Ti-mn-o composite oxide catalyst, and preparation method and application thereof

Abstract

This invention discloses a Ti-Mn-O composite oxide catalyst, its preparation method, and its application. The catalyst is mainly composed of Ti, Mn, and O, with the main phases including Mn₂O₃ and anatase TiO₂. The preparation method involves preparing a titanium-manganese composite dry gel precursor using a citric acid-assisted sol-gel method, followed by calcination at 350–500°C to obtain the Ti-Mn-O composite oxide catalyst. This invention also discloses the application of this catalyst in hydrogen storage: under a protective atmosphere, 2–8 wt% of the catalyst is ball-milled with MgH₂ to obtain a Ti-Mn-O / MgH₂ composite hydrogen storage material. TPD test results show that the hydrogen release temperature of this composite hydrogen storage material is significantly lower than that of undoped MgH₂, with the main hydrogen release range being 245–310°C and the total hydrogen release being 6.7–7.3 wt%. The catalyst of this invention has a simple preparation process, and the Ti and Mn components are uniformly dispersed. It can effectively improve the dehydrogenation behavior of MgH2 and reduce the hydrogen release temperature, and has good application prospects in the field of magnesium-based solid hydrogen storage materials.

Description

Technical Field

[0001] This invention belongs to the field of hydrogen storage materials technology, and relates to a Ti-Mn-O composite oxide catalyst, its preparation method and application. Background Technology

[0002] Hydrogen energy is considered a promising renewable energy source due to its high energy density, environmental friendliness, and wide range of applications. Solid-state hydrogen storage offers higher safety and volumetric hydrogen storage density compared to compressed gaseous hydrogen storage and cryogenic liquid hydrogen storage. Among various solid-state hydrogen storage materials, magnesium-based materials (especially MgH2) have attracted widespread attention due to their high theoretical hydrogen storage capacity, abundant resources, and low cost.

[0003] However, MgH2 itself has strong Mg-H bonds and high thermodynamic stability, which leads to problems in practical applications such as high hydrogen desorption temperature, slow hydrogen absorption and desorption kinetics, insufficient reactivity at low temperatures, and the need to improve cycle stability. These problems seriously restrict the application of magnesium-based hydrogen storage materials.

[0004] Currently, researchers commonly employ methods such as catalyst doping, alloying, microstructure control, and nanoengineering to improve the performance of magnesium-based hydrogen storage materials. Among these, adding catalysts is considered one of the simplest and most effective strategies. In numerous catalyst systems, transition metals and their compounds can, to some extent, promote the dissociation of hydrogen molecules, the migration of hydrogen atoms, and interfacial reactions during the dehydrogenation process of MgH2. Therefore, transition metal oxides, nitrides, and multi-component composite catalysts are widely used to improve the hydrogen absorption and desorption performance of MgH2 hydrogen storage systems.

[0005] In the existing technology, although some transition metal or transition metal compound catalysts can reduce the hydrogen desorption temperature of MgH2, they still generally have the following shortcomings: First, the preparation process of some catalysts is complex, with many reaction steps, and high requirements for equipment and conditions; second, some catalyst particles are large or not sufficiently dispersed, making it difficult to form a sufficient and uniform contact interface with the MgH2 matrix; third, although some catalytic systems have a certain modifying effect on MgH2, they are still insufficient in further reducing the hydrogen desorption temperature, increasing the reaction rate, and maintaining the effective hydrogen storage phase content.

[0006] Furthermore, there is relatively little research on the regulation of MgH2 hydrogen storage performance by Ti-Mn bicomponent composite oxide catalysts in existing technologies. Ti-based oxides and Mn-based oxides have different interfacial characteristics and catalytic activities. If Ti and Mn can be uniformly dispersed at the microscale through the sol-gel method and a Ti-Mn-O composite oxide system can be formed during subsequent calcination, it is expected that more catalytic interfaces can be constructed and the hydrogen diffusion path can be shortened, thereby improving the hydrogen desorption behavior of MgH2.

[0007] Although existing studies have used transition metals and their oxides, nitride doping, or synergistic catalysis to modify MgH2, its hydrogen storage performance still has shortcomings in practical applications. These shortcomings mainly include high hydrogen desorption temperature, poor hydrogen desorption kinetics, insufficient contact interface between the catalyst and the MgH2 matrix, and difficulty in optimizing the amount of catalyst added.

[0008] Therefore, developing a Ti-Mn-O composite oxide catalyst with low raw material cost, simple preparation process, and significant ability to reduce the hydrogen desorption temperature of MgH2 is of great significance for promoting the practical application of magnesium-based solid hydrogen storage materials. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the present invention aims to provide a Ti-Mn-O composite oxide catalyst, its preparation method, and its application.

[0010] This invention is achieved through the following technical solution:

[0011] A Ti-Mn-O composite oxide catalyst, wherein the catalyst comprises elements Ti, Mn, and O, and the main phases of the catalyst include Mn2O3 and anatase TiO2.

[0012] This invention also provides a method for preparing the above-mentioned Ti-Mn-O composite oxide catalyst, comprising the following steps:

[0013] Step 1): Dissolve the titanium source in an organic solvent to obtain a titanium source solution; dissolve the manganese source and citric acid in an aqueous solvent to obtain a manganese source-chelating agent solution;

[0014] Step 2), the manganese source-chelating agent solution is mixed with the titanium source solution, a hydrolysis catalyst is added, and the mixture is heated and stirred to form a gel. After aging and drying, a titanium-manganese composite dry gel precursor is obtained.

[0015] Step 3) The titanium-manganese composite dry gel precursor is calcined to obtain the Ti-Mn-O composite oxide catalyst.

[0016] Preferably, in step 1), the titanium source is tetraisopropyl titanate, the organic solvent is anhydrous ethanol, the manganese source is manganese acetate tetrahydrate, the citric acid is citric acid monohydrate, and the aqueous solvent is a mixture of water and ethanol.

[0017] Preferably, in step 1), the molar ratio of titanium source to manganese source is 1:2, and the molar ratio of citric acid to manganese source is 2:1 to 3:1.

[0018] Preferably, in step 2), the hydrolysis catalyst is concentrated nitric acid, and the ratio of the amount of concentrated nitric acid added to the amount of titanium source used in step 1) is 0.3-0.5 mL of concentrated nitric acid per millimole of titanium source.

[0019] Preferably, in step 2), the heating and stirring conditions are 80°C for 4 hours, the aging conditions are sealed aging for 2 hours, and the drying conditions are 80°C for 48 hours.

[0020] Preferably, in step 2), the method for mixing the manganese source-chelating agent solution with the titanium source solution is to slowly add the manganese source-chelating agent solution dropwise to the titanium source solution under stirring conditions.

[0021] Preferably, in step 3), the titanium-manganese composite dry gel precursor is spread evenly in an open crucible with a thickness ≤3mm, placed in a muffle furnace, heated to a calcination temperature of 350-500°C at a heating rate of 1-2°C / min, held at that temperature for 2h, and then cooled to room temperature to obtain the Ti-Mn-O composite oxide catalyst; more preferably, the calcination temperature is 450°C.

[0022] The present invention also provides the application of the above-mentioned Ti-Mn-O composite oxide catalyst in the preparation of MgH2-based hydrogen storage materials: the Ti-Mn-O composite oxide catalyst is mixed with MgH2 and ball-milled to obtain Ti-Mn-O / MgH2 composite hydrogen storage materials.

[0023] Preferably, the Ti-Mn-O composite oxide catalyst has a mass fraction of 2-8% in the Ti-Mn-O / MgH2 composite hydrogen storage material; more preferably, the Ti-Mn-O composite oxide catalyst has a mass fraction of 4-6% in the Ti-Mn-O / MgH2 composite hydrogen storage material.

[0024] Preferably, the ball milling process is carried out under an argon protective atmosphere, with a ball-to-material ratio of 30:1 to 50:1, a ball milling speed of 350 to 450 rpm, a ball milling time of 8 to 12 hours, and a ball milling method of alternating forward and reverse rotation; more preferably, the ball-to-material ratio is 40:1, the ball milling speed is 400 rpm, the ball milling time is 10 hours, the single forward rotation time of the alternating forward and reverse rotation ball milling is 12 minutes, the ball milling interval is 6 minutes, and the single reverse rotation time is 12 minutes.

[0025] The beneficial effects of this invention are:

[0026] 1. This invention uses the sol-gel method to prepare Ti-Mn-O composite oxide catalysts. By mixing the titanium source and the manganese source in solution, uniform dispersion of Ti and Mn components is achieved, avoiding the local segregation problem that may occur in traditional solid-phase mixing systems, and ensuring the consistency and stability of the catalyst composition.

[0027] 2. The Ti-Mn-O composite oxide catalyst provided by this invention has Ti, Mn, and O as the main constituent elements, and the main phases include Mn2O3 and anatase TiO2. This multiphase composite structure is conducive to building abundant interfacial contact sites, making it easier for the catalyst to be uniformly dispersed in the MgH2 matrix during subsequent ball milling, thereby fully exerting its catalytic effect.

[0028] 3. The Ti-Mn-O composite oxide catalyst obtained in this invention has a micron-sized particle profile and a relatively rough surface structure, locally exhibiting fine lamellar or particle characteristics. This morphology facilitates the formation of a sufficient and uniform interfacial contact with MgH2 during ball milling, thereby improving catalytic efficiency.

[0029] 4. The present invention uses the sol-gel method to prepare catalysts, which does not require expensive raw materials and complex equipment. The process conditions are mild, the operation is simple, and it is easy to scale up production.

[0030] 5. The Ti-Mn-O composite oxide catalyst prepared in this invention is ball-milled with MgH2 at a doping amount of 2-8 wt%. The dehydrogenation performance of the resulting composite hydrogen storage material is significantly improved: the initial hydrogen release temperature is reduced from about 330°C in the undoped state to 230-270°C, the main hydrogen release range is reduced from 350-390°C to 245-310°C, the hydrogen release initiation temperature is reduced by about 60-100°C, and the total hydrogen release is still maintained at a high level of 6.7-7.3 wt%. Attached Figure Description

[0031] Figure 1 TG-DSC curve of the titanium-manganese composite dry gel precursor prepared in Example 1;

[0032] Figure 2 The image shows the XRD pattern of the Ti-Mn-O composite oxide catalyst obtained by calcination at 350°C in Example 1.

[0033] Figure 3 The image shown is the XRD pattern of the Ti-Mn-O composite oxide catalyst obtained by calcination at 400°C in Example 1.

[0034] Figure 4 The image shows the XRD pattern of the Ti-Mn-O composite oxide catalyst obtained by calcination at 450°C in Example 1.

[0035] Figure 5The image shows the XRD pattern of the Ti-Mn-O composite oxide catalyst obtained by calcination at 500°C in Example 1.

[0036] Figure 6 The XRD patterns of the catalysts obtained by calcination at different temperatures (350-500°C) in Example 1 are shown in comparison.

[0037] Figure 7 This is a SEM image of the Ti-Mn-O composite oxide catalyst obtained by calcination at 450°C in Example 1;

[0038] Figure 8 TPD curves of Ti-Mn-O / MgH2 composite hydrogen storage materials with different doping amounts prepared in Example 2 Detailed Implementation

[0039] The following embodiments further illustrate the content of the present invention, but should not be construed as limiting the present invention. Any modifications or substitutions made to the methods, steps, or conditions of the present invention without departing from the spirit and essence of the invention are within the scope of the present invention.

[0040] Example 1: Preparation method of Ti-Mn-O composite oxide catalyst

[0041] Step 1): Dissolve 1 mmol tetraisopropyl titanate in 10 mL anhydrous ethanol and stir magnetically for 10 min to obtain a titanium source solution. Then, dissolve 2 mmol manganese acetate tetrahydrate and 4 mmol citric acid monohydrate in a mixed solution of 10 mL deionized water and 5 mL ethanol and stir until clear to obtain a manganese source-chelating agent solution.

[0042] Step 2): Under vigorous stirring, the manganese source-chelating agent solution was slowly added dropwise to the titanium source solution. After the addition was complete, 0.3 mL of concentrated nitric acid was slowly added dropwise to the mixture as a hydrolysis catalyst. The mixture was heated and stirred at 80°C for 4 hours to allow the solution to gradually form a viscous gel. The gel was sealed and aged for 2 hours, and then dried in an oven at 80°C for 48 hours to obtain the titanium-manganese composite dry gel precursor powder.

[0043] Step 3) Take a portion of the dried titanium-manganese composite dry gel precursor for thermogravimetric-differential scanning calorimetry (TG-DSC) to analyze its weight loss behavior and thermal effect changes, in order to determine the removal temperature range of adsorbed water, residual solvent, and organic complexes, as well as the temperature range for the formation and structural stability of composite oxides.

[0044] Test results are as follows Figure 1As shown, the sample exhibited distinct phased weight loss behavior during the heating process: below 80°C, the main process involved the removal of adsorbed water and residual solvent; from 180 to 280°C, a significant decomposition of organic complexes and residual organic groups occurred; from 280 to 360°C, further removal of residual organic matter and formation of complex oxides took place; and from 360 to 460°C, the weight loss of the sample tended to moderate. These results indicate that the catalyst precursor had essentially completed its thermal conversion at approximately 450°C, providing a basis for determining the subsequent calcination temperature.

[0045] Step 4): Gently grind the dried titanium-manganese composite dry gel precursor in an agate mortar, then spread it thinly and evenly on the bottom of an open alumina crucible, with a thickness controlled below 3 mm. Heat the muffle furnace to the target temperature at a programmed heating rate of 1 °C / min, and hold at the target temperature for 2 hours. After holding, cool the furnace to room temperature to obtain the calcined sample.

[0046] In this embodiment, a temperature gradient experiment was set up to calcine the precursor at 350°C, 400°C, 450°C and 500°C respectively, in order to study the effects of different heat treatment temperatures on the oxidation degree, crystal phase composition and crystallinity of the catalyst.

[0047] To verify the phase composition of the products obtained at different calcination temperatures, X-ray diffraction (XRD) analysis was performed on each calcined sample prepared in step 4). The test results are as follows: Figures 2-6 As shown in the figure, the phase composition of the samples differs significantly under different heat treatment temperatures. The main phases of the sample treated at 450°C can be attributed to Mn₂O₃ and anatase TiO₂, indicating the successful preparation of a Ti-Mn-O composite oxide catalyst. However, samples treated at lower temperatures (e.g., 350°C, 400°C) show more diffraction peaks of low-valence manganese oxides such as MnO, indicating insufficient oxidation of the precursor, requiring adjustment of the heating rate or extension of the holding time to promote complete oxidation. The diffraction peak intensity of the sample treated at 500°C increases, indicating improved crystallinity, but the phase composition remains essentially the same as the 450°C sample.

[0048] To observe the microstructure of the prepared Ti-Mn-O composite oxide catalyst, scanning electron microscopy (SEM) was performed on the sample after heat treatment at 450°C. The test results are as follows: Figure 7 As shown. By Figure 7 As can be seen, the catalyst exhibits a micron-sized particle profile with a relatively rough surface, and fine lamellar or granular features are observed in local areas. This rough surface structure and fine secondary structure facilitate the formation of a sufficient and uniform interfacial contact with the MgH2 matrix during subsequent ball milling, thereby enhancing its catalytic effect.

[0049] Example 2: Application of Ti-Mn-O composite oxide catalyst in MgH2-based hydrogen storage materials

[0050] In this embodiment, the Ti-Mn-O composite oxide catalyst obtained by calcination at 450°C in Example 1 was used to prepare MgH2-based hydrogen storage materials, and its effect on the hydrogen desorption performance of MgH2 was evaluated.

[0051] 1. Preparation of Ti-Mn-O / MgH2 composite hydrogen storage materials

[0052] Under argon atmosphere, the above-mentioned Ti-Mn-O composite oxide catalyst was mixed with MgH2 at a set mass ratio and placed in a ball mill jar for high-energy ball milling. The ball milling conditions were: ball-to-material ratio of 40:1, ball milling speed of 400 rpm, and total ball milling time of 10 h; the ball milling method was intermittent ball milling with forward and reverse rotation, wherein the single forward rotation time was 12 min, the ball milling interval was 6 min, and the single reverse rotation time was 12 min.

[0053] This embodiment sets up five groups of samples, namely M0, M2, M4, M6, and M8, where M0 is a blank control sample without catalyst, and M2, M4, M6, and M8 represent Ti-Mn-O / MgH2 composite hydrogen storage materials with catalyst doping amounts of 2wt%, 4wt%, 6wt%, and 8wt%, respectively. Based on a total mass of 1.000g, the composition of each sample is as follows:

[0054] M0: MgH2 1.000g, catalyst 0g;

[0055] M2: MgH2 0.980g, catalyst 0.020g;

[0056] M4: MgH2 0.960g, catalyst 0.040g;

[0057] M6: MgH2 0.940g, catalyst 0.060g;

[0058] M8: MgH2 0.920g, catalyst 0.080g.

[0059] 2. TPD hydrogen desorption performance test of composite hydrogen storage materials

[0060] To evaluate the hydrogen desorption behavior of the aforementioned composite hydrogen storage materials, temperature-programmed desorption (TPD) tests were conducted on samples M0, M2, M4, M6, and M8. The test results are as follows: Figure 8 As shown.

[0061] The results showed that the blank control sample M0, without catalyst doping, began to rapidly release hydrogen after approximately 330°C, with the main hydrogen release range being approximately 350–390°C. In contrast, the dehydrogenation curves of samples M2, M4, M6, and M8, doped with Ti-Mn-O composite oxide catalysts, all shifted to the lower temperature region, with significant hydrogen release beginning at approximately 230–270°C, and the main hydrogen release range shifting to 245–310°C, with a total hydrogen release of approximately 6.7–7.3 wt%.

[0062] Further analysis of the effects of different doping amounts revealed that the 8wt% doped sample (M8) showed a more pronounced trend of earlier hydrogen decomposition at low temperatures, indicating that increasing the catalyst content can provide more active interfaces; while the 4-6wt% doped samples (M4, M6) had a better overall advantage in reducing the hydrogen decomposition temperature and maintaining the effective hydrogen storage phase content of MgH2.

[0063] The above results indicate that the Ti-Mn-O composite oxide catalyst prepared in this invention can significantly improve the hydrogen desorption behavior of MgH2, effectively reduce the hydrogen desorption temperature, and maintain good hydrogen desorption capacity.

Claims

1. A Ti-Mn-O composite oxide catalyst, characterized in that: The catalyst contains the elements Ti, Mn, and O, and the main phases of the catalyst include Mn2O3 and anatase TiO2.

2. The preparation method of the Ti-Mn-O composite oxide catalyst according to claim 1, characterized in that, Includes the following steps: Step 1): Dissolve the titanium source in an organic solvent to obtain a titanium source solution; dissolve the manganese source and citric acid in an aqueous solvent to obtain a manganese source-chelating agent solution; Step 2), the manganese source-chelating agent solution is mixed with the titanium source solution, a hydrolysis catalyst is added, and the mixture is heated and stirred to form a gel. After aging and drying, a titanium-manganese composite dry gel precursor is obtained. Step 3) The titanium-manganese composite dry gel precursor is calcined to obtain the Ti-Mn-O composite oxide catalyst.

3. The preparation method according to claim 2, characterized in that: In step 1), the titanium source is tetraisopropyl titanate, the organic solvent is anhydrous ethanol, the manganese source is manganese acetate tetrahydrate, the citric acid is citric acid monohydrate, and the aqueous solvent is a mixture of water and ethanol.

4. The preparation method according to claim 2, characterized in that: In step 1), the molar ratio of titanium source to manganese source is 1:2, and the molar ratio of citric acid to manganese source is 2:1 to 3:

1.

5. The preparation method according to claim 2, characterized in that: In step 2), the hydrolysis catalyst is concentrated nitric acid, and the ratio of the amount of concentrated nitric acid added to the amount of titanium source used in step 1) is 0.3-0.5 mL of concentrated nitric acid per millimole of titanium source.

6. The preparation method according to claim 2, characterized in that: In step 3), the titanium-manganese composite dry gel precursor is spread in an open crucible with a thickness of ≤3mm, placed in a muffle furnace, heated to a calcination temperature of 350-500°C at a heating rate of 1-2°C / min, held for 2 hours, and then cooled to room temperature to obtain the Ti-Mn-O composite oxide catalyst.

7. The application of the Ti-Mn-O composite oxide catalyst according to claim 1 in the preparation of MgH2-based hydrogen storage materials, characterized in that: The Ti-Mn-O composite oxide catalyst was mixed with MgH2 and ball-milled to obtain a Ti-Mn-O / MgH2 composite hydrogen storage material.

8. The application according to claim 7, characterized in that: The mass fraction of the Ti-Mn-O composite oxide catalyst in the Ti-Mn-O / MgH2 composite hydrogen storage material is 2-8%.

9. The application according to claim 7, characterized in that: The ball milling process is carried out under an argon protective atmosphere, with a ball-to-material ratio of 30:1 to 50:1, a ball milling speed of 350 to 450 rpm, a ball milling time of 8 to 12 hours, and a ball milling method of alternating forward and reverse rotation.

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