Gradient nitrogen-doped iron-based catalyst capable of accurately controlling powder conveying mode as well as preparation method and application of gradient nitrogen-doped iron-based catalyst

Abstract

The invention discloses a gradient nitrogen-doped iron-based catalyst capable of accurately controlling a powder conveying mode and a preparation method and application thereof, and relates to the technical field of catalysts.The preparation method comprises the following steps that ferric salt and ferricyanide powder are added into deionized water at the same time to be stirred and mixed, aging, centrifuging, washing and drying are conducted, and the gradient nitrogen-doped iron-based catalyst is obtained; a precursor is obtained; and grinding, granulating and calcining to obtain the catalyst. The gradient nitrogen-doped carbon-coated iron-based catalyst is successfully prepared in an accurate powder conveying mode, and the gradient nitrogen-doped carbon-coated iron-based catalyst is used for Fischer-Tropsch synthesis, has high selectivity on high-carbon hydrocarbons, and is beneficial to efficient production of aviation energy.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and in particular to an iron-based catalyst with gradient nitrogen doping and precise control of powder delivery mode, as well as a preparation method and application thereof. Background Art

[0002] The aviation industry is an important component and supporting industry of the global economy. A large amount of aviation kerosene is consumed during transportation. Aviation kerosene, also known as jet fuel, is mainly used as fuel for jet aircraft engines. Its main components are C8~C 16 of normal isomerized paraffins, cycloalkanes, etc. Due to the increasing depletion of petroleum resources, the production routes of non-petroleum-based aviation kerosene have received more and more widespread attention. Among them, the process of preparing aviation kerosene from synthesis gas is one of the most promising production routes for alternative aviation fuels. Limited by the distribution law of ASF, the product selectivity of direct production of aviation kerosene by Fischer-Tropsch synthesis is limited. How to improve the selectivity of aviation kerosene is still an important challenge currently facing this field. In Fischer-Tropsch synthesis, iron-based catalysts have the advantages of low price, abundant resource reserves, low requirements for the H2 / CO ratio in synthesis gas, rich and adjustable product variety, and high activity, and therefore have broad application prospects. Regarding the synthesis of iron-based catalysts, more research is done on iron carbide catalysts wrapped in carbon shells, but the selectivity of such catalysts for long-chain hydrocarbons is often relatively low, so it is necessary to find a method for synthesizing highly active catalysts.

[0003] Effective nitrogen doping can regulate the dispersibility of metal nanoparticles, which is beneficial to improving the activity of the catalyst; at the same time, nitrogen doping can act as an electron donor atom, and nitrogen modification can enhance the interaction between the metal and the carrier, which is beneficial to regulate the adsorption and dissociation of carbon monoxide in Fischer-Tropsch synthesis and improve the selectivity of the product; nitrogen doping can inhibit the agglomeration of the catalyst and make the catalyst more stable.

[0004] CN117065781A discloses a method for preparing an alkali metal modified carbon nitride supported iron-based catalyst, comprising the following steps: (1) taking a certain amount of melamine, iron nitrate nonahydrate and alkali metal nitrate, putting them into a ball mill for a period of time to obtain a precursor; (2) putting the precursor into a tubular furnace for calcination to obtain the catalyst.

[0005] However, previous reports on nitrogen-doped catalysts often result in random distribution of nitrogen atoms, limiting further regulation of catalyst performance. Here, the present invention provides a method for synthesizing a gradient nitrogen-doped iron-based catalyst for use in Fischer-Tropsch synthesis, which has high selectivity for high-carbon hydrocarbons and can be used for aviation fuel.

[0006] A nitrogen-rich environment can change the electronic properties of the catalyst, thereby optimizing the catalyst's adsorption capacity for reactants and making the reaction easier to occur. In Fischer-Tropsch synthesis, synthesis gas often reacts on the surface of the catalyst, so it is necessary to design a catalyst with nitrogen-rich surface to improve the performance of the catalyst. In the synthesis of the catalyst, various powder precursors need to be added to the reaction solution for mixed reaction, but the powder precursor is often added to the reaction solution manually at one time using the traditional method. This traditional manual powder feeding method cannot achieve uniform, continuous and controllable introduction of powder materials. Here, the present invention utilizes a high-precision continuous powder conveying device to simultaneously add an iron salt precursor and ferrocyanide at different rates to dissolve in deionized water, so that iron ions and cyanide ions react slowly and continuously at a certain speed, regulate the binding sites of nitrogen elements and iron elements, and synthesize Fe@NC catalysts with gradient nitrogen distribution, which is of great significance to the development of efficient Fischer-Tropsch synthesis iron-based catalysts. Summary of the invention

[0007] In order to address the deficiencies in the prior art, the purpose of the present invention is to provide a powder conveying method that precisely controls an iron-based catalyst with gradient nitrogen doping, and a preparation method and application thereof. The present invention successfully prepares an iron-based catalyst coated with gradient nitrogen doping carbon through a precise powder conveying method, and uses it in Fischer-Tropsch synthesis. It has high selectivity for high-carbon hydrocarbons, and is conducive to the efficient production of aviation energy.

[0008] In order to achieve the above object, the present invention adopts the following technical solution:

[0009] A method for preparing an iron-based catalyst with gradient nitrogen doping by precisely controlling the powder delivery mode comprises the following steps:

[0010] (1) adding iron salt and ferrocyanide powders to deionized water respectively through a powder conveying device, stirring and mixing, aging, centrifuging, washing, and drying to obtain a precursor;

[0011] (2) Grinding, granulating and calcining the precursor to obtain the iron-based catalyst with gradient nitrogen doping.

[0012] Preferably, in step (1), the iron salt is one or more of FeCl3, FeSO4, Fe(NO3)3, FeCl2, Fe(C2H3O2)3, and Fe2(C2O4)3.

[0013] Preferably, in step (1), the ferrocyanide is one or more of Na4[Fe(CN)6], K3[Fe(CN)6], K4[Fe(CN)6], and Na3[Fe(CN)6].

[0014] Preferably, in step (1), the usage ratio of iron salt, ferrocyanide and deionized water is 1.825-5.01 g: 2.179-6.539 g: 50-150 mL.

[0015] Preferably, in step (1), the conveying speed of the iron salt powder is 0.012 to 0.72 g / min, the conveying speed of the ferrocyanide powder is 0.012 to 0.72 g / min, the stirring and mixing speed is 300 to 500 r / min, and stirring is continued for 20 to 60 min after the powder is added.

[0016] Preferably, in step (1), the aging condition is room temperature aging for 12 to 18 hours; the centrifugation condition is 8000 to 10000 r / min centrifugation for 5 to 15 minutes; the washing condition is washing with deionized water and anhydrous ethanol for 3 to 6 times respectively; and the drying condition is drying in a vacuum drying oven at 60 to 80° C. for 12 to 24 hours.

[0017] Preferably, in step (2), the precursor is ground and granulated and passed through a 20-120 mesh sieve.

[0018] Preferably, in step (2), the calcination conditions are to increase the temperature to 450-750° C. at a rate of 1-10° C. / min and keep the temperature for 60-600 min under an inert atmosphere to obtain an iron-based catalyst with gradient nitrogen doping.

[0019] The present invention also claims protection for an iron-based catalyst with gradient nitrogen doping prepared by the preparation method with precise control of the powder delivery mode.

[0020] The present invention also claims to protect the use of the gradient nitrogen-doped iron-based catalyst in Fischer-Tropsch synthesis.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention provides a preparation method with precise control of powder delivery mode, and adopts a coprecipitation method with synchronous and precise delivery of two components to prepare an iron-based catalyst, which overcomes the problems of local supersaturation and reaction runaway caused by the traditional one-time feeding method. Through the continuous and slow delivery process, the iron ions and cyanide ions can react in a controllable manner as expected, and the precise regulation of each component in the precursor is achieved. The method has good process repeatability and product stability, and is easy to achieve large-scale production.

[0023] 2. The powder conveying device used in the present invention can achieve accurate speed control of iron salt and ferrocyanide in the range of 0.012-0.72 g / min, ensuring the simultaneous addition of the two reactants and accurate control of the reaction process. By adjusting the powder conveying speed, the dynamic change of ion concentration in the solution can be accurately controlled, avoiding the problem of uneven precipitation caused by instantaneous reaction in traditional methods.

[0024] 3. The present invention successfully achieves a gradient distribution structure of nitrogen from the surface to the inside by precisely controlling the reaction kinetics of iron ions and cyanide ions. This unique gradient nitrogen-doped structure provides abundant active sites and enhances the electron transfer ability of the catalyst surface. In the Fischer-Tropsch synthesis reaction, the gradient-distributed nitrogen atoms can effectively adjust the electronic structure and adsorption properties of the iron-based catalyst, significantly improve the selectivity for high-carbon hydrocarbon products, and provide a new technical approach for the directional synthesis of aviation fuel. The present invention not only enriches the structural types of iron-based catalysts, but also provides an important scientific basis for the rational design of Fischer-Tropsch synthesis catalysts. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show schematic diagrams of certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 This is the XPS full spectrum of the catalyst obtained in Example 3 of the present invention after argon ion etching. Its surface mainly contains C, N, O, and Fe, indicating that the nitrogen-doped Fe@NC-S catalyst was successfully synthesized (the nitrogen content analysis results before and after etching are shown in Figure 2). Figure 3 );

[0027] Figure 2 This is the N1s spectrum of the XPS of the catalyst obtained in Example 3 of the present invention, which is mainly convoluted into three peaks, which belong to pyridine N, pyrrole N and graphite N, respectively, indicating that the catalyst doped with different types of nitrogen is successfully prepared;

[0028] Figure 3 This is a graph of N content before and after argon ion etching for 120 seconds by XPS in a vacuum system in Example 3 of the present invention. The nitrogen content before and after etching is analyzed. It can be seen that the nitrogen content is reduced after etching, indicating that nitrogen is distributed in a gradient in the catalyst;

[0029] Figure 4 This is the XRD spectrum of the catalyst in Case 3 of the present invention, indicating that the phase of the catalyst is a single Fe3C;

[0030] Figure 5 This is the full XPS spectrum of the catalyst before and after C etching in Comparative Example 1 of the present invention. The nitrogen content does not change much after etching, indicating that the catalyst does not have a structure with gradient nitrogen distribution. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with embodiments. Of course, the specific embodiments described here are only used to explain the present invention and are not used to limit the present invention.

[0032] Unless otherwise specified, the chemical reagents and materials in the present invention are purchased from commercial sources or synthesized from raw materials purchased from commercial sources.

[0033] A method for preparing an iron-based catalyst with gradient nitrogen doping by precisely controlling the powder delivery mode comprises the following steps:

[0034] (1) adding 1.825-5.01 g of iron salt into a feed funnel of a powder conveying device, adding 2.179-6.539 g of ferricyanide into another feed funnel of a powder conveying device, turning on the power supply and turning on the control switch at the same time, slowly and continuously adding the iron salt powder at a rate of 0.012-0.72 g / min and the ferricyanide powder at a rate of 0.012-0.72 g / min into 50-150 mL of deionized water, stirring and mixing at 300-500 r / min, stirring for 20-60 min after the powder is added, aging at room temperature for 12-18 h, centrifuging at 8000-10000 r / min for 5-15 min, washing with deionized water and anhydrous ethanol for 3-6 times respectively, and then drying in a vacuum drying oven at 60-80° C. for 12-24 h to obtain a precursor;

[0035] Specifically, the iron salt may be FeCl3, FeSO4, Fe(NO3)3, FeCl2, Fe(C2H3O2)3, or Fe2(C2O4)3.

[0036] Specifically, the ferrocyanide is Na4[Fe(CN)6], K3[Fe(CN)6], K4[Fe(CN)6], Na3[Fe(CN)6].

[0037] Specifically, the usage ratio of iron salt, ferrocyanide and deionized water can be 1.825g:2.179g:50mL, 1.825g:2.179g:150mL, 1.825g:6.539g:50mL, 1.825g:6.539g:150mL, 5.01g:2.179g:50mL, 5.01g:2.179g:150mL, 5.01g:6.539g:50mL, 5.01g:6.539g:150mL, and 3.649g:4.359g:150mL.

[0038] Specifically, the conveying speed of the iron salt powder can be 0.012, 0.024, 0.036, 0.048, 0.060, 0.072, 0.084, 0.096, 0.108, 0.12, 0.24, 0.36, 0.48, 0.60, or 0.72 g / min.

[0039] Specifically, the conveying speed of the ferrocyanide powder can be 0.012, 0.024, 0.036, 0.048, 0.060, 0.072, 0.084, 0.096, 0.108, 0.12, 0.24, 0.36, 0.48, 0.60, or 0.72 g / min.

[0040] Specifically, the stirring and mixing speed can be 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500 r / min.

[0041] Specifically, stirring was continued for 20, 25, 30, 35, 40, 45, 50, 55, and 60 minutes after the powder was added.

[0042] Specifically, the aging conditions may be room temperature aging for 12, 13, 14, 15, 16, 17, or 18 hours.

[0043] Specifically, the centrifugation conditions can be 8000, 8500, 9000, 9500, 10000 r / min for 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 min.

[0044] Specifically, the washing conditions may be washing with deionized water and anhydrous ethanol for 3, 4, 5, or 6 times respectively.

[0045] Specifically, the drying conditions may be drying in a vacuum drying oven at 60, 65, 70, 75, or 80° C. for 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, or 24 h.

[0046] (2) Grinding the precursor into powder, pressing into tablets to obtain a catalyst with a mesh size of 20 to 120, placing the catalyst in an inert atmosphere, heating the temperature to 450 to 750° C. at a rate of 1 to 10° C. / min and maintaining the temperature for 60 to 600 min to obtain the iron-based catalyst with gradient nitrogen doping.

[0047] Specifically, the precursor is ground and granulated and passed through 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, or 120 mesh sieves.

[0048] Specifically, the calcination conditions can be to increase the temperature to 450, 500, 550, 600, 650, 700, 750°C at 1, 2, 3, 4, 5, 6, 7, 8, 9, 10°C / min in an inert atmosphere and keep it for 60, 120, 180, 240, 300, 360, 420, 480, 540, 600 min.

[0049] The present invention will be further described below through specific embodiments.

[0050] Example 1

[0051] A method for preparing an iron-based catalyst with gradient nitrogen doping by precisely controlling the powder delivery mode comprises the following steps:

[0052] (1) Add 3.649 g FeCl3 into the feeding funnel of the powder conveying device, add 4.359 g Na4[Fe(CN)6] into the feeding funnel of another powder conveying device, turn on the power and turn on the control switch at the same time, slowly and continuously add the iron salt powder at a rate of 0.243 g / min and the ferrocyanide powder at a rate of 0.291 g / min into 150 mL deionized water, stir and mix at 350 r / min, continue stirring for 30 min after the powder is added, stand at room temperature for aging for 15 h, centrifuge at 8500 r / min for 5 min, wash with deionized water and anhydrous ethanol for 4 times respectively, and then put into a vacuum drying oven at 60°C for 24 h to obtain a precursor;

[0053] (2) Grind the precursor into powder, press into tablets to obtain a catalyst with a mesh size of 20 to 40, take 2 g of the catalyst and place it in a quartz tube, heat it to 550° C. at a rate of 5° C. / min under a N 2 atmosphere and keep it for 1 hour to obtain the iron-based catalyst with gradient nitrogen doping.

[0054] Example 2

[0055] A method for preparing an iron-based catalyst with gradient nitrogen doping by precisely controlling the powder delivery mode comprises the following steps:

[0056] (1) Add 3.649 g FeCl3 into the feeding funnel of the powder conveying device, add 4.359 g Na4[Fe(CN)6] into the feeding funnel of another powder conveying device, turn on the power and turn on the control switch at the same time, slowly and continuously add the iron salt powder at a rate of 0.182 g / min and the ferrocyanide powder at a rate of 0.218 g / min into 150 mL deionized water, stir and mix at 350 r / min, continue stirring for 30 min after the powder is added, stand at room temperature for aging for 15 h, centrifuge at 8500 r / min for 5 min, wash with deionized water and anhydrous ethanol for 4 times respectively, and then put into a vacuum drying oven at 60°C for 24 h to obtain a precursor;

[0057] (2) Grind the precursor into powder, press into tablets to obtain a catalyst with a mesh size of 20 to 40, take 2 g of the catalyst and place it in a quartz tube, heat it to 550° C. at a rate of 5° C. / min under a N 2 atmosphere and keep it for 1 hour to obtain the iron-based catalyst with gradient nitrogen doping.

[0058] Example 3

[0059] A method for preparing an iron-based catalyst with gradient nitrogen doping by precisely controlling the powder delivery mode comprises the following steps:

[0060] (1) Add 3.649 g FeCl3 into the feeding funnel of the powder conveying device, add 4.359 g Na4[Fe(CN)6] into the feeding funnel of another powder conveying device, turn on the power and turn on the control switch at the same time, slowly and continuously add the iron salt powder at a rate of 0.156 g / min and the ferrocyanide powder at a rate of 0.174 g / min into 150 mL deionized water, stir and mix at 350 r / min, continue stirring for 30 min after the powder is added, stand at room temperature for aging for 15 h, centrifuge at 8500 r / min for 5 min, wash with deionized water and anhydrous ethanol for 4 times respectively, and then put into a vacuum drying oven at 60°C for 24 h to obtain a precursor;

[0061] (2) Grind the precursor into powder, press into tablets to obtain a catalyst with a mesh size of 20 to 40, take 2 g of the catalyst and place it in a quartz tube, heat it to 550° C. at a rate of 5° C. / min under a N 2 atmosphere and keep it for 1 hour to obtain the iron-based catalyst with gradient nitrogen doping.

[0062] Example 4

[0063] A method for preparing an iron-based catalyst with gradient nitrogen doping by precisely controlling the powder delivery mode comprises the following steps:

[0064] (1) Add 3.649 g FeCl3 into the feeding funnel of the powder conveying device, add 4.359 g Na4[Fe(CN)6] into the feeding funnel of another powder conveying device, turn on the power and turn on the control switch at the same time, slowly and continuously add the iron salt powder at a rate of 0.122 g / min and the ferrocyanide powder at a rate of 0.145 g / min into 150 mL deionized water, stir and mix at 350 r / min, continue stirring for 30 min after the powder is added, stand at room temperature for aging for 15 h, centrifuge at 8500 r / min for 5 min, wash with deionized water and anhydrous ethanol for 4 times respectively, and then put into a vacuum drying oven at 60°C for 24 h to obtain a precursor;

[0065] (2) Grind the precursor into powder, press into tablets to obtain a catalyst with a mesh size of 20 to 40, take 2 g of the catalyst and place it in a quartz tube, heat it to 550° C. at a rate of 5° C. / min under a N 2 atmosphere and keep it for 1 hour to obtain the iron-based catalyst with gradient nitrogen doping.

[0066] Comparative Example 1

[0067] A method for preparing a nitrogen-doped iron-based catalyst comprises the following steps:

[0068] (1) 3.78 g of Fe2(C2O4)3 was added to 50 mL of deionized water stirred at 350 r / min and stirred for 15 min to obtain solution A; 4.359 g of Na4[Fe(CN)6] was added to 100 mL of deionized water stirred at 350 r / min and stirred for 15 min to obtain solution B;

[0069] (2) At room temperature, solution B was slowly added to solution A using a microchannel under the action of a peristaltic pump at a pump speed of 18.5 r / min. After the addition was completed, the mixed solution was continuously stirred for 30 min, aged at room temperature for 15 h, and then centrifuged at a speed of 8500 r / min for 5 min. The mixture was washed with deionized water and anhydrous ethanol for 6 times, respectively, and then dried in a vacuum drying oven at 60° C. for 24 h to obtain a precursor.

[0070] (3) Grind the precursor into powder, press into tablets to obtain a catalyst with a mesh size of 20 to 40, take 2 g of the catalyst and place it in a quartz tube, heat it to 550° C. at a rate of 5° C. / min under a N 2 atmosphere and keep it for 1 hour to obtain the nitrogen-doped iron-based catalyst.

[0071] Comparative Example 2

[0072] A method for preparing a nitrogen-doped iron-based catalyst comprises the following steps:

[0073] (1) 3.78 g of FeCl3 and 4.359 g of Na4[Fe(CN)6] were added directly to 150 mL of deionized water stirred at 350 r / min, stirred at 350 r / min for 30 min, aged at room temperature for 15 h, centrifuged at 8500 r / min for 5 min, washed with deionized water and anhydrous ethanol for 4 times, and then dried in a vacuum drying oven at 60°C for 24 h to obtain a precursor;

[0074] (2) The precursor is ground into powder and pressed into tablets to obtain a catalyst with a mesh size of 20 to 40. 2 g of the catalyst is placed in a quartz tube and heated to 550° C. at a rate of 5° C. / min under a N2 atmosphere and maintained for 1 h to obtain the nitrogen-doped iron-based catalyst.

[0075] Comparative Example 3

[0076] A method for preparing a nitrogen-doped iron-based catalyst comprises the following steps:

[0077] (1) Add 3.649 g of FeCl3 to 50 mL of deionized water stirred at 350 r / min and stir for 15 min to obtain solution A; add 4.359 g of Na4[Fe(CN)6] to 100 mL of deionized water stirred at 350 r / min and stir for 15 min to obtain solution B;

[0078] (2) At room temperature, solution B was slowly added to solution A using a microchannel under the action of a peristaltic pump at a pump speed of 18.5 r / min. After the addition was completed, the mixed solution was continuously stirred for 30 min, aged at room temperature for 15 h, and then centrifuged at a speed of 8500 r / min for 5 min. The mixture was washed with deionized water and anhydrous ethanol for 4 times, respectively, and then dried in a vacuum drying oven at 60° C. for 24 h to obtain a precursor.

[0079] (3) Grind the precursor into powder, press into tablets to obtain a catalyst with a mesh size of 20 to 40, take 2 g of the catalyst and place it in a quartz tube, heat it to 550° C. at a rate of 5° C. / min under a N 2 atmosphere and keep it for 1 hour to obtain the nitrogen-doped iron-based catalyst.

[0080] Comparative Example 4

[0081] A method for preparing a nitrogen-doped iron-based catalyst comprises the following steps:

[0082] (1) Weigh 0.706 g Fe(C5H7O2)3 and 0.9 g C6H 12 O6 was dissolved in 50 mL of ethylene glycol, mixed and stirred for 30 min at a speed of 500 r / min. After stirring evenly, it was transferred to the reactor, sealed, and placed in an oven at 200 °C for reaction for 15 h.

[0083] (2) After the reaction is completed, the mixture is cooled naturally, then centrifuged at 8500 r / min for 5 min, washed with deionized water and anhydrous ethanol for 4 times, and then dried in a vacuum drying oven at 60° C. for 12 h to obtain a precursor;

[0084] (3) Grinding the precursor into powder, pressing into tablets to obtain a catalyst with a mesh size of 20 to 40, taking 2 g of the catalyst and placing it in a quartz tube, heating it to 600° C. at a rate of 5° C. / min under an Ar atmosphere and maintaining it for 2 h, thereby obtaining the nitrogen-doped iron-based catalyst.

[0085] The catalysts prepared in Examples 1 to 4 and Comparative Examples 1 to 4 were tested for the performance of syngas to long-chain hydrocarbons. The specific test method is as follows: 0.2 g of the prepared catalyst was loaded into a fixed bed reactor. The reaction conditions were 300° C., H2 / CO=2 (molar ratio), 2 MPa, 6000 h -1 , Fischer-Tropsch synthesis reaction was carried out, and the specific test results are shown in Table 1.

[0086] Table 1 Performance test of catalysts for synthesis gas to long-chain hydrocarbons

[0087]

[0088] As shown in Table 1, the CO conversion rate of the catalysts provided in Comparative Examples 1 to 4 is low, all lower than 60%. The CO conversion rate of the catalysts provided in Examples 1 to 4 of the present invention is relatively high, and the CO conversion rate of the catalysts provided in Example 3 is relatively high. 8～16 The hydrocarbon selectivity is as high as 67.8%. Combined with the XPS spectrum and XRD spectrum, it can be obtained that the iron-based catalyst doped with gradient nitrogen has high selectivity for high-carbon hydrocarbons, which is beneficial to solving aviation energy problems. The catalyst with a special structure obtained by this catalyst synthesis method has obtained good results in performance tests.

[0089] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing an iron-based catalyst with gradient nitrogen doping by precisely controlling the powder delivery mode, characterized in that: The steps include: (1) adding iron salt and ferrocyanide powders to deionized water respectively through a powder conveying device, stirring and mixing, aging, centrifuging, washing, and drying to obtain a precursor; (2) Grinding, granulating and calcining the precursor to obtain the iron-based catalyst with gradient nitrogen doping.

2. The preparation method according to claim 1, characterized in that: In step (1), the iron salt is one or more of FeCl3, FeSO4, Fe(NO3)3, FeCl2, Fe(C2H3O2)3, and Fe2(C2O4)3.

3. The preparation method according to claim 1, characterized in that: In step (1), the ferrocyanide is one or more of Na4[Fe(CN)6], K3[Fe(CN)6], K4[Fe(CN)6], and Na3[Fe(CN)6].

4. The preparation method according to claim 1, characterized in that: In step (1), the usage ratio of iron salt, ferrocyanide and deionized water is 1.825-5.01 g: 2.179-6.539 g: 50-150 mL.

5. The preparation method according to claim 1, characterized in that: In step (1), the conveying speed of the iron salt powder is 0.012 to 0.72 g / min, the conveying speed of the ferrocyanide powder is 0.012 to 0.72 g / min, the stirring and mixing speed is 300 to 500 r / min, and stirring is continued for 20 to 60 min after the powder is added.

6. The preparation method according to claim 1, characterized in that: In step (1), the aging condition is aging at room temperature for 12 to 18 hours; the centrifugation condition is centrifugation at 8000 to 10000 r / min for 5 to 15 minutes; the washing condition is washing with deionized water and anhydrous ethanol for 3 to 6 times respectively; and the drying condition is drying in a vacuum drying oven at 60 to 80° C. for 12 to 24 hours.

7. The preparation method according to claim 1, characterized in that: In step (2), the precursor is ground into granules and passed through a 20-120 mesh sieve.

8. The preparation method according to claim 1, characterized in that: In step (2), the calcination conditions are to increase the temperature to 450-750° C. at a rate of 1-10° C. / min and keep the temperature for 60-600 min under an inert atmosphere to obtain an iron-based catalyst with gradient nitrogen doping.

9. An iron-based catalyst with gradient nitrogen doping prepared by the preparation method with precise control of the powder conveying mode as described in any one of claims 1 to 8.

10. Use of the gradient nitrogen-doped iron-based catalyst as claimed in claim 9 in Fischer-Tropsch synthesis.

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