Manganese-based denitration catalyst with core-shell structure as well as preparation method and application of manganese-based denitration catalyst

Abstract

The invention relates to a manganese-based denitration catalyst with a core-shell structure as well as a preparation method and application thereof, and belongs to the technical field of environment-friendly catalysts. The technical problems that a catalyst cannot meet the purification requirement of a wide temperature range, the nitrogen selectivity is poor, the reaction path is difficult to control, new pollutants are generated through excessive oxidation, and the denitration capacity in the wide temperature range is poor are solved. The invention relates to a manganese-based denitration catalyst with a core-shell structure. The composition of the manganese-based denitration catalyst is AMnOx (at) BOy, aMnOx is a composite oxide of coated manganese and doped elements, and BOy is an acidic metal oxide shell; and a reverse coprecipitation method is adopted for preparation. The manganese-based denitration catalyst with the core-shell structure has high surface acidity and oxidation-reduction capacity, the adsorption capacity of the catalyst to NH3 can be enhanced, and the manganese-based denitration catalyst has high catalytic activity and nitrogen selectivity at the active temperature of 150-400 DEG C.

Description

Technical Field

[0001] The present invention discloses a manganese-based denitration catalyst with a core-shell structure, a preparation method thereof, and an application thereof, belonging to the technical field of environmentally friendly catalysts. Background Art

[0002] Nitrogen oxides (NO x ) is the main source of air pollution, mainly from the combustion of fossil fuels and the growth of motor vehicle ownership. Excessive emissions will cause environmental and climate problems such as acid rain, photochemical smog and global warming. Traditional denitrification technology uses ammonia selective catalytic reduction (NH3-SCR) method, with V2O5-WO3 / TiO2 or its modified substances as catalysts. The active temperature range is relatively narrow, usually 150℃~300℃ or 250℃~400℃, and the cost of the catalyst is relatively high. However, it cannot simultaneously meet the requirements of nitrogen oxides (NO) within a wide temperature range such as 150℃~400℃. x ) purification requirements.

[0003] Currently, in practical applications, manganese oxide (MnO2) and modified manganese oxide catalysts are widely studied due to their excellent low-temperature catalytic activity and environmentally friendly properties. However, manganese-based selective catalytic reduction (SCR) denitrification catalysts need to consider the issue of nitrogen selectivity. Although the variable chemical states and abundant lattice defects of manganese oxides exhibit excellent redox performance, these characteristics may also make it difficult to precisely control the reaction path in the SCR reaction. At high temperatures, NH3 will be over-oxidized to N2O, leading to the formation of new pollutants. This side reaction is very significant in the medium and high temperature range above 250°C. Compared with other transition metals, manganese has more variable valence states and can easily convert between various oxidation states under low temperature conditions, thus having good low-temperature denitrification performance and a relatively low price. Therefore, there is an urgent need to develop a manganese-based denitrification catalyst with strong nitrogen selectivity and strong denitrification ability over a wide temperature range. Summary of the Invention

[0004] In order to solve the technical problems such as the catalyst cannot meet the purification requirements in a wide temperature range, poor nitrogen selectivity, difficulty in controlling the reaction path, excessive oxidation to generate new pollutants, and poor denitrification ability in a wide temperature range, the present invention proposes a core-shell structured manganese-based denitrification catalyst and its preparation method and application.

[0005] In order to solve the above technical problems, the technical solutions of the present invention are as follows:

[0006] A core-shell structured manganese-based denitrification catalyst, the composition of the manganese-based denitrification catalyst is AMnO x @BO y ;AMnO x It is a composite oxide of coated manganese and doping elements, BO yIt is an acidic metal oxide shell;

[0007] Wherein, A is a doping element, and the doping element is a rare earth element;

[0008] B is an acidic metal element, and the acidic metal element is a transition metal element;

[0009] x is the active component of the composite oxide of manganese and doping elements AMnO x The number of oxygen atoms in , 1≤x≤2;

[0010] y is an acidic metal oxide shell BO y The number of oxygen atoms in , 1≤y≤3.

[0011] Preferably, the rare earth element is selected from any one of cerium, neodymium, samarium, europium, yttrium, dysprosium, ytterbium, lanthanum or praseodymium; wherein,

[0012] The molar ratio of the rare earth element to the manganese element is (0.05-0.3):1, and can be 0.05:1, 0.10:1, 0.15:1, 0.20:1, 0.25:1 or 0.30:1, but is not limited to the listed values.

[0013] Furthermore, the rare earth element is selected from any one of cerium, neodymium or lanthanum.

[0014] Preferably, the transition metal element is selected from any one of tungsten, molybdenum, niobium, chromium, iron, cobalt, nickel or titanium; wherein,

[0015] The molar ratio of the transition metal element to the manganese element is (2.0-15.0):1, and can be 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1 or 15:1, but is not limited to the listed values.

[0016] Furthermore, the transition metal element is selected from any one of molybdenum and titanium.

[0017] A method for preparing a core-shell structured manganese-based denitration catalyst, wherein the manganese-based denitration catalyst is prepared by a reverse coprecipitation method.

[0018] The specific steps are as follows:

[0019] (1) A rare earth element compound and a manganese nitrate compound are mixed, and 60.0 mL of deionized water is added and stirred thoroughly to form a mixed solution. The mixed solution is then added dropwise to a precipitant at a dropping speed of 5 to 20 mL / min while stirring. After a precipitate is formed, the precipitate is allowed to stand for 2 h to 24 h, and filtered to obtain a precipitate. The precipitate is then centrifuged and dried at a temperature of 80°C to 105°C. The dried precipitate is then calcined for the first time in a muffle furnace, wherein the calcination temperature is 400°C to 600°C, the heating rate is 1.0°C / min to 10.0°C / min, and the calcination time is 3.0 h to 10.0 h to obtain a composite oxide AMnO. x The composite oxide obtained after calcination is cooled to room temperature, and then the composite oxide is placed in a ball mill and ball-milled using zirconium beads. During the ball milling, the mass ratio of the calcined composite oxide to the zirconium beads is 1: (5.0-20.0), the ball milling time is 2.0h-5.0h, and the ball milling speed is 300 rpm-900 rpm to obtain a composite oxide AMnO that is uniformly dispersed after ball milling. x powder;

[0020] (2) The ball-milled composite oxide powder was added to a mixed solution of an acidic metal compound and ethanol containing a metal ion concentration of 0.01 mol / L to 0.1 mol / L. The mixed solution was then ultrasonically dispersed for 20 min to 60 min. The mixed solution was then dried at a drying temperature of 80°C to 105°C. The dried mixture was then sent to a muffle furnace for a second calcination at a calcination temperature of 400°C to 600°C, a heating rate of 1.0°C to 10.0°C / min, and a calcination time of 3.0 h to 10.0 h to obtain a core-shell structured manganese-based denitrification catalyst AMnO x @BO y .

[0021] Preferably, in step (1), the rare earth element compound is selected from cerium nitrate, neodymium nitrate, samarium nitrate, europium nitrate,

[0022] Any one of yttrium nitrate, dysprosium nitrate, ytterbium nitrate, lanthanum nitrate or praseodymium nitrate; the nitrate compound of manganese element is selected from manganese nitrate.

[0023] Furthermore, the rare earth element compound is selected from any one of cerium nitrate, neodymium nitrate or lanthanum nitrate.

[0024] Preferably, in step (1), the precipitant is a mixture of 30% concentrated ammonia water and deionized water, and the 30% concentrated ammonia water

[0025] The volume ratio of the precipitant to the deionized water is 1:9; wherein the molar ratio of the precipitant to the sum of the metal ions is (1-3):1, which can be 1:1, 1.5:1, 2:1, 2.5:1 or 3:1, but is not limited to the values listed;

[0026] It should be noted that the sum of metal ions refers to the sum of rare earth ions in rare earth element compounds and manganese ions in nitrate compounds.

[0027] Preferably, in step (2), the acidic metal compound is selected from ammonium metatungstate, ammonium molybdate, tetrabutyl titanate, niobate

[0028] Any of ammonium oxalate, chromium nitrate, iron nitrate, cobalt nitrate or nickel nitrate;

[0029] Furthermore, in step (2), the acidic metal compound is selected from any one of ammonium molybdate and tetrabutyl titanate.

[0030] In addition, in the above preparation method:

[0031] In step (1), the mixed solution is added dropwise to the precipitant at a rate of 5 mL / min to 20 mL / min, which may be 5 mL / min, 10 mL / min, 15 mL / min or 20 mL / min, but is not limited to the values listed;

[0032] The first calcination temperature is 400°C to 600°C, and can be 400°C, 420°C, 440°C, 460°C, 480°C, 500°C, 520°C, 540°C, 580°C or 600°C, but is not limited to the listed values;

[0033] During ball milling, the mass ratio of the calcined composite oxide to the zirconium beads is 1:(5.0-20.0), which may be 1:5, 1:10, 1:15 or 1:20, but is not limited to the values listed. The ball milling time is 2.0 h to 5.0 h, which may be 2 h, 3 h, 4 h or 5 h, but is not limited to the values listed. The ball milling speed is 300 rpm to 900 rpm, which may be 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm or 900 rpm, but is not limited to the values listed.

[0034] In step (2), the mixed solution is ultrasonically dispersed for 20 min to 60 min, which can be 20 min, 30 min, 40 min, 50 min or 60 min, but is not limited to the listed values;

[0035] The first calcination temperature is 400°C to 600°C, and can be 400°C, 420°C, 440°C, 460°C, 480°C, 500°C, 520°C, 540°C, 580°C or 600°C, but is not limited to the listed values.

[0036] The present invention also includes a core-shell structure manganese-based denitrification catalyst for the treatment of nitrogen oxides (NO x ) catalytic applications. Its applications mainly include treating NO in waste gas emitted by coal-fired power plants, sintering plants, cement plants, etc. x , among which, NO x It refers to oxides of nitrogen in different valence states or mixtures thereof.

[0037] Beneficial effects of the present invention:

[0038] 1. The present invention provides a core-shell structured manganese-based denitration catalyst, its preparation method, and application. The manganese-based denitration catalyst has high surface acidity and redox ability. The coated manganese and composite oxide of doped elements and the acidic metal oxide shell can balance the redox ability and acidity of the catalyst. At the same time, the core-shell structured manganese-based denitration catalyst of the present invention has high catalytic activity and nitrogen selectivity at an active temperature of 150°C to 400°C, while meeting purification requirements within a wide active temperature range.

[0039] 2. By doping rare earth elements with manganese, the redox ability of manganese can be regulated. Combining acidic metal oxides as a shell can enhance the catalyst's adsorption capacity for NH3. x The asymmetric oxygen vacancy structure of AO-Mn in the catalyst improves the oxygen activation ability of the catalyst, thereby enhancing the activation and dehydrogenation rate of NH3, improving the denitrification efficiency of the catalyst, and inhibiting the side reaction of NH3 to N2O, thereby improving the nitrogen selectivity of the catalyst and avoiding the generation of new pollutants due to excessive reaction caused by poor nitrogen selectivity;

[0040] 3. By regulating the molar ratio of manganese to acidic metal elements and keeping it within a range of 1:(2.0-15.0), an acidic metal oxide shell with controllable thickness can be prepared. This allows the core-shell manganese-based denitrification catalyst to maintain both high-temperature and low-temperature catalytic activity, with very low N2O production and high N2 selectivity, resulting in enhanced denitrification performance over a wide active temperature range (150°C-400°C). When the ratio is controlled within a range of 1:(2.0-15.0), the catalyst shell thickness is not too thick due to a low manganese content, which would weaken the catalyst's redox ability and prevent NH3 from reacting with NO at suitable sites after adsorption, leading to a decrease in low-temperature performance. Furthermore, the shell thickness is not too thin due to a high manganese content, which would prevent the acidic metal elements from effectively adsorbing and activating NH3, resulting in an overly strong redox ability of the catalyst, which would easily lead to over-oxidation of NH3 to N2O and a decrease in N2 selectivity.

[0041] 4. The preparation method of the core-shell structured manganese-based denitration catalyst provided by the present invention is simple and easy to operate, with low synthesis cost, short time and high success rate, and does not contain heavy metal substances such as vanadium, and is relatively environmentally friendly; compared with the forward co-precipitation method used in the prior art, the active component of the core-shell structured manganese-based denitration catalyst synthesized by the reverse co-precipitation method used in the present invention has good crystallinity, which is because when a mixed solution of a rare earth element compound and a manganese nitrate compound with a low pH value is added to a precipitant with a high pH value, the pH value of the reaction environment of the metal ions and the precipitant is always maintained at a high value, resulting in more complete precipitation of the metal ions, thereby making the acidity and redox ability of the manganese-based denitration catalyst highly controllable; Before the manganese-based denitrification catalyst is coated with the acidic metal oxide, it needs to be dispersed by ball milling. The particle size of the manganese-based denitrification catalyst particles is significantly reduced after ball milling, which can enhance the interaction with the acidic metal oxide shell, thereby improving the NH3 adsorption capacity of the catalyst; during ball milling, the quality of the zirconium beads used must be controlled within a certain range. If there are too many zirconium beads, the catalyst particle size will be too small and the lattice will be broken, thereby reducing the redox ability of the catalyst and causing a decrease in catalytic performance; if there are too few zirconium beads, the catalyst particle size will be increased, resulting in low utilization of active sites; similarly, the ball milling time and speed must also be controlled within a reasonable range to control the particle size of the catalyst and make the composite oxide AMnO x It is easily coated by acidic metal oxides to form a good core-shell structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1This is a graph showing the catalytic reduction performance of a core-shell manganese-based denitration catalyst for nitrogen oxides versus temperature as shown in Example 1 of a core-shell manganese-based denitration catalyst and its preparation method and application according to the present invention. This graph is also used as an abstract figure.

[0043] Figure 2 This is a comparison chart of the XRD diffraction of a core-shell structured manganese-based denitration catalyst prepared by the reverse co-precipitation method in Example 1 of the present invention and a preparation method and application thereof, and a manganese-based denitration catalyst prepared by the forward co-precipitation method in Comparative Example 3. DETAILED DESCRIPTION

[0044] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0045] Example 1

[0046] (1) 0.4340 g of cerium nitrate hexahydrate and 1.7895 g of 50% manganese nitrate solution were mixed, and 60 mL of deionized water was added. The mixture was stirred thoroughly to form a mixed solution. The mixed solution was then heated to 10 mL / min was added dropwise to a mixed solution of 6mL30% concentrated ammonia water and 54mL deionized water, stirring while adding dropwise. After the addition was completed and a precipitate was formed, the solution and the precipitate were allowed to stand for 10h and filtered to obtain a precipitate, which was then centrifuged and dried at a temperature of 90°C. The dried precipitate was then calcined for the first time in a muffle furnace, wherein the precipitate was calcined at a temperature of 500°C in a muffle furnace at a heating rate of 5°C / min for 4h. At this time, the molar ratio of Ce to Mn in the obtained composite oxide powder was 0.2:1; the composite oxide obtained after calcination was cooled to room temperature, 1.0g of the calcined composite oxide powder was taken, and then the composite oxide was placed in a ball mill and ball milled with zirconium beads. The mass of the added zirconium beads was 10.0g, the ball milling time was 3.0h, and the ball milling speed was 450 rpm to obtain a composite oxide AMnO that was uniformly dispersed after ball milling. x powder;

[0047] (2) 1.0 g of the above-mentioned ball-milled composite oxide powder was added to a mixed solution of 26.146 g of tetrabutyl titanate and 100 mL of ethanol. The mixed solution was then ultrasonically dispersed for 30 minutes and dried at 90 °C. The dried mixture was then sent to a muffle furnace for a second calcination at a calcination temperature of 500 °C, a heating rate of 5 °C / min, and a calcination time of 4 h. At this time, the molar ratio of Ti to Mn in the obtained manganese-based denitration catalyst was 10:1, thereby obtaining a core-shell structured manganese-based denitration catalyst AMnO x @BO y ;

[0048] Among them, the XRD diffraction pattern of the core-shell structured manganese-based denitrification catalyst is as follows: Figure 2 shown.

[0049] Example 2

[0050] The only difference between this example and Example 1 is that, when preparing the core-shell manganese-based denitration catalyst, 0.4340 g of cerium nitrate hexahydrate was replaced with 0.4344 g of lanthanum nitrate hexahydrate. The molar ratio of La to Mn in the composite oxide was now 0.2:1. All other conditions and parameters were identical to those in Example 1.

[0051] Example 3

[0052] The only difference between this example and Example 1 is that, when preparing the core-shell manganese-based denitration catalyst, 0.4340 g of cerium nitrate hexahydrate was replaced with 0.4380 g of neodymium nitrate hexahydrate. The molar ratio of Nd to Mn in the composite oxide was now 0.2:1. All other conditions and parameters were identical to those in Example 1.

[0053] Comparative Example 1

[0054] The only difference between this comparative example and Example 1 is that only manganese nitrate is added when preparing the composite oxide of the manganese-based denitration catalyst, and the other conditions and parameters are exactly the same as those in Example 1.

[0055] Comparative Example 2

[0056] The only difference between this comparative example and Example 1 is that, when preparing the manganese-based denitration catalyst, tetrabutyl titanate is not added during the ultrasonic dispersion stage in step (2), but only ethanol is added. The other conditions and parameters are exactly the same as those in Example 1.

[0057] Comparative Example 3

[0058] The only difference between this comparative example and Example 1 is that, when preparing the manganese-based denitration catalyst, a forward precipitation method is adopted, wherein a mixed solution containing 6 mL of 30% concentrated ammonia water and 54 mL of deionized water is added dropwise to a mixed solution of cerium nitrate hexahydrate and manganese nitrate. Other conditions and parameters are exactly the same as those in Example 1. The XRD diffraction pattern of the core-shell structured manganese-based denitration catalyst is as follows: Figure 2 shown.

[0059] Comparative Example 4

[0060] 0.4340 g of cerium nitrate hexahydrate and 1.7895 g of 50% manganese nitrate solution were mixed, and 60 mL of deionized water was added. The mixed solution was then added dropwise at a rate of 10 mL / min to a mixed solution containing 6 mL of 30% concentrated ammonia water, 5.681 g of titanium dioxide powder and 54 mL of deionized water. The mixture was added dropwise while stirring. After the addition was completed, the stirring was stopped, and the mixed solution was allowed to stand for 10 hours and filtered to obtain a precipitate. The precipitate was dried at 90°C, and then the precipitate was heated to 500°C in a muffle furnace at a heating rate of 5°C / min and calcined for 4 hours to obtain a manganese-based denitration catalyst.

[0061] Comparative Example 5

[0062] This comparative example differs from Example 1 only in that, when preparing the core-shell manganese-based denitration catalyst, 26.146 g of tetrabutyl titanate was replaced with 13.580 g of ammonium molybdate, and 100 mL of ethanol was replaced with 100 mL of water. The molar ratio of Mo to Mn in the manganese-based denitration catalyst was now 10:1. All other conditions and parameters were identical to those in Example 1.

[0063] Comparative Example 6

[0064] This comparative example differs from Example 1 only in that, when preparing the core-shell manganese-based denitration catalyst, 0.4340 g of cerium nitrate hexahydrate was replaced with 0.0217 g of cerium nitrate hexahydrate. The molar ratio of Ce to Mn in the composite oxide was now 0.01:1. All other conditions and parameters were identical to those in Example 1.

[0065] Comparative Example 7

[0066] The only difference between this comparative example and Example 1 is that, when preparing the manganese-based denitration catalyst, 0.4340 g of cerium nitrate hexahydrate was replaced with 1.3020 g of cerium nitrate hexahydrate, and the molar ratio of Ce to Mn in the composite oxide was now 0.6:1. Other conditions and parameters were identical to those in Example 1.

[0067] Comparative Example 8

[0068] The only difference between this comparative example and Example 1 is that, when preparing the manganese-based denitration catalyst, 26.146 g of tetrabutyl titanate was replaced with 1.307 g of tetrabutyl titanate, and the molar ratio of Ti to Mn in the manganese-based denitration catalyst was now 0.5:1. Other conditions and parameters were identical to those in Example 1.

[0069] Comparative Example 9

[0070] The only difference between this comparative example and Example 1 is that, when preparing the manganese-based denitration catalyst, 26.146 g of tetrabutyl titanate was replaced with 52.292 g of tetrabutyl titanate, and the molar ratio of Ti to Mn in the manganese-based denitration catalyst was now 20:1. Other conditions and parameters were identical to those in Example 1.

[0071] Comparative Example 10

[0072] The only difference between this comparative example and Example 1 is that, in the ball milling stage, 1 g of powder is mixed with 50 g of zirconium beads and ball milled. Other conditions and parameters are exactly the same as those in Example 1.

[0073] Comparative Example 11

[0074] The only difference between this comparative example and Example 1 is that, in the ball milling stage, 1 g of powder is mixed with 1 g of zirconium beads and ball milled. Other conditions and parameters are exactly the same as those in Example 1.

[0075] Comparative Example 12

[0076] The only difference between this comparative example and Example 1 is that, in the ball milling stage, the ball milling time is set to 10 h, and the other conditions and parameters are exactly the same as those in Example 1.

[0077] Comparative Example 13

[0078] The only difference between this comparative example and Example 1 is that, in the ball milling stage, the ball milling time is set to 1 h, and the other conditions and parameters are exactly the same as those in Example 1.

[0079] Comparative Example 14

[0080] The only difference between this comparative example and Example 1 is that, when preparing the manganese-based denitration catalyst, in the ultrasonic dispersion stage in step (2), the ultrasonic dispersion time is set to 3 h, and the other conditions and parameters are exactly the same as those in Example 1.

[0081] Comparative Example 15

[0082] The only difference between this comparative example and Example 1 is that, when preparing the manganese-based denitration catalyst, in the ultrasonic dispersion stage in step (2), the ultrasonic dispersion time is set to 5 minutes, and the other conditions and parameters are exactly the same as those in Example 1.

[0083] Comparative Example 16

[0084] The only difference between this comparative example and Example 1 is that the calcination temperature for both times when preparing the manganese-based denitration catalyst is 900° C., and the other conditions and parameters are exactly the same as those in Example 1.

[0085] Comparative Example 17

[0086] The only difference between this comparative example and Example 1 is that the calcination temperature for both times during the preparation of the manganese-based denitration catalyst is 300° C., and the other conditions and parameters are exactly the same as those in Example 1.

[0087] Performance testing:

[0088] The catalysts prepared in the above examples and comparative examples were used to conduct denitrification activity tests on flue gas in simulated air pollution control. The flue gas in simulated air pollution control contained 500ppm NH3, 500ppm NO, and 5% O2, with nitrogen as the balance gas. The NO activity of the catalysts at different temperatures was tested under the above conditions. x The conversion rate and N2 selectivity test results are shown in Table 1:

[0089]

[0090] The test results show that:

[0091] (1) Combination Figure 1 Comparing the data in Table 1 with Examples 1 to 3, it can be seen that the type of rare earth doping element in the manganese-based denitration catalysts of the present invention has a significant impact on the denitration performance of the catalysts, but has little effect on nitrogen selectivity. The catalyst doped with the rare earth element Ce exhibits the best performance. This is because, compared to La and Nd, Ce, upon incorporation into the crystal lattice, releases surrounding lattice oxygen more readily, resulting in a lower oxygen vacancy formation energy and a stronger redox ability.

[0092] (2) Combining the data in Table 1, it can be seen from Example 1 and Comparative Example 1 that the presence of a rare earth doping element has a significant effect on the denitration performance and nitrogen selectivity of the catalyst. Without the doping of a rare earth element, the MnO2 active component has poor acidity and excessive redox ability, which can lead to excessive oxidation of NH3 to byproducts such as NO or N2O, thereby reducing the denitration performance and nitrogen selectivity of the catalyst.

[0093] (3) Combining the data in Table 1, Example 1 and Comparative Example 2 show that the presence of an acidic metal oxide shell has a significant effect on the denitration performance and nitrogen selectivity of the catalyst. Without the use of an acidic metal oxide shell for coating, the acidity of the catalyst cannot be enhanced, resulting in excessive oxidation of NH3 to byproducts such as NO or N2O, thereby reducing the denitration performance and nitrogen selectivity of the catalyst.

[0094] (4) Combination Figure 2 As shown in Table 1, Example 1 and Comparative Example 3 demonstrate that the order of solution addition significantly influences the catalyst's denitration performance and nitrogen selectivity when preparing manganese-based composite oxides using the coprecipitation method. The forward coprecipitation method results in the metal ions forming corresponding hydroxide precipitates at low pH. Excessively low pH can lead to partial dissolution of the hydroxide precipitate, thereby reducing the catalyst's crystallinity.

[0095] (5) Combining the data in Table 1, it can be seen from Example 1 and Comparative Example 4 that the interaction strength between titanium dioxide and the active component has a significant effect on the denitrification performance and nitrogen selectivity of the catalyst. When titanium dioxide is used as a carrier, part of CeMnO x The nanoparticles cannot fully contact Ti, resulting in reduced interaction; however, when titanium dioxide is used as the shell, most of the active sites of the catalyst (i.e., the Ce-O-Mn-O-Ti interface) can be fully exposed, improving the utilization of active sites.

[0096] (6) In conjunction with the data in Table 1, by comparing Example 1 with Comparative Example 4, it can be seen that in the manganese-based denitration catalysts of the present invention, the type of acidic element has a significant effect on the denitration performance of the catalyst, but has a smaller effect on the nitrogen selectivity. Among them, the Ti-coated catalyst has the best performance. This is because, compared with elements such as Mo, Ti not only has a certain degree of acidity, but also the lattice oxygen of Ti is more easily released, which also improves the catalyst's NH3 activation dehydrogenation ability.

[0097] (7) In conjunction with the data in Table 1, by comparing Example 1 with Comparative Examples 5 and 6, it can be seen that the amount of rare earth element doping in the manganese-based denitration catalyst of the present invention has a significant effect on the denitration performance and nitrogen selectivity of the catalyst. If the amount of doping element is too small, the catalyst's redox ability is too strong, causing the catalyst to over-oxidize NH3 to byproducts such as NO or N2O. On the other hand, if the amount of rare earth element doping is too large, the catalyst's redox ability is too weak, and after NH3 adsorption, NO cannot be adsorbed, thereby reducing the catalytic performance.

[0098] (8) In conjunction with the data in Table 1, by comparing Example 1 with Comparative Examples 7 and 8, it can be seen that the thickness of the acidic element oxide shell, that is, the molar ratio of the acidic element to the Mn element, in the manganese-based denitration catalyst of the present invention has a significant effect on the denitration performance and nitrogen selectivity of the catalyst. If the amount of acidic element added is too much, the shell thickness will be too large, affecting the mass transfer process of reactants such as NH3 and NO to the active sites of the catalyst; if the amount of acidic element added is too low, the acidity of the catalyst will be too low, which is not compatible with the redox capacity, resulting in excessive oxidation of NH3 to byproducts such as NO or N2O.

[0099] (9) In combination with the data in Table 1, it can be seen from Example 1 and Comparative Examples 9 to 12 that the conditions during ball milling have a significant impact on the denitrification performance and nitrogen selectivity of the catalyst. If the amount of zirconium beads added during ball milling is too large or the ball milling time is too long, the lattice structure of the catalyst will be destroyed, the crystallinity will decrease, and the catalytic performance will be reduced. If the amount of zirconium beads added is too small or the ball milling time is too short, the ball milling effect will be less obvious, the catalyst particle size will be larger, and the acidic metal shell will be unevenly formed. The interaction at the core-shell interface cannot be enhanced, resulting in reduced catalyst performance.

[0100] (10) Combined with the data in Table 1, it can be seen from Example 1 and Comparative Examples 13 and 14 that the ultrasonic time has a significant effect on the denitration performance and nitrogen selectivity of the catalyst. If the ultrasonic time is too long, the crystal lattice of the manganese-based active component will be destroyed, resulting in the deintercalation of the doping element, a decrease in the number of active sites, and a decrease in catalytic performance. If the ultrasonic time is too short, the ultrasonic effect is not obvious, the particle dispersion of the catalyst is poor, and the acidic metal shell is unevenly formed, resulting in a decrease in catalyst performance.

[0101] (11) Combining the data in Table 1, it can be seen from Example 1 and Comparative Examples 15-16 that the calcination temperature has a significant effect on the denitration performance and nitrogen selectivity of the catalyst. When the calcination temperature is too low, the catalyst has poor crystallinity and excessive surface defects, which is not conducive to the adsorption of NH3. Instead, it causes NH3 oxidation, generates more NO, and reduces the denitration performance of the catalyst. When the calcination temperature is too high, the catalyst nanoparticles easily agglomerate, the specific surface area is greatly reduced, which is not conducive to the diffusion of reactants and reduces the utilization rate of active sites.

[0102] The above embodiments are merely examples for clarity of explanation and are not intended to limit the embodiments. Those skilled in the art will appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all embodiments here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A manganese-based denitration catalyst with a core-shell structure, characterized in that: The composition of manganese-based denitrification catalyst is AMnO x @BO y ;AMnO x It is a composite oxide of coated manganese and doping elements, BO y It is an acidic metal oxide shell; Wherein, A is a doping element, and the doping element is a rare earth element; B is an acidic metal element, and the acidic metal element is a transition metal element; x is the active component of the composite oxide of manganese and doping elements AMnO x The number of oxygen atoms in , 1≤x≤2; y is an acidic metal oxide shell BO y The number of oxygen atoms in , 1≤y≤3.

2. The core-shell manganese-based denitration catalyst according to claim 1, characterized in that: The rare earth element is selected from any one of cerium, neodymium, samarium, europium, yttrium, dysprosium, ytterbium, lanthanum or praseodymium; Among them, the molar ratio of rare earth elements to manganese elements is (0.05~0.3):

1.

3. The core-shell manganese-based denitration catalyst according to claim 1, characterized in that: Transition metal elements are selected from any one of tungsten, molybdenum, niobium, chromium, iron, cobalt, nickel or titanium Among them, the molar ratio of transition metal elements to manganese elements is (2.0~15.0):

1.

4. A method for preparing a core-shell structured manganese-based denitration catalyst, characterized in that: The manganese-based denitrification catalyst is prepared by the reverse coprecipitation method, and the specific steps are as follows: (1) A rare earth element compound and a manganese nitrate compound are mixed, and 60.0 mL of deionized water is added and stirred thoroughly to form a mixed solution. The mixed solution is then added dropwise to a precipitant at a dropping speed of 5 to 20 mL / min while stirring. After a precipitate is formed, the precipitate is allowed to stand for 2 h to 24 h, and filtered to obtain a precipitate. The precipitate is then centrifuged and dried at a temperature of 80°C to 105°C. The dried precipitate is then calcined for the first time in a muffle furnace, wherein the calcination temperature is 400°C to 600°C, the heating rate is 1.0°C / min to 10.0°C / min, and the calcination time is 3.0 h to 10.0 h to obtain a composite oxide AMnO. x The composite oxide obtained after calcination is cooled to room temperature, and then the composite oxide is placed in a ball mill and ball-milled using zirconium beads. During the ball milling, the mass ratio of the calcined composite oxide to the zirconium beads is 1: (5.0-20.0), the ball milling time is 2.0h-5.0h, and the ball milling speed is 300 rpm-900 rpm to obtain a composite oxide AMnO that is uniformly dispersed after ball milling. x powder; (2) The ball-milled composite oxide powder was added to a mixed solution of an acidic metal compound and ethanol containing a metal ion concentration of 0.01 mol / L to 0.1 mol / L. The mixed solution was then ultrasonically dispersed for 20 min to 60 min. The mixed solution was then dried at a drying temperature of 80°C to 105°C. The dried mixture was then sent to a muffle furnace for a second calcination at a calcination temperature of 400°C to 600°C, a heating rate of 1.0°C to 10.0°C / min, and a calcination time of 3.0 h to 10.0 h to obtain a core-shell structured manganese-based denitrification catalyst AMnO x @BO y .

5. The method for preparing a core-shell manganese-based denitration catalyst according to claim 4, characterized in that: In the step (1), the rare earth element compound is selected from any one of cerium nitrate, neodymium nitrate, samarium nitrate, europium nitrate, yttrium nitrate, dysprosium nitrate, ytterbium nitrate, lanthanum nitrate or praseodymium nitrate; The nitrate compound of the manganese element is selected from manganese nitrate.

6. The method for preparing a core-shell manganese-based denitration catalyst according to claim 4, characterized in that: The rare earth element compound is selected from any one of cerium nitrate, neodymium nitrate or lanthanum nitrate.

7. The method for preparing a core-shell manganese-based denitration catalyst according to claim 4, characterized in that: In the step (1), the precipitant is a mixed solution of 30% concentrated ammonia water and deionized water, and the volume ratio of 30% concentrated ammonia water to deionized water is 1:9; The molar ratio of the precipitant to the sum of the metal ions is (1-3):

1.

8. The method for preparing a core-shell manganese-based denitration catalyst according to claim 4, characterized in that: In the step (2), the acidic metal compound is selected from any one of ammonium metatungstate, ammonium molybdate, tetrabutyl titanate, ammonium niobate oxalate, chromium nitrate, iron nitrate, cobalt nitrate or nickel nitrate.

9. The method for preparing a core-shell manganese-based denitration catalyst according to claim 4, characterized in that: The acidic metal compound is selected from any one of ammonium molybdate and tetrabutyl titanate.

10. Use of a core-shell manganese-based denitration catalyst according to claim 1 or a core-shell manganese-based denitration catalyst prepared by the method according to claim 4 for catalyzing nitrogen oxides in air pollution control at an active temperature of 150°C to 400°C.

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