Lanthanum oxycarbonate catalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of lanthanum oxycarbonate, and discloses a lanthanum oxycarbonate catalyst and a preparation method and application thereof, and the lanthanum oxycarbonate catalyst comprises hexagonal crystal phase lanthanum oxycarbonate and hexagonal crystal phase lanthanum oxycarbonate containing a doping element R. The method comprises the following steps: (1) adding alkali liquor into a solution of a lanthanum source, and then carrying out solid-liquid separation and drying to obtain lanthanum hydroxide; (2) contacting a solution of a compound containing a doping element R with lanthanum hydroxide, and then drying; and (3) roasting the dried product in the step (2) in a carbon-containing atmosphere to obtain the lanthanum oxycarbonate catalyst. When the catalyst prepared by the method is used for the oxidative coupling reaction of methane, the yield of C2 hydrocarbon is relatively high.

Description

Lanthanum oxycarbonate catalyst and its preparation method and application Technical Field

[0001] The invention relates to a lanthanum oxycarbonate catalyst, and a preparation method and application thereof. Background Art

[0002] Lanthanum oxycarbonate is a novel material primarily used in water treatment, optoelectronics, catalysis, and other fields. Currently, the main methods for synthesizing lanthanum oxycarbonate include precipitation, thermal decomposition, and hydrothermal methods. However, lanthanum oxycarbonate is typically prepared in a two-step process: first, synthesizing a La(OH)3 precursor, followed by low-temperature calcination. Current improvements to lanthanum oxycarbonate materials primarily involve modifying the preparation method to obtain lanthanum oxycarbonate with varying morphologies or structures.

[0003] CN113797949A discloses a method for preparing lanthanum oxycarbonate, which includes synthesizing rod-shaped nanostructured lanthanum oxycarbonate under ultrasonic conditions. The prepared lanthanum oxycarbonate can efficiently undergo methane oxidative coupling reaction at a relatively low temperature, but the yield of carbon dihydrocarbons of the lanthanum oxycarbonate is relatively low.

[0004] There are few reports in the prior art on element doping of lanthanum oxycarbonate materials. Only a few literatures have reported on impregnating lanthanum oxycarbonate materials with solutions containing doping elements. However, there is no report in the prior art on completing element doping during the preparation process of lanthanum oxycarbonate.

[0005] Summary of the Invention

[0006] The present invention provides a lanthanum oxycarbonate catalyst, a preparation method and an application thereof. The catalyst is particularly suitable for activated methane oxidative coupling and has a high C2 hydrocarbon yield at, for example, 500-650°C.

[0007] In order to achieve the above-mentioned object, the present invention provides a lanthanum oxycarbonate catalyst on the one hand, which comprises hexagonal lanthanum oxycarbonate and hexagonal lanthanum oxycarbonate containing a doping element R; the total content of hexagonal lanthanum oxycarbonate and hexagonal lanthanum oxycarbonate containing a doping element R in the lanthanum oxycarbonate catalyst is not less than 98 wt% (preferably not less than 99 wt%), wherein the molar ratio of lanthanum element to doping element R is 1:0.01-1:0.3; and the doping element R is selected from at least one of Mg, Ca, Sr, Ba, Fe and Zn elements.

[0008] Preferably, no characteristic peak of the doping element in the form of a metal salt appears in the XRD spectrum of the present invention.

[0009] Another aspect of the present invention provides a method for preparing the lanthanum oxycarbonate catalyst of the present invention, the method comprising:

[0010] (1) adding an alkali solution to a solution of a lanthanum source, and then subjecting the solution to optional aging, solid-liquid separation, and drying to obtain solid lanthanum hydroxide; wherein the drying comprises a first drying and a second drying, wherein the conditions for the first drying comprise: a temperature of 70-90° C. and a time of 10-20 hours, and the second drying is performed at a higher temperature and for a shorter time than the first drying;

[0011] Determine the saturated water absorption of the second dried lanthanum hydroxide: Under nitrogen protection, take 1 g of the second dried lanthanum hydroxide and place it in a container. Add water to mix evenly with the lanthanum hydroxide until the lanthanum hydroxide no longer absorbs water. Record the amount of water added at this time as the saturated water absorption of the lanthanum hydroxide.

[0012] (2) optionally, under a protective atmosphere, adding a solution of a compound containing a doping element R to the solid lanthanum hydroxide obtained in step (1) so that the solution is in contact with the lanthanum hydroxide in an amount less than or equal to the saturated water absorption capacity of the lanthanum hydroxide, and then drying; wherein the contacting method is selected from surface precipitation, atomic layer deposition, and single atomic layer plating;

[0013] (3) calcining the dried product of step (2) in a carbon-containing (e.g., CO and / or CO2) atmosphere to obtain a lanthanum oxycarbonate catalyst.

[0014] Another aspect of the present invention provides a lanthanum oxycarbonate catalyst prepared by the method described above.

[0015] Another 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.

[0016] Another aspect of the present invention provides a method for preparing C2 and higher hydrocarbons from methane, the method comprising: in the presence of oxygen and under the conditions of a methane oxidative coupling reaction, contacting methane with the lanthanum oxycarbonate catalyst of the present invention for reaction; or,

[0017] The lanthanum oxycarbonate catalyst is prepared according to the method of the present invention, and then methane is contacted with the obtained lanthanum oxycarbonate catalyst for reaction in the presence of oxygen and under the conditions of methane oxidative coupling reaction.

[0018] The catalyst provided by the present invention contains both hexagonal lanthanum oxycarbonate and hexagonal lanthanum oxycarbonate containing the doping element R, which can effectively promote the occurrence of methane oxidative coupling reaction and improve the yield of carbon dihydrocarbons.

[0019] The present invention first prepares lanthanum hydroxide by adding an alkaline solution to a solution containing a lanthanum element, and then contacts the lanthanum hydroxide with a solution containing a doping element R to prepare a catalyst. The prepared catalyst includes hexagonal lanthanum oxycarbonate and hexagonal lanthanum oxycarbonate containing the doping element R. When used in a methane oxidative coupling reaction, the catalyst prepared by the present invention has a high yield of carbon dihydrocarbons. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG1 is an XRD spectrum of the lanthanum oxycarbonate catalyst prepared in Example 1;

[0021] FIG2 is a transmission scanning electron micrograph of the lanthanum oxycarbonate catalyst prepared in Example 1;

[0022] FIG3 is an XRD spectrum of the lanthanum oxycarbonate catalyst prepared in Comparative Example 4. DETAILED DESCRIPTION

[0023] 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.

[0024] Unless otherwise specified, all percentages, parts, ratios, etc. mentioned herein are based on weight, unless based on weight, they are not in accordance with the common understanding of those skilled in the art.

[0025] As used herein, unless otherwise indicated, the terms "comprises," "includes," "contains," "has," and similar expressions are intended to be open ended, but should also be understood to explicitly disclose closed ended situations. For example, "comprises" indicates that other elements not listed may also be included, but also explicitly discloses situations where only the listed elements are included. Furthermore, as used herein, "comprises / comprising" is interpreted as explicitly stating the presence of the referenced features, integers, steps, or components, but does not exclude the presence or addition of one or more other features, integers, steps, components, or groups thereof. Additionally, the term "comprising" is intended to include embodiments encompassed by the terms "consisting essentially of" and "consisting of." Similarly, the term "consisting essentially of" is intended to include embodiments encompassed by the term "consisting of."

[0026] On one hand, the present invention provides a lanthanum oxycarbonate catalyst, which includes hexagonal lanthanum oxycarbonate and hexagonal lanthanum oxycarbonate containing a doping element R; the total content of hexagonal lanthanum oxycarbonate and hexagonal lanthanum oxycarbonate containing the doping element R in the lanthanum oxycarbonate catalyst is not less than 98wt% (preferably not less than 99wt%), wherein the molar ratio of lanthanum element to doping element R is 1:0.01-1:0.3; and the doping element R is selected from at least one of Mg, Ca, Sr, Ba, Fe and Zn elements.

[0027] Without being limited to any known theory, it is believed that the present invention benefits from factors including but not limited to the following: appropriate control of the molar ratio of the lanthanum element to the doping element R, and especially a specific preparation process so that the majority (not less than 98 wt%, preferably not less than 99 wt%) of the lanthanum oxycarbonate and lanthanum oxycarbonate containing the doping element R in the obtained lanthanum oxycarbonate catalyst are present in the form of a hexagonal crystal phase, which can ensure a satisfactory catalyst structure, including the doping element content and its distribution; thereby being beneficial to the catalyst activity, especially when it is used to activate methane oxidative coupling, it has a higher methane conversion rate, as well as a higher selectivity and yield of carbon dihydrocarbons.

[0028] According to the present invention, the total content of hexagonal lanthanum oxycarbonate and hexagonal lanthanum oxycarbonate containing the doping element R in the lanthanum oxycarbonate catalyst is not less than 98% wt%, preferably not less than 99% wt%, and can even be not less than 99.5% wt%, or close to 100 wt%; this means that although the lanthanum oxycarbonate is treated in multiple steps in the present invention, the hexagonal phase in the obtained lanthanum oxycarbonate catalyst is absolutely dominant, ensuring the high purity of the hexagonal phase relative to other crystalline phases.

[0029] For the purposes of the present invention, the hexagonal crystal content, for example, the total content of hexagonal lanthanum oxycarbonate and hexagonal lanthanum oxycarbonate containing the doping element R, is determined by XRD patterns. Specifically, for example, the bulk crystal structure information is measured by XRD patterns, and the ratio of the diffraction peak areas of the hexagonal lanthanum oxycarbonate and the crystal structure containing the doping element to the total peak area is calculated to obtain the weight percentage of the hexagonal lanthanum oxycarbonate and the hexagonal lanthanum oxycarbonate containing the doping element in the product.

[0030] According to the present invention, the doping element R may preferably be selected from at least one of elements from Groups IIA, VIII, IB, and IIB, more preferably at least one of Mg, Ca, Sr, Ba, Fe, and Zn, and further preferably Sr and / or Ba. For other applications, there are some reports in the prior art of adding Ni to lanthanum oxycarbonate; however, without being limited by any known theory, it is believed that, especially when used to activate methane oxidative coupling, a doping element R selected from Mg, Ca, Sr, Ba, Fe, and Zn is particularly advantageous for higher methane conversion, as well as higher selectivity and yield of C2 hydrocarbons, particularly higher C2 hydrocarbon yields.

[0031] According to the present invention, preferably, the molar ratio of lanthanum to doping element R in the lanthanum oxycarbonate catalyst is 1:0.03-1:0.2, preferably 1:0.04-1:0.15. The molar ratio of lanthanum to doping element R in the lanthanum oxycarbonate catalyst can be calculated based on the feed amounts of lanthanum and doping element R.

[0032] According to the present invention, preferably, the lanthanum oxycarbonate catalyst has a fibrous nanostructure, the diameter of the lanthanum oxycarbonate catalyst is 10 nm-30 nm, preferably 10 nm-20 nm, and the aspect ratio is 5-50:1, more preferably 15-40:1.

[0033] In the present invention, the "particle size / diameter" and "aspect ratio" of the lanthanum oxycarbonate catalyst are both average values. The specific testing method for the "average particle size / diameter" is to select 5-10 samples within a viewing window using a transmission electron microscope ruler, measure the diameter of each sample, and then calculate the average value. The specific testing method for the "average aspect ratio" is to select 5-10 samples within a viewing window using a transmission electron microscope ruler, measure the diameter and length of each sample, calculate the aspect ratio of each sample, and then calculate the average value.

[0034] According to the present invention, preferably, the specific surface area of ​​the lanthanum oxycarbonate catalyst is 35m 2 / g-90m 2 / g, preferably 45m 2 / g-85m 2 / g, preferably 50m 2 / g-60m 2 / g, pore volume is 0.15cm 3 / g-0.5cm 3 / g, preferably 0.26cm 3 / g-0.4cm 3 / g, and an average pore diameter of 8nm-16nm, preferably 8nm-15nm, and further preferably 10nm-13.5nm.

[0035] Another aspect of the present invention provides a method for preparing the lanthanum oxycarbonate catalyst of the present invention, the method comprising:

[0036] (1) adding an alkali solution to a solution of a lanthanum source, and then subjecting the solution to optional aging, solid-liquid separation, and drying to obtain solid lanthanum hydroxide; wherein the drying comprises a first drying and a second drying, wherein the conditions for the first drying comprise: a temperature of 70-90° C. and a time of 10-20 hours, and the second drying is performed at a higher temperature and for a shorter time than the first drying;

[0037] Determine the saturated water absorption of the second dried lanthanum hydroxide: Under nitrogen protection, take 1 g of the second dried lanthanum hydroxide and place it in a container. Add water to mix evenly with the lanthanum hydroxide until the lanthanum hydroxide no longer absorbs water. Record the amount of water added at this time as the saturated water absorption of the lanthanum hydroxide.

[0038] (2) optionally, under a protective atmosphere, adding a solution of a compound containing a doping element R to the solid lanthanum hydroxide obtained in step (1) so that the solution contacts the lanthanum hydroxide, and then drying, wherein the amount of the solution of the compound containing the doping element R in contact with the lanthanum hydroxide is less than or equal to (preferably equal to or substantially equal to) the saturated water absorption capacity of the lanthanum hydroxide; wherein the contacting method is selected from surface precipitation, atomic layer deposition, and single atomic layer plating;

[0039] (3) calcining the dried product of step (2) in a carbon-containing (e.g., CO and / or CO2) atmosphere to obtain a lanthanum oxycarbonate catalyst.

[0040] According to the present invention, the above-mentioned specific preparation process makes the lanthanum oxycarbonate and lanthanum oxycarbonate containing the doping element R in the obtained lanthanum oxycarbonate catalyst mostly exist in the form of hexagonal phase, so that in the obtained lanthanum oxycarbonate catalyst, the total content of hexagonal phase lanthanum oxycarbonate and hexagonal phase lanthanum oxycarbonate containing the doping element R is not less than 98wt%, preferably not less than 99wt%, and can even be not less than 99.5wt%, or close to 100wt%.

[0041] According to the present invention, in order to make the generated lanthanum hydroxide more fibrous in morphology, preferably, the concentration of the alkali solution is 3 wt%-25 wt%.

[0042] According to the present invention, preferably, the alkali in the alkali solution is a compound of a Group IA metal.

[0043] According to the present invention, preferably, the addition rate of the alkali solution is 5 mL / min-150 mL / min per kilogram of the lanthanum source solution.

[0044] According to the present invention, preferably, the concentration of the lanthanum source solution is 0.01 wt%-10 wt%.

[0045] According to the present invention, preferably, the amount of the alkali solution used is such that the final pH value of the mixed system of the alkali solution and the lanthanum source solution is 10-12.5.

[0046] According to the present invention, the lanthanum source can be any substance that can provide lanthanum elements. Preferably, the lanthanum source is a water-soluble salt of lanthanum, more preferably at least one of lanthanum nitrate, lanthanum chloride and lanthanum acetate; further preferably, it is lanthanum nitrate.

[0047] According to the present invention, when performing the aging process, there are no particular limitations on the aging apparatus, as long as the aging temperature and stirring conditions are met. However, based on experimental safety and comprehensive catalyst performance, the aging process is preferably performed under condensation reflux. Preferably, the aging conditions include a temperature of 80-100°C and a time of 10-50 hours.

[0048] The present invention may further include performing solid-liquid separation on the aged product and then washing it with deionized water until it is neutral. The solid-liquid separation may be performed by conventional solid-liquid separation methods in the art, such as separation using a centrifuge.

[0049] According to the present invention, preferably, in step (1), the drying includes a first drying and a second drying, thereby obtaining the solid lanthanum hydroxide.

[0050] According to the present invention, preferably, the first drying conditions include: temperature of 70-90° C. and time of 10-20 h.

[0051] According to the present invention, preferably, the conditions for the second drying include: relative pressure of 10kPa-91kPa, preferably 20kPa-70kPa, temperature of 120-160°C, and time of 2-10h; wherein the second drying is performed for a shorter time than the first drying.

[0052] Without being limited by any known theory, it is believed that implementing the first drying and the second drying separately in the above step (1) and accurately controlling the drying conditions (such as temperature and time) are particularly beneficial to the purpose of the present invention, such as the control of the crystal phase.

[0053] According to the present invention, when the protective atmosphere is used, preferably, the protective atmosphere is provided by an inert gas and / or nitrogen.

[0054] In the present invention, the protective atmosphere can be provided by using Schlenk technology (double-row pipeline operation) or in a glove box with a protective atmosphere.

[0055] According to the present invention, preferably, step (1) further comprises measuring the saturated water absorption of lanthanum hydroxide. Then, a solution of a compound containing the doping element R is prepared based on the measured saturated water absorption of lanthanum hydroxide and the amount of the doping element R.

[0056] According to the present invention, preferably, in step (2), based on the measured saturated water absorption of lanthanum hydroxide, a solution of a compound containing the doping element R is added to the solid lanthanum hydroxide obtained in step (1) in an amount less than or equal to (or substantially equal to) the saturated water absorption of lanthanum hydroxide. For the purposes of the present invention, the amount of the solution containing the compound containing the doping element R added can preferably be "equal to" the saturated water absorption of lanthanum hydroxide; however, the solution and the solid may cause slight changes in volume after mixing, and thus, the amount of the solution containing the compound containing the doping element R added calculated without considering the slight change in volume can be regarded as "substantially equal to" the saturated water absorption of the lanthanum hydroxide. Without being limited to any known theory, it is believed that adding the solution containing the compound containing the doping element R based on the measured saturated water absorption of lanthanum hydroxide is particularly beneficial to the purposes of the present invention, such as controlling the amount of solution and the amount of doping element during the preparation process, thereby enabling a desired doping amount to be obtained without causing a change in the crystal phase.

[0057] According to the present invention, preferably, the concentration of the solution containing the compound of the doping element R is 0.01-0.2 g / mL.

[0058] According to the present invention, preferably, the molar ratio of the lanthanum element to the doping element R in the lanthanum hydroxide is 1:0.01-1, preferably 1:0.03-0.5, and more preferably 1:0.04-0.2.

[0059] According to the present invention, preferably, the compound containing the doping element R is selected from compounds of at least one element in Groups IIA, VIII, IB, and IIB, more preferably a compound of at least one element in Groups Mg, Ca, Sr, Ba, Fe, and Zn, and further preferably a compound of Sr and / or Ba. The compound containing the doping element R can be at least one of a nitrate (e.g., magnesium nitrate, calcium nitrate, strontium nitrate, barium nitrate, iron nitrate, zinc nitrate), a chloride (e.g., magnesium chloride, calcium chloride, strontium chloride, barium chloride, iron chloride, zinc chloride), and an acetate (e.g., magnesium acetate, calcium acetate, strontium acetate, barium acetate, iron acetate, zinc acetate) of the doping element R, preferably a nitrate.

[0060] According to the present invention, preferably, in step (2), a solution of a compound containing the doping element R is added to the solid lanthanum hydroxide obtained in step (1) using a specific contact method, rather than adding the solution of the compound containing the doping element R to the lanthanum hydroxide obtained in step (1). Without being limited to any known theory, it is believed that this specific addition method is conducive to the realization of the purpose of the present invention, especially, for example, the distribution of the doping element; and the corresponding higher conversion rate and selectivity, and especially the yield, brought about by the obtained catalyst. Thus, for the purpose of the present invention, a suitable specific contact method can be selected from lattice doping, surface precipitation, atomic layer deposition and single atomic layer plating. An example of a specific contact method that can be mentioned is surface precipitation, which comprises: adding a solution of a compound containing the doping element R dropwise to lanthanum hydroxide under stirring conditions, and continuing to stir after the addition is complete. More preferably, the addition rate of the solution of the compound containing the doping element R is 0.1 mL / min-10 mL / min, preferably 0.1 mL / min-8 mL / min, relative to each gram of lanthanum hydroxide.

[0061] According to the present invention, preferably, the contact conditions include: temperature of 15-50° C., and time of 2-5 h.

[0062] According to the present invention, in order to fully contact the solution containing the compound of the doping element R with lanthanum hydroxide, the contact is carried out in a vortex mixer.

[0063] According to the present invention, preferably, in step (2), the drying conditions include: a temperature of 60-100° C. and a drying time of 10-24 h.

[0064] According to the present invention, preferably, in step (3), the calcination conditions include: a temperature of 450-550°C and a time of 2-8 hours. According to the present invention, the carbon-containing atmosphere can be any atmosphere that can provide carbon for the purpose of the present invention and is not detrimental to obtaining the desired lanthanum oxycarbonate catalyst, in particular, an atmosphere containing CO and / or CO2. Preferably, the carbon-containing (e.g., CO and / or CO2) atmosphere can be an air atmosphere; accordingly, the carbon element in the lanthanum oxycarbonate catalyst is derived from carbon dioxide in the CO2-containing atmosphere.

[0065] According to the present invention, preferably, the lanthanum oxycarbonate catalyst having a specific structure obtained by the specific preparation method of the present invention exhibits clear characteristic peaks of the hexagonal phase when subjected to XRD measurement of the lanthanum oxycarbonate catalyst of the present invention, without the presence of characteristic peaks of the doping element in the form of a metal salt. For the purposes of the present invention, "absence of characteristic peaks" means the absence of measurable characteristic peaks in the XRD spectrum. Without being bound by any known theory, it is believed that this specific structure contributes to the catalytic activity of the lanthanum oxycarbonate catalyst of the present invention.

[0066] Another aspect of the present invention provides a lanthanum oxycarbonate catalyst prepared by the method described above.

[0067] Another 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.

[0068] Another aspect of the present invention provides a method for preparing C2 and higher hydrocarbons from methane, the method comprising: contacting methane with the above-mentioned lanthanum oxycarbonate catalyst in the presence of oxygen and under methane oxidative coupling reaction conditions;

[0069] Alternatively, the lanthanum oxycarbonate catalyst is prepared according to the method of the present invention, 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.

[0070] According to the present invention, preferably, the molar ratio of the methane to the oxygen is 2:1-9:1.

[0071] According to the present invention, preferably, the temperature of the contact reaction is 500-650°C.

[0072] According to the present invention, preferably, the space velocity of methane is 5000 mL / (g·h)-200000 mL / (g·h).

[0073] Example

[0074] The present invention will be described in detail below by way of examples, but the present invention is not limited to these examples. In the following examples:

[0075] TEM imaging was performed using a JEOL 2100F FEG TEM with a Schottky field emission source. The accelerating voltage was 200 kV. Representative images were selected from imaging of at least six different grid areas.

[0076] The length and diameter of the fibrous catalyst were measured using the ruler in the software provided with the transmission electron microscope image.

[0077] The analysis of the reaction product components was carried out on a gas chromatograph (Model 7890A) purchased from Agilent.

[0078] The XRD diffraction pattern was obtained by using an X-ray diffractometer (XRD) manufactured by PANalytical, model Empyrean, Cu target generator, working tube voltage 40KV, working tube current 40mA, PixCel 3DDetector: divergence slit 1 / 4°, anti-scatter slit 1 / 2°, light barrier 10 mm, Soller slit 0.04 rad, receiving slit 7.5 mm, scanning speed 0.013° / step, scanning time 30 s / step, scanning range: 5°-90°, measurement in reflection mode.

[0079] The hexagonal phase content is determined by an XRD spectrum. Specifically, the bulk crystal structure information is measured by the XRD spectrum, and the ratio of the diffraction peak area of ​​the hexagonal lanthanum oxycarbonate and the crystal structure containing the doped element to the total peak area is calculated, which is the weight percentage of the hexagonal lanthanum oxycarbonate and the hexagonal lanthanum oxycarbonate containing the doped element in the product.

[0080] The contents of lanthanum and doping element R in the catalyst were measured using an iCAP TQ ICP-MS purchased from Thermo Scientific.

[0081] The pore structure of the catalyst was characterized by BET analysis using an automatic adsorption analyzer ASAP2420M purchased from MICROMERITICS (Micromeritics Instruments, Inc., USA).

[0082] The methane conversion rate is calculated as follows:

[0083] Methane conversion rate = amount of methane consumed in the reaction / initial amount of methane × 100%.

[0084] The ethylene selectivity is calculated as follows:

[0085] Ethylene selectivity = amount of methane consumed by produced ethylene / total methane consumption × 100%.

[0086] The ethane selectivity is calculated as follows:

[0087] Ethane selectivity = amount of methane consumed by produced ethane / total methane consumption × 100%.

[0088] The calculation method of C2 hydrocarbon yield is as follows:

[0089] C2 hydrocarbon yield = methane conversion × (ethane selectivity + ethylene selectivity).

[0090] Example 1

[0091] (1) 5 g of lanthanum nitrate hexahydrate was dissolved in 210 g of deionized water and stirred at 25° C. and 900 rpm for 30 min. Then, sodium hydroxide solution was added dropwise to the lanthanum nitrate aqueous solution (the concentration of the sodium hydroxide solution was 10 wt %, and the addition rate of the alkali solution was 7 mL / min for each kilogram of the lanthanum source solution. The amount of the alkali solution was such that the final pH value of the mixed system of the alkali solution and the lanthanum source solution was 11.6). After the addition was completed, the mixture was stirred at 25° C. and 9000 rpm for 10 min. The mixture was then heated to 90° C. and kept under condensation reflux and stirred for 12 h. After the solution was cooled to room temperature, the solid material was separated by centrifugation at 1000 rpm and washed with deionized water until the pH value of the washing solution was neutral. The obtained solid was dried first and then dried second. The conditions for the first drying included: temperature of 80° C. and time of 12 h; the conditions for the second drying included: relative pressure of 60 kPa, temperature of 140° C. and time of 5 h.

[0092] Determine the saturated water absorption of the lanthanum hydroxide after the second drying: Under nitrogen, place 1 g of the second dried lanthanum hydroxide in a round-bottom flask. Add deionized water dropwise using a syringe and mix with the lanthanum hydroxide using a vortex mixer. Stop adding deionized water until the lanthanum hydroxide no longer absorbs significant water. Record the amount of deionized water added at this point. The saturated water absorption of the lanthanum hydroxide was determined to be 2 mL / g.

[0093] (2) 0.08 g of strontium nitrate was dissolved in 1.5 mL of deionized water to obtain an aqueous strontium nitrate solution. Under nitrogen protection, 0.8 g of the second dried lanthanum hydroxide was weighed and placed in a round-bottom flask. The aqueous strontium nitrate solution was then added dropwise to the round-bottom flask using a syringe at 25° C. (the addition rate of the solution containing the doping element compound was 1 mL / min per gram of the lanthanum hydroxide) and thoroughly mixed using a vortex mixer for 5 h. The resulting mixture was then dried at 80° C. for 12 h.

[0094] (3) Lanthanum carbonate catalyst was prepared by calcining at 500 °C for 2 h in air atmosphere.

[0095] The molar ratio of the catalyst lanthanum element to the strontium element is 1:0.091.

[0096] According to BET analysis, the specific surface area of ​​lanthanum oxycarbonate catalyst is 52m 2 / g, pore volume is 0.31cm 3 / g, and the average pore diameter is 10.1nm.

[0097] Figure 1 is an XRD spectrum of the lanthanum oxycarbonate catalyst prepared in Example 1, with the abscissa representing 2θ and the ordinate representing intensity. Comparison with the PXRD database (Bruker Diffrac.Eva, Version 4.2.1) shows that the catalyst prepared by this method exhibits characteristic peaks of a hexagonal phase, and due to its nanoscale nature, has low crystallinity. It can also be seen that only characteristic peaks of the hexagonal phase are observed in this XRD spectrum, while no characteristic peaks of the doping element in the form of a metal salt are present. The total content of hexagonal lanthanum oxycarbonate and hexagonal lanthanum oxycarbonate containing the doping element in the product, as determined by the XRD spectrum, is 98.0 wt%.

[0098] FIG2 is a transmission scanning electron micrograph of the lanthanum oxycarbonate catalyst prepared in Example 1. As can be seen from FIG2 , the lanthanum oxycarbonate catalyst has a fibrous nanostructure, and calculations show that the average diameter is 13 nm and the average aspect ratio is 40:1.

[0099] Example 2

[0100] (1) 5.15 g of lanthanum nitrate hexahydrate was dissolved in 155 g of deionized water and stirred at 25° C. and 900 rpm for 30 min. Then, sodium hydroxide solution was added dropwise to the lanthanum nitrate aqueous solution (the concentration of the sodium hydroxide solution was 10 wt %, and the addition rate of the alkali solution was 5 mL / min for each kilogram of the lanthanum source solution. The amount of the alkali solution was such that the final pH value of the mixed system of the alkali solution and the lanthanum source solution was 12.2). After the addition was completed, the mixture was stirred at 25° C. and 9000 rpm for 10 min. The mixture was then heated to 100° C. and kept under condensation reflux and stirred for 15 h. After the solution was cooled to room temperature, the solid material was separated by centrifugation at 9000 rpm and washed with deionized water until the pH value of the washing solution was neutral. The obtained solid was dried first and then dried second. The conditions for the first drying included: temperature of 80° C. and time of 15 h; the conditions for the second drying included: relative pressure of 50 kPa, temperature of 150° C. and time of 5 h.

[0101] Determine the saturated water absorption capacity of the lanthanum hydroxide after the second drying: Under nitrogen, place 1 g of the second dried lanthanum hydroxide in a round-bottom flask. Add deionized water dropwise using a syringe and mix with the lanthanum hydroxide using a vortex mixer. Stop adding deionized water until the lanthanum hydroxide no longer absorbs significant water. Record the amount of deionized water added at this point. The saturated water absorption capacity of the lanthanum hydroxide was determined to be 2.1 mL / g.

[0102] (2) 0.04 g of strontium nitrate was dissolved in 1.68 mL of deionized water to obtain an aqueous strontium nitrate solution. Under nitrogen protection, 0.9 g of the second dried lanthanum hydroxide was weighed and placed in a round-bottom flask. The aqueous strontium nitrate solution was then added dropwise to the round-bottom flask using a syringe at 30° C. (the addition rate of the solution containing the doping element compound was 4 mL / min per gram of the lanthanum hydroxide) and thoroughly mixed using a vortex mixer for 2 h. The resulting mixture was then dried at 80° C. for 13 h.

[0103] (3) Lanthanum carbonate catalyst was prepared by calcining at 500 °C for 2 h in air atmosphere.

[0104] The molar ratio of the catalyst lanthanum element to the strontium element is 1:0.046.

[0105] According to BET analysis, the specific surface area of ​​lanthanum oxycarbonate catalyst is 56m 2 / g, pore volume is 0.4cm 3 / g, and the average pore diameter is 13.4nm.

[0106] The XRD spectrum (similar to Example 1 and not shown here) shows only the characteristic peaks of the hexagonal phase, without any characteristic peaks of the doping element in its metal salt form. The total content of hexagonal lanthanum carbonate and hexagonal lanthanum carbonate containing the doping element in the product, as determined by XRD, was 98.6 wt%.

[0107] From the transmission scanning electron microscopy image (similar to Example 1, not shown again), it can be seen that the lanthanum oxycarbonate catalyst has a fibrous nanostructure, and it is calculated that the average diameter is 14 nm and the average aspect ratio is 35:1.

[0108] Example 3

[0109] (1) 10 g of lanthanum nitrate hexahydrate was dissolved in 155 g of deionized water and stirred at 25° C. and 900 rpm for 30 min. Then, sodium hydroxide solution was added dropwise to the lanthanum nitrate aqueous solution (the concentration of the sodium hydroxide solution was 10 wt %, and the addition rate of the alkali solution was 7 mL / min for each kilogram of the lanthanum source solution. The amount of the alkali solution was such that the final pH value of the mixed system of the alkali solution and the lanthanum source solution was 12). After the addition was completed, the mixture was stirred at 25° C. and 9000 rpm for 10 min. The mixture was then heated to 100° C. and kept under condensation reflux and stirred for 15 h. After the solution was cooled to room temperature, the solid material was separated by centrifugation at 900 rpm and washed with deionized water until the pH value of the washing solution was neutral. The obtained solid was dried first and then dried second. The conditions for the first drying included: temperature of 90° C. and time of 20 h; the conditions for the second drying included: relative pressure of 50 kPa, temperature of 160° C. and time of 3 h.

[0110] Determine the saturated water absorption of the lanthanum hydroxide after the second drying: Under nitrogen, place 1 g of the second dried lanthanum hydroxide in a round-bottom flask. Add deionized water dropwise using a syringe and mix with the lanthanum hydroxide using a vortex mixer. Stop adding deionized water until the lanthanum hydroxide no longer absorbs significant water. Record the amount of deionized water added at this point. The saturated water absorption of the lanthanum hydroxide was determined to be 2.4 mL / g.

[0111] (2) 0.13 g of strontium nitrate was dissolved in 1.92 mL of deionized water to obtain an aqueous strontium nitrate solution. Under nitrogen protection, 0.9 g of the second dried lanthanum hydroxide was weighed and placed in a round-bottom flask. The aqueous strontium nitrate solution was then added dropwise to the round-bottom flask using a syringe at 40° C. (the addition rate of the solution containing the doping element compound was 3 mL / min per gram of the lanthanum hydroxide) and thoroughly mixed using a vortex mixer for 2 h. The resulting mixture was then dried at 80° C. for 10 h.

[0112] (3) Lanthanum carbonate catalyst was prepared by calcining at 500 °C for 2 h in air atmosphere.

[0113] The molar ratio of the catalyst lanthanum element to the strontium element is 1:0.148.

[0114] According to BET analysis, the specific surface area of ​​lanthanum oxycarbonate catalyst is 51m 2 / g, pore volume is 0.3cm 3 / g, and the average pore diameter is 10.5nm.

[0115] The XRD spectrum (similar to Example 1 and not shown here) shows only the characteristic peaks of the hexagonal phase, without any characteristic peaks of the doping element in its metal salt form. The total content of hexagonal lanthanum carbonate and hexagonal lanthanum carbonate containing the doping element in the product, as determined by XRD, was 99.1 wt%.

[0116] From the transmission scanning electron microscopy image (similar to Example 1, not shown again), it can be seen that the lanthanum oxycarbonate catalyst has a fibrous nanostructure, and it is calculated that the average diameter is 18 nm and the average aspect ratio is 20:1.

[0117] Example 4

[0118] (1) 15 g of lanthanum nitrate hexahydrate was dissolved in 155 g of deionized water and stirred at 25° C. and 9000 rpm for 30 min. Then, sodium hydroxide solution was added dropwise to the lanthanum nitrate aqueous solution (the concentration of the sodium hydroxide solution was 10 wt %, and the addition rate of the alkali solution was 10 mL / min relative to each kilogram of the lanthanum source solution, based on the compound of the Group IA metal. The amount of the alkali solution was such that the final pH value of the mixed system of the alkali solution and the lanthanum source solution was 10). After the addition was completed, the mixture was stirred at 25° C. and 900 rpm for 10 min. The mixture was then heated to 100° C. and kept under condensation reflux and stirred for 15 h. After the solution was cooled to room temperature, the solid material was separated by centrifugation at 9000 rpm and washed with deionized water until the pH value of the washing solution was neutral. The obtained solid was subjected to first drying and second drying in sequence. The conditions for the first drying included: temperature of 80° C. and time of 15 h; the conditions for the second drying included: relative pressure of 40 kPa, temperature of 140° C. and time of 5 h.

[0119] Determine the saturated water absorption capacity of the lanthanum hydroxide after the second drying: Under nitrogen, place 1 g of the second dried lanthanum hydroxide in a round-bottom flask. Add deionized water dropwise using a syringe and mix with the lanthanum hydroxide using a vortex mixer. Stop adding deionized water until the lanthanum hydroxide no longer absorbs significant water. Record the amount of deionized water added at this point. The saturated water absorption capacity of the lanthanum hydroxide was determined to be 1.9 mL / g.

[0120] (2) 0.24 g of strontium nitrate was dissolved in 1.52 mL of deionized water to obtain an aqueous strontium nitrate solution. Under nitrogen protection, 0.9 g of the second dried lanthanum hydroxide was weighed and placed in a round-bottom flask. The aqueous strontium nitrate solution was then added dropwise to the round-bottom flask using a syringe at 35° C. (the addition rate of the solution containing the doping element compound was 1.5 mL / min per gram of the lanthanum hydroxide) and thoroughly mixed using a vortex mixer for 3 h. The resulting mixture was then dried at 80° C. for 15 h.

[0121] (3) Lanthanum carbonate catalyst was prepared by calcining at 500 °C for 2 h in air atmosphere.

[0122] The molar ratio of the catalyst lanthanum element to the strontium element is 1:0.146.

[0123] According to BET analysis, the specific surface area of ​​lanthanum oxycarbonate catalyst is 50m 2 / g, pore volume is 0.26cm 3 / g, and the average pore diameter is 11.6nm.

[0124] The XRD spectrum (similar to Example 1 and not shown here) shows only the characteristic peaks of the hexagonal phase, without any characteristic peaks of the doping element in its metal salt form. The total content of hexagonal lanthanum carbonate and hexagonal lanthanum carbonate containing the doping element in the product, as determined by XRD, was 99.4 wt%.

[0125] From the transmission scanning electron microscopy image (similar to Example 1, not shown again), it can be seen that the lanthanum oxycarbonate catalyst has a fibrous nanostructure, and it is calculated that the average diameter is 16 nm and the average aspect ratio is 15:1.

[0126] Example 5

[0127] Lanthanum oxycarbonate was prepared according to the method of Example 1, except that strontium nitrate was replaced by an equimolar amount of barium nitrate.

[0128] According to BET analysis, the specific surface area of ​​lanthanum carbonate catalyst is 49m 2 / g, pore volume is 0.29cm 3 / g, and the average pore diameter is 12.6nm.

[0129] From the transmission scanning electron microscopy image (similar to Example 1, not shown again), it can be seen that the lanthanum oxycarbonate catalyst has a fibrous nanostructure, and it is calculated that the average diameter is 22 nm and the average aspect ratio is 19:1.

[0130] Example 6

[0131] Lanthanum oxycarbonate was prepared according to the method of Example 1, except that, in step (1), the second drying process was not included.

[0132] According to BET analysis, the specific surface area of ​​lanthanum oxycarbonate catalyst is 68m 2 / g, pore volume is 0.39cm 3 / g, and the average pore diameter is 8.5nm.

[0133] The XRD spectrum (similar to Example 1 and not shown here) shows only the characteristic peaks of the hexagonal phase, without any characteristic peaks of the doping element in its metal salt form. The total content of hexagonal lanthanum carbonate and hexagonal lanthanum carbonate containing the doping element in the product, as determined by XRD, was 98.7 wt%.

[0134] From the transmission scanning electron microscopy, it can be seen that the lanthanum oxycarbonate catalyst has a fibrous nanostructure, and it is calculated that the average diameter is 21 nm and the average aspect ratio is 16:1.

[0135] Example 7

[0136] Lanthanum oxycarbonate was prepared according to the method of Example 1, except that strontium nitrate was replaced by an equimolar amount of zinc nitrate.

[0137] According to BET analysis, the specific surface area of ​​lanthanum oxycarbonate catalyst is 42m 2 / g, pore volume is 0.21cm 3 / g, and the average pore diameter is 9.8nm.

[0138] The XRD spectrum (similar to Example 1 and not shown here) shows only the characteristic peaks of the hexagonal phase, without any characteristic peaks of the doping element in its metal salt form. The total content of hexagonal lanthanum carbonate and hexagonal lanthanum carbonate containing the doping element in the product, as determined by XRD, was 98.2 wt%.

[0139] From the transmission scanning electron microscopy image (similar to Example 1, not shown again), it can be seen that the lanthanum oxycarbonate catalyst has a fibrous nanostructure, and it is calculated that the average diameter is 23 nm and the average aspect ratio is 18:1.

[0140] Example 8

[0141] Lanthanum oxycarbonate was prepared according to the method of Example 1, except that strontium nitrate was replaced by an equimolar amount of magnesium nitrate.

[0142] According to BET analysis, the specific surface area of ​​lanthanum oxycarbonate catalyst is 39m 2 / g, pore volume is 0.46cm 3 / g, and the average pore diameter is 15.2nm.

[0143] The XRD spectrum (similar to Example 1 and not shown here) shows only the characteristic peaks of the hexagonal phase, without any characteristic peaks of the doping element in its metal salt form. The total content of hexagonal lanthanum carbonate and hexagonal lanthanum carbonate containing the doping element in the product, as determined by XRD, was 98.9 wt%.

[0144] From the transmission scanning electron microscopy image (similar to Example 1, not shown again), it can be seen that the lanthanum oxycarbonate catalyst has a fibrous nanostructure, and it is calculated that the average diameter is 20 nm and the average aspect ratio is 16:1.

[0145] Example 9

[0146] Lanthanum oxycarbonate was prepared according to the method of Example 1, except that in step (2), the lanthanum hydroxide after the second drying was added to the strontium nitrate aqueous solution, mixed and stirred for 5 hours, and then the obtained mixture was dried at 80°C for 12 hours.

[0147] According to BET analysis, the specific surface area of ​​lanthanum oxycarbonate catalyst is 39m 2 / g, pore volume is 0.31cm3 / g, and the average pore diameter is 12.8nm.

[0148] The XRD spectrum (similar to Example 1 and not shown here) shows only the characteristic peaks of the hexagonal phase, without any characteristic peaks of the doping element in its metal salt form. The total content of hexagonal lanthanum carbonate and hexagonal lanthanum carbonate containing the doping element in the product, as determined by XRD, was 99.3 wt%.

[0149] From the transmission scanning electron microscopy image (similar to Example 1, not shown again), it can be seen that the lanthanum oxycarbonate catalyst has a fibrous nanostructure, and it is calculated that the average diameter is 16 nm and the average aspect ratio is 19:1.

[0150] Example 10

[0151] Lanthanum oxycarbonate was prepared according to the method of Example 1, except that the addition rate of the solution containing the compound of the doping element was 20 mL / min per gram of the lanthanum hydroxide.

[0152] According to BET analysis, the specific surface area of ​​lanthanum carbonate catalyst is 44m 2 / g, pore volume is 0.28cm 3 / g, and the average pore diameter is 11.2nm.

[0153] The XRD spectrum (similar to Example 1 and not shown here) shows only the characteristic peaks of the hexagonal phase, without any characteristic peaks of the doping element in its metal salt form. The total content of hexagonal lanthanum carbonate and hexagonal lanthanum carbonate containing the doping element in the product, as determined by XRD, was 99.5 wt%.

[0154] From the transmission scanning electron microscopy image (similar to Example 1, not shown again), it can be seen that the lanthanum oxycarbonate catalyst has a fibrous nanostructure, and it is calculated that the average diameter is 20 nm and the average aspect ratio is 18.6:1.

[0155] Example 11

[0156] Lanthanum oxycarbonate was prepared according to the method of Example 1, except that in step (2), the amount of deionized water used was 5 mL.

[0157] According to BET analysis, the specific surface area of ​​lanthanum oxycarbonate catalyst is 38m 2 / g, pore volume is 0.2cm 3 / g, and the average pore diameter is 13.3nm.

[0158] The XRD spectrum (similar to Example 1 and not shown here) shows only the characteristic peaks of the hexagonal phase, without any characteristic peaks of the doping element in its metal salt form. The total content of hexagonal lanthanum carbonate and hexagonal lanthanum carbonate containing the doping element in the product, as determined by XRD, was 99.6 wt%.

[0159] From the transmission scanning electron microscopy image (similar to Example 1, not shown again), it can be seen that the lanthanum oxycarbonate catalyst has a fibrous nanostructure, and it is calculated that the average diameter is 21 nm and the average aspect ratio is 17:1.

[0160] Example 12

[0161] (1) 15 g of lanthanum nitrate hexahydrate was dissolved in 155 g of deionized water and stirred at 25° C. and 900 rpm for 30 min. Then, sodium hydroxide solution was added dropwise to the lanthanum nitrate aqueous solution (the concentration of the sodium hydroxide solution was 10 wt %, and the addition rate of the alkali solution was 10 mL / min relative to each kilogram of the lanthanum source solution, based on the compound of the Group IA metal. The amount of the alkali solution was such that the final pH value of the mixed system of the alkali solution and the lanthanum source solution was 10). After the addition was completed, the mixture was stirred at 25° C. and 9000 rpm for 10 min. The mixture was then heated to 100° C. and kept under condensation reflux and stirred for 15 h. After the solution was cooled to room temperature, the solid material was separated by centrifugation at 9000 rpm and washed with deionized water until the pH value of the washing solution was neutral. The obtained solid was subjected to first drying and second drying in sequence. The conditions for the first drying included: temperature of 80° C. and time of 15 h; the conditions for the second drying included: relative pressure of 40 kPa, temperature of 140° C. and time of 5 h.

[0162] Determine the saturated water absorption capacity of the lanthanum hydroxide after the second drying: Under nitrogen, place 1 g of the second dried lanthanum hydroxide in a round-bottom flask. Add deionized water dropwise using a syringe and mix with the lanthanum hydroxide using a vortex mixer. Stop adding deionized water until the lanthanum hydroxide no longer absorbs significant water. Record the amount of deionized water added at this point. The saturated water absorption capacity of the lanthanum hydroxide was determined to be 1.9 mL / g.

[0163] (2) 0.24 g of ferric nitrate was dissolved in 1.52 mL of deionized water to obtain an aqueous strontium nitrate solution. Under nitrogen protection, 0.9 g of the second dried lanthanum hydroxide was weighed and placed in a round-bottom flask. Then, the ferric nitrate aqueous solution was added dropwise to the round-bottom flask using a syringe at 35° C. (the addition rate of the solution containing the doping element compound was 1.5 mL / min per gram of the lanthanum hydroxide) and the solution was thoroughly mixed using a vortex mixer for 3 hours. The resulting mixture was then dried at 80° C. for 15 hours.

[0164] (3) Lanthanum carbonate catalyst was prepared by calcining at 500 °C for 2 h in air atmosphere.

[0165] The molar ratio of the catalyst lanthanum element to the iron element is 1:0.13.

[0166] According to BET analysis, the specific surface area of ​​lanthanum oxycarbonate catalyst is 48m 2 / g, pore volume is 0.36cm 3 / g, and the average pore diameter is 13.8nm.

[0167] The XRD spectrum (similar to Example 1 and not shown here) shows only the characteristic peaks of the hexagonal phase, without any characteristic peaks of the doping element in its metal salt form. The total content of hexagonal lanthanum carbonate and hexagonal lanthanum carbonate containing the doping element in the product, as determined by XRD, was 98.1 wt%.

[0168] From the transmission scanning electron microscopy image (similar to Example 1, not shown again), it can be seen that the lanthanum oxycarbonate catalyst has a fibrous nanostructure, and it is calculated that the average diameter is 20 nm and the average aspect ratio is 20:1.

[0169] Example 13

[0170] (1) 5 g of lanthanum nitrate hexahydrate was dissolved in 210 g of deionized water and stirred at 25° C. and 900 rpm for 30 min. Then, sodium hydroxide solution was added dropwise to the lanthanum nitrate aqueous solution (the concentration of the sodium hydroxide solution was 10 wt %, and the addition rate of the alkali solution was 7 mL / min for each kilogram of the lanthanum source solution. The amount of the alkali solution was such that the final pH value of the mixed system of the alkali solution and the lanthanum source solution was 11.6). After the addition was completed, the mixture was stirred at 25° C. and 9000 rpm for 10 min. The mixture was then heated to 90° C. and kept under condensation reflux and stirred for 12 h. After the solution was cooled to room temperature, the solid material was separated by centrifugation at 1000 rpm and washed with deionized water until the pH value of the washing solution was neutral. The obtained solid was dried first and then dried second. The conditions for the first drying included: temperature of 80° C. and time of 12 h; the conditions for the second drying included: relative pressure of 60 kPa, temperature of 140° C. and time of 5 h.

[0171] Determine the saturated water absorption of the lanthanum hydroxide after the second drying: Under nitrogen, place 1 g of the second dried lanthanum hydroxide in a round-bottom flask. Add deionized water dropwise using a syringe and mix with the lanthanum hydroxide using a vortex mixer. Stop adding deionized water until the lanthanum hydroxide no longer absorbs significant water. Record the amount of deionized water added at this point. The saturated water absorption of the lanthanum hydroxide was determined to be 2 mL / g.

[0172] (2) 0.06 g of calcium nitrate was dissolved in 1.5 mL of deionized water to obtain a calcium nitrate aqueous solution. Under nitrogen protection, 1.0 g of the second dried lanthanum hydroxide was weighed and placed in a round-bottom flask. The calcium nitrate aqueous solution was then added dropwise to the round-bottom flask using a syringe at 25° C. (the addition rate of the solution containing the doping element calcium compound was 1 mL / min per gram of the lanthanum hydroxide) and thoroughly mixed using a vortex mixer for 5 h. The resulting mixture was then dried at 80° C. for 12 h.

[0173] (3) Lanthanum carbonate catalyst was prepared by calcining at 500 °C for 2 h in air atmosphere.

[0174] The molar ratio of the catalyst lanthanum element to the calcium element is 1:0.11.

[0175] According to BET analysis, the specific surface area of ​​lanthanum carbonate catalyst is 49m 2 / g, pore volume is 0.3cm 3 / g, and the average pore diameter is 10.2nm.

[0176] The XRD spectrum (similar to Example 1 and not shown here) shows only the characteristic peaks of the hexagonal phase, without any characteristic peaks of the doping element in its metal salt form. The total content of hexagonal lanthanum carbonate and hexagonal lanthanum carbonate containing the doping element in the product, as determined by XRD, was 99.3 wt%.

[0177] From the transmission scanning electron microscopy image (similar to Example 1, not shown again), it can be seen that the lanthanum oxycarbonate catalyst has a fibrous nanostructure, and it is calculated that the average diameter is 18 nm and the average aspect ratio is 20:1.

[0178] Comparative Example 1

[0179] (1) 5 g of lanthanum nitrate hexahydrate was dissolved in 210 g of deionized water and stirred at 25° C. and 900 rpm for 30 min. Then, sodium hydroxide solution was added dropwise to the lanthanum nitrate aqueous solution (the concentration of the sodium hydroxide solution was 10 wt %, and the addition rate of the alkali solution was 7 mL / min for each kilogram of the lanthanum source solution. The amount of the alkali solution was such that the final pH value of the mixed system of the alkali solution and the lanthanum source solution was 11.6). After the addition was completed, the mixture was stirred at 25° C. and 9000 rpm for 10 min. The mixture was then heated to 90° C. and kept under condensation reflux and stirred for 12 h. After the solution was cooled to room temperature, the solid material was separated by centrifugation at 10,000 rpm and washed with deionized water until the pH value of the washing solution was neutral. The obtained solid was dried first and then dried second in sequence. The conditions for the first drying included: temperature of 80° C. and time of 12 h; the conditions for the second drying included: relative pressure of 60 kPa, temperature of 140° C. and time of 5 h. Lanthanum oxycarbonate catalyst was prepared by calcining at 500℃ for 2h in air atmosphere.

[0180] According to BET analysis, the specific surface area of ​​lanthanum oxycarbonate catalyst is 68m 2 / g, pore volume is 6cm 3 / g, and the average pore diameter is 42nm.

[0181] The XRD spectrum (similar to Example 1 and not shown here) shows only the characteristic peaks of the hexagonal phase, without the characteristic peaks of the doping element in the form of a metal salt. The total content of hexagonal lanthanum carbonate in the product was determined to be 98.2 wt%.

[0182] From the transmission scanning electron microscopy image (similar to Example 1, not shown again), it can be seen that the lanthanum oxycarbonate catalyst has a fibrous nanostructure, and it is calculated that the average diameter is 12 nm and the average aspect ratio is 15:1.

[0183] Comparative Example 2

[0184] (1) Lanthanum hydroxide was prepared according to the method of step (1) of Example 1.

[0185] (2) 0.08 g of strontium nitrate was calcined at 500°C for 2 h in an air atmosphere.

[0186] (3) 0.8 g of lanthanum hydroxide was calcined at 500°C for 2 h in an air atmosphere.

[0187] (4) The product obtained in step (2) and the product obtained in step (3) are then mixed uniformly to obtain a catalyst.

[0188] According to BET analysis, the specific surface area of ​​lanthanum oxycarbonate catalyst is 40m 2 / g, pore volume is 2.3cm3 / g, and the average pore diameter is 14.2nm.

[0189] The XRD spectrum (similar to Example 1 and not shown here) shows only the characteristic peaks of the hexagonal phase, without any characteristic peaks of the doping element in its metal salt form. The total content of hexagonal lanthanum carbonate and hexagonal lanthanum carbonate containing the doping element in the product, as determined by XRD, was 82.3 wt%.

[0190] Comparative Example 3

[0191] (1) 5 g of lanthanum nitrate hexahydrate was dissolved in 210 g of deionized water and stirred at 25° C. and 900 rpm for 30 min. Then, sodium hydroxide solution was added dropwise to the lanthanum nitrate aqueous solution (the concentration of the sodium hydroxide solution was 10 wt %, and the addition rate of the alkali solution was 7 mL / min for each kilogram of the lanthanum source solution. The amount of the alkali solution was such that the final pH value of the mixed system of the alkali solution and the lanthanum source solution was 11.6). After the addition was completed, the mixture was stirred at 25° C. and 9000 rpm for 10 min. The mixture was then heated to 90° C. and kept under condensation reflux and stirred for 12 h. After the solution was cooled to room temperature, the solid material was separated by centrifugation at 10,000 rpm and washed with deionized water until the pH value of the washing solution was neutral. The obtained solid was dried first and then dried second in sequence. The conditions for the first drying included: temperature of 80° C. and time of 12 h; the conditions for the second drying included: relative pressure of 60 kPa, temperature of 140° C. and time of 5 h.

[0192] Determine the saturated water absorption of the lanthanum hydroxide after the second drying: Under nitrogen, place 1 g of the second dried lanthanum hydroxide in a round-bottom flask. Add deionized water dropwise using a syringe and mix with the lanthanum hydroxide using a vortex mixer. Stop adding deionized water until the lanthanum hydroxide no longer absorbs significant water. Record the amount of deionized water added at this point. The saturated water absorption of the lanthanum hydroxide was determined to be 2 mL / g.

[0193] (2) Dissolve 0.08 g of strontium nitrate in 1.5 mL of deionized water to obtain a strontium nitrate aqueous solution. Under nitrogen protection, weigh 0.8 g of the second dried lanthanum hydroxide, and then add the lanthanum hydroxide solid directly to the strontium nitrate solution at 25°C. The resulting mixture is then dried at 80°C for 12 h.

[0194] (3) Lanthanum carbonate catalyst was prepared by calcining at 500 °C for 2 h in air atmosphere.

[0195] Comparative Example 4

[0196] Dissolve 0.26 g of barium nitrate in 10 mL of deionized water and stir to dissolve it completely. Weigh 2 g of the prepared hexagonal lanthanum carbonate, drop the barium nitrate aqueous solution into the hexagonal lanthanum carbonate, stir to mix evenly, place in an 80°C oven for 24 hours, then transfer to a muffle furnace, heat to 500°C at 2°C / min, and maintain for 2 hours to prepare Ba / La2O2CO3.

[0197] FIG3 is an XRD spectrum of the lanthanum oxycarbonate catalyst prepared in Comparative Example 4. It can be seen that the XRD results show that in addition to the peak of lanthanum oxycarbonate, a characteristic peak of BaCO4 is also obtained in the sample.

[0198] Comparative Example 5

[0199] Dissolve 0.3 g of nickel nitrate hexahydrate in 10 mL of deionized water and stir to dissolve it completely. Weigh 2 g of the prepared hexagonal lanthanum carbonate, drop the nickel nitrate aqueous solution into the hexagonal lanthanum carbonate, stir to mix evenly, place in an 80°C oven for 24 h, then transfer to a muffle furnace, heat to 500°C at 2°C / min, and maintain for 2 h to prepare Ni / La2O2CO3.

[0200] Test Example 1

[0201] The catalysts prepared in the above examples and comparative examples were tableted and sieved through 40-60 mesh. Then, 0.1 g was taken and loaded into an Inconel fixed bed reactor. Under normal pressure, methane and oxygen (the molar ratio of methane to oxygen was 3:1) were introduced to react. Other reaction conditions and results are shown in Table 1.

[0202] Table 1

[0203] It can be seen from the results in Table 1 that, compared with Comparative Example 1, the lanthanum oxycarbonate catalyst containing the doping element R of the present invention has a higher yield of two carbon hydrocarbons at 500-650°C. Particularly preferably, the yield of two carbon hydrocarbons using the catalysts of Examples 1-5 is higher than 15% at 550-650°C.

[0204] In Comparative Example 2, the catalyst obtained by directly mixing lanthanum oxycarbonate and strontium oxide has a carbon dihydrogen yield of less than 10%, while the carbon dihydrogen yield of the catalyst prepared by the method of Example 1 of the present invention is 16.8%. Therefore, compared with the direct mixing method of Comparative Example 2, the element doping method of the present invention can improve the carbon dihydrogen yield.

[0205] In Comparative Example 3, solid lanthanum hydroxide was added to a strontium nitrate solution, rather than the method of the present invention of dropwise adding the strontium nitrate aqueous solution to the solid lanthanum hydroxide. The resulting catalyst had a C2 hydrocarbon yield of less than 10%.

[0206] Comparative Example 4, using a conventional impregnation method for doping, yielded a catalyst with low methane conversion, C2 selectivity, and yield. In particular, the performance of the catalyst obtained using this method was significantly affected by temperature, with conversion, selectivity, and yield all being very low at 500°C.

[0207] Comparative Example 5 uses Ni instead of the specific doping element of the present invention for doping, which obviously results in the production of the target product, carbon dihydrocarbon, failing to achieve the desired purpose. The selectivity and yield of carbon dihydrocarbon at various temperatures are very low.

[0208] 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 oxycarbonate catalyst, characterized in that The catalyst includes hexagonal lanthanum oxycarbonate and hexagonal lanthanum oxycarbonate containing a doping element R, and the total content of the hexagonal lanthanum oxycarbonate and the hexagonal lanthanum oxycarbonate containing the doping element R in the catalyst is not less than 98wt%, wherein the molar ratio of the lanthanum element to the doping element R is 1:0.01-1:0.3; and the doping element R is selected from at least one of Mg, Ca, Sr, Ba, Fe and Zn.

2. The lanthanum oxycarbonate catalyst according to claim 1, wherein The doping element R is Sr and / or Ba.

3. The lanthanum oxycarbonate catalyst according to claim 1, wherein The total content of hexagonal lanthanum oxycarbonate and hexagonal lanthanum oxycarbonate containing the doping element R in the lanthanum oxycarbonate catalyst is not less than 99 wt %; and / or, The molar ratio of the lanthanum element to the doping element R in the lanthanum oxycarbonate catalyst is 1:0.03-1:0.2, preferably 1:0.04-1:0.

15.

4. The lanthanum oxycarbonate catalyst according to any one of claims 1 to 3, wherein The lanthanum oxycarbonate catalyst has a fibrous nanostructure; the diameter of the lanthanum oxycarbonate catalyst is 10 nm-30 nm, preferably 10 nm-20 nm, and the aspect ratio is 5:1-50:1, preferably 15:1-40:1; and / or, The specific surface area of ​​the lanthanum oxycarbonate catalyst is 35m 2 / g-90m 2 / g, preferably 50m 2 / g-60m 2 / g, pore volume is 0.15cm 3 / g-0.5cm 3 / g, preferably 0.26cm 3 / g-0.4cm 3 / g, and the average pore diameter is 8nm-16nm, preferably 10nm-13.5nm.

5. The lanthanum oxycarbonate catalyst according to any one of claims 1 to 3, wherein The XRD spectrum of the lanthanum oxycarbonate catalyst does not have the characteristic peak of the doping element in the form of a metal salt.

6. A method for preparing the lanthanum oxycarbonate catalyst according to any one of the preceding claims, characterized in that The method includes: (1) adding an alkali solution to a solution of a lanthanum source, and then performing solid-liquid separation and drying to obtain solid lanthanum hydroxide; wherein the drying comprises a first drying and a second drying, wherein the conditions of the first drying comprise: a temperature of 70-90° C. and a time of 10-20 hours, and the second drying is performed at a higher temperature and a shorter time than the first drying; Determine the saturated water absorption of the second dried lanthanum hydroxide: Under nitrogen protection, take 1 g of the second dried lanthanum hydroxide and place it in a container. Add water to mix evenly with the lanthanum hydroxide until the lanthanum hydroxide no longer absorbs water. Record the amount of water added at this time as the saturated water absorption of the lanthanum hydroxide. (2) adding a solution of a compound containing a doping element R to the solid lanthanum hydroxide obtained in step (1) so that the solution contacts the lanthanum hydroxide in an amount less than or equal to the saturated water absorption capacity of the lanthanum hydroxide, and then drying; wherein the contacting method is selected from lattice doping, surface precipitation, atomic layer deposition, and single atomic layer plating; (3) calcining the dried product of step (2) in a carbon-containing atmosphere to obtain a lanthanum oxycarbonate catalyst.

7. The method according to claim 6, wherein the alkali in the alkali solution is a compound of a Group IA metal, preferably the concentration of the alkali solution is 3 wt% to 25 wt%; and / or, The amount of the alkali solution is such that the final pH value of the mixed system of the alkali solution and the lanthanum source solution is 10-12.5; and / or, The lanthanum source is a water-soluble salt of lanthanum, preferably at least one of lanthanum nitrate, lanthanum chloride and lanthanum acetate. The concentration of the lanthanum source solution is preferably 0.01 wt%-10 wt%.

8. The method according to claim 6, wherein: In step (1), aging is performed before solid-liquid separation, and the aging conditions include: temperature of 80-100° C. and time of 10-50 h; and / or, Preferably, the second drying conditions include: relative pressure of 10 kPa-91 kPa, preferably 20 kPa-70 kPa, temperature of 120-160° C., and time of 2-10 h.

9. The method according to claim 6, wherein: Step (2) is carried out under a protective atmosphere provided by an inert gas and / or nitrogen; and / or, The concentration of the solution containing the compound of the doping element R is 0.01-0.2 g / mL; and / or, The molar ratio of the lanthanum element to the doping element R in the lanthanum hydroxide is 1:0.01-1:1; and / or, The compound containing the doping element R is a compound of at least one element selected from Mg, Ca, Sr, Ba, Fe and Zn, preferably a compound of Sr and / or Ba; and / or, The contact conditions include: temperature of 15-50°C and time of 2-5 hours.

10. The method according to claim 6, wherein In step (2), the addition rate of the solution of the compound containing the doping element R is 0.1 mL / min-10 mL / min, preferably 0.1 mL / min-8 mL / min, relative to each gram of the lanthanum hydroxide; And or, the drying conditions include: temperature of 60-100°C and time of 10-24h.

11. The method according to claim 6, wherein In step (3), the carbon-containing atmosphere is an atmosphere containing CO and / or CO2; and / or The calcination conditions include: temperature of 450-550° C. and time of 2-8 hours.

12. The method according to claim 6, wherein the amount of the solution containing the compound of the doping element R in contact with the lanthanum hydroxide is equal to or substantially equal to the saturated water absorption capacity of the lanthanum hydroxide.

13. Use of the lanthanum oxycarbonate catalyst according to any one of claims 1 to 5 in the oxidative coupling reaction of methane to produce C2 or higher hydrocarbons.

14. A method for preparing hydrocarbons with a carbon content of two or more from methane, characterized in that: The method includes: In the presence of oxygen and under the conditions of methane oxidative coupling reaction, methane is contacted with the lanthanum oxycarbonate catalyst according to any one of claims 1 to 5 for reaction; or, A lanthanum oxycarbonate catalyst is prepared according to the method according to any one of claims 6 to 12, and then methane is contacted with the obtained lanthanum oxycarbonate catalyst in the presence of oxygen and under the conditions of a methane oxidative coupling reaction.

15. The method according to claim 13, wherein: The molar ratio of the methane to the oxygen is 2:1-9:1; and / or, The temperature of the contact reaction is 500-650°C; and / or, The space velocity of the methane is 5000 mL / (g·h)-200000 mL / (g·h).

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