A preparation method of an iron-based composite catalyst, the obtained catalyst and application thereof

Abstract

The application relates to a preparation method of an iron-based composite catalyst, the obtained catalyst and application of the catalyst, a solution containing a Fe salt and a precipitator are reacted together under supercritical reaction conditions to obtain catalyst core powder; then a solution containing the catalyst core powder and a shell component salt is mixed with the precipitator under supercritical reaction conditions to carry out reaction, the reactants are washed, dried and calcined to obtain an iron-based composite catalyst with a core-shell structure. The obtained iron-based composite catalyst is applied in a water vapor shift reaction and has the characteristics of water heat resistance and high-temperature sintering resistance.

Description

Technical Field

[0001] The present invention relates to an iron-based catalyst for water-gas shift reaction, in particular to a preparation method of an iron-based composite catalyst, the obtained catalyst and application thereof. Background Art

[0002] Hydrogen energy has attracted considerable attention as a potential alternative to traditional fossil fuels. With a gross calorific value of 141.8 MJ / kg, hydrogen fuel is twice as calorific as natural gas (54.0 MJ / kg), offering excellent economic benefits. While hydrogen resources are abundant, such as water and biomass, most hydrogen today is extracted from traditional fossil fuels such as crude oil and natural gas. Currently, steam methane reforming (SRM) is the primary, established industrial hydrogen production technology. To increase hydrogen yield, the reforming process is followed by a water-gas shift reaction (WGS) to remove excess CO and further increase the H₂ content in the atmosphere, thereby increasing hydrogen yield. In recent years, another important application of the WGS reaction has been in new energy vehicles. Fuel cell electrode materials are primarily composed of platinum, which is easily deactivated in the presence of carbon monoxide. Therefore, a WGS reactor is placed before the fuel cell to convert CO into hydrogen and CO₂. Therefore, the WGS reaction plays an important industrial role in regulating and increasing H₂ concentrations.

[0003] Commercial iron oxide catalysts using chromium oxide as a structural additive have a history of application for more than 60 years. In addition to being a structural additive to prevent the sintering of iron oxide crystals, Cr2O3 / CrO3 can also improve the inherent catalytic activity of Fe2O3. Under high-temperature hydrothermal conditions during the reaction, Cr2O3 will inhibit the growth of iron oxide grains and avoid a significant reduction in the specific surface area of ​​the catalyst. Although chromium oxide has been proven to be a good additive, hexavalent chromium is a heavy metal that is toxic to humans, organisms or cells, and is also a serious environmental pollutant. The water solubility of hexavalent chromium causes it to leach from the catalyst through condensed steam or cold water. The hexavalent chromium (Cr6+) of fresh and discarded commercial high-temperature conversion Fe-Cr catalysts has a very high cost of disposal. Due to the hexavalent chromium (Cr 6+ ) and its impact on the environment, it is necessary to develop a highly stable and active chromium-free catalyst for HT-WGSR.

[0004] CN107649142B discloses a low-density iron-chromium CO conversion catalyst, which uses Mn, Mg, and Cr as additives to improve the high-temperature stability of the Fe-based catalyst. The catalyst is Fe2O3, Cr2O3, CuO, Mn, and Cr. x O Y The mixture is mainly composed of the following by weight percentage: Fe2O370%~92%, Cr2O3 4%~15%, CuO 0.5%~10%, M xO Y 4%~15%, wherein M is one or more of Ti, Mg, Mn, Al, Ca, Si.

[0005] CN103272600B discloses a supported copper iron water gas shift catalyst, and the catalyst is prepared by using modified bauxite as carrier and Cu and Fe as active components, and the content of CuO is 10-15wt%, and the content of Fe2O3 is 5-30wt%.

[0006] CN104014345B discloses a CuO-CeO2 catalyst for water gas shift reaction, and the catalyst is prepared by using complex deposition precipitation method.

[0007] The problems of the water gas shift reaction reported in the literatures and patents include serious methanation side reaction, low space-time yield, high catalyst cost, and serious chromium pollution. SUMMARY

[0008] The present application aims to provide a preparation method of an iron-based composite catalyst, the obtained catalyst and the application thereof on the basis of the prior art, so as to solve the problem of poor hydrothermal stability of the iron-based catalyst in the water gas shift reaction in the prior art.

[0009] The present application provides a preparation method of an iron-based composite catalyst, which comprises the following steps:

[0010] (1) providing a solution A containing Fe salt, auxiliary salt and carbon source, and a solution B containing precipitator;

[0011] The auxiliary is selected from one or more of Mn, Mo, Co, Al, V, Ni, Mg, Ca and Cu, the molar ratio of Fe element and auxiliary element is 20:1-1:2, and the molar ratio of Fe element and carbon source molecule is 5-20;

[0012] (2) solution A and solution B enter a supercritical reactor in a parallel flow mode, and reaction is carried out under supercritical reaction conditions, then pressure reduction cooling is carried out after the reaction is completed, and the obtained solid material I is washed, dried and ground to obtain a catalyst inner core powder;

[0013] (3) providing a solution C containing a catalyst core powder and a shell component salt, wherein the solution C and the solution B are fed into a supercritical reactor in parallel, reacting under supercritical reaction conditions, and cooling after the reaction. After solid-liquid separation, the solid material II is washed, dried, and calcined to obtain an iron-based composite catalyst having a core-shell structure;

[0014] The outer shell component is selected from one or more of Zr, Ce, La, In, and Si.

[0015] In one embodiment of the present invention, the carbon source is selected from at least one of sodium polyacrylamide, sodium formate, sodium acetate, sodium oxalate, sodium citrate, sodium succinate, sucrose, starch, glucose, maltose, cellulose, citric acid, glutamic acid, maleic acid, fumaric acid, succinic acid, tartaric acid, malic acid, gluconic acid, terephthalic acid, ethylenediaminetetraacetic acid, dipicolinic acid, and trimesic acid. Preferably, the carbon source is selected from at least one of glucose, maltose, citric acid, and sodium citrate.

[0016] In one embodiment of the present invention, solution A contains a solvent, and the solvent is deionized water and / or ethanol, preferably the solvent is an ethanol aqueous solution with a volume ratio of deionized water to ethanol of 0.1:1-1:0.1;

[0017] In solution A, the total concentration of iron and auxiliary elements is 0.05-5 mol / L, preferably 0.1-2 mol / L.

[0018] In one embodiment of the present invention, the auxiliary agent is selected from one or more of Al, Ni, Cu, and Co.

[0019] In one embodiment of the present invention, the Fe salt and the auxiliary salt are each independently selected from at least one of Fe and auxiliary nitrate, sulfate, formates, acetates and halides.

[0020] In one embodiment of the present invention, the precipitant used is selected from one or more of ammonia water, sodium acetate, potassium acetate, cesium acetate, potassium hydroxide, potassium carbonate, cesium hydroxide, cesium carbonate, ammonium carbonate, urea, sodium carbonate, and sodium hydroxide; preferably, the mass fraction of ammonia in the ammonia water is 25-28%.

[0021] In one embodiment of the present invention, the molar amount of the precipitant is 1-5 times the theoretical stoichiometric ratio of Fe and the number of atoms of the auxiliary metal for precipitation.

[0022] In one embodiment of the present invention, in step (2), the reaction temperature of the supercritical reaction is 350-550° C.; the reaction pressure is 20-40 MPa; and the reaction time is 30-600 s.

[0023] In step (2), the drying temperature is 60-120° C., the time is 0.5-4 h, and the process is carried out in an N 2 or Ar atmosphere.

[0024] In one embodiment of the present invention, in step (2), solution A and solution B are pumped into a supercritical reactor in parallel using respective pumps, and the flow rate range of the solution A feed pump and the solution B feed pump is 5-20 mL / min; deionized water is pumped into the supercritical reactor using a pump, and the deionized water is heated to a supercritical state by passing through a heater in the middle, and the flow rate range of the deionized water feed pump is 15-35 mL / min; the supercritical reactor is a tubular split flow reactor, and the reacted fluid passes through a cooling system and a filtration system.

[0025] In one embodiment of the present invention, in step (3), the solution C contains a solvent, the solvent is deionized water and / or ethanol, preferably the solvent is an ethanol aqueous solution with a volume ratio of deionized water to ethanol of 0.1:1-1:0.1,

[0026] In solution C, the total molar concentration of the shell component elements is 0.05-5 mol / L, preferably 0.1-2 mol / L.

[0027] In one embodiment of the present invention, in step (3), the outer shell component is selected from one or more of Zr, Ce, and La.

[0028] In one embodiment of the present invention, the molar ratio of the outer shell component element to the Fe element is 1:1-3:1.

[0029] In one embodiment of the present invention, the shell component salt is selected from at least one of nitrates, sulfates, formates, acetates, and halides of the shell component.

[0030] In one embodiment of the present invention, in step (3), the reaction temperature of the supercritical reaction is 350-550° C.; the reaction pressure is 20-40 MPa; and the reaction time is 30-600 s.

[0031] In step (3), the drying temperature is 50-100°C, the time is 0.5-5h, and it is carried out in a N2 or Ar atmosphere;

[0032] In step (3), the calcination temperature is 300-500° C., the time is 0.5-5 h, and the calcination is carried out in a N 2 or Ar atmosphere.

[0033] In one embodiment of the present invention, in step (3), solution C and solution B are pumped into the supercritical reactor in a parallel manner using respective pumps, and the flow rate range of the solution C feed pump and the solution B feed pump is 5-20 mL / min; deionized water is pumped into the supercritical reactor using a pump, and the deionized water is heated to a supercritical state by passing through a heater in the middle, and the flow rate range of the deionized water feed pump is 15-35 mL / min; the supercritical reactor is a tubular split flow reactor, and the reacted fluid passes through a cooling system and a filtration system.

[0034] The second aspect of the present invention provides an iron-based composite catalyst obtained according to the above-mentioned preparation method, wherein the iron-based composite catalyst is composed of a core component and a shell component, wherein the core component includes iron and auxiliary elements, and the oxide of the core component accounts for 20%-70% of the catalyst by weight based on the entire catalyst; and the iron oxide content is 60-90% and the auxiliary oxide content is 10%-40% by weight based on the core component.

[0035] The third aspect of the present invention provides an application method of the iron-based composite catalyst obtained according to the above preparation method, wherein the iron-based composite catalyst is loaded in a fixed bed reactor for a water gas shift reaction, and the reaction conditions are: pressure 0.1-5MPa, temperature 300-500°C, space velocity 2000-100000h -1 ,原料气中nH2O:nCO=2-6。

[0036] In one embodiment of the present invention, the iron-based composite catalyst is not subjected to reduction pretreatment before use.

[0037] 本发明的特点:

[0038] (1) The present invention utilizes a supercritical reactor during the catalyst preparation process, allowing the materials to reach the required temperature and pressure instantaneously, resulting in a very short reaction time. On the one hand, the generated metal oxides are all precipitated as ultrafine particles, resulting in a fast nucleation rate and uniform dispersion of the active components, and a high nucleation rate. On the other hand, the shell components are well encapsulated, the reaction time is short, and the preparation efficiency is greatly improved.

[0039] (2) The Fe-based composite catalyst obtained by the present invention exhibits excellent hydrothermal resistance and high-temperature sintering resistance. It can withstand the harsh conditions of high temperature, high pressure, and high water vapor required for the water-gas shift reaction. The Fe-based composite catalyst of the present invention has good hydrothermal stability and is suitable for low water-gas ratio conditions. It can improve the hydrogen yield of the water-gas shift reaction without side reactions. The catalyst also has good heat resistance and activity, and its specific surface area and activity remain good after high-temperature treatment.

[0040] (3) The present invention provides an application in the field of water-gas conversion, which has the advantage that the catalyst does not need to undergo reduction pretreatment and industrial sulfur removal steps before use, which greatly saves costs and realizes a chromium-free and sulfur-free catalyst that is green and environmentally friendly.

[0041] (4) The iron-based composite catalyst provided by the present invention has a water-to-carbon ratio as low as 2.5 at a temperature of 400°C in a water-gas shift fixed-bed reactor, a CO conversion rate of over 70%, a hydrogen production rate of 44 μmol / (gcat.s) at 400°C, no methanation and CO disproportionation side reactions, and a heat-resistant activity retention of over 78%. DETAILED DESCRIPTION

[0042] The present invention will be further described below with reference to the examples, but the present invention is not limited thereto.

[0043] Example 1

[0044] The preparation process of the iron-based composite catalyst of this embodiment is as follows:

[0045] (1) 40 g of Fe(NO3)3·9H2O, 3.72 g of Al(NO3)3·9H2O, and 5.98 g of Cu(NO3)2·3H2O were added to 200 mL of 1:1 ethanol-water solution, 2.0 g of glucose was added, and the mixture was stirred at room temperature for 1 h to obtain solution A. 80 g of 25% ammonia water was added to obtain solution B.

[0046] (2) Solution A was pumped into the supercritical reactor using feed pump 1 at a flow rate of 20 mL / min. Solution B was simultaneously pumped into the supercritical reactor using feed pump 2 at a flow rate of 10 mL / min. At the same time, feed pump 3 delivered 200 mL of deionized water to a heater, heated to 380°C, and heated the deionized water to a supercritical state. The deionized water was then delivered to the supercritical reactor at a flow rate of 20 mL / min. The supercritical reactor used was a tubular split flow reactor. The operating conditions of the supercritical reactor were: temperature 380°C, pressure 20 MPa, and reaction time 60 s.

[0047] After the reaction is completed, the pressure is reduced, the mixture is cooled and filtered, and the filtered solid material I is washed and dried at 80° C. under N 2 atmosphere for 2 h to obtain a catalyst core powder.

[0048] (3) 17.49 g of Ce(NO3)3·6H2O and 12.07 g of Zr(NO3)4·5H2O were added to 200 mL of 1:1 ethanol-water solution, and then 6.93 g of the catalyst core powder obtained in step (2) was added. The mixture was stirred at room temperature for 1 h to obtain solution C, and 120 g of 25% ammonia water was added to obtain solution B.

[0049] Solution C was pumped into the supercritical reactor using feed pump 4 at a flow rate of 10 mL / min. Simultaneously, solution B was pumped into the supercritical reactor using feed pump 5 at a flow rate of 12 mL / min. Simultaneously, feed pump 6 delivered 200 mL of deionized water to a heater, heated to 380°C, bringing the deionized water to a supercritical state. The deionized water was then delivered to the supercritical reactor at a flow rate of 20 mL / min. The supercritical reactor used was a tubular split-flow reactor. The operating conditions for the supercritical reactor were: temperature of 380°C, pressure of 20 MPa, and reaction time of 60 s.

[0050] After the reaction, the reaction mixture was cooled and filtered under reduced pressure. The filtered solid material II was washed, dried at 80°C in a N2 atmosphere for 2 h, and then calcined at 450°C in a N2 atmosphere for 3 h to obtain a core-shell structured Fe-based composite catalyst C-1.

[0051] Example 2

[0052] The preparation process of the iron-based composite catalyst of this embodiment is as follows:

[0053] (1) 40 g of Fe(NO3)3·9H2O, 9.60 g of Ni(NO3)2·6H2O, and 8.0 g of Cu(NO3)2·3H2O were added to 200 mL of a 1:1 ethanol-water solution, 2.0 g of glucose was added, and the mixture was stirred at room temperature for 1 h to obtain solution A. 4.0 g of NaAc was dissolved in 100 mL of a 1:1 ethanol-water solution to obtain solution B.

[0054] (2) Solution A was pumped into the supercritical reactor using feed pump 1 at a flow rate of 20 mL / min. Solution B was simultaneously pumped into the supercritical reactor using feed pump 2 at a flow rate of 10 mL / min. At the same time, feed pump 3 delivered 200 mL of deionized water to a heater, heated to 380°C, and heated the deionized water to a supercritical state. The deionized water was then delivered to the supercritical reactor at a flow rate of 20 mL / min. The supercritical reactor used was a tubular split flow reactor. The operating conditions of the supercritical reactor were: temperature 380°C, pressure 20 MPa, and reaction time 60 s.

[0055] After the reaction is completed, the pressure is reduced, the mixture is cooled and filtered, and the filtered solid material I is washed and dried at 80° C. under N 2 atmosphere for 2 h to obtain a catalyst core powder.

[0056] (3) 59.4 g of Ce(NO3)3·6H2O and 31.3 g of La(NO3)3·6H2O were added to 200 mL of a 1:1 ethanol-water solution, and 11.7 g of the catalyst core powder obtained in step (2) was added. The mixture was stirred at room temperature for 1 h to obtain solution C. 4.0 g of NaAc was dissolved in 100 mL of a 1:1 ethanol-water solution to obtain solution B.

[0057] Solution C was pumped into the supercritical reactor using feed pump 4 at a flow rate of 20 mL / min. Simultaneously, solution B was pumped into the supercritical reactor using feed pump 5 at a flow rate of 10 mL / min. Simultaneously, feed pump 6 delivered 200 mL of deionized water to a heater, heated to 380°C, bringing the deionized water to a supercritical state. The deionized water was then delivered to the supercritical reactor at a flow rate of 20 mL / min. The supercritical reactor used was a tubular split-flow reactor, and the operating conditions for the supercritical reactor were: temperature of 380°C, pressure of 20 MPa, and reaction time of 60 s.

[0058] After the reaction, the pressure was reduced, the mixture was cooled and filtered. The filtered solid material II was washed, dried at 80°C in a N2 atmosphere for 2 hours, and then calcined at 450°C in a N2 atmosphere for 3 hours to obtain a core-shell structured Fe-based composite catalyst C-2.

[0059] Example 3

[0060] The preparation process of the iron-based composite catalyst of this embodiment is as follows:

[0061] (1) 20 g of Fe(NO3)3·9H2O, 4.80 g of Ni(NO3)2·6H2O, and 4.0 g of Cu(NO3)2·3H2O were added to 100 mL of a 1:1 ethanol-water solution, 1.5 g of sodium citrate was added, and the mixture was stirred at room temperature for 1 h to obtain solution A. 2.0 g of NaAc was dissolved in 50 mL of a 1:1 ethanol-water solution to obtain solution B.

[0062] (2) Solution A was pumped into the supercritical reactor using feed pump 1 at a flow rate of 10 mL / min. Solution B was simultaneously pumped into the supercritical reactor using feed pump 2 at a flow rate of 5 mL / min. At the same time, feed pump 3 delivered 100 mL of deionized water to a heater, heated to 380°C, and heated the deionized water to a supercritical state. The deionized water was then delivered to the supercritical reactor at a flow rate of 10 mL / min. The supercritical reactor used was a tubular split flow reactor. The operating conditions of the supercritical reactor were: temperature 380°C, pressure 20 MPa, and reaction time 60 s.

[0063] After the reaction is completed, the pressure is reduced, the mixture is cooled and filtered, and the filtered solid material I is washed and dried at 80° C. under N 2 atmosphere for 2 h to obtain a catalyst core powder.

[0064] (3) 19.8 g of Ce(NO3)3·6H2O and 13.8 g of Zr(NO3)4·5H2O were added to 100 mL of a 1:1 ethanol-water solution, and 5.87 g of the catalyst core powder obtained in step (2) was added. The mixture was stirred at room temperature for 1 h to obtain solution C. 2.0 g of NaAc was dissolved in 50 mL of a 1:1 ethanol-water solution to obtain solution B.

[0065] Solution C was pumped into the supercritical reactor using feed pump 4 at a flow rate of 20 mL / min. Simultaneously, solution B was pumped into the supercritical reactor using feed pump 5 at a flow rate of 5 mL / min. Simultaneously, feed pump 6 delivered 100 mL of deionized water to a heater, heated to 380°C, bringing the deionized water to a supercritical state. The water was then delivered to the supercritical reactor at a flow rate of 10 mL / min. The supercritical reactor used was a tubular split-flow reactor, operating under the following conditions: a temperature of 380°C, a pressure of 20 MPa, and a reaction time of 60 seconds.

[0066] After the reaction, the pressure was reduced, the mixture was cooled and filtered. The filtered solid material II was washed, dried at 80°C in a N2 atmosphere for 2 hours, and then calcined at 450°C in a N2 atmosphere for 3 hours to obtain a core-shell structured Fe-based composite catalyst C-3.

[0067] Example 4

[0068] The preparation process of the iron-based composite catalyst of this embodiment is as follows:

[0069] (1) 40 g of FeCl₃·6H₂O, 3.57 g of AlCl₃·6H₂O, and 1.3 g of CuCl₂·2H₂O were added to 200 mL of a 1:1 ethanol-water solution, 3.0 g of glucose was added, and the mixture was stirred at room temperature for 1 h to obtain solution A. 4.0 g of NaOH was dissolved in 100 mL of a 1:1 ethanol-water solution to obtain solution B.

[0070] (2) Solution A was pumped into the supercritical reactor using feed pump 1 at a flow rate of 20 mL / min. Solution B was simultaneously pumped into the supercritical reactor using feed pump 2 at a flow rate of 10 mL / min. At the same time, feed pump 3 delivered 200 mL of deionized water to a heater, heated to 380°C, and heated the deionized water to a supercritical state. The deionized water was then delivered to the supercritical reactor at a flow rate of 20 mL / min. The supercritical reactor used was a tubular split flow reactor. The operating conditions of the supercritical reactor were: temperature 380°C, pressure 20 MPa, and reaction time 60 s.

[0071] After the reaction is completed, the pressure is reduced, the mixture is cooled and filtered, and the filtered solid material I is washed and dried at 80° C. under N 2 atmosphere for 2 h to obtain a catalyst core powder.

[0072] (3) 34.97 g of Ce(N03)3-6H20 and 24.14 g of Zr(N03)4-5H20 were added to 200 mL of an ethanol aqueous solution with a volume ratio of 1:1, and 14.2 g of the catalyst core powder obtained in step (2) was added, and stirred at room temperature for 1 h to obtain solution C. 4.0 g of NaOH was dissolved in 100 mL of an ethanol aqueous solution with a volume ratio of 1:1 to obtain solution B.

[0073] Solution C was pumped into the supercritical reactor by feed pump 4 at a flow rate of 20 mL / min, and solution B was pumped into the supercritical reactor by feed pump 5 at a flow rate of 10 mL / min, and feed pump 6 was used to send 100 mL of deionized water to the heater, heated to 380°C, so that the deionized water was heated to a supercritical state, and then sent to the supercritical reactor at a flow rate of 20 mL / min. The supercritical reactor used was a tubular split reactor, and the operating conditions of the supercritical reactor were: temperature 380°C, pressure 20 MPa, and the reaction was carried out for 60 s.

[0074] After the reaction was completed, pressure reduction cooling and filtration were carried out, and the solid material II after filtration was washed and dried at 80°C under N2atmosphere for 2 h, and then calcined at 450°C under N2atmosphere for 3 h to obtain the Fe-based composite catalyst C-4 with core-shell structure.

[0075] Comparative Example 1

[0076] The preparation process of the iron-based catalyst of the present comparative example is as follows:

[0077] 20 g of Fe(N03)3-9H20, 4.8 g of Ni(N03)2-6H20 and 4.0 g of Cu(N03)2-3H20 were added to 200 mL of deionized water, and 12 g of Ce02powder was added and stirred to dissolve at room temperature. The obtained solution was subjected to concurrent titration with an ammonia solution with a mass concentration of 25%, and the pH was controlled to be about ~ 9.0. After the titration was completed, stirring was continued for 1 h. After standing overnight, the supernatant was poured and centrifuged, washed with deionized water 4 times, and the centrifuged solid was dried at 60°C for 2 h. The catalyst powder was placed in a tubular furnace and calcined at 450°C in an air atmosphere for 3 h to obtain the Fe-based catalyst D-1.

[0078] Comparative Example 2

[0079] The preparation process of the iron-based catalyst of the present comparative example is as follows:

[0080] 40g Fe(NO3)3·9H2O, 3.72g Al(NO3)3·9H2O, 5.98g Cu(NO3)2·3H2O, 34.97g Ce(NO3)3·6H2O and 24.14g Zr(NO3)4·5H2O were added to 400mL of ethanol aqueous solution with a volume ratio of 1:1, and stirred at room temperature for 1h to obtain solution A. Solution A was pumped into the supercritical reactor by feed pump 1 at a flow rate of 20mL / min. At the same time, 120g of 25% ammonia water was pumped into the supercritical reactor by feed pump 2 at a flow rate of 6mL / min. At the same time, feed pump 3 sent 400mL of deionized water to the heater, heated to 380℃, so that the deionized water was heated to a supercritical state, and then sent to the supercritical reactor at a flow rate of 20mL / min. The supercritical reactor used is a tubular split flow reactor, and the operating conditions of the supercritical reactor are: temperature 380° C., pressure 20 MPa, and reaction for 60 seconds.

[0081] After the reaction, the pressure was reduced, the mixture was cooled and filtered. The filtered solid material II was washed, dried at 80°C in a N2 atmosphere for 2 hours, and then calcined at 450°C in a N2 atmosphere for 3 hours to obtain an Fe-based catalyst D-2.

[0082] Comparative Example 3

[0083] (1) 15 g of Fe(NO₃)₃·9H₂O, 2.32 g of Al(NO₃)₃·9H₂O, and 0.22 g of Cu(NO₃)₂·3H₂O were added to 200 mL of a 1:1 ethanol-water solution, and 1.0 g of glucose was added. The mixture was stirred at room temperature for 1 h to obtain solution A. 80 g of 25% aqueous ammonia was added to obtain solution B. Solution B was added to solution A at a flow rate of 20 mL / min to allow the reaction to proceed. After the reaction, the mixture was cooled and filtered. The filtered solid material I was washed and dried at 80°C under a nitrogen atmosphere for 2 h to obtain a catalyst core powder.

[0084] (2) 4.24 g of Ce(NO3)3·6H2O and 5.5 g of Zr(NO3)4·5H2O were added to 200 mL of 1:1 ethanol-water solution, and then 5.0 g of the catalyst core powder obtained in step (1) was added. The mixture was stirred at room temperature for 1 h to obtain solution C, and 120 g of 25% ammonia water was added to obtain solution B.

[0085] Solution B was added to solution C at a flow rate of 20 mL / min to allow the reaction to proceed. After the reaction, the mixture was cooled and filtered. The filtered solid material II was washed, dried at 80°C in an N2 atmosphere for 2 h, and then calcined at 450°C in an N2 atmosphere for 3 h to obtain a core-shell Fe-based catalyst D-3.

[0086] Examples 5-8, Comparative Examples 4-6

[0087] The following examples and comparative examples are applications of the catalysts obtained in Examples 1-4 and Comparative Examples 1-3.

[0088] 0.5 g of the screened catalyst was loaded into a reaction tube with an inner diameter of 8 mm, and a water gas shift reaction was performed.

[0089] Reduction pretreatment:

[0090] (1) The catalysts C-1, C-2, C-3, C-4 obtained in Examples 1-4 were not subjected to reduction pretreatment.

[0091] (2) The catalysts D-1, D-2, D-3 obtained in Comparative Examples 1-3 were subjected to reduction pretreatment: the pretreatment atmosphere was CO / CO2 / H2 / N2 (volume fraction) = 12.4% / 5.3% / 49.5% / 32.8%; the pretreatment temperature was 400°C, the pretreatment time was 2 h, the pressure was atmospheric pressure, and the pretreatment space velocity was 20000 h-1. -1 , H2O / CO (molar ratio) = 1.6.

[0092] The raw material gas used in the formal water gas shift reaction was composed of dry gas and water, wherein the composition of the dry gas was as follows: CO / CO2 / H2 / N2 = 12.4% / 5.3% / 49.5% / 32.8% (volume fraction); and the H2O / CO (molar ratio) in the raw material gas was 2.5.

[0093] The reaction conditions used were: 0.5 MPa, 350°C, 40000 h -1 .

[0094] After the formal reaction, a heat-resistant activity test was performed. The conditions for the heat-resistant activity test were as follows: the reaction pressure, the raw material gas, and the space velocity were consistent with those of the formal reaction, the temperature was increased to 530°C and maintained for 2 h, and then decreased to 400°C and maintained for 1 h before sampling and analysis, and the obtained carbon monoxide conversion rate was taken as the heat-resistant activity data. The liquid product was collected in an ice water bath, and the product composition was analyzed by gas chromatography. The specific evaluation results are shown in Table 1.

[0095] Table 1

[0096]

[0097] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the present application and fall within the protection scope of the present application.

Claims

1. A method for preparing an iron-based composite catalyst, comprising the following steps: (1) providing a solution A containing an Fe salt, a builder salt, and a carbon source, and a solution B containing a precipitant; The auxiliary agent is selected from one or more of Mn, Co, Al, Ni, and Cu, the molar ratio of Fe element to auxiliary element is 20:1-1:2, and the molar ratio of Fe element to carbon source molecule is 5-20; The carbon source is selected from at least one of sodium polyacrylamide, sodium formate, sodium acetate, sodium oxalate, sodium citrate, sodium succinate, sucrose, starch, glucose, maltose, cellulose, citric acid, glutamic acid, maleic acid, fumaric acid, succinic acid, tartaric acid, malic acid, gluconic acid, terephthalic acid, ethylenediaminetetraacetic acid, dipicolinic acid and trimesic acid; The precipitant used is one or more selected from ammonia water, sodium acetate, potassium acetate, cesium acetate, potassium hydroxide, potassium carbonate, cesium hydroxide, cesium carbonate, ammonium carbonate, urea, sodium carbonate, and sodium hydroxide; the molar amount of the precipitant is 1-5 times the theoretical stoichiometric ratio of Fe and the number of auxiliary metal atoms for precipitation; (2) Solution A and Solution B are fed into a supercritical reactor in parallel, reacting under supercritical conditions. After the reaction is complete, the pressure is reduced and the solution is cooled. After solid-liquid separation, the solid material I obtained is washed and dried to obtain a catalyst core powder. (3) providing a solution C containing a catalyst core powder and a shell component salt, wherein the solution C and the solution B are fed into a supercritical reactor in parallel, reacting under supercritical reaction conditions, and cooling after the reaction. After solid-liquid separation, the solid material II is washed, dried, and calcined to obtain an iron-based composite catalyst having a core-shell structure; The outer shell component is selected from one or more of Zr, Ce and La.

2. The preparation method according to claim 1, characterized in that The carbon source is selected from at least one of glucose, maltose, citric acid and sodium citrate.

3. The preparation method according to claim 1, characterized in that Solution A contains a solvent, which is deionized water and / or ethanol; In solution A, the total concentration of iron and auxiliary elements is 0.05-5 mol / L.

4. The preparation method according to claim 3, characterized in that The solvent is an ethanol-water solution with a volume ratio of deionized water to ethanol of 0.1:1-1:0.1; In solution A, the total concentration of iron and auxiliary elements is 0.1-2 mol / L.

5. The preparation method according to claim 1, characterized in that The additive is selected from one or more of Al, Ni, Cu, and Co. The Fe salt and the auxiliary salt are independently selected from at least one of Fe and auxiliary nitrate, sulfate, formates, acetates and halides.

6. The preparation method according to claim 1, characterized in that In step (2), the reaction temperature of the supercritical reaction is 350-550° C.; the reaction pressure is 20-40 MPa; and the reaction time is 30-600 s. The drying temperature is 60-120°C, the time is 0.5-4h, and it is carried out in N2 or Ar atmosphere.

7. The preparation method according to claim 1 or 6, characterized in that In step (2), solution A and solution B are pumped into the supercritical reactor in a parallel manner using respective pumps, and the flow rate range of the solution A feed pump and the solution B feed pump is 5-20 mL / min; deionized water is pumped into the supercritical reactor using a pump, and passes through a heater in the middle to heat the deionized water to a supercritical state, and the flow rate range of the deionized water feed pump is 15-35 mL / min; the supercritical reactor is a tubular split flow reactor, and the reacted fluid passes through a cooling system and a filtration system.

8. The preparation method according to claim 1, characterized in that In step (3), solution C contains a solvent, and the solvent is deionized water and / or ethanol, In solution C, the total molar concentration of the shell component elements is 0.05-5 mol / L.

9. The preparation method according to claim 8, characterized in that The solvent is an ethanol aqueous solution with a volume ratio of deionized water and ethanol of 0.1:1-1:0.

1. In solution C, the total molar concentration of the shell component elements is 0.1-2 mol / L.

10. The preparation method according to claim 1, characterized in that In step (3), the shell component is selected from one or more of Zr, Ce, and La; The molar ratio of the shell component elements to the Fe element is 1:1-3:1; The shell component salt is selected from at least one of nitrates, sulfates, formates, acetates and halides of the shell component.

11. The preparation method according to claim 1, characterized in that In step (3), the reaction temperature of the supercritical reaction is 350-550° C., the reaction pressure is 20-40 MPa, and the reaction time is 30-600 s; Drying temperature is 50-100℃, time is 0.5-5h, and it is carried out in N2 or Ar atmosphere; The calcination temperature is 300-500°C, the time is 0.5-5h, and it is carried out in N2 or Ar atmosphere.

12. The preparation method according to claim 1, characterized in that In step (3), solution C and solution B are pumped into the supercritical reactor in a parallel manner using respective pumps, and the flow rate range of the solution C feed pump and the solution B feed pump is 5-20 mL / min; deionized water is pumped into the supercritical reactor using a pump, and the deionized water is heated to a supercritical state by passing through a heater in the middle, and the flow rate range of the deionized water feed pump is 15-35 mL / min; the supercritical reactor is a tubular split flow reactor, and the reacted fluid passes through a cooling system and a filtration system.

13. An iron-based composite catalyst obtained by the preparation method according to any one of claims 1 to 12, wherein the iron-based composite catalyst consists of a core component and a shell component, the core component includes iron and promoter elements, and the oxide of the core component accounts for 20% to 70% of the catalyst by weight based on the entire catalyst; the iron oxide content is 60% to 90% by weight, and the promoter oxide content is 10% to 40% by weight based on the core component.

14. A method for using the iron-based composite catalyst obtained by any one of the preparation methods of claims 1 to 12, characterized in that: The iron-based composite catalyst is loaded in a fixed bed reactor for water gas shift reaction. The reaction conditions are: pressure 0.1-5MPa, temperature 300-500℃, space velocity 2000-100000h -1 , nH2O:nCO in the raw gas = 2-6.

15. The application method according to claim 14, characterized in that: The iron-based composite catalyst is not subjected to reduction pretreatment before use.

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