Cuo@ceo2 catalyst for low-temperature simultaneous denitration and demercuration

Abstract

The application provides a CuO@CeO2 catalyst for low-temperature synergistic denitration and demercuration, and belongs to the technical field of denitration and demercuration catalysts.The catalyst is a nanoscale CuO@CeO2 catalyst which is synthesized by a flame synthesis method in one time.The CuO@CeO2 catalyst is a core-shell catalyst, the alkaline active site CuO is used as the shell of the catalyst, and CeO2 is used as the core oxidation active site of the catalyst.The alkaline active site CuO is used as the shell of the catalyst, and is used for adsorbing acid gases such as NO, SO2 and HCl, the adsorbed NO is converted into NO2, NH3, NO is converted into N2 and H2O through a rapid denitration reaction, and VOCs are converted into CO2 and H2O.Thus, the denitration region and the Hg 0 oxidation reaction region are effectively separated, and the purpose of synergistic purification of multiple pollutants is achieved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of denitration and demercuration catalysts, in particular to a CuO@CeO2 catalyst for low-temperature synergistic denitration and demercuration. BACKGROUND

[0002] The flue gas temperature of the steel sintering and waste incineration industries is generally in the range of 150-250 DEG C, and the low temperature leads to the fact that general catalysts cannot meet the requirements of low-temperature conditions for the synergistic removal of NOx and Hg. Under low-temperature conditions, the NH3 adsorption sites of the denitration reaction are the same as the Hg 0 adsorption sites, and the difference between the NH3 and Hg concentrations causes Hg 0 to be difficult to be adsorbed to the active sites, thereby reducing the oxidation performance of Hg 0 . Commercial catalysts generally have a reaction temperature of 350-450 DEG C, and are V-based single-activity oxidation sites, and thus cannot meet the requirements of the synergistic management of NOx reduction and Hg0 oxidation. The prior art CN107715867A discloses a catalyst preparation method for removing NO x and Hg 0 from coal-fired waste gas at low temperature, which is prepared by uniformly loading metal salts on gamma-Al2O3 according to a certain ratio by means of an equal-volume impregnation method and calcining at a certain temperature, so as to obtain a sample for removing NOx and Hg0 at low temperature and with high efficiency. However, the preparation method is complex. Therefore, the market urgently needs a catalyst for the synergistic removal of NOx and Hg from low-temperature flue gas of the steel sintering and waste incineration industries, which can distinguish the reaction regions of denitration and demercuration and improve the catalytic performance of the catalyst. SUMMARY

[0003] The application provides a CuO@CeO2 catalyst for low-temperature synergistic denitration and demercuration.

[0004] To solve the above-mentioned application purposes, the technical scheme provided by the application is as follows:

[0005] The CuO@CeO2 catalyst for low-temperature synergistic denitration and demercuration is synthesized in one step by means of flame synthesis, the CuO@CeO2 catalyst is a core-shell catalyst, the alkaline active site CuO serves as the shell of the catalyst, and CeO2 serves as the core oxidation active site of the catalyst.

[0006] The preparation process of the CuO@CeO2 catalyst is as follows:

[0007] S1, dissolving a catalyst precursor in a solvent, wherein the precursor:solvent ratio is 1 g:5 ml;

[0008] S2, preparing a premixed gas and igniting the premixed gas to form a flame;

[0009] S3, the mixed solution of the catalyst precursor and the solvent obtained in step S1 is formed into aerosol by high-pressure air in an atomizer and sprayed into the flame in step S2;

[0010] S4, the aerosol is heated, combusted, evaporated, solute precipitated, and agglomerated in the flame to form a catalyst, and the catalyst is adsorbed on the stagnation plate under the action of thermal phoresis;

[0011] S5, the cooled catalyst on the stagnation plate is collected, which is a nanoscale CuO@CeO2 catalyst.

[0012] The catalyst precursor in step S1 is Ce(NO3)3 and carbonyl copper, and the molar ratio of Ce to Cu in Ce(NO3)3 and carbonyl copper is 1:1 or 1:4 or 4:1.

[0013] The solvent in step S1 is prepared by mixing extra-pure ethanol and n-hexane at a volume ratio of 1:1.

[0014] The premixed gas in step S2 is a mixture of ethanol and pure oxygen, and the molar ratio of ethanol to pure oxygen is 1:3.5.

[0015] The flow rate of the pure oxygen is 10 L·min -1 By controlling the flow rate of pure oxygen, the atomization size of particulate matter is reduced, and sufficient temperature for catalyst pyrolysis is provided.

[0016] The flame temperature in step S2 is stabilized at 1800-2200℃.

[0017] The aerosol particle size in step S3 is 500-1000 nm.

[0018] The stagnation plate in step S4 is an aluminum plate with a thickness of 1-2 mm, and the back of the stagnation plate has a water cooling device to ensure that the temperature of the stagnation plate is below 50℃, and the distance between the stagnation plate and the atomizer nozzle is 40-60 cm.

[0019] In step S1, tungsten hexacarbonyl is added as a precursor to obtain a catalyst CuO(0.5)@CeO2(0.5)-W, wherein the molar ratio of W in tungsten hexacarbonyl to the whole precursor is 10%.

[0020] The CuO@CeO2 catalyst obtained in step S5 is further subjected to acidification treatment, specifically: 0.1 mol / L sulfuric acid and phosphoric acid are respectively used to soak CuO@CeO2 catalyst at a solid-liquid ratio of 1:5 for 2h, then filtered, dried at 150℃, and finally calcined at 450℃ for 4h, to obtain catalysts CuO(0.5)@CeO2(0.5)-S and CuO(0.5)@CeO2(0.5)-P.

[0021] Compared with the prior art, the technical scheme has at least the following beneficial effects:

[0022] The scheme is synthesized by flame synthesis to synthesize CuO@CeO2 catalyst in one time, CuO with basic active sites is used as the shell of the catalyst to adsorb acid gases such as NO, SO2 and HCl, adsorbed NO is converted into NO2, NH3 and NO are converted into N2 and H2O by rapid reaction of denitration, and VOCs are converted into CO2 and H2O; because NH3 in the CuO shell inhibits Hg 0 Adsorption oxidation has a strong inhibitory effect, so Hg 0 By entering the CuO@CeO2 catalyst core oxidation active site CeO2 through the shell, active sites are formed by adsorbing NO and HCl gas to make Hg 0 Convert into oxidized mercury (HgO, Hg(NO3)2, etc.), so that the denitration region and the Hg 0 oxidation reaction region are effectively separated, and the purpose of multi-pollutant synergistic purification is achieved. In addition, by further acidification treatment, the denitration performance of the catalyst can be effectively increased, and the denitration efficiency is improved. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0024] Figure 1 It is a synthesis diagram of the CuO@CeO2 catalyst for low-temperature synergistic denitration and mercury removal according to the present application;

[0025] Figure 2 It is a performance curve of the CuO(0.5)@CeO2(0.5) catalyst for synergistic denitration and mercury oxidation in the embodiment of the present application;

[0026] Figure 3 It is the denitration performance of the CuO(0.5)@CeO2(0.5) catalyst in the embodiment of the present application;

[0027] Figure 4 It is the NH3 adsorption performance of the CuO(0.5)@CeO2(0.5) catalyst in the embodiment of the present application;

[0028] Figure 5 It is a crystal phase analysis of the CuO(0.5)@CeO2(0.5)-W catalyst prepared in the embodiment of the present application;

[0029] Figure 6 is a surface element valence change of the catalyst prepared in the embodiment of the present application, wherein,Figure 6A CuO(0.5)@CeO2(0.5)-WO3, Figure 6B CuO(0.5)@CeO2(0.5)-WO3, Figure 6C CuO(0.5)@CeO2(0.5)-sulfuric acid, Figure 6D CuO(0.5)@CeO2(0.5)-phosphoric acid. DETAILED DESCRIPTION

[0030] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions of the embodiments of the present application will be described clearly and completely below with reference to the drawings of the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the described embodiments of the present application, all other embodiments obtained by a person of ordinary skill in the art without any inventive effort fall within the scope of protection of the present application.

[0031] Unless otherwise defined, technical terms or scientific terms used in the present application shall have the usual meaning understood by a person of ordinary skill in the art to which the present application belongs.

[0032] The present application provides a CuO@CeO2 catalyst for low-temperature synergistic denitration and demercuration.

[0033] The catalyst is a nanoscale CuO@CeO2 catalyst synthesized by flame synthesis, and the CuO@CeO2 catalyst is a core-shell catalyst, with basic active site CuO as the shell of the catalyst and CeO2 as the core oxidation active site of the catalyst.

[0034] As shown in the preparation process of the CuO@CeO2 catalyst: Figure 1

[0035] S1, dissolving the catalyst precursor in a solvent;

[0036] S2, preparing a premixed gas and igniting to form a flame;

[0037] S3, forming an aerosol of the mixed solution of the catalyst precursor and the solvent obtained in step S1 by high-pressure air in an atomizer, and spraying into the flame in step S2;

[0038] S4, the aerosol is heated, combusted, evaporated, solute precipitated, and agglomerated to form a catalyst in the flame, and the catalyst is adsorbed on the stagnation plate under the action of thermal phoresis;

[0039] S5, collecting the cooled catalyst on the stagnation plate, which is a nanoscale CuO@CeO2 catalyst.

[0040] ​In a specific preparation, ethanol is used as fuel and mixed with pure oxygen to form a premixed gas with a molar mixing ratio of 1:3.5, i.e. the oxygen is slightly higher than the air-fuel ratio of ethanol, to ensure sufficient combustion of ethanol and prevent the formation of carbon black in the combustion flame from blocking the pore structure of the catalyst. The oxygen flow is controlled at 10 L·min -1 , and the flame temperature is stabilized at about 2000°C. The catalyst precursor is formed into an aerosol of 500-1000 nm in the atomizer by high-pressure air, and then enters the flame for heating, combustion, evaporation, solute precipitation, and agglomeration to form a high-efficiency catalyst. The flame-synthesized catalyst is adsorbed on a stagnation plate (1 mm aluminum plate) under the action of thermal force. The back of the stagnation plate has a water cooling device to ensure that the stagnation plate temperature is below 50°C, so that the collected catalyst can be quickly cooled down. After the reaction is completed, the catalyst on the stagnation plate is collected.

[0041] In a specific application, Ce(NO3)3 and copper carbonyl are selected as the precursors of the core-shell catalyst, and 1:1 high-purity ethanol and n-hexane are used as solvents. As shown in Table 1, by systematically adjusting the solvent and gas flow, combustion temperature and other factors of the catalyst synthesis, CuO@CeO2 catalysts with different Cu:Ce ratios are successfully synthesized. Through testing, it is found that CuO(0.5)@CeO2(0.5) with a Cu:Ce ratio of 1:1 has better synergistic multi-pollutant purification performance, so CuO(0.5)@CeO2(0.5) is used as the target research catalyst.

[0042] Table 1 Element ratio of CuO@CeO2 catalyst

[0043]

[0044] Catalyst performance evaluation

[0045] (1) DeNOx and mercury oxidation performance of CuO(0.5)@CeO2(0.5) catalyst

[0046] As Figure 2 (reaction conditions: N2+6% O2+500 ppm NO+500 ppm NH3; mercury concentration: 80.0 μg·m -3 ; space velocity: 50000 h -1) The CuO(0.5)@CeO2(0.5) core-shell catalyst was tested for the synergistic performance of de-NOx and mercury oxidation under the condition of high concentration (500 ppm) of NO and NH3. The de-NOx efficiency of the traditional catalyst was less than 30% at 200°C, and the de-NOx efficiency of the CuO(0.5)@CeO2(0.5) core-shell catalyst increased from 35.4% to 75.8% in the range of 100-200°C. The de-NOx performance of the CuO(0.5)@CeO2(0.5) core-shell catalyst was greatly improved. The mercury oxidation efficiency reached 80.7% at 100°C, and the mercury oxidation rate reached 95.2%-97.7% above 250°C. The de-NOx and de-mercury reactions were in different regions, which significantly reduced the inhibition of NH3 on the mercury oxidation performance of the catalyst and improved the de-NOx and de-mercury performance of the CuO(0.5)@CeO2(0.5) core-shell catalyst.

[0047] (2) Catalytic reaction mechanism of the CuO(0.5)@CeO2(0.5) catalyst

[0048] In the embodiments of the present application, 10-20 nm size nanoparticle catalysts were prepared, and the catalysts had good sulfur resistance and hydrothermal resistance. Research shows that the Cu element of the CuO(0.5)@CeO2(0.5) core-shell catalyst is mainly distributed in the outer shell part, and the Ce element is mainly distributed in the inner core part. The NO and Hg 0 adsorption reaction regions are effectively separated by the different acidities and basicities of the active sites.

[0049] After the de-NOx and de-mercury reactions, the N and Hg elements of the catalyst were characterized. The N element is mainly distributed in the CuO(0.5)@CeO2(0.5) core-shell catalyst outer shell CuO part. Considering the strong basicity of the CuO active site and the de-NOx reaction efficiency, it is speculated that the outer shell CuO mainly adsorbs NO to form NO2. The Hg element is mainly distributed in the inner core part CeO2, which proves that the Hg 0 catalytic oxidation process is mainly distributed in the inner core part. Therefore, the CuO(0.5)@CeO2(0.5) core-shell catalyst effectively separates the NO and Hg 0 adsorption regions, the de-NOx reaction mainly occurs in the outer shell region, and the mercury oxidation mainly occurs in the inner core region. The de-NOx and de-mercury reaction regions are effectively separated, so that the NH3 adsorption of the de-NOx reaction is controlled in the outside of the CuO(0.5)@CeO2(0.5) core-shell catalyst, the adsorption competition between NH3 and Hg on the surface of CeO2 is avoided, and the mercury oxidation performance of the CeO2 in the catalyst is improved.

[0050] Further, the obtained catalyst can be subjected to acid treatment in order to improve the de-NOx performance of the catalyst.

[0051] The CuO@CeO2 catalyst was soaked in 0.1 mol / L sulfuric acid and phosphoric acid at a solid-liquid ratio of 1:5 for 2 h, then filtered, dried at 150 °C, and finally calcined at 450 °C for 4 h to obtain the catalysts CuO(0.5)@CeO2(0.5)-S and CuO(0.5)@CeO2(0.5)-P, as shown in Table 2.

[0052] Meanwhile, in step S1, tungsten hexacarbonyl is added as a precursor to obtain the catalyst CuO(0.5)@CeO2(0.5)-W.

[0053] Table 2 Elemental Ratios of CuO@CeO2 Acidification Catalysts

[0054]

[0055] like Figure 3 As shown, in the presence of N2 + 6% O2 + 500 ppm NH3 and a mercury concentration of 80.0 μg·m -3 Airspeed 50,000 h -1 Under the reaction conditions, acid treatment significantly increased the denitrification performance of the catalysts at reaction temperatures above 300℃, achieving denitrification efficiencies of 77.6%-99.5%. Sulfuric acid treatment of the CuO(0.5)@CeO2(0.5)-S catalyst resulted in a denitrification efficiency of 77.6%-77.9% in the 300-450℃ range. Phosphoric acid treatment significantly improved the denitrification efficiency, with the CuO(0.5)@CeO2(0.5)-P catalyst achieving a denitrification efficiency of 89.6%-91.4% in the 300-450℃ range. WO3-doped catalysts exhibited the best denitrification efficiency, with CuO(0.5)@CeO2(0.5)-W achieving a denitrification efficiency of 95.9%-99.5% in the 300-450℃ range, demonstrating good denitrification efficiency, and maintaining a relatively good denitrification efficiency (45.3%-90.6%) even at 100-250℃.

[0056] The above results indicate that the excellent oxidation ability significantly improves the mercury oxidation ability of the CuO(0.5)@CeO2(0.5) core-shell catalyst. In order to further stabilize the catalyst and increase the surface acidity, acid treatment was adopted. The results show that WO3 doping significantly improves the denitrification ability of the catalyst.

[0057] like Figure 4As shown, the NH3 desorption peak of CuO(0.5)@CeO2(0.5) catalyst mainly exists in the form of weak acid at 100-200 ℃, which is consistent with the good denitration performance of CuO(0.5)@CeO2(0.5) at low temperature. When the temperature rises to 300 ℃, NH3 is completely desorbed from the CuO(0.5)@CeO2(0.5) catalyst, at which time NH3 cannot contact the active site, reducing the reaction efficiency of NH3 and NO. The catalyst CuO(0.5)@CeO2(0.5)-S treated with sulfuric acid exhibits the best NH3 adsorption performance. The catalyst still has high NH3 adsorption performance in the strong acid range of 300-400 ℃, which is the result of the formation of a large number of sulfate and B-acid sites on the catalyst surface by sulfuric acid acidification. WO3 doping and phosphoric acid treatment have similar effects at high temperatures, indicating that WO3 doping and phosphoric acid treatment improve the high-temperature acid sites of the catalyst.

[0058] By Figure 5 analysis, the test shows that WO3 does not appear obvious crystal grains in the CuO(0.5)@CeO2(0.5)-W catalyst, and is uniformly distributed on the surface of the catalyst, providing the acidity and active sites of the catalyst, so that the WO3 doping of the CuO(0.5)@CeO2(0.5) catalyst exhibits good acidity and catalytic activity.

[0059] As Figure 6A shown, the valence state change of the surface O element of the CuO(0.5)@CeO2(0.5) catalyst before and after acidification treatment is shown. The spectrum contains two bond energy peaks: 529.0-530.6 eV and 530.7-532.0 eV. The low bond energy peak (529.0-530.6 eV) represents the energy spectrum peak of lattice oxygen (O L ); the high bond energy peak (530.7-532.0 eV) represents active oxygen components (O a ), such as chemisorbed oxygen or oxygen vacancy adsorbed oxygen. As Figure 6B shown, the O a proportion of the CuO(0.5)@CeO2(0.5)-WO3 catalyst doped with WO3 increases, indicating that the active sites of the catalyst increase, promoting the progress of the denitration reaction, which is consistent with the reaction performance of the catalyst. As Figure 6C shown, the O a proportion of the catalyst CuO(0.5)@CeO2(0.5)-sulfuric acid treated with sulfuric acid is significantly reduced, accounting for only 12.3%, indicating that the active sites of the catalyst surface are acidified during the sulfuric acid acidification process, and the active oxygen on the catalyst surface is stabilized, forming lattice oxygen or sulfate, thereby increasing the proportion of O L . As Figure 6D shown, the Oa The proportion is also reduced, indicating that the active oxygen on the catalyst surface is also stabilized during the phosphoric acid oxidation process, forming lattice oxygen or phosphates, thereby improving the O L The proportion.

[0060] In summary, the catalyst of the present application effectively separates the denitration region from the Hg 0 oxidation reaction region at low temperature, achieving the effect of multi-pollutant synergistic purification, and after further acidification treatment, the denitration performance can be significantly improved, especially the WO3 doping meets the requirements of increasing the catalyst surface acidity and improving the active structure of the catalyst surface, and the catalyst has good reaction activity.

[0061] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto, and the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A CuO@CeO 2 catalyst for low-temperature synergistic denitration and demercuration, characterized in that, The CuO@CeO2 catalyst in nanometer size is synthesized by one-time synthesis of flame synthesis, the CuO@CeO2 catalyst is a core-shell catalyst, the basic active site CuO is used as the shell of the catalyst, and the CeO2 is used as the core oxidation active site of the catalyst; The preparation process of the CuO@CeO2 catalyst is as follows: S1, the catalyst precursor is dissolved in a solvent, wherein the precursor:solvent ratio is 1g:5ml; S2, a premixed gas is prepared and ignited to form a flame; S3, the mixed solution of the catalyst precursor and the solvent obtained in step S1 is formed into an aerosol by high-pressure air in an atomizer and sprayed into the flame in step S2; S4, the aerosol is heated, combusted, evaporated, solute precipitated, and agglomerated to form a catalyst in the flame, and the catalyst is adsorbed on the stagnation plate under the action of thermal force; S5, the cooled catalyst on the stagnation plate is collected, which is the CuO@CeO2 catalyst in nanometer size; The catalyst precursor in step S1 is Ce(NO3)3 and carbonyl copper; The solvent in step S1 is prepared by mixing high-purity ethanol and n-hexane at a volume ratio of 1:1; The flame temperature in step S2 is stabilized at 1800-2200℃.

2. The CuO@CeO2 catalyst for low-temperature synergetic removal of mercury and nitrogen oxides according to claim 1, characterized in that, The molar ratio of Ce to Cu in Ce(NO3)3 and carbonyl copper in S1 is 1:1 or 1:4 or 4:

1. 3.The CuO@CeO 2 catalyst for low-temperature synergetic removal of mercury and NO x according to claim 1, characterized in that, The premixed gas in the step S2 is formed by mixing ethanol and pure oxygen, wherein the molar ratio of ethanol to pure oxygen is 1:3.5, and the flow rate of pure oxygen is 10 L·min -1 . 4.The CuO@CeO 2 catalyst for low-temperature synergetic removal of mercury and NO x according to claim 1, characterized in that, The particle size of the aerosol in step S3 is 500-1000 nm. 5.The CuO@CeO 2 catalyst for low-temperature synergetic removal of mercury and NO x according to claim 1, characterized in that, The stagnation plate in step S4 is an aluminum plate with a thickness of 1-2mm, and the back of the stagnation plate has a water cooling device to ensure that the temperature of the stagnation plate is below 50℃; the distance between the stagnation plate and the atomizer nozzle is 40-60cm. 6.The CuO@CeO 2 catalyst for low-temperature synergetic removal of mercury and NO x according to claim 2, characterized in that, In step S1, tungsten hexacarbonyl is added as a precursor to obtain a catalyst CuO@CeO2-W, wherein the molar ratio of W in tungsten hexacarbonyl to the whole catalyst precursor is 10%.

7. The CuO@CeO2 catalyst for low-temperature synergetic removal of mercury and NOx according to claim 2, characterized in that, The CuO@CeO2 catalyst obtained in step S5 is further subjected to acidification treatment, specifically: 0.1mol / L sulfuric acid and phosphoric acid are used to soak the CuO@CeO2 catalyst at a solid-liquid ratio of 1:5 for 2h, then filtered, dried at 150℃, and finally calcined at 450℃ for 4h, to obtain catalysts CuO@CeO2-S and CuO@CeO2-P, respectively.

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