Photocatalyst for preparing ethanol by coupling methane with carbon dioxide, preparation method and application thereof
By using cerium dioxide composite zinc oxide nanoparticle photocatalyst to promote the coupling of methane and carbon dioxide to produce ethanol under light, the problem of converting methane into high-value-added liquids at low temperatures is solved, achieving an efficient, green and environmentally friendly catalytic effect.
Patent Information
- Application Number
- CN202311187563.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-09-14
- Publication Date
- 2025-09-09
- Estimated Expiration
- 2043-09-14
AI Technical Summary
Existing technologies make it difficult to efficiently convert methane into high-value-added liquid compounds such as ethanol at low temperatures. In addition, commonly used oxidants are expensive, the reaction conditions are harsh, and carbon dioxide emissions are serious.
Cerium dioxide composite zinc oxide nanoparticles are used as photocatalysts to produce ethanol through the coupling reaction of methane and carbon dioxide under photocatalysis. Cerium oxide activates carbon dioxide and zinc oxide activates methane to produce active intermediates CO and CH3OOH, which are finally selectively coupled to produce ethanol.
The highly efficient conversion of methane and carbon dioxide into ethanol was achieved under mild conditions, with a yield of up to 580 μmol·g-1·h-1. It has good chemical stability and photocatalytic activity and is suitable for large-scale industrial production.
Smart Images
Figure CN117427627B_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of methane photocatalytic oxidation, and particularly relates to a photocatalyst for preparing ethanol by coupling methane with carbon dioxide, and a preparation method and application thereof. Background Art
[0002] Methane is a byproduct of oil production and is widely found in natural gas, shale gas, and combustible ice. Due to its abundance and low price, methane is becoming an important precursor for chemicals and fuels that can replace coal and oil. Therefore, its rational utilization provides a basis for decarbonization of the current oil industry. However, methane is currently in a flammable and explosive gaseous form, making it unsuitable for long-distance transportation, thus limiting its application. Converting methane into higher-value, easily transportable liquids such as ethanol, acetic acid, or methanol is an ideal approach.
[0003] The tetrahedral configuration of methane shows high symmetry and low polarity, and it is an extremely stable inert molecule. At the same time, the dissociation energy of carbon-hydrogen bonds is higher than its valuable conversion products (such as CH3CH2OH, CH3OH, etc.). Therefore, the selective oxidation of methane remains a major challenge. The industrial conversion of methane adopts the synthesis gas route, which requires a lot of energy and capital costs, and is subject to harsh reaction conditions (temperature>900K and pressure>3MPa), and will emit a large amount of carbon dioxide, further exacerbating global warming. In order to reduce the maintenance cost of factory equipment and carbon dioxide emissions, a method of directly converting methane into oxidation products at lower temperatures (<500K) has been developed. However, this type of method often uses expensive oxidants, such as H2O2, NO x In recent years, photocatalytic conversion of methane to high value-added products has been considered a promising route. Among them, the introduction of soft oxidant CO in the photochemical process 2， The simultaneous conversion of two greenhouse gases, CH4 and CO2, into ethanol is of great significance and is a win-win strategy for both clean substitution and the harvest of high-energy-density multi-carbon chemicals. Summary of the Invention
[0004] The first object of the present invention is to provide a photocatalyst for preparing ethanol by coupling methane with carbon dioxide, which has high activity and low price.
[0005] The second object of the present invention is to provide a method for preparing the photocatalyst.
[0006] The third object of the present invention is to provide use of the photocatalyst in preparing ethanol by coupling methane and carbon dioxide.
[0007] The photocatalyst for preparing ethanol from methane by coupling carbon dioxide provided by the present invention is a cerium dioxide composite zinc oxide nanoparticle; it is prepared by grinding and mixing a cerium salt and a zinc salt and then reacting them at a high temperature of 500-600°C for 1-3 hours;
[0008] The molar ratio of the cerium salt to the zinc salt is 1:(1-25), preferably 1:(5-25), and more preferably 1:10.
[0009] Preferably, the cerium salt is one or more of cerium chloride, cerium acetate, cerium sulfate, and cerium nitrate; and the zinc salt is one or more of zinc chloride, zinc acetate, zinc sulfate, and zinc nitrate.
[0010] The present invention also provides a method for preparing a photocatalyst, the specific steps of which are as follows:
[0011] (1) Mechanically mix zinc salt, cerium salt, and urea in a mortar at 20-25° C. The total amount of zinc salt and cerium salt is 1.2-3.2 mmol, and the amount of urea is 83-167 mmol. Stir for more than 1 hour (e.g., 1-2 hours);
[0012] (2) Place the mixture in a porcelain crucible with a lid and heat at 2-6℃·min -1 The temperature was raised to 520-600°C at a rate of 1-3 hours, and the reaction was carried out; after the reaction was completed, the mixture was naturally cooled to obtain a light yellow powder, which was a ceria-zinc oxide nanoparticle photocatalyst; the powder was stored in a glove box filled with pure Ar gas for further use;
[0013] The ratio of the active components of the cerium zinc oxide is within a reasonable range, and the yield and selectivity of the target product obtained are high; the photocatalytic effect is good; if the ratio of cerium oxide is too low, the components for activating carbon dioxide are insufficient, resulting in a low yield of multi-carbon liquid phase products; if the ratio is too high, methane is guided to follow the self-oxidation path rather than the coupling path, resulting in a decrease in the yield of multi-carbon liquid phase products.
[0014] The present invention provides a method for using the above-mentioned photocatalyst to produce ethanol by coupling methane with carbon dioxide. The method utilizes the close connection between the adsorption and activation sites of methane and carbon dioxide on the catalyst surface under light to promote the photocatalytic coupling of methane and carbon dioxide to produce ethanol. The specific steps are as follows:
[0015] The cerium dioxide composite zinc oxide nanoparticle photocatalyst is ultrasonically dispersed in deionized water, and then CO2 and CH4 are introduced in sequence. The reaction under light produces a multi-carbon product mainly composed of ethanol. The reaction is carried out in a high-pressure reactor with a light-transmitting window on the top.
[0016] The present invention also provides the use of a photocatalyst in the preparation of ethanol by coupling methane with carbon dioxide. Methane and carbon dioxide are used as raw materials, serving as an oxidant and a reductant to each other. Under the combined action of light and a photocatalyst, methane and carbon dioxide are converted into ethanol. By controlling appropriate photocatalyst components, dosages, and gas ratios, the main product ethanol has a high yield and selectivity, the reaction conditions are mild, and the catalytic reaction process is simple and environmentally friendly. A zinc oxide carrier supported by cerium dioxide is used as the photocatalyst. The loading of cerium oxide can promote the activation of carbon dioxide to generate active oxygen species and an active intermediate CO. The zinc oxide carrier promotes the oxidation of methane to generate an active intermediate product CH3OOH under the action of water. Finally, CO and CH3OOH are selectively coupled, thereby achieving efficient conversion of methane and carbon dioxide to ethanol.
[0017] Preferably, the solid-liquid ratio of the catalyst to deionized water is (5-25) mg:15 ml.
[0018] The dosage of the photocatalyst must be controlled within a reasonable range to efficiently photocatalyze the conversion of methane and carbon dioxide into ethanol. Too little photocatalytic reaction slows down the reaction, resulting in a decrease in product yield. Too much photocatalytic reaction diminishes the catalytic effect, leading to a waste of resources.
[0019] Preferably, the high-pressure reactor is placed in a cold water pool for reaction, and the air in the reactor is replaced by the carbon dioxide.
[0020] Preferably, the total pressure of the introduced gas raw materials CO2 and CH4 is 1-2 MPa; the pressure ratio is 1:(1-3).
[0021] If the partial pressure of the carbon dioxide is too low, the target product and selectivity obtained are low; if the partial pressure is too high, the gas phase product CO is easily generated.
[0022] Preferably, the reaction time is 0.5-4h.
[0023] Preferably, the reaction temperature is 25-50°C.
[0024] Preferably, the light source used for the illumination includes a xenon lamp, and the wavelength of the xenon lamp is 350nm-1000nm.
[0025] In the present invention, the ethanol-based multi-carbon product is specifically one or more of methanol, peroxymethanol, ethanol, and acetic acid; wherein the main product is ethanol.
[0026] Compared with the prior art, the present invention has the following beneficial effects:
[0027] In the present invention, methane and carbon dioxide are used as raw materials, acting as oxidants and reductants respectively. Under the combined action of light and a photocatalyst composed of cerium dioxide and zinc oxide nanoparticles, methane and carbon dioxide are coupled to ethanol. By controlling the ratio and combination form of the cerium and zinc components, the amount of photocatalyst used, and the mixing ratio of the two gases, the yield of ethanol can reach as high as 580 μmol·g. -1 ·h -1 , has good chemical stability and photocatalytic activity; the reaction conditions in the photocatalytic methane coupling system of carbon dioxide to ethanol are mild, the process is simple and green and environmentally friendly, and is suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS
[0028] Figure 1 This is a diagram illustrating the principle of the method of the present invention. Under light, the cerium dioxide component in the photocatalyst activates carbon dioxide, and the zinc oxide component activates methane. Under the cooperation of water, the activated intermediates of the two gases, CO and CH3OOH, selectively combine to produce ethanol.
[0029] Figure 2 This is the morphology of the ceria-zinc oxide nano-photocatalyst provided in Example 1 of the present invention. Figure a is an electron microscope image of ceria-zinc oxide nanoparticles; and figure b is the distribution of zinc, cerium, and oxygen elements.
[0030] Figure 3 This is the NMR spectrum of the reaction product provided in Example 2 of the present invention.
[0031] Figure 4 This is the X-ray diffraction image of the cerium dioxide composite zinc oxide nanoparticles before and after the reaction provided in Example 1 of the present invention.
[0032] Figure 5 This is the morphology of the cerium dioxide composite zinc oxide nanophotocatalyst provided in Example 3 of the present invention.
[0033] Figure 6 This is the NMR spectrum of the reaction product provided in Example 4 of the present invention. DETAILED DESCRIPTION
[0034] The present invention will be further described by way of examples, which will help to understand the present invention but are not intended to limit the present invention.
[0035] Example 1
[0036] This embodiment provides a cerium zinc oxide photocatalyst for photocatalytic coupling of methane and carbon dioxide to produce ethanol. The specific steps of preparation are as follows:
[0037] Cerium-zinc mixed oxide nanoparticles with a ratio of 1:10 were synthesized by calcination method; 83 mmol CO(NH2)2, 0.2 mmol Ce(NO3)3·6H2O and 2.0 mmol Zn(NO3)2·6H2O were mechanically mixed at 25 °C for 1.5 h; the mixture was then heated in air at 4 °C·min -1 Heat to 520℃ at a rate of 1000 ℃ and keep warm for 2h;
[0038] The TEM image of the photocatalyst is shown in FIG. Figure 2 As shown in a; From the figure, it can be seen that the cerium oxide particles are loaded on the zinc oxide sheet; the elemental analysis diagram of the photocatalyst is as shown Figure 2 As shown in b, it can be clearly seen that the cerium oxide nanoparticles are all loaded on the zinc oxide and are evenly distributed, without existing alone.
[0039] Example 2
[0040] This embodiment provides a method for producing ethanol by photocatalytic coupling of methane and carbon dioxide, the specific steps of which are as follows:
[0041] 5 mg of the photocatalyst provided in Example 1 was dispersed in 15 mL of DI water under continuous stirring at 700 rpm. After replacing the air in the autoclave with CO2, CO2 and CH4 were introduced in sequence at a total pressure of 1.4 MPa (ratio of CO2:CH4=1:2), and stirring was continued in the dark for 20 minutes. Then, a 300 W xenon lamp was used in the autoclave at 25°C for full spectrum irradiation. After the reaction for 1 hour, methanol, acetic acid, and the ethanol were obtained. The NMR spectrum is shown in FIG. Figure 3 As shown; (the single peak at the abscissa 2.6 is the added internal standard);
[0042] The XRD spectra of the photocatalyst before and after the reaction are as follows: Figure 4 As shown, zinc oxide and cerium oxide can respectively match well with the hexagonal zinc oxide standard card (JCPDS No.36-1451) and the tetragonal cerium dioxide standard card (JCPDS No.34-0394). It can be seen that the catalyst maintains stable results before and after the reaction.
[0043] Example 3
[0044] This embodiment provides a cerium zinc oxide photocatalyst for photocatalytic coupling of methane and carbon dioxide to produce ethanol. The specific steps of preparation are as follows:
[0045] Cerium-zinc mixed oxide nanoparticles with a ratio of 1:20 were synthesized by calcination method; 83 mmol CO(NH2)2, 0.1 mmol Ce(NO3)3·6H2O and 2.0 mmol Zn(NO3)2·6H2O were mechanically mixed at 25 °C for 1.5 h; the mixture was then heated in air at 2 °C·min -1 Heat to 520℃ at a rate of 1000 ℃ and keep warm for 2h;
[0046] The TEM image of the photocatalyst is shown in FIG. Figure 5 As shown; the composite structure of cerium oxide particles and zinc oxide can be seen from the figure.
[0047] Example 4
[0048] This embodiment provides a method for producing ethanol by photocatalytic coupling of methane and carbon dioxide, the specific steps of which are as follows:
[0049] 5 mg of the photocatalyst provided in Example 3 was dispersed in 15 mL of DI water under continuous stirring at 700 rpm. After replacing the air in the autoclave with CO2, CO2 and CH4 were introduced sequentially at a total pressure of 1.4 MPa (ratio of CO2:CH4=1:2). Then, full spectrum irradiation was performed in the autoclave at 25°C using a 300 W xenon lamp. After 2 hours of reaction, ethanol was obtained. The NMR spectrum is shown in FIG. Figure 6 As shown (the single peak at the abscissa 2.6 is the added internal standard).
Claims
1. A photocatalyst for producing ethanol by coupling methane with carbon dioxide, characterized in that: The photocatalyst is a cerium dioxide-zinc oxide composite nanoparticle. It is prepared by grinding and mixing a cerium salt and a zinc salt, and then reacting them at a high temperature of 500-600°C for 1-3 hours. The molar ratio of the cerium salt to the zinc salt is 1:(1-25). Under light, the close connection between the methane and carbon dioxide adsorption and activation sites on the catalyst surface is utilized to promote the photocatalytic coupling of methane and carbon dioxide to produce ethanol. The specific application steps are as follows: The cerium dioxide composite zinc oxide nanoparticle photocatalyst is ultrasonically dispersed in deionized water, and then CO2 and CH4 are introduced in sequence. The reaction under light produces a multi-carbon product mainly composed of ethanol. The reaction is carried out in a high-pressure reactor with a light-transmitting window on the top.
2. The use according to claim 1, characterized in that The solid-liquid ratio of the catalyst to deionized water is (5-25) mg: 15 ml.
3. The use according to claim 1, characterized in that The total pressure of the CO2 and CH4 introduced is 1-2 MPa; the pressure ratio is 1:1-3.
4. The use according to claim 1, characterized in that The reaction time is 0.5-4 h; the reaction temperature is 25-50°C.
5. The use according to claim 1, characterized in that The light source used for illumination is a xenon lamp, and the wavelength of the xenon lamp is 350nm-1000nm.
6. The use according to claim 1, characterized in that The ethanol-based multi-carbon product refers to a product in which ethanol is the main product and the rest is one or more of methanol, methanol peroxide, ethanol, and acetic acid.
7. The use according to claim 1, characterized in that The cerium salt is selected from cerium chloride, cerium acetate, cerium sulfate, and cerium nitrate; and the zinc salt is selected from zinc chloride, zinc acetate, zinc sulfate, and zinc nitrate.