阅读说明：本技术 铁基催化剂及其制备方法和应用 (Iron-based catalyst and preparation method and application thereof ) 是由 王锐 张奉波 吕毅军 张魁 门卓武 孟祥堃 孙琦 于 2019-04-18 设计创作，主要内容包括：本发明涉及费托合成领域,公开了一种铁基催化剂及其制备方法和应用,该催化剂含有Fe元素、Mn元素、Zn元素、S元素和助剂,所述助剂选自碱金属和碱土金属中的至少一种；其中,以所述铁基催化剂的总量为基准,所述S元素的含量为0.02-0.5重量％,以元素计,所述助剂的含量为0.1-10重量％；Fe：Mn：Zn的摩尔比为1：(0.1-4)：(0.01-1)。与常规沉淀法相比,采用本发明所述方法制备得到的铁基催化剂BET比表面高、孔体积大,将该铁基催化剂用于高温费托合成反应时,具有反应活性高、低碳烷烃选择性低和低碳烯烃选择性高的优点。(The invention relates to the field of Fischer-Tropsch synthesis and discloses an iron-based catalyst, a preparation method and application thereof, wherein the catalyst contains Fe element, Mn element, Zn element, S element and auxiliary agent, and the auxiliary agent is selected from at least one of alkali metal and alkaline earth metal; wherein, based on the total amount of the iron-based catalyst, the content of the S element is 0.02-0.5 wt%, and the content of the auxiliary agent is 0.1-10 wt% calculated by the element; fe: mn: the molar ratio of Zn is 1: (0.1-4): (0.01-1). Compared with the conventional precipitation method, the iron-based catalyst prepared by the method has the advantages of high BET specific surface area and large pore volume, and has the advantages of high reaction activity, low-carbon alkane selectivity and high low-carbon olefin selectivity when the iron-based catalyst is used in high-temperature Fischer-Tropsch synthesis reaction.)

1. An iron-based catalyst, which contains Fe element, Mn element, Zn element, S element and an auxiliary agent, wherein the auxiliary agent is at least one of alkali metal and alkaline earth metal;

wherein, based on the total amount of the iron-based catalyst, the content of the S element is 0.02-0.5 wt%, and the content of the auxiliary agent is 0.1-10 wt% calculated by the element;

fe: mn: the molar ratio of Zn is 1: (0.1-4): (0.01-1).

2. The iron-based catalyst according to claim 1, wherein the content of the S element is 0.05-0.45 wt% and the content of the promoter is 0.5-4 wt% in terms of element, based on the total amount of the iron-based catalyst;

fe: mn: the molar ratio of Zn is 1: (0.5-1.3): (0.09-0.15).

3. The iron-based catalyst of claim 1 or 2, wherein the promoter is selected from at least one of Na, K, Ca and Mg.

4. The iron-based catalyst according to any one of claims 1-3, wherein the iron-based catalyst has a BET specific surface area of 300-580m²Per g, preferably 400-580m²Per g, pore volume of 0.3-0.8m³A/g, preferably of 0.5 to 0.8m³/g。

5. A method of preparing an iron-based catalyst, the method comprising:

1) mixing a solution containing a ferrous salt, a manganese source and a zinc source, and optionally a promoter precursor, with C₂-C₄Mixing the dicarboxylic acids to obtain a mixed material;

2) carrying out hydrothermal treatment on the mixed material to obtain a precipitate;

3) sequentially carrying out first drying and first roasting on the precipitate to obtain a composite oxide; optionally, the method further comprises: dipping the composite oxide by adopting an auxiliary agent precursor solution, and then sequentially carrying out second drying and second roasting;

wherein at least one of the ferrous salt, the manganese source, the zinc source and the auxiliary agent precursor is sulfate;

the auxiliary agent is selected from at least one of alkali metal and alkaline earth metal;

the dosage of the auxiliary agent precursor is 0.1-10 wt% of the prepared catalyst calculated by elements.

6. The method as claimed in claim 5, wherein, in the step 1), the amount of the auxiliary agent precursor is such that the content of the auxiliary agent in the prepared catalyst is 0.5-4 wt% calculated on element;

preferably, the metals in the solution are in elemental form with C₂-C₄In a molar ratio of 1: (0.1-2), preferably 1: (0.7-1.2);

preferably, in the step 1), the molar ratio of the ferrous salt to the manganese source to the zinc source is 1: (0.1-4): (0.01-1), preferably 1: (0.5-1.3): (0.09-0.15);

preferably, in step 1), the concentration of the solution is 0.01-0.1 g/ml.

7. The process according to claim 5 or 6, wherein the amount of the divalent iron salt, the manganese source, the zinc source and the promoter precursor is such that the S element is contained in the obtained iron-based catalyst in an amount of 0.02 to 0.5 wt%, preferably 0.05 to 0.45 wt%, based on the total amount of the iron-based catalyst.

8. The process according to any one of claims 5 to 7, wherein the hydrothermal treatment in step 2) is carried out in the presence of a surfactant;

preferably, the volume ratio of the surfactant to the mixed material is (0.1-9): 1, preferably (0.3-2): 1;

preferably, the surfactant is selected from C₂-C₆Monohydric alcohol of (A) and (C)₂-C₆At least one of the polyols of (a);

preferably, the conditions of the hydrothermal treatment include: the temperature is 60-180 deg.C, preferably 80-120 deg.C, and the time is 1-24 hr, preferably 6-12 hr.

9. The method according to any one of claims 5 to 8, wherein in step 1), the ferrous salt, the manganese source and the zinc source are each independently selected from at least one of a sulfate, a nitrate and a carbonate;

preferably, in the step 1), the ferrous salt, the manganese source and the zinc source are all sulfates;

preferably, in step 1), the dicarboxylic acid is selected from oxalic acid and/or tartaric acid, more preferably oxalic acid;

preferably, the auxiliary agent is selected from at least one of Na, K, Ca and Mg.

10. The method according to any one of claims 5-9,

the conditions of the first drying include: the temperature is 90-120 ℃, and the time is 4-24 h;

the conditions of the first firing include: the temperature is 300-500 ℃ and the time is 2-4 h;

the conditions of the second drying include: the temperature is 90-120 ℃, and the time is 4-24 h;

the conditions of the second roasting include: the temperature is 300 ℃ and 500 ℃, and the time is 2-4 h.

11. An iron-based catalyst prepared by the method of any one of claims 5 to 10;

preferably, the iron-based catalyst has a BET specific surface area of 300-580m²Per g, preferably 400-580m²Per g, pore volume of 0.3-0.8m³A/g, preferably of 0.5 to 0.8m³/g。

12. Use of an iron-based catalyst according to any one of claims 1 to 4 and 11 in fischer-tropsch synthesis.

Technical Field

The invention relates to the field of Fischer-Tropsch synthesis, in particular to an iron-based catalyst, and a preparation method and application thereof.

Background

Coal indirect liquefaction is to obtain synthesis gas (CO + H) by converting coal through gasification process₂) The synthesis gas is converted into hydrocarbons and oxygenates by the catalyst. The coal indirect liquefaction is generally divided into two process routes of low-temperature Fischer-Tropsch synthesis and high-temperature Fischer-Tropsch synthesis, wherein the former industrially mainly uses cobalt catalysts and iron catalysts, the reaction temperature is 200 ℃ and 280 ℃, and the main process is to produce hydrocarbons such as gasoline, diesel oil, paraffin and the like; the latter uses iron catalyst, the reaction temperature is 300-350 ℃, and the product can produce a large amount of oxygen-containing organic substances and olefin and other chemical products besides the oil product.

With the rapid fall-back of petroleum prices in recent years, the coal-to-liquid industry is seriously impacted, and the improvement of the added value of products becomes the way of the development of the coal-to-liquid technology under the current situation, so that the high-temperature Fischer-Tropsch synthesis technology for producing more chemical products as by-products has the characteristics of high added value of the products, consideration of oil products, chemical industry and the like, and shows certain advantages under the current market environment.

Iron-based fischer-tropsch catalysts have been commercialized in 50 s by Sasol corporation of south africa mainly for the production of fuels and waxes, etc. There have been many studies on low temperature synthesis of fischer-tropsch catalysts, but few studies on high temperature fischer-tropsch catalysts. At present, the industrial application adopts a molten iron catalyst, raw material iron is added into K₂And smelting the O and the auxiliary agent in an electric arc furnace to obtain the alloy. However, the molten iron catalyst has the defects of lower specific surface area, uneven auxiliary agent content, more impurity content and the like. In addition Yan mine also developed a precipitated iron based high temperature Fischer-Tropsch catalyst, and the results of pilot tests were less than 10% methane selectivity and about 25% C2-C4 olefin selectivity.

CN1695803A disclosesThe preparation method comprises dissolving ferric nitrate, adding ammonia water solution to form precipitate slurry, filtering, washing to obtain coprecipitation filter cake, adding water, pulping, adding Na-containing solution⁺、K⁺、Cr³⁺、Cu²⁺The solution is directly added into the slurry, the slurry is obtained after a certain time of dipping, and then the high-temperature Fischer-Tropsch synthesis catalyst is obtained through drying and roasting. The catalyst contains Fe 50-70 wt%, Cu 0.01-10 wt%, Cr 0.01-10 wt%, and K₂0.01-8 wt% of O and Na₂The weight percentage of O is 0.01-8.

CN1817451A discloses a microspheric iron-based catalyst for Fischer-Tropsch synthesis at high temperature and a preparation method thereof, wherein the catalyst comprises the following components in percentage by weight: cu: cr: k₂O：Na₂O100: 0.01-10: 0.03-10: 0.01-6: 0.01-5. The preparation method comprises the steps of dissolving iron powder in nitric acid to obtain an iron nitrate solution, diluting, adding an ammonium bicarbonate solution, precipitating to obtain a slurry, filtering and washing to obtain a filter cake, adding a certain amount of water and an auxiliary agent for pulping, soaking for a certain time to obtain a slurry, and performing centrifugal spray drying and roasting to obtain the microspheric Fischer-Tropsch synthesis catalyst.

CN101024192A discloses a preparation method of a catalyst for preparing low-carbon olefins from synthesis gas, which comprises the following steps: (1) mixing Fe (NO)₃)₃·9H₂O and Mn (NO)₃)₂Preparing a uniform mixed solution of 0.2-1.0 mol/L; (2) by NH₄OH is a precipitator and is (Fe + Mn)/NH according to the molar weight of the substance₄Measuring OH as 1: 2-3, and weighing NH₄OH and preparing NH with the same volume as (1)₄The OH solution and the Fe/Mn mixed solution prepared in the step (1) are dripped into a container in a parallel flow mode, the mixture is continuously stirred for 4-8 hours after precipitation is finished, and the mixture is stood for 8-12 hours at normal temperature and normal pressure; (3) filtering and washing the precipitate obtained in the step (2), and then drying at 30-80 ℃ to obtain a dried precipitate A; (4) roasting the obtained substance A at the roasting temperature of 400-550 ℃ for 60-120 min, and recording the obtained product as B; (5) weighing K according to the composition of the catalyst₂CO₃Mixing ofPreparing a solution having the same volume as the obtained product B, and immersing the obtained product B in K₂CO₃Stirring and standing the solution for 4 to 8 hours, drying the solution at the temperature of 80 to 120 ℃, tabletting and molding the obtained dried substance, and crushing the dried substance to 40 to 60 meshes to obtain the catalyst.

It can be seen that the prior art adopts alkaline precipitant (such as ammonia water, sodium carbonate and ammonium hydroxide) to precipitate the iron-based catalyst for Fischer-Tropsch synthesis at high temperature, and then the iron-based catalyst is filtered, washed and re-pulped, and then the auxiliary agent salt solution is added into the slurry, and after the slurry is soaked for a period of time, the catalyst is prepared by drying and roasting.

In view of this, it is necessary to provide an iron-based catalyst suitable for high temperature fischer-tropsch synthesis and a preparation method thereof, so that the catalyst has the advantages of high CO activity, low methane hydrocarbon selectivity, high low carbon olefin selectivity, high strength and the like when being used for high temperature fischer-tropsch synthesis.

Disclosure of Invention

The invention aims to overcome the defect that the prior art adopts an iron-based catalyst prepared by alkaline precipitator (such as ammonia water, sodium carbonate and ammonium hydroxide), C₂-C₄Low selectivity to olefin, CH₄The iron-based catalyst has the advantages of high reaction activity, low selectivity of low-carbon alkane and high selectivity of low-carbon olefin when being used for high-temperature Fischer-Tropsch synthesis reaction.

In the method for producing the iron-based catalyst of the present invention, the catalyst C₂-C₄The dicarboxylic acid can form a coordination precursor solution with a solution containing a ferrous salt, a manganese source, a zinc source and optionally an auxiliary precursor, wherein at least one of the ferrous salt, the manganese source, the zinc source and the auxiliary precursor is a sulfate; thereby simplifying the flow, shortening the time, simultaneously obtaining the iron-based catalyst with specific sulfur content through hydrothermal treatment, and when the iron-based catalyst is used for high-temperature Fischer-Tropsch synthesis reaction, the iron-based catalyst has high reaction activity, low selectivity of low-carbon alkane and low-carbon olefinHigh selectivity.

In order to achieve the above object, a first aspect of the present invention provides an iron-based catalyst containing an Fe element, an Mn element, a Zn element, an S element, and an auxiliary agent selected from at least one of alkali metals and alkaline earth metals;

wherein, based on the total amount of the iron-based catalyst, the content of the S element is 0.02-0.5 wt%, and the content of the auxiliary agent is 0.1-10 wt% calculated by the element;

fe: mn: the molar ratio of Zn is 1: (0.1-4): (0.01-1).

In a second aspect, the present invention provides a method of preparing an iron-based catalyst, the method comprising:

1) mixing a solution containing a ferrous salt, a manganese source and a zinc source, and optionally a promoter precursor, with C₂-C₄Mixing the dicarboxylic acids to obtain a mixed material;

2) carrying out hydrothermal treatment on the mixed material to obtain a precipitate;

3) sequentially carrying out first drying and first roasting on the precipitate to obtain a composite oxide;

optionally, the method further comprises: dipping the composite oxide by adopting an auxiliary agent precursor solution, and then sequentially carrying out second drying and second roasting;

wherein at least one of the ferrous salt, the manganese source, the zinc source and the auxiliary agent precursor is sulfate;

the auxiliary agent is selected from at least one of alkali metal and alkaline earth metal;

the dosage of the auxiliary agent precursor is 0.1-10 wt% of the prepared catalyst calculated by elements.

In a third aspect, the invention provides an iron-based catalyst prepared by the method of the second aspect of the invention.

In a fourth aspect, the invention provides the use of an iron-based catalyst according to the invention in fischer-tropsch synthesis.

In the preparation method of the iron-based catalyst of the invention, C₂-C₄Can be reacted with a compound containingAnd (2) forming a coordination precursor solution by using a solution of a ferrous salt, a manganese source, a zinc source and optionally an auxiliary agent precursor, wherein at least one of the ferrous salt, the manganese source, the zinc source and the auxiliary agent precursor is sulfate, and obtaining the iron-based catalyst with a specific composition by hydrothermal treatment. Through the technical scheme, the iron-based catalyst is particularly suitable for Fischer-Tropsch synthesis reaction, and particularly has the advantages of high catalytic activity, high selectivity of low-carbon olefin and low selectivity of methane when being used for high-temperature Fischer-Tropsch synthesis reaction of a fixed bed. In addition, the preparation method of the iron-based catalyst provided by the invention has simple process and shortens the time required by preparation.

Detailed Description

The following describes in detail specific embodiments of the present invention. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.

As described above, the first aspect of the present invention provides an iron-based catalyst containing an Fe element, an Mn element, a Zn element, an S element, and an auxiliary agent selected from at least one of an alkali metal and an alkaline earth metal;

wherein, based on the total amount of the iron-based catalyst, the content of the S element is 0.02-0.5 wt%, and the content of the auxiliary agent is 0.1-10 wt% calculated by the element; fe: mn: the molar ratio of Zn is 1: (0.1-4): (0.01-1).

In order to further improve the selectivity of the low-carbon olefin and reduce the selectivity of the low-carbon alkane, the content of the S element is preferably 0.05 to 0.45 wt% and the content of the auxiliary agent is preferably 0.5 to 4 wt% calculated on the element basis, based on the total amount of the iron-based catalyst.

According to a preferred embodiment of the present invention, Fe: mn: the molar ratio of Zn is 1: (0.25-1.3): (0.09-0.15).

In the present invention, preferably, the auxiliary is at least one selected from Na, K, Ca and Mg, and more preferably, the auxiliary is Na and/or K. When Na and/or K are/is selected as the auxiliary agent, the catalytic performance of the iron-based catalyst can be better improved.

In the present invention, the form in which the auxiliary is present is not particularly limited, and may be present in an oxidized state, for example.

In the present invention, it is preferable that the iron-based catalyst has a BET specific surface area of 300-580m²(ii)/g, more preferably 400-²Per g, pore volume of 0.3-0.8m³A ratio of 0.5 to 0.8 m/g is more preferable³/g。

The BET specific surface area and pore volume of the iron-based catalyst of the invention may be measured according to conventional means in the art, such as nitrogen physisorption.

In a second aspect, the present invention provides a method of preparing an iron-based catalyst, the method comprising:

1) mixing a solution containing a ferrous salt, a manganese source and a zinc source, and optionally a promoter precursor, with C₂-C₄Mixing the dicarboxylic acids to obtain a mixed material;

2) carrying out hydrothermal treatment on the mixed material to obtain a precipitate;

3) sequentially carrying out first drying and first roasting on the precipitate to obtain a composite oxide; optionally, the method further comprises: dipping the composite oxide by adopting an auxiliary agent precursor solution, and then sequentially carrying out second drying and second roasting;

wherein at least one of the ferrous salt, the manganese source, the zinc source and the auxiliary agent precursor is sulfate;

the auxiliary agent is selected from at least one of alkali metal and alkaline earth metal;

the dosage of the auxiliary agent precursor is 0.1-10 wt% of the prepared catalyst calculated by elements.

According to the invention, the "optional" in step 1) and step 2) can be explained as follows: namely, the auxiliary agent can be introduced by the following three methods:

first, the auxiliaries, i.e. the solution containing the divalent iron, manganese and zinc salts and the auxiliary precursor and C, are introduced only in step 1)₂-C₄Mixing the dicarboxylic acids to obtain a precipitate; sequentially carrying out first drying and first roasting on the precipitate to obtain composite oxideSubstance (iron-based catalyst).

Secondly, the auxiliaries, i.e. the solution containing the ferrous salt, the manganese source and the zinc source and C, are introduced only in step 2)₂-C₄Mixing the dicarboxylic acids to obtain a precipitate; sequentially carrying out first drying and first roasting on the precipitate to obtain a composite oxide; and then, dipping the composite oxide by adopting an auxiliary agent precursor solution, and sequentially carrying out second drying and second roasting to obtain the iron-based catalyst.

Thirdly, the addition agent is introduced in the step 1) and the step 2), namely, the solution containing ferrous salt, manganese source, zinc source and addition agent precursor and C₂-C₄Mixing the dicarboxylic acids to obtain a precipitate; sequentially carrying out first drying and first roasting on the precipitate to obtain a composite oxide; and then, dipping the composite oxide by adopting an auxiliary agent precursor solution, and sequentially carrying out second drying and second roasting to obtain the iron-based catalyst.

According to the invention, no matter what way the auxiliary agent is introduced, the amount of the auxiliary agent precursor is required to be enough to enable the content of the auxiliary agent in the prepared catalyst to be 0.1-10 wt% calculated by elements.

In order to obtain an iron-based catalyst with higher catalytic performance, the promoter precursor is preferably used in an amount such that the content of the promoter in the obtained catalyst is 0.5 to 4 wt% on an elemental basis.

According to a preferred embodiment of the invention, the auxiliary is introduced in the second way described above. When the promoter is introduced by the second method, i.e. only in step 2), an iron-based catalyst with higher catalytic performance can be obtained better.

In order to further improve the selectivity of the low-carbon olefin and reduce the selectivity of the low-carbon alkane, preferably, the metal calculated by elements in the solution is mixed with C₂-C₄In a molar ratio of 1: (0.1-2), more preferably 1: (0.7-1.2). That is, when the solution in step 1) contains a divalent iron salt, a manganese source, a zinc source, and an auxiliary precursor, the total amount of the divalent iron salt, the manganese source, the zinc source, and the auxiliary precursor, and C are preferably calculated on the basis of the metal element₂-C₄In a molar ratio of 1: (0.1-2), more preferably 1: (0.7-1.2); when the solution in the step 1) contains ferrous salt, a manganese source and a zinc source, the molar ratio of the total amount of the ferrous salt, the manganese source and the zinc source to the dicarboxylic acid with the carbon number of 2-4 is preferably 1: (0.1-2), more preferably 1: (0.7-1.2).

Preferably, in the step 1), the molar ratio of the ferrous salt to the manganese source to the zinc source is 1: (0.1-4): (0.01-1), more preferably 1: (0.5-1.3): (0.09-0.15).

In the present invention, the concentration of the solution in step 1) is not particularly limited, and in the case where the contents of the above components are satisfied, it is preferable that the concentration of the solution in step 1) may be 0.01 to 0.1 g/ml.

According to the invention, in a particular embodiment, C₂-C₄The dicarboxylic acid(s) may be introduced in the form of a solution, for example in step 1), a solution containing the divalent iron, manganese and zinc salts and optionally the promoter precursor is mixed with a solution containing C₂-C₄The dicarboxylic acid solution of (2) is mixed. The invention is to the compound containing C₂-C₄The concentration of the dicarboxylic acid (C) solution is not particularly limited as long as the metal and dicarboxylic acid charging relationship of the present invention is satisfied, and for example, the solution contains C₂-C₄The concentration of the solution of the dicarboxylic acid(s) of (2) may be 0.01 to 0.1 g/ml.

According to the present invention, preferably, the step 2) further comprises washing the material obtained after the hydrothermal treatment to obtain the precipitate. The washing may be performed by a method conventional in the art, and for example, the material obtained after the hydrothermal treatment may be washed with a mixed solution of water and ethanol or ethanol.

According to the present invention, the ferrous salt, the manganese source, the zinc source and the promoter precursor are preferably used in such amounts that the content of the S element in the resulting iron-based catalyst is 0.02 to 0.5 wt%, more preferably 0.05 to 0.45 wt%, based on the total amount of the iron-based catalyst. By adopting the preferred embodiment, the sulfur content in the iron-based catalyst is controlled, so that the selectivity of the low-carbon olefin is further improved, and the selectivity of the low-carbon alkane is reduced. When the content of the sulfur element in the iron-based catalyst is too low, the low-carbon olefin selectivity of the iron-based catalyst is reduced, and the low-carbon alkane selectivity is increased, and when the content of the sulfur element is too high, the low-carbon olefin selectivity of the iron-based catalyst is reduced, the low-carbon alkane selectivity of the iron-based catalyst is increased, and even the iron-based catalyst is completely inactivated. At least one of the ferrous salt, the manganese source, the zinc source and the auxiliary agent precursor is sulfate, and the sulfur content in the prepared catalyst can be regulated and controlled by controlling the using amounts of the ferrous salt, the manganese source, the zinc source and the auxiliary agent precursor and washing, and the person skilled in the art can know how to control the sulfur content in the catalyst through the above description.

According to the present invention, in order to further increase the pore volume and specific surface area of the prepared catalyst, preferably, the hydrothermal treatment in step 2) is performed in the presence of a surfactant.

Preferably, the volume ratio of the surfactant to the mixed material is (0.1-9) based on the total amount of the solution used in the hydrothermal treatment process: 1, preferably (0.3-2): 1.

preferably, the surfactant is selected from C₂-C₆Monohydric alcohol of (A) and (C)₂-C₆At least one of the polyols of (A), C₂-C₆The monohydric alcohol of (b) may be, for example, ethanol, n-propanol, 2-propanol, n-butanol, etc.; said C is₂-C₆The polyol (b) may be ethylene glycol, glycerin, etc., and more preferably is ethanol or glycerin.

According to the present invention, preferably, the conditions of the hydrothermal treatment include: the temperature is 60-180 deg.C, preferably 80-120 deg.C, and the time is 1-24 hr, preferably 6-12 hr. According to the present invention, the hydrothermal treatment process is not particularly limited, and specifically, a solution containing a divalent iron salt, a manganese source, and a zinc source, and optionally a promoter precursor, and C₂-C₄The materials obtained after the dicarboxylic acid is mixed are subjected to hydrothermal treatment under the condition of hydrothermal treatment, and the precipitate is obtained after suction filtration and washing. Thus, the method can better obtain high low-carbon olefin selectivity and low carbonAn alkane-selective iron-based catalyst.

According to the present invention, in the case where at least one of the ferrous salt, the manganese source, the zinc source, and the auxiliary precursor is a sulfate, the species of the ferrous salt, the manganese source, and the zinc source are not particularly limited as long as the corresponding ferrous iron, manganese, and zinc can be provided, and preferably, the ferrous salt, the manganese source, and the zinc source are each independently selected from at least one of a sulfate, a nitrate, and a carbonate; further preferably, the ferrous salt, the manganese source and the zinc source are all sulfates. The above-mentioned substances are all conventional in the art and are commercially available.

In the present invention, the above-mentioned C is preferable₂-C₄The dicarboxylic acid of (a) is oxalic acid and/or tartaric acid. When oxalic acid and/or tartaric acid are selected, the iron-based catalyst with high catalytic performance can be better obtained. The oxalic acid and tartaric acid are all conventional choices in the art and are all commercially available.

In a particularly preferred embodiment of the present invention, when the ferrous salt, the manganese source and the zinc source are all sulfates, and the dicarboxylic acid is oxalic acid, not only can the introduction of impurities in the catalyst be avoided, but also the sulfate solutions of the ferrous salt, the manganese source and the zinc source can better form a coordination precursor solution with the dicarboxylic acid, so as to obtain an iron-based catalyst with more excellent catalytic performance.

In the invention, the solution of ferrous salt, manganese source and zinc source and optional auxiliary agent precursor and C₂-C₄The mixing method of the dicarboxylic acid (2) is not particularly limited.

According to a preferred embodiment of the present invention, the mixing process may be slowly adding the solution of the ferrous salt, the manganese source and the zinc source and optionally the promoter precursor to the solution containing C under the action of magnetic stirring₂-C₄The dicarboxylic acid (b) is stirred for 0.5-4h, and precipitation occurs.

According to the method of the present invention, preferably, the conditions of the first drying include: the temperature is 90-120 ℃, and the time is 4-24 h.

According to the method of the present invention, preferably, the conditions of the first firing include: the temperature is 300 ℃ and 500 ℃, and the time is 2-4 h.

According to the method of the present invention, preferably, the conditions of the second drying include: the temperature is 90-120 ℃, and the time is 4-24 h.

According to the method of the present invention, preferably, the conditions of the second firing include: the temperature is 300 ℃ and 500 ℃, and the time is 2-4 h.

The drying and calcining processes can be performed according to conventional procedures in the art and are not described herein.

In the invention, under the condition that the dosage of the auxiliary agent precursor is satisfied to enable the content of the auxiliary agent in the prepared catalyst to be 0.1-10 wt% in terms of elements, the concentration of the auxiliary agent precursor solution is not particularly limited, and a person skilled in the art can determine the concentration of the auxiliary agent precursor solution according to the water absorption rate of the composite oxide and the content of the auxiliary agent in the prepared catalyst, which is not repeated herein.

In the present invention, the kind of the precursor of the additive is not particularly limited as long as the corresponding additive element can be provided, and the precursor of the additive is a substance capable of obtaining an oxide of the corresponding additive element through subsequent processing. For example, at least one selected from nitrate, carbonate, acetate and sulfate of an auxiliary agent. Specifically, the auxiliary may contain at least one selected from Na, K, Ca, and Mg, more preferably Na and/or K. When Na and/or K are/is selected, the catalytic performance of the iron-based catalyst can be better improved.

In a third aspect, the invention provides an iron-based catalyst prepared by the method of the second aspect of the invention.

In the present invention, the BET specific surface area of the iron-based catalyst is 300-580m²(ii)/g, more preferably 400-²Per g, pore volume of 0.3-0.8m³A ratio of 0.5 to 0.8 m/g is more preferable³/g。

The iron-based catalyst provided by the invention has the advantages of high reaction activity, low selectivity of low-carbon alkane and high selectivity of low-carbon olefin when being used in high-temperature Fischer-Tropsch synthesis reaction. Therefore, the fourth aspect of the invention also provides the application of the iron-based catalyst in Fischer-Tropsch synthesis.

The iron-based catalyst has the advantages of high reaction activity, low selectivity of low-carbon alkane and high selectivity of low-carbon olefin when used in high-temperature Fischer-Tropsch synthesis reaction, and preferably, the temperature of the high-temperature Fischer-Tropsch synthesis reaction is 300-350 ℃.

The present invention will be described in detail below by way of examples.

In the following examples and comparative examples, all materials used were commercially available unless otherwise specified;

the pore diameter and the BET specific surface area pore volume of the catalyst are measured by nitrogen physical adsorption;

the composition of the catalyst was determined by XRF.