Porous lanthanum-doped manganese-based carbon nitride composite catalyst as well as preparation method and application thereof

Abstract

The invention discloses a porous lanthanum-doped manganese-based carbon nitride composite catalyst as well as a preparation method and application thereof, and belongs to the field of catalyst preparation. The lanthanum-doped manganese-based carbon nitride composite catalyst with a porous structure is prepared by adopting a method of combining a sol-gel method and a polymerization reaction method, lanthanum-doped manganous-manganic oxide is an active oxide, porous carbon nitride is a carrier, the porous structure is generated in situ in a high-temperature thermal decomposition reaction process, and the lanthanum-doped manganese-based carbon nitride composite catalyst is prepared. Meanwhile, rich oxygen vacancies and surface defects can be generated on the surface of the catalyst through the reducing atmosphere, it is guaranteed that the catalyst has efficient CO catalytic oxidation performance, and the method is simple in technological process and low in equipment requirement and has a good application prospect in CO treatment through flue gas.

Description

Technical Field

[0001] The invention belongs to the field of catalyst preparation, and specifically relates to a porous lanthanum-doped manganese-based carbon nitride composite catalyst and a preparation method and application thereof. Background Art

[0002] CO is the largest and most widely distributed pollutant among all air pollutants. Focusing on the purification of CO in flue gas, low-temperature CO catalytic oxidation catalysts are divided into precious metal catalysts and non-precious metal catalysts. As the earliest catalyst to be used, precious metals have excellent catalytic performance and usually have better performance than non-precious metal catalysts. Therefore, they are an important direction for the design and development of high-performance CO low-temperature catalytic oxidation catalysts. However, precious metals have high costs and are prone to poisoning, which limits their further practical application. Non-precious metal oxide catalysts such as Co, Mn, Ce, and Cu have attracted widespread attention due to their large reserves and low prices. In recent years, focusing on the regulation of active substances and the controllable preparation of carriers, researchers have regulated the morphology, grain size, surface dispersion state, and loading amount of precious metals, and carried out extensive research on them on carriers such as Al2O3, TiO2, ZrO2, and SiO2.

[0003] Graphitic carbon nitride (g-C3N4) is a two-dimensional non-metallic semiconductor. It has attracted widespread attention due to its excellent thermal and chemical stability, high temperature resistance and acid and alkali resistance. g-C3N4 can not only enrich the CO catalytic oxidation catalyst system, but also has important practical significance for expanding the application of catalytic materials. At present, there are few reports on the preparation of CO catalytic oxidation catalysts using g-C3N4 as a carrier.

[0004] Therefore, the development of efficient and stable CO catalytic oxidation catalysts with carbon nitride as the carrier provides a new path to expand CO treatment. Summary of the invention

[0005] In order to provide an efficient and stable CO catalytic oxidation catalyst, the present invention provides a porous lanthanum-doped manganese-based carbon nitride composite catalyst and a preparation method and application thereof. The composite catalyst uses porous carbon nitride as a carrier, adopts a sol-gel method and a polymerization reaction combination method, first synthesizes a lanthanum manganese-organic polymer precursor, and then prepares a lanthanum-doped manganese-based carbon nitride composite catalyst with a porous structure by high-temperature heat treatment. The catalyst has efficient CO removal performance under relatively low temperature conditions and exhibits good water resistance.

[0006] Technical solution: A method for preparing a porous lanthanum-doped manganese-based carbon nitride composite catalyst, comprising the following steps: Step (1), adding a certain amount of lanthanum salt, manganese salt, citric acid and organic monomer into an alcohol solvent, stirring evenly to obtain a mixed solution; Step (2), reacting the mixed solution under stirring conditions at a certain temperature for a period of time, and then centrifuging, washing, and drying to obtain a lanthanum manganese citrate gel-resin composite precursor; Step (3), pyrolyzing the lanthanum manganese citrate gel-resin composite precursor at high temperature to obtain a porous lanthanum-doped manganese-based carbon nitride composite catalyst.

[0007] Preferably, the lanthanum salt in step (1) is lanthanum acetate, the manganese salt is manganese acetate, and the organic monomer is a mixture of melamine and hexamethylenetetramine.

[0008] Preferably, in step (1), the molar ratio of lanthanum, manganese, citric acid, melamine and hexamethylenetetramine is 0.05-0.1:1:0.5-1:5-19:1-3.

[0009] Preferably, in step (1), the alcohol solvent is methanol or ethanol.

[0010] Preferably, in step (2), the reaction temperature is 50-100° C. and the reaction time is 20-50 hours.

[0011] Preferably, the lanthanum manganese citrate gel-resin composite precursor obtained in step (2) is a composite of lanthanum manganese citrate gel and melamine resin.

[0012] Preferably, in step (3), the high temperature pyrolysis temperature is 400-600°C, the pyrolysis atmosphere is nitrogen, and the time is 1.5-5 hours.

[0013] In the lanthanum-doped manganese-based carbon nitride composite catalyst prepared by the method of the present invention, lanthanum-doped manganese tetraoxide is composited in a graphitized carbon nitride (g-C3N4) structure, and the catalyst has a porous structure and exposes a large number of oxygen vacancies; wherein, lanthanum-doped manganese tetraoxide is an active oxide, porous carbon nitride is a carrier, and the active oxide is uniformly dispersed in the porous carbon nitride carrier structure.

[0014] The lanthanum-doped manganese-based carbon nitride composite catalyst prepared by the method of the present invention can be used to remove CO from industrial flue gas. When used, preferably, the initial concentration of CO is 20000 ppm, the concentration of O2 is 2-3%, and the space velocity is 10000 h -1 The particle size of the lanthanum-doped manganese-based carbon nitride composite catalyst is 20-40 mesh, and the reaction temperature ranges from 80-200°C.

[0015] Beneficial effects: Compared with the prior art, the present invention combines the sol-gel method with the organic polymerization reaction method, synthesizes lanthanum manganese citrate gel and melamine resin by in-situ inorganic and organic polymerization growth, and uses them as precursors. After high-temperature heat treatment, the lanthanum manganese citrate gel and melamine resin are pyrolyzed at high temperature. The lanthanum manganese citrate gel decomposes to generate lanthanum-doped manganese tetraoxide, and the melamine resin decomposes at high temperature in situ to generate porous graphitized carbon nitride (g-C3N4), so as to prepare a lanthanum-doped manganese-based carbon nitride composite catalyst, and the lanthanum-doped manganese tetraoxide is uniformly dispersed in the porous carbon nitride structure.

[0016] The catalyst prepared by the present invention forms a strong interaction with the active oxide through the carrier. The catalyst is a composite material formed by using lanthanum-doped manganese tetraoxide as the active oxide and porous carbon nitride as the carrier. The catalyst has a high specific surface area and a porous structure, exposing a large number of oxygen vacancy active sites and surface and interface defects. The active oxide is uniformly dispersed in the structure of the porous carrier, and can exhibit high-efficiency catalytic oxidation of CO performance under relatively low temperature conditions. At the same time, the active oxide is stably dissolved in the porous carrier, so that the catalyst exhibits good stability.

[0017] In addition, the raw materials used in the present invention are cheap, the catalyst preparation process is simple, and the composite catalyst exhibits efficient CO removal performance under complex flue gas working conditions, and has broad application prospects in the field of flue gas treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Graph showing the CO removal efficiency of the lanthanum-doped manganese-based carbon nitride composite catalyst prepared under different conditions in Example 2 of the present invention. DETAILED DESCRIPTION

[0019] The technical scheme of the present invention is described in detail below through examples, but the protection scope of the present invention is not limited to the examples. The test methods in the following examples are conventional methods unless otherwise specified; the reagents and materials are commercially available unless otherwise specified.

[0020] Example 1: (1) 0.19 g of lanthanum acetate, 1.73 g of manganese acetate, 1.15 g of citric acid, 6.93 g of melamine and 1.68 g of hexamethylenetetramine were weighed and added into 80 mL of ethanol, and stirred to disperse uniformly to obtain a mixed solution 1, wherein the molar ratio of La, Mn, citric acid, melamine and hexamethylenetetramine added was 0.06:1:0.6:5.5:1.2; (2) The mixed solution 1 was reacted at 60° C. for 48 hours, naturally cooled to room temperature, centrifuged, washed, and dried to obtain a lanthanum manganese citrate gel-resin composite precursor A.

[0021] (3) The lanthanum manganese citrate gel-resin composite precursor A was treated at 450°C for 4 hours under nitrogen atmosphere to obtain a porous lanthanum-doped manganese-based carbon nitride composite catalyst A with a measured surface area of ​​251 m 2 / g, pore volume 0.72 cm 3 / g.

[0022] (4) Test the CO removal performance, the initial CO concentration is 20000 ppm, the O2 concentration is 3%, and the space velocity is 10000 h -1 The CO removal efficiency of porous lanthanum-doped manganese-based carbon nitride composite catalyst A in the range of 130-200 °C is 99.1-100%. Figure 1 shown.

[0023] Example 2: (1) 0.25 g of lanthanum acetate, 1.73 g of manganese acetate, 1.54 g of citric acid, 10.08 g of melamine and 2.80 g of hexamethylenetetramine were weighed and added into 80 mL of ethanol, and stirred to disperse uniformly to obtain a mixed solution 1, wherein the molar ratio of La, Mn, citric acid, melamine and hexamethylenetetramine added was 0.08:1:0.8:8:2; (2) The mixed solution 1 is reacted at 90° C. for 24 hours, naturally cooled to room temperature, centrifuged, washed, and dried to obtain a lanthanum manganese citrate gel-resin composite precursor B.

[0024] (3) The lanthanum manganese citrate gel-resin composite precursor B was treated at 500 °C for 3 hours under nitrogen atmosphere to obtain a porous lanthanum-doped manganese-based carbon nitride composite catalyst B with a measured surface area of ​​269 m 2 / g, pore volume 0.85 cm 3 / g.

[0025] (4) Test the CO removal performance, the initial CO concentration is 20000 ppm, the O2 concentration is 2.5%, and the air velocity is 10000 h -1 The CO removal efficiency of porous lanthanum-doped manganese-based carbon nitride composite catalyst B is 99.2-100% in the range of 120-200 °C. Figure 1 shown.

[0026] Example 3: (1) 0.28 g of lanthanum acetate, 1.73 g of manganese acetate, 1.34 g of citric acid, 18.90 g of melamine and 3.50 g of hexamethylenetetramine were weighed and added into 80 mL of ethanol, and stirred to disperse uniformly to obtain a mixed solution 1, wherein the molar ratio of La, Mn, citric acid, melamine and hexamethylenetetramine added was 0.09:1:0.7:15:2.5; (2) The mixed solution 1 was reacted at 80° C. for 30 hours, naturally cooled to room temperature, centrifuged, washed, and dried to obtain a lanthanum manganese citrate gel-resin composite precursor C.

[0027] (3) The lanthanum manganese citrate gel-resin composite precursor C was treated at 550°C for 2 hours under nitrogen atmosphere to obtain a porous lanthanum-doped manganese-based carbon nitride composite catalyst C with a measured surface area of ​​243 m 2 / g, pore volume 0.71 cm 3 / g.

[0028] (4) Test the CO removal performance, the initial CO concentration is 20000 ppm, the O2 concentration is 2.5%, and the air velocity is 10000 h -1 The CO removal efficiency of porous lanthanum-doped manganese-based carbon nitride composite catalyst C is 99.3-100% in the range of 140-200 °C. Figure 1 shown.

[0029] Example 4: (1) 0.28 g of lanthanum acetate, 1.73 g of manganese acetate, 1.73 g of citric acid, 23.94 g of melamine and 3.92 g of hexamethylenetetramine were weighed and added into 80 mL of ethanol, and stirred to disperse uniformly to obtain a mixed solution 1, wherein the molar ratio of La, Mn, citric acid, melamine and hexamethylenetetramine added was 0.09:1:0.9:19:2.8; (2) The mixed solution 1 was reacted at 75° C. for 36 hours, naturally cooled to room temperature, centrifuged, washed, and dried to obtain a lanthanum manganese citrate gel-resin composite precursor D.

[0030] (3) The lanthanum manganese citrate gel-resin composite precursor D was treated at 550°C for 2.5 hours under nitrogen atmosphere to obtain a porous lanthanum-doped manganese-based carbon nitride composite catalyst D with a measured surface area of ​​261 m 2 / g, pore volume 0.79 cm 3 / g.

[0031] (4) Test the CO removal performance, the initial CO concentration is 20000 ppm, the O2 concentration is 2.5%, and the air velocity is 10000 h -1 The CO removal efficiency of porous lanthanum-doped manganese-based carbon nitride composite catalyst D is 99.5-100% in the range of 130-200 °C. Figure 1 shown.

[0032] Comparative Example 1 (1) Weigh 0.19 g of lanthanum acetate, 1.73 g of manganese acetate and 6.93 g of melamine into 80 mL of ethanol, stir and disperse evenly to obtain a mixed solution 1, wherein the molar ratio of La, Mn and melamine added is 0.06:1:5.5; (2) The mixed solution 1 is reacted at 60° C. for 48 hours, naturally cooled to room temperature, centrifuged, washed, and dried to obtain a lanthanum manganese-melamine precursor A.

[0033] (3) The lanthanum-manganese-melamine precursor A was treated at 450 °C for 4 hours under nitrogen atmosphere to obtain a lanthanum-doped manganese-based carbon nitride catalyst E with a measured surface area of ​​47 m 2 / g, pore volume 0.15 cm 3 / g.

[0034] (4) Test the CO removal performance, the initial CO concentration is 20000 ppm, the O2 concentration is 3%, and the space velocity is 10000 h -1 The CO removal efficiency of the lanthanum-doped manganese-based carbon nitride catalyst E in the range of 190-200 °C is 69.3-75%. Figure 1 shown.

[0035] In summary, the present invention adopts a method combining a sol-gel method and a polymerization reaction method to synthesize a precursor material, and prepares a porous structure metal composite through a high-temperature heat treatment process. Specifically, as shown in Examples 1-4, a porous composite catalyst with a high specific surface area is prepared, which exhibits an efficient CO removal effect at a relatively low temperature and has good application prospects.

[0036] As described above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the present invention itself. Various changes in form and details may be made without departing from the spirit and scope of the present invention.

Claims

1. A method for preparing a porous lanthanum-doped manganese-based carbon nitride composite catalyst, characterized in that: The following steps are involved: Step (1), adding a certain amount of lanthanum salt, manganese salt, citric acid and organic monomer into an alcohol solvent, stirring evenly to obtain a mixed solution; Step (2), reacting the mixed solution under stirring conditions at a certain temperature for a period of time, and then centrifuging, washing, and drying to obtain a lanthanum manganese citrate gel-resin composite precursor; Step (3), pyrolyzing the lanthanum manganese citrate gel-resin composite precursor at high temperature to obtain a porous lanthanum-doped manganese-based carbon nitride composite catalyst.

2. The preparation method according to claim 1, characterized in that: The lanthanum salt in step (1) is lanthanum acetate, the manganese salt is manganese acetate, and the organic monomer is a mixture of melamine and hexamethylenetetramine.

3. The preparation method according to claim 2, characterized in that: In step (1), the molar ratio of lanthanum, manganese, citric acid, melamine and hexamethylenetetramine is 0.05-0.1: 1: 0.5-1: 5-19: 1-3.

4. The preparation method according to claim 1, characterized in that: In step (1), the alcohol solvent is methanol or ethanol.

5. The preparation method according to claim 1, characterized in that: In step (2), the reaction temperature is 50-100°C and the reaction time is 20-50 hours.

6. The preparation method according to claim 1, characterized in that: The lanthanum manganese citrate gel-resin composite precursor obtained in step (2) is a composite of lanthanum manganese citrate gel and melamine resin.

7. The preparation method according to claim 1, characterized in that: In step (3), the temperature of high temperature pyrolysis is 400-600°C, the pyrolysis atmosphere is nitrogen, and the time is 1.5-5 hours.

8. A porous lanthanum-doped manganese-based carbon nitride composite catalyst prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the porous lanthanum-doped manganese-based carbon nitride composite catalyst prepared by the preparation method according to any one of claims 1 to 7 in removing CO from industrial flue gas.

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