阅读说明：本技术 一种碳层嵌入式的碳化铁及其制备方法和碳层嵌入式的碳化铁作为费托合成催化剂的应用 (Carbon layer embedded iron carbide, preparation method thereof and application of carbon layer embedded iron carbide as Fischer-Tropsch synthesis catalyst ) 是由 王铁军 仇松柏 张浅 古桔文 于 2019-11-13 设计创作，主要内容包括：本发明属于费托合成催化剂技术领域,尤其涉及一种碳层嵌入式的碳化铁及其制备方法和碳层嵌入式的碳化铁作为费托合成催化剂的应用。本发明提供了一种碳层嵌入式的碳化铁,碳层嵌入式的碳化铁包括碳层和碳化铁纳米颗粒；碳化铁纳米颗粒负载于碳层上且碳化铁纳米颗粒非全包裹于碳层内。本发明中,碳层嵌入式的碳化铁具有独特的微观结构,碳化铁纳米颗粒均匀负载于碳层上且碳化铁纳米颗粒非全包裹于碳层内,使得该碳层嵌入式的碳化铁作为费托合成催化剂能够防止碳化铁纳米颗粒在长时间的高温反应中烧结,作为费托合成催化剂具有高的稳定性和机械强度；实验结果表明,该碳层嵌入式的碳化铁作为费托合成催化剂具有很高的催化活性,CO转化率高。(The invention belongs to the technical field of Fischer-Tropsch synthesis catalysts, and particularly relates to carbon layer embedded iron carbide, a preparation method of the carbon layer embedded iron carbide and application of the carbon layer embedded iron carbide as a Fischer-Tropsch synthesis catalyst. The invention provides a carbon layer embedded iron carbide, which comprises a carbon layer and iron carbide nano-particles; the iron carbide nano-particles are loaded on the carbon layer and are not completely wrapped in the carbon layer. According to the invention, the iron carbide with the embedded carbon layer has a unique microstructure, the iron carbide nanoparticles are uniformly loaded on the carbon layer, and the iron carbide nanoparticles are not completely wrapped in the carbon layer, so that the iron carbide with the embedded carbon layer as a Fischer-Tropsch synthesis catalyst can prevent the iron carbide nanoparticles from sintering in a long-time high-temperature reaction, and has high stability and mechanical strength as the Fischer-Tropsch synthesis catalyst; experimental results show that the carbon layer embedded iron carbide has high catalytic activity and high CO conversion rate when being used as a Fischer-Tropsch synthesis catalyst.)

1. A carbon-layer embedded iron carbide, comprising a carbon layer and iron carbide nanoparticles;

the iron carbide nanoparticles are loaded on the carbon layer and are not completely wrapped in the carbon layer.

2. The carbon layer embedded iron carbide of claim 1, wherein the iron carbide nanoparticles have a particle size of 10nm to 50 nm;

the thickness of the carbon layer is 1.5 nm-3 nm;

the specific surface area of the carbon layer embedded iron carbide is 80m ²/g～350m ²/g。

3. The carbon layer embedded iron carbide according to claim 1, wherein the loading amount of the iron element in the carbon layer embedded iron carbide is 15 wt% to 80 wt%.

4. A method for preparing the carbon layer embedded iron carbide according to any one of claims 1 to 3, comprising the steps of:

a) carrying out heating reaction on an iron source, a polycarboxyl complex and an alkali source in water to obtain an intermediate product;

b) drying the intermediate product to obtain a complex precursor, and roasting the complex precursor at 550-1100 ℃ in an inert atmosphere to obtain carbon-layer-embedded iron carbide;

wherein the molar ratio of the iron element in the iron source to the carboxyl in the polycarboxyl complex is 1: 1-1: 2.9.

5. The method according to claim 4, wherein the iron source is one or more of ferroferric oxide, iron oxide, ferrous oxide, iron carbonate, reduced iron powder, and iron ore;

the polycarboxyl complex is selected from one or more of citric acid, ethylenediamine tetraacetic acid, tartaric acid and nitrilotriacetic acid;

the alkali source is one or more selected from potassium hydroxide, sodium hydroxide, ammonia water, ethylenediamine, ethanolamine and calcium hydroxide.

6. The method according to claim 4, wherein the pH of the reaction system formed by the iron source, the polycarboxy complex, the alkali source and water in step a) is 2 to 10.

7. The preparation method according to claim 4, wherein the temperature of the heating reaction in the step a) is 40-100 ℃;

the heating reaction time is 6-24 h.

8. The preparation method of claim 4, wherein the roasting time in the step b) is 2-10 h;

the heating rate before roasting is 1-30 ℃/min.

9. The method according to claim 4, wherein the drying temperature in step b) is 60-170 ℃;

the drying time is 12-120 h.

10. Use of the carbon layer embedded iron carbide according to any one of claims 1 to 3 and/or the carbon layer embedded iron carbide prepared by the preparation method according to any one of claims 4 to 9 as a fischer-tropsch synthesis catalyst.

Technical Field

The invention belongs to the technical field of Fischer-Tropsch synthesis catalysts, and particularly relates to carbon layer embedded iron carbide, a preparation method of the carbon layer embedded iron carbide and application of the carbon layer embedded iron carbide as a Fischer-Tropsch synthesis catalyst.

Background

The Fischer-Tropsch synthesis is a reaction which is discovered in the twentieth century and is used for catalytically synthesizing hydrocarbon liquid fuel from synthesis gas (mixed gas of carbon monoxide and hydrogen) on a catalyst, is invented by German scientists Fischer and Tropsh, and is called Fischer-Tropsch synthesis or F-T synthesis for short; wherein, the synthesis gas is prepared by converting natural gas or coal gasification. The Fischer-Tropsch synthesis has the characteristics of no dependence on petroleum, clean products and the like, and has very wide application prospect.

Research shows that most of VIII family metals have catalytic action on Fischer-Tropsch synthesis, but only four transition metals of Fe, Co, Ni and Ru are generally considered to have strong enough catalytic capability, and the reaction activity sequence of the transition metals is Ru>Fe>Co>Rh>And (3) Ni. Because Ru and Rh are expensive, and Ni has the defects of easy carbonyl compound loss, serious methanation trend and the like in high-pressure reaction, the Fischer-Tropsch synthesis mostly adopts an iron-based or cobalt-based catalyst. The Fischer-Tropsch synthesis reaction process is divided into low-temperature Fischer-Tropsch synthesis and high-temperature Fischer-Tropsch synthesis, the iron-based catalyst can be suitable for the two Fischer-Tropsch synthesis processes, and the cobalt-based catalyst can only be used for the low-temperature Fischer-Tropsch synthesis process. In addition, Fe is low in price and wide in reserves, and the total reserves of iron ores in the world are about 8000 hundred million tons. In addition, the Fe-based catalyst has higher activity and higher olefin selectivity, and can obtain liquid fuels such as gasoline, diesel oil, kerosene and the like with higher octane number or bulk chemical raw materials such as low-carbon olefin and the like with high selectivity through proper modification. Meanwhile, the iron-based catalyst has excellent water-vapor conversion performance and can adjust H ₂The ratio of/CO is more suitable for low H obtained by taking biomass or coal as raw material than that of Co-based catalyst ₂The Fischer-Tropsch synthesis reaction of the ratio of/CO is more widely concerned.

In the iron-based Fischer-Tropsch synthesis catalyst, precipitated iron or molten iron is generally used industrially and is used for medium-temperature or high-temperature Fischer-Tropsch reaction. However, the conventional precipitated and molten iron catalysts are easily deposited with carbon and sintered, the catalyst channels are easily clogged, the specific surface is lost, and the mechanical strength is reduced, which results in gradual reduction of the catalyst activity and severe reduction of the service life. The supported catalyst can improve the mechanical strength of the catalyst by utilizing the carrier, can improve the dispersibility and the sintering resistance of the iron particles, but on one hand, the strong interaction between the iron particles and the carrier can greatly reduce the activity of the catalyst; on the other hand, carriers with lower interaction will cause the iron particles to agglomerate and deactivate. Therefore, there is a need for an iron-based fischer-tropsch synthesis catalyst that combines high catalytic activity and mechanical strength with good sintering resistance.

Disclosure of Invention

In view of the above, the invention provides a carbon layer embedded iron carbide, a preparation method thereof and an application of the carbon layer embedded iron carbide as a fischer-tropsch synthesis catalyst, and is used for providing an iron fischer-tropsch synthesis catalyst with high catalytic activity, high mechanical strength and good sintering resistance.

The specific technical scheme of the invention is as follows:

a carbon-layer embedded iron carbide comprising a carbon layer and iron carbide nanoparticles;

the iron carbide nanoparticles are loaded on the carbon layer and are not completely wrapped in the carbon layer.

Preferably, the particle size of the iron carbide nano-particles is 10 nm-50 nm;

the thickness of the carbon layer is 1.5 nm-3 nm;

the specific surface area of the carbon layer embedded iron carbide is 80m ²/g～350m ²/g。

Preferably, the loading amount of the iron element in the iron carbide embedded in the carbon layer is 15 wt% to 80 wt%.

The invention also provides a preparation method of the carbon layer embedded iron carbide in the technical scheme, which comprises the following steps:

a) carrying out heating reaction on an iron source, a polycarboxyl complex and an alkali source in water to obtain an intermediate product;

b) drying the intermediate product to obtain a complex precursor, and roasting the complex precursor at 550-1100 ℃ in an inert atmosphere to obtain carbon-layer-embedded iron carbide;

wherein the molar ratio of the iron element in the iron source to the carboxyl in the polycarboxyl complex is 1: 1-1: 2.9.

Preferably, the iron source is one or more of ferroferric oxide, ferric oxide, ferrous oxide, ferric carbonate, reduced iron powder and iron ore;

the polycarboxyl complex is selected from one or more of citric acid, ethylenediamine tetraacetic acid, tartaric acid and nitrilotriacetic acid;

the alkali source is one or more selected from potassium hydroxide, sodium hydroxide, ammonia water, ethylenediamine, ethanolamine and calcium hydroxide.

Preferably, the pH value of a reaction system formed by the iron source, the polycarboxyl complex, the alkali source and water in the step a) is 2-10.

Preferably, the temperature of the heating reaction in the step a) is 40-100 ℃;

the heating reaction time is 6-24 h.

Preferably, the roasting time in the step b) is 2-10 h;

the heating rate before roasting is 1-30 ℃/min.

Preferably, the drying temperature in the step b) is 60-170 ℃;

the drying time is 12-120 h.

The invention also provides the application of the carbon layer embedded iron carbide in the technical scheme and/or the carbon layer embedded iron carbide prepared by the preparation method in the technical scheme as a Fischer-Tropsch synthesis catalyst.

In summary, the present invention provides a carbon-layer-embedded iron carbide, which includes a carbon layer and iron carbide nanoparticles; the iron carbide nanoparticles are loaded on the carbon layer and are not completely wrapped in the carbon layer. According to the invention, the iron carbide with the embedded carbon layer has a unique microstructure, the iron carbide nanoparticles are uniformly loaded on the carbon layer, and the iron carbide nanoparticles are not completely wrapped in the carbon layer, so that the iron carbide with the embedded carbon layer as a Fischer-Tropsch synthesis catalyst can prevent the iron carbide nanoparticles from sintering in a long-time high-temperature reaction, and has high stability and mechanical strength as the Fischer-Tropsch synthesis catalyst; experimental results show that the carbon layer embedded iron carbide has high catalytic activity and high CO conversion rate when being used as a Fischer-Tropsch synthesis catalyst.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below.

Fig. 1 is an XRD pattern of carbon-layer-embedded iron carbide prepared in example 1, example 10 and example 11 of the present invention;

FIG. 2 is Fe ₃C. XRD standard spectra of Fe and FeO;

FIG. 3 is a scanning electron micrograph of a carbon-layer-embedded iron carbide prepared according to example 1 of the present invention;

FIG. 4 is a TEM image of the carbon-layer-embedded iron carbide prepared in example 1 of the present invention, wherein FIGS. 4-A, 4-B and 4-C are TEM images of the carbon-layer-embedded iron carbide prepared in example 1 at different magnifications, and FIG. 4-D is a TEM image of the carbon-layer-embedded iron carbide prepared in example 1 after pickling with 10 wt% dilute sulfuric acid solution;

fig. 5 is a graph showing the CO conversion change of the carbon layer-embedded iron carbide prepared in example 1 of the present invention.

Detailed Description

The invention provides a carbon layer embedded iron carbide, a preparation method thereof and application of the carbon layer embedded iron carbide as a Fischer-Tropsch synthesis catalyst, which are used for providing an iron Fischer-Tropsch synthesis catalyst with high catalytic activity, high mechanical strength and good sintering resistance.

The technical solutions in the embodiments of the present invention will be 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.

A carbon layer embedded iron carbide, the carbon layer embedded iron carbide comprises a carbon layer and iron carbide nano-particles;

the iron carbide nano-particles are loaded on the carbon layer and are not completely wrapped in the carbon layer.

In the embodiment of the invention, the iron carbide embedded in the carbon layer has a unique microstructure, the iron carbide nano particles are uniformly loaded on the carbon layer, and the iron carbide nano particles are not completely wrapped in the carbon layer, so that the iron carbide embedded in the carbon layer as the Fischer-Tropsch synthesis catalyst can prevent the iron carbide nano particles from being sintered in a long-time high-temperature reaction, and has high stability and mechanical strength as the Fischer-Tropsch synthesis catalyst; experimental results show that the carbon layer embedded iron carbide has high catalytic activity and high CO conversion rate when being used as a Fischer-Tropsch synthesis catalyst.

Further, the carbon-layer-embedded iron carbide is of a carbon-layer-embedded semi-wrapped structure, and the iron carbide nanoparticles are semi-wrapped by the carbon layer just like honeybee homing.

In the embodiment of the invention, the particle size of the iron carbide nano-particles is 10 nm-50 nm, preferably 20 nm-40 nm;

the thickness of the carbon layer is 1.5 nm-3 nm, preferably 2 nm-2.5 nm;

the specific surface area of the carbon layer-embedded iron carbide is 80m ²/g～350m ²/g。

In the embodiment of the invention, the loading amount of the iron element in the carbon layer embedded iron carbide is 15-80 wt%.

The invention also provides a preparation method of the carbon layer embedded iron carbide in the technical scheme, which comprises the following steps:

a) carrying out heating reaction on an iron source, a polycarboxyl complex and an alkali source in water to obtain an intermediate product;

b) drying the intermediate product to obtain a complex precursor, and roasting the complex precursor at 550-1100 ℃ in an inert atmosphere to obtain carbon-layer-embedded iron carbide;

wherein the molar ratio of the iron element in the iron source to the carboxyl in the polycarboxyl complex is 1: 1-1: 2.9.

In the embodiment of the invention, an alkali source can be used as a catalyst to promote the dissolution of an iron source in water, firstly, a polycarboxyl complex reacts with the alkali source to generate polycarboxyl complex ions, the polycarboxyl complex ions then react with the iron source in a complex manner, iron elements in the iron source are extracted and dissolved in water to obtain a complex precursor, and the complex precursor is roasted in an inert atmosphere to carry out pyrolysis self-reduction to obtain the carbon-layer-embedded iron carbide.

When the polycarboxyl complex is citric acid, the citric acid reacts with an alkali source to generate citrate ions, the citrate ions then undergo a complexing reaction with an iron source, and the iron element is extracted from the iron source based on the following reactions:

H ₃C ₆H ₅O ₇+OH ^-→H ₂C ₆H ₅O ₇ ^-+H ₂O

H ₂C ₆H ₅O ₇ ^-+Fe→FeC ₆H ₅O ₇ ^-+H ₂

H ₂C ₆H ₅O ₇ ^-+FeO→FeC ₆H ₅O ₇ ^-+H ₂O

2H ₂C ₆H ₅O ₇ ^-+Fe ₂O ₃→2FeC ₆H ₅O ₇+H ₂O+2OH ^-

3H ₂C ₆H ₅O ₇ ^-+Fe ₃O ₄→FeC ₆H ₅O ₇ ^-+2FeC ₆H ₅O ₇+2H ₂O+2OH ^-

H ₂C ₆H ₅O ₇ ^-+FeCO ₃→FeC ₆H ₅O ₇ ^-+H ₂O+CO ₂

in the embodiment of the invention, the roasting temperature is preferably 700-1100 ℃, and more preferably 700-900 ℃;

the molar ratio of the iron element in the iron source to the carboxyl in the polycarboxyl complex is preferably 1: 1.4-1: 2.

At present, iron salts with high purity such as ferric nitrate, ferric chloride, ferric sulfate, ferric acetylacetonate and the like are mostly adopted for preparing the iron carbide Fischer-Tropsch synthesis catalyst, a large amount of acid and alkali are needed in the iron salt industrial process, the process flow is long, the quality requirement of the iron salt is high, a large amount of waste gas is generated during the preparation of the iron salt, the environmental pressure is high, and the price is high.

In the embodiment of the invention, the iron source is one or more of ferroferric oxide, ferric oxide, ferrous oxide, ferric carbonate, reduced iron powder and iron ore, and the iron ore is one or more selected from magnetite, hematite, limonite and siderite;

the polycarboxyl complex is selected from one or more of citric acid, ethylene diamine tetraacetic acid, tartaric acid and nitrilotriacetic acid;

the alkali source is one or more selected from potassium hydroxide, sodium hydroxide, ammonia water, ethylenediamine, ethanolamine and calcium hydroxide.

In the embodiment of the invention, the iron source is ferroferric oxide or ferric oxide (Fe) ₂O ₃) One or more of reduced iron powder and iron ore are not needed to be used as an iron source, so that the problems that iron salt is needed to be used for preparing the iron carbide Fischer-Tropsch synthesis catalyst, a large amount of acid and alkali is needed to be used for preparing the iron salt, the process flow is long, and the cost is high are solved.

Magnetite is a kind of ferrimagnetism mineral, it is rich in ferriferrous oxide, produce in metamorphic deposit and endogenous deposit, it is the main iron ore raw materials of our country, the stock volume is enormous in our country, distribute extensively. Becomes hematite or limonite after oxidation and is the main raw material for iron making. Currently, magnetite is mainly used for iron making, but the magnetite needs to be reduced by carbon monoxide at high temperature for refining, the current iron making process consumes extremely large energy, a large amount of waste gas and waste residues are generated in the iron making process, certain environmental protection pressure exists, and the risk problems of poisoning, explosion and the like exist in the reduction by carbon monoxide.

In an embodiment of the invention, the iron source may be iron ore selected from one or more of magnetite, hematite, limonite and siderite. Extracting iron element from magnetite under mild condition, preferably filtering and drying to obtain complex precursor, and roasting the complex precursor to obtain the carbon-layer embedded iron carbide. The method can adopt cheap natural magnetite resources as an iron source, provides a new way for the application of the magnetite, directly prepares the carbon-layer-embedded iron carbide by utilizing the magnetite, has very important industrial application value, has simple preparation process and low cost of the carbon-layer-embedded iron carbide, is easy to implement large-scale production, has high stability and feasibility of operation, avoids the industrial iron-making of the natural magnetite and the deep processing process of iron salt industry, and has the characteristics of energy conservation, environmental protection. In addition, the preparation method can avoid intermediate smelting and preparation and purification of iron salt when the iron source is derived from natural minerals.

In the embodiment of the invention, the preparation method of the carbon-layer embedded iron carbide can fully utilize lean iron ores in China, iron elements are enriched by a dissolving and filtering method to prepare the carbon-layer embedded iron carbide, and the prepared carbon-layer embedded iron carbide as a Fischer-Tropsch synthesis catalyst has high CO conversion rate and stability.

In the embodiment of the invention, the pH value of a reaction system formed by the iron source, the polycarboxyl complex, the alkali source and water in the step a) is 2-10.

In the embodiment of the invention, the temperature of the heating reaction in the step a) is 40-100 ℃;

the heating reaction time is 6-24 h, preferably 6-12 h.

In the embodiment of the invention, the roasting time in the step b) is 2-10 h;

the heating rate before roasting is 1-30 deg.c/min.

In the embodiment of the invention, the drying temperature in the step b) is 60-170 ℃;

the drying time is 12-120 h.

The invention also provides the application of the carbon layer embedded iron carbide prepared by the preparation method in the technical scheme and/or the carbon layer embedded iron carbide prepared by the preparation method in the technical scheme as a Fischer-Tropsch synthesis catalyst.

The carbon layer embedded iron carbide of the invention has high catalytic activity and high CO conversion rate when being used as a Fischer-Tropsch synthesis catalyst.

For a further understanding of the invention, reference will now be made in detail to the following examples.