CN112169799A - Method for synthesizing low-carbon olefin by carbon dioxide hydrogenation by iron-based catalyst - Google Patents
Method for synthesizing low-carbon olefin by carbon dioxide hydrogenation by iron-based catalyst Download PDFInfo
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Abstract
The invention relates to an iron-based catalyst for synthesizing low-carbon olefin by carbon dioxide hydrogenation and a preparation method and application thereof,mainly realizes the direct CO synthesis on a single catalyst2Hydrogenation is carried out to convert the mixture into low-carbon olefin, so that high low-carbon olefin selectivity and high stability are obtained. The catalyst adopted by the invention comprises the following components in parts by mass: a) 5-88% of iron element or oxide thereof; b) any one or more than two of oxides of cobalt, nickel and magnesium, the weight percentage is 10-80%. c) One or more than two oxides selected from lithium, sodium, potassium, rubidium and cesium, and the weight percentage of the oxides is 0.001-20%. The catalyst provided by the invention can directly react CO2Conversion to light olefins, CO2The conversion rate can reach 43.5%, the selectivity of methane is lower than 10%, and the carbon-based selectivity of the low-carbon olefin reaches 46%.
Description
Technical Field
The invention relates to an iron-based catalyst for synthesizing low-carbon olefin by carbon dioxide hydrogenation, and a preparation method and application thereof.
Background
In recent years, atmospheric CO2The concentration is gradually increased, which causes a series of environmental problems such as global warming and ocean acidification, and the like, and the method has attracted wide attention of people all over the world. CO 22Not only a greenhouse gas, but also a carbon resource, should be comprehensively utilized. H obtained by using renewable energy2With CO2The hydrogenation reaction is carried out to obtain CO and CH4Low carbon olefin, gasoline, aromatic hydrocarbon and other valuable chemicals, wherein the low carbon olefin is one of the most basic raw materials in the chemical industry. The traditional production method of the low-carbon olefin is mainly obtained by naphtha cracking and low-carbon alkane dehydrogenation. By using CO2The low-carbon olefin obtained by hydrogenation not only can realize CO2The resource utilization of the method also provides a technology for generating the low-carbon olefin by a non-petroleum route, and is expected to realize the carbon recycling. Thus, CO2The technology for synthesizing the low-carbon olefin by hydrogenation has important significance in the aspects of environmental protection and resource utilization.
Reported in the literature, CO on Fe-based catalysts2Firstly, RW GS reaction is carried out to convert the RW GS into CO, and the CO is subjected to F-T synthesis reaction to generate low-carbon olefin. Due to CO2Relative inertness of the molecule and kinetic barrier to C-C bond formation, CO2Activation and conversion to high carbon products of more than two carbon atoms remains a significant challenge. The pure Fe-based catalyst has lower activity, and the product is mainly low-carbon alkane. Additive for foodThe addition of alkali metal auxiliary agent such as Na can promote CO2Adsorption of (2), inhibition of H2The adsorption of the catalyst can effectively inhibit the secondary hydrogenation reaction of the low-carbon olefin, thereby improving the selectivity of the low-carbon olefin. Creep and autophoresis and the like Fe modified by Na auxiliary agent3O4Catalyst for CO2Hydrogenation synthesis of low-carbon olefin. At 320 deg.C, 3MPa, H2/CO2＝3、2000h-1Under reaction conditions of (3), CO2Conversion of (3%) was 40.3%, C2 ＝-C4 ＝The selectivity of (A) was 38.7% (Catalysis Science)&Technolo gy,2016,6: 4786-. The method researches different alkali metal auxiliary agent modified Fe-based catalysts in CO2Influence of the Performance in the hydrogenation reaction, it was found that the order of activity is Rb>K≈Cs>Li>Na (Chinese Journal of Catalysis,2013,34: 956-. However, the activity of bulk Fe-based catalysts and selectivity to lower olefins still need to be improved due to material limitations.
At present, some have been used for CO2The catalyst for synthesizing low-carbon olefin by hydrogenation applies for related patents. Several reported patents are listed below for details:
chinese patent CN201510116355 discloses the name: CO (carbon monoxide)2An iron-based catalyst for preparing low-carbon olefin by hydrogenation, and a preparation method and application thereof. This patent reports the use of an added oxide promoter Fe3O4A catalyst. In CO2CO in hydrogenation reactions2The conversion is higher, but the selectivity of the low-carbon olefin is only 28 percent.
Chinese patent CN201611098885 discloses a name: preparation of iron-based catalyst for preparing alpha-low carbon olefin by carbon dioxide hydrogenation, catalyst and application. This patent reports the use of an adjuvant modified Fe-based catalyst in CO2CO in hydrogenation reactions2The conversion rate is 31 percent, the selectivity of the low-carbon olefin is 22 percent, and the selectivity of the high-carbon hydrocarbon in the product is higher.
CO2The reaction for synthesizing the low-carbon olefin by hydrogenation is a strong exothermic reaction, and the reaction performance is closely related to the particle size of Fe species. However, Fe species in the bulk phase catalyst are easy to agglomerate and grow in the reaction process, so that the catalyst activity is causedThe sexual performance is reduced. To further increase the activity of the catalyst, the properties of the Fe species need to be modulated and kept stable under the reaction conditions.
Hydrotalcite is a layered anionic clay having the general composition: [ M ] A2+ 1-xM3+ x(OH)2]x+·An- x/n·mH2O, wherein M2+Is a divalent metal ion, M3+Is a trivalent metal ion, An-Is an interlayer anion. The ideal molecular formula is Mg6Al2(OH)16CO3·4H2O, partial or complete substitution of Mg by divalent or trivalent transition metal cations of similar radius2+，Al3+Ions can synthesize various hydrotalcite-like compounds. After the hydrotalcite is roasted, various components interact to form a composite oxide with high specific surface area and high stability, and metal particles with small particle size and high stability can be obtained after reduction treatment. The second component is introduced by using the hydrotalcite precursor containing Fe, so that the property of Fe species can be modulated, and the stability of the Fe species can be expected to be realized. Further develops a Fe-based catalyst with high activity, high selectivity of low-carbon olefin and high stability.
Disclosure of Invention
One of the technical problems to be solved by the invention is to solve the problem of the catalyst for synthesizing the low-carbon olefin by carbon dioxide hydrogenation, and provide a novel catalyst for synthesizing the low-carbon olefin by carbon dioxide hydrogenation, wherein the catalyst has high CO content2High conversion rate, high selectivity of low-carbon olefin and high stability.
The second technical problem to be solved by the present invention is to adopt the method for preparing the catalyst described in the first technical problem. The catalyst has controllable content of each component, and the method has simple preparation process and good reliability.
The invention aims to solve the third technical problem of realizing the catalytic reaction process of synthesizing the low-carbon olefin by hydrogenating the carbon dioxide by adopting the catalyst in one of the technical problems.
1. In order to solve one of the technical problems, the invention adopts the following technical scheme: cO2The iron-based catalyst for synthesizing the low-carbon olefin by hydrogenation comprises the following components in parts by mass: a) 5-88% of one or more than two of iron element or oxides thereof; b) any one or more than two of oxides of cobalt, nickel and magnesium in 10-80%; c) one or more than two oxides selected from lithium, sodium, potassium, rubidium and cesium, and the weight percentage of the oxides is 0.001-20%.
In order to solve the second technical problem, the invention adopts the following technical scheme:
1) dissolving soluble ferric salt and soluble salt of M in deionized water to obtain solution A, and separating metal
The concentration of the seed is 0.1-2 mol/L, wherein M is one or more than two of cobalt, nickel and magnesium;
2) dissolving alkali in deionized water to prepare a precipitator to obtain a solution B with the concentration of 0.001-10 mol/L;
3) placing the solution B in a water bath kettle at 20-60 ℃, adding the solution A into the solution B under the stirring state, wherein a precipitate is generated in the mixed solution; wherein the volume ratio of the solution B to the solution A is 0.5-10, and the pH value of the system is adjusted to 9-11 after full precipitation; then stirring and aging the obtained mixture in a water bath at the temperature of 60-95 ℃ for 0.5-24 h;
4) filtering and washing the obtained turbid liquid, and drying a filter cake in air at 50-200 ℃ for 12-48 h to obtain a hydrotalcite precursor C;
5) dissolving one or more soluble salts of lithium, sodium, potassium, rubidium and cesium in deionized water to prepare a solution D, wherein the concentration of alkali metal ions is 0.001-10 mol/L;
6) taking a solid C, dropwise adding the prepared solution D into the solid C or pouring the solution D into the solid C, wherein the volume ratio of the solution D to the solid C is 0.1-10, and uniformly mixing;
7) soaking the mixture in the step (6) at room temperature for 0.5-48 h;
8) drying the mixture obtained in the step (7) at the temperature of 60-120 ℃ for 4-24 hours;
9) and roasting the dried mixture at 350-700 ℃ for 1-8 h to obtain the iron-based catalyst.
The soluble ferric salt in the step 1) is one or two of nitrate and chloride; the soluble salt of M is one or two of nitrate and chloride;
the alkali in the step 2) is an aqueous solution of sodium hydroxide and sodium carbonate, and the molar ratio of the sodium hydroxide to the sodium carbonate is 0.5-2: 1;
in the step 5), the soluble salts of lithium, sodium, potassium, rubidium and cesium are nitrates.
In the step 9), roasting can be carried out in a flowing or static air atmosphere; wherein the temperature is raised from room temperature or drying temperature to roasting temperature by adopting a program, and the temperature raising rate is 0.5-10 ℃/min; the preferable roasting temperature is 380-500 ℃, and the roasting time is 0.5-6 h.
The iron-based catalyst of claim 1, wherein: the reduction activation process of the catalyst comprises the following steps: reducing the gas to pure H2The purity is more than or equal to 99.9 percent, and the volume space velocity of the reducing gas is 1000-3600 h-1The temperature rising rate from room temperature to the reduction temperature is 1-10 ℃/min, the reduction temperature is 200-600 ℃, the pressure is normal pressure, and the reduction time is 1-24 h.
In order to solve the third technical problem, the invention adopts the following technical scheme: application of catalyst in fixed bed reactor for CO (carbon monoxide)2The reaction conditions for synthesizing the low-carbon olefin by hydrogenation are as follows: the reaction gas is CO2And H2In which the molar ratio is H2:CO2The volume space velocity is 600-30000 ml/(g)catH), the reaction temperature is 200-600 ℃, and the reaction pressure is 0.1-6 MPa.
The invention has the advantages that:
(1) the catalyst provided by the invention has the advantages of cheap and easily available raw materials, simple preparation method and contribution to realizing mass production.
(2) The catalyst provided by the invention has stable property and higher stability.
(3) The catalyst provided by the invention can directly react CO2Converted into low-carbon olefin and has high catalytic activity and selectivity.
Drawings
FIG. 1K/MgFe-HT- (1/1) catalyst in CO2The reaction performance in the reaction of synthesizing low-carbon olefin by hydrogenation. (a) CO 22The conversion of (a); (b) and (4) selecting low-carbon olefins. Reaction conditions are as follows: h2/CO2＝3；3MPa；320℃；2000ml h-1gcat -1。
Detailed Description
The technical details of the present invention are described in detail by the following examples. The embodiments are described for further illustrating the technical features of the invention, and are not to be construed as limiting the invention.
Catalyst preparation and Performance evaluation
Example 1
11.84g of magnesium nitrate (Mg (NO)3)2) And 96.96g of iron nitrate (Fe (NO)3)3·9H2O) was dissolved in 200ml of deionized water to prepare a solution A. 50.88g of anhydrous sodium carbonate (NaCO) was weighed3) And 20.48g of sodium hydroxide (NaOH) was dissolved in 100ml of deionized water to obtain solution B. Putting the solution B into a water bath kettle at 40 ℃, adding the solution A into the solution B at the speed of 3ml/min under the condition of vigorous stirring, and adding 10ml of 1mol/L NaOH solution to adjust the pH value to be about 10. The mixture was then aged for 12h in a 70 ℃ water bath with stirring. And filtering and washing the obtained turbid liquid, and drying the filter cake at 80 ℃ for 12h to obtain a hydrotalcite precursor C.
2.0g of the above solid C and 0.052g of potassium nitrate (KNO) were weighed3) Dissolving in 2ml deionized water to obtain solution, and soaking the solid C sample in the KNO3And (3) dissolving the mixture in the solution, and uniformly mixing the mixture. Dipping for 12h at room temperature, drying for 12h at 60 ℃, roasting for 4h at 400 ℃, and finally grinding, tabletting, crushing and sieving (20-40 meshes) to obtain the iron-based catalyst, wherein the molar ratio of Mg/Fe is 1: 3, K content of 1 wt%, MgO content of 14.1 wt%, Fe2O3The mass content is 84.9 percent and is marked as K/MgFe-HT- (1/3).
Catalyst reduction activation conditions: reducing the gas to pure H2Purity of>99.9 percent and the airspeed of 2000h-1The heating rate is 5 ℃/min, and the reduction temperature isThe temperature is 400 ℃, the pressure is normal pressure, and the reduction time is 6 h. Reaction conditions are as follows: molar ratio H2:CO2The space velocity is 2000 ml/(g)catH) pressure of 3MPa and temperature of 320 ℃ and the results are given in Table 1.
Example 2
11.84g of magnesium nitrate (Mg (NO)3)2) And 64.64g of iron nitrate (Fe (NO)3)3·9H2O) was dissolved in 200ml of deionized water to prepare a solution A. 33.92g of anhydrous sodium carbonate (NaCO) was weighed out3) And 15.36g of sodium hydroxide (NaOH) were dissolved in 100ml of deionized water to obtain solution B. Putting the solution B in a water bath kettle at 40 ℃, adding the solution A into the solution B at the speed of 3ml/min under the condition of vigorous stirring, and adding 10ml of 1mol/L NaOH solution to adjust the pH value to be about 10. The mixture was then aged for 12h in a 70 ℃ water bath with stirring. And filtering and washing the obtained turbid liquid, and drying the filter cake at 80 ℃ for 12h to obtain a hydrotalcite precursor C.
2.0g of the above solid C and 0.052g of potassium nitrate (KNO) were weighed3) Dissolving in 2ml deionized water to obtain solution, and soaking the solid C sample in the KNO3And (3) dissolving the mixture in the solution, and uniformly mixing the mixture. Dipping for 12h at room temperature, drying for 12h at 60 ℃, roasting for 4h at 400 ℃, and finally grinding, tabletting, crushing and sieving (20-40 meshes) to obtain the iron-based catalyst, wherein the molar ratio of Mg/Fe is 1: 2, the mass content of K is 1 percent, the mass content of MgO is 19.8 percent, and Fe2O3The mass content is 79.2 percent and is marked as K/MgFe-HT- (1/2).
Catalyst reduction activation conditions: reducing the gas to pure H2Purity of>99.9 percent and the airspeed of 2000h-1The heating rate is 5 ℃/min, the reduction temperature is 400 ℃, the pressure is normal pressure, and the reduction time is 6 h. Reaction conditions are as follows: molar ratio H2:CO2The space velocity is 2000 ml/(g)catH) pressure of 3MPa and temperature of 320 ℃ and the results are given in Table 1.
Example 3
11.84g of magnesium nitrate (Mg (NO)3)2) And 32.32g of iron nitrate (Fe (NO)3)3·9H2O) was dissolved in 200ml of deionized water to prepare a solution A. Weighing 16.96g anhydrous sodium carbonate (NaCO)3) And 10.24g of sodium hydroxide (NaOH) was dissolved in 100ml of deionized water to obtain solution B. The solution B is placed in a water bath at 40 ℃, the solution A is added into the solution B at the speed of 3ml/min under the condition of vigorous stirring, and 10ml of 1mol/L NaOH solution is added to adjust the pH value to 10. The mixture was then aged for 12h in a 70 ℃ water bath with stirring. And filtering and washing the obtained turbid liquid, and drying the filter cake at 80 ℃ for 12h to obtain a hydrotalcite precursor C.
2.0g of the above solid C and 0.052g of potassium nitrate (KNO) were weighed3) Dissolving in 2ml deionized water to obtain solution, and soaking the solid C sample in the KNO3And (3) dissolving the mixture in the solution, and uniformly mixing the mixture. Dipping for 12h at room temperature, drying for 12h at 60 ℃, roasting for 4h at 400 ℃, and finally grinding, tabletting, crushing and sieving (20-40 meshes) to obtain the iron-based catalyst, wherein the molar ratio of Mg/Fe is 1:1, K content of 1 wt%, MgO content of 33 wt%, Fe2O3The mass content is 66 percent and is recorded as K/MgFe-HT- (1/1).
Catalyst reduction activation conditions: reducing the gas to pure H2Purity of>99.9 percent and the airspeed of 2000h-1The heating rate is 5 ℃/min, the reduction temperature is 400 ℃, the pressure is normal pressure, and the reduction time is 6 h. Reaction conditions are as follows: molar ratio H2:CO2The space velocity is 2000 ml/(g)catH) pressure of 3MPa and temperature of 320 ℃ and the results are given in Table 1.
Example 4
11.84g of magnesium nitrate (Mg (NO)3)2) And 16.16g of iron nitrate (Fe (NO)3)3·9H2O) was dissolved in 200ml of deionized water to prepare a solution A. 8.48g of anhydrous sodium carbonate (NaCO) was weighed in3) And 7.68g of sodium hydroxide (NaOH) were dissolved in 100ml of deionized water to obtain solution B. The solution B is placed in a water bath at 40 ℃, the solution A is added into the solution B at the speed of 3ml/min under the condition of vigorous stirring, and 10ml of 1mol/L NaOH solution is added to adjust the pH value to 10. The mixture was then aged for 12h in a 70 ℃ water bath with stirring. And filtering and washing the obtained turbid liquid, and drying the filter cake at 80 ℃ for 12h to obtain a hydrotalcite precursor C.
Weigh 2.0g of the above solidsBody C, 0.052g of potassium nitrate (KNO) was weighed3) Dissolving in 2ml deionized water to obtain solution, and soaking the solid C sample in the KNO3And (3) dissolving the mixture in the solution, and uniformly mixing the mixture. Dipping for 12h at room temperature, drying for 12h at 60 ℃, roasting for 4h at 400 ℃, and finally grinding, tabletting, crushing and sieving (20-40 meshes) to obtain the iron-based catalyst, wherein the molar ratio of Mg/Fe is 1: 2, K content of 1 wt%, MgO content of 49.5 wt%, Fe2O3The mass content is 49.5 percent and is marked as K/MgFe-HT- (2/1).
Catalyst reduction activation conditions: reducing the gas to pure H2Purity of>99.9 percent and the airspeed of 2000h-1The heating rate is 5 ℃/min, the reduction temperature is 400 ℃, the pressure is normal pressure, and the reduction time is 6 h. Reaction conditions are as follows: molar ratio H2:CO2The space velocity is 2000 ml/(g)catH) pressure of 3MPa and temperature of 320 ℃ and the results are given in Table 1.
Example 5
11.84g of magnesium nitrate (Mg (NO)3)2) And 10.77g of iron nitrate (Fe (NO)3)3·9H2O) was dissolved in 200ml of deionized water to prepare a solution A. 5.65g of anhydrous sodium carbonate (NaCO) was weighed in addition3) And 6.83g of sodium hydroxide (NaOH) was dissolved in 100ml of deionized water to obtain solution B. The solution B is placed in a water bath at 40 ℃, the solution A is added into the solution B at the speed of 3ml/min under the condition of vigorous stirring, and 10ml of 1mol/L NaOH solution is added to adjust the pH value to 10. The mixture was then aged for 12h in a 70 ℃ water bath with stirring. And filtering and washing the obtained turbid liquid, and drying the filter cake at 80 ℃ for 12h to obtain a hydrotalcite precursor C.
2.0g of the above solid C and 0.052g of potassium nitrate (KNO) were weighed3) Dissolving in 2ml deionized water to obtain solution, and soaking the solid C sample in the KNO3And (3) dissolving the mixture in the solution, and uniformly mixing the mixture. Dipping for 12h at room temperature, drying for 12h at 60 ℃, roasting for 4h at 400 ℃, and finally grinding, tabletting, crushing and sieving (20-40 meshes) to obtain the iron-based catalyst, wherein the molar ratio of Mg/Fe is 1: 2, the mass content of K is 1 percent, the mass content of MgO is 59.4 percent, and Fe2O3The mass content is 39.6 percent and is recorded as K/MgFe-HT-(3/1)。
Catalyst reduction activation conditions: reducing the gas to pure H2Purity of>99.9 percent and the airspeed of 2000h-1The heating rate is 5 ℃/min, the reduction temperature is 400 ℃, the pressure is normal pressure, and the reduction time is 6 h. Reaction conditions are as follows: molar ratio H2:CO2The space velocity is 2000 ml/(g)catH) pressure of 3MPa and temperature of 320 ℃ and the results are given in Table 1.
Example 6
Catalyst stability test
The catalyst prepared in example 3 was subjected to a stability test as described in example 3 and the results are shown in figure 1.
Comparative example 7
11.84g of magnesium nitrate (Mg (NO)3)2) And 32.32g of iron nitrate (Fe (NO)3)3·9H2O) was dissolved in 200ml of deionized water to prepare a solution A. Another 16.96g of anhydrous sodium carbonate (NaCO) was weighed3) And 10.24g of sodium hydroxide (NaOH) was dissolved in 100ml of deionized water to obtain solution B. The solution B is placed in a water bath at 40 ℃, the solution A is added into the solution B at the speed of 3ml/min under the condition of vigorous stirring, and 10ml of 1mol/L NaOH solution is added to adjust the pH value to 10. The mixture was then aged for 12h in a 70 ℃ water bath with stirring. And filtering and washing the obtained turbid liquid, and drying the filter cake at 80 ℃ for 12h to obtain a hydrotalcite precursor C. Roasting the catalyst at 400 ℃ for 4h, and finally grinding, tabletting, crushing and sieving (20-40 meshes) to obtain the iron-based catalyst, wherein the molar ratio of Mg/Fe is 1:1, K content of 1%, MgO content of 33.3%, Fe2O3The mass content is 66.7 percent and is recorded as MgFe-HT- (1/1).
Catalyst reduction activation conditions: reducing the gas to pure H2Purity of>99.9 percent and the airspeed of 2000h-1The heating rate is 5 ℃/min, the reduction temperature is 400 ℃, the pressure is normal pressure, and the reduction time is 6 h. Reaction conditions are as follows: molar ratio H2:CO2The space velocity is 2000 ml/(g)catH) pressure of 3MPa and temperature of 320 ℃ and the results are given in Table 1.
Comparative example 8
The catalyst of K and Fe loaded by MgO is prepared by an impregnation method. Weigh 0.052g of potassium nitrate (KNO)3) And 1.63g of iron nitrate (Fe (NO)3)3·9H2O) it was dissolved in 2ml of deionized water to prepare a solution. 2.0g of magnesium oxide (MgO) was weighed and added to the above KNO3And (3) dissolving the mixture in the solution, and uniformly mixing the mixture. Soaking at room temperature for 12h, drying at 60 deg.C for 12h, calcining at 400 deg.C for 4h, grinding, tabletting, crushing, and sieving (20-40 mesh) to obtain iron-based catalyst with K content of 1 wt%, MgO content of 74.2 wt%, and Fe content2O3The mass content is 24.8 percent and is recorded as K-Fe/MgO.
Catalyst reduction activation conditions: reducing the gas to pure H2Purity of>99.9 percent and the airspeed of 2000h-1The heating rate is 5 ℃/min, the reduction temperature is 400 ℃, the pressure is normal pressure, and the reduction time is 6 h. Reaction conditions are as follows: molar ratio H2:CO2The space velocity is 2000 ml/(g)catH) pressure of 3MPa and temperature of 320 ℃ and the results are given in Table 1.
Example analysis of results:
from the data analysis in table 1, it can be seen that the catalyst prepared by using the hydrotalcite containing Fe as the precursor is used in CO2The catalyst shows excellent performance in the synthesis of low-carbon olefin by hydrogenation. CO with increasing Mg/Fe ratio2The conversion and the selectivity of the lower olefins are gradually increased and then gradually decreased. The preferred Mg/Fe molar ratio is 1: 1. K-Mg-Fe-HT- (1/1) catalyst obtained by optimizing the Mg/Fe molar ratio, its CO2Conversion of (2) was 43.5%, lower olefins (C)2 ＝-C4 ＝) The selectivity of (a) was 46.4% and the selectivity of methane was only 9.8%. The catalyst (K-Fe/MgO) prepared by the traditional impregnation method and the CO thereof2The conversion of (A) is only 8.2%, the products are mainly CO, C2 ＝-C4 ＝The selectivity of (a) is only 1.5%. The comparison shows that the catalyst prepared by adopting the hydrotalcite containing Fe as the precursor is used in CO2The performance of the reaction for synthesizing the low-carbon olefin by hydrogenation is far higher than that of the catalyst prepared by an impregnation method. In addition, as can be seen from FIG. 1, the Fe-containing hydrotalcite is good for preparing the catalyst by using the Fe-containing hydrotalcite as the precursorStability, during the reaction for 100h, CO2The conversion rate and the selectivity of the low-carbon olefin are basically unchanged.
TABLE 1 CO on different iron-based catalysts2Effect of hydrogenation Performance
In Table 1, product selectivities refer to carbon-based selectivities; c2 ＝-C4 ＝Is a low-carbon olefin product with carbon number from 2 to 4; c2 0-C4 0Is an alkane product with the carbon number from 2 to 4; c5+Hydrocarbon products with carbon number of 5 and above; the alkylene ratio (O/P) is C in the product2 ＝-C4 ＝And C2 0-C4 0The molar ratio of (a) to (b). Reaction conditions are as follows: h2/CO2＝3；3MPa；320℃；2000ml h-1gcat -1。
Claims (8)
1. The method for synthesizing the low-carbon olefin by carbon dioxide hydrogenation by adopting the iron-based catalyst is characterized by comprising the following steps of: the iron-based catalyst comprises the following components in parts by weight: a) 5-88% of one or more than two of iron element or oxides thereof; b) any one or more than two of oxides of cobalt, nickel and magnesium in 10-80%; c) one or more than two oxides selected from lithium, sodium, potassium, rubidium and cesium, and the weight percentage of the oxides is 0.001-20%.
2. The method of claim 1, wherein: component a) preferably the oxide of iron is Fe3O4Or Fe2O3One or more than two of the components, the preferable content of the component a) is 25-70%;
the component b) is preferably any one or more than two of cobalt, nickel and magnesium oxides, and the content of the component b) is preferably 20-70%;
the component c) is preferably one or more of oxides of lithium, sodium, potassium and cesium, and the content of the component c) is preferably 0.01-15%.
3. The method according to any one of claims 1 to 2, wherein: the preparation process of the iron-based catalyst comprises the following steps:
1) dissolving soluble ferric salt and soluble salt of M in deionized water to obtain a solution A, wherein the concentration of metal ions is 0.1-2 mol/L, and M is one or more than two of cobalt, nickel and magnesium;
2) dissolving alkali in deionized water to prepare a precipitator to obtain a solution B with the concentration of 0.001-10 mol/L;
3) placing the solution B in a water bath kettle at 20-60 ℃, adding the solution A into the solution B under the stirring state, wherein a precipitate is generated in the mixed solution; wherein the volume ratio of the solution B to the solution A is 0.5-10, and the pH value of the system is adjusted to 9-11 after full precipitation; then stirring and aging the obtained mixture in a water bath at the temperature of 60-95 ℃ for 0.5-24 h;
4) filtering and washing the obtained turbid liquid, and drying a filter cake in air at 50-200 ℃ for 12-48 h to obtain a hydrotalcite precursor C;
5) dissolving one or more soluble salts of lithium, sodium, potassium, rubidium and cesium in deionized water to prepare a solution D, wherein the concentration of alkali metal ions is 0.001-10 mol/L;
6) taking a solid C, dropwise adding the prepared solution D into the solid C or pouring the solution D into the solid C, wherein the volume ratio of the solution D to the solid C is 0.1-10, and uniformly mixing;
7) soaking the mixture in the step (6) at room temperature for 0.5-48 h;
8) drying the mixture obtained in the step (7) at the temperature of 60-120 ℃ for 4-24 hours;
9) and roasting the dried mixture at 350-700 ℃ for 1-8 h to obtain the iron-based catalyst.
4. The method of claim 3, wherein:
the soluble ferric salt in the step 1) is one or two of nitrate and chloride; the soluble salt of M is one or two of nitrate and chloride;
the alkali in the step 2) is an aqueous solution of sodium hydroxide and sodium carbonate, and the molar ratio of the sodium hydroxide to the sodium carbonate is 0.5-2: 1;
in the step 5), the soluble salts of lithium, sodium, potassium, rubidium and cesium are nitrates.
5. The method of claim 3, wherein:
in the step 9), roasting can be carried out in a flowing or static air atmosphere; wherein the temperature is raised from room temperature or drying temperature to roasting temperature by adopting a program, and the temperature raising rate is 0.5-10 ℃/min; the preferable roasting temperature is 380-500 ℃, and the roasting time is 0.5-6 h.
6. The method according to any one of claims 1 to 5, wherein: before the catalyst is used, the catalyst needs to be subjected to reduction activation, and the reduction activation process of the catalyst is as follows: reducing the gas to pure H2The molar purity is more than or equal to 99.9 percent, and the volume space velocity of the reducing gas is 1000-3600 h-1The temperature rising rate from room temperature to the reduction temperature is 1-10 ℃/min, the reduction temperature is 200-600 ℃, the pressure is normal pressure, and the reduction time is 1-24 h.
7. The method according to any one of claims 1 to 6, wherein: the catalyst is used for CO2Hydrogenation synthesis of low-carbon olefin; the low-carbon olefin is a low-carbon olefin product with the carbon number from 2 to 4.
8. The method according to any one of claims 1 to 7, wherein: application of catalyst in fixed bed reactor for CO (carbon monoxide)2The reaction conditions for synthesizing the low-carbon olefin by hydrogenation are as follows: the reaction gas is CO2And H2In which the molar ratio is H2:CO2The volume space velocity is 600-30000 ml/(g)catH), the reaction temperature is 200-600 ℃, and the reaction pressure is 0.1-6 MPa.
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