A nitrogen-doped perovskite catalyst, its preparation method and application

Abstract

The present invention belongs to the technical fields of material catalysis and catalyst preparation, and discloses a nitrogen-doped perovskite catalyst, a preparation method thereof and an application thereof. The perovskite-type catalyst is prepared by a hydrothermal method, a sol-gel method or a co-precipitation method, and DBD is used to cooperate with the catalyst to remove NO x , and in the process of DBD cooperating with the high-efficiency removal of NO in industrial waste gas x , using nitrogen oxide pollutants as a nitrogen source, a nitrogen-doped perovskite-type catalyst capable of being applied to the photocatalytic removal of Hg 0 is synthesized. This not only omits the pretreatment process of forming a nitrogen-doped catalyst by introducing a nitrogen component in the prior art, but also enables the prepared nitrogen-doped perovskite catalyst to have the advantages of high visible light utilization rate, low photogenerated electron-hole recombination rate, excellent mercury removal efficiency and stable catalytic performance. This method is simple and easy to implement, has low energy consumption and high recycling rate, and realizes the resource utilization of the catalyst after denitrification.

Description

Technical Field

[0001] The present invention relates to the technical fields of material catalysis and catalyst preparation, and particularly relates to a nitrogen-doped perovskite catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] As one of the main pollutants in the atmosphere, nitrogen oxides (NOx) mostly come from coal-fired power plants, steel (iron) mills, coking plants, non-ferrous metal smelters, etc. The excessive emission of nitrogen oxides will cause a series of environmental problems such as acid rain, ozone layer depletion, smog, and greenhouse effect. In this regard, China has made clear regulations on the emission of nitrogen oxides in various industrial waste gases, requiring that the emission in the coal power industry be less than 50 mg / m 3 , and the emission in the coke oven industry be less than 150 mg / m 3 etc. The main component of nitrogen oxides in industrial waste gas is nitric oxide (NO), and its removal technologies include selective catalytic reduction (SCR), selective non-catalytic reduction (SNCR), adsorption, and low-temperature plasma, etc.

[0003] At present, the relatively mature SCR technology can achieve a removal rate of 80-95% and excellent N2 selectivity. However, as known from patent CN116408132, although the denitration catalyst of zero-valent iron supported on 13X molecular sieve disclosed therein can achieve 100% denitration efficiency at 240-375°C, it faces problems such as catalyst poisoning, agglomeration, and difficult regeneration.

[0004] The denitration rate of the SNCR technology is generally 30-80%, which can meet the needs of small and medium-sized enterprises. However, there are still problems such as ammonia escape and inability to be used on a large scale. Although the adsorption method for denitration has the characteristics of good purification effect and realization of waste gas reuse, it cannot solve the problems of large consumption of adsorbent and difficult regeneration.

[0005] Moreover, dielectric barrier discharge (DBD), as a high-efficiency and low-cost low-temperature plasma treatment technology, can ionize and activate gas molecules at a relatively low temperature, generating high-energy electrons, free radicals, active groups, etc. After being synergistic with the catalyst, it can provide sufficient activation energy for chemical reactions. However, as disclosed in patent CN115155307A for low-temperature plasma synergistic manganese-cerium-titanium catalyst, although it can achieve a denitration efficiency of 70-99% at a relatively low temperature (100-200°C), it also faces problems of large-scale use and difficult catalyst regeneration. Combining the above, the treatment of the catalyst after denitration has become an important issue.

[0006] For coal-fired power plants, the renewable rate of denitration catalysts is about 60%, and a large amount of energy is consumed during the regeneration process. Generally, after the currently used catalysts are regenerated 2-3 times, they can only be disposed of as hazardous waste. From the perspectives of economic practicality and environmental friendliness, reusing denitration catalysts after regeneration treatment is not a reasonable solution. Therefore, a new way for the resource utilization of post-denitration catalysts is imminent.

[0007] Meanwhile, elemental mercury (Hg 0 ) as a heavy metal pollutant in industrial waste gases such as coal-fired flue gas and non-ferrous metal smelting, the "Emission Standards for Pollutants from Lead and Zinc Industries" (GB25466-2010) stipulates that the emission standard of mercury and its compounds should be lower than 0.05 mg / m 3 . Currently, among the technologies for removing Hg 0 , photocatalytic technology has great application prospects due to its advantages such as environmental friendliness and high-efficiency purification. It can be seen from Patent CN107362817A that although the disclosed titanium dioxide-modified graphitic carbon nitride photocatalyst achieves a mercury removal efficiency of more than 70%, titanium dioxide has the defect of insufficient utilization of visible light.

[0008] Perovskite-type catalysts have excellent electronic structures, are easy for electron excitation and migration, and have a very high utilization rate of visible light. However, due to the significantly smaller band gap (1.2-1.6 eV) of perovskite than that of titanium dioxide (3-3.2 eV), photo-generated electron-hole recombination is more likely to occur. Doping perovskite with nitrogen as a modification method, the formed independent valence band after hybridization is easy for photo-generated electron transition and effectively prevents the recombination process. And although Patent CN116174000A discloses the formation of a low-defect nitrogen-doped RTaON2 photocatalyst under the action of an ammonia gas stream, the pretreatment of the ammonia gas stream faces problems of complex operation and high cost. Summary of the Invention

[0009] In view of this, in combination with the problems of difficult regeneration of post-denitration catalysts and low visible light response of mercury removal photocatalysts, the present invention provides a nitrogen-doped perovskite catalyst, its preparation method and application. On the premise of efficiently removing NO x , nitrogen-doped perovskite catalysts are formed by using industrial waste gas NO x , improving the performance of perovskite-type catalysts in photocatalytic mercury removal and realizing the resource utilization of hazardous waste.

[0010] One of the technical solutions of the present invention: provides a preparation method of a nitrogen-doped perovskite catalyst, and the method specifically includes the following steps:

[0011] (1) Prepare a perovskite-type catalyst ABO3 by using a hydrothermal method, a sol-gel method or a co-precipitation method;

[0012] (2) The perovskite catalyst ABO3 is used in cooperation with DBD for denitrification to prepare the nitrogen-doped perovskite catalyst; wherein,

[0013] A is a rare earth element, at least one of lanthanum, cerium, and samarium; B is a transition metal, at least one of titanium, iron, cobalt, nickel, copper, manganese, and chromium.

[0014] Optionally, the specific operation in step (2) is as follows:

[0015] Place the perovskite catalyst in a dielectric barrier discharge reactor, introduce gas at room temperature, with a flow rate of 300 - 500 ml / min, and the flue gas atmosphere is a mixed gas of 300 - 800 ppm NO, 5 - 10% O2, and high-purity N2. While carrying out cooperative denitrification, using nitrogen oxides NO x as the nitrogen source, and finally obtain the nitrogen-doped perovskite catalyst.

[0016] Furthermore, the reaction temperature in step (2) is 50 - 100 °C, the discharge frequency is 8 - 12 KHz, and the output voltage is 20 - 50 V.

[0017] Optionally, in step (1), the specific steps for preparing the perovskite catalyst ABO3 by the hydrothermal method are as follows: Dissolve the same amount of rare earth and transition metal salts, specifically lanthanum nitrate hexahydrate and tetrabutyl titanate, in 50 - 100 ml of deionized water, and magnetically stir for 10 - 30 min until completely dissolved. Then add 2 - 5 g of citric acid, and continue to stir for 10 - 30 min to obtain a mixed solution; Transfer the mixed solution to a stainless steel reaction kettle with a polytetrafluoroethylene lining and react at 120 - 180 °C for 8 - 15 h. After the product cools, filter, wash, and dry it, and then place it in a muffle furnace and program the temperature to 400 - 700 °C for calcination for 4 - 6 h, press it into tablets and pass through a 40 - 60 mesh sieve to obtain the perovskite catalyst.

[0018] Optionally, in step (1), the specific steps for preparing the perovskite catalyst ABO3 by the sol-gel method are as follows: Dissolve the same amount of rare earth and transition metal salts, specifically cerium nitrate hexahydrate, iron(III) nitrate nonahydrate, and manganese(II) nitrate tetrahydrate, in 50 - 100 ml of deionized water, and magnetically stir for 10 - 30 min until completely dissolved. Then, according to the molar ratio of citric acid:metal cation = 2:1, add the chelating agent citric acid to this solution and stir for 10 - 30 min, and adjust the pH value to 6.5 - 7.5 with ammonia water. Subsequently, raise the water bath stirring temperature to 60 - 80 °C, and add 8 - 10 ml of polyethylene glycol, and continue to stir for 4 - 6 h to obtain a wet gel;

[0019] The wet gel is placed in an oven at 80 - 100 °C and dried for 10 - 12 h to obtain a dry gel. Then, the dry gel is ground into powder and calcined in a muffle furnace at 400 - 700 °C for 4 - 6 h. After pressing and screening through a 40 - 60 mesh sieve, a perovskite-type catalyst is obtained.

[0020] Optionally, in step (1), the specific steps for preparing the perovskite-type catalyst ABO3 by the co-precipitation method are as follows: The same amounts of rare earth and transition metal salts, specifically lanthanum nitrate hexahydrate, cerium nitrate hexahydrate, copper nitrate trihydrate, and chromium nitrate nonahydrate, are dissolved in 50 - 100 ml of deionized water, and magnetically stirred for 10 - 30 min until completely dissolved to obtain a mixed solution. Then, the rotation speed of the magnetic stirrer is reduced, and a 1 - 3 mol / L NaOH solution is gradually added to the mixed solution to adjust the pH value to 9 - 13. After maintaining slow magnetic stirring for 4 - 6 h, filtration is carried out to obtain a yellow-brown precipitate.

[0021] The yellow-brown precipitate is placed in an oven at 80 - 100 °C and dried for 10 - 12 h, then ground into powder and calcined in a muffle furnace at 400 - 700 °C for 4 - 6 h. After pressing and screening through a 40 - 60 mesh sieve, a perovskite-type catalyst is obtained.

[0022] The second technical solution of the present invention: Provide a nitrogen-doped perovskite catalyst.

[0023] The third technical solution of the present invention: Provide an application of the nitrogen-doped perovskite catalyst in the field of photocatalysis.

[0024] Specifically, the nitrogen-doped perovskite catalyst can be applied to catalytic removal of elemental mercury Hg 0 .

[0025] Further, the specific steps for the nitrogen-doped perovskite catalyst to catalytically remove elemental mercury Hg 0 are as follows:

[0026] The nitrogen-doped perovskite catalyst is recovered and placed in a gas-solid photocatalytic device. A mixed gas with a gas flow rate of 300 - 500 ml / min and a gas composition of 80 - 400 μg / Nm 3 Hg 0 , 1 - 5% O2, and high-purity N2 is introduced. First, react and adsorb under dark conditions for 10 - 30 min. Subsequently, turn on a visible light source with a wavelength of 400 - 760 nm, and carry out photocatalytic reaction for 10 - 30 min to remove Hg 0 . After that, turn off the light source and react and adsorb again for 10 - 30 min. Repeat the cycle to enable the nitrogen-doped CeFe 0.4 Mn 0.6 O3 photocatalyst to efficiently remove Hg 0 .

[0027] The principle of the present invention for DBD synergistic catalysis of NO X and the formation of a nitrogen-doped perovskite catalyst includes: First, under the action of a high-strength electric field, high-speed electrons collide with molecules such as NO x , N2, O2, etc., causing the N-O bond, O-O bond, and a small amount of N-N bond to break, and recombining and fixing with the broken metal bond-oxygen bond (M-O) of the perovskite catalyst, ultimately forming the form of M-N-O or M-O-N; meanwhile, DBD generates a large number of free radicals and active species (O3, ·OH, and ·O, etc.) that react with NO x to occur an oxidation reaction, mainly generating N2, nitrates, etc. that remain on the surface of the perovskite catalyst; and because the radius of N 3- (0.13nm) is smaller than that of O 2- (0.14nm), it is easier for it to replace part of O 2- and enter the lattice or lattice interstitial of the perovskite catalyst.

[0028] And from the above technical solutions, it can be seen that compared with the prior art, the beneficial effects of the present invention are:

[0029] (1) The present invention provides a method of "treating waste with waste". The perovskite catalyst prepared by different methods such as hydrothermal method, sol-gel method or co-precipitation method synergistically removes NO in industrial waste gas with dielectric barrier discharge (DBD) x After that, rich nitrogen species are incorporated into the surface or lattice interstitial of the catalyst, enabling it to be used for catalytic removal of Hg under visible light 0 . Compared with traditional catalysts, the nitrogen-doped perovskite catalyst of the present invention has a special structure. The introduction of nitrogen components can effectively regulate the acid-base properties of the catalyst, improve its activation ability for reactant or product molecules, and the present invention utilizes the interaction between nitrogen species and active components such as metal components or metal oxides to effectively improve the dispersion and stability of active species, and realizes the effect of improving its catalytic performance by modulating its redox properties.

[0030] (2) The present invention adopts the method of DBD synergistic catalyst to remove NO x , making the process of removing NO x at a relatively low temperature (50-100 °C), thereby effectively reducing the inactivation of active sites, and using NO x as a nitrogen source, enabling the catalyst after denitrification to form a structure that can reuse nitrogen doping and applying it to the removal of polluted gases in the field of photocatalysis, such as elemental mercury Hg 0 , further expanding its promotion and application in the catalytic field, effectively overcoming the problems in the existing thermal catalysis (150-350 °C) process, such as catalyst sintering and agglomeration due to too high temperature, resulting in inactivation of catalytic active sites, and the removal of NO xAfter the catalyst is regenerated 2-3 times, it faces the defects of being scrapped and difficult to handle.

[0031] (3) During the low-temperature and high-pressure removal process of the present invention, NO x molecules are broken by the high-speed electrons generated by DBD, and then a catalyst with a nitrogen-doped structure is formed. The pretreatment process of introducing a nitrogen component to form a nitrogen-doped catalyst in the prior art is omitted. Moreover, the nitrogen-doped perovskite catalyst prepared by the present invention has excellent photo-generated electron transition ability, can effectively prevent the recombination of photo-generated electrons and holes, and realizes the effect of nitrogen doping while removing NO x , improving the performance of the perovskite catalyst in photocatalytic removal of Hg 0 , effectively controlling the emissions of NO x and Hg 0 , and realizing the resource utilization of hazardous waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0033] Figure 1 Schematic diagram of the device structure for DBD synergistic catalysis of NO x and formation of a nitrogen-doped perovskite catalyst in Examples 1-3.

[0034] Figure 2 Schematic diagram of the device structure for gas-solid photocatalytic removal of Hg 0 in Examples 1-3.

[0035] Figure 3 Efficiency comparison diagram of DBD synergistic nitrogen-doped LaTiO3 catalyst and DBD synergistic undoped LaTiO3 catalyst for Hg 0 removal in Example 1.

[0036] Figure 4 Efficiency comparison diagram of DBD synergistic nitrogen-doped CeFe 0.4 Mn 0.6 O3 catalyst and DBD synergistic undoped CeFe 0.4 Mn 0.6 O3 catalyst for Hg 0 removal in Example 2.

[0037] Figure 5 Efficiency comparison diagram of DBD synergistic nitrogen-doped La 0.8 Ce0.2 Cu 0.9 Cr 0.1 O3 catalyst and DBD synergistically un-nitrogen-doped modified La 0.8 Ce 0.2 Cu 0.9 Cr 0.1 O3 catalyst for Hg removal 0 Efficiency comparison chart.

[0038] Figure 6 XRD pattern of the LaTiO3 perovskite catalyst prepared in Example 1.

[0039] Figure 7 XPS spectrum of the nitrogen-doped LaTiO3 catalyst in Example 1.

[0040] Figure 8 For the nitrogen-doped CeFe in Example 2 0.4 Mn 0.6 Fourier transform infrared spectroscopy (FIRT) pattern of the O3 perovskite catalyst.

[0041] Figure 1-2 In

[0042] 1. Corundum electrode; 2. Voltage regulator; 3. Dielectric barrier discharge power supply; 4. Oscilloscope; 5. Copper mesh; 6. Catalyst; 7. Quartz wool; 8. Quartz tube reaction chamber; 9. Flue gas analyzer; 10. Photocatalytic device power supply; 11. Visible light source; 12. Sealed box; 13. VM3000 mercury analyzer. Detailed implementation manners

[0043] Now, various exemplary implementation manners of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0044] It should be understood that the terms described in the present invention are only for describing specific implementation manners and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0045] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although this invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of this invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the said documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0046] Without departing from the scope or spirit of this invention, various improvements and changes can be made to the specific embodiments of the specification of this invention, which are obvious to those skilled in the art. Other embodiments obtained from the specification of this invention are obvious to those skilled in the art. The specification and examples of this application are merely exemplary.

[0047] Regarding the use of "comprising", "including", "having", "containing", etc. in this invention, they are all open-ended terms, meaning including but not limited to.

[0048] Example 1

[0049] (1) Preparation of LaTiO3 perovskite catalyst by hydrothermal method

[0050] Dissolve 0.02 mol of lanthanum nitrate hexahydrate and 0.02 mol of tetrabutyl titanate in 70 ml of deionized water. After magnetically stirring in a water bath for 10 min until completely dissolved, add 2 g of citric acid monohydrate thereto, and continue stirring for 30 min to obtain a mixed solution;

[0051] Transfer the mixed solution to a stainless steel reactor with a polytetrafluoroethylene lining and react at 160 °C for 12 h. After the product is cooled, filter, wash, and dry it, then place it in a muffle furnace and program the temperature to 650 °C for calcination for 6 h, press it into tablets and sieve through a 40 - 60 mesh sieve to obtain the LaTiO3 perovskite catalyst for standby.

[0052] (2) Preparation of nitrogen-doped LaTiO3 catalyst by DBD-assisted denitrification

[0053] Place 2 g of the LaTiO3 perovskite catalyst in a dielectric barrier discharge reactor, and then introduce a mixed gas with a gas flow rate of 300 ml / min and a flue gas atmosphere of 400 ppm NO, 5% O2, and high-purity N2 for DBD-assisted denitrification treatment; among them, the reaction temperature is 85 °C, the discharge frequency is 9.5 KHz, the output voltage starts from 30 V and finally reaches 50 V, and it is increased by 5 V every 30 min to enable the DBD to cooperate with the LaTiO3 perovskite catalyst to remove NO xMeanwhile, a rich layer of nitrogen species is incorporated on the surface or lattice interstitial sites of the LaTiO3 perovskite catalyst by using nitrogen oxides in the flue gas to form a nitrogen-doped LaTiO3 catalyst. And the energy density is calculated to be 0 - 6000 J / L, with each energy density interval set at 1000 J / L. Finally, it is determined that when the input voltage is 40 V and the energy density is approximately 4650 J / L, the optimal NO removal efficiency of the LaTiO3 catalyst is measured by a flue gas analyzer. x is 78%.

[0054] (3) Recycling the nitrogen-doped LaTiO3 catalyst for Hg removal 0

[0055] After placing 0.2 g of the nitrogen-doped LaTiO3 catalyst formed after denitrification in step (2) into a gas-solid photocatalytic device, a mixed gas with a gas flow rate of 300 ml / min and a gas composition of 100 μg / Nm 3 Hg0, 2% O2, and high-purity N2 is introduced. First, the reaction is adsorbed for 15 min under dark conditions, and then the visible light source with a wavelength of 500 nm is turned on, and the Hg is removed by photocatalytic reaction for 30 min. 0 After that, the light source is turned off and the reaction is adsorbed again for 15 min, and this cycle is repeated to enable the nitrogen-doped LaTiO3 catalyst to efficiently remove Hg. 0 And the VM-3000 mercury analyzer is used to measure the Hg removal 0 efficiency of the nitrogen-doped LaTiO3 catalyst.

[0056] Figure 6 is the XRD pattern of the LaTiO3 perovskite catalyst prepared in Example 1. The figure shows the crystalline properties of the LaTiO3 perovskite catalyst. The characteristic diffraction peaks appearing at 2θ = 19.3° and 22.4° are attributed to the anatase structure of TiO2. The sharp peaks shown at 2θ = 32° and 39.65° and the characteristic peaks appearing at 45.8°, 51.6°, 56.9°, 60.8°, and 66.8° are all in correspondence with the PDF card (LaTiO3, PDF#70 - 2293), which indicates that the LaTiO3 perovskite catalyst was successfully prepared and synthesized in Example 1.

[0057] Figure 7 is the XPS spectrum of the nitrogen-doped LaTiO3 catalyst in Example 1. It can be seen that two peaks are observed in the N1s spectrum of the LaTiO3 sample, located at approximately 399.6 eV and 407 eV respectively. Among them, the peak located at 399.6 eV may be attributed to the N element in Ti - O - N, that is, interstitial N, indicating that N atoms are successfully doped in the interstitial positions of the LaTiO3 lattice, and the other peak located near 407 eV is attributed to nitrogen oxides such as NO 2- and NO3- , which proves that during the process of removing NO by the DBD combined with the LaTiO3 catalyst in Example 1, a nitrogen-doped LaTiO3 catalyst was formed.

[0058] Example 2

[0059] (1) Prepare the CeFe 0.4 Mn 0.6 O3 perovskite-type catalyst

[0060] Dissolve 1.0855 g of cerium nitrate hexahydrate, 0.3232 g of iron nitrate nonahydrate, and 0.4394 g of manganese nitrate tetrahydrate in 50 ml of deionized water. After completely dissolving it by magnetic stirring in a water bath for 15 min, add the chelating agent citric acid to the above solution according to the molar ratio of citric acid: metal cations = 2:1 and stir for 10 min. Adjust the pH value to 6.5 - 7.5 with ammonia water. Then raise the temperature of the water bath stirring to 80 °C, add 8 ml of polyethylene glycol, and continue stirring for 6 h to obtain a wet gel;

[0061] Place the wet gel in an oven at 100 °C and dry it for 10 h to obtain a dry gel. Then grind the dry gel into powder and calcine it in a muffle furnace at 600 °C for 4 h. After pressing and screening through a 40 - 60 mesh sieve, obtain the CeFe 0.4 Mn 0.6 O3 perovskite-type catalyst. Set aside for later use.

[0062] (2) Prepare the nitrogen-doped CeFe 0.4 Mn 0.6 O3 catalyst by DBD combined denitrification

[0063] Place 2 g of the CeFe 0.4 Mn 0.6 O3 perovskite-type catalyst in a dielectric barrier discharge reactor, and then introduce a mixed gas with a gas flow rate of 400 ml / min and a flue gas atmosphere of 500 ppm NO, 10% O2, and high-purity N2 for combined denitrification treatment. Among them, the reaction temperature is 80 °C, the discharge frequency is 10.2 KHz, the output voltage starts from 30 V and finally reaches 50 V, and it is increased by 5 V every 30 min, so that the DBD combines with the CeFe 0.4 Mn 0.6 O3 perovskite-type catalyst to remove NO x At the same time, use the nitrogen oxides in the flue gas to incorporate a rich layer of nitrogen species on the surface or lattice interstitial sites of the CeFe 0.4 Mn 0.6 O3 perovskite-type catalyst to form a nitrogen-doped CeFe 0.4 Mn 0.6O3 catalyst. And the calculated energy density is 0 - 6000 J / L, and each energy density interval is set to 1000 J / L. Finally, it is determined that when the input voltage is 45 V and the energy density is about 5260 J / L, CeFe was measured by a flue gas analyzer 0.4 Mn 0.6 The best NO removal efficiency of the O3 catalyst x is 82%.

[0064] (3) Recycling the nitrogen-doped CeFe 0.4 Mn 0.6 O3 catalyst for Hg removal 0

[0065] Put 0.2 g of the nitrogen-doped CeFe formed after denitrification in step (2) 0.4 Mn 0.6 O3 catalyst into the gas-solid photocatalytic device, and then introduce a mixed gas with a gas flow rate of 400 ml / min and a gas composition of 200 μg / Nm 3 Hg 0 , 4% O2, and high-purity N2. First, react and adsorb for 15 min under dark conditions, then turn on the visible light source with a wavelength of 540 nm, and perform photocatalytic reaction for 30 min to remove Hg 0 After that, turn off the light source and react and adsorb again for 15 min. Repeat the cycle to make the nitrogen-doped CeFe 0.4 Mn 0.6 O3 catalyst efficiently remove Hg 0 , and use a VM-3000 mercury analyzer to measure the Hg removal efficiency of the catalyst 0 efficiency.

[0066] In the atmosphere composed of NO, O2, and N2, the catalytic behavior of NOx on the surface of the nitrogen-doped CeFe 0.4 Mn 0.6 O3 perovskite-type catalyst in Example 2 was characterized by Fourier transform infrared spectroscopy (FIRT), and its test results were recorded in Figure 7 in.

[0067] Figure 8 is the Fourier transform infrared spectroscopy (FIRT) of the nitrogen-doped CeFe 0.4 Mn 0.6 O3 catalyst in Example 2. It can be seen from Figure 8 that the absorption peak at 1438 cm -1 belongs to the characteristic vibration peak of monodentate nitrate, and 1331 cm -1 is attributed to the vibration peak of Fe 3+ -NO 3- ; 1243 cm -1The characteristic peak at 1168 cm-1 is attributed to monodentate nitrite or nitro group. -1 The vibration peak attributed to monodentate nitrite (NO) is 1086 cm -1 Belong to the transition state N2O2 2- , 1000cm -1 The following is a weakly adsorbed NO. This proves that Example 2 has a strong effect on the DBD-assisted CeFe 0.4 Mn 0.6 Removal of NO with O3 perovskite catalyst x In the process, nitrogen-doped CeFe 0.4 Mn 0.6 O3 catalyst.

[0068] Example 3

[0069] (1) Preparation of La by coprecipitation method 0.8 Ce 0.2 Cu 0.9 Cr 0.1 O3 perovskite catalyst

[0070] 0.8034 g of lanthanum nitrate hexahydrate, 0.1554 g of cerium nitrate hexahydrate, 0.9549 g of copper nitrate trihydrate and 0.1042 g of chromium nitrate nonahydrate were dissolved in 50 ml of deionized water, and the mixture was completely dissolved by magnetic stirring in a water bath for 10 min to obtain a mixed solution; then the speed of the magnetic stirrer was reduced, and a 1 mol / L NaOH solution (prepared by 2 g of NaOH in a 50 ml quantitative bottle) was gradually added to the mixed solution, the pH value was adjusted to 12, and the mixture was filtered after slow magnetic stirring for 4 h to obtain a yellow-brown precipitate;

[0071] The yellow-brown precipitate was dried in an oven at 100°C for 10 h, ground into powder and calcined in a muffle furnace at 600°C for 4 h, pressed into tablets and passed through a 40-60 mesh sieve to obtain La 0.8 Ce 0.2 Cu 0.9 Cr 0.1 O3 perovskite catalyst.

[0072] (2) DBD synergistic denitrification and preparation of nitrogen-doped La 0.8 Ce 0.2 Cu 0.9 Cr 0.1 O3 Catalyst

[0073] 2gLa 0.8 Ce 0.2 Cu 0.9 Cr 0.1The O3 perovskite catalyst is placed in a dielectric barrier discharge reactor, and then a gas with a flow rate of 500 ml / min is introduced. The flue gas atmosphere is a mixture of 600 ppm NO, 10% O2, and high-purity N2 for synergistic denitrification treatment. Among them, the reaction temperature is 70 °C, the discharge frequency is 11 KHz, the output voltage starts from 30 V and finally reaches 50 V, and it is increased by 5 V every 30 minutes, so that DBD synergistically combines with La 0.8 Ce 0.2 Cu 0.9 Cr 0.1 The O3 perovskite catalyst removes NO x While using the nitrogen oxides in the flue gas to incorporate a rich layer of nitrogen species on the surface or lattice interstices of the La 0.8 Ce 0.2 Cu 0.9 Cr 0.1 O3 perovskite catalyst to form a nitrogen-doped La 0.8 Ce 0.2 Cu 0.9 Cr 0.1 O3 catalyst. And after calculation, the energy density is 0 - 6000 J / L, and each energy density interval is set at 1000 J / L. Finally, it is determined that when the input voltage is 50 V and the energy density is about 6000 J / L, the La 0.8 Ce 0.2 Cu 0.9 Cr 0.1 O3 catalyst removes NO x with an efficiency of 85%.

[0074] (3) Recycling the nitrogen-doped La 0.8 Ce 0.2 Cu 0.9 Cr 0.1 O3 catalyst to remove Hg 0

[0075] After placing 0.2 g of the nitrogen-doped La 0.8 Ce 0.2 Cu 0.9 Cr 0.1 O3 photocatalyst formed after denitrification in step (2) into a gas-solid photocatalytic device, a gas with a flow rate of 500 ml / min is introduced. The gas composition is 300 μg / Nm 3 Hg 0 、5% O2, and a mixture of high-purity N2. First, react and adsorb for 15 minutes under dark conditions, then turn on the visible light source with a wavelength of 560 nm, and carry out photocatalytic reaction for 30 minutes to remove Hg 0 After that, turn off the light source and react and adsorb again for 15 minutes. Repeat the cycle to make the nitrogen-doped La 0.8 Ce 0.2Cu 0.9 Cr 0.1 Hg Removal by O3 Catalyst with High Efficiency 0 and the mercury removal efficiency of the catalyst was measured by a VM-3000 mercury analyzer 0 .

[0076] Figure 1 FIG. is a schematic structural diagram of the device for DBD co-catalyzing NO and forming nitrogen-doped perovskite in Examples 1-3, and its purpose is to simulate the situation after the catalyst removes NO; Figure 2 is a schematic structural diagram of the device for gas-solid photocatalytic mercury removal in Examples 1-3 0 .

[0077] Comparative Example 1

[0078] A DBD was used in combination with an undoped LaTiO3 perovskite catalyst, and the other conditions were the same as those in Example 1.

[0079] Comparative Example 2

[0080] A DBD was used in combination with a photocatalyst of undoped CeFe 0.4 Mn 0.6 O3, and the other conditions were the same as those in Example 2.

[0081] Comparative Example 3

[0082] A DBD was used in combination with an undoped La 0.8 Ce 0.2 Cu 0.9 Cr 0.1 O3 perovskite catalyst, and the other conditions were the same as those in Example 1.

[0083] In order to verify the influence of the nitrogen-doped modified materials in Examples 1-3 on the photocatalytic reaction, Comparative Examples 1-3 of DBD combined with undoped perovskite catalysts were set up, and under the same conditions as in Examples 1-3, the mercury removal 0 efficiency test of the DBD combined with the undoped perovskite catalyst was carried out, and a comparison chart of the mercury removal 0 efficiency of the DBD combined with the undoped perovskite catalyst and the DBD combined with the nitrogen-doped perovskite catalyst was drawn, specifically as Figures 3-5 shown.

[0084] Figure 3 is a comparison chart of the mercury removal 0 efficiency of the DBD combined with the nitrogen-doped LaTiO3 catalyst and the DBD combined with the undoped LaTiO3 photocatalyst in Example 1.

[0085] It can be seen that the photocatalyst of DBD combined with un-nitrogen-doped modified LaTiO3 in Comparative Example 1 has a Hg removal rate of 16.8% under dark conditions and a photocatalytic effect on Hg of 63.9% under visible light; while the photocatalyst of DBD combined with nitrogen-doped LaTiO3 in Example 1 has a Hg removal rate of 14.2% under dark conditions and a photocatalytic effect on Hg reaching 82.6% under visible light. 0 under visible light for Hg 0 The photocatalytic effect is 63.9%; while the photocatalyst of DBD combined with nitrogen-doped LaTiO3 in Example 1 has a Hg 0 removal rate of 14.2% under dark conditions and a photocatalytic effect on Hg 0 reached 82.6%.

[0086] Figure 4 For the efficiency comparison diagram of the DBD combined with nitrogen-doped CeFe 0.4 Mn 0.6 O3 catalyst and the DBD combined with un-nitrogen-doped modified CeFe 0.4 Mn 0.6 O3 catalyst for Hg 0 removal.

[0087] It can be seen that the photocatalyst of DBD combined with un-nitrogen-doped modified CeFe 0.4 Mn 0.6 O3 has a Hg 0 removal rate of 18.8% under dark conditions and a photocatalytic effect on Hg 0 of 79.6% under visible light; while the photocatalyst of DBD combined with nitrogen-doped CeFe 0.4 Mn 0.6 O3 has a Hg 0 removal rate of 16.1% under dark conditions and a photocatalytic effect on Hg 0 reached 90.3%.

[0088] Figure 5 For the efficiency comparison diagram of the DBD combined with nitrogen-doped La 0.8 Ce 0.2 Cu 0.9 Cr 0.1 O3 catalyst and the DBD combined with un-nitrogen-doped modified La 0.8 Ce 0.2 Cu 0.9 Cr 0.1 O 33 catalyst for Hg 0 removal.

[0089] It can be seen that the photocatalyst of DBD combined with un-nitrogen-doped modified La 0.8 Ce 0.2 Cu 0.9 Cr 0.1 O3 has a Hg 0The removal rate was 20.8% for Hg under visible light. 0 The photocatalytic effect of DBD in Example 3 is 82.9%. 0.8 Ce 0.2 Cu 0.9 Cr 0.1 O3 photocatalyst for Hg 0 The removal rate of Hg was 22.4% under visible light. 0 The photocatalytic effect reached 93.8%.

[0090] Depend on Figures 3-5 It can be seen that compared with the DBD-cooperative non-nitrogen-doped perovskite-type catalysts in Comparative Examples 1-3, the DBD-cooperative nitrogen-doped perovskite-type catalysts prepared in Examples 1-3 of the present invention have a lower degradation rate than that of the perovskite-type catalysts prepared in Comparative Examples 1-3. 0 The photocatalytic effect is significantly improved.

[0091] The present invention utilizes nitrogen oxides in industrial waste gas to synthesize a perovskite photocatalyst for mercury removal. The perovskite catalyst is first prepared by a hydrothermal method, a sol-gel method or a co-precipitation method. Then, in the process of coordinating DBD to remove nitrogen oxides in industrial waste gas at low temperature and with high efficiency, the nitrogen oxide pollutants are used as a nitrogen source to prepare a nitrogen-doped perovskite photocatalyst, thereby omitting a pretreatment process of introducing a nitrogen component to form a nitrogen-doped catalyst. At the same time, when the synthesized nitrogen-doped perovskite photocatalyst is used for photocatalytic removal of zero-valent mercury, the photocatalyst has the advantages of high visible light utilization rate, low photogenerated electron-hole recombination rate, excellent mercury removal efficiency and stable catalytic performance.

[0092] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. Application of a nitrogen-doped perovskite catalyst in photocatalytic removal of elemental mercury Hg 0 characterized in that The preparation method of the nitrogen-doped perovskite catalyst specifically includes the following steps: (1) Prepare the perovskite-type catalyst ABO3 by hydrothermal method, sol-gel method or co-precipitation method; (2) Use DBD to cooperate with the perovskite-type catalyst ABO3 for denitrification to prepare the nitrogen-doped perovskite catalyst; where A is a rare earth, at least one of lanthanum, cerium, and samarium; B is a transition metal, at least one of titanium, iron, cobalt, nickel, copper, manganese, and chromium.

2. The application according to claim 1, characterized in that, The specific operation in step (2) is as follows: Place the perovskite catalyst in a dielectric barrier discharge reactor, introduce gas at room temperature with a flow rate of 300-500 ml / min, and the flue gas atmosphere is a mixed gas of 300-800 ppm NO, 5-10% O2, and high-purity N2. While carrying out synergistic denitrification, use nitrogen oxides NO x as the nitrogen source, and finally obtain the nitrogen-doped perovskite catalyst.

3. The application according to claim 2, characterized in that, In step (2), the reaction temperature is 50-100 °C, the discharge frequency is 8-12 KHz, and the output voltage is 20-50 V.

4. The application according to any one of claims 1 to 3, characterized in that, In step (1), the specific operation of preparing the perovskite-type catalyst ABO3 by the hydrothermal method is as follows: Dissolve the same amount of rare earth and transition metal salts in 50-100 ml of deionized water, stir magnetically for 10-30 min, add 2-5 g of citric acid after complete dissolution, and continue to stir for 10-30 min to obtain a mixed solution; Transfer the mixed solution to a stainless steel reaction kettle with a polytetrafluoroethylene lining, react at 120-180 °C for 8-15 h, filter, wash and dry the product after cooling; then place it in a muffle furnace and program the temperature to 400-700 °C for roasting for 4-6 h, press tablets and pass through a 40-60 mesh sieve to obtain the perovskite-type catalyst ABO3.

5. The application according to any one of claims 1 to 3, characterized in that In step (1), the specific operation of preparing the perovskite-type catalyst ABO3 by the sol-gel method is as follows: Dissolve the same amount of rare earth and transition metal salts in 50-100 ml of deionized water, stir magnetically for 10-30 min, and after complete dissolution, add the chelating agent citric acid to the mixed solution according to the molar ratio of citric acid: metal cation = 2:1 and stir for 10-30 min, adjust the pH to 6.5-7.5 with ammonia water, then raise the water bath temperature to 60-80 °C, add 8-10 ml of polyethylene glycol, and continue to stir for 4-6 h to obtain a wet gel; Place the wet gel in an oven at 80-100 °C and dry for 10-12 h to obtain a dry gel, then grind the dry gel into powder and calcine it in a muffle furnace at 400-700 °C for 4-6 h, press tablets and pass through a 40-60 mesh sieve to obtain the perovskite-type catalyst ABO3.

6. The application according to any one of claims 1 to 3, characterized in that, In step (1), the specific operation of preparing the perovskite-type catalyst ABO3 by the co-precipitation method is as follows: Dissolve the same amount of rare earth and transition metal salts in 50-100 ml of deionized water, stir magnetically for 10-30 min to obtain a mixed solution; slowly add 1-3 mol / L NaOH solution dropwise to the mixed solution, adjust the pH to 9-13, filter after stirring for 4-6 h to obtain a yellowish-brown precipitate; Place the yellowish-brown precipitate in an oven at 80-100 °C and dry for 10-12 h, then grind it into powder and calcine it at 400-700 °C for 4-6 h, press tablets and pass through a 40-60 mesh sieve to obtain the perovskite-type catalyst ABO3.

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