Method for producing ethane by methanol carbon-carbon coupling promoted by oxygen vacancies

Abstract

The application discloses a kind of oxygen vacancy promotes methanol carbon-carbon coupling ethane production method, comprising the following steps: synthesizing H2Ti4O9;The obtained H2Ti4O9 is stripped into colloidal sheet, obtains two-dimensional TiO2 nanosheet;Hydrogenation treatment obtains the TiO2 nanosheet with oxygen vacancy;The TiO2 nanosheet with oxygen vacancy is dissolved in methanol / water solution, drop into H2PtCl6 solution, solution is in vacuum state, then it is irradiated with arc lamp while stirring N1 hour, obtain brown white precipitate, after washing vacuum drying catalyst is obtained;Methanol / water solution is placed into reactor, catalyst is uniformly dispersed in methanol / water solution, when reaction, first the reactor is evacuated to remove air, then xenon lamp is opened to carry out illumination, after reaction, obtain ethane.The application uses the TiO2 nanosheet with oxygen vacancy as catalyst to produce ethane, and a large number of oxygen vacancies increase a large number of methanol dissociation sites, thereby reducing the distance between adjacent methoxyl groups, and then promoting coupling to generate ethane.

Description

Technical Field

[0001] The invention relates to a method for producing ethane by promoting carbon-carbon coupling of methanol with oxygen vacancies, and belongs to the technical field of ethane production. Background Art

[0002] The chemistry of converting C1 molecules into value-added products is experiencing a resurgence due to the rapidly expanding demand for carbon-based energy and chemical production from non-petroleum sources, such as shale gas in the United States, coal in China, renewable biomass, and the emergence of carbon dioxide (CO2). Traditional homogeneous and heterogeneous catalysis plays an important role in C1 chemistry, converting C1 molecules such as carbon monoxide (CO), carbon dioxide, methane (CH4), and methanol (CH3OH) into liquid fuels (such as gasoline, diesel, and jet fuel) or basic chemicals (such as ethylene (C2H4), propane (C3H6), aromatics, and ethanol (C2H5OH). Methanol is an abundant, renewable C1 resource. Currently, methanol can be used to make a variety of compounds, such as formaldehyde, acetic acid, methyl esters, methylamines, dimethyl ether, and lower olefins. Among them, creating carbon-carbon (CC) bonds is the most desirable and difficult process in methanol chemistry.

[0003] Photocatalysis has emerged as a promising tool for activating C1 molecules and selectively converting them into a variety of products under mild conditions. However, to our knowledge, there is limited literature on the photocatalytic conversion of methanol requiring C-C bond formation, and these studies are mostly limited to methanol-to-olefin and methanol-to-ethylene glycol processes. For example, Wang et al. created a molybdenum disulfide nanofoam-modified cadmium sulfide nanorod catalyst that produced ethylene glycol with 90% selectivity and good efficiency, while also producing hydrogen. Yu et al. found that silicoaluminophosphate (SAPO-34) with three-dimensional (3D) channels and moderate acid strength exhibited particularly good selectivity for light olefins because the tiny pore openings prevented larger reaction intermediates from passing through the channels. Despite all these applications, the methanol-to-ethane process remains quite uncommon.

[0004] Therefore, a method for producing ethane by promoting carbon-carbon coupling of methanol with oxygen vacancies is needed to solve the above problems. Summary of the Invention

[0005] The purpose of the present invention is to overcome the problems existing in the prior art and provide a method for producing ethane by promoting the carbon-carbon coupling of methanol by using oxygen vacancies.

[0006] The present invention provides a method for producing ethane by promoting carbon-carbon coupling of methanol using oxygen vacancies, comprising the following steps:

[0007] 1) Synthesis of H2Ti4O9;

[0008] 2) Exfoliating the H2Ti4O9 obtained in step 1) into colloidal sheets to obtain two-dimensional TiO2 nanosheets;

[0009] 3) hydrogenating the two-dimensional TiO2 nanosheets obtained in step 2) to obtain TiO2 nanosheets with oxygen vacancies;

[0010] 4) Dissolve the TiO2 nanosheets with oxygen vacancies obtained in step 3) in a methanol / water solution, add H2PtCl6 solution dropwise, place the solution in a vacuum state, and then irradiate nitrogen with an arc lamp for 1 hour while stirring to obtain a brown-white precipitate, which is then washed and dried in a vacuum to obtain a catalyst;

[0011] 5) Put the methanol / water solution into the reactor, and evenly disperse the catalyst obtained in step 4) in the methanol / water solution. During the reaction, the reactor is first evacuated to remove air, and then a xenon lamp is turned on for illumination. After the reaction, ethane is obtained.

[0012] Furthermore, the method for synthesizing H2Ti4O9 in step 1) comprises the following steps:

[0013] 11) Grind K2CO3 and TiO2 together in a molar ratio of 1.3:1 to form a uniform powder and spread it evenly in a crucible;

[0014] 12) Place the crucible in a muffle furnace and anneal at 960°C for 10 hours to obtain K2Ti4O9;

[0015] 13) Place the K2Ti4O9 powder obtained in step 12) into the first hydrochloric acid solution and stir at room temperature for at least 24 hours;

[0016] 14) The titanate is then filtered out of the solution, rinsed with deionized water, added to the second hydrochloric acid solution, and stirred for at least 24 hours;

[0017] 15) Repeat steps 13)-14) multiple times, then wash with water multiple times and dry in vacuum to obtain acid-treated H2Ti4O9.

[0018] Furthermore, in step 13), the first hydrochloric acid solution is a 1.0 M hydrochloric acid solution, and the mass volume ratio of K2Ti4O9 powder to the first hydrochloric acid solution is 1 g:100 mL.

[0019] Furthermore, in step 14), the concentration of the second hydrochloric acid solution is the same as the concentration of the first hydrochloric acid solution.

[0020] Furthermore, in step 2), the H2Ti4O9 obtained in step 1) is peeled off into colloidal sheets to obtain two-dimensional TiO2 nanosheets, which includes the following steps:

[0021] 21) Adding H2Ti4O9 to a 50% ethylamine solution at a molar ratio of 1:30, stirring at room temperature for at least 24 hours, then centrifuging, rinsing with acetone several times to obtain a suspension, and obtaining a precipitate from the suspension by centrifugation;

[0022] 22) Dissolve the precipitate in TBAOH solution and shake for at least 7 days, where H + The molar ratio of ions to TBAOH is 1:5; the colloidal suspension is collected by high-speed centrifugation, washed with deionized water and ethanol multiple times to remove excess TBAOH, and then redispersed in water. After centrifugation again, it is freeze-dried for at least 12 hours and then ground to obtain two-dimensional TiO2 nanosheets.

[0023] Furthermore, in step 22), the TBAOH solution is a 10 wt % TBAOH solution, and the high-speed centrifugation speed is not less than 15,000 rpm.

[0024] Furthermore, in step 3), the two-dimensional TiO2 nanosheets obtained in step 2) are hydrogenated to obtain TiO2 nanosheets with oxygen vacancies. Specifically, the two-dimensional TiO2 nanosheets are placed in a tubular furnace, calcined at 450°C in a 10% concentration of H2 / Ar mixed gas environment, and cooled to room temperature to obtain TiO2 nanosheets with oxygen vacancies.

[0025] Furthermore, in step 4), the methanol / water solution is a 50% methanol / water solution, the concentration of the H2PtCl6 solution is 25 mg / ml, and the arc lamp is a 300W Xe arc lamp.

[0026] Furthermore, in step 4), N1 hours is 2-8 hours.

[0027] Furthermore, in step 5), the methanol / water solution is 50% methanol / water solution, and the mass volume ratio of the catalyst to the methanol / water solution is 30 mg:50 mL.

[0028] Beneficial effect: The oxygen vacancy-promoted methanol carbon-carbon coupling ethane production method of the present invention uses TiO2 nanosheets with oxygen vacancies as catalysts to produce ethane. Compared with TiO2 nanosheets without vacancies, the CH3OH molecules adsorbed on the TiO2 nanosheets with oxygen vacancies have greater negative adsorption energy. CH3OH is mainly adsorbed on the five-fold coordinated TiO2 surface. 5c Molecular adsorption on the site ( * CH3OH), and dissociate at the surface oxygen vacancy site to form methoxyl radicals ( * A large number of oxygen vacancies increase the dissociation sites of methanol, thereby reducing the distance between adjacent methoxy groups and promoting the coupling to ethane. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Atomic force microscopy (AFM) images of two-dimensional TiO2 nanosheets;

[0030] Figure 2 The first distance and height curve of the atomic force microscope (AFM) image of the two-dimensional TiO2 nanosheet;

[0031] Figure 3 The second distance and height curve of the atomic force microscope (AFM) image of the two-dimensional TiO2 nanosheet;

[0032] Figure 4 is the X-ray diffraction pattern of two-dimensional TiO2 nanosheets;

[0033] Figure 5 O v0 -Transmission electron microscopy (TEM) image of TO (1 nm);

[0034] Figure 6 O v0 -Transmission electron microscopy (TEM) image of TO (10 nm);

[0035] Figure 7 The figure is a comparison of the X-ray photoelectron spectra of TiO2 before and after hydrogenation treatment;

[0036] Figure 8 The figure is a comparison of the X-ray photoelectron spectra of TiO2 before and after hydrogenation treatment;

[0037] Figure 9 The ESR signal intensity of TiO2 at different hydrogenation times is compared with the ESR signal intensity of TiO2 before hydrogenation.

[0038] Figure 10 The PL emission intensity of TiO2 with different hydrogenation treatment times is compared with the PL emission intensity of TiO2 before hydrogenation treatment;

[0039] Figure 11 The graph is a comparison of the ethane and methane yields using TiO2 as a catalyst with a hydrogenation time of 8 h;

[0040] Figure 12 This is the production graph of ethane and methane within 12 hours using TiO2 as a catalyst with a hydrogenation treatment time of 8 hours. Implementation Method

[0041] The present invention will now be described in further detail with reference to the accompanying drawings. Example

[0042] To address the problem of methanol to ethane, the present invention synthesized two-dimensional (2D) TiO2 nanosheets with oxygen defects, and promoted CH3OH coupling through oxygen defects. The method includes the following steps:

[0043] Step 1: Synthesis of K2Ti4O9 and H2Ti4O9. K2CO3 and TiO2 were first ground together at a molar ratio of 1.3:1 to form a uniform powder, which was then spread evenly in a crucible. The crucible was then annealed at 960°C for 10 hours in a muffle furnace to produce K2Ti4O9. For the synthesis of H2Ti4O9, the resulting K2Ti4O9 powder (1.0 g) was stirred in a 1.0 M hydrochloric acid solution (100 mL) at room temperature for 24 hours. The titanate was then filtered from the solution, rinsed with deionized water, and added to a fresh solution of equal concentration of HCl, where it was stirred for an additional 24 hours. This process (stirring in a 1.0 M hydrochloric acid solution (100 mL) for 12 hours and then washing with deionized water) was repeated three times. The mixture was then washed with water several times and dried in vacuo to produce the acid-treated titanate (H2Ti4O9).

[0044] Step 2: Exfoliate H2Ti4O9 into colloidal sheets to obtain two-dimensional TiO2 nanosheets. H2Ti4O9 was added to a 50% ethylamine solution at a molar ratio of 1:30, stirred at room temperature for 24 hours, then centrifuged and rinsed three times with acetone. Finally, a precipitate was obtained from the suspension by centrifugation. In order to fully exfoliate, the precipitate was dissolved in a TBAOH solution (10wt%) and shaken vigorously for 7 days. + The molar ratio of TBAOH was 1:5. -1 The colloidal suspension was collected and washed three times with deionized water and ethanol to remove excess TBAOH, then redispersed in water, centrifuged again and freeze-dried for 12 hours. After freeze-drying, two-dimensional TiO2 nanosheets (called O V0 -TO).

[0045] Step 3: Hydrogenation treatment to obtain TiO2 nanosheets with oxygen vacancies. The two-dimensional TiO2 nanosheets are placed in a tube furnace and calcined at 450°C in a 10% H2 / Ar environment and cooled to room temperature to obtain TiO2 nanosheets with oxygen vacancies.

[0046] The amount of oxygen vacancies can be controlled by controlling the calcination time: TiO2 nanosheets with oxygen vacancies removed are obtained by calcining in air. The hydrogenated two-dimensional TiO2 nanosheets are placed in a muffle furnace, calcined at 450°C and cooled to room temperature to obtain TiO2 nanosheets with oxygen vacancies removed (called Air-TO).

[0047] Step 4: Platinum-loaded TiO2 nanosheets. All platinum deposition reactions were performed by dissolving 100 mg of TiO2 nanosheets in 50 mL of a 50% (v / v) methanol / water solution and adding 200 μl of a 25 mg / mL HPtCl6 solution. The solution was placed under vacuum and then irradiated with a 300 W Xe arc lamp for 8 hours while stirring. The resulting brownish-white precipitate was centrifuged, washed four times with water, and then dried under vacuum.

[0048] Step 5: Methanol coupling to produce ethane. The photocatalytic reactor consists of a sealed reactor, a recessed window made of quartz glass, and a liquid sampling port sealed with a silicone gasket. The reactor is connected to a Pfizer 6A autosampler for online sampling to an Agilent 8890 gas chromatograph. 50 mL of a 50% (v / v) methanol / water solution is added to the reactor, and 30 mg of TiO2 nanosheets are evenly dispersed in the solution. During the reaction, the system is first evacuated to remove air, and then a xenon lamp is turned on for illumination. After a one-hour reaction, the gas and liquid products are detected by an analytical system.

[0049] The experiment shows that the hydrogenation time of the two-dimensional TiO2 nanosheets in this embodiment is 8h. V8 -TO catalyst has good catalytic activity. When the catalyst dosage is 30 mg, the C2H6 yield is 1.44 μmol g -1 h -1 .

[0050] Other embodiments: Other things remain unchanged, and the hydrogenation time of the two-dimensional TiO2 nanosheets is changed to: 2h and 4h respectively.

[0051] Invention principle and result verification:

[0052] The present invention discloses a surfactant exfoliation method, which synthesizes two-dimensional TiO2 nanosheets by exfoliating layered oxide materials. The TiO2 nanosheets are in a foamy state. The TiO2 nanosheets are hydrogenated with 10% hydrogen in an argon environment for 2 hours, 4 hours, and 8 hours to adjust the defect distribution of the photocatalyst, which is expressed as O v2 -TO、O v4 -TO and O v8 In contrast, TiO2 nanosheets were calcined in air at the same temperature for 8 h and named O v0 -TO. The color of the sample changed from white to gray after hydrogenation, and the color became darker as the hydrogenation time increased.

[0053] See Figure 1-3As shown, atomic force microscopy (AFM) confirmed that the exfoliated layered oxide material was exfoliated into two-dimensional TiO2 nanosheets. Based on the corresponding height curve, the thickness of the nanosheets was approximately 4 nanometers, which is consistent with the thickness of TiO2 nanosheets containing 3-4 unit cells. Figure 4 The X-ray diffraction (XRD) pattern corresponds to two series of peaks of anatase and rutile and O v2 -TO、O v4 -TO and O v8 XRD patterns of -TO and O v0 -TO, indicating that hydrogenation has no effect on the crystal structure of titanium dioxide. Figure 5-6 O v0 The transmission electron microscopy (TEM) image of -TO shows that the sample is a two-dimensional TiO2 nanosheet with a large surface area, and its BET surface area reaches 24.34 m 2 g -1 , providing a large number of sites for the generation of oxygen vacancies.

[0054] The nanosheets were hydrogenated with 10% hydrogen in an argon atmosphere for 2, 4, and 8 hours to adjust the defect distribution of the photocatalyst. Electron spin resonance (EPR) spectroscopy was used to study the concentration of oxygen vacancies in the samples. Figure 9 As shown in Figure 2, both samples exhibit similar ESR signals (g = 2.003), and the ESR signal intensity increases significantly with the increase of hydrogenation time. As we all know, oxygen vacancies can emit photoluminescence (PL) under the excitation of light, so PL spectroscopy is further performed to study the defects in the samples. Figure 10 As shown in Figure 3, the PL emission intensity of TiO2 after hydrogenation is lower than that of TiO2 before hydrogenation, which means that oxygen vacancies can hinder the recombination of photogenerated carriers in the nanosheets. Figure 7-8 As shown in Figure 2, X-ray photoelectron spectroscopy (XPS) can further support the increase of oxygen vacancies after hydrogenation treatment. 2p The peak is attributed to lattice oxygen, while the other peak at 531.5 eV is the signal of oxygen atoms near oxygen vacancies. Figure 12 The figure clearly shows that the sample after 8 hours of hydrogenation has more oxygen vacancies than the sample before hydrogenation, with a ratio of about 18.2%. However, the energy spectrum of Ti does not change before and after hydrogenation.

[0055] See also Figure 11 and 12 As shown in Figure 2, after the photocatalytic reaction, it was found that the production of ethane gradually increased while the production of methane gradually decreased with the increase of oxygen vacancies. When the hydrogenation time was 8h and the catalyst dosage was 30mg, O V8The production of C2H6 and CH4 gradually increased over the 12h period of the -TO catalyst. The final average production of C2H6 was 1.44μmolg -1 h -1 . And O V0 The final average C2H6 yield of -TO was 0.49 μmol g -1 h -1 , much lower than O V8 -TO catalyst. No methanol was added during the reaction, and no ethane was produced, confirming that ethane is indeed produced by methanol coupling. Furthermore, to demonstrate the anchoring effect of oxygen vacancies, no ethane was produced in Air-TO after oxygen vacancies were removed, confirming the anchoring effect of oxygen vacancies.

Claims

1. A method for producing ethane by promoting carbon-carbon coupling of methanol using oxygen vacancies, characterized in that: The following steps are involved: 1) Synthesis of H2Ti4O9; 2) Exfoliating the H2Ti4O9 obtained in step 1) into colloidal sheets to obtain two-dimensional TiO2 nanosheets; 3) hydrogenating the two-dimensional TiO2 nanosheets obtained in step 2) to obtain TiO2 nanosheets with oxygen vacancies; 4) Dissolve the TiO2 nanosheets with oxygen vacancies obtained in step 3) in a methanol / water solution, add H2PtCl6 solution dropwise, place the solution in a vacuum state, and then irradiate nitrogen with an arc lamp for 1 hour while stirring to obtain a brown-white precipitate, which is then washed and dried in a vacuum to obtain a catalyst; 5) Put the methanol / water solution into the reactor, and evenly disperse the catalyst obtained in step 4) in the methanol / water solution. During the reaction, the reactor is first evacuated to remove air, and then a xenon lamp is turned on for illumination. After the reaction, ethane is obtained.

2. The method for producing ethane by promoting carbon-carbon coupling of methanol using oxygen vacancies as claimed in claim 1, wherein: The method for synthesizing H2Ti4O9 in step 1) comprises the following steps: 11) Grind K2CO3 and TiO2 together in a molar ratio of 1.3:1 to form a uniform powder and spread it evenly in a crucible; 12) Place the crucible in a muffle furnace and anneal at 960°C for 10 hours to obtain K2Ti4O9; 13) Place the K2Ti4O9 powder obtained in step 12) into the first hydrochloric acid solution and stir at room temperature for at least 24 hours; 14) The titanate is then filtered out of the solution, rinsed with deionized water, added to the second hydrochloric acid solution, and stirred for at least 24 hours; 15) Repeat steps 13)-14) multiple times, then wash with water multiple times and dry in vacuum to obtain acid-treated H2Ti4O9.

3. The method for producing ethane by promoting carbon-carbon coupling of methanol using oxygen vacancies as claimed in claim 2, wherein: In step 13), the first hydrochloric acid solution is a 1.0 M hydrochloric acid solution, and the mass volume ratio of K2Ti4O9 powder to the first hydrochloric acid solution is 1 g:100 mL.

4. The method for producing ethane by promoting carbon-carbon coupling of methanol using oxygen vacancies as claimed in claim 2, wherein: The concentration of the second hydrochloric acid solution in step 14) is the same as that of the first hydrochloric acid solution.

5. The method for producing ethane by promoting carbon-carbon coupling of methanol using oxygen vacancies as claimed in claim 1, wherein: In step 2), the H2Ti4O9 obtained in step 1) is peeled off into colloidal sheets to obtain two-dimensional TiO2 nanosheets, which includes the following steps: 21) Adding H2Ti4O9 to a 50% ethylamine solution at a molar ratio of 1:30, stirring at room temperature for at least 24 hours, then centrifuging, rinsing with acetone several times to obtain a suspension, and obtaining a precipitate from the suspension by centrifugation; 22) Dissolve the precipitate in TBAOH solution and shake for at least 7 days, wherein H + The molar ratio of ions to TBAOH is 1:5; the colloidal suspension is collected by high-speed centrifugation, washed with deionized water and ethanol multiple times to remove excess TBAOH, and then redispersed in water. After centrifugation again, it is freeze-dried for at least 12 hours and then ground to obtain two-dimensional TiO2 nanosheets.

6. The method for producing ethane by promoting carbon-carbon coupling of methanol using oxygen vacancies as claimed in claim 5, wherein: In step 22), the TBAOH solution is a 10 wt % TBAOH solution, and the high-speed centrifugation speed is not less than 15,000 rpm.

7. The method for producing ethane by promoting carbon-carbon coupling of methanol using oxygen vacancies as claimed in claim 1, wherein: In step 3), the two-dimensional TiO2 nanosheets obtained in step 2) are hydrogenated to obtain TiO2 nanosheets with oxygen vacancies. Specifically, the two-dimensional TiO2 nanosheets are placed in a tubular furnace, calcined at 450°C in a 10% H2 / Ar mixed gas environment, and cooled to room temperature to obtain TiO2 nanosheets with oxygen vacancies.

8. The method for producing ethane by promoting carbon-carbon coupling of methanol using oxygen vacancies as claimed in claim 1, wherein: In step 4), the methanol / water solution is a 50% methanol / water solution, the concentration of the H2PtCl6 solution is 25 mg / ml, and the arc lamp is a 300W Xe arc lamp.

9. The method for producing ethane by promoting carbon-carbon coupling of methanol using oxygen vacancies as claimed in claim 1, wherein: In step 4), N1 hour is 2-8 hours.

10. The method for producing ethane by promoting carbon-carbon coupling of methanol using oxygen vacancies as claimed in claim 1, wherein: In step 5), the methanol / water solution is a 50% methanol / water solution, and the mass volume ratio of the catalyst to the methanol / water solution is 30 mg:50 mL.

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