Amino-functionalized rodlike silicon dioxide loaded monometal Pd nano-catalyst and application thereof

Abstract

The invention discloses an amino-functionalized rodlike silicon dioxide loaded monometal Pd nano-catalyst and application thereof, after rodlike silicon dioxide is subjected to surface modification by 3-aminopropyltrimethoxysilane, a Pd precursor solution and amino-functionalized rodlike silicon dioxide are mixed, and loaded Pd nano-particles are subjected to reduction treatment by sodium borohydride. Compared with a traditional spherical silicon dioxide carrier, the unique morphology of the rod-like silicon dioxide carrier adopted by the catalyst provides a high specific surface area and a short mass transfer channel, the anchoring capacity of Pd nanoparticles is improved through amino functionalization, sintering is inhibited, and efficient and uniform loading and small size control of single metal Pd are achieved. The catalyst is used for room-temperature formic acid decomposition hydrogen production reaction, and shows 100% formic acid conversion rate, 100% hydrogen selectivity, good cycling stability and high initial TOF (Time of Flight) value.

Description

Technical Field

[0001] The present invention belongs to the field of catalyst preparation and sustainable development of environment and energy, and specifically relates to an amino-functionalized rod-shaped silica-supported single-metal Pd nanocatalyst and the application of the catalyst in catalyzing the decomposition of formic acid to produce hydrogen. Background Art

[0002] With the rapid development of the global economy, the world's demand for energy is constantly increasing. The energy crisis and environmental pollution caused by the gradual depletion of traditional fossil energy are becoming increasingly serious. The development of renewable clean energy to replace the use of traditional fossil fuels is the key to current research. Hydrogen is considered to be a clean energy alternative to traditional fossil fuels due to its cleanliness, high energy density (144MJ / kg) and renewability. In addition, hydrogen can be easily converted into electricity through fuel cells, and the only product is water. Due to the extremely low density and critical point of hydrogen, the safe and efficient storage and transportation of hydrogen remains a major problem for its industrial application. Formic acid (FA), as a liquid organic hydrogen carrier (LOHC), has the advantages of being non-toxic, having a high hydrogen content (4.4wt%) and hydrogen volume density (53.4g H2 / L), and being easy to store and transport. It is considered to be a safe and sustainable hydrogen storage material. Formic acid can be derived from CO2 hydrogenation and biomass conversion.

[0003] Catalysts for hydrogen production from formic acid decomposition are categorized into homogeneous and heterogeneous catalysts. Homogeneous catalysts have attracted widespread attention due to their high formic acid decomposition activity, but the difficulty in separating and recovering homogeneous catalysts limits their industrial application. Heterogeneous catalysts, on the other hand, are widely used in FA dehydrogenation reactions due to their excellent cyclic stability and ease of separation and recovery. Among heterogeneous catalysts, supported Pd metal nanoparticles (NPs) have attracted considerable attention due to their high activity and cyclic stability for FA decomposition to produce hydrogen. The catalytic activity of supported Pd metal catalysts is closely related to the particle size, coordination number, and electronic properties of the Pd NPs. In particular, smaller Pd NPs typically possess abundant metal active sites and exhibit excellent catalytic activity for FA decomposition to produce hydrogen. However, the surface energy of Pd metal increases with decreasing particle size, and Pd NPs often aggregate, resulting in decreased activity and stability. Therefore, selecting an appropriate support to enhance the dispersion of metal NPs and modulating the geometric and electronic structures of Pd NPs through metal-support interactions (MSIs) are crucial for improving catalyst activity and stability.

[0004] To date, carbon materials, silica, metal-organic frameworks (MOFs), and metal oxides have been widely used as support materials for the FA decomposition reaction to produce hydrogen. Mesoporous silica, with its large surface area, controllable pore structure, and high thermal and chemical stability, has shown promise as a palladium-loaded support for catalyzing the formic acid decomposition reaction to produce hydrogen. However, new silica supports are still under development to enhance their catalytic activity. Summary of the Invention

[0005] In view of the problems existing in the above-mentioned prior art, the present invention provides an amino-functionalized rod-shaped silica-supported single-metal Pd nanocatalyst with high specific surface area and short mass transfer channels.

[0006] The amino-functionalized rod-shaped silica-supported monometallic Pd nanocatalyst provided by the present invention is prepared by using rod-shaped silica with a long diameter of 50 to 200 nm and a short diameter of 10 to 50 nm as a carrier after being surface-modified with 3-aminopropyltriethoxysilane, using sodium tetrachloropalladate as a palladium source, and sodium borohydride as a reducing agent. The Pd loading amount in the catalyst is 5 wt% to 20 wt%, and the Pd particle size is 1.0 to 2.4 nm.

[0007] The preparation method of the rod-shaped silica is as follows: dissolving cetyltrimethylammonium bromide (CTAB) in a mixed solution of N,N-dimethylformamide (DMF) and deionized water under stirring, adding aqueous ammonia to adjust the pH to 8-10, stirring at 25-35°C for 0.5-2 hours, then adding tetraethyl orthosilicate (TEOS), heating to 70-80°C for hydrolysis and polycondensation for 2-24 hours, centrifuging, washing, vacuum drying, and calcining to obtain the rod-shaped silica. Preferably, the molar ratio of cetyltrimethylammonium bromide to tetraethyl orthosilicate is 1:5-20, and the aqueous ammonia concentration is 0.5-4 mol / L.

[0008] The amino-functionalized rod-shaped silica is prepared by dispersing the rod-shaped silica in anhydrous toluene, adding 3-aminopropyltriethoxysilane (APTES), and reacting at 60-90°C for 6-24 hours. The mixture is then centrifuged, washed, and vacuum-dried to obtain the amino-functionalized rod-shaped silica. The ratio of 3-aminopropyltriethoxysilane to rod-shaped silica is preferably 2-10 mL / g.

[0009] The preparation method of the amino-functionalized rod-shaped silica-supported monometallic Pd nanocatalyst comprises dispersing the amino-functionalized rod-shaped silica in an aqueous sodium tetrachloropalladate solution, sonicating for 20 to 60 minutes, adding an aqueous sodium borohydride solution, stirring at room temperature for 20 to 60 minutes, centrifuging, washing, and vacuum drying to obtain the amino-functionalized rod-shaped silica-supported monometallic Pd nanocatalyst. Preferably, the concentration of the aqueous sodium tetrachloropalladate solution is 0.01 to 0.5 mol / L, and the molar ratio of sodium borohydride to the Pd element in the sodium tetrachloropalladate is 20 to 40:1.

[0010] The present invention also provides a use of the amino-functionalized rod-shaped silica-supported monometallic Pd nanocatalyst for catalyzing the decomposition of formic acid to produce hydrogen. The specific method is: freshly prepared amino-functionalized rod-shaped silica-supported monometallic Pd nanocatalyst is added to deionized water, followed by a formic acid-sodium formate mixed solution, and the formic acid decomposition reaction is carried out at 20-70°C to produce hydrogen. Preferably, the molar ratio of the Pd element to formic acid in the catalyst is 1:10-500, the molar ratio of formic acid to sodium formate in the formic acid-sodium formate mixed solution is 1:1-3, and the formic acid concentration in the reaction system is 0.1-2.5 mol / L.

[0011] The beneficial effects of the present invention are as follows:

[0012] 1. The present invention uses amino-functionalized rod-shaped silica as a carrier to load single-metal Pd nanoparticles. Compared with traditional spherical silica, the shorter mesoporous channels of rod-shaped silica are more conducive to the mass transfer of reactant molecules. The abundant silanol groups on its surface are easy to amino-functionalize, which can anchor ultrafine Pd nanoparticles and inhibit metal agglomeration, so that the catalyst exhibits good catalytic activity and stability in the formic acid decomposition hydrogen production reaction.

[0013] 2. The catalyst of the present invention is used to catalyze the reaction of preparing hydrogen with formic acid as raw material, and has excellent catalytic performance. When the Pd loading in the catalyst is 5wt%, the TOF values ​​can reach 2129h at 25℃ and 50℃ respectively. -1 and 4500h -1 , with 100% formic acid conversion, 100% hydrogen selectivity and good cycle stability, providing a new way to develop safe and efficient formic acid hydrogen production catalysts. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1These are the SEM image (a) and TEM image (b) of RMS-NH2 in Example 1, the SEM image (c) and TEM image (d) of 10wt% Pd / RMS-NH2, the TEM image of 10wt% Pd / RMS-NH2 and the particle size distribution of Pd NPs (e), and the TEM image of Pd / RMS and the particle size distribution of Pd NPs (f) in Comparative Example 1.

[0015] Figure 2 This is the N1s spectrum of RMS-NH2 in Example 1.

[0016] Figure 3 This is the Pd 3d spectrum of 10 wt% Pd / RMS-NH2 in Example 1.

[0017] Figure 4 This is a composition diagram of the gas products of hydrogen production by decomposition of formic acid catalyzed by 10 wt % Pd / RMS-NH2 in Example 1, where (a) is the TCD channel and (b) is the FID channel.

[0018] Figure 5 This is a cyclic stability diagram of the 10wt% Pd / RMS-NH2 catalytic decomposition of formic acid to produce hydrogen in Example 1.

[0019] Figure 6 These are the SEM image (a) and TEM image of Pd / YSMSNs-NH2 in Comparative Example 2 and the particle size distribution of Pd NPs (b).

[0020] Figure 7 This is a comparison chart of the catalytic performance of Pd / RMS-NH2 with different Pd loading amounts in Example 2 for the decomposition of formic acid to produce hydrogen.

[0021] Figure 8 This is a comparison chart of the catalytic performance of 10wt% Pd / RMS-NH2 in Example 1 for catalytic decomposition of formic acid to produce hydrogen at different temperatures. DETAILED DESCRIPTION

[0022] The present invention will be further described in detail below with reference to the accompanying drawings and examples, but the examples do not limit the scope of protection claimed in the present invention.

[0023] Example 1

[0024] 1. Preparation of amino-functionalized rod-shaped silica-supported monometallic Pd nanocatalysts

[0025] Step 1: Under stirring at room temperature, 0.596 g CTAB (1.6 mmol) was dissolved in a mixed solution of 5 mL DMF and 65 mL deionized water until a transparent solution was formed; then 2 mol / L ammonia water was added to the transparent solution to adjust the pH of the system to 9, and stirred at 30°C for 1 hour. Then, 2 mL TEOS (8.9 mmol) was added, and the mixture was heated to 80°C and stirred for 4 hours. The resulting white emulsion was centrifuged and washed with ethanol, and then vacuum-dried at 80°C for 12 hours. Finally, it was calcined at 550°C for 6 hours to remove CTAB to obtain rod-shaped SiO2 (denoted as RMS).

[0026] Step 2: Disperse 0.5 g of RMS in 30 mL of anhydrous toluene, add 3 mL of APTES, and react with stirring and reflux at 80°C for 24 h. Then, the reaction mixture is cooled to room temperature, centrifuged and washed with ethanol, and finally dried in vacuum at 50°C for 12 h to obtain amino-functionalized rod-shaped silica (denoted as RMS-NH2).

[0027] Step 3: 47.9 mg of RMS-NH2 was dispersed in 5 mL of deionized water containing 0.05 mmol of sodium tetrachloropalladate, and the mixed solution was sonicated for 30 minutes. Subsequently, an excess of NaBH4 (37.8 mg, 1 mmol) aqueous solution was added to the above mixed solution and stirred at room temperature for 30 minutes; the mixed solution was then centrifuged and washed with deionized water, and finally vacuum dried at 50°C for 12 hours to obtain an amino-functionalized rod-shaped silica-supported monometallic Pd nanocatalyst with a Pd loading of 10 wt%, recorded as 10 wt% Pd / RMS-NH2.

[0028] SEM and TEM of RMS-NH2 and 10wt% Pd / RMS-NH2 are shown in Figure 1 , indicating that RMS has a rod-like structure with a long diameter of about 50nm and a short diameter of about 20nm. The rod-like structure of RMS does not change after loading with Pd NPs, and the average particle size of Pd NPs is about 1.3nm. The N1s and Pd 3d spectra of RMS-NH2 and 10wt% Pd / RMS-NH2 are shown in Figure 2. Figure 2 and Figure 3 , Pd 0 The shift of the peak toward higher binding energy indicates that Pd NPs transfer electrons to the support, and the shift of the N1s peak toward increasing binding energy indicates the existence of a strong metal-support interaction between PdNPs and RMS-NH2.

[0029] 2. Amino-functionalized rod-shaped silica supported on single-metal Pd nanocatalyst to catalyze formic acid decomposition and hydrogen production

[0030] 53.2 mg (the molar amount of Pd element is 0.05 mmol) of 10 wt% Pd / RMS-NH2 was added to a two-necked flask filled with 3 mL of deionized water, and then 2 mL of a formic acid-sodium formate mixed solution with a molar ratio of 1:2 (the molar amount of formic acid is 2.5 mmol) was added. The formic acid was decomposed and hydrogen was produced at 50°C under stirring. The resulting gas product was collected by drainage method and analyzed by gas chromatography. The composition of the gas product is shown in FIG. Figure 4 The formic acid conversion rate, H2 selectivity and initial TOF value are shown in Table 1. The results show that the formic acid conversion rate and H2 selectivity are both 100%, and the initial TOF value is 4500h -1 Subsequently, the stability test of 10wt% Pd / RMS-NH2 catalyst was carried out. Figure 5 It can be seen that after 5 cycles of experiments, the activity of 10wt% Pd / RMS-NH2 for formic acid decomposition and hydrogen production decreased slightly.

[0031] Comparative Example 1

[0032] In this comparative example, the RMS in step 1 of Example 1 was directly loaded with Pd according to the method in step 3 to obtain a catalyst 10 wt% Pd / RMS. The TEM results of the obtained 10 wt% Pd / RMS are shown in FIG. Figure 1 , indicating that the average particle size of PdNPs loaded on the RMS support without amino functionalization is larger, about 7.5 nm.

[0033] Further, 10 wt% Pd / RMS was used to catalyze formic acid decomposition for hydrogen production according to the method of Example 1. The formic acid conversion, H2 selectivity, and TOF values ​​are shown in Table 1. The results show that when TEM is not amino-functionalized with APTES, the gas production is less than 20 mL within 20 minutes, and the catalyst activity is negligible. This indicates that the amino groups grafted onto RMS facilitate the formation of well-dispersed PdNPs, thereby enhancing catalyst activity.

[0034] Comparative Example 2

[0035] In this comparative example, 0.64 g of CTAB (1.7 mmol) and 1.6 g of 1,3,5-trimethylbenzene (TMB) were dissolved in a mixture of 75 mL of deionized water and 30 mL of ethanol at room temperature with stirring until a transparent solution formed. 1 mL of 2 mol / L ammonia was then added to the transparent solution to adjust the pH to 9. The mixture was stirred at 30°C for 1 hour, followed by the addition of 1 mL of LTEOS (4.4 mmol) and 1 mL of 1,2-bis(triethoxysilyl)ethane (BTSE). The mixture was heated to 80°C and stirred for 4 hours. The resulting white emulsion was centrifuged and washed with ethanol, then vacuum-dried at 80°C for 12 hours and finally calcined at 550°C for 6 hours to obtain yolk-shell structured mesoporous SiO2 (denoted as YSMSNs). The YSMSNs were then amino-functionalized according to the method of step 2 of Example 1 and loaded with Pd according to the method of step 3 of Example 1 to obtain the catalyst 10 wt% Pd / YSMSNs-NH2. The SEM and TEM results of the obtained 10wt% Pd / YSMSNs-NH2 are shown in Figure 6 , indicating that the yolk-shell structured mesoporous SiO2 carrier was successfully prepared, and the average particle size of Pd NPs was about 1.5 nm.

[0036] 10 wt% Pd / YSMSNs-NH2 was further used to catalyze formic acid decomposition to produce hydrogen according to the method of Example 1. The formic acid conversion rate, H2 selectivity and TOF value are shown in Table 1. The results show that when YSMSNs-NH2 is used as the carrier and the reaction temperature is 50°C, the initial TOF value is 2783h -1 , which is lower than the level of 10 wt% Pd / RMS-NH2 catalyst in Example 1, indicating that RMS is more conducive to reaction mass transfer than YSMSNs.

[0037] Example 2

[0038] The molar amount of sodium tetrachloropalladate in step 3 of Example 1 was replaced with 0.025mmol, 0.075mmol, and 0.1mmol, respectively. The other steps were the same as in Example 1 to obtain Pd / RMS-NH2 catalysts with different Pd loadings (Pd loadings were 5wt%, 15wt% and 20wt%, respectively). Then, the formic acid decomposition to produce hydrogen was carried out according to the method of Example 1. The formic acid conversion rate, H2 selectivity and TOF value are shown in Table 1. The results show that when the reaction temperature is 50°C, the initial TOF values ​​of the Pd / RMS-NH2 catalysts with different Pd loadings for catalyzing the decomposition of formic acid to produce hydrogen are 3629h, 1576h and 1576h, respectively. -1 , 1500h -1 and 1125h -1 Comparison of the reaction performance of Pd / RMS-NH2 catalysts with different Pd loadings, see Figure 7With the increase of Pd loading, the reaction rate of formic acid decomposition to produce hydrogen shows a trend of first increasing and then decreasing. The optimal Pd loading is 10wt% and the initial TOF value is 4500h -1 .

[0039] Example 3

[0040] 53.2 mg (the molar amount of Pd element is 0.05 mmol) of 10 wt% Pd / RMS-NH2 prepared in Example 1 was added to a two-necked flask filled with 3 mL of deionized water, and then 2 mL of a formic acid-sodium formate mixed solution with a molar ratio of 1:2 (the molar amount of formic acid is 2.5 mmol) was added. The formic acid was decomposed and hydrogen was produced at 25°C, 40°C, 60°C, and 70°C under stirring. The resulting gas products were collected by drainage method and analyzed by gas chromatography. The formic acid conversion rate, H2 selectivity, and TOF value are shown in Table 1. Figure 8 The results show that the conversion of formic acid and the selectivity of H2 are both 100% at different reaction temperatures. The initial TOF values ​​corresponding to the reaction temperatures of 25℃, 40℃, 50℃, 60℃ and 70℃ are 2129h -1 、2573h -1 , 4500h -1 、5994h -1 and 7163h -1 According to the Arrhenius equation, the activation energy (Ea) of the formic acid decomposition reaction to produce hydrogen catalyzed by 10 wt% Pd / RMS-NH2 in the formic acid-sodium formate system is 30.3 kJ / mol.

[0041] Table 1

[0042] catalyst Pd loading amount / wt% Formic acid conversion rate / % <![CDATA[H2 Selectivity / %]]> <![CDATA[Initial TOF value / h -1 > Example 1 10 100 100 4500 Comparative Example 1 10 100 100 0 Comparative Example 2 10 100 100 2783 Example 2 5 100 100 3629 Example 2 15 100 100 1500 Example 2 20 100 100 1125

[0043] Table 2

[0044] catalyst Reaction temperature / ℃ Formic acid conversion rate / % <![CDATA[H2 Selectivity / %]]> <![CDATA[Initial TOF value / h -1 > Example 3 25 100 100 2129 Example 3 40 100 100 2573 Example 1 50 100 100 4500 Example 3 60 100 100 5994 Example 3 70 100 100 7163

[0045] Note: Initial TOF = PV / (2n metal RTt), P represents atmospheric pressure (1.013×10 5 Pa), V represents the gas production when the conversion rate is 20%, and R represents the ideal gas constant (R = 8.314 J·mol -1 ·K -1 ), n metal represents the total molar amount of Pd, T represents the reaction temperature, and t represents the time taken for the formic acid conversion to reach 20%.

Claims

1. An amino-functionalized rod-shaped silica-supported monometallic Pd nanocatalyst, characterized by: The long diameter of the rod-shaped silica is 50 to 200 nm, and the short diameter is 10 to 50 nm. The amino-functionalized rod-shaped silica is prepared by modifying the rod-shaped silica with 3-aminopropyltriethoxysilane. The catalyst is prepared using the amino-functionalized rod-shaped silica as a carrier, sodium tetrachloropalladate as a palladium source, and sodium borohydride as a reducing agent. The Pd loading in the catalyst is 5 wt% to 20 wt%, and the Pd particle size is 1.0 to 2.4 nm.

2. The amino-functionalized rod-shaped silica-supported monometallic Pd nanocatalyst according to claim 1, characterized in that: The preparation method of the rod-shaped silica comprises the following steps: dissolving hexadecyltrimethylammonium bromide in a mixed solution of N,N-dimethylformamide and deionized water under stirring, adding ammonia water to adjust the pH to 8-10, stirring at 25-35° C. for 0.5-2 hours, adding ethyl orthosilicate, heating to 70-80° C. for hydrolysis and polycondensation for 2-24 hours, centrifuging, washing, vacuum drying and calcining to obtain the rod-shaped silica.

3. The amino-functionalized rod-shaped silica-supported monometallic Pd nanocatalyst according to claim 2, characterized in that: The molar ratio of hexadecyltrimethylammonium bromide to ethyl orthosilicate is 1:5-20, and the concentration of ammonia water is 0.5-4 mol / L.

4. The amino-functionalized rod-shaped silica-supported monometallic Pd nanocatalyst according to claim 1, characterized in that: The preparation method of the amino-functionalized rod-shaped silica comprises the following steps: dispersing the rod-shaped silica in anhydrous toluene, adding 3-aminopropyltriethoxysilane, reacting under reflux at 60-90° C. for 6-24 hours, centrifuging, washing and vacuum drying to obtain the amino-functionalized rod-shaped silica.

5. The amino-functionalized rod-shaped silica-supported monometallic Pd nanocatalyst according to claim 4, characterized in that: The ratio of the amount of 3-aminopropyltriethoxysilane to the amount of rod-shaped silica is 2-10 mL / g.

6. The amino-functionalized rod-shaped silica-supported monometallic Pd nanocatalyst according to claim 1, characterized in that: The preparation method of the amino-functionalized rod-shaped silica supported single metal Pd nanocatalyst comprises the following steps: dispersing the amino-functionalized rod-shaped silica in a sodium tetrachloropalladate aqueous solution, ultrasonicating for 20 to 60 minutes, adding a sodium borohydride aqueous solution, stirring at room temperature for 20 to 60 minutes, centrifuging, washing and vacuum drying to obtain the amino-functionalized rod-shaped silica supported single metal Pd nanocatalyst.

7. The amino-functionalized rod-shaped silica-supported monometallic Pd nanocatalyst according to claim 6, characterized in that: The concentration of the sodium tetrachloropalladate aqueous solution is 0.01-0.5 mol / L, and the molar ratio of sodium borohydride to the Pd element in the sodium tetrachloropalladate is 20-40:

1.

8. Use of the amino-functionalized rod-shaped silica-supported monometallic Pd nanocatalyst according to any one of claims 1 to 7 for catalyzing the decomposition of formic acid to produce hydrogen, characterized in that: Freshly prepared amino-functionalized rod-shaped silica-supported single-metal Pd nanocatalyst was added to deionized water, and then a formic acid-sodium formate mixed solution was added to carry out a formic acid decomposition hydrogen production reaction at 20-70°C.

9. Use of the amino-functionalized rod-shaped silica-supported monometallic Pd nanocatalyst for catalyzing the decomposition of formic acid to produce hydrogen according to claim 8, characterized in that: The molar ratio of Pd element to formic acid in the catalyst is 1:10-500, the molar ratio of formic acid to sodium formate in the formic acid-sodium formate mixed solution is 1:1-3, and the formic acid concentration in the reaction system is 0.1-2.5 mol / L.

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