A supported nano-palladium-silver bimetallic catalyst, a preparation method and application thereof

Abstract

This invention discloses a supported nano-palladium-silver bimetallic catalyst, its preparation method, and its application. The preparation method includes: (1) synthesizing MIL-125 metal-organic framework material by solvothermal method in a mixed solvent of N,N-dimethylformamide and methanol using terephthalic acid and tetrabutyl titanate as raw materials; (2) subjecting MIL-125 to programmed temperature carbonization treatment under an inert gas atmosphere to obtain carbonized MIL-125 support; (3) using the carbonized MIL-125 as support, loading palladium and silver bimetallic active components by co-reduction method to prepare the supported nano-palladium-silver bimetallic catalyst. This invention obtains a porous carbon@titanium oxide composite support by high-temperature pyrolysis of MIL-125, and utilizes the synergistic confinement effect of porous carbon structure and titanium oxide nanoparticles to effectively inhibit the growth and aggregation of PdAg nanoparticles. The prepared catalyst exhibits excellent catalytic performance in the low-temperature liquid-phase formic acid decomposition to hydrogen production reaction, with a TOF value of up to 2550 h⁻¹. ‑1 .

Description

Technical Field

[0001] This invention belongs to the field of catalytic hydrogen production technology, specifically relating to a supported palladium-silver catalyst, its preparation method, and its application in the liquid-phase formic acid decomposition for hydrogen production. Background Technology

[0002] With the global energy crisis and environmental problems becoming increasingly severe, hydrogen energy, due to its outstanding advantages such as being renewable, pollution-free, and having a high calorific value, has become one of the most promising clean energy sources. Among many hydrogen storage materials, formic acid is considered one of the most promising liquid organic hydrogen carriers due to its wide availability, renewable nature, low price, and convenient storage and transportation.

[0003] However, existing liquid-phase formic acid decomposition hydrogen production catalysts often suffer from insufficient catalytic activity, low selectivity, or poor stability, making it difficult to meet the practical requirements for efficient hydrogen production under low-temperature conditions. Therefore, developing a low-temperature nanocatalytic liquid-phase formic acid decomposition hydrogen production system with high stability, high selectivity, and high catalytic efficiency is of significant research and application value.

[0004] Based on a review and analysis of existing literature and patents related to heterogeneous catalysts, bimetallic catalysts using a porous structure and special components to support palladium (Pd) and silver (Ag) alloys as active components have shown good catalytic potential in the formic acid decomposition reaction.

[0005] For example, patent application CN114950544A provides an MXene-supported metal catalyst modified with aniline groups. It uses the reaction of isoamyl nitrite and p-phenylenediamine to modify the surface of the MXene material with aniline groups. Then, palladium metal ions or a palladium bimetallic ion solution are reduced by a liquid-phase reducing agent to realize the construction of palladium metal or its alloy particles loaded on the MXene support modified with aniline groups. This solves the problems of metal particle agglomeration and / or poor catalytic activity of formic acid decomposition to produce hydrogen, and has a great promoting effect on the application of formic acid decomposition to produce hydrogen.

[0006] MIL-125 is a titanium-based metal-organic framework (MOF) material assembled from titanium oxide clusters and terephthalic acid ligands. It is widely used in research fields such as photocatalysis, gas separation, and energy storage. It possesses a microporous structure and a large specific surface area, with a BET specific surface area reaching 1300 m² / g. By controlling the carbonization atmosphere and temperature during pyrolysis, a novel structural material composed of porous carbon and titanium oxide can be obtained.

[0007] For example, patent application CN119368213A discloses a porous nanocomposite Co / TiO2@CN catalyst and its preparation and application. It utilizes a MOF epitaxial growth strategy to synthesize a ZIF-67@NH2-MIL-125 composite structure, which is further prepared into a metal / titanium dioxide / carbon-nitrogen composite (Co / TiO2@CN) through high-temperature pyrolysis. This method has the advantages of simple preparation process and low cost, and the resulting composite material exhibits excellent photocatalytic activity, effectively solving the problem of low photocatalytic efficiency of single semiconductor materials.

[0008] Based on this, the present invention uses palladium and silver as active metal components. By pyrolyzing titanium-based metal-organic framework compound (MIL-125) at high temperature, and by screening catalyst supports and optimizing the palladium-silver component ratio, the aim is to prepare a supported nano-palladium-silver bimetallic catalyst with high catalytic activity, high selectivity and high stability, so as to achieve a high formic acid to hydrogen production efficiency. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a method for preparing a supported palladium-silver bimetallic catalyst for hydrogen production by formic acid decomposition, so as to overcome the defects of existing catalysts such as low activity, poor selectivity and insufficient stability.

[0010] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A method for preparing a supported nano-palladium-silver bimetallic catalyst for hydrogen production by low-temperature liquid-phase formic acid decomposition includes the following steps: (1) MIL-125 metal-organic framework material was synthesized by solvothermal method using terephthalic acid and tetrabutyl titanate as raw materials in a mixed solvent of N,N-dimethylformamide and methanol. (2) The MIL-125 is carbonized under a protective atmosphere by programmed temperature rise to obtain a carbonized MIL-125 carrier; (3) Using the carbonized MIL-125 as a support, palladium-silver bimetallic active components with different molar ratios were loaded by co-reduction method to prepare the supported nano-palladium-silver bimetallic catalyst.

[0011] Further, in step (1), the volume ratio of N,N-dimethylformamide to methanol is 1:1 to 18:1; most preferably, the volume ratio of N,N-dimethylformamide to methanol is 9:1.

[0012] Further, in step (1), the ratio of terephthalic acid, tetrabutyl titanate and N,N-dimethylformamide is 1-10 mmol : 1-10 mmol : 13.3 mL; most preferably, the ratio of terephthalic acid, tetrabutyl titanate and N,N-dimethylformamide is 4 mmol : 1 mmol : 13.3 mL.

[0013] Further, in step (1), the temperature of the solvothermal reaction is 100–180°C, and the reaction time is 6–24 h. Most preferably, the temperature of the solvothermal reaction is 160°C, and the reaction time is 20 h.

[0014] Furthermore, in step (2), the heating rate of the programmed heating carbonization is 1 to 10 °C / min, the final carbonization temperature is 500 to 1000 °C, and the holding time is 2 to 6 h.

[0015] Furthermore, in step (3), the molar ratio of the palladium-silver bimetallic compound Pd:Ag is 1:0.1 to 1:5.

[0016] Furthermore, in step (3), the co-reduction method uses sodium borohydride or hydrazine hydrate as a reducing agent and carries out the reduction reaction at room temperature to 80°C.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The present invention does not directly use MIL-125 metal-organic framework material as catalyst support, but instead performs programmed temperature carbonization treatment of MIL-125 at different temperatures under nitrogen atmosphere to obtain porous carbon@titanium oxide composite support. (2) The palladium-silver bimetallic active components are loaded onto the porous carbon@titanium oxide composite support. The synergistic confinement effect of the porous carbon structure and titanium oxide nanoparticles effectively inhibits the growth and aggregation of PdAg nanoparticles, thereby obtaining better catalytic performance. Attached Figure Description

[0018] Figure 1 This is a low-magnification transmission electron microscopy image of the supported palladium-silver catalyst prepared in Example 1 of the present invention; Figure 2 The X-ray diffraction patterns of the supported palladium-silver catalysts prepared in Examples 1-4 of this invention are shown below. Figure 3 This is a high-magnification transmission electron microscopy image of the supported palladium-silver catalyst prepared in Example 1 of the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below with reference to specific embodiments. The following embodiments are for illustrative purposes only and should not be considered as limitations on this invention.

[0020] Example 1

[0021] Preparation of a supported nano-palladium-silver alloy catalyst: (1) Dissolve 2492 mg of terephthalic acid and 1276 mg of tetrabutyl titanate together in 50 mL of a mixed solvent of N,N-dimethylformamide (DMF) and methanol, wherein the volume ratio of N,N-dimethylformamide to methanol is 9:1; (2) The above mixed solution was transferred to a 100 mL polytetrafluoroethylene (PTFE) liner, and the PTFE liner was placed in a stainless steel reactor. The reaction was carried out at 160 °C for 20 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature to obtain the MIL-125 powder product. (3) The MIL-125 powder was washed twice each with N,N-dimethylformamide and methanol, and then dried at 60°C to obtain MIL-125 powder. (4) The MIL-125 powder was placed in a tube furnace and pre-carbonized at 300°C for 4 h under a nitrogen atmosphere; then, the temperature was increased to 900°C at a rate of 5°C / min and held for 2 h. After the holding period, the powder was allowed to cool naturally to room temperature in the furnace to obtain a black carbonized product. The black carbonized product was named MIL-125-900. (5) Add 100 mg of MIL-125-900 to 10 mL of deionized water and sonicate for 10 min to obtain a uniform dispersion. Then, add a mixed solution of 0.1 mmol silver nitrate and 0.9 mmol palladium chloroacetic acid to the dispersion and stir for 3 h. (6) Under vigorous stirring conditions, 0.5 mL of sodium borohydride aqueous solution was rapidly added to the above mixed solution, wherein the mass of sodium borohydride in the sodium borohydride aqueous solution was 37 mg; after the addition was completed, the mixture was stirred continuously for 10 min and centrifuged at 6000 r / min for 5 min to obtain the supported nano-palladium-silver alloy catalyst.

[0022] Example 2

[0023] Preparation of a supported nano-palladium-silver alloy catalyst: (1) Dissolve 2492 mg of terephthalic acid and 1276 mg of tetrabutyl titanate together in 50 mL of a mixed solvent of N,N-dimethylformamide (DMF) and methanol, wherein the volume ratio of N,N-dimethylformamide to methanol is 9:1; (2) The above mixed solution was transferred to a 100 mL polytetrafluoroethylene (PTFE) liner, and the PTFE liner was placed in a stainless steel reactor. The reaction was carried out at 160 °C for 20 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature to obtain the MIL-125 powder product. (3) The MIL-125 powder was washed twice each with N,N-dimethylformamide and methanol, and then dried at 60°C to obtain MIL-125 powder. (4) The MIL-125 powder was placed in a tube furnace and pre-carbonized at 300°C for 4 h under a nitrogen atmosphere; then, the temperature was increased to 800°C at a rate of 5°C / min and held for 2 h. After the holding period, the powder was allowed to cool naturally to room temperature in the furnace to obtain a black carbonized product. The black carbonized product was named MIL-125-800. (5) Add 100 mg of MIL-125-800 to 10 mL of deionized water and sonicate for 10 min to obtain a uniform dispersion. Then, add a mixed solution of 0.1 mmol silver nitrate and 0.9 mmol palladium chloroacetic acid to the dispersion and stir for 3 h. (6) Under vigorous stirring conditions, 0.5 mL of sodium borohydride aqueous solution was rapidly added to the above mixed solution, wherein the mass of sodium borohydride in the sodium borohydride aqueous solution was 37 mg; after the addition was completed, the mixture was stirred continuously for 10 min and centrifuged at 6000 r / min for 5 min to obtain the supported nano-palladium-silver alloy catalyst.

[0024] Example 3

[0025] Preparation of a supported nano-palladium-silver alloy catalyst: (1) Dissolve 2492 mg of terephthalic acid and 1276 mg of tetrabutyl titanate together in 50 mL of a mixed solvent of N,N-dimethylformamide (DMF) and methanol, wherein the volume ratio of N,N-dimethylformamide to methanol is 9:1; (2) The above mixed solution was transferred to a 100 mL polytetrafluoroethylene (PTFE) liner, and the PTFE liner was placed in a stainless steel reactor. The reaction was carried out at 160 °C for 20 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature to obtain the MIL-125 powder product. (3) The MIL-125 powder was washed twice each with N,N-dimethylformamide and methanol, and then dried at 60°C to obtain MIL-125 powder. (4) The MIL-125 powder was placed in a tube furnace and pre-carbonized at 300°C for 4 h under a nitrogen atmosphere; then, the temperature was increased to 1000°C at a rate of 5°C / min and held for 2 h. After the holding period, the powder was allowed to cool naturally to room temperature in the furnace to obtain a black carbonized product. The black carbonized product was named MIL-125-1000. (5) Add 100 mg of MIL-125-1000 to 10 mL of deionized water and sonicate for 10 min to obtain a uniform dispersion. Then, add a mixed solution of 0.1 mmol silver nitrate and 0.9 mmol palladium chloride to the dispersion and stir for 3 h. (6) Under vigorous stirring conditions, 0.5 mL of sodium borohydride aqueous solution was rapidly added to the above mixed solution, wherein the mass of sodium borohydride in the sodium borohydride aqueous solution was 37 mg; after the addition was completed, the mixture was stirred continuously for 10 min and centrifuged at 6000 r / min for 5 min to obtain the supported nano-palladium-silver alloy catalyst.

[0026] Example 4

[0027] Preparation of a supported nano-palladium-silver alloy catalyst: (1) Dissolve 2492 mg of terephthalic acid and 1276 mg of tetrabutyl titanate together in 50 mL of a mixed solvent of N,N-dimethylformamide (DMF) and methanol, wherein the volume ratio of N,N-dimethylformamide to methanol is 9:1; (2) The above mixed solution was transferred to a 100 mL polytetrafluoroethylene (PTFE) liner, and the PTFE liner was placed in a stainless steel reactor. The reaction was carried out at 160 °C for 20 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature to obtain the MIL-125 powder product. (3) The MIL-125 powder was washed twice each with N,N-dimethylformamide and methanol, and then dried at 60°C to obtain MIL-125 powder. (4) The MIL-125 powder was placed in a tube furnace and pre-carbonized at 300°C for 4 h under a nitrogen atmosphere; then, the temperature was increased to 900°C at a rate of 5°C / min and held for 2 h. After the holding period, the powder was allowed to cool naturally to room temperature in the furnace to obtain a black carbonized product. The black carbonized product was named MIL-125-900. (5) Add MIL-125-900 to a 40% hydrofluoric acid aqueous solution, stir and etch for 12 h, centrifuge at 6000 r / min, wash with deionized water until neutral, and dry at 60℃ for 12 h to obtain a porous carbon support. (6) 100 mg of porous carbon support was added to 10 mL of deionized water and ultrasonically dispersed for 10 min to obtain a uniform dispersion. Subsequently, a mixed solution of 0.1 mmol silver nitrate and 0.9 mmol palladium chloroacetic acid was added to the dispersion and stirred for 3 h. (7) Under vigorous stirring conditions, 0.5 mL of sodium borohydride aqueous solution was rapidly added to the above mixed solution, wherein the mass of sodium borohydride in the sodium borohydride aqueous solution was 37 mg; after the addition was completed, the mixture was stirred continuously for 10 min and centrifuged at 6000 r / min for 5 min to obtain the supported nano-palladium-silver alloy catalyst.

[0028] Comparative Example 1

[0029] The only difference between this comparative example and Example 1 is that hydrofluoric acid is used to dissolve and remove the titanium oxide component in the carrier. The specific steps are the same as step (5) in Example 4, and the remaining steps are the same as in Example 1.

[0030] Example 5

[0031] Application of a supported palladium-silver catalyst in the production of hydrogen from formic acid: Take 5 mg of each catalyst prepared in Examples 1-4 and disperse it in 5 mL of formic acid / sodium formate aqueous solution (formic acid concentration 1M, sodium formate concentration 1M). Control the reaction temperature at 50°C, determine the volume of gas produced by water displacement method, and analyze the gas composition by gas chromatography.

[0032] Catalyst performance is characterized by the time-of-conversion (TOF) of the catalyst during the dehydrogenation of a chemical hydrogen storage medium. The TOF formula is: TOF = P o V / (2RTnt), where P o The atmospheric pressure is 101325 Pa, and V is the amount of hydrogen produced by the catalytic decomposition process (m³). 3 T is the room temperature (K), n is the total molar amount of Pd in ​​the catalyst (mol), and R is the ideal gas constant (8.3145m). 3 ·Pa·mol -1 ·K -1 The conversion frequency (TOF) of the catalyst can be calculated by taking the average of V and t from the addition of formic acid to the cessation of gas production. For each catalyst, three experiments were conducted, and the TOF was calculated using the average of V and t.

[0033] Table 1. TOF values ​​of catalysts in Examples 1-4

[0034] As shown in Table 1, the supported palladium-silver catalysts provided in Examples 1-3 of this invention, by selecting MIL-125 supports carbonized at different temperatures, can achieve a TOF value of 2550 h⁻¹ for the formic acid to hydrogen production reaction at 50°C. -1 The level can significantly increase the rate of hydrogen production from formic acid decomposition; however, in Example 4, after removing the titanium oxide component from the carbonized MIL-125 support using hydrofluoric acid aqueous solution, the reaction rate of the palladium-silver catalyst with only porous carbon support for hydrogen production from formic acid decreased significantly, and it could not completely decompose formic acid.

[0035] Depend on Figure 1 It can be seen that the active component PdAg particles of the catalyst prepared in Example 1 have a particle size of approximately 5-20 nm, and the larger particles (black spherical) are titanium oxide particles. This indicates that the present invention can achieve efficient hydrogen production from formic acid using a catalyst with highly dispersed active components, and the catalyst preparation process is short and easy to separate.

[0036] Depend on Figure 2 It can be seen that the catalyst supports prepared in Examples 1-3 contain titanium oxide components with different crystal forms. The titanium oxide components in Example 3 are significantly different from those in Examples 1 and 2. Furthermore, the TOF value of the catalyst in Example 3 is significantly lower than that in Examples 1 and 2, indicating that the catalyst prepared by high-temperature carbonization within a specific temperature range has higher catalytic reaction efficiency.

[0037] In summary, the supported palladium-silver catalyst provided by this invention can be well applied to the production of hydrogen from formic acid.

[0038] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a supported nanoscale palladium-silver bimetallic catalyst, characterized in that, Includes the following steps: (1) MIL-125 metal-organic framework material was synthesized by solvothermal method using terephthalic acid and tetrabutyl titanate as raw materials in a mixed solvent of N,N-dimethylformamide and methanol. (2) The MIL-125 described in step (1) is subjected to programmed temperature carbonization in an inert gas atmosphere to obtain a carbonized MIL-125 carrier; (3) Using the carbonized MIL-125 described in step (2) as a support, palladium and silver bimetallic active components are loaded by co-reduction method to prepare the supported nano-palladium-silver bimetallic catalyst.

2. The production method according to claim 1, characterized by, In step (1), the volume ratio of N,N-dimethylformamide to methanol is 1:1 to 18:

1.

3. The preparation method according to claim 2, characterized in that, In step (1), the volume ratio of N,N-dimethylformamide to methanol is 9:

1.

4. The preparation method according to claim 3, characterized in that, In step (1), the ratio of terephthalic acid, tetrabutyl titanate and N,N-dimethylformamide is 1-10 mmol : 1-10 mmol : 13.3 mL.

5. The preparation method according to claim 4, characterized in that, In step (1), the ratio of terephthalic acid, tetrabutyl titanate and N,N-dimethylformamide is 4 mmol : 1 mmol : 13.3 mL.

6. The preparation method according to claim 5, characterized in that, In step (1), the temperature of the solvothermal reaction is 100-180°C and the reaction time is 6-24 h.

7. The preparation method according to claim 6, characterized in that, In step (1), the temperature of the solvothermal reaction is 160°C and the reaction time is 20 h; In step (2), the heating rate of the programmed heating carbonization is 1 to 10 °C / min, the final carbonization temperature is 500 to 1000 °C, and the holding time is 2 to 6 h. In step (3), the molar ratio of palladium to silver is 1:0.1 to 1:5, and the co-reduction method uses sodium borohydride or hydrazine hydrate as a reducing agent to carry out the reduction reaction at room temperature to 80°C.

8. The supported nano-palladium-silver bimetallic catalyst prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the supported nano-palladium-silver bimetallic catalyst according to claim 8 in the liquid-phase formic acid decomposition for hydrogen production.

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