CN112755993B

CN112755993B - Carbon-coated nickel oxide nanocomposite and preparation method and application thereof

Info

Publication number: CN112755993B
Application number: CN201911001538.3A
Authority: CN
Inventors: 荣峻峰; 于鹏; 徐国标; 吴耿煌; 谢婧新; 宗明生; 林伟国; 纪洪波
Original assignee: Sinopec Research Institute of Petroleum Processing; China Petroleum and Chemical Corp
Current assignee: Sinopec Research Institute of Petroleum Processing; China Petroleum and Chemical Corp
Priority date: 2019-10-21
Filing date: 2019-10-21
Publication date: 2022-07-15
Anticipated expiration: 2039-10-21
Also published as: CN112755993A

Abstract

The invention provides a carbon-coated nickel oxide nano composite material, a preparation method and an application thereof, wherein the nano composite material comprises a nuclear membrane structure with an outer membrane and an inner core, the outer membrane is a graphitized carbon membrane, and the inner core comprises nickel oxide nano particles, wherein the carbon content is not more than 5 wt% of the nano composite material. The nano composite material has excellent activity as a catalyst, can effectively catalyze and decompose nitrous oxide, and is beneficial to solving the problem of high-concentration N generated in the production processes of adipic acid plants, nitric acid plants and the like₂The elimination of O is of great significance for protecting the environment and reducing the atmospheric pollution, and has good industrial application prospect.

Description

Carbon-coated nickel oxide nanocomposite and preparation method and application thereof

Technical Field

The invention relates to the technical field of catalysis, in particular to a carbon-coated nickel oxide nano composite material and a preparation method and application thereof.

Background

The transition metal oxide has excellent catalytic performance and electromagnetic performance, is a research hotspot in the field of inorganic materials, and has wide application in energy storage materials, catalytic materials, magnetic recording materials and biomedicine. The carbon material has good conductivity, good chemical/electrochemical stability and high structural strength. The nano particles of active metal or metal oxide are coated by carbon material, so that the conductivity and stability of the nano material are effectively improved, and the nano particles are not easy to agglomerate due to the action of a limited domain. In recent years, carbon-coated nanomaterials are widely applied to the fields of electrocatalysis, supercapacitor materials, lithium ion battery negative electrode materials, bioengineering and the like, but the carbon-coated nanomaterials are not applied to the field of catalytic science in many ways.

Nitrous oxide (N)₂O), also known as laughing gas, is an important greenhouse gas whose Global Warming Potential (GWP) is CO₂310 times of, CH₄21 times of the total weight of the composition; furthermore, N₂The average life of O in the atmosphere is about 150 years, and the O is also a main source of NOx in the stratosphere, not only can seriously damage the ozone layer, but also has strong greenhouse effect.

The domestic production of adipic acid mainly adopts a cyclohexanol nitric acid oxidation method, and the cyclohexanol is subjected to nitric acid oxidation to produce adipic acid, and the method is mature in technology, high in product yield and purity, but large in nitric acid consumption, and capable of producing a large amount of N in the reaction process₂And the tail gas discharged in the production process is concentrated, large in quantity and high in concentration (36-40%). At present, 15 ten thousand tons of adipic acid and N are produced annually by a nitric acid oxidation method of cyclohexanol₂The annual emission of O can reach 4.5 ten thousand tons. Therefore, the tail gas of the adipic acid device is purified, and N is effectively controlled and eliminated₂O has become a research hotspot in the field of environmental catalysis at present.

By direct catalytic decomposition of N₂O is decomposed into nitrogen and oxygen to eliminate N₂O is the most effective and clean technique. Wherein the catalyst is a technique of direct catalytic decompositionAnd (4) a core. Decomposition of N reported in the present study₂The O catalyst mainly comprises a noble metal catalyst, an ion exchange molecular sieve catalyst and a transition metal oxide catalyst. Noble metal catalysts (e.g. Rh and Ru) vs. N₂The O catalytic decomposition has higher low-temperature catalytic activity (within the range of 250-350 ℃) and can efficiently decompose N₂O), but the expensive price limits the large-scale application of noble metal catalysts. The molecular sieve type catalyst and the transition metal oxide catalyst are obviously cheaper than the noble metal, but the two types of catalysts are used for N₂The activity of O catalytic decomposition is low, the temperature range of efficient decomposition is 450-550 ℃, and the decomposition can be carried out only by diluting high-concentration laughing gas to about 0.5-2% concentration, thereby greatly improving the industrial cost.

Thus, a low cost, highly active catalyst is developed which is N₂The field of O emission reduction is an urgent problem to be solved.

It is noted that the information disclosed in the foregoing background section is only for enhancement of background understanding of the invention and therefore it may contain information that does not constitute prior art that is already known to a person of ordinary skill in the art.

Disclosure of Invention

It is a primary object of the present invention to overcome at least one of the above-mentioned drawbacks of the prior art and to provide a carbon-coated nickel oxide nanocomposite, which has a core-film structure including a graphitized carbon film and a nickel oxide core, has excellent activity as a catalyst, can effectively catalyze decomposition of nitrous oxide, and helps to solve high concentration of N generated during the production of adipic acid plants, nitric acid plants, etc., and a method for preparing the same and use thereof₂The elimination of O is of great significance for protecting the environment and reducing the atmospheric pollution, and has good industrial application prospect.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect of the invention there is provided a carbon-coated nickel oxide nanocomposite material comprising a core-film structure having an outer film comprising a graphitized carbon film and an inner core comprising nickel oxide nanoparticles, wherein the carbon content comprises no more than 5 wt% of the nanocomposite material.

According to one embodiment of the invention, the carbon content is not more than 1wt% of the nanocomposite.

According to one embodiment of the present invention, the ratio of the carbon element in the nanocomposite material as determined by X-ray photoelectron spectroscopy to the carbon element content as determined by elemental analysis is not less than 10 in terms of a mass ratio.

According to one embodiment of the invention, the Raman spectrum of the nanocomposite is at 1580cm^-1Intensity of nearby G peak at 1320cm^-1The ratio of the intensities of the nearby D peaks is greater than 2.

According to one embodiment of the invention, the particle size of the nuclear membrane structure is between 1nm and 100 nm.

The second aspect of the present invention provides a method for preparing the carbon-coated nickel oxide nanocomposite, comprising the steps of: putting a nickel-containing compound and polybasic organic carboxylic acid into a solvent to be mixed to form a homogeneous solution; removing the solvent in the homogeneous solution to obtain a precursor; pyrolyzing the precursor in inert atmosphere or reducing atmosphere; and carrying out oxygen treatment on the product after pyrolysis to obtain the nano composite material.

According to one embodiment of the invention, the oxygen treatment comprises introducing standard gas into the pyrolysis product and heating, wherein the standard gas contains oxygen and balance gas, and the volume concentration of the oxygen is 10-40%.

According to one embodiment of the present invention, the temperature of the oxygen treatment is 200 ℃ to 500 ℃ and the time of the oxygen treatment is 0.5h to 10 h.

According to one embodiment of the present invention, the mass ratio of the nickel-containing compound to the polybasic organic carboxylic acid is 1 (0.1-100), preferably 1: 0.5-5, and more preferably 1: 0.8-2; the nickel-containing compound is selected from one or more of organic acid salt of nickel, nickel carbonate, basic nickel carbonate, nickel hydroxide and nickel oxide; the polybasic organic carboxylic acid is selected from one or more of citric acid, maleic acid, trimesic acid, terephthalic acid, gluconic acid and malic acid.

According to one embodiment of the invention, pyrolysis comprises: heating the precursor to a constant temperature section in an inert atmosphere or a reducing atmosphere, and keeping the constant temperature in the constant temperature section;

wherein the heating rate is 0.5 ℃/min-30 ℃/min, the temperature of the constant temperature section is 400-800 ℃, the constant temperature time is 20-600 min, the inert atmosphere is nitrogen or argon, and the reducing atmosphere is the mixed gas of inert gas and hydrogen.

A third aspect of the invention provides the use of the above nanocomposite as a catalyst.

A fourth aspect of the present invention provides the use of the above nanocomposite as a catalyst for the decomposition of nitrous oxide, comprising: the catalyst is contacted with nitrous oxide to carry out catalytic decomposition reaction to generate nitrogen and oxygen.

According to one embodiment of the present invention, the temperature of the catalytic decomposition reaction is 300 ℃ to 400 ℃.

According to one embodiment of the invention, the space velocity of the catalytic decomposition reaction is 1000h^-1～3000h^-1。

According to one embodiment of the invention, the nitrous oxide has a volume concentration comprised between 30% and 40%.

According to the technical scheme, the carbon-coated nickel oxide nano composite material and the preparation method and application thereof have the advantages and positive effects that:

the carbon-coated nickel oxide nano composite material provided by the invention comprises a nuclear membrane structure with a graphitized carbon membrane and a nickel oxide inner core, and the carbon-coated nickel oxide nano composite material is used as a catalyst to catalyze N through unique structure and composition₂Has excellent activity in O decomposition reaction. Compared with the prior catalyst, the catalyst must remove N in industrial waste gas₂The catalyst can directly catalyze and decompose high-concentration nitrous oxide waste gas generated in industrial production at a lower temperature, the decomposition rate can reach more than 99 percent, and the catalyst has important significance for protecting the environment and reducing air pollution and has good industrial application prospect.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention.

FIG. 1 is an X-ray diffraction pattern of the nanocomposite material of example 1;

FIG. 2 is a transmission electron micrograph of the nanocomposite material of example 1;

FIG. 3 is a Raman spectrum of the nanocomposite material of example 1;

FIG. 4 is an X-ray diffraction pattern of the nanocomposite material of example 2;

FIG. 5 is a transmission electron micrograph of the nanocomposite material of example 2;

FIG. 6 is a Raman spectrum of the nanocomposite material of example 2;

FIG. 7 is an X-ray diffraction pattern of the material obtained in comparative example 1;

FIGS. 8a and 8b are transmission electron micrographs of the material obtained in comparative example 1 at different magnifications, respectively.

Detailed Description

The following presents various embodiments, or examples, in order to enable one of ordinary skill in the art to practice the invention with reference to the description herein. These are, of course, merely examples and are not intended to be limiting. The endpoints of the ranges and any values disclosed in the present application are not limited to the precise range or value and should be understood to encompass values close to these ranges or values. For numerical ranges, combinations of values between the endpoints of each of the ranges, between the endpoints of each of the ranges and individual values, and between individual values can result in one or more new numerical ranges, and such numerical ranges should be considered as being specifically disclosed herein.

Any terms not directly defined herein should be understood to have meanings associated with them as commonly understood in the art of the present invention. The following terms as used throughout this specification should be understood to have the following meanings unless otherwise indicated.

The term "nuclear membrane structure" in the present invention means a nuclear membrane structure having an outer membrane which is a graphitized carbon membrane and an inner core containing nickel oxide nanoparticles. The composite material formed after the graphitized carbon film is coated with the nickel oxide nano particles is spherical or quasi-spherical.

The term "graphitized carbon film" refers to a thin film structure composed mainly of graphitized carbon.

The term "carbon element content determined by X-ray photoelectron spectroscopy" refers to the relative content of carbon elements on the surface of a material measured by quantitative elemental analysis using an X-ray photoelectron spectrometer as an analysis tool.

The term "carbon content determined in elemental analysis" refers to the relative content of total carbon elements of a material measured by elemental quantitative analysis using an elemental analyzer as an analysis tool.

A first aspect of the present invention provides a carbon-coated nickel oxide nanocomposite, the nanocomposite comprising a core film structure having an outer film and an inner core, the outer film comprising a graphitized carbon film and the inner core comprising nickel oxide nanoparticles, wherein the carbon content is not more than 5 wt% of the nanocomposite. In some embodiments, the carbon content is no greater than 1wt% of the nanocomposite.

According to the invention, the carbon-coated nickel oxide nano composite material is a nuclear membrane structure comprising an outer membrane layer and an inner nuclear layer, wherein the outer membrane layer mainly comprises a graphitized carbon membrane, and the graphitized carbon membrane is a thin membrane structure mainly comprising graphitized carbon and is coated on the surface of nickel oxide nano particles. The inventor of the invention unexpectedly finds that the core membrane structure coated with the graphitized carbon membrane on the outer layer has relatively little carbon content in the thin membrane layer, but greatly improves the performance of the whole material, particularly the catalytic performance, specifically, the core membrane structure not only can generate a certain confinement effect, effectively avoids the aggregation and growth of nickel oxide nanoparticles in the core, and enables the catalytic activity of the composite material to be stable, but also can synergistically increase the catalytic activity of the whole composite material, and obviously improves the catalytic activity compared with the catalytic activity of pure nickel oxide which is not coated with the graphite carbon membrane.

In some embodiments, the nanocomposite material of the present invention has a ratio of the content of carbon element determined by X-ray photoelectron spectroscopy to the content of carbon element determined by elemental analysis of not less than 10 in terms of mass ratio. As mentioned above, the carbon content determined by X-ray photoelectron spectroscopy refers to the relative carbon content on the surface of the material measured by quantitative element analysis using an X-ray photoelectron spectrometer as an analysis tool. The carbon element content determined in the element analysis refers to the relative content of the total carbon elements of the material, which is measured by carrying out element quantitative analysis by taking an element analyzer as an analysis tool. When the ratio of the carbon element determined by X-ray photoelectron spectroscopy to the carbon element content determined by element analysis is larger, most of carbon in the whole nano composite material is concentrated on the surface of the material to form a carbon film layer, so that the nuclear film structure is formed.

In some embodiments, the present nanocomposites have Raman spectra at 1580cm^-1Intensity of nearby G peak at 1320cm^-1The ratio of the intensities of the nearby D peaks is greater than 2. As will be understood by those skilled in the art, the D peak and the G peak are both characteristic Raman peaks of the C atom crystal, the D peak represents a defect of the carbon atom lattice, and the G peak represents a C atom sp²Hybrid in-plane stretching vibration. It is understood that a greater ratio of the intensity of the G peak to the intensity of the D peak indicates that more graphitic carbon is present in the nanocomposite than amorphous carbon. That is, the carbon element in the nanocomposite material of the present invention exists mainly in the form of graphitic carbon. The graphite carbon has better oxidation resistance, and can increase the catalytic activity with the nickel oxide nano-particles of the kernel in a synergistic manner, thereby improving the performance of the whole composite material.

In some embodiments, the aforementioned nuclear membrane structure generally has a particle size of 1nm to 100nm, preferably 2nm to 40 nm.

The second aspect of the present invention also provides a method for preparing the carbon-coated nickel oxide nanocomposite, comprising the following steps:

putting a nickel-containing compound and polybasic organic carboxylic acid into a solvent to be mixed to form a homogeneous solution;

removing the solvent in the homogeneous solution to obtain a precursor;

pyrolyzing the precursor in inert atmosphere or reducing atmosphere;

and carrying out oxygen treatment on the product after pyrolysis to obtain the nano composite material.

Specifically, the precursor is a water-soluble mixture, which refers to a nickel-containing water-soluble mixture obtained by dissolving a nickel-containing compound and a polybasic organic carboxylic acid in a solvent such as water and ethanol to form a homogeneous solution, and then directly evaporating and removing the solvent. The aforementioned temperature and process of evaporating the solvent may be any available prior art, for example, spray drying at 80 ℃ to 120 ℃ or drying in an oven.

In addition, other organic compounds than the two aforementioned compounds can be added to form a homogeneous solution, and the other organic compounds can be any organic compounds which can supplement the carbon source required in the product and do not contain other doping atoms. Organic compounds having no volatility such as organic polyols, lactic acid and the like are preferable.

In some embodiments, the mass ratio of the nickel-containing compound, the poly-organic carboxylic acid, and the other organic compound is 1:0.1 to 10:0 to 10, preferably 1:0.5 to 5:0 to 5, more preferably 1:0.8 to 3:0 to 3; the nickel-containing compound is one or more of organic acid salt of nickel, nickel carbonate, basic nickel carbonate, nickel hydroxide and nickel oxide; preferably, the organic acid salt is an organic carboxylate salt of nickel free of other heteroatoms. The polybasic organic carboxylic acid is selected from one or more of citric acid, maleic acid, trimesic acid, terephthalic acid, gluconic acid and malic acid.

In some embodiments, the pyrolyzing comprises: heating the precursor to a constant temperature section in an inert atmosphere or a reducing atmosphere, and keeping the constant temperature in the constant temperature section;

wherein the heating rate is 0.5-30 ℃/min, preferably 1-10 ℃/min; the temperature of the constant temperature section is 400-800 ℃, and preferably 500-800 ℃; the constant temperature time is 20min to 600min, preferably 60min to 480 min; the inert atmosphere is nitrogen or argon, and the reducing atmosphere is a mixed gas of an inert gas and hydrogen, for example, a small amount of hydrogen is doped in the inert atmosphere.

In some embodiments, the oxygen treatment comprises introducing standard gas into the pyrolyzed product and heating, wherein the standard gas contains oxygen gas and balance gas, and the volume concentration of the oxygen gas is 10% to 40%, optionally 10% to 30%. The balance gas may be an inert gas such as nitrogen or argon, but the present invention is not limited thereto.

In some embodiments, the temperature of the oxygen treatment is 200 ℃ to 500 ℃, preferably 300 ℃ to 400 ℃; the time of the oxygen treatment is 0.5h to 10h, and then the carbon-coated nickel oxide nano composite material can be obtained.

As known to those skilled in the art, carbon is oxidized to generate gas after contacting with oxygen at high temperature, and it can be understood that the product after high temperature pyrolysis forms a nanocomposite material in which a graphite carbon shell coats an inner core nickel, wherein the carbon content is about 15% to 60%. After the pyrolysis product is treated with oxygen, most of the carbon in the material is lost along with the oxidation reaction. However, the inventors of the present invention have unexpectedly found that the oxygen treated material burns off most of the carbon while oxidizing not only the nickel of the core but also a small portion of the carbon remains. As mentioned above, XPS and Raman spectrum detection analysis prove that the carbon is a graphitized carbon film layer coated on the surface of the nickel oxide, and the carbon film layer further enables the nanocomposite material to have a plurality of excellent properties, especially catalytic activity.

In a third aspect, the present invention provides the use of the above nanocomposite as a catalyst. That is, the nanocomposite of the present invention has catalytic activity and can be used as a catalyst in various industrial production reactions.

In a fourth aspect, the present invention provides the use of the nanocomposite described above as a catalyst for decomposing nitrous oxide, comprising contacting the catalyst with nitrous oxide to effect a catalytic decomposition reaction to produce nitrogen and oxygen. Specifically, a gas containing dinitrogen monoxide is introduced into a reactor containing the catalyst to perform a catalytic decomposition reaction.

In some embodiments, the temperature of the catalytic decomposition reaction is from 300 ℃ to 400 ℃, preferably from 350 ℃ to 380 ℃. Space velocity of the catalytic decomposition reaction is1000h^-1～3000h^-1. The space velocity of the reaction is the amount of gas treated per unit volume of catalyst per unit time under the specified conditions, and is expressed in m³/(m³Catalyst h) can be simplified to h^-1. The high reaction space velocity allowed by the invention shows that the catalyst of the invention has high activity and large device processing capacity when the reaction is applied.

According to the invention, as mentioned above, the currently reported decomposition N₂The O catalyst mainly comprises a noble metal catalyst, an ion exchange molecular sieve catalyst and a transition metal oxide catalyst. Although the decomposition temperature of the noble metal catalyst is low, the expensive price of the noble metal catalyst is not suitable for large-scale industrial production; the high-efficiency decomposition temperature of other molecular sieve catalysts and transition metal oxide catalysts is 450-550 ℃, and the high temperature required by the reaction greatly improves the industrial cost; in addition, the decomposition of nitrous oxide generates oxygen, which tends to deactivate the catalyst.

However, the inventors of the present invention have found that the carbon-coated nickel oxide nanocomposite of the present invention can effectively decompose nitrous oxide into nitrogen and oxygen using the catalyst, and exhibits excellent catalytic activity stability in the reaction. In addition, when the prior catalyst is used for catalyzing and decomposing the nitrous oxide, the high-concentration nitrous oxide obtained by industrial production generally needs to be diluted to be about 0.5 to 2 percent, but the catalyst can be directly decomposed to achieve high decomposition rate without further dilution. Namely, the nitrous oxide can be subjected to catalytic decomposition reaction when the volume concentration is 30-40%, and the decomposition rate can reach over 99%, so that the industrial cost is greatly reduced, and the method has a good industrial application prospect.

The invention will now be further illustrated by the following examples, but is not to be construed as being limited thereto. Unless otherwise specified, all reagents used in the invention are analytically pure.

The invention detects elements on the surface of the material by an X-ray photoelectron spectrum analyzer (XPS). The X-ray photoelectron spectrum analyzer was prepared by software Avantage V5.926, produced by VG scientific IncThe ESCALb 220i-XL type ray electron spectrometer has the following analysis and test conditions of X-ray photoelectron spectroscopy: the excitation source is monochromatized A1K alpha X-ray, the power is 330W, and the basic vacuum is 3X 10 during analysis and test^-9mbar。

The analysis of carbon (C) element is carried out on an Elementar Micro Cube element analyzer which is mainly used for analyzing four elements of carbon (C), hydrogen (H), oxygen (O) and nitrogen (N), and the specific operation method and conditions are as follows: weighing 1-2 mg of a sample in a tin cup, putting the sample into an automatic sample feeding disc, feeding the sample into a combustion tube through a ball valve for combustion, wherein the combustion temperature is 1000 ℃ (in order to remove atmospheric interference during sample feeding, helium gas is adopted for blowing), and then reducing the combusted gas by using reduced copper to form nitrogen, carbon dioxide and water. The mixed gas is separated by three desorption columns and sequentially enters a TCD detector for detection. The oxygen element is analyzed by converting oxygen in a sample into CO under the action of a carbon catalyst by utilizing pyrolysis, and then detecting the CO by adopting TCD. Since the composite material of the present invention contains only carbon and metal oxide, the total content of the metal oxide can be known from the content of the carbon element.

The ratio of the different metal oxides is measured by an X-ray fluorescence spectrometer (XRF), and the content of the different metal oxides in the composite material is calculated according to the known content of carbon element. The X-ray fluorescence spectrum analyzer (XRF) adopted by the invention is a Rigaku 3013X-ray fluorescence spectrometer, and the X-ray fluorescence spectrum analysis and test conditions are as follows: the scanning time was 100s and the atmosphere was air.

The Raman detection adopts a LabRAM HR UV-NIR laser confocal Raman spectrometer produced by HORIBA company of Japan, and the laser wavelength is 325 nm.

The high-resolution transmission electron microscope (HRTEM) adopted by the invention is JEM-2100(HRTEM) (Nippon electronic Co., Ltd.), and the test conditions of the high-resolution transmission electron microscope are as follows: the acceleration voltage was 200 kV.

The XRD diffractometer adopted by the invention is an XRD-6000X-ray powder diffractometer (Shimadzu, Japan), and the XRD test conditions are as follows: the Cu target was irradiated with K α rays (wavelength λ is 0.154nm), tube voltage was 40kV, tube current was 200mA, and scanning speed was 10 ° (2 θ)/min.

Example 1

This example serves to illustrate the preparation of a carbon-coated nickel oxide nanocomposite material according to the invention.

(1) Weighing 10g of nickel carbonate and 10g of citric acid, adding the nickel carbonate and the citric acid into a beaker containing 100mL of deionized water, stirring the mixture at 70 ℃ to obtain a homogeneous solution, and continuously heating and evaporating the solution to dryness to obtain a solid precursor.

(2) And (2) placing the solid precursor obtained in the step (1) in a porcelain boat, then placing the porcelain boat in a constant temperature area of a tube furnace, introducing nitrogen with the flow of 100mL/min, heating to 600 ℃ at the speed of 4 ℃/min, keeping the temperature for 2h, stopping heating, and cooling to room temperature under the nitrogen atmosphere to obtain a black solid.

(3) And (3) placing the black solid obtained in the step (2) in a porcelain boat, then placing the porcelain boat in a constant temperature area of a tube furnace, introducing standard gas (15% of oxygen and 15% of nitrogen as balance gas) with the flow rate of 100mL/min, heating to 350 ℃ at the speed of 2 ℃/min, keeping the temperature for 8 hours, stopping heating, and cooling to room temperature under the atmosphere of the standard gas to obtain the black solid, namely the nano composite material.

Material characterization:

FIG. 1 is an X-ray diffraction (XRD) spectrum of the nanocomposite material of example 1, and it can be seen from FIG. 1 that nickel in the nanocomposite material exists in the form of an oxide after the mild oxidation treatment. FIG. 2 is a Transmission Electron Microscope (TEM) image of the nanocomposite material of example 1, in which it can be observed that the surface of the material has a carbon layer film, and the particle size is about 5 to 20 nm.

As can be seen from X-ray fluorescence spectrum analysis (XRF) and elemental analysis, the carbon content in the nanocomposite was 0.64 wt% and the nickel oxide content was 99.36 wt%. It was found by X-ray photoelectron spectroscopy (XPS) analysis that carbon, oxygen, and nickel were detected as surface layer elements of the nanocomposite. Wherein the ratio of the carbon element content of the surface layer to the total carbon element content is 32.7/1. It can be seen that the carbon in the nanocomposite is mainly present on the surface of the core film structure. FIG. 3 shows the Raman spectrum of the nanocomposite, with the G peak (1580 cm)^-1) Intensity of (3) and intensity of D peak (1320 cm)^-1) The ratio of (A) to (B) is 2.2/1. It can be seen that most of the carbon in this material is graphitic carbon.

Example 2

(1) Weighing 10g of nickel acetate and 10g of citric acid, adding the nickel acetate and the citric acid into a beaker containing 100mL of deionized water, stirring the mixture at 70 ℃ to obtain a homogeneous solution, and continuously heating and evaporating the solution to dryness to obtain a solid precursor.

(2) And (2) placing the solid precursor obtained in the step (1) in a porcelain boat, then placing the porcelain boat in a constant temperature area of a tube furnace, introducing nitrogen with the flow of 100mL/min, heating to 650 ℃ at the speed of 2 ℃/min, keeping the temperature for 2h, stopping heating, and cooling to room temperature under the nitrogen atmosphere to obtain a black solid.

(3) And (3) placing the black solid obtained in the step (2) in a porcelain boat, then placing the porcelain boat in a constant temperature area of a tube furnace, introducing standard gas (15% of oxygen and 15% of nitrogen as balance gas) with the flow rate of 100mL/min, heating to 330 ℃ at the speed of 2 ℃/min, keeping the temperature for 8 hours, stopping heating, and cooling to room temperature under the atmosphere of the standard gas to obtain the black solid, namely the nano composite material.

Material characterization:

fig. 4 shows the X-ray diffraction pattern of the nanocomposite material of example 2, and it can be seen from fig. 4 that nickel in the nanocomposite material exists in the form of oxide after the mild oxidation treatment. FIG. 5 shows a transmission electron microscope image of the nanocomposite material of example 2, in which it can be observed that the material surface has a carbon layer film with a particle size of about 5 to 20 nm.

As can be seen from X-ray fluorescence spectrum analysis (XRF) and elemental analysis, the carbon content in the nanocomposite was 0.91 wt% and the nickel oxide content was 99.09 wt%. It was found by X-ray photoelectron spectroscopy (XPS) analysis that carbon, oxygen, and nickel were detected as surface layer elements of the nanocomposite. Wherein the ratio of the carbon element content of the surface layer to the total carbon element content is 22.4/1. It can be seen that the carbon in the nanocomposite is mainly present on the surface of the core film structure. FIG. 6 shows the nanocompositeRaman spectrum of the material, wherein the peak G (1580 cm)^-1) Intensity of (2) and intensity of D peak (1320 cm)^-1) The ratio of (A)/(B) is 2.4/1. It can be seen that most of the carbon in this material is graphitic carbon.

Comparative example 1

And (3) placing 10g of nickel acetate solid in a porcelain boat, then placing the porcelain boat in a constant temperature area of a tube furnace, introducing air with the flow rate of 150mL/min, heating to 500 ℃ at the speed of 2 ℃/min, keeping the temperature for 2h, stopping heating, and cooling to room temperature in an air atmosphere to obtain a sample material.

Fig. 7 is an X-ray diffraction pattern of the material obtained in comparative example 1, and as can be seen from fig. 7, the XRD pattern of the material shows characteristic peaks of nickel oxide, indicating that nickel is mainly present in the form of nickel oxide. Fig. 8a and 8b show transmission electron micrographs of the material obtained in comparative example 1 at different magnifications, respectively, and it can be seen that nickel oxide is greatly agglomerated, indicating that nickel oxide nanoparticles without a carbon film coating are very easily agglomerated. XRF and elemental analysis showed that the material of comparative example 1 had a carbon content of 0.12 wt% and a nickel oxide content of 99.88 wt%.

Application example 1

This application example serves to illustrate the reaction of catalyzing the decomposition of nitrous oxide using the nanocomposite of example 1 as a catalyst.

0.5g of catalyst was placed in a continuous flow fixed bed reactor and the reaction gas consisted of 38.0% by volume N₂O, using nitrogen as balance gas, the flow rate of the reaction gas is 15ml/min, and the space velocity is 1800h^-1The activity evaluation temperature range is 300-500 ℃, and the catalyst is used for catalyzing and decomposing N at different temperatures₂The conversion of O is shown in Table 1.

Application example 2

N Using the method of application example 1₂O decomposition reaction except that the nanocomposite of example 2 was used as a catalyst, the results are shown in Table 1.

Comparative application example 1

N Using the method of application example 1₂O decomposition reaction except that the material of comparative example 1 was used asThe catalyst, results are shown in Table 1.

Comparative application example 2

N Using the method of application example 1₂O decomposition reaction except that commercially available nickel oxide (NiO) (analytical grade, lot: 20160803, manufacturer: national pharmaceutical group chemical Co., Ltd.) was used as a catalyst, the results are shown in Table 1.

TABLE 1

As can be seen from Table 1 above, the nanocomposite of carbon-coated nickel oxide prepared using the method of the present invention is comparable to uncoated pure nickel oxide, for N₂O has better catalytic decomposition performance, and N can be decomposed with high efficiency in a relatively low temperature range₂O, whereas the material of comparative example 1 requires a temperature of at least 490 ℃ for N₂The conversion rate of O reaches more than 99 percent, and the decomposition can be relatively complete. Commercial nickel oxide requires higher relative decomposition temperatures. It can be seen that the nanocomposite material of the invention has good catalytic effect on the decomposition of nitrous oxide, and can efficiently decompose and eliminate N at a lower temperature₂O, application thereof to industrial process waste gas N₂In the treatment of O, e.g. high concentrations of N produced during the production in adipic acid plants and nitric acid plants₂The elimination of the O tail gas can greatly reduce the reaction temperature and the energy consumption, and has good industrial application prospect.

It should be noted by those skilled in the art that the described embodiments of the present invention are merely exemplary and that various other substitutions, alterations, and modifications may be made within the scope of the present invention. Accordingly, the present invention is not limited to the above-described embodiments, but is only limited by the claims.

Claims

1. A carbon-coated nickel oxide nanocomposite, comprising a core-film structure having an outer film which is a graphitized carbon film and an inner core comprising nickel oxide nanoparticles, wherein the carbon content is not more than 1wt% of the nanocomposite;

the ratio of the carbon element determined by X-ray photoelectron spectroscopy in the nanocomposite material to the carbon element determined by element analysis is not less than 10 in terms of mass ratio;

in the Raman spectrum of the nano composite material, the Raman spectrum is positioned at 1580cm^-1Intensity of G peak nearby and at 1320cm^-1The ratio of the intensities of the nearby D peaks is greater than 2.

2. The nanocomposite of claim 1, wherein the inner core is a nickel oxide nanoparticle.

3. The nanocomposite as claimed in claim 1, wherein the core-film structure has a particle size of 1nm to 100 nm.

4. A method for preparing the carbon-coated nickel oxide nanocomposite according to any one of claims 1 to 3, comprising the steps of:

removing the solvent in the homogeneous solution to obtain a precursor;

pyrolyzing the precursor in an inert atmosphere or a reducing atmosphere;

5. The preparation method of claim 4, wherein the oxygen treatment comprises introducing standard gas into the pyrolyzed product and heating, wherein the standard gas contains oxygen gas and balance gas, and the volume concentration of the oxygen gas is 10-40%.

6. The preparation method according to claim 4, wherein the temperature of the oxygen treatment is 200 to 500 ℃ and the time of the oxygen treatment is 0.5 to 10 hours.

7. The production method according to claim 4, wherein the mass ratio of the nickel-containing compound to the polyvalent organic carboxylic acid is 1 (0.1 to 100); the nickel-containing compound is selected from one or more of organic acid salt of nickel, nickel carbonate, basic nickel carbonate, nickel hydroxide and nickel oxide; the polybasic organic carboxylic acid is selected from one or more of citric acid, maleic acid, trimesic acid, terephthalic acid, gluconic acid and malic acid.

8. The method of claim 4, wherein the pyrolyzing comprises: heating the precursor to a constant temperature section in an inert atmosphere or a reducing atmosphere, and keeping the constant temperature in the constant temperature section;

the heating rate is 0.5-30 ℃/min, the temperature of the constant temperature section is 400-800 ℃, the constant temperature time is 20-600 min, the inert atmosphere is nitrogen or argon, and the reducing atmosphere is a mixed gas of inert gas and hydrogen.

9. Use of a nanocomposite according to any one of claims 1 to 3 as a catalyst.

10. Use of a nanocomposite according to any one of claims 1 to 3 as a catalyst for decomposing nitrous oxide, comprising: and contacting the catalyst with nitrous oxide to perform a catalytic decomposition reaction to generate nitrogen and oxygen.

11. The use of claim 10, wherein the temperature of the catalytic decomposition reaction is 300 ℃ to 400 ℃.

12. Use according to claim 10, wherein the catalytic decomposition reaction has a space velocity of 1000h^-1～3000h^-1。

13. Use according to claim 10, wherein the nitrous oxide has a volume concentration of 30% to 40%.