The curve fitting is carried out, and a fitting equation y = 7.50206 + 0.03231x (wherein y is the concentration of sulfate, and x is time, the correlation coefficient of the fitting equation is 0.99195) is obtained. The oxidation rate constant (K value) without adding the catalyst is about 0.03231, which is far lower than the oxidation rate constant 0.077-0.122 after adding the catalyst, so it is further proved that the cobalt-based microgel material has good catalytic performance, and can catalyze the oxidation of sulfite to sulfate.

[0118] In summary, by regulating the n(NaBH4) / n(Co 2+ ) molar ratio, the cobalt-based microgel catalyst CoB-1.25 with optimal composition and three-dimensional network structure is successfully prepared. The material exhibits high activity, high stability and good working adaptability for sulfite oxidation under mild conditions, far exceeding traditional catalysts and non-catalytic systems, and has broad application prospects in the field of wet desulfurization and the like.

[0119] It can be understood that the technical features of the above-described embodiments can be combined in any manner. In order to make the description concise, all possible combinations of the technical features in the above-described embodiments are not described, however, as long as the combination of the technical features does not exist contradictory, it should be considered as the scope of the present disclosure.

[0120] The above is only a preferred embodiment of the present application, and only the technical principles of the present application are specifically described, and these descriptions are only for explaining the principles of the present application, and cannot be explained as a limitation on the protection scope of the present application in any way. Based on the explanation here, any modification, equivalent replacement and improvement made within the spirit and principle of the present application, and other specific embodiments of the present application which can be conceived by those skilled in the art without creative labor, should be included in the protection scope of the present application.

Claims

1. A method for the preparation of a cobalt-based microgel material, characterized in that, Includes the following steps: Cobalt salt is added to water to obtain solution A; Sodium borohydride was added to water to obtain solution B; Solution A was added dropwise to solution B to carry out a co-reduction reaction. After the reaction was completed, the material was aged, centrifuged, washed, and dried to obtain a cobalt-based microgel material. The molar ratio of sodium borohydride to cobalt in the cobalt salt is (0.5~3.0):

1.

2. The method of claim 1, wherein the cobalt-based microgel material is prepared by the process comprising: The molar ratio of sodium borohydride to cobalt in the cobalt salt is 1.25:

1.

3. The method of claim 1, wherein the cobalt-based microgel material is prepared by the process comprising: The cobalt salt includes at least one of cobalt nitrate, cobalt sulfate, and cobalt chloride.

4. The method for preparing the cobalt-based microgel material as described in claim 1, characterized in that, At 20~25℃, solution A is added dropwise to solution B at a rate of 1~5 mL / min to carry out a co-reduction reaction.

5. The method for preparing the cobalt-based microgel material as described in claim 1, characterized in that, Solution A is added dropwise to solution B to carry out a co-reduction reaction. After the reaction is completed, an aging step is performed with an aging temperature of 20~25℃ and an aging time of 4~8h.

6. The method of claim 1, wherein the cobalt-based microgel material is prepared by the process comprising: In the step of adding sodium borohydride to water to obtain solution B, the molar volume ratio of sodium borohydride to water is (2~12) mmol:(30~40) mL; The volume ratio of solution A to solution B is (50~60):(30~40).

7. The method for preparing the cobalt-based microgel material as described in claim 1, characterized in that, Solution A was added dropwise to solution B to carry out a co-reduction reaction. After the reaction was completed, the material was aged, centrifuged, washed with ethanol and / or water, and then dried to obtain cobalt-based microgel material. The drying temperature was 50~80℃ and the time was 8~12 h.

8. A cobalt-based microgel material, characterized in that, It is prepared by any one of the preparation methods described in claims 1 to 7.

9. The application of a cobalt-based microgel material prepared by any one of the preparation methods described in claims 1 to 7, or the cobalt-based microgel material described in claim 8, in the catalytic oxidation of sulfite.

10. The application as described in claim 9, characterized in that, The sulfite includes at least one of zinc sulfite, sodium sulfite, ammonium sulfite, and magnesium sulfite; The application conditions are as follows: pH value of 7.0~9.0, reaction temperature of 45~60℃, air as the oxidizing gas source, and air flow rate of 0.5~1.5 L / min.

Images