Carbon-coated nickel oxide nanocomposites, their preparation methods and applications

Abstract

A carbon-coated nickel oxide nanocomposite material, its preparation method, and its applications are disclosed. This nanocomposite material comprises carbon-coated nickel oxide nanoparticles with a core-membrane structure, wherein the core-membrane structure includes an outer membrane and a core. The outer membrane is an optionally nitrogen-doped graphitized carbon membrane, and the core comprises nickel oxide nanoparticles. The carbon content of the nanocomposite material is greater than 0 wt% and no more than about 5 wt% by weight. This nanocomposite material exhibits excellent activity as a catalyst and can be effectively used to catalyze various reactions, showing promising prospects for industrial applications.

Description

[Technical Field] This application relates to the field of catalysis technology, specifically to a carbon-coated nickel oxide nanocomposite material, its preparation method, and its application. Cross-reference is made to related applications claiming priority to the following patent applications filed on October 21, 2019: Patent Application No. 201911001538.3, entitled "Carbon-coated Nickel Oxide Nanocomposite Material, its Preparation Method, and Application"; Patent Application No. 201911002419.X, filed on October 21, 2019, entitled "Method for Catalytic Combustion of Volatile Organic Compounds"; Patent Application No. 202010503595.8, filed on June 5, 2020, entitled "Carbon-coated Nickel Oxide Nanocomposite Material, its Preparation Method, and Application"; and Patent Application No. 202010503588.8, filed on June 5, 2020, entitled "Method for Catalytic Combustion of Volatile Organic Compounds," the contents of which are hereby incorporated herein by reference in their entirety. [Previous Technology] Transition metal oxides possess excellent catalytic and photoelectric properties, making them a research hotspot in the field of inorganic materials. They have wide applications in energy storage materials, catalytic materials, magnetic recording materials, and biomedicine. Carbon materials exhibit good conductivity, chemical / electrochemical stability, and high structural strength. Coating active metal or metal oxide nanoparticles with carbon materials effectively improves the conductivity and stability of the nanoparticles and provides a confined domain effect, making them less prone to aggregation. In recent years, carbon-coated nanomaterials have been widely used in electrocatalysis, supercapacitor materials, lithium-ion battery anode materials, and bioengineering, but their application in catalysis science is still relatively limited. Nitrous oxide (N2O), also known as laughing gas, is a significant greenhouse gas with a global warming potential (GWP) 310 times that of CO2 and 21 times that of CH4. Furthermore, N2O has an average atmospheric lifetime of approximately 150 years and is a major source of NOx in the stratosphere, severely damaging the ozone layer and exhibiting a strong greenhouse effect. Domestic production of adipic acid mainly employs the cyclohexanol-nitric acid oxidation method. Cyclohexanol is oxidized with nitric acid to produce adipic acid. This method is technically mature, with relatively high product yield and purity. However, it consumes a large amount of nitric acid, generates significant amounts of N2O during the reaction, and produces concentrated, high-concentration tail gas emissions (36%-40%). Currently, a cyclohexanol-nitric acid oxidation method producing 150,000 tons of adipic acid annually results in annual N2O emissions of up to 45,000 tons. Therefore, purifying the tail gas from adipic acid plants and effectively controlling and eliminating N2O has become a research hotspot in the field of environmental catalysis. Direct catalytic decomposition can decompose N2O into nitrogen and oxygen, making it the most effective and cleanest technology for eliminating N2O. The catalyst is the core technology of direct catalytic decomposition. Currently reported catalysts for N2O decomposition mainly include noble metal catalysts, ion-exchange molecular sieve catalysts, and transition metal oxide catalysts. Noble metal catalysts (such as Rh and Ru) exhibit high low-temperature catalytic activity for the decomposition of N2O (250℃-350℃ range, capable of efficiently decomposing N2O), but their high price limits their large-scale application. Molecular sieve catalysts and transition metal oxide catalysts are significantly cheaper than noble metals, but currently, these two types of catalysts have relatively low activity for the decomposition of N2O, with efficient decomposition temperatures in the 450℃-550℃ range. Furthermore, the decomposition requires diluting high-concentration nitrous oxide to approximately 0.5%-2%, greatly increasing industrial costs. Volatile organic compounds (VOCs) are a class of organic compounds with a saturated vapor pressure greater than 70 Pa at room temperature and a boiling point below 260℃ at atmospheric pressure.VOCs are diverse, mainly including alkanes, aromatics, esters, aldehydes, and halogenated hydrocarbons. Most have pungent odors and can cause poisoning and cancer. VOCs are also a significant source of photochemical smog and PM2.5. As a major manufacturing country, China has the world's largest VOC emissions. Industrial VOC emissions, due to their high concentration, long duration, and diverse types, not only harm human health but also severely damage the ecological environment. In recent years, China has systematically controlled VOCs as a pollutant, and developing efficient VOC purification technologies to control emissions has become a crucial issue in environmental protection. There are two main types of VOC purification methods: the first is physical absorption and adsorption, commonly used to recover high concentrations (>5000 mg / m3) of VOCs. However, this method is not ideal for purifying low concentrations (<1000 mg / m3) of VOCs, exhibiting low adsorption efficiency, and the adsorption, absorption, and elution processes generate secondary wastewater or solid waste. The second category is the chemical reaction method, which introduces oxidants into VOCs to oxidize them into non-toxic chemical substances. This method is mainly for treating medium or low concentrations of VOCs. Combustion technology is widely used in chemical reaction methods, specifically divided into direct flame combustion and catalytic combustion. Direct flame combustion uses VOCs as fuel and burns them directly, requiring high temperatures of around 600-900℃, resulting in high energy consumption and producing black smoke and odors due to incomplete combustion. Catalytic combustion, on the other hand, is a typical gas-solid catalytic reaction. Essentially, it catalytically reacts VOCs adsorbed on the catalyst surface with O2 to produce harmless CO2 and H2O. The reaction typically takes place at 300-500℃, with lower energy consumption and no secondary pollution, making it an energy-saving, efficient, economical, and environmentally friendly technology. The catalyst is the core of catalytic combustion technology. Currently reported catalysts for catalytic combustion of VOCs mainly include noble metal catalysts and non-noble metal oxide catalysts. Among these, noble metal catalysts (such as Pt, Ru, Au, Pd, etc.) exhibit good performance but are expensive and susceptible to poisoning; non-noble metal oxide catalysts (such as Co2O3, MnO2, CeO2, CuO, TiO2, and perovskite, etc.) are inexpensive and less prone to poisoning, but their catalytic activity is relatively low. Therefore, developing low-cost, high-performance catalysts suitable for the aforementioned fields is an urgent problem to be solved. It should be noted that the information disclosed in the foregoing prior art is only used to enhance the background understanding of this application, and therefore may include information that does not constitute prior art known to those skilled in the art. [Summary of the Invention] One objective of this application is to provide a carbon-coated nickel oxide nanocomposite material, its preparation method, and its applications. This nanocomposite material comprises carbon-coated nickel oxide nanoparticles with a core-membrane structure consisting of a graphitized carbon film optionally doped with nitrogen and a nickel oxide core. As a catalyst active component, it exhibits excellent activity and can be effectively used for the catalytic decomposition of nitrous oxide and the catalytic combustion of volatile organic compounds. It addresses the problem of eliminating high concentrations of N2O generated during the production processes of adipic acid and nitric acid plants, as well as the purification of VOCs. This is of great significance for environmental protection and reducing air pollution, and has promising prospects for industrial applications. To achieve the above objectives, this application provides, in one aspect, a carbon-coated nickel oxide nanocomposite material comprising carbon-coated nickel oxide nanoparticles with a core-membrane structure. The core-membrane structure includes an outer membrane and a core. The outer membrane is a graphitized carbon film optionally doped with nitrogen, and the core comprises nickel oxide nanoparticles. The carbon content of the nanocomposite material is greater than 0 wt% and not greater than about 5 wt% by weight. Preferably, the carbon content of the nanocomposite material, as determined by X-ray photoelectron spectroscopy, is about 15-60 mol%; and / or, the ratio of the mass content of carbon in the nanocomposite material determined by X-ray photoelectron spectroscopy to the mass content of carbon in the nanocomposite material determined by elemental analysis is not less than about 10. Preferably, in the Raman spectrum of the nanocomposite material, the ratio of the intensity of the G peak near 1580 cm⁻¹ to the intensity of the D peak near 1320 cm⁻¹ is greater than about 2. On the other hand, this application provides a method for preparing carbon-coated nickel oxide nanocomposite materials, comprising the following steps: i) mixing a nickel source, a polycarboxylic acid, and optionally a nitrogen-containing compound in a solvent to form a homogeneous solution; ii) removing the solvent from the homogeneous solution to obtain a precursor; iii) pyrolyzing the precursor under an inert or reducing atmosphere; and iv) heat-treating the pyrolyzed product in the presence of oxygen to obtain the nanocomposite material, wherein the nickel source is preferably selected from one or more of nickel powder, nickel hydroxide, nickel oxide, soluble organic acid salts of nickel, basic carbonates of nickel, and carbonates of nickel; the polycarboxylic acid is preferably selected from one or more of citric acid, maleic acid, trimesic acid, terephthalic acid, gluconic acid, malic acid, ethylenediaminetetraacetic acid, pyridine dicarboxylic acid, iminodiacetic acid, diethylenetriaminepentaacetic acid, and 1,3-propanediaminetetraacetic acid; and the nitrogen-containing compound is preferably selected from one or more of urea, melamine, dicyandiamine, hexamethylenetetramine, and amino acids. Preferably, the heat treatment in step iv) includes introducing oxygen-containing gas into the pyrolysis product and heating it, wherein the volume concentration of oxygen in the oxygen-containing gas is about 10-40%, the heat treatment temperature is about 200-500°C, and the heat treatment time is about 0.5-10 h.On the other hand, this application provides a method for catalytic decomposition of nitrous oxide, comprising contacting nitrous oxide with a catalyst to carry out a catalytic decomposition reaction to generate nitrogen and oxygen, wherein the catalyst comprises the nanocomposite material according to this application as an active component. On yet another aspect, this application provides a method for treating volatile organic compounds, comprising contacting the volatile organic compounds with a catalyst to carry out an oxidation reaction, wherein the catalyst comprises the nanocomposite material according to this application as an active component. Preferably, the oxidation reaction is carried out by catalytic combustion of a mixed gas containing the volatile organic compounds and oxygen with the catalyst. The carbon-coated nickel oxide nanocomposite material of this application has a core-film structure comprising a graphitized carbon film optionally doped with nitrogen and a nickel oxide core. Through its unique structure and composition, it exhibits excellent activity as a catalyst for the decomposition of N2O. Compared to existing catalysts that require dilution of N2O in industrial waste gas before treatment, the nanocomposite material of this application can directly catalytically decompose high-concentration nitrous oxide waste gas generated in industrial production at lower temperatures, with a decomposition rate of over 99%, which is of great significance for environmental protection and reducing air pollution. Furthermore, this nanocomposite material can efficiently catalyze the oxidation and combustion of VOCs at lower temperatures, which helps to solve the problem of VOCs purification and reduce air pollution.

Implementation Method

Claims

1. A carbon-coated nickel oxide nanocomposite material, the nanocomposite material comprising carbon-coated nickel oxide nanoparticles having a core-film structure, the core-film structure comprising an outer film and a core, the outer film being an optionally nitrogen-doped graphitized carbon film, and the core comprising nickel oxide nanoparticles, wherein, The carbon content of the nanocomposite material is greater than 0 wt% and not greater than about 5 wt% by weight; the graphitized carbon film is a thin film structure mainly composed of graphitized carbon; the ratio of the surface carbon content of the nanocomposite material determined by X-ray photoelectron spectroscopy to the carbon content determined by elemental analysis is not less than about 10, and the ratio of the intensity of the G peak near 1580 cm⁻¹ to the intensity of the D peak near 1320 cm⁻¹ in the Raman spectrum of the nanocomposite material is greater than about 2, wherein the surface carbon content of the nanocomposite material determined by X-ray photoelectron spectroscopy is about 15-60 mol.

2. The nanocomposite material according to claim 1, wherein the ratio of the surface carbon content determined by X-ray photoelectron spectroscopy to the carbon content determined by elemental analysis is 20-40.

3. The nanocomposite material according to claim 1 or 2, wherein the outer membrane of the core membrane structure is a nitrogen-doped graphitized carbon membrane, and the nitrogen content of the nanocomposite material, as determined by X-ray photoelectron spectroscopy, is about 0.1-5 mol.

4. The nanocomposite material according to claim 1 or 2, wherein the carbon-coated nickel oxide nanoparticles have a particle size of about 1-100 nm.

5. The nanocomposite material according to claim 1 or 2, wherein the carbon content is about 0.4-0.95 wt% by weight of the nanocomposite material.

6. A method for preparing a graphitized carbon-coated nickel oxide nanocomposite material according to any one of claims 1 to 5, comprising the steps of: i) mixing a nickel source, a polycarboxylic acid and optionally a nitrogen-containing compound in a solvent to form a homogeneous solution; ii) removing the solvent from the homogeneous solution to obtain a precursor; iii) pyrolyzing the precursor under an inert or reducing atmosphere; and iv) heat-treating the pyrolyzed product in the presence of oxygen to obtain the nanocomposite material.

7. The preparation method according to claim 6, wherein the nickel source is selected from one or more of nickel powder, nickel hydroxide, nickel oxide, soluble organic acid salts of nickel, basic carbonates of nickel, and carbonates of nickel; the polycarboxylic acid is selected from one or more of citric acid, maleic acid, trimesic acid, terephthalic acid, gluconic acid, malic acid, ethylenediaminetetraacetic acid, pyridine dicarboxylic acid, iminodiacetic acid, diethylenetriaminepentaacetic acid, and 1,3-propanediaminetetraacetic acid; and the nitrogen-containing compound is selected from one or more of urea, melamine, dicyandiamine, hexamethylenetetramine, and amino acids.

8. The preparation method according to claim 6 or 7, wherein the heat treatment in step iv) comprises introducing an oxygen-containing gas into the pyrolysis product and heating it, wherein the oxygen-containing gas has a volume concentration of about 10-40%, the heat treatment temperature is about 200-500°C, and the heat treatment time is about 0.5-10 h.

9. The preparation method according to claim 6 or 7, wherein in step i), a nickel source is mixed with a polycarboxylic acid in a solvent, the polycarboxylic acid being selected from one or more of citric acid, maleic acid, trimesic acid, terephthalic acid, gluconic acid, and malic acid, and the mass ratio of the nickel source to the polycarboxylic acid is about 1:(0.1-100).

10. The preparation method according to claim 6 or 7, wherein in step i), a nickel source is mixed with a polycarboxylic acid in a solvent, the polycarboxylic acid being selected from one or more of ethylenediaminetetraacetic acid, pyridinedicarboxylic acid, iminodiacetic acid, diethylenetriaminepentaacetic acid, and 1,3-propanediaminetetraacetic acid, and the mass ratio of the nickel source to the polycarboxylic acid is about 1:(0.1-10).

11. The preparation method according to claim 6 or 7, wherein in step i), a nickel source, a polycarboxylic acid and a nitrogen-containing compound are mixed in a solvent, the polycarboxylic acid being selected from one or more of citric acid, maleic acid, trimesic acid, terephthalic acid, gluconic acid and malic acid, and the mass ratio of the nickel source, the polycarboxylic acid and the nitrogen-containing compound is about 1:(0.1-10):(0.1-10).

12. The preparation method according to claim 6 or 7, wherein the pyrolysis in step iii) comprises: The precursor is heated to a constant temperature range under an inert or reducing atmosphere and maintained at that constant temperature range for a period of time. The heating rate is approximately 0.5-30°C / min, the constant temperature range is approximately 400-800°C, and the constant temperature range is approximately 20-600min. The inert atmosphere is nitrogen or argon, and the reducing atmosphere is a mixture of inert gas and hydrogen.

13. A method for catalytic decomposition of nitrous oxide, comprising contacting nitrous oxide with a catalyst to carry out a catalytic decomposition reaction to generate nitrogen and oxygen, wherein the catalyst comprises a nanocomposite material according to any one of claims 1-5 as an active component.

14. The method according to claim 13, wherein the conditions for the catalytic decomposition reaction include: The reaction temperature is about 300-400℃, the reaction space velocity is about 1000-3000 mL of reaction gas / (h•g catalyst), and the volume concentration of nitrous oxide in the reaction gas is about 5-40%.

15. A method for treating volatile organic compounds, comprising contacting the volatile organic compounds with a catalyst to carry out an oxidation reaction, wherein the catalyst comprises a nanocomposite material according to any one of claims 1-5 as an active component.

16. The method according to claim 15, wherein a nanocomposite material according to any one of claims 1-5 is used as a catalyst, and the oxidation reaction is carried out by catalytic combustion by contacting a mixed gas containing the volatile organic compound and oxygen with the catalyst.

17. The method according to claim 15, wherein the volume percentage of the volatile organic compounds in the mixed gas is about 0.01-2%, and the volume percentage of oxygen is about 5-20%.

18. The method according to claim 15 or 16, wherein the conditions for said oxidation reaction include: The reaction temperature is approximately 300-450℃, and the reaction space velocity is approximately 1000-5000 mL of reaction gas / (h•g catalyst).

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