CN110201665B - Pd-Rh nano-catalyst, preparation method and application thereof - Google Patents
Pd-Rh nano-catalyst, preparation method and application thereof Download PDFInfo
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- 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
- B01J23/46—Ruthenium, rhodium, osmium or iridium
- B01J23/464—Rhodium
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Abstract
The invention provides a preparation method of a Pd-Rh nano-catalyst, which comprises the following steps: mixing and dissolving palladium source solution, rhodium source solution, potassium iodide aqueous solution and polyvinylpyrrolidone in a solvent to obtain a mixture, heating, cooling, centrifuging and cleaning the mixture to obtain the Pd-Rh nano catalyst; the palladium source is sodium chloropalladate; the rhodium source is sodium hexachlororhodate. According to the invention, an element doping mode is used, rhodium atoms are doped on the palladium nanocrystals, so that a nano catalyst is constructed, and a unique m-nitrophenylethylene adsorption structure different from that of the Pd nanocrystals is obtained by doping of the rhodium atoms in the nano catalyst, so that hydrogenation of nitro groups is difficult to perform, and the selectivity of carbon-carbon double bonds is improved. The Pd-Rh nano-catalyst has the advantages of good catalytic activity, high double-bond hydrogenation selectivity of m-nitrostyrene and stable catalytic performance.
Description
Technical Field
The invention relates to the technical field of catalysts, in particular to a Pd-Rh nano catalyst, and a preparation method and application thereof.
Background
For catalytic reactions, the activity of the catalyst is often sacrificed in exchange for high selectivity to a particular product. Therefore, it is of great value to develop heterogeneous catalysts with both high activity and high selectivity. In particular, for selective hydrogenation reactions, the selective hydrogenation of carbon-carbon double bonds is important for the synthesis of drugs, perfumes, polymers, pesticides, and other products. When more than one hydroreducible group is present on the substrate, conventional noble metal catalysts reduce these reducible groups simultaneously, resulting in lower product selectivity.
Traditional solutions include the introduction of ligands, zeolites, metal organic frameworks, poisoning aids, etc., which either occupy or inactivate the active sites in nature, in effect trading activity for selectivity. For selective hydrogenation reaction, how to improve the selectivity of the product without reducing the activity is an important direction of research.
Disclosure of Invention
In view of the above, the technical problem to be solved by the present invention is to provide a method for preparing a Pd-Rh nano catalyst, which has high catalytic selectivity, good catalytic activity and stable catalytic performance in hydrogenation reaction of m-nitroaniline.
The invention provides a preparation method of a Pd-Rh nano-catalyst, which comprises the following steps:
mixing and dissolving palladium source solution, rhodium source solution, potassium iodide aqueous solution and polyvinylpyrrolidone in a solvent to obtain a mixture, heating, cooling, centrifuging and cleaning the mixture to obtain the Pd-Rh nano catalyst; the palladium source is sodium chloropalladate; the rhodium source is sodium hexachlororhodate.
Preferably, the concentration of the sodium chloropalladate solution is 19.5 mM-20.5 mM; the concentration of the sodium hexachlororhodate solution is 19.5 mM-20.5 mM; the concentration of the aqueous solution of potassium iodide is 0.9-1.1M.
Preferably, the weight volume ratio of the sodium chloropalladate solution, the sodium hexachlororhodate solution, the aqueous solution of potassium iodide, the polyvinylpyrrolidone and the solvent is (1.5-1.9) mL: (0.2-0.4) mL: (0.8-1.2) mL: (130-170) mg: (9-11) mL.
Preferably, the solvent is dimethylformamide.
Preferably, the heating is heating in an oven; the heating temperature is 130-150 ℃; the heating time is 3-5 h; the cooling is to cool the mixture to room temperature in air.
Preferably, the centrifugal rotating speed is 9000-11000 rpm; the centrifugation time is 4-6 min; the cleaning specifically comprises the following steps: washing with water for 1-3 times, and then washing with ethanol for 1-3 times.
Preferably, the method further comprises the step of keeping the cleaned product for 25-35 min at a position 4-6 mm away from the lamp of the ultraviolet ozone cleaning machine, and then taking out the product.
The invention provides a Pd-Rh nano-catalyst which is prepared by any one of the preparation methods in the technical schemes.
The invention provides a preparation method of m-nitroanisole, which comprises the step of catalyzing selective hydrogenation reaction of m-nitroanisole by using a Pd-Rh nano catalyst prepared by the preparation method in any one of the technical schemes.
The invention provides application of the Pd-Rh nano-catalyst prepared by the preparation method in any one of the technical schemes in selective hydrogenation reaction of m-nitroaniline.
Compared with the prior art, the invention provides a preparation method of a Pd-Rh nano-catalyst, which comprises the following steps: mixing and dissolving palladium source solution, rhodium source solution, potassium iodide aqueous solution and polyvinylpyrrolidone in a solvent to obtain a mixture, heating, cooling, centrifuging and cleaning the mixture to obtain the Pd-Rh nano catalyst; the palladium source is sodium chloropalladate; the rhodium source is sodium hexachlororhodate. According to the invention, an element doping mode is used, rhodium atoms are doped on the palladium nanocrystals, so that a nano catalyst is constructed, and a unique m-nitrophenylethylene adsorption structure different from that of the Pd nanocrystals is obtained by doping of the rhodium atoms in the nano catalyst, so that hydrogenation of nitro groups is difficult to perform, and the selectivity of carbon-carbon double bonds is improved. The Pd-Rh nano-catalyst has the advantages of good catalytic activity, high double-bond hydrogenation selectivity of m-nitrostyrene and stable catalytic performance.
Drawings
FIG. 1 shows Pd (a) obtained in example 1 of the present invention94Rh6Transmission electron microscope image of nanocubes, (b) scanning transmission electron microscope image of atomic resolution of individual nanocubes, (c) high-angle annular dark field image-scanning transmission electron microscope image of typical single-particle nanocubes and corresponding energy dispersive X-ray detection element resolution map, (d) elemental linear scan map along the dashed line in map (c), (e) Pd94Rh6X-ray diffraction pattern of nanocube, (f) Pd94Rh6A photoelectron spectroscopy spectrum of the nanocube;
FIG. 2 shows Pd-Rh nano-catalyst Pd obtained in example 1 of the present invention94Rh6In the catalytic hydrogenation of 3-nitrostyrene, ln (C/C0) as a function of time;
FIG. 3 shows Pd-Rh nano-catalyst Pd obtained in example 1 of the present invention94Rh6And (3) testing the stability of the hydrogenated 3-nitrostyrene.
Detailed Description
The invention provides a Pd-Rh nano-catalyst, a preparation method and application thereof, and a person skilled in the art can use the contents for reference and appropriately improve the process parameters to realize the Pd-Rh nano-catalyst. It is expressly intended that all such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the scope of the invention. While the methods and applications of this invention have been described in terms of preferred embodiments, it will be apparent to those of ordinary skill in the art that variations and modifications in the methods and applications described herein, as well as other suitable variations and combinations, may be made to implement and use the techniques of this invention without departing from the spirit and scope of the invention.
The invention provides a preparation method of a Pd-Rh nano-catalyst, which comprises the following steps:
mixing and dissolving palladium source solution, rhodium source solution, potassium iodide aqueous solution and polyvinylpyrrolidone in a solvent to obtain a mixture, heating, cooling, centrifuging and cleaning the mixture to obtain the Pd-Rh nano catalyst; the palladium source is sodium chloropalladate; the rhodium source is sodium hexachlororhodate.
Firstly, mixing a palladium source solution, a rhodium source solution, a potassium iodide aqueous solution and polyvinylpyrrolidone, and dissolving in a solvent.
According to the invention, the palladium source is preferably sodium chloropalladate; the source of rhodium is preferably sodium hexachlororhodium. The source of the present invention is not limited and may be commercially available.
Wherein the concentration of the sodium chloropalladate solution is preferably 19.5 mM-20.5 mM; more preferably 20 mM; the concentration of the sodium hexachlororhodate solution is preferably 19.5 mM-20.5 mM; more preferably 20 mM; the concentration of the aqueous solution of potassium iodide is preferably 0.9 to 1.1; most preferably 1M.
According to the invention, the weight-volume ratio of the sodium chloropalladate solution, the sodium hexachlororhodate solution, the aqueous solution of potassium iodide, the polyvinylpyrrolidone and the solvent is preferably (1.5-1.9) mL: (0.2-0.4) mL: (0.8-1.2) mL: (130-170) mg: (9-11) mL; most preferably 1.7 mL: 0.3 mL: 1mL of: 150 mg: 10 mL.
The solvent is dimethylformamide. The source of the present invention is not limited and may be commercially available.
The proportion of the raw materials can ensure that the Pd-Rh nanocubes with expected rhodium doping proportion can be obtained.
In the process of implementing the invention, the proportion is adopted, the catalytic activity is better, the hydrogenation selectivity to carbon-carbon double bonds is very high, and other hydrogenation products are hardly generated.
After mixing the above components in dimethylformamide, the mixture was heated.
The heating is preferably heating in an oven; the heating temperature is preferably 130-150 ℃; more preferably 135-145 ℃; the heating time is preferably 3-5 h; more preferably 3.5 to 4.5 hours.
Heating, cooling, centrifuging at a specific rotating speed, and cleaning to obtain a Pd-Rh nanocube, namely the Pd-Rh nanocatalyst.
The cooling according to the invention is preferably in air to room temperature. The centrifugal rotating speed is preferably 9000-11000 rpm; the centrifugal time is preferably 4-6 min; the cleaning is preferably as follows: washing with water for 1-3 times, and then washing with ethanol for 1-3 times.
After the reaction is finished, water and ethanol are used for washing, so that other impurities can be dissolved, and the Pd-Rh nanocubes can be precipitated for centrifugal separation.
According to the invention, the cleaned product is kept for 25-35 min at a position 4-6 mm away from the lamp of the ultraviolet ozone cleaning machine, and then taken out.
The invention is put into an ultraviolet ozone cleaning machine for cleaning again so as to further remove the polyvinylpyrrolidone remained on the surface of the product.
The specification of the ultraviolet ozone cleaning machine type number is not limited, and the ultraviolet ozone cleaning machine type number is well known to those skilled in the art.
The invention provides a Pd-Rh nano-catalyst which is prepared by any one of the preparation methods in the technical schemes.
The invention provides a preparation method of m-nitroanisole, which comprises the step of catalyzing selective hydrogenation reaction of m-nitroanisole by using a Pd-Rh nano catalyst prepared by the preparation method in any one of the technical schemes.
The invention is not limited to the remaining conditions of the reaction, as will be familiar to those skilled in the art.
The invention provides application of the Pd-Rh nano-catalyst prepared by the preparation method in any one of the technical schemes in selective hydrogenation reaction of m-nitroaniline.
The Pd-Rh nano-catalyst has the advantages of good catalytic activity, high double-bond hydrogenation selectivity of m-nitrostyrene and stable catalytic performance.
The invention further provides the application of the Pd-Rh nano-catalyst in the selective hydrogenation reaction of the nitrostyrene.
The invention provides a preparation method of a Pd-Rh nano-catalyst, which comprises the following steps: mixing and dissolving palladium source solution, rhodium source solution, potassium iodide aqueous solution and polyvinylpyrrolidone in a solvent to obtain a mixture, heating, cooling, centrifuging and cleaning the mixture to obtain the Pd-Rh nano catalyst; the palladium source is sodium chloropalladate; the rhodium source is sodium hexachlororhodate. According to the invention, an element doping mode is used, rhodium atoms are doped on the palladium nanocrystals, so that a nano catalyst is constructed, and a unique m-nitrophenylethylene adsorption structure different from that of the Pd nanocrystals is obtained by doping of the rhodium atoms in the nano catalyst, so that hydrogenation of nitro groups is difficult to perform, and the selectivity of carbon-carbon double bonds is improved. The Pd-Rh nano-catalyst has the advantages of good catalytic activity, high double-bond hydrogenation selectivity of m-nitrostyrene and stable catalytic performance.
In order to further illustrate the present invention, the following will describe in detail a Pd-Rh nanocatalyst, its preparation method and application in conjunction with the examples.
Example 1
A Pd-Rh nano-catalyst comprises Pd-Rh nano-crystals with rhodium doped in the palladium crystals.
The preparation method of the Pd-Rh nano-catalyst comprises the following steps:
mixing 1.7ml of 20mM sodium chloropalladate aqueous solution, 0.3ml of 20mM sodium hexachlororhodate aqueous solution, 1ml of 1M potassium iodide aqueous solution and 150mg of polyvinylpyrrolidone in 10ml of dimethylformamide, putting the homogeneous mixture into an oven at 140 ℃ for heating for 4 hours, cooling, centrifuging at 10000rpm, washing with water for three times, washing with ethanol for three times, putting the mixture at a position 5mM away from a lamp in an ultraviolet ozone cleaning machine for holding for 30 minutes, and taking out the mixture to obtain the Pd-Rh nano catalyst.
The Pd-Rh nano-catalyst prepared in the example 1 is used for the catalytic performance test of the nitrostyrene selective hydrogenation reaction:
in the catalytic test, we added 2ml of ethanol, 0.5mmol of m-nitrophenylethylene, 0.1mg of catalyst and one magneton into a 100ml glass reaction flask, and the flask was mounted on a magnetic stirrer. The whole catalytic reaction was carried out at 25 ℃ in a hydrogen atmosphere of one atmosphere and with a magnetic stirring speed of 300 rpm. After the catalytic reaction is finished, the liquid phase product is separated from the catalyst in a centrifugal mode, the centrifugal rotating speed is 10,000rpm, and the liquid phase product is centrifuged for 2 min. Then, 100. mu.l of the liquid phase product was taken, 20. mu.l of naphthalene was added as an internal standard and dispersed in 5 ml of ethanol, and the analysis and the test were carried out by a gas chromatography-mass spectrometer.
The transmission electron microscope image of the Pd-Rh nano-catalyst before catalysis in the selective hydrogenation reaction of m-nitroaniline by the Pd-Rh nano-catalyst is shown in figure 1 (a). Referring to fig. 1 and fig. 2, the Pd-Rh nano catalyst obtained by the present invention has extremely high hydrogenation selectivity, excellent catalytic effect and high catalytic activity in the m-nitroaniline selective hydrogenation reaction. Referring to FIG. 3, the Pd-Rh nano-catalyst obtained by the invention is used in the m-nitroaniline selective hydrogenation reaction at 25 ℃ and 1bar H2The reaction is carried out for 40 hours in a circulating way, the selectivity of the intermediate nitroethylbenzene in the product is nearly 100%, meanwhile, the conversion rate of the m-nitrostyrene is nearly 100%, and in the continuous measurement process of 40 hours, the selectivity and the conversion rate of the product basically keep stable, thereby showing excellent stability. FIG. 1 shows Pd (a) obtained in example 1 of the present invention94Rh6Transmission electron microscope image of nanocubes, (b) scanning transmission electron microscope image of atomic resolution of individual nanocubes, (c) a typical single particle nanocubesHigh angle annular dark field image-scanning transmission electron microscope image and corresponding energy dispersive X-ray detection element resolution map, (d) elemental linear scan along the dotted line in map (c), (e) Pd94Rh6X-ray diffraction pattern of nanocube, (f) Pd94Rh6A photoelectron spectroscopy spectrum of the nanocube; FIG. 2 shows Pd-Rh nano-catalyst Pd obtained in example 1 of the present invention94Rh6In the catalytic hydrogenation of 3-nitrostyrene, ln (C/C0) as a function of time; FIG. 3 shows Pd-Rh nano-catalyst Pd obtained in example 1 of the present invention94Rh6And (3) testing the stability of the hydrogenated 3-nitrostyrene. Reaction conditions are as follows: 3-Nitrostyrene (0.5mmol), catalyst (0.1mg), ethanol (2mL), H2Pressure (1atm), reaction temperature (25 ℃), reaction time (4 h).
Example 2
A Pd-Rh nano-catalyst comprises Pd-Rh nano-crystals with rhodium doped in the palladium crystals.
The preparation method of the Pd-Rh nano-catalyst comprises the following steps:
mixing 1.7ml of 20mM sodium chloropalladate aqueous solution, 0.3ml of 20mM sodium hexachlororhodate aqueous solution, 1ml of 1M potassium iodide aqueous solution and 130mg of polyvinylpyrrolidone in 10ml of dimethylformamide, putting the homogeneous mixture into an oven at 140 ℃ for heating for 4 hours, cooling, centrifuging at 10000rpm, washing with water for three times, washing with ethanol for three times, putting the mixture at a position 5mM away from a lamp in an ultraviolet ozone cleaning machine for holding for 30 minutes, and taking out the mixture to obtain the Pd-Rh nano catalyst.
The Pd-Rh nano-catalyst prepared in the example 2 is adopted to carry out the catalytic performance test of the nitrostyrene selective hydrogenation reaction:
in the catalytic test, we added 2ml of ethanol, 0.5mmol of m-nitrophenylethylene, 0.1mg of catalyst and one magneton into a 100ml glass reaction flask, and the flask was mounted on a magnetic stirrer. The whole catalytic reaction was carried out at 25 ℃ in a hydrogen atmosphere of one atmosphere and with a magnetic stirring speed of 300 rpm. After the catalytic reaction is finished, the liquid phase product is separated from the catalyst in a centrifugal mode, the centrifugal rotating speed is 10,000rpm, and the liquid phase product is centrifuged for 2 min. Then 100 microliters of liquid phase product is taken, 20 microliters of naphthalene is added to be used as an internal standard and dispersed into 5 milliliters of ethanol, and the product is analyzed and tested by a gas chromatography-mass spectrometer to determine that the product is a m-nitrophenylethane structure.
Example 3
A Pd-Rh nano-catalyst comprises Pd-Rh nano-crystals with rhodium doped in the palladium crystals.
The preparation method of the Pd-Rh nano-catalyst comprises the following steps:
mixing 1.7ml of 20mM sodium chloropalladate aqueous solution, 0.3ml of 20mM sodium hexachlororhodate aqueous solution, 1ml of 1M potassium iodide aqueous solution and 140mg of polyvinylpyrrolidone in 10ml of dimethylformamide, putting the homogeneous mixture into an oven at 140 ℃ for heating for 4 hours, cooling, centrifuging at 10000rpm, washing with water for three times, washing with ethanol for three times, putting the mixture at a position 5mM away from a lamp in an ultraviolet ozone cleaning machine for holding for 30 minutes, and taking out the mixture to obtain the Pd-Rh nano catalyst.
The Pd-Rh nano-catalyst prepared in example 3 is used for the catalytic performance test of the nitrostyrene selective hydrogenation reaction:
in the catalytic test, we added 2ml of ethanol, 0.5mmol of m-nitrophenylethylene, 0.1mg of catalyst and one magneton into a 100ml glass reaction flask, and the flask was mounted on a magnetic stirrer. The whole catalytic reaction was carried out at 25 ℃ in a hydrogen atmosphere of one atmosphere and with a magnetic stirring speed of 300 rpm. After the catalytic reaction is finished, the liquid phase product is separated from the catalyst in a centrifugal mode, the centrifugal rotating speed is 10,000rpm, and the liquid phase product is centrifuged for 2 min. Then, 100. mu.l of the liquid phase product was taken, 20. mu.l of naphthalene was added as an internal standard and dispersed in 5 ml of ethanol, and the analysis and the test were carried out by a gas chromatography-mass spectrometer.
Example 4
A Pd-Rh nano-catalyst comprises Pd-Rh nano-crystals with rhodium doped in the palladium crystals.
The preparation method of the Pd-Rh nano-catalyst comprises the following steps:
mixing 1.7ml of 20mM sodium chloropalladate aqueous solution, 0.3ml of 20mM sodium hexachlororhodate aqueous solution, 1ml of 1M potassium iodide aqueous solution and 160mg of polyvinylpyrrolidone in 10ml of dimethylformamide, putting the homogeneous mixture into an oven at 140 ℃ for heating for 4 hours, cooling, centrifuging at 10000rpm, washing with water for three times, washing with ethanol for three times, putting the mixture at a position 5mM away from a lamp in an ultraviolet ozone cleaning machine for holding for 30 minutes, and taking out the mixture to obtain the Pd-Rh nano catalyst.
The Pd-Rh nano-catalyst prepared in the example 4 is adopted to carry out the catalytic performance test of the nitrostyrene selective hydrogenation reaction:
in the catalytic test, we added 2ml of ethanol, 0.5mmol of m-nitrophenylethylene, 0.1mg of catalyst and one magneton into a 100ml glass reaction flask, and the flask was mounted on a magnetic stirrer. The whole catalytic reaction was carried out at 25 ℃ in a hydrogen atmosphere of one atmosphere and with a magnetic stirring speed of 300 rpm. After the catalytic reaction is finished, the liquid phase product is separated from the catalyst in a centrifugal mode, the centrifugal rotating speed is 10,000rpm, and the liquid phase product is centrifuged for 2 min. Then, 100. mu.l of the liquid phase product was taken, 20. mu.l of naphthalene was added as an internal standard and dispersed in 5 ml of ethanol, and the analysis and the test were carried out by a gas chromatography-mass spectrometer.
The Pd-Rh nano-catalyst obtained in the example 2-4 is also used for carrying out the catalytic performance test of the m-nitroaniline selective hydrogenation reaction, and the hydrogenation selectivity is extremely high, the catalytic effect is excellent and the catalytic activity is high in the reaction. Similar to example 1, the selectivity of the intermediate nitroethylbenzene is nearly 100%, and the conversion rate of the intermediate nitroethylbenzene is nearly 100%, and the selectivity and the conversion rate of the intermediate nitroethylbenzene are basically stable during continuous measurement for 40h, and the intermediate nitroethylbenzene also shows excellent stability.
Comparative example 1
A Pd-Rh nano-catalyst comprises Pd-Rh nano-crystals with rhodium doped in the palladium crystals.
The preparation method of the Pd-Rh nano-catalyst comprises the following steps:
1.7ml of 20mM palladium nitrate aqueous solution, 0.3ml of 20mM sodium hexachlororhodate aqueous solution, 1ml of 1M potassium iodide aqueous solution and 130mg of polyvinylpyrrolidone are mixed in 10ml of dimethylformamide, the homogeneous mixture is put into an oven at 140 ℃ for heating for 4 hours, cooled, centrifuged again at 10000rpm, washed with water for three times, washed with ethanol for three times, placed in an ultraviolet ozone cleaning machine and kept away from a lamp for 5mM for 30 minutes, and taken out to obtain the Pd-Rh nano catalyst.
The Pd-Rh nano-catalyst prepared in comparative example 1 was used for the catalytic performance test of the nitrostyrene selective hydrogenation reaction:
in the catalytic test, we added 2ml of ethanol, 0.5mmol of m-nitrophenylethylene, 0.1mg of catalyst and one magneton into a 100ml glass reaction flask, and the flask was mounted on a magnetic stirrer. The whole catalytic reaction was carried out at 25 ℃ in a hydrogen atmosphere of one atmosphere and with a magnetic stirring speed of 300 rpm. After the catalytic reaction is finished, the liquid phase product is separated from the catalyst in a centrifugal mode, the centrifugal rotating speed is 10,000rpm, and the liquid phase product is centrifuged for 2 min. Then, 100. mu.l of the liquid phase product was taken, 20. mu.l of naphthalene was added as an internal standard and dispersed in 5 ml of ethanol, and the analysis and the test were carried out by a gas chromatography-mass spectrometer.
The Pd-Rh nano-catalyst obtained in comparative example 1 is used for carrying out the catalytic performance test of the m-nitroaniline selective hydrogenation reaction, the selectivity of the intermediate nitroethylbenzene in the product is only 70%, and the conversion rate of the m-nitroaniline is 87%.
Comparative example 2
A Pd-Rh nano-catalyst comprises Pd-Rh nano-crystals with rhodium doped in the palladium crystals.
The preparation method of the Pd-Rh nano-catalyst comprises the following steps:
mixing 1.7ml of 20mM sodium chloropalladate aqueous solution, 0.3ml of 20mM sodium hexachlororhodate aqueous solution, 1ml of 1M potassium iodide aqueous solution and 130mg of polyvinylpyrrolidone in 10ml of dimethylformamide, putting the homogeneous mixture into an oven at 170 ℃ for heating for 4 hours, cooling, centrifuging at 10000rpm, washing with water for three times, washing with ethanol for three times, putting the mixture at a position 5mM away from a lamp in an ultraviolet ozone cleaning machine for holding for 30 minutes, and taking out the mixture to obtain the Pd-Rh nano catalyst.
The Pd-Rh nano-catalyst prepared in comparative example 2 was used for the catalytic performance test of the nitrostyrene selective hydrogenation reaction:
in the catalytic test, we added 2ml of ethanol, 0.5mmol of m-nitrophenylethylene, 0.1mg of catalyst and one magneton into a 100ml glass reaction flask, and the flask was mounted on a magnetic stirrer. The whole catalytic reaction was carried out at 25 ℃ in a hydrogen atmosphere of one atmosphere and with a magnetic stirring speed of 300 rpm. After the catalytic reaction is finished, the liquid phase product is separated from the catalyst in a centrifugal mode, the centrifugal rotating speed is 10,000rpm, and the liquid phase product is centrifuged for 2 min. Then, 100. mu.l of the liquid phase product was taken, 20. mu.l of naphthalene was added as an internal standard and dispersed in 5 ml of ethanol, and the analysis and the test were carried out by a gas chromatography-mass spectrometer.
The Pd-Rh nano-catalyst obtained in comparative example 2 is used for carrying out the catalytic performance test of the m-nitroaniline selective hydrogenation reaction, the selectivity of the intermediate nitroethylbenzene in the product is only 66%, and the conversion rate of the m-nitroaniline is 93%.
Comparative example 3
The Pd nano-catalyst has the same appearance as the Pd-Rh nano-crystal in the example 1.
The preparation method of the Pd nano-catalyst comprises the following steps:
mixing 2ml of 20mM sodium chloropalladate aqueous solution, 1ml of 1M potassium iodide aqueous solution and 130mg of polyvinylpyrrolidone in 10ml of dimethylformamide, putting the homogeneous mixture into an oven at 140 ℃ for heating for 4 hours, cooling, centrifuging at 10000rpm, washing with water for three times, washing with ethanol for three times, putting the mixture at a position 5mM away from a lamp in an ultraviolet ozone cleaning machine for 30 minutes, and taking out the mixture to obtain the Pd-Rh nano catalyst.
The Pd nano-catalyst prepared in comparative example 3 was used for the catalytic performance test of the nitrostyrene selective hydrogenation reaction:
in the catalytic test, we added 2ml of ethanol, 0.5mmol of m-nitrophenylethylene, 0.1mg of catalyst and one magneton into a 100ml glass reaction flask, and the flask was mounted on a magnetic stirrer. The whole catalytic reaction was carried out at 25 ℃ in a hydrogen atmosphere of one atmosphere and with a magnetic stirring speed of 300 rpm. After the catalytic reaction is finished, the liquid phase product is separated from the catalyst in a centrifugal mode, the centrifugal rotating speed is 10,000rpm, and the liquid phase product is centrifuged for 2 min. Then, 100. mu.l of the liquid phase product was taken, 20. mu.l of naphthalene was added as an internal standard and dispersed in 5 ml of ethanol, and the analysis and the test were carried out by a gas chromatography-mass spectrometer.
The Pd nano-catalyst obtained in comparative example 2 is used for the catalytic performance test of the m-nitroaniline selective hydrogenation reaction, the selectivity of the intermediate nitroethylbenzene in the product is only 52%, and the conversion rate of the m-nitroaniline is 98%.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (9)
1. A preparation method of a Pd-Rh nano-catalyst is characterized by comprising the following steps:
mixing and dissolving palladium source solution, rhodium source solution, potassium iodide aqueous solution and polyvinylpyrrolidone in a solvent to obtain a mixture, heating, cooling, centrifuging and cleaning the mixture to obtain the Pd-Rh nano catalyst; the palladium source is sodium chloropalladate; the rhodium source is sodium hexachlororhodate; the concentration of the sodium chloropalladate solution is 19.5 mM-20.5 mM; the concentration of the sodium hexachlororhodate solution is 19.5 mM-20.5 mM; the heating is heating in an oven; the heating temperature is 130-150 ℃; the heating time is 3-5 h; the weight volume ratio of the sodium chloropalladate solution, the sodium hexachlororhodate solution, the aqueous solution of potassium iodide to the polyvinylpyrrolidone to the solvent is (1.5-1.9) mL: (0.2-0.4) mL: (0.8-1.2) mL: (130-170) mg: (9-11) mL;
the Pd-Rh nano-catalyst is used for the selective hydrogenation reaction of m-nitroaniline.
2. The method according to claim 1, wherein the concentration of the aqueous solution of potassium iodide is 0.9 to 1.1M.
3. The method according to claim 1, wherein the solvent is dimethylformamide.
4. The method of claim 1, wherein the cooling is air cooling to room temperature.
5. The preparation method according to claim 1, wherein the centrifugal rotation speed is 9000-11000 rpm; the centrifugation time is 4-6 min; the cleaning specifically comprises the following steps: washing with water for 1-3 times, and then washing with ethanol for 1-3 times.
6. The preparation method according to claim 1, further comprising maintaining the cleaned product at a position 4-6 mm away from the lamp in an ultraviolet ozone cleaning machine for 25-35 min, and then taking out.
7. A Pd-Rh nano-catalyst, which is prepared by the preparation method of any one of claims 1 to 6.
8. The preparation method of m-nitroanisole is characterized by comprising the step of catalyzing selective hydrogenation reaction of m-nitroanisole by using the Pd-Rh nano catalyst prepared by the preparation method of any one of claims 1-6.
9. The application of the Pd-Rh nano-catalyst prepared by the preparation method of any one of claims 1 to 6 in the selective hydrogenation reaction of m-nitroaniline.
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