Preparation of d-orbital metal surface plasmon heterostructure photocatalyst and application of d-orbital metal surface plasmon heterostructure photocatalyst in conversion of low-carbon hydrogen into acetic acid through activation

Abstract

The invention discloses preparation of a d-orbital metal surface plasmon heterostructure photocatalyst and application of the d-orbital metal surface plasmon heterostructure photocatalyst in conversion of low-carbon hydrogen into acetic acid through activation. According to the invention, by reasonably selecting metal and a carrier, the plasmon photocatalyst with strong interaction between metal nanoparticles and the carrier is successfully prepared, and the plasmon photocatalyst is used for solving the key scientific problem of driving activation and functionalization of methane and other low-carbon hydrocarbons at room temperature. The catalyst generates a long-life charge carrier separation state under excitation of visible light, and surface chemical reaction is effectively accelerated. Activation and conversion reactions of low carbon and hydrogen such as methane are carried out at room temperature, the reaction is mild and efficient, the yield of an acetic acid product is high, the selectivity is good, and a practical solution is provided for activation and conversion of inert C (sp3)-H bonds such as light-driven methane.

Description

Technical Field

[0001] The invention belongs to the technical field of plasmon photocatalysis, and specifically relates to the preparation of a d-orbital metal surface plasmon heterostructure photocatalyst and its application in the activation and conversion of low-carbon hydrogen into acetic acid. Background Art

[0002] The activation of carbon-hydrogen bonds is a hot area that is increasingly attracting attention. Against the backdrop of rising energy demand and increasingly scarce oil resources, the efficient utilization, activation and conversion of clean energy small molecules (such as methane) will become a way to meet people's growing demand for liquid fuels and basic chemicals in the future. Methane (CH4) is the main component of natural gas, shale gas, combustible ice, etc. It is widely present in nature and is an abundant and readily available natural resource. Due to its high tetrahedral symmetry, C(sp 3 )-H bond energy is up to 435 KJ / mol, so the activation and directional conversion of methane under mild conditions is extremely challenging and is considered the holy grail in the field of catalysis. Its greenhouse effect is 20 times that of CO2, and the activation and conversion of CH4 saturated carbon-hydrogen bonds also have extremely important environmental protection value.

[0003] Photocatalysis is a technology with broad application prospects and is one of the ideal methods to drive CH4 conversion. Under the excitation of ultraviolet or visible light photons, the photocatalyst is excited to a high-energy excited state, which will change the reaction path, reduce the activation energy of the reaction, and even provide the possibility of thermodynamic uphill reactions under mild conditions. It can collect solar energy and convert it into chemical energy. Therefore, using the abundant and clean solar energy in nature to drive methane conversion will meet the requirements of green energy and dual carbon goals at the same time, and can also break the thermodynamic limitations to a certain extent.

[0004] The localized surface plasmon resonance effect (Surface Plasmon Resonance, SPR) has unique properties in the interaction between light and matter. The present invention loads d-orbital metal nanoparticles on carbon material electron acceptors to produce a strong coupling effect. The modified composite catalytic material has excellent photocatalytic performance. Due to SPR, the photogenerated hot electrons of the catalyst are directly transferred to the carbon material, and the holes are collected on the metal surface, thereby inhibiting the recombination of photogenerated hot electrons and holes, generating a long-lived carrier separation state, and significantly improving the plasmon-induced catalytic activity. In this process, the photogenerated electrons are excited to the conduction band to promote the reduction half-reaction, while the oxidation half-reaction is carried out by the photogenerated holes left in the valence band. Preparation, screening, and optimization of high-performance d-orbital metal heterostructure photocatalysts, and their application in gaseous alkanes C(sp 3 The activation and transformation of )-H bonds will be an important breakthrough in organic synthesis and heterogeneous gas-phase reactions.

[0005] At present, there is no report on the conversion of methane to acetic acid under mild conditions by plasmon photocatalysis. In the literature on semiconductor photocatalytic CH4 oxidation, it has been found that methanol, formic acid, acetic acid, ethanol, methanol peroxide, carbon dioxide and other small organic molecule products exist simultaneously, but the yield and selectivity of acetic acid products are very low. The research goal of converting low-carbon alkanes into acetic acid products with high selectivity and good yield has not been achieved so far. More importantly, uncontrollable oxidation degree and over-oxidation have become important challenges for CH4 activation and conversion. Therefore, it is of great significance to develop a method for preparing acetic acid by photocatalytic methane oxidation with high yield and high selectivity. Summary of the invention

[0006] The present invention provides a preparation of a d-orbital metal surface plasmon heterostructure photocatalyst and its application in the activation and conversion of low-carbon hydrogen into acetic acid. The method of the present invention realizes the synthesis of a high-concentration acetic acid solution through photocatalytic CH4 oxidation, and the acetic acid selectivity is close to 100%. The method avoids the peroxidation of CH4 to form formaldehyde, formic acid or carbon dioxide, and reduces the cost of separating mixed liquid products. In the method of the present invention, the output concentration of acetic acid can reach up to 2.2 mol / L, and after cyclically performing the photocatalytic reaction for 5 times, its output efficiency is still maintained at more than 90% of the highest output efficiency.

[0007] The method for preparing the d-orbital metal surface plasmon heterostructure photocatalyst of the present invention comprises the following steps: Step 1: Disperse the d-orbital metal compound in a protic solvent, add a biomass carbon source / semiconductor material, and react at 120-200° C. for 4-24 hours to obtain a preliminary product.

[0008] Step 2: The preliminary product is centrifuged, washed with deionized water and ethanol, and vacuum dried at a drying temperature of 50-80° C. for 8-24 h to obtain a hydrothermal product.

[0009] Step 3: calcining the hydrothermal product under an inert atmosphere at a calcination temperature of 600-1000° C. for a calcination time of 2-6 h to obtain the target catalyst.

[0010] In step 1, the d-orbital metal compound is selected from one or more metal compounds such as Fe, Co, Mn, Cu, Ce, Mo, V, Au, etc. Specifically, it can be a metal halide, nitrate, oxide, etc., such as ferric chloride, cerium chloride, etc. The concentration of the d-orbital metal compound in the reaction system is 0.0001-0.01 mmol / mL.

[0011] In step 1, the biomass carbon source / semiconductor material is selected from one or more of glucose, cellulose, sodium alginate, starch, lapis lazuli blue, methylene blue, etc. The concentration of the biomass carbon source / semiconductor material in the reaction system is 0.01-1.0 mmol / mL.

[0012] In step 1, the protic solvent is selected from one or more common protic solvents such as water, methanol, ethanol, ethylene glycol, etc.

[0013] In step 3, the inert atmosphere protective gas is argon. Different metal precursors have different optimal calcination conditions. Taking (Cu, Fe)@C as an example, its optimal calcination condition is a heating rate of 5°C / min to 900°C and keeping it for 2 h. Different calcination conditions have an impact on the size, micromorphology and catalytic performance of the photocatalyst.

[0014] The invention discloses an application of a d-orbital metal surface plasmon heterostructure photocatalyst in the activation and conversion of low-carbon hydrogen into acetic acid.

[0015] The low-carbon hydrogen includes small molecular gaseous alkanes such as methane, ethane, propane, and butane.

[0016] The method specifically comprises the following steps: adding a photocatalyst into an oxidant solution, placing the solution in a stainless steel high-pressure reactor in a small molecule gas alkane atmosphere, and reacting the solution for 10-48 hours under closed and light conditions to obtain a final product.

[0017] The oxidant solution is a hydrogen peroxide aqueous solution with a concentration (g / g) of 3-30 wt % and a dosage of 2-10 mL.

[0018] The added amount of the photocatalyst is 0.1-3.0 mg / mL, such as 0.5 mg / mL, 1.0 mg / mL, 2.0 mg / mL or 2.5 mg / mL.

[0019] The amount of the small molecule gas alkane is measured by atmospheric pressure or high pressure reactor pressure, and the pressure is 0.1-6.0 MPa, for example 0.1 MPa, 1.0 MPa, 2.0 MPa, 3.0 MPa, 4.0 MPa, 5.0 MPa or 6.0 MPa.

[0020] Furthermore, the wavelength of the light is in the range of 390-480 nm, such as 390 nm, 400 nm, 450 nm or 480 nm, etc., the light intensity is 10-100 W, and the distance between the light source and the reaction system is 0.5-5 cm. Preferably, the light source is an LED light source with a wavelength of 390 nm and a power of 100 W; a xenon lamp, sunlight, etc. can be selected as the light source.

[0021] Furthermore, the reaction temperature is 20-90°C.

[0022] The catalytic reaction scheme is shown below:

[0023] The photocatalytic reaction system of the present invention comprises three phases of solid, liquid and gas, two phases of liquid and solid, or two phases of gas and solid, preferably three phases of solid, liquid and gas.

[0024] The present invention focuses on the conversion and utilization of carbon-based energy, provides a method for preparing a d-orbital metal surface plasmon heterostructure photocatalyst, and uses it to solve the key scientific problem of driving the activation and functionalization of low-carbon hydrogens such as methane at room temperature. By rationally selecting metals and carriers, plasmon photocatalysts with strong interactions between metal nanoparticles and carriers were successfully prepared, which produced long-lived charge carrier separation states under visible light excitation, effectively accelerating surface chemical reactions. The activation and conversion reactions of low-carbon hydrogens such as methane are carried out at room temperature, the reactions are mild and efficient, the yield of acetic acid products is high, and the selectivity is good, which is a promising method for light-driven methane and other inert C (sp 3 )-H bond activation and transformation provide practical solutions.

[0025] The d-orbital plasmon photocatalyst of the present invention can effectively utilize sunlight to drive the catalytic oxidation of alkanes, the energy is clean and easy to obtain, and saturated C (sp 3 )-H direct dehydrogenation and CC reaction, the acetic acid conversion selectivity can reach 90% at room temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The prepared (Cu,Fe)@C photocatalyst is a black powder.

[0027] Figure 2 This is the SEM morphology of (Cu,Fe)@C photocatalyst. Figure 2 As shown, copper nanoparticles and graphene-like materials form an encapsulating structure.

[0028] Figure 3 is the XRD spectrum of (Cu,Fe)@C photocatalyst. Figure 3 As shown, the diffraction peaks at 43.3°, 50.4° and 74.0° are attributed to the metallic copper nanophase, which is consistent with PDF card #04-0836. The 23° broadened diffraction peak is attributed to the graphene-like phase.

[0029] Figure 4 This is a high-resolution transmission electron microscopy image of the (Cu,Fe)@C photocatalyst. Figure 4 As shown, copper nanoparticles are distributed in the graphene-like layer.

[0030] Figure 5This is a high-resolution transmission electron microscopy image of the (Cu,Fe,Pd)@C photocatalyst with double spherical aberration. As shown in the figure, the copper and palladium elements exist in the form of an alloy to form a Pd3Cu alloy; the iron element exists in the form of a single atom and is distributed on the Pd3Cu alloy.

[0031] Figure 6 The prepared Al@CN photocatalyst is a light yellow powder.

[0032] Figure 7 It is a schematic diagram of the catalytic reaction principle of the present invention.

[0033] Figure 8 This is the standard curve of the (Cu,Fe)@C photocatalyst-driven conversion of alkanes into acetic acid with DSS as the internal standard.

[0034] Fig. 9 This is the H NMR spectrum of the activation of methane into acetic acid driven by a plasmon heterostructure photocatalyst. DETAILED DESCRIPTION

[0035] The technical solution of the present invention is further analyzed and explained below through specific embodiments. Embodiment 1:

[0036] Dissolve 150 mg of copper chloride and 200 mg of ferric chloride in 60 mL of water, add 2 g of glucose, disperse the solution system evenly by ultrasonication, transfer it to a stainless steel reactor with a polytetrafluoroethylene liner, and react at 180 ° C for 24 hours. Take out the hydrothermal reaction system, centrifuge it, wash it with deionized water and ethanol, and dry it in a vacuum drying oven at 60 ° C for 12 hours to obtain a catalyst precursor powder. The above precursor powder was raised to 900 ° C at a program-controlled temperature of 5 ° C / min in an argon atmosphere and calcined for 2 hours to obtain the target photocatalyst, that is, a graphene-like material loaded with metals Cu and Fe, named (Cu, Fe) @ C.

[0037] like Figure 1 The (Cu, Fe)@C photocatalyst is a black powder, and its scanning electron microscope image is as follows Figure 2 The X-ray diffraction spectrum is shown in Figure 3 As shown in the high-resolution transmission electron microscopy image Figure 4 shown. Embodiment 2:

[0038] Dissolve 150 mg of copper chloride, 200 mg of ferric chloride and 220 mg of palladium chloride in 60 mL of water, add 2 g of glucose, disperse the solution system evenly by ultrasonication, transfer it to a stainless steel reactor with a polytetrafluoroethylene liner, and react at 180 ° C for 24 hours. Take out the hydrothermal reaction system, centrifuge it, wash it with deionized water and ethanol, and dry it in a 60 ° C vacuum oven for 12 hours to obtain a catalyst precursor powder. The above precursor powder was raised to 900 ° C at a program-controlled temperature of 5 ° C / min in an argon atmosphere, and calcined for 2 hours to obtain the target photocatalyst, that is, a graphene-like material loaded with metals Cu, Fe, and Pd, named (Cu, Fe, Pd) @ C. Its double spherical aberration high-resolution transmission electron microscope image is shown in the figure Figure 5 shown. Embodiment 3:

[0039] Dissolve 250 mg of aluminum nitrate in 60 mL of water, add 2 g of melamine, disperse the solution system evenly by ultrasonication, transfer it to a stainless steel reactor with a polytetrafluoroethylene liner, and react at 180 ° C for 24 hours. Take out the hydrothermal reaction system, centrifuge it, wash it with deionized water and ethanol, and dry it in a 60 ° C vacuum drying oven for 12 hours to obtain a catalyst precursor powder. The above precursor powder was raised to 600 ° C at a program-controlled temperature of 5 ° C / min under an argon atmosphere, and calcined for 2 hours to obtain the target photocatalyst, that is, a graphene-like material loaded with metal Al, named Al@CN. Figure 6 The Al@CN photocatalyst shown is a light yellow powder. Embodiment 4:

[0040] 20 mg (Cu, Fe) @ C photocatalyst was dispersed in 8 mL of 30 wt% hydrogen peroxide aqueous solution, transferred to a high pressure reactor, and 5 MPa of methane was introduced. The reaction was carried out at room temperature for 24 h under 100 W, 390 nm LED light. 3-Trimethylsilyl-1-propanesulfonic acid sodium (DSS) was used as the NMR internal standard, the acetic acid concentration gradient was used as the horizontal coordinate, and the NMR hydrogen spectrum integral area ratio of acetic acid and DSS in D2O was used as the vertical coordinate to draw a standard curve, as shown in the figure below: Figure 6 The target product acetic acid was analyzed by nuclear magnetic resonance spectrometer, D2O was selected as deuterated reagent, DSS was used as internal standard, and nuclear magnetic resonance hydrogen spectrum was obtained, as shown in FIG. Figure 7 As shown in the figure, the chemical shift of 2.10 ppm corresponds to the hydrogen on the methyl group of acetate, confirming that the product is acetic acid (selectivity > 95%), with a maximum concentration of 0.54 mol / L and a yield of 9.00 mmol·g -1 ·h -1 . Embodiment 5:

[0041] 20 mg (Cu, Fe)@C photocatalyst was dispersed in 8 mL of 30 wt% hydrogen peroxide aqueous solution, transferred to a high-pressure reactor, and introduced into 4 MPa ethane. The reaction was carried out at room temperature for 24 h under 100W, 390 nm LED illumination. DSS was used as the internal standard of NMR. The reaction system was confirmed to have acetic acid as the product (selectivity>95%) by NMR analysis. The maximum concentration could reach 1.22 mol / L, and the yield was 25.42 mmol·g -1 ·h -1 . Embodiment 6:

[0042] 20 mg (Cu, Fe)@C photocatalyst was dispersed in 8 mL of 30 wt% hydrogen peroxide aqueous solution, transferred to a high-pressure reactor, and introduced into 0.8 MPa propane. The reaction was carried out at room temperature for 24 h under 100W, 390 nm LED illumination. DSS was used as the internal standard of NMR. The reaction system was confirmed by NMR analysis to be acetic acid (selectivity>95%), with a maximum concentration of 0.48 mol / L and a yield of 8.00 mmol·g -1 ·h -1 . Embodiment 7:

[0043] 20 mg (Cu, Fe, Pd)@C photocatalyst was dispersed in 8 mL of 30 wt% hydrogen peroxide aqueous solution, transferred to a high-pressure reactor, and introduced into 5 MPa methane. The reaction was carried out at room temperature for 24 h under 100W, 390 nm LED illumination. DSS was used as the internal standard of NMR. The reaction system was confirmed to have acetic acid as the product (selectivity>95%) by NMR analysis. The maximum concentration could reach 0.43 mol / L, and the yield was 7.17 mmol·g -1 ·h -1 . Embodiment 8:

[0044] 10 mg of Al@C photocatalyst was dispersed in 8 mL of 30 wt% hydrogen peroxide aqueous solution, transferred to a high-pressure reactor, and introduced into 5 MPa of methane. The reaction was carried out at room temperature for 24 h under 100 W, 390 nm LED illumination. DSS was used as an internal standard for NMR analysis of the reaction system, and the product was confirmed to be acetic acid (selectivity > 95%), with a maximum concentration of 0.36 mol / L and a yield of 12.00 mmol·g -1 ·h -1 .

Claims

1. A method for preparing a d-orbital metal surface plasmon heterostructure photocatalyst, characterized in that The steps include: Step 1: Disperse the d-orbital metal compound in a protic solvent, add a biomass carbon source / semiconductor material, and react at 120-200° C. for 4-24 hours to obtain a preliminary product; Step 2: centrifugally separating the preliminary product, washing with deionized water and ethanol, and vacuum drying to obtain a hydrothermal product; Step 3: calcining the hydrothermal product under an inert atmosphere to obtain the target catalyst.

2. The preparation method according to claim 1, characterized in that: In step 1, the d-orbital metal compound is selected from one or more of the metal compounds of Fe, Co, Mn, Cu, Ce, Mo, V, and Al.

3. The preparation method according to claim 2, characterized in that: The metal compound is a metal halide, nitrate or oxide.

4. The preparation method according to claim 1, characterized in that: In step 1, the biomass carbon source / semiconductor material is selected from one or more of glucose, cellulose, sodium alginate, starch, melamine, and methylene blue.

5. The preparation method according to claim 1, characterized in that: In step 3, the calcination temperature is 600-1000° C., and the calcination time is 2-6 hours.

6. Use of the d-orbital metal surface plasmon heterostructure photocatalyst prepared by the preparation method of any one of claims 1 to 5 in the activation and conversion of low-carbon hydrogen into acetic acid.

7. The use according to claim 6, characterized in that: The low-carbon hydrogen is a small-molecule gaseous alkane.

8. The use according to claim 6, characterized in that: The photocatalyst is added to the oxidant solution, placed in a stainless steel high-pressure reactor in a small molecule gas alkane atmosphere, and reacted for 10-48 hours under closed and light conditions to obtain the final product.

9. The use according to claim 8, characterized in that: The oxidant solution is a hydrogen peroxide solution with a concentration of 3-30wt%.

10. The use according to claim 8, characterized in that: The added amount of the photocatalyst is 0.1-3.0 mg / mL.

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