Preparation method of catalyst for selective photothermal catalytic reduction denitrification of low-temperature flue gas

Abstract

The present invention discloses a method for preparing a catalyst for selective photothermal catalytic reduction denitrification of low-temperature flue gas, comprising the steps of: preparing CoMnAlO x ‑LDO; Step 2, using the CoMnAlO prepared in step 1 x ‑LDO was used as raw material to prepare alkaline CoMnAlO x ‑LDO; Step 3, using the alkaline CoMnAlO obtained in Step 2 x CeO x / CoMnAlO x Composite photothermal catalyst. This method for preparing a catalyst for selective photothermal catalytic reduction denitrification of low-temperature flue gas solves the problem that the performance of existing low-temperature SCR denitrification catalysts is difficult to meet the actual needs under ultra-low-temperature denitrification conditions.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and in particular relates to a method for preparing a catalyst for selective photothermal catalytic reduction denitrification of low-temperature flue gas. Background Art

[0002] Nitrogen oxides (NO x ) is one of the main atmospheric pollutants that cause acid rain, photochemical smog and haze, and it strengthens NO x Emission control and treatment has become an urgent task for the sustainable green development of my country's economy and society. Selective catalytic reduction (SCR) is currently the most widely used and most effective denitrification technology. Most non-power enterprises adopt the "dust removal and desulfurization + flue gas heating + medium-temperature NH3-SCR denitrification" process route in ultra-low emission transformation. However, the temperature of the flue gas drops significantly after desulfurization and dust removal, mostly below 150°C or even lower. The use of conventional medium-temperature (280°C ~ 420°C) catalysts requires a large amount of heat energy to heat the entire system, greatly increasing energy consumption and equipment investment, resulting in resource waste and greenhouse gas emissions.

[0003] At present, the research on low-temperature SCR denitrification catalysts mainly focuses on modified manganese-based, titanium-based, cerium-based, tungsten-based and other metal oxides. To this end, various transition metal oxides have been prepared and developed for the reduction of NO in non-power industries. x However, their performance is difficult to meet the actual needs of ultra-low temperature denitrification conditions. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing a catalyst for selective photocatalytic reduction denitration of low-temperature flue gas, so as to solve the problem that the performance of existing low-temperature SCR denitration catalysts is difficult to meet the actual needs under denitration conditions below 150°C.

[0005] In order to solve the above technical problems, the present invention discloses a method for preparing a catalyst for selective photothermal catalytic reduction denitrification of low-temperature flue gas, which is specifically implemented according to the following steps:

[0006] Step 1, preparation of CoMnAlO x -LDO;

[0007] Step 2: Prepare the CoMnAlO x -LDO was used as raw material to prepare alkaline CoMnAlO x -LDO;

[0008] Step 3: using the alkaline CoMnAlO obtained in step 2 x -LDO and cerium salt were used as raw materials to prepare CeO x / CoMnAlOx Composite photothermal catalyst.

[0009] The technical solution of the present invention also has the following characteristics:

[0010] As a preferred embodiment of the present invention, in step 1, CoMnAlO is prepared x -LDO specifically:

[0011] Step 1.1, take Co(NO3)2·6H2O, Mn(NO3)2·4H2O, Al(NO3)3·9H2O and urea into a beaker, where n(NO -3 ) / n(urea) ratio is 1:1, regulating n(Co 2+ ) / n(Mn 2+ ) / n(Al 3+ ) is in the ratio of (1-5):(1-5):1;

[0012] Step 1.2: Add deionized water to a beaker and stir with a magnetic stirrer for 15-20 minutes to completely dissolve the solution.

[0013] Step 1.3, the solution obtained in step 1.2 was sealed and placed in a stainless steel reactor lined with polytetrafluoroethylene, and heated in an oven. After the reaction temperature dropped to room temperature, the solid sample was alternately washed with deionized water and anhydrous ethanol, and then dried in a drying oven. After drying and grinding, CoMnAl-LDH powder was obtained;

[0014] Step 1.4: Place the CoMnAl-LDH powder in a crucible and place it in a muffle furnace, and calcine it in an air atmosphere to obtain CoMnAlO x -LDO.

[0015] As a preferred embodiment of the present invention, in step 1.2, the stirring time of the magnetic stirrer is 15 min-20 min.

[0016] As a preferred embodiment of the present invention, in step 1.3, the heating temperature in the oven is 100° C.-180° C., and the heating time is 16 h-28 h.

[0017] As a preferred embodiment of the present invention, in step 1.4, the calcination is carried out at 300° C.-700° C. for 4 h-10 h at a heating rate of 2-5° C. / min.

[0018] As a preferred embodiment of the present invention, in step 2, alkaline CoMnAlO x -LDO specifically:

[0019] Step 2.1: CoMnAlO obtained in step 1 x-LDO is dispersed in H2O to obtain a dispersion with a concentration of 5g / L-50g / L;

[0020] Step 2.2, after ultrasonic treatment, add 0.5 mol / L-4 mol / L NaOH aqueous solution, with the volume ratio of the dispersion to the NaOH solution being 1:1.5, and continue stirring until the solution is uniformly mixed;

[0021] Step 2.3, transfer the mixed solution to a polytetrafluoroethylene-lined stainless steel reactor and maintain it at 100°C-170°C for 0.5h-6h. After the reaction temperature drops to room temperature, wash the solid sample alternately with deionized water and ethanol;

[0022] Step 2.4: After washing, the product is placed in a vacuum drying oven and dried under vacuum to obtain alkaline CoMnAlO x -LDO.

[0023] As a preferred embodiment of the present invention, in step 2.4, the vacuum drying temperature is 60° C.-120° C., and the drying time is 16 h-28 h.

[0024] As a preferred embodiment of the present invention, in step 3, CeO x / CoMnAlO x Composite photothermal catalyst, specifically:

[0025] Step 3.1, alkaline CoMnAlO x -LDO is dispersed in oxygen-free water, and after ultrasonication, stirring is continued to make it dispersed evenly to obtain a dispersion liquid;

[0026] Step 3.2, add alkaline CoMnAlO x -LDO molar ratio of (2-5): 1 cerium salt, then stir until the solution is mixed evenly, then quickly inject 1mol / L-4mol / L NH3·H2O to make the pH reach 8-9 and continue stirring for 5-10min;

[0027] Step 3.3, the mixed solution was centrifuged, and after the centrifugation, it was placed in an oven for drying. Finally, the dried and ground sample was placed in a muffle furnace and calcined in an air atmosphere to obtain CeO x / CoMnAlO x Composite photothermal catalyst.

[0028] As a preferred embodiment of the present invention, in step 3.3, the calcination is carried out at 300° C.-700° C. for 4 h-10 h at a heating rate of 2-5° C. / min.

[0029] As a preferred embodiment of the present invention, it is used for selective photothermal catalytic reduction denitrification of low-temperature flue gas.

[0030] Compared with the existing technology: the preparation method of the catalyst for selective photothermal catalytic reduction denitrification of low-temperature flue gas of the present invention has the multifunctional effects of photothermal conversion and photocatalytic reduction denitrification. After being exposed to light, local high temperature can be formed on the surface of the catalyst, thereby achieving efficient removal of ultra-low temperature flue gas. The catalyst body CoMnAlO x The multi-metal oxide is obtained by the topological transformation process of CoMnAl-LDH hydrotalcite material through high-temperature calcination. It not only has a porous lamellar structure and a large specific surface area, which is conducive to the adsorption and mass transfer of reaction gas molecules, but also its photothermal conversion metals (Co and Mn), denitrification active metals (Mn) and carrier metals (Al) can maintain a high degree of dispersion at the atomic scale, promoting the effective synergy of photothermal and catalytic activity between different metal oxides and improving the thermal stability of the catalyst. In addition, CeO prepared by electrostatic adsorption and calcination method x / CoMnAlO x Composite photothermal catalyst, CeO x It is an ultra-small nanocluster with a size of less than 10nm and is uniformly dispersed in CoMnAlO x -LDO surface has a high exposure ratio of active sites, which can fully exert its catalytic effect in the low-temperature denitrification process and maintain high stability, thereby improving the denitrification activity of the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 CoMnAlO obtained in Examples 1 and 4 of the present invention x -LDO transmission electron microscope;

[0032] Figure 2 The CoMnAlO obtained in Example 5 of the present invention x - XRD pattern of LDO (base);

[0033] Figure 3 The CoMnAlO obtained in Example 5 of the present invention x - Zeta potential diagram of LDO (base);

[0034] Figure 4 The CeO obtained in Example 1 of the present invention x / CoMnAlO x TEM and HRTEM images;

[0035] Figure 5 The CeO obtained in Example 1 of the present invention x / CoMnAlO x Element distribution diagram;

[0036] Figure 6 The CeO obtained in Example 1 of the present invention x / CoMnAlO x XRD pattern of

[0037] Figure 7 The CeO obtained in Example 1 of the present invention x / CoMnAlO x Photothermal performance diagram;

[0038] Figure 8 The CeO obtained in Example 1 of the present invention x / CoMnAlO x XPS graph;

[0039] Figure 9 The CeO obtained in Example 1 of the present invention x / CoMnAlO x Denitrification activity diagram; DETAILED DESCRIPTION

[0040] The method for preparing a catalyst for selective photothermal catalytic reduction denitrification of low-temperature flue gas of the present invention is specifically implemented according to the following steps:

[0041] Step 1, preparation of CoMnAlO x -LDO, specifically:

[0042] Step 1.1, take Co(NO3)2·6H2O, Mn(NO3)2·4H2O, Al(NO3)3·9H2O and urea into a beaker, where n(NO -3 ) / n(urea) ratio is 1:1, regulating n(Co 2+ ) / n(Mn 2+ ) / n(Al 3+ ) is in the ratio of (1-5):(1-5):1;

[0043] Step 1.2: Add deionized water to a beaker and stir with a magnetic stirrer for 15-20 minutes to completely dissolve the solution.

[0044] Step 1.3, the solution obtained in step 1.2 is sealed and placed in a polytetrafluoroethylene-lined stainless steel reactor, and heated in an oven at 100-180°C for 16-28 hours. After the reaction cools to room temperature, the solid sample is alternately washed with deionized water and anhydrous ethanol, and then placed in a drying oven for drying. After drying and grinding, CoMnAl-LDH powder is obtained;

[0045] Step 1.4: Place the CoMnAl-LDH powder in a crucible and place it in a muffle furnace. Sinter the mixture at 300-700°C for 4-10 h at a heating rate of 2-5°C / min in air atmosphere to obtain CoMnAlO x -LDO;

[0046] Step 2: Prepare the CoMnAlO x -LDO was used as raw material to prepare alkaline CoMnAlO x -LDO, specifically:

[0047] Step 2.1: CoMnAlO obtained in step 1 x -LDO is dispersed in H2O to obtain a dispersion with a concentration of 5g / L-50g / L;

[0048] Step 2.2, after ultrasonic treatment, add 0.5 mol / L-4 mol / L NaOH aqueous solution, with the volume ratio of the dispersion to the NaOH solution being 1:1.5, and continue stirring until the solution is uniformly mixed;

[0049] Step 2.3, transfer the mixed solution to a polytetrafluoroethylene-lined stainless steel reactor and maintain it at 100°C-170°C for 0.5h-6h. After the reaction temperature drops to room temperature, wash the solid sample alternately with deionized water and ethanol;

[0050] Step 2.4: After washing, the product is placed in a vacuum drying oven at 60°C-120°C and dried for 16h-28h to obtain alkaline CoMnAlO x -LDO;

[0051] Step 3: using the alkaline CoMnAlO obtained in step 2 x -LDO and cerium salt were used as raw materials to prepare CeO x / CoMnAlO x Composite photothermal catalyst, specifically:

[0052] Step 3.1, alkaline CoMnAlO x -LDO is dispersed in oxygen-free water, and after ultrasonication, stirring is continued to make it dispersed evenly to obtain a dispersion liquid;

[0053] Step 3.2, add alkaline CoMnAlO x -LDO molar ratio of (2-5): 1 cerium salt, then stir until the solution is mixed evenly, then quickly inject 1mol / L-4mol / L NH3·H2O to make the pH reach 8-9 and continue stirring for 5min-10min;

[0054] Step 3.3, the mixed solution was centrifuged and placed in an oven for drying. Finally, the dried and ground sample was placed in a muffle furnace and calcined at 300-600°C for 4-12 hours at a heating rate of 5°C / min in air atmosphere to obtain CeO x / CoMnAlO x Composite photothermal catalyst.

[0055] The present invention discloses a method for preparing a catalyst for selective photothermal catalytic reduction denitrification of low-temperature flue gas, wherein CoMnAlO x It is prepared from CoMnAl-LDH hydrotalcite-like layered nanomaterials. The main layer of hydrotalcite-like metal elements are rich and adjustable. The CoMnAl-LDH in the present invention covers the photothermal conversion metals Co and Mn required for photothermal catalytic denitrification, the denitrification active metal Mn and the carrier metal Al, and the different metal elements in the main layer are arranged in an orderly and uniform manner, which can keep the multi-metal elements as active sites highly dispersed at the atomic scale. The main structure of LDHs in the present invention is composed of charged hydroxyl layer plates and negatively charged interlayer anions. As the calcination temperature increases, the interlayer anions and layer hydroxyl groups decompose, causing the layer plates to collapse and the structural topology to transform into hydrotalcite-like derived multi-metal oxides CoMnAlO x -LDO. Prepared CoMnAlO x -LDO exhibits high denitrification activity and nitrogen selectivity due to its advantages, including a two-dimensional porous structure, large specific surface area, uniformly dispersed active centers, good thermal stability, fully exposed strong acidic sites, and excellent redox capacity. Based on these structural advantages, hydrotalcite-like multimetal oxides can achieve excellent high-temperature photothermal conversion on their surfaces, which is beneficial for low-temperature flue gas denitrification activity.

[0056] The metal ion complexing agent can complex multiple ions together to form a complete CoMnAl-LDH. Compared with the existing preparation method, the metal ion complexing agent selected for the preparation of CoMnAl-LDH in the present invention is urea, which has the advantages of stable structural skeleton and large size after calcination.

[0057] The present invention adopts electrostatic adsorption nucleation method to prepare ultra-small nano-sized CeO x Loaded CoMnAlO x -LDO catalyst, including Ce 3+ In a weakly alkaline solution (preferably, the pH is controlled within the range of 8.5-9), [Ce(OH) x ] y+ Complex positive ions, while CoMnAlO x -LDO has an electronegative surface after alkali etching, which can be used to etch [Ce(OH) x ] y+ Positive ions produce good electrostatic adsorption, which makes Ce species in CoMnAlO x -LDO (alkali) surface nuclei are formed in large quantities and are extremely small in size. During the subsequent calcination process, the Ce species adsorbed on the surface will react with oxygen to form CeO x, and due to the high dispersion of its crystal nuclei, ultra-small CeO with a size less than 10nm can be prepared x Nanoclusters. If CoMnAlO x -LDO has not been alkali etched, and the positively charged [Ce(OH) x ] y+ With positively charged CoMnAlO x - LDOs repel each other and ultimately cannot form a composite CeO x / CoMnAlO x .

[0058] CeO x It is an effective low-temperature denitrification co-catalyst. However, in previous studies, Ce species were usually introduced into the support surface in the form of impregnated species, forming large and isolated cerium oxide particles in mixed oxide materials, or doped in the oxide crystals in the form of Ce ions. Since most of the Ce element exists in the bulk phase, both methods are not conducive to the Ce sites fully playing the role of active sites in the catalytic process. In the present invention, during the high-temperature calcination process, the atomically dispersed Ce species self-assemble into ultra-small, isolated CeO x Nanoclusters. Compared to the lower thermal stability of cerium oxide particles in high-temperature catalytic reactions, the nanoclusters in the present invention have excellent oxygen storage capacity, a high proportion of exposed surface active sites, and unique redox properties. The redox properties of cerium oxide promote the formation of oxygen vacancies, thereby promoting the oxidation of NO to NO2, resulting in better low-temperature flue gas denitrification activity.

[0059] Example 1

[0060] The method for preparing a catalyst for selective photothermal catalytic reduction denitrification of low-temperature flue gas of the present invention is specifically implemented according to the following steps:

[0061] Step 1, preparation of CoMnAlO x -LDO, specifically:

[0062] Step 1.1, take Co(NO3)2·6H2O, Mn(NO3)2·4H2O, Al(NO3)3·9H2O and urea into a beaker, where n(NO -3 ) / n(urea) ratio is 1:1, regulating n(Co 2+ ) / n(Mn 2+ ) / n(Al 3+ ) is in a ratio of 2:1:1;

[0063] Step 1.2: Add deionized water to the beaker and stir with a magnetic stirrer for 15 minutes to completely dissolve the solution.

[0064] Step 1.3, the solution obtained in step 1.2 was sealed and placed in a polytetrafluoroethylene-lined stainless steel reactor, and heated in a 120°C oven for 28 hours. After the reaction cooled to room temperature, the solid sample was alternately washed with deionized water and anhydrous ethanol, and then dried in a drying oven. After drying and grinding, CoMnAl-LDH powder was obtained;

[0065] Step 1.4: Place the CoMnAl-LDH powder in a crucible and place it in a muffle furnace. Sinter it at 400 °C for 7 h at a heating rate of 5 °C / min in air to obtain CoMnAlO x -LDO;

[0066] Step 2: Prepare the CoMnAlO x -LDO was used as raw material to prepare alkaline CoMnAlO x -LDO, specifically:

[0067] Step 2.1: CoMnAlO obtained in step 1 x -LDO was dispersed in H2O to obtain a dispersion with a concentration of 6 g / L;

[0068] Step 2.2, after ultrasonic treatment, add 1 mol / L NaOH aqueous solution, with the volume ratio of dispersion to NaOH solution being 1:1.5, and continue stirring until the solution is uniformly mixed;

[0069] Step 2.3, the mixed solution was transferred to a polytetrafluoroethylene-lined stainless steel reactor and maintained at 100°C for 4 h. After the reaction temperature dropped to room temperature, the solid sample was washed alternately with deionized water and ethanol;

[0070] Step 2.4: After washing, the product was placed in a vacuum drying oven at 60°C and dried for 28 hours to obtain alkaline CoMnAlO x -LDO;

[0071] Step 3: using the alkaline CoMnAlO obtained in step 2 x -LDO and cerium salt were used as raw materials to prepare CeO x / CoMnAlO x Composite photothermal catalyst, specifically:

[0072] Step 3.1, alkaline CoMnAlO x -LDO is dispersed in oxygen-free water, and after ultrasonication, stirring is continued to make it dispersed evenly to obtain a dispersion liquid;

[0073] Step 3.2, add alkaline CoMnAlO x-LDO molar ratio of cerium salt is 2:1, then stirred until the solution is mixed evenly, then quickly injected 1mol / L NH3·H2O to make the pH reach 8-9 and continued stirring for 5min;

[0074] Step 3.3, the mixed solution was centrifuged and placed in an oven for drying. Finally, the dried and ground sample was placed in a muffle furnace and calcined at 500°C for 12 h at a heating rate of 5°C / min in an air atmosphere to obtain CeO x / CoMnAlO x Composite photothermal catalyst.

[0075] Example 2

[0076] The method for preparing a catalyst for selective photothermal catalytic reduction denitrification of low-temperature flue gas of the present invention is specifically implemented according to the following steps:

[0077] Step 1, preparation of CoMnAlO x -LDO, specifically:

[0078] Step 1.1, take Co(NO3)2·6H2O, Mn(NO3)2·4H2O, Al(NO3)3·9H2O and urea into a beaker, where n(NO -3 ) / n(urea) ratio is 1:1, regulating n(Co 2+ ) / n(Mn 2+ ) / n(Al 3+ ) is in a ratio of 3:5:1;

[0079] Step 1.2: Add deionized water to a beaker and stir with a magnetic stirrer for 20 minutes to completely dissolve the solution.

[0080] Step 1.3: The solution obtained in step 1.2 was sealed and placed in a polytetrafluoroethylene-lined stainless steel reactor, and heated in an oven at 180°C for 16 hours. After the reaction cooled to room temperature, the solid sample was alternately washed with deionized water and anhydrous ethanol, and then dried in a drying oven. After drying and grinding, CoMnAl-LDH powder was obtained;

[0081] Step 1.4: Place the CoMnAl-LDH powder in a crucible and place it in a muffle furnace. Sinter it at 700 °C for 4 h at a heating rate of 4 °C / min in air to obtain CoMnAlO x -LDO;

[0082] Step 2: Prepare the CoMnAlO x -LDO was used as raw material to prepare alkaline CoMnAlO x -LDO, specifically:

[0083] Step 2.1: CoMnAlO obtained in step 1 x -LDO was dispersed in H2O to obtain a dispersion with a concentration of 50 g / L;

[0084] Step 2.2, after ultrasonic treatment, add 4 mol / L NaOH aqueous solution, with the volume ratio of dispersion to NaOH solution being 1:1.5, and continue stirring until the solution is uniformly mixed;

[0085] Step 2.3, transfer the mixed solution to a polytetrafluoroethylene-lined stainless steel reactor and maintain it at 170°C for 0.5 h. After the reaction temperature cools to room temperature, wash the solid sample alternately with deionized water and ethanol;

[0086] Step 2.4: After washing, the product was placed in a vacuum drying oven at 120°C for 16 h to obtain alkaline CoMnAlO x -LDO;

[0087] Step 3: using the alkaline CoMnAlO obtained in step 2 x -LDO and cerium salt were used as raw materials to prepare CeO x / CoMnAlO x Composite photothermal catalyst, specifically:

[0088] Step 3.1, alkaline CoMnAlO x -LDO is dispersed in oxygen-free water, and after ultrasonication, stirring is continued to make it dispersed evenly to obtain a dispersion liquid;

[0089] Step 3.2, add alkaline CoMnAlO x -LDO molar ratio of cerium salt is 5:1, then stirred until the solution is mixed evenly, then quickly injected 4mol / L NH3·H2O to make the pH reach 8-9 and continued stirring for 10min;

[0090] Step 3.3, the mixed solution was centrifuged and placed in an oven for drying. Finally, the dried and ground sample was placed in a muffle furnace and calcined at 600 °C for 4 h at a heating rate of 3 °C / min in an air atmosphere to obtain CeO x / CoMnAlO x Composite photothermal catalyst.

[0091] Example 3

[0092] The method for preparing a catalyst for selective photothermal catalytic reduction denitrification of low-temperature flue gas of the present invention is specifically implemented according to the following steps:

[0093] Step 1, preparation of CoMnAlO x -LDO, specifically:

[0094] Step 1.1, take Co(NO3)2·6H2O, Mn(NO3)2·4H2O, Al(NO3)3·9H2O and urea into a beaker, where n(NO -3 ) / n(urea) ratio is 1:1, regulating n(Co 2+ ) / n(Mn 2+ ) / n(Al 3+ ) is in a ratio of 4:2:1;

[0095] Step 1.2: Add deionized water to a beaker and stir with a magnetic stirrer for 18 minutes to completely dissolve the solution.

[0096] Step 1.3, the solution obtained in step 1.2 was sealed and placed in a polytetrafluoroethylene-lined stainless steel reactor, and heated in a 140°C oven for 22 hours. After the reaction cooled to room temperature, the solid sample was alternately washed with deionized water and anhydrous ethanol, and then dried in a drying oven. After drying and grinding, CoMnAl-LDH powder was obtained;

[0097] Step 1.4: Place the CoMnAl-LDH powder in a crucible and place it in a muffle furnace. Sinter it at 500 °C for 6 h at a heating rate of 2 °C / min in air atmosphere to obtain CoMnAlO x -LDO;

[0098] Step 2: Prepare the CoMnAlO x -LDO was used as raw material to prepare alkaline CoMnAlO x -LDO, specifically:

[0099] Step 2.1: CoMnAlO obtained in step 1 x -LDO was dispersed in H2O to obtain a dispersion with a concentration of 28 g / L;

[0100] Step 2.2, after ultrasonic treatment, add 2.5 mol / L NaOH aqueous solution, with the volume ratio of dispersion to NaOH solution being 1:1.5, and continue stirring until the solution is uniformly mixed;

[0101] Step 2.3, transfer the mixed solution to a polytetrafluoroethylene-lined stainless steel reactor and maintain it at 135°C for 3.5 hours. After the reaction temperature cools to room temperature, wash the solid sample alternately with deionized water and ethanol;

[0102] Step 2.4: After washing, the product was placed in a vacuum drying oven at 70°C for 22 hours to obtain alkaline CoMnAlO x -LDO;

[0103] Step 3: using the alkaline CoMnAlO obtained in step 2 x-LDO and cerium salt were used as raw materials to prepare CeO x / CoMnAlO x Composite photothermal catalyst, specifically:

[0104] Step 3.1, alkaline CoMnAlO x -LDO is dispersed in oxygen-free water, and after ultrasonication, stirring is continued to make it dispersed evenly to obtain a dispersion liquid;

[0105] Step 3.2, add alkaline CoMnAlO x -LDO molar ratio of cerium salt is 3:1, then stirred until the solution is mixed evenly, then quickly injected 2mol / L NH3·H2O to make the pH reach 8-9 and continued stirring for 8min;

[0106] Step 3.3, the mixed solution was centrifuged and placed in an oven for drying after the centrifugation. Finally, the dried and ground sample was placed in a muffle furnace and calcined at 450 °C for 8 h at a heating rate of 5 °C / min in an air atmosphere to obtain CeO x / CoMnAlO x Composite photothermal catalyst.

[0107] Example 4

[0108] In research step 1, CoMnAlO x -The influence of different calcination temperatures of LDO

[0109] The CoMnAlO in step 1 of Example 1 was x -LDO calcination temperatures were set at 300℃, 400℃, 500℃, 600℃ and 700℃ respectively, and all other operation steps and parameters remained unchanged. x -LDO times are recorded as CoMnAlO x -300, CoMnAlO x -400, CoMnAlO x -500, CoMnAlO x -600, CoMnAlO x -700. Calcination temperature is one of the important factors affecting the morphology, structure and catalytic performance of the catalyst. With the increase of temperature, CoMnAlO x -LDO catalyst crystal sintering is more obvious, the catalyst specific surface area shows a downward trend, while the pore size shows an upward trend. Therefore, the calcination temperature can be used to control the catalyst microstructure and thus the catalyst activity.

[0110] Example 5

[0111] Study the impact of different alkaline etching preparation methods in step 2

[0112] The hydrothermal method in step 2 of Example 1 was replaced by a low-temperature liquid phase treatment. The specific steps were as follows: 300 mg of CoMnAl-LDO was dispersed in 20 mL of H2O and ultrasonicated for 30 min, and then a NaOH aqueous solution was injected into the dispersion. The solution was placed on a magnetic stirrer and stirred at 60 ° C for 12 h. After washing with water, the product was vacuum dried at 60 ° C for 24 h to obtain CoMnAlO x -LDO (alkaline). After alkaline etching, the surface charge of the sample changes from positive to negative, and different alkaline etching methods have different degrees of conversion of the surface charge of the sample.

[0113] Example 6

[0114] Study the effect of the concentration of NH3·H2O added in step 3 on the catalyst.

[0115] The concentrations of NH3·H2O in step 3 of Example 1 were set to 1.5 and 2.5 mol / L respectively, and all other operation steps and parameters remained unchanged. - The ion is Ce 3+ The ion is a strong complexing agent for the formation of cationic complexes, but excess hydroxide can lead to precipitation of Ce(OH)3. In order to avoid the formation of Ce(OH)3 precipitates from the solution phase, the hydroxide concentration needs to be carefully controlled to maintain a soluble [Ce(OH) x ] y+ The complex is a relatively stable aqueous solution.

[0116] The main steps of the denitrification activity test method are as follows:

[0117] Take 0.2g CeO x / CoMnAlO x The composite photothermal catalyst was dispersed in deionized water and ultrasonicated for 0.5 hours to achieve uniform dispersion. A quartz fiber was laid flat in a filtration device, and the dispersion was poured into the filtration device for filtration. The filtered sample was then dried in a drying oven to obtain a catalyst-loaded quartz fiber membrane. The catalyst-loaded quartz fiber membrane was placed in a photothermal catalytic denitrification reactor. The reaction conditions were: 0.1-0.5g of catalyst, 300-1000ppm NO, 300-1000ppm NH3, an oxygen content of 3-6%, a flow rate of 200-1000mL / min, and a flue gas temperature of 80-200°C.

[0118] Structural performance characterization

[0119] Figure 1 It can be seen that CoMnAl-LDH has a more complete crystal structure and better hexagonal sheet morphology, while after calcination, CoMnAlO x-LDO surface presents a porous structure. This is because as the temperature rises, the interlayer anions and hydroxyl groups of LDHs decompose, causing the layer collapse and structural topology transformation, destroying the original layered structure. And as the temperature rises, the specific surface area of ​​the catalyst shows a downward trend, while the pore size shows an upward trend. Among them, CoMnAlO x -300 has the largest specific surface area, which is 142.7m 2 g, which is much higher than other catalysts. It also has the smallest average pore size, which is due to the small pores formed by the overflow of gas during the calcination process. x The -700 catalyst has the largest pore size, resulting from the collapse and accumulation of large pores during high-temperature calcination. Therefore, the calcination temperature can be used to control the catalyst's microstructure and, in turn, its performance.

[0120] Figure 2 For sample CoMnAlO x -LDO and CoMnAlO x -LDO (alkali) XRD pattern, from which we can see that the sample after alkali etching is different from CoMnAlO x -LDO has similar diffraction peak positions and intensities, and its crystal form is relatively complete, with high crystallinity and no impurity phase, indicating that alkaline etching does not change its crystal form.

[0121] Figure 3 For sample CoMnAlO x -LDO and CoMnAlO x -LDO (alkali) Zeta potential diagram. It can be seen from the figure that after alkaline etching, the surface charge of the sample changes from positive to negative. Therefore, [Ce(OH) x ] y+ The ions produce good electrostatic adsorption, which provides a good foundation for the later CeO x Better loading on CoMnAlO x The surface lays the foundation.

[0122] Figure 4 For sample CeO x / CoMnAlO x From the TEM and HRTEM images, it can be seen that the catalyst is a porous sheet structure with isolated and evenly dispersed ultra-small CeO x Nanoclusters, whose size is less than 10nm.

[0123] Figure 5 For sample CeO x / CoMnAlO xFrom the element distribution diagram, it can be seen that the Ce, Cm, Mn, Al, Ce, and O elements that make up the catalyst have a uniform element distribution, which is beneficial to the synergistic effect between different metal units in the catalytic process and improves the stability of the catalyst.

[0124] Figure 6 Sample CeO x / CoMnAlO x XRD pattern of CeO x / CoMnAlO x The XRD diffraction peak position of the sample is similar to that of CoMnAlO x -LDO standard peak position is basically the same, indicating that in the composite CeO x During the process of CoMnAlO x The main body of the crystal structure can remain stable. In addition, compared with the bulk CeO2 crystal prepared separately, CeO x / CoMnAlO x CeO x The diffraction peak is not obvious, which is partly because CeO x The ultra-small particles of nanoclusters are not enough to form a highly crystalline structure. On the other hand, CeO x Lower content.

[0125] Figure 7 CeO x / CoMnAlO x The photothermal performance diagram shows that this catalyst has good photothermal conversion performance. 2 Under the illumination of , its surface temperature can finally reach 451.3 ℃, indicating that the catalyst surface can carry out high-temperature photothermal conversion very well, which can provide a sufficient local high-temperature environment for the photothermal catalytic reduction denitrification reaction, and is beneficial to the denitrification treatment of ultra-low temperature flue gas.

[0126] Figure 8 CeO x / CoMnAlO x The XPS graph shows CeO x Successfully loaded on CoMnAlO x -LDO, and it shows that the catalyst is 4+ and Ce 3+ The advantages of the redox performance of the conversion between Ce 4+ and Ce 3+ The conversion between them can promote the oxidation of NO to NO2, which is beneficial to the photothermal catalytic reduction denitrification reaction of low-temperature flue gas.

[0127] Depend on Figure 9 It can be seen that CeO x / CoMnAlOx The denitrification activity diagram of CeO x / CoMnAlO x than CoMnAlO x -LDO has better denitrification performance and nitrogen selectivity. NO x The overall trend of conversion rate can be summarized as follows: it increases continuously at the beginning, gradually approaches a steady state as the temperature rises, and shows a downward trend as the temperature further rises.

Claims

1. A method for preparing a catalyst for selective photothermal catalytic reduction denitrification of low-temperature flue gas, characterized in that: Please follow the steps below to implement it: Step 1, preparation of CoMnAlO x -LDO; Step 2: Prepare the CoMnAlO x -LDO was used as raw material to prepare alkaline CoMnAlO x -LDO; Step 3: using the alkaline CoMnAlO obtained in step 2 x -LDO and cerium salt were used as raw materials to prepare CeO x / CoMnAlO x Composite photothermal catalyst; In step 1, CoMnAlO is prepared x -LDO specifically: Step 1.1, take Co(NO3)2·6H2O, Mn(NO3)2·4H2O, Al(NO3)3·9H2O and urea into a beaker, where n(NO3 - ) / n(urea) ratio is 1:1, regulating n(Co 2+ ) / n(Mn 2+ ) / n(Al 3+ ) is in the ratio of (1-5):(1-5):1; Step 1.2: Add deionized water to a beaker and stir with a magnetic stirrer for 15-20 minutes to completely dissolve the solution. Step 1.3, the solution obtained in step 1.2 was sealed and placed in a stainless steel reactor lined with polytetrafluoroethylene, and heated in an oven. After the reaction temperature dropped to room temperature, the solid sample was alternately washed with deionized water and anhydrous ethanol, and then dried in a drying oven. After drying and grinding, CoMnAl-LDH powder was obtained; Step 1.4: Place the CoMnAl-LDH powder in a crucible and place it in a muffle furnace, and calcine it in an air atmosphere to obtain CoMnAlO x -LDO; In the step 1.2, the stirring time of the magnetic stirrer is 15 min-20 min; In the step 1.3, the temperature of heating in the oven is 100° C.-180° C., and the heating time is 16 h-28 h; In the step 1.4, calcining at 300°C-700°C for 4h-10h at a heating rate of 2-5°C / min; In step 2, alkaline CoMnAlO x -LDO specifically: Step 2.1: CoMnAlO obtained in step 1 x -LDO is dispersed in H2O to obtain a dispersion with a concentration of 5g / L-50g / L; Step 2.2, after ultrasonic treatment, add 0.5 mol / L-4 mol / L NaOH aqueous solution, with the volume ratio of the dispersion to the NaOH solution being 1:1.5, and continue stirring until the solution is uniformly mixed; Step 2.3, transfer the mixed solution to a polytetrafluoroethylene-lined stainless steel reactor and maintain it at 100°C-170°C for 0.5h-6h. After the reaction temperature drops to room temperature, wash the solid sample alternately with deionized water and ethanol; Step 2.4: After washing, the product is placed in a vacuum drying oven and dried under vacuum to obtain alkaline CoMnAlO x -LDO.

2. The method for preparing a catalyst for selective photothermal catalytic reduction denitrification of low-temperature flue gas according to claim 1, characterized in that: In step 2.4, the vacuum drying temperature is 60° C.-120° C., and the time is 16 h-28 h.

3. The method for preparing a catalyst for selective photothermal catalytic reduction denitrification of low-temperature flue gas according to claim 2, characterized in that: In step 3, CeO is prepared x / CoMnAlO x Composite photothermal catalyst, specifically: Step 3.1, alkaline CoMnAlO x -LDO is dispersed in oxygen-free water, and after ultrasonication, stirring is continued to make it dispersed evenly to obtain a dispersion liquid; Step 3.2, add alkaline CoMnAlO x -LDO molar ratio of (2-5): 1 cerium salt, then stir until the solution is mixed evenly, then quickly inject 1mol / L-4mol / L NH3·H2O to make the pH reach 8-9 and continue stirring for 5-10min; Step 3.3, the mixed solution was centrifuged, and after the centrifugation, it was placed in an oven for drying. Finally, the dried and ground sample was placed in a muffle furnace and calcined in an air atmosphere to obtain CeO x / CoMnAlO x Composite photothermal catalyst.

4. The method for preparing a catalyst for selective photothermal catalytic reduction denitrification of low-temperature flue gas according to claim 3, characterized in that: In the step 3.3, calcination is performed at 300° C.-700° C. for 4 h-10 h at a heating rate of 2-5° C. / min.

5. The method for preparing a catalyst for selective photothermal catalytic reduction denitrification of low-temperature flue gas according to claim 4, characterized in that: Used for selective photothermal catalytic reduction denitrification of low-temperature flue gas.

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