Ni / Mo2C@CQDs catalytic method for selective hydrogenation / hydrodeoxygenation of fatty acid methyl esters

Abstract

This invention belongs to the field of biomass utilization and biomass energy, and provides a method for selectively hydrogenating fatty acid methyl esters to prepare long-chain fatty alcohols or for preparing high-carbon green advanced hydrocarbon fuels by hydrogenation deoxygenation and carbon conversion under mild conditions using Ni / Mo2C@CQDs catalyst.

Description

Technical Field

[0001] This invention belongs to the field of biomass utilization and biomass energy, and relates to a method for selectively hydrogenating fatty acid methyl esters to prepare long-chain fatty alcohols or for hydrogenating and deoxygenating them to obtain high-carbon-content green advanced hydrocarbon fuels using Ni / Mo2C@CQDs catalysts under mild conditions. Background Technology

[0002] Long-chain fatty alcohols (from decadecyl alcohols to octadecyl alcohols with 10-18 carbon atoms) are a renewable biomass resource and an important industrial raw material for the production of surfactants, detergents, plasticizers, other personal care products, and fatty tertiary amines. Currently, the hydrogenation of renewable fatty acid methyl esters using CuO / CuCr2O4 catalysis to prepare fatty alcohols is one industrial production technique, achieving a molar yield of >90%. However, the reaction is often carried out at 200–300℃ and 20–30 MPa H2, and the reaction process involves the highly toxic substance Cr. 6+ Leaching is detrimental to the environment. Because noble metals such as palladium, platinum, iridium, rhodium, and ruthenium exhibit good hydrogenation activity under mild conditions, they are considered effective alternatives to chromium-based catalysts in the production of fatty alcohols. However, their high price, limited reserves, and poor sintering resistance hinder their large-scale application. Therefore, the rational design and development of highly selective non-noble metal hydrogenation catalysts is of great significance.

[0003] Nickel exhibits noble metal-like hydrogenation activity and has been applied to the hydrogenation of various biomass diffractions, such as phenol, furfural, and fatty acids. More importantly, the cost of nickel (¥0.15 / g) is significantly lower than that of noble metals like platinum (¥191.39 / g). Although Ni-catalyzed hydrogenation reduction of fatty acids to fatty alcohols shows good catalytic activity, there are no reports of Ni-based catalysts catalyzing below 200℃. At higher reaction temperatures, while Ni catalytic activity is enhanced, it tends to follow a decarbonylation / decarboxylation reaction pathway, yielding nC... N-1Alkanes, rather than fatty alcohols, are produced. Studies have shown that modifying the charge and coordination environment of Ni sites by forming Ni-M alloys or Ni-M intermetallic compounds (M = Fe, Mo, Sn, and In) can effectively suppress decarbonylation / decarboxylation reactions and C / C bond cleavage. Based on this concept, Ni-Fe intermetallic compounds (Ni / Fe atomic molar ratio 1 / 1) were embedded in a mesoporous carbon array to catalyze the selective hydrogenation of stearic acid to stearyl alcohol. The reaction was carried out at 250 °C and 5 MPa H₂ for 5 h, achieving 100% stearic acid conversion and 98% stearyl alcohol selectivity. This was attributed to the synergistic effect between Ni and Fe. DFT simulation results indicate that suitable Ni-H bond forces and the strong affinity of Fe for carbonyl oxygen are key to high stearyl alcohol selectivity. Ni-In intermetallic compounds (Ni / In atomic molar ratio 1 / 1.3) were used in a fixed-bed reactor at 270 °C and 3.5 MPa H₂ to catalyze the hydrogenation of methyl palmitate to palmitol, with a WHSV of 1.2 h. -1 A 100% conversion of methyl palmitate and a 94.8% selectivity for palmitol were achieved. However, the high reaction temperature limits the further application of these two intermetallic compound catalysts. Jun Ni modulates the Ni site charge density by adjusting the oxygen hole concentration on the ZrO2 surface, resulting in an abundant Ni on the Ni / ZrO2 catalyst surface. δ- -O V -Zr 3+ The interface sites, in turn, greatly enhance the charge density on the d orbitals of Ni sites. A reaction at 240℃ and 4MPa for 1 h yielded a stearic acid conversion of 7.47% and a stearyl alcohol selectivity of 93.5%. Although extending the reaction time to 37 h improved the stearic acid conversion to 93.77%, it significantly reduced the stearyl alcohol selectivity to 26.5%, while simultaneously increasing nC. 17 Selectivity up to 64.6%.

[0004] As can be seen above, anchoring nano-Ni uniformly onto a support with abundant surface sites through strong intermetallic forces, and suppressing its sintering or agglomeration during high-temperature calcination reduction and reactions, is an effective method. In addition, transition metal carbides (TMCs) have attracted research interest in recent years due to their high mechanical strength and thermal stability. Among various transition metal carbides, molybdenum carbide (Mo2C) possesses advantages such as green and controllable synthesis, a platinum-like d-band electronic structure, and superior performance. However, due to its poor H2 adsorption and dissociation capabilities and slow interfacial reaction rate, the catalytic selective hydrogenation activity of pure Mo2C is far from satisfactory, and a reaction temperature above 350℃ is required to initiate the hydrogenation reaction. An effective method is to modify Mo2C with transition metals M (M = Pt, Ni, and Co, etc.) to weaken the Mo2C-H bond strength, increase the generation rate of active H species during the reaction, and thus improve catalytic activity. Chemically coupling Ni and Mo₂C at the nanoscale to achieve strong intermetallic interactions between Ni and Mo₂C is beneficial for reducing the binding energy of active hydrogen species on the catalyst surface, thereby achieving thermal and kinetic equilibrium between the adsorption and desorption of active hydrogen species and promoting enhanced catalytic activity. However, the synthesis of Mo₂C catalysts is complex, and the preparation of Mo₂C often involves expensive reagents such as molybdenum hexacarbonyl. Furthermore, the preparation of Mo₂C-based materials is usually carried out at high temperatures (650°C) and uses expensive and explosive CH₄ as a carbon source, posing potential safety concerns. Therefore, developing new strategies to prepare Mo₂C catalysts under mild conditions using inexpensive and readily available biomass as a carbon source is of great significance.

[0005] Using citric acid, a renewable resource, to prepare carbon quantum dots (CQDs) offers advantages such as abundant reserves, low cost, good biocompatibility, and environmental friendliness. Furthermore, CQDs possess a unique electronic structure and high specific surface area, making them an excellent renewable carbon source. In addition, the abundant functional groups (-OH, -COOH, -NH2) on the surface of CQDs are conducive to the formation of metal ions (M... δ+ A strong M-shaped relationship is formed between CQDs. δ+ -Ideal coordination sites for CQDs coordination. Strong M δ+ The coordination of CQDs effectively suppresses the uncontrolled growth of metal nanoparticles between CQDs. To date, most reports on CQDs have focused on their fluorescence properties and their use as metal-free promoters to enhance photocatalytic performance. There are few reports on using CQDs as a green substitute for CH4 for the synthesis of Mo2C-based materials. Therefore, using CQDs as a carbon source to synthesize Mo2C-based materials, chemically coupling nano-Ni and Mo2C at the nanoscale, and thus achieving strong intermetallic interactions between Ni and Mo2C, provides a new method for constructing highly efficient Ni / Mo2C-type catalysts for the selective hydrogenation of fatty acids.

[0006] Therefore, a low-cost hydrothermal process using CQDs as a carbon source was employed to prepare Ni / Mo2C@CQDs catalysts via temperature-programmed reduction at lower temperatures for the selective hydrogenation of fatty acid methyl esters. Results showed that at a mass ratio of 1:5 (Ni / Mo2C@CQDs catalyst to fatty acid methyl ester), at 180℃ and 4 MPa H2 for 18 hours, a methyl stearate conversion of 98.8% and a stearyl alcohol selectivity of 95.7% were achieved. This performance surpasses that of most noble metal catalysts reported to date. Furthermore, the catalysts were used to selectively hydrogenate non-edible bio-oils such as jatropha oil and waste edible oils to fatty alcohols, achieving conversion rates of 92.4% and 87.1%, and total selectivity of the target products of 86.5% and 81.7%, respectively. Such Ni-based catalysts exhibiting high fatty acid hydrogenation activity at low reaction temperatures have not been previously reported. In-situ XRD patterns confirmed the formation of strong Ni-Mo2C interactions, and in-situ XPS spectroscopy revealed changes in these strong interactions during the reduction process. Thanks to the strong interaction between Ni and Mo2C, the electron transfer rate from Mo2C to Ni is significantly improved, and the charge density of Ni sites is greatly enhanced, thereby promoting the dissociation of H2 at low temperature. The electron-deficient Mo2C has a strong adsorption effect on carbonyl oxygen with lone pair electrons, promoting the adsorption and activation of C=O bonds and accelerating the C=O hydrogenation reaction rate.

[0007] Furthermore, the Ni / Mo2C@CQDs catalyst, by increasing the reaction temperature to 220℃, can also catalyze the hydrodeoxygenation of fatty acid methyl esters, yielding high-carbon-conversion, high-carbon-content advanced hydrocarbon fuels. The Ni / Mo2C@CQDs catalyst and the reactant fatty acid methyl ester are added to the reactor at a mass ratio of 1:5, and then a pressure of 3.5 MPa is introduced. H2 was reacted at 220℃ for 8 hours. After separating the catalyst, the resulting liquid product was hydrocarbon fuel: the hydrodeoxygenation of methyl decanoate yielded a 96.5% selectivity for decane, methyl laurate yielded a 96.1% selectivity for dodecane, methyl myristate yielded a 95.9% selectivity for tetradecane, methyl palmitate yielded a 96.3% selectivity for hexadecane, and methyl stearate yielded a 94.7% selectivity for octadecane. The conversion rates of these hydrodeoxygenation reactions were all greater than 95%. The hydrodeoxygenation of jatropha oil yielded a 94.7% conversion rate, producing a mixture of tetradecane, hexadecane, and octadecane with a total molar yield of 91.5%. The reaction of waste cooking oil yielded a 93.4% conversion rate, producing a mixture of tetradecane, hexadecane, and octadecane with a total molar yield of 89.6%. All of the above reactions reduced the reaction temperature and H2 pressure of existing catalytic fatty acid methyl ester hydrodeoxygenation to hydrocarbon fuels technology, achieving the goal of improving product yield by Ni / Mo2C@CQDs catalytic hydrodeoxygenation of fatty acid methyl esters to hydrocarbon fuels under mild conditions. Summary of the Invention

[0008] The purpose of this invention

[0009] This invention aims to provide a method for selectively hydrogenating fatty acid methyl esters to prepare long-chain fatty alcohols, or for hydrogenating and deoxygenating them to obtain high-carbon, green, advanced hydrocarbon fuels, using Ni / Mo2C@CQDs catalysts under mild conditions.

[0010] Technical solution of the present invention

[0011] The method for selective hydrogenation / hydrodeoxygenation of fatty acid methyl esters catalyzed by Ni / Mo2C@CQDs is as follows:

[0012] (1) The fatty acid methyl ester is any one of methyl decanoate, methyl laurate, methyl myristate, methyl palmitate, and methyl stearate; the fatty acid methyl ester is also derived from inedible natural oils such as jatropha oil or waste cooking oils from catering.

[0013] The Ni / Mo2C@CQDs catalyst and the reactants, fatty acid methyl esters, jatropha oil, or waste cooking oil, were added to the reactor at a mass ratio of 1:5. Then, 4 MPa of H2 was introduced, and the reaction was carried out at 180°C for 18 hours. After separating the catalyst, the resulting liquid product was the long-chain fatty alcohol, as detailed below:

[0014] 1) Ni / Mo2C@CQDs catalyzed the selective hydrogenation of methyl decanoate to decanol with a selectivity of 81.7%, the selective hydrogenation of methyl laurate to laurol with a selectivity of 87.9%, the selective hydrogenation of methyl myristate to myristol with a selectivity of 90.2%, the selective hydrogenation of methyl palmitate to palmitol with a selectivity of 94.3%, and the selective hydrogenation of methyl stearate to stearyl alcohol with a selectivity of 95.7%. The conversion rates of all of them were greater than 95%.

[0015] 2) The selective hydrogenation of jatropha oil catalyzed by Ni / Mo2C@CQDs yielded jatropha oil with a conversion rate of 92.4%. The product was a mixture of tetradecanol, hexadecyl alcohol, and octadecyl alcohol, with a total selectivity of 87.1%. The selectivities of tetradecanol, hexadecyl alcohol, and octadecyl alcohol were 5.6%, 11.7%, and 69.8%, respectively.

[0016] 3) Ni / Mo2C@CQDs catalyzes selective hydrogenation of waste cooking oil to obtain waste cooking oil with a reaction conversion rate of 86.5%. The product is a mixture of tetradecyl alcohol, hexadecyl alcohol, and octadecyl alcohol, with a total selectivity of 81.7%, of which the selectivities of tetradecyl alcohol, hexadecyl alcohol, and octadecyl alcohol are 1.7%, 37.3%, and 42.7%, respectively.

[0017] Reactions 1), 2), and 3) above all reduce the reaction temperature and H2 pressure of existing catalytic hydrogenation of fatty acid methyl esters to prepare fatty alcohols, thus achieving the goal of selective hydrogenation of fatty acid methyl esters to prepare long-chain fatty alcohols under mild conditions.

[0018] (2) The Ni / Mo2C@CQDs catalyst and the reactant fatty acid methyl ester were added to the reactor at a mass ratio of 1:5. Then, 3.5 MPa H2 was introduced, and the reaction was carried out at 220°C for 8 hours. After separating the catalyst, the resulting liquid product was hydrocarbon fuel, as detailed below:

[0019] 1) The selectivity of Ni / Mo2C@CQDs for the hydrodeoxygenation of methyl decanoate to decane is 96.5%, the selectivity of the hydrodeoxygenation of methyl laurate to dodecane is 96.1%, the selectivity of the hydrodeoxygenation of methyl myristate to tetradecane is 95.9%, the selectivity of the hydrodeoxygenation of methyl palmitate to hexadecane is 96.3%, and the selectivity of the hydrodeoxygenation of methyl stearate to octadecane is 94.7%. The conversion rates of these hydrodeoxygenation reactions are all greater than 95%.

[0020] 2) The conversion rate of jatropha oil hydrodeoxygenation reaction catalyzed by Ni / Mo2C@CQDs was 94.7%, and the product was a mixture of tetradecane, hexadecane and octadecane, with a total molar yield of 91.5%.

[0021] 3) Ni / Mo2C@CQDs catalyzed the reaction of waste cooking oil with a conversion rate of 93.4%, and the product was a mixture of tetradecane, hexadecane and octadecane, with a total molar yield of 89.6%.

[0022] Reactions 1), 2), and 3) above all reduce the reaction temperature and H2 pressure of existing catalytic fatty acid methyl ester hydrodeoxygenation to prepare hydrocarbon fuels, thus achieving the goal of preparing high-carbon hydrocarbon fuels by catalytic fatty acid methyl ester hydrodeoxygenation and carbon conversion under mild conditions.

[0023] (3) The Ni / Mo2C@CQDs catalyst is prepared by using renewable carbon quantum dots (CQDs) as carbon source support, utilizing the hydrothermal solubility of carbon quantum dots, Ni ions and molybdate ions, through hydrothermal chelation, polymerization, dialysis, centrifugation and freeze drying to first obtain the Ni / Mo2C@CQDs catalyst precursor, and then by temperature-programmed reduction.

[0024] This avoids the use of expensive, flammable, and explosive CH4 to prepare Mo2C carbon source carriers that require high-temperature calcination above 650℃ and have poor stability.

[0025] The carbon quantum dots have a large number of oxygen-containing functional groups -OH and -COOH on their surface, thus avoiding the need to pretreat the carbon source carrier material with concentrated nitric acid to generate oxygen-containing functional groups -OH and -COOH on the surface, which would otherwise produce acidic wastewater.

[0026] Utilizing the hydrothermal solubility of carbon quantum dots, Ni ions, and molybdate ions, the numerous oxygen-containing functional groups -OH and -COOH on the surface of carbon quantum dots react with Ni. 2+ and Mo7O 24 6- Mo in 6+ Sufficient chelation avoids the need for the expensive and inconvenient glove box to impregnate the supported Ni metal with unstable Mo2C in traditional methods, and then obtain the catalyst precursor through polymerization, dialysis, centrifugation and freeze drying, thus avoiding the agglomeration of Ni and Mo2C nanoparticles during the subsequent calcination reduction of the catalyst precursor.

[0027] The catalyst precursor is reduced in hydrogen gas at a programmed temperature of 500°C, forming a strong Ni-Mo2C interaction in the catalyst to obtain a Ni / Mo2C@CQDs catalyst. This reduces the reduction temperature of more than 650°C required by existing technologies to prepare Mo2C type catalysts in a CH4 / H2 mixed atmosphere.

[0028] The specific steps for preparing Ni / Mo2C@CQDs catalysts are as follows:

[0029] 1) Dissolve 1.0507 g of citric acid in 20 mL of double-distilled water. After dissolution, transfer the solution to a 100 mL polytetrafluoroethylene hydrothermal reactor and heat at 200 °C for 5 hours. Citric acid dehydrates and polymerizes to form carbon quantum dots. Then cool to 25 °C and transfer the reaction solution to a dialysis bag for dialyzing with double-distilled water to remove unreacted citric acid and oligomers with a molecular weight of less than 2000. Dialyze at 25 °C for 2 days, changing the double-distilled water every 8 hours. Transfer the dialyzed reaction solution to a centrifuge tube and centrifuge at high speed to remove large particulate impurities precipitated in the reaction solution. Place the centrifuged liquid in a freeze dryer at -20 °C for 24 hours. The dark brown solid powder obtained after drying is carbon quantum dots (CQDs).

[0030] The specifications of the dialysis bag are as follows: cellulose dialysis bag, molecular weight cutoff 500-1000, flat width 24mm, and unit length volume 1.8mL / cm.

[0031] The high-speed centrifugation involves centrifuging at 12,000 rpm for 30 minutes to remove large particulate impurities precipitated in the reaction solution. These large particulate impurities are polymers with a molecular weight exceeding 10,000 formed by excessive polymerization of citric acid under hydrothermal conditions at 200°C. If the centrifugation speed exceeds 15,000 rpm, carbon quantum dots will precipitate.

[0032] 2) Dissolve 1 gram of carbon quantum dots in 100 mL of double-distilled water to obtain a carbon quantum dot solution concentration of 10 mg / mL. Then add 0.9 mmol Ni(CH3COO)2·4H2O and 0.76 mmol (NH4)6Mo7O respectively. 24 After slowly stirring until completely dissolved, the resulting solution was transferred to a hydrothermal reactor and heated at 200°C for 6 hours. After natural cooling, it was centrifuged at 8000 rpm for 30 minutes. The resulting dark brown precipitate was washed three times with double-distilled water and anhydrous ethanol, respectively. After drying in an oven at 80°C for 12 hours, the resulting solid powder was placed in a tube furnace and a hydrogen-nitrogen mixture containing 20% ​​H2 and 80% N2 was introduced. The temperature was programmed to rise to 500°C for 4 hours at a rate of 5°C / min. The resulting silvery-white solid powder is the Ni / Mo2C@CQDs catalyst, with a Ni mass content of 10%.

[0033] The physicochemical properties of the prepared carbon quantum dots are as follows: average particle size 3.84 nm, height not exceeding 5 nm, no obvious lattice fringes, and amorphous carbon nano-ellipsoidal particles; the carbon quantum dots exhibit a series of infrared characteristic peaks: 3385 cm⁻¹ -1 (C-OH stretching vibration), 2923cm -1 and 2851cm -1 (CH stretching vibration), 1632cm -1 (CO / C=O stretching vibration), 1585cm -1 (C=C stretching vibration / benzene ring skeleton vibration), 1416cm -1 and 1466cm -1 (CC stretching vibration), 1026cm -1 and 1123cm -1 (CH in-plane bending vibration) indicates that the carbon quantum dot surface has aromatic structures and oxygen-containing functional groups, which facilitate chelation with Ni and molybdate ions in aqueous solution. This prevents molybdate ions from decomposing and agglomerating into larger MoO3 nanoparticles during catalyst reduction, thereby promoting Mo… 6+ Xiang Mo 2+ The reduction of (Mo2C); the UV-Vis absorption spectrum of carbon quantum dots shows maximum UV absorption peaks at 228 and 342 nm, which are attributed to the π→π* transition of the C=C double bond on the aromatic ring and sp, respectively. 2 The n→π* transition of the hybrid C=O double bond, when 0.02 mg·mL -1 When the aqueous solution of carbon quantum dots is excited by 365nm ultraviolet light, the carbon quantum dots exhibit strong blue fluorescence, showing obvious photoinduced blue fluorescence emission characteristics, with the center of the fluorescence peak located at 490nm.

[0034] The physicochemical properties of the prepared Ni / Mo2C@CQDs catalyst are as follows:

[0035] The catalyst exhibits a type IV isothermal adsorption-desorption curve, with a distinctly steep H1-type hysteresis loop in the relative pressure range of P / P0 = 0.4–0.9, indicating that the catalyst possesses a uniformly distributed mesoporous structure with a narrow pore size distribution. Some of the catalyst's physicochemical properties are shown in Tables 1 and 2.

[0036] Table 1

[0037]

[0038] a Specific surface area b At a specific pore volume of P / P0 = 0.99, c Average aperture determined by the BJH method, d ICP-OES measurement, e H2 chemisorption measurement of Ni nanoparticle dispersion on catalyst surface f The amount of Ni-H species on the catalyst surface determined by H2-TPD within the temperature range of 50–300℃

[0039] Table 2

[0040]

[0041] a Based on NH3-TPD calculations, b Weak (<250℃), Medium (250~500℃), Strong (>500℃) c Calculated based on Py-FTIR

[0042] In-situ XRD characterization of the catalyst revealed characteristic diffraction peaks of the β-Mo2C phase at 34.4°, 38.0°, 39.5°, 52.2°, 61.8°, 69.6°, 72.6°, 74.8°, and 75.8°. These peaks belong to the (100), (002), (101), (102), (110), (103), (200), (112), and (201) crystal planes of the β-Mo2C phase, respectively. Compared with the standard card of pure β-Mo2C, the peak positions of these β-Mo2C phases shifted to higher angle regions, indicating that some Ni entered the β-Mo2C lattice and caused lattice distortion, forming a strong Ni-Mo2C inter-phase force. In addition, there were weak Ni-Mo characteristic diffraction peaks, but no obvious Ni-Mo2C inter-phase forces. 0 The characteristic diffraction peaks indicate that strong Ni-Mo2C and weak Ni-Mo interactions are formed within the catalyst, thereby inhibiting the agglomeration and sintering of Ni nanoparticles during the high-temperature reduction process.

[0043] H2-TPD characterization of the catalyst showed that there were many Ni-H species on the catalyst surface. The characteristic diffraction peak was located at 97℃, indicating that the catalyst has the ability to dissociate H2 at low temperature to generate active H. A broad peak was observed at 284℃, which was attributed to the desorption of chemically adsorbed H species (Mo2C-H) on Mo2C nanoparticles. The contents of Ni-H species and Mo2C-H species in the catalyst were 167.9 and 53.5 μmol / g, respectively.

[0044] In-situ XPS spectroscopy of the catalyst indicates that Ni exposed on the catalyst surface 0 Percentage 76.37%; Mo in the catalyst 2+ The binding energy is 227.64 eV. After introducing Ni, the Mo in the catalyst... 2+ The binding energy increased to 228.88 eV, indicating that Mo2C in the catalyst lost electrons and Ni... 0 The catalyst gains electrons, forming a strong Ni-Mo2C interaction, resulting in the formation of a large amount of Ni on the catalyst surface. δ --Mo2C δ+ Interfacial sites; the enhanced charge density of Ni sites in the catalyst not only improves its ability to generate active hydrogen through low-temperature dissociation, but also promotes the hydrogenation conversion of aliphatic aldehyde intermediates into alcohol products, rather than generating C through direct decarbonylation. N-1 Product: This is because, unlike normal Ni nanoparticles that homogenize upon adsorption and dissociation of H2 to produce two H· particles, Ni nanoparticles with excess charge density heterogenize H2 upon adsorption and dissociation to produce active H, thus generating a single H· particle. + And an H - H + It reacts with the -OH (O=C-OH) in the carboxyl functional group of the fatty acid intermediate to produce water, or combines with CH3O- in the fatty acid methyl ester to form methanol and is thus removed. The remaining fatty aldehyde intermediate is then removed by H. - The attack generates fatty alcohol products; in addition, the electron-deficient Mo2C adsorbs the O atoms with lone pairs of electrons in the C=O bond of furfural, thereby promoting the adsorption and activation of the C=O bond.

[0045] Technical features and advantages of this invention

[0046] 1. Green and renewable carbon quantum dots are used as the carbon source carrier. Carbon quantum dots are inexpensive and easy to synthesize, making them an ideal alternative to CH4. In addition, the large number of oxygen-containing functional groups -OH and -COOH on the surface of carbon quantum dots avoids the need for pretreatment of carbon materials with concentrated nitric acid, thereby avoiding the generation of harmful wastewater.

[0047] 2. Utilizing the hydrothermal solubility of carbon quantum dots, Ni ions, and molybdate ions, a Ni / Mo2C@CQDs catalyst precursor is prepared through hydrothermal chelation, polymerization, dialysis, centrifugation, and freeze-drying. Then, it is reduced in hydrogen at a programmed temperature of 500℃ to obtain the Ni / Mo2C@CQDs catalyst. This avoids the need for a high-temperature reduction method above 650℃ to prepare the Mo2C carbon source support and the use of expensive glove box equipment for the operation of impregnating Mo2C with Ni active sites.

[0048] 3. In the hydrothermal process described in 2, due to the excellent water solubility of carbon quantum dots, Ni ions, and molybdate ions, the numerous oxygen-containing functional groups -OH and -COOH on the surface of carbon quantum dots can react with Ni. 2+ Mo7O 24 6- Mo in 6+ Sufficient chelation is achieved, thereby preventing the aggregation of Ni and Mo2C nanoparticles during high-temperature reduction.

[0049] 4. Under the conditions of Ni / Mo2C@CQDs catalyst and reactant fatty acid methyl esters (mass ratio 1:5), at 180℃ and 4MPa H2 for 18 hours, the selective hydrogenation of methyl decanoate to decyl alcohol yielded a selectivity of 81.7%, methyl laurate to lauryl alcohol 87.9%, methyl myristate to myristol 90.2%, methyl palmitate to palmitol 94.3%, and methyl stearate to stearyl alcohol 95.7%, all with conversion rates greater than 95%. The selective hydrogenation of jatropha oil yielded a 92.4% conversion rate, with a total selectivity of 87.1% for tetradecanol, hexadecyl alcohol, and octadecyl alcohol. The selective hydrogenation of waste cooking oil yielded an 86.5% conversion rate, with a total selectivity of 81.7% for tetradecanol, hexadecyl alcohol, and octadecyl alcohol. These reactions reduce the reaction temperature and H2 pressure of existing catalytic hydrogenation techniques for fatty acid methyl esters to prepare long-chain fatty alcohols, achieving the goal of selectively hydrogenating fatty acid methyl esters to prepare long-chain fatty alcohols under mild conditions.

[0050] 5. By increasing the reaction temperature to 220℃, the Ni / Mo2C@CQDs catalyst can also catalyze the hydrodeoxygenation of fatty acid methyl esters, yielding high carbon-to-carbon conversion and high carbon content green advanced hydrocarbon fuels. The hydrodeoxygenation of methyl decanoate yields a 96.5% selectivity for decane, methyl laurate yields a 96.1% selectivity for dodecane, methyl myristate yields a 95.9% selectivity for tetradecane, methyl palmitate yields a 96.3% selectivity for hexadecane, and methyl stearate yields a 94.7% selectivity for octadecane. All these hydrodeoxygenation reactions have conversion rates greater than 95%. The hydrodeoxygenation of jatropha oil yields a 94.7% conversion rate, with a total molar yield of a mixture of tetradecane, hexadecane, and octadecane products of 91.5%. The reaction of waste cooking oil yields a 93.4% conversion rate, with a total molar yield of a mixture of tetradecane, hexadecane, and octadecane products of 89.6%. These reactions reduce the reaction temperature and H2 pressure of existing catalytic fatty acid methyl ester hydrodeoxygenation to produce hydrocarbon fuels, achieving the goal of producing high-carbon, green, advanced hydrocarbon fuels through catalytic hydrodeoxygenation and decarbonization of fatty acid methyl esters under mild conditions. Detailed Implementation

[0051] The technical solution and implementation method of the present invention will be described below through embodiments, but the technical solution and implementation method of the present invention are not limited to the following embodiments.

[0052] Example 1: Preparation of catalyst Ni / Mo2C@CQDs and comparative catalyst Mo2C@CQDs

[0053] (1) Preparation of carbon quantum dots: 1.0507 g of citric acid was dissolved in 20 mL of double-distilled water. After dissolution, the solution was transferred to a 100 mL polytetrafluoroethylene hydrothermal reactor and heated at 200 °C for 5 hours. Citric acid was dehydrated and polymerized to form carbon quantum dots. The solution was then cooled to 25 °C and transferred to a dialysis bag for dialyzing with double-distilled water to remove unreacted citric acid and oligomers with a molecular weight less than 2000. Dialysis was continued at 25 °C for 2 days, with the double-distilled water changed every 8 hours. The dialyzed solution was transferred to a centrifuge tube and centrifuged at high speed to remove large particulate impurities precipitated in the solution. The centrifuged solution was then freeze-dried at -20 °C for 24 hours. The resulting dark brown solid powder was carbon quantum dots (CQDs). The specifications of the dialysis bag were: cellulose dialysis bag, molecular weight cutoff 500-1000, flat width 24 mm, and unit length volume 1.8 mL / cm. The high-speed centrifugation involves centrifuging at 12,000 rpm for 30 minutes to remove large particulate impurities precipitated in the reaction solution. These large particulate impurities are polymers with a molecular weight exceeding 10,000 formed by excessive polymerization of citric acid under hydrothermal conditions at 200°C. If the centrifugation speed exceeds 15,000 rpm, carbon quantum dots will precipitate.

[0054] (2) Dissolve 1 gram of carbon quantum dots in 100 mL of double-distilled water to obtain a carbon quantum dot solution concentration of 10 mg / mL. Then add 0.9 mmol Ni(CH3COO)2·4H2O and 0.76 mmol (NH4)6Mo7O respectively. 24 Slowly stir to dissolve. After complete dissolution, transfer the resulting solution to a hydrothermal reactor and heat at 200°C for 6 hours. After natural cooling, centrifuge at 8000 rpm for 30 minutes. Wash the resulting dark brown precipitate three times with double-distilled water and anhydrous ethanol, respectively. Dry in an oven at 80°C for 12 hours. Place the resulting solid powder in a tube furnace and purge with a hydrogen-nitrogen mixture containing 20% ​​H2 and 80% N2. Reduce the temperature to 500°C for 4 hours at a rate of 5°C / min. The resulting silvery-white solid powder is the Ni / Mo2C@CQDs catalyst, with a Ni mass content of 10%.

[0055] (3) Prepare comparative catalyst Mo2C@CQDs according to the steps (1) and (2) above, but do not add Ni(CH3COO)2·4H2O in step (2) above.

[0056] Example 2: Transmission electron microscopy (TEM) characterization of the prepared carbon quantum dots showed that the carbon quantum dots were uniformly dispersed with an average particle size of 3.84 nm. The carbon quantum dots exhibited no obvious lattice fringes and were amorphous carbon nanoparticles. Atomic force microscopy (AFM) characterization showed that the carbon quantum dots had a height of no more than 5 nm and were ellipsoidal. Fourier transform infrared spectroscopy characterization showed that the carbon quantum dots exhibited a series of characteristic infrared peaks, including those at 3385 cm⁻¹. -1 (C-OH stretching vibration), 2923cm -1 and 2851cm -1 (CH stretching vibration), 1632cm -1 (CO / C=O stretching vibration), 1585cm -1 (C=C stretching vibration / benzene ring skeleton vibration), 1416cm -1 and 1466cm -1 (CC stretching vibration), 1026cm -1 and 1123cm -1 (CH in-plane bending vibration) indicates that the carbon quantum dot surface has aromatic structures and oxygen-containing functional groups, which facilitates chelation with Ni and molybdate ions in aqueous solution and prevents molybdate ions from decomposing and agglomerating into larger MoO3 nanoparticles during catalyst reduction, thereby promoting Mo… 6 + Xiang Mo 2+Reduction of (Mo2C); UV-Vis absorption spectroscopy characterization of carbon quantum dots showed that there were maximum UV absorption peaks at 228 and 342 nm, which were attributed to the π→π* transition of the C=C double bond on the aromatic ring and the sp transition, respectively. 2 The n→π* transition of the hybrid C=O double bond, when 0.02 mg·mL -1 When the aqueous solution of carbon quantum dots is excited by 365nm ultraviolet light, the carbon quantum dots exhibit strong blue fluorescence, showing obvious photoinduced blue fluorescence emission characteristics, with the center of the fluorescence peak located at 490nm.

[0057] Example 3: The Ni / Mo2C@CQDs catalyst exhibits a type IV isothermal adsorption-desorption curve and a distinctly steep H1-type hysteresis loop within the relative pressure range of P / P0 = 0.4 to 0.9, indicating that the catalyst has a uniformly distributed mesoporous structure with a narrow pore size distribution.

[0058] Table 3. Physical property data of Ni / Mo2C@CQDs prepared at different calcination temperatures

[0059]

[0060] a Specific surface area b At a specific pore volume of P / P0 = 0.99, c Average aperture determined by the BJH method, d ICP-OES measurement, e H2 chemisorption measurement of Ni nanoparticle dispersion on catalyst surface f Based on the amount of Ni-H species on the catalyst surface determined by H2-TPD within the temperature range of 50–300℃, g Used catalyst.

[0061] As can be seen from Table 1, the physical property data of Ni / Mo2C@CQDs calcined at 500℃ are the best.

[0062] Example 4: In-situ XRD patterns of Ni / Mo2C@CQDs prepared at different reduction temperatures reveal the effect of reduction temperature on the catalyst crystal structure and crystal phase transition: During the reduction stage from 25 to 200 °C, no obvious diffraction peaks were observed. As the reduction temperature increased to 300–400 °C, two weak and broad peaks appeared at 37.9 °C and 43.4 °C, which are attributed to face-centered cubic α-MoC. 1-x Nanoparticles (JCPDS:15-0457); reduction temperature increased to 500℃, α-MoC 1-xThe XRD diffraction peaks corresponding to the nanoparticles disappeared rapidly, while characteristic diffraction peaks of the β-Mo2C phase appeared. These peaks were at 34.4°, 38.0°, 39.5°, 52.2°, 61.8°, 69.6°, 72.6°, 74.8°, and 75.8° (JCPDS: 35-0787), belonging to the (100), (002), (101), (102), (110), (103), (200), (112), and (201) crystal planes of the β-Mo2C phase, respectively. Compared with the standard card of pure β-Mo2C, the peak positions of these β-Mo2C phases shifted to the higher angle region, indicating that some Ni entered the β-Mo2C lattice and caused lattice distortion, forming a strong Ni-Mo2C inter-phase force. In addition, there were weak Ni-Mo characteristic diffraction peaks, but no obvious Ni-Mo2C inter-phase forces. 0 Characteristic diffraction peaks indicate that at 500℃, reduction leads to the formation of strong Ni-Mo2C and weak Ni-Mo intermetallic forces within the catalyst, thereby inhibiting the agglomeration and sintering of Ni nanoparticles during high-temperature reduction. As the reduction temperature increases to 600–800℃, the strong Ni-Mo2C intermetallic forces weaken, with new peaks appearing at 30.1°, 40.8°, 43.2°, and 45.4°. Peaks at 30.1° and 45.4° belong to the MoNi4 alloy phase, while peaks at 40.8° and 43.2° belong to Ni-Mo intermetallic compounds, indicating that the surface structure of Mo2C is disrupted, and the Mo content within Mo2C decreases. 2+ Further reduction to elemental Mo and formation of Ni-Mo alloys or Ni-Mo intermetallic compounds with elemental Ni, along with a significant increase in the intensity of the catalyst diffraction peaks, indicates that the corresponding species crystals grow and aggregate. These factors are not conducive to the selective hydrogenation of fatty acid methyl esters to fatty alcohols.

[0063] Example 5: In the catalytic hydrodeoxygenation reaction of biolipids, the metal active site adsorbs and dissociates H2 to generate active H+. * Attacking oxygen-containing functional groups (C=O, CO, C) Ar The ability of Ni-H species to dissociate H2 at low temperatures is closely related to the catalyst activity. H2-TPD characterization of the catalyst showed that there were many Ni-H species on the catalyst surface. The characteristic diffraction peak was located at 97℃, indicating that the catalyst has the ability to dissociate H2 at low temperatures to generate active H. A broad peak was observed at 284℃, which was attributed to the desorption of chemically adsorbed H species (Mo2C-H) on Mo2C nanoparticles. Compared with other reduction temperatures, the catalyst prepared at 500℃ had the highest content of Ni-H species and Mo2C-H species, at 167.9 and 53.5 μmol / g, respectively.

[0064] Example 6: In-situ XPS spectroscopy reveals the formation of strong Ni-Mo2C interactions and charge transfer processes within the catalyst: Ni was detected when the catalyst reduction temperature reached 200°C. 0(binding energy 853.27 eV), Mo 2+ The formation of (binding energy 229.26 eV) and the comparison of the Mo 3d spectra of the catalyst and Mo2C@CQDs in the low-temperature region indicate that the introduction of Ni significantly promotes the formation of Mo2C. The Ni-Mo2C interaction begins to form at relatively low catalyst reduction temperatures, and the Ni-Mo2C interaction, in turn, promotes the NiO→Ni conversion and the formation of Mo2C species. The Ni-Mo2C interaction increases the charge density of Ni sites in the catalyst, increases the ability to dissociate H2, and the more active hydrogen on the catalyst surface, the easier it is to convert Mo. 6+ Restored to Mo 2+ Mo2C is formed; as the reduction temperature and time of the catalyst increase, the number of Ni sites in the catalyst continuously increases. At 500℃ for 4 hours of reduction, the exposed Ni sites on the catalyst surface... 0 76.37% (based on peak fitting of the XPS spectrum of Ni element obtained after reduction at 500℃ for 4 hours, for Ni) 2+ Ni 0 The corresponding peak area integral calculation, Ni 0 The peak area accounts for 76.37%.

[0065] When the catalyst reduction temperature is increased from 200℃ to 500℃, Ni 0 The binding energy decreased from 853.27 eV to 852.03 eV in Ni / Mo2C@CQDs and Mo2C@CQDs. 2+ The binding energies decreased from 229.26 eV to 228.88 eV and from 228.81 eV to 227.64 eV, respectively, indicating that during the catalyst reduction process from 200 °C to 500 °C, Ni... 0 As electrons are continuously gained, the charge density increases, resulting in a total charge of 1.24 eV. This also means that Mo₂C loses the same total charge of 1.24 eV. Further comparison of Mo in Ni / Mo₂C@CQDs and Mo₂C@CQDs reveals… 2+ The difference in binding energy at 200℃ and 500℃ is as follows: at 200℃, the difference is 229.26-228.81=0.45eV, and at 500℃, the difference is 228.88-227.64=1.24eV. ​​This difference increases with increasing reduction temperature, indicating that the Ni-Mo2C charge transfer in the catalyst prepared by reduction at 500℃ is increased, and the Ni-Mo2C intermolecular forces are stronger. Furthermore, at a reduction temperature of 500℃, the Mo in the catalyst... 2+ The binding energy is 227.64 eV. After introducing Ni, the Mo in the catalyst... 2+ The binding energy increased to 228.88 eV, indicating that Mo2C in the catalyst lost electrons, and Ni... 0The catalyst gains electrons, forming a strong Ni-Mo2C interaction, resulting in the formation of a large amount of Ni on the catalyst surface. δ --Mo2C δ+ Interface sites.

[0066] The increased charge density at Ni sites in the catalyst not only enhances its ability to generate active hydrogen through low-temperature dissociation, but also promotes the hydrogenation conversion of aliphatic aldehyde intermediates into alcohol products, rather than generating C through direct decarbonylation. N-1 The product; this is because, unlike normal Ni nanoparticles that homogenize upon adsorption and dissociation of H2 to produce two H· particles, Ni nanoparticles with excess charge density heterogenize H2 upon adsorption and dissociation to produce active H, thus generating a single H· particle. + And an H - H + It reacts with the -OH (O=C-OH) in the carboxyl functional group of the fatty acid intermediate to produce water, or combines with CH3O- in the fatty acid methyl ester to form methanol and is thus removed. The remaining fatty aldehyde intermediate is then removed by H. - The attack generates fatty alcohol products; in addition, the electron-deficient Mo2C adsorbs the O atoms with lone pairs of electrons in the C=O bond of furfural, thereby promoting the adsorption and activation of the C=O bond.

[0067] Table 2 shows the characterization results of Ni / Mo2C@CQDs and Mo2C@CQDs using NH3-TPD and Py-FTIR in Example 7. The catalyst showed one strong peak at 133℃ indicating the desorption of NH3 at a weakly acidic site, and two weak peaks at 335℃ and 456℃ indicating the desorption of NH3 at moderately acidic sites. The number of acidic sites in the catalyst was 0.21 mmol / g (weak acid) and 0.008 mmol / g (moderately strong acid), respectively. Mo2C@CQDs showed two relatively strong NH3 desorption peaks in the moderate acidity site region, with the number of acidic sites being 0.13 mmol / g (weak acid) and 0.177 mmol / g (moderate acidity), respectively.

[0068] Table 4. Different acid sites and acid strengths of Ni / Mo2C@CQDs and Mo2C@CQDs

[0069]

[0070] a Based on NH3-TPD calculations, b Weak (<250℃), Medium (250~500℃), Strong (>500℃) c Calculated based on Py-FTIR.

[0071] In Example 8, the catalyst Ni / Mo2C@CQDs was reacted with the reactant fatty acid methyl esters at a mass ratio of 1:5, at 180°C, and at 4 MPa H2 for 18 hours. The selective hydrogenation of methyl stearate yielded stearyl alcohol with a selectivity of 95.7%, the selective hydrogenation of methyl decanoate yielded decanol with a selectivity of 81.7%, the selective hydrogenation of methyl laurate yielded lauryl alcohol with a selectivity of 87.9%, the selective hydrogenation of methyl myristate yielded myristyl alcohol with a selectivity of 90.2%, and the selective hydrogenation of methyl palmitate yielded palmitol with a selectivity of 94.3%. The conversion rates of all reactions were greater than 95%.

[0072] Example 9: The catalyst Ni / Mo2C@CQDs reacted with the natural oil Jatropha curcas oil in a mass ratio of 1:5 at 180°C and 4MPa H2 for 18 hours. The fatty acid methyl ester was derived from an inedible source. The selective hydrogenation reaction of Jatropha curcas oil catalyzed by Ni / Mo2C@CQDs achieved a conversion rate of 92.4%, and the product was a mixed alcohol of tetradecanol, hexadecylol, and octadecylol. The total selectivity of the mixed alcohol was 87.1%, with the selectivities of tetradecanol, hexadecylol, and octadecylol being 5.6%, 11.7%, and 69.8%, respectively.

[0073] In Example 10, the catalyst Ni / Mo2C@CQDs reacted with waste cooking oil in a mass ratio of 1:5 at 180°C and 4MPa H2 for 18 hours. The selective hydrogenation of waste cooking oil catalyzed by Ni / Mo2C@CQDs achieved a conversion rate of 86.5%, and the product was a mixed alcohol of tetradecanol, hexadecyl alcohol, and octadecyl alcohol. The total selectivity of the mixed alcohol was 81.7%, with the selectivities of tetradecanol, hexadecyl alcohol, and octadecyl alcohol being 1.7%, 37.3%, and 42.7%, respectively.

[0074] In Example 11, Ni / Mo2C@CQDs catalyst and fatty acid methyl ester were added to a reactor at a mass ratio of 1:5. H2 was then introduced at 3.5 MPa, and the reaction was carried out at 220°C for 8 hours. After separating the catalyst, the resulting liquid product was hydrocarbon fuel, specifically as follows: Ni / Mo2C@CQDs catalyzed the hydrodeoxygenation of methyl decanoate to decane with a selectivity of 96.5%; the hydrodeoxygenation of methyl laurate to dodecane with a selectivity of 96.1%; the hydrodeoxygenation of methyl myristate to tetradecane with a selectivity of 95.9%; the hydrodeoxygenation of methyl palmitate to hexadecane with a selectivity of 96.3%; and the hydrodeoxygenation of methyl stearate to octadecane with a selectivity of 94.7%. The conversion rates of these hydrodeoxygenation reactions were all greater than 95%.

[0075] In Example 12, Ni / Mo2C@CQDs catalyst and natural jatropha oil were added to a reactor at a mass ratio of 1:5. H2 was then introduced at 3.5 MPa, and the reaction was carried out at 220°C for 8 hours. After separating the catalyst, the resulting liquid product was hydrocarbon fuel. The conversion rate of the hydrodeoxygenation reaction of jatropha oil catalyzed by Ni / Mo2C@CQDs was 94.7%, and the product was a mixture of tetradecane, hexadecane, and octadecane, with a total molar yield of 91.5%.

[0076] In Example 13, Ni / Mo2C@CQDs catalyst and waste cooking oil from catering were added to a reactor at a mass ratio of 1:5. H2 was then introduced at 3.5 MPa, and the reaction was carried out at 220°C for 8 hours. After separating the catalyst, the resulting liquid product was hydrocarbon fuel. The conversion rate of waste cooking oil catalyzed by Ni / Mo2C@CQDs was 93.4%, and the product was a mixture of tetradecane, hexadecane, and octadecane, with a total molar yield of 89.6%.

Claims

1. A Ni / Mo2C@CQDs catalyst for the selective hydrogenation / hydrodeoxygenation of fatty acid methyl esters, characterized by: (1) The physicochemical properties of the Ni / Mo2C@CQDs catalyst are shown in Table 1 and Table 2: Table 1 D in Table 1 N i represents the dispersion of Ni nanoparticles on the catalyst surface, and Ni-H represents the species content of Ni-H species on the catalyst surface. Table 2 (2) The selective hydrogenation / hydrodeoxygenation of catalytic fatty acid methyl esters is carried out by adding the Ni / Mo2C@CQDs catalyst and the reactants fatty acid methyl esters, jatropha oil, or waste cooking oil to the reactor at a mass ratio of 1:5, then introducing 4MPa H2, reacting at 180°C for 18 hours, and separating the catalyst to obtain a long-chain fatty alcohol as the liquid product; the reaction conditions are changed to adding the Ni / Mo2C@CQDs catalyst and the reactants fatty acid methyl esters, jatropha oil, or waste cooking oil to the reactor at a mass ratio of 1:5, then introducing 3.5MPa H2, reacting at 220°C for 8 hours, and separating the catalyst to obtain a hydrocarbon fuel as the liquid product; the fatty acid methyl ester is any one of methyl decanoate, methyl laurate, methyl myristate, methyl palmitate, and methyl stearate; the fatty acid methyl ester is also derived from inedible natural oils such as jatropha oil or waste cooking oil from catering.

2. The Ni / Mo2C@CQDs catalyst for selective hydrogenation / hydrodeoxygenation of fatty acid methyl esters according to claim 1, characterized in that: Using renewable carbon quantum dots (CQDs) as the carbon source carrier, and leveraging the hydrothermal solubility of carbon quantum dots, Ni ions, and molybdate ions, a Ni / Mo2C@CQDs catalyst precursor was first prepared through hydrothermal chelation, polymerization, dialysis, centrifugation, and freeze-drying. Then, the Ni / Mo2C@CQDs catalyst was obtained through programmed temperature reduction. The specific steps are as follows: 1) Dissolve 1.0507 g of citric acid in 20 mL of double-distilled water. After dissolution, transfer the solution to a 100 mL polytetrafluoroethylene hydrothermal reactor and heat at 200 °C for 5 hours. The citric acid undergoes dehydration and polymerization to form carbon quantum dots. Then, cool to 25 °C and transfer the reaction solution to a dialysis bag for dialysis with double-distilled water to remove unreacted citric acid and oligomers with a molecular weight less than 2000. Dialyze at 25 °C for 2 days, changing the double-distilled water every 8 hours. Transfer the dialyzed reaction solution to centrifuge tubes. In the process, after removing large particulate impurities precipitated in the reaction solution by high-speed centrifugation, the centrifuged liquid is placed in a freeze dryer at -20℃ for 24 hours. The resulting dark brown solid powder is carbon quantum dots (CQDs). The specifications of the dialysis bag are: cellulose dialysis bag, molecular weight cutoff 500-1000, flat width 24mm, and unit length volume 1.8mL / cm. The high-speed centrifugation is performed at 12000rpm for 30 minutes to remove large particulate impurities precipitated in the reaction solution. These large particulate impurities are polymers with a molecular weight exceeding 10,000 formed by excessive polymerization of citric acid under hydrothermal conditions at 200℃. If the centrifugation speed exceeds 15000rpm, carbon quantum dots will precipitate. 2) Dissolve 1 gram of carbon quantum dots in 100mL of double-distilled water to obtain a carbon quantum dot solution concentration of 10mg / mL, and then add 0.9mmol Ni(CH3COO)2·4H2O and 0.76mmol (NH4)6Mo7O. 24 After slowly stirring until completely dissolved, the resulting solution was transferred to a hydrothermal reactor and heated at 200°C for 6 hours. After natural cooling, it was centrifuged at 8000 rpm for 30 minutes. The resulting dark brown precipitate was washed three times with double-distilled water and anhydrous ethanol, respectively. After drying in an oven at 80°C for 12 hours, the resulting solid powder was placed in a tube furnace and a hydrogen-nitrogen mixture containing 20% ​​H2 and 80% N2 was introduced. The temperature was programmed to rise to 500°C for 4 hours at a rate of 5°C / min. The resulting silvery-white solid powder is the Ni / Mo2C@CQDs catalyst.

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