A catalyst for reduction recovery of sulfur dioxide and a synthesis method and application thereof

Abstract

The application discloses a catalyst for reducing and recovering sulfur dioxide and a synthesis method and application thereof, and belongs to the technical field of waste recovery. The catalyst for reducing and recovering sulfur dioxide comprises nitrogen-doped carbon microspheres and metal sulfides on surfaces of the carbon microspheres. The catalyst can obtain a catalytic performance equivalent to that of a platinum / carbon catalyst, has a lower price and a longer service life. The application further provides a synthesis method and application of the catalyst.

Description

Technical Field

[0001] This invention relates to the field of waste gas recovery technology, and in particular to a catalyst for the reduction and recovery of sulfur dioxide, its synthesis method, and its application. Background Technology

[0002] Metallurgical enterprises and thermal power plants generate large amounts of flue gas containing sulfur dioxide (SO2 concentration ranging from 500 to 3000 ppm). Direct emission into the atmosphere causes environmental problems such as acid rain, ozone layer depletion, and sulfuric acid fumes. Currently, sulfur dioxide is often treated using liquid solvent absorption. For example, flue gas desulfurization processes using ammonia or wet limestone as adsorbents can remove approximately 90-95% of the sulfur dioxide from flue gas. However, these flue gas desulfurization processes suffer from a series of problems, including high energy consumption, equipment corrosion, fine particulate pollution, and the generation of large amounts of wastewater and waste residue. Furthermore, the adsorbed sulfur dioxide cannot be recovered from these absorbents, leading to a significant waste of sulfur resources. As an important raw material for the synthesis of sulfur-containing fine chemicals, sulfur dioxide itself has high market value. Against this backdrop, it is essential to develop a new, environmentally friendly, and clean desulfurization process that simultaneously achieves sulfur resource recovery.

[0003] Compared to traditional flue gas desulfurization technologies, electrochemical methods for treating sulfur dioxide flue gas offer several advantages. Firstly, they reduce the use of chemical reagents such as sodium hydroxide, resulting in less environmental pollution. Secondly, they are easy to operate, consume less energy, and operate under mild reaction conditions. More importantly, by adjusting voltage and current at room temperature, they can selectively catalytically convert sulfur dioxide into high-value-added sulfur-containing chemicals, simultaneously achieving sulfur dioxide emission reduction and sulfur resource recovery. However, a key issue in this conversion process is the selection of electrode materials; more specifically, the choice of catalyst type. Currently, most commercially available sulfur dioxide catalytic conversion materials are based on platinum / carbon catalysts. Their high cost significantly limits their practical industrial application, and the corrosive nature of sulfur dioxide severely damages the lifespan of platinum-carbon catalysts, making them difficult to recover, further increasing catalyst costs and environmental pollution.

[0004] In summary, it is crucial to find a low-cost catalytic material that can rival the catalytic performance of platinum / carbon and also possesses high stability. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a catalyst for the reduction and recovery of sulfur dioxide, which can achieve catalytic performance comparable to platinum / carbon catalysts, but at a lower cost and with a longer lifespan.

[0006] The present invention also provides a method for synthesizing the above-mentioned catalyst.

[0007] The present invention also provides an electrode comprising the above-described catalyst.

[0008] The present invention also provides a method for preparing the above-mentioned electrode.

[0009] The present invention also provides a method for reducing and recovering sulfur dioxide using the above-described electrodes.

[0010] According to an embodiment of a first aspect of the present invention, a catalyst for the reduction and recovery of sulfur dioxide is provided, the catalyst comprising nitrogen-doped carbon microspheres and metal sulfides on the surface of the carbon microspheres.

[0011] The catalyst according to embodiments of the present invention has at least the following beneficial effects:

[0012] Carbon microspheres enhance the adsorption of sulfur dioxide molecules by the catalyst; nitrogen doping in the carbon microspheres significantly improves the conductivity of the catalyst; nitrogen doping also helps to change the electronic structure of carbon and metal elements at the doping sites, promoting electron transfer reactions, accelerating the adsorption and activation of sulfur dioxide molecules, and improving catalytic performance; metal sulfides have excellent catalytic activity; the catalyst exhibits excellent performance in the reduction and recovery of sulfur dioxide. Specifically, the catalyst provided by this invention has catalytic activity for sulfur dioxide comparable to that of platinum / carbon, but its hydrogen evolution activity is inferior to that of platinum / carbon catalysts; it also has advantages such as a wide reduction potential window, strong resistance to sulfur poisoning, long lifetime, and low cost. Therefore, the catalyst provided by this invention significantly suppresses side reactions while ensuring high catalytic activity; and the yield of sulfur per unit time is higher, making it a highly promising new catalyst to replace platinum / carbon materials.

[0013] According to some embodiments of the present invention, the metal sulfide comprises Co9S8. The metal sulfide has a flocculent structure.

[0014] According to some embodiments of the present invention, the metal sulfide is in a crystalline state.

[0015] According to some embodiments of the present invention, the particle size of the carbon microspheres is 10–30 μm.

[0016] According to some embodiments of the present invention, the carbon content in the catalyst is 90-95 wt%. For example, it can be 92-93 wt%.

[0017] According to some embodiments of the present invention, the metal content in the catalyst is 1 to 2 wt%. For example, it may be about 1.2 wt% or 1.3 wt%.

[0018] According to some embodiments of the present invention, the sulfur content in the catalyst is 2-3 wt%. Specifically, it may be about 2.5 wt% or 2.8 wt%.

[0019] According to some embodiments of the present invention, the nitrogen content in the catalyst is 3 to 4 wt%. For example, it may be about 3.5 wt% or 3.8 wt%.

[0020] According to some embodiments of the present invention, the SO2 reduction potential window of the catalyst is -0.3 to 0.05 V (vsRHE). This represents a potential window 0.1 V larger than that of conventional commercial platinum / carbon electrodes.

[0021] According to some embodiments of the present invention, the catalyst is a black solid.

[0022] According to an embodiment of a second aspect of the present invention, a method for synthesizing the catalyst is provided, the method comprising mixing and calcining a sulfur-containing organometallic compound and a nitrogen-containing organic compound in a protective atmosphere.

[0023] The mechanism of the synthesis method is as follows: the nitrogen-containing organic matter serves as a solid carbon / nitrogen source to increase the nitrogen / carbon content. At high temperature, through in-situ carbonization / nitridation, the carbon in the nitrogen-containing organic matter is converted into nitrogen-doped carbon microspheres, forming a heterogeneous structure in which metal sulfides encapsulate the carbon microspheres.

[0024] The raw materials used in this invention include sulfur-containing organometallic compounds, which have unique metal-ligand interactions and 3d unoccupied orbitals that can accommodate foreign electrons. Therefore, the catalysts prepared have excellent potential for catalytic reduction of sulfur dioxide.

[0025] The synthesis method provided by this invention is simple to operate, and the resulting catalyst exhibits excellent catalytic activity and anti-poisoning properties, which is of great significance for the industrial application and sustainable development of catalysts for purifying sulfur dioxide flue gas.

[0026] According to some embodiments of the present invention, the sulfur-containing organometallic material includes at least one selected from (C3H6NS2)2Co, (C3H6NS2)2Ni, and (C3H6NS2)2Fe. More specifically, it may be (C3H6NS2)2Co. The sulfur-containing organometallic material serves as both a metal source and a sulfur source.

[0027] According to some embodiments of the present invention, the nitrogen-containing organic compound includes at least one selected from polyacrylonitrile, melamine, dicyandiamide, and urea. More specifically, it may be polyacrylonitrile. The nitrogen-containing organic compound serves as a solid carbon and nitrogen source, which can increase the nitrogen / carbon content in the resulting catalyst and improve the material's electrical conductivity and catalytic performance.

[0028] According to some embodiments of the present invention, the mass ratio of the sulfur-containing organometallic compound to the nitrogen-containing organic compound is 0.5–1.2:0.8. Specifically, it can be 1.1:0.8. Specifically, it can be approximately 1:1.

[0029] According to some embodiments of the present invention, when the nitrogen-containing organic compound is polyacrylonitrile, the weight-average molecular weight of the polyacrylonitrile is 120,000 to 180,000. For example, it can be about 150,000.

[0030] According to some embodiments of the present invention, the temperature of the mixed calcination is 600–1200°C.

[0031] According to some embodiments of the present invention, the temperature of the mixed calcination is 900–1100°C. Specifically, it can be about 1000°C.

[0032] According to some embodiments of the present invention, the duration of the mixed roasting is 90 to 120 minutes. For example, it can be approximately 120 minutes.

[0033] According to some embodiments of the present invention, the heating rate of the mixed roasting is 2 to 10 °C / min.

[0034] According to some embodiments of the present invention, the heating rate of the mixed calcination is 2 to 5 °C / min.

[0035] According to some embodiments of the present invention, the protective atmosphere includes at least one of vacuum, argon, and nitrogen. Specifically, it may be argon.

[0036] According to some embodiments of the present invention, the synthesis method further includes washing and drying sequentially after the mixing and calcination.

[0037] According to some embodiments of the present invention, the washing includes sequentially performing a dilute sulfuric acid wash, a water wash, and an alcohol wash. The concentration of the dilute sulfuric acid used in the dilute sulfuric acid wash is 0.3–1.5 g / L. For example, it can be approximately 0.5 g / L. More specifically, the duration of the dilute sulfuric acid wash is 3–10 minutes, and more specifically, it can be approximately 5 minutes.

[0038] According to some embodiments of the present invention, the total washing time is 20 to 40 minutes.

[0039] According to some embodiments of the present invention, the drying temperature is 50–80°C. Specifically, it can be about 60°C.

[0040] According to an embodiment of a third aspect of the present invention, an electrode for reducing and recovering sulfur dioxide is provided, the electrode comprising a conductive substrate and a catalyst supported on the conductive substrate.

[0041] Since the electrode employs all the technical solutions of the catalysts described in the above embodiments, it possesses at least all the beneficial effects brought about by the technical solutions of the above embodiments. That is, the electrode has advantages such as a wide operating potential, low potential, long lifespan, and high sulfur yield during the catalytic reduction and recovery of sulfur dioxide.

[0042] According to some embodiments of the present invention, the conductive substrate includes at least one selected from glassy carbon electrode, stainless steel sheet, stainless steel mesh, carbon paper, copper mesh, and copper sheet. Specifically, it may be a stainless steel mesh.

[0043] According to some embodiments of the present invention, the apparent area of ​​one side of the electrode is 0.25 to 3 cm². 2 For example, it could be approximately 2cm. 2 .

[0044] According to an embodiment of a fourth aspect of the present invention, a method for preparing the electrode is provided, the method comprising coating a slurry containing the catalyst onto the conductive substrate.

[0045] Since the preparation method employs all the technical solutions of the electrodes described in the above embodiments, it possesses at least all the beneficial effects brought about by the technical solutions of the above embodiments. Furthermore, the use of a slurry coating method makes it easier to control the amount of catalyst used, minimizes material consumption, and can also improve the bonding strength between the catalyst and the conductive substrate, thereby increasing the conductivity of the electrode.

[0046] According to some embodiments of the present invention, the slurry further includes a liquid phase component.

[0047] According to some embodiments of the present invention, the liquid phase composition includes ethanol, N-methylpyrrolidone, and a 5 wt% Nafion solution. The volume ratio of ethanol to N-methylpyrrolidone is 1.5–2.5:1; specifically, it can be 2–2.1:1. The mass ratio of ethanol to the 5 wt% Nafion solution is 15–25:1; specifically, it can be 19–20:1.

[0048] The 5wt% Nafion solution contains Nafion (CAS: 31175-20-9) as the solute and a mixture of ethanol and water in a mass ratio of 55:45 as the solvent.

[0049] The 5wt% Nafion solution also acts as a binder, increasing the bonding strength between the catalyst and the conductive matrix.

[0050] According to some embodiments of the present invention, the solid-liquid ratio of the slurry is 1g:5 to 20mL. For example, it can be approximately 1g:15mL.

[0051] According to some embodiments of the present invention, the method for preparing the slurry includes mixing the components of the slurry. The mixing method includes grinding. Specifically, the grinding time is 2-5 minutes. In actual production, this time is not strictly limited, as long as a viscous liquid is formed.

[0052] According to some embodiments of the present invention, the temperature of the slurry is 20–37°C. Specifically, it can be about 25°C.

[0053] According to some embodiments of the present invention, the area of ​​the paste coating on the conductive substrate is 0.25 to 2 cm². 2 For example, it could be approximately 1cm. 2 .

[0054] According to some embodiments of the present invention, the preparation method further includes drying after coating.

[0055] According to some embodiments of the present invention, the drying process in the preparation method is carried out at a temperature of 60–80°C.

[0056] According to some embodiments of the present invention, the drying process in the preparation method lasts for 12 to 24 hours.

[0057] According to some embodiments of the present invention, the drying process in the preparation method includes vacuum drying.

[0058] According to an embodiment of the fifth aspect of the present invention, a method for reducing and recovering sulfur dioxide is provided, the method comprising electrolyzing sulfur dioxide introduced into an electrolyte using the electrode as a cathode.

[0059] The mechanism of the method involves first adsorbing sulfur dioxide from the electrolyte onto the catalyst surface, and then reducing the sulfur dioxide to sulfur under the action of metal sulfides and electrolysis. The specific mechanism is as follows:

[0060] SO2 + 4e - +4H + →2H2O+S↓.

[0061] The method according to embodiments of the present invention has at least the following beneficial effects:

[0062] In actual production, the capacity for sulfur dioxide reduction and recovery can be adjusted by regulating the voltage and current of the electrolysis. Furthermore, the method provided by this invention can achieve both sulfur dioxide removal from flue gas and the resource recovery of sulfur. Sulfur has a higher value, significantly improving economic benefits and promoting the green concept of waste resource utilization. Specifically:

[0063] (1) In the traditional Cluas sulfur production process, the process gas needs to undergo multiple cooling, capture, and desulfurization processes, which is cumbersome and requires additional tail gas treatment equipment. This invention converts sulfur dioxide into sulfur through one-step electrochemical electrolysis. Compared to traditional methods, this is simpler to operate, requires no large amounts of chemical reagents, reduces the generation of waste residue and waste liquid, and improves the environmental friendliness of the sulfur production process. On the other hand, the direct emission of sulfur dioxide pollutants from flue gas not only causes significant environmental pollution but also results in a large waste of sulfur resources. This invention uses sulfur dioxide as a raw material for sulfur production, enabling resource-based sulfur production and turning waste into treasure, which has high economic benefits and broad market prospects.

[0064] (2) While commercial platinum / carbon materials, as cathode catalysts, exhibit high electrocatalytic activity, their high selectivity for the hydrogen evolution reaction (HER) leads to interference from HER side reactions and a narrow SO2 reduction potential window during the electroreduction of sulfur dioxide to produce sulfur (SO2RR). This invention, through a catalyst preparation method and the synergistic effect of its components, produces a catalyst with catalytic activity comparable to commercial platinum / carbon materials, but with stronger resistance to sulfur poisoning and a wider sulfur dioxide reduction potential window, effectively suppressing the HER side reaction. Compared to commercial platinum / carbon catalysts, the preferred metal-based carbon / nitrogen material catalyzes higher sulfur yields and lower energy consumption per unit, making it a promising new catalyst to replace platinum / carbon materials.

[0065] According to some embodiments of the present invention, the anode used in the electrolysis is an inert electrode. For example, it can be a platinum electrode.

[0066] According to some embodiments of the present invention, the electrolysis temperature is 15–40°C. Specifically, it can be about 25°C.

[0067] According to some embodiments of the present invention, the electrolysis time is 30 to 120 minutes. For example, it can be approximately 60 minutes.

[0068] According to some embodiments of the present invention, the electrolyte includes one of sulfuric acid, hydrochloric acid, potassium hydroxide, sulfate, and phosphate buffer. For example, it may specifically be sulfuric acid.

[0069] According to some embodiments of the present invention, the pH of the electrolyte is 0 to 14.

[0070] According to some embodiments of the present invention, the pH of the electrolyte is 0 to 2.0.

[0071] According to some embodiments of the present invention, the electrolyte is at least one of an aqueous solution of sulfuric acid and an aqueous solution of hydrochloric acid.

[0072] According to some embodiments of the present invention, the concentration of the solute in the electrolyte is 0.005 to 1 mol / L.

[0073] According to some embodiments of the present invention, the electrolyte is an aqueous sulfuric acid solution with a concentration of 0.005–0.5 mol / L. Specifically, the concentration of the aqueous sulfuric acid solution is approximately 0.5 mol / L.

[0074] According to some embodiments of the present invention, a carrier gas is also introduced into the electrolyte along with the sulfur dioxide. The carrier gas is argon.

[0075] The mixture of sulfur dioxide and the carrier gas is referred to as a gas.

[0076] According to some embodiments of the present invention, the gas flow rate is 10 to 80 sccm.

[0077] According to some embodiments of the present invention, the gas flow rate is 50 to 70 sccm.

[0078] According to some embodiments of the present invention, the volume concentration of sulfur dioxide in the gas is 2% to 10%. Specifically, it can be about 5%.

[0079] According to some embodiments of the present invention, the electrolysis current is 0 to -0.1A.

[0080] According to some embodiments of the present invention, the electrolysis current is 0 to -80 mA.

[0081] According to some embodiments of the present invention, the electrolysis current is -15 to -55 mA.

[0082] According to some embodiments of the present invention, the voltage of the electrolysis is 0.2 to -0.8V (vs. RHE).

[0083] According to some embodiments of the present invention, the voltage of the electrolysis is 0.2 to -0.6V (vs. RHE).

[0084] According to some embodiments of the present invention, the voltage of the electrolysis is 0.1 to -0.5V (vs. RHE). Specifically, it can be about -0.1V, -0.2V, -0.3V or -0.4V.

[0085] Within the aforementioned voltage and current range, the start and stop processes of the electrolysis reaction can be controlled to avoid reactions such as hydrogen evolution and oxygen evolution, and to selectively convert sulfur dioxide into sulfur with high added value.

[0086] According to some embodiments of the present invention, the yield of sulfur synthesized by electrolysis of SO2 is 100-200 μmol / mgh of catalyst. For example, it can be about 110 μmol / mgh, 120 μmol / mgh, 130 μmol / mgh, 140 μmol / mgh, 150 μmol / mgh or 190 μmol / mgh.

[0087] According to some embodiments of the present invention, the unit energy consumption of the electrolysis of sulfur is 1.4 to 4.1 kWh / kg. For example, it can be approximately 1.5 kWh / kg, 2.0 kWh / kg, 2.4 kWh / kg, 2.5 kWh / kg, 2.8 kWh / kg, 3.0 kWh / kg, or 4.0 kWh / kg.

[0088] According to some embodiments of the present invention, the electrolysis product, including sulfur, is a pale yellow solid.

[0089] According to some embodiments of the present invention, the method further includes, after electrolysis, performing solid-liquid separation, washing with water to obtain a solid product, and drying the obtained solid product.

[0090] The solid-liquid separation method includes filtration. The filtration uses an aqueous organic PTFE nylon filter membrane; more specifically, the pore size of the aqueous organic PTFE nylon filter membrane is 0.2–0.45 μm. For example, it can be approximately 0.22 μm.

[0091] The washing time for the resulting solid product is not strictly limited, as long as it effectively removes residual electrolyte. For example, it could be a 10-minute wash, or 3-5 washes.

[0092] The temperature at which the solid product is obtained after drying is 50–80°C. For example, it could be approximately 60°C. The drying time is not strictly limited; for example, it could be approximately 1 hour.

[0093] Unless otherwise specified, "room temperature" in this invention means 25℃±2℃.

[0094] Unless otherwise specified, the term "about" in this invention actually means that the error is allowed to be within ±2%, for example, about 100 is actually 100 ± 2% × 100.

[0095] Unless otherwise specified, "between" in this invention includes the number itself, for example, "between 2 and 3" includes the endpoint values ​​2 and 3.

[0096] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0097] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0098] Figure 1 These are the SEM test results of the catalysts obtained in Example 1(a) and Comparative Example 1(b) of this invention.

[0099] Figure 2 These are the XRD test results of the catalysts obtained in Example 1 and Comparative Example 1 of this invention.

[0100] Figure 3 These are the XPS test results of the catalysts obtained in Example 1 and Comparative Example 1 of this invention.

[0101] Figure 4 The results are linear sweep voltammetry test results of the catalysts obtained in Example 1 and Comparative Example 1 of this invention with commercial 20% Pt / C in SO2RR.

[0102] Figure 5 The double-layer capacitance curves of the catalysts obtained in Example 1 and Comparative Example 1 of this invention and commercial 20% Pt / C in SO2RR are shown.

[0103] Figure 6 The results are the stability test results of the catalyst obtained in Example 1 of this invention and commercial 20% Pt / C in SO2RR.

[0104] Figure 7 The result is the XRD test result of the pale yellow solid described in Example 3 of this invention.

[0105] Figure 8 This is the Raman spectrum of the pale yellow solid described in Example 3 of this invention. Detailed Implementation

[0106] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0107] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0108] The (C3H6NS2)2Co used in the following examples was obtained by the following processing method:

[0109] 10.5 g of sodium dimethyl dithiocarbamate (CAS: 128-04-1) and 10.2 g of CoSO4·7H2O were mixed in 100 mL of water and stirred at room temperature for 1 h. The mixture was then filtered to obtain a green solid. The solid was then washed 3-5 times with deionized water and ethanol at room temperature and dried at 80 °C to obtain (C3H6NS2)2Co material.

[0110] Example 1

[0111] This embodiment prepares a catalyst for the reduction and recovery of sulfur dioxide, and the specific steps are as follows:

[0112] Grind and mix 1.1g of (C3H6NS2)2Co with 0.8g of polyacrylonitrile (CAS: 25014-41-9, Mw = 150,000, Sigma-Aldrich) until homogeneous;

[0113] The resulting mixture was heated to 1000℃ for 2 hours under an argon atmosphere at a heating rate of 5℃ / min.

[0114] The calcined product was washed in 0.5 g / L sulfuric acid for 5 min, and then washed with deionized water and ethanol to remove residual sulfuric acid and impurities. It was dried at 60 °C overnight to obtain a black solid catalyst (abbreviated as MN / C-0.8).

[0115] Example 2

[0116] This embodiment prepares an electrode, and the specific steps are as follows:

[0117] At room temperature, 15 mg of the catalyst obtained in Example 1, 195 μL of ethanol, 95 μL of N-methylpyrrolidone, and 10 μL of 5% Nafion solution were ground for 2–5 min to form a slurry, which was then coated onto a 2 cm thick surface. 2 The electrode is obtained by vacuum drying at 80°C overnight (about 15 hours) on a stainless steel mesh electrode.

[0118] Example 3

[0119] This embodiment provides a method for reducing and recovering sulfur dioxide, the specific steps of which are as follows:

[0120] The electrode obtained in Example 2 was used as the cathode, the platinum sheet as the anode, and a 0.5 mol / L sulfuric acid aqueous solution as the electrolyte;

[0121] 5% sulfur dioxide gas (sulfur dioxide + argon, sulfur dioxide volume percentage 5%, flow rate 50 sccm) was continuously introduced into the electrolyte, and electrolysis was performed at room temperature under constant potential (E = -0.1V vs RHE), with the current fluctuating within the range of -0.02 to -0.08A. The electrolysis product was filtered through a 0.22μm (pore size) aqueous organic PTFE nylon filter membrane, washed 3–5 times with deionized water, and dried at approximately 60°C for 1 hour to obtain a pale yellow solid.

[0122] Example 4

[0123] This embodiment provides a method for reducing and recovering sulfur dioxide. The specific steps differ from those in Embodiment 3 in that:

[0124] The electrolysis was performed at a constant potential of -0.2V.

[0125] Example 5

[0126] This embodiment provides a method for reducing and recovering sulfur dioxide. The specific steps differ from those in Embodiment 3 in that:

[0127] The electrolysis was performed at a constant potential of -0.3V.

[0128] Example 5

[0129] This embodiment provides a method for reducing and recovering sulfur dioxide. The specific steps differ from those in Embodiment 3 in that:

[0130] The electrolysis was performed at a constant potential of -0.4V.

[0131] Comparative Example 1

[0132] This example prepares a catalyst for the reduction and recovery of sulfur dioxide. The specific process differs from that in Example 1 in that:

[0133] The mixture used for calcination does not include polyacrylonitrile, and the resulting catalyst is referred to as MN / C-0.

[0134] Comparative Example 2

[0135] This example prepares an electrode, and the specific steps differ from those in Example 2 in that:

[0136] The catalyst used was from Comparative Example 1.

[0137] Comparative Example 3

[0138] This example provides a method for reducing and recovering sulfur dioxide. The specific steps differ from those in Example 3 in that:

[0139] The electrodes used were from Comparative Example 2.

[0140] Comparative Example 4

[0141] This example provides a method for reducing and recovering sulfur dioxide. The specific steps differ from those in Example 4 in that:

[0142] The electrodes used were from Comparative Example 2.

[0143] Comparative Example 5

[0144] This example provides a method for reducing and recovering sulfur dioxide. The specific steps differ from those in Example 5 in that:

[0145] The electrodes used were from Comparative Example 2.

[0146] Comparative Example 6

[0147] This example provides a method for reducing and recovering sulfur dioxide. The specific steps differ from those in Example 6 in that:

[0148] The electrodes used were from Comparative Example 2.

[0149] Comparative Example 7

[0150] This example provides a method for reducing and recovering sulfur dioxide, with the following specific steps:

[0151] S1. At room temperature, grind 15 mg of commercial 20% Pt / C powder, 195 μL of ethanol, 95 μL of N-methylpyrrolidone, and 10 μL of 5% Nafion solution for 2–5 min to prepare a slurry, and apply it to a 2 cm thick surface. 2 A 20% Pt / C electrode was obtained by vacuum drying overnight at 80°C on a stainless steel mesh electrode.

[0152] S2. 5% sulfur dioxide gas (sulfur dioxide + argon, sulfur dioxide volume percentage 5%) is introduced into a 0.5 mol / L sulfuric acid electrolyte. The electrode obtained in step S1 is used as the cathode, and a platinum sheet as the anode. Electrolysis is performed at room temperature under constant potential (E = -0.1 V vs RHE). The electrolysis product is filtered through a 0.22 μm (pore size) aqueous organic PTFE nylon filter membrane, washed 3–5 times with deionized water, and dried for 1 hour to obtain a pale yellow solid.

[0153] Test Example 1

[0154] In this example, the structure, morphology, crystallinity, and elemental composition of the catalysts obtained in Example 1 and Comparative Example 1 were tested using SEM, XRD, and XPS, respectively. The results showed that the catalyst obtained by calcining (C3H6NS2)2Co alone exhibited a large number of disordered flocculent structures; while the incorporation of polyacrylonitrile introduced a large amount of carbon / nitrogen source, resulting in a material with a large number of carbon / nitrogen spheres in addition to the basic flocculent structure, with carbon sphere diameters ranging from 10 to 30 μm. The presence of these carbon / nitrogen spheres effectively promoted the adsorption and activation of sulfur dioxide molecules on the surface of the obtained catalyst, enhancing the electrocatalytic activity of the material. Specific test results are as follows: Figure 1 As shown; where Figure 1 (a) shows the morphology of the catalyst obtained in Example 1. Figure 1 (b) shows the morphology of the catalyst obtained in Comparative Example 1.

[0155] The phase composition and crystallization state of the obtained catalyst were obtained by XRD testing. The XRD results showed that the cobalt-based catalyst prepared in this invention consisted only of the Co9S8 phase, without any other impurity phases. The diffraction peaks at 29.8, 31.3, 39.5, 44.6, 47.6, 52.0, 60.9, and 61.9 were attributed to the (311), (222), (331), (422), (511), (440), (533), and (622) crystal planes of cubic Co9S8, respectively. Specific test results are as follows... Figure 2 As shown.

[0156] The composition of other elements in the catalysts obtained in Example 1 and Comparative Example 1 was obtained by XPS analysis. The results showed that the polyacrylonitrile in the synthesis raw materials mainly existed in the form of carbon / nitrogen (nitrogen-doped carbon microspheres) after high-temperature calcination. Specifically, the C1s peak of the catalyst prepared in Example 1 was significantly stronger than that in Comparative Example 1, and the carbon / nitrogen content increased by 9.84% and 0.57%, respectively. Correspondingly, the carbon / nitrogen material obtained from the pyrolysis of polyacrylonitrile, as a supporting substrate, could disperse the Co9S8 particles. Therefore, the intensity peaks of Co2p3 and S2p in the XPS spectrum decreased slightly, and the elemental contents also decreased to 1.23% and 2.74%, respectively. Specific test results are as follows: Figure 3 As shown in Table 1.

[0157] Table 1. Percentage (%) of each element in the catalysts obtained in Example 1 and Comparative Example 1

[0158] Group Co S N C Example 1 1.23 2.74 3.71 92.31 Comparative Example 1 6.20 8.19 3.14 82.47

[0159] Test Example 2

[0160] This example aims to evaluate the SO2RR catalytic performance and stability of the catalysts obtained in Example 1, Comparative Example 1, and the commercial 20% Pt / C powder catalyst used in Comparative Example 7. Specific test methods are as follows:

[0161] Take 5 mg of the above catalyst, 495 μL of anhydrous ethanol, 495 μL of deionized water, and 10 μL of Nafion and disperse them separately by sonication for at least 45 min. Then, transfer 10 μL of the suspension and drop it onto a 1×1 cm plate. 2 The stainless steel mesh electrode, after drying, was used as the working electrode. An electrochemical workstation and a three-electrode system (platinum sheet as counter electrode and Ag-AgCl as reference electrode) were used to perform linear scan voltammetry, chronoamperometry, and cyclic voltammetry at different scan rates in 0.5 mol / L H2SO4 solution, and the double-layer capacitance curve was obtained.

[0162] Linear sweep voltammetry (LSV, scan rate 10 mV / s, voltage range 0.2 to -0.6 V vs RHE) results showed that the catalyst obtained in Example 1 only underwent hydrogen evolution reaction (HER) in a pure argon atmosphere. After introducing sulfur dioxide, a very obvious SO2 reduction peak appeared in the range of -0.3 to 0.05 V. Compared with the commercial Pt / C catalyst, its SO2 reduction potential window increased by 0.1 V, and the HER potential shifted significantly negatively, indicating that the catalyst obtained in Example 1 can effectively inhibit the HER reaction. In the range of -0.2 to 0.05 V, the LSV curve of the catalyst obtained in the example basically coincided with that of 20% Pt / C, indicating that it has SO2RR catalytic activity comparable to that of the commercial Pt / C catalyst. Comparing the test results of the catalysts obtained in Example 1 and Comparative Example 1, it can be seen that the inclusion of nitrogen-containing organic matter in the raw materials, i.e., the inclusion of nitrogen-doped carbon microspheres in the product, helps to improve the catalytic activity of the material. Specific test results are as follows: Figure 4 As shown.

[0163] The double-layer capacitance (test voltage 0.1–0.2 V vs RHE) can be used to evaluate the size of the electrochemical active area of ​​a catalyst. A larger capacitance value indicates a larger electrochemical active area and higher electrocatalytic activity. Comparing the double-layer capacitance curves of the catalysts in Example 1 and Comparative Example 1 shows that the catalyst obtained in Example 1 has a larger electrochemical active area than the catalyst obtained in Comparative Example 1, and its electrocatalytic activity is even slightly higher than that of the commercial Pt / C electrode. This is because the presence of nitrogen-doped carbon microspheres provides a large number of SO2 adsorption sites for the catalyst; simultaneously, the nitrogen-doped carbon microspheres, as a support, effectively disperse the Co9S8 particles, thereby improving the utilization rate of the Co9S8 material. Therefore, overall, the catalyst obtained in Example 1 exhibits a larger electrochemical active area than the catalyst obtained in Comparative Example 1 and the commercial Pt / C catalyst. Specific test results are as follows: Figure 5 As shown.

[0164] This invention also used a chronoamperometry method (test voltage -0.3V vs RHE) to test the current retention rate of the catalyst obtained in the examples and the commercial Pt / C catalyst within 3600 s to evaluate their stability in the SO2RR reaction process. The results showed that the catalyst obtained in the examples had stronger resistance to sulfur poisoning and a longer lifespan than the commercial Pt / C catalyst. Specifically, the Pt / C catalyst experienced a sharp decline in current around 2000 s due to sulfur poisoning, and the current retention rate was only 50% after 3600 s; in contrast, the catalyst obtained in Example 1 showed a slight decrease in current around 3000 s, and the current retention rate still reached 85% after 3600 s. This may be because metallic Pt is more prone to sulfidation with the product sulfur than Co9S8, thus losing its activity. Specific test results are as follows... Figure 6 As shown.

[0165] Test Example 3

[0166] In this example, XRD and Raman spectroscopy were used to test the phase composition and material structure of the pale yellow solid obtained in Example 3. The XRD results showed that the solid product obtained in Example 3 of this invention was sulfur, composed of eight sulfur atoms (S8), and no other impurities were present. The diffraction peaks of 2θ at 19.6°, 22.1°, 23.3°, 24.3°, 25.4°, 26.0°, 26.9°, 27.9°, 28.9°, 31.7°, 35.1°, 43.0°, and 51.3° were attributed to the (212), (220), (222), (125), (133), (026), (311), (206), (135), (044), (333), (319), and (266) crystal planes of the orthorhombic S8. Specific test results are as follows: Figure 7 As shown.

[0167] Raman spectroscopy results show that standard sulfur at 84 cm⁻¹ -1 153cm -1 219cm -1 247cm -1 436cm -1 472cm -1 Characteristic Raman peaks are found in various locations, including 153cm. -1 219cm -1 472cm -1 The characteristic peak intensity is highest at 153 cm⁻¹. -1 The characteristic peak at 219 cm⁻¹ originates from the antisymmetric bending vibration of the S8 ring. -1 The characteristic peak at 472 cm corresponds to bending vibration. -1 The characteristic peak at 84 cm corresponds to the symmetrical stretching vibration of the S8 ring, while the peak at 84 cm corresponds to the symmetrical stretching vibration of the S8 ring. -1 247cm-1 436cm -1 The characteristic peak at that location corresponds to other vibrational modes of the S8 ring. Clearly, the product of the electrocatalytic reduction of SO2 in Example 3 of this invention shows a high degree of agreement with the Raman peaks of standard sulfur, indicating that the product is sulfur with high purity and free of other impurities. Specific test results are as follows... Figure 8 As shown.

[0168] Test Example 4

[0169] In this example, the sulfur production, unit energy consumption, and Faraday efficiency synthesized in Examples 3-6 and Comparative Examples 3-7 were tested respectively.

[0170] The method for testing sulfur yield is as follows:

[0171] Weigh the pale yellow sulfur solids from Examples 3-6 and Comparative Examples 3-7, and the mass of the catalyst supported in the cathode used. Calculate the sulfur yield based on the time taken for the SO2RR reaction. The specific calculation formula is as follows:

[0172]

[0173] The unit energy consumption test method is as follows:

[0174] Weigh the pale yellow sulfur solids from Examples 3-6 and Comparative Examples 3-7 respectively, and calculate the unit energy consumption based on the total charge consumed in the reaction and the voltage and time used for electrolysis. The specific calculation formula is as follows:

[0175]

[0176]

[0177] The Faraday efficiency test method is as follows:

[0178] Weigh the pale yellow sulfur solids from Examples 3-6 and Comparative Examples 3-7 respectively, and calculate the Faraday efficiency based on the total charge consumed in the reaction. The specific calculation formula is as follows:

[0179]

[0180] The results of the above tests and calculations are shown in Table 2 below.

[0181] Table 2 shows the sulfur yield, energy consumption per unit, and Faraday efficiency for Examples 3-6 and Comparative Examples 3-7.

[0182] Group Sulfur production (umol / mgh) Energy consumption per unit (kWh / kg) Faraday efficiency / % Example 3 113.1 1.45 69.2 Example 4 123.3 2.49 53.7 Example 5 143.4 2.99 55.9 Example 6 197.1 4.09 49.1 Comparative Example 3 23.5 2.72 36.9 Comparative Example 4 86.7 2.22 60.1 Comparative Example 5 128.1 3.21 52.1 Comparative Example 6 159.1 4.27 47.0 Comparative Example 7 73.6 1.60 62.8

[0183] Examples 3-6 and Comparative Examples 3-6 show that increasing the electrolysis voltage increases sulfur production, but also increases overall energy consumption. Clearly, under the same reaction conditions, sulfur production is positively correlated with the electrical energy consumed in the reaction. Correspondingly, as the voltage increases, the hydrogen evolution side reaction becomes increasingly significant, especially after -0.3V, the Faraday efficiency of the sulfur product shows a significant downward trend.

[0184] As demonstrated in Examples 3, 3, and 7, under the same electrolysis voltage (E = -0.1 V vs RHE), MC / N-0.8 (Example 3) exhibits higher sulfur yield, Faradaic efficiency, and lower energy consumption than MC / N-0 (Comparative Example 3) due to the introduction of a large number of nitrogen-doped carbon microspheres. Furthermore, the catalyst obtained in Example 3 demonstrates better SO2RR catalytic performance than commercial noble metal catalysts. Specifically, the sulfur yield and Faradaic efficiency of the SO2RR reaction catalyzed by MC / N-0.8 are higher than those of the 20% Pt / C catalyst (Comparative Example 7), and the energy consumption is also lower than that of the commercial Pt / C catalyst.

[0185] Although the catalytic performance of the MC / N-0.8 material is the best within the value range verified in the embodiments of the present invention, it is not excluded that better results may be obtained under other conditions provided by the present invention.

[0186] In summary, the catalyst for reducing and recovering sulfur dioxide provided by this invention exhibits superior catalytic performance compared to traditional precious metal catalysts when used in electrochemical methods to treat sulfur dioxide and recover it as sulfur. This is due to the synergistic effect of its composition, structure, raw materials, and preparation process. Overall, compared to traditional sulfur production processes, the technical solution provided by this invention offers superior environmental friendliness and economic efficiency.

[0187] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A method for reducing and recovering sulfur dioxide, characterized in that, The method includes electrolyzing sulfur dioxide introduced into an electrolyte; The anode used for electrolysis includes a conductive substrate and a catalyst supported on the conductive substrate; The catalyst comprises nitrogen-doped carbon microspheres and metal sulfides on the surface of the carbon microspheres; The metal sulfide includes Co9S8.

2. The method according to claim 1, characterized in that, The catalyst has an SO2 reduction potential window of -0.3 to 0.05 V.

3. The method according to claim 1 or 2, characterized in that, The catalyst is synthesized by mixing and calcining a sulfur-containing organometallic compound and a nitrogen-containing organic compound in a protective atmosphere.

4. The method according to claim 3, characterized in that, The sulfur-containing organometallic compounds include (C3H6NS2)2Co; The (C3H6NS2)2Co was obtained by the following treatment method: 10.5 g of sodium dimethyl dithiocarbamate and 10.2 g of CoSO4·7H2O were mixed in 100 mL of water and stirred at room temperature for 1 h. The mixture was then filtered to obtain a green solid. The solid was then washed with deionized water and ethanol at room temperature. The solid obtained by drying at 80℃ five times yielded (C3H6NS2)2Co material.

5. The method according to claim 3, characterized in that, The nitrogen-containing organic compound includes at least one of polyacrylonitrile, melamine, dicyandiamide, and urea.

6. The method according to claim 3, characterized in that, The mass ratio of the sulfur-containing organometallic compound to the nitrogen-containing organic compound is 0.5~1.2:0.

8.

7. The method according to claim 3, characterized in that, The temperature for the mixed roasting is 600~1200℃.

8. The method according to claim 3, characterized in that, The roasting time for the mixture is 90-120 minutes.

9. The method according to claim 3, characterized in that, The protective atmosphere includes at least one of vacuum, argon, and nitrogen.

10. The method according to claim 1, characterized in that, The method for preparing the anode includes coating a slurry containing the catalyst onto the conductive substrate.

11. The method according to claim 1, characterized in that, The electrolyte includes one of sulfuric acid, hydrochloric acid, potassium hydroxide, sulfate, and phosphate buffer.

12. The method according to claim 1, characterized in that, The pH of the electrolyte is 0~14.

0.

13. The method according to claim 1, characterized in that, The flow rate of the sulfur dioxide is 50~70 sccm.

14. The method according to claim 1, characterized in that, The electrolysis current is 0 to -0.1A; and the electrolysis current is not 0.

15. The method according to claim 1, characterized in that, The voltage for electrolysis is -0.8 to 0.2V.

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