CN110586081B - Palladium-carbon catalyst and preparation method and application thereof - Google Patents

Palladium-carbon catalyst and preparation method and application thereof Download PDF

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CN110586081B
CN110586081B CN201910850029.1A CN201910850029A CN110586081B CN 110586081 B CN110586081 B CN 110586081B CN 201910850029 A CN201910850029 A CN 201910850029A CN 110586081 B CN110586081 B CN 110586081B
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palladium
catalyst
carrier
carbon
solution
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CN110586081A (en
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王勇
吕国锋
马啸
毛善俊
王哲
于丽丽
李建清
王柳枫
李其川
鲍晓冰
陈宇卓
毛建拥
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Shandong Nhu Pharmaceutical Co ltd
Shandong Nhu Vitamin Co ltd
Shangyu Nhu Biochemical Industry Co ltd
Zhejiang University ZJU
Zhejiang NHU Co Ltd
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Shandong Nhu Pharmaceutical Co ltd
Shandong Nhu Vitamin Co ltd
Shangyu Nhu Biochemical Industry Co ltd
Zhejiang University ZJU
Zhejiang NHU Co Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B01J23/40—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals of the platinum group metals
    • B01J23/42—Platinum
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/30—
    • B01J35/60—
    • B01J35/61—
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/34—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation
    • B01J37/348—Electrochemical processes, e.g. electrochemical deposition or anodisation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00—Manufacture or treatment of nanostructures
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C29/00—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring
    • C07C29/17—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring by hydrogenation of carbon-to-carbon double or triple bonds
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C2601/00—Systems containing only non-condensed rings
    • C07C2601/12—Systems containing only non-condensed rings with a six-membered ring
    • C07C2601/16—Systems containing only non-condensed rings with a six-membered ring the ring being unsaturated

Abstract

The invention provides a preparation method of a palladium-carbon catalyst, and also provides the palladium-carbon catalyst prepared by the preparation method and application thereof. Compared with the prior art, the method has the advantages that the palladium ions adsorbed on the carrier are subjected to in-situ reduction through electrochemical in-situ reduction, compared with the traditional method of adding a reducing agent or electrochemical deposition, the preparation method is high in reduction speed, the metal palladium is flaky, more contact area is formed between the metal palladium and the carrier, the migration and falling of the palladium metal can be well prevented, the stability is high, the utilization rate of palladium atoms is high, the catalytic performance is good, meanwhile, the higher conversion rate and yield can be stably achieved without adding other metals on a catalyst, and the separation problem and the palladium metal recovery problem caused by the traditional preparation method are avoided.

Description

Palladium-carbon catalyst and preparation method and application thereof
Technical Field
The invention relates to the technical field of catalysts, in particular to a palladium-carbon catalyst and a preparation method and application thereof.
Background
The palladium-based catalyst is a general catalyst with wide application and good performance, has high catalytic activity and selectivity, is widely applied to the fields of petrochemical industry, chemical pharmacy, environmental protection engineering and the like, and can be used for the conversion of hydrocarbon compounds, such as catalytic hydrogenation and catalytic cracking. The palladium carbon catalyst loads noble metal palladium on active carbon, the active palladium is distributed on the surface of carrier carbon, and the internal palladium crystal is beneficial to prolonging the service life of an active agent of the catalyst.
The preparation of palladium on carbon catalysts generally involves pretreatment of the carbon support, impregnation of a palladium-containing solution, and reduction of the palladium. Wherein, the reduction of palladium can be reduced by a chemical reducing agent, or the palladium ions dissociating in the electrolyte are reduced and deposited by electrochemical plating deposition. However, in the reduction process of the chemical reducing agent, the palladium nanoparticles tend to aggregate, and the agglomeration phenomenon is serious, so that the catalytic activity of the palladium nanoparticles is influenced; the agglomerated palladium nano particles are easy to separate, and have poor stability, so that the loss of noble metal palladium is caused; the formed palladium nano-particles are basically surrounded by Pd (111) crystal faces, and the crystal faces are single and have poor catalytic performance. In the electrochemical plating deposition preparation, the formation of palladium metal crystals comprises the processes of metal ion migration and reduction, nucleation of metal atoms and nucleus growth, wherein the migrated metal ions can be reduced on the nucleated metal atoms, so that the nucleated palladium metal atoms grow and aggregate to form large-size granular nano particles, most of atoms are wrapped inside the nano particles, the metal atom utilization rate is low, the contact area between the granular nano particles and a carrier is small, the nano particles are easy to fall off, and poor catalyst stability and palladium metal loss are caused.
In addition, the conventional palladium-carbon catalyst inevitably introduces or generates other substances during the preparation process, which causes problems in separation and recovery of reaction products from additives or byproducts, and particularly, palladium metal is an expensive noble metal, which causes an increase in cost.
In conclusion, the traditional preparation method of the palladium-carbon catalyst is complex and faces the problems of easy agglomeration, easy shedding, poor stability, low utilization rate of palladium atoms, poor catalytic activity and difficult recovery.
Disclosure of Invention
The first technical problem to be solved by the present invention is to provide a method for preparing a palladium-carbon catalyst which is not easy to agglomerate and fall off, has high catalytic activity and high stability, and is easy to recover, aiming at the above-mentioned current state of the art.
The second technical problem to be solved by the present invention is to provide a palladium-carbon catalyst which is not easy to agglomerate and fall off, has high catalytic activity and high stability, and is easy to recover, in view of the above-mentioned current state of the art.
The third technical problem to be solved by the present invention is to provide an application of a palladium-carbon catalyst, which is not easily agglomerated and dropped off, has high catalytic activity and high stability, and is easily recycled, in catalytic hydrogenation reaction aiming at the current state of the prior art.
The technical scheme adopted by the invention for solving the first technical problem is as follows: the preparation method of the palladium-carbon catalyst comprises the following steps:
soaking a carrier into a palladium metal precursor solution to obtain a catalyst precursor, wherein the carrier is a carbon material;
and carrying out electrochemical in-situ reduction on the catalyst precursor in an alkaline electrolyte so that palladium ions are reduced into metal palladium to obtain the palladium-carbon catalyst.
In one embodiment, the alkaline electrolyte is at least one of potassium hydroxide, sodium hydroxide or calcium hydroxide, and the solution concentration of the alkaline electrolyte is 0.5 mol/L-3 mol/L.
Electrochemically reducing the catalyst precursor in situ comprises: and mixing the catalyst precursor and the blend in proportion and coating the mixture on a working electrode, wherein the mass ratio of the catalyst precursor to the blend is 1 (50-150).
In one embodiment, the blend is a perfluorosulfonic acid resin solution in which a perfluorosulfonic acid resin is dissolved in water and ethanol, wherein the mass ratio of the perfluorosulfonic acid resin to the water and ethanol is 1: (7.6-13.3): (200-600).
In one embodiment, the electrochemical in situ reduction comprises: under the action of alkaline electrolyte, the mixture of the catalyst precursor, the blend A and the blend B is coated on a working electrode, and an electrochemical hydrogen evolution test is carried out through a three-electrode system until a hydrogen evolution reaction occurs on the working electrode, and palladium ions are reduced into metal palladium under the action of hydrogen. The obtained catalyst precursor was substantially black powder.
In one embodiment, the working electrode of the three-electrode system comprises a glassy carbon electrode, the reference electrode comprises a calomel electrode, and the auxiliary electrode comprises a gold foil electrode.
In one embodiment, the step of immersing the carrier in a palladium metal precursor solution to obtain the catalyst precursor comprises: ultrasonically dispersing the carrier in water, soaking the carrier in a palladium metal precursor solution, ultrasonically dispersing the carrier uniformly to enable the carrier to fully adsorb a palladium-containing compound to obtain a catalyst precursor, repeatedly centrifuging the obtained catalyst precursor, ultrasonically washing the catalyst precursor until no palladium-containing compound exists in liquid, and drying the obtained catalyst precursor.
Preferably, the ultrasonic time is 20 minutes to 120 minutes, and the drying method comprises vacuum freeze drying, wherein the drying time is 4 hours to 24 hours.
In one embodiment, the preparation method further comprises pretreating a carrier, wherein the carrier comprises at least one of activated carbon, carbon nanotubes and carbon fibers, and it is understood that the carrier can be a carbon material doped with other elements, such as nitrogen-doped carbon material, in addition to a carbonaceous carrier. The pretreatment comprises the following steps:
acid treatment, dissolving the carrier in 0.1-5 mol/L acid solution, heating and refluxing for 4-12 hours at 70-100 ℃, and then washing with water to be neutral; and/or the presence of a catalyst in the reaction mixture,
heat treatment, the carrier is placed in an inert gas atmosphere to be calcined for 1 to 6 hours, and the calcination temperature is 600 to 1200 ℃; and/or the presence of a catalyst in the reaction mixture,
and (2) carrying out foaming treatment, namely mixing the carrier and an activating agent, calcining for 1-6 hours in an inert gas atmosphere at the calcining temperature of 500-1200 ℃, and then washing to be neutral.
In one embodiment, the acid solution is at least one of sulfuric acid, hydrochloric acid or nitric acid, the inert gas is at least one of nitrogen, helium and argon, the activating agent is at least one of sodium bicarbonate, potassium bicarbonate, ammonium bicarbonate and ammonium carbonate, and the mass ratio of the activating agent to the carrier is 1: (1-10).
In one embodiment, the palladium metal precursor solution is at least one of a palladium chloride solution, a palladium acetate solution and a palladium nitrate solution, and the palladium concentration in the palladium metal precursor solution is 0.01 g/ml to 1 g/ml.
The technical scheme adopted by the invention for solving the second technical problem is as follows: provides a palladium-carbon catalyst, which is prepared by the preparation method.
In one embodiment, the palladium-carbon catalyst comprises a carrier and palladium metal loaded on the carrier, wherein the palladium metal is attached to the surface of the carrier, and the loading thickness of the palladium metal is less than or equal to 2 nm.
Preferably, the supported thickness of the palladium metal is 1nm or less.
The technical scheme adopted by the invention for solving the third technical problem is as follows: the application of the palladium-carbon catalyst in catalytic hydrogenation reaction is provided, and the palladium-carbon catalyst is used as a catalyst in selective hydrogenation reaction of alkynol.
In one embodiment, the alkynol is at least one of 3, 7-dimethyl-9- (2 ', 6 ', 6 ' -trimethyl-1-cyclohexene) yl-2, 7-diene-4-yne-1, 6-diol, dehydroisophytol, 2-methyl-3-butyn-2-ol, and dehydrolinalool.
Compared with the prior art, the invention has the beneficial effects that:
(1) the preparation method comprises the steps of adsorbing palladium ions on a carrier, and then carrying out in-situ reduction on the palladium ions adsorbed on the carrier by utilizing electrochemical in-situ reduction, wherein the reduction speed of the preparation method is higher compared with that of the traditional method of adding a reducing agent or electrochemical deposition;
(2) under the initial voltage, a series of processes of ion exchange, reduction, dissociation and the like are carried out to form a series of hydroxyl, hydrogen ions and Pd (OH)XUnder the protection of the intermediates, palladium ions adsorbed on the carrier are reduced to form palladium sheets with different crystal faces such as Pd (111), Pd (200) and Pd (311). The palladium sheet is in a very thin sheet nano-shape, compared with the spherical particle-state nano-particles obtained by the traditional preparation method, the palladium sheet prepared by the preparation method has more contact area with the carrier, and can well prevent the migration and falling of palladium metal, so that the catalyst has higher stability in the reaction process;
(3) the palladium-carbon catalyst prepared by the traditional chemical reducing agent and electrochemical plating deposition method is easy to generate irregular aggregation, so that most of palladium atoms are wrapped in the nano particles, the atom utilization rate is low, and strong acting force exists between the palladium atomic nucleus formed in the preparation method and the defect position of the carrier, so that the palladium atoms grow along the plane of the carrier to form a flaky palladium structure;
(4) in addition, the palladium atom on the palladium-carbon catalyst prepared by the preparation method can expose more crystal faces, so that the palladium-carbon catalyst has better catalytic performance;
(5) in the catalytic hydrogenation reaction, due to the special crystal face structure and particle shape of the palladium-carbon catalyst, additives serving as poisoning agents are not required to be added in the reaction, and other metals are not required to be added on the catalyst, so that high conversion rate and yield can be stably achieved, and the problems of separation and palladium metal recovery caused by the traditional preparation method are avoided.
Drawings
FIG. 1 is a graph showing the application results of hydrogenation reaction 1 of palladium-carbon catalysts prepared in different examples;
FIG. 2 is a High Resolution Transmission Electron Micrograph (HRTEM) of Pd on C catalyst;
FIG. 3 is a high angle annular dark field image-scanning transmission electron image (HAADF-STEM) of palladium on carbon catalyst C;
FIG. 4 is another High Resolution Transmission Electron Microscopy (HRTEM) photograph of palladium on carbon catalyst C;
FIG. 5 is a High Resolution Transmission Electron Microscope (HRTEM) photograph and a Fourier transform photograph of palladium on carbon catalyst C;
fig. 6 is a high-resolution transmission electron microscope (HRTEM) photograph of palladium on carbon catalyst C.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
The invention provides a preparation method of a palladium-carbon catalyst. The preparation method comprises the following steps:
s1, preprocessing the carrier;
s2, soaking the carrier in a palladium metal precursor solution, cleaning and drying to obtain a catalyst precursor;
and S3, carrying out electrochemical in-situ reduction on the catalyst precursor so that palladium ions are reduced into metal palladium to prepare the palladium-carbon catalyst.
In the step S1, the carrier used for pre-treating the carrier includes at least one of activated carbon, carbon nanotubes and carbon fibers, and nitrogen-doped hierarchical pore carbon, and compared with a common carbon material, the nitrogen-doped carbon material has some unique advantages, such as that the nitrogen doping can change the local electronic structure of the carbon material, facilitate the dispersion of the noble metal nanoparticles, and improve the activity and stability of the catalyst through the interaction between nitrogen and metal.
The preprocessing in step S1 includes:
acid treatment, dissolving the carrier in 0.1-5 mol/L acid solution, heating and refluxing for 4-12 hours at 70-100 ℃, and then washing with water to be neutral; and/or the presence of a catalyst in the reaction mixture,
heat treatment, putting the carrier in an inert gas atmosphere to calcine for 1 to 6 hours, wherein the calcining temperature is 600 to 1200 ℃; and/or the presence of a catalyst in the reaction mixture,
and (2) carrying out foaming treatment, namely mixing the carrier and the activating agent, calcining for 1-6 hours in an inert gas atmosphere at the calcining temperature of 500-1200 ℃, and then washing to be neutral.
It can be understood that the surface of the carbon material after pretreatment exposes more defect sites, and strong force is generated between the palladium atomic nucleus formed in the preparation method and the defect sites of the carrier.
Preferably, the acid solution is at least one of sulfuric acid, hydrochloric acid or nitric acid, the inert gas is at least one of nitrogen, helium and argon, and the activator is at least one of sodium bicarbonate, potassium bicarbonate, ammonium bicarbonate and ammonium carbonate. Wherein the mass ratio of the activating agent to the carrier is 1: (1-10).
In step S2, the palladium metal precursor solution is at least one of a palladium chloride solution, a palladium acetate solution, and a palladium nitrate solution, and the palladium concentration in the palladium metal precursor solution is not limited without affecting the effect of the present invention, and is preferably 0.01 g/ml to 1 g/ml.
Specifically, step S2 includes ultrasonically dispersing the carrier in water, immersing the carrier in a palladium metal precursor solution, ultrasonically dispersing the carrier uniformly so that the carrier sufficiently adsorbs a palladium-containing compound to obtain a catalyst precursor, repeatedly centrifuging the obtained catalyst precursor, ultrasonically washing the catalyst precursor until the liquid is free of the palladium-containing compound, and drying the obtained catalyst precursor.
Preferably, the ultrasonic time is 20 minutes to 120 minutes, and the drying method comprises vacuum freeze drying, wherein the drying time is 4 hours to 24 hours.
In step S3, the electrochemical in-situ reduction includes coating the catalyst precursor on the working electrode under the action of an alkaline electrolyte, and performing an electrochemical hydrogen evolution test (HER) through a three-electrode system until a hydrogen evolution reaction occurs on the working electrode, and palladium ions are reduced to metallic palladium under the action of hydrogen. The obtained catalyst precursor was substantially black powder.
Preferably, the alkaline electrolyte is at least one of potassium hydroxide, sodium hydroxide or calcium hydroxide, and the solution concentration of the alkaline electrolyte is 0.5 mol/L-3 mol/L.
The working electrode of the three-electrode system comprises a glassy carbon electrode, the reference electrode comprises a calomel electrode, and the auxiliary electrode comprises a gold foil electrode.
Preferably, in electrochemical in situ reduction, the scanning is performed by linear sweep voltammetry (L SV) at a sweep rate of 1 mV/s to 100 mV/s, and/or,
the scanning frequency of the linear scanning voltammetry is 2-10 times.
Preferably, applying the catalyst precursor to the working electrode comprises: and mixing the catalyst precursor and the blend in proportion and coating the mixture on a working electrode, wherein the mass ratio of the catalyst precursor to the blend is 1 (50-150).
The blend is a perfluorinated sulfonic acid resin solution prepared by dissolving perfluorinated sulfonic acid resin in water and ethanol, wherein the mass ratio of the perfluorinated sulfonic acid resin to the water to the ethanol is 1: (7.6-13.3): (200-600).
Referring to fig. 2 to 6, the present invention further provides a palladium-carbon catalyst prepared by the above preparation method, wherein the palladium-carbon catalyst comprises a carrier and palladium metal loaded on the carrier, and the palladium metal is attached to the surface of the carrier. Preferably, the palladium metal is attached to the surface of the carrier in a sheet shape, and it can be understood that the palladium metal can be in a micro-nano sheet structure with uniform interval distribution, and can also be in an irregular shape with non-uniform interval distribution, which are all within the protection scope of the present invention.
The supported thickness of the palladium metal is not limited without affecting the precursor which does not affect the technical effect of the invention. Preferably, the supported thickness of the palladium metal is 2nm or less, and more preferably, the supported thickness of the palladium metal is 1nm or less.
Wherein the formation of palladium metal in a sheet form is accompanied by the reduction of a palladium metal precursor and the generation of hydrogen by hydrolysis, both reactions being carried out simultaneously. The specific process is as follows:
(1) at an initial voltage, the palladium metal precursor solution is subjected to ion exchange in an alkaline environment to form PdX6-y(OH)y 2-Hydroxide, wherein X is chloride ion, acetate ion or nitrate ion;
(2)PdX6-y(OH)y 2-the hydroxide is reduced to Pd (OH) by hydrogenyAnd metal Pd, and form Pd (OH)yPd boundary, and Pd (OH) formed at the same timeyThe dissociation of water is promoted to form a large amount of intermediate hydrogen ions and hydroxyl;
(3) the newly reduced palladium atoms are selectively deposited on the surface of the already formed palladium crystals, and Pd (OH)yPd (OH) formed by further reductiony-1OH adsorbed on low level surfaces-Will desorb and form vacant sites leading to the formation of more stepped atoms;
(4) the active substance is preferentially adsorbed on the stepped atoms, the palladium atoms subjected to reduction after induction are selectively deposited and grown, finally, a high-index surface is formed in the environment, and the palladium atoms subjected to reduction after the reduction are grown along the stepped atom surface to form the flaky nano sheet.
The invention also provides an application of the palladium-carbon catalyst in catalytic hydrogenation reaction, and the palladium-carbon catalyst is used as a catalyst in selective hydrogenation reaction of alkynol.
Preferably, the alkynol is at least one of 3, 7-dimethyl-9- (2 ', 6 ', 6 ' -trimethyl-1-cyclohexene) yl-2, 7-diene-4-yne-1, 6-diol, dehydroisophytol, 2-methyl-3-butyn-2-ol, and dehydrolinalool, and the alkynol used in the present invention is not limited thereto.
Compared with the prior art, the invention has the beneficial effects that:
(1) the preparation method comprises the steps of adsorbing palladium ions on a carrier, and then carrying out in-situ reduction on the palladium ions adsorbed on the carrier by utilizing electrochemical in-situ reduction, wherein the reduction speed of the preparation method is higher compared with that of the traditional method of adding a reducing agent or electrochemical deposition;
(2) under the initial voltage, a series of processes of ion exchange, reduction, dissociation and the like are carried out to form a series of hydroxyl, hydrogen ions and Pd (OH)XUnder the protection of the intermediates, palladium ions adsorbed on the carrier are reduced to form palladium sheets with different crystal faces such as Pd (111), Pd (200) and Pd (311). The palladium sheet is in a very thin sheet nano-shape, compared with the spherical particle-state nano-particles obtained by the traditional preparation method, the palladium sheet prepared by the preparation method has more contact area with the carrier, and can well prevent the migration and falling of palladium metal, so that the catalyst has higher stability in the reaction process;
(3) the palladium-carbon catalyst prepared by the traditional chemical reducing agent and electrochemical plating deposition method is easy to generate irregular aggregation, so that most of palladium atoms are wrapped in the nano particles, the atom utilization rate is low, and strong acting force exists between the palladium atomic nucleus formed in the preparation method and the defect position of the carrier, so that the palladium atoms grow along the plane of the carrier to form a flaky palladium structure;
(4) in addition, the palladium atom on the palladium-carbon catalyst prepared by the preparation method can expose more crystal faces, so that the palladium-carbon catalyst has better catalytic performance;
(5) in the catalytic hydrogenation reaction, due to the special crystal face structure and particle shape of the palladium-carbon catalyst, additives serving as poisoning agents are not required to be added in the reaction, and other metals are not required to be added on the catalyst, so that high conversion rate and yield can be stably achieved, and the problems of separation and palladium metal recovery caused by the traditional preparation method are avoided.
Further, the palladium-carbon catalyst prepared by the invention can be subjected to performance evaluation through the following catalytic reaction:
(1) reaction 1:
preparation of vitamin A intermediate 3, 7-dimethyl-9- (2 ', 6', 6 '-trimethyl-1-cyclohexene) yl-2, 7-diene-4-alkyne-1, 6-diol by hydrogenation of 3, 7-dimethyl-9- (2', 6 ', 6' -trimethyl-1-cyclohexene) yl-2, 4, 7-triene-1, 6-diol
The reaction equation is as follows:
Figure BDA0002196569740000091
the catalytic reaction process comprises the steps of adding 200g of dichloromethane into 50g of reaction substrate, adding 0.4g of catalyst, adding the mixture into a 500m L stainless steel reaction kettle, replacing air with nitrogen for 4 times, replacing nitrogen with hydrogen for 4 times, continuously introducing hydrogen and ensuring the hydrogen pressure to be 0.1-0.2 MPa, stirring and controlling the temperature to be 10-50 ℃, sampling and analyzing the composition of products after the reaction end point is reached, cooling, filtering and separating the catalyst, wherein the catalyst can be recycled.
(2) Reaction 2:
preparation of vitamin E intermediate isophytol by hydrogenation of dehydrogenated isophytol
The reaction equation is as follows:
Figure BDA0002196569740000092
the catalytic reaction process comprises the steps of adding 100g of dehydroisophytol into 100g of ethanol, adding 0.4g of catalyst, adding the mixture into a 500m L stainless steel reaction kettle, replacing air with nitrogen for 4 times, replacing nitrogen with hydrogen for 4 times, continuously introducing hydrogen and ensuring the hydrogen pressure to be 1.0-2.0 MPa, stirring and controlling the temperature to be 30-50 ℃, sampling and analyzing the composition of products after the reaction end point is reached, cooling, filtering and separating out the catalyst, wherein the catalyst can be recycled.
(3) Reaction 3:
2-methyl-3-butyne-2-alcohol hydrogenation for preparing 2-methyl-3-butene-2-alcohol
The reaction equation is as follows:
Figure BDA0002196569740000101
the catalytic reaction process comprises the steps of adding 50g of deionized water into 150g of 2-methyl-3-butyn-2-ol, adding 0.4g of catalyst, adding the mixture into a 500m L stainless steel reaction kettle, replacing air with nitrogen for 4 times, replacing nitrogen with hydrogen for 4 times, continuously introducing hydrogen, ensuring the hydrogen pressure to be 1.0-2.0 MPa, stirring, controlling the temperature to be 60-80 ℃, sampling and analyzing the composition of a product after the reaction end point is reached, cooling, filtering and separating the catalyst, and recycling the catalyst.
(4) Reaction 4:
hydrogenation preparation of linalool by dehydrolinalool
The reaction equation is as follows:
Figure BDA0002196569740000102
the catalytic reaction process comprises the steps of adding 100g of dehydrolinalool into 100g of ethanol, adding 0.4g of catalyst, adding the mixture into a 500m L stainless steel reaction kettle, replacing air with nitrogen for 4 times, replacing nitrogen with hydrogen for 4 times, continuously introducing hydrogen and ensuring the hydrogen pressure to be 1.0-2.0 MPa, stirring and controlling the temperature to be 30-50 ℃, sampling and analyzing the composition of products after the reaction end point is reached, cooling, filtering and separating out the catalyst, wherein the catalyst can be recycled.
(5) Reaction 5:
hydrogenation of 1, 4-butynediol to cis-1, 4-butenediol
The reaction equation is as follows:
Figure BDA0002196569740000103
the catalytic reaction process comprises the steps of adding 100g of 1, 4-butylene glycol into 100g of ethanol, adding 0.3g of catalyst, adding the mixture into a 500m L stainless steel reaction kettle, replacing air with nitrogen for 4 times, replacing nitrogen with hydrogen for 4 times, continuously introducing hydrogen, ensuring the hydrogen pressure to be 0.5-2.0 MPa, stirring, controlling the temperature to be 40-70 ℃, sampling and analyzing the composition of products after the reaction end point is reached, cooling, filtering and separating out the catalyst, and recycling the catalyst.
The catalytic hydrogenation reaction can be used for preparing intermediates of vitamin A, vitamin E and vitamin B6, the vitamin A, the vitamin E and the vitamin B6 are indispensable vitamins for human bodies, the important effect is achieved on the health and development of the human bodies, and the final cost of the medicine is directly determined by the yield and the selectivity of selective hydrogenation of the alkynol intermediates in the production of the vitamin A, the vitamin E and the vitamin B6.
The palladium-carbon catalyst of the present invention, its preparation method and application will be further described by examples.
Example 1
Weighing 1g of carbon nano tube, firstly carrying out acid treatment on the carbon nano tube, putting the carbon nano tube into 1 mol/L H of 50m L2SO4Heating and refluxing the mixture for 8 hours at the temperature of 80 ℃, cooling the mixture to room temperature, filtering the mixture to obtain black powder, and washing the black powder with deionized water for multiple times until the aqueous solution of the black powder becomes neutral. Then, the carbon nanotubes were subjected to heat treatment, and the black powder was calcined at 1000 ℃ for 2 hours in an atmosphere of high-purity nitrogen gas.
0.5g of the treated carbon nanotubes are weighed into 20m L deionized water, the mixture is subjected to ultrasonic treatment for 1 hour, and 0.05m L of PdCl is measured and added2The method comprises the following steps of carrying out ultrasonic treatment on a solution (the concentration of palladium is 0.05g/m L) for 1 hour, carrying out centrifugal separation, removing the solution, adding 20m L deionized water for washing, carrying out centrifugation, repeating the ultrasonic treatment for 5 times, collecting black powder, carrying out vacuum freeze drying for 12 hours to obtain a catalyst precursor, carrying out ultrasonic mixing on the collected black powder, 2.5m L perfluorosulfonic acid resin solution and 60m L ethanol for 60 minutes and uniformly mixing under a three-electrode system with an electrolyte of KOH solution of 1 mol/L, coating the mixture on a working electrode for an electrochemical hydrogen evolution test (HER), wherein the scanning rate of a linear scanning voltammetry (L SV) is 50mV/s, carrying out repeated scanning for 5 times, taking off black solids on the working electrode, carrying out filtration and washing for five times, wherein the obtained solids are the prepared palladium-carbon catalyst A, and the palladium loading (namely the mass fraction) is.
Example 2
This example is substantially the same as example 1, except that 0.1m L of PdCl was measured2Solution (palladium concentration 0.05g/m L) was prepared to give palladium on carbon catalyst B with a palladium loading of 1%.
Example 3
This embodiment is substantially the same as embodiment 1,the difference is that PdCl with the dosage of 0.15m L is measured2Solution (palladium concentration 0.05g/m L) was prepared to give palladium on carbon catalyst C with a palladium loading of 1.5%.
Example 4
This example is substantially the same as example 1, except that 0.2m L of PdCl was measured2Solution (palladium concentration 0.05g/m L) was prepared to give palladium on carbon catalyst D with a palladium loading of 2%.
Example 5
This example is substantially the same as example 1, except that 0.25m L of PdCl was measured2Solution (palladium concentration 0.05g/m L) was prepared to give palladium on carbon catalyst E with a palladium loading of 2.5%.
Example 6
This example is substantially the same as example 1, except that 0.05m L of PdCl was measured2Solution (palladium concentration 0.01g/m L) was prepared to give palladium on carbon catalyst F with a palladium loading of 0.1%.
Example 7
This example is substantially the same as example 1, except that 0.05m L of PdCl was measured2Solution (palladium concentration 1G/m L) was prepared to give palladium on carbon catalyst G with a palladium loading of 10%.
Example 8
This example is substantially the same as example 3 except that the carbon nanotubes were subjected to acid treatment by introducing 25m L of 4 mol/L HNO3And 4 mol/L of H of 25m L2SO4And (3) heating and refluxing the mixed solution at the temperature of 80 ℃ for 8 hours, cooling the mixed solution to room temperature, filtering the mixed solution to obtain black powder, washing the black powder with deionized water for multiple times until the aqueous solution of the black powder becomes neutral, and preparing the palladium-carbon catalyst H in the same way as in example 3.
Example 9
This embodiment is substantially the same as embodiment 3 except that: the carbon nanotube carrier of example 3 was directly subjected to heat treatment without acid treatment, and the palladium on carbon catalyst I was prepared as in example 3.
Example 10
This embodiment is substantially the same as embodiment 3 except that: and (2) carrying out foaming treatment on the carbon nanotube carrier in the embodiment 3, namely weighing 1g of carbon nanotube and 5g of ammonium bicarbonate, mixing the carbon nanotube and the ammonium bicarbonate uniformly, placing the mixture in a high-purity nitrogen atmosphere, heating the mixture to 1000 ℃, calcining the mixture for 2 hours, then washing the mixture to be neutral, and drying the mixture, wherein the palladium-carbon catalyst J is prepared by the same method as the embodiment 3.
Example 11
This embodiment is substantially the same as embodiment 3 except that: the carrier was changed to activated carbon, and the same procedure as in example 3 was repeated to prepare palladium on carbon catalyst K.
Example 12
This example is substantially the same as example 3 except that the carrier is replaced with carbon fiber, and a palladium on carbon catalyst L is prepared in the same manner as in example 3.
Example 13
This embodiment is substantially the same as embodiment 11 except that: the carrier was replaced with nitrogen-doped activated carbon, and palladium on carbon catalyst M was prepared as in example 11.
Example 14
This example is substantially the same as example 11, except that the palladium metal precursor solution was changed to a palladium acetate solution having a palladium solubility of 0.05g/m L, and the palladium on carbon catalyst N was prepared as in example 11.
Example 15
This example is substantially the same as example 11, except that the palladium metal precursor solution was changed to a palladium nitrate solution having a palladium solubility of 0.05g/m L, and a palladium on carbon catalyst O was prepared as in example 11.
Comparative example 1
Reducing by conventional chemical reduction method, weighing 1g carbon nanotube, adding 50m L H1 mol/L mol2SO4Heating at 80 deg.C for 8 hr, filtering, washing with deionized water to neutral, oven drying, measuring PdCl 0.2m L2The solution (palladium concentration 0.05g/m L) was added to 20m L deionized water, 0.5g of treated carbon nanotubes was added, and 14m L of NaBH was added4Ultrasonic treating the solution (10mg/m L) for 1 hour, centrifuging to remove the solution, washing with 20m L deionized water, centrifuging, repeating for 5 times, and oven drying at 40 deg.C for 12 hours to obtain catalyst P.
Comparative example 2
Reduction is carried out by electrochemical deposition method, wherein 1g of carbon nano-tube is weighed and added with 1 mol/L mol of H with 50m of L2SO4Heating at 80 deg.C for 8 hr, filtering, washing with deionized water to neutral, oven drying, weighing 0.5g treated carbon nanotube, 2.5m L perfluorosulfonic acid resin solution, 60m L ethanol, mixing and ultrasonic treating for 60min, mixing, coating on working electrode, adding 0.2m L PdCl into 1 mol/L KOH electrolyte2The solution (palladium concentration 0.05g/m L) was subjected to electrochemical hydrogen evolution test (HER) and repeatedly scanned 5 times, and the black solid on the working electrode was removed and washed with water by filtration five times, and the obtained solid was the catalyst prepared and the catalyst prepared was catalyst Q.
Experimental conclusion and analysis:
1) the results of the catalytic performance evaluation (reaction conversion and reaction yield) of each of the palladium on carbon catalysts obtained in the above examples 1 to 15, and comparative examples 1 and 2 were shown in table 1, with respect to the reactions 1 and 2.
TABLE 1
Figure BDA0002196569740000141
And (4) conclusion:
comparison of palladium loading: in examples 1 to 7, palladium metal precursor solutions with different palladium loadings are compared and subjected to electrochemical in-situ reduction in an alkaline electrolyte, respectively, so that in the intermediate hydrogenation catalytic reaction of the reaction 1 and the reaction 2, a palladium carbon catalyst with a palladium loading of 1.5-2% is better in catalytic effect.
Alignment of vector pretreatment: in the four methods of pretreating the carrier, the conversion rate and yield of the palladium-carbon catalyst obtained by pretreating the carrier by the foaming method are better in the example 3 in which the carrier is subjected to acid treatment by sulfuric acid, the example 8 in which the carrier is subjected to acid treatment by mixed acid of sulfuric acid and nitric acid, the example 9 in which the carrier is not subjected to acid treatment but is directly subjected to heat treatment, and the example 10 in which the carrier is treated by the foaming method. The pore channels of the carrier can be increased by processing the carrier by using a foaming method, so that the specific surface area of the carrier is enlarged, and palladium atoms have better dispersibility on the surface of the carrier.
Alignment to vector: in example 3, carbon nanotubes were selected as a carrier, in example 11, activated carbon was selected as a carrier, in example 12, carbon fibers were selected as a carrier, in example 13, nitrogen-doped activated carbon was selected as a carrier, and among the four palladium-carbon catalysts prepared by carrying different carriers, the palladium-carbon catalyst prepared by using carbon nanotubes as a carrier had the best conversion rate and yield. Meanwhile, referring to fig. 1, the number of times of applying the catalyst prepared by using the carbon nanotube as the carrier is more than that of the catalyst prepared by using the activated carbon as the carrier, which shows that the catalyst is more stable, and this is probably because the carbon nanotube carrier can expose more defect sites compared with other two carriers, so that the palladium atom has better dispersibility on the surface of the carrier, and the palladium atom and the carrier are more tightly combined, so that the catalyst has better activity and stability.
Comparing different types of palladium metal precursor solutions: in the embodiment 11, palladium chloride is selected as a palladium metal precursor, in the embodiment 14, palladium acetate is selected as a palladium metal precursor, in the embodiment 15, palladium nitrate is selected as a palladium metal precursor, and the three palladium carbon catalysts prepared from different palladium metal precursors have no obvious difference in reaction conversion rate and yield, which indicates that the three solutions can be used as precursor solutions of palladium metal in the method.
Comparison of preparation methods: compared with the traditional chemical reduction method and the electrochemical deposition method in the comparative example 1 and the comparative example 2, on the same palladium-loaded catalyst, the catalyst prepared by the electrochemical in-situ reduction method provided by the invention is obviously superior to the traditional preparation methods provided by the comparative examples 1 and 2 in conversion rate and yield.
2) The results of the catalytic performance evaluation (reaction conversion and reaction yield) of each of the palladium on carbon catalysts obtained in example 3, comparative example 1 and comparative example 2 were shown in Table 2, wherein reactions 3 and 4 were carried out.
TABLE 2
Figure BDA0002196569740000161
And (4) conclusion: the catalytic effect of the palladium-carbon catalysts prepared by electrochemical in-situ reduction in examples 3 and 13 is significantly better than that of the conventional chemical reduction and electrochemical deposition methods provided in comparative examples 1 and 2.
3) The hydrogenation reaction 1 was performed on each of the palladium on carbon catalysts obtained in the above examples 3, 9, 11 and 13, and the application results are shown in fig. 1.
Conclusion in examples 3, 9, 11, and 13, the number of times of applying the palladium-carbon catalyst prepared by electrochemical in-situ reduction is significantly better than that in comparative examples 1 and 2, which shows that the palladium-carbon catalyst prepared by the electrochemical in-situ reduction method provided by the present invention has better stability than the traditional chemical reduction and electrochemical deposition methods.
4) The palladium-carbon catalyst prepared in the above example 3 is characterized, and the characterization results are shown in fig. 2 to fig. 6:
it can be seen from fig. 3 that the palladium nanoparticles are obviously supported on the surface of the palladium-carbon catalyst;
fig. 2 and fig. 4 show that the palladium nanoparticles supported by the carbon nanotube carrier on the palladium-carbon catalyst C have different sheet structures;
from fig. 5, it is clearly observed that the surface of the palladium-carbon catalyst C has three different crystal planes (311) (200) (111).
It can be seen at the edge of the image of fig. 6 that the thickness of a part of the palladium nanosheet is only about 1nm, indicating that the palladium nanoparticle supported on the prepared palladium on carbon catalyst C is a nanosheet having a very thin thickness.
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims (9)

1. The preparation method of the palladium-carbon catalyst is characterized by comprising the following steps of:
soaking a carrier into a palladium metal precursor solution to obtain a catalyst precursor, wherein the carrier is a carbon material;
mixing the catalyst precursor and the blend according to a mass ratio of 1 (50-150), coating the mixture on a working electrode, and performing an electrochemical hydrogen evolution test on the catalyst precursor coated on the working electrode through a three-electrode system under the action of an alkaline electrolyte until a hydrogen evolution reaction occurs on the working electrode, wherein palladium ions are reduced into metal palladium under the action of hydrogen to obtain the palladium-carbon catalyst, wherein the blend is a perfluorinated sulfonic acid resin solution prepared by dissolving perfluorinated sulfonic acid resin in water and ethanol, and the mass ratio of the perfluorinated sulfonic acid resin to the water to the ethanol is 1: (7.6-13.3): (200-600).
2. The method of claim 1, wherein the alkaline electrolyte is at least one of potassium hydroxide, sodium hydroxide, and calcium hydroxide, and the solution concentration of the alkaline electrolyte is 0.5 mol/L-3 mol/L.
3. The method of preparing a palladium on carbon catalyst as recited in claim 1 further comprising pretreating the support, wherein the support comprises at least one of nitrogen-doped hierarchical pore carbon, activated carbon, carbon nanotubes and carbon fibers, the pretreating comprising:
acid treatment, dissolving the carrier in 0.1-5 mol/L acid solution, heating and refluxing for 4-12 hours at 70-100 ℃, and then washing with water to be neutral; and/or the presence of a catalyst in the reaction mixture,
heat treatment, the carrier is placed in an inert gas atmosphere to be calcined for 1 to 6 hours, and the calcination temperature is 600 to 1200 ℃; and/or the presence of a catalyst in the reaction mixture,
and (2) carrying out foaming treatment, namely mixing the carrier and an activating agent, calcining for 1-6 hours in an inert gas atmosphere at the calcining temperature of 500-1200 ℃, and then washing to be neutral.
4. The method of preparing a palladium-on-carbon catalyst according to claim 3, wherein the acid solution is at least one of sulfuric acid, hydrochloric acid or nitric acid, the inert gas is at least one of nitrogen, helium and argon, the activator is at least one of sodium bicarbonate, potassium bicarbonate, ammonium bicarbonate and ammonium carbonate, and the mass ratio of the activator to the support is 1: (1-10).
5. The method of claim 1, wherein the palladium metal precursor solution is at least one of a palladium chloride solution, a palladium acetate solution, and a palladium nitrate solution, and the palladium concentration in the palladium metal precursor solution is 0.01 g/ml to 1 g/ml.
6. A palladium-carbon catalyst, characterized by being prepared by the preparation method of any one of claims 1 to 5.
7. The palladium-carbon catalyst according to claim 6, wherein the palladium-carbon catalyst comprises a carrier and palladium metal loaded on the carrier, the palladium metal is attached to the surface of the carrier, and the loading thickness of the palladium metal is less than or equal to 2 nm.
8. Use of a palladium on carbon catalyst according to claim 6 or 7 as a catalyst in the selective hydrogenation of alkynols.
9. The use of a palladium on carbon catalyst in a catalytic hydrogenation reaction according to claim 8, wherein the alkynol is at least one of 3, 7-dimethyl-9- (2 ', 6 ', 6 ' -trimethyl-1-cyclohexene) yl-2, 7-diene-4-yne-1, 6-diol, dehydroisophytol, 2-methyl-3-butyn-2-ol, dehydrolinalool, and 1, 4-butynediol.
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