Flaky lanthanum oxide catalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of lanthanum oxide, and discloses a flaky lanthanum oxide catalyst and a preparation method and application thereof.The flaky lanthanum oxide catalyst comprises flaky lanthanum oxide formed by rod-shaped lanthanum oxide in a self-assembly mode, and the average thickness of the flaky lanthanum oxide is 100-500 nm. The preparation method of the lanthanum oxide catalyst comprises the following steps: mixing a lanthanum precursor and an aqueous solution of urea and alcohol to obtain a mixed solution, adjusting the pH value of the mixed solution to 8.5-9 by adopting a first alkali solution, then adjusting the pH value of the mixed solution to 10-13 by adopting a second alkali solution, and then sequentially carrying out reaction, separation and first roasting. The lanthanum oxide catalyst provided by the invention is easy to form, has relatively high forming strength, and has relatively high methane conversion rate and C2 and above hydrocarbon selectivity when being used for a methane oxidative coupling reaction.

Description

Technical Field

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

[0002] Rare earth oxides are key building blocks for the preparation of high-tech materials, including rare earth magnetic materials, luminescent materials, hydrogen storage materials, crystalline materials, and catalytic materials. With the continuous expansion of rare earth applications and their potential applications, high-tech materials are placing increasingly stringent quality demands on rare earth oxides, shifting towards controlling physical properties such as particle size, purity, morphology, and specific surface area. Lanthanum oxide, one of the key rare earth oxide compounds, is widely used in catalysis, luminescent materials, magnetic materials, and other fields due to its strong ability to gain or lose electrons and its propensity to undergo redox reactions. Studies have found that lanthanum oxide and its composite catalysts with alkaline earth metals exhibit high catalytic activity and selectivity for the oxidative coupling of methane and exhibit excellent stability at high temperatures. CN109663587 reports the preparation of a nanoflower-shaped lanthanum oxide catalyst. Fern-shaped La2O3 nanostructures as potential scaffolds for efficient hydroquinone chemicals in applications. Ceramics International 2020, 46(4), 5141-5148. A fern-shaped nano-lanthanum oxide was reported. The obtained lanthanum oxide material showed a 3D fern-like structure with dendritic arms of different lengths and a triangular outline. The dendritic arms were connected to a long common trunk in a beaded shape and were evenly arranged along the central trunk. This material was used in an electrochemical sensor for hydroquinone. The above-mentioned lanthanum oxide has the disadvantages of poor catalytic performance and low molding strength when used for methane oxidative coupling. Summary of the Invention

[0003] The purpose of the present invention is to overcome the problem of low molding strength of lanthanum oxide powder in the prior art and to provide a flaky lanthanum oxide catalyst and a preparation method and application thereof.

[0004] To achieve the above objectives, the present invention provides a lanthanum oxide catalyst in a first aspect. The lanthanum oxide catalyst comprises sheet-like lanthanum oxide formed by self-assembly of rod-like lanthanum oxide, wherein the average thickness of the sheet-like lanthanum oxide is 100-500 nm.

[0005] A second aspect of the present invention provides a method for preparing a lanthanum oxide catalyst, the method comprising: mixing a lanthanum precursor and an aqueous solution of urea and alcohol to obtain a mixed solution, adjusting the pH value of the mixed solution to 8.5-9 using a first alkaline solution, then adjusting the pH value of the mixed solution to 10-13 using a second alkaline solution, and then sequentially performing a reaction, separation, and a first calcination.

[0006] The present invention uses different alkaline solutions to adjust the pH value of the mixed solution in two steps, and then reacts. During the reaction, small rod-shaped lanthanum oxide particles can be formed, and the rod-shaped lanthanum oxide particles can self-assemble to form flaky lanthanum oxide. The flaky lanthanum oxide prepared by the present invention is conducive to molding, and the strength of the particles after molding is relatively high. This may be because the interaction between the flaky lanthanum oxide particles formed by the self-assembly of the rod-shaped lanthanum oxide is enhanced, resulting in a higher strength of the lanthanum oxide after molding. The lanthanum oxide of the present invention has a higher molding strength, which greatly reduces the risk of catalyst particle pulverization during the methane oxidative coupling process, resulting in catalyst loss and clogging of the reactor.

[0007] The third aspect of the present invention provides a lanthanum oxide catalyst prepared by the method described above.

[0008] A fourth aspect of the present invention provides the use of the above-mentioned lanthanum oxide catalyst in the oxidative coupling reaction of methane to produce C2 and higher hydrocarbons.

[0009] A fifth aspect of the present invention provides a method for preparing C2 or higher hydrocarbons from methane, the method comprising: contacting methane with the above-mentioned lanthanum oxide catalyst in the presence of oxygen and under methane oxidative coupling reaction conditions;

[0010] Alternatively, the lanthanum oxide catalyst is prepared according to the method described above, and then methane is contacted with the obtained lanthanum oxide catalyst in the presence of oxygen and under the conditions of methane oxidative coupling reaction.

[0011] The technical solution of the present invention can achieve the following beneficial effects:

[0012] The lanthanum oxide catalyst provided by the present invention is easy to shape and has high molding strength. When used in the methane oxidative coupling reaction, it has a high methane conversion rate and selectivity for C2 and higher hydrocarbons.

[0013] The present invention prepares flaky lanthanum oxide with a specific thickness by adjusting the pH value of a mixed solution of a lanthanum precursor, urea, alcohol and water in a two-step method, and the flaky lanthanum oxide is loaded with rod-shaped lanthanum oxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a scanning electron microscope image of the lanthanum oxide catalyst prepared in Example 1;

[0015] Figure 2 This is a scanning electron microscope image of the lanthanum oxide catalyst prepared in Example 1. DETAILED DESCRIPTION

[0016] The endpoints of the ranges and any values ​​disclosed herein 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 endpoints of each range, the endpoints of each range and 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 to be specifically disclosed herein.

[0017] A first aspect of the present invention provides a lanthanum oxide catalyst, which comprises sheet-like lanthanum oxide formed by self-assembly of rod-like lanthanum oxide, wherein the average thickness of the sheet-like lanthanum oxide is 100-500 nm.

[0018] According to the present invention, preferably, the average thickness of the flaky lanthanum oxide is 200-250 nm.

[0019] According to the present invention, preferably, the average length of the flaky lanthanum oxide is 2-10 μm, more preferably 5-10 μm, and even more preferably 4-5 μm.

[0020] According to the present invention, preferably, the average width of the flaky lanthanum oxide is 1-5 μm, preferably 1-3 μm.

[0021] According to the present invention, preferably, the rod-shaped lanthanum oxide has a length of 100-300 nm and a width of 10-30 nm.

[0022] According to the present invention, preferably, the lanthanum oxide catalyst further comprises a modifying element, and the modifying element is cerium.

[0023] According to the present invention, preferably, the molar ratio of the modifying element to the lanthanum element in the lanthanum oxide catalyst is 1:1-10, more preferably 1:3-10. In the present invention, the molar ratio of the lanthanum element in the lanthanum oxide catalyst to the modifying element is calculated based on the feed amount of the raw materials.

[0024] In the present invention, unless otherwise indicated, the thickness, length, and width described herein are measured using a scanning electron microscope. The dimensional testing method for flaky lanthanum oxide materials is as follows: 6-8 samples within the field of view are selected and the length, width, and thickness are measured using the scanning electron microscope's built-in measuring instrument. The average length, width, and thickness of the 6-8 samples within the field of view are then calculated. The length and width of rod-shaped lanthanum oxide are measured using the scanning electron microscope's built-in measuring instrument.

[0025] A second aspect of the present invention provides a method for preparing a lanthanum oxide catalyst, the method comprising: mixing a lanthanum precursor and an aqueous solution of urea and alcohol to obtain a mixed solution, adjusting the pH value of the mixed solution to 8.5-9 using a first alkaline solution, then adjusting the pH value of the mixed solution to 10-13 using a second alkaline solution, and then sequentially performing a reaction, separation, and a first calcination.

[0026] According to the present invention, the lanthanum precursor can be a substance containing lanthanum element conventionally used in the art. Preferably, the lanthanum precursor is a water-soluble salt of lanthanum (such as nitrate, chloride, etc.), preferably lanthanum nitrate.

[0027] According to the present invention, the alcohol is preferably a C1-C4 alcohol, more preferably a C1-C4 monohydric alcohol and / or a C1-C4 dihydric alcohol, and further preferably at least one of methanol, ethanol, propylene glycol, ethylene glycol, and glycerol. Limiting the type of alcohol in the mixed solution to the above range can further improve the molding strength of the lanthanum oxide catalyst.

[0028] According to the present invention, preferably, the mass fraction of alcohol in the alcohol aqueous solution is 10-60 wt%, more preferably 40-55 wt%.

[0029] According to the present invention, in order to further improve the molding strength of the lanthanum oxide catalyst, preferably, the weight ratio of the lanthanum precursor: urea: alcohol aqueous solution is (1-10): (20-50): (100-500), more preferably (1.5-5): (25-50): (150-400).

[0030] According to the present invention, preferably, the weight ratio of the lanthanum precursor to urea is 1:5-40 (for example, 1:5, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, and a range consisting of any two of the above points), more preferably 1:10-25.

[0031] According to the present invention, preferably, the weight ratio of the lanthanum precursor to the alcohol aqueous solution is 1:50-250 (for example, 1:50, 1:60, 1:70, 1:80, 1:90, 1:100, 1:110, 1:120, 1:140, 1:150, 1:180, 1:200, 1:250, and the range composed of any two of the above points), more preferably 1:60-200.

[0032] According to the present invention, preferably, the first alkali solution is aqueous ammonia, and more preferably, the mass fraction of aqueous ammonia is 20-30 wt%.

[0033] According to the present invention, preferably, the second alkali solution is a sodium hydroxide aqueous solution, and more preferably, the concentration of the sodium hydroxide aqueous solution is 3-5 mol / L.

[0034] According to the present invention, preferably, the reaction method includes water bath reaction and / or hydrothermal reaction. That is, the reaction of the present invention can be carried out in a water bath or in a hydrothermal reactor, as long as the reaction temperature and reaction time are met.

[0035] According to the present invention, the reaction is preferably carried out in a water bath. The reaction pressure is typically atmospheric pressure. More preferably, the reaction conditions include a temperature of 40-100°C and a time of 1-10 hours. Further preferably, the reaction is carried out with stirring at a speed of 100-500 rpm.

[0036] According to the present invention, preferably, the conditions of the hydrothermal reaction include: reaction temperature of 80-180° C. and reaction time of 12-24 h.

[0037] According to the present invention, preferably, the method further comprises: standing the reaction solution obtained at 60-80° C. for 10-50 h (e.g., 10 h, 20 h, 30 h, 40 h, 50 h, and a range consisting of any two of the above points).

[0038] According to the present invention, preferably, the conditions for the first calcination include: heating to 700-800° C. at a rate of 2-10° C. / min, and then maintaining the temperature for 2-10 h.

[0039] According to the present invention, preferably, the atmosphere of the first calcination is air or nitrogen, more preferably air.

[0040] According to the present invention, preferably, the method further comprises: before roasting, subjecting the separated solid to a first drying process, wherein the conditions for the first drying process include: a temperature of 80-120° C. and a time of 12-100 h.

[0041] 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.

[0042] According to the present invention, in order to further improve the molding strength and catalytic performance of the lanthanum oxide catalyst, preferably, the method further comprises: modifying the first calcined product with a modifying element; wherein the modifying element is cerium.

[0043] According to the present invention, preferably, the molar ratio of the modifying element to the lanthanum element in the first calcined product is 1:1-10, more preferably 1:3-10.

[0044] According to the present invention, preferably, the modification method is: impregnating the product of the first calcination with a solution containing a modifying element precursor, and then performing a second calcination.

[0045] According to the present invention, preferably, the modifying element precursor is a cerium salt (such as cerium nitrate, chloride, sulfate, etc.), more preferably cerium nitrate.

[0046] According to the present invention, preferably, the impregnation can be equal volume impregnation, excess impregnation, etc., more preferably equal volume impregnation.

[0047] According to the present invention, preferably, the second calcination conditions include: heating to 650-750° C. at a rate of 5-10° C. / min, and then maintaining the temperature for 2-5 hours.

[0048] According to the present invention, preferably, the atmosphere of the second calcination is air or nitrogen, more preferably air.

[0049] According to the present invention, preferably, the modification method further comprises: performing a second drying before calcination, wherein the second drying temperature is 80-120° C. and the time is 4-24 hours.

[0050] XRD characterization shows that the lanthanum oxide catalyst of the present invention has characteristic peaks of lanthanum oxide and is lanthanum oxide.

[0051] The third aspect of the present invention provides a lanthanum oxide catalyst prepared by the method described above.

[0052] A fourth aspect of the present invention provides the use of the above-mentioned lanthanum oxide catalyst in the oxidative coupling reaction of methane to produce C2 and higher hydrocarbons.

[0053] A fifth aspect of the present invention provides a method for preparing C2 or higher hydrocarbons from methane, the method comprising: contacting methane with the above-mentioned lanthanum oxide catalyst in the presence of oxygen and under methane oxidative coupling reaction conditions;

[0054] Alternatively, the lanthanum oxide catalyst is prepared according to the method described above, and then methane is contacted with the obtained lanthanum oxide catalyst in the presence of oxygen and under the conditions of methane oxidative coupling reaction.

[0055] According to the present invention, preferably, the molar ratio of the methane to the oxygen (hereinafter referred to as the alkoxygen ratio) is 6-12:1.

[0056] According to the present invention, preferably, the temperature of the contact reaction is 600-750°C.

[0057] According to the present invention, preferably, the space velocity of methane is 600,000-180,000 mL / (g·h).

[0058] According to a particularly preferred embodiment of the present invention, the method for preparing a lanthanum oxide catalyst comprises:

[0059] (1) Weighing 2.5-3 g of lanthanum nitrate hexahydrate and 40-42 g of urea, adding them to 150-200 g of ethanol aqueous solution (ethanol content in the ethanol aqueous solution is 40-45 wt%), stirring to completely dissolve, adding ammonia water to adjust the pH to 8.9-9, and then adding sodium hydroxide solution (3-3.5 mol / L) dropwise to continue adjusting the pH to 12-12.5; then transferring to a water bath, stirring at 60-70° C. and 400-500 rpm for 2-3 h, and standing at 75-80° C. for 45-50 h to obtain a suspension; centrifuging the suspension, washing with water and ethanol, and drying the solid at 100-120° C. for 12-14 h; and calcining at 740-750° C. at 4-5° C. / min under a nitrogen atmosphere for 5-6 h to obtain a lanthanum oxide catalyst.

[0060] (2) Accurately weigh 0.5-0.6 g of cerium nitrate and dissolve it in 5-10 g of deionized water, stirring to completely dissolve it, adding the cerium nitrate solution dropwise to 2-2.5 g of the lanthanum oxide catalyst obtained in step (1), stirring at 80-90° C. to allow the solvent to evaporate completely, drying at 120-140° C. for 24-26 h, and then heating to 720-750° C. at 4.5-5° C. / min in an air atmosphere and maintaining it for 4.5-5 h to prepare a cerium-modified lanthanum oxide catalyst.

[0061] According to a particularly preferred embodiment of the present invention, the method for preparing a lanthanum oxide catalyst comprises: weighing 2.5-3g of lanthanum nitrate hexahydrate and 40-42g of urea, adding them to 150-200g of propylene glycol aqueous solution (propylene glycol content in the propylene glycol aqueous solution is 40-45wt%), stirring to completely dissolve them, adding ammonia water to adjust the pH to 8.9-9, and then adding sodium hydroxide solution (3-3.5mol / L) dropwise to continue adjusting the pH to 12-12.5; then transferring to a water bath and stirring at 60-70°C and 400-500rpm for 2-3h, and standing at 75-80°C for 45-50h to obtain a suspension; centrifuging the suspension, washing with water and ethanol, and drying the solid at 100-120°C for 12-14h; and calcining at 740-750°C at 4-5°C / min under a nitrogen atmosphere for 5-6h.

[0062] The present invention will be described in detail below by way of examples.

[0063] The mass fraction of ammonia water is 25wt%.

[0064] The methane conversion rate is calculated as follows:

[0065] Methane conversion rate = amount of methane consumed in the reaction / initial amount of methane × 100%.

[0066] The ethylene selectivity is calculated as follows:

[0067] Ethylene selectivity = amount of methane consumed by produced ethylene / total methane consumption × 100%.

[0068] The ethane selectivity is calculated as follows:

[0069] Ethane selectivity = amount of methane consumed by produced ethane / total methane consumption × 100%.

[0070] The selectivity of C2 and higher hydrocarbons includes the sum of ethylene, ethane, propylene, propane and higher hydrocarbons.

[0071] Example 1

[0072] Weigh 2.5g of lanthanum nitrate hexahydrate and 42g of urea and add them to 150g of ethanol aqueous solution (ethanol content in ethanol aqueous solution is 45wt%), stir to completely dissolve, add ammonia water to adjust the pH to 8.9, then add sodium hydroxide solution (3mol / L) dropwise to continue adjusting the pH to 12; then transfer to a water bath and keep stirring at 60℃ and 400rpm for 2h, and let it stand at 80℃ for 50h to obtain a suspension; centrifuge the suspension, wash it three times with water, wash it once with ethanol, place it in an oven, and dry it at 120℃ for 12h; move it to a muffle furnace, and in a nitrogen atmosphere, heat it to 750℃ at 5℃ / min and calcine it for 5h. The lanthanum oxide catalyst cat1 was prepared, and the scanning electron micrograph of the lanthanum oxide catalyst (electron microscope images at different magnifications) is shown as follows: Figure 1-2 As shown in the scanning electron micrograph, the lanthanum oxide catalyst has a flaky structure, and the flaky structure is formed by self-assembly of rod-shaped lanthanum oxide particles; the length of the rod-shaped lanthanum oxide is in the range of 100-200 nm, and the length of the rod-shaped lanthanum oxide is in the range of 10-20 nm.

[0073] Example 2

[0074] 2g of lanthanum nitrate hexahydrate and 25g of urea were weighed and added to 300g of an aqueous ethanol solution (50wt% ethanol), stirred until completely dissolved, and then ammonia was added to adjust the pH to 8.5. Then, sodium hydroxide solution (3mol / L) was added dropwise to further adjust the pH to 13. The mixture was then transferred to a water bath and stirred at 40°C and 250rpm for 5 hours, followed by 20 hours at 85°C to obtain a suspension. The suspension was centrifuged, washed three times with water and once with ethanol, and dried in an oven at 80°C for 12 hours. The mixture was then transferred to a muffle furnace and calcined at 700°C under a nitrogen atmosphere at a rate of 2°C / min for 10 hours. This yielded the lanthanum oxide catalyst Cat2.

[0075] The lanthanum oxide catalyst prepared in Example 2 has a similar morphology to that of Example 1, with the length of the rod-shaped lanthanum oxide being in the range of 100-200 nm and the length of the rod-shaped lanthanum oxide being in the range of 10-20 nm.

[0076] Example 3

[0077] 5g of lanthanum nitrate hexahydrate and 45g of urea were weighed and added to 400g of an aqueous ethanol solution (53wt% ethanol content). The mixture was stirred until completely dissolved, and aqueous ammonia was added to adjust the pH to 8.5. Then, sodium hydroxide solution (5mol / L) was added dropwise to further adjust the pH to 11. The mixture was then transferred to a water bath with stirring at 40°C and 200rpm for 5 hours, and then allowed to stand at 80°C for 20 hours to obtain a suspension. The suspension was centrifuged, washed three times with water and once with ethanol, dried in an oven at 80°C for 12 hours, and then transferred to a muffle furnace and calcined at 700°C under a nitrogen atmosphere at a rate of 4°C / min for 10 hours. This yielded the lanthanum oxide catalyst Cat3.

[0078] The lanthanum oxide catalyst prepared in Example 3 has a similar morphology to that of Example 1. The length of the rod-shaped lanthanum oxide is in the range of 100-200 nm, and the length of the rod-shaped lanthanum oxide is in the range of 10-20 nm.

[0079] Example 4

[0080] Accurately weigh 0.5 g of cerium nitrate and dissolve it in 5 g of deionized water, stir to completely dissolve it, add the cerium nitrate solution dropwise to 2 g of the lanthanum oxide catalyst prepared in Example 1, stir evenly, stir at 80°C to allow the solvent to evaporate completely, place in a muffle furnace at 120°C for 24 h, and heat to 750°C at 5°C / min in an air atmosphere and hold for 5 h to prepare a cerium-modified lanthanum oxide catalyst cat4.

[0081] The lanthanum oxide catalyst prepared in Example 4 has a similar morphology to that of Example 1, with the length of the rod-shaped lanthanum oxide being in the range of 100-200 nm and the length of the rod-shaped lanthanum oxide being in the range of 10-20 nm.

[0082] Example 5

[0083] The method of Example 1 was followed, except that the ethanol in the ethanol aqueous solution was replaced by an equal weight of propylene glycol.

[0084] The lanthanum oxide catalyst prepared in Example 5 has a similar morphology to that of Example 1, with the length of the rod-shaped lanthanum oxide being in the range of 100-200 nm and the length of the rod-shaped lanthanum oxide being in the range of 10-20 nm.

[0085] Example 6

[0086] The method of Example 1 was followed, except that the ethanol in the ethanol aqueous solution was replaced by an equal weight of n-octanol.

[0087] The lanthanum oxide catalyst prepared in Example 6 has a similar morphology to that of Example 1. The length of the rod-shaped lanthanum oxide is in the range of 100-200 nm, and the length of the rod-shaped lanthanum oxide is in the range of 10-20 nm.

[0088] Example 7

[0089] The method of Example 1 was followed, except that the ethanol content in the ethanol aqueous solution was 10 wt %.

[0090] The lanthanum oxide catalyst prepared in Example 7 has a similar morphology to that of Example 1, with the length of the rod-shaped lanthanum oxide being in the range of 100-200 nm and the length of the rod-shaped lanthanum oxide being in the range of 10-20 nm.

[0091] Example 8

[0092] The method of Example 1 was followed, except that “transfer to a water bath and stir at 60°C and 400 rpm for 2 h” was replaced by “transfer to a hydrothermal autoclave and maintain at 120°C for 12 h”.

[0093] The lanthanum oxide catalyst prepared in Example 8 has a similar morphology to that of Example 1, with the length of the rod-shaped lanthanum oxide being in the range of 100-200 nm and the length of the rod-shaped lanthanum oxide being in the range of 10-20 nm.

[0094] Comparative Example 1

[0095] The method of Example 1 was followed, except that urea was replaced by an equal weight of ethanol.

[0096] Scanning electron microscopy observation of the lanthanum oxide catalyst prepared in Comparative Example 1 revealed no flake lanthanum oxide formed by self-assembly of rod-shaped lanthanum oxide particles.

[0097] Comparative Example 2

[0098] The method of Example 1 was followed, except that the "ethanol aqueous solution" was replaced with an equal weight of "water".

[0099] Scanning electron microscopy observation of the lanthanum oxide catalyst prepared in Comparative Example 2 revealed no flake lanthanum oxide formed by self-assembly of rod-shaped lanthanum oxide particles.

[0100] Test Example 1

[0101] The dimensional testing method for lanthanum oxide flakes is to select 6-8 samples within the field of view and measure their length, width, and thickness using the measuring instrument included in the scanning electron microscope. The average length, width, and thickness of the 6-8 samples within the field of view are then calculated. The test results are shown in Table 1.

[0102] Table 1

[0103]

[0104]

[0105] Test Example 2

[0106] (1) Testing Method for Molding Strength: The lanthanum oxide materials of the above-described embodiments and comparative examples were filled into a mold, and then the mold was placed in a tablet press for tableting. The pressure of the tablet press was controlled to increase uniformly to 20 kN to obtain tablets of lanthanum oxide material having a diameter of 4 mm and a thickness of 5-6 mm. The tablets were then placed in a strength tester for strength testing to test the radial mechanical strength of the formed lanthanum oxide material (radial crushing strength, i.e., the pressure applied by the strength tester when the tablets were broken). The test results are shown in Table 2.

[0107] (2) The catalyst formed into tablets in step (1) was loaded into a quartz tube fixed-bed reactor with an inner diameter of 4 mm. Methane and oxygen were introduced at an alkoxy-alkane ratio of 6, a methane space velocity of 100,000 mL / (g·h), and a reaction temperature of 720°C. The methane conversion and selectivity for C2 and higher hydrocarbons were calculated based on the product composition. The results are shown in Table 2.

[0108] Table 2

[0109] Radial mechanical strength / N Methane conversion rate (%) Selectivity of C2 and above hydrocarbons (%) Example 1 41 24.6 51 Example 2 42 26.1 53 Example 3 41 24.4 52.1 Example 4 49 26.3 56.1 Example 5 45 24.1 53.2 Example 6 32 24.2 53.6 Example 7 35 23.9 52.4 Example 8 21 23.5 52.3 Comparative Example 1 12 22.3 50.4 Comparative Example 2 11 23.2 50.2

[0110] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A lanthanum oxide catalyst, characterized in that The lanthanum oxide catalyst comprises sheet-like lanthanum oxide formed by self-assembly of rod-like lanthanum oxide, wherein the average thickness of the sheet-like lanthanum oxide is 100-500 nm.

2. The lanthanum oxide catalyst according to claim 1, wherein The average length of the flake lanthanum oxide is 2-10 μm, and the average width is 1-5 μm; And / or, the rod-shaped lanthanum oxide has a length of 100-300 nm and a width of 10-30 nm.

3. The lanthanum oxide catalyst according to claim 1, wherein The lanthanum oxide catalyst also includes a modifying element, and the modifying element is cerium; Preferably, the molar ratio of the modifying element to the lanthanum element in the lanthanum oxide catalyst is 1:1-10, more preferably 1:3-10.

4. A method for preparing a lanthanum oxide catalyst, characterized in that: The method comprises: mixing a lanthanum precursor and an aqueous solution of urea and alcohol to obtain a mixed solution, adjusting the pH value of the mixed solution to 8.5-9 with a first alkali solution, adjusting the pH value of the mixed solution to 10-13 with a second alkali solution, and then sequentially performing reaction, separation and first calcination.

5. The method according to claim 4, wherein: The lanthanum precursor is a water-soluble salt of lanthanum, preferably lanthanum nitrate; And / or, the alcohol is a C1-C4 alcohol, preferably at least one of methanol, ethanol, propylene glycol, ethylene glycol and glycerol; more preferably, the mass fraction of the alcohol in the aqueous solution of the alcohol is 10-60wt%; And / or, the weight ratio of the lanthanum precursor: urea: alcohol aqueous solution is (1-10): (20-50): (100-500), preferably (1.5-5): (25-50): (150-400).

6. The method according to claim 4, wherein: The first alkali solution is aqueous ammonia, preferably, the mass fraction of aqueous ammonia is 20-30wt%; And / or, the second alkali solution is a sodium hydroxide aqueous solution, preferably, the concentration of the sodium hydroxide aqueous solution is 3-5 mol / L.

7. The method according to claim 4, wherein: The reaction conditions include: temperature of 40-100°C; time of 1-10h; And / or, the method further comprises: allowing the reaction solution obtained by the reaction to stand at 60-80° C. for 10-50 hours; And / or, the first calcination conditions include: heating to 700-800° C. at 2-10° C. / min, and then maintaining the temperature for 2-10 h.

8. The method according to claim 4, wherein: The method further comprises: modifying the first calcined product by using a modifying element; wherein the modifying element is cerium; Preferably, the molar ratio of the modifying element to the lanthanum element in the first calcined product is 1:1-10, preferably 1:3-10.

9. The method according to claim 8, 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 5-10° C. / min, and then maintaining the temperature for 2-5 hours.

10. A lanthanum oxide catalyst prepared by the method according to any one of claims 4 to 9.

11. Use of the lanthanum oxide catalyst according to any one of claims 1 to 3 and 10 in the oxidative coupling reaction of methane to produce C2 or higher hydrocarbons.

12. A method for preparing hydrocarbons with carbon 2 or higher content 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 catalyst described in any one of claims 1 to 3 and 10 for reaction; Alternatively, the lanthanum oxide catalyst is prepared according to the method described in any one of claims 4 to 9, and then methane is contacted with the obtained lanthanum oxide for reaction in the presence of oxygen and under the conditions of methane oxidative coupling reaction.

13. The method according to claim 12, wherein: The molar ratio of the methane to the oxygen is 6-12:1; And / or, the contact reaction temperature is 600-750°C; And / or, the space velocity of methane is 60000-180000 mL / (g·h).

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