Catalyst for dehydrogenation of liquid organic hydrogen energy carrier as well as preparation method and dehydrogenation method of catalyst

Abstract

The invention discloses a catalyst for dehydrogenation of a liquid organic hydrogen energy carrier as well as a preparation method and a dehydrogenation method of the catalyst. The catalyst for dehydrogenation of the liquid organic hydrogen energy carrier comprises an active component, an auxiliary agent and a carrier, the active component is Pt, the auxiliary agent is CeO2, and the carrier is MgO-Al2O3 composite oxide; the CeO2 is dispersed on the surface of the MgO-Al2O3 composite oxide in an island form; pt is selectively dispersed on the CeO2 islands. The catalyst can inhibit agglomeration and growth of Pt particles and deposition of organic carbides on the surface of the catalyst in the dehydrogenation reaction process, and shows excellent activity and stability.

Description

Technical Field

[0001] The present invention belongs to the field of chemical hydrogen storage, and in particular relates to a catalyst for dehydrogenation of a liquid organic hydrogen energy carrier, a preparation method thereof, and a dehydrogenation method. Background Art

[0002] With the development of social economy and the growth of population, the global demand for energy is gradually increasing. Fossil fuels include coal, oil and natural gas, which have low calorific value and release a large amount of harmful and greenhouse gases during combustion, causing extremely serious environmental pollution. Hydrogen energy, as an emerging energy source that is green, environmentally friendly, abundant in source and widely used, has become a powerful means for energy users to achieve green and low-carbon transformation. However, the storage and transportation of hydrogen in the hydrogen storage process remains a key problem that restricts the large-scale application of hydrogen energy. There is an urgent need to find a large-scale hydrogen storage technology with low energy consumption, high hydrogen storage density, and safe operation and transportation at normal temperature and pressure.

[0003] At present, hydrogen storage methods are mainly divided into four categories, namely high-pressure gaseous hydrogen storage, low-temperature liquid hydrogen storage, organic liquid hydrogen storage, and solid material hydrogen storage. Traditional gaseous and liquid hydrogen storage methods have limitations in practical applications. In contrast, liquid organic hydride hydrogen storage technology has excellent hydrogenation-dehydrogenation reversible cycle characteristics. Its principle is to use unsaturated liquid organic hydrogen storage agents and hydrogen to undergo catalytic hydrogenation reactions under the action of catalysts to generate liquid organic hydrogen carriers to achieve the purpose of hydrogen storage, and then use the catalyst to undergo dehydrogenation reactions at a certain temperature to release and use the stored hydrogen. The International Energy Agency stipulates that the mass hydrogen storage density of practical hydrogen storage systems must reach 5wt%, and the volume hydrogen storage density is also required to be greater than 40kg / m 3 , and when hydrogen is released, other gas components in the hydrogen, such as H2S, CO, and NH3, must be strictly controlled. Therefore, cycloalkanes such as cyclohexane, methylcyclohexane, and decalin are considered to be the most suitable organic hydrogen energy carriers. However, the dehydrogenation reaction is a highly endothermic heterogeneous reaction that needs to be carried out under low-pressure and high-temperature heterogeneous conditions. However, it is plagued by heat and mass transfer and reaction equilibrium limits. The key to achieving reversible recycling of cycloalkanes for hydrogen storage is the development of efficient dehydrogenation catalysts.

[0004] In recent years, a variety of catalysts for the dehydrogenation of organic hydrides have been reported, often with the addition of additional components to further enhance their activity and stability. For example, [International Journal of Hydrogen Energy, 2018, 43: 9343] reported that the introduction of alkaline MgO into Al2O3 inhibited catalyst deactivation due to carbon deposition and improved catalyst stability. [Chin J Chem Eng 2020, 28, 2337] reported that the decrease in catalyst dehydrogenation activity was primarily due to agglomeration of the active components during the reaction, resulting in an increase in particle size and a decrease in the number of active sites. Although current catalysts exhibit good dehydrogenation activity and stability, the active components are primarily directly loaded onto the support via impregnation, making their dispersion difficult to effectively control. Therefore, the industrial preparation of catalysts, the dispersion of the active components, and the sufficient exposure of active sites remain challenges. Summary of the Invention

[0005] The purpose of the present invention is to provide a catalyst for the dehydrogenation of a liquid organic hydrogen energy carrier, a preparation method thereof, and a dehydrogenation method. The catalyst for the dehydrogenation of the liquid organic hydrogen energy carrier is Pt / CeO2 / MgO-Al2O3, wherein CeO2 is dispersed in the form of isolated islands on the surface of the MgO-Al2O3 composite oxide carrier, and Pt is selectively dispersed on the CeO2 isolated islands, which can effectively promote the dispersion of the active component Pt, and inhibit the agglomeration and growth of Pt particles and the deposition of organic carbides on the catalyst surface during the dehydrogenation reaction, thereby exhibiting excellent activity and stability.

[0006] To achieve the above object, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a catalyst for dehydrogenation of a liquid organic hydrogen energy carrier, comprising an active component, a promoter, and a carrier, wherein the active component is Pt, the promoter is CeO2, and the carrier is a MgO-Al2O3 composite oxide; The CeO2 is dispersed on the surface of the MgO-Al2O3 composite oxide in the form of isolated islands; The Pt is selectively dispersed on the CeO2 islands.

[0007] Based on the above technical solution, unlike the prior art in which the active component Pt is directly dispersed on the carrier surface, the CeO2 in the catalyst of the present invention is dispersed in the form of islands on the surface of the MgO-Al2O3 composite oxide carrier, and Pt is selectively dispersed on the CeO2 islands, which can effectively promote the dispersion of the active component Pt, and inhibit the migration and agglomeration of Pt particles and the deposition of organic carbides on the catalyst surface during the dehydrogenation reaction of the organic hydrogen energy carrier, and exhibit excellent activity and stability in the dehydrogenation reaction of the liquid organic hydrogen energy carrier.

[0008] In the above catalyst, further, the diameter of the CeO2 islands is 5 to 10 nm. In the present invention, the term "islands" refers to nanoparticles dispersed on a carrier.

[0009] In the above catalyst, further, based on the total weight of the catalyst, the percentage of CeO2 is 2% to 30%, preferably 2.5 to 28wt%, 3.0 to 25wt%, 4.0 to 22wt%, 5.0 to 20wt%, for example, 6.0wt%, 7.0wt%, 8.0wt%, 9.0wt%, 10.0wt%, 11.0wt%, 12.0wt%, 13.0wt%, 14.0wt%, 15.0wt%, 16.0wt%, 17.0wt%, 18.0wt%, and 19.0wt%; the percentage of Pt is 0.1% to 2%, preferably 0.2 to 1.8wt%, 0.3 to 1.5wt%, 0.4 to 1.2wt%, and 0.5 to 1.0wt%, for example, 0.6wt%, 0.7wt%, 0.8wt%, and 0.9wt%; And / or, in the catalyst, Mg 2+ With Al 3+ The molar ratio is (2-8):1, preferably (3-6):1, more preferably (4-5):1, for example 6:1, 2:1, 4:1, 8:1.

[0010] In a second aspect, the present invention provides a method for preparing a catalyst for dehydrogenation of a liquid organic hydrogen energy carrier as described in any one of the above, comprising the following steps: S1, adding a CeO2 solution to Mg-Al hydrotalcite for impregnation treatment, then removing the solvent and calcining to obtain a CeO2 / MgO-Al2O3 carrier; S2, adding the CeO2 / MgO-Al2O3 support to a Pt salt solution for impregnation treatment, and then drying and calcining in sequence to obtain a catalyst precursor; S3. Reducing the catalyst precursor under a hydrogen atmosphere to obtain the catalyst for dehydrogenation of the liquid organic hydrogen energy carrier.

[0011] Based on the above technical scheme, the present invention first adopts the impregnation method to load pseudo-homogeneous CeO2 on the surface of Mg-Al hydrotalcite, and then obtains a CeO2 / MgO-Al2O3 carrier after calcination, wherein CeO2 is dispersed in the form of isolated islands on the surface of the MgO-Al2O3 composite oxide, and then utilizes the strong metal-support interaction between Pt and CeO2 to prepare a Pt / CeO2 / MgO-Al2O3 catalyst by impregnation and loading Pt salt, calcination and hydrogen reduction. Due to the strong metal-support interaction, Pt is mainly adsorbed on the CeO2 isolated islands. The operation method is simple and easy.

[0012] In the above preparation method, further, the concentration of the CeO2 solution is 0.001 to 0.2 g / mL, for example, 16 mg / mL, 32 mg / mL, 21 mg / mL, 2.1 mg / mL, and can be adjusted within a reasonable range according to the loading amount of CeO2; as an example, 2 g of the Mg-Al hydrotalcite is added to every 20 mL of the CeO2 solution; The CeO2 solution solvent is one or more of cyclohexane, n-heptane, and methylcyclohexane; The CeO2 solution is a clear and transparent solution; the CeO2 is monodisperse CeO2 nanoparticles, which can be obtained by referring to the preparation method disclosed in US 9,090,468 B2 "Method for preparing metal sulfide compound particles". The average particle size can be about 2 nm to about 100 nm, about 2 nm to about 20 nm, about 2 nm to about 50 nm, about 5 nm to about 50 nm, about 10 nm to about 100 nm or about 50 nm to about 100 nm, and the particle size distribution is narrow. The steepness ratio of the final particles in the dispersed system is less than about 3, less than about 2, less than about 1.8, less than about 1.5 or less than about 1.3.

[0013] In step S1, the immersion treatment temperature is 5 to 60°C, such as 30°C, 5°C, 60°C, 40°C, and 20°C, and the time is 1 to 12 hours, preferably 2 to 10 hours, and more preferably 4 to 8 hours, such as 6 hours, 12 hours, 1 hour, 10 hours, and 8 hours; As an example, the Mg-Al hydrotalcite is prepared according to a method comprising the following steps: 1) preparing a metal salt mixed solution of an aluminum salt and a magnesium salt; 2) preparing an alkaline mixed solution comprising sodium hydroxide and ammonium carbonate; 3) simultaneously dripping the metal salt mixed solution and the alkaline mixed solution into a reaction flask, controlling the pH value of the suspension within the range of 9.5 to 10.5, stopping the dripping of the alkaline mixed solution B, continuing the reaction for 30 minutes, transferring the suspension into a hydrothermal reactor, and crystallizing at 95° C. for 10 hours to obtain the Mg-Al hydrotalcite; As an example, the solvent is removed by rotary evaporation, such as rotary evaporation of n-heptane at 105°C.

[0014] In the above preparation method, further, in step S1, the calcination temperature is 400-600°C, preferably 450-550°C, for example, 500°C, 600°C, or 400°C, and the time is 2-8 hours, for example, 4 hours, 2 hours, or 8 hours. In step S1, the calcination is performed in an air atmosphere. In the resulting support, CeO2 is dispersed in the form of isolated islands on the surface of the MgO-Al2O3 composite oxide.

[0015] In the above preparation method, further, the concentration of the Pt salt solution is 1 to 100 mg / mL, preferably 1 to 4 mg / mL, for example 1 mg / mL, 4 mg / mL, 0.2 mg / mL, 2 mg / mL; the Pt loading amount is regulated by adjusting the amount of the Pt salt solution added and / or the concentration of the Pt salt; as an example, 16 mL or 20 mL of the Pt salt solution is added to every 2 g of the CeO2 / MgO-Al2O3 carrier; The solvent of the Pt salt solution is acetone, methanol, ethanol or water; The Pt salt is one or more of tetraammineplatinum sulfate, tetraammineplatinum nitrate, tetraammineplatinum hydrogenphosphate, tetraammineplatinum chloride, platinum nitrate, and chloroplatinic acid; Taking advantage of the strong metal-support interaction between Pt and CeO2, when the support is impregnated with Pt salt, Pt ions are selectively adsorbed on CeO2 islands, which is beneficial to promote the dispersion of Pt and inhibit the formation of large Pt particles.

[0016] In step S2, the immersion treatment is ultrasonic immersion, the temperature is 15-30°C, such as room temperature 25°C, and the time is 5-60 min, such as 60 min.

[0017] In the above preparation method, further, in step S2, the calcination temperature is 300-360°C, for example, 350°C, 360°C, 300°C, 330°C, and the calcination time is 2-8 h, for example, 4 h, 2 h, 8 h, 5 h; In step S2, the calcination is carried out in an air atmosphere; As an example, the drying is performed at 105° C. for 12 h; And / or, the reduction temperature is 360-450° C., such as 375° C., 400° C., 360° C., 380° C., and the reduction time is 2-12 h, such as 4 h, 8 h.

[0018] In a third aspect, the present invention provides a method for dehydrogenating a liquid organic hydrogen energy carrier, comprising the following steps: The liquid organic hydrogen energy carrier is subjected to a dehydrogenation reaction under the catalytic action of the catalyst described in any one of the above items or the catalyst obtained by the preparation method described in any one of the above items.

[0019] In the above dehydrogenation method, the liquid organic hydrogen energy carrier is cyclohexane, methylcyclohexane, ethylcyclohexane or decahydronaphthalene; The temperature of the dehydrogenation reaction is 280-450°C, for example 350°C; As an example, the temperature of the dehydrogenation reaction of methylcyclohexane is 350° C., and the feeding rate of methylcyclohexane corresponding to each 0.5 g of the catalyst precursor after reduction is 0.1 mL / min; The temperature of the cyclohexane dehydrogenation reaction is 350° C., and the feed rate of cyclohexane corresponding to each 0.5 g of the catalyst precursor after reduction is 0.1 mL / min; The temperature of the dehydrogenation reaction of ethylcyclohexane is 350° C., and the feeding rate of ethylcyclohexane corresponding to each 1.0 g of the catalyst precursor after reduction is 0.1 mL / min; The temperature of the decalin dehydrogenation reaction was 350° C., and the feeding rate of decalin after reduction per 0.5 g of the catalyst precursor was 0.1 mL / min.

[0020] The present invention has the following beneficial effects: The catalyst preparation method of the present invention utilizes the high dispersibility of a pseudo-homogeneous dispersion to load CeO2 onto the surface of Mg-Al hydrotalcite. After calcination, CeO2 is dispersed in the form of islands on the surface of the MgO-Al2O3 composite oxide. During the loading process, the CeO2 can fully exert its effect. The strong metal-support interaction between Pt and CeO2 is then utilized to selectively disperse Pt ions on the CeO2 islands, promoting Pt dispersion. In particular, during the dehydrogenation reaction of an organic hydrogen energy carrier, due to the island effect, Pt in the catalyst migrates only on the CeO2 islands at high temperatures. Pt particles on different islands are difficult to agglomerate, effectively suppressing Pt particle growth. In addition, the area outside the islands is composed of the MgO-Al2O3 composite oxide. The presence of alkaline MgO significantly suppresses the deposition of organic carbides. Therefore, the catalyst exhibits excellent activity and stability in the dehydrogenation reaction of liquid organic hydrogen energy carriers. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the XRD pattern of the Pt / CeO2 / MgO-Al2O3 catalyst of Example 1.

[0022] Figure 2 TEM and STEM-HAADF images of the Pt / CeO2 / MgO-Al2O3 catalyst of Example 1, where the white bright spots are Pt nanoparticles. It can be clearly seen that Pt is mainly attached to CeO2. DETAILED DESCRIPTION

[0023] The present invention will be further described in detail below in conjunction with specific embodiments. The examples provided are only for illustrating the present invention and are not intended to limit the scope of the present invention. The examples provided below can serve as a guide for further improvements by those skilled in the art and are not intended to limit the present invention in any way.

[0024] Unless otherwise specified, the methods used in the following examples are all conventional methods and are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. The materials, reagents, etc. used in the following examples are all commercially available unless otherwise specified.

[0025] The CeO2 used in the following examples was prepared according to the method disclosed in Example 2.1 of US009090468B2. The specific steps are as follows: 4.27 g of Ce(NO3)3·6H2O was dissolved in 50 ml of water in a three-necked round-bottom flask (RBF). 25% aqueous ammonia was diluted with 47.5 ml of water and mixed with a cerium nitrate solution under vigorous stirring. The reaction system temperature was maintained at 80°C. After the aqueous ammonia and cerium nitrate solution were mixed for 4 to 7 minutes, 20 ml of a 0.04 mol / L sodium oleate solution was added to the reaction solution. The reaction solution was vigorously stirred for 1 hour to obtain a yellow powder in a clear aqueous solution. The yellow powder dissolved almost immediately upon addition of n-hexane, and the aqueous phase was removed using a separatory funnel. Approximately 30 ml of isopropanol was added to the n-hexane solution, forming a flocculent precipitate. The precipitate was centrifuged and washed with methanol and isopropanol.

[0026] The reagents used in the examples were all analytically pure, and the water was ultrapure water.

[0027] Preparation Example 1 Weigh 9.4g of aluminum nitrate and press Mg 2+ / Al 3+ Magnesium nitrate was weighed and dissolved in 200 mL of deionized water at a molar ratio of 6 to prepare metal salt mixed solution A. 12.0 g of NaOH and 2.0 g of anhydrous Na2CO3 were weighed and dissolved in 250 mL of deionized water to prepare alkaline mixed solution B. Under room temperature and vigorous stirring, metal salt mixed solution A and alkaline mixed solution B were simultaneously added dropwise to a three-necked flask at a rate of 4 mL / min using a peristaltic pump. The pH of the suspension in the three-necked flask was controlled within the range of 9.5 to 10.5. After stopping the addition of alkaline mixed solution B and continuing the reaction for 30 minutes, the suspension was transferred to a hydrothermal reactor and crystallized at 95°C for 10 hours. The suspension was then filtered, and the filtered solid was washed and dried to obtain Mg-Al hydrotalcite.

[0028] Preparation Example 2 According to the preparation process of hydrotalcite-like in Preparation Example 1, only Mg 2+ / Al 3+ The molar ratio was adjusted to 2.

[0029] Preparation Example 3 According to the preparation process of hydrotalcite-like in Preparation Example 1, only Mg 2+ / Al 3+ The molar ratio was adjusted to 4.

[0030] Preparation Example 4 According to the preparation process of hydrotalcite-like in Preparation Example 1, only Mg 2+ / Al 3+ The molar ratio was adjusted to 8.

[0031] Example 1, Preparation of 0.4wt%Pt / 15wt%CeO2 / MgO-Al2O3 Catalyst (Mg 2+ / Al 3+ The molar ratio is 6) CeO2 was weighed and dispersed in an n-heptane solution at a CeO2 loading of 15 wt% to form a transparent solution (16 mg / mL). 2 g of the Mg-Al hydrotalcite obtained in Preparation Example 1 was then added to 20 mL of the solution and impregnated at 30 °C for 6 h. The n-heptane was then rotary evaporated to dryness at 105 °C. The solid was removed and calcined at 500 °C in air for 4 h to obtain a CeO2 / MgO-Al2O3 composite oxide support. Then, 2 g of the above CeO2 / MgO-Al2O3 support was added to 16 mL of a 1 mg / mL chloroplatinic acid acetone solution at a Pt loading of 0.4 wt%. After ultrasonic impregnation at room temperature for 1 h, the solution was transferred to a 105 °C drying oven and dried for 12 h. The solution was then calcined at 350 °C in air for 4 h to obtain a catalyst precursor.

[0032] 0.5 g of the above-mentioned catalyst precursor was weighed and filled into a fixed-bed reaction tube. After reduction under a hydrogen atmosphere at 375°C for 4 hours (to prepare the catalyst), the reaction temperature was adjusted to 350°C, and methylcyclohexane was introduced for dehydrogenation reaction at a feed rate of 0.1 mL / min. Surprisingly, the methylcyclohexane conversion rate was 99.3%, the toluene selectivity was 99.9%, and after 50 hours of continuous reaction, the dehydrogenation activity did not change.

[0033] Figure 1 This is the XRD spectrum of the Pt / CeO2 / MgO-Al2O3 catalyst in Example 1. Figure 2 These are the TEM and STEM-HAADF images of the Pt / CeO2 / MgO-Al2O3 catalyst of Example 1, where the white bright spots are Pt nanoparticles. It can be clearly seen that CeO2 is dispersed in the form of islands on the surface of the MgO-Al2O3 composite oxide, and Pt is mainly attached to the CeO2 islands, with a diameter of about 5 to 10 nm.

[0034] Example 2, Preparation of 0.4wt%Pt / 15wt%CeO2 / MgO-Al2O3 Catalyst (Mg 2+ / Al 3+ The molar ratio is 2) CeO2 was weighed and dispersed in an n-heptane solution to form a transparent solution (16 mg / mL) at a CeO2 loading of 15 wt%. 2 g of the Mg-Al hydrotalcite obtained in Preparation Example 2 was then added to 20 mL of the solution. The mixture was impregnated at 5 °C for 12 h. The n-heptane was then rotary evaporated to dryness at 105 °C. The solid was removed and calcined at 600 °C in air for 2 h to obtain a CeO2 / MgO-Al2O3 composite oxide support. Subsequently, 2 g of the CeO2 / MgO-Al2O3 support was added to 16 mL of a 1 mg / mL tetraammine platinum sulfate acetone solution to obtain a Pt loading of 0.4 wt%. After ultrasonic impregnation at room temperature for 1 h, the mixture was transferred to a 105 °C drying oven and dried for 12 h. The mixture was then calcined at 360 °C in air for 2 h to obtain a catalyst precursor.

[0035] 0.5 g of the catalyst precursor was weighed and filled into a fixed-bed reaction tube. After reduction under a hydrogen atmosphere at 400°C for 4 h, the reaction temperature was adjusted to 350°C, and cyclohexane was introduced for dehydrogenation at a cyclohexane feed rate of 0.1 mL / min. Chromatographic analysis of the sample showed a conversion of 96.4% and a benzene selectivity of 99.9%. After 50 h of reaction, the dehydrogenation activity remained unchanged.

[0036] Example 3, Preparation of 2wt%Pt / 30wt%CeO2 / MgO-Al2O3 Catalyst (Mg 2+ / Al 3+ The molar ratio is 4) CeO2 was weighed and dispersed in an n-heptane solution to form a transparent solution (32 mg / mL) at a CeO2 loading of 30 wt%. Then, 2 g of the Mg-Al hydrotalcite obtained in Preparation Example 3 was added to 20 mL of the solution. The mixture was impregnated at 60 °C for 1 h. The n-heptane was then rotary evaporated to dryness at 105 °C. The solid was removed and calcined at 400 °C in air for 8 h to obtain a CeO2 / MgO-Al2O3 composite oxide support. Then, 2 g of the above CeO2 / MgO-Al2O3 support was added to 20 mL of a 4 mg / mL tetraammineplatinum nitrate acetone solution to obtain a Pt loading of 2 wt%. After ultrasonic impregnation at room temperature for 1 h, the mixture was transferred to a 105 °C drying oven and dried for 12 h. The mixture was then calcined at 300 °C in air for 8 h to obtain a catalyst precursor.

[0037] 0.5 g of the above catalyst precursor was weighed and filled into a fixed-bed reaction tube. After reduction under a hydrogen atmosphere at 360°C for 8 h, the reaction temperature was adjusted to 350°C, and methylcyclohexane was introduced for dehydrogenation reaction at a feed rate of 0.1 mL / min. Chromatographic analysis of the sample showed a conversion rate of 99.6% and a toluene selectivity of 99.9%. After continuing the reaction for 50 h, the dehydrogenation activity did not change.

[0038] Example 4, Preparation of 0.1wt%Pt / 20wt%CeO2 / MgO-Al2O3 Catalyst (Mg 2+ / Al 3+ The molar ratio is 8) CeO2 was weighed and dispersed in an n-heptane solution to form a transparent solution (21 mg / mL) at a CeO2 loading of 20 wt%. Then, 2 g of the Mg-Al hydrotalcite obtained in Preparation Example 4 was added to 20 mL of the solution and impregnated at 30 °C for 10 h. The n-heptane was then rotary evaporated to dryness at 105 °C. The solid was removed and calcined at 500 °C in air for 4 h to obtain a CeO2 / MgO-Al2O3 composite oxide support. Then, 2 g of the above CeO2 / MgO-Al2O3 support was added to 20 mL of a 0.2 mg / mL tetraammine platinum hydrogen phosphate acetone solution at a Pt loading of 0.1 wt%. After ultrasonic impregnation at room temperature for 1 h, the solution was transferred to a 105 °C drying oven and dried for 12 h. It was then calcined at 330 °C in air for 5 h to obtain a catalyst precursor.

[0039] 1.0 g of the catalyst precursor was weighed and placed in a fixed-bed reaction tube. After reduction under a hydrogen atmosphere at 380°C for 4 h, the reaction temperature was adjusted to 350°C, and ethylcyclohexane was introduced for dehydrogenation at a feed rate of 0.1 mL / min. Chromatographic analysis of the sample showed a conversion of 95.1% and a selectivity for ethylbenzene of 99.9%. After 50 h of reaction, the dehydrogenation activity remained unchanged.

[0040] Example 5, Preparation of 1wt%Pt / 2wt%CeO2 / MgO-Al2O3 Catalyst (Mg 2+ / Al 3+ The molar ratio is 6) CeO2 was weighed and dispersed in an n-heptane solution to form a transparent solution (2.1 mg / mL) at a CeO2 loading of 2 wt%. Then, 2 g of the Mg-Al hydrotalcite obtained in Preparation Example 1 was added to 20 mL of the solution and impregnated at 40 °C for 8 h. The n-heptane was then rotary evaporated to dryness at 105 °C. The solid was removed and calcined at 500 °C in air for 4 h to obtain a CeO2 / MgO-Al2O3 composite oxide support. Then, 2 g of the above CeO2 / MgO-Al2O3 support was added to 20 mL of a 2 mg / mL tetraammineplatinum chloride acetone solution at a Pt loading of 1 wt%. After ultrasonic impregnation at room temperature for 1 h, the solution was transferred to a 105 °C drying oven and dried for 12 h. The solution was then calcined at 350 °C in air for 4 h to obtain a catalyst precursor.

[0041] 0.5 g of the above catalyst precursor was weighed and filled into a fixed-bed reaction tube. After reduction under a hydrogen atmosphere at 400°C for 4 h, the reaction temperature was adjusted to 350°C, and decalin was introduced for dehydrogenation. The feed rate of decalin was 0.1 mL / min. Chromatographic analysis of the sample showed a conversion rate of 99.2% and a naphthalene selectivity of 99.9%. After continuing the reaction for 50 h, the dehydrogenation activity did not change.

[0042] Example 6, Preparation of 1.5wt%Pt / 15wt%CeO2 / MgO-Al2O3 Catalyst (Mg 2+ / Al 3+ The molar ratio is 6) CeO2 was weighed and dispersed in an n-heptane solution at a CeO2 loading of 15 wt% to form a transparent solution (16 mg / mL). 2 g of the Mg-Al hydrotalcite obtained in Preparation Example 1 was then added to 20 mL of the solution. The mixture was impregnated at 20 °C for 8 h. The n-heptane was then rotary evaporated to dryness at 105 °C. The solid was removed and calcined at 500 °C for 4 h to obtain a CeO2 / MgO-Al2O3 composite oxide support. Then, 2 g of the above CeO2 / MgO-Al2O3 support was added to 20 mL of a 2 mg / mL platinum nitrate acetone solution at a Pt loading of 1.5 wt%. After ultrasonic impregnation at room temperature for 1 h, the mixture was transferred to a 105 °C drying oven and dried for 12 h. The mixture was then calcined at 350 °C in air for 4 h to obtain a catalyst precursor.

[0043] 0.5 g of the above catalyst precursor was weighed and filled into a fixed-bed reaction tube. After reduction under a hydrogen atmosphere at 400°C for 4 h, the reaction temperature was adjusted to 350°C, and methylcyclohexane was introduced for dehydrogenation reaction. The feed rate of methylcyclohexane was 0.1 mL / min. Chromatographic analysis of the sample showed a conversion rate of 99.2% and a toluene selectivity of 99.9%. After continuing the reaction for 50 h, the dehydrogenation activity did not change.

[0044] Comparative Example 1 The same as Example 1, except that Mg-Al hydrotalcite is directly used as the carrier and the CeO2 loading amount is 0. The specific steps are as follows: 2 g of the Mg-Al hydrotalcite obtained in Preparation Example 1 was calcined at 500°C for 4 h to obtain a MgO-Al2O3 composite oxide support. Then, 2 g of the MgO-Al2O3 support was added to 16 mL of a 1 mg / mL chloroplatinic acid acetone solution, achieving a Pt loading of 0.4 wt%. After ultrasonic impregnation at room temperature for 1 h, the support was dried in a 105°C drying oven for 12 h, and then calcined at 350°C in air for 4 h to obtain a catalyst precursor.

[0045] 0.5 g of the catalyst precursor was weighed and placed in a fixed-bed reaction tube. After reduction under a hydrogen atmosphere at 375°C for 4 h, the reaction temperature was adjusted to 350°C, and methylcyclohexane was introduced for dehydrogenation at a feed rate of 0.1 mL / min. Under the same reaction conditions as in Example 1, the conversion of methylcyclohexane was reduced to 66.7%.

[0046] From the comparison results of Example 1 and Comparative Example 1, it can be seen that when Pt is directly loaded on the MgO-Al2O3 carrier, the conversion rate of methylcyclohexane is greatly reduced. This is because the addition of CeO2 additive improves the dehydrogenation activity of the catalyst.

[0047] Comparative Example 2 Same as Ce in Example 1 3+ / Mg 2+ / Al 3+ The difference is that the Ce-Mg-Al hydrotalcite is obtained by co-precipitation of aluminum nitrate, magnesium nitrate and cerium nitrate solution. The specific steps are as follows: Weigh 9.4g of aluminum nitrate and press Mg 2+ / Al 3+A molar ratio of 6:1 and a CeO₂ content of 15% by mass in the carrier were calculated. A certain amount of magnesium nitrate and cerium nitrate were weighed and dissolved in 200 mL of deionized water to prepare metal salt mixed solution A. 12.0 g of NaOH and 2.0 g of anhydrous Na₂CO₃ were weighed and dissolved in 250 mL of deionized water to prepare alkaline mixed solution B. Under vigorous stirring at room temperature, metal salt mixed solution A and alkaline mixed solution B were simultaneously added dropwise to a three-necked flask at a rate of 4 mL / min using a peristaltic pump. The pH of the suspension in the flask was controlled within the range of 9.5-10.5. After the addition of alkaline mixed solution B was stopped and the reaction continued for 30 minutes, the suspension was transferred to a hydrothermal reactor and crystallized at 95°C for 10 hours. The suspension was then filtered, and the filtered solid was washed and dried to obtain Ce-Mg-Al hydrotalcite.

[0048] The Ce-Mg-Al hydrotalcite was calcined at 500°C for 4 h to obtain a CeO2-MgO-Al2O3 composite oxide support. Subsequently, 2 g of the CeO2-MgO-Al2O3 support was added to 16 mL of a 1 mg / mL chloroplatinic acid acetone solution, achieving a Pt loading of 0.4 wt%. After ultrasonic impregnation at room temperature for 1 h, the support was dried in a 105°C drying oven for 12 h, and then calcined in air at 350°C for 4 h to obtain a catalyst precursor.

[0049] 0.5 g of the catalyst precursor was weighed and placed in a fixed-bed reaction tube. After reduction under a hydrogen atmosphere at 375°C for 4 h, the reaction temperature was adjusted to 350°C, and methylcyclohexane was introduced for dehydrogenation at a feed rate of 0.1 mL / min. Under the same reaction conditions as in Example 1, the conversion of methylcyclohexane was reduced to 65.2%.

[0050] From the comparison results of Example 1 and Comparative Example 2, it can be seen that when Pt is directly loaded on the CeO2-MgO-Al2O3 composite oxide support, the conversion rate of methylcyclohexane is greatly reduced. This is because in Example 1, CeO2 is dispersed in the form of islands on the surface of the MgO-Al2O3 composite oxide, and Pt is selectively dispersed on the CeO2 islands, which promotes the dispersion of Pt. The addition improves the dehydrogenation activity of the catalyst. The dispersion of Pt in Comparative Example 2 is difficult to effectively control.

[0051] Comparative Example 3 0.46 g of Ce(NO₃)₃·6H₂O was weighed and dissolved in 10 mL of water. Then, 2 g of the Mg-Al hydrotalcite obtained in Preparation Example 1 was added. The mixture was impregnated at 30°C for 6 h. The mixture was then rotary evaporated to dryness at 105°C. The solid was removed and calcined at 500°C for 4 h to obtain a CeO₂ / MgO-Al₂O₃ composite oxide support. CeO₂ was randomly dispersed on the MgO-Al₂O₃ composite oxide, and a uniform CeO₂ particle size distribution was not achieved. Subsequently, 2 g of the CeO₂ / MgO-Al₂O₃ support was added to 16 mL of a 1 mg / mL chloroplatinic acid acetone solution, achieving a Pt loading of 0.4 wt%. After ultrasonic impregnation at room temperature for 1 h, the mixture was transferred to a 105°C drying oven and dried for 12 h. The mixture was then calcined at 350°C in air for 4 h to obtain the catalyst precursor.

[0052] 0.5 g of the above catalyst precursor was weighed and filled into a fixed-bed reaction tube. After reduction under a hydrogen atmosphere at 375°C for 4 h, the reaction temperature was adjusted to 350°C, and methylcyclohexane was introduced for dehydrogenation reaction. The feed rate of methylcyclohexane was 0.1 mL / min. Sampling chromatographic analysis showed a conversion rate of 55.2%.

[0053] From the comparison results of Example 1 and Comparative Example 3, it can be seen that when an aqueous solution of Ce salt is used for impregnation, the catalyst of Comparative Example 3 cannot form CeO2 with uniformly dispersed particles, and it is difficult to achieve high dispersion and sufficient exposure of Pt, resulting in the catalyst activity being significantly lower than the dehydrogenation activity of the catalyst prepared in Example 1.

[0054] The present invention has been described in detail above. For those skilled in the art, without departing from the purpose and scope of the present invention, can implement the present invention in a wider range under equivalent parameters, concentration and conditions. Although the present invention provides specific embodiments, it should be understood that the present invention can be further improved. In a word, according to the principle of the present invention, the application is intended to include any variation, purposes or improvements of the present invention, including departing from the disclosed scope in the application and the changes made with conventional techniques known in the art.

Claims

1. A catalyst for dehydrogenation of liquid organic hydrogen energy carrier, characterized in that: It includes an active component, an auxiliary agent and a carrier, wherein the active component is Pt, the auxiliary agent is CeO2, and the carrier is a MgO-Al2O3 composite oxide; The CeO2 is dispersed on the surface of the MgO-Al2O3 composite oxide in the form of isolated islands; The Pt is selectively dispersed on the CeO2 islands.

2. The catalyst for dehydrogenation of liquid organic hydrogen energy carrier according to claim 1, characterized in that: The diameter of the CeO2 island is 5 to 10 nm.

3. The catalyst for dehydrogenation of a liquid organic hydrogen energy carrier according to any one of claims 1 to 2, characterized in that: Based on the total weight of the catalyst, the percentage of CeO2 is 2% to 30%, and the percentage of Pt is 0.1% to 2%; And / or, in the catalyst, Mg 2+ With Al 3+ The molar ratio is (2~8):

1.

4. The method for preparing a catalyst for dehydrogenation of a liquid organic hydrogen energy carrier according to any one of claims 1 to 3, characterized in that: The steps include: S1, adding a CeO2 solution to Mg-Al hydrotalcite for impregnation treatment, then removing the solvent and calcining to obtain a CeO2 / MgO-Al2O3 carrier; S2, adding the CeO2 / MgO-Al2O3 support to a Pt salt solution for impregnation treatment, and then drying and calcining in sequence to obtain a catalyst precursor; S3. Reducing the catalyst precursor under a hydrogen atmosphere to obtain the catalyst for dehydrogenation of the liquid organic hydrogen energy carrier.

5. The method for preparing a catalyst for dehydrogenation of a liquid organic hydrogen energy carrier according to claim 4, characterized in that: The concentration of the CeO2 solution is 0.001 to 0.2 g / mL; And / or, the solvent of the CeO2 solution is one or more of cyclohexane, n-heptane, and methylcyclohexane; And / or, in step S1, the immersion treatment temperature is 5 to 60° C. and the time is 1 to 12 hours.

6. The method for preparing a catalyst for dehydrogenation of a liquid organic hydrogen energy carrier according to claim 4 or 5, characterized in that: In step S1, the calcination temperature is 400-600°C and the time is 2-8 hours; In step S1, the calcination treatment is performed in an air atmosphere.

7. The method for preparing a catalyst for dehydrogenation of a liquid organic hydrogen energy carrier according to any one of claims 4 to 6, characterized in that: The concentration of the Pt salt solution is 1 to 100 mg / mL; and / or, the solvent of the Pt salt solution is acetone, methanol, ethanol or water; And / or, the Pt salt is one or more of tetraammineplatinum sulfate, tetraammineplatinum nitrate, tetraammineplatinum hydrogenphosphate, tetraammineplatinum chloride, platinum nitrate, and chloroplatinic acid; And / or, in step S2, the immersion treatment is ultrasonic immersion, the temperature is 15-30°C, and the time is 5-60 minutes.

8. The method for preparing a catalyst for dehydrogenation of a liquid organic hydrogen energy carrier according to any one of claims 4 to 7, characterized in that: In step S2, the calcination temperature is 300-360°C and the calcination time is 2-8 hours; And / or, the reduction temperature is 360-450° C., and the reduction time is 2-12 h.

9. A method for dehydrogenating a liquid organic hydrogen energy carrier, characterized in that: The steps include: The liquid organic hydrogen energy carrier is subjected to a dehydrogenation reaction under the catalytic action of the catalyst according to any one of claims 1 to 3 or the catalyst obtained by the preparation method according to any one of claims 4 to 8.

10. The dehydrogenation method of the liquid organic hydrogen energy carrier according to claim 9, characterized in that: The liquid organic hydrogen energy carrier is cyclohexane, methylcyclohexane, ethylcyclohexane or decahydronaphthalene; The temperature of the dehydrogenation reaction is 280-450°C.

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