CN116273135B - Nitrogen-doped oxide supported metal catalyst and preparation method and application thereof - Google Patents

Nitrogen-doped oxide supported metal catalyst and preparation method and application thereof Download PDF

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CN116273135B
CN116273135B CN202310561654.0A CN202310561654A CN116273135B CN 116273135 B CN116273135 B CN 116273135B CN 202310561654 A CN202310561654 A CN 202310561654A CN 116273135 B CN116273135 B CN 116273135B
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孙正宗
肖太师
曾事成
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Suzhou Xiangcheng District Qingzhi Intelligent Connected Vehicle Innovation Center
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Abstract

The invention relates to a nitrogen-doped oxide supported metal catalyst, and a preparation method and application thereof, and belongs to the technical field of formic acid hydrogen production catalysts. The method comprises the following steps: placing the oxide in a vacuum environment, introducing hydrogen, generating active hydrogen plasma by using a plasma generator to reduce the oxide, and cooling to obtain a modified oxide; preparing a complex solution from a metal salt solution, an organic ligand and a carbon source, adding a modified oxide, uniformly mixing, and sequentially performing heating treatment and calcination treatment to obtain a nitrogen-doped oxide supported metal catalyst; the organic ligand is 2,4, 6-tri (2-pyridine) -1,3, 5-triazine and/or dicyandiamide, and the carbon source is melamine and/or glucose. The high nitrogen doped oxide supported metal catalyst prepared by the invention obviously improves the catalytic activity of the catalyst, and can effectively inhibit the generation of carbon monoxide during the hydrogen production of formic acid due to high nitrogen doping content.

Description

Nitrogen-doped oxide supported metal catalyst and preparation method and application thereof
Technical Field
The invention belongs to the technical field of formic acid hydrogen production catalysts, and particularly relates to a nitrogen-doped oxide supported metal catalyst, and a preparation method and application thereof.
Background
Along with the development of science and technology and the continuous progress of society, energy consumption is also increasing, environmental problems such as greenhouse effect are serious due to the use of a large amount of fossil fuels, and people are promoted to search for novel renewable energy sources. The characteristics of high heat value, no pollution and the like of hydrogen are attracting great attention, and students focus on the research of hydrogen fuel cells so as to completely replace fossil fuels in future society.
Formic acid has relatively high hydrogen storage amount, is liquid at normal temperature and normal pressure, and has good safety and transportation feasibility. Therefore, the high-efficiency catalytic formic acid decomposition hydrogen storage hydrogen production has great potential for the field of hydrogen storage and transportation. The formic acid hydrogen production catalyst is mainly divided into two types, one is homogeneous and the other is heterogeneous. The homogeneous catalyst is mainly some metal complexes, such as ruthenium complex, and has large contact area, high activity, single catalyst structure, high selectivity and high reaction rate, but the catalyst is difficult to separate from formic acid, the reactor size is difficult to reduce, and the reaction device is complex in design. The heterogeneous catalyst mainly takes a metal catalyst, particularly a noble metal catalyst, such as a palladium-based catalyst and the like, has unique selectivity for generating hydrogen through formic acid decomposition, is easy to separate from formic acid, and the reaction device can be greatly simplified, thereby being beneficial to practical application; but heterogeneous catalysts suffer from low catalytic efficiency or higher carbon monoxide content in the resulting product.
In summary, it is highly necessary to provide a nitrogen-doped oxide supported metal catalyst, and a preparation method and application thereof.
Disclosure of Invention
In order to solve one or more technical problems in the prior art, the invention provides a nitrogen-doped oxide supported metal catalyst, and a preparation method and application thereof.
The present invention provides in a first aspect a method for preparing a nitrogen-doped oxide supported metal catalyst, the method comprising the steps of:
(1) Placing the oxide in a vacuum environment, then introducing hydrogen, generating active hydrogen plasma by using a plasma generator to reduce the oxide, and then cooling to obtain a modified oxide; when the reduction treatment is carried out, the flow rate of the introduced hydrogen is 10-20 sccm, and when the cooling treatment is carried out, the flow rate of the introduced hydrogen is 100-150 sccm, and the cooling rate is 30-50 ℃/min;
(2) Preparing a complex solution from a metal salt solution, an organic ligand and a carbon source, and then adding the modified oxide into the complex solution and uniformly mixing to obtain a complex solution; the organic ligand is 2,4, 6-tri (2-pyridine) -1,3, 5-triazine and/or dicyandiamide, and the carbon source is melamine and/or glucose;
(3) And sequentially carrying out heating treatment and calcination treatment on the composite solution to obtain the nitrogen-doped oxide supported metal catalyst.
Preferably, in step (1): the temperature of the reduction treatment is 500-1150 ℃, and the time of the reduction treatment is 10-120 min.
Preferably, the molar ratio of the metal ions contained in the metal salt solution, the organic ligand, and the amount of the carbon source is 1: (1.5 to 4): (8-15); the concentration of metal ions in the metal salt solution is 0.05-0.2 mol/L; and/or the complex solution adopts an ethanol water solution, wherein the ethanol water solution contains 40-60% of ethanol by volume.
Preferably, the complex solution contains 15-25% of the sum of the mass percentages of metal salt, organic ligand and carbon source; and/or the molar ratio of the modified oxide to the metal salt contained in the metal salt solution is (10-20): 1.
preferably, the organic ligand is 2,4, 6-tris (2-pyridine) -1,3, 5-triazine and the carbon source is melamine; or the organic ligand is dicyandiamide, and the carbon source is glucose.
Preferably, in the step (2), the mixing is performed in the following manner: stirring for 18-30 h at room temperature under the rotating speed of 100-800 r/min; the heating treatment is as follows: heating at 80-120 ℃ until the compound solution becomes solid; and/or the calcination treatment is: calcining at 400-600 ℃ for 2-4 hours, and then calcining at 700-1100 ℃ for 1-3 hours.
Preferably, the metal ions contained in the metal salt solution are one or more of iron ions, cobalt ions, nickel ions and palladium ions; and/or the oxide is one or more of titanium oxide, cerium oxide, zirconium oxide and aluminum oxide.
Preferably, the metal salt solution is a chloropalladite solution, and the pH of the chloropalladite solution is 0-2.
The present invention provides in a second aspect a nitrogen-doped oxide supported metal catalyst produced by the production process of the invention described in the first aspect.
The present invention provides in a third aspect the use of a nitrogen doped oxide supported metal catalyst prepared by the preparation method of the invention as described in the first aspect in the production of hydrogen from formic acid.
Compared with the prior art, the invention has at least the following beneficial effects:
(1) When the nitrogen-doped oxide supported metal catalyst is prepared, a complex solution formed by taking 2,4, 6-tris (2-pyridine) -1,3, 5-triazine and/or dicyandiamide as an organic ligand and melamine and/or glucose as a carbon source is coordinated with metal palladium to form a stable complex, and modified oxide is added to synthesize the high nitrogen-doped oxide supported metal catalyst, and compared with the conventional nitrogen-doped raw material, the nitrogen-doped metal catalyst obviously increases the nitrogen doping content and the metal loading capacity and obviously improves the activity and stability of a metal active center; in addition, the invention discovers that the high nitrogen doped oxide supported metal catalyst prepared by the invention can effectively inhibit the generation of carbon monoxide during the hydrogen production of formic acid due to high nitrogen doping content, and obviously reduces the content of carbon monoxide in the product.
(2) According to the nitrogen-doped oxide supported metal catalyst, reducing gas hydrogen is introduced into a vacuum environment, active hydrogen is excited by hydrogen plasma to reduce an oxide, and then rapid cooling treatment is carried out in a high-flow hydrogen atmosphere, so that the obtained modified oxide is used as a carrier, the nitrogen-doped oxide supported metal can be more effectively adsorbed in a pore channel of the modified oxide, the interaction between the modified oxide carrier and the metal catalyst can be enhanced, strong coordination can be carried out with metal ions, the effective load of the metal can be improved, and compared with the conventional oxide carrier, the catalyst can be more plastic and stable and is easy to separate, and meanwhile, the catalytic efficiency of the metal catalyst is more beneficial to being improved.
Drawings
FIG. 1 is a schematic illustration of hydrogen production from formic acid catalyzed by a nitrogen-doped black titania supported palladium catalyst made in accordance with some embodiments of the present invention;
FIG. 2 is an X-ray photoelectron spectrum of a black titanium oxide and a white titanium oxide (white titanium oxide powder P25) obtained in example 1 of the present invention;
FIG. 3 is a transmission electron microscopic image of a nitrogen-doped oxide supported metal catalyst (nitrogen-doped black titanium oxide supported palladium catalyst) obtained in example 1 of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be clearly and completely described below in connection with the embodiments of the present invention. It will be apparent that the described embodiments are some, but not all, embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The present invention provides in a first aspect a method for preparing a nitrogen-doped oxide supported metal catalyst, the method comprising the steps of:
(1) Placing the oxide in a vacuum environment, then introducing hydrogen, generating active hydrogen plasma by using a plasma generator to reduce the oxide, and then cooling to obtain a modified oxide; when the reduction treatment is carried out, the flow rate of the introduced hydrogen is 10-20 sccm, when the cooling treatment is carried out, the flow rate of the introduced hydrogen is 100-150 sccm, the cooling rate is 30-50 ℃/min (for example, 30 ℃/min, 35 ℃/min, 40 ℃/min, 45 ℃/min or 50 ℃/min), and the cooling rate is 30-50 ℃/min and the temperature is reduced to the room temperature; in the invention, the room temperature is, for example, 15-35 ℃; in the invention, the pressure of the vacuum environment can be controlled to be 30-500 Pa; the power of the plasma generator is 80-150W, for example; specifically, for example, oxide powder or oxide microspheres are subjected to washing, impurity removal and drying, then placed in a vacuum environment, then hydrogen is introduced into the vacuum environment, and meanwhile, active hydrogen plasma generated by a plasma generator is used for carrying out reduction treatment on the oxide powder, so that the vacancy concentration on the surface of the oxide is regulated and controlled in an auxiliary manner, the forbidden band width of the oxide can be regulated, and a proper modified oxide is obtained;
(2) Preparing a complex solution from a metal salt solution, an organic ligand and a carbon source, and then modifying an oxide in the complex solution and uniformly mixing to obtain a complex solution; the organic ligand is 2,4, 6-tri (2-pyridine) -1,3, 5-triazine (TPTZ) and/or dicyandiamide (alias: dicyandiamide), and the carbon source is melamine and/or glucose; in the present invention, the metal salt solution is, for example, a metal salt aqueous solution; in the invention, for example, an ethanol water solution with the volume ratio of ethanol to water of 1:1 is adopted to uniformly mix a metal salt solution, an organic ligand and a carbon source for 2-4 hours at room temperature (for example, the room temperature is 15-35 ℃) under the rotating speed of 100-800 r/min, so as to prepare a complex solution; the present invention is not particularly limited, and the sum of the mass percentages of the metal salt, the organic ligand, and the carbon source contained in the complex solution may be, for example, 15 to 25%; the sources of 2,4, 6-tris (2-pyridine) -1,3, 5-triazine (TPTZ), dicyandiamide, melamine or glucose and the like are not particularly limited, and products which can be purchased in the market or synthesized by the existing method can be adopted;
(3) Sequentially carrying out heating treatment and calcination treatment on the composite solution to obtain a nitrogen-doped oxide supported metal catalyst; in the present invention, the heat treatment means that the complex solution is slowly evaporated to dryness into a solid state at a certain temperature; the calcination treatment is, for example, a two-step calcination in an inert atmosphere.
When the nitrogen-doped oxide supported metal catalyst is prepared, a complex solution formed by taking 2,4, 6-tris (2-pyridine) -1,3, 5-triazine and/or dicyandiamide as an organic ligand and melamine and/or glucose as a carbon source is coordinated with metal palladium to form a stable complex, and modified oxide is added to synthesize the high nitrogen-doped oxide supported metal catalyst, and compared with the conventional nitrogen-doped raw material, the nitrogen-doped metal catalyst obviously increases the nitrogen doping content and the metal loading capacity and obviously improves the activity and stability of a metal active center; in addition, the invention discovers that the high nitrogen doped oxide supported metal catalyst prepared by the invention has high nitrogen doping content, can effectively inhibit the generation of carbon monoxide during the hydrogen production of formic acid, and obviously reduces the content of carbon monoxide in the product; according to the nitrogen-doped oxide supported metal catalyst, reducing gas hydrogen is introduced into a vacuum environment, active hydrogen is excited by hydrogen plasma to reduce an oxide, and then rapid cooling treatment is carried out in a high-flow hydrogen atmosphere, so that the obtained modified oxide is used as a carrier, the nitrogen-doped oxide supported metal can be more effectively adsorbed in a pore channel of the modified oxide, the interaction between the modified oxide carrier and the metal catalyst can be enhanced, strong coordination can be carried out with metal ions, the effective load of the metal can be improved, and compared with the conventional oxide carrier, the catalyst can be more plastic and stable and is easy to separate, and meanwhile, the catalytic efficiency of the metal catalyst is more beneficial to being improved.
According to some preferred embodiments, in step (1): the temperature of the reduction treatment is 500 to 1150 ℃ (e.g., 500 ℃, 550 ℃, 600 ℃, 650 ℃, 700 ℃, 750 ℃, 800 ℃, 850 ℃, 900 ℃, 950 ℃, 1000 ℃, 1050 ℃, 1100 ℃, or 1150 ℃), the time of the reduction treatment is 10 to 120min (e.g., 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, or 120 min), more preferably the temperature of the reduction treatment is 700 ℃, the reduction treatment time is 30min, and in the present invention, the temperature rate of the reduction treatment to the temperature may be 5 to 10 ℃/min, for example.
According to some preferred embodiments, the molar ratio of the metal ions contained in the metal salt solution, the organic ligand and the carbon source used is 1: (1.5 to 4): (8-15); the concentration of metal ions contained in the metal salt solution is 0.05-0.2 mol/L; the complex solution adopts an ethanol aqueous solution, and the ethanol aqueous solution contains 40-60% by volume of ethanol; the complex solution contains 15-25% of the sum of the mass percentages of metal salt, organic ligand and carbon source; and/or the molar ratio of the modified oxide to the metal salt contained in the metal salt solution is (10-20): 1 (e.g., 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, or 20:1).
According to some preferred embodiments, the organic ligand is 2,4, 6-tris (2-pyridine) -1,3, 5-triazine and the carbon source is melamine; or the organic ligand is dicyandiamide, and the carbon source is glucose; in the present invention, when the organic ligand is 2,4, 6-tris (2-pyridine) -1,3, 5-triazine, melamine is preferably used as a carbon source, and it is preferable that the molar ratio of the metal ion contained in the metal salt solution, the organic ligand, and the carbon source is 1: (1.5 to 4): (8-15), so that the nitrogen doping content of the nitrogen doped oxide supported metal catalyst is improved, the catalytic activity of the catalyst is improved obviously, and the effect of reducing the content of carbon monoxide in a product is more obvious.
According to some preferred embodiments, in step (2), the mixing is performed in such a way that: stirring at room temperature (for example, at a temperature of 15-35 ℃) for 18-30 hours, preferably 24 hours, under the rotating speed of 100-800 r/min; in step (3), the heat treatment is: heating (heating evaporation drying) at 80-120 ℃ until the complex solution becomes solid, for example, under stirring at a speed of 100-800 r/min; and/or the calcination treatment is: calcining at 400-600 ℃ for 2-4 hours, and then calcining at 700-1100 ℃ for 1-3 hours; the temperature rising rate in the calcination treatment process is not particularly limited, and may be, for example, 5-10 ℃/min.
According to some preferred embodiments, the metal ions contained in the metal salt solution are one or more of iron ions, cobalt ions, nickel ions, palladium ions; and/or the oxide is one or more of titanium oxide, cerium oxide, zirconium oxide and aluminum oxide.
According to some preferred embodiments, the metal salt solution is a palladium salt solution, the palladium salt being one or more of palladium dichloride, sodium tetrachloropalladate, palladium tetraammine dichloride; preferably, the palladium salt solution is a palladium chloride acid solution, and the pH value of the palladium chloride acid solution is 0-2; in the invention, the preparation of the chloropalladite solution is a conventional technology in the field, and hydrochloric acid is adopted to dissolve palladium dichloride, and the pH value is 0-2.
According to some specific embodiments, the preparation of the nitrogen-doped oxide supported metal catalyst comprises the steps of:
(1) washing commercial titanium dioxide powder (white titanium oxide powder P25) or titanium oxide microbeads with ethanol and deionized water to remove impurities, and drying for later use; specifically, commercial titanium dioxide powder (P25) or titanium oxide microbeads are soaked in an ethanol water solution of ethanol and water, ultrasonic treatment is carried out to remove residual organic attachments, the volume ratio of the ethanol to the water in the ethanol water solution is 1:1, the ultrasonic power is 200W, the time is 30min, the titanium oxide powder (P25) or the titanium oxide microbeads after ultrasonic treatment are subjected to vacuum suction filtration and are washed three times with deionized water to remove the residual ethanol, the residual ethanol is dried in a vacuum oven for 12 hours, and then the adsorbed water is further removed in a tube furnace for standby, the temperature of the vacuum oven is 80 ℃, and the treatment temperature of the tube furnace is 150 ℃ for 1 hour.
(2) Uniformly placing the titanium oxide powder or titanium oxide microbeads treated in the step (1) in a quartz boat, placing the quartz boat in a movable vacuum tube furnace vacuum environment provided with a plasma generator, controlling the power of the plasma generator to be 100W, introducing hydrogen, generating active hydrogen plasma by using the plasma generator to reduce the oxide, controlling the hydrogen flow to be 15sccm during the reduction treatment, keeping the vacuum low pressure (controlling the pressure to be 30-200 Pa) during the whole process, utilizing the low-pressure hydrogen plasma glow to strike the titanium oxide surface, reducing the titanium oxide at the temperature of 500-1150 ℃ for 10-120 min, removing a high-temperature region after the color change of the white titanium oxide surface is observed to be stable, turning off the plasma generator, adjusting the hydrogen flow to be 100sccm, keeping the hydrogen low pressure (controlling the pressure to be 300-500 Pa), cooling the atmosphere, and cooling to the room temperature at the cooling rate of 30 ℃/min, thus obtaining the black titanium oxide.
(3) Mixing a chloropalladite solution with the concentration of 0.05-0.2 mol/L, pH =0-2 with 2,4, 6-tris (2-pyridine) -1,3, 5-triazine (TPTZ) and melamine by adopting an ethanol aqueous solution, stirring for 2 hours at room temperature to obtain a uniformly mixed complex solution, adding the black titanium oxide obtained in the step (2) into the complex solution, and stirring for 18-30 hours at room temperature under the rotating speed of 100-800 r/min to uniformly mix to obtain a complex solution; in the step (3), the ethanol aqueous solution is prepared from ethanol and water according to the volume ratio of 1:1, wherein the complex solution contains 15-25% of the sum of the mass percentages of palladium dichloride, 2,4, 6-tri (2-pyridine) -1,3, 5-triazine and melamine, and the molar ratio of palladium ions contained in the chloropalladite solution to the dosage of the 2,4, 6-tri (2-pyridine) -1,3, 5-triazine to the melamine is 1: (1.5 to 4): (8-15); the molar ratio of the black titanium oxide to the palladium dichloride contained in the palladium chloride acid solution is (10-20): 1, a step of; in the present invention, the concentration of the palladium chloride acid solution means a concentration of palladium dichloride contained in the palladium chloride acid solution.
(4) Heating the compound solution obtained in the step (3) at 80-120 ℃ until the compound solution is evaporated to dryness, so that the compound solution becomes solid, obtaining a solid precursor, grinding the solid precursor into powder, then placing the powder into a heating furnace for calcination, maintaining a nitrogen atmosphere (the nitrogen flow is 120-180 sccm for example), and performing calcination treatment in two steps to obtain the nitrogen-doped oxide supported metal catalyst; the two steps of calcination are as follows: calcining at 400-600 ℃ for 2-4 hours, and then calcining at 700-1100 ℃ for 1-3 hours; the grinding is not particularly limited, and is a conventional technology in the art, for example, grinding can be performed for 30-40 min.
The present invention provides in a second aspect a nitrogen-doped oxide supported metal catalyst produced by the production process of the invention described in the first aspect.
The present invention provides in a third aspect the use of a nitrogen-doped oxide supported metal catalyst prepared by the preparation method of the invention as described in the first aspect in the production of hydrogen from formic acid; the nitrogen-doped black titanium oxide supported palladium catalyst prepared in some embodiments of the invention catalyzes the formic acid to prepare hydrogen schematically, as shown in fig. 1; as can be seen from fig. 1, the nitrogen-doped oxide supported metal catalyst prepared by the invention takes a nitrogen-doped nano cage coated black oxide (such as black titanium oxide) structure as a carrier, and utilizes oxygen vacancies of the black oxide and high nitrogen-doped nitrogen sites to regulate the activity and stability of palladium sites, thereby greatly improving the selectivity of the formic acid hydrogen production reaction and the efficiency of the formic acid hydrogen production reaction.
In the invention, when the nitrogen-doped oxide supported metal catalyst is adopted to carry out formic acid hydrogen production, the nitrogen-doped oxide supported metal catalyst and hydrogen production stock solution are uniformly mixed to carry out hydrogen production reaction; in the invention, for example, the hydrogen production stock solution contains formic acid and/or sodium formate, the hydrogen production stock solution takes water as a solvent, the concentration of the formic acid in the hydrogen production stock solution is 1-3 mol/L, and/or the concentration of the sodium formate in the hydrogen production stock solution is 3-7 mol/L, and the dosage of the nitrogen-doped oxide supported metal catalyst is as follows: adding 0.01-0.03 g of nitrogen-doped oxide supported metal catalyst into each 20mL of hydrogen production stock solution; the temperature of the hydrogen production reaction is 60-80 ℃.
The invention will be further illustrated by way of example, but the scope of the invention is not limited to these examples. The present invention is capable of other and further embodiments and its several details are capable of modification and variation in accordance with the present invention, as will be apparent to those skilled in the art, without departing from the spirit and scope of the invention as defined in the appended claims.
Example 1
(1) Soaking titanium dioxide powder (white titanium oxide powder P25) in an ethanol water solution of ethanol and deionized water, carrying out ultrasonic treatment to remove residual organic attachments, wherein the volume ratio of the ethanol to the deionized water is 1:1 in the ethanol water solution, the power of ultrasonic treatment is 200W, the time is 30min, carrying out vacuum suction filtration on the titanium dioxide powder after ultrasonic treatment, flushing the titanium dioxide powder with the deionized water for three times to remove the residual ethanol, drying the titanium dioxide powder in a vacuum oven at 80 ℃ for 12 hours, and then further removing adsorbed water in a tubular furnace at 150 ℃ for 1 hour for later use.
(2) Uniformly placing the titanium dioxide powder processed in the step (1) in a quartz boat, placing the quartz boat in a vacuum environment of a movable vacuum tube furnace provided with a plasma generator, controlling the power of the plasma generator to be 100W, introducing hydrogen, generating active hydrogen plasma by using the plasma generator to reduce the titanium dioxide, controlling the hydrogen flow to be 15sccm during the reduction, maintaining the vacuum low pressure (controlling the pressure to be 30-200 Pa) during the whole process, reducing the titanium dioxide at 700 ℃ for 30min, removing a high temperature area, closing the plasma generator, adjusting the hydrogen flow to be 100sccm, maintaining the hydrogen low pressure (controlling the pressure to be 300-500 Pa) atmosphere, and cooling to room temperature at a cooling rate of 30 ℃/min to obtain the modified titanium dioxide (black titanium oxide).
(3) Mixing 7.5mL of a chloropalladite solution with the concentration of 0.1mol/L, pH =1 with 1.5mmol of 2,4, 6-tris (2-pyridine) -1,3, 5-triazine (TPTZ) and 7.5mmol of melamine by adopting an ethanol aqueous solution, stirring at the room temperature of 25 ℃ at the rotating speed of 300r/min for 2 hours to obtain a uniformly mixed complex solution, adding 0.8g of black titanium oxide obtained in the step (2) into the complex solution, and stirring at the room temperature of 25 ℃ at the rotating speed of 300r/min for 24 hours to uniformly mix to obtain a complex solution; in the step (3), the ethanol aqueous solution is formed by mixing ethanol and water (deionized water) according to a volume ratio of 1:1, and the volumes of the ethanol and the water are 21.2mL.
(4) Heating the compound solution obtained in the step (3) at 110 ℃ and the rotating speed of 300r/min until the compound solution is evaporated to dryness to enable the compound solution to become solid, so as to obtain a solid precursor, grinding the solid precursor into powder, then placing the powder into a heating furnace for calcination, maintaining a nitrogen atmosphere (the nitrogen flow is 150 sccm), and performing calcination treatment in two steps to obtain a nitrogen-doped oxide-supported metal catalyst (nitrogen-doped black titanium oxide-supported palladium (Pd)) catalyst; the two steps of calcination are as follows: calcination was performed at 550℃for 3 hours, followed by calcination at 800℃for 2 hours.
As shown in FIG. 2, the X-ray photoelectron spectrum of the modified titanium dioxide (black titanium oxide) and white titanium oxide P25 obtained in the embodiment shows that the content of +3 valent titanium ions in the modified titanium dioxide is obviously increased and the peak of Ti2P is subjected to overall red shift, wherein Ti is 3+ The peak represents a change in the electron structure of Ti due to an increase in oxygen vacancies; the modified titanium dioxide is used as a carrier, so that the catalytic activity of the catalyst is increased, and electron transfer exists between the modified titanium dioxide carrier with high oxygen vacancy and the nitrogen-doped carrier, so that the prepared nitrogen-doped oxide supported metal catalyst has high catalytic efficiency, and simultaneously, the generation of carbon monoxide can be effectively inhibited, and the content of the carbon monoxide in the product is obviously reduced; as shown in fig. 3, in a transmission electron microscope image of the nitrogen-doped black titanium oxide supported palladium nano catalyst obtained in the embodiment, as can be seen from fig. 3, metal palladium nano particles are uniformly supported on a carrier, and the size is about 5-10 nm.
Example 2
Example 2 is substantially the same as example 1 except that:
(3) mixing 7.5mL of a chloropalladite solution with the concentration of 0.1mol/L, pH =1 with 1.5mmol of dicyandiamide and 7.5mmol of glucose by adopting an ethanol aqueous solution, stirring for 2 hours at the room temperature of 25 ℃ and the rotation speed of 300r/min to obtain a uniformly mixed complex solution, adding 0.8g of the black titanium oxide obtained in the step (2) into the complex solution, and stirring for 24 hours at the room temperature of 25 ℃ and the rotation speed of 300r/min to uniformly mix to obtain a complex solution; in the step (3), the ethanol aqueous solution is formed by mixing ethanol and water (deionized water) according to a volume ratio of 1:1, and the volumes of the ethanol and the water are 21.2mL.
Example 3
Example 3 is substantially the same as example 1 except that:
(3) mixing 7.5mL of a chloropalladite solution with the concentration of 0.1mol/L, pH =1 with 1.5mmol of 2,4, 6-tris (2-pyridine) -1,3, 5-triazine (TPTZ) and 7.5mmol of glucose by adopting an ethanol aqueous solution, stirring at the room temperature of 25 ℃ at the rotating speed of 300r/min for 2 hours to obtain a uniformly mixed complex solution, adding 0.8g of black titanium oxide obtained in the step (2) into the complex solution, and stirring at the room temperature of 25 ℃ at the rotating speed of 300r/min for 24 hours to uniformly mix to obtain a complex solution; in the step (3), the ethanol aqueous solution is formed by mixing ethanol and water (deionized water) according to a volume ratio of 1:1, and the volumes of the ethanol and the water are 21.2mL.
Example 4
Example 4 is substantially the same as example 1 except that:
(3) mixing 7.5mL of a chloropalladite solution with the concentration of 0.1mol/L, pH =1 with 1.5mmol of dicyandiamide and 7.5mmol of melamine by adopting an ethanol aqueous solution, stirring for 2 hours at the room temperature of 25 ℃ and the rotation speed of 300r/min to obtain a uniformly mixed complex solution, adding 0.8g of black titanium oxide obtained in the step (2) into the complex solution, and stirring for 24 hours at the room temperature of 25 ℃ and the rotation speed of 300r/min to uniformly mix to obtain a complex solution; in the step (3), the ethanol aqueous solution is formed by mixing ethanol and water (deionized water) according to a volume ratio of 1:1, and the volumes of the ethanol and the water are 21.2mL.
Example 5
Example 5 is substantially the same as example 1 except that:
(3) mixing 7.5mL of a chloropalladite solution with the concentration of 0.1mol/L, pH =1 with 0.75mmol of 2,4, 6-tris (2-pyridine) -1,3, 5-triazine (TPTZ) and 3.75mmol of melamine by adopting an ethanol aqueous solution, stirring at the room temperature of 25 ℃ at the rotating speed of 300r/min for 2 hours to obtain a uniformly mixed complex solution, adding 0.8g of black titanium oxide obtained in the step (2) into the complex solution, and stirring at the room temperature of 25 ℃ at the rotating speed of 300r/min for 24 hours to uniformly mix to obtain a complex solution; in the step (3), the ethanol aqueous solution is formed by mixing ethanol and water (deionized water) according to a volume ratio of 1:1, and the volumes of the ethanol and the water are 21.2mL.
Example 6
Example 6 is substantially the same as example 1 except that:
(3) mixing 7.5mL of a chloropalladite solution with the concentration of 0.1mol/L, pH =1 with 3.75mmol of 2,4, 6-tris (2-pyridine) -1,3, 5-triazine (TPTZ) and 15mmol of melamine by adopting an ethanol aqueous solution, stirring at the room temperature of 25 ℃ at the rotating speed of 300r/min for 2 hours to obtain a uniformly mixed complex solution, adding 0.8g of black titanium oxide obtained in the step (2) into the complex solution, and stirring at the rotating speed of 300r/min for 24 hours at the room temperature of 25 ℃ to uniformly mix to obtain the complex solution; in the step (3), the ethanol aqueous solution is formed by mixing ethanol and water (deionized water) according to a volume ratio of 1:1, and the volumes of the ethanol and the water are 21.2mL.
Comparative example 1
Comparative example 1 is substantially the same as example 1 except that:
in the step (2), after the reduction treatment is carried out for 30min, a high-temperature area is removed, a plasma generator is turned off, the flow rate of hydrogen is kept at 15sccm, the atmosphere of low pressure of hydrogen (the pressure is controlled at 30-200 Pa)) is kept for natural cooling, and the temperature is reduced to the room temperature, so that modified titanium dioxide is obtained; the modified titanium dioxide in example 1 was replaced with the modified titanium dioxide to carry out the subsequent step (3) and step (4).
Comparative example 2
(1) Soaking titanium dioxide powder (white titanium oxide powder P25) in an ethanol water solution of ethanol and deionized water, carrying out ultrasonic treatment to remove residual organic attachments, wherein the volume ratio of the ethanol to the deionized water is 1:1 in the ethanol water solution, the power of ultrasonic treatment is 200W, the time is 30min, carrying out vacuum suction filtration on the titanium dioxide powder after ultrasonic treatment, flushing the titanium dioxide powder with the deionized water for three times to remove the residual ethanol, drying the titanium dioxide powder in a vacuum oven at 80 ℃ for 12 hours, and then further removing adsorbed water in a tubular furnace at 150 ℃ for 1 hour for later use.
(2) Mixing 7.5mL of a chloropalladite solution with the concentration of 0.1mol/L, pH =1 with 1.5mmol of 2,4, 6-tris (2-pyridine) -1,3, 5-triazine (TPTZ) and 7.5mmol of melamine by adopting an ethanol aqueous solution, stirring at the room temperature of 25 ℃ at the rotating speed of 300r/min for 2 hours to obtain a uniformly mixed complex solution, adding 0.8g of white titanium oxide treated in the step (1) into the complex solution, and stirring at the room temperature of 25 ℃ at the rotating speed of 300r/min for 24 hours to uniformly mix to obtain a complex solution; in the step (2), the ethanol aqueous solution is formed by mixing ethanol and water (deionized water) according to a volume ratio of 1:1, wherein the volumes of the ethanol and the water are 21.2mL.
(3) Heating the compound solution obtained in the step (2) at 110 ℃ and the rotating speed of 300r/min until the compound solution is evaporated to dryness, so that the compound solution becomes solid, obtaining a solid precursor, grinding the solid precursor into powder, then placing the powder into a heating furnace for calcination, maintaining a nitrogen atmosphere (the nitrogen flow is 150 sccm), and carrying out calcination treatment in two steps to obtain the nitrogen-doped oxide supported metal catalyst; the two steps of calcination are as follows: calcination was performed at 550℃for 3 hours, followed by calcination at 800℃for 2 hours.
Comparative example 3
(1) Soaking titanium dioxide powder (white titanium oxide powder P25) in an ethanol water solution of ethanol and deionized water, carrying out ultrasonic treatment to remove residual organic attachments, wherein the volume ratio of the ethanol to the deionized water is 1:1 in the ethanol water solution, the power of ultrasonic treatment is 200W, the time is 30min, carrying out vacuum suction filtration on the titanium dioxide powder after ultrasonic treatment, flushing the titanium dioxide powder with the deionized water for three times to remove the residual ethanol, drying the titanium dioxide powder in a vacuum oven at 80 ℃ for 12 hours, and then further removing adsorbed water in a tubular furnace at 150 ℃ for 1 hour for later use.
(2) Uniformly placing the titanium dioxide powder processed in the step (1) in a quartz boat, placing the quartz boat in a vacuum environment of a movable vacuum tube furnace provided with a plasma generator, controlling the power of the plasma generator to be 100W, introducing hydrogen, generating active hydrogen plasma by using the plasma generator to reduce the titanium dioxide, controlling the hydrogen flow to be 15sccm during the reduction, maintaining the vacuum low pressure (controlling the pressure to be 30-200 Pa) during the whole process, reducing the titanium dioxide, controlling the reduction temperature to be 700 ℃ for 30min, removing a high temperature area, closing the plasma generator, adjusting the hydrogen flow to be 100sccm, maintaining the hydrogen low pressure (controlling the pressure to be 300-500 Pa) atmosphere, and cooling to room temperature at a cooling rate of 30 ℃/min to obtain the modified titanium dioxide (black titanium oxide).
(3) Uniformly mixing 7.5mL of a chloropalladite solution with the concentration of 0.1mol/L, pH =1 by adopting an ethanol aqueous solution, then adding 0.8g of the black titanium oxide obtained in the step (2), and stirring at the room temperature of 25 ℃ for 24 hours at the rotating speed of 300r/min, uniformly mixing to obtain a mixed solution; in the step (3), the ethanol aqueous solution is formed by mixing ethanol and water (deionized water) according to a volume ratio of 1:1, and the volumes of the ethanol and the water are 21.2mL.
(4) Adding sodium borohydride aqueous solution with the concentration of 2mg/mL into the mixed solution obtained in the step (3), and stirring at the room temperature of 25 ℃ and the rotating speed of 300r/min for reacting for 2 hours to obtain a reaction solution; wherein the molar ratio of sodium borohydride contained in the sodium borohydride aqueous solution to palladium dichloride contained in the palladium chloride acid solution in the step (3) is 6:1.
(5) And (3) carrying out suction filtration on the reaction liquid to obtain a solid, and then drying the solid in a vacuum oven at 60 ℃ for 24 hours to obtain the palladium catalyst.
Comparative example 4
(1) 7.5mL of a chloropalladite solution with the concentration of 0.1mol/L, pH =1, 1.5mmol of 2,4, 6-tris (2-pyridine) -1,3, 5-triazine (TPTZ) and 7.5mmol of melamine are mixed by adopting an ethanol aqueous solution, and stirred for 2 hours at the room temperature of 25 ℃ and the rotating speed of 300r/min to obtain a uniformly mixed complex solution; the ethanol aqueous solution is formed by mixing ethanol and water (deionized water) according to the volume ratio of 1:1, and the volumes of the ethanol and the water are 21.2mL.
(2) Heating the complex solution obtained in the step (1) at 110 ℃ and the rotating speed of 300r/min until the complex solution is evaporated to dryness, so that the complex solution becomes solid, obtaining a solid precursor, grinding the solid precursor into powder, then calcining the powder in a heating furnace, maintaining the nitrogen atmosphere (the nitrogen flow is 150 sccm), and calcining the powder in two steps to obtain the nitrogen-doped carbon-supported metal catalyst; the two steps of calcination are as follows: calcination was performed at 550℃for 3 hours, followed by calcination at 800℃for 2 hours.
Comparative example 5
Comparative example 5 is substantially the same as example 1 except that:
(3) mixing 7.5mL of a chloropalladite solution with the concentration of 0.1mol/L, pH =1 with 1.5mmol of 2,4, 6-tris (2-pyridine) -1,3, 5-triazine (TPTZ) by adopting an ethanol aqueous solution, stirring for 2 hours at the room temperature of 25 ℃ and the rotation speed of 300r/min to obtain a uniformly mixed complex solution, adding 0.8g of black titanium oxide obtained in the step (2) into the complex solution, and stirring for 24 hours at the room temperature of 25 ℃ and uniformly mixing at the rotation speed of 300r/min to obtain a complex solution; in the step (3), the ethanol aqueous solution is formed by mixing ethanol and water (deionized water) according to a volume ratio of 1:1, and the volumes of the ethanol and the water are 21.2mL.
Comparative example 6
Comparative example 6 is substantially the same as example 1 except that:
(3) mixing 7.5mL of a chloropalladite solution with the concentration of 0.1mol/L, pH =1 with 7.5mmol of melamine by adopting an ethanol aqueous solution, stirring for 2 hours at the room temperature of 25 ℃ and the rotating speed of 300r/min to obtain a uniformly mixed complex solution, adding 0.8g of black titanium oxide obtained in the step (2) into the complex solution, and stirring for 24 hours at the room temperature of 25 ℃ and the rotating speed of 300r/min to uniformly mix to obtain a complex solution; in the step (3), the ethanol aqueous solution is formed by mixing ethanol and water (deionized water) according to a volume ratio of 1:1, and the volumes of the ethanol and the water are 21.2mL.
The nitrogen content of the catalysts finally obtained in each example and each comparative example was measured according to the present invention, and the nitrogen content of the catalysts was obtained by characterization of X-ray photoelectron spectroscopy, and the results are shown in table 1.
The invention also tests the catalytic effect of the hydrogen production reaction of formic acid on the catalysts finally prepared in each example and each comparative example, and the test method comprises the following steps:
preparing a mixed solution of formic acid and sodium formate by using water as a solvent to serve as a hydrogen production stock solution, wherein the concentration of the formic acid in the hydrogen production stock solution is 1mol/L, and the concentration of the sodium formate in the hydrogen production stock solution is 3mol/L; adding a catalyst into the hydrogen production stock solution to carry out hydrogen production reaction, wherein 0.01g of catalyst is added into each 20mL of hydrogen production stock solution; after hydrogen production reaction is carried out at 80 ℃ for 10min, a conversion frequency value (TOF value) is obtained, the result is shown in table 1, and the result of measuring the content of CO in the gas product in the first 10min is shown in table 1, wherein the content of CO in the gas product is detected by a gas chromatograph equipped with a hydrogen flame detector.
TABLE 1
The invention is not described in detail in a manner known to those skilled in the art.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and are not limiting; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (9)

1. A method for preparing a nitrogen-doped oxide supported metal catalyst, which is characterized by comprising the following steps:
(1) Placing the oxide in a vacuum environment, then introducing hydrogen, generating active hydrogen plasma by using a plasma generator to reduce the oxide, and then cooling to obtain a modified oxide; when the reduction treatment is carried out, the flow rate of the introduced hydrogen is 10-20 sccm, and when the cooling treatment is carried out, the flow rate of the introduced hydrogen is 100-150 sccm, and the cooling rate is 30-50 ℃/min; the oxide is one or more of titanium oxide, cerium oxide, zirconium oxide and aluminum oxide;
(2) Preparing a complex solution from a metal salt solution, an organic ligand and a carbon source, and then adding the modified oxide into the complex solution and uniformly mixing to obtain a complex solution; the organic ligand is 2,4, 6-tri (2-pyridine) -1,3, 5-triazine and/or dicyandiamide, and the carbon source is melamine and/or glucose; the metal ions contained in the metal salt solution are one or more of iron ions, cobalt ions, nickel ions and palladium ions;
(3) And sequentially carrying out heating treatment and calcination treatment on the composite solution to obtain the nitrogen-doped oxide supported metal catalyst.
2. The method of claim 1, wherein in step (1):
the temperature of the reduction treatment is 500-1150 ℃, and the time of the reduction treatment is 10-120 min.
3. The method of manufacturing according to claim 1, characterized in that:
the molar ratio of the metal ions contained in the metal salt solution, the organic ligand and the carbon source is 1: (1.5 to 4): (8-15);
the concentration of metal ions in the metal salt solution is 0.05-0.2 mol/L; and/or
The complex solution adopts an ethanol aqueous solution, and the ethanol aqueous solution contains 40-60% by volume of ethanol.
4. The method of manufacturing according to claim 1, characterized in that:
the complex solution contains 15-25% of the sum of the mass percentages of metal salt, organic ligand and carbon source; and/or
The molar ratio of the modified oxide to the metal salt contained in the metal salt solution is (10-20): 1.
5. the method of manufacturing according to claim 1, characterized in that:
the organic ligand is 2,4, 6-tri (2-pyridine) -1,3, 5-triazine, and the carbon source is melamine; or (b)
The organic ligand is dicyandiamide, and the carbon source is glucose.
6. The method of manufacturing according to claim 1, characterized in that:
in the step (2), the mode of uniform mixing is as follows: stirring for 18-30 h at room temperature under the rotating speed of 100-800 r/min;
the heating treatment is as follows: heating at 80-120 ℃ until the compound solution becomes solid; and/or
The calcination treatment is as follows: calcining at 400-600 ℃ for 2-4 hours, and then calcining at 700-1100 ℃ for 1-3 hours.
7. The method of manufacturing according to claim 1, characterized in that:
the metal salt solution is a chloropalladite solution, and the pH value of the chloropalladite solution is 0-2.
8. A nitrogen-doped oxide supported metal catalyst produced by the production method according to any one of claims 1 to 7.
9. Use of a nitrogen-doped oxide supported metal catalyst prepared by the preparation method of any one of claims 1 to 7 in hydrogen production from formic acid.
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