Metal-doped MoSe2 piezoelectric catalyst as well as preparation method and application thereof

Abstract

The invention discloses a metal-doped MoSe2 piezoelectric catalyst and a preparation method and application thereof, the catalyst is formed by loading metal monatomic on the surface of MoSe2 and presenting a nanoflower-shaped structure formed by ultrathin nanosheets, the catalyst is obtained by generating the metal monatomic on the surface of MoSe2 in situ, and the metal is Ag, Ru, Ni, Pt or Pd. According to the preparation method, metal single atoms are introduced into MoSe2, active sites are enriched, the carrier separation efficiency is improved, the MoSe2 is used for catalyzing plastic to be converted into H2 and CO, the conversion rate is high, and the content of by-product CH4 is extremely low.

Description

Technical Field

[0001] This invention relates to a piezoelectric catalyst, its preparation method and application, and particularly to a metal-doped MoSe2 piezoelectric catalyst, its preparation method and application. Background Technology

[0002] The continuous accumulation of plastic waste has become a pressing global ecological problem. Plastics, with their excellent durability and low production cost, are widely used in all aspects of production and daily life. However, their extremely strong chemical stability and recalcitrant nature mean that only a small amount of plastic waste is effectively recycled globally, with the remainder disposed of through landfills, incineration, or environmental dumping. Landfilling releases greenhouse gases such as methane, exacerbating global warming; incineration produces toxic and harmful pollutants that threaten ecosystems; and microplastics scattered in the environment accumulate through the food chain, harming biological health and creating a vicious cycle of "production-consumption-waste." Against this backdrop, developing sustainable plastic recycling strategies that combine environmental and economic benefits is urgently needed. Among these, chemical upgrading and recycling technologies for waste plastics, which can convert low-value waste into high-value fuels, chemicals, and functional materials, have become a current research focus.

[0003] In the innovative exploration of chemical upgrading and recycling technologies, piezoelectric catalysis, with its direct conversion characteristic from mechanical energy to chemical energy, is gradually developing into a core technological path for the high-value utilization of plastics. Piezoelectric catalysis can efficiently break chemical bonds such as CC and CHC in plastic molecular chains under low-energy mechanical excitation, achieving directional conversion. Especially in the field of syngas (CO / H2) production, it not only recovers high-energy-density clean fuels from waste but also reduces dependence on fossil resources, truly achieving synergistic effects of "environmental governance and energy recovery." As a typical transition metal chalcogenide, molybdenum diselenide (MoSe2) provides an ideal material substrate for piezoelectric catalysis-driven plastic recycling due to its significant piezoelectric response, excellent mechanical flexibility, and high specific surface area. However, MoSe2 still faces key bottlenecks in practical applications: the easy aggregation of nanosheets leads to insufficient exposure of active sites, and the intrinsic piezoelectric coefficient and carrier separation efficiency need to be improved. Summary of the Invention

[0004] Objectives of the Invention: The first objective of this invention is to provide a metal-doped MoSe2 piezoelectric catalyst with abundant active sites and high carrier separation efficiency; the second objective of this invention is to provide a method for preparing the metal-doped MoSe2 piezoelectric catalyst; and the third objective of this invention is to provide applications of the metal-doped MoSe2 piezoelectric catalyst.

[0005] Technical solution: The metal-doped MoSe2 piezoelectric catalyst of the present invention is a MoSe2 surface loaded with metal single atoms, exhibiting a nanoflower-like structure formed by ultrathin nanosheets, obtained by generating metal single atoms in situ on the MoSe2 surface, wherein the metal is Ag, Ru, Ni, Pt or Pd.

[0006] Preferably, the content of gold single atoms in the catalyst is 0.76%~4.57% (mole fraction). When the loading of metal single atoms is too low, there are insufficient active sites; when the loading is too high, some active sites are masked, leading to changes in electronic structure or limited mass transfer, thereby reducing catalytic efficiency.

[0007] More preferably, the content of metal single atoms in the catalyst is 1.5% to 3.8% (mole fraction).

[0008] The preparation method of the metal-doped MoSe2 piezoelectric catalyst of the present invention includes the following steps: uniformly dispersing MoSe2 powder in a solvent, adding a metal salt solution dropwise while stirring, stirring until uniform, adding a reducing agent dropwise, stirring to react, washing, and drying to obtain a MoSe2 piezoelectric catalyst supported on a single metal atom.

[0009] Preferably, the reducing agent is sodium borohydride or hydrazine hydrate.

[0010] Preferably, when the reducing agent is sodium borohydride, the molar ratio of MoSe2, metal salt, and sodium borohydride is 400:3 to 18:40.

[0011] Preferably, the reaction temperature is 20~30℃. More preferably, the reaction time is 11~15 h.

[0012] Preferably, the washing process uses deionized water and anhydrous ethanol respectively.

[0013] Preferably, the drying is vacuum drying, the drying temperature is 50~65℃, and the drying time is 12~18 h.

[0014] Preferably, the method for preparing MoSe2 powder includes the following steps: dissolving sodium borohydride in deionized water, then adding selenium powder and sodium molybdate and mixing evenly, and carrying out a hydrothermal reaction; after cooling, washing and drying to obtain MoSe2 powder.

[0015] Preferably, the molar ratio of sodium borohydride, selenium powder, and sodium molybdate is 4:2:1.

[0016] Preferably, the hydrothermal temperature is 200~220℃; more preferably, the hydrothermal reaction time is 18~22h.

[0017] Preferably, the reaction solvent is deionized water.

[0018] Preferably, the washing is performed using deionized water and anhydrous ethanol, respectively.

[0019] Preferably, the drying is vacuum drying, the drying temperature is 50~65℃, and the drying time is 12~18 h.

[0020] The application of the metal-doped MoSe2 piezoelectric catalyst described in this invention in the catalytic conversion of plastics into CO and H2.

[0021] The application method is as follows: the prepared catalyst is uniformly dispersed in the microplastic hydrothermal pretreatment solution to initiate a piezoelectric catalytic reaction.

[0022] Preferably, the piezoelectric catalytic reaction is carried out in a closed gas system using an ultrasonic cleaner with an ultrasonic power of 120~200 W and a reaction time of 4~8 h.

[0023] Invention Mechanism:

[0024] Piezoelectric catalysis can efficiently break chemical bonds such as CC and CHC in plastic molecular chains under low-energy mechanical excitation, achieving directional conversion. Especially in the field of syngas production, it can recover high-energy-density clean fuels from waste and reduce dependence on fossil resources, truly achieving synergistic effects of "environmental governance and energy recovery".

[0025] This invention utilizes MoSe2 loaded with metal single atoms (Ag, Ru, Ni, Pt, or Pd) as a piezoelectric catalyst, which offers advantages such as high metal atom utilization, tunable coordination environment, and excellent catalytic activity. By loading metal single atoms onto MoSe2, aggregation is avoided and atom utilization is maximized, promoting charge transfer between the metal single atoms and MoSe2 and improving carrier separation efficiency. Furthermore, by adjusting the loading amount of metal single atoms on MoSe2, optimized syngas yields can be obtained, with CO yields reaching up to 6637 μmol / g and H2 yields reaching up to 2047 μmol / g, and the syngas composition ratio is adjustable within the range of 1.24:1 to 3.24:1.

[0026] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The present invention enriches the active sites and improves the carrier separation efficiency by introducing metal single atoms (Ag, Ru, Ni, Pt or Pd) into MoSe2; (2) By adjusting the loading amount of metal single atoms on MoSe2, the optimized syngas yield can be obtained, and the composition ratio of syngas can be adjusted within a certain range; (3) The catalyst preparation method is simple and easy to industrialize; (4) The piezoelectric catalyst of the present invention is used to convert plastics into H2 and CO with high conversion rate and extremely low content of by-product CH4. Attached Figure Description

[0027] Figure 1 These are the XRD patterns of the catalysts in Examples 1-5 and Comparative Example 1;

[0028] Figure 2 These are Raman characterization diagrams of the catalysts in Example 3 and Comparative Example 1;

[0029] Figure 3 This is a transmission electron microscope image of the catalyst in Comparative Example 1;

[0030] Figure 4 This is a transmission electron microscope image of the catalyst in Example 3;

[0031] Figure 5 The graphs show the performance of the catalysts in Examples 1-5 and Comparative Example 1 in converting polylactic acid hydrothermal pretreatment solution (polylactic acid concentration of 0.05 g / mL) into syngas.

[0032] Figure 6 This is a graph showing the yield of syngas converted from polylactic acid hydrothermal pretreatment liquid (with different polylactic acid concentrations) by the catalyst in Example 3;

[0033] Figure 7 This is a stability graph of the catalyst in Example 3 converting polylactic acid hydrothermal pretreatment solution (polylactic acid concentration of 0.05 g / mL) into syngas.

[0034] Figure 8 The graph shows the yield of syngas converted from polylactic acid hydrothermal pretreatment liquid (polylactic acid concentration of 0.05 g / mL) by the catalyst in Examples 6-9 and Example 3. Detailed Implementation

[0035] The technical solution of the present invention will be further described below with reference to the embodiments.

[0036] Example 1

[0037] The metal-doped MoSe2 piezoelectric catalyst of the present invention is prepared by means of the following steps:

[0038] (1) Preparation of MoSe2 powder

[0039] 0.608 g of sodium borohydride was dissolved in 150 mL of deionized water, and then 0.632 g of selenium powder and 0.968 g of sodium molybdate were thoroughly mixed with it and stirred for 30 min. The resulting mixture was then transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave and kept at 210 °C for 20 h. After natural cooling, the mixture was washed three times each with deionized water and anhydrous ethanol, and dried under vacuum at 60 °C for 12 h to obtain MoSe2 powder.

[0040] (2) Preparation of 0.15Pd-MoSe2

[0041] 100 mg of MoSe2 powder was uniformly dispersed in 100 mL of deionized water. 0.15 mL of 20 mM sodium tetrachloropalladium solution was added dropwise under vigorous stirring. After thorough mixing, 2 mL of 20 mM sodium borohydride solution was added dropwise, and the mixture was stirred for 12 h. The catalyst was then washed three times each with deionized water and anhydrous ethanol, and dried under vacuum at 60 °C for 12 h to obtain a Pd-supported MoSe2 piezoelectric catalyst, named 0.15Pd-MoSe2, with a palladium content of 0.76% (mole fraction).

[0042] Example 2

[0043] The metal-doped MoSe2 piezoelectric catalyst of the present invention is prepared by means of the following steps:

[0044] (1) The preparation of MoSe2 powder is the same as in Example 1.

[0045] (2) Preparation of 0.3Pd-MoSe2

[0046] 100 mg of MoSe2 powder was uniformly dispersed in 100 mL of deionized water. 0.3 mL of 20 mM sodium tetrachloropalladium solution was added dropwise under vigorous stirring. After thorough mixing, 2 mL of 20 mM sodium borohydride solution was added dropwise, and the mixture was stirred overnight. The catalyst was then washed three times each with deionized water and anhydrous ethanol, and dried under vacuum at 60 °C for 12 h to obtain a Pd-supported MoSe2 piezoelectric catalyst, named 0.3Pd-MoSe2. The palladium content in the catalyst was 1.5% (mole fraction).

[0047] Example 3

[0048] The metal-doped MoSe2 piezoelectric catalyst of the present invention is prepared by means of the following steps:

[0049] (1) The preparation of MoSe2 powder is the same as in Example 1.

[0050] (2) Preparation of 0.6Pd-MoSe2

[0051] 100 mg of MoSe2 powder was uniformly dispersed in 100 mL of deionized water. 0.6 mL of 20 mM sodium tetrachloropalladium solution was added dropwise under vigorous stirring. After thorough mixing, 2 mL of 20 mM sodium borohydride solution was added dropwise, and the mixture was stirred overnight. The catalyst was then washed three times each with deionized water and anhydrous ethanol, and dried under vacuum at 60 °C for 12 h to obtain a Pd-supported MoSe2 piezoelectric catalyst, named 0.6Pd-MoSe2. The palladium content in the catalyst was 3% (mole fraction).

[0052] Example 4

[0053] The metal-doped MoSe2 piezoelectric catalyst of the present invention is prepared by means of the following steps:

[0054] (1) The preparation of MoSe2 powder is the same as in Example 1.

[0055] (2) Preparation of 0.75Pd-MoSe2

[0056] 100 mg of MoSe2 powder was uniformly dispersed in 100 mL of deionized water. 0.75 mL of 20 mM sodium tetrachloropalladium solution was added dropwise under vigorous stirring. After thorough mixing, 2 mL of 20 mM sodium borohydride solution was added dropwise, and the mixture was stirred overnight. The catalyst was then washed three times each with deionized water and anhydrous ethanol, and dried under vacuum at 60 °C for 12 h to obtain a Pd-supported MoSe2 piezoelectric catalyst, named 0.75Pd-MoSe2, with a palladium content of 3.8% (mole fraction).

[0057] Example 5

[0058] The metal-doped MoSe2 piezoelectric catalyst of the present invention is prepared by means of the following steps:

[0059] (1) The preparation of MoSe2 powder is the same as in Example 1.

[0060] (2) Preparation of 0.9Pd-MoSe2

[0061] 100 mg of MoSe2 powder was uniformly dispersed in 100 mL of deionized water. 0.9 mL of 20 mM sodium tetrachloropalladium solution was added dropwise under vigorous stirring. After thorough mixing, 2 mL of 20 mM sodium borohydride solution was added dropwise, and the mixture was stirred overnight. The catalyst was then washed three times each with deionized water and anhydrous ethanol, and dried under vacuum at 60 °C for 12 h to obtain a Pd-supported MoSe2 piezoelectric catalyst, named 0.9Pd-MoSe2, with a palladium content of 4.57% (mole fraction).

[0062] Example 6

[0063] Based on Example 3, silver nitrate was used to replace sodium tetrachloropalladium, and the catalyst was named 0.6Ag-MoSe2. The Ag content in the catalyst was 3% (mole fraction).

[0064] Example 7

[0065] Based on Example 3, ruthenium chloride was used to replace sodium tetrachloropalladium, and the catalyst was named 0.6Ru-MoSe2 with a Ru content of 3% (mole fraction).

[0066] Example 8

[0067] Based on Example 3, nickel chloride was used to replace sodium tetrachloropalladium, and the catalyst was named 0.6Ni-MoSe2 with a Ni content of 3% (mole fraction).

[0068] Example 9

[0069] Based on Example 3, sodium tetrachloropalladium was replaced with chloroplatinic acid and named 0.6Pt-MoSe2. The Pt content in the catalyst was 3% (mole fraction).

[0070] Comparative Example 1 (MoSe2)

[0071] By performing only step (1) of Example 1, the MoSe2 piezoelectric catalyst was obtained.

[0072] Structural characterization

[0073] X-ray diffraction (XRD) was used to characterize the different catalysts prepared in Examples 1-5 and Comparative Example 1, such as... Figure 1 As shown.

[0074] Depend on Figure 1 It can be seen that Examples 1-5 and Comparative Example 1 all have 1T phase MoSe2 (JCPDS No: 87-2419) and do not contain other crystalline impurities. Among them, no obvious diffraction peaks related to Pd appeared in the XRD patterns of Examples 1-5, indicating that Pd exists in the form of single atoms.

[0075] Raman spectroscopy characterization was performed on the different catalysts prepared in Example 3 and Comparative Example 1, such as... Figure 2 As shown.

[0076] Depend on Figure 2 Therefore, at 237.7 cm -1 At this location, a small and weak peak was observed, which corresponds to the out-of-plane mode (A) of the Mo-Se mode in the 2H phase. 1g The peak intensity was lower in Example 3 and Comparative Example 1. Furthermore, J1, J2, and E... 1g J3 and E 2g 1 The vibration modes appeared at 116.6, 148.0, 197.3, 277.2, and 343.4 cm, respectively. -1 The α signal is the main signal distinguishing between the 1T and 2H phases. Both catalysts exhibit similar characteristic peaks, with the 1T phase signal being significantly stronger than the 2H phase signal, indicating that the 1T phase is mainly present in the sample. Compared to the 2H phase MoSe2, the 1T phase MoSe2 exhibits better catalytic activity due to its relatively higher electronic conductivity.

[0077] The different catalysts prepared in Comparative Example 1 and Example 3 were characterized by transmission electron microscopy (TEM), and the results are as follows: Figures 3-4 As shown.

[0078] from Figure 3 and Figure 4 It can be seen that the prepared MoSe2 and 0.6Pd-MoSe2 are both composed of randomly layered ultrathin nanosheets, forming a nanoflower-like structure. This helps to increase the specific surface area of ​​the catalyst, provide more edge active sites, and thus improve the catalytic efficiency.

[0079] application

[0080] The application of the metal-doped MoSe2 piezoelectric catalyst of the present invention in the catalytic conversion of plastics into H2 and CO, specifically in the conversion of polylactic acid (PLA) hydrothermal pretreatment liquid into syngas, includes the following steps:

[0081] (1) A certain amount of PLA was placed in 20 mL of deionized water, and then the resulting mixture was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave and kept at 180 °C for 12 h to obtain a PLA hydrothermal pretreatment solution.

[0082] (2) 5 mg of catalyst was placed in the reactor, which contained 20 mL of PLA hydrothermal pretreatment solution;

[0083] (3) The sealed reactor was flushed three times with an oil pump while being kept under an argon atmosphere to ensure complete removal of air. The reactor was then pressurized to 1 bar with argon.

[0084] (4) The piezoelectric catalytic reaction was carried out in a gas-closed system using an ultrasonic cleaner (120 W, 40 kHz). The reaction system was kept at 25°C under the control of a low-temperature circulating pump. The gas mixture was collected after 4 h of reaction.

[0085] (5) CO and CH4 concentrations were detected by a flame ionization detector (FID) and H2 concentration was detected by a thermal conductivity detector (TCD).

[0086] When using PLA hydrothermal pretreatment solution (PLA content of 1g in 20 mL of deionized water), the gas production in Examples 1-5 and Comparative Example 1 is as follows: Figure 5 As shown.

[0087] Depend on Figure 5It can be seen that within 4 hours, the CH4 yield of Comparative Example 1 was extremely low and negligible, with CO yield of 370 μmol / g and H2 yield of 258.93 μmol / g; the CH4 yield of Example 1 was 96.47 μmol / g, CO yield was 868.54 μmol / g, and H2 yield was 690.18 μmol / g; the CH4 yield of Example 2 was 290.99 μmol / g, CO yield was 3137.93 μmol / g, and H2 yield was 2217.86 μmol / g; and the yield of Example 3 was... The yields of CH4 in Example 1 were 344.95 μmol / g, CO was 6637.24 μmol / g, and H2 was 2047.32 μmol / g; in Example 4, the yields were 299.58 μmol / g, CO was 3175.39 μmol / g, and H2 was 2196.43 μmol / g; and in Example 5, the yields were 127.23 μmol / g, CO was 1096.25 μmol / g, and H2 was 885.71 μmol / g. Compared to Comparative Example 1, the conversion rates of PLA in Examples 1-5 were significantly improved. This is likely because Pd loading can improve carrier separation efficiency and enhance piezoelectric catalytic performance. Therefore, Pd-loaded MoSe2 can serve as a highly efficient piezoelectric catalyst for the upgrading and conversion of microplastics. Among them, the catalyst prepared in Example 3 had the highest syngas yield. This may be because when the loading is too low, there are not enough active sites, while when the loading is too high, it will mask the active sites, resulting in a decrease in catalytic efficiency.

[0088] When using PLA hydrothermal pretreatment solution (20 mL of deionized water with different PLA contents), the gas production in Example 3 is as follows: Figure 6 As shown.

[0089] Depend on Figure 6 It can be seen that within 4 hours, when the PLA content in 20 mL of deionized water is 0.5 g, the CH4 production is 134.34 μmol / g, the CO production is 1116.52 μmol / g, and the H2 production is 891.96 μmol / g; when the PLA content in 20 mL of deionized water is 1 g, the CH4 production is 344.95 μmol / g, the CO production is 6637.24 μmol / g, and the H2 production is 2047.32 μmol / g; when the PLA content in 20 mL of deionized water is 1.5 g, the CH4 production is 488.91 μmol / g, the CO production is 2614.54 μmol / g, and the H2 production is 2026.79 μmol / g; 20 When the PLA content in deionized water is 2g / mL, the CH4 yield is 275.59μmol / g, the CO yield is 2348.17μmol / g, and the H2 yield is 1791.96μmol / g. Therefore, the optimal reaction condition is a PLA content of 0.05g / mL.

[0090] The catalyst prepared in Example 3 was subjected to cyclic stability testing using a PLA hydrothermal pretreatment solution (PLA content of 1 g in 20 mL deionized water). The testing method was as follows: after each gas measurement experiment, the catalyst was collected, thoroughly washed, and dried before the next catalytic experiment. The results are as follows: Figure 7 As shown.

[0091] from Figure 7 It can be seen that after four consecutive cycles, the yields of CO and H2 decreased slightly, but the yields of CO and H2 still reached 5990.73 μmol / g and 1772.32 μmol / g, respectively. This slight decrease may be due to the intermediates generated during the PLA reaction covering the active sites of the catalyst. Overall, the catalyst still exhibits good stability and excellent reusability.

[0092] When using PLA hydrothermal pretreatment solution (PLA content of 1g in 20 mL of deionized water), the gas production of comparative examples 2-5 is as follows: Figure 8 As shown.

[0093] Depend on Figure 8 It can be seen that in Example 6, the CH4 yield was 133.24 μmol / g, the CO yield was 1079.11 μmol / g, and the H2 yield was 1004.46 μmol / g within 4 hours; in Example 7, the CH4 yield was 145.09 μmol / g, the CO yield was 1378.71 μmol / g, and the H2 yield was 1018.75 μmol / g within 4 hours; in Example 8, the CH4 yield was 220.64 μmol / g, the CO yield was 2120.82 μmol / g, and the H2 yield was 1583.93 μmol / g within 4 hours; and in Example 9, the CH4 yield was 303.01 μmol / g, the CO yield was 2596.96 μmol / g, and the H2 yield was 2206.25 μmol / g within 4 hours. This proves that doping MoSe2 with metals such as Ag, Ru, Ni, Pt, or Pd is effective, with Pd doping showing the best results.

Claims

1. A metal-doped MoSe2 piezoelectric catalyst, characterized in that, The catalyst is a MoSe2 surface loaded with metal single atoms, exhibiting a nanoflower-like structure formed by ultrathin nanosheets. It is obtained by generating metal single atoms in situ on the MoSe2 surface, and the metal is Ag, Ru, Ni, Pt or Pd.

2. The metal-doped MoSe2 piezoelectric catalyst according to claim 1, characterized in that, The catalyst contains 0.76-4.57% metal single atoms.

3. A method for preparing the metal-doped MoSe2 piezoelectric catalyst according to claim 1 or 2, characterized in that, The process includes the following steps: MoSe2 powder is uniformly dispersed in a solvent, a metal salt solution is added dropwise while stirring, a reducing agent is added dropwise after stirring, the reaction is stirred, and the mixture is washed and dried to obtain a MoSe2 piezoelectric catalyst supported on a single metal atom.

4. The method for preparing the metal-doped MoSe2 piezoelectric catalyst according to claim 3, characterized in that, The reducing agent is sodium borohydride or hydrazine hydrate.

5. The method for preparing the metal-doped MoSe2 piezoelectric catalyst according to claim 3, characterized in that, When the reducing agent is sodium borohydride, the molar ratio of MoSe2, metal salt, and sodium borohydride is 400:3 to 18:

40.

6. The method for preparing the metal-doped MoSe2 piezoelectric catalyst according to claim 3, characterized in that, The reaction temperature is 20~30℃.

7. The method for preparing the metal-doped MoSe2 piezoelectric catalyst according to claim 6, characterized in that, The reaction time is 11-15 h.

8. The method for preparing the metal-doped MoSe2 piezoelectric catalyst according to claim 3, characterized in that, The method for preparing MoSe2 powder includes the following steps: dissolving sodium borohydride in deionized water, then adding selenium powder and sodium molybdate and mixing evenly, and carrying out a hydrothermal reaction; cooling, washing, and drying to obtain MoSe2 powder.

9. The method for preparing the metal-doped MoSe2 piezoelectric catalyst according to claim 3, characterized in that, The hydrothermal temperature is 200~220℃.

10. The application of a metal-doped MoSe2 piezoelectric catalyst according to any one of claims 1 to 3 in the catalytic conversion of plastics to CO and H2.

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