A perovskite-type Fe-based high-temperature CO shift catalyst, preparation method and application

Abstract

The present invention belongs to the technical field of catalyst materials, and specifically relates to a perovskite-type Fe-based high-temperature CO conversion catalyst, and further discloses its preparation method and application. The perovskite-type Fe-based catalyst of the present invention synthesizes Fe-based perovskite, and introduces a high-surface-area carrier precursor into the catalytic system during the synthesis of perovskite, so that there is a strong interaction between the perovskite phase and the high-surface-area carrier. At the same time, the perovskite phase can be highly dispersed on the carrier surface, and due to the strong interaction between the perovskite structure and the carrier for the active component Fe element, the degree of reduction of the Fe element in the catalyst during the reduction and reaction process can be significantly reduced, effectively avoiding Fe 0 The formation of by-products of Fischer-Tropsch synthesis can be effectively avoided, which helps to obtain a catalyst with a stable structure and thus improve its catalytic performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst materials, and specifically relates to a perovskite-type Fe-based high-temperature CO shift catalyst, and further discloses a preparation method and application thereof. Background Art

[0002] The high-temperature water-gas shift (WGS) reaction is a crucial step in the production of hydrogen from hydrocarbons. Currently, Fe-Cr catalysts are commonly used in the industry for this reaction. However, because Cr is a highly polluting heavy metal, improper handling of used Fe-Cr catalysts can easily cause environmental pollution. Therefore, developing a Cr-free, yet highly efficient, high-temperature shift catalyst is of great significance.

[0003] In the traditional Fe-Cr catalyst system, the presence of Cr components plays a role in stabilizing the catalyst structure, preventing catalyst sintering, and improving stability. If a Fe-based high-temperature conversion catalyst with a stable structure can be synthesized, the use of Cr components can be effectively avoided, and thus the pollution of the environment by Cr components can be avoided. At the same time, since the catalyst also needs to have a high structural stability, it can keep the structure of the catalyst stable during the calcination and reaction process, and at the same time have a high catalytic activity. In Fe-Cr catalysts, it is generally believed that Fe3O4 is the active center in the high-temperature conversion process. During the pre-reduction and high-temperature conversion reaction process, Fe 3+ Cannot be over-reduced to Fe 0 This is because Fe 0 The presence of is likely to cause side reactions in Fischer-Tropsch synthesis, which significantly reduces the content of hydrogen produced and increases the content of by-products, making subsequent separation more difficult. In addition to adding a certain amount of water vapor to the reaction system, if a strong interaction can be created between the Fe phase and the surrounding environment, then the excessive reduction of the Fe phase can be significantly prevented, thereby significantly improving the stability of the catalyst and significantly reducing the occurrence of side reactions.

[0004] The perovskite structure is a relatively stable octahedral structure with a general molecular formula of ABO3, where A is usually an atom with a relatively large radius and element B usually serves as the catalytic active center. However, the specific surface area of ​​traditional perovskite structures is usually small, and the activity of the catalyst is relatively low. The existing technology attempts to increase the surface area of ​​perovskite to improve its catalytic performance. For example, the use of a shaped high-specific surface area carrier to load the perovskite phase disclosed in Chinese patent CN114177912A can significantly increase the specific surface area of ​​the catalyst; another example is the porous perovskite phase synthesized in Chinese patent CN106238066A, which further increases the specific surface area of ​​the catalyst, thereby significantly increasing the catalyst activity.

[0005] The present invention expects to synthesize Fe-based perovskite structure catalysts, attempts to introduce a carrier with a relatively high specific surface area in the process of preparing perovskite, and at the same time controls the strong interaction between the carrier and the perovskite active center, which helps to improve the catalytic activity and stability of the catalyst. Summary of the Invention

[0006] To this end, the technical problem to be solved by the present invention is to provide a perovskite-type Fe-based high-temperature CO shift catalyst having a stable structure and efficient catalytic performance;

[0007] The second technical problem to be solved by the present invention is to provide a preparation method and application of the above-mentioned titanium ore-type Fe-based high-temperature CO shift catalyst.

[0008] In order to solve the above technical problems, the present invention provides a method for preparing a perovskite-type Fe-based high-temperature CO shift catalyst, comprising the following steps:

[0009] (1) Add Fe salt solution to citric acid solution and mix well for later use;

[0010] (2) adding a rare earth metal salt solution to the mixed solution obtained in step (1) and mixing the mixture for later use;

[0011] (3) adding a carrier precursor to the mixed solution obtained in step (2), mixing the mixture, and heating to evaporate water to form a gel;

[0012] (4) Drying the obtained gel to a solid state, and then calcining the obtained solid to obtain the product.

[0013] Specifically, in the step (1), the molar ratio of the Fe salt to the citric acid is 1:1-1:4.

[0014] Specifically, in step (1), the Fe salt solution is selected from one or a mixed solution of ferric nitrate, ferric sulfate, ferrous sulfate or ferrous chloride solution;

[0015] The concentration of the Fe salt solution is 0.2-2 mol / L;

[0016] The concentration of the citric acid solution is 0.4-3 mol / L.

[0017] Specifically, in step (2), the molar ratio of the rare earth metal salt to the Fe salt is 1:2-2:1.

[0018] Specifically, the rare earth metal salt solution includes one or a mixed solution of lanthanum nitrate and cerium nitrate solutions;

[0019] The concentration of the rare earth metal salt solution is 0.2-2 mol / L.

[0020] Specifically, in step (3), the carrier precursor is a carrier precursor with a high specific surface area;

[0021] The carrier precursor includes a mixture of one or more of pseudo-boehmite, aluminum isopropoxide, aluminum nitrate, tetrabutyl titanate, metatitanic acid, tetraethyl orthosilicate, zirconyl nitrate, and zirconium nitrate;

[0022] The added amount of the carrier precursor accounts for 10-80 wt% of the catalyst.

[0023] Specifically, in step (3), the heating temperature is 40-80°C.

[0024] Specifically, in step (4):

[0025] The temperature of the drying step is 80-150°C;

[0026] The temperature of the calcination step is 400-1300°C.

[0027] The present invention also discloses a perovskite-type Fe-based high-temperature CO conversion catalyst prepared by the method. In the catalyst, the catalyst carrier accounts for 10-80wt% of the catalyst.

[0028] The present invention also discloses the application of the perovskite-type Fe-based high-temperature CO shift catalyst in a high-temperature water-gas shift reaction.

[0029] The perovskite-type Fe-based catalyst of the present invention synthesizes Fe-based perovskite and introduces a high specific surface area carrier precursor into the catalytic system during the perovskite synthesis process, so that there is a strong interaction between the perovskite phase and the high specific surface area carrier. At the same time, the perovskite phase can be highly dispersed on the carrier surface. Moreover, due to the strong interaction between the perovskite structure and the carrier for the active component Fe component, the reduction degree of the Fe component in the catalyst during the reduction and reaction process can be significantly reduced, effectively avoiding the Fe 0 The Fe-based perovskite catalyst of the present invention exhibits high catalytic activity and stability and can be used to efficiently catalyze high-temperature water-gas shift reactions.

[0030] The perovskite-type Fe-based catalyst of the present invention fully utilizes the special semiconductor properties and strong stability of the perovskite phase. The catalyst has a stable structure, a high specific surface area, and excellent catalytic activity. The catalytic activity is significantly higher than that of traditional Fe-Cr catalysts. In addition, the catalyst does not contain the Cr element, effectively avoiding environmental pollution and having the advantage of being green and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0032] Figure 1 The H2-TPR spectra of the catalysts prepared in Example 1 and Comparative Example 1 are shown. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention.

[0034] In the following embodiments of the present invention, the performance testing methods and operations involved include:

[0035] H2-TPR testing was conducted in a quartz tube reactor at atmospheric pressure, using a H2-N2 mixture containing 5% H2 by volume as the reducing gas at a rate of 30 ml / min. The catalyst required pretreatment prior to TPR testing. This pretreatment involved heating the catalyst to 120°C at room temperature under a nitrogen atmosphere, purging it for 1 hour, then cooling it to room temperature. The catalyst was then switched to a hydrogen-argon mixture and heated from room temperature to 900°C at a rate of 10°C / min. Online TCD detection was used.

[0036] The specific surface area (SSA) of the catalyst was determined using nitrogen adsorption using the ASAP2020 surface analyzer and low-temperature nitrogen adsorption. Test conditions: A certain amount of sample was weighed and placed in a sample tube. The gas in the tube was evacuated, heated to 150°C and degassed for 40 minutes. The tube was then back-flushed with helium, cooled, and weighed to obtain the dry weight. Physical adsorption and desorption of the catalyst were performed to generate a measurement curve, and the SSA was calculated using the BET equation.

[0037] Example 1

[0038] Take 200g of citric acid and add it to deionized water, mix it evenly until it is fully dissolved, and set aside; take another 83.3g of FeSO4·7H2O and 56.2g of Fe2(SO4)3·9H2O aqueous solutions and drop them into the above citric acid solution respectively, and mix them evenly.

[0039] Take 216.5g of La(NO3)3·6H2O aqueous solution and drop it into the above liquid mixture, mix it evenly to obtain a new liquid mixture, and keep it at 60℃ for 2h. Then add 50g of pseudo-boehmite and mix it. Continue to heat it to 80℃ and stir it to gradually turn it into a gel.

[0040] The obtained gel was dried at 120° C. to a solid, and the obtained solid was calcined at 650° C. to obtain the desired catalyst, which was recorded as CAT-1.

[0041] Comparative Example 1

[0042] Add 200g of citric acid to deionized water, mix thoroughly until fully dissolved, and set aside. Separately, dropwise add 83.3g of FeSO4·7H2O, 56.2g of Fe2(SO4)3·9H2O, and 216.5g of La(NO3)3·6H2O aqueous solutions into the citric acid solution and mix thoroughly. Then, add 50g of pseudo-boehmite and mix thoroughly. Heat the mixture to 80°C and stir thoroughly. Continue stirring at 60°C until the solid becomes a gel and no longer flows.

[0043] The obtained product was dried at 120° C. to obtain a solid, and the obtained solid was calcined at 650° C. to obtain a catalyst, which was recorded as D-CAT-1.

[0044] The H2-TPR spectra of the catalysts obtained in Example 1 and Comparative Example 1 are shown in the attached Figure 1 As shown, the reduction peak area of ​​the Fe component in the catalyst of Example 1 is significantly lower than that of the Fe component in the catalyst of Comparative Example 1. This is because the Fe element forms a relatively pure perovskite, and Fe can form a perovskite structure with the rare earth metal in a one-to-one correspondence, forming a relatively dispersed state in the catalyst phase, and thus the corresponding characteristic peak area is relatively small. This shows that the method of the present invention can significantly improve the interaction between the Fe component and the various components and its dispersion.

[0045] Example 2

[0046] Take 200g of citric acid and add it to deionized water, mix it evenly until it is fully dissolved, and set aside; take another 83.3g of FeSO4·7H2O and 56.2g of Fe2(SO4)3·9H2O aqueous solutions and drop them into the citric acid solution respectively, and mix them evenly.

[0047] Take 216.5g of Ce(NO3)3·6H2O aqueous solution and drop it into the above liquid mixture, mix evenly to obtain a new liquid mixture, and keep it at 60℃ for 2h. Then add 60g of ethyl orthosilicate and mix it. Continue to heat it to 80℃ and stir it to gradually turn it into a gel.

[0048] The obtained gel was dried at 80° C. to a solid, and the obtained solid was calcined at 750° C. to obtain the desired catalyst, which was recorded as CAT-2.

[0049] Example 3

[0050] Take 300g of citric acid and add it to deionized water, mix it evenly until it is fully dissolved, and set aside; take another 202g of Fe(NO3)3·9H2O aqueous solution and drop it into the above citric acid solution and mix it evenly.

[0051] Take 300g of Ce(NO3)3·6H2O aqueous solution and add it dropwise to the above liquid mixture, mix it evenly to obtain a new liquid mixture, and keep it at 60℃ for 2h. Then add 100g of zirconium oxynitrate and mix it. Continue to heat it to 80℃ and stir it to gradually turn it into a gel.

[0052] The obtained gel was dried at 100° C. to a solid, and the obtained solid was calcined at 850° C. to obtain the desired catalyst, which was recorded as CAT-3.

[0053] Example 4

[0054] Take 300g of citric acid and add it to deionized water, mix it evenly until it is fully dissolved, and set aside; take another 100g of FeCl2·4H2O aqueous solution and drop it into the citric acid solution respectively, and mix it evenly.

[0055] Take 200g of La(NO3)3·6H2O aqueous solution and drop it into the above liquid mixture, mix it evenly to obtain a new liquid mixture, and keep it at 60℃ for 2h. Then add 100g of ethyl orthosilicate and mix it. Continue to heat it to 80℃ and stir it to gradually turn it into a gel.

[0056] The obtained gel was dried at 100° C. to a solid, and the obtained solid was calcined at 850° C. to obtain the desired catalyst, which was designated as CAT-4.

[0057] Example 5

[0058] Take 100g of citric acid and add it to deionized water, mix it evenly until it is fully dissolved, and set aside; take another 115g of FeCl2·4H2O aqueous solution and add it dropwise to the citric acid solution and mix it evenly.

[0059] Take 400g of La(NO3)3·6H2O aqueous solution and drop it into the above liquid mixture, mix it evenly to obtain a new liquid mixture, and keep it at 60℃ for 2h. Then add 300g of ethyl orthosilicate and mix it. Continue to heat it to 80℃ and stir it to gradually turn it into a gel.

[0060] The obtained gel was dried at 120° C. to a solid, and the obtained solid was calcined at 850° C. to obtain the desired catalyst, which was recorded as CAT-5.

[0061] Comparative Example 2

[0062] Take 83.3g FeSO4·7H2O and 56.2g Fe2(SO4)3·9H2O and dissolve them in deionized water and mix them evenly.

[0063] Take 200g of NaCO3 and dissolve it in deionized water, and then drop the above-mentioned Fe-containing liquid mixture to obtain a precipitate. Then keep it at 60°C for 2h. Take out the precipitate and dry it at 120°C until it becomes solid. The obtained solid is then calcined at 550°C to obtain a catalyst, which is recorded as D-CAT-2.

[0064] Comparative Example 3

[0065] 83.3g of FeSO4·7H2O, 56.2g of Fe2(SO4)3·9H2O, and 5.65g of CrO3 were dissolved in deionized water and mixed thoroughly. 200g of NaCO3 was dissolved in deionized water and the Fe-containing liquid mixture was added dropwise to form a precipitate. The mixture was then kept at 60°C for 2 hours. The precipitate was removed and dried at 120°C until solid. The resulting solid was then calcined at 550°C to obtain a catalyst, designated D-CAT-3.

[0066] Comparative Example 4

[0067] Add 200g of citric acid to deionized water, mix thoroughly until fully dissolved, and set aside. Separately, dropwise add 83.3g of FeSO4·7H2O and 56.2g of Fe2(SO4)3·9H2O aqueous solutions into the citric acid solution and mix thoroughly. Maintain the mixture at 60°C for 2 hours, then add 50g of pseudo-boehmite. Continue heating to 80°C and stirring until the mixture gradually transforms into a gel.

[0068] The obtained gel was dried at 120° C. until solid, and the obtained solid was calcined at 650° C. to obtain the desired catalyst, which was recorded as DCAT-4.

[0069] Comparative Example 5

[0070] Take 300g of citric acid and add it to deionized water, mix it evenly until it is fully dissolved, and set aside; take another 100g of FeCl2·4H2O aqueous solution and drop it into the citric acid solution respectively, and mix it evenly.

[0071] The mixture was kept at 60°C for 2 hours, and then 100 g of ethyl orthosilicate was added and mixed. The mixture was heated to 80°C and stirred to gradually turn into a gel.

[0072] The obtained gel was dried at 100° C. to a solid, and the obtained solid was calcined at 850° C. to obtain the desired catalyst, which was recorded as CAT-5.

[0073] Experimental example

[0074] 1. Specific surface area test

[0075] The specific surface areas of the catalysts obtained in Examples 1-4 and Comparative Examples 1-5 were tested according to the aforementioned method, and the results are recorded in Table 1 below.

[0076] Table 1 Specific surface area of ​​catalyst

[0077] serial number <![CDATA[Fresh catalyst BET surface area (m 2 / g)]]> Example 1 128.1 Example 2 98.3 Example 3 97.5 Example 4 130.1 Comparative Example 1 56.3 Comparative Example 2 9.5 Comparative Example 3 20.3 Comparative Example 4 19.6 Comparative Example 5 55.2

[0078] The results in the table show that the specific surface area of ​​the catalyst of the present invention is significantly higher than that of the catalyst in the comparative example, indicating that the dispersion of the active components in the catalyst is high, thereby significantly increasing the number of active sites in the catalyst.

[0079] 2. Catalytic performance test

[0080] This experimental example scheme uses a pressurized activity evaluation device in the prior art to simulate industrial conditions and compare the conversion activity and stability of the catalyst. The reaction tube is a Ø45×5mm stainless steel tube with a Ø8×2mm thermocouple tube in the center. The reactor specifications are: inner diameter 26.1mm, length 1434mm.

[0081] The feed gas is depressurized by a pressure reducing valve, then controlled by a mass flowmeter. It is then mixed with water and fed into a preheater for preheating. After preheating, it enters the reactor, where it comes into contact with the catalyst bed and reacts. A certain amount of water is added according to the requirements of different water-gas ratios. After high-temperature gasification, it enters the reaction tube along with the feed gas for a water-gas shift reaction. The post-reaction gas is condensed in a condenser and fed into a liquid storage tank. After drying in a dryer, the gas enters a gas chromatograph for tail gas detection using a thermal conductivity cell. The tail gas after the reaction is analyzed by chromatography.

[0082] The catalytic activity results of the catalysts in Examples 1-4 and Comparative Examples 1-5 are shown in Table 2 below.

[0083] Table 2 Catalytic activity evaluation results of finished catalysts

[0084] serial number CO conversion rate Example 1 78％ Example 2 79％ Example 3 80％ Example 4 81％ Comparative Example 1 52％ Comparative Example 2 20％ Comparative Example 3 60％ Comparative Example 4 21％ Comparative Example 5 43％

[0085] It can be seen that the catalyst prepared by the method of the present invention has better catalytic performance and higher catalytic efficiency.

[0086] The embodiments of the present invention are described in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core ideas. At the same time, for those skilled in the art, according to the ideas of the present invention, there may be changes in the specific implementation methods and application scopes. In summary, the contents of this specification should not be understood as limiting the present invention.

Claims

1. A method for preparing a perovskite-type Fe-based CO shift catalyst, characterized in that: The steps include: (1) Add Fe salt solution to citric acid solution and mix well for later use; (2) Add the rare earth metal salt solution to the mixed solution obtained in step (1), mix well, keep at 60°C for 2 hours, and set aside; (3) adding the carrier precursor to the mixed solution obtained in step (2), mixing the mixture, and heating to evaporate the water to form a gel; (4) drying the obtained gel to a solid, and calcining the obtained solid to obtain; Wherein, in step (1), the molar ratio of the Fe salt to the citric acid is 1:1-1:4; the molar ratio of the rare earth metal salt to the Fe salt is 1:2-2:1; The carrier precursor includes a mixture of one or more of pseudo-boehmite, aluminum isopropoxide, aluminum nitrate, tetrabutyl titanate, metatitanic acid, tetraethyl orthosilicate, zirconyl nitrate, and zirconium nitrate; The temperature of the calcination step is 400-1300°C.

2. The method for preparing a perovskite-type Fe-based CO shift catalyst according to claim 1, characterized in that: In the step (1), the Fe salt solution is selected from one or a mixed solution of ferric nitrate, ferric sulfate, ferrous sulfate or ferrous chloride solution; The concentration of the Fe salt solution is 0.2-2 mol / L; The concentration of the citric acid solution is 0.4-3 mol / L.

3. The method for preparing a perovskite-type Fe-based CO shift catalyst according to claim 1 or 2, characterized in that: The rare earth metal salt solution includes one or a mixed solution of lanthanum nitrate and cerium nitrate solutions; The concentration of the rare earth metal salt solution is 0.2-2 mol / L.

4. The method for preparing a perovskite-type Fe-based CO shift catalyst according to claim 1 or 2, characterized in that: The added amount of the carrier precursor accounts for 10-80 wt % of the catalyst.

5. The method for preparing a perovskite-type Fe-based CO shift catalyst according to claim 1 or 2, characterized in that: In the step (3), the heating temperature is 40-80°C.

6. The method for preparing a perovskite-type Fe-based CO shift catalyst according to claim 1 or 2, characterized in that: In step (4): The temperature of the drying step is 80-150°C.

7. Use of the perovskite-type Fe-based CO shift catalyst obtained by the preparation method according to any one of claims 1 to 6 in a water-gas shift reaction.

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