A method for preparing a sodium-promoted zinc-aluminum spinel-supported iron-based catalyst and its application in the synthesis of olefins.

Abstract

This invention belongs to the field of carbon dioxide hydrogenation catalyst technology, and discloses a method for preparing a sodium-promoted zinc-aluminum spinel-supported iron-based catalyst and its application in olefin synthesis. The catalyst comprises a zinc-aluminum spinel oxide support prepared with a zinc salt to aluminum salt molar ratio of 1:2. The zinc-aluminum spinel oxide, iron salt, and sodium salt are mixed and uniformly blended by physical mixing, followed by calcination at 550℃~600℃ for 2~5h to obtain the sodium-promoted zinc-aluminum spinel-supported iron-based catalyst. This catalyst is used in the carbon dioxide hydrogenation reaction. Optimal catalytic reaction conditions are selected by adjusting different reaction conditions, such as reaction temperature and space velocity. Furthermore, the prepared catalyst exhibits good olefin selectivity and high thermal stability during the carbon dioxide hydrogenation reaction.

Description

Technical Field

[0001] This invention relates to a method for preparing and applying a sodium-promoted zinc-aluminum spinel-supported iron-based catalyst. Background Technology

[0002] The scarcity of fossil fuels and the problem of carbon emissions severely impact human development. The need to develop sustainable clean energy technologies has driven research into CO2 utilization. Light olefins are important precursors for manufacturing plastics, solvents, and paints. Carbon dioxide hydrogenation can effectively solve these problems, producing light olefins. The entire carbon dioxide hydrogenation process involves reverse water-gas reaction (RWGS) and Fischer-Tropsch synthesis (FTS). In iron-based catalysts, Fe3O4 and Fe5C2 are the active phases in these two steps, respectively, thus iron-based catalysts are widely used in carbon dioxide hydrogenation to olefins. Spinel structure is a special crystal structure with a highly ordered arrangement. Spinel catalysts have an octahedral crystal structure, exhibiting high stability and activity. This structure gives spinel catalysts a large surface area and good catalytic performance. In carbon dioxide hydrogenation, spinel-structured nanocatalysts have numerous advantages, including accelerating CO2 bond breaking and enhancing catalytic performance through the formation and stabilization of active sites.

[0003] Currently, there are patent applications for catalysts used in the hydrogenation of carbon dioxide to produce low-carbon olefins, but none specifically using zinc-aluminum spinel as a catalyst for this purpose. However, there are patents for its use in the production of aromatics. The following is a detailed description of a reported patent regarding the use of zinc-aluminum spinel catalysts in the hydrogenation of carbon dioxide to produce aromatics: Chinese patent CN110496639A, entitled "A Catalyst for Aromatics Synthesis and Its Preparation Method and Application," reports the use of zinc-aluminum spinel oxide and an acidic molecular sieve catalyst for the hydrogenation of carbon dioxide to synthesize aromatics. Results show that all catalysts exhibit high selectivity for aromatics, but their CO2 conversion rate is generally low, around 10%. Summary of the Invention

[0004] To address the problems in the background art, this invention prepares a sodium-promoted zinc-aluminum spinel-supported iron-based catalyst. This catalyst exhibits good catalytic performance in the hydrogenation of carbon dioxide to olefins, especially in terms of CO2 conversion rate, and also shows good stability. Therefore, it is expected to be scaled up for industrial application.

[0005] Therefore, one object of the present invention is to provide a catalyst for olefin synthesis, the catalyst comprising a zinc-aluminum spinel support in a molar ratio of 1:2, iron as the active phase on the surface, and sodium as an auxiliary agent.

[0006] Another object of the present invention is to provide a method for preparing the above-described catalyst.

[0007] Another object of the present invention is to provide a method for producing olefins by hydrogenation of carbon dioxide using the above-mentioned catalyst, and to explore the optimal reaction conditions thereunder.

[0008] The specific preparation method is as follows:

[0009] Zinc-aluminum spinel: A mixed metal salt aqueous solution is prepared by mixing zinc salt and aluminum salt; the mixed metal salt aqueous solution is contacted with a precipitant aqueous solution until a fixed pH value of 10 is reached, so that the metal ions in the mixed metal salt aqueous solution are co-precipitated; the mixture is stirred until complete precipitation; the precipitate is washed, dried and calcined to obtain the zinc-aluminum spinel oxide;

[0010] Furthermore, the zinc salt is selected from one or more of zinc acetate, zinc sulfate, and zinc nitrate; the aluminum salt is selected from one or more of aluminum acetate, aluminum sulfate, aluminum nitrate, and aluminum isopropoxide.

[0011] The precipitant is selected from one or more of sodium carbonate, potassium carbonate, ammonium carbonate, sodium bicarbonate, potassium bicarbonate, ammonium bicarbonate, ammonia, sodium hydroxide, and potassium hydroxide.

[0012] Furthermore, zinc-aluminum spinel supports were prepared by using a zinc salt to aluminum salt molar ratio of 1:2;

[0013] The coprecipitation is carried out at 40℃ to 80℃; the carrier is calcined at 600℃ to 900℃.

[0014] Sodium-enhanced zinc-aluminum spinel supported iron-based catalyst: Iron and sodium elements are loaded onto the catalyst via a physical mixing method, followed by calcination.

[0015] Sodium-promoted zinc-aluminum spinel supported iron-based catalyst: Zinc-aluminum spinel oxide, iron salt and sodium salt are mixed and uniformly mixed by physical mixing, and then calcined at 550℃~600℃ for 2~5h to obtain the catalyst.

[0016] Furthermore, the mass ratio of iron salt to zinc-aluminum spinel carrier is 1:1 to 1.5, and the molar ratio of iron to sodium is 7:1.5 to 1.8.

[0017] This invention provides an application of sodium-promoted zinc-aluminum spinel-supported iron-based catalyst material in chemical catalysis, specifically for the production of high-value chemicals, particularly olefins, through the reaction of carbon dioxide and hydrogen under high temperature and pressure.

[0018] It is used as a catalyst in the hydrogenation reaction of carbon dioxide. The catalyst is loaded into a catalytic reactor, and hydrogen is first pretreated for reduction for 18 hours. Then, a mixture of H2 and CO2 in a ratio of 2:1 to 4:1 is introduced. Hydrogenation to olefins is carried out under the conditions of temperature 280 to 380℃, pressure 2.4 to 2.6 MPa, and space velocity 1400 to 3000 ml / (g*h) for 75 hours.

[0019] This invention provides a sodium-promoted zinc-aluminum spinel-supported iron-based catalyst for the carbon dioxide hydrogenation reaction under the above-mentioned reaction conditions. Finally, comparisons were made to select the optimal reaction conditions. The optimal reaction conditions are: reaction temperature 360℃, reaction pressure 2.5MPa, and space velocity 2600ml / (g*h).

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: the zinc-aluminum spinel support in the catalyst of the present invention is simple to prepare and has low raw material cost. The present invention is the first to use it in the hydrogenation of carbon dioxide to olefins. The iron on the surface as the active phase and the sodium as the promoter show excellent catalytic performance in the reaction, especially in terms of CO2 conversion rate, and at the same time, it shows good reaction catalytic stability. Attached Figure Description

[0021] Figure 1 XRD patterns of the catalyst supports in Examples 1-10 and Comparative Examples 1-4;

[0022] Figure 2 The XRD patterns are of the catalysts after loading in Examples 1-10 and Comparative Examples 1-4.

[0023] Figure 3 The graph shows the change of CO2 conversion rate over time in the catalytic reaction of Examples 9 and Comparative Examples 1-4. Detailed Implementation

[0024] Example 1

[0025] Zinc-aluminum spinel: 3.86g Zn(NO3)2·6H2O, 9.75g Al(NO3)3·9H2O, and 150ml deionized water were mixed to prepare a mixed metal salt aqueous solution; 5.6g NaOH was dissolved in 100ml deionized water to form a precipitant solution, and the precipitant solution was added dropwise to the metal salt aqueous solution. The precipitation reaction temperature was controlled at 60℃ until a fixed pH value of 10 was reached, so that the metal ions in the mixed metal salt aqueous solution were co-precipitated; the mixture was stirred until complete precipitation; the precipitate was washed 5 times with deionized water, dried overnight at 70℃, and calcined at 700℃ for 4h to obtain the zinc-aluminum spinel oxide;

[0026] Sodium-promoted zinc-aluminum spinel supported iron-based catalyst: 0.59 g zinc-aluminum spinel oxide, 0.81 g Fe(NO3)3·9H2O and 0.04 g NaNO3 were mixed and uniformly mixed by physical mixing, and then calcined at 550 °C for 4 h to obtain the catalyst.

[0027] The catalyst was loaded into the reaction tube and subjected to carbon dioxide hydrogenation on a high-pressure catalytic evaluation system. First, hydrogen reduction was pretreated for 18 hours, then a mixture of H2 and CO2 in a volume ratio of 3:1 was introduced. Hydrogenation to olefins was carried out at a reaction temperature of 280℃, a pressure of 2.5 MPa, and a space velocity of 1800 ml / (g*h) for 75 hours. The catalytic performance is shown in Table 1.

[0028] Example 2

[0029] The catalyst preparation was the same as in Example 1; the difference in application was that the carbon dioxide hydrogenation reaction conditions were 300℃, 2.5MPa, and space velocity 1800ml / (g*h). The catalytic performance is shown in Table 1.

[0030] Example 3

[0031] The catalyst preparation was the same as in Example 1, but the application differed in that the carbon dioxide hydrogenation reaction conditions were 320°C, 2.5 MPa, and a space velocity of 1800 ml / (g*h). The catalytic performance is shown in Table 1.

[0032] Example 4

[0033] The catalyst preparation was the same as in Example 1, but the application differed in that the carbon dioxide hydrogenation reaction conditions were 340℃, 2.5MPa, and space velocity 1800ml / (g*h). The catalytic performance is shown in Table 1.

[0034] Example 5

[0035] The catalyst preparation was the same as in Example 1, but the application differed in that the carbon dioxide hydrogenation reaction conditions were 360°C, 2.5 MPa, and a space velocity of 1800 ml / (g*h). The catalytic performance is shown in Table 1.

[0036] Example 6

[0037] The catalyst preparation was the same as in Example 1, but the application differed in that the carbon dioxide hydrogenation reaction conditions were 380℃, 2.5MPa, and space velocity 1800ml / (g*h). The catalytic performance is shown in Table 1.

[0038] From the catalytic results of Examples 1-6, it can be seen that the higher the reaction temperature, the higher the CO2 conversion rate, the lower the CO selectivity, but the higher the CH4 selectivity; when the reaction temperature increases from 280℃ to 300℃, C2＝ -C4 ＝ Selectivity increases as the reaction temperature further increases, C2 ＝ -C4 ＝ Selectivity begins to decrease. While the O / P ratio increases when the reaction temperature rises from 280℃ to 320℃, it begins to decrease again as the reaction temperature further increases. Overall, although the C2O / P ratio increases after the reaction temperature reaches 300℃... ＝ -C4 ＝ Selectivity began to decrease, but the STY value was the highest at 360°C, thus confirming that 360°C was the optimal reaction temperature. Next, the reaction temperature was kept constant at 360°C, and different space velocities were changed to study the optimal reaction space velocity.

[0039] Example 7

[0040] The catalyst preparation was the same as in Example 1, except that the carbon dioxide hydrogenation reaction conditions were 360°C, 2.5 MPa, and space velocity 1400 ml / (g*h). The catalytic performance is shown in Table 1.

[0041] Example 8

[0042] The catalyst preparation was the same as in Example 1, except that the carbon dioxide hydrogenation reaction conditions were 360°C, 2.5 MPa, and space velocity 2200 ml / (g*h). The catalytic performance is shown in Table 1.

[0043] Example 9

[0044] The catalyst preparation was the same as in Example 1, except that the carbon dioxide hydrogenation reaction conditions were 360°C, 2.5 MPa, and space velocity 2600 ml / (g*h). The catalytic performance is shown in Table 1.

[0045] Example 10

[0046] The catalyst preparation was the same as in Example 1, except that the carbon dioxide hydrogenation reaction conditions were 360°C, 2.5 MPa, and space velocity 3000 ml / (g*h). The catalytic performance is shown in Table 1.

[0047] From the catalytic results of Examples 7-10, it can be seen that as the space velocity increases, the CO2 conversion rate decreases, the CO selectivity increases, and the methane content remains basically unchanged; when the reaction space velocity increases from 1400 ml / (g*h) to 1800 ml / (g*h), C2 ＝ -C4 ＝ Selective increase, as airspeed further increases, C2 ＝ -C4 ＝Selectivity decreased slightly. While the O / P ratio increased when the reaction space velocity increased from 1400 ml / (g*h) to 2200 ml / (g*h), the O / P ratio showed a decreasing trend with further increases in space velocity, though this was not significant. Overall, although the C2 ratio decreased after the reaction space velocity reached 1800 ml / (g*h), the selectivity remained relatively stable. ＝ -C4 ＝ Selectivity began to decrease, but STY was highest at a reaction space velocity of 2600 ml / (g*h), thus establishing 2600 ml / (g*h) as the optimal reaction space velocity. Combining the catalytic results from Examples 1-6, the optimal reaction conditions were a temperature of 360°C, a pressure of 2.5 MPa, and a space velocity of 2600 ml / (g*h).

[0048] Comparative Example 1

[0049] The catalyst preparation differs from that in Example 1, except that the calcination temperature of the support is changed to 800°C, while the rest is the same as in Example 1.

[0050] The carbon dioxide hydrogenation reaction was carried out under the same conditions as in Example 9, namely, a temperature of 360°C, a pressure of 2.5 MPa, and a space velocity of 2600 ml / (g*h). The catalytic performance is shown in Table 1.

[0051] Comparative Example 2

[0052] The catalyst preparation differed from that in Example 1, except that the support calcination temperature was changed to 900°C. The carbon dioxide hydrogenation reaction was the same as in Example 9. The catalytic performance is shown in Table 1.

[0053] Comparative Example 3

[0054] The catalyst preparation differed from that in Example 1, except that the calcination temperature of the support was changed to 600°C. The carbon dioxide hydrogenation reaction was the same as in Example 9, and the catalytic performance is shown in Table 1.

[0055] Comparative Example 4

[0056] The catalyst preparation method is different from that in Example 1.

[0057] Zinc-aluminum spinel: 1.49g Zn(NO3)2·6H2O and 3.75g Al(NO3)3·9H2O were uniformly mixed by mechanical synthesis, and the resulting mixture was calcined at 700℃ for 4h to obtain the zinc-aluminum spinel oxide.

[0058] Sodium-promoted zinc-aluminum spinel-supported iron-based catalyst: 0.59 g of zinc-aluminum spinel oxide, 0.81 g of Fe(NO3)3·9H2O, and 0.04 g of NaNO3 were mixed uniformly by physical mixing, followed by calcination at 550 °C for 4 h. The carbon dioxide hydrogenation reaction conditions were 360 ​​°C, 2.5 MPa, and space velocity 2600 ml / (g*h). The catalytic performance is shown in Table 1.

[0059] Under the same reaction conditions—temperature 360°C, pressure 2.5 MPa, and space velocity 2600 ml / (g*h)—for 75 h, Example 9 exhibited the highest olefin selectivity and STY compared to Comparative Examples 1-4. Notably, the CO2 conversion rates of all samples in this invention were above 20%, higher than the CO2 conversion rates exhibited by all samples in Chinese Patent CN110496639A.

[0060] Table 1 Catalytic performance of Examples 1-10 and Comparative Examples 1-4

[0061]

[0062] X-ray powder diffraction (XRD) experiments were performed on the catalysts of all embodiments, and the results are as follows: Figure 1 and 2 As shown.

[0063] The catalysts of Example 9 and Comparative Examples 1-4 were subjected to stability tests under the carbon dioxide hydrogenation reaction conditions of Example 9: The results are as follows. Figure 3 As shown in the figure, experimental verification revealed a good catalytic effect and good thermal stability. Even after a relatively long time (75h), it still maintained good catalytic activity, showing great potential application in the field of carbon dioxide hydrogenation.

Claims

1. A method for preparing a sodium-promoted zinc-aluminum spinel-supported iron-based catalyst, characterized in that: (1) Prepare a mixed metal salt aqueous solution by mixing zinc salt and aluminum salt; contact the mixed metal salt aqueous solution with the precipitant aqueous solution until a fixed pH value of 10 is reached, so that the metal ions in the mixed metal salt aqueous solution are co-precipitated; The mixture was heated and stirred until complete precipitation was achieved; the precipitate was washed, dried, and then calcined to obtain a zinc-aluminum spinel oxide support; the molar ratio of zinc salt to aluminum salt was 1:

2. (2) Iron salt, sodium salt and zinc aluminum spinel oxide support are mixed by physical mixing method and calcined to obtain sodium-promoted zinc aluminum spinel supported iron-based catalyst; the mass ratio of iron salt to support is 1:1~1.5; the molar ratio of iron salt to sodium salt is 7:1.5~1.

8.

2. The method for preparing the sodium-promoted zinc-aluminum spinel-supported iron-based catalyst according to claim 1, characterized in that: The zinc salt is selected from one or more of zinc acetate, zinc sulfate, and zinc nitrate; the aluminum salt is selected from one or more of aluminum acetate, aluminum sulfate, aluminum nitrate, and aluminum isopropoxide; the precipitant is selected from one or more of sodium carbonate, potassium carbonate, ammonium carbonate, sodium bicarbonate, potassium bicarbonate, ammonium bicarbonate, ammonia, sodium hydroxide, and potassium hydroxide.

3. The method for preparing the sodium-promoted zinc-aluminum spinel-supported iron-based catalyst according to claim 1, characterized in that: Coprecipitation was carried out at 40℃~80℃.

4. The method for preparing the sodium-promoted zinc-aluminum spinel-supported iron-based catalyst according to claim 1, characterized in that: Step (1) The calcination temperature is 600℃~900℃.

5. The method for preparing the sodium-promoted zinc-aluminum spinel-supported iron-based catalyst according to claim 1, characterized in that: Step (2) The calcination temperature is 550℃~600℃.

6. A method for producing olefins by hydrogenation of carbon dioxide, characterized in that: The sodium-promoted zinc-aluminum spinel-supported iron-based catalyst prepared by any one of claims 1-5 is loaded into a catalytic reactor. After hydrogen reduction, a mixture of H2 and CO2 with a volume ratio of 2:1 to 4:1 is introduced, and hydrogenation to olefins is carried out under the conditions of reaction temperature of 280 to 380°C, pressure of 2.4 to 2.6 MPa, and space velocity of 1400 to 3000 ml / (g*h).

7. The method for producing olefins by hydrogenation of carbon dioxide according to claim 6, characterized in that: The reaction temperature was 360℃, the reaction pressure was 2.5MPa, and the space velocity was 2600ml / (g*h).

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