Multi-element metal-based catalyst as well as preparation method and application thereof

Abstract

The invention discloses a multi-element metal-based catalyst as well as a preparation method and application thereof, and belongs to the technical field of metal-based catalysts. The multi-metal-based catalyst takes an iron-based spinel oxygen carrier AB2O4 as a matrix, the A site is multi-metal compounding, and the B site uses a transition element to replace part of Fe; the general formula is MFe2-xNxO4, M is a multi-metal compound, N is a transition element, and x is more than or equal to 0.05 and less than or equal to 0.5. The multi-element metal-based catalyst MFe2-xNxO4 provided by the invention can be applied to a two-step thermochemical CO2 or H2O decomposition system and a two-step thermochemical methane dry / wet reforming system. According to the invention, the concentrated solar energy can be used for providing reaction heat for the reaction, CO2, H2O and other substances with wide sources are used as raw materials to prepare CO, H2, synthesis gas and other high value-added chemicals, the whole process can realize no coal consumption and zero carbon emission, and the method is a very clean and promising green fuel preparation technology.

Description

Technical Field

[0001] This invention belongs to the field of metal-based catalyst technology, specifically relating to a multi-metal-based catalyst, its preparation method, and its application. Background Technology

[0002] Currently, there are three main types of oxygen carriers used for the two-step thermochemical decomposition of CO2: CeO2-based materials, perovskite-type metal oxides (ABO3), and Fe-based materials. 3+ / Fe 2+ Ferrite materials with redox pairs. However, due to the high process temperature (1400℃ and above), the oxygen carrier inevitably suffers from high-temperature sintering deactivation, resulting in low decomposition efficiency (low CO yield). How to solve the problem of high-temperature sintering deactivation of the oxygen carrier is a major challenge of this technology. Summary of the Invention

[0003] The purpose of this invention is to provide a multi-metal-based catalyst, its preparation method, and its application.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] One of the technical solutions of this invention is to provide a multi-metal-based catalyst, wherein the multi-metal-based catalyst uses iron-based spinel oxygen support AB2O4 as the parent material, the A-site is a multi-metal composite, and the B-site uses transition elements to replace part of the Fe; its general formula is MFe. 2-x N x O4, where M is a multimetallic composite, N is a transition element, and 0.05≤x≤0.5.

[0006] This invention utilizes multi-metallic element composites at the A-site of an iron-based spinel oxygen support. The composite of multiple metal elements increases the material's configurational entropy, which in turn enhances the disordered arrangement of atoms in the crystal lattice and reduces surface defects. Furthermore, the inventors discovered that partial substitution of the Fe sites in iron-based spinels with transition elements also exhibits excellent thermochemical CO2 decomposition performance, with a certain increase in oxygen ion migration rate. Therefore, this invention combines the idea of ​​multi-metallic doping at the A-site of iron-based spinels with partial substitution at the Fe site, utilizing the synergistic effect of A- and B-site metals on thermochemical reaction driving to provide a highly efficient and stable thermochemical catalyst.

[0007] A two-step thermochemical cycle reaction based on a multi-metal-based catalyst can convert CO2 / H2O into CO / H2 and CH4-CO2 / H2O into syngas through reforming.

[0008] The reaction steps of two-step thermochemical decomposition of CO2 / H2O to CO / H2 are: (1) the active material is reduced at high temperature (1200-1450℃) in an inert atmosphere, releasing oxygen; (2) the active material after releasing oxygen reacts with CO2 / H2O at relatively low temperature (800-1100℃) to generate CO / H2. The representative expression of the reaction is as follows:

[0009]

[0010] wherein MFe 2-x N x O 4(oxidized) and MFe 2-x N x O 4-δ(reduced) represent the active material in oxidized and reduced states, respectively.

[0011] The reaction steps of two-step thermochemical CH4-CO2 / H2O reforming to synthesis gas are: (1) the active material is activated in CH4 atmosphere at a certain temperature (500-900℃), releasing lattice oxygen, and the reaction generates CO and H2; (2) the active material after releasing lattice oxygen is then supplemented with lattice oxygen in CO2 / H2O atmosphere, and the reaction generates CO / H2. The representative expression of the reaction is as follows:

[0012]

[0013] wherein MFe 2-x N x O 4(oxidized) and MFe 2-x N x O 4-δ(reduced) represent the active material in oxidized and reduced states, respectively.

[0014] Preferably, the multi-metal complex is at least two of Mn, Zn, Co, Ni, Mg and Cu.

[0015] Preferably, the transition element includes Ce, Zr, Y, Al or Sc.

[0016] The second technical solution of the present application provides a preparation method of the above-mentioned multi-metal-based catalyst, including co-precipitation method, solid phase reaction method or sol-gel method.

[0017] Preferably, the steps of the co-precipitation method include: weighing the metal salt of the corresponding metal according to the chemical dosage ratio, dissolving and adding alkali for precipitation, separating the obtained precipitate, washing and drying, and then calcining to obtain the multi-metal-based catalyst.

[0018] More preferably, the metal salt is selected from one or more of nitrate, chlorate, acetate and sulfate.

[0019] More preferably, the base comprises one or more of NaOH, KOH and ammonia.

[0020] More preferably, the temperature of the calcination is 1000℃ and the time is 5h.

[0021] Preferably, the steps of the solid phase reaction method comprise: weighing the precursors of the corresponding metals according to the chemical dosage ratio, mixing by grinding, pre-calcination, tabletting after grinding the obtained powder after pre-calcination, calcination, to obtain the multi-metallic catalyst.

[0022] More preferably, the precursors are selected from carbonates and / or metal oxides.

[0023] More preferably, the temperature of the pre-calcination is 1000℃ and the time is 10h; the temperature of the calcination is 1300℃ and the time is 12h.

[0024] Preferably, the steps of the sol-gel method comprise: weighing the metal salts of the corresponding metals according to the chemical dosage ratio, dissolving in water and adding a complexing agent, then adding ammonia to adjust the pH value to 8, stirring at 80℃ to obtain a viscous gel, drying and calcining to obtain the multi-metallic catalyst.

[0025] More preferably, the metal salts are selected from one or more of nitrate, chlorate and carbonate.

[0026] More preferably, the complexing agent is selected from citric acid, glucose, glycine or ethylenediaminetetraacetic acid.

[0027] More preferably, the temperature of the calcination is 800℃ and the time is 5h.

[0028] Technical solution three of the present application: provide a kind of above-mentioned multi-metallic catalyst in two-step thermochemical decomposition CO 2 It is the application of CO or decomposition H 2 In H 2, The metal element of the multi-metallic catalyst of the metal complex does not include Cu and Zn.

[0029] Technical solution four of the present application: provide a kind of above-mentioned multi-metallic catalyst in two-step thermochemical CH 4 -CO 2 Reforming or CH 4 -H 2 O reforming to the application of synthesis gas.

[0030] The beneficial technical effects of the present application are as follows:

[0031] 1, the present application combines the idea of multi-metal complexation at the A site of iron-based spinel and partial substitution at the Fe site, and provides a highly efficient and stable thermochemical catalyst.

[0032] 2, the present application provides a multi-metallic catalyst MFe 2-x N xO4 is suitable for a variety of thermochemical applications and has been experimentally verified to be successfully applied in two-step thermochemical decomposition of CO2 or H2O system, two-step thermochemical dry / wet reforming of methane system.

[0033] 3、The present application can utilize concentrated solar energy to provide reaction heat, utilize widely-sourced CO2, H2O and other substances as raw materials to prepare CO, H2 and synthesis gas and other high-value-added chemicals, and the whole process can realize zero coal consumption and zero carbon emission, and is a very clean and promising green fuel preparation technology. DETAILED DESCRIPTION

[0034] The various illustrative embodiments of the present application will now be described in detail in connection with the following figures. This description is not to be taken in a limiting sense but is made merely for the purpose of providing a full and enabling disclosure of the present application. The best mode contemplated for the application is described in connection with the detailed description.

[0035] It should be noted that the present application does not describe in detail the conventional operation means in the art, and is not the focus of the present application.

[0036] In addition, for the numerical range in the present application, it should be understood that each intermediate value between the upper limit and the lower limit of the range is also specifically disclosed. Each smaller range between any stated value or stated range of values, and any other stated value or stated range of values, is also encompassed within the scope of the present application. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0037] 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 this application belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, preferred methods and materials are described. Any and all

[0038] As used herein, the terms "comprise", "comprising", "include", "including", "have", "having" and the like are open-ended terms that are intended to mean including, but not limited to.

[0039] Example 1

[0040] Ni 0.5 Co 0.5 Fe 1.7 Y 0.3 O4 two-step thermochemical CO2 decomposition:

[0041] Preparation by co-precipitation: the corresponding mass of nitrate is taken according to the metal molar ratio of Ni:Co:Fe:Y=5:5:17:3, the nitrate is dissolved in deionized water to obtain a mixed salt solution with a concentration of 2 mol / L, and a sodium hydroxide solution with a concentration of 1 mol / L is prepared as a precipitant. The sodium hydroxide solution is added to the mixed salt solution for co-precipitation, the pH of the solution is kept at 10, and the precipitate is washed and filtered several times until the pH value reaches neutral, dried at 100°C and calcined at 1000°C for 5h to obtain Ni 0.5 Co 0.5 Fe 1.7 Y 0.3 O4.

[0042] As a control, the non-element-doped NiFe2O4 in this embodiment is prepared by co-precipitation.

[0043] The two-step thermochemical CO2 decomposition reaction of this embodiment is carried out on a fixed bed reactor. The specific reaction steps are: the material is heated to 1400°C in an argon atmosphere for activation, the activation time is 20 min, and then cooled to 1000°C under argon atmosphere; CO2 is introduced at 1000°C for decomposition reaction, the reaction time is 30 min. The product is detected by chromatograph, and the reaction results in three cycles are shown in Table 1.

[0044] Table 1

[0045]

[0046] As can be seen from Table 1, compared with traditional iron-based spinel materials, after A-site multi-metal element complexing and B-site transition element partial substitution of Fe, the performance of the metal-based catalyst of the present application is significantly improved, especially it still maintains considerable CO generation rate in the later reaction period.

[0047] Example 2

[0048] Ni 0.2 Mg 0.3 Co 0.5 Fe 1.8 Sc 0.2 O4 two-step thermochemical H2O decomposition:

[0049] Preparation by sol-gel method: the corresponding mass of nitrate is taken according to the metal molar ratio of Ni:Mg:Co:Fe:Sc=2:3:5:18:2, the nitrate is dissolved in deionized water at 80°C to obtain a mixed salt solution with a concentration of 0.8 mol / L, citric acid is added to the mixed salt solution and stirred, the molar ratio of citric acid to metal ions is 2:1, after sufficient dissolution, ammonia water is added to adjust the pH to 8, continue to stir at 80°C until the gel is generated, then dry at 120°C, and calcine at 800°C for 5h to obtain Ni0.2 Mg 0.3 Co 0.5 Fe 1.8 Sc 0.2 O4.

[0050] The two-step thermochemical H2O decomposition of the embodiment was carried out on a fixed bed reactor. The specific reaction steps were as follows: the material was activated by being heated to 1350 DEG C in an argon atmosphere for 30 min, and then H2O was introduced at 900 DEG C for a decomposition reaction for 30 min. The product was detected by a chromatograph, and the reaction results in three cycles are shown in Table 2.

[0051] Table 2

[0052]

[0053] As can be seen from Table 2, after the metal-based catalyst of the application was subjected to the A-site multi-metal element compounding and the B-site transition element partial substitution of Fe, a very good H2 generation rate was maintained in the later reaction stage.

[0054] Example 3

[0055] Zn 0.5 Cu 0.5 Fe 1.9 Ce 0.1 O4 two-step thermochemical methane dry reforming:

[0056] Preparation by a coprecipitation method, and the preparation method is the same as that of Example 1.

[0057] As a control, the B-site element-doped Zn 0.5 Cu 0.5 Fe2O4 was prepared by a coprecipitation method.

[0058] The two-step thermochemical CH4-CO2 decomposition reaction (methane dry reforming) of the embodiment was carried out on a fixed bed reactor. The specific reaction steps were as follows: the material was first heated to 900 DEG C in an argon atmosphere, then the argon was replaced by CH4 for activation at 900 DEG C for 15 min, and then CO2 was introduced at the same temperature for a reaction for 25 min, and the product was detected by a chromatograph, and the reaction results in three cycles are shown in Table 3.

[0059] Table 3

[0060]

[0061]

[0062] As can be seen from Table 3, after the metal-based catalyst of the application was subjected to the B-site transition element partial substitution of Fe, the CH4 conversion rate and the CO generation rate can be significantly improved.

[0063] Example 4

[0064] Zn 0.1 Ni 0.6 Mn 0.3 Fe 1.5 Al 0.5 O4 two-step thermo-chemical methane wet reforming:

[0065] The material was prepared by a solid phase reaction method. Metal oxide powders were weighed according to the metal molar ratio of Zn:Ni:Mn:Fe:Al = 1:6:3:15:5, mixed thoroughly by grinding, pre-baked at 1000℃ for 10h, then the pre-baked powder was ground, and then baked at 1300℃ for 12h to obtain Zn 0.1 Ni 0.6 Mn 0.3 Fe 1.5 Al 0.5 O4.

[0066] The two-step thermo-chemical CH4-H2O decomposition reaction (methane wet reforming) of this example was carried out in a fixed bed reactor. The specific reaction steps were as follows: first, the material was heated to 800℃ in an argon atmosphere, then the argon was replaced with CH4 and activated at 800℃ for 20min, then replaced with H2O at the same temperature and reacted for 30min, the product was detected by a chromatograph, and the reaction results in three cycles are shown in Table 4.

[0067] Table 4

[0068]

[0069] As can be seen from Table 4, after the A-site multi-metal element composite and the B-site transition element partial substitution of Fe, the multi-metallic catalyst of the present application can maintain a high CH4 conversion rate and H2 generation rate.

[0070] The above-described embodiments are only to describe the preferred modes of the present application, and not to limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements to the technical solutions of the present application made by those of ordinary skill in the art shall fall within the protection scope determined by the claims of the present application.

Claims

1. A multi-metal-based catalyst, characterized in that, The multi-metal-based catalyst uses iron-based spinel oxygen support AB₂O₄ as the parent material, with a multi-metal composite at the A-site and partial Fe substitution at the B-site by transition elements; its general formula is MFe. 2-x N x O4, where M is a multimetallic composite, N is a transition element, and 0.05≤x≤0.

5.

2. The multi-metal-based catalyst according to claim 1, characterized in that, The multimetallic composite is a composite of at least two of Mn, Zn, Co, Ni, Mg and Cu.

3. The multi-metal-based catalyst according to claim 1, characterized in that, The transition elements include Ce, Zr, Y, Al, or Sc.

4. A method for preparing a multi-metal-based catalyst according to any one of claims 1 to 3, characterized in that, These include coprecipitation, solid-phase reaction, or sol-gel methods.

5. The preparation method according to claim 4, characterized in that, The steps of the coprecipitation method include: weighing the metal salt of the corresponding metal according to the chemical dosage ratio, dissolving it, adding alkali to precipitate it, separating the obtained precipitate, washing and drying it, and then calcining it to obtain the multi-metal-based catalyst.

6. The preparation method according to claim 4, characterized in that, The solid-phase reaction method includes the following steps: weighing the precursor of the corresponding metal according to the chemical dosage ratio, mixing it thoroughly by grinding, pre-calcining, grinding the powder obtained by pre-calcination again, pressing it into tablets, calcining it, and obtaining the multi-metal-based catalyst.

7. The preparation method according to claim 4, characterized in that, The steps of the sol-gel method include: weighing the metal salts of the corresponding metals according to the chemical dosage ratio, dissolving them in water and adding a complexing agent, then adding ammonia to adjust the pH value to 8, stirring at 80°C to obtain a viscous colloid, drying and calcining to obtain the multi-metal-based catalyst.

8. The application of the multi-metal-based catalyst according to any one of claims 1 to 3 in a two-step thermochemical decomposition of CO2 to CO or decomposition of H2O to H2, characterized in that, The multi-metal composite metal elements in the multi-metal based catalyst do not include Cu and Zn.

9. The use of a multi-metal-based catalyst according to any one of claims 1 to 3 in a two-step thermochemical reforming process for producing syngas from CH4-CO2 or CH4-H2O.

Images