NPF co-doped carbon nanotube supported Pd catalyst, and preparation method and application thereof

Abstract

This invention discloses an NPF co-doped carbon nanotube-supported Pd catalyst, its preparation method, and its application, belonging to the field of catalyst technology. The catalyst uses multi-walled carbon nanotubes as a support, obtained by one-step co-doping of N, P, and F elements with ammonium hexafluorophosphate to obtain an NPF-CNT support, which is then loaded with Pd nanoparticles. The Pd nanoparticles in the catalyst have a face-centered cubic structure with Pd(111) as the main crystal plane and an average particle size of 2.25-3.73 nm. The preparation method of this invention is simple, cost-controllable, and reproducible. Through the synergistic effect of N, P, and F co-doping, electron-deficient Pd active centers are constructed, improving the hydrophobicity of the catalyst and significantly inhibiting irreversible dissociation of O-O bonds, thereby improving the selectivity and yield of H2O2. When applied to the direct synthesis of H2O2 from H2 and O2, under conditions of 2℃ and 4.00 MPa, the H2O2 selectivity reaches 94.71%, and the yield reaches 33.44 mol·gPd. ‑1 ·h ‑1 It exhibits excellent cycle stability, with the yield decreasing by only 14.3% after 5 cycles. It can replace the traditional anthraquinone process and has broad prospects for industrial application.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to an NPF co-doped carbon nanotube supported Pd catalyst, its preparation method and application, and particularly to a highly efficient catalyst for the direct synthesis of hydrogen peroxide from H2 and O2. Background Technology

[0002] Hydrogen peroxide is a green oxidant whose decomposition product is only water. It is widely used in industrial oxidation, environmental protection, and pharmaceutical disinfection. Currently, H2O2 is almost entirely produced industrially using the anthraquinone (AO) process. This process requires multiple steps, including continuous hydrogenation, oxidation, and liquid-liquid extraction of alkyl anthraquinones. It not only involves huge equipment investment but also generates a large amount of organic waste, resulting in a cumbersome process and poor environmental performance.

[0003] The process of directly synthesizing H2O2 from H2 and O2 using transition metal palladium (Pd)-based catalysts offers advantages such as mild reaction conditions, environmental friendliness, no need for organic substrates, ease of small-scale production, and coupling with downstream processes, making it an ideal alternative to the traditional anthraquinone process. However, traditional Pd-based catalysts have significant drawbacks: the active centers of Pd readily return electrons to adsorbed species, leading to irreversible dissociation of OO bonds (O2*, OOH*, and HOOH*), significantly reducing the selectivity for H2O2; simultaneously, the catalyst surface has poor wettability, hindering the desorption of the product H2O2 and further affecting reaction efficiency.

[0004] To address the aforementioned issues, existing technologies often employ alloying Pd with other metals (such as Pd-Au, Pd-Pt, etc.) to reduce electron feedback. However, this method involves complex preparation processes, high costs, and poses toxicity risks. Another approach is to modify the support by doping, such as using N-doped titanium dioxide to support Pd. However, the H2O2 yield of this type of catalyst is low, making it difficult to meet industrial demands. Furthermore, existing technologies do not adequately focus on controlling the wettability of the catalyst surface, failing to achieve a synergistic effect between electronic structure regulation and wettability improvement, thus limiting further improvements in H2O2 synthesis efficiency.

[0005] Therefore, developing a Pd-based catalyst that is simple to prepare, cost-controllable, can simultaneously optimize the electronic structure of Pd and improve catalyst wettability, and has excellent H2O2 selectivity and yield is of great significance for promoting the industrial application of the direct synthesis of H2O2. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing Pd-based catalysts, such as low selectivity, insufficient yield, and complex preparation, and to provide an NPF co-doped carbon nanotube supported Pd catalyst, its preparation method, and its application.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A Pd catalyst supported on NPF co-doped carbon nanotubes is disclosed. The multi-walled carbon nanotubes are used as the support. The support is modified by N, P and F co-doping through mixing with ammonium hexafluorophosphate and then calcining at high temperature to obtain NPF-CNTs. Pd nanoparticles are loaded on the NPF-CNTs. In the catalyst, the Pd nanoparticles have a face-centered cubic structure with Pd(111) as the main crystal plane and an average particle size of 2.25-3.73 nm.

[0008] Preferably, the aforementioned NPF co-doped carbon nanotube-supported Pd catalyst uses commercially available conventional multi-walled carbon nanotubes, requiring no additional pretreatment.

[0009] Preferably, the aforementioned NPF co-doped carbon nanotube-supported Pd catalyst has a Pd nanoparticle loading of 1-1.5 wt%.

[0010] A method for preparing an NPF co-doped carbon nanotube-supported Pd catalyst as described above includes the following steps: Step 1: Preparation of NPF-CNTs vectors Ammonium hexafluorophosphate was mixed evenly with multi-walled carbon nanotubes, placed in a nitrogen atmosphere, heated and calcined, and then naturally cooled to obtain NPF co-doped carbon nanotubes, namely: NPF-CNTs. Step 2: Preparation of Pd / NPF-CNTs catalyst Measure out H2PdCl4 solution, add it to anhydrous ethanol, and stir until homogeneous; then weigh out the NPF-CNTs prepared in step 1, disperse them in the above solution, and stir at room temperature for 4-8 hours; then add NaBH4 to carry out a reduction reaction for 20-30 minutes; after the reaction is completed, centrifuge, wash, and dry to obtain the Pd catalyst supported on NPF co-doped carbon nanotubes, namely: Pd / NPF-CNTs.

[0011] Preferably, in the aforementioned preparation method, the ammonium hexafluorophosphate and multi-walled carbon nanotubes are prepared at a mass ratio of 0.1-1:1.

[0012] Preferably, in the aforementioned preparation method, in step 1, the calcination temperature is 450-550℃, and the calcination time is 1-3 hours.

[0013] Preferably, in the aforementioned preparation method, step 2 involves washing with distilled water 1-5 times.

[0014] Preferably, in the aforementioned preparation method, step 2, the drying conditions are drying in a vacuum oven at 70-90℃ for 5-15 hours.

[0015] An application of the aforementioned NPF co-doped carbon nanotube supported Pd catalyst, wherein the catalyst is used for the direct synthesis of hydrogen peroxide from H2 and O2.

[0016] Preferably, in the aforementioned applications, the catalyst can be reused. After use, it can be washed 1-5 times by centrifugation with distilled water, dried in a vacuum oven at 70-90℃ for 5-15 hours, and then reused in the reaction. After 5 cycles, the H2O2 yield remains at 26.929 mol·gPd. -1 ·h -1 The selectivity remained above 80.73%. Beneficial effects

[0017] Compared with the prior art, the present invention has the following advantages: 1. This invention uses ammonium hexafluorophosphate and carbon nanotubes in a one-step calcination process to achieve co-doping of N, P and F elements. The preparation method is simple, cost-controllable, and reproducible. It does not require complex equipment and is suitable for large-scale industrial production. 2. The three elements N, P, and F have a synergistic effect: F element constructs an electron-deficient Pd active center through electron-withdrawing effect, reduces the electron feedback from the d orbital of Pd to the π* orbital of O2*, raises the OO bond breaking energy barrier, and inhibits the irreversible dissociation of OO bond; N, P, and F co-doping can also improve the hydrophobicity of the catalyst, promote the desorption of hydrophilic product H2O2, and further improve the selectivity and yield of H2O2; 3. The Pd nanoparticles in the catalyst of this invention have a face-centered cubic structure with Pd(111) as the main crystal plane. They have a small average particle size and are uniformly dispersed. 2+ / Pd 0 The ratio was 0.69, which optimized the electronic structure of Pd and further enhanced its catalytic activity; 4. When the catalyst of this invention is applied to the direct synthesis of H2O2 from H2 and O2, under mild conditions (2℃, 4.00 MPa), the selectivity for H2O2 can reach 94.71%, and the yield can reach 33.44 mol·gPd. -1 ·h -1 Compared with undoped Pd / CNTs catalysts, the yield is increased by 4.97 times and the selectivity is increased by 2.49 times. At the same time, the catalyst has excellent cycling stability, with the yield decreasing by only 14.3% after 5 cycles and the selectivity basically maintained, which solves the problems of low activity and poor stability of existing catalysts. 5. The catalyst of this invention does not require the introduction of a second metal, thus avoiding the drawbacks of high cost and high toxicity of alloy catalysts. Moreover, the reaction process is environmentally friendly, with no large amount of organic waste generated. It can effectively replace the traditional anthraquinone process and has broad prospects for industrial application. Attached Figure Description

[0018] Appendix Figure 1The XRD pattern of the catalyst of this invention is shown below. A D8 Advance X-ray diffractometer was used, with a scanning rate of 2°·min. -1 The scanning range is 5-90° (2θ), and the results are as follows: Figure 1 As shown, the catalyst exhibits characteristic diffraction peaks of the C(002) crystal plane of carbon nanotubes at 2θ=25.6°, and characteristic diffraction peaks of the Pd(111), Pd(200), Pd(220) and Pd(311) crystal planes at 40.1, 46.7, 68.1 and 82.1°, respectively. Among them, the Pd(111) crystal plane diffraction peak has the strongest intensity, indicating that the Pd nanoparticles have a face-centered cubic structure and the main crystal plane is Pd(111).

[0019] Appendix Figure 2 This is the XPS plot of the catalyst of the present invention; Using a K-AlphaPlus X-ray photoelectron spectrometer with non-monochromatic Al-Kα radiation and a power of 150 W, the results show that in the Pd3d spectrum, Pd 0 The 3d5 / 2 binding energy is 336.34 eV, Pd 0 The 3d³ / ² binding energy is 341.49 eV, Pd 2+ The 3d5 / 2 binding energy is 338.55 eV, Pd 2+ The 3d³ / ² binding energy is 343.81 eV, Pd 2+ / Pd 0 The ratio is 0.69; the F1s binding energy shifts towards the direction of lower binding energy, and N is in a state of electron loss, indicating that there is a strong interfacial interaction between N, P, F and Pd, and Pd is in a state of electron deficiency.

[0020] Appendix Figure 3 The above are the H2-TPD and O2-TPD diagrams of the catalyst of this invention. As shown in the figure, the H2-TPD curves of all catalysts exhibit a broad peak near 390℃, but the peak intensities of Pd / F-CNTs and Pd / NPF-CNTs are slightly weaker than those of Pd / N-CNTs and Pd / P-CNTs, indicating that Pd / N-CNTs and Pd / P-CNTs have stronger hydrogen adsorption capabilities. Notably, compared to Pd / N-CNTs, Pd / P-CNTs, and Pd / F-CNTs, the H2-TPD curve of Pd / NPF-CNTs shows a weak peak at 347.5℃, and a characteristic peak at a low temperature of 130℃, attributed to H2* desorption. The weak intensity and low temperature position of this characteristic peak indicate that Pd / NPF-CNTs exhibit the weakest H2 adsorption. These findings suggest that the introduction of N, P, and F reduces the adsorption of molecules or atoms at the Pd active center. This promotes the transfer of dissociated H* to adjacent sites to react with O2* or OOH*, and promotes the desorption of the formed HOOH*.

[0021] Two peaks were observed near 170.6℃ and 330.1℃ on the O2-TPD curves, which were attributed to the desorption characteristic peaks of the superoxide-like O2 (O2*) and the O* intermediate state, respectively [55, 60, 61]. Notably, the O2* peak was observed only on Pd / P-CNTs and Pd / NPF-CNTs, and the weaker characteristic peak of Pd / NPF-CNTs was located at a lower temperature. The O* peak was observed in all four sample groups. These findings indicate that the adsorption strength of the reactants on the Pd / NPF-CNTs sample has weakened, resulting in weaker Pd-O bond binding, particularly significantly inhibiting the dissociation of the OO bond on O2. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0023] Example 1: Preparation of Pd catalyst supported on NPF co-doped carbon nanotubes Step 1: Preparation of NPF-CNTs vectors Weigh 0.5g of ammonium hexafluorophosphate and 1.0g of multi-walled carbon nanotubes (purchased from Shenzhen Suiheng Graphene Technology Co., Ltd.), mix them evenly, put them into a high-temperature tube furnace, introduce nitrogen gas at a flow rate of 50mL / min, heat to 500℃, calcine for 2h, and cool naturally to room temperature to obtain NPF-CNTs carrier.

[0024] Step 2: Preparation of Pd / NPF-CNTs catalyst Measure 0.185 mL of 0.075 M H2PdCl4 solution (prepared from PdCl2 and HCl, PdCl2 purity 59%), add it to 30 mL of anhydrous ethanol, and stir magnetically for 5 min until homogeneous; weigh 0.1 g of NPF-CNTs prepared in step 1, disperse it in the above solution, and stir magnetically at room temperature for 6 h; then add 0.3 g of NaBH4, and continue stirring for 25 min to carry out the reduction reaction; after the reaction is completed, centrifuge at 8000 rpm for 10 min, collect the precipitate, wash it 3 times with distilled water, centrifuge after each washing, and then place the precipitate in an 80℃ vacuum oven to dry for 10 h to obtain the Pd / NPF-CNTs catalyst.

[0025] Example 2: Preparation of Pd catalyst supported on NPF co-doped carbon nanotubes Step 1: Preparation of NPF-CNTs vectors Weigh 0.1g of ammonium hexafluorophosphate and 1.0g of multi-walled carbon nanotubes (purchased from Shenzhen Suiheng Graphene Technology Co., Ltd.), mix them evenly, put them into a high-temperature tube furnace, introduce nitrogen gas at a flow rate of 50mL / min, heat to 450℃, calcine for 3h, and cool naturally to room temperature to obtain NPF-CNTs carrier.

[0026] Step 2: Preparation of Pd / NPF-CNTs catalyst Measure 0.142 mL of 0.075 M H2PdCl4 solution (prepared from PdCl2 and HCl, PdCl2 purity 59%), add it to 30 mL of anhydrous ethanol, and stir magnetically for 5 min until homogeneous; weigh 0.1 g of NPF-CNTs prepared in step 1, disperse it in the above solution, and stir magnetically at room temperature for 4 h; then add 0.3 g of NaBH4, and continue stirring for 20 min to carry out the reduction reaction; after the reaction is completed, centrifuge at 8000 rpm for 10 min, collect the precipitate, wash it once with distilled water, and then dry the precipitate in a vacuum oven at 70℃ for 15 h to obtain the Pd / NPF-CNTs catalyst.

[0027] Example 3: Preparation of Pd catalyst supported on NPF co-doped carbon nanotubes Step 1: Preparation of NPF-CNTs vectors Weigh 1.0 g of ammonium hexafluorophosphate and 1.0 g of multi-walled carbon nanotubes (purchased from Shenzhen Suiheng Graphene Technology Co., Ltd.), mix them evenly, put them into a high-temperature tube furnace, introduce nitrogen gas at a flow rate of 50 mL / min, heat to 550 °C, calcine for 1 h, and cool naturally to room temperature to obtain NPF-CNTs carrier.

[0028] Step 2: Preparation of Pd / NPF-CNTs catalyst Measure 0.213 mL of 0.075 M H2PdCl4 solution (prepared from PdCl2 and HCl, PdCl2 purity 59%), add it to 30 mL of anhydrous ethanol, and stir magnetically for 5 min until homogeneous; weigh 0.1 g of NPF-CNTs prepared in step 1, disperse it in the above solution, and stir magnetically at room temperature for 8 h; then add 0.4 g of NaBH4, and continue stirring for 30 min to carry out the reduction reaction; after the reaction is completed, centrifuge at 8000 rpm for 10 min, collect the precipitate, wash it 5 times with distilled water, centrifuge after each washing, and then place the precipitate in a 90℃ vacuum oven to dry for 5 h to obtain the Pd / NPF-CNTs catalyst.

[0029] Example 4: Application of catalysts in the direct synthesis of H2O2 A three-phase jacketed reactor was used. 0.0100 g of the Pd / NPF-CNTs catalyst prepared in Example 1 was added to the reactor, followed by the addition of 40 mL of methanol (99.5% purity) and 450 μL of 2 mol·L⁻¹. -1 The reaction medium is sulfuric acid. First, the reactor is purged with a 5% H2-N2 mixed gas for 10 minutes to remove air. Then, the above H2-N2 mixed gas is injected into the reactor to raise the pressure to 2.80 MPa. Next, a 25% O2-N2 mixed gas is injected to raise the total pressure to 4.00 MPa. The reactor temperature is controlled at 2℃, the stirring speed is adjusted to 1200 rpm, and the reaction is carried out for 30 minutes.

[0030] After the reaction, the H2 content in the reactor was detected by GC-2014C gas chromatograph, and the H2 conversion rate was calculated. The H2O2 content in the reaction solution was determined by iodometric titration, and the H2O2 selectivity and yield were calculated. The results showed that the H2 conversion rate was excellent, the H2O2 selectivity was 94.71%, and the yield was 33.44 mol·gPd. -1 ·h -1 .

[0031] Example 5: Cyclic stability test of the catalyst The catalyst after the reaction in Example 4 was washed three times with distilled water by centrifugation at 8000 rpm for 10 min each time, and then dried in a vacuum oven at 80°C for 10 h to obtain the recovered catalyst. The recovered catalyst was then subjected to a cyclic reaction under the reaction conditions of Example 3, and the reaction was repeated five times.

[0032] The results showed that after 5 cycles, the yield of H2O2 was 26.929 mol·gPd. -1 ·h -1 The yield decreased by only 14.3% compared to the initial yield; the H2O2 selectivity was 80.73%, which remained basically stable, indicating that the catalyst of this invention has excellent cycle stability.

[0033] Comparative Example 1: Preparation and Performance Testing of Undoped Pd / CNT Catalysts Weigh 0.1 g of pure multi-walled carbon nanotubes and disperse them in 20 mL of anhydrous ethanol. Use a pipette to take 185 μL (0.075 M) H2PdCl4 and stir until homogeneous. After stirring at room temperature for 6 h, add 0.3 g of NaBH4 and reduce for 25 min. Centrifuge and dry to obtain Pd / CNTs catalyst.

[0034] The performance of the catalyst was tested according to the reaction conditions of Example 4. The results showed that the H2O2 selectivity was 38.13% and the yield was 6.73 mol·gPd. -1 ·h -1It is significantly lower than that of the Pd / NPF-CNTs catalyst of this invention.

[0035] Comparative Example 2: Preparation and Performance Testing of Single-Element Doped Pd / CNT Catalysts Pd / N-CNTs, Pd / P-CNTs, and Pd / F-CNTs catalysts were prepared separately. The preparation methods were the same as in Example 1, except for the different support modification methods. Among them, the Pd / N-CNTs support was prepared by mixing melamine and CNTs at a mass ratio of 1:2 and calcining at 500°C under a nitrogen atmosphere for 2 hours. The Pd / P-CNTs and Pd / F-CNTs supports were prepared by mixing and calcining CNTs with the corresponding single-element dopants.

[0036] The performance of the catalyst was tested according to the reaction conditions of Example 4. The results showed that the H2O2 selectivity and yield of the single-element doped catalyst were lower than those of the Pd / NPF-CNTs catalyst of the present invention, indicating that the co-doping of N, P and F elements has a significant synergistic effect.

[0037] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A Pd catalyst supported on NPF co-doped carbon nanotubes, characterized in that: Using multi-walled carbon nanotubes as a carrier, the carrier is modified by N, P and F co-doping through high-temperature calcination after mixing with ammonium hexafluorophosphate. Pd nanoparticles are loaded on the NPF-CNTs. In the catalyst, the Pd nanoparticles have a face-centered cubic structure with Pd(111) as the main crystal plane and an average particle size of 2.25-3.73 nm.

2. The Pd catalyst supported on NPF co-doped carbon nanotubes according to claim 1, characterized in that: The multi-walled carbon nanotubes are commercially available conventional multi-walled carbon nanotubes and require no additional pretreatment.

3. The Pd catalyst supported on NPF co-doped carbon nanotubes according to claim 1, characterized in that: The loading of the Pd nanoparticles is 1-1.5 wt%.

4. A method for preparing an NPF co-doped carbon nanotube-supported Pd catalyst as described in any one of claims 1-3, characterized in that, Includes the following steps: Step 1: Preparation of NPF-CNTs vectors Ammonium hexafluorophosphate was mixed evenly with multi-walled carbon nanotubes, placed in a nitrogen atmosphere, heated and calcined, and then naturally cooled to obtain NPF co-doped carbon nanotubes, namely: NPF-CNTs. Step 2: Preparation of Pd / NPF-CNTs catalyst Measure out H2PdCl4 solution, add it to anhydrous ethanol, and stir until homogeneous; then weigh out the NPF-CNTs prepared in step 1, disperse them in the above solution, and stir at room temperature for 4-8 hours; then add NaBH4 to carry out a reduction reaction for 20-30 minutes; after the reaction is completed, centrifuge, wash, and dry to obtain the Pd catalyst supported on NPF co-doped carbon nanotubes, namely: Pd / NPF-CNTs.

5. The preparation method according to claim 4, characterized in that: The ammonium hexafluorophosphate and multi-walled carbon nanotubes are mixed at a mass ratio of 0.1-1:

1.

6. The preparation method according to claim 4, characterized in that: In step 1, the calcination temperature is 450-550℃, and the calcination time is 1-3 hours.

7. The preparation method according to claim 4, characterized in that: In step 2, the washing process involves washing with distilled water 1-5 times.

8. The preparation method according to claim 4, characterized in that: In step 2, the drying conditions are drying in a vacuum oven at 70-90℃ for 5-15 hours.

9. The application of the NPF co-doped carbon nanotube supported Pd catalyst as described in any one of claims 1-3, characterized in that: The catalyst was used in the direct synthesis of hydrogen peroxide from H2 and O2.

10. The application according to claim 9, characterized in that, The catalyst can be reused. After use, it can be washed 1-5 times by centrifugation with distilled water and dried in a vacuum oven at 70-90℃ for 5-15 hours before being used again in the reaction.

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