Defective silver-based catalysts, methods for their preparation and use

Abstract

The application provides a defective silver-based catalyst and a preparation method and application thereof, and belongs to the technical field of ammonia treatment. The preparation method of the defective silver-based catalyst provided by the application comprises the following steps: first calcining H-ZSM-5 zeolite molecular sieve to obtain pretreated molecular sieve; mixing the pretreated molecular sieve with a tetrapropylammonium hydroxide solution, and performing hydrothermal reaction to obtain a molecular sieve precursor; second calcining the molecular sieve precursor to obtain a defective molecular sieve; mixing the defective molecular sieve with a soluble silver salt solution, and performing impregnation treatment to obtain a catalyst precursor; third calcining the catalyst precursor to obtain a defective silver-based catalyst. The defective silver-based catalyst prepared by the application has high catalytic performance and high stability in the reaction of selective catalytic oxidation of ammonia.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of ammonia treatment, and particularly relates to a defective silver-based catalyst and a preparation method and application thereof. BACKGROUND

[0002] A large amount of ammonia-nitrogen compounds in motor vehicle exhaust can not only cause environmental problems such as photochemical smog and acid rain, but also seriously threaten human health. Therefore, sufficient treatment of ammonia-nitrogen compounds in motor vehicle exhaust is a hot spot in the field of environmental catalysis. Selective catalytic reduction technology is one of the most practical ammonia-nitrogen compound post-treatment technologies, but in actual application, in order to ensure that ammonia-nitrogen compounds are completely treated, an excess of ammonia gas is usually introduced, which can easily cause ammonia gas leakage. Ammonia gas is also a pollutant, which is harmful to the surrounding environment and human health, and therefore needs to be reasonably and effectively treated.

[0003] ZSM-5 zeolite molecular sieve has the characteristics of high specific surface area, rich pore structure, strong hydrophobicity, adjustable acidity and alkalinity, complex channel and excellent thermal stability, and is often used in the field of waste gas treatment. However, the catalyst prepared by loading metal on ZSM-5 zeolite molecular sieve is easy to form large particles by agglomeration of the loaded metal on the surface of ZSM-5 zeolite molecular sieve, resulting in uneven dispersion and thus reducing the stability and catalytic activity of the catalyst. SUMMARY

[0004] The present application provides a defective silver-based catalyst and a preparation method and application thereof. The defective silver-based catalyst prepared by the method provided by the present application has high catalytic performance and high stability in the reaction of selective catalytic oxidation of ammonia.

[0005] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0006] The present application provides a preparation method of a defective silver-based catalyst, comprising the following steps:

[0007] The H-ZSM-5 zeolite molecular sieve is first calcined to obtain a pretreated molecular sieve;

[0008] The pretreated molecular sieve is mixed with a tetrapropylammonium hydroxide solution to perform a hydrothermal reaction, and a molecular sieve precursor is obtained;

[0009] The molecular sieve precursor is secondly calcined to obtain a defective molecular sieve;

[0010] The defective molecular sieve is mixed with a soluble silver salt solution to perform an impregnation treatment, and a catalyst precursor is obtained;

[0011] The catalyst precursor is thirdly calcined to obtain a defective silver-based catalyst.

[0012] Preferably, the first calcination temperature is 500-600 DEG C, and the holding time is 2-5h.

[0013] Preferably, the concentration of the tetrapropylammonium hydroxide solution is 0.2-0.7mol / L; and the ratio of the pretreated molecular sieve to the tetrapropylammonium hydroxide solution is 3-10g:60-200mL.

[0014] Preferably, the hydrothermal reaction temperature is 150-180 DEG C, and the time is 24-84h.

[0015] Preferably, the second calcination temperature is 500-600 DEG C, and the holding time is 5-8h.

[0016] Preferably, the third calcination temperature is 500-600 DEG C, and the holding time is 2-4h.

[0017] The application provides a defective silver-based catalyst prepared by the preparation method, which comprises a defective ZSM-5 carrier and silver particles loaded on the defective ZSM-5 carrier.

[0018] Preferably, the mass fraction of the silver particles in the defective silver-based catalyst is 0.1-10%, and the particle size of the silver particles is 2.0-20nm.

[0019] The application provides an application of the defective silver-based catalyst in selective catalytic oxidation of ammonia.

[0020] Preferably, before the defective silver-based catalyst is used in selective catalytic oxidation of ammonia, the defective silver-based catalyst is subjected to reduction treatment; and the reduction treatment temperature is 400-800 DEG C, and the holding time is 1-10h.

[0021] The application provides a preparation method of a defective silver-based catalyst, comprising the following steps: performing first calcination on H-ZSM-5 zeolite molecular sieve to obtain pretreated molecular sieve; mixing the pretreated molecular sieve with a tetrapropylammonium hydroxide solution and polytetrafluoroethylene, and performing hydrothermal reaction to obtain a molecular sieve precursor; performing second calcination on the molecular sieve precursor to obtain a defective molecular sieve; mixing the defective molecular sieve with a soluble silver salt solution, and performing impregnation treatment to obtain a catalyst precursor; and performing third calcination on the catalyst precursor to obtain the defective silver-based catalyst. The first calcination removes some impurities on the surface of the molecular sieve, and the pretreated H-ZSM-5 zeolite molecular sieve is dissolved in the tetrapropylammonium hydroxide solution through the hydrothermal reaction. Since the tetrapropylammonium hydroxide solution can dissolve the silicon on the surface of the H-ZSM-5 zeolite molecular sieve, more aluminum is exposed, so that more active sites are formed on the surface of the H-ZSM-5 zeolite molecular sieve for anchoring of silver particles, the silver particles can be uniformly dispersed in the H-ZSM-5 zeolite molecular sieve containing defects, and thus the defective silver-based catalyst with uniformly dispersed silver particles is obtained. Meanwhile, the second calcination removes the organic matter precursor remaining in the aforementioned hydrothermal reaction, and the third calcination loads the silver particles in the defective molecular sieve and limits the agglomeration and migration of the silver particles, which is beneficial to maintaining the size and high dispersity of the silver particles, and thus the defective silver-based catalyst obtained has high catalytic performance and high stability in the reaction of selective catalytic oxidation of ammonia. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed in the embodiments. Obviously, the drawings described below only show some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative labor.

[0023] Figure 1 The NH3 conversion rate diagram of sample A prepared in Example 1 of the present application and sample M prepared in Comparative Example 1 at different temperatures;

[0024] Figure 2 The NH3 conversion rate diagram of sample B, sample C and sample D prepared in Example 2-4 of the present application and sample N, sample O and sample P prepared in Comparative Example 2-4 after reduction treatment at different temperatures. DETAILED DESCRIPTION

[0025] The application provides a preparation method of a defective silver-based catalyst, comprising the following steps:

[0026] performing first calcination on H-ZSM-5 zeolite molecular sieve to obtain pretreated molecular sieve;

[0027] mixing the pretreated molecular sieve with a solution of tetrapropylammonium hydroxide, and performing a hydrothermal reaction to obtain a molecular sieve precursor;

[0028] performing a second calcination on the molecular sieve precursor to obtain a defective molecular sieve;

[0029] mixing the defective molecular sieve with a solution of a soluble silver salt, and performing an impregnation treatment to obtain a catalyst precursor;

[0030] performing a third calcination on the catalyst precursor to obtain a defective silver-based catalyst.

[0031] In the present application, the raw materials used are all commercially available goods well known to those skilled in the art, unless otherwise specified.

[0032] In the present application, the H-ZSM-5 zeolite molecular sieve is subjected to a first calcination to obtain a pretreated molecular sieve. In the present application, the silicon-aluminum ratio of the H-ZSM-5 zeolite molecular sieve is preferably 25-50, and more preferably 40-50. The temperature of the first calcination in the present application is preferably 500-600℃, and more preferably 550-580℃; the holding time is preferably 2-5h, and more preferably 3-4h. The first calcination in the present application is preferably performed in an air atmosphere. In the examples of the present application, the first calcination is performed in a muffle furnace. In the present application, the first calcination is preferably followed by cooling the first material obtained by the first calcination to room temperature. The manner of cooling in the present application is not particularly limited, and any cooling manner well known to those skilled in the art can be used. The first calcination in the present application removes some impurities on the surface of the molecular sieve, facilitating the subsequent operation steps.

[0033] After obtaining the pretreated molecular sieve, the present application mixes the pretreated molecular sieve with a tetrapropylammonium hydroxide solution to perform a hydrothermal reaction to obtain a molecular sieve precursor. In the present application, the concentration of the tetrapropylammonium hydroxide solution is preferably 0.2-0.7 mol / L, and more preferably 0.3-0.4 mol / L. The ratio of the amount of the pretreated molecular sieve to the amount of the tetrapropylammonium hydroxide solution is preferably 3-10 g: 60-200 mL, and more preferably 5-7 g: 80-120 mL. In the present application, the pretreated molecular sieve and the tetrapropylammonium hydroxide solution are preferably mixed under first stirring; the rate of the first stirring is preferably 450-550 r / min, and more preferably 500-520 r / min; and the time of the first stirring is preferably 4-6 h, and more preferably 4.5-5.5 h. In the embodiments of the present application, the first stirring is specifically performed by using a magnetic stirrer. The present application preferably pours the mixture obtained after the first stirring into a polytetrafluoroethylene liner to seal, and then fixes the liner in an outer kettle of a reaction kettle and places it in a homogeneous reactor to perform the hydrothermal reaction. In the present application, the filling ratio of the mixture is preferably 50-70%, and more preferably 60%. The temperature of the hydrothermal reaction is preferably 150-180°C, and more preferably 170-180°C; and the time is preferably 24-84 h, and more preferably 72-84 h. In the present application, the hydrothermal reaction preferably includes cooling the second material obtained after the hydrothermal reaction to room temperature. The present application does not have special limitations on the cooling method, and any cooling method known to those skilled in the art can be used. In the present application, the cooling preferably includes water washing and first drying performed in sequence. The number of times of water washing is preferably 1-5 times, and more preferably 3 times. The present application does not have special limitations on the water washing method, and any method capable of eluting the water washing eluent to neutral after water washing can be used. The temperature of the first drying is preferably 50-100°C, and more preferably 60-80°C; the time of the first drying is preferably 12-18 h, and more preferably 12 h; and the method of the first drying is preferably oven drying. In the present application, the pretreated H-ZSM-5 zeolite molecular sieve is dispersed in the tetrapropylammonium hydroxide solution through the hydrothermal reaction. Since the tetrapropylammonium hydroxide solution can dissolve the silicon on the surface of the H-ZSM-5 zeolite molecular sieve, more aluminum is exposed, so that defects are formed on the surface of the H-ZSM-5 zeolite molecular sieve, more active sites are provided for the anchoring of silver particles, and the silver particles can be uniformly dispersed in the H-ZSM-5 zeolite molecular sieve containing defects, so that a defect-type silver-based catalyst with uniformly dispersed silver particles can be obtained.

[0034] After obtaining the molecular sieve precursor, the molecular sieve precursor is subjected to a second calcination to obtain a defective molecular sieve. In the present application, the temperature of the second calcination is preferably 500-600°C, more preferably 550-600°C; the holding time of the second calcination is preferably 5-8h, more preferably 6-8h. The second calcination in the present application is preferably carried out in an air atmosphere. In the examples of the present application, the second calcination is carried out in a muffle furnace. In the present application, the second calcination is preferably followed by cooling the third material obtained by the second calcination to room temperature. The present application does not have special limitations on the cooling method, and any cooling method known to those skilled in the art can be used. The present application removes the organic precursor remaining in the aforementioned hydrothermal reaction by the second calcination.

[0035] After obtaining the defective molecular sieve, the defective molecular sieve is mixed with a soluble silver salt solution to perform impregnation treatment to obtain a catalyst precursor. In the present application, the concentration of the soluble silver salt solution is preferably 0.5-1.1 mol / L, more preferably 0.9-1 mol / L; the mass ratio of the defective molecular sieve to the soluble silver salt solution is preferably 1:0.1-1, more preferably 1:0.1. The soluble silver salt solution in the present application is preferably a silver nitrate solution. The present application preferably first disperses the defective molecular sieve in water to obtain a defective molecular sieve dispersion; then the soluble silver salt solution is added dropwise to the defective molecular sieve dispersion. The present application does not have special limitations on the dropping method, and any dropping method known to those skilled in the art can be used. The impregnation treatment in the present application is preferably carried out under second stirring. The rate of the second stirring in the present application is preferably 450-500r / min, more preferably 480-500r / min. In the present application, the impregnation treatment is preferably followed by drying the fourth material obtained by the impregnation treatment. The drying in the present application preferably includes sequentially performing second drying and third drying. The temperature of the second drying in the present application is preferably 60-100°C, more preferably 85-95°C; the time is preferably 10-15h, more preferably 12-14h; the method of the second drying is preferably rotary evaporation. The temperature of the third drying in the present application is preferably 90-120°C, more preferably 105-115°C; the time of the third drying is preferably 8-12h, more preferably 10-11h; the method of the third drying is preferably oven drying. The impregnation treatment in the present application highly disperses the silver salt on the surface of the carrier and in the defects, which can inhibit the migration and growth of the silver salt during high-temperature calcination and reduction atmosphere, is conducive to maintaining the high dispersity of the silver salt, and can improve the stability and universality of the obtained defective silver-based catalyst; at the same time, by accurately adjusting the ratio of the defective molecular sieve to the soluble silver salt solution, the catalytic performance of the obtained defective silver-based catalyst can be significantly optimized.

[0036] After obtaining the catalyst precursor, the catalyst precursor is subjected to third calcination to obtain the defective silver-based catalyst. In the present application, the temperature of the third calcination is preferably 450-550 DEG C, more preferably 550-600 DEG C; the holding time of the third calcination is preferably 2-4 h, more preferably 2.5-3.5 h. The third calcination in the present application is preferably carried out in an air atmosphere. In the embodiments of the present application, the third calcination is carried out in a muffle furnace. Through the third calcination, the silver species is loaded on the defective molecular sieve.

[0037] The present application also provides the defective silver-based catalyst prepared by the preparation method described in the above technical solution, which comprises a defective ZSM-5 carrier and silver particles loaded on the defective ZSM-5 carrier. In the present application, the mass fraction of the silver particles in the defective silver-based catalyst is preferably 1-2%, more preferably 1-1.5%; the particle size of the silver particles is preferably 2-20 nm, more preferably 2-5 nm. The defective silver-based catalyst provided in the present application has high catalytic performance and high stability in the selective catalytic oxidation reaction of ammonia.

[0038] The present application also provides the application of the defective silver-based catalyst described in the above technical solution in the selective catalytic oxidation reaction of ammonia. The present application preferably carries out the selective catalytic oxidation reaction of ammonia on the coal flue gas in the presence of the defective silver-based catalyst. In the present application, the defective silver-based catalyst preferably comprises a reduction treatment before the selective catalytic oxidation reaction of ammonia. In the present application, the reduction treatment is preferably carried out in a mixed gas atmosphere; the mixed gas atmosphere preferably comprises H2 and N2; the volume ratio of H2 to N2 in the mixed gas atmosphere is preferably 1:5-15, more preferably 1:9. The temperature of the reduction treatment in the present application is preferably 400-800 DEG C, more preferably 500-700 DEG C; the holding time is preferably 1-10 h, more preferably 2 h. The present application does not have special limitations on the source of the coal flue gas, and any coal flue gas containing NH3 can be used. The selective catalytic oxidation reaction of ammonia in the present application is preferably carried out in a fixed-bed continuous evaluation device. In the embodiments of the present application, the coal flue gas is composed of NH3, NO, NO2, O2 and N2O; the conditions of the selective catalytic oxidation reaction of ammonia are as follows: the concentration of NH3 is 500 ppm, the volume percentage content of O2 is 10%, the amount of the defective silver-based catalyst is 30 mg, the space velocity is 120000 h-1, and the reaction temperature is 100-300 DEG C; the fixed-bed continuous evaluation device comprises a quartz tube reactor with a specification of Φ4*300 mm, an electric resistance furnace with a constant temperature region length of 150 mm, and a Fourier transform infrared spectrometer equipped with a 2 m optical path gas cell. -1

[0039] ​The technical solutions in the present application will be clearly and completely described below in combination with the embodiments in the present application. Apparently, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the protection scope of the present application.

[0040] The chemical formula of the H-ZSM-5 zeolite molecular sieve used in the embodiments is H-ZSM-5 SiO2 / Al2O3, and the silicon-aluminum ratio is 50; the product is commercially available from Nankai Catalyst Factory;

[0041] The reagents used in the embodiments are commercially available.

[0042] The fixed-bed continuous evaluation device used in the embodiments includes a quartz tube reactor with a specification of Φ4*300 mm, an electric resistance furnace with a constant temperature region length of 150 mm, and a Fourier transform infrared spectrometer provided with a 2 m optical path gas cell.

[0043] Embodiment 1

[0044] 5 g of H-ZSM-5 molecular sieve with a silicon-aluminum ratio of 50 was weighed into a muffle furnace, and was calcined at 550 ℃ for 3 h; the obtained first material was cooled to room temperature to obtain a pretreated molecular sieve.

[0045] The obtained pretreated molecular sieve was mixed with 100 mL of a tetrapropylammonium hydroxide solution with a concentration of 0.4 mol / L, and a magnetic stirrer was started to stir at a speed of 500 r / min for 5 h. The obtained mixture was poured into a polytetrafluoroethylene lining, sealed, filled at a ratio of 60%, and the lining was installed in an outer kettle of a reaction kettle, and was fixed and placed in a homogeneous reaction instrument, and was hydrothermally reacted at 170 ℃ for 72 h. Then the reaction kettle was naturally cooled to room temperature, and the obtained second material was washed with water for 3 times until the obtained water washing effluent was neutral, and was dried at 60 ℃ for 12 h to obtain a molecular sieve precursor.

[0046] The obtained molecular sieve precursor was placed into a muffle furnace, and was calcined at 550 ℃ for 6 h; the obtained third material was cooled to room temperature to obtain a defective molecular sieve.

[0047] 2 g of the obtained defective molecular sieve was weighed, and deionized water was added dropwise to the above defective molecular sieve until the molecular sieve was fully dispersed to obtain a defective molecular sieve dispersion liquid. 1.2 mL of a silver nitrate solution with a concentration of 1 mol / L was added dropwise to the above defective molecular sieve dispersion liquid, and stirring was started, and was stirred at a speed of 500 r / min at 22 ℃ for 2 h (at this time, the mass ratio of the defective molecular sieve to the silver nitrate solution was 1:0.1) to obtain a fourth material. The obtained fourth material was rotary evaporated to remove excess water at 85 ℃, and was then dried at 105 ℃ for 10 h to obtain a catalyst precursor.

[0048] The obtained catalyst precursor was placed in a muffle furnace and calcined at 550°C for 3 hours to obtain a defective silver-based catalyst, denoted as sample A.

[0049] Comparative Example 1

[0050] Weigh 2g of H-ZSM-5 molecular sieve, add deionized water dropwise to the molecular sieve until it is fully dispersed, and obtain a molecular sieve dispersion; add 1.2mL of 1mol / L silver nitrate solution dropwise to the molecular sieve solution, start stirring, and stir at 500r / min at 22℃ for 2h (at this time, the mass ratio of H-ZSM-5 molecular sieve to silver nitrate solution is 1:0.1), then remove excess water by rotary evaporation at 85℃, and then dry at 105℃ for 10h to obtain the catalyst precursor;

[0051] The obtained catalyst precursor was placed in a muffle furnace and calcined at 550°C for 3 hours to obtain a silver-based catalyst, denoted as sample M.

[0052] Defective silver-based catalysts and activity evaluation of silver-based catalysts:

[0053] In a fixed-bed continuous evaluation apparatus, ammonia selective catalytic oxidation of flue gas was carried out in the presence of sample A and sample M, respectively. The flue gas consisted of NH3, NO, NO2, O2, and N2O. The reaction conditions were: NH3 concentration of 500 ppm, O2 volume percentage of 10 vol%, sample A or sample M amount of 30 mg, and space velocity of 120,000 h⁻¹. -1 The reaction temperature was 100–300℃; the concentrations of NH3, NO, NO2, O2, and N2O were detected using a Fourier transform infrared spectrometer in a fixed-bed continuous evaluation device. Specific results are as follows: Figure 1 As shown.

[0054] Depend on Figure 1 It can be seen that within the temperature range of 100–175℃, there is no significant difference in the NH3 conversion rate between sample A prepared in Example 1 and sample M prepared in Comparative Example 1 as the temperature increases. Within the temperature range of 175–300℃, the NH3 conversion rates of both samples A and M show a significant upward trend with increasing temperature. Furthermore, under the same conditions, sample A exhibits a higher NH3 conversion rate than sample M. For example, at 225℃, the NH3 conversion rate of sample A is approximately 85%, while that of sample M is only 20%. This indicates that hydrothermal reaction using tetrapropylammonium hydroxide solution can improve the catalytic performance of defective silver-based catalysts, thereby achieving efficient NH3 removal.

[0055] Example 2

[0056] The defective molecular sieve was prepared according to the method and conditions of Example 1.

[0057] 2 g of the defective molecular sieve was weighed out, and deionized water was added dropwise to the defective molecular sieve until the molecular sieve was fully dispersed, to obtain a defective molecular sieve dispersion. 1.2 mL of a silver nitrate solution having a concentration of 1 mol / L was added dropwise to the defective molecular sieve dispersion, and stirring was started, and the mixture was stirred at 500 r / min for 2 h at 22°C (at this time, the mass ratio of the defective molecular sieve to the silver nitrate solution was 1:0.1), to obtain a fourth material. The fourth material was then rotary evaporated at 85°C to remove excess water, and then dried at 105°C for 10 h, to obtain a catalyst precursor.

[0058] The catalyst precursor was placed in a muffle furnace, and calcined at 550°C for 3 h, to obtain a defective silver-based catalyst.

[0059] Reduction treatment of the defective silver-based catalyst: the defective silver-based catalyst was placed in a mixed atmosphere of H2 and N2 (the volume content of H2 was 10%), and subjected to reduction treatment at 400°C for 2 h, and the resulting product was recorded as Sample B.

[0060] Example 3

[0061] The defective silver-based catalyst was prepared according to the method and conditions of Example 2.

[0062] Reduction treatment of the defective silver-based catalyst: the defective silver-based catalyst was placed in a mixed atmosphere of H2 and N2 (the volume content of H2 was 10%), and subjected to reduction treatment at 600°C for 2 h, and the resulting product was recorded as Sample C.

[0063] Example 4

[0064] The defective silver-based catalyst was prepared according to the method and conditions of Example 2.

[0065] Reduction treatment of the defective silver-based catalyst: the defective silver-based catalyst was placed in a mixed atmosphere of H2 and N2 (the volume content of H2 was 10%), and subjected to reduction treatment at 800°C for 2 h, and the resulting product was recorded as Sample D.

[0066] Comparative Example 2

[0067] 2 g of H-ZSM-5 molecular sieve was weighed, and deionized water was added dropwise to the molecular sieve until the molecular sieve was fully dispersed to obtain a molecular sieve dispersion liquid; 1.2 mL of a silver nitrate solution with a concentration of 1 mol / L was added dropwise to the molecular sieve solution, stirring was started, and stirring was performed at a rate of 500 r / min for 2 h at 22 ℃ (at this time, the mass ratio of the H-ZSM-5 molecular sieve to the silver nitrate solution was 1:0.1), and then excess water was removed by rotary evaporation at 85 ℃, and then drying was performed at 105 ℃ for 10 h to obtain a catalyst precursor;

[0068] The obtained catalyst precursor was placed in a muffle furnace and calcined at 550 ℃ for 3 h to obtain a silver-based catalyst.

[0069] Reduction treatment of the silver-based catalyst: the obtained silver-based catalyst was placed in a mixed gas atmosphere of H2 and N2 (the volume content of H2 was 10%), and reduction treatment was performed at 400 ℃ for 2 h, and the obtained product was recorded as sample N.

[0070] Comparative Example 3

[0071] The silver-based catalyst was prepared according to the method and conditions of Comparative Example 2.

[0072] Reduction treatment of the silver-based catalyst: the obtained silver-based catalyst was placed in a mixed gas atmosphere of H2 and N2 (the volume content of H2 was 10%), and reduction treatment was performed at 600 ℃ for 2 h, and the obtained product was recorded as sample O.

[0073] Comparative Example 4

[0074] The silver-based catalyst was prepared according to the method and conditions of Comparative Example 2.

[0075] Reduction treatment of the silver-based catalyst: the obtained silver-based catalyst was placed in a mixed gas atmosphere of H2 and N2 (the volume content of H2 was 10%), and reduction treatment was performed at 800 ℃ for 2 h, and the obtained product was recorded as sample P.

[0076] Activity evaluation of the defect-type silver-based catalyst and the silver-based catalyst after reduction treatment:

[0077] In a fixed-bed continuous evaluation device, coal flue gas was subjected to selective catalytic oxidation of ammonia in the presence of sample B, sample C, sample D, sample N, sample O, and sample P, respectively, wherein the coal flue gas was composed of NH3, NO, NO2, O2, and N2O, the concentration of NH3 was 500 ppm, the volume percentage of O2 was 10 vol%, the amount of sample B or sample C or sample D or sample N or sample O or sample P was 30 mg, the space velocity was 120000 h-1, and the reaction temperature was 300 ℃. -1, the reaction temperature was 100-300°C; the concentrations of NH3, NO, NO2, O2 and N2O were detected by Fourier transform infrared spectrometer in a fixed bed continuous evaluation device, and the specific results are shown in Table 1 and Figure 2

[0078] Table 1 NH3 conversion rates of samples B, C, D, N, O and P at different temperatures

[0079]

[0080]

[0081] From Figure 2 and Table 1, it can be seen that in the temperature range of 100-300°C, the NH3 conversion rates of samples B, C and D prepared in Examples 2-4 and samples N, O and P prepared in Comparative Examples 2-4 all have an obvious upward trend with the increase of temperature. Obviously, the defective silver-based catalysts still have good NH3 removal effect after high-temperature reduction treatment. Moreover, in the temperature range of 100-190°C, the NH3 conversion rate of the defective silver-based catalysts also increases with the increase of reduction treatment temperature under the same conditions. In the temperature range of 190-300°C, the NH3 conversion rate of the defective silver-based catalysts is also greater than or equal to that of the conventional silver-based catalysts under the same reduction treatment temperature conditions; for example, under the temperature condition of 200°C, the NH3 conversion rate of sample B is about 51%, and the NH3 conversion rate of sample N is about 52%; the NH3 conversion rate of sample C is about 89%, and the NH3 conversion rate of sample O is about 74%; the NH3 conversion rate of sample D is about 83%, and the NH3 conversion rate of sample P is only 22%. This shows that the defective silver-based catalysts after high-temperature reduction treatment still have high catalytic performance and stability. In addition, from Figures 1-2 and Table 1, it can be seen that under the condition of 225°C, the NH3 conversion rates of samples A, B, C and D are about 85%, 80%, 96% and 95% respectively, and thus it can be seen that the catalytic performance of the defective silver-based catalysts after high-temperature reduction treatment does not decrease obviously.

[0082] Although the above examples have described the present application in detail, it is only a part of the embodiments of the present application, but not all the embodiments, and other embodiments can be obtained from the present embodiments without creativity, which all belong to the protection scope of the present application.​

Claims

1. A method for preparing a defective silver-based catalyst for selective catalytic oxidation of ammonia, comprising the following steps: carrying out first calcination on a H-ZSM-5 zeolite molecular sieve to obtain a pretreated molecular sieve; mixing the pretreated molecular sieve with a tetrapropylammonium hydroxide solution to carry out a hydrothermal reaction, to obtain a molecular sieve precursor; the temperature of the hydrothermal reaction is 150-180 ℃, and the time is 24-84 h; the concentration of the tetrapropylammonium hydroxide solution is 0.2-0.7 mol / L; the ratio of the amount of the pretreated molecular sieve to the amount of the tetrapropylammonium hydroxide solution is 3-10 g:60-200 mL; carrying out second calcination on the molecular sieve precursor to obtain a defective molecular sieve; mixing the defective molecular sieve with a soluble silver salt solution to carry out impregnation treatment, to obtain a catalyst precursor; carrying out third calcination on the catalyst precursor to obtain a defective silver-based catalyst; the temperature of the third calcination is 550 ℃.

2. The production method according to claim 1, characterized by, the temperature of the first calcination is 500-600 ℃, and the holding time is 2-5 h.

3. The preparation method according to claim 1, characterized in that, the temperature of the second calcination is 500-600 ℃, and the holding time is 5-8 h.

4. The method of claim 1, wherein, the holding time of the third calcination is 2-4 h. 5.A defective silver-based catalyst for selective catalytic oxidation of ammonia, prepared by the method of any one of claims 1-4, comprising a defective ZSM-5 carrier and silver particles supported on the defective ZSM-5 carrier.

6. The defective silver-based catalyst of claim 5, wherein, The mass fraction of the silver particles in the defective silver-based catalyst is 0.1-10%, and the particle size of the silver particles is 2-20 nm. 7.Use of the defective silver-based catalyst for selective catalytic oxidation of ammonia of any one of claims 5-6 in selective catalytic oxidation of ammonia.

8. Use according to claim 7, characterized in that, Before the defective silver-based catalyst is used in selective catalytic oxidation of ammonia, the defective silver-based catalyst is subjected to reduction treatment; the temperature of the reduction treatment is 400-800 ℃, and the holding time is 1-10 h.

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