A cerium-embedded zinc-iron spinel structure oxide catalyst, a preparation method and application thereof

Abstract

The application relates to the technical field of catalyst materials, and discloses an oxide catalyst with cerium embedded in a zinc-iron spinel structure, a preparation method and application thereof. The preparation method comprises the following steps: dissolving iron salt, zinc salt and cerium salt in deionized water, and slowly adding an ammonium hydroxide solution; after stirring, a precipitate is formed, the solution is subjected to hydrothermal treatment, washing and drying to obtain a catalyst precursor; finally, sodium is loaded onto the prepared catalyst by an impregnation method, and the catalyst is calcined to obtain a zinc-iron spinel catalyst with cerium embedded therein. The catalyst prepared by the application has rich active sites, can promote the adsorption and activation of reaction gas, has high thermal stability, and finally exhibits excellent catalytic performance. The preparation method is simple, low in cost, and can be widely applied, and the final purpose is to efficiently and stably prepare light olefins and other high-value chemicals.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalyst materials, in particular to an oxide catalyst with cerium embedded in a zinc-iron spinel structure and a preparation method and application thereof. BACKGROUND

[0002] At present, global energy shortage and environmental problems are becoming increasingly serious. Therefore, it is urgent to find a series of clean, sustainable and alternative green energy. Carbon dioxide hydrogenation is a clean energy conversion technology that can convert coal, biomass and synthetic gas (a mixture of H2 and CO2) in the atmosphere into high-value carbon hydrocarbon chemicals and liquid oils, such as olefins, gasoline and diesel. However, catalysts are needed as intermediates to direct the regulation of products in the synthesis of these products.

[0003] Traditional iron-based catalysts are widely used in carbon dioxide hydrogenation catalysis due to their simple production and rich products. However, traditional iron-based catalysts also have a series of problems, such as insufficient catalytic performance and large reaction particles. Through improvement, spinel oxide catalysts have emerged, but ordinary spinel oxides are difficult to catalyze reactions under relatively mild conditions and have the problem of few active sites, and the selectivity of the final olefin products is still unsatisfactory. At present, some modified zinc-iron catalysts have been used for the synthesis of low-carbon olefins from CO2, but there are more or less some problems such as harsh reaction conditions and low target products. Therefore, it is crucial to develop a catalyst with high activity, high selectivity and mild reaction conditions for the process of carbon dioxide hydrogenation to light olefins. SUMMARY

[0004] The technical problem to be solved by the present application is to overcome the deficiencies in the prior art and provide an oxide catalyst with cerium embedded in a zinc-iron spinel structure and a preparation method and application thereof. The present application forms a single-phase stable spinel catalyst by solid-solution of multiple different metal components, thereby improving the catalytic activity of the catalyst. The embedding of cerium replaces the position of iron in the lattice to form new active sites, and on the other hand, forms cerium dioxide on its surface to promote the conversion and dissociation of CO2, thereby obtaining a catalyst material for CO2 hydrogenation to light olefins with high activity, selectivity and simple production under relatively mild conditions.

[0005] The technical scheme adopted by the present application to solve its technical problem is:

[0006] A preparation method of an oxide catalyst with cerium embedded in a zinc-iron spinel structure, specifically comprising the following steps:

[0007] Step S1, dissolve iron salt, zinc salt and cerium salt in deionized water, slowly add 28% NH4OH solution and stir uniformly to obtain a mixed solution; the mixed solution is subjected to hydrothermal reaction; the hydrothermal reaction conditions are 120-180℃;

[0008] Step S2, after the hydrothermal reaction is cooled to room temperature, the solution after the reaction is collected, centrifuged and washed, and then placed in an oven for drying, the drying temperature is 60-100℃, and the drying is maintained for 10-14h, to obtain a metal composite material;

[0009] Step S3, the dried metal composite material is loaded with a sodium salt by an impregnation method;

[0010] Step S4, placed in a tubular furnace and calcined under argon, the calcination temperature is 300-500℃, and the calcination is maintained for 2-5h, to obtain a finished product of a cerium-embedded zinc-iron spinel structure oxide catalyst.

[0011] Further, in the step S1, the iron salt is one or more of ferric chloride trihydrate, anhydrous ferric chloride, ferric nitrate nonahydrate, and ferric sulfate pentahydrate; the zinc salt is one or more of zinc chloride tetrahydrate, zinc nitrate hexahydrate, and zinc sulfate heptahydrate; and the cerium salt is one or more of cerium nitrate hexahydrate and cerium chloride hexahydrate.

[0012] Further, in the step S1, the molar ratio of the iron salt, the zinc salt, and the cerium salt is (1.95-1.99):1:(0.01-0.05).

[0013] Further, in the step S1, the reaction temperature of the hydrothermal reaction is 180℃, and the reaction time is 24h.

[0014] Further, in the step S2, the drying temperature is 80℃, and the drying is maintained for 12h.

[0015] Further, in the step S3, the loading amount of the sodium salt is 1%.

[0016] Further, in the step S4, the calcination temperature is 400℃, and the calcination is maintained for 3h.

[0017] A cerium-embedded zinc-iron spinel structure oxide catalyst is prepared by the preparation method of any one of claims 1-7.

[0018] An application of the above-mentioned cerium-embedded zinc-iron spinel structure oxide catalyst, wherein the cerium-embedded zinc-iron spinel structure oxide catalyst is applied in carbon dioxide hydrogenation catalysis.

[0019] Further, the application is specifically: a cerium-embedded zinc-iron spinel structure oxide catalyst is reduced by H2, and then loaded into a fixed fluidized bed, a mixed gas composed of CO2 and H2 is introduced, and the hydrogenation reaction is carried out under the conditions of a temperature of 290℃ and a pressure of 2MPa, wherein the molar ratio of CO2 to H2 is 1:3.

[0020] The present application has the advantages of reasonable design, simple preparation method and the following advantages.

[0021] (1) The zinc-iron spinel structure oxide catalyst prepared by the present application is prepared by a precipitation-hydrothermal method, which is simple in production and preparation, and the raw materials are cheap, thus being conducive to industrialized production; meanwhile, the content of embedded cerium can be regulated to regulate the physical and chemical properties of the catalyst; on one hand, the embedded cerium can greatly improve the adsorption and activation capacity of the catalytic material to the reaction gas, and accelerate the reaction process; on the other hand, the rich active sites improve the carburizing capacity of the catalytic material, and improve the O / P ratio, which is beneficial to the synthesis of the target product.

[0022] (2) The cerium-embedded zinc-iron spinel structure oxide catalyst prepared by the present application shows excellent catalytic activity under relatively mild conditions, and the CO2 conversion rate, olefin selectivity and space-time yield are all excellent, which can provide extensive prospects for subsequent industrial application and olefin production. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings needed to be used in the description of the specific embodiments or the prior art. Obviously, the drawings described below are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0024] Figure 1 is the X-ray powder diffraction (XRD) pattern of the catalyst after reaction in Example 1 to Example 3, Comparative Example 1 to Comparative Example 2;

[0025] Figure 2 is the X-ray powder diffraction (XRD) pattern of the fresh catalyst in Example 1 to Example 3, Comparative Example 1 to Comparative Example 2;

[0026] Figure 3 is the morphology diagram (TEM) of the fresh catalyst in Example 1;

[0027] Figure 4 is the N2 adsorption-desorption isotherm of the catalyst in Example 1 to Example 3, Comparative Example 1 to Comparative Example 2;

[0028] Figure 5 is the CO2 conversion rate-time change graph of the catalyst in Example 1 to Example 3, Comparative Example 1 to Comparative Example 2. DETAILED DESCRIPTION

[0029] It should be noted that the following detailed description is illustrative only, and is intended to provide further description in order to provide a thorough understanding of the exemplary embodiments according to the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the exemplary embodiments according to the present application belong.

[0030] It is also important to note that the term "or" as used herein is intended to mean an inclusive "or," such that "A or B" means any or all of the items listed with no options of "and / or." Unless otherwise indicated, the use of relational terms, if any, such as "first," "second," and the like, are used solely to distinguish one from another entity or action without necessarily implying a physical or chronological precedence or relation.

[0031] The technical solutions of the present application will be described clearly and completely below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0032] A method for preparing a cerium-embedded zinc-iron spinel structure oxide catalyst, specifically comprising the following steps:

[0033] A. Dissolve different three kinds of metal salt solutions in deionized water, stir for 10 minutes, then slowly add 28% NH4OH solution, continue to stir for 1 h to obtain a brown precipitated solution;

[0034] B. Put the above metal precursor solution into a reaction kettle, heat to 120-180℃ and keep for 24 h;

[0035] C. After the reaction is completed, the reaction kettle is completely cooled, the solution is washed with deionized water and anhydrous ethanol by centrifugation for 3 times, and the sample with surface solvent removed is collected and placed in a culture dish;

[0036] D. The sample in the culture dish is placed in an oven for drying, the temperature is 60-80℃, and the keeping time is 10-14 h;

[0037] E. The sample is taken out from the reaction dish, 200 ml deionized water is added and stirred, and then NaNO3 aqueous solution is added dropwise;

[0038] F. The sample after step completion is placed in an oven for drying, the temperature is 80℃, and the keeping time is 12 h;

[0039] G. Put into a tubular furnace with argon gas, calcine at a temperature of 300-500℃ for 2-5 h at a rate of 5℃ / min, and finally obtain the finished product of cerium-embedded zinc-iron spinel.

[0040] Further, the molar ratio of the iron salt, zinc salt, and cerium salt is 1.95-1.99:1:0.01-0.05.

[0041] The application provides the oxide catalyst with the zinc-iron spinel structure embedded with cerium, which is prepared by the method.

[0042] The application provides the application of the oxide catalyst with the zinc-iron spinel structure embedded with cerium in chemical catalysis, and specifically, the oxide catalyst is used for catalyzing carbon dioxide and hydrogen to obtain high-value chemicals, such as light olefins, under relatively mild conditions.

[0043] Specific application is that the oxide catalyst is used as a catalyst in a carbon dioxide hydrogenation reaction, first reduction is performed at a temperature of 400 DEG C, a pressure of 0.4 MPa, and a space velocity of 2500 ml / (g*h) for 18 h. After the reduction is completed, the catalyst is loaded into a reactor, a CO2 / H2 mixed gas with a molar ratio of 1:3 is introduced, and hydrogenation is performed at a temperature of 290 DEG C, a pressure of 2 MPa, and a space velocity of 2500 ml / (g*h) to prepare olefins, and the reaction time is 70 h.

[0044] Example 1

[0045] The application provides a preparation method of the oxide catalyst with the zinc-iron spinel structure embedded with cerium.

[0046] A, Fe(NO3)3.9H2O (8.03g), Ce(NO3)3.6H2O (0.04g), and Zn(NO3)2.6H2O (2.97g) are dissolved in 60ml of deionized water (wherein the molar ratio of Fe:Zn:Ce is 1.99:1:0.01);after stirring for 10 minutes, 9ml of 28% NH4OH solution is slowly added, and stirring is continued for 1h;

[0047] B, the above metal precursor solution is placed into a reaction kettle, and kept at 180 DEG C for 24h;

[0048] C, after the reaction is completed, the reaction kettle is completely cooled, the solution is centrifuged and washed with deionized water and anhydrous ethanol for three times, and the sample after removal of surface solvent is collected and placed into a culture dish;

[0049] D, the sample in the culture dish is placed into an oven for drying, the temperature is 100 DEG C, and the drying is kept for 12h;

[0050] E, the sample is taken out from the reaction dish, 1.8g is added into 200ml of deionized water for stirring, and then 0.07g of NaNO3 is added dropwise;

[0051] F, the sample after the step E is placed into an oven for drying, the temperature is 100 DEG C, and the drying is kept for 12h.

[0052] G, put into a tubular furnace with argon, calcination temperature is 400℃, keep 4h, rate 5℃ / min. Finally get catalyst material Ce1ZFO.

[0053] The experimental operation steps of the catalytic evaluation system are as follows: first, a certain amount of catalyst material and quartz sand are weighed and mixed uniformly, then the reaction tube in the high-pressure catalytic evaluation system is disassembled, and a small amount of quartz wool and quartz sand are put into it from top to bottom, and the catalyst is put in when the height of the quartz sand reaches half of the height, then the quartz sand is put in until the top of the reaction tube, and finally a small amount of quartz sand is filled at the top. Tighten the screws at each position, and reconnect to the high-pressure catalytic evaluation system. Under the premise that the entire system is not leaking, first reduce the above catalyst by hydrogen, specifically: first reduce by H2, reduction conditions 0.4 MPa pressure, temperature 400℃, space velocity 2500 ml / (g*h), for 18h, and after reduction, it is used for subsequent catalytic reaction. After reduction, the catalyst is loaded into the reactor, and a mixture of CO2 / H2 with a molar ratio of 1:3 is introduced, and under the conditions of temperature 290℃, pressure 2 MPa, space velocity 2500 ml / (g*h), the hydrogenation of olefins is carried out, and the reaction time is 70h.

[0054] After calculating the average data in 70h, the CO2 conversion rate of the catalyst is 38.1%, the CH4 selectivity is 16.7%, the C2 ＝ -C4 ＝ selectivity is 46.5%, and the C5 + selectivity is 28.6%.

[0055] Example 2

[0056] The difference between this example and Example 1 is that in this example, step A is: A, Fe(NO3)3·9H2O (7.95g), Ce(NO3)3·6H2O (0.12g), Zn(NO3)2·6H2O (2.97g) is dissolved in 60ml deionized water (molar ratio of Fe:Zn:Ce is 1.97:1:0.3); after stirring for 10 minutes, slowly add 9ml of 28% NH4OH solution, continue stirring for 1h.

[0057] This example finally gets catalyst material Ce3ZFO.

[0058] The catalytic reaction process is the same as Example 1, and after calculating the average data in 70h, the CO2 conversion rate of the catalyst is 32.8%, the CH4 selectivity is 23.5%, the C2 ＝ -C4 ＝ selectivity is 40.8%, and the C5 + selectivity is 26%.

[0059] Example 3

[0060] The difference between this example and Example 1 is that in this example, step A is: A, Fe(N03)3*9H20 (7.87 g), Ce(N03)3*6H20 (0.2 g), Zn(N03)2*6H20 (2.97 g) are dissolved in 60 ml of deionized water (wherein the molar ratio of Fe:Zn:Ce is 1.95:1:0.5); after stirring for 10 minutes, 9 ml of 28% NH4OH solution is slowly added, and stirring is continued for 1 h.

[0061] The final catalyst material obtained in this example is Ce5ZFO.

[0062] The catalytic reaction process is the same as in Example 1. After calculating the average data within 70 h, the CO2 conversion rate of the catalyst is 31.6%, the CH4 selectivity is 26.9%, the C2 ＝ -C4 ＝ selectivity is 39%, and the C5 + selectivity is 24.2%.

[0063] Comparative Example 1

[0064] The difference between this example and Example 1 is that in this example, step A is: A, Fe(N03)3*9H20 (7.87 g), Ce(N03)3*6H20 (0.2 g), Zn(N03)2*6H20 (2.97 g) are dissolved in 60 ml of deionized water (wherein the molar ratio of Fe:Zn:Ce is 1.95:1:0.5); after stirring for 10 minutes, 9 ml of 28% NH4OH solution is slowly added, and stirring is continued for 1 h.

[0065] A, Fe(N03)3*9H20 (8.08 g), Zn(N03)2*6H20 (2.96 g) are dissolved in 60 ml of deionized water (wherein the molar ratio of Fe:Zn is 2:1); after stirring for 10 minutes, 9 ml of 28% NH4OH solution is slowly added, and stirring is continued for 1 h.

[0066] The final catalyst material obtained in this example is ZnFe2O4.

[0067] The catalytic reaction process is the same as in Example 1. After calculating the average data within 70 h, the CO2 conversion rate of the catalyst is 31.6%, the CH4 selectivity is 26.9%, the C2 ＝ -C4 ＝ selectivity is 39.8%, and the C5 + selectivity is 26.9%.

[0068] Comparative Example 2

[0069] The difference between this example and Example 1 is that in this example, step A is: A, Fe(N03)3*9H20 (7.87 g), Ce(N03)3*6H20 (0.2 g), Zn(N03)2*6H20 (2.97 g) are dissolved in 60 ml of deionized water (wherein the molar ratio of Fe:Zn:Ce is 1.95:1:0.5); after stirring for 10 minutes, 9 ml of 28% NH4OH solution is slowly added, and stirring is continued for 1 h.

[0070] A, Fe(NO3)3.9H2O (8.08 g), Zn(NO3)2.6H2O (2.97 g), Ce(NO3)3.6H2O (0.04 g) were dissolved in 60 ml deionized water (molar ratio of Fe:Zn:Ce was 2:1:0.01); after stirring for 10 minutes, 9 ml of 28% NH4OH solution was slowly added, and stirring was continued for 1 h.

[0071] The comparative example finally obtained a catalyst material Ce1@ZFO.

[0072] The catalytic reaction process was the same as that of Example 1, and after calculating the average data within 70 h, the CO2 conversion rate of the catalyst was 28.6%, the CH4 selectivity was 24.9%, the C2 ＝ -C4 ＝ selectivity was 39.4%, and the C5 + selectivity was 14.4%.

[0073] The catalysts prepared in Examples 1-3 and Comparative Examples 1-2 were tested for catalytic performance, and the test results are shown in Table 1.

[0074] Table 1: Catalytic performance of Examples 1-3 and Comparative Examples 1-3

[0075]

[0076] Table 1 shows the average performance of the catalysts within 70 h at different calcination temperatures. The CO2 conversion rate of Ce1ZFO of the present application reached 38.1%, the carbon monoxide selectivity was only 11.8%, the CH4 selectivity was 16.7%, and the selectivity of C2 ＝ -C4 ＝ was 46.5%.

[0077] Comparing Example 1, Example 2 and Example 3, it can be seen that as the embedded Ce content increases, the CO2 conversion rate decreases from 38.1% to 31.6%, the CH4 selectivity increases from 16.7% to 26.9%, and at the same time, the selectivity of C2 ＝ -C4 ＝ decreases from 46.5% to 39%. The results show that the increase of Ce content is not conducive to the conversion of CO2, thereby inhibiting C-C coupling and forming a large amount of methane. In combination Figure 1 with Table 1, Examples 1-3, it can be seen that the embedding of a small amount of Ce in ZFO is more conducive to the formation of Fe5C2, thereby improving the carburizing ability and promoting C-C coupling to form light olefins. At the same time, as Figure 2As shown, the main phase of the five samples is ZnFe2O4, and no other impurities are found, indicating that the embedded Ce is well integrated into ZnFe2O4, which is conducive to maintaining the stability of the crystal. By observing the TEM picture of Ce1ZFO Figure 3 , it can be seen that Ce1ZFO is composed of uniformly dispersed small particles, and the particle size is between 11-14 nm, which indicates that it has abundant active sites and catalytic activity. In addition, as shown in Figure 4 , the embedding of Ce does not affect the stable structure of the single-phase spinel, and still shows a mesoporous structure, which promotes the adsorption of gas. Through performance data analysis, it is found that the regulation of the content of Ce is crucial for the preparation of light olefins by carbon dioxide hydrogenation. A small amount of Ce can greatly improve the yield of olefins. Similarly, by adding 1% Ce, there is a significant difference between Ce1ZFO in Example 1 and Ce1@ZFO in Comparative Example 2, the CO2 conversion rate decreases from 38.1% to 28.6%, and the O / P decreases from 5.6 to 4.4. As shown in Figure 5 , the five catalysts are continuously reacted for 70h, and no obvious downward trend is found. It shows that it has high thermal stability and anti-inactivation ability. Combining the above advantages, Ce1ZFO has the best catalytic activity and excellent olefin selectivity.

[0078] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. Use of a cerium-embedded zinc-iron spinel-structured oxide catalyst in the catalysis of carbon dioxide hydrogenation, characterized in that: The preparation method of the cerium-embedded zinc-iron spinel structure oxide catalyst specifically comprises the following steps: Step S1, dissolving iron salt, zinc salt and cerium salt in deionized water, slowly adding 28% NH4OH solution and stirring uniformly to obtain a mixed solution; the mixed solution is subjected to hydrothermal reaction; the hydrothermal reaction condition is 120-180°C; Step S2, after the hydrothermal reaction is completed and cooled to room temperature, the reacted solution is collected, centrifuged and washed, and then placed in an oven for drying; the drying temperature is 60-100°C, and the drying is maintained for 10-14h to obtain a metal composite material; Step S3, loading sodium salt on the dried metal composite material by impregnation method; Step S4, placing in a tubular furnace and calcining under argon condition; the calcining temperature is 300-500°C, and the calcining is maintained for 2-5h; the finished product cerium-embedded zinc-iron spinel structure oxide catalyst is obtained after calcining; In the step S1, the molar ratio of the iron salt, the zinc salt and the cerium salt is (1.95-1.99):1:(0.01-0.05).

2. Use of a cerium-embedded zinc-iron spinel structure oxide catalyst according to claim 1 in the catalysis of carbon dioxide hydrogenation, characterized in that: In the step S1, the iron salt is one or more of ferric chloride trihydrate, anhydrous ferric chloride, ferric nitrate nonahydrate, and ferric sulfate pentahydrate; the zinc salt is one or more of zinc chloride tetrahydrate, zinc nitrate hexahydrate, and zinc sulfate heptahydrate; and the cerium salt is one or more of cerium nitrate hexahydrate and cerium chloride hexahydrate.

3. Use of a cerium-embedded zinc-iron spinel structure oxide catalyst according to claim 1 in the catalysis of carbon dioxide hydrogenation, characterized in that: In the step S1, the reaction temperature of the hydrothermal reaction is 180°C, and the reaction time is 24h.

4. Use of a cerium-embedded zinc-iron spinel structure oxide catalyst according to claim 1 in the catalysis of carbon dioxide hydrogenation, characterized in that: In the step S2, the drying temperature is 80°C, and the drying is maintained for 12h.

5. Use of a cerium-embedded zinc-iron spinel structure oxide catalyst according to claim 1 in the catalysis of carbon dioxide hydrogenation, characterized in that: In the step S3, the loading amount of the sodium salt is 1%.

6. Use of a cerium-embedded zinc-iron spinel structure oxide catalyst according to claim 1 in the catalysis of carbon dioxide hydrogenation, characterized in that: In the step S4, the calcining temperature is 400°C, and the calcining is maintained for 3h.

7. Use of a cerium-embedded zinc-iron spinel structure oxide catalyst according to claim 1 in the catalysis of carbon dioxide hydrogenation, characterized in that: The application specifically is that: after the cerium-embedded zinc-iron spinel structure oxide catalyst is reduced by H2, the catalyst is loaded into a fixed fluidized bed, a mixed gas composed of CO2 and H2 is introduced, and a hydrogenation reaction is carried out under the conditions of a temperature of 290°C and a pressure of 2MPa, wherein the molar ratio of CO2 to H2 is 1:3.

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