Ligand-modified supported palladium-based catalysts, methods of making and using the same

Abstract

The application belongs to the technical field of bio-energy and chemical industry, and particularly relates to a ligand-modified supported palladium-based catalyst, a preparation method and application thereof. The ligand-modified supported palladium-based catalyst is composed of an active component, a modified organic ligand and a carrier, wherein the active component is palladium nanoparticles; the modified organic ligand is at least one of ethylenediamine, methoxyethylamine, aminopropyltriethoxysilane, dodecyl mercaptan, tetradecyl mercaptan, hexadecyl mercaptan, octadecyl mercaptan, cyclopentyl mercaptan, cyclohexyl mercaptan, benzyl mercaptan or furfuryl mercaptan. The ligand-modified supported palladium-based catalyst is modified by a single-layer self-assembled organic ligand with controllable density, the adsorption mode of phenolic derivatives on the catalyst surface is controlled, and the catalyst has the advantages of high catalytic activity, high selectivity of target products, high stability and long catalyst service life.

Description

Technical Field

[0001] This invention belongs to the field of bioenergy chemical technology, specifically relating to a ligand-modified supported palladium-based catalyst, its preparation method, and its application. Background Technology

[0002] With the increasing depletion of fossil fuels globally, the development and utilization of biomass energy is an effective way to achieve sustainable development for human society. The essence of biomass energy is that plants store solar energy through photosynthesis using chemical bonds; the process of utilizing biomass energy is the process of releasing the solar energy stored in biomass. Biomass is mainly composed of cellulose, hemicellulose, and up to 30% lignin. In the resource utilization of biomass, lignin, as a non-food biomass, does not compete with the food chain and is an ideal source of renewable fuels and chemicals. Lignin is most similar to petroleum in composition, with an oxygen-to-carbon ratio between 0.32 and 0.46 and a hydrogen-to-carbon ratio between 1.1 and 1.3; while ordinary crude oil has an oxygen-to-carbon ratio of 0.03 and a hydrogen-to-carbon ratio between 1.6 and 2.1. Under completely oxygen-deficient or limited oxygen supply conditions, lignin undergoes rapid thermal cracking and depolymerization to obtain a large amount of brownish-red liquid product, namely bio-oil. Compared to traditional fossil fuels, bio-oils generally have drawbacks such as high kinematic viscosity, high water content, low calorific value, high oxygen content, and poor stability, making them unsuitable for direct use as fuel in internal combustion engines and resulting in low utilization efficiency. Therefore, it is essential to refine and improve the quality of bio-oils to enable them to replace traditional fossil fuels.

[0003] The main methods for refining and upgrading bio-oils include catalytic hydrogenation, catalytic cracking, catalytic esterification, and emulsification. Problems include poor selectivity of the target product, catalyst deactivation due to carbon buildup, and blockage of reaction equipment. Therefore, it is essential to explore new refining methods to improve the quality of bio-oils and make it possible for them to replace traditional fossil fuels on a large scale. Based on the composition and characteristics of bio-oils, they are pre-separated into oil-soluble and water-soluble phases through extraction. The oil-soluble phase is mainly composed of phenolic derivatives, while the water-soluble phase is mainly composed of carboxylic acid derivatives. Phenolic derivatives are one of the main reasons for the poor stability of bio-oils and are also the most difficult substances to convert during the refining and upgrading process. Therefore, the conversion of phenolic derivatives is particularly important in the refining and upgrading of bio-oils.

[0004] The hydrodeoxygenation of phenolic derivatives from bio-oils to produce aromatic compounds is an effective method for refining and upgrading bio-oils by minimizing hydrogen consumption and effectively reducing the oxygen content and improving the stability of the bio-oils. Highly active, selective, and stable catalysts are crucial for the targeted conversion of phenolic derivatives from bio-oils into aromatic compounds via hydrodeoxygenation. In traditional hydrodeoxygenation catalysts, phenolic derivatives preferentially adsorb horizontally onto the catalyst surface. Because the energy barrier for cyclohydrogenation is lower than that for CO bond breaking, cyclohydrogenation readily occurs first, generating cyclohexanols, which then further undergo CO bond breaking and dehydration to generate cyclohexanes. Currently reported catalyst systems generally exhibit over-hydrogenation, resulting in high selectivity for cyclohexanes but poor selectivity for the target aromatic compounds; furthermore, the catalysts deactivate after a period of reaction, leading to a significant decline in catalytic performance. How to achieve catalysts with high activity, high selectivity, and high stability remains a key technical challenge in this field.

[0005] Therefore, in order to overcome the above-mentioned defects of the existing technology and prepare a catalyst with high activity, high selectivity and high stability, this invention is proposed. Summary of the Invention

[0006] The purpose of this application is to provide a ligand-modified supported palladium-based catalyst. This catalyst exhibits high catalytic activity, high selectivity for the target product, high stability, and long catalyst lifetime. Furthermore, this invention also proposes its preparation method and applications.

[0007] The ligand-modified supported palladium-based catalyst of the present invention comprises an active component, a modified organic ligand, and a support. The active component is palladium nanoparticles; the modified organic ligand is at least one selected from ethylenediamine, methoxyethylamine, aminopropyltriethoxysilane, dodecyl mercaptan, tetradecyl mercaptan, hexadecyl mercaptan, octadecyl mercaptan, cyclopentyl mercaptan, cyclohexyl mercaptan, benzyl mercaptan, or furfuryl mercaptan; and the support is at least one selected from alumina, zinc oxide, magnesium oxide, zirconium oxide, cerium oxide, silicon oxide, titanium dioxide, activated carbon, Y molecular sieve, MCM-41 molecular sieve, 13X molecular sieve, ZSM-5 molecular sieve, carbon nanotubes, or graphene.

[0008] Preferably, the modified organic ligand is octadecyl mercaptan.

[0009] Preferably, the carrier is a Y molecular sieve; more preferably, the Y molecular sieve is at least one of sodium-type Y molecular sieve, hydrogen-type Y molecular sieve, or ammonium-type Y molecular sieve; even more preferably, the Y molecular sieve is a sodium-type Y molecular sieve.

[0010] The mass ratio of active component to carrier is 0.5-5:100.

[0011] The molar ratio of modified organic ligand to active component is 0.01-110:100.

[0012] The preparation method of the ligand-modified supported palladium catalyst of the present invention comprises the following steps:

[0013] (1) The palladium precursor was dissolved and dispersed in a solvent, and then subjected to ultrasonic and stirring treatment to obtain system I;

[0014] (2) Add the carrier to system I and stir until homogeneous to obtain system II;

[0015] (3) Heat system II obtained in step (2) until the solvent evaporates to dryness, and then calcine and reduce to obtain system III;

[0016] (4) The modified organic ligand was dissolved and dispersed in ethanol, and then subjected to ultrasonic and stirring treatment to obtain system IV;

[0017] (5) The system III obtained in step (3) is added to the system IV obtained in step (4) for impregnation and adsorption, and then separated and dried to prepare a ligand-modified supported palladium catalyst.

[0018] in:

[0019] The palladium precursor mentioned in step (1) is at least one of palladium acetate, palladium nitrate, palladium chloride, potassium hexachloropalladium, potassium tetrachloropalladium, palladium acetylacetone, dichlorodiamminepalladium, or dichlorotetraamminepalladium; preferably, the palladium precursor is palladium acetate.

[0020] The solvent mentioned in step (1) is at least one of water, methanol, ethanol, acetone, benzene, toluene, dichloromethane, chloroform, dimethyl sulfoxide, tetrahydrofuran or dimethylformamide; preferably, the solvent is acetone.

[0021] In step (1), the mass ratio of the palladium precursor to the volume ratio of the solvent is 0.1-3:1, with units of g / L.

[0022] In step (1), the dissolution and dispersion temperature is room temperature, the ultrasonic time is 0.5-3h, and the stirring time is 5-10h.

[0023] The mass ratio of palladium precursor to support is 1-20:100.

[0024] In step (3), the evaporation temperature is 50-150℃ and the evaporation time is 4-8h; the calcination temperature is 150-500℃ and the calcination time is 1-12h; the reduction temperature is 200-400℃ and the reduction time is 1-6h, and the reduction atmosphere is hydrogen.

[0025] In step (4), the dissolution and dispersion temperature is room temperature, the ultrasonic time is 0.5-1h, and the stirring time is 1-5h.

[0026] In step (5), the impregnation and adsorption temperature is room temperature, and the impregnation and adsorption time is 10-16 hours; the separation is centrifugal separation, and the centrifugation speed is 3000-6000 r / min; the drying temperature is 20-150℃, and the drying time is 1-12 h.

[0027] The application of the ligand-modified supported palladium-based catalyst of the present invention comprises the following steps: adding bio-oil rich in phenolic derivatives into a high-pressure reactor, using n-octane as a solvent and hexadecane as an internal standard, adding the ligand-modified supported palladium-based catalyst, and simultaneously introducing H2 reaction gas. Under the conditions of a reaction temperature of 100-400℃, a reaction pressure of 0.1-10MPa, and a reaction time of 1-10h, the phenolic derivatives in the bio-oil undergo a hydrodeoxygenation reaction to prepare aromatic compounds.

[0028] in:

[0029] The phenolic derivatives in bio-oils rich in phenolic derivatives are at least one of phenol, p-phenol, m-cresol, hydroquinone, nitrophenol, chlorophenol, guaiacol, or phenyl ether.

[0030] The mass ratio of bio-oil rich in phenolic derivatives to ligand-modified supported palladium catalyst is 1:0.2.

[0031] The mass ratio of bio-oil rich in phenolic derivatives to solvent is 1:50.

[0032] Preferably, the reaction temperature is 200-300℃, the reaction pressure is 3-8MPa, and the reaction time is 3-5 hours.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] (1) The ligand-modified supported palladium catalyst of the present invention modifies the adsorption mode of phenolic derivatives on the catalyst surface by modifying the monolayer self-assembled organic ligands with controllable density, and has the advantages of high catalytic activity, high selectivity of target products, high stability and long catalyst lifetime.

[0035] (2) The preparation method of the ligand-modified supported palladium catalyst of the present invention firstly involves uniformly dispersing the Pd precursor onto the surface of the support by impregnation, and then forming uniformly dispersed Pd nanoparticles on the support surface by drying, calcination, and reduction; secondly, taking advantage of the characteristic that -SH in alkyl thiols or -NH2 in silane coupling agents or alkyl ammonium readily coordinate with Pd, an array of alkyl thiols is formed on the surface of the Pd particles, forming a steric hindrance effect, which only allows phenolic substances to be adsorbed onto the surface of Pd particles in a vertical manner to undergo hydrogenation and deoxygenation reactions, and inhibits the horizontal adsorption of phenolic substances on the surface of Pd particles to undergo cyclohydrogenation side reactions.

[0036] (3) The application of the ligand-modified supported palladium-based catalyst of the present invention is to apply the catalyst to the reaction of hydrodeoxygenation of phenolic derivatives in bio-oil to prepare aromatic compounds. A single-layer self-assembled organic ligand array with controllable density is modified on the surface of the active component of the catalyst. The adsorption mode of phenolic derivatives on the surface of the active component of the catalyst is mainly vertical adsorption through confinement effect, so that the oxygen-containing groups in the phenolic derivatives are in direct contact with the active component of the catalyst, avoiding the contact between the benzene ring in the phenolic derivatives and the active component of the catalyst, effectively reducing the possibility of ring hydrogenation reaction, thereby realizing the control of reaction path, directional CO bond breaking reaction, and highly selective hydrodeoxygenation of phenolic derivatives to prepare aromatic compounds.

[0037] (4) The application of the ligand-modified supported palladium catalyst described in this invention has the advantages of high activity, high selectivity and high stability under the synergistic effect of palladium nanoparticles (activating H2) and monolayer self-assembled modified organic ligand array (confining effect) and the efficient catalytic effect of Bronsted acidic support to promote dehydration reaction. Attached Figure Description

[0038] Figure 1 The bar chart shows the results of investigating the conversion rate of phenol, the selectivity of benzene, cyclohexane, and cyclohexanol, and the stability of the number of cycles in the reaction of the catalyst CAT-1 prepared in Example 1 for the hydrodeoxygenation of phenolic derivatives in bio-oil to prepare aromatic compounds. Detailed Implementation

[0039] The present invention will be further described below with reference to embodiments.

[0040] Examples 1-13

[0041] The preparation method of the ligand-modified supported palladium-based catalyst described in Examples 1-13 consists of the following steps:

[0042] (1) A certain amount of palladium precursor was dissolved in 20 mL of solvent for dissolution and dispersion (dissolution and dispersion temperature was room temperature), and then subjected to ultrasonic treatment (ultrasonic time was 1.75 h) and stirring (stirring time was 7.5 h) to obtain system I;

[0043] (2) Add 1g of carrier and stir thoroughly to obtain system II;

[0044] (3) Heat the system II obtained in step (2) until the solvent evaporates to dryness, and then calcine and reduce (in a hydrogen atmosphere) to obtain system III;

[0045] (4) The modified organic ligand was added to 20 mL of ethanol for dissolution and dispersion (dissolution and dispersion temperature was room temperature), and then subjected to ultrasonic treatment (ultrasonic time was 0.75 h) and stirring (stirring time was 3 h) to obtain system IV;

[0046] (5) The system III obtained in step (3) is added to the system IV obtained in step (4) for impregnation and adsorption, and then separated (centrifuged at 4500 r / min) and dried to prepare the ligand-modified supported palladium catalyst.

[0047] Table 1. Detailed preparation conditions for Examples 1-13

[0048]

[0049]

[0050]

[0051] The elemental composition of catalysts CAT-1 to CAT-13 prepared in Examples 1-13 was determined using a JOBIN YVON ULTIMA 2 inductively coupled plasma atomic emission spectrometer (ICP) and an ELEMENTAR VARIO EL CUBE elemental analyzer (EA). The results are shown in Table 2.

[0052] Table 2. Elemental composition of catalysts prepared in Examples 1-13

[0053]

[0054]

[0055] The application of the ligand-modified supported palladium-based catalysts described in Examples 1-13 consists of the following steps: 0.2g of catalysts CAT-1 to CAT-13 are taken respectively, 1g of phenol and 50g of n-octane are placed in a high-pressure reactor, 5MPa H2 is introduced, the reaction temperature is 250℃, the reaction time is 4 hours, and hexadecane is used as an internal standard to evaluate the catalytic performance of phenol hydrogenation deoxygenation to benzene. The phenol conversion rate and product selectivity of catalysts CAT-1 to CAT-13 are detailed in Table 3.

[0056] The product was detected using an Agilent GC7890 gas chromatograph with an SE-30 column and an FID detector.

[0057] The conversion rate of phenol was calculated using the following method:

[0058] Phenol conversion rate (%) = ([phenol]) in -[phenol] out ) / [phenol] in ×100%

[0059] The selectivity of benzene was calculated using the following method:

[0060] Benzene selectivity (%) = [Benzene] out / ([benzene] out +[cyclohexane] out +[cyclohexanol] out )

[0061] The selectivity of cyclohexane was calculated using the following method:

[0062] Cyclohexane selectivity (%) = [Cyclohexane] out / ([benzene] out +[cyclohexane] out +[cyclohexanol] out )

[0063] The selectivity of cyclohexanol was calculated using the following method:

[0064] Cyclohexanol selectivity (%) = [cyclohexanol] out / ([benzene] out +[cyclohexane] out +[cyclohexanol] out )

[0065] Note: [Phenol] in ,[phenol] out These represent the concentrations of phenol before and after the reaction, respectively; [benzene] out [Cyclohexane] out [Cyclohexanol] out These represent the concentrations of the products benzene, cyclohexane, and cyclohexanol generated after the reaction.

[0066] The stability study results of catalyst CAT-1 are as follows: Figure 1 As shown, after five cycles, the conversion rate of phenol remained around 75%, and the selectivity of benzene was always greater than 80%, indicating that the catalyst has good stability.

[0067] Table 3. Phenol conversion and product selectivity of catalysts CAT-1 to CAT-13

[0068]

[0069]

[0070] In Example 2, no organic ligand modification was used. Since no spatial array was formed on the surface of the Pd nanoparticles, phenolic substances were more preferentially adsorbed on the surface of the Pd nanoparticles than in a planar manner. At this time, hydrogenation of the aromatic ring was more likely to occur, resulting in a decrease in the selectivity of hydrogenation deoxygenation products (such as benzene) and an increase in the selectivity of cyclohydrogenation byproducts (such as cyclohexane and cyclohexanol).

[0071] The acidity or basicity of the support has a significant impact on the efficiency and product distribution of the hydrogenation reaction of phenol. The stronger the acidity of the support, the higher the phenol conversion rate, the easier the deoxygenation reaction, and the higher the selectivity of benzene in the product.

[0072] By using -SH from alkyl thiols or -NH2 or alkylammonium from silane coupling agents to coordinate with Pd nanoparticles, a spatial array with a confinement effect is formed on the surface of Pd nanoparticles. This can promote the vertical adsorption of phenol on the catalyst surface, with the phenolic hydroxyl end adsorbed onto the surface of Pd nanoparticles, and the phenolic hydroxyl end undergoes a directional hydrogenation and deoxygenation reaction, inhibiting the aromatic ring hydrogenation side reaction and effectively improving the selectivity of benzene.

Claims

1. The application of a ligand-modified supported palladium-based catalyst, characterized in that: The ligand-modified supported palladium-based catalyst comprises an active component, a modified organic ligand, and a support. The active component is palladium nanoparticles. The modified organic ligand is at least one of ethylenediamine, methoxyethylamine, aminopropyltriethoxysilane, dodecyl mercaptan, tetradecyl mercaptan, octadecyl mercaptan, cyclopentane mercaptan, cyclohexane mercaptan, benzyl mercaptan, or furfuryl mercaptan. The support is at least one of alumina, zinc oxide, magnesium oxide, zirconium oxide, cerium oxide, silicon oxide, activated carbon, Y molecular sieve, MCM-41 molecular sieve, 13X molecular sieve, or ZSM-5 molecular sieve. Wherein: the mass ratio of active component to carrier is 0.5-5 : 100; the molar ratio of modified organic ligand to active component is 0.01-110 : 100; The application of the ligand-modified supported palladium catalyst comprises the following steps: adding bio-oil rich in phenolic derivatives into a high-pressure reactor, using n-octane as a solvent and hexadecane as an internal standard, adding the ligand-modified supported palladium catalyst, and simultaneously introducing H2 reaction gas. Under the conditions of a reaction temperature of 100-400 ℃, a reaction pressure of 0.1-10 MPa, and a reaction time of 1-10 h, the phenolic derivatives in the bio-oil undergo a hydrodeoxygenation reaction to prepare aromatic compounds.

2. The application of the ligand-modified supported palladium-based catalyst according to claim 1, characterized in that: The modified organic ligand is octadecyl mercaptan; the support is Y molecular sieve.

3. The application of the ligand-modified supported palladium-based catalyst according to claim 1, characterized in that: The preparation method of the ligand-modified supported palladium-based catalyst comprises the following steps: (1) The palladium precursor was added to a solvent for dissolution and dispersion, and then subjected to ultrasonic and stirring treatment to obtain system I; (2) Add the carrier to system I and stir until homogeneous to obtain system II; (3) Heat system II obtained in step (2) until the solvent evaporates to dryness, and then calcine and reduce to obtain system III; (4) The modified organic ligand was dissolved and dispersed in ethanol, and then subjected to ultrasonic and stirring treatment to obtain system IV; (5) The system III obtained in step (3) is added to the system IV obtained in step (4) for impregnation and adsorption, and then separated and dried to prepare a ligand-modified supported palladium catalyst.

4. The application of the ligand-modified supported palladium-based catalyst according to claim 3, characterized in that: The palladium precursor mentioned in step (1) is at least one of palladium acetate, palladium nitrate, palladium chloride, potassium hexachloropalladate, potassium tetrachloropalladate, palladium acetylacetone, dichlorodiamminepalladium, or dichlorotetraamminepalladium. The solvent mentioned in step (1) is at least one of water, methanol, ethanol, acetone, benzene, toluene, dichloromethane, chloroform, dimethyl sulfoxide, tetrahydrofuran, or dimethylformamide; In step (1), the mass ratio of the palladium precursor to the volume ratio of the solvent is 0.1-3:1, in g / L. In step (1), the dissolution and dispersion temperature is room temperature, the ultrasonic time is 0.5-3h, and the stirring time is 5-10h.

5. The application of the ligand-modified supported palladium-based catalyst according to claim 4, characterized in that: The palladium precursor is palladium acetate; the solvent is acetone.

6. The application of the ligand-modified supported palladium-based catalyst according to claim 3, characterized in that: The mass ratio of palladium precursor to support is 1-20:100; In step (3), the evaporation temperature is 50-150℃ and the evaporation time is 4-8h; the calcination temperature is 150-500℃ and the calcination time is 1-12h; the reduction temperature is 200-400℃ and the reduction time is 1-6h, and the reduction atmosphere is hydrogen.

7. The application of the ligand-modified supported palladium-based catalyst according to claim 3, characterized in that: In step (4), the dissolution and dispersion temperature is room temperature, the ultrasonic time is 0.5-1h, and the stirring time is 1-5h. In step (5), the impregnation and adsorption temperature is room temperature, and the impregnation and adsorption time is 10-16 hours; the separation is centrifugal separation, and the centrifugation speed is 3000-6000 r / min; the drying temperature is 20-150℃, and the drying time is 1-12h.

8. The application of the ligand-modified supported palladium-based catalyst according to claim 1, characterized in that: The phenolic derivatives in bio-oils rich in phenolic derivatives are at least one of phenol, p-phenol, m-cresol, hydroquinone, nitrophenol, chlorophenol, guaiacol, or phenyl ether. The mass ratio of bio-oil rich in phenolic derivatives to ligand-modified supported palladium catalyst is 1:0.2; The mass ratio of bio-oil rich in phenolic derivatives to solvent is 1:50.

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