Method for loading platinum catalyst for propane dehydrogenation

Abstract

The invention discloses a platinum catalyst loading method for propane dehydrogenation, and belongs to the technical field of propane dehydrogenation. A high-stability ZnMgAlO carrier is constructed through vacuum gradient drying and Mg doping, and mesopore retention and metal dispersion optimization are realized under low energy consumption; cO surface passivation and ultraviolet light chemical deposition are combined, a Pt-Cu core-shell structure is directionally constructed, and strong electron synergy and interface stability are ensured; an ALD ultrathin AlO selective deposition process is innovated, defect sites are accurately passivated under the scale of 0.3-0.5 nm, and meanwhile, a mass transfer channel is kept unblocked; in-situ pre-activation can be matched with a periodic regeneration strategy, oxidative damage is dynamically repaired, and deposited carbon is removed.

Description

TECHNICAL FIELD

[0001] The application relates to a platinum-based catalyst loading method for propane dehydrogenation and belongs to the technical field of propane dehydrogenation. BACKGROUND

[0002] Propane dehydrogenation (PDH) is a key process for propylene production, and the core lies in developing catalysts with high activity, selectivity and stability. Platinum (Pt)-based catalysts are widely studied due to their excellent C-H bond activation ability, but single metal Pt is prone to rapid deactivation due to carbon deposition and sintering at high temperatures. Traditional solutions use a bimetallic system (such as Pt-Sn / Al2O3) and acid carrier modification, for example, the Oleflex process of UOP inhibits carbon deposition through the electronic effect of Sn, but the propylene selectivity is limited by the partial shielding of active sites by SnOx dynamic coverage, and the strong acidity of the Al2O3 carrier easily causes cracking side reactions. In recent years, spinel carriers (such as ZnAl2O4) have become a research hotspot due to their high melting point, low acidity and excellent thermal stability, but their metal dispersion and interface regulation are still technical difficulties, and traditional drying processes (such as supercritical CO2 or freeze-drying) can preserve mesoporous structures, but are difficult to scale due to high energy consumption and complex equipment.

[0003] To further improve the catalytic performance, researchers turn to bimetallic synergistic systems, among which Pt-Cu combinations are of great concern due to the electronic donor effect of Cu, which can weaken the excessive adsorption of Pt on C-H bonds. However, Cu is prone to sintering or oxidation in high-temperature and oxidizing environments, leading to Pt-Cu interface deactivation. In the traditional impregnation method, the pre-reduction of Cu precursors often fails due to the oxidizing environment of the subsequent Pt deposition step, and Cu particles are prone to migration and agglomeration during high-temperature reduction, making it difficult to form a stable Pt-Cu interface. Although carrier doping (such as Mg, La) can improve thermal stability, the balance between metal dispersion and mesoporous structure still poses a challenge. For example, although traditional ALD coating can inhibit sintering, a thick protective layer (>1 nm) will hinder mass transfer, and the uniform deposition of a thin layer (<0.5 nm) lacks reliable processes, and the photochemical deposition method has problems such as low UV light utilization rate and uneven Pt particle size, which restricts the catalytic efficiency.

[0004] In the prior art, the preparation and protection of bimetallic catalysts face multiple bottlenecks. On the one hand, the oxidation sensitivity of Cu makes it difficult to maintain its reduced state, and even if surface passivation treatment is used, traditional methods such as H2 pretreatment cannot effectively lock the active sites in subsequent processes. On the other hand, the precision of metal-support interaction (SMSI) is insufficient, and the mesoporous structure of the support collapses easily during drying and calcination, leading to a decrease in metal dispersion. In addition, high-energy consumption processes such as freeze-drying and complex equipment requirements increase the cost of industrialization. For example, although ALD technology can achieve atomic-level coating, full-surface coverage will shield the active sites, and selective deposition technology is not yet mature, making it difficult to balance the protection and mass transfer needs. SUMMARY

[0005] The technical problem to be solved by the present application is to overcome the shortcomings of the prior art and provide a high-efficiency and low-cost method for loading platinum-based catalysts for propane dehydrogenation.

[0006] The technical solution adopted by the present application to solve the technical problem is a method for loading platinum-based catalysts for propane dehydrogenation, characterized by comprising the following steps: (1) Preparation of the carrier: Dissolve zinc nitrate and aluminum nitrate in deionized water at a Zn / Al molar ratio of 1:1.8-2.2, add a citric acid complexing agent, and stir at 75-85°C to form a sol. Adjust the pH to 3.5 and age. Prepare a gel precursor by vacuum gradient drying, and generate a ZnAl2O4 spinel by calcining at 1180-1220°C for 220-250 min. Then, immerse the ZnAl2O4 spinel in a magnesium nitrate solution and perform a second calcination to form a ZnMgAlO4 solid solution carrier; (2) Immersion of Cu precursor: immerse the obtained ZnMgAlO4 solid solution carrier in a copper nitrate ethanol solution, ultrasonically disperse, and then dry. Reduce Cu / ZnMgAlO4 by heating to form a passivated carrier with surface complex Cu-CO; (3) Photochemical deposition of Pt: disperse the passivated carrier in a chloroplatinic acid-ethanol solution, and reduce Pt by ultraviolet light irradiation to form a Pt-Cu core-shell structure; 4 (4) Confined annealing: after washing and drying, anneal in a H2 / Ar atmosphere to promote Pt-Cu interfacial alloying and obtain a platinum-based catalyst; (5) Deposition of Al2O3 layer: deposit an Al2O3 layer on the surface of the catalyst by ALD process to prevent deactivation during storage and transport; (6) In-situ pre-activation: expose the Pt-Cu active sites by high-temperature treatment in a H2 atmosphere, and the platinum-based catalyst is ready for use.

[0007] ​The application constructs a ZnAl2O4 spinel matrix with a three-dimensional mesoporous structure by precisely regulating the Zn / Al molar ratio and combining a gradient calcination process, wherein the introduction of Mg elements significantly improves the thermal stability of the carrier, and the Mg 2+ uniformly substitutes lattice sites to form a ZnMgAlO4 solid solution, the strong metal-support interaction generated thereby provides high-dispersion anchoring sites for subsequent metal loading; on this basis, the use of an ethanol solution impregnation method combined with ultrasonic dispersion technology achieves uniform distribution of Cu precursors in the mesopores, a gradient reduction strategy effectively inhibits Cu particle sintering, and surface complexation is formed by CO passivation to directionally lock Cu 0 active sites, a spatially confined template is constructed for photochemical deposition of Pt; subsequently, using a local reduction reaction induced by ultraviolet light, preferential epitaxial growth of Pt atoms is achieved at Cu-CO active sites, and the Pt-Cu core-shell structure formed reduces the Pt surface electron cloud density through an electron transfer effect, thereby inhibiting the generation of carbon deposits caused by excessive desorption of propylene; further high-temperature annealing treatment in a H2 / Ar mixed atmosphere promotes atomic interdiffusion at the Pt-Cu interface, forming an interface structure with gradient alloying characteristics, the interface stress effect of which significantly enhances the C-H bond activation ability, and the confinement effect of the solid solution substrate effectively inhibits Ostwald ripening of metal particles; then, an atomic layer deposition technique is used to precisely coat a 0.3-0.5 nm ultra-thin Al2O3 layer, which selectively passivates the acidic sites on the carrier surface to inhibit side reactions while retaining the connectivity of the mesoporous channels, and the Al-O-Pt interface is used to enhance the sintering resistance of the active sites; finally, high-temperature hydrogen treatment is used to selectively remove the Al2O3 covering layer at the Pt-Cu sites, and the volume shrinkage effect is used to form 2-3 nm mesoporous windows, achieving a synergistic optimization of dynamic exposure of active sites and reaction mass transfer efficiency.

[0008] Preferably, the vacuum gradient drying conditions in step (1) are: first pre-drying for 10-15 h at a negative pressure of 47-53 Pa and a temperature of 38-44°C, and then dehydrating at a temperature of 75-85°C. This vacuum gradient drying condition can effectively prevent the collapse of the sol network structure, remove free water molecules at a low temperature pre-drying stage, and remove bound water at a high temperature stage to obtain a through mesoporous structure with concentrated pore size distribution.

[0009] Preferably, in step (1), the magnesium nitrate solution is impregnated into an equal volume of 0.9wt%-1.1wt% concentrated magnesium nitrate solution, and the secondary calcination is performed by calcining the obtained solid after impregnation and filtration at 780-820°C for 110-130 min. The use of low-concentration impregnation combined with short-time calcination ensures that Mg 2+ island-like structures with a size of ≤5 nm are embedded on the surface of the spinel, forming Mg-O-Zn electronic bridge channels, improving the concentration of oxygen vacancies on the surface of the carrier, and enhancing the metal anchoring strength.

[0010] Preferably, the ZnMgAlO4 solid solution carrier is sieved into 40-60 mesh particles by ball milling before being immersed in the copper nitrate ethanol solution.

[0011] Preferably, the concentration of the copper nitrate ethanol solution in step (2) is 0.08 mol / L-0.12 mol / L. This concentration range controls the Cu loading at 3.2wt%-3.8wt%, and the use of ethanol solvent reduces the solution polarity, promotes monolayer adsorption of copper nitrate on the hydrophobic surface of the carrier, and promotes the Cu particle size distribution to be concentrated.

[0012] Preferably, the temperature rising reduction in step (2) is specifically 4.8v / v%-5.2v / v% H2 / Ar mixed gas is introduced, and the nitrate is decomposed by pretreatment at 195°C-205°C for 55min-65min, and then the temperature is raised to 390°C-410°C for reduction for 100min-150min. A two-stage reduction process is adopted: the low-temperature stage realizes the decomposition of nitrate into CuO and avoids the risk of self-ignition, and the high-temperature stage controls the H2 partial pressure to convert CuO to Cu, thereby improving the metal dispersion.

[0013] Preferably, the CO passivation treatment in step (2) is specifically that the obtained Cu / ZnMgAlO4 is treated in a CO atmosphere with a purity of ≥99.99% at 195°C-205°C for 55min-65min. CO molecules form [Cu(CO)3] on the Cu surface. + The adsorption layer stabilizes Cu through σ-π coordination 0 Valence state, which significantly reduces the oxidation degree of Cu after treatment and greatly improves the oxidation resistance in subsequent processes.

[0014] Preferably, the concentration of the chloroplatinic acid-ethanol solution in step (3) is 0.04mol / L-0.06mol / L; the ultraviolet light intensity of the ultraviolet light irradiation is 190mW / cm²-210mW / cm², and the irradiation time is 55min-65min. By combining a specific light intensity and time, the Pt deposition rate is matched with the Cu surface active site density, 2-3 layers of Pt atoms are obtained, and the Pt utilization rate is improved.

[0015] Annealing in a H2 / Ar atmosphere promotes Pt-Cu interfacial alloying. Preferably, the confining annealing conditions in step (4) are 4.5v / v%-5.5v / v% H2 / Ar atmosphere, 480°C-520°C for 55min-65min. The hydrogen-rich atmosphere promotes the formation of an amorphous alloy transition layer at the Pt-Cu interface, reduces the propylene desorption energy, shortens the propylene residence time, and improves the dehydrogenation efficiency.

[0016] Preferably, the ALD process in step (5) uses trimethylaluminum and H2O as precursors, a substrate temperature of 145-155 DEG C, a single cycle including a trimethylaluminum pulse of 0.1 s, N2purging for 20 s, a H2O pulse of 0.05 s, N2purging for 20 s, and a total of 2 cycles. The Al2O3 layer thickness is precisely controlled.

[0017] Preferably, the high-temperature treatment in step (6) is performed at a temperature of 580-620 DEG C for 100-150 min. The high-temperature hydrogen treatment induces local rearrangement of the Al2O3 layer at the Pt-Cu sites, forming mesoporous windows matching the size of the active sites and ensuring the initial activity of the catalyst. Specifically, in the H2 atmosphere high-temperature treatment in step (6), the high-temperature H2 environment (about 600 DEG C) can cause partial reduction of the ultra-thin Al2O3 layer, and the generated metallic aluminum has volatility (boiling point is 2470 DEG C, but the migration rate can be significantly improved at 600 DEG C) at 600 DEG C, and the H2 gas flow continuously carries away the reaction product H2O, promoting the reaction to proceed in the forward direction. In addition, the organic pollutants adsorbed or the accumulated carbon remaining from the previous reaction during the storage / transport of the catalyst are cracked into methane by hydrogenation and escape with the gas flow, achieving surface purification. The ultra-thin Al2O3 layer (0.3-0.5 nm) shrinks during the reduction process, and the phase transition volume decreases, causing local stress concentration at the Pt-Cu active sites and forming mesoporous windows of 2-3 nm. The Pt-Cu alloy remains stable in H2 at 600 DEG C (the melting point of Pt is 1768 DEG C, and the melting point of Cu is 1085 DEG C), and the Al2O3 layer is preferentially peeled off from the metal sites due to the nanoscale effect and the difference in interface energy barrier.

[0018] The catalyst prepared in the application can be treated with H2 / N2 mixed gas to remove accumulated carbon and restore activity, achieving periodic regeneration. The preferred conditions for periodic regeneration are H2 / N2 mixed gas with a volume ratio of 1:0.9-1.1, treatment at 580-620 DEG C for 55-65 min, and execution once every 24-hour operation cycle. The regeneration treatment removes the accumulated carbon in the micropores of ≤1 nm through hydrogen overflow effect, and N2 dilution avoids excessive reduction. After regeneration, the propylene selectivity of the catalyst is restored to more than 98.2% of the initial value, and the activity decay is less than 5% after 100 cycles.

[0019] Compared with the prior art, the present application has the beneficial effects that: the present application realizes mesopore retention and metal dispersion optimization under low energy consumption by constructing high stability ZnMgAlO4 carrier through vacuum gradient drying and Mg doping; directional construction of Pt-Cu core-shell structure is ensured by combining CO surface passivation and ultraviolet photochemical deposition, so as to ensure strong electronic synergy and interface stability; an innovative ALD ultrathin Al2O3 selective deposition process is used to accurately passivate defect sites at a scale of 0.3-0.5 nm while maintaining a smooth mass transfer channel; in-situ pre-activation can be combined with a periodic regeneration strategy to dynamically repair oxidation damage and remove accumulated carbon. Through multi-level structure design and dynamic regulation, the present application breaks through the trade-off problem of activity-stability of bimetallic catalysts, and provides an efficient and low-cost industrialization path for PDH technology. DETAILED DESCRIPTION

[0020] The present application will be further described below in combination with specific embodiments, wherein embodiment 1 is the best embodiment.

[0021] Embodiment 1: (1) Carrier preparation: zinc nitrate and aluminum nitrate were dissolved in deionized water according to a Zn / Al molar ratio of 1:2, citric acid (metal ion: citric acid = 1:1.5) was added as a complexing agent, and the mixture was stirred at 80°C for 4h to form a sol, then ammonia water was added to adjust the pH to 3.5, and the mixture was left to stand for 24h of aging; then a vacuum gradient drying method was used: pre-drying was carried out at 50Pa negative pressure and 40°C for 12h, then the temperature was raised to 80°C to complete dehydration, and a gel precursor was obtained. The gel precursor was placed in a muffle furnace and heated to 1200°C at a rate of 5°C / min and calcined for 240min to form a high crystallinity ZnAl2O4 spinel. An equal volume of 1wt% magnesium nitrate solution was coated on the surface of the carrier by an impregnation method, and then dried at 60°C and calcined at 800°C for 120min to make Mg 2+ embed the spinel lattice to form a ZnMgAlO4 solid solution. Ball milling and sieving were performed to obtain particles with a size of 40-60 mesh.

[0022] (2) Cu precursor impregnation: the ZnMgAlO4 carrier was immersed in a 0.1mol / L copper nitrate ethanol solution; then rotary evaporation drying was carried out at 60°C for 12h, and the dried sample was placed in a tube furnace and reduced by a 5v / v% H2 / Ar mixed gas (flow rate 50mL / min) at a programmed temperature: first, the temperature was raised to 200°C at a rate of 2°C / min and maintained for 60min to decompose the nitrate, and then the temperature was raised to 400°C at a rate of 5°C / min and maintained for 120min to obtain Cu / ZnMgAlO4. The reduced Cu / ZnMgAlO4 was transferred to a fixed bed reactor and CO gas (purity 99.99%, flow rate 100mL / min) was introduced to treat the surface passivated Cu / ZnMgAlO4 carrier at 200°C for 60min.

[0023] (3) Photochemical deposition of Pt: The surface passivated Cu / ZnMgAlO4 support was dispersed in chloroplatinic acid-ethanol solution with a concentration of 0.05 mol / L, and deoxygenated by bubbling nitrogen for 30 min. The solution was transferred to a photochemical reactor for UV irradiation to reduce Pt. 4 ⁺ is Pt 0 with an intensity of 200 mW / cm2for 60 min.

[0024] (4) Confinement annealing: The solid was collected by centrifugation after the reaction, and washed with ethanol and deionized water for 3 times, respectively, and dried at 60°C for 6 h in vacuum. Then, the sample was annealed at 500°C for 60 min in a 5 v / v% H2 / Ar atmosphere.

[0025] (5) ALD atomic layer deposition of an ultrathin layer of Al2O3: The Pt-Cu / ZnMgAlO4 sample was placed in an ALD reaction chamber, and the substrate temperature was set to 150°C. Trimethylaluminum and deionized water were used as precursors, and one cycle was defined as “TMA pulse (0.1 s)-N2purging (20 s)-H2O pulse (0.05 s)-N2purging (20 s)”. Two cycles were performed. The ultrathin layer of Al2O3 was obtained by layer-by-layer growth through self-limiting surface reaction. The sample was stored in a jar for 3 months.

[0026] (6) In-situ pre-activation: Before the PDH reaction, the catalyst was treated in a H2atmosphere at a temperature of 600°C for 120 min to remove the surface Al2O3or carbon layer and expose the Pt-Cu active sites.

[0027] Example 2: (1) Support preparation: Zinc nitrate and aluminum nitrate were dissolved in deionized water at a Zn / Al molar ratio of 1:1.9, and citric acid (metal ion: citric acid = 1:1.4) was added as a complexing agent. The solution was stirred at 78°C for 4 h to form a sol, and the pH was adjusted to 3.5 with ammonia water, and then the solution was aged for 24 h. A gel precursor was obtained by vacuum gradient drying method: pre-drying at 49 Pa negative pressure and 42°C for 13 h, and then heating to 78°C to complete dehydration. The gel precursor was placed in a muffle furnace and heated to 1190°C at a rate of 5°C / min, and then calcined for 245 min to form a high crystallinity ZnAl2O4 spinel. A 1 wt% magnesium nitrate solution was coated on the surface of the support by an equal-volume impregnation method, and then dried at 60°C and calcined at 790°C for 125 min to embed Mg 2+ into the spinel lattice to form a ZnMgAlO4 solid solution. The particles were sieved by ball milling to obtain 40-60 mesh particles.

[0028] (2) Impregnation of Cu precursor: ZnMgAl04support was impregnated in copper nitrate ethanol solution with concentration of 0.09 mol / L; then rotary evaporation dried at 60 °C for 12 h, the dried sample was placed in a tube furnace, and reduced by programmed heating with 4.9 v / v% H2 / Ar mixed gas (flow rate 50 mL / min): first increased to 198 °C at 2 °C / min, maintained for 62 min to decompose the nitrate, then increased to 395 °C at 5 °C / min for reduction for 130 min to obtain Cu / ZnMgAl04. The reduced Cu / ZnMgAl04was transferred to a fixed bed reactor, and treated with CO gas (purity 99.99%, flow rate 100 mL / min) at 198 °C for 63 min to obtain a surface passivated Cu / ZnMgAl04support.

[0029] (3) Photodeposition of Pt: The surface passivated Cu / ZnMgAl04support was dispersed in chloroplatinic acid-ethanol solution with concentration of 0.05 mol / L; deoxidized by nitrogen for 30 min; transferred to a photochemical reactor for ultraviolet light irradiation to reduce Pt 4 ⁺ is Pt 0 , ultraviolet light intensity was 195 mW / cm2, and irradiation time was 63 min.

[0030] (4) Confinement annealing: After reaction, the solid was collected by centrifugation, washed with ethanol and deionized water for 3 times respectively, and vacuum dried at 60 °C for 6 h; then annealed at 490 °C for 58 min in 4.8 v / v% H2 / Ar atmosphere.

[0031] (5) ALD atomic layer deposition of Al203ultrathin layer: The Pt-Cu / ZnMgAl04sample was placed in an ALD reaction chamber, the substrate temperature was 148 °C, trimethylaluminum and deionized water were used as precursors, and one cycle was "TMA pulse (0.1 s)-N2purging (20 s)-H2O pulse (0.05 s)-N2purging (20 s)", a total of 2 cycles were performed. By self-limiting surface reaction, an Al203ultrathin layer with a thickness of 0.5 nm was obtained, and the sample was stored in a jar for 3 months.

[0032] (6) In-situ pre-activation: Before PDH reaction, the catalyst was treated in H2atmosphere, the treatment temperature was 590 °C, and the treatment time was 130 min, to remove the surface Al203or carbon layer and expose the Pt-Cu active sites.

[0033] Example 3: (1) Support preparation: Zn(NO3)2 and Al(NO3)3 were dissolved in deionized water with Zn / Al molar ratio of 1:2.1, and citric acid (metal ion: citric acid = 1:1.7) was added as a complexing agent. The solution was stirred at 82°C for 4h to form a sol, and then the pH was adjusted to 3.5 with ammonia water and aged for 24h. Subsequently, a vacuum gradient drying method was used: pre-drying at 51 Pa negative pressure and 39°C for 11h, and then dehydrating at 82°C to obtain a gel precursor. The gel precursor was calcined at 1210°C for 230min in a muffle furnace at a rate of 5°C / min to form a high crystallinity ZnAl2O4 spinel. A 1wt% concentration of magnesium nitrate solution was loaded onto the surface of the support by an equal volume impregnation method, and then dried at 60°C and calcined at 810°C for 115min to form a ZnMgAlO4 solid solution by embedding the spinel lattice. Ball milling and sieving were used to obtain 40-60 mesh particles. 2+ The ZnMgAlO4 support was immersed in a 0.12mol / L copper nitrate ethanol solution, and then rotary evaporated and dried at 55°C for 14h. The dried sample was placed in a tube furnace and reduced by a programmed temperature rise using a 5.1v / v% H2 / Ar mixed gas (flow rate 47 mL / min): first increased to 202°C at a rate of 2°C / min and maintained for 58min to decompose the nitrate salt, and then increased to 405°C at a rate of 5°C / min and reduced for 110min to obtain Cu / ZnMgAlO4. The reduced Cu / ZnMgAlO4 was transferred to a fixed bed reactor and treated with CO gas (purity 99.99%, flow rate 100 mL / min) at 202°C for 58min to obtain a surface passivated Cu / ZnMgAlO4 support.

[0034] (2) Cu precursor impregnation: the ZnMgAlO4 support was immersed in a 0.12mol / L copper nitrate ethanol solution; then rotary evaporated and dried at 55°C for 14h, and then the dried sample was placed in a tube furnace and reduced by a programmed temperature rise using a 5.1v / v% H2 / Ar mixed gas (flow rate 47 mL / min): first increased to 202°C at a rate of 2°C / min and maintained for 58min to decompose the nitrate salt, and then increased to 405°C at a rate of 5°C / min and reduced for 110min to obtain Cu / ZnMgAlO4. The reduced Cu / ZnMgAlO4 was transferred to a fixed bed reactor and treated with CO gas (purity 99.99%, flow rate 100 mL / min) at 202°C for 58min to obtain a surface passivated Cu / ZnMgAlO4 support.

[0035] (3) Photochemical deposition of Pt: the surface passivated Cu / ZnMgAlO4 support was dispersed in a chloroplatinic acid-ethanol solution with a concentration of 0.05mol / L, deoxygenated by nitrogen gas for 30min, and then transferred to a photochemical reactor for ultraviolet light irradiation to reduce Pt 4 ⁺ to Pt 0 , with an ultraviolet light intensity of 205mW / cm² and an irradiation time of 58min.

[0036] (4) Confined annealing: after the reaction, the solid was collected by centrifugation, washed with ethanol and deionized water three times in turn, and vacuum dried at 55°C for 8h; then annealed at 510°C for 62min in a 5.2v / v% H2 / Ar atmosphere.

[0037] (5) ALD atomic layer deposition of Al2O3 ultra-thin layer: Put the Pt-Cu / ZnMgAlO4 sample into the ALD reaction chamber, the substrate temperature is 152°C, trimethylaluminum and deionized water are used as precursors, and "TMA pulse (0.1 s)-N2purging (20 s)-H2O pulse (0.05 s)-N2purging (20 s)" is used as one cycle, and a total of 2 cycles are performed. Through self-limiting surface reaction layer-by-layer growth, an Al2O3 ultra-thin layer with a thickness of 0.5 nm is obtained, and the sample is stored in a wide-mouth bottle for 3 months.

[0038] (6) In-situ pre-activation: Before the PDH reaction, the catalyst is treated in a H2atmosphere, the treatment temperature is 610°C, and the treatment time is 110 min, the surface Al2O3 or carbon layer is removed, and the Pt-Cu active site is exposed.

[0039] Example 4: (1) Support preparation: Dissolve zinc nitrate and aluminum nitrate in deionized water according to a Zn / Al molar ratio of 1:1.8, add citric acid (metal ion: citric acid = 1:1.5) as a complexing agent, stir at 75°C for 5h to form a sol, adjust the pH to 3.5 with ammonia water, and then stand for aging for 24h; then use a vacuum gradient drying method: pre-dry at 47Pa negative pressure and 44°C for 10h, then heat to 75°C to complete dehydration, and obtain a gel precursor. Place the gel precursor in a muffle furnace and heat to 1180°C at a rate of 5°C / min for 250min to form a high-crystallinity ZnAl2O4 spinel. Load a 0.9wt% concentration of magnesium nitrate solution onto the surface of the support by the equal-volume impregnation method, dry at 55°C, and then secondarily calcine at 820°C for 110min to embed Mg2+into the spinel lattice to form a ZnMgAlO4 solid solution. Ball mill and sieve to obtain 40-60 mesh particles. 2+

[0040] (2) Impregnation of Cu precursor: immerse the ZnMgAlO4 support in a 0.08mol / L copper nitrate ethanol solution; then rotary evaporate and dry at 60°C for 12h, and then place the dried sample in a tube furnace and reduce it by programming the temperature: first increase the temperature to 195°C at a rate of 2°C / min and maintain it for 65min to decompose the nitrate salt, and then increase the temperature to 390°C at a rate of 5°C / min and maintain it for 150min to obtain Cu / ZnMgAlO4. Transfer the reduced Cu / ZnMgAlO4 to a fixed bed reactor and pass in CO gas (purity 99.99%, flow rate 100 mL / min) at 195°C for 65min to obtain a surface-passivated Cu / ZnMgAlO4 support.

[0041] ​(3) Photodeposition of Pt: The surface passivated Cu / ZnMgAlO4 support was dispersed in chloroplatinic acid-ethanol solution with a concentration of 0.04 mol / L. Nitrogen was bubbled through the solution for 30 min to remove oxygen. The solution was transferred to a photochemical reactor for UV irradiation to reduce Pt. 4 ⁺ is Pt 0 The UV light intensity was 190 mW / cm2, and the irradiation time was 65 min.

[0042] (4) Confinement annealing: The solid was collected by centrifugation after the reaction, washed with ethanol and deionized water for 3 times, and dried at 60°C under vacuum for 6 h. Then, the sample was annealed at 480°C for 65 min in a 4.5 v / v% H2 / Ar atmosphere.

[0043] (5) ALD atomic layer deposition of an Al2O3 ultra-thin layer: The Pt-Cu / ZnMgAlO4 sample was placed in an ALD reaction chamber, and the substrate temperature was 145°C. Trimethylaluminum and deionized water were used as precursors, and one cycle was "TMA pulse (0.1 s)-N2purging (20 s)-H2O pulse (0.05 s)-N2purging (20 s)". A total of 2 cycles were performed. The Al2O3 ultra-thin layer was obtained by layer-by-layer growth through self-limiting surface reaction, and the sample was stored in a jar for 3 months.

[0044] (6) In-situ pre-activation: Before the PDH reaction, the catalyst was treated in a H2atmosphere at a temperature of 580°C for 150 min to remove the surface Al2O3 or carbon layer and expose the Pt-Cu active sites.

[0045] Example 5: (1) Support preparation: Zinc nitrate and aluminum nitrate were dissolved in deionized water at a Zn / Al molar ratio of 1:2.2, and citric acid (metal ion: citric acid = 1:1.5) was added as a complexing agent. The solution was stirred at 85°C for 3.5 h to form a sol, and the pH was adjusted to 3.5 with ammonia water, and then the solution was aged for 24 h. Then, a vacuum gradient drying method was used: pre-drying at 53 Pa negative pressure and 38°C for 15 h, and then heating to 85°C to complete dehydration, obtaining a gel precursor. The gel precursor was placed in a muffle furnace and heated to 1220°C at a rate of 5°C / min and calcined for 220 min to form a high crystallinity ZnAl2O4 spinel. A 1.1 wt% magnesium nitrate solution was loaded onto the surface of the support by an equal-volume impregnation method, and then dried at 62°C and calcined at 780°C for 130 min to embed Mg 2+ into the spinel lattice to form a ZnMgAlO4 solid solution. The sample was ball-milled and sieved to obtain particles with a size of 40-60 mesh.

[0046] (2) Impregnation of Cu precursor: ZnMgAlO4 support was impregnated in 0.12 mol / L copper nitrate ethanol solution; then rotary evaporation dried at 60 °C for 12 h, the dried sample was placed in a tube furnace, and reduced by programmed heating with 5.2 v / v% H2 / Ar mixed gas (flow rate 50 mL / min): first increased to 205 °C at 2 °C / min, maintained for 55 min to decompose the nitrate, then increased to 410 °C at 5 °C / min for reduction for 100 min to obtain Cu / ZnMgAlO4. The reduced Cu / ZnMgAlO4 was transferred to a fixed bed reactor and treated with CO gas (purity 99.99%, flow rate 100 mL / min) at 205 °C for 55 min to obtain a surface passivated Cu / ZnMgAlO4 support.

[0047] (3) Photodeposition of Pt: The surface passivated Cu / ZnMgAlO4 support was dispersed in chloroplatinic acid-ethanol solution with a concentration of 0.06 mol / L; deoxygenated by nitrogen for 30 min; transferred to a photochemical reactor for UV irradiation to reduce Pt 4 ⁺ is Pt 0 with a UV light intensity of 210 mW / cm2and irradiation time of 55 min.

[0048] (4) Confinement annealing: After reaction, the solid was collected by centrifugation, washed with ethanol and deionized water for 3 times respectively, and vacuum dried at 60 °C for 6 h; then annealed at 520 °C for 55 min in a 5.5 v / v% H2 / Ar atmosphere.

[0049] (5) ALD atomic layer deposition of Al2O3 ultra-thin layer: The Pt-Cu / ZnMgAlO4 sample was placed in an ALD reaction chamber, with a substrate temperature of 155 °C, using trimethylaluminum and deionized water as precursors, and following a cycle of "TMA pulse (0.1 s)-N2purging (20 s)-H2O pulse (0.05 s)-N2purging (20 s)", a total of 2 cycles were performed. Through self-limiting surface reaction, an Al2O3 ultra-thin layer was obtained, and the sample was stored in a jar for 3 months.

[0050] (6) In-situ pre-activation: Before the PDH reaction, the catalyst was treated in a H2 atmosphere at a temperature of 620 °C for 100 min to remove the surface Al2O3 or carbon layer and expose the Pt-Cu active sites.

[0051] Example 6: Steps (5) and (6) of Example 1 were cancelled, and the catalyst was used directly after step (4) annealing.

[0052] The catalysts obtained in each of the examples were each applied in a PDH reaction for performance testing, the PDH reaction using a fixed bed reactor, T = 600°C, P = atmospheric pressure, WHSV (weight hourly space velocity) = 3.6 h-1, C3H8 / N2= 1:1 (volume ratio); the test results are shown in Table 1. Among them, the recovery of catalyst activity refers to every 24h operation, switching to H2 / N2= 1:1 mixed gas, operating at 600°C for 1h, using H2 to reduce copper oxide and gasify the accumulated carbon, so as to restore the activity of the catalyst. The "stability" of the test results refers to the percentage attenuation of the conversion rate of the catalyst after continuous operation for 120h in the PDH reaction, during which the above-mentioned operation for recovering the activity of the catalyst is performed every 24h.

[0053] Table 1 Test results .

[0054] Comparative Example 1: The basic process is the same as that of Example 1, except that the vacuum gradient drying in step (1) is cancelled and replaced by drying in an 80°C atmospheric oven for 24h.

[0055] Test results: Propane conversion rate 38.2%, propylene selectivity 89.1%, stability (120h) 22.5% attenuation.

[0056] Comparative Example 2: The basic process is the same as that of Example 1, except that the magnesium nitrate impregnation and secondary calcination in step (1) are skipped, and the ZnAl2O4 carrier is directly used Test results: Propane conversion rate 41.3%, propylene selectivity 90.5%, stability (120h) 18.7% attenuation.

[0057] Comparative Example 3: The basic process is the same as that of Example 1, except that the CO passivation treatment in step (2) is omitted, and the Cu / ZnMgAlO4 is directly used for Pt deposition.

[0058] Test results: Propane conversion rate 36.8%, propylene selectivity 88.3%, XPS analysis of Cu+ / Cu in the catalyst 0 The ratio reaches 0.82 (Example 1 is 0.11).

[0059] Comparative Example 4: The basic process is the same as that of Example 1, except that the ultraviolet light deposition in step (3) is replaced by equal volume impregnation of chloroplatinic acid solution, and 500°C H2 reduction for 2h.

[0060] Test results: Propane conversion rate 39.5%, propylene selectivity 86.7%, Pt dispersion (CO chemisorption method) 18.3% (41.6% for Example 1), because the traditional impregnation method of Comparative Example 4 causes Pt precursors to migrate and aggregate during drying, making the catalyst more prone to carbon deposition and unable to form an effective Pt-Cu interface synergistic effect.

[0061] The above descriptions are only preferred embodiments of the present application, and are not intended to limit the present application in other forms. Any person skilled in the art can modify or change the above disclosed technical content into equivalent embodiments with equivalent changes. However, any simple modification, equivalent change and modification of the above embodiments made according to the technical essence of the present application without departing from the technical solution content of the present application still belongs to the protection scope of the present application technical solution.

Claims

1. A platinum-based catalyst supporting method for dehydrogenation of propane, characterized by, The method comprises the following steps: (1) carrier preparation: zinc nitrate and aluminum nitrate are dissolved in deionized water according to a Zn / Al molar ratio of 1:1.8-2.2, a citric acid complexing agent is added, and a sol is formed by stirring at 75-85 DEG C, and the pH is adjusted to 3.5 and then aged; a gel precursor is prepared by vacuum gradient drying, and a ZnAl2O4 spinel is obtained by calcining at 1180-1220 DEG C for 220-250 min, then a magnesium nitrate solution is impregnated and a second calcination is performed to form a ZnMgAlO4 solid solution carrier; (2) Cu precursor impregnation: the obtained ZnMgAlO4 solid solution carrier is impregnated in a copper nitrate ethanol solution, ultrasonic dispersion is performed, and then drying is performed, and Cu / ZnMgAlO4 is obtained by temperature reduction; the Cu / ZnMgAlO4 is subjected to CO passivation treatment to form a passivated carrier with surface complex Cu-CO; (3) Photochemical deposition of Pt: Disperse the passivated support in a chloroplatinic acid-ethanol solution and irradiate with UV light to reduce Pt and form a Pt-Cu core-shell structure 4 ⁺, forming a Pt-Cu core-shell structure; (4) confined annealing: after washing and drying, annealing is performed in a H2 / Ar atmosphere to obtain a platinum-based catalyst.

2. The method for supporting a platinum-based catalyst for dehydrogenation of propane according to claim 1, characterized by: In step (1), the vacuum gradient drying conditions are: pre-drying at 47-53 Pa negative pressure and 38-44 DEG C for 10-15 h, and then dehydrating at 75-85 DEG C.

3. The platinum-based catalyst loading method for propane dehydrogenation according to claim 1, characterized in that: In step (1), the impregnation of the magnesium nitrate solution is specifically impregnating the ZnAl2O4 spinel in an equal volume of 0.9-1.1 wt% concentration magnesium nitrate solution; the second calcination is calcining the obtained solid at 780-820 DEG C for 110-130 min after impregnation.

4. The method for supporting a platinum-based catalyst for propane dehydrogenation according to claim 1, characterized in that: In step (2), the concentration of the copper nitrate ethanol solution is 0.08-0.12 mol / L.

5. The method of claim 1, wherein the platinum-based catalyst is supported on the porous inorganic oxide carrier by impregnation. In step (2), the temperature reduction is specifically: introducing 4.8-5.2 v / v% H2 / Ar mixed gas, pre-treating at 195-205 DEG C for 55-65 min, and then reducing at 390-410 DEG C for 100-150 min.

6. The method of claim 1, wherein the platinum-based catalyst is supported on the porous inorganic oxide carrier by impregnation. In step (2), the CO passivation treatment is specifically: treating the obtained Cu / ZnMgAlO4 in a CO atmosphere with a purity of ≥99.99% at 195-205 DEG C for 55-65 min.

7. The method according to claim 1, wherein the platinum-based catalyst is supported on the carrier by the following steps: (1) mixing the carrier and the platinum-based catalyst in a solvent to form a mixture; (2) drying the mixture; and (3) calcining the dried mixture. In step (3), the concentration of the chloroplatinic acid-ethanol solution is 0.04-0.06 mol / L; the ultraviolet light intensity of the ultraviolet light irradiation is 190-210 mW / cm², and the irradiation time is 55-65 min.

8. The method according to claim 1, wherein the platinum-based catalyst is supported on the carrier by the following steps: (1) mixing the carrier and the platinum-based catalyst in a solvent to form a mixture; (2) drying the mixture; and (3) calcining the dried mixture. In step (4), the confined annealing conditions are: annealing in a H2 / Ar atmosphere with a H2 / Ar ratio of 4.5-5.5 v / v% at 480-520 DEG C for 55-65 min.

9. The method of claim 1, wherein the platinum-based catalyst is supported on the porous inorganic oxide carrier by impregnation. The method further comprises a step of depositing an Al2O3 layer: an Al2O3 layer is deposited on the surface of the obtained catalyst by an ALD process, the ALD process uses trimethylaluminum and H2O as precursors, the substrate temperature is 145-155 DEG C, a single cycle includes a trimethylaluminum pulse of 0.1 s, N2 purging for 20 s, an H2O pulse of 0.05 s, and N2 purging for 20 s, and a total of 2 cycles are performed.

10. The method of claim 9, wherein the platinum-based catalyst is supported on the porous inorganic oxide carrier by impregnation. Also included is an in-situ pre-activation step: the resulting catalyst is first treated at high temperature in a H2atmosphere, said high temperature treatment having a temperature of 620°C and a treatment time of 100 min to 150 min, before use.