Pt cluster catalyst, preparation method and application

Abstract

According to the Pt cluster catalyst, the preparation method and the application, an aluminum oxide composite metal oxide carrier is prepared by adopting a pH swing method, a defect oxide nano island is formed through high-temperature reduction treatment, and oxygen vacancies contained on the surface can firmly anchor a subsequently loaded Pt cluster, so that the coking phenomenon of the Pt-based catalyst is reduced, and the catalytic activity of the Pt-based catalyst is improved. The catalytic activity and the stability of the Pt cluster catalyst are obviously improved. Meanwhile, Pt clusters are prepared through a heating reflux method, so that the Pt clusters have high dispersity and rich active sites, the finally prepared Pt cluster catalyst is small in Pt particle size and high in atom utilization rate, and when the Pt cluster catalyst is used for catalyzing a dehydrogenation reaction of a liquid organic hydrogen carrier, the Pt cluster catalyst is weak in adsorption capacity to a product, and the catalytic activity of the liquid organic hydrogen carrier is improved. The catalyst can show high conversion rate and hydrogen release rate at low temperature, can still keep stable structure at high temperature, and provides an efficient and reliable solution for engineering application of an LOHC dehydrogenation link.

Description

Technical Field

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

[0002] LOHC technology is a technology that utilizes organic compounds containing unsaturated carbon-carbon double bonds to carry out reversible hydrogenation and dehydrogenation reactions to achieve the storage and transportation of hydrogen. At present, petroleum-based aromatic compounds are considered to be extremely promising hydrogen storage carriers due to their low cost, high hydrogen storage density, good chemical stability and excellent reversibility. With these advantages, LOHC technology has become one of the few technologies that can achieve long-term, large-scale storage of hydrogen, and can be matched with existing fossil energy transportation infrastructure, so that the storage, transportation and refueling of hydrogen can be similar to the way petroleum is handled. However, in the entire aromatic hydrogen storage cycle, although the hydrogenation technology of unsaturated organic matter is relatively mature, the dehydrogenation reaction process of liquid organic hydrogen carriers still faces many challenges.

[0003] At present, platinum-based catalysts are widely used in dehydrogenation reactions due to their excellent dehydrogenation performance. However, the dehydrogenation process involves a complex gas-liquid-solid three-phase reaction. Existing catalysts have problems such as low reaction conversion rate and slow hydrogen release rate at low temperatures and poor catalyst stability 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, preparation method and application, a composite metal oxide carrier is prepared by pH swing method, and defect oxide nano-islands are formed on the surface of the composite metal oxide carrier by high temperature reduction treatment, and the rich oxygen vacancies contained in the surface can firmly anchor the Pt clusters loaded subsequently, thereby reducing the coking phenomenon of Pt-based catalysts, and significantly improving the catalytic activity and stability of Pt cluster catalysts. At the same time, Pt clusters are prepared by heating reflux method, so that they have high dispersibility and rich active sites, so that the Pt particle size in the finally prepared Pt cluster catalyst is small, the atomic utilization rate is high, and when used to catalyze the dehydrogenation reaction of liquid organic hydrogen carriers, the Pt cluster catalyst has weak adsorption capacity for products, can show 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 LOHC dehydrogenation link.

[0005] In a first aspect, the present invention provides a method for preparing a Pt cluster catalyst, the preparation method comprising: Step 1: dissolving sodium aluminate and a metal oxide precursor in deionized water to obtain a mixed turbid solution; Step 2: using a pH swing method, the mixed turbid liquid is mixed with a sulfuric acid solution to form a suspension, and the suspension is centrifuged, washed, dried and calcined for the first time to obtain a composite metal oxide carrier; Step 3: The composite metal oxide support is subjected to high-temperature reduction treatment to obtain a composite metal oxide support with surface defects; Step 4: mixing the platinum acid solution, the additive and the ethanol aqueous solution, heating the mixed system under reflux, cooling and filtering to obtain Pt clusters; Step 5: dissolving the Pt clusters in a solvent to obtain an impregnation solution, and dropping the impregnation solution onto the composite metal oxide support with surface defects by equal volume impregnation, sealing and standing, and then drying and performing a second calcination treatment to obtain the Pt cluster catalyst.

[0006] Optionally, in step 1, the mass ratio of the sodium aluminate to the metal oxide precursor is (5-30):1.

[0007] 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.

[0008] Optionally, in step 2, the pH swing method is used to mix the mixed turbid liquid with a sulfuric acid solution, so that the pH of the obtained 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, and the number of pH swings is 2-6.

[0009] 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.

[0010] Optionally, in step 3, the high-temperature reduction treatment is carried out in a CO / inert gas atmosphere, wherein the volume fraction of CO in the CO / inert gas atmosphere 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.

[0011] Optionally, in step 4, the additive is selected from any one of polyvinyl pyrrolidone, polyvinyl alcohol and polyethylene glycol.

[0012] Optionally, 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 additive in the mixed system is (2-20):1.

[0013] Optionally, in step 4, the temperature of the heating reflux treatment is 80°C-95°C.

[0014] 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%; The solvent is selected from at least one of water, ethanol, methanol and acetone.

[0015] Optionally, in step 5, the second calcination is performed at a temperature of 200°C-500°C and for a time of 3 h-6 h.

[0016] In a second aspect, the present invention provides a Pt cluster catalyst prepared by the preparation method described in the first aspect above; The Pt cluster catalyst is formed by a composite metal oxide carrier supporting a Pt cluster; 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%.

[0017] Optionally, the composite metal oxide support comprises MgO-Al 2 O 3 , Ga 2 O 3 -Al 2 O 3 、ZrO 2 -Al 2 O 3 ,La 2 O 3 -Al 2 O 3 、CeO 2 -Al 2 O 3 MgO-La 2 O 3 -Al 2 O 3 MgO-CeO 2 -Al 2 O 3 Any one of .

[0018] 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 a dehydrogenation reaction of a liquid organic hydrogen carrier; The dehydrogenation reaction process comprises: Placing the Pt cluster catalyst in a catalyst bed of a reactor, and introducing a reducing mixed gas to activate the Pt cluster catalyst; 4 h -1 -150 h -1 The liquid organic hydrogen carrier is continuously supplied to the catalyst bed of the reactor at a mass space velocity of , and the liquid organic hydrogen carrier undergoes a dehydrogenation reaction under the action of the Pt cluster catalyst to produce hydrogen; Wherein, the reducing mixed gas is composed of H 2 Mixed with inert gases to form; After the dehydrogenation reaction was continuously carried out for 96 h, the deactivation rate of the Pt cluster catalyst was no more than 10%.

[0019] Optionally, the liquid organic hydrogen carrier is cyclohexane or methylcyclohexane.

[0020] In summary, the present invention has at least the following beneficial technical effects: 1. The present invention provides a preparation method of a Pt cluster catalyst, comprising dissolving sodium aluminate and a metal oxide precursor in water, adjusting precipitation by a pH swing method, and obtaining a composite metal oxide carrier by centrifugation, drying, and calcining; treating the carrier at high temperature in a reducing atmosphere to form a defect structure on the surface; mixing a platinum acid solution with an ethanol aqueous solution containing a steric hindrance additive, and heating and refluxing to prepare nanoscale Pt clusters; and loading the Pt clusters on the composite metal oxide carrier with surface defects by equal volume impregnation, and obtaining a Pt cluster catalyst by drying and calcining. The preparation method realizes the confined growth of Pt clusters in a nanoreactor by combining sodium aluminate and a metal oxide precursor to form a nano-island carrier structure on an alumina substrate, and combining defect construction and the steric hindrance effect of the additive. The Pt particles in the obtained Pt cluster catalyst are smaller in size and have a strong metal-carrier interaction. In the dehydrogenation reaction of a liquid organic hydrogen carrier, low-temperature and high-efficiency dehydrogenation and high-temperature anti-sintering / anti-coking can be achieved, and the dehydrogenation efficiency of the liquid organic hydrogen carrier can be significantly improved. 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 low loading, and the utilization rate of precious metals is significantly improved while ensuring the catalytic efficiency, thereby reducing the production cost; 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 96 hours of continuous dehydrogenation reaction, the deactivation rate of the Pt cluster catalyst is not higher than 10%. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the description of the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0022] Figure 1 The flowchart of the preparation method of Pt cluster catalysis proposed in the embodiment of the present invention is shown; Figure 2 The spherical aberration electron microscope image of Pt cluster catalysis proposed in the embodiment of the present invention is shown. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0024] In the drawings, the size of the constituent elements, the thickness of the layer or the area may be exaggerated for the sake of clarity. Therefore, any implementation of the present disclosure is not necessarily limited to the size shown in the drawings, and the shapes and sizes of the components in the drawings 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.

[0025] Among the related technologies, LOHC technology is a technology that utilizes organic compounds containing unsaturated carbon-carbon double bonds to carry out reversible hydrogenation and dehydrogenation reactions to achieve the storage and transportation of hydrogen. At present, petroleum-based aromatic compounds are considered to be extremely 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 matter is 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. These problems have become one of the key bottlenecks restricting the further development of LOHC technology.

[0026] The present invention finds that although the existing platinum-based catalyst has excellent dehydrogenation performance, it still has problems such as low dehydrogenation efficiency, high dehydrogenation temperature, and easy catalyst deactivation during the dehydrogenation reaction. For example, CN116393124B discloses a Pt-based catalyst and its preparation method and application, using PtCl 6 2-The strong electrostatic interaction between the catalyst and the magnesium-aluminum hydrotalcite layer (positively charged) and the change of Pt loading amount can achieve the microstructural 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 increased by 3.3 times, but the hydrogen release rate was only 769 mmol / (gPt·min).

[0027] The present invention further studies and finds that the dehydrogenation reaction process of liquid organic hydrogen carrier involves a complex gas-liquid-solid three-phase reaction, which results in low conversion rate and slow hydrogen release rate of existing platinum-based catalysts at low temperatures; at high temperatures, the catalyst has poor stability. 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 high hydrogen release rate and good stability. The specific implementation content of the present invention is as follows: In a first aspect, the present invention provides a method for preparing a Pt cluster catalyst. Figure 1 The flow chart of the preparation method of the Pt cluster catalyst provided in the embodiment of the present invention is shown as follows: Figure 1 As shown, the preparation method comprises: S1: dissolving sodium aluminate and a metal oxide precursor in deionized water to obtain a mixed turbid solution; In the present invention, the concentration of sodium aluminate is 1 mol / L-5 mol / L; In some embodiments, the mass ratio of the sodium aluminate to the metal oxide precursor is (5-30):1.

[0028] 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; The metal oxide precursors may be selected from one or two in the present invention; In one case, when two metal oxide precursors are selected, the mass ratio of the two metal oxide precursors is (5-15):1; In this step, sodium aluminate and metal oxide precursors are combined in a mass ratio of (5-30):1, which 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. 2 O 3 The synergistic effect with metal oxides can regulate the number of oxygen vacancies to reduce the dehydrogenation barrier (e.g. Ce 3+ / Ce 4+ The redox couple promotes H 2 desorption, etc.), so that the final Pt cluster catalyst can achieve stable dehydrogenation at low temperature.

[0029] 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.

[0030] The metal oxide precursors in the present invention optimize the performance of Pt cluster catalysts through their unique physical and chemical properties. The metal oxides formed by these metal oxide precursors after calcination react with γ-Al 2 O 3 The synergistic effect of the carrier enables the catalyst to have high-density oxygen vacancies, excellent Pt dispersion and low-temperature dehydrogenation activity. At the same time, the interfacial effect inhibits Pt sintering and carbon deposition, ultimately achieving efficient and stable dehydrogenation of liquid organic hydrogen carriers.

[0031] In the present invention, the reaction process of obtaining the mixed turbid solution includes: dissolving sodium aluminate and dissolving the metal salt precursor; for example, NaAlO 2 As a strong base and weak acid salt, it dissociates and hydrolyzes in water to produce amorphous Al(OH) 3 Colloid (one of the main components of turbid solution), the solution is alkaline, which promotes the coprecipitation of subsequent metal ions; the second metal ion (metal ion other than Al) and OH - Combine to form metal hydroxide colloid; finally Al(OH) 3 It forms a heterogeneous colloidal network with metal hydroxides through hydrogen bonds and electrostatic interactions to obtain a mixed turbid solution.

[0032] S2: using a pH swing method, mixing the mixed turbid liquid with a sulfuric acid solution to form a suspension, and subjecting the suspension to centrifugation, washing, drying and a first calcination treatment to obtain a composite metal oxide carrier; In specific implementation, when this step adopts the pH swing method to prepare the composite metal oxide carrier, the pH value during precipitation changes alternately between acid and base, and the amorphous aluminum hydroxide impurities and some unstable edge sites of γ-AlOOH are dissolved on the acid side. When alkali is added again, they will be precipitated on the generated pseudo-boehmite crystalline particles. Such a cycle can generate a composite metal oxide carrier with relatively uniform crystal particles and relatively concentrated pore size.

[0033] In specific implementation, this step adopts the pH swing method, mixing the mixed turbid liquid with the sulfuric acid solution, so that the pH of the obtained 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, and the number of pH swings is 2-6.

[0034] In the specific implementation, an appropriate amount of mixed turbid liquid is slowly added to an appropriate amount of sulfuric acid solution to change the pH of the obtained mixed system to alkaline, and after maintaining for 3 min-5 min, an appropriate amount of sulfuric acid solution is continuously slowly added to the mixed system to change the pH of the obtained mixed system to acidic, and maintained for 3 min-5 min. The pH of the mixed system undergoes multiple swings until all the mixed turbid liquid is mixed with the sulfuric acid solution. By setting the pH swing time to 3 min-5 min, Al(OH) can be ensured in the alkaline stage. 3 It can fully co-precipitate with the formed metal hydroxide; in the acidic stage, it can moderately dissolve the edge unstable particles, thereby improving the crystallinity.

[0035] In this step, the pH swing method repeatedly cycles from alkaline to acidic to alkaline, so that the metal ions precipitate, dissolve, and reprecipitate, thereby forming a precipitate of uniform size, avoiding rapid agglomeration of particles, and forming an amorphous structure carrier. In the present invention, the composite metal oxide carrier with surface defects obtained by calcining and high-temperature reduction 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 structure is complete, so that H 2 The desorption energy is lower, and H is more easily desorbed than traditional Pt-based catalysts. 2 . In addition, the hierarchical pore structure formed by alternating pH can accelerate the diffusion of liquid organic hydrogen carriers and reduce the activation energy of the reaction; In this step, the pH of the alkaline stage is set to 9.5-10.5, which can ensure that AlO 2- The metal ions are completely co-precipitated to form a hydroxide carrier, which is converted into a composite metal oxide carrier structure with a high specific surface area after calcination; the pH of the acidic stage is set to 2.5-3.5 to selectively dissolve small particles and impurity phases, retaining the highly active Al 2 O 3 The skeleton improves the defect concentration; the pH swing frequency is set to 2-6 times, and the formed composite metal oxide carrier is more suitable for the diffusion of macromolecular liquid organic hydrogen carrier. For example, under the catalytic action of the Pt cluster catalyst provided by the present invention, the apparent activation energy of methylcyclohexane dehydrogenation is reduced.

[0036] In this step, the Al 2 O 3 The shell covers the metal oxide core and also helps to inhibit the subsequent high-temperature migration of Pt clusters.

[0037] In this step, the mass fraction of the sulfuric acid solution is 5 wt%-15 wt%; the concentration of the sulfuric acid solution affects the dissolution-precipitation equilibrium of the metal, thereby affecting the pore structure and vacancy concentration of the final composite metal oxide support. The present invention sets the mass fraction of the sulfuric acid solution to 5 wt%-15 wt%, which helps to form a uniform mesoporous structure in the subsequent process, and the obtained composite metal oxide support is conducive to the subsequent Pt cluster loading and can avoid Pt particle agglomeration.

[0038] Preferably, the mass fraction of the sulfuric acid solution is 8 wt%-12 wt%, which is beneficial to the partial Al 3+ dissolves to form Al vacancies, which are subsequently converted into oxygen vacancies, which are beneficial to the deposition and adhesion of metal oxides; wherein, after calcination, the metal oxide precursor is in the γ-Al 2 O 3 Metal oxide nano-islands are formed on the surface of the carrier, so that each nested metal atom is isolated in the nanoreactor. In the subsequent processing process, the metal atoms are confined in the nanoreactor, solving the problems of metal atom agglomeration growth and decreased stability.

[0039] In this step, the precipitate obtained after centrifugal washing is dried to remove free water and part of bound water in the precipitate to prevent the carrier from cracking due to rapid evaporation of water during subsequent calcination. A vacuum drying oven or other equipment may be used for drying; wherein the drying temperature is 60°C-110°C and the drying time is 2 h-24 h.

[0040] In this step, the first calcination treatment is to achieve carrier crystallization; the temperature of the first calcination is 400 ℃-600 ℃, the heating rate is 2 ℃ / min-10 ℃ / min, and the time is 2 h-24 h.

[0041] In specific implementation, this step sets the first calcination temperature between 400°C and 600°C to promote the conversion of hydroxides in the precipitate into a composite metal oxide carrier with a high specific surface area, which is beneficial to the subsequent diffusion of liquid organic hydrogen carriers; the lower limit of the temperature is set to 400°C to ensure complete crystallization and avoid residual amorphous phase to reduce the specific surface area; the upper limit of the temperature is set to 600°C to inhibit the formation of γ-Al 2 O 3The crystalline phase of the composite material is transformed into the θ phase; during calcination, the surface hydroxyl groups (-OH) can be appropriately removed and appropriate oxygen vacancies can be generated to avoid structural collapse caused by excessive defects; by setting the heating rate between 2 ℃ / min-10 ℃ / min, it is helpful to gradually remove physically adsorbed water and bound water, avoid pore collapse, make the carrier grain size uniform, reduce stress cracks, and shorten the process time and reduce energy consumption; by setting the calcination time between 2 h and 24 h, it is possible to avoid excessive grain growth, ensure a high surface oxygen vacancy density, and enhance dehydrogenation activity.

[0042] The composite metal oxide support obtained in this step is a composite support comprising aluminum and a second metal, wherein the second metal is a metal atom provided by the metal oxide precursor.

[0043] S3: The composite metal oxide support is subjected to high-temperature reduction treatment to obtain a composite metal oxide support with surface defects; In specific implementation, this step performs a high-temperature reduction treatment on the composite metal oxide carrier to reduce the metal oxide and generate oxygen vacancies; in the high-temperature reduction treatment, the reducing atmosphere can induce the chemical reduction of metal ions in the composite metal oxide carrier at high temperature, and the surface oxygen atoms are removed to form oxygen vacancies, thereby obtaining a composite metal oxide carrier with surface defects; the electronic defect state induced by the oxygen vacancies can adjust the downward shift of the d-band center of the subsequently loaded Pt clusters, weaken the CH bond binding energy, enable the dehydrogenation reaction to proceed at a lower temperature, and reduce the catalyst's adsorption capacity for the product; and the energy provided by the high-temperature environment can overcome the energy barrier of the metal-oxygen bond breakage, promote the diffusion of oxygen atoms, and make the oxygen vacancies evenly distributed rather than just enriched on the surface.

[0044] In some embodiments, the high-temperature reduction treatment can be carried out in a CO / inert gas atmosphere, in which 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.

[0045] It should be noted that the volume fraction of inert gas in the CO / inert gas mixed atmosphere 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, surface oxygen vacancies can be slowly generated to avoid the collapse of the carrier structure caused by excessive reduction of the bulk phase; the high temperature of 300℃-750℃ can form abundant oxygen vacancies on the surface of the composite metal oxide carrier, which is conducive to the subsequent uniform and sufficient loading of Pt clusters; the heating rate is maintained at 2℃ / min-10℃ / min to ensure the uniform distribution of oxygen vacancies and avoid the agglomeration of metal particles caused by local overheating. Finally, by limiting the reduction time to 5h-9h, it can ensure that the oxygen vacancies in the bulk phase of the composite metal oxide carrier are fully formed, and the oxygen vacancies generated by reduction cooperate with the oxygen storage capacity of the metal oxide to achieve low-temperature and efficient dehydrogenation.

[0046] S4: mixing the platinum acid solution, the additive and the ethanol aqueous solution, heating the mixed system under reflux, cooling it and filtering it to obtain the Pt clusters; In specific implementation, the platinum acid solution used in this step is selected from any one of chloroplatinic acid, platinum nitrate, platinum acetylacetonate, and tetraammine platinum nitrate; the additive is selected from any one of polyvinyl pyrrolidone, polyvinyl alcohol, and polyethylene glycol.

[0047] In specific implementation, the long-chain molecules of polyvinyl pyrrolidone / polyvinyl alcohol / polyethylene glycol are adsorbed on the surface of the Pt clusters, preventing the particles from colliding and agglomerating through steric barriers; for example, the polar amide group (-CONH-) of polyvinyl pyrrolidone or the ether bond (-O-) of polyethylene glycol can form a coordination bond with the Pt surface, enhancing the stability of the final Pt cluster catalyst. During the subsequent second calcination, polyvinyl pyrrolidone / polyethylene glycol is partially carbonized to form an ultra-thin carbon shell that wraps the Pt clusters, inhibiting the high-temperature migration of the Pt clusters.

[0048] In a 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 mass ratio of the additive in the obtained mixed system is (2-20):1.

[0049] In the present invention, the volume ratio of ethanol to water in the ethanol-water solution and the mass ratio of the additive to platinum are set to achieve controllable preparation and stable loading of Pt clusters. 4+ The reduction kinetics of the Pt clusters are controlled within a small range; the additives effectively prevent Pt agglomeration through steric hindrance and maintain stability at high temperatures. The ratio of the additives to the platinum acid solution is set to ensure that the additives completely cover the surface of the Pt clusters, avoiding the agglomeration of Pt clusters and achieving size controllability, high dispersibility and high-temperature stability of the Pt clusters.

[0050] In specific implementation, the present invention sets the heating reflux temperature between 80°C and 95°C, which can ensure the effective redox of ethanol and avoid the coarsening of Pt particles caused by violent reactions, and has significantly improved performance compared with traditional methods. During the heating reflux process, additives and ethanol aqueous solution are added to the platinum acid solution, and the resulting system is heated to the reflux temperature, wherein ethanol releases electrons after being oxidized by heat, so that the Pt in the system 4+ The Pt atoms are reduced to Pt atoms, which form Pt nanoclusters through nucleation and aggregation. The additives are adsorbed on the surface of the Pt nanoclusters to form a protective layer. After filtration, Pt clusters with a protective layer are obtained. Under the reducing effect of the additives and ethanol, the platinum acid solution slowly nucleates and grows into Pt clusters of uniform size, avoiding the particle agglomeration of the traditional reduction method.

[0051] S5: dissolving the Pt clusters in a solvent to obtain an impregnation solution, and dropping the impregnation solution onto the composite metal oxide support with surface defects by equal volume impregnation, sealing and standing the support, and then drying and performing a second calcination treatment to obtain the Pt cluster catalyst.

[0052] In specific implementation, the mass ratio of Pt in the impregnation solution used in this step to the mass ratio 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.

[0053] In this step, the impregnation liquid is added dropwise to the composite metal oxide support with surface defects by equal volume impregnation, which can avoid excessive local concentration, make the Pt clusters uniformly adsorbed on the composite metal oxide support with surface defects, and ensure that the impregnation liquid fully infiltrates the pores of the support, thereby improving the loading efficiency of the Pt clusters; sealed and static can make the Pt clusters better embed into oxygen vacancies, form a strong metal-support interaction, and inhibit Pt agglomeration during subsequent calcination.

[0054] In specific implementation, the temperature of the second calcination is 200 ℃-500 ℃, and the time is 3 h-6 h. The second calcination is for Pt-carrier bonding, so that the Pt clusters and the carrier form a strong interaction, inhibit coking, and maintain small-sized Pt clusters. The drying treatment before the second calcination can avoid the problem of local concentration of Pt clusters and particle coarsening caused by rapid evaporation during calcination.

[0055] In this step, the temperature of the second calcination is set between 200℃ and 500℃, while evaporating free water and decomposing part of the additives, the carbonized protective layer is retained to prevent the migration of Pt clusters. After the second calcination is completed, the additives are carbonized into a conductive carbon layer, which enhances the electron transport of the Pt clusters, moves the d-band center of the Pt clusters downward, weakens the strong adsorption of Pt on H atoms, and reduces the activation energy of CH bond breaking; the oxygen vacancies on the composite metal oxide carrier act as electron reservoirs to inject electrons into the Pt clusters, and the electron delocalization of ultra-small Pt clusters or single-atom Pt is stronger, which promotes H 2 Desorption; Rapid electron transfer can also prevent excessive retention of H atoms on the Pt surface, and electron-enriched Pt clusters are more likely to release H 2 Setting the calcination time between 3 h and 6 h helps retain more surface defects on the catalyst surface, thereby improving the dehydrogenation activity.

[0056] The Pt cluster catalyst prepared by the preparation method provided by the present invention can effectively solve the problems of low dehydrogenation efficiency, high reaction temperature, easy deactivation of catalyst, low hydrogen release rate, etc. Specifically include: preparing a composite metal oxide carrier with surface defects by pH swing method, enhancing the metal-carrier interaction when loading Pt clusters later, inhibiting the coking during Pt calcination, and improving the stability of Pt cluster catalyst; synthesizing Pt clusters by heating reflux method, which can increase the exposure and dispersion of its active sites, thereby improving the catalytic efficiency; finally, impregnating Pt clusters into composite metal oxide carriers with surface defects, oxygen vacancies can anchor Pt clusters and optimize electronic structure. In addition, the high specific surface area of ​​Pt clusters and the synergistic effect of oxygen vacancies on composite metal oxide carriers can significantly improve the conversion rate and hydrogen release rate of liquid organic hydrogen carriers, and oxygen vacancies and Pt electronic regulation can reduce the activation energy, realizing low-temperature and efficient dehydrogenation.

[0057] In a second aspect, the present invention further provides a Pt cluster catalyst, wherein the Pt cluster catalyst is formed by a composite metal oxide carrier supporting a Pt cluster; 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%.

[0058] In some embodiments, the composite metal oxide support is selected from MgO-Al 2 O 3 , Ga 2 O 3 -Al 2 O 3 、ZrO 2 -Al 2 O 3 ,La 2 O 3 -Al 2 O3 、CeO 2 -Al 2 O 3 MgO-La 2 O 3 -Al 2 O 3 MgO-CeO 2 -Al 2 O 3 Any one of .

[0059] In specific implementation, in the Pt cluster catalyst provided by the present invention, the Pt cluster size is extremely small and evenly dispersed, and the atomic utilization rate is higher. Under the condition of the same Pt ​​loading, the Pt cluster catalyst prepared by the present invention has better catalytic performance than the traditional catalyst; therefore, under the premise of meeting most LOHC dehydrogenation requirements, the Pt cluster catalyst provided by the present invention greatly reduces the Pt loading in the catalyst, thereby greatly reducing the catalyst preparation cost.

[0060] In a third aspect, the present invention further provides an application of a Pt cluster catalyst, wherein the Pt cluster catalyst is prepared by the preparation method provided by the present invention, and the Pt cluster catalyst is used to catalyze a dehydrogenation reaction of a liquid organic hydrogen carrier; The dehydrogenation reaction process comprises: Placing the Pt cluster catalyst in a catalyst bed of a reactor, and introducing a reducing mixed gas to activate the Pt cluster catalyst; 4 h -1 -150 h -1 The liquid organic hydrogen carrier is continuously supplied to the catalyst bed of the reactor at a mass space velocity of , and the liquid organic hydrogen carrier undergoes a dehydrogenation reaction under the action of the Pt cluster catalyst to produce hydrogen; Wherein, the reducing mixed gas is composed of H 2 Mixed with inert gases to form; After the dehydrogenation reaction was continuously carried out for 96 h, the deactivation rate of the Pt cluster catalyst was no more than 10%.

[0061] In the present invention, the flow rate of the reducing mixed gas is 10 mL / min-50 mL / min, and the activation time is 3 h-5 h; Inert gases include nitrogen, argon, etc. In the present invention, a single inert gas is preferred; In the present invention, during activation, the activation temperature and the dehydrogenation reaction temperature are kept consistent. 2 The initial volume ratio of H to inert gas is 1:(10-15). After each first time interval, H 2 The flow rate increases by 5%, and the inert gas flow rate decreases by 5%, until H2 The volume ratio with inert gas is (10-15), and the total activation time is 3 h-5 h; In the present invention, the first time interval is the unit time of each activation process; the first time interval may be 8 min-12 min; In some embodiments, the liquid organic hydrogen carrier is cyclohexane or methylcyclohexane.

[0062] In the present invention, the mass space velocity is the mass of the liquid organic hydrogen carrier passing through a unit mass of the Pt cluster catalyst per unit time.

[0063] In the present invention, the temperature of the dehydrogenation reaction is 280°C-320°C.

[0064] In the dehydrogenation reaction system provided by the present invention, the reactor used is a batch reactor or a fixed bed reactor.

[0065] The Pt cluster catalyst prepared by the present invention has excellent activity and stability for the dehydrogenation reaction of liquid organic hydrogen carrier. Before the dehydrogenation reaction, the present invention uses a reducing mixed gas for activation, and then gradually reduces the inert gas flow rate, increases H 2 The flow rate is adjusted to form a more uniform distribution of active sites on the surface of the Pt clusters; this mild activation process avoids the problem of Pt particle aggregation caused by traditional high-concentration hydrogen rapid reduction, ensuring that the Pt cluster catalyst has excellent dehydrogenation activity at the beginning of the reaction. The catalyst system can adapt to the needs of dehydrogenation devices of different scales and provide complete support for the LOHC system to achieve efficient and stable hydrogen release.

[0066] Specifically, the present invention adopts 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 effect of the catalyst during the cooling process during offline reduction, which helps to maintain its stability and extend the shelf life. The nitrogen-hydrogen ratio (i.e., the ratio of inert gas to H 2 The increase or decrease of the ratio of the catalyst to the catalyst can avoid the sudden exposure of the catalyst to high concentration of hydrogen, which may cause the aggregation of metal particles, and ensure that the catalyst bed is evenly reduced from top to bottom.

[0067] In order to enable those skilled in the art to more clearly understand the present invention, the Pt cluster catalyst, preparation method and application of the present invention are now described in detail through the following examples.

[0068] Example 1 Prepare a 2 mol / L sodium aluminate solution and add it to magnesium nitrate hexahydrate at a molar ratio of Al:Mg=10:1 to form a mixed turbid solution; Under the action of a rotating stirring paddle, 2 mol / L of a mixed turbid solution of sodium aluminate and magnesium nitrate hexahydrate was slowly added to 50 mL of 11.6 wt% sulfuric acid solution until the pH reached 10 and then the addition was stopped to complete the first pH swing. After holding for 3 min, an appropriate amount of sulfuric acid solution was slowly added until the pH reached 3 and then the addition was stopped. After holding for 3 min, 2 mol / L of a mixed turbid solution of sodium aluminate and magnesium nitrate hexahydrate was continued to be added until the pH reached 10 and then the addition was stopped to complete the second pH swing. After holding for 3 min, an appropriate amount of sulfuric acid solution was slowly added until the pH reached 3 and then the addition was stopped. After holding for 3 min, 2 mol / L of a mixed turbid solution of sodium aluminate and magnesium nitrate hexahydrate was continued to be added until the pH reached 10 and then the addition was stopped to complete the third pH swing. After continuing to stir for 4 h, a suspension containing a composite metal oxide carrier was obtained. The suspension was centrifuged, washed four times, and then dried in an oven at 80 °C for 8 h. The dried powder (MgO-Al 2 O 3 The composite metal oxide support) was ground and placed in a muffle furnace and calcined for the first time at 600 ° C for 12 h to obtain MgO-Al 2 O 3 Composite metal oxide support; MgO-Al 2 The O composite metal oxide support was placed in a tube furnace and reduced at 550 °C for 5 h in a CO / Ar mixed atmosphere with a CO volume fraction of 5% to obtain MgO-Al with surface defects. 2 O 3 Composite metal oxide support; Pipette 20 mL of 50 mg / mL chloroplatinic acid aqueous 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 to 90 °C, reflux for 5 h, and after natural cooling, filter and collect the synthesized PVP-protected Pt clusters.

[0069] Weigh 1 g of MgO-Al with surface defects 2 O 3 Composite carrier, add 3.33 mL of 1.5 mg / mL Pt cluster ethanol impregnation solution dropwise to the surface defective MgO-Al 2 O 3The composite metal oxide carrier was impregnated for 1 h, sealed and allowed to stand for 12 h, and then dried at 80 °C for 6 h. The obtained solid product was ground into powder and placed in a muffle furnace. The second calcination treatment was performed at 350 °C for 12 h to obtain a Pt cluster catalyst. The Pt cluster catalyst was pressed into 40-60 mesh particles. The MgO content in the Pt cluster catalyst was 12 wt%, and the Pt loading was 0.5 wt%, expressed as Pt / MgO-Al 2 O 3 -550.

[0070] Example 2 The difference between Example 2 and Example 1 is that: 2 O 3 During the preparation of the composite support, the pH swings twice, expressed as Pt / MgO-Al 2 O 3 -2-550.

[0071] Example 3 The difference between Example 3 and Example 1 is that: 2 O 3 During the preparation of the composite support, the pH swings four times, expressed as Pt / MgO-Al 2 O 3 -4-550.

[0072] Example 4 The difference between Example 4 and Example 1 is that: 2 O 3 During the preparation of the composite support, when the pH swings, the end point pH on the acid side is 2.5, and the end point pH on the alkaline side is 9.5. The expression is Pt / MgO-Al 2 O 3 -L-550.

[0073] Example 5 The difference between Example 5 and Example 1 is that: 2 O 3 During the preparation of the composite support, when the pH swings, the end point pH on the acid side is 3.5, and the end point pH on the alkaline side is 10.5. The expression is Pt / MgO-Al 2 O 3 -H-550.

[0074] Example 6 The difference between Example 6 and Example 1 is that Ga(NO 3 ) 3 9H 2 O replaces Mg(NO3 ) 2 6H 2 O, finally Ga 2 O 3 The content of Pt / Ga is 8 wt%. 2 O 3 -Al 2 O 3 -550.

[0075] Example 7 The difference between Example 7 and Example 1 is that Zr(NO 3 ) 4 Replace Mg(NO 3 ) 2 6H 2 O, eventually ZrO 2 The content of Pt / ZrO is 8 wt%. 2 -Al 2 O 3 -550.

[0076] Example 8 The difference between Example 8 and Example 1 is that La(NO 3 ) 3 6H 2 O replaces Mg(NO 3 ) 2 6H 2 O, finally La 2 O 3 The content is 10 wt%, and the expression is Pt / La 2 O 3 -Al 2 O 3 -550.

[0077] Example 9 The difference between Example 9 and Example 1 is that Ce(NO 3 ) 3 6H 2 O replaces Mg(NO 3 ) 2 6H 2 O, finally CeO 2 The content is 8 wt%, expressed as Pt / CeO 2 -Al 2 O 3 -550.

[0078] Example 10 The difference between Example 10 and Example 1 is that Mg(NO 3 )2 6H 2 O and La (NO 3 ) 3 6H 2 O composite metal solution to replace Mg(NO 3 ) 2 6H 2 O, MgO and La 2 O 3 The molar ratio of MgO and La is 12:1. 2 O 3 The content of Pt / MgO-La is 8 wt%. 2 O 3 -Al 2 O 3 -550.

[0079] Embodiment 11 The difference between Example 11 and Example 1 is that Mg(NO 3 ) 2 6H 2 O and Ce(NO 3 ) 3 6H 2 O composite metal solution to replace Mg(NO 3 ) 2 6H 2 O, MgO and CeO 2 The molar ratio of MgO and CeO is 12:1. 2 The content is 8wt%, expressed as Pt / MgO-CeO 2 -Al 2 O 3 -550.

[0080] Example 12 The difference between Example 12 and Example 8 is that: La 2 O 3 -Al 2 O 3 The composite carrier was reduced in a reducing atmosphere containing CO at a temperature of 300 °C. The expression is Pt / La 2 O 3 -Al 2 O 3 -300.

[0081] Embodiment 13 The difference between Example 13 and Example 8 is that: La 2 O 3 -Al 2 O 3The composite carrier was reduced in a reducing atmosphere containing CO at a temperature of 450 °C. The expression is Pt / La 2 O 3 -Al 2 O 3 -450.

[0082] Embodiment 14 The difference between Example 14 and Example 8 is that: La 2 O 3 -Al 2 O 3 The reduction temperature of the composite carrier was adjusted to 650 °C, and the expression was Pt / La 2 O 3 -Al 2 O 3 -650.

[0083] Embodiment 15 The difference between Example 15 and Example 8 is that: La 2 O 3 -Al 2 O 3 The reduction temperature of the composite carrier was adjusted to 750 °C, and the expression was Pt / La 2 O 3 -Al 2 O 3 -750.

[0084] Example 16 The only difference between Example 16 and Example 9 is that the additive used to stabilize the Pt clusters is polyvinyl alcohol, and the expression is Pt / CeO 2 -Al 2 O 3 -550-E.

[0085] Embodiment 17 The only difference between Example 17 and Example 9 is that the additive used to stabilize the Pt clusters is polyethylene glycol, and the expression is Pt / CeO 2 -Al 2 O 3 -550-P.

[0086] Embodiment 18 The difference between Example 18 and Example 9 is that CeO 2 -Al 2 O 3 The composite carrier is reduced in a CO / Ar reducing atmosphere with a CO volume fraction of 2%, and the expression is Pt CO-2 / CeO 2 -Al 2 O3 -550.

[0087] Embodiment 19 The difference between Example 19 and Example 9 is that CeO 2 -Al 2 O 3 The composite carrier is reduced in a CO / Ar reducing atmosphere with a CO volume fraction of 6%, and the expression is Pt CO-6 / CeO 2 -Al 2 O 3 -550.

[0088] The following Comparative Examples 1-8 were set up based on Examples 1-19.

[0089] Comparative Example 1 Add 1.5 mL of chloroplatinic acid ethanol solution dropwise to the γ-Al 2 O 3 The carrier was impregnated for 1 h and sealed 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. The expression is Pt / Al 2 O 3 .

[0090] Comparative Example 2 1.5 mL of chloroplatinic acid ethanol solution was added dropwise to the MgO carrier for 1 h of impregnation and 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, expressed as Pt / MgO.

[0091] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that Comparative Example 3 adopts coprecipitation method to prepare MgO-Al 2 O 3 The composite carrier specifically comprises: Weigh 7.3583 g Al(NO 3)3 9H 2 O, 0.3037 g Mg(NO 3 ) 2 6H 2 O, 100 mL of water was added to form a mixed solution, and then concentrated ammonia was added to adjust the pH to about 9 and continued to stir for 20 min. The obtained mixture was filtered through a sand core funnel, and the precipitate was dried at 80 °C for 6 h, and then calcined in air at 500 °C in a muffle furnace for 8 h to obtain MgO-Al 2 O 3 Composite support. MgO-Al 2 O 3The composite support was reduced in a tube furnace at 550 °C for 5 h in a CO / Ar reducing atmosphere with a CO volume fraction of 5% to obtain the reduced MgO-Al 2 O 3 Composite carrier, the remaining steps are consistent with implementation 1, the catalyst expression is Pt / MgO-Al 2 O 3 -550-C.

[0092] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that: MgO-Al 2 O 3 The composite support is not subjected to reduction treatment, and the catalyst obtained is expressed as Pt / MgO-Al 2 O 3 .

[0093] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that the Pt clusters are not treated with PVP protection, and chloroplatinic acid is directly prepared into a 1 mg / m-2 mg / mL Pt carrier solution, and is impregnated into the MgO-Al2O3 containing oxygen vacancies on the surface in an equal volume manner. 2 O 3 The catalyst is expressed as Pt / MgO-Al 2 O 3 -W.

[0094] Comparative Example 6 The difference between Comparative Example 6 and Example 1 is that the suspension is centrifuged, washed four times, and then placed in an oven at 80°C for 8 h. The dried powder is placed in a tube furnace and reduced at 550°C for 5 h in a CO / Ar reducing atmosphere with a CO volume fraction of 5% to obtain a reduced MgO-Al 2 O 3 Composite carrier, the catalyst expression is Pt / MgO-Al 2 O 3 -K.

[0095] Comparative Example 7 The difference between Comparative Example 7 and Example 1 is that the reduction is carried out under H 2 The volume fraction of 5% H 2 / N 2 The catalyst obtained is expressed as PtH 2 -5 / MgO-Al 2 O 3 -550.

[0096] Catalytic performance test of catalyst The catalysts prepared in Examples 1-19 and Comparative Examples 1-7 were activated by in-situ induction, and the catalyst performance test was performed after activation, specifically including: (1) Take 0.1 g of catalyst (40-60 mesh) and mix it with 0.1 g of silicon carbide, and load it into a 12 mm × 8 mm quartz reaction tube in the order of quartz wool + catalyst silicon carbide mixture + quartz wool; (2) Place the reaction tube into the reactor, close all outlets, and check for leaks using nitrogen; (3) After the leak detection is completed, open the exhaust gas outlet and 2 is the activation gas, N 2 The total flow rate is controlled at 10 mL / min-50 mL / min and the initial N 2 :H 2 =15:1, the activation temperature is set to 300 °C; (4) Every 10 minutes, N 2 Flow rate reduced by 5%, H 2 The flow rate increases by 5% until N 2 :H 2 =1:10, keep this ratio for 3 h; (5) After activation, set the reaction conditions: 300 °C, cyclohexane / methylcyclohexane flow rate 27 mL / min, N 2 Flow rate 30mL / min, mass space velocity 32 h -1 Cyclohexane / methylcyclohexane was injected into the N2 solution preheated at 220 °C through a syringe pump. 2 Dehydrogenation reaction test was carried out in the gas flow.

[0097] Table 1 Hydrogen release rate of cyclohexane / methylcyclohexane catalyzed by catalysts

[0098] 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 the activity of the catalyst does not decrease after 96 hours of dehydrogenation reaction. 2 O 3 When the composite carrier is treated with hydrogen, the activity of the catalyst decreases to varying degrees.

[0099] In Comparative Example 3, MgO-Al was prepared by coprecipitation method. 2 O 3 Composite carrier, the final Pt / MgO-Al 2 O 3The initial hydrogen release rate of -550-C was 2341 mmol / (gPt·min), and the deactivation rate was 33.3% after 96 hours of dehydrogenation reaction. 2 O 3 The composite carrier, that is, the pH value in the preparation process changes alternately between acid and alkali. The acid side dissolves the amorphous aluminum hydroxide contained in the crystalline pseudo-boehmite, and when alkali is added, it will precipitate on the already generated pseudo-boehmite crystalline particles. Such a cycle can generate a composite alumina carrier with relatively uniform crystal particles and relatively concentrated pore size. The requirements on process parameters (such as pH value and temperature) are more stringent than those of the co-precipitation method. The co-precipitation method is very prone to local oversaturation leading to component segregation, and the carrier pore size dispersion span is large, which leads to poor stability of the final catalyst.

[0100] Comparative Example 4 is different from Example 1 in that the preparation conditions are not 2 O 3 The composite carrier is reduced to obtain Pt / MgO-Al 2 O 3 The deactivation rate is 41.4%. In the process of reducing the composite carrier, the present invention removes oxygen from the surface of the catalyst carrier, generates surface defects to anchor the Pt metal, enhances the interaction between the Pt and the carrier containing vacancy defects, obtains sub-nanometer-sized Pt metal particles, and limits the movement and aggregation of Pt gold in the high-temperature hydrogen-rich atmosphere in the organic liquid dehydrogenation system, thereby effectively improving the stability of the catalyst.

[0101] Comparative Example 5 is different from Example 1 in that the only difference is that PVP is not used to disperse and protect Pt, which further limits the aggregation of Pt during the subsequent catalyst calcination process. 2 O 3 -550-W has a deactivation rate of 31.4%. In the present invention, PVP acts as a steric hindrance and is adsorbed on the surface of Pt nanoparticles through its long-chain molecular structure to form a stable protective layer. During the calcination process, PVP has a low thermal decomposition temperature and can be gradually decomposed at high temperatures, while effectively inhibiting the surface migration and agglomeration of Pt particles and maintaining their high dispersibility. This mechanism ensures that the Pt particles still have a small particle size and a high specific surface area after calcination, thereby maintaining excellent catalytic activity.

[0102] Comparative Example 6 is prepared under the conditions of Example 1 only by adding MgO-Al 2 O 3 After the composite carrier is directly reduced, it is impregnated and loaded. 2 O 3-550-K stability is significantly reduced, and the deactivation rate is 45.2%. In the present invention, the composite alumina carrier with relatively uniform crystal particles and relatively concentrated pore size is first solidified by calcination to ensure the stability of the carrier's pore structure, and then reduced to form surface defects to anchor the Pt metal. The catalyst structure formed at that time is stable and effectively limits the movement of the Pt metal on the limited carrier surface, thereby obtaining a highly dispersed Pt sub-nano cluster catalyst, thereby inhibiting its agglomeration phenomenon during the high temperature reaction process.

[0103] Comparative Example 7 is only prepared under the conditions of MgO-Al 2 O 3 When the composite carrier is reduced, H 2 The volume fraction of 5% H 2 / N 2 The results showed that this change led to a significant decrease in the stability of the catalyst, with a deactivation rate of up to 47.5%. Specifically, when CO was used as a reducing agent, the M X+ metal ions and form oxygen vacancies by removing surface oxygen atoms, and the CO generated in this process 2 It is an acidic gas and does not contain water molecules. On the contrary, when hydrogen (H 2 ) will generate relatively more water during the reduction reaction, which may have an adverse effect on the stability of the catalyst support. Especially during the impregnation loading operation, excessive water may lead to the loss of oxygen vacancies, thereby weakening the anchoring effect between platinum (Pt) and the support, and ultimately affecting the overall performance and stability of the catalyst.

[0104] Take 0.1 g of Pt / MgO-Al prepared in Example 1 2 O 3 -550 catalyst was activated in a tubular furnace under the same activation conditions as in-situ induced activation. After activation, the catalyst was loaded into the reactor for the catalyst performance test shown in step (5). The results showed that the initial activity of the catalyst was only 2176mmol / (gPt·min) when the in-situ induced reduction was changed to offline reduction of the catalyst, and the stability of the catalyst was significantly reduced, with a deactivation rate of 41.7%. During the offline reduction process, the catalyst will have a cooling process after the reduction is completed. The temperature change will produce thermal stress, and the catalyst will undergo some unnecessary physical and chemical changes, further affecting the microstructure and electronic effects of the catalyst, resulting in 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.

[0105] In summary, the present invention provides a Pt cluster catalyst, preparation method and application, wherein an alumina composite metal oxide carrier is prepared by a pH swing method, and defective oxide nano-islands are formed by high-temperature reduction treatment, which can firmly anchor the subsequently loaded Pt clusters, reduce the coking phenomenon of Pt-based catalysts, and significantly improve the catalytic activity and stability of Pt cluster catalysts. At the same time, Pt clusters are prepared by a heating reflux method, so that they have high dispersibility and abundant active sites. The Pt cluster catalyst finally prepared has a small Pt particle size and a high atomic utilization rate. When used to catalyze the dehydrogenation reaction of liquid organic hydrogen carriers, the Pt cluster catalyst has a weak adsorption capacity for the product, can show 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.

[0106] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0107] Although the preferred embodiments of the present application have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the embodiments of the present application.

[0108] Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or terminal device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or terminal device. In the absence of further restrictions, the elements defined by the sentence "including one..." do not exclude the existence of other identical elements in the process, method, article or terminal device including the elements.

[0109] The above is a detailed introduction to a Pt cluster catalyst, preparation method and application provided by the present application. Specific examples are used in this article to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method of the present application and its core idea; at the same time, for general technical personnel in this field, according to the idea of ​​the present application, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A method for preparing a Pt cluster catalyst, characterized in that: The preparation method comprises: Step 1: dissolving sodium aluminate and a metal oxide precursor in deionized water to obtain a mixed turbid solution; Step 2: using a pH swing method, the mixed turbid liquid is mixed with a sulfuric acid solution to form a suspension, and the suspension is centrifuged, washed, dried and calcined for the first time to obtain a composite metal oxide carrier; Step 3: The composite metal oxide support is subjected to high-temperature reduction treatment to obtain a composite metal oxide support with surface defects; Step 4: mixing the platinum acid solution, the additive and the ethanol aqueous solution, heating the mixed system under reflux, cooling and filtering to obtain Pt clusters; Step 5: dissolving the Pt clusters in a solvent to obtain an impregnation solution, and dropping the impregnation solution onto the composite metal oxide support with surface defects by equal volume impregnation, sealing and standing, and then drying and performing a second calcination treatment to obtain the Pt cluster catalyst.

2. The method for preparing the Pt cluster catalyst according to claim 1, characterized in that: In step 1, the mass ratio of the sodium aluminate to the metal oxide precursor is (5-30): 1, and 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.

3. The method for preparing the Pt cluster catalyst according to claim 1, characterized in that: In step 2, the pH swing method is adopted to mix the mixed turbid liquid with the sulfuric acid solution, so that the pH of the obtained 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, and the number of pH swings is 2-6.

4. The method for preparing 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 method for preparing the Pt cluster catalyst according to claim 1, characterized in that: In step 3, the high temperature reduction treatment is carried out in a CO / inert gas atmosphere, wherein the volume fraction of CO in the CO / inert gas atmosphere 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.

6. The method for preparing the Pt cluster catalyst according to claim 1, characterized in that: In step 4, the additive is selected from any one of polyvinyl pyrrolidone, polyvinyl alcohol and polyethylene glycol.

7. The method for preparing 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 additive in the mixed system is (2-20):

1.

8. The method for preparing the Pt cluster catalyst according to claim 1, characterized in that: In step 4, the temperature of the heating reflux treatment is 80°C-95°C.

9. The method for preparing the Pt cluster catalyst according to claim 1, characterized in that: 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%; The solvent is selected from at least one of water, ethanol, methanol and acetone; In step 5, the second calcination temperature is 200°C-500°C, and the time is 3 h-6 h.

10. A Pt cluster catalyst, characterized in that: The Pt cluster catalyst is prepared by the preparation method according to any one of claims 1 to 9 above; The Pt cluster catalyst is formed by a composite metal oxide carrier supporting a Pt cluster; 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%.

11. The Pt cluster catalyst according to claim 10, characterized in that: The composite metal oxide carrier includes any one of MgO-Al2O3, Ga2O3-Al2O3, ZrO2-Al2O3, La2O3-Al2O3, CeO2-Al2O3, MgO-La2O3-Al2O3, and MgO-CeO2-Al2O3.

12. An application of a Pt cluster catalyst prepared by the preparation method according to any one of claims 1 to 9, characterized in that: The Pt cluster catalyst is used to catalyze the dehydrogenation reaction of the liquid organic hydrogen carrier; The dehydrogenation reaction process comprises: Placing the Pt cluster catalyst in a catalyst bed of a reactor, and introducing a reducing mixed gas to activate the Pt cluster catalyst; 4 h -1 -150 h -1 The liquid organic hydrogen carrier is continuously supplied to the catalyst bed of the reactor at a mass space velocity of , and the liquid organic hydrogen carrier undergoes a dehydrogenation reaction under the action of the Pt cluster catalyst to produce hydrogen; Wherein, the reducing mixed gas is formed by mixing H2 and an inert gas; After the dehydrogenation reaction was continuously carried out for 96 h, the deactivation rate of the Pt cluster catalyst was no more than 10%.

13. The use of the Pt cluster catalyst according to claim 12, characterized in that: The liquid organic hydrogen carrier is cyclohexane or methylcyclohexane.

Images