Lanthanum oxide carbonate catalyst, method for preparing same, and use thereof

Abstract

The present application relates to the technical field of oxy-lanthanum carbonate, and discloses an oxy-lanthanum carbonate catalyst, a preparation method and application thereof, the oxy-lanthanum carbonate catalyst comprising hexagonal crystal phase oxy-lanthanum carbonate and hexagonal crystal phase oxy-lanthanum carbonate containing doping element R.The method comprises the following steps: (1) adding an alkali solution into a solution of a lanthanum source, and then performing solid-liquid separation and drying to obtain lanthanum hydroxide; (2) contacting a solution containing a compound of doping element R with the lanthanum hydroxide, and then performing drying; (3) performing calcination on the dried product of step (2) in a carbon-containing atmosphere to obtain the oxy-lanthanum carbonate catalyst.The catalyst prepared by the present application has a high carbon dihydrocarbon yield when used in a methane oxidative coupling reaction.

Description

Technical Field

[0001] This invention relates to lanthanum oxycarbonate catalysts, their preparation methods, and applications. Background Technology

[0002] Lanthanum oxycarbonate is a novel material primarily used in water treatment, optoelectronics, and catalysis. Currently, the main methods for synthesizing lanthanum oxycarbonate include precipitation, thermal decomposition of lanthanum carbonate, and hydrothermal synthesis. However, lanthanum oxycarbonate is typically prepared via a two-step process: first, the La(OH)3 precursor is synthesized, followed by calcination at low temperature. Current improvements to lanthanum oxycarbonate materials mainly focus on modifying the preparation method to obtain lanthanum oxycarbonate with different 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 C2 hydrocarbons from this lanthanum oxycarbonate is low.

[0004] In existing technologies, there are very few methods for elemental doping of lanthanum oxycarbonate materials. Only a few documents have reported on impregnating lanthanum oxycarbonate materials with solutions containing dopant elements. However, there are no reports in existing technologies on completing elemental doping during the preparation of lanthanum oxycarbonate. Summary of the Invention

[0005] This invention provides a lanthanum oxycarbonate catalyst, its preparation method, and its application. This catalyst is particularly suitable for activating the oxidative coupling of methane and exhibits, for example, a high yield of C2 hydrocarbons at 500-650°C.

[0006] To achieve the above objectives, the present invention provides a lanthanum oxycarbonate catalyst comprising hexagonal lanthanum oxycarbonate and hexagonal lanthanum oxycarbonate containing dopant element R; the total content of hexagonal lanthanum oxycarbonate and hexagonal lanthanum oxycarbonate containing dopant 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 to dopant element R is 1:0.01-1:0.3; and the dopant element R is selected from at least one of Mg, Ca, Sr, Ba, Fe and Zn.

[0007] Preferably, the XRD spectrum of the present invention does not show characteristic peaks of the dopant element in the form of metal salt.

[0008] In another aspect, the present invention provides a method for preparing the lanthanum oxycarbonate catalyst of the present invention, the method comprising:

[0009] (1) An alkaline solution is added to a solution of a lanthanum source, and then, optionally, aging, solid-liquid separation and drying are performed to obtain solid lanthanum hydroxide; wherein the drying includes a first drying and a second drying, wherein the conditions for the first drying include a temperature of 70-90°C and a time of 10-20 h, and the second drying is performed at a higher temperature and for a shorter time than the first drying.

[0010] Determine the saturated water absorption of the second dried lanthanum hydroxide: Under nitrogen protection, take 1g of the second dried lanthanum hydroxide and place it in a container. Add water to mix it evenly with the lanthanum hydroxide until the lanthanum hydroxide no longer absorbs water significantly. Record the amount of water added at this time as the saturated water absorption of the lanthanum hydroxide.

[0011] (2) Optionally, under a protective atmosphere, the solid lanthanum hydroxide obtained in step (1) is contacted with lanthanum hydroxide in an amount less than or equal to the saturated water absorption of lanthanum hydroxide, and then dried; wherein the contact method is selected from surface precipitation, atomic layer deposition and monoatom layer plating.

[0012] (3) The dried product from step (2) is calcined in a carbon-containing atmosphere (e.g., CO and / or CO2) to obtain a lanthanum oxycarbonate catalyst.

[0013] In another aspect, the present invention provides a lanthanum oxycarbonate catalyst prepared by the method described above.

[0014] In another aspect, the present invention provides the application of the above-described lanthanum oxycarbonate catalyst in the oxidative coupling reaction of methane to produce C2 and above hydrocarbons.

[0015] Another aspect of the present invention provides a method for preparing C2 and above hydrocarbons from methane, the method comprising: reacting methane with the lanthanum oxycarbonate catalyst described in the present invention in the presence of oxygen and under conditions of methane oxidative coupling reaction; or,

[0016] A lanthanum oxycarbonate catalyst was prepared according to the method described in this invention, and then methane was reacted with the obtained lanthanum oxycarbonate catalyst in the presence of oxygen and under the conditions of methane oxidative coupling reaction.

[0017] The catalyst provided by this invention contains both hexagonal lanthanum oxycarbonate and hexagonal lanthanum oxycarbonate with dopant element R, which can effectively promote the occurrence of methane oxidative coupling reaction and improve the yield of C2 hydrocarbons.

[0018] This invention first prepares lanthanum hydroxide by adding an alkaline solution to a lanthanum-containing solution, and then prepares a catalyst by contacting a solution containing dopant element R with the lanthanum hydroxide. The prepared catalyst comprises hexagonal lanthanum oxycarbonate and hexagonal lanthanum oxycarbonate containing dopant element R. The catalyst prepared by this invention exhibits a high yield of C2 hydrocarbons when used in the oxidative coupling reaction of methane. Attached Figure Description

[0019] Figure 1 This is the XRD pattern of the lanthanum oxycarbonate catalyst prepared in Example 1;

[0020] Figure 2 This is a transmission scanning electron microscope image of the lanthanum oxycarbonate catalyst prepared in Example 1;

[0021] Figure 3 This is the XRD pattern of the lanthanum oxycarbonate catalyst prepared in Comparative Example 4. Detailed Implementation

[0022] The endpoints and any values ​​of the ranges 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 endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0023] Unless otherwise specified, all percentages, portions, ratios, etc., mentioned herein are based on weight, unless being based on weight would not be in accordance with the common understanding of those skilled in the art.

[0024] In this document, unless otherwise stated, the terms “comprising,” “including,” “containing,” “having,” and similar terms indicate an open-ended meaning, but should also be understood to explicitly disclose a closed-ended meaning. For example, “comprising” means that other elements not listed may also be included, but also explicitly discloses the inclusion of only the listed elements. Furthermore, as used herein, “comprising / including” is interpreted as explicitly stating the presence of the mentioned feature, integer, step, or component, 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 covered by the terms “substantially constitutes…” and “consisting of…”. Similarly, the term “substantially constitutes…” is intended to include embodiments covered by the term “consisting of…”.

[0025] This invention provides a lanthanum oxycarbonate catalyst comprising hexagonal lanthanum oxycarbonate and hexagonal lanthanum oxycarbonate containing dopant element R; the total content of hexagonal lanthanum oxycarbonate and hexagonal lanthanum oxycarbonate containing dopant 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 to dopant element R is 1:0.01-1:0.3; and the dopant element R is selected from at least one of Mg, Ca, Sr, Ba, Fe and Zn.

[0026] Not 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 lanthanum to dopant element R, and especially a specific preparation process that ensures that the majority (not less than 98 wt%, preferably not less than 99 wt%) of lanthanum oxycarbonate and lanthanum oxycarbonate containing dopant element R in the obtained lanthanum oxycarbonate catalyst exists in the form of a hexagonal crystal phase, which can guarantee a desirable catalyst structure, including the content and distribution of dopant elements; thereby benefiting the catalyst activity, especially when it is used to activate methane oxidative coupling, resulting in a high methane conversion rate, as well as a high C2 hydrocarbon selectivity and yield.

[0027] According to the present invention, the total content of hexagonal lanthanum oxycarbonate and hexagonal lanthanum oxycarbonate containing dopant element R in the lanthanum oxycarbonate catalyst is not less than 98% wt%, preferably not less than 99% wt%, and even not less than 99.5 wt%, or close to 100 wt%. This means that although the lanthanum oxycarbonate is processed in multiple steps in the present invention, the hexagonal lanthanum oxycarbonate catalyst obtained is absolutely dominant in terms of crystal phase, which ensures the high purity of the hexagonal lanthanum oxycarbonate phase relative to other crystal phases.

[0028] For the purposes of this invention, the content of hexagonal phases, such as the total content of hexagonal lanthanum oxycarbonate and hexagonal lanthanum oxycarbonate containing dopant element R, is determined by XRD patterns. Specifically, for example, the bulk crystal structure information is obtained by XRD patterns, and the ratio of the peak area of ​​the diffraction peaks of the hexagonal lanthanum oxycarbonate and the dopant crystal structure to the total peak area is calculated, which represents the weight percentage of hexagonal lanthanum oxycarbonate and the dopant hexagonal lanthanum oxycarbonate in the product.

[0029] According to the present invention, preferably, the dopant element R is selected from at least one element selected from Group IIA, VIII, IB and IIB, more preferably at least one element selected from Mg, Ca, Sr, Ba, Fe and Zn, and even more 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 to any known theory, it is believed that dopant element R selected from Mg, Ca, Sr, Ba, Fe and Zn is particularly beneficial for higher methane conversion, as well as higher C2 hydrocarbon selectivity and yield, especially higher C2 hydrocarbon yield, especially when used for activating methane oxidative coupling.

[0030] According to the present invention, preferably, the molar ratio of lanthanum to dopant R in the lanthanum oxycarbonate catalyst is 1:0.03-1:0.2, more preferably 1:0.04-1:0.15. The molar ratio of lanthanum to dopant R in the lanthanum oxycarbonate catalyst can be calculated based on the amount of lanthanum and dopant R fed.

[0031] According to the present invention, preferably, the lanthanum oxycarbonate catalyst has a fibrous nanostructure, the diameter of the lanthanum oxycarbonate catalyst is 10nm-30nm, preferably 10nm-20nm, and the aspect ratio is 5-50:1, more preferably 15-40:1.

[0032] In this invention, the "particle size / diameter" and "aspect ratio" of the lanthanum oxycarbonate catalyst are both average values. The specific method for testing the "average particle size / diameter" is to use a transmission electron microscope (TEM) scale, select 5-10 samples within the viewing window, measure the diameter of each sample, and then calculate the average value. The specific method for testing the "average aspect ratio" is to use a TEM scale, select 5-10 samples within the viewing window, measure the diameter and length of each sample, calculate the aspect ratio of each sample, and then calculate the average value.

[0033] According to the present invention, preferably, the specific surface area of ​​the lanthanum oxycarbonate catalyst is 35 m². 2 / g-90m 2 / g, preferably 45m 2 / g-85m 2 / g, preferably 50m 2 / g-60m 2 / g, pore volume 0.15cm 3 / g-0.5cm 3 / g, preferably 0.26cm 3 / g-0.4cm 3 / g, with an average pore size of 8nm-16nm, preferably 8nm-15nm, and even more preferably 10nm-13.5nm.

[0034] Another aspect of the present invention provides a method for preparing the lanthanum oxycarbonate catalyst of the present invention, the method comprising:

[0035] (1) An alkaline solution is added to a solution of a lanthanum source, and then, optionally, aging, solid-liquid separation and drying are performed to obtain solid lanthanum hydroxide; wherein the drying includes a first drying and a second drying, wherein the conditions for the first drying include a temperature of 70-90°C and a time of 10-20 h, and the second drying is performed at a higher temperature and for a shorter time than the first drying.

[0036] Determine the saturated water absorption of the second dried lanthanum hydroxide: Under nitrogen protection, take 1g of the second dried lanthanum hydroxide and place it in a container. Add water to mix it evenly with the lanthanum hydroxide until the lanthanum hydroxide no longer absorbs water significantly. Record the amount of water added at this time as the saturated water absorption of the lanthanum hydroxide.

[0037] (2) Optionally, under a protective atmosphere, the solid lanthanum hydroxide obtained in step (1) is brought into contact with lanthanum hydroxide by adding a solution of a compound containing dopant element R, and then dried, wherein the amount of the solution of the compound containing dopant element R in contact with lanthanum hydroxide is less than or equal to (preferably equal to or substantially equal to) the saturated water absorption of lanthanum hydroxide; wherein the contact method is selected from surface precipitation, atomic layer deposition and monolayer plating.

[0038] (3) The dried product from step (2) is calcined in a carbon-containing atmosphere (e.g., CO and / or CO2) to obtain a lanthanum oxycarbonate catalyst.

[0039] According to the present invention, the specific preparation process described above results in the lanthanum oxycarbonate catalyst obtained being predominantly in the form of hexagonal crystalline phase, thereby the total content of hexagonal crystalline lanthanum oxycarbonate and hexagonal crystalline lanthanum oxycarbonate containing dopant R in the obtained lanthanum oxycarbonate catalyst is not less than 98 wt%, preferably not less than 99 wt%, and may even be not less than 99.5 wt%, or close to 100 wt%.

[0040] According to the present invention, in order to make the morphology of the generated lanthanum hydroxide more fibrous, the concentration of the alkaline solution is preferably 3wt%-25wt%.

[0041] According to the present invention, preferably, the alkali in the alkaline solution is a compound of a Group IA metal.

[0042] According to the present invention, preferably, the alkaline solution is added at a rate of 5 mL / min to 150 mL / min relative to each kilogram of the lanthanum source solution.

[0043] According to the present invention, preferably, the concentration of the lanthanum source solution is 0.01wt%-10wt%.

[0044] According to the present invention, preferably, the amount of alkaline solution used is such that the final pH value of the mixture of alkaline solution and lanthanum source solution is 10-12.5.

[0045] According to the present invention, the lanthanum source can be any substance capable of providing lanthanum. Preferably, the lanthanum source is a water-soluble salt of lanthanum, more preferably at least one of lanthanum nitrate, lanthanum chloride, and lanthanum acetate; and even more preferably lanthanum nitrate.

[0046] According to the present invention, when performing the aging process, the present invention does not particularly limit the aging apparatus, as long as it can meet the aging temperature and stirring conditions. However, based on experimental safety and overall catalyst performance, the aging is carried out under reflux conditions. Preferably, the aging conditions include: a temperature of 80-100°C and a time of 10-50 hours.

[0047] The present invention may further include solid-liquid separation of the aged products, followed by washing with deionized water until neutral. The solid-liquid separation can be a conventional solid-liquid separation method in the art, such as using a centrifuge.

[0048] 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.

[0049] According to the present invention, preferably, the conditions for the first drying include: a temperature of 70-90°C and a time of 10-20 hours.

[0050] According to the present invention, preferably, the conditions for the second drying include: a relative pressure of 10 kPa-91 kPa, preferably 20 kPa-70 kPa, a temperature of 120-160°C, and a time of 2-10 h; wherein the time for the second drying is shorter than the time for the first drying.

[0051] Without being limited to any known theory, it is believed that performing the first drying and the second drying in step (1) above, and having relatively accurate control over the drying conditions (e.g., temperature and time), is particularly beneficial to the purposes of the present invention, such as for the control of the crystal phase.

[0052] According to the present invention, when the protective atmosphere is used, preferably, the protective atmosphere is provided by an inert gas and / or nitrogen.

[0053] In this invention, the protective atmosphere can be provided by Schlenk technique (double-line operation) or in a glove box with a protective atmosphere.

[0054] According to the present invention, preferably, step (1) further includes the process of determining the saturated water absorption of lanthanum hydroxide. Then, a solution containing the compound of dopant element R is prepared based on the determined saturated water absorption of lanthanum hydroxide and the amount of dopant element R used.

[0055] According to the present invention, preferably, in step (2), a solution of a compound containing dopant 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, based on the measured saturated water absorption of lanthanum hydroxide. For the purposes of the present invention, the amount of the solution containing dopant element R added can preferably be “equal to” the saturated water absorption of lanthanum hydroxide; however, slight volume changes may occur after the solution is mixed with the solid, and thus, the amount of the solution containing dopant element R added, calculated without considering such slight volume changes, can be regarded as “substantially equal to” the saturated water absorption of lanthanum hydroxide. Not limited to any known theory, it is believed that adding a solution containing dopant element R based on the measured saturated water absorption of lanthanum hydroxide is particularly advantageous for the purposes of the present invention, for example, to control the amount of solution and the amount of dopant element in the process, thereby enabling the desired doping amount to be obtained without causing a change in crystal phase.

[0056] According to the present invention, preferably, the concentration of the solution containing the dopant element R is 0.01-0.2 g / mL.

[0057] According to the present invention, preferably, the molar ratio of lanthanum to dopant element R in lanthanum hydroxide is 1:0.01-1, more preferably 1:0.03-0.5, and more preferably 1:0.04-0.2.

[0058] According to the present invention, preferably, the compound containing dopant element R is selected from compounds of at least one element from Groups IIA, VIII, IB, and IIB, more preferably from compounds of at least one element from Mg, Ca, Sr, Ba, Fe, and Zn, and even more preferably from compounds of Sr and / or Ba. The compound containing dopant element R can be at least one of the following: nitrates (e.g., magnesium nitrate, calcium nitrate, strontium nitrate, barium nitrate, ferric nitrate, zinc nitrate), chlorides (e.g., magnesium chloride, calcium chloride, strontium chloride, barium chloride, ferric chloride, zinc chloride), and acetates (e.g., magnesium acetate, calcium acetate, strontium acetate, barium acetate, ferric acetate, zinc acetate), preferably nitrates.

[0059] According to the present invention, preferably, in step (2), a specific contact method is used to add the solid lanthanum hydroxide obtained in step (1) to a solution of a compound containing dopant element R, rather than adding the solution of the compound containing dopant element R to the lanthanum hydroxide obtained in step (1). Without being limited by any known theory, it is believed that this specific addition method is beneficial to the achievement of the objectives of the present invention, particularly, for example, the distribution of the dopant element; and consequently, the higher conversion and selectivity, and especially the yield, resulting from the catalyst. Thus, for the objectives of the present invention, a suitable specific contact method may be selected from lattice doping, surface deposition, atomic layer deposition, and monolayer deposition. An example of a specific contact method that may be mentioned is surface deposition, which includes: adding a solution of a compound containing dopant element R dropwise to lanthanum hydroxide under stirring conditions, followed by continued stirring. More preferably, the addition rate of the solution of the compound containing dopant element R is 0.1 mL / min to 10 mL / min, preferably 0.1 mL / min to 8 mL / min, relative to each gram of said lanthanum hydroxide.

[0060] According to the present invention, preferably, the contact conditions include a temperature of 15-50°C and a time of 2-5 hours.

[0061] According to the present invention, in order to ensure sufficient contact between a solution of a compound containing doped element R and lanthanum hydroxide, the contact is carried out in a vortex mixer.

[0062] According to the present invention, preferably, in step (2), the drying conditions include: a temperature of 60-100°C and a time of 10-24h.

[0063] 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 capable of providing carbon to the purpose of the present invention and not detrimental to obtaining the desired lanthanum oxycarbonate catalyst, particularly, for example, an atmosphere containing CO and / or CO2. Preferably, the carbon-containing (e.g., CO and / or CO2) atmosphere can be an air atmosphere; correspondingly, the carbon element in the lanthanum oxycarbonate catalyst is derived from carbon dioxide in a CO2-containing atmosphere.

[0064] According to the present invention, preferably, the lanthanum oxycarbonate catalyst with a specific structure obtained by the specific preparation method of the present invention exhibits clear hexagonal characteristic peaks in its XRD spectrum when XRD measurements are performed, without the characteristic peaks of the dopant element in the form of a metal salt. For the purposes of this invention, "without...characteristic peaks" means that no measurable characteristic peaks are present in the XRD spectrum. Without being limited by any known theory, it is believed that this specific structure is beneficial to the catalytic activity of the lanthanum oxycarbonate catalyst of the present invention.

[0065] In another aspect, the present invention provides a lanthanum oxycarbonate catalyst prepared by the method described above.

[0066] In another aspect, the present invention provides the application of the above-described lanthanum oxycarbonate catalyst in the oxidative coupling reaction of methane to produce C2 and above hydrocarbons.

[0067] Another aspect of the present invention provides a method for preparing C2 and above hydrocarbons from methane, the method comprising: reacting methane with the above-described lanthanum oxycarbonate catalyst in the presence of oxygen and under the conditions of methane oxidative coupling reaction;

[0068] Alternatively, a lanthanum oxycarbonate catalyst can be prepared according to the method described in this invention, and then methane can be reacted with the obtained lanthanum oxycarbonate catalyst in the presence of oxygen and under the conditions of methane oxidative coupling reaction.

[0069] According to the present invention, preferably, the molar ratio of methane to oxygen is 2:1 to 9:1.

[0070] According to the present invention, preferably, the temperature of the contact reaction is 500-650°C.

[0071] According to the present invention, preferably, the space velocity of the methane is 5000 mL / (g·h)-200000 mL / (g·h).

[0072] Example

[0073] The present invention will be described in detail below through embodiments, but the present invention is not limited to these embodiments. The following embodiments include:

[0074] TEM imaging was performed using a JEOL 2100F FEG TEM and a Schottky field emission source. The accelerating voltage was 200 kV. Images obtained from at least six different grid regions were selected as representative.

[0075] The length and diameter of the fibrous catalyst were determined using the scale bar in the built-in software of the transmission scanning electron microscope.

[0076] The analysis of the reaction product components was performed on a gas chromatograph (model 7890A) purchased from Agilent Technologies.

[0077] XRD diffraction patterns were obtained from an X-ray diffractometer (Empyrean) manufactured by Panaco, with a Cu target generator, operating voltage 40 kV, operating current 40 mA, and PixCel. 3DThe detector has a divergence slit of 1 / 4°, an anti-scattering slit of 1 / 2°, an aperture of 10 mm, a Sola slit of 0.04 rad, a receiving slit of 7.5 mm, a scanning speed of 0.013° / step, a scanning time of 30 s / step, and a scanning range of 5°-90°. Measurements are performed in reflection mode.

[0078] The content of the hexagonal phase was determined by XRD pattern. Specifically, the bulk crystal structure information was obtained by XRD pattern. The ratio of the peak area of ​​the hexagonal lanthanum oxycarbonate and the doped element crystal structure to the total peak area was calculated, which is the weight percentage of the hexagonal lanthanum oxycarbonate and the doped element hexagonal lanthanum oxycarbonate in the product.

[0079] The contents of lanthanum and dopant element R in the catalyst were measured using an iCAP TQICP-MS purchased from Thermo Scientific.

[0080] The pore structure of the catalyst was characterized by BET analysis using an ASAP2420M fully automated adsorption system purchased from Microtics, USA.

[0081] The method for calculating methane conversion rate is as follows:

[0082] Methane conversion rate = Amount of methane consumed in the reaction / Initial amount of methane × 100%.

[0083] The method for calculating ethylene selectivity is as follows:

[0084] Ethylene selectivity = Amount of methane consumed to produce ethylene / Total methane consumption × 100%.

[0085] The method for calculating ethane selectivity is as follows:

[0086] Ethane selectivity = Amount of methane consumed to produce ethane / Total methane consumption × 100%.

[0087] The method for calculating the yield of C2 hydrocarbons is as follows:

[0088] C2 hydrocarbon yield = methane conversion rate × (ethane selectivity + ethylene selectivity).

[0089] Example 1

[0090] (1) Dissolve 5g of lanthanum nitrate hexahydrate in 210g of deionized water and stir at 25℃ and 900rpm for 30min. Then, add sodium hydroxide solution dropwise to the lanthanum nitrate aqueous solution (the concentration of sodium hydroxide solution is 10wt%, and the addition rate of the alkali solution is 7mL / min relative to each kilogram of the lanthanum source solution, and the amount of alkali solution used is such that the final pH value of the mixture of alkali solution and lanthanum source solution is 11.6). After the addition is completed, continue stirring at 25℃ and 9000rpm for 10min. Then, raise the temperature to 90℃ and keep stirring under reflux for 12h. After the solution cools to room temperature, centrifuge the solid material at 1000rpm and wash with deionized water until the pH value of the washing liquid is neutral. The obtained solid is subjected to a first drying and a second drying in sequence. The conditions for the first drying are: temperature 80℃ and time 12h; the conditions for the second drying are: relative pressure 60kPa, temperature 140℃ and time 5h.

[0091] The saturated water absorption capacity of lanthanum hydroxide after the second drying step was determined as follows: Under nitrogen protection, 1 g of the second dried lanthanum hydroxide was placed in a round-bottom flask. Deionized water was added dropwise to the flask using a syringe, and the mixture was stirred with the lanthanum hydroxide using a vortex mixer until no further water absorption was observed. The amount of deionized water added at this point was recorded. The saturated water absorption capacity of lanthanum hydroxide was determined to be 2 mL / g.

[0092] (2) Dissolve 0.08 g of strontium nitrate in 1.5 mL of deionized water to obtain an aqueous solution of strontium nitrate. Under nitrogen protection, weigh 0.8 g of the second dried lanthanum hydroxide into a round-bottom flask, and then add the aqueous solution of strontium nitrate dropwise into the round-bottom flask using a syringe at 25 °C (the addition rate of the solution containing the dopant element is 1 mL / min relative to each gram of lanthanum hydroxide), and use a vortex mixer to mix it thoroughly for 5 h. Then dry the resulting mixture at 80 °C for 12 h.

[0093] (3) Lanthanum oxycarbonate catalyst was prepared by calcination at 500°C for 2 hours in air atmosphere.

[0094] The molar ratio of lanthanum to strontium in the catalyst is 1:0.091.

[0095] BET analysis showed that the specific surface area of ​​the lanthanum oxycarbonate catalyst was 52 m². 2 / g, pore volume is 0.31cm 3 / g, with an average pore size of 10.1nm.

[0096] Figure 1The image shows the XRD pattern of the lanthanum oxycarbonate catalyst prepared in Example 1, where the horizontal axis represents 2θ and the vertical axis represents intensity. Compared with the PXRD database (BrukerDiffrac.Eva, version 4.2.1), it can be seen that the catalyst prepared by this method has characteristic peaks of the hexagonal crystal phase, and due to its nanoscale nature, it has low crystallinity. It can also be observed that only the characteristic peaks of the hexagonal crystal phase are seen in this XRD pattern, without the characteristic peaks of the dopant element in the form of a metal salt. The total content of hexagonal lanthanum oxycarbonate and doped hexagonal lanthanum oxycarbonate in the product, determined by XRD pattern, is 98.0 wt%.

[0097] Figure 2 This is a transmission scanning electron microscope (SEM) image of the lanthanum oxycarbonate catalyst prepared in Example 1. Figure 2 It can be seen that the lanthanum oxycarbonate catalyst has a fibrous nanostructure, and the average diameter is calculated to be 13 nm with an average aspect ratio of 40:1.

[0098] Example 2

[0099] (1) Dissolve 5.15g of lanthanum nitrate hexahydrate in 155g of deionized water and stir at 25℃ and 900rpm for 30min. Then, add sodium hydroxide solution dropwise to the lanthanum nitrate aqueous solution (the concentration of sodium hydroxide solution is 10wt%, and the addition rate of the alkali solution is 5mL / min relative to each kilogram of the lanthanum source solution, and the amount of alkali solution used is such that the final pH value of the mixture of alkali solution and lanthanum source solution is 12.2). After the addition is completed, continue stirring at 25℃ and 9000rpm for 10min. Then, raise the temperature to 100℃ and keep stirring under reflux for 15h. After the solution cools to room temperature, centrifuge the solid material at 9000rpm and wash with deionized water until the pH value of the washing liquid is neutral. The obtained solid is subjected to a first drying and a second drying in sequence. The conditions for the first drying are: temperature of 80℃ and time of 15h; the conditions for the second drying are: relative pressure of 50kPa, temperature of 150℃ and time of 5h.

[0100] The saturated water absorption capacity of lanthanum hydroxide after the second drying step was determined as follows: Under nitrogen protection, 1 g of the second dried lanthanum hydroxide was placed in a round-bottom flask. Deionized water was added dropwise to the flask using a syringe, and the mixture was stirred with the lanthanum hydroxide using a vortex mixer until no further water absorption was observed. The amount of deionized water added at this point was recorded. The saturated water absorption capacity of lanthanum hydroxide was determined to be 2.1 mL / g.

[0101] (2) 0.04 g of strontium nitrate was dissolved in 1.68 mL of deionized water to obtain an aqueous solution of strontium nitrate. Under nitrogen protection, 0.9 g of the second dried lanthanum hydroxide was weighed and placed in a round-bottom flask. The aqueous solution of strontium nitrate was then added dropwise to the round-bottom flask using a syringe at 30 °C (the addition rate of the solution containing the dopant element was 4 mL / min relative to each gram of lanthanum hydroxide), and the mixture was thoroughly mixed using a vortex mixer for 2 h. The resulting mixture was then dried at 80 °C for 13 h.

[0102] (3) Lanthanum oxycarbonate catalyst was prepared by calcination at 500°C for 2 hours in air atmosphere.

[0103] The molar ratio of lanthanum to strontium in the catalyst is 1:0.046.

[0104] BET analysis showed that the specific surface area of ​​the lanthanum oxycarbonate catalyst was 56 m². 2 / g, pore volume 0.4cm 3 / g, with an average pore size of 13.4nm.

[0105] The XRD pattern (similar to Example 1, not shown again) only showed the characteristic peaks of the hexagonal phase, without the characteristic peaks of the dopant element in its metal salt form. The total content of hexagonal lanthanum oxycarbonate and doped hexagonal lanthanum oxycarbonate in the product was determined to be 98.6 wt% by XRD pattern.

[0106] As can be seen from the transmission scanning electron microscope images (similar to Example 1, not shown again), the lanthanum oxycarbonate catalyst has a fibrous nanostructure, and the calculated average diameter is 14 nm and the average aspect ratio is 35:1.

[0107] Example 3

[0108] (1) Dissolve 10g of lanthanum nitrate hexahydrate in 155g of deionized water and stir at 25℃ and 900rpm for 30min. Then, add sodium hydroxide solution dropwise to the lanthanum nitrate aqueous solution (the concentration of sodium hydroxide solution is 10wt%, and the addition rate of the alkali solution is 7mL / min relative to each kilogram of the lanthanum source solution, and the amount of alkali solution used is such that the final pH value of the mixture of alkali solution and lanthanum source solution is 12). After the addition is completed, continue stirring at 25℃ and 9000rpm for 10min. Then, raise the temperature to 100℃ and keep stirring under reflux for 15h. After the solution cools to room temperature, centrifuge the solid material at 900rpm and wash it with deionized water until the pH value of the washing liquid is neutral. The obtained solid is subjected to a first drying and a second drying in sequence. The conditions for the first drying are: temperature of 90℃ and time of 20h; the conditions for the second drying are: relative pressure of 50kPa, temperature of 160℃ and time of 3h.

[0109] The saturated water absorption capacity of lanthanum hydroxide after the second drying step was determined as follows: Under nitrogen protection, 1 g of the second dried lanthanum hydroxide was placed in a round-bottom flask. Deionized water was added dropwise to the flask using a syringe, and the mixture was stirred with the lanthanum hydroxide using a vortex mixer until no further water absorption was observed. The amount of deionized water added at this point was recorded. The saturated water absorption capacity of lanthanum hydroxide was determined to be 2.4 mL / g.

[0110] (2) 0.13 g of strontium nitrate was dissolved in 1.92 mL of deionized water to obtain an aqueous solution of strontium nitrate. Under nitrogen protection, 0.9 g of the second dried lanthanum hydroxide was weighed and placed in a round-bottom flask. Then, the aqueous solution of strontium nitrate was added dropwise to the round-bottom flask using a syringe at 40 °C (the addition rate of the solution containing the dopant element was 3 mL / min relative to each gram of lanthanum hydroxide), and the mixture was thoroughly mixed using a vortex mixer for 2 h. The resulting mixture was then dried at 80 °C for 10 h.

[0111] (3) Lanthanum oxycarbonate catalyst was prepared by calcination at 500°C for 2 hours in air atmosphere.

[0112] The molar ratio of lanthanum to strontium in the catalyst is 1:0.148.

[0113] BET analysis showed that the specific surface area of ​​the lanthanum oxycarbonate catalyst was 51 m². 2 / g, pore volume 0.3cm 3 / g, with an average pore size of 10.5nm.

[0114] The XRD pattern (similar to Example 1, not shown again) only showed the characteristic peaks of the hexagonal phase, without the characteristic peaks of the dopant element in its metal salt form. The total content of hexagonal lanthanum oxycarbonate and doped hexagonal lanthanum oxycarbonate in the product was determined to be 99.1 wt% by XRD pattern.

[0115] As can be seen from the transmission scanning electron microscope images (similar to Example 1, not shown again), the lanthanum oxycarbonate catalyst has a fibrous nanostructure, and the calculated average diameter is 18 nm and the average aspect ratio is 20:1.

[0116] Example 4

[0117] (1) Dissolve 15g of lanthanum nitrate hexahydrate in 155g of deionized water and stir at 25°C and 9000rpm for 30min. Then, add sodium hydroxide solution dropwise to the lanthanum nitrate aqueous solution (the concentration of sodium hydroxide solution is 10wt%, and the addition rate of the alkali solution is 10mL / min relative to the lanthanum source solution per kilogram, based on the compound of Group IA metals, and the amount of alkali solution used is such that the final pH value of the mixture of alkali solution and lanthanum source solution is 10). After the addition is complete, continue stirring at 25°C and 900rpm for 10min. Then, raise the temperature to 100°C and maintain reflux for stirring for 15h. After the solution cools to room temperature, centrifuge the solid material at 9000rpm and wash with deionized water until the pH value of the washing liquid is neutral. The obtained solid is subjected to a first drying and a second drying in sequence. The conditions for the first drying are: temperature 80°C and time 15h; the conditions for the second drying are: relative pressure 40kPa, temperature 140°C and time 5h.

[0118] The saturated water absorption capacity of lanthanum hydroxide after the second drying step was determined as follows: Under nitrogen protection, 1 g of the second dried lanthanum hydroxide was placed in a round-bottom flask. Deionized water was added dropwise to the flask using a syringe, and the mixture was stirred with the lanthanum hydroxide using a vortex mixer until no further water absorption was observed. The amount of deionized water added at this point was recorded. The saturated water absorption capacity of lanthanum hydroxide was determined to be 1.9 mL / g.

[0119] (2) Dissolve 0.24 g of strontium nitrate in 1.52 mL of deionized water to obtain an aqueous solution of strontium nitrate. Under nitrogen protection, weigh 0.9 g of the second dried lanthanum hydroxide into a round-bottom flask, and then add the aqueous solution of strontium nitrate dropwise into the round-bottom flask using a syringe at 35 °C (the addition rate of the solution containing the dopant element is 1.5 mL / min relative to each gram of lanthanum hydroxide), and use a vortex mixer to mix it thoroughly for 3 h. Then dry the resulting mixture at 80 °C for 15 h.

[0120] (3) Lanthanum oxycarbonate catalyst was prepared by calcination at 500°C for 2 hours in air atmosphere.

[0121] The molar ratio of lanthanum to strontium in the catalyst is 1:0.146.

[0122] BET analysis showed that the specific surface area of ​​the lanthanum oxycarbonate catalyst was 50 m². 2 / g, pore volume 0.26cm 3 / g, with an average pore size of 11.6nm.

[0123] The XRD pattern (similar to Example 1, not shown again) only showed the characteristic peaks of the hexagonal phase, without the characteristic peaks of the dopant element in its metal salt form. The total content of hexagonal lanthanum oxycarbonate and doped hexagonal lanthanum oxycarbonate in the product was determined to be 99.4 wt% by XRD pattern.

[0124] As can be seen from the transmission scanning electron microscope images (similar to Example 1, not shown again), the lanthanum oxycarbonate catalyst has a fibrous nanostructure, and the calculated average diameter is 16 nm and the average aspect ratio is 15:1.

[0125] Example 5

[0126] The method of Example 1 was followed to prepare lanthanum oxycarbonate, except that strontium nitrate was replaced with an equimolar amount of barium nitrate.

[0127] BET analysis showed that the specific surface area of ​​the lanthanum oxycarbonate catalyst was 49 m². 2 / g, pore volume is 0.29cm 3 / g, with an average pore size of 12.6nm.

[0128] As can be seen from the transmission scanning electron microscope images (similar to Example 1, not shown again), the lanthanum oxycarbonate catalyst has a fibrous nanostructure, and the calculated average diameter is 22 nm and the average aspect ratio is 19:1.

[0129] Example 6

[0130] The preparation of lanthanum oxycarbonate was carried out according to the method of Example 1, except that step (1) did not include the second drying process.

[0131] BET analysis showed that the specific surface area of ​​the lanthanum oxycarbonate catalyst was 68 m². 2 / g, pore volume is 0.39cm 3 / g, with an average pore size of 8.5nm.

[0132] The XRD pattern (similar to Example 1, not shown again) only showed the characteristic peaks of the hexagonal phase, without the characteristic peaks of the dopant element in its metal salt form. The total content of hexagonal lanthanum oxycarbonate and doped hexagonal lanthanum oxycarbonate in the product was determined to be 98.7 wt% by XRD pattern.

[0133] The transmission scanning electron microscope (SEM) images show that the lanthanum oxycarbonate catalyst has a fibrous nanostructure, with an average diameter of 21 nm and an average aspect ratio of 16:1.

[0134] Example 7

[0135] The method of Example 1 was followed to prepare lanthanum oxycarbonate, except that strontium nitrate was replaced with an equimolar amount of zinc nitrate.

[0136] BET analysis showed that the specific surface area of ​​the lanthanum oxycarbonate catalyst was 42 m². 2 / g, pore volume is 0.21cm 3 / g, with an average pore size of 9.8nm.

[0137] The XRD pattern (similar to Example 1, not shown again) only showed the characteristic peaks of the hexagonal phase, without the characteristic peaks of the dopant element in its metal salt form. The total content of hexagonal lanthanum oxycarbonate and doped hexagonal lanthanum oxycarbonate in the product was determined to be 98.2 wt% by XRD pattern.

[0138] As can be seen from the transmission scanning electron microscope images (similar to Example 1, not shown again), the lanthanum oxycarbonate catalyst has a fibrous nanostructure, and the calculated average diameter is 23 nm and the average aspect ratio is 18:1.

[0139] Example 8

[0140] The method of Example 1 was followed to prepare lanthanum oxycarbonate, except that strontium nitrate was replaced with an equimolar amount of magnesium nitrate.

[0141] BET analysis showed that the specific surface area of ​​the lanthanum oxycarbonate catalyst was 39 m². 2 / g, pore volume is 0.46cm 3 / g, with an average pore size of 15.2nm.

[0142] The XRD pattern (similar to Example 1, not shown again) only showed the characteristic peaks of the hexagonal phase, without the characteristic peaks of the dopant element in its metal salt form. The total content of hexagonal lanthanum oxycarbonate and doped hexagonal lanthanum oxycarbonate in the product was determined to be 98.9 wt% by XRD pattern.

[0143] As can be seen from the transmission scanning electron microscope images (similar to Example 1, not shown again), the lanthanum oxycarbonate catalyst has a fibrous nanostructure, and the calculated average diameter is 20 nm and the average aspect ratio is 16:1.

[0144] Example 9

[0145] The method of Example 1 was followed to prepare lanthanum hydroxide, except that in step (2), the second dried lanthanum hydroxide was added to an aqueous solution of strontium nitrate, mixed and stirred for 5 h, and then the resulting mixture was dried at 80 °C for 12 h.

[0146] BET analysis showed that the specific surface area of ​​the lanthanum oxycarbonate catalyst was 39 m². 2 / g, pore volume is 0.31cm3 / g, with an average pore size of 12.8nm.

[0147] The XRD pattern (similar to Example 1, not shown again) only showed the characteristic peaks of the hexagonal phase, without the characteristic peaks of the dopant element in its metal salt form. The total content of hexagonal lanthanum oxycarbonate and doped hexagonal lanthanum oxycarbonate in the product was determined to be 99.3 wt% by XRD pattern.

[0148] As can be seen from the transmission scanning electron microscope images (similar to Example 1, not shown again), the lanthanum oxycarbonate catalyst has a fibrous nanostructure, and the calculated average diameter is 16 nm and the average aspect ratio is 19:1.

[0149] Example 10

[0150] The preparation of lanthanum oxycarbonate was carried out according to the method of Example 1, except that the rate of addition of the solution containing the dopant element was 20 mL / min relative to each gram of lanthanum hydroxide.

[0151] BET analysis showed that the specific surface area of ​​the lanthanum oxycarbonate catalyst was 44 m². 2 / g, pore volume 0.28cm 3 / g, with an average pore size of 11.2nm.

[0152] The XRD pattern (similar to Example 1, not shown again) only showed the characteristic peaks of the hexagonal phase, without the characteristic peaks of the dopant element in its metal salt form. The total content of hexagonal lanthanum oxycarbonate and doped hexagonal lanthanum oxycarbonate in the product was determined to be 99.5 wt% by XRD pattern.

[0153] As can be seen from the transmission scanning electron microscope images (similar to Example 1, not shown again), the lanthanum oxycarbonate catalyst has a fibrous nanostructure, and the calculated average diameter is 20 nm and the average aspect ratio is 18.6:1.

[0154] Example 11

[0155] The preparation of lanthanum oxycarbonate was carried out according to the method of Example 1, except that in step (2), the amount of deionized water used was 5 mL.

[0156] BET analysis showed that the specific surface area of ​​the lanthanum oxycarbonate catalyst was 38 m². 2 / g, pore volume 0.2cm 3 / g, with an average pore size of 13.3nm.

[0157] The XRD pattern (similar to Example 1, not shown again) only showed the characteristic peaks of the hexagonal phase, without the characteristic peaks of the dopant element in its metal salt form. The total content of hexagonal lanthanum oxycarbonate and doped hexagonal lanthanum oxycarbonate in the product was determined to be 99.6 wt% by XRD pattern.

[0158] As can be seen from the transmission scanning electron microscope images (similar to Example 1, not shown again), the lanthanum oxycarbonate catalyst has a fibrous nanostructure, and the calculated average diameter is 21 nm and the average aspect ratio is 17:1.

[0159] Example 12

[0160] (1) Dissolve 15g of lanthanum nitrate hexahydrate in 155g of deionized water and stir at 25°C and 900rpm for 30min. Then, add sodium hydroxide solution dropwise to the lanthanum nitrate aqueous solution (the concentration of sodium hydroxide solution is 10wt%, and the addition rate of the alkali solution is 10mL / min relative to the lanthanum source solution per kilogram, based on the compound of Group IA metals, and the amount of alkali solution used is such that the final pH value of the mixture of alkali solution and lanthanum source solution is 10). After the addition is completed, continue stirring at 25°C and 9000rpm for 10min. Then, raise the temperature to 100°C and maintain reflux for stirring for 15h. After the solution cools to room temperature, centrifuge the solid material at 9000rpm and wash with deionized water until the pH value of the washing liquid is neutral. The obtained solid is subjected to a first drying and a second drying in sequence. The conditions for the first drying are: temperature of 80°C and time of 15h; the conditions for the second drying are: relative pressure of 40kPa, temperature of 140°C and time of 5h.

[0161] The saturated water absorption capacity of lanthanum hydroxide after the second drying step was determined as follows: Under nitrogen protection, 1 g of the second dried lanthanum hydroxide was placed in a round-bottom flask. Deionized water was added dropwise to the flask using a syringe, and the mixture was stirred with the lanthanum hydroxide using a vortex mixer until no further water absorption was observed. The amount of deionized water added at this point was recorded. The saturated water absorption capacity of lanthanum hydroxide was determined to be 1.9 mL / g.

[0162] (2) Dissolve 0.24 g of ferric nitrate in 1.52 mL of deionized water to obtain an aqueous solution of strontium nitrate. Under nitrogen protection, weigh 0.9 g of the second dried lanthanum hydroxide into a round-bottom flask, and then add the ferric nitrate aqueous solution dropwise into the round-bottom flask using a syringe at 35 °C (the addition rate of the solution containing the dopant element is 1.5 mL / min relative to each gram of lanthanum hydroxide), and use a vortex mixer to mix thoroughly for 3 h. Then dry the resulting mixture at 80 °C for 15 h.

[0163] (3) Lanthanum oxycarbonate catalyst was prepared by calcination at 500°C for 2 hours in air atmosphere.

[0164] The molar ratio of lanthanum to iron in the catalyst is 1:0.13.

[0165] BET analysis showed that the specific surface area of ​​the lanthanum oxycarbonate catalyst was 48 m². 2 / g, pore volume is 0.36cm 3 / g, with an average pore size of 13.8nm.

[0166] The XRD pattern (similar to Example 1, not shown again) only showed the characteristic peaks of the hexagonal phase, without the characteristic peaks of the dopant element in its metal salt form. The total content of hexagonal lanthanum oxycarbonate and doped hexagonal lanthanum oxycarbonate in the product was determined to be 98.1 wt% by XRD pattern.

[0167] As can be seen from the transmission scanning electron microscope images (similar to Example 1, not shown again), the lanthanum oxycarbonate catalyst has a fibrous nanostructure, and the calculated average diameter is 20 nm and the average aspect ratio is 20:1.

[0168] Example 13

[0169] (1) Dissolve 5g of lanthanum nitrate hexahydrate in 210g of deionized water and stir at 25℃ and 900rpm for 30min. Then, add sodium hydroxide solution dropwise to the lanthanum nitrate aqueous solution (the concentration of sodium hydroxide solution is 10wt%, and the addition rate of the alkali solution is 7mL / min relative to each kilogram of the lanthanum source solution, and the amount of alkali solution used is such that the final pH value of the mixture of alkali solution and lanthanum source solution is 11.6). After the addition is completed, continue stirring at 25℃ and 9000rpm for 10min. Then, raise the temperature to 90℃ and keep stirring under reflux for 12h. After the solution cools to room temperature, centrifuge the solid material at 1000rpm and wash with deionized water until the pH value of the washing liquid is neutral. The obtained solid is subjected to a first drying and a second drying in sequence. The conditions for the first drying are: temperature 80℃ and time 12h; the conditions for the second drying are: relative pressure 60kPa, temperature 140℃ and time 5h.

[0170] The saturated water absorption capacity of lanthanum hydroxide after the second drying step was determined as follows: Under nitrogen protection, 1 g of the second dried lanthanum hydroxide was placed in a round-bottom flask. Deionized water was added dropwise to the flask using a syringe, and the mixture was stirred with the lanthanum hydroxide using a vortex mixer until no further water absorption was observed. The amount of deionized water added at this point was recorded. The saturated water absorption capacity of lanthanum hydroxide was determined to be 2 mL / g.

[0171] (2) Dissolve 0.06 g of calcium nitrate in 1.5 mL of deionized water to obtain an aqueous solution of calcium nitrate. Under nitrogen protection, weigh 1.0 g of the second dried lanthanum hydroxide into a round-bottom flask, and then add the aqueous solution of calcium nitrate dropwise into the round-bottom flask using a syringe at 25 °C (the addition rate of the solution containing the dopant calcium compound is 1 mL / min relative to each gram of lanthanum hydroxide), and use a vortex mixer to mix it thoroughly for 5 h. Then dry the resulting mixture at 80 °C for 12 h.

[0172] (3) Lanthanum oxycarbonate catalyst was prepared by calcination at 500°C for 2 hours in air atmosphere.

[0173] The molar ratio of lanthanum and calcium in the catalyst is 1:0.11.

[0174] BET analysis showed that the specific surface area of ​​the lanthanum oxycarbonate catalyst was 49 m². 2 / g, pore volume 0.3cm 3 / g, with an average pore size of 10.2nm.

[0175] The XRD pattern (similar to Example 1, not shown again) only showed the characteristic peaks of the hexagonal phase, without the characteristic peaks of the dopant element in its metal salt form. The total content of hexagonal lanthanum oxycarbonate and doped hexagonal lanthanum oxycarbonate in the product was determined to be 99.3 wt% by XRD pattern.

[0176] As can be seen from the transmission scanning electron microscope images (similar to Example 1, not shown again), the lanthanum oxycarbonate catalyst has a fibrous nanostructure, and the calculated average diameter is 18 nm and the average aspect ratio is 20:1.

[0177] Comparative Example 1

[0178] (1) Dissolve 5g of lanthanum nitrate hexahydrate in 210g of deionized water and stir at 25℃ and 900rpm for 30min. Then, add sodium hydroxide solution dropwise to the lanthanum nitrate aqueous solution (the concentration of sodium hydroxide solution is 10wt%, and the addition rate of the alkali solution is 7mL / min relative to each kilogram of the lanthanum source solution, and the amount of alkali solution used is such that the final pH value of the mixture of alkali solution and lanthanum source solution is 11.6). After the addition is completed, continue stirring at 25℃ and 9000rpm for 10min. Then, raise the temperature to 90℃ and keep stirring under reflux for 12h. After the solution cools to room temperature, centrifuge the solid material at 10000rpm and wash with deionized water until the pH value of the washing liquid is neutral. The obtained solid is subjected to a first drying and a second drying in sequence. The conditions for the first drying are: temperature of 80℃ and time of 12h; the conditions for the second drying are: relative pressure of 60kPa, temperature of 140℃ and time of 5h. Lanthanum oxycarbonate catalyst was prepared by calcination at 500°C for 2 hours in air atmosphere.

[0179] BET analysis showed that the specific surface area of ​​the lanthanum oxycarbonate catalyst was 68 m². 2 / g, pore volume 6cm 3 / g, with an average pore size of 42nm.

[0180] The XRD pattern (similar to Example 1, not shown again) only showed characteristic peaks of the hexagonal phase, without the characteristic peaks of the dopant element in its metal salt form. The total content of the hexagonal lanthanum oxycarbonate phase in the product was determined to be 98.2 wt% by XRD pattern.

[0181] As can be seen from the transmission scanning electron microscope images (similar to Example 1, not shown again), the lanthanum oxycarbonate catalyst has a fibrous nanostructure, and the calculated average diameter is 12 nm and the average aspect ratio is 15:1.

[0182] Comparative Example 2

[0183] (1) Lanthanum hydroxide was prepared according to the method of step (1) in Example 1.

[0184] (2) 0.08g of strontium nitrate was roasted at 500°C for 2 hours in air.

[0185] (3) 0.8g of lanthanum hydroxide was calcined at 500°C for 2 hours in air.

[0186] (4) Then the product obtained in step (2) and the product obtained in step (3) are mixed evenly to obtain the catalyst.

[0187] BET analysis showed that the specific surface area of ​​the lanthanum oxycarbonate catalyst was 40 m². 2 / g, pore volume 2.3cm3 / g, with an average pore size of 14.2nm.

[0188] The XRD pattern (similar to Example 1, not shown again) only showed characteristic peaks of the hexagonal phase, without the characteristic peaks of the dopant element in its metal salt form. The total content of hexagonal lanthanum oxycarbonate and doped hexagonal lanthanum oxycarbonate in the product was determined to be 82.3 wt% by XRD pattern.

[0189] Comparative Example 3

[0190] (1) Dissolve 5g of lanthanum nitrate hexahydrate in 210g of deionized water and stir at 25℃ and 900rpm for 30min. Then, add sodium hydroxide solution dropwise to the lanthanum nitrate aqueous solution (the concentration of sodium hydroxide solution is 10wt%, and the addition rate of the alkali solution is 7mL / min relative to each kilogram of the lanthanum source solution, and the amount of alkali solution used is such that the final pH value of the mixture of alkali solution and lanthanum source solution is 11.6). After the addition is completed, continue stirring at 25℃ and 9000rpm for 10min. Then, raise the temperature to 90℃ and keep stirring under reflux for 12h. After the solution cools to room temperature, centrifuge the solid material at 10000rpm and wash with deionized water until the pH value of the washing liquid is neutral. The obtained solid is subjected to a first drying and a second drying in sequence. The conditions for the first drying are: temperature of 80℃ and time of 12h; the conditions for the second drying are: relative pressure of 60kPa, temperature of 140℃ and time of 5h.

[0191] The saturated water absorption capacity of lanthanum hydroxide after the second drying step was determined as follows: Under nitrogen protection, 1 g of the second dried lanthanum hydroxide was placed in a round-bottom flask. Deionized water was added dropwise to the flask using a syringe, and the mixture was stirred with the lanthanum hydroxide using a vortex mixer until no further water absorption was observed. The amount of deionized water added at this point was recorded. The saturated water absorption capacity of lanthanum hydroxide was determined to be 2 mL / g.

[0192] (2) Dissolve 0.08 g of strontium nitrate in 1.5 mL of deionized water to obtain an aqueous solution of strontium nitrate. Under nitrogen protection, weigh 0.8 g of the second dried lanthanum hydroxide and add the solid lanthanum hydroxide directly to the strontium nitrate solution at 25 °C. Then dry the resulting mixture at 80 °C for 12 h.

[0193] (3) Lanthanum oxycarbonate catalyst was prepared by calcination at 500°C for 2 hours in air atmosphere.

[0194] Comparative Example 4

[0195] 0.26 g of barium nitrate was dissolved in 10 mL of deionized water and stirred until completely dissolved. 2 g of the prepared hexagonal lanthanum oxycarbonate was weighed out and the barium nitrate aqueous solution was added dropwise to the hexagonal lanthanum oxycarbonate. The mixture was stirred until homogeneous and placed in an oven at 80 °C for 24 h. Then it was transferred to a muffle furnace and heated to 500 °C at a rate of 2 °C / min, and held for 2 h to prepare Ba / La2O2CO3.

[0196] Figure 3 The XRD pattern of the lanthanum oxycarbonate catalyst prepared in Comparative Example 4 shows that, in addition to the peak of lanthanum oxycarbonate, the sample also contains a characteristic peak of BaCO4.

[0197] Comparative Example 5

[0198] 0.3 g of nickel nitrate hexahydrate was dissolved in 10 mL of deionized water and stirred until completely dissolved. 2 g of the prepared hexagonal lanthanum oxycarbonate was weighed out and the nickel nitrate aqueous solution was added dropwise to the hexagonal lanthanum oxycarbonate. The mixture was stirred until homogeneous and placed in an oven at 80 °C for 24 h. Then it was transferred to a muffle furnace and heated to 500 °C at a rate of 2 °C / min, and held for 2 h to prepare Ni / La2O2CO3.

[0199] Test Example 1

[0200] The catalysts prepared in the above examples and comparative examples were compressed into tablets, sieved through a 40-60 mesh, and then 0.1 g was loaded into an Inconel fixed-bed reactor. Under normal pressure, methane and oxygen (methane to oxygen molar ratio of 3:1) were introduced to carry out the reaction. Other reaction conditions and results are shown in Table 1.

[0201] Table 1

[0202]

[0203]

[0204]

[0205] As can be seen from the results in Table 1, compared with Comparative Example 1, the lanthanum oxycarbonate catalyst containing doped element R of the present invention has a higher C2 hydrocarbon yield at 500-650℃. In particular, the catalysts of Examples 1-5 have a C2 hydrocarbon yield of more than 15% at 550-650℃.

[0206] The catalyst obtained by directly mixing lanthanum oxycarbonate and strontium oxide in Comparative Example 2 had a C2 hydrocarbon yield of less than 10%, while the catalyst prepared by the method of Example 1 of the present invention had a C2 hydrocarbon yield of 16.8%. Therefore, the element doping method of the present invention can improve the C2 hydrocarbon yield compared with the direct mixing method of Comparative Example 2.

[0207] In Comparative Example 3, solid lanthanum hydroxide was added to a strontium nitrate solution, instead of adding an aqueous strontium nitrate solution to solid lanthanum hydroxide as described in this invention. The resulting catalyst had a C2 hydrocarbon yield of less than 10%.

[0208] Comparative Example 4 used a conventional impregnation method for doping, and the resulting catalyst exhibited low methane conversion, C2 hydrocarbon selectivity, and yield. In particular, the performance of the catalyst obtained by this method was significantly affected by temperature, especially at 500°C, where the three key indicators of conversion, selectivity, and yield were all very low.

[0209] Comparative Example 5 uses Ni instead of the specific doping element of this invention for doping, which obviously makes the production of the target product C2 hydrocarbons unsatisfactory, with very low C2 hydrocarbon selectivity and yield at various temperatures.

[0210] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A lanthanum oxycarbonate catalyst, characterized in that, The catalyst comprises hexagonal lanthanum oxycarbonate and hexagonal lanthanum oxycarbonate containing dopant element R, and the total content of hexagonal lanthanum oxycarbonate and hexagonal lanthanum oxycarbonate containing dopant element R in the catalyst is not less than 98 wt%, wherein the molar ratio of lanthanum to dopant element R is 1:0.01-1:0.3; and the dopant 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 dopant element R in the lanthanum oxycarbonate catalyst is not less than 99 wt%; and / or, In the lanthanum oxycarbonate catalyst, the molar ratio of lanthanum to dopant R is 1:0.03-1:0.

2.

4. The lanthanum oxycarbonate catalyst according to any one of claims 1-3, wherein, The lanthanum oxycarbonate catalyst has a fibrous nanostructure; the diameter of the lanthanum oxycarbonate catalyst is 10 nm-30 nm, and the aspect ratio is 5:1-50:1; and / or, The specific surface area of ​​the lanthanum oxycarbonate catalyst is 35 m². 2 / g-90m 2 / g, pore volume 0.15cm 3 / g-0.5cm 3 / g, with an average pore size of 8nm-16nm.

5. The lanthanum oxycarbonate catalyst according to any one of claims 1-3, wherein, The XRD pattern of this lanthanum oxycarbonate catalyst does not show characteristic peaks of the dopant element in its metal salt form.

6. The lanthanum oxycarbonate catalyst according to claim 3, wherein, The molar ratio of lanthanum to dopant R in the lanthanum oxycarbonate catalyst is 1:0.04-1:0.

15.

7. The lanthanum oxycarbonate catalyst according to claim 4, wherein, The lanthanum oxycarbonate catalyst has a fibrous nanostructure; the diameter of the lanthanum oxycarbonate catalyst is 10 nm-20 nm, and the aspect ratio is 15:1-40:1; and / or, the specific surface area of ​​the lanthanum oxycarbonate catalyst is 50 m². 2 / g-60m 2 / g, pore volume 0.26cm 3 / g-0.4cm 3 / g, with an average pore size of 10nm-13.5nm.

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

9. The method according to claim 8, wherein the alkali in the alkaline solution is a compound of a Group IA metal; and / or, The amount of alkali solution used ensures that the final pH value of the mixture of alkali solution and lanthanum source solution is 10-12.5; and / or, The lanthanum source is a water-soluble salt of lanthanum.

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

11. The method according to claim 8, 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 dopant element R is 0.01-0.2 g / mL; and / or, The molar ratio of lanthanum to dopant R in lanthanum hydroxide is 1:0.01-1:1; and / or, The compound containing dopant element R is selected from compounds containing at least one element selected from Mg, Ca, Sr, Ba, Fe and Zn; And / or, The contact conditions include a temperature of 15-50℃ and a time of 2-5 hours.

12. The method according to claim 8, wherein, In step (2), the rate at which the solution containing the dopant element R is added is 0.1 mL / min to 10 mL / min, relative to each gram of lanthanum hydroxide. And / or, drying conditions include: a temperature of 60-100°C and a time of 10-24 hours.

13. The method according to claim 8, wherein, In step (3), the carbon-containing atmosphere is an atmosphere containing CO and / or CO2; and / or The roasting conditions include a temperature of 450-550℃ and a time of 2-8 hours.

14. The method according to claim 8, wherein the amount of the solution of the compound containing dopant element R in contact with lanthanum hydroxide is equal to or substantially equal to the saturated water absorption of lanthanum hydroxide.

15. The method according to claim 9, wherein the concentration of the alkaline solution is 3 wt%-25 wt%; and / or, the lanthanum source is at least one of lanthanum nitrate, lanthanum chloride, and lanthanum acetate, and the concentration of the lanthanum source solution is 0.01 wt%-10 wt%.

16. The use of the lanthanum oxycarbonate catalyst according to any one of claims 1-7 in the oxidative coupling reaction of methane to produce C2 and above hydrocarbons.

17. A method for preparing C2 and above hydrocarbons from methane, characterized in that, The method includes: In the presence of oxygen and under the conditions of methane oxidative coupling reaction, methane is reacted with the lanthanum oxycarbonate catalyst according to any one of claims 1-7; or, A lanthanum oxycarbonate catalyst is prepared according to any one of claims 8-14, and then methane is reacted with the obtained lanthanum oxycarbonate catalyst in the presence of oxygen and under the conditions of methane oxidative coupling reaction.

18. The method according to claim 17, wherein, The molar ratio of methane to oxygen is 2:1 to 9:1; and / or, The temperature of the contact reaction is 500-650℃; and / or, The space velocity of the methane is 5000 mL / (g·h)-200000 mL / (g·h).

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