A method for studying the activity mechanism of a chemical looping oxygen carrier

Abstract

The application belongs to the field of catalysis technology, and particularly relates to a method for studying the mechanism of a chemical chain oxygen carrier, the core of the method being to prepare a core-shell structure of an inert oxide coated with an active component of the oxygen carrier, and using the chemically inert oxide shell as a fixed marker layer for monitoring the dynamic migration path of the bulk metal ions of the oxygen carrier during the oxidation-reduction experiment, and determining the reaction interface of the oxygen carrier for activating the reactant methane, and summarizing the activity mechanism thereof in the oxidation-reduction reaction, and providing ideas for designing a new type of efficient oxygen carrier.

Description

Technical Field

[0001] This invention belongs to the field of catalysis technology, and in particular relates to a method for studying the active mechanism of chemically chained oxygen carriers. Background Technology

[0002] Chemical looping technology mainly consists of two parts: chemical looping reforming (CLR) and chemical looping combustion (CLC). CLR enables the reforming of natural gas, primarily composed of methane, to effectively produce high-purity H2 and syngas (H2 and CO). CLC enables the clean combustion of fossil fuels and the capture of CO2, effectively protecting the environment and reducing greenhouse gas emissions.

[0003] The core of chemical chaining technology lies in the reactivity of the oxygen carrier, which is closely related to the migration of bulk active ions. However, current research on the reaction mechanism of oxygen carriers mainly focuses on the migration of lattice oxygen, and there is a lack of in-depth and systematic understanding of the spatiotemporal evolution characteristics of the bulk metal active components of oxygen carrier particles. Therefore, to prepare more efficient and novel oxygen carriers, it is necessary to conduct in-depth research on their activity mechanism in redox reactions.

[0004] Therefore, providing a method for studying the active mechanism of chemically chained oxygen carriers is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides a method for studying the activity mechanism of chemically chained oxygen carriers. By using an inert oxide film as the shell layer for inert labeling experiments, the inert labeling can realize the oxidation-reduction of the oxygen carrier and monitor the migration of bulk metal ions under different reduction and oxidation degrees, thus demonstrating the reaction interface of the oxygen carrier activating methane.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for studying the activity mechanism of chemically chained oxygen carriers is disclosed. In this method, the oxygen carrier employs a core-shell structure, wherein the core is the active component and the shell is an inert oxide. The inert oxide shell maintains structural and morphological integrity under high-temperature conditions, and its chemical inertness further ensures that the encapsulated metal nanoparticles exhibit their inherent catalytic performance without being affected by metal-oxide interactions, thus ensuring the accuracy of inert labeling experiments.

[0008] Preferably, the inert oxide is SiO2 or Al2O3, which is abundant, inexpensive, has good mechanical properties, high thermal stability, and good chemical inertness. As an inert shell of the active component of the oxygen carrier, it can meet the needs of high-temperature chemical chain reactions.

[0009] The active component is Ce 0.8 Fe 0.2 O2, Ce 0.8 Zr 0.2 O2 and Ce 0.8 Ni 0.2 Any of the O2 molecules has a fairly stable cubic fluorite crystal structure, which remains stable even at 2000℃.

[0010] Preferably, the method for preparing the core-shell structured oxygen carrier includes the following steps:

[0011] (1) A microemulsion was prepared using cyclohexane, polyethylene glycol octylphenyl ether and n-hexanol;

[0012] (2) After ultrasonically dispersing the suspension of the active component and the microemulsion, ammonia and silicon source are added sequentially, and the mixture is stirred for 12-20 hours to obtain the sample;

[0013] (3) After drying the sample, calcination is performed to obtain a core-shell structured oxygen carrier.

[0014] Cyclohexane serves as the oil phase, and polyethylene glycol octylphenyl ether is a nonionic surfactant. It binds to the inorganic ionic precursor via hydrogen bonds, undergoing a chemical reaction to obtain oxygen-carrying nanoparticles. This type of nanomaterial exhibits good stability and high purity. Hexanol acts as a co-surfactant, reducing interfacial tension and improving interfacial curvature in the microemulsion system. The stable microemulsion system formulated with these three components facilitates the dispersion of the precursor active components and allows for control over particle size. Ammonia is added later to provide an alkaline environment, which is beneficial for the hydrolysis and condensation of tetraethyl orthosilicate.

[0015] Preferably, the volume ratio of cyclohexane, polyethylene glycol octylphenyl ether and n-hexanol in step (1) is 2-5:1:1, preferably 4:1:1.

[0016] The volume ratio of cyclohexane, polyethylene glycol octylphenyl ether, and n-hexanol is 4:1:1. At this ratio, the Brownian motion of the reactants will not be significantly affected by the oil phase cyclohexane. Moreover, the effect of polyethylene glycol octylphenyl ether on the nucleation of particles is also in line with the requirements. The interfacial tension and interfacial curvature of the microemulsion system affected by n-hexanol meet the nucleation rate requirements for the oxygen carrier. Otherwise, the microemulsion system would not be conducive to the nucleation of the precursor.

[0017] Within the above-mentioned ratio range, the Brownian motion of the reactants will not be excessively interfered with by the cyclohexane in the oil phase, and the effect of polyethylene glycol octylphenyl ether on the nucleation of particles is also in line with the requirements. The interfacial tension and interfacial curvature of the microemulsion system affected by n-hexanol meet the nucleation rate required for the oxygen carrier; otherwise, the microemulsion system would not be conducive to the nucleation of the precursor.

[0018] Preferably, the ultrasonic dispersion time in step (2) is 20-60 min;

[0019] The concentration of the ammonia water is 25-28%, the volume ratio of the ammonia water to the silicon source is 14-30:1, preferably 27:1, and the volume ratio of the ammonia water to the microemulsion is 0.3-0.6:1, preferably 0.44:1.

[0020] The mass ratio of the silicon source to the active component is 3.5-7:1, preferably 5.64:1;

[0021] The suspension is an aqueous solution of the active component, and the volume ratio of the suspension to the microemulsion is 0.5-1:1, preferably 0.928:1.

[0022] The silicon source is tetraethyl silicate (TEOS).

[0023] When the volume ratio of ammonia to TEOS is 10-26:1 and the mass ratio of TEOS to active components is 5.64:1, the hydrolysis rate of TEOS is too slow and takes too long. When the volume ratio of ammonia to TEOS is 30-80:1 and the mass ratio of TEOS to active components is 5.64:1, the increase in ammonia concentration will lead to a faster hydrolysis rate of TEOS. Although the amount of silicate ions generated per unit time increases, the excessively high ammonia concentration will cause partial dissolution of the SiO2 shell. Therefore, the optimal volume ratio of ammonia to TEOS is about 27:1.

[0024] When the volume ratio of ammonia to TEOS is 27:1 and the mass ratio of TEOS to active component is 5.64:1, the amount of TEOS used is used to control the thickness of the shell. Too little TEOS will not be enough to coat the active component particles, while too much TEOS will result in an excessively thick shell, affecting the properties of the active component itself. Therefore, the mass ratio of TEOS to active component is chosen to be 5.64:1.

[0025] Preferably, the roasting procedure in step (3) is as follows: the temperature is increased from room temperature to 500-850℃ at a heating rate of 1-5℃ / min, and then kept at 500-850℃ for 3-5 hours, and finally cooled naturally to room temperature.

[0026] Preferably, the roasting procedure in step (3) is as follows: the temperature is increased from room temperature to 500°C at a heating rate of 1°C / min, held at 500°C for 4 hours, and finally cooled naturally to room temperature.

[0027] Preferably, the active component is prepared using the sol-gel method.

[0028] Preferably, the specific steps of the sol-gel method are as follows: citric acid is added to a metal salt solution and stirred at 60-80°C until a gel state is reached, then dried and calcined to obtain the active component.

[0029] Preferably, the molar ratio of citric acid to metal ions is 1-3:1;

[0030] The drying temperature is 100-120℃, and the time is 12-18h;

[0031] The roasting procedure is as follows: heat from room temperature to 250-300℃ at a heating rate of 1-5℃ / min, hold at 250-300℃ for 0.5-1h, then heat from 250-300℃ to 500-700℃ at a heating rate of 1-5℃ / min, hold at 500-700℃ for 2-5h, and then allow to cool naturally to room temperature.

[0032] Preferably, the steps for studying the oxidation or reduction mechanism of the oxygen carrier in the core-shell structure are as follows:

[0033] The core-shell structured oxygen carrier is placed in a reactor and oxidized or reduced using oxidizing or reducing gases. The degree of oxidation or reduction of the oxygen carrier is controlled by time. The position and dispersion of the bulk metal ions of the oxygen carrier relative to the shell will continuously change under different reduction degrees, thereby qualitatively determining their migration direction and migration rate. At the same time, the fixed-bed circulation activity results of uncoated oxygen carriers and coated oxygen carriers are compared to determine the reaction interface of methane, the oxygen carrier activation reactant.

[0034] Preferably, the oxidation or reduction temperature is 500-900℃, and the flow rate of the oxidizing or reducing gas is 50-150 mL / min.

[0035] Preferably, when using oxidizing or reducing gases for oxidation or reduction, it is necessary to purge with inert gas for 5-20 minutes to remove impurity gases, and then switch between oxidizing or reducing gases according to the program settings to carry out the oxidation or reduction experiment.

[0036] As can be seen from the above technical solution, compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] This invention provides a method for studying the activity mechanism of chemically chained oxygen carriers. By using an inert oxide film as the shell layer for inert labeling experiments, the inert labeling can monitor the migration of bulk metal ions during redox experiments on the oxygen carrier and demonstrate that the oxygen carrier activates the reaction interface of methane. Attached Figure Description

[0038] The accompanying drawings, which are included to provide a further understanding of the invention and form part of the invention, show:

[0039] Figure 1 This invention is Ce 0.8 Fe0.2 Schematic diagram of the principle of monitoring metal ion migration in the inert shell of O2@SiO2 core-shell oxygen carrier;

[0040] Figure 2 The fresh Ce described in Embodiment 1 of this invention 0.8 Fe 0.2 Transmission electron microscopy morphology of O2@SiO2 core-shell oxygen carrier;

[0041] Figure 3 The fresh Ce described in Embodiment 1 of this invention 0.8 Fe 0.2 Morphology of O2@SiO2 core-shell oxygen carrier for Si, Ce and Fe by surface scanning;

[0042] Figure 4 The Ce after the redox reaction described in Example 2 of this invention 0.8 Fe 0.2 Morphology images of Si, Ce, Fe, and O elements obtained by transmission electron microscopy of O2@SiO2 core-shell oxygen carriers (surface scan).

[0043] Figure 5 The Ce after the redox reaction described in Example 2 of this invention 0.8 Fe 0.2 TEM (EDS) elemental packing map of O2@SiO2 with its inert shell for monitoring metal ion migration;

[0044] Figure 6 The Ce before and after the redox reaction described in Example 2 of this invention 0.8 Fe 0.2 XRD test results of O2@SiO2 core-shell structure;

[0045] Figure 7 The uncoated oxygen carrier Ce described in Embodiment 1 of this invention 0.8 Fe 0.2 Graph showing the activity results of O2 in a fixed-bed circulation experiment;

[0046] Figure 8 The coated oxygen carrier Ce described in Embodiment 1 of this invention 0.8 Fe 0.2 Figure showing the activity results of the fixed-bed circulating experiment of O2@SiO2. Detailed Implementation

[0047] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0048] Example 1

[0049] This invention provides a coated oxygen carrier Ce 0.8 Fe 0.2 The preparation method of O2@SiO2 is as follows:

[0050] (1) Active ingredient Ce 0.8 Fe 0.2 Preparation of O2 solid solution

[0051] 1-1) Weigh 11.19g Ce(NO3)3·6H2O and dissolve it in 100mL of deionized water. Then weigh 2.60g Fe(NO3)3·9H2O and dissolve it in the above solution. Transfer the solution into a magnetic stirrer, set the speed to 250r / min and the temperature to 70℃. Then weigh 18.56g anhydrous citric acid and dissolve it in the stirring solution. Stir the mixture until it reaches a wet gel state, where the anhydrous citric acid acts as a complexing agent.

[0052] 1-2) The obtained wet gel was transferred into a drying oven and dried at 110°C for 12 hours to obtain a dry gel;

[0053] 1-3) The obtained dry gel was transferred into a muffle furnace for calcination. The calcination procedure was as follows: the temperature was increased from room temperature to 280℃ at a heating rate of 1℃ / min, held at 280℃ for 0.5h, then increased from 280℃ to 600℃ at a heating rate of 2℃ / min, held at 600℃ for 4h, and finally cooled naturally to room temperature. After grinding, Ce was obtained. 0.8 Fe 0.2 O2 powder;

[0054] (2)Ce 0.8 Fe 0.2 Preparation of O2@SiO2

[0055] 2-1) Accurately measure 120 mL of cyclohexane, 30 mL of polyethylene glycol octylphenyl ether, and 30 mL of n-hexanol using a graduated cylinder to prepare 180 mL of microemulsion, and then mix it evenly under magnetic stirring.

[0056] 2-2) Accurately weigh 0.5g of the prepared Ce using an electronic balance. 0.8 Fe 0.2 O2 solid solution powder was dispersed in 167 mL of deionized water and ultrasonically dispersed for 45 min. Using an ultrasonic cleaner helped to uniformly disperse the solid solution particles and form a uniform suspension aqueous solution.

[0057] 2-3) Mix the microemulsion prepared in step 2-1) with the homogeneous suspension prepared in step 2-2) under magnetic stirring until homogeneous, then transfer to an ultrasonic cleaner for ultrasonic dispersion for 30 min, then transfer to magnetic stirring and add 80 mL of ammonia (28%), mix until homogeneous, then add 3 mL of tetraethyl orthosilicate (TEOS) dropwise, stirring continuously for 16 h to obtain the mixture;

[0058] 2-4) Let the obtained mixture stand for 1 hour to stabilize it, then centrifuge it, and then wash it 4 times with anhydrous ethanol and deionized water by ultrasonic oscillation to remove organic matter on the surface of the oxygen carrier and obtain filter material.

[0059] 2-5) The obtained filter material was dried at 110℃ overnight, and then calcined in a muffle furnace. The calcination procedure was as follows: the temperature was increased from room temperature to 500℃ at a heating rate of 1℃ / min, held at 500℃ for 4 hours, and finally cooled naturally to room temperature. Calcination further removed organic matter, and finally Ce was obtained. 0.8 Fe 0.2 O2@SiO2 powder.

[0060] Example 2

[0061] A method for studying the redox activity mechanism of chemically chained oxygen carriers, the specific operation steps of which are as follows:

[0062] (1) The Ce prepared in Example 1 0.8 Fe 0.2 0.32 g of O2@SiO2 core-shell oxygen carrier was placed in a fixed-bed reactor. The temperature was raised from room temperature to 850°C at a rate of 10°C / min. The reaction tube was then purged with N2 at a rate of 150 mL / min for 10 min to remove impurity gases.

[0063] (2) According to the program setting, switch to 150 mL / min CH4 to reduce the oxygen carrier. The reduction program lasts for 1 hour. Then, purge with 150 mL / min N2 for 10 minutes to remove CH4 gas. Then switch to 150 mL / min O2 to re-oxidize the oxygen carrier. The oxidation program lasts for 1 hour. After the re-oxidation process is completed, purge with 150 mL / min N2 and allow natural cooling to protect the oxygen carrier from being reduced.

[0064] The above methods can be used to effectively monitor the positional changes of bulk metal ions relative to the inert labeled SiO2 shell during the redox reaction process. The basic principle is as follows: Figure 1 As shown, the microscopic particle structure of the core-shell oxygen carrier is as follows: Figure 2 As shown, the relative positions of the original SiO2 shell and the active metal elements in the oxygen carrier bulk phase are as follows: Figure 3As shown, both cerium and iron are encased in an inert shell. After the reaction, the positions of some elements relative to the inert shell are as follows: Figure 4 , Figure 5 As shown, some Ce and some Fe elements have migrated outside the inert shell, and Fe exhibits severe segregation, which is consistent with the XRD results. Figure 6 As shown, Fe3O4 and Fe2O3 phases appeared in the sample after the reaction, indicating that Fe migrated from the bulk phase to the surface during the redox reaction, which is consistent with the TEM surface scan results.

[0065] Based on the results of the redox cycle experiment, as follows Figure 7 and Figure 8 As shown, the methane conversion rate and product selectivity of the active component did not fluctuate much before and after being coated with inert oxide, but the carbon deposition results were greatly reduced. This indicates that the methane reaction tends to occur on the SiO2 surface, that is, lattice oxygen migrates from the bulk phase to the surface through the silicon layer to react with methane, thus avoiding direct contact between methane and metal active species and the resulting cracking reaction.

[0066] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for studying the active mechanism of chemically chained oxygen carriers, characterized in that, In the method, the oxygen carrier adopts a core-shell structure, wherein the core is an active component and the shell is an inert oxide. The inert oxide is SiO2 or Al2O3, and the active component is Ce. 0.8 Fe 0.2 O2, Ce 0.8 Zr 0.2 O2 and Ce 0.8 Ni 0.2 Any one of O2; The steps for studying the oxidation or reduction mechanism of the oxygen carrier in the core-shell structure are as follows: The core-shell structured oxygen carrier is placed in a reactor and partially oxidized or reduced using oxidizing or reducing gases. The degree of oxidation or reduction of the oxygen carrier is controlled by time. The position and dispersion of the bulk metal ions of the oxygen carrier relative to the shell layer will continuously change under different reduction degrees, thereby qualitatively determining their migration direction and migration rate. At the same time, the fixed-bed circulation activity results of uncoated oxygen carriers and coated oxygen carriers are compared to determine the reaction interface of methane, the oxygen carrier activation reactant. The method for preparing the core-shell structured oxygen carrier includes the following steps: (1) A microemulsion was prepared using cyclohexane, polyethylene glycol octylphenyl ether and n-hexanol; (2) After ultrasonically dispersing the suspension of the active component and the microemulsion, ammonia and silicon source are added sequentially, and the mixture is stirred for 12-20 hours to obtain the sample; (3) After drying the sample, calcination is performed to obtain a core-shell structured oxygen carrier.

2. The method for studying the activity mechanism of chemically chained oxygen carriers according to claim 1, characterized in that, The volume ratio of cyclohexane, polyethylene glycol octylphenyl ether and n-hexanol in step (1) is 2-5:1:

1.

3. The method for studying the activity mechanism of chemically chained oxygen carriers according to claim 1, characterized in that, The ultrasonic dispersion time in step (2) is 20-60 min; The volume ratio of the ammonia water to the silicon source is 14-30:1, and the volume ratio of the ammonia water to the microemulsion is 0.3-0.6:

1. The mass ratio of the silicon source to the active component is 3.5-7:1; The suspension is an aqueous solution of the active component, and the volume ratio of the suspension to the microemulsion is 0.5-1:

1. The silicon source is tetraethyl silicate.

4. The method for studying the activity mechanism of chemically chained oxygen carriers according to claim 1, characterized in that, The roasting procedure in step (3) is as follows: heat from room temperature to 500-850℃ at a heating rate of 1-5℃ / min, keep at 500-850℃ for 3-5 hours, and finally cool down naturally to room temperature.

5. The method for studying the activity mechanism of chemically chained oxygen carriers according to claim 1, characterized in that, The active component was prepared using the sol-gel method; The specific steps of the sol-gel method are as follows: citric acid is added to a metal salt solution and stirred at 60-80°C until a gel state is reached. After drying, the active component is obtained by calcination.

6. The method for studying the activity mechanism of chemically chained oxygen carriers according to claim 5, characterized in that, The molar ratio of citric acid to metal ions is 1-3:1; The drying temperature is 100-120℃, and the time is 12-18h; The roasting procedure is as follows: heat from room temperature to 250-300℃ at a heating rate of 1-5℃ / min, hold at 250-300℃ for 0.5-1h, then heat from 250-300℃ to 500-700℃ at a heating rate of 1-5℃ / min, hold at 500-700℃ for 2-5h, and then allow to cool naturally to room temperature.

7. The method for studying the activity mechanism of chemically chained oxygen carriers according to claim 1, characterized in that, The oxidation or reduction temperature is 500-900℃, and the flow rate of the oxidizing or reducing gas is 50-150mL / min.

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