An alkali metal-doped iron-based perovskite catalyst, a preparation method and application thereof

Abstract

An alkali metal-doped iron-based perovskite catalyst, its preparation method, and its application are disclosed. The catalyst uses an iron-based perovskite catalyst as a matrix, in which alkali metals are in-situ doped. The method includes mixing Nd(NO3)3·6H2O, Fe(NO3)3·9H2O, and deionized water to obtain a metal salt solution; mixing the metal salt solution with a complexing agent and adding ammonia to adjust the pH to neutral to obtain a sol; subjecting the sol to aging, drying, calcining, and grinding sequentially to obtain NdFeO3; mixing NdFeO3, carbonate, and deionized water to obtain an alkali metal-doped iron-based perovskite catalyst; introducing alkali metal elements into the iron-based perovskite catalyst through impregnation and physical mixing processes; constructing locally electron-rich regions on the surface of the iron-based perovskite catalyst with alkali metals; achieving surface enrichment of active sites; and significantly improving the catalyst activity and selectivity for low-carbon olefins.

Description

Technical Field

[0001] This invention relates to the field of petrochemical catalysis technology, specifically to an alkali metal-doped iron-based perovskite catalyst, its preparation method, and its application. Background Technology

[0002] Carbon monoxide hydrogenation conversion is of great significance for carbon resource utilization and carbon neutrality. Traditional iron-based catalysts have been widely studied due to their advantages such as low cost, strong adaptability to feedstocks (able to withstand high CO partial pressures), and high activity in water-gas shift (WGS) (suitable for coal-based syngas with low H2 / CO ratios). However, the system has problems such as excessive hydrogenation activity, high methane selectivity, and complex and uncontrollable active phase composition. The activity of traditional iron-based catalysts depends on specific active phases (such as ε'-Fe2.2C, χ-Fe5C2), but the formation and stability of the active phase require precise control of the preparation process (such as precursor selection, reducing atmosphere, and carbonization conditions), and are extremely sensitive to preparation parameters. The performance of different batches of catalysts fluctuates greatly, making it difficult to meet the stability requirements of industrial plants.

[0003] Perovskite oxides possess stable crystal structures and excellent thermal stability. Introducing active components into the perovskite structure can effectively suppress the sintering of active components and improve catalyst stability. However, there is still room for improvement in the catalytic activity and product selectivity of pure iron-based perovskite catalysts in the hydrogenation reaction of carbon monoxide.

[0004] Alkali metal promoters have been shown to regulate product distribution by adjusting the electron density on the surface of the active phase, thereby affecting hydrogenation capacity. The regulatory mechanism of alkali metal promoters (Li, Na, K) on iron-based Fischer-Tropsch catalysts is a highly dynamic and complex process. Their effect depends not only on the electronic properties of the alkali metal (such as electronegativity and ionic radius) but also on the type of iron active phase (such as Fe5C2, Fe3C, Fe3O4) and its dynamic evolution.

[0005] Therefore, it is necessary to efficiently and stably dope alkali metals into iron-based perovskite catalysts through modification methods to improve catalyst activity, suppress by-products, and enhance the catalyst's anti-sintering performance. Summary of the Invention

[0006] To overcome the shortcomings of the existing technology, the present invention aims to provide an alkali metal-doped iron-based perovskite catalyst, its preparation method and application. Alkali metal elements are introduced into the iron-based perovskite catalyst through impregnation and physical mixing processes. The alkali metals construct local electron-rich regions on the surface of the iron-based perovskite catalyst, thereby achieving surface enrichment of active sites and significantly improving the activity of the catalyst and the selectivity of low-carbon olefins.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: An alkali metal-doped iron-based perovskite catalyst is prepared by in-situ doping an alkali metal into an iron-based perovskite catalyst matrix; the chemical formula of the alkali metal-doped iron-based perovskite catalyst is A. x -BFeO3, where A is one of Li, Na, and K, and B is Nd; based on the number of moles of Fe in BFeO3, x is the number of moles of component A, with a value range of 0.25~0.5, that is, the number of moles of component A is 25%~50% of the number of moles of Fe.

[0008] A method for preparing an alkali metal-doped iron-based perovskite catalyst includes the following steps: Step S1: Mix Nd(NO3)3·6H2O, Fe(NO3)3·9H2O and deionized water until homogeneous to obtain a metal salt solution; Step S2: Mix the metal salt solution and complexing agent, and add ammonia dropwise to adjust the pH to neutral to obtain a sol; Step S3: The sol is subjected to aging, drying, calcination and grinding in sequence to obtain NdFeO3; Step S4: Mix NdFeO3, carbonate, and deionized water at a mass ratio of 1:(0.25~0.5):4 until homogeneous, then dry, calcine, and grind sequentially to obtain an alkali metal-doped iron-based perovskite catalyst.

[0009] Further, in step S1, the mass ratio of Nd(NO3)3·6H2O, Fe(NO3)3·9H2O and deionized water is (2.5~3.5):(1.5~2.5):(4~6), the mixing time is 30~60 min, and the mixing speed is 500~900 rpm.

[0010] Further, in step S2, the mass ratio of the metal salt solution to the complexing agent is (0.8~1.2):1; the complexing agent is one of citric acid monohydrate and anhydrous citric acid.

[0011] Further, in step S3, the aging time is 3~5h, the aging temperature is 35~45℃, the drying time is 12~18h, the drying temperature is 80~110℃, during calcination, the temperature is increased from 20~30℃ to 800~900℃ at a rate of 1.5~2.5℃ / min, and maintained at 800~900℃ for 2~4h, the calcination atmosphere is air, and after calcination, the temperature is cooled to 20~30℃, and then ground to a particle size distribution of 10~20 nm.

[0012] Furthermore, in step S4, the carbonate is one of lithium carbonate, sodium carbonate, and potassium carbonate.

[0013] Further, in step S4, the mixing and stirring time is 30-60 min, the mixing and stirring rate is 600-800 rpm, the drying time is 6-12 h, the drying temperature is 85-110℃, and during calcination, the temperature is increased from 20-30℃ to 800-900℃ at a rate of 1.5-2.5℃ / min and maintained at 800-900℃ for 4-6 h. The calcination atmosphere is air. After calcination, the temperature is cooled to 20-30℃ and then ground until the particle size distribution is 15-25 nm.

[0014] An application of an alkali metal-doped iron-based perovskite catalyst as described above, or an alkali metal-doped iron-based perovskite catalyst prepared by any of the above methods, in the catalytic conversion of carbon monoxide and hydrogen into low-carbon olefins via co-feed reaction, involves loading the alkali metal-doped iron-based perovskite catalyst into a fixed-bed reactor, pumping in syngas formed from carbon monoxide and hydrogen, and using nitrogen or argon as the carrier gas. Low-carbon olefins are prepared under preset reaction conditions; the volume ratio of carbon monoxide to hydrogen is 1:(1~3), and the mass hourly space velocity (MSV) of the alkali metal-doped iron-based perovskite catalyst is 500~3600 mL·g. - ¹·h - ¹; The preset reaction conditions are: reaction temperature 300~400℃, reaction pressure 1~3 MPa.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention provides an alkali metal-doped iron-based perovskite catalyst, which, compared with existing iron-based perovskite catalysts, has the advantages of multiple active sites, strong structural stability, and precise controllability of electronic properties. Alkali metals are doped into the iron-based perovskite catalyst in a composite manner of "mainly in-situ doping and supplemented by surface impregnation". The alkali metals (Li, Na, K) replace some of the lattice sites of Nd by doping, and regulate the electronic state of Fe species through the dual effects of "intralattice charge transfer" and "surface electron enrichment". The surface-impregnated alkali metals form local electron-rich regions on the catalyst surface, which inhibits the dissociation and adsorption of H2, while improving the adsorption capacity of CO, thus solving the problem of "excessive hydrogenation activity" of iron-based perovskite catalysts.

[0016] 2. In the process of preparing alkali metal-doped iron-based perovskite catalysts, the present invention first prepares iron-based perovskite catalysts through sol-gel to ensure the stability of the crystal structure, and then loads alkali metals onto the catalysts through impregnation to achieve surface enrichment of active sites. During calcination in step S4, the heating rate is controlled within the range of 1.5~2.5℃ / min for slow heating, allowing the precursor distribution to decompose and the lattice to recombine. In the initial heating stage (20~300℃), nitrates and citric acid are gradually dehydrated and decomposed (avoiding catalyst pore collapse caused by rapid gas release). In the middle heating stage (300~600℃), the metal oxides undergo a solid-state reaction, and slow heating ensures the reaction proceeds fully, reducing lattice defects. In the later heating stage (600~900℃), the perovskite lattice is recombined, and slow heating inhibits excessive grain growth (the final grain size is controlled at 15~25 nm, much smaller than the 35 nm or more of the prior art). At the same time, the calcination temperature of 800~900℃ and the holding time of 4~6 h further consolidate the pure phase structure of the perovskite.

[0017] 3. When the alkali metal-doped iron-based perovskite catalyst of the present invention catalyzes the co-feeding conversion of carbon monoxide and hydrogen into low-carbon olefins, the selectivity of low-carbon olefins is increased from 0.72% to 20-30% through catalyst activity testing, which significantly improves the selectivity of the target product. It has significant advantages such as high selectivity of low-carbon hydrocarbons, low selectivity of methane, stable and controllable active phase, and good repeatability of catalytic performance.

[0018] In summary, the alkali metal-doped iron-based perovskite catalyst of the present invention is prepared by conventional methods such as simple impregnation and physical mixing. The introduction of alkali metal elements is simple and does not require complicated post-processing. The alkali metals construct local electron-rich regions on the surface of the iron-based perovskite catalyst, thereby achieving surface enrichment of active sites and significantly improving the activity of the catalyst and the selectivity of low-carbon olefins. Attached Figure Description

[0019] Figure 1 In the embodiments of the present invention, NdFeO3 and Li 0.25 -NdFeO3, Na 0.25 -NdFeO3 and K 0.25 XRD pattern of NdFeO3 catalyst.

[0020] Figure 2 In the embodiments of the present invention, NdFeO3 and Li 0.5 -NdFeO3, Na 0.5 -NdFeO3 and K 0.5 XRD pattern of NdFeO3 catalyst.

[0021] Figure 3This is a flowchart of the preparation method of the alkali metal-doped iron-based perovskite catalyst of the present invention.

[0022] Figure 4 In the embodiments of the present invention, NdFeO3 and Li 0.5 -NdFeO3, Na 0.5 -NdFeO3 and K 0.5 - Hydrocarbon selectivity distribution of NdFeO3 catalyst in the co-feed reaction of carbon monoxide and hydrogen to low-carbon olefins.

[0023] Figure 5 In the embodiments of the present invention, NdFeO3 and Li 0.5 -NdFeO3, Na 0.5 -NdFeO3 and K 0.5 - Line graph of CO conversion rate in the co-feed reaction of carbon monoxide and hydrogen to low-carbon olefins using NdFeO3 catalyst. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments: An alkali metal-doped iron-based perovskite catalyst is prepared by in-situ doping an alkali metal into an iron-based perovskite catalyst matrix; the chemical formula of the alkali metal-doped iron-based perovskite catalyst is A. x -BFeO3, where A is one of Li, Na, or K, and B is Nd; based on the molar number of Fe in BFeO3, x is the molar number of component A, ranging from 0.25 to 0.5, meaning the molar number of component A is 25% to 50% of the molar number of Fe. See also Figure 1 and Figure 2 The XRD patterns of the doped catalysts all showed sharp diffraction peaks that perfectly matched those of perovskite NdFeO3. The positions of the main characteristic diffraction peaks corresponded one-to-one with the standard diffraction peaks of NdFeO3, and no impurity peaks were observed, indicating that the doped catalysts have good crystallinity and a pure phase structure. This invention, through a "sol-gel + composite impregnation" preparation process, successfully doped Li, Na, and K into the NdFeO3 perovskite matrix within a doping range of 25% to 50%. The catalysts maintained a complete perovskite pure phase structure, with no impurity phase formation, good crystallinity, and a stable lattice structure.

[0025] Example 1 See Figure 3 A method for preparing an alkali metal-doped iron-based perovskite catalyst includes the following steps: Step S1: Mix Nd(NO3)3·6H2O, Fe(NO3)3·9H2O and deionized water in a mass ratio of 3:2:5 After mixing, place the mixture in a DF-101S magnetic stirrer and stir at 800 rpm for 45 min to obtain a metal salt solution. Step S2: Mix the metal salt solution and citric acid monohydrate at a mass ratio of 1:1, and add ammonia dropwise to adjust the pH to neutral to obtain a sol; Step S3: The sol was aged at 35℃ for 5 hours, then dried in an 80℃ oven for 12 hours. After drying, it was placed in a muffle furnace and heated from 20℃ to 900℃ at a rate of 2℃ / min in air, and calcined at 900℃ for 4 hours. After calcination, it was cooled to 20℃ and then placed in an agate mortar and manually ground until the particle size distribution was 10~20 nm to obtain NdFeO. 3; Step S4: Mix NdFeO3, potassium carbonate, and deionized water at a mass ratio of 1:0.25:4, place in an F-101S magnetic stirrer, and stir at 800 rpm for 30 min. After stirring evenly, dry in an 85℃ oven for 6 h, then transfer to a muffle furnace and calcine at 800℃ for 4 h at a rate of 2℃ / min under air atmosphere, heating from 20℃ to 800℃. After calcination, cool to 20℃, place in an agate mortar, and manually grind until the particle size distribution is 15~25 nm to obtain a potassium-doped iron-based perovskite catalyst, i.e., K. 0.25 -NdFeO3.

[0026] Example 2 Step S1: Mix Nd(NO3)3·6H2O, Fe(NO3)3·9H2O and deionized water in a mass ratio of 2.5:1.5:4, place the mixture in a DF-101S magnetic stirrer, and stir at 500 rpm for 30 min to obtain a metal salt solution. Step S2: Mix the metal salt solution and anhydrous citric acid at a mass ratio of 0.8:1, and add ammonia water dropwise to adjust the pH to neutral to obtain a sol; Step S3: The sol was aged at 45℃ for 3 hours, then dried in an 80℃ oven for 12 hours. After drying, it was placed in a muffle furnace and heated from 20℃ to 800℃ at a rate of 1.5℃ / min in air, and calcined at 800℃ for 2 hours. After calcination, it was cooled to 20℃ and then placed in an agate mortar and manually ground until the particle size distribution was 10~20 nm to obtain NdFeO. 3; Step S4: Mix NdFeO3, sodium carbonate, and deionized water at a mass ratio of 1:0.25:4, place in an F-101S magnetic stirrer, and stir at 800 rpm for 30 min. After stirring evenly, dry in an 85℃ oven for 6 h, then transfer to a muffle furnace and calcine at 800℃ for 4 h at a rate of 1.5℃ / min under air atmosphere, increasing the temperature from 20℃ to 800℃. After calcination, cool to 20℃, place in an agate mortar, and manually grind until the particle size distribution is 15~25 nm to obtain sodium-doped iron-based perovskite catalyst, i.e., Na. 0.25 -NdFeO3.

[0027] Example 3 Step S1: Mix Nd(NO3)3·6H2O, Fe(NO3)3·9H2O and deionized water in a mass ratio of 3.5:2.5:6, place the mixture in a DF-101S magnetic stirrer, and stir at 900 rpm for 60 min to obtain a metal salt solution. Step S2: Mix the metal salt solution and citric acid monohydrate at a mass ratio of 1.2:1, and add ammonia dropwise to adjust the pH to neutral to obtain a sol; Step S3: The sol was aged at 40℃ for 4 hours, then dried in an oven at 110℃ for 18 hours. After drying, it was placed in a muffle furnace and heated from 30℃ to 900℃ at a rate of 2.5℃ / min in air, and calcined at 900℃ for 4 hours. After calcination, it was cooled to 30℃ and then placed in an agate mortar and manually ground until the particle size distribution was 10~20 nm to obtain NdFeO. 3; Step S4: NdFeO3, lithium carbonate, and deionized water are mixed at a mass ratio of 1:0.25:4 and placed in an F-101S magnetic stirrer. The mixture is stirred at 800 rpm for 30 min. After thorough mixing, it is dried in a 110℃ oven for 12 h, then transferred to a muffle furnace and calcined at 900℃ for 6 hours at a rate of 2.5℃ / min under air atmosphere, increasing the temperature from 30℃ to 900℃. After calcination, the mixture is cooled to 30℃, placed in an agate mortar, and manually ground until the particle size distribution is 15~25 nm, yielding a lithium-doped iron-based perovskite catalyst, i.e., Li. 25 -NdFeO3.

[0028] Example 4 Step S1: Mix Nd(NO3)3·6H2O, Fe(NO3)3·9H2O and deionized water in a mass ratio of 3:2:5 After mixing, place the mixture in a DF-101S magnetic stirrer and stir at 800 rpm for 45 min to obtain a metal salt solution. Step S2: Mix the metal salt solution and citric acid monohydrate at a mass ratio of 1:1, and add ammonia dropwise to adjust the pH to neutral to obtain a sol; Step S3: The sol was aged at 35℃ for 5 hours, then dried in an 80℃ oven for 12 hours. After drying, it was placed in a muffle furnace and heated from 20℃ to 900℃ at a rate of 2℃ / min in air, and calcined at 900℃ for 4 hours. After calcination, it was cooled to 20℃ and then placed in an agate mortar and manually ground until the particle size distribution was 10~20 nm to obtain NdFeO. 3; Step S4: NdFeO3, lithium carbonate, and deionized water are mixed in a mass ratio of 1:0.5:4 and placed in an F-101S magnetic stirrer. The mixture is stirred at 700 rpm for 35 min. After thorough mixing, it is dried in a 90℃ oven for 10 h, then transferred to a muffle furnace and calcined at 850℃ for 5 h at a rate of 2℃ / min under air atmosphere, starting from 25℃. After calcination, it is cooled to 25℃, placed in an agate mortar, and manually ground until the particle size distribution is 15~25 nm, yielding a lithium-doped iron-based perovskite catalyst, i.e., Li. 0.5 -NdFeO3.

[0029] Example 5 Step S1: Mix Nd(NO3)3·6H2O, Fe(NO3)3·9H2O and deionized water in a mass ratio of 3:2:5 After mixing, place the mixture in a DF-101S magnetic stirrer and stir at 800 rpm for 45 min to obtain a metal salt solution. Step S2: Mix the metal salt solution and citric acid monohydrate at a mass ratio of 1:1, and add ammonia dropwise to adjust the pH to neutral to obtain a sol; Step S3: The sol was aged at 35℃ for 5 hours, then dried in an 80℃ oven for 12 hours. After drying, it was placed in a muffle furnace and heated from 20℃ to 900℃ at a rate of 2℃ / min in air, and calcined at 900℃ for 4 hours. After calcination, it was cooled to 20℃ and then placed in an agate mortar and manually ground until the particle size distribution was 10~20 nm to obtain NdFeO. 3; Step S4: Mix NdFeO3, potassium carbonate, and deionized water at a mass ratio of 1:0.5:4, place the mixture in an F-101S magnetic stirrer, and stir at 800 rpm for 60 min. After thorough mixing, dry the mixture in a 100℃ oven for 11 h, then transfer it to a muffle furnace and calcine it at 850℃ for 5 h at a rate of 2℃ / min under air atmosphere, heating from 28℃ to 850℃. After calcination, cool the mixture to 26℃, place it in an agate mortar, and manually grind it until the particle size distribution is 15~25 nm to obtain the potassium-doped iron-based perovskite catalyst, i.e., K. 0.5 -NdFeO3.

[0030] Example 6 Step S1: Mix Nd(NO3)3·6H2O, Fe(NO3)3·9H2O and deionized water in a mass ratio of 3:2:5 After mixing, place the mixture in a DF-101S magnetic stirrer and stir at 800 rpm for 45 min to obtain a metal salt solution. Step S2: Mix the metal salt solution and citric acid monohydrate at a mass ratio of 1:1, and add ammonia dropwise to adjust the pH to neutral to obtain a sol; Step S3: The sol was aged at 35℃ for 5 hours, then dried in an 80℃ oven for 12 hours. After drying, it was placed in a muffle furnace and heated from 20℃ to 900℃ at a rate of 2℃ / min in air, and calcined at 900℃ for 4 hours. After calcination, it was cooled to 20℃ and then placed in an agate mortar and manually ground until the particle size distribution was 10~20 nm to obtain NdFeO. 3; Step S4: Mix NdFeO3, sodium carbonate, and deionized water at a mass ratio of 1:0.5:4, place the mixture in an F-101S magnetic stirrer, and stir at 600 rpm for 30 min. After thorough mixing, dry the mixture in a 100℃ oven for 10 h, then transfer it to a muffle furnace and calcine at 800℃ for 6 h at a rate of 2℃ / min under air atmosphere, starting from 30℃. After calcination, cool the mixture to 25℃, place it in an agate mortar, and manually grind it until the particle size distribution is 15~25 nm to obtain the sodium-doped iron-based perovskite catalyst, i.e., Na. 0.5 -NdFeO3.

[0031] Comparative Example 1 Step S1: Mix Nd(NO3)3·6H2O, Fe(NO3)3·9H2O and deionized water in a mass ratio of 3:2:5 After mixing, place the mixture in a DF-101S magnetic stirrer and stir at 850 rpm for 50 min to obtain a metal salt solution; Step S2: Mix the metal salt solution and citric acid monohydrate at a mass ratio of 1:1, and add ammonia dropwise to adjust the pH to neutral to obtain a sol; Step S3: The sol was aged at 40℃ for 5 hours, and then dried in an oven at 100℃ for 18 hours. After drying, it was placed in a muffle furnace and heated from 30℃ to 850℃ at a rate of 2℃ / min in air atmosphere, and calcined at 850℃ for 4 hours. After calcination, it was cooled to 30℃ and then placed in an agate mortar and manually ground until the particle size distribution was 10~20 nm to obtain NdFeO3.

[0032] Catalyst activity test Test conditions: Catalyst activity tests were conducted on a stainless steel pressurized fixed-bed reactor. The inner diameter of the reaction tube in the fixed-bed reactor was 10 mm and the tube length was 50 cm. The feed gas was controlled by a mass flow meter. The catalyst to be tested was placed in the constant temperature zone of the reaction tube. The temperature conditions required for the test were controlled by thermocouples, temperature controllers and heating furnaces. The pressure was controlled by a pressure gauge.

[0033] Test steps: a) Weigh 0.3g of NdFeO3 from Comparative Example 1 and Li from Examples 1-6. 0.25 -NdFeO3, Na 0.25 -NdFeO3, K 0.25 -NdFeO3, Li 0.5 -NdFeO3, Na 0.5 -NdFeO3 and K 0.5 -NdFeO3 catalyst, without any pretreatment, was filled into the isothermal zone of the reaction tube; b) Place the thermocouple on top of the catalyst bed; c) Heat the fixed-bed reactor to 400°C using a temperature controller; d) A syngas stream of carbon monoxide and hydrogen (volume ratio 1:2) is passed through the catalyst bed. After 2 hours, the fixed-bed reactor is cooled to 350°C using a temperature controller, and then the pressure in the fixed-bed reactor is increased to 2 MPa using a pressure gauge. The syngas flow rate is set to 25 ml / min, and the mass hourly space velocity of the catalyst is 3600 mL·g. - ¹·h - ¹, the reaction products are obtained; the reaction products are mainly low-carbon olefins, including CH4 4， C2-C4 alkanes (mainly ethane, propane, and butane), C2-C4 alkenes (mainly ethylene, propylene, and butene); e) The synthesized reaction products were determined using Thermo Fisher Scientific chromatography to obtain the following results: Figure 4 The diagram shows the hydrocarbon selectivity distribution of the reaction products. Figure 5The CO conversion rates of the reactants are shown in Table 1; Table 1. Catalytic performance of NdFeO3 and alkali metal-doped NdFeO3 in the synthesis of CO hydrogenation. Catalyst number raw material CO conversion rate (%) Low carbon olefin selectivity (%) NdFeO3 Carbon monoxide and hydrogen in a volume ratio of 1:2 25.18 0.71 K0.25-NdFeO3 Carbon monoxide and hydrogen in a volume ratio of 1:2 79.95 30.63 Li0.25-NdFeO3 Carbon monoxide and hydrogen in a volume ratio of 1:2 37.19 11.82 Na0.25-NdFeO3 Carbon monoxide and hydrogen in a volume ratio of 1:2 38.34 32.77 K0.5-NdFeO3 Carbon monoxide and hydrogen in a volume ratio of 1:2 89.42 34.37 Li0.5-NdFeO3 Carbon monoxide and hydrogen in a volume ratio of 1:2 14.68 21.46 Na0.5-NdFeO3 Carbon monoxide and hydrogen in a volume ratio of 1:2 50.38 31.49 from Figure 4 , Figure 5 As shown in Table 1, the CO conversion rate of the undoped NdFeO3 catalyst is 25.18%. After K metal doping, the CO conversion rate of the catalyst is increased to a maximum of 89.42%, with the selectivity of low-carbon olefins (C2-C4=) increasing from 0.71% to 34.37%. After Na metal doping, the CO conversion rate of the catalyst is increased to a maximum of 50.38%, with the selectivity of low-carbon olefins (C2-C4) increasing from 0.71% to 31.49%. After Li metal doping, the selectivity of low-carbon olefins increases from 0.71% to 21.46%. The preparation method using alkali metal introduction in this invention achieves a synergistic effect of high activity and high selectivity. After the introduction of alkali metal, the dissociation of H2 is suppressed, avoiding the decrease in selectivity caused by excessive hydrogenation. Furthermore, by enhancing CO adsorption and dissociation, the conversion rate is improved, enabling the reaction to both efficiently convert CO and directionally generate low-carbon olefins.

[0034] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. An alkali metal-doped iron-based perovskite catalyst, characterized in that: The alkali metal-doped iron-based perovskite catalyst was prepared by in-situ doping an alkali metal into the iron-based perovskite catalyst as a matrix; the chemical formula of the alkali metal-doped iron-based perovskite catalyst is A. x -BFeO3, where A is one of Li, Na, and K, and B is Nd; based on the number of moles of Fe in BFeO3, x is the number of moles of component A, with a value range of 0.25~0.5, that is, the number of moles of component A is 25%~50% of the number of moles of Fe.

2. A method for preparing an alkali metal-doped iron-based perovskite catalyst, characterized in that: Includes the following steps: Step S1: Mix Nd(NO3)3·6H2O, Fe(NO3)3·9H2O and deionized water until homogeneous to obtain a metal salt solution; Step S2: Mix the metal salt solution and complexing agent, and add ammonia dropwise to adjust the pH to neutral to obtain a sol; Step S3: The sol is subjected to aging, drying, calcination and grinding in sequence to obtain NdFeO3; Step S4: Mix NdFeO3, carbonate, and deionized water at a mass ratio of 1:(0.25~0.5):4 until homogeneous, then dry, calcine, and grind sequentially to obtain an alkali metal-doped iron-based perovskite catalyst.

3. The method for preparing the alkali metal-doped iron-based perovskite catalyst according to claim 2, characterized in that: In step S1, the mass ratio of Nd(NO3)3·6H2O, Fe(NO3)3·9H2O and deionized water is (2.5~3.5):(1.5~2.5):(4~6), the mixing time is 30~60 min, and the mixing speed is 500~900 rpm.

4. The method for preparing the alkali metal-doped iron-based perovskite catalyst according to claim 2, characterized in that: In step S2, the mass ratio of the metal salt solution to the complexing agent is (0.8~1.2):1; the complexing agent is one of citric acid monohydrate and anhydrous citric acid.

5. The method for preparing the alkali metal-doped iron-based perovskite catalyst according to claim 2, characterized in that: In step S3, the aging time is 3-5 hours, the aging temperature is 35-45°C, the drying time is 12-18 hours, the drying temperature is 80-110°C, and during calcination, the temperature is increased from 20-30°C to 800-900°C at a rate of 1.5-2.5°C / min, and maintained at 800-900°C for 2-4 hours. The calcination atmosphere is air. After calcination, the temperature is cooled to 20-30°C, and then the particles are ground to a particle size distribution of 10-20 nm.

6. The method for preparing the alkali metal-doped iron-based perovskite catalyst according to claim 2, characterized in that: In step S4, the carbonate is one of lithium carbonate, sodium carbonate, or potassium carbonate.

7. The method for preparing the alkali metal-doped iron-based perovskite catalyst according to claim 2, characterized in that: In step S4, the mixing and stirring time is 30-60 min, the mixing and stirring rate is 600-800 rpm, the drying time is 6-12 h, the drying temperature is 85-110℃, and during calcination, the temperature is increased from 20-30℃ to 800-900℃ at a rate of 1.5-2.5℃ / min and maintained at 800-900℃ for 4-6 h. The calcination atmosphere is air. After calcination, the temperature is cooled to 20-30℃ and then ground until the particle size distribution is 15-25 nm.

8. A method for preparing an alkali metal-doped iron-based perovskite catalyst, characterized in that: Includes the following steps: Step S1: Mix Nd(NO3)3·6H2O, Fe(NO3)3·9H2O and deionized water in a mass ratio of 3:2:5 After mixing, place the mixture in a magnetic stirrer and stir at 800 rpm for 45 min to obtain a metal salt solution; Step S2: Mix the metal salt solution and citric acid monohydrate at a mass ratio of 1:1, and add ammonia dropwise to adjust the pH to neutral to obtain a sol; Step S3: The sol was aged at 35°C for 5 hours, and then dried in an 80°C oven for 12 hours. After drying, it was placed in a muffle furnace and heated from 20°C to 900°C at a rate of 2°C / min in air atmosphere, and calcined at 900°C for 4 hours. After calcination, it was cooled to 20°C and then placed in an agate mortar and ground until the particle size distribution was 10~20 nm to obtain NdFeO3. Step S4: Mix NdFeO3, potassium carbonate, and deionized water at a mass ratio of 1:0.5:4, place in a magnetic stirrer, and stir at 800 rpm for 60 min. After stirring evenly, dry in a 100℃ oven for 11 h, then transfer to a muffle furnace and calcine at 850℃ for 5 h at a rate of 2℃ / min under air atmosphere, heating from 28℃ to 850℃. After calcination, cool to 26℃, place in an agate mortar, and grind until the particle size distribution is 15~25 nm to obtain K. 0.5 -NdFeO3.

9. The application of the alkali metal-doped iron-based perovskite catalyst as described in claim 1 or the alkali metal-doped iron-based perovskite catalyst prepared by any of the methods of claims 2-8 in the catalytic conversion of carbon monoxide and hydrogen into low-carbon olefins, characterized in that: Alkali metal-doped iron-based perovskite catalyst is loaded into a fixed-bed reactor, and syngas formed from carbon monoxide and hydrogen is pumped in. Nitrogen or argon is used as the carrier gas. Low-carbon olefins are prepared under preset reaction conditions. The volume ratio of carbon monoxide to hydrogen is 1:(1~3), and the mass hourly space velocity of the alkali metal-doped iron-based perovskite catalyst is 500~3600 mL·g. - ¹·h - ¹; The preset reaction conditions are: reaction temperature 300~400℃, reaction pressure 1~3 MPa.

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