High-entropy oxygen carrier with delayed oxidation characteristic

Abstract

The invention discloses a high-entropy oxygen carrier with a delayed oxidation effect. The high-entropy oxygen carrier with the delayed oxidation effect is of a spinel structure, and high mechanical strength and good sintering agglomeration resistance can be maintained while high reaction activity is achieved. Different from a conventional oxygen carrier which is low in reduction rate and high in oxidation rate, the oxidation-reduction characteristic of the high-entropy oxygen carrier is opposite to that of the conventional oxygen carrier, the reduction rate of the high-entropy oxygen carrier is higher than that of conventional copper-based, perovskite-based and ore oxygen carriers, but the oxidation rate of the high-entropy oxygen carrier is only 1 / 3 of that of the reference oxygen carrier. The high-entropy oxygen carrier generates a large number of oxygen vacancies based on the lattice distortion effect; based on the hysteresis diffusion effect, the oxygen carrier shows excellent sintering / agglomeration resistance. By introducing the aluminum element, the anti-sintering performance is remarkably enhanced, and meanwhile, the synergistic improvement of the reaction activity and the cycling stability is realized by enhancing the solid solution effect. The addition of the sodium element further promotes the formation of oxygen vacancies through an electronic compensation mechanism, and the kinetic performance of the oxidation-reduction reaction is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical looping combustion oxygen carrier preparation, and in particular to a high entropy oxide oxygen carrier with delayed oxidation characteristics. Background Art

[0002] Oxygen carriers act as transporters of oxygen and heat during the step-by-step reactions of chemical looping combustion, directly impacting carbon capture efficiency and energy conversion efficiency. Transition metal oxides are the primary oxygen carrier, but there is no consensus on the selection of the primary element, and it remains difficult to find a single oxygen carrier that fully meets all the requirements of chemical looping combustion. An ideal oxygen carrier should possess excellent thermodynamic properties, a high reaction rate, sufficient oxygen loading, uniform redox exothermicity, good fluidization, high mechanical strength, and resistance to sintering and agglomeration. However, these various oxygen carrier properties often constrain each other. For example, increasing the oxygen loading rate and reaction rate may exacerbate sintering and agglomeration, while increasing mechanical strength may reduce reactivity. Currently, the development trend of oxygen carriers is towards multi-primary element integration, aiming to complement the strengths of different elements, promote synergistic effects, avoid significant deficiencies in individual performance, and achieve a balanced and optimal overall performance.

[0003] When the number of principal elements in an oxygen carrier reaches five, the concept of high entropy becomes relevant. High-entropy oxides (HEOs) are single-phase oxides formed by the solid dissolution of five or more elements in equimolar or near-molar ratios. They disregard the traditional concept of principal elements, with the constituent elements randomly dissolving in a highly disordered state, resulting in a high mixed configurational entropy. HEOs benefit from four core effects: high entropy, lattice distortion, delayed diffusion, and the cocktail effect. They have demonstrated exceptional mechanical, catalytic, and reactive properties in electrocatalysis, thermochemical conversion, and battery energy storage. These four effects are highly consistent with the performance requirements of oxygen carriers. The high entropy effect significantly enhances the mechanical strength of the oxygen carrier; the lattice distortion effect modifies the electronic band structure, promotes surface adsorption of reactants, and provides a large number of oxygen vacancies and active sites; the delayed diffusion effect reduces the diffusion rate of metal atoms, inhibits grain growth, and enhances the oxygen carrier's resistance to sintering and agglomeration. The cocktail effect, through the optimization of constituent elements and their content, modulates the adsorption strength of the target reactants, achieving reaction selectivity and stimulating interelement synergy. Oxygen carrier materials prepared based on the high entropy concept are expected to break the balance between reactivity and anti-wear / agglomeration performance, and achieve both high strength and high activity. Summary of the Invention

[0004] The purpose of the present invention is to overcome the inherent limitations of traditional oxygen carriers that they cannot simultaneously possess high reactivity, high mechanical strength, wear resistance and anti-agglomeration / sintering properties. Based on the high entropy material design theory, the present invention proposes a design and preparation method for a new type of high entropy oxide oxygen carrier, which achieves maximum mixing entropy through the molar ratio of the target elements. High entropy oxygen carriers rely on four high entropy effects to exhibit unique redox characteristics: different from the reverse redox characteristics of low reduction rate and high oxidation rate of traditional oxygen carriers, that is, high reduction rate and low oxidation rate characteristics, and can effectively enhance the reaction activity while improving anti-agglomeration and anti-wear properties. Based on the high entropy material design principles and combined with the oxygen carrier modification strategy, the present invention proposes four high entropy oxide oxygen carriers: (Mn 0.2 Fe 0.2 Co 0.2 Ni 0.2 Cu 0.2 )O,(Mn 0.2125 Fe 0.2125 Co 0.2125 Cu 0.2125 Al 0. 15 )O,(Mn 0.2125 Fe 0.2125 Ni 0.2125 Cu 0.2125 Al 0.15 )O,(Na 0.15 Mn 0.175 Fe 0.175 Co 0.175 Cu 0.175 Al 0.15 The addition of inert carrier Al2O3 can improve the dispersion of active components of the oxygen carrier and enhance the solid solution effect; the addition of alkali metal NaO can promote the formation of oxygen vacancies in the oxygen carrier and enhance the reaction activity.

[0005] The technical solution adopted by the present invention is:

[0006] A high entropy oxygen carrier based on a transition metal oxide, including a high entropy oxygen carrier free of alkali metal sodium, the chemical formula of which is (Mn 0.2 Fe 0.2 Co 0.2 Ni 0.2 Cu 0.2 )O,(Mn 0.2125 Fe 0.2125 Co 0.2125 Cu 0.2125 Al 0.15 )O,,(Mn 0.2125 Fe 0.212 5Ni 0.2125 Cu 0.2125 Al 0.15)O, or a high entropy oxygen carrier containing alkali metal sodium, the chemical formula is (Na 0.15 Mn 0.175 Fe 0.175 Co 0.175 Cu 0.175 Al 0.15 )O.

[0007] As an improvement, the high entropy oxygen carrier is a high entropy oxygen carrier that does not contain alkali metal sodium, and the preparation method includes the following steps:

[0008] Step 1: weigh at least five nitrates selected from the group consisting of manganese nitrate, iron nitrate, cobalt nitrate, nickel nitrate, copper nitrate, and aluminum nitrate according to the target molar amount of each metal element as precursors, dissolve the nitrates in deionized water, and stir to obtain a precursor solution.

[0009] Step 2, preparing a 20% NaOH solution and a 20% Na2CO3 solution;

[0010] Step 3: Mix NaOH solution and Na2CO3 solution as precipitant, add them to the precursor solution, stir to obtain precipitate, let it stand for solid-liquid separation, and filter with deionized water to remove Na + The filtrate was filtered to obtain a precipitate;

[0011] Step 4: After drying the precipitate, transfer it to a muffle furnace for calcination. After calcination, crush and screen it to a target particle size of 0.1-0.2 mm to obtain a high entropy oxygen carrier free of alkali metal sodium.

[0012] A further improvement is that the drying temperature in step 4 is 120° C. and the drying time is 8 hours.

[0013] A further improvement is that the calcination temperature in step 4 is 950° C. and the calcination time is 12 hours.

[0014] As an improvement, when the high entropy oxygen carrier is a high entropy oxygen carrier containing alkali metal sodium, the preparation method includes the following steps:

[0015] Step 1: weighing at least five nitrates of manganese nitrate, iron nitrate, cobalt nitrate, nickel nitrate, copper nitrate, and aluminum nitrate in equal molar amounts of each metal element as precursors, dissolving them in deionized water, and stirring to obtain a precursor solution;

[0016] Step 2, adding aluminum isopropoxide to deionized water and stirring uniformly to obtain aluminum gel;

[0017] Step 3, hydrolyzing the aluminum gel at 75°C for 0.5 hours with stirring, followed by condensation at 90°C for 2 hours;

[0018] Step 4, preparing a 20% NaOH solution;

[0019] Step 5: Add the NaOH solution and the precursor solution to the aluminum gel, heat and dry to obtain a precipitate, transfer the precipitate to a muffle furnace for calcination, and finally crush and sieve the calcined product to a target particle size of 0.2-0.3 mm to obtain a high entropy oxygen carrier containing alkali metal sodium.

[0020] As an improvement, the drying temperature in step 5 is 100° C. and the drying time is 12 hours.

[0021] As an improvement, the calcination temperature in step 5 is 950° C., the calcination time is 4 hours, and the calcination atmosphere is air. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a summary of the XRD characterization of the high entropy oxide oxygen carriers prepared in Example 1 and Example 2;

[0023] Figure 2 Schematic diagram of the structure of four high entropy oxide oxygen carriers of the present invention;

[0024] Figure 3 A comparison chart of the redox performance of four high entropy oxide oxygen carriers of the present invention;

[0025] Figure 4 The graph shows the mass change over time of the four high entropy oxide oxygen carriers of the present invention after 30 cycles of hydrogen-oxygen redox reaction tests on a fluidized bed-thermogravimetric analyzer;

[0026] Figure 5 This is a comparison diagram of XRD characterization of the four high entropy oxide oxygen carriers of the present invention before and after 30 redox cycles. DETAILED DESCRIPTION

[0027] The following is a detailed description of the embodiments of the present invention in conjunction with specific examples, which aims to fully reflect the creative features of the present invention through the description of specific implementation methods and operation processes. It should be noted that this embodiment is only an illustrative description based on the technical solution of the present invention, and its purpose is to provide a complete understanding solution for those skilled in the art, but the scope of the present invention is not limited to the embodiment.

[0028] Based on the technical content disclosed in this application, those skilled in the art may make appropriate adjustments to the specific embodiments of the present invention without departing from the spirit and scope defined by the appended claims. It should be understood that the scope of protection of the present invention is not limited to the specific process steps, physical properties or component combinations described in the specification, and the embodiments are only used to illustrate the technical features of the present invention. In fact, any reasonable changes and improvements made by those skilled in the art and related fields based on this application are within the scope of protection required by the claims.

[0029] To accurately define the technical boundaries of the present invention, all numerical indicators such as amounts and percentages involved in this application should be understood as approximate values. Unless otherwise specified, all numerical parameters listed in the specification and claims are assumed to include the modified meaning of "about". Therefore, unless otherwise specified, the numerical parameters listed in the specification and the appended claims are approximate values ​​and may vary depending on the desired properties to be obtained.

[0030] Example 1 Preparation of high entropy oxygen carrier (Mn 0.2 Fe 0.2 Co 0.2 Ni 0.2 Cu 0.2 )O,(Mn 0.2125 Fe 0.2125 Co 0.2125 Cu 0.2125 Al 0.15 )O,(Mn 0.2125 Fe 0.2125 Ni 0.2125 Cu 0.2125 Al 0.15 )O.

[0031] According to the target molar amount of each metal element, at least five nitrates of manganese nitrate, iron nitrate, cobalt nitrate, nickel nitrate, copper nitrate, and aluminum nitrate are weighed as precursors, dissolved in deionized water, and stirred for 30 minutes to ensure uniformity to obtain a precursor solution;

[0032] Prepare a 20% NaOH solution and a 20% Na2CO3 solution, and stir and mix the two for 30 minutes to form an alkaline precipitant;

[0033] Add the alkaline precipitant dropwise to the precursor solution over 2 hours, stirring until a stable suspension is formed. After all the precipitant has been added to the precursor salt solution and stirring for 2 hours, continue stirring for 2 hours to complete precipitation. After standing for 6 hours, filter using a circulating water vacuum pump. Wash the filter residue three times with deionized water to remove the sodium ions and obtain a precipitate.

[0034] The obtained precipitate was placed in a 120° C. forced air drying oven and dried for 8 hours, and then transferred to a muffle furnace and calcined at a high temperature of 950° C. for 4 hours to obtain a high entropy oxide oxygen carrier free of alkali metal sodium.

[0035] According to the above method, (Mn 0.2 Fe 0.2 Co 0.2 Ni 0.2 Cu 0.2 )O,(Mn 0.2125 Fe 0.2125 Co 0.2125 Cu 0.2125 Al 0.15 )O,,(Mn 0.2125 Fe 0.2125 Ni 0.2125 Cu 0.2125 Al 0.15 )O.

[0036] Example 2 Preparation of high entropy oxygen carrier containing alkali metal sodium (Na 0.15 Mn 0.175 Fe 0.175 Co 0.175 Cu 0.175 Al 0.15 )O.

[0037] According to the molar ratio of each element, the corresponding manganese nitrate, iron nitrate, cobalt nitrate, and copper nitrate solutions were weighed as precursors, dissolved in deionized water, and stirred for 30 minutes to mix them evenly to form a precursor salt solution.

[0038] Aluminum isopropoxide was added to deionized water, stirred at 75° C. for 30 minutes to mix uniformly to form aluminum gel, and then condensed at 90° C. for 2 hours. At the same time, a 20% NaOH solution was prepared.

[0039] The NaOH solution and the target metal nitrate solution were added to the aluminum gel, stirred and mixed for 30 minutes, and heated at 90° C. for 12 hours to obtain a final precipitate.

[0040] The obtained precipitate was placed in a 120°C forced air drying oven and dried for 8 hours, then transferred to a muffle furnace and calcined at 950°C for 4 hours, crushed and sieved to the target particle size of 0.2-0.3 mm to obtain a high entropy oxide oxygen carrier containing alkali metal sodium (Na 0.15 Mn 0.175 Fe 0.175 Co 0.175 Cu 0.175 Al 0.15 )O.

[0041] Example 3 Test of the physical and chemical properties of high entropy oxygen carriers

[0042] The four high entropy oxygen carriers prepared in Example 1-2 were subjected to XRD phase analysis, and the results were as follows: Figure 1 As shown in the test results, it can be seen that the four high entropy oxygen carriers designed and prepared according to the target component molar ratio of the present invention have spinel structure oxides as their main crystal phase, and the content of this crystal phase is higher than 95wt.%. In addition, each sample shows a trace of CuO second phase diffraction peak, among which (Na 0.15 Mn 0.175 Fe 0.175 Co 0.175 Cu 0.175 Al 0.15) O samples showed trace amounts of Na2O third phase diffraction peaks, (Mn 0.2 Fe 0.2 Co 0.2 Ni 0.2 Cu 0.2 )O sample showed a trace level of NiO third phase diffraction peak, indicating that the prepared high entropy oxygen carrier has basically achieved the construction of a single-phase solid solution. The specific XRD characterization spectrum and structure diagram are shown in the figure below. Figure 1-2 shown.

[0043] The four high entropy oxygen carriers prepared in Example 1-2 were subjected to XRD tests, and the results were as follows: Figure 1 As shown. It can be seen that the main crystal phases of the four high entropy oxygen carriers based on the target molar ratio of the present invention are all spinel structure oxides, and the mass fraction of this phase is greater than 95wt.%. Each sample shows a second phase diffraction peak of CuO, among which (Na 0.15 Mn 0.175 Fe 0.175 Co 0.175 Cu 0.175 Al 0.15 )O sample showed a trace level of Na2O third phase diffraction peak, (Mn 0.2 Fe 0.2 Co 0.2 Ni 0.2 Cu 0.2 )O sample shows a trace level of NiO third phase diffraction peak, indicating that the prepared high entropy oxygen carriers have basically formed a single-phase solid solution. The structure of each high entropy oxygen carrier is shown in Figure 2 shown.

[0044] The high entropy oxide oxygen carrier of the present invention exhibits excellent reduction performance through the synergy of oxygen vacancies and rapid diffusion of the product layer. 0.2125 Fe 0.2125 Ni 0.2125 Cu 0.2125 Al 0.15)O high entropy oxygen carrier as an example, under the same reaction conditions, although its BET surface area is only 1m 2 / g, but the reduction rate is as high as 0.88mmol / g·s, which is comparable to the BET surface area of ​​50m 2 The reduction rate of Cu-Al oxygen carrier is equivalent to that of the natural ilmenite oxygen carrier in Norway (0.33mmol / g·s), which is 2.6 times that of CaMn 0.5 Ti 0.375 Fe 0.125 O 3-δ The reduction rate of the perovskite oxygen carrier is 1.9 times that of the perovskite oxygen carrier (0.346mmol / g·s). Due to the hysteresis diffusion effect, the oxidation rate of the high entropy oxygen carrier is slower, only 0.37mmol / g·s, and the reduction rate is 2-3 times that of the oxidation rate. The specific comparison results are as follows Figure 3 shown.

[0045] The high entropy oxygen carrier prepared in Example 1-2 was subjected to 30 deep reduction-oxidation cycle tests to evaluate the stability of the high entropy oxygen carrier. 2g of the prepared oxygen carrier particles were selected and first reduced with 250mL / min hydrogen (concentration 50%) at 900°C for 2 minutes, then purged with 250mL / min nitrogen for 2 minutes, and finally oxidized with 66.5mL / min oxygen (concentration 21%) for 5 minutes. The experimental results are shown in Figure 2. Figure 4 As shown, the high entropy oxide oxygen carrier does not show a significant rate decrease until the reduction degree reaches 80-90%, showing a higher product layer diffusion rate and good reaction stability.

[0046] The XRD analysis of the high entropy oxide oxygen carrier after 30 deep redox cycles was carried out. The experimental results are as follows: Figure 5 All four groups of high entropy oxide oxygen carriers maintain spinel structure without obvious phase separation, and their composition and structure remain stable during the cycle. (Mn 0.2 Fe 0.2 Co 0.2 Ni 0.2 Cu 0.2 The redox characteristics of the )O high-entropy oxygen carrier are similar to those of the ilmenite-type oxygen carrier. It does not achieve complete reoxidation and has obvious surface sintering. Compared with the high-entropy oxygen carrier doped with aluminum, it has a significant difference in maintaining stable cycle quality.

[0047] The high entropy oxygen carrier (Mn 0.2 Fe 0.2 Co 0.2 Ni 0.2 Cu 0.2 )O,(Mn 0.2125 Fe 0.2125 Co 0.2125 Cu0.2125 Al 0.15 )O,(Mn 0.2125 Fe 0.2125 Ni 0.2125 Cu 0.2125 Al 0.15 )O,(Na 0.15 Mn 0.175 Fe 0.175 Co 0.175 Cu 0.175 Al 0.15 The theoretical oxygen loading rates of )O were 24.27%, 22.04%, 22.37%, and 21.91%, respectively. However, in deep redox cycling experiments, the actual oxygen loading rates were 15.62-19.66 wt.%, 4.4-6.3 wt.% lower than the theoretical oxygen loading rates, indicating that the actual oxygen loading performance of high-entropy oxides still has room for further optimization.

[0048] In summary, the high entropy oxygen carrier described in the present invention breaks through the concept of traditional solid solution and element doping through the design of nearly equimolar components, realizes the maximization of solid solubility and doping concentration, and significantly improves the oxygen vacancy concentration. Among them, the addition of inert metal aluminum element effectively promotes the formation of single-phase solid solution and inhibits the formation of secondary phases, thereby improving the structural stability and mechanical strength of the material; aluminum element preferentially occupies the octahedral site, prompting the heterovalent elements to concentrate in the tetrahedral site, inducing lattice distortion and increasing the oxygen vacancy concentration. This structural optimization is not only beneficial to the reaction in the initial reduction stage, but also improves the cyclic stability of the material. At the same time, the addition of alkali metal sodium element significantly increases the oxygen vacancy concentration and optimizes the redox kinetics through electron compensation and lattice expansion. The present invention provides a new paradigm for the development of efficient and stable oxygen carriers.

[0049] The above is a schematic description of the present invention and its embodiments, which is not restrictive. The drawings show only one embodiment of the present invention, and the actual structure is not limited thereto. Therefore, if a person skilled in the art is inspired by this and, without departing from the purpose of the present invention, designs a structure and embodiment similar to this technical solution without inventiveness, they shall fall within the scope of protection of the present invention.

Claims

1. A high entropy oxygen carrier based on transition metal oxides, characterized in that: It includes a high entropy oxygen carrier that does not contain alkali metal sodium, and its chemical formula is (Mn 0.2 Fe 0.2 Co 0.2 Ni 0.2 Cu 0.2 )O,(Mn 0.2125 Fe 0.2125 Co 0.2125 Cu 0.2125 Al 0.15 )O,(Mn 0.2125 Fe 0.2125 Ni 0.2125 Cu 0.2125 Al 0.15 )O, or a high entropy oxygen carrier containing alkali metal sodium, the chemical formula is (Na 0.15 Mn 0.175 Fe 0.175 Co 0.175 Cu 0.175 Al 0.15 )O.

2. The high entropy oxygen carrier based on transition metal oxide according to claim 1, characterized in that When the high entropy oxygen carrier is a high entropy oxygen carrier that does not contain alkali metal sodium, the preparation method includes the following steps: Step 1: weighing at least five nitrates of manganese nitrate, iron nitrate, cobalt nitrate, nickel nitrate, copper nitrate, and aluminum nitrate as precursors according to the target molar amount of each metal element, dissolving them in deionized water, and stirring them evenly to obtain a precursor solution; Step 2, preparing a 20% NaOH solution and a 20% Na2CO3 solution; Step 3: Evenly mix NaOH solution and Na2CO3 solution, add them into the precursor solution as precipitant, stir to obtain precipitate, stand for solid-liquid separation, and filter to remove Na + The filtrate was filtered to obtain a precipitate; Step 4: After drying the precipitate, transfer it to a muffle furnace for calcination. After calcination, crush and screen it to a target particle size of 0.1-0.2 mm to obtain high entropy oxygen carrier particles that do not contain alkali metal sodium.

3. The high entropy oxygen carrier based on transition metal oxide according to claim 2, characterized in that The drying temperature in step 4 is 120° C. and the drying time is 8 hours.

4. The high entropy oxygen carrier based on transition metal oxide according to claim 2, characterized in that The calcination temperature in step 4 is 950° C., and the calcination atmosphere is air.

5. The high entropy oxygen carrier based on transition metal oxide according to claim 1, characterized in that When the high entropy oxygen carrier is a high entropy oxygen carrier containing alkali metal sodium, the preparation method comprises the following steps: Step 1: weighing at least five nitrates of manganese nitrate, iron nitrate, cobalt nitrate, nickel nitrate, copper nitrate, and aluminum nitrate as precursors according to the target molar amount of each metal element, dissolving them in deionized water, and stirring them evenly to obtain a precursor solution; Step 2, adding aluminum isopropoxide to deionized water and stirring uniformly to obtain aluminum gel; Step 3, hydrolyzing the aluminum gel at 75°C for 0.5 hours with stirring, followed by condensation at 90°C for 2 hours; Step 4, preparing a 20% NaOH solution; Step 5: Add the NaOH solution and the precursor solution to the aluminum gel, heat and dry to obtain a precipitate, transfer the precipitate to a muffle furnace for calcination, and finally crush and sieve the calcined product to a target particle size of 0.2-0.3 mm to obtain a high entropy oxygen carrier containing alkali metal sodium.

6. The high entropy oxygen carrier based on transition metal oxide according to claim 5, characterized in that The drying temperature in step 5 is 100° C. and the drying time is 12 hours.

7. The high entropy oxygen carrier based on transition metal oxide according to claim 5, characterized in that The calcination temperature in step 5 is 950° C., the calcination time is 4 hours, and the calcination atmosphere is air.

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