A synergistic modification of activated carbon containing oxygen and nitrogen functional groups and its preparation method

Abstract

This invention relates to activated carbon with synergistic modification of oxygen-nitrogen functional groups and its preparation method, belonging to the technical field of activated carbon preparation. The preparation method of the activated carbon with synergistic modification of oxygen-nitrogen functional groups includes: introducing oxygen-containing gas at 200-300℃ to safely pre-introduce oxygen-containing functional groups; introducing inert gas for protection at 300-900℃; activating with steam at 900-950℃; and introducing a mixture of oxygen-containing gas and nitrogen-containing precursor volatiles at 650-500℃ to simultaneously introduce oxygen- and nitrogen-containing functional groups. This invention employs a multi-stage temperature and atmosphere coupling control strategy to safely introduce oxygen-containing functional groups during high-temperature activation, avoiding activated carbon burn-off; and simultaneously introduces nitrogen-containing functional groups, resulting in a synergistic catalytic effect between the oxygen- and nitrogen-containing functional groups, significantly improving the low-temperature denitrification performance of the activated carbon. This invention is safe and controllable in operation, and the resulting activated carbon is particularly suitable for flue gas denitrification.

Description

Technical Field

[0001] This invention belongs to the technical field of activated carbon preparation, and more specifically, relates to an activated carbon modified by synergistic modification of oxygen- and nitrogen-containing functional groups and its preparation method. Background Technology

[0002] With the continuous acceleration of my country's industrialization, nitrogen oxides (NOx) emitted from coal-fired power plants, steel smelting, cement production, and industrial boilers have become one of the main sources of air pollution. Developing efficient and economical flue gas denitrification technologies has become an important issue in the field of environmental protection.

[0003] Activated carbon, as a cheap, readily available, and porous carbon-based material, exhibits unique advantages in low-temperature denitrification. On one hand, its well-developed porous structure provides ample adsorption sites for NOx and NH3; on the other hand, the functional groups on the surface of activated carbon can participate in the catalytic cycle of the denitrification reaction. Studies have shown that oxygen-containing functional groups on the surface of activated carbon (such as carboxyl groups)... COOH, hydroxyl group OH groups, lactone groups, carbonyl groups (C=O, etc.) can significantly affect adsorption selectivity by altering surface acidity and basicity, and can also act as catalytic active centers in NOx reduction reactions. Meanwhile, nitrogen-containing functional groups on the activated carbon surface (such as amino groups) NH2, pyridine N, pyrrole N, quaternary ammonium N, etc., can provide basic sites, effectively adsorb acidic NOx gas, and act as electron donors to promote catalytic reactions. However, how to efficiently and stably introduce oxygen- and nitrogen-containing functional groups onto the surface of activated carbon and fully utilize their synergistic catalytic effect remains a current research challenge.

[0004] In conventional activated carbon activation and modification processes, oxygen-containing functional groups are typically introduced through oxidation reactions in an oxygen-containing atmosphere (air, water vapor, ozone, etc.). However, when the surface temperature of the activated carbon is too high, the oxidation reaction becomes violent, easily leading to surface burn-off or even fire, posing serious safety hazards. It also damages the specific surface area and pore structure of the activated carbon. The introduction of nitrogen-containing functional groups usually requires the pyrolysis reaction of nitrogen-containing precursors (such as urea, ammonia, melamine, etc.) at high temperatures. However, nitrogen-containing functional groups are extremely sensitive to temperature and easily decompose at excessively high temperatures. Furthermore, the atmosphere must be strictly controlled when introducing nitrogen-containing functional groups at high temperatures to prevent activated carbon burn-off.

[0005] Existing patent literature also discloses some methods for modifying activated carbon. However, these methods have problems such as complex operation, inability to simultaneously introduce oxygen- and nitrogen-containing functional groups, difficulty in avoiding excessive decomposition of oxygen- and nitrogen-containing functional groups during high-temperature activation, and limited functional group incorporation and synergistic effects.

[0006] Therefore, there is an urgent need to develop a method for preparing activated carbon that can simultaneously introduce oxygen- and nitrogen-containing functional groups while ensuring production safety and fully leveraging their synergistic catalytic effect. Summary of the Invention

[0007] The purpose of this invention is to provide activated carbon with synergistic modification of oxygen- and nitrogen-containing functional groups and its preparation method, so as to solve the problems of how to safely introduce oxygen-containing functional groups during high-temperature activation and simultaneously introduce nitrogen-containing functional groups while ensuring production safety.

[0008] The objective of this invention can be achieved through the following technical solutions: A method for preparing activated carbon with synergistic modification of oxygen- and nitrogen-containing functional groups includes the following steps: Step 1: Heat the activated carbon raw material to 200°C Within a temperature range of 300℃, a first oxygen-containing gas is introduced into the activated carbon raw material, with the flow rate of the oxygen-containing gas controlled at 0.3. 1.2 L / min·g carbon, heat preservation treatment for 20 days 60 minutes; Step 2: Raise the system temperature from the temperature in Step 1 to a range of 800-900℃. During the heating process, continuously introduce an inert protective gas into the system, controlling the flow rate of the inert protective gas to be 0.3. 0.6 L / min·g carbon; Step 3: Once the system reaches a temperature range of 900-950℃, stop the introduction of the inert protective gas and instead introduce water vapor into the system for high-temperature activation, controlling the water vapor flow rate to be 0.6. 1.5 g / min·g carbon, heat treatment for 60°C 150 minutes; Step 4: Cool the system to 380-420℃, and then cool it down to 650℃. At temperatures around 500℃, a mixture of a second oxygen-containing gas and the volatile gas of a nitrogen-containing precursor is introduced into the system, and the mixture is kept at this temperature for 30 minutes. The nitrogen-containing precursor volatile gas is generated by heating and pyrolysis or sublimation of the nitrogen-containing precursor over 90 minutes. The nitrogen-containing precursor is selected from at least one of urea, ammonium bicarbonate or melamine.

[0009] Preferably, in step 1, the first oxygen-containing gas is air or water vapor; in step 4, the second oxygen-containing gas is air.

[0010] Preferably, the oxygen-containing gas in step 1 is air or water vapor; the activated carbon raw material is selected from at least one of coal-based activated carbon, wood-based activated carbon, and fruit shell activated carbon, and the specific surface area of ​​the activated carbon raw material is 400-800 m². 2 / g, iodine adsorption value is 400-800mg / g.

[0011] The activated carbon raw material described in this invention refers to activated carbon precursor materials that have undergone preliminary carbonization treatment but have not yet undergone deep high-temperature activation, including but not limited to at least one of coal-based activated carbon, wood-based activated carbon, coconut shell activated carbon, apricot shell activated carbon, and walnut shell activated carbon. The specific surface area of ​​the activated carbon raw material is typically 400... 800m 2 / g, iodine adsorption value 400 800 mg / g. Raw materials within the above-mentioned range contain a certain amount of volatile matter, which can further develop the porous structure through steam vaporization reaction during the subsequent high-temperature activation process, while providing sufficient reaction sites for the simultaneous grafting of functional groups in the cooling stage.

[0012] More preferably, the temperature range in step 1 is 240°C. 280℃.

[0013] Preferably, the inert protective gas in step 2 is N2 or Ar.

[0014] Preferably, in step 4, the volume ratio of oxygen-containing gas to nitrogen-containing precursor volatiles is (0.5). 2):1.

[0015] Preferably, the mixed gas is introduced in step 4 by continuous introduction or alternating pulse introduction.

[0016] Preferably, in step 4, the nitrogen-containing precursor is preheated to 150°C via a separate evaporator. After reaching 250°C, the gas is carried into the reaction system by a carrier gas. Preferably, the carrier gas is N2 or Ar.

[0017] Specifically, the nitrogen-containing precursor volatiles mentioned in this invention refer to gaseous nitrogen-containing species produced by the pyrolysis or sublimation of nitrogen-containing precursors under heating conditions, including but not limited to NH3, HCN, HNCO, etc. These gaseous nitrogen-containing species can penetrate deep into the carbon skeleton surface along the pores of activated carbon, react with the carbon skeleton, and introduce nitrogen-containing functional groups.

[0018] Preferably, the heating rate in steps 1 and 2 is 2-10℃ / min, more preferably 4℃ / min. 6℃ / min; the cooling rate in step 4 is 2 8℃ / min, preferably 4 6℃ / min.

[0019] An activated carbon modified by the synergistic effect of oxygen- and nitrogen-containing functional groups is prepared by the above-described method.

[0020] The above-mentioned applications of activated carbon in the low-temperature denitrification treatment of toxic and harmful gases such as coal-fired flue gas and industrial kiln exhaust gas.

[0021] In step 1 of this technical solution, in 200 Within the temperature range of 300℃, activated carbon is in a state where a large amount of tar volatiles are released. At this temperature, the reaction between the activated carbon surface and oxygen-containing gases is mainly surface oxidation, while the oxidation and ablation reaction rate of the carbon skeleton itself is low. Therefore, it is possible to safely and controllably pre-introduce C=O (carbonyl) groups and... The presence of oxygen-containing functional groups, primarily COOH (carboxyl groups), avoids the problem of activated carbon burn-off caused by vigorous oxidation reactions at high temperatures. The core reason for choosing this temperature range is that: below 200℃, the oxidation reaction rate between oxygen-containing gas and the activated carbon surface is too low, making it difficult to effectively form sufficient oxygen-containing functional groups; above 300℃, activated carbon begins to enter the stage of concentrated volatile matter release, and at the same time, the oxidation reaction rate increases sharply, easily leading to severe oxidation of the activated carbon surface or even ignition.

[0022] In step 2, an inert protective gas is continuously introduced throughout the process of raising the temperature from step 1 to 800-900℃. This temperature range covers the 300-800℃ range where the volatiles of activated carbon are concentrated. The protective effect of the inert atmosphere completely prevents the activated carbon from contacting oxygen-containing gases, preventing burn-off or ignition caused by the large-scale release of volatiles. When the system reaches the activation temperature range of 900-950℃, step 3 stops the introduction of inert gas and instead introduces water vapor for high-temperature activation. At this point, the volatiles of the activated carbon have been almost completely released, and the gasification reaction between the water vapor and carbon proceeds under controlled conditions, without causing a risk of burn-off.

[0023] In step 3, at 900 Within a temperature range of 950℃, water vapor reacts with carbon in a gasification reaction (C + H₂O → CO + H₂). After activation by high-temperature water vapor, the activated carbon develops numerous defect sites and oxygen-containing vacancies on its carbon skeleton surface, resulting in a fully developed pore structure. This achieves deep pore expansion and forms a stable microporous structure, providing ideal reaction sites for the subsequent introduction of functional groups. This step is completed under an inert atmosphere to ensure that the activated carbon does not burn up due to contact with oxygen at high temperatures.

[0024] In step 4, during the gradual cooling process, when the temperature drops to 650... At temperatures around 500℃, the pores of the activated carbon have been fully opened by the high-temperature steam activation in step 3. Nitrogen-containing precursors (such as urea) undergo pyrolysis, further generating nitrogen-containing active species such as NH3 and HCN. These nitrogen-containing active species, in synergy with oxygen-containing gases (such as oxygen and carbon dioxide in the air), penetrate deep into the surface of the activated carbon framework along the opened pores, undergoing grafting reactions at the original defect sites of the carbon framework, and simultaneously forming… Nitrogen-containing functional groups such as NH2 (amino), pyridine N, and others COOH (carboxyl group), C OH (hydroxyl group) Oxygen-containing functional groups such as CHO (aldehyde group). This in-situ synchronous grafting method avoids the problem of functional groups being destroyed by subsequent high-temperature treatment in traditional stepwise modification methods. At the same time, because oxygen-containing gas and nitrogen-containing precursor volatiles are fully mixed and contacted in the pores, the resulting functional groups are more uniformly distributed and the spatial distance between oxygen and nitrogen groups is closer, which is conducive to exerting a synergistic catalytic effect in the denitrification reaction.

[0025] The technical significance of selecting the temperature range in step 4 is as follows: When the temperature is above 650℃, the pyrolysis rate of nitrogen-containing precursors (especially urea and melamine) is too fast, making it difficult for nitrogen-containing active species to effectively remain on the activated carbon surface and react with the carbon skeleton; when the temperature is below 500℃, the pyrolysis of nitrogen-containing precursors is insufficient, the effective amount of nitrogen-containing species generated is insufficient, and the oxidation reaction rate of oxygen-containing gas with the carbon surface is too low. 650℃ The temperature window of 500℃ is precisely the ideal range for the nitrogen-containing precursor to fully pyrolyze and for the pyrolysis products to effectively react with the activated carbon surface. At the same time, the activated carbon pores are fully opened, allowing oxygen-containing gas to enter the pores in tandem with the volatile gas of the nitrogen-containing precursor, thus achieving uniform grafting of oxygen-containing groups and nitrogen-containing groups on the carbon skeleton surface.

[0026] At low temperature NH3 In the SCR denitrification reaction, oxygen-containing and nitrogen-containing functional groups play different but synergistic roles. Oxygen-containing functional groups (especially carboxyl and hydroxyl groups) enhance the polarity of the activated carbon surface, facilitating the adsorption of NOx and NH3 molecules. Simultaneously, oxygen-containing functional groups can serve as centers for redox reactions, participating in electron transfer processes within the catalytic cycle. Nitrogen-containing functional groups (especially pyridine N and amino groups) provide lone pairs of electrons, enhancing the basicity of the activated carbon surface, which is beneficial for the adsorption of acidic NOx gases. They can also act as electron donors to promote the activation of NH3 to generate key reaction intermediates such as ·NH2.

[0027] When oxygen-containing and nitrogen-containing functional groups coexist on the surface of activated carbon, they exert a synergistic effect through spatial proximity, forming a reaction microenvironment with higher catalytic activity. The nitrogen-containing group transfers electrons to the oxygen-containing group, enhancing its redox activity; conversely, the oxygen-containing group effectively stabilizes reaction intermediates on the nitrogen-containing group surface, preventing premature deactivation. This synergistic effect enables the activated carbon surface to more efficiently catalyze the reaction between NH3 and NOx (4NO + 4NH3 + O2 → 4N2 + 6H2O).

[0028] Compared with the prior art, the present invention has the following beneficial effects: (1) In this invention, the modification process of activated carbon is divided into multiple characteristic temperature ranges, each temperature range is matched with a different reaction atmosphere, forming a "low temperature introduction of oxygen-containing atmosphere" Medium and high temperature inert protection High-temperature deep activation A multi-stage process route of "simultaneous grafting of oxygen and nitrogen at cooling" was adopted. This design not only utilizes the differences in physicochemical properties exhibited by activated carbon in different temperature ranges, but also establishes a delicate balance among safety, functional group introduction efficiency, and pore structure development. This achieves the safe introduction of oxygen-containing functional groups throughout the preparation process, and the activated carbon at 300°C... The 800℃ volatile matter precipitation stage is protected by inert gas throughout, avoiding severe oxidation or ignition caused by the large amount of volatile matter precipitation, thus fundamentally eliminating the safety hazard of activated carbon burn-off in traditional oxidation modification methods.

[0029] (2) In step 1, oxygen-containing functional groups are pre-introduced in the low-temperature zone. In step 4, during the cooling phase, a mixture of oxygen-containing gas and nitrogen-containing precursor volatiles is used to simultaneously graft oxygen-containing and nitrogen-containing functional groups in situ while the activated carbon pores are fully open. The oxygen-containing and nitrogen-containing functional groups are spatially adjacent on the surface of the activated carbon, forming a highly efficient synergistic catalytic microenvironment. Simultaneously, combined with the deep pore-forming effect of high-temperature steam activation in step 3, the porous structure of the activated carbon is preserved to the maximum extent while efficiently introducing functional groups. Compared with traditional liquid-phase oxidation modification methods, which often lead to pore blockage and a significant decrease in specific surface area, this invention significantly improves the specific surface area of ​​activated carbon and its resistance to low-temperature NH3. Catalytic activity of SCR denitrification reaction.

[0030] (3) This invention achieves precise control of the atmosphere composition and gas flow rate in each temperature range, resulting in fine regulation of the modification process. The process has good repeatability, strong controllability, and wide applicability. It is suitable for activated carbon raw materials from various sources (coal-based, wood, coconut shell, etc.) and has good prospects for industrial application. The synergistic catalytic effect of oxygen-containing and nitrogen-containing functional groups is significant. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described below with reference to specific embodiments, but the scope of protection of this invention is not limited thereto. Experimental methods not specifically described in the embodiments are generally performed under conventional conditions or according to the manufacturer's recommendations. Unless otherwise specified, all reagents and materials used are commercially available.

[0032] Raw material description: The coconut shell activated carbon precursor used in this embodiment is industrial-grade coconut shell carbonized material with a specific surface area of ​​approximately 650 m². 2 / g, the iodine adsorption value is approximately 600mg / g.

[0033] Example 1 A method for preparing activated carbon with synergistic modification of oxygen- and nitrogen-containing functional groups, the specific steps of which are as follows: Step 1: Low-temperature pre-oxidation Take 100g of coconut shell activated carbon precursor and place it in a tubular activation reactor. Under the protection of N2 atmosphere with a flow rate of 0.4L / min·g carbon, raise the furnace temperature to 260℃ at a heating rate of 5℃ / min. After reaching 260℃, switch the gas to air and adjust the air flow rate to 0.5L / min·g carbon. Hold the temperature for 40 minutes.

[0034] Step 2: Medium-temperature inert protection After step 1 is completed, close the air intake valve, switch back to N2 atmosphere, maintain N2 flow rate at 0.4 L / min·g carbon, and continue to raise the furnace temperature to 900℃ at a heating rate of 5℃ / min.

[0035] Step 3: High-temperature steam activation When the temperature stabilizes at 900℃, stop the N2 flow and introduce water vapor at a flow rate of 1.0 g / min·g carbon, and maintain the temperature for 120 minutes.

[0036] Step 4: Simultaneously introduce oxygen- and nitrogen-containing functional groups during the cooling stage. After steam activation, the steam supply is stopped, and the atmosphere is switched to N2 (0.3 L / min·g carbon). A cooling program is initiated at a rate of 5 °C / min. When the furnace temperature drops to 600 °C, the N2 supply is shut off, and a mixture of air and urea pyrolysis volatilization gas is continuously introduced. The air flow rate is 0.3 L / min·g carbon. The urea is preheated to 180 °C via an independent evaporator. The N2 (0.2 L / min·g carbon) carries the volatilization gas generated from urea decomposition in the evaporator into the reaction system. The volume ratio of air to urea volatilization gas in the mixed gas is approximately 1.5:1. The mixture is held at 600 °C for 60 minutes.

[0037] After the cooling phase (400℃) is completed, the mixed gas supply is shut off, and the system is switched to an N2 atmosphere (0.2 L / min·g carbon). The system is then allowed to cool naturally to room temperature. The resulting product is an oxygen-containing gas. Activated carbon modified by nitrogen-containing functional groups.

[0038] Example 2 Compared to Example 1, the difference between this example and Example 1 is as follows: Step 4 of this example is as follows: After steam activation, the steam supply is stopped, and the atmosphere is switched to N2 (0.3 L / min·g carbon). The cooling program is started at a rate of 8°C / min. When the furnace temperature drops to 600°C, N2 is turned off, and a mixture of air and ammonium bicarbonate pyrolysis volatiles is continuously introduced. The air flow rate is 0.4 L / min·g carbon. The ammonium bicarbonate is preheated to 150°C via an independent evaporator. The N2 (0.2 L / min·g carbon) carries the volatiles generated from the decomposition of ammonium bicarbonate in the evaporator into the reaction system. The volume ratio of air to ammonium bicarbonate volatiles in the mixed gas is approximately 1.5:1. The mixture is kept at 600°C for 60 minutes.

[0039] The remaining steps are the same as in Example 1.

[0040] Example 3 Compared to Example 1, the difference between this example and Example 1 lies in the following steps: Step 4 of this example involves stopping the steam injection after steam activation and switching to an N2 atmosphere (0.3 L / min·g carbon). A cooling program is initiated at a rate of 2°C / min. When the furnace temperature drops to 600°C, the N2 atmosphere is shut off, and a mixture of air and melamine pyrolysis volatiles is continuously introduced. The air flow rate is 0.3 L / min·g carbon. The melamine is preheated to 250°C via an independent evaporator. The N2 atmosphere (0.3 L / min·g carbon) carries the volatiles generated from the melamine decomposition in the evaporator into the reaction system. The volume ratio of air to melamine volatiles in the mixed gas is approximately 1:1. The mixture is then kept at a constant temperature of 600°C for 60 minutes.

[0041] The remaining steps are the same as in Example 1.

[0042] Example 4 Compared with Example 1, the difference between this example and Example 1 is that the mixed gas is introduced in step 4 of this example by alternating pulse introduction: first, air is introduced in a pulse for 20 seconds (flow rate 0.4 L / min·g carbon), then urea volatilized gas is introduced in a pulse for 40 seconds (carrier gas N2 flow rate 0.2 L / min·g carbon), and this alternation cycle is repeated 3 times, with a total processing time of 60 minutes. The remaining steps are the same as in Example 1.

[0043] Comparative Example 1 Compared with Example 1, the difference between this comparative example and Example 1 is that in step 4 of this comparative example, no urea pyrolysis volatile gas is introduced (i.e., no nitrogen-containing precursor volatile gas), only air is introduced, wherein the air flow rate is 0.5 L / min·g carbon, and the treatment is carried out at 600°C for 60 minutes. The remaining steps are the same as in Example 1.

[0044] Comparative Example 2 Compared with Example 1, the difference between this comparative example and Example 1 is that: in step 4 of this comparative example, no air is introduced (i.e., no second oxygen-containing gas), only the volatile gas from urea pyrolysis is introduced. The urea is preheated to 180°C through an independent evaporator, and the volatile gas generated from urea decomposition in the evaporator is carried into the reaction system by N2 (0.3 L / min·g carbon), and the system is kept at a constant temperature of 600°C for 60 minutes. The remaining steps are the same as in Example 1.

[0045] Comparative Example 3 This comparative example uses a traditional stepwise modification method. The specific steps are as follows: 100g of coconut shell activated carbon precursor is immersed in a 3mol / L nitric acid solution and treated at 80℃ for 3 hours. After washing and drying, oxygen-containing functional group modified activated carbon is obtained. Then, the activated carbon is immersed in a 15% ammonia solution and treated at room temperature for 12 hours. After washing and drying, oxygen-containing and nitrogen-containing modified activated carbon is obtained.

[0046] Comparative Example 4 Compared with Example 1, the difference between this comparative example and Example 1 is that step 4 is omitted in this comparative example. That is, after the high-temperature steam activation in step 3, the temperature is directly lowered to room temperature in N2 atmosphere without the introduction of oxygen / nitrogen-containing gases.

[0047] Comparative Example 5 Compared with Example 1, the difference between this comparative example and Example 1 is that the low-temperature pre-oxidation stage in step 1 is omitted in this comparative example. That is, the specific steps of this comparative example are as follows: 100g of coconut shell activated carbon precursor is placed in a tubular activation reactor. Under the protection of N2 atmosphere with a flow rate of 0.4L / min·g carbon, the furnace temperature is raised to 900℃ at a heating rate of 5℃ / min. Then, high-temperature activation and simultaneous grafting during the cooling stage are carried out according to steps 3-4 of Example 1.

[0048] Comparative Example 6 Compared with Example 1, the difference between this comparative example and Example 1 is that: the specific steps of step 2 in this comparative example are as follows: after step 1, the temperature is continued to rise to 900°C while maintaining an air atmosphere and not switching back to N2 atmosphere. In step 3, the temperature is switched to water vapor for high-temperature activation. The subsequent steps are the same as in Example 1.

[0049] Comparative Example 7 Compared with Example 1, the difference between this comparative example and Example 1 is as follows: Step 4 of this comparative example is as follows: After steam activation, the steam supply is stopped, and the atmosphere is switched to N2 (0.3 L / min·g carbon). The cooling program is started at a rate of 5°C / min. Instead of waiting for the furnace temperature to drop to 600°C, a mixture of air and urea pyrolysis volatilization gas (flow rate the same as in Example 1) is directly introduced from 900°C until 400°C. Then, the mixed gas supply is stopped, and the atmosphere is switched to N2 (0.2 L / min·g carbon), allowing the system to cool naturally to room temperature.

[0050] Performance testing solution The activated carbon samples obtained from the above embodiments and comparative examples were subjected to the following performance tests: (1) Specific surface area and pore structure test (BET method) The adsorption of N2 on activated carbon samples was determined using a physical adsorption analyzer with N2 as the adsorbate gas at 77K. Desorption isotherms were determined. The specific surface area of ​​the samples was calculated using the BET method, and the average pore size and pore volume distribution were calculated using the BJH method.

[0051] (2) Determination of activated carbon burn-off rate The activated carbon burn-off rate is calculated using the following formula: α=(m0) m1) / m0×100%. Where m0 is the mass (g) of activated carbon before activation and modification, and m1 is the mass (g) of activated carbon after activation and modification.

[0052] (3) Characterization of surface functional groups (XPS method) X-ray photoelectron spectroscopy was used to analyze the elemental composition and functional group types of the activated carbon sample surface. AlKα rays (hv = 1486.6 eV) were used as the excitation source, with a passing energy of 30 eV. High-resolution spectra of C1s, O1s, and N1s were subjected to peak fitting to analyze the types, contents, and relative proportions of oxygen-containing functional groups (percentage of O1s peak area or C1s fitted peak area) and nitrogen-containing functional groups (percentage of N1s peak area).

[0053] (4) Low-temperature denitrification performance test The denitrification performance of activated carbon samples was evaluated using a fixed-bed quartz tube reactor. The simulated flue gas composition was as follows: NO concentration 500 ppm, NH3 concentration 500 ppm, O2 volume fraction 5%, N2 as the balance gas, total gas flow rate 500 mL / min, and space velocity 5000 h⁻¹. -1The reaction temperature was set at five points: 80℃, 100℃, 120℃, 150℃, and 180℃ (with 120℃ as the primary evaluation temperature). The NO concentration at the reactor inlet and outlet was continuously monitored using a flue gas analyzer, and the denitrification efficiency was calculated using the following formula: η = (C(NO)input) / (NO2) C(NO)_out / C(NO)_in × 100%. Where C(NO)_in and C(NO)_out represent the NO concentration (ppm) at the reactor inlet and outlet, respectively.

[0054] The performance test results are shown in Tables 1, 2 and 3.

[0055] Table 1

[0056] Table 2

[0057] Table 3

[0058] As can be seen from the test results in Table 1, the modified activated carbon obtained in each embodiment of the present invention has higher overall performance in terms of specific surface area, oxygen content, nitrogen content, and burn-off rate. This indicates that the present invention achieves higher performance through a four-stage temperature control. The atmosphere coupling control strategy effectively avoids the problems of pore blockage and sharp decrease in specific surface area in traditional liquid-phase modification methods while successfully introducing oxygen- and nitrogen-containing functional groups. Comparative Example 1, which only introduced air without a nitrogen source in step 4, resulted in a significantly reduced nitrogen content in the obtained sample; Comparative Example 2, which only introduced urea volatilization gas without oxygen in step 4, also resulted in a significantly reduced oxygen content in the obtained sample. This demonstrates that the mixed gas synchronous introduction strategy in step 4 of this application can efficiently introduce both oxygen- and nitrogen-containing functional groups simultaneously, obtaining an activated carbon surface with both types of functional groups coexisting. Comparative Example 3, using traditional liquid-phase oxidation modification, showed an increased burn-off rate, indicating that the safety of the method of this invention is significantly superior to traditional liquid-phase oxidation modification methods. Comparative Example 6, with air introduced throughout the 200-800℃ process, observed severe oxidation during the heating process, resulting in a high burn-off rate and no detectable specific surface area; the obtained sample could not meet the requirements for subsequent characterization and denitrification performance testing. This indicates that step 2 of the present invention, which introduces inert protection in the temperature range of 300-900°C where a large amount of volatiles of activated carbon are released, is the key to ensuring the safety and feasibility of this method.

[0059] As shown in Table 2, all embodiments of the present invention achieved efficient simultaneous introduction of oxygen-containing and nitrogen-containing functional groups, and the distribution of each type of functional group was relatively balanced. The oxygen-containing functional groups were mainly C-OH and -COOH, while the nitrogen-containing functional groups were mainly pyridine N and pyrrole N, with a considerable proportion of -NH2. Comparative Example 1 (oxygen only) did not effectively introduce nitrogen; Comparative Example 2 (nitrogen only) did not effectively introduce oxygen (oxygen mainly came from the background of the raw materials and oxidation of trace amounts of oxygen in the air). Comparative Example 3 (traditional stepwise modification), although containing both oxygen and nitrogen, had a significantly lower surface nitrogen content than the embodiments, and the distribution of the two types of functional groups was limited by the order and conditions of the two-step operation, resulting in poor spatial proximity and affecting the synergistic effect. Comparative Example 4 had a nitrogen content of only 0.6 at%, indicating that step 4 was the key pathway for introducing nitrogen-containing functional groups. Comparative Example 5 had a low oxygen content, indicating that the low-temperature pre-oxidation in step 1 was crucial for the efficient introduction of oxygen-containing functional groups. Comparative Example 6 did not obtain a valid XPS spectrum due to severe burn-off. The nitrogen content of Comparative Example 7 was significantly lower than that of Example 7, indicating that the introduction of nitrogen-containing precursor volatiles at temperatures above 650°C would lead to excessively rapid decomposition of nitrogen-containing active species and low inoculation efficiency.

[0060] As shown in Table 3, the modified activated carbon obtained in each embodiment of the present invention exhibits superior denitrification efficiency. Comparative Examples 1 and 2, which only involve oxygen / nitrogen modification, show lower denitrification efficiencies than the embodiments of the present invention, demonstrating the existence of a synergistic catalytic effect between oxygen-containing and nitrogen-containing functional groups—the catalytic activity generated by the coexistence of these two types of functional groups far exceeds the simple sum of their effects. Comparative Example 3, employing a traditional stepwise modification method of nitric acid oxidation followed by ammonia impregnation, also shows a significantly lower denitrification efficiency than the embodiments of the present invention. This indicates that the "simultaneous in-situ grafting during cooling" strategy of the present invention offers an advantage in synergistic catalytic efficiency that cannot be replaced by traditional stepwise modification methods.

[0061] Observing the denitrification efficiency of each embodiment with temperature, it can be found that all samples reach the highest denitrification efficiency around 120℃, and the denitrification efficiency decreases slightly after exceeding 150℃. This is mainly due to the decrease in stability of the functional groups on the surface of activated carbon at excessively high temperatures. However, even so, each embodiment of the present invention still maintains a high denitrification efficiency of more than 80% at 180℃, indicating that the modified activated carbon obtained by the present invention has a wide effective temperature window.

[0062] The above performance test results show that the present invention resolves the contradiction between safety and functional group introduction efficiency during activated carbon modification, and improves safety and pore structure retention while ensuring activity, making it particularly suitable for large-scale application in low-temperature flue gas denitrification industry.

[0063] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing activated carbon with synergistic modification of oxygen- and nitrogen-containing functional groups, characterized in that, Includes the following steps: Step 1: Heat the activated carbon raw material to 200°C Within a temperature range of 300℃, a first oxygen-containing gas is introduced into the activated carbon raw material, with the flow rate of the oxygen-containing gas controlled at 0.

3. 1.2 L / min·g carbon, heat preservation treatment for 20 days 60 minutes; Step 2: Raise the system temperature from the temperature in Step 1 to a range of 800-900℃. During the heating process, continuously introduce an inert protective gas into the system, controlling the flow rate of the inert protective gas to be 0.

3. 0.6 L / min·g carbon; Step 3: Once the system reaches a temperature range of 900-950℃, stop the introduction of the inert protective gas and instead introduce water vapor into the system for high-temperature activation, controlling the water vapor flow rate to be 0.

6. 1.5 g / min·g carbon, heat treatment for 60°C 150 minutes; Step 4: Cool the system to 380-420℃, and then cool it down to 650℃. At temperatures around 500℃, a mixture of a second oxygen-containing gas and the volatile gas of a nitrogen-containing precursor is introduced into the system, and the mixture is kept at this temperature for 30 minutes. The nitrogen-containing precursor volatile gas is generated by heating and pyrolysis or sublimation of the nitrogen-containing precursor over 90 minutes. The nitrogen-containing precursor is selected from at least one of urea, ammonium bicarbonate or melamine.

2. The method for preparing activated carbon with synergistic modification of oxygen- and nitrogen-containing functional groups according to claim 1, characterized in that, In step 1, the first oxygen-containing gas is air or water vapor; in step 4, the second oxygen-containing gas is air.

3. The method for preparing activated carbon with synergistic modification of oxygen- and nitrogen-containing functional groups according to claim 1, characterized in that, The oxygen-containing gas mentioned in step 1 is air or water vapor; the activated carbon raw material is selected from at least one of coal-based activated carbon, wood-based activated carbon, and fruit shell activated carbon, and the specific surface area of ​​the activated carbon raw material is 400-800 m². 2 / g, iodine adsorption value is 400-800mg / g.

4. The method for preparing activated carbon with synergistic modification of oxygen- and nitrogen-containing functional groups according to claim 1, characterized in that, The inert protective gas mentioned in step 2 is N2 or Ar.

5. The method for preparing activated carbon with synergistic modification of oxygen- and nitrogen-containing functional groups according to claim 1, characterized in that, In step 4, the volume ratio of oxygen-containing gas to nitrogen-containing precursor volatiles is (0.5). 2):

1.

6. The method for preparing activated carbon with synergistic modification of oxygen- and nitrogen-containing functional groups according to claim 1, characterized in that, In step 4, the mixed gas is introduced either continuously or by alternating pulses.

7. The method for preparing activated carbon with synergistic modification of oxygen- and nitrogen-containing functional groups according to claim 1, characterized in that, In step 4, the nitrogen-containing precursor is preheated to 150°C using a separate evaporator. After reaching 250°C, the gas is carried into the reaction system by a carrier gas, which is N2 or Ar.

8. The method for preparing activated carbon with synergistic modification of oxygen- and nitrogen-containing functional groups according to claim 1, characterized in that, The heating rate in steps 1 and 2 is 2-10℃ / min; the cooling rate in step 4 is 2℃ / min. 8℃ / min.

9. An activated carbon with synergistic modification of oxygen- and nitrogen-containing functional groups, characterized in that, The activated carbon is prepared by the preparation method according to any one of claims 1-8.

10. The application of activated carbon according to claim 9 in the low-temperature denitrification treatment of toxic and harmful gases such as coal-fired flue gas and industrial kiln exhaust gas.

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