Lanthanum oxycarbonate catalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of methane oxidative coupling, and discloses a lanthanum oxycarbonate catalyst and a preparation method and application thereof.The preparation method of the lanthanum oxycarbonate catalyst comprises the steps that 1, solid lanthanum salt and an optional solid substance containing doping elements are mixed with alkali liquor, and turbid liquid is obtained; (2) standing the turbid liquid, removing supernatant liquid, and then adding water to adjust the pH value to 11-13; and (3) carrying out a hydrothermal reaction on the material obtained in the step (2), separating the product of the hydrothermal reaction, and roasting the separated solid in a carbon dioxide-containing atmosphere. When the prepared lanthanum oxycarbonate catalyst is used for oxidative coupling of methane, the selectivity of hydrocarbon with two or more carbon atoms can be improved.

Description

Technical Field

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

[0002] Natural gas refers to all gases that exist naturally in nature, including gases formed by various natural processes in the atmosphere, hydrosphere, and lithosphere (including oilfield gas, gas field gas, mud volcano gas, coalbed methane, and biogenic gas, etc.). The definition of "natural gas" that people have long used is a narrow definition from an energy perspective, which refers to a mixture of hydrocarbons and non-hydrocarbon gases naturally stored in the strata. In petroleum geology, it usually refers to oilfield gas and gas field gas. Its composition is mainly hydrocarbons and contains non-hydrocarbon gases. On May 6, 2020, PetroChina Southwest Oil and Gas Field Company disclosed that the company had discovered a new zone rich in natural gas, with an estimated potential resource volume of more than one trillion cubic meters. On February 28, 2023, the National Bureau of Statistics released the "Statistical Communiqué of the People's Republic of China on the National Economic and Social Development in 2022". According to preliminary calculations, natural gas consumption fell by 1.2%, and clean energy consumption such as natural gas, hydropower, nuclear power, wind power, and solar power generation accounted for 25.9% of total energy consumption, an increase of 0.4 percentage points. With the continuous development of mining methods, the consumption of natural gas in clean energy will continue to rise. The conversion and utilization of methane, the main component of natural gas, is particularly important. Oxidative coupling of methane (OCM) technology refers to the reaction of directly converting methane into ethylene. Since it was proposed in the 1980s, it has been the research focus of the catalytic, chemical and new energy fields. A large number of scientists have devoted themselves to the development and research of catalysts for OCM reactions, and have studied more than 2,000 catalyst compositions that can almost cover all elements in the periodic table. Due to some technical problems in engineering amplification, there is still no industrial device in the world. Therefore, there is still a long way to go for the development of catalysts and the research of reaction processes. In the past few years, the research interest in OCM reactions has further increased, and catalysts with higher activity and selectivity have been continuously discovered. It is worth noting that the OCM reaction is a highly exothermic reaction, which is easy to generate hot spots in the reactor. If the selectivity of the product is high enough, the strong exothermicity of the reaction process can be effectively reduced. Rare earth oxides and their composite catalysts with alkaline earth metals have high catalytic activity and selectivity for methane oxidative coupling reaction, and also show good stability at high temperature. The document Structure Sensitivity of La2O2CO3 Catalysts in the Oxidative Coupling of Methane, ACS Catal. 2015, 5, 1663-1674 reports that different preparation methods have different methane oxidative coupling reaction performances. In order to further improve the catalytic performance of lanthanum carbonate catalyst, the present invention prepares a lanthanum carbonate catalyst, and applies the catalyst to the methane oxidative coupling reaction to achieve good carbon dihydrocarbon selectivity. Summary of the invention

[0003] The purpose of the present invention is to further improve the catalytic performance of a lanthanum oxycarbonate catalyst in a methane oxidative coupling reaction, and to provide a lanthanum oxycarbonate catalyst and a preparation method and application thereof.

[0004] In order to achieve the above object, the first aspect of the present invention provides a method for preparing a lanthanum oxycarbonate catalyst, the method comprising:

[0005] (1) mixing a solid lanthanum salt and an optional solid substance containing a doping element with an alkali solution to obtain a suspension;

[0006] (2) After the suspension is allowed to stand, the supernatant is removed, and then water is added to adjust the pH to 11-13;

[0007] (3) subjecting the material obtained in step (2) to a hydrothermal reaction, separating the product of the hydrothermal reaction, and then calcining the separated solid in an atmosphere containing carbon dioxide.

[0008] The second aspect of the present invention provides a lanthanum oxycarbonate catalyst prepared by the method described above.

[0009] The third aspect of the present invention provides a lanthanum oxycarbonate catalyst, which has a linear structure, a length of the linear structure of 1-50 μm, a diameter of the linear structure of 5-100 nm, and an aspect ratio of 50-500.

[0010] A fourth aspect of the present invention provides the use of the above-mentioned lanthanum oxycarbonate catalyst in the oxidative coupling reaction of methane to produce C2 and higher hydrocarbons.

[0011] A fifth aspect of the present invention provides a method for preparing hydrocarbons having two or more carbon atoms from methane, the method comprising: contacting methane with the above-mentioned lanthanum carbonate catalyst in the presence of oxygen and under the conditions of methane oxidative coupling reaction;

[0012] Alternatively, the lanthanum oxycarbonate catalyst is prepared according to the method described above, and then methane is contacted with the obtained lanthanum oxycarbonate catalyst in the presence of oxygen and under the conditions of methane oxidative coupling reaction.

[0013] The present invention can prepare a lanthanum carbonate catalyst with a linear structure by controlling the contact mode between the lanthanum salt and the alkali solution - contacting the solid lanthanum salt with the alkali solution, adjusting the pH of the lower particle sedimentation layer with water, and then performing a hydrothermal reaction. The lanthanum carbonate catalyst prepared by the present invention can improve the selectivity of carbon two and above hydrocarbons when used for methane oxidative coupling. The lanthanum carbonate catalyst of the present invention can obtain a higher methane conversion rate and selectivity of carbon two and above hydrocarbons at a lower reaction temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1This is a scanning electron microscope image of the lanthanum carbonate catalyst prepared in Example 1. DETAILED DESCRIPTION

[0015] 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.

[0016] The first aspect of the present invention provides a method for preparing a lanthanum oxycarbonate catalyst, the method comprising:

[0017] (1) mixing a solid lanthanum salt and an optional solid substance containing a doping element with an alkali solution to obtain a suspension;

[0018] (2) After the suspension is allowed to stand, the supernatant is removed, and then water is added to adjust the pH to 11-13;

[0019] (3) subjecting the material obtained in step (2) to a hydrothermal reaction, separating the product of the hydrothermal reaction, and then calcining the separated solid in an atmosphere containing carbon dioxide.

[0020] The inventors of the present invention unexpectedly discovered that a lanthanum carbonate catalyst prepared by directly mixing a lanthanum salt with an alkaline solution to obtain a suspension, removing the supernatant, adjusting the pH with water, and then performing a hydrothermal reaction has a linear structure, and the lanthanum carbonate catalyst has good catalytic performance when used for methane oxidative coupling.

[0021] According to the present invention, the type of the lanthanum salt can be a lanthanum salt commonly used in the art. Preferably, the lanthanum salt is at least one of lanthanum nitrate (eg, lanthanum nitrate hexahydrate), lanthanum chloride and lanthanum acetate.

[0022] According to the present invention, preferably, the alkali solution is an alkali metal hydroxide aqueous solution, more preferably a sodium hydroxide aqueous solution and / or a potassium hydroxide aqueous solution. When the type of the alkali solution is limited to the above range, not only can a lanthanum oxycarbonate catalyst with a linear structure be obtained, but also the lanthanum oxycarbonate catalyst can further improve the conversion rate of methane and the selectivity of C2 and above hydrocarbons when used for methane oxidative coupling.

[0023] According to the present invention, in order to further improve the conversion rate of methane and the selectivity of C2 and above hydrocarbons, preferably, the concentration of the alkali solution is 1-3 mol / L. In the present invention, the concentration of the alkali solution can be 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, and a range consisting of any two of the above points.

[0024] According to the present invention, preferably, the weight ratio of the lanthanum salt to the alkali solution is 1:2-40, preferably 1:5-30. In the present invention, the weight ratio of the lanthanum salt to the alkali solution can be 1:2, 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.

[0025] According to the present invention, preferably, the mixing time is 10-100 min, more preferably 25-60 min.

[0026] According to the present invention, in order to allow the lanthanum salt to react fully with the alkali solution, preferably, the mixing is performed under stirring.

[0027] According to the present invention, the standing time is not particularly limited, as long as the suspension can be separated into an upper clear liquid and a lower particle sedimentation layer after standing. Preferably, in order to fully settle the particles in the suspension, preferably, the standing time is 10-100 hours. The standing time in the present invention can be 10 hours, 20 hours, 30 hours, 40 hours, 50 hours, 60 hours, 70 hours, 80 hours, 90 hours, 100 hours, and a range consisting of any two of the above points.

[0028] According to the present invention, the standing temperature is not particularly limited. Preferably, the standing temperature is 25-50°C.

[0029] According to the present invention, preferably, in step (2), the process of adding water to adjust the pH is carried out under stirring.

[0030] According to the present invention, preferably, the substance containing the doping element is at least one of alkaline earth metal compounds, more preferably at least one of magnesium nitrate, calcium nitrate, strontium nitrate and barium nitrate.

[0031] According to the present invention, preferably, the molar ratio of the lanthanum salt to the substance containing the doping element is 1:0.01-1 (for example, 1:0.01, 1:0.05, 1:0.09, 1:0.1, 1:0.11, 1:0.12, 1:0.13, 1:0.14, 1:0.15, 1:0.16, 1:0.17, 1:0.18, 1:0.19, 1:0.2, 1:0.3, 1:0.5, 1:0.8, 1:1, and a range consisting of any two of the above points), more preferably 1:0.05-0.5, and further preferably 1:0.09-0.3.

[0032] According to the present invention, preferably, the hydrothermal conditions include: temperature of 150-180° C. and time of 10-24 h.

[0033] According to the present invention, preferably, in step (3), the separation method is centrifugal separation, and more preferably, the conditions for centrifugal separation include: a rotation speed of 8000-11000 rpm, a temperature of 5-20° C., and a time of 10-30 min.

[0034] According to the present invention, preferably, step (3) further comprises drying the separated solid, and more preferably, the drying conditions comprise: a temperature of 80-150° C. and a drying time of 5-20 h.

[0035] According to the present invention, preferably, the calcination conditions include: a temperature of 500-600° C. and a time of 2-10 h.

[0036] According to the present invention, preferably, the calcination is carried out at a heating rate of 1-5°C / min to a calcination temperature.

[0037] According to the present invention, preferably, the atmosphere containing carbon dioxide is an air atmosphere.

[0038] The second aspect of the present invention provides a lanthanum oxycarbonate catalyst prepared by the method described above.

[0039] The third aspect of the present invention provides a lanthanum oxycarbonate catalyst, which has a linear structure, a length of the linear structure of 1-50 μm, a diameter of the linear structure of 5-100 nm, and an aspect ratio of 50-500.

[0040] According to the present invention, preferably, the length of the linear structure is 2-10 μm, the diameter of the linear structure is 5-50 nm, and the aspect ratio is 100-400.

[0041] According to the present invention, preferably, the specific surface area of ​​the lanthanum carbonate catalyst is 65-100m 2 / g, pore volume is 0.2-0.5cm 3 / g, and the average pore size is 10-20 angstroms.

[0042] In the present invention, It is a unit of length, 10 angstroms = 1 nm.

[0043] According to the present invention, preferably, the lanthanum oxycarbonate catalyst further contains a doping element, and the doping element includes at least one of magnesium, calcium, strontium and barium.

[0044] According to the present invention, preferably, the molar ratio of lanthanum to doping element in the lanthanum oxycarbonate catalyst is 1: 0.01-3. In the present invention, the molar ratio of lanthanum to doping element in the lanthanum oxycarbonate catalyst is calculated based on the feed amount of raw materials.

[0045] A fourth aspect of the present invention provides the use of the above-mentioned lanthanum oxycarbonate catalyst in the oxidative coupling reaction of methane to produce C2 and higher hydrocarbons.

[0046] A fifth aspect of the present invention provides a method for preparing hydrocarbons having two or more carbon atoms from methane, the method comprising: contacting methane with the above-mentioned lanthanum carbonate catalyst in the presence of oxygen and under the conditions of methane oxidative coupling reaction;

[0047] Alternatively, the lanthanum oxycarbonate catalyst is prepared according to the method described above, and then methane is contacted with the obtained lanthanum oxycarbonate catalyst in the presence of oxygen and under the conditions of methane oxidative coupling reaction.

[0048] According to the present invention, preferably, the molar ratio of the methane to the oxygen (referred to as the alkoxygen ratio) is 5-8:1.

[0049] According to the present invention, preferably, the temperature of the contact reaction is 500-750°C.

[0050] According to the present invention, preferably, the space velocity of methane is 40000-140000 mL / (g·h).

[0051] According to a particularly preferred embodiment of the present invention, the preparation method of the lanthanum carbonate catalyst comprises: adding 5.8-6g of lanthanum nitrate hexahydrate and 0.3-0.2g of barium nitrate to 100-120g of sodium hydroxide solution (1.5-2mol / L), and rapidly stirring for 50-60min to obtain a suspension; after the suspension is allowed to stand for 50-60h, stratification occurs (the upper layer is a clear liquid, and the lower layer is a particle sedimentation layer), the upper clear liquid is poured off, and then deionized water is added to the particle sedimentation layer while stirring, and the reaction solution is measured. The pH value of the liquid is 11-11.3, stop dropping, stir for 30-40 minutes, react at 160-165°C for 20-24 hours, wash and separate with a centrifuge (centrifugal conditions include: speed of 10000-11000rpm, temperature of 10-15°C, time of 15-20min), wash with water and ethanol, dry at 120-140°C for 10-12h, then heat to 620-650°C at 1.5-2°C / min in an air atmosphere and keep for 2-3h.

[0052] The present invention will be described in detail below by way of examples. In the following examples,

[0053] The reaction was allowed to stand at room temperature (about 25°C).

[0054] The calculation method of methane conversion rate is as follows:

[0055] Methane conversion rate = amount of methane consumed in the reaction / initial amount of methane × 100%.

[0056] The ethylene selectivity is calculated as follows:

[0057] Ethylene selectivity = amount of methane consumed by produced ethylene / total methane consumption x 100%.

[0058] The ethane selectivity is calculated as follows:

[0059] Ethane selectivity = amount of methane consumed by produced ethane / total methane consumption x 100%.

[0060] The selectivity of C2 and above hydrocarbons includes the sum of ethylene, ethane, propylene, propane and higher carbon hydrocarbons.

[0061] Example 1

[0062] Weigh 5.8g of lanthanum nitrate hexahydrate and add it to 100g of sodium hydroxide solution (3mol / L), stir rapidly for 30min to obtain a suspension; after the suspension is left standing for 100h, stratification occurs (the upper layer is a clear liquid, and the lower layer is a particle sedimentation layer), the upper clear liquid is poured off, and then deionized water is added to the particle sedimentation layer while stirring, the pH value of the reaction solution is measured to be 12, the dropwise addition is stopped, and after stirring for 30min, it is placed in a high-pressure hydrothermal reactor lined with polytetrafluoroethylene, and the hydrothermal reactor is placed at 160°C for reaction for 12h, and after cooling to room temperature, the hydrothermal reactor is opened, and washed and separated by a centrifuge (the centrifugal conditions include: a speed of 10000rpm, a temperature of 10°C, and a time of 15min), washed three times with water, washed once with ethanol, placed in a 120°C oven, kept for 12h, and then moved to a muffle furnace (the calcination atmosphere is an air atmosphere), heated to 550°C at 2°C / min, and kept for 2h. Lanthanum carbonate catalyst A1 is prepared. The XRD spectrum of the lanthanum oxycarbonate catalyst prepared in Example 1 shows that it has characteristic peaks of lanthanum oxycarbonate, indicating that the catalyst prepared in Example 1 is lanthanum oxycarbonate.

[0063] Example 2

[0064] 5.8 g of lanthanum nitrate hexahydrate and 0.32 g of barium nitrate were weighed and added to 100 g of sodium hydroxide solution (2 mol / L), and the mixture was rapidly stirred for 60 min to obtain a suspension; after the suspension was allowed to stand for 50 h, stratification occurred (the upper layer was a clear liquid, and the lower layer was a particle sedimentation layer), the upper clear liquid was poured off, and then deionized water was added to the particle sedimentation layer while stirring, the pH value of the reaction solution was measured to be 11.3, the dropwise addition was stopped, and after stirring for 30 min, the mixture was placed in a high-pressure hydrothermal reactor lined with polytetrafluoroethylene, and the hydrothermal reactor was placed at 160° C. for reaction for 24 h. After cooling to room temperature, the hydrothermal reactor was opened, and the mixture was washed and separated by a centrifuge (the centrifugal conditions included: a speed of 11000 rpm, a temperature of 10° C., and a time of 15 min), washed three times with water, washed once with ethanol, placed in a 120° C. oven, kept for 12 h, and then moved to a muffle furnace (the calcination atmosphere was an air atmosphere), heated to 600° C. at 2° C. / min, and kept for 2 h. Lanthanum oxycarbonate catalyst A2 was prepared.

[0065] Example 3

[0066] 5.8 g of lanthanum nitrate hexahydrate and 0.36 g of strontium nitrate were weighed and added to 100 g of sodium hydroxide solution (3 mol / L), and the suspension was rapidly stirred for 25 min. After the suspension was allowed to stand for 24 h, stratification occurred (the upper layer was a clear liquid, and the lower layer was a particle sedimentation layer). The upper clear liquid was poured off, and then deionized water was added to the particle sedimentation layer while stirring. The pH value of the reaction solution was measured to be 11.5, and the dropwise addition was stopped. After stirring for 30 min, the mixture was placed in a high-pressure hydrothermal reactor lined with polytetrafluoroethylene, and the hydrothermal reactor was placed at 180° C. for reaction for 12 h. After cooling to room temperature, the hydrothermal reactor was opened, and the mixture was washed and separated by a centrifuge (the centrifugal conditions included: a speed of 8500 rpm, a temperature of 10° C., and a time of 15 min), washed three times with water, washed once with ethanol, placed in a 120° C. oven, kept for 12 h, and then moved to a muffle furnace (the calcination atmosphere was an air atmosphere), heated to 600° C. at 2° C. / min, and kept for 2 h. Lanthanum oxycarbonate catalyst A3 was prepared.

[0067] Example 4

[0068] 5.8 g of lanthanum nitrate hexahydrate and 0.4 g of magnesium nitrate were weighed and added to 150 g of sodium hydroxide solution (3 mol / L), and the suspension was rapidly stirred for 30 min. After the suspension was allowed to stand for 100 h, stratification occurred (the upper layer was a clear liquid, and the lower layer was a particle sedimentation layer). The upper clear liquid was poured off, and then deionized water was added to the particle sedimentation layer while stirring. The pH value of the reaction solution was measured to be 11.5, and the dropwise addition was stopped. After stirring for 30 min, the mixture was placed in a high-pressure hydrothermal reactor lined with polytetrafluoroethylene, and the hydrothermal reactor was placed at 180° C. for reaction for 24 h. After cooling to room temperature, the hydrothermal reactor was opened, and the mixture was washed and separated by a centrifuge (the centrifugal conditions included: a speed of 9000 rpm, a temperature of 15° C., and a time of 15 min), washed three times with water, washed once with ethanol, placed in a 120° C. oven, kept for 12 h, and then moved to a muffle furnace (the calcination atmosphere was an air atmosphere), heated to 500° C. at 2° C. / min, and kept for 2 h. Lanthanum oxycarbonate catalyst A4 was prepared.

[0069] Comparative Example 1

[0070] Weigh 5.8g of lanthanum nitrate hexahydrate, add 100g of deionized water, drop sodium hydroxide solution (3mol / L), adjust the end point pH value to 12, stir evenly, place in a high-pressure reactor lined with polytetrafluoroethylene, stand at 160°C for 12h, wash and separate with a centrifuge, wash three times with water, wash once with ethanol, place in an oven, 120°C, keep for 12h, then move to a muffle furnace (calcination atmosphere is air atmosphere), heat to 500°C at 2°C / min, and keep for 5h. Lanthanum carbonate catalyst D1 is prepared.

[0071] Comparative Example 2

[0072] The method of Example 1 was followed, except that the pH value of the reaction solution was measured to be 9, and the dropwise addition was stopped.

[0073] Test Example 1

[0074] The shape and size, specific surface area, pore volume, average pore diameter and other results of the above catalysts are shown in Table 1.

[0075] The shape of the lanthanum carbonate catalyst was determined by scanning electron microscopy. The size of the lanthanum carbonate catalyst was tested by selecting 5-10 samples in the field of view, measuring the length and diameter using the measuring instrument provided by the scanning electron microscope, and then calculating the average length and average diameter of the 5-10 samples in the field of view as the data of the length and diameter of the sample, and calculating the aspect ratio based on the average length and average diameter of the sample.

[0076] The test method for the specific surface area, pore volume and average pore size of the lanthanum carbonate catalyst is as follows: the automatic physical adsorption instrument ASAP2420 is used for measurement, 100 mg of sample is weighed and placed in a sample tube, the sample tube is placed in the instrument degassing station for degassing, the degassing condition is 350°C for 4 hours, and after natural cooling to room temperature, the sample tube is placed in the instrument analysis station for analysis, and the nitrogen adsorption and desorption isotherm is fully analyzed 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 by the BJH (Barret, Joyner, Halenda) method according to the desorption (adsorption) branch.

[0077] Table 1

[0078]

[0079] Test Example 2

[0080] After the catalyst tablets were sieved through 40-60 mesh, 100 mg was weighed and loaded into a quartz tube fixed bed reactor with an inner diameter of 4 mm, and methane and oxygen were introduced, with a methane space velocity of 140000 mL / (g·h), an alkoxy ratio of 8, and a reaction temperature as shown in Table 2. The product composition was detected online by Agilent gas chromatography, and the results are shown in Table 2.

[0081] Table 2

[0082]

[0083] It can be seen from the results in Table 2 that the lanthanum oxycarbonate catalyst prepared by the method of the present invention has a higher methane conversion rate and selectivity for C2 and above hydrocarbons.

[0084] 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 method for preparing a lanthanum oxycarbonate catalyst, characterized in that: The method includes: (1) mixing a solid lanthanum salt and an optional solid substance containing a doping element with an alkali solution to obtain a suspension; (2) After the suspension is allowed to stand, the supernatant is removed, and then water is added to adjust the pH to 11-13; (3) subjecting the material obtained in step (2) to a hydrothermal reaction, separating the product of the hydrothermal reaction, and then calcining the separated solid in an atmosphere containing carbon dioxide.

2. The method according to claim 1, wherein: The lanthanum salt is at least one of lanthanum nitrate, lanthanum chloride and lanthanum acetate; and / or, the substance containing the doping element is at least one of alkaline earth metal compounds, preferably at least one of magnesium nitrate, calcium nitrate, strontium nitrate and barium nitrate; And / or, the alkali solution is an alkali metal hydroxide aqueous solution, preferably a sodium hydroxide aqueous solution and / or a potassium hydroxide aqueous solution.

3. The method according to claim 1 or 2, wherein: The molar ratio of the lanthanum salt to the substance containing the doping element is 1:0.01-1; And / or, the concentration of the alkali solution is 1-3 mol / L; And / or, the weight ratio of the lanthanum salt solid to the alkali solution is 1:2-40, preferably 1:5-30.

4. The method according to claim 1 or 2, wherein: The standing time is 10-100h.

5. The method according to claim 1 or 2, wherein: The hydrothermal conditions include: temperature of 150-180°C and time of 10-24h; And / or, the calcination conditions include: temperature of 500-600° C. and time of 2-10 h.

6. A lanthanum oxycarbonate catalyst prepared by the method described in any one of claims 1 to 5.

7. A lanthanum oxycarbonate catalyst, characterized in that The lanthanum oxycarbonate catalyst has a linear structure, the length of the linear structure is 1-50 μm, the diameter of the linear structure is 5-100 nm, and the aspect ratio is 50-500.

8. The lanthanum oxycarbonate catalyst according to claim 1, wherein The length of the linear structure is 2-10 μm, the diameter of the linear structure is 5-50 nm, and the aspect ratio is 100-400; And / or, the specific surface area of ​​the lanthanum carbonate catalyst is 65-100m 2 / g, pore volume is 0.2-0.5cm 3 / g, and the average pore size is 10-20 angstroms.

9. The lanthanum oxycarbonate catalyst according to claim 1, wherein The lanthanum oxycarbonate catalyst also contains a doping element, and the doping element includes at least one of magnesium, calcium, strontium and barium.

10. Use of the lanthanum oxycarbonate catalyst described in any one of claims 6 and 7-9 in the oxidative coupling reaction of methane to produce C2 and higher hydrocarbons.

11. 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 carbonate catalyst described in any one of claims 6 and 7-9 for reaction; Alternatively, a lanthanum oxycarbonate catalyst is prepared according to the method described in any one of claims 1 to 5, and then methane is contacted with the obtained lanthanum oxycarbonate catalyst in the presence of oxygen and under the conditions of methane oxidative coupling reaction.

12. The method according to claim 11, wherein: The molar ratio of the methane to the oxygen is 5-8:1; And / or, the contact reaction temperature is 500-750°C; And / or, the space velocity of methane is 40000-140000 mL / (g·h).

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