CN113751005A - Catalyst of carbon-coated transition metal oxide and preparation method and application thereof - Google Patents
Catalyst of carbon-coated transition metal oxide and preparation method and application thereof Download PDFInfo
- Publication number
- CN113751005A CN113751005A CN202010503583.5A CN202010503583A CN113751005A CN 113751005 A CN113751005 A CN 113751005A CN 202010503583 A CN202010503583 A CN 202010503583A CN 113751005 A CN113751005 A CN 113751005A
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- China
- Prior art keywords
- transition metal
- catalyst
- carbon
- metal oxide
- mass
- Prior art date
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 182
- 229910052799 carbon Inorganic materials 0.000 title claims abstract description 159
- 239000003054 catalyst Substances 0.000 title claims abstract description 150
- 229910000314 transition metal oxide Inorganic materials 0.000 title claims abstract description 77
- 238000002360 preparation method Methods 0.000 title claims abstract description 22
- 239000002114 nanocomposite Substances 0.000 claims abstract description 58
- 239000000463 material Substances 0.000 claims abstract description 45
- 238000000034 method Methods 0.000 claims abstract description 43
- 229910002804 graphite Inorganic materials 0.000 claims abstract description 21
- 239000010439 graphite Substances 0.000 claims abstract description 21
- 238000006243 chemical reaction Methods 0.000 claims abstract description 18
- 230000008569 process Effects 0.000 claims abstract description 9
- 150000003624 transition metals Chemical class 0.000 claims description 79
- 229910052723 transition metal Inorganic materials 0.000 claims description 74
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 57
- 229910052760 oxygen Inorganic materials 0.000 claims description 57
- 239000001301 oxygen Substances 0.000 claims description 57
- GQPLMRYTRLFLPF-UHFFFAOYSA-N Nitrous Oxide Chemical group [O-][N+]#N GQPLMRYTRLFLPF-UHFFFAOYSA-N 0.000 claims description 44
- 239000012298 atmosphere Substances 0.000 claims description 44
- 239000007789 gas Substances 0.000 claims description 41
- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical compound OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 claims description 39
- 238000010438 heat treatment Methods 0.000 claims description 39
- IJGRMHOSHXDMSA-UHFFFAOYSA-N nitrogen Substances N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 39
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- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 24
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 claims description 22
- 229910052757 nitrogen Inorganic materials 0.000 claims description 21
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- GNRSAWUEBMWBQH-UHFFFAOYSA-N oxonickel Chemical compound [Ni]=O GNRSAWUEBMWBQH-UHFFFAOYSA-N 0.000 claims description 12
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- VXAUWWUXCIMFIM-UHFFFAOYSA-M aluminum;oxygen(2-);hydroxide Chemical compound [OH-].[O-2].[Al+3] VXAUWWUXCIMFIM-UHFFFAOYSA-M 0.000 claims description 10
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- 150000004649 carbonic acid derivatives Chemical class 0.000 claims description 2
- 229910000428 cobalt oxide Inorganic materials 0.000 claims description 2
- IVMYJDGYRUAWML-UHFFFAOYSA-N cobalt(ii) oxide Chemical compound [Co]=O IVMYJDGYRUAWML-UHFFFAOYSA-N 0.000 claims description 2
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- URGAHOPLAPQHLN-UHFFFAOYSA-N sodium aluminosilicate Chemical compound [Na+].[Al+3].[O-][Si]([O-])=O.[O-][Si]([O-])=O URGAHOPLAPQHLN-UHFFFAOYSA-N 0.000 description 4
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Images
Classifications
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- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
- B01J23/74—Iron group metals
- B01J23/755—Nickel
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
- B01D53/86—Catalytic processes
- B01D53/8621—Removing nitrogen compounds
- B01D53/8625—Nitrogen oxides
- B01D53/8628—Processes characterised by a specific catalyst
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- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/02—Impregnation, coating or precipitation
- B01J37/0201—Impregnation
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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- B01J37/02—Impregnation, coating or precipitation
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
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- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/12—Oxidising
- B01J37/14—Oxidising with gases containing free oxygen
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y40/00—Manufacture or treatment of nanostructures
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2257/00—Components to be removed
- B01D2257/40—Nitrogen compounds
- B01D2257/402—Dinitrogen oxide
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
- Y02C20/00—Capture or disposal of greenhouse gases
- Y02C20/10—Capture or disposal of greenhouse gases of nitrous oxide (N2O)
Abstract
The invention provides a catalyst of carbon-coated transition metal oxide and a preparation method and application thereof, wherein the catalyst comprises a carrier and an active component loaded on the carrier, wherein the active component is a graphite carbon-coated transition metal oxide nano composite material, and the transition metal oxide is selected from one or more of oxides of VIII group, VIB group, IB group and IIB group. The invention adopts the graphite carbon-coated transition metal oxide nano composite material as the active component and loads the graphite carbon-coated transition metal oxide nano composite material on the carrier through a specific process, so that the obtained catalyst not only has higher catalytic activity, but also has certain mechanical strength, is not easy to crack and pulverize in the reaction process, can meet the requirements of actual industrial production, and has good application prospect.
Description
Technical Field
The invention relates to the field of catalysts, in particular to a catalyst of carbon-coated transition metal oxide and a preparation method and application thereof.
Background
The transition metal oxide has excellent catalytic performance and electromagnetic performance, and is a research hotspot in the field of inorganic materials. The carbon material has good conductivity, good chemical/electrochemical stability and high structural strength. The nano particles of the transition metal oxide are coated by the carbon material, so that the conductivity and the stability of the nano material can be improved, and the nano material has the effect of a limited domain and is not easy to agglomerate. In recent years, carbon-coated transition metal oxide nano materials have shown good application prospects in the fields of electrocatalysis, supercapacitor materials, lithium ion battery cathode materials, bioengineering and the like.
Generally, carbon-coated nanomaterials are small in particle size, powdery, and have poor self-moldability. However, in industrial applications, especially for fixed bed processes, the catalyst is required to have not only certain activity and selectivity, but also certain properties such as particle size and mechanical strength. If the catalyst is not strong enough, the catalyst is broken and pulverized, which easily causes the catalyst carrying loss or the device blockage in the reaction process, greatly increases the pressure drop of the catalyst bed layer, and even causes the forced shutdown of the device. Therefore, the carbon-coated nano material needs to be subjected to molding treatment to meet the industrial reaction requirements of compressive strength, pressure drop after filling, stability and the like. The molding treatment is a process of aggregating raw materials such as catalyst raw powder and molding aid to prepare solid particles having a certain size, shape and mechanical strength. The forming process has an effect on the activity, strength and service life of the catalyst to a certain extent. How to improve the strength and not influence the activity as much as possible is the key point of research on the carbon-coated nano material forming method.
N2O is an important greenhouse gas, and its 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, which is also NO in the stratospherexThe main source of the compound can not only 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, the wave quantity is large, and the concentration is high (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 most preferablyEfficiency and cleaning techniques. Among them, the catalyst is the core of the direct catalytic decomposition method. Decomposition of N reported in the present study2The catalyst of O mainly comprises noble metal catalyst, ion-exchanged molecular sieve catalyst and 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 price of molecular sieve catalyst and transition metal oxide catalyst is obviously lower than that of noble metal, but at present, the two catalysts are used for N2The activity of O catalytic decomposition is low, and the temperature range of efficient decomposition is 450-550 ℃. Therefore, the development of a new non-noble metal, low cost and efficient new material catalyst couple N2The emission reduction of O has important significance.
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
The invention aims to overcome at least one defect of the prior art and provides a catalyst of carbon-coated transition metal oxide, a preparation method and application thereof.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention provides a catalyst of carbon-coated transition metal oxide, which comprises a carrier and an active component loaded on the carrier, wherein the active component is a nano composite material of graphite carbon-coated transition metal oxide.
According to one embodiment of the invention, the transition metal oxide is selected from one or more of the group VIII, VIB, IB and IIB oxides, preferably one or more of iron oxide, cobalt oxide and nickel oxide.
According to one embodiment of the invention, the inner core further comprises alumina.
According to one embodiment of the present invention, the content of the transition metal oxide is 10% to 90% and the content of the carrier is 10% to 90% based on the mass of the catalyst; preferably, the content of the transition metal oxide is 40 to 90 percent, and the content of the carrier is 10 to 60 percent.
According to an embodiment of the present invention, the carbon content is not more than 5%, preferably 0.1% to 5%, more preferably 0.1% to 1%, based on 100% by mass of the total of carbon and the transition metal oxide.
According to one embodiment of the present invention, the ratio of the carbon element in the catalyst determined by X-ray photoelectron spectroscopy to the carbon element content determined by elemental analysis is not less than 10 in terms of mass ratio.
According to one embodiment of the invention, the catalyst has a Raman spectrum at 1580cm-1Intensity of nearby G peak at 1320cm-1The ratio of the intensities of the nearby D peaks is greater than 1, preferably greater than 2.
According to one embodiment of the invention, the catalyst has a Raman spectrum only at 1580cm-1Nearby G peak, not located at 1320cm-1Nearby D peak.
According to one embodiment of the present invention, the support is selected from the group consisting of alumina, silica, and a composite oxide of silica and alumina.
According to one embodiment of the invention, the catalyst has a specific surface area of 90m2/g～160m2Per g, pore volume 0.12cm3/g～0.18cm3(iv) g, the crushing strength is 120N/cm-160N/cm.
According to one embodiment of the present invention, the nanocomposite comprises a core film structure having an outer film which is a graphitized carbon film and an inner core comprising transition metal oxide nanoparticles.
The invention also provides a preparation method of the catalyst, which comprises the following steps: providing a carbon-coated transition metal nanocomposite; carrying out oxygen treatment on the carbon-coated transition metal nanocomposite to obtain a carbon-coated transition metal oxide nanocomposite; and molding the carbon-coated transition metal oxide nano composite material to obtain the catalyst.
According to one embodiment of the present invention, a method for preparing a carbon-coated transition metal nanocomposite includes: placing a transition metal-containing compound and a carboxylic acid in a solvent to mix to form a homogeneous solution; removing the solvent in the homogeneous solution to obtain a precursor; and pyrolyzing the precursor in inert atmosphere or reducing atmosphere to obtain the carbon-coated transition metal nanocomposite.
According to one embodiment of the invention, the transition metal-containing compound is selected from one or more of soluble organic acid salts, basic carbonates, hydroxides and oxides of transition metals, the carboxylic acid is 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 transition metal-containing compound to the carboxylic acid is 1 (0.1-10).
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.
According to an embodiment of the present invention, the method further comprises performing the oxygen treatment after performing the acid washing treatment on the pyrolyzed product.
According to one embodiment of the present invention, the carbon-coated transition metal nanocomposite may have an acid loss rate of 60% or less, may be 40% or less, may be 30% or less, may be 20% or less, and may be 10% or less.
According to one embodiment of the invention, the oxygen treatment comprises introducing standard gas into the product after pyrolysis and heating, wherein the standard gas contains oxygen and balance gas, and the volume concentration of the oxygen is 10-40%; the temperature of the oxygen treatment is 200-500 ℃, and the time of the oxygen treatment is 0.5-10 h.
According to one embodiment of the invention, the forming process comprises: adding a binder into the carbon-coated transition metal oxide nano composite material, and uniformly mixing to obtain a wet material mass; the wet mass is shaped after drying and optional firing. Wherein the shaping may be selected from one or more of extruding, rolling, tabletting and granulating.
According to one embodiment of the invention, the drying temperature is 20-100 ℃, the drying time is 3-24 h, and the drying atmosphere is inert atmosphere or air atmosphere; the roasting comprises the following steps: heating the dried product to 400-800 ℃ at a heating rate of 1-20 ℃/min under an inert atmosphere, and keeping the temperature constant for 1-10 h; the second roasting comprises the following steps: and heating the product obtained after the molding treatment to 300-400 ℃ at a heating rate of 1-20 ℃/min in the air atmosphere, and keeping the temperature for 4-10 h.
According to one embodiment of the invention, the binder is selected from the group consisting of an aluminium sol, a silica sol or a silica-alumina sol. The aluminum sol, silica sol or silica alumina sol is conveniently commercially available or can be made by itself using existing methods, such as by acidifying pseudo-boehmite.
According to one embodiment of the present invention, the binder is prepared from pseudoboehmite and a peptizing agent selected from one or more of an aqueous nitric acid solution, an aqueous hydrochloric acid solution and an aqueous citric acid solution.
According to one embodiment of the invention, the binder further comprises a lubricant selected from one or more of sesbania powder, citric acid, starch and carboxymethyl cellulose.
According to one embodiment of the invention, the liquid-solid mass ratio in the wet dough is 0.8-1.5, the carbon-coated transition metal oxide nano composite material accounts for 20-80% of the mass of the solids in the wet dough, and the binder accounts for 20-80% of the mass of the solids in the wet dough; the mass of the lubricant is 1-6% of that of the carbon-coated transition metal oxide nanocomposite, and the mass of the peptizing agent is 1-5%, preferably 2-3% of that of the binder.
The invention also provides another preparation method of the catalyst, which comprises the following steps:
introducing a transition metal onto a support;
(II) carrying out graphite carbon coating on the transition metal loaded on the carrier to obtain a graphite carbon coated transition metal simple substance composite structure;
(III) carrying out oxygen treatment on the graphite carbon coated transition metal simple substance composite structure, and removing amorphous carbon to obtain the catalyst containing the graphite carbon coated transition metal oxide composite structure.
According to the aforementioned production method, the transition metal described in (I) is in a zero-valent state and/or an oxidized state.
According to an embodiment of the present invention, the loss rate of the transition metal in the graphite carbon-coated transition metal composite structure is not higher than 60%, may not be higher than 40%, may not be higher than 30%, may not be higher than 20%, and may not be higher than 10% after acid washing.
According to one embodiment of the invention, the oxygen treatment comprises introducing standard gas and heating, wherein the standard gas comprises oxygen and balance gas, and the volume concentration of the oxygen is 10-40%; the temperature of the oxygen treatment is 200-500 ℃, and the time of the oxygen treatment is 0.5-10 h.
According to an embodiment of the present invention, the support is alumina, silica, or a composite oxide of silica and alumina.
The invention also provides another catalyst prepared by any one of the methods.
According to one embodiment of the present invention, the transition metal oxide content is 10% to 90% and the support content is 10% to 90% based on the mass of the catalyst; the Raman spectrum of the catalyst is 1580cm-1Intensity of nearby G peak at 1320cm-1The ratio of the intensities of the nearby D peaks is greater than 1, preferably greater than 2.
According to one embodiment of the inventionBased on the mass of the catalyst, the content of the transition metal oxide is 40-90%, and the content of the carrier is 10-60%; the Raman spectrum of the catalyst is only 1580cm-1Nearby G peak, not located at 1320cm-1Nearby D peak.
The invention also provides a method for catalyzing the decomposition of nitrous oxide, which comprises the step of contacting a catalyst with the nitrous oxide to perform a catalytic decomposition reaction to generate nitrogen and oxygen, wherein the catalyst is the catalyst.
According to one embodiment of the invention, in the catalytic decomposition reaction, the reaction temperature is 300-420 ℃, the reaction space velocity is 500-3000 ml reaction gas/(h.g catalyst), and the volume concentration of nitrous oxide is 5-40%, preferably 30-40%.
According to the technical scheme, the invention has the beneficial effects that:
the carbon-coated transition metal oxide supported catalyst provided by the invention adopts a nano composite material of an ultrathin graphite carbon layer-coated transition metal oxide as an active component. The invention firstly utilizes the action of the transition metal simple substance to form a graphitized carbon film with good coating on the outside of the carbon film, then converts the transition metal simple substance into the transition metal oxide through oxygen treatment, and simultaneously removes amorphous carbon, thereby obtaining the nano composite material of the transition metal oxide tightly coated by a small amount of graphitic carbon. The invention discovers that the unique structure and composition enable the catalyst to be used as a catalyst active component to catalyze N2The catalyst has excellent activity during O decomposition reaction, and the prepared supported catalyst has good mechanical property and can maintain the catalytic activity. Compared with the prior catalyst, the catalyst can reduce the content of N in industrial waste gas2The catalyst can directly catalyze and decompose the 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 the 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 product obtained in step (3) of example 1;
FIG. 2 is a transmission electron microscope photograph of the product obtained in step (3) of example 1;
FIG. 3 is a Raman spectrum of the product obtained in step (3) of example 1;
FIG. 4 is an X-ray diffraction pattern of the product obtained in step (3) of example 2;
FIG. 5 is a transmission electron microscope photograph of a product obtained in step (3) of example 2;
FIG. 6 is a Raman spectrum of the product obtained in step (3) of example 2.
Detailed Description
The following presents various embodiments or examples in order to enable those skilled in the art to practice the invention with reference to the description herein. These are, of course, merely examples and are not intended to limit the invention. The endpoints of the ranges and any values disclosed in the present application are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For wave value ranges, one or more new wave value ranges may be obtained from combinations of the end point values of each range, the end point values of each range and the individual point values, and these wave value ranges should be considered as specifically disclosed herein.
The term "nuclear membrane structure" in the present invention refers to a nuclear membrane structure having an outer membrane which is a graphitized carbon membrane and an inner core which contains transition metal oxide nanoparticles. The composite material formed after the graphitized carbon film is coated with the transition metal 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.
The invention provides a catalyst of carbon-coated transition metal oxide, which comprises a carrier and an active component loaded on the carrier, wherein the active component is a nano composite material of graphite carbon-coated transition metal oxide.
According to the present invention, there is no particular limitation on the kind of the transition metal, and those of the existing graphite carbon-coated transition metal composite materials can be used in the present invention. For example, the transition metal oxide may be selected from one or more oxides of group VIII, group VIB, group IB, and group IIB metals; more specifically, it may be selected from one or more of the oxides of iron, cobalt, nickel and, optionally, one or more of the oxides of aluminum, copper, zinc, chromium, molybdenum, tungsten.
According to the present invention, the nanocomposite material has a core-film structure having an outer film which is a graphitized carbon film and an inner core containing transition metal oxide nanoparticles.
According to the present invention, the catalyst is a supported catalyst having a nanocomposite of a transition metal oxide coated with graphitic carbon as an active component, and in general, the nanocomposite of the transition metal oxide coated with graphitic carbon has a core film structure having an integral outer film layer and an inner core layer, and the outer film is mainly composed of a graphitized carbon film, which is a thin film structure mainly composed of graphitized carbon and completely or substantially completely coats the surface of the transition metal oxide nanoparticle, and in general, it is considerably difficult to completely coat graphitic carbon on the outside of the transition metal oxide. The inventor of the invention unexpectedly finds that the core film structure coated with the graphitized carbon film on the outer layer has relatively little carbon content in the film layer, but greatly improves the performance of the whole material, particularly the catalytic performance, specifically, the core film structure not only can generate a certain limited domain effect and effectively avoid the aggregation and growth of core nanoparticles, so that the catalytic activity of the composite material is 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 a pure transition metal oxide which is not coated with a graphite carbon film. The catalyst has high mechanical strength, can meet the industrial application requirements, can well maintain the catalytic performance of the active component, and has good application prospect.
In some embodiments, the transition metal oxide is present in an amount of 40% to 90%, e.g., 40%, 43%, 50%, 55%, 57%, 67%, 79%, 80%, 85%, etc., and the support is present in an amount of 10% to 60%, e.g., 10%, 16%, 22%, 31%, 35%, 40%, 50%, 60%, etc., based on the mass of the catalyst. The carbon content is not more than 2% of the catalyst content, such as 1%, 0.8%, 0.5%, 0.3%, 0.2%, 0.1%, etc.
In some embodiments, the catalyst of the present invention has a ratio of carbon element determined by X-ray photoelectron spectroscopy to carbon element content 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 content ratio of carbon element determined by X-ray photoelectron spectroscopy to carbon element determined by element analysis is larger, most of carbon in the whole catalyst is concentrated on the surface of the material to form a carbon film layer, and further the nuclear film structure is formed.
In some embodiments, the catalyst of the present invention has a Raman spectrum 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 peak D and the peak G are both Raman characteristic peaks of a crystal of C atoms, the peak D represents a defect in a lattice of carbon atoms, and the peak G represents a sp of C atoms2Hybrid in-plane stretching vibration. It is understood that a larger ratio of the intensity of the G peak to the intensity of the D peak indicates that more graphitic carbon is present in the catalyst than amorphous carbon. That is, the carbon element in the catalyst of the present invention is mainly present in the form of graphitic carbon. The graphite carbon has better oxidation resistance, and can be used for increasing the catalytic activity with the transition metal oxide nanoparticles of the inner core in a synergistic manner, so that the performance of the whole catalyst is improved.
In some embodiments, the catalyst of the present invention has a Raman spectrum at 1580cm-1Nearby G peak, not located at 1320cm-1Nearby D peak.
According to the invention, the aforementioned support may be alumina and/or silica. The catalyst has a certain pore structure, and in some embodiments, the specific surface area of the catalyst of the present invention is 90m2/g～160m2Per g, pore volume 0.12cm3/g～0.18cm3(iv) g, the crushing strength is 120N/cm-160N/cm.
It should be noted that, for the present invention, the specific surface area and pore volume of the catalyst obtained by different binders (such as alumina sol, silica sol, pseudo-boehmite, etc.) and different forming conditions (such as pressure) and forming manners (tabletting, extruding, granulating) are greatly different, so that the ranges of the specific surface area, pore volume and crush strength can be adjusted according to the actual operating conditions and the requirements for the catalyst strength, etc., and the present invention is not limited thereto.
The invention also provides a preparation method of the catalyst, which comprises the following steps: providing a carbon-coated transition metal nanocomposite; carrying out oxygen treatment on the carbon-coated transition metal nanocomposite to obtain a carbon-coated transition metal oxide nanocomposite; and (3) molding the carbon-coated transition metal oxide nano composite material to obtain the catalyst.
The preparation of the catalyst is described in detail below.
First, a carbon-coated transition metal nanocomposite is provided. The carbon-coated transition metal nanocomposite can be prepared by the existing method or can be obtained commercially. The preparation method preferably adopts the following steps:
placing a transition metal-containing compound and a carboxylic acid in a solvent to mix to form a homogeneous solution; removing the solvent in the homogeneous solution to obtain a precursor; and pyrolyzing the precursor in inert atmosphere or reducing atmosphere to obtain the carbon-coated transition metal nanocomposite.
Specifically, the precursor is a water-soluble mixture, which refers to a water-soluble mixture containing nickel obtained by dissolving a transition metal-containing compound and a carboxylic acid in a solvent such as water, ethanol, etc. to form a homogeneous solution, and then directly evaporating the solvent. The foregoing temperature and process of evaporating the solvent may be by any available prior art, for example, spray drying at 80 ℃ to 120 ℃ or drying in an oven.
In some embodiments, the transition metal-containing compound is selected from one or more of a soluble organic acid salt, basic carbonate, hydroxide, and oxide of the transition metal.
According to the present invention, there is no particular limitation on the kind of the carboxylic acid, and carboxylic acids used in such a method of producing a carbon-coated transition metal composite material as known may be used in the present invention, including nitrogen-containing or nitrogen-free polycarboxylic acids. In some embodiments, the carboxylic acid is 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 transition metal-containing compound to the carboxylic acid is 1 (0.1-10).
In addition, other organic compounds than the two mentioned above, which may be any organic compound that can supplement the carbon source required in the product, with or without other doping atoms, can also be added to form a homogeneous solution. Organic compounds having no volatility such as organic polyols, lactic acid and the like are preferable. In some embodiments, the mass ratio of the transition metal-containing compound, the 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, and more preferably 1:0.8 to 3:0 to 3.
In some embodiments, 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 ℃/min to 30 ℃/min, such as 2.5 ℃/min, 4.5 ℃/min, 5 ℃/min, 6.5 ℃/min, 7 ℃/min, 8.5 ℃/min, 9 ℃/min, 10 ℃/min, 20 ℃/min, and the like; the temperature of the constant temperature section is 400-800 ℃, preferably 500-700 ℃, such as 500 ℃, 550 ℃, 570 ℃, 610 ℃, 660 ℃, 680 ℃ and the like; the constant temperature time is 20min to 600min, preferably 30min to 300min, such as 30min, 45min, 55min, 70min, 86min, 97min, 100min, 180min, 270min, 300min and the like; 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 present invention further comprises acid washing the pyrolyzed product.
In fact, the product obtained after the aforementioned pyrolysis is a nanocomposite material in which a graphitized carbon layer is coated with a transition metal. The graphitized carbon layer is a carbon structure with a layered structure, but not an amorphous structure, which can be obviously observed under a high-resolution transmission electron microscope, and the interlayer distance is about 0.34 nm. The nano composite material of transition metal coated by the graphitized carbon layer is a composite material consisting of transition metal nano particles which are tightly coated (not contacted with the outside) by the graphitized carbon layer, transition metal nano particles which can be contacted with the outside and are limited in domain and carbon materials with mesoporous structures. After acid pickling, the nickel in the composite material has certain loss, and can be characterized by the acid pickling loss rate. That is, the "acid pickling loss ratio" refers to the loss ratio of the transition metal after the acid pickling of the prepared carbon-coated transition metal nanocomposite product. Which reflects how tightly the graphitized carbon layer coats the transition metal. If the graphitized carbon layer does not cover the transition metal tightly, the transition metal of the core is dissolved by the acid and lost after the acid treatment. The larger the acid washing loss rate is, the lower the degree of tightness of the transition metal coating by the graphitized carbon layer is, and the smaller the acid washing loss rate is, the higher the degree of tightness of the transition metal coating by the graphitized carbon layer is.
In general, the specific conditions of the pickling treatment are: adding 1g of sample into 20mL of sulfuric acid aqueous solution (1mol/L), treating the sample at 90 ℃ for 8h, then washing the sample to be neutral by using deionized water, weighing and analyzing the sample after drying, and calculating the pickling loss rate according to the following formula.
The calculation formula is as follows: the acid pickling loss rate is [1- (mass partial wave of transition metal in the composite material after acid pickling × mass of the composite material after acid pickling) ÷ (mass partial wave of transition metal in the composite material to be treated × mass of the composite material to be treated) ] × 100%. It should be noted that the "composite" in this formula is a composite that has not been treated with oxygen. In some embodiments, the composite material generally has a pickling loss ratio of 40% or less, can be 30% or less, can be 20% or less, and can be 10% or less.
Then, the carbon-coated transition metal nanocomposite obtained after pyrolysis or after acid washing is further subjected to oxygen treatment, wherein the oxygen treatment comprises introducing standard gas into the pyrolyzed product and heating, wherein the standard gas contains oxygen gas and equilibrium gas, and the volume concentration of the oxygen gas is 10% to 40%, such as 10%, 12%, 15%, 17%, 20%, 22%, 25%, 28%, 30%, and the like. 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 from 200 ℃ to 500 ℃, preferably from 300 ℃ to 400 ℃, such as 320 ℃, 340 ℃, 350 ℃, 380 ℃, and the like; the time of the oxygen treatment is 0.5 to 10 hours, for example, 1 hour, 3 hours, 5 hours, 7 hours, 8 hours, 10 hours, etc.
One skilled in the art will recognize that carbon can be oxidized with oxygen to form a gas. It will be appreciated that the precursor pyrolytically forms a carbon-clad transition metal core nanocomposite material which, after high temperature oxygen treatment, may be such that carbon in the material is oxidised and lost. However, the inventors of the present invention have unexpectedly found that, after appropriate oxygen treatment, a small portion of the carbon remains while a large portion of the carbon is burned off. As mentioned above, the XRD, XPS and Raman spectroscopy analysis prove that a composite structure with a very thin graphite carbon film coated on the surface of the transition metal oxide is formed. Surprisingly, this is also true for nanocomposites in which carbon tightly coats the elemental core of the transition metal (which is not substantially lost in transition metal when treated with strong non-oxidizing acids at temperatures near boiling for extended periods of time). Further research finds that not only the transition metal of the inner core is oxidized, but also the thin film carbon layer enables the nano composite material to further have a plurality of excellent properties, so that the nano composite material has great application potential in catalytic materials, energy storage materials and electromagnetic materials.
And finally, molding the product after the oxygen treatment, namely the carbon-coated transition metal oxide nano composite material to obtain the catalyst. The forming process specifically comprises the following steps:
adding a binder, an optional lubricant and the like into the carbon-coated transition metal oxide nanocomposite, and then uniformly mixing to obtain a wet mass; drying and roasting the wet dough for the first time; and forming the product after the first roasting treatment, and roasting the formed product for the second time to obtain the catalyst.
Specifically, the binder is selected from an aluminum sol, a silica sol, or a silicon aluminum sol. The alumina sol is commercially available or prepared by a known method from hydrated alumina (e.g., pseudoboehmite or boehmite) and a peptizing agent selected from one or more of aqueous nitric acid, aqueous hydrochloric acid and aqueous citric acid. Further, the binder can also comprise a lubricant, namely the binder is prepared from hydrated alumina, peptizer and lubricant, and the lubricant can be one or more selected from sesbania powder, citric acid, starch and carboxymethyl cellulose.
In some embodiments, the mass ratio of liquid to solid in the wet mass is 0.8 to 1.5, such as 0.8, 0.9, 1, 1.2, etc., preferably 0.85 to 1. The carbon-coated transition metal oxide nanocomposite accounts for 20% to 80% of the mass of solids in the wet mass, for example, 20%, 25%, 31%, 47%, 56%, 60%, 75%, etc. The binder accounts for 20-80% of the mass of solids in the wet mass, such as 22%, 36%, 41%, 47%, 55%, 67%, 80%, etc.; the amount of the lubricant added may be 1% to 6%, for example, 1%, 2%, 4%, 5%, 6%, etc., preferably 2% to 3% based on the mass of the carbon-coated transition metal oxide nanocomposite. The mass of the peptizing agent is 1-5%, preferably 2-3% of the mass of the binder.
After obtaining a wet mass of the desired composition, the wet mass is dried at a temperature of 20 ℃ to 100 ℃, for example 20 ℃, 25 ℃, 30 ℃, 45 ℃, 50 ℃, 65 ℃, 70 ℃, 72 ℃, 82 ℃, 88 ℃ and the like. The drying time is 3h to 24h, for example, 3h, 4h, 6h, 7h, 10h, 12h, 13h, 17h, 20h, 24h and the like. The drying atmosphere is an inert atmosphere or an air atmosphere.
The dried product may be first calcined in an inert atmosphere, such as pseudoboehmite, which is converted to gamma-Al2O3As a carrier for the active ingredient. The heating rate of the calcination is 1 to 20 ℃/min, preferably 2.5 to 10 ℃/min, for example, 2.5, 3.5, 4, 5, 6, 8, 10 ℃/min, etc. When the temperature is raised to the roasting temperature of 400-800 ℃, keeping the constant temperature for 1-10 h, preferably 450-600 ℃, and keeping the constant temperature for 3-8 h.
The product after drying or first roasting can be shaped, and then second roasting is carried out, wherein the shaping method is one or more of extruding, rolling, tabletting and granulating, and the invention is not limited by the method.
The invention also provides another preparation method of the catalyst, which comprises the following operations:
an operation of introducing a transition metal onto a support;
(II) preparing a graphite carbon-coated transition metal composite structure; and
(III) an operation of converting the zero-valent transition metal in the composite structure into a transition metal oxide by oxygen treatment while removing amorphous carbon.
According to the above-mentioned preparation process, the transition metal in (I) is in a zero-valent state and/or an oxidized state.
According to the preparation method, one mode is as follows: firstly, loading oxidized transition metal on a carrier by using existing loading methods such as dipping and the like, (II) then introducing gas containing a carbon source at high temperature in an inert atmosphere or a hydrogen atmosphere, and simultaneously carrying out reduction and carbon coating on the transition metal; (III) finally, oxygen treatment is carried out to convert the zero-valent transition metal into the transition metal oxide and simultaneously remove the amorphous carbon. The other mode is as follows: firstly, loading oxidized transition metal on a carrier by using existing loading methods such as dipping and the like, then reducing the transition metal to a zero valence state, and (II) introducing gas containing a carbon source at a high temperature in an inert atmosphere or a hydrogen atmosphere to carry out carbon coating; (III) finally, oxygen treatment is carried out to convert the zero-valent transition metal into the transition metal oxide and simultaneously remove the amorphous carbon.
According to the foregoing production method, the carrier is alumina or silica, or the carrier is a composite oxide of silica and alumina.
In some embodiments, the graphitic carbon-coated transition metal composite structure is pickled, and the loss rate of transition metal is not higher than 60%, may not be higher than 40%, may not be higher than 30%, may not be higher than 20%, and may not be higher than 10%.
In some embodiments, the oxygen treatment comprises introducing standard gas and heating, wherein the standard gas comprises oxygen and balance gas, and the volume concentration of the oxygen is 10-40%; the temperature of the oxygen treatment is 200-500 ℃, and the time of the oxygen treatment is 0.5-10 h.
In conclusion, the carbon-coated transition metal oxide nano composite material is used as an active component and is loaded on the carrier through a specific process, so that the obtained catalyst not only has high catalytic activity, but also has certain mechanical strength, is not easy to break and pulverize in the reaction process, can meet the requirements of actual industrial production, and has good application prospect.
The invention also provides a catalyst prepared by any one of the methods.
In some embodiments, the transition metal oxide content is 10% to 90% and the support content is 10% to 90% based on the mass of the catalyst; preferably, the content of the transition metal oxide is 40-90%, and the content of the carrier is 10-60%.
In some embodiments, the catalyst has a Raman spectrum at 1580cm-1Intensity of nearby G peak at 1320cm-1The ratio of the intensities of the nearby D peaks is greater than 2.
In some embodiments, the catalyst has a Raman spectrum at 1580cm-1Nearby G peak, not located at 1320cm-1Nearby D peak.
The invention also provides a specific application of the catalyst, which comprises a method for catalyzing the decomposition of nitrous oxide by using the catalyst, and specifically, a gas containing nitrous oxide is introduced into a reactor provided with the catalyst to carry out a catalytic decomposition reaction to generate nitrogen and oxygen.
In some embodiments, the temperature of the catalytic decomposition reaction is from 300 ℃ to 420 ℃, preferably from 350 ℃ to 420 ℃. The space velocity of the catalytic decomposition reaction is 500-3000 ml of reaction gas/(h.g of catalyst). The high concentration of the nitrous oxide allowed by the invention and the large reaction space velocity show that the catalyst of the invention has high activity and large treatment capacity of the device when the reaction is applied.
According to the invention, as mentioned above, the currently reported decomposition N2The catalyst of O mainly comprises noble metal catalyst, ion-exchanged molecular sieve catalyst and 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.
The inventors of the present invention have found that the nanocomposite using the carbon-coated transition metal oxide of the present invention as a catalyst can effectively decompose nitrous oxide into nitrogen and oxygen, and exhibits excellent catalytic activity stability in the reaction. In addition, when the existing 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 0.5-2 percent, and the catalyst can be directly decomposed to achieve a high decomposition rate without being diluted. Namely, the nitrous oxide can be subjected to catalytic decomposition reaction with the volume concentration of 30-40%, and the decomposition rate can reach more than 99%, so that the industrial cost is greatly reduced, and the method has a good industrial application prospect.
The invention will 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 adopted X-ray photoelectron spectrum analyzer is an ESCALB 220i-XL type ray photoelectron spectrum analyzer which is manufactured by VG scientific company and is provided with Avantage V5.926 software, and the X-ray photoelectron spectrum analysis test conditions are as follows: 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, placing the sample in an automatic sample feeding disc, feeding the sample into a combustion tube through a ball valve for combustion, wherein the combustion temperature is 1000 ℃ (the atmosphere interference during sample feeding is removed, helium 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 a metal oxide, the total content of the metal oxide can be determined from the content of the carbon element.
The ratio between the different metal oxides was measured by an X-ray fluorescence spectrometer (XRF), and the content of the different metal oxides in the composite material was calculated from 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 HRUV-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 electronics Co., Ltd.), and the test conditions of the high-resolution transmission electron microscope are as follows: the acceleration voltage was 200 kV.
The model of 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.
The pore structure property of the material is detected by a BET test method. Specifically, a Quantachrome AS-6B type analyzer is adopted for determination, and the specific surface area, pore volume and average pore diameter of the catalyst are the most probable pore diameters.
The crushing strength of the invention refers to the pressure when each catalyst is crushed, the strength is measured by adopting an ZQJ-III type intelligent particle strength tester of Dalian intelligent tester factory, the catalyst is pressed into tablets under the condition of 2.5MPa, and the diameter of a die is 10 mm. 20 samples of the same batch of catalyst are randomly selected for carrying out a crushing strength test, after the maximum value and the minimum value are removed, the arithmetic mean value is a Newton value F (N) when single particles are crushed, and the radial crushing strength sigma (N/cm) of the single particles is calculated according to a formula sigma F/L, wherein L is the length (cm) of the single particles.
Example 1
This example illustrates the preparation of a catalyst 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 homogeneous 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 product 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 (the volume partial wave of oxygen is 15%, nitrogen is balance gas) with the flow rate of 100mL/min, heating to 350 ℃ at the speed of 2 ℃/min, keeping the temperature for 8h, stopping heating, and cooling to room temperature under the atmosphere of the standard gas to obtain the carbon-coated nickel oxide nanocomposite, namely the raw powder.
(4) And (3) uniformly mixing the pseudoboehmite with the mass partial wave accounting for 50% of the total powder mass and the product obtained in the step (3) at room temperature, adding sesbania powder with the mass partial wave accounting for 1.5% of the total powder mass, uniformly mixing, preparing 1mol/L nitric acid aqueous solution from nitric acid with the mass partial wave accounting for 2.5% of the pseudoboehmite mass, dropwise adding, and continuously stirring until the materials are uniformly mixed to obtain a wet material mass.
(5) And (3) placing the wet material mass in an oven at 80 ℃, drying for 12 hours, then placing in a tube furnace, introducing nitrogen, heating to 500 ℃ at the speed of 5 ℃/min, keeping the temperature for 4 hours, stopping heating, and cooling to room temperature under the nitrogen atmosphere to obtain a product after roasting treatment.
(6) And crushing the roasted product, sieving the crushed product with a 100-mesh sieve, tabletting the powder with the granularity smaller than 100 meshes in a tabletting machine, then placing the tabletted product in a tube furnace, introducing air, heating to 350 ℃ at the speed of 5 ℃/min, and keeping the temperature for 8 hours to carry out secondary roasting treatment. And then stopping heating, and cooling to room temperature in an air atmosphere to obtain the molded catalyst. XRF elemental analysis showed that the shaped catalyst contained 0.49 wt% carbon, 56.32 wt% nickel oxide and 43.19 wt% alumina. The specific surface, pore volume, pore diameter and crush strength of the catalyst are shown in Table 1.
FIG. 1 is an X-ray diffraction pattern (XRD) of the product obtained in step (3) of example 1, and it can be seen from FIG. 1 that nickel in the product obtained in step (3) is present as an oxide after mild oxidation treatment. FIG. 2 is a TEM image of the product obtained in step (3) of example 1, and it can be seen from FIG. 2 that the nickel oxide surface is covered with a thin layer of graphitized carbon, and the particle size of the nanocomposite is about 5nm to 20 nm. Elemental analysis revealed that the product obtained in step (3) had a carbon content of 0.64% by weight and nickel oxide contentThe amount was 99.36 wt%. The XPS analysis revealed that the surface layer of the product obtained in step (3) contained carbon, oxygen and nickel. Wherein the ratio of the carbon element content of the surface layer to the total carbon element content is 32.7/1. It is found from the elemental analysis and the XPS result that carbon in the product obtained in step (3) is mainly present on the surface of the particles. FIG. 3 shows a laser Raman spectrum of the product obtained in step (3) of example 1, from which a 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, namely, the surface of the material is coated by a graphitized carbon film.
Example 2
This example illustrates the preparation of a catalyst according to the invention
(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 homogeneous 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 product 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 (the volume partial wave of oxygen is 15%, nitrogen is balance gas) with the flow rate of 100mL/min, heating to 330 ℃ at the speed of 2 ℃/min, keeping the temperature for 8h, stopping heating, and cooling to room temperature under the atmosphere of the standard gas to obtain the carbon-coated nickel oxide nanocomposite.
(4) Uniformly mixing the pseudoboehmite with the mass partial wave accounting for 25% of the total powder mass and the product obtained in the step (3) at room temperature, adding sesbania powder with the mass partial wave accounting for 1.5% of the total powder mass, uniformly mixing, preparing 1mol/L nitric acid aqueous solution from nitric acid with the mass partial wave accounting for 2.5% of the pseudoboehmite mass, dropwise adding, and continuously stirring until the materials are uniformly mixed; obtaining wet dough;
(5) and (3) placing the wet material mass in an oven at 80 ℃, drying for 12 hours, then placing in a tube furnace, introducing nitrogen, heating to 500 ℃ at the speed of 5 ℃/min, keeping the temperature for 4 hours, stopping heating, and cooling to room temperature under the nitrogen atmosphere to obtain a roasted product.
(6) And crushing the roasted product, sieving the crushed product with a 100-mesh sieve, tabletting the powder with the granularity smaller than 100 meshes in a tabletting machine, then placing the tabletted product in a tube furnace, introducing air, heating to 350 ℃ at the speed of 5 ℃/min, and keeping the temperature for 8 hours to carry out secondary roasting. And then stopping heating, and cooling to room temperature in an air atmosphere to obtain the molded catalyst. XRF elemental analysis showed that the shaped catalyst contained 0.72 wt% carbon, 78.46 wt% nickel oxide, and 20.82 wt% alumina. The specific surface, pore volume, pore diameter and crush strength of the catalyst are shown in Table 1.
FIG. 4 is an X-ray diffraction pattern (XRD) of the product obtained in step (3) of example 2, and it can be seen from FIG. 4 that nickel in the product obtained in step (3) exists as an oxide after the mild oxidation treatment. FIG. 5 is a TEM image of the product obtained in step (3) of example 2, and it can be seen from FIG. 5 that the nickel oxide surface is covered with a thin layer of graphitized carbon, and the particle size of the nanocomposite is about 5nm to 20 nm. Elemental analysis revealed that the product obtained in step (3) had a carbon content of 0.91 wt% and a nickel oxide content of 99.09 wt%. The XPS analysis revealed that the elements of the surface layer were carbon, oxygen, and nickel. Wherein the ratio of the carbon element content of the surface layer to the total carbon element content is 22.4/1. It is known from elemental analysis and XPS results that carbon in the material is mainly present on the surface of the particles. FIG. 6 shows a laser Raman spectrum of the product obtained in step (3) of example 2, from which a G peak (1580 cm)-1) Intensity of (3) and intensity of D peak (1320 cm)-1) The ratio of (A) to (B) is 2.4/1, namely, the surface of the material is coated by a graphitized carbon film.
Comparative example 1
A catalyst was prepared by the method of example 1 except that step (4) was not performed to obtain a carbon-coated nickel oxide catalyst which was not subjected to a molding treatment.
Comparative example 2
A catalyst was prepared by the method of example 2 except that step (4) was not performed to obtain a carbon-coated nickel oxide catalyst which was not subjected to a molding treatment.
Application example 1
The tablets were crushed and 0.5 g of the catalyst of example 1, 20-40 mesh sieved, placed in a continuous flow fixed bed reactor with a reaction gas composition of 38.0% by volume N2O, using nitrogen as balance gas, and the flow rate of reaction gas is 15 ml/min. The activity evaluation temperature range is 300-500 ℃, and the catalyst is used for catalyzing and decomposing N2The conversion of O is shown in Table 2.
Application example 2
The tablets were crushed and 0.5 g of the catalyst of example 2, 20-40 mesh sieved, placed in a continuous flow fixed bed reactor with a reaction gas composition of 38.0% by volume N2O, using nitrogen as balance gas, and the flow rate of reaction gas is 15 ml/min. The activity evaluation temperature range is 300-500 ℃, and the catalyst is used for catalyzing and decomposing N2The conversion of O is shown in Table 2.
Comparative application example 1
0.5 g of the catalyst of comparative example 1 was placed in a continuous flow fixed bed reactor with a reaction gas composition of 38.0% N2O, using nitrogen as balance gas, and the flow rate of reaction gas is 15 ml/min. The activity evaluation temperature range is 300-500 ℃, and the catalyst is used for catalyzing and decomposing N2The conversion of O is shown in Table 2.
Comparative application example 2
0.5 g of the catalyst of comparative example 2 was placed in a continuous flow fixed bed reactor with a reaction gas composition of 38.0% N2O, using nitrogen as balance gas, and the flow rate of reaction gas is 15 ml/min. The activity evaluation temperature range is 300-500 ℃, and the catalyst is used for catalyzing and decomposing N2The conversion of O is shown in Table 2.
TABLE 1
TABLE 2
As can be seen from the above tables 1 and 2, the shaped catalyst prepared by the method of the present invention not only has high mechanical strength and can meet the requirements of industrial application, but also well maintains N of the original active component2O catalytic decomposition performance, and N can be efficiently eliminated at 360-420 DEG C2And O. When the formed catalyst provided by the invention is applied to the treatment of the waste gas in the adipic acid production process, the reaction temperature can be greatly reduced, the energy consumption is reduced, the activity is high, and the stability is good.
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 (32)
1. The catalyst of the carbon-coated transition metal oxide is characterized by comprising a carrier and an active component loaded on the carrier, wherein the active component is a graphite carbon-coated transition metal oxide nano composite material.
2. The catalyst of claim 1 wherein the transition metal oxide is selected from one or more of the group VIII, VIB, IB and IIB oxides.
3. The catalyst of claim 1, wherein the transition metal oxide is selected from one or more of iron oxide, cobalt oxide, and nickel oxide.
4. The catalyst of claim 1, wherein the nanocomposite comprises a core membrane structure having an outer membrane that is a graphitized carbon membrane and an inner core comprising transition metal oxide nanoparticles.
5. The catalyst according to claim 1, wherein the transition metal oxide content is 10% to 90% and the support content is 10% to 90% based on the mass of the catalyst.
6. The catalyst according to claim 1, wherein the carbon content is not more than 5%, preferably 0.1 to 5%, based on 100% by mass of the total of carbon and transition metal oxide.
7. The catalyst according to claim 1, wherein the catalyst contains carbon in a mass ratio of not less than 10 as determined by X-ray photoelectron spectroscopy to the content of carbon as determined by elemental analysis.
8. The catalyst of claim 1, wherein the catalyst has a Raman spectrum at 1580cm-1Intensity of nearby G peak at 1320cm-1The ratio of the intensities of the nearby D peaks is greater than 1, preferably greater than 2.
9. The catalyst according to claim 1, wherein the carrier is alumina, silica, or a composite oxide of silica and alumina.
10. The catalyst of claim 4, wherein the inner core further comprises alumina.
11. A preparation method of the catalyst comprises the following steps:
providing a carbon-coated transition metal nanocomposite;
carrying out oxygen treatment on the carbon-coated transition metal nanocomposite to obtain a carbon-coated transition metal oxide nanocomposite; and
and molding the carbon-coated transition metal oxide nano composite material to obtain the catalyst.
12. The method of claim 11, wherein the carbon-coated transition metal nanocomposite is prepared by:
placing a transition metal-containing compound and a carboxylic acid in a solvent to mix to form a homogeneous solution;
removing the solvent in the homogeneous solution to obtain a precursor; and
and pyrolyzing the precursor in an inert atmosphere or a reducing atmosphere to obtain the carbon-coated transition metal nanocomposite.
13. The preparation method according to claim 12, wherein the transition metal-containing compound is selected from one or more of soluble organic acid salts, basic carbonates, hydroxides and oxides of transition metals, the carboxylic acid is 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 transition metal-containing compound to the carboxylic acid is 1 (0.1-10).
14. The method of claim 12, 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.
15. The method according to claim 14, further comprising subjecting the pyrolyzed product to acid washing treatment and then to oxygen treatment.
16. The method according to claim 12, wherein the carbon-coated transition metal nanocomposite has an acid loss of 60% or less.
17. The preparation method according to claim 11, wherein the oxygen treatment comprises introducing standard gas into the pyrolyzed product and heating, wherein the standard gas contains oxygen and balance gas, and the volume concentration of the oxygen is 10-40%; the temperature of the oxygen treatment is 200-500 ℃, and the time of the oxygen treatment is 0.5-10 h.
18. The production method according to claim 11, wherein the molding process includes:
adding a binder into the carbon-coated transition metal oxide nano composite material and uniformly mixing to obtain a wet material mass;
drying and roasting the wet dough for the first time, and then molding;
and roasting the molded product for the second time to obtain the molded catalyst.
19. The preparation method according to claim 18, wherein the drying temperature is 20 ℃ to 100 ℃, the drying time is 3h to 24h, and the drying atmosphere is an inert atmosphere or an air atmosphere; the first roasting comprises: heating the dried product to 400-800 ℃ at a heating rate of 1-20 ℃/min under an inert atmosphere, and keeping the temperature constant for 1-10 h; the second roasting comprises: and heating the formed product to 300-400 ℃ at a heating rate of 1-20 ℃/min in the air atmosphere, and keeping the temperature constant for 4-10 h.
20. The method of claim 18, wherein the binder is selected from the group consisting of an aluminum sol, a silica sol, and a silica-alumina sol.
21. The preparation method according to claim 18, wherein the binder is prepared from pseudoboehmite and a peptizing agent, the peptizing agent is selected from one or more of nitric acid aqueous solution, hydrochloric acid aqueous solution and citric acid aqueous solution, and the mass of the peptizing agent is 1-5%, preferably 2-3% of the mass of the binder.
22. The method of claim 21, wherein the binder further comprises a lubricant selected from one or more of sesbania powder, citric acid, starch and carboxymethyl cellulose, and the mass of the lubricant is 1% to 6% of the mass of the nanocomposite of the carbon-coated transition metal oxide.
23. The method according to claim 22, wherein the wet mass ratio of the liquid to the solid in the wet mass is 0.8 to 1.5, the nanocomposite of the carbon-coated transition metal oxide accounts for 20 to 80% of the mass of the solids in the wet mass, and the binder accounts for 20 to 80% of the mass of the solids in the wet mass.
24. A preparation method of the catalyst comprises the following steps:
introducing a transition metal onto a support;
carrying out graphite carbon coating on the transition metal loaded on the carrier to obtain a graphite carbon coated transition metal simple substance composite structure; and
and carrying out oxygen treatment on the graphite carbon coated transition metal simple substance composite structure, and removing amorphous carbon to obtain the catalyst containing the graphite carbon coated transition metal oxide composite structure.
25. The method of claim 24, wherein the graphitic carbon-coated transition metal elemental composite structure is acid-washed, and the loss rate of transition metal is not higher than 60%, preferably not higher than 10%.
26. The preparation method of claim 24, wherein the oxygen treatment comprises introducing standard gas and heating, wherein the standard gas comprises oxygen and balance gas, and the volume concentration of the oxygen is 10-40%; the temperature of the oxygen treatment is 200-500 ℃, and the time of the oxygen treatment is 0.5-10 h.
27. The production method according to claim 24, wherein the support is alumina, silica, or a composite oxide of silica and alumina.
28. A catalyst prepared by the method of any one of claims 24 to 27.
29. The catalyst of claim 28, wherein the transition metal oxide content is 10% to 90% and the support content is 10% to 90% based on the mass of the catalyst; the Raman spectrum of the catalyst is 1580cm-1Intensity of nearby G peak at 1320cm-1The ratio of the intensities of the nearby D peaks is greater than 1, preferably greater than 2.
30. The catalyst of claim 28, wherein the transition metal oxide content is 40% to 90% and the support content is 10% to 60% based on the mass of the catalyst.
31. A method for catalyzing decomposition of nitrous oxide, comprising contacting nitrous oxide with the catalyst of any one of claims 1 to 10 and 28 to 30 to perform a catalytic decomposition reaction to produce nitrogen and oxygen.
32. The method as claimed in claim 31, wherein in the catalytic decomposition reaction, the reaction temperature is 300-420 ℃, the reaction space velocity is 500-3000 ml reaction gas/(hr-g catalyst), and the volume concentration of the nitrous oxide is 30-40%.
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| CN115233170B (en) * | 2022-06-22 | 2023-12-12 | 中国科学院宁波材料技术与工程研究所 | Ultrathin metal oxide-based nanomaterial with high catalytic performance as well as preparation method and application thereof |
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