CN113751005B - Catalyst of carbon-coated transition metal oxide, preparation method and application thereof - Google Patents
Catalyst of carbon-coated transition metal oxide, preparation method and application thereof Download PDFInfo
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- CN113751005B CN113751005B CN202010503583.5A CN202010503583A CN113751005B CN 113751005 B CN113751005 B CN 113751005B CN 202010503583 A CN202010503583 A CN 202010503583A CN 113751005 B CN113751005 B CN 113751005B
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- transition metal
- carbon
- catalyst
- metal oxide
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 172
- 229910052799 carbon Inorganic materials 0.000 title claims abstract description 154
- 239000003054 catalyst Substances 0.000 title claims abstract description 135
- 229910000314 transition metal oxide Inorganic materials 0.000 title claims abstract description 72
- 238000002360 preparation method Methods 0.000 title claims abstract description 21
- 239000002114 nanocomposite Substances 0.000 claims abstract description 57
- 239000000463 material Substances 0.000 claims abstract description 50
- 238000000034 method Methods 0.000 claims abstract description 43
- 238000006243 chemical reaction Methods 0.000 claims abstract description 19
- 229910002804 graphite Inorganic materials 0.000 claims abstract description 16
- 239000010439 graphite Substances 0.000 claims abstract description 16
- 150000003624 transition metals Chemical class 0.000 claims description 73
- 229910052723 transition metal Inorganic materials 0.000 claims description 68
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 52
- 229910052760 oxygen Inorganic materials 0.000 claims description 52
- 239000001301 oxygen Substances 0.000 claims description 52
- 239000012298 atmosphere Substances 0.000 claims description 43
- IJGRMHOSHXDMSA-UHFFFAOYSA-N nitrogen Substances N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 43
- 239000007789 gas Substances 0.000 claims description 38
- 238000010438 heat treatment Methods 0.000 claims description 35
- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical compound OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 claims description 33
- GQPLMRYTRLFLPF-UHFFFAOYSA-N Nitrous Oxide Chemical group [O-][N+]#N GQPLMRYTRLFLPF-UHFFFAOYSA-N 0.000 claims description 28
- 229910052757 nitrogen Inorganic materials 0.000 claims description 27
- 239000002131 composite material Substances 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 21
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 20
- 239000011230 binding agent Substances 0.000 claims description 20
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- GNRSAWUEBMWBQH-UHFFFAOYSA-N oxonickel Chemical compound [Ni]=O GNRSAWUEBMWBQH-UHFFFAOYSA-N 0.000 claims description 12
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- RGHNJXZEOKUKBD-SQOUGZDYSA-N D-gluconic acid Chemical compound OC[C@@H](O)[C@@H](O)[C@H](O)[C@@H](O)C(O)=O RGHNJXZEOKUKBD-SQOUGZDYSA-N 0.000 claims description 6
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- BJEPYKJPYRNKOW-REOHCLBHSA-N (S)-malic acid Chemical compound OC(=O)[C@@H](O)CC(O)=O BJEPYKJPYRNKOW-REOHCLBHSA-N 0.000 claims description 3
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- RGHNJXZEOKUKBD-UHFFFAOYSA-N D-gluconic acid Natural products OCC(O)C(O)C(O)C(O)C(O)=O RGHNJXZEOKUKBD-UHFFFAOYSA-N 0.000 claims description 3
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- 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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- 150000005323 carbonate salts Chemical class 0.000 claims 1
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- 150000005324 oxide salts Chemical class 0.000 claims 1
- NDLPOXTZKUMGOV-UHFFFAOYSA-N oxo(oxoferriooxy)iron hydrate Chemical compound O.O=[Fe]O[Fe]=O NDLPOXTZKUMGOV-UHFFFAOYSA-N 0.000 claims 1
- 230000003197 catalytic effect Effects 0.000 abstract description 16
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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 3
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
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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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- B—PERFORMING OPERATIONS; TRANSPORTING
- 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, a preparation method and application thereof, wherein the catalyst comprises a carrier and an active component loaded on the carrier, the active component is a nano composite material of graphite carbon-coated transition metal oxide, and the transition metal oxide is selected from one or more of oxides of VIII, VIB, IB and IIB. According to the invention, the graphite 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 has high catalytic activity, certain mechanical strength and difficult fragmentation and pulverization in the reaction process, can meet the requirements of actual industrial production, and has a good application prospect.
Description
Technical Field
The invention relates to the field of catalysts, in particular to a carbon-coated transition metal oxide catalyst, and a preparation method and application thereof.
Background
The transition metal oxide has excellent catalytic performance and photoelectromagnetic performance, and is a research hot spot in the field of inorganic materials. The carbon material has good conductivity, good chemical/electrochemical stability and high structural strength. The carbon material is used for coating the nano particles of the transition metal oxide, so that the conductivity and the stability of the nano material can be improved, and the limited domain of the nano particles 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 anode materials, bioengineering and the like.
In general, carbon-coated nano-materials have small particles, are powdery, and have poor self-formability. However, in industrial applications, particularly in the case of fixed bed processes, not only are certain activities and selectivities required for the catalysts, but also certain properties such as particle size and mechanical strength are required. If the catalyst is not strong enough and disintegrated and pulverized, the catalyst is easy to carry loss or block the device in the reaction process, the pressure drop of the catalyst bed is greatly increased, and even the device is forced to stop. Therefore, the carbon-coated nano material needs to be subjected to forming treatment to meet the industrial reaction requirements of compressive strength, pressure drop after filling, stability and the like. The molding process is a process of forming solid particles having a certain size, shape and mechanical strength by mutually aggregating raw materials such as a catalyst raw powder and a molding aid by an external force. The molding process can have 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 research focus of the carbon-coated nano material forming method.
N 2 O is an important greenhouse gas, and its Global Warming Potential (GWP) is CO 2 310 times of CH 4 21 times of (2); in addition, N 2 The average life of O in the atmosphere is about 150 years, also known as NO in the stratosphere x The main source of the composition is not only capable of seriously destroying the ozone layer, but also has strong greenhouse effect.
The domestic adipic acid production mainly adopts a cyclohexanol nitric acid oxidation method, and the cyclohexanol is subjected to nitric acid oxidation to produce adipic acid, the technology of the method is mature, the product yield and purity are relatively high, but the nitric acid consumption is large, and a large amount of N is produced in the reaction process 2 O, and 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 adopting a cyclohexanol nitric acid oxidation method 2 The annual discharge of O can reach 4.5 ten thousand tons. Therefore, the tail gas of the adipic acid purifying device can effectively control and eliminate N 2 O has become a research hotspot in the field of environmental catalysis today.
The direct catalytic decomposition method can decompose N 2 O is decomposed into nitrogen and oxygen to eliminate N 2 O is the most effective and clean technique. Wherein, the catalyst is the technical core of the direct catalytic decomposition method. Decomposition N reported in the current study 2 The catalyst of O 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) on N 2 The O catalytic decomposition has higher low-temperature catalytic activity (the temperature is 250-350 ℃ and N can be efficiently decomposed) 2 O), the expensive price limits the large-scale use of noble metal catalysts. Molecular sieve-type catalysts and transition metal oxide catalysts are significantly less expensive than noble metals, but currently these two types of catalysts are relatively more expensive than noble metals for N 2 O catalytic decompositionThe activity of the catalyst is low, and the high-efficiency decomposition temperature is 450-550 ℃. Thus, new materials catalyst pair N was developed that are new non-noble metals, low cost and efficient 2 The emission reduction of O has important significance.
It is noted that the information disclosed in the foregoing background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the 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 above purpose, the present 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 oxides of group VIII, group VIB, group IB and group IIB, preferably one or more of iron oxide, cobalt oxide and nickel oxide.
According to one embodiment of the invention, the core further comprises alumina.
According to one embodiment of the invention, the content of the transition metal oxide is 10-90% based on the mass of the catalyst, and the content of the carrier is 10-90%; preferably, the content of the transition metal oxide is 40% -90% and the content of the carrier is 10% -60%.
According to one 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 mass of carbon and transition metal oxide.
According to one embodiment of the present invention, the ratio of the carbon element determined by the X-ray photoelectron spectroscopy to the carbon element content determined by elemental analysis in the catalyst is not less than 10 in terms of mass ratio.
According to one embodiment of the invention, the raman spectrum of the catalyst is located at 1580cm -1 G peak intensity in the vicinity and at 1320cm -1 The ratio of nearby D peak intensities is greater than 1, preferably greater than 2.
According to one embodiment of the invention, the raman spectrum of the catalyst is only at 1580cm -1 G peak in the vicinity, not located at 1320cm -1 A nearby D peak.
According to one embodiment of the invention, the support is selected from the group consisting of alumina, silica, or a composite oxide of silica and alumina.
According to one embodiment of the invention, the specific surface area of the catalyst is 90m 2 /g～160m 2 Per gram, pore volume of 0.12cm 3 /g～0.18cm 3 And/g, the crushing strength is 120N/cm-160N/cm.
According to one embodiment of the invention, the nanocomposite comprises a nuclear membrane structure having an outer membrane that is a graphitized carbon membrane 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; oxygen treatment is carried out on the carbon-coated transition metal nanocomposite material to obtain a carbon-coated transition metal oxide nanocomposite material; and molding the nano composite material of the carbon-coated transition metal oxide to obtain the catalyst.
According to one embodiment of the present invention, a method for preparing a carbon-coated transition metal nanocomposite includes: mixing a transition metal-containing compound and carboxylic acid in a solvent 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 present invention, the transition metal-containing compound is selected from one or more of soluble organic acid salts, basic carbonate, hydroxide and oxide of transition metal, and 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 0.5-30 ℃/min, the constant temperature section temperature 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 one embodiment of the invention, the method further comprises the step of carrying out acid washing treatment on the pyrolyzed product and then carrying out oxygen treatment.
According to one embodiment of the present invention, the carbon-coated transition metal nanocomposite has a pickling 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 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.
According to one embodiment of the present invention, the molding process includes: adding a binder into the nano composite material of the carbon-coated transition metal oxide, and uniformly mixing to obtain a wet dough; the wet dough is shaped after drying and optionally baking. Wherein the shaping can be selected from one or more of extrusion, rolling, tabletting and granulating.
According to one embodiment of the invention, the drying temperature is 20-100 ℃, the drying time is 3-24 hours, 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 inert atmosphere, and keeping the temperature constant for 1-10 h; the second roasting comprises the following steps: heating the product obtained after the molding treatment to 300-400 ℃ at a heating rate of 1-20 ℃ per minute under the air atmosphere, and keeping the temperature constant for 4-10 hours.
According to one embodiment of the invention, the binder is selected from the group consisting of an aluminum sol, a silica sol or a silica-alumina sol. The alumina sol, silica sol or silica alumina sol is readily commercially available or may be self-produced by existing methods, such as by acidification of pseudoboehmite.
According to one embodiment of the invention, the binder is made of pseudo-boehmite and a peptizing agent selected from one or more of aqueous nitric acid, aqueous hydrochloric acid and aqueous citric acid.
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 nanocomposite material of the carbon-coated transition metal oxide accounts for 20-80% of the solid mass in the wet dough, and the binder accounts for 20-80% of the solid mass in the wet dough; the mass of the lubricant is 1-6% of the mass of the nanocomposite of carbon-coated transition metal oxide, and the mass of the peptizing agent is 1-5%, preferably 2-3% of the mass 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) coating graphite carbon on transition metal loaded on the carrier to obtain a graphite carbon coated transition metal simple substance composite structure;
and (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 preparation method, the transition metal in the (I) is in a zero-valent state and/or an oxidation state.
According to one embodiment of the invention, the graphite carbon coated transition metal composite structure is subjected to acid washing, and the loss rate of transition metal is not higher than 60%, not higher than 40%, not higher than 30%, not higher than 20%, not higher than 10%.
According to one embodiment of the invention, the oxygen treatment comprises introducing a 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 one embodiment of the invention, the support is alumina, silica, or a composite oxide of silica and alumina.
The invention also provides another catalyst prepared by any of the methods described above.
According to one embodiment of the invention, the content of the transition metal oxide is 10-90% based on the mass of the catalyst, and the content of the carrier is 10-90%; the Raman spectrum of the catalyst is positioned at 1580cm -1 G peak intensity in the vicinity and at 1320cm -1 The ratio of nearby D peak intensities is greater than 1, preferably greater than 2.
According to one embodiment of the invention, the content of the transition metal oxide is 40-90% and the content of the carrier is 10-60% based on the mass of the catalyst; in the Raman spectrum of the catalyst, only the catalyst is positioned at 1580cm -1 G peak in the vicinity, not located at 1320cm -1 A nearby D peak.
The invention also provides a method for catalyzing the decomposition of nitrous oxide, which comprises the step of enabling a catalyst to be in contact with nitrous oxide to perform 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 of reaction gas/(hr-g of catalyst), and the volume concentration of nitrous oxide is 5% -40%, preferably 30% -40%.
According to the technical scheme, the beneficial effects of the invention are as follows:
the invention provides a carbon-coated transition metal oxide supported catalyst, which adopts an ultrathin graphite carbon layer coated transition metal oxide nanocomposite as an active component. According to the invention, a graphitized carbon film with good coating is formed outside the graphitized carbon film by utilizing the action of a transition metal simple substance, then the transition metal simple substance is converted into a transition metal oxide by oxygen treatment, and amorphous carbon is removed at the same time, so that a nanocomposite material with a small amount of graphite carbon tightly coating the transition metal oxide is obtained. The present invention has found that this unique structure and composition allows it to catalyze N as a catalyst active component 2 The O decomposition reaction has excellent activity, and the prepared supported catalyst has good mechanical property and can maintain catalytic activity. N in industrial waste gas compared with the existing catalyst 2 O is diluted and then treated, the 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%, and the catalyst has great significance in protecting environment and reducing atmospheric pollution and has good industrial application prospect.
Drawings
The following drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate the invention and together with the description serve to explain the invention, without limitation to the invention.
FIG. 1 is an X-ray diffraction chart of the product obtained in the step (3) of example 1;
FIG. 2 is a transmission electron micrograph of the product obtained in step (3) of example 1;
FIG. 3 is a Raman spectrum of the product obtained in the step (3) of example 1;
FIG. 4 is an X-ray diffraction chart of the product obtained in the step (3) of example 2;
FIG. 5 is a transmission electron micrograph of the product obtained in step (3) of example 2;
FIG. 6 is a Raman spectrum of the product obtained in the step (3) of example 2.
Detailed Description
The following provides various embodiments or examples to enable those skilled in the art to practice the invention as described herein. These are, of course, merely examples and are not intended to limit the invention from that described. The endpoints of the ranges and any values disclosed in the present invention are not limited to the precise range or value, and the range or value should be understood to include values close to the range or value. For a range of wave values, one or more new ranges of wave values may be obtained in combination with each other between the endpoints of each range, between the endpoints of each range and the individual point values, and between the individual point values, and these ranges of wave values 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 comprising transition metal oxide nanoparticles. The composite material formed by coating transition metal oxide nano particles with the graphitized carbon film is spherical or spheroidic.
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, which is measured by performing element quantitative analysis by using an X-ray photoelectron spectrometer as an analysis tool.
The term "carbon element content determined in elemental analysis" refers to the relative content of total carbon elements of a material as 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, the kind of the transition metal is not particularly limited, and those of the existing graphitic 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 of oxides of group VIII, group VIB, group IB, and group IIB metals; more specifically, 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 may be selected.
According to the invention, the nanocomposite comprises a nuclear membrane structure having an outer membrane, which is a graphitized carbon membrane, and an inner core comprising transition metal oxide nanoparticles.
According to the present invention, the catalyst is a supported catalyst using a nanocomposite material of a graphitic carbon-coated transition metal oxide as an active component, and in general, the nanocomposite material of a graphitic carbon-coated transition metal oxide includes a nuclear membrane structure having an intact outer membrane layer and an inner core layer, the outer membrane is mainly composed of a graphitized carbon membrane, and the graphitized carbon membrane is a thin membrane structure mainly composed of graphitized carbon, and is completely or substantially completely coated on the surface of the transition metal oxide nanoparticle, and in general, it is quite difficult to completely coat the graphitic carbon outside the transition metal oxide. The inventor of the invention surprisingly found that, although the carbon content of the film layer is relatively small, the performance, especially the catalytic performance, of the whole material is greatly improved, and particularly, the film layer can not only generate a certain limiting effect, effectively avoid the aggregation and growth of the inner core nano particles, ensure that the catalytic activity of the composite material is stable, but also synergistically increase the catalytic activity of the whole composite material, and compared with the catalytic activity of a pure transition metal oxide without a graphite carbon film, the catalytic activity of the composite material is obviously improved. The nanocomposite with good catalytic activity is used as an active component and is loaded on a carrier through a specific process, so that the catalyst has high mechanical strength, can be suitable for 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 content is 40% to 90%, e.g., 40%, 43%, 50%, 55%, 57%, 67%, 79%, 80%, 85%, etc., and the support content is 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, for example, 1%, 0.8%, 0.5%, 0.3%, 0.2%, 0.1%, etc.
In some embodiments, the ratio of elemental carbon determined by X-ray photoelectron spectroscopy to elemental carbon content determined by elemental analysis in the catalyst of the present invention is not less than 10 by mass ratio. As described above, the carbon element content determined by the X-ray photoelectron spectroscopy refers to the relative content of carbon element on the surface of the material measured by performing elemental quantitative analysis using the X-ray photoelectron spectrometer as an analysis tool. The carbon element content determined in the elemental analysis refers to the relative content of the total carbon element of the material measured by elemental quantitative analysis using an elemental analyzer as an analysis tool. When the ratio of the carbon element determined by the X-ray photoelectron spectroscopy to the carbon element content determined by the elemental analysis is larger, it is shown that most of carbon is concentrated on the surface of the material in the whole catalyst, a carbon film layer is formed, and the nuclear film structure is formed.
In some embodiments, the catalyst of the invention is located at 1580cm in the Raman spectrum -1 G peak intensity in the vicinity and at 1320cm -1 The ratio of nearby D peak intensities is greater than 2. As known to those skilled in the art, the D peak and the G peak are Raman characteristic peaks of C atom crystals, the D peak represents a defect of a carbon atom lattice, and the G peak represents a C atom sp 2 Hybrid in-plane stretching vibration. It will be appreciated that a greater ratio of G-peak intensity to D-peak intensity 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 exists mainly in the form of graphitic carbon. The graphite carbon has better oxidation resistance, and can synergistically increase catalytic activity with transition metal oxide nano particles of the inner core, thereby improving the performance of the whole catalyst.
In some embodiments, the catalyst of the invention has a Raman spectrum located only at 1580cm -1 G peak in the vicinity, not located at 1320cm -1 A nearby D peak.
According to the invention, the aforementioned support may be alumina and/or silica. The catalyst has a pore structure, and in some embodiments, the specific surface area of the catalyst of the present invention is 90m 2 /g～160m 2 Per gram, pore volume of 0.12cm 3 /g～0.18cm 3 And/g, the crushing strength is 120N/cm-160N/cm.
In the present invention, the specific surface area, pore volume and crush strength ranges of the catalyst obtained by different binders (such as alumina sol, silica sol, pseudo-boehmite, etc.) and different molding conditions (such as pressure) and molding modes (tabletting, extruding and granulating) are greatly different, so the present invention is not limited to this, and the specific surface area, pore volume and crush strength ranges can be adjusted according to the actual operating conditions and the requirements for catalyst strength, etc.
The invention also provides a preparation method of the catalyst, which comprises the following steps: providing a carbon-coated transition metal nanocomposite; oxygen treatment is carried out on the carbon-coated transition metal nanocomposite material to obtain a carbon-coated transition metal oxide nanocomposite material; and (3) carrying out molding treatment on the nano composite material of the carbon-coated transition metal oxide 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 an existing method, and can also be obtained by commercial purchase. Preferably prepared by the following method:
mixing a transition metal-containing compound and carboxylic acid in a solvent 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 is a nickel-containing water-soluble mixture obtained by dissolving a transition metal-containing compound and a carboxylic acid in a solvent such as water, ethanol, or the like into a homogeneous solution, and then directly evaporating the solvent. The aforementioned temperature and process of evaporating the solvent may be any available prior art technique, for example, spray drying at 80-120 ℃, 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, a basic carbonate, a hydroxide, and an oxide of a transition metal.
According to the present invention, the kind of the carboxylic acid is not particularly limited, and carboxylic acids used in such a method for producing a carbon-coated transition metal composite material, including polycarboxylic acids containing nitrogen or no nitrogen, have been used in the present invention. 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 above may be added together to form a homogeneous solution, and the other organic compounds may be any organic compound that may supplement the carbon source desired in the product, with or without other doping atoms. Organic compounds which are not volatile, such as organic polyols, lactic acid, etc., are preferred. In some embodiments, the mass ratio of transition metal containing compound, carboxylic acid, and 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.
In some embodiments, 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 0.5-30 ℃/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, etc.; the constant temperature section temperature is 400-800 ℃, preferably 500-700 ℃, such as 500 ℃, 550 ℃, 570 ℃, 610 ℃, 660 ℃, 680 ℃, and the like; the constant temperature is maintained for 20 min-600 min, preferably 30 min-300 min, such as 30min, 45min, 55min, 70min, 86min, 97min, 100min, 180min, 270min, 300min, etc.; the inert atmosphere is nitrogen or argon, the reducing atmosphere is a mixed gas of inert gas and hydrogen, for example, a small amount of hydrogen is doped in the inert atmosphere.
In some embodiments, the invention further comprises subjecting the aforementioned pyrolyzed product to an acid wash treatment.
In fact, the product obtained after the pyrolysis is a nanocomposite material with graphitized carbon layers coated with transition metal. Wherein the "graphitized carbon layer" refers to a carbon structure in which a layered structure is clearly observed under a high resolution transmission electron microscope, not an amorphous structure, and the interlayer spacing is about 0.34nm. The nano composite material of the graphitized carbon layer coated transition metal is a composite material composed of transition metal nano particles which are tightly coated by the graphitized carbon layer (not contacted with the outside), transition metal nano particles which can be contacted with the outside and limited by the domain and a carbon material with a mesoporous structure. After pickling treatment, nickel in the composite material has a certain loss, and can be characterized by a pickling loss rate. That is, "pickling loss rate" refers to the loss ratio of transition metal after pickling of the prepared carbon-coated transition metal nanocomposite product. Reflecting 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 inner core is dissolved by the acid after the acid treatment and is lost. The higher the acid washing loss rate, the lower the tightness degree of the graphitized carbon layer on the transition metal coating is, and the lower the acid washing loss rate is, the higher the tightness degree of the graphitized carbon layer on the transition metal coating is.
In general, specific conditions for the acid washing treatment are: 1g of the sample was added in a proportion of 20mL of an aqueous sulfuric acid solution (1 mol/L), the sample was treated at 90℃for 8 hours, then washed with deionized water to neutrality, dried, weighed, analyzed, and the acid washing loss rate was calculated as follows.
The calculation formula is as follows: the acid washing loss rate = [1- (mass wavelet of transition metal in composite material after acid washing x mass of composite material after acid washing)/(mass wavelet of transition metal in composite material to be treated x mass of 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 of 40% or less, may be 30% or less, may be 20% or less, and may be 10% or less.
The carbon-coated transition metal nanocomposite obtained after pyrolysis or after acid washing is then further subjected to an oxygen treatment comprising introducing a standard gas into the pyrolyzed product and heating, wherein the standard gas contains oxygen and an equilibrium gas, and the volume concentration of the oxygen is 10% -40%, for example 10%, 12%, 15%, 17%, 20%, 22%, 25%, 28%, 30%, etc. 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 ℃, such as 320 ℃, 340 ℃, 350 ℃, 380 ℃, etc.; the oxygen treatment time is 0.5 to 10 hours, for example, 1 hour, 3 hours, 5 hours, 7 hours, 8 hours, 10 hours, etc.
It is known to those skilled in the art that carbon can undergo an oxidation reaction with oxygen to produce a gas. It will be appreciated that pyrolysis of the precursor forms a nanocomposite material having a carbon-coated transition metal core, which is subjected to high temperature oxygen treatment, possibly with loss of carbon from the material by oxidation. However, the inventors of the present invention have unexpectedly found that after proper oxygen treatment, a small portion of carbon remains while a large portion of carbon is burned off. As described above, 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 the case for nanocomposite materials with carbon tightly coated elemental cores of transition metals (which materials are treated with strong non-oxidizing acids at temperatures near boiling for long periods of time without substantial loss of transition metals). Further research shows that the transition metal of the inner core is oxidized, and the thin film carbon layer further has 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, carrying out molding treatment on the oxygen treated product, namely the carbon-coated transition metal oxide nanocomposite material to obtain the catalyst. The forming process specifically comprises the following steps:
adding a binder, an optional lubricant and the like into the nano composite material of the carbon-coated transition metal oxide, and uniformly mixing to obtain a wet dough; drying and roasting the wet dough for the first time; and (3) forming the product after the first roasting treatment, and carrying out second roasting on the formed product to obtain the catalyst.
Specifically, the binder is selected from an aluminum sol, a silica sol, or a silica-alumina sol. The alumina sol can be obtained from commercial sources or from hydrated alumina (e.g. pseudo-boehmite or boehmite) and a peptizing agent selected from one or more of aqueous nitric acid, aqueous hydrochloric acid and aqueous citric acid according to well known methods. Further, the binder may further comprise a lubricant, i.e. the binder is made of hydrated alumina, peptizing agent, and lubricant, and the lubricant may be one or more selected from sesbania powder, citric acid, starch, and carboxymethyl cellulose.
In some embodiments, the aforementioned wet mass has a liquid to solid mass ratio of 0.8 to 1.5, e.g., 0.8, 0.9, 1, 1.2, etc., preferably 0.85 to 1. The carbon-coated transition metal oxide nanocomposite material accounts for 20% -80% of the mass of solids in the wet mass, such as 20%, 25%, 31%, 47%, 56%, 60%, 75%, etc. The binder accounts for 20% -80% of the solid mass in the wet dough, such as 22%, 36%, 41%, 47%, 55%, 67%, 80% and the like; 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 the wet dough having a desired composition is obtained, the wet dough is dried at a drying 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, etc. The drying atmosphere is an inert atmosphere or an air atmosphere.
The dried product may be subjected to a first calcination in an inert atmosphere, for example pseudo-boehmite, in which case the product is pseudo-Conversion of boehmite to gamma-Al 2 O 3 As carrier for the active ingredient. The temperature rising rate of the roasting is 1-20 ℃ per minute, preferably 2.5-10 ℃ per minute, such as 2.5, 3.5, 4, 5, 6, 8, 10, etc. When the temperature is raised to the roasting temperature of 400-800 ℃, keeping the constant temperature for 1-10 h, wherein the preferable roasting temperature is 450-600 ℃, and the constant temperature time is 3-8 h.
The dried or first baked product may be formed and then second baked, wherein the forming method is one or more of extruding, rolling, tabletting and granulating, and the invention is not limited thereto.
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 preparation method, the transition metal in the (I) is in a zero-valent state and/or an oxidation state.
According to the preparation method, one mode is as follows: firstly, loading oxidized transition metal on a carrier by using an existing loading method such as impregnation and the like, and then, introducing a gas containing a carbon source at a high temperature under an inert atmosphere or a hydrogen atmosphere, and simultaneously carrying out reduction and carbon coating of the transition metal; (III) finally, carrying out oxygen treatment again to convert the zero-valent transition metal into transition metal oxide and simultaneously removing amorphous carbon. Another way is: firstly, loading oxidized transition metal on a carrier by using an existing loading method such as dipping and the like, then reducing the transition metal to a zero-valent state, and (II) introducing gas containing carbon source at high temperature under inert atmosphere or hydrogen atmosphere for carbon coating; (III) finally, carrying out oxygen treatment again to convert the zero-valent transition metal into transition metal oxide and simultaneously removing amorphous carbon.
According to the aforementioned preparation 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 acid washed with no more than 60%, may be no more than 40%, may be no more than 30%, may be no more than 20%, may be no more than 10% of the transition metal lost.
In some embodiments, the oxygen treatment comprises passing a standard gas and heating, wherein the standard gas comprises oxygen and a balance gas, the oxygen having a volume concentration of 10% to 40%; the temperature of the oxygen treatment is 200-500 ℃, and the time of the oxygen treatment is 0.5-10 h.
In summary, the nano composite material of the carbon-coated transition metal oxide is used as an active component and is loaded on the carrier through a specific process, so that the obtained catalyst has high catalytic activity, certain mechanical strength and difficult fragmentation and pulverization 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 is located at 1580cm in the raman spectrum -1 G peak intensity in the vicinity and at 1320cm -1 The ratio of nearby D peak intensities is greater than 2.
In some embodiments, the catalyst has a Raman spectrum that is only at 1580cm -1 G peak in the vicinity, not located at 1320cm -1 A nearby D peak.
The invention also provides a specific application of the catalyst, which comprises a method for catalyzing the decomposition of nitrous oxide by adopting the catalyst, specifically, the gas containing nitrous oxide is introduced into a reactor filled with the catalyst for catalytic decomposition reaction to generate nitrogen and oxygen.
In some embodiments, the catalytic decomposition reaction is at a temperature of 300 ℃ to 420 ℃, preferably 350 ℃ to 420 ℃. The space velocity of the catalytic decomposition reaction is 500-3000 ml of reaction gas/(hr.g of catalyst). The catalyst has high nitrous oxide concentration and high reaction space velocity, and the catalyst has high activity and high device treatment capacity when the catalyst is applied to the reaction.
According to the invention, as previously described, the decomposition N reported in the current research 2 The catalyst of O mainly comprises a noble metal catalyst, an ion-exchange molecular sieve catalyst and a transition metal oxide catalyst. Noble metal catalysts, although having a low decomposition temperature, are not suitable for large-scale industrial production at an expensive price; 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 material of the carbon-coated transition metal oxide of the present invention can effectively decompose nitrous oxide into nitrogen and oxygen as a catalyst, and exhibits excellent stability of catalytic activity in the reaction. In addition, when the existing catalyst is used for catalyzing and decomposing nitrous oxide, the high-concentration nitrous oxide obtained in industrial production is generally required to be diluted to about 0.5% -2%, and the catalyst can be directly decomposed to reach a high decomposition rate without dilution. Namely, the volume concentration of the nitrous oxide is 30% -40%, the catalytic decomposition reaction can be carried out, and the decomposition rate can reach more than 99%, so that the industrial cost is greatly reduced, and the method has good industrial application prospect.
The invention will be further illustrated by the following examples, but the invention is not limited thereby. Unless otherwise indicated, all reagents used in the present invention were analytically pure.
The invention detects the elements on the surface of the material by an X-ray photoelectron spectroscopy (XPS). The X-ray photoelectron spectrum analyzer used was produced by VG scientific and equipped with AvantagThe ESCALab220i-XL type ray electron spectrometer of e V5.926 software has the following X-ray photoelectron spectroscopy analysis test conditions: the excitation source is monochromized A1K alpha X-ray with power of 330W and basic vacuum of 3X 10 during analysis and test -9 mbar。
Analysis of carbon (C) was performed on a Elementar Micro Cube elemental analyzer, which was used mainly for analysis of four elements, carbon (C), hydrogen (H), oxygen (O), and nitrogen (N), with the following specific methods and conditions: 1 mg-2 mg of sample is weighed in a tin cup, is put into an automatic sample feeding disc, enters a combustion tube through a ball valve for combustion, the combustion temperature is 1000 ℃ (in order to remove atmospheric interference during sample feeding, helium is adopted for blowing), and then reduction copper is used for reducing the burnt gas 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 analysis of oxygen element is to convert oxygen in the sample into CO by pyrolysis under the action of a carbon catalyst, and then detect the CO by TCD. Since the composite material of the present invention contains only carbon and metal oxide, the total content of metal oxide can be known from the content of carbon element.
The ratio between the different metal oxides was determined by X-ray fluorescence spectroscopy (XRF) and the content of the different metal oxides in the composite was calculated from the known carbon content. The model of the X-ray fluorescence spectrum analyzer (XRF) adopted by the invention is Rigaku 3013X-ray fluorescence spectrum analyzer, and the X-ray fluorescence spectrum analysis test conditions are as follows: the scan time was 100s and the atmosphere was air.
The Raman detection of the invention adopts a LabRAM HRUV-NIR laser confocal Raman spectrometer manufactured by HORIBA company of Japan, and the laser wavelength is 325nm.
The model of the high-resolution transmission electron microscope (HRTEM) adopted by the invention is JEM-2100 (HRTEM) (Japanese electronics Co., ltd.) and the test conditions of the high-resolution transmission electron microscope are as follows: the acceleration voltage was 200kV.
The model of the XRD diffractometer adopted by the invention is XRD-6000 type X-ray powder diffractometer (Shimadzu), and XRD testing conditions are as follows: cu target, ka radiation (wavelength λ=0.154 nm), tube voltage 40kV, tube current 200mA, scan speed 10 ° (2θ)/min.
The invention detects the pore structure property of the material by a BET test method. Specifically, the specific surface area, the pore volume and the average pore diameter of the catalyst are measured by a Quantachrome AS-6B type analyzer, and the pore diameter is the most probable.
The crushing strength of the invention refers to the pressure of each catalyst when being crushed, the strength is measured by adopting a ZQJ-III intelligent particle strength tester of a large-connection intelligent tester factory, and the catalyst is pressed into tablets under the condition of 2.5MPa, and the diameter of a die is 10mm. The crushing strength test is carried out on 20 samples randomly extracted from the same batch of catalyst, after the maximum value and the minimum value are removed, the arithmetic average value is taken as 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 of the catalyst.
Example 1
This example is illustrative of the preparation of the catalyst of the present invention
(1) 10g of nickel carbonate and 10g of citric acid are weighed into a beaker containing 100mL of deionized water, stirred at 70 ℃ to obtain a homogeneous solution, and continuously heated and evaporated to dryness to obtain a solid precursor.
(2) And (3) placing the solid precursor obtained in the step (1) in a porcelain boat, 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 2 hours, stopping heating, and cooling to room temperature under the nitrogen atmosphere to obtain 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 with the flow rate of 100mL/min (the volume wave of oxygen is 15 percent, nitrogen is balance gas), heating to 350 ℃ at the speed of 2 ℃/min, stopping heating after keeping the temperature for 8 hours, and cooling to room temperature under the atmosphere of the standard gas to obtain the nano composite material of the carbon-coated nickel oxide, namely the raw powder.
(4) At room temperature, uniformly mixing pseudo-boehmite accounting for 50% of the total powder mass and the product of the step (3), adding sesbania powder accounting for 1.5% of the total powder mass, uniformly mixing, preparing nitric acid accounting for 2.5% of the pseudo-boehmite mass into 1mol/L nitric acid aqueous solution, dropwise adding, and continuously stirring until the materials are uniformly mixed, thus obtaining wet dough.
(5) And (3) placing the wet dough in an oven at 80 ℃, drying for 12 hours, then placing in a tube furnace, introducing nitrogen, heating to 500 ℃ at a speed of 5 ℃/min, keeping the temperature for 4 hours, stopping heating, and cooling to room temperature under nitrogen atmosphere to obtain a roasted product.
(6) Crushing the roasted product, sieving with a 100-mesh sieve, tabletting with powder with granularity smaller than 100 meshes in a tablet press, then placing the tabletting product in a tube furnace, introducing air, heating to 350 ℃ at a speed of 5 ℃/min, and performing secondary roasting treatment at constant temperature for 8 hours. And then stopping heating, and cooling to room temperature under the air atmosphere to obtain the formed catalyst. As is clear from XRF and elemental analysis, the carbon content of the molded catalyst was 0.49 wt%, the nickel oxide content was 56.32 wt%, and the alumina content was 43.19 wt%. The specific surface area, pore volume, pore size and crush strength of the catalyst are shown in Table 1.
FIG. 1 shows the X-ray diffraction pattern (XRD) of the product obtained in step (3) of example 1. As can be seen from FIG. 1, the nickel in the product obtained in step (3) is present in the form of an oxide after a 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. As a result of elemental analysis, the carbon content of the product obtained in the step (3) was 0.64 wt% and the nickel oxide content was 99.36 wt%. As is evident from XPS analysis, the surface layer of the product obtained in the step (3) contains 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. As can be seen from the elemental analysis and XPS results, the 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 the step (3) of example 1, from which the G peak (1580 cm -1 ) Intensity of (C) and intensity of D peak (1320 cm) -1 ) The ratio of (2) to (1) is 2.2/1, namely, the surface of the material is coated by a graphitized carbon film.
Example 2
This example is illustrative of the preparation of the catalyst of the present invention
(1) 10g of nickel acetate and 10g of citric acid are weighed into a beaker containing 100mL of deionized water, stirred at 70 ℃ to obtain a homogeneous solution, and continuously heated and evaporated to dryness to obtain a solid precursor.
(2) And (3) placing the solid precursor obtained in the step (1) in a porcelain boat, 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, stopping heating after keeping the temperature for 2 hours, and cooling to room temperature under the nitrogen atmosphere to obtain 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 with the flow rate of 100mL/min (the volume wave of oxygen is 15 percent, nitrogen is balance gas), heating to 330 ℃ at the speed of 2 ℃/min, stopping heating after keeping the temperature constant for 8 hours, and cooling to room temperature under the atmosphere of the standard gas to obtain the carbon-coated nickel oxide nanocomposite.
(4) Uniformly mixing pseudo-boehmite accounting for 25% of the total powder mass and the product of the step (3) at room temperature, adding sesbania powder accounting for 1.5% of the total powder mass, uniformly mixing, preparing nitric acid accounting for 2.5% of the pseudo-boehmite mass into 1mol/L nitric acid aqueous solution, dropwise adding, and continuously stirring until the materials are uniformly mixed; obtaining wet dough;
(5) And (3) placing the wet dough in an oven at 80 ℃, drying for 12 hours, then placing in a tube furnace, introducing nitrogen, heating to 500 ℃ at a 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) Crushing the roasted product, sieving with a 100-mesh sieve, tabletting with powder with granularity smaller than 100 meshes in a tablet press, then placing the tabletting product in a tube furnace, introducing air, heating to 350 ℃ at a speed of 5 ℃/min, and performing secondary roasting at constant temperature for 8 hours. And then stopping heating, and cooling to room temperature under the air atmosphere to obtain the formed catalyst. As is clear from XRF and elemental analysis, the carbon content of the molded catalyst was 0.72 wt%, the nickel oxide content was 78.46 wt%, and the alumina content was 20.82 wt%. The specific surface area, pore volume, pore size and crush strength of the catalyst are shown in Table 1.
FIG. 4 shows the X-ray diffraction pattern (XRD) of the product obtained in step (3) of example 2, and it is apparent from FIG. 4 that nickel in the product obtained in step (3) exists as an oxide after a 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. As a result of elemental analysis, the carbon content of the product obtained in the step (3) was 0.91 wt% and the nickel oxide content was 99.09 wt%. The XPS analysis shows that the surface layer contains 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. From elemental analysis and XPS results, it is known 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 the step (3) of example 2, from which the G peak (1580 cm -1 ) Intensity of (C) and intensity of D peak (1320 cm) -1 ) The ratio of (2) to (1) 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 the 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 the molding treatment.
Application example 1
The tablets were crushed and 0.5 g of the catalyst of example 1, which was sieved out to 20-40 mesh, was placed in a continuous flow fixed bed reactor with a reaction gas composition of 38.0% by volume N 2 O, nitrogen was used as an equilibrium gas, and the flow rate of the reaction gas was 15ml/min. The activity evaluation temperature is 300-500 ℃, and the catalyst catalyzes and decomposes N 2 The conversion of O is shown in Table 2.
Application example 2
Crushing the pressed tablets, and sieving0.5 g of the catalyst of example 2, 20-40 mesh, was placed in a continuous flow fixed bed reactor with a reaction gas composition of 38.0% N by volume 2 O, nitrogen was used as an equilibrium gas, and the flow rate of the reaction gas was 15ml/min. The activity evaluation temperature is 300-500 ℃, and the catalyst catalyzes and decomposes N 2 The 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, and the reaction gas composition was 38.0% N 2 O, nitrogen was used as an equilibrium gas, and the flow rate of the reaction gas was 15ml/min. The activity evaluation temperature is 300-500 ℃, and the catalyst catalyzes and decomposes N 2 The 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, and the reaction gas composition was 38.0% N 2 O, nitrogen was used as an equilibrium gas, and the flow rate of the reaction gas was 15ml/min. The activity evaluation temperature is 300-500 ℃, and the catalyst catalyzes and decomposes N 2 The conversion of O is shown in Table 2.
TABLE 1
TABLE 2
As can be seen from tables 1 and 2 above, the shaped catalyst prepared by the method of the present invention has high mechanical strength, can meet the requirements of industrial application, and well maintains the N of the original active components 2 The catalytic decomposition performance of O can efficiently eliminate N at 360-420 DEG C 2 O. The formed catalyst provided by the invention is applied to adipic acid production processWhen the waste gas is treated, the reaction temperature can be greatly reduced, the energy consumption is reduced, the activity is high, and the stability is good.
It will be appreciated by persons skilled in the art that the embodiments described herein are merely exemplary and that various other alternatives, modifications and improvements may be made within the scope of the invention. Thus, the present invention is not limited to the above-described embodiments, but only by the claims.
Claims (18)
1. A catalyst of carbon-coated transition metal oxide, characterized in that the catalyst comprises a carrier and an active component loaded on the carrier, wherein the active component is a nanocomposite of graphite carbon-coated transition metal oxide;
the transition metal oxide is selected from one or more of ferric oxide, cobalt oxide and nickel oxide;
the nanocomposite comprises a nuclear membrane structure having an outer membrane and an inner core, the outer membrane being a graphitized carbon membrane and the inner core comprising transition metal oxide nanoparticles;
the carbon content is 0.1% -1% based on 100% of the total mass of carbon and transition metal oxide;
the ratio of carbon element determined by X-ray photoelectron spectroscopy to the content of carbon element determined by elemental analysis in the catalyst is not less than 10;
the Raman spectrum of the catalyst is positioned at 1580cm -1 G peak intensity in the vicinity and at 1320cm -1 The ratio of nearby D peak intensities is greater than 2;
the carrier is alumina, silicon oxide or composite oxide of silicon oxide and alumina.
2. The catalyst according to claim 1, wherein the content of the transition metal oxide is 10% -90% and the content of the carrier is 10% -90% based on the mass of the catalyst.
3. A process for preparing the catalyst of claim 1 or 2, comprising the steps of:
providing a carbon-coated transition metal nanocomposite;
oxygen treatment is carried out on the carbon-coated transition metal nanocomposite material to obtain a carbon-coated transition metal oxide nanocomposite material; a kind of electronic device with high-pressure air-conditioning system
And (3) carrying out molding treatment on the nano composite material of the carbon-coated transition metal oxide to obtain the catalyst.
4. The method of preparing a nanocomposite of a carbon-coated transition metal according to claim 3, comprising:
mixing a transition metal-containing compound and carboxylic acid in a solvent to form a homogeneous solution;
removing the solvent in the homogeneous solution to obtain a precursor; a kind of electronic device with high-pressure air-conditioning system
And pyrolyzing the precursor in an inert atmosphere or a reducing atmosphere to obtain the carbon-coated transition metal nanocomposite.
5. The method according to claim 4, wherein the transition metal-containing compound is one or more selected from the group consisting of soluble organic acid salts, basic carbonate salts, hydroxide salts and oxide salts of transition metals, the carboxylic acid is one or more selected from the group consisting 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).
6. The method of preparation 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 temperature rise rate is 0.5-30 ℃/min, the constant temperature section temperature 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.
7. The method according to claim 6, further comprising subjecting the pyrolyzed product to acid washing treatment and then to the oxygen treatment.
8. The method according to claim 4, wherein the carbon-coated transition metal nanocomposite has a pickling loss rate of 60% or less.
9. The method according to claim 3, wherein the oxygen treatment comprises introducing a 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.
10. A method of manufacturing according to claim 3, wherein the shaping process comprises:
adding a binder into the nano composite material of the carbon-coated transition metal oxide, and uniformly mixing to obtain a wet dough;
drying and roasting the wet dough for the first time, and then forming;
and roasting the formed product for the second time to obtain the formed catalyst.
11. The preparation method according to claim 10, wherein the drying temperature is 20-100 ℃, the drying time is 3-24 hours, and the drying atmosphere is an inert atmosphere or an air atmosphere; the first firing includes: heating the dried product to 400-800 ℃ at a heating rate of 1-20 ℃ per minute under inert atmosphere, and keeping the temperature constant for 1-10 hours; the second firing includes: and heating the molded product to 300-400 ℃ at a heating rate of 1-20 ℃ per minute under an air atmosphere, and keeping the temperature constant for 4-10 hours.
12. The method of claim 10, wherein the binder is selected from the group consisting of aluminum sol, silica sol, and silica alumina sol.
13. The preparation method according to claim 10, wherein the binder is prepared from pseudo-boehmite and a peptizing agent, wherein the peptizing agent is selected from one or more of aqueous nitric acid, aqueous hydrochloric acid and aqueous citric acid, and the mass of the peptizing agent is 1% -5% of the mass of the binder.
14. The method of claim 13, wherein the peptizing agent is 2% -3% of the binder by mass.
15. The preparation method according to claim 13, 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% -6% of the mass of the nanocomposite of carbon-coated transition metal oxide.
16. The preparation method according to claim 15, wherein the mass ratio of liquid to solid in the wet mass is 0.8-1.5, the nanocomposite material of the carbon-coated transition metal oxide accounts for 20-80% of the mass of solid in the wet mass, and the binder accounts for 20-80% of the mass of solid in the wet mass.
17. A method of catalyzing the decomposition of nitrous oxide comprising contacting nitrous oxide with the catalyst of claim 1 or 2 to produce nitrogen and oxygen.
18. The method according to claim 17, wherein in the catalytic decomposition reaction, the reaction temperature is 300-420 ℃, the reaction space velocity is 500-3000 ml of reaction gas/(hour.g of catalyst), and the volume concentration of the nitrous oxide is 30-40%.
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