CN103041816A - Self-protection nano-cobalt catalyst with high cyclic stability - Google Patents

Abstract

The invention provides a self-protecting nano-cobalt catalyst with high cycle stability. The nano-cobalt catalyst, after the nano-metal cobalt Co catalyzes the hydrolysis of boronamine AB to generate hydrogen under room temperature air, oxidizes the Co nanometer in the etching solution. Catalyst particles to convert them into Co ²⁺ ions, Co ²⁺ ions can be stored in the solution for a long _time to realize the self-protection function of the catalyst; then quickly reduce Co ²⁺ ions to Co nanoparticles realize the recycling of Co catalysts; the regenerated Co nanocatalyst particles have the same high catalytic activity as the original Co nanocatalyst particles. The method is simple, effective, and low-cost, and overcomes the oxidation passivation of the non-precious metal catalyst Co nanoparticles when catalyzing AB hydrogen production, making it stable for long-term cycles, and promoting the practical application of hydrogen storage-dehydrogenation in vehicle-mounted mobile hydrogen source materials .

Description

A self-protected nano-cobalt catalyst with high cycle stability

technical field

The invention relates to a self-protected nano-cobalt catalyst with high cycle stability prepared by a metal-metal ion reversible transformation method. the

Background technique

With the generation of the energy crisis and the large amount of greenhouse effect gases (carbon dioxide, methane, etc.) being discharged into the ambient atmosphere, it is very important to find an alternative clean new energy source. Hydrogen energy has surfaced as an abundant, renewable, and pollution-free energy source. Therefore, in the process of leading to a hydrogen energy society, finding an efficient and safe hydrogen storage material has become the most difficult challenge. Boronamine (NH ₃ BH ₃ , AB) can be used as a very promising hydrogen storage material due to its high hydrogen content (19.6 wt%), high solubility, non-toxicity and stability. However, one of the biggest obstacles to the extensive application of AB as a hydrogen storage material is to find a catalyst that is simple, efficient, economical, and has good cycle stability to further improve its hydrogen desorption kinetics under appropriate conditions.

Compared with ordinary bulk catalyst materials, nano catalyst materials have been widely used in many important chemical reactions due to their large surface-to-volume ratio and high catalytic activity. An important goal of nanocatalyst materials is to make them have high selectivity, excellent catalytic activity, strong reaction stability and low cost. the

In many important reactions, cobalt element (Co) is not only abundant in the earth's crust compared to the non-noble metals of noble metal elements, but also has a lower cost than noble metal elements, and in many important reactions such as: synthesis of high Carbon (C3 or higher) alcohol reactions, dehydrogenation reactions, hydrogen and oxygen production reactions, etc., all have good catalytic activity, so they have received more and more attention as catalytic materials. However, Co nanoparticles are more easily oxidized in air than noble metal particles, which will lead to oxidation passivation of catalyst particles and poor cycle stability, especially when the time interval between two cycle reactions is long, which greatly limits its practical application. Recently, the main method to overcome this problem is to add a layer of stable wrapping materials on the surface of Co nanoparticles, such as silicon, carbon, transition metal oxides, etc.; or to apply and store nano-Co catalysts under inert gas. However, these methods have more or less disadvantages, such as the stable outer coating material occupying the active site of the Co catalyst, reducing its catalytic activity; under the protection of inert gas, the complexity and high cost of catalyst synthesis and application, etc. To sum up, it is very meaningful to find a simple and effective new method to avoid the problem of Co nanocatalysts being degraded by long-term use. the

Contents of the invention

The object of the present invention is to provide a self-protected nano-Co catalyst with high cycle stability prepared by the catalyst through the free and reversible transformation method of metal (Co)-metal ion (Co ²⁺ ). The self-protected nano-cobalt catalyst with high cycle stability, in the air environment at room temperature, after the nano-metallic Co catalyzes the hydrolysis of AB to generate hydrogen, the Co nanoparticles in the solution are oxidized and etched to convert them into Co ²⁺ ions , and Co ²⁺ ions can be stored in the solution for a long time to realize the self-protection function of the catalyst; then the Co ²⁺ ions can be quickly reduced to Co nanoparticles by sodium borohydride (NaBH ₄ ) and AB to realize the recycling of the catalyst ; while the regenerated Co nanocatalyst particles have the same high catalytic activity as the original Co nanocatalyst particles.

Technical scheme of the present invention is:

A self-protected nano-cobalt catalyst with high cycle stability, the nano-cobalt catalyst is prepared by the following method:

The selection of chemicals required for the AB hydrogen production process: boronamine AB, cobalt chloride hexahydrate CoCl ₂ 6H ₂ O, sodium borohydride NaBH ₄ and ammonia water H ₅ NO, the specific steps for the preparation of nano-Co catalyst particles are as follows:

Step 1, dissolving 0.01-0.05 mmol of CoCl ₂ ·6H ₂ O in 2-10 mL of distilled water to obtain a pink CoCl ₂ aqueous solution;

Step 2, dissolving 30-70 mg of AB and 5-30 mg of _NaBH in 2-10 mL of distilled water;

Step 3, the solution in step 2 is added to the solution of step 1;

Step 4, at 10-40°C, magnetically stir the solution obtained in Step 3 in the air, and black suspended particles can be seen, which are Co nano metal catalysts;

Step 5, measure the hydrogen produced in step 4 through the gas measuring tube, and the hydrolysis hydrogen production equation is:

AB+2H ₂ O=NH ₄ ⁺ +BO ₂ ^- +3H ₂ ;

Step 6: At 10-40°C, after the solution in step 4 generates hydrogen, magnetically stir the black suspension in the air for 10-200 minutes, and the black suspension turns into a pink liquid, which is CoCl ₂ solution;

Step 7, 30-70 mg of AB and 5-30 mg of NaBH ₄ are dissolved in 2-10 mL of distilled water;

Step 8, pour the solution of step 7 into the solution of step 6, and the pink solution becomes a black suspension again;

Step 9, at 10-40°C, magnetically stir the solution obtained in step 8 in the air, and black suspended particles can be seen, and the black suspended particles are Co nano metal catalysts;

The chemicals used are AB with 90wt% boronamine, CoCl ₂ ·6H ₂ O with 99wt% cobalt chloride hexahydrate, >96wt% sodium borohydride NaBH ₄ and 25wt%-28wt% ammonia water H ₅ NO.

The steps 1 to 4 are to convert the metal ion Co ²⁺ into the nano-metal catalyst Co; step 6 is to convert the nano-metal catalyst Co into the metal ion Co ²⁺ , so that the nano-metal catalyst Co can be self-protected and realize the high circulation of the catalyst Stability; Step 9 is to convert metal ion Co ²⁺ into nano-metal catalyst Co; the above steps 1 to 9 are a reaction cycle, so as to realize the self-protected nano-Co catalyst with high cycle stability prepared by metal-metal ion reversible transformation method .

Co nanoparticles synthesized for the first time have a size of 20 nm and aggregate together like nanochain structures. the

The re-synthesized Co nano metal particles are in a dispersed state, and the size of the nanoparticles is about 4nm. the

Technical effect of the present invention is:

The simple but effective metal-metal ion reversible transformation method used to prepare nano-Co catalysts can effectively avoid the oxidation passivation of non-noble metal catalysts Co, making it easy to store, achieving self-protection and making nano-Co catalysts have a high cycle stability. In other words, we can completely convert Co nanoparticles into Co ions and preserve them in air for a long time, and then easily convert Co ^ions into Co nanoparticles with similar or ^identical high catalytic activity as before preservation , to achieve recycling, so that the non-noble metal nanocatalyst Co has high cycle stability. This approach also saves costs in catalyst selection, synthesis and application.

Description of drawings

Fig. 1 Schematic diagram of free and reversible transformation of metal (Co)-metal ion (Co ²⁺ ).

Fig. 2 UV-Vis spectrum diagram, wherein: (a) is CoCl ₂ solution, (b) is Co nanoparticle, (c) is the solution after oxidative etching of Co nanoparticle in air.

The XPS diagram of the elements in Figure 3Co nanoparticles, where:

Figure 3(a) is the XPS diagram of Co,

Figure 3(b) is the XPS diagram of B. the

Figure 4. Hydrogen production curves of AB catalyzed by different catalysts, where: (a) is the Co nanoparticles produced for the first time, (b) is the Co nanoparticles regenerated in the fifth cycle, and (c) is the Co nanoparticles regenerated in the tenth cycle . Insert: AB hydrogen production curves catalyzed by Co nanoparticles after storage in pure water for 7 days. the

Fig. 5 TEM and SAED images of different catalysts, where: (a) is the Co nanoparticles synthesized for the first time, and (b) is the Co nanoparticles regenerated in the 10th cycle. the

Detailed ways

Comparative Example 1

Dissolve 0.03 mmol of CoCl ₂ 6H ₂ O in 5 mL of distilled water to obtain a pink CoCl ₂ aqueous solution; 50 mg of AB and 10 mg of NaBH ₄ are dissolved in 5 mL of distilled water, and add this solution to the pink color at 25 °C In the colored _CoCl2 aqueous solution, the magnetic force stirs evenly, and the pink solution rapidly becomes a black suspension, as shown in Figure 3, X-ray photoelectron spectroscopy (XPS) results show that the black suspended particles are Co nanometer metal catalysts; in the AB solution After the hydrogen production was finished, the black suspended Co nanoparticles were stirred for 200 min under an argon atmosphere. The black suspension remained unchanged, which means that the Co nanoparticles were stable in argon. It shows that Co nanoparticles cannot realize the interconversion between nano-metal Co and Co ²⁺ under the condition of argon atmosphere, and cannot realize the self-protection function when the nano-Co catalyst is recycled.

Comparative Example 2

Dissolve 0.03 mmol of CoCl ₂ 6H ₂ O in 5 mL of distilled water to obtain a pink CoCl ₂ aqueous solution; 50 mg of AB and 10 mg of NaBH ₄ are dissolved in 5 mL of distilled water, and add this solution to the pink color at 25 °C In the colored _CoCl2 aqueous solution, the magnetic force stirs evenly, and the pink solution rapidly becomes a black suspension, as shown in Figure 3, X-ray photoelectron spectroscopy (XPS) results show that the black suspended particles are Co nanometer metal catalysts; in the AB solution After the hydrogen production was finished, the water-washed black suspended Co nanoparticles were placed in distilled water, and the solution was stirred for 200 minutes under an air atmosphere, and it was found that the black suspension remained unchanged. It shows that Co nanoparticles cannot realize the interconversion between nano-metal Co and Co ²⁺ in the air without C1 ^- , BO ₂ ^- and NH ₄ ⁺ , and cannot realize the self-protection function when the nano-Co catalyst is recycled.

Comparative Example 3

Dissolve 0.03 mmol of CoCl ₂ 6H ₂ O in 5 mL of distilled water to obtain a pink CoCl ₂ aqueous solution; 50 mg of AB and 10 mg of NaBH ₄ are dissolved in 5 mL of distilled water, and add this solution to the pink color at 25 °C In the colored CoCl ₂ aqueous solution, the magnetic force stirred evenly, and the pink solution quickly turned into a black suspension, as shown in Figure 3, and the X-ray photoelectron spectroscopy (XPS) results showed that the black suspended particles were Co nano-metal catalysts; After the hydrogen was over, the water-washed black suspended Co nanoparticles were placed in ammonia water at pH = 9.4, and the solution was stirred for 200 min under an air atmosphere, and it was found that the black suspension remained unchanged. It shows that Co nanoparticles cannot realize the interconversion between nano-metal Co and Co ²⁺ in the air with NH ₄ ⁺ , and cannot realize the self-protection function when the nano-Co catalyst is recycled.

Comparative example 4 (embodiment of the present invention)

Dissolve 0.03 mmol of CoCl ₂ 6H ₂ O in 5 mL of distilled water to obtain a pink CoCl ₂ aqueous solution; 50 mg of AB and 10 mg of NaBH ₄ are dissolved in 5 mL of distilled water, and add this solution to the pink color at 25 °C Magnetically stir the colored CoCl ₂ aqueous solution evenly, and the pink solution quickly turns into a black suspension, as shown in Figure 3. X-ray photoelectron spectroscopy (XPS) results show that the black suspended particles are Co nano-metal catalysts, and the initial reaction produces The size of the Co nanoparticles is about 20nm and they are agglomerated together like a nanochain structure, as shown in Figure 5a; after the hydrogen production of the AB solution is completed, the black suspension is magnetically stirred in the air for 30 minutes at 25 ° C, and the black The suspension turned into a pink liquid. 50 mg of AB and 10 mg of NaBH were dissolved in 5 mg of distilled water, and the solution was poured into a pink solution, which turned into a black suspension again; the invention used ultraviolet _- visible absorption spectroscopy (UV-Vis) to detect the transformation ( figure 2). At a wavelength of 510nm, we saw an absorption peak corresponding to CoCl ₂ (Fig. 2a). After adding 50 mg of AB and 10 mg of NaBH ₄ dissolved in 5 mL of distilled water, the absorption peak disappeared, indicating that the Co ²⁺ ion was transformed into into Co nanoparticles (Fig. 2b). When the black suspension turned into a clear pink solution, the absorption peak at 510nm appeared again (Figure 2c), indicating that the nano-metallic Co was transformed into nano-Co ²⁺ ions again, and at the wavelength of 420nm due to the new reaction product ion resulting in a new absorption peak. The graph of hydrogen production (mL) and time (minutes) of the nano-Co catalyzed AB hydrogen production process is shown in Figure 4a. The initial reduction of Co nanoparticles catalyzed AB hydrolysis hydrogen production can be completed within 11 minutes. The amount of hydrogen gas was 125 mL.

Comparative Example 5

Dissolve 0.03 mmol of CoCl ₂ 6H ₂ O in 5 mL of distilled water to obtain a pink CoCl ₂ aqueous solution; 50 mg of AB and 10 mg of NaBH ₄ are dissolved in 5 mL of distilled water, and add this solution to the pink color at 25 °C Magnetically stir the colored CoCl ₂ aqueous solution evenly, and the pink solution quickly turns into a black suspension, as shown in Figure 3. X-ray photoelectron spectroscopy (XPS) results show that the black suspended particles are Co nano-metal catalysts, and the initial reaction produces The size of the Co nanoparticles is about 20nm and they are agglomerated together like a nanochain structure, as shown in Figure 5a; after the hydrogen production of the AB solution is completed, the black suspension is magnetically stirred in the air for 30 minutes at 25 ° C, and the black The suspension turned into a pink liquid. This shows that after Co nanoparticles are converted into Co ²⁺ ions with self-protection function through oxidation etching, they are stored in air at room temperature for 7 days, and after adding 50 mg of AB and 10 mg of NaBH ₄ dissolved in 5 mL of distilled water, they are reduced to Co nanoparticles and applied to the same catalytic reaction. This was repeated 5 times for a total of 35 days. As a result, the regenerated Co nanoparticles for the fifth time had the same reactivity as the Co nanoparticles for the initial reaction. This time, the catalyzed hydrolysis of AB to produce hydrogen could be completed within 11.4 minutes, and the amount of hydrogen produced was 125mL.

Comparative Example 6

Dissolve 0.03 mmol of CoCl ₂ 6H ₂ O in 5 mL of distilled water to obtain a pink CoCl ₂ aqueous solution; 50 mg of AB and 10 mg of NaBH ₄ are dissolved in 5 mL of distilled water, and add this solution to the pink color at 25 °C Magnetically stir the colored CoCl ₂ aqueous solution evenly, and the pink solution quickly turns into a black suspension, as shown in Figure 3. X-ray photoelectron spectroscopy (XPS) results show that the black suspended particles are Co nano-metal catalysts, and the initial reaction produces The size of the Co nanoparticles is about 20nm and they are agglomerated together like a nanochain structure, as shown in Figure 5a; after the hydrogen production of the AB solution is completed, the black suspension is magnetically stirred in the air for 30 minutes at 25 ° C, and the black The suspension turned into a pink liquid. This shows that after Co nanoparticles are converted into Co ²⁺ ions with self-protection function through oxidation etching, they are stored in air at room temperature for 7 days, and after adding 50 mg of AB and 10 mg of NaBH ₄ dissolved in 5 mL of distilled water, they are reduced to Co again. nanoparticles and applied to the same catalytic reaction. This was repeated 10 times for a total of 70 days. As a result, the regenerated Co nanoparticles for the 10th time had the same reactivity as the Co nanoparticles for the initial reaction. The TEM of the Co nanoparticles after the 10th reaction (Fig. The particle size is about 4nm. The catalytic AB hydrolysis to produce hydrogen can be completed within 11 minutes, and the amount of hydrogen produced at 25°C is 125mL.

Comparative Example 7

Dissolve 0.03 mmol of CoCl ₂ 6H ₂ O in 5 mL of distilled water to obtain a pink CoCl ₂ aqueous solution; 50 mg of AB and 10 mg of NaBH ₄ are dissolved in 5 mL of distilled water, and add this solution to the pink color at 25 °C Magnetically stir the colored CoCl ₂ aqueous solution evenly, and the pink solution quickly turns into a black suspension, as shown in Figure 3. X-ray photoelectron spectroscopy (XPS) results show that the black suspended particles are Co nano-metal catalysts, and the initial reaction produces The size of the Co nanoparticles is about 20nm and agglomerated together like a nanochain structure, as shown in Figure 5a; in air, the washed Co nanoparticles were stored in pure water for 7 days, and then the catalyst particles were applied to the AB In the catalytic hydrogen production reaction (the reaction without NaBH ₄ ), the reaction can only be completed within 216 min (as shown in the inset of Fig. 4). In general, the metal-metal ion reversible transformation can be used as a new method to overcome the oxidation passivation of Co nanoparticles. After long-term storage in air, Co nanocatalysts still have high activity, so that Co The catalyst is capable of numerous commercial applications.

Although the invention has been described in detail with reference to the embodiments, it will be understood by those skilled in the art that changes in some of the details may be made within the scope of the appended claims. the

Industrial application:

The preparation of nano-Co catalysts by metal-metal ion reversible transformation can simply and effectively avoid the oxidation passivation of non-noble metal catalysts, make them easy to store, realize their own protection and make nano-Co catalysts have high cycle stability. It has greatly promoted the practical application of hydrogen storage-dehydrogenation in vehicle-mounted mobile hydrogen source materials. the

Claims (5)

1. the self-shield nanometer cobalt catalyst of a high cyclical stability is characterized in that, described nanometer cobalt catalyst prepares by the following method:

The selection of the required chemicals of AB hydrogen production process: boron amide AB, CoCL2 6H2O CoCl ₂6H ₂O, sodium borohydride NaBH ₄With ammoniacal liquor H ₅NO, the concrete steps of nano Co catalyst granules preparation are as follows:

Step 1 is with the CoCl of 0.01～0.05mmol ₂6H ₂O is dissolved in the distilled water of 2～10mL, obtains peach CoCl ₂The aqueous solution;

Step 2 is with the AB of 30～70mg and the NaBH of 5～30mg ₄Be dissolved in the distilled water of 2～10mL;

Step 3 joins the solution in the step 2 solution of step 1;

Step 4, under 10-40 ℃ that solution magnetic agitation in air of step 3 gained is even, can see that the suspended particulate that black is arranged produces, the black suspension particle is the Co metallic catalyst;

Step 5, by the hydrogen that produces in the gas burette measuring process four, the hydrolytic hydrogen production equation is:

AB+2H ₂O=NH ₄ ⁺+BO ₂ ^-+3H ₂；

Step 6, under 10-40 ℃, step 4 solution produces hydrogen finish after, in air behind the magnetic agitation 10-200min, black suspension has become pink liquid with black suspension, this peach liquid is CoCl ₂Solution;

Step 7, the AB of 30～70mg and the NaBH of 5～30mg ₄Be dissolved in the distilled water of 2～10mL;

Step 8 is poured step 7 solution in the step 6 solution into, and pink solution becomes black suspension again;

Step 9, under 10-40 ℃ that solution magnetic agitation in air of step 8 gained is even, can see that the suspended particulate that black is arranged produces, the black suspension particle is the Co metallic catalyst;

2. the self-shield nanometer cobalt catalyst of a kind of high cyclical stability according to claim 1 is characterized in that, used chemicals is the AB of boron amide 90wt%, the CoCl of CoCL2 6H2O 99wt% ₂6H ₂O,〉the sodium borohydride NaBH of 96wt% ₄And the ammoniacal liquor H of 25wt%～28wt% ₅NO.

3. the self-shield nanometer cobalt catalyst of a kind of high cyclical stability according to claim 1 and 2 is characterized in that, described step 1 to four is with metal ion Co ²⁺Change metallic catalyst Co into; Described step 6 is to change metallic catalyst Co into metal ion Co ²⁺Thereby, make metallic catalyst Co obtain self-protection, realize the high cyclical stability of catalyst; Described step 9 is with metal ion Co ²⁺Change again metallic catalyst Co into; Above-mentioned steps one to nine is a reaction cycle, thereby realizes the self-shield nano Co catalyst with the standby high cyclical stability of metal-metal ion reversible transition legal system.

4. the self-shield nanometer cobalt catalyst of a kind of high cyclical stability according to claim 3 is characterized in that, synthetic Co nano-particles size is 20nm and reunites and arrive together as the nano chain structure first.

5. the self-shield nanometer cobalt catalyst of a kind of high cyclical stability according to claim 3 is characterized in that, synthetic Co nano-metal particle is dispersity again, and its nano particle size is about 4nm.

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