CN116328749A - Modified magnesium-aluminum hydrotalcite catalyst and preparation method and application thereof - Google Patents
Modified magnesium-aluminum hydrotalcite catalyst and preparation method and application thereof Download PDFInfo
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- 239000003054 catalyst Substances 0.000 title claims abstract description 89
- GDVKFRBCXAPAQJ-UHFFFAOYSA-A dialuminum;hexamagnesium;carbonate;hexadecahydroxide Chemical compound [OH-].[OH-].[OH-].[OH-].[OH-].[OH-].[OH-].[OH-].[OH-].[OH-].[OH-].[OH-].[OH-].[OH-].[OH-].[OH-].[Mg+2].[Mg+2].[Mg+2].[Mg+2].[Mg+2].[Mg+2].[Al+3].[Al+3].[O-]C([O-])=O GDVKFRBCXAPAQJ-UHFFFAOYSA-A 0.000 title claims abstract description 45
- 229960001545 hydrotalcite Drugs 0.000 title claims abstract description 31
- 229910001701 hydrotalcite Inorganic materials 0.000 title claims abstract description 31
- GANNOFFDYMSBSZ-UHFFFAOYSA-N [AlH3].[Mg] Chemical class [AlH3].[Mg] GANNOFFDYMSBSZ-UHFFFAOYSA-N 0.000 title claims abstract description 27
- 238000002360 preparation method Methods 0.000 title claims abstract description 24
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims abstract description 102
- 238000006243 chemical reaction Methods 0.000 claims abstract description 65
- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical compound OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 claims abstract description 63
- 239000000243 solution Substances 0.000 claims abstract description 56
- 239000012266 salt solution Substances 0.000 claims abstract description 33
- 238000005336 cracking Methods 0.000 claims abstract description 31
- 238000001354 calcination Methods 0.000 claims abstract description 29
- 239000011259 mixed solution Substances 0.000 claims abstract description 27
- 238000001035 drying Methods 0.000 claims abstract description 26
- 229910052746 lanthanum Inorganic materials 0.000 claims abstract description 24
- 238000002156 mixing Methods 0.000 claims abstract description 22
- -1 polyethylene Polymers 0.000 claims abstract description 22
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 21
- 238000003756 stirring Methods 0.000 claims abstract description 20
- FZLIPJUXYLNCLC-UHFFFAOYSA-N lanthanum atom Chemical compound [La] FZLIPJUXYLNCLC-UHFFFAOYSA-N 0.000 claims abstract description 19
- 229910001868 water Inorganic materials 0.000 claims abstract description 17
- 229920003171 Poly (ethylene oxide) Polymers 0.000 claims abstract description 15
- 229920000428 triblock copolymer Polymers 0.000 claims abstract description 15
- 239000004698 Polyethylene Substances 0.000 claims abstract description 14
- 239000004743 Polypropylene Substances 0.000 claims abstract description 14
- 229920000573 polyethylene Polymers 0.000 claims abstract description 14
- 229920001155 polypropylene Polymers 0.000 claims abstract description 14
- 238000000975 co-precipitation Methods 0.000 claims abstract description 11
- 238000002791 soaking Methods 0.000 claims abstract description 11
- 238000007598 dipping method Methods 0.000 claims abstract description 10
- AZDRQVAHHNSJOQ-UHFFFAOYSA-N alumane Chemical class [AlH3] AZDRQVAHHNSJOQ-UHFFFAOYSA-N 0.000 claims abstract description 9
- 150000002815 nickel Chemical class 0.000 claims abstract description 9
- 150000002603 lanthanum Chemical class 0.000 claims abstract description 8
- 159000000003 magnesium salts Chemical class 0.000 claims abstract description 8
- 238000000967 suction filtration Methods 0.000 claims abstract description 8
- 238000005406 washing Methods 0.000 claims abstract description 8
- 238000005216 hydrothermal crystallization Methods 0.000 claims abstract description 7
- 239000002994 raw material Substances 0.000 claims abstract description 7
- 238000005185 salting out Methods 0.000 claims abstract description 7
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 35
- 239000002041 carbon nanotube Substances 0.000 claims description 32
- 229910021393 carbon nanotube Inorganic materials 0.000 claims description 32
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical group [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 claims description 30
- 229910052739 hydrogen Inorganic materials 0.000 claims description 27
- 239000001257 hydrogen Substances 0.000 claims description 27
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 25
- 238000000034 method Methods 0.000 claims description 21
- 238000010438 heat treatment Methods 0.000 claims description 17
- 229910000029 sodium carbonate Inorganic materials 0.000 claims description 15
- YIXJRHPUWRPCBB-UHFFFAOYSA-N magnesium nitrate Chemical group [Mg+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O YIXJRHPUWRPCBB-UHFFFAOYSA-N 0.000 claims description 12
- 239000011343 solid material Substances 0.000 claims description 10
- 229910001453 nickel ion Inorganic materials 0.000 claims description 9
- VEQPNABPJHWNSG-UHFFFAOYSA-N Nickel(2+) Chemical compound [Ni+2] VEQPNABPJHWNSG-UHFFFAOYSA-N 0.000 claims description 8
- FYDKNKUEBJQCCN-UHFFFAOYSA-N lanthanum(3+);trinitrate Chemical group [La+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O FYDKNKUEBJQCCN-UHFFFAOYSA-N 0.000 claims description 8
- KBJMLQFLOWQJNF-UHFFFAOYSA-N nickel(ii) nitrate Chemical group [Ni+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O KBJMLQFLOWQJNF-UHFFFAOYSA-N 0.000 claims description 8
- BNGXYYYYKUGPPF-UHFFFAOYSA-M (3-methylphenyl)methyl-triphenylphosphanium;chloride Chemical group [Cl-].CC1=CC=CC(C[P+](C=2C=CC=CC=2)(C=2C=CC=CC=2)C=2C=CC=CC=2)=C1 BNGXYYYYKUGPPF-UHFFFAOYSA-M 0.000 claims description 7
- 230000008569 process Effects 0.000 claims description 7
- 229910052782 aluminium Inorganic materials 0.000 claims description 6
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 4
- JLVVSXFLKOJNIY-UHFFFAOYSA-N Magnesium ion Chemical compound [Mg+2] JLVVSXFLKOJNIY-UHFFFAOYSA-N 0.000 claims description 2
- 150000002431 hydrogen Chemical group 0.000 claims description 2
- 150000002500 ions Chemical class 0.000 claims description 2
- 229910001425 magnesium ion Inorganic materials 0.000 claims description 2
- 239000004411 aluminium Substances 0.000 claims 1
- 150000002680 magnesium Chemical class 0.000 claims 1
- 230000003197 catalytic effect Effects 0.000 abstract description 17
- 238000004939 coking Methods 0.000 abstract description 4
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 29
- 241000877463 Lanio Species 0.000 description 25
- 239000000725 suspension Substances 0.000 description 16
- 239000002131 composite material Substances 0.000 description 11
- 230000000052 comparative effect Effects 0.000 description 9
- 230000000694 effects Effects 0.000 description 9
- 238000000197 pyrolysis Methods 0.000 description 9
- 239000011148 porous material Substances 0.000 description 8
- 239000003795 chemical substances by application Substances 0.000 description 7
- 239000011777 magnesium Substances 0.000 description 7
- 238000001027 hydrothermal synthesis Methods 0.000 description 6
- 229910000510 noble metal Inorganic materials 0.000 description 6
- 230000009467 reduction Effects 0.000 description 6
- 229910052799 carbon Inorganic materials 0.000 description 5
- 238000005470 impregnation Methods 0.000 description 5
- CZMAIROVPAYCMU-UHFFFAOYSA-N lanthanum(3+) Chemical compound [La+3] CZMAIROVPAYCMU-UHFFFAOYSA-N 0.000 description 5
- 238000004519 manufacturing process Methods 0.000 description 5
- 238000001179 sorption measurement Methods 0.000 description 5
- TWRXJAOTZQYOKJ-UHFFFAOYSA-L Magnesium chloride Chemical compound [Mg+2].[Cl-].[Cl-] TWRXJAOTZQYOKJ-UHFFFAOYSA-L 0.000 description 4
- NIPNSKYNPDTRPC-UHFFFAOYSA-N N-[2-oxo-2-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)ethyl]-2-[[3-(trifluoromethoxy)phenyl]methylamino]pyrimidine-5-carboxamide Chemical compound O=C(CNC(=O)C=1C=NC(=NC=1)NCC1=CC(=CC=C1)OC(F)(F)F)N1CC2=C(CC1)NN=N2 NIPNSKYNPDTRPC-UHFFFAOYSA-N 0.000 description 4
- 239000008367 deionised water Substances 0.000 description 4
- 229910021641 deionized water Inorganic materials 0.000 description 4
- 229910052751 metal Inorganic materials 0.000 description 4
- 239000002184 metal Substances 0.000 description 4
- 229910044991 metal oxide Inorganic materials 0.000 description 4
- 150000004706 metal oxides Chemical class 0.000 description 4
- 229910052759 nickel Inorganic materials 0.000 description 4
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 3
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- 230000009471 action Effects 0.000 description 3
- 238000005054 agglomeration Methods 0.000 description 3
- 230000002776 aggregation Effects 0.000 description 3
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 3
- 238000011068 loading method Methods 0.000 description 3
- 229910052749 magnesium Inorganic materials 0.000 description 3
- 239000013528 metallic particle Substances 0.000 description 3
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 description 2
- 230000004913 activation Effects 0.000 description 2
- VSCWAEJMTAWNJL-UHFFFAOYSA-K aluminium trichloride Chemical compound Cl[Al](Cl)Cl VSCWAEJMTAWNJL-UHFFFAOYSA-K 0.000 description 2
- 238000004523 catalytic cracking Methods 0.000 description 2
- 239000007809 chemical reaction catalyst Substances 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 238000001514 detection method Methods 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- 229910001629 magnesium chloride Inorganic materials 0.000 description 2
- 229920000642 polymer Polymers 0.000 description 2
- 239000002243 precursor Substances 0.000 description 2
- 239000000376 reactant Substances 0.000 description 2
- IHCCLXNEEPMSIO-UHFFFAOYSA-N 2-[4-[2-(2,3-dihydro-1H-inden-2-ylamino)pyrimidin-5-yl]piperidin-1-yl]-1-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)ethanone Chemical compound C1C(CC2=CC=CC=C12)NC1=NC=C(C=N1)C1CCN(CC1)CC(=O)N1CC2=C(CC1)NN=N2 IHCCLXNEEPMSIO-UHFFFAOYSA-N 0.000 description 1
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical class [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 1
- 229910002340 LaNiO3 Inorganic materials 0.000 description 1
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 1
- 229910001051 Magnalium Inorganic materials 0.000 description 1
- 229910021586 Nickel(II) chloride Inorganic materials 0.000 description 1
- 125000004429 atom Chemical group 0.000 description 1
- 239000012752 auxiliary agent Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 229910002090 carbon oxide Inorganic materials 0.000 description 1
- 239000000969 carrier Substances 0.000 description 1
- CETPSERCERDGAM-UHFFFAOYSA-N ceric oxide Chemical compound O=[Ce]=O CETPSERCERDGAM-UHFFFAOYSA-N 0.000 description 1
- 229910000422 cerium(IV) oxide Inorganic materials 0.000 description 1
- 239000006258 conductive agent Substances 0.000 description 1
- 230000008021 deposition Effects 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 239000010881 fly ash Substances 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 239000003365 glass fiber Substances 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- ICAKDTKJOYSXGC-UHFFFAOYSA-K lanthanum(iii) chloride Chemical compound Cl[La](Cl)Cl ICAKDTKJOYSXGC-UHFFFAOYSA-K 0.000 description 1
- 229910001416 lithium ion Inorganic materials 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- QMMRZOWCJAIUJA-UHFFFAOYSA-L nickel dichloride Chemical compound Cl[Ni]Cl QMMRZOWCJAIUJA-UHFFFAOYSA-L 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 229910052763 palladium Inorganic materials 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- 230000035484 reaction time Effects 0.000 description 1
- 230000002787 reinforcement Effects 0.000 description 1
- 239000012744 reinforcing agent Substances 0.000 description 1
- 238000005245 sintering Methods 0.000 description 1
- 238000003980 solgel method Methods 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
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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
- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/0009—Use of binding agents; Moulding; Pressing; Powdering; Granulating; Addition of materials ameliorating the mechanical properties of the product catalyst
- B01J37/0018—Addition of a binding agent or of material, later completely removed among others as result of heat treatment, leaching or washing,(e.g. forming of pores; protective layer, desintegrating by heat)
-
- 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
- B01J21/10—Magnesium; Oxides or hydroxides thereof
-
- 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
- B01J23/76—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
- B01J23/83—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with rare earths or actinides
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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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- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/02—Impregnation, coating or precipitation
- B01J37/03—Precipitation; Co-precipitation
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- B01J37/08—Heat treatment
- B01J37/10—Heat treatment in the presence of water, e.g. steam
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- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
- C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
- C01B3/22—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by decomposition of gaseous or liquid organic compounds
- C01B3/24—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by decomposition of gaseous or liquid organic compounds of hydrocarbons
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Abstract
The application relates to the technical field of methane cracking catalyst preparation, in particular to a preparation method of a modified magnesium aluminum hydrotalcite catalyst, which comprises the following steps: (1) raw material mixing: mixing a salt solution and a polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer solution, and uniformly stirring to obtain a reaction solution, wherein the salt solution is formed by mixing aluminum salt, magnesium salt and water; (2) precipitation crystallization: adding a precipitant into the reaction solution to perform coprecipitation reaction, performing hydrothermal crystallization after the reaction is finished, and performing suction filtration, washing, drying and calcination to obtain modified hydrotalcite; (3) dipping: and adding a mixed solution formed by nickel salt, lanthanum salt, citric acid and water into the modified hydrotalcite, soaking and stirring, and drying and calcining to obtain the lanthanum nickelate loaded modified hydrotalcite catalyst. The preparation method of the modified magnesium aluminum hydrotalcite catalyst can slow down the coking of the catalyst and promote the catalytic activity of the catalyst.
Description
Technical Field
The application relates to the technical field of methane cracking catalyst preparation, in particular to a modified magnesium aluminum hydrotalcite catalyst and a preparation method and application thereof.
Background
The carbon nano tube is used as a one-dimensional quantum material, has low density, excellent mechanical property and conductivity and good physical and chemical stability, and has wide application prospect in the fields of lithium ion battery conductive agents, high polymer composite materials, catalyst carriers and the like. In addition, carbon nanotubes have other good properties such as optical properties and hydrogen storage, making carbon nanotubes an ideal reinforcement for polymer composites. The methane catalytic cracking process can simultaneously obtain carbon nanotubes and hydrogen without carbon oxides, and the atom utilization rate of the hydrogen reaches the maximum value, so that the technical route is focused widely. In order to improve the methane cracking catalytic efficiency, related reaction catalysts are also being researched more and more.
Currently, methane cracking catalysts mainly use noble metals (Pt, pd) and small amounts of non-noble metals (Ni, cu, fe) as active sites. Noble metal catalysts have good catalytic activity, but cannot be produced on a large scale in an industrial manner due to the high price. The non-noble metal catalyst reduces the reaction cost and can obtain ideal reaction activity, so that the catalyst is widely applied. The existing catalyst is prepared by adopting silicon-aluminum-titanium composite oxide as a carrier, noble metal palladium as an active component and glass fiber as a reinforcing agent, then extruding and molding a honeycomb catalyst, drying and calcining the honeycomb catalyst, and has stronger mechanical strength and better methane hydrogen production activity, but the use of the noble metal catalyst greatly improves the process cost. The catalyst is prepared by taking fly ash as a carrier, taking metal Ni and Fe as active components and CeO2 as a metal auxiliary agent and adopting a method of dipping after coprecipitation, and is applied to methane pyrolysis, and has good cycle performance but low catalytic activity. The method for improving the yield of the generated hydrogen and the carbon nano tube by changing the carbon source is characterized in that the catalyst is a nickel catalyst and an iron catalyst prepared by a sol-gel method, the carbon source comprises methane and multi-carbon alkane, the methane cracking can be obviously promoted by the cracking acting effect of the multi-carbon alkane on a reaction system, the production efficiency of the carbon nano tube is improved, the production cost is reduced, but the methane conversion rate is lower and always lasts at about 49 percent. Therefore, developing an anti-carbon deposition catalyst with high activity, high stability and difficult sintering is still a key problem for developing large-scale methane catalytic cracking hydrogen production.
Disclosure of Invention
In order to slow down catalyst coking and improve catalyst activity of the catalyst, the application provides a modified magnesium aluminum hydrotalcite catalyst and a preparation method and application thereof.
The preparation method and application of the modified magnesium aluminum hydrotalcite catalyst provided by the application adopt the following technical scheme:
in a first aspect, the present application provides a method for preparing a modified magnesium aluminum hydrotalcite catalyst, comprising the steps of:
(1) Mixing the raw materials: mixing a salt solution and a polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer solution, and uniformly stirring to obtain a reaction solution, wherein the salt solution is formed by mixing aluminum salt, magnesium salt and water;
(2) And (3) precipitation crystallization: adding a precipitant into the reaction solution to perform coprecipitation reaction, performing hydrothermal crystallization after the reaction is finished, and performing suction filtration, washing, drying and calcination to obtain modified hydrotalcite;
(3) Dipping: and adding a mixed solution formed by nickel salt, lanthanum salt, citric acid and water into the modified hydrotalcite, soaking and stirring, and drying and calcining to obtain the lanthanum nickelate loaded modified hydrotalcite catalyst.
According to the preparation method, the polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer solution is used as a template agent, so that the polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer solution can be inserted into a laminate space of precursor hydrotalcite in a coprecipitation process, a stable forming process of crystals is guaranteed through a hydrothermal process, and the template agent is removed through roasting to obtain a composite oxide carrier with a porous structure, so that the structure of the catalyst is radically improved, more reduction sites are exposed, the dispersity of nickel and lanthanum metals on the surface is improved, the catalytic activity is improved, the average pore diameter of the catalyst is larger, the diffusion of reactant molecules is facilitated, the coking of the catalyst is slowed down, the adsorption capacity to methane is greatly improved, and the reaction activity of the catalyst is improved; meanwhile, the preparation method of the catalyst is simple, the operability is strong, and the carbon nano tube prepared by catalyzing methane pyrolysis by using the catalyst has uniform tube diameter and high yield
Preferably, in the step (1), the molar ratio of aluminum ions to magnesium ions in the salt solution is 1 (2-4), the aluminum salt is aluminum nitrate, and the magnesium salt is magnesium nitrate.
Preferably, the concentration of the polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer solution is 2-5 g/L, and the volume ratio of the polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer solution to the salt solution is 1 (1-3).
By adjusting the volume ratio of the polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer solution to the salt solution, the modified hydrotalcite can be further promoted to form a composite oxide carrier with a porous structure, and the internal structure of the catalyst is radically improved.
Preferably, in the step (2), the precipitant is a sodium carbonate solution, and the concentration of the sodium carbonate solution is 0.5-1.5 mol/L.
Preferably, in the step (2), the temperature of the hydrothermal crystallization is 200-220 ℃, and the time of the hydrothermal crystallization is 10-20 hours; the drying temperature is 90-150 ℃ and the drying time is 8-12 h; the calcination temperature is 600-750 ℃ and the calcination time is 4-5 h.
Preferably, in the step (3), the nickel salt is nickel nitrate, the lanthanum salt is lanthanum nitrate, and the molar ratio of nickel ions to lanthanum ions in the mixed solution is 4: (5-6); the mole ratio of the citric acid to the total ions of nickel ions and lanthanum ions is 1:1.
Preferably, in the step (3), the soaking and stirring time is 8-12 h, and the soaking temperature is 35-55 ℃; the drying temperature is 80-120 ℃ and the drying time is 18-24 h.
Preferably, in the step (3), the calcining includes: decomposing for 1-2 h at 450-500 ℃ at a heating rate of 2-3 ℃/min, then raising the temperature to 650-750 ℃ at the same heating rate, and calcining for 4-8 h.
In order to improve the loading degree of metallic nickel and lanthanum in the catalyst, the impregnation time is controlled, and meanwhile, a program sectional calcining mode is adopted to generate strong action force between metallic nickel and lanthanum and oxides of magnesium and aluminum, so that agglomeration among metallic particles is reduced, and the overall catalytic activity is improved.
In a second aspect of the invention, a modified magnalium hydrotalcite catalyst is provided, which is prepared by the preparation method.
In the third aspect of the invention, the prepared modified magnesium aluminum hydrotalcite catalyst is placed in a fluidized bed and reduced in a reducing atmosphere, wherein the reducing atmosphere is hydrogen, the reducing airspeed is 0.2-0.5/h, and the reducing temperature is 600-650 ℃; then the temperature of the fluidized bed is raised to 650-700 ℃, methane is introduced to carry out cracking reaction, and the flow rate of the methane is 0.3-0.5 m 3 And/h, the time of the cracking reaction is 180-210 min, and the hydrogen and carbon nano tube solid material is obtained.
The modified magnesium aluminum hydrotalcite catalyst prepared by the method is applied to the preparation of hydrogen and carbon nanotubes by methane pyrolysis, and can achieve the optimal catalytic effect by adjusting preparation parameters, so that the yield of the hydrogen and carbon nanotube solid materials is effectively improved.
The application has the following beneficial technical effects:
1. the lanthanum nickelate modified magnesium aluminum hydrotalcite catalyst prepared by the method adopts polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer solution as a template agent, so that the polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer solution can be inserted into a laminate space of precursor hydrotalcite in a coprecipitation process, a stable forming process of crystals is ensured through a hydrothermal process, and then the template agent is removed through roasting to obtain a composite oxide carrier with a porous structure, so that the structure of the catalyst is radically improved, more reduction sites are exposed, the dispersion degree of nickel and lanthanum metal loaded on the surface is improved, the catalytic activity is improved, the average pore diameter of the catalyst is larger, the diffusion of reactant molecules is facilitated, the coking of the catalyst is slowed down, the adsorption capacity to methane is greatly improved, and the reaction activity of the catalyst is improved; meanwhile, the preparation method of the catalyst is simple, the operability is strong, and the carbon nano tube prepared by catalyzing methane pyrolysis by using the catalyst has uniform tube diameter and high yield.
2. In the impregnation and activation step, in order to improve the loading degree of metallic nickel and lanthanum in the catalyst, the impregnation time is controlled, and meanwhile, a program sectional calcining mode is adopted to generate strong action force between metallic nickel and lanthanum and oxides of magnesium and aluminum, so that agglomeration among metallic particles is reduced, and the overall catalytic activity is improved.
3. The modified magnesium aluminum hydrotalcite catalyst prepared by the method is applied to the preparation of hydrogen and carbon nanotubes by methane pyrolysis, and can achieve the optimal catalytic effect by adjusting preparation parameters, so that the yield of the hydrogen and carbon nanotube solid materials is effectively improved.
Drawings
FIG. 1 shows LaNiO 3 LaNiO 3 Comparative graph of specific surface area and average pore size curves of two catalysts @ MgAl-LDO.
Detailed Description
Along with the continuous improvement of research heat of carbon nanotubes, the demand for carbon nanotubes is also continuously improved, and the existing carbon nanotube preparation method adopts a mode of obtaining carbon nanotubes and hydrogen by methane pyrolysis, so that more and more workers start to put into the research of reaction catalysts of the carbon nanotubes in order to improve the conversion rate of methane pyrolysis into the carbon nanotubes. The inventor finds that when lanthanum nickelate modified magnesium aluminum hydrotalcite is used as a methane cracking catalyst, the catalyst has high catalytic activity and low preparation cost, and can meet the requirements of industrial carbon nanotube production.
The present application is further illustrated below with reference to examples.
Example 1
The preparation method of the modified magnesium aluminum hydrotalcite catalyst comprises the following steps:
(1) Mixing the raw materials: mixing a salt solution and a polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer solution, and uniformly stirring to obtain a reaction solution, wherein the salt solution is formed by mixing aluminum salt, magnesium salt and water.
Specifically, aluminum salt, magnesium salt and water are mixed to form a salt solution, wherein the aluminum salt can be aluminum nitrate or aluminum chloride, and the aluminum salt is specifically selected as aluminum nitrate in the application; the magnesium salt may be magnesium nitrate or magnesium chloride, in this case magnesium chloride. Al in salt solution 3+ 、Mg 2+ The molar ratio is 1:2 Al in salt solution 3+ 1mol/L, mg 2+ The salt solution was mixed with 2g/L of a solution of a polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer (P123) and 50mL of deionized water at 2mol/L, and stirred to obtain a reaction solution. The volume ratio of the P123 solution to the salt solution is 1 (1-3), the specific volume ratio of the P123 solution to the salt solution in the application is 1:2, namely the P123 solution is 25mL, and the salt solution is 50mL.
By adjusting the volume ratio of the polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer solution to the salt solution, the modified hydrotalcite can be further promoted to form a composite oxide carrier with a porous structure, the internal structure of the catalyst is radically improved, and the catalytic efficiency of the catalyst is improved.
(2) And (3) precipitation crystallization: adding a precipitant into the reaction solution to perform coprecipitation reaction, performing hydrothermal crystallization after the reaction is finished, and performing suction filtration, washing, drying and calcination to obtain the modified hydrotalcite.
Specifically, a precipitant is gradually added dropwise into the reaction solution obtained in the step (1) to carry out coprecipitation reaction, wherein the precipitant can be sodium carbonate solution or mixed solution of sodium hydroxide and sodium carbonate, and the specific choice in the application is sodium carbonate solution. The concentration of the sodium carbonate solution may be 0.5 to 1.5mol/L, specifically 1mol/L in this application. And (3) dropwise adding the sodium carbonate solution until the pH value of the solution is 10, stopping dropwise adding, stirring at the temperature of 30 ℃ for 30min, and obtaining a suspension after the reaction is finished. Transferring the suspension into a hydrothermal synthesis kettle, crystallizing for 10 hours at 200 ℃, carrying out suction filtration, washing and drying for 8-12 hours at 90-150 ℃, specifically selecting the suspension to be dried for 8 hours at 120 ℃, then sending the suspension into a muffle furnace, and calcining for 5 hours at 600 ℃ to obtain the template modified magnesium aluminum hydrotalcite composite metal oxide (MgAl-LDO).
(3) Dipping: and adding a mixed solution formed by nickel salt, lanthanum salt, citric acid and water into the modified hydrotalcite, soaking and stirring, and drying and calcining to obtain the lanthanum nickelate loaded modified hydrotalcite catalyst.
Specifically, a nickel salt, lanthanum salt, citric acid and water are mixed to form a mixed solution, wherein the nickel salt can be nickel nitrate or nickel chloride, and the nickel salt is specifically selected as nickel nitrate in the application; the lanthanum salt can be lanthanum nitrate or lanthanum chloride, and is specifically selected as lanthanum nitrate in the application; nickel ion (Ni) 3+ ) And lanthanum ion (La) 3+ ) The molar ratio of (2) is 4:6, namely Ni in the mixed solution 3+ 4mol/L, la 3+ At 6mol/L, citric acid and Ni 3+ And La (La) 3+ The molar ratio of the sum is 1:1, namely, the citric acid in the mixed solution is 10mol/L. Adding the mixed solution into MgAl-LDO prepared in the step (2), soaking and stirring for 8-12 h at 35-45 ℃, specifically selecting in the application to soak and stir for 8h at 45 ℃, then drying for 18-24 h at 80-120 ℃, specifically selecting in the application to dry for 18h at 120 ℃, then decomposing for 1-2 h at 500 ℃ at the heating rate of 2 ℃/min, specifically selecting in the application to decompose for 1h, then calcining for 4-8 h at the same heating rate to 750 ℃, specifically selecting in the application to calcine for 6h, and obtaining lanthanum nickelate modified magnesium aluminum hydrotalcite catalyst LaNiO 3 @MgAl-LDO。
In the impregnation and activation step, in order to improve the loading degree of metallic nickel and lanthanum in the catalyst, the impregnation time is controlled, and meanwhile, a program sectional calcining mode is adopted to generate strong action force between metallic nickel and lanthanum and oxides of magnesium and aluminum, so that agglomeration among metallic particles is reduced, and the overall catalytic activity is improved.
LaNiO prepared in example 1 3 The @ MgAl-LDO catalyst is applied to methane cracking reaction.
Specifically, 2g of self-prepared LaNiO was taken 3 The @ MgAl-LDO is placed in a fluidized bed and reduced in the hydrogen atmosphere, the space velocity of the reduction is 0.2 to 0.5/h, and the specific selection is thatThe reduction temperature is 600-650 ℃ at 0.2/h, the specific selection in the application is 600 ℃, then the temperature of the fluidized bed is raised to 700 ℃, methane is introduced for cracking reaction, and the flow rate of the methane is 0.3m 3 /h; the time of the cracking reaction is 180min, and the hydrogen and carbon nano tube solid material is obtained.
The modified magnesium aluminum hydrotalcite catalyst prepared by the method is applied to the preparation of hydrogen and carbon nanotubes by methane pyrolysis, and can achieve the optimal catalytic effect by adjusting preparation parameters, so that the yield of the hydrogen and carbon nanotube solid materials is effectively improved.
Example 2
(1) Mixing the raw materials:
mixing aluminum nitrate, magnesium nitrate and water to form a salt solution, wherein Al is contained in the salt solution 3+ 、Mg 2+ The molar ratio is 1:3 Al in salt solution 3+ 1mol/L, mg 2+ The salt solution was mixed with 3g/L of P123 solution and 50mL of deionized water at 3mol/L, and stirred to obtain a reaction solution.
(2) And (3) precipitation crystallization:
and (3) gradually dropwise adding a sodium carbonate solution into the reaction solution obtained in the step (1) to carry out coprecipitation reaction. And (3) dropwise adding the sodium carbonate solution until the pH value of the solution is 10, stopping dropwise adding, stirring at the temperature of 30 ℃ for 30min, and obtaining a suspension after the reaction is finished. Transferring the suspension into a hydrothermal synthesis kettle, crystallizing for 12 hours at 180 ℃, carrying out suction filtration, washing and drying for 8 hours at 120 ℃ on the crystallized suspension, then sending the suspension into a muffle furnace, and calcining for 4 hours at 700 ℃ to obtain the template agent modified magnesium aluminum hydrotalcite composite metal oxide (MgAl-LDO).
(3) Dipping:
mixing nickel nitrate, lanthanum nitrate, citric acid and water to form a mixed solution, wherein nickel ions (Ni 3+ ) And lanthanum ion (La) 3+ ) The molar ratio of (2) is 4:5, namely Ni in the mixed solution 3+ 4mol/L, la 3+ 5mol/L, citric acid and Ni 3+ And La (La) 3+ The molar ratio of the sum to the solution is 1:1, namely, the citric acid in the mixed solution is 9mol/L. Adding the mixed solution into the MgAl-LDO prepared in the step (2), soaking and stirring for 8 hours at 45 ℃, then drying for 18 hours at 120 ℃,then decomposing for 1h at 500 ℃ at a heating rate of 3 ℃/min, then calcining for 6h at the same heating rate to 750 ℃ to obtain the lanthanum nickelate modified magnesium aluminum hydrotalcite catalyst LaNiO 3 @MgAl-LDO。
LaNiO prepared in example 2 3 The @ MgAl-LDO catalyst is applied to methane cracking reaction.
Specifically, 3g of self-prepared LaNiO was taken 3 Placing @ MgAl-LDO in fluidized bed, reducing under hydrogen atmosphere at space velocity of 0.2/h and reducing temperature of 600deg.C, heating the fluidized bed to 650deg.C, introducing methane to perform cracking reaction, and the flow rate of methane is 0.3m 3 /h; the time of the cracking reaction is 210min, and the hydrogen and carbon nano tube solid material is obtained.
Example 3
(1) Mixing the raw materials:
mixing aluminum nitrate, magnesium nitrate and water to form a salt solution, wherein Al is contained in the salt solution 3+ 、Mg 2+ The molar ratio is 1:4 Al in salt solution 3+ 1mol/L, mg 2+ The salt solution was mixed with 5g/L of P123 solution and 50mL of deionized water at 4mol/L, and stirred to obtain a reaction solution.
(2) And (3) precipitation crystallization:
and (3) gradually dropwise adding a sodium carbonate solution into the reaction solution obtained in the step (1) to carry out coprecipitation reaction. And (3) dropwise adding the sodium carbonate solution until the pH value of the solution is 10, stopping dropwise adding, stirring at the temperature of 30 ℃ for 30min, and obtaining a suspension after the reaction is finished. Transferring the suspension into a hydrothermal synthesis kettle, crystallizing for 20 hours at 220 ℃, carrying out suction filtration, washing and drying for 8 hours at 120 ℃ on the crystallized suspension, then sending the suspension into a muffle furnace, and calcining for 4 hours at 750 ℃ to obtain the template agent modified magnesium aluminum hydrotalcite composite metal oxide (MgAl-LDO).
(3) Dipping:
mixing nickel nitrate, lanthanum nitrate, citric acid and water to form a mixed solution, wherein nickel ions (Ni 3+ ) And lanthanum ion (La) 3+ ) The molar ratio of (2) is 4:6, namely Ni in the mixed solution 3+ 4mol/L, la 3+ At 6mol/L, citric acid and Ni 3+ And La (La) 3+ The molar ratio of the sum is1:1, namely 10mol/L of citric acid in the mixed solution. Adding the mixed solution into the MgAl-LDO prepared in the step (2), soaking and stirring for 8 hours at 45 ℃, drying for 18 hours at 120 ℃, decomposing for 1 hour at 450 ℃ at the heating rate of 3 ℃/min, and calcining for 6 hours at the same heating rate to 650 ℃ to obtain the lanthanum nickelate modified magnesium aluminum hydrotalcite catalyst LaNiO 3 @MgAl-LDO。
LaNiO prepared in example 3 3 The @ MgAl-LDO catalyst is applied to methane cracking reaction.
Specifically, 5g of self-prepared LaNiO was taken 3 Placing @ MgAl-LDO in fluidized bed, reducing under hydrogen atmosphere at space velocity of 0.2/h and reducing temperature of 600deg.C, heating the fluidized bed to 650deg.C, introducing methane to perform cracking reaction, and the flow rate of methane is 0.5m 3 /h; the time of the cracking reaction is 210min, and the hydrogen and carbon nano tube solid material is obtained.
Example 4
(1) Mixing the raw materials:
mixing aluminum nitrate, magnesium nitrate and water to form a salt solution, wherein Al is contained in the salt solution 3+ 、Mg 2+ The molar ratio is 1:4 Al in salt solution 3+ 1mol/L, mg 2+ The salt solution was mixed with 5g/L of P123 solution and 50mL of deionized water at 4mol/L, and stirred to obtain a reaction solution.
(2) And (3) precipitation crystallization:
and (3) gradually dropwise adding a sodium carbonate solution into the reaction solution obtained in the step (1) to carry out coprecipitation reaction. And (3) dropwise adding the sodium carbonate solution until the pH value of the solution is 10, stopping dropwise adding, stirring at the temperature of 30 ℃ for 30min, and obtaining a suspension after the reaction is finished. Transferring the suspension into a hydrothermal synthesis kettle, crystallizing for 20 hours at 220 ℃, carrying out suction filtration, washing and drying for 8 hours at 120 ℃ on the crystallized suspension, then sending the suspension into a muffle furnace, and calcining for 4 hours at 750 ℃ to obtain the template agent modified magnesium aluminum hydrotalcite composite metal oxide (MgAl-LDO).
(3) Dipping:
mixing nickel nitrate, lanthanum nitrate, citric acid and water to form a mixed solution, wherein nickel ions (Ni 3+ ) And lanthanum ion (La) 3+ ) A kind of electronic deviceThe molar ratio is 4:6, namely Ni in the mixed solution 3+ 4mol/L, la 3+ At 6mol/L, citric acid and Ni 3+ And La (La) 3+ The molar ratio of the sum is 1:1, namely, the citric acid in the mixed solution is 10mol/L. Adding the mixed solution into the MgAl-LDO prepared in the step (2), soaking and stirring for 8 hours at 45 ℃, drying for 18 hours at 120 ℃, decomposing for 1 hour at 450 ℃ at the heating rate of 3 ℃/min, and calcining for 6 hours at the same heating rate to 700 ℃ to obtain the lanthanum nickelate modified magnesium aluminum hydrotalcite catalyst LaNiO 3 @MgAl-LDO。
LaNiO prepared in example 4 3 The @ MgAl-LDO catalyst is applied to methane cracking reaction.
Specifically, 5g of self-prepared LaNiO was taken 3 Placing @ MgAl-LDO in fluidized bed, reducing under hydrogen atmosphere at space velocity of 0.2/h and reducing temperature of 600deg.C, heating the fluidized bed to 700deg.C, introducing methane to perform cracking reaction, and the flow rate of methane is 0.3m 3 /h; the time of the cracking reaction is 210min, and the hydrogen and carbon nano tube solid material is obtained.
Comparative example 1: catalyst LaNiO 3 Is prepared from
Mixing nickel nitrate, lanthanum nitrate, citric acid and water to form a mixed solution, wherein nickel ions (Ni 3+ ) And lanthanum ion (La) 3+ ) The molar ratio of (2) is 4:6, namely Ni in the mixed solution 3+ 4mol/L, la 3+ At 6mol/L, citric acid and Ni 3+ And La (La) 3+ The molar ratio of the sum is 1:1, namely, the citric acid in the mixed solution is 10mol/L. Soaking and stirring the mixed solution at 45 ℃ for 8 hours, drying at 120 ℃ for 18 hours, decomposing at 500 ℃ for 1 hour at the heating rate of 2 ℃/min, and calcining at the same heating rate to 750 ℃ for 6 hours to obtain the catalyst LaNiO 3 。
Placing 2g of LaNiO3 prepared by the method into a fluidized bed, reducing under hydrogen atmosphere, wherein the reduction airspeed is 0.2/h, the reduction temperature is 600 ℃, then raising the temperature of the fluidized bed to 700 ℃, introducing methane for cracking reaction, and the flow rate of the methane is 0.3m 3 /h; the time of the cracking reaction is 180min, and the hydrogen and carbon nano tube solid material is obtained.
Performance detection
The catalysts prepared in examples 1 to 4 and comparative example 1 were applied to methane cracking, and performance measurements were performed on the parameters related to the cracking reaction, and the results are shown in table 1.
Table 1 results of methane cracking related parameters for examples and comparative examples
| Example 1 | Example 2 | Example 3 | Example 4 | Comparative example 1 | |
| Catalyst amount (g) | 2.0 | 3.0 | 3.0 | 5.0 | 2.0 |
| Methane reaction quantity (m) 3 /h) | 0.3 | 0.3 | 0.5 | 0.3 | 0.3 |
| Reaction temperatureDegree (. Degree. C.) | 700 | 650 | 650 | 700 | 700 |
| Reaction time (min) | 180 | 210 | 210 | 210 | 180 |
| Yield of carbon nanotubes (g) | 160.5 | 158.9 | 267.5 | 154.1 | 94.3 |
| Purity of carbon nanotube (%) | 99.8 | 99.3 | 99.6 | 99.2 | 72.6 |
| Methane conversion (%) | 98.3 | 97.6 | 98.0 | 95.3 | 80.2 |
As can be seen from table 1, the catalyst prepared in the examples of the present application can effectively promote methane cracking in the methane cracking reaction, and the conversion rate of methane and the yield of carbon nanotubes in all examples are far higher than those in the comparative examples, which indicates that the catalytic efficiency of the lanthanum nickelate modified magnesium aluminum hydrotalcite catalyst used in the examples of the present application is higher than that of the lanthanum nickelate catalyst used alone.
LaNiO in example 1 3 @MgAl-LDO catalyst and LaNiO in comparative example 1 3 Specific surface area of catalyst (S BET ) The average pore diameters are shown in Table 2, and the pressure and adsorption curves are shown in FIG. 1.
Table 2 specific surface area and average pore size detection results of example 1 and comparative example 1
| Catalyst | S BET (m 2 ·g -1 ) | Average pore diameter (nm) |
| LaNiO 3 | 10.2 | 15.3 |
| LaNiO 3 @MgAl-LDO | 27.3 | 26.7 |
As can be seen from Table 2, laNiO prepared in example 1 of the present application 3 The specific surface area and the average pore diameter of the @ MgAl-LDO catalyst are far higher than those of LaNiO prepared in comparative example 1 3 The catalyst has higher surface area and average pore diameter and can promote catalysisThe adsorption quantity of the catalyst to methane can enable methane to react on the surface of the catalyst, so that the catalytic efficiency and the reaction activity of the catalyst are improved, and the methane cracking conversion rate and the carbon nano tube generation quantity are improved. As can be seen from FIG. 1, the LaNiO prepared in the present application was prepared under the same relative pressure 3 The adsorption quantity of the @ MgAl-LDO catalyst is higher than that of LaNiO 3 The results of the catalyst are consistent with those of the previous results, and further illustrate the LaNiO prepared in the present application 3 The @ MgAl-LDO catalyst can effectively adsorb methane gas and improve the catalytic efficiency of methane pyrolysis.
The present embodiment is merely illustrative of the present application and is not intended to be limiting, and those skilled in the art, after having read the present specification, may make modifications to the present embodiment without creative contribution as required, but is protected by patent laws within the scope of the claims of the present application.
Claims (10)
1. The preparation method of the modified magnesium aluminum hydrotalcite catalyst is characterized by comprising the following steps of:
(1) Mixing the raw materials: mixing a salt solution and a polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer solution, and uniformly stirring to obtain a reaction solution, wherein the salt solution is formed by mixing aluminum salt, magnesium salt and water;
(2) And (3) precipitation crystallization: adding a precipitant into the reaction solution to perform coprecipitation reaction, performing hydrothermal crystallization after the reaction is finished, and performing suction filtration, washing, drying and calcination to obtain modified hydrotalcite;
(3) Dipping: and adding a mixed solution formed by nickel salt, lanthanum salt, citric acid and water into the modified hydrotalcite, soaking and stirring, and drying and calcining to obtain the lanthanum nickelate loaded modified hydrotalcite catalyst.
2. The method according to claim 1, wherein in the step (1), the molar ratio of aluminum ions to magnesium ions in the salt solution is 1 (2-4), the aluminum salt is aluminum nitrate, and the magnesium salt is magnesium nitrate.
3. The preparation method according to claim 1 or 2, wherein the concentration of the polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer solution is 2-5 g/L, and the volume ratio of the polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer solution to the salt solution is 1 (1-3).
4. The method according to claim 1 or 2, wherein in the step (2), the precipitant is a sodium carbonate solution, and the concentration of the sodium carbonate solution is 0.5 to 1.5mol/L.
5. The method according to claim 4, wherein in the step (2), the hydrothermal crystallization is performed at a temperature of 200 to 220 ℃ for a time of 10 to 20 hours; the drying temperature is 90-150 ℃ and the drying time is 8-12 h; the calcination temperature is 600-750 ℃ and the calcination time is 4-5 h.
6. The method according to claim 1, wherein in the step (3), the nickel salt is nickel nitrate, the lanthanum salt is lanthanum nitrate, and the molar ratio of nickel ions to lanthanum ions in the mixed solution is 4: (5-6); the mole ratio of the citric acid to the total ions of nickel ions and lanthanum ions is 1:1.
7. The method according to claim 6, wherein in the step (3), the dipping and stirring time is 8 to 12 hours, and the dipping temperature is 35 to 55 ℃; the drying temperature is 80-120 ℃ and the drying time is 18-24 h.
8. The method according to claim 7, wherein in the step (3), the calcining comprises: decomposing for 1-2 h at 450-500 ℃ at a heating rate of 2-3 ℃/min, then raising the temperature to 650-750 ℃ at the same heating rate, and calcining for 4-8 h.
9. A modified magnesium aluminium hydrotalcite catalyst, characterised in that it is obtainable by a process according to any one of claims 1 to 8.
10. The use of the modified magnesium aluminum hydrotalcite catalyst according to claim 9, wherein the prepared modified magnesium aluminum hydrotalcite catalyst is placed in a fluidized bed and reduced in a reducing atmosphere, wherein the reducing atmosphere is hydrogen, the reducing space velocity is 0.2-0.5/h, and the reducing temperature is 600-650 ℃; then the temperature of the fluidized bed is raised to 650-700 ℃, methane is introduced to carry out cracking reaction, and the flow rate of the methane is 0.3-0.5 m 3 And/h, the time of the cracking reaction is 180-210 min, and the hydrogen and carbon nano tube solid material is obtained.
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