Preparation method and application of composite catalyst for hydrogenation of carbon dioxide to aromatics

Abstract

The present invention discloses a preparation method and application of a composite catalyst for hydrogenating carbon dioxide to aromatics. The composite catalyst is composed of an iron-based catalyst and an HZSM-5 molecular sieve. The main active components of the iron-based catalyst are Fe3O4 and iron carbide. The preparation method includes the steps of preparing modified ferric oxide, modified ferrosoferric oxide, and the iron-based catalyst. The preparation method of the present invention improves the adsorption activation ability of carbon dioxide on the composite catalyst and the anti-poisoning stability of the composite catalyst, while also improving the selectivity of the aromatics product.

Description

Technical Field

[0001] The present invention relates to a method for preparing a catalyst, in particular to a method for preparing a catalyst for catalyzing the hydrogenation of carbon dioxide to produce aromatic hydrocarbons. Background Art

[0002] The capture and utilization of CO2 can consume greenhouse gases. CO2 is widely present in nature and is cheap and easy to obtain. Using CO2 as raw material to prepare high-value-added hydrocarbon products can not only effectively alleviate the global greenhouse effect, but also replace increasingly depleted fossil fuels.

[0003] Aromatic hydrocarbons, particularly benzene, toluene, xylene, and durene, are widely used in polymers, coatings, pharmaceuticals, and military applications. Market demand is substantial and growing annually. Currently, the process of converting coal to syngas (a mixture of CO and H₂) is maturing, and extensive research is underway into technologies for producing aromatics using syngas as a feedstock. Consequently, CO₂-to-aromatics technology has begun to attract research attention as a more economical and clean non-petroleum-based method for producing aromatics.

[0004] Direct CO2 to aromatics production includes routes through oxygenated intermediates (methanol route) and Fischer-Tropsch synthesis (CO2-FT) intermediates. The methanol route involves hydrogenating CO2 to produce a methanol intermediate, which is then used to produce aromatics through methanol-to-aromatics technology. While this route produces aromatics with high selectivity among hydrocarbons, its conversion is generally below 20%, accompanied by the formation of a large amount of CO as a byproduct, resulting in a relatively low space-time yield. The CO2-FT intermediate to aromatics route involves CO2 undergoing a reverse water-gas shift reaction to produce CO, which is then hydrogenated to produce a light olefin intermediate through the Fischer-Tropsch synthesis (CO-FT) reaction. These light olefins are then aromatized to produce aromatics. This route, also known as direct CO2-FT to aromatics, offers advantages in achieving industrial production, including high CO2 conversion and high space-time yield of aromatics. However, its product distribution is complex, with a high concentration of aliphatic hydrocarbons in the liquid product, leading to high separation costs. Therefore, it is necessary to conduct in-depth research on the reaction process of direct production of aromatics from CO2-FT, develop efficient CO2-FT iron-based catalysts and molecular sieve composite catalysts, and improve the reaction conversion rate and aromatics selectivity. These are key issues that need to be solved for the industrial application of CO2-FT technology to produce aromatics.

[0005] Patent CN107840778A discloses a method for producing aromatic hydrocarbons by hydrogenating carbon dioxide. The active components of the iron-based metal oxide catalyst used in this technology are Fe, FeO, Fe2O3, and Fe3O4. The soluble iron salt used is a mixture of divalent and trivalent iron salts. At a pH of 2-3, both the iron salt and the additive precipitate. This means that the iron salt and additive described in this technology do not completely dissolve in the aqueous solution and are uniformly mixed, resulting in a precipitate mixture.

[0006] Patent CN108160104A discloses a catalyst for the one-step hydrogenation of carbon dioxide to produce aromatic hydrocarbons, as well as its preparation method and application. The active component of the iron-based metal oxide catalyst used in this technology is Fe₃O₄, and the additive is present in the catalyst as an oxide. Furthermore, the pH value of the iron salt and additive salt solutions used in this technology is not specified. The aqueous solution prepared using one or more of hydrochlorides, nitrates, bromides, acetates, oxalates, and ammonium salts as raw materials cannot dissolve most metal elements even with the aid of ultrasound, resulting in precipitation. In other words, the iron salt and additive in this technology cannot completely dissolve in the aqueous solution and mix evenly, resulting in a precipitate mixture.

[0007] Patent CN111229303A discloses a composite catalyst for directly producing high-value aromatic hydrocarbons from carbon dioxide, as well as its preparation method and application. The catalyst used in this technology has a three-layer porous core-shell structure, the inner layer is a metal-modified iron-based metal oxide, the middle layer is a microporous SiO2 thin layer coated with a metal-modified metal oxide, and the outer layer is a HZSM-5 molecular sieve layer. A variety of additives are used, and the additives can preferably be added to the aqueous solution in the form of one or more of chlorides, nitrates, and acetates. In addition, this technology does not specify the pH of the iron salt and additive salt solution. When the pH value is 2-3, both the iron salt and the additive salt have precipitated and cannot be completely dissolved. The precipitate formed is a precipitate mixture. In addition, when the pH reaches 3.2-10, the titration endpoint is reached and the addition of the alkaline precipitant is stopped, which may cause the additives, including copper salts, to not precipitate out in the aqueous solution and be discarded with the mother liquor. This technology uses

[0008] Patent CN114369002A discloses a method for synthesizing linear α-olefins from syngas. This technology uses potassium and manganese salts as additives. The surface of the iron-based catalyst's primary iron components, Fe₃O₄ and Fe₂O₃, is modified using an equal-volume impregnation method. The resulting additive-containing Fe-Cat is K-Mn-Fe₂O₃. The additive is anchored only on the surfaces of the primary iron components, Fe₃O₄ and Fe₂O₃. At these anchoring locations, the additive maintains its original structure or forms a small amount of new material. The original structure of Fe₃O₄ and Fe₂O₃ remains unchanged in areas uncovered by the additive and within the bulk of the iron-based catalyst.

[0009] During the catalytic reaction of carbon dioxide to aromatics, carbon dioxide is relatively stable, difficult to activate catalytically, and has a low conversion rate. In addition, iron-based catalysts for carbon dioxide to aromatics are easily poisoned by impurities such as sulfur and have low stability. These problems have restricted the industrial application of carbon dioxide to aromatics technology. Summary of the Invention

[0010] To address the current shortcomings of carbon dioxide-to-aromatics technology, the present invention proposes a method for preparing a catalyst for the hydrogenation of carbon dioxide to aromatics. First, rare earth metals are added to increase oxygen vacancies, improving carbon dioxide activation performance. Secondly, based on the presence of iron and auxiliary elements in aqueous solution under different acidic conditions, the auxiliary element is prepared to be highly dispersed in the iron phase in a nearly monoatomic state, thereby forming a large amount of iron-metal alloy in the composite catalyst. The formation of the iron-metal alloy greatly enhances the electronic and structural effects of the metal auxiliary on the composite catalyst, improving the adsorption and activation ability of carbon dioxide on the composite catalyst and the anti-poisoning stability of the composite catalyst. It also improves the selectivity of the product aromatics, showing great potential for industrial application.

[0011] To achieve the above-mentioned object, the present invention provides a method for preparing a composite catalyst for hydrogenating carbon dioxide to aromatics, which is composed of an iron-based catalyst and an HZSM-5 molecular sieve. The main active components of the iron-based catalyst are Fe3O4 and iron carbide. The preparation method comprises the following steps:

[0012] (1) Preparation of modified ferric oxide:

[0013] A soluble Fe(III) salt is mixed with an additive to form a saline solution, hydrochloric acid or nitric acid is added to adjust the pH, heated and stirred, and then an alkaline solution is added dropwise to adjust the pH. The colloidal state of the solution is converted into a suspended precipitation state, aged, separated, washed, dried, and calcined to obtain modified ferric oxide;

[0014] (2) Preparation of modified ferroferric oxide:

[0015] A soluble Fe(II) salt, a soluble Fe(III) salt and an auxiliary agent are mixed to form a saline solution, nitrogen is introduced for protection, hydrochloric acid or nitric acid solution is added to adjust the pH, heated and stirred, and then an alkaline solution is added dropwise to adjust the pH, the solution becomes a suspended precipitation state, aged, separated, washed, dried and calcined to obtain modified ferrosoferric oxide;

[0016] (3) Preparation of iron-based catalysts:

[0017] The modified ferric oxide and the modified ferrosoferric oxide are ground and mixed, then immersed in a solution of sodium carbonate or potassium carbonate, dried and calcined to obtain an iron-based catalyst;

[0018] (4) Preparation of composite catalyst:

[0019] The iron-based catalyst and the HZSM-5 molecular sieve are respectively pressed into tablets, sieved, and then evenly mixed in the form of particles to obtain a composite catalyst;

[0020] Wherein, in step (1), the auxiliary agent includes two or more of Na, K, Mn, Cu, Zr, V, Zn, Ce, La, Ni, Cr, and Co;

[0021] In step (2), the auxiliary agent includes two or more of Mn, Ce, La, Pr, Nd, Gd, and Sm, wherein the number of rare earth elements is two or more.

[0022] In the preparation method of the composite catalyst of the present invention, in step (1), the soluble Fe(III) salt refers to a salt compound that can be dissolved in water, and is one or more of Fe chloride, nitrate, and acetate.

[0023] In the preparation method of the composite catalyst of the present invention, in step (1), the auxiliary agent is added in the form of a soluble salt, including one or more of chloride, nitrate, and acetate.

[0024] In the preparation method of the composite catalyst of the present invention, in step (1), the content of the auxiliary agent, calculated as metal oxide, accounts for 0.01 to 35% of the total mass of the iron-based catalyst.

[0025] In the preparation method of the composite catalyst of the present invention, in step (2), the soluble Fe(II) salt and the soluble Fe(III) salt refer to salt compounds that can be dissolved in water, and are one or more of the chloride, nitrate, and acetate of Fe.

[0026] In the preparation method of the composite catalyst of the present invention, in step (2), the auxiliary agent is added in the form of a soluble salt, including one or more of chloride, nitrate, and acetate.

[0027] The preparation method of the composite catalyst of the present invention, in step (2), when Mn is added, Fe 2+ The molar ratio of Fe to Mn is 0.5-2. 3+ The molar ratio of Fe to Mn is 0.1-0.5, 3+ The molar ratio of rare earth elements is 0.5-2.

[0028] In the preparation method of the composite catalyst of the present invention, in step (1), the concentration of Fe(III) in the saline solution is 0.05-1 mol / L; the concentration of the hydrochloric acid or nitric acid is 4-12 mol / L; and the pH value is 0-2.

[0029] In the preparation method of the composite catalyst of the present invention, in step (1), the heating temperature is 60-80° C.; the stirring speed is 400-800 rpm, and the stirring time is 0.5-3 h, preferably 1 h.

[0030] In the preparation method of the composite catalyst of the present invention, in step (1), the alkaline solution is added at a rate of 0.5-1.5 drops / second, and the pH value is adjusted to 9-11 by adding the alkaline solution dropwise; and the aging time is 1-5 hours, preferably 1 hour.

[0031] In the preparation method of the composite catalyst of the present invention, in step (1), the alkaline solution refers to an alkaline solution capable of adjusting the pH value of the solution, which is one or more solutions of NaOH, KOH, Na2CO3, NaHCO3, K2CO3, KHCO3, Na2C2O4, K2C2O4, RCOONa, RCOOK, and ammonia water, preferably NaOH, wherein R is an organic functional group; the concentration of the alkaline solution is 0.1 to 5 mol / L, preferably 1 mol / L.

[0032] The preparation method of the composite catalyst of the present invention comprises the following steps: in step (1), the separation is carried out by centrifugation or filtration; the washing is carried out by fully washing with deionized water until the mixture is neutral; the drying temperature is 110°C and the drying time is 12 hours; the calcination condition is 2°C·min -1 The heating rate is increased from room temperature to 400-600°C and calcined for 3-6 hours.

[0033] In the preparation method of the composite catalyst of the present invention, in step (2), the concentration of Fe(III) in the saline solution is 0.05-1 mol / L; the concentration of the hydrochloric acid or nitric acid is 4-12 mol / L; and the pH value is 0-2.

[0034] In the preparation method of the composite catalyst of the present invention, in step (2), the heating temperature is 60-80° C.; the stirring speed is 400-800 rpm, and the stirring time is 0.5-3 h, preferably 1 h.

[0035] In the preparation method of the composite catalyst of the present invention, in step (2), the alkaline solution is added at a dripping speed of 0.5-1.5 drops / second, and the pH value is adjusted to 9-11 by dripping the alkaline solution; and the aging time is 1-5 hours, preferably 1 hour.

[0036] In the preparation method of the composite catalyst of the present invention, in step (2), the alkaline solution refers to an alkaline solution capable of adjusting the pH value of the solution, which is one or more solutions of NaOH, KOH, Na2CO3, NaHCO3, K2CO3, KHCO3, Na2C2O4, K2C2O4, RCOONa, RCOOK, and ammonia water, preferably NaOH, wherein R refers to an organic functional group; the concentration of the alkaline solution is 0.1 to 5 mol / L, preferably 1 mol / L.

[0037] The preparation method of the composite catalyst of the present invention, in step (2), the separation is carried out by centrifugation or filtration; the washing is carried out by fully washing with deionized water until neutral; the drying temperature is 110°C and the drying time is 12h; the calcination condition is 2°C·min -1 The heating rate is increased from room temperature to 400-600°C and calcined for 3-6 hours.

[0038] In the preparation method of the composite catalyst of the present invention, in step (3), the grinding to 80-100 mesh is performed for 1 hour.

[0039] In the preparation method of the composite catalyst of the present invention, in step (3), the mass ratio of the modified ferric oxide to the modified ferrosoferric oxide is 20:1-1:20.

[0040] The preparation method of the composite catalyst of the present invention, in step (3), the concentration of the sodium carbonate or potassium carbonate solution is 0.1 to 5 mol / L, preferably 1 mol / L; the solid-liquid ratio of the mixture of the modified ferric oxide and the modified ferrosoferric oxide to the sodium carbonate or potassium carbonate solution is 0.1-1 g / mL. The impregnation conditions are: standing under ultrasound, then centrifuging to separate the solid; the drying temperature is 110°C, the time is 12 hours; the calcination conditions are: 2°C·min -1 The heating rate is increased from room temperature to 400-600°C and calcined for 3-6 hours.

[0041] In the preparation method of the composite catalyst of the present invention, in step (4), the mass ratio of the iron-based catalyst to the HZSM-5 molecular sieve is 1:10 to 10:1, preferably 1:3 to 3:1; the silicon-aluminum ratio of the HZSM-5 molecular sieve is 20-50; and the particle size of the iron-based catalyst and the HZSM-5 molecular sieve is 20-60 mesh.

[0042] The present invention also provides a method for producing aromatic hydrocarbons by hydrogenating carbon dioxide, wherein a mixed gas consisting of carbon dioxide and hydrogen is used as raw gas and directly converted into aromatic hydrocarbons by reaction under the catalytic action of a composite catalyst.

[0043] The method for preparing aromatic hydrocarbons by hydrogenating carbon dioxide of the present invention is as follows: at 0.1-3.0 MPa and 300-500°C, H2 is introduced into the reactor to reduce the composite catalyst for 4-24 hours, with a hydrogen space velocity of 100-5000 mL / (h·g cat ), then switch the reducing gas under the same conditions, first use 100~5000 mL / (h·g cat ) Purge with N2 at an air velocity for 0.5-5h, then switch to reducing gas (CO / N2=3:2~10:1) and reduce at a constant temperature for 4-24h.

[0044] The method for preparing aromatic hydrocarbons by hydrogenating carbon dioxide of the present invention comprises the following steps: cooling the reaction temperature to 300-350°C in nitrogen, the reaction temperature being 250-450°C, the reaction pressure being 0.01-10.0 MPa, the feed gas space velocity being 500-50000 mL / (h·g cat ), the H2 / CO2 molar ratio in the raw gas is 0.5 to 8.0.

[0045] The method for preparing aromatic hydrocarbons by hydrogenating carbon dioxide of the present invention comprises any one or more of industrial waste gas containing carbon dioxide, automobile exhaust, coal combustion waste gas, carbon dioxide absorbed from the atmosphere and seawater.

[0046] The composite catalyst obtained by the preparation method of the present invention is composed of three active components: modified ferroferric oxide, iron carbide generated after carbonization of modified ferric oxide, and HZSM-5 molecular sieve. The oxygen vacancies of ferroferric oxide are active sites for carbon dioxide activation. At present, in the process of carbon dioxide to aromatics reaction, the ferroferric oxide phase content and the number of oxygen vacancies of iron-based catalysts vary greatly with the reaction conditions or even decrease and disappear, affecting the catalytic activity of carbon dioxide. The present invention can stabilize the ferroferric oxide phase and oxygen vacancies by adding auxiliary agents such as manganese and rare earth in a high proportion, and increase the number of oxygen vacancies, thereby increasing the carbon dioxide activation performance and improving the carbon dioxide conversion rate.

[0047] The iron and additive elements in the aqueous solution exist in different states under different acidic conditions. By adding an acid solution to the aqueous solution mixed with the Fe salt and additive to adjust the pH to 0-2, and then heating and stirring, the Fe salt and additive salt can be completely dissolved and evenly dispersed in an ionic state. After the gradual addition of alkaline solution, the additive element is highly dispersed in the iron phase in an almost monoatomic state, thereby forming a large amount of iron metal alloy in the composite catalyst. The formation of the iron metal alloy greatly enhances the electronic and structural effects of the metal additive on the composite catalyst, improving the adsorption and activation ability of carbon dioxide on the composite catalyst and the anti-poisoning stability of the composite catalyst. It also improves the selectivity of the product aromatics and reduces the yield of gaseous byproducts.

[0048] The iron oxide phase with increased oxygen vacancy content and the modified ferric oxide phase are ground to achieve uniform dispersion and chemical adhesion between the two phases. During the carbon dioxide hydrogenation reaction, carbon dioxide is activated at the iron oxide oxygen vacancies to form a carbon monoxide intermediate. The carbon monoxide then rapidly undergoes carbon chain growth at the nearby active sites of iron carbides formed by the ferric oxide to form hydrocarbons. The hydrocarbons enter the molecular sieve pores and undergo aromatization to form aromatic products. Due to the matched contact between the activities, the entire carbon dioxide reaction process forms a chemical reaction chain coupling effect. The formation of aromatic products further drives the carbon dioxide conversion reaction, improving the carbon dioxide conversion rate and aromatic product selectivity. The present invention has promising industrial applications. DETAILED DESCRIPTION

[0049] The present invention will be further described in detail below with reference to specific embodiments, but is not limited to the embodiments.

[0050] Comparative Example 1

[0051] (1) Preparation of Na-FeMnO by co-precipitation and impregnation x Oxide:

[0052] 60.6 g of Fe(NO3)3·9H2O and 10.7372 g of 50 wt% Mn(NO3)2 solution were weighed and dissolved in 300 mL of deionized water to prepare the precursor solution; 21.4716 g of NaOH was weighed and dissolved in 500 mL of deionized water to prepare the precipitant. The precursor solution was stirred continuously at 70°C, and an alkaline solution was added. The resulting suspension was aged at 70°C for 1 hour and then filtered. It was washed thoroughly several times to remove a large amount of residual sodium in preparation for the impregnation operation. Then, 12.56 g of FeMnO x The powder was put into 31.4 mL of 0.696 mol / l sodium carbonate solution, ultrasonicated for 30 min, and then allowed to stand and soak for 12 hours. Finally, it was dried in an oven at 110 °C overnight, calcined at 400 °C for 4 hours, ground, and sieved to obtain 40-60 mesh Na-FeMnO x catalyst.

[0053] (2) Preparation of ZSM-5 molecular sieve by hydrothermal method:

[0054] 45.756 g of tetrapropylammonium hydroxide (TPAOH) was added dropwise to 62.499 g of tetraethyl orthosilicate (TEOS) and stirred for 24 hours to form Solution I. 4.500 g of Al(NO3)3·9H2O and an excess of alkali (2.400 g of NaOH) were dissolved in an appropriate amount of deionized water to form Solution II. Solution II was slowly added dropwise to Solution I under stirring to obtain the zeolite precursor. This was then transferred to a Teflon-sealed autoclave and heated at 170 °C and 45 rpm for 10 min.-1 The molecular sieve was subjected to hydrothermal crystallization treatment for 48 hours under the following conditions. The molecular sieve was centrifuged and washed until neutral. It was dried at 105°C for 12 hours and calcined in air at 550°C for 5 hours. The obtained molecular sieve was heated to 1 mol·L -1 NH4Cl solution at 80℃ for 2 h (zeolite / liquid is 50 g·L -1 ), filter and separate by suction, repeat the ion exchange 3 times, wash the molecular sieve to neutrality, filter and separate, dry the filter cake at 105℃ for 12h, calcine in air at 550℃ for 5h, press into tablets, grind and sieve 40-60 mesh HZSM-5 molecular sieve.

[0055] (3) Mix 40 to 60 mesh Na-FeMnO x The catalyst and 40-60 mesh HZSM-5 molecular sieve were mechanically mixed uniformly at a mass ratio of 1:1 to obtain composite catalyst A-1.

[0056] (4) Catalyst evaluation:

[0057] 2 g of catalyst A-1 was loaded into the constant temperature section of the reaction tube and heated by nitrogen gas at a rate of 2°C / min to a reduction temperature of 400°C. Reducing gas (CO / N2 = 3 / 2) was introduced into the reaction tube at a flow rate of 75 mL / min. After 12 hours of isothermal reduction, the reaction tube was cooled to a reaction temperature of 320°C in nitrogen. The reaction gas (N2 / H2 / CO2 = 4 / 24 / 72) was then introduced into the fixed-bed reactor at a space velocity of 1000 mL / g / min. The reaction was carried out at a reaction pressure of 3 MPa for 24 hours. The CO2 conversion and aromatics product selectivity are listed in Table 1.

[0058] Example 1

[0059] (1) Preparation of Mn-modified ferric oxide by colloidal precipitation method:

[0060] Weigh 30.3 g of Fe(NO3)3·9H2O and 5.3686 g of 50 wt% Mn(NO3)2 solution and dissolve them in 150 mL of deionized water to prepare an aqueous solution. Add 5 mol / L nitric acid to adjust the pH to ~1.5, and stir the aqueous solution at 70°C for 1 hour. Weigh 10.7358 g of NaOH and dissolve it in 250 mL of deionized water to prepare a precipitant. Add the alkaline solution dropwise to the acidic salt solution at a constant temperature while stirring, and gradually adjust the pH value of the solution from 1.5 to 10. After the addition is complete, age the resulting suspension at 70°C for 1 hour. Separate the suspension by centrifugation at room temperature, wash the solid thoroughly with deionized water until it is neutral, dry it at 110°C for 12 hours, and simmer for 1 hour at 2°C·min -1The heating rate was increased from room temperature to a calcination temperature of 450°C and calcined for 4 hours to obtain modified ferric oxide.

[0061] (2) Preparation of modified ferroferric oxide:

[0062] Fe 2+ The molar ratio of Fe to Mn is 1. 3+ The molar ratio of Fe to Mn is 0.4, 3+ The molar ratio of Fe to Ce is 1. The Fe(III) concentration is 0.1 mol / L. The specific steps are as follows:

[0063] According to the catalyst composition ratio, soluble FeCl3·6H2O, FeCl2·4H2O, MnSO4·H2O and Ce2(SO4)3·8H2O were mixed to form a salt solution, nitrogen was introduced for protection, 10 mol / L hydrochloric acid solution was added to adjust the pH value to 1, and the solution was heated to 70°C with a stirring speed of 400 rpm and a stirring time of 1 h.

[0064] Under constant temperature and nitrogen protection, add NaOH alkaline solution dropwise at a concentration of 1 mol / L at a rate of 1.5 drops / second while stirring. Gradually adjust the pH of the solution from 1 to a basic pH of 10, until the solution becomes a suspended precipitate. After the addition is complete, age at this constant temperature for 1 hour.

[0065] The precipitate was separated by centrifugation at room temperature, washed thoroughly with deionized water until neutral, dried at 110 °C for 12 h, and heated at 2 °C·min -1 The heating rate is increased from room temperature to the calcination temperature, the calcination temperature is 400°C, and the calcination time is 3 hours. Thus, the additive-modified ferrosoferric oxide is obtained.

[0066] (3) Preparation of iron-based catalysts:

[0067] 2g of modified ferric oxide and 6g of modified ferroferric oxide were ground and sieved into 80-100 mesh respectively. The two iron-based catalyst oxides, modified ferric oxide and modified ferroferric oxide, were ground and mixed for 1 hour. The mixed iron-based catalyst oxide powder was put into the sodium carbonate solution with a solid-liquid ratio of 0.3g / mL. After ultrasonication for 30 minutes, it was allowed to stand and soak for 12 hours. The concentration of the sodium carbonate deionized water solution was 1mol / L. The solid was separated by centrifugation at a speed of 3800 rpm. The solid was dried at 110℃ for 12 hours and at 2℃·min -1 The heating rate was increased from room temperature to calcination temperature, the calcination temperature was 400°C, and calcination was carried out for 3 hours to obtain an iron-based catalyst.

[0068] (4) Preparation of composite catalyst:

[0069] A commercial HZSM-5 catalyst with a silicon-to-aluminum ratio of 27 was purchased from the Nankai University Catalyst Factory. The catalyst was calcined at 400°C in air for 4 hours, pressed into pellets, and then ground and sieved with 40-60 mesh HZSM-5 molecular sieves. (The following examples all use the same commercial HZSM-5 and treatment method.)

[0070] 5g of iron-based catalyst and 5g of HZSM-5 molecular sieve catalyst powder were weighed, pressed into tablets, sieved, and mixed uniformly in a 1:1 mass ratio to obtain composite catalyst S-1. The iron-based catalyst and HZSM-5 molecular sieve catalyst had a particle size of 40-60 mesh.

[0071] (5) Catalyst evaluation:

[0072] 2g of composite catalyst S-1 was loaded into the thermostatic section of the reactor tube and heated at a rate of 2°C / min to a reduction temperature of 350°C. Reduction conditions were as follows: at atmospheric pressure and 400°C, H2 was introduced into the reactor at a flow rate of 75mL / min for 12 hours. This was followed by a 0.5-hour N2 purge under the same conditions, followed by a switch to a reducing gas (CO / N2 = 3 / 2) and a 12-hour constant temperature reduction. The reaction was then cooled to 320°C under nitrogen, and the reaction gases (N2 / H2 / CO2 = 4 / 24 / 72) were introduced into the fixed-bed reactor at a space velocity of 1000mL / g / min. The reaction was carried out at a pressure of 3MPa for 24 hours. The CO2 conversion and aromatics product selectivity are listed in Table 1.

[0073] Comparative Example 2

[0074] The difference from Example 1 is that the modifications of step (1) and step (2) are carried out in one step.

[0075] (1) Preparation of modified iron oxide mixture:

[0076] 30.3 g of Fe(NO3)3·9H2O, 1.208 g of Cu(NO3)2·3H2O, and soluble FeCl3·6H2O, FeCl2·4H2O, MnSO4·H2O, and Ce2(SO4)3·8H2O were weighed and dissolved in 150 mL of deionized water. 5 mol / L nitric acid was added to adjust the pH to 1.5, and the aqueous solution was stirred continuously at 70°C for 1 hour. 10.7358 g of NaOH was weighed and dissolved in 250 mL of deionized water to prepare a precipitant. Alkaline solution was added dropwise to the acidic salt solution at a constant temperature while stirring, gradually adjusting the pH of the solution from 1.5 to 10. After the addition was complete, the resulting suspension was aged at 70°C for 1 hour. The suspension was separated by centrifugation at room temperature, and the solid was thoroughly washed with deionized water until neutral, dried at 110°C for 12 hours, and sintered at 2°C·min-1 The heating rate was increased from room temperature to a calcination temperature of 400°C and calcined for 4 hours to obtain a modified iron oxide mixture.

[0077] (2) Preparation of iron-based catalysts:

[0078] The modified iron oxide mixture obtained in step 1 was ground and sieved, and the rest was the same as in Example 1.

[0079] (3) Preparation of composite catalyst:

[0080] The same method as in Example 1 was used to obtain a composite catalyst A-2.

[0081] (4) Catalyst evaluation:

[0082] Same as Example 1. The CO2 conversion rate and product selectivity are listed in Table 1.

[0083] Example 2

[0084] (1) Preparation of Cu-modified ferric oxide by colloidal precipitation method:

[0085] Weigh 30.3 g of Fe(NO3)3·9H2O and 1.208 g of Cu(NO3)2.3H2O and dissolve them in 150 mL of deionized water to prepare an aqueous solution. Add 5 mol / L nitric acid to adjust the pH to 2, and stir the aqueous solution at 70°C for 1 hour. Weigh 10.7358 g of NaOH and dissolve it in 250 mL of deionized water to prepare a precipitant. Add the alkaline solution dropwise to the acidic salt solution at a constant temperature, keep stirring, and gradually adjust the pH value of the solution from 2 to pH 10. After the addition is complete, age the resulting suspension at 70°C for 1 hour. Separate the suspension by centrifugation at room temperature, wash the solid thoroughly with deionized water until it is neutral, dry it at 110°C for 12 hours, and simmer for 1 hour at 2°C·min -1 The heating rate was increased from room temperature to a calcination temperature of 400°C and calcined for 4 hours to obtain modified ferric oxide.

[0086] (2) Preparation of modified ferroferric oxide:

[0087] The rare earth metal is La(NO3)3·6H2O, and other conditions are the same as in Example 1.

[0088] (3) Preparation of iron-based catalysts:

[0089] The impregnation liquid for the iron-based oxide precursor is potassium carbonate, and the rest is the same as in Example 1.

[0090] (4) Preparation of composite catalyst:

[0091] The same method as in Example 1 was used to obtain the composite catalyst S-2.

[0092] (5) Catalyst evaluation:

[0093] Same as Example 1. The CO2 conversion rate and product selectivity are listed in Table 1.

[0094] Example 3

[0095] (1) Preparation of Cu and Zn modified ferric oxide by colloidal precipitation method:

[0096] Weigh 30.3 g of Fe(NO3)3·9H2O, 1.208 g of Cu(NO3)2.3H2O and 0.1 g of Zn(NO3)2·6H2O and dissolve them in 150 mL of deionized water to prepare an aqueous solution. Add 5 mol / L nitric acid to adjust the pH to 1.5, and stir the aqueous solution at 80°C for 1 hour. Weigh 10.7358 g of NaOH and dissolve it in 250 mL of deionized water to prepare a precipitant. Add the alkaline solution dropwise to the acidic salt solution at a constant temperature, keep stirring, and gradually adjust the pH value of the solution from 1.5 to 10. After the addition is complete, age the resulting suspension at 80°C for 2 hours. Separate the suspension by centrifugation at room temperature, wash the solid thoroughly with deionized water until it is neutral, dry it at 110°C for 12 hours, and simmer for 2 hours at 2°C·min -1 The heating rate was increased from room temperature to a calcination temperature of 400°C and calcined for 4 hours to obtain modified ferric oxide.

[0097] (2) Preparation of modified ferroferric oxide:

[0098] The rare earth metal is Pr(NO3)3·6H2O, and other conditions are the same as in Example 1.

[0099] (3) Preparation of iron-based catalysts:

[0100] Same as Example 1.

[0101] (4) Preparation of composite catalyst:

[0102] The same method as in Example 1 was used to obtain the composite catalyst S-3.

[0103] (5) Catalyst evaluation:

[0104] Same as Example 1. The CO2 conversion rate and aromatic product selectivity are listed in Table 1.

[0105] Example 4

[0106] (1) Preparation of Cu and Zr modified ferric oxide by colloidal precipitation method:

[0107] 30.3 g of Fe(NO3)3·9H2O, 1.208 g of Cu(NO3)2.3H2O and 0.08 g of Zr(NO3)4·5H2O were weighed and dissolved in 150 mL of deionized water to prepare an aqueous solution. 5 mol / L nitric acid was added to adjust the pH to 2. The aqueous solution was stirred continuously at 70°C for 1 hour. 10.7358 g of NaOH was weighed and dissolved in 250 mL of deionized water to prepare a precipitant. Alkaline solution was added dropwise to the acidic salt solution at a constant temperature while stirring. The pH value of the solution was gradually adjusted from 2 to 10. After the addition was complete, the resulting suspension was aged at 70°C for 1 hour. The suspension was separated by centrifugation at room temperature, the solid was thoroughly washed with deionized water until neutral, dried at 110°C for 12 hours, and spun at 2°C·min -1 The heating rate was increased from room temperature to a calcination temperature of 500°C and calcined for 6 hours to obtain modified ferric oxide.

[0108] (2) Preparation of modified ferroferric oxide:

[0109] The rare earth metal is Sm(NO3)3·6H2O, and other conditions are the same as in Example 1.

[0110] (3) Preparation of iron-based catalysts:

[0111] Same as Example 1.

[0112] (4) Preparation of composite catalyst:

[0113] The same method as in Example 1 was used to obtain the composite catalyst S-4.

[0114] (5) Catalyst evaluation:

[0115] Same as Example 1. The CO2 conversion rate and aromatic product selectivity are listed in Table 1.

[0116] Example 5

[0117] (1) Preparation of Cu and Ni modified ferric oxide by colloidal precipitation method:

[0118] Weigh 30.3 g of Fe(NO3)3·9H2O, 1.208 g of Cu(NO3)2.3H2O and 0.06 g of Ni(NO3)2·6H2O and dissolve them in 150 mL of deionized water to prepare an aqueous solution. Add 5 mol / L nitric acid to adjust the pH to 2, and stir the aqueous solution at 80°C for 1 hour. Weigh 10.7358 g of NaOH and dissolve it in 250 mL of deionized water to prepare a precipitant. Add the alkaline solution dropwise to the acidic salt solution at a constant temperature, keep stirring, and gradually adjust the pH value of the solution from 2 to pH 10. After the addition is complete, age the resulting suspension at 80°C for 1 hour. Separate the suspension by centrifugation at room temperature, wash the solid thoroughly with deionized water until it is neutral, dry it at 110°C for 12 hours, and simmer for 1 hour at 2°C·min -1 The heating rate was increased from room temperature to a calcination temperature of 500°C and calcined for 6 hours to obtain modified ferric oxide.

[0119] (2) Preparation of modified ferroferric oxide:

[0120] The rare earth metal is Gd(NO3)3·6H2O, and other conditions are the same as in Example 1.

[0121] (3) Preparation of iron-based catalysts:

[0122] The impregnation liquid for the iron-based oxide precursor is potassium carbonate, and the rest is the same as in Example 1.

[0123] (4) Preparation of composite catalyst:

[0124] The same method as in Example 1 was used to obtain the composite catalyst S-5.

[0125] (5) Catalyst evaluation:

[0126] Same as Example 1. The CO2 conversion rate and aromatic product selectivity are listed in Table 1.

[0127] Example 6

[0128] (1) Preparation of Cu, Ni and Zr modified ferric oxide by colloidal precipitation method:

[0129] 30.3 g of Fe(NO3)3·9H2O, 1.208 g of Cu(NO3)2.3H2O, 0.05 g of Ni(NO3)2·6H2O, and 0.1 g of Zr(NO3)4·5H2O were weighed and dissolved in 150 mL of deionized water to prepare an aqueous solution. 5 mol / L nitric acid was added to adjust the pH to 2, and the aqueous solution was stirred continuously at 70°C for 1 hour. 10.7358 g of NaOH was weighed and dissolved in 250 mL of deionized water to prepare a precipitant. The alkaline solution was added dropwise to the acidic salt solution at a constant temperature while stirring, gradually adjusting the pH of the solution from 2 to 9. After the addition was complete, the resulting suspension was aged at 70°C for 1 hour. The suspension was separated by centrifugation at room temperature, and the solid was thoroughly washed with deionized water until neutral, dried at 110°C for 12 hours, and sintered at 2°C·min -1 The heating rate was increased from room temperature to a calcination temperature of 400°C and calcined for 6 hours to obtain modified ferric oxide.

[0130] (2) Preparation of modified ferroferric oxide:

[0131] The rare earth metal is Nd(NO3)3·6H2O, and other conditions are the same as in Example 1.

[0132] (3) Preparation of iron-based catalysts:

[0133] Same as Example 1.

[0134] (4) Preparation of composite catalyst:

[0135] The same method as in Example 1 was used to obtain the composite catalyst S-6.

[0136] (5) Catalyst evaluation:

[0137] Same as Example 1. The CO2 conversion rate and aromatic product selectivity are listed in Table 1.

[0138] Example 7

[0139] (1) Preparation of Cu, Zn and Ni modified ferric oxide by colloidal precipitation method:

[0140] Weigh 20.27 g FeCl3·6H2O, 0.762 g CuCl2·2H2O, 0.1 g ZnCl2 and 0.2 g NiCl2·6H2O and dissolve them in 150 mL deionized water to prepare an aqueous solution. Add 5 mol / L hydrochloric acid to adjust the pH value to 2, and stir the aqueous solution at 70°C for 1 hour. Weigh 10.7358 g NaOH and dissolve it in 250 mL deionized water to prepare a precipitant. Add the alkaline solution dropwise to the acidic saline solution at a constant temperature, keep stirring, and gradually adjust the pH value of the solution from 2 to pH 10. After the addition is complete, age the resulting suspension at 70°C for 1 hour. Separate the suspension by centrifugation at room temperature, wash the solid thoroughly with deionized water to neutrality, dry it at 110°C for 12 hours, and sieve it at 2°C·min -1 The heating rate was increased from room temperature to a calcination temperature of 400°C and calcined for 6 hours to obtain modified ferric oxide.

[0141] (2) Preparation of modified ferroferric oxide:

[0142] The rare earth metals are Ce2(SO4)3·8H2O and La(NO3)3·6H2O, the molar ratio of Ce to La is 1, and the other conditions are the same as in Example 1.

[0143] (3) Preparation of iron-based catalysts:

[0144] Same as Example 1.

[0145] (4) Preparation of composite catalyst:

[0146] The same method as in Example 1 was used to obtain the composite catalyst S-7.

[0147] (5) Catalyst evaluation:

[0148] Same as Example 1. The CO2 conversion rate and aromatic product selectivity are listed in Table 1.

[0149] Example 8:

[0150] (1) Preparation of Cu and Mn modified ferric oxide by colloidal precipitation method

[0151] Weigh 14.319 g Fe(OH)(CH3COO)2, 0.892 g Cu(CH3COO)2·H2O and 0.05 g Mn(CH3COO)2 and dissolve them in 150 mL deionized water to prepare an aqueous solution. Add 5 mol / L nitric acid to adjust the pH to 1, and stir the aqueous solution at 70°C for 1 hour. Weigh 10.7358 g NaOH and dissolve it in 250 mL deionized water to prepare a precipitant. Add the alkaline solution dropwise to the acidic salt solution at a constant temperature, keep stirring, and gradually adjust the pH value of the solution from 1 to pH 9. After the addition is complete, age the resulting suspension at 70°C for 1 hour. Separate the suspension by centrifugation at room temperature, wash the solid thoroughly with deionized water until it is neutral, dry it at 110°C for 12 hours, and simmer at 2°C·min -1 The heating rate was increased from room temperature to a calcination temperature of 400°C and calcined for 6 hours to obtain modified ferric oxide.

[0152] (2) Preparation of modified ferroferric oxide:

[0153] The rare earth metals are Sm(NO3)3·6H2O, Ce2(SO4)3·8H2O and La(NO3)3·6H2O, Ce:La:Sm=1:1:1 (molar ratio), and other conditions are the same as in Example 1.

[0154] (3) Preparation of iron-based catalysts:

[0155] The impregnation liquid for the iron-based oxide precursor is potassium carbonate, and the rest is the same as in Example 1.

[0156] (4) Preparation of composite catalyst:

[0157] The same method as in Example 1 was used to obtain the composite catalyst S-8.

[0158] (5) Catalyst evaluation:

[0159] Same as Example 1. The CO2 conversion rate and aromatic product selectivity are listed in Table 1.

[0160] Table 1

[0161]

[0162] From the results in Table 1, it can be seen that the composite catalyst obtained by the method of the present invention has a higher carbon dioxide conversion rate and aromatic product selectivity, or has a lower gas-phase by-product yield compared with the prior art; thus, it can be confirmed that the composite catalyst obtained by the preparation method of the present invention can improve the carbon dioxide conversion rate and aromatic product selectivity during the catalytic reaction, and also reduce the yield of gas-phase by-products.

[0163] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for preparing a composite catalyst for hydrogenating carbon dioxide to aromatics, characterized in that: The invention is a composite of an iron-based catalyst and HZSM-5 molecular sieve, wherein the main active components of the iron-based catalyst are Fe3O4 and iron carbide, and the preparation method comprises the following steps: (1) Preparation of modified ferric oxide: A soluble Fe(III) salt is mixed with an additive to form a saline solution, hydrochloric acid or nitric acid is added to adjust the pH to 0-2, heated and stirred, and then an alkaline solution is added dropwise to adjust the pH. The colloidal state of the solution is changed to a suspended precipitation state, aged, separated, washed, dried, and calcined to obtain modified ferric oxide; (2) Preparation of modified ferroferric oxide: A soluble Fe(II) salt, a soluble Fe(III) salt and an additive are mixed to form a brine solution, nitrogen is introduced for protection, hydrochloric acid or nitric acid solution is added to adjust the pH to 0-2, the solution is heated and stirred, and then an alkaline solution is added dropwise to adjust the pH. The solution turns into a suspended precipitate state, and the solution is aged, separated, washed, dried and calcined to obtain modified ferrosoferric oxide. (3) Preparation of iron-based catalysts: The modified ferric oxide and the modified ferrosoferric oxide are ground and mixed, then immersed in a solution of sodium carbonate or potassium carbonate, dried and calcined to obtain an iron-based catalyst; (4) Preparation of composite catalyst: The iron-based catalyst and the HZSM-5 molecular sieve are respectively pressed into tablets, sieved, and then evenly mixed in the form of particles to obtain a composite catalyst; Wherein, in step (1), the auxiliary agent includes two or more of Na, K, Mn, Cu, Zr, V, Zn, Ce, La, Ni, Cr, and Co; In step (2), the auxiliary agent includes two or more of Mn, Ce, La, Pr, Nd, Gd, and Sm, wherein the number of rare earth elements is two or more; In step (3), the mass ratio of the modified ferric oxide to the modified ferrosoferric oxide is 20:1-1:20; In step (4), the mass ratio of the iron-based catalyst to the HZSM-5 molecular sieve is 1:10 to 10:

1.

2. The preparation method according to claim 1, characterized in that In step (1) or step (2), the soluble Fe(III) salt is one or more of Fe chloride, nitrate, and acetate.

3. The preparation method according to claim 1, characterized in that In step (1), the auxiliary agent is added in the form of a soluble salt, including one or more of chloride, nitrate, and acetate.

4. The preparation method according to claim 1, characterized in that In step (1), the content of the auxiliary agent, calculated as metal oxide, accounts for 0.01 to 35% of the total mass of the iron-based catalyst.

5. The preparation method according to claim 1, characterized in that In step (2), the auxiliary agent is added in the form of a soluble salt, including one or more of chloride, nitrate, and acetate.

6. The preparation method according to claim 1, characterized in that In step (2), when Mn is added, Fe 2+ The molar ratio of Fe to Mn is 0.5-2. 3+ The molar ratio of Fe to Mn is 0.1-0.5, 3+ The molar ratio of rare earth elements is 0.5-2.

7. The preparation method according to claim 1, characterized in that In step (1), the concentration of Fe(III) in the brine solution is 0.05 to 1 mol / L; the concentration of the hydrochloric acid or nitric acid is 4 to 12 mol / L.

8. The preparation method according to claim 1, characterized in that In step (1), an alkaline solution is added dropwise to adjust the pH to 9-11; and the aging time is 1-5 hours.

9. The preparation method according to claim 1, characterized in that In step (1) or step (2), the alkaline solution is one or more solutions of NaOH, KOH, Na2CO3, NaHCO3, K2CO3, KHCO3, Na2C2O4, K2C2O4, RCOONa, RCOOK, and ammonia water, wherein R is an organic functional group; and the concentration of the alkaline solution is 0.1 to 5 mol / L.

10. The preparation method according to claim 1, characterized in that In step (2), the concentration of Fe(III) in the brine solution is 0.05 to 1 mol / L; the concentration of the hydrochloric acid or nitric acid is 4 to 12 mol / L.

11. The preparation method according to claim 1, characterized in that In step (2), an alkaline solution is added dropwise to adjust the pH to 9-11; and the aging time is 1-5 hours.

12. The preparation method according to claim 1, characterized in that In step (3), the grinding is to 80-100 mesh.

13. The preparation method according to claim 1, characterized in that In step (3), the concentration of the sodium carbonate or potassium carbonate solution is 0.1-5 mol / L; the solid-to-liquid ratio of the ground mixture of modified ferric oxide and modified ferrosoferric oxide to the sodium carbonate or potassium carbonate solution is 0.1-1 g / mL.

14. The preparation method according to claim 1, characterized in that In step (4), the silicon-aluminum ratio of the HZSM-5 molecular sieve is 20-50; the particle size of the iron-based catalyst and the HZSM-5 molecular sieve is 20-60 mesh.

15. A method for preparing aromatic hydrocarbons by hydrogenating carbon dioxide, characterized in that: The method uses a mixed gas consisting of carbon dioxide and hydrogen as raw material gas, and directly converts the mixed gas into aromatic hydrocarbons under the catalytic action of the composite catalyst prepared by the preparation method according to any one of claims 1 to 14.

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