Core-shell structure CeO2 (at) mSiO2 (at) Ni2P catalyst as well as preparation method and application thereof

Abstract

The invention discloses a CeO2 (at) mSiO2 (at) Ni2P catalyst with a core-shell structure as well as a preparation method and application of the CeO2 (at) mSiO2 (at) Ni2P catalyst. CeO2 is taken as a core and is coated with a mesoporous silica layer, and the outermost layer is subjected to phosphating treatment to form a Ni2P active phase, so that the composite catalyst with a core-shell structure is formed. The catalyst is prepared through the steps of a hydrothermal method, a template method, dipping precipitation, phosphating reduction and the like, and has a high specific surface area, a rich pore structure and highly dispersed active sites. In catalytic elimination of chlorine-containing volatile organic compounds such as chlorobenzene, the catalyst shows high catalytic activity, excellent deep mineralization efficiency and outstanding chlorine poisoning resistance stability through a series reduction-oxidation reaction path, and efficient conversion and degradation of chlorobenzene can be realized at a relatively low temperature.

Description

Technical Field

[0001] This invention belongs to the field of catalyst materials technology, specifically relating to a core-shell structured catalyst and its preparation method, as well as the application of the catalyst in the tandem reduction and oxidation of chlorine-containing volatile organic compounds. Background Technology

[0002] Volatile organic compounds (VOCs) are a class of harmful pollutants widely found in industrial waste gas, vehicle exhaust, and indoor air, posing significant threats to human health and the ecological environment. Chlorinated volatile organic compounds (CVOCs), such as chlorobenzene and dichloromethane, in particular, are among the most challenging aspects of air pollution control due to their high chemical stability, strong toxicity, and difficulty in degradation.

[0003] Among various CVOCs mitigation technologies, catalytic oxidation is widely used due to its simplicity, maturity, and high purification efficiency. Catalytic oxidation can selectively convert CVOCs into harmless final products, reducing the formation of harmful byproducts. As the core of catalytic oxidation technology, the selection of a superior catalyst for CVOCs removal is crucial. Since noble metal catalysts inherently possess excellent catalytic activity, their performance in CVOCs removal can be further enhanced by rationally adjusting their redox properties. Nickel phosphide catalysts are particularly outstanding in the hydrodechlorination of polychlorinated compounds, with generally higher activity than other phosphides. Supported nickel phosphide is considered a highly promising dechlorination catalyst. Studies have shown that nickel phosphide species possess good hydrogen transfer properties, and hydrogen species overflowing from their surface can further promote the HDC reaction. Cerium oxide-based materials are considered promising catalysts for CVOCs decomposition because they exhibit outstanding redox performance, high activity of CeO2 in CVOCs oxidation, and unique oxygen storage capacity. However, in the oxidation reaction of CVOCs, CeO2 may react with HCl or Cl2 to form metal chlorides, leading to the loss of the active components of the catalyst.

[0004] Existing core-shell catalytic mechanisms are essentially single, direct oxidation pathways, which significantly limit their effectiveness in dealing with more stable and toxic complex pollutants, especially in systems requiring multi-step co-transformation, such as chlorinated volatile organic compounds. Pure oxidation mechanisms lack protective designs for the catalyst itself. When treating chlorinated pollutants, the chlorine species released during the reaction readily combine with metal active sites on the catalyst surface, forming metal chlorides, leading to the loss of active components and structural damage—a condition known as chlorine poisoning. Studies have shown that formaldehyde degradation primarily occurs through direct attack of formaldehyde molecules by oxygen vacancies and reactive oxygen species on the catalyst surface, followed by mineralization into CO2 and H2O via intermediates such as dioxane and formate. This mechanism is effective in degrading simple, halogen-free small-molecule aldehydes because it mainly depends on the abundance and activity of the oxidative active sites. However, for chlorinated organic compounds such as chlorobenzene, their C-Cl bond energy is high and their chemical stability is strong. It is difficult to break the C-Cl bond under mild conditions by relying solely on oxidation mechanisms. This can easily lead to the reaction stopping at the intermediate product stage or even generating more toxic polychlorinated byproducts (Gang Xing, Xuan Liu, Yazhen Jia, et al. Oxygen vacancy-rich K-Mn3O4@CeO2 catalyst for efficient oxidationdegradation of formaldehyde at near room temperature [J]. Journal of ColloidAnd Interface Science, 2025, 677, 417-428.). Summary of the Invention

[0005] The purpose of this invention is to provide a core-shell structured CeO2@mSiO2@Ni2P catalyst and its preparation method, as well as the application of this catalyst in the catalytic reduction and oxidation of CVOCs. Through a rational structural design, this catalyst combines the reducing properties of Ni2P with the oxidizing properties of CeO2, achieving a tandem process of reductive dechlorination and deep oxidation. While maintaining high activity, it significantly improves resistance to chlorine poisoning and reaction stability.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] In a first aspect, the present invention provides a core-shell structure CeO2@mSiO2@Ni2P catalyst, which is a core-shell structure with CeO2 nanoparticles as the core, and sequentially coated with a mesoporous SiO2 (mSiO2) layer and a Ni2P active phase.

[0008] Furthermore, the CeO2 nanoparticles have a particle size of 100-200 nm.

[0009] Furthermore, the thickness of the mSiO2 layer is 300-400 nm.

[0010] Furthermore, the molar ratio of Ni to P in the Ni2P active phase is 1:(0.8-1.2).

[0011] In a second aspect, the present invention provides a method for preparing the catalyst described in the first aspect, comprising the following steps:

[0012] (1) Preparation of CeO2 nanoparticles: CeO2 nanoparticles were prepared by hydrothermal method using cerium nitrate as cerium source, PVP as template agent and ethylene glycol as solvent.

[0013] (2) Preparation of CeO2@mSiO2: Using TEOS as silicon source, CTAB as template and ammonia as catalyst, mSiO2 layer was coated on CeO2 surface by sol-gel method;

[0014] (3) Preparation of CeO2@mSiO2@Ni3(PO4)2: The nickel source and phosphorus source were loaded onto CeO2@mSiO2 by impregnation method, and Ni3(PO4)2 precursor was obtained after drying;

[0015] (4) Preparation of CeO2@mSiO2@Ni2P: The precursor was converted into Ni2P by temperature-programmed phosphating reduction in H2 / Ar atmosphere to obtain the target catalyst.

[0016] Furthermore, in step (1), CeO2 nanoparticles are prepared by hydrothermal reaction at 160°C for 8 hours.

[0017] Furthermore, in step (2), the mass ratio of the template agent CTAB to the silicon source TEOS is 1:(1-2.5), the reaction is carried out under the catalysis of ammonia water for 20-24 hours at room temperature, and CeO2@mSiO2 catalyst is prepared.

[0018] Furthermore, in step (3), the nickel source is nickel nitrate and the phosphorus source is diammonium hydrogen phosphate. Loading is achieved through co-impregnation and solvent evaporation. The molar ratio of Ni to P is 1:(0.8-1.2), and the evaporation temperature is 80-95℃ to prepare CeO2@mSiO2@Ni3(PO4)2 precursor.

[0019] Furthermore, in step (4), in an H2 / Ar atmosphere, the temperature is first raised from room temperature to 100-150℃ at a rate of 3-5℃ / min and held for 1-2 hours to remove physically adsorbed water; then the temperature is raised to 300-500℃ at a rate of 1-3℃ / min; then the temperature is raised to 500-700℃ at a slow rate of 1-2℃ / min, and is kept at this final temperature for 1-3 hours to prepare CeO2@mSiO2@Ni2P catalyst.

[0020] Thirdly, the present invention also provides the application of the catalyst described in the first aspect in the catalytic reduction and oxidation reaction of CVOCs.

[0021] Furthermore, the CVOCs are chlorobenzene, and the catalytic elimination reaction adopts a tandem reduction-oxidation reaction pathway.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] (1) By designing a core-shell structure and introducing the active phase of Ni2P, the reducing property of Ni2P and the oxidizing property of CeO2 are organically combined to construct an efficient reduction-oxidation tandem reaction pathway, thereby achieving efficient and highly selective degradation of chlorobenzene.

[0024] (2) The mesoporous SiO2 layer not only increases the specific surface area and promotes reaction mass transfer, but also acts as a physical barrier to effectively protect CeO2 cores from chlorine poisoning, significantly improving catalyst lifetime.

[0025] (3) Using non-precious metal Ni2P as the main active component, the cost is much lower than that of precious metal catalysts such as Pt and Pd, and it has greater potential for industrial application.

[0026] (4) The preparation process is simple, the parameters are easy to control, and the repeatability is good, making it suitable for large-scale production;

[0027] (5) The catalyst exhibits high activity, high selectivity and long lifespan in the catalytic oxidation of chlorobenzene, and has broad prospects for industrial application. Attached Figure Description

[0028] Figure 1 SEM image of the core-shell structure CeO2@mSiO2@Ni2P catalyst material prepared in the example;

[0029] Figure 2 TEM image of the core-shell structure CeO2@mSiO2@Ni2P catalyst material prepared in the example;

[0030] Figure 3 The XRD pattern of the core-shell structure CeO2@mSiO2@Ni2P catalyst material prepared in the example is shown below.

[0031] Figure 4 XPS spectra of the core-shell structure CeO2@mSiO2@Ni2P catalyst material prepared for the example, including Ni 2p, P 1s, O 1s, Ce 3d;

[0032] Figure 5 The nitrogen adsorption curves of the core-shell structure CeO2@mSiO2@Ni2P catalyst material prepared in the example are shown.

[0033] Figure 6 The performance curves of the CeO2, CeO2@mSiO2, CeO2@mSiO2@Ni2P, and Ni2P / CeO2 catalyst materials prepared in this invention in the catalytic oxidation of chlorobenzene are shown. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the scope of protection of the present invention is not limited to the following embodiments.

[0035] This invention attempts to combine the reducing properties of nickel phosphide catalysts with the oxidizing properties of cerium dioxide catalysts to synthesize a CeO2@mSiO2@Ni2P core-shell structured catalyst, thereby constructing a system for the tandem reduction and oxidation of chlorobenzene to overcome the aforementioned problems. Therefore, a core-shell structured catalyst with highly dispersed active sites, excellent resistance to chlorine poisoning, and good stability is developed.

[0036] The core-shell CeO2@mSiO2@Ni2P catalyst proposed in this invention employs a more advanced tandem reduction-oxidation reaction mechanism: firstly, reductive hydrogenation and dechlorination occur at the Ni2P active site, breaking the C–Cl bond to generate a low-chlorine or chlorine-free intermediate (such as benzene); subsequently, the intermediate migrates to the CeO2 core surface, undergoing deep oxidation under the action of oxygen species, ultimately mineralizing into CO2 and H2O. This stepwise, synergistic mechanism not only improves reaction efficiency but also inhibits the formation of toxic byproducts, thereby achieving complete harmlessness of pollutants.

[0037] Example:

[0038] (1) Preparation of CeO2 nanoparticles: 500 mg Ce(NO3)3·6H2O, 200 mg PVP, 15 mL ethylene glycol and 1 mL ultrapure water were added to a 50 mL polytetrafluoroethylene reactor. After stirring for 30 minutes, the mixture was placed in a 160℃ oven for hydrothermal reaction for 8 hours. After the reaction, the product was collected by centrifugation, washed three times with ethanol, and dried at 60℃ for 12 hours to obtain CeO2 nanoparticles. To facilitate subsequent characterization or application, 1.0 g of the synthesized CeO2 nanoparticles were accurately weighed and placed in a certain amount of anhydrous ethanol. The mixture was then sonicated to ensure thorough dispersion. Subsequently, the suspension was transferred to a 100 mL volumetric flask and diluted to the mark with anhydrous ethanol. The solution was shaken well to obtain an ethanol dispersion of CeO2 nanoparticles with a concentration of 10 mg / mL.

[0039] (2) Preparation of CeO2@mSiO2: 5.0 mL of pre-synthesized CeO2 nanoparticle stock solution was placed in a 250 mL beaker, and 155 mL of anhydrous ethanol, 38 mL of ultrapure water, 200 mg of CTAB, 1.0 mL of ammonia, and 0.5 mL of tetraethyl orthosilicate were added sequentially. The mixture was continuously magnetically stirred at a constant speed for 24 hours at room temperature. During this process, TEOS underwent hydrolysis and condensation reactions in an alkaline environment, and under the guidance of the CTAB micelle template, it self-assembled on the surface of CeO2 nanoparticles to form a silica / surfactant composite shell. After the reaction was completed, the preliminary product was collected by centrifugation (10,000 rpm, 10 minutes) and washed three times with anhydrous ethanol to remove residual ammonia and unreacted organic matter. Subsequently, the product was dried in a vacuum drying oven at 60 °C for 6 hours to obtain a white powder. Finally, the powder was placed in a muffle furnace and heated to 550°C at a rate of 1°C / min under static air atmosphere, and calcined at this temperature for 5 hours to completely remove the CTAB template agent, thereby obtaining CeO2@mSiO2 core-shell nanomaterials with mesoporous structure.

[0040] (3) Preparation of CeO2@mSiO2@Ni3(PO4)2: First, 1.350 g of nickel nitrate hexahydrate was weighed into a beaker, and 15 mL of ultrapure water was added. The mixture was magnetically stirred until completely dissolved, forming a clear green solution. Then, 306 mg of diammonium hydrogen phosphate was added to the solution, and the mixture was sonicated for 10 minutes to disperse it evenly. Under continuous stirring, 30% nitric acid aqueous solution was slowly added dropwise using a dropper until the solution changed from turbid to clear. This clear solution indicated the formation of a soluble nickel-phosphorus precursor complex. Subsequently, CeO2@mSiO2 support, which had been ultrasonically dispersed in 15 mL of ultrapure water, was slowly added to the above clear solution. The entire mixture was continuously stirred in a 60°C water bath and evaporated to dryness to ensure that the active component precursor was uniformly distributed on the surface and in the pores of the support. The resulting wet paste was transferred to a forced-air drying oven and dried overnight at 100°C. The dried solid powder was placed in a muffle furnace and heated to 550°C at a programmed heating rate of 2°C / min under static air atmosphere, and calcined at this temperature for 5 hours. This process decomposes the nickel-phosphorus precursor and transforms it into species such as nickel oxide (Ni2O) and nickel phosphate, while stabilizing the support structure.

[0041] (4) Preparation of CeO2@mSiO2@Ni2P: Temperature-programmed reduction was performed. The calcined sample was placed in a tube furnace and reduced under a mixed H2 / Ar gas flow (e.g., 10% H2, 50 mL / min) according to the following program: the temperature was increased from room temperature to 120 °C at a rate of 5 °C / min and held for 0.5 hours to remove physically adsorbed water; then the temperature was increased from 120 °C to 400 °C at a rate of 2 °C / min; then the temperature was increased from 400 °C to 600 °C at a slow rate of 1 °C / min and held at this final temperature for 2 hours. After the reduction was completed, the sample was cooled to room temperature under H2 atmosphere protection to obtain the final CeO2@mSiO2@Ni2P catalyst.

[0042] Comparative example:

[0043] Mechanically mixed Ni2P / CeO2 catalyst: Physically mixing Ni2P and CeO2 results in a significantly lower activity than the core-shell structure catalyst of this invention, demonstrating the unique advantages of the core-shell structure in constructing tandem reaction interfaces and protecting active centers.

[0044] Characterization and performance testing

[0045] Catalyst characterization: The CeO2@mSiO2@Ni2P catalysts prepared in the examples were characterized by SEM, TEM, XRD, XPS, BET, etc., as shown below. Figures 1 to 5 As shown in the figure. The results indicate that CeO2@mSiO2@Ni2P possesses a regular spherical core-shell structure. Its BET specific surface area reaches 389 m².2 / g, pore volume approximately 0.227 cm³ 3 / g. XPS confirmed that Ni exists in the phosphide state, and CeO2 contains abundant Ce. 3+ Species and oxygen vacancies.

[0046] Performance testing: The catalytic performance of four catalysts (CeO2, CeO2@mSiO2, CeO2@mSiO2@Ni2P, Ni2P / CeO2) on chlorobenzene (500 ppm) was evaluated in a fixed-bed reactor at a space velocity of 120,000 mL·g. -1 ·h -1 The results showed that... Figure 6 As shown, the chlorobenzene degradation curves of pure CeO2 and CeO2@mSiO2 catalysts almost completely overlap, indicating similar activity levels. Their T90 values ​​are both around 400 degrees Celsius. This result directly proves that the mesoporous silica coating layer itself does not possess significant catalytic activity; its main function is structural support and protection, without altering the intrinsic catalytic behavior of CeO2. Furthermore, the degradation rate of the mechanically mixed Ni2P / CeO2 catalyst at 425 degrees Celsius did not even reach 80%, indicating that the direct addition of nickel phosphide affects the intrinsic oxidation capacity of cerium dioxide. The CeO2@mSiO2@Ni2P catalyst significantly improves the degradation rate of chlorobenzene, with a T90 of approximately 345 degrees Celsius, reaching reaction equilibrium at 375 degrees Celsius, where the chlorobenzene degradation rate stabilizes at around 95%. Therefore, the core-shell structure CeO2@mSiO2@Ni2P catalyst exhibits the best reduction-oxidation capacity.

[0047] This invention successfully prepared a CeO2@mSiO2@Ni2P catalyst with a core-shell structure, which exhibited excellent performance in the catalytic oxidation of CVOCs such as chlorobenzene. The reaction conditions were 500 ppm CB and a space velocity of 120,000 mL·g. -1 ·h -1 In an air atmosphere, chlorobenzene molecules first undergo hydrogenation and dechlorination at the Ni2P site to generate benzene. Subsequently, the benzene intermediate is deeply oxidized to CO2 and H2O on the CeO2 core surface. This tandem pathway effectively avoids the formation of polychlorinated byproducts, while the mesoporous SiO2 layer effectively blocks the poisoning of the CeO2 core by chlorine species, thus endowing the catalyst with excellent stability.

Claims

1. A core-shell structured CeO2@mSiO2@Ni2P catalyst, characterized in that, It has a core-shell structure, including: (1) Using CeO2 nanoparticles as the core; (2) A mesoporous silica mSiO2 layer coating CeO2 nanoparticles; (3) Ni2P active phase loaded on the outside of mSiO2 layer and formed by phosphating.

2. The catalyst according to claim 1, characterized in that, The CeO2 nanoparticles have a particle size of 100~200 nm, the mSiO2 layer thickness is 300~400 nm, the Ni2P layer thickness is 20~30 nm, and the catalyst particle size is 700~800 nm.

3. The catalyst according to claim 1 or 2, characterized in that, The molar ratio of Ni to P in the Ni2P active phase is 1:(0.8-1.2).

4. A method for preparing the catalyst according to any one of claims 1-3, characterized in that, Includes the following steps: (1) CeO2 nanoparticles were prepared by hydrothermal method; (2) Using CTAB as a template agent and TEOS as a silicon source, a mesoporous silica layer was coated on the CeO2 surface by the sol-gel method to obtain CeO2@mSiO2; (3) The nickel precursor and phosphorus source were loaded onto CeO2@mSiO2 by impregnation-precipitation method to obtain CeO2@mSiO2@Ni3(PO4)2 precursor; (4) The precursor was subjected to phosphating heat treatment under a reducing atmosphere to obtain CeO2@mSiO2@Ni2P catalyst.

5. The preparation method according to claim 4, characterized in that, In step (1), the hydrothermal reaction temperature is 150~180℃ and the reaction time is 6~10 hours.

6. The preparation method according to claim 4, characterized in that, In step (2), the mass ratio of CTAB to TEOS is 1:(1-2.5), and the reaction is carried out under the catalysis of ammonia water.

7. The preparation method according to claim 4, characterized in that, In step (3), the nickel precursor is nickel nitrate and the phosphorus source is diammonium hydrogen phosphate.

8. The preparation method according to claim 4, characterized in that, In step (4), the phosphating heat treatment conditions are as follows: in an H2 / Ar atmosphere, the temperature is first raised from room temperature to 100-150℃ at a rate of 3-5℃ / min and held for 1-2 hours to remove physically adsorbed water; then the temperature is raised to 300-500℃ at a rate of 1-3℃ / min; then the temperature is raised to 500-700℃ at a slow rate of 1-2℃ / min, and the temperature is kept constant at this final temperature for 1-3 hours.

9. The use of a catalyst as described in any one of claims 1-3 in the catalytic reaction of chlorine-containing volatile organic compounds.

10. The application according to claim 9, characterized in that, The chlorine-containing volatile organic compound is chlorobenzene.

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