Iron-based catalyst for catalyzing CO2 hydrogenation to prepare low-carbon olefin and preparation method of iron-based catalyst

Abstract

The invention relates to an iron-based catalyst for catalyzing CO2 hydrogenation to prepare low-carbon olefin and a preparation method thereof, and the preparation method comprises the following steps: preparing a zirconium oxide carrier, grinding ZrOCl2. 8H2O, calcining in a muffle furnace to obtain ZrO2, and grinding to obtain the zirconium oxide carrier; the preparation method comprises the following steps: respectively dissolving a Fe source, a Co source and a K source in water, adding the zirconia carrier, stirring and evaporating to obtain a suspension, drying the suspension, and calcining to obtain a FeCoK / ZrO2 catalyst; wherein in the FeCoK / ZrO2 catalyst, the loading capacity of Fe-Co is 12.2 wt%, the molar ratio of Co / (Fe + Co) is 0.15 to 2, and the molar ratio of K to Fe is 0.2 to 0.7. The FeCoK / ZrO2 catalyst prepared by the preparation method disclosed by the invention has a very high conversion rate on CO2 and selectivity on low-carbon olefins, optimizes the adsorption activation path on CO2, and has very good catalytic activity.

Description

Technical Field

[0001] The present invention relates to the technical field of catalyst preparation, and in particular to an iron-based catalyst for catalyzing CO2 hydrogenation to produce light olefins and a preparation method thereof. Background Art

[0002] Light olefins (C2 ＝ -C4 ＝ ) includes ethylene (C2H4), propylene (C3H6), and butene (C4H8), which are important raw materials for organic chemical products and are widely used in synthetic resins, synthetic rubber, pesticides, dyes and other fields. At present, the global scale production capacity of low-carbon olefins exceeds 1.5 million tons. The conventional technical routes for producing low-carbon olefins include steam cracking (SC) using naphtha as raw material, fluid catalytic cracking (FCC) and deep catalytic cracking (DCC) technology using zeolite, and methanol to olefins (MTO) technology using methanol as raw material. With the growth of the economy and the increase in demand for related consumer goods, the demand for low-carbon olefins has increased year by year. At present, the global petrochemical industry's demand for ethylene exceeds 155 million tons per year. Over the years, although my country's production of low-carbon olefins has increased year by year, it still cannot meet the needs of the rapid development of the domestic economy. At present, from the perspective of ethylene demand, my country's low-carbon olefin gap is very large. Driven by the market, many ethylene projects across the country are under construction, put into production or approved for project approval. It can be seen that ethylene production has entered a period of rapid development in my country. Under the situation that my country is highly dependent on crude oil imports and international oil prices are rising, the traditional method of producing low-carbon olefins from naphtha has been gradually restricted in China. In order to meet the needs of national economic development, it is inevitable to develop a low-cost, high-efficiency and energy-saving low-carbon olefin production route.

[0003] CO2 is an important carbon resource. Its application in the preparation of low-carbon olefins, an important raw material for the organic chemical industry, can not only alleviate the greenhouse effect, but also help solve the energy crisis. To this end, researchers have conducted research on combining CO2 with renewable H2 to prepare low-carbon olefins. Iron-based catalysts can achieve CO2 hydrogenation to produce low-carbon olefins, but their activity is not high. Loading iron-based catalysts on carriers such as ZrO2 and Al2O3 can disperse active metals and control the growth of carbon chains, thereby improving the activity of CO2 catalytic hydrogenation to produce low-carbon olefins to a certain extent. Summary of the invention

[0004] The main purpose of the present invention is to overcome the defects of the existing iron-based catalysts for catalyzing the hydrogenation of CO2 to produce light olefins, and to provide a new iron-based catalyst for catalyzing the hydrogenation of CO2 to produce light olefins and a preparation method thereof. The technical problem to be solved is to improve the CO2 conversion rate and at the same time promote the growth of the carbon chain, thereby being more suitable for practical use and having industrial utilization value.

[0005] The purpose of the present invention and the technical problem to be solved are achieved by adopting the following technical solutions.

[0006] Compared with the prior art, the present invention has obvious advantages and beneficial effects. From the above technical scheme, it can be seen that in order to achieve the above-mentioned invention purpose, the main technical contents of the present invention are as follows:

[0007] The present invention provides a method for preparing an iron-based catalyst for catalyzing CO2 hydrogenation to produce light olefins, characterized in that it comprises:

[0008] preparing a zirconia carrier, grinding ZrOCl2·8H2O, calcining it in a muffle furnace to obtain ZrO2, and grinding it to obtain a zirconia carrier;

[0009] Dissolving Fe source, Co source and K source in water respectively, adding to the zirconia carrier, stirring and evaporating to obtain a suspension, drying and calcining the suspension to obtain a FeCoK / ZrO2 catalyst;

[0010] Among them, in the FeCoK / ZrO2 catalyst, the loading amount of Fe-Co is 12.2wt%, the molar ratio of Co / (Fe+Co) is 0.15-2, and the molar ratio of K to Fe is 0.2-0.7.

[0011] In an optional embodiment, the Fe source is Fe(NO3)3·9H2O.

[0012] In an optional embodiment, the Co source is Co(NO3)3·6H2O.

[0013] In an optional embodiment, the K source is KNO3.

[0014] In an optional embodiment, the step of preparing the zirconium oxide carrier includes grinding ZrOCl2·8H2O by direct calcination method, heating it to 700℃-900℃ at a rate of 2℃ / min in a muffle furnace, calcining it for 3-4h to obtain ZrO2, grinding it, and obtaining the zirconium oxide carrier.

[0015] In an optional embodiment, the Fe source, Co source and K source are respectively dissolved in water and added to the zirconia carrier, and stirred and evaporated at 70°C-80°C to obtain a suspension, and the suspension is dried at 100°C-120°C and calcined to obtain a FeCoK / ZrO2 catalyst.

[0016] In an optional embodiment, the reaction temperature of the FeCoK / ZrO2 catalyst is 280°C-310°C.

[0017] In an optional embodiment, the selectivity of the FeCoK / ZrO2 catalyst is between 44% and 69%.

[0018] In an optional embodiment, the particle size of the FeCoK / ZrO2 catalyst is 50nm to 200nm.

[0019] On the other hand, an iron-based catalyst is provided, wherein the iron-based catalyst is prepared by any of the above-mentioned methods for preparing an iron-based catalyst for catalyzing the hydrogenation of CO2 to produce light olefins.

[0020] From the above, it can be seen that the present invention provides a method for preparing an iron-based catalyst containing an alkali metal additive K for CO2 hydrogenation to prepare low-carbon olefins, so as to investigate the influence of the K additive on the catalytic performance and reaction mechanism of CO2 hydrogenation, thereby optimizing the CO2 adsorption activation path, and improving the CO2 conversion rate and selectivity for low-carbon olefins. The present invention adopts different methods to prepare ZrO2 carriers, and then uses an impregnation method to obtain FeCoK / ZrO2, and investigates the influence of different carrier preparation methods and K additives on the CO2 catalytic hydrogenation reaction performance. The main conclusions are as follows: (1) ZrO2 is prepared by hydrothermal method, precipitation method, direct calcination method and sol-gel method, and is used as a carrier. FeCoK / ZrO2 catalyst is prepared by impregnation method, and the influence of carrier preparation method on CO2 catalytic hydrogenation reaction performance is studied. The results show that ZrO2 prepared by hydrothermal method, precipitation method and direct calcination method is mainly monoclinic, while ZrO2 prepared by sol-gel method contains monoclinic and tetragonal crystals. The activity test results show that the mixed crystalline ZrO2 prepared by the sol-gel method is not conducive to the adsorption of CO2 and has low reaction activity. (2) The effect of potassium (K) content on the catalytic activity of CO2 hydrogenation reaction of ZrO2-supported iron-cobalt catalysts (FeCo / ZrO2 and FeCoK / ZrO2 catalysts) prepared by direct calcination was investigated. The results show that the addition of K increases the electron cloud density of Fe species, enhances the adsorption of CO2 on the surface of Fe species, promotes the formation of iron carbide (χ-Fe5C2), and optimizes the CO2 adsorption activation pathway, thereby improving the CO2 conversion rate and light olefin selectivity, and increasing the space-time yield (STY) of light olefins from 0.013mmol·gcat to 1.08mmol·gcat. -1 ·h -1 Improved to 4.11

[0021] mmol·gcat -1 ·h -1 .

[0022] By means of the above technical solution, the present invention (name) has at least the following advantages:

[0023] The method provided in the embodiment of the present invention adopts a direct calcination method to prepare a catalyst carrier. The catalyst carrier prepared based on this method has good stability and good hydrogenation performance; and based on the added Fe source, Co source and K source, and limiting the Fe-Co loading in the FeCoK / ZrO2 catalyst to 12.2wt%, the molar ratio of Co / (Fe+Co) to 0.15-2, and the molar ratio of K to Fe to 0.2-0.7, the prepared FeCoK / ZrO2 catalyst has a very high conversion rate for CO2 and selectivity for light olefins, optimizes the adsorption and activation path of CO2, and has good catalytic activity.

[0024] In summary, the present invention provides a special iron-based catalyst for catalyzing the hydrogenation of CO2 to produce light olefins and a preparation method thereof. The catalyst carrier prepared based on the method has good stability and good hydrogenation performance; and based on the added Fe source, Co source and K source, and limiting the Fe-Co loading in the FeCoK / ZrO2 catalyst to 12.2wt%, the molar ratio of Co / (Fe+Co) to 0.15-2, and the molar ratio of K to Fe to 0.2-0.7, the prepared FeCoK / ZrO2 catalyst has a very high conversion rate for CO2 and selectivity for light olefins, optimizes the adsorption and activation path of CO2, and has good catalytic activity. It has the above-mentioned many advantages and practical values, and there is no similar design publicly published or used in the similar iron-based catalyst for catalyzing the hydrogenation of CO2 to produce light olefins and its preparation method, so it is indeed innovative. It has great improvements in both the iron-based catalyst for catalyzing the hydrogenation of CO2 to produce light olefins and its preparation method and in function, and has great progress in technology, and has produced easy-to-use and practical effects. It has improved many functions compared with the existing iron-based catalyst for catalyzing the hydrogenation of CO2 to produce light olefins and its preparation method, and is therefore more suitable for practical use and has wide industrial utilization value. It is truly a novel, progressive and practical new design.

[0025] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention in conjunction with the accompanying drawings.

[0026] The specific iron-based catalyst for catalyzing CO2 hydrogenation to produce light olefins and the preparation method thereof of the present invention are described in detail in the following examples and their accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the flow chart of the device for producing light olefins by hydrogenating CO2.

[0028] Figure 2This is the reaction performance diagram of ZrO2-supported FeCoK catalysts obtained by different preparation methods in CO2 hydrogenation to produce light olefins.

[0029] Figure 3 This is the reaction performance diagram of FeCoK catalysts with different K contents in CO2 hydrogenation to produce light olefins.

[0030] Figure 4 These are the catalytic stability test results of 0-FCK / ZrO2 and 0.3-FCK / ZrO2.

[0031] Figure 5 TEM images of 0-FCK / ZrO2 and (c, d) 0.3-FCK / ZrO2.

[0032] Figure 6 XRD spectra of different catalysts and XPS-Co2p spectra of the reduced catalyst.

[0033] Figure 7 H2-TPR of catalysts with different K contents.

[0034] Figure 8 CO2-TPD spectra of different K / Fe catalysts.

[0035] Fig. 9 H2-TPD spectra of different x-FCK / ZrO2. DETAILED DESCRIPTION

[0036] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the specific implementation method of the preparation method of the iron-based catalyst for catalyzing CO2 hydrogenation to prepare light olefins proposed in accordance with the present invention is described in detail below in combination with the accompanying drawings and preferred embodiments.

[0037] The method for preparing an iron-based catalyst for catalyzing CO2 hydrogenation to produce light olefins according to a preferred embodiment of the present invention mainly comprises the following steps:

[0038] The zirconia carrier is prepared by grinding ZrOCl2·8H2O, calcining it in a muffle furnace to obtain ZrO2, and grinding it to obtain the zirconia carrier.

[0039] The Fe source, Co source and K source are dissolved in water respectively, and then added into the zirconium oxide carrier, and then stirred and evaporated to obtain a suspension, and the suspension is dried and calcined to obtain a FeCoK / ZrO2 catalyst.

[0040] Among them, in the FeCoK / ZrO2 catalyst, the loading amount of Fe-Co is 12.2wt%, the molar ratio of Co / (Fe+Co) is 0.15-2, and the molar ratio of K to Fe is 0.2-0.7.

[0041] The method for preparing an iron-based catalyst for catalyzing CO2 hydrogenation to produce light olefins according to an embodiment of the present invention has at least the following beneficial effects:

[0042] The method provided in the embodiment of the present invention adopts a direct calcination method to prepare a catalyst carrier. The catalyst carrier prepared based on this method has good stability and good hydrogenation performance; and based on the added Fe source, Co source and K source, and limiting the Fe-Co loading in the FeCoK / ZrO2 catalyst to 12.2wt%, the molar ratio of Co / (Fe+Co) to 0.15-2, and the molar ratio of K to Fe to 0.2-0.7, the prepared FeCoK / ZrO2 catalyst has a very high conversion rate for CO2 and selectivity for light olefins, optimizes the adsorption and activation path of CO2, and has good catalytic activity.

[0043] The catalyst preparation method provided by the present invention will be further explained and illustrated by optional embodiments below.

[0044] In an optional embodiment, the Fe source is Fe(NO3)3·9H2O.

[0045] In an optional embodiment, the Co source is Co(NO3)3·6H2O.

[0046] In an optional embodiment, the K source is KNO3.

[0047] In an optional embodiment, the step of preparing the zirconium oxide carrier includes grinding ZrOCl2·8H2O by direct calcination method, heating it to 700℃-900℃ in a muffle furnace at a rate of 2℃ / min, calcining it for 3-4h to obtain ZrO2, grinding it, and obtaining the zirconium oxide carrier.

[0048] In an optional embodiment, the Fe source, Co source and K source are respectively dissolved in water and added to a zirconium oxide carrier, and stirred and evaporated at 70°C-80°C to obtain a suspension, and the suspension is dried at 100°C-120°C and calcined to obtain a FeCoK / ZrO2 catalyst.

[0049] In an optional embodiment, the reaction temperature of the FeCoK / ZrO2 catalyst is 280°C-310°C.

[0050] In an optional embodiment, the selectivity of the FeCoK / ZrO2 catalyst is between 44% and 69%.

[0051] Illustratively, the selectivity of the FeCoK / ZrO2 catalyst prepared in the embodiments of the present invention is between 44%, 44.4%, 45%, 46%, 47%, 47.2%, 48%, 49%, 50%, 51%, 52%, 55%, 56%, 60%, 61%, 65%, 65.5%, 66%, 67%, 68.6%, and 69%.

[0052] In an optional embodiment, the particle size of the FeCoK / ZrO2 catalyst is 50nm to 200nm.

[0053] Illustratively, the particle size of the FeCoK / ZrO2 catalyst prepared in an embodiment of the present invention can be 50nm, 53nm, 54nm, 55nm, 56nm, 59nm, 60nm, 65nm, 69nm, 70nm, 75nm, 80nm, 88nm, 90nm, 94nm, 96nm, 100nm, 107nm, 110nm, 117nm, 120nm, 127nm, 130nm, 147nm, 150nm, 157nm, 160nm, 166nm, 170nm, 175nm, 180nm, 187nm, 190nm, 197nm or 200nm, etc.

[0054] On the other hand, an iron-based catalyst is provided, which is prepared by any of the above-mentioned methods for preparing an iron-based catalyst for catalyzing the hydrogenation of CO2 to produce light olefins.

[0055] The iron-based catalyst for preparing low-carbon olefins by hydrogenation of CO2 of the present invention is prepared by the following steps:

[0056] After grinding ZrOCl2·8H2O, heat it to 800℃ in a muffle furnace at a rate of 2℃ / min, and calcine it for 4h to obtain ZrO2, which is ground and set aside. Fe(NO3)3·9H2O, Co(NO3)3·6H2O, and KNO3 are used as Fe source, Co source, and K source respectively, dissolved in water, and ZrO2 powder is added. Stir and evaporate at 70℃, and the obtained suspension is dried at 110℃, and then calcined at 500℃ for 4h to finally obtain FeCoK / ZrO2 catalyst. Among them, the loading amount of Fe-Co is 12.2wt%, and Co / (Fe+Co)=0.17 (molar ratio).

[0057] The present invention explores the effect of catalyst carriers obtained by different preparation methods on the mechanism of action of CO2 hydrogenation to light olefins. ZrO2 is prepared by hydrothermal method, precipitation method and sol-gel method respectively. For the convenience of expression, the catalyst carrier prepared by hydrothermal method is represented as ZrO2(H), the catalyst carrier prepared by precipitation method is represented as ZrO2(P), and the catalyst carrier prepared by sol-gel method is represented as ZrO2(S). Subsequently, FeCoK / ZrO2 catalyst is prepared by impregnation method, and the effect of impregnation method on the catalytic CO2 hydrogenation reaction activity is investigated. Similarly, the catalyst after FeCoK is loaded on ZrO2 prepared by hydrothermal method is represented as FCK / ZrO2(H), the catalyst after FeCoK is loaded on ZrO2 prepared by precipitation method is represented as FCK / ZrO2(P), the catalyst after FeCoK is loaded on ZrO2 prepared by sol-gel method is represented as FCK / ZrO2(S), and the catalyst after FeCoK is loaded on ZrO2 prepared by direct calcination method is represented as FCK / ZrO2(D).

[0058] In the embodiment of the present invention, catalysts with different K contents were prepared by changing the amount of K source added, and were named x-FCK / ZrO2, where x represents K / Fe (molar ratio).

[0059] The CO2 hydrogenation performance of FeCoK / ZrO2 was tested using a high pressure fixed bed reactor. Figure 1 The test method is as follows: first, 1g of FeCoK / ZrO2 catalyst is loaded into the reaction tube, and the catalyst is pre-reduced by introducing a mixed gas (V(H2) / V(N2)=4) at a flow rate of 50mL / min at 400℃ for 4h, and then the catalyst is heated at 1.5MPa, 1500mL·h -1 ·gcat -1 The reaction gas (H2 / CO2=4 / 1, volume ratio) was introduced under the conditions, and the product experimental part was analyzed by gas chromatography after the reaction stabilized.

[0060] Compared with the prior art, the present invention has the following characteristics:

[0061] 1. The present invention adopts different methods to prepare ZrO2, uses it as a carrier, and applies the impregnation method to prepare FeCoK / ZrO2 catalyst, and investigates its effect on the catalytic CO2 hydrogenation reaction activity, thereby optimizing the best preparation method of the carrier.

[0062] 2. FeCoK / ZrO2 catalyst was prepared using ZrO2 carrier obtained by the optimal preparation method as raw material, and the effect of K additive on the catalytic performance and reaction mechanism of CO2 hydrogenation was systematically studied.

[0063] 3. Adding K additive to iron-based catalysts can increase the orbital electron cloud density of Fe species, enhance the adsorption of CO2 on the surface of Fe species, promote the formation of iron carbide (χ-Fe5C2), and optimize the CO2 adsorption activation path, thereby improving the CO2 conversion rate and low-carbon olefin selectivity.

[0064] The invention can obtain an iron-based catalyst containing an alkali metal additive K and used for preparing light olefins by hydrogenating CO2.

[0065] The present invention is further explained below through specific implementation cases. The described embodiments are part of the present invention, and the protection scope of the present invention is not limited to the described contents.

[0066] Example 1

[0067] This example uses different methods to prepare the carrier ZrO2, and studies the effect of different carrier preparation methods on the performance of ZrO2-supported iron-based catalysts. The CO2 hydrogenation performance of different catalysts was tested at 260-350°C. The test results are shown in Figure 2. Figure 2 As shown. With the increase of reaction temperature, the CO2 conversion rate of all catalysts gradually increased, while the selectivity of light olefins first increased and then decreased. By changing the preparation method of the carrier, it was found that FCK / ZrO2(H) (catalyst after FeCoK was loaded on ZrO2 prepared by hydrothermal method), FCK / ZrO2(P) (catalyst after FeCoK was loaded on ZrO2 prepared by precipitation method), FCK / ZrO2(D) (catalyst after FeCoK was loaded on ZrO2 prepared by direct calcination method) showed similar CO2 conversion rate and light olefin selectivity at each temperature, while FCK / ZrO2(S) (catalyst after FeCoK was loaded on ZrO2 prepared by sol-gel method) had significantly lower CO2 conversion rate and light olefin selectivity than the other three catalysts. In addition, FCK / ZrO2(H), FCK / ZrO2(P), and FCK / ZrO2(D) reached the highest light olefin selectivity at 290°C, while FCK / ZrO2(S) reached the highest light olefin selectivity at 320°C. By Figure 2 It can be seen that ZrO2 prepared by hydrothermal method, precipitation method and direct calcination method showed similar CO2 hydrogenation performance after loading FeCoK. In view of the simpler preparation method of direct calcination method, direct calcination method was used to prepare ZrO2 as catalyst carrier.

[0068] Example 2

[0069] This example studies the effect of K in iron-based catalysts and tests the reaction performance of catalysts with different K contents. Figure 3 .Depend on Figure 3From Figures 3a and 3b, it can be seen that with the increase of reaction temperature, the CO2 conversion rate of all catalysts gradually increases, while the yield of light olefins first increases and then decreases, and reaches the maximum at 300°C. By changing the K content, it is found that the CO2 conversion rate and light olefin selectivity first increase and then decrease with the increase of K / Fe (molar ratio), and reach the maximum when the K / Fe molar ratio is 0.3. The results show that at 300°C, 0.3-FCK / ZrO2 has the highest CO2 conversion rate and light olefin selectivity, which are 44.4% and 68.6%, respectively. Figure 3 c It can be seen that the addition of K increases the space-time yield (STY) of light olefins from 0.013 mmol·gcat -1 ·h -1 Increased to 4.11mmol·gcat -1 ·h -1 . Figure 3 d is the mass spectrometry analysis result of the CO2 hydrogenation product catalyzed by 0.3-FCK / ZrO2. It can be seen from the figure that the product contains substances such as olefins, alkanes, CO and CO2. The results of mass spectrometry further qualitatively verify the reaction products.

[0070] Example 3

[0071] This example studies the catalytic stability of 0-FCK / ZrO2 (K / Fe molar ratio 0, i.e. K content 0) and 0.3-FCK / ZrO2 (K / Fe molar ratio 0.3, i.e. K content 0.3). The test results are shown in Figure 4 .Depend on Figure 4 It can be seen that when the reaction was carried out for 85 hours, the CO2 conversion rate of 0-FCK / ZrO2 dropped from 40.8% to 35.6%, and the selectivity of light olefins was still less than 0.1%. The reaction performance of 0.3-FCK / ZrO2 was almost unchanged, because alkali metal ions can promote the further conversion of the intermediate product CO, inhibit the formation of inert carbonaceous compounds on the catalyst surface, and thus improve the stability of the catalytic reaction.

[0072] Example 4

[0073] TEM was used to observe 0-FCK / ZrO2 and 0.3-FCK / ZrO2. The results are as follows: Figure 5 As shown. Figure 5 It can be seen that 0-FCK / ZrO2 and 0.3-FCK / ZrO2 are irregular particles with particle sizes ranging from 50 to 200 nm. Figure 6 a and 6b are XRD spectra of catalysts with different K contents after calcination and reduction. Figure 6 a It can be seen that the calcined catalyst has an undecomposed KNO3 diffraction peak at 2Theta = 23.5°, while Figure 6b was not found, indicating that KNO3 may decompose into K2O after hydrogen pre-reduction. In addition, the characteristic peak of Fe2O3 appeared at 33.2°. After hydrogen reduction, the Fe2O3 peak disappeared ( Figure 6 b), and an obvious characteristic peak of elemental Fe appeared at 44.7°, indicating that Fe2O3 was reduced to elemental Fe. The XPS-Co 2p spectrum of the catalyst after reduction is shown in Figure 6 c and 6d. As shown in the figure, the Co element in the catalyst after reduction mainly exists in the form of CoO. The catalysts with different K contents were characterized by H2-TPR. The results are shown in Figure 7 As shown. Five peaks appeared in the catalyst during the reduction process. Combined with XRD, it can be inferred that peaks I and II are the reduction peaks of KNO3, peaks III and IV correspond to the reduction of Fe2O3 to Fe3O4 and Fe3O4 to elemental Fe, respectively, and peak V may be caused by the loss of lattice oxygen at high temperature. At the same time, with the increase of K content, peaks III and IV gradually shift to high temperature, indicating that the reduction performance of x-FCK / ZrO2 gradually decreases with the increase of K content. This may be because the addition of K increases the strength of Fe-O, thereby increasing the reduction temperature of iron species.

[0074] Example 5

[0075] The chemical adsorption of CO2 on the catalyst surface is one of the key steps in the catalytic hydrogenation reaction. Therefore, CO2-TPD tests were carried out on catalysts with different K contents. The results are shown in Figure 8 . From the characterization results, it can be seen that two broad peaks appeared below 500°C. Among them, the low-temperature peak (100-200°C) corresponds to physically adsorbed CO2, and the medium-temperature peak (300-500°C) corresponds to chemically adsorbed CO2. From the peak area of ​​the medium-temperature peak, it can be seen that with the increase of K content, the adsorption amount of CO2 gradually increases, indicating that the addition of K can improve the chemical adsorption of CO2 by the catalyst. From the position of the medium-temperature peak, it can be found that with the increase of K content, the adsorption intensity of CO2 first increases and then weakens. When K / Fe=0.3, the adsorption intensity of CO2 is the highest.

[0076] Example 6

[0077] The H2-TPD test results of catalysts with different K contents are shown in Fig. 9 As can be seen from the figure, after K is added, the chemical adsorption of H2 by the catalyst at the reaction temperature is weakened. This weakens the excessive hydrogenation of the catalyst, inhibits the further hydrogenation of olefins to alkanes, and thus improves the selectivity of light olefins in the product.

[0078] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes by using the methods and technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing an iron-based catalyst for catalyzing CO2 hydrogenation to produce light olefins, characterized in that: include: preparing a zirconia carrier, grinding ZrOCl2·8H2O, calcining it in a muffle furnace to obtain ZrO2, and grinding it to obtain a zirconia carrier; Dissolving Fe source, Co source and K source in water respectively, adding to the zirconia carrier, stirring and evaporating to obtain a suspension, drying and calcining the suspension to obtain a FeCoK / ZrO2 catalyst; Among them, in the FeCoK / ZrO2 catalyst, the loading amount of Fe-Co is 12.2wt%, the molar ratio of Co / (Fe+Co) is 0.15-2, and the molar ratio of K to Fe is 0.2-0.

7.

2. The method for preparing an iron-based catalyst for catalyzing CO2 hydrogenation to produce light olefins according to claim 1, characterized in that: The Fe source is Fe(NO3)3·9H2O.

3. The method for preparing an iron-based catalyst for catalyzing CO2 hydrogenation to produce light olefins according to claim 1, characterized in that: The Co source is Co(NO3)3·6H2O.

4. The method for preparing an iron-based catalyst for catalyzing CO2 hydrogenation to produce light olefins according to claim 1, characterized in that: The K source is KNO3.

5. The method for preparing an iron-based catalyst for catalyzing CO2 hydrogenation to produce light olefins according to claim 1, characterized in that: The steps of preparing the zirconium oxide carrier include grinding ZrOCl2·8H2O by direct calcination, heating it to 700℃-900℃ at a rate of 2℃ / min in a muffle furnace, calcining it for 3-4h to obtain ZrO2, and grinding it to obtain the zirconium oxide carrier.

6. The method for preparing an iron-based catalyst for catalyzing CO2 hydrogenation to produce light olefins according to claim 1, characterized in that: The Fe source, Co source and K source are dissolved in water respectively and then added into the zirconia carrier, and then stirred and evaporated at 70°C-80°C to obtain a suspension, and then the suspension is dried at 100°C-120°C and calcined to obtain a FeCoK / ZrO2 catalyst.

7. The method for preparing an iron-based catalyst for catalyzing CO2 hydrogenation to produce light olefins according to claim 1, characterized in that: The reaction temperature of the FeCoK / ZrO2 catalyst is 280°C-310°C.

8. The method for preparing an iron-based catalyst for catalyzing CO2 hydrogenation to produce light olefins according to claim 1, characterized in that: The selectivity of the FeCoK / ZrO2 catalyst is between 44% and 69%.

9. The method for preparing an iron-based catalyst for catalyzing CO2 hydrogenation to produce light olefins according to claim 1, characterized in that: The particle size of the FeCoK / ZrO2 catalyst is 50nm to 200nm.

10. An iron-based catalyst, characterized in that The iron-based catalyst is prepared by the preparation method of the iron-based catalyst for catalyzing CO2 hydrogenation to produce light olefins as described in any one of claims 1-9.

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