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 as well as a preparation method and application thereof. The lanthanum oxycarbonate catalyst comprises hexagonal crystal phase lanthanum oxycarbonate, monoclinic crystal phase lanthanum oxycarbonate containing doping elements and tetragonal crystal phase lanthanum oxycarbonate containing doping elements. When the catalyst provided by the invention is used for the oxidative coupling reaction of methane, the catalyst has a relatively high C2 hydrocarbon yield at a low temperature.

Description

Lanthanum oxycarbonate catalyst and its preparation method and application Technical Field

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

[0002] Ethylene is an important basic organic chemical raw material. Its production has long relied on the steam cracking route of petroleum fractions, resulting in increasingly serious environmental pollution and other problems. In recent years, the continuous rise in crude oil prices has led to an increase in the price of ethylene cracking feedstocks, while also significantly outstripping the supply of ethylene cracking feedstocks. Faced with this situation, countries around the world are adjusting their energy utilization structures and continuously searching for new ethylene production routes. Oxidative coupling of methane (OCM), which converts methane into ethylene and ethane (collectively referred to as C2H2O) in a single step, has been widely studied as a method for directly producing ethylene and ethane due to its environmentally friendly properties. Since its proposal in 1982, researchers have conducted extensive research on catalysts, catalytic processes, and reactors. Various catalyst systems for the OCM reaction have been developed over the past four decades, focusing on uncovering active sites, improving C2H2 yields, and improving catalyst stability. These include Mn2O3-Na2WO4 / SiO2, perovskite systems, MgO-based catalysts, supported La materials, and nanoscale La-based catalysts. However, problems that limit the commercialization of the OCM process still exist: (1) high reaction temperatures (700-900°C) are required to achieve high yields of C2H; (2) the concentration of C2H in the product is low, which makes the separation cost of the product high; and (3) when the methane conversion rate is high, the selectivity of the corresponding C2H is low, making it very difficult to achieve high methane conversion and C2H selectivity at the same time.

[0003] The prior art does not mention how to prepare a catalyst containing hexagonal lanthanum oxycarbonate, monoclinic lanthanum oxycarbonate and tetragonal lanthanum oxycarbonate at the same time by a one-step method, nor does it explore the effect of lanthanum oxycarbonate having these three crystal phases on catalytic performance.

[0004] Summary of the Invention

[0005] The purpose of the present invention is to overcome the above-mentioned problems of the prior art and to provide a lanthanum oxycarbonate catalyst and a preparation method and application thereof.

[0006] To achieve the above objectives, the first aspect of the present invention provides a lanthanum oxycarbonate catalyst, comprising the following three coexisting crystalline phases: a hexagonal lanthanum oxycarbonate, a monoclinic lanthanum oxycarbonate containing a doping element, and a tetragonal lanthanum oxycarbonate containing a doping element. Preferably, the ratio of the molar amount of the hexagonal lanthanum oxycarbonate to the total molar amount of the tetragonal lanthanum oxycarbonate and the monoclinic lanthanum oxycarbonate is 1:0.01-1. Also preferably, the ratio of the molar amount of the tetragonal lanthanum oxycarbonate to the monoclinic lanthanum oxycarbonate is 1:0.1-10, preferably 1:0.2-5, or 1:0.25-3.

[0007] Another aspect of the present invention provides a method for preparing a lanthanum oxycarbonate catalyst, which comprises: adding an alkali solution to a mixed solution containing a lanthanum source and a compound containing a doping element to make the pH value of the mixed system greater than 9, and then sequentially carrying out reaction, solid-liquid separation, drying and calcination; wherein, relative to each kilogram of the mixed solution, the addition rate of the alkali solution is 0.01g / min-10g / min, preferably 0.03g / min-8g / min, and more preferably 0.5g / min-6g / min, calculated as the alkali in the alkali solution; and wherein, the alkali solution is first added dropwise to the mixed solution at a first addition rate until the pH of the solution reaches a set value, which is between 8 and 9, and then the alkali solution is added dropwise to the mixed solution at a second addition rate until the pH of the system is 10-13, wherein the second addition rate is 0.5-4.5g / min higher than the first addition rate.

[0008] Another aspect of the present invention provides a lanthanum oxycarbonate catalyst prepared by the method described in the present invention.

[0009] Another aspect of the present invention provides a lanthanum oxycarbonate catalyst composition formed by combining the lanthanum oxycarbonate catalyst of the present invention with a binder or a carrier.

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

[0011] In another aspect, the present invention provides a method for preparing C2 and higher hydrocarbons from methane, comprising: contacting methane with the lanthanum oxycarbonate catalyst of the present invention in the presence of oxygen and under conditions of a methane oxidative coupling reaction.

[0012] The present invention proposes for the first time a catalyst comprising hexagonal lanthanum oxycarbonate, monoclinic lanthanum oxycarbonate containing a doping element, and tetragonal lanthanum oxycarbonate containing a doping element. The catalyst is prepared by controlling the crystal phase formation conditions by adding an alkaline solution to a mixed solution containing a lanthanum source and a compound containing the doping element. The content of the monoclinic and tetragonal lanthanum oxycarbonates in the catalyst can be regulated by the amount of doping element added and the crystal phase formation conditions (for example, by controlling the rate of alkaline solution addition and the reaction conditions). When used in the methane oxidative coupling reaction, the catalyst of the present invention exhibits a high C2 hydrocarbon yield at low temperatures (450-650°C). BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG1 is a scanning electron microscope (SEM) image of the lanthanum oxycarbonate catalyst prepared in Example 1;

[0014] FIG2 is an X-ray (XRD) spectrum of the lanthanum oxycarbonate catalyst prepared in Example 1;

[0015] FIG3 is an X-ray (XRD) spectrum of the lanthanum oxycarbonate catalyst prepared in Example 4;

[0016] FIG4 is an X-ray (XRD) spectrum of the lanthanum oxycarbonate catalyst prepared in Example 6;

[0017] FIG5 is an X-ray (XRD) spectrum of the lanthanum oxycarbonate catalyst prepared in Example 7;

[0018] FIG6 is an X-ray (XRD) spectrum of the lanthanum oxycarbonate catalyst prepared in Comparative Example 1;

[0019] FIG7 is an X-ray (XRD) spectrum of the lanthanum oxycarbonate catalyst prepared in Comparative Example 3. DETAILED DESCRIPTION

[0020] 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.

[0021] In this article, the "crystalline coexistence" means that, unlike simple mechanical mixing, the three crystalline phases of hexagonal, monoclinic and tetragonal are uniformly mixed not only on a macroscopic scale, but also on a microscopic scale. Specifically, the three crystalline phases described in the present invention can be measured by XRD testing; accordingly, the "crystalline coexistence" described in the present invention is manifested in that when an XRD test is performed on a sample of the product of the present invention, the simultaneous presence of the three crystalline phases is measured for each unit weight of the test sample required for the test. For the purpose of the present invention, for example, the "unit weight" of the test sample is no more than 1g, no more than 0.5g, or preferably no more than 0.3g. It is also preferred that, for the product of the present invention, the unit weight of the test sample subjected to the XRD test is at least 3 parts, or at least 5 parts, or at least 10 parts.

[0022] For example, in the present invention, a batch of products produced by the method of the present invention can be divided into several test samples of unit weight required for measurement, evenly or unevenly in weight; several batches of products produced by the method of the present invention can also be divided into several test samples of unit weight required for measurement, evenly or unevenly in weight; several batches of products produced by the method of the present invention can also be mixed with each other and then divided into several test samples of unit weight required for measurement, evenly or unevenly in weight.

[0023] In this article, the "carbon two" hydrocarbon refers to hydrocarbons with 2 carbon atoms, especially alkenes and alkanes, such as ethylene and ethane. The remaining hydrocarbons expressed in terms of carbon number each have similar meanings.

[0024] A first aspect of the present invention provides a lanthanum oxycarbonate catalyst, which includes the following three crystalline phases coexisting in a crystalline state: a hexagonal lanthanum oxycarbonate phase, a monoclinic lanthanum oxycarbonate phase containing a doping element, and a tetragonal lanthanum oxycarbonate phase containing a doping element.

[0025] According to the present invention, preferably, the doping element in the monoclinic lanthanum oxycarbonate and the tetragonal lanthanum oxycarbonate is selected from at least one of the elements of Groups IIA, VIII, IB, IIB and lanthanide elements other than lanthanum, preferably at least one of Mg, Ca, Sr, Ba, Fe, Zn, Ce and Cd, more preferably at least one of Mg, Ca, Sr and Ba.

[0026] According to the present invention, preferably, the molar ratio of lanthanum element to doping element in the lanthanum oxycarbonate catalyst is 1:0.01-0.1, preferably 1:0.01-0.08, and more preferably 1:0.012-0.06.

[0027] According to the present invention, preferably, the molar amount of the hexagonal lanthanum oxycarbonate to the total molar amount of the tetragonal lanthanum oxycarbonate and the monoclinic lanthanum oxycarbonate is 1: 0.01-1, preferably 1: 0.1-1, more preferably 1: 0.25-0.9. Wherein, the content of each crystalline phase in the catalyst is calculated according to the XRD full spectrum fitting method (Rietveld method), specifically using Highscore plus 4.0 software for standardless quantitative calculation, first determining the background, peak finding, and object matching, then inserting the structural information (unit cell parameters) of the hexagonal lanthanum oxycarbonate and the monoclinic lanthanum oxycarbonate, and automatically and manually refining the global parameters and the parameters of each component, the error parameter (Rwp) is as small as possible, and when Rwp is less than 10, the quantitative end is completed, and the computer outputs the calculation result (i.e., the molar amount of the hexagonal lanthanum oxycarbonate to the total molar amount of the tetragonal lanthanum oxycarbonate and the monoclinic lanthanum oxycarbonate).

[0028] For the purpose of the present invention, for the convenience of calculation, as described above, when examining the molar relationship between the three crystalline phases of hexagonal, monoclinic and tetragonal, the total molar amount of the tetragonal lanthanum oxycarbonate and the monoclinic lanthanum oxycarbonate is examined, wherein the unit cell parameters of the monoclinic lanthanum oxycarbonate are used as representatives of the unit cell parameters of the tetragonal lanthanum oxycarbonate. Accordingly, in the calculation process of the XRD full spectrum fitting method, the crystal structure data of the hexagonal lanthanum oxycarbonate and the monoclinic lanthanum oxycarbonate are assigned as initial values. In the present invention, the standard XRD pattern of the hexagonal lanthanum oxycarbonate is PDF: 00-37-0804, the standard XRD pattern of the tetragonal lanthanum oxycarbonate is PDF: 00-23-0320, and the standard XRD pattern of the orthorhombic lanthanum oxycarbonate is PDF 04-22-8421.

[0029] Surprisingly, the XRD pattern of the catalyst prepared by element doping using the specific method of the present invention clearly shows the formation of lanthanum oxycarbonate in different crystalline phases, and in particular, lanthanum oxycarbonate in which the hexagonal, monoclinic and tetragonal crystalline phases coexist.

[0030] Some skilled in the art have speculated that lanthanum oxycarbonate may interconvert between its tetragonal and monoclinic phases. However, the inventors have found no literature or other published reports confirming this speculation, nor any studies providing relevant data and / or other experimental evidence. Accordingly, the inventors have found no reports providing lanthanum oxycarbonate in which the three crystalline phases described in the present invention coexist, particularly, for example, by quantitatively analyzing the three crystalline phases to confirm their coexistence and analyzing the amount of one or more of these phases present.

[0031] Correspondingly, as measured by the XRD pattern, the ratio R1 of the molar amount of the hexagonal lanthanum oxycarbonate to the total molar amount of the tetragonal lanthanum oxycarbonate and the monoclinic lanthanum oxycarbonate is 1:0.01-1.

[0032] Also preferably, the molar ratio R2 of the tetragonal lanthanum oxycarbonate to the monoclinic lanthanum oxycarbonate is 1:0.1-10, preferably 1:0.2-5, or 1:0.25-3. According to one embodiment of the present invention, the ratio R2 is determined by peak separation based on an XRD pattern using a spectrum fitting method to determine the relative contents of the two structures; the peak separation method is known in the art. Preferably, the ratio R2 is determined based on the XRD pattern from which the ratio R1 was measured. After calculation and statistics, the calculation error of the fitting calculation of the ratio R2 is less than or equal to 25%.

[0033] According to the present invention, the lanthanum oxycarbonate catalyst can be a particle with a nanostructure, especially when it is prepared by the method of the present invention. In the art, the morphology of a solid can be described in three dimensions. In this regard, regardless of the specific morphology of the catalyst particle, when the smallest dimension of its three-dimensional scale is at the nanometer level, for example, not exceeding 1000nm, preferably not exceeding 500nm, it is considered to have the "nano" structure described in the present invention. For example, it is widely known in the art that for catalyst particles of different morphologies, scales such as aspect ratio and thickness are often used to provide descriptions; accordingly, in this article, as long as the diameter or thickness of the particle is at the nanometer level, it is considered to have the "nano" structure described in the present invention.

[0034] In the present invention, the "diameter" and "aspect ratio" of the lanthanum oxycarbonate catalyst particles are both average values. The specific testing method for the "average diameter" is to use a transmission electron microscope ruler to select 5-10 samples within a viewing window, measure the diameter of each sample, and then calculate the average value. The specific testing method for the "average aspect ratio" is to use a transmission electron microscope ruler to select 5-10 samples within a viewing window, measure the diameter and length of each sample, calculate the aspect ratio of each sample, and then calculate the average value.

[0035] According to the present invention, preferably, the lanthanum oxycarbonate catalyst particles have a rod-like nanostructure. It will be appreciated by those skilled in the art that, for catalyst particles, when the present invention refers to "rod-like", it is in accordance with the conventional understanding of the art, and need not be a rod-like in a strict geometric sense. For example, particle forms such as oblong, elliptical, and needle-like are common in this area and are also described as belonging to the "rod-like" structure of the present invention, as long as they meet the diameter and / or aspect ratio requirements of the present invention. Specifically, in one embodiment, the diameter of the lanthanum oxycarbonate catalyst of the rod-like nanostructure is 10nm-30nm (for example, it can be 10nm, 12nm, 14nm, 15nm, 18nm, 20nm, 22nm, 24nm, 26nm, 28nm, 30nm, and the range of any two of the above). In one embodiment, the aspect ratio of the rod-like nanostructured lanthanum oxycarbonate catalyst is 5-30:1 (e.g., 5:1, 7:1, 9:1, 11:1, 13:1, 15:1, 17:1, 19:1, 20:1, 22:1, 24:1, 26:1, 28:1, 30:1, and ranges consisting of any two of the foregoing), more preferably 10-26:1.

[0036] According to the present invention, preferably, the specific surface area of ​​the rod-shaped nanostructured lanthanum oxycarbonate catalyst is 40 m 2 / g-100m 2 / g (for example, it can be 40m 2 / g, 50m 2 / g, 60m 2 / g、65m 2 / g、70m 2 / g、75m 2 / g、80m 2 / g、85m 2 / g、90m 2 / g、100m 2 / g, and the range consisting of any two of the above points). In one embodiment, the pore volume of the rod-shaped nanostructured lanthanum oxycarbonate catalyst is 0.2 cm 3 / g-0.7cm 3 / g (for example, it can be 0.2cm 3 / g, 0.3cm 3 / g, 0.35cm 3 / g, 0.4cm 3 / g, 0.45cm 3 / g, 0.5cm 3 / g, 0.55cm 3 / g, 0.6cm 3 / g, 0.65cm 3 / g, 0.7cm 3 / g, and ranges consisting of any two of the above points). In one embodiment, the average pore size of the rod-shaped nanostructured lanthanum oxycarbonate catalyst is 5 nm-300 nm (for example, 5 nm, 8 nm, 10 nm, 10.5 nm, 11 nm, 11.5 nm, 12 nm, 12.5 nm, 13 nm, 15 nm, 20 nm, 25 nm, 30 nm, 50 nm, 80 nm, 100 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, 210 nm, 220 nm, 230 nm, 240 nm, 250 nm, 260 nm, 270 nm, 280 nm, 290 nm, 300 nm, and ranges consisting of any two of the above points), more preferably 8 nm-290 nm, and more preferably 180 nm-260 nm.

[0037] According to the present invention, the lanthanum oxycarbonate catalyst particles may have a lamellar structure. It will be understood by those skilled in the art that, for catalyst particles, the present invention's reference to "lamellar" is in accordance with conventional knowledge in the art. For example, a "lamellar" structure may generally refer to a structural form in which the scale in the "thickness" direction is significantly smaller than the scales in the remaining two dimensional directions. For the purposes of the present invention, the plane formed by the two dimensions other than the thickness direction of the lamellar structure particles is referred to as the "cross-section" of the particles. For the purposes of the present invention, the particles of the lamellar structure may have cross-sections of various shapes, such as circular, elliptical, parallelogram, or shapes close to these shapes. Preferably, for example, the particles of the lamellar structure of the present invention may have a "nearly parallelogram" cross-section.

[0038] According to the present invention, the term "near parallelogram" includes a parallelogram and a quadrilateral that is close to a parallelogram, that is, the sum of two adjacent internal angles of the near parallelogram is equal to or close to 180°.

[0039] Preferably, two adjacent interior angles of the nearly parallelogram are denoted as ∠A and ∠B, wherein ∠A is set to an acute angle or a right angle, and ∠B is set to an obtuse angle or a right angle, 60°<∠A<90°, and 170°<(∠A+∠B)<195°. For example, ∠A can be 65°, 68°, 70°, 72°, 75°, 78°, 80°, 82°, 85°, or 88°. ∠A+∠B can be 172°, 175°, 178°, 180°, 182°, 185°, 188°, 190°, or 193°.

[0040] According to the present invention, a rectangular or square cross section also belongs to the “nearly parallelogram” cross section.

[0041] The angle can be measured by using the angle measuring scale provided by the scanning electron microscope.

[0042] According to the present invention, the side length of the nearly parallelogram can vary in a wide range, preferably 1 μm-5 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, preferably 1.5 μm-3.5 μm.

[0043] The side length can be measured by a ruler provided by a scanning electron microscope.

[0044] According to the present invention, preferably, the thickness of the nearly parallelogram lanthanum oxycarbonate can vary in a wide range, preferably 100 nm-500 nm, for example, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, preferably 200 nm-400 nm.

[0045] The thickness can be measured by a ruler provided by a scanning electron microscope.

[0046] According to the present invention, the lanthanum oxycarbonate catalyst particles may have a spherical structure. Those skilled in the art will appreciate that the term "spherical" herein, when used with respect to catalyst particles, is consistent with conventional understanding in the art. For example, a "spherical" structure generally refers to particles having a sphericity greater than 0.5, greater than 0.6, greater than 0.7, greater than 0.8, or greater than 0.9.

[0047] According to the present invention, preferably, the diameter of the spherical lanthanum oxycarbonate can vary in a wide range, preferably 100 nm-800 nm, for example 200 nm-600 nm.

[0048] For the purposes of the present invention, it is preferred that the lanthanum oxycarbonate catalyst of the present invention has a rod-like nanostructure.

[0049] Another aspect of the present invention provides a method for preparing the lanthanum oxycarbonate catalyst particles described herein, comprising: adding an alkaline solution to a mixed solution containing a lanthanum source and a compound containing a doping element, adjusting the pH of the mixed system to greater than 9 (the pH at this point refers to the pH of the mixed system when the addition of the alkaline solution is stopped), and then sequentially performing a reaction, solid-liquid separation, drying, and calcination. In the present invention, the reaction described herein specifically refers to the reaction of a lanthanum nitrate solution with an alkaline solution to produce solid lanthanum hydroxide.

[0050] The inventors discovered that by adding an alkaline solution to a mixed solution containing a lanthanum source and a compound containing a doping element, followed by a reaction, solid-liquid separation, drying, and calcination, the relatively stable hexagonal lanthanum carbonate can be partially converted into the less stable tetragonal and monoclinic lanthanum carbonate phases. The mixture then exists as a relatively stable mixture of these three phases. This mixed phase can enhance the catalyst's low-temperature activation performance.

[0051] 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, and further preferably lanthanum nitrate.

[0052] According to the present invention, the type of compound containing the doping element can be selected from a wide range, as long as the required doping element can be provided. Preferably, the compound containing the doping element is a compound containing at least one element selected from Groups IIA, VIII, IB, IIB, and the lanthanide series other than lanthanum, more preferably a compound of at least one element selected from Mg, Ca, Sr, Ba, Fe, Zn, and Cd, and further preferably a compound of at least one element selected from Mg, Ca, Sr, and Ba. The compound containing the doping element can be at least one of a nitrate (e.g., magnesium nitrate, calcium nitrate, strontium nitrate, barium nitrate, iron nitrate, zinc nitrate, and cadmium nitrate), a chloride (e.g., magnesium chloride, calcium chloride, strontium chloride, barium chloride, iron chloride, zinc chloride, and cadmium chloride), and an acetate (e.g., magnesium acetate, calcium acetate, strontium acetate, barium acetate, iron acetate, zinc acetate, and cadmium acetate) of the doping element, preferably a nitrate.

[0053] According to the present invention, the amount of the lanthanum source and the compound containing the doping element can be selected in a wide range, but in order to increase the yield of carbon dihydrocarbons and reduce the temperature of the methane oxidative coupling reaction, and at the same time to reduce the preparation cost, preferably, the amount of the lanthanum source and the compound containing the doping element is such that the molar ratio of lanthanum element to doping element in the lanthanum oxycarbonate catalyst is 1:0.01-0.1, more preferably 1:0.01-0.08, and further preferably 1:0.012-0.06.

[0054] According to the present invention, preferably, the amounts of the lanthanum source and the compound containing the doping element are used so that the ratio of the molar amount of the hexagonal lanthanum oxycarbonate to the total molar amount of the tetragonal lanthanum oxycarbonate and the monoclinic lanthanum oxycarbonate in the lanthanum oxycarbonate catalyst is 1:0.01-1, preferably 1:0.1-1, and more preferably 1:0.25-0.9.

[0055] According to the present invention, the primary purpose of the alkali solution is to provide an alkaline environment for the system. Therefore, it can be any liquid substance capable of providing alkaline conditions, such as aqueous ammonia, hydroxide solution, carbonate solution, or bicarbonate solution. Without being bound by any known theory, it is believed that selecting a specific base for the alkali solution helps control the crystal morphology of the resulting product. Accordingly, the base in the alkali solution is preferably a compound of a Group IA metal; more preferably, the base is sodium hydroxide and / or potassium hydroxide. Without being bound by any known theory, it is believed that such bases are particularly conducive to the formation of rod-shaped nanostructured lanthanum oxycarbonate particles.

[0056] According to the present invention, preferably, the amount of the alkali solution used makes the pH value of the mixed system greater than 9, more preferably 10 to 13. Without being limited by any known theory, it is believed that the pH value of the mixed system is particularly conducive to the formation of rod-shaped nanostructured lanthanum oxycarbonate particles.

[0057] According to the present invention, the concentration of the alkali solution is preferably 2 wt% to 25 wt%, preferably 3 wt% to 20 wt%, and more preferably 5 wt% to 18 wt%. Without being limited by any known theory, it is believed that the alkali solution concentration of the mixed system is particularly conducive to the formation of rod-shaped nanostructured lanthanum oxycarbonate particles.

[0058] According to the present invention, preferably, the method further comprises:

[0059] S1. Mixing the lanthanum source and the compound containing the doping element with water under a first stirring condition to obtain a mixed solution; preferably, the first stirring condition comprises: a temperature of 10-50° C., a rotation speed of 300-1000 rpm, and a time of 10-40 min;

[0060] S2. Under a second stirring condition, adding alkali solution to the mixed solution to obtain a mixed system; preferably, the second stirring condition includes: a temperature of 20-60° C. and a rotation speed of 500-1500 rpm.

[0061] According to the present invention, a specific alkali solution addition rate is adopted. Preferably, the alkali solution is added at a rate of 0.01 g / min to 10 g / min, preferably 0.03 g / min to 8 g / min, and more preferably 0.5 g / min to 6 g / min, calculated as the Group IA metal compound per kilogram of the mixed solution.

[0062] According to the specific alkali solution addition rate of the present invention, in order to further increase the content of the doping element in the lanthanum oxycarbonate catalyst, preferably, the alkali solution dropwise addition rate during the addition of the alkali solution to the mixed solution comprising the lanthanum source and the compound containing the doping element is controlled. Specifically, in step S2, under the second stirring condition, the alkali solution is added dropwise to the mixed solution comprising the lanthanum source and the compound containing the doping element at a first addition rate until the pH of the solution reaches a set value, which is between 8 and 9. Then, the alkali solution is added dropwise to the mixed solution comprising the lanthanum source and the compound containing the doping element at a second addition rate. When the pH of the system is 10-13, the addition of the alkali solution is stopped.

[0063] More preferably, in step S2, the second addition rate is 0.5-4.5 g / min (for example, 0.5 g / min, 1 g / min, 1.5 g / min, 2 g / min, 2.5 g / min, 3 g / min, 3.5 g / min, 4 g / min, 5.5 g / min, 5 g / min, and a range consisting of any two of the above values) higher than the first addition rate.

[0064] More preferably, in step S2, under the second stirring condition, the alkali solution is added dropwise to the mixed solution comprising the lanthanum source and the compound containing the doping element at a first addition rate of 0.01-1 g / min (for example, 0.01 g / min, 0.1 g / min, 0.2 g / min, 0.3 g / min, 0.4 g / min, 0.5 g / min, 0.6 g / min, 0.7 g / min, 0.8 g / min, 0.9 g / min, 1 g / min, and a range consisting of any two of the above) per kilogram of the mixed solution comprising the lanthanum source and the compound containing the doping element, calculated as the compound of Group IA metal, until the pH of the solution reaches a set value, which is between 8 and 9. and then, the alkali solution is added dropwise to the mixed solution comprising the lanthanum source and the compound containing the doping element at a second addition rate of 0.5-5 g / min (for example, 0.5 g / min, 0.6 g / min, 0.7 g / min, 0.8 g / min, 0.9 g / min, 1 g / min, 1.5 g / min, 2 g / min, 2.5 g / min, 3 g / min, 3.5 g / min, 4 g / min, 4.5 g / min, 5 g / min, and a range consisting of any two of the above) per kilogram of the mixed solution comprising the lanthanum source and the compound containing the doping element, calculated as the compound of Group IA metal, and the addition of the alkali solution is stopped when the pH of the system is 10-13.

[0065] Without being bound by any known theory, it is believed that the specific alkali solution addition rate of the present invention is particularly conducive to the formation of the various crystalline forms desired by the present invention. For example, the specific alkali solution addition rate of the present invention is believed to be conducive to controlling the supersaturation of the solution.

[0066] According to the present invention, preferably, the reaction temperature is 80-200°C (for example, it can be 80°C, 85°C, 90°C, 95°C, 100°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, and the range consisting of any two of the above), and the reaction time is 10h-50h (for example, it can be 10h, 15h, 20h, 25h, 30h, 35h, 40h, 45h, 50h, and the range consisting of any two of the above).

[0067] According to the present invention, the reaction can be carried out in an aging manner or a hydrothermal manner.

[0068] According to the present invention, preferably, the aging is carried out under stirring at a speed of 500-1500 rpm. The present invention does not particularly limit 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 is carried out under condensation reflux. More preferably, the aging conditions include a temperature of 80-100°C and a time of 10-50 hours. Aging is carried out at atmospheric pressure (0.1 MPa).

[0069] Preferably, the hydrothermal conditions include a temperature of 100-200° C. and a time of 10 h to 50 h. The hydrothermal pressure is the pressure generated by the hydrothermal reaction itself.

[0070] According to the present invention, preferably, the method further comprises: washing the aged product before drying, wherein the washing solvent is water and / or a C1-C4 monohydric alcohol. According to a preferred embodiment of the present invention, the aged product is first washed with water (distilled water) until neutral, and then washed with ethanol 1-2 times.

[0071] According to the present invention, the drying conditions can be changed within a wide range. Preferably, the drying temperature is 60°C-100°C, for example, 60°C, 70°C, 80°C, 90°C, 100°C, and the drying time is 12h-24h, for example, 12h, 14h, 16h, 18h, 20h, 22h, 24h.

[0072] According to the present invention, the roasting conditions can be changed within a wide range. Preferably, the roasting temperature is 450°C-550°C, for example, it can be 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, 510°C, 520°C, 530°C, 550°C, and the roasting time is 2h-8h, for example, it can be 2h, 3h, 4h, 5h, 6h, 7h, 8h.

[0073] According to the present invention, the calcination atmosphere is not particularly limited and may be an air atmosphere or a carbon dioxide atmosphere.

[0074] Another aspect of the present invention provides a lanthanum oxycarbonate catalyst prepared by the method described in the present invention.

[0075] Another aspect of the present invention provides the use of the lanthanum oxycarbonate catalyst of the present invention in the oxidative coupling reaction of methane to produce C2 and higher hydrocarbons.

[0076] The lanthanum oxycarbonate catalyst prepared by the method of the present invention is preferably a nanostructured particle, which can be used directly, such as in the application of methane oxidative coupling reaction to produce carbon two and above hydrocarbons. However, for reasons such as efficiency of use and engineering requirements, such as in the application of methane oxidative coupling reaction to produce carbon two and above hydrocarbons, the lanthanum oxycarbonate catalyst can be further processed and formed, especially when used in a fixed bed reactor. For example, the lanthanum oxycarbonate particles of the present invention can be tableted to have a size of, for example, 40-60 mesh.

[0077] The lanthanum oxycarbonate particles of the present invention can be used in combination with a binder, which can be those conventionally used in the art, such as alumina, soluble starch, silica sol, polyethylene glycol, etc.

[0078] The lanthanum oxycarbonate particles of the present invention can be supported on a carrier. The carrier can be those commonly used in the art, such as aluminum oxide, silicon oxide, molecular sieves (mesoporous molecular sieves, microporous molecular sieves), diatomaceous earth, ceramics, etc.

[0079] Another aspect of the present invention provides a method for preparing C2 and higher hydrocarbons from methane, comprising: contacting methane with the lanthanum oxycarbonate catalyst of the present invention in the presence of oxygen and under the conditions of a methane oxidative coupling reaction.

[0080] According to the present invention, the conditions for the methane oxidative coupling reaction are not particularly limited and can be conventionally selected in the art. The methane oxidative coupling reaction conditions may include: a molar ratio of methane to oxygen of 2-9:1, a contact reaction temperature of 450°C-650°C (for example, 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, 520°C, 530°C, 550°C, 570°C, 580°C, 600°C, 650°C), and a methane space velocity of 5000 mL / (g·h)-200000 mL / (g·h).

[0081] The present invention will be described in detail below by way of examples.

[0082] 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.

[0083] The length and diameter of the rod-shaped catalyst were measured using the ruler in the software provided with the transmission electron microscope image.

[0084] The analysis of the reaction product components was carried out on a gas chromatograph (Model 7890A) purchased from Agilent.

[0085] The XRD diffraction patterns were measured as follows: X-ray diffractometer (XRD) was manufactured by PANalytical, model Empyrean, Cu target generator, working tube voltage 40KV, working tube current 40mA, PixCel 3D Detector, 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.

[0086] Sample preparation: uniformly select samples, place them in an agate mortar, grind them thoroughly for 10 minutes, and then select 300-mesh powder after sieving. Use the back pressure method to press the powder sample into the sample cell and measure it in reflection mode.

[0087] The lanthanum and doping element contents in the catalysts were measured using an iCAP TQ ICP-MS purchased from Thermo Scientific.

[0088] The pore structure of the catalyst was characterized by BET analysis using an automatic adsorption analyzer ASAP2420M purchased from MICROMERITICS (Micromeritics Instruments, Inc., USA).

[0089] The methane conversion rate is calculated as follows:

[0090] Methane conversion rate = amount of methane consumed in the reaction / initial amount of methane × 100%.

[0091] The ethylene selectivity is calculated as follows:

[0092] Ethylene selectivity = amount of methane consumed by produced ethylene / total methane consumption × 100%.

[0093] The ethane selectivity is calculated as follows:

[0094] Ethane selectivity = amount of methane consumed by produced ethane / total methane consumption × 100%.

[0095] The selectivity of C2 and higher hydrocarbons includes the sum of ethylene, ethane, propylene, propane and higher hydrocarbons.

[0096] The calculation method of C2 hydrocarbon yield is as follows:

[0097] C2 hydrocarbon yield = methane conversion × (ethane selectivity + ethylene selectivity).

[0098] Example 1

[0099] Accurately weigh 3.15 g of lanthanum nitrate hexahydrate, 0.18 g of barium nitrate, and 155 g of deionized water into a beaker, and stir at 900 rpm for 30 min at 25° C. to prepare a solution. Then, 10 wt% sodium hydroxide solution was added dropwise to the solution at 25° C. and 900 rpm. The first addition rate was 0.5 g / min in terms of sodium hydroxide per kilogram of the solution containing lanthanum nitrate and barium nitrate, which was equivalent to adding 0.5 g of sodium hydroxide per minute to the solution containing lanthanum nitrate and barium nitrate. After the pH of the system reached 9, the addition rate of the sodium hydroxide solution was increased to 0.5 g / min in terms of sodium hydroxide per kilogram of the solution containing lanthanum nitrate and barium nitrate. The addition rate is 1 g / min, which is equivalent to adding 1 g of sodium hydroxide per minute to each kilogram of lanthanum nitrate and barium nitrate solution. When the pH of the system reaches 12, the addition of sodium hydroxide solution is stopped, and the temperature is maintained at 25°C and stirring is continued for 10 minutes. The solution is then heated to 100°C and condensed and refluxed (dynamic aging, normal pressure) for 15 hours under stirring. The stirring speed is 1500 rpm. After the solution is cooled to room temperature, the solid material is separated by centrifugation at 9000 rpm in a centrifuge and washed with deionized water until the pH value of the washing liquid is neutral. The obtained solid is dried at 80°C for 15 hours and then calcined in air at 500°C for 2 hours to prepare a lanthanum carbonate catalyst.

[0100] ICP analysis showed that the content of lanthanum in the catalyst was 72.9 wt %, and the content of barium was 0.96 wt %, that is, the molar ratio of lanthanum to barium in the catalyst was 1:0.013.

[0101] According to BET analysis, the specific surface area of ​​lanthanum oxycarbonate catalyst is 46.36m 2 / g, pore volume is 0.23cm 3 / g, and the average pore diameter is 201.48nm.

[0102] FIG1 is a scanning electron microscope image of the lanthanum oxycarbonate catalyst prepared in Example 1. As can be seen from FIG1 , the lanthanum oxycarbonate catalyst has a rod-like nanostructure, and calculations show that the average diameter is 15 nm and the average aspect ratio is 20:1.

[0103] FIG2 is an XRD pattern of the lanthanum oxycarbonate catalyst prepared in Example 1, wherein the abscissa is 2θ and the ordinate is intensity. Compared with the PXRD database (Bruker Diffrac.Eva, version 4.2.1), the characteristic peaks of the hexagonal lanthanum oxycarbonate in FIG2 include 11.1°, 22.2°, 25.2°, 25.8°, 27.6°, 30.3°, 33.7°, 33.9°, 42.5°, 44.4°, 45.9°, 47.4°, 50.2°, 51.7°, 52.1°, 53.1°, 54.7°, 56.9°, 57.8°, 58.2°, 63.2°, 64.0°, 67.0°, 70. 8°, 71.6°, 73.0°, 75.0°, 75.7°, 76.0°; the characteristic peaks of tetragonal lanthanum carbonate include 13.1°, 22.9°, 26.3°, 29.6°, 31.1°, 33.9°, 40.0°, 41.3°, 44.6°, 46.6°, 51.7°, 54.4°, 61.4°; the characteristic peaks of monoclinic lanthanum carbonate include 13.1°, 22.8°, 25.5°, 26.4°, 29.5°, 30.7°, 31.3°, 33.5°, 34.0°, 34.4°, 37.2°, 40.0°, 40.9°, 41.4°, 44.4°, 45.0°, 46.4°, 50.2°, 50.9°, 51.6°, 52.4°, 53.9°, 54.6°, 57.1°, 57.7°, 61.0°, 61.3°, 61.6°, 64.0°, 64.4°, 65.3°, 66 .3°, 66.7°, 69.5°; and no characteristic peaks attributable to elemental barium (characteristic peaks at 25.1°, 35.8°, 44.2°), barium oxide (characteristic peaks at 26.7°, 34.7°, 40.4°, 41.0°), barium hydroxide (characteristic peaks at 26.3°, 26.9°, 27.4°, 34.2°), or barium carbonate (characteristic peaks at 22.1°, 25°, 36.5°, 43.1°). This indicates that the lanthanum oxycarbonate catalyst prepared in Example 1 contains hexagonal lanthanum oxycarbonate, tetragonal lanthanum oxycarbonate, and monoclinic lanthanum oxycarbonate.

[0104] According to the XRD full spectrum fitting method, it was calculated that the ratio of the molar amount of the hexagonal lanthanum oxycarbonate to the total molar amount of the tetragonal lanthanum oxycarbonate and the monoclinic lanthanum oxycarbonate was 1:0.26; the ratio of the total molar amount of the monoclinic lanthanum oxycarbonate to the tetragonal lanthanum oxycarbonate was 0.27:1.

[0105] Example 2

[0106] Accurately weigh 3 g of lanthanum nitrate hexahydrate, 0.72 g of barium nitrate and 150 g of deionized water into a beaker, and stir at 900 rpm for 30 min at 30° C. to prepare a solution. Then, 15 wt% sodium hydroxide solution was added dropwise to the solution at 30° C. and 850 rpm. The first addition rate was 0.1 g / min in terms of sodium hydroxide per kilogram of the solution containing lanthanum nitrate and barium nitrate, which was equivalent to adding 0.1 g of sodium hydroxide per minute to each kilogram of the solution containing lanthanum nitrate and barium nitrate. After the pH of the system reached 8.5, the addition rate of the sodium hydroxide solution was increased to a second addition rate of 1 g / min in terms of sodium hydroxide per kilogram of the solution containing lanthanum nitrate and barium nitrate. min, which is equivalent to adding 1 g of sodium hydroxide per minute to the solution of lanthanum nitrate and barium nitrate per kilogram. When the pH of the system reaches 11.8, the dropwise addition of sodium hydroxide solution is stopped, the temperature is maintained at 30°C and stirring is continued for 10 minutes, and then the solution is heated to 90°C and condensed and refluxed (dynamic aging, normal pressure) for 12 hours under stirring, with a stirring speed of 1200 rpm. After the solution is cooled to room temperature, the solid material is separated by centrifugation at a speed of 10000 rpm in a centrifuge, and washed with deionized water until the pH value of the washing liquid is neutral, and then washed once with ethanol. The resulting solid is dried at 100°C for 10 hours and then calcined in air at 550°C for 4 hours to prepare a lanthanum oxycarbonate catalyst.

[0107] ICP analysis showed that the content of lanthanum in the catalyst was 76.44 wt %, and the content of barium was 2.94 wt %, that is, the molar ratio of lanthanum to barium in the catalyst was 1:0.038.

[0108] According to BET analysis, the specific surface area of ​​lanthanum oxycarbonate catalyst is 48.3m 2 / g, pore volume is 0.26cm 3 / g, and the average pore size is 200.1nm.

[0109] The scanning electron microscope image (similar to Example 1, not shown) shows that the lanthanum oxycarbonate catalyst has a rod-like nanostructure, and calculations show that the average diameter is 18 nm and the average aspect ratio is 26:1.

[0110] The XRD pattern of the lanthanum oxycarbonate catalyst prepared in Example 2 is similar to that in Example 1 (not shown), indicating that the lanthanum oxycarbonate catalyst prepared in Example 2 contains hexagonal lanthanum oxycarbonate, tetragonal lanthanum oxycarbonate and monoclinic lanthanum oxycarbonate.

[0111] According to the XRD full spectrum fitting method, it was calculated that the ratio of the molar amount of the hexagonal lanthanum oxycarbonate to the total molar amount of the tetragonal lanthanum oxycarbonate and the monoclinic lanthanum oxycarbonate was 1:0.64; the ratio of the total molar amount of the monoclinic lanthanum oxycarbonate to the tetragonal lanthanum oxycarbonate was 2.91:1.

[0112] Example 3

[0113] Accurately weigh 3 g of lanthanum nitrate hexahydrate, 0.54 g of barium nitrate, and 150 g of deionized water into a beaker, and stir at 900 rpm for 30 min at 30° C. to prepare a solution. Then, 15 wt% sodium hydroxide solution was added dropwise to the solution at 35° C. and 950 rpm. The first addition rate was 0.6 g / min in terms of sodium hydroxide per kilogram of the solution containing lanthanum nitrate and barium nitrate, which was equivalent to adding 0.6 g of sodium hydroxide per minute per kilogram of the solution containing lanthanum nitrate and barium nitrate. After the pH of the system reached 8, the addition rate of the sodium hydroxide solution was increased to a second addition rate of 5 g / min in terms of sodium hydroxide per kilogram of the solution containing lanthanum nitrate and barium nitrate. in, which is equivalent to adding 5 g of sodium hydroxide per minute to the solution of per kilogram of lanthanum nitrate and barium nitrate. When the pH of the system reaches 10.8, the dropwise addition of sodium hydroxide solution is stopped, the temperature is maintained at 30°C and stirring is continued for 10 minutes, and then the solution is heated to 80°C and condensed and refluxed (dynamic aging, normal pressure) for 12 hours under stirring, with a stirring speed of 1500 rpm. After the solution is cooled to room temperature, the solid material is separated by centrifugation at a speed of 10000 rpm in a centrifuge, and washed with deionized water until the pH value of the washing liquid is neutral, and then washed once with ethanol. The resulting solid is dried at 100°C for 10 hours and then calcined in air at 480°C for 4 hours to prepare a lanthanum carbonate catalyst.

[0114] ICP analysis showed that the content of lanthanum in the catalyst was 75.48 wt %, and the content of barium was 2.04 wt %, that is, the molar ratio of lanthanum to barium in the catalyst was 1:0.027.

[0115] According to BET analysis, the specific surface area of ​​lanthanum oxycarbonate catalyst is 46.87m 2 / g, pore volume is 0.23cm 3 / g, and the average pore diameter is 203nm.

[0116] From the scanning electron microscope image (similar to Example 1, not shown), it can be seen that the lanthanum oxycarbonate catalyst has a rod-like nanostructure, and it is calculated that the average diameter is 21 nm and the average aspect ratio is 21:1.

[0117] The XRD pattern of the lanthanum oxycarbonate catalyst prepared in Example 3 is similar to that in Example 1 (not shown), indicating that the lanthanum oxycarbonate catalyst prepared in Example 3 contains hexagonal lanthanum oxycarbonate, tetragonal lanthanum oxycarbonate and monoclinic lanthanum oxycarbonate.

[0118] According to the XRD full spectrum fitting method, it is calculated that the ratio of the molar amount of the hexagonal lanthanum oxycarbonate to the total molar amount of the tetragonal lanthanum oxycarbonate and the monoclinic lanthanum oxycarbonate is 1:0.49; the ratio of the total molar amount of the monoclinic lanthanum oxycarbonate to the tetragonal lanthanum oxycarbonate is 1.34:1.

[0119] Example 4

[0120] Accurately weigh 3 g of lanthanum nitrate hexahydrate, 0.18 g of magnesium nitrate hexahydrate, and 150 g of deionized water into a beaker, and stir at 900 rpm for 30 min at 30° C. to prepare a solution. Then, 15 wt% sodium hydroxide solution was added dropwise to the solution at 30° C. and 950 rpm. The first addition rate was 0.6 g / min in terms of sodium hydroxide per kilogram of the solution containing lanthanum nitrate and magnesium nitrate, which was equivalent to adding 0.6 g of sodium hydroxide per minute to the solution containing lanthanum nitrate and magnesium nitrate. After the pH of the system reached 8.8, the addition rate of the sodium hydroxide solution was increased to a second addition rate of 2 g in terms of sodium hydroxide per kilogram of the solution containing lanthanum nitrate and magnesium nitrate. / min, which is equivalent to adding 2g of sodium hydroxide per minute to the solution of lanthanum nitrate and magnesium nitrate per kilogram. When the pH of the system reaches 11.6, the dropwise addition of sodium hydroxide solution is stopped, the temperature is maintained at 30°C and stirring is continued for 10 minutes, and then the solution is heated to 90°C and condensed and refluxed (dynamic aging, normal pressure) for 12 hours under stirring, with a stirring speed of 1250 rpm. After the solution is cooled to room temperature, the solid material is separated by centrifugation at a speed of 10000 rpm in a centrifuge, and washed with deionized water until the pH value of the washing liquid is neutral, and then washed once with ethanol. The resulting solid is dried at 100°C for 10 hours and then calcined in air at 475°C for 4 hours to prepare a lanthanum carbonate catalyst.

[0121] ICP analysis showed that the content of lanthanum in the catalyst was 72.3 wt %, and the content of magnesium was 0.75 wt %, that is, the molar ratio of lanthanum to magnesium in the catalyst was 1:0.059.

[0122] According to BET analysis, the specific surface area of ​​lanthanum oxycarbonate catalyst is 72.93m 2 / g, pore volume is 0.42cm 3 / g, and the average pore diameter is 184.2nm.

[0123] The scanning electron microscope image (similar to Example 1, not shown) shows that the lanthanum oxycarbonate catalyst has a rod-like nanostructure, and calculations show that the average diameter is 25 nm and the average aspect ratio is 20:1.

[0124] FIG3 is an XRD pattern of the lanthanum carbonate catalyst prepared in Example 4, wherein the abscissa is 2θ and the ordinate is intensity, which is consistent with the PXRD database (Bruker 3 has characteristic peaks attributable to hexagonal lanthanum oxycarbonate (the same as the characteristic peaks attributable to hexagonal lanthanum oxycarbonate in Example 1), characteristic peaks attributable to tetragonal lanthanum oxycarbonate (the same as the characteristic peaks attributable to tetragonal lanthanum oxycarbonate in Example 1), and characteristic peaks attributable to monoclinic lanthanum oxycarbonate (the same as the characteristic peaks attributable to monoclinic lanthanum oxycarbonate in Example 1); it does not have characteristic peaks attributable to elemental magnesium (characteristic peaks 32.2°, 34.4°, 36.6°, 63.1°), magnesium oxide (characteristic peaks 36.9°, 42.8°, 62.2°, 78.4°), magnesium hydroxide (characteristic peaks 18.6°, 38.0°, 50.9°, 58.7°), and magnesium carbonate (characteristic peaks 32.6°, 43.0°, 53.9°, 70.3°). It is shown that the lanthanum oxycarbonate catalyst prepared in Example 4 contains hexagonal lanthanum oxycarbonate, tetragonal lanthanum oxycarbonate and monoclinic lanthanum oxycarbonate.

[0125] According to the XRD full spectrum fitting method, it is calculated that the ratio of the molar amount of the hexagonal lanthanum oxycarbonate to the total molar amount of the tetragonal lanthanum oxycarbonate and the monoclinic lanthanum oxycarbonate is 1:0.67; the ratio of the total molar amount of the monoclinic lanthanum oxycarbonate to the tetragonal lanthanum oxycarbonate is 0.70:1.

[0126] Example 5 - Sodium hydroxide solution is added at a constant rate

[0127] Accurately weigh 3.15 g of lanthanum nitrate hexahydrate, 0.18 g of barium nitrate, and 155 g of deionized water into a beaker, and stir at 900 rpm for 30 min at 25° C. to prepare a solution. Then, 10 wt% sodium hydroxide solution was added dropwise to the solution at 25° C. and 900 rpm. The addition rate was 2 g / min as sodium hydroxide per kilogram of the solution containing lanthanum nitrate and barium nitrate, which is equivalent to adding 2 g of sodium hydroxide per minute per kilogram of the solution containing lanthanum nitrate and barium nitrate. After the pH of the system reached 12, the mixture was stirred for 30 min at 900 rpm. , stop adding sodium hydroxide solution, maintain the temperature at 25°C and continue stirring for 10 minutes, then heat the solution to 100°C and reflux under stirring (dynamic aging, normal pressure) for 15 hours, with a stirring speed of 1500 rpm. After the solution is cooled to room temperature, the solid material is separated by centrifugation at 9000 rpm in a centrifuge, and washed with deionized water until the pH value of the washing liquid is neutral. The obtained solid is dried at 80°C for 15 hours, and then calcined in air at 500°C for 2 hours to prepare a lanthanum carbonate catalyst.

[0128] ICP analysis showed that the content of lanthanum in the catalyst was 76.44 wt %, and the content of barium was 0.9 wt %, that is, the molar ratio of lanthanum to barium in the catalyst was 1:0.012.

[0129] According to BET analysis, the specific surface area of ​​lanthanum oxycarbonate catalyst is 74.1m 2 / g, pore volume is 0.46cm 3 / g, and the average pore diameter is 111.6nm.

[0130] The scanning electron microscope image (similar to Example 1, not shown) shows that the lanthanum oxycarbonate catalyst has a rod-like nanostructure, and calculations show that the average diameter is 24 nm and the average aspect ratio is 16.7:1.

[0131] The XRD pattern of the lanthanum oxycarbonate catalyst prepared in Example 5 is similar to that in Example 1 (not shown), indicating that the lanthanum oxycarbonate catalyst prepared in Example 5 contains hexagonal lanthanum oxycarbonate, tetragonal lanthanum oxycarbonate and monoclinic lanthanum oxycarbonate.

[0132] According to the XRD full spectrum fitting method, it is calculated that the ratio of the molar amount of the hexagonal lanthanum oxycarbonate to the total molar amount of the tetragonal lanthanum oxycarbonate and the monoclinic lanthanum oxycarbonate is 1:0.2; the ratio of the total molar amount of the monoclinic lanthanum oxycarbonate to the tetragonal lanthanum oxycarbonate is 1.75:1.

[0133] Example 6 - Hydrothermal method

[0134] Accurately weigh 3.15 g of lanthanum nitrate hexahydrate, 0.18 g of barium nitrate, and 155 g of deionized water into a beaker, and stir at 900 rpm for 30 min at 25° C. to prepare a solution. Then, 10 wt% sodium hydroxide solution was added dropwise to the solution at 25° C. and 920 rpm. The first addition rate was 1 g / min in terms of sodium hydroxide per kilogram of the solution containing lanthanum nitrate and barium nitrate, which was equivalent to adding 1 g of sodium hydroxide per minute per kilogram of the solution containing lanthanum nitrate and barium nitrate. After the pH of the system reached 8.6, the addition rate of the sodium hydroxide solution was increased to 10 wt% sodium hydroxide per kilogram of the solution containing lanthanum nitrate and barium nitrate. The second addition rate of the sodium hydroxide meter is 5 g / min, which is equivalent to adding 5 g of sodium hydroxide per minute per kilogram of lanthanum nitrate and barium nitrate solution. When the pH of the system reaches 12, the addition of sodium hydroxide solution is stopped, and the temperature is maintained at 25°C and stirring is continued for 10 minutes. The solution is then transferred to a hydrothermal kettle lined with polytetrafluoroethylene and statically reacted at 180°C for 15 hours. After the hydrothermal kettle is cooled to room temperature, the solid material is separated by centrifugation at 9000 rpm in a centrifuge and washed with deionized water until the pH value of the washing liquid is neutral. The resulting solid is dried at 80°C for 15 hours and then calcined in air at 500°C for 2 hours to prepare a lanthanum carbonate catalyst.

[0135] ICP analysis showed that the content of lanthanum in the catalyst was 72 wt %, and the content of barium was 1.2 wt %, that is, the molar ratio of lanthanum to barium in the catalyst was 1:0.017.

[0136] According to BET analysis, the specific surface area of ​​lanthanum oxycarbonate catalyst is 64.2m 2 / g, pore volume is 0.5cm 3 / g, and the average pore diameter is 253nm.

[0137] The scanning electron microscope image (similar to Example 1, not shown) shows that the lanthanum oxycarbonate catalyst has a rod-like nanostructure, and calculations show that the average diameter is 26 nm and the average aspect ratio is 15:1.

[0138] FIG4 is an XRD pattern of the lanthanum carbonate catalyst prepared in Example 6, wherein the abscissa is 2θ and the ordinate is intensity, which is consistent with the PXRD database (Bruker Diffrac.Eva, version 4.2.1), Figure 4 has characteristic peaks attributable to hexagonal lanthanum oxycarbonate (the same as the characteristic peaks attributable to hexagonal lanthanum oxycarbonate in Example 1), characteristic peaks attributable to tetragonal lanthanum oxycarbonate (the same as the characteristic peaks attributable to tetragonal lanthanum oxycarbonate in Example 1), and characteristic peaks attributable to monoclinic lanthanum oxycarbonate (the same as the characteristic peaks attributable to monoclinic lanthanum oxycarbonate in Example 1); it does not have characteristic peaks attributable to elemental barium, but has characteristic peaks attributable to elemental barium (characteristic peaks 25.1°, 35.8°, 44.2°), barium oxide (characteristic peaks 26.7°, 34.7°, 40.4°, 41.0°), barium hydroxide (characteristic peaks 26.3°, 26.9°, 27.4°, 34.2°), and barium carbonate (characteristic peaks 22.1°, 25°, 36.5°, 43.1°). It is shown that the lanthanum oxycarbonate catalyst prepared in Example 6 contains hexagonal lanthanum oxycarbonate, tetragonal lanthanum oxycarbonate and monoclinic lanthanum oxycarbonate.

[0139] According to the XRD full spectrum fitting method, it is calculated that the ratio of the molar amount of the hexagonal lanthanum oxycarbonate to the total molar amount of the tetragonal lanthanum oxycarbonate and the monoclinic lanthanum oxycarbonate is 1:0.3; the ratio of the total molar amount of the monoclinic lanthanum oxycarbonate to the tetragonal lanthanum oxycarbonate is 0.41:1.

[0140] Example 7

[0141] Accurately weigh 3.15 g of lanthanum nitrate hexahydrate, 0.18 g of strontium nitrate, and 155 g of deionized water into a beaker, and stir at 900 rpm for 30 min at 25° C. to prepare a solution. Then, 10 wt% sodium hydroxide solution was added dropwise to the solution at 25° C. and 900 rpm. The first addition rate was 0.1 g / min in terms of sodium hydroxide per kilogram of the solution containing lanthanum nitrate and strontium nitrate, which is equivalent to adding 0.1 g of sodium hydroxide per minute per kilogram of the solution containing lanthanum nitrate and strontium nitrate. After the pH of the system reached 9, The addition rate of the sodium hydroxide solution was increased to a second addition rate of 2 g / min in terms of sodium hydroxide per kilogram of the solution containing lanthanum nitrate and strontium nitrate, which was equivalent to adding 2 g of sodium hydroxide per minute per kilogram of the solution containing lanthanum nitrate and barium nitrate. When the pH of the system reached 12, the dropwise addition of the sodium hydroxide solution was stopped, and the temperature was maintained at 25°C and stirring was continued for 10 minutes. The solution was then heated to 80°C and refluxed under stirring (dynamic aging, normal pressure) for 15 hours at a stirring speed of 1500 rpm. 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 of the washing liquid was neutral. The resulting solid was dried at 80°C for 15 hours and then calcined in air at 500°C for 2 hours to prepare a strontium-doped lanthanum carbonate catalyst.

[0142] ICP analysis showed that the content of lanthanum in the catalyst was 71.3 wt %, and the content of strontium was 0.99 wt %, that is, the molar ratio of lanthanum to strontium in the catalyst was 1:0.022.

[0143] According to BET analysis, the specific surface area of ​​lanthanum oxycarbonate catalyst is 57m 2 / g, pore volume is 0.37cm 3 / g, and the average pore diameter is 253nm.

[0144] The scanning electron microscope image (similar to Example 1, not shown) shows that the lanthanum oxycarbonate catalyst has a rod-like nanostructure, and calculations show that the average diameter is 30 nm and the average aspect ratio is 14:1.

[0145] FIG5 is an XRD pattern of the lanthanum carbonate catalyst prepared in Example 7, wherein the abscissa is 2θ and the ordinate is intensity, which is consistent with the PXRD database (Bruker Diffrac.Eva, version 4.2.1), Figure 5 has characteristic peaks attributable to hexagonal lanthanum oxycarbonate (the same as the characteristic peaks attributable to hexagonal lanthanum oxycarbonate in Example 1), characteristic peaks attributable to tetragonal lanthanum oxycarbonate (the same as the characteristic peaks attributable to tetragonal lanthanum oxycarbonate in Example 1), and characteristic peaks attributable to monoclinic lanthanum oxycarbonate (the same as the characteristic peaks attributable to monoclinic lanthanum oxycarbonate in Example 1); it does not have characteristic peaks attributable to elemental strontium (characteristic peaks 25.4°, 29.4°, 42.0°, 49.7°), strontium oxide (characteristic peaks 27.2°, 28.6°, 35.7°, 45.5°), hydrated strontium hydroxide (characteristic peaks 19.5°, 31.8°, 39.2°, 40.4°), and strontium carbonate (characteristic peaks 22.2°, 27.5°, 43.1°, 45.6°). It is shown that the lanthanum oxycarbonate catalyst prepared in Example 7 contains hexagonal lanthanum oxycarbonate, tetragonal lanthanum oxycarbonate and monoclinic lanthanum oxycarbonate.

[0146] According to the XRD full spectrum fitting method, it was calculated that the ratio of the molar amount of the hexagonal lanthanum oxycarbonate to the total molar amount of the tetragonal lanthanum oxycarbonate and the monoclinic lanthanum oxycarbonate was 1:0.9; and the ratio of the total molar amount of the monoclinic lanthanum oxycarbonate to the tetragonal lanthanum oxycarbonate was 1.37:1.

[0147] Example 8

[0148] The method of Example 1 was followed, except that “0.18 g of barium nitrate” was replaced by “0.23 g of cerium nitrate”.

[0149] ICP analysis showed that the content of lanthanum in the catalyst was 69.2 wt %, and the content of cerium was 3.2 wt %, that is, the molar ratio of lanthanum to cerium in the catalyst was 1:0.045.

[0150] According to BET analysis, the specific surface area of ​​lanthanum oxycarbonate catalyst is 79.2m 2 / g, pore volume is 0.43cm 3 / g, and the average pore diameter is 211nm.

[0151] The scanning electron microscope image (similar to Example 1, not shown) shows that the lanthanum oxycarbonate catalyst has a rod-like nanostructure, and calculations show that the average diameter is 19 nm and the average aspect ratio is 25:1.

[0152] The XRD pattern of the lanthanum oxycarbonate catalyst prepared in Example 8 is similar to that in Example 1 (not shown). It can be seen from the figure that the lanthanum oxycarbonate catalyst prepared in Example 8 has characteristic peaks attributable to hexagonal lanthanum oxycarbonate (the same as the characteristic peaks attributable to the hexagonal lanthanum oxycarbonate in Example 1), characteristic peaks attributable to tetragonal lanthanum oxycarbonate (the same as the characteristic peaks attributable to tetragonal lanthanum oxycarbonate in Example 1), and characteristic peaks attributable to monoclinic lanthanum oxycarbonate (the same as the characteristic peaks attributable to monoclinic lanthanum oxycarbonate in Example 1). The lanthanum oxycarbonate catalyst prepared in Example 8 has the same characteristic peaks as those of the orthorhombic lanthanum oxycarbonate); it does not have the characteristic peaks of elemental cerium (characteristic peaks at 30.0°, 34.8°, 50.1°, 59.5°), cerium oxide (characteristic peaks at 28.5°, 33.1°, 47.5°, 56.3°), cerium hydroxide (characteristic peaks at 15.8°, 27.4°, 28.2°, 48.9°), or cerium carbonate (characteristic peaks at 17.0°, 29.7°, 34.5°, 42.6°). This indicates that the lanthanum oxycarbonate catalyst prepared in Example 8 contains hexagonal lanthanum oxycarbonate, tetragonal lanthanum oxycarbonate, and monoclinic lanthanum oxycarbonate.

[0153] According to the XRD full spectrum fitting method, it is calculated that the ratio of the molar amount of the hexagonal lanthanum oxycarbonate to the total molar amount of the tetragonal lanthanum oxycarbonate and the monoclinic lanthanum oxycarbonate is 1:0.7; the ratio of the total molar amount of the monoclinic lanthanum oxycarbonate to the tetragonal lanthanum oxycarbonate is 1.10:1.

[0154] Comparative Example 1

[0155] Accurately weigh 3.15 g of lanthanum nitrate hexahydrate and 155 g of deionized water and add them to a beaker. Stir at 900 rpm for 30 min at 25 ° C to prepare a solution. Then, 10 wt% sodium hydroxide solution is added dropwise to the solution at 25 ° C and 900 rpm. The addition rate is 0.5 g / min in terms of sodium hydroxide per kilogram of solution containing lanthanum nitrate, which is equivalent to adding 0.5 g of sodium hydroxide per minute per kilogram of solution containing lanthanum nitrate. After the pH of the system reaches 12, the addition of sodium hydroxide solution is stopped, and the temperature is maintained at 25 ° C and stirring is continued for 10 min. The solution is then heated to 100 ° C and condensed and refluxed (dynamic aging) for 15 h under stirring at a stirring speed of 1200 rpm. After the solution is cooled to room temperature, the solid material is separated by centrifugation at 9000 rpm and washed with deionized water until the pH of the washing liquid is neutral. The resulting solid is dried at 80 ° C for 15 h and then calcined in air at 500 ° C for 2 h to prepare a lanthanum carbonate catalyst.

[0156] ICP analysis showed that the content of lanthanum in the catalyst was 85 wt%.

[0157] According to BET analysis, the specific surface area of ​​lanthanum oxycarbonate catalyst is 83m 2 / g, pore volume is 0.43cm 3 / g, and the average pore size is 95nm.

[0158] The scanning electron microscope image (similar to Example 1, not shown) shows that the lanthanum oxycarbonate catalyst has a rod-like nanostructure, and calculations show that the average diameter is 20 nm and the average aspect ratio is 20:1.

[0159] Figure 6 is an XRD pattern of the lanthanum oxycarbonate catalyst prepared in Comparative Example 1, where the abscissa is 2θ and the ordinate is intensity. Compared with the PXRD database (Bruker Diffrac.Eva, Version 4.2.1), Figure 6 shows only characteristic peaks attributable to the hexagonal lanthanum oxycarbonate phase (the same as the characteristic peaks attributable to the hexagonal lanthanum oxycarbonate phase in Example 1). This indicates that the lanthanum oxycarbonate catalyst prepared in Comparative Example 1 is pure hexagonal lanthanum oxycarbonate.

[0160] Example 9

[0161] The method of Example 1 was followed, except that the aging temperature was 40°C.

[0162] ICP analysis showed that the content of lanthanum in the catalyst was 73 wt %, and the content of barium was 2.1 wt %, that is, the molar ratio of lanthanum to barium in the catalyst was 1:0.03.

[0163] According to BET analysis, the specific surface area of ​​lanthanum oxycarbonate catalyst is 45m 2 / g, pore volume is 0.3cm 3 / g, and the average pore diameter is 86nm.

[0164] The scanning electron microscope image (similar to Example 1, not shown) shows that the lanthanum oxycarbonate catalyst has a rod-shaped nanostructure, and it is calculated that the average diameter is 16 nm and the average aspect ratio is 20:1; the ratio of the total molar amount of the monoclinic lanthanum oxycarbonate to the tetragonal lanthanum oxycarbonate is 0.79:1.

[0165] Example 10

[0166] The method of Example 1 was followed, except that the first addition rate was 5 g / min and the second addition rate was 0.5 g / min.

[0167] ICP analysis showed that the content of lanthanum in the catalyst was 66 wt %, and the content of barium was 3 wt %, that is, the molar ratio of lanthanum to barium in the catalyst was 1:0.045.

[0168] According to BET analysis, the specific surface area of ​​lanthanum carbonate catalyst is 49m 2 / g, pore volume is 0.2cm 3 / g, and the average pore diameter is 45nm.

[0169] The scanning electron microscope image (similar to Example 1, not shown) shows that the lanthanum oxycarbonate catalyst has a rod-like nanostructure, and calculations show that the average diameter is 13 nm and the average aspect ratio is 25:1.

[0170] The XRD pattern of the lanthanum oxycarbonate catalyst prepared in Example 10 is similar to that in Example 1 and is not shown again.

[0171] According to the XRD full spectrum fitting method, it is calculated that the ratio of the molar amount of the hexagonal lanthanum oxycarbonate to the total molar amount of the tetragonal lanthanum oxycarbonate and the monoclinic lanthanum oxycarbonate is 1:0.2; the ratio of the total molar amount of the monoclinic lanthanum oxycarbonate to the tetragonal lanthanum oxycarbonate is 0.57:1.

[0172] Comparative Example 2

[0173] The method of Example 1 was followed, except that a 10 wt % sodium hydroxide solution was added dropwise to the solution at 25° C. and 900 rpm. The addition rate was 0.5 g / min as sodium hydroxide per kilogram of the solution containing lanthanum nitrate and barium nitrate, i.e., 0.5 g of sodium hydroxide was added per minute per kilogram of the solution containing lanthanum nitrate and barium nitrate. The addition of the sodium hydroxide solution was stopped when the pH of the system reached 8.

[0174] The catalyst prepared by the method of Comparative Example 2 does not have a rod-like structure, and no hexagonal lanthanum oxycarbonate, tetragonal lanthanum oxycarbonate, or monoclinic lanthanum oxycarbonate is found.

[0175] Comparative Example 3

[0176] 1.95 g of lanthanum nitrate hexahydrate and 5.4 g of urea were weighed and dissolved in 300 ml of deionized water. The mixture was stirred until completely dissolved. Aqueous ammonia was added to the resulting solution, and the pH was adjusted to 8.5. The solution was stirred in a 90°C oil bath for 3 hours. The resulting white suspension was naturally cooled to room temperature and centrifuged. The resulting precipitate was washed twice with anhydrous ethanol and centrifuged. The white precipitate was dried at 80°C for 12 hours and then calcined at 500°C for 2 hours. Lanthanum oxycarbonate was prepared.

[0177] 0.018 g of cerium nitrate hexahydrate was completely dissolved in deionized water, and 0.105 g of lanthanum carbonate was impregnated with the obtained solution, wherein the molar ratio of cerium nitrate hexahydrate to lanthanum carbonate was 0.15:1. The obtained sample was completely dried at 80°C and calcined at 600°C for 2 hours to prepare a solid sample.

[0178] XRD analysis showed that the obtained solid had hexagonal and monoclinic lanthanum carbonate phases but no tetragonal phase.

[0179] Test Example 1

[0180] The catalyst directly obtained from the preparation process of the above examples and comparative examples is in the form of particles. The particles are pressed into tablets and sieved through a 40-60 mesh screen. Then, 0.1 g of the pellets are loaded into an Inconel fixed-bed reactor. Methane and oxygen are introduced under normal pressure to carry out the reaction. Other reaction conditions and results are shown in Table 1.

[0181] Table 1

[0182]

[0183] Test Example 2

[0184] Example 1: 0.1 g of the granular powder obtained directly from the preparation process was directly loaded into an Inconel fixed bed reactor. The upper and lower sides of the catalyst were fixed with quartz wool. Methane and oxygen were introduced under normal pressure to carry out the reaction. The reaction conditions and results are listed in Table 2.

[0185] Table 2

[0186]

[0187] The short-term catalytic performance of powder and tablets is not much different. The difference is that the powder particle size is small, resulting in high bed pressure, which is a problem for engineering scale-up.

[0188] The results in Table 1 show that, compared to Comparative Examples 1-2, the catalysts prepared using the present invention containing hexagonal lanthanum oxycarbonate, tetragonal lanthanum oxycarbonate, and monoclinic lanthanum oxycarbonate can achieve higher C2 hydrocarbon yields at low temperatures when used in the methane oxidative coupling reaction. Furthermore, using the preferred embodiments of the present invention, Examples 1-4 and Examples 6-8, even higher C2 hydrocarbon yields can be achieved.

[0189] 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 lanthanum oxycarbonate catalyst comprises the following three crystalline phases coexisting in a crystalline state: a hexagonal lanthanum oxycarbonate, a monoclinic lanthanum oxycarbonate containing a doping element, and a tetragonal lanthanum oxycarbonate containing a doping element; wherein the ratio of the molar amount of the hexagonal lanthanum oxycarbonate to the total molar amount of the tetragonal lanthanum oxycarbonate and the monoclinic lanthanum oxycarbonate is 1:0.01-1, and the ratio of the molar amount of the tetragonal lanthanum oxycarbonate to the monoclinic lanthanum oxycarbonate is 1:0.1-10.

2. The lanthanum oxycarbonate catalyst according to claim 1, wherein The doping element in the monoclinic lanthanum oxycarbonate and the tetragonal lanthanum oxycarbonate is selected from at least one of Groups IIA, VIII, IB, and IIB elements and lanthanide elements other than lanthanum, preferably at least one of Mg, Ca, Sr, Ba, Fe, Zn, Ce, and Cd, more preferably at least one of Mg, Ca, Sr, and Ba; And / or, the molar ratio of lanthanum element to doping element in the lanthanum oxycarbonate catalyst is 1:0.01-0.1, preferably 1:0.01-0.08, more preferably 1:0.012-0.

06.

3. The lanthanum oxycarbonate catalyst according to claim 1, wherein The ratio of the molar amount of the hexagonal lanthanum oxycarbonate to the total molar amount of the tetragonal lanthanum oxycarbonate and the monoclinic lanthanum oxycarbonate is 1:0.1-1, more preferably 1:0.25-0.9; and / or The molar ratio of the tetragonal lanthanum oxycarbonate to the monoclinic lanthanum oxycarbonate is 1:0.2-5, preferably 1:0.25-3.

4. The lanthanum oxycarbonate catalyst according to any one of claims 1 to 3, wherein The lanthanum oxycarbonate catalyst has a nanostructure, preferably the catalyst is in rod form with a hydraulic diameter of 10nm-40nm, preferably 10nm-30nm, and further preferably 15nm-30nm; or preferably the catalyst is in sheet form with a thickness of 100nm-500nm, preferably 200nm-400nm; or preferably the catalyst is in spherical form with a hydraulic diameter of 100nm-800nm, preferably 200nm-600nm.

5. The lanthanum oxycarbonate catalyst according to any one of claims 1 to 3, wherein The specific surface area of ​​the lanthanum oxycarbonate catalyst is 40 m 2 / g-100m 2 / g, pore volume is 0.2cm 3 / g-0.7cm 3 / g, and the average pore diameter is 5nm-300nm, preferably 8nm-290nm, and more preferably 180nm-260nm.

6. The lanthanum oxycarbonate catalyst according to any one of claims 1 to 3, wherein The lanthanum oxycarbonate catalyst has a rod-shaped nanostructure, a diameter of the lanthanum oxycarbonate catalyst is 10 nm-30 nm, and an aspect ratio is 5-30:1, preferably 10-26:

1.

7. A method for preparing the lanthanum oxycarbonate catalyst according to any one of claims 1 to 6, characterized in that: The method comprises: adding an alkali solution to a mixed solution containing a lanthanum source and a compound containing a doping element, making the pH value of the mixed system greater than 9, and then sequentially performing reaction, solid-liquid separation, drying and roasting; Wherein, relative to each kilogram of the mixed solution, the addition rate of the alkali solution is 0.01g / min-10g / min, preferably 0.03g / min-8g / min, more preferably 0.5g / min-6g / min, calculated as the alkali in the alkali solution; and wherein, the alkali solution is first added dropwise to the mixed solution at a first addition rate until the pH of the solution reaches a set value, which is between 8 and 9, and then the alkali solution is added dropwise to the mixed solution at a second addition rate until the pH of the system is 10-13, wherein the second addition rate is 0.5-4.5g / min higher than the first addition rate.

8. The method according to claim 7, wherein: The lanthanum source is a water-soluble salt of lanthanum, preferably at least one of lanthanum nitrate, lanthanum chloride and lanthanum acetate, more preferably lanthanum nitrate.

9. The method according to claim 7 or 8, wherein The concentration of the alkali solution is 2 wt%-25 wt%, preferably 3 wt%-20 wt%, more preferably 5 wt%-18 wt%.

10. The method according to claim 7 or 8, wherein The alkali in the alkali solution is a compound of a Group IA metal.

11. The method according to claim 7, wherein: The first addition rate is 0.01-1 g / min; and / or the second addition rate is 0.5-5 g / min.

12. The method according to claim 7 or 8, wherein: The reaction temperature is 80-200°C, and the reaction time is 10h-50h; And / or, the drying temperature is 60°C-100°C, and the drying time is 12h-24h; And / or, the calcination temperature is 450° C.-550° C., and the calcination time is 2 h-8 h.

13. The method according to claim 7 or 8, wherein: The method further includes: S1. Mixing the lanthanum source and the compound containing the doping element with water under a first stirring condition to obtain a mixed solution; preferably, the first stirring condition comprises: a temperature of 10-50° C., a rotation speed of 300-1000 rpm, and a time of 10-40 min; S2. Under a second stirring condition, adding alkali solution to the mixed solution to obtain a mixed system; preferably, the second stirring condition includes: a temperature of 20-60° C. and a rotation speed of 500-1500 rpm.

14. A lanthanum oxycarbonate catalyst composition, comprising the lanthanum oxycarbonate catalyst according to any one of claims 1 to 6 and a binder, wherein the binder comprises alumina, soluble starch, silica sol and polyethylene glycol.

15. A lanthanum oxycarbonate catalyst composition comprising the lanthanum oxycarbonate catalyst according to any one of claims 1 to 6 and a carrier, wherein the carrier comprises alumina, silica, molecular sieve, diatomaceous earth and ceramic.

16. Use of the lanthanum oxycarbonate catalyst according to any one of claims 1 to 6, the lanthanum oxycarbonate catalyst composition according to claim 14, or the lanthanum oxycarbonate catalyst composition according to claim 15 in the oxidative coupling reaction of methane to produce C2 or higher hydrocarbons.

17. A method for preparing hydrocarbons with a carbon content of two or more from methane, characterized in that: The method comprises: in the presence of oxygen and under the conditions of a methane oxidative coupling reaction, contacting methane with the lanthanum oxycarbonate catalyst according to any one of claims 1 to 6, the lanthanum oxycarbonate catalyst composition according to claim 14, or the lanthanum oxycarbonate catalyst composition according to claim 15 for reaction.

18. The method according to claim 17, wherein The molar ratio of the methane to the oxygen is 2-9:1; And / or, the temperature of the contact reaction is 450°C-650°C; And / or, the space velocity of methane is 5000 mL / (g·h)-200000 mL / (g·h).

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