Cerium dioxide nano-catalyst rich in grain boundary defect and preparation method of cerium dioxide nano-catalyst

Abstract

The invention provides a grain boundary defect-enriched cerium dioxide nano catalyst and a preparation method thereof, and the preparation method comprises the following steps: preparing a cerium salt solution with nitrate radicals, reacting to obtain cerium formate and basic cerium carbonate precursor products, and washing, drying and roasting to obtain the grain boundary defect-enriched cerium dioxide nano catalyst. The cerium dioxide nano-catalyst prepared by the method can form an oxygen vacancy defect, promote the adsorption and activation of O2, form peroxy, superoxide and other active oxygen species, and improve the catalytic oxidation activity. According to the method, the covalence of Ce-O bonds is effectively reduced by destroying the periodicity of CeO2 crystal lattices. The reduction of covalence can weaken the constraint strength that surface lattice oxygen atoms are surrounded by Ce atoms and enhance the release reactivity of the surface lattice oxygen atoms essentially, so that the formation of oxygen deficiency is further promoted, the CeO2 adsorption is enhanced, the activity of activating O2 to form active oxygen for oxidation reaction is enhanced, and the oxidation reaction efficiency is improved. Furthermore, the catalyst has good catalytic performance on toxic and harmful substances such as chlorobenzene, sarin toxic agent simulation agents, CO and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst preparation, and particularly relates to a cerium dioxide nanocatalyst rich in grain boundary defects and a preparation method thereof. Background Art

[0002] Oxide nanomaterials such as cerium oxide (CeO2), as active components or carriers, play a key role in a variety of catalytic applications, including heterogeneous catalysis, photocatalysis, electrocatalysis, and environmental catalysis. Their role in metal-support interactions, as well as their catalytic activity and selectivity, especially in oxidation and hydrogenation reactions, are fundamentally determined by the activity of surface lattice oxygen. Generally speaking, when the binding strength of the oxide lattice to surface lattice oxygen is relatively low, it can promote the tendency of metal-oxide interfacial bonding and adhesion, prompt the release of surface lattice oxygen to form oxygen vacancies, and generate H2O and CO2 in the catalytic cycle, while activating O2 to form reactive oxygen species. Therefore, regulating the activity of surface lattice oxygen is crucial for improving the catalytic performance of oxide nanomaterials. There are various ways to regulate the surface activity of oxide nanomaterials, including adjusting particle size, morphology, and exposed crystal planes, doping transition metals (such as Cu, Co) or rare earth elements (such as La, Sm), and introducing defects (such as oxygen vacancies, strain, and grain boundaries), etc. Although some current methods have made progress in regulating surface lattice oxygen synthesis and modification, how to synthesize stable metal oxide nanomaterials with a high concentration of defects remains a difficult point in research.

[0003] Therefore, it is crucial to design a material preparation system starting from the intrinsic physical and chemical mechanisms that drive the intrinsic activity of oxide nanomaterials and develop CeO2 nanometal oxide materials rich in defects. Highly active CeO2 is of great significance in national defense and civilian applications, such as in the fields of eliminating toxic agents, volatile organic compounds, and industrial toxic and harmful gases. Summary of the Invention

[0004] (1) Technical Problems to be Solved

[0005] The present invention proposes a cerium dioxide nanocatalyst rich in grain boundary defects and a preparation method thereof to solve the technical problem of preparing stable cerium dioxide nanomaterials with a high concentration of defects.

[0006] (2) Technical Solutions

[0007] To solve the above technical problems, the present invention proposes a preparation method for a cerium dioxide nanocatalyst rich in grain boundary defects. This preparation method for the nanocatalyst includes the following steps:

[0008] S1. Add 5 - 40 g of cerium salt into 30 - 100 mL of ethylene glycol and 0 - 10 mL of deionized water, stir and dissolve at room temperature for 5 - 200 min, then add 0 - 50 g of sodium nitrate, stir and dissolve at room temperature for 5 - 30 min to obtain a cerium salt solution with nitrate ions; wherein, the cerium salt is cerium nitrate, cerium chloride or cerium sulfate;

[0009] S2. Place the cerium salt solution with nitrate ions in a reaction kettle, and obtain a precursor product of cerium formate and basic cerium carbonate after reaction;

[0010] S3. Wash the precursor product with deionized water and ethanol in sequence; after vacuum drying, calcine the product in an air atmosphere to obtain a cerium dioxide nanocatalyst with rich grain boundary defects.

[0011] Further, in step S1, the molar ratio of cerium ions to nitrate ions in the cerium salt solution with nitrate ions is (1:6) - (1:3).

[0012] Further, in step S2, react in the reaction kettle at 140 - 220 °C for 4 - 24 hours.

[0013] Further, in step S3, wash the precursor product with 10 - 50 mL of deionized water and 10 - 50 mL of ethanol in sequence for 3 - 6 times; vacuum dry at 50 - 120 °C for 3 - 12 hours; after drying, calcine the product in an air atmosphere, the calcination temperature is 300 - 700 °C, the heating rate is 5 - 30 °C / min, and the calcination time is 1 - 6 hours to obtain a cerium dioxide nanocatalyst with rich grain boundary defects.

[0014] In addition, the present invention also provides a cerium dioxide nanocatalyst with rich grain boundary defects, which is prepared by the above method.

[0015] (III) Beneficial effects

[0016] The present invention provides a cerium dioxide nanocatalyst with rich grain boundary defects and a preparation method thereof, including preparing a cerium salt solution with nitrate ions, reacting to obtain a cerium formate and basic cerium carbonate precursor product, and after washing, drying, and calcining, obtaining a cerium dioxide nanocatalyst with rich grain boundary defects. The cerium dioxide nanocatalyst prepared by this method can form oxygen vacancy defects, promote the adsorption and activation of O2, form reactive oxygen species such as peroxide and superoxide, and enhance the catalytic oxidation activity. This method effectively reduces the covalency of the Ce-O bond by destroying the periodicity of the CeO2 lattice. The reduction of covalency can weaken the binding strength of surface lattice oxygen atoms surrounded by Ce atoms, essentially enhancing their release reactivity. The above effects further promote the formation of oxygen defects, enhance the activity of CeO2 to adsorb and activate O2 to form reactive oxygen for oxidation reactions, and thus exhibit good catalytic performance for toxic and harmful substances such as chlorobenzene, sarin simulant, and CO. Description of the Drawings

[0017] Figure 1 XRD phase diagram of cerium formate and basic cerium carbonate precursors prepared in Example 1; in the figure, # is the peak of the basic cerium carbonate precursor, and * is the peak of the cerium formate precursor; the abscissa is 2θ, in degrees;

[0018] Figure 2 XRD phase diagram of the cerium dioxide nanocatalyst with rich grain boundary defects prepared in Example 1; in the figure, the abscissa is 2θ, in degrees;

[0019] Figure 3 Transmission electron microscope photograph of cerium formate and basic cerium carbonate precursors prepared in Example 1;

[0020] Figure 4 Transmission electron microscope photograph of the cerium dioxide nanocatalyst with rich grain boundary defects prepared in Example 1;

[0021] Figure 5 High-resolution transmission electron microscope photograph of the cerium dioxide nanocatalyst with rich grain boundary defects prepared in Example 1;

[0022] Figure 6 Protection performance of the cerium dioxide nanocatalyst with rich grain boundary defects prepared in Example 1 against chlorobenzene;

[0023] Figure 7 Protection performance of the cerium dioxide nanocatalyst with rich grain boundary defects prepared in Example 1 against the sarin simulant dimethyl methylphosphonate (DMMP);

[0024] Figure 8 Protection performance of the cerium dioxide nanocatalyst with rich grain boundary defects prepared in Example 1 against CO;

[0025] Figure 9Schematic diagram of the formation process of the cerium dioxide nanomaterial with rich grain boundary defects of the present invention. Specific embodiments

[0026] To make the objectives, content and advantages of the present invention clearer, the following further describes in detail the specific embodiments of the present invention in conjunction with the drawings and embodiments.

[0027] Example 1

[0028] 10 g of Ce(NO3)3·6H2O was added to 30 mL of ethylene glycol and stirred at 25 °C for 180 min to obtain a cerium salt solution with nitrate ions. It was placed in a pressure-resistant reaction kettle and reacted at 180 °C for 6 hours. The product was collected to obtain a cerium formate and basic cerium carbonate precursor. The precursor product was washed 5 times with 20 mL of deionized water and 20 mL of ethanol in sequence; vacuum dried at 60 °C for 8 hours; calcined in an air atmosphere, the calcination temperature was 400 °C, the heating rate was 10 °C / min, and the calcination time was 2 hours to obtain a CeO2 nanocatalyst with rich grain boundary defects.

[0029] The XRD patterns of the cerium formate and basic cerium carbonate precursors prepared in this example are as Figure 1 shown. Characteristic peaks of cerium formate and basic cerium carbonate appear on the phase diagram. The XRD pattern of the CeO2 nanocatalyst with rich grain boundary defects is as Figure 2 shown. It can be seen from the figure that the CeO2 nanocatalyst was successfully prepared. The relatively wide diffraction peaks indicate that CeO2 has extremely small grain sizes. The microscopic morphologies of the cerium formate and basic cerium carbonate precursors are as Figure 3 shown. The morphology is nanorods with a diameter of about 20 nanometers. The microscopic morphology of the CeO2 nanocatalyst with rich grain boundary defects is as Figure 4 shown. The CeO2 nanocatalyst with rich grain boundary defects obtained after calcination of the precursor is a nanoporous nanorod morphology and is composed of polycrystalline nanoparticles. The high-resolution transmission electron microscopy image of the CeO2 nanocatalyst with rich grain boundary defects is as Figure 5 shown. It can be seen from the figure that the grain size is 3 - 6 nm and the lattice orientation is significantly misaligned, confirming the existence of grain boundary defects.

[0030] Example 2

[0031] 5 g of Ce(NO3)3·6H2O was added to a mixed solvent of 30 mL of ethylene glycol and 2 mL of water, and stirred at 25 °C for 30 min to dissolve. Then 3 g of sodium nitrate was added and stirred at 25 °C for 20 min to dissolve, obtaining a cerium salt solution with nitrate ions. It was placed in a pressure-resistant reaction kettle and reacted at 180 °C for 6 hours to obtain a precursor product of cerium formate and basic cerium carbonate. The precursor product was washed 5 times successively with 20 mL of deionized water and 20 mL of ethanol; vacuum dried at 60 °C for 8 hours; calcined in an air atmosphere, the calcination temperature was 400 °C, the heating rate was 10 °C / min, and the calcination time was 2 hours, obtaining a CeO2 nanocatalyst rich in grain boundary defects.

[0032] Example 3

[0033] 10 g of CeCl3·7H2O was added to a mixed solvent of 30 mL of ethylene glycol and 2 mL of water, and stirred at 25 °C for 20 min to dissolve. Then 5 g of sodium nitrate was added and stirred at 25 °C for 20 min to dissolve, obtaining a cerium salt solution with nitrate ions. It was placed in a pressure-resistant reaction kettle and reacted at 180 °C for 8 hours to obtain a precursor product of cerium formate and basic cerium carbonate. The precursor product was washed 5 times successively with 20 mL of deionized water and 20 mL of ethanol; vacuum dried at 60 °C for 8 hours; calcined in an air atmosphere, the calcination temperature was 400 °C, the heating rate was 10 °C / min, and the calcination time was 2 hours, obtaining a CeO2 nanocatalyst rich in grain boundary defects.

[0034] To verify the catalytic performance of the catalyst prepared by the present invention, the catalytic performances of the CeO2 nanocatalyst rich in grain boundary defects prepared in Example 1 for chlorobenzene ( Figure 6 ), DMMP ( Figure 7 ), and CO ( Figure 8 ) were respectively tested. At a chlorobenzene concentration of 1000 ppm, an airspeed of 10000 h -1 , and a catalytic temperature of 300 °C, the protection time with a chlorobenzene conversion rate of more than 90% was 150 min; at a DMMP concentration of 5.6 g / m 3 , an airspeed of 6000 h -1 , and a catalytic temperature of 400 °C, the protection time with a DMMP conversion rate of more than 99% was 800 min; at a CO concentration of 2500 ppm, an airspeed of 10000 h -1 , and a catalytic temperature of 250 °C, the protection time with a CO conversion rate of 100% was more than 700 min. Through the above tests, it can be seen that the CeO2 nanocatalyst rich in grain boundary defects prepared by the present invention shows good elimination performance for the three pollutants.

[0035] The structural formation process of the CeO2 nanocatalyst rich in grain boundary defects prepared by the present invention is as Figure 9As shown, in the cerium salt solution with nitrate in ethylene glycol solution, ethylene glycol is oxidized by nitrate at 140-220°C to generate cerium formate and basic cerium carbonate precursors. The precursors are calcined to release carbon dioxide, and the original precursor structure partially collapses and decomposes to form CeO2 nanorods rich in grain boundary defects. This structural adjustment method can reduce the covalency of the Ce-O bond, thereby weakening the lattice binding of surface atoms, which in turn leads to an increase in the activity of surface oxygen atoms to leave the lattice, promotes the formation of oxygen vacancies, and further promotes the adsorption and activation of O2. These changes can ultimately enhance the catalytic reaction activity of catalytic oxidation of toxic and harmful pollutants such as chlorobenzene, DMMP and CO.

[0036] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A preparation method of a cerium dioxide nanocatalyst rich in grain boundary defects, characterized in that, The method for preparing the nano-catalyst comprises the following steps: S1. Add 5 - 40 g of cerium salt into 30 - 100 mL of ethylene glycol and 0 - 10 mL of deionized water, stir and dissolve at room temperature for 5 - 200 min, then add 0 - 50 g of sodium nitrate, stir and dissolve at room temperature for 5 - 30 min to obtain a cerium salt solution with nitrate ions; wherein, the cerium salt is cerium nitrate, cerium chloride or cerium sulfate; S2. Place the cerium salt solution with nitrate ions in a reaction kettle, and obtain a precursor product of cerium formate and basic cerium carbonate after the reaction; S3. Wash the precursor product successively with deionized water and ethanol; after vacuum drying, calcine the product in an air atmosphere to obtain a cerium dioxide nano-catalyst with rich grain boundary defects.

2. The preparation method of the cerium dioxide nanocatalyst rich in grain boundary defects according to claim 1, wherein, In step S1, the molar ratio of cerium ions to nitrate ions in the cerium salt solution with nitrate ions is (1:6) - (1:3).

3. The preparation method of the cerium dioxide nanocatalyst rich in grain boundary defects according to claim 1, characterized in that, In step S2, react in the reaction kettle at 140 - 220 °C for 4 - 24 hours.

4. The preparation method of the cerium dioxide nanocatalyst rich in grain boundary defects according to claim 1, wherein, In step S3, wash the precursor product successively with 10 - 50 mL of deionized water and 10 - 50 mL of ethanol for 3 - 6 times; vacuum dry at 50 - 120 °C for 3 - 12 hours; after drying, calcine the product in an air atmosphere, the calcination temperature is 300 - 700 °C, the heating rate is 5 - 30 °C / min, and the calcination time is 1 - 6 hours to obtain a cerium dioxide nano-catalyst with rich grain boundary defects.

5. A cerium dioxide nanocatalyst rich in grain boundary defects, characterized in that, The cerium dioxide nano-catalyst with rich grain boundary defects is prepared by the method described in any one of claims 1 - 4.

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