Spherical and flaky lanthanum oxide as well as preparation method and application thereof

Abstract

The invention relates to the technical field of oxidative coupling of methane, and discloses spherical and flaky lanthanum oxide as well as a preparation method and application thereof. The lanthanum oxide comprises spherical lanthanum oxide and flaky lanthanum oxide, the average diameter of the spherical lanthanum oxide is 0.1-1 [mu] m, and the average thickness of the flaky lanthanum oxide is 100-200 nm. The method for preparing the lanthanum oxide comprises the following steps: mixing a lanthanum precursor and an aqueous solution of urea and alcohol to obtain a mixed solution, adding alkali liquor to adjust the pH value of the mixed solution to 7.5-8, then reacting at 80-100 DEG C for 2-12 hours, and then separating and primarily roasting. By adopting the method disclosed by the invention, spherical and flaky lanthanum oxide can be prepared, and the lanthanum oxide has relatively high reaction stability when being used for methane oxidative coupling reaction.

Description

Technical Field

[0001] The invention relates to the technical field of methane oxidative coupling, and in particular to spherical and flaky lanthanum oxide and a preparation method and application thereof. Background Art

[0002] The technology of producing ethylene by oxidative coupling of methane is a route for direct conversion and utilization of natural gas. Compared with the anaerobic conversion of methane, the reaction temperature of oxidative coupling technology is lower, and ethylene, an important industrial raw material, is the main product. It has a broad industrial prospect and is a generally promising technology route. However, although the technology has been around for more than 40 years, high-performance catalysts are the core issue of whether the oxidative coupling technology of methane can be applied industrially. At present, from a general perspective, the oxidative coupling reaction of methane still requires a relatively high temperature to obtain a high methane conversion rate. High temperature is not only prone to deep oxidation of methane and product olefins, but also high temperature is prone to loss of active components, and a series of problems such as sintering and difficulty in removing heat at high temperature may occur. With the continuous emergence of new materials, researchers have been working hard to find catalysts for the efficient activation of methane oxidative coupling reactions. The literature Fern shaped La2O3 nanostructures as potential scaffold for efficient hydroquinone chemicalsensing application. Ceramics International 2020, 46 (4), 5141-5148. reported a fern-shaped nano lanthanum oxide, lanthanum nitrate solution (20mL, 0.1M) and hexamethylenetetramine solution (20mL, 0.1M) were mixed under stirring. The pH value of the solution was adjusted to 10 by adding ammonia solution dropwise to the mixture. The resulting solution was then transferred to a 100ml solution of polytetrafluoroethylene-lined stainless steel autoclave and aged at 160-170°C for 6 hours. After cooling to room temperature, the solid portion was filtered and washed with deionized water and ethanol, and the resulting product was then dried at 80°C for 3 hours. Subsequently, the material was calcined in air at 800°C for 4 hours. The obtained lanthanum oxide material shows a 3D fern-like structure with dendritic arms of different lengths, a triangular outline, and the dendritic arms are connected to a long common trunk like beads and evenly arranged along the central trunk. This material is used in electrochemical sensors for hydroquinone. However, the above lanthanum oxide has low catalytic activity when used in oxidative coupling reactions. Summary of the invention

[0003] The purpose of the present invention is to overcome the above technical problems of the prior art and provide a spherical and flaky lanthanum oxide and a preparation method and application thereof.

[0004] In order to achieve the above object, the first aspect of the present invention provides a lanthanum oxide, which includes spherical lanthanum oxide and flake lanthanum oxide, wherein the average diameter of the spherical lanthanum oxide is 0.1-1 μm, and the average thickness of the flake lanthanum oxide is 100-200 nm.

[0005] The second aspect of the present invention provides a method for preparing lanthanum oxide, which comprises: mixing a lanthanum precursor and an aqueous solution of urea and alcohol to obtain a mixed solution, adding an alkali solution to adjust the pH value of the mixed solution to 7.5-8, then reacting at 80-100°C for 2-12h, and then separating and performing a first calcination.

[0006] The third aspect of the present invention provides lanthanum oxide prepared by the method described above.

[0007] A fourth aspect of the present invention provides the use of the above-mentioned lanthanum oxide in the oxidative coupling reaction of methane to produce C2 and higher hydrocarbons.

[0008] A fifth aspect of the present invention provides a method for preparing hydrocarbons having two or more carbon atoms from methane, characterized in that the method comprises: in the presence of oxygen and under the conditions of methane oxidative coupling reaction, contacting methane with the above-mentioned lanthanum oxide for reaction;

[0009] Alternatively, lanthanum oxide is prepared according to the method described above, and then methane is contacted with the obtained lanthanum oxide in the presence of oxygen and under the conditions of methane oxidative coupling reaction.

[0010] The method of the invention can be used to prepare spherical and flaky lanthanum oxide, and the lanthanum oxide can have high reaction stability when used in methane oxidative coupling reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a scanning electron microscope image of the lanthanum oxide prepared in Example 1. DETAILED DESCRIPTION

[0012] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0013] A first aspect of the present invention provides a lanthanum oxide, which includes spherical lanthanum oxide and flake lanthanum oxide, wherein the average diameter of the spherical lanthanum oxide is 0.1-1 μm, and the average thickness of the flake lanthanum oxide is 100-200 nm.

[0014] According to the present invention, preferably, the average length of the flake lanthanum oxide is 0.4-1 μm, and the average width is 0.2-0.5 μm.

[0015] In the present invention, unless otherwise stated, the thickness, length and width described herein are measured by scanning electron microscopy. The method for testing the size of the lanthanum oxide material is as follows: 6-8 samples in the field of view are selected, and the diameter, length, width and thickness are measured using a measuring instrument provided by the scanning electron microscope, and then the average diameter, average length, average width and average thickness of the 6-8 samples in the field of view are calculated.

[0016] According to the present invention, preferably, the specific surface area of ​​the lanthanum oxide is 10-20m 2 / g, pore volume is 0.1-0.2cm 3 / g, and the average pore size is 50-150 angstroms. It is a unit of length, 10 angstroms = 1 nm.

[0017] According to the present invention, in order to improve the catalytic performance of the catalyst, preferably, the lanthanum oxide also includes a modifying element, and the modifying element includes at least one element selected from the group consisting of sodium, potassium, magnesium, calcium, strontium, barium, titanium, iron, boron and cerium.

[0018] According to the present invention, preferably, the molar ratio of the modifying element to the lanthanum element in lanthanum oxide is 1:1-30 (for example, 1:1, 1:5, 1:10, 1:15, 1:20, 1:22, 1:24, 1:26, 1:28, 1:30, and a range consisting of any two of the above points), more preferably 1:12-25. In the present invention, the molar ratio of the modifying element to the lanthanum element is calculated based on the feed amount.

[0019] The second aspect of the present invention provides a method for preparing lanthanum oxide, wherein a lanthanum precursor and an aqueous solution of urea and alcohol are mixed to obtain a mixed solution, an alkali solution is added to adjust the pH value of the mixed solution to 7.5-8, and then the mixed solution is reacted at 80-100°C for 2-12h, followed by separation and a first calcination.

[0020] According to the present invention, preferably, the reaction is carried out in a water bath. More preferably, the reaction is carried out under stirring at a speed of 200-500 rpm.

[0021] According to the present invention, the lanthanum precursor may be a conventional substance containing lanthanum element; preferably, the lanthanum precursor is a water-soluble salt of lanthanum (such as nitrate, chloride, etc.), more preferably lanthanum nitrate.

[0022] According to the present invention, in order to better control the morphology and size of lanthanum oxide; preferably, the alcohol is a C1-C4 monohydric alcohol and / or a C1-C4 dihydric alcohol, more preferably at least one of methanol, ethanol and propylene glycol.

[0023] According to the present invention, preferably, the mass fraction of alcohol in the alcohol aqueous solution is 20-50 wt %, more preferably 25-30 wt %.

[0024] According to the present invention, preferably, the weight ratio of lanthanum precursor: urea: water: alcohol in the mixed solution is (2-10): (3-15): (200-400): (40-100), more preferably (2-6); (6-12): (210-300): (40-100).

[0025] According to the present invention, preferably, the weight ratio of the lanthanum precursor to urea in the mixed solution is 1:0.5-5 (for example, 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, and a range consisting of any two of the above points), and more preferably 1:1.5-3.

[0026] According to the present invention, preferably, the weight ratio of the lanthanum precursor to the alcohol aqueous solution in the mixed solution is 1:40-120 (for example, 1:40, 1:50, 1:60, 1:70, 1:80, 1:90, 1:100, 1:110, 1:120, and a range consisting of any two of the above points), more preferably 1:50-100.

[0027] According to the present invention, preferably, an alkali solution is used to adjust the pH value of the mixed solution, and the alkali solution is aqueous ammonia; more preferably, the mass fraction of aqueous ammonia is 20-36wt%.

[0028] According to the present invention, preferably, the method further comprises: standing the reaction solution obtained after the reaction for a period of time, and then performing separation and roasting steps. More preferably, the standing temperature is 15-40°C and the time is 12-100 hours.

[0029] According to the present invention, preferably, the temperature of the first calcination is 750-850°C and the time is 2-10 hours. The atmosphere of the first calcination can be an air atmosphere or an inert atmosphere, and the gas providing the inert atmosphere can be selected from at least one of nitrogen, helium, neon, argon, krypton or xenon, preferably nitrogen.

[0030] According to the present invention, preferably, the method further comprises: before the first roasting, subjecting the separated solid to a first drying, and the conditions for the first drying include: a temperature of 80-120° C. and a time of 10-24 h.

[0031] According to the present invention, preferably, the method further comprises: washing the separated solid with water and alcohol (ethanol) in sequence, and then performing a first drying. The number of water washings may be 2-4 times, and the number of alcohol washings may be 1-2 times.

[0032] According to the present invention, in order to improve the catalytic performance of the catalyst, preferably, the method further comprises: modifying the first calcined product with a modifying element; wherein the modifying element comprises at least one element selected from the group consisting of sodium, potassium, magnesium, calcium, strontium, barium, titanium, iron, boron and cerium.

[0033] According to the present invention, preferably, the molar ratio of the modifying element to the lanthanum element in the first calcined product is 1:1-30 (for example, 1:1, 1:5, 1:10, 1:15, 1:20, 1:22, 1:24, 1:26, 1:28, 1:30, and a range consisting of any two of the above points), and more preferably 1:12-25.

[0034] According to the present invention, preferably, the modification method is: using a solution containing a modifying element precursor to impregnate the product of the first calcination, and then performing a second calcination.

[0035] According to the present invention, preferably, the content of the modifying element precursor in the solution containing the modifying element precursor is 0.001-0.1 wt %, more preferably 0.009-0.012 wt %.

[0036] According to the present invention, preferably, the impregnation can be equal volume impregnation, excess impregnation, etc., preferably equal volume impregnation.

[0037] According to the present invention, preferably, the second calcination conditions include: heating to 650-750°C at 10-20°C / min, and then maintaining the temperature for 2-10 hours. More preferably, the second calcination atmosphere is air atmosphere.

[0038] According to the present invention, preferably, the modification method further comprises: performing a second drying before the second calcination, the second drying temperature is 80-100° C., and the time is 2-12 hours.

[0039] The third aspect of the present invention provides lanthanum oxide prepared by the method described above.

[0040] A fourth aspect of the present invention provides the use of the above-mentioned lanthanum oxide in the oxidative coupling reaction of methane to produce C2 and higher hydrocarbons.

[0041] A fifth aspect of the present invention provides a method for preparing hydrocarbons having two or more carbon atoms from methane, characterized in that the method comprises: in the presence of oxygen and under the conditions of methane oxidative coupling reaction, contacting methane with the above-mentioned lanthanum oxide for reaction;

[0042] Alternatively, lanthanum oxide is prepared according to the method described above, and then methane is contacted with the obtained lanthanum oxide in the presence of oxygen and under the conditions of methane oxidative coupling reaction.

[0043] According to the present invention, preferably, the molar ratio of the methane to the oxygen (hereinafter referred to as the alkoxygen ratio) is 3-10:1.

[0044] According to the present invention, preferably, the temperature of the contact reaction is 700-850°C.

[0045] According to the present invention, preferably, the space velocity calculated as methane is 10000-150000 mL / (g·h).

[0046] According to a particularly preferred embodiment of the present invention, the method for preparing lanthanum oxide comprises: adding 4-4.5g of lanthanum nitrate hexahydrate and 6-6.5g of urea to 290-300g of ethanol aqueous solution (ethanol content in the ethanol aqueous solution is 28-30wt%), stirring to completely dissolve, adding ammonia water to adjust the pH to 7.8-8, and then transferring to a water bath at 85-90°C and 350-400rpm for 2-2.5h, and then standing at room temperature for 50-55h, the solid and liquid are centrifuged, washed with water and ethanol, dried at 80-90°C for 12-14h, and calcined at 800-810°C for 2-3h under a nitrogen atmosphere.

[0047] The present invention will be described in detail below by way of examples. In the following examples,

[0048] The room temperature is about 20-25℃.

[0049] The concentration of the ammonia water was 25 wt %.

[0050] The calculation method of methane conversion rate is as follows:

[0051] Methane conversion rate = amount of methane consumed in the reaction / initial amount of methane × 100%.

[0052] The ethylene selectivity is calculated as follows:

[0053] Ethylene selectivity = amount of methane consumed by produced ethylene / total methane consumption x 100%.

[0054] The ethane selectivity is calculated as follows:

[0055] Ethane selectivity = amount of methane consumed by produced ethane / total methane consumption x 100%.

[0056] The selectivity of C2 and above hydrocarbons includes the sum of ethylene, ethane, propylene, propane and higher carbon hydrocarbons.

[0057] Example 1

[0058] 6g of lanthanum nitrate hexahydrate and 10g of urea were added to 300g of ethanol aqueous solution (ethanol content in ethanol aqueous solution was 25wt%), stirred to completely dissolve, ammonia water was added to adjust the pH to 7.5, and then transferred to a water bath at 80°C and 250rpm for 10h, and then allowed to stand overnight at room temperature (about 12h), the solid and liquid were centrifuged, washed three times with water, washed once with ethanol, placed in an oven, dried at 120°C for 12h, moved to a muffle furnace, and calcined at 750°C for 2h under a nitrogen atmosphere. The lanthanum oxide catalyst cat1 was prepared, and the scanning electron microscope image of the lanthanum oxide catalyst is shown as follows: Figure 1 As shown by Figure 1 It can be seen that the lanthanum oxide catalyst contains spherical lanthanum oxide and flake lanthanum oxide.

[0059] Example 2

[0060] 4g of lanthanum nitrate hexahydrate and 6g of urea were added to 300g of ethanol aqueous solution (ethanol content in ethanol aqueous solution was 30wt%), stirred to completely dissolve, ammonia water was added to adjust the pH to 8, and then transferred to a water bath at 90°C and 400rpm for 2h, and then allowed to stand at room temperature for 50h, the solid and liquid were centrifuged, washed three times with water, washed once with ethanol, placed in an oven, dried at 80°C for 12h, moved to a muffle furnace, and calcined at 800°C for 2h under a nitrogen atmosphere. Lanthanum oxide catalyst cat2 was prepared.

[0061] Example 3

[0062] 0.1 g of magnesium nitrate was dissolved in 10 mL of deionized water, 5 g of lanthanum oxide prepared in Example 1 was weighed, and the magnesium nitrate solution was added dropwise on the surface of the lanthanum oxide, stirred at 80 ° C for 12 h until dry, and then transferred to a muffle furnace, and heated to 750 ° C at 15 ° C / min in an air atmosphere, and maintained for 5 h to obtain the modified lanthanum oxide catalyst cat3.

[0063] Example 4

[0064] The procedure described in Example 3 was followed except that magnesium nitrate was replaced by an equimolar amount of titanium chloride.

[0065] Example 5

[0066] The method of Example 1 was followed, except that ethanol was replaced with an equal weight of propylene glycol.

[0067] Example 6

[0068] The method of Example 1 was followed, except that ethanol was replaced with an equal weight of n-octanol.

[0069] Example 7

[0070] The method of Example 1 was followed, except that the ethanol content in the ethanol aqueous solution was 50 wt %.

[0071] Comparative Example 1

[0072] The method of Example 1 was followed, except that no urea was added. The product obtained was in the form of flakes.

[0073] Comparative Example 2

[0074] The method of Example 1 was followed, except that the ethanol aqueous solution was replaced by an equal weight of water. The product obtained was in the form of flakes.

[0075] Comparative Example 3

[0076] The method of Example 1 was followed, except that "transfer to a water bath at 80°C and 250 rpm for 10 h" was replaced by "transfer to a hydrothermal kettle and maintain at 180°C for 10 h". The product obtained was in the form of flakes.

[0077] Test Example 1

[0078] The specific surface area, pore volume, average pore size, diameter of spherical lanthanum oxide, thickness, length and width of flake lanthanum oxide, and mass ratio of spherical and flake lanthanum oxide of the above catalyst were tested. The test results are shown in Table 1.

[0079] The test method for the specific surface area, pore volume and average pore size of the catalyst is as follows: weigh 2000 mg of sample and put it into a sample tube, put the sample tube into the instrument degassing station for degassing, the degassing condition is 350 degrees for 4 hours, and after naturally cooling to room temperature, put the sample tube into the instrument analysis station for analysis, and perform a full analysis of the nitrogen adsorption and desorption isotherm at liquid nitrogen temperature. The specific surface area of ​​the sample is calculated by the BET (Brunauer, Emmett, Teller) method, and the pore volume and average pore size of the sample are calculated according to the desorption (adsorption) branch by the BJH (Barret, Joyner, Halenda) method. Instrument model: fully automatic physical adsorption instrument ASAP2420, Mack Instrument Company, USA.

[0080] The method for testing the diameter of spherical lanthanum oxide is: take 6-8 spherical lanthanum oxides in the field of view, use the software provided by the SEM software to measure the diameter, and take the average value.

[0081] The testing method for the thickness, length and width of the flaky lanthanum oxide is as follows: take 6-8 flaky lanthanum oxides in the field of view, use the software provided by the SEM software to measure the thickness, length and width of the flakes, and take the average value.

[0082] Table 1

[0083]

[0084]

[0085] Test Example 2

[0086] After the catalyst tablets were sieved through 40-60 mesh, 200 mg was weighed and loaded into a quartz tube fixed bed reactor with an inner diameter of 8 mm, and methane and oxygen were introduced. The methane space velocity was 40000 mL / (g·h), the alkoxy ratio was 3, and the reaction temperature was 750°C. The analysis of the reaction product components was carried out on a gas chromatograph model 7890A purchased from Agilent. The methane conversion rate and the selectivity of C2 and above hydrocarbons were calculated based on the composition of the product. The results are shown in Table 2.

[0087] Table 2

[0088] Methane conversion rate (%) Selectivity of C2 and above hydrocarbons (%) Example 1 34 47.4 Example 2 35.6 49.8 Example 3 34.7 48.2 Example 4 34.5 48.5 Example 5 34.6 47.9 Example 6 33.9 46.8 Example 7 34.1 40.3 Comparative Example 1 32.1 35.6 Comparative Example 2 26.7 33.6 Comparative Example 3 29.3 34.2

[0089] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A lanthanum oxide, characterized in that The lanthanum oxide comprises spherical lanthanum oxide and flake lanthanum oxide, wherein the average diameter of the spherical lanthanum oxide is 0.1-1 μm, and the average thickness of the flake lanthanum oxide is 100-200 nm.

2. The lanthanum oxide according to claim 1, wherein The average length of the flake lanthanum oxide is 0.4-1 μm, and the average width is 0.2-0.5 μm.

3. The lanthanum oxide according to claim 1, wherein The specific surface area of ​​the lanthanum oxide is 10-20m 2 / g, pore volume is 0.1-0.2cm 3 / g, and the average pore size is 50-150 angstroms.

4. The lanthanum oxide according to claim 1, wherein The lanthanum oxide further comprises a modifying element, wherein the modifying element comprises at least one element selected from the group consisting of sodium, potassium, magnesium, calcium, strontium, barium, titanium, iron, boron and cerium; Preferably, the molar ratio of the modifying element to the lanthanum element in lanthanum oxide is 1:1-30, preferably 1:12-25.

5. A method for preparing lanthanum oxide, characterized in that: The method comprises: mixing a lanthanum precursor and an aqueous solution of urea and alcohol to obtain a mixed solution, adding an alkali solution to adjust the pH value of the mixed solution to 7.5-8, then reacting at 80-100°C for 2-12h, and then separating and first calcining.

6. The method according to claim 5, wherein: The lanthanum precursor is a water-soluble salt of lanthanum, preferably lanthanum nitrate; And / or, the alcohol is a C1-C4 monohydric alcohol and / or a C1-C4 dihydric alcohol, preferably at least one of methanol, ethanol and propylene glycol; more preferably, the mass fraction of the alcohol in the aqueous solution of the alcohol is 20-50wt%; and / or, the weight ratio of lanthanum precursor: urea: water: alcohol in the mixed solution is (2-10): (3-15): (200-400): (40-100), preferably (2-6); (6-12)：(210-300)：(40-100)。 7. The method according to claim 5, wherein: The pH value of the mixed solution is adjusted by using an alkali solution, wherein the alkali solution is aqueous ammonia; preferably, the mass fraction of aqueous ammonia is 20-36wt%.

8. The method according to claim 5, wherein: The temperature of the first calcination is 750-850° C., and the time is 2-10 hours.

9. The method according to claim 5, wherein: The method further comprises: modifying the first calcined product with a modifying element; wherein the modifying element comprises at least one element selected from the group consisting of sodium, potassium, magnesium, calcium, strontium, barium, titanium, iron, boron and cerium; Preferably, the molar ratio of the modifying element to the lanthanum element in the first calcined product is 1:1-30, preferably 1:12-25.

10. The method according to claim 9, wherein: The modification method is: impregnating the product of the first calcination with a solution containing a precursor of a modification element, and then performing a second calcination; Preferably, the second calcination conditions include: heating to 650-750° C. at a rate of 10-20° C. / min, and then maintaining the temperature for 2-10 h.

11. Lanthanum oxide prepared by the method according to any one of claims 5 to 10.

12. Use of the lanthanum oxide described in any one of claims 1 to 4 and 11 in the oxidative coupling reaction of methane to produce C2 or higher hydrocarbons.

13. A method for preparing hydrocarbons with carbon content of two or more carbon atoms from methane, characterized in that: The method comprises: in the presence of oxygen and under the conditions of methane oxidative coupling reaction, contacting methane with the lanthanum oxide described in any one of claims 1 to 4 and 11 for reaction; Alternatively, lanthanum oxide is prepared according to the method described in any one of claims 5 to 10, and then methane is contacted with the obtained lanthanum oxide to react in the presence of oxygen and under the conditions of methane oxidative coupling reaction.

14. The method according to claim 13, wherein: The molar ratio of the methane to the oxygen is 3-10:1; And / or, the temperature of the contact reaction is 700-850°C; And / or, the space velocity calculated in terms of methane is 10000-150000 mL / (g·h).

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