CN111889120A - Fe core-shell nano catalyst, preparation method and application thereof - Google Patents
Fe core-shell nano catalyst, preparation method and application thereof Download PDFInfo
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- CN111889120A CN111889120A CN201910366883.0A CN201910366883A CN111889120A CN 111889120 A CN111889120 A CN 111889120A CN 201910366883 A CN201910366883 A CN 201910366883A CN 111889120 A CN111889120 A CN 111889120A
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- 239000011258 core-shell material Substances 0.000 title claims abstract description 69
- 239000011943 nanocatalyst Substances 0.000 title claims abstract description 58
- 238000002360 preparation method Methods 0.000 title claims abstract description 41
- 150000001336 alkenes Chemical class 0.000 claims abstract description 84
- 238000006243 chemical reaction Methods 0.000 claims abstract description 82
- JRZJOMJEPLMPRA-UHFFFAOYSA-N olefin Natural products CCCCCCCC=C JRZJOMJEPLMPRA-UHFFFAOYSA-N 0.000 claims abstract description 71
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 211
- SZVJSHCCFOBDDC-UHFFFAOYSA-N ferrosoferric oxide Chemical compound O=[Fe]O[Fe]O[Fe]=O SZVJSHCCFOBDDC-UHFFFAOYSA-N 0.000 claims description 104
- 239000007789 gas Substances 0.000 claims description 55
- 239000002243 precursor Substances 0.000 claims description 29
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- 238000000635 electron micrograph Methods 0.000 description 2
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- 239000002028 Biomass Substances 0.000 description 1
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 1
- 238000004833 X-ray photoelectron spectroscopy Methods 0.000 description 1
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- URGAHOPLAPQHLN-UHFFFAOYSA-N sodium aluminosilicate Chemical compound [Na+].[Al+3].[O-][Si]([O-])=O.[O-][Si]([O-])=O URGAHOPLAPQHLN-UHFFFAOYSA-N 0.000 description 1
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Images
Classifications
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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
- B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
- B01J27/20—Carbon compounds
- B01J27/22—Carbides
-
- B01J35/397—
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
-
- 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
-
- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
- C10G2/00—Production of liquid hydrocarbon mixtures of undefined composition from oxides of carbon
- C10G2/30—Production of liquid hydrocarbon mixtures of undefined composition from oxides of carbon from carbon monoxide with hydrogen
- C10G2/32—Production of liquid hydrocarbon mixtures of undefined composition from oxides of carbon from carbon monoxide with hydrogen with the use of catalysts
- C10G2/33—Production of liquid hydrocarbon mixtures of undefined composition from oxides of carbon from carbon monoxide with hydrogen with the use of catalysts characterised by the catalyst used
- C10G2/331—Production of liquid hydrocarbon mixtures of undefined composition from oxides of carbon from carbon monoxide with hydrogen with the use of catalysts characterised by the catalyst used containing group VIII-metals
- C10G2/332—Production of liquid hydrocarbon mixtures of undefined composition from oxides of carbon from carbon monoxide with hydrogen with the use of catalysts characterised by the catalyst used containing group VIII-metals of the iron-group
Abstract
The invention provides a Fe core-shell nano catalyst, a preparation method and application thereof2C5Active phase shell layer. The catalyst of the invention has good catalytic activity and high selectivity of short-chain olefin. In the Fischer-Tropsch olefin preparation process, the conversion frequency of the supported nano catalyst is as high as 1.32s‑1Far exceeds the conversion frequency of the Fischer-Tropsch olefin preparation catalyst reportedThe highest rate, and the selectivity of short chain olefin of the catalyst can reach 63.0C% in the prepared hydrocarbon. Fe supported on SiC in the invention3O4@χ‑Fe5C2The nanocube catalyst is the only catalyst which can simultaneously achieve the conversion frequency higher than 1.0s‑1And short-chain olefin selectivity of more than 60.0C%.
Description
Technical Field
The invention relates to the technical field of catalysts, in particular to a Fe core-shell nano catalyst, and a preparation method and application thereof.
Background
The short chain olefin of C2-C4 is the basic carbon-based raw material of some high value-added products such as high polymer, surfactant, plastic and the like. Currently, most short-chain olefins are produced by thermal or catalytic cracking of petroleum-derived hydrocarbons; the rapid consumption of petroleum has accelerated the worldwide progress of research on the production of short-chain olefins from other feedstocks. A typical petroleum substitute is synthesis gas, which is a raw material gas used as a chemical raw material and mainly comprises carbon monoxide and hydrogen; it can easily pass through coal, biomass, CO2And natural gas production.
The Fischer-Tropsch olefin preparation reaction provides a mode for directly preparing short-chain olefin from synthesis gas, wherein the short-chain olefin is CHx(x ═ 1,2,3) by surface polymerization. To achieve this goal, researchers have developed a number of fischer-tropsch olefin producing catalysts. For example, there is a catalyst prepared by supporting Fe nanocrystals on carbon nanofibers, which has selectivity of as high as 61C% for short chain olefins in fischer-tropsch reaction, but CO conversion is less than 1%, i.e. the catalyst has high selectivity for short chain olefins but low activity. In addition, there are catalysts for preparing iron carbide embedded in a porous carbon matrix, which exhibit higher activity with a conversion frequency of up to 0.11s-1However, the selectivity to the C2-C5 short chain olefins is only 28.8C percent.
Although the high activity and selectivity of the existing fischer-tropsch olefin production catalysts have been achieved separately, none of the reported catalysts is able to achieve both high activity and high selectivity.
Disclosure of Invention
In view of the above, the invention aims to provide a Fe core-shell nano catalyst, and a preparation method and application thereof, and the nano catalyst provided by the invention has the advantages of good catalytic activity and high selectivity of C2-C4 olefin, and is beneficial to application in Fischer-Tropsch olefin preparation reaction.
The invention provides a Fe core-shell nano catalyst which takes a Fe nanocube with a core-shell structure as an effective component, wherein the Fe nanocube with the core-shell structure takes a ferroferric oxide nanocube as a core, and the surface of the ferroferric oxide nanocube is coated with chi-Fe2C5Active phase shell layer.
Preferably, the Fe core-shell nanocatalyst further comprises an inert carrier, and the Fe nanocubes with the core-shell structure are loaded on the inert carrier.
Preferably, the inert support is selected from one or more of silicon carbide, silica and carbon supports.
Preferably, the total content of iron in the Fe core-shell nano-catalyst is 24-32 mol%.
Compared with the prior art, the catalyst provided by the invention can be expressed as Fe3O4@χ-Fe5C2The active ingredient of the nanocube catalyst is Fe with a core-shell structure3O4@χ-Fe2C5Of nanocubes, i.e. Fe3O4Chi-Fe with a layer of (020) crystal face on the surface of a nano cube5C2An active phase. Fe according to the invention3O4@χ-Fe5C2The nanocube catalyst has high Fischer-Tropsch olefin selectivity due to a unique reaction path, namely the hydrogen-assisted CO dissociation path reduces the activation energy to activate CO. Further, the Fe3O4@χ-Fe2C5The nanocubes have weak adsorption effect on C2-C4 olefins, so that the process of preparing paraffin and C5+ products by carbon-carbon coupling through secondary hydrogenation can be inhibited. Therefore, the nano-catalyst provided by the invention has better catalytic activity and higher selectivity of C2-C4 olefin. In the Fischer-Tropsch olefin preparation process of the embodiment of the invention, Fe loaded on SiC3O4@χ-Fe5C2The conversion frequency of the nanocube catalyst is as high as 1.32s-1Far exceeds the highest value (0.22 s) of the conversion frequency of the Fischer-Tropsch olefin preparation catalyst reported-1) Meanwhile, the selectivity of the C2-C4 olefin of the catalyst is inThe obtained hydrocarbon can reach 63.0C%. In particular, Fe supported on SiC in the present invention3O4@χ-Fe5C2The nanocube catalyst is the only catalyst which can simultaneously achieve the conversion frequency higher than 1.0s-1And C2-C4 olefin selectivity over 60.0C%.
The invention provides a preparation method of a Fe core-shell nano catalyst, which comprises the following steps:
s1, providing a ferroferric oxide nanocube;
s2, reducing the surface of the ferroferric oxide nano cube into an iron simple substance to obtain a precursor nano cube;
s3, reconstructing the surface of the precursor nanocube in an atmosphere containing CO to enable the surface of the ferroferric oxide nanocube to form chi-Fe2C5And optionally loading the active phase shell layer with an inert carrier material to obtain the Fe core-shell nano catalyst.
Preferably, in the step S1, ferric acetylacetonate is used as an iron source, and a heating reaction is performed in a solvent in the presence of 4-phenylbenzoic acid and oleic acid to obtain the ferroferric oxide nanocube.
Preferably, the step S2 is specifically: and carrying out reduction reaction on the ferroferric oxide nanocube in a reducing gas atmosphere, wherein the reducing gas is a mixed gas of hydrogen and argon, the temperature of the reduction reaction is 300-350 ℃, and the surface of the ferroferric oxide nanocube is reduced into an iron simple substance to obtain a precursor nanocube.
Preferably, in step S2, before reducing to elemental iron, the method further includes:
mixing the ferroferric oxide nanocubes and an inert carrier material, and grinding to obtain a compound; reducing the surface of the ferroferric oxide nanocube in the compound into an iron simple substance to obtain a precursor substance loaded with a precursor nanocube;
the step S3 is: performing surface reconstruction on the precursor substance loaded with the precursor nanocubes in an atmosphere containing CO to ensure that the ferroferric oxide nanocubesThe surface of the body forms chi-Fe2C5And obtaining the Fe core-shell nano catalyst by using an active phase shell layer.
Preferably, in the step S3, the precursor substance loaded with the precursor nanocube is heated to 350 ℃ under the atmosphere of synthesis gas to perform surface reconstruction, so that chi-Fe is formed on the surface of the ferroferric oxide nanocube2C5And obtaining the Fe core-shell nano catalyst by using an active phase shell layer.
The invention provides the Fe core-shell nano-catalyst or the application of the Fe core-shell nano-catalyst obtained by the preparation method in the Fischer-Tropsch olefin preparation reaction.
Compared with the prior art, the method takes ferroferric oxide nanocubes as raw materials, and mainly reconstructs Fe on the surface3O4Chi-Fe of (020) crystal face is constructed in a manner of nanocubes5C2And (3) optionally loading the active phase with an inert carrier material to construct the Fe core-shell nano catalyst. The nano-catalyst synthesized by the method has the advantages of good catalytic activity, high selectivity of C2-C4 olefin and stable catalytic performance. Meanwhile, the method is simple and easy to implement, and is convenient for large-scale popularization. In the Fischer-Tropsch olefin preparation process of the embodiment of the invention, Fe loaded on SiC3O4@χ-Fe5C2The conversion frequency of the nanocube catalyst is as high as 1.32s-1Far exceeds the highest value (0.22 s) of the conversion frequency of the Fischer-Tropsch olefin preparation catalyst reported-1) Meanwhile, the selectivity of C2-C4 olefin of the catalyst can reach 63.0C% in the prepared hydrocarbon, and the catalyst is favorable for application in Fischer-Tropsch olefin preparation reaction.
Drawings
FIG. 1 shows Fe obtained in example 1 of the present invention3O4Transmission electron microscopy of nanocubes;
FIG. 2 shows Fe obtained in example 2 of the present invention3O4@χ-Fe5C2High resolution transmission electron microscopy of nanocubes;
FIG. 3 shows Fe obtained in example 2 of the present invention3O4@χ-Fe5C2Powder X-ray diffraction spectra of nanocubes;
FIG. 4 shows Fe obtained in example 2 of the present invention3O4@χ-Fe5C2X-ray photoelectron spectroscopy of nanocubes;
FIG. 5 shows Fe obtained in example 2 of the present invention3O4@χ-Fe5C2A data graph of catalytic performance of the Fischer-Tropsch olefin preparation reaction catalyzed by the nano cubic catalyst;
FIG. 6 shows Fe obtained in example 2 of the present invention3O4@χ-Fe5C2A catalytic performance data graph of the nanocube catalyst subjected to 100-hour catalytic test on-line detection;
FIG. 7 shows Fe obtained in example 2 of the present invention3O4@χ-Fe5C2Transmission electron microscopy images of nanocube catalysts after 100 hours of catalytic testing;
FIG. 8 shows Fe obtained in comparative example 1 of the present invention3O4Transmission electron microscopy of nanooctahedra.
Detailed Description
The technical solutions in the embodiments of the present invention are clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention provides a Fe core-shell nano catalyst which takes a Fe nanocube with a core-shell structure as an effective component, wherein the Fe nanocube with the core-shell structure takes a ferroferric oxide nanocube as a core, and the surface of the ferroferric oxide nanocube is coated with chi-Fe2C5Active phase shell layer.
The nano-catalyst provided by the invention has high catalytic activity, high selectivity of C2-C4 olefin and stable catalytic performance, and is beneficial to application in Fischer-Tropsch olefin preparation reaction.
The invention provides a catalystContains Fe nanocubes with a core-shell structure, which are effective components of the catalyst. The Fe nanocubes are iron-containing nanocubes and have core-shell structures with nanocubes, and the phases are mainly Fe3O4And chi-Fe2C5. In the Fe nanocube core-shell structure, the core containing Fe component is ferroferric oxide (Fe)3O4) The shell layer coating the core of the nanocube is chi-Fe2C5An active phase, which is a cubic shell. In an embodiment of the present invention, the Fe nanocubes having the core-shell structure may be expressed as Fe3O4@χ-Fe5C2The average size of the nanocubes is 42nm, and the thickness of a shell layer is generally 2-3 nm.
The existing catalyst with Fischer-Tropsch olefin preparation activity can generally stabilize the transition state of CO based on
The Evans-Polanyi relationship, the activation energy and adsorption energy of which are linearly related to each other, and the adsorption energies of the intermediates are linearly related to each other. This being the case, promoting the activation of CO is equivalent to the stabilization of CO, i.e. corresponding to a strong adsorption of low olefins. The strong bond between the lower olefin and the catalyst results in further hydrogenation to paraffins or in carbon-carbon coupling to long chain products. Thus, high activity for CO conversion is somewhat contradictory with high selectivity for low olefins. Therefore, it is difficult to develop an effective fischer-tropsch olefin catalyst, because both easy dissociation of CO and weak bonding of low olefins are achieved.
In the present invention, said Fe3O4@χ-Fe5C2The nanocube catalyst has a unique reaction path, so that the nanocube catalyst has high Fischer-Tropsch olefin selectivity, namely the hydrogen-assisted CO dissociation path reduces the activation energy to activate CO. Further, the Fe3O4@χ-Fe2C5The nanocubes have weak adsorption effect on C2-C4 olefins, so that the process of preparing paraffin and C5+ products by carbon-carbon coupling through secondary hydrogenation can be inhibited.
In the practice of the inventionIn an example, the Fe core-shell nanocatalyst further comprises an inert carrier, and the Fe nanocubes with the core-shell structure are loaded on the inert carrier. The inert carrier mainly plays a role in dispersing the effective ingredients; the inert carrier of the present invention may be selected from one or more of silicon carbide (SiC), silica and carbon carriers (e.g., activated carbon, carbon nanofibers, carbon nanotubes, etc.), and is preferably SiC. The catalyst comprising the inert carrier is a supported Fe core-shell nano catalyst, and the Fe nanocubes with the core-shell structure are preferably supported on the surface of SiC particles. In the supported Fe core-shell nano-catalyst, the total iron content is preferably 24-32 mol%. In the process of implementing the invention, the proportion is adopted, the catalytic activity is better, and Fe is generated in the reaction process3O4The nanocubes are not easy to agglomerate to cause catalyst deactivation.
In the Fischer-Tropsch olefin preparation process of the embodiment of the invention, Fe loaded on SiC3O4@χ-Fe5C2The conversion frequency of the nanocube catalyst is as high as 1.32s-1Far exceeds the highest value (0.22 s) of the conversion frequency of the Fischer-Tropsch olefin preparation catalyst reported-1) Meanwhile, the selectivity of C2-C4 olefin of the catalyst can reach 63.0 percent in the prepared hydrocarbon. In particular, Fe supported on SiC in the present invention3O4@χ-Fe5C2The nanocube catalyst is the only catalyst which can simultaneously achieve the conversion frequency higher than 1.0s-1And C2-C4 olefin selectivity over 60.0C%.
Correspondingly, the embodiment of the invention provides a preparation method of a Fe core-shell nano catalyst, which comprises the following steps:
s1, providing a ferroferric oxide nanocube;
s2, reducing the surface of the ferroferric oxide nano cube into an iron simple substance to obtain a precursor nano cube;
s3, reconstructing the surface of the precursor nanocube in an atmosphere containing CO to enable the surface of the ferroferric oxide nanocube to form chi-Fe2C5Active phase shell, optionally with inert carrierAnd loading the substance to obtain the Fe core-shell nano catalyst.
The Fe core-shell nano-catalyst prepared by the method has the advantages of good catalytic activity, high selectivity of short-chain olefin and stable catalytic performance, and the method is simple, convenient and easy to implement and is beneficial to application.
The examples of the present invention first provide Fe3O4Nanocubes, which are crystal structures on the order of nanometers in size, with an average size of 40 nm. Said Fe3O4Nanocubes can be prepared by general methods known to those skilled in the art, and the present invention is preferably prepared by the following steps: mainly adopts iron acetylacetonate (Fe (acac)3) Is an iron source, and is heated and reacted in a solvent in the presence of 4-phenylbenzoic acid and oleic acid to obtain the ferroferric oxide nanocube.
Wherein 4-phenylbenzoic acid and oleic acid are mainly used for controlling the shape of ferroferric oxide; such solvents include, but are not limited to, diphenyl ether. In the embodiment of the invention, ferric acetylacetonate, 4-phenylbenzoic acid and oleic acid can be dissolved in dibenzyl ether, oxygen in the benzyl ether is removed, and the mixture is stirred and reacted for 30-60min after the temperature is preferably raised to 250-300 ℃. After the reaction is finished, the substance obtained by the reaction is cooled to room temperature, ethanol is added to precipitate a product, and then the product is separated, washed and dried to obtain the Fe3O4A nanocube.
In the embodiment of the invention, the weight volume ratio of the ferric acetylacetonate, the 4-phenylbenzoic acid, the oleic acid and the dibenzyl ether is preferably 1-2 g: 0.9-1.1 g: 2-3 mL: 15-25 mL; the raw material proportion can ensure that the Fe with uniform size can be obtained3O4A nanocube. Specifically, in the embodiment of the invention, a certain proportion of ferric acetylacetonate, 4-phenylbenzoic acid and oleic acid are dissolved in dibenzyl ether, heated to 110-. After the reaction was completed, the temperature was cooled to 150 ℃, and 20mg of sodium oleate and 5mg of sulfur powder were dissolved in the solution at a stirring rate of 300rpm and maintained for 30 minutes; recoolingCooling to room temperature, adding ethanol to precipitate a product, separating the product by using a magnet, ultrasonically washing the product for 3-4 times by using n-hexane, and drying the product overnight in vacuum to finally obtain dry Fe3O4A nanocube.
Wherein, the heating of the raw material solution can ensure the removal of residual oxygen in the solution; other specific limitations of the reaction conditions favor obtaining uniform-sized Fe3O4A nanocube. After the reaction is finished, ethanol is added to dissolve other impurities and enable Fe3O4The nanocubes are precipitated for magnet separation; fe to be finally obtained3O4The nanocubes can be dispersed in n-hexane for storage, and can prevent Fe3O4The nanocubes are oxidized.
After the ferroferric oxide nanocube is obtained, the ferroferric oxide nanocube can be put into a fixed bed reactor in the embodiment of the invention, and is heated and reduced in the atmosphere of reducing gas, so that the surface of the ferroferric oxide nanocube is reduced into a simple substance of iron, and the precursor nanocube is obtained. The preparation method of the precursor nanocube comprises the following steps: a certain amount of the ferroferric oxide nanocubes are filled into a fixed bed reactor (the inner diameter of the reactor can be 9mm) commonly used in the field, and mixed gas (H) of hydrogen and argon is added2and/Ar) in airflow atmosphere, carrying out reduction reaction to reduce the surface of the ferroferric oxide nano cube into an iron simple substance. Wherein the reducing gas is preferably H2Mixed gas of Ar, H2Ar may be in a volume ratio of 1: 7-12; the temperature of the reduction reaction is preferably 300-350 ℃, and Fe can be converted3O4Fully reducing into iron simple substance.
After the reduction reaction is finished, the obtained precursor nanocube sample can be heated in a fixed bed reactor under the atmosphere of a synthesis gas flow containing CO to carry out surface reconstruction (or called surface reconstruction) reaction, so that chi-Fe is formed on the surface of the ferroferric oxide nanocube2C5Active phase shell layer to obtain Fe with core-shell structure3O4@χ-Fe5C2The nanocubes can be called as Fe nanocubes with core-shell structures for short.
The Fe nanocubes with the core-shell structure obtained by the embodiment of the invention have higher catalytic activity, and meanwhile, the selectivity of short alkenes in the Fischer-Tropsch olefin preparation reaction is high; it may be expressed as Fe3O4@χ-Fe5C2A nanocube catalyst. In order to further enhance the stability of the catalytic active component, the embodiment of the invention can also prepare supported Fe3O4@χ-Fe5C2A nanocube catalyst.
In some embodiments of the invention, the resulting Fe may be used3O4@χ-Fe5C2Mixing the nanocubes with an inert carrier material to obtain the supported Fe core-shell nanocatalyst. The inert carrier material may be selected from one or more of silicon carbide, silicon dioxide and carbon carriers, preferably SiC powder; the particle size of the inert carrier material may be 20-40 mesh.
In other embodiments of the present invention, before reducing to elemental iron, the method further comprises: mixing the ferroferric oxide nanocubes and an inert carrier material, and grinding to obtain a compound; then, reducing the surface of the ferroferric oxide nano cube in the compound into an iron simple substance to obtain a precursor substance loaded with a precursor nano cube; finally, performing surface reconstruction on the precursor substance loaded with the precursor nanocubes in an atmosphere containing CO to form chi-Fe on the surfaces of the ferroferric oxide nanocubes2C5And obtaining the Fe core-shell nano catalyst by using an active phase shell layer.
Wherein the inert support material may be selected from one or more of silicon carbide, silica and carbon support. Taking SiC powder as an example, in these examples, Fe3O4Mixing the nanocubes with SiC powder, preferably adding the mixture into a solvent, grinding the mixture, and drying the mixture to obtain Fe supported on the surface3O4A nanocube SiC composite. The solvent is preferably one or more of n-hexane, ethanol, toluene, acetone and tetrahydrofuran; the solvent and Fe3O4The volume-to-weight ratio of the nanocubes is preferably 7-15 mL: 1g of the total weight of the composition. The above solventBy addition and grinding of Fe3O4The nanocube loading is more uniform. Further, the Fe3O4The weight ratio of the nanocubes to the SiC powder may be 1: 8-11.
After loading, the obtained composite is subjected to a reduction reaction in a reducing gas atmosphere, and then a surface reconstruction reaction in a synthetic gas atmosphere, so as to obtain the Fe core-shell nano catalyst. Specifically, the compound is preferably heated to 300-350 ℃ at the speed of 1-3 ℃/min in a reducing gas atmosphere with the gas flow rate of 80-120mL/min and the pressure of 0.8-1.2bar, and the reduction reaction is carried out for 10-15h at constant temperature. Wherein the reducing gas is preferably H2Mixed gas of Ar, H2And the volume ratio of Ar is 1: 7-12. The reduction reaction under the above conditions can convert Fe3O4Fully reducing the iron into simple substance, and heating at a specific heating rate to ensure that Fe is not damaged3O4The morphology of nanocubes.
After the reduction reaction is finished, in the embodiment of the present invention, the precursor loaded with the precursor nanocube is preferably heated to 350 ℃ under the atmosphere of the synthesis gas to perform surface reconstruction. Specifically, the air speed can be 2000-3000 mL-h-1·gcat-1And in the synthetic gas atmosphere with the pressure of 15-25bar, heating to 350 ℃ at the speed of 1-3 ℃/min, carrying out surface reconstruction at constant temperature, and reacting for 10-15h to obtain the supported Fe core-shell nano catalyst.
Wherein the synthesis gas is preferably H2Mixed gas of CO and Ar, H2The volume ratio of CO to Ar is 10-15: 10-15: 1. the above reaction temperature facilitates the carbonization of iron to form Fe3O4@χ-Fe5C2The core-shell structure can ensure that Fe is not damaged when the temperature is raised at a specific temperature raising rate3O4The morphology of nanocubes. In addition, the reaction gas, pressure and space velocity may be in accordance with the conditions of the catalytic reaction.
The embodiment of the invention further provides application of the Fe core-shell nano catalyst in Fischer-Tropsch olefin preparation reaction, namely a method for preparing short-chain olefin through Fischer-Tropsch reaction.
In a specific embodiment of the invention, the Fischer-Tropsch olefin production reaction can be carried out in a fixed bed reactor at 330 ℃ and 350 ℃ under 1bar of synthesis gas. For example, 100-900 mg of supported Fe core-shell nanocatalyst is loaded into a fixed bed reactor with an inner diameter of 9mm, and then 1bar of synthesis gas (48 vol% H)248 vol% CO and 4 vol% Ar, Ar as internal standard) as raw material gas, and 15-35 mL/min-1Is introduced into the reactor.
In the embodiment of the invention, two gas chromatographs are used for detecting products and reactants on line, and H is analyzed by a carbon molecular sieve column (TDX-1) with a Thermal Conductivity Detector (TCD)2，CO，CO2，CH4And Ar; analysis of hydrocarbons using PONA capillary column with Flame Ionization Detector (FID) for CH4As a reference bridge between the TCD and the FID. The CO conversion was calculated according to the internal standard method, assuming that the amount of Ar remained constant after the reaction.
The CO conversion is calculated based on carbon atoms and is given by the formula:
CO conversion rate (CO)inlet-COoutlet)/COinlet×100％；
Wherein, COinletAnd COoutletAre the moles of CO at the inlet and outlet, respectively.
Hydrocarbons CnHmThe selectivity of (a) is calculated according to the following formula:
wherein, CnHm outletRepresents the moles of the single-species hydrocarbon product at the outlet; the denominator represents the total number of moles of carbon atoms in all hydrocarbon products at the outlet, and m, n, i, and j are the numbers of carbon and hydrogen. The selectivity of the oxygen-containing compound is lower than 1.0 percent; the carbon balance is over 94.0%.
The conversion frequency value is calculated based on the following equation:
conversion frequency ═ CO conversion × moles of CO in the syngas × gas flow rate ÷ moles of surface Fe atoms.
According to detection, the Fe core-shell nano-catalyst has excellent catalytic effect and high catalytic activity in the Fischer-Tropsch olefin preparation reaction. In addition, in the continuous measurement process of the Fe core-shell nano-catalyst, the selectivity of C2-C4 olefin and the selectivity of CO are basically kept stable, and the excellent stability is shown.
For further understanding of the present application, the Fe core-shell nanocatalyst provided by the present invention, its preparation method and application are specifically described below with reference to examples.
Example 1
1.4g of Fe (acac)3And 1.0g of 4-biphenylcarboxylic acid was dissolved in a mixture of 20.0mL of benzyl ether and 2.5mL of oleic acid, and the resulting mixed solution was degassed at 120 ℃ for 30 min. Subsequently, the solution was heated at 10 ℃ for min-1Heating to 290 ℃ and maintaining for 30min, and stirring at the speed of 300rpm to react to obtain the Fe-containing material3O4A solution of nanocubes. After cooling the temperature to 150 ℃, 20mg of sodium oleate and 5mg of sulfur powder were dissolved in the solution at a stirring rate of 300rpm and held for 30 minutes. Cooling the obtained solution to room temperature, adding ethanol to precipitate a product, separating the product by using a magnet, ultrasonically washing the product by using n-hexane for three times, drying the product in vacuum, and standing overnight to obtain dry Fe3O4The nanocubes, the electron micrograph of which is shown in FIG. 1. As can be seen from FIG. 1, this example yielded Fe of uniform size3O4A nanocube.
Example 2
1. 0.2g of Fe prepared in example 1 was added3O4The nanocubes were packed into a fixed bed reactor with an internal diameter of 9mm, the Fe3O4Nanocubes in H2/Ar(10vol％H2And 90 vol% Ar) at a pressure of 1bar at 100mL min-1The gas flow rate of (A) is reduced for 10h at 350 ℃, and the heating rate is 1 ℃ min-1. The sample obtained was then treated in a fixed bed reactor with 1bar of synthesis gas (48 vol% H)248 vol% CO and 4 vol% Ar) at a gas flow rate of 20 mL. min-1Heating at 340 deg.C for 10 hr at 1 deg.C·min-1To obtain Fe3O4@χ-Fe5C2A nanocube.
The resulting Fe3O4@χ-Fe5C2The transmission electron microscopy of the nanocubes is shown in FIG. 2, the powder X-ray diffraction spectrum is shown in FIG. 3, and the X-ray photoelectron spectrum is shown in FIG. 4. As can be seen from the figure, the average size of the obtained nanocubes is 42 nm; it has a core-shell structure, the core is Fe3O4Nano cube, shell is Chi-Fe of (020) crystal face5C2The thickness of the active phase and the shell layer is 2-3 nm.
2. 0.2g of prepared Fe3O4@χ-Fe5C2The nanocubes were mixed with 1.8g of 20-40 mesh SiC powder and the resulting composite was charged into a fixed bed reactor with an internal diameter of 9 mm. Subsequently, 1bar of synthesis gas (48 vol% H) was fed248 vol% CO and 4 vol% Ar, Ar as internal standard) as a raw material gas, and 20 mL. min-1Is introduced into the reactor. The Fischer-Tropsch olefin preparation reaction is carried out in a fixed bed reactor under the condition of 1bar of synthesis gas and at the temperature of 340 ℃.
According to the method, the product and the reactant of the Fischer-Tropsch olefin preparation reaction are detected, and the CO conversion rate, the olefin selectivity and the like are respectively calculated. The results are shown in FIG. 5, and FIG. 5 shows the data of catalytic performance of the Fischer-Tropsch olefin preparation reaction. Fig. 6 is catalytic performance data measured on-line after 100 hours of catalytic testing, and fig. 7 is a transmission electron microscope image of the catalyst after 100 hours of catalytic testing.
With reference to fig. 5-6, in the fischer-tropsch olefin production reaction, the Fe core-shell nano-catalyst obtained by the present invention has the following reaction conditions: 1bar of synthesis gas (48 vol% H248 vol% CO, 4 vol% Ar), flow rate 20 mL. min-1And the reaction temperature was 340 ℃. As shown in FIG. 5, the C2-C4 olefin selectivity in the product was as high as 63C%, the C2-C4 alkylene ratio reached 7.2, and there was 52.2% CO conversion. Therefore, the Fe core-shell nano-catalyst has excellent catalytic effect and high catalytic activity in the Fischer-Tropsch olefin preparation reaction.
To more accurately evaluate the activity of the catalyst, based on Fe atoms per mole of surfaceThe conversion frequency, Fe, was calculated per second of CO conversion3O4@χ-Fe5C2The nanocube/SiC was 1.32s-1. As shown in FIG. 6, the C2-C4 olefin selectivity and CO selectivity remained essentially stable during 100h of continuous measurement, showing excellent stability.
Example 3
Mixing 1g Fe (acac)3And 1.1g of 4-biphenylcarboxylic acid was dissolved in a mixture of 20.0mL of benzyl ether and 2.5mL of oleic acid, and the resulting mixed solution was degassed at 110 ℃ for 40 min. Subsequently, the solution was heated at 8 ℃ for min-1Heating to 300 deg.C and maintaining for 30min, stirring at 500rpm to obtain Fe-containing solution3O4A solution of nanocubes. After cooling the temperature to 150 ℃, 20mg of sodium oleate and 5mg of sulfur powder were dissolved in the solution at a stirring rate of 300rpm and held for 30 minutes. Cooling the obtained solution to room temperature, adding ethanol to precipitate a product, separating the product by using a magnet, ultrasonically washing the product by using n-hexane for three times, drying the product in vacuum, and standing overnight to obtain dry Fe3O4A nanocube.
Example 4
0.2g of Fe prepared in example 33O4The nanocubes were packed into a fixed bed reactor with an internal diameter of 9mm, the Fe3O4Nanocubes in H2/Ar(10vol％H2And 90 vol% Ar) at a pressure of 1bar at 100mL min-1The gas flow rate of (A) is reduced for 10h at 350 ℃, and the heating rate is 1 ℃ min-1. The sample obtained was then treated in a fixed bed reactor with 1bar of synthesis gas (48 vol% H)248 vol% CO and 4 vol% Ar) at a gas flow rate of 20 mL. min-1At 340 ℃ for 10 hours at a heating rate of 1 ℃ min-1To obtain Fe3O4@χ-Fe5C2A nanocube.
Example 5
Dissolving 2.0g of ferric acetylacetonate, 0.9g of 4-phenylbenzoic acid and 3.0mL of oleic acid in 15.0mL of dibenzyl ether at normal temperature, heating the obtained solution to 130 ℃ in a nitrogen atmosphere, and stirring for 20min to remove oxygen in the solution; then, the process of the present invention is carried out,heating to 250 ℃ at the heating rate of 13 ℃/min, stirring and reacting for 60min at the stirring speed of 200rpm to obtain the Fe-containing iron3O4A solution of nanocubes. After cooling the temperature to 150 ℃, 20mg of sodium oleate and 5mg of sulfur powder were dissolved in the solution at a stirring rate of 300rpm and held for 30 minutes. Cooling the obtained solution to room temperature, adding ethanol to precipitate a product, separating the product by using a magnet, ultrasonically washing the product by using n-hexane for three times, drying the product in vacuum, and standing overnight to obtain dry Fe3O4A nanocube.
Example 6
0.5g of Fe prepared in example 5 was added3O4The nanocubes were packed into a fixed bed reactor with an internal diameter of 9mm, the Fe3O4Nanocubes in H2/Ar(10vol％H2And 90 vol% Ar) at a pressure of 1bar at 100mL min-1The gas flow rate of (A) is reduced for 10h at 350 ℃, and the heating rate is 1 ℃ min-1. The sample obtained was then treated in a fixed bed reactor with 1bar of synthesis gas (48 vol% H)248 vol% CO and 4 vol% Ar) at a gas flow rate of 20 mL. min-1At 340 ℃ for 10 hours at a heating rate of 1 ℃ min-1To obtain Fe3O4@χ-Fe5C2A nanocube.
Example 7
Dissolving 1.5g of ferric acetylacetonate, 1.0g of 4-phenylbenzoic acid and 2.5mL of oleic acid in 20.0mL of dibenzyl ether at normal temperature, heating the obtained solution to 120 ℃ in a nitrogen atmosphere, and stirring for 30min to remove oxygen in the solution; then, the temperature is raised to 280 ℃ at the temperature raising rate of 12 ℃/min, the stirring reaction is carried out for 40min, the stirring speed is 300rpm, and the Fe-containing material is obtained3O4A solution of nanocubes. After cooling the temperature to 150 ℃, 20mg of sodium oleate and 5mg of sulfur powder were dissolved in the solution at a stirring rate of 300rpm and held for 30 minutes. Cooling to room temperature after the reaction is finished, adding 10mL of ethanol to precipitate a product, separating the product by using a magnet, ultrasonically washing the product by using n-hexane for 4 times, wherein the ultrasonic time is 1.5min each time, separating the product by using the magnet, drying the product in vacuum at 50 ℃, and standing overnight to obtain Fe3O4A nanocube.
Example 8
0.3g of Fe prepared in example 73O4The nanocubes were packed into a fixed bed reactor with an internal diameter of 9mm, the Fe3O4Nanocubes in H2/Ar(10vol％H2And 90 vol% Ar) at a pressure of 1bar at 100mL min-1The gas flow rate of (A) is reduced for 10h at 350 ℃, and the heating rate is 1 ℃ min-1. The sample obtained was then treated in a fixed bed reactor with 1bar of synthesis gas (48 vol% H)248 vol% CO and 4 vol% Ar) at a gas flow rate of 20 mL. min-1At 340 ℃ for 10 hours at a heating rate of 1 ℃ min-1To obtain Fe3O4@χ-Fe5C2A nanocube.
Example 9
0.2g of Fe prepared in example 4, example 6 and example 83O4@χ-Fe5C2And mixing the nanocubes with 1.8g of 20-40 mesh SiC powder respectively, and filling the obtained compounds into fixed bed reactors with the inner diameter of 9mm respectively to perform Fischer-Tropsch olefin preparation reaction. The reaction conditions include: 1bar of synthesis gas (48 vol% H248 vol% CO, 4 vol% Ar), flow rate 20 mL. min-1And the reaction temperature was 340 ℃.
The catalyst of example 4 has 60C% selectivity of C2-C4 olefin in the Fischer-Tropsch olefin reaction product, 6.9% C2-C4 alkene ratio and 48.3% CO conversion. The conversion frequency of the Fe core-shell nano-catalyst is 1.12s-1And the selectivity of C2-C4 olefin and CO are basically kept stable during 100h of continuous measurement, and the excellent stability is shown.
The catalyst of example 6 has 61.5C% selectivity of C2-C4 olefin in the Fischer-Tropsch olefin reaction product, 7.1% alkene ratio of C2-C4, and 51.6% CO conversion. The conversion frequency of the Fe core-shell nano catalyst is 1.32s-1And the selectivity of C2-C4 olefin and CO are basically kept stable during 100h of continuous measurement, and the excellent stability is shown.
The catalyst of example 8 has C2-C4 olefin selectivity of 62.8C%, C2-C4 olefin ratio of 7.2, and CO conversion of 50.4%. The conversion frequency of the Fe core-shell nano-catalyst is 1.12s-1And the selectivity of C2-C4 olefin and CO are basically kept stable during 100h of continuous measurement, and the excellent stability is shown.
Comparative example 1
1.0g of Fe (acac)3Dissolved in a mixture of 20.0mL benzyl ether, 2.3mL oleylamine and 1.6mL oleic acid and degassed at 120 ℃ for 30 min. The degassed solution was cooled to 20 ℃ for min-1The mixture was heated to 220 ℃ and stirred at 300rpm for 1 hour. Then, the resulting solution was heated at 20 ℃ for min-1Heat to 300 ℃ and hold for 2 hours. After cooling the temperature to 150 ℃, 13mg of sodium oleate and 5mg of sulfur powder were dissolved in the solution at a stirring rate of 300rpm and maintained for 30 minutes to obtain Fe3O4The electron micrograph of the nano-octahedron is shown in FIG. 8.
0.2g of the obtained Fe3O4The nano octahedron is loaded on a silicon carbide carrier of 0.8g and 40-60 meshes and is loaded into a fixed bed reactor with the inner diameter of 9 mm. Obtained Fe3O4Nano octahedron load in H2/Ar(10vol％H2And 90 vol% Ar) gas atmosphere at a pressure of 1bar at 100 mL. min-1The gas flow rate of (2) is reduced for 10h at 350 ℃, and the heating rate is 1 ℃ min-1. The sample obtained was then treated in a fixed bed reactor with 1bar of synthesis gas (48 vol% H)248 vol% CO and 4 vol% Ar) at a gas flow rate of 20 mL. min-1At 340 ℃ for 10 hours at a heating rate of 1 ℃ min-1To obtain Fe3O4@χ-Fe5C2Octahedral nanocatalyst.
Using the obtained Fe3O4@χ-Fe5C2The octahedral nano catalyst is used for carrying out the catalytic performance test of the Fischer-Tropsch olefin preparation reaction under the reaction condition of 1bar of synthesis gas (48 vol% H)248 vol% CO, 4 vol% Ar), flow rate 20 mL. min-1And the reaction temperature was 340 ℃. C2-C4 in the productThe olefin selectivity is only 49.1C percent, the CO conversion rate is 11.2 percent, and the conversion frequency is only 0.21s-1。
Comparative example 2
0.2g of Fe-MIL-88BNH2 was placed in a tube furnace and heated at 500 ℃ for 4 hours; the obtained sample was charged into a fixed bed reactor having an inner diameter of 9 mm. At a rate of 60 mL/min-1At 340 ℃ for 4 hours. 1bar of synthesis gas (48 vol% H) was subsequently passed in248 vol% CO and 4 vol% Ar) at a gas flow rate of 20 mL. min-1At 340 ℃ for 10 hours at a heating rate of 1 ℃ min-1To obtain Fe3O4@χ-Fe5C2Spherical nano-catalyst.
Using the obtained Fe3O4@χ-Fe5C2The spherical nano catalyst is used for carrying out the catalytic performance test of the Fischer-Tropsch olefin preparation reaction under the reaction condition of 20bar of synthesis gas (CO/H)2Volume ratio of 1), flow rate of 30 mL/min-1The reaction temperature was 300 ℃. The selectivity of C2-C4 olefin in the product is only 21.4C percent, the CO conversion rate is 81.8 percent, and the conversion frequency is only 0.091s-1。
From the above examples, it can be seen that in the fischer-tropsch olefin production process of the embodiment of the invention, Fe supported on SiC3O4@χ-Fe5C2The conversion frequency of the nanocube catalyst is as high as 1.32s-1Far exceeds the highest value (0.22 s) of the conversion frequency of the Fischer-Tropsch olefin preparation catalyst reported-1) Meanwhile, the selectivity of C2-C4 olefin of the catalyst can reach 63.0 percent in the prepared hydrocarbon.
In particular, Fe supported on SiC in the present invention3O4@χ-Fe5C2The nanocube catalyst is the only catalyst which can simultaneously achieve the conversion frequency higher than 1.0s-1And C2-C4 olefin selectivity over 60.0C%. In addition, in the continuous measurement process of the Fe core-shell nano-catalyst, the selectivity of C2-C4 olefin and the selectivity of CO are basically kept stable, and the excellent stability is shown.
The above description is only a preferred embodiment of the present invention, and it should be noted that various modifications to these embodiments can be implemented by those skilled in the art without departing from the technical principle of the present invention, and these modifications should be construed as the scope of the present invention.
Claims (10)
1. The Fe core-shell nano catalyst is characterized in that a Fe nanocube with a core-shell structure is used as an effective component, a ferroferric oxide nanocube is used as a core in the Fe nanocube core-shell structure, and the surface of the ferroferric oxide nanocube is coated with chi-Fe2C5Active phase shell layer.
2. The Fe core-shell nanocatalyst of claim 1, further comprising an inert support, wherein the Fe core-shell nanocatalyst having a core-shell structure is supported on the inert support.
3. The Fe core shell nanocatalyst of claim 2 wherein the inert support is selected from one or more of silicon carbide, silica and carbon supports.
4. The Fe core-shell nanocatalyst of claim 2, wherein the total iron content of the Fe core-shell nanocatalyst is from 24 mol% to 32 mol%.
5. A preparation method of a Fe core-shell nano catalyst comprises the following steps:
s1, providing a ferroferric oxide nanocube;
s2, reducing the surface of the ferroferric oxide nano cube into an iron simple substance to obtain a precursor nano cube;
s3, reconstructing the surface of the precursor nanocube in an atmosphere containing CO to enable the surface of the ferroferric oxide nanocube to form chi-Fe2C5And optionally loading the active phase shell layer with an inert carrier material to obtain the Fe core-shell nano catalyst.
6. The preparation method according to claim 5, characterized in that in step S1, ferric acetylacetonate is used as an iron source, and the heating reaction is carried out in a solvent in the presence of 4-phenylbenzoic acid and oleic acid to obtain the ferroferric oxide nanocubes.
7. The preparation method according to claim 5, wherein the step S2 specifically comprises: and carrying out reduction reaction on the ferroferric oxide nanocube in a reducing gas atmosphere, wherein the reducing gas is a mixed gas of hydrogen and argon, the temperature of the reduction reaction is 300-350 ℃, and the surface of the ferroferric oxide nanocube is reduced into an iron simple substance to obtain a precursor nanocube.
8. The method according to any one of claims 5 to 7, wherein the step S2 further comprises, before reducing the iron into elemental iron:
mixing the ferroferric oxide nanocubes and an inert carrier material, and grinding to obtain a compound; reducing the surface of the ferroferric oxide nanocube in the compound into an iron simple substance to obtain a precursor substance loaded with a precursor nanocube;
the step S3 is: performing surface reconstruction on the precursor substance loaded with the precursor nanocubes in an atmosphere containing CO to enable the ferroferric oxide nanocubes to form chi-Fe on the surfaces2C5And obtaining the Fe core-shell nano catalyst by using an active phase shell layer.
9. The method as claimed in claim 8, wherein in step S3, the precursor loaded with the precursor nanocubes is heated to 350 ℃ in a syngas atmosphere to perform surface reconstruction, such that χ -Fe is formed on the surface of the ferroferric oxide nanocubes2C5And obtaining the Fe core-shell nano catalyst by using an active phase shell layer.
10. The Fe core-shell nano-catalyst according to any one of claims 1 to 4 or the Fe core-shell nano-catalyst obtained by the preparation method according to any one of claims 5 to 9 is applied to a Fischer-Tropsch olefin preparation reaction.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
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| CN201910366883.0A CN111889120B (en) | 2019-05-05 | 2019-05-05 | Fe core-shell nano catalyst, and preparation method and application thereof |
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| CN114602469A (en) * | 2022-02-14 | 2022-06-10 | 清华大学 | Catalyst for preparing olefin from synthesis gas, preparation method and use method |
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