CN107686105B - Preparation method of high-efficiency nitrogen-doped carbon nano tube and application of nitrogen-doped carbon nano tube - Google Patents
Preparation method of high-efficiency nitrogen-doped carbon nano tube and application of nitrogen-doped carbon nano tube Download PDFInfo
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- 239000010949 copper Substances 0.000 claims description 76
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- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 claims description 27
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 24
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- 230000002194 synthesizing effect Effects 0.000 claims description 13
- 239000002243 precursor Substances 0.000 claims description 11
- XTVVROIMIGLXTD-UHFFFAOYSA-N copper(II) nitrate Chemical group [Cu+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O XTVVROIMIGLXTD-UHFFFAOYSA-N 0.000 claims description 10
- 239000000463 material Substances 0.000 claims description 7
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- 239000007795 chemical reaction product Substances 0.000 claims description 2
- ORTQZVOHEJQUHG-UHFFFAOYSA-L copper(II) chloride Chemical compound Cl[Cu]Cl ORTQZVOHEJQUHG-UHFFFAOYSA-L 0.000 claims description 2
- OPQARKPSCNTWTJ-UHFFFAOYSA-L copper(ii) acetate Chemical compound [Cu+2].CC([O-])=O.CC([O-])=O OPQARKPSCNTWTJ-UHFFFAOYSA-L 0.000 claims description 2
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- XOJVVFBFDXDTEG-UHFFFAOYSA-N Norphytane Natural products CC(C)CCCC(C)CCCC(C)CCCC(C)C XOJVVFBFDXDTEG-UHFFFAOYSA-N 0.000 description 1
- AAMATCKFMHVIDO-UHFFFAOYSA-N azane;1h-pyrrole Chemical compound N.C=1C=CNC=1 AAMATCKFMHVIDO-UHFFFAOYSA-N 0.000 description 1
- DLGYNVMUCSTYDQ-UHFFFAOYSA-N azane;pyridine Chemical compound N.C1=CC=NC=C1 DLGYNVMUCSTYDQ-UHFFFAOYSA-N 0.000 description 1
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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
-
- 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
- B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
- B01J21/18—Carbon
- B01J21/185—Carbon nanotubes
-
- 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
- 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
- B01J23/72—Copper
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- B01J35/615—
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- B01J35/635—
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- B01J35/647—
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C68/00—Preparation of esters of carbonic or haloformic acids
- C07C68/01—Preparation of esters of carbonic or haloformic acids from carbon monoxide and oxygen
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2002/00—Crystal-structural characteristics
- C01P2002/50—Solid solutions
- C01P2002/52—Solid solutions containing elements as dopants
- C01P2002/54—Solid solutions containing elements as dopants one element only
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/12—Surface area
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/14—Pore volume
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/16—Pore diameter
- C01P2006/17—Pore diameter distribution
Abstract
A preparation method of a high-efficiency nitrogen-doped carbon nanotube comprises the steps of adding a multi-walled carbon nanotube into a nitric acid solution, sealing the multi-walled carbon nanotube in a high-pressure kettle, pressurizing to 0.4-1.0MPa, stirring, heating to 120-200 ℃ and keeping for 1-4h, cooling the high-pressure kettle to room temperature, washing to neutrality, performing suction filtration and drying; mixing the carbon nano tube and the melamine solid according to the mass ratio of 1:1-4, uniformly grinding by using a mortar, roasting at high temperature in nitrogen, washing to be neutral, and drying to obtain the nitrogen-doped carbon nano tube. The nitrogen doping amount of the invention is 4.6wt% -10.3 wt%.
Description
Technical Field
The invention relates to a preparation method of a high-efficiency nitrogen-doped carbon nano tube and application of the nitrogen-doped carbon nano tube.
Background
Carbon materials are widely used in the field of catalysis due to the characteristics of rich pore channel structure, easy surface modification and the like, for example, carbon-supported copper catalysts are often used for synthesizing dimethyl carbonate, and particularly, activated carbon-supported copper is used for catalyzing methanol gas phase oxidation carbonylation reactions, for example, patents CN102600843A and CN 102872879A. Although the activated carbon supported copper catalyst shows higher initial activity, the activated carbon is mainly microporous, and most copper species fall on the outer surface of the activated carbon, so that the activated carbon is easy to agglomerate in the catalyst preparation process and the reaction process to cause the reduction of dispersibility, thereby causing the rapid reduction of catalytic activity. The chemical properties of the surface of the activated carbon can be regulated and controlled by modifying the activated carbon, so that the interaction between copper species and the activated carbon carrier is enhanced, and further, the metal dispersion is promoted. Although increasing the oxygen-containing functional groups on the surface of the activated carbon can promote the dispersion of copper species and improve the anti-agglomeration capability thereof to some extent, thereby slowing down the deactivation rate of the catalyst (Zhang g.appl.catal, B,179(2015),95-105), during the reaction process, the copper species can still agglomerate, thereby causing the catalyst to be deactivated.
Carbon Nanotubes (CNTs) have attracted much attention in recent years due to their good thermal stability, mechanical stability and electronic conduction properties. The pore channels may provide a special limited-area environment for the metal catalyst and the catalytic reaction, and can prevent the agglomeration of metal particles, thereby promoting the dispersion of active species and the improvement of anti-agglomeration capacity. And due to the unique electronic structure of the bent graphene wall, the performance of the metal catalyst can be modified, so that the catalytic performance is improved.
Compared with the oxygen-containing functional group, the nitrogen-containing functional group added on the surface of the carbon material can enhance the interaction between the loaded metal species and the carrier to a greater extent, thereby obviously improving the dispersion degree of the metal and the agglomeration resistance of the catalyst, and further enhancing the catalytic activity and the stability. Meanwhile, the nitrogen doping amount is closely related to the performance of the nitrogen-doped carbon material. The nitrogen doping amount of the carbon nano tube is lower and is not more than 4.05 percent (L.M.Ombaka.J.solid State Chem,235(2016),202-211) by using a one-step method, thereby affecting the performance of the carbon nano tube.
Disclosure of Invention
In view of the background technology, the present invention aims at providing a preparation method of a high-efficiency nitrogen-doped carbon nanotube with high nitrogen doping amount, a copper-based catalyst prepared by using the nitrogen-doped carbon nanotube as a carrier, and a method for synthesizing dimethyl carbonate by using the copper-based catalyst through methanol gas phase oxidation and carbonylation.
The specific technical scheme of the invention is implemented by the following steps:
the invention provides a preparation method of a high-efficiency nitrogen-doped carbon nanotube, which comprises the following steps:
(1) hydrothermal oxidation of carbon nanotubes
According to the multi-wall carbon nano tube: 1-2g of nitric acid solution: 50-100mL, adding the multi-walled carbon nanotube into a nitric acid solution with the concentration of 0.05-0.5mol/L, transferring the mixture into an autoclave provided with a temperature controller and a propeller type stirring system, sealing the autoclave, flushing and discharging the nitrogen for three times to exhaust the dissolved oxygen in the solution, further pressurizing the system to 0.4-1.0MPa, stirring at the speed of 100 plus 300r/min, then heating to 120 plus 200 ℃ and keeping for 1-4h, finally cooling the autoclave to room temperature and then discharging the pressure, washing to be neutral by using ionized water, performing suction filtration, and drying in an oven at the temperature of 80-100 ℃ for 8-12 h;
(2) mixing the carbon nano tube subjected to hydrothermal oxidation in the step (1) with melamine solid in a mass ratio of 1:1-4, uniformly grinding the mixture by using a mortar, roasting the mixture for 2-4 hours at a high temperature of 600-900 ℃ in nitrogen, washing the roasted mixture to be neutral by using distilled water, and drying the washed mixture to obtain the nitrogen-doped carbon nano tube.
The Carbon Nanotubes (CNTs) described in the step (1) are multi-walled carbon nanotubes with a specific surface area of 180-2The pore volume is 0.70-0.98ml/g, and the average pore diameter is 7.6-12.8 nm.
The nitrogen content of the nitrogen-doped carbon nanotube is 4.6 to 10.3 weight percent, and the specific surface area is 134-180m2The pore volume is 0.60-0.80ml/g, and the average pore diameter is 12.6-15.2 nm.
The catalyst of the invention is composed of active components of copper and nitrogen-doped carbon nano-tubes, wherein Cu3.0-10.0 wt% and the nitrogen-doped carbon nano-tubes are 90-97 wt%.
The catalyst of the invention is prepared by the following preparation method:
(1) according to the composition of the catalyst, dropwise adding a soluble non-chlorine copper salt aqueous solution with the concentration of 0.156-0.52mol/L into the nitrogen-doped carbon nano tube, stirring in an ultrasonic reactor for 30-60min, and then drying at 30-50 ℃ for 8-15h to obtain a dried precursor;
(2) and (3) heating the dried precursor to 450 ℃ at the speed of 2-10 ℃/min in the inert atmosphere, roasting at the constant temperature for 240min, naturally cooling to room temperature, and taking out to obtain the nitrogen-doped carbon nanotube supported copper catalyst.
The soluble non-chloride copper salt is copper nitrate or copper acetate.
The inert atmosphere as described above is nitrogen or argon.
The catalyst of the invention is used for the reaction of synthesizing dimethyl carbonate by methanol gas phase oxidation carbonylation, and the reaction steps and the process conditions are as follows:
the mixture of the catalyst and the quartz sand is loaded into a fixed bed reactor, and the temperature of a catalyst bed layer in the reactor is heated to 120-140 ℃ under the nitrogen atmosphere; the volume flow ratio of the reaction gas is as follows: o is2: heating the raw material of methanol 8:1:0.01-11:1:0.01 to 110-; the material from the preheater enters the tubular reactor from the upper end of the reactor, and the gas phase volume space velocity of the material is 4980--1Reacting at the temperature of 120-140 ℃ and under the pressure of normal pressure-2.0 MPa, and condensing the material from the reactor by a condenser to obtain a reaction product.
The addition amount of the catalyst and the quartz sand is that the mass ratio of the catalyst to the quartz sand is as follows: 1:2-5 of quartz sand.
The technical advantages of the invention are as follows:
the catalyst prepared by the invention adopts the idea of firstly carrying out hydrothermal oxidation on the carbon nano tube and then carrying out high-temperature nitrogen doping on the copper-loaded catalyst in a breakthrough manner, and has the advantages of simple operation, advanced process, high nitrogen doping amount, small copper nano particle size, uniform dispersion, large number of active centers, strong agglomeration resistance, good catalytic activity and stability and the like.
The carbon nano tube after being subjected to hydrothermal oxidation and high-temperature nitrogen doping has good physical and chemical properties, and the nitrogen content on the surface of the carbon nano tube is obviously improved, namely nitrogen-containing functional groups on the surface of the carbon nano tube, including pyridine nitrogen, pyrrole nitrogen, tetravalent nitrogen and the like, are increased through the hydrothermal oxidation and high-temperature nitrogen doping treatment.
Compared with the prior art, the invention has obvious advancement, aims at the defect of preparation of carbon material loaded copper catalyst, and adopts a method of firstly hydrothermal oxidation and then high-temperature nitrogen dopingThe preparation method is simple to operate, advanced in process and accurate in data, copper nanoparticles are uniformly dispersed (about 4 nm) by dispersing copper species in the nitrogen-doped carbon nanotube cavity, the anti-agglomeration capacity of the active component copper is improved by the confinement effect and the nitrogen doping of the carbon nanotube, and the prepared supported copper catalyst shows better catalytic activity and stability in the reaction of catalyzing methanol gas-phase oxidative carbonylation to synthesize dimethyl carbonate. The methanol conversion rate is 8.5-20%, and the space-time yield of DMC reaches 300--1·h-1The DMC selectivity is 86-99%, and the stability is 30-60 h.
The embodiment of the invention adopts the steps of firstly carrying out hydrothermal oxidation and then carrying copper on the high-temperature nitrogen-doped carbon nano tube to prepare the supported copper-based catalyst, and the supported copper-based catalyst is applied to the reaction of catalyzing methanol gas-phase oxidation carbonylation to synthesize dimethyl carbonate (DMC). Compared with a comparative example without the composite treatment, the method has the advantages of high nitrogen doping amount, high methanol conversion rate, high DMC space-time yield and selectivity, good stability and the like.
Drawings
FIG. 1 is an XPS chart of the total elemental analysis of N-doped carbon nanotubes prepared in example 3 of the present invention;
FIG. 2 is a N1sXPS plot of N doped carbon nanotubes prepared in example 3 of the present invention;
fig. 3 is a nitrogen adsorption and desorption graph of the nitrogen-doped carbon nanotube prepared in example 3 of the present invention;
fig. 4 is a TEM topography of the nitrogen doped carbon nanotube confined copper catalyst prepared in example 3 of the present invention. As can be seen from FIG. 4, the prepared copper nanoparticles have good dispersion and high dispersion degree;
fig. 5 is a TEM topography of the nitrogen-doped carbon nanotube confinement copper catalyst prepared in example 3 of the present invention after activity evaluation for 60h, and it can be seen from fig. 5 that the nitrogen-doped carbon nanotube can effectively limit migration and agglomeration of copper nanoparticles.
Detailed Description
Comparative example 1 an ultrasonic-assisted isometric impregnation method was used to prepare a Cu-supported catalyst for pristine carbon nanotubes CNTs, the specific steps of Cu/CNTs were as follows:
①, weighing 0.113g Cu (NO)3)2·3H2Measuring 3mL of deionized water, adding the deionized water into a beaker, and magnetically stirring the mixture for 10min to obtain 0.156mol/L copper nitrate aqueous solution;
②, weighing the powder with a specific surface area of 195m2Adding 1g of original multi-walled carbon nano-tubes with the pore volume of 0.90ml/g and the average pore diameter of 12.8nm into the solution, placing the solution in an ultrasonic reactor, and stirring the solution for 60min, wherein the ultrasonic frequency is 60 KHz;
③, standing the mixture after ultrasonic treatment for 24 hours at room temperature;
④, standing, and then placing the beaker in an oven for drying at the drying temperature of 40 ℃ for 8h to obtain the original carbon nanotube confinement copper catalyst precursor;
⑤, introducing 30ml/min nitrogen into the dried precursor in a tube furnace, raising the temperature to 350 ℃ at the speed of 2 ℃/min, roasting at constant temperature for 240min, naturally cooling to room temperature, and taking out to obtain the Cu/CNT catalyst, wherein the composition of the Cu/CNT catalyst is Cu-3 wt% and CNT-97 wt%.
The specific reaction steps of the catalyst for evaluating the reaction activity of synthesizing the dimethyl carbonate by the methanol gas-phase oxidation carbonylation are as follows:
loading a uniform mixture of 0.3g of catalyst and 0.6g of quartz sand into a stainless steel tubular reactor, setting a temperature-raising program, starting a preheating furnace, and starting CO and O when the temperature is raised to 140 DEG C2Methanol is pumped by Series III type micro-sampling pump, gasified in a preheating gasification furnace and mixed with CO and O2Mixing the two gases thoroughly, timing when the temperature rises to the required temperature, performing gas chromatography every 1h at methanol feed rate of 0.02ml/min, and introducing CO and O2The feeding speed is 22ml/min and 2.0ml/min respectively, and the material gas phase volume space velocity is 7040h-1The reaction pressure is normal pressure. Space-time yield STY for synthesizing DMC by catalyzing methanol oxidation carbonylation with original carbon nano tube confined copper catalystDMCOnly 86.2mg g-1·h-1Methanol conversion was 2.4%, DMC selectivity was 70.3%, and deactivation was rapid within 5 h.
Comparative example 2 hydrothermal oxidation of carbon nanotubes
①, measuring 2.34mL of nitric acid and 72.66mL of deionized water, adding into a beaker, and stirring for 10min to prepare a 0.5mol/L nitric acid aqueous solution;
②, weighing the powder with a specific surface area of 220m22g of original carbon nano-tubes with the pore volume of 0.78ml/g and the average pore diameter of 8.7nm are added into the nitric acid aqueous solution;
③ transferring the mixture into an autoclave equipped with a temperature controller and a propeller type stirring system, sealing the autoclave, flushing with nitrogen for three times to exhaust dissolved oxygen in the solution, further pressurizing the system to 0.8MPa, stirring at 100r/min, heating to 140 ℃ and maintaining for 3h, cooling the autoclave to room temperature, releasing pressure, washing with ionized water to neutrality, filtering, drying in an oven at 100 ℃, drying for 10h to obtain the hydrothermally oxidized carbon nanotube with specific surface area of 230m2The pore volume is 0.76ml/g, the average pore diameter is 9.2nm, and the atomic percentage of elemental analysis is that the content of carbon element is 90.8 percent, the content of oxygen element is 8.4 percent, and the content of nitrogen element is 0.8 percent.
Preparation of hydrothermal oxidized carbon nanotube-loaded copper catalyst Cu/OCNT
①, weighing 0.189g Cu (NO)3)2·3H2Measuring 3mL of deionized water, adding the deionized water into a beaker, and magnetically stirring the mixture for 10min to obtain 0.260mol/L copper nitrate aqueous solution;
②, weighing 1g of multi-walled carbon nanotubes subjected to hydrothermal oxidation, adding into the solution, and placing in an ultrasonic reactor to stir for 40min at an ultrasonic frequency of 50 KHz;
③, standing the mixture after ultrasonic treatment for 12h at room temperature,
④, standing, and then placing the beaker in an oven for drying at the drying temperature of 40 ℃ for 10h to obtain a direct nitrogen-doped carbon nanotube confinement copper catalyst precursor;
⑤, introducing 20ml/min nitrogen into the dried precursor in a tube furnace, heating to 300 ℃ at the speed of 3 ℃/min, roasting for 240min at constant temperature, naturally cooling to room temperature, and taking out to obtain the Cu/OCNT catalyst, wherein the composition of the Cu/OCNT catalyst is Cu-5 wt% and OCNT-95 wt%.
The specific reaction steps of the catalyst for evaluating the reaction activity of synthesizing the dimethyl carbonate by the methanol gas-phase oxidation carbonylation are as follows:
①, mixing 0.3g of catalyst and 1.0g of quartz sand uniformly and then loading the mixture into a stainless steel tubular reactor;
② setting temperature raising program, heating the catalyst bed in the reactor to 120 deg.C, turning on CO and O2Methanol is pumped by Series III type micro-sampling pump, gasified in a preheating gasification furnace and mixed with CO and O2Mixing the two gases, and analyzing by on-line gas chromatography at methanol feed rate of 0.03ml/min and CO and O2The feeding speed is respectively 30ml/min and 3.0ml/min, and the volume space velocity is 9960h-1The reaction pressure was 0.3 MPa. Space-time yield STY of synthesizing DMC by catalyzing methanol oxidation carbonylation with oxidized carbon nanotube confined copper catalystDMCOnly 187.5mg g-1·h-1Methanol conversion was 5.0%, DMC selectivity was 68.5%, and deactivation began at 10h and was faster.
Comparative example 3 direct nitrogen-doped carbon nanotubes
(1) 1.0g of a specific surface area of 229m2The volume of each hole is 0.73ml/g, the original carbon nano tube with the average aperture of 8.5nm and 2g of melamine solid are placed in a mortar and are uniformly ground and then are placed in a quartz boat; (2) placing the quartz boat containing the mixture in a high-temperature tube furnace, introducing 20ml/min of nitrogen into the tube furnace, roasting at the constant temperature of 700 ℃ for 240min, naturally cooling to room temperature, taking out, washing to neutrality, performing suction filtration, placing in an oven, drying at the drying temperature of 110 ℃, and drying for 10h to obtain the nitrogen-doped carbon nano tube, wherein the specific surface area of the nitrogen-doped carbon nano tube is 182m2The pore volume is 0.69ml/g, the average pore diameter is 12.6nm, and the atomic percentage of elemental analysis is that the content of carbon element is 97.0 percent, the content of oxygen element is 1.6 percent, and the content of nitrogen element is 1.4 percent.
Preparation of direct nitrogen-doped carbon nanotube confinement copper catalyst
①, weighing 0.378g Cu (NO)3)2·3H2Measuring 3mL of deionized water, adding the deionized water into a beaker, and magnetically stirring the mixture for 10min to obtain 0.520mol/L copper nitrate aqueous solution;
②, weighing 1g of nitrogen-doped multi-walled carbon nanotubes, adding into the solution, and stirring in an ultrasonic reactor for 60min at an ultrasonic frequency of 50 KHz;
③, standing the mixture after ultrasonic treatment for 30h at room temperature;
④, standing, and then placing the beaker in an oven for drying at the drying temperature of 35 ℃ for 12h to obtain a direct nitrogen-doped carbon nanotube confinement copper catalyst precursor;
⑤, introducing 25ml/min nitrogen into a tube furnace, roasting at 350 ℃ for 240min, naturally cooling to room temperature, and taking out to obtain the Cu/NCNT catalyst, wherein the composition of the Cu/NCNT catalyst is Cu-10 wt%, and the NCNT-90 wt%, and the specific reaction steps of the catalyst in the evaluation of the activity of the methanol gas phase oxidation carbonylation synthesis dimethyl carbonate reaction are as follows:
①, mixing 0.3g of catalyst and 1.5g of quartz sand uniformly and then putting into a stainless steel tubular reactor;
② setting temperature raising program, heating the catalyst bed in the reactor to 130 deg.C, turning on CO and O2Methanol is pumped by Series III type micro-sampling pump, gasified in a preheating gasification furnace and mixed with CO and O2Mixing the two gases, and analyzing by on-line gas chromatography at methanol feed rate of 0.04ml/min and CO and O2The feeding speed is respectively 36ml/min and 4.0ml/min, and the volume space velocity is 12480h-1The reaction pressure is normal pressure. The nitrogen-doped carbon nanotube confined copper catalyst catalyzes the space-time yield STY of methanol oxidative carbonylation synthesis DMCDMCIs 164.2mg g-1·h-1Methanol conversion was 4.5%, DMC selectivity was 73.2%, and faster deactivation began at 7 h.
Example 1 hydrothermal Oxidation of carbon nanotubes
①, measuring nitric acid 0.23mL and deionized water 74.77mL, adding into a beaker, and stirring for 10min to prepare a nitric acid aqueous solution of 0.05 mol/L;
②, weighing the powder with a specific surface area of 180m2Per g, pore volume of0.90ml/g of original multi-walled carbon nano-tubes with the average pore diameter of 12.8nm is added into the nitric acid aqueous solution by 2 g;
③, transferring the mixture into an autoclave provided with a temperature controller and a propeller type stirring system, sealing the autoclave, flushing and discharging the nitrogen for three times to exhaust the dissolved oxygen in the solution, further pressurizing the system to 0.4MPa, stirring at the speed of 100r/min, heating to 120 ℃ and keeping for 1h, finally cooling the autoclave to room temperature, then releasing pressure, washing with ionized water to neutrality, filtering, placing in an oven for drying at the drying temperature of 90 ℃, and drying for 12 h.
Carbon nano tube after high-temperature nitrogen doping oxidation
① carbon nanotubes and melamine after oxidation
Respectively weighing 1.5g of carbon nano tube and 3g of melamine;
② preparation of the mixture
Placing the weighed carbon nano tube and melamine solid in a mortar, uniformly grinding, and placing in a quartz boat;
③ high-temperature nitrogen-doped carbon oxide nanotube
Placing the quartz boat containing the mixture in a high-temperature tube furnace, introducing 30ml/min nitrogen into the tube furnace, roasting at 700 ℃ for 240min at constant temperature, naturally cooling to room temperature, taking out, washing to neutrality, performing suction filtration, placing in an oven, drying at 100 ℃, and drying for 10h to obtain nitrogen-doped carbon nanotubes with specific surface area of 171m2The pore volume is 0.88ml/g, the average pore diameter is 14.1nm, and the atomic percentage of elemental analysis is that the content of carbon element is 92.2 percent, the content of oxygen element is 3.2 percent, and the content of nitrogen element is 4.6 percent.
Preparation of nitrogen-doped carbon nanotube confinement copper catalyst
①, weighing 0.113g Cu (NO)3)2·3H2Measuring 3mL of deionized water, adding the deionized water into a beaker, and magnetically stirring the mixture for 10min to obtain 0.156mol/L copper nitrate aqueous solution;
②, weighing 1g of nitrogen-doped multi-walled carbon nanotubes, adding into the solution, and stirring in an ultrasonic reactor for 60min at an ultrasonic frequency of 60 KHz;
③, standing the mixture after ultrasonic treatment for 24 hours at room temperature,
④, standing, and then placing the beaker in an oven for drying at the drying temperature of 30 ℃ for 14h to obtain a nitrogen-doped carbon nanotube confinement copper catalyst precursor;
⑤, introducing 30ml/min nitrogen into the dried precursor in a tube furnace, raising the temperature to 350 ℃ at the speed of 5 ℃/min, roasting for 240min at constant temperature, naturally cooling to room temperature, and taking out to obtain the Cu/NCNT catalyst, wherein the composition of the Cu/NCNT catalyst is Cu-3 wt% and NCNT-97 wt%.
The specific reaction steps of the catalyst for evaluating the reaction activity of synthesizing the dimethyl carbonate by the methanol gas-phase oxidation carbonylation are as follows:
①, mixing 0.3g of catalyst and 1g of quartz sand uniformly and then loading the mixture into a stainless steel tubular reactor;
② setting temperature raising program to heat the catalyst bed in the reactor to 140 deg.C, and turning on CO and O2Methanol is pumped by Series III type micro-sampling pump, gasified in a preheating gasification furnace and mixed with CO and O2Mixing the two gases, and analyzing by on-line gas chromatography at methanol feed rate of 0.05ml/min and CO and O2The feeding speed is respectively 50ml/min and 5.0ml/min, and the volume space velocity is 16600h-1The reaction pressure is normal pressure. The nitrogen-doped carbon nanotube confined copper catalyst catalyzes the space-time yield STY of methanol oxidative carbonylation synthesis DMCDMCReaches 313.5mg g-1·h-1The methanol conversion was 8.5%, the DMC selectivity was 86.0%, and began to decline slowly at 30 h.
Example 2
The same operation and procedure as in example 1 were carried out except that the concentration of nitric acid used in the oxidation was changed to 0.5mol/L, the oxidation temperature was changed to 180 ℃, the oxidation pressure was changed to 0.8MPa, the stirring speed was changed to 200r/min, and the oxidation time was changed to 2 hours; when the high-temperature nitrogen is doped, the mass of the melamine is changed to 4.5g, the high-temperature nitrogen-doped multi-walled carbon nano-tube is obtained, and the specific surface area of the nitrogen-doped carbon nano-tube is 171m2The volume of pores is 0.87ml/g, the average pore diameter is 12.7nm, the atomic percentage of carbon element is 83.6 percent and the oxygen element content is 6 percent in elemental analysis.8 percent and the content of nitrogen element is 9.6 percent.
Preparation of nitrogen-doped carbon nanotube confinement copper catalyst
①, weighing 0.189g Cu (NO)3)2·3H2Measuring 3mL of deionized water, adding the deionized water into a beaker, and magnetically stirring the mixture for 10min to obtain 0.260mol/L copper nitrate aqueous solution;
②, weighing 1g of nitrogen-doped multi-walled carbon nanotubes, adding into the solution, and stirring in an ultrasonic reactor for 60min at an ultrasonic frequency of 40 KHz;
③, standing the mixture after ultrasonic treatment for 12h at room temperature,
④, standing, and then placing the beaker in an oven for drying at the drying temperature of 30 ℃ for 15h to obtain a nitrogen-doped carbon nanotube confinement copper catalyst precursor;
⑤, introducing 20ml/min nitrogen into the dried precursor in a tube furnace, raising the temperature to 300 ℃ at the speed of 6 ℃/min, roasting for 240min at constant temperature, naturally cooling to room temperature, and taking out to obtain the Cu/NCNT catalyst, wherein the components of the Cu/NCNT catalyst are Cu-5 wt% and NCNT-95 wt%.
The specific reaction steps of the catalyst for evaluating the reaction activity of synthesizing the dimethyl carbonate by the methanol gas-phase oxidation carbonylation are as follows:
①, mixing 0.2g of catalyst and 0.8g of quartz sand uniformly and then putting into a stainless steel tubular reactor;
② setting temperature raising program, heating the catalyst bed in the reactor to 125 deg.C, turning on CO and O2Methanol is pumped by Series III type micro-sampling pump, gasified in a preheating gasification furnace and mixed with CO and O2Mixing the two gases, and analyzing by on-line gas chromatography at methanol feed rate of 0.01ml/min and CO and O2The feeding speed is respectively 10ml/min and 1.0ml/min, and the volume space velocity is 4980h-1The reaction pressure was 0.5 MPa. The nitrogen-doped carbon nanotube confined copper catalyst catalyzes the space-time yield STY of methanol oxidative carbonylation synthesis DMCDMCReaches 514.5mg g-1·h-1The methanol conversion was 18.8%, the DMC selectivity was 90.5%, and started to decline slowly at 50 h.
Example 3
The same operation and procedure as in example 1 were carried out except that the concentration of the aqueous solution of hydrothermal nitric acid oxide was changed to 0.5mol/L, the oxidation temperature was changed to 200 deg.C, the oxidation pressure was changed to 1.0MPa, the stirring speed was changed to 300r/min, and the oxidation time was changed to 3 hours; when the high-temperature nitrogen is doped, the mass of the melamine is changed to 6g, the high-temperature nitrogen-doped multi-walled carbon nano tube is obtained, and the specific surface area of the nitrogen-doped carbon nano tube is 135m2The pore volume is 0.76ml/g, the average pore diameter is 15.1nm, and the atomic percentage of elemental analysis is that the content of carbon element is 82.3 percent, the content of oxygen element is 7.4 percent and the content of nitrogen element is 10.3 percent.
Preparation of nitrogen-doped carbon nanotube confinement copper catalyst
①, weighing 0.265g Cu (NO)3)2·3H2Measuring 3mL of deionized water, adding the deionized water into a beaker, and magnetically stirring the mixture for 10min to obtain 0.375mol/L copper nitrate aqueous solution;
②, weighing 1g of nitrogen-doped multi-walled carbon nanotubes, adding into the solution, and stirring in an ultrasonic reactor for 60min at an ultrasonic frequency of 45 KHz;
③, standing the mixture after ultrasonic treatment for 14h at room temperature,
④, standing, and then placing the beaker in an oven for drying at the drying temperature of 30 ℃ for 15h to obtain a nitrogen-doped carbon nanotube confinement copper catalyst precursor;
⑤, introducing 25ml/min nitrogen into the dried precursor in a tube furnace, roasting at 350 ℃ for 240min, naturally cooling to room temperature, and taking out to obtain the Cu/NCNT catalyst, wherein the composition of the Cu/NCNT catalyst is Cu-7 wt% and NCNT-93 wt%.
The specific reaction steps of the catalyst for evaluating the reaction activity of synthesizing the dimethyl carbonate by the methanol gas-phase oxidation carbonylation are as follows:
①, mixing 0.3g of catalyst and 1.5g of quartz sand uniformly and then putting into a stainless steel tubular reactor;
② setting temperature raising program, heating the catalyst bed in the reactor to 130 deg.C, turning on CO and O2Methanol is pumped by Series III type micro-sampling pump, gasified in a preheating gasification furnace and mixed with CO and O2The two gases are fully mixed by adopting on-line gasThe methanol feed rate was 0.02ml/min, CO and O by phase chromatography2The feeding speed is respectively 16ml/min and 2.0ml/min, and the volume space velocity is 5840h-1The reaction pressure was 2.0 MPa. The nitrogen-doped carbon nanotube confined copper catalyst catalyzes the space-time yield STY of methanol oxidative carbonylation synthesis DMCDMCReaches 547.7mg g-1·h-1Methanol conversion was 20.0%, DMC selectivity was 91.3%, and there was no significant deactivation within 60 h.
Example 4
The same operation and procedure as in example 1 were carried out except that the concentration of the aqueous solution of hydrothermal nitric acid oxide was changed to 0.1mol/L, the oxidation temperature was changed to 140 ℃, the oxidation pressure was changed to 0.4MPa, the stirring speed was changed to 150r/min, and the oxidation time was changed to 2 hours; during high-temperature nitrogen doping, the mass of melamine is changed to 6g, and the high-temperature nitrogen-doped multi-walled carbon nanotube is obtained, wherein the specific surface area of the nitrogen-doped carbon nanotube is 117m2The pore volume is 0.6ml/g, the average pore diameter is 14.1nm, and the atomic percentage of elemental analysis is that the content of carbon element is 89.8%, the content of oxygen element is 3.4%, and the content of nitrogen element is 6.8%.
Preparation of nitrogen-doped carbon nanotube confinement copper catalyst
①, weighing 0.340g Cu (NO)3)2·3H2Measuring 3mL of deionized water, adding the deionized water into a beaker, and magnetically stirring the mixture for 10min to obtain 0.469mol/L copper nitrate aqueous solution;
②, weighing 1g of nitrogen-doped multi-walled carbon nanotubes, adding into the solution, and stirring in an ultrasonic reactor for 60min at an ultrasonic frequency of 50 KHz;
③, standing the mixture after ultrasonic treatment for 16h at room temperature,
④, standing, and then placing the beaker in an oven for drying at the drying temperature of 30 ℃ for 10h to obtain a nitrogen-doped carbon nanotube confinement copper catalyst precursor;
⑤, introducing 20ml/min nitrogen into the dried precursor in a tube furnace, heating to 350 ℃ at the speed of 10 ℃/min, roasting for 240min at constant temperature, naturally cooling to room temperature, and taking out to obtain the Cu/NCNT catalyst, wherein the components of the Cu/NCNT catalyst are Cu-9 wt% and NCNT-91 wt%.
The specific reaction steps of the catalyst for evaluating the reaction activity of synthesizing the dimethyl carbonate by the methanol gas-phase oxidation carbonylation are as follows:
①, mixing 0.6g of catalyst and 3g of quartz sand uniformly and then loading the mixture into a stainless steel tubular reactor;
② setting temperature raising program, heating the catalyst bed in the reactor to 135 deg.C, turning on CO and O2Methanol is pumped by Series III type micro-sampling pump, gasified in a preheating gasification furnace and mixed with CO and O2Mixing the two gases, and analyzing by on-line gas chromatography at methanol feed rate of 0.04ml/min and CO and O2The feeding speed is 36ml/min and 4.0ml/min respectively, and the volume space velocity is 6240h-1The reaction pressure was 0.8 MPa. The nitrogen-doped carbon nanotube confined copper catalyst catalyzes the space-time yield STY of methanol oxidative carbonylation synthesis DMCDMCReaches 416.8mg g-1·h-1Methanol conversion was 15.2%, DMC selectivity was 92.0%, and activity began to decline slowly at 45 h.
Example 5
The same operation and procedure as in example 1 were carried out except that the concentration of the aqueous solution of hydrothermal nitric acid oxide was changed to 1.0mol/L, the oxidation temperature was changed to 160 ℃, the oxidation pressure was changed to 0.8MPa, the stirring speed was changed to 250r/min, and the oxidation time was changed to 4 hours; when the high-temperature nitrogen is doped, the mass of melamine is changed to 1.5g, the high-temperature nitrogen-doped multi-wall carbon nano tube is obtained, and the specific surface area of the nitrogen-doped carbon nano tube is 169m2The pore volume is 0.7ml/g, the average pore diameter is 15.2nm, and the atomic percentage of elemental analysis is that the content of carbon element is 88.6 percent, the content of oxygen element is 5.6 percent, and the content of nitrogen element is 5.8 percent.
Preparation of nitrogen-doped carbon nanotube confinement copper catalyst
①, weighing 0.378g Cu (NO)3)2·3H2Measuring 3mL of deionized water, adding the deionized water into a beaker, and magnetically stirring the mixture for 10min to obtain 0.520mol/L copper nitrate aqueous solution;
②, weighing 1g of nitrogen-doped multi-walled carbon nanotubes, adding into the solution, and stirring in an ultrasonic reactor for 60min at an ultrasonic frequency of 60 KHz;
③, standing the mixture after ultrasonic treatment for 18h at room temperature,
④, standing, and then placing the beaker in an oven for drying at the drying temperature of 35 ℃ for 12h to obtain a nitrogen-doped carbon nanotube confinement copper catalyst precursor;
⑤, introducing 35ml/min nitrogen into the dried precursor in a tube furnace, roasting at 350 ℃ for 240min, naturally cooling to room temperature, and taking out to obtain the Cu/NCNT reagent, wherein the components of the Cu/NCNT reagent are Cu-10 wt% and NCNT-90 wt%.
The specific reaction steps of the catalyst for evaluating the reaction activity of synthesizing the dimethyl carbonate by the methanol gas-phase oxidation carbonylation are as follows:
①, mixing 0.8g of catalyst and 2.5g of quartz sand uniformly and then putting into a stainless steel tubular reactor;
② setting temperature raising program to heat the catalyst bed in the reactor to 140 deg.C, and turning on CO and O2Methanol is pumped by Series III type micro-sampling pump, gasified in a preheating gasification furnace and mixed with CO and O2Mixing the two gases, and analyzing by on-line gas chromatography at methanol feed rate of 0.06ml/min and CO and O2The feeding speed is respectively 60ml/min and 6.0ml/min, and the volume space velocity is 7470h-1The reaction pressure was 1.5 MPa. The nitrogen-doped carbon nanotube confined copper catalyst catalyzes the space-time yield STY of methanol oxidative carbonylation synthesis DMCDMCReaches 345.2mg g-1·h-1The methanol conversion was 12.6%, the DMC selectivity was 93.4%, and the activity started to decline slowly at 40 h.
Claims (9)
1. A preparation method of a high-efficiency nitrogen-doped carbon nanotube is characterized by comprising the following steps:
(1) hydrothermal oxidation of carbon nanotubes
According to the multi-wall carbon nano tube: 1-2g of nitric acid solution: 50-100mL, adding the multi-walled carbon nanotube into a nitric acid solution with the concentration of 0.05-0.5mol/L, transferring the mixture into an autoclave provided with a temperature controller and a propeller type stirring system, sealing the autoclave, flushing and discharging the nitrogen for three times to exhaust the dissolved oxygen in the solution, further pressurizing the system to 0.4-1.0MPa, stirring at the speed of 100 plus 300r/min, then heating to 120 plus 200 ℃ and keeping for 1-4h, finally cooling the autoclave to room temperature and then discharging the pressure, washing to be neutral by using ionized water, performing suction filtration, and drying in an oven at the temperature of 80-100 ℃ for 8-12 h;
(2) mixing the carbon nano tube subjected to hydrothermal oxidation in the step (1) with melamine solid in a mass ratio of 1:1-4, uniformly grinding the mixture by using a mortar, roasting the mixture for 2-4 hours at a high temperature of 600-900 ℃ in nitrogen, washing the roasted mixture to be neutral by using distilled water, and drying the washed mixture to obtain the nitrogen-doped carbon nano tube.
2. The method as claimed in claim 1, wherein the carbon nanotubes obtained in step (1) are multi-walled carbon nanotubes with a specific surface area of 180-2Per g, pore volume of 0.70-0.98ml/g, and average pore diameter of 7.6-12.8 nm.
3. The method as claimed in claim 1 or 2, wherein the N content of the N-doped carbon nanotube is 4.6wt% -10.3wt%, and the specific surface area is 134-180m2The pore volume is 0.60-0.80ml/g, and the average pore diameter is 12.6-15.2 nm.
4. The catalyst prepared by the nitrogen-doped carbon nanotube of claim 3, wherein the catalyst is composed of copper and nitrogen-doped carbon nanotube as active components, wherein Cu is 3.0-10.0wt%, and nitrogen-doped carbon nanotube is 90-97 wt%.
5. The method for preparing the catalyst according to claim 4, comprising the steps of:
(1) according to the composition of the catalyst, dropwise adding a soluble non-chlorine copper salt aqueous solution with the concentration of 0.156-0.52mol/L into the nitrogen-doped carbon nano tube, stirring in an ultrasonic reactor for 30-60min, and then drying at 30-50 ℃ for 8-15h to obtain a dried precursor;
(2) and (3) heating the dried precursor to 450 ℃ at the speed of 2-10 ℃/min in the inert atmosphere, roasting at the constant temperature for 240min, naturally cooling to room temperature, and taking out to obtain the nitrogen-doped carbon nanotube supported copper catalyst.
6. The method of claim 5, wherein the soluble non-chloride copper salt is copper nitrate or copper acetate.
7. The method of claim 5, wherein the inert atmosphere is nitrogen or argon.
8. Use of a catalyst according to claim 4, characterized in that it comprises the following steps:
the catalyst is used for the reaction of synthesizing dimethyl carbonate by methanol gas-phase oxidation carbonylation, the mixture of the catalyst and quartz sand is loaded into a fixed bed reactor, and the temperature of a catalyst bed layer in the reactor is heated to 120-140 ℃ under the atmosphere of nitrogen; the volume flow ratio of the reaction gas is as follows: o is2: the raw material of methanol =8:1:0.01-11:1:0.01 is heated to 110-; the material from the preheater enters the tubular reactor from the upper end of the reactor, and the gas phase volume space velocity of the material is 4980--1Reacting at the temperature of 120-140 ℃ and under the pressure of normal pressure-2.0 MPa, and condensing the material from the reactor by a condenser to obtain a reaction product.
9. The use of the catalyst according to claim 8, wherein the catalyst and the quartz sand are added in such an amount that the mass ratio of the catalyst to the quartz sand is as follows: quartz sand =1: 2-5.
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