Single-atom catalyst, and preparation method therefor and use thereof

Abstract

The present invention relates to the technical field of methane oxidation coupling, and disclosed are a single-atom catalyst comprising a carrier and an active metal loaded on the carrier, and a preparation method therefor and the use thereof. In the single-atom catalyst provided in the present invention, the active metal forms a single-atom active site on the carrier, and a better catalytic effect of methane oxidation coupling reaction is obtained by using the synergistic effects between the active metal and the carrier and between the active metal.

Description

Single-atom catalysts, their preparation methods and applications Technical Field

[0001] This invention relates to the field of catalyst technology, specifically to a single-atom catalyst, its preparation method, and its application in methane oxidative coupling. Background Technology

[0002] The high temperature required for the methane oxidative coupling reaction, which leads to rapid catalyst deactivation, is one of the reasons why current methane oxidative coupling technology is difficult to industrialize. Although researchers have made improvements in various aspects, the reaction results are still not satisfactory.

[0003] Single-atom catalysts refer to catalysts in which an active metal is supported on a support surface as a single atom, primarily through bonding with other atoms. A single-atom catalyst does not mean that a single zero-valent metal atom is the active center; the single atom also undergoes coordination interactions with other atoms on the support, such as electron transfer, and often exhibits a certain charge. Single-atom catalysts have been extensively and deeply studied due to their extremely high atom utilization and excellent catalytic performance, becoming a hot topic in the field of catalysis in recent years. Single-atom catalysts have also shown good performance in the oxidative coupling reaction of methane. However, conventional single-atom catalysts in current technology contain only one type of metal center, resulting in an insufficient number of atoms in the single-atom state. Furthermore, the distance between active metal atoms is too large, making it difficult to break the linear relationships present in many catalytic processes, and their performance still needs significant improvement. In addition, most existing single-atom catalysts suffer from low metal loading and relatively weak interactions between individual atoms and the support material, which greatly limits their practical application in the field of catalysis. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems existing in the prior art, such as the need to improve the catalytic performance of single-atom catalysts for methane oxidative coupling, and to provide a single-atom catalyst containing at least one active metal, its preparation method, and its applications. Compared with existing single-atom catalysts, the single-atom catalyst of this invention effectively improves the catalytic activity of the active metal in the catalyst, and can significantly reduce the reaction temperature of methane oxidative coupling, making the industrial production of methane oxidative coupling possible.

[0005] In particular, the single-atom catalyst of the present invention contains two active metals as active components, which have a synergistic effect and form active sites of the two active metals on the support.

[0006] In a first aspect, the present invention provides a single-atom catalyst comprising a support and an active metal supported on the support, wherein the support is an oxide support, and the active metal is selected from at least one of Group IA, Group IIA, Group IIB, Group IIIB, Group VIB, and Group VIIB metals.

[0007] Of these, active metals in a single-atom state on the carrier account for ≥70% of the total active metals.

[0008] A second aspect of the present invention provides a method for preparing a single-atom catalyst, the method comprising: step 1: preparing a mixed solution of at least one metal precursor, a nitrogen-containing compound ligand containing two or more nitrogen atoms, and a solvent, and contacting it with an optional reduced support to obtain a mixture; step 2: dispersing the mixture obtained in step 1 by ultrasonication, filtering and drying to obtain a catalyst precursor; and step 3: drying and calcining the catalyst precursor obtained in step 2, and cooling to obtain a single-atom catalyst.

[0009] The support is an oxide support, and the metal is selected from at least one of Group IA, Group IIA, Group IIB, Group IIIB, Group VIB, and Group VIIB metals.

[0010] The third aspect of the present invention provides a single-atom catalyst prepared by the method described in the second aspect.

[0011] The fourth aspect of the present invention provides the application of the catalyst described in the first or third aspect or the method described in the second aspect in the oxidative coupling reaction of methane.

[0012] The fifth aspect of the present invention provides a method for preparing C2 and above hydrocarbons, the method comprising contacting a feed gas with a catalyst described in the first or third aspect to perform a methane oxidative coupling reaction, wherein the feed gas comprises CH4 and O2. Attached Figure Description

[0013] Figures 1-A and 1-B are XAFS (X-ray absorption fine structure) spectra of the metal sites Ba and Sr in the present invention in single-atom form;

[0014] Figures 2-A to 2-F show the XAFS (Fit) fitted spectra of the single-atom catalyst CAT-A prepared in Example 1 in krq space;

[0015] Figures 3-A to 3-F show the XAFS fitting spectra of the single-atom catalyst CAT-B prepared in Example 2 in krq space; Detailed Implementation

[0016] In a first aspect, the present invention provides a single-atom catalyst comprising a support and an active metal supported on the support, wherein the support is an oxide support, and the active metal is selected from at least one of Group IA, Group IIA, Group IIB, Group IIIB, Group VIB, and Group VIIB metals.

[0017] The active metal in a single-atom state on the carrier accounts for ≥70% of the total active metal, preferably ≥80%, and more preferably ≥90%.

[0018] In this invention, the active metal exists in a single-atom state, but this does not mean that the active metal cannot exist in other forms.

[0019] The active metal in the single-atom catalyst can be characterized by synchrotron radiation methods (such as XAFS), and the test results can be fitted and determined.

[0020] The determination of the proportion of single-atom active metals in the total amount of active metals is carried out as follows: Synchrotron radiation is used for characterization. Ten locations are randomly selected from the sample to be tested. The fitting results represent the ratio of the number of locations with single-atom states to the total number. For example, if nine out of ten test locations on the same sample are single-atom states, then single-atom active metals are considered to account for 90% of the total amount of active metals. Here, ten locations are used only to explain the calculation method; in actual testing, more than ten locations may be used.

[0021] In some embodiments, in the single-atom catalyst of the present invention, the support is calculated as a non-oxygen element, and the active metal is calculated as a metal element, and the molar ratio of the support (hereinafter also referred to as S) to the active metal is 2-500:1, preferably 4-500:1, and more preferably 4-400:1. "Molar ratio of support to active metal" refers to the molar ratio of the total loading of non-oxygen elements in the oxide used as the support to the total loading of metal elements in the active metal supported on the support.

[0022] In some embodiments, in the single-atom catalyst of the present invention, the molar ratio of the support S to the active metal can be 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, 21:1, 22:1, 23:1, 24:1, 25:1, 30... The ratios are 1, 40:1, 50:1, 80:1, 100:1, 120:1, 150:1, 180:1, 200:1, 220:1, 250:1, 280:1, 300:1, 320:1, 350:1, 280:1, 400:1, 420:1, 450:1, 480:1, 500:1, or any range of any two of the above ratios or any intermediate value within that range.

[0023] In some embodiments, the spacing between active metal atoms in the single-atom catalyst of the present invention is [missing information]. In cases such as approximately Preferably, the spacing between the active metal atoms is The proportion of monatomic metals in the total monatomic active metals is ≥25%, for example 28% and 40%.

[0024] In some embodiments, the single-atom catalyst of the present invention contains M1-(O). n -M2 structure, where M1 and M2 represent the same active metal or two different active metals, n represents 1 or 2, preferably 1, and the spacing between M1 and M2 is [missing information]. For example, about Preferably, the distance between M1 and M2 is The proportion of the single-atom states M1 and M2 in the total single-atom active metal is ≥25%, for example 28% and 40%.

[0025] In some embodiments, the support is selected from at least one of lanthanum oxide, aluminum oxide, cerium oxide, and silicon oxide, with lanthanum oxide being preferred.

[0026] Preferably, the carrier is crystalline or amorphous.

[0027] Preferably, the specific surface area of ​​the carrier can be 1-500 m². 2 / g, more preferably 20-400m 2 / g.

[0028] Preferably, the active metal is selected from at least one of Sr, Ba, Mn, Mg, Ce, Ca, Li, Na, K, Zn and W, preferably a combination of any two, and particularly preferably Sr and Ba.

[0029] In the single-atom catalyst of the present invention, when at least two active metals are present, preferably two active metals, the active metals may be a combination of at least two metals selected from the same group, or a combination of at least two metals selected from different groups.

[0030] Preferably, the active metal can be Ba and / or Sr.

[0031] Preferably, the active metal can be any combination of the following: Sr and Ba, Sr and Mn, Ba and Mg, Ce and Mg, Ba and Li, Ca and K, Ba and Mn, Zn and W, or Mn and Na, with Sr and Ba being particularly preferred.

[0032] In particular, the presence of two active metals in the single-atom catalyst of the present invention forms a single-atom catalyst containing two active metals, wherein the two active metals, for example, form M1-(O). n -M2 structure, where M1 and M2 represent two different active metals, n represents 1 or 2, preferably 1, and the spacing between M1 and M2 is preferably... For example, about

[0033] In a single-atom catalyst containing two active metals, the two different active metals exist simultaneously in single-atom form and exhibit certain interactions (such as synergistic effects, geometric effects, and electronic effects), for example, the distance between them is... This interaction between the two active metals is not merely a simple summation of the functions of individual metal atoms; rather, it helps to regulate the electronic structure of the catalytic active sites, effectively improving catalytic performance and thus resulting in better catalytic activity and effect in the methane oxidative coupling reaction.

[0034] In the case of a single-atom catalyst containing two active metals, the active metals are preferably selected from any combination of two of Sr, Ba, Mn, Mg, Ce, Ca, Li, Na, K, Zn and W, with Sr and Ba being particularly preferred.

[0035] In the case of a single-atom catalyst containing two active metals, the active metals can be a combination of two metals from the same group or a combination of two metals from different groups.

[0036] In the case of a single-atom catalyst containing two active metals, the active metals are preferably any of the following combinations: Sr and Ba, Sr and Mn, Ba and Mg, Ce and Mg, Ba and Li, Ca and K, Ba and Mn, Zn and W, or Mn and Na, with Sr and Ba being particularly preferred.

[0037] In the case of a single-atom catalyst containing two active metals, the single-atom catalyst of the present invention can be denoted as M1M2 / S, where M1 and M2 represent the active metals respectively, and S represents the support.

[0038] According to some preferred embodiments of the present invention, the support is calculated as non-oxygen elements, and the active metal is calculated as metal elements. The molar ratio of support S to active metal M1M2 (i.e., the total amount of active components) is 2-500:1, preferably 4-500:1, and more preferably 4-400:1. The "molar ratio of support to active metal" refers to the molar ratio of the non-oxygen elements in the oxide used as the support to the total molar amount of metal elements in the two different active metals supported on the support. For example, in a catalyst using lanthanum oxide as the support and Sr and Ba as the active metals, the "molar ratio of support to active metal" is the ratio of the molar amount of La in the support to the total molar amount of Sr and Ba supported on the support; as another example, in a catalyst using silicon oxide as the support and Sr and Ba as the active metals, the "molar ratio of support to active metal" is the ratio of the molar amount of Si in the support to the total molar amount of Sr and Ba supported on the support.

[0039] In the case of a single-atom catalyst containing two active metals, the molar ratio of the support S to the active components M1 and M2 can be 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, 21:1, 22:1, 23:1, 24:1, or 25:1. 30:1, 40:1, 50:1, 80:1, 100:1, 120:1, 150:1, 180:1, 200:1, 220:1, 250:1, 280:1, 300:1, 320:1, 350:1, 280:1, 400:1, 420:1, 450:1, 480:1, 500:1, or any range formed by any two of the above ratios or any intermediate value within that range.

[0040] In the case of a single-atom catalyst containing two active metals, the present invention does not impose any particular limitation on the content ratio of the two active metals in the single-atom catalyst. However, in order to obtain better catalytic performance, according to some preferred embodiments of the present invention, in the single-atom catalyst M1M2 / S containing two active metals, the molar ratio of M1 and M2, based on the metal elements, can be 1:0.1-10, preferably 1:0.1-5. For example, it can be 1:0.1, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, or any intermediate ratio within the range of any two of the above ratios.

[0041] A second aspect of the present invention provides a method for preparing a single-atom catalyst, the method comprising:

[0042] Step 1: Prepare a mixed solution by mixing at least one metal precursor, a nitrogen-containing compound ligand containing two or more nitrogen atoms and a solvent, and contact it with an optional reduced support to obtain a mixture;

[0043] Step 2: The mixture obtained in Step 1 is ultrasonically dispersed, filtered, and dried to obtain the catalyst precursor;

[0044] Step 3: The catalyst precursor obtained in Step 2 is dried, calcined, and cooled to obtain a single-atom catalyst;

[0045] The support is an oxide support, and the metal is selected from at least one of Group IA, Group IIA, Group IIB, Group IIIB, Group VIB, and Group VIIB metals.

[0046] In some embodiments, the support is selected from at least one of lanthanum oxide, aluminum oxide, cerium oxide, and silicon oxide, with lanthanum oxide being preferred.

[0047] In some embodiments, the metal is selected from at least one of Sr, Ba, Mn, Mg, Ce, Ca, Li, Na, K, Zn, and W, preferably a combination of any two, with Sr and Ba being particularly preferred.

[0048] When using at least two active metals, the metals can be a combination of at least two metals selected from the same group or a combination of at least two metals selected from different groups.

[0049] Preferably, the metal can be Ba and / or Sr.

[0050] Preferably, the metal can be any combination of the following: Sr and Ba, Sr and Mn, Ba and Mg, Ce and Mg, Ba and Li, Ca and K, Ba and Mn, Zn and W, or Mn and Na, with Sr and Ba being particularly preferred.

[0051] Preferably, the precursor is a salt, which is preferably selected from water-soluble salts, and more particularly from at least one of nitrates, sulfates, and halides. The halides are, for example, fluorides, chlorides, and bromides.

[0052] In some embodiments, the nitrogen-containing compound ligand is selected from (organic) compounds containing amine groups.

[0053] In some embodiments, the nitrogen-containing compound ligand is selected from at least one of diethylenetriamine, ethylenediaminetetraacetic acid, bipyridine, porphyrin, and phthalocyanine.

[0054] Preferably, the solvent is water or an organic solvent; more preferably, the solvent is at least one of water, an alcohol with no more than 5 carbon atoms, and a ketone with no more than 5 carbon atoms; and even more preferably, the solvent is at least one of water, methanol, ethanol, and acetone.

[0055] In some embodiments, the molar ratio of the precursor to the ligand, expressed as metal ions, in the mixed solution is 2-5:1. For example, it can be 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, or any range of any two of the above ratios or any intermediate value within that range.

[0056] To create defects on the support surface that facilitate the loading and dispersion of ligands and metal atoms, according to a preferred embodiment of the invention, the support is pretreated before contacting the mixed solution. Any method capable of creating these defects on the support surface is applicable to the invention. According to some preferred embodiments of the invention, the pretreatment may be a heat treatment A of the support under a reducing atmosphere.

[0057] Preferably, the reducing atmosphere is provided by H2 and / or CO.

[0058] Preferably, the conditions for heat treatment A include: a temperature of 300-500°C and a time of 0.5-5 hours. For example, the carrier can be left to stand under the above conditions.

[0059] According to a preferred embodiment of the present invention, the amount of support used, based on metal ions, is such that the molar ratio of support to metal precursor is 2-500:1, preferably 4-500:1, and most preferably 4-400:1. The "molar ratio of support to metal precursor" refers to the molar ratio of the non-oxygen element in the oxide used as the support to the total amount of metal ions generated by the metal precursor in the mixed solution. For example, using lanthanum oxide as the support and water-soluble salts of Sr and Ba as precursors, the molar ratio of support to metal precursor is the ratio of the molar amount of La provided by lanthanum oxide to the sum of the molar amounts of Sr and Ba provided by the metal precursor.

[0060] In the method provided by this invention, the amount of carrier used is such that the molar ratio of carrier to metal precursor can be 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, 21:1, 22:1, 23:1, 24:1, 25:1, or 30:1. 40:1, 50:1, 80:1, 100:1, 120:1, 150:1, 180:1, 200:1, 220:1, 250:1, 280:1, 300:1, 320:1, 350:1, 280:1, 400:1, 420:1, 450:1, 480:1, 500:1, or any range formed by any two of the above ratios or any intermediate value within that range.

[0061] In order to make the distribution of the loaded metal precursor more uniform, according to a preferred embodiment of the present invention, in step 2, after ultrasonic treatment, heat treatment B is performed.

[0062] Preferably, the conditions for ultrasonic treatment include: temperature 40-70℃, ultrasonic frequency 20-100kHz, ultrasonic power 200-500w, and ultrasonic time 0.5-5h.

[0063] For example, the ultrasonic frequency can be 20kHz, 30kHz, 40kHz, 50kHz, 60kHz, 70kHz, 80kHz, 90kHz, or 100kHz, or it can be any range of any two of the above values ​​or any intermediate value in that range.

[0064] For example, the ultrasonic power can be 200W, 250W, 300W, 350W, 400W, 450W, or 500W, or it can be a range consisting of any two of the above values ​​or any intermediate value in that range.

[0065] Preferably, stirring is performed during the ultrasonic treatment process. The purpose of stirring is mainly to increase the uniformity of mixing between the metal precursor and the carrier, and any stirring conditions that can achieve this purpose are applicable to this invention. For example, a stirring speed of 100-500 rpm can be used for a 500 mL treatment system.

[0066] Preferably, the conditions for heat treatment B include: a temperature of 40-90°C and a time of 1-10 hours. Stirring is preferably performed during heat treatment B. The purpose of stirring is mainly to prevent uneven distribution of active components caused by the evaporation of surface solvents; any stirring conditions that achieve this purpose are applicable to this invention. For example, for a 500 mL treatment system, a stirring speed of 200-600 rpm can be used.

[0067] According to a preferred embodiment of the invention, the drying conditions are such that the solvent content in the carrier loaded with the metal precursor and ligand does not exceed 1 wt%, preferably 0.1-0.7 wt%. "Solvent content" refers to the amount of residual solvent in the carrier loaded with the precursor and ligand.

[0068] Preferably, the drying conditions include: a temperature of 70-120°C and a time of 10-30 hours.

[0069] According to a preferred embodiment of the present invention, the calcination method includes calcining at 100-650°C for 30-300 min.

[0070] Preferably, the roasting is carried out under a protective atmosphere, which is provided, for example, by air and / or nitrogen.

[0071] A third aspect of the present invention provides a single-atom catalyst prepared according to the method described in the second aspect.

[0072] The fourth aspect of this invention provides the application of the single-atom catalyst described in the first or third aspect in the oxidative coupling reaction of methane, or the application of the method described in the second aspect in the oxidative coupling reaction of methane. "Application in the oxidative coupling reaction of methane" can be understood as using the single-atom catalyst of this invention in a methane oxidative coupling reaction (on any scale), which may also include, when using methane oxidative coupling for industrial production (e.g., production of C2 and above hydrocarbons), using the method of this invention to prepare the single-atom catalyst and using the prepared single-atom catalyst for the reaction.

[0073] The fifth aspect of the present invention provides a method for preparing C2 and above hydrocarbons, the method comprising contacting a feed gas with a single-atom catalyst as described in the first or third aspect to perform a methane oxidative coupling reaction, wherein the feed gas comprises CH4 and O2.

[0074] According to a preferred embodiment of the present invention, the molar ratio of CH4 to O2 in the raw material gas is 2-10:1, preferably 2-8:1.

[0075] For example, the molar ratio of CH4 to O2 in the feed gas can be 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, or any range of any two of the above ratios or any intermediate value within that range.

[0076] According to a preferred embodiment of the present invention, the conditions for the methane oxidative coupling reaction include: a reaction temperature not lower than 450°C, preferably 480-800°C; and a feed gas space velocity (CGH) of 20,000-200,000 mL / (g·h), preferably 30,000-180,000 mL / (g·h). mL / (g·h) refers to the amount of feed gas (mL) passing through a unit amount (g) of catalyst per unit time (h).

[0077] For example, the temperature of the methane oxidative coupling reaction can be 450℃, 460℃, 470℃, 480℃, 490℃, 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 575℃, 600℃, 625℃, 650℃, 675℃, 700℃, 725℃, or 750℃, or it can be any range of any two of the above values ​​or any intermediate value within that range.

[0078] For example, the gas hourly space velocity (GHSV) of the feed gas in the methane oxidative coupling reaction, calculated as CH4, can be 20,000 mL / (g·h), 30,000 mL / (g·h), 40,000 mL / (g·h), 50,000 mL / (g·h), 60,000 mL / (g·h), 70,000 mL / (g·h), 80,000 mL / (g·h), 90,000 mL / (g·h), or 100,000 mL / (g·h). The values ​​can be 110000mL / (g·h), 120000mL / (g·h), 130000mL / (g·h), 140000mL / (g·h), 150000mL / (g·h), 160000mL / (g·h), 180000mL / (g·h), 200000mL / (g·h), or any range of any two of the above values ​​or any intermediate value within that range.

[0079] For the single-atom catalyst of the present invention, such as a single-atom catalyst containing two active metals, barium and strontium (e.g., catalyst CAT-A in Example 1), XAFS was used to characterize and compare the coordination environments of barium and strontium atoms respectively (see Figures 1-A and 1-B). It can be seen that, compared with the standard sample barium oxide, the main peak in the R space of the single-atom catalyst of the present invention containing two active metals is consistent with the Ba-O peak in barium oxide, proving that the coordination form of barium in this sample is a barium-oxygen bond; barium-barium bonds exist in the barium oxide sample (peaks between 3-4.5 in the figure), while there is no corresponding peak in the catalyst of the present invention, proving that barium-barium bonds do not exist, and the barium coordination form is a Ba-O bond; similarly, the catalyst of the present invention shows that strontium-strontium bonds do not exist, and the strontium coordination form is a Sr-O bond. Based on the bond length and coordination number, combined with the DFT fitting results, it is confirmed that the active metal atoms Ba and Sr in the single-atom catalyst of the present invention exist in single-atom form. Further characterization using synchrotron radiation and fitting revealed that the spacing between strontium and barium in structures existing as single-atom forms of barium and strontium, respectively, could be [value missing]. The situation.

[0080] Through the above technical solution, the present invention can achieve at least the following beneficial effects:

[0081] (1) The single-atom catalyst provided by the present invention can effectively improve the adjustability in the methane oxidative coupling reaction through the synergistic effect between the support and the supported active metal, and further through the synergistic effect between the active metals in the presence of at least two active metals.

[0082] (2) The preparation method of the single-atom catalyst provided by the present invention is simple and easy to implement, the raw materials are readily available, and it can be mass-produced and has the potential for industrial application.

[0083] (3) When the single-atom catalyst provided by the present invention is used in the methane oxidative coupling reaction, it can improve the selectivity of C2 and above hydrocarbons while maintaining a low methane activation temperature, thereby reducing the energy consumption of the methane oxidative coupling reaction and laying the foundation for industrial application.

[0084] Example

[0085] The present invention will be described in detail below through embodiments. It should be understood that the following embodiments are only used to further explain and illustrate the content of the present invention by way of example, and are not intended to limit the present invention.

[0086] Unless otherwise specified, all reagents used in the following examples are commercially available products purchased from legitimate chemical suppliers and are of analytical purity.

[0087] The structure of single-atom sites in the catalyst was characterized by XAFS, for example, the K-edge X-ray absorption spectra of Ba and Sr were obtained by XAS beamline (BL14W1) at the Shanghai Synchrotron Radiation Facility (SSRF, 3.5 GeV, 250 mA). Hard X-ray monochromatization was achieved using a Si(311) dual-crystal monochromator. Pd foil and PdO were used as standard compounds for testing, and energy calibration was performed.

[0088] The method for determining the proportion of active metals in a single-atom state in a single-atom catalyst is as follows: Synchrotron radiation is used for characterization. Ten locations on the sample are randomly selected for testing. The fitting result represents the ratio of the number of locations in a single-atom state to the total number of locations. For example, if nine out of ten locations on the same sample are in a single-atom state, then the active metal in a single-atom state is considered to account for 90% of the total active metal. The ten locations mentioned here are only used to explain the calculation method; in actual testing, more than ten locations may be used.

[0089] The spacing between metals M1 and M2 is The proportions of the single-atom states M1 and M2 in the total single-atom active metal are calculated as follows: Based on the bond length differences between Ba-O-Ba / La and Ba-O-Sr, the proportion of Ba-O-Sr is obtained by EXAFS (Extended X-ray Absorption Spectroscopy) fitting. The specific EXAFS fitting method is as follows: The acquired EXAFS data is processed according to standard procedures using Athena and Artemis modules implemented in the IFEFFIT software package. The accessory details are as follows: The acquired EXAFS data is processed according to standard procedures using the Athena module implemented in the IFEFFIT software package. The EXAFS spectrum is obtained by subtracting the back-edge background from the overall absorption and then normalizing it relative to the edge skip step. Subsequently, a hanning window is used. The x(k) data were Fourier transformed to R space to separate EXAFS contributions from different shells. To obtain quantitative structural parameters around the central atom, least-squares curve parameter fitting was performed using the ARTEMIS module in the IFEFFIT package. The fitting yielded the second shell.

[0090] The following EXAFS equations were used:

[0091] Among them, S0 2 F is the amplitude reduction factor. j (k) represents the effective backscattering amplitude of the bent wave, N j Let R be the neighborhood number of the j-th atomic shell. jλ is the distance between the central atom absorbing X-rays and the j-th atomic shell atom (backscatterer). The mean free path in the middle, For phase shift (including the phase shift of each shell and the total phase shift of the central atom), σ j The Debye-Waller parameters of the j-th shell (average R) j (Changes in surrounding distances). Function F j (k), λ and φ j (k) Calculation was performed using the ab initio code FEFF8.2. The coordination number of the model samples was fixed at the nominal value. The resulting S0 2 These parameters are fixed in the subsequent fitting. However, the internal atomic distance R, the Debye-Waller factor σ², and the edge energy displacement ΔE₀ are allowed to run freely.

[0092] Example 1

[0093] The single-atom catalyst CAT-A containing barium and strontium was prepared using the following method:

[0094] Support pretreatment: Lanthanum oxide was subjected to heat treatment A by reducing it with H2 at 350℃ for 1 hour. The reduced lanthanum oxide surface has oxygen vacancy sites, and the support specific surface area is 58 m². 2 / g.

[0095] Active metal and ligand loading: 10 g of reduced lanthanum oxide was ultrasonically dispersed in 20 mL of ethanol solution (95% concentration). Then, 1.8 g of strontium nitrate and 1.5 g of barium nitrate were dissolved in 25 mL of deionized water, and 5 mol% (calculated based on lanthanum oxide) of diethylenetriamine polydentate ligand was added to obtain a solution. This solution was then added to the aforementioned lanthanum oxide ethanol solution. The mixture was ultrasonically dispersed at 50 °C for 4 h with stirring (ultrasonic frequency 40 kHz, ultrasonic power 300 W). After drying and filtration, the catalyst precursor was obtained and dried in a drying oven at 80 °C for 12 h. Finally, it was calcined at 500 °C for 2 h and cooled to obtain catalyst CAT-A. Synchrotron radiation characterization (XAFS spectrum) showed that Ba mainly existed in the Ba-O bond coordination form, with a bond length of approximately [missing value]. The coordination number is 3.9; Sr also coordinates with O to form an Sr-O bond with a bond length of approximately The coordination number is 2.9. Fitting the results (see Figures 2-A to 2-F) reveals that the catalyst CAT-A contains sites for two active metal single atoms: Ba and O-Sr, with a spacing of [missing information - likely a value]. The situation.

[0096] In single-atom catalysts, the proportion of active metals in the single-atom state is 92% of the total active metals.

[0097] The spacing between Ba and Sr is The proportion of single-atom Ba and Sr in the total single-atom active metal is 40%.

[0098] Example 2

[0099] The single-atom catalyst CAT-B containing barium and strontium was prepared using the following method:

[0100] Support pretreatment: Lanthanum oxide was subjected to heat treatment A by reducing it with H2 at 350℃ for 1 hour. The reduced lanthanum oxide surface has oxygen vacancy sites, and the support specific surface area is 58 m². 2 / g.

[0101] Active metal and ligand loading: 10 g of reduced lanthanum oxide was ultrasonically dispersed in 25 mL of ethanol solution (95% concentration). Then, 0.9 g of strontium nitrate and 1.5 g of barium nitrate were dissolved in 25 mL of deionized water. A 5 mol% (calculated based on lanthanum oxide) solution of ethylenediaminetetraacetic acid (EDTA) multidentate ligand was added to the lanthanum oxide ethanol solution. The mixture was ultrasonically dispersed at 60 °C for 4 h with stirring (ultrasonic frequency 50 kHz, ultrasonic power 200 W). After drying and filtration, the catalyst precursor was obtained and dried in a drying oven at 80 °C for 24 h. Finally, the precursor was calcined at 550 °C for 2 h and cooled to obtain catalyst CAT-B. Synchrotron radiation characterization (XAFS spectrum) revealed that Ba mainly exists in the form of Ba-O bonds with a bond length of approximately [missing value]. The coordination number is 3.9; Sr also coordinates with O to form an Sr-O bond with a bond length of approximately The coordination number is 3.0. Fitting the results (see Figures 3-A to 3-F) reveals that the catalyst CAT-B contains sites for two active metal single atoms: Ba and O-Sr, with a spacing of [missing information - likely a value] between Ba and Sr. The situation.

[0102] In single-atom catalysts, the proportion of active metals in the single-atom state is 95% of the total active metals.

[0103] The spacing between Ba and Sr is The proportion of single-atom Ba and Sr in the total single-atom active metal is 28.8%.

[0104] Example 3

[0105] The single-atom catalyst CAT-C containing barium and strontium was prepared using the following method:

[0106] Support pretreatment: Lanthanum oxide was subjected to heat treatment A by reducing it with H2 at 500℃ for 1 hour. The reduced lanthanum oxide surface has oxygen vacancy sites, and the support specific surface area is 58 m². 2 / g.

[0107] Active metal and ligand loading: 10 g of reduced lanthanum oxide was ultrasonically dispersed in 15 mL of ethanol solution (95% concentration). Then, 0.9 g of strontium nitrate and 1.5 g of barium nitrate were dissolved in 25 mL of deionized water. 5 mol% (calculated based on lanthanum oxide) of bipyridine polydentate ligand was added to obtain a solution, which was then added to the aforementioned lanthanum oxide ethanol solution. The mixture was ultrasonically dispersed at 60 °C for 4 h with stirring (ultrasonic frequency 80 kHz, ultrasonic power 400 W). After drying and filtration, the catalyst precursor was obtained and dried in a drying oven at 80 °C for 24 h. Finally, it was calcined at 550 °C for 2 h and cooled to obtain catalyst CAT-C. Synchrotron radiation characterization (XAFS spectrum) revealed that Ba mainly exists in the form of Ba-O bonds with a bond length of [missing information]. The coordination number is 3.32, and Sr also coordinates with O to form an Sr-O bond with a bond length of approximately [missing information]. The coordination number is 2.54. Fitting the results revealed that the catalyst CAT-C contains sites for two active metal single atoms: Ba-O-Sr, with a spacing between Ba and Sr of [missing information]. The situation.

[0108] In single-atom catalysts, the proportion of active metals in the single-atom state is 89% of the total active metals.

[0109] The spacing between Ba and Sr is The proportion of single-atom Ba and Sr in the total single-atom active metal is 32%.

[0110] Example 4

[0111] The single-atom catalyst CAT-D containing barium and strontium was prepared using the following method:

[0112] Support pretreatment: Lanthanum oxide was subjected to heat treatment A by reducing it with H2 at 450℃ for 1 hour. The reduced lanthanum oxide surface has oxygen vacancy sites, and the support specific surface area is 58 m². 2 / g.

[0113] Active metal and ligand loading: 10 g of reduced lanthanum oxide was ultrasonically dispersed in 20 mL of ethanol solution (95% concentration). Then, 1.8 g of strontium nitrate and 1.3 g of barium nitrate were dissolved in 25 mL of deionized water. A 5 mol% (calculated based on lanthanum oxide) solution of porphyrin polydentate ligand was added, and this solution was added to the aforementioned lanthanum oxide ethanol solution. The mixture was ultrasonically dispersed at 60 °C for 4 h with stirring (ultrasonic frequency 100 kHz, ultrasonic power 200 W). After drying and filtration, the catalyst precursor was obtained and dried in a drying oven at 80 °C for 24 h. Finally, it was calcined at 550 °C for 2 h and cooled to obtain catalyst CAT-D. Synchrotron radiation characterization (XAFS spectrum) revealed that Ba mainly exists in the form of Ba-O bonds with a bond length of [missing information]. The coordination number is 3.11, and Sr also coordinates with O to form an Sr-O bond with a bond length of approximately [missing information]. The coordination number is 2.13. R-space fitting of the results revealed that the catalyst CAT-A contains sites for two active metal single atoms: Ba and O-Sr, with a spacing between Ba and Sr of [missing information]. The situation.

[0114] In single-atom catalysts, the proportion of active metals in the single-atom state is 85% of the total active metals.

[0115] The spacing between Ba and Sr is The proportion of single-atom Ba and Sr in the total single-atom active metal is 35%.

[0116] Example 5

[0117] The single-atom catalyst CAT-E containing metallic barium was prepared using the following method:

[0118] Support pretreatment: Lanthanum oxide was subjected to heat treatment A by reducing it with H2 at 450℃ for 1 hour. The reduced lanthanum oxide surface has oxygen vacancy sites, and the support specific surface area is 58 m². 2 / g.

[0119] Active metal and ligand loading: 10 g of reduced lanthanum oxide was ultrasonically dispersed in 20 mL of ethanol solution (95% concentration). Then, 1.3 g of barium nitrate was dissolved in 25 mL of deionized water, and 5 mol% (calculated based on lanthanum oxide) of porphyrin polydentate ligand was added to obtain a solution. This solution was then added to the above lanthanum oxide ethanol solution. The mixture was ultrasonically dispersed at 60 °C for 4 h with stirring (ultrasonic frequency 100 kHz, ultrasonic power 200 W). After drying and filtration, the catalyst precursor was obtained and dried in a drying oven at 80 °C for 24 h. Finally, it was calcined at 550 °C for 2 h and cooled to obtain catalyst CAT-E. Synchrotron radiation characterization (XAFS spectrum) revealed that Ba mainly exists in the form of Ba-O bonds with a bond length of [missing information]. The coordination number is 3.11. R-space fitting of the results revealed that the catalyst CAT-E contains active metal single-atom sites of Ba-O-Ba, with a spacing of [missing information - likely a specific value]. The situation.

[0120] In single-atom catalysts, the proportion of active metals in the single-atom state is 90% of the total active metals.

[0121] The spacing between Ba and Ba is The proportion of single-atom Ba in the total single-atom active metal is 25%.

[0122] Comparative Example 1

[0123] This comparative example is used to compare the effects of different ligands used in the preparation process on the structure of the prepared materials.

[0124] The single-atom catalyst CAT-F containing barium and strontium was prepared using the following method:

[0125] Support pretreatment: Lanthanum oxide was subjected to heat treatment A by reducing it with H2 at 350℃ for 1 hour. The reduced lanthanum oxide surface has oxygen vacancy sites, and the support specific surface area is 58 m². 2 / g.

[0126] Active metal and ligand loading: 10 g of reduced lanthanum oxide was ultrasonically dispersed in 20 mL of ethanol solution (95% concentration). Then, 1.8 g of strontium nitrate and 1.5 g of barium nitrate were dissolved in 25 mL of deionized water. A 5 mol% (calculated based on lanthanum oxide) solution of pyridine was added, and this solution was added to the above lanthanum oxide ethanol solution. The mixture was ultrasonically dispersed at 50 °C for 4 h with stirring (ultrasonic frequency 50 kHz, ultrasonic power 200 W). After drying and filtration, the catalyst precursor was obtained and dried in a drying oven at 80 °C for 12 h. Finally, it was calcined at 500 °C for 2 h and cooled to obtain catalyst CAT-F. Synchrotron radiation characterization (XAFS spectrum) revealed the presence of Ba-O bond coordination, with a bond length of approximately [missing value]. Sr also coordinates with O to form Sr-O bonds, with a bond length of approximately [missing information]. Fitting the results revealed that the distance between Ba and Sr was not detected. The situation.

[0127] In single-atom catalysts, the proportion of active metals in the single-atom state is 2% of the total active metals.

[0128] Comparative Example 2

[0129] This comparative example is used to compare the effect of not using ultrasonic dispersion after adding active metals during the preparation process on the material structure.

[0130] The single-atom catalyst CAT-G containing barium and strontium was prepared using the following method:

[0131] Support pretreatment: Lanthanum oxide was subjected to heat treatment A by reducing it with H2 at 350℃ for 1 hour. The reduced lanthanum oxide surface has oxygen vacancy sites, and the support specific surface area is 58 m². 2 / g.

[0132] Active metal and ligand loading: 10 g of reduced lanthanum oxide was ultrasonically dispersed in 20 mL of ethanol solution (95% concentration). Then, 1.8 g of strontium nitrate and 1.5 g of barium nitrate were dissolved in 25 mL of deionized water. 5 mol% (calculated based on lanthanum oxide) of diethylenetriamine polydentate ligand was added to obtain a solution, which was then added to the aforementioned lanthanum oxide ethanol solution. The mixture was stirred and dispersed at 50 °C for 4 h. After drying and filtration, the catalyst precursor was obtained and dried in a drying oven at 80 °C for 12 h. Finally, the precursor was calcined at 500 °C for 2 h and cooled to obtain catalyst CAT-G. Synchrotron radiation characterization (XAFS spectrum) revealed the presence of Ba and Sr sites and Ba-O bond coordination, with a bond length of approximately [missing value]. Sr also coordinates with O to form Sr-O bonds, with a bond length of approximately [missing information]. Fitting the results revealed that the distance between Ba and Sr was not detected. The situation.

[0133] In a single-atom catalyst, the proportion of active metal in the single-atom state is 5% of the total active metal.

[0134] Catalyst effect testing in examples and comparative examples

[0135] Test Example 1

[0136] This test example illustrates the catalytic performance of the catalysts obtained in the above embodiments in the methane oxidative coupling reaction.

[0137] 0.1 g of catalyst was charged into a fixed-bed quartz reactor. Under atmospheric pressure, the molar ratio of methane to oxygen was 6:1, and the methane space velocity was 40,000 mL / gh. The activation temperature of the reaction was measured, and the methane conversion and the conversion of C2 and higher hydrocarbons (C4 and C5) of the catalyst were measured at reaction temperatures of 500 °C and 600 °C. 2+ The selectivity of methane is detailed in Table 1. The activation temperature refers to the reaction temperature at which both methane conversion is greater than 2% and the selectivity for C2 hydrocarbons and above is greater than 5%.

[0138] The specific testing methods are as follows:

[0139] The reaction products were analyzed using an Agilent 7890A gas chromatograph, and the methane conversion rate and the percentage of C2 and higher hydrocarbons (C4 and C5) were calculated based on the analytical results. 2+ The selectivity of C2 and above hydrocarbons can be calculated by multiplying the methane conversion rate by the selectivity of C2 and above hydrocarbons.

[0140] In equation (1), CH4 conversion (or CH4 conversion rate) is the conversion rate of methane. This refers to the methane concentration at the reactor inlet. This refers to the methane concentration at the reactor outlet.

[0141] In equation (2), C2+sel (or C 2+ Selectivity refers to the selectivity of hydrocarbons with two or more carbon atoms. C2H4 C C2H6 C C3H6 C C3H8 C C4H8 C CO2 C CO These are the concentrations of C2H4, C2H6, C3H6, C3H8, C4H8, CO2, and CO at the reactor outlet, respectively.

[0142] Table 1

[0143] Test Example 2

[0144] This test example illustrates the changes in the catalytic performance of the catalyst of the present invention under different methane oxidative coupling reaction conditions.

[0145] The catalytic performance of the catalyst CAT-A obtained in Example 1 was tested using the method in Test Example 1 and according to the conditions in Table 2. The results are detailed in Table 2.

[0146] Table 2

[0147] Note: In Table 2, "alkane-to-oxygen ratio" refers to the molar ratio of methane to oxygen in the feed gas; space velocity is the feed gas space velocity measured based on methane in the feed gas, methane conversion rate, and C2 and above hydrocarbons (C4H2O). 2+ The selectivity of ) is detected and calculated using the method in Test Example 1.

[0148] Through comparison of examples and comparative examples, it was found that the technical solution of the present invention effectively improves the catalytic activity of the active metal in the catalyst and can significantly reduce the reaction temperature of methane oxidative coupling, making the industrial production of methane oxidative coupling possible.

[0149] The catalysts obtained in Examples 1-5 were further tested for stability. Under the conditions in Tables 1 and 2, the catalysts were reacted continuously for 50 hours. It was observed that the catalyst performance remained unchanged or essentially unchanged during the reaction.

[0150] 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.

[0151] 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 single-atom catalyst, the single-atom catalyst comprising a support and an active metal supported on the support, wherein the support is an oxide support, and the active metal is selected from at least one of Group IA, Group IIA, Group IIB, Group IIIB, Group VIB, and Group VIIB metals. The active metal in a single-atom state on the carrier accounts for ≥70% of the total active metal, preferably ≥80%, and more preferably ≥90%.

2. The single-atom catalyst according to claim 1, wherein it has at least one of the following characteristics: The carrier is calculated as a non-oxygen element, and the active metal is calculated as a metal element. The molar ratio of the carrier to the active metal is 2-500:1, preferably 4-500:1, and more preferably 4-400:

1. The spacing between active metal atoms in a single-atom catalyst is The situation; M1-(O) is present in single-atom catalysts. n -M2 structure, where M1 and M2 represent the same active metal or two different active metals, n represents 1 or 2, preferably 1, and the spacing between M1 and M2 is [missing information]. and The active metal is selected from at least one of Sr, Ba, Mn, Mg, Ce, Ca, Li, Na, K, Zn and W, preferably a combination of any two, and particularly preferably Sr and Ba.

3. The single-atom catalyst according to claim 1 or 2, having at least one of the following characteristics: The spacing between active metal atoms is The proportion of monatomic metals in the total number of monatomic active metals is ≥25%; The distance between M1 and M2 is The proportion of the single-atom states M1 and M2 in the total single-atom active metal is ≥25%; The support is selected from at least one of lanthanum oxide, aluminum oxide, cerium oxide, and silicon oxide, with lanthanum oxide being preferred; The carrier is in a crystalline or amorphous state; and The specific surface area of ​​the carrier is 1-500m². 2 / g, more preferably 20-400m 2 / g.

4. The single-atom catalyst according to any one of claims 1-3, having at least one of the following characteristics: The single-atom catalyst contains at least two active metals, preferably two active metals, which are selected from a combination of at least two metals of the same group or a combination of at least two metals of different groups. The active metal is Ba and / or Sr; The active metal is any one of the following combinations: Sr and Ba, Sr and Mn, Ba and Mg, Ce and Mg, Ba and Li, Ca and K, Ba and Mn, Zn and W, or Mn and Na; and In a single-atom catalyst M1M2 / S containing two active metals, the molar ratio of M1 to M2, based on the metal elements, can be 1:0.1-10, preferably 1:0.1-5.

5. A method for preparing a single-atom catalyst according to any one of claims 1-4, the method comprising: Step 1: Prepare a mixed solution by mixing at least one metal precursor, a nitrogen-containing compound ligand containing two or more nitrogen atoms and a solvent, and contact it with an optional reduced support to obtain a mixture; Step 2: The mixture obtained in Step 1 is ultrasonically dispersed, filtered, and dried to obtain the catalyst precursor; Step 3: The catalyst precursor obtained in Step 2 is dried, calcined, and cooled to obtain a single-atom catalyst; The support is an oxide support, and the metal is selected from at least one of Group IA, Group IIA, Group IIB, Group IIIB, Group VIB, and Group VIIB metals.

6. The preparation method according to claim 5, wherein it has at least one of the following characteristics: The support is selected from at least one of lanthanum oxide, aluminum oxide, cerium oxide, and silicon oxide, with lanthanum oxide being preferred; The metal is selected from at least one of Sr, Ba, Mn, Mg, Ce, Ca, Li, Na, K, Zn and W, preferably a combination of any two, and particularly preferably Sr and Ba; When using at least two active metals, preferably two active metals, the metals are selected from a combination of at least two metals from the same group, or from a combination of at least two metals from different groups; The metal is Ba and / or Sr; and The metal can be any of the following combinations: Sr and Ba, Sr and Mn, Ba and Mg, Ce and Mg, Ba and Li, Ca and K, Ba and Mn, Zn and W, or Mn and Na.

7. The preparation method according to claim 5 or 6, wherein it has at least one of the following characteristics: The precursor is a salt, preferably selected from water-soluble salts, and more preferably at least one of nitrates, sulfates and halides, wherein the halide is, for example, a fluoride, a chloride and a bromide; The nitrogen-containing compound ligands are selected from (organic) compounds containing amine groups; The nitrogen-containing compound ligand is selected from at least one of diethylenetriamine, ethylenediaminetetraacetic acid, bipyridine, porphyrin and phthalocyanine; The solvent is water or an organic solvent; more preferably, the solvent is at least one selected from water, an alcohol having no more than 5 carbon atoms, and a ketone having no more than 5 carbon atoms; even more preferably, the solvent is at least one selected from water, methanol, ethanol, and acetone; and In the mixed solution, the molar concentration ratio of the ligand to the precursor, calculated as metal ions, is 2-5:

1.

8. The preparation method according to any one of claims 5-7, comprising at least one of the following characteristics: The carrier is pretreated before contacting the mixed solution. Preferably, the pretreatment method is heat treatment of the carrier under a reducing atmosphere. Based on metal ions, the amount of support used is such that the molar ratio of support to metal precursor is 2-500:1, preferably 4-500:1, and more preferably 4-400:

1. In step 2, after ultrasonic treatment, heat treatment B is performed; The conditions for ultrasonic treatment include: temperature 40-70℃, ultrasonic frequency 20-100kHz, ultrasonic power 200-500w, and ultrasonic time 0.5-5h. Stirring is performed during the ultrasonic treatment process; The drying conditions are such that the solvent content in the carrier loaded with the metal precursor and ligand does not exceed 1% by weight, preferably 0.1-0.7% by weight; The roasting method includes: roasting at 100-650℃ for 30-300 minutes; and The roasting is carried out under a protective atmosphere.

9. The preparation method according to any one of claims 5-8, comprising at least one of the following features: The reducing atmosphere is provided by H2 and / or CO; The conditions for heat treatment A include: Temperature 300-500℃, time 0.5-5h, for example, the carrier can be left to stand under the above conditions; The conditions for heat treatment B include: temperature 40-90℃, time 1-10h; and The drying conditions include: a temperature of 70-120℃ and a time of 10-30 hours.

10. The use of the single-atom catalyst according to any one of claims 1-4 or the single-atom catalyst obtained by the preparation method according to any one of claims 5-9 in the oxidative coupling reaction of methane.

11. The application of the preparation method according to any one of claims 5-9 in the oxidative coupling reaction of methane.

12. A method for preparing C2 and above hydrocarbons, the method comprising contacting a feed gas with a single-atom catalyst according to any one of claims 1-4 or a single-atom catalyst obtained by the preparation method according to any one of claims 5-9 to perform a methane oxidative coupling reaction, wherein the feed gas comprises CH4 and O2.

13. The method of claim 12, wherein In the feed gas, the molar ratio of CH4 to O2 is 2-10:1, preferably 2-8:1; and / or The conditions for the methane oxidative coupling reaction include: The reaction temperature is not lower than 450℃, preferably 480-800℃; the gas hourly space velocity of the feed gas, calculated as CH4, is 20000-200000 mL / (g·h), preferably 30000-180000 mL / (g·h).

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