Composite oxygen carrier as well as preparation method and application thereof in chemical looping process

Abstract

The invention belongs to the technical field of oxygen carriers, and discloses a composite oxygen carrier and application thereof in a chemical looping process, the chemical general formula of the composite oxygen carrier is gamma-Fe2O3 / CeO2, and the molar ratio of Fe / (Fe + Ce) is 0.6-0.8; the preparation method comprises the following steps: synthesizing FexCe1-xO by adopting a one-step coprecipitation method, and promoting Fe species to generate directional migration and crystal form transformation by adopting a three-step activation process, specifically, enriching an iron element to the surface, and converting the crystal form into high-activity gamma-Fe2O3 from alpha-Fe2O3. In addition, the gamma-Fe2O3 / CeO2 composite oxygen carrier subjected to activating treatment shows breakthrough performance advantages that ultra-deep removal with the CO concentration being lower than 100 ppm or so is achieved in the chemical looping hydrogen production process, meanwhile, the H2 recovery rate is kept to be larger than or equal to 95%, and the index is remarkably superior to that of a traditional membrane separation method (the recovery rate is about 85%) and a metal hydride method (CO residue gt; 200 ppm).

Description

Technical Field

[0001] The present invention belongs to the technical field of oxygen carriers, and in particular relates to a composite oxygen carrier, a preparation method thereof, and an application thereof in a chemical chaining process. Background Art

[0002] Carbon monoxide (CO), a harmful impurity, is rigorously removed across multiple industrial systems to ensure process safety, product quality, and environmental compliance. In the energy industry, the commercialization of proton exchange membrane fuel cells (PEMFCs), highly efficient hydrogen-to-electricity conversion devices, is hampered by electrode poisoning caused by trace amounts of CO in hydrogen-rich feed gas, leading to irreversible catalyst deactivation and significantly reduced cell life. In chemical production, trace amounts of CO in hydrogen-rich feed gas can poison and deactivate iron catalysts in ammonia synthesis. In the metallurgical industry, blast furnace and converter gases contain CO and H₂, which need to be removed for subsequent resource utilization. Furthermore, in the environmental protection sector, CO also needs to be removed from industrial waste gases to meet emission standards. Therefore, the need for CO removal spans multiple sectors, including metallurgy, chemical engineering, environmental protection, and energy, and treatment technologies are flexibly selected based on concentration, impurity composition, and end-use application. Future trends include the development of low-cost catalysts, high-efficiency adsorption materials, and integrated purification processes to improve economic efficiency and sustainability.

[0003] Taking the removal of CO from hydrogen-rich gas as an example, the CO preferential oxidation (PROX) technology can achieve mild conditions (100-200°C) purification of hydrogen fuel by adding molecular oxygen oxidant to the hydrogen-rich atmosphere and selectively catalyzing the conversion of CO to CO2 at the catalyst interface. Compared with traditional methods such as pressure swing adsorption, this technology has significant advantages such as near-zero hydrogen loss (theoretical recovery rate 100%) and low operating energy consumption. However, the existing catalytic system still faces dual challenges: although precious metal catalysts such as Pt and Au have excellent CO conversion rate and selectivity, their scarcity leads to high costs; although transition metal-based catalysts such as Cu / Co / Fe are low-cost, they have inherent defects such as deactivation of Cu-based materials due to carbonate accumulation and methanation side reactions induced by Co-based materials.

[0004] More importantly, the traditional PROX process relies on an air separation unit (ASU) to obtain a gaseous oxygen source, which not only increases operating costs but also seriously restricts system safety due to the explosion risk of the O2 / H2 mixed system. The innovation of chemical looping technology lies in decoupling the redox reaction into two stages: oxygen carrier reduction (CO oxidation) and regeneration (O2 replenishment) separated in time and space. By replacing the gaseous oxygen source with a solid oxygen carrier, the explosion risk is fundamentally avoided and the ASU unit is eliminated, achieving process intensification and energy efficiency improvement. Under this technical framework, the performance of the oxygen carrier becomes the core factor determining the efficiency of the system, and it must simultaneously meet the requirements of high oxygen storage capacity, excellent sintering resistance and cyclic stability. Metal oxides, as oxygen carriers, play the role of transporting oxygen between the reduction / oxidation cycles. Their cost, reactivity and selectivity have an important impact on the feasibility and economy of the process. Therefore, the key to this research is to design and synthesize high-performance and highly selective oxygen carriers. Summary of the Invention

[0005] The present invention addresses the technical issues related to the removal of CO in hydrogen-rich gas and provides a composite oxygen carrier, a preparation method thereof, and an application in a chemical chaining process. The composite oxygen carrier not only realizes the crystal transformation of α-Fe2O3 species, but also achieves ultra-deep removal of CO in the chemical chaining hydrogen production process while maintaining a high H2 recovery rate.

[0006] In order to solve the above technical problems, the present invention is implemented through the following technical solutions:

[0007] According to one aspect of the present invention, a composite oxygen carrier is provided, comprising γ-Fe2O3 and CeO2, with a general chemical formula of γ-Fe2O3 / CeO2; wherein the molar ratio of Fe / (Fe+Ce) is 0.6-0.8.

[0008] According to another aspect of the present invention, there is provided a method for preparing the composite oxygen carrier, comprising:

[0009] (1) Obtaining bimetallic oxide Fe by coprecipitation method x Ce 1-x O; where x is greater than 0 and less than 1;

[0010] (2) The bimetallic oxide Fe x Ce 1-x O is loaded into the reactor, heated to the activation temperature and stabilized;

[0011] (3) alternately introducing steam / nitrogen and hydrogen-rich feed gas into the reactor;

[0012] (4) Under oxidation temperature conditions, air is introduced into the reactor for oxidation for a period of time to obtain a γ-Fe2O3 / CeO2 composite oxygen carrier; wherein the molar ratio of Fe / (Fe+Ce) is 0.6-0.8.

[0013] Preferably, the activation temperature in step (2) is 300-500°C.

[0014] Preferably, in step (3), the cumulative introduction time of the hydrogen-rich feed gas is 80-130 minutes.

[0015] More preferably, the single introduction time of the hydrogen-rich feed gas is 5-8 minutes, and the single introduction time of the water vapor / nitrogen is 10 minutes.

[0016] Preferably, the oxidation temperature in step (4) is 200-400° C., and the oxidation time is 1-5 min.

[0017] According to another aspect of the present invention, there is provided an application of the above-mentioned composite oxygen carrier in a chemical chaining process, comprising: placing a γ-Fe2O3 / CeO2 composite oxygen carrier in a reactor, heating it to a reaction temperature and stabilizing it; the reaction comprises a purification stage and a regeneration stage: in the purification stage, hydrogen-rich gas is introduced, and the γ-Fe2O3 / CeO2 composite oxygen carrier uses lattice oxygen to oxidize CO to CO2; in the regeneration stage, the reacted γ-Fe2O3 / CeO2 composite oxygen carrier reacts in an oxidizing atmosphere to replenish lattice oxygen, thereby completing the cyclic regeneration process.

[0018] Preferably, the reaction temperature is 260-280°C.

[0019] The beneficial effects of the present invention are:

[0020] (1) This invention develops a novel preparation method based on the transition conditions between various iron oxides. It designs and synthesizes a highly active iron-based oxygen carrier, γ-Fe2O3 / CeO2, enabling the controllable construction of the oxygen carrier structure. This oxygen carrier, γ-Fe2O3 / CeO2, can effectively reduce CO concentrations to below 100 ppm and achieve H2 recovery rates exceeding 95%.

[0021] (2) The composite oxygen carrier of the present invention is applied to a chemical looping process. To avoid non-selective oxidation of H2, the operating temperature of the reaction is lower than 300°C, which is significantly lower than the operating temperature of conventional chemical looping processes (>800°C).

[0022] (3) The composite oxygen carrier of the present invention is applied to a chemical looping process, which decouples the CO oxidation reaction and utilizes the lattice oxygen of the oxygen carrier. Compared to conventional preferential oxidation processes, this not only achieves the transfer of oxygen species but also eliminates the need for pure oxygen, ultimately improving operational safety and saving air separation plant costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The present invention relates to the preparation process of composite oxygen carrier.

[0024] Figure 2 Fe prepared in Example 1-4 x Ce 1-x XRD pattern of O.

[0025] Figure 3 is Fe in Example 3 0.6 Ce 0.4 O and the γ-Fe2O3 / CeO2 (Fe / (Fe+Ce)=0.6) oxygen carrier in Example 10 and the XRD patterns of the samples recovered in the purification stage and regeneration stage during the reaction.

[0026] Figure 4 is Fe in Example 3 0.6 Ce 0.4 (a) Raman spectra and (b) FTIR spectra of the γ-Fe2O3 / CeO2 (Fe / (Fe+Ce)=0.6) oxygen carrier in O and Example 10 and the sample recovered in the purification stage.

[0027] Figure 5 is Fe in Example 4 0.8 Ce 0.2 O and the γ-Fe2O3 / CeO2 (Fe / (Fe+Ce)=0.8) oxygen carrier in Example 9 and the XRD patterns of the samples recovered in the purification stage and regeneration stage during the reaction.

[0028] Figure 6 is Fe in Example 3 0.6 Ce 0.4 H2-TPR patterns of the γ-Fe2O3 / CeO2 (Fe / (Fe+Ce)=0.6) oxygen carrier and its CO pre-reduced oxygen carrier in Example 10. DETAILED DESCRIPTION

[0029] like Figure 1 As shown, the present invention provides a composite oxygen carrier comprising γ-Fe2O3 and CeO2, with a general chemical formula of γ-Fe2O3 / CeO2; wherein the molar ratio of Fe / (Fe+Ce) is 0.6-0.8; and the preparation method thereof is as follows:

[0030] (1) Obtaining bimetallic oxide Fe by coprecipitation method x Ce 1-x O; where x is greater than 0 and less than 1.

[0031] (2) The bimetallic oxide Fe x Ce1-x O is loaded into the reactor, heated to an activation temperature of 300-500°C and stabilized.

[0032] (3) Water vapor / nitrogen and hydrogen-rich feed gas are alternately introduced into the reactor; the cumulative introduction time of the hydrogen-rich feed gas is 80-130 minutes.

[0033] In some preferred embodiments of the present invention, the single introduction time of the hydrogen-rich feed gas is 5-8 minutes, and the single introduction time of the water vapor / nitrogen gas is 10 minutes.

[0034] (4) Under oxidation temperature conditions, air is introduced into the reactor, and oxidation is carried out at a temperature of 200-400° C. for 1-5 minutes to obtain a γ-Fe2O3 / CeO2 composite oxygen carrier; wherein the molar ratio of Fe / (Fe+Ce) is 0.6-0.8.

[0035] The application of the composite oxygen carrier of the present invention in the chemical chaining process includes: placing the γ-Fe2O3 / CeO2 composite oxygen carrier in a reactor, heating it to a reaction temperature of 260-280°C and stabilizing it; the reaction includes a purification stage and a regeneration stage: in the purification stage, hydrogen-rich gas is introduced, and the γ-Fe2O3 / CeO2 composite oxygen carrier uses lattice oxygen to oxidize CO to CO2; in the regeneration stage, the reacted γ-Fe2O3 / CeO2 composite oxygen carrier reacts in an oxidizing atmosphere to replenish lattice oxygen, completing the cyclic regeneration process.

[0036] The present invention will be further described in detail below through specific examples. The following examples may enable those skilled in the art to have a more comprehensive understanding of the present invention, but are not intended to limit the present invention in any way.

[0037] Example 1

[0038] The iron-cerium bimetallic oxide was prepared by the co-precipitation method: 1.0517g Fe(NO3)3·9H2O and 4.5213g Ce(NO3)3·6H2O were accurately weighed in a beaker, 50mL deionized water was added, and the mixture was stirred at room temperature for half an hour to fully dissolve the mixture into a transparent solution. Under continuous stirring, ammonia water was used as a precipitant to adjust the pH of the solution, and the solution was added dropwise and evenly. At the same time, the pH of the solution was measured with a pH meter to stabilize it between 8.5-9, and then aged in an oven at 80°C for 3h. The sample was then filtered and washed until the washing liquid was neutral. The resulting precipitate was placed in an oven at 120°C and dried for 12h. The sample was then taken out, ground into powder in a mortar, and calcined at 500°C for 4h to obtain a fresh bimetallic oxide, namely Fe with x=0.2. 0.2 Ce 0.8 O.

[0039] Example 2

[0040] The bimetallic oxide was prepared according to the method of Example 1, the only difference being that Fe(NO3)3·9H2O was 2.3904 g and Ce(NO3)3·6H2O was 3.8538 g. After the preparation, Fe(NO3)3·9H2O was obtained. 0.4 Ce 0.6 O bimetallic oxides.

[0041] Example 3

[0042] The bimetallic oxide was prepared according to the method of Example 1, the only difference being that Fe(NO3)3·9H2O was 4.1523 g and Ce(NO3)3·6H2O was 2.9753 g. After the preparation, Fe(NO3)3·9H2O was obtained. 0.6 Ce 0.4 O bimetallic oxides.

[0043] Example 4

[0044] The bimetallic oxide was prepared according to the method of Example 1, the only difference being that Fe(NO3)3·9H2O was 6.5759 g and Ce(NO3)3·6H2O was 1.7669 g. After the preparation, Fe(NO3)3·9H2O was obtained. 0.8 Ce 0.2 O bimetallic oxides.

[0045] Figure 2 The XRD patterns of the bimetallic oxides prepared in Examples 1-4 are shown in the figure. x Ce 1-x O oxide was successfully synthesized, and with the increase of Fe content, obvious diffraction peaks of Fe2O3 gradually appeared.

[0046] The activity of the bimetallic oxides prepared in Examples 1-4 was tested in a fixed-bed quartz tubular reactor at atmospheric pressure. 0.8 g of an oxygen carrier with a particle size of 20-40 mesh was mixed uniformly with 1 mL of quartz sand. The mixture was then placed in a quartz tube and heated to the reaction temperature. Reduction stage: 1% CO + 50% H₂ + 49% N₂ reaction gas was used at a flow rate of 100 mL / min and a mass space velocity of 7500 mL·g -1 ·h -1 Oxidation stage: 21% O2 / N2 at 100 mL / min. Between the reduction and oxidation reactions, N2 was purged (100 mL / min) to prevent explosions caused by mixing of the reducing gas and air. H2, N2, CO, CH4, and CO2 at the reactor outlet were analyzed online by gas chromatograph.

[0047] The CO conversion rate, H2 recovery rate and tail gas CO concentration are calculated as follows:

[0048]

[0049] Among them, F co,in Indicates the concentration of CO in the hydrogen-rich feed gas, F co,out Indicates the concentration of CO in the exhaust gas; F H2,in Indicates the concentration of H2 in the hydrogen-rich feed gas, F H2,out Indicates the concentration of H2 in the exhaust gas, F N2,out Indicates the concentration of N2 in the exhaust gas, F CO2,out Indicates the concentration of CO2 in the exhaust gas.

[0050] The present invention investigates the effect of the Fe2O3 content in the bimetallic oxides prepared in Examples 1-4 on the reaction performance. Based on the above conditions, when the reaction temperature is 260°C, the test results of the bimetallic oxides in Examples 1-4 are shown in Table 1:

[0051] Table 2 Effect of Fe2O3 content on reaction performance

[0052]

[0053] According to the results in Table 1, it can be seen that Fe x Ce 1-x The CO content in the tail gas of O is not lower than 100ppm, which cannot meet the requirements for use in fuel cells.

[0054] Example 5

[0055] 0.8 g of the bimetallic oxide from Example 3 was loaded into a fixed bed and heated to 400°C and stabilized. Water vapor / nitrogen and hydrogen-rich feed gas were then introduced alternately, with each addition lasting 10 minutes for each addition of water vapor / nitrogen and 6 minutes for each addition of hydrogen-rich feed gas, for a total of 30 minutes. Finally, the oxidation temperature was adjusted to 300°C and air was introduced for 1 minute to produce a γ-Fe2O3 / CeO2 oxygen carrier (Fe / (Fe+Ce)=0.6). Testing was then initiated at 300°C.

[0056] Example 6

[0057] The bimetallic oxide was activated according to the method of Example 5, except that the hydrogen-rich feed gas was introduced for 60 minutes.

[0058] Example 7

[0059] 0.8 g of the bimetallic oxide from Example 3 was loaded into a fixed bed and heated to 400°C and stabilized. Water vapor / nitrogen and hydrogen-rich feed gas were then introduced alternately, with each addition of water vapor / nitrogen for 10 minutes and the hydrogen-rich feed gas for 8 minutes, for a total of 80 minutes. Finally, the oxidation temperature was adjusted to 300°C and air was introduced for 1 minute to produce a γ-Fe2O3 / CeO2 oxygen carrier (Fe / (Fe+Ce)=0.6). Testing was then initiated at 300°C.

[0060] Example 8

[0061] 0.8 g of the bimetallic oxide from Example 4 was loaded into a fixed bed and heated to 400°C and stabilized. Water vapor / nitrogen and hydrogen-rich feed gas were then introduced alternately, with each steam / nitrogen injection lasting 10 minutes, and the hydrogen-rich feed gas being introduced for a total of 70 minutes. Finally, the oxidation temperature was adjusted to 300°C and air was introduced for 2 minutes to produce a γ-Fe2O3 / CeO2 oxygen carrier (Fe / (Fe+Ce)=0.8). Testing was then initiated at 300°C.

[0062] Example 9

[0063] The bimetallic oxide was activated according to the method of Example 8, except that the hydrogen-rich feed gas was introduced for 5 minutes each time, for a total of 130 minutes.

[0064] Example 10

[0065] The bimetallic oxide was activated according to the method of Example 7, except that the oxidation temperature and the reaction temperature were both 260°C.

[0066] Example 11

[0067] The bimetallic oxide was activated according to the method of Example 10, except that the hydrogen-rich feed gas and water vapor / nitrogen were introduced together for 80 minutes.

[0068] Example 12

[0069] 0.8 g of the bimetallic oxide from Example 3 was loaded into a fixed bed and heated to 400°C and stabilized. Water vapor / nitrogen and hydrogen-rich feed gas were then introduced alternately, with each steam / nitrogen injection lasting 10 minutes and the hydrogen-rich feed gas lasting 8 minutes, for a total of 80 minutes. Finally, the oxidation temperature was adjusted to 220°C and air was introduced for 1 minute to produce a γ-Fe2O3 / CeO2 oxygen carrier (Fe / (Fe+Ce)=0.6). Testing was then initiated at 260°C.

[0070] Example 13

[0071] The bimetallic oxide was activated according to the method of Example 12, except that the oxidation temperature was adjusted to 200°C.

[0072] Example 14

[0073] 0.8 g of the bimetallic oxide from Example 3 was loaded into a fixed bed and heated to 400°C and stabilized. Steam / nitrogen and hydrogen-rich feed gas were then introduced alternately, with steam / nitrogen introduced for 10 minutes each and hydrogen-rich feed gas introduced for 8 minutes each, for a total of 80 minutes. Finally, the oxidation temperature was adjusted to 400°C and air was introduced for 5 minutes to produce a γ-Fe2O3 / CeO2 oxygen carrier (Fe / (Fe+Ce)=0.6). Testing was then initiated at 260°C.

[0074] Example 15

[0075] The bimetallic oxide was activated according to the method of Example 14, except that air was introduced for oxidation for 10 minutes.

[0076] Example 16

[0077] The bimetallic oxide was activated according to the method of Example 12, except that the test temperature was 300°C.

[0078] Example 17

[0079] The bimetallic oxide was activated according to the method of Example 12, except that the test temperature was 280°C.

[0080] Example 18

[0081] The bimetallic oxide was activated according to the method of Example 12, except that the test temperature was 250°C.

[0082] Examples 3, 5-7 explored the effect of the introduction time of hydrogen-rich feed gas on the performance of the oxygen carrier when the Fe / (Fe+Ce) molar ratio was 0.6. The test results are shown in Table 2:

[0083] Table 2 Effect of hydrogen-rich feed gas introduction time on oxygen carrier performance

[0084]

[0085] Examples 8-9 investigated the effect of the introduction time of hydrogen-rich feed gas on the performance of the oxygen carrier when the Fe / (Fe+Ce) molar ratio was 0.8. The test results are shown in Table 3:

[0086] Table 3 Effect of hydrogen-rich feed gas introduction time on oxygen carrier performance

[0087]

[0088]

[0089] According to the results in Tables 2 and 3, when the introduction time of the hydrogen-rich feed gas is greater than 80 minutes, the requirement of a CO concentration lower than 100 ppm can be achieved; therefore, the preferred introduction time of the hydrogen-rich feed gas is 80-130 minutes.

[0090] Examples 10-11 investigated the effect of the reducing gas introduction method on the performance of the oxygen carrier. The test results are shown in Table 4:

[0091] Table 4 Effects of hydrogen-rich feed gas and steam / nitrogen introduction methods on performance

[0092]

[0093] According to the results in Table 4, the requirement of CO concentration below 100 ppm can be achieved when water vapor / nitrogen and hydrogen-rich feed gas are introduced alternately.

[0094] Examples 12-16 explored the effects of oxidation temperature and oxidation time on the performance of oxygen carriers. The test results are shown in Table 5:

[0095] Table 5 Effect of oxidation temperature and oxidation time on oxygen carrier performance

[0096]

[0097] According to the results in Table 5, when the oxidation temperature is 200-400°C and the oxidation time is 1-5 minutes, the requirement of CO concentration below 100 ppm can be achieved; therefore, the preferred oxidation temperature is 200-400°C and the oxidation time is 1-5 minutes.

[0098] Examples 12, 16-18 explored the effect of test temperature on the performance of oxygen carriers. The test results are shown in Table 6:

[0099] Table 6 Effect of test temperature on oxygen carrier performance

[0100]

[0101] According to the results of the embodiment, the requirement of a CO concentration lower than 100 ppm can be achieved when the reaction temperature is 260-280°C.

[0102] In order to further determine the crystal phases of the two oxygen carriers, XRD characterization tests were performed on the oxygen carriers of Example 3 and Example 10.

[0103] Figure 3 is Fe in Example 3 0.6 Ce 0.4The XRD patterns of the oxygen carriers O and γ-Fe2O3 / CeO2 (Fe / (Fe+Ce) molar ratio = 0.6) in Example 10 and the samples recovered during the purification and regeneration stages of the reaction. From the XRD, it can be seen that the γ-Fe2O3 crystal phase appears on the oxygen carrier of Example 10. However, the XRD characteristic peaks of γ-Fe2O3 and Fe3O4 are similar, so it is difficult to accurately determine whether the oxygen carriers after activation and reduction have two different iron oxides by XRD. Raman and Fourier transform infrared spectroscopy further confirmed the presence of γ-Fe2O3, as shown in Figure 2. Figure 4 The Raman spectrum of the oxygen carrier of Example 10 is at 350 and 500 cm -1 and 700cm -1 Three relatively broad characteristic peaks appeared, which matched the characteristic peaks of γ-Fe2O3. In addition, the FTIR spectrum of the oxygen carrier of Example 10 was at 728, 694, 637, 554, 479, and 440 cm -1 and 419cm -1 There are also seven characteristic peaks of γ-Fe2O3. 0.6 Ce 0.4 O oxygen carrier surface weak α-Fe2O3, the oxygen carrier surface of Example 10 has obvious iron species, namely γ-Fe2O3, indicating that the preparation process causes the iron species to migrate and aggregate to the surface of the oxygen carrier, and forms a γ-Fe2O3 species with higher activity on the surface.

[0104] Figure 5 is Fe in Example 4 0.8 Ce 0.2 O and the γ-Fe2O3 / CeO2 (Fe / (Fe+Ce) molar ratio = 0.8) oxygen carrier in Example 9 and the XRD patterns of the samples recovered in the purification stage and regeneration stage during the reaction. Similar to the γ-Fe2O3 / CeO2 (Fe / (Fe+Ce) molar ratio = 0.6) oxygen carrier, Figure 5 It can be seen that γ-Fe2O3 crystal phase also appears on the γ-Fe2O3 / CeO2 (Fe / (Fe+Ce) molar ratio = 0.8) oxygen carrier.

[0105] Figure 6 is Fe in Example 3 0.6 Ce 0.4 O and the H2-TPR spectra of the γ-Fe2O3 / CeO2 (Fe / (Fe+Ce)=0.6) oxygen carrier in Example 10 and its CO pre-reduced oxygen carrier. First, Fe 0.6 Ce 0.4The first peak of O appears at 419℃. The broad reduction peak may be the result of the overlap of the reduction peaks of isolated Fe2O3 and CeO2 on the surface. The oxygen carrier of Example 10 has two obvious reduction peaks in the low temperature region, of which the reduction peak at the higher temperature is the same as that of Fe 0.6 Ce 0.4 The reduction peak of O appears at the same position, likely due to the surface reduction of CeO2. Combined with the previous XRD, Raman, and IR structural characterization results, the newly appearing reduction peak at a lower temperature of around 300°C is likely due to the reduction of γ-Fe2O3 enriched on the surface during the activation process. Subsequently, it can be seen that the sample after pre-reduction (the oxygen carrier of Example 10 was fully reduced with 5% CO / He at 260°C) disappears compared to the oxygen carrier of Example 10, while a second reduction peak associated with the surface reduction of CeO2 remains. This structure indicates that γ-Fe2O3 has been reduced by CO at a reaction temperature of 260°C, meaning that the primary active species in the CO selective oxidation process is γ-Fe2O3. Furthermore, the significant forward shift in the reduction peak position of the oxygen carrier of Example 10 indicates improved reducibility and better reaction activity. Therefore, the preparation method of the present invention effectively enriches the iron species of the oxygen carrier on the surface of the oxygen carrier and forms a highly active γ-Fe2O3 species on the surface, thereby significantly improving the reaction performance.

[0106] Although the preferred embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments. The above-mentioned specific embodiments are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms of specific changes without departing from the scope of protection of the present invention and the claims. These all fall within the scope of protection of the present invention.

Claims

1. A composite oxygen carrier, characterized in that: It comprises gamma-Fe2O3 and CeO2, and its general chemical formula is gamma-Fe2O3 / CeO2; wherein the molar ratio of Fe / (Fe+Ce) is 0.6-0.

8.

2. A method for preparing a composite oxygen carrier according to any one of claims 1 to 3, characterized in that: include: (1) Obtaining bimetallic oxide Fe by coprecipitation method x Ce 1-x O; where x is greater than 0 and less than 1; (2) The bimetallic oxide Fe x Ce 1-x O is loaded into the reactor, heated to the activation temperature and stabilized; (3) alternately introducing steam / nitrogen and hydrogen-rich feed gas into the reactor; (4) Under oxidation temperature conditions, air is introduced into the reactor for oxidation for a period of time to obtain a γ-Fe2O3 / CeO2 composite oxygen carrier; wherein the molar ratio of Fe / (Fe+Ce) is 0.6-0.

8.

3. The method for preparing a composite oxygen carrier according to claim 2, characterized in that: The activation temperature in step (2) is 300-500°C.

4. The method for preparing a composite oxygen carrier according to claim 2, characterized in that: In step (3), the cumulative introduction time of the hydrogen-rich feed gas is 80-130 minutes.

5. The method for preparing a composite oxygen carrier according to claim 4, characterized in that: The single injection time of hydrogen-rich raw gas is 5-8 minutes, and the single injection time of water vapor / nitrogen is 10 minutes.

6. The method for preparing a composite oxygen carrier according to claim 2, characterized in that: The oxidation temperature in step (4) is 200-400° C., and the oxidation time is 1-5 minutes.

7. Use of the composite oxygen carrier according to claim 1 in a chemical looping process, characterized in that: include: A γ-Fe2O3 / CeO2 composite oxygen carrier is placed in a reactor, heated to the reaction temperature and stabilized; the reaction includes a purification stage and a regeneration stage: in the purification stage, hydrogen-rich gas is introduced, and the γ-Fe2O3 / CeO2 composite oxygen carrier uses lattice oxygen to oxidize CO to CO2; in the regeneration stage, the reacted γ-Fe2O3 / CeO2 composite oxygen carrier reacts in an oxidizing atmosphere to replenish lattice oxygen, completing the cyclic regeneration process.

8. Use of the composite oxygen carrier in a chemical looping process according to claim 7, characterized in that: The reaction temperature is 260-280°C.

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