CN102861576A - Pd/ZnO/C composite nano catalyst and preparation method thereof - Google Patents

Abstract

The invention discloses a Pd/ZnO/C composite nano catalyst and a preparation method thereof. The Pd/ZnO/C composite nano catalyst, wherein Pd, ZnO, and C are calculated by mass ratio, that is, Pd:ZnO:C is A nano-catalyst compounded at a ratio of 0.5:1:1; wherein the C is activated carbon passing through a 200-mesh sieve. The preparation method is to first prepare ZnO nanoparticles, and then according to the mass ratio of 1:1, stir the activated carbon and ZnO nanoparticles that have passed through a 200-mesh sieve in an aqueous solution of ethylene glycol and mix them well. The Pd/ZnO/C composite nano-catalyst is obtained by loading nano-Pd particles. The Pd/ZnO/C composite nano-catalyst of the invention has strong anti-poisoning ability and good catalytic oxidation performance to ethanol in alkaline solution.

Description

A kind of Pd/ZnO/C composite nano catalyst and preparation method thereof

technical field

The invention belongs to the technical field of preparation of nano-catalyst materials, in particular to a Pd/ZnO/C composite nano-catalyst with high catalytic activity to ethanol and its preparation method

Background technique

At present, there are more and more researches on fuel cells, mainly because some small molecular compounds such as methanol, ethanol and other substances have a wide range of sources, and can be used directly as fuel in fuel cells. However, methanol has certain volatility and toxicity, which will cause harm to the human body, while ethanol has high energy density and can be used in some electronic devices and electric vehicles. Research on direct ethanol fuel cells has attracted more attention ^[1-5] . Pt is a metal that has been studied more on the oxidation of ethanol, but the complete oxidation reaction of ethanol is a 12-electron reaction, the reaction on pure metal Pt is slow, and most of the final products of its oxidation of ethanol are acetic acid, not CO ₂ ^[6-7] , in the oxidation process of ethanol, some CO-like intermediate products will be generated, which will cause Pt catalyst poisoning, and the catalytic activity will decrease significantly.

Studies have shown that adding oxides to the catalyst will improve the ability to oxidize ethanol and resist CO poisoning. Pang ^[8] prepared SnO ₂ -CNTs/Pt catalyst by sol-gel method. The catalyst has high catalytic activity to ethanol in acidic solution. The introduction of SnO ₂ makes the long-term cycle performance of the catalyst better. Zhang ^[9] et al. synthesized a Pt/CNTSnO ₂ catalyst with a core-shell structure (thickness about 2nm), and the oxidation current of ethanol in acidic solution was 1.57 times that of Pt/C. B.RuizCamacho ^[10] found that adding oxides SnO ₂ , TiO ₂ , ZnO to prepare Pt/SnO ₂ /C, Pt/TiO ₂ /C and Pt/ZnO/C have better electricity than Pt/C Catalytic performance, but the catalytic stability of Pt/ZnO/C is not good. Moreover, Pt itself is expensive and its reserves are limited, so there are certain limitations in practical applications. In comparison, the price of Pd is relatively cheap and the reserves are abundant. Using Pd instead of Pt can reduce the cost of the anode catalyst for alcohol fuel cells. Compared with Pt/C in alkaline solution, Pd/C has better catalytic activity for ethanol, Stability and anti-CO poisoning ability ^[11] .

In view of the catalytic activity of ZnO, the present invention has prepared a kind of novel catalyst Pd/ZnO/C that ethanol has good catalytic activity and stability in alkaline solution, and traditional laboratory preparation Pt/ZnO/C catalyst needs The equipment is complicated and the yield is low. The present invention first synthesizes zinc oxide, the raw material is cheap, the operation is simple, and the yield is high. The particle size of the loaded metal Pd is small and evenly distributed. Compared with the Pd/C catalyst, the catalytic activity is relatively high. Significantly improved. Due to the limited research on direct ethanol fuel cells at present and the different experimental systems, there is no similar report of the present invention.

references

[1] Song SQ, Zhou WJ, Zhou ZH, Jiang LH, Sun GQ, Xin Q, et al. Direct ethanol PEM fuel cells: the case of platinum based anodes[J]. Int J Hydrogen Energy 2005;30:995- 1001

[2] Lamy C, Rousseau S, Belgsir EM, Coutanceau C, Leger JM.Recent progress in the direct ethanol fuel cell: development of new platinum -tin electrocatalysts[J]. Electrochim Acta 2004; 49:3901-3018

[3] Rousseau S, Coutanceau C, Lamy C. Direct ethanol fuel cell (DEFC): electrical performances and reaction ion products distribution under operating conditions with different platinum-based anodes[J]. J Power Sources 2006-258:18

[4]Antolini E. Catalysts for direct ethanol fuel cells[J]. J. Power Sources 2007; 170: 1-12

[5] E. Antolini, F. Colmati, ER Gonzalez. Ethanol oxidation on carbon supported (PtSn) alloy/SnO ₂ and (PtSnPd) alloy/SnO ₂ catalysts with a fixed Pt/SnO ₂ atomic ratio:Effect of the alloy phase characteristics[J]. Journal of Power Sources 193 (2009) 555-561

[6]H. Wang, Z. Jusys, R.J. Behm. Ethanol Electro oxidation on a Carbon-Supported Pt Catalyst: Reaction Kinetics and Product Yields[J]. J. Phys. Chem. B., 2004, 108, 19413-19424

[7] G.A. Camara, T. Iwasita, Parallel pathways of ethanol oxidation: The effect of ethanol concentration[J]. Journal of Electroanalytical Chemistry.2005,578,315-321

[8]H.L. Pang, J.P. Lu, J.H. Chen, C.T. Huang, B. Liu, X.H. Zhang. Preparation of SnO2-CNTs supported Pt catalysts and their electrocatalytic properties for ethanol oxidation [J]. Electrochimica (261 Acta 54)

[9]Xinwei Zhang, Hong Zhu, Zhijun Guo, et al.Design and preparation of CNTSnO2 core-shell composites with thin shell and its application for ethanol oxidation[J].International Journal of Hydrogen Energy 35 (2010) 8841-8847

[10]B.RuizCamachoa, C. Moraisa, et al. Enhancing oxygen reduction reaction activity and stability of platinum via oxide-carbon composites[J]. Catalysis Today, 2012, 1-8

[11]Liang Ma, Deryn Chu, Rongrong Chen. Comparison of ethanol electro-oxidation on Pt/C and Pd/C catalysts in alkaline media[J]. International Journal of Hydrogen Energy, 37(2012) 11185-11194

Contents of the invention

One of the purposes of the present invention is to provide a Pd/ZnO/C composite nano-catalyst with high catalytic activity, stability and anti-poisoning ability in order to solve technical problems such as low catalytic activity of the above-mentioned catalyst and poor stability.

The second object of the present invention is to provide a method for preparing the above-mentioned Pd/ZnO/C composite nano-catalyst.

Technical principle of the present invention

Considering that Pd has a higher activity than Pt in the catalytic oxidation of ethanol in an alkaline environment, and has good stability in acid and alkali media, ZnO has good electrochemical activity and hydrothermal stability, and is a A kind of electrocatalyst and catalyst carrier with excellent performance. Pd/ZnO/C composite nanocatalyst was prepared by introducing ZnO into the Pd catalyst system for the catalytic oxidation of ethanol. The research results showed that the catalyst had high catalytic activity for the oxidation of ethanol.

Technical scheme of the present invention

A Pd/ZnO/C composite nano-catalyst, wherein Pd, ZnO, and C are calculated by mass ratio, that is, a nano-catalyst composited by a ratio of Pd:ZnO:C of 0.5:1:1;

Wherein said C is the activated carbon that crosses 200 mesh sieves, and the described activated carbon that crosses 200 mesh sieves is preferably Vulcan XC-72 activated carbon powder.

The preparation method of above-mentioned a kind of Pd/ZnO/C composite nano-catalyst specifically comprises the following steps:

(1) Preparation of ZnO nanoparticles

React ZnSO ₄ solution, NaOH solution and ammonium bicarbonate under stirring conditions to form fine basic zinc carbonate particles, then dry the basic zinc carbonate particles at 80°C, and then calcinate at 400°C to obtain white Particles are ZnO particles;

(2) Then according to the mass ratio of 1:1, stir the activated carbon passed through a 200-mesh sieve and the ZnO nanoparticles obtained in step (1) in an aqueous ethylene glycol solution and mix them well to obtain a mixed solution;

The ethylene glycol aqueous solution, that is, ethylene glycol and deionized water is calculated by volume ratio, that is, a solution composed of ethylene glycol: deionized water at a ratio of 1:3;

The pretreated Vulcan XC-72 activated carbon powder, that is, the temperature is controlled at 90°C, the activated carbon Vulcan XC-72 is vigorously stirred and refluxed in 5mol/L HNO ₃ for 5h, cooled to room temperature, filtered and washed with water, the temperature is controlled at Vacuum drying at 130°C, grinding, and passing through a 200-mesh sieve to obtain pretreated Vulcan XC-72 activated carbon powder;

(3) Loading nano Pd particles by liquid phase reduction method;

Add PdCl _aqueous solution dropwise to the mixed solution obtained in step (2), stir evenly, add trisodium citrate containing two crystal waters as a stabilizer, and control the molar ratio of metal Pd to trisodium citrate to be 1:5 , and ultrasonically oscillate to mix evenly, then adjust the pH value of the solution to 11 with alkaline solution NaOH, then add sodium borohydride as a reducing agent, continue the constant temperature reaction for 3 hours, then cool to room temperature, filter and wash until there is no Cl ^- in the filter cake, Control the temperature at 90°C and vacuum dry to obtain a black powdery Pd/ZnO/C composite nanocatalyst, in which the metal Pd loading is wt.20%;

The amount of _PdCl2 aqueous solution, trisodium citrate and sodium borohydride added in the above mixed solution is based on the Zn contained in the mixed solution: the metal Pd contained in the _PdCl2 aqueous solution: trisodium citrate: the mole of sodium borohydride The ratio is 2.6:1:5:6.

The Pd/ZnO/C composite nano-catalyst obtained above has high catalytic activity for the oxidation reaction of ethanol.

Beneficial effects of the present invention

The Pd/ZnO/C composite nano catalyst of the present invention contains ZnO, thereby improving the anti-poisoning ability of the Pd/ZnO/C composite nano catalyst, and the Pd/ZnO/C composite nano catalyst has better stability.

Further, a Pd/ZnO/C composite nano-catalyst of the present invention has good catalytic oxidation performance for ethanol in alkaline solution.

In summary, a Pd/ZnO/C composite nanocatalyst of the present invention has better effects in terms of particle size distribution, catalytic performance on ethanol, and stability. the

Description of drawings

Figure 1. TEM images of Pd/ZnO/C composite nanocatalysts;

Figure 2. XRD pattern of Pd/ZnO/C composite nanocatalyst;

Figure 3. Stripping voltammetry curve of Pd/ZnO/C composite nanocatalyst in 1mol L ^-1 KOH solution;

Figure 4. Cyclic voltammetry curves of Pd/C catalyst and Pd/ZnO/C composite nanocatalyst in 1mol/LCH ₃ CH ₂ OH and 1mol/L KOH solutions respectively;

Fig. 5. Time-current curves of Pd/C catalyst and Pd/ZnO/C composite nanocatalyst in 1M KOH+1M C ₂ H ₅ OH.

Detailed ways

The present invention will be further described below through specific embodiments in conjunction with the accompanying drawings, but the present invention is not limited.

(

 =0.15418nm)，步长0.0167°，每步停留1s，扫描范围为20-90°； The X-ray powder diffractometer is a German Bruker D8-ADVANCE type, and the radiation source is CuK

(

=0.15418nm), the step size is 0.0167°, each step stays for 1s, and the scanning range is 20-90°;

Shanghai Chenhua Instrument Company CHI660A Electrochemical Workstation;

The specifications and manufacturer's information of reagents or raw materials used in the present invention are as follows:

Palladium chloride (PdCl ₂ , Shanghai Institute of Fine Chemical Materials, analytically pure);

Vulcan XC-72 (Cabot, USA, 98%); Ethanol (Jiangsu Qiangsheng Functional Chemistry Co., Ltd., analytically pure);

Ethylene glycol (Sinopharm Chemical Reagent Co., Ltd., analytically pure);

Sodium hydroxide (Shanghai Chemical Reagent Co., Ltd., analytically pure);

Ammonium bicarbonate (Shanghai Junhui Chemical Co., Ltd., analytically pure);

Zinc sulfate heptahydrate (Nanjing Chemical Reagent Co., Ltd., analytically pure);

Nafion solution (5 (wt)%, DuPont, USA).

Example 1

A kind of preparation method of Pd/ZnO/C composite nano-catalyst, concrete steps are as follows:

(1) Preparation of ZnO nanoparticles

Get 50ml of 1.0mol/L _ZnSO4 solution, add 10ml of NaOH solution with a concentration of 0.5mol/L dropwise under rapid stirring, add 6g of ammonium bicarbonate after the dropwise addition and continue stirring. Basic zinc carbonate particles, put the zinc carbonate particles in an oven to control the temperature at 80°C and dry them, then calcinate them at 400°C for 1 hour to obtain white particles, which are ZnO nanoparticles;

(2), preparation of composite catalyst

According to the mass ratio of 1:1, add a total of 40mg of pretreated Vulcan XC-72 activated carbon powder and ZnO nanoparticles obtained in step (1) to 120ml by volume ratio of ethylene glycol and deionized water, that is, ethylene glycol : Deionized water is ethylene glycol aqueous solution with a composition of 1:3, the temperature is controlled at 60°C, and the magnetic stirrer is used to vigorously stir and mix well to obtain a mixed solution;

The pretreated Vulcan XC-72 activated carbon powder is to add Vulcan XC-72 activated carbon powder to 5mol/L HNO ₃ , control the temperature at 90°C, stir vigorously for 5h, filter and wash with water after cooling to room temperature; then control the temperature at Vacuum dry at 130°C for 6 hours, then grind and pass through a 200-mesh sieve to obtain pretreated Vulcan XC-72 activated carbon powder;

(3) Loading nano-Pd particles by liquid phase reduction method

Add 46.99 mL of 2 mmol/L PdCl ₂ solution dropwise to the mixture obtained in step (2), stir for 1 hour, then add 138.18 mg of trisodium citrate containing two crystal waters as a stabilizer, that is, to control the interaction between metal Pd and lemon The molar ratio of trisodium acid is 1:5, ultrasonically oscillate for 30 minutes, mix well, then adjust the pH value of the solution to 11 with alkaline solution NaOH, then add 21.33 mg of sodium borohydride as a reducing agent, continue the reaction for 3 hours, and then cool to room temperature, filter and wash until there is no Cl ^- in the filter cake, and vacuum-dry at a temperature of 90°C for 12 hours to obtain a black powdery Pd/ZnO/C composite nanocatalyst with a metal Pd loading of wt.20%.

The Pd/ZnO/C composite nano-catalyst obtained above is scanned by a transmission electron microscope, and the resulting TEM picture is shown in Figure 1. From Figure 1, it can be seen that Pd is evenly dispersed in the catalyst, and the catalyst made has a good Dispersion, Pd particle size is about 2-4nm.

(

=0.15418nm)，步长0.0167°，每步停留1s，扫描范围为20－90°，获得Pd/ZnO/C复合纳米催化剂的XRD图如图2所示，并将图2所得的XRD图与Pd的标准卡片（JCPDS, No. 65-6174）Pd的特征衍射峰出现在40.11°（111），46.65°（200），68.11°（220），82.03°（311），86.60°（222）位置，同时对比ZnO的标准卡片（JCPDS, No. 65-3358），ZnO衍射峰出现在82.09°（112），86.54°（201），由此表明此制备方法成功制备出了含有Pd和ZnO的复合纳米催化剂。 Utilize X-ray powder diffractometer to carry out XRD scanning to the Pd/ZnO/C composite nano-catalyst of above-mentioned gain, used X-ray powder diffractometer is German Bruker D8-ADVANCE type, radiation source is CuK

(

=0.15418nm), the step length is 0.0167°, each step stays for 1s, and the scanning range is 20-90°. The XRD pattern of the Pd/ZnO/C composite nanocatalyst is shown in Figure 2, and the XRD pattern obtained in Figure 2 is compared with Pd's standard card (JCPDS, No. 65-6174) Pd's characteristic diffraction peaks appear at 40.11° (111), 46.65° (200), 68.11° (220), 82.03° (311), 86.60° (222) , and compared with the standard card of ZnO (JCPDS, No. 65-3358), the diffraction peaks of ZnO appear at 82.09° (112), 86.54° (201), which shows that this preparation method successfully prepared a composite containing Pd and ZnO nanocatalyst.

The Pd/ZnO/C composite nano-catalyst obtained above is prepared as a catalytic electrode, and the specific steps are as follows:

Weigh a certain amount of Pd/ZnO/C composite nano-catalyst prepared above, and calculate by mass ratio, that is, Pd/ZnO/C composite nano-catalyst: deionized water: ethanol: 5% Nafion solution is 1:160:32:22 Mix the Pd/ZnO/C composite nanocatalyst with deionized water, ethanol and 5% Nafion solution, and oscillate ultrasonically for 30 minutes to obtain a black ink-like Pd/ZnO/C composite nanocatalyst mixed solution. Use a pipette to measure 4 μl of Pd /ZnO/C composite nano-catalyst mixed solution, covering the surface of the glassy carbon electrode, after natural drying, the electrode is fabricated, and the catalytic electrode covered with Pd/ZnO/C composite nano-catalyst is obtained.

 m的Al₂O₃粉末在麂皮上磨至镜面，再分别用去离子水和无水乙醇超声洗涤。 For the glassy carbon (GC) electrode (d=3mm), use 0.3

The Al ₂ O ₃ powder of m was ground on suede to a mirror surface, and then ultrasonically washed with deionized water and absolute ethanol, respectively.

Characterization of Catalytic Properties of the Pd/ZnO/C Composite Nanocatalysts Obtained Above

The prepared catalytic electrode with Pd/ZnO/C composite nano-catalyst was used as the working electrode, the saturated calomel electrode (SCE) was used as the reference electrode, and the metal platinum electrode was used as the auxiliary electrode to form a three-electrode test system, which was cycled on CHI660A Volt-ampere test and time-current curve test.

Firstly, the stripping voltammetry curve of the Pd/ZnO/C composite nanocatalyst in 1mol L ^-1 KOH solution is measured, as shown in Figure 3. From Figure 3, it can be seen that there is a hydrogen adsorption peak at -0.5V, indicating that Pd /ZnO/C composite nanocatalyst has a certain active specific surface area.

The cyclic voltammetry curves of the Pd/C catalyst and Pd/ZnO/C composite nanocatalyst prepared under the same conditions were further measured in 1mol/LCH ₃ CH ₂ OH and 1mol/L KOH solutions respectively, as shown in Figure 4, from Figure 4 It can be seen that the catalytic performance of the Pd/ZnO/C composite nanocatalyst is much higher than that of the Pd/C catalyst, and the Pd/ZnO/C composite nanocatalyst is about -0.6V at a very low potential during the positive sweep process. (vs.SCE), ethanol begins to catalyze oxidation, reaching the maximum at -0.2 V, and its peak current density is about 85mA/cm ² ; at this time, the peak current density of Pd/C catalyst is only 28.8mA/cm ² , adding ZnO, the current density increased by 2.95 times. In the reverse scanning, because the Pd in the Pd/ZnO/C composite nanocatalyst is transformed into active Pd atoms again, the ethanol adsorbed on it is catalyzed and oxidized, and the oxidation peak reaches the maximum value at -0.40 V, and the catalytic current As can be seen from Figure ⁴ , the catalytic activity of the Pd/C catalyst is significantly lower than that of the Pd/ZnO/C composite nanocatalyst.

Further measurement of the time-current curves of Pd/C catalyst and Pd/ZnO/C composite nano-catalyst in 1M KOH+1M C ₂ H ₅ OH is shown in Figure 5. It can be seen from Figure 5 that with the prolongation of the reaction time, the Pd /C catalyst and Pd/ZnO/C composite nanocatalyst have a decrease in the peak current density of ethanol oxidation, but the Pd/C catalyst declines faster. The magnitude of the density is 0.96 mA/cm ² , and the magnitude of the current density of the Pd/C catalyst is 0.73 mA/cm ² . Over time, the intermediate product of ethanol oxidation will poison the catalyst and reduce its activity, but the attenuation of the Pd/ZnO/C composite nanocatalyst is small, indicating that the addition of ZnO improves the anti-poisoning ability of the Pd/ZnO/C composite nanocatalyst. /ZnO/C composite nanocatalysts have better stability.

The above content is only a basic description of the concept of the present invention, and any equivalent transformation made according to the technical solution of the present invention shall belong to the protection scope of the present invention.

Claims (5)

1. a Pd/ZnO/C composite nano-catalyst is characterized in that wherein Pd, ZnO, C calculate in mass ratio, and namely Pd:ZnO:C is the nanocatalyst that the ratio of 0.5:1:1 is composited;

Wherein said C was the active carbon of 200 mesh sieves.

2. a kind of Pd/ZnO/C composite nano-catalyst as claimed in claim 1, the active carbon that it is characterized in that described mistake 200 mesh sieves is pretreated Vulcan XC-72 activated carbon powder;

Described pretreated Vulcan XC-72 activated carbon powder, namely controlling temperature is 90 ℃, with the HNO of active carbon Vulcan XC-72 at 5mol/L ₃Middle strong stirring backflow 5h is cooled to and filters after the room temperature and washing, the control temperature in 130 ℃ of vacuum drying, grinding, cross 200 mesh sieves, namely get pretreated Vulcan XC-72 activated carbon powder.

3. the preparation method of a kind of Pd/ZnO/C composite nano-catalyst as claimed in claim 1 or 2 is characterized in that specifically comprising the steps:

(1), ZnO nano particle preparation

With ZnSO ₄Solution, NaOH solution and carbonic hydroammonium react under stirring condition and generate the zinc carbonate particle, again with the zinc carbonate particle after drying under 80 ℃ of conditions, under 400 ℃ of conditions, calcine, obtain white particle, be the ZnO particle;

(2), be 1:1 according to mass ratio, the ZnO nano particle of the active carbon of crossing 200 mesh sieves and step (1) gained stirred in glycol water fully mix, obtain mixed solution;

(3), with liquid phase reduction loaded with nano Pd particle;

Dropwise add PdCl in the mixed liquor that step (2) obtains ₂The aqueous solution, after stirring, add and contain the trisodium citrate of two crystallizations water as stabilizing agent, the mol ratio of control metal Pd and trisodium citrate is 1:5, and ultrasonic concussion mixes, and uses the pH value to 11 of alkaline solution NaOH regulator solution again, then add sodium borohydride as reducing agent, continue isothermal reaction 3h, then be cooled to room temperature, filter and wash to the filter cake without Cl ^-, the control temperature is 90 ℃ of lower vacuum drying, namely obtains the Pd/ZnO/C composite nano-catalyst of black;

The PdCl that adds in the above-mentioned mixed liquor ₂The amount of the aqueous solution, trisodium citrate, sodium borohydride is pressed Zn:PdCl contained in the mixed liquor ₂Contained metal Pd in the aqueous solution: trisodium citrate: the mol ratio of sodium borohydride is 2.6:1:5:6.

4. the preparation method of a kind of Pd/ZnO/C composite nano-catalyst as claimed in claim 3, it is characterized in that pretreated Vulcan XC-72 active carbon in the step (2), the ZnO nano particle of step (1) gained and the consumption of glycol water, press mass volume ratio and calculate, be i.e. pretreated Vulcan XC-72 active carbon: the ZnO nano particle of step (1) gained: glycol water is 1g:1g:6L.

5. the preparation method of a kind of Pd/ZnO/C composite nano-catalyst as claimed in claim 4, it is characterized in that the glycol water described in the step (2), be that ethylene glycol and deionized water are calculated by volume, i.e. ethylene glycol: deionized water is the glycol water that the ratio of 1:3 forms.

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