CN113101964B - A kind of mesoporous cerium oxide photocatalyst and its preparation method and application - Google Patents

Abstract

The invention provides a mesoporous cerium oxide photocatalyst, and a preparation method and application thereof, wherein the preparation method comprises the following steps: (1) Mixing a mesoporous molecular sieve with a solvent, adding a cerium source, and heating and drying to obtain a precursor; (2) Calcining the precursor obtained in the step (1), mixing with alkali liquor, and drying to obtain the mesoporous cerium oxide photocatalyst; wherein the mesoporous molecular sieve is KIT-6. The invention prepares mesoporous CeO by using KIT-6 molecular sieve as matrix through template roasting method ₂ As a catalyst for preparing methanol by activating photocatalytic methane, the catalyst has the characteristics of regular shape, stable mesoporous structure, good crystallinity, high purity, high photocatalytic activity under visible light and the like.

Description

A kind of mesoporous cerium oxide photocatalyst and its preparation method and application

technical field

The invention belongs to the technical field of inorganic nanometer materials, and relates to a mesoporous cerium oxide photocatalyst and a preparation method and application thereof.

Background technique

The conversion of methane to methanol has always been a hot research direction in the field of catalysis. Traditional thermal catalytic methane activation to methanol is limited by thermodynamic equilibrium, often requires high temperature and high pressure conditions, complex operation and high cost, and it is difficult to achieve the ideal level of methanol yield and selectivity at the same time. The photocatalytic conversion of methane to methanol driven by solar energy can reduce the energy barrier of the reaction and realize the activation of methane to methanol under mild conditions.

CN110038591A discloses a copper-iridium composite oxide catalyst for direct oxidation of methane to methanol and a preparation method thereof. The catalyst is composed of iridium oxide, copper oxide and promoter zinc, cobalt or iron oxide. Based on the weight of the catalyst as 100%, the weight percentage of the noble metal iridium is 0.1-10.0%, and the weight percentage of the cocatalyst _MOx is 0-20.0%. The catalyst has a simple preparation method, and has the characteristics of high methanol yield in the methane oxidation to methanol reaction and can be used repeatedly. However, it uses the noble metal iridium, which is expensive and not suitable for industrial production.

CN110252302A discloses a catalyst for catalyzing the low-temperature selective oxidation of methane to prepare methanol. The catalyst is a copper-zirconium-aluminum composite metal oxide with the following general structural formula: Cu _a Zr _{b Al c} O _d , wherein a, b, c, and d are the atomic numbers of Cu, Zr, Al, and O elements in the catalyst, and the value range of a is 1-2, the value range of b is 1-2, and the value range of c is 1-2; d is the oxygen atom required to meet the oxidation state of other elements number. The disclosed catalyst has a simple synthesis method, can catalyze methane to prepare methanol at 100-200° C., has high methane conversion rate and good methanol selectivity.

The above scheme has the disadvantages of using noble metals or requiring high temperature conditions. Therefore, it is very necessary to develop a photocatalyst that can convert methane into methanol without adding noble metals and at room temperature.

Contents of the invention

The object of the present invention is to provide a mesoporous cerium oxide photocatalyst and its preparation method and application. The preparation method comprises the following steps: (1) mixing a mesoporous molecular sieve with a solvent, adding a cerium source, heating and drying to obtain a precursor; (2) calcining the precursor obtained in step (1) and mixing it with lye, and drying to obtain the mesoporous cerium oxide photocatalyst; wherein the mesoporous molecular sieve is KIT-6. The invention obtains a mesoporous _CeO2 photocatalyst with regular shape, stable mesoporous structure, good crystallinity and high purity through a template roasting method, and has outstanding performance of photocatalytic activation of methane to produce methanol.

To achieve this purpose of the invention, the present invention adopts the following technical solutions:

In a first aspect, the present invention provides a method for preparing a mesoporous cerium oxide photocatalyst, the preparation method comprising the following steps:

(1) After mixing the mesoporous molecular sieve with the solvent, add the cerium source, and obtain the precursor after heating and drying;

(2) mixing the precursor obtained in step (1) with lye after calcining, and drying to obtain the mesoporous cerium oxide photocatalyst;

Wherein, the mesoporous molecular sieve is KIT-6.

The present invention uses KIT-6 molecular sieve as a substrate to prepare mesoporous _CeO2 as a photocatalytic methane catalyst for methanol production through a template roasting method. The catalyst has the characteristics of regular morphology, stable mesoporous structure, good crystallinity, high purity, and high photocatalytic activity under visible light. Mesoporous CeO ₂ is dispersed into a closed quartz glass reactor filled with water, and methane is introduced after the air in the reactor is exhausted. Under the condition of light, methane can be activated to produce methanol through photocatalytic process, which is beneficial to practical application.

Preferably, the ratio of the mass of the mesoporous molecular sieve to the volume of the solvent in step (1) is (0.1-1) g/10mL, for example: 0.1g/10mL, 0.2g/10mL, 0.3g/10mL, 0.5g/10mL, 0.7g/10mL, 0.8g/10mL, or 1g/10mL.

Preferably, the solvent includes deionized water and/or ethanol.

Preferably, the mesoporous molecular sieve is mixed with the solvent while stirring.

Preferably, the stirring speed is 150-600r/min, for example: 150r/min, 200r/min, 250r/min, 300r/min, 400r/min, 500r/min or 600r/min, etc., preferably 200-400r/min.

Preferably, the cerium source in step (1) includes any one or a combination of at least two of cerous nitrate hexahydrate, cerous chloride heptahydrate or cerium acetate hydrate.

Preferably, the mass ratio of the cerium source to the mesoporous molecular sieve is 1:(0.1-1), such as 1:0.1, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9 or 1:1, etc., preferably 1:(0.25-0.75).

Preferably, standing before heating and drying described in step (1).

Preferably, the standing time is 0.5-12h, such as 0.5h, 1.5h, 8h or 12h, etc., preferably 1-3h.

Preferably, the heating and drying temperature in step (1) is 40-120°C, such as 40°C, 60°C, 65°C, 80°C or 120°C, preferably 50-80°C.

Preferably, the heating and drying time in step (1) is 8-48 hours, such as 8 hours, 14 hours, 16 hours, 24 hours, 30 hours or 48 hours, etc., preferably 10-24 hours.

Preferably, the calcination temperature in step (2) is 400-900°C, for example, 400°C, 440°C, 480°C, 520°C, 560°C, 600°C, 640°C, 660°C, 680°C, 700°C, 720°C, 800°C, 860°C or 900°C, etc., preferably 750-800°C.

Preferably, the heating rate of the calcination is 1-20°C/min, such as 1°C/min, 4°C/min, 6°C/min, 8°C/min, 10°C/min, 12°C/min, 14°C/min, 16°C/min or 20°C/min, etc., preferably 3-5°C/min.

Preferably, the calcination time is 3-12 h, such as 3 h, 5 h, 7 h, 9 h, 10 h or 12 h, etc., preferably 4-8 h.

Preferably, the lye in step (2) includes any one or a combination of NaOH solution or KOH solution.

Preferably, the concentration of the lye is 1-5 mol/L, for example: 1 mol/L, 2 mol/L, 3 mol/L, 4 mol/L or 5 mol/L, etc., preferably 2-3 mol/L.

Preferably, centrifugation, filtration and washing are carried out before the drying in step (2).

Preferably, the rotational speed during the centrifugation is 6000-12000r/min, such as 6000r/min, 8000r/min, 900r/min, 10000r/min or 12000r/min, etc., preferably 8000-10000r/min.

Preferably, the centrifugation time is 3-15 minutes, preferably 5-10 minutes.

Preferably, the washing detergent includes ethanol and/or deionized water.

Preferably, the number of washings is 2-5 times, for example: 2 times, 3 times, 4 times or 5 times.

Preferably, the drying temperature in step (2) is 50-150°C, such as 50°C, 60°C, 70°C, 100°C or 150°C, etc., preferably 60-90°C.

Preferably, the drying time in step (2) is 8-48 hours, such as 8 hours, 10 hours, 13 hours, 14 hours, 16 hours, 20 hours, 25 hours, 32 hours, 36 hours, 40 hours or 48 hours, etc., preferably 10-24 hours.

As a preferred version of the present invention, the preparation method comprises the following steps:

(1) mix the mesoporous molecular sieve and the solvent according to the ratio of the mass of the mesoporous molecular sieve to the volume value of the solvent (0.1-1):10, add a cerium source after mixing, heat and dry to obtain a precursor;

(2) Calcining the precursor obtained in step (1) for 3 to 12 hours at 400 to 900° C., mixing it with lye, and drying to obtain the mesoporous cerium oxide photocatalyst;

Wherein, the mesoporous molecular sieve is KIT-6.

In a second aspect, the present invention provides a mesoporous cerium oxide photocatalyst, which is prepared by the method described in the first aspect; the specific surface area of the catalyst is 75-100 cm ² /g, for example: 75 cm ² /g, 80 cm ² /g, 85 cm ² /g, 90 cm ² /g, 95 cm ² /g or 100 cm ² /g, etc., and the average pore diameter of the catalyst is 5-30 nm, for example: 5 nm, 10 nm, 15 nm nm, 20nm, 25nm or 30nm etc.

The mesoporous cerium oxide photocatalyst of the present invention has an adjustable band gap and can effectively absorb ultraviolet or visible light. Nanoscale mesoporous CeO ₂ has a larger specific surface area, an ordered pore structure, and better optical and catalytic properties than bulk ceria.

In the third aspect, the present invention provides an application of the mesoporous cerium oxide photocatalyst as described in the second aspect, and the mesoporous cerium oxide photocatalyst is used for photocatalytic activation of methane to produce methanol.

Compared with the prior art, the present invention has the following beneficial effects:

(1) The present invention uses KIT-6 molecular sieve as a substrate to prepare mesoporous _CeO2 as a photocatalyst for methane activation to produce methanol through template roasting method. The catalyst has regular morphology, stable mesoporous structure, good crystallinity, high purity, and has the characteristics of high photocatalytic activity under visible light. Mesoporous CeO ₂ is dispersed into a closed quartz glass reactor filled with water, and methane is introduced after the air in the reactor is exhausted. Under the condition of light, methane can be activated to produce methanol through photocatalytic process, which is beneficial to practical application.

(2) The preparation method of the present invention is simple to operate, environmentally friendly, and low in cost, which is beneficial to practical application.

Description of drawings

Figure 1 is a TEM image of the catalyst prepared in Example 1 of the present invention.

Figure 2 is the XRD pattern of the catalyst prepared in Example 1 of the present invention.

Fig. 3 is a comparison chart of the photocatalytic methane activation methanol production performance of the catalyst prepared in Example 1 of the present invention and the catalyst prepared in Comparative Example 1.

Detailed ways

The technical solutions of the present invention will be further described below through specific embodiments. It should be clear to those skilled in the art that the examples are only for helping to understand the present invention, and should not be regarded as specific limitations on the present invention.

Example 1

This embodiment provides a kind of mesoporous cerium oxide photocatalyst, the preparation method of described catalyst is as follows:

(1) Mix 0.25g KIT-6 mesoporous molecular sieve with 10mL water;

(2) Add 1 g of cerous nitrate hexahydrate to the above mixed solution, and heat the liquid after standing for 2 hours at 60° C. for 12 hours to obtain a dry solid powder;

(3) The dry solid powder was calcined at 800°C and then mixed with 2mol/L alkaline solution at a stirring rate of 300r/min and reacted for 0.5h. The liquid after removing the template was centrifuged at a rate of 8000r/min for 6min. The obtained precipitate was washed with ethanol and deionized water three times and dried at 80°C for 12h to obtain a mesoporous cerium oxide photocatalyst with a specific surface area of ^85cm2 /g and an average pore diameter of 11nm.

The TEM image of the catalyst is shown in FIG. 1 . It can be seen from FIG. 1 that the catalyst has a regular morphology and a uniform and stable mesopore structure.

The XRD pattern of the catalyst is shown in FIG. 2 . It can be seen from FIG. 2 that the catalyst is a face-centered cubic fluorite crystal form, and there are no other crystal forms, and the purity is high.

Example 2

This embodiment provides a kind of mesoporous cerium oxide photocatalyst, the preparation method of described catalyst is as follows:

(1) Mix 0.8g KIT-6 mesoporous molecular sieve with 10mL water;

(2) Add 3 g of cerous nitrate hexahydrate to the above mixed solution, and heat the liquid after standing for 2 hours at 80° C. for 12 hours to obtain a dry solid powder;

(3) After calcining the dried solid powder at a high temperature at 830°C, mix it with a 2.5mol/L alkaline solution at a stirring rate of 300r/min and react for 0.5h, centrifuge the liquid after removing the template at a rate of 8000r/min for 6min, wash the obtained precipitate with ethanol and deionized water for 3 times, and dry at 80°C for 12h to obtain a mesoporous cerium oxide photocatalyst with a specific surface area of 75cm ² /g and an average pore diameter of 10nm .

Example 3

The only difference between this example and Example 1 is that the high-temperature calcination temperature in step (3) is 400° C., and other conditions and parameters are exactly the same as those in Example 1.

Example 4

The only difference between this example and Example 1 is that the high temperature calcination in step (3) is 900° C., and other conditions and parameters are exactly the same as those in Example 1.

Example 5

The only difference between this example and Example 1 is that the temperature of the high-temperature calcination in step (3) is 300° C., and other conditions and parameters are exactly the same as those of Example 1.

Example 6

The only difference between this example and Example 1 is that the high temperature calcination in step (3) is 950° C., and other conditions and parameters are exactly the same as those in Example 1.

Comparative example 1

The only difference between this comparative example and Example 1 is that the KIT-6 described in step (1) is replaced by SBA-15, and other conditions and parameters are exactly the same as in Example 1.

Comparative example 2

The only difference between this comparative example and Example 1 is that the KIT-6 described in step (1) is replaced with mesoporous silicon, and other conditions and parameters are exactly the same as those in Example 1.

Performance Testing:

Take 10 mg of the photocatalysts described in Examples 1-6 and Comparative Examples 1-2 and add them into 30 mL of deionized water, and ultrasonically disperse them uniformly for 10 minutes. The photocatalyst dispersion was transferred to a 50 mL reactor, and the reactor was sealed with a rubber stopper. Argon gas was passed into the reactor for 30 minutes, and the air in the reactor was purged. Then, methane gas was introduced into the dispersion liquid by bubbling method for 10 min at a rate of 100 mL/min to ensure that methane was fully dissolved in water and in close contact with the photocatalyst. Then, place the reactor directly under the xenon lamp light source, about 10 cm away from the lamp port, turn on the stirring and cooling water, and illuminate for 1 hour. Use a gas-tight needle to suck the gas in the reactor and inject it into a gas chromatograph to detect the gas product content. The liquid after the reaction is extracted, and the content of the liquid product is detected by hydrogen nuclear magnetic resonance spectroscopy. The test results are shown in Table 1:

Table 1

Methanol productivity/μmol/g/h Example 1 27.8 Example 2 27.5 Example 3 24.3 Example 4 26.1 Example 5 22.7 Example 6 22.9 Comparative example 1 0 Comparative example 2 0

As can be seen from Table 1, it can be obtained from Examples 1-6 that the catalyst prepared by the method of the present invention catalyzes the activation of methane to produce methanol with a yield of more than 22.7 μmol/g/h.

From the comparison of Example 1 and Examples 3-6, it can be seen that the calcination temperature in step (2) will affect the catalytic activity of the prepared catalyst, and a catalyst with higher catalytic activity can be obtained by controlling the calcination temperature at 400-900°C. If the calcination temperature is lower than 400°C, the crystallinity of the catalyst is poor, the purity is low, and the mesopore structure is unstable and easy to collapse. If the calcination temperature is higher than 900°C, the specific surface area of the catalyst will decrease significantly, and the pore size will be uneven.

The comparison chart of the photocatalytic methane activation to methanol performance of the catalyst obtained in Example 1 and the catalyst obtained in Comparative Example 1 is shown in Figure 3. From the comparison of Example 1 and Comparative Example 1, it can be obtained that the present invention uses KIT-6 mesoporous molecular sieves as a carrier to prepare mesoporous cerium oxide as a catalyst, which can have high photocatalytic activity under visible light, and can be used under light conditions to realize the activation of methane to prepare methanol, which is beneficial to practical applications.

The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection scope and disclosure scope of the present invention.

Claims (33)

1. an application of mesoporous cerium oxide photocatalyst, it is characterized in that, described mesoporous cerium oxide photocatalyst is used for photocatalytic methane activation and makes methanol, and the preparation method of described mesoporous cerium oxide photocatalyst comprises the following steps: (1) Mix the mesoporous molecular sieve with the solvent, add the cerium source, heat and dry to obtain the precursor; (2) Calcining the precursor obtained in step (1), mixing it with lye, and drying to obtain the mesoporous cerium oxide photocatalyst; Wherein, the mesoporous molecular sieve is KIT-6, the mass ratio of the cerium source to the mesoporous molecular sieve is 1:(0.25~0.75), the solvent is deionized water, and the calcination temperature is 750~800°C. 2. The application according to claim 1, characterized in that the ratio of the mass of the mesoporous molecular sieve to the volume of the solvent in step (1) is (0.1-1) g/10mL. 3. The application according to claim 1, wherein the mesoporous molecular sieve is mixed with a solvent while stirring. 4. application as claimed in claim 3, is characterized in that, the speed of described stirring is 150～600r/min. 5. application as claimed in claim 4, is characterized in that, the speed of described stirring is 200～400r/min. 6 . The application according to claim 1 , wherein the cerium source in step (1) comprises any one or a combination of at least two of cerous nitrate hexahydrate, cerous chloride heptahydrate or cerium acetate hydrate. 7. The application according to claim 1, characterized in that, in the step (1), the drying is carried out before heating and drying. 8. The application according to claim 7, wherein the standing time is 0.5 to 12 hours. 9. application as claimed in claim 8, is characterized in that, the time of described standing still is 1～3h. 10. The application according to claim 1, characterized in that the heating and drying temperature in step (1) is 40-120°C. 11. The application according to claim 10, characterized in that, the heating and drying temperature is 50-80°C. 12. The application according to claim 1, characterized in that the heating and drying time in step (1) is 8-48 hours. 13. The application according to claim 12, wherein the heating and drying time is 10 to 24 hours. 14. The application according to claim 1, characterized in that the heating rate of the calcination is 1-20°C/min. 15. The application according to claim 14, characterized in that the heating rate of the calcination is 3-5°C/min. 16. The application according to claim 1, wherein the calcination time is 3 to 12 hours. 17. The application according to claim 16, wherein the calcination time is 4 to 8 hours. 18. The application according to claim 1, characterized in that the lye in step (2) includes any one or a combination of NaOH solution or KOH solution. 19. The application according to claim 1, wherein the concentration of the lye is 1 to 5 mol/L. 20. application as claimed in claim 19, is characterized in that, the concentration of described lye is 2～3 mol/L. 21. The application according to claim 1, characterized in that centrifugation, filtration and washing are performed before drying in step (2). 22. The application according to claim 21, characterized in that, the rotational speed during the centrifugation is 6000~12000r/min. 23. The application according to claim 22, characterized in that, the rotational speed during the centrifugation is 8000~10000r/min. 24. The application according to claim 21, wherein the centrifugation time is 3 to 15 minutes. 25. The application according to claim 24, wherein the centrifugation time is 5 to 10 minutes. 26. Use according to claim 21, characterized in that said washing detergent comprises ethanol and/or deionized water. 27. The application according to claim 21, wherein the number of times of said washing is 2 to 5 times. 28. The application according to claim 1, characterized in that the drying temperature in step (2) is 50-150°C. 29. The application according to claim 28, characterized in that, the drying temperature is 60-90°C. 30. The application according to claim 1, characterized in that the drying time in step (2) is 8-48 hours. 31. The application according to claim 30, wherein the drying time is 10 to 24 hours. 32. application as claimed in claim 1, is characterized in that, described preparation method comprises the following steps: (1) Mix the mesoporous molecular sieve and the solvent according to the ratio of the mass of the mesoporous molecular sieve to the volume value of the solvent (0.1-1) g/10mL, add the cerium source, heat and dry to obtain the precursor; (2) Calcining the precursor obtained in step (1) at 750-800° C. for 3-12 hours, mixing it with lye, and drying to obtain the mesoporous cerium oxide photocatalyst; Wherein, the mesoporous molecular sieve is KIT-6. 33. The application according to claim 1, characterized in that the specific surface area of the catalyst is 75-100 cm ² /g, and the average pore diameter of the catalyst is 5-30 nm.