Low-temperature dehydrogenation catalyst for organic hydrogen storage liquid as well as preparation method and application of low-temperature dehydrogenation catalyst

Abstract

The invention discloses an organic hydrogen storage liquid low-temperature dehydrogenation catalyst as well as a preparation method and application thereof, and belongs to the technical field of catalysts. According to the present invention, the carrier is modified by using the metal, the electron structure of the carrier is optimized by modifying the electron supply of the metal, the pore size of the carrier is adjusted, the active metal is loaded on the carrier by using the impregnation method, the catalyst with the high dehydrogenation ability is prepared, the dehydrogenation temperature of the hydrogen storage liquid is reduced, and the reaction activity and the stability of the catalyst are improved. According to the low-temperature dehydrogenation catalyst for the organic hydrogen storage liquid, the conversion rate of the organic hydrogen storage liquid reaches 99.6% at the temperature of 140 DEG C. According to the invention, dehydrogenation of the organic hydrogen storage liquid is realized at low temperature by using the metal modified carrier catalyst, and a new method is provided for efficient storage and utilization of hydrogen energy.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and particularly to a low-temperature dehydrogenation catalyst for organic hydrogen storage liquids, a preparation method thereof, and an application thereof. Background Art

[0002] As a highly efficient and clean energy source, hydrogen energy is widely used in multiple fields such as transportation, chemical industry, and aerospace. However, due to the low energy density, inflammability, and explosiveness of hydrogen itself, how to store and transport hydrogen safely and efficiently has become a major problem in large-scale hydrogen energy utilization. At present, the liquid organic hydrogen carriers (LOHC) technology has received extensive attention due to its advantages such as large hydrogen storage capacity, high efficiency, and environmental friendliness. The LOHC technology mainly uses liquid aromatic compounds as hydrogen storage carriers, and realizes the storage and release of hydrogen through the reversible catalytic addition and dehydrogenation reactions of unsaturated bonds in the molecular structure, and has the advantage of being able to directly utilize the existing conventional oil tanker transportation methods and gas station equipment. However, the temperature requirement for the dehydrogenation reaction in the current LOHC technology is still relatively high, generally exceeding 300 °C. At high temperatures, side reactions such as cracking and carbon deposition are likely to occur, resulting in a decrease in the catalyst activity and even deactivation, and reducing the dehydrogenation reaction efficiency.

[0003] In order to reduce the dehydrogenation reaction energy barrier, avoid side reactions, and improve the hydrogen conversion efficiency, researchers are looking for hydrogen storage liquids with better performance and have developed a series of new dehydrogenation catalysts. A series of unsaturated aromatic heterocyclic organic compounds such as N-ethylcarbazole, carbazole, N-propylcarbazole, phenazine, indole, and 2-methylindole have relatively high hydrogen storage densities, and the N element in the molecule can reduce the standard enthalpy of the hydrogen compound, and the C-H bond energy adjacent to N is lower than the C-H bond energy in cycloalkanes. Therefore, the dehydrogenation temperature required for unsaturated aromatic heterocyclic organic compounds is lower.

[0004] For example, a Chinese invention patent with the publication number CN117920265A discloses a FePd bimetallic nanocatalyst with high dehydrogenation activity, its preparation method and application. Using poly-dopamine modified Al2O3 as the carrier, a Fe@Pd bimetallic nanocatalyst was prepared by an electro-displacement reaction, achieving complete dehydrogenation of dodecahydro-N-ethylcarbazole at 180 °C. The Chinese invention patent with the publication number CN116803520A provides a mesoporous SiO2 supported palladium-ruthenium catalyst that is simultaneously suitable for hydrogen storage and dehydrogenation of liquid organic hydrogen carriers and its preparation method. It uses electrostatic adsorption and glow discharge plasma reduction technology to load noble metals Pd and Ru on the mesoporous SiO2 carrier, and the dehydrogenation rate of dodecahydro-N-ethylcarbazole is increased to 99.5% at 170 °C. In the Chinese patent with the publication number CN115945209A, a Ni@Pd core-shell nanocatalyst for organic liquid hydrogen storage, its preparation method and application are provided. A core-shell nanocatalyst was prepared by loading Ni@Pd on KIT-6 molecular sieve, catalyzing the dehydrogenation of dodecahydro-N-ethylcarbazole, and further reducing the dehydrogenation reaction temperature to 160 °C under atmospheric pressure while improving the cycle stability of the catalyst.

[0005] In summary, the dehydrogenation temperature of the dehydrogenation catalysts developed for unsaturated aromatic heterocyclic organic compounds currently ranges from 160 to 190 °C. However, most of the catalysts proposed currently can only correspondingly reduce the dehydrogenation temperature of a single hydrogen storage liquid compound. And in practical applications, in order to extend the catalyst life and improve the portability and practicality of the dehydrogenation system, it is necessary to further reduce the dehydrogenation temperature of organic liquids. Therefore, in this context, developing catalysts with lower dehydrogenation temperature and stronger anti-coking ability and applying them to the dehydrogenation of mixed organic hydrogen storage liquids has important strategic significance for the efficient storage and large-scale application of hydrogen energy in the future. Summary of the Invention

[0006] In view of the above-mentioned defects of the prior art, in the first aspect of the present invention, a preparation method of a low-temperature dehydrogenation catalyst for organic hydrogen storage liquids with simple process and good economic benefits is provided, including the following steps: (1) Mix a metal compound for modification with a catalyst carrier in a certain proportion to obtain a mixture; (2) Calcinate the mixture in an inert atmosphere, and after completion, cool, acid-leach, and dry to obtain a metal-doped modified carrier (M-C); (3) Add the metal-doped modified carrier to an aqueous solution of an active metal precursor and mix to obtain a mixed solution; (4) Under an inert atmosphere, dropwise add an aqueous solution of NaBH4 to the mixed solution, mix, filter, wash, dry, and grind to obtain a metal catalyst precursor; (5) The metal catalyst precursor is heat-treated to obtain a catalyst for low-temperature dehydrogenation of organic hydrogen storage liquids.

[0007] Preferably, in the step (1), the metal compound includes at least one of MgCl2·6H2O, MnCl2·4H2O, and ZnCl2.

[0008] Preferably, in the step (1), the catalyst support includes at least one of SiC, Al2O3, ZSM-5, MCM-41, SBA-15, BN, and active carbon (AC).

[0009] Preferably, in the step (1), the metal compound accounts for 10 wt.% - 50 wt.% of the catalyst support.

[0010] In step (1), it is appropriate to use raw materials with a suitable particle size to improve the mixing effect. During this process, grinding can be carried out to refine the raw materials and make the mixing more sufficient. Those skilled in the art can select a suitable grinding time according to the actual conditions and the state of the raw materials, such as 15 - 45 min, with 30 min being the best.

[0011] Preferably, in the step (2), the calcination temperature is 550 - 950 °C and the calcination time is 0.5 - 6 h.

[0012] Preferably, in the step (2), the type of acid used for acid leaching includes one of H2SO4, HCl, and HNO3; the concentration of the acid is 1 - 8 mol / L.

[0013] Preferably, in the step (2), the drying temperature is 50 - 70 °C and the drying time is 4 - 12 h.

[0014] Preferably, in the step (3), the active metal precursor includes at least one of Na2PdCl4, Na2PtCl4, RuCl3, Ni(NO3)2·6H2O, CoCl2·6H2O, CuCl2, and Fe(NO3)3·9H2O.

[0015] Preferably, in the step (3), the loading amount of the active metal in the active metal precursor on the catalyst support is 1 wt.% - 20 wt.%.

[0016] Further preferably, when the active metal provided by the active metal precursor is a bimetal, the mass ratio of the bimetal is 0.3 - 3:1.

[0017] Preferably, in the step (3), the stirring time for mixing is 0.5 - 2 h.

[0018] Preferably, in the step (4), the mass of NaBH4 added is 60% - 80% of the mass of the active metal in the active metal precursor.

[0019] Preferably, in the step (4), the stirring time for mixing is 1.5 - 4 h.

[0020] Preferably, in the step (4), the drying temperature is 50 - 70 °C and the drying time is 4 - 12 h.

[0021] Preferably, in the step (5), the heating temperature for heat treatment is 300 - 550 °C and the heating time is 8 - 24 h.

[0022] In the preparation process of the organic hydrogen storage liquid low-temperature dehydrogenation catalyst, those skilled in the art can select appropriate gases according to actual conditions to create an inert atmosphere, such as using nitrogen, argon, helium, etc. Unless otherwise specified, the operations in the steps are carried out at room temperature.

[0023] In the second aspect of the present invention, there is provided an organic hydrogen storage liquid low-temperature dehydrogenation catalyst with a lower noble metal loading and catalytic dehydrogenation temperature, excellent dehydrogenation effect, cycle stability and renewable performance, and good applicability, which is prepared by the preparation method of the first aspect of the present invention.

[0024] In the third aspect of the present invention, there is provided the application of the organic hydrogen storage liquid low-temperature dehydrogenation catalyst of the second aspect of the present invention, including the following steps: S1. Mix an organic hydrogen storage compound with the organic hydrogen storage liquid low-temperature dehydrogenation catalyst in a certain proportion; S2. Under an inert atmosphere, carry out a dehydrogenation reaction at a certain temperature.

[0025] Preferably, in the S1, the organic hydrogen storage compound includes at least one of N-ethylcarbazole hydride, N-propylcarbazole hydride, and 2-methylindole hydride.

[0026] More preferably, the organic hydrogen storage compound is N-ethylcarbazole hydride, N-propylcarbazole hydride, and 2-methylindole hydride, and the mass ratio is 1.25 - 1.75:1:1.25 - 1.75 in sequence.

[0027] N-ethylcarbazole, N-propylcarbazole, and 2-methylindole are solids at room temperature and liquids during the hydrogenation and dehydrogenation reactions. When the organic hydrogen storage compound is a mixture of the three, the ratio of 1.5:1:1.5 is the best, and at this time, the mixed hydrogen storage compound starts to liquefy at room temperature.

[0028] Preferably, in the S1, the mass ratio of the organic hydrogen storage compound to the organic hydrogen storage liquid low-temperature dehydrogenation catalyst is 1 - 10:1.

[0029] Preferably, in the step S2, the gas pressure of the inert atmosphere is 0.1 MPa.

[0030] Preferably, in the step S2, the temperature of the dehydrogenation reaction is 110-180 °C, and the reaction time is 2-12 h.

[0031] More preferably, the temperature of the dehydrogenation reaction is 110-150 °C, and the reaction time is 4-10 h.

[0032] Based on the above technical solutions, the design concept and principle of the present invention are as follows: Taking the dehydrogenation reaction mechanism of the present invention by using a Pd, Ni bimetal supported on a magnesium-modified SiC support as an example, in the reaction of catalytic dehydrogenation of hydrogen storage liquids, the modified metal Mg optimizes the electronic structure of the support through the electron donor effect, reduces the binding energy of the supported noble metal Pd, promotes the cleavage of C-H bonds and the rapid dissociation and desorption of H2, and at the same time increases the oxidation state of the non-noble metal Ni. The strong interaction between Ni ions and the intermediate stabilizes some dehydrogenated species, inhibiting side reactions caused by their excessive adsorption; the modified metal also significantly increases the specific surface area and mesopore volume of the support, promoting the diffusion of reactants and the desorption of products. The synergistic effect of Pd and Ni forms a metal oxide active center, in which Pd dominates the stepwise cleavage of C-H bonds to release H2, and Ni prevents the formation of deep dehydrogenation by-products by regulating the adsorption strength of intermediates.

[0033] Therefore, the preparation method of the low-temperature dehydrogenation catalyst for organic hydrogen storage liquids designed by the present invention can reduce the catalytic dehydrogenation temperature of hydrogen storage liquids to 140 °C through the synergistic effect of the modified support and the loaded active metal, greatly reducing the reaction energy consumption. In addition, by loading highly dispersed active metal particles on the modified support, the noble metal loading amount is reduced, which has good economic benefits. The low-temperature dehydrogenation catalyst for organic hydrogen storage liquids has good dehydrogenation effects on various hydrogen storage liquids, can be used in different systems as needed, and has good applicability.

[0034] Compared with the prior art, the present invention has the following advantages and beneficial effects: The present invention provides a preparation method of a low-temperature dehydrogenation catalyst for organic hydrogen storage liquids, which has the advantages of simple process and good economic benefits.

[0035] The present invention provides a low-temperature dehydrogenation catalyst for organic hydrogen storage liquids, which has excellent dehydrogenation effects and reduces the noble metal loading amount. The catalytic dehydrogenation temperature of the catalyst is lower, and it has good cycle stability and renewability, and has good applicability.

[0036] The present invention provides an application of an organic hydrogen storage liquid low-temperature dehydrogenation catalyst, which has good dehydrogenation effects on various hydrogen storage liquids, can be used in different systems as needed, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is the catalyst preparation flow chart of the preparation method of the organic hydrogen storage liquid low-temperature dehydrogenation catalyst; Figure 2 is the schematic diagram of the experimental operation process of the catalytic dehydrogenation of the organic hydrogen storage liquid of the preparation method of the organic hydrogen storage liquid low-temperature dehydrogenation catalyst; Figure 3 is the structural formula and hydrogen storage density of the hydrogen storage liquid used in the preparation method of the organic hydrogen storage liquid low-temperature dehydrogenation catalyst. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] The present invention will be further described below by way of examples, but the present invention is not limited to the scope of the described examples. The experimental methods without specific conditions in the following examples are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0039] The present invention prepares an active metal catalyst supported on a modified carrier (SiC, Al2O3, ZSM-5, MCM-41, SBA-15, BN, AC) by an impregnation method.

[0040] The preparation of a bimetallic (taking Pd and Ni as examples) catalyst supported on a modified SiC carrier is as Figure 1 shown: (1) Weigh 4.1667 g of SiC and 6.9674 g of magnesium chloride hexahydrate (MgCl2·6H2O) and mix and grind for 1 h; (2) Then send it into a tubular furnace, under a nitrogen atmosphere, heat it to 800 °C at a heating rate of 5 °C / min and keep it for 1 h; after calcination and cooling, grind it into powder, soak it in 4M HCl for 6 h; then send it into an oven and dry it overnight at 60 °C to obtain a Mg-SiC carrier; (3) Dissolve 0.3456 g of Na2PdCl4 and 0.6194 g of Ni(NO3)2·6H2O in 30 mL of deionized water, add the Mg-SiC carrier, and stir for 1 h; (4) Dissolve 0.156 g of NaBH4 in 10 mL of deionized water. Under a nitrogen atmosphere, add the NaBH4 solution dropwise to the stirred mixture while stirring, and stir at 800 rpm for 2 h; after stirring, filter, wash it with water many times, then send it into an oven and dry it overnight at 60 °C, take it out and grind it to obtain a bimetallic carrier catalyst precursor; (5) Place the catalyst precursor in a muffle furnace and heat it at 350 °C for 12 h to obtain Pd 2.5% Ni 2.5% O / Mg-SiC catalyst (2.5% indicates that the loadings of Pd and Ni are 2.5 wt.%).

[0041] Change the catalyst support and obtain Pd in the same way 2.5% Ni 2.5% O / Mg-Al2O3, Pd 2.5% Ni 2.5% O / Mg-ZSM-5, Pd 2.5% Ni 2.5% O / Mg-MCM-41, Pd 2.5% Ni 2.5% O / Mg-SBA-15, Pd 2.5% Ni 2.5% O / Mg-BN, Pd 2.5% Ni 2.5% O / Mg-AC; change the types and ratios of active metals and obtain Pt in the same way 2.5% Ni 2.5% O / Mg-SiC, Ru 2.5% Ni 2.5% O / Mg-SiC, Pd 2.5% Co 2.5% O / Mg-SiC, Pd 2.5% Cu 2.5% O / Mg-SiC, Pd 2.5% Fe 2.5% O / Mg-SiC, Pd 1.25% Ni 3.75 %O / Mg-SiC, Pd 3.75% Ni 1.25% O / Mg-SiC and other bimetallic catalysts and Pd 5% O / Mg-SiC, Ni 5% O / Mg-SiC and other monometallic catalysts; change the types of modified metals and obtain Pd in the same way 2.5% Ni 2.5% O / Mn-SiC, Pd 2.5% Ni 2.5% O / Zn-SiC. Use these catalysts to conduct dehydrogenation experiments of hydrogen storage liquids under different conditions respectively. The hydrogen storage liquids used in the following examples are a mixture of N-ethylcarbazole, N-propylcarbazole, and 2-methylindole hydride in a ratio of 1.5:1:1.5.

[0042] Example 1 This example studied the dehydrogenation effect of the catalyst for low-temperature dehydrogenation of organic hydrogen storage liquids in applications. The steps are as follows: S1. Weigh 0.5 g of the hydrogen storage liquid and 0.25 g of the Pd 2.5% Ni 2.5% O / Mg - SiC catalyst prepared above and place them in a reactor; S2. Flush and fill the reactor with normal pressure nitrogen 5 times repeatedly. Heat the reactor to 140 °C and keep it for 8 h. After the reaction ends, place the reactor in ice water for rapid cooling.

[0043] As Figure 2 shown, collect the gas generated by the reaction with an aluminum foil gas collection bag and conduct qualitative analysis. Rinse the reaction kettle with 5 mL of acetone to collect all the catalyst and dehydrogenation products into a test tube, and then centrifuge to separate the catalyst. The separated catalyst is repeatedly rinsed with ethanol and water and then dried overnight in a vacuum drying oven at 50 °C and used as the catalyst for subsequent cycle experiments. Add 1 mg of the internal standard dodecane to the acetone solution, and take 1 mL of the acetone solution for qualitative and quantitative analysis by GC - MS (FID). The structural formula and hydrogen storage density of the hydrogen storage liquid used in the preparation method of the organic hydrogen storage liquid low - temperature dehydrogenation catalyst are as Figure 3 shown. After analyzing the reaction products, it is found that the dehydrogenation rate of the hydrogen storage liquid (dodecahydro - N - ethylcarbazole, dodecahydro - N - propylcarbazole, octahydro - 2 - methylindole) is 99.6%, and the sum of the yields of the dehydrogenation products (N - ethylcarbazole, N - propylcarbazole, 2 - methylindole) is 93.1%. This is because the dehydrogenation reaction proceeds step by step, and some hydrogen storage intermediates are not completely dehydrogenated.

[0044] Example 2 This example is basically the same as Example 1, except that the catalyst used is Pd 2.5% Ni 2.5% O / Mg - Al2O3.

[0045] Example 3 This example is basically the same as Example 1, except that the catalyst used is Pd 2.5% Ni 2.5% O / Mg - ZSM - 5.

[0046] Example 4 This example is basically the same as Example 1, except that the catalyst used is Pd 2.5% Ni 2.5% O / Mg - MCM - 41.

[0047] Example 5 This example is basically the same as Example 1, except that the catalyst used is Pd 2.5% Ni 2.5% O / Mg - SBA - 15.

[0048] Example 6 This example is basically the same as Example 1, except that the catalyst is Pd 2.5% Ni 2.5% O / Mg-BN.

[0049] Example 7 This example is basically the same as Example 1, except that the catalyst is Pd 2.5% Ni 2.5% O / Mg-AC.

[0050] Test and count the influence of catalysts with different carriers in Examples 2 to 7 on the dehydrogenation reaction of hydrogen storage liquid. The test results are shown in Table 1.

[0051] Table 1: Influence of catalysts with different carriers on the dehydrogenation reaction of hydrogen storage liquid

[0052] According to Table 1 and Example 1, the influence of the catalyst carrier on the dehydrogenation effect is very small. Therefore, SiC is still selected as the carrier in the follow-up to explore the influence of factors such as the type of modified metal, the type of active metal, the ratio of active metals, reaction temperature, and reaction time on the dehydrogenation reaction.

[0053] Example 8 On the basis of Example 1, replace the modified metal Mg of the carrier with Mn, that is, the catalyst uses the above Pd 2.5% Ni 2.5% O / Mn-SiC, and other conditions remain unchanged, and the same operation steps as in Example 1 are carried out.

[0054] Example 9 This example is basically the same as Example 1, except that the catalyst is Pd 2.5% Ni 2.5% O / Zn-SiC.

[0055] Test and count the influence of catalysts with different modified metals in Examples 8 and 9 on the dehydrogenation reaction of hydrogen storage liquid. The test results are shown in Table 2.

[0056] Table 2: Influence of catalysts using different modified metals on the dehydrogenation reaction of hydrogen storage liquid

[0057] According to Table 2 and Example 1, the catalyst modified by Mg has the best dehydrogenation effect. The conversion rate of the hydrogen storage liquid of the catalyst modified by Mn exceeds 90%, but the total yield of the fully dehydrogenated product is relatively low. The overall dehydrogenation effect of the catalyst modified by Zn is the worst.

[0058] Example 10 On the basis of Example 1, change the types of active bimetals, keep other conditions unchanged, and use Pt as the catalyst 2.5% Ni 2.5% O / Mg-SiC, and perform the same operation steps as in Example 1.

[0059] Example 11 This example is basically the same as Example 1, except that Ru is used as the catalyst 2.5% Ni 2.5% O / Mg-SiC.

[0060] Example 12 This example is basically the same as Example 1, except that Pd is used as the catalyst 2.5% Co 2.5% O / Mg-SiC.

[0061] Example 13 This example is basically the same as Example 1, except that Pd is used as the catalyst 2.5% Cu 2.5% O / Mg-SiC.

[0062] Example 14 This example is basically the same as Example 1, except that Pd is used as the catalyst 2.5% Fe 2.5% O / Mg-SiC.

[0063] Test and count the influence of the types of active metal particles on the dehydrogenation reaction of hydrogen storage liquid in Examples 10 to 14. The test results are shown in Table 3.

[0064] Table 3: Influence of the types of active metal particles on the dehydrogenation reaction of hydrogen storage liquid

[0065] According to Table 3, when using Pt and Ru noble metal particles, the dehydrogenation effects of the two catalysts are similar, and both are weaker than the Pd-supported catalysts (Examples 1, 12, 13, 14). The hydrogen storage liquid conversion rates of the catalysts loaded with Pd noble metal particles and different non-noble metals Co, Cu, and Fe are quite the same, but the total yield of their fully dehydrogenated products is lower than that of the catalyst loaded with Ni particles (Example 1). Overall, the combination of Pd and Ni still has the best dehydrogenation effect.

[0066] Example 15 On the basis of Example 1, change the loadings of active metals Pd and Ni, that is, the Pd 5% O / Mg-SiC prepared above, keep other conditions unchanged. Perform the same operation steps as in Example 1.

[0067] Example 16 This example is basically the same as Example 1, except that the catalyst used is Pd 3.75% Ni 1.25% O / Mg-SiC.

[0068] Example 17 This example is basically the same as Example 1, except that the catalyst used is Pd 1.25% Ni 3.75 %O / Mg-SiC.

[0069] Example 18 This example is basically the same as Example 1, except that the catalyst used is Ni 5% O / Mg-SiC.

[0070] Test and statistically analyze the effects of catalysts with different active metal ratios in Examples 15 to 18 on the dehydrogenation reaction of hydrogen storage liquids. The test results are shown in Table 4.

[0071] Table 4: Effects of catalysts with different active metal ratios on the dehydrogenation reaction of hydrogen storage liquids

[0072] According to Table 4, using different active metal ratios has a significant impact on the dehydrogenation reaction of hydrogen storage liquids. During the dehydrogenation reaction, the noble metal Pd dominates the gradual cleavage of C-H bonds. Therefore, when the relative content of Pd element is low, the conversion rate of hydrogen storage liquids decreases; when the relative content of Pd element is high, the hydrogen storage liquid will undergo over-dehydrogenation reaction to form coke, reducing the yield of the desired fully dehydrogenated product, and the coke is easily deposited on the catalyst surface, resulting in a decrease in the catalyst cycle stability and even deactivation. Therefore, the best ratio of noble metal to non-noble metal is 1:1.

[0073] Example 19 On the basis of Example 1, use Pd 2.5% Ni 2.5% O / Mg-SiC catalyst, and under a reaction time of 8 h, change the dehydrogenation reaction temperature of the hydrogen storage liquid to 110 °C, and then perform the same operation steps as in Example 1.

[0074] Example 20 This example is basically the same as Example 1, except that the dehydrogenation reaction temperature is 120 °C Example 21 This example is basically the same as Example 1, except that the dehydrogenation reaction temperature is 130 °C Example 22 This example is basically the same as Example 1, except that the dehydrogenation reaction temperature is 150 °C Test and statistically analyze the influence of reaction temperature on the dehydrogenation reaction of hydrogen storage liquid in Examples 19 to 22. The test results are shown in Table 5.

[0075] Table 5: Influence of Reaction Temperature on the Dehydrogenation Reaction of Hydrogen Storage Liquid

[0076] According to Table 5 and Example 1, the higher the temperature, the more favorable it is for the dehydrogenation of hydrogen storage liquid. When the temperature exceeds 130 °C, the conversion rate of hydrogen storage liquid exceeds 95% and increases slowly, while the total yield of fully dehydrogenated products rises rapidly. At 110 °C, the conversion rate of hydrogen storage liquid reaches 85.1%, and the total yield of fully dehydrogenated products reaches 58.9%. This indicates that the catalyst effectively reduces the energy barrier of the dehydrogenation reaction and realizes the dehydrogenation of hydrogen storage liquid at a lower temperature. The dehydrogenation temperature of 140 °C corresponding to Example 1 enables the conversion rate of hydrogen storage liquid to reach 99.6%, and the total yield of fully dehydrogenated products reaches 93.1%, with the overall dehydrogenation effect being the best.

[0077] Example 23 On the basis of Example 1, use Pd 2.5% Ni 2.5% O / Mg-SiC catalyst. At a reaction temperature of 140 °C, change the dehydrogenation time of the hydrogen storage liquid to 2 h, and then perform the same operation steps as in Example 1.

[0078] Example 24 This example is basically the same as Example 1, except that the dehydrogenation reaction time is 4 h.

[0079] Example 25 This example is basically the same as Example 1, except that the dehydrogenation reaction time is 6 h.

[0080] Example 26 This example is basically the same as Example 1, except that the dehydrogenation reaction time is 10 h.

[0081] Test and statistically analyze the influence of reaction time on the dehydrogenation reaction of hydrogen storage liquid in Examples 23 to 26. The test results are shown in Table 6.

[0082] Table 6: Influence of Reaction Time on the Dehydrogenation Reaction of Hydrogen Storage Liquid

[0083] According to Table 6 and Example 1, at a reaction temperature of 140 °C and a reaction time of 2 h, the conversion rate of the hydrogen storage liquid has exceeded 75%, but the total yield of the fully dehydrogenated product is only 3.2%. This is because the dehydrogenation of the hydrogen storage liquid is a continuous process. After the reaction proceeds for 2 h, a large amount of dehydrogenation intermediates such as decahydro-N-ethylcarbazole, decahydro-N-propylcarbazole, hexahydro-2-methylindole, octahydro-N-ethylcarbazole, octahydro-N-propylcarbazole, and tetrahydro-2-methylindole are initially produced from the dehydrogenation of the hydrogen storage liquid. Therefore, the total yield of the fully dehydrogenated product is relatively low. After extending the reaction time, the total yield of the fully dehydrogenated product increases rapidly. After the reaction time exceeds 8 h, the conversion rate of the hydrogen storage liquid and the total yield of the fully dehydrogenated product basically remain unchanged.

[0084] Example 27 On the basis of Example 1, Pd 2.5% Ni 2.5% O / Mg-SiC catalyst was used to react at a reaction temperature of 140 °C for 8 h. The mass ratio of the hydrogen storage liquid to the catalyst was changed to 10:1 while keeping the total mass unchanged, and the same operating steps as in Example 1 were carried out.

[0085] Example 28 This example is basically the same as Example 1, except that the mass ratio of the hydrogen storage liquid to the catalyst is 5:1.

[0086] Example 29 This example is basically the same as Example 1, except that the mass ratio of the hydrogen storage liquid to the catalyst is 3:1.

[0087] Example 30 This example is basically the same as Example 1, except that the mass ratio of the hydrogen storage liquid to the catalyst is 1:1.

[0088] The effects of different ratios of reactants to catalysts in Examples 27 to 30 on the dehydrogenation reaction of the hydrogen storage liquid were tested and statistically analyzed. The test results are shown in Table 7.

[0089] Table 7: Effects of different ratios of reactants to catalysts on the dehydrogenation reaction of the hydrogen storage liquid

[0090] According to Table 7 and Example 1, the larger the mass fraction of the catalyst, the better the dehydrogenation effect. When the mass ratio of the hydrogen storage liquid to the catalyst is 1:1, the hydrogen storage liquid is almost completely dehydrogenated. However, in this case, the amount of catalyst used is too large. To balance the dehydrogenation effect and the catalyst cost, the mass ratio of the hydrogen storage liquid to the catalyst of 2:1 is still used to explore the effects of other factors on the dehydrogenation effect.

[0091] Example 31 On the basis of Example 1, the catalyst was recovered and recycled once, and its dehydrogenation effect was also tested on the basis of Example 1.

[0092] Example 32 In this example, the catalyst of Example 31 was recovered and recycled again, with a total of 2 cycles, and its dehydrogenation effect was tested on the basis of Example 1.

[0093] Example 33 In this example, the catalyst of Example 32 was recovered and recycled again, with a total of 3 cycles, and its dehydrogenation effect was tested on the basis of Example 1.

[0094] Example 34 In this example, the catalyst of Example 32 was recovered, and the catalyst after 3 cycles of recycling was regenerated, and its dehydrogenation effect was tested on the basis of Example 1.

[0095] Test and statistically analyze Pd in Examples 31 to 34 2.5% Ni 2.5% The cycle stability and regenerability of the O / Mg-SiC catalyst, and the results are shown in Table 8.

[0096] Table 8: Cycle stability and regenerability of Pd 2.5% Ni 2.5% O / Mg-SiC catalyst

[0097] According to Table 8 and Example 1, after being reused 4 times (with 3 cycles), the conversion rate of the hydrogen storage liquid was 83.6%, which was 16.1% lower than that of the non-recycled catalyst, but the total yield of the fully dehydrogenated product decreased sharply to 23.3%. After the catalyst was regenerated, the conversion rate of the hydrogen storage liquid recovered to 98.1%, and the total yield of the fully dehydrogenated product lost 6.3%. This indicates that the catalyst can restore its catalytic activity through reactivation, but its performance is slightly lower than that of a brand-new catalyst.

[0098] Comparative Example 1 To prove the necessity of the catalyst, a comparative experiment was carried out in this comparative example without adding a catalyst. The specific implementation method was the same as that of Example 1, with a reaction temperature of 140 °C and a reaction time of 8 h.

[0099] Comparative Example 2 In this comparative example, a comparative experiment was carried out under the condition of only adding a SiC catalyst. The specific implementation method was the same as that of Example 1, with a reaction temperature of 140 °C and a reaction time of 8 h.

[0100] Comparative Example 3 In this comparative example, Pd with active metals Pd and Ni added but SiC not modified 2.5%Ni 2.5% A comparative experiment was carried out under the NiO / SiC catalyst. The specific implementation method was the same as that of Example 1, with a reaction temperature of 140 °C and a reaction time of 8 h.

[0101] The effects of non-catalysis, only adding SiC, and the unmodified SiC catalyst on the dehydrogenation reaction of the hydrogen storage liquid were tested and statistically analyzed. The results are shown in Table 9.

[0102] Table 9: Effects of non-catalysis, only adding SiC, and the unmodified SiC catalyst on the dehydrogenation reaction of the hydrogen storage liquid

[0103] According to Table 9, in the case of not adding a catalyst and only using SiC as a catalyst, the dehydrogenation reaction is difficult to proceed and the difference between the two is not significant. Single SiC is difficult to activate the dehydrogenation reaction. When using the unmodified Pd 2.5% Ni 2.5% O / SiC catalyst, the conversion rate of the hydrogen storage liquid decreased by 6.4% compared with the catalyst modified by magnesium, and the total yield of the fully dehydrogenated product decreased by 22%. This is mainly because the Mg modification enhanced the electron density of Pd, promoted the cleavage of the C-H bond and the rapid desorption of H2. Therefore, the modified catalyst has a higher total yield of the fully dehydrogenated product.

[0104] In summary, in order to reduce the dehydrogenation temperature of the hydrogen storage liquid, improve the reaction activity and stability of the catalyst at the same time, the present invention proposes to use a metal-modified carrier, optimize the electronic structure of the carrier by the electron-donating of the modified metal, adjust the pore size of the carrier at the same time, and load the active metal on the carrier by the impregnation method to prepare a catalyst with high dehydrogenation ability. At 140 °C, the conversion rate of the organic hydrogen storage liquid reaches 99.6%. The present invention proposes to use a metal-modified carrier catalyst to realize the dehydrogenation of organic hydrogen storage liquid at low temperature, providing a new method for the efficient storage and utilization of hydrogen energy.

[0105] The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations according to the concept of the present invention without creative work. Therefore, all technical solutions that can be obtained by those skilled in the art in the technical field of the present invention based on the concept of the present invention through logical analysis, reasoning or limited experiments on the basis of the prior art should be within the protection scope determined by the claims.

Claims

1. A preparation method of a catalyst for low-temperature dehydrogenation of an organic hydrogen storage liquid, characterized in that, It includes the following steps: (1) Mix the metal compound for modification with the catalyst support in a certain proportion to obtain a mixture; (2) Calcinate the mixture under an inert atmosphere. After completion, cool, acid-leach, and dry it to obtain a metal-doped modified support; (3) Add the metal-doped modified support to an aqueous solution of the active metal precursor and mix to obtain a mixed solution; (4) Under an inert atmosphere, dropwise add an aqueous solution of NaBH4 to the mixed solution. After mixing, filter, wash, dry, and grind it to obtain a metal catalyst precursor; (5) Heat-treat the metal catalyst precursor to obtain a catalyst for low-temperature dehydrogenation of organic hydrogen storage liquids.

2. The preparation method of the organic hydrogen storage liquid low-temperature dehydrogenation catalyst according to claim 1, characterized in that: In the step (1), the metal compound includes at least one of MgCl2·6H2O, MnCl2·4H2O, and ZnCl2; the catalyst support includes at least one of SiC, Al2O3, ZSM-5, MCM-41, SBA-15, BN, and activated carbon; the metal compound accounts for 10 wt.% - 50 wt.% of the catalyst support.

3. The preparation method of the organic hydrogen storage liquid low-temperature dehydrogenation catalyst according to claim 1, characterized in that: In the step (2), the calcination temperature is 550 - 950 °C, and the calcination time is 0.5 - 6 h; the type of acid used for acid-leaching includes one of H2SO4, HCl, and HNO3; the concentration of the acid is 1 - 8 mol / L; the drying temperature is 50 - 70 °C, and the drying time is 4 - 12 h.

4. The preparation method of the organic hydrogen storage liquid low-temperature dehydrogenation catalyst according to claim 1, wherein: In the step (3), the active metal precursor includes at least one of Na2PdCl4, Na2PtCl4, RuCl3, Ni(NO3)2·6H2O, CoCl2·6H2O, CuCl2, and Fe(NO3)3·9H2O; the loading amount of the active metal on the catalyst support in the active metal precursor is 1 wt.% - 20 wt.%; when the active metal provided by the active metal precursor is a bimetal, the mass ratio of the bimetal is 0.3 - 3:1; the stirring time for mixing is 0.5 - 2 h.

5. The preparation method of the organic hydrogen storage liquid low-temperature dehydrogenation catalyst according to claim 1, characterized in that: In the step (4), the mass of added NaBH4 is 60% - 80% of the mass of the active metal in the active metal precursor; the stirring time for mixing is 1.5 - 4 h; the drying temperature is 50 - 70 °C, and the drying time is 4 - 12 h.

6. The preparation method of the low-temperature dehydrogenation catalyst for organic hydrogen storage liquid according to claim 1, wherein: In the step (5), the heating temperature for heat-treatment is 300 - 550 °C, and the heating time is 8 - 24 h.

7. An organic hydrogen storage liquid low-temperature dehydrogenation catalyst, characterized in that: It is prepared by using the preparation method described in any one of claims 1 - 6.

8. Use of the organic hydrogen storage liquid low-temperature dehydrogenation catalyst as described in claim 7, characterized in that, It includes the following steps: S1. Mix the organic hydrogen storage compound with the catalyst for low-temperature dehydrogenation of organic hydrogen storage liquids in a certain proportion; S2. Under an inert atmosphere, carry out a dehydrogenation reaction at a certain temperature.

9. Use of the organic hydrogen storage liquid low-temperature dehydrogenation catalyst according to claim 8, characterized in that: In the S1, the organic hydrogen storage compound includes at least one of N-ethylcarbazole hydride, N-propylcarbazole hydride, and 2-methylindole hydride; the mass ratio of the organic hydrogen storage compound to the catalyst for low-temperature dehydrogenation of organic hydrogen storage liquids is 1 - 10:1; when the organic hydrogen storage compound is N-ethylcarbazole hydride, N-propylcarbazole hydride, or 2-methylindole hydride, their mass ratios are 1.25 - 1.75:1:1.25 - 1.75 in sequence.

10. Use of the organic hydrogen storage liquid low-temperature dehydrogenation catalyst according to claim 8, characterized in that: The temperature of the dehydrogenation reaction is 110~180 °C, and the reaction time is 2~12 h.

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