CN111821976A

CN111821976A - Threshold-limited iron-based Fischer-Tropsch synthesis catalyst and preparation method thereof

Info

Publication number: CN111821976A
Application number: CN201910323146.2A
Authority: CN
Inventors: 卓欧; 刘萌; 高福杰; 王喜章; 吴强; 杨立军; 胡征
Original assignee: Nanjing University
Current assignee: Nanjing University
Priority date: 2019-04-22
Filing date: 2019-04-22
Publication date: 2020-10-27
Anticipated expiration: 2039-04-22
Also published as: CN111821976B

Abstract

The invention provides a threshold-limited iron-based Fischer-Tropsch synthesis catalyst and a preparation method thereof, belonging to the technical field of Fischer-Tropsch synthesis catalysts. The threshold-limited iron-based Fischer-Tropsch synthesis catalyst provided by the invention comprises a carbon-based nanocage and iron-based nanoparticles, wherein the iron-based nanoparticles are threshold-limited in a cage cavity of the carbon-based nanocage. In the invention, the iron-based nanoparticles are used as active components, the carbon-based nanocages are used as carriers, the iron-based nanoparticles are confined in the cage cavities of the carbon-based nanocages, and the catalyst shows high catalytic activity, selectivity of target products, strong carbon deposition resistance and sintering resistance in the reaction of catalyzing Fischer-Tropsch synthesis by utilizing the three-dimensional threshold limiting effect of the carbon-based nanocages and the limitation of micropores of the cage walls on mass transfer of various molecules in the reaction.

Description

Threshold-limited iron-based Fischer-Tropsch synthesis catalyst and preparation method thereof

Technical Field

The invention relates to the technical field of Fischer-Tropsch synthesis catalysts, in particular to a threshold-limited iron-based Fischer-Tropsch synthesis catalyst and a preparation method thereof.

Background

Fischer-Tropsch Synthesis (Fischer-Tropsch Synthesis) is a Synthesis of Synthesis gas (CO and H) under conditions₂Mixed gas) catalytic conversion into hydrocarbon, and can be used for producing low-carbon olefin

Gasoline, diesel oil, paraffin and other oxygen-containing organic matters. Fixed fluidized bed (SAS) and slurry bed (SSPD) processes from Sasol of south africa, fixed bed SMDS process from Shell, GTL process from Syntrolem, AGC-21 process from Exxon, and GasCat process from energy international, among others, are currently large-scale fischer-tropsch processes, producing primarily fuel oil (appl.catal.a: gen.1999,186,3.catal.sci.technol.2014,4,2210). Fischer-Tropsch synthetic liquid fuel has no nitrogen and sulfur and low aromatic hydrocarbon content, is rather favored by the market as a clean fuel, and currently 2 percent of fuel oil in the world comes from Fischer-Tropsch synthesis (nat. chem.2016,8, 929-934).

Although the Fischer-Tropsch synthesis has been applied to the production of fuel oil on a large scale, a plurality of scientific problems still remain to be solved. Firstly, the regulation and control of product selectivity is one of the scientific problems to be solved urgently in Fischer-Tropsch synthesis, according to the Anderson-Schulz-Flory (ASF) product distribution rule, the selectivity of gasoline fraction in Fischer-Tropsch synthesis product is not higher than 45%, the selectivity of diesel fraction is not higher than 30%, and C is₂-C₄The selectivity of the components is not higher than 60% (ACS cat.2013, 3,2130.); secondly, the Fischer-Tropsch synthesis catalysts all have the problem of sintering, and the sintering of the catalysts can cause the reduction of catalytic performance, which is one of the serious problems faced in industrial application. The supported iron-based catalyst commonly used at present can obtain higher fuel oil fraction or

Component selectivity, but such catalysts are prone to sintering leading to catalystsThe performance is rapidly reduced, and large-scale industrial application is difficult to realize (chem.Soc.Rev.2008,37,2758; ACS Catal.2016,6,4017.); in addition, carbon deposition is generated on the surface of the catalyst in the fischer-tropsch reaction process, especially, the Fe-based catalyst is more easily deposited under the condition of high-temperature reaction, so that the performance of the catalyst is reduced, the structure of the catalyst is damaged, even a reaction tube is blocked, and the like, and how to improve the carbon deposition resistance of the catalyst is also a great difficulty problem in catalyst design (chem.soc.rev.2008,37,2758.). Therefore, the Fischer-Tropsch synthesis catalyst still has the problems of poor selectivity and stability.

Disclosure of Invention

The invention aims to provide a threshold-limiting type iron-based Fischer-Tropsch synthesis catalyst and a preparation method thereof.

In order to achieve the above object, the present invention provides the following technical solutions:

the invention provides a threshold-limited iron-based Fischer-Tropsch synthesis catalyst, which comprises a carbon-based nano cage and iron-based nano particles, wherein the iron-based nano particles are limited in a cage cavity of the carbon-based nano cage.

Preferably, the carbon-based nanocages are carbon nanocages, nitrogen-doped carbon nanocages or sulfur-doped carbon nanocages; the size of a cage cavity of the carbon-based nano cage is 5-100 nm; the specific surface area of the carbon-based nano cage is 500-2500 m²(ii)/g; the pore volume of the carbon-based nano cage is 0.5-5 cm³/g。

Preferably, the average particle size of the iron-based nanoparticles is 1-30 nm, and the phase composition of the iron-based nanoparticles comprises ferroferric oxide.

Preferably, the loading amount of the iron-based nanoparticles is 1-60 wt.% based on the content of iron element.

Preferably, the threshold-limiting type iron-based Fischer-Tropsch synthesis catalyst further comprises a first auxiliary agent, and the first auxiliary agent is Na⁺Or K⁺And the loading amount of the first auxiliary agent is 0.5-5 wt.%.

Preferably, the threshold-limited iron-based Fischer-Tropsch synthesis catalyst further comprises a second auxiliary agent, the second auxiliary agent is sulfur, and the loading amount of the second auxiliary agent is 0.1-1 wt.%.

The invention also provides a preparation method of the threshold-limited type iron-based Fischer-Tropsch synthesis catalyst, which comprises the following steps:

(1) providing a carbon-based nanocage;

(2) mixing the carbon-based nano cage with the iron precursor solution under a vacuum condition, and then filtering and drying to obtain the carbon-based nano cage filled with the iron precursor;

(3) sequentially carrying out first roasting and passivation on the carbon-based nano cage filled with the iron precursor to obtain a threshold-limited iron-based Fischer-Tropsch synthesis catalyst primary product;

(4) taking the primary threshold-limited iron-based Fischer-Tropsch synthesis catalyst as a carbon-based nano cage, and repeating the steps (2) to (3) until the required iron-based nano particle filling amount is obtained, so as to obtain the threshold-limited iron-based Fischer-Tropsch synthesis catalyst;

when the threshold-limiting type iron-based Fischer-Tropsch synthesis catalyst contains the first auxiliary agent or contains the first auxiliary agent and the second auxiliary agent, the method further comprises the following steps:

carrying out heat treatment on the product obtained in the step (4), then mixing the product with an ethanol aqueous solution of sodium salt or potassium salt, and drying to obtain the threshold-limited iron-based Fischer-Tropsch synthesis catalyst added with the auxiliary agent precursor; the sodium salt or the potassium salt is at least one of nitrate, hydrochloride, acetate, citrate, formate, carbonate and sulfate;

and carrying out second roasting on the threshold-limited type iron-based Fischer-Tropsch synthesis catalyst added with the auxiliary agent precursor to obtain the threshold-limited type iron-based Fischer-Tropsch synthesis catalyst.

Preferably, the iron precursor in the iron precursor solution is at least one of ferric nitrate, ferrous nitrate, ferric sulfate, ferrous sulfate, ferric ammonium citrate, ferric acetate, ferric acetylacetonate, ferrocene, ferrous acetate, ferrous lactate, ferrous citrate, ferric chloride and ferrous chloride.

Preferably, the first calcination is carried out in H₂、N₂Or in an inert gas stream(ii) a The temperature of the first roasting is 300-600 ℃; the first roasting time is 0.5-6 h.

Preferably, the second calcination is performed in N₂Or in an inert gas stream; the temperature of the second roasting is 300-600 ℃, and the time of the second roasting is 0.5-6 h. .

The invention provides a threshold-limited iron-based Fischer-Tropsch synthesis catalyst, which comprises a carbon-based nano cage and iron-based nano particles, wherein the iron-based nano particles are limited in a cage cavity of the carbon-based nano cage. In the invention, the iron-based nanoparticles are used as active components, the carbon-based nanocages are used as carriers, the iron-based nanoparticles are confined in the cage cavities of the carbon-based nanocages, and the catalyst shows high catalytic activity, selectivity of a target product, strong carbon deposition resistance and sintering resistance in the reaction of catalyzing Fischer-Tropsch synthesis by utilizing the three-dimensional threshold limiting effect of the cage cavities of the carbon-based nanocages and the limitation of micropores of the cage walls on mass transfer of various molecules in the reaction. In addition, compared with the traditional iron-based Fischer-Tropsch synthesis catalyst, the distribution of the product obtained by using the threshold-limited iron-based Fischer-Tropsch synthesis catalyst provided by the invention is obviously deviated from the limitation of Anderson-Schulz-Flory theory, and the selectivity of the product can be effectively regulated and controlled by combining other conventional methods, for example, the selectivity of low-carbon olefin can be favorably improved under the high-temperature reaction condition, the selectivity of a gasoline component and the gasoline component (C) can be favorably improved under the low-temperature reaction condition₅～C₁₁) And lower olefins (C)₂～C₄) The selectivity can reach 59% and 64% respectively.

Drawings

FIG. 1 Transmission Electron micrograph of Fe @ CNC catalyst obtained in example 1;

FIG. 2 XRD spectrum of Fe @ CNC catalyst obtained in example 1;

FIG. 3 high-power transmission electron micrograph of Fe @ NCNC catalyst obtained in example 4;

FIG. 4 is a graph showing the change in particle size of iron nanoparticles before and after the reaction between the supported catalyst and the filled catalyst.

Detailed Description

In the present invention, the carbon-based nanocage is preferably a carbon nanocage (may be abbreviated as CNC), a nitrogen-doped carbon nanocage (may be abbreviated as NCNC), or a sulfur-doped carbon nanocage (may be abbreviated as SCNC); the size of a cage cavity of the carbon-based nano cage is 5-100 nm, preferably 10-30 nm, the cage cavity is of an irregular three-dimensional structure, and the size of the cage cavity refers to the longest length passing through the center of the three-dimensional structure; the specific surface area of the carbon-based nano cage is preferably 500-2500 m²(ii)/g, more preferably 800 to 1200m²(ii)/g; the pore volume of the carbon-based nano cage is preferably 0.5-5 cm³A concentration of 3 to 5cm³(ii)/g; pore channels preferably exist on the cage walls of the carbon-based nano cage, and the pore diameter of each pore channel is preferably 0.4-0.8 nm, and more preferably 0.6 nm; the content of nitrogen in the nitrogen-doped carbon nanocages is preferably 3-12 at%; the content of sulfur in the sulfur-doped carbon nanocage is preferably 1-5 at.%. In the invention, the proper specific surface area is beneficial to the dispersion of active components, and the carbon-based nano cage with too high specific surface area has too thin cage wall, thus being not beneficial to improving the threshold limiting effect; the carbon-based nano cage with too low specific surface area has too thick cage wall and too strong threshold limiting effect, thus being not beneficial to mass transfer of reaction; the larger pore volume is beneficial to the mass transfer in the reaction process.

In the embodiment of the present invention, the carbon-based nanocages are preferably prepared by the methods disclosed in chinese patents CN101284663A and CN102530922A, wherein the preparation method of SCNC is the same as that of CNC and NCNC, and only the carbon source is replaced by thiophene.

In the invention, the average particle size of the iron-based nanoparticles is preferably 1-30 nm, and more preferably 8-15 nm; the phase composition of the iron-based nanoparticles comprises ferroferric oxide.

In the invention, the loading amount of the iron-based nanoparticles (i.e. the content of the iron-based nanoparticles in the threshold-limited iron-based Fischer-Tropsch synthesis catalyst) is preferably 1 to 60 wt.%, and more preferably 30 to 50 wt.%, based on the content of iron element.

In the invention, the threshold-limiting type iron-based Fischer-Tropsch synthesis catalyst preferably further comprises a first auxiliary agent, wherein the first auxiliary agent is Na⁺Or K⁺The loading amount of the first auxiliary agent (namely the percentage of the first auxiliary agent in the total mass of the catalyst) is 0.5-5 wt.%; the first auxiliary agent is preferably loaded on the threshold-limited type iron-based Fischer-Tropsch synthesis catalyst in a salt form (namely sodium salt or potassium salt), and then is obtained by second roasting; the salt includes at least one of nitrate, hydrochloride, acetate, citrate, formate, and carbonate. In the invention, the first auxiliary agent has alkalinity, and can promote the dissociation and adsorption of CO, thereby being beneficial to improving the activity of the catalyst and the selectivity of olefin. The addition of the basic auxiliary agent can make the catalyst easier to deposit carbon, and the threshold-limiting type iron-based Fischer-Tropsch synthesis catalyst provided by the invention still has excellent stability when containing the basic auxiliary agent.

In the invention, the threshold-limited iron-based Fischer-Tropsch synthesis catalyst preferably further comprises a first auxiliary agent and a second auxiliary agent, wherein the second auxiliary agent is sulfur element, and the loading amount (namely the percentage of the second auxiliary agent in the total mass of the catalyst) of the second auxiliary agent is 0.1-1 wt.%; the sulfur element is preferably loaded on the threshold-limited iron-based Fischer-Tropsch synthesis catalyst in the form of sulfate and then is obtained through second roasting. In the invention, the second auxiliary agent can reduce the chain growth probability of the reaction, improve the selectivity of olefin and inhibit carbon deposition.

(1) providing a carbon-based nanocage;

carrying out heat treatment on the product obtained in the step (4), and then mixing the product with an ethanol aqueous solution of sodium salt or potassium salt to obtain a threshold-limited type iron-based Fischer-Tropsch synthesis catalyst added with an auxiliary agent precursor; the sodium salt or the potassium salt is at least one of nitrate, hydrochloride, acetate, citrate, formate, carbonate and sulfate;

The present invention first provides a carbon-based nanocage.

In the embodiment of the present invention, the carbon-based nanocages are preferably prepared by the methods disclosed in chinese patents CN101284663A and CN 102530922A.

After the carbon-based nano cage is obtained, the carbon-based nano cage and the iron precursor solution are mixed under the vacuum condition, and then the mixture is filtered and dried to obtain the carbon-based nano cage filled with the iron precursor.

In the present invention, the absolute pressure of the vacuum is preferably 0 to 100Pa, and more preferably 0 to 20 Pa. In the invention, the iron precursor solution can enter the cage cavity of the nanocage under the vacuum condition, and the vacuum condition is preferably obtained by firstly placing the carbon-based nanocage into a reactor and then vacuumizing the reactor.

In the invention, the iron precursor in the iron precursor solution is preferably at least one of ferric nitrate, ferrous nitrate, ferric sulfate, ferrous sulfate, ferric ammonium citrate, ferric acetate, ferric acetylacetonate, ferrocene, ferrous acetate, ferrous lactate, ferrous citrate, ferric trichloride and ferrous chloride; the concentration of the iron element in the iron precursor solution is preferably 0.05-2 mol/L, and more preferably 0.2-0.8 mol/L; the solvent of the iron precursor solution is preferably an ethanol water solution, and the volume percentage content of ethanol in the ethanol water solution is preferably 5-40%, and more preferably 15-25%. In the invention, the ethanol aqueous solution is used as a solvent of the iron precursor solution, and the ethanol can reduce the surface tension of the solution and promote the solution of the metal compound to be uniformly dispersed on the surface of the carbon-based nano cage, in the cage and in other various types of holes of the carbon-based nano cage.

In the invention, the dosage ratio of the carbon-based nano cage to the iron precursor solution is preferably 1 g/10-100 mL, and more preferably 1 g/25-50 mL. In the invention, the dosage of the iron precursor solution is properly increased, which is beneficial to reducing the viscosity of the liquid after the carbon-based nano cage and the iron precursor solution are mixed.

In the invention, the mixing is preferably stirring mixing, the rotating speed of the stirring is preferably 50-200 r/min, and the stirring time is preferably 0.5-24 h, and more preferably 10-24 h.

In the present invention, the drying is preferably air-blast drying; the drying temperature is preferably 50-120 ℃, and more preferably 80-100 ℃; the drying time is preferably 1-24 h, more preferably 5-20 h, and most preferably 10-15 h; in the drying process, the solvent is gradually volatilized, the iron precursor is gradually nucleated and crystallized in the carbon-based nanocages and on the surfaces of the carbon-based nanocages to form iron precursor particles, and then the iron precursor particles are decomposed into iron-based nanoparticles through first roasting.

After drying, the dried product is preferably ground, washed and then dried again in sequence to obtain the carbon-based nano cage filled with the iron precursor. In the invention, the product obtained by drying is ground and washed, so that the iron precursor outside the carbon-based nano cage can be removed, and the iron precursor filled into the cage cannot be washed away because of the protection of the limiting threshold action of the cage wall.

The grinding mode is not particularly limited, and a powdery product can be obtained.

In the invention, the washing solution for washing is preferably deionized water, and the specific mode of washing is not particularly limited in the invention, and a conventional washing mode, such as soaking washing, can be adopted.

In the present invention, the manner of drying again is the same as the manner of drying, and is not described herein again.

After the carbon-based nano cage filled with the iron precursor is obtained, the carbon-based nano cage filled with the iron precursor in the cage is subjected to first roasting and passivation in sequence to obtain a threshold-limited iron-based Fischer-Tropsch synthesis catalyst primary product.

In the present invention, the first calcination is preferably in H₂、N₂Or in an inert gas stream; the first roasting temperature is preferably 300-600 ℃, and more preferably 380-500 ℃; the first roasting time is preferably 0.5-6 h, and more preferably 1-3 h; the time of the first calcination is preferably from the time of raising the temperature to the temperature required for the first calcination; the heating rate of the first roasting to the temperature required by the first roasting is not particularly limited, and a conventional heating rate is adopted, and in the embodiment of the invention, the heating rate is preferably 1-20 ℃/min. In the present invention, when the iron precursor used is ferric chloride or ferrous chloride, the first calcination is carried out in H₂The method is carried out in air flow, and an iron precursor is converted into elemental iron; when the used iron precursor is ferric nitrate, ferrous nitrate, ferric sulfate and ferrous sulfate, the first roasting is carried out on N₂Or in inert gas flow, the iron precursor is converted into ferroferric oxide, and part of the ferroferric oxide can generate simple substance iron or iron carbide; when the used iron precursor is ferric ammonium citrate, ferric acetate, ferric acetylacetonate, ferrocene, ferrous acetate, ferrous lactate or ferrous citrate, the first roasting is carried out in N₂Or in an inert gas stream, the iron precursor is converted to iron carbide.

In the invention, the passivation is preferably carried out in a flow of an oxygen-containing inert gas, the volume content of oxygen in the flow of the oxygen-containing inert gas is preferably 0.5-2%, more preferably 1-1.5%, and the flow rate of the flow of the oxygen-containing inert gas is preferably 50-500 mL/min; the passivation time is preferably 0.5-2 h, and more preferably 1-1.5 h; the passivation temperature is preferably 0-40 ℃, and more preferably room temperature (namely 20-30 ℃). In the invention, after the first passivation is finished, the equipment temperature is preferably reduced to the temperature required by passivation, and then oxygen-containing inert gas is introduced for passivation; the temperature reduction rate of the temperature required for the passivation is not particularly limited, and in the embodiment of the invention, the temperature reduction is preferably natural temperature reduction. In the present invention, elemental iron or iron carbide particles in the first calcined product are oxidized to ferroferric oxide during the passivation process. The passivation is carried out under the condition of lower oxygen content, so that the reaction rate of converting simple substance iron or iron carbide into ferroferric oxide can be reduced, the reaction heat release is reduced, and the combustion of the carbon-based nano cage carrier is prevented.

After the threshold-limited iron-based Fischer-Tropsch synthesis catalyst primary product is obtained, the threshold-limited iron-based Fischer-Tropsch synthesis catalyst primary product is used as a carbon-based nano cage, and the steps are repeated until the required iron-based nano particle filling amount is obtained, so that the threshold-limited iron-based Fischer-Tropsch synthesis catalyst is obtained. In the invention, when the filling amount of the iron-based nanoparticles in the primary threshold-limited iron-based Fischer-Tropsch synthesis catalyst product meets the requirement, the primary threshold-limited iron-based Fischer-Tropsch synthesis catalyst product is the threshold-limited iron-based Fischer-Tropsch synthesis catalyst.

carrying out heat treatment on the threshold-limiting type iron-based Fischer-Tropsch synthesis catalyst obtained in the previous step, then mixing the catalyst with an ethanol aqueous solution of sodium salt or potassium salt, and drying to obtain the threshold-limiting type iron-based Fischer-Tropsch synthesis catalyst added with an auxiliary agent precursor; the sodium salt or the potassium salt is at least one of nitrate, hydrochloride, acetate, citrate, formate, carbonate and sulfate; when the first aid is contained alone, the sodium salt or the potassium salt is preferably at least one of nitrate, acetate, citrate and formate, and when the first aid and the second aid are contained together, the sodium salt or the potassium salt preferably includes sulfate.

And carrying out second roasting on the threshold-limited iron-based Fischer-Tropsch synthesis catalyst added with the auxiliary agent precursor to obtain the threshold-limited iron-based Fischer-Tropsch synthesis catalyst containing the auxiliary agent.

The threshold-limiting type iron-based Fischer-Tropsch synthesis catalyst obtained in the previous step is subjected to heat treatment, then is mixed with an ethanol water solution of sodium salt or potassium salt, and is dried to obtain the threshold-limiting type iron-based Fischer-Tropsch synthesis catalyst added with the auxiliary agent precursor.

In the invention, the heat treatment is preferably carried out under a vacuum condition, and the vacuum degree of the heat treatment is preferably 0.1-1000 Pa; the temperature is preferably 200-250 ℃, and the time is preferably 2-2.5 h. In the invention, after the threshold-limited iron-based Fischer-Tropsch synthesis catalyst is subjected to heat treatment, the threshold-limited iron-based Fischer-Tropsch synthesis catalyst is mixed with the ethanol water solution of the auxiliary agent, so that other impurities adsorbed on the surface of the metal oxide or the elemental iron can be removed, and after the ethanol solution of the auxiliary agent is added, the interaction between the auxiliary agent and the metal oxide/elemental iron can be enhanced, and the catalytic performance can be further improved.

In the invention, the concentration of the sodium salt or the potassium salt in the ethanol water solution of the sodium salt or the potassium salt is preferably 0.005-0.1 mol/L, and more preferably 0.005-0.06 mol/L; the volume percentage content of ethanol in the ethanol water solution of the sodium salt or the potassium salt is preferably 10-50%, and more preferably 30-40%. In the invention, the ethanol aqueous solution is a solvent of sodium salt or potassium salt, and the ethanol can reduce the surface tension of the solution and promote the solution of the sodium salt or the potassium salt to be uniformly dispersed on the surface of the carrier and in various pores of the carrier.

In the present invention, the mixing of the heat-treated fischer-tropsch synthesis catalyst with an aqueous ethanol solution of sodium or potassium salt is preferably a mechanical stirring mixing; the mixing speed is preferably 50-200 r/min; the mixing time is preferably 12-24 h.

In the invention, the drying temperature is preferably 80-120 ℃, and more preferably 100 ℃; the drying time is preferably 1-3 h, and more preferably 2 h; the drying is preferably air-blast drying.

After the threshold-limited iron-based Fischer-Tropsch synthesis catalyst added with the auxiliary agent precursor is obtained, the threshold-limited iron-based Fischer-Tropsch synthesis catalyst added with the auxiliary agent precursor is subjected to second roasting to obtain the threshold-limited iron-based Fischer-Tropsch synthesis catalyst containing the auxiliary agent.

In the present invention, the second calcination is preferably in N₂Or in an inert gas stream; the second roasting temperature is preferably 300-600 ℃, and more preferably 380-500 ℃; the second roasting time is preferably 0.5-6 h, and more preferably 2-4 h; the time of the second roasting is preferably started when the temperature is raised to the roasting required temperature; the heating rate of the temperature to be heated to the temperature required by roasting is not particularly limited, and a conventional heating rate is adopted, and in the embodiment of the invention, the heating rate is preferably 1-20 ℃/min. In the present invention, the second firing can decompose the promoter precursor, improving the interaction of the promoter with the active component.

After the second roasting is finished, the second roasted product is preferably cooled to room temperature, and the threshold-limited type iron-based Fischer-Tropsch synthesis catalyst loaded with the auxiliary agent is obtained. The cooling rate is not particularly limited in the present invention, and may be any cooling rate, and in the embodiment of the present invention, the cooling is preferably natural cooling.

The threshold-limiting type iron-based Fischer-Tropsch synthesis catalyst and the preparation method thereof provided by the present invention will be described in detail with reference to the following examples, which should not be construed as limiting the scope of the present invention.

Example 1

Weighing 4g of basic magnesium carbonate, adding the basic magnesium carbonate into a vertically placed quartz reaction tube, uniformly spreading, vacuumizing the reaction tube by using a mechanical pump, introducing argon gas serving as carrier gas (100sccm), heating to 800 ℃ at the speed of 10 ℃/min, inputting benzene into the reaction tube by using a constant flow pump at the flow rate of 0.020mL/min, reacting for 30min, cooling to room temperature to obtain black powder in the quartz reaction tube, soaking the obtained black powder in 1mol/L hydrochloric acid solution for 30min, filtering, washing with deionized water to be neutral, and drying to obtain 0.2g of carbon nanocages (namely CNC) with the specific surface area of 1700m²G, pore volume of 4.2cm³(ii)/g; the size range of the cage cavity is 10-30 nm, and sufficient CNC is obtained by repeating the steps;

weighing 20.2g of ferric nitrate nonahydrate, dissolving with deionized water, and preparing into 50mL of solution with the concentration of 1mol/L for later use;

weighing 0.5g of CNC, adding the CNC into a two-neck flask, sealing one port of the two-neck flask by using a rubber flanging plug, connecting the other port of the two-neck flask to a vacuum pump, vacuumizing the two-neck flask until the pressure is below 20Pa, keeping the pressure for 0.5h, injecting ferric nitrate solution into the two-neck flask from the flanging plug by using an injector, stirring for 24h at room temperature, filtering, and drying for 10h at 100 ℃; grinding the dried sample into powder, adding 50mL of deionized water, stirring for 0.5h, washing, filtering, drying the solid obtained by filtering in a forced air drying oven at 100 ℃ for 10h, placing the sample in a porcelain boat, placing the porcelain boat in a tubular furnace, heating to 400 ℃ at the speed of 10 ℃/min under the protection of 200sccm Ar gas flow, and roasting for 4 h; after completion of the calcination, the sample was cooled to room temperature, and oxygen was introduced into the sample to produce 1% by volume of O₂And (3) keeping the flow rate of the/Ar mixed gas at 50mL/min, and taking out a sample after 1h to obtain the Fe @ CNC catalyst (namely the threshold-limited Fischer-Tropsch synthesis catalyst).

The filling amount of iron in the obtained Fe @ CNC catalyst was determined to be 37 wt.% by using a thermogravimetric analyzer under an oxygen-containing gas flow at a temperature rise rate of 10 ℃/min, the average particle size of the iron-based nanoparticles was counted to be 10nm by a transmission electron microscope photograph, the obtained transmission electron microscope photograph is shown in fig. 1, as shown in the figure, the shape and position of the iron nanoparticles change with the morphology and structure of the carbon nanocage walls, indicating that the iron nanoparticles are in the carbon nanocage.

Fig. 2 is an XRD spectrum of Fe @ CNC catalyst showing that the main phase of the Fe nanoparticles is ferroferric oxide.

100mg of the Fe @ CNC catalyst obtained in the example was placed in a fixed bed Fischer-Tropsch synthesis reactor at 380 ℃ and 10mL/min of H₂Reducing in situ for 4H under the air flow, switching to synthesis gas (volume ratio H) after the temperature is reduced to 300 DEG C₂The space velocity of the synthetic gas is 1500 mL/(h.g), then the reaction is carried out for 24h under the conditions of 300 ℃ and 20bar, the CO conversion rate is 76 percent, and the low-carbon olefin is reacted

Selectivity of 9% and methane selectivity of 12%, C₅₊The selectivity was 36%.

Example 2

CNC was prepared as in example 1;

weighing 4.04g of ferric nitrate nonahydrate, dissolving with deionized water, and preparing into 50mL of 0.2mol/L solution for later use;

weighing 0.5g of CNC, adding the CNC into a two-neck flask, sealing one port of the two-neck flask by using a rubber flanging plug, connecting the other port of the two-neck flask to a vacuum pump, vacuumizing the two-neck flask until the pressure is below 20Pa, keeping the pressure for 0.5h, injecting ferric nitrate solution into the two-neck flask from the flanging plug by using an injector, stirring for 12h at room temperature, filtering, and drying for 10h at 100 ℃; grinding the dried sample into powder, adding 50mL of deionized water, stirring for 0.5h, washing, filtering, drying the solid obtained by filtering in a forced air drying oven at 100 ℃ for 10h, placing the sample in a porcelain boat, placing the porcelain boat in a tubular furnace, heating to 400 ℃ at the speed of 10 ℃/min under the protection of 100sccm Ar gas flow, and roasting for 4 h; after completion of the calcination, the sample was cooled to room temperature, and oxygen was introduced into the sample to produce 1% by volume of O₂And (3) keeping the flow rate of the/Ar mixed gas at 50mL/min, and taking out a sample after 1h to obtain the Fe @ CNC catalyst (namely the threshold-limited Fischer-Tropsch synthesis catalyst).

The iron loading in the resulting Fe @ CNC catalyst was determined to be 15 wt.% using a thermogravimetric analyzer at a temperature rise rate of 10 ℃/min under an oxygen-containing gas flow, and the average particle size of the iron-based nanoparticles was counted to be 6nm by transmission electron microscope photographs.

100mg of the Fe @ CNC catalyst obtained in the example was placed in a fixed bed Fischer-Tropsch synthesis reactor at 380 ℃ and 10mL/min of H₂Reducing in situ for 3H under the air flow, switching to synthesis gas (volume ratio H) after the temperature is reduced to 300 DEG C₂1/CO), the space velocity of the synthetic gas is 1500 mL/(h.g), then the reaction is carried out for 24h under the conditions of 300 ℃ and 20bar, the conversion rate of CO is 45 percent, the selectivity of the low-carbon olefin is 5 percent, the selectivity of the methane is 22 percent, and C₅₊The selectivity was 25%.

Example 3

Weighing 0.5g of the Fe @ CNC catalyst prepared in the example 2, adding the weighed material into a Teflon beaker, putting the beaker into a vacuum drying oven, carrying out heat treatment at the temperature of 200 ℃ for 2h under the high vacuum condition of less than 10Pa, and naturally cooling to room temperature; weighing 0.0258g of anhydrous potassium nitrate, dissolving the anhydrous potassium nitrate in 10mL of 40% ethanol water solution, pouring the anhydrous potassium nitrate into a Teflon beaker, violently stirring the mixture for 5 hours at the rotating speed of 250r/min, and then placing the beaker in a forced air drying oven to dry the beaker for 12 hours at the temperature of 100 ℃; and (3) heating the dried product to 350 ℃ at the heating rate of 10 ℃/min under the protection of Ar gas flow of 100sccm, roasting for 2h, and naturally cooling to room temperature to obtain the KFe @ CNC catalyst (namely the threshold-limited Fischer-Tropsch synthesis catalyst containing the auxiliary agent potassium).

100mg of the KFe @ CNC catalyst obtained in this example was placed in a fixed bed Fischer-Tropsch synthesis reactor at 380 ℃ and 10mL/min H₂Reducing in situ for 2H under the air flow, switching to synthesis gas (volume ratio H) after the temperature is reduced to 300 DEG C₂1) and the space velocity of the synthesis gas is 6000 mL/(h.g), then the reaction is carried out for 24 hours under the conditions of 300 ℃ and 20bar, the conversion rate of CO is 76 percent, the selectivity of the low-carbon olefin is 18 percent, the selectivity of the methane is 5 percent, and C is₅-C₁₁Selectivity 57%, C₁₂₊The selectivity was 15%.

Reacting for 24 hours at 340 ℃ and 10bar under the condition that the space velocity of the synthesis gas is 12000 mL/(h.g), the conversion rate of CO is 57 percent, the selectivity of the low-carbon olefin is 51 percent, the selectivity of the methane is 7 percent, and C₅₊The selectivity was 32%.

Example 4

Weighing 4g of basic magnesium carbonate, adding the basic magnesium carbonate into a vertically placed quartz reaction tube, uniformly spreading, vacuumizing the reaction tube by using a mechanical pump, introducing argon gas serving as carrier gas (100sccm), heating to 800 ℃ at the speed of 10 ℃/min, inputting pyridine into the reaction tube by using a constant flow pump at the flow rate of 0.020mL/min, reacting for 20min, cooling to room temperature to obtain black powder in the reaction tube, soaking the obtained black powder in 1mol/L hydrochloric acid solution for 30min, filtering, washing with deionized water to be neutral, and drying to obtain 0.2g of carbon nanocage NCNC with the specific surface area of about 1800m²Per g, pore volume of 4.8cm³(ii)/g; the size of the cage cavity is 10-30 nm, and the nitrogen content is 10 at.%. Repeating the above steps to obtain a sufficient amount of NCNC;

0.5g of NCNC was weighed and added to each of the two portsIn the flask, one mouth of the two-mouth flask is sealed by a rubber flanging plug, the other mouth is connected with a vacuum pump, the two-mouth flask is vacuumized until the pressure is below 20Pa and kept for 0.5h, then an injector is used for injecting ferric nitrate solution into the two-mouth flask from the flanging plug, the mixture is stirred for 5h at room temperature, filtered and dried for 10h at 100 ℃; grinding the dried sample into powder, adding 50mL deionized water, stirring for 0.5h, washing, filtering, drying the solid in a forced air drying oven at 100 deg.C for 10h, placing the sample in a porcelain boat, placing in a tubular furnace, and drying at 100sccm N₂Under the protection of airflow, heating to 400 ℃ at the speed of 10 ℃/min, and roasting for 4 h; after completion of the calcination, the sample was cooled to room temperature, and oxygen was introduced into the sample to produce 1% by volume of O₂And (3) keeping the flow rate of the/Ar mixed gas at 50mL/min, and taking out a sample after 1h to obtain the Fe @ NCNC catalyst (namely the threshold-limited Fischer-Tropsch synthesis catalyst).

The loading of iron in the resulting Fe @ NCNC catalyst was measured to be 38 wt.% using a thermogravimetric analyzer under an oxygen-containing gas flow at a temperature increase rate of 10 ℃/min, and the average particle size of the iron-based nanoparticles was counted to be 10nm by transmission electron microscope photographs, which are shown in fig. 3, showing that the iron nanoparticles were indeed loaded into the cavities of the nitrogen-doped carbon nanocages.

100mg of the Fe @ NCNC catalyst obtained in the example was placed in a Fischer-Tropsch synthesis reactor at 380 ℃ and 10mL/min of H₂Reducing in situ for 4H under the air flow, switching to synthesis gas (volume ratio H) after the temperature is reduced to 300 DEG C₂1 percent of synthetic gas, the space velocity of the synthetic gas is 3000 mL/(h.g), the reaction is carried out for 24 hours under the conditions of 300 ℃ and 20bar, the conversion rate of CO is 71 percent, the selectivity of low-carbon olefin is 19 percent, the selectivity of methane is 9 percent, and C₅₊The selectivity was 46%.

Example 5

Weighing 0.5g of the Fe @ NCNC catalyst prepared in the example 4, adding the Fe @ NCNC catalyst into a Teflon beaker, putting the beaker into a vacuum drying oven, carrying out heat treatment at 200 ℃ for 2h under the high vacuum condition of less than 10Pa, and then cooling to room temperature; weighing 0.0258g of anhydrous potassium nitrate, dissolving the anhydrous potassium nitrate in 10mL of 40% ethanol water solution, pouring the anhydrous potassium nitrate into a Teflon beaker, violently stirring the mixture for 0.5h at the rotating speed of 250r/min, and then placing the beaker in a forced air drying oven to dry the beaker for 12h at the temperature of 100 ℃; and (3) heating the dried product to 350 ℃ at the heating rate of 10 ℃/min under the protection of Ar gas flow of 100sccm, roasting for 2h, and naturally cooling to room temperature to obtain the KFe @ NCNC catalyst (namely the threshold-limited Fischer-Tropsch synthesis catalyst containing the potassium additive).

100mg of KFe @ NCNC catalyst obtained in this example was placed in a Fischer-Tropsch synthesis reactor at 350 ℃ and 10mL/min H₂Reducing in situ for 3H under the air flow, switching to synthesis gas (volume ratio H) after the temperature is reduced to 300 DEG C₂1/CO), the space velocity of the synthetic gas is 6000 mL/(h.g), then the reaction is carried out for 24 hours under the conditions of 300 ℃ and 20bar, the conversion rate of CO is 86 percent, the selectivity of the low-carbon olefin is 21 percent, the selectivity of the methane is 4 percent, and C is obtained₅-C₁₁Selectivity 59%, C₁₂₊The selectivity was 12%.

Reacting for 24 hours at 340 ℃ and 10bar under the condition that the space velocity of the synthesis gas is 12000 mL/(h.g), the conversion rate of CO is 63 percent, the selectivity of the low-carbon olefin is 59 percent, the selectivity of the methane is 4 percent, and C₅₊The selectivity was 28%.

Example 6

Weighing 0.5g of the Fe @ NCNC catalyst obtained in the example 4, adding the Fe @ NCNC catalyst into a Teflon beaker, putting the beaker into a vacuum drying oven, carrying out heat treatment at 200 ℃ for 2h under the high vacuum condition of less than 10Pa, and then cooling to room temperature; weighing 0.0067g of anhydrous sodium sulfate and 0.0290g of sodium nitrate, dissolving in 10mL of 40% ethanol water solution, pouring into a Teflon beaker, violently stirring at the rotation speed of 250r/min for 0.5h at room temperature, and then placing in a forced air drying oven for drying at 100 ℃ for 10 h; the dried product was at 100sccm N₂Under the protection of airflow, heating to 350 ℃ at a heating rate of 10 ℃/min, roasting for 2h, and naturally cooling to room temperature to obtain the NaSFe @ NCNC catalyst.

100mg of the NaSFe @ CNC catalyst obtained in this example was placed in a Fischer-Tropsch synthesis reactor at 350 ℃ and 10mL/min H₂Reducing in situ for 2H under the air flow, switching to synthesis gas (volume ratio H) after the temperature is reduced to 340 DEG C₂1) and the space velocity of the synthesis gas is 12000 mL/(h.g), then the reaction is carried out for 24h under the conditions of 340 ℃ and 10bar, the CO conversion rate is 71 percent, and the selectivity of the low-carbon olefin is 64% methane selectivity 3%, C₅₊The selectivity was 25%.

Example 7

Weighing 4g of basic magnesium carbonate, adding the basic magnesium carbonate into a vertically placed quartz reaction tube, uniformly spreading, vacuumizing the reaction tube by using a mechanical pump, introducing argon as carrier gas (100sccm), heating to 800 ℃ at the speed of 10 ℃/min, inputting thiophene into the reaction tube by using a constant flow pump, reacting for 30min, and cooling to room temperature to obtain black powder; soaking the obtained black powder in 1mol/L hydrochloric acid solution for 30min, filtering, washing with deionized water to neutrality, and oven drying to obtain about 0.2g carbon nanocage SCNC (sulfur-doped carbon nanocage) with specific surface area of about 1500m²G, pore volume of 3.9cm³(ii)/g, the cage cavity size is 10-30 nm, and the sulfur content is 3 at.%; repeating the steps to obtain enough SCNC;

weighing 20.2g of ferric nitrate nonahydrate, dissolving with deionized water, and preparing into 50mL of solution with the solubility of 1.0mol/L for later use;

weighing 0.5g of SCNC with the sulfur content of 3 at.%, adding the SCNC into a two-neck flask, sealing one port of the two-neck flask by using a rubber flanging plug, connecting the other port of the two-neck flask to a vacuum pump, vacuumizing the two-neck flask until the pressure is below 20Pa, keeping the pressure for 0.5h, injecting a ferric nitrate solution into the two-neck flask from the flanging plug by using an injector, stirring for 10h at room temperature, filtering, and drying for 10h at 100 ℃; grinding the dried sample into powder, adding 50mL of deionized water, stirring for 0.5h, washing, filtering, drying the solid obtained by filtering in a forced air drying oven at 100 ℃ for 10h, placing the sample in a porcelain boat, placing the porcelain boat in a tubular furnace, heating to 400 ℃ at the speed of 10 ℃/min under the protection of 100sccm Ar gas flow, and roasting for 4 h; after completion of the calcination, the sample was cooled to room temperature, and oxygen was introduced into the sample to produce 1% by volume of O₂And (3) keeping the flow rate of the/Ar mixed gas at 50mL/min, and taking out a sample after 1h to obtain the Fe @ SCNC catalyst (namely the threshold-limited Fischer-Tropsch synthesis catalyst).

The loading of iron in the resulting Fe @ SCNC catalyst was determined to be 34 wt.% using a thermogravimetric analyzer, and the average particle size of the iron-based nanoparticles was found to be 9nm by transmission electron microscopy photographs.

100mg of the Fe @ SCNC catalyst obtained in the example was placed in a Fischer-Tropsch synthesis reactor at 350 ℃ and 10mL/min of H₂Reducing in situ for 3H under the air flow, switching to synthesis gas (volume ratio H) after the temperature is reduced to 340 DEG C₂1/CO), the space velocity of the synthetic gas is 1500 mL/(h.g), then the reaction is carried out for 24h under the conditions of 340 ℃ and 10bar, the CO conversion rate is 43 percent, the selectivity of the low-carbon olefin is 19 percent, the selectivity of the methane is 21 percent, and C₅₊The selectivity was 19%.

Example 8

Weighing 0.5g of the Fe @ SCNC catalyst obtained in the example 7, adding the Fe @ SCNC catalyst into a Teflon beaker, putting the beaker into a vacuum drying oven, carrying out heat treatment at 200 ℃ for 2h under the high vacuum condition of less than 10Pa, and then cooling to room temperature; weighing 0.0258g of anhydrous potassium nitrate, dissolving the anhydrous potassium nitrate in 10mL of 40% ethanol water solution, pouring the anhydrous potassium nitrate into a Teflon beaker, violently stirring the mixture for 0.5h at the rotating speed of 250r/min, and then placing the beaker in a forced air drying oven to dry the beaker for 12h at the temperature of 100 ℃; and (3) heating the dried product to 350 ℃ at the heating rate of 10 ℃/min under the protection of Ar gas flow of 100sccm, roasting for 2h, and naturally cooling to room temperature to obtain the KFe @ SCNC catalyst.

100mg of KFe @ SCNC catalyst from this example was placed in a Fischer-Tropsch synthesis reactor at 350 ℃ and 10mL/min H₂Reducing in situ for 3H under the air flow, switching to synthesis gas (volume ratio H) after the temperature is reduced to 340 DEG C₂1/CO), the space velocity of the synthetic gas is 1500 mL/(h.g), then the reaction is carried out for 24h under the conditions of 340 ℃ and 10bar, the conversion rate of CO is 74 percent, the selectivity of the low-carbon olefin is 62 percent, the selectivity of the methane is 5 percent, and C₁₂₊The selectivity was 21%.

Example 9

NCNC was prepared according to the method of example 4;

weighing 0.5g of NCNC, adding the NCNC into a two-mouth flask, sealing one mouth of the two-mouth flask by using a rubber flanging plug, connecting the other mouth of the two-mouth flask to a vacuum pump, vacuumizing the two-mouth flask until the pressure is below 20Pa, keeping the pressure for 0.5h, and injecting the ferric nitrate solution into the two-mouth flask from the flanging plug by using an injectorStirring at room temperature for 5h in a bottle, filtering, and drying at 100 deg.C for 10 h; grinding the dried sample into powder, adding 50mL deionized water, stirring for 0.5h, washing, filtering, drying the solid in a forced air drying oven at 100 deg.C for 10h, placing the sample in a porcelain boat, placing in a tubular furnace, and drying at 100sccm N₂Under the protection of airflow, heating to 400 ℃ at the speed of 10 ℃/min, and roasting for 4 h; after completion of the calcination, the sample was cooled to room temperature, and oxygen was introduced into the sample to produce 1% by volume of O₂Keeping the flow rate of the mixed gas/Ar at 50mL/min, and taking out a sample after 1h to obtain a primary product of the Fe @ NCNC catalyst; then repeating the above method for refilling to obtain the Fe @ NCNC catalyst;

weighing 0.5g of the Fe @ NCNC catalyst, adding the Fe @ NCNC catalyst into a Teflon beaker, putting the beaker into a vacuum drying oven, carrying out heat treatment for 2h at 200 ℃ under the high vacuum condition of less than 10Pa, and cooling to room temperature; weighing 0.0258g of anhydrous potassium nitrate, dissolving the anhydrous potassium nitrate in 10mL of 40% ethanol water solution, pouring the solution into a Teflon beaker, violently stirring the solution for 0.5h, and then placing the beaker in a forced air drying oven to dry the beaker for 12h at 100 ℃; and (3) heating the dried product to 350 ℃ at the heating rate of 10 ℃/min under the protection of 100sccm Ar gas flow, roasting for 2h, and naturally cooling to room temperature to obtain the KFe @ NCNC catalyst.

The loading of iron in the resulting KFe @ NCNC catalyst was determined to be 54 wt.% using a thermogravimetric analyzer, and the average particle size of the iron-based nanoparticles was counted as 12nm by transmission electron microscopy photographs.

100mg of KFe @ NCNC catalyst obtained in this example was placed in a Fischer-Tropsch synthesis reactor at 350 ℃ and 10mL/min H₂Reducing in situ for 4H under the air flow, switching to synthesis gas (volume ratio H) after the temperature is reduced to 300 DEG C₂1) and the space velocity of the synthesis gas is 6000 mL/(h.g), then the reaction is carried out for 24 hours under the conditions of 300 ℃ and 20bar, the CO conversion rate is 91 percent, the selectivity of the low-carbon olefin is 19 percent, the selectivity of the methane is 3 percent, and C is₅-C₁₁Selectivity 56%, C₁₂₊The selectivity was 16%.

Reacting for 24 hours at 340 ℃ and 10bar under the condition that the space velocity of the synthesis gas is 12000 mL/(h.g), the CO conversion rate is 67 percent, and the selectivity of the low-carbon olefin is 60 percentSelectivity to methane of 4%, C₅₊The selectivity was 31%.

Comparative example 1

The preparation method of the supported Fischer-Tropsch synthesis catalyst by adopting a common impregnation method comprises the following specific steps:

NCNC was prepared using the method of example 4;

preparing 50mL of 0.5mol/L ferric nitrate solution; soaking 0.5g of NCNC in 12.8mL of ferric nitrate solution, stirring at the rotating speed of 160r/min for 0.5h, soaking at room temperature for 24h, and drying the soaked product in a drying oven at 100 ℃ for 10 h; grinding the dried powder, placing the ground powder into a porcelain boat, placing the porcelain boat into a tubular furnace, heating the porcelain boat to 400 ℃ at the speed of 10 ℃/min under the protection of Ar gas flow of 200sccm, and roasting the porcelain boat for 4 hours; after completion of the calcination, the sample was cooled to room temperature, and oxygen was introduced into the sample to produce 1% by volume of O₂And maintaining the flow rate of the/Ar mixed gas at 50mL/min, and taking out a sample after 1h to obtain the Fe/NCNC catalyst.

The content of iron in the obtained Fe/NCNC catalyst was determined to be 36 wt.% using a thermogravimetric analyzer, and the average particle diameter of the iron-based nanoparticles was counted to be 9nm by transmission electron microscope photographs.

Weighing 0.5g of Fe/NCNC catalyst, adding the Fe/NCNC catalyst into a Teflon beaker, putting the beaker into a vacuum drying oven, carrying out heat treatment for 2h at 200 ℃ under the high vacuum condition of less than 10Pa, and then cooling to room temperature; weighing 0.0258g of anhydrous potassium nitrate, dissolving the anhydrous potassium nitrate in 10mL of 40% ethanol water solution, pouring the anhydrous potassium nitrate into a Teflon beaker, violently stirring the mixture for 0.5h at the rotating speed of 250r/min, and then placing the beaker in a forced air drying oven to dry the beaker for 12h at the temperature of 100 ℃; and (3) heating the dried product to 350 ℃ at the heating rate of 10 ℃/min under the protection of Ar gas flow of 100sccm, roasting for 2h, and naturally cooling to room temperature to obtain the KFe/NCNC catalyst (namely the supported Fischer-Tropsch synthesis catalyst containing the auxiliary agent potassium).

100mg of the KFe/NCNC catalyst obtained in this example was placed in a Fischer-Tropsch synthesis reactor at 350 ℃ and 10mL/min H₂Reducing in situ for 4H under the air flow, switching to synthesis gas (volume ratio H) after the temperature is reduced to 300 DEG C₂1/CO), the space velocity of the synthetic gas is 3000 mL/(h.g), and then the reaction is carried out for 24h under the conditions of 300 ℃ and 20bar, and the CO is converted intoConversion rate of 54%, selectivity of low-carbon olefin of 19%, selectivity of methane of 13%, C₅-C₁₁Selectivity 37%, C₁₂₊The selectivity was 13%.

Reacting for 24 hours at 340 ℃ and 10bar under the condition that the space velocity of the synthesis gas is 12000 mL/(h.g), the conversion rate of CO is 43 percent, the selectivity of the low-carbon olefin is 25 percent, the selectivity of the methane is 15 percent, and C₅₊The selectivity was 34%.

From the above test results, when the threshold type Fischer-Tropsch synthesis catalyst KFe @ NCNC catalyst obtained in example 5 is used, the CO conversion rate of example 5 reaches 86% when the reaction is carried out at 300 ℃ and 20bar, and the low-carbon olefin (C)₂～C₄) Selectivity of (2) is 21%, selectivity of methane is 4%, C₅-C₁₁Selectivity 59%, C₁₂₊The selectivity is 12 percent, the conversion rate of CO is 63 percent, the selectivity of low-carbon olefin is 59 percent, the selectivity of methane is 4 percent, and C is C when the reaction is carried out under the conditions of 340 ℃ and 10bar₅₊The selectivity is 28 percent, the CO conversion rate of the supported Fischer-Tropsch synthesis catalyst obtained in the comparative example 1 is obviously reduced, and the supported Fischer-Tropsch synthesis catalyst is used for treating low-carbon olefin and gasoline component (C)₅-C₁₁) The selectivity of (a) also decreases.

The particle size change of the iron nanoparticles after the supported catalyst (comparative example 1) and the filled catalyst (example 5) were tested after continuous use for 40h, as shown in fig. 4, where a is the particle size distribution of the iron-based nanoparticles before the reaction of the supported catalyst, c is the particle size distribution of the iron-based nanoparticles after the reaction of the supported catalyst, b is the particle size distribution of the iron-based nanoparticles before the reaction of the filled catalyst, and d is the particle size distribution of the iron-based nanoparticles after the reaction of the filled catalyst. As can be seen from FIG. 4, the average particle size of the iron-based nanoparticles before the reaction of the supported catalyst was 9nm, and the average particle size of the iron-based nanoparticles after the reaction was 20nm, while the average particle size of the iron-based nanoparticles before the reaction of the filled catalyst was 10nm, and the average particle size of the iron-based nanoparticles after the reaction was 12nm, indicating that the filled catalyst had better sintering resistance.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims

1. A threshold-limited iron-based Fischer-Tropsch synthesis catalyst is characterized by comprising a carbon-based nanocage and iron-based nanoparticles, wherein the iron-based nanoparticles are limited in a cage cavity of the carbon-based nanocage.

2. The threshold-limited iron-based fischer-tropsch synthesis catalyst of claim 1, wherein the carbon-based nanocages are carbon nanocages, nitrogen-doped carbon nanocages, or sulfur-doped carbon nanocages; the size of a cage cavity of the carbon-based nano cage is 5-100 nm; the specific surface area of the carbon-based nano cage is 500-2500 m²(ii)/g; the pore volume of the carbon-based nano cage is 0.5-5 cm³/g。

3. The threshold-limiting iron-based Fischer-Tropsch synthesis catalyst of claim 1, wherein the iron-based nanoparticles have an average particle size of 1 to 30nm, and the phase of the iron-based nanoparticles comprises ferroferric oxide.

4. The threshold-limited iron-based fischer-tropsch synthesis catalyst of claim 1, wherein the iron-based nanoparticles are loaded at a loading of 1 to 60 wt.%, based on the amount of iron element.

5. The threshold iron-based fischer-tropsch synthesis catalyst of claim 1, further comprising a first promoter, the first promoter being Na⁺Or K⁺And the loading amount of the first auxiliary agent is 0.5-5 wt.%.

6. The threshold iron-based fischer-tropsch synthesis catalyst of claim 5, further comprising a second promoter, wherein the second promoter is elemental sulfur, and wherein the second promoter is present at a loading of from 0.1 to 1 wt.%.

7. The preparation method of the threshold-limited type iron-based Fischer-Tropsch synthesis catalyst according to any one of claims 1 to 6, characterized by comprising the following steps:

(1) providing a carbon-based nanocage;

8. The method according to claim 7, wherein the iron precursor in the iron precursor solution is at least one of ferric nitrate, ferrous nitrate, ferric sulfate, ferrous sulfate, ferric ammonium citrate, ferric acetate, ferric acetylacetonate, ferrocene, ferrous acetate, ferrous lactate, ferrous citrate, ferric chloride, and ferrous chloride.

9. As claimed in claimThe production method of 7, wherein the first calcination is carried out in H₂、N₂Or in an inert gas stream; the temperature of the first roasting is 300-600 ℃; the first roasting time is 0.5-6 h.

10. The method of claim 7, wherein the second firing is at N₂Or in an inert gas stream; the temperature of the second roasting is 300-600 ℃, and the time of the second roasting is 0.5-6 h.