Preparation method and application of composite catalyst for preparing aromatic hydrocarbon through hydrogenation of carbon dioxide

Abstract

The invention discloses a preparation method and application of a composite catalyst for preparing aromatic hydrocarbon through hydrogenation of carbon dioxide, the composite catalyst is formed by compounding 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 steps of preparation of modified ferric oxide, preparation of modified ferroferric oxide, preparation of the iron-based catalyst and the like. The preparation method provided by the invention improves the adsorption activation capability of carbon dioxide on the composite catalyst and the anti-poisoning stability of the composite catalyst, and also improves the aromatic hydrocarbon selectivity of the product.

Description

Technical Field

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

[0002] The capture and utilization of CO2 can consume greenhouse gases. CO2 is widely present in nature, 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, especially benzene, toluene, xylene and durene, are widely used in polymers, coatings, medicine, military industry and other fields. The market demand is huge and growing year by year. At present, the production of aromatic hydrocarbons is still dominated by petroleum catalytic reforming, and my country's resource structure of "rich in coal, poor in oil, and little gas" has led to my country's aromatic hydrocarbon sources being heavily dependent on the import of crude oil or naphtha. Using coal as raw material to produce aromatic hydrocarbons is not only more in line with my country's national conditions, but also can alleviate my country's dependence on imported petroleum resources. At present, the process of coal-to-syngas (CO and H2 mixed gas) has become mature, and the technology of preparing aromatic hydrocarbons using synthesis gas as raw material has also been widely studied. On this basis, as a more economical and clean non-petroleum route to produce aromatic hydrocarbons, the technology of carbon dioxide to aromatic hydrocarbons has begun to attract the attention of researchers.

[0004] CO2 direct production of aromatics includes the route of producing aromatics through oxygen-containing intermediates (methanol route) and the route of producing aromatics through Fischer-Tropsch synthesis intermediates (CO2-FT route). The methanol route is that CO2 is first hydrogenated to generate methanol intermediates, and the intermediates are then used to produce aromatics through methanol to aromatics technology. Although the aromatics prepared by this route have high selectivity among hydrocarbons, their conversion rate is generally less than 20%, and are accompanied by the generation of a large amount of by-product CO, so the time-space yield of this route is low. The route of producing aromatics through Fischer-Tropsch synthesis intermediates is that CO2 is subjected to the reverse water gas shift reaction to produce CO, CO is hydrogenated to produce Fischer-Tropsch synthesis reaction (CO-FT) to produce light olefin intermediates, and light olefins are then aromatized to produce aromatics, so this route is also called CO2-FT direct production of aromatics. This route has the characteristics of high CO2 conversion rate and high time-space yield of aromatics, and has more advantages in the direction of realizing industrial production. However, its product distribution is complex, and there are more aliphatic hydrocarbons in the liquid phase product, which will result in higher 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 the 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, and the soluble iron salt used is a mixture of divalent and trivalent iron salts. When the pH value is 2 to 3, both the iron salt and the auxiliary agent have precipitated, that is, the iron salt and the auxiliary agent described in this technology cannot be completely dissolved in the aqueous solution but are evenly mixed, and the precipitate formed is a precipitate mixture.

[0006] Patent CN108160104A discloses a catalyst for preparing aromatic hydrocarbons by one-step hydrogenation of carbon dioxide, and its preparation method and application. The active component of the iron-based metal oxide catalyst used in this technology is Fe3O4, and the additive appears in the catalyst in the form of an oxide. In addition, the pH value of the iron salt and additive salt solution used in this technology is not clear. The aqueous solution is prepared with one or more of hydrochloride, nitrate, bromide, acetate, oxalate and ammonium salt as raw materials. Most of the metal elements cannot be dissolved with the help of ultrasound, and precipitation will occur. That is, the iron salt and additive of this technology cannot be completely dissolved in the aqueous solution and are evenly mixed, and the precipitate formed is a precipitate mixture.

[0007] Patent CN111229303A discloses a composite catalyst for directly producing high-value aromatic hydrocarbons from carbon dioxide, as well as a 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 between 2 and 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 result in the additives, including copper salts, not being precipitated in the aqueous solution and being discarded with the mother liquor. This technology uses

[0008] Patent CN114369002A discloses a method for synthesizing linear α-olefins from synthesis gas. The additives of the technology are K and Mn salts. The surface of the main iron components Fe3O4 and Fe2O3 of the iron-based catalyst is modified by an equal volume impregnation method. The Fe-Cat containing the additives is K-Mn-Fe2O3. The additives are only anchored on the surface of the main iron components Fe3O4 and Fe2O3. The original material structure of the additives is still maintained at the anchoring position or a small amount of new substances are formed. The original material structure of Fe3O4 and Fe2O3 is still maintained at the uncovered part of the additive and inside the body of the iron-based catalyst, that is, there is no change in the material structure.

[0009] In the catalytic reaction of carbon dioxide to aromatics, carbon dioxide is relatively stable, not easy to be catalytically activated, and the conversion rate is low. In addition, the iron-based catalyst for carbon dioxide to aromatics is easily poisoned by impurities such as sulfur and has low stability. These problems have restricted the industrial application of carbon dioxide to aromatics technology. Summary of the invention

[0010] In view of the current technical deficiencies in the production of aromatics from carbon dioxide, the present invention proposes a method for preparing a catalyst for the hydrogenation of carbon dioxide to produce aromatics. First, rare earth metals are added to increase oxygen vacancies and improve the activation performance of carbon dioxide; secondly, according to the presence of iron elements and auxiliary elements in aqueous solution under different acidic conditions, auxiliary elements are prepared to be highly dispersed in the iron phase in a single atomic state, thereby forming a large amount of iron metal alloys in the composite catalyst. The formation of the iron metal alloy greatly improves the electronic effect and structural effect of the metal auxiliary on the composite catalyst, improves the adsorption and activation ability of carbon dioxide on the composite catalyst and the anti-poisoning stability of the composite catalyst, and also improves the selectivity of the product aromatics, which has industrial application prospects.

[0011] To achieve the above object, the present invention provides a method for preparing a composite catalyst for hydrogenating carbon dioxide to aromatics, which is composited with an iron-based catalyst and a 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:

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

[0013] A soluble Fe(III) salt is mixed with an auxiliary agent 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 solution colloid state is changed to a suspended precipitation state, aged, separated, washed, dried, and roasted 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 roasted 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 mixed evenly 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 soluble in water, which 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 soluble in water, which 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 to the rare earth element is 0.5-2.

[0028] The preparation method of the composite catalyst of the present invention comprises the following steps: 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] The preparation method of the composite catalyst of the present invention comprises the following steps: in step (1), the heating temperature is 60-80°C; the stirring speed is 400-800 rpm; the stirring time is 0.5-3h, preferably 1h.

[0030] The preparation method of the composite catalyst of the present invention comprises the following steps: 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; and the aging time is 1-5 hours, preferably 1 hour.

[0031] 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 0.1-5 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 suction 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 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.

[0033] 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; 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] The preparation method of the composite catalyst of the present invention comprises the following steps: in step (2), the dropping speed of the alkaline solution is 0.5-1.5 drops / second, and the pH value is adjusted to 9-11 by dropping 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 suction filtration; the washing is carried out by washing with deionized water until it is fully 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 meshes is carried out for 1 hour.

[0039] In the method for preparing 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 0.1-5 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 condition is to stand the impregnation under ultrasound and then centrifuge to separate the solid; the drying temperature is 110°C and the 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.

[0041] The preparation method of the composite catalyst of the present invention comprises the following steps: 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 preparing aromatic hydrocarbons by hydrogenating carbon dioxide. 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 a composite catalyst.

[0043] The method for preparing aromatic hydrocarbons by hydrogenating carbon dioxide of the present invention comprises the following steps: introducing H2 into a reactor at 0.1-3.0 MPa and 300-500° C. to reduce the composite catalyst for 4-24 h, with a hydrogen space velocity of 100-5000 mL / (h·g cat ), then switch the reducing gas under the same conditions, first use 100~5000mL / (h·g cat ) purge with N2 at an air velocity of 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 is 250-450°C, the reaction pressure is 0.01-10.0 MPa, the raw gas space velocity is 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: iron carbide generated after the carbonization of modified ferroferric oxide and modified ferric sesquioxide, 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 additives 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 element and the auxiliary element in the aqueous solution exist in different states under different acidic conditions. By adding an acid solution to the mixed aqueous solution of the Fe salt and the auxiliary agent to adjust the pH value to 0-2, the Fe salt and the auxiliary agent salt can be completely dissolved and evenly dispersed in an ionic state under heating and stirring. After gradually adding alkaline solution, the auxiliary element is highly dispersed in the iron phase in a single atomic state, thereby forming a large amount of iron metal alloy in the composite catalyst. The formation of the iron metal alloy greatly improves the electronic effect and structural effect of the metal auxiliary agent on the composite catalyst, improves the adsorption and activation ability of carbon dioxide on the composite catalyst and the anti-poisoning stability of the composite catalyst, and also improves the selectivity of the product aromatics and reduces the yield of gas phase by-products.

[0048] The iron oxide phase with increased oxygen vacancy content and the modified ferric oxide phase are ground to make the two phases uniformly dispersed and chemically adhered. In the carbon dioxide hydrogenation reaction, carbon dioxide is activated at the iron oxide oxygen vacancy to generate a carbon monoxide intermediate, and then the carbon monoxide quickly grows the carbon chain at the active site of the iron carbide formed by the ferric oxide nearby to form hydrocarbons, and the hydrocarbons enter the molecular sieve pores to undergo aromatization reaction to form aromatic products. Due to the matched contact of the activities, the entire carbon dioxide reaction process forms a chemical reaction chain coupling effect, and further through the formation of aromatic products, the carbon dioxide conversion reaction is driven, and the carbon dioxide conversion rate and the selectivity of aromatic products are improved. The present invention has industrial application prospects. DETAILED DESCRIPTION

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

[0050] Comparative Example 1

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

[0052] Weigh 60.6g Fe(NO3)3·9H2O and 10.7372g 50wt% Mn(NO3)2 solution and dissolve them in 300ml deionized water to prepare the precursor solution; weigh 21.4716g NaOH and dissolve it in 500ml deionized water to prepare the precipitant. The precursor solution is stirred continuously at 70℃, and the alkaline solution is added. After the obtained suspension is aged at 70℃ for 1 hour, it is filtered and needs to be thoroughly washed several times to remove a large amount of residual sodium in preparation for the impregnation operation. Then, 12.56g 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 for 12 hours. Finally, it was dried in an oven at 110 °C overnight, roasted at 400 °C for 4 hours, ground, and sieved to 40-60 mesh Na-FeMnO x catalyst.

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

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

[0055] (3) Place 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 a composite catalyst A-1.

[0056] (4) Catalyst evaluation:

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

[0058] Example 1

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

[0060] Weigh 30.3g Fe(NO3)3·9H2O and 5.3686g 50wt% Mn(NO3)2 solution and dissolve them in 150ml deionized water to prepare an aqueous solution. Add 5mol / L nitric acid to adjust the pH value to ~1.5, and stir the aqueous solution at 70℃ for 1h. Weigh 10.7358g NaOH and dissolve it in 250ml deionized water to prepare a precipitant. Add alkaline solution dropwise at a constant temperature to the acidic saline solution, 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 70℃ for 1 hour. Separate the suspension by centrifugation at room temperature, wash the solid thoroughly with deionized water to neutrality, dry it at 110℃ for 12h, and dry it at 2℃·min -1 The 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, the concentration of the alkaline solution is 1 mol / L, the dropping speed is 1.5 drops / second, and stirring is maintained. Gradually adjust the pH value of the solution from 1 to an alkaline pH value of 10, and the solution becomes a suspended precipitation state. After the addition is completed, age at a constant temperature for 1 hour.

[0065] The precipitate was separated by centrifugation at room temperature, washed 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] Grind and sieve 2g of modified ferric oxide and 6g of modified ferrosoferric oxide into 80-100 meshes respectively. Grind and mix the two iron-based catalyst oxides, modified ferric oxide and modified ferrosoferric oxide, for 1 hour. Put the mixed iron-based catalyst oxide powder into sodium carbonate solution with a solid-liquid ratio of 0.3g / ml. Ultrasonicate for 30 minutes and let it stand for 12 hours. The concentration of sodium carbonate deionized water solution is 1mol / L. Centrifuge to separate the solid at a speed of 3800 rpm. Dry the solid at 110°C for 12 hours and at 2°C·min -1 The heating rate was increased from room temperature to calcination temperature, the calcination temperature was 400°C, and the 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-aluminum ratio of 27 was purchased from the catalyst factory of Nankai University, calcined at 400°C in air for 4 hours, pressed into tablets, ground and sieved into 40-60 mesh HZSM-5 molecular sieves. (The following examples all use the same commercial HZSM-5 and treatment method).

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

[0071] (5) Catalyst evaluation:

[0072] 2g of composite catalyst S-1 was loaded into the constant temperature section of the reaction tube, and nitrogen was introduced to increase the temperature, and the temperature was increased to 350°C at a rate of 2°C / min. The reduction conditions were: at normal pressure and 400°C, H2 was introduced into the reactor for reduction for 12h, with a flow rate of 75ml / min, and then N2 was purged for 0.5h under the same conditions, and then the reduction gas (CO / N2=3 / 2) was switched to constant temperature reduction for 12h. The reaction conditions were: cooling to a reaction temperature of 320°C in nitrogen, and the reaction gas (N2 / H2 / CO2=4 / 24 / 72) was fed into the fixed bed reactor at an air velocity of 1000ml / g / min, and the reaction was carried out at a reaction pressure of 3MPa for 24h. The CO2 conversion rate and aromatic product selectivity are listed in Table 1.

[0073] Comparative Example 2

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

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

[0076] Weigh 30.3g Fe(NO3)3·9H2O, 1.208g Cu(NO3)2.3H2O, soluble FeCl3·6H2O, FeCl2·4H2O, MnSO4·H2O and Ce2(SO4)3·8H2O and dissolve them in 150ml deionized water to prepare an aqueous solution. Add 5mol / L nitric acid to adjust the pH value to 1.5, and stir the aqueous solution at 70℃ for 1h. Weigh 10.7358g NaOH and dissolve it in 250ml deionized water to prepare a precipitant. Add alkaline solution dropwise at a constant temperature to the acidic saline solution, 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 70℃ for 1 hour. Separate the suspension by centrifugation at room temperature, wash the solid thoroughly with deionized water to neutrality, dry at 110℃ for 12h, and dry at 2℃·min -1The 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 is ground and sieved, and the rest is 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. CO2 conversion 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 30.3g Fe(NO3)3·9H2O and 1.208g Cu(NO3)2.3H2O and dissolve them in 150ml deionized water to prepare an aqueous solution. Add 5mol / L nitric acid to adjust the pH value to 2. Stir the aqueous solution at 70℃ for 1h. Weigh 10.7358g NaOH and dissolve it in 250ml deionized water to prepare a precipitant. Add alkaline solution dropwise at a constant temperature to the acidic saline solution, keep stirring, and gradually adjust the pH value of the solution from 2 to 10. After the addition is complete, age the resulting suspension at 70℃ for 1 hour. Separate the suspension by centrifugation at room temperature, wash the solid thoroughly with deionized water to neutrality, dry it at 110℃ for 12h, and dry it at 2℃·min -1 The heating rate was increased from room temperature to a calcination temperature of 400°C, and the calcination was performed 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 those 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. CO2 conversion 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 30.3g Fe(NO3)3·9H2O, 1.208g Cu(NO3)2.3H2O and 0.1g Zn(NO3)2·6H2O and dissolve them in 150ml deionized water to prepare an aqueous solution. Add 5mol / L nitric acid to adjust the pH value to 1.5. Stir the aqueous solution at 80℃ for 1h. Weigh 10.7358g NaOH and dissolve it in 250ml deionized water to prepare a precipitant. Add alkaline solution dropwise at a constant temperature to the acidic saline solution, 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℃ 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℃ for 12h, and dry it at 2℃·min -1 The heating rate was increased from room temperature to a calcination temperature of 400°C, and the calcination was performed 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 those 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] Weigh 30.3g Fe(NO3)3·9H2O, 1.208g Cu(NO3)2.3H2O and 0.08g Zr(NO3)4·5H2O and dissolve them in 150ml deionized water to prepare an aqueous solution. Add 5mol / L nitric acid to adjust the pH value to 2. Stir the aqueous solution at 70℃ for 1h. Weigh 10.7358g NaOH and dissolve it in 250ml deionized water to prepare a precipitant. Add alkaline solution dropwise at a constant temperature to the acidic saline solution, keep stirring, and gradually adjust the pH value of the solution from 2 to 10. After the addition is complete, age the resulting suspension at 70℃ for 1 hour. Separate the suspension by centrifugation at room temperature, wash the solid thoroughly with deionized water to neutrality, dry it at 110℃ for 12h, and dry it at 2℃·min -1 The heating rate was increased from room temperature to a calcination temperature of 500°C, and the calcination was performed 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 those 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 30.3g Fe(NO3)3·9H2O, 1.208g Cu(NO3)2.3H2O and 0.06g Ni(NO3)2·6H2O and dissolve them in 150ml deionized water to prepare an aqueous solution. Add 5mol / L nitric acid to adjust the pH value to 2. Stir the aqueous solution at 80℃ for 1h. Weigh 10.7358g NaOH and dissolve it in 250ml deionized water to prepare a precipitant. Add alkaline solution dropwise at a constant temperature to the acidic saline solution, keep stirring, and gradually adjust the pH value of the solution from 2 to 10. After the addition is complete, age the resulting suspension at 80℃ for 1 hour. Separate the suspension by centrifugation at room temperature, wash the solid thoroughly with deionized water to neutrality, dry it at 110℃ for 12h, and dry it at 2℃·min -1 The heating rate was increased from room temperature to a calcination temperature of 500°C, and the calcination was performed 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 those 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] Weigh 30.3g Fe(NO3)3·9H2O, 1.208g Cu(NO3)2.3H2O, 0.05g Ni(NO3)2·6H2O and 0.1g Zr(NO3)4·5H2O and dissolve them in 150ml deionized water to prepare an aqueous solution. Add 5mol / L nitric acid to adjust the pH value to 2. Stir the aqueous solution at 70℃ for 1h. Weigh 10.7358g NaOH and dissolve it in 250ml 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 9. After the addition is complete, age the resulting suspension at 70℃ 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℃ for 12h, and dry it at 2℃·min -1 The heating rate was increased from room temperature to a calcination temperature of 400°C, and the calcination was carried out 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 those 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 20.27g FeCl3·6H2O, 0.762g CuCl2·2H2O, 0.1g ZnCl2 and 0.2g NiCl2·6H2O and dissolve them in 150ml deionized water to prepare an aqueous solution. Add 5mol / L hydrochloric acid to adjust the pH value to 2, and stir the aqueous solution continuously at 70℃ for 1h. Weigh 10.7358g NaOH and dissolve it in 250ml 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 10. After the addition is complete, age the resulting suspension at 70℃ for 1 hour. Separate the suspension by centrifugation at room temperature, wash the solid thoroughly with deionized water to neutrality, dry it at 110℃ for 12h, and dry it at 2℃·min -1 The heating rate was increased from room temperature to a calcination temperature of 400°C, and the calcination was carried out 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] Embodiment 8:

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

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

[0161] 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.

[0162] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope 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 composited with an iron-based catalyst and a 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 auxiliary agent 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 solution colloid state is changed to a suspended precipitation state, aged, separated, washed, dried, and roasted to obtain modified ferric oxide; (2) Preparation of modified ferroferric oxide: 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 roasted 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 mixed evenly 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.

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, Fe nitrate and Fe 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 to the rare earth element 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 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.

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 0.05-1 mol / L; the concentration of the hydrochloric acid or nitric acid is 4-12 mol / L; and the pH value is 0-2.

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 mass ratio of the modified ferric oxide to the modified ferrosoferric oxide is 20:1-1:

20.

14. 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.

15. The preparation method according to claim 1, characterized in that: In step (4), the mass ratio of the iron-based catalyst to the HZSM-5 molecular sieve is 1:10 to 10:1; 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.

16. A method for preparing aromatics 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 15.

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