Transition metal modified iron-based catalyst and application of transition metal modified iron-based catalyst in preparation of low-carbon olefin through carbon dioxide hydrogenation

Abstract

The invention belongs to the technical field of catalyst preparation, and particularly relates to a transition metal modified iron-based catalyst and application thereof in preparation of low-carbon olefin through carbon dioxide hydrogenation. The preparation method comprises the following steps: dissolving transition metal salt and iron salt in water to prepare a mixed solution, then uniformly mixing the mixed solution with a porous material, drying and calcining to obtain a catalyst precursor; and carrying out alkali metal modification on the catalyst precursor, and roasting to obtain the transition metal modified iron-based catalyst. According to the invention, the transition metal is doped into the Fe-based catalyst to improve the performance of the catalyst, the transition metal is introduced into the Fe-based catalyst as an auxiliary agent by using a simple equivalent-volume impregnation method, and for the CO2 hydrogenation reaction, the used raw materials are non-toxic, environment-friendly and low in price, the preparation method is simple, and the catalyst can be used for industrial catalyst production.

Description

Technical Field

[0001] The invention belongs to the technical field of catalyst preparation, and more specifically relates to a transition metal-modified iron-based catalyst and its application in preparing light olefins by hydrogenating carbon dioxide. Background Art

[0002] CO 2 As a raw material, CO can be reduced by hydrogen. 2 Convert to CH 4 However, low-carbon olefins (C 2 ＝ -C 4 ＝ ) is currently mainly produced by the cracking of naphtha. 2 The CO intermediate pathway for hydrogenation to produce low-carbon olefins has been widely accepted. First, CO 2 The reaction of CO and hydrogen on the catalyst surface is carried out through reverse water gas shift (RWGS), and then olefins are selectively generated through carbon chain growth in the FT process. However, the product is uncontrollable after the FT reaction begins, and the product distribution follows the ASF (Anderson-Schulz-Flory) law. Due to the limitation of ASF distribution, C 2 -C 4 The selectivity of olefins and alkanes in the range cannot be higher than 56.7%, so it is necessary to develop a catalyst with high reverse water gas shift activity, flexible operating conditions and low cost, which is still a CO 2 Hydrogenation to produce light olefins is an important research direction.

[0003] The current Fe-based catalysts have good activity, are cheap and easy to obtain, and are widely studied. Moreover, most of the current iron-based catalysts are prepared by coprecipitation, and the reaction process involves secondary hydrogenation of olefins to produce alkanes, which reduces the olefin-alkane ratio. At present, the inhibition of secondary hydrogenation leads to a decrease in olefin selectivity, which is one of the reasons for the high selectivity of by-products in this process. Therefore, there are still key technical difficulties in inhibiting the secondary hydrogenation activity, improving the catalyst olefin selectivity, reducing CO selectivity, and regulating product distribution. It is particularly important to design an efficient iron-based catalyst.

[0004] The Fe-based catalysts reported so far have poor activity stability and cannot maintain a good catalytic effect for a long time. In addition, the internal catalysts are prone to aggregation and sintering during the reaction, which reduces the activity of the catalyst or even deactivates it. Therefore, how to prepare a catalyst that can inhibit the deactivation of the catalyst caused by the aggregation and sintering of the catalyst during the reaction and greatly enhance the stability of the reaction has become a difficult problem that technicians in this field need to solve urgently. Summary of the invention

[0005] The purpose of the present invention is to provide a transition metal-modified iron-based catalyst and its application in the preparation of light olefins by hydrogenation of carbon dioxide. Specifically, based on the isovolumetric impregnation method, the electronic and geometric structures of the catalyst surface are adjusted through the synergistic effect of other elements to prepare a highly efficient catalytic CO 2 A sheet-shaped composite iron-based catalyst for preparing low-carbon olefins by hydrogenation is provided to solve the problems existing in the above-mentioned prior art.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] One of the technical solutions of the present invention is to provide a method for preparing a transition metal-modified iron-based catalyst, the steps comprising:

[0008] Dissolving a transition metal salt and an iron salt in water to prepare a mixed solution, then uniformly mixing the mixed solution with a porous material, drying and calcining to obtain a catalyst precursor;

[0009] The catalyst precursor is modified with an alkali metal and then calcined to obtain the transition metal-modified iron-based catalyst.

[0010] Furthermore, the transition metal salt is nitrate, acetate and chlorate of transition metal.

[0011] Optionally, the transition metal in the transition metal salt includes at least one of Zn, Ni, Cu, Co and Mn.

[0012] Furthermore, the iron salt includes Fe(NO 3 ) 3 and / or FeCl 3 .

[0013] Furthermore, the molar ratio of the transition metal salt to the iron salt is 1:1-5.

[0014] Optionally, the molar ratio of the transition metal salt to the iron salt is 1:1, 1:2, 1:3, 1:4 or 1:5.

[0015] Furthermore, the concentration of the iron salt in the mixed solution is 1-10 mmol / mL.

[0016] Furthermore, the porous material is a carbon-containing high-temperature removable material.

[0017] Optionally, the porous material includes carbon nanotubes and / or carbon nanofibers.

[0018] Furthermore, the porous material also includes water washing and acid washing steps before use.

[0019] Furthermore, the drying is first vacuum drying for 12 hours, and then oven drying for 10 hours at a temperature of 100°C.

[0020] Furthermore, the usage ratio of the iron salt and the porous material is 9-50 mmol: 1-4 g.

[0021] Furthermore, the calcination temperature is not less than 500° C. and the calcination time is not less than 3 hours.

[0022] Optionally, the calcination temperature is 500-800° C. and the calcination time is 3-5 h.

[0023] Furthermore, the alkali metal includes Na, K or Rb.

[0024] Furthermore, the alkali metal modification step includes: using an alkali metal salt solution as a precursor, and adopting an equal volume impregnation method to impregnate the alkali metal into the catalyst precursor.

[0025] Optionally, the alkali metal salt in the alkali metal salt solution is an alkali metal nitrate.

[0026] Furthermore, the amount of alkali metal in the transition metal-modified iron-based catalyst is 1-5% of the total molar amount of iron and transition metal.

[0027] The electron density on the catalyst surface was adjusted by alkali metal impregnation method.

[0028] Furthermore, the calcination temperature is 400-500°C and the calcination time is 4-5h.

[0029] The present invention uses a template method to obtain a sheet-like Fe-based catalyst, wherein transition metals such as Zn, Ni, Cu, Co or Mn are used as structural additives, and Na, K and Rb are alkali metal additives.

[0030] Doping transition metals (such as Zn, Cu, Ni, Co, Mn, etc.) into Fe-based catalysts can improve the performance of the catalyst. Transition metals are introduced into Fe-based catalysts as additives using a simple isovolumetric impregnation method. 2 The hydrogenation reaction uses non-toxic and environmentally friendly raw materials, which are cheap and have a simple preparation method and can be used for industrial catalyst production.

[0031] A second technical solution of the present invention provides a transition metal-modified iron-based catalyst, wherein the transition metal-modified iron-based catalyst is prepared by the above-mentioned preparation method.

[0032] The third technical solution of the present invention is to provide an application of the above-mentioned transition metal-modified iron-based catalyst in the preparation of light olefins by hydrogenation of carbon dioxide.

[0033] The fourth technical solution of the present invention is to provide a method for preparing low-carbon olefins, comprising the steps of: using the above-mentioned transition metal-modified iron-based catalyst to catalyze the hydrogenation reaction of carbon dioxide to prepare the low-carbon olefins.

[0034] The present invention discloses the following technical effects:

[0035] The method for preparing a transition metal-modified iron-based catalyst of the present invention regulates the electron density on the metal surface of the iron-based catalyst to promote CO 2 and CO surface absorption, increasing the CO 2 On the other hand, the reaction process prevents the agglomeration of phase particles and stabilizes Fe 5 C 2 The presence of the phase synergistically accelerates the desorption of olefins on the catalyst surface and inhibits the secondary hydrogenation of olefins, thereby stabilizing the olefin-alkane ratio for a longer time.

[0036] The transition metal-modified iron-based catalyst prepared by the present invention is a flaky porous iron-based catalyst, which can be used to catalyze CO 2 In the reaction of hydrogenation to produce light olefins, the catalytic performance is obvious and remains stable after 80 hours. It has an excellent olefin-alkane ratio and the overall light olefin yield is significantly improved.

[0037] The preparation method of the invention has simple operation steps, saves time, is environmentally friendly, has high reaction stability, and has good economic utilization value. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0039] Figure 1 This is the SEM image of FeZnNa.

[0040] Figure 2 The reaction performance of the catalysts prepared in Examples 1-3 and Comparative Example 1.

[0041] Figure 3 The reaction performance of the catalysts prepared in Example 1 and Examples 4-5. DETAILED DESCRIPTION

[0042] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0043] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0044] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0045] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0046] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0047] The raw materials used in the specific embodiments of the present invention are all commercially available products; unless otherwise specified, "normal temperature" and "room temperature" both refer to 20-30° C.; the parts not described in detail in the preparation method are all conventional processes in the art.

[0048] The porous material (carbon nanotube) used in the specific embodiment of the present invention was washed with water and acid-washed before use. Specifically, an appropriate amount of porous material (3 g) was added to a beaker, 100 mL of dilute hydrochloric acid (conventional dilution) was added, and the mixture was stirred at room temperature for 2 h, filtered, and rinsed with deionized water until the filtrate showed neutral or weak acidity, and then dried in a 100°C oven for 4 h.

[0049] Example 1

[0050] The preparation method of the transition metal modified iron-based catalyst comprises the following steps:

[0051] S1. Weigh 5.52 g of zinc nitrate hexahydrate and 7.5 g of iron nitrate nonahydrate, dissolve in 10 mL of water, stir for 0.5 h to fully dissolve, add dropwise to 4 g of porous material (carbon nanotubes), continue stirring for 1 h, ultrasonicate for 1 h, then vacuum dry (100 ° C) for 12 h, then oven dry (100 ° C) for 10 h, and calcine in a muffle furnace at 3 ° C / min to 500 ° C for 4 h to obtain a catalyst precursor;

[0052] S2. Sodium nitrate is dissolved in water to prepare a sodium nitrate aqueous solution, and then sodium nitrate is impregnated into the catalyst precursor by an equal volume impregnation method. After drying, the catalyst is calcined at 400° C. for 4 h to obtain a transition metal-modified iron-based catalyst, which is denoted as FeZnNa. The SEM image is as follows: Figure 1 As shown;

[0053] The molar amount of Na is 1% of the sum of the molar amounts of Fe and Zn.

[0054] Example 2

[0055] Compared with Example 1, the only difference is that zinc nitrate hexahydrate is replaced by an equimolar amount of nickel acetate tetrahydrate, and the product is recorded as FeNiNa.

[0056] Example 3

[0057] Compared with Example 1, the only difference is that zinc nitrate hexahydrate is replaced by an equimolar amount of copper (II) perchlorate hexahydrate, and the product is recorded as FeCuNa.

[0058] Example 4

[0059] Compared with Example 1, the only difference is that the amount of iron nitrate nonahydrate is adjusted to 15 g, and the product is recorded as Fe2Zn1Na.

[0060] Example 5

[0061] Compared with Example 1, the only difference is that the amount of zinc nitrate hexahydrate is adjusted to 22.5 g, and the product is recorded as Fe3Zn1Na.

[0062] Comparative Example 1

[0063] Compared with Example 1, the only difference is that zinc nitrate hexahydrate is not added, and the product is recorded as FeNa.

[0064] Test example

[0065] The catalysts prepared in Examples 1-3 and Comparative Example 1 were used to catalyze the hydrogenation of carbon dioxide, and characterization analysis and catalytic performance tests were performed. The results are as follows: Figure 2 shown.

[0066] Carbon dioxide is hydrogenated to produce light olefins at a reaction temperature of 320°C, a reaction pressure of 2 MPa, and H 2 / CO 2 =3 (volume ratio), space velocity 8000mL / (g cat h) under the conditions of CO 2 The hydrogenation reaction was carried out for 20 h.

[0067] The catalytic performance was judged based on the carbon dioxide conversion rate.

[0068] Figure 2 The reaction performance of the catalysts prepared in Examples 1-3 and Comparative Example 1 is shown in the figure. It can be seen that the doping of transition metals does improve the iron-based CO 2 The performance of the hydrogenation catalyst mainly improves the CO 2 The conversion rate and stability of the catalyst. At 320℃, 2MPa, the space velocity is 8000mL / (g cat h), the FeZnNa catalyst has the best performance, CO 2 The maximum conversion rate was 35.5%, and the activity remained relatively stable after the reaction time of 80 h.

[0069] The reaction performance of the catalysts prepared in Example 1 and Example 4-5 was analyzed and characterized. The results are as follows: Figure 3 As shown. (Method as above).

[0070] Figure 3 The reaction performance of the catalysts prepared in Example 1 and Example 4-5 is shown in the figure. As can be seen from the figure, the catalysts with different Zn contents have different reaction performances for CO 2 Hydrogenation has different activities. At 320℃, 2MPa, and a space velocity of 8000mL / (g cat h), the performance of Fe2Zn1Na catalyst is the best, CO 2 The maximum conversion rate was 38.1%, and the activity remained more stable after the reaction time of 80 h.

[0071] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0072] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a transition metal-modified iron-based catalyst, characterized in that the steps include: Dissolving a transition metal salt and an iron salt in water to prepare a mixed solution, then uniformly mixing the mixed solution with a porous material, drying and calcining to obtain a catalyst precursor; The catalyst precursor is modified with an alkali metal and then calcined to obtain the transition metal-modified iron-based catalyst.

2. The preparation method according to claim 1, characterized in that The transition metal salt is a nitrate, acetate and chlorate of a transition metal; and / or the iron salt includes Fe(NO3)3 and / or FeCl3; and / or the molar ratio of the transition metal salt to the iron salt is 1:1-5; and / or the concentration of the iron salt in the mixed solution is 1-10mmol / mL; and / or the porous material is a high-temperature removable carbon-containing material; and / or the porous material further includes water washing and acid washing steps before use.

3. The preparation method according to claim 2, characterized in that: The transition metal in the transition metal salt includes at least one of Zn, Ni, Cu, Co and Mn; and / or the porous material includes carbon nanotubes and / or carbon nanofibers.

4. The preparation method according to claim 1, characterized in that: The drying is first vacuum drying for 12 hours and then oven drying for 10 hours at a temperature of 100°C; and / or the usage ratio of the iron salt and the porous material is 9-50mmol:1-4g; and / or the calcination temperature is not less than 500°C and the time is not less than 3 hours.

5. The preparation method according to claim 1, characterized in that: The alkali metal includes Na, K or Rb; and / or, the alkali metal modification step includes: using an alkali metal salt solution as a precursor, and impregnating the alkali metal into the catalyst precursor by an equal volume impregnation method.

6. The preparation method according to claim 5, characterized in that: The alkali metal salt in the alkali metal salt solution is nitrate of alkali metal.

7. The preparation method according to claim 1, characterized in that: The amount of alkali metal in the transition metal-modified iron-based catalyst is 1-5% of the total molar number of iron and transition metal; and / or, the calcination temperature is 400-500° C. and the calcination time is 4-5 hours.

8. A transition metal-modified iron-based catalyst, wherein the transition metal-modified iron-based catalyst is prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the transition metal-modified iron-based catalyst according to claim 8 in the preparation of light olefins by hydrogenation of carbon dioxide.

10. A method for preparing light olefins, characterized in that: The steps include: The light olefins are prepared by catalyzing the hydrogenation reaction of carbon dioxide using the transition metal-modified iron-based catalyst described in claim 8.

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