Catalyst, preparation method thereof and method for preparing low-carbon olefin through carbon dioxide hydrogenation

Abstract

The invention relates to the technical field of catalysis, in particular to a catalyst, a preparation method of the catalyst and a method for preparing low-carbon olefin through carbon dioxide hydrogenation. The catalyst comprises an active component, alkali metal and an auxiliary agent, wherein the active component is an oxide of iron; the alkali metal is selected from one or more of Li, Na, K, Rb and Cs; the auxiliary agent is selected from one or more of Al, Zn, Mn, Cu, Co, Zr and Ce; in the catalyst, the molar ratio of the iron element to the additive element is 1: (0.1-1), and the mass percent of the alkali metal in the catalyst is 0.5-1.5%. The catalyst provided by the invention can have high CO2 conversion rate and high low-carbon olefin selectivity under the condition of high space velocity (such as 30000 mL / (gcat.h)); the stability is high, and no obvious inactivation phenomenon is shown after the reaction is performed for 200 hours.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of catalysis, in particular to a catalyst, a preparation method and application thereof, and a method for preparing low-carbon olefins by hydrogenation of carbon dioxide. BACKGROUND

[0002] The continuous increase in the concentration of CO2 in the atmosphere has caused a series of environmental problems, such as global warming, ocean acidification and glacier melting. The catalytic hydrogenation of CO2 to produce olefins is a way to realize the resource utilization of CO2, and is also one of the important ways to achieve "carbon peak" and "carbon neutral". Low-carbon olefins such as ethylene, propylene and butene are raw materials for the synthesis of high polymers such as fibers, rubbers and plastics, and their main sources are petroleum cracking products and gas products of Fischer-Tropsch synthesis. Ethylene is mainly used to synthesize polyethylene (PE), polyvinyl chloride (PVC), polystyrene (PS) and ABS plastic. Propylene can be used to prepare chemical products such as propylene oxide and acetone. Butene can be used to prepare butadiene, epoxy butane and high molecular polymers. China is relatively short of fossil energy and has a high degree of dependence on imports. The rapid economic development has further exacerbated the demand for low-carbon olefins. Therefore, the development of CO2 catalytic hydrogenation to produce low-carbon olefins not only realizes "waste to treasure", but also alleviates the dependence on foreign oil resources, which has very important practical significance.

[0003] CO2 is a thermodynamically stable gas. At present, there are two types of catalyst systems for the production of low-carbon olefins by hydrogenation of CO2, namely iron-based catalyst system and bifunctional catalyst system. The iron-based catalyst system takes CO as the key reaction intermediate, and first generates CO by the reverse water-gas shift reaction of CO2 and H2 on the catalyst, and then generates low-carbon olefins by the Fischer-Tropsch synthesis reaction of CO and H2. The key intermediate of the bifunctional catalyst is methanol, and CO2 is first hydrogenated to generate CH3OH, and then CH3OH is dehydrated on the molecular sieve to generate low-carbon olefins. Although the selectivity of low-carbon olefins in the reaction product of CO2 hydrogenation on the iron-based catalyst is relatively high, the single-component iron-based catalyst still cannot meet the requirements of industrial application. Therefore, it is generally necessary to introduce an additive to improve the reaction activity, low-carbon olefin selectivity and stability of the catalyst. According to research reports, alkali metal additives such as Na and K can promote the adsorption of CO2, inhibit the adsorption of H2, and effectively inhibit the secondary hydrogenation reaction of low-carbon olefins, thereby improving the selectivity of low-carbon olefins.

[0004] At present, some catalysts for the synthesis of low-carbon olefins by hydrogenation of CO2 have been applied for related patents. The following are several reported patents, which are described in detail.

[0005] Chinese patent CN 112169815 A discloses the application of an iron-based catalyst in the synthesis of low-carbon olefins from carbon dioxide and hydrogen. The iron-based catalyst reported in this patent can directly convert CO2 into low-carbon olefins. Under the condition of a space velocity of 2000 mL / (g cat.· h), the conversion rate of CO2 can reach more than 40%, the selectivity of methane is less than 10%, and the carbon-based selectivity of low-carbon olefins can reach 46.6%.

[0006] Chinese patent CN 112174764 A discloses the application of an iron-based catalyst in the synthesis of low-carbon olefins from carbon dioxide and hydrogen. The iron-based catalyst reported in this patent can directly convert CO2 into low-carbon olefins. Under the condition of a space velocity of 1200 h -1 , the conversion rate of CO2 can reach more than 42%, the selectivity of methane is less than 10%, and the carbon-based selectivity of low-carbon olefins can reach 44.6%.

[0007] Chinese patent CN 106031871 A discloses an iron-based catalyst for the synthesis of low-carbon olefins from CO2 and hydrogen, as well as its preparation and application. The single-pass conversion rate of the iron-based catalyst reported in this patent can reach more than 40%, the selectivity of methane in the hydrocarbon product is less than 15%, the selectivity of low-carbon olefins is higher than 40%, and the olefin / alkane ratio is 2-12.

[0008] Chinese patent CN 112169799 A discloses a method for the synthesis of low-carbon olefins from carbon dioxide and hydrogen using an iron-based catalyst. The CO2 conversion rate of the iron-based catalyst reported in this patent can reach more than 43.5% under the condition of a space velocity of 2000 mL / (g cat.· h), the selectivity of low-carbon olefins is as high as 46%, and the stability is only 100 h.

[0009] Chinese patent CN 108620089 A discloses a catalyst for the synthesis of low-carbon olefins from carbon dioxide and hydrogen, as well as its preparation method and application. The CO2 conversion rate of the iron-based catalyst reported in this patent can reach more than 44.7% under the condition of a space velocity of 4000 h -1 , the selectivity of low-carbon olefins is as high as 46.2%, and the stability is only 120 h. The catalysts reported in the above patents are all evaluated at low space velocities, and the stability needs to be further improved. SUMMARY

[0010] To overcome the problems existing in the prior art, the inventors of the present application have conducted extensive and in-depth research and provided a catalyst, a preparation method thereof, and a method for the synthesis of low-carbon olefins from carbon dioxide and hydrogen. For example, one of the objectives of the present application is to provide a catalyst for the synthesis of low-carbon olefins from carbon dioxide and hydrogen, which has a high space velocity (such as 30000 mL / (g cat.Under the condition of the above-mentioned catalyst, the carbon dioxide conversion rate and the low-carbon olefin selectivity can be high, and the stability is high, and no obvious deactivation phenomenon is shown after 200 hours of reaction. In addition, another object of the present application is to provide a preparation method corresponding to the above-mentioned catalyst, which has simple and reliable preparation technology and can accurately control the content of each component in the catalyst.

[0011] In order to achieve the above-mentioned object, the first aspect of the present application provides a catalyst, which comprises an active component, an alkali metal and an additive; wherein,

[0012] The active component is an oxide of iron; the alkali metal is selected from one or more of Li, Na, K, Rb and Cs; and the additive is selected from one or more of Al, Zn, Mn, Cu, Co, Zr and Ce;

[0013] In the catalyst, the molar ratio of iron element to the additive element is 1:0.1-1, and the mass percentage of the alkali metal in the catalyst is 0.5-1.5%.

[0014] In the present application, the oxide of iron includes Fe3O4, Fe2O3, FeO, etc. The oxide of iron is generated in the calcination process of preparing the catalyst, and is also generated in the reaction process when the catalyst is applied to the carbon dioxide hydrogenation to prepare low-carbon olefins.

[0015] In some embodiments of the present application, in the catalyst, the molar ratio of iron element to the additive element is 1:0.4-0.6, and the mass fraction of the alkali metal in the catalyst is 0.7-0.9%.

[0016] In some embodiments of the present application, the catalyst is a composite metal oxide containing Fe, Zn and K, wherein the molar ratio of Fe to Zn is (1-10):1, and the mass fraction of K in the catalyst is 0.5-1.5%. Preferably, the molar ratio of Fe to Zn is 1:0.4-0.6, and the mass fraction of K in the catalyst is 0.7-0.9%.

[0017] The second aspect of the present application provides a preparation method of the catalyst as described in the above-mentioned first aspect, which comprises the following steps:

[0018] S1, providing a solution I containing an active component source and an additive source; and providing a solution II containing an alkali metal source;

[0019] S2, mixing the solution I and the solution II to obtain a suspension;

[0020] S3, performing several times of centrifugal treatment and washing treatment on the suspension to obtain a precipitated intermediate product;

[0021] S4, sequentially performing drying treatment and calcination treatment on the precipitated intermediate product to obtain the catalyst.

[0022] In some embodiments of the present application, in step S1, the active component source is selected from at least one of ferric chloride, ferric nitrate, ferric sulfate and ferrous chloride.

[0023] In some embodiments of the present application, in step S1, the assistant source is selected from one or more of nitrate, chloride, sub-chloride, sulfate or sub-sulfate of Al, Zn, Mn, Cu, Co, Zr and Ce which are soluble in alcohol. Preferably, the assistant source is selected from one or more of zinc chloride, magnesium chloride, copper chloride, manganese chloride, cobalt chloride, zirconium chloride and cerium chloride.

[0024] In some embodiments of the present application, in step S1, the alkali metal source is selected from one or more of hydroxide or carbonate of Li, Na, K, Rb and Cs. Preferably, the alkali metal source is selected from one or more of potassium carbonate, potassium bicarbonate, potassium chloride, potassium sulfate and potassium nitrate.

[0025] In some embodiments of the present application, in step S1, the molar ratio of iron element and assistant element in the solution I is 1:0.1-1; preferably 1:0.4-0.6.

[0026] In some embodiments of the present application, in step S1, the total molar concentration of the assistant element in the solution I is 0.1-1.0 mol / L.

[0027] In some embodiments of the present application, in step S1, the solution I further comprises a solvent I, and the solvent I is selected from at least one of ethylene glycol, glycerol, ethanol and isopropanol.

[0028] According to the present application, the temperature for preparing the solution I is -20- -1℃. The active component source and the assistant source are ultrasonically dissolved in the solvent I, and the solution I is prepared by constant temperature stirring at -20- -1℃.

[0029] In some embodiments of the present application, in step S1, the molar concentration of the alkali metal in the solution II is 0.1-2.0 mol / L.

[0030] In some embodiments of the present application, in step S1, the solution II further comprises a solvent II, and the solvent II is water. The alkali metal source is added to deionized water, and the solution II is obtained by constant temperature (room temperature) stirring.

[0031] In some embodiments of the present application, in step S2, the conditions for performing the mixing include: the temperature is -20- -1℃; and / or, the pH value is 8-12.

[0032] In some embodiments of the present application, the solution II is added dropwise into the solution I to obtain the suspension in step S2; preferably, the dropwise adding speed is 1-10 mL / min.

[0033] In the present application, after the solution II is added dropwise into the solution I and the reaction is completed, 1-20 times volume of water can be added into the post-reaction product to obtain the suspension.

[0034] In some embodiments of the present application, the solution II is slowly added dropwise into the solution I under the condition of constant temperature stirring at-20 to-1℃, and after the dropwise adding is completed, the stirring is continued to age for 1-24 hours, the pH value is maintained at 8-12, and 1-20 times volume of water of the post-reaction product is added to obtain the suspension.

[0035] In the present application, in step S3, the centrifugal speed for centrifugal treatment is not strictly limited, and any speed can be used as long as the suspension can be separated. For example, the centrifugal treatment is performed at a speed of 5000 rpm.

[0036] In the present application, the suspension can be divided into several parts, and each part is subjected to centrifugal treatment and subsequent washing treatment.

[0037] In some embodiments of the present application, in step S3, the washing treatment is performed on the centrifugal precipitate obtained by centrifugal treatment using water.

[0038] In the present application, the mass percentage of alkali metal elements can be measured by an inductively coupled plasma optical emission spectrometer (ICP-OES).

[0039] In the present application, the mass percentage of alkali metal in the precipitated intermediate product can be controlled by the number of washing treatments.

[0040] In some embodiments of the present application, the suspension is divided into several parts and subjected to centrifugal treatment, and then several times of deionized water are added into the centrifugal product obtained after centrifugal treatment to perform washing treatment and centrifugal treatment, and the precipitate is separated; the residual amount of alkali metal in the precipitate is controlled by controlling the number of centrifugal treatments.

[0041] In some embodiments of the present application, in step S4, the drying treatment is performed under the conditions of a temperature of 40-80℃ and a time of 1-24 hours.

[0042] In the present application, the drying treatment can be vacuum drying under a vacuum degree of-0.1 MPa or less to obtain a post-drying product.

[0043] In some embodiments of the present application, the conditions for the calcination treatment in step S4 include a temperature of 300-600℃ and a time of 1-24 hours. The calcination treatment in the present application is performed in an air atmosphere.

[0044] In the present application, the heating rate during the calcination treatment is 1-5℃ / min.

[0045] In the present application, the dried product obtained after the drying treatment can be further subjected to a grinding treatment to facilitate the calcination treatment.

[0046] The third aspect of the present application provides a catalyst as described in the first aspect above or a catalyst obtained by the preparation method described in the second aspect above for use in the hydrogenation of carbon dioxide to produce low-carbon olefins.

[0047] In the present application, low-carbon olefins refer to olefins with a carbon atom number of 2-4, i.e., small-molecule olefins such as ethylene, propylene and butylene.

[0048] When the catalyst of the present application is used in the hydrogenation of carbon dioxide to produce low-carbon olefins, the electronic effect of the alkali metal can regulate the charge distribution on the surface of the catalyst, thereby affecting the product distribution.

[0049] The fourth aspect of the present application provides a method for the hydrogenation of carbon dioxide to produce low-carbon olefins, which comprises the steps of:

[0050] carrying out the hydrogenation reaction of carbon dioxide in the presence of hydrogen, carbon dioxide and a catalyst, wherein the catalyst is the catalyst described in the first aspect above or the catalyst obtained by the preparation method described in the second aspect above.

[0051] In the present application, low-carbon olefins refer to olefins with a carbon atom number of 2-4, i.e., small-molecule olefins such as ethylene, propylene and butylene.

[0052] In some embodiments of the present application, the molar ratio of hydrogen to carbon dioxide is 1-5:1.

[0053] In some embodiments of the present application, the conditions for the hydrogenation reaction include a reaction temperature of 250-400℃, a space velocity of 10000-50000 mL / (g cat. ·h) and a pressure of 0.1-5.0 MPa.

[0054] In some embodiments of the present application, the catalyst is subjected to an activation treatment before the hydrogenation reaction. The conditions for the activation treatment include:

[0055] The activation atmosphere is a mixture of CO and Ar; the volume ratio of Ar to CO in the mixture is 5-20:1; the space velocity of the mixture is 10000-50000 mL / (g cat. ·h);

[0056] The activation pressure is 0.1-1 MPa.

[0057] The activation temperature is 200-400℃; preferably, the temperature rising rate is 2-10℃ / min.

[0058] The activation time is 1-50 h.

[0059] Before the hydrogenation reaction, the catalyst is activated and reduced, aiming to reduce the iron oxide in the catalyst to iron carbide to form active centers. The iron carbide includes, but is not limited to, Fe5C2, Fe3C, Fe7C3, etc. After activation, no iron oxide is detected in the catalyst by XRD detection, which is inferred to be very little iron oxide and no crystal structure is formed.

[0060] According to the present application, the reaction process of carbon dioxide hydrogenation to low-carbon olefins can be analyzed online by gas chromatography to monitor the reaction. In the reaction product, there may be a small amount of liquid phase (aqueous phase and oil phase), and the content of hydrocarbons and oxygen-containing organic compounds in the aqueous phase product collected by a cold trap is very low (negligible), while the oil phase product can be analyzed by offline GC-MS. The carbon balance of all the obtained products and the raw gas is above 95%.

[0061] In some embodiments of the present application, the method for carbon dioxide hydrogenation to low-carbon olefins comprises the following steps:

[0062] 50-300 mg of the catalyst obtained by the preparation method of the second aspect is loaded into a fixed bed reactor, and the catalyst is activated and treated using CO / Ar mixed gas under the conditions of a temperature of 200-400℃ and a pressure of 0.1-1.0 MPa, the volume ratio of Ar to CO in the CO / Ar mixed gas is 5-20:1, the space velocity of the CO / Ar mixed gas is 10000-50000 mL / (g cat. ·h), and the activation time is 1-50 h;

[0063] After the activation is completed, the catalyst bed in the fixed bed reactor is purged with high-purity argon (99.999%) for 0-3 h, the temperature of the catalyst bed in the fixed bed reactor is adjusted to 250-400℃, then a mixed reaction gas with a molar ratio of H2 to CO2 of (1-5):1 is introduced into the fixed bed reactor, the reaction pressure is adjusted to 0.1-5.0 MPa, and the space velocity of the mixed reaction gas is 10000-50000 mL / (g cat. ·h).

[0064] Compared with the prior art, the present application comprises at least one of the following beneficial effects:

[0065] 1) The catalyst provided by the present application has high CO2 conversion rate and high low-carbon olefin selectivity under the condition of high space velocity (such as up to 30000 mL / (g cat. ·h), and high stability, and no obvious deactivation phenomenon is shown after 200 h of reaction;

[0066] 2) The preparation method of the catalyst provided by the present application, each raw material is cheap and easy to obtain, the production condition is easy to control, the preparation process is simple and reliable, the production cycle is short, the environment is not polluted, and batch production can be realized;

[0067] 3) When the catalyst provided by the present application is applied to the preparation of low-carbon olefins (olefins with carbon atom number between 2 and 4) from carbon dioxide and hydrogen, the service life of the catalyst under high space velocity is lower than that under low space velocity, but the catalyst provided by the present application does not show obvious deactivation trend after 200 h of high space velocity continuous reaction in the reaction process, so the catalyst provided by the present application has high stability and good industrialization prospect. BRIEF DESCRIPTION OF DRAWINGS

[0068] Figure 1 A performance change diagram of carbon dioxide conversion rate and low-carbon olefin selectivity of the catalyst 0.8% K-Fe10Zn5 of Example 1 of the present application operated for 200 h is shown;

[0069] Figure 2 An XRD diagram of the catalyst 0.8% K-Fe10Zn5 of Example 1 of the present application operated for 200 h is shown. DETAILED DESCRIPTION

[0070] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The endpoints of the ranges and any values are understood to be approximate values. The exact numerical values of the endpoints of the ranges and the separate points are not to be understood as being strictly limited to the exact numerical values recited. At the very least, each minimum numerical limitation should at least be construed in the context as permitting some slack between the minimum and maximum values to allow for experimentation and / or variation.

[0071] In the present application, unless otherwise specified, the terms “active component”, “active phase metal” and “metal active phase” are used interchangeably, and all refer to the metal component used as the active phase of the catalyst.

[0072] The present application is described in detail below through examples, but the protection scope of the present application is not limited to the following description.

[0073] In the following examples, the molar ratio of iron element and auxiliary element in the catalyst and the mass percentage of alkali metal in the catalyst can be set before the catalyst is prepared (which can be set in advance according to the water washing process), and the amount of raw materials is calculated according to the set content. It should be noted that compared with the catalyst designed before preparation, the numerical value of the composition of the actually prepared catalyst will have a small error around the designed value, but the overall deviation will not be too large.

[0074] In the following examples, the mass percentage of alkali metal in the catalyst is measured by inductively coupled plasma optical emission spectrometer (ICP-OES).

[0075] In the following examples, the product components of the carbon dioxide hydrogenation reaction for producing low-carbon olefins are collected and analyzed online by gas chromatography. A small amount of liquid phase (aqueous phase and oil phase) is collected by a cold trap. The content of hydrocarbons and oxygen-containing organic compounds in the aqueous phase product is extremely low (negligible), and the oil phase product can be analyzed by offline gas chromatography-mass spectrometry (GC-MS). The carbon balance of all the obtained products and raw gas is above 95%.

[0076] In the examples, the specific conditions are not specified, and the conventional conditions or the conditions recommended by the manufacturer are used. The raw materials, reagents or instruments used are not specified by the manufacturer, and are conventional products that can be obtained by market purchase or prepared according to the preparation method disclosed in the prior art.

[0077] Example 1

[0078] 1. The preparation method of the catalyst of the present embodiment comprises the following steps:

[0079] A 200 mL solution of 0.2 mol / L K2CO3 was prepared; 4.323 g of FeCl3·6H2O and 1.091 g of ZnCl2 were weighed and dissolved in 80 mL of ethylene glycol, and ultrasonic stirring was performed for 15 min to uniformly dissolve the raw materials; then, the mixed solution was transferred to a three-necked flask, and water bath was performed under magnetic stirring, and the temperature was maintained at -10 degrees Celsius; after maintaining for 30 min, the prepared 200 mL solution of 0.2 mol / L K2CO3 was added dropwise to the mixed solution at a rate of 1 mL / min, and after the dropwise addition was completed, the precipitate was allowed to stand for 2 h, then the reaction liquid was transferred from the three-necked flask to a beaker, 200 mL of deionized water was added to the three-necked flask and transferred to the beaker, and the suspension was obtained after standing for 1-2 h until the temperature returned to room temperature; then the suspension was divided into 6 50 mL centrifuge tubes for centrifugal separation, and the precipitate in the centrifuge tube was washed with 2500 mL of deionized water for 6 times to obtain the precipitated intermediate product; the precipitated intermediate product was placed in a vacuum oven at 60 degrees Celsius, the vacuum degree was -0.1 MPa, and drying was performed overnight; finally, the dried precipitated intermediate product was ground and placed in a muffle furnace for calcination, the atmosphere was air, the heating rate was 2 degrees Celsius / min, the temperature was raised to 500 degrees Celsius and maintained for 5 h, then the temperature was naturally lowered to below 100 degrees Celsius, and the catalyst product was obtained after grinding.

[0080] In the catalyst product, Fe exists in the form of an oxide, the molar ratio of Zn to Fe is 1:2, and the mass percentage of K is 0.8 wt%, denoted as 0.8%K-Fe10Zn5.

[0081] 2. Carbon dioxide hydrogenation to low-carbon olefin experiment

[0082] 0.1 g of the above-prepared catalyst 0.8%K-Fe10Zn5 was loaded into a fixed bed reactor. The catalyst 0.8%K-Fe10Zn5 was reduced in a CO / Ar mixed gas containing 10% CO at 350 degrees Celsius and 0.1 MPa for 6 h, the space velocity of the CO / Ar mixed gas was 30000 mL / (g cat. ·h), and the heating rate was 5 degrees Celsius / min.

[0083] After activation, high-purity argon (99.999%) was blown for 1 h, the temperature was lowered to 320 degrees Celsius, then the hydrogen and CO2 mixed gas (H2 / CO2 molar ratio was 3) was switched on, the pressure was 2.0 MPa, the temperature was 320 degrees Celsius, and the CO2 hydrogenation reaction was performed at a H2 / CO2 mixed gas space velocity of 30000 mL / (g cat. ·h).

[0084] The results are shown in Table 1.

[0085] Figure 1The performance change diagram of carbon dioxide conversion rate and low carbon olefin selectivity of catalyst 0.8%K-Fe10Zn5 running 200h is shown; Figure 2 The XRD diagram of catalyst 0.8%K-Fe10Zn5 after running 200h is shown. Figure 1 and Figure 2 It can be seen that the catalyst 0.8%K-Fe10Zn5 within the protection scope of the present application has high CO2 conversion rate and high low carbon olefin selectivity under high space velocity (30000mL / (g cat. ·h); and no obvious deactivation phenomenon is shown after reaction for 200h, and the stability is high.

[0086] Example 2

[0087] 1、The preparation method of the catalyst of the present example is basically the same as that of example 1, except that "1.091g ZnCl2" is changed to "2.182g ZnCl2".

[0088] In the catalyst product, Fe exists in the form of oxide, the molar ratio of Zn to Fe is 1:1, and the mass percentage of K is 0.8wt%, which is recorded as 0.8%K-Fe10Zn10.

[0089] 2、Carbon dioxide hydrogenation to low carbon olefin experiment

[0090] 0.1g of the above prepared catalyst 0.8%K-Fe10Zn10 is taken and packed in a fixed bed reactor. Other steps are the same as those of example 1.

[0091] The results are shown in table 1.

[0092] Example 3

[0093] 1、The preparation method of the catalyst of the present example is basically the same as that of example 1, except that "1.091g ZnCl2" is changed to "1.527g ZnCl2".

[0094] In the catalyst product, Fe exists in the form of oxide, the molar ratio of Zn to Fe is 0.7:1, and the mass percentage of K is 0.8wt%, which is recorded as 0.8%K-Fe10Zn7.

[0095] 2、Carbon dioxide hydrogenation to low carbon olefin experiment

[0096] 0.1g of the above prepared catalyst 0.8%K-Fe10Zn7 is taken and packed in a fixed bed reactor. Other steps are the same as those of example 1.

[0097] The results are shown in table 1.

[0098] Example 4

[0099] 1、The preparation method of the catalyst of this example is basically the same as that of Example 1, except that "1.091 g of ZnCl2" is changed to "0.727 g of ZnCl2".

[0100] In the catalyst product, Fe exists in the form of oxide, the molar ratio of Zn to Fe is 0.3:1, and the mass percentage of K is 0.8wt%, which is recorded as 0.8% K-Fe10Zn3.

[0101] 2, Carbon dioxide hydrogenation to low carbon olefin experiment

[0102] 0.1 g of the above-prepared catalyst 0.8% K-Fe10Zn3 was taken and packed in a fixed bed reactor. The other steps were the same as those of Example 1.

[0103] The results are shown in Table 1.

[0104] Example 5

[0105] 1、The preparation method of the catalyst of this example is basically the same as that of Example 1, except that "1.091 g of ZnCl2" is changed to "0.218 g of ZnCl2".

[0106] In the catalyst product, Fe exists in the form of oxide, the molar ratio of Zn to Fe is 0.1:1, and the mass percentage of K is 0.8wt%, which is recorded as 0.8% K-Fe10Zn1.

[0107] 2, Carbon dioxide hydrogenation to low carbon olefin experiment

[0108] 0.1 g of the above-prepared catalyst 0.8% K-Fe10Zn1 was taken and packed in a fixed bed reactor. The other steps were the same as those of Example 1.

[0109] The results are shown in Table 1.

[0110] Example 6

[0111] 1、The preparation method of the catalyst of this example is basically the same as that of Example 1, except that "1.091 g of ZnCl2" is changed to "1.075 g of CuCl2".

[0112] In the catalyst product, Fe exists in the form of oxide, the molar ratio of Cu to Fe is 0.5:1, and the mass percentage of K is 0.8wt%, which is recorded as 0.8% K-Fe10Cu5.

[0113] 2, Carbon dioxide hydrogenation to low carbon olefin experiment

[0114] 0.1 g of the above-prepared catalyst 0.8% K-Fe10Cu5 was loaded into a fixed bed reactor. The other steps were the same as in Example 1.

[0115] The results are shown in Table 1.

[0116] Example 7

[0117] 1. The preparation method of the catalyst of this example was basically the same as that of Example 1, except that "1.091 g of ZnCl2" was changed to "1.006 g of MnCl2".

[0118] In the catalyst product, Fe existed in the form of oxide, the molar ratio of Mn to Fe was 0.5:1, and the mass percentage of K was 0.8 wt%, which was denoted as 0.8% K-Fe10Mn5.

[0119] 2. Experiment of carbon dioxide hydrogenation to low-carbon olefins

[0120] 0.1 g of the above-prepared catalyst 0.8% K-Fe10Mn5 was loaded into a fixed bed reactor. The other steps were the same as in Example 1.

[0121] The results are shown in Table 1.

[0122] Example 8

[0123] 1. The preparation method of the catalyst of this example was basically the same as that of Example 1, except that "1.091 g of ZnCl2" was changed to "1.038 g of CoCl2".

[0124] In the catalyst product, Fe existed in the form of oxide, the molar ratio of Co to Fe was 0.5:1, and the mass percentage of K was 0.8 wt%, which was denoted as 0.8% K-Fe10Co5.

[0125] 2. Experiment of carbon dioxide hydrogenation to low-carbon olefins

[0126] 0.1 g of the above-prepared catalyst 0.8% K-Fe10Co5 was loaded into a fixed bed reactor. The other steps were the same as in Example 1.

[0127] The results are shown in Table 1.

[0128] Comparative Example 1

[0129] 1. The preparation method of the catalyst of this example was basically the same as that of Example 1, except that "4.323 g of FeCl3·6H2O and 1.091 g of ZnCl2" were changed to "4.323 g of FeCl3·6H2O".

[0130] The catalyst product contains Fe in the form of oxide, and the mass percentage of K is 0.8wt%, which is recorded as 0.8%K-Fe.

[0131] 2. Experiment of preparing low-carbon olefins from carbon dioxide and hydrogen

[0132] 0.1 g of the catalyst 0.8%K-Fe prepared above was taken and packed in a fixed bed reactor. Other steps were the same as those in Example 1.

[0133] The results are shown in Table 1.

[0134] Comparative Example 2

[0135] 1. The preparation method of the catalyst in this comparative example was basically the same as that in Example 1, except that "washing the precipitate in the centrifuge tube with 2500 mL of deionized water for 6 times" was changed to "washing the precipitate in the centrifuge tube with 10000 mL of deionized water for 24 times".

[0136] The catalyst product contains Fe in the form of oxide, and the molar ratio of Zn to Fe is 0.5:1, and the content of K reaches the lower limit of detection (less than 0.01%wt), which is recorded as Fe10Zn5.

[0137] 2. Experiment of preparing low-carbon olefins from carbon dioxide and hydrogen

[0138] 0.1 g of the catalyst Fe10Zn5 prepared above was taken and packed in a fixed bed reactor. Other steps were the same as those in Example 1.

[0139] The results are shown in Table 1.

[0140] Comparative Example 3

[0141] 1. The preparation method of the catalyst in this comparative example was basically the same as that in Example 1, except that "1.091 g of ZnCl2" was changed to "2.618 g of ZnCl2".

[0142] The catalyst product contains Fe in the form of oxide, and the molar ratio of Zn to Fe is 1.2:1, and the mass percentage of K is 0.8wt%, which is recorded as 0.8%K-Fe10Zn12.

[0143] 2. Experiment of preparing low-carbon olefins from carbon dioxide and hydrogen

[0144] 0.1 g of the catalyst 0.8%K-Fe10Zn12 prepared above was taken and packed in a fixed bed reactor. Other steps were the same as those in Example 1.

[0145] The results are shown in Table 1.

[0146] Comparative Example 4

[0147] 1. The preparation method of the catalyst of this comparative example is basically the same as that of Example 1, except that "1.091 g of ZnCl2" is changed to "0.109 g of ZnCl2".

[0148] In the catalyst product, Fe exists in the form of oxide, the molar ratio of Zn to Fe is 0.05:1, and the mass percentage of K is 0.8wt%, which is denoted as 0.8%K-Fe10Zn0.5.

[0149] 2. Carbon dioxide hydrogenation to low-carbon olefins experiment

[0150] 0.1 g of the above-prepared catalyst 0.8%K-Fe10Zn0.5 was taken and packed in a fixed bed reactor. The other steps were the same as those of Example 1.

[0151] The results are shown in Table 1.

[0152]

[0153]

[0154] In Table 1, C2-C4 o represents C2-C4 alkanes; C2-C4 ＝ represents C2-C4 olefins; C 5+ represents hydrocarbons with a carbon number greater than 5.

[0155] From the carbon dioxide hydrogenation reaction results of Comparative Examples 1-5 and Comparative Example 1, it can be seen that under the same reaction conditions, the CO2 conversion rate, the C2-C4 low-carbon olefin selectivity in the product, and the O / P (olefin / alkane) ratio of the low-carbon olefins all show a trend of first increasing and then decreasing with the addition of zinc promoter, and the methane selectivity shows a trend of first decreasing and then increasing, indicating that the zinc promoter can effectively promote the adsorption and activation of CO2 and inhibit the excessive hydrogenation activity of olefins, and the 0.8%K-Fe10Zn5 in the above Example 1 has the best reaction activity and low-carbon olefin selectivity.

[0156] From the reaction results of Comparative Example 1 and Comparative Example 2, it can be seen that the addition of potassium alkali significantly improves the catalytic reaction activity, inhibits the generation of methane, and improves the olefin selectivity and O / P ratio, which is because the electronic effect of the alkali metal regulates the charge distribution on the surface of the catalyst, thereby affecting the product distribution.

[0157] Comparing Example 1 with Comparative Examples 3-4, when the molar ratio of Zn to Fe is within the range of the present application, the CO2 conversion rate, the C2-C4 low-carbon olefin selectivity in the product, and the O / P (olefin / alkane) ratio of the low-carbon olefins are significantly higher.

[0158] In summary, the catalyst provided by the present application can keep stable reaction activity and low-carbon olefin selectivity, and has no obvious deactivation phenomenon during 200 hours of continuous reaction under high space velocity reaction conditions. It can be seen that the catalyst provided by the present application has good industrial application prospect when used for preparing low-carbon olefins from carbon dioxide hydrogenation.

[0159] Any numerical values recited herein include all values from the lower value and the upper value. For example, if a concentration range is stated as 1% to 50%, it is intended that values such as 15% to 35%, 22% to 29%, or 10%, 11%, 12%, 13%, 14%, 15%, etc., to 50%, 51%, 52%, 53%, 54%, 55%, etc., are expressly enumerated in this specification. For values which are less than one, one unit in the high is considered to be 0.1, 0.01, 0.001, or 0.0001, as appropriate. These are only examples of what is specifically enumerated herein and are not intended to limit the application in any way. Any numerical value, however, can only be achieved with the consent of this specification.

[0160] It should be noted that the foregoing examples have been provided merely for the purposes of explanation and are in no way to be construed as limiting. The present application is described with reference to exemplary embodiments, but it is understood that the words which have been used herein are words of description, and that the application is not limited to the particulars of the embodiments described. The present application is capable of modification in various respects, and the applicant intends to be bound by the application only as modified and limited insofar as it is involved in the scope of the present claims. Although the present application has been described with reference to particular means, materials and embodiments, from the foregoing description, one skilled in the art can effect a variety of changes and modifications with respect to the partical methods and embodiments without departing from the scope and spirit of the application. Although the application described herein relates to particular methods, materials and embodiments, it is not intended to be limited to the particular examples disclosed herein, but includes all alternatives consistent with the scope of the present application.

Claims

1. A catalyst comprising an active component, an alkali metal and an auxiliary agent; wherein, the active component is an iron oxide; the alkali metal is selected from one or more of Li, Na, K, Rb and Cs; the auxiliary agent is selected from one or more of Al, Zn, Mn, Cu, Co, Zr and Ce; in the catalyst, the molar ratio of iron element to the auxiliary agent element is 1:0.1-1, and the mass percentage of the alkali metal in the catalyst is 0.5-1.5%.

2. The catalyst according to claim 1, characterized in that, in the catalyst, the molar ratio of iron element to the auxiliary agent element is 1:0.4-0.6, and the mass percentage of the alkali metal in the catalyst is 0.7-0.9%.

3. A method for preparing the catalyst of claim 1 or 2, comprising the steps of: S1, providing a solution I containing a source of active component and a source of auxiliary agent; providing a solution II containing a source of alkali metal; S2, mixing the solution I and the solution II to obtain a suspension; S3, performing centrifugal treatment and washing treatment on the suspension to obtain a precipitated intermediate product; S4, sequentially performing drying treatment and calcination treatment on the precipitated intermediate product to obtain the catalyst.

4. The production method according to claim 3, characterized by, in step S1, the source of active component is selected from at least one of ferric chloride, ferric nitrate, ferric sulfate and ferrous chloride; and / or, in step S1, the source of auxiliary agent is selected from one or more of nitrate, chloride, subchloride, sulfate or sub-sulfate of Al, Zn, Mn, Cu, Co, Zr and Ce that is soluble in alcohol; preferably, the source of auxiliary agent is selected from one or more of zinc chloride, magnesium chloride, copper chloride, manganese chloride, cobalt chloride, zirconium chloride and cerium chloride; and / or, in step S1, the source of alkali metal is selected from one or more of hydroxide or carbonate of Li, Na, K, Rb and Cs; preferably, the source of alkali metal is selected from one or more of potassium carbonate, potassium bicarbonate, potassium chloride, potassium sulfate and potassium nitrate; and / or, in step S1, the molar ratio of iron element to the auxiliary agent element in the solution I is 1:0.1-1; preferably, 1:0.4-0.6; and / or, in step S1, the total molar concentration of the auxiliary agent element in the solution I is 0.1-1.0 mol / L; and / or, in step S1, the solution I further comprises a solvent I, and the solvent I is selected from at least one of ethylene glycol, glycerol, ethanol and isopropanol; and / or, in step S1, the molar concentration of the alkali metal in the solution II is 0.1-2.0 mol / L; and / or, in step S1, the solution II further comprises a solvent II, and the solvent II is water.

5. The production method according to claim 3 or 4, characterized by, in step S2, the conditions for the mixing include: temperature of -20 to -1℃; and / or, pH value of 8-12; and / or, in step S2, the solution II is added dropwise into the solution I to obtain the suspension; preferably, the dropwise adding speed is 1-10 mL / min; and / or, in step S3, water is used for the washing treatment.

6. The production method according to any one of claims 3 to 5, characterized by, in step S4, the conditions for the drying treatment include: temperature of 40-80℃; time of 1-24 h; And / or, in step S4, the conditions for the calcination treatment include: temperature of 300-600℃; time of 1-24h.

7. Use of the catalyst of claim 1 or 2 or the catalyst obtained by the preparation method of any one of claims 3-6 in the hydrogenation of carbon dioxide to produce low-carbon olefins.

8. A method for producing low carbon olefins by hydrogenation of carbon dioxide, comprising the step of: allowing carbon dioxide to undergo a hydrogenation reaction in the presence of hydrogen, carbon dioxide, and a catalyst; wherein, The catalyst is the catalyst of claim 1 or 2 or the catalyst obtained by the preparation method of any one of claims 3-6.

9. The method of claim 8, wherein, The molar ratio of the hydrogen and carbon dioxide is 1-5:1; And / or, the conditions of the hydrogenation reaction include: the reaction temperature is 250℃-400℃; the space velocity is 10000-50000 mL / (g cat. ·h); the pressure is 0.1-5.0 MPa.

10. The method according to claim 8 or 9, characterized in that, Before the hydrogenation reaction is performed, the catalyst is subjected to an activation treatment; the conditions for the activation treatment include: The activation atmosphere is a mixed gas of CO and Ar; the volume ratio of Ar to CO in the mixed gas is 5-20:1; The air speed of the mixed gas is 10000-50000 mL / (g cat. ·h); And / or, the activation pressure is 0.1-1 MPa; And / or, the activation temperature is 200-400℃; And / or, the time is 1-50h.

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