Carbon-supported palladium-gold nanoheterogeneous catalyst, preparation method and use

Abstract

The present invention discloses a carbon-supported palladium-gold nano-heterogeneous catalyst, a preparation method, and uses thereof. The catalyst comprises a carbon support and active component palladium-gold alloy nanoparticles, with a total metal loading of 3.0 to 15.0 wt.%, including 0.46 to 9.28 wt.% palladium and 1.14 to 12.71 wt.%. The method comprises: 1) dispersing the carbon support in water to obtain a suspension A; 2) adding chloroauric acid to a sodium citrate solution to obtain a suspension B; 3) adding chloropalladic acid to the sodium citrate solution to obtain a solution C; 4) simultaneously adding suspensions B and C to suspension A to obtain a suspension D; 5) ultrasonically treating suspension D, stirring at room temperature, and impregnating the suspension; 6) reducing the suspension with a sodium carbonate solution containing sodium borohydride, filtering, washing, and drying to obtain the catalyst. The method is simple, has mild conditions, and an adjustable ratio of catalytic components. When used for formic acid decomposition to produce hydrogen, the catalyst has the advantages of high catalytic activity, high conversion rate, easy recovery, and multiple uses.

Description

Technical Field

[0001] The invention relates to a heterogeneous catalyst using a series of carbons as carriers and palladium-gold nanoparticles composed of different molar ratios as active centers, a preparation method, and use of the catalyst in a formic acid decomposition hydrogen production reaction. Background Art

[0002] Hydrogen has an extremely high mass energy density, nearly three times that of gasoline. Its combustion product is water, making it a truly zero-carbon energy source. It is a crucial alternative to fossil fuels and has become a crucial component of my country's energy landscape. However, hydrogen's low volume energy density, flammability, explosiveness, and difficulty in storage and transportation have hindered its widespread adoption, primarily due to high technical barriers and economic costs associated with its development. Researching and developing "hydrogen carriers" for efficient hydrogen storage and transportation has become a research goal for many researchers.

[0003] Formic acid (HCOOH, Formic Acid, FA) is the simplest carboxylic acid with low toxicity and high hydrogen density (4.4wt.%, 53.4g·L -1 ), and is inexpensive. Moreover, it is liquid at room temperature, has low volatility and is not easy to burn, can be safely stored and transported, and is considered to be an organic liquid hydrogen storage material with great application potential. Compared with other hydrogen storage technologies, formic acid hydrogen storage technology has very low cost and high safety, and has incomparable advantages in storage and transportation. At room temperature and pressure, formic acid can only be decomposed to produce hydrogen under the action of a catalyst. Under the action of a catalyst, formic acid can be decomposed through two pathways: a dehydrogenation pathway (HCOOH→H2+CO2), the products of which are carbon dioxide and hydrogen; and a dehydration pathway (HCOOH→H2O+CO), the products of which are water and carbon monoxide. Both pathways are thermodynamically favorable reactions (standard Gibbs free energy change is less than 0), of which the dehydration pathway is a side reaction.

[0004] Compared to homogeneous catalysts, heterogeneous catalysts offer advantages such as easy recovery and recycling, high resistance to carbon monoxide (CO) poisoning, long lifespan, avoidance of large amounts of organic solvents during preparation, and easy control of the reaction process, thus holding promising prospects for development. Heterogeneous catalysts consist of a support and an active component supported on the support. Catalysts can be categorized as monometallic catalysts or binary / multimetallic alloy catalysts based on the active component. Among monometallic catalysts, palladium is the most active catalyst for the decomposition of formic acid to produce hydrogen. However, because carbon monoxide can form stable adsorption on precious metal surfaces, even trace amounts of carbon monoxide can poison and deactivate the catalyst, making side reactions essential to avoid. While some monopalladium catalysts exhibit good performance, most suffer from poor stability due to susceptibility to poisoning by carbon monoxide, a byproduct of formic acid decomposition. By alloying or doping palladium with elements such as Ag, Au, Ni, Co, Cr, and B, the valence electron density of palladium can be modulated, thereby reducing its adsorption of carbon monoxide or facilitating its adsorption of formate. Among them, the weak adsorption of Au atoms on CO and H2 molecules is not only beneficial to the precipitation of H2, but also because CO is difficult to form a stable complex on the Au surface, it is beneficial to alleviate the poisoning phenomenon of Pd / C, thereby improving the stability of the catalyst.

[0005] Existing reports on palladium-gold nano-heterogeneous catalysts for catalytic decomposition of formic acid to produce hydrogen have the following problems:

[0006] (1) Some catalysts require higher temperatures to function, which cannot meet actual needs (DOI: 10.1016 / j.jcat.2012.12.009); (2) The preparation methods of carriers for highly active catalysts are often more complicated, resulting in high catalyst costs and unfavorable promotion (DOI: 10.1021 / acsanm.1c00266); (3) The preparation methods of some catalysts use a high-temperature hydrogen / hydrogen-argon reduction process, and the reduction conditions are relatively harsh (DOI: 10.1016 / j.cattod.2020.08.009).

[0007] Therefore, developing a method for preparing palladium-gold nano-heterogeneous nanocatalysts with simple preparation process, low cost, mild conditions, and large-scale preparation, which has uniform dispersion of active components, high catalytic activity and good stability, has become an urgent problem to be solved. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the above-mentioned shortcomings and provide a carbon-supported palladium-gold nano-heterogeneous catalyst for catalyzing the decomposition of formic acid to produce hydrogen and a preparation method thereof. The catalyst comprises a carbon support and palladium-gold nanoparticles as active components supported on the carbon support. The total metal loading is 3.0 to 15.0 wt.%, of which the palladium content is 0.46 to 9.28 wt.%, and the gold content is 1.14 to 12.71 wt.%. The preparation method is simple and the preparation conditions are mild. The catalyst is applicable to various carbon supports and the ratio of its active components is adjustable. The catalyst can also be used to catalyze the rapid decomposition of formic acid to produce hydrogen.

[0009] Specifically, the present invention utilizes the preparation method to prepare a series of catalysts by fixing the metal loading, adjusting the molar ratio between active components (palladium and gold), and changing the type of carbon carrier; when such catalysts are used for the decomposition of formic acid to produce hydrogen, the occurrence of side reactions can be effectively avoided, and they have the advantages of high catalytic activity, high conversion rate, easy recovery, and repeated use, are suitable for industrial scale-up production, and have promotion value.

[0010] The technical solution adopted by the preparation method of the present invention is as follows:

[0011] (1) Step 1, preparation of carrier suspension A: First, weigh 190.2 mg of carbon carrier (such as ECP, ECP600JD, XC-72, SAC-02, etc.) and disperse it in 20 mL of deionized water. Ultrasonic dispersion is performed for 30 minutes, and then stirring is performed for 30 minutes to form a uniformly dispersed carrier suspension A. Finally, while stirring, wait for the addition of gold nanoparticle suspension B and palladium precursor solution C.

[0012] (2) Step 2, preparation of gold nanoparticle suspension B: First, weigh 78.4 mg of sodium citrate and dissolve it in 4 mL of water. Then, add 1.65 mL of 0.02 M chloropalladic acid H2PdCl4 solution. After rapid mixing, let it stand at room temperature for 15 minutes. The color of the solution changes from yellow to black, forming gold nanoparticle suspension B. Finally, add it together with palladium precursor solution C to the carrier suspension A under stirring.

[0013] (3) Step 3, preparation of palladium precursor solution C: first weigh 78.4 mg of sodium citrate and dissolve it in 2.6 mL of water, then add palladium salt (chloropalladic acid H2PdCl4, sodium chloropalladate Na2PdCl4, potassium chloropalladate K2PdCl4, palladium nitrate Pd(NO3)2 and palladium acetate Pd(CH3COO)2, etc.) solution, mix well and let it stand at room temperature for 15 minutes to form palladium precursor solution C, and finally add it together with suspension B to the carrier suspension A under stirring.

[0014] (4) Step 4, mixed suspension D: Add the gold nanoparticle suspension B and the palladium precursor solution C to the carrier suspension A under stirring, and stir at room temperature for 5 minutes to form a mixed suspension D.

[0015] (5) Step 5, ultrasonic mixing: ultrasonically mix the mixed suspension D for 20 min.

[0016] (6) Step 6, stirring and soaking: transfer the mixed suspension D to a low-temperature reaction bath, and stir and soak for 1 to 4 hours under temperature control (0 to 50°C).

[0017] (7) Step 7, reduction: add 6.4 mL of 0.05 mol / L sodium carbonate Na2CO3 aqueous solution (containing 25.5 mg of sodium borohydride NaBH4) dropwise at a rate of 0.5 mL / min, and continue to reduce and stir at 0-50 °C for 2-16 h.

[0018] (8) Step 8, filtration and drying: Filter by suction, rinse the filter cake with a large amount of deionized water, dry the filter cake in a vacuum oven at 50°C for 12 hours, grind it into powder, and obtain Pd x Au 1-x / C catalyst. The catalyst is named Pd x Au 1-x / The name of the carbon support. For example, the catalyst with a molar ratio of palladium to gold prepared using ECP as a support is named Pd 0.5 Au 0.5 / ECP.

[0019] A carbon-supported palladium-gold nano-heterogeneous catalyst is used in catalyzing the decomposition of formic acid to produce hydrogen.

[0020] Catalytic performance test: 32 mg of catalyst was weighed and placed into a 25 mL branched reaction tube containing a magnetic rod. 0.5 mL of deionized water was then added, and the tube was placed in a water bath and stirred for 10 minutes. Then, 1.5 mL of a solution containing 84 μL of formic acid (AR, 99%) and 502 mg of sodium formate dihydrate (AR, 99.5%) was rapidly injected into the tube via syringe. A timer was started, and the gas volume was recorded using the displacement method. Using the modified formula PV = nRT: Calculate the total volume of gas that can be produced by 100% decomposition of formic acid under the ambient temperature and pressure conditions during the test, and then calculate the total volume of 25% of the gas; finally, use the formula Calculate the Turnover Frequency (TOF), where P is the local atmospheric pressure (unit, Pa); V 25％It refers to 25% of the total volume of gas (carbon dioxide and hydrogen, unit, L) that can be produced by 100% decomposition of formic acid under the test conditions; R is the gas constant 8.314; T is the reaction temperature (unit, K); n metal It refers to the total molar amount of palladium and gold in the catalyst used (unit, mol); t is the reaction time (unit, h).

[0021] Catalyst reusability test: After the first catalytic formic acid decomposition hydrogen production reaction is completed, the reacted catalyst is recovered by filtering, washing, and drying; then the catalytic performance of the recovered catalyst is tested according to the same operating steps as above.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. Compared with pure palladium-carbon catalysts, under the condition of the same molar amount of active component metal, the carbon-supported palladium-gold nano-heterogeneous catalyst prepared by the method of the present invention has substantially the same catalytic activity as the pure palladium-carbon catalyst, but the carbon-supported palladium-gold nano-heterogeneous catalyst prepared by the stepwise reduction method of the present invention has better stability;

[0024] 2. Compared with carbon-supported palladium-gold catalysts prepared using the same raw materials but with a different feeding order (co-reduction method or one-pot method), the palladium-gold nanoheterogeneous catalyst prepared by the step-by-step reduction method of the present invention has higher catalytic activity;

[0025] 3. Compared with palladium-gold catalysts prepared by other methods, the catalyst prepared by the method of the present invention can achieve hydrogen production under mild conditions, has high catalytic activity, good selectivity, and can be recycled repeatedly.

[0026] 4. Compared with other preparation methods of palladium-gold catalysts, the preparation method of the present invention has the advantages of simple process, convenient operation, short preparation time, low cost, good reproducibility, etc., and is more suitable for industrial scale-up production. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 :Schematic diagram of the preparation process flow of carbon-supported palladium-gold nanoheterogeneous catalysts.

[0028] Figure 2 : Pd prepared in Example 1 0.5 Au 0.5 TEM image and particle size distribution of / ECP.

[0029] Figure 3 : Pd prepared in Example 1 0.5 Au 0.5 / ECP element mapping diagram.

[0030] Figure 4 : Pd prepared in Example 1 0.5 Au 0.5 XPS patterns of Pd 3d and Au 4f in / ECP.

[0031] Figure 5 : Pd prepared in Example 1 0.5 Au 0.5 / ECP XRD pattern.

[0032] Figure 6 : Pd prepared in Example 1 0.5 Au 0.5 / ECP catalytic performance diagram of formic acid decomposition to produce hydrogen at different temperatures. DETAILED DESCRIPTION

[0033] The present invention will be further described below with reference to specific embodiments. The illustrative embodiments and descriptions of the present invention are used to explain the present invention but are not intended to limit the present invention.

[0034] Example 1

[0035] Disperse 185.7 mg of superconducting carbon Ketjen Black ECP with 20 mL of deionized water and sonicate for 30 minutes to uniformly disperse it to form a carrier suspension A for later use. Weigh 111.7 mg of sodium citrate (AR, 99%) and dissolve it in 3.75 mL of deionized water. Then add it to 2.35 mL of 0.02 M chloroauric acid, mix well, and let it stand at room temperature for 10 to 15 minutes until the solution completely turns from yellow to black, forming a gold nanoparticle suspension B. At the same time, take 0.94 mL of 0.05 M chloropalladic acid, 111.7 mg of sodium citrate, and 3.75 mL of deionized water to form an orange-yellow palladium precursor solution C. Finally, the black gold nanoparticle suspension B and the orange-yellow palladium precursor solution C are added to the carrier suspension A simultaneously. After stirring at 0°C for 1 hour, 7.25 mL of 0.05 M sodium carbonate aqueous solution containing 29 mg of sodium borohydride was added dropwise at 0.5 mL / min. After the addition was completed, the mixture was stirred at this temperature for 4 hours, filtered, and the filter cake was washed with a large amount of deionized water. The filter cake was dried in vacuo at 50°C for 12 hours to obtain the target catalyst Pd with a total loading of 5 wt.% of palladium and gold. 0.5 Au 0.5 / ECP. According to the test method of catalyst catalytic performance, the catalyst was tested at 303K, 313K, 323K, and 333K. FA :n SF =1.1M:2.4M catalytic performance, the results are shown in Figure 6The process was repeated four times according to the method described in the catalyst reusability test. The results are shown in Table 2. The prepared catalyst has good cyclic stability for catalyzing the formic acid dehydrogenation reaction. After three reactions, the conversion rate and hydrogen selectivity of the catalyst for the decomposition of formic acid to produce hydrogen can still reach 100%.

[0036] Example 2

[0037] Disperse 185.7 mg of conductive carbon black XC-72 with 20 mL of deionized water and sonicate for 30 minutes to uniformly disperse it to form a carrier suspension A, which is set aside. Weigh 111.7 mg of sodium citrate (AR, 99%) and dissolve it in 3.75 mL of deionized water. Then add it to 2.35 mL of 0.02 M chloroauric acid, mix well, and let it stand at room temperature for 10 to 15 minutes until the solution completely turns from yellow to black, forming a gold nanoparticle suspension B. At the same time, take 0.94 mL of 0.05 M chloropalladic acid, 111.7 mg of sodium citrate, and 3.75 mL of deionized water and mix to form an orange-yellow palladium precursor solution C. Finally, the black gold nanoparticle suspension B and the orange-yellow palladium precursor solution C are added to the carrier suspension A simultaneously. After stirring at 0 ° C for 1 hour, 7.25 mL of 0.05 M sodium carbonate aqueous solution containing 29.0 mg of sodium borohydride was added dropwise at 0.5 mL / min. After the addition was completed, the mixture was stirred for 4 hours. The mixture was filtered and the filter cake was washed with a large amount of deionized water. The filter cake was dried in vacuum at 50 ° C for 12 hours to obtain the target catalyst Pd 0.5 Au 0.5 / XC-72.

[0038] Example 3

[0039] Disperse 185.7 mg of high-purity coconut shell carbon powder SAC-02 with 20 mL of deionized water and sonicate for 30 minutes to uniformly disperse it to form carrier suspension A, which is set aside. Weigh 111.7 mg of sodium citrate (AR, 99%) and dissolve it in 3.75 mL of deionized water. Then add it to 2.35 mL of 0.02 M chloroauric acid, mix thoroughly, and let it stand at room temperature for 10-15 minutes until the solution completely turns from yellow to black, forming gold nanoparticle suspension B. Simultaneously, take 0.94 mL of 0.05 M chloropalladic acid, 111.7 mg of sodium citrate, and 3.75 mL of deionized water to form orange-yellow palladium precursor solution C. Finally, the black gold nanoparticle suspension B and the orange-yellow palladium precursor solution C are simultaneously added to carrier suspension A. After stirring at 0 ° C for 1 hour, 7.25 mL of 0.05 M sodium carbonate aqueous solution containing 29.0 mg of sodium borohydride was added dropwise at 0.5 mL / min. After the addition was completed, the mixture was kept warm and stirred for 4 hours, filtered, and the filter cake was washed with a large amount of deionized water. It was vacuum dried at 50 ° C for 12 hours to obtain the target catalyst Pd 0.5 Au 0.5 / SAC-02.

[0040] Example 4

[0041] Disperse 185.7 mg of superconducting carbon Ketjen Black ECP600JD with 20 mL of deionized water and sonicate for 30 minutes to uniformly disperse it to form a carrier suspension A for later use. Weigh 111.7 mg of sodium citrate (AR, 99%) and dissolve it in 3.75 mL of deionized water. Then add it to 2.35 mL of 0.02 M chloroauric acid, mix well, and let it stand at room temperature for 10 to 15 minutes until the solution completely turns from yellow to black, forming a gold nanoparticle suspension B. At the same time, take 0.94 mL of 0.05 M chloropalladic acid, 111.7 mg of sodium citrate, and 3.75 mL of deionized water to form an orange-yellow palladium precursor solution C. Finally, the black gold nanoparticle suspension B and the orange-yellow palladium precursor solution C are added to the carrier suspension A simultaneously. After stirring at 0 ° C for 1 hour, 7.25 mL of 0.05 M sodium carbonate aqueous solution containing 29.0 mg of sodium borohydride was added dropwise at 0.5 mL / min. After the addition was completed, the mixture was kept warm and stirred for 4 hours. The mixture was filtered and the filter cake was washed with a large amount of deionized water. The filter cake was vacuum dried at 50 ° C for 12 hours to obtain the target catalyst Pd 0.5 Au 0.5 / ECP600JD.

[0042] Example 5

[0043] Disperse 187.9 mg of superconducting carbon Ketjen Black ECP with 20 mL of deionized water and sonicate for 30 minutes to uniformly disperse it to form carrier suspension A, which is set aside. Weigh 55.8 mg of sodium citrate and dissolve it in 1.9 mL of deionized water. Add it to 1.175 mL of 0.02 M chloroauric acid, mix thoroughly, and let it stand at room temperature for 10-15 minutes until the solution completely turns from yellow to black, forming gold nanoparticle suspension B. Simultaneously, mix 1.41 mL of 0.05 M chloropalladic acid, 167.5 mg of sodium citrate, and 5.6 mL of deionized water to form orange-yellow palladium precursor solution C. Finally, add the black gold nanoparticle suspension B and orange-yellow palladium precursor solution C simultaneously to the carrier suspension. After stirring at 0 ° C for 1 hour, 7.25 mL of 0.05 M sodium carbonate aqueous solution containing 29 mg of sodium borohydride was added dropwise at 0.5 mL / min. After the addition was completed, stirring was continued for 4 hours, filtered, washed with a large amount of water, and dried in vacuo at 50 ° C for 12 hours to obtain the target catalyst Pd 0.75 Au 0.25 / ECP.

[0044] Example 6

[0045] Disperse 183.6 mg of superconducting carbon Ketjen Black ECP with 20 mL of deionized water and sonicate for 30 minutes to uniformly disperse it to form carrier suspension A, which is set aside. Dissolve 167.5 mg of sodium citrate in 5.6 mL of deionized water and add it to 3.52 mL of 0.02 M chloroauric acid. Mix thoroughly and let stand at room temperature for 10-15 minutes until the solution completely turns from yellow to black, forming gold nanoparticle suspension B. Simultaneously, mix 0.47 mL of 0.05 M chloropalladic acid, 55.8 mg of sodium citrate, and 1.9 mL of deionized water to form yellow palladium precursor solution C. Finally, add both the black gold nanoparticle suspension B and the yellow palladium precursor solution C to the carrier suspension. After stirring at 0 ° C for 1 hour, 7.25 mL of 0.05 M sodium carbonate aqueous solution containing 29 mg of sodium borohydride was added dropwise at 0.5 mL / min. After the addition was completed, stirring was continued for 4 hours, filtered, washed with a large amount of water, and dried in vacuo at 50 ° C for 12 hours to obtain the target catalyst Pd 0.25 Au 0.75 / ECP.

[0046] Comparative Example 1

[0047] Weigh 318 mg of superconducting carbon Ketjen black ECP and 370.6 mg of sodium citrate, dissolve them in 40 mL of water, and ultrasonically disperse them for 30 minutes. Then add 3.15 mL of 0.05 M chloropalladic acid solution, continue ultrasonicating for 20 minutes, transfer to a low-temperature reaction bath, stir at 0°C for 1 hour, and then add 10 mL of sodium carbonate solution (containing 40 mg of sodium borohydride) dropwise at a rate of 0.5 mL / min. After the addition is completed, continue to keep warm and stir for 4 hours, filter, and wash the filter cake with a large amount of water. After vacuum drying at 50°C for 12 hours, the Pd / ECP catalyst is obtained.

[0048] Comparative Example 2

[0049] Weigh 318 mg of conductive carbon black XC-72 and 370.6 mg of sodium citrate, dissolve them in 40 mL of water, and ultrasonically disperse for 30 minutes. Then add 3.15 mL of 0.05 M chloropalladic acid solution, continue ultrasonicating for 20 minutes, transfer to a low-temperature reaction bath, stir at 0°C for 1 hour, and then add 10 mL of sodium carbonate solution (containing 40 mg of sodium borohydride) at a rate of 0.5 mL / min. After the addition is completed, continue to keep warm and stir for 4 hours, filter, and wash the filter cake with a large amount of water. After vacuum drying at 50°C for 12 hours, the Pd / XC-72 catalyst is obtained.

[0050] Comparative Example 3

[0051] Weigh 318 mg of high-purity coconut shell carbon powder SAC-02 and 370.6 mg of sodium citrate, dissolve them in 40 mL of water, and ultrasonically disperse them for 30 minutes. Then add 3.15 mL of 0.05 M chloropalladic acid solution, continue ultrasonicating for 20 minutes, transfer to a low-temperature reaction bath, stir at 0°C for 1 hour, and then add 10 mL of sodium carbonate solution (containing 40 mg of sodium borohydride) dropwise at a rate of 0.5 mL / min. After the addition is completed, continue to keep warm and stir for 4 hours, filter, and wash the filter cake with plenty of water. After vacuum drying at 50°C for 12 hours, the Pd / SAC-02 catalyst is obtained.

[0052] Comparative Example 4

[0053] Weigh 318 mg of superconducting carbon Ketjen black ECP600JD and 370.6 mg of sodium citrate, dissolve them in 40 mL of water, and ultrasonically disperse them for 30 minutes. Then add 3.15 mL of 0.05 M chloropalladic acid solution, continue ultrasonicating for 20 minutes, transfer to a low-temperature reaction bath, stir at 0°C for 1 hour, and then add 10 mL of sodium carbonate solution (containing 40 mg of sodium borohydride) dropwise at a rate of 0.5 mL / min. After the addition is completed, continue to keep warm and stir for 4 hours, filter, and wash the filter cake with a large amount of water. After vacuum drying at 50°C for 12 hours, the Pd / ECP600JD catalyst is obtained.

[0054] Comparative Example 5

[0055] Disperse 318 mg of superconducting carbon Ketjen Black (ECP) in 20 mL of deionized water and sonicate for 30 minutes to achieve uniform dispersion, forming Support Suspension A. Weigh 202 mg of sodium citrate and dissolve it in 6.4 mL of deionized water. Add the mixture to 4.25 mL of 0.02 M chloroauric acid, mix thoroughly, and let it stand at room temperature for 10-15 minutes until the solution completely changes from yellow to black, forming Gold Nanoparticle Suspension B. This suspension is then added to Support Suspension A. After stirring at 0°C for 1 hour, add 26.3 mg of sodium borohydride in 6.6 mL of 0.05 M sodium carbonate aqueous solution dropwise at 0.5 mL / min. Continue stirring for 4 hours after the addition is complete. Filter, wash with copious amounts of water, and dry under vacuum at 50°C for 12 hours to obtain the target catalyst, Au / ECP.

[0056] Comparative Example 6

[0057] 185.7 mg of superconducting carbon Ketjen black ECP was dispersed with 20 mL of deionized water and ultrasonicated for 30 minutes to form a carrier suspension A for later use. 223.4 mg of sodium citrate (AR, 99%) was weighed and dissolved with 7.25 mL of deionized water. 0.94 mL of 0.05 M chloropalladic acid was added and mixed evenly. 2.35 mL of 0.02 M chloroauric acid was added and mixed evenly. The mixture was quickly added to the carrier suspension A and ultrasonicated for 20 minutes. After stirring at 0 ° C for 1 hour, 7.25 mL of 0.05 M sodium carbonate aqueous solution containing 29 mg of sodium borohydride was added dropwise at 0.5 mL / min. After the addition was completed, the mixture was kept warm and stirred for 4 hours, filtered, and the filter cake was washed with a large amount of deionized water. The filter cake was vacuum dried at 50 ° C for 12 hours to obtain the target catalyst Pd 0.5 Au 0.5 / ECP (One Pot Process).

[0058] The catalytic performance of the catalysts prepared in Examples 1 to 6 and Comparative Examples 1 to 6 in the formic acid dehydrogenation (FAD) reaction was evaluated, and the results are shown in Table 1. In order to investigate the stability of the examples and comparative examples, the catalysts of Example 1, Comparative Example 1, Comparative Example 5, and Comparative Example 6 were tested for reusability, and the results are shown in Table 2. It can be seen that by alloying or doping Pd with Au elements, the valence electron density of Pd can be adjusted, thereby reducing the adsorption of carbon monoxide by Pd or facilitating the adsorption of formate. Among them, the weak adsorption of CO and H2 molecules by Au atoms is not only conducive to the precipitation of H2, but also because CO is difficult to form a stable complex on the Au surface, it is beneficial to reduce the poisoning phenomenon of Pd / C, thereby improving the stability of the catalyst.

[0059] Table 1 TOF values ​​of formic acid decomposition to hydrogen produced by carbon-supported palladium-gold nanoparticle heterogeneous catalysts

[0060]

[0061] Table 2 Test on the reusability of catalysts for catalytic decomposition of formic acid to produce hydrogen

[0062]

[0063] It can be seen from the above examples and comparative examples that the present invention can be used as a simple catalyst preparation method, and can be applied to different supports, metal precursors, and palladium-gold molar ratios to prepare a series of carbon-supported palladium-gold nanoheterogeneous catalysts. The prepared catalysts are applied to the formic acid decomposition reaction to produce hydrogen, and have very good catalytic activity and stability. This provides a new approach for the development of inexpensive, safe, and efficient heterogeneous catalysts, and further promotes the application of formic acid as a hydrogen storage material in actual production and life.

Claims

1. A carbon-supported palladium-gold nano-heterogeneous catalyst for catalyzing hydrogen production from formic acid-sodium formate aqueous solution, characterized in that The catalyst comprises a carbon support and active components, palladium-gold nanoparticles, supported on the carbon support. The total metal loading is 3.0 to 15.0 wt%, wherein the palladium content is 0.46 to 9.28 wt% and the gold content is 1.14 to 12.71 wt%. The preparation method comprises the following steps: Step 1, preparation of carrier suspension A: dispersing the carbon carrier in deionized water, ultrasonically dispersing and stirring to form carrier suspension A; Step 2, preparation of gold nanoparticle suspension B: dissolving sodium citrate in water, and then adding chloroauric acid solution to form gold nanoparticle suspension B; Step 3, preparation of palladium precursor solution C: dissolving sodium citrate in water, and then adding palladium precursor solution to form palladium precursor solution C; Step 4, mixing suspension D: adding gold nanoparticle suspension B and palladium precursor solution C to the stirred carrier suspension A, and stirring at room temperature to form a mixed solution D; Step 5, ultrasonic mixing: ultrasonically mixing the mixed suspension D; Step 6, stirring and soaking: transfer the mixed suspension D to a low-temperature constant temperature reaction bath, stir and soak at a temperature of 0-50°C for 1-4 hours; Step 7, reduction: add dropwise a sodium carbonate aqueous solution containing sodium borohydride, and continue reducing and stirring at 0-50°C; Step 8, filtration and drying: Filter and rinse the filter cake with plenty of water, dry the filter cake in a vacuum oven, grind it, and obtain Pd x Au 1-x / C catalyst.

2. The use according to claim 1, characterized in that: The carbon-supported palladium-gold nanoheterogeneous catalyst is dispersed in water, and a formic acid-sodium formate aqueous solution is injected to produce hydrogen at a reaction temperature of 303K to 333K. In the reaction system, the molar concentrations of formic acid and sodium formate are 1.1 mol / L and 2.4 mol / L, respectively.

3. The use according to claim 1, characterized in that: In step 1, the carbon support includes conductive carbon black XC-72, superconducting carbon Ketjen black ECP, superconducting carbon Ketjen black ECP600JD, and high-purity coconut shell carbon powder SAC-02.

4. The use according to claim 1, characterized in that: In step 3, the palladium precursor includes chloropalladic acid, sodium chloropalladate, potassium chloropalladate, palladium nitrate and palladium acetate.

5. The use according to claim 1, characterized in that In step 2: The ratio of the molar amount of gold contained in chloroauric acid to the molar amount of sodium citrate is 1:8; The mixed solution of chloroauric acid and sodium citrate is allowed to stand for reduction at room temperature for 10 to 30 minutes.

6. The use according to claim 1, characterized in that: In step 3, the molar ratio of palladium contained in the palladium precursor to the molar ratio of sodium citrate is 1:

8.

7. The use according to claim 1, characterized in that: In step 4, the molar ratio of gold in the gold nanoparticle suspension B to palladium in the palladium precursor solution C is 1:0.333-3, and the total mass of palladium and gold in the catalyst accounts for 3.0-15.0 wt % of the catalyst.

8. The use according to any one of claims 1 to 7, characterized in that: In step 7, the ratio of the total molar amount of palladium and gold in the mixed suspension D to the molar amount of sodium borohydride in the sodium carbonate solution is 1:8 to 1:20; the reduction time is 2 h to 16 h, and the reduction temperature is 0 to 50° C.

9. The use according to any one of claims 1 to 7, characterized in that: In step 7, the molar concentration of sodium borohydride in the 0.05 mol / L sodium carbonate aqueous solution is 0.1 mol / L; the dropping speed of the mixed suspension D is 0.5 mL / min.

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