A porous lanthanum-doped manganese-based carbon nitride composite catalyst, its preparation method and application

Abstract

The present invention discloses a porous lanthanum-doped manganese-based carbon nitride composite catalyst, its preparation method and application, belonging to the field of catalyst preparation. The present invention combines the sol-gel method and the polymerization reaction method to prepare a porous lanthanum-doped manganese-based carbon nitride composite catalyst. Among them, lanthanum-doped manganese tetroxide is the active oxide, and porous carbon nitride is the carrier. The porous structure is generated in-situ during the high-temperature thermal decomposition reaction. At the same time, the reducing atmosphere will cause rich oxygen vacancies and surface defects on the catalyst surface, ensuring that the catalyst has high-efficiency catalytic oxidation performance for CO. This method has a simple process flow and low equipment requirements, and has good application prospects in the treatment of CO in flue gas.

Description

Technical Field

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

[0002] CO is the most abundant and widely distributed pollutant among all air pollutants. Regarding the purification of CO in flue gas, low-temperature CO catalytic oxidation catalysts are divided into noble metal catalysts and non-noble metal catalysts. As the earliest applied catalysts, noble metals have excellent catalytic performance and usually have better performance than non-noble metal catalysts. Therefore, they are an important direction for designing and developing high-performance low-temperature CO catalytic oxidation catalysts. However, noble metals have high costs and problems such as easy poisoning, which limit their further practical applications. Non-noble metal oxide catalysts such as Co, Mn, Ce, and Cu have attracted extensive attention due to their large reserves and low prices. In recent years, researchers have regulated the morphology, grain size, surface dispersion state, and loading amount of noble metals, and carried out extensive research on loading them on carriers such as Al2O3, TiO2, ZrO2, and SiO2.

[0003] Graphitic carbon nitride (g-C3N4) is a two-dimensional non-metallic semiconductor. Due to its excellent thermal stability, chemical stability, high temperature resistance, and acid and alkali resistance, it has attracted extensive attention. 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. Currently, there are few reports on preparing CO catalytic oxidation catalysts using g-C3N4 as a carrier.

[0004] Therefore, the development of an efficient and stable CO catalytic oxidation catalyst using carbon nitride as a carrier provides a new path for expanding CO treatment. Summary of the Invention

[0005] To provide an efficient and stable CO catalytic oxidation catalyst, the purpose of the present invention is to provide a porous lanthanum-doped manganese-based carbon nitride composite catalyst, a preparation method thereof, and an application thereof. The composite catalyst uses porous carbon nitride as a carrier, and combines the sol-gel method and polymerization reaction. First, a lanthanum-manganese-organic polymer precursor is synthesized, and then a porous lanthanum-doped manganese-based carbon nitride composite catalyst with a porous structure is prepared by high-temperature heat treatment. The catalyst has high-efficiency CO removal performance at low temperature conditions and also shows good water resistance.

[0006] Technical Solution: A preparation method of a porous lanthanum-doped manganese-based carbon nitride composite catalyst includes the following steps:

[0007] Step (1): Add a certain amount of lanthanum salt, manganese salt, citric acid, and organic monomers into an alcohol solvent, and stir evenly to obtain a mixed solution;

[0008] Step (2): React the mixed solution under stirring at a certain temperature for a period of time, then centrifuge, wash, and dry to obtain a lanthanum-manganese-citric acid gel-resin composite precursor;

[0009] Step (3): Pyrolyze the lanthanum-manganese-citric acid gel-resin composite precursor at a high temperature to obtain a porous lanthanum-doped manganese-based carbon nitride composite catalyst.

[0010] Preferably, the lanthanum salt in step (1) is lanthanum acetate, the manganese salt is manganese acetate, and the organic monomers are a mixture of melamine and hexamethylenetetramine.

[0011] 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.

[0012] Preferably, in step (1), the alcohol solvent is methanol or ethanol.

[0013] Preferably, the reaction temperature in step (2) is 50 - 100 °C, and the time is 20 - 50 hours.

[0014] Preferably, the lanthanum-manganese-citric acid gel-resin composite precursor obtained in step (2) is composed of a lanthanum-manganese-citric acid gel and a melamine resin.

[0015] Preferably, the high-temperature pyrolysis temperature in step (3) is 400 - 600 °C, the pyrolysis atmosphere is nitrogen, and the time is 1.5 - 5 hours.

[0016] In the lanthanum-doped manganese-based carbon nitride composite catalyst prepared by the method of the present invention, lanthanum-doped manganese tetroxide is compounded in the graphitized carbon nitride (g-C3N4) structure. The catalyst has a porous structure and exposes a large number of oxygen vacancies; among them, lanthanum-doped manganese tetroxide is the active oxide, porous carbon nitride is the carrier, and the active oxide is uniformly dispersed in the porous carbon nitride carrier structure.

[0017] 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 applied, preferably, the initial concentration of CO is 20000 ppm, the O2 concentration is 2 - 3%, 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 range is 80 - 200 °C.

[0018] Beneficial effects:

[0019] Compared with the prior art, the present invention combines the sol-gel method and the organic polymerization reaction method. By in-situ inorganic and organic polymerization growth, lanthanum manganese citrate gel and melamine resin are synthesized. Taking these as precursors, through high-temperature heat treatment, during the high-temperature pyrolysis process of lanthanum manganese citrate gel and melamine resin, the lanthanum manganese citrate gel decomposes to generate lanthanum-doped manganese tetroxide, and at the same time, the melamine resin in-situ decomposes at high temperature to generate porous graphitized carbon nitride (g-C3N4), and a lanthanum-doped manganese-based carbon nitride composite catalyst is prepared, with lanthanum-doped manganese tetroxide uniformly dispersed in the porous carbon nitride structure.

[0020] The catalyst prepared by the present invention forms a strong interaction between the carrier and the active oxide. This catalyst is a composite material with lanthanum-doped manganese tetroxide as the active oxide and porous carbon nitride as the carrier, having a high specific surface area and a porous structure, exposing a large number of oxygen vacancy active sites and surface and interface defects, and the active oxide is uniformly dispersed in the structure of the porous carrier, and can exhibit high-efficiency catalytic oxidation of CO performance under lower temperature conditions. At the same time, the active oxide is stably dissolved in the porous carrier, making the catalyst show good stability.

[0021] In addition, the raw materials used in the present invention are cheap, and the catalyst preparation process is simple. This composite catalyst shows high-efficiency CO removal performance under complex flue gas conditions and has broad application prospects in the field of flue gas treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a CO removal efficiency diagram of the lanthanum-doped manganese-based carbon nitride composite catalyst prepared under different conditions in the examples and comparative examples of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] The technical solution of the present invention will be described in detail below through examples, but the protection scope of the present invention is not limited to the described examples.

[0024] The test methods described in the following examples are all conventional methods unless otherwise specified; the reagents and materials, unless otherwise specified, can be obtained from commercial channels.

[0025] Example 1

[0026] (1) Weigh 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 and add them to 80 mL of ethanol, stir and disperse evenly to obtain a mixed solution 1. The molar ratio of added La, Mn, citric acid, melamine, and hexamethylenetetramine is 0.06:1:0.6:5.5:1.2;

[0027] (2) React the mixture 1 at 60 °C for 48 hours, naturally cool it to room temperature, centrifuge, wash, and dry to obtain the lanthanum-manganese-citric acid gel-resin composite precursor A.

[0028] (3) Treat the lanthanum-manganese-citric acid gel-resin composite precursor A at 450 °C for 4 hours under a nitrogen atmosphere to obtain the porous lanthanum-doped manganese-based carbon nitride composite catalyst A, and measure its surface area to be 251 m 2 / g and the pore volume to be 0.72 cm 3 / g.

[0029] (4) Test the CO removal performance. The initial concentration of CO is 20,000 ppm, the O2 concentration is 3%, and the space velocity is 10,000 h -1 , and the CO removal efficiency of the porous lanthanum-doped manganese-based carbon nitride composite catalyst A is 99.1 - 100% in the range of 130 - 200 °C. The CO removal efficiency of this catalyst is as Figure 1 shown.

[0030] Example 2

[0031] (1) Weigh 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 and add them to 80 mL of ethanol, stir and disperse evenly to obtain the mixture 1. The molar ratio of La, Mn, citric acid, melamine, and hexamethylenetetramine added is 0.08:1:0.8:8:2;

[0032] (2) React the mixture 1 at 90 °C for 24 hours, naturally cool it to room temperature, centrifuge, wash, and dry to obtain the lanthanum-manganese-citric acid gel-resin composite precursor B.

[0033] (3) Treat the lanthanum-manganese-citric acid gel-resin composite precursor B at 500 °C for 3 hours under a nitrogen atmosphere to obtain the porous lanthanum-doped manganese-based carbon nitride composite catalyst B, and measure its surface area to be 269 m 2 / g and the pore volume to be 0.85 cm 3 / g.

[0034] (4) Test the CO removal performance. The initial concentration of CO is 20,000 ppm, the O2 concentration is 2.5%, and the space velocity is 10,000 h -1 , and the CO removal efficiency of the porous lanthanum-doped manganese-based carbon nitride composite catalyst B is 99.2 - 100% in the range of 120 - 200 °C. The CO removal efficiency of this catalyst is as Figure 1 shown.

[0035] Example 3

[0036] (1) Weigh 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, add them to 80 mL of ethanol, stir and disperse evenly to obtain mixture 1. The molar ratio of La, Mn, citric acid, melamine to hexamethylenetetramine added is 0.09:1:0.7:15:2.5;

[0037] (2) React mixture 1 at 80 °C for 30 hours, naturally cool to room temperature, centrifuge, wash and dry to obtain the lanthanum-manganese-citric acid gel-resin composite precursor C.

[0038] (3) Treat the lanthanum-manganese-citric acid gel-resin composite precursor C at 550 °C for 2 hours under a nitrogen atmosphere to obtain the porous lanthanum-doped manganese-based carbon nitride composite catalyst C. The measured surface area is 243 m 2 / g, and the pore volume is 0.71 cm 3 / g.

[0039] (4) Test the CO removal performance. The initial concentration of CO is 20,000 ppm, the O2 concentration is 2.5%, and the space velocity is 10,000 h -1 , and the CO removal efficiency of the porous lanthanum-doped manganese-based carbon nitride composite catalyst C is 99.3 - 100% in the range of 140 - 200 °C. The CO removal efficiency of this catalyst is as Figure 1 shown.

[0040] Example 4

[0041] (1) Weigh 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, add them to 80 mL of ethanol, stir and disperse evenly to obtain mixture 1. The molar ratio of La, Mn, citric acid, melamine to hexamethylenetetramine added is 0.09:1:0.9:19:2.8;

[0042] (2) React mixture 1 at 75 °C for 36 hours, naturally cool to room temperature, centrifuge, wash and dry to obtain the lanthanum-manganese-citric acid gel-resin composite precursor D.

[0043] (3) Treat the lanthanum-manganese-citric acid gel-resin composite precursor D at 550 °C for 2.5 hours under a nitrogen atmosphere to obtain the porous lanthanum-doped manganese-based carbon nitride composite catalyst D. The measured surface area is 261 m 2 / g, and the pore volume is 0.79 cm 3 / g.

[0044] (4) Test the CO removal performance. The initial concentration of CO is 20,000 ppm, the O2 concentration is 2.5%, and the space velocity is 10,000 h -1, the CO removal efficiency of the porous lanthanum-doped manganese-based carbon nitride composite catalyst D is 99.5 - 100% in the range of 130 - 200 °C, and the efficiency of this catalyst for removing CO is as Figure 1 shown.

[0045] Comparative Example 1

[0046] (1) Weigh 0.19 g of lanthanum acetate, 1.73 g of manganese acetate and 6.93 g of melamine, add them to 80 mL of ethanol, stir and disperse evenly to obtain a mixed solution 1. The molar ratio of La, Mn and melamine added is 0.06:1:5.5;

[0047] (2) React the mixed solution 1 at 60 °C for 48 hours, naturally cool to room temperature, centrifuge, wash and dry to obtain the lanthanum-manganese-melamine precursor A.

[0048] (3) Treat the lanthanum-manganese-melamine precursor A at 450 °C for 4 hours under a nitrogen atmosphere to obtain the lanthanum-doped manganese-based carbon nitride catalyst E. The measured surface area is 47 m 2 / g, and the pore volume is 0.15 cm 3 / g.

[0049] (4) Test the CO removal performance. The initial concentration of CO is 20000 ppm, the concentration of O2 is 3%, and the space velocity is 10000 h -1 . The CO removal efficiency of the lanthanum-doped manganese-based carbon nitride catalyst E is 69.3 - 75% in the range of 190 - 200 °C, and the efficiency of this catalyst for removing CO is as Figure 1 shown.

[0050] In summary, the present invention combines the sol-gel method and the polymerization reaction method to synthesize a precursor material, and through a high-temperature heat treatment process, a porous structure metal composite is prepared. Specifically, the porous composite catalyst with a high specific surface prepared in Examples 1 - 4 has a structure and shows an efficient CO removal effect at a lower temperature, and has a good application prospect.

[0051] As described above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as a limitation of the present invention itself. Various changes can be made to it in form and detail 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; 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; the molar ratio of lanthanum, manganese, citric acid, melamine and hexamethylenetetramine is 0.05-0.1:1:0.5-1:5-19:1-3.

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

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

4. 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.

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

6. A porous lanthanum-doped manganese-based carbon nitride composite catalyst prepared by the preparation method according to any one of claims 1 to 5.

7. Application of the porous lanthanum-doped manganese-based carbon nitride composite catalyst prepared by the preparation method according to any one of claims 1 to 5 in removing CO from industrial flue gas.

Images