Preparation method of acid etching modified CoMn2O4 spinel wide-temperature SCR (Selective Catalytic Reduction) catalyst

Abstract

The invention discloses optimization and application research on a CoMn2O4 spinel SCR catalyst through acid etching modification, and belongs to the technical field of environment-friendly catalytic materials. The CoMn2O4 spinel catalyst has the advantages that raw materials are easy to obtain, the structure is controllable, valence states are variable, the oxidation-reduction capacity is high, and the catalyst is environmentally friendly. The CoMn2O4 spinel catalyst prepared by a hydrothermal method is subjected to defect construction by utilizing acid etching, so that the specific surface area of the catalyst can be obviously increased, oxygen vacancies can be enriched, and the acid amount of Bronsted acid and Lewis acid can be increased, and therefore, the performances such as denitration efficiency, temperature operation window and poisoning resistance of the catalyst can be obviously improved. The preparation technology is simple, the requirement for equipment is low, all the used raw materials are common chemical reagents, the source is wide, the price is low, the raw materials are easy to obtain, industrial production is easy to achieve, and good application prospects are achieved in the aspect of coal-fired flue gas denitration.

Description

Technical Field

[0001] The invention belongs to the technical field of environmentally friendly catalytic materials and specifically relates to a CoMn 2 O 4 Method for preparing spinel SCR catalyst, especially a method for acid etching modified CoMn 2 O 4 Research on optimization and application of spinel SCR catalyst. Background Art

[0002] In order to achieve the strategic goal of building a new power system with new energy as the main body, my country has vigorously developed renewable energy such as wind power, nuclear energy, and solar energy. However, due to the randomness, volatility, and intermittency of new energy power generation, the energy structure dominated by coal power will not change significantly in the short term. Nitrogen oxides (NO x ) is the main source of atmospheric pollutants, and under certain conditions it will form photochemical smog, destroy the ozone layer, and seriously disrupt the ecological balance. x Among various treatment processes for gaseous pollutants, Selective Catalytic Reduction (SCR) has become the mainstream technology in the field of flue gas denitrification and has been widely used in the fields of coal-fired flue gas denitrification and diesel vehicle exhaust control. At present, the traditional commercial vanadium-titanium system (V 2 O 5 -WO 3 / TiO 2 However, the SCR catalyst has the disadvantages of narrow active temperature window (300~400 ℃), easy poisoning, poor thermal stability, and leaching toxicity. In order to ensure the stable supply of electricity and the consumption of clean energy, coal-fired power units with good peak-shaving potential are playing an important role in the basic regulation of energy in the power grid. However, when coal-fired units participate in deep peak-shaving, the furnace flue gas temperature will change with the unit load fluctuations, and it is difficult to ensure that the SCR catalyst operates within the optimal active temperature window for a long time. Therefore, the coal-fired units face more severe pollutant emission reduction challenges during flexible peak-shaving. In order to adapt to the NO x The need for efficient treatment of pollutants to achieve NO x Effective control and efficient purification of pollutants, and the development of a new wide-temperature SCR catalyst with high efficiency, excellent anti-poisoning performance and environmental friendliness, play an important role in improving the level and competitiveness of key technical equipment for clean utilization of coal in my country, and have broad application prospects and significant social and environmental benefits.

[0003] Spinel metal oxides (Spinel oxides, AB 2 O 4) has become an important basic catalytic material in the energy and chemical industry due to its unique metal-oxygen tetrahedron and metal-oxygen octahedron interlaced structure, abundant reserves, controllable structure and variable valence state. 2 O 4 Compared with other elements (Cu, Ni, Fe), spinel exhibits excellent low-temperature SCR activity and water and sulfur resistance, which is attributed to the variable valence states of Co and Mn ions, which have better redox properties and the strong bond between Mn and Co. 2 O 4 Spinel can be controlled by structure, composition, phase, valence, morphology and defects to polarize the charge of two different atoms A and B in its structure to form an "alienation effect", thereby improving the catalytic performance of the catalyst. Acid etching is an important method for defect construction, which can improve the catalyst structure, increase surface active oxygen vacancies, enrich surface acid sites, etc. Therefore, the present invention uses acid etching to construct defects in the Co-Mn spinel catalyst prepared by the hydrothermal method, which can significantly improve the denitrification efficiency, widen the temperature operation window and enhance the anti-poisoning ability. Summary of the invention

[0004] The object of the present invention is to provide a CoMn 2 O 4 Preparation method of spinel wide temperature SCR catalyst, and further improvement of CoMn by acid etching modification 2 O 4 Catalytic performance of spinel wide temperature SCR catalyst, the CoMn 2 O 4 The raw materials of spinel catalysts are easily available and have simple components. They have the advantages of a wide temperature operating window, excellent anti-poisoning ability, environmental friendliness, high efficiency and stability.

[0005] To achieve the above object, the present invention adopts the following technical solution: The present invention provides an acid-etched modified CoMn 2 O 4 The method for preparing a spinel wide temperature SCR catalyst comprises the following steps: Step 1. CoMn 2 O 4 Preparation of spinel SCR catalyst (1) dissolving the manganese precursor and the cobalt precursor in anhydrous ethanol solvent and stirring continuously until they are completely dissolved and become a clear solution; (2) Add the precipitant dropwise to the clear solution until the pH of the solution is 9-10, so that the precipitation is complete and a suspension is obtained; (3) Pour the suspension into a container with a polytetrafluoroethylene liner, place the hydrothermal synthesis reactor in an oven, and heat at 180-200 °C for 20-24 h; (4) The reactor was naturally cooled to room temperature, the obtained dark brown suspension was filtered, and washed several times with anhydrous ethanol to collect the precipitate; (5) Place the precipitate in an oven and dry it at 80-100 °C for 10-12 h; (6) The dried precipitate is calcined in a muffle furnace at 400-600 °C for 4-6 h in an atmosphere of air or inert gas, and then ground to obtain CoMn 2 O 4 Spinel catalyst powder.

[0006] Step 2. Acid Etching Modification The CoMn obtained in step 1 2 O 4 The spinel catalyst powder was immersed in the acid solution and stirred for 10-30 min. The obtained suspension was filtered and the separated precipitate was placed in an oven at 80-100 °C for 8-12 h to obtain the material, which was the acid-etched modified CoMn 2 O 4 Spinel catalyst.

[0007] The inventors found in experiments that changes in parameters such as manganese salt precursor, cobalt salt precursor, calcination temperature, hydrothermal reaction temperature, acid solution, etc. will bring about changes in the catalyst structure, thereby affecting the denitration performance of the catalyst.

[0008] Preferably, the manganese precursor selected in the above step 1(1) is at least one manganese salt such as manganese nitrate, manganese phosphate, manganese acetate or manganese acetate.

[0009] The cobalt precursor selected in the above step 1(1) is at least one cobalt salt such as cobalt nitrate, cobalt phosphate, cobalt oxalate, cobalt sulfate or cobalt acetate.

[0010] The precipitating agent selected in the above step 1 (2) is at least one of urea, ammonia water, ammonium carbonate, ammonium bicarbonate, etc.

[0011] The acid solution selected in the above step 2 is at least one of a nitric acid solution, an oxalic acid solution, a sulfuric acid solution, and the like. Beneficial Effects

[0012] CoMn prepared by the technical solution of the present invention 2 O 4 Spinel catalysts have the advantages of easy availability of raw materials, controllable structure, variable valence, strong redox ability and environmental friendliness. 2 O 4The spinel catalyst exhibits high catalytic activity, excellent durability and a wide active temperature window. The present invention has the characteristics of simple process and no liquid waste, and meets the requirements of green synthesis. 2 O 4 The spinel wide temperature SCR catalyst can be used in the selective catalytic reduction of nitrogen oxides by ammonia. Within the temperature window of 200-400 °C, the NO conversion rate can be maintained at more than 92%. Compared with the existing process, the present invention has the following innovations: (1) The preparation process of the present invention is simple, the preparation conditions are easy to control, the raw materials used are cheap, and the energy utilization rate is high; (2) The surface modification of the acid-etched catalyst increased the original CoMn 2 O 4 The specific surface area of ​​spinel exposes more active sites. At the same time, acid etching causes more structural defects on the catalyst surface, resulting in an increase in oxygen vacancies, which promotes the transfer of surface oxygen and bulk oxygen, and is conducive to the rapid SCR reaction. Most importantly, after acid etching, the acidity of the catalyst Brønsted acid and Lewis acid increases significantly, which is conducive to the NH 3 The adsorption and activation of the catalyst are the key to improving the SCR activity of the catalyst; (3) CoMn modified by acid etching 2 O 4 Spinel effectively improves the denitrification activity of the catalyst under the test conditions of 500 ppm NH 3 , 500 ppm NO, 5 vol. %O 2 , the balance gas is N 2 , at 100000 mLg -1 h -1 At the mass space velocity, within the temperature window of 200-400 °C, the NO conversion rate can be maintained at more than 92%, which greatly broadens the active reaction temperature window of the catalyst. After the cumulative use time of 60 hours, it can maintain the highest efficiency and has ideal stability. 2 +10 vol. % H 2 After O, acid etching modified CoMn 2 O 4 The NO conversion efficiency of spinel decreased by only 9.29% compared with the initial value, and it has excellent sulfur and water resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 The NH of the catalyst No. 1 prepared in Comparative Example 1 and the catalyst No. 1, No. 2, and No. 3 prepared in Examples 1, 2, and 3 is 3-SCR catalytic activity comparison curve.

[0014] Figure 2 The NH ions of the catalyst samples 1# prepared in comparative example 1 and 2# prepared in example 2 within the cumulative catalytic period of 60 h were 3 -SCR catalytic activity comparison curve.

[0015] Figure 3 The catalyst samples 1# prepared in comparative example 1 and 2# prepared in example 2 were subjected to the introduction of 200 ppm SO 2 +10 vol.% H 2 NH O at 250 °C 3 -SCR catalytic activity comparison curve.

[0016] Figure 4 X-ray diffraction (XRD) of catalyst #1 prepared in comparative example 1 and catalyst #1, #2, #3 samples prepared in examples 1, 2, 3.

[0017] Figure 5 The nitrogen isothermal adsorption-desorption curves of catalyst No. 1 prepared in comparative example 1 and catalyst No. 1 and catalyst No. 2 prepared in examples 1 and 2 are shown.

[0018] Figure 6 Scanning electron microscope (SEM) images of catalyst #1 prepared in comparative example 1 and catalyst #2 prepared in example 2.

[0019] Figure 7 Electron paramagnetic resonance (EPR) of catalyst sample 1# prepared in comparative example 1 and catalyst sample 2# prepared in example 2.

[0020] Figure 8 This is the pyridine infrared test (Py-IR) of catalyst #1 prepared in comparative example 1 and catalyst #2 prepared in example 2. Implementation

[0021] The present invention will be described below in conjunction with embodiments, but the present invention is not limited to the following embodiments.

[0022] Comparative Example: Accurately weigh 5.36 g of manganese acetate dihydrate {(CH 3 COO 3 Mn·2H 2 O} and 2.91 g of cobalt nitrate hexahydrate {Co(NO 3 ) 2 6H 2 O} was added to a beaker containing 80 mL of anhydrous ethanol and stirred on a magnetic stirrer for 30 min to completely dissolve into a clear solution. 3 ·H2 O (25wt%) precipitant was added dropwise to the above clarified solution, the pH of the solution was adjusted to 9, and stirring was continued for 30 min. The suspension was poured into a hydrothermal synthesis reactor with a polytetrafluoroethylene liner and placed in an oven heated at 180 °C for 24 h. The reactor was naturally cooled to room temperature, the dark brown suspension was filtered, and the separated precipitate was washed 4 times with anhydrous ethanol. The precipitate was placed in an oven at 80 °C and dried for 10 h, and finally calcined at 600 °C in a muffle furnace for 4 h. CoMn was obtained after grinding. 2 O 4 catalyst.

[0023] Embodiment 1: Accurately weigh 5.36 g of manganese acetate dihydrate {(CH 3 COO 3 Mn·2H 2 O} and 2.91 g of cobalt nitrate hexahydrate {Co(NO 3 ) 2 6H 2 O} was added to a beaker containing 80 mL of anhydrous ethanol and stirred on a magnetic stirrer for 30 min to completely dissolve into a clear solution. 3 ·H 2 O (25wt%) precipitant was added dropwise to the above clear solution, the pH of the solution was adjusted to 9, and stirring was continued for 30 min. The suspension was poured into a hydrothermal synthesis reactor with a polytetrafluoroethylene liner and placed in an oven at 180°C for heating for 24 h. The reactor was naturally cooled to room temperature, the dark brown suspension was filtered, and the separated precipitate was washed 4 times with anhydrous ethanol. The precipitate was placed in an oven at 100°C for drying for 12 h, and then calcined at 600°C in a muffle furnace for 4 h. After grinding, 0.3 g of the catalyst was placed in a beaker containing 50 mL of 0.05 mol / L nitric acid solution, placed on a magnetic stirrer and stirred for 20 min to fully stir it, then filtered to obtain the acid-washed catalyst, and finally placed in an oven at 80°C for drying for 6 h to obtain acid-etched modified CoMn 2 O 4 -0.05M catalyst.

[0024] Embodiment 2: Accurately weigh 5.36 g of manganese acetate dihydrate {(CH 3 COO 3 Mn·2H 2 O} and 2.91 g of cobalt nitrate hexahydrate {Co(NO 3 ) 2 6H 2O} was added to a beaker containing 80 mL of anhydrous ethanol and stirred on a magnetic stirrer for 30 min to completely dissolve into a clear solution. 3 ·H 2 O (25wt%) precipitant was added dropwise to the above clear solution, the pH of the solution was adjusted to 9, and stirring was continued for 30 min. The suspension was poured into a hydrothermal synthesis reactor with a polytetrafluoroethylene liner and placed in an oven at 180 °C for heating for 24 h. The reactor was naturally cooled to temperature, the dark brown suspension was filtered, and the separated precipitate was washed 4 times with anhydrous ethanol. The precipitate was placed in an oven at 100 °C for 12 h and then calcined at 600 °C in a muffle furnace for 4 h. After grinding, 0.3 g of the catalyst was placed in a beaker containing 50 mL of 0.10 mol / L nitric acid solution, placed on a magnetic stirrer and stirred for 20 min to fully stir it, then filtered to obtain the acid-washed catalyst, and finally placed in an oven at 80 °C for 6 h to obtain acid-etched modified CoMn 2 O 4 -0.10M catalyst.

[0025] Embodiment 1: Accurately weigh 5.36 g of manganese acetate dihydrate {(CH 3 COO 3 Mn·2H 2 O} and 2.91 g of cobalt nitrate hexahydrate {Co(NO 3 ) 2 6H 2 O} was added to a beaker containing 80 mL of anhydrous ethanol and stirred on a magnetic stirrer for 30 min to completely dissolve into a clear solution. 3 ·H 2 O (25wt%) precipitant was added dropwise to the above clear solution, the pH of the solution was adjusted to 9, and stirring was continued for 30 min. The suspension was poured into a hydrothermal synthesis reactor with a polytetrafluoroethylene liner and placed in an oven at 180 °C for heating for 24 h. The reactor was naturally cooled to room temperature, the dark brown suspension was filtered, and the separated precipitate was washed 4 times with anhydrous ethanol. The precipitate was placed in an oven at 100 °C for 12 h and then calcined at 600 °C in a muffle furnace for 4 h. After grinding, 0.3 g of the catalyst was placed in a beaker containing 50 mL of 0.15 mol / L nitric acid solution, placed on a magnetic stirrer and stirred for 20 min to fully stir it, then filtered to obtain the acid-washed catalyst, and finally placed in an oven at 80 °C for 6 h to obtain acid-etched modified CoMn 2 O 4 -0.15M catalyst.

[0026] NH of the catalysts in the comparative examples and examples 3 -SCR catalytic activity comparison Figure 1 It can be seen that the catalyst prepared in Example 2 has a NO conversion rate of more than 92% at 200-400 °C, and its catalyst activity is significantly higher than that of Comparative Example 1, indicating that acid etching modification is beneficial to broadening the active reaction temperature window of the catalyst. 2 +10 vol.% H 2 NH after O 3 -SCR catalytic activity comparison curve Figure 2 It can be seen that the catalyst prepared in Example 2 has good sulfur and water resistance. 2 and H 2 After addition of O, the NO conversion rate dropped from 99% to 90%, while the NO conversion rate of the catalyst prepared in Comparative Example 1 dropped from 77% to a minimum of 62%, indicating that acid etching modification is beneficial to improving the sulfur and water resistance of metal catalysts.

[0027] The XRD patterns of the catalysts in the comparative examples and embodiments are shown in Figure 4 It can be seen that the main diffraction peak angle of the catalyst is completely consistent with the standard card JCPDS 18-0408 of the Joint Committee on Powder Diffraction Standards, indicating that the spinel CoMn 2 O 4 The catalyst was successfully prepared. The pore size distribution of the comparative example and the example catalyst is as follows Figure 5 The specific surface area of ​​the catalyst prepared in Comparative Example 1 is 10.81 m 2 / g, while the specific surface area of ​​the catalyst prepared in Example 2 is 25.73 m 2 / g, proving that acid etching modification can indeed increase the specific surface area of ​​the catalyst and provide more active sites. Figure 6 The particle distribution of the catalyst prepared in Example 2 is more uniformly dispersed. Figure 7 The number of oxygen vacancies in the catalyst prepared in Example 2 is significantly greater than that in the catalyst prepared in Comparative Example 1, which promotes the 3 The Py-IR of the catalysts in the comparative examples and embodiments is as follows Figure 8 This indicates that the catalyst prepared in Example 2 contains more surface Lewis and Bronsted acid sites, which is conducive to the adsorption of NH 3 and NH 4 + .

[0028] The above description is only a preferred embodiment of the present invention and is not any formal or substantial limitation of the present invention. It should be pointed out that a person skilled in the art can make several improvements and supplements without departing from the present invention, and these improvements and supplements should also be regarded as the protection scope of the present invention.

Claims

1. A kind of acid-etched modified CoMn provided by the present invention 2 O 4 Preparation method of spinel wide temperature SCR catalyst, It is characterized in that The following steps are involved: (1) dissolving a manganese precursor and a cobalt precursor in an anhydrous ethanol solvent, and continuously stirring until they are completely dissolved and become a clear solution; (2) adding a precipitant dropwise to the clarified solution until the pH of the solution is 9-10, so that the precipitation is complete and a suspension is obtained; (3) Pour the suspension into a polytetrafluoroethylene liner, place the hydrothermal synthesis reactor in an oven, and heat at 180-200 °C for 20-24 h; (4) The reactor was naturally cooled to room temperature, the obtained dark brown suspension was filtered, and washed several times with anhydrous ethanol to collect the precipitate; (5) Place the precipitate in an oven and dry it at 80-100 °C for 10-12 h; (6) The dried precipitate is calcined in a muffle furnace at 400-600 °C for 4-6 h in an atmosphere of air or inert gas, and then ground to obtain CoMn 2 O 4 Spinel catalyst powder; (7) The catalyst powder obtained in step (6) is immersed in an acid solution, fully stirred, and the obtained suspension is filtered, and the separated precipitate is placed in an oven at 80-100°C and dried for 8-12 hours to obtain the acid-etched modified CoMn 2 O 4 Spinel catalyst.

2. The acid-etched modified CoMn according to claim 1 2 O 4 Preparation method of spinel wide temperature SCR catalyst, It is characterized in that The cobalt precursor in step (1) is cobalt nitrate hexahydrate {Co(NO 3 ) 2 6H 2 O}, the manganese precursor is manganese acetate dihydrate {(CH 3 COO 3 Mn·2H 2 O}, and the molar ratio is 2:

1.

3. The acid-etched modified CoMn according to claim 1 2 O 4 Preparation method of spinel wide temperature SCR catalyst, It is characterized in that The precipitant in step (2) is NH 3 ·H 2 O (25wt%), the solution pH=9.

4. The acid-etched modified CoMn as claimed in claim 1 2 O 4 Preparation method of spinel wide temperature SCR catalyst, It is characterized in that The oven temperature in step (3) is 180° C. and the heating time is 24 h.

5. The acid-etched modified CoMn as claimed in claim 1 2 O 4 Preparation method of spinel wide temperature SCR catalyst, It is characterized in that The oven temperature in step (5) is 100° C. and the drying time is 12 h.

6. The acid-etched modified CoMn as claimed in claim 1 2 O 4 Preparation method of spinel wide temperature SCR catalyst, It is characterized in that The calcination temperature in the muffle furnace in step (6) is 600° C. and the calcination time is 4 h.

7. The acid-etched modified CoMn as claimed in claim 1 2 O 4 Preparation method of spinel wide temperature SCR catalyst, It is characterized in that The oven temperature in step (7) is 80° C. and the drying time is 6 h.

8. The acid-etched modified CoMn as claimed in claim 1 2 O 4 Preparation method of spinel wide temperature SCR catalyst, It is characterized in that The stirring time in step (1) and step (7) is 30 min.

9. The acid-etched modified CoMn according to any one of claims 1 to 8 2 O 4 Application of spinel wide temperature SCR catalyst in SCR flue gas denitrification treatment.

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