Preparation method and application of core-shell catalyst for oxidizing CO and reducing NO at low temperature

Abstract

The invention relates to a preparation method and application of a core-shell catalyst for oxidizing CO and reducing NO at low temperature, and belongs to the technical field of flue gas purification. According to the core-shell catalyst, coconut shell activated carbon CSAC serves as a core, the outer side of the CSAC is coated with active components CeO2 and CoO to form a shell structure, the total mass of Ce and Co in the active components accounts for 2%-4% of that of the CSAC, and the molar weight of Co accounts for 80%-90% by taking the total molar weight of Co and Ce as 100%. The CSAC catalyst is coated with Co and Ce step by step or at the same time through acetic acid activation pretreatment, step-by-step impregnation or co-impregnation, microwave pyrolysis activation and plasma surface treatment, and CO and NO are synchronously removed under low-temperature activation of water vapor. According to the core-shell catalyst, CSAC is used as a physical support and reactant enrichment platform, a Co layer is used for leading redox cycle, a Ce layer is used for regulating oxygen species migration, Co and Ce reaction sites are used for constructing a bifunctional catalyst, coupling of two reactions of CO catalytic oxidation and NO catalytic reduction is achieved, CO and NO are efficiently removed at the same time, and the core-shell catalyst is environmentally friendly and free of pollution.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method and application of a core-shell catalyst for low-temperature oxidation of CO and reduction of NO, and belongs to the technical field of flue gas purification. BACKGROUND

[0002] Currently, the commonly used technologies for eliminating NO x and CO in sintering flue gas are CO selective catalytic reduction of NO (CO-SCR) and CO selective catalytic oxidation (CO-SCO), wherein the CO-SCR technology can simultaneously remove CO and NO x and convert them into CO2 and N2, and the CO-SCO technology can process low-concentration CO, has the characteristics of low reaction temperature and high oxidation rate, and is one of the economic and effective emission reduction technologies. If the two technologies of CO-SCR and CO-SCO can be combined, the green development concept can be met, and waste can be treated with waste to avoid secondary pollution.

[0003] To realize the combined application of the CO-SCR and CO-SCO technologies, a composite catalyst with the dual functions of selective reduction of NO x and catalytic oxidation of CO needs to be developed, and the structure of the catalyst includes a porous carrier and a high-efficiency active component. Activated carbon (AC) is the most commonly used carrier for removal of NO x , SO2 and VOCs in the field of environmental catalysis. The activated carbon is beneficial to low cost, flexible working conditions, high specific surface area and developed pore structure, and especially, coconut shell-based activated carbon (CSAC) has a unique honeycomb pore system and excellent adsorption properties, and thus exhibits significant advantages in treatment of industrial flue gas pollutants and becomes an optimal carrier in industrial application. However, the unmodified activated carbon has a pore distribution and surface chemical property which are not fully optimized, the mass transfer efficiency of reaction molecules is limited by the narrow micropore structure, and the surface active site density is insufficient, so that the efficient dispersion of active metals is difficult to realize, and thus the removal of CO and NO is significantly limited. SUMMARY

[0004] In view of the problems of poor activity of existing activated carbon loaded with metal active components in low-temperature removal of NO x and CO, and low removal rates of NO x and CO, the application provides a preparation method and application of a core-shell catalyst for low-temperature oxidation of CO and reduction of NO, a cheap coconut shell activated carbon is used as a carrier, Co and Ce are step-by-step or synchronously coated on the activated carrier CSAC activated by an acetic acid solution, and different core-shell catalysts are prepared through microwave pyrolysis activation-plasma surface treatment, so that the synchronous removal of CO and NO under the conditions of low-temperature activation of water vapor and 100-250 DEG C is realized; and the problems of poor activity of existing low-temperature removal of NO x and CO in flue gas, and low removal rates of NO xand low removal rate of CO. The core-shell catalyst of the application takes CSAC as a physical support and a reactant enrichment platform, takes Co layer as a main body of redox cycle, takes Ce layer as a regulator of oxygen species migration, constructs a dual-functional catalyst with Co and Ce reaction sites, and realizes coupling of CO catalytic oxidation and NO catalytic reduction, which not only simultaneously and efficiently removes CO and NO, but also is environmentally friendly and pollution-free.

[0005] A preparation method of a core-shell catalyst for low-temperature oxidation of CO and reduction of NO, the core-shell catalyst taking coconut shell activated carbon (CSAC) as a core, active components CeO2 and CoO being coated outside the CSAC to form a shell structure, the total mass of Ce and Co elements in the active components accounting for 2-4 wt% of the CSAC, the molar amount of Co accounting for 80-90% of the total molar amount of Co and Ce, which is 100%; The specific steps are as follows: (1) The coconut shell activated carbon is cleaned with deionized water, ultrasonically treated in a water bath at a temperature of 60-80℃ for 2-4 h, solid-liquid separated, and dried to obtain pretreated coconut shell activated carbon (CSAC); (2) The pretreated coconut shell activated carbon (CSAC) is added into an acetic acid solution for surface activation treatment, solid-liquid separated, and dried to obtain activated coconut shell activated carbon (CH3COOH / CSAC); (3) The activated coconut shell activated carbon (CH3COOH / CSAC) is added into a mixed solution of cobalt nitrate and cerium nitrate, a cobalt nitrate solution, and a cerium nitrate solution respectively, and is stirred and impregnated at a temperature of 80-100℃ for 2-4 h, and is then left to stand at room temperature for 24-36 h, and is vacuum dried to obtain CSAC@CoCe precursor, Co / CSAC precursor, and Ce / CSAC precursor; (4) In a microwave high-temperature sintering furnace, the CSAC@CoCe precursor, the Co / CSAC precursor, and the Ce / CSAC precursor are uniformly heated to a temperature of 470-490℃ and are microwave vacuum sintered for 90-110 min, and are then subjected to plasma surface treatment to obtain CSAC@CoCe core-shell catalyst, Co / CSAC catalyst, or Ce / CSAC catalyst; (5) The Co / CSAC catalyst is added into a cerium nitrate solution and is stirred and impregnated at a temperature of 80-100℃ for 2-4 h, and is then left to stand at room temperature for 24-36 h, and is vacuum dried to obtain Co / CSAC@Ce precursor, and the Ce / CSAC catalyst is added into a cobalt nitrate solution and is stirred and impregnated at a temperature of 80-100℃ for 2-4 h, and is then left to stand at room temperature for 24-36 h, and is vacuum dried to obtain Ce / CSAC@Co precursor; (6) in the microwave high-temperature sintering furnace, the Co / CSAC@Ce precursor and the Ce / CSAC@Co precursor are uniformly heated to 470-490 ℃ and microwave vacuum sintered for 90-110 min, and then the Co / CSAC@Ce core-shell catalyst and the Ce / CSAC@Co core-shell catalyst are obtained through plasma surface treatment.

[0006] Preferably, the concentration of the acetic acid solution in the step (2) is 6-8 mol / L, the temperature of the surface active treatment is 80-100 ℃, and the time is 2-4 h.

[0007] Preferably, the concentration of the cerium nitrate in the mixed solution of the cobalt nitrate and the cerium nitrate is 0.05-0.09 mol / L, the concentration of the cobalt nitrate is 0.025-0.075 mol / L, the concentration of the cerium nitrate solution is 0.05-0.09 mol / L, and the concentration of the cobalt nitrate solution is 0.025-0.075 mol / L.

[0008] Preferably, the microwave power in the step (4) and the step (6) is 2-4 KW, the plasma surface treatment power is 300-400 W, the time is 20-40 min, and the plasma discharge gas is hydrogen-nitrogen mixed gas.

[0009] More preferably, the volume ratio of hydrogen to nitrogen in the hydrogen-nitrogen mixed gas is 1-2:10, and the flow rate of the hydrogen-nitrogen mixed gas is 13-15 ml / min.

[0010] The core-shell catalyst can be used for catalytic removal of CO and NO in flue gas at low temperature, and the catalytic removal temperature is 100-250 ℃.

[0011] Performance test of the core-shell catalyst for removing CO and NO: (1) the temperature of the water bubbler is maintained at 25 ℃ to obtain a stable water vapor flow, N2 is introduced to purge the Co / CSAC@Ce catalyst, and the temperature of the CO+NO removal fixed bed reactor is increased to 100 ℃; (2) the mixed flue gas (simulation gas) to be removed CO+NO is sent into the fixed bed reactor, the reaction temperature is controlled at 100-250 ℃, the NO flow in the mixed flue gas (simulation gas) to be removed CO+NO is 2.4 ml·min -1 (2.4×10 3 ppm), the volume concentration of O2 is 10% (volume ratio), the CO flow is 4 ml·min -1 (4×10 3 ppm), and the total flow of the mixed gas is 1000 ml·min -1 (1×10 6ppm), N2 is the balance gas, CO+NO in the flue gas is oxidized to CO2 and reduced to N2 gas under the action of different core-shell catalysts; (3) The components in the flue gas before and after the removal of CO+NO by the different core-shell catalysts are recorded by a flue gas analyzer, and the removal efficiency of CO+NO is calculated; (4) The reacted gas is discharged into the atmosphere after the unreacted CO and NO are absorbed by a limestone solution.

[0012] The coconut shell activated carbon activated by acetic acid pretreatment is used as the carrier to increase the specific surface area of the catalyst, improve the internal pore volume and pore size of the coconut shell activated carbon, greatly increase the oxygen-containing functional groups on the surface of the coconut shell activated carbon, enhance the hydrophilicity of the coconut shell activated carbon, improve the subsequent water vapor activation efficiency, and realize the simultaneous and efficient removal of CO and NO; the impregnation method can improve the dispersity of Co and Ce elements on the surface of the catalyst, effectively reduce the metal oxide agglomeration phenomenon on the surface of the catalyst, and thus ensure that the catalyst has high CO+NO removal activity; the microwave sintering technology can enrich the pore structure of the catalyst and improve the uniformity of the active components; the plasma surface treatment can promote the transformation of the valence state of the metal active components and generate more oxygen vacancies; the low-temperature activation of water vapor can significantly improve the low-temperature activity and stability of the catalyst, reduce the reaction temperature, enhance the sintering resistance, and optimize the surface oxygen species; the double-functional core-shell catalyst for CO oxidation and NO reduction is prepared by the acetic acid activation pretreatment-stepwise / impregnation method-microwave pyrolysis activation-plasma surface treatment, and has the advantages of simple preparation process, easy operation, low energy consumption, environmental protection, no pollution, high CO+NO removal efficiency, and easy industrialization.

[0013] The beneficial effects of the present application are: (1) The core-shell catalyst for low-temperature oxidation of CO and reduction of NO has good low-temperature CO+NO removal activity, can realize the simultaneous removal of CO+NO at 100-250 DEG C, and can solve the problems of poor low-temperature NO and CO removal activity of the metal active components supported on the existing activated carbon, and low NO and CO removal rate; x x (2) The coconut shell activated carbon activated by acetic acid pretreatment is used as the carrier to increase the specific surface area of the catalyst, improve the internal pore volume and pore size of the coconut shell activated carbon, greatly increase the oxygen-containing functional groups on the surface of the coconut shell activated carbon, enhance the hydrophilicity of the coconut shell activated carbon, improve the subsequent water vapor activation efficiency, and realize the simultaneous and efficient removal of CO and NO; the impregnation method can improve the dispersity of Co and Ce elements on the surface of the catalyst, effectively reduce the metal oxide agglomeration phenomenon on the surface of the catalyst, and thus ensure that the catalyst has high CO+NO removal activity; the microwave sintering technology can enrich the pore structure of the catalyst and improve the uniformity of the active components; the plasma surface treatment can promote the transformation of the valence state of the metal active components and generate more oxygen vacancies; ​​(3) The application cooperates with CO-SCR (simultaneously removing CO and NO x and converting into CO2 and N2) and CO-SCO (processing low-concentration CO, with the characteristics of low reaction temperature and high oxidation rate), which not only conforms to the green development concept, but also realizes waste treatment and avoids secondary pollution, and can provide a theoretical basis for the low-temperature and high-efficiency development of double-effect catalysts. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a curve diagram of removal of CO+NO by different core-shell catalysts at different temperatures; Figure 2 is an SEM diagram of different core-shell catalysts. DETAILED DESCRIPTION

[0015] The application will be further described in detail below in combination with specific embodiments, but the protection scope of the application is not limited to the content described.

[0016] In the embodiment of the application, the catalytic reactor is a fixed bed reactor, the temperature of the water bubbler is 25 DEG C, the raw gas is preheated to enter the reactor, the reaction temperature is 100-250 DEG C, the total gas flow is 1000 ml / min, and the GHSV is 30000 h -1 -1. The simulated flue gas composition is: the NO flow is 2.4 ml·min -1 (2.4*10 3 ppm), the O2 volume concentration is 10% (volume ratio), the CO flow is 4 ml·min -1 (4*10 3 ppm), and N2 is the balance gas, the simulated flue gas is mixed and sent into the fixed bed reactor, and the gas flow is controlled by a rotameter; The purities of CO, NO, N2 and O2 used in the application are all 99.99%; The CO+NO removal activity of the catalyst is evaluated by using CO conversion rate and NO conversion rate, and the calculation method is as follows: (1); (2); In the formula, ------ the CO concentration at the reactor inlet, ppm; ----- the CO concentration at the reactor outlet, ppm; ------ the NO concentration at the reactor inlet, ppm; ----- the NO concentration at the reactor outlet, ppm.

[0017] In this embodiment, the core-shell catalyst has coconut shell activated carbon CSAC as the core, and active components CeO2 and CoO are coated outside the CSAC to form a shell structure. The total mass of Ce and Co in the active components accounts for 2% of the mass of the CSAC, and the molar amount of Co accounts for 80% of the total molar amount of Co and Ce, which is taken as 100%. The core-shell catalyst in this embodiment is prepared by acetic acid activation pretreatment, co-impregnation, microwave pyrolysis activation, and plasma surface treatment to coat Co and Ce on the surface of the CSAC at the same time. A preparation method of a core-shell catalyst for low-temperature oxidation of CO and reduction of NO, and the specific steps are as follows: (1) Coconut shell activated carbon is washed with deionized water for 7 times, ultrasonic treated in a water bath at a temperature of 60°C for 4 hours, and then dried to obtain pretreated activated carbon CSAC. (2) The pretreated coconut shell activated carbon CSAC is added into an acetic acid solution with a concentration of 6 mol / L, and surface activation treatment is performed at a temperature of 80°C for 2 hours. After solid-liquid separation and drying, activated coconut shell activated carbon CH3COOH / CSAC is obtained. (3) The activated coconut shell activated carbon CH3COOH / CSAC is added into a mixed solution of cobalt nitrate and cerium nitrate (cobalt nitrate 0.025 mol / L, cerium nitrate 0.05 mol / L), and stirred and impregnated at a temperature of 80°C for 2 hours. After standing at room temperature for 24 hours, vacuum drying is performed to obtain a CSAC@CoCe precursor. (4) In a microwave high-temperature sintering furnace, the CSAC@CoCe precursor is uniformly heated at a rate of 10°C / min to a temperature of 470°C and microwave vacuum sintered for 90 minutes, and then plasma surface treatment is performed for 20 minutes to obtain a CSAC@CoCe core-shell catalyst. The microwave power is 2 KW, the plasma surface treatment power is 300 W, the plasma discharge gas is hydrogen-nitrogen mixed gas, the volume ratio of hydrogen to nitrogen in the hydrogen-nitrogen mixed gas is 1:10, and the hydrogen-nitrogen mixed gas flow is 13 ml / min. The core-shell catalyst for low-temperature oxidation of CO and reduction of NO in this embodiment is used for NO removal reaction at a temperature of 100-250°C, and the catalyst loading amount is 8g. Before the experiment starts, the temperature of the water bubbler is maintained at 25°C to obtain a stable water vapor flow, and N2 is introduced into the fixed bed reactor to discharge other gases in the reactor to avoid interference of other gases. Then, CO+NO in the simulated flue gas is introduced for 1 hour to allow the CSAC@CoCe catalyst with co-impregnated Co and Ce to adsorb CO+NO to saturation, thereby reducing experimental errors. The total flow rate of the simulated gas is 1000 ml / min, and the GHSV is 30000 h -1 , the NO flow rate is 2.4 ml·min -1 (2.4×10 3ppm), O2 volume concentration of 10% (volume ratio), CO flow of 4 ml·min -1 (4×10 3 ppm), N2 as the balance gas; the simulated gas was mixed in a gas mixing box and then sent into a fixed bed reactor, where CO was oxidized to CO2 and NO was reduced to N2 under the action of the CSAC@CoCe catalyst which was simultaneously impregnated with Co and Ce. The reacted gas was discharged into the atmosphere after the unreacted CO and NO were absorbed by a limestone solution, and the CO and NO concentrations at the inlet and outlet were detected by a flue gas analyzer; The CO+NO removal efficiency of the CSAC@CoCe catalyst which was simultaneously impregnated with Co and Ce is shown in Table 1 and Figure 1 , Table 1 CO+NO removal efficiency of the CSAC@CoCe catalyst which was simultaneously impregnated with Co and Ce ; From Table 1 and Figure 1 , it can be seen that the CO removal rate of the CSAC@CoCe catalyst maintained 100% at 100-120℃, and slightly decreased to 97.95% as the temperature increased to 250℃, which may be due to the gradual saturation of the adsorption capacity of CSAC. The NO removal rate gradually decreased from 93.67% to 59.33%, which may be due to the gradual saturation of the adsorption capacity of CSAC and the fact that the active sites for the catalytic reduction of NO are less than those for the catalytic oxidation of CO, resulting in less significant effect on the removal of NO.

[0019] Example 2: In this example, the core-shell catalyst has CSAC as the core structure, and active components CeO2 and CoO are coated on the outside of CSAC to form a shell structure. The total mass of Ce and Co in the active components accounts for 3wt% of CSAC, and the molar amount of Co accounts for 85% of the total molar amount of Co and Ce, which is taken as 100%. The core-shell catalyst in this example is prepared by acetic acid activation pretreatment-distributed impregnation-microwave pyrolysis activation-plasma surface treatment to coat Co and Ce on the surface of CSAC in sequence; A preparation method of a core-shell catalyst for low-temperature oxidation of CO and reduction of NO, and the specific steps are as follows: (1) The CSAC is washed with deionized water for 7 times, ultrasonic treated in a water bath at a temperature of 70℃ for 3h, and then solid-liquid separated and dried to obtain pretreated CSAC; (2) The pretreated CSAC is added into an acetic acid solution with a concentration of 7 mol / L, and then surface activated at a temperature of 90℃ for 3h, and then solid-liquid separated and dried to obtain activated CSAC CH3COOH / CSAC; (3) The activated coconut shell activated carbon CH3COOH / CSAC is added into a cobalt nitrate solution with a concentration of 0.05 mol / L, and is stirred and impregnated at a temperature of 90 ℃ for 3 h, is placed at room temperature for 30 h, and is then vacuum dried to obtain a Co / CSAC precursor; (4) The Co / CSAC precursor is uniformly heated at a rate of 10 ℃ / min to a temperature of 480 ℃ in a microwave high-temperature sintering furnace and is microwave vacuum sintered for 100 min, and is then subjected to plasma surface treatment for 30 min to obtain a Co / CSAC catalyst; the microwave power is 3 KW, the plasma surface treatment power is 350 W, the plasma discharge gas is hydrogen-nitrogen mixed gas, the volume ratio of hydrogen to nitrogen in the hydrogen-nitrogen mixed gas is 1.5:10, and the hydrogen-nitrogen mixed gas flow rate is 14 ml / min; (5) The Co / CSAC catalyst is added into a cerium nitrate solution with a concentration of 0.075 mol / L and is stirred and impregnated at a temperature of 90 ℃ for 3 h, is placed at room temperature for 30 h, and is vacuum dried to obtain a Co / CSAC@Ce precursor; (6) The Co / CSAC@Ce precursor is uniformly heated at a rate of 10 ℃ / min to a temperature of 480 ℃ in a microwave high-temperature sintering furnace and is microwave vacuum sintered for 100 min, and is then subjected to plasma surface treatment to obtain a Co / CSAC@Ce core-shell catalyst; the microwave power is 3 KW, the plasma surface treatment power is 350 W, the plasma discharge gas is hydrogen-nitrogen mixed gas, the volume ratio of hydrogen to nitrogen in the hydrogen-nitrogen mixed gas is 1.5:10, and the hydrogen-nitrogen mixed gas flow rate is 14 ml / min; The core-shell catalyst for low-temperature oxidation of CO and reduction of NO in this embodiment is subjected to a NO removal reaction at 100-250 ℃, and the catalyst loading amount is 8 g; before the experiment is started, the temperature of a water bubbler is maintained at 25 ℃ to obtain a stable water vapor flow rate, and N2 is introduced into the fixed bed reactor to discharge other gases in the reactor, so as to avoid interference of other gases; then CO+NO in the simulated flue gas is introduced for 1 h, so that the Co / CSAC@Ce catalyst impregnated with Co first and then impregnated with Ce is saturated with adsorption of CO+NO, and the experimental error is reduced; The total flow rate of the simulated gas is 1000 ml / min, and the GHSV is 30000 h -1 , the NO flow rate is 2.4 ml·min -1 (2.4×10 3ppm), O2 volume concentration of 10% (volume ratio), CO flow of 4 ml·min-1 (4×103ppm), N2 as the balance gas; the simulated gas was mixed in a gas mixing box, then was sent into a fixed bed reactor, CO was oxidized to CO2 and NO was reduced to N2 under the action of Co / CSAC@Ce catalyst which was impregnated with Co first and then impregnated with Ce; the reacted gas was discharged into the atmosphere after the unreacted CO and NO were absorbed by a limestone solution, and the CO and NO concentrations at the inlet and outlet were detected by a flue gas analyzer; The CO+NO removal efficiency of Co / CSAC@Ce catalyst which was impregnated with Co first and then impregnated with Ce is shown in Table 2 and Figure 1 , Table 2 CO+NO removal efficiency of Co / CSAC@Ce catalyst which was impregnated with Co first and then impregnated with Ce

[0020] ; From Table 2 and Figure 1 It can be seen that the NO removal rate and the CO removal rate of Co / CSAC@Ce catalyst decreased from 99.99% and 99.93% to 70.17% and 98.73% respectively at 100-250℃, and the NO removal rate of the catalyst was the highest among the three catalysts, mainly because the Ce layer maximally regulated the migration of oxygen species, and the dynamic conversion of Ce 3+ / Ce 4+ efficiently transferred electrons, accelerated the adsorption and activation of NO.

[0022] In this embodiment, the core-shell catalyst has CSAC as the core, and active components CeO2 and CoO are coated outside the CSAC to form a shell structure, and the total mass of Ce and Co elements in the active components accounts for 4wt% of CSAC, and the mole amount of Co accounts for 90% of the total mole amount of Co and Ce, which is 100%; A preparation method of a core-shell catalyst for low-temperature oxidation of CO and reduction of NO, and the specific steps are as follows: (1) The coconut shell activated carbon is washed with deionized water for 7 times, ultrasonic treated in a water bath at a temperature of 80℃ for 2h, solid-liquid separated, and dried to obtain pretreated coconut shell activated carbon CSAC; (2) The pretreated coconut shell activated carbon CSAC is added into an acetic acid solution with a concentration of 8mol / L, and surface activated at a temperature of 100℃ for 4h, solid-liquid separated, and dried to obtain activated coconut shell activated carbon CH3COOH / CSAC; (3) The activated coconut shell activated carbon CH3COOH / CSAC is added into a cerium nitrate solution with a concentration of 0.09 mol / L, and is stirred and impregnated at a temperature of 100 ℃ for 4 h, is placed at room temperature for 36 h, and is then vacuum dried to obtain a Ce / CSAC precursor; (4) The Ce / CSAC precursor is uniformly heated at a rate of 10 ℃ / min to a temperature of 490 ℃ in a microwave high-temperature sintering furnace, and is microwave vacuum sintered for 110 min, and is then subjected to plasma surface treatment for 40 min to obtain a Ce / CSAC catalyst; the microwave power is 4 KW, the plasma surface treatment power is 400 W, the plasma discharge gas is hydrogen-nitrogen mixed gas, the volume ratio of hydrogen to nitrogen in the hydrogen-nitrogen mixed gas is 2:10, and the hydrogen-nitrogen mixed gas flow is 15 ml / min; (5) The Ce / CSAC catalyst is added into a cobalt nitrate solution with a concentration of 0.075 mol / L, and is stirred and impregnated at a temperature of 100 ℃ for 4 h, is placed at room temperature for 36 h, and is vacuum dried to obtain a Ce / CSAC@Co precursor; (6) The Ce / CSAC@Co precursor is uniformly heated at a rate of 10 ℃ / min to a temperature of 490 ℃ in a microwave high-temperature sintering furnace, and is microwave vacuum sintered for 110 min, and is then subjected to plasma surface treatment for 40 min to obtain a Ce / CSAC@Co core-shell catalyst; the microwave power is 4 KW, the plasma surface treatment power is 400 W, the plasma discharge gas is hydrogen-nitrogen mixed gas, the volume ratio of hydrogen to nitrogen in the hydrogen-nitrogen mixed gas is 2:10, and the hydrogen-nitrogen mixed gas flow is 15 ml / min; The core-shell catalyst for low-temperature oxidation of CO and reduction of NO in this embodiment is subjected to a NO removal reaction at 100-250 ℃, and the catalyst loading amount is 8 g; before the experiment test, the temperature of the water bubbler is maintained at 25 ℃ to obtain a stable water vapor flow, and N2 is introduced into the fixed bed reactor to discharge other gases in the reactor, so as to avoid interference of other gases; then CO+NO in the simulated flue gas is introduced for 1 h, so that the Ce / CSAC@Co catalyst impregnated with Ce first and then Co is saturated with adsorption of CO+NO, and the experimental error is reduced; The total flow of the simulated gas is 1000 ml / min, and the GHSV is 30000 h -1 -1 -1 (2.4×10 3 ppm), the volume concentration of O2 is 10% (volume ratio), the flow of CO is 4 ml·min -1 (4×10 3ppm), N2 is the balance gas; the simulated gas is mixed in a gas mixing box, and then is sent into a fixed bed reactor, and CO is oxidized to CO2 and NO is reduced to N2 under the action of the Ce / CSAC@Co catalyst which is impregnated with Ce first and then impregnated with Co; the reacted gas is discharged into the atmosphere after the unreacted CO and NO are absorbed by a limestone solution, and the CO and NO concentrations at the inlet and outlet are detected by a flue gas analyzer; The CO+NO removal efficiency of the Ce / CSAC@Co catalyst impregnated with Ce first and then impregnated with Co is shown in Table 3 and Figure 1 , Table 3 CO+NO removal efficiency of the Ce / CSAC@Co catalyst impregnated with Ce first and then impregnated with Co ; As shown in Table 3 and Figure 1 , the NO removal rate and the CO removal rate of the Ce / CSAC@Co catalyst decrease from 95% and 100% to 61.83% and 98.88% respectively at 100-250 DEG C, wherein the CO removal rate of the catalyst is the highest among the three catalysts, and the main reason is that the Co layer dominates the redox cycle, directly catalyzing CO oxidation, reducing the reaction energy barrier, and making the CO catalytic oxidation efficiency the highest; The SEM images of different core-shell catalysts are shown in Figure 2 , the NO and CO can be efficiently removed simultaneously by the different core-shell catalysts at 100-250 DEG C; under the same temperature, the Co / CSAC@Ce catalyst with lamellar CeO2 has the highest NO removal efficiency, up to 99.99%, the lamellar CeO2 covers the surface of the activated carbon to form a microporous-mesoporous hierarchical structure, preventing blockage and providing diffusion channels for the reaction gas; the Ce / CSAC@Co catalyst with needle-like CeO2 has the highest CO removal efficiency, up to 100%, the needle-like CeO2 increases the specific surface area of the activated carbon and enriches oxygen vacancies, significantly optimizing the CO oxidation path and efficiency; the CSAC@CoCe catalyst with cluster-like CeO2 has a CO removal efficiency of 100% and a NO removal efficiency of 93.67%, the cluster-like CeO2 causes pore blockage and active site coverage, leading to insufficient active sites and reducing the activity of the catalyst in removing CO+NO.

[0024] The specific embodiments of the present application are described in detail above, but the present application is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the purpose of the present application.

Claims

1. A method for preparing a core-shell catalyst for low-temperature oxidation of CO and reduction of NO, characterized in that, The core-shell catalyst uses coconut shell activated carbon (CSAC) as the core, with active components CeO2 and CoO coating the outside of the CSAC to form a shell structure. The total mass of Ce and Co elements in the active components accounts for 2-4 wt% of the CSAC, and with the total molar amount of Co and Ce being 100%, the molar amount of Co accounts for 80-90%. The specific steps are as follows: (1) Coconut shell activated carbon is washed with deionized water, ultrasonically treated in a water bath at 60~80℃ for 2~4h, solid-liquid separation is performed, and dried to obtain pretreated coconut shell activated carbon CSAC. (2) The pretreated coconut shell activated carbon CSAC was added to an acetic acid solution for surface activation treatment, solid-liquid separation was performed, and the activated coconut shell activated carbon CH3COOH / CSAC was obtained by drying. (3) Activated coconut shell activated carbon CH3COOH / CSAC was added to a cobalt nitrate-cerium nitrate mixed solution, a cobalt nitrate solution, and a cerium nitrate solution, respectively. The mixture was stirred and impregnated at 80~100℃ for 2~4h, and then allowed to stand at room temperature for 24~36h. Finally, it was dried under vacuum to obtain CSAC@CoCe precursor, Co / CSAC precursor, and Ce / CSAC precursor. (4) In a microwave high-temperature sintering furnace, the CSAC@CoCe precursor, Co / CSAC precursor and Ce / CSAC precursor are heated at a constant rate to a temperature of 470~490℃ and microwave vacuum sintered for 90~110 min, and then plasma surface treatment is performed to obtain CSAC@CoCe core-shell catalyst, Co / CSAC catalyst or Ce / CSAC catalyst. (5) Add the Co / CSAC catalyst to the cerium nitrate solution and stir and impregnate at 80~100℃ for 2~4h, let stand at room temperature for 24~36h, and vacuum dry to obtain the Co / CSAC@Ce precursor; add the Ce / CSAC catalyst to the cobalt nitrate solution and stir and impregnate at 80~100℃ for 2~4h, let stand at room temperature for 24~36h, and vacuum dry to obtain the Ce / CSAC@Co precursor; (6) In a microwave high-temperature sintering furnace, the Co / CSAC@Ce precursor and the Ce / CSAC@Co precursor are heated at a constant rate to a temperature of 470~490℃ and microwave vacuum sintered for 90~110 min, and then plasma surface treatment is performed to obtain the Co / CSAC@Ce core-shell catalyst and the Ce / CSAC@Co core-shell catalyst.

2. The method for preparing a core-shell catalyst for low-temperature oxidation of CO and reduction of NO according to claim 1, characterized in that: Step (2) The concentration of acetic acid solution is 6~8 mol / L, the temperature of surface activity treatment is 80~100℃, and the time is 2~4h.

3. The method for preparing a core-shell catalyst for low-temperature oxidation of CO and reduction of NO according to claim 1, characterized in that: The concentration of cerium nitrate in the cobalt nitrate-cerium nitrate mixed solution is 0.05~0.09 mol / L, the concentration of cobalt nitrate is 0.025~0.075 mol / L, the concentration of cerium nitrate solution is 0.05~0.09 mol / L, and the concentration of cobalt nitrate solution is 0.025~0.075 mol / L.

4. The method for preparing a core-shell catalyst for low-temperature oxidation of CO and reduction of NO according to claim 1, characterized in that: In steps (4) and (6), the microwave power is 2-4KW, the plasma surface treatment power is 300-400W, the time is 20-40min, and the plasma discharge gas is a hydrogen-nitrogen mixture.

5. The method for preparing a core-shell catalyst for low-temperature oxidation of CO and reduction of NO according to claim 4, characterized in that: The volume ratio of hydrogen to nitrogen in the hydrogen-nitrogen mixture is 1~2:10, and the flow rate of the hydrogen-nitrogen mixture is 13~15 ml / min.

6. The application of the core-shell catalyst according to any one of claims 1 to 5 in the catalytic removal of CO and NO from flue gas.

7. The application according to claim 6, characterized in that: The temperature for catalytic removal is 100~250℃.

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