Assistant-modified nano iron-based catalyst as well as preparation method and application thereof

Abstract

The invention provides an auxiliary-modified nano iron-based catalyst as well as a preparation method and application thereof. Specifically, the nano iron-based catalyst comprises an iron metal oxide, a zirconium metal oxide, an auxiliary agent and an optional carrier, the auxiliary agent comprises a metal oxide auxiliary agent and a non-metal auxiliary agent; and the carrier accounts for 10-80% of the total mass fraction of the catalyst. According to the present invention, the multi-element layered LDH precursor is formed during the preparation process, the efficient FeCx-MOx metal carbide / oxide interface is constructed during the reaction process through the reduction carbonization, and the high CO2 hydrogenation reaction activity, the low CH4 selectivity and the excellent long-chain alpha-olefin selectivity are achieved through the efficient synergistic effect of different assistants and the multi-interface active site; meanwhile, the catalyst keeps excellent reaction stability and is more suitable for large-scale industrial application.

Description

Technical Field

[0001] The present invention relates to the technical field of iron-based catalysts, and in particular to an auxiliary agent-modified iron-based catalyst and a preparation method and application thereof. Background Art

[0002] At present, my country and the world's energy supply mainly relies on fossil energy such as coal, oil, and natural gas. The use of fossil energy inevitably produces a large amount of carbon dioxide. Faced with increasingly severe emission reduction pressure and a huge carbon emission trading market, how to efficiently utilize carbon dioxide resources is a hot topic in C1 chemistry research. The development of efficient carbon dioxide conversion and utilization technology is of great significance to my country's sustainable development strategy and emission reduction tasks.

[0003] Long-chain α-olefins refer to olefins with more than five carbon atoms and unsaturated bonds at the end of the hydrocarbon chain. They are widely used as olefin comonomers, surfactants, plasticizers, etc. Long-chain α-olefins are important high-value-added chemical raw materials and occupy a very important position in the national economy. They are mainly used in synthetic detergents, flavors and fragrances, plasticizers, etc. At present, the main way to synthesize long-chain olefins is based on the polymerization reaction of ethylene, and ethylene mainly comes from petroleum resources. Therefore, the industrial synthesis of long-chain olefins needs to rely on the petrochemical industry. In contrast, using renewable energy to electrolyze water to produce hydrogen, and then reacting it with carbon dioxide to directly prepare long-chain olefins, can produce huge environmental benefits.

[0004] CN112973698A discloses a CO 2 A method for preparing a catalyst for hydrogenating high-carbon linear α-olefins and its application, a carbon-doped Fe catalyst is prepared by a hydrothermal synthesis method, the main active component is Fe, and one or more alkali metal elements such as K, Mg, Ca, etc. are used as electronic additives for the Fe catalyst, which can 2 Efficient conversion of linear α-olefins, CO 2 The conversion rate is about 30%, and its α-C 4+ The selectivity of olefins is about 60%, the selectivity of by-product CO is about 21%, and the selectivity of CH 4 Selectivity is about 10%.

[0005] CN116265091A discloses a CO 2Catalyst for preparing high-carbon linear alpha olefins by hydrogenation, and its preparation and application. The catalyst is a composite metal oxide catalyst containing Fe, alkali metal, Zn and Al; wherein the molar ratio of Fe to (Zn+Al) is 1:0.11:1, and the content of alkali metal Na or K is 0.1-10wt%. The catalyst preparation process is to first dissolve Fe salt in deionized water, then add Al salt and Zn salt to the Fe salt solution to prepare solution I; then dissolve at least one of the Na compound and the K compound in water to prepare solution II; and then synthesize solution I and solution II in one step by coprecipitation method. The synthesized catalyst is used for CO 2 Hydrogenation to produce alpha olefins, CO 2 The conversion rate is 30-36%, the selectivity of αC4+ olefins is 50-55%, the selectivity of by-product CO is 15-25%, and the selectivity of CH 4 Selectivity 10-16%.

[0006] Patent CN108144617A discloses the preparation of an iron-based catalyst for hydrogenating carbon dioxide to produce alpha olefins, as well as the catalyst and its application. The preparation method of the iron-based catalyst for hydrogenating carbon dioxide to produce alpha olefins includes: 1) preparation of an auxiliary agent: first pre-treating the biomass powder, calcining it in an air atmosphere at 300-800°C for 3-10 hours to remove carbon-containing organic compounds and obtain a powder auxiliary agent rich in mineral elements; 2) mechanically mixing the Fe-based catalyst and the auxiliary agent into a composite catalyst, and the mass ratio of the Fe-based catalyst to the auxiliary agent is controlled at 10:0.110:5; the Fe-based catalyst is a loaded catalyst with an iron mass content of 540%. The iron-based catalyst disclosed in the patent is used for CO 2 Hydrogenation to produce alpha olefins, αC 4+ The olefin selectivity reached 30.6%, CO 2 The conversion rate is 30.5%, but 23.2% CO and 12.6% alkane are produced during the reaction. 2 Hydrogenation catalysts usually have problems such as poor catalytic activity, complex preparation process or short service life.

[0007] Therefore, there is an urgent need in the art to develop an additive-modified nano-iron-based catalyst that is simple to prepare, has good catalytic activity, low by-product selectivity and long service life. Summary of the invention

[0008] The purpose of the present invention is to provide an additive-modified nano iron-based catalyst which is simple to prepare, has good catalytic activity, low by-product selectivity and long service life, and to apply the catalyst to CO 2 In the hydrogenation reaction to produce long-chain α-olefins.

[0009] In the first aspect of the present invention, a nano iron-based catalyst modified by an additive is provided, wherein the nano iron-based catalyst comprises iron metal oxide, zirconium metal oxide, an additive and an optional carrier; the molar ratio of iron element to zirconium element is 1:0.5-2;

[0010] The additives include metal oxide additives and non-metal additives; the molar ratio of iron element to metal element in the metal oxide additive is 1:0.01-0.05;

[0011] The carrier accounts for 10%-80% of the total mass fraction of the catalyst.

[0012] In a preferred embodiment, the nano iron-based catalyst comprises the following components:

[0013] 20-60 parts by weight of iron metal oxide;

[0014] 20-60 parts by weight of zirconium metal oxide;

[0015] 5-30 parts by weight of an auxiliary agent; and / or

[0016] 0-30 parts by weight of carrier.

[0017] In a preferred embodiment, the nano iron-based catalyst comprises the following components by mass:

[0018] 10-60% iron metal oxides;

[0019] 10-60% zirconium metal oxide;

[0020] 0.1-10% adjuvant; and / or

[0021] 10-60% carrier.

[0022] In a preferred embodiment, the iron metal oxide comprises Fe 2 O 3 and FeO, preferably Fe 2 O 3 .

[0023] In a preferred embodiment, the metal element in the metal oxide additive is selected from at least one of transition metals and alkaline metals.

[0024] In a preferred embodiment, the transition metal is selected from at least one of nickel, molybdenum, chromium and copper.

[0025] In a preferred embodiment, the alkaline metal is selected from at least one of sodium, potassium, magnesium, calcium and palladium.

[0026] In a preferred embodiment, the non-metallic additive is selected from at least one of boron and phosphorus.

[0027] In a preferred embodiment, the carrier is selected from Al 2 O 3 Powder, SiO 2 Powder, TiO 2 Powder, Al 2 O 3 Sol, acidic silica sol and TiO 2 One or more of the sol.

[0028] In the second aspect of the present invention, a method for preparing the nano iron-based catalyst according to the first aspect of the present invention is provided, comprising the following steps:

[0029] When the carrier in the catalyst is 0, the preparation method 1 comprises the following steps:

[0030] S1: According to the composition ratio of the catalyst, a soluble salt solution of Fe, Zr and the metal elements in the metal oxide additive is prepared into a mixed salt solution; preferably nitrate;

[0031] S2: preparing a precipitant solution with a precipitant containing an alkaline metal according to the composition ratio of the catalyst;

[0032] S3: co-precipitating the mixed salt solution in S1 and the precipitant solution in S2 in parallel;

[0033] S4: After the precipitation is completed, the slurry is aged, filtered and washed to obtain the slurry;

[0034] S5: adding non-metallic additives to the slurry obtained by washing in S4, drying, and calcining to obtain the catalyst.

[0035] In a preferred embodiment, the method further comprises the following steps:

[0036] When the carrier in the catalyst is greater than 0, the preparation method 2 comprises the following steps:

[0037] S1: According to the composition ratio of the catalyst, a soluble salt solution of Fe, Zr and the metal elements in the metal oxide additive is prepared into a mixed salt solution; preferably nitrate;

[0038] S2: preparing a precipitant solution with a precipitant containing an alkaline metal according to the composition ratio of the catalyst;

[0039] S3: In the presence of a carrier, the mixed salt solution in S1 and the precipitant solution in S2 are co-precipitated in parallel;

[0040] S4: After the precipitation, aging, dynamic crystallization, filtration and washing are performed to obtain mud;

[0041] S5: adding non-metallic additives to the slurry obtained by washing in S4, re-slurrying the filter cake, drying, and calcining to obtain the catalyst.

[0042] In a preferred embodiment, the molar concentration of the total metal salt in the mixed salt solution is in the range of 0.1-5 mol / L, such as 0.1-4 mol / L, 0.2-3 mol / L, 0.5-2 mol / L.

[0043] In a preferred embodiment, the mixed salt solution includes at least one of nickel nitrate, chromium nitrate, copper nitrate, magnesium nitrate, calcium nitrate, barium nitrate, zirconium nitrate, aluminum nitrate or acidic silica sol.

[0044] In a preferred embodiment, the precipitant is selected from at least one of sodium carbonate, sodium bicarbonate, sodium hydroxide, potassium carbonate, potassium bicarbonate or potassium hydroxide; the precipitant is more preferably a combination of sodium bicarbonate and sodium hydroxide, or potassium bicarbonate and potassium hydroxide.

[0045] In a preferred embodiment, the molar concentration of the precipitant solution is in the range of 0.1-5 mol / L, such as 0.1-4 mol / L, 0.2-3 mol / L, 0.5-2 mol / L.

[0046] In a preferred embodiment, the carrier is selected from Al 2 O 3 Powder, SiO 2 Powder, TiO 2 Powder, Al 2 O 3 Sol, acidic silica sol and TiO 2 One or more of the sols, preferably acidic silica sol.

[0047] In a preferred embodiment, the coprecipitation conditions are: the coprecipitation temperature is 10-100°C, such as 10-25°C, 25-50°C, 50-60°C, 60-65°C, 65-70°C or 70-100°C, and the coprecipitation pH is 6-12, such as 6-8, 8-9, 9-10 or 10-12.

[0048] In a preferred embodiment, the metal element mass content of the precipitant in the mud obtained after washing is controlled at 0.1-3%, such as 0.1-0.2%, 0.2-0.3%, 0.3-0.4%, 0.4-0.5%, 0.5-0.7%, 0.7-1%, 1-2.5% or 2.5-3%.

[0049] In a preferred embodiment, the aging conditions are: the aging temperature is 10-100°C, such as 10-25°C, 25-50°C, 50-60°C, 60-65°C, 65-70°C or 70-100°C, and the aging time is 0.5-24h, such as 0.5-2h, 2-3h, 3-4h, 4-5h, 5-6h, 6-15h or 15-24h.

[0050] In a preferred embodiment, the conditions for dynamic crystallization are: the dynamic crystallization temperature is 50-300°C, such as 50-250°C, 80-200°C, 100-180°C or 120-160°C, and the dynamic crystallization time is 1-48h, such as 10-40h, 15-35h or 15-24h.

[0051] In a preferred embodiment, the non-metallic additive is selected from at least one of boric acid or phosphoric acid.

[0052] In a preferred embodiment, the conductivity of the filtered filtrate is controlled to be 500-3000 μs / cm.

[0053] In a preferred embodiment, after the filter cake is slurried, the solid content of the slurry is controlled to be 15-25%, a certain amount of boric acid or phosphoric acid solution is added for impregnation, and then the pH of the slurry is adjusted to 7-9, and dried at 80-120° C. for 10-30 hours.

[0054] In a preferred embodiment, the drying conditions are: drying temperature is 50-300°C, such as 70-200°C, 100-150°C or 120-140°C, and drying time is 0.5-24h, such as 0.5-1h, 1-2h, 2-4h, 4-6h, 6-8h, 85-10h or 10-24h.

[0055] In a preferred embodiment, the calcination is carried out under a nitrogen atmosphere.

[0056] In a preferred embodiment, the calcination conditions are: the calcination temperature is 200-800°C, such as 200-300°C, 300-350°C, 350-400°C, 400-500°C, 500-550°C, 550-600°C, 600-700°C or 700-800°C, and the calcination time is 0.5-24h, such as 0.5-1h, 1-2h, 2-4h, 4-6h, 6-8h, 85-10h or 10-24h.

[0057] In the third aspect of the present invention, there is provided a use of the nano iron-based catalyst according to the first aspect of the present invention for CO 2 In the hydrogenation reaction to produce long-chain α-olefins.

[0058] In a preferred embodiment, the reaction comprises: pre-reducing and carbonizing the nano-iron-based catalyst described in the first aspect of the present invention, and using the reduced and carbonized catalyst for CO 2 Hydrogenation reaction.

[0059] In a preferred embodiment, the reduction carbonization conditions are: the reducing gas is H 2 , CO or CO and H 2 , space velocity is 5000-20000mL / gcat / h, temperature is 300-400℃, pressure is 0.1-1.0MPa, and time is 10-40h.

[0060] In a preferred embodiment, in the CO 2 In the hydrogenation reaction, the reaction conditions are: space velocity of 2000-20000 mL / gcat / h, reaction temperature of 280-350°C, reaction pressure of 0.1-3.0 MPa, H 2 and CO 2 The molar ratio is 2-7:1.

[0061] It should be understood that within the scope of the present invention, the above-mentioned technical features of the present invention and the technical features specifically described below (such as embodiments) can be combined with each other to form a new or preferred technical solution. Due to space limitations, they will not be described one by one here.

[0062] Compared with the prior art, the present invention has the following technical effects:

[0063] (1) The catalyst of the present invention uses LDH as a catalyst precursor, which has the advantages of large specific surface area, rich pore structure, highly dispersed active components, good thermal stability, etc., and the catalyst surface has abundant basic sites, which is beneficial to CO 2 The adsorption of α-olefins can improve the catalytic activity; at the same time, the addition of additives in the LDH synthesis stage is conducive to the interaction between the additives and the active component iron phase, improving the electronic properties and acid-base properties of the active site, and promoting the formation of iron carbide χ-Fe 5 C 2 The formation of , improves the selectivity for long-chain α-olefins;

[0064] (2) The present invention uses a variety of additives, including transition metals Ni, Mo, Cr, Cu, etc., alkaline metal additives Na, K, Mg, Ca, Ba, etc., and non-metal additives B, P, etc. The various additives can regulate the acidity and alkalinity of the catalyst surface, have good synergistic catalysts, and make the catalyst have a higher CO 2 High hydrogenation reaction activity, low CO selectivity and high carbon efficiency;

[0065] (3) The raw materials of the catalyst prepared by the present invention are cheap and readily available, the preparation process is simple, the catalyst has high mechanical strength, the active components are evenly dispersed, and it can operate stably for a long period of time in the reactor, and is easy to be mass-produced industrially;

[0066] (4) The catalyst prepared by the present invention is used in the reaction of carbon dioxide hydrogenation to synthesize hydrocarbon compounds. 2 The conversion rate exceeded 50%, and the by-product CH 4 The selectivity for CO is lower than 15%, the selectivity for α-olefin is higher than 40%, and the catalyst has good reaction stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 The results of the catalyst stability test in Example 3 of the present invention are shown. DETAILED DESCRIPTION

[0068] The present invention will be further described below in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope limited by the appended claims of the present application. The various commonly used reagents used in the examples are all commercially available products.

[0069] Example 1

[0070] 202 g Fe(NO 3 ) 3 9H 2 O, 26.15 g Ba(NO 3 ) 2 、215g Zr(NO 3 ) 4 ·5H 2 O, 28.5gCu(NO 3 ) 2 ·3H 2 O is prepared into a 2 mol / L metal mixed salt solution A, and then 2 mol / LNa 2 CO 3and NaOH solution as precipitant B; 100g of 20% acidic silica sol was added to the three-necked flask in advance, and solution A and solution B were added to the three-necked flask in parallel for co-precipitation reaction, the reaction temperature was 80℃, the precipitation reaction pH value was 8.0, and the reaction time was 0.5h. After the reaction, the solution was stirred and aged at 80℃ for 5h; after the aging, the solution was transferred to a purification reactor, dynamically crystallized at 160℃ for 24h, then filtered and washed with water, and when the conductivity of the filtrate reached 1200μs / cm; the filter cake was re-slurried, 0.48g of phosphoric acid was added, and the pH value was adjusted to 8.0 after stirring evenly; it was dried at 120℃ for 24h to obtain the LDH precursor of multi-component iron oxide; it was treated at 420℃ in a nitrogen roasting furnace for 6 hours to obtain catalyst S1.

[0071] Take 20-40 mesh catalyst S1 and quartz sand of the same mesh, mix them in a mass ratio of 1:3 and load them into a fixed bed reaction tube. The reduction conditions are: pressure 0.3MPa, temperature 320℃, 50% CO / Ar reduction carbonization treatment for 12h, space velocity 15000h -1 After the reduction, the synthesis reaction was carried out under the conditions of 1.5 MPa, 330 °C, H 2 / CO 2 =4, airspeed 10000h -1 The catalyst was tested for activity for 70 hours and the reaction results are listed in Table 1.

[0072] Example 2

[0073] 202 g Fe(NO 3 ) 3 9H 2 O, 26.15 g Ba(NO 3 ) 2 、215g Zr(NO 3 ) 4 ·5H 2 O, 28.5gCu(NO 3 ) 2 ·3H 2 O is prepared into a 2 mol / L metal mixed salt solution A, and then 2 mol / LNa 2 CO 3and NaOH solution as precipitant B; solution A and solution B are added to a three-necked flask in parallel for co-precipitation reaction, the reaction temperature is 80°C, the precipitation reaction pH value is 8.0, and the reaction time is 0.5h. After the reaction is completed, the solution is stirred and aged at 80°C for 5h; after the aging, the solution is transferred to a purification reactor, dynamically crystallized at 160°C for 24h, then filtered and washed with water, and when the conductivity of the filtrate reaches 1200μs / cm; the filter cake is re-slurried, 0.48g of boric acid is added, stirred evenly, and the pH value is adjusted to 8.0; dried at 120°C for 24h to obtain the LDH precursor of multi-component iron oxide; treated at 420°C in a nitrogen calciner for 6 hours to obtain catalyst S2.

[0074] Take 20-40 mesh catalyst S2 and quartz sand of the same mesh, mix them in a mass ratio of 1:3 and fill them into a fixed bed reaction tube. The reduction conditions are: pressure 0.3MPa, temperature 320℃, 50% CO / Ar reduction carbonization treatment for 12h, space velocity 15000h -1 After the reduction, the synthesis reaction was carried out under the conditions of 1.5 MPa, 330 °C, H 2 / CO 2 =4, airspeed 10000h -1 The catalyst was tested for activity for 70 hours and the reaction results are listed in Table 1.

[0075] Example 3

[0076] 202 g Fe(NO 3 ) 3 9H 2 O, 26.15 g Ba(NO 3 ) 2 、215g Zr(NO 3 ) 4 ·5H 2 O, 28.5gCu(NO 3 ) 2 ·3H 2 O is prepared into a 2 mol / L metal mixed salt solution A, and then 2 mol / LNa 2 CO 3and NaOH solution as precipitant B; solution A and solution B are added to a three-necked flask in parallel for co-precipitation reaction, the reaction temperature is 80°C, the precipitation reaction pH value is 8.0, and the reaction time is 0.5h. After the reaction is completed, the solution is stirred and aged at 80°C for 5h; after the aging, the solution is transferred to a purification reactor, dynamically crystallized at 160°C for 24h, then filtered and washed with water, and when the conductivity of the filtrate reaches 1200μs / cm; the filter cake is re-slurried, 0.48g of phosphoric acid is added, stirred evenly, and the pH value is adjusted to 8.0; dried at 120°C for 24h to obtain the LDH precursor of multi-component iron oxide; treated at 420°C in a nitrogen calciner for 6 hours to obtain catalyst S3.

[0077] Take 20-40 mesh catalyst S3 and quartz sand of the same mesh, mix them in a mass ratio of 1:3 and fill them into a fixed bed reaction tube. The reduction conditions are: pressure 0.3MPa, temperature 320℃, 50% CO / Ar reduction carbonization treatment for 12h, space velocity 15000h -1 After the reduction, the synthesis reaction was carried out under the conditions of 1.5 MPa, 330 °C, H 2 / CO 2 =4, airspeed 10000h -1 The catalyst was tested for activity for 70 hours and the reaction results are listed in Table 1.

[0078] Example 4

[0079] 202 g Fe(NO 3 ) 3 9H 2 O, 26.15 g Ba(NO 3 ) 2 、215g Zr(NO 3 ) 4 ·5H 2 O, 28.5gCu(NO 3 ) 2 ·3H 2 O is prepared into 2 mol / L metal mixed salt solution A, and then 2 mol / L K 2 CO 3and KOH solution as precipitant B; solution A and solution B are added to a three-necked flask in parallel for co-precipitation reaction, the reaction temperature is 80°C, the precipitation reaction pH value is 8.0, and the reaction time is 0.5h. After the reaction is completed, the solution is stirred and aged at 80°C for 5h; after the aging is completed, the solution is transferred to a purification reactor, dynamically crystallized at 160°C for 24h, then filtered and washed with water, and when the conductivity of the filtrate reaches 1200μs / cm; the filter cake is re-slurried, 0.48g of phosphoric acid is added, stirred evenly, and the pH value is adjusted to 8.0; dried at 120°C for 24h to obtain the LDH precursor of multi-component iron oxide; treated at 420°C in a nitrogen calciner for 6 hours to obtain catalyst S4.

[0080] Take 20-40 mesh catalyst S4 and quartz sand of the same mesh, mix them in a mass ratio of 1:3 and fill them into a fixed bed reaction tube. The reduction conditions are: pressure 0.3MPa, temperature 320℃, 50% CO / Ar reduction carbonization treatment for 12h, space velocity 15000h -1 After the reduction, the synthesis reaction was carried out under the conditions of 1.5 MPa, 330 °C, H 2 / CO 2 =4, airspeed 10000h -1 The catalyst was tested for activity for 70 hours, and the reaction results are listed in Table 1.

[0081] Example 5

[0082] 202 g Fe(NO 3 ) 3 9H 2 O, 26.15 g Ba(NO 3 ) 2 、215g Zr(NO 3 ) 4 ·5H 2 O, 28.5gCu(NO 3 ) 2 ·3H 2 O, 40.0 g Cr(NO 3 ) 3 9H 2 O is prepared into a 2 mol / L metal mixed salt solution A, and then 2 mol / LNa 2 CO 3and NaOH solution as precipitant B; solution A and solution B are added to a three-necked flask in parallel for co-precipitation reaction, the reaction temperature is 80°C, the precipitation reaction pH value is 8.0, and the reaction time is 0.5h. After the reaction is completed, the mixture is stirred and aged at 80°C for 5h; after the aging, the solution is transferred to a purification reactor, dynamically crystallized at 160°C for 24h, then filtered and washed with water, and when the conductivity of the filtrate reaches 1200μs / cm; the filter cake is re-slurried, 0.48g of phosphoric acid is added, stirred evenly, and the pH value is adjusted to 8.0; dried at 120°C for 24h to obtain the LDH precursor of multi-component iron oxide; treated at 420°C in a nitrogen calciner for 6 hours to obtain catalyst S5.

[0083] Take 20-40 mesh catalyst S5 and quartz sand of the same mesh, mix them in a mass ratio of 1:3 and fill them into a fixed bed reaction tube. The reduction conditions are: pressure 0.3MPa, temperature 320℃, 50% CO / Ar reduction carbonization treatment for 12h, space velocity 15000h -1 After the reduction, the synthesis reaction was carried out under the conditions of 1.5 MPa, 330 °C, H 2 / CO 2 =4, airspeed 10000h -1 The catalyst was tested for activity for 70 hours, and the reaction results are listed in Table 1.

[0084] Comparative Example 1

[0085] 202 g Fe(NO 3 ) 3 9H 2 O, 26.15 g Ba(NO 3 ) 2 、28.5g Cu(NO 3 ) 2 ·3H 2 O is prepared into a 2 mol / L metal mixed salt solution A, and then 2 mol / LNa 2 CO 3 and NaOH solution as precipitant B; solution A and solution B are added to a three-necked flask in parallel for co-precipitation reaction, the reaction temperature is 80°C, the precipitation reaction pH value is 8.0, and the reaction time is 0.5h. After the reaction is completed, the mixture is stirred and aged at 80°C for 5h; after the aging, the solution is transferred to a purification reactor, dynamically crystallized at 160°C for 24h, then filtered and washed with water, and when the conductivity of the filtrate reaches 1200μs / cm; the filter cake is re-slurried, 0.48g of phosphoric acid is added, stirred evenly, and the pH value is adjusted to 8.0; dried at 120°C for 24h to obtain the LDH precursor of multi-component iron oxide; treated at 420°C in a nitrogen calciner for 6 hours to obtain catalyst D1.

[0086] Take 20-40 mesh catalyst D1 and quartz sand of the same mesh, mix them in a mass ratio of 1:3 and load them into a fixed bed reaction tube. The reduction conditions are: pressure 0.3MPa, temperature 320℃, 50% CO / Ar reduction carbonization treatment for 12h, space velocity 15000h -1 After the reduction, the synthesis reaction was carried out under the conditions of 1.5 MPa, 330 °C, H 2 / CO 2 =4, airspeed 10000h -1 The catalyst was tested for activity for 70 hours and the reaction results are listed in Table 1.

[0087] Comparative Example 2

[0088] 202 g Fe(NO 3 ) 3 9H 2 O, 26.15 g Ba(NO 3 ) 2 、215g Zr(NO 3 ) 4 ·5H 2 O, 28.5gCu(NO 3 ) 2 ·3H 2 O is prepared into a 2 mol / L metal mixed salt solution A, and then 2 mol / LNa 2 CO 3 and NaOH solution as precipitant B; solution A and solution B are added to a three-necked flask in parallel for co-precipitation reaction, the reaction temperature is 80°C, the precipitation reaction pH value is 8.0, and the reaction time is 0.5h. After the reaction is completed, the solution is stirred and aged at 80°C for 5h; after the aging, the solution is transferred to a purification reactor, dynamically crystallized at 160°C for 24h, then filtered and washed with water, and when the conductivity of the filtrate reaches 1200μs / cm; the filter cake is re-slurried, stirred evenly, and the pH value is adjusted to 8.0; dried at 120°C for 24h to obtain the LDH precursor of multi-component iron oxide; treated at 420°C in a nitrogen calciner for 6 hours to obtain catalyst D2.

[0089] Take 20-40 mesh catalyst D2 and quartz sand of the same mesh, mix them in a mass ratio of 1:3 and load them into a fixed bed reaction tube. The reduction conditions are: pressure 0.3MPa, temperature 320℃, 50% CO / Ar reduction carbonization treatment for 12h, space velocity 15000h -1 After the reduction, the synthesis reaction was carried out under the conditions of 1.5 MPa, 330 °C, H 2 / CO 2 =4, airspeed 10000h -1 The catalyst was tested for activity for 70 hours and the reaction results are listed in Table 1.

[0090] Experimental Results

[0091] Based on the catalyst prepared in the above Examples 1-5 and Comparative Examples 1-2, the stability test conditions were the same as the activity test conditions. The catalyst was continuously reacted until the CO 2 The conversion rate decreased significantly.

[0092] The performance of the catalyst depends on the CO 2 The conversion rate and selectivity of hydrocarbons in the product are calculated.

[0093] According to the reaction process CO 2 The performance of the catalyst is calculated by the conversion rate and the selectivity of hydrocarbons in the product. The specific calculation formula is shown below, and the technical results are shown in Table 1 below:

[0094] CO 2 Conversion rate:

[0095]

[0096] CO selectivity:

[0097]

[0098] CH 4 Optional:

[0099]

[0100] C 2 -C 4 Olefin selectivity:

[0101]

[0102] C 5+ Optional:

[0103]

[0104] Table 1 Comparative Examples and Examples Catalysts for Carbon Dioxide Hydrogenation Reaction Performance Results

[0105]

[0106] From Table 1 and Figure 1 It can be seen that the iron-based catalyst obtained in Example 3 can still have good reaction stability after long-term operation for 1600 hours. During the entire carbon dioxide hydrogenation reaction process, the catalyst always maintains a high CO 2 Conversion rate (conversion rate ≥ 40%), and the selectivity of by-products is very low, CO and CH 4 The selectivity is kept below 15%, C5+ The selectivity of hydrocarbons is more than 50%, and the C 4+ α-olefin selectivity> 40%. This shows that the catalyst of the present invention greatly improves the iron-based catalyst in CO 2 Catalytic reaction stability in hydrogenation reactions.

[0107] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the attached claims.

Claims

1. A nano iron-based catalyst modified by an additive, characterized in that: The nano iron-based catalyst comprises iron metal oxide, zirconium metal oxide, an additive and an optional carrier; the molar ratio of iron element to zirconium element is 1:0.5-2; The additives include metal oxide additives and non-metal additives; the molar ratio of iron element to metal element in the metal oxide additive is 1:0.01-0.05; The carrier accounts for 10%-80% of the total mass fraction of the catalyst.

2. The nano iron-based catalyst according to claim 1, characterized in that: The nano iron-based catalyst comprises the following components: 20-60 parts by weight of iron metal oxide; 20-60 parts by weight of zirconium metal oxide; 5-30 parts by weight of an auxiliary agent; and / or 0-30 parts by weight of carrier.

3. The nano iron-based catalyst according to claim 1, characterized in that: The iron metal oxide includes Fe2O3 and FeO, preferably Fe2O3.

4. The nano iron-based catalyst according to claim 1, characterized in that: The metal element in the metal oxide additive is selected from at least one of transition metals and alkaline metals.

5. The nano iron-based catalyst according to claim 1, characterized in that: The carrier is selected from one or more of Al2O3 powder, SiO2 powder, TiO2 powder, Al2O3 sol, acidic silica sol and TiO2 sol.

6. A method for preparing the nano iron-based catalyst according to claim 1, characterized in that: The steps include: When the carrier in the catalyst is 0, the preparation method 1 comprises the following steps: S1: According to the composition ratio of the catalyst, a soluble salt solution of Fe, Zr and the metal elements in the metal oxide additive is prepared into a mixed salt solution; preferably nitrate; S2: preparing a precipitant solution with a precipitant containing an alkaline metal according to the composition ratio of the catalyst; S3: co-precipitating the mixed salt solution in S1 and the precipitant solution in S2 in parallel; S4: After the precipitation is completed, the slurry is aged, filtered and washed to obtain the slurry; S5: adding non-metallic additives to the slurry obtained by washing in S4, drying, and calcining to obtain the catalyst.

7. A method for preparing the nano iron-based catalyst according to claim 1, characterized in that: When the carrier in the catalyst is greater than 0, the preparation method 2 comprises the following steps: S1: According to the composition ratio of the catalyst, a soluble salt solution of Fe, Zr and the metal elements in the metal oxide additive is prepared into a mixed salt solution; preferably nitrate; S2: preparing a precipitant solution with a precipitant containing an alkaline metal according to the composition ratio of the catalyst; S3: In the presence of a carrier, the mixed salt solution in S1 and the precipitant solution in S2 are co-precipitated in parallel; S4: After the precipitation, aging, dynamic crystallization, filtration and washing are performed to obtain mud; S5: adding non-metallic additives to the slurry obtained by washing in S4, re-slurrying the filter cake, drying, and calcining to obtain the catalyst.

8. The method for preparing a nano iron-based catalyst according to claim 6 or 7, characterized in that: The molar concentration of the total metal salt in the mixed salt solution is in the range of 0.1-5 mol / L, such as 0.1-4 mol / L, 0.2-3 mol / L, 0.5-2 mol / L.

9. The method for preparing a nano iron-based catalyst according to claim 6 or 7, characterized in that: The molar concentration of the precipitant solution is in the range of 0.1-5 mol / L, such as 0.1-4 mol / L, 0.2-3 mol / L, 0.5-2 mol / L.

10. The use of the nano iron-based catalyst according to claim 1, characterized in that: Used in the CO2 hydrogenation reaction to produce long-chain α-olefins.

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