Preparation method of Fe-based catalyst for CO2 hydrogenation to light olefins

Abstract

The present invention discloses a preparation method of an Fe-based catalyst for CO2 hydrogenation to produce light olefins, comprising the following steps: (1) mixing potassium bromide and manganese nitrate to obtain a promoter mixture; (2) mixing the promoter mixture obtained in step (1) with NaY molecular sieve and ferric nitrate and grinding the mixture; (3) subjecting the ground product in step (2) to a melt infiltration treatment; (4) calcining the product after the melt infiltration in step (3) under the protection of an inert gas to obtain FeMnKBr / Y meso The Fe-based catalyst prepared by the present invention has a better product distribution. The bromine element can control the electron density around the active center of the catalyst through its own electronegativity and ability to accept electrons, thereby changing the catalyst's hydrogenation ability in a hydrogen-rich atmosphere. At a reaction temperature of 300°C, a CO2 conversion rate of 35.0%, a CO selectivity of 13.2%, and a light olefin selectivity of 56.2% were achieved.

Description

Technical Field

[0001] The invention belongs to the field of catalysts and relates to a co-catalyst composition of an Fe-based catalyst acting on CO2 hydrogenation to produce light olefins. Background Art

[0002] Fe-based catalysts are widely used in the catalytic production of light olefins using CO2 and H2 as raw materials. Traditional Fe-based catalysts will sinter and agglomerate during calcination and the reaction process, resulting in a decrease in conversion rate and a reduction in the selectivity of the target product. Especially in a hydrogen-rich atmosphere, most of the products are alkanes. Different preparation methods and the addition of different additives have a great influence on the conversion rate and selectivity of iron-based catalysts. Therefore, it is necessary to improve the dispersion of active components and adjust the surface electron density, thereby improving the activity and selectivity of the catalyst in the process of CO2 hydrogenation to light olefins.

[0003] Traditional Fe-based catalysts report that the halogen bromine element is a harmful substance that poisons the catalyst. During the reaction process, it can rob electrons from the catalyst surface, inhibit the adsorption and dissociation of carbon dioxide, reduce the catalytic activity of the catalyst, and change the product distribution. Summary of the Invention

[0004] The object of the present invention is to provide a co-catalyst composition for an Fe-based catalyst for CO2 hydrogenation to produce light olefins.

[0005] The technical solutions for achieving the purpose of the present invention are as follows:

[0006] The preparation method of Fe-based catalyst for CO2 hydrogenation to light olefins is prepared by melt infiltration, and the specific steps are as follows:

[0007] (1) mixing potassium bromide and manganese nitrate to obtain a promoter mixture;

[0008] (2) mixing the co-catalyst mixture obtained in step (1) with NaY molecular sieve and ferric nitrate and grinding the mixture;

[0009] (3) subjecting the ground product of step (2) to melt infiltration treatment;

[0010] (4) The product after melt infiltration in step (3) is calcined under the protection of an inert gas to obtain an Fe-based catalyst.

[0011] Furthermore, in step (1), the mass ratio of Br:Mn in the co-catalyst mixture is (1-2):1.

[0012] Furthermore, in step (2), the NaY molecular sieve is Y meso -Na molecular sieve.

[0013] Furthermore, the Ymeso -Na molecular sieve is prepared by the following method: Y micro -Na molecular sieves were first treated with EDTA solution, micro The mass ratio of -Na to hexamethylenediaminetetraacetic acid is 2.35:1, the concentration of EDTA aqueous solution is 0.07 mol / L, the temperature of condensation reflux is 80 ° C, the treatment time is 6 hours, centrifugal drying, and then the mass ratio of solid powder to sodium hydroxide is 2.22:1, the concentration of sodium hydroxide solution is 0.4 mol / L, the temperature of heating and stirring is 40~80 ° C, and the treatment time is 0.5 hours.

[0014] Furthermore, the mass ratio of the co-catalyst mixture, NaY molecular sieve and ferric nitrate is (2-3):3:(18-19).

[0015] Furthermore, in step (3), the temperature of the melt infiltration treatment is 60° C., and the treatment time is 48 h.

[0016] Furthermore, in step (4), the inert gas is nitrogen.

[0017] Furthermore, in step (4), the calcination heating rate is 2°C / min, the temperature is 550°C, and the calcination time is 4h.

[0018] The Fe-based catalyst obtained by the preparation method described above is used in catalytic CO2 hydrogenation to produce light olefins.

[0019] Furthermore, the catalytic temperature is 300 ° C, the catalytic pressure is 1 MPa, and the space velocity is 2160 mL·g cat -1 ·h -1 .

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] (1) The present invention prepares FeMnKBr / Y by melt infiltration with the addition of molecular sieves meso -Na, the active component of the catalyst has a good degree of dispersion, which reduces the degree of sintering and agglomeration during calcination and reaction, and is beneficial to improving catalytic performance.

[0022] (2) Compared with other iron-based catalysts with potassium additives, the FeMnKBr / Y meso-Na has a better product distribution. In the preparation method of this catalyst, bromine element can control the electron density around the active center of the catalyst through its own electronegativity and ability to gain electrons, thereby changing the catalyst's hydrogenation ability in a hydrogen-rich atmosphere. The optimal ratio of bromine element addition is obtained through experiments, thereby improving the catalytic activity of the catalyst. At the same time, it can also effectively adjust the product distribution, thereby improving the selectivity of the target product, achieving a CO2 conversion rate of 35.0%, a CO selectivity of 13.2%, and a light olefin selectivity of 56.2% at a reaction temperature of 300°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 FeMnKBr / Y prepared in Example 1 meso -Scanning electron microscopy image of Na catalyst.

[0024] Figure 2 FeMnKBr / Y prepared in Example 1 meso -Na catalyst EDS element distribution diagram, Figure (b~i) is FeMnKBr / Y mseo -Element distribution of Al, Br, C, Fe, K, Mn, O, and Si in Na. DETAILED DESCRIPTION

[0025] The present invention is further described in detail below by means of specific examples and accompanying drawings, but the scope of the present invention is not limited thereto. Unless otherwise specified, the reagents, raw materials, reaction gases, etc. used in the examples are all commercially available, and the testing and experimental methods are all conventional operations in the art unless otherwise specified.

[0026] Y micro -Na molecular sieves were purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0027] Example 1

[0028] First, 0.52g KBr and 0.26g Mn(NO3)2·4H2O were fully mixed, and then the selected Y micro -Na treatment to obtain Y meso - Na, 13.4 g of Y micro -Na molecular sieves and EDTA aqueous solution (containing EDTA 4.09g, 200ml, 0.07mol / L) were added to a distillation flask and condensed under reflux and stirred at 80℃ for 6h. The solid product was centrifuged, washed and dried for subsequent sodium hydroxide treatment. For NaOH treatment, 1.7g of solid powder was added to NaOH aqueous solution (50ml, 0.4mol / L) and heated and stirred at 60℃ for 0.5h. Then centrifuged and dried to form Y meso- Na. The mixed catalyst mixture and 1.51g Y meso -Na and 1.73gFe(NO3)3·9H2O were fully mixed, ground to a moist state, transferred to a small sample bottle, and melt-infiltrated at 60°C for 48h. The solid was then further calcined at 550°C for 4h in a N2 (40ml / min) gas flow with a heating rate of 2°C / min to obtain FeMnKBr / Y meso - Na catalyst.

[0029] Example 2

[0030] This embodiment is basically the same as embodiment 1, the only difference being that the amount of KBr added is 0.26 g, and the amount of Y-Na molecular sieve is 1.6 g. The remaining steps are the same as embodiment 1.

[0031] Example 3

[0032] This embodiment is basically the same as Example 1, the only difference being the potassium salt used, 0.3 g K2CO3 being added, and the remaining steps being the same as Example 1.

[0033] Example 4

[0034] This embodiment is basically the same as embodiment 1, the only difference being that different potassium salts are used, 0.72 g KI is added. ， The remaining steps are the same as in Example 1.

[0035] Application experimental testing

[0036] The catalysts prepared in Examples 1-4 were used to catalyze CO2 hydrogenation to produce light olefins, and the specific steps were as follows:

[0037] All catalysts were tested for activity in the catalytic hydrogenation of CO2 in a fixed-bed stainless steel reactor. Before testing, 1 g of catalyst and 2.0 g of quartz sand were weighed, mixed, and loaded into the thermostatic section of the fixed-bed reactor. Reduction was carried out for 8 h at a temperature of 440°C, a pressure of 0.5 MPa, a reducing gas mixture of 80% N2 / 20% CO, and a space velocity of 7200 mL / (g·h). After reduction, the temperature was naturally cooled to 50°C, and the reaction gas mixture (V(H2) / V(CO2) / V(Ar) = 73.0%:24.0%:3.0%) was then introduced into the reactor. Fischer-Tropsch synthesis (FTS) reactions were then carried out at a temperature of 300°C, a pressure of 1 MPa, and a space velocity of 2160 mL / (g·h). To prevent product condensation, all off-gas lines before entering the chromatograph were insulated at 100°C, and the products were immediately analyzed by a thermal conductivity detector (TCD) and a flame ionization detector (FID). The sample collection started 4 hours after the reaction started. The activity evaluation and evaluation results of all catalysts in CO2 hydrogenation to light olefins are shown in Table 1.

[0038] Table 1 Catalytic effects of the catalysts prepared in Examples 1-3 and References 1-3

[0039] catalyst Temperature / ℃ Pressure / MPa <![CDATA[Air speed / mL·g cat −1 ·h −1 > <![CDATA[CO2 conversion rate / %]]> CO selectivity / % Light olefin selectivity / % Example 1 300 1.0 2160 35.0 13.2 56.2 Example 2 300 1.0 2160 29.6 40.6 42.6 Example 3 300 1.0 2160 31.0 19.0 42.6 Example 4 300 1.0 2160 29.2 21.7 47.9 Comparative Literature 1 340 2.0 1200 21.0 55.0 43.0

[0040] The catalytic performance of Examples 1-4 was evaluated in a fixed bed reactor to test the performance of CO2 hydrogenation to light olefins. The results are shown in Table 1. From the data of Examples 1-4 and the comparative literature, it can be seen that the catalytic performance improves with the different potassium salts and the selectivity of the target product. The optimal catalyst is FeMnKBr / Y meso - Na, at a reaction temperature of 300°C, the CO2 conversion rate was 35.0%, the CO selectivity was 13.2%, and the light olefin selectivity was 56.2%. This is because the addition of molecular sieves promotes the dispersion of metal components, thereby exposing more active components and improving the conversion rate. The addition of bromine promoters can adjust the electron density on the surface of active components and change the product distribution.

[0041] To further explore the effect of the preparation method on the catalytic performance of the catalyst, compared with Reference 1, the performance improvement was attributed to the fact that the melt infiltration method with the addition of molecular sieves can promote the dispersion of metal components, while the synergistic effect of the dual promoters can control the hydrogen density around the active components of the catalyst during the reaction by regulating the electron density on the catalyst surface.

[0042] Regarding Fe-based catalysts, different preparation methods and different additives result in poor and widely varying catalytic performance for CO2 hydrogenation to light olefins. The catalysts in Reference 1 (Wang, Jingjuan, et al. "Synthesis of lower olefins by hydrogenation of carbon dioxide oversupported iron catalysts." Catalysis Today 215.41(2013):186-193) all exhibit lower light olefin conversion than the catalysts in the present invention. Furthermore, the Fe catalysts reported in the reference all operate at reaction temperatures above 300°C and pressures above 1 MPa, resulting in relatively low activity. The catalysts in Examples 1-4 of the present invention achieve relatively excellent CO2 conversion and light olefin selectivity at a reaction temperature of 300°C.

Claims

1. A method for preparing an Fe-based catalyst for CO2 hydrogenation to produce light olefins, characterized in that: The steps are as follows: (1) mixing potassium bromide and manganese nitrate to obtain a promoter mixture, wherein the mass ratio of Br to Mn in the promoter mixture is (1-2):1; (2) The co-catalyst mixture obtained in step (1) is mixed with NaY molecular sieve and ferric nitrate and then ground. The NaY molecular sieve is Y meso -Na molecular sieve, (3) subjecting the ground product of step (2) to a melt infiltration treatment at a temperature of 60° C. for 48 h; (4) calcining the product after melt infiltration in step (3) under the protection of inert gas to obtain FeMnKBr / Y meso -Na.

2. The preparation method according to claim 1, characterized in that The Y meso -Na molecular sieve is prepared by the following method: Y micro -Na molecular sieve was first treated with ethylenediaminetetraacetic acid EDTA aqueous solution condensation reflux treatment, Y micro -Na and ethylenediaminetetraacetic acid mass ratio is 2.35:1, the concentration of ethylenediaminetetraacetic acid EDTA aqueous solution is 0.04 mol / L, the condensation reflux temperature is 80 ° C, the treatment time is 6 hours, centrifugal drying, and then the obtained solid powder is added to a sodium hydroxide solution and heated with stirring. The mass ratio of the solid powder to sodium hydroxide is 2.22:1, the concentration of the sodium hydroxide solution is 0.4 mol / L, the heating and stirring temperature is 60 ° C, and the treatment time is 0.5 hours.

3. The preparation method according to claim 1, wherein The mass ratio of the co-catalyst mixture, NaY molecular sieve and iron is (2-3):3:(18-19).

4. The preparation method according to claim 1, characterized in that In step (4), the inert gas is nitrogen.

5. The preparation method according to claim 1, characterized in that In step (4), the calcination heating rate is 2°C / min, the temperature is 550°C, and the calcination time is 4h.

6. Use of the Fe-based catalyst obtained by the preparation method according to any one of claims 1 to 5 in catalyzing CO2 hydrogenation to produce light olefins.

7. The use according to claim 6, characterized in that The catalytic temperature is 300℃, the catalytic pressure is 1MPa, and the space velocity is 2160mL·g cat -1 ·h -1 .

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