CN106179402A - A kind of preparation method of nanoporous palladium catalytic membrane - Google Patents

Abstract

The invention discloses a method for preparing a nanoporous palladium catalytic membrane, which belongs to the technical field of nanoporous materials and catalysis. The present invention adopts electroless plating and dealloying methods to prepare nanoporous palladium, first chemically deposits a layer of Pd-based (Pd/Cu) precursor alloy nano-film on the organic film carrier, and then removes the organic film carrier and homogenizes the alloy by heat treatment The chemical composition of the nano-membrane is dealloyed in an acidic solution, and finally washed to neutral in distilled water to obtain a three-dimensional catalytic self-supporting nano-porous membrane with a film thickness and a pore size of nanometer scale (1-100nm).

Description

A kind of preparation method of nanoporous palladium catalytic membrane

technical field

The invention relates to a preparation method of a nanoporous palladium catalytic membrane, in particular to a preparation method of a three-dimensional catalytic self-supporting nanoporous palladium catalytic membrane, belonging to the technical field of preparation methods of nanoporous metal materials.

Background technique

Due to the atomic structure characteristics of palladium, it has excellent catalytic activity for many important reactions, high catalytic selectivity and good stability. Pd catalysts also have broad application prospects in environmental protection, especially in the treatment of automobile exhaust, which can convert toxic gases such as hydrocarbons, carbon monoxide and nitrogen oxides in exhaust gases into Harmless gas; In addition, Pd catalyst has shown potential application value in proton exchange membrane fuel cells due to its excellent methanol electrocatalytic activity, formic acid electrocatalytic activity and oxygen electroreduction activity.

At present, dealloying is the main method to prepare nanoporous palladium catalytic membrane. The preparation method is usually to obtain a certain thickness of alloy film by alloy smelting and rolling, or by depositing (PVD, electroplating, etc.) on the substrate ( Metal, ceramics, activated carbon and other non-organic substances) film is deposited on a layer of alloy film, and then the alloy is dealloyed to form a three-dimensional continuous nanoporous film on the surface of the substrate. In the method of smelting-rolling-dealloying, due to the plasticity limit of noble metal alloys, the thickness of the alloy film is usually ≥ 20 μm. The part is still a solid alloy, the noble metal in the core alloy has not been fully utilized, and its nanopore structure is blocked by the core solid alloy in the thickness direction; for the deposition-dealloying method, the final porous The structure of the membrane is a three-dimensional continuous nanoporous noble metal on the surface, the core is a matrix membrane, and its nanopore structure is also blocked by the matrix in the thickness direction, and it is not a three-dimensional continuous nanoporous membrane in the true sense.

Contents of the invention

In order to overcome the shortcomings of particle-supported catalysts, the present invention provides a method for preparing a nano-porous palladium catalytic membrane with a novel structure. An alloy film with a thickness of nanometers is electrolessly plated on an organic film carrier, and then the organic film is removed by heat treatment. Carrier and homogenize the chemical composition of the alloy nano-membrane, and finally use the method of de-alloying to obtain a three-dimensional nano-porous palladium catalytic membrane with a film thickness and a pore size of nanometer scale.

The preparation method of nanoporous palladium catalytic membrane of the present invention specifically comprises the following steps:

(1) Pretreatment of organic film

Wash the surface of the organic film with deionized water. After drying, place the organic film in a roughening solution at 60-70°C for 5-15 minutes. After washing with water, place it in an ionic palladium solution at 40-50°C for activation. Add 1%~5% sodium hypophosphite after the adsorption of complex ions reaches equilibrium.

(2) Composite plating

①Mix sodium hypophosphite solution and ammonium chloride solution to obtain a reducing agent, the concentration of sodium hypophosphite in the reducing agent is 10~20g/L, and the solubility of ammonium chloride is 27~54g/L;

②Add hydrochloric acid and ammonia water to the palladium chloride and copper chloride solution in turn to make a plating solution. The concentration of palladium chloride in the plating solution is 1~10g/L, the concentration of copper chloride is 1~20g/L, and the concentration of ammonia water The concentration is 160~320mL/L (that is, the amount of ammonia added), and the concentration of hydrochloric acid is 2~10mL/L (that is, the amount of hydrochloric acid added). After the solution is prepared according to the above ratio, use ammonia to adjust the pH of the plating solution to 8 ~10; hydrochloric acid used is commercially available mass percent concentration and is 37.2wt% hydrochloric acid; ammoniacal liquor is commercially available mass percent concentration and is the ammoniacal liquor of 28wt%;

③Immerse the pretreated organic film in the reducing agent for 2~10min, take it out and place it at room temperature for 1~5min, then immerse it in the plating solution at 50~60℃ for 20~60min, wash it with deionized water until the pH value is neutral The Pd/Cu alloy film (thickness 1-100nm) attached to the organic film can be obtained.

(3) heat treatment

Dry the Pd/Cu alloy film attached to the organic film obtained in step (2) and put it into an electric furnace for heat treatment. After removing the organic film, the Pd/Cu alloy film can be obtained; the drying temperature is 40~50°C, The time is 1~2h; the heat treatment temperature is 500~700℃, and the time is 1~2h.

(3) dealloying

The nanoporous palladium catalytic membrane is prepared by de-alloying by free corrosion method, that is, the Pd/Cu alloy film is immersed in nitric acid for free corrosion and de-alloying, after de-alloying, it is cleaned with deionized water until the pH value is neutral, and it is ready A three-dimensional catalytic self-supporting nanoporous palladium catalytic membrane can be obtained.

The organic film of the present invention is one of polyester film and polypropylene film, with a thickness of 1-2mm.

The roughening solution of the present invention is the mixed solution of sulfuric acid and chromic anhydride, and the concentration of sulfuric acid in the mixed solution is 100～300mL/L (adopting commercially available sulfuric acid preparation), and the concentration of chromic anhydride is 350～450g/L; Sulfuric acid used is The commercially available mass percentage is 98wt% sulfuric acid.

The preparation method of the activating solution of the present invention is: dissolving palladium chloride in the aqueous solution of ammonium chloride to make solution A, dissolving α-aminopyridine in water to obtain an aqueous solution of α-aminopyridine, and mixing solution A with The α-aminopyridine aqueous solution is mixed to obtain an activation solution. The concentration of palladium chloride in the activation solution is 0.3~0.6 g/L, the concentration of ammonium chloride is 0.2~0.4 g/L; the concentration of α-aminopyridine is 1~3 g/L.

The concentration of nitric acid used in the free corrosion dealloying method of the present invention is 60-70wt%, the temperature is 10-30°C, and the time is 5-40h.

Invention principle:

(1) Alloy film preparation

The electrochemical mechanism of electroless plating of metals is that cathodic metal deposition and anodic oxidation of reducing agent proceed simultaneously.

anode:

anode:

According to the reaction of cathode and anode, the chemical reaction formula of electroless palladium plating and copper plating with sodium hypophosphite as reducing agent is as follows:

(2) dealloying

The chemical properties of palladium are stable and insoluble in strong acids and strong alkalis. Therefore, nitric acid is used as the etching solution. Nitric acid only reacts with copper. After the copper in the Pd/Cu alloy film is completely corroded, nanoporous palladium can be obtained. The reaction formula is as follows:

(3) Quantitative characterization of pore structure (pore size, porosity) and film thickness

The thickness of the Pd/Cu alloy film is adjusted by the number of repeated immersions of the organic film in the reducing agent and the plating solution. The thickness of the Pd/Cu alloy film increases by about 7-10nm each time the immersion is performed, and the optimal number of immersions is 4-8 times. Nitric acid does not react with palladium but only corrodes copper, so the film thickness, pore size and porosity can be controlled by adjusting the molar ratio of palladium chloride and copper chloride addition (the pore size and porosity increase with the increase of copper chloride addition. Big).

Its quantitative relationship is:

In the formula, X is the mole fraction of palladium, and Y is the mole fraction of copper.

Beneficial effects of the present invention:

(1) The nanoporous palladium membrane prepared by the dealloying method is used as a catalyst, which eliminates the influence of the substrate and is beneficial to improve the stability of palladium catalytic activity.

(2) The thickness and pore diameter of the nanoporous palladium film obtained by the present invention are both on the order of nanometers and have three-dimensional self-supporting catalytic properties. Through the nanoporous membrane, it is catalyzed and converted, so as to realize the three-dimensional catalytic performance of the noble metal nanoporous membrane, and greatly improve the catalytic performance and utilization rate of the nanoporous palladium catalytic membrane.

Description of drawings

Figure 1 is a process flow diagram for the preparation of nanoporous palladium catalytic membrane.

detailed description

The present invention will be described in further detail below in conjunction with specific examples, but the protection scope of the present invention is not limited to the content described.

Example 1

(1) Pretreatment of organic film

Wash the surface of the polyester film with a thickness of 1 mm with deionized water, and after drying, place the polyester film in a roughening solution at 60°C (including sulfuric acid: 150mL/L, chromic anhydride: 350g/L) for 5 minutes, and wash it with water. Put it into ionic palladium solution (including palladium chloride: 0.3g/L, ammonium chloride: 0.2 g/L, α-aminopyridine: 1 g/L) at 40°C for activation until the complex ion adsorption of palladium reaches equilibrium Then add 1% sodium hypophosphite.

(2) Composite film

1. sodium hypophosphite solution and ammonium chloride solution are mixed to obtain reducing agent, the concentration of sodium hypophosphite in the reducing agent is 10g/L, the solubility of ammonium chloride is 27g/L;

② Add hydrochloric acid and ammonia water to the palladium chloride and copper chloride solution in turn to make a plating solution. The concentration of palladium chloride in the plating solution is 5.3g/L, the concentration of copper chloride is 8g/L, and the concentration of ammonia water is 160mL /L, the concentration of hydrochloric acid is 10mL/L, and the pH value of the plating solution is adjusted to 8 with ammonia water after the solution is prepared according to the above ratio.

③Immerse the pretreated polyester film in the reducing agent for 10 minutes, take it out, and place it at room temperature for 2 minutes, then immerse it in the plating solution at 60°C for 20 minutes, wash it with deionized water until the pH value is neutral, and then adhere to the organic film. nanometer-thick Pd/Cu alloy film.

(3) heat treatment

Dry the Pd/Cu alloy film attached to the organic film obtained in step (2) ③, dry it at 40°C for 1 hour, then put it into an electric furnace for heat treatment (heat treatment temperature is 500°C, time is 1 hour), and remove the organic film. A Pd/Cu alloy thin film was obtained.

(4) dealloying

The nanoporous palladium catalytic membrane is prepared by free corrosion method dealloying, that is, the Pd/Cu alloy film is immersed in concentrated nitric acid at a temperature of 10°C and a concentration of 65wt% for free corrosion dealloying, and the dealloying time is 40h. After alloying, wash with deionized water until the pH value is neutral, and dry at 40°C for 1 hour to obtain a three-dimensional catalytic self-supporting nanoporous palladium catalytic membrane with a film thickness of 2.7nm and a pore diameter of 7.2nm. was 72.7%.

Example 2

(1) Pretreatment of organic film

Wash the surface of the polyester film with a thickness of 2mm with deionized water, and after drying, place the polyester film in a roughening solution at 65°C (including dilute sulfuric acid: 200mL/L, chromic anhydride: 400g/L) for 8 minutes, and wash with water. Then put it into 45°C ionic palladium solution (including palladium chloride: 0.4 g/L, ammonium chloride: 0.3 g/L, α-aminopyridine: 2 g/L) for activation, until the complex ion adsorption of palladium reaches Add 2% sodium hypophosphite after equilibrium.

(2) Composite plating

1. sodium hypophosphite solution and ammonium chloride solution are mixed to obtain reducing agent, the concentration of sodium hypophosphite in the reducing agent is 15g/L, the solubility of ammonium chloride is 36g/L;

②Add hydrochloric acid and ammonia water to the palladium chloride and copper chloride solution in turn to make a plating solution. The concentration of palladium chloride in the plating solution is 5g/L, the concentration of copper chloride is 10g/L, and the concentration of ammonia water is 200mL/L 1. The concentration of hydrochloric acid is 4mL/L, after the solution is prepared according to the above ratio, the pH value of the plating solution is adjusted to 9 with ammonia water.

③Immerse the pretreated polyester film in the reducing agent for 5 minutes, take it out and place it at room temperature for 3 minutes, then immerse it in the plating solution at 55°C for 30 minutes, and wash it with deionized water until the pH value is neutral to obtain the adhesion to the organic film. nanometer-thick Pd/Cu alloy film.

(3) heat treatment

Dry the Pd/Cu alloy film attached to the organic film obtained in step (2)③ at 45°C for 1.5h, then put it into an electric furnace for heat treatment (heat treatment temperature is 600°C, time is 1.5h), after removing the organic film A Pd/Cu alloy thin film can be obtained.

(3) dealloying

Prepare the nanoporous palladium alloy thin film by free corrosion method dealloying, that is, immerse the Pd/Cu alloy film in nitric acid with a temperature of 20 °C and a concentration of 66wt% for free corrosion and dealloying, and the dealloying time is 15h. After deionization, wash with deionized water until the pH value is neutral, and dry at 45°C for 1 hour to obtain a three-dimensional catalytic self-supporting nanoporous palladium catalytic membrane with a film thickness of 2.5nm, a pore diameter of 7.5nm, and a porosity of 75%.

Example 3

(1) Pretreatment of organic film

Wash the surface of the polypropylene film with a thickness of 1 mm with deionized water, and after drying, place the polypropylene film in a roughening solution at 65°C (including sulfuric acid: 200mL/L, chromic anhydride: 400g/L) for 10 minutes, and wash it with water. Put it into ionic palladium solution (including palladium chloride: 0.5 g/L, ammonium chloride: 0.3 g/L, α-aminopyridine: 2 g/L) at 45°C for activation until the complex ion adsorption of palladium reaches equilibrium Then add 3% sodium hypophosphite.

(2) Composite plating

1. sodium hypophosphite solution and ammonium chloride solution are mixed to obtain reducing agent, the concentration of sodium hypophosphite in the reducing agent is 15g/L, the solubility of ammonium chloride is 45g/L;

② Add hydrochloric acid and ammonia water to the palladium chloride and copper chloride solutions in turn to make a plating solution. The concentration of palladium chloride in the plating solution is 7g/L, the concentration of copper chloride is 12.5g/L, and the concentration of ammonia water is 240mL/L. L, the concentration of hydrochloric acid is 6mL/L, adjusts the pH value of plating solution to be 9 with ammoniacal liquor after the solution preparation is finished by above-mentioned ratio.

③Immerse the pretreated polypropylene film in the reducing agent for 7 minutes, take it out and place it at room temperature for 4 minutes, then immerse it in the plating solution at 55°C for 40 minutes, and wash it with deionized water until the pH value is neutral to obtain the adhesion to the organic film. nanometer-thick Pd/Cu alloy film.

(3) heat treatment

Dry the Pd/Cu alloy film attached to the organic film obtained in step (2)③ at 45°C for 1.5h, then put it into an electric furnace for heat treatment (heat treatment temperature is 600°C, time is 1.5h), after removing the organic film A Pd/Cu alloy thin film can be obtained.

(3) dealloying

Prepare the nanoporous palladium alloy film by free corrosion method dealloying, that is, immerse the Pd/Cu alloy film in nitric acid with a temperature of 20 °C and a concentration of 67wt%g for free corrosion dealloying, and the dealloying time is 25h. After alloying, wash with deionized water until the pH value is neutral, and dry at 45°C for 1.5 hours to obtain a three-dimensional catalytic self-supporting nanoporous palladium catalytic membrane with a film thickness of 1.43nm and a pore diameter of 8.57nm. The rate is 85%.

Example 4

(1) Pretreatment of organic film

Wash the surface of the polypropylene film with a thickness of 2 mm with deionized water, and after drying, place the polypropylene film in a roughening solution at 70°C (including sulfuric acid: 300mL/L, chromic anhydride: 450g/L) for 12 minutes, and wash it with water. Put it into an ionic palladium solution (including palladium chloride: 0.6 g/L, ammonium chloride: 0.4 g/L, α-aminopyridine: 3 g/L) at 50°C for activation until the complex ion adsorption of palladium reaches equilibrium Then add 5% sodium hypophosphite.

(2) Composite plating

1. sodium hypophosphite solution and ammonium chloride solution are mixed to obtain reducing agent, the concentration of sodium hypophosphite in the reducing agent is 20g/L, the solubility of ammonium chloride is 54g g/L;

② Add hydrochloric acid and ammonia water to the palladium chloride and copper chloride solution in turn to make a plating solution. The concentration of palladium chloride in the plating solution is 8g/L, the concentration of copper chloride is 20g/L, and the concentration of ammonia water is 240mL/L 1. The concentration of hydrochloric acid is 8mL/L, and the pH value of the plating solution is adjusted to 10 with ammonia water after the solution is prepared according to the above ratio.

③Immerse the pretreated polypropylene film in the reducing agent for 2 minutes, take it out and place it at room temperature for 5 minutes, then immerse it in the plating solution at 50°C for 60 minutes, and wash it with deionized water until the pH value is neutral to obtain the adhesion to the organic film. nanometer-thick Pd/Cu alloy film.

(3) heat treatment

Dry the Pd/Cu alloy film attached to the organic film obtained in step (2)③, dry it at 50°C for 2 hours, then put it into an electric furnace for heat treatment (heat treatment temperature is 700°C, time is 2 hours), and remove the organic film. A Pd/Cu alloy thin film was obtained.

(3) dealloying

Prepare the nanoporous palladium alloy thin film by free corrosion method for alloying, that is, immerse the Pd/Cu alloy thin film in nitric acid with a temperature of 30°C and a concentration of 68wt% for free corrosion and alloying, and the alloying time is 5h. After deionization, wash with deionized water until the pH value is neutral, and dry at 50°C for 2 hours to obtain a three-dimensional catalytic self-supporting nanoporous palladium catalytic membrane with a film thickness of 2nm, a pore diameter of 8nm, and a porosity of 80%. .

Claims (5)

1. a preparation method of nanoporous palladium catalytic membrane, is characterized in that, specifically comprises the following steps: (1) Pretreatment of organic film Wash the surface of the organic film with deionized water. After drying, place the organic film in a roughening solution at 60-70°C for 5-15 minutes. After washing with water, place it in an ionic palladium solution at 40-50°C for activation. Add sodium hypophosphite with a mass percentage concentration of 1% to 5% after the complex ion adsorption reaches equilibrium; (2) Composite plating ①Mix sodium hypophosphite solution and ammonium chloride solution to obtain a reducing agent, the concentration of sodium hypophosphite in the reducing agent is 10~20g/L, and the solubility of ammonium chloride is 27~54g/L; ②Add hydrochloric acid and ammonia water to the palladium chloride and copper chloride solution in turn to make a plating solution. The concentration of palladium chloride in the plating solution is 1~10g/L, the concentration of copper chloride is 1~20g/L, and the concentration of ammonia water The concentration is 160~320mL/L, and the concentration of hydrochloric acid is 2~10mL/L. After the solution is prepared according to the above ratio, adjust the pH value of the plating solution to 8~10 with ammonia water; ③Immerse the pretreated organic film in the reducing agent for 2~10min, take it out and place it at room temperature for 1~5min, then immerse it in the plating solution at 50~60℃ for 20~60min, wash it with deionized water until the pH value is neutral The Pd/Cu alloy film attached to the organic film can be obtained; (3) heat treatment Dry the Pd/Cu alloy film attached to the organic film obtained in step (2) and put it into an electric furnace for heat treatment. After removing the organic film, the Pd/Cu alloy film can be obtained; the drying temperature is 40~50°C, the time 1~2h; heat treatment temperature is 500~700℃, time is 1~2h; (3) dealloying The nanoporous palladium catalytic membrane is prepared by de-alloying by free corrosion method, that is, the Pd/Cu alloy film is immersed in nitric acid for free corrosion and de-alloying, after de-alloying, it is cleaned with deionized water until the pH value is neutral, and it is ready A three-dimensional catalytic self-supporting nanoporous palladium catalytic membrane can be obtained. 2. the preparation method of nanoporous palladium catalytic membrane according to claim 1, is characterized in that: organic film is a kind of in polyester film and polypropylene film, and thickness is 1～2mm. 3. the preparation method of nanoporous palladium catalytic membrane according to claim 1 is characterized in that: the roughening solution is the mixed solution of sulfuric acid and chromic anhydride, and the concentration of sulfuric acid in the mixed solution is 100～300mL/L, and the concentration of chromic anhydride The concentration is 350~450g/L. 4. the preparation method of nanoporous palladium catalytic membrane according to claim 1 is characterized in that: palladium chloride is dissolved in the aqueous solution of ammonium chloride and is made solution A, and α-aminopyridine is dissolved in water to obtain α- Aminopyridine aqueous solution, under constant stirring, mix solution A and α-aminopyridine aqueous solution to obtain an activation solution, the concentration of palladium chloride in the activation solution is 0.3~0.6g/L, and the concentration of ammonium chloride is 0.2~0.4 g/L ; The concentration of α-aminopyridine is 1~3 g/L. 5. the preparation method of nanoporous palladium catalytic membrane according to claim 1 is characterized in that: the concentration of nitric acid used in free corrosion dealloying method is 60～70wt%, and temperature is 10～30 ℃, and the time is 5～40h .