General deposition-in-situ reduction preparation method of nano medium / high-entropy metal oxide catalyst

Abstract

The invention discloses a general deposition-in-situ reduction preparation method of a nano medium / high-entropy metal oxide catalyst, the medium / high-entropy metal oxide catalyst comprises more than three metal elements, the metal elements comprise active metal elements and inactive metal elements, the active metal elements comprise at least one of Ti, Cr, Nb, Zr and V, and the inactive metal elements comprise at least one of Ti, Cr, Nb, Zr and V; the inactive metal element comprises at least one of Pd, Pt, Ir, Cu, Ru, Fe, Ni, Mo, Co, Sn, Mn and W; the preparation method comprises the following steps: mixing a raw material solution containing uniformly distributed and stable active metal element ions and inactive metal element ions with a carrier, removing a solvent, and uniformly depositing the active metal element ions and the inactive metal element ions on the surface of the carrier to obtain a medium / high-entropy ion precursor; the precursor is uniformly dispersed in water containing or not containing sodium hydroxide, and ammonia borane is added for in-situ reduction synthesis of the nano medium / high-entropy metal oxide catalyst.

Description

Technical Field

[0001] The present invention relates to the field of energy catalysis, and in particular to a universal deposition-in-situ reduction method for synthesizing nanometer medium / high entropy metal oxide catalysts at room temperature, a prepared nanometer medium / high entropy metal oxide catalyst having high catalytic activity and cyclic stability, and application of the nanometer medium / high entropy metal oxide catalyst in catalyzing the hydrolysis of ammonia borane. Background Art

[0002] Hydrogen (H 2 ) energy density (120MJ·kg -1 ) is much higher than gasoline (44MJ·kg -1 ), and only water is a by-product when burned. It is considered to be one of the most promising energy carriers to solve the energy crisis.

[0003] Ammonia borane (NH 3 BH 3 ) is one of the most promising liquid-phase chemical hydrogen storage materials, with a mass hydrogen storage capacity of 19.6%, and has the characteristics of low molecular weight, non-toxicity, high solubility in water, and stability in atmospheric environment. Therefore, the hydrolysis reaction of ammonia borane is used to produce high-purity hydrogen. However, at room temperature, the kinetics of ammonia borane hydrolysis is significantly limited, and a suitable catalyst needs to be selected to promote the reaction. Therefore, the synthesis of catalysts with cost-effectiveness, high catalytic activity and cyclic stability has become an important issue in the process of realizing the hydrogen economy.

[0004] A large number of researchers have focused on the structure and composition design of catalysts, and are committed to synthesizing catalysts with high activity or stability. Generally speaking, the catalyst components that have been developed are mainly divided into precious metal (Pt, Pd, Ag, Au, etc.) based and non-precious metal (Cu, Co, Ni, Fe, etc.) based. Precious metal-based catalysts usually have very efficient catalytic activity due to their unique outer electron structure, but the active outer electrons also doom them to have poor stability and high costs. Although the stability of non-precious metal-based catalysts has been improved compared to precious metal-based catalysts, it is still difficult to meet the needs in actual production, and the activity is far apart. Activity and stability seem to have become two contradictory properties, which are difficult to meet simultaneously in the same catalytic system.

[0005] To solve the above problems, medium / high-entropy materials are applied in the catalytic field, which have four major effects (high-entropy effect, cocktail effect, lattice distortion effect, and sluggish diffusion effect). Among them, the cocktail effect is regarded as a very feasible design strategy for breaking through the limitations of activity and stability. This effect promotes the interaction between components through the blending of various raw materials, enabling the material to exhibit a beneficial composite effect as a whole. The high-entropy effect is due to the increase in configurational entropy caused by multiple major components in high-entropy materials, endowing them with excellent structural stability, which is beneficial for maintaining activity.

[0006] Currently, the preparation of medium / high-entropy materials usually requires extreme environments (rapid heating and rapid cooling), resulting in a cumbersome preparation process and high cost. Moreover, due to the diverse elemental composition of high-entropy materials, the chemical reaction path for material forming is complex, making it difficult to ensure the uniform distribution of components and the precise control of morphology and size. In the hydrolysis of ammonia borane to produce hydrogen, due to the reducibility of the reactants, it becomes a natural advantage for the in-situ synthesis of high-entropy materials. There is a phenomenon of enhanced catalyst activity during the in-situ reaction process, that is, the catalytic activity in the second cycle is higher than that in the first cycle, which is a typical catalyst activation phenomenon. By reasonably designing the catalyst composition and leveraging the unique reaction thermodynamics and kinetics pathways of the oxidation activation process, it is possible to in-situ synthesize high-performance nano medium / high-entropy metal oxide catalysts at room temperature. Summary of the Invention

[0007] In a first aspect, the present invention provides a general deposition-in-situ reduction (D-ISR) preparation method for nano medium / high-entropy metal oxide catalysts. The medium / high-entropy metal oxide catalysts contain three or more (including three) metal elements, and the metal elements include active metal elements and inactive metal elements. The active metal elements include at least one of Ti, Cr, Nb, Zr, and V, and the inactive metal elements include at least one of Pd, Pt, Ir, Cu, Ru, Fe, Ni, Mo, Co, Sn, Mn, and W;

[0008] The preparation method includes:

[0009] Prepare a raw material solution, which contains uniformly distributed and stable active metal element ions and inactive metal element ions;

[0010] Mix the raw material solution with a carrier and remove the solvent to uniformly deposit the active metal element ions and inactive metal element ions in the raw material solution on the surface of the carrier, obtaining a medium / high-entropy ion precursor;

[0011] Disperse the medium / high-entropy ion precursor uniformly in water with or without sodium hydroxide, add ammonia borane, and in-situ reduce and synthesize nano medium / high-entropy metal oxide catalysts.

[0012] See Figure 1 , in the present invention, metal elements are classified into the above-mentioned active metal elements and inactive metal elements according to their oxidation ability.

[0013] The preparation method of the present invention can ultrashortly synthesize medium / high entropy materials at room temperature.

[0014] The medium / high entropy ion precursor prepared by the deposition process of the present invention has excellent stability. Components including active metal elements do not crystallize within at least 48 hours in the atmospheric environment, enabling the preparation of catalysts rich in active metal elements in an aqueous environment.

[0015] In the preparation method of the present invention, active metal elements and inactive metal elements must coexist, and it is preferably that the total number of metal element types is not less than three. The presence of inactive metal elements can ensure the stability of active metal elements in the medium / high entropy ion precursor prepared by deposition.

[0016] See Figure 2 , in the in-situ reduction synthesis reaction of the present invention, there is an enthalpy-driven dynamic oxidation (DO) mechanism. In this process, metal ions are first reduced by ammonia borane into uneven clusters, and then dissolved oxygen rapidly connects the clusters into a solid solution under the action of active metal elements. The introduction of active metal elements is one of the keys to realizing the above DO mechanism. The catalyst is enriched with active metal elements, significantly reducing the rate difference of oxygen binding of different components, inhibiting the segregation of inactive metal elements, and thus realizing the synthesis of single-phase medium / high entropy metal oxides at room temperature. Without active metal elements, there will be impurity phases such as single-phase of inactive metal elements and segregated single-metal oxide phases in the products of in-situ reduction synthesis; while the introduction of active metal elements can inhibit the formation of these impurity phases.

[0017] The preparation method of the present invention can prepare nano medium / high entropy metal oxides on a large scale and is universal for the synthesis of ternary to ultra-multicomponent metal oxide catalysts.

[0018] In some embodiments, in the medium / high entropy metal oxide catalyst, the metal elements can have an equimolar ratio.

[0019] In some embodiments, the active metal elements may include Ti, and the inactive metal elements may include Co, Cu, and Ni.

[0020] In some embodiments, the carrier may include activated carbon.

[0021] In some embodiments, the raw material solution and the carrier can be mixed according to the mass ratio of the total molar number of metal element ions in the raw material solution to the carrier of 0.001 - 10 mmol:72 mg (such as 0.05 mmol:72 mg, 0.1125 mmol:72 mg, etc.).

[0022] In some embodiments, the solvent may include absolute ethanol.

[0023] In some embodiments, the solvent can be removed by heating and evaporation to dryness.

[0024] In some embodiments, the medium / high-entropy ion precursor can be uniformly dispersed in water containing sodium hydroxide. Further, the concentration of sodium hydroxide in the water containing sodium hydroxide may not exceed 4 mol / L.

[0025] In a second aspect, the present invention provides a nano medium / high-entropy metal oxide catalyst prepared by the general deposition-in-situ reduction preparation method of the nano medium / high-entropy metal oxide catalyst described in the first aspect. Further, the medium / high-entropy metal oxide in the nano medium / high-entropy metal oxide catalyst is single-phase.

[0026] In a third aspect, the present invention provides an application of the nano medium / high-entropy metal oxide catalyst described in the second aspect in catalyzing the hydrolysis of ammonia borane.

[0027] The present invention can solve problems such as the cumbersome preparation process, high energy consumption, and low efficiency of current medium / high-entropy catalysts, provides a process for efficiently and cost-effectively synthesizing multi-component nano-oxide catalysts on a large scale with precision, and demonstrates a multi-component supported catalyst prepared by this strategy. Through this process, a catalyst rich in active metal elements is prepared in an aqueous environment, and this catalyst simultaneously has excellent activity and stability.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The present invention firstly proposes an enthalpy-driven deposition-in-situ reduction method, which has a dynamic oxidation (DO) mechanism and can be used to ultrashortly synthesize nano medium / high-entropy metal oxide catalysts at room temperature. Among them, the DO mechanism involves the process of oxygen acting as a "bridge" to connect heterogeneous metal clusters to form a solid solution. Thanks to the deposition step, a catalyst rich in active metal elements is prepared in an aqueous environment. The coordination of active metal elements can reduce the energy barrier of the oxygen-linking reaction in the DO process, narrow the difference in the bonding rates of oxygen with different components, inhibit component segregation, and thus achieve the ultrashort synthesis of medium / high-entropy metal oxides under mild conditions.

[0030] 2. The deposition-in-situ reduction method proposed by the present invention successfully synthesized a high-entropy metal oxide containing up to nine metal elements (Co, Cu, Ni, Ti, Fe, Cr, Mn, Mo, Pt), demonstrating the universality of this method for the synthesis of ternary to multi-component catalysts. In the catalyst system scale-up experiment, the synchronous increase in the magnification factor and the hydrogen production rate proved the industrial potential of this method. The unique thermodynamic and kinetic pathways of the oxygen connection process enable this process to break through the limitations of rapid temperature fluctuations and long reaction times, making it a preparation method with high efficiency and low energy consumption.

[0031] 3. The CoCuNiTi metal oxide catalyst prepared by the present invention has a high-entropy effect, which increases the lattice disorder and distortion degree, and then promotes the enrichment of O around Co. The enrichment of O is beneficial to the splitting and broadening of the Co 3d orbitals, intensifies the Co-Cu coupling effect, and makes the turnover frequency (TOF) value of catalytic hydrolysis of ammonia borane at 25 °C reach 236.6 min -1 . In addition, the high-entropy effect effectively slows down the Ostwald ripening of the active particles, and the particle swelling rate after six cycles is 14.1%, ensuring excellent structural and catalytic stability. Brief Description of the Drawings

[0032] Figure 1 is the change of the Gibbs free energy of formation of different oxides with temperature (Ellingham diagram).

[0033] Figure 2 is a schematic diagram of the process for synthesizing single-phase nano-scale medium / high-entropy oxides based on the dynamic oxidation (DO) mechanism according to the element activity properties.

[0034] Figure 3 is the X-ray diffraction (XRD) pattern of CoCuNiTi-O / AC obtained in Example 1 of the present invention.

[0035] Figure 4 are the low / high-resolution transmission electron microscopy (HR-TEM) photos (a, b), the statistical curve of the active particle size (c), and the aberration-corrected transmission electron microscopy (AC-TEM) photo (d) of CoCuNiTi-O / AC obtained in Example 1 of the present invention.

[0036] Figure 5 are the X-ray absorption fine structure spectrum (EXAFS) and the density of states (DOS) result diagram calculated by density functional theory (DFT) of CoCuNiTi-O / AC obtained in Example 1 of the present invention.

[0037] Figure 6The cyclic hydrogen production test (a), the hydrogen evolution curves of the catalytic reaction at different temperatures (b), and the corresponding Arrhenius plot (c) of CoCuNiTi-O / AC obtained in Example 1 of the present invention at 25 °C.

[0038] Figure 7 The TEM images (a) of CoCuNiTi-O / AC obtained in Example 1 of the present invention after the cyclic hydrogen production test and the graph of the expansion of the active particle size (b).

[0039] Figure 8 The XRD pattern (a) and AC-TEM images (b) of the nonary CoCuNiTiFeCrMnMoPt-O / AC obtained in Example 2 of the present invention.

[0040] Figure 9 The hydrogen production performance test graph of the nonary CoCuNiTiFeCrMnMoPt-O / AC obtained in Example 2 of the present invention at 25 °C for the catalytic hydrolysis of ammonia borane.

[0041] Figure 10 The hydrogen production performance test graph (a) and the linear relationship graph of the magnification factor - activity (b) of CoCuNiTi-O / AC in Example 3 of the present invention for the catalytic hydrolysis of ammonia borane at 25 °C after the catalyst system was expanded to 1, 5, 10, 15, and 20 times respectively.

[0042] Figure 11 The XRD pattern (a), transmission electron microscope (TEM) images (b), and the statistical graph of the active particle size (c) of the ternary CoCuNi-O / AC obtained in Comparative Example 1 of the present invention.

[0043] Figure 12 The hydrogen production performance test graph of the ternary CoCuNi-O / AC obtained in Comparative Example 1 of the present invention at 25 °C for the catalytic hydrolysis of ammonia borane.

[0044] Figure 13 The TEM images (a) of the ternary CoCuNi-O / AC obtained in Comparative Example 1 of the present invention after the cyclic hydrogen production test and the graph of the expansion of the active particle size (b).

[0045] Figure 14 The XRD pattern (a), TEM images (b), and the statistical graph of the active particle size (c) of the binary CoCu-O / AC obtained in Comparative Example 2 of the present invention.

[0046] Figure 15 The hydrogen production performance test graph of the binary CoCu-O / AC obtained in Comparative Example 2 of the present invention at 25 °C for the catalytic hydrolysis of ammonia borane.

[0047] Figure 16 The TEM photograph (a) and the graph of the expansion of the active particle size of the binary CoCu-O / AC obtained in Comparative Example 2 of the present invention after cyclic hydrogen production testing.

[0048] Figure 17 For Comparative Example 3 of the present invention, the CoCuNi-O / AC prepared by the traditional NaBH 4 XRD spectrum (a) and TEM photograph (b) of CoCuNi-O / AC prepared by the liquid-phase reduction method.

[0049] Figure 18 For Comparative Example 3 of the present invention, the CoCuNi-O / AC prepared by the traditional NaBH 4 Activity graph of CoCuNi-O / AC prepared by the liquid-phase reduction method for catalyzing the hydrolysis of ammonia borane to produce hydrogen at room temperature.

[0050] Figure 19 XRD spectrum (a) and TEM photograph (b) of CoCuNi-O / AC prepared by the traditional in-situ coprecipitation method in Comparative Example 4 of the present invention.

[0051] Figure 20 Activity graph of CoCuNi-O / AC prepared by the traditional in-situ coprecipitation method in Comparative Example 4 of the present invention for catalyzing the hydrolysis of ammonia borane to produce hydrogen at room temperature. Detailed implementation manners

[0052] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention.

[0053] Example 1: Preparation of CoCuNiTi-O / AC by deposition-in-situ reduction method and its structure and performance evaluation.

[0054] The medium-entropy metal oxide catalyst can be expressed as CoCuNiTi-O / AC.

[0055] 72 mg of activated carbon (AC) and 0.5 mL each of CoCl 2 ·6H 2 O (0.025 mol / L), CuCl 2 ·2H 2 O (0.025 mol / L), NiCl 2 ·6H 2 O (0.025 mol / L), and TiCl 4 (0.025 mol / L) in absolute ethanol solution were respectively measured. The above raw materials were mixed, stirred, heated and evaporated to dryness at 35 °C and 600 r / min to obtain the Co-Cu-Ni-Ti / AC precursor.

[0056] 80 mg of the Co-Cu-Ni-Ti / AC precursor obtained according to the above process was transferred to a reactor placed in a constant temperature water bath at 25 °C, and 4 mL of an aqueous solution of sodium hydroxide (2 mol / L) was added. Under the condition of magnetic stirring at 1200 r / min, 200 μL of an aqueous solution of ammonia borane (0.60 mol / L) was added to obtain the CoCuNiTi-O / AC catalyst.

[0057] In the synthesis reaction, metal ions are first reduced by ammonia borane to metal clusters, and then the dissolved oxygen in water quickly links the metal clusters together and promotes their solid solution to form a single-phase medium / high entropy metal oxide. To characterize the crystal structure of CoCuNiTi-O / AC in the present invention, XRD tests were carried out on it, and the results are as Figure 3 shown. This catalyst has a rock salt-type oxide crystal structure, and the main crystal plane is (200). The single Bragg peak means the solid solution of multiple components. In the subsequent TEM images, the catalyst shows a uniform nanoparticle morphology ( Figure 4 a), with an average particle size of 9.9 nm ( Figure 4 c). The crystal plane spacing of the catalyst is 0.210 nm ( Figure 4 b), corresponding to the rock salt structure of the above XRD results. The AC-TEM results show that Co, Cu, Ni, and Ti form a homogeneous single-phase solid solution ( Figure 4 d), indicating that the deposition-in-situ reduction method is an effective method for synthesizing single-phase medium / high entropy metal oxides.

[0058] The EXAFS results obtained by quantitative fitting ( Figure 5 a) show that the Co-M (M = Co, Cu, Ni, Ti) bond length is longer than the Co-O bond length in CoO This can be attributed to the introduction of large-sized Ti atoms, meaning that the medium entropy oxide has a high degree of lattice distortion. In addition, the Co-O coordination number in CoCuNiTi-O / AC is 10.2, while the Co-M coordination number is 10.9, and an abnormally large amount of O is enriched around the active center Co. The DOS results show ( Figure 5 b) that the oxygen enrichment in the Co 3d orbital promotes the expansion and splitting of this orbital. The separated Co 3d and Cu 3d orbitals significantly overlap, indicating a strong d-d coupling between Co and Cu. This interaction greatly promotes electron transfer, thereby enhancing the catalytic activity.

[0059] The performance of the medium entropy metal oxide in catalyzing the hydrolysis of ammonia borane to produce hydrogen was calculated by a water displacement gas collection system. In the cyclic test, 200 μL of an aqueous solution of ammonia borane (0.60 mol / L) was added each time, for a total of six times. The TOF of CoCu-O / AC is 236.6 min -1 (Figure 6 a), the stability after six cycles is 82.8%, and the activation energy is 43.7 kJ·mol -1 ( Figure 6 b, Figure 6 c). The good structural stability of the catalyst of the present invention promotes the high stability of the catalyst performance. The TOF value after six cycles of hydrogen release is 195.8 min -1 . As Figure 7 shown, after six cycles of testing, the particle size of CoCuNiTi-O / AC increased from 9.9 nm to 11.3 nm, with a growth rate of 14.1%. This is because the high configurational entropy enhances the structural stability of the catalyst and effectively resists Ostwald ripening.

[0060] Example 2: Synthesis of CoCuNiTiMoMnCrFePt-O / AC by deposition-in-situ reduction method and its structural and performance evaluation.

[0061] Prepare anhydrous ethanol solutions of MoCl 5 , MnCl 2 , CrCl 3 , FeCl 3 and H 2 PtCl 6 with a concentration of 0.025 mol / L respectively. Take 0.5 mL of each of the above solutions and the Co 2+ , Cu 2+ , Ni 2+ , Ti 4+ anhydrous ethanol solutions prepared in Example 1, and mix them evenly with 72 mg of activated carbon. Under the conditions of magnetic rotation stirring at 35 °C and 600 r / min, prepare the Co-Cu-Ni-Ti-Mo-Mn-Cr-Fe-Pt / AC precursor by deposition method.

[0062] Transfer 80 mg of the Co-Cu-Ni-Ti-Mo-Mn-Cr-Fe-Pt / AC precursor obtained according to the above process to a reactor placed in a 25 °C constant temperature water bath, and add 4 mL of an aqueous solution of sodium hydroxide (2 mol / L). Under the condition of magnetic rotation stirring at 1200 r / min, add 200 μL of an aqueous solution of ammonia borane (0.60 mol / L) to obtain CoCuNiTiMoMnCrFePt-O / AC. The single Bragg peak in the XRD pattern ( Figure 8 a) and the clear active particles in the AC-TEM image illustrate the formation of a nine-component single-phase solid solution ( Figure 8 b), verifying the universality of the D-ISR method. The multi-component uniform solid solution achieved by the D-ISR method endows CoCuNiTiMoMnCrFePt-O / AC with excellent catalytic activity ( Figure 9 ).

[0063] Example 3: Synthesis and performance testing of CoCuNiTi-O / AC with the catalytic system scaled up by 1, 5, 10, 15, and 20 times.

[0064] Take 72×X mg of activated carbon (X is 1, 5, 10, 15, and 20 respectively), and take the corresponding 0.5×X mL of the anhydrous ethanol solutions of Co 2+ , Cu 2+ , Ni 2+ , and Ti 4+ and mix them evenly. Prepare the Co-Cu-Ni-Ti / AC×X precursor by the deposition method of evaporating the solvent by stirring under the conditions of 35 °C and 600 r / min.

[0065] Transfer 80×X mg of the Co-Cu-Ni-Ti / AC×X precursor obtained according to the above process to a reactor placed in a 25 °C constant temperature water bath, and add 4×X mL of an aqueous solution of sodium hydroxide (2 mol / L). Under the condition of magnetic stirring at 1200 r / min, add 200×X μL of an aqueous solution of ammonia borane (0.60 mol / L) to obtain the CoCuNiTi-O / AC×X catalyst, and conduct catalytic performance evaluation ( Figure 10 a). It can be observed that there is a strict linear correlation between the scaling factor and the increase in the hydrogen evolution rate ( Figure 10 b), indicating that this method has significant potential in the controllable scale preparation of medium / high entropy materials.

[0066] Comparative Example 1: Preparation of the ternary CoCuNi-O / AC catalyst by the deposition-in-situ reduction method.

[0067] Take 72 mg of activated carbon, and take 0.5 mL of the anhydrous ethanol solutions of Co 2+ , Cu 2+ , and Ni 2+ and mix them evenly. Prepare the Co-Cu-Ni / AC precursor by the deposition method of evaporating the solvent by stirring under the conditions of 35 °C and 600 r / min.

[0068] Transfer 80 mg of the Co-Cu-Ni / AC precursor obtained according to the above process to a 25 °C constant temperature water bath reactor, add 4 mL of an aqueous solution of sodium hydroxide (2 mol / L), and add 200 μL of an aqueous solution of ammonia borane (0.60 mol / L) under the condition of magnetic stirring at 1200 r / min to obtain the CoCuNi-O / AC catalyst. Figure 11 The XRD pattern in a shows the Bragg peak representing the (200) crystal plane of the rock salt-type oxide, but there is Cu component segregation, proving that the addition of active metal elements is the key factor promoting the formation of single-phase medium / high entropy metal oxides. Figure 11Clear particle formation can be observed in the TEM image of b, and the particle size is 13.3 nm( Figure 11 c).

[0069] In the cyclic test, 200 μL of an aqueous solution of ammonia borane (0.60 mol / L) was added each time, for a total of six times. The TOF value of CoCuNi-O / AC was 216.0 min -1 , and the cyclic durability was 60.4%( Figure 12 ). The morphology of CoCuNi-O / AC after the cyclic test was characterized, Figure 13 The TEM image of a shows that the active particles have expanded, and the grown particle size is 21.1 nm( Figure 13 b), and the particle size expansion rate is 58.6%.

[0070] Comparative Example 2: Preparation of binary CoCu-O / AC catalyst by deposition-in-situ reduction method.

[0071] Take 72 mg of activated carbon, and take 0.5 mL of Co 2+ and Cu 2+ anhydrous ethanol solutions were mixed evenly, and Co-Cu / AC precursor was prepared by the deposition method of heating and evaporating the solvent at 35 °C and 600 r / min.

[0072] 80 mg of the Co-Cu / AC precursor obtained according to the above process was transferred to a reactor placed in a 25 °C constant temperature water bath, and 4 mL of an aqueous solution of sodium hydroxide (2 mol / L) was added. 200 μL of an aqueous solution of ammonia borane (0.60 mol / L) was added under the condition of magnetic stirring at 1200 r / min to obtain CoCu-O / AC catalyst. Figure 14 The XRD pattern in a shows the Bragg peak representing the (200) crystal plane of the rock salt type oxide, but there are partial precipitation peaks of CuO, proving that there is partial segregation of Cu components in CoCu-O / AC. Figure 14 Clear particle formation can be observed in the TEM image of b, and the particle size is 13.6 nm( Figure 14 c).

[0073] In the cyclic test, 200 μL of an aqueous solution of ammonia borane (0.60 mol / L) was added each time, for a total of six times. The TOF value of CoCu-O / AC was 198.6 min -1 , and the cyclic durability was 41.9%( Figure 15 ). The morphology of CoCu-O / AC after the cyclic test was characterized, and the TEM image confirmed that the active particles grew significantly during the cycle( Figure 16 a), and the grown particle size is 47.9 nm( Figure 16 b), and the particle size expansion rate is 252.2%.

[0074] Comparative Example 3: Preparation of ternary CoCuNi-O / AC catalyst by sodium borohydride liquid-phase reduction method.

[0075] Dissolve 1.25 mmol CoCl 2 ·6H 2 O, CuCl 2 ·2H 2 O, NiCl 2 ·6H 2 O together in 150 mL of deionized water, and ultrasonicate for 15 min to obtain an aqueous solution of a mixture of three metal salts with a concentration of 0.0083 mol / L. Dissolve 0.3 g of sodium borohydride in 5 mL of deionized water to obtain a reducing agent for synthesizing the catalyst. Mix 2.4 mL of the aqueous solution of the metal salts with activated carbon, and then add 10 mL of H 2 O, and let it stand for 10 min to evenly distribute various metal salts and activated carbon in the liquid phase. Under the condition that the rotational speed of the magnetic stirrer is 600 r / min, slowly add the aqueous solution of sodium borohydride at 25 °C to ensure uniform synthesis of the catalyst. After stirring for 1 hour, centrifuge the mixture 3 times at a rotational speed of 10,000 r / min in a high-speed centrifuge with deionized water and absolute ethanol respectively to wash the mixture. Dry the catalyst in vacuum at 75 °C for 2 h to obtain a dried catalyst. Use the water displacement method to evaluate the catalytic performance of the catalyst for hydrogen production by ammonia borane hydrolysis.

[0076] The CoCuNi-O / AC catalyst was prepared by the method of sodium borohydride liquid-phase reduction. The XRD pattern and TEM images ( Figure 17 a, Figure 17 b) confirmed the successful synthesis of the single-phase catalyst, and the activity decreased significantly compared with the catalyst prepared by the deposition-in-situ reduction method ( Figure 18 ), and the TOF value was 98.7 min -1 . The TEM images confirmed that the reason for the decrease in activity was the dissociation and aggregation of oxide particles. Moreover, compared with the in-situ technique, the traditional reduction method involves the cleaning and extraction of the catalyst in the liquid phase, and this non-loading phenomenon increases the possibility of particles being eluted.

[0077] Comparative Example 4: Preparation of ternary CoCuNi-O / AC catalyst by in-situ co-precipitation method.

[0078] Add a mixture of an aqueous solution of 1.2 ml CoCl 2 , CuCl 2 and NiCl 2 together with 72 mg of activated carbon into a round-bottom flask reactor containing 4 ml of an aqueous solution of 2 mol / L sodium hydroxide. To prevent metal ions from reacting with OH -Hydrolysis reaction occurred and ultrasonic treatment was not adopted. The catalyst was rapidly synthesized in-situ and its catalytic activity for the hydrolysis of ammonia borane was tested. Then, the catalyst in the liquid phase was dried by the same method to characterize the microstructure and phase composition. According to Figure 19 the XRD results of a and Figure 19 the TEM images of b showed that the catalyst prepared by this method was also successfully obtained. Figure 20 The hydrogen evolution curve of the catalyst was shown, and its TOF value was 56.4 min -1 . Combining with the TEM images of the catalyst prepared by in-situ co-precipitation, although the catalyst was also synthesized by in-situ route, the nano-oxide particles did not form a supported relationship with the carbon support, but were free outside the support, and the oxide particles without support restriction showed serious aggregation and growth phenomena, which was the main factor for the low activity of the catalyst.

[0079] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

Claims

1. A universal deposition-in-situ reduction preparation method for nano-medium / high entropy metal oxide catalysts, characterized in that: The medium / high entropy metal oxide catalyst comprises three or more metal elements, wherein the metal elements comprise active metal elements and inactive metal elements, wherein the active metal elements comprise at least one of Ti, Cr, Nb, Zr, and V, and the inactive metal elements comprise at least one of Pd, Pt, Ir, Cu, Ru, Fe, Ni, Mo, Co, Sn, Mn, and W; The preparation method comprises: Preparing a raw material solution, wherein the raw material solution contains active metal element ions and inactive metal element ions that are evenly distributed and stable; The raw material solution and the carrier are mixed, and the solvent is removed, so that the active metal element ions and the inactive metal element ions in the raw material solution are uniformly deposited on the surface of the carrier to obtain a medium / high entropy ion precursor; The medium / high entropy ion precursor is uniformly dispersed in water containing or not containing sodium hydroxide, ammonia borane is added, and nanometer medium / high entropy metal oxide catalyst is synthesized by in-situ reduction.

2. The universal deposition-in-situ reduction preparation method of nano medium / high entropy metal oxide catalysts according to claim 1, characterized in that: In the medium / high entropy metal oxide catalyst, each of the metal elements is in an equal molar ratio.

3. The universal deposition-in-situ reduction preparation method of nano medium / high entropy metal oxide catalysts according to claim 1 or 2, characterized in that: The active metal element includes Ti, and the inactive metal element includes Co, Cu and Ni.

4. The universal deposition-in-situ reduction preparation method of nano medium / high entropy metal oxide catalysts according to claim 1, characterized in that: The support includes activated carbon.

5. The universal deposition-in-situ reduction preparation method of nano medium / high entropy metal oxide catalysts according to claim 1 or 4, characterized in that: The raw material liquid and the carrier are mixed in a mass ratio of 0.001-10 mmol:72 mg of the total molar number of metal element ions in the raw material liquid to the carrier.

6. The universal deposition-in-situ reduction preparation method of nano-medium / high entropy metal oxide catalysts according to claim 1, characterized in that: The solvent includes anhydrous ethanol; The solvent was removed by heating and evaporating to dryness.

7. The universal deposition-in-situ reduction preparation method of nano medium / high entropy metal oxide catalysts according to claim 1, characterized in that: The medium / high entropy ion precursor is uniformly dispersed in water containing sodium hydroxide, and the concentration of sodium hydroxide in the water containing sodium hydroxide does not exceed 4 mol / L.

8. The nanometer medium / high entropy metal oxide catalyst prepared according to the universal deposition-in-situ reduction preparation method of the nanometer medium / high entropy metal oxide catalyst according to any one of claims 1 to 7.

9. The nano medium / high entropy metal oxide catalyst according to claim 8, characterized in that: The medium / high entropy metal oxide in the nano medium / high entropy metal oxide catalyst is single-phase.

10. Use of the nano medium / high entropy metal oxide catalyst according to claim 8 or 9 in catalyzing the hydrolysis of ammonia borane.

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