Foamed metal-based catalyst for denitration at ultra-low temperature and method for preparing the same

Abstract

The application discloses a kind of foam metal-based catalyst for denitration under ultralow temperature and preparation method thereof, the preparation method includes: (1) foam metal pretreatment: using alkali solution to pretreat foam metal, to obtain surface etched foam metal;(2) the surface etched foam metal obtained in step (1) is immersed in binder solution containing glass fiber silk, and the glass fiber silk is adsorbed on the pore surface of the foam metal, then dried, calcined, to obtain a modified matrix;(3) prepare coating slurry: mix denitration catalyst powder with inorganic binder and organic binder evenly to obtain coating slurry;(4) slurry coating: immerse the modified matrix obtained in step (2) in the above coating slurry, dry and calcine after taking out, to obtain foam metal-based denitration catalyst product.The application uses foam metal as matrix, and the mechanical strength of the catalyst is good at low temperature.

Description

Technical Field

[0001] This invention belongs to the field of industrial waste gas treatment and the development and research of green and efficient low-temperature SCR catalysts. More specifically, it relates to a foam metal-based catalyst for denitrification at ultra-low temperatures and its preparation method, which is mainly applied to low-temperature SCR denitrification in coal-fired power plants or coking plants, cement plants, steel plants, etc. Background Technology

[0002] Nitrogen oxides (NO) x Nitrogen oxides (NOx) are among the major air pollutants, a significant contributor to acid rain formation, a major precursor to ozone and photochemical smog, and a major cause of regional PM2.5 pollution and haze. Selective catalytic reduction (NH3-SCR) using NH3 as a reducing agent is currently the most widely used method for treating nitrogen oxides (NOx). x In purification technology, the denitrification catalyst is a crucial core component of NH3-SCR denitrification technology.

[0003] In recent years, coal-fired power plants have fully implemented ultra-low emission standards, and non-power industries have become the leading contributors to air pollution emissions. Pollution control requirements for flue gas from non-power industries such as steel, non-ferrous metals, cement, and glass are becoming increasingly stringent. The flue gas temperature of non-power industrial furnaces is mostly below 200℃, while the temperature of flue gas after dust removal and desulfurization is below 150℃. Therefore, NH3-SCR catalysts must possess high catalytic activity at ultra-low temperatures (<150℃) to effectively avoid the impact of dust and SO2 on catalyst performance, extend catalyst lifespan, and save energy consumption from flue gas reheating. Given the practical needs of ultra-low emissions and low-temperature flue gas treatment, the research and application of low-temperature denitrification technology are increasingly urgent. There is a desire to provide foam metal-based ultra-low temperature catalysts that can solve the above problems and adapt to this operating condition with high water and sulfur resistance.

[0004] CN106925294A discloses a low-temperature SCR catalyst supported on nickel foam and its preparation method. The method involves using nickel foam as a support and Mn oxide as the active component, wherein the loading of Mn element is 5-20% of the weight of the nickel foam. The active component is loaded onto the support using an impregnation method, followed by magnetic stirring and drying, and finally calcination in air to obtain the low-temperature SCR denitrification catalyst. However, the direct bonding ability between the foam metal surface and the catalyst is poor, resulting in a low catalyst loading and failing to guarantee the target catalyst loading, thus affecting the denitrification effect of the coated catalyst. Summary of the Invention

[0005] The purpose of this invention is to provide a foam metal-based catalyst for denitrification at ultra-low temperatures and its preparation method, wherein the catalyst exhibits good low-temperature activity.

[0006] To achieve the first aspect of the above-mentioned objective, the method for preparing the foamed metal-based catalyst provided by the present invention adopts the following technical solution:

[0007] A method for preparing a foamed metal-based catalyst for denitrification at ultra-low temperatures includes the following steps:

[0008] (1) Foam metal pretreatment: Foam metal is pretreated with an alkaline solution to obtain surface-etched foam metal;

[0009] (2) The surface-etched foam metal obtained in step (1) is immersed in an adhesive solution containing glass fiber filaments, so that the glass fiber filaments are adsorbed on the pore surface of the foam metal, and then dried and calcined to obtain a modified matrix.

[0010] (3) Preparation of coating slurry: The denitrification catalyst powder is mixed evenly with inorganic binder and organic binder to obtain coating slurry. The proportion of catalyst powder is 15-30%, inorganic binder is 2-10%, organic binder is 0.2-0.7%, and the remainder is water, according to the mass of the slurry.

[0011] (4) Slurry coating: The modified matrix obtained in step (2) is immersed in the above coating slurry, taken out, dried and calcined to obtain the foam metal-based denitrification catalyst product.

[0012] In step (1) of the present invention, the foam metal is subjected to etching pretreatment; in one embodiment, in step (1), the foam metal is one or more of foam aluminum, foam copper, and foam nickel; in one embodiment, the alkaline solution is one or more of sodium hydroxide, sodium bicarbonate, and ammonia water; in one embodiment, the pH range of the alkaline solution is 8-13, preferably 10-12, such as 9 or 11.

[0013] In one embodiment, in step (1), after the etched foam metal is rinsed several times with deionized water and dried, the foam metal loses 0.5-4% weight after etching, for example, 0.8%, 1%, 2%, 3% or 3.5%.

[0014] In step (2) of the present invention, the foam metal is soaked in a binder solution containing glass fiber for a certain period of time, and then dried and calcined so that the glass fiber is adsorbed on the pore surface of the foam metal, which can produce a catalyst coating substrate with strong adsorption, high mechanical strength and high geometric specific surface area.

[0015] According to the preparation method of the present invention, preferably, in step (2), the binder solution containing glass fibers is a silica sol solution, wherein the silica sol content is 4-10%, for example 5%, 6% or 8%, and the glass fiber content is 30-50%, for example 35%, 40% or 45%. In one embodiment, in step (2), the calcination temperature is 300-500℃, for example 350, 400 or 450℃, and maintained for 3-5 hours, preferably with a heating rate of 5-8℃ / min.

[0016] In step (3) of this invention, a coating slurry for the denitrification catalyst is prepared, for example, by mixing the denitrification catalyst powder with an inorganic binder and an organic binder, and ball milling for 1 hour to obtain a coating slurry. Preferably, the denitrification catalyst is a supported manganese-based denitrification catalyst. In one embodiment, the denitrification catalyst includes a first active component A, a second active component B, an auxiliary agent C, and a support D; in this invention, setting the support D is beneficial to the better activity of the final catalyst. Those skilled in the art will understand that the catalyst powder can be prepared by using an aqueous solution of the precursor salts of the catalyst active component A, active component B, and auxiliary agent C, and by any one of the following methods: impregnation, hydrothermal, or precipitation, using the support D. For example, after impregnation adsorption, the powder is dried and calcined at 500-600°C for 4-8 hours. The specific preparation method is well known in the art and will not be described in detail here.

[0017] In one embodiment, the first active component A is an oxide of metallic manganese, and its corresponding soluble precursor salt includes, but is not limited to, manganese nitrate, manganese acetate, manganese sulfate, and manganese chloride. In one embodiment, the second active component B is an oxide of cerium or lanthanum, preferably cerium oxide, and its corresponding soluble precursor salt includes, but is not limited to, cerium nitrate, cerium nitrate, cerium ammonium nitrate, cerium carbonate, cerium chloride, lanthanum nitrate, and lanthanum chloride.

[0018] In one embodiment, the additive C is one or more oxides of tungsten, molybdenum, antimony, niobium, cobalt, and iron, preferably oxides of antimony and niobium. The corresponding soluble precursor salts include, but are not limited to, ammonium metatungstate, ammonium tungstate, ammonium paratungstate, ammonium heptamolybdate, ammonium phosphomolybdate, ammonium paramolybdate, antimony acetate, antimony chloride, niobium oxalate, ammonium niobium oxalate, cobalt nitrate, cobalt chloride, ferric nitrate, and ferric chloride.

[0019] In one embodiment, the support D is titanium dioxide or a zeolite molecular sieve, wherein the zeolite molecular sieve includes β-type, Y-type, ZSM-5, SAPO-34, and SSZ-13 zeolite molecular sieves; preferably, it is a Y-type molecular sieve. In one embodiment, the denitrification catalyst contains 10-25% of a first active component, such as 12%, 15%, 18%, 20%, or 23%; 15-35% of a second active component, such as 18%, 20%, 25%, 30%, or 33%; 4-12% of an additive, such as 5%, 7%, 10%, or 11%; and 28-71% of a support, such as 30%, 40%, 55%, or 65%.

[0020] In one embodiment of step (3) of the present invention, the inorganic binder is one of aluminum sol and silica sol; the organic binder is one or more of polyvinyl alcohol, hydroxypropyl methylcellulose, methylcellulose or polyethylene oxide, which are well known in the art and will not be described in detail here.

[0021] In step (4) of the present invention, in one embodiment, the modified matrix is ​​immersed in the above slurry for a certain period of time, then taken out and optionally left to stand or blown to remove excess slurry, and then dried.

[0022] In one embodiment, before the modified matrix is ​​immersed, the pH value of the coating slurry obtained in step (3) is adjusted to 2-4, for example, by adjusting the pH value with acetic acid; preferably, the calcination temperature in step (4) is 350-500°C, for example, 380, 400 or 450°C, and the calcination time is 2-8 hours.

[0023] To achieve the second aspect of the above-mentioned objective, the present invention also provides a foamed metal-based catalyst prepared by the above-described preparation method.

[0024] In this invention, unless otherwise specified, all percentages appearing in the text are mass percentages.

[0025] This invention uses an alkaline solution to pretreat foamed metal. The foamed metal is immersed in the alkaline solution for a period of time, and the alkaline solution etches the surface of the foamed metal. After etching, the foamed metal is rinsed several times with deionized water and dried. Then, it is immersed in a binder solution of a certain concentration containing glass fiber for a certain period of time. After immersion, the foamed metal is subjected to low-pressure blowing, drying, and calcination, so that the glass fiber is adsorbed on the pore surface of the foamed metal, thus producing a catalyst-coated modified matrix with strong adsorption, high mechanical strength, and high geometric specific surface area.

[0026] Ultra-low temperature denitrification catalyst powder was prepared using one of the following methods: impregnation, hydrothermal method, or precipitation method. The catalyst powder was added to a slurry with a certain viscosity. The slurry was ball-milled to a certain particle size and then impregnated onto a glass fiber foam metal substrate. This yielded a foam metal substrate coated low-temperature catalyst with uniform coating distribution, no cracks, high activity at ultra-low temperatures, and high water and sulfur resistance.

[0027] Compared with the prior art, the present invention has the following advantages

[0028] 1) The addition of elements such as Nb with special electron layer distribution to the catalyst powder formulation can improve the hydrophobicity of the catalyst surface, which is beneficial to suppressing the adsorption of H2O on the catalyst surface at low temperature.

[0029] 2) The alkali pretreatment of the foam metal increases the geometric specific surface area of ​​the foam metal matrix, and the surface fixation of glass fiber filaments improves the surface adsorption of the foam metal.

[0030] 3) Using foamed metal as a matrix can improve the mechanical strength of the catalyst, increase the contact area between the gas and the catalyst due to its high geometric specific surface area, and increase the thickness of the catalyst coating due to its high adsorption capacity, thereby improving the low-temperature denitrification efficiency of the catalyst. Detailed Implementation

[0031] The present invention will be further described below with reference to the embodiments, but the present invention is not limited to the listed embodiments.

[0032] Example 1:

[0033] Pretreatment of aluminum foam: The aluminum foam is pretreated with a sodium hydroxide solution of pH=12. The aluminum foam is immersed in the sodium hydroxide solution and the alkaline solution is used to etch the surface of the aluminum foam (weight reduction of about 3%). The etched aluminum foam is rinsed several times with deionized water and then dried at 110℃ for 10h. The pretreated aluminum foam is then immersed in a mixed solution of 6% silica sol binder containing 50% glass fiber for 5min. After immersion, it is blown with compressed air gun at low speed for 0.5min. The foam metal is dried at 120℃ for 10h and calcined at 400℃ for 3h to allow the glass fiber to be adsorbed on the pore surface of the foam metal.

[0034] Catalyst powder preparation: Catalyst powder was prepared by impregnation method. 36g of manganese acetate and 69g of cerium nitrate were added to 1500ml of deionized water and heated and stirred in a 90℃ water bath until dissolved to form a mixed solution of Mn and Ce salts. 29g of antimony acetate was then added, and the mixture was heated and stirred until the solution was homogeneous. 68g of Y-type molecular sieve was added to the solution, and the mixture was stirred until all the water in the solution evaporated. The resulting wet material was placed in an oven and dried at 110℃ for 10h. After drying, the material was placed in a muffle furnace and calcined at 500℃ for 5h to obtain the catalyst powder.

[0035] Mix 300g of catalyst powder, 225g of aluminum sol with a mass fraction of 20%, 2g of methylcellulose, and 500g of deionized water, and ball mill in a ball mill for 60 minutes to obtain the slurry to be coated.

[0036] 10 ml of acetic acid was added to the obtained slurry, and the pH of the slurry was measured to be 3.2. The pretreated aluminum foam matrix was immersed in the above slurry for 5 min, and excess slurry was blown off with a compressed air gun at a low speed. It was then placed under a hot air gun for drying, purging at 60℃ for 10 min, 90℃ for 10 min, and 400℃ for 5 min. After drying, the same immersion-drying steps were repeated once. After processing with the same drying temperature curve, it was placed in a muffle furnace for high-temperature calcination at 400℃ for 5 h. The quality of the aluminum foam before and after coating was recorded. After two coatings, the loading was 200 g / L, and the aluminum foam-based ultra-low temperature denitrification catalyst product was obtained.

[0037] Example 2:

[0038] Pretreatment of aluminum foam: The aluminum foam was pretreated with a sodium bicarbonate solution with pH=9. The aluminum foam was immersed in the sodium bicarbonate solution and the alkaline solution etched the surface of the aluminum foam (weight loss of about 1%). The etched aluminum foam was rinsed several times with deionized water and dried at 110℃ for 10h. The pretreated aluminum foam was then immersed in a mixed solution of 8% silica sol binder containing 30% glass fiber for 5min. After immersion, it was blown with compressed air gun at low speed for 0.5min. The aluminum foam was dried at 120℃ for 10h and calcined at 300℃ for 5h to allow the glass fiber to be adsorbed on the pore surface of the aluminum foam.

[0039] Catalyst powder preparation: Catalyst powder was prepared by impregnation method. 41g of manganese acetate and 54g of cerium nitrate were added to 1500ml of deionized water and heated and stirred in a 90℃ water bath until dissolved to form a mixed solution of Mn and Ce salts. 24g of antimony acetate and 8g of niobium oxalate were then added and heated and stirred until the solution was homogeneous. 57g of Y-type molecular sieve was added to the solution and stirred until the water in the solution was completely evaporated. The resulting wet material was placed in an oven and dried at 110℃ for 10h. After drying, it was placed in a muffle furnace and calcined at 500℃ for 5h to obtain the catalyst powder.

[0040] Mix 300g of catalyst powder, 225g of aluminum sol with a mass fraction of 15%, 2g of methylcellulose, and 500g of deionized water, and ball mill in a ball mill for 60 minutes to obtain the slurry to be coated.

[0041] 10 ml of acetic acid was added to the obtained slurry, and the pH of the slurry was measured to be 3.2. The pretreated aluminum foam matrix was immersed in the above slurry for 5 min, and excess slurry was blown off with a compressed air gun at low speed. It was then placed under a hot air gun for drying, purging at 60℃ for 10 min, 90℃ for 10 min, and 400℃ for 5 min. After drying, the same immersion-drying steps were repeated once. After processing with the same drying temperature curve, it was placed in a muffle furnace for high-temperature calcination at 400℃ for 5 h. The quality of the aluminum foam before and after coating was recorded. After two coatings, the loading was 200 g / L, and the aluminum foam-based ultra-low temperature denitrification catalyst product was obtained.

[0042] Example 3:

[0043] Pretreatment of aluminum foam: The aluminum foam is pretreated with a sodium hydroxide solution of pH=10. The aluminum foam is immersed in the sodium hydroxide solution and the alkaline solution is used to etch the surface of the aluminum foam (weight loss of about 2%). The etched aluminum foam is rinsed several times with deionized water and then dried at 110℃ for 10h. The pretreated aluminum foam is then immersed in a mixed solution of 4% silica sol binder containing 50% glass fiber for 5min. After immersion, it is blown with compressed air gun at low speed for 0.5min. The foam metal is dried at 120℃ for 10h and calcined at 400℃ for 4h to allow the glass fiber to be adsorbed on the pore surface of the foam metal.

[0044] Catalyst powder preparation: Catalyst powder was prepared by impregnation method. 41g of manganese acetate and 54g of lanthanum nitrate were added to 1500ml of deionized water and heated and stirred in a 90℃ water bath until dissolved to form a mixed solution of Mn and La salts. 24g of niobium oxalate was then added and heated and stirred until the solution was homogeneous. 54g of Y-type molecular sieve was added to the solution and stirred until the water in the solution was completely evaporated. The resulting wet material was placed in an oven and dried at 110℃ for 10h. After drying, it was placed in a muffle furnace and calcined at 500℃ for 5h to obtain the catalyst powder.

[0045] Mix 300g of catalyst powder, 225g of aluminum sol with a mass fraction of 15%, 2g of methylcellulose, and 500g of deionized water, and ball mill in a ball mill for 60 minutes to obtain the slurry to be coated.

[0046] 10 ml of acetic acid was added to the obtained slurry, and the pH of the slurry was measured to be 3.2. The pretreated aluminum foam matrix was immersed in the above slurry for 5 min, and excess slurry was blown off with a compressed air gun at low speed. It was then placed under a hot air gun for drying, purging at 60℃ for 10 min, 90℃ for 10 min, and 400℃ for 5 min. After drying, the same immersion-drying steps were repeated once. After processing with the same drying temperature curve, it was placed in a muffle furnace for high-temperature calcination at 400℃ for 5 h. The quality of the aluminum foam before and after coating was recorded. After two coatings, the loading was 200 g / L, and the aluminum foam-based ultra-low temperature denitrification catalyst product was obtained.

[0047] Comparative Example 1:

[0048] The procedure is the same as in Example 1, except that only etching is performed during the pretreatment of the aluminum foam, and no glass fiber filament attachment is performed. Everything else is the same.

[0049] Comparative Example 2:

[0050] The procedure is the same as in Example 2, except that the aluminum foam was not etched. The unetched aluminum foam was immersed in a 30% silica sol binder mixed solution containing 50% glass fiber for 5 minutes, and then purged with compressed air at low speed for 0.5 minutes. The foam metal was then dried at 120°C for 10 hours to allow the glass fiber to adhere to the pore surface of the foam metal. The rest is the same.

[0051] Comparative Example 3:

[0052] The difference from Example 1 is that the denitrification catalyst used in this example does not contain a support; instead, the precursor soluble salts of the active components and additives are directly added to the slurry to be coated. Everything else is the same.

[0053] Test method:

[0054] 1. Catalyst performance testing: An experimental platform was built, and the catalysts from the above examples / comparative examples were placed in a stainless steel fixed-bed reactor. The temperature was raised to 360°C, and simulated flue gas (SO2 = 50 ppm, NO) was introduced. x =NH3=300ppm, O2=8%, H2O=20%, N2 is the balance gas), space velocity=3000h-1. MKS flue gas analyzer tests NO at the catalyst inlet and outlet. x The concentration.

[0055] NO conversion rate:

[0056]

[0057] In the formula: NO at reactor inlet x Concentration, in ppm; NO at reactor outlet x Concentration, in ppm. Results are shown in Appendix Table 1:

[0058] Table 1. Denitrification efficiency of the catalyst (%)

[0059]

Claims

1. A method for preparing a foamed metal-based catalyst for denitrification at ultra-low temperatures, characterized in that, The preparation method includes the following steps: (1) Foam metal pretreatment: Foam metal is pretreated with an alkaline solution to obtain surface-etched foam metal; (2) The surface-etched foam metal obtained in step (1) is immersed in a binder solution containing glass fiber filaments, so that the glass fiber filaments are adsorbed on the surface of the foam metal pores, and then dried and calcined to obtain a modified matrix. (3) Preparation of coating slurry: The denitrification catalyst powder is mixed evenly with inorganic binder and organic binder to obtain coating slurry. The proportion of catalyst powder is 15-30%, inorganic binder is 2-10%, organic binder is 0.2-0.7%, and the remainder is water, according to the mass of the slurry. The denitrification catalyst is a supported manganese-based denitrification catalyst. (4) Slurry coating: The modified matrix obtained in step (2) is immersed in the above coating slurry, taken out, dried and calcined to obtain the foam metal-based denitrification catalyst product.

2. The preparation method according to claim 1, characterized in that, The denitrification catalyst is supported by titanium dioxide or zeolite molecular sieves, wherein the zeolite molecular sieves are selected from one of β-type, Y-type, ZSM-5, SAPO-34 and SSZ-13 molecular sieves.

3. The preparation method according to claim 1, characterized in that, The denitrification catalyst is supported by titanium dioxide or zeolite molecular sieve, wherein the zeolite molecular sieve is a Y-type molecular sieve.

4. The preparation method according to any one of claims 1-3, characterized in that, In step (3), the inorganic binder is one of aluminum sol and silica sol; the organic binder is one or more of polyvinyl alcohol, hydroxypropyl methylcellulose, methylcellulose or polyethylene oxide.

5. The preparation method according to claim 1, characterized in that, The denitrification catalyst comprises a first active component, a second active component, an additive, and a support; wherein the first active component is an oxide of metallic manganese; the second active component is an oxide of cerium or lanthanum; and the additive is one or more oxides of tungsten, molybdenum, antimony, niobium, cobalt, and iron.

6. The preparation method according to claim 5, characterized in that, The second active component is cerium oxide; the auxiliary agents are oxides of antimony and niobium. In the denitrification catalyst, the content of the first active component is 10-25%, the content of the second active component is 15-35%, the content of the auxiliary agent is 4-12%, and the content of the support is 28-71%.

7. The preparation method according to any one of claims 1-3 and 5-6, characterized in that, In step (1), the foam metal is one or more of aluminum foam, copper foam, and nickel foam; The pH of the alkaline solution is 8-13.

8. The preparation method according to claim 7, characterized in that, The alkaline solution is one or more of sodium hydroxide, sodium bicarbonate, and ammonia water; the pH of the alkaline solution is 10-12.

9. The preparation method according to any one of claims 1-3, 5-6 and 8, characterized in that, In step (1), the foam metal is etched to reduce its weight by 0.5-4%.

10. The preparation method according to any one of claims 1-3, 5-6 and 8, characterized in that, In step (2), the adhesive solution containing glass fiber filaments is a silica sol solution, wherein the silica sol content is 4-10% and the glass fiber filament content is 30-50%.

11. The preparation method according to claim 10, characterized in that, In step (2), the calcination temperature is 300-500℃ and maintained for 3-5 hours.

12. The preparation method according to any one of claims 1-3, 5-6, 8 and 11, characterized in that, In step (4), before the modified matrix is ​​immersed, the pH value of the coating slurry obtained in step (3) is adjusted to 2-4.

13. The preparation method according to claim 12, characterized in that, In step (4), the roasting temperature is 350-500℃ and the roasting time is 2-8 hours.

14. The foamed metal-based catalyst prepared by any one of claims 1-13.

Images