A Pt cluster catalyst, preparation method and application

Abstract

The present invention provides a Pt cluster catalyst, a preparation method and an application thereof. The alumina composite metal oxide support is prepared by the pH swing method, and defect oxide nanoislands are formed through high-temperature reduction treatment. The oxygen vacancies contained on the surface can firmly anchor the subsequently loaded Pt clusters, thereby reducing the coking phenomenon of the Pt-based catalyst and significantly improving the catalytic activity and stability of the Pt cluster catalyst. At the same time, Pt clusters are prepared by the heating reflux method, so that they have high dispersibility and rich active sites, and the Pt particle size in the finally prepared Pt cluster catalyst is small and the atomic utilization rate is high. When used for catalyzing the dehydrogenation reaction of liquid organic hydrogen carriers, the Pt cluster catalyst has a weak adsorption capacity for products, can exhibit high conversion rate and hydrogen release rate at low temperature, and can still maintain structural stability at high temperature, providing an efficient and reliable solution for the engineering application of the LOHC dehydrogenation link.

Description

Technical Field

[0001] This application relates to the technical field of organic liquid hydrogen storage, and specifically, to a Pt cluster catalyst, a preparation method, and an application thereof. Background Art

[0002] The LOHC technology is a technology that uses organic compounds containing unsaturated carbon-carbon double bonds for reversible hydrogenation and dehydrogenation reactions to achieve the storage and transportation of hydrogen. Currently, petroleum-based aromatic compounds are considered to be potential hydrogen storage carriers due to their low cost, high hydrogen storage density, good chemical stability, and excellent reversibility. With these advantages, the LOHC technology has become one of the few technologies that can achieve long-term and large-scale hydrogen storage and can match the existing fossil energy transportation infrastructure, making the processes of hydrogen storage, transportation, and refueling similar to those of petroleum. However, in the entire aromatic hydrogen storage cycle, although the hydrogenation technology of unsaturated organic compounds has been relatively mature, the dehydrogenation reaction process of liquid organic hydrogen carriers still faces many challenges.

[0003] Currently, platinum-based catalysts are widely used in dehydrogenation reactions due to their excellent dehydrogenation performance. However, the dehydrogenation process involves complex gas-liquid-solid three-phase reactions, and existing catalysts have problems such as low reaction conversion rate and slow hydrogen release rate at low temperatures, and poor stability of the catalyst at high temperatures. Therefore, it is necessary to develop a platinum-based catalyst suitable for three-phase interface reactions. Summary of the Invention

[0004] To solve the above problems, the present invention provides a Pt cluster catalyst, a preparation method, and an application thereof. The composite metal oxide support is prepared by the pH swing method, and defect oxide nanoislands are formed on the surface of the composite metal oxide support through high-temperature reduction treatment. The rich oxygen vacancies contained on the surface can firmly anchor the subsequent loaded Pt clusters, thereby reducing the coking phenomenon of the Pt-based catalyst and significantly improving the catalytic activity and stability of the Pt cluster catalyst. At the same time, Pt clusters are prepared by the heating reflux method, making them have high dispersibility and rich active sites, so that the Pt particle size in the finally prepared Pt cluster catalyst is small and the atomic utilization rate is high. When used to catalyze the dehydrogenation reaction of liquid organic hydrogen carriers, the Pt cluster catalyst has a weak adsorption capacity for products and can exhibit high conversion rate and hydrogen release rate at low temperatures, and still maintain structural stability at high temperatures, providing an efficient and reliable solution for the engineering application of the LOHC dehydrogenation link.

[0005] In the first aspect, the present invention provides a preparation method of a Pt cluster catalyst, and the preparation method includes:

[0006] Step 1: Dissolve sodium aluminate and a metal oxide precursor in deionized water to obtain a mixed turbid solution;

[0007] Step 2: Using the pH swing method, mix the mixed turbid solution with a sulfuric acid solution to form a suspension. After centrifuging, washing, drying, and first calcining the suspension, a composite metal oxide support is obtained;

[0008] Step 3: Subject the composite metal oxide support to high-temperature reduction treatment to obtain a composite metal oxide support with surface defects;

[0009] Step 4: Mix a platinic acid solution, an additive, and an ethanol aqueous solution, and perform heat reflux treatment on the mixed system. After cooling, filter to obtain Pt clusters;

[0010] Step 5: Dissolve the Pt clusters in a solvent to obtain an impregnation solution, and drop the impregnation solution onto the composite metal oxide support with surface defects by equal-volume impregnation. After sealing and standing, perform drying and second calcining treatment to prepare the Pt cluster catalyst.

[0011] Optionally, in Step 1, the mass ratio of sodium aluminate to the metal oxide precursor is (5 - 30):1.

[0012] Optionally, in Step 1, the metal oxide precursor is selected from at least one of magnesium nitrate hexahydrate, gallium nitrate nonahydrate, zirconium nitrate, lanthanum nitrate hexahydrate, cerium nitrate hexahydrate, calcium nitrate, manganese nitrate tetrahydrate, zinc nitrate hexahydrate, and barium nitrate.

[0013] Optionally, in Step 2, in the pH swing method, mix the mixed turbid solution with a sulfuric acid solution to make the pH of the resulting suspension swing back and forth between alkaline and acidic. When the pH swings to the alkaline side, the pH value is 9.5 - 10.5, and when the pH swings to the acidic side, the pH value is 2.5 - 3.5. The number of pH swings is 2 - 6.

[0014] Optionally, in Step 2, the temperature of the first calcination is 400 °C - 600 °C, the heating rate is 2 °C / min - 10 °C / min, and the time is 2 h - 24 h.

[0015] Optionally, in Step 3, the high-temperature reduction treatment is carried out in a CO / inert gas atmosphere. In the CO / inert gas atmosphere, the volume fraction of CO is 1% - 10%;

[0016] The temperature of the high-temperature reduction treatment is 300 °C - 750 °C, the heating rate is 2 °C / min - 10 °C / min, and the time is 5 h - 9 h.

[0017] Optionally, in Step 4, the additive is selected from any one of polyvinylpyrrolidone, polyvinyl alcohol, and polyethylene glycol.

[0018] Optionally, in step 4, the volume ratio of ethanol to water in the ethanol aqueous solution is (1-7):1;

[0019] The mass ratio of platinum to additive in the mixed system is (2-20):1.

[0020] Optionally, in step 4, the temperature of the heating reflux treatment is 80°C-95°C.

[0021] Optionally, in step 5, the mass ratio of Pt in the impregnation solution to the mass ratio of the composite metal oxide support with surface defects is 0.1 wt%-0.7 wt%;

[0022] The solvent is selected from at least one of water, ethanol, methanol and acetone.

[0023] Optionally, in step 5, the second calcination temperature is 200° C.-500° C., and the time is 3 h-6 h.

[0024] In a second aspect, the present invention provides a Pt cluster catalyst prepared by the preparation method described in the first aspect above;

[0025] The Pt cluster catalyst is formed by a composite metal oxide carrier supporting Pt clusters;

[0026] In the Pt cluster catalyst, the mass ratio of the Pt cluster to the composite metal oxide support is 0.1 wt%-0.7 wt%.

[0027] Optionally, the composite metal oxide support includes any one of MgO-Al2O3, Ga2O3-Al2O3, ZrO2-Al2O3, La2O3-Al2O3, CeO2-Al2O3, MgO-La2O3-Al2O3, and MgO-CeO2-Al2O3.

[0028] In a third aspect, the present invention provides an application of a Pt cluster catalyst prepared by the preparation method described in the first aspect, wherein the Pt cluster catalyst is used to catalyze the dehydrogenation reaction of a liquid organic hydrogen carrier;

[0029] The dehydrogenation reaction process comprises:

[0030] Placing the Pt cluster catalyst in a catalyst bed of a reactor, and introducing a reducing mixed gas to activate the Pt cluster catalyst;

[0031] 4 h -1 -150 h -1At a mass space velocity, continuously supply the liquid organic hydrogen carrier to the catalyst bed of the reactor. The liquid organic hydrogen carrier undergoes a dehydrogenation reaction under the action of the Pt cluster catalyst to produce hydrogen;

[0032] Among them, the reducing gas mixture is formed by mixing H2 and an inert gas;

[0033] After continuously performing the dehydrogenation reaction for 96 h, the inactivation rate of the Pt cluster catalyst is not higher than 10%.

[0034] Optionally, the liquid organic hydrogen carrier is cyclohexane or methylcyclohexane.

[0035] In summary, the present invention at least has the following beneficial technical effects:

[0036] 1. The present invention provides a preparation method of a Pt cluster catalyst. Dissolve sodium aluminate and a metal oxide precursor in water, adjust the precipitation by the pH swing method, and obtain a composite metal oxide support through centrifugation, drying, and calcination; heat-treat the support at a high temperature in a reducing atmosphere to form a defect structure on the surface; then mix a platinum acid solution with an ethanol aqueous solution containing a steric hindrance additive, and prepare nano-scale Pt clusters through heating and reflux; then use equal-volume impregnation to load the Pt clusters on the composite metal oxide support with surface defects, and obtain the Pt cluster catalyst through drying and calcination; this preparation method can form a nano-island support structure with an alumina substrate through the combination of sodium aluminate and the metal oxide precursor, and then combine defect construction and the steric hindrance effect of the additive to realize the confined growth of Pt clusters in the nano-reactor. The Pt particles in the obtained Pt cluster catalyst are smaller in size and have strong metal-support interaction, and can achieve low-temperature and high-efficiency dehydrogenation and high-temperature anti-sintering / anti-coking in the dehydrogenation reaction of liquid organic hydrogen carriers, significantly improving the dehydrogenation efficiency of liquid organic hydrogen carriers;

[0037] 2. The present invention provides a Pt cluster catalyst. The Pt cluster catalyst prepared by the preparation method provided by the present invention has atomic-level dispersion and high surface activity, so that sufficient active sites can still be provided at a low loading amount, significantly improving the utilization rate of precious metals and reducing production costs on the premise of ensuring catalytic efficiency;

[0038] 3. The present invention provides an application of Pt cluster catalysis. The Pt cluster catalyst prepared by the present invention has excellent activity and stability for the dehydrogenation reaction of liquid organic hydrogen carriers, and the hydrogen release rate reaches more than 3000 mmol / (gPt·min). After continuously performing the dehydrogenation reaction for 96 h, the inactivation rate of the Pt cluster catalyst is not higher than 10%. Description of the Drawings

[0039] To more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments of the present application. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0040] Figure 1 Shows the flow chart of the preparation method catalyzed by Pt clusters proposed in the embodiments of the present invention;

[0041] Figure 2 Shows the aberration-corrected electron microscope image of the Pt cluster catalysis proposed in the embodiments of the present invention. Detailed implementation manners

[0042] The following will clearly and completely describe the technical solutions in the embodiments of the present application in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of them. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0043] In the drawings, sometimes for clarity, the sizes of the constituent elements, the thicknesses of the layers, or the areas may be exaggerated. Therefore, any implementation of the present disclosure is not necessarily limited to the sizes shown in the figures, and the shapes and sizes of the components in the figures do not reflect the true proportions. In addition, the drawings schematically show ideal examples, and any implementation of the present disclosure is not limited to the shapes or values shown in the drawings.

[0044] In the related art, the LOHC technology is a technology that uses organic compounds containing unsaturated carbon-carbon double bonds for reversible hydrogenation and dehydrogenation reactions to achieve the storage and transportation of hydrogen. Currently, petroleum-based aromatic compounds are considered to be potential hydrogen storage carriers due to their low cost, high hydrogen storage density, good chemical stability, and excellent reversibility. However, in the entire aromatic hydrogen storage cycle, although the hydrogenation technology of unsaturated organic compounds has been relatively mature, the dehydrogenation reaction of liquid organic hydrogen carriers still faces many challenges. For example, the dehydrogenation process has low efficiency, high energy consumption, and poor stability, etc. These problems have become one of the key bottlenecks restricting the further development of the LOHC technology.

[0045] The present invention finds that although the existing platinum-based catalysts have excellent dehydrogenation performance, in the dehydrogenation reaction process, there are still problems such as low dehydrogenation efficiency, high dehydrogenation temperature, and easy deactivation of the catalyst. For example, CN116393124B discloses a Pt-based catalyst and its preparation method and application, using PtCl6 2-The strong electrostatic interaction between the positively charged layered double hydroxide of magnesium and aluminum, as well as the change in Pt loading, are used to achieve the microstructure regulation of Pt in the Pt-based catalyst. Compared with the catalyst prepared by the traditional impregnation method, under the same reaction conditions, the conversion rate of methylcyclohexane is increased by 3.3 times, but the hydrogen release rate is only 769 mmol / (gPt·min).

[0046] The present invention further studies and finds that the dehydrogenation reaction process of liquid organic hydrogen carriers involves complex gas-liquid-solid three-phase reactions, which results in the existing platinum-based catalysts having a low conversion rate and a slow hydrogen release rate at low temperatures; and poor stability at high temperatures. In order to meet the requirements of engineering applications for the reliability of organic hydride dehydrogenation devices, the present invention provides a Pt cluster catalyst suitable for three-phase interface reactions to achieve a high hydrogen release rate and good stability. The specific implementation content of the present invention is as follows:

[0047] In the first aspect, the present invention provides a preparation method of a Pt cluster catalyst, Figure 1 which shows the flowchart of the preparation method of the Pt cluster catalyst provided by the embodiment of the present invention, as Figure 1 shown, the preparation method includes:

[0048] S1: Dissolve sodium metaaluminate and a metal oxide precursor in deionized water to obtain a mixed turbid solution;

[0049] In the present invention, the concentration of sodium metaaluminate is 1 mol / L - 5 mol / L;

[0050] In some embodiments, the mass ratio of the sodium metaaluminate to the metal oxide precursor is (5 - 30):1.

[0051] In the present invention, the metal in the metal oxide precursor is selected from one of Mg, Ca, Ga, Mn, Zn, Zr, Ba, La, and Ce;

[0052] One or two metal oxide precursors can be selected in the present invention;

[0053] In one case, when two metal oxide precursors are selected, the mass ratio of the two metal oxide precursors is (5 - 15):1;

[0054] In this step, the composite of sodium metaaluminate and the metal oxide precursor with a mass ratio of (5 - 30):1 helps to balance the acid-base sites, adjust the d-band center of Pt, and optimize the adsorption-desorption equilibrium of liquid organic hydrogen carriers, thereby improving the conversion rate. Among them, the synergistic effect of Al2O3 and the metal oxide can regulate the number of oxygen vacancies to reduce the dehydrogenation energy barrier (such as Ce 3+ / Ce 4+The redox couple promotes H2 desorption, etc., enabling the finally prepared Pt cluster catalyst to achieve stable dehydrogenation at low temperatures.

[0055] In some embodiments, the metal oxide precursor is selected from at least one of magnesium nitrate hexahydrate, gallium nitrate nonahydrate, zirconium nitrate, lanthanum nitrate hexahydrate, cerium nitrate hexahydrate, calcium nitrate, manganese nitrate tetrahydrate, zinc nitrate hexahydrate, and barium nitrate.

[0056] The metal oxide precursors in the present invention synergistically optimize the performance of the Pt cluster catalyst through their unique physical and chemical properties. The metal oxides formed after calcination of these metal oxide precursors cooperate with the γ-Al2O3 support, endowing the catalyst with high-density oxygen vacancies, excellent Pt dispersion, and low-temperature dehydrogenation activity. At the same time, the interface effect inhibits Pt sintering and carbon deposition, ultimately achieving efficient and stable dehydrogenation of liquid organic hydrogen carriers.

[0057] In the present invention, the reaction process for obtaining the mixed turbid solution includes: dissolution of sodium aluminate and dissolution of the metal salt precursor; for example, NaAlO2, as a salt of a strong base and a weak acid, dissociates and hydrolyzes in water to form amorphous Al(OH)3 colloid (one of the main components of the turbid solution), and the solution is alkaline, promoting the subsequent coprecipitation of metal ions; the second metal ion (metal ion other than Al) combines with OH - to form a metal hydroxide colloid; finally, Al(OH)3 and the metal hydroxide form a heterogeneous colloid network through hydrogen bonding and electrostatic interactions to obtain a mixed turbid solution.

[0058] S2: Using the pH swing method, mixing the mixed turbid solution with a sulfuric acid solution to form a suspension, and after centrifuging, washing, drying, and first calcination treatment of the suspension, a composite metal oxide support is obtained;

[0059] Specifically, when preparing the composite metal oxide support by the pH swing method in this step, the pH value during precipitation alternates between acid and base. The acid side dissolves amorphous aluminum hydroxide impurities and some unstable sites on the edge of γ-AlOOH, and when adding alkali again, it will precipitate on the formed pseudo-boehmite crystal particles. Such cycling can generate a composite metal oxide support with relatively uniform crystal particles and relatively concentrated pore sizes.

[0060] Specifically, in this step, using the pH swing method, the mixed turbid solution is mixed with a sulfuric acid solution to make the pH of the obtained suspension swing back and forth between alkaline and acidic. When the pH swings to the alkaline side, the pH value is 9.5 - 10.5, when the pH swings to the acidic side, the pH value is 2.5 - 3.5, and the number of pH swings is 2 - 6.

[0061] In specific implementation, an appropriate amount of the mixed turbid solution is slowly added to an appropriate amount of sulfuric acid solution to make the pH of the obtained mixed system turn alkaline. After maintaining for 3 min - 5 min, an appropriate amount of sulfuric acid solution is continuously and slowly added to the mixed system to make the pH of the obtained mixed system turn acidic, and maintained for 3 min - 5 min. The pH of the mixed system swings multiple times until all the mixed turbid solution and sulfuric acid solution are mixed; by setting the pH swing time to 3 min - 5 min, it can ensure the full coprecipitation of Al(OH)3 and the formed metal hydroxide in the alkaline stage; in the acidic stage, it can moderately dissolve the edge-unstable particles, thereby improving the crystallinity.

[0062] In this step, the pH swing method makes the metal ions precipitate - dissolve - reprecipitate through repeated alkaline → acidic → alkaline cycles, thereby forming precipitates with uniform size, avoiding rapid particle aggregation, and forming an amorphous structure support. In the present invention, the surface-defect composite metal oxide support obtained after calcination and high-temperature reduction treatment of the precipitate generated by the pH swing method has a stepped defect distribution, that is, the surface is enriched with oxygen vacancies and the bulk phase structure is complete, which reduces the H2 desorption energy and is easier to desorb H2 than traditional Pt-based catalysts. Moreover, the hierarchical pore structure formed by alternating pH can accelerate the diffusion of liquid organic hydrogen carriers and reduce the reaction activation energy;

[0063] In this step, the pH in the alkaline stage is set to 9.5 - 10.5, which can ensure the complete coprecipitation of metal ions such as AlO 2- to form a hydroxide support, which is transformed into a high specific surface area composite metal oxide support structure after calcination; the pH in the acidic stage is set to 2.5 - 3.5, which can selectively dissolve small particles and impurity phases, retain the high-activity Al2O3 skeleton, and increase the defect concentration; the number of pH swings is set to 2 - 6 times, and the formed composite metal oxide support is more suitable for the diffusion of macromolecular liquid organic hydrogen carriers. For example, under the catalysis of the Pt cluster catalyst provided in the present invention, the apparent activation energy of methylcyclohexane dehydrogenation is reduced, etc.

[0064] In this step, the Al2O3 shell formed by pH swing coats the metal oxide core, which also helps to inhibit the high-temperature migration of subsequent Pt clusters.

[0065] In this step, the mass fraction of the sulfuric acid solution is 5 wt% - 15 wt%; the concentration of the sulfuric acid solution will affect the dissolution - precipitation equilibrium of the metal, and thus affect the pore structure and vacancy concentration of the final composite metal oxide support. By setting the mass fraction of the sulfuric acid solution to 5 wt% - 15 wt% in the present invention, it helps to form a uniform mesoporous structure subsequently, and the obtained composite metal oxide support is beneficial for the subsequent loading of Pt clusters and can avoid the aggregation of Pt particles.

[0066] Preferably, the mass fraction of the sulfuric acid solution is 8 wt%-12 wt%, and this concentration is conducive to the partial dissolution of Al 3+ to form Al vacancies, which are subsequently transformed into oxygen vacancies, facilitating the deposition and attachment of metal oxides; among them, after the metal oxide precursor is calcined, metal oxide nanodomains are formed on the surface of the γ-Al2O3 support. Therefore, each nested metal atom is isolated in the nano-reactor, and during subsequent treatment processes, the metal atoms are confined in the nano-reactor, solving problems such as agglomeration growth and decreased stability of metal atoms.

[0067] In this step, drying the precipitate obtained after centrifugal washing is to remove free water and partial bound water in the precipitate, preventing the support from cracking due to rapid evaporation of water during subsequent calcination. Equipment such as a vacuum drying oven can be used for drying; among them, the drying temperature is 60 °C - 110 °C, and the drying time is 2 h - 24 h.

[0068] In this step, the first calcination treatment is to achieve the crystallization of the support; the temperature of the first calcination is 400 °C - 600 °C, the heating rate is 2 °C / min - 10 °C / min, and the time is 2 h - 24 h.

[0069] Specifically, in this step, by setting the temperature of the first calcination between 400 °C and 600 °C, the hydroxides in the precipitate are promoted to be transformed into a composite metal oxide support with a high specific surface area, facilitating the diffusion of subsequent liquid organic hydrogen carriers; setting the lower temperature limit at 400 °C is to ensure complete crystallization and avoid reducing the specific surface area due to residual amorphous phases; setting the upper temperature limit at 600 °C is to inhibit the transformation of γ-Al2O3 to the θ phase; during calcination, surface hydroxyl groups (-OH) can be moderately removed and moderate oxygen vacancies are generated, avoiding structural collapse due to excessive defects; by setting the heating rate between 2 °C / min and 10 °C / min, it helps to gradually remove physically adsorbed water and bound water, avoid pore collapse, make the grain size of the support uniform, reduce stress cracks, and shorten the process time and reduce energy consumption; by setting the calcination time between 2 h and 24 h, excessive grain growth can be avoided, ensuring a high density of surface oxygen vacancies and enhancing dehydrogenation activity.

[0070] The composite metal oxide support obtained in this step is a composite support containing aluminum and a second metal, and the second metal is the metal atom provided by the metal oxide precursor.

[0071] S3: The composite metal oxide support is subjected to high-temperature reduction treatment to obtain a composite metal oxide support with surface defects;

[0072] In specific implementation, this step performs high-temperature reduction treatment on the composite metal oxide support to reduce the metal oxide and generate oxygen vacancies. During the high-temperature reduction treatment, the reducing atmosphere can induce the chemical reduction of metal ions in the composite metal oxide support at high temperature, and surface oxygen atoms are removed to form oxygen vacancies, thereby obtaining a composite metal oxide support with surface defects. The electron defect state induced by oxygen vacancies can adjust the downward shift of the d-band center of the subsequently loaded Pt clusters, weaken the C-H bond binding energy, enable the dehydrogenation reaction to proceed at a lower temperature, and reduce the adsorption capacity of the catalyst for the product. Moreover, the energy provided by the high-temperature environment can overcome the energy barrier for the cleavage of the metal-oxygen bond, promote the diffusion of oxygen atoms, and make the oxygen vacancies evenly distributed rather than only enriched on the surface.

[0073] In some embodiments, the high-temperature reduction treatment can be carried out in a CO / inert gas atmosphere. In the CO / inert gas atmosphere, the volume fraction of CO is 1%-10%; the temperature of the high-temperature reduction treatment is 300 °C - 750 °C, the heating rate is 2 °C / min - 10 °C / min, and the time is 5 h - 9 h.

[0074] It should be noted that in the CO / inert gas mixed atmosphere, the volume fraction of the inert gas is 90%-99%, and the volume fraction of CO in the mixed atmosphere is 1%-10%. By controlling the volume fraction of CO in the mixed atmosphere, slow generation of surface oxygen vacancies can be achieved, avoiding the collapse of the support structure caused by excessive reduction of the bulk phase. The high temperature of 300 °C - 750 °C can enable an abundant amount of oxygen vacancies to be formed on the surface of the composite metal oxide support, which is beneficial for the subsequent uniform and sufficient loading of Pt clusters. Maintaining a heating rate of 2 °C / min - 10 °C / min can ensure the even distribution of oxygen vacancies and avoid the aggregation of metal particles caused by local overheating. Finally, by limiting the reduction time to 5 h - 9 h, it can ensure the full formation of oxygen vacancies in the bulk phase of the composite metal oxide support, and the oxygen vacancies generated by reduction cooperate with the oxygen storage capacity of the metal oxide to achieve low-temperature and high-efficiency dehydrogenation.

[0075] S4: Mix the platinum acid solution, additive, and ethanol aqueous solution, and perform heating and reflux treatment on the mixed system. After cooling, filter to obtain Pt clusters.

[0076] In specific implementation, the platinum acid solution used in this step is selected from any one of chloroplatinic acid, platinum nitrate, platinum acetylacetonate, and tetraammineplatinum nitrate; the additive is selected from any one of polyvinylpyrrolidone, polyvinyl alcohol, and polyethylene glycol.

[0077] In specific implementation, long-chain molecules of polyvinylpyrrolidone / polyvinyl alcohol / polyethylene glycol are adsorbed on the surface of Pt clusters, preventing particle collision and aggregation through steric hindrance. For example, the polar amide group (-CONH-) of polyvinylpyrrolidone or the ether bond (-O-) of polyethylene glycol can form coordination bonds with the Pt surface, enhancing the stability of the final Pt cluster catalyst. During the subsequent second calcination, polyvinylpyrrolidone / polyethylene glycol is partially carbonized to form an ultrathin carbon shell to wrap the Pt clusters, inhibiting the high-temperature migration of Pt clusters.

[0078] In specific implementation, the volume ratio of ethanol to water in the ethanol aqueous solution used in this step is (1-7):1; the mass ratio of platinum to the additive in the obtained mixed system is (2-20):1.

[0079] In the present invention, by setting the volume ratio of ethanol to water in the ethanol aqueous solution and the mass ratio of the additive to platinum, the controllable preparation and stable loading of Pt clusters are realized. The ratio of ethanol to water regulates the reduction kinetics of Pt 4+ so that the size of Pt clusters is controlled within a small range; while the additive effectively prevents Pt aggregation through steric hindrance and maintains stability at high temperatures. By further setting the ratio of the additive to the platinum acid solution, it is ensured that the additive completely covers the surface of the Pt clusters, avoiding the aggregation of Pt clusters, and realizing the controllable size, high dispersion and high-temperature stability of Pt clusters.

[0080] In specific implementation, by setting the heating reflux temperature between 80 °C and 95 °C in the present invention, it can not only ensure the effective redox of ethanol, but also avoid the coarsening of Pt particles caused by violent reactions, and the performance is significantly improved compared with the traditional method. During the heating reflux process, an additive and an ethanol aqueous solution are added to the platinum acid solution, and the obtained system is heated to the reflux temperature. Among them, ethanol is oxidized by heat to release electrons, making the Pt 4+ in the system reduced to Pt atoms, which form Pt nanoclusters through nucleation and aggregation. The additive is adsorbed on the surface of the Pt nanoclusters to form a protective layer, and the Pt clusters with the protective layer are obtained after filtration; the platinum acid solution slowly nucleates and grows into Pt clusters with uniform size under the reduction action of the additive and ethanol, avoiding particle aggregation in the traditional reduction method.

[0081] S5: Dissolve the Pt clusters in a solvent to obtain an impregnation solution, and drop the impregnation solution onto the composite metal oxide support with surface defects by equal-volume impregnation. After sealing and standing, drying and a second calcination treatment are carried out to prepare the Pt cluster catalyst.

[0082] In specific implementation, the mass ratio of Pt in the impregnation solution used in this step to the mass of the composite metal oxide support with surface defects is 0.1 wt%-0.7 wt%; the solvent is selected from at least one of water, ethanol, methanol, and acetone.

[0083] In this step, the impregnation solution is dropped onto the composite metal oxide carrier with surface defects by equal-volume impregnation, which can avoid excessive local concentration, enable Pt clusters to be evenly adsorbed on the composite metal oxide carrier with surface defects, and ensure that the impregnation solution fully infiltrates the carrier pores, improving the loading efficiency of Pt clusters; sealed static standing can make Pt clusters better embed into oxygen vacancies to form strong metal-support interactions, thereby inhibiting Pt agglomeration during subsequent calcination.

[0084] Specifically, during implementation, the temperature of the second calcination is 200 °C - 500 °C, and the time is 3 h - 6 h. The second calcination is for Pt-support bonding, enabling Pt clusters to form strong interactions with the support, inhibiting coking, and maintaining small-sized Pt clusters. The drying treatment before the second calcination can avoid the problems of local concentration and particle coarsening of Pt clusters caused by rapid evaporation during calcination.

[0085] In this step, by setting the temperature of the second calcination between 200 °C and 500 °C, while evaporating free water and decomposing some additives, its carbonized protective layer is retained to prevent Pt cluster migration. After the second calcination is completed, the additive is carbonized into a conductive carbon layer, enhancing the electron transport of Pt clusters, shifting the d-band center of Pt clusters downward, weakening the strong adsorption of Pt to H atoms, and reducing the activation energy for C-H bond cleavage; while the oxygen vacancies on the composite metal oxide carrier act as an electron reservoir, injecting electrons into Pt clusters, and the electron delocalization of ultra-small Pt clusters or single-atom Pt is stronger, promoting H2 desorption; rapid electron transport can also avoid excessive retention of H atoms on the Pt surface, and the electron-rich Pt clusters are more likely to release H2. By setting the calcination time between 3 h and 6 h, it helps to retain more surface defects on the catalyst surface, thereby enhancing the dehydrogenation activity.

[0086] The Pt cluster catalyst prepared by the preparation method provided by the present invention can effectively solve problems such as low dehydrogenation efficiency, high reaction temperature, easy deactivation of the catalyst, and low hydrogen release rate. Specifically, it includes: using the pH swing method to prepare a composite metal oxide carrier with surface defects, enhancing the metal-support interaction during subsequent Pt cluster loading, inhibiting coking during Pt calcination, and improving the stability of the Pt cluster catalyst; then synthesizing Pt clusters by the heating reflux method, which can increase the exposure and dispersion of its active sites, thereby enhancing the catalytic efficiency; finally, impregnating the Pt clusters onto the composite metal oxide carrier with surface defects, and the oxygen vacancies can anchor the Pt clusters and optimize the electronic structure. Moreover, the synergistic effect of the high specific surface area of Pt clusters and the oxygen vacancies on the composite metal oxide carrier can significantly improve the conversion rate and hydrogen release rate of liquid organic hydrogen carriers, and the oxygen vacancy and Pt electron regulation can reduce the activation energy to achieve low-temperature and high-efficiency dehydrogenation.

[0087] In a second aspect, the present invention also provides a Pt cluster catalyst, which is formed by loading Pt clusters on a composite metal oxide support;

[0088] In the Pt cluster catalyst, the mass ratio of the Pt clusters to the mass of the composite metal oxide support is 0.1 wt% - 0.7 wt%.

[0089] In some embodiments, the composite metal oxide support is selected from any one of MgO - Al2O3, Ga2O3 - Al2O3, ZrO2 - Al2O3, La2O3 - Al2O3, CeO2 - Al2O3, MgO - La2O3 - Al2O3, and MgO - CeO2 - Al2O3.

[0090] In specific implementation, in the Pt cluster catalyst provided by the present invention, the Pt clusters are extremely small in size and uniformly dispersed, and the atomic utilization rate is higher. When the Pt loading amount is the same, the Pt cluster catalyst prepared by the present invention has better catalytic performance than the traditional catalyst; therefore, on the premise of meeting most of the LOHC dehydrogenation requirements, the Pt cluster catalyst provided by the present invention greatly reduces the Pt loading amount in the catalyst, thereby significantly reducing the catalyst preparation cost.

[0091] In a third aspect, the present invention also provides an application of a Pt cluster catalyst, which is prepared by the preparation method provided by the present invention, and the Pt cluster catalyst is used to catalyze the dehydrogenation reaction of liquid organic hydrogen carriers;

[0092] The dehydrogenation reaction process includes:

[0093] Placing the Pt cluster catalyst in the catalyst bed layer of the reactor, and introducing a reducing gas mixture to activate the Pt cluster catalyst;

[0094] At a mass space velocity of 4 h -1 - 150 h -1 to continuously supply the liquid organic hydrogen carrier to the catalyst bed layer of the reactor, and the liquid organic hydrogen carrier undergoes a dehydrogenation reaction under the action of the Pt cluster catalyst to produce hydrogen;

[0095] wherein, the reducing gas mixture is formed by mixing H2 and an inert gas;

[0096] After continuously performing the dehydrogenation reaction for 96 h, the deactivation rate of the Pt cluster catalyst is not higher than 10%.

[0097] In the present invention, the flow rate of the reducing gas mixture is 10 mL / min - 50 mL / min, and the activation time is 3 h - 5 h;

[0098] The inert gases include nitrogen, argon, etc., and a single inert gas is preferably used in the present invention;

[0099] In the present invention, during activation, the activation temperature is kept the same as the dehydrogenation reaction temperature. The initial volume ratio of H2 to the inert gas is 1:(10 - 15). Every time a first time interval passes, the H2 flow rate increases by 5%, and the inert gas flow rate decreases by 5% until the volume ratio of H2 to the inert gas is (10 - 15), and the total activation time is 3 h - 5 h;

[0100] In the present invention, the first time interval is the unit time passed each time during the activation process; the first time interval can be 8 min - 12 min;

[0101] In some embodiments, the liquid organic hydrogen carrier is cyclohexane or methylcyclohexane.

[0102] In the present invention, the mass space velocity is the mass of the liquid organic hydrogen carrier passing through the unit mass of the Pt cluster catalyst per unit time.

[0103] In the present invention, the temperature of the dehydrogenation reaction is 280 °C - 320 °C.

[0104] In the dehydrogenation reaction system provided by the present invention, the reactor used is a batch reactor or a fixed bed reactor.

[0105] The Pt cluster catalyst prepared by the present invention has excellent activity and stability for the dehydrogenation reaction of liquid organic hydrogen carriers. Before the dehydrogenation reaction, the present invention uses a reducing gas mixture for activation, and then by gradually reducing the inert gas flow rate and increasing the H2 flow rate, a more uniform active site distribution is formed on the surface of the Pt cluster; this mild activation process avoids the problem of Pt particle aggregation caused by the rapid reduction of traditional high-concentration hydrogen, ensuring that the Pt cluster catalyst has excellent dehydrogenation activity at the initial stage of the reaction. This catalyst system can meet the requirements of dehydrogenation devices of different scales, providing complete support for the LOHC system to achieve efficient and stable hydrogen release.

[0106] Specifically, the present invention uses in-situ induced activation to flexibly adjust the activation parameters (such as temperature, time, concentration, etc.), avoiding the secondary damage to the microstructure and electronic effects of the catalyst during the cooling process in offline reduction, which helps to maintain its stability and extend the storage period. Gradient setting of the nitrogen-hydrogen ratio (i.e., the ratio of the inert gas to H2) rise and fall can avoid the possible aggregation of metal particles caused by the sudden exposure of the catalyst to high-concentration hydrogen, ensuring uniform reduction of the catalyst bed from top to bottom.

[0107] To make those skilled in the art understand the present invention more clearly, the following examples are now used to detail a Pt cluster catalyst, its preparation method and application described in the present invention.

[0108] Example 1

[0109] Prepare a 2 mol / L sodium aluminate solution, and add it to magnesium nitrate hexahydrate in a molar ratio of Al:Mg = 10:1 to form a mixed turbid solution;

[0110] Under the action of a rotating stirring paddle, slowly add the mixed turbid solution of 2 mol / L sodium aluminate and magnesium nitrate hexahydrate to 50 mL of 11.6 wt% sulfuric acid solution until the pH reaches 10, then stop adding. Complete the first pH swing. After maintaining for 3 min, slowly add an appropriate amount of sulfuric acid solution until the pH reaches 3, then stop adding. After maintaining for 3 min, continue to add the mixed turbid solution of 2 mol / L sodium aluminate and magnesium nitrate hexahydrate until the pH reaches 10, then stop adding. Complete the second pH swing. After maintaining for 3 min, slowly add an appropriate amount of sulfuric acid solution until the pH reaches 3, then stop adding. After maintaining for 3 min, continue to add the mixed turbid solution of 2 mol / L sodium aluminate and magnesium nitrate hexahydrate until the pH reaches 10, then stop adding. Complete the third pH swing. Continue stirring for 4 h to obtain a suspension containing the composite metal oxide support. Centrifuge the suspension, wash it four times, and then place it in an oven at 80 °C for drying for 8 h. Grind the dried powder (MgO-Al2O3 composite metal oxide support) and put it into a muffle furnace for the first calcination treatment at 600 °C for 12 h to obtain the MgO-Al2O3 composite metal oxide support;

[0111] Place the MgO-Al2O composite metal oxide support in a tubular furnace, and carry out high-temperature reduction at 550 °C for 5 h in a CO / Ar mixed atmosphere with a CO volume fraction of 5% to obtain a MgO-Al2O3 composite metal oxide support with surface defects;

[0112] Transfer 20 mL of a 50 mg / mL aqueous chloroplatinic acid solution, 0.4 g of polyvinylpyrrolidone (hereinafter referred to as PVP), 25 mL of water, and 75 mL of ethanol into a 200 mL round-bottom flask, heat it to 90 °C, and reflux for 5 h. After natural cooling, filter and collect the synthesized PVP-protected Pt clusters.

[0113] Weigh 1 g of the MgO-Al2O3 composite support with surface defects. Dropwise add 3.33 mL of the prepared ethanol impregnation solution of Pt clusters with a concentration of 1.5 mg / mL onto the MgO-Al2O3 composite metal oxide support with surface defects, impregnate for 1 h, then seal and let stand for 12 h, and then dry at 80 °C for 6 h. After grinding the obtained solid product into powder, put it into a muffle furnace and conduct the second calcination treatment at 350 °C for 12 h to prepare the Pt cluster catalyst. Press the Pt cluster catalyst into 40-60 mesh particles. In this Pt cluster catalyst, the content of MgO is 12 wt%, and the loading amount of Pt is 0.5 wt%, with the expression Pt / MgO-Al2O3-550.

[0114] Example 2

[0115] The difference between Example 2 and Example 1 is only that: during the preparation of the MgO-Al2O3 composite support, the number of pH swings is 2 times, with the expression Pt / MgO-Al2O3-2-550.

[0116] Example 3

[0117] The difference between Example 3 and Example 1 is only that: during the preparation of the MgO-Al2O3 composite support, the number of pH swings is 4 times, with the expression Pt / MgO-Al2O3-4-550.

[0118] Example 4

[0119] The difference between Example 4 and Example 1 is only that: during the preparation of the MgO-Al2O3 composite support, when the pH swings, the end-point pH on the acid side is 2.5 and the end-point pH on the base side is 9.5, with the expression Pt / MgO-Al2O3-L-550.

[0120] Example 5

[0121] The difference between Example 5 and Example 1 is only that: during the preparation of the MgO-Al2O3 composite support, when the pH swings, the end-point pH on the acid side is 3.5 and the end-point pH on the base side is 10.5, with the expression Pt / MgO-Al2O3-H-550.

[0122] Example 6

[0123] The difference between Example 6 and Example 1 is only that: use Ga(NO3)3·9H2O to replace Mg(NO3)2·6H2O, and finally the content of Ga2O3 is 8 wt%, with the expression Pt / Ga2O3-Al2O3-550.

[0124] Example 7

[0125] Example 7 is only different from Example 1 in that Zr(NO3)4 is used instead of Mg(NO3)2·6H2O, and the final content of ZrO2 is 8 wt%, with the expression Pt / ZrO2-Al2O3-550.

[0126] Example 8

[0127] Example 8 is only different from Example 1 in that La(NO3)3·6H2O is used instead of Mg(NO3)2·6H2O, and the final content of La2O3 is 10 wt%, with the expression Pt / La2O3-Al2O3-550.

[0128] Example 9

[0129] Example 9 is only different from Example 1 in that Ce(NO3)3·6H2O is used instead of Mg(NO3)2·6H2O, and the final content of CeO2 is 8 wt%, with the expression Pt / CeO2-Al2O3-550.

[0130] Example 10

[0131] Example 10 is only different from Example 1 in that a composite metal solution of Mg(NO3)2·6H2O and La(NO3)3·6H2O is used instead of Mg(NO3)2·6H2O, the molar ratio of MgO to La2O3 is 12:1, and the final contents of MgO and La2O3 are 8 wt%, with the expression Pt / MgO-La2O3-Al2O3-550.

[0132] Example 11

[0133] Example 11 is only different from Example 1 in that a composite metal solution of Mg(NO3)2·6H2O and Ce(NO3)3·6H2O is used instead of Mg(NO3)2·6H2O, the molar ratio of MgO to CeO2 is 12:1, and the final contents of MgO and CeO2 are 8 wt%, with the expression Pt / MgO-CeO2-Al2O3-550.

[0134] Example 12

[0135] Example 12 is only different from Example 8 in that the reduction treatment temperature of the La2O3-Al2O3 composite support in a reducing atmosphere containing CO is adjusted to 300 °C, with the expression Pt / La2O3-Al2O3-300.

[0136] Example 13

[0137] Example 13 is different from Example 8 only in that: in a reducing atmosphere containing CO, the reduction treatment temperature of the La2O3-Al2O3 composite support is adjusted to 450 °C, and the expression is Pt / La2O3-Al2O3-450.

[0138] Example 14

[0139] Example 14 is different from Example 8 only in that: the reduction treatment temperature of the La2O3-Al2O3 composite support is adjusted to 650 °C, and the expression is Pt / La2O3-Al2O3-650.

[0140] Example 15

[0141] Example 15 is different from Example 8 only in that: the reduction treatment temperature of the La2O3-Al2O3 composite support is adjusted to 750 °C, and the expression is Pt / La2O3-Al2O3-750.

[0142] Example 16

[0143] Example 16 is different from Example 9 only in that: the additive used to stabilize the Pt clusters is polyvinyl alcohol, and the expression is Pt / CeO2-Al2O3-550-E.

[0144] Example 17

[0145] Example 17 is different from Example 9 only in that: the additive used to stabilize the Pt clusters is polyethylene glycol, and the expression is Pt / CeO2-Al2O3-550-P.

[0146] Example 18

[0147] Example 18 is different from Example 9 only in that: when the CeO2-Al2O3 composite support is reduced, it is reduced in a CO / Ar reducing atmosphere with a CO volume fraction of 2%, and the expression is Pt CO-2 / CeO2-Al2O3-550.

[0148] Example 19

[0149] Example 19 is different from Example 9 only in that: when the CeO2-Al2O3 composite support is reduced, it is reduced in a CO / Ar reducing atmosphere with a CO volume fraction of 6%, and the expression is Pt CO-6 / CeO2-Al2O3-550.

[0150] Based on Examples 1-19, the following Comparative Examples 1-8 are set up.

[0151] Comparative Example 1

[0152] 1.5 mL of chloroplatinic acid ethanol solution was added dropwise to the γ-Al2O3 carrier for 1 h of impregnation and then sealed and allowed to stand for 12 h. The obtained solid was dried at 80 °C for 6 h, ground into powder, and the catalyst was pressed into 40-60 mesh particles with the expression of Pt / Al2O3.

[0153] Comparative Example 2

[0154] 1.5 mL of chloroplatinic acid ethanol solution was added dropwise to the MgO support for 1 hour of impregnation and then sealed and allowed to stand for 12 hours. The obtained solid was dried at 80°C for 6 hours, ground into powder, and the catalyst was pressed into 40-60 mesh particles, expressed as Pt / MgO.

[0155] Comparative Example 3

[0156] The difference between Comparative Example 3 and Example 1 is that Comparative Example 3 adopts a coprecipitation method to prepare the MgO-Al2O3 composite carrier, which specifically includes:

[0157] Weigh 7.3583 g Al(NO 3)3 ·9H2O, 0.3037 g Mg(NO3)2·6H2O, and 100 mL of water were added to form a mixed solution. Concentrated ammonia was then added to adjust the pH to approximately 9 and stirred continuously for 20 minutes. The resulting mixture was filtered through a sand core funnel, and the precipitate was dried at 80°C for 6 hours. It was then calcined in air at 500°C in a muffle furnace for 8 hours to obtain a MgO-Al2O3 composite support. The MgO-Al2O3 composite support was then reduced in a tube furnace at 550°C for 5 hours in a CO / Ar reducing atmosphere with a CO volume fraction of 5% to obtain the reduced MgO-Al2O3 composite support. The remaining steps were consistent with those in Example 1. The catalyst is represented by Pt / MgO-Al2O3-550-C.

[0158] Comparative Example 4

[0159] The difference between Comparative Example 4 and Example 1 is that the MgO-Al2O3 composite carrier is not subjected to reduction treatment, and the obtained catalyst expression is Pt / MgO-Al2O3.

[0160] Comparative Example 5

[0161] The difference between Comparative Example 5 and Example 1 is that the Pt clusters are not subjected to PVP protection treatment, and chloroplatinic acid is directly prepared into a 1 mg / m-2 mg / mL Pt carrier solution, which is impregnated onto the MgO-Al2O3 composite carrier with oxygen vacancies on the surface in an equal volume manner. The catalyst expression is Pt / MgO-Al2O3-W.

[0162] Comparative Example 6

[0163] The difference between Comparative Example 6 and Example 1 is as follows: The suspension was centrifuged, washed four times, and then dried in an oven at 80 °C for 8 h. The dried powder was placed in a tubular furnace and reduced at 550 °C for 5 h in a reducing atmosphere of CO / Ar with a CO volume fraction of 5%, obtaining a reduced MgO-Al2O3 composite support. The catalyst is expressed as Pt / MgO-Al2O3-K.

[0164] Comparative Example 7

[0165] The difference between Comparative Example 7 and Example 1 is that the reduction was carried out in a reducing atmosphere of H2 / N2 with a H2 volume fraction of 5%, and the obtained catalyst is expressed as PtH2-5 / MgO-Al2O3-550.

[0166] Catalytic performance test of the catalyst

[0167] For the catalysts prepared in Examples 1-19 and Comparative Examples 1-7, in-situ induction activation was carried out, and after activation, the catalyst performance test was carried out, specifically including:

[0168] (1) Take 0.1 g of the catalyst (40 mesh - 60 mesh) and mix it with 0.1 g of silicon carbide, and fill it into a 12 mm × 8 mm quartz reaction tube in the order of quartz wool + catalyst silicon carbide mixture + quartz wool;

[0169] (2) Place the reaction tube into the reaction furnace, close all outlets, and leak-check with nitrogen;

[0170] (3) After leak-checking, open the tail gas outlet. Using H2 as the activation gas and N2 as the inert gas, control the total flow rate at 10 mL / min - 50 mL / min, with an initial N2:H2 = 15:1, and set the activation temperature at 300 °C;

[0171] (4) Every 10 min, reduce the N2 flow rate by 5% and increase the H2 flow rate by 5% until N2:H2 = 1:10, and maintain this ratio for activation for 3 h;

[0172] (5) After activation, set the reaction conditions: 300 °C, cyclohexane / methylcyclohexane flow rate 27 mL / min, N2 flow rate 30 mL / min, mass space velocity 32 h -1 , and inject cyclohexane / methylcyclohexane into the N2 gas stream preheated to 220 °C through an injection pump for dehydrogenation reaction testing.

[0173] Table 1 Hydrogen release rate table of the catalyst for cyclohexane / methylcyclohexane dehydrogenation

[0174]

[0175] As can be seen from Table 1, the hydrogen release rate of the Pt cluster catalyst prepared in Example 1 for methylcyclohexane is 3301 mmol / (gPt·min), and after the dehydrogenation reaction proceeds for 96 hours, the activity of the catalyst does not decrease; when changing the preparation process of the pH swing method, the doped metal, and the hydrogen treatment conditions of the MgO-Al2O3 composite support, the activity of the catalyst decreases to varying degrees.

[0176] In Comparative Example 3, the MgO-Al2O3 composite support was prepared by the co-precipitation method, and the initial hydrogen release rate of the finally prepared Pt / MgO-Al2O3-550-C was 2341 mmol / (gPt·min). After the dehydrogenation reaction proceeded for 96 hours, the inactivation rate was 33.3%. In the present invention, the MgO-Al2O3 composite support is prepared by the pH swing method, that is, the pH value during the preparation process alternates between acid and base. The amorphous aluminum hydroxide contained in the crystalline pseudo-boehmite is dissolved on the acid side, and when alkali is added again, it will precipitate on the formed pseudo-boehmite crystal particles. Such cycling can generate a composite alumina support with relatively uniform crystal particles and relatively concentrated pore sizes. The requirements for process parameters (such as pH value, temperature) are more stringent than those of the co-precipitation method. The co-precipitation method is prone to local supersaturation, resulting in composition segregation and a large dispersion span of the support pore size, and further leading to poor stability of the finally prepared catalyst.

[0177] Compared with the preparation conditions of Example 1, in Comparative Example 4, only the MgO-Al2O3 composite support was not subjected to reduction treatment, and the inactivation rate of the prepared Pt / MgO-Al2O3 was 41.4%. In the present invention, during the process of reducing the composite support, the oxygen on the surface of the catalyst support is removed, and surface defects are generated to anchor the Pt metal, enhancing the interaction between Pt and the support with vacancy defects, obtaining sub-nanometer-sized Pt metal particles, restricting the migration and aggregation of Pt gold in the high-temperature hydrogen-rich gas atmosphere in the organic liquid dehydrogenation system, and effectively improving the stability of the catalyst.

[0178] Compared with the preparation conditions of Example 1, in Comparative Example 5, only PVP was not used to disperse and protect Pt to further restrict the agglomeration of Pt during the subsequent calcination of the catalyst. The inactivation rate of the obtained Pt / MgO-Al2O3-550-W was 31.4%. In the present invention, PVP is used as a steric hindrance agent, and its long-chain molecular structure adsorbs on the surface of Pt nanoparticles to form a stable protective layer. During the calcination process, the thermal decomposition temperature of PVP is relatively low, and it can be gradually decomposed at high temperature, effectively inhibiting the surface migration and agglomeration of Pt particles and maintaining its high dispersion. This mechanism ensures that the Pt particles still have a small particle size and a high specific surface area after calcination, thus maintaining excellent catalytic activity.

[0179] Comparative Example 6 only impregnated and loaded directly after reducing the MgO-Al2O3 composite support compared with the preparation conditions of Example 1. The stability of its catalyst - Pt / MgO-Al2O3-550-K decreased significantly, and the deactivation rate was 45.2%. In the present invention, the composite alumina support with relatively uniform crystal particles and relatively concentrated pore diameters is first calcined to solidify it, ensuring the stability of the pore structure of the support, and then reduced to form surface defects for anchoring Pt metal. At this time, the formed catalyst structure is stable, and the movement of Pt metal on the limited support surface is effectively restricted, obtaining a highly dispersed Pt sub-nanocluster catalyst, achieving the inhibition of its agglomeration phenomenon during high-temperature reactions.

[0180] Comparative Example 7 only used a H2 / N2 reducing atmosphere with a H2 volume fraction of 5% during the reduction of the MgO-Al2O3 composite support compared with the preparation conditions of Example 1. The results showed that this change led to a significant decrease in the stability of the catalyst, and the deactivation rate was as high as 47.5%. Specifically, in the case of using CO as a reducing agent, it can effectively reduce the metal ions in the support and form oxygen vacancies by removing surface oxygen atoms, and the CO2 generated during this process is an acidic gas and there is no water molecule. On the contrary, when hydrogen (H2) is used for the reduction reaction, relatively more water will be generated, which may have an adverse effect on the stability of the catalyst support. Especially during the impregnation and loading operation, excessive water may lead to the loss of oxygen vacancies, thereby weakening the anchoring effect between platinum (Pt) and the support, ultimately affecting the overall performance and stability of the catalyst. X+ metal ions, and form oxygen vacancies by removing surface oxygen atoms, and the CO2 generated during this process is an acidic gas and there is no water molecule. On the contrary, when hydrogen (H2) is used for the reduction reaction, relatively more water will be generated, which may have an adverse effect on the stability of the catalyst support. Especially during the impregnation and loading operation, excessive water may lead to the loss of oxygen vacancies, thereby weakening the anchoring effect between platinum (Pt) and the support, ultimately affecting the overall performance and stability of the catalyst.

[0181] Another 0.1 g of the Pt / MgO-Al2O3-550 catalyst prepared in Example 1 was taken and activated in a tubular furnace. The activation conditions were the same as those of in-situ induced activation. After the activation was completed, the catalyst was loaded into the reactor for the catalyst performance test shown in step (5). It was found that when the in-situ induced reduction was changed to off-line reduction of the catalyst, the initial activity of the catalyst was only 2176 mmol / (gPt·min), and the stability of the catalyst decreased significantly, with a deactivation rate of 41.7%. During the off-line reduction process, there will be a cooling process after the reduction of the catalyst, and the temperature change will generate thermal stress, and the catalyst will undergo some unnecessary physical and chemical changes, further affecting the microstructure and electronic effect of the catalyst, resulting in an increased deactivation during the use of the catalyst. In-situ induced activation can activate the catalyst under actual operating conditions. The catalyst activated in this way has better stability and durability, which is particularly important for long-term industrial processes.

[0182] In summary, the present invention provides a Pt cluster catalyst, a preparation method and an application thereof. The alumina composite metal oxide support is prepared by the pH swing method, and defect oxide nanoislands are formed through high-temperature reduction treatment, which can firmly anchor the subsequently loaded Pt clusters, reduce the coking phenomenon of the Pt-based catalyst, and significantly improve the catalytic activity and stability of the Pt cluster catalyst. At the same time, the Pt clusters are prepared by the heating reflux method, so that they have high dispersibility and abundant active sites. Finally, the prepared Pt cluster catalyst has a small Pt particle size and a high atomic utilization rate. When used in the dehydrogenation reaction of liquid organic hydrogen carriers, the Pt cluster catalyst has a weak adsorption capacity for products, can exhibit a high conversion rate and hydrogen release rate at low temperatures, and can still maintain structural stability at high temperatures, providing an efficient and reliable solution for the engineering application of the LOHC dehydrogenation link.

[0183] Each embodiment in this specification is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. The same or similar parts among the various embodiments can be referred to each other.

[0184] Although the preferred embodiments of the embodiments of the present application have been described, those skilled in the art can make additional changes and modifications once they know the basic creative concept. Therefore, the appended claims are intended to be construed as including the preferred embodiments and all changes and modifications falling within the scope of the embodiments of the present application.

[0185] Finally, it should also be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover a non-exclusive inclusion, so that a process, method, article or terminal device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or terminal device. Without further limitation, an element defined by the statement "comprising a..." does not exclude the existence of additional identical elements in the process, method, article or terminal device comprising the element.

[0186] The above provides a detailed introduction to a Pt cluster catalyst, a preparation method and an application thereof provided by the present application. Specific examples are used in this article to elaborate on the principle and implementation manner of the present application. The description of the above embodiments is only used to help understand the method and its core idea of the present application; at the same time, for those of ordinary skill in the art, according to the idea of the present application, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present application.

Claims

1. A preparation method of a Pt cluster catalyst, characterized in that, The preparation method includes the following steps: Step 1: Dissolve sodium aluminate and a metal oxide precursor in deionized water to obtain a mixed turbid solution; Step 2: Using the pH swing method, mix the mixed turbid solution with a sulfuric acid solution to form a suspension. After centrifuging, washing, drying, and first calcination of the suspension, a composite metal oxide support is obtained; Step 3: Subject the composite metal oxide support to high-temperature reduction treatment to obtain a composite metal oxide support with surface defects; Step 4: Mix a platinic acid solution, an additive, and an ethanol aqueous solution, and perform heat reflux treatment on the mixed system. After cooling, filter to obtain Pt clusters; Step 5: Dissolve the Pt clusters in a solvent to obtain an impregnation solution, and drop the impregnation solution onto the composite metal oxide support with surface defects by equal-volume impregnation. After sealing and standing still, perform drying and second calcination treatment to prepare the Pt cluster catalyst; Among them, in Step 1, the mass ratio of sodium aluminate to the metal oxide precursor is (5 - 30):1; In Step 1, the metal oxide precursor is selected from at least one of magnesium nitrate hexahydrate, gallium nitrate nonahydrate, zirconium nitrate, lanthanum nitrate hexahydrate, cerium nitrate hexahydrate, calcium nitrate, manganese nitrate tetrahydrate, zinc nitrate hexahydrate, and barium nitrate; In Step 3, the high-temperature reduction treatment is carried out in a CO / inert gas atmosphere. In the CO / inert gas atmosphere, the volume fraction of CO is 1% - 10%; The temperature of the high-temperature reduction treatment is 300 °C - 750 °C, the heating rate is 2 °C / min - 10 °C / min, and the time is 5 h - 9 h; In Step 4, the additive is selected from any one of polyvinylpyrrolidone, polyvinyl alcohol, and polyethylene glycol.

2. The preparation method of the Pt cluster catalyst according to claim 1, characterized in that, The composite metal oxide support includes any one of MgO - Al2O3, Ga2O3 - Al2O3, ZrO2 - Al2O3, La2O3 - Al2O3, CeO2 - Al2O3, MgO - La2O3 - Al2O3, and MgO - CeO2 - Al2O3.

3. The preparation method of the Pt cluster catalyst according to claim 1, characterized in that, In Step 2, when using the pH swing method to mix the mixed turbid solution with the sulfuric acid solution, the pH of the resulting suspension swings back and forth between alkaline and acidic. When the pH swings to the alkaline side, the pH value is 9.5 - 10.5, and when the pH swings to the acidic side, the pH value is 2.5 - 3.

5. The number of pH swings is 2 - 6.

4. The preparation method of the Pt cluster catalyst according to claim 1, characterized in that In Step 2, the temperature of the first calcination is 400 °C - 600 °C, the heating rate is 2 °C / min - 10 °C / min, and the time is 2 h - 24 h.

5. The preparation method of the Pt cluster catalyst according to claim 1, characterized in that, In Step 4, the volume ratio of ethanol to water in the ethanol aqueous solution is (1 - 7):1; The mass ratio of platinum to the additive in the mixed system is (2 - 20):

1.

6. The preparation method of the Pt cluster catalyst according to claim 1, characterized in that, In Step 4, the temperature of the heat reflux treatment is 80 °C - 95 °C.

7. The preparation method of the Pt cluster catalyst according to claim 1, wherein, In Step 5, the mass ratio of Pt in the impregnation solution to the mass of the composite metal oxide support with surface defects is 0.1 wt% - 0.7 wt%; The solvent is selected from at least one of water, ethanol, methanol, and acetone; In Step 5, the temperature of the second calcination is 200 °C - 500 °C, and the time is 3 h - 6 h.

8. A Pt cluster catalyst, characterized in that, The Pt cluster catalyst is prepared by the preparation method described in any one of the above claims 1 - 7; The Pt cluster catalyst is formed by loading Pt clusters on a composite metal oxide support; In the Pt cluster catalyst, the mass ratio of the Pt clusters to the mass of the composite metal oxide support is 0.1 wt% - 0.7 wt%.

9. Use of the Pt cluster catalyst prepared by the preparation method according to any one of claims 1-7, characterized in that, The Pt cluster catalyst is used to catalyze the dehydrogenation reaction of liquid organic hydrogen carriers; The dehydrogenation reaction process includes: Placing the Pt cluster catalyst in the catalyst bed layer of the reactor, and introducing a reducing gas mixture to activate the Pt cluster catalyst; At a mass space velocity of 4 h -1 - 150 h -1 the liquid organic hydrogen carrier is continuously supplied to the catalyst bed of the reactor, and the dehydrogenation reaction of the liquid organic hydrogen carrier occurs under the action of the Pt cluster catalyst to produce hydrogen; Among them, the reducing gas mixture is formed by mixing H2 and an inert gas; After continuously performing the dehydrogenation reaction for 96 h, the deactivation rate of the Pt cluster catalyst is not higher than 10%.

10. The application of the Pt cluster catalyst according to claim 9, characterized in that, The liquid organic hydrogen carrier is cyclohexane or methylcyclohexane.

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