NH3-SCR (selective catalytic reduction) catalyst as well as preparation method and application thereof

Abstract

The invention discloses an NH3-SCR (Selective Catalytic Reduction) catalyst as well as a preparation method and application thereof. The NH3-SCR catalyst is a cerium oxide composite oxide catalyst and contains Ce, M and R elements, and 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); based on the total mass of the NH3-SCR catalyst, the loading amount of the R element is 0.1-3 wt%; the NH3-SCR catalyst is in a spherical shape; the cerium oxide exposes a crystal face [111], and the surface active oxygen content accounts for 35-70% of the total surface oxygen content of the NH3-SCR catalyst; the acid content is 7500-9000 [mu] L, the hydrogen consumption is 1500-2500 [mu] L, and the specific surface area is 50-90 m < 2 > / g. The catalyst disclosed by the invention has the advantages that nitrogen oxides are subjected to ammonia selective catalytic reduction at the low temperature of less than or equal to 200 DEG C, the conversion rate of NOx is high, the selectivity of N2 is high, and the generation amount of a byproduct N2O is small.

Description

Technical Field

[0001] The invention relates to an NH3-SCR catalyst and a preparation method and application thereof. Background Art

[0002] Nitrogen oxides (mainly NO and NO2, collectively referred to as NO x ) is one of the atmospheric pollutants that causes acid rain, photochemical smog and haze, and has caused great harm to the environment in which humans live. At present, NO in non-electricity industries such as coking enterprises (coke oven flue gas), steel enterprises (sintering flue gas, coke oven flue gas, blast furnace flue gas and converter flue gas), chemical enterprises (waste liquid incineration flue gas, nitric acid preparation tail gas) and cement industry (rotary kiln flue gas) is increasing. x Control and emission reduction have become the focus and difficulty of flue gas pollution prevention and control.

[0003] In view of the low temperature of flue gas emissions in non-power industries, ammonia selective catalytic reduction (NH3-SCR) technology is currently the most effective NO x Emission reduction technology. my country has developed SCR technology and its catalyst system with good application effects in the range of 180-420°C, but catalytic reduction under conditions below 200°C still needs to be broken through, that is, the catalyst is required to achieve 90% NO reduction at below 200°C. x In order to achieve the best catalytic efficiency, strict NO x According to emission regulations, the industry basically adopts the heating and heat exchange mode, equipped with traditional V2O5-WO3 (MoO3) / TiO2 catalysts, and increases the low-temperature activity of the catalyst to a certain extent by increasing the vanadium content. This process route is complex, with high overall investment, high system resistance, and consumes additional fuel and produces additional CO2. In addition, the selective catalytic reduction reaction of ammonia also produces nitrous oxide (N2O) as a byproduct. N2O is not only a pollutant, but also a strong greenhouse gas.

[0004] CN106423139A discloses a rare earth-based SCR denitration catalyst and a preparation method thereof. The catalyst is a medium-low temperature CeO2 and TiO2 composite denitration catalyst, the active component of the catalyst is cerium dioxide, the carrier is titanium dioxide, and the auxiliary agent is transition metal and rare earth metal oxide. The catalyst has good NO x Conversion and N2 selectivity.

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

[0006] CN112316940A discloses a method for preparing a rare earth-based redox catalyst for flue gas denitration in a coking plant, 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 water, filtering, extruding, and drying to obtain a catalyst. The catalyst requires ammonia and carbon monoxide as reducing agents, and the denitration efficiency still has room for improvement.

[0007] CN117019136A discloses a low-temperature manganese / cerium honeycomb denitration catalyst, which is prepared by extrusion method using cerium dioxide and manganese oxide as main active ingredients, titanium dioxide as paste material, and adding structural additives. The denitration efficiency of the catalyst is still low. Summary of the invention

[0008] In view of this, an object of the present invention is to provide an NH3-SCR catalyst which can selectively catalyze the reduction of nitrogen oxides, NO x High conversion rate, high N2 selectivity, and low amount of by-product N2O generated.

[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 use of the NH3-SCR catalyst as described above in the selective catalytic reduction of nitrogen oxides by ammonia at a temperature below 200°C to generate nitrogen.

[0011] The present invention adopts the following technical solutions to achieve the above-mentioned purpose.

[0012] In one aspect, the present invention provides an NH3-SCR catalyst, which is a cerium oxide composite oxide catalyst, comprising 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 to 10:1; based on the total mass of the NH3-SCR catalyst, the loading amount of the R element is 0.1 to 3 wt%;

[0013] The NH3-SCR catalyst has a spherical shape; the cerium oxide exposes the

[111] crystal plane, and the surface active oxygen content accounts for 35-70% of the total oxygen content on the surface of the NH3-SCR catalyst; its acid content is 7500-9000 μL, its hydrogen consumption is 1500-2500 μL, and its specific surface area is 50-90 m 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) mixing a water-soluble cerium salt, a C2-C5 alkanediol, a surface stabilizer and water to obtain a solution A; reacting the solution A under microwave conditions at 80-180° C., separating and obtaining a first solid after the reaction, and drying the first solid to obtain a CeO2 precursor;

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

[0018] 3) reacting solution B under microwave conditions at 80-180° C., separating to obtain a second solid after the reaction, and drying and calcining the second solid to obtain a cerium oxide composite;

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

[0020] 5) dispersing the salt of the R element in the solution C, and then concentrating and drying the solution. The concentrated and dried product is calcined in an atmosphere of carbon dioxide and an inert gas to obtain an 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, cerous nitrate, ammonium cerium nitrate, and cerium carbonate; the C2-C5 alkanediol is ethylene glycol; and the surface stabilizer is selected from one of polyvinyl pyrrolidone, polyethylene glycol, triethylenetetramine, sorbitol, and xylene.

[0022] According to the preparation method of the present invention, preferably, in step 1), the mass volume ratio of the water-soluble cerium salt to the C2-C5 alkane diol 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; the volume ratio of the C2-C5 alkane diol to water is 6-20:1; in step 1), solution A is reacted under microwave conditions at 80-180°C for 8-48 hours.

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

[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, a second solid is separated after the reaction, the second solid is dried, and the dried solid is then calcined at 480-550°C for 2-8 hours to obtain a 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; and the pH value of solution C is 2-6.

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

[0027] In another aspect, the present invention further provides use of the NH3-SCR catalyst as described above in the selective catalytic reduction of nitrogen oxides with ammonia at a temperature below 200°C to generate nitrogen.

[0028] The NH3-SCR catalyst of the present invention can selectively catalyze the reduction of nitrogen oxides by ammonia at a low temperature of less than or equal to 200°C. x The conversion rate is high, the N2 selectivity is high, and the amount of byproduct N2O generated is small. According to the preferred technical scheme of the present invention, the preparation method of the present invention controls the morphology of the CeO2 precursor by microwave reaction, and the NH3-SCR catalyst obtained by specific calcination atmosphere and specific process parameters has better denitration performance. The specific surface area, acid content, 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 denitration performance of the obtained catalyst, so that the NO of the catalyst x The conversion rate is high, the N2 selectivity is high, and the amount of by-product N2O generated is small. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0030] Figure 2 This is a TEM image of the rod-shaped cerium oxide composite obtained in Comparative Preparation Example 1.

[0031] Figure 3 This is a TEM image of the granular cerium oxide composite obtained in Comparative Preparation Example 2.

[0032] Figure 4 This is a TEM image of the cubic cerium oxide composite obtained in Comparative Preparation Example 3.

[0033] Figure 5 These are activity diagrams of cerium oxide composites 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 the TEM image of the catalyst prepared in Example 1.

[0035] Figure 7 This is the TEM image of the catalyst prepared in Example 2. DETAILED DESCRIPTION

[0036] The present invention is further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0037] <Catalyst>

[0038] The present invention provides an NH3-SCR catalyst, which is a cerium oxide composite oxide catalyst, comprising 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 to 10:1; based on the total mass of the NH3-SCR catalyst, the loading amount of the R element is 0.1 to 3 wt%;

[0039] The NH3-SCR catalyst has a spherical shape; the cerium oxide exposes the

[111] crystal face, and the surface active oxygen content accounts for 40-70% of the total oxygen content on the surface of the NH3-SCR catalyst; the acid content of the NH3-SCR catalyst is 7500-9000 μL, the hydrogen consumption is 1500-2500 μL, and the specific surface area is 60-90 m 2 Such a catalyst has excellent denitration efficiency and nitrogen selectivity at low temperatures of 200°C or less, and produces a small amount of nitrous oxide N2O.

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

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

[0042] In the present invention, the morphology of the NH3-SCR catalyst is basically spherical. The cerium oxide exposes the

[111] crystal plane (the lattice fringes on the catalyst surface can be photographed under a high-resolution transmission electron microscope TEM, and then the exposed cerium oxide

[111] crystal plane on the catalyst surface can be determined by using software and comparing with the data in the database), and the percentage of surface active oxygen content to the total oxygen content on the surface of the NH3-SCR catalyst is preferably 43-60%, and more preferably 45-55%. The acid content of the NH3-SCR catalyst is preferably 7800-8800 μL, and more preferably 8100-8700 μL. The hydrogen consumption is preferably 1600-2400 μL, and more preferably 1700-2000 μL. The specific surface area is preferably 64-85 m 2 / g, more preferably 65 to 82 m 2 The catalyst of the present invention has a mesoporous structure and has 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) a step of preparing a CeO2 precursor; (2) a step of preparing a solution B; (3) a step of preparing a cerium oxide composite; (4) a step of preparing a solution C; and (5) a step of obtaining the NH3-SCR catalyst. This is described in detail below.

[0045] Preparation steps of CeO2 precursor

[0046] A water-soluble cerium salt, a C2-C5 alkanediol, a surface stabilizer and water are mixed to obtain a solution A; the solution A is reacted under microwave conditions at 80-180°C, a first solid is separated after the reaction, and the first solid is dried to obtain a CeO2 precursor. The present invention finds that this is conducive to improving the catalytic reduction performance of the obtained catalyst and improving NO x The conversion rate (i.e., high denitrification efficiency) is high, the N2 selectivity is high, and the amount of N2O generated is small.

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

[0048] In the present invention, the C2-C5 alkanediol is an alkyldiol having 2 to 5 carbon atoms, and examples of the C2-C5 alkanediol include ethylene glycol, propylene glycol, butylene glycol, pentanediol, preferably ethylene glycol. The surface stabilizer is selected from one of polyvinyl pyrrolidone, polyethylene glycol, triethylenetetramine, sorbitol and xylene, preferably selected from one of polyvinyl pyrrolidone, polyethylene glycol, sorbitol, more preferably polyvinyl pyrrolidone (abbreviated as PVP). The present invention believes that such a surface stabilizer can prevent particle aggregation, which is beneficial to controlling the growth and exposure of specific crystal faces of cerium oxide.

[0049] In the present invention, the mass volume ratio of the water-soluble cerium salt to the C2-C5 alkane diol is 1 g: 12-32 mL, preferably 1 g: 15-32 mL, and more preferably 1 g: 20-30 mL. The mass ratio of the water-soluble cerium salt to the 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 the C2-C5 alkane diol to water is 6-20: 1, preferably 9-18: 1, and more preferably 10-16: 1.

[0050] According to a specific embodiment of the present invention, cerium nitrate and polyvinyl pyrrolidone (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 the present invention, microwave conditions can be achieved by a microwave workstation. In the microwave workstation, specific parameters include: microwave frequency is 400-3000MHz, preferably 900-3000MHz, for example, it can be 2450MHz. The reaction temperature can be 80-180°C, preferably 100-180°C, and more preferably 120-160°C. The reaction pressure is 0.2-1.0MPa, preferably 0.5-1.0MPa, and more preferably 0.7-1.0MPa. The reaction time can be 8-48h, preferably 12-36h, more preferably 18-30h, for example, it can be 24h. After the reaction, the temperature is lowered to room temperature. After cooling, it can be filtered. When filtering, water and alcohol can be used to wash the filter cake in sequence to obtain a first solid, and the first solid is dried to obtain a CeO2 precursor. The alcohol used for washing can be methanol, ethanol or isopropanol, preferably ethanol. The drying temperature may be 50 to 90°C, preferably 50 to 80°C, and more preferably 55 to 65°C.

[0052] Preparation steps of solution B

[0053] The CeO2 precursor and the water-soluble salt of the M element are dispersed in water to obtain solution B. This is beneficial to improving the catalytic reduction performance of the obtained catalyst and improving NO xThe conversion rate (i.e., high denitrification efficiency) is high, the N2 selectivity is high, and the amount of N2O generated is small.

[0054] In the present invention, the CeO2 precursor prepared above and the water-soluble salt of the M element can be dispersed in water by ultrasound or stirring. The water-soluble salt of the M element may contain water of crystallization or may not contain water of crystallization. The water-soluble salt of the M element may be a nitrate, an acetate or an oxalate, for example, specifically copper nitrate, niobium oxalate, iron nitrate, cobalt nitrate, manganese nitrate, nickel nitrate, zinc nitrate. The present invention believes that the addition of the water-soluble salt of the M element is conducive to the formation of oxygen defects and acts as an acidic site inducer, thereby helping to improve the denitration performance of the resulting catalyst.

[0055] The molar ratio of the Ce element in the CeO2 precursor to the M element in the water-soluble salt of the 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 CeO2 precursor can be 0.03-5 g / mL, preferably 0.05-4.5 g / mL, and 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, and more preferably 0.08-2 g / mL.

[0057] Preparation steps of cerium oxide composite

[0058] Solution B is reacted under microwave conditions at 80-180°C, and a second solid is separated after the reaction. The second solid is dried and calcined to obtain a cerium oxide composite. This is beneficial to improving the catalytic reduction performance of the obtained catalyst and improving NO x Conversion rate, high N2 selectivity and low N2O generation.

[0059] In this step, the microwave conditions can be a microwave workstation. In the microwave workstation, the specific parameters include: the microwave frequency is 400 to 3000 MHz, preferably 900 to 3000 MHz, for example, it can be 2450 MHz. The reaction temperature can be 80 to 180°C, preferably 100 to 160°C, more preferably 110 to 150°C, for example, it can be 120°C. The reaction pressure is 0.2 to 1.0 MPa, preferably 0.5 to 1.0 MPa, more preferably 0.7 to 1.0 MPa. The reaction time can be 6 to 30 hours, preferably 8 to 24 hours, more preferably 10 to 20 hours, for example, it can be 12 hours.

[0060] According to one embodiment of the present invention, solution B is transferred to a reactor in a microwave workstation, and then reacted in the microwave workstation at 80 to 180° C., and separated to obtain a second solid after the reaction. Separation may be by centrifugation or filtration. The reactor in the microwave workstation may be a reaction vessel having a polytetrafluoroethylene liner, and the reaction vessel may be formed of a polyetheretherketone resin.

[0061] The second solid is dried at 50-90°C for 2-10 hours, and can be dried 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 is dispersed in water, and then an acid is added to continue dispersion to obtain a solution C. This is beneficial to improving the denitration performance of the obtained catalyst.

[0064] In the present invention, the acid is selected from one of nitric acid, acetic acid and citric acid, preferably citric acid. The pH value of solution C is 2 to 6, preferably 3 to 5, and more preferably 4 to 5. The present invention believes that the acid here can play the role of a pore former and a pH regulator. Adding acid to continue dispersing can adopt stirring dispersion or ultrasonic dispersion, and the dispersion time can be 30 to 60 minutes. The addition of such an acid is conducive to the diffusion of the R element in the solution and prevents the aggregation of particles containing the R element.

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

[0066] Steps to obtain the catalyst

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

[0068] In the present invention, the salt of the R element may be a nitrate, chloride, acetate, acetylacetonate or dodecyl salt of the R element, preferably acetylacetonate. Concentrated drying may be rotary evaporation drying. The concentrated dried product may have a water content of less than or equal to 5wt%.

[0069] During calcination, the volume ratio of carbon dioxide to inert gas is 10-20:80-90, for example, 15:85. The present invention finds that the use of such a calcination atmosphere is better than calcination in an air atmosphere, that is, it is more conducive to improving the performance of the obtained catalyst. The calcination temperature can be 450-550°C, preferably 480-550°C, preferably 500-520°C. The calcination time can be 2-6h, preferably 2.5-5h, and more preferably 3-4h.

[0070] The inert gas can 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] <Purpose>

[0072] The present invention also provides a use of the NH3-SCR catalyst as described above in the selective catalytic reduction of nitrogen oxides by ammonia at a temperature below 200°C to generate nitrogen. x The conversion rate is high, the N2 selectivity is high, and the amount of N2O generated is small.

[0073] The NH3-SCR catalyst of the present invention has a NO x The conversion rate is greater than or equal to 84%, preferably greater than or equal to 91%, and can reach 97%; at 175°C, NO x The conversion rate is greater than or equal to 99%, and can reach 100%; at 200℃, NO x The conversion rate is basically 100%. In addition, the N2 selectivity is relatively high, with the N2 selectivity at 150°C being greater than or equal to 96%, and can reach 100%; the N2 selectivity at 175°C being greater than or equal to 96%, and can reach 100%; and the N2 selectivity at 200°C being greater than or equal to 97%, and can reach 100%. In the catalytic reduction reaction below (or less than or equal to) 200°C, the amount of byproduct nitrous oxide N2O generated is less than or equal to 20.0ppm. At 200°C, the amount of N2O generated is less than or equal to 13.7ppm, and at 175°C, the amount of N2O generated is less than or equal to 18.3ppm. In addition, the amount of N2O generated can reach less than 10ppm.

[0074] <Test Method>

[0075] Specific surface area test: The specific surface area of ​​the catalyst was tested using an American Micromeritics ASAP 2460 physical adsorption instrument. The degassing temperature was 105°C and the degassing time was 2 hours. The test was repeated three times and the average value was taken.

[0076] Morphology test: The Thermo Scientific Talos F200i transmission electron microscope (USA) was used to test the microscopic morphology and crystal surface of the catalyst.

[0077] Acid content and hydrogen consumption test: The ammonia adsorption and desorption performance of the catalyst was tested using the American Quantachrome ASAP 292011 chemical adsorption instrument. The acid content or hydrogen consumption was calculated based on the ammonia desorption peak area or hydrogen peak area. The acid content can measure the ammonia storage performance of the catalyst, and the hydrogen consumption can measure the redox ability of the catalyst.

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

[0079] Activity test: A certain amount of prepared composite or catalyst of 40-60 mesh was loaded into a fixed bed quartz reactor with an inner diameter of 6mm for NH3-SCR activity test. The reaction mixture gas composition was 500ppm NO, 500ppm NH3, 10% O2 and 5% H2O, with N2 as the balance. The total gas flow rate was 750mL / min, and the gas hourly space velocity (GHSV) was 50000-150000h -1 The concentration of test gases at 100-500°C was measured using an FTIR spectrometer in Antaris IGS (Thermo Scientific) at standard atmospheric pressure. x ) conversion rate (same as NO x The conversion rate) and N2 selectivity (same as N2 selectivity) were calculated according to the following formulas.

[0080]

[0081] In the following examples, the microwave workstation used was purchased from Beijing Xianghu Technology Development Co., Ltd., model XH-300PE, with a microwave frequency of 2450 MHz and equipped with a polytetrafluoroethylene-lined reactor (formed with polyetheretherketone resin).

[0082] In the following examples, the cerium nitrate used is Ce(NO3)3·6H2O.

[0083] Preparation Example 1 - Preparation of the composite

[0084] Dissolve 2.5g of cerium nitrate and 1g of polyvinyl pyrrolidone (PVP) in 70mL of ethylene glycol, then add 5mL of deionized water to the above solution and stir for 30min to obtain solution A. Transfer solution A to a 100mL reactor in a microwave workstation, set the microwave workstation to heat up to 160°C for 30min, and then react in the microwave workstation at 160°C and 0.8MPa for 24h. After cooling to room temperature, separate the first solid, and wash the first solid with deionized water and anhydrous ethanol respectively to obtain the washed first solid. Then dry the washed first solid at 60°C to obtain a CeO2 precursor, recorded as s-CeO2.

[0085] Niobium oxalate (C2NbO4) was mixed with the s-CeO2 prepared above in a molar ratio (Ce:Nb=1:1), and then added into 60 mL of deionized water and stirred for 30 min to obtain solution B.

[0086] Solution B was transferred to a 100 mL reactor in a microwave workstation, and the microwave workstation was set to heat up to 120°C for 30 minutes, and then reacted in the microwave workstation at 120°C and 0.7 MPa for 12 hours. After the reaction, centrifugation was performed to obtain a second solid, and the second solid was washed with deionized water. The washed second solid was dried at 60°C, ground, and then placed in a muffle furnace, heated to 500°C at a heating rate of 2°C / min, and calcined at 500°C for 4 hours to obtain a spherical cerium oxide composite, recorded as Nb / s-CeO2 composite.

[0087] The TEM results of Nb / s-CeO2 composites are shown in Figure 1 . Figure 1 In the figure, the morphology of the Nb / s-CeO2 composite is spherical, and the

[111] crystal plane of cerium oxide is exposed.

[0088] Comparative Preparation Example 1

[0089] 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 cerium nitrate aqueous solution to the cooled NaOH solution. Continue stirring for 30 minutes, transfer the resulting mixture to a 100 mL polytetrafluoroethylene-lined reactor, and perform a hydrothermal reaction at 100 ° C for 24 hours. After the reaction is completed, centrifuge to separate and collect the solid particles, and wash them alternately with deionized water and ethanol three times, and finally dry them at 60 ° C to obtain a CeO2 precursor, recorded as r-CeO2.

[0090] Niobium oxalate (C2NbO4) was mixed with the r-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.

[0091] Solution B was transferred to a 100 mL reactor in a microwave workstation, and the microwave workstation was set to heat up to 120°C for 30 minutes, and then reacted in the microwave workstation at 120°C and 0.7 MPa for 12 hours. After the reaction was completed, centrifugation was performed to obtain a solid, and the solid was washed with deionized water. The washed solid was dried at 60°C, ground, and then placed in a muffle furnace, heated to 500°C at a heating rate of 2°C / min, and calcined at 500°C for 4 hours to obtain a rod-shaped Nb / r-CeO2 composite.

[0092] The TEM results of Nb / r-CeO2 composites are shown in Figure 2 . Figure 2 In the figure, the morphology of the Nb / r-CeO2 composite is rod-shaped, and the

[111] crystal plane of cerium oxide is exposed.

[0093] Comparative Preparation Example 2

[0094] 15 g of ammonium cerium nitrate and 50 g of urea were dispersed in 500 mL of deionized water, fully stirred and heated to 90°C, and stirred at 90°C for 27 hours. Then filtered, the solid was washed with deionized water during filtration, and then the washed solid was dried at 100°C to obtain a CeO2 precursor, which was recorded as g-CeO2.

[0095] 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.

[0096] Solution B was transferred to a 100 mL reactor in a microwave workstation, and the microwave workstation was set to heat up to 120°C for 30 minutes. Then, the solution was hydrothermally reacted in the microwave workstation at 120°C and 0.7 MPa for 12 hours. After the reaction, the solution was centrifuged. The solid obtained by centrifugation was washed with deionized water. The washed solid was dried at 60°C, ground, placed in a muffle furnace, heated to 500°C at a heating rate of 2°C / min, and calcined at 500°C for 4 hours to obtain a granular Nb / g-CeO2 composite.

[0097] The TEM results of Nb / g-CeO2 composites are shown in Figure 3 . Figure 3 In the example, cerium oxide exposes the

[111] and

[220] crystal planes.

[0098] Comparative Preparation Example 3

[0099] Dissolve an appropriate amount of sodium hydroxide in 30 mL of deionized water and cool to room temperature to obtain a NaOH solution with a concentration of 36 wt%. Dissolve 1.92 g of cerium nitrate in 40 mL of deionized water and cool to room temperature to obtain a cerium nitrate solution. Mix and stir the two solutions for 30 minutes, then transfer the resulting flocculent mixture to a reactor and hydrothermally treat it at 180 ° C for 24 hours. After the reaction is completed, cool it, centrifuge it, wash the solid with distilled water until the washing liquid is neutral, and then dry the washed solid at 60 ° C to obtain a CeO2 precursor, recorded as c-CeO2.

[0100] Niobium oxalate (C2NbO4) was mixed with the c-CeO2 prepared above in a molar ratio (Ce:Nb=1:1), added into 60 mL of deionized water and stirred for 30 min to obtain solution B.

[0101] Solution B was transferred to a 100 mL reactor in a microwave workstation, and the microwave workstation was set to heat up to 120°C for 30 minutes, and then reacted in the microwave workstation at 120°C and 0.7 MPa for 12 hours. After the reaction was completed, centrifugation was performed, and the solid obtained by centrifugation was washed with deionized water. The washed solid was dried at 60°C, ground, placed in a muffle furnace, heated to 500°C at a heating rate of 2°C / min, and calcined at 500°C for 4 hours to obtain a cubic Nb / c-CeO2 composite.

[0102] The TEM results of Nb / c-CeO2 composites are shown in Figure 4 . Figure 4 In the figure, the morphology of the Nb / c-CeO2 composite is basically cubic, and cerium oxide exposes the

[200] and

[220] crystal planes.

[0103] Comparative Preparation Example 4

[0104] Compared with Preparation Example 1, the heating method in the microwave workstation was changed to ordinary oven heating, and other conditions were the same.

[0105] The activity of the composites in Preparation Example 1 and Comparative Preparation Examples 1 to 4 was tested. 0.77 g of the prepared composites of 40 to 60 meshes were loaded into a fixed bed quartz reactor with an inner diameter of 6 mm for NH3-SCR activity test. The gas hourly space velocity (GHSV) was 60000 h -1 The results are shown in Figure 5 and Table 1.

[0106] 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 shows the best SCR activity. xThe conversion rate is 76%, and NO x The conversion rate is greater than 90%.

[0107] It can also be seen from Table 1 that the performance of the composite synthesized by microwave hydrothermal method (Preparation Example 1) is significantly better than that by ordinary oven heating (Comparative Example 4).

[0108] Table 1

[0109]

[0110] Example 1 - Preparation of NH3-SCR Catalyst

[0111] The Nb / s-CeO2 composite prepared in Preparation Example 1 is used to load the precious metal Rh. The specific method is as follows:

[0112] 3 g of the Nb / s-CeO2 composite prepared in Preparation Example 1 was added into 10 mL of deionized water and ultrasonically dispersed for 30 min. Citric acid was added to adjust the pH value of the solution to 4, and ultrasonic dispersion was continued for 40 min to obtain Solution C.

[0113] 0.0704 g of rhodium triacetylacetonate was added to solution C, and ultrasonic dispersion was continued for 30 min. The product was dried by rotary evaporation. The product was calcined at 500° C. for 3 h in a 15% CO 2 / Ar atmosphere to obtain an NH 3 -SCR catalyst, recorded as 0.6% Rh / CeNbOx.

[0114] The TEM microstructure of the obtained NH3-SCR catalyst is shown in Figure 6 .Depend on Figure 6 It can be seen that the morphology of the catalyst is basically spherical. After testing, its hydrogen consumption is 1811μL, the ratio of surface active oxygen content to total oxygen content on the catalyst surface is 46%, the acid content is 8550μL, and the specific surface area is 76m 2 / g.

[0115] Example 2

[0116] The Nb / s-CeO2 composite prepared in Preparation Example 1 is used to load the precious metal Pt. The specific method is as follows:

[0117] 3 g of the Nb / s-CeO2 composite prepared in Preparation Example 1 was added into 10 mL of deionized water and ultrasonically dispersed for 30 min. Citric acid was added to adjust the pH value of the solution to 4, and ultrasonic dispersion was continued for 40 min to obtain Solution C.

[0118] 0.03 g of platinum nitrate was added to solution C, and ultrasonic dispersion was continued for 30 min. Then, the rotary evaporation drying product was calcined at 500° C. for 3 h in a 15% CO 2 / Ar atmosphere to obtain an NH 3 -SCR catalyst, recorded as 0.6% Pt / CeNbOx.

[0119] The TEM microstructure of the obtained NH3-SCR catalyst is shown in Figure 7 ,Depend on Figure 7 It can be seen that the morphology of the catalyst is basically spherical. After testing, its hydrogen consumption is 1738μL, the ratio of surface active oxygen content to total oxygen content on the catalyst surface is 49%, the acid content is 8231μL, and the specific surface area is 67m 2 / g.

[0120] Example 3

[0121] The Nb / s-CeO2 composite prepared in Preparation Example 1 is used to load the precious metal Pt. The specific method is as follows:

[0122] 3 g of the Nb / s-CeO2 composite prepared in Preparation Example 1 was added into 10 mL of deionized water and ultrasonically dispersed for 30 min. Citric acid was added to adjust the pH value of the solution to 4, and ultrasonic dispersion was continued for 40 min to obtain Solution C.

[0123] 0.02 g of platinum nitrate was added to solution C, and ultrasonic dispersion was continued for 30 min. The product was dried by rotary evaporation. The dried product was calcined at 500° C. for 3 h in a 15% CO 2 / Ar atmosphere to obtain an NH 3 -SCR catalyst, recorded as 0.4% Pt / CeNbOx.

[0124] Example 4

[0125] The Nb / s-CeO2 composite prepared in Preparation Example 1 is used to load the precious metal Pt. The specific method is as follows:

[0126] 3 g of the Nb / s-CeO2 composite prepared in Preparation Example 1 was added into 10 mL of deionized water and ultrasonically dispersed for 30 min. Citric acid was added to adjust the pH value of the solution to 4, and ultrasonic dispersion was continued for 40 min to obtain Solution C.

[0127] 0.04 g of platinum nitrate was added to solution C, and ultrasonic dispersion was continued for 30 min. The product was dried by rotary evaporation. The dried product was calcined at 500° C. for 3 h in a 15% CO 2 / Ar atmosphere to obtain an NH 3 -SCR catalyst, recorded as 0.8% Pt / CeNbOx.

[0128] Comparative Example 1 (without addition of niobium oxalate)

[0129] Dissolve 2.5g of cerium nitrate and 1g of polyvinyl pyrrolidone (PVP) in 70mL of ethylene glycol, and then add 5mL of deionized water to the above solution. Stir for 30min to obtain solution A. Transfer solution A to a 100mL reactor in a microwave workstation, set the microwave workstation to heat up to 160°C for 30min, and then react in the microwave workstation at 160°C and 0.8MPa for 24h. After cooling to room temperature, separate and collect the first solid, wash the first solid with deionized water and anhydrous ethanol respectively, and then dry the washed first solid at 60°C to obtain a spherical CeO2 precursor. Calcinate the CeO2 precursor at 500°C for 4h (the heating rate during calcination is 2°C / min) to obtain spherical CeO2.

[0130] 3 g of spherical CeO2 was added into 10 mL of deionized water and ultrasonically dispersed for 30 min. Citric acid was added to adjust the pH value of the solution to 4, and ultrasonic dispersion was continued for 40 min to obtain solution C.

[0131] Add 0.03 g of platinum nitrate to solution C, continue ultrasonic dispersion for 30 min, and dry by rotary evaporation. The rotary evaporation dried product is calcined at 500° C. for 3 h in a 15% CO2 / Ar atmosphere to obtain an NH3-SCR catalyst, recorded as 0.6% Pt / CeO2.

[0132] The test showed that the catalyst consumed 651 μL of hydrogen, the ratio of surface active oxygen content to total oxygen content on the catalyst surface was 26%, the acid content was 2350 μL, and the specific surface area was 36 m 2 / g.

[0133] Comparative Example 2 (no spherical CeO2 precursor added)

[0134] 3.618 g of niobium oxalate (C2NbO4) was added to 60 mL of deionized water and stirred for 30 min. The mixture was 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 in the microwave workstation. After the reaction was completed, the solid obtained by centrifugation was dried at 60 ° C, and the dried product was calcined at 500 ° C for 4 h (the heating rate during calcination was 2 ° C / min) to obtain NbOx.

[0135] 3 g of NbOx was added into 10 mL of deionized water, and ultrasonically dispersed for 30 min. Citric acid was added to adjust the pH value of the solution to 4, and ultrasonic dispersion was continued for 40 min to obtain solution C.

[0136] 0.03 g of platinum nitrate was added to solution C, and ultrasonic dispersion was continued for 30 min. The product was dried by rotary evaporation. The dried product was calcined at 500° C. for 3 h in a 15% CO 2 / Ar atmosphere to obtain an NH 3 -SCR catalyst, recorded as 0.6% Pt / NbOx.

[0137] The test showed that the catalyst consumed 961 μL of hydrogen, the ratio of surface active oxygen content to total oxygen content on the catalyst surface was 19%, the acid content was 1236 μL, and the specific surface area was 23 m 2 / g.

[0138] Comparative Example 3

[0139] Compared with Example 1, the only difference is that in Comparative Example 3, the calcination atmosphere is air atmosphere.

[0140] After testing, the hydrogen consumption of the catalyst obtained in Comparative Example 3 was 1023 μL, the ratio of surface active oxygen content to total oxygen content on the catalyst surface was 35%, the acid content was 3624 μL, and the specific surface area was 57 m 2 / g.

[0141] Table 2

[0142] serial number Hydrogen consumption / μL Oxygen content ratio / % Acid volume / 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

[0143] Note: In this table, oxygen content ratio refers to the percentage of active oxygen content on the catalyst surface to the total oxygen content on the catalyst surface.

[0144] It can be seen from the table that the catalyst prepared by the present invention has abundant surface oxygen concentration and acidic sites.

[0145] Experimental Example 1

[0146] The NH3-SCR catalysts obtained in Examples 1 to 4 and Comparative Examples 1 to 3 were tested for activity. 0.62 g of the prepared NH3-SCR catalyst of 40 to 60 mesh was loaded into a fixed bed quartz reactor with an inner diameter of 6 mm for NH3-SCR activity test. The gas hourly space velocity (GHSV) was 100,000 h -1 The results are shown in Tables 3, 4 and 5.

[0147] As shown in Table 3, the denitration efficiency of the NH3-SCR catalyst obtained by the present invention at 150-225°C is 84-100%. As shown in Comparative Example 1, Comparative Example 2 and Example 1, the NH3-SCR catalyst with good performance of the present invention cannot be obtained by omitting cerium oxide or niobium oxalate. As shown in Comparative Example 3 and Example 1, compared with calcination in air atmosphere, calcination in 15% CO2 / Ar atmosphere can significantly improve the NO of the obtained catalyst. x Conversion rate.

[0148] It can be seen from Table 4 that the N2 selectivity of the NH3-SCR catalyst obtained in the present invention at 125-225°C is ≥95%.

[0149] It can be seen from Table 5 that the N2O generation amount of the NH3-SCR catalyst obtained by the present invention at 125-225°C can be below 20 ppm, and most of them are below 10 ppm.

[0150] Table 3

[0151]

[0152] Table 4

[0153]

[0154] Table 5

[0155]

[0156] As can be seen from the table, the NH3-SCR catalyst obtained by the present invention has excellent denitration performance, especially at a relatively low temperature (125-225°C). x The conversion rate is high, the N2 selectivity is high and the byproduct N2O generation amount is low. The NH3-SCR catalyst obtained by the invention still has good denitration efficiency at a temperature below 200°C.

[0157] The present invention is not limited to the above-mentioned embodiments. Without departing from the essential content of the present invention, any deformation, improvement and substitution that can be conceived by those skilled in the art shall fall within the scope of the present invention.

Claims

1. An NH3-SCR catalyst, characterized in that: The invention discloses a cerium oxide composite oxide catalyst, comprising 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 to 10:1; and the loading amount of the R element is 0.1 to 3 wt% based on the total mass of the NH3-SCR catalyst; The NH3-SCR catalyst has a spherical shape; the cerium oxide exposes the [111] crystal plane, and the surface active oxygen content accounts for 35-70% of the total oxygen content on the surface of the NH3-SCR catalyst; its acid content is 7500-9000 μL, its hydrogen consumption is 1500-2500 μL, and its specific surface area is 50-90 m 2 / g.

2. The NH3-SCR catalyst according to claim 1, characterized in that: 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.

3. A method for preparing the NH3-SCR catalyst according to claim 1 or 2, characterized in that: The following steps are involved: 1) mixing a water-soluble cerium salt, a C2-C5 alkanediol, a surface stabilizer and water to obtain a solution A; reacting the solution A under microwave conditions at 80-180° C., separating and obtaining a first solid after the reaction, and drying the first solid to obtain a CeO2 precursor; 2) dispersing a CeO2 precursor and a water-soluble salt of the M element in water to obtain a solution B; 3) reacting solution B under microwave conditions at 80-180° C., separating to obtain a second solid after the reaction, and drying and calcining the second solid to obtain a cerium oxide composite; 4) dispersing the cerium oxide complex obtained in step 3) in water, and then adding acid to continue dispersing to obtain solution C; 5) dispersing the salt of the R element in the solution C, and then concentrating and drying the solution. The concentrated and dried product is calcined in an atmosphere of carbon dioxide and an inert gas to obtain an NH3-SCR catalyst.

4. The preparation method according to claim 3, characterized in that: In step 1), the water-soluble cerium salt is selected from at least one of cerium nitrate, cerium acetate, cerous nitrate, ammonium cerium nitrate, and cerium carbonate; the C2-C5 alkanediol is ethylene glycol; and the surface stabilizer is selected from one of polyvinyl pyrrolidone, polyethylene glycol, triethylenetetramine, sorbitol, and xylene.

5. The preparation method according to claim 3, characterized in that: In step 1), the mass volume ratio of the water-soluble cerium salt to the C2-C5 alkanediol 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; the volume ratio of the C2-C5 alkanediol to water is 6-20:1; In step 1), solution A is reacted under microwave conditions at 80-180° C. for 8-48 h.

6. The preparation method according to claim 3, characterized in that: In step 2), CeO2 precursor and water-soluble salt of element M are dispersed in water by ultrasound.

7. The preparation method according to claim 3, characterized in that: In step 3), solution B is reacted under microwave conditions at 80-180° C. for 8-48 hours, and a second solid is separated 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 a cerium oxide composite.

8. The preparation method according to claim 3, 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 solution C is 2-6.

9. The preparation method according to claim 3, characterized in that: In step 5), the calcination temperature is 450-550° C. and the calcination time is 2-6 hours.

10. Use of the NH3-SCR catalyst according to claim 1 or 2 in the selective catalytic reduction of nitrogen oxides by ammonia at a temperature below 200°C to generate nitrogen.

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