Method for preparing surface-roughened pd nanospheres without surfactant and application of the pd nanospheres

Abstract

The application relates to a method for preparing Pd nanospheres with rough surfaces without surfactants and application of the Pd nanospheres, wherein an ethanol aqueous solution or a methanol aqueous solution is configured, a certain amount of Pd precursors is added into the ethanol aqueous solution or the methanol aqueous solution, a reaction container is gently shaken to uniformly mix the reaction system, the reaction system is allowed to stand and react in dark conditions, the reaction product is centrifugally separated after the reaction is completed, the obtained precipitate is centrifugally washed with ultrapure water, and drying is carried out under the condition of 20-60 DEG C, so that Pd nanospheres with rough surfaces are obtained. The application does not need to use surfactants, hard templates, does not need to additionally add a reducing agent, does not need high temperature and high pressure, does not need stirring and does not need light conditions, the reaction condition is mild, and the reaction step is simple. The prepared Pd nanospheres have rough surface structures and rich pore structures, are high in purity, and have high catalytic activity and conversion rate in selective hydrogenation reaction of 4-nitrobenzaldehyde.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of single metal nanomaterials, and particularly relates to a method for preparing Pd nanospheres with a rough surface structure under mild conditions without adding any surfactant in an alcohol solution and application of the Pd nanospheres in selective hydrogenation catalysis. BACKGROUND

[0002] Due to the fact that changes in size, morphology, composition and structural order of nanomaterials can bring unique optical, electrical and chemical properties, in recent years, people have launched a large number of researches on nanomaterials with special functions, among which, noble metals are particularly prominent. Design and construction of noble metal nanomaterials with special properties have become a major research hotspot in the field of catalytic materials in recent years.

[0003] In most of the methods for synthesizing noble metal nanoparticles reported in the literature, polyvinylpyrrolidone (PVP), cetyltrimethylammonium bromide (CTAB) and other surfactants are introduced. The introduction of surfactants can effectively control the morphology, stability and uniformity of noble metal nanoparticles, but at the same time, because of the strong adsorption of surfactants and the surface of nanocrystals, the active sites of nanomaterials are covered, resulting in a decrease in catalytic activity. Therefore, it is still a great challenge to use a simple and mild method to prepare nanomaterials with uniform particle size and high activity.

[0004] Pd nanomaterials have a wide range of applications in the field of catalysis, such as fuel cells, CO2 electro-reduction, CO2 hydrogenation, coupling reactions, cyclohexane oxidation and formic acid decomposition hydrogenation, and their catalytic performance is closely related to their morphology and chemical composition. Pd metals with different morphologies and structures have been successfully prepared, for example, the Chinese invention patent with application number CN201711134807.4 uses K2PdCl4 as a precursor, mixes it with NaOH, and then heats and calcines it in anhydrous ethanol at 150-200℃ in the dark for 1-2h to prepare porous Pd nanochalices. The reaction conditions are harsh, requiring high temperature and strong base conditions, which not only increases energy consumption and causes environmental pollution, but also makes the reaction process highly dangerous. The Chinese invention patent with application number CN201610261081.X first reduces the CuCl2 and polyethyleneimine (PEI) mixed solution with a pH of 10-13 at room temperature to prepare Cu2O nanospheres, then adds hydrazine hydrate and PdCl2 under alkaline conditions at 50-80℃ for 40min, and then stirs at room temperature for 16-24h to obtain hollow Pd nanospheres. The reaction operation process is long, requires the use of a surfactant, and the nanoparticles are difficult to clean. The Chinese invention patent with application number CN201010175023.8 mixes PdCl2 and ammonia water, and then sequentially adds ditetradecyl dimethyl quaternary ammonium salt, hypophosphite and cyclohexane, stirs uniformly, slowly raises the temperature to 60℃, and reacts for 60-90min to obtain a black product. The surfactant is extracted with anhydrous ethanol at 80℃ for 4h, ultrasonically cleaned for 30min, and washed with acetone and anhydrous ethanol multiple times, and then centrifuged to obtain clean multi-shell Pd nanospheres. The reaction process requires the use of flammable and explosive hypophosphite, which is dangerous to operate. A surfactant is also required to assist in the preparation of special-shaped products, and organic solvents are used, which causes environmental pollution. In addition, a large amount of organic solvent is required for repeated cleaning to obtain nanoparticles with high activity. Therefore, it is necessary to develop a mild and simple preparation technique without a surfactant for the synthesis of Pd nanomaterials. SUMMARY

[0005] The purpose of the present application is to provide a surfactant-free method for preparing Pd nanospheres with rough surfaces and the application of the Pd nanospheres. The preparation method of the present application is carried out in an alcohol solution, does not require the use of a surfactant, a hard template, or the additional addition of a reducing agent, does not require high temperature and high pressure, does not require stirring or light conditions, has mild reaction conditions, a simple reaction step, and can prepare samples with a "clean" surface, thus having high catalytic activity. The prepared Pd nanospheres have rough surface structures and rich pore structures, high purity, and high catalytic activity and conversion rate for selective hydrogenation of 4-nitrobenzaldehyde.

[0006] The application is realized by the following technical scheme, and the method for preparing Pd nanospheres with rough surface without surfactant comprises the following steps:

[0007] (1) a certain amount of anhydrous ethanol or methanol is configured into an ethanol aqueous solution or a methanol aqueous solution with water, and is prepared for use;

[0008] (2) a certain volume of the ethanol aqueous solution or the methanol aqueous solution in step (1) is added into a reaction container, a certain amount of Pd precursor is added into the reaction container, the reaction container is gently shaken to uniformly mix the reaction system, and then the reaction system is placed in the dark for reaction;

[0009] (3) the reaction product prepared in step (2) is centrifuged to discard the supernatant to obtain the lower layer precipitate, the obtained precipitate is centrifugally washed with ultrapure water for 3-5 times, and then is dried at 20-60℃ for 8-12h to obtain Pd nanospheres with rough surface.

[0010] Preferably, the volume ratio of the anhydrous ethanol or methanol to water in step (1) is 5:5-10:0.

[0011] Preferably, the temperature for the reaction in step (2) is 20-50℃, and the time is 1-4h.

[0012] Preferably, the molar concentration of the Pd precursor in the ethanol aqueous solution or the methanol aqueous solution in step (2) is 1.0-6.0mmol / L.

[0013] Preferably, the Pd precursor can be Pd(OAc)2.

[0014] The method for preparing Pd nanospheres with rough surface without surfactant has the Pd nanospheres with rough surface structure, the rough surface of the Pd nanospheres is composed of smaller nanoparticles, the diameter of the Pd nanospheres is 140nm, the diameter of the smaller nanoparticles constituting the rough surface of the Pd nanospheres is 12nm, the Pd nanospheres are face-centered cubic structure, the specific surface area is 31.19m 2 ·g -1 , the pore size range of the Pd nanospheres spans from micropore 0.7nm to mesopore 36.0nm, mainly with micropore 1.4nm, and Pd mainly exists in Pd 0 valence state in the nanospheres.

[0015] Further, the reaction container in the preparation method can be a round-bottom flask, a conical flask or a beaker, etc.

[0016] The application also provides application of the Pd nanospheres prepared according to the method in selective hydrogenation conversion of 4-nitrobenzaldehyde into 4-aminobenzaldehyde, and the specific method comprises the following steps: dispersing the prepared Pd nanospheres in a certain volume of anhydrous ethanol, shaking gently to make the Pd nanospheres uniformly dispersed, then adding the Pd nanospheres into a certain volume of anhydrous ethanol containing 4-nitrobenzaldehyde, so that the concentration of the Pd nanospheres and the 4-nitrobenzaldehyde in the mixed system is 0.1-0.3 g / L and 0.05-0.30 mol / L respectively. Then the mixed system is reacted under the conditions of 35 ℃, hydrogen atmosphere and normal pressure, and a gas chromatograph-mass spectrometer is used to track the reaction process. After 1.5 h of reaction, the conversion rate of the 4-nitrobenzaldehyde is ≥98%, and the selectivity of the conversion of the 4-nitrobenzaldehyde into 4-aminobenzaldehyde is ≥98%, which indicates that the prepared Pd nanospheres have good catalytic activity and selectivity in the catalytic hydrogenation reaction of 4-nitrobenzaldehyde.

[0017] Compared with the prior art, the application has obvious advantages and beneficial effects. By means of the above technical scheme, the application can achieve considerable technical progress and practicability, and has wide utilization value, and at least has the following advantages:

[0018] (1) The preparation method of the application is carried out in an alcohol solution, and no surfactant needs to be added in the reaction process, so that a sample with clean surface can be easily prepared, and thus the catalytic activity is high.

[0019] (2) The application does not need to add an additional reducing agent, and after the precursor Pd(OAc)2 is added into an ethanol aqueous solution or a methanol aqueous solution, the reaction can be carried out, so that the experimental steps are simpler. The methanol or ethanol used has a dual role, which not only serves as a solvent component, but also serves as a reducing agent due to its weak reducing property, so that the Pd(OAc)2 is reduced into metallic Pd.

[0020] (3) The technical route for preparing the Pd nanospheres in the application does not need to use a surfactant or a hard template, and does not need to add an additional reducing agent or high temperature and high pressure. The reaction condition is mild, and the reaction can be carried out at 20-50 ℃ in the dark, without stirring or light irradiation. The operation is simple, the separation is easy, and the energy consumption is low.

[0021] (4) The prepared Pd nanospheres have a rough surface structure, and the rough surface is composed of smaller nanoparticles. The diameter of the Pd nanospheres is about 140 nm, and the diameter of the small nanoparticles constituting the rough surface of the Pd nanospheres is about 12 nm. The Pd nanospheres have a face-centered cubic structure, and the peak type is obviously widened, which indicates that the Pd nanospheres are composed of smaller nanoparticles. No other impurity peaks appear, which proves that the purity of the purified sample is high. The specific surface area of the Pd nanospheres is about 31.19 m 2 ·g-1 The pore size range spans from micropores 0.7 nm to mesopores 36.0 nm, mainly micropores 1.4 nm, and Pd mainly exists in Pd 0 valence in the nanospheres.

[0022] (5) The Pd nanospheres prepared by the method have high catalytic activity and conversion rate in selective hydrogenation of 4-nitrobenzaldehyde, and the catalytic reaction is safe, low in energy consumption, and mild in conditions, and the conversion rate of 4-nitrobenzaldehyde in the catalytic hydrogenation is ≥98%, and the selectivity to 4-aminobenzaldehyde is ≥98%. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a SEM image of the Pd nanospheres prepared in Example 1, magnified 20000 times;

[0024] Figure 2 is a SEM image of the Pd nanospheres prepared in Example 1, magnified 50000 times;

[0025] Figure 3 is a TEM image of the Pd nanospheres prepared in Example 1;

[0026] Figure 4 is an XRD spectrum of the Pd nanospheres prepared in Example 1;

[0027] Figure 5 is an XPS spectrum of the Pd nanospheres prepared in Example 1;

[0028] Figure 6 is a N2 adsorption-desorption isotherm curve of the Pd nanospheres prepared in Example 1;

[0029] Figure 7 is a pore size distribution graph of the Pd nanospheres prepared in Example 1;

[0030] Figure 8 is a conversion rate and selectivity curve of the Pd nanospheres prepared in Example 1 in catalytic hydrogenation of 4-nitrobenzaldehyde with time. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme of the present application will be described clearly and completely below in combination with specific embodiments. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0032] Example 1:

[0033] 1) A certain amount of methanol and water were taken to prepare a methanol aqueous solution, and the volume ratio of methanol to water was 10:0;

[0034] 2) 10 mL of the methanol aqueous solution in step 1) was taken into a round-bottom flask, and 0.033 mmol of Pd(OAc)2 was added thereto, so that the molar concentration of Pd(OAc)2 in the methanol aqueous solution was 3.3 mmol / L; the round-bottom flask was gently shaken to mix the reaction system uniformly, and then the reaction was carried out at 40°C for 2 h in the dark;

[0035] 3) The reaction mixture prepared in step 2) was subjected to centrifugal separation, and the supernatant was discarded to obtain a lower layer of precipitate, which was then washed by centrifugation with ultrapure water for 3 times, and then vacuum dried at 40°C for 8 h to obtain Pd nanospheres with rough surfaces.

[0036] Figure 1 and Figure 2 are scanning electron microscope (SEM) images of the Pd nanospheres prepared in Example 1, which are enlarged 20,000 times and 50,000 times, respectively; it can be seen from the SEM images at different magnifications that the prepared Pd nanospheres have a spherical structure with rough surfaces, and the rough surfaces are composed of smaller nanoparticles.

[0037] Figure 3 is a TEM image of the Pd nanospheres prepared in Example 1, and it can be seen that the diameters of the nanospheres are about 140 nm, and the diameters of the smaller nanoparticles constituting the rough surfaces of the nanospheres are about 12 nm.

[0038] Figure 4 is an XRD pattern of the Pd nanospheres prepared in Example 1; it can be seen that the Pd nanospheres have a face-centered cubic structure, and the peak type is obviously widened, indicating that the Pd nanospheres are composed of smaller nanoparticles. No other impurity peaks appear, proving that the sample after purification has high purity.

[0039] Figure 5 is an XPS spectrum of the Pd nanospheres prepared in Example 1, which shows that Pd in the nanospheres mainly exists in the Pd 0 valence state.

[0040] Figure 6 is the N2 adsorption-desorption isotherm curve of the Pd nanospheres prepared in Example 1, which shows a type III curve, and the specific surface area of the Pd nanospheres is determined to be as high as 31.19 m 2 ·g -1 .

[0041] Figure 7 is the pore size distribution graph of the Pd nanospheres prepared in Example 1, and it can be seen that the pore size range of the Pd nanospheres spans from micropores of 0.7 nm to mesopores of 36.0 nm, and the micropores of 1.4 nm are mainly present.

[0042] The prepared surface-roughened Pd nanospheres were used to catalyze selective hydrogenation of 4-nitrobenzaldehyde. The specific method comprises: dispersing the prepared Pd nanospheres in 1 mL of anhydrous ethanol, gently shaking to uniformly disperse the Pd nanospheres, and then adding the Pd nanospheres to 4 mL of anhydrous ethanol containing 4-nitrobenzaldehyde, so that the concentration of the Pd nanospheres and the 4-nitrobenzaldehyde in the mixed system is 0.2 g / L and 0.10 mol / L, respectively. Then, the mixed system was reacted at 35°C under a hydrogen atmosphere at normal pressure, and a gas chromatograph-mass spectrometer was used to track the reaction process. Figure 8 Figure is a curve of the conversion rate of Pd nanospheres catalyzing hydrogenation of 4-nitrobenzaldehyde and the selectivity of 4-aminobenzaldehyde with time. After 1.5 h of reaction, the conversion rate of 4-nitrobenzaldehyde is ≥98%, and the selectivity of the conversion to generate 4-aminobenzaldehyde is ≥98%, indicating that the prepared Pd nanospheres have good catalytic activity and selectivity in the catalytic hydrogenation reaction of 4-nitrobenzaldehyde.

[0043] Example 2:

[0044] 1) A certain amount of anhydrous ethanol and water were configured into an ethanol aqueous solution, and the volume ratio of anhydrous ethanol to water was 10:0.

[0045] 2) 10 mL of the ethanol aqueous solution in step 1) was taken into a round-bottom flask, 0.02 mmol of Pd(OAc)2 was added to the ethanol aqueous solution, so that the molar concentration of Pd(OAc)2 in the ethanol aqueous solution was 2.0 mmol / L; the round-bottom flask was gently shaken to uniformly mix the reaction system, and then the reaction system was statically reacted at 30°C in the dark for 2 h.

[0046] 3) The reaction mixture prepared in step 2) was centrifuged to discard the supernatant and obtain the precipitate, and then the precipitate was washed with ultrapure water for 3 times, and then vacuum dried at 50°C for 8 h, to obtain the surface-roughened Pd nanospheres.

[0047] Example 3:

[0048] 1) A certain amount of methanol and water were configured into a methanol aqueous solution, and the volume ratio of methanol to water was 8:2.

[0049] 2) 10 mL of the methanol aqueous solution in step 1) was taken into a round-bottom flask, 0.025 mmol of Pd(OAc)2 was added to the methanol aqueous solution, so that the molar concentration of Pd(OAc)2 in the methanol aqueous solution was 2.5 mmol / L; the round-bottom flask was gently shaken to uniformly mix the reaction system, and then the reaction system was statically reacted at 20°C in the dark for 1 h.

[0050] 3) centrifuging the reaction mixture prepared in step 2) to discard the supernatant and obtain the precipitate, then washing the precipitate with ultrapure water for 3 times, and drying the precipitate at 40°C under vacuum for 8h to obtain the Pd nanospheres with rough surface.

[0051] Example 4:

[0052] 1) a certain amount of methanol and water were taken to prepare a methanol aqueous solution, and the volume ratio of methanol to water was 5:5;

[0053] 2) 10mL of the methanol aqueous solution in step 1) was taken into a round-bottom flask, and 0.06mmol of Pd(OAc)2 was added to the round-bottom flask to make the molar concentration of Pd(OAc)2 in the methanol aqueous solution 6.0mmol / L; the round-bottom flask was gently shaken to mix the reaction system, and then the reaction was carried out at 50°C under dark condition for 4h;

[0054] 3) the reaction mixture prepared in step 2) was centrifuged to discard the supernatant and obtain the precipitate, then the precipitate was washed with ultrapure water for 5 times, and the precipitate was dried at 20°C under vacuum for 10h to obtain the Pd nanospheres with rough surface.

[0055] Example 5:

[0056] 1) a certain amount of anhydrous ethanol and water were taken to prepare an ethanol aqueous solution, and the volume ratio of anhydrous ethanol to water was 7:3;

[0057] 2) 10mL of the ethanol aqueous solution in step 1) was taken into a round-bottom flask, and 0.05mmol of Pd(OAc)2 was added to the round-bottom flask to make the molar concentration of Pd(OAc)2 in the ethanol aqueous solution 5.0mmol / L; the round-bottom flask was gently shaken to mix the reaction system, and then the reaction was carried out at 30°C under dark condition for 3h;

[0058] 3) the reaction mixture prepared in step 2) was centrifuged to discard the supernatant and obtain the precipitate, then the precipitate was washed with ultrapure water for 5 times, and the precipitate was dried at 60°C under vacuum for 12h to obtain the Pd nanospheres with rough surface.

[0059] Example 6:

[0060] 1) a certain amount of methanol and water were taken to prepare a methanol aqueous solution, and the volume ratio of methanol to water was 6:4;

[0061] 2) Take 10 mL of the methanol aqueous solution in step 1) into a round-bottom flask, and add 0.045 mmol of Pd(OAc)2 into the round-bottom flask, so that the molar concentration of Pd(OAc)2 in the methanol aqueous solution is 4.5 mmol / L; shake the round-bottom flask gently to mix the reaction system uniformly, and then place the round-bottom flask in dark condition at 30°C for 1 h of reaction;

[0062] 3) Centrifuge the reaction mixture prepared in step 2), discard the supernatant, and then wash the precipitate with ultrapure water for 4 times, and then dry the precipitate in vacuum at 30°C for 10 h, so that the Pd nanospheres with rough surface are obtained.

[0063] It should be noted that the preparation method of the present application is not limited to using a round-bottom flask as a reaction container, and in other embodiments, a transparent glass reaction container such as a conical flask or a beaker can also be used, and the description of the specific embodiments is not considered as any form of limitation on the present application.

[0064] The above description is only an embodiment of the present application, and is not considered as any form of limitation on the present application, and the present application can also have other forms of embodiments according to the above structure and function, and the above embodiments are not listed one by one. Therefore, any skilled person in the art, without departing from the technical solution range of the present application, according to the technical essence of the present application, any simple modification, equivalent change and modification of the above embodiments, still belongs to the technical solution range of the present application.

Claims

1. A method for preparing surface-roughened Pd nanospheres without surfactants, characterized by The method comprises the following steps: (1) a certain amount of anhydrous ethanol or methanol is taken and configured into an ethanol aqueous solution or a methanol aqueous solution with water, for standby; or a certain amount of anhydrous ethanol or methanol is taken, for standby; (2) a certain volume of the ethanol aqueous solution or the methanol aqueous solution in step (1) or anhydrous ethanol or methanol is taken and added into a reaction container, and a certain amount of Pd(OAc)2 is added into the reaction container as a Pd precursor, so that the molar concentration of the Pd precursor in the ethanol aqueous solution or the methanol aqueous solution or anhydrous ethanol or methanol is 1.0-6.0 mmol / L, the reaction system is mixed uniformly by gently shaking the reaction container, and then the reaction system is placed at 20-50 °C in the dark for 1-4 h; (3) the reaction product prepared in step (2) is centrifuged and separated, the supernatant is discarded, the obtained precipitate is washed by centrifugation with ultrapure water for 3-5 times, and then dried at 20-60 °C for 8-12 h, so that the Pd nanospheres with a rough surface are obtained, the Pd nanospheres have a rough surface structure, the rough surface is composed of smaller nanoparticles, the diameter of the Pd nanospheres is 140 nm, and the diameter of the smaller nanoparticles constituting the rough surface of the Pd nanospheres is 12 nm.

2. The surfactant-free method for preparing surface-roughened Pd nanospheres according to claim 1, characterized in that The Pd nanospheres are face-centered cubic structures with a specific surface area of 31.19 m 2 ·g -1 , mainly with 1.4 nm micropores, and Pd mainly exists in Pd 0 valence state in the nanospheres.

3. The Pd nanospheres prepared by the method of claim 1.

4. The application of the Pd nanospheres prepared by the method of claim 1 in catalyzing the selective hydrogenation conversion of 4-nitrobenzaldehyde into 4-aminobenzaldehyde, wherein the conversion rate of the Pd nanospheres in the selective hydrogenation conversion of 4-nitrobenzaldehyde is ≥98%, and the selectivity of the Pd nanospheres to 4-aminobenzaldehyde is ≥98%.

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