NH3-SCR catalyst, its preparation method and applications

Abstract

The application discloses an NH3-SCR catalyst and a preparation method and application thereof. The NH3-SCR catalyst is a cerium oxide composite oxide catalyst, which comprises Ce, M and R elements, the M element is selected from at least one of Cu, Nb, Fe, Co, Mn, Ni and Zn; the R element is selected from at least one of Ru, Pt, Pd, Rh, Ag and Au; the molar ratio of the Ce element to the M element is 0.5:1-10:1; the loading amount of the R element is 0.1-3 wt% based on the total mass of the NH3-SCR catalyst; the morphology of the NH3-SCR catalyst is spherical; the cerium oxide exposes [111] crystal surface, the content of surface active oxygen accounts for 35-70% of the total oxygen content on the surface of the NH3-SCR catalyst; the acid amount of the catalyst is 7500-9000 muL, the hydrogen consumption amount is 1500-2500 muL, and the specific surface area is 50-90 m 2 / g. The catalyst of the application can selectively catalyze the reduction of nitrogen oxide NO x at a low temperature of less than or equal to 200 DEG C by using ammonia, and has high conversion rate, high N2 selectivity and low N2O byproduct generation amount.

Description

Technical Field

[0001] This invention relates to an NH3-SCR catalyst, its preparation method, and its uses. Background Technology

[0002] Nitrogen oxides (mainly NO and NO2, collectively referred to as NO) x NOx is one of the air pollutants that causes acid rain, photochemical smog, and haze, posing a significant threat to the environment for human survival. Currently, non-power industries such as coking plants (coke oven gas), steel plants (sintering gas, coke oven gas, blast furnace gas, and converter gas), chemical plants (waste liquid incineration gas, nitric acid preparation tail gas), and the cement industry (rotary kiln gas) are major contributors to NOx emissions. x Control and emission reduction have become the key and difficult points in the prevention and control of flue gas pollution.

[0003] Given the low emission temperature of flue gas from non-power industries, ammonia selective catalytic reduction (NH3-SCR) technology is currently the most effective method for NO emission control. x Emission reduction technologies. my country has developed SCR technology and its catalyst system with good application performance in the 180–420℃ range, but breakthroughs are still needed in catalytic reduction below 200℃, specifically requiring the catalyst to achieve 90% NO reduction below 200℃. x Conversion rate. To achieve optimal catalytic efficiency and meet stringent NO requirements. x Emission regulations dictate that industrial processes primarily employ a heating and heat exchange method, using traditional V₂O₅-WO₃(MoO₃) / TiO₂ catalysts, and increasing the vanadium content to some extent improves the catalyst's low-temperature activity. This process is complex, involves high overall investment, has significant system resistance, consumes additional fuel, and generates additional CO₂. Furthermore, the selective catalytic reduction of ammonia produces nitrous oxide (N₂O) as a byproduct; N₂O is not only a pollutant but also a potent greenhouse gas.

[0004] CN106423139A discloses a rare earth-based SCR denitration catalyst and its preparation method. This catalyst is a medium-to-low temperature CeO2 / TiO2 composite denitration catalyst. The active component is cerium dioxide, the support is titanium dioxide, and the promoters are transition metals and rare earth metal oxides. This catalyst exhibits good NO removal efficiency in the temperature range of 200–500℃. x Conversion rate and N2 selectivity.

[0005] CN106861674A discloses a low-temperature SCR flue gas high-efficiency denitrification catalyst and its preparation method. The catalyst uses titanium dioxide as a support and contains tungsten oxide, vanadium oxide, antimony oxide, or rare earth metal cerium oxide. There is still room for improvement in denitrification efficiency.

[0006] CN112316940A discloses a method for preparing a rare earth-based redox catalyst for denitrification of flue gas in coking plants, comprising: S1 preparing cerium oxide, palladium oxide, rhodium oxide, and deionized water, and then preparing a solid solution matrix material; S2 mixing the prepared solid solution matrix material with glass fiber, aminocellulose, polyethylene oxide, deionized water, and ammonia, filtering, extruding, and drying to obtain the catalyst. This catalyst requires ammonia and carbon monoxide as reducing agents, and there is still room for improvement in its denitrification efficiency.

[0007] CN117019136A discloses a low-temperature manganese / cerium honeycomb denitrification catalyst, which uses cerium dioxide and manganese oxide as the main active components, titanium dioxide as the paste material, and adds structural additives, and is prepared by extrusion. The denitrification efficiency of this catalyst is still relatively low. Summary of the Invention

[0008] In view of this, one object of the present invention is to provide an NH3-SCR catalyst that can selectively catalytically reduce nitrogen oxides (NOx) with ammonia at a low temperature of less than or equal to 200°C. x It has a high conversion rate, high N2 selectivity, and low N2O byproduct generation.

[0009] Another object of the present invention is to provide a method for preparing the NH3-SCR catalyst as described above.

[0010] Another object of the present invention is to provide the use of the NH3-SCR catalyst as described above in the selective catalytic reduction of nitrogen oxides by ammonia to produce nitrogen at temperatures below 200°C.

[0011] The present invention achieves the above objectives using the following technical solutions.

[0012] On one hand, the present invention provides an NH3-SCR catalyst, which is a cerium oxide composite oxide catalyst containing Ce, M and R elements, wherein the M element is selected from at least one of Cu, Nb, Fe, Co, Mn, Ni and Zn; the R element is selected from at least one of Ru, Pt, Pd, Rh, Ag and Au; the molar ratio of Ce element to M element is 0.5:1 to 10:1; and the loading of R element is 0.1 to 3 wt% based on the total mass of the NH3-SCR catalyst.

[0013] The NH3-SCR catalyst has a spherical morphology; cerium oxide has exposed

[111] crystal faces, and the percentage of active oxygen content on the surface of the NH3-SCR catalyst is 35-70% of the total oxygen content on the surface; its acidity is 7500-9000 μL, its hydrogen consumption is 1500-2500 μL, and its specific surface area is 50-90 m². 2 / g.

[0014] According to the NH3-SCR catalyst of the present invention, preferably, the M element is selected from at least one of Cu, Nb and Zn; and the R element is selected from at least one of Ru, Pt, Pd and Rh.

[0015] On the other hand, the present invention also provides a method for preparing the NH3-SCR catalyst as described above, comprising the following steps:

[0016] 1) Mix water-soluble cerium salt, C2-C5 alkyldiol, surface stabilizer and water to obtain solution A; react solution A under microwave conditions at 80-180℃, separate the first solid after reaction, and dry the first solid to obtain CeO2 precursor;

[0017] 2) Disperse the CeO2 precursor and the water-soluble salt of element M in water to obtain solution B;

[0018] 3) Solution B was reacted under microwave conditions at 80–180 °C. After the reaction, the second solid was separated. The second solid was dried and calcined to obtain the cerium oxide complex.

[0019] 4) Disperse the cerium oxide complex obtained in step 3) in water, then add acid to continue dispersing, to obtain solution C;

[0020] 5) Disperse the salt of element R in the solution C, then concentrate and dry it. Calcine the concentrated and dried product in an atmosphere of carbon dioxide and inert gas to obtain the NH3-SCR catalyst.

[0021] According to the preparation method of the present invention, preferably, in step 1), the water-soluble cerium salt is selected from at least one of cerium nitrate, cerium acetate, cerium nitrate, cerium ammonium nitrate, and cerium carbonate; the C2-C5 alkyldiol is ethylene glycol; and the surface stabilizer is selected from one of polyvinylpyrrolidone, polyethylene glycol, triethylenetetramine, sorbitol, and xylene.

[0022] According to the preparation method of the present invention, preferably, in step 1), the mass-to-volume ratio of water-soluble cerium salt to C2-C5 alkyldiol is 1 g: 12-32 mL; the mass ratio of water-soluble cerium salt to surface stabilizer is 2.5: 0.8-1.5; the volume ratio of C2-C5 alkyldiol to water is 6-20:1; in step 1), solution A is reacted under microwave conditions at 80-180°C for 8-48 h.

[0023] According to the preparation method of the present invention, preferably, in step 2), the water-soluble salt of CeO2 precursor and element M is dispersed in water by ultrasonication.

[0024] According to the preparation method of the present invention, preferably, in step 3), solution B is reacted under microwave conditions at 80-180°C for 8-48 hours, and a second solid is obtained after the reaction. The second solid is dried, and then the dried solid is calcined at 480-550°C for 2-8 hours to obtain the cerium oxide composite.

[0025] According to the preparation method of the present invention, preferably, in step 4), the acid is selected from one of nitric acid, acetic acid and citric acid; the pH value of solution C is 2 to 6.

[0026] According to the preparation method of the present invention, preferably, in step 5), the calcination temperature is 450-550℃ and the calcination time is 2-6h.

[0027] In another aspect, the present invention also provides the use of the NH3-SCR catalyst as described above in the selective catalytic reduction of nitrogen oxides by ammonia to produce nitrogen at temperatures below 200°C.

[0028] The NH3-SCR catalyst of this invention can selectively catalytically reduce nitrogen oxides (NO) with ammonia at low temperatures of less than or equal to 200°C. x It exhibits high conversion rate, high N2 selectivity, and low N2O byproduct formation. According to a preferred embodiment of the present invention, the preparation method utilizes microwave reaction to control the morphology of the CeO2 precursor, employs a specific calcination atmosphere, and employs specific process parameters to obtain an NH3-SCR catalyst with superior denitrification performance. The specific surface area, acidity, hydrogen consumption, and surface active oxygen content of the NH3-SCR catalyst obtained by the present invention are within a specific range, which is more conducive to improving the denitrification performance of the catalyst, resulting in lower NO content. x It has a high conversion rate, high N2 selectivity, and low amount of N2O byproduct generated. Attached Figure Description

[0029] Figure 1 TEM image of the spherical cerium oxide composite obtained in Example 1.

[0030] Figure 2 TEM images of the rod-shaped cerium oxide composite obtained in Preparation Example 1 are shown for comparison.

[0031] Figure 3 TEM image of the particulate cerium oxide composite obtained in Preparation Example 2 for comparison.

[0032] Figure 4 TEM images of the cubic cerium oxide composite obtained in Preparation Example 3 are shown for comparison.

[0033] Figure 5 Activity diagrams of cerium oxide complexes with different morphologies in Preparation Example 1, Comparative Preparation Example 1, Comparative Preparation Example 2, and Comparative Preparation Example 3.

[0034] Figure 6 This is a TEM image of the catalyst prepared in Example 1.

[0035] Figure 7 This is a TEM image of the catalyst prepared in Example 2. Detailed Implementation

[0036] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0037] Catalyst

[0038] This invention provides an NH3-SCR catalyst, which is a cerium oxide composite oxide catalyst containing Ce, M, and R elements. The M element is selected from at least one of Cu, Nb, Fe, Co, Mn, Ni, and Zn; the R element is selected from at least one of Ru, Pt, Pd, Rh, Ag, and Au; the molar ratio of Ce to M element is 0.5:1 to 10:1; and the loading of R element is 0.1 to 3 wt% based on the total mass of the NH3-SCR catalyst.

[0039] The NH3-SCR catalyst has a spherical morphology. Cerium oxide exposes the

[111] crystal face. The percentage of surface active oxygen content to the total oxygen content on the surface of the NH3-SCR catalyst is 35-70%, preferably 40-70%. The acidity of the NH3-SCR catalyst is 7500-9000 μL. The hydrogen consumption is 1500-2500 μL. The specific surface area is 50-90 m². 2 / g, preferably 60-90m 2 / g. Such catalysts exhibit superior denitrification efficiency and nitrogen selectivity at low temperatures of 200℃ or less, with low N2O formation.

[0040] In this invention, element M is preferably selected from at least one of Cu, Nb, Fe, Co, Ni, and Zn, more preferably from at least one of Cu, Nb, and Zn, and even more preferably from one of Cu, Nb, and Zn. Element R is preferably selected from at least one of Ru, Pt, Pd, Rh, and Au, more preferably from at least one of Ru, Pt, Pd, and Rh, and even more preferably from one of Ru, Pt, Pd, and Rh.

[0041] In this invention, the molar ratio of Ce to M is preferably 0.5:1 to 8:1, more preferably 0.8:1 to 7:1, and even more preferably 1:1 to 7:1. Based on the total mass of the NH3-SCR catalyst, the loading of R is 0.1 to 3 wt%, preferably 0.3 to 2 wt%, more preferably 0.4 to 1.5 wt%, even more preferably 0.6 to 1 wt%, and even more preferably 0.6 to 0.8 wt%. The loading of R in this invention is relatively low.

[0042] In this invention, the morphology of the NH3-SCR catalyst is basically spherical. Cerium oxide

[111] crystal planes are exposed (the lattice fringes on the catalyst surface can be captured under a high-resolution transmission electron microscope (TEM), and the exposed cerium oxide

[111] crystal planes on the catalyst surface can be determined by comparing the data with data in a database using software). The percentage of surface active oxygen content to the total oxygen content on the NH3-SCR catalyst surface is preferably 43-60%, more preferably 45-55%. The acidity of the NH3-SCR catalyst is preferably 7800-8800 μL, more preferably 8100-8700 μL. The hydrogen consumption is preferably 1600-2400 μL, more preferably 1700-2000 μL. The specific surface area is preferably 64-85 m². 2 / g, more preferably 65-82m 2 / g. The catalyst of this invention has a mesoporous structure with abundant surface oxygen concentration and acidic sites.

[0043] <Preparation Method>

[0044] The present invention also provides a method for preparing the NH3-SCR catalyst as described above, comprising the following steps: (1) preparation of CeO2 precursor; (2) preparation of solution B; (3) preparation of cerium oxide complex; (4) preparation of solution C; and (5) obtaining the NH3-SCR catalyst. These steps are described in detail below.

[0045] Preparation steps of CeO2 precursor

[0046] A solution A is prepared by mixing a water-soluble cerium salt, a C2-C5 alkyldiol, a surface stabilizer, and water. Solution A is then reacted under microwave conditions at 80-180°C. After the reaction, a first solid is obtained and dried to yield the CeO2 precursor. This invention demonstrates that this method is beneficial for improving the catalytic reduction performance of the obtained catalyst and increasing the NO reduction efficiency. x It has a high conversion rate (i.e., high denitrification efficiency), high N2 selectivity, and low N2O generation.

[0047] In this invention, the water-soluble cerium salt is selected from at least one of cerium nitrate, cerium acetate, cerium nitrate, cerium ammonium nitrate, and cerium carbonate, preferably from one of cerium nitrate, cerium acetate, cerium nitrate, cerium ammonium nitrate, and cerium carbonate. The water-soluble cerium salt may or may not contain water of crystallization.

[0048] In this invention, the C2-C5 alkyldiol is an alkyldiol with 2 to 5 carbon atoms. Examples of C2-C5 alkyldiols include ethylene glycol, propylene glycol, butanediol, and pentanediol, with ethylene glycol being preferred. The surface stabilizer is selected from one of polyvinylpyrrolidone, polyethylene glycol, triethylenetetramine, sorbitol, and xylene, preferably from one of polyvinylpyrrolidone, polyethylene glycol, and sorbitol, and more preferably from polyvinylpyrrolidone (PVP). This invention has found that such a surface stabilizer can prevent particle aggregation and is beneficial for controlling the growth and exposure of specific cerium oxide crystal faces.

[0049] In this invention, the mass-to-volume ratio of water-soluble cerium salt to C2-C5 alkyldiol is 1 g:12-32 mL, preferably 1 g:15-32 mL, and more preferably 1 g:20-30 mL. The mass ratio of water-soluble cerium salt to surface stabilizer is 2.5:0.8-1.5, preferably 2.5:0.9-1.5, and more preferably 2.5:1.0-1.3. The volume ratio of C2-C5 alkyldiol to water is 6-20:1, preferably 9-18:1, and more preferably 10-16:1.

[0050] According to one specific embodiment of the present invention, cerium nitrate and polyvinylpyrrolidone (PVP) are dissolved in ethylene glycol, and then water is added to the above solution and stirred to obtain solution A. The water can be deionized water, distilled water, or purified water.

[0051] In this invention, microwave conditions can be achieved using a microwave workstation. Specific parameters of the microwave workstation include: a microwave frequency of 400–3000 MHz, preferably 900–3000 MHz, for example, 2450 MHz; a reaction temperature of 80–180°C, preferably 100–180°C, more preferably 120–160°C; a reaction pressure of 0.2–1.0 MPa, preferably 0.5–1.0 MPa, more preferably 0.7–1.0 MPa; and a reaction time of 8–48 h, preferably 12–36 h, more preferably 18–30 h, for example, 24 h. After the reaction, the temperature is lowered to room temperature. After cooling, the mixture can be filtered. During filtration, the filter cake can be washed sequentially with water and alcohol to obtain a first solid. The first solid is dried to obtain the CeO2 precursor. The alcohol used for washing can be methanol, ethanol, or isopropanol, preferably ethanol. The drying temperature can be 50-90℃, preferably 50-80℃, and more preferably 55-65℃.

[0052] Preparation steps of solution B

[0053] Dispersing the CeO2 precursor and a water-soluble salt of element M in water yields solution B. This method is beneficial for improving the catalytic reduction performance of the obtained catalyst and increasing NO reduction. x It has a high conversion rate (i.e., high denitrification efficiency), high N2 selectivity, and low N2O generation.

[0054] In this invention, the CeO2 precursor and the water-soluble salt of element M prepared above can be dispersed in water by ultrasonication or stirring. The water-soluble salt of element M may or may not contain water of crystallization. The water-soluble salt of element M can be a nitrate, acetate, or oxalate, such as copper nitrate, niobium oxalate, ferric nitrate, cobalt nitrate, manganese nitrate, nickel nitrate, or zinc nitrate. This invention has found that the addition of the water-soluble salt of element M is beneficial for the formation of oxygen vacancies and for acting as an acidic site inducing agent, thereby improving the denitrification performance of the obtained catalyst.

[0055] The molar ratio of Ce element in the CeO2 precursor to M element in the water-soluble salt of M element is preferably 0.5:1 to 8:1, more preferably 0.8:1 to 7:1, and even more preferably 1:1 to 7:1.

[0056] In solution B, the concentration of the CeO2 precursor can be 0.03–5 g / mL, preferably 0.05–4.5 g / mL, more preferably 0.1–4 g / mL; the concentration of the water-soluble salt of element M can be 0.01–3 g / mL, preferably 0.03–2.5 g / mL, more preferably 0.08–2 g / mL.

[0057] Preparation steps of cerium oxide complex

[0058] Solution B was reacted under microwave conditions at 80–180 °C. After the reaction, a second solid was obtained, which was then dried and calcined to yield a cerium oxide complex. This process is beneficial for improving the catalytic reduction performance of the obtained catalyst and increasing NO reduction. x The conversion rate is high, with high N2 selectivity and low N2O generation.

[0059] In this step, the microwave conditions can be achieved using a microwave workstation. Specific parameters of the microwave workstation include: a microwave frequency of 400–3000 MHz, preferably 900–3000 MHz, for example, 2450 MHz; a reaction temperature of 80–180°C, preferably 100–160°C, more preferably 110–150°C, for example, 120°C; a reaction pressure of 0.2–1.0 MPa, preferably 0.5–1.0 MPa, more preferably 0.7–1.0 MPa; and a reaction time of 6–30 h, preferably 8–24 h, more preferably 10–20 h, for example, 12 h.

[0060] According to one embodiment of the present invention, solution B is transferred to a reaction vessel in a microwave workstation, and then reacted in the microwave workstation at 80–180°C. After the reaction, a second solid is obtained by separation. Separation can be achieved by centrifugation or filtration. The reaction vessel in the microwave workstation can be a reaction vessel with a polytetrafluoroethylene liner, and the reaction vessel can be formed of polyetheretherketone resin.

[0061] The second solid is dried at 50–90°C for 2–10 hours, preferably in an oven. After drying, it is ground and then calcined. The calcination temperature can be 480–550°C, preferably 490–550°C, and more preferably 500–530°C. The calcination time can be 2–8 hours, preferably 3–7 hours, and more preferably 4–6 hours, for example 5 hours.

[0062] Preparation steps of solution C

[0063] The obtained cerium oxide complex was dispersed in water, and then acid was added to continue the dispersion, yielding solution C. This method is beneficial for improving the denitrification performance of the obtained catalyst.

[0064] In this invention, the acid is selected from nitric acid, acetic acid, and citric acid, preferably citric acid. The pH value of solution C is 2-6, preferably 3-5, and more preferably 4-5. This invention has found that the acid here can act as a pore-forming agent and a pH adjuster. Further dispersion after adding the acid can be achieved by stirring or ultrasonic dispersion, with a dispersion time of 30-60 minutes. The addition of this acid facilitates the diffusion of element R in the solution and prevents the aggregation of particles containing element R.

[0065] The mass concentration of the cerium oxide complex in solution C can be 10–35 wt%, preferably 15–30 wt%, and more preferably 18–25 wt%.

[0066] Steps to obtain a catalyst

[0067] The salt of element R is dispersed in solution C, then concentrated and dried. The concentrated and dried product is calcined in an atmosphere of carbon dioxide and inert gas to obtain the NH3-SCR catalyst. This method is beneficial to improving the catalytic reduction performance of the obtained catalyst and increasing NO reduction. x It has a high conversion rate (i.e., high denitrification efficiency), high N2 selectivity, and low N2O generation.

[0068] In this invention, the salt of element R can be a nitrate, chloride, acetate, acetylacetonate, or dodecyl hydroxyl salt of element R, preferably an acetylacetonate. Concentration and drying can be performed by rotary evaporation. The water content of the concentrated and dried product can be less than or equal to 5 wt%.

[0069] During calcination, the volume ratio of carbon dioxide to inert gas is 10–20:80–90, for example, 15:85. This invention has found that using such a calcination atmosphere is superior to calcination in an air atmosphere, i.e., it is more conducive to improving the performance of the obtained catalyst. The calcination temperature can be 450–550°C, preferably 480–550°C, and more preferably 500–520°C. The calcination time can be 2–6 hours, preferably 2.5–5 hours, and more preferably 3–4 hours.

[0070] The inert gas may be selected from at least one of helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe); preferably, the inert gas is selected from at least one of helium, neon, and argon; more preferably, the inert gas is selected from at least one of helium and argon.

[0071] <Application>

[0072] The present invention also provides the use of the NH3-SCR catalyst as described above in the selective catalytic reduction of nitrogen oxides by ammonia to produce nitrogen at temperatures below 200°C. x It has a high conversion rate, high N2 selectivity, and low N2O generation.

[0073] The NH3-SCR catalyst of the present invention at 150°C produces NO x The conversion rate is greater than or equal to 84%, preferably greater than or equal to 91%, and can reach 97%. NO at 175℃ x The conversion rate is greater than or equal to 99%, and can reach 100%. NO at 200℃... x The conversion rate is essentially 100%. The NH3-SCR catalyst of this invention exhibits high N2 selectivity. At 150°C, the N2 selectivity is greater than or equal to 96%, reaching 100%. At 175°C, the N2 selectivity is greater than or equal to 96%, reaching 100%. At 200°C, the N2 selectivity is greater than or equal to 97%, reaching 100%. In catalytic reduction reactions below (or less than or equal to) 200°C, the amount of nitrous oxide (N2O) generated as a byproduct is less than or equal to 20.0 ppm. At 200°C, the N2O generation is less than or equal to 13.7 ppm. At 175°C, the N2O generation is less than or equal to 18.3 ppm. In some embodiments, the N2O generation can be less than 10 ppm.

[0074] <Testing Methods>

[0075] Specific surface area test: The specific surface area of ​​the catalyst was tested using a Micromeritics ASAP 2460 physical adsorption instrument (USA). The degassing temperature was 105℃ and the degassing time was 2 hours. The test was repeated three times, and the average value was taken.

[0076] Morphology testing: The microstructure and crystal faces of the catalyst were tested using a Thermo Scientific Talos F200i transmission electron microscope.

[0077] Acidity and hydrogen consumption tests: The ammonia adsorption and desorption performance of the catalyst was tested using a Quanta ASAP 292011 chemisorption analyzer. The acidity or hydrogen consumption was calculated based on the ammonia desorption peak area or hydrogen peak area. Acidity can measure the ammonia storage performance of the catalyst, and hydrogen consumption can measure the redox capacity of the catalyst.

[0078] Surface oxygen content and oxygen vacancy testing: The surface elemental properties of the catalyst were analyzed using an X-ray photoelectron spectrometer (XPS) from Thermo Scientific ESCALAB QXi.

[0079] Activity testing: A certain amount of the prepared composite or catalyst (40-60 mesh) was loaded into a fixed-bed quartz reactor with an inner diameter of 6 mm for NH3-SCR activity testing. The reaction mixture consisted of 500 ppm NO, 500 ppm NH3, 10% O2, and 5% H2O, with the balance being N2. The total gas flow rate was 750 mL / min, and the gas hourly space velocity (GHSV) was 50,000–150,000 h⁻¹. -1 The concentrations of the analyte gas were measured at standard atmospheric pressure and temperatures ranging from 100 to 500 °C using an FTIR spectrometer in an Antaris IGS (Thermo Scientific) instrument. Nitrogen oxides (NOx) x Conversion rate of NO x The conversion rate and the selectivity of N2 (same as N2 selectivity) are calculated according to the following formulas.

[0080]

[0081] In the following preparation examples, comparative preparation examples, and comparative examples, the microwave workstations used were purchased from Beijing Xianghu Technology Development Co., Ltd., model XH-300PE, with a microwave frequency of 2450MHz, and were equipped with polytetrafluoroethylene-lined reactors (formed from polyetheretherketone resin). All cerium nitrates used were Ce(NO3)3·6H2O.

[0082] Preparation Example 1 - Preparation of the Complex

[0083] 2.5 g of cerium nitrate and 1 g of polyvinylpyrrolidone (PVP) were dissolved in 70 mL of ethylene glycol. Then, 5 mL of deionized water was added to the solution, and the mixture was stirred for 30 min to obtain solution A. Solution A was transferred to a 100 mL reactor in a microwave workstation, and the microwave workstation was set to heat to 160 °C over 30 min. The reaction was then carried out in the microwave workstation at 160 °C and 0.8 MPa for 24 h. After cooling to room temperature, the first solid was separated. The first solid was washed with deionized water and anhydrous ethanol to obtain the washed first solid. The washed first solid was then dried at 60 °C to obtain the CeO2 precursor, denoted as s-CeO2.

[0084] Niobium oxalate (C2NbO4) was mixed with the s-CeO2 prepared above in a molar ratio (Ce:Nb = 1:1), and then added to 60 mL of deionized water and stirred for 30 min to obtain solution B.

[0085] Solution B was transferred to a 100 mL reaction vessel in a microwave workstation, which was then set to heat to 120 °C over 30 min. The reaction was then carried out in the microwave workstation at 120 °C and 0.7 MPa for 12 h. After the reaction, centrifugation was performed to obtain a second solid. The second solid was washed with deionized water, dried at 60 °C, ground, and then placed in a muffle furnace. The temperature was increased to 500 °C at a rate of 2 °C / min, and calcined at 500 °C for 4 h to obtain a spherical cerium oxide composite, denoted as the Nb / s-CeO2 composite.

[0086] TEM results of the Nb / s-CeO2 complex are shown in [the image]. Figure 1 . Figure 1 In the Nb / s-CeO2 composite, the morphology is spherical with exposed cerium oxide crystal faces

[111] .

[0087] Comparative Preparation Example 1

[0088] Dissolve 19.2 g of sodium hydroxide (NaOH) in 70 mL of deionized water to obtain a NaOH solution. At room temperature, slowly add 10 mL of a 0.4 mmol / mL aqueous solution of cerium nitrate to the cooled NaOH solution. Stir continuously for 30 min, then transfer the resulting mixture to a 100 mL polytetrafluoroethylene-lined reactor and carry out a hydrothermal reaction at 100 °C for 24 h. After the reaction is complete, centrifuge to separate and collect the solid particles, wash three times alternately with deionized water and ethanol, and finally dry at 60 °C to obtain the CeO2 precursor, denoted as r-CeO2.

[0089] Niobium oxalate (C2NbO4) was mixed with the above-prepared r-CeO2 in a molar ratio (Ce:Nb = 1:1), and then 60 mL of deionized water was added and stirred for 30 min to obtain solution B.

[0090] Solution B was transferred to a 100 mL reaction vessel in a microwave workstation, which was set to heat to 120 °C over 30 min. The reaction was then carried out in the microwave workstation at 120 °C and 0.7 MPa for 12 h. After the reaction, the mixture was centrifuged to obtain a solid. The solid was washed with deionized water, dried at 60 °C, ground, and then placed in a muffle furnace. The temperature was increased to 500 °C at a rate of 2 °C / min, and calcined at 500 °C for 4 h to obtain rod-shaped Nb / r-CeO2 composites.

[0091] TEM results of the Nb / r-CeO2 complex are shown in [the image]. Figure 2 . Figure 2 In the Nb / r-CeO2 composite, the morphology is rod-shaped with exposed cerium oxide crystal faces

[111] .

[0092] Comparative Preparation Example 2

[0093] 15g of cerium ammonium nitrate and 50g of urea were dispersed in 500mL of deionized water, stirred thoroughly, and heated to 90℃. The mixture was stirred at 90℃ for 27h, and then filtered. The solid was washed with deionized water during filtration. The washed solid was then dried at 100℃ to obtain the CeO2 precursor, denoted as g-CeO2.

[0094] Niobium oxalate (C2NbO4) was mixed with the g-CeO2 prepared above in a molar ratio (Ce:Nb = 1:1), and then 60 mL of deionized water was added and stirred for 30 min to obtain solution B.

[0095] Solution B was transferred to a 100 mL reactor in a microwave workstation, which was then set to heat to 120 °C over 30 min. The mixture was then subjected to a hydrothermal reaction at 120 °C and 0.7 MPa for 12 h in the microwave workstation. After the reaction, the mixture was centrifuged, and the resulting solid was washed with deionized water. The washed solid was dried at 60 °C, ground, and placed in a muffle furnace. The temperature was increased to 500 °C at a rate of 2 °C / min, and then calcined at 500 °C for 4 h to obtain granular Nb / g-CeO2 composites.

[0096] TEM results of the Nb / g-CeO2 complex are shown in [the image]. Figure 3 . Figure 3 In the middle, cerium oxide exposes the

[111] and

[220] crystal planes.

[0097] Comparative preparation example 3

[0098] A suitable amount of sodium hydroxide was dissolved in 30 mL of deionized water and cooled to room temperature to obtain a 36 wt% NaOH solution. 1.92 g of cerium nitrate was dissolved in 40 mL of deionized water and cooled to room temperature to obtain a cerium nitrate solution. The two solutions were mixed and stirred for 30 min. The resulting flocculent mixture was then transferred to a reaction vessel and hydrothermally treated at 180 °C for 24 h. After the reaction was complete, the mixture was cooled, centrifuged, and the solid was washed with distilled water until the washings were neutral. The washed solid was then dried at 60 °C to obtain the CeO2 precursor, denoted as c-CeO2.

[0099] Niobium oxalate (C2NbO4) was mixed with the c-CeO2 prepared above in a molar ratio (Ce:Nb = 1:1), and then added to 60 mL of deionized water and stirred for 30 min to obtain solution B.

[0100] Solution B was transferred to a 100 mL reaction vessel in a microwave workstation, which was then set to heat to 120 °C over 30 min. The reaction was then carried out in the microwave workstation at 120 °C and 0.7 MPa for 12 h. After the reaction, the mixture was centrifuged, and the resulting solid was washed with deionized water. The washed solid was dried at 60 °C, ground, and placed in a muffle furnace. The temperature was increased to 500 °C at a rate of 2 °C / min, and then calcined at 500 °C for 4 h to obtain a cubic Nb / c-CeO2 composite.

[0101] TEM results of the Nb / c-CeO2 complex are shown in [the image]. Figure 4 . Figure 4 In the Nb / c-CeO2 composite, the morphology is basically cubic, with cerium oxide exposing the

[200] and

[220] crystal planes.

[0102] Comparative preparation example 4

[0103] Compared to Preparation Example 1, the heating method in the microwave workstation will be changed to ordinary oven heating, while other conditions remain the same.

[0104] The complexes from Preparation Example 1 and Comparative Preparation Examples 1-4 were subjected to activity testing. 0.77 g of the prepared complex (40-60 mesh) was loaded into a fixed-bed quartz reactor with an inner diameter of 6 mm for NH3-SCR activity testing. The gas hourly space velocity (GHSV) was 60,000 h⁻¹. -1 The results are shown below. Figure 5 See Table 1.

[0105] Combination Figure 5 It can be seen that, compared with comparative preparation examples 1 to 3, the spherical cerium oxide composite prepared in preparation example 1 of the present invention exhibits the best SCR activity, with NO at 200°C. xThe conversion rate was 76% within a temperature window of 225–425℃. x Conversion rate greater than 90%.

[0106] As shown in Table 1, the composite synthesized by microwave hydrothermal method (Preparation Example 1) has significantly better performance than that synthesized by conventional oven heating (Comparative Preparation Example 4).

[0107] Table 1

[0108]

[0109] Example 1 - Preparation of NH3-SCR catalyst

[0110] The Nb / s-CeO2 composite prepared in Preparation Example 1 was used to support the noble metal Rh. The specific method is as follows:

[0111] Add 3g of the Nb / s-CeO2 complex prepared in Preparation Example 1 to 10mL of deionized water, sonicate for 30min, add citric acid to adjust the pH of the solution to 4, and continue sonication for 40min to obtain solution C.

[0112] 0.0704 g of rhodium triacetylacetone was added to solution C, and the mixture was ultrasonically dispersed for 30 min. The product was then dried by rotary evaporation. The product was calcined at 500 °C for 3 h under a 15% CO2 / Ar atmosphere to obtain the NH3-SCR catalyst, denoted as 0.6% Rh / CeNbOx.

[0113] The TEM microstructure of the obtained NH3-SCR catalyst is shown in the figure. Figure 6 .Depend on Figure 6 It can be seen that the catalyst has a basically spherical morphology. Tests showed that its hydrogen consumption was 1811 μL, the ratio of surface active oxygen content to total oxygen content on the catalyst surface was 46%, the acid content was 8550 μL, and the specific surface area was 76 m². 2 / g.

[0114] Example 2

[0115] The Nb / s-CeO2 composite prepared in Preparation Example 1 was used to support the noble metal Pt. The specific method is as follows:

[0116] Add 3g of the Nb / s-CeO2 complex prepared in Preparation Example 1 to 10mL of deionized water, sonicate for 30min, add citric acid to adjust the pH of the solution to 4, and continue sonication for 40min to obtain solution C.

[0117] 0.03 g of platinum nitrate was added to solution C, and the mixture was ultrasonically dispersed for 30 min. Then, it was dried by rotary evaporation. The product dried by rotary evaporation was calcined at 500 °C for 3 h under a 15% CO2 / Ar atmosphere to obtain the NH3-SCR catalyst, denoted as 0.6% Pt / CeNbOx.

[0118] The TEM microstructure of the obtained NH3-SCR catalyst is shown in the figure. Figure 7 ,Depend on Figure 7 It can be seen that the catalyst has a basically spherical morphology. Tests showed that its hydrogen consumption was 1738 μL, the ratio of surface active oxygen content to total oxygen content on the catalyst surface was 49%, the acid content was 8231 μL, and the specific surface area was 67 m². 2 / g.

[0119] Example 3

[0120] The Nb / s-CeO2 composite prepared in Preparation Example 1 was used to support the noble metal Pt. The specific method is as follows:

[0121] Add 3g of the Nb / s-CeO2 complex prepared in Preparation Example 1 to 10mL of deionized water, sonicate for 30min, add citric acid to adjust the pH of the solution to 4, and continue sonication for 40min to obtain solution C.

[0122] 0.02 g of platinum nitrate was added to solution C, and the mixture was ultrasonically dispersed for 30 min. The product was then dried by rotary evaporation. The product was calcined at 500 °C for 3 h under a 15% CO2 / Ar atmosphere to obtain the NH3-SCR catalyst, denoted as 0.4% Pt / CeNbOx.

[0123] Example 4

[0124] The Nb / s-CeO2 composite prepared in Preparation Example 1 was used to support the noble metal Pt. The specific method is as follows:

[0125] Add 3g of the Nb / s-CeO2 complex prepared in Preparation Example 1 to 10mL of deionized water, sonicate for 30min, add citric acid to adjust the pH of the solution to 4, and continue sonication for 40min to obtain solution C.

[0126] 0.04 g of platinum nitrate was added to solution C, and the mixture was ultrasonically dispersed for 30 min. The product was then dried by rotary evaporation. The product was calcined at 500 °C for 3 h under a 15% CO2 / Ar atmosphere to obtain the NH3-SCR catalyst, denoted as 0.8% Pt / CeNbOx.

[0127] Comparative Example 1 (without niobium oxalate)

[0128] 2.5 g of cerium nitrate and 1 g of polyvinylpyrrolidone (PVP) were dissolved in 70 mL of ethylene glycol, and then 5 mL of deionized water was added to the solution. The mixture was stirred for 30 min to obtain solution A. Solution A was transferred to a 100 mL reactor in a microwave workstation, and the microwave workstation was set to heat to 160 °C over 30 min. The reaction was then carried out in the microwave workstation at 160 °C and 0.8 MPa for 24 h. After cooling to room temperature, the first solid was separated and collected. The first solid was washed with deionized water and anhydrous ethanol, and then dried at 60 °C to obtain spherical CeO2 precursors. The CeO2 precursors were calcined at 500 °C for 4 h (heating rate of 2 °C / min) to obtain spherical CeO2.

[0129] Add 3g of spherical CeO2 to 10mL of deionized water, sonicate for 30min, add citric acid to adjust the pH of the solution to 4, and continue sonication for 40min to obtain solution C.

[0130] 0.03 g of platinum nitrate was added to solution C, and the mixture was ultrasonically dispersed for 30 min. The product was then dried by rotary evaporation. The product was calcined at 500 °C for 3 h under a 15% CO2 / Ar atmosphere to obtain the NH3-SCR catalyst, denoted as 0.6% Pt / CeO2.

[0131] The tested catalyst had a hydrogen consumption of 651 μL, a surface active oxygen content to total catalyst surface oxygen content ratio of 26%, an acid content of 2350 μL, and a specific surface area of ​​36 m². 2 / g.

[0132] Comparative Example 2 (without spherical CeO2 precursor)

[0133] 3.618 g of niobium oxalate (C2NbO4) was added to 60 mL of deionized water and stirred for 30 min. The mixture was then transferred to a 100 mL reactor in a microwave workstation and subjected to hydrothermal reaction at 120 °C and 0.7 MPa for 12 h. After the reaction was completed, the mixture was centrifuged, and the resulting solid was dried at 60 °C. The dried product was then calcined at 500 °C for 4 h (heating rate of 2 °C / min) to obtain NbOx.

[0134] Add 3g NbOx to 10mL of deionized water, sonicate for 30min, add citric acid to adjust the pH of the solution to 4, and continue sonication for 40min to obtain solution C.

[0135] 0.03 g of platinum nitrate was added to solution C, and the mixture was ultrasonically dispersed for 30 min. The product was then dried by rotary evaporation. The product was calcined at 500 °C for 3 h under a 15% CO2 / Ar atmosphere to obtain the NH3-SCR catalyst, denoted as 0.6% Pt / NbOx.

[0136] The tested catalyst had a hydrogen consumption of 961 μL, a surface active oxygen content to total catalyst surface oxygen content ratio of 19%, an acid content of 1236 μL, and a specific surface area of ​​23 m². 2 / g.

[0137] Comparative Example 3

[0138] Compared with Example 1, the only difference is that in Comparative Example 3, the roasting atmosphere is an air atmosphere.

[0139] The catalyst obtained in Comparative Example 3 was tested and found to have a hydrogen consumption of 1023 μL, a surface active oxygen content to total catalyst surface oxygen content ratio of 35%, an acid content of 3624 μL, and a specific surface area of ​​57 m². 2 / g.

[0140] Table 2

[0141] serial number Hydrogen consumption / μL Oxygen content percentage / % Acidity / μL <![CDATA[Specific surface area / m 2 / g]]> Example 1 1811 46 8550 76 Example 2 1738 49 8231 67 Comparative Example 1 651 26 2350 36 Comparative Example 2 961 19 1236 23 Comparative Example 3 1023 35 3624 57

[0142] Note: In this table, the oxygen content ratio refers to the percentage of active oxygen content on the catalyst surface relative to the total oxygen content on the catalyst surface.

[0143] As can be seen from the table, the catalyst prepared by this invention has abundant surface oxygen concentration and acidic sites.

[0144] Experimental Example 1

[0145] The NH3-SCR catalysts obtained in Examples 1-4 and Comparative Examples 1-3 were subjected to activity tests. 0.62 g of the prepared NH3-SCR catalyst (40-60 mesh) was loaded into a fixed-bed quartz reactor with an inner diameter of 6 mm for NH3-SCR activity testing. The gas space velocity (GHSV) was 100,000 h⁻¹. -1 The results are shown in Tables 3, 4, and 5.

[0146] Table 3 shows that the NH3-SCR catalyst obtained in this invention has a denitrification efficiency of 84-100% at 150-225℃. A comparison of Comparative Example 1, Comparative Example 2, and Example 1 shows that omitting cerium oxide or niobium oxalate cannot yield the high-performance NH3-SCR catalyst of this invention. A comparison of Comparative Example 3 and Example 1 shows that calcination in a 15% CO2 / Ar atmosphere significantly improves the NO content of the obtained catalyst compared to calcination in air. x Conversion rate.

[0147] As shown in Table 4, the NH3-SCR catalyst obtained in this invention has an N2 selectivity of ≥95% at 125–225 °C.

[0148] As shown in Table 5, the N2O generation of the NH3-SCR catalyst obtained in this invention can be below 20 ppm at 125-225℃, with most of it below 10 ppm.

[0149] Table 3

[0150]

[0151] Table 4

[0152]

[0153] Table 5

[0154]

[0155] As shown in the table, the NH3-SCR catalyst obtained in this invention exhibits excellent denitrification performance, especially at lower temperatures (125–225 °C) for NO removal. x The catalyst exhibits high conversion rate, high N2 selectivity, and low N2O byproduct formation. The NH3-SCR catalyst obtained in this invention still maintains good denitrification efficiency below 200℃.

[0156] This invention is not limited to the above-described embodiments. Any modifications, improvements, or substitutions that can be conceived by those skilled in the art without departing from the essential content of this invention fall within the scope of this invention.

Claims

1. A method for preparing an NH3-SCR catalyst, characterized by, The NH3-SCR catalyst is a cerium oxide composite oxide catalyst, which comprises Ce, M and R elements, wherein the M element is selected from at least one of Cu, Nb, Fe, Co, Mn, Ni and Zn; the R element is selected from at least one of Ru, Pt, Pd, Rh, Ag and Au; the molar ratio of the Ce element to the M element is 0.5:1-10:1; and the loading of the R element is 0.1-3 wt% based on the total mass of the NH3-SCR catalyst; The NH3-SCR catalyst has a spherical shape; cerium exposes [111] crystal surface, the percentage of surface active oxygen content in total oxygen content of the NH3-SCR catalyst is 35-70%; the acid amount is 7500-9000 muL, the hydrogen consumption amount is 1500-2500 muL, the specific surface area is 50-90 m 2 / g; The preparation method of the NH3-SCR catalyst comprises the following steps: 1) mixing a water-soluble cerium salt, a C2-C5 alkylene glycol, a surface stabilizer and water to obtain a solution A; reacting the solution A under microwave conditions at 80-180°C, and then separating a first solid after the reaction, drying the first solid to obtain a CeO2 precursor; 2) dispersing the CeO2 precursor and a water-soluble salt of the M element in water to obtain a solution B; 3) reacting the solution B under microwave conditions at 80-180°C, and then separating a second solid after the reaction, drying and calcining the second solid to obtain a cerium oxide composite; 4) dispersing the cerium oxide composite obtained in step 3) in water, and then adding an acid for further dispersion to obtain a solution C; 5) dispersing a salt of the R element in the solution C, and then concentrating and drying, and calcining the concentrated and dried product in an atmosphere containing carbon dioxide and an inert gas to obtain the NH3-SCR catalyst.

2. The production method according to claim 1, characterized by, In step 1), the water-soluble cerium salt is selected from at least one of cerium nitrate, cerium acetate, cerous nitrate, cerium ammonium nitrate and cerium carbonate; the C2-C5 alkylene glycol is ethylene glycol; and the surface stabilizer is selected from one of polyvinylpyrrolidone, polyethylene glycol, triethylenetetramine and sorbitol.

3. The preparation method according to claim 1, characterized in that: In step 1), the mass-volume ratio of the water-soluble cerium salt to the C2-C5 alkylene glycol is 1 g:12-32 mL; the mass ratio of the water-soluble cerium salt to the surface stabilizer is 2.5:0.8-1.5; and the volume ratio of the C2-C5 alkylene glycol to water is 6-20:

1. In step 1), the solution A is reacted under microwave conditions at 80-180°C for 8-48 h.

4. The method of claim 1, wherein, In step 2), the CeO2 precursor and the water-soluble salt of the M element are dispersed in water by ultrasonic.

5. The preparation method according to claim 1, characterized in that, In step 3), the solution B is reacted under microwave conditions at 80-180°C for 8-48 h, and then a second solid is separated after the reaction, and the second solid is dried, and then the dried solid is calcined at 480-550°C for 2-8 h to obtain the cerium oxide composite.

6. The preparation method according to claim 1, characterized in that, In step 4), the acid is selected from one of nitric acid, acetic acid and citric acid; and the pH value of the solution C is 2-6.

7. The preparation method according to claim 1, characterized in that, In step 5), the calcination temperature is 450-550°C, and the calcination time is 2-6 h.

8. The method of claim 1, wherein, The M element is selected from at least one of Cu, Nb and Zn; and the R element is selected from at least one of Ru, Pt, Pd and Rh.

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